Flash Photography

Introduction to Flash Photography

By Desmond Downs

1 Basic info about Flash Photography

Why should you use flash or consider purchasing an external flash to add to your camera? If you've seen professional images taken using flash I'm pretty sure you know the answer to that! Flash can make your images look very different and a lot more professional when used correctly. You may even find that many images that impress you were taken using subtle flash that doesn't seem to show in the images until you actually see a comparison of the same image without flash. Once you learn more and more about flash you start to understand how many uses it has, besides simply providing extra light when “it's too dark”. You'll probably be surprised to learn that you need flash more in bright sunlight than indoors!

Perhaps that's a good starting point for discussion, the effect of flash on an image. This can vary between blatantly obvious like direct flash casting harsh shadows on the wall behind your subject in a dark room – where it is obvious that flash is the one and only light source, all the way to an image where you don't actually realize that flash was involved until you are told or shown a comparison with and without it, - plus everything in between. In other words there is a ratio of flash to ambient in an image.

So what is Ambient lighting then? For the purpose of this book it is any lighting that has an effect on our image that is not flash. Well actually if you are in a huge stadium with lots of cameras and flashes firing all the time then those other flashes are also part of the ambient lighting so ambient is any light that you are not adding to the scene with your flash :).

Something that many people battle to come to grips with is the fact that when you use flash you are creating two exposures in one image. Think about it for a while because it is perhaps the most important aspect of flash to understand. We have ambient light which would give one exposure during the time that the shutter is open, then we have the flash which, if you were to totally underexpose the ambient light would give you an image usually very different to the ambient, this happens in about 1/1000th sec during the exposure. This is best illustrated with pictures of course which we will see later.

Most cameras have a built in flash which is usually more accurate than an external flash due to the fact that there are less variables involved with its operation. It stays in the same place, it is always pointing forward and there are seldom any light modifiers placed in front of it. Minimal variables makes it easier for manufacturers to calculate exposure based on reflected light and the ever important distance information from the lens which will be discussed later.

For now let's get onto the absolute basics of flash.

Pin Configuration

Have a look at the following image of various flashes.

Some are really old while the one at upper left is a modern video led that also works as a flash, the big one on the right is an old 'hammer-head' style flash.

All except the hammer head flash have something in common – the hotshoe mount at the bottom.

Now have a look at the bases of those flashes, this is the 'foot' that mounts into the hotshoe of your camera. Each one of them, regardless of how many other pins they have, has a centre pin which is the 'trigger' pin for the flash circuit.

On the side of the hotshoe foot is something else that is common to all of them, the earthing contact.

If you were to take a piece of wire from the earthing contact and touch it to the trigger pin, with the flash turned on and charged up, the flash will fire.

In the next image we see the old hammer head flash with a pc cable coming out the side. Some cameras have a pc socket to trigger a flash with a pc plug and the more professional flashes have a pc socket as well as a hotshoe foot.

The vast majority of flashes today have the standard type hotshoe foot and in this book we will be discussing those flashes . The pc type connection has its uses but they are very seldom used today, though in some cases they can be very useful as with high speed photography and other manual applications.

Inside the flash we have a capacitor to store high voltages. Don't try to pull them apart unless you know exactly what you are doing and understand the risks! These capacitors store voltages ranging from about 100 volts to 600 volts and are made to discharge at a very rapid rate and can kill you! Even when the flash has been off for a while they remain charged and dangerous.

So, what's with the little “Starblitz” flash at the bottom? Well as an experiment I took out the smaller black capacitor on the left which was rated as 200 micro farads and wired up an external 800 micro farad capacitor to it instead. Highly dangerous I know but it gave my 4 times the power!

So there's a bit of a lesson in energy storage and output. Bigger capacitors store more energy, just like batteries, and can supply more power as well.

If you add a capacitor that is 5 times bigger than the one that goes in the flash it will take 5X longer to charge but will also produce 5X as much light. But be careful, the flash tube can melt if it gets too many full power blasts beyond what it is made to handle.

In the following modification I added a 1330 microfarad capacitor to the existing 800uf cap. This resulted in almost 3 times the power. The external capacitor is wired in parallel directly to the existing capacitor. Once again, don't try this at home!

This shows the distance it was from the house.and the lighting.

The ambient was under-exposed to let the flash light the subject. A D50 with a ccd sensor was used to allow for full flash synch at any speed.

The results don't necessarily look professional but do demonstrate the amount of power that was available to the flash.

Those two wires from the capacitor, where do they go to?

Straight to the flash tube! So don't think that it is safe to touch the wires on the ends of the flash tube just because the flash isn't firing at the time! Those two wires with high voltage and a capacitor load of energy can kill you ! How does it work then? The short version is that there is a third wire that goes near the one end which the flash circuit uses to trigger the flash.

We have the two main wires pointing outwards and then on the left we have another shielded wire that fires a high voltage which ionizes the gas inside the flash tube and allows electricity to conduct and light up the flash tube. This happens at very high speeds, a Nikon SB800 fires at 1/128 th power in less than 1/40 000 th of a second. At full power it takes longer, about 1/700 th of a second obviously because it is dumping more energy and will therefore take longer to do so

On top of most cameras there is a hotshoe for connecting the camera to an external flash. We have the commonly used centre 'trigger pin' while the metal part that holds the flash down also serves as the earthing contact, along with the other pins that are used for communication between the camera and flash. If you are using an external flash for the first time, or haven't used one for a while these contacts may need cleaning to make proper contact. Usually the act of sliding the flash back and forth a few times in the holder accomplishes this.

Now let's have a look at one of many accessories available for camera flash. This is an optic trigger which can fire a flash some distance from your camera when it detects another flash triggered by your camera. It has the same earthing contact and trigger pin plus a pc plug on the side. The pc plug is connected directly to the other two contacts so either can be used to fire a flash.

Something else that this can be used for is high speed photography where you use something besides your camera to fire the flash. A pc cable with the wires cut back can be used for this. Either connect them to an electronic circuit, a sound activated switch for example, or simply touch those two wires together and the flash will fire. Just like the 'test' button on some flashes, all it does is join the centre pin to the earthing contact.

Here's an example, discussed later in the section on high speed photography.

A switch is mounted on the side of two boards with a spring between them and the wires are connected directly to a pc plug that has a flash mounted on it.

When a light bulb is smacked with a hammer the spring is pushed down, making the switch join the two wires connected to the pc plug, which effectively touches the trigger pin to the earthing contact of the flash and Bang!

So what speed was the breaking glass exposed at? The manual for the Nikon SB26 flash gives the following speeds:

Full power flash (1/1) fires at 1/1000th sec

½ output = 1/1100th sec

¼ output = 1/2500th sec

1/8 output = 1/5000th sec

1/16 output = 1/8700th sec

1/32 output = 1/12000th sec

1/64 output = 1/23000th sec

This varies between flashes as well, the SB800 fires full power at 1/700th sec and down at 1/128th power it fires at 1/41600th sec. Having the ambient totally underexposed means we can choose what speed to use to freeze motion based on flash power, and adjust our aperture, iso and distance from the subject to get the exposure we want.

That's the absolute basics of how a flash works and all we really need to know for now. Next we will look at something else that is very relevant to flash photography because because of the 'distance' variable – the inverse square law.

The inverse square law:

It is useful to understand the inverse square law when dealing with flash, especially outdoors when you are competing with the sun and need all the power you can get to be able to work at a reasonable distance.

At first it takes a bit to grasp the concept that at twice the distance you have ¼ the power. 3X the distance = 1/9th of the power. The initial thought would be that at twice the distance you would need twice the power right? But because we are dealing with area, and doubling the distance you are working at doubles the length of both sides of the area you are working with, it doesn’t quite work out like that. You take the number you are multiplying the distance by, put a one over it and square it. 5X the distance = 1/5 squared or 1/25th of the power. As always a decent picture explains it much easier.

That’s much easier to understand isn’t it? If your subject is 1 meter away from you it will take, a certain amount of energy from your flash to light. If the subject is 2 meters or twice that distance away, because the length and breadth of your flash pattern both double the area is now 4X bigger, the light is now ¼ as powerful as it was before, because it is spread out over 4X the area, so you need 4X that amount of energy from your flash to light the same subject. Each factor you increase the distance by makes the light \'7b1/[that factor] squared\'7d weaker. 2X=1/4, 3X=1/9, 4X=1/16, etc.

This gives rise to “flash fall-off” which is demonstrated in the next picture of several objects each the same distance apart. The histogram of each image shows the varying degrees of exposure as the subjects get further from the light source. This looks like the typical amateur direct flash shot that we try to avoid.

Flash settings:

First curtain or 'normal flash'

When your camera is simply set at 'flash' with no fancy names added to it that means that the flash fires as soon as the shutter opens. In other words the 'first curtain' of the shutter has opened all the way. This is explained more in the chapter on HSS/auto-fp flash. Once this curtain is open the entire frame is available for the flash to fire and light it up all the way from top to bottom with no obstructions from the shutter curtains. If you are taking a one second exposure the first curtain opens, the entire frame is ready to be exposed for one second [less the time it took for that curtain to open, usually around 1/250th sec, and the time it will take for the second curtain to close.] and then the second curtain closes heading across the frame to the first curtain. Example, dropping a ball with a deliberate slow shutter speed. The result does not look natural, something at the beginning of the exposure frozen in time with blur moving away from it. It looks more like the ball is bouncing upwards when in fact it is falling.

With faster shutter speeds there is no subject blur so it really doesn't make much difference then.

Second/rear curtain

The first curtain opens, we have a pause while the sensor soaks up the ambient light, then the flash fires near the end of the exposure, just before the second curtain closes.

Example, the previous subject now looks more natural as the blur is behind the frozen image because the flash fired near the end of the exposure rather than the beginning. Ok so I cheated and used the same image flipped upside down to maintain consistency.

3) slow synch

This will be explained better in the section on balancing flash with ambient but basically if you are taking pictures indoors and turn your flash on then quite often the camera will assume that flash is going to light the entire scene for you, as the only light source, and defaults to a set shutter speed. This is normally around 1/60th sec [usually a setting that you can change in your camera]. This means that the background will go very dark and flash will be obvious in the picture when you are in a dark environment. Selecting “slow synch” basically tells your camera “Expose correctly for the ambient as well!” so that instead of jumping to 1/60th sec it will choose whatever shutter speed would be necessary to have the ambient correctly exposed if the flash were not on.

Here is an example, first image is ambient only, no flash.

Then we turn on the flash and it defaults to 1/60th of a second which kills the ambient “mood”.

This is not an exercise in good lighting so the built in flash was used in these images. When it is relevant to the subject we will discuss better quality light but when we are discussing technical matters my model “Iris” will be the subject to avoid “distractions” and biased opinions based on how attractive the subject is. She was rescued from Borg and hasn't fully recovered. I once saw a thread on a forum where someone had a girl in a bikini on an old sofa on the beach. The comments from the male audience were nothing but praise and “I wish I could take pictures like that!” while basically the photographer had broken all the rules and used direct flash from the camera's built in flash and fully auto settings , there were long shadows behind her – but onlookers [Ooglers] were prepared to overlook those 'minor' technicalities based on the appearance of the model in a bikini.

So we set the flash mode to “slow synch” and it exposes the ambient correctly and adds light to the subject. If you're shooting in manual mode this becomes easier because your settings won't change when you turn on the flash. Also be mindful that some cameras assume that when you choose “rear curtain” you actually want a slower exposure for the effect so they will also default to “slow synch” when you use that mode. The image hardly looks like it has flash in it mainly due to the fact that the built in flash works in TTL-BL mode which backs of by 1.7 stops when the ambient is correctly exposed.

In the chapter on “balancing with ambient” we will discuss further steps to achieving the correct colours in an image with two different light sources like this [flash and ambient]

For now let's have a re-cap of first curtain [normal], second/rear curtain and slow synch flash:

First curtain flash fires as soon as the shutter opens. If there is movement this means the subject is lit by the flash at the beginning of that movement while with second curtain flash the subject is lit at the end of that movement.

If the subject below were a car we would see the red tail light trailing behind it with second curtain flash which would look more normal. Slow synch flash is demonstrated in both of these images in that a slower shutter speed was used to capture the ambient light along with the flash on the subject, which results in movement being shown in some conditions.

Red eye reduction.

Don't even go there! We're discussing how to avoid direct flash and red-eye reduction is for dealing with direct flash and the horrible red eyes that result from this. Basically the flash fires several times before the picture is taken to make the person't pupils contract and reduce the area that the flash has to reflect off. The best red-eye reduction is to not use direct flash! A better solution is flash-value lock as described below.

Dealing with blinking blinkers!

Sometimes you're taking photos of a group of people and there's this one guy who blinks in every shot you take! It's the pre-flash, some people are very sensitive to it and blink when it happens and their eyes aren't open again by the time the camera takes the actual photo. Film cameras just used the reflection off the film surface to measure the flash bouncing off it. Digital sensors are too reflective for this so the camera has to take a measurement off the flash meter before the picture is taken. Basically what happens is that as soon as you press the shutter to take a picture the camera fires a weak burst of flash and does its measurements before the mirror lifts up and exposes the sensor for the picture to be taken. Once it's done its calculations the mirror lifts up and the shutter opens to expose the sensor for the picture to be taken. This usually takes exactly enough time for people to blink and still have their eyes closed for the picture when it is taken. But there is a way around this!

Some cameras have the option of using “fv-lock” or “flash value” lock. What this means is that when you press the ae/af lock button [it can be assigned to do various things, check your manual] the camera fires its pre-flash to measure the reflected light and determine what power will be needed to light the subject/s. Don't change your working distance now if you're using on camera flash [in sunlight for example when red-eye isn't an issue because peoples pupils are dilated]. When this pre-flash happens the blinker will obviously close his eyes for a fraction of a second which is ok since you haven't taken a picture yet. But once you have that flash value 'locked' the pre-flash will not fire again so you can happily take some pictures of the group and the main flash will light them correctly and the blinker will have his eyes open in the picture but closed a fraction of a second after the picture has been taken, which we don't mind at all :) .

Catchlights:

The light source you use will likely be reflected in your subject's eyes.

Even my model “Iris” has catch-lights added to make her look more life-like. Notice how the 'natural' look for catch-lights in the eyes is a bit to one side and in the upper half of the eye. That's where most light comes from in normal conditions. Keep that in mind when you add lighting in an image. When reviewing the sample images of Iris keep this in mind – they are not from the flash!

So we're all ready to start taking pictures using flash now but not before we have learned a very important lesson: Just because you have the tools doesn't mean you have to use them!

2 Lesson one – you don't have to use flash!

When I got my first external flash I used it for every shot until one day when I proudly presented an image on the forums with a bride standing next to a large window, I had used bounce flash as per the advice I had read online, and for bounce flash it looked pretty good.

The first comment I got was “Why on earth would you destroy that lovely window light with flash!?”. Oops!

Then I had a look at some of the images without flash and noticed what lovely lighting the window was producing and realized I had made the mistake of thinking that just because flash can improve a lot of photos doesn't mean it will improve every situation. In reality a certain amount of bounced flash can improve almost every photo but be very wary of totally destroying good natural light with it, keep an eye on the natural light and know when to turn the flash off!

This is taken from the chapter on flash in my other book “Photography Masterclass”.

A while ago a group of us did a shoot with some volunteer models out at Raglan harbor in New Zealand. One of the guys managed to catch a very well timed shot of me shooting in the water with the flash lighting up the umbrella. This helps to give an idea of what the setup was and the angle of the light. Now I won’t profess to be a professional photographer because I was doing this just for fun and as a learning experience, but the results do look very different to the average snapshot. I was shooting with my 6 MP D40 and the 18-200mm lens.

The big advantage of a zoom lens is the wide variety of images you can get without having to change lenses, and realistically, if you are shooting at smaller apertures, there is very little difference at F8 between a prime and a zoom, I’ve done tests to confirm this.

Here we have about 200mm.

This is the image I was aiming for but I decided to zoom back just to include an image showing how we accomplished this shot and I ended up liking it more, though the biggest issue with the image is probably the “spill”, or unwanted flash in the foreground on the water. It would have taken quite a bit to set up something to block that light while lighting the model properly while also shooting in water.

