“Light makes photography. Embrace light. Admire it. Love it. But above all, know light. Know it for all you are worth, and you will know the key to photography.”

– GEORGE EASTMAN, INVENTOR

t’s no mistake that we started this guide with a quote about light, because today’s topic (like most things relating to photography) is all about light. Specifically, how your camera reacts to light. ISO is the third – often overlooked – corner of the exposure triangle, and after reading this guide you’ll wonder how you ever got along without it.

We recently discussed the other two corners of the triangle in “Understanding Aperture: Controlling Light Based on the Exposure Triangle” and “Mastering Shutter Speed to Capture and Freeze Motion.” As with aperture and shutter speed, ISO plays a specific role regarding exposure and light, and a seemingly simple role at that. Simply put, increasing the number on your ISO will increase your camera sensor’s sensitivity to light, brightening your image. So then, if you’re shooting in a low-light situation and your photos are coming out underexposed, just increase the ISO level and brighten it up. Easy, right?

Yes and no. This would be a pretty short guide if that’s all there was to it… and you can tell by scrolling down, that isn’t the case. Adjusting any corner of the exposure triangle will introduce a number of variables that affect how your image appears. Once you understand these variables you can learn to anticipate them when you’re shooting in manual mode, balancing the entire triangle to get the best exposure for your needs.

This guide will round out our trilogy by focusing on all things related to ISO, including how ISO interacts with the other two aspects of the exposure triangle. Specifically, we’ll answer these important questions:

• What is ISO?

• What are the pros and cons of using ISO?

• What do variations in ISO levels look like?

• What happens if increasing ISO is the only available option?

Let’s take a look at the world of ISO.

What Is ISO?

A good way to begin defining ISO is with the meaning of the acronym itself. ISO refers to the International Organization of Standardization, the organization responsible for setting the standards for a digital camera’s sensitivity rating. In reference to your camera, ISO has a bit of a history. You may have heard it referred to as “film speed” because in film-based photography the actual film you use determines your ISO.

Film is made with different levels of sensitivity to light, so a film speed (or ISO) of 100 shoots very differently from a film speed of 800. That means when you’re shooting with film, you determine your ISO once (when you select a roll of film to put in your camera) and then you’re stuck with that ISO until you finish the roll. It’s a lot more flexible with digital photography! The ISO setting on your DSLR is simply a measure of how sensitive your camera sensor is to light, and you can change it quickly and easily between snaps.

While aperture and shutter speed describe mechanical functions – with aperture being determined by the size of the opening in your lens, and shutter speed being controlled by the timed opening and closing of a curtain-like shutter – ISO as we know it in the digital age is more of a computerized function. All digital cameras contain computers, and one role of these computers is to translate the information gathered by your camera’s aperture and shutter speed. Once the information is obtained and stored, the camera’s computer can be used, via the ISO feature, to brighten a given image. In this sense, using ISO on your camera is much like using image-editing software on your personal computer or laptop.

ISO Values and Exposure

ISO values (or ISO settings) are measured in whole numbers. On most cameras, ISO values range from ISO 100 to ISO 6400 (although some high-tech lenses allow for values far beyond that), with ISO 100 considered to be a low setting and ISO 6400 a high setting. This seems like a good time for a visual aid:

As you can see, these numbers correspond to the level of brightness you are introducing via the ISO function. A higher number equals a brighter exposure, while a lower number equals a darker exposure.

We can see that the image at ISO 100 is underexposed, making it difficult for us to make out the features of LEGO Darth Vader. This isn’t a problem for him, since he’s pretty comfortable with the dark side, but this level of underexposure is considered poor quality in most photography. Even at ISO 200, he still appears too dark for us to see any significant detail. Once we hit about ISO 400, we start to see some details emerge. Remember that the “right” ISO setting will be different for every image, based on the lighting situation you’re working with.

How Your ISO Setting Affects Your Photos

As we saw in the last section, increasing your ISO can do wonders for your exposure. However, it can cause some complications as well.

When you increase your ISO, you are essentially trading a certain level of quality in your image for a brightness boost. In some cases, as with the images above, increasing your ISO setting will have little to no effect on the overall quality and clarity of your photos. In others, you’ll see a visible change in sharpness and detail.