Now: I have been going on about how much difference flash can make to a plain image and how you should use it more and get it off the camera for good side lighting etc. etc. but I also want to add a lesson I learned while doing this shoot. An important principle of photography is ‘Just because you have it doesn’t mean you have to use it!’ At one stage I was shooting pretty fast and the flash was battling to keep up. Eventually I hit a stage where the batteries were just too far down to recharge the flash fast enough and I got a ‘misfire’, the flash didn’t go off. After looking at the image later I realized that I got a happy accident and need to stay aware of the possibilities of images without flash even when my main purpose is to learn to use it.

So if you're learning flash then by all means practice with it and learn to make it look good but still be aware that every now and then you should just turn it off if the natural light is good.

Since we'll be discussing the fact that flash photography involves two exposures in one we may as well include the chapter on exposure from my other book. This includes ambient exposure and a discussion on histograms.

3 Exposure

When I got my first decent digital camera I would take a picture, look at the resulting image on the screen and think to myself ‘Oh, so that’s how it is supposed to look then?!’ fully believing that such an expensive camera must obviously know exactly what it is doing and would therefore give me a perfect exposure. How wrong I was, even in its most advanced modes the cameras’ metering system is only the result of a computer program, written by an imperfect human being trying to work out what the camera will be pointed at and what the main subject will be, based on many variables that are impossible to predict in absolutely every situation. Is the subject the bright mountains in the distance or the person standing in the shade of the tree? Which is more important in the final exposure? Is the person under the tree important to the photographer or just another tourist getting in the way? For that matter the photographer may have the camera on a tripod and want an image exposed perfectly for the background first and then for the subject under the tree to combine them later in editing software. Obviously some of these variables cannot be calculated by the limited electronics of a camera, or even for that matter by another human standing next to the photographer, unless he can read minds. This is one of the reasons why the hardest part of photography for most beginners is getting the correct exposure – or even understanding what is ‘correct’ exposure.

Here is an image and its associated histogram just to show a few basics.

This is what the histogram looks like. A spike on the left representing black with no detail, a spike on the right representing white with no detail, and then everything else goes in between them with darks on the left, lights on the right and mid tones in the centre.

Here are some more images, along with some more histogram basics, that should help to explain why it is so difficult for manufacturers to write a program to give correct exposure in all situations. Have a look at this image and the resulting histogram. On the left of the histogram we have the dark part of the image and on the right we have the light part of the image, shown as two separate ‘hills’. So what is this picture of?

It’s actually a sheet of white paper so everything is white to a person looking at it. But half of the paper is in sunlight and the other half is in shade. This shows that there are many situations where the camera has to make compromises while trying to achieve correct exposure. Don’t think that the histogram gets the tones the right way around according to how the picture looks on the screen, it always shows darks on the left and lights on the right

So what if we only take a picture of the area of the paper that is in the sunlight, or just in the shade? What will the exposure and histogram look like? Like this, for BOTH!

This could be either the sunlight or the shade image, they both came out the same.

When it’s a neutral color the camera’s meter aims for ‘average gray’, somewhere near the middle. The camera does not know the difference between gray in normal light, white in shade or black in sunlight! How could it? Something to think about when trying to work out why your camera does what it does.

So how do we get ‘correct’ exposure in an image when we have such a variety of lighting to deal with? In a later chapter ‘exposure compensation’ will be discussed which deals with correcting the exposure when the camera gets it wrong, which is actually quite often!

What happens when we introduce a third variable to the scene, besides the shadow and sunlit areas of the paper? Let’s introduce a black lens cap in the shaded area. Compare the histogram of this image with that of the first image. Do you notice how the left peak has dropped a little, but we now have an extra spike to the very left of that? Why has this happened? Well the lens cap is now using up some of the space in the shadow area, so that original left peak has less of that particular tone to represent, but since the lens cap is even darker than the shaded paper it creates another hill on the very left, which represents black with very little detail.

Next we add something lighter than the shadow area but not as light as the sunlit part of the paper. Can you predict where the histogram will show this? Somewhere between the left and right peak perhaps? Definitely! It now shows as a rather spread out mound between the two, because it is a more average tone.

Try to predict what the histogram will look like if we introduce our black lens cap to the shadow area again. Where will we see it represented on the above histogram? Obviously if it is darker than the white paper in shade it must fall to the left of the left hand peak once again. And here we have a more complete histogram! On the very left we have the spike of the black object in shade, after that we have a nice sharp hill representing the white paper in shade, then we have a shallow hill with a little peak on it representing the various tones of the leaf, and finally we have the steep hill on the right representing the white area in sunlight. Be aware that there will be some overlapping of tones between the different subjects on almost any histogram so they are not always this clear-cut to interpret.

A large hurdle to overcome is understanding ‘how the brain sees’ compared to how the camera sees, because often a lot of confusion is created by taking a picture and seeing that it looks nothing like how you expected it to look. Take the picture of the white paper in sunlight and shade for an example, both sides looked white to me when I looked at it on the table. It’s all about something called ‘dynamic range’. This is basically the limit of what you can see from the darkest part to the lightest part of an image.

A camera’s dynamic range is very limited compared to how our brain ‘sees’. The example that best illustrates this is when you look at a bright window and see something like this and stare at it for a while

It all looks pretty ‘normal’ to you until you look away and blink and you see this pattern when your eyes are closed………

Why does this happen? Perhaps the simplest way to describe it is that your brain/eye combination ‘fixes’ the situation by darkening the bright areas so that the exposure looks right for the inside and outside at the same time (realistically it is caused by a chemical (rhodopsin) in the retina of your eye being depleted by the bright light), and when you turn away and blink it takes a while for it to ‘reset’ the pattern it created in the process which is why you see that shape. It involves a lot of hard work for your brain because the scene has a high dynamic range, from very dark all the way to very bright. Let’s have a look at how the camera sees this scene. When I take a photo of it I get this …..

The camera’s sensor doesn’t have enough dynamic range to capture the dark interior of the house and the bright exterior all in one image. The window has become totally white with no detail and is therefore beyond the limits of the sensor’s dynamic range. Your brain-eye combination has a very high dynamic range, it can see the bright exterior and dark interior all in one scene.

Now here is another image of the same scene with the exposure set correctly for the outside light.

Now the outside detail can be seen but the inside has become totally black with no detail. Once again capturing detail inside and outside at the same time is beyond the dynamic range of the sensor – you have to choose what you want to have correctly exposed because what you can capture, all in one exposure, is limited by the dynamic range of the sensor.

Try this: Set your camera to spot metering and find a scene like this – bright window and dark room. Turn off auto ISO, use ‘A’ mode or ‘Aperture priority’ and take a photo with the window in the centre of the frame – spot metering is only seeing the light outside. Now take another picture with the window to the side and the centre focus point of your camera on the wall inside. You will see a vast difference in the exposure – in one image the light outside the window will look right while the wall inside is close to being black, and in the other image the wall will look right while the window is white.

Now when we compare these images how much difference is there between the shutter speeds chosen by the camera? Well compare 1/5th sec to 1/250th sec. 250 divided by 5 = 50. The light outside is 50 times brighter than inside! Of course depending on conditions where you are there will be variations in this experiment so don’t think there is something wrong if you don’t see a difference of 50 X .

The initial image in this chapter is the result of combining the two images in Photoshop – it’s not nice to have to resort to editing images to get what you want but sometimes it is unavoidable. This combining of the two images results in a rather crude ‘High Dynamic Range’ or ‘HDR’ image.

Another solution would be to use flash to light up the inside of the house while exposing correctly for the outside light.

So what about an image where the light is even enough not to have to do this and what does the camera’s metering system aim to achieve to obtain ‘correct’ exposure?

Try this: put your camera in ‘P’ mode. Use centre weighted or matrix/pattern metering mode and take a picture of something in an even lighting arrangement – perhaps a dull color or simply a patch of grass or blue sky with nothing else in the image. Now check your histogram.

Side note: If anyone asks why you are using Program mode tell them ‘P’ stands for ‘Professional’ but if you reach the stage where you don’t need to use it then you tell them ‘P’ stands for ‘Panic’ because it tries to do everything for you besides turn on the flash. (That’s why it’s best to stay away from the fully automatic modes because you never know when it will pop the flash up when you don’t want it to.)

With an even patch of dark blue sky the histogram should look something like this: Very low contrast, because there is very little difference in the tones of the scene.

The camera’s metering system is designed to try and produce an average gray in each scene whenever possible. When reading a histogram always bear in mind the context of the image. On the very left is ‘black with no detail’ and on the very right is ‘white with no detail’. ‘Average Gray’ does not necessarily mean the color gray but rather an average tone in any color.

Using the same settings I took a picture of the (dry) grass in front of me. Now there’s a difference! It may not look like it but there’s a lot going on in this image all the way from black with no detail to white with no detail (The two spikes at either end) and everything in between. That’s why you have to look at the context of the image and resulting histogram. The meter may aim for an average reading and this has a hump in the middle in the same place as the image of the sky and both exposures are correct, but this one has a lot more contrast, there is information at both ends of the histogram, that’s what contrast is all about!

Now we move lower in the sky where there is some haze on the horizon and a greater contrast in colors, not as much as with the grass but still a lot more than previously. I used the same exposure settings as the previous images. We have some of the neutral tone blue sky near the top of the image, white clouds at the bottom which account for the high spike on the right of the histogram, and the tip of a tree and some darker looking cloud which accounts for the flat line at the very left of the histogram.

Now we add some more variables to the scene by once again using the same exposure so we know the different parts of that histogram will stay in the same place. Because I have gone to wide angle the original white spike is lower because the white clouds are a smaller part of the final image. Look at the picture for a while and try to work out what that spike is at the very right of the histogram.

Remember ‘white with no detail’? Look at the lower left of the image and the bright reflections off the white paint of the closest house. This is the tricky part of reading histograms, what do you ignore? In this case the histogram is really good for the rest of the image and the bright part of that house is not all that important to the image so the exposure is good enough for that scene. If you were to back off the exposure to show some detail in that white area the rest of the image would be under-exposed. If you print it out as it is there won’t be any detail in the white part of that house but if it’s for your own personal use and the white part of that house isn’t important to you then don’t worry about it, the rest of the image is well exposed. Either way, it would be rejected by an image library, due to that spike, but there isn’t much other option besides going back when the lighting is better or taking two different exposures and blending them later in Photoshop. Our original example shows this concept quite well.

Look at the spike on the right, that’s the blown out highlights of the bright window or ‘white with no detail’. The hump in the middle is formed mainly from the lighter part of the brown wood of the walls and the white appliances plus the white ceiling. The left part of the histogram is the darker part of the walls and other shadows.

What about the picture where the window is correctly exposed? Let’s have a look.

As we can see there is a large spike of ‘black with no detail’ on the left, a very small amount of ‘correct’ exposure across the middle of the frame, a small hump of ‘white with detail’ of the clouds and a small spike of ‘white with no detail’ on the right.

So which image is correctly exposed? It depends what you wanted to show and what is important in the image. If you only wanted to show what it looks like inside then the first image is ok. If you wanted to show someone how nice the weather was outside then the second image is fine. If you are taking pictures for a real estate agent to show how nice the house is inside and outside then you had better either combine the images or add flash inside with the outside correctly exposed.

And when the images are combined we have a more even histogram – not perfect by any means due to the spikes at either end but sufficient to illustrate what we are aiming for and give an idea of what the various areas of the histogram mean.

This also helps to explain why some scenes are more relaxing to look at than others. It depends how much work your brain/eye combination has to do to make a scene look right, and when the lighting is nice and even it doesn’t have to work very hard so the scene is more relaxing to look at. Like this shot of the Taranaki coast in New Zealand when the setting sun just dipped under the clouds on the horizon. The lighting is so even that contrast had to be added later, but basically the lighting of the scene was well within the limits of the sensor’s dynamic range to capture detail in everything quite easily. This makes the resulting scene easy to look at in person and in the photos, because it involves very little adjustments of your brain/eye combination to be seen easily.

An example of a potentially good looking scene that never had the right light and is harder to look at is this shot of a mountain at the beginning of New Zealand’s best one day walk, the Tongariro crossing. It takes a bit of work for your brain to even out the lighting in this image and even more so when you are there in real life trying to adjust your eyes for the bright sky and dark shadows.

Once you come to grips with the fact that the camera doesn’t capture exactly what you see due to its limitations, and learn to work around those limitations, you will be closer to capturing the images you have envisioned in your mind before pressing the shutter release.

Exposure compensation- Ambient

Once you have an idea what correct exposure is and how the different metering modes work you will realize that no metering mode is perfect in every possible situation. A metering system doesn’t know what the lighting is like. It sees something white and assumes it is gray in bright light so it backs off the exposure. It sees something black and assumes it is gray in dark lighting and increases the exposure – all it knows is ‘average gray.’ Though Nikon’s color matrix metering generally knows a little more than that, spot and centre weighted and most other cameras’ pattern metering systems only know one thing ‘average gray’. And that is what they aim to achieve regardless of whether the subject is black or white or anything in between.

This is where exposure compensation comes into the equation. Once you have chosen a mode to work in and are comfortable with judging when exposure is correct you can start using exposure compensation to fix images that aren’t properly exposed. If you take a picture and can see it is definitely not exposed correctly then all you need to do is push the little +/- [EV or ‘exposure value’] button on your camera, usually near the shutter release button with Nikon DSLR’s, and turn the back dial while holding that button down [depending on how your particular camera works] and take another picture, of course. If the results are still not where you want them try another adjustment until it’s right. As you do this more often you will find it easier to get close to the correct exposure with only one adjustment.

Remember that a ‘stop’ is either twice as much or half as much light depending which way you make the adjustment. Most cameras are set to dial in 1/3 of a stop increments while some are set at ½ increments. If your camera has the ability to choose between the two then it is best set at 1/3 increments because that is generally how the shutter speed adjustments work as well. That way if you are in manual mode and adjust the shutter speed 3 ‘clicks’ then you know that adjusting the aperture 3 ‘clicks’ in the other direction will result in the same exposure. Once you have made an adjustment the rear LCD, and usually inside the viewfinder, shows a +/- symbol to remind you that the metering is set to behave differently.

Let’s go back to the image of the white paper half in sunlight and half in shade as an extreme example.

We’ll start by adding a reason to ‘take sides’ between light and dark. Let’s add some subjects. This is what they looked like on the page as the clouds blocked the sun for a while.

Once the sun came through the clouds again I used aperture priority mode and took a picture and the camera chose 1/800th sec. at ISO 100.

The first image was taken with the active focus point on the roach on the right of the image. I had my camera in matrix metering mode and moved the active focus point over to the mantis on the left and the metering system realized my subject was now in the dark but was not prepared to change by too much. As I’ve noted in the past Nikon’s matrix metering system seems to have a cap of 2 stops that it is prepared to change in any situation. [With most of their newer models, that is]. Centre weighted metering would have maintained exactly the same exposure for both images.

So now we see that the shutter speed dropped to brighten the dark areas and this resulted in totally blown highlights. In this situation we have no choice, we have to blow the highlights to get our exposure right for the subject we have selected. Since the subject is still too dark, remembering that it is on a white surface, I dialed in ‘+2’ EV compensation so the shutter speed dropped to 1/50th sec [two extra stops of exposure gives us 4 times as much light so we go from 1/200th to 1/50th]. Our histogram now shows the whites in the shaded area as just above ‘average gray’ judging by where the histogram is sitting. We can see the thin spike on the right of the histogram representing our blown out whites on the right side of the image.

I dialed in another two stops of compensation resulting in a total of ‘+4’. Two stops down from 1/50th is 1/12.5th. Shown as 1/13th. Now the left hand whites are shown as a hill sloping down to the very right of the histogram, just before the spike caused by the right hand half of blown out whites. Right where it should be to give us a white with some details and expose our subject correctly as well. This has come at the cost of a total loss of detail on the right hand side of the image.

These are the decisions we have to make in a really high contrast situation. Which is the subject? What are we prepared to sacrifice to get the subject correctly exposed and what options do we have anyway? The camera doesn’t know what our subject is and where it is in the image except what it figures out based on the focus points [when in matrix or pattern metering mode]. The camera is disadvantaged in the fact that it cannot read our minds [some would be a shorter read than others]. That is why cameras have EV compensation buttons, to be used when necessary!

Here is a more realistic ‘real world’ example, an image I took a few months ago of Lake Waikaremoana [try to say that without hurting yourself] in New Zealand. When I checked the histogram it was bunched up to the right a little too much and had a thin spike at the far right meaning ‘white with no detail’, Matrix metering saw all the dark greens and overdid the clouds a bit while trying to expose properly for the greens.

As with previous situations like this, with this particular camera and metering system, I’ve become accustomed to dialing in compensation of ‘-0.7’. Hold down the ‘+/-’ button and turn the back dial until the exposure shows ‘-0.7’ which is usually two out of three lines on a scale showing 1/3 increments, it’s actually 2/3 which is 0.666666 , rounded off to 0.7. Some cameras have an LCD screen on top that actually shows ‘-0.7’. In this particular case I felt that it was more than 1/3 over, perhaps close to 1 stop over, but 0.7 gave me a happy medium to try, and in this case it worked first time.

It may not look much different on screen but the first image would be rejected from a stock library because the spike indicates an imperfect exposure. The second image was accepted when submitted.

Note how the histogram is no longer bunched up against the side, no spikes showing overexposure? And if you analyze it for a while you start seeing what the different ‘hills’ represent. The solitary hill on the right is predominantly bright sky and possibly includes the brighter reflections on the surface of the water. Histograms very seldom look like the ‘ideal’ the meter aims for because we seldom photograph something totally plain so it pays to have a look at the histograms you are getting and to learn to read the information and decipher the exposure in varied situations. Just remember ‘pitch black on the left, pure white on the right and everything else in between’.

Of course it’s not always negative compensation that we have to use, it depends on the scene and what ‘fools’ your metering system when it tries to produce an ‘average gray’. Here’s a shot with a lot of white in it, a bright lighthouse and clouds in the background. Our metering system decides things are too bright and backs off the exposure resulting in an image with a lot of detail in the whites but underexposed grass and blue sky, which should be our real ‘average gray’ tone.

Look at the ‘hills’ just left of the centre and to the right of centre. That’s supposed to be whites, we have a lot of white in the scene and that should give us a hill touching the right but instead it’s to the left meaning that the image is badly underexposed.

In this case it was so badly underexposed that I dialed in ‘+1.7’ and could have made it ‘+2’ or even ‘2.3 but anyway it made the image look more like it should have been, ‘next time’ I will check the resulting histogram more closely but it’s still a huge improvement on the initial image where any metering system would be fooled by the massive amount of bright light in the image.

Have a look at the resulting histogram above. See that gap on the right that we could still use? There is also a small spike at the end, which is the unavoidable spike of the bright light reflecting off that window. There’s no way we can save that because it’s the sun’s reflection and it is totally acceptable because a reflection like that can’t have detail. Think about the image in the chapter on exposure with the house with the bright white wall. If the rest of the image is properly exposed we sometimes have to ignore a minor imperfection elsewhere, we can’t always get everything properly exposed, due to the limits of the sensor’s dynamic range we dealt with earlier as well. The sun and its reflections in a normal image will always be a spike of white with no detail but we can still use that space on the right before that to push our histogram over even more and expose further to the right. As mentioned adding another 1/3 to 2/3 of a stop of exposure would brighten the image further without throwing away much detail and would result in a more accurate exposure and better image quality and print. The resulting histogram would fill that gap.

Flash exposure compensation:

The same principles apply to flash exposure compensation. You need to determine though how your flash output is affected when you use exposure compensation for ambient. With Nikons the flash takes on the same compensation as the ambient adjustment so if I set my exposure compensation for ambient to “-1” the flash will also be “-1” without having touched any flash settings. The Canon brand generally only affects ambient and leaves flash compensation as a totally separate adjustment though possibly in some models you can choose how you want it to work. It's dangerous to assume any brand will act in any particular way because you never know when they will change how things work on the next model so test yours out and see how it responds to an adjustment for ambient – have the flash on and see if it does what you tell the ambient to do – try it indoors when it is dark so you can basically only see the flash output.

This is generally where the buttons sit for flash and exposure compensation. Check your camera to make sure where they are. The Nikons with two command dials usually allow for the front button being used for flash exposure compensation and the rear dial for the flash modes when the flash button itself is held down. With the single command dial you will need to also hold the +/- button down to adjust flash exposure compensation.

With the Nikons and the way the exposure compensation adjustment is “global” [affects ambient and flash], if for example you only want to adjust ambient to under-expose the background in a scene and you are not shooting manual you would have to dial in your normal exposure compensation for ambient, let's say “-1,7” and then you would have to adjust the flash compensation by dialing in “+1,7” which would cancel out the “-1,7” that the global adjustment caused. This would leave you with the flash 'back to normal'. Of course when we analyze flash metering modes “normal” can mean different things to different situations and models of camera so “normal” is very seldom “correct” exposure.

Our next chapter will involve a rule meant for ambient lighting which is actually very useful for calculations when you know you will be using flash.

4 The Sunny 16 rule

Basically this rule states that on the brightest, clearest, sunniest day you could possibly get, if your ISO and shutter speed are equal your aperture will need to be at F16 to get the correct exposure. That is, if the subject is in the sunlight of course. Believe me I had to mention that last part because I’ve learned that very little is ‘obvious’ when someone is learning something new.

How or why does this work? First of all we have to establish a standard to base our measurements on and an easy way to do this is to make our ISO and shutter speed the same because no matter what their value, as long as they are the both the same, the exposure will be the same at any given aperture. Let’s assume the brightest day possible and you are at F16. If your ISO is 100 and your shutter speed is 1/100th sec you will get the same exposure at that aperture at ISO 200 and 1/200th sec, ISO 400 and 1/400th sec, ISO 8000 and 1/8000th sec and so on.

Think about it for a while so it becomes clear in your mind. At ISO 100 and 1/100th at F16 you have correct exposure on a ‘sunny 16’ day. If you stay at F16 and change your shutter speed to 1/200th sec you are halving the amount of time you allow the light into the camera. But by changing your ISO to 200 you are doubling the exposure you had at ISO 100. 2 X 1/2 = 1, which is the same exposure. And the same with any other combination that is different to ISO 100 and 1/100th sec, as long as the two numbers are the same they will give the same exposure with any combination because any number you multiply the shutter speed by divides the exposure but if you multiply the ISO by that same number it multiplies the exposure by the same factor, giving the same result.

So why did I use F11 in my example image when we are discussing the sunny 16 rule? Because I want this number to stick in your mind, since you will very rarely see an F16 day! Depending where you live of course, but just because there is sunlight between the clouds that does not make it a sunny 16 day. Even if there is not a cloud in the sky, if you can see a little haze on the horizon it will most likely be an F11 day because that haze is also above you and is obstructing the sunlight above you as well.

Try this: On a sunny set your camera to manual mode and turn off auto ISO. Choose an equal shutter speed and ISO, let’s say ISO 200 and 1/200th sec. Point your camera at the blue sky or green grass, or just move it around in random directions and see what aperture the camera chooses. [Don’t point it at the sun!]. Most of the time if the sun is shining you will see apertures around F11, very rarely will you see F16.

So what? Why does it even matter if the camera is going to choose the right settings for you anyway? Even though the sunny 16 rule was developed a long time ago and used a lot for manual shooting that does not mean it no longer has any use! It serves as a pivotal calculation point.

For example imagine you want to use flash for an outdoor event tomorrow but don’t know what the effective range will be for the flash. Now you have a pivotal value to use to calculate the worst-case scenario for the day. In bright sunlight you need powerful flash because you are competing with the sun and have to use smaller apertures to block out the sun’s light, which also blocks out the flash’s light.

So the worst-case scenario, if we are at ISO 200 and the camera’s maximum flash sync speed [1/200th in this case], is the brightest possible day at F16. So you set up your camera and flash the night before and manually dial in ISO200 1/200th and F16, and with the flash attached you see what settings it tells you that you will have. The flash is telling us, before we even venture outdoors, that with a 24mm lens we will be able to work at up to 2.7m at these settings, for full power flash! Cool eh? [My wife is Canadian eh!]

Then we change to a more realistic setting of ISO 200, 1/200th and F11, which is the brightest day we are most likely to get, and the camera now tells us we will have a safe working distance of 3.8m. F11 lets in twice as much light as F16, which benefits our flash power. [Mathematically speaking, due to the inverse square law, discussed later, twice the power gives us 1.4X the working distance because that will spread the flash over twice the area. 1.4 X 2.7m = 3.8m].

And then we set it to an optimistic ISO 200, 1/200th and F7.1 just to see what we might have to work with if it’s fairly cloudy. 6m is what we get and though it’s unlikely that we will be at F7.1 it only took a few seconds to check with the knowledge we now have of the sunny 16 rule!

Another application it has besides working out flash distances involves shutter speeds. Suppose it is a sporting event and you haven’t a clue what speeds you could be shooting at. Now F16 is a best case scenario and you optimistically calculate from ISO 200 1/200th and F16. You won’t shoot at F16 so you move to F8 to help your calculations and, knowing that F8 lets in 4X as much light as F16, you now know that at ISO 200 you can shoot at 1/800th sec on a sunny 16 day. Then we go to a more realistic F11 day, which is half as bright [F11 lets in twice as much light as F16, so there would have to be half the maximum light available to have an F11 day], so we know that instead of being able to shoot at 1/800th at F8 we would have to drop to 1/400th on an F11 day [With half the light available]. But of course lenses go wider than F8 so at F5.6, one more stop wider, we could achieve our 1/800th again. It takes a bit of mathematics but it’s good to know it’s not impossible to work out, ahead of the time, what you may have to work with, and even if you can’t do the maths yourself you now know what the pivotal settings are and someone will be able to work it out for you perhaps.

Next we will discuss metering modes because besides affecting what the camera deems to be 'correct' exposure for the ambient they will give us an insight into flash metering modes as well.

5 Metering modes

We'll start off discussing metering for ambient only at first and then progress to flash metering. This is a chapter from my other book and I feel that since ambient and flash are often in the same image it is beneficial to discuss both metering systems to gain a full understanding of the subject. Flash metering will be a separate chapter after this.

A metering system tries to get an average gray out of a scene, as shown with the image of the grass. It tries to achieve a similar pattern with anything it sees, relative to the content of course, because as we’ve seen a solid patch of blue sky will give a narrower hill.

Note: A camera’s metering system can be affected by light coming in through the viewfinder so if you’re not looking through the viewfinder make sure you block it with something when taking photos so the images aren’t under-exposed. Most manufacturers supply an adapter for blocking the viewfinder for situations like this.

Spot metering:

Spot metering measures off one small area in the centre of the frame. Some cameras allow you to set it to measure off the active focus point so that, if you move your focus point when in single area mode, whichever focus point is lit up is the one it will spot meter off. This is a very basic ‘what you see is what you get’ mode and many people who shoot in manual mode use it to measure off a specific area of the image so they can choose their settings based on that measurement.

If you look through a drinking straw you will get an idea of what spot metering ‘sees’. Nothing but a very small area that it does all it’s measuring from. If you spot meter off a black surface it will assume it is average gray in bad light and will overexpose the entire image. If it is pointed at something white it will once again assume it is average gray in bright lighting and underexpose the entire image. To use spot metering you must know what you are doing. If you measure off something you know is an average tone, like blue sky or green grass, you will be ok. If you measure off something white and dial in the correct positive compensation your image will be correctly exposed. I would not advise beginners to shoot in this mode unless they have practised with it and are fully aware of how it works, before using it on an important shoot.

Mathematically speaking spot metering is like: ‘Centre spot = 100% of exposure’.

Let’s have a look at some examples to help understand its behavior.

If we have a high contrast scene like this burned out house we can get an idea of how it behaves. [Disclaimer: I had nothing to do with the fact that this house burned down, it was not a victim of any of my experiments!] In the first image I had pointed the spot metering at the white paint and it tried to get a gray and succeeded.

So spot metering destroyed the bright areas by making them too dark, what happens if we point it at the dark area? Now it tries to make the dark area gray and totally blows the whites! Who would seriously think of using such an extreme metering mode?

Photographers who know what they are doing, actually. Spot metering is a very precise method of choosing exactly what you want to meter off without any uncertainties. Once you know what to meter off you can choose your average tones and meter off them to get the correct exposure. Another method that works quite well for this house, which is a high contrast scene, is to measure off the brightest part of the house and use exposure compensation. In the following image I used spot metering to measure off the white walls, dialed in ‘+1.3’ exposure compensation, and got the histogram pretty close to the ideal exposure. By knowing what we want to achieve, and how much different it is to how our metering mode will react, we can meter off a known tone, use exposure compensation, and take more control of where our histogram will sit. +1.7 would have given a slightly better exposure.

This is when we use the EV-Lock button. Sometimes you don’t want the exposure to change while you recompose your image. For the above photo I zoomed in on a white patch using spot metering, set EV-compensation to ‘+1.3’, then I held down the EV-Lock [exposure value lock] button, shown below, so the exposure wouldn’t change as I went wide again and recomposed my picture.

Remember where this button sits and get used to placing your thumb on it without taking your eye from the viewfinder, it can be very useful in some situations. Also make sure you set it up properly in the menu because generally you can choose to set it to lock focus as well if you want to. Read your manual and set it up properly from the beginning.

Centre weighted metering:

This is almost like ‘large spot metering’ but it doesn’t only use the centre of the screen. It uses the entire screen but assigns 75% priority to the large centre area. This means that it takes an average reading but concentrates on the centre of the frame.

This is a safer mode to use because it is not as erratic as spot metering which would have the exposure jumping all over the place as you point the camera at differently lit parts of the scene. Centre-weighted metering is pretty standard between different camera makes and bodies, and as long as you get used to using it and making the necessary compensation adjustments for various scenes you won’t have to bother about learning how a new camera meters each time you replace yours.

Mathematically speaking centre-weighted metering is like: ‘exposure = (centre pattern X3 + outer area X1) divided by 4’. This would result in the outer measurement only being ¼ or 25% of the equation while the inner circle would be ¾ or 75% of the equation.

Let’s have a look at the sample images now. As mentioned previously centre-weighted is just that, weighted toward the centre of the image. If there is comparatively more darkness near the centre it will cause over-exposure in the rest of the image. If there is comparatively more lightness near the centre it will cause under-exposure.

As we zoom back the scene starts to average out and the average calculated by centre-weighted metering starts to give a better exposure.

And when we go wider and there is more variety in the scene the average still works fairly well for the image.

Matrix/pattern metering:

Ok now this is the point where you ask yourself why you didn’t take the blue pill because now the matrix has you. On saying that I use matrix, also known as pattern metering, 99% of the time. Matrix metering is designed to get you as close as possible to the best exposure for any given scene. It won’t be the same for all cameras because it is basically a computer program that changes slightly with each new release. Each time they try to make it cleverer but, as with computer programs, sometimes they just frustrate people who are used to it behaving a certain way. Here is an image to help picture how it works:

Matrix metering concentrates it’s measurements on the focus point area because obviously that is where your subject will be 99% of the time, under a focus point. But it still pays attention to the outer areas and factors them into its equation. Nikon has what is called ‘3D color matrix metering’ which means that the metering screen can detect colors, it uses the focus points to determine which is the most important color to expose for in the scene, since if you are focused on something it is most likely your subject, and it also uses the distance information from your lens, along with information based on the focus points that light up at the same time - to calculate the ‘3D’ aspect of its equation.

Nikon also claims that it has 30 000 images stored in a database in the camera, to compare with the scene you are photographing, to help calculate the best exposure. It is more likely a collection of equations based on 30 000 images than actual images that you could display if you were able to get into the metering program. Matrix metering also varies its calculations depending on your active focus point. If you set up your camera on a tripod and take the same image, with the focus point moved from one spot to another, matrix metering will sometimes give different exposures based on where your active focus point is and what the dominant light is like in that area. After all if you have sunlight and shade in a scene, and your subject is standing either in the sun or the shade you would want them to be properly exposed, and that’s not going to happen if matrix metering exposes exactly the same for the scene no matter where you have focused. If your subject is in the shaded half of the image and that is where your focus point is then matrix metering will expose brighter than if your subject were in the sunlight. On my D90 this exposure varies by up to 2 stops [4X brighter or darker] in the same scene.

Whatever, there is no perfect metering mode and each one has its strengths and weaknesses. Just learn how they act and choose one that you understand best and go with that.

Mathematically speaking matrix metering is like: ? Hmmmm , depends what model camera you have , who the manufacturer is, is it for the beginner or professional market, what focus mode are you using, does your lens have distance information ? …….

And the list goes on ‘Exposure = (lens distance info, color of subject, brightness of background, active focus point info, size of subject, difference between brightest and darkest areas, size of brightest area (it might be programmed like TTL-BL flash mode and can ignore an area it deems to be a reflection), reference to 30 000 image database) all multiplied and divided by an equation depending on the make and model of camera and depending on whether a firmware update has changed something that early users complained about, and of course whether you have done that update.’