When dealing with higher ISO values, the diminishment of image quality is far more apparent:

In this series of images, a great deal of quality is being sacrificed as the ISO increases. In the previous series, we were faced with an image that was noticeably underexposed. By doubling the setting twice on the low end of the ISO scale, we were able to increase the brightness without losing any quality. In this series however, what we see is an image becoming increasingly overexposed instead. The image becomes too bright, to the point of details being “washed out” and the crispness of the image has decreased as well.

Artifacts, Grain, and Noise – Oh My!

Imagine that you’ve conducted an interview, using a digital recorder with a built-in microphone. When you upload the audio to your computer, you realize that the sound isn’t loud enough to make out what’s being said. Of course you want to make the interview intelligible, so you use sound-editing software to increase the audio level.

As you increase the audio level, you realize that, while the voices captured in the interview are becoming much louder, other noises are increasing as well. Electrical noise from the microphone itself and ambient noise from your surroundings are now audible, muddying the clarity of the most important sounds: your voice and that of the person you interviewed. In this case, louder doesn’t mean better; rather, it means noisier. It’s the same with ISO and brightness.

As you increase the ISO setting, although it will technically make the details in your image brighter, it will also introduce little artifacts into your image that negatively impact your sharpness and color purity. In film photography, these artifacts are called grain and they are linked to the coating on your film. In digital photography, they are called noise and they’re linked to your camera sensor. Although grain and noise are kind of caused by the same thing (ISO), they are not one and the same. Feelings about grain in the photography community range from neutral to positive (many think of it as a textural effect that adds character), while excessive noise is almost universally considered to be a sign of poor quality.

Luminance vs. Chromatic Noise

When it comes to digital noise, there are two varieties:

• Luminance noise is caused by the level of light in a photo. This is similar in appearance to film grain and as a result, you can get away with more of it in your photos before it becomes “unsightly.”

• Chromatic noise is also known as color noise, and it’s pretty easy to spot by the pixelated variations of color you see in areas of an image that would otherwise be a more or less uniform color range.

The issue with both of these, as we’ve hinted at already, is the loss of detail. If sharpness is important to you (and in photography, it usually will be), you’ll want to keep noise to a minimum when possible. That means that with your ISO, as with so many other elements of photography we’ve discussed, it’s always going to be about finding the right balance.

Managing Noise in Post-Processing

Any photo editing software worth using these days will have some way of managing noise in your images. Adobe Lightroom and Photoshop each allow you to make adjustments to both luminance and color noise. (Lightroom uses a pretty foolproof slider system that’s perfect for beginners.)

Here’s the issue you’re going to run into: your editing software doesn’t know what your scene looked like without all that noisy interference. So it’s rarely a good idea to hike up your ISO to accomodate for a miserable lighting condition, with the mindset that you’re going to make all the resulting noise magically disappear on your computer. Yes, you technically can get all of the noise out of your image that way (usually), but what will be left is a waxy-looking, muddy-colored shell of the vision you had when you pressed the shutter button.

When it comes to editing out noise, the best approach is to minimize the noise to the point that it’s not distracting while maintaining as much detail as you can. (That, and balancing your exposure correctly in-camera!)

When to Use Higher ISO Settings

Don’t let that last section scare you away from ever increasing your ISO. This third of the exposure triangle can be a powerful one when used correctly, and in less-than-desirable lighting conditions, it really can be a solid option for achieving the right exposure for your needs. For example, you may wish to get a brighter exposure without impacting the appearance of motion or the depth of field in your image. In that case, a mild bump in your ISO is just what the doctor ordered.

You may also find that the simplest way of getting a correct exposure for a dark indoor or night shot is to increase your ISO, in addition to opening up your aperture and setting a longer shutter speed.

Lastly, you might want to embrace noise for artistic effect.

For example, this photo of a row of antique books is enhanced by the coarse, textured appearance of noise. It resembles that vintage appearance of grain in this context, rather than appearing pixelated and disruptive. So in the right situation, feel free to throw caution (and ISO limitations) to the wind.

When to Use Lower ISO Settings

As stated earlier, the most basic function of ISO is to brighten photos that are too dark and/or underexposed, often because they were taken in environments with insufficient light. However, when there is sufficient (or abundant) light, you will want to keep your ISO value reasonably low. If too high an ISO setting is used in such a situation, you could find yourself with overexposed images and clipped highlights.