What I like most about matrix metering is the fact that it has a degree of consistency in a scene and most of the time I can just forget about it and carry on with my picture taking. Occasionally for a picture I consider important I will check the histogram and adjust exposure compensation if needed to get as close as possible to the right exposure, and most of the time it is only about 1/3 – 2/3 of a stop out.

Here is what matrix metering did with the sample scene, it always gets me pretty close to what I want to achieve from the first image.

Now let’s have a look at a really high contrast scene to test matrix metering to its limits. We’ll move the tripod closer to the house. Hold on while I battle my way through those thorny plants, I don’t mind having to pick all manner of strange seeds off my socks when I get home just to get some interesting images for my book!

Ok, here is where things get a little more complicated. I have the camera on a tripod pointing at our test scene and will not move anything beside the active focus point. Just excuse me while I go and rescue my wife from a man-eating Tarantula about to rip her arms off! Ok then, it was just a piece of grass seed [once again], she’ll survive. Now where were we again? Ok, I have chosen a focus mode that only uses one focus point but I can move it around on the screen to decide where I want it to focus. Let’s move it to the dark wall at the back, essentially telling the program that our subject is in the dark. This is the resulting exposure.

It totally blew the highlights in favor of the dark wall inside, and after all that is what I told it I wanted to be the subject so it had little choice. Now all I am going to do is use the rear control pad of my camera [D90] to move my active focus point onto the white frame, basically telling the program that my subject is no longer in the dark. Nothing else was changed here and this is how matrix metering decided to expose exactly the same scene.

Pretty cool when you think about it, the matrix metering program exposed the whites very well because it took into account the amount of darkness in the scene and pushed the whites to the right thereby saving detail while still giving some exposure for the dark areas. The biggest advantage of matrix metering is that it is not as dependent on exact sizes as the other two metering modes, it can choose for itself what the subject is without it having to be a specific size. I’m almost always in matrix metering mode.

So why didn’t I show the matrix metering pattern on top of these sample images? Because it’s not that simple. Matrix metering ‘maps out’ its subject mainly using the area around the focus points, which I call ‘the focus point diamond.’ Here is a rough idea of what I am talking about, in the image where the focus point was on the whites matrix metering could choose its own pattern, independent of size, and determine its exposure from that, along with a lot of other information including a reading off the darker areas. Notice how I’ve made the white bits darker in the red metering area? That is my perception of how matrix metering would have read this scene, and given priority to the areas and colors in the focus plane that I chose with my active focus point.

So which mode will you choose to work with? It doesn’t really matter if you simply choose the one you understand best because nobody can tell you that you are using the wrong mode if you are getting the results you want, they can all work for you depending on your style, that’s why there are options.

Next we progress to flash metering but don't think for one moment that means forgetting about ambient metering because they are both important when using flash. We seldom use flash as the only light source so keep in mind the fact that adding flash to the equation is like........ getting married! Ambient and flash are two different light sources but when the correct formula is applied they can complement each other nicely, and live happily ever after! With a little work of course...

6 Flash metering

This is where things get interesting as we add another dimension to the equation. This is best demonstrated by a sample of a scene where flash was used. What do you think of this image? I set my flash compensation to +1.3.

Now even a 90 year old grandma who has never touched a camera will probably ask “Will the flash actually have an effect at that distance?”. Of course not granny, well done for thinking about it! There's the factor that makes flash very different from ambient, DISTANCE ! We never have to worry about the distance light has to travel when we meter for ambient lighting because it is already there and we can see it and adjust settings accordingly.

Flash is different, it's biggest limitation due to its limited power supply is the fact that it can only be effective up to a certain distance and, since much of the time it is mounted on the camera, we can see a change in the light from it as we get further from the subject; often called “flash fall-off” due to the inverse square law we learned earlier. This is not as noticeable if we have one subject lit by flash but if there are several at various distances the ones closest will look much brighter than the ones progressively further away and this will look unnatural, apart from the fact that it is a challenge to meter correctly to get the right exposure for only one subject.

Disclaimer: I am not trying to tell anyone that they should use any particular method be it manual mode, A mode, TTL mode or Pattern/TTL-BL/ETTL mode. All I'm trying to do is provide a background to how each mode works and while stating my preferences I will still say “use whatever works for you, if it gets you the result that you want then it is the right way - for you, just don't try to push it on others as “the only way””.

For all situations where I declare “Flash only” in an image it means that the ambient is so far underexposed in the image that it will not be noticeable or have any effect on the flash calculations.

“A” metering.

Very few people will use this as it is more like “A” for “Ah-bsolete”. Sounds like an American talking doesn't it? I met this American from a place called “Noo Yaak” which sounds like some little settlement out in the boondocks but anyway; Basically the first flashes that were automatic used a sensor on the flash itself to measure the flash. A little 'eye' on the front of the flash took the reading and turned the flash off when it had 'seen enough', based on the settings involved telling it what aperture and iso you were at, so it would know how much light to let in. So if you are at an aperture of f2.8 and iso 100 and the flash determines that it needs 1/8th of its power based on the reading it got from the light reflected off the subject, and you adjusted your aperture to f5.6 [and changed that setting in the flash as well] you would be letting in ¼ of the light with the aperture settings so the flash would take its reading and multiply its output by 4 compared to the first photo giving ½ power [1/8thX4]. Some of the really old flashes simply had a graduated filter that slid in front of the 'eye' thereby blocking the amount of reflected light it got as you adjusted the 'aperture' setting forcing it to keep the flash on longer before it would turn off – giving the correct exposure for your new setting.

We won't dwell on “A” mode because very few new flashes have it and TTL is far superior as it sees what you see Through-The-Lens [TTL].

TTL metering.

The flash meters off a sensor inside the camera and uses the light coming in Through-The-Lens. This is a mode that has changed slightly over the years. I will not state any facts for all cameras but I do know that the Nikon system has changed a bit over the years. The original TTL systems metered from a circle in the centre of the frame, basically moving the metering from the “A” mode sensor that sat above the camera in the flash and sometimes 'saw' over the top of close up subjects, right to the middle of the frame you see when looking through the viewfinder, and is hence unaffected by a change in focal length because the metering system sees the centre of the frame at the same size regardless of the focal length you are working at. The “A” mode sensor saw one size regardless of how big it appeared in the final image so the percentage of the image that was metered off changed depending on the focal length you were working with. Here is a comparison taken recently showing the difference between TTL flash with a Nikon D50 and a D5200. I left the settings the same for both, auto wb and no ambient in the equation, flash only. Notice how 'cool' the auto-wb is in the D50 and how 'warm' it is in the D5200? Also the D50 may look underexposed while in fact the grey rock has a good histogram, the D5200 has in fact over-exposed the image.

Another thing we notice is that the D50 wasn't as badly affected by the introduction of a white object to the outer focus point while the D5200 changed its exposure quite a bit [closer to 'correct' actually] when a white subject appeared under the outer focus point. This is because the original TTL metering pattern looked something like this, a circle in the middle of the frame.

With the older TTL flash metering it only knows the area it meters off, nothing around it. No matter what you have in the area around that red spot the flash metering only sees what is in the centre and meters for that. It is still possible that the D50 meters off a larger area than the original circle because it made a subtle change in output when the white object was put in front of a focus point but the TTL metering program may not have been tweaked to the same degree as the D5200 has been. What about the D5200 image? It appears that this metering algorithm has grown to include a larger area in its calculations. Metering systems tend to favour focus points, as this is where we generally have our subjects, and I like to refer to this area as the “focus point diamond”. Here is what TTL metering appears to 'see' in the D5200.

A larger area concentrating on the focus point diamond which is where our subjects are 99% of the time – which makes sense. Of course this could change with the next model so don't get caught in the trap of over-thinking each shot because when you finally work out exactly how your camera meters it will all change with the next model, and also don't try to tell someone with a different model “exactly” how it meters, because theirs will probably be slightly different. :) The D50 most likely uses the same area but more “centre weighted” in that it gives greater priority to the very centre of the frame so reacts less to objects under the outer focus points. It is not easy stating facts in these cases because there is also the variable of slight changes in output in the very same scene from the camera metering system, or the flash system not doing exactly what it was told due to all the variables involved in electronic components etc. etc. But by doing the same tests several times over we get a 'good average' to make an analysis from. In reality as has been mentioned these variables change slightly with each new body so don't obsess about them, just learn to work around the imperfections in a mode you like to shoot with or go fully manual and never have to worry about camera metering again – instead you can worry about your own failings and whether you will make the right decision. Personally I prefer to let the camera meter for flash because when it makes a mistake it's still close enough to fix later while a mistake in manual mode could cost you the entire image being either totally blown out or too dark to see depending on the shooting conditions.

The older TTL flash also relied on the centre circle being filled with the subject so if the subject was smaller than that circle and only half filled it for example, the flash would fire twice as bright to get the same 'average' that it looked for. Here is an example of this in action.

When the subject is large enough in the frame exposure was good.

Now look what happens when the subject is smaller in the frame, to get the same reflective value from the subject the flash needed to fire much brighter to satisfy the requirements of the average reading it was looking for. It ended up totally blowing the highlights which were in fact the entire subject, by doing this it manages to get an average grey for the whole centre of the frame. In a way this system is like a large spot meter for flash.

I get similar results from the newer D5200 so it appears that even though the metering area has changed TTL flash hasn't gotten all that much smarter though once again it depends which camera body you have and how much it cost. I've had comments from people with professional cameras that TTL and TTL-BL flash both give “perfect” results for them in all situations. There's another variable to think about, same year, same age technology, but different processor in the professional bodies.

One major difference between the older flash modes and the pattern/TTL-BL/ETTL is that plain old TTL doesn't take the ambient into account. All it knows is that you are at a certain aperture and iso and it will produce an output based on the assumption that it is the only light source. If you already have the ambient correctly exposed and use TTL flash you will end up with twice the brightness you need, which is why people accustomed to using TTL flash use exposure compensation. If you have an F2.8 lens it will measure the light at F2.8 [because no matter what you set your aperture to it stays at its widest until you actually take the picture.] Then it will base its output on your selected aperture. So if you have set your aperture at F5.6 for example that would mean you are letting in ¼ of the light of F2.8 so as you take the picture the lens closes down to F5.6 and the flash would fire 4X brighter than what it decided would be the right exposure at F2.8.

When to use TTL flash: basically it is good for when flash will be the only lighting in the scene but if you are accustomed to how it meters and the results it produces there is nothing wrong with using it all the time along with exposure compensation for any situation where you want to add flash to a scene. There are no hard and fast rules for any particular mode in photography because all that matters is the end result. You may see two amazing pictures side by side. One photographer says “I used manual exposure and a hand-held light meter and manual flash settings”. The other photographer says “I was in Aperture priority mode with exposure compensation set to -0,7 for ambient and flash dialed up to + 1.3 to counter-act the global exposure compensation and add some light because the subject had white in it which would have caused under-exposure.” Who is shooting the right way? Both of them because they both knew how to use their settings to achieve their desired result. There are a lot of people who could try both methods and still not get good results because they don't fully understand the basics of either.

Now we delve deeper into the mind of the camera and flash as metering tries harder to think for us, which can be both good and bad, depending on whether it is thinking what we are thinking.

Pattern/TTL-BL/ETTLII flash metering

No matter what you call it all the manufacturers are competing to see who can deliver the most accurate automatic flash exposure to users. Always keep in mind that these modes are very much like pattern/matrix metering in your camera and change or get tweaked with each new model that is released, which is sometimes for the better but sometimes just plain frustrating as things no longer work the way they used to, and you have to once again adjust the way you approach the subject. From here on I will refer to Nikon's TTL-BL mode because that is what I used for all my tests. BUT: much of what we discuss applies in one way or another to every camera brand, as they generally use the same variables to calculate flash exposure, so while we are now discussing the way one particular brand applies these variables everyone can benefit by learning this because it is most likely to tie in one way or another with the way their particular camera works.

Distance information is a biggie with TTL-BL. Because of this the built in flash is often more accurate than an external flash using bounce mode because it uses distance info quite strongly, assuming that it will always be pointed straight forward. Notice how exposure changes in the same scene with a simple twist of the focus ring on the lens and with no other adjustments having been made.

The only variable that changed here was distance information from the lens. When we focused closer the flash output decreased and when we focused further it increased. This is one of the variables programmed into the TTL-BL algorithm.

Setting flash output based on distance is a very accurate way of achieving correct exposure, as long as you know there is nothing in front of the flash to diffuse the light [and weaken it], and the flash is pointing right at the subject [which is generally how the built in flash is]. But since this is based on assumptions the manufacturers can't bias metering too much toward distance info. Imagine setting your guide number to 3m and you get perfect exposure on the subject 3m away, but then you place a diffuser in front of the flash – suddenly the image will be darker as the diffuser wastes light in all directions.

However, when we look at the picture of the lens below and the row of numbers regarding distance at the top we see that the distance the focusing moves from 1,5m to 3m is the same as the distance from 3m to infinity which means that beyond 3m we can't rely too much on distance info from the lens, the distance info reported to the camera is no longer as simple, and accurate, as the difference between 1,5m and 3m.

We also need to take into account that with wear and tear a lens may occasionally report the wrong distance which will mess with the final exposure. Add to this the possibility that a 3rd party lens may not give the right info. This happened with a batch of Tamron 17-50mm F2.8 lenses a few years ago, they caused TTL-BL to over-expose because they were giving the wrong output for the distance that the lens was focused on. This is mainly a problem with regard to direct flash, because the flash head has a little switch in it that tells it when it is moved from the forward position [as with bounce flash], then it assigns less importance to distance info because it no longer knows how far the light has to travel after bouncing off whatever it is pointing at. At this point it relies very much on reflected reading. Of course as with computer operating systems this changes with different bodies.

My interest in analyzing TTL-BL arose from reading discussions [read “arguments”] on the forums as to how it worked. Much of the confusion was caused by the fact that the manual's description made very little sense and I was informed by a person from Japan that it wasn't a translation issue as his manual also made little sense in Japanese. Also the way it worked changed quite drastically at one point where it was no longer only for back-lit situations. I was informed by someone who apparently worked on the electronic chip for TTL-BL that even though the “BL” was originally designed for flash in Back-Lit situations it actually stood for “balanced fill flash”. Whatever! It used to be for situations where the sun was behind the subject, hence the addition of distance info from the lens in case the sun messed up the pre-flash reading, then the camera could fall back on the distance info from the lens and get a good enough exposure from it. But my thoughts are that Nikon soon realized they had some very useful technology, like the distance info, that they were confining to a rather small area of flash photography, and decided to introduce it to all aspects of flash photography. During another back and forth “discussion” it was agreed that with the earlier digital cameras, before the D200, TTL-BL was only for back-lit situations and if you tried to use it in the dark then the flash would balance the subject with the background – which was 'darkness' and under-expose the image.

The description in the manual stated something like this “The flash output level is automatically adjusted for a well balanced exposure of the main subject and background”. This had many people thinking that the flash would also try to light what is behind the subject and in the process would over-expose the subject. What it should say is “the flash output level is automatically adjusted for correct exposure on the subject while taking the ambient [background] lighting into account”. That is a more accurate description of how it actually works.

In back-lit situations this means that if a person has the sun behind them and their whole body is shaded then the TTL-BL system evaluates the well lit areas and then adds flash to the subject to light the shadows and make it the same exposure as everything in sunlight. With that in mind imagine what happens with the system at night when everything is really dark – it would then, in theory, evaluate the entire scene and see that it is under-exposed and decide to fire really weak so as to keep the subject the same exposure as the background – under-exposed. This is how TTL-BL used to work.

But with the D200 as the first updated body, and from then on, the camera is programmed to “lie” to the TTL-BL system when it is used in darkness and instead of telling it to balance flash with the ambient [which would end up in under-exposed flash due to under-exposed ambient] it tells the flash system “Hey, the ambient is perfectly exposed [nudge nudge, wink wink], do the same with the subject!”. This was verified in a discussion with a technician working on the modern TTL-BL chips.

It has reached the stage where the older style TTL flash is not an option in many cases – the built in flash may be set to “TTL” but it in fact works as TTL-BL flash using distance info from the lens, metering off the focus point diamond and backing off its output depending on how well the ambient is already exposed. It's the same with wireless flash, one author warned against the dangers of using TTL-BL based on the manual's description of how it would try to light the background as well,[“The flash output level is automatically adjusted for a well balanced exposure of the main subject and background”], and over-expose the subject, while in fact the wireless flash mode that he praised so highly was actually using TTL-BL metering. With Nikon's wireless flash modes even though the flash head says “TTL” on it, it is in fact metering in TTL-BL mode. It also backs off the same way TTL-BL does when the ambient is correctly exposed so it appears to be using a similar program to TTL-BL less the distance info of course – because it doesn't know how far the flash is when it is used wirelessly and mounted somewhere else, so what good will distance info from the lens do?!

So how does this work then, taking the ambient into account to determine its output? When I got my first external flash on an old film camera the very first thing I did was aim it at the bright light hanging from the ceiling and take a picture. I then wondered “why did the flash fire, there was more than enough light?”. That was my first lesson in flash metering, plain old TTL flash did not care what other light was in the scene because as far as it was concerned there was no other light and its job was to provide it all. TTL-BL is the natural advancement on that system, it knows what your meter is reading in your camera. For example the D90, if you are using manual mode and adjust your settings so that the meter shows “-1”, or below, for ambient then TTL-BL will assume it is the sole light source and fire at the power it would need to light the scene in total darkness. If however your settings have the needle at zero, TTL-BL 'sees' this and backs off to “-1,7” stops of the exposure it would need to light the scene, in other words almost down to ¼ of what it would have fired at if it was the main light source. Then it is acting as “fill-flash”.

So for test purposes we need to devise a method of measuring the flash output with todays cameras that fire a pre-flash just before taking the picture, because this can make it difficult to get an accurate reading from a flash meter since the pre-flash is always the same output and will interfere with the reading of the main flash.

Using a flash meter and rear-curtain flash we can achieve this by having the flash meter covered for the pre-flash firing before the exposure and then, if the exposure is long enough like 2.5 seconds, we can uncover the flash meter after the pre-flash so it can measure the output of the main flash when it fires near the end of the exposure.

TTL flash decided that an equivalent power for F9 was necessary in this situation which is the same power that TTL-BL chose when the shutter speed was at 1 second (giving us more than 1 stop under-exposure). But when we chose a shutter speed that exposed the ambient correctly TTL-BL backed off to -1,7 of what it would have needed to expose the scene correctly were it the only light source.

TTL flash fired at the same power regardless of where we had our ambient settings, even if we had the ambient totally over exposed TTL flash would still fire at a power of F9 in this situation because its job is to light the scene all on its own and it doesn't know or care what you do with your other settings. This is a reason why many people who still prefer shooting in TTL mode, mainly because they have been doing it for years and are comfortable with it, will back off the flash output by dialing in flash compensation when they have the ambient correctly exposed. There is absolutely nothing wrong with using that method either if it gets them the results they are after.

At this point we can talk about another “discussion” that was taking place on the forums. Some people were saying that when they use CLS [Nikon's “Creative Lighting System”] with several flashes in wireless mode the flash output would sometimes change through the simple act of moving a focus point. This was hotly debated, though it is actually possible when using matrix metering because matrix metering is “3D” in that it can change its mind as to what is correct exposure simply by where the active focus point is and what 'plane' that is in the scene.

Watch the exposure in this breath-taking scene change. In the first image with wireless flash being used, and matrix metering, the camera meter deemed the exposure to be “-0,7” for the ambient, not quite dark enough for TTL-BL to take over the exposure, so it was still at “-1,7” of correct output.

Nothing else was touched but the controls for the focus point, as it was moved to the black body of the camera, and then the picture was taken. As the camera focused on the black object matrix metering decided that it was the new subject and concluded that we were now at “-1” for ambient exposure. TTL-BL 'saw' this and fired brighter!

Now realistically I can't really say that “TTL-BL “saw” the meter was at -1” because quite possibly it's rather a matter of “the camera knew its meter was at -1 and “told” TTL-BL to assume full output” - either way it shows that TTL-BL responds to what the meter says, which affects the final output of the flash.

Another way this affects TTL-BL flash is regarding the metering mode you choose, because that determines what the meter will show and how TTL-BL will therefore react. Let's take a scene where we know centre weighted metering will give very different results to matrix metering. My model “Stinky” [who often gets the response “Oh no not the creepy doll again!”] happily poses for us. Centre Weighted metering is happy with the exposure in the middle of the frame even if it means our subject looks a little dark – CW metering only cares about the average it is programmed to achieve.

TTL-BL fired at “-1,7” because the scene was correctly exposed. Now we see what the simple act of changing the exposure mode does. Matrix metering watches your focus points and if the active focus point is on Stinky it says “If that is our subject we are 2 stops under-exposed regardless of how blown out the sky would be at that setting! Hey TTL-BL flash, take over please because you need to light the subject for us!”

None of the settings were changed besides switching to a different metering mode and the flash fired nearly 4 X brighter.

This demonstrates several things.

Matrix metering meters according to the active focus point and is not confined to the centre of the frame, it can “choose” where its subject is.

TTL-BL can also work with a subject that is off centre, like matrix metering. It is not strictly “centre weighted” as with TTL flash especially since it has the added advantage of distance info from the lens.

With exactly the same settings for ambient two different metering programs can give very different TTL-BL flash results to each other because TTL-BL is “watching the meter”.

Starting to see a pattern? TTL-BL is starting to look very much like “matrix metering for flash”. Have a look at the comparisons between matrix metering for ambient on the D90 and TTL-BL flash for the same scene. Two sets of images, one taken with the available light exposed according to matrix metering and the other taken with the ambient totally under-exposed and only TTL-BL flash lighting it.

What really made this stand out is that the D90 has some 'quirks' in its metering, such as the subject going darker when it is off centre, and metering affected strongly by the introduction of something white under one of the outer focus points. This originally caused several comments about TTL-BL and under-exposure which changed with the introduction of newer bodies. This seems to be strong evidence that TTL-BL actually hijacks the matrix metering program and pattern to do its calculations, which would actually make sense because if they put so much effort into improving matrix metering they may as well take advantage of that technology and let the flash metering system use it. Disclaimer: I have no physical evidence that this does in fact happen – only what I can surmise from the results below.

The first row of images were ambient only while the second row were flash only. Now moving the subject to the side should either keep exposure the same or perhaps make it brighter because of the darker background. Not so with the D90, it actually decreases the exposure with matrix metering as does TTL-BL flash. Now some people may say “Perhaps it is matrix metering doing that to it when you use flash!” but in the images with flash only CW metering was selected for the ambient, matrix metering was not used! :)

Why would it go darker when the subject is off centre? I suppose that's like asking why was windows Vista released? Who knows, it just does and had the beneficial side effect of revealing something about the relationship between TTL-BL and matrix metering.

What about wireless flash? What few people realize is that when they are using wireless flash and it says “TTL” on the flash head they are actually using TTL-BL metering [less the distance info which doesn't count when the camera doesn't know how far away the flash is from the subject]. This is how wireless flash behaves on the D90 in the same situations.

This varies between camera bodies and with the newer bodies I have done the same tests and seen that Matrix metering has changed to the same degree that TTL-BL metering has.

Coincidence? I think not! …............... Ok, moving on.

There are many variables involved with automatic flash modes and we could spend weeks analyzing them, but due to the fact that each new body seems to bring out a new program for automatic flash it would be more of a mind exercise that is interesting for 0.1% of the population but a pure waste of time for someone simply wanting to go out and improve their photos by learning how to use flash. Analyzing these variables has taught me that:

Someone who learns to use flash in manual mode never needs to worry about changes in software of the next model of camera or flash. But due to the variables involved, such as distance from subject and what modifier is being used which can greatly affect the result, I personally only use manual flash when I have lots of spare time and the option to re-take a photo if it doesn't look right. When the action speeds up I know that the auto modes will be less likely to make a complete mess of the exposure than if I were to use the wrong manual setting, like when you're photographing the bride 4m away and something really interesting happens behind you and you swing around and take a shot of a priceless moment 1m away and realize your flash exposure is now 16X what it was for the bride.

The old TTL flash does not take the ambient into account, if you're accustomed to using it and know how to work around this then by all means use whatever works for you.

TTL-BL/ETTL/Pattern flash is the auto mode that does the most thinking for you. Depending on your model of camera and style of shooting this can be good or bad. For the vast majority of photographers who don't want to spend too much time analyzing a situation these auto modes will take the ambient lighting into account, read the distance info from your lens, decide how relevant the distance info is based on whether the flash head is pointing forward or not, take a reflective reading off the subject using the pre-flash, adjust the white balance based on the power of the flash [if “auto” wb or “flash” wb is selected] and produce an image that generally errs on the safe side. This means that you will sometimes get an under-exposed flash output when flash is the only light source, that protects the highlights, which you can always brighten up later. It is not ideal to have to brighten images but it is a pure waste of time and energy to have over-exposed images. Most of the time we hope to be adding flash to the existing ambient, which should already be set at the exposure you want, so the ambient won't be affected by a cautious flash metering system. Besides, many photographers prefer a more subtle flash in their images so they don't “look flashed”.

Based on these conclusions my advice would be to a.) Learn how to use manual flash if you have time to set up the image or simply to have a plan-B if the auto mode frustrates you. b.) Use the auto mode that works for you along with exposure compensation to achieve the result you are after when time is not on your side.

How reliable are the auto modes? Consider this, the SB800 flash has a switch on the head that is pushed in when the diffuser dome is fitted.

What is the purpose of this switch? When you are in the old TTL mode it makes no difference, because the metering is working purely off reflected light, but when you are in the fully auto TTL-BL mode it actually makes the flash fire hotter to compensate for the diffuser dome which is wasting light in all directions. Why is this significant? Because it shows that the auto mode is far from perfect if it can't work out for itself that there is less light in an image from its reflected reading. It must work on assumptions as well or else why does it need to be told something is in front of the flash?

Having said that I have found that exposure is more accurate when this dome is on. Here is a comparison of two images testing the effect of the diffuser dome with direct flash, both shot in TTL-BL mode to show the difference.

Realistically we could spend ages discussing the many different metering options and variables, and much of what I have discussed in the last section of this chapter is simply brain exercise for those who wish to understand the deeper aspects of flash metering programs. Hopefully it also serves as a guide/warning for everyone to understand that there's a reason why there are so many options – because none of them are perfect and they all have their quirks, so please don't fall into the trap of listening to someone who suggests that there is one mode and one compensation setting for all situations!

Next we move on to a chapter that discusses the raft of options out there ready to entice you to part with your money to “get professional results!”.... Flash Modifiers!

7 Flash modifiers and accessories

Fishing lures are designed to catch ….......... fishermen! Ok, they are also designed to catch fish but the main reason they are mass produced is to make money by selling them to fishermen. Flash accessories are the same, they are mass produced for the sole purpose of making money from whoever will buy them. And there are all sorts of accessories you can buy that make you look like a dork or like you have a mini toilet bowl on top of your camera. I've been caught many times, buying gear that looks cool but eventually never gets used. Of course many of them do have their uses so the best thing you can do is gain practical knowledge of what the modifiers do and where you would need them. You may be surprised at how few you actually need!

Just remember, you will have to carry it all as well!

So what are we after in a light modifier?

Quality light depends on “Relative size” and “Diffusion”!

Why “relative” size? Well look at the sun for example [no don't look at it! You know what I mean don't you?] The sun is the largest light source within 8 light minutes of our planet, but if you stretch your arm out it's about the size of a marble between your fingers. Try it with the moon, they're the same size right? Actually the moon is much smaller than the sun but is capable of blocking it out during an eclipse because it is closer but “relatively” the same size because of the difference in distance. So relative size depends on the distance from your subject. Diffusion is the other important aspect of quality light. The sun's rays come at us parallel to each other because it is so far away that, understandably, any light that is not heading directly for the earth finds somewhere else in our galaxy to land. This means that parallel light, more commonly known as “hard light”, is not very flattering on a subject. There is a strong defining line between the light areas and the darker areas of an image as opposed to the type of light you get when the biggest diffuser we encounter, an overcast day, gives us light that 'wraps around' our subject to the point where it is hard to differentiate between the areas that show the direction the light is coming from and the areas that are on the 'darker' side. Let's have a look at a few flash modifiers that demonstrate this.

Reflectors can be very useful not only for reflecting sunlight but also for reflecting light from a flash. Many of them also have the option of removing the white/gold/silver cover to reveal a diffuser which can also help to create really nice light when a flash is fired through it. Their biggest disadvantage is that they either need more accessories to hold them in place, or an assistant or two to help you, which is why I personally steer away from using them, however I did take some sample images to show how they could be used. Here is an example of lighting that is not ideal and we will assume the ceiling is the wrong colour/height to bounce off and the walls are too far away.

It's possible to hold a reflector over your shoulder, perhaps let an assistant do that for you if you have the luxury of one [Referred to as a “VALS” or “voice activated light stand” in the profession], and then you can angle the flash head towards it and bounce your flash off of it.

In this example the face is totally shaded and the nose actually looks like it has dirt on it due to the shadows.

Once again we have several variables to play with. Do we expose the ambient correctly and simply add flash as a fill?

Or under-expose the ambient by two stops and let the flash light the scene.....

And of course there are many options between those two as well for you to experiment with.

Another option with many reflectors is to take off the outer layer to reveal a soft diffuser in the centre that can be used to either diffuse bright sunlight and prevent it from causing bright patches on a subject outdoors, or to provide “window light” indoors. This is what our subject looks like indoors with overhead lighting.

To totally take control of the lighting all we have to do is choose a fast enough shutter speed, and perhaps a lower iso, to under-expose the ambient. Then we place a large shoot-through diffuser in the doorway and fire a flash through it using a wireless trigger.

And we have created “window light”.

The softbox is a popular tool used in flash photography. It is reasonably cheap, comes in a variety of sizes, and can make your images look very different to straight flash lighting. Depending on the metering mode you are using, if you're not in full manual, it may require various degrees of flash exposure compensation to allow for consistent results. [Due to the flash metering system not knowing you are wasting some energy on something that only lets through 50% of the light]. Here are some comparison images. Even with the softbox mounted on a flash facing directly forward the results improve dramatically, depending on your distance of course – as you get further away the difference between the two images will decrease.

If we move the softbox [and flash of course] to the side we see a more dramatic difference in the results. Look at the difference in size between the two light sources.

Even at a quick glance the difference is obvious, and when we look closer we see it's because we have more pleasing skin tones and a more gradual dividing line between the lit areas and the shadow areas. Look particularly under the chin in the following images.

Look at the very strong dividing line between light and dark on the image with plain flash.

Now look at the image taken using the softbox, where does the flash stop having an effect? Good question. There is a very gradual transition from the lit area to the shadow area which makes the light more pleasing.

Theoretically a softbox from a distance would give harsh light because it gets relatively smaller as its distance increases and eventually looks the same size as the flash head does when it's close up. But when we try to demonstrate this the whole room lights up since the softbox, being further away, spreads more light which bounces off other surfaces and so the flash has to fire much stronger than if it were closer. [remember inverse square law?] This results in reasonably soft light due to the bouncing light.

However if the subject were outdoors with nothing for the light to bounce off we would not see that extra light bouncing onto the subject from all sides and the lighting would be harsher, but either way in both situations if we look close-up we are back to harsh light, because even though the flash has a softbox on it, the relative size is pretty small because of the distance.

On a side note I have read that hard light seems to work better for bodybuilders so keep that in mind as well – sometimes you can use hard light to convey a different mood. “Perfect” light can mean different things in different situations.

The ceiling and walls are the quickest and easiest light modifiers available to anyone in a room with a white [light coloured] ceiling and perhaps walls. It is probably also the most under-estimated light source of them all because people seem to feel they have to spend money on something to gain an improvement in their images. Here's an image taken using wireless flash to demonstrate the size of the light source we get with bounce flash. This was a particularly low ceiling so it is perhaps the most efficient surface to bounce from but also the smallest light source we will get using bounce flash, further is better but also keep in mind the fact that the flash has limits to its power. The wide diffuser was pulled out to spread the light as much as possible. There is one fairly small hot-spot in the centre and then a wide area of softly spread light that eventually makes for a pretty large and effective light source.

Umbrellas are a cheap alternative to the softbox and handy to have when there is nothing to bounce the light off.