Pro Tip: Native ISO

One way to preserve the clarity and quality of your photos when using ISO is to shoot at your camera’s “native ISO.” The native ISO on digital cameras is generally ISO 100 or ISO 200. How do you know what your camera’s native ISO is? Simple: Enter your camera model (brand name and number, etc.) into a Google search, along with the words “native ISO,” and the results should come up immediately. Knowing your camera’s native ISO will also give you a reference point when raising and lowering your ISO settings.

ISO, Aperture, and Shutter Speed

Manipulating aperture and shutter speed can allow you to explore a vast range of aesthetic and stylistic variations in your work. Changing your aperture not only changes how much light is exposed to your camera sensor, but also the relative level of focus and depth of field in a given image. Shutter speed also affects light exposure by raising and lowering your camera’s shutter, but also functions as a tool for freezing an object in motion or allowing motion blur to appear.

Often times, photographers will refer to ISO as the “third” aspect of the exposure triangle. This is not because it’s less important than the other two, but rather because many photographers determine their aperture and shutter speed settings before they make any adjustments in their ISO values. This approach allows you to select your more dynamic settings first in order to tell whether raising your ISO value is necessary or if you can leave your native ISO in place.

Let’s use some visual examples to demonstrate how ISO works organically with aperture and shutter speed:

This photo was taken with a low ISO value of 200, which seems distinctly low given that it seems to have been taken in low light as the sun was setting. However, it was also taken with a wide aperture setting of f/1.8, with the lens almost wide open to allow for an increased amount of light to enter in order to avoid poor exposure. Using the wider aperture setting also allowed for the photographer to use a faster shutter speed (which allows less light in) of 1/500 of a second in order to capture and freeze the subject in motion.

This image was taken with a little bit higher ISO (400) than the previous example, as, once again, it seems to have been taken as the sun was rising or falling, and therefore with less light. A faster shutter speed, 1/500 of a second, was used again in order to freeze any movement by the subject, even while this reduced the amount of light entering the camera. In addition, in this case, a mid-range aperture of f/5.6 was used in order to achieve a greater depth of field, which also allows less light to reach the camera’s sensor. In this way, by using a higher ISO the photographer was able to use shutter speed and aperture settings that allowed them to achieve the desired effect.

Lastly, this beautiful night photo was taken with a very slow shutter shutter speed of nearly 30 minutes, and a medium level aperture setting of f/4. The long shutter speed allows as much of the available light as possible (the light coming from the sunset and the stars) to enter the camera, and also to capture a movement effect in the stars due to the Earth’s rotation during the extended interval that the shutter was open.

The medium aperture allows for the photographer to achieve a shallower depth of field, keeping the subject in the foreground in high focus while allowing for a dreamlike effect to be achieved in the background by allowing for less focus. But given the extreme lack of light in the shooting environment, the photographer used a significantly increased ISO value of 1600 in order to brighten up the image and achieve proper exposure.

Each of these examples represent perfectly balanced photos, with various ISO levels used for particular reasons so that the photographer could achieve their desired effects.

Pro Tip: Using ISO Wisely

It’s important to keep in mind that while you always want to capture the cleanest, sharpest image you can, this is no reason to shoot with a low ISO in every situation simply because a higher ISO value increases image noise. In fact, an image with a minimal degree of noise is preferable to an image with unwanted motion blur or unbalanced focus. Always seek a balance that works for the entire triangle, but prioritize your depth of field and motion capture over your noise level when it comes down to it.

Now you’ve got one more tool in your image-maker’s toolkit and a highly useful one at that. Not only can ISO bail you out of a low-lighting jam, exploring different combinations of ISO can also be every bit as artistically satisfying as experimenting with aperture and shutter speed. This last corner of the exposure triangle is just one more way for you to enjoy the process of developing your own taste and artistic style while you learn.

We hope that you’ll keep our guides to aperture, shutter speed, and ISO close by and accessible as you continue to experiment with manual photography. You never know when you might need a quick refresher. When you’re ready to learn more about which file type to take all your amazing new exposures in, join us for the RAW vs. JPG Showdown!