There is a large selection of very reasonably priced umbrellas available out there. They are not quite designed for windy days but still have many uses and are easier to work with in a variety of situations than a soft-box of the same size. The reflective umbrellas with the silver or gold surface have never been my style. This is partly due to the fact that, even though that they are made to reflect pretty well, this can make for a slightly harder light partly due to their design and the working distance they have to be at which can become a problem. The shoot-through umbrellas allow you to get much closer to the subject with a softer light output and are a favourite of many photographers on a budget. Compare these two images where a rather versatile umbrella has the option of a silver reflective backing going over the back of the white part to reflect light forward or, with it removed, provides the option of a plain shoot-through umbrella. Look how much closer we can get with the shoot-through option and how much softer the light is. Also take note how much bigger the light source is in comparison to the subject in the upper right of the image.

With the backing on it we have a “satellite dish” style of light on our subject but the design means that we have to have the light source further away to accommodate the handle. This means the light is not quite as soft because of the distance factor and the fact that the light source is relatively smaller and we have more direct light. The question is whether anyone would notice that difference in a side-by-side comparison. Again, look at the upper right image, the light source does not look as big in comparison to the subject as in the previous image.

One would also expect the final output to be weaker because of the distance and the inverse square law, but is it? With flash power set manually to 1/10th a comparison shows that the reflective umbrella actually gives us more light than the shoot through option because it is “focusing” the light from the flash onto the subject while the shoot-through style is much closer but wastes a lot of light in all directions.

The Stofen diffuser is generally meant for spreading light in all directions when shooting indoors. Outdoors it simply wastes a lot of energy since there is nothing to bounce off, and it is the same size as the flash head, which means no advantage regarding the size of our light source. Some flash heads have a little switch to tell them when the diffuser is on which makes them fire hotter to compensate. This does not always result in the same exposure as direct flash – just learn what difference it makes and what compensation to use if you're not using manual flash.

The ring light modifier has become my tool of choice with flash modifiers. It can be slightly awkward to use sometimes but once you have the focal length you want and all your settings have been adjusted it is quite nice to work with. Even though we try to avoid aiming light directly from our camera position it is something that, when the light is nicely diffused, eliminates just about all shadows. Granny with the wrinkles will love the effect, and I had a model tell me that she absolutely loves the ring flash because it smooths out all blemishes. It may not gain a lot of praise from other photographers if the lighting isn't more creative but it certainly helps to have a smiling model and granny in a good mood.

In this image there is some shadow on the right of the subject. This is because of the imperfect design of the diffuser which means it does not diffuse the light totally evenly and the fact that I was holding it slightly sideways. You can use this to your advantage if you want a little more shape to you lighting while flattening out wrinkles at the same time.

Remember in the early chapter when catch-lights in the eyes were mentioned? The ring flash creates donut shaped catch-lights which some love and others hate.

This extension cord is what makes it possible to shoot with the flash off the camera, besides the many wireless options, and it is very reliable too. Keep in mind though that your metering system doesn't know the flash is off the camera when you use this cord since all the wiring pins are still connected to the camera, and will assume that its distance from the subject is what the lens distance info suggests, so you may need to make compensation adjustments for this at times or shoot in the old TTL mode which does not use distance info. Adjusting the flash head to point straight up relative to the body will generally trip an internal switch which reminds the camera not to worry so much about distance info because it thinks the light is no longer pointed directly at the subject.

The ring flash can be used like a softbox or umbrella as well by simply holding it at arms length or closer to the subject. This makes it a very versatile tool.

Within seconds it can be moved to the ideal position and a photo snapped before changing its position again for a different effect.

Compared to an umbrella this device can be mounted on a tripod for a reasonably wind resistant light modifier. With cameras that can control a flash in command mode it is easy enough to trigger especially because there is nothing to block the signal as with an umbrella or softbox. If you use a wireless trigger it becomes a potentially costly balancing act if it decides to break off at one of the mountings and then you will need to think about securing it in another way.

Occasionally you may want to use wireless flash in bright sunlight and not everyone has the option of wireless control at their disposal. Here's a trick for using a cheap optic trigger in the sun. Normally the sun is too bright for an optic trigger to work because the bright light prevents it 'seeing' the flash but if you tape a tube on it and face it directly at the master flash it will work in sunlight. Looks 'factory' doesn't it?

The last word: When I was into fresh water fishing back in South Africa there were some fishermen who were passionate about it and had large fold out trays on a stand with 40 bottles of corn of various flavours, and they would have a notebook and write down the two different flavours they had just cast in on the two separate hooks so that they could tell which the fish preferred, on that day with those weather conditions, temperature, time of year etc. etc. Or was it just that the fish found that piece of corn first and would have eaten both? I was talking to an elderly man, who sold fishing gear and bait, and he was honest with me because I didn't shop for bait since I made my own. He said to me “Do you think a hungry fish will swim past strawberry flavour because that's not its favourite? Will that starving fish think 'I don't feel like strawberry today, let me swim over to the other fishing lines and see if they have cherry flavour rather'?”. He then went on to show me the 'latest' flavour in bait. There is a large dam in South Africa called the “Vaal” dam, and one of the top selling baits was called “The Vaal dam special”, which was a mixture of flavours that supposedly worked really well with Carp. As he proudly produced a bottle of “Vaal dam special mkII” he said “This is selling really well at the moment and people tell me it's much better than the original version. What they don't know is that it's exactly the same stuff with a different label on it, we sell twice as much that way.”

I suppose what I'm trying to say is “Beware of the flavour of the month!”. It's all about the size and direction of the light source and its diffusion. Don't think that you need to rush out and buy the “Jong Dong mk VI” just because you saw a really nice photo taken with it, of course they paid a professional to take that photo to make it look good or just downloaded a nice picture taken with a shoot-through umbrella to help sell their product. Look at the light it creates and ask yourself whether it is any different from what you could do with a softbox or bounce flash. Will anyone else see the difference? I recently posted a picture on Facebok of an elliptical exercise machine we bought for our 'home gym' and the first comment I got was “We've also got a clothes drier like that!” Think about how much you will use something before parting with hard earned cash for it. Will you use it or will it be a “clothes drier”?

8 Manual Flash

Manual flash has its advantages and disadvantages. If you have enough time to go manual and experiment then all is well, but if time is limited and the variables like distance and lighting are changing fairly quickly then manual can result in some serious mis-haps. Auto flash isn't always as consistent as we would like but when you don't have the luxury of time to experiment with it then it will give you more reliable results than manual flash with changing distances. For example if you are at a wedding shooting the bride walking past 4 metres away and have your flash set to the perfect output for that distance and suddenly something really interesting happens to your side 2 metres away and you swing around and take a picture your flash will be 4 times as powerful as it needed to be. [Inverse square law, half the distance = 4X the power]. In those circumstances automatic flash will give you more reliable results. But for situations where you have a constant distance and your subject will be around long enough for you to make several adjustments then you can't beat the consistency, and comfort of having the knowledge of working with manual flash. Once you have found the right setting every picture will have the same exposure at that distance and in those conditions.

At this point we will discuss using an older flash in manual mode, including the ever important trigger voltage of the hotshoe pins. Remember the earth pin and trigger pin on the foot of the flash? Well some of the older flashes had very high trigger voltages that were fine to use with an old film camera, that had metal contacts to switch the flash rather than an electronic circuit, but put them on a modern digital camera and you could fry the electrics! With the advancement of modern electronics many newer flashes only have a switching voltage around 6 volts, and most compact cameras with a hotshoe are only designed to handle 6 volts. Put 600 volts on that and things could go Pop! [Get a video if you try it!]

Obviously then the first thing you need to do with an older flash [any flash you are not sure of for that matter] is to measure the trigger voltage. You do this by placing the black lead of a multimeter on the earth contact and the red lead on the trigger pin [I came across a freak flash that was the other way round once] and see what voltage those pins are when the flash has been turned on and is fully charged, usually indicated by a red light coming on.

It turned out that this old flash had an exceptionally low trigger voltage of 5 volts. This is quite rare with older flashes.

There is also a good online reference at http://www.botzilla.com/photo/strobeVolts.html where the author has collected data from various sources so you can check before you buy an older flash whether it will be safe with your camera – measure it yourself as well, there is the chance that someone measured wrong or the voltage changed between two different 'series' of that flash. My Nikons can handle 250 volts so they are pretty strong in this area, check the specs of your camera before putting a flash on it that you are not sure of.

Looking at the back of the flash we have a scale showing ASA [like iso], aperture and working distance. The red ready light is on in this picture showing that the flash is charged and ready to fire. We put it in manual mode because auto mode will not “talk to” our digital camera. That white button at the base is the 'test' button that fires the flash by joining the centre pin to the earthing contact.

Realistically the scale on the back is a guide to the aperture and iso we are working at and what distance we should be from the subject at those settings. Using this flash in manual mode would mean accepting the one power it fires at, which is not adjustable, and using your camera settings to control the exposure in the final image.

A slightly newer flash like the SB26 has that scale on the display for us. Let's take an SB26 and put it in manual mode and see if we can work out how to get the right flash power without any information like that. After all if we are using a modifier to make the light more diffused than all those settings go out the window anyway, because the light reaching our subject will no longer be what is assumed by those settings.

The camera is set at 1/200th sec to kill the ambient indoors – this gives us “flash only” in the resulting image. We're at iso 200 and F5.6 and about 1.5 m from our subject so we choose ¼ power. Can you see a problem with this setting before reading further?

The flash head is assuming we are using iso 100 when in fact we are at iso 200. We are also less than 2 m away from the subject.

When we take the picture it is badly over-exposed. This gives us two options: Either change the flash power or the camera settings.

A logical approach, if you have chosen your aperture for a reason, is to decrease the flash power, so we drop it to 1/8th. That way we also get longer life out of the batteries because we're now using half the power we were before. Look at the distance it gives us now.

This knocks the exposure back and recovers most of the highlights, but it's still too bright.

Taking the flash power down to 1/16th does the job. It may say we should be 1 m away but we're also not at iso 100, we're at 200.

Now we're well on our way to getting a good exposure.

Our other option was to close down the aperture rather than decreasing flash power. We have gone from ¼ flash power to 1/16th, halving our flash power each time. This results in two stops less power. If we were at aperture f5.6 and wanted to reduce the incoming light by two stops what would we do? Go to f11 of course which lets in ¼ of the light of f5.6.

So 1/16th flash power at f5.6 gives us the same exposure as ¼ flash power at f11! The histogram may not look precisely the same but keep in mind the imperfections involved. The aperture blades may not have been at exactly f5.6 and f11 due to the mechanical side of the lens and camera not being perfect, and also the flash may not fire at exactly the same power each time it says it is firing at ¼ power – nothing is perfect in the system. Back to ¼ power, close the aperture to f11.

After all those warnings on direct flash not looking good I will mention that this was purely an exercise in learning manual flash settings. Of course bounce flash is better for two reasons: It gives much more pleasing light and it almost does away with the distance issue (the light spreads out and the ceiling is usually the same height for all the photos inside the same room). In the above example those final settings would only work at that exact distance. Half that distance would make it 4X as bright and twice that distance would make it ¼ the brightness so we would have to keep changing our settings with direct flash. We were at f11 and ¼ power for the last image. Let's simply aim the flash head upwards and bounce the light off the ceiling to make it more diffused.

The lighting looks much better but now it's too dark!

Let's open the aperture to f5.6 again and make it 4X brighter.

That's getting better!

Now we can walk around taking pictures knowing that our distance to the ceiling is the same anywhere in the room and the distance from the subject is no longer such an issue. Our exposure will be pretty much the same for any picture in that room with bounce flash. Direct flash would be a nightmare of changing settings each time you were a different distance from your subject.

From this little exercise we can see that if we have the option of adjusting flash power we can decide on the aperture and iso we want to work at, take a test shot, and then adjust flash power until the image looks right.

OR: If the flash power can't be adjusted [or is already where we want it to be] we can either adjust the aperture or the iso, both of which will affect the exposure of the flash.

I would not advise using manual flash in a fast moving environment. However I would advise learning how to use it, as it will greatly increase your understanding of the subject. One day it could also come in very useful if you're suddenly stuck with a flash that can only work with manual settings. Or perhaps you are using wireless flash with your subject being quite small in the frame so TTL mode has trouble reading the reflected light. Rather have it and not need it than need it and not have it.

On the internet forums you will often read statements like “Shutter speed controls ambient, aperture and iso control flash!”. That is a partial truth actually bordering on being a silly statement because aperture and iso also control the ambient.

Basically what they are trying to say is that if you want to only adjust the ambient then you can do that with your shutter speed without affecting flash output.

9 Balancing with ambient

Usually the biggest step in understanding flash is comprehending the fact that you are dealing with two exposures in one when you use flash in a scene. Probably the best way to understand it is through an image where you know flash is not having an effect on a part of a scene, like “environmental portraiture”. In the following image taken at night an exposure of iso 3200, F2,8 and 30 seconds was needed to expose the landscape lit by the moon. At the beginning of the exposure the flash fired and lit our two subjects, then they walked away allowing the background to show through them where they had been standing. This is a very obvious example of two exposures in one. One ambient exposure to get the background to show and one flash exposure to light our subjects.

A common application of balancing flash with ambient is indoor photography including real estate photography. Have you ever looked at photos of a house for sale and though “What a dark looking place!”? The reality is that quite often someone will do a quick walk through the place snapping away to get the pictures done in a hurry with no thought to lighting, and they are either going to end up with the inside looking very dark or the outside looking very bright. So you're paging through listings of houses for sale and you keep in mind this sobering fact: “A happy wife is a happy life”, and even though you daren't tell her that her place is “bare-foot in the kitchen” [let's leave out the 'and pregnant' part] you still keep in mind the fact that, to the wife, a nice kitchen and bathroom are as important as a decent garage is to you. You like the look of this one house in particular and check out the kitchen photos and the first thing you think of when you look at this image is “Oh no, it's sooooo dark! The wife will not be happy in that kitchen!” The bright light from the window made the camera's meter under-expose the interior.

Basically the estate agent “saved money” by taking the pictures himself or paid his cousin's kid $10 to take them for him. Next you look at another listing and without realizing it is the same house listed by the owner this time [whose camera metered differently] you think “Oh noooo that is even worse, it's so bright outside that window she will have a constant headache!”[ definitely not good!]

Imagine if the photographer had exposed for the sunlight outside to make it look less harsh and then used bounce flash inside to light the kitchen.

Now it doesn't look too dark inside, and the outside sunlight doesn't look too bright either! Now all I can hope for is that my wife doesn't find out I used these pictures without letting her 'make it look tidy first!

When it is relevant to the subject we will discuss better quality light but when we are discussing technical matters my model “Iris” will be the subject to avoid “distractions” and biased opinions based on how attractive the subject is. I once saw a thread on a forum where someone had a girl in a bikini on an old sofa on the beach. The comments from the male audience were nothing but praise and “I wish I could take pictures like that!” while basically the photographer had broken all the rules and used direct flash from the camera's built in flash and auto settings – but onlookers [Ooglers] were prepared to overlook those 'minor technicalities' based on the appearance of the model in a bikini.

But balancing with ambient is not only about the outside lighting – we also have to balance flash with indoor lighting. Here is an example, first image is ambient only, no flash. Auto-wb often doesn't do well with yellow toned [incandescent] interior lighting – a reason to do a custom wb setting unless you're one of those people like me that forgets to change it when you move to another location. Besides the fact that we sometimes want to add light to prevent motion blur, in some parts of the room the model would have darker shadows around her eyes due to downward lighting which is a good enough reason to use flash. Let's assume our model is working out on the elliptical and we can't use slow shutter speeds because of the motion blur. In this image we were at iso 100, F3.5 and 1/15th sec.

The room light casts a shadow to the side and adds a bit of a yellow glow to the ambient. So we turn on the flash and what does it do? It suddenly assumes it is in full control of the situation, increases the shutter speed to 1/60th which is often the shutter speed that cameras are set to as a minimum speed for flash, and the ambient goes darker and we have a nasty shadow behind the subject.

Then we decide to use bounce flash with the white diffuser dome to spread the light a little more and make it less direct. This improves the general apearance of the background and in some cases may suffice for our needs.

What if the ambient lighting is adding a 'mood' that improves the scene? Perhaps the colour of the lighting or the shadows on the side, but we still want to light our subject and remove unwanted shadows from their face. That's when we use slow-synch flash, either by manually changing our settings to expose for the ambient or through the auto modes of the flash.

If we use the “slow synch” mode of the flash setting then most likely the camera will return to 1/15th shutter speed which, in this case, would be too slow for the movement of our subject exercising. When the flash was turned on the shutter speed defaulted to 1/60th and going from 1/15th to 1/60th is two stops of exposure that the background was underexposed by. We were at iso 100 so we can change that to iso 400 to gain two stops of exposure for the ambient and still keep our 1/60th shutter speed. If we were more serious about avoiding blur we could go further and use 1/125th sec and iso 800 and so on, for exactly the same exposure of the ambient.

Now because the ambient is correctly exposed and we are in TTL-BL mode the flash automatically backs off by -1.7 stops because it has “seen” our meter sitting at zero. If your settings for ambient are manual and you turn around to a darker area of the room and the meter suddenly decides you are under-exposing the ambient by -1 or more, the flash decides to totally take over again and will fire hotter [in TTL-BL or ETTL mode]. Keep this in mind when you choose between shooting manually or adjusting auto modes in the camera because if you had it in slow-synch mode it would adjust accordingly as you change positions and the flash will remain at -1.7 of the required output for darkness.

What if the ambient lights are very yellow and you have mixed lighting, white light from your flash and yellow light from the ambient? Fight fire with fire! In the last image the subject had good skin tones but the background had a yellow cast to it. If you like that effect then leave it like that but if you want things to look “correct” then you could change your flash to a yellow cast as well and correct both light sources at the same time to make them even.

So now all of our lighting looks yellow, a bit too much so.

The red channel is dominating in the scene.

So we dive into the wb settings and find that we can “add blue” to help cancel the yellow.

Now we have provided a similar colour light from our flash and made an adjustment to back off that colour cast from both sources at once.

This is also important for processing images later. I hate to rely on photoshop to “fix” bad technique but it isn't always possible to spend a lot of time perfecting an image when you are in a hurry. The best thing you can do is make a 'cushion' to soften the blow, and by having our light sources the same colour we don't have to select parts of an image to make separate adjustments, we can do it globally.

This is with a global adjustment for correcting a colour cast. After clicking on the white ceiling and forcing it to go white Photoshop has made the entire scene look more “correct” and the skin tones are more natural on our subject. But what is “correct”? Is it when an image is as accurate as possible or when it looks like it did to you at the time? In some cases the yellow cast reproduces the emotions you felt at the time as your “brain eye” combination adjusted the image to what it “knew” was right while making you feel “happy” with the yellow light. If the light had a blue tinge you would still see the skin tones “correctly” with your “brain eye” combination and the whites would still look white to you but you may feel slightly depressed like you “have the blues”- that's what blue lighting does – you can recreate these emotions with the colour cast of your images. You decide what you want your images to look like and learn how to achieve that look on purpose, not by accident. I could have got closer to the image below by setting my wb to B6 and introducing more blue to cancel the yellow cast. It's seldom as simple as one magic setting so all we can do is minimize the variables making it easier to edit later if we have to.

People who aren't photographers don't seem to notice whether we use direct flash or bounce flash, they generally react to the facial expressions of someone they know – they say things like “Hey look, uncle Charlie is actually smiling in that picture, I love it!” when you were trying to demonstrate to them how nasty direct flash looks. Then there's the aspect of whether an image of them is flattering or not. I once took what I thought was a really natural looking photo inside a room using bounce flash while all the other people were using compact cameras and direct flash. Aunty “Oldie von Mouldy” looked at the picture I took of her with horror and exclaimed “I don't like your camera, it shows all the wrinkles!”.

Keep that in mind in future, angled lighting can show textures very nicely but your subject may not always want their “facial textures” to show in the final image that everyone else gets to see.

Bouncing flash directly upwards from the ceiling can produce “natural looking lighting and wrinkles” but it doesn't only have to be directed at the ceiling, it can accomplish more pleasing results from a wall to the side or a combination of wall and ceiling to give better lighting.

With most people who are not overly wrinkled you can still accomplish professional looking results that don't show all their flaws, sometimes you can even reduce them. Which way do you bounce it? If you have the option then keep in mind that “short lighting” [slimming] is more pleasing to the ladies than “broad lighting” which makes them look 'wider'.

Notice how the shadows on the right make the face look slimmer? What about when we bounce the flash from the other side and light the larger area of the face. This gives us broad lighting which is actually better for the guys to make them look more masculine.

Different angles can make a big difference in your results and how your subjects feel about you pointing a camera at them, so don't be afraid to angle your flash head to the side, as long as you press the correct release button and there's no cracking sounds coming out of it when you do so.

There are various options for the flash head when bouncing flash, besides the angle it is aimed at. Much of this depends on how much forward light you want. In most cases direct light is not desirable but sometimes some is necessary, for example when bounce flash produces shadows like when the subject has deep set eyes or is wearing a hat.

So let's start with the worst amount of forward light, direct flash. This is the part where the beginner shouts out “See, I told you flash will ruin your photos!”

So we go to bounce flash again with the flash head straight up, a noticeable improvement but we have a shadow under the hat meaning we need some forward light.

The flash head was like this …..

The best solution is to bounce some light off a nearby wall for diffused frontal light but sometimes there isn't a wall around when you need it. So we pull the diffuser out and this flash has a built in white card. If yours doesn't then the old trick is to use a rubber band and any white card you can find to provide some forward bounce light.

With the white card all the way out we can see the effect of the forward light by the shadow behind the subject. Shadow behind the subject is not desirable as it “looks flashed”.

As always there are other options, the card doesn't have to be all the way out and pushing it back down so it is only slightly sticking out can add enough forward light to remove those shadows under the hat without making the shadow behind the subject too obvious.

Like this. Don't worry too much about that small bit of white card and how much of its light will reach your subject, you will find that the diffuser panel that is now on the face of the flash throws a surprising amount of light forward as well from its edge.

It's worth taking a sequence of photos for comparison for later reference.

It always comes in handy for later reference and for sharing information when you document your tests.

So what if our subject is wearing glasses that reflect light whenever you take a picture? Once again it's good old bounce flash to the rescue and again, we have more variables [like reflections]. Here is our subject wearing glasses in pure ambient light, a soft diffused side light taken at a very slow shutter speed indoors. The shutter speed was too low to prevent blur if the subject moved.

Now we turn on the lights and since iris is under a light we have introduced shadows under her glasses.

So we turn on the flash and point the flash head straight up and improve the situation by adding some diffused light. But it's still not perfect because even though the flash has replaced the room light it is also coming downward and we have shadows under her glasses again.

What about that fancy wide diffuser built into the flash head that makes the light spread over a larger area, that should make a difference shouldn't it?

Yep, it throws some light forward and gives us reflections in the glasses.

Look how that wide diffuser throws light forward. Even though it's “flat” it still has thickness and that edge throws light forward, something we don't really want right now.

We want as little forward light from the flash itself because the glasses are highly reflective so we resort to bounce flash with no forward light from the flash head.

If we look at the glasses on her right there is still a mild white reflection from the flash but it is not too noticeable.

We seldom have the luxury of totally controlling our environment, and your subject may not want to sit for long periods while you take test photos so we can't always be fussy. Also you may be following guests at a wedding or some other event where you have to think quickly and “adapt” as you go along. That's why it is important to always be aware of your surroundings so you can use what you have. If there is nothing to bounce off and time is of the essence then direct flash is a last resort. If the shot is that important then people will just have to take what they get. If it's a massive news event then 95% of the population don't even know the difference between a good and bad picture, and if you're the only one who got the shot someone will buy it off you regardless.

Perhaps the ultimate “balancing with ambient” scenario is with a back-lit subject outdoors in sunlight. That's why TTL-BL was originally created and distance info from the lens was used as a back-up for if the pre-flash reading was messed up by sunlight.

Our subject is a bride during an outdoor ceremony so you can't 'drag her off to better light” as many “available light only” photographers insist is the solution for bad light.

In this kind of light direct flash is better than nothing, better than the 'natural light' that is already on her face in fact. It has also made the grass look better by removing the harsh shadows.

Perhaps the worst lighting we can have outdoors is dappled sunlight as when we're shooting under a tree. The dominant light is in the background, so the auto wb has set itself for that, making the shadow area look more blue. If we spot-metered the subject's face the dappled sunlight would get really bright and ugly as the exposure increased.

Adding some direct flash has improved the situation. Once again in TTL-BL mode.

If we want to make the dappling effect look less harsh we can adjust our settings for ambient to halve the strength of the sun by dialing in “-1” exposure compensation [and if you have a Nikon “+1” on the flash to compensate]

We can take that a step further and drop the ambient exposure another stop and allow the flash to dominate, with the sun not looking too harsh. By doing this we have also made the flash lighting look more obvious and it becomes the dominant light. We would now need to think about whether we should rather be using a softbox to diffuse it more or settle for a normally exposed background with fill-flash simply adding to the existing shadows. Always more variables to weigh up and consider when we have two light sources aren't there? :).

Essentially when we're taking a picture with flash we are almost always balancing it with the ambient to a degree, unless we're in a pitch black cave. Just how well we are doing that depends on how much we actually understand or how 'lucky' we get with the camera's automatic modes. Understand how your camera meters for ambient, how your flash meters and how the flash interacts with the ambient metering of the camera with the mode you are using and you will remove the guesswork from the equation.

10 Fun and games

Now we know how to balance flash with ambient and have a better understanding of how flash works let's go out and play around a bit. There's a toy dinosaur, let's make it look different to the usual snapshot. It is quite strongly back-lit so we know flash will come in handy.

First we get down low and set our exposure for the clouds in the background.

Then we turn on the flash. And that's just a quick test with direct flash, it can get a lot better.

If we have a flash in a softbox on an extension cord we can hold it above a flower ...

Or behind the flower giving two very different images within seconds of each other.

Even an accessory that you think you may never use can come in handy in other ways.

This one turned into a moon.

Textures can be created by placing the flash to the extreme side of the subject thereby turning a rather flat looking surface into one with a lot of texture.

Even a rather smooth looking garage door can be transformed. The crop in the middle is of exactly the same scene taken seconds after the main image with the flash turned on. The difference between the textures is rather dramatic.

Even those cheesy looking wedding photos can be created with some side lighting. Of course most of the time you will be able to move a subject like this to the light you are after but occasionally if you are stuck with bad lighting you can always create your own side lighting.

And a close up view.

The image in the preface was taken with the ring flash diffuser at arms length. It takes a bit of thinking to get your subject on the opposite side of the background and light her correctly while you take a photo of the mirror.

You can practice on yourself. Set up your umbrella or ring-light.

Look down the lens.

You'll get an idea of what the lighting will look like when you have a better looking subject and can zoom in to frame your image better.

The results can be well worth it though.

Here are a few taken with the softbox. This is the scene.

And this is what an 'available light only' photo would look like.

These are some of the options we have with a softbox.

The results can be very different.

A tunnel can give us a large area to bounce flash off to avoid getting a silhouette, unless of course you wanted that effect.

A simple statue outdoors will yield the same image to every snap-shooter.

Underexposing the ambient and adding some side flash can make for a different image.

If you put your flash on a stand and gel it orange it can appear that the flames are lighting your subject when in fact they aren't strong enough to do so.

Of course if the flames die down while you're shooting it doesn't give the same effect. This was actually shot in the afternoon. Wb was set to “Tungsten” to make the sky look more blue as if it were night.

Once you understand the principle of controlling ambient and adding flash you can confuse people by presenting an image taken during the day as a bad direct-flash shot at night.

By simply increasing our shutter speed in the same image we make it look nice and dark outdoors.

My D50 can synch manual flash at any speed due to the type of sensor it has. This could also be done using HSS or auto-fp mode. Underexposing the ambient and adding direct flash has turned a normal daylight image into what looks like a snapshot at night. You could go a step further and change the wb to a tungsten setting to make the sky look bluer and more 'night-like' if you wanted.

In my other book on high speed photography we discuss how to freeze motion at 1/41600th sec using 1/128th power of the flash and a sound activated trigger.

11 Wireless flash

This is where things can get really complicated if you don't understand the basics. When you first start learning to shoot with flash it can be confusing enough but when you start to go wireless with multi channels you open up a whole new can of worms. Wireless flash can involve a simple manual trigger where you set the output of the flash manually or a multi-channel TTL system. Now with regard to the Nikon system, when you work with wireless flash in automatic mode even though the flash head says “TTL” it is actually metering in TTL-BL mode. You will notice that if the ambient is under-exposed by more than one stop the flash will take control of the lighting, but if your subject is already exposed correctly it will back off to -1.7 of the output it would have used for full control of the situation, and simply act as fill-flash. Distance info however is not included in the equation because the camera no longer knows how far your flash is from the subject.

This makes sense when you think that today's automatic flash modes are mathematicians. They can add and subtract values to arrive at a final result working with ambient and the pre-flash reading. The next logical advancement in this equation is to have more channels for the flash to work with so you can control them independently while they still have the ability to adjust exposure if one channel starts to add to the area the other channel is lighting. Even though we don't see this at the time of writing this book I will not make any definite statements on this, as technology is rapidly changing and “facts” can become obsolete as the next model is released.

Let's look at a fairly clear cut example of two separate channels. A D90 camera is our 'command' camera and the built in flash acts as our controller. The flash on the left is set to channel a while the flash on the right is set to channel b. At this stage everything is turned on and ready to fire, we set our ambient to total under-exposure so everything will look dark without the flash, and actually that's what the command camera sees for now – darkness, it does not know how many flashes or channels there are yet. So how does it work then?

When you push the shutter release to take the picture the command flash starts 'talking', we can think of it as something like Morse code because it's a series of rapid flashes that sends out a signal that says “channel a, if you're there fire a pre-flash” and Bam, its meter sees this and knows there is a channel a.

Then, because we have the command camera also set to work with a channel b, the command flash says “Channel b, if you're there fire a pre-flash please” and again Bam, it sees this and knows we have a channel b lighting up the other side of the subject. Some systems also have a channel c which is just another step to what we are discussing so we don't need to include it here.

So this all happened in a fraction of a second and some people won't have noticed it while the 'blinkers' will have closed their eyes for a fraction of a second. Now the camera does its maths and says “The meter for ambient shows 4 stops under-exposure so the flash will need to fully light the subject, without blowing any highlights if possible, depending on the angle of the flash and what TTL-BL deems to be a reflection. We have one half of a shape on the left that needs 10% flash power [making up numbers here] and the other side needs 15% power [that flash was slightly further] ” As the mirror lifts and the camera takes the picture the flash sends another signal “Channel a 10%, channel b 15% …..... NOW!” and the scene is lit.

Let's have another look at the metering system by introducing a white object on one side.

To demonstrate how separate the two channels are when it comes to metering we dangle a white object in an area under the right focus points where channel b can 'see' it but channel a can't. Notice how the light from channel b goes darker? The white object reflected more light for the pre-flash causing the exposure to drop considerably on that channel.

So what happens when two flashes light the same side then? The ultimate 'evolution' of the system dictates that it should add the combined pre-flashes and adjust them individually to an output that gives the same exposure that one flash would give. Experiments seem to prove that this stage has not been reached yet and the one simply adds to the other, though this statement will probably be obsolete a day after this book is released. The best thing to do then is to experiment and learn how your system works or basically avoid situations where you have two different channels lighting the same area until you are sure how your system works.

My advice for now is to stick to the same channel for flashes lighting the same area of the subject AND when one flash is the rim light. Why the bit about the rim light? Because it is very difficult for a flash to meter the light that is coming from behind the subject. Let's test it out with a softbox lighting the subject from the front and a rim light behind the subject to separate it from the scene.

When we have the front flash on channel a and the rear flash on channel b we find that the rear flash fires very aggressively because all the flash metering sees from its pre-flash is a thin bright white line that can be rejected as a reflection so ends up firing really strong and even lighting up the reflector behind our subject from the reflections off her head.

Now here's a trick to keep in mind. The command camera does not know how many flashes you have on each channel – it simply measures the pre-flash from channel a and then sends out a signal for channel a to fire at a set power, and all flashes on channel a will fire at that same power. So that tells us that setting the rear flash to channel a can make sure that it does not fire stronger than the front flash because they will both fire at the same power and we can now adjust the strength of our rim light by adjusting its distance from the subject or even by covering half of it, because no matter what we do now it will still fire at the same strength as the front flash!

So let's go back to lighting up the background. Both of our wireless controlled flashes are used up so all that's left is an older flash with SU mode – that 'eye' on the front of the flash that makes it fire when it 'sees' another flash go off. So we set the old flash to 1/16th power and point it at our background to blow it out. “So”, you say, “what about the pre-flash then? Surely that will make our old flash fire before the actual exposure!?”. Yes it will, and if you're at full power the flash will not have time to charge for the actual photo. But when it is at 1/16th power it can fire several times rapidly which means it fires for the pre-flash and again for the main flash – problem solved.

Annnnnnd, we introduce a new problem, part of our subject's face disappears when we blow out the white background and she has a white rim light on the side of her face which reminds us that a rim light is useful for separating the subject from a dark background but causes problems with a bright background.

12 Auto fp

This will be divided into ‘Beginners : All you need to know,’ ‘Intermediate: other interesting info, and ‘Techno Geek : just if you’re interested in straining your brain a bit.’

Beginners:

This is a trick mode that gives you about ¼ of the flash power you would get from normal flash. This can be useful in bright sunlight where you only want fill flash and don’t want the hassle of being limited in your choice of aperture and shutter speed.

At this stage I’ll state that beginners who are only interested in going out and taking photos could skip the rest of this chapter because realistically all you need to know is that you have about ¼ the power which gives you half your working distance [due to the inverse square law]. Try to use 1/2000th sec and faster when in this mode. From here on it gets technical.

Intermediate:

What is it and why is it necessary? Basically 99% of cameras that can take an external flash use a focal plane shutter. This involves the two ‘curtains’ of the shutter. Think of a stage with the left curtain pulled all the way open, and the right curtain pulled closed, all the way across to the left side as well. When you take a picture the right curtain moves back to the right hand side, the stage is fully exposed, then the left curtain follows the right curtain all the way across to the right hand side. Once this is over they both move back together across to the left hand side waiting for the next exposure. This is how a focal plane shutter works but from the bottom to the top of the sensor.

Now imagine this with the shutter of a camera that can move across the frame at 1/250th sec. If you were to use a shutter speed of 1/200th sec once the first curtain opens you could trigger the flash to expose the entire sensor and then close the second curtain. But what if you wanted to use a faster shutter speed when the curtain can only move across at 1/250th sec? Let’s take 1/500th sec as an example. Because the curtain can only move at 1/250th sec you couldn’t have the full sensor exposed all at once, the curtain can’t move fast enough to do that all at 1/500th sec. The way they get around that is to start opening the first curtain and once it gets halfway start chasing it with the second curtain. That way we are only letting in half as much light because, compared to 1/250th sec., the second curtain has started closing already only halfway through the exposure.

This is the concept of a focal plane shutter, it is limited to the speed it can open and close so they adjust the time of the exposure by the size of the slit that travels across it. Imagine now what has been described with regard to faster shutter speeds. If 1/500th results in the second curtain starting to close halfway through the exposure than 1/1000th will mean that the second curtain has to start closing ¼ of the way through the exposure. This means that the first curtain gets ¼ of the way across the stage/sensor and the second curtain starts chasing it across the screen already and we have a slit ¼ of the width of the full sensor sliding in front of it. Now imagine 1/4000th sec. Someone starts opening that first curtain and almost immediately the second curtain follows it leaving only a small slit to slide across our sensor.

So there we have the concept of the focal plane shutter.

Realistically with a camera that has a shutter that takes 1/250th sec. to move across the sensor the flash synchronization [sync] speed is limited to about 1/200th sec. because we still have to allow up to 1/500th sec. for a full power flash to complete it’s firing.

So what if we want flash at 1/1000th sec.? The trick mode they use is auto-fp or high-fp mode. ‘fp’ stands for ‘focal plane’ [HSS for Canon]. With a flash capable of this mode it acts as a continuous light while the two curtains are having their race across the stage. But a lot of light is wasted, think of taking a flash photo of those two curtains on the stage at 1/500th sec. with a slit half the size of the stage, some of your light will reach the people on the stage while the rest is wasted on the back of the curtain. Here’s an illustration to show what I mean and most people don’t need to go any further.

At 1/2000th sec. we have auto-fp flash turned on and the first curtain opens and the second one follows close behind. All the time this is happening the flash is firing continuously ‘bzzzzzzzzzzzzzz’

And the slit keeps moving up while the flash keeps buzzing away.

‘bzzzzzzz’

‘bzzzzzzzz’

‘bzzzzzzzz’

‘bzzzzzzzzz’, and the flash turns off as soon as the slit closes.

And the exposure is over– all this [short] time the flash was buzzing away, spreading the energy it normally uses in an instant over a longer period of time.

Techno Geek:

Now this is where it gets a little complicated, realistically all you have to remember now is that if you use this mode get away from the slower speeds and as close to 1/2000th sec, and faster, if possible. You will get more power that way. It doesn’t make sense at first when you think that at 1/500th you have half the sensor exposed so half the light should reach your sensor and at 1/4000th you have 1/16th of a slit with the rest being wasted on the curtain so you’d think it will be much weaker, but there’s a lot more to the equation.

If you are in fp flash mode you will be in bright light or you wouldn’t need it. If you are shooting at 1/250th sec. with normal flash and you change over to auto-fp mode this is what happens. By going to 1/500th you open your aperture one stop to let in more light so you make the flash that reaches your sensor twice as powerful. Sounds simple enough until we realize that the flash has to keep ‘buzzing’ for the 1/250th sec. that the first curtain spent opening plus the 1/500th sec. that the second curtain, which was halfway across when the first curtain reached the end of its travel, takes to complete its journey.

Try to stay focused here, each time we increase the shutter speed by one stop the first curtain still takes 1/250th sec. to complete its journey, then we open the aperture one more stop making the flash we are cutting in half twice as powerful again, BUT the total shutter travel decreases each time! Think about it, when we go from 1/500th to 1/1000th the second curtain of the slit leaves twice as early as previously meaning that after the first curtain completes its 1/250th sec. journey the second curtain is closer behind and halves its time to finish, it is now 1/1000th sec. behind the first curtain.

Keep doing this calculation all the way up to 1/4000th and we have 1/250th sec. first curtain travel plus 1/4000th for the second curtain to finish after that. In the graph below the x-axis represent shutter speed and the y-axis represents shutter travel time, the blue line is the 4ms time that the first curtain takes to open. The red line represents the total curtain travel time after adding the shutter speed you are working at. At 1/250th sec the total time is double that but once we get to speeds around 1/2000th sec the total travel time is not much different to 1/250th sec.

There is also a difference in power loss between dx and fx cameras. The more professional full frame [fx] cameras work a bit better in that their shutter travels faster than with the cheaper dx sensor cameras. Because of this, auto-fp flash doesn’t have to stay on as long, because it’s all over much faster, so the flash can fire at a higher power for a shorter time thereby releasing the same amount of energy but with a brighter resulting image. Below we have the same graph as above but with yellow and green lines added showing how long the same shutter speeds take on a full frame camera with a shutter curtain travel of 2ms [1/500th sec]. Notice how much faster the entire event is, remembering that these are at the same shutter speeds, meaning that we can get more power out of high-fp flash with a full frame camera.

This all means that the auto-fp flash has to keep firing for a shorter period of time and therefore can fire stronger for that shorter period of time and use the same total amount of energy. Think of it in terms of a candle. You can burn one candle for 10 minutes or you can cut the same candle in half and burn both those halves for 5 minutes which is half that time but twice the light, and it’s still the same amount of energy, one candle! If that were to depict a dx camera at faster speeds in auto-fp mode then an fx camera would be like cutting the same candle into 4 pieces and getting more light again but a shorter ‘burn-time’ of 2 ½ minutes.

Let’s see what this looks like in a graph of tests I did. I set the camera to expose for a ‘sunny 16’ day so as to duplicate what we might have to deal with in a real life situation. The y-axis represents the distance I could work at to get the same histogram from a white wall, which should be the same exposure. The x-axis represents shutter speed. With a camera that can sync flash at 1/200th sec I get the most power at 1/200th when exposing for daylight. If I use slower speeds than 1/200th I need to close the aperture down which also affects the flash, making it much weaker. As I go to 1/250th I now have to move twice as close to get the same exposure, meaning that I am losing two stops of light based on the inverse square law. Once I start using faster shutter speeds the situation improves due to the fact that total shutter travel time decreases, leaving the camera/flash combination with the ability to use a stronger flash power over a shorter time period, to get the same energy use.

In review: Each time you halve the shutter duration you open the aperture one more stop canceling the fact that the slit just halved in size wasting more of the flash. But each time you use a faster shutter speed the total travel time, and hence the amount of time auto-fp flash stays on, decreases meaning a slightly higher output can be used during that time - making auto-fp more effective at the higher shutter speeds than at those closer to normal flash sync speed.

13 Something a little different

This is another chapter from my previous ebook, the pre-cursor to the second one called “Understanding Explosure”. I like to explore the technical limits of the mechanical and electronic aspects of photography. Realistically I’d much rather make a living photographing beautiful scenery but when I’m stuck at home for a while I start doing ‘experiments’.

A while ago I bought a sound activated switch and wired it up to my camera flash. Mostly using a two second exposure at night the background is pitch black at F9 and ISO200, so that saved having to use a fancy studio and dig the pellets out of their wall. The first images involved a black dot on a balloon, I had the microphone right under the air rifle and it triggered the flash so soon that I had a photo of a pellet touching the balloon’s surface.

Slowly moving the microphone further and further, to give the sound further to travel before triggering the flash, allowed me to capture the split in the balloon all the way up to the edges, with the pellet touching the back of the balloon, then I could go back to filling them with water.

With the first image I got using this method I stared at the screen for a while thinking there was something wrong with it, I had never seen anything like this. As the balloon splits the rubber pulls up the water into a fine spray making it look like a starfish clinging to the balloon.

Of course there are many possibilities with high speed photography and a little imagination, and hanging a half-filled balloon up and shooting the top away yielded some interesting images of water hanging in the air with colored rubber flying in all directions, but one image in particular turned out pretty ‘unique’, if there is such a thing in photography these days, in that it gave me a vertical split. In this image I had added a flash behind the balloon, which made things nice and ‘sparkly’.

After cleaning up the mess I half filled the balloons and shot downwards on them, I find it fascinating seeing events like this frozen in time.

Shooting from the side shows the water jumping towards the air rifle [to the right].

The splits weren’t all the same but most were 4, 6 or 8 way splits.

After posting these images on the forums someone suggested I should be using safety goggles so I tried it but it just doesn’t work for me?

Fill a balloon halfway and shoot the top away.

There is a limit to how much you can ‘freeze’ motion. That is based on the speed of your flash in this case. The flash I was using fired full power for about 1/700th sec. which is quite a long time when doing this type of photography. At its lower power settings I was getting 1/11000th sec. but that wasn’t fast enough for a light bulb shot with an air rifle, there was still movement in it.

There are many avenues to explore and some pictures take a lot of time to set up. This one involved a pre-charged capacitor firing in series with a 240 volt light bulb to make the filament glow, and a second flash wired up to a sound activated switch to light the background as the axe breaks the bulb.

There are many opportunities for ‘different’ photography and a little bit of inventiveness, though you need to be careful when playing with something as dangerous as a flash capacitor because they have enough energy inside them to kill you if you don’t handle them properly.

“Superspeed photography”: Something that I consider ‘my invention’, since I haven’t seen it done anywhere before is ‘Super-speed photography’. Now normal high-speed photography involves either a very fast camera at a high frame rate or the act of ‘freezing’ the motion using flash, while the actual exposure is actually quite long. For much of my high-speed photography with flash I was using shutter speeds of two seconds to give me time to break or shoot whatever my subject was and trigger the flash with a sound activated device. But then I started playing with the idea of using the flash trigger of the camera to actually cause the event.

By wiring up an electrical device to the trigger circuit of the camera one can actually make an event happen by the act of pressing the shutter while you photograph it at the same time! That’s why I call it ‘Super-speed photography’ because it all happens faster than with normal high-speed photography and is actually caused by the act of taking a photograph, at any speed.

My first experiments involved wiring a diesel fuel shut-off solenoid [I was training as a diesel fuel technician while on the farm but am actually an automotive-electrician] in series with the camera flash’s capacitor. As the flash fires a certain portion of the energy gets used in the winding of the solenoid causing it to propel the solenoid plunger forward as the picture is taken. The first few attempts involved the needle on the end of the plunger only piercing the balloon full of water after the image was over, due to the relatively slow mechanical movement and the fact that the balloon had to be a reasonable distance away to prevent accidents due to movement. Finally at 1/30th sec there was enough time to get a bit of exposure of the balloon in its un-burst state and then some of the actually bursting rubber and water flying everywhere.

Thus Super-speed Photography was born, but it is still in the primary stage of its life and has a long way to go to reach its full potential.

Watch this space!

My latest attempts involve using an SCR or ‘Silicon controlled rectifier’. This means that it can switch very high voltages and currents when needed. It can trigger 800 volts at up to 3800 amps in fact. I’ve wired it up to a large capacitor that gets charged to 325 volts by an old flash I picked up cheap. I have the trigger wire connected up to the hot-shoe of my camera, a 6 MP Nikon D40, which means that when I take a picture the SCR dumps the capacitor across a piece of wire and literally blows it up with the massive surge of energy in such a short period of time.

This is ‘The Rig’. I try not to take it out in public and have given up the idea of ever taking it anywhere through airport security. The big blue thing is a 3300uf Capacitor that gets charged by the old hammer-head flash in the centre, powered by the gray battery holder with six AA batteries. The wires all go up to four 240 volt switches on the lid to disconnect everything from the system when I am connecting the wires to something. On the right is a 12 volt security battery that switches the SCR via the flash hot-shoe of my camera. I use the 240 volt light bulb to discharge the capacitor when I am finished to prevent any nasty surprises when I use it the next time. Don’t anyone even think of trying this at home, the capacitor gets charged to 325 volts and has enough energy to blow off your finger-tips, in the process of frying your heart.

Let me just lock the door, I think the black sedan just pulled up outside my house … again!

There are many possibilities that arise with an exploding wire in images. One option is to freeze the wire in an ice cube and trigger the explosion to see what happens with the ice. From experience not much happens if the wire isn’t properly secured in the ice, it makes a nice bright flash but the wire simply blasts out of the ice from the force of the rapidly expanding water/steam. I was hoping to see the ice exploding in all directions.

Now if you sprinkle some gunpowder on top of that wire and add a stone it makes for an interesting ‘shot’ [Get it, “gunpowder”, “shot” ???? …… no? Never mind!] .

This is what happens when you start studying into how a camera and its electronics work and start doing experiments. The difficult part of photographing explosions of any sort with this method is timing, because an explosion is relatively slow compared to the speed of a camera flash triggering system and quite often the event happens after the picture has been taken. As with this image of a wire exploding around a balloon full of propane gas [don’t try this at home], the wire explodes in about 1/4000th of a second or less [1/4000th was the fastest speed I tested it at] and all you get is a picture of a bright flash which is over long before the balloon even starts to split open, relatively speaking. This image was taken at 1/500th sec. and shows the piece of wire held by two alligator clips exploding. Microseconds later the balloon burst but by then the exposure (or should that be “explosure”?) was over.

Just for interest the gas did not ignite, it turns out the mixture was too rich to give me the fireball I was looking for. Placing a candle close to the balloon however, makes for a very different photo but tends to freak the neighbors out. In one of my videos recording my experiments on the following weekend you can hear the little girl next door saying ‘Mummy he’s making fires again!’ so I had to work quickly.

Another option for triggering events when you press the shutter release is to use an ignition coil. Now I’m not going to say too much because people can get killed fiddling with the capacitor of a flash and 30 000 volt coils but for those of you capable of doing it you will understand when I say that the coil needs to be in series with the flash tube. That’s as much info as I’m going to give out because I don’t want anyone getting hurt trying this – it is very dangerous if you don’t know what you’re doing!

This is the flash-activated coil setup.

And this is what it does.

A teaspoon of Calcium Carbide in water releases acetylene gas, and a spark from a coil connected to a camera flash ignited via a very conveniently placed spark plug in the back of the microwave makes for interesting photo opportunities. You just have to use a fast frame rate so that by the second or third exposure you catch the fireball, I still need to perfect this shot, by this time I had moved the spark lead to the front because the plug had fouled up from foaming Calcium Carbide earlier.

Once again I will ask readers not to try any of the dangerous stuff unless you are qualified to work with high voltages and know exactly what you are doing. Even then it's better not to try it just to be safe, you probably won't be covered by your life insurance!

For now rather go out and practice your flash photography and have fun!