This is a beginners guide to help you get started in astro-imaging with a DSLR.

I do not profess to be an expert but I am told my explanations in simple terms are often very helpful to beginners.

Originally written in 2011 when I was using a Canon 450D

I can only tell it from my point of view and using the equipment and software that I use and only to my own ability. Hopefully this will help some beginners get started on this rather steep learning curve and I will have “paid back” some of the help that I have been given.

This was originally written for my friend Ian, but others have found it and found it very useful, so although somewhat out of date I am keeping this on my new website.

When I first started I used Canon Utility as my capture software, this is very simple and does the job, but had no "bells and whistles" so later I changed to using APT (Astrophotography tool) and in 2012 I changed over to using a Cooled Mono CCD camera and have continued to do so since only using the DSLR on odd occasions, for instance when imaging abroad, and the Lunar eclipse and occasional comet.

However, I decided to leave this tutorial as it is because it is simple and from the feedback page you will see many people find it easy to follow and that's what this tutorial is all about - to help you get started.

1. Equipment needed

2. Focal Ratio

3. DSLR Camera

4. Laptop and connections

5. Software

6. Polar Alignment

7. Balancing the mount

8. Alignment procedure

9. Connection to the laptop

10. Getting Focus

11. Capturing your first image

12. Viewing your first image

13. Calibration frames (Darks, Flats and Bias)

14. Stacking

15. Simple Processing

16. Guiding

17. Modifying your DSLR

18. Dithering

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1. Equipment

Warning:

This hobby is not a cheap one, you will need deep pockets and lots of patience and endurance. However it becomes addictive and you’ll find yourself continuing to dig into your pocket long after you think you have bought everything you need.

Remember this is for imaging with a DSLR so I will not be covering planetary imaging though this can be done from the same set up. Planetary imaging does not require an equatorial mount and a guide camera, though having said that I think you would find it easier to do this if you do have these things.

Mount:

The single most important thing for Deep Sky Imaging is a decent solid Equatorial mount with guiding capability.

I initially had a CG5 GT and this sufficed for quite a while, but it developed some guiding issues and then I bought a larger telescope and was advised to get myself a sturdier mount, and so I bought an NEQ6. An HEQ5 is also a good mount if you don’t think you will be buying a heavier telescope at some stage.

Telescope:

This is a matter of personal choice and budget, however for a beginner a small refractor is probably the best choice, you can always change to something grander once you have acquired your skills rather than jumping in at the deep end. I started with a Megrez 72 doublet APO and found it to be a good telescope producing some good results. I only sold it because there were a couple of practical reasons why I wanted to get an ED80 which had convenient mounting rings on which I could mount a guidescope and a decent finderscope.

In my opinion when you are starting out you will make life more difficult if you use a more powerful telescope with a small field of view as guiding will become more critical as will actually finding the object become more of a chore. Start small and work up as you learn the skill. A smaller telescope is never wasted as there are times when you will need that wide field of view for some of the larger objects like the Andromeda galaxy which will not fit into the FOV of a more powerful scope. Most imagers have more than one telescope - but watch the focal ratio (see next paragraph).

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2. Focal ratio:

This is something I learnt as I went along. Focal ratio is the focal length divided by the diameter of your objective lens. For example, a refractor with a focal length of 900mm and an aperture of 100mm has a focal ratio of 900/100 = 9 or f/9.

The larger the focal ratio the slower and more difficult it will be to acquire data as it will take much much longer.

I am not going into technical details here, just summarising in simple terms, you can do your own research on this on the internet.

Generally the rule of thumb is:

For planetary imaging - the slower high F ratios such as F11 - F15 are suitable

For deep sky imaging - middle F ratios such as f6 - F10 are suitable and can also be used on planets with a barlow. Skilled accuracy is needed for F2 - F5 as these are much faster and the technical demands are high.

Websites can vary a little on this, but the above is a reasonable guide.

Example:

An f/5 system can photograph a nebula or other faint deep space object in one-fourth the time of an f/10 system, but the image will be only half as large. Plus if you add say a 2 x barlow, you might double the size of the object, but you will quadruple the amount of time needed to capture the same data.

(This does not apply to planetary imaging which is not done with long exposure)

If you find the above difficult to get your head around, just buy yourself a small/middle sized refractor which is an APO and you can’t go far wrong. The ED80 is much recommended, and I suggest make sure you buy yourself one with a decent finderscope.

I find the following two pages really helpful in working out what I can get into the FOV (Field of view):

http://www.12dstring.me.uk/fov.htm

https://www.blackwaterskies.co.uk/imaging-toolbox/

Focal Reducers can lower the focal ratio (making the capture of photons quicker), but this also makes the object smaller. So for instance, if you have a telescope a F7.5 and you buy a Focal reducer x 0.8 this reduces the focal ratio to 6. (7.5 x 0.8)

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3. DSLR Camera

Ok, so you’ve bought a suitable mount and telescope and we are assuming you already have your DSLR. If not the one that is generally recommended is Canon and I personally recommend you get one capable of live view and that will do longer exposures than 30secs which is a disadvantage of some models. I used a 450D to start with and currently own an 1100D. Live view is pretty essential to getting good focus and seeing if you have the target in the FOV without you having to bend in awkward positions. Many model DSLRs have a flip out LCD screen which is even more helpful.

Other makes can be used but I have no experience of these. I understand there are problems modifying some other makes of DSLR cameras which is a necessity if you are going to be able to capture the best data, but we will come to this later.

The camera will be supplied with an interface cable so you can attach the camera to a laptop, if not I recommend you get yourself one as trying to see through the viewfinder on the back of a DSLR and focus (just think of the awkward angles your camera might be at in pointing at your chosen object) I think must be an extremely - not mention back and neck achingly - difficult job. Some people like to be more mobile than this and not have to take a laptop to a temporary location, but this is entirely up to you.

I like to use a laptop as it is much more comfortable, you can even network your laptop so you can sit in the warm and do it, focus is easier to see and do and downloading the files directly to your laptop I also find easier, so I am going to explain imaging using a laptop.

I recommend that you buy yourself a 2nd battery for the DSLR so one can be charging while the other is being used, although lately I have bought myself a cabled battery, as this runs off 12V and doesn’t need re-charging which means I can go to bed for a few hours and leave the imaging running without having to get up to change the battery. It also slightly reduces the amount of heat in the camera and thus slightly reduces the noise, which is a problem in the warmer weather with DSLRs as they are not cooled.

You will also need some means of attaching your DSLR to your telescope. You will need a T Ring (which fixes to the DSLR) and a T adapter which has a 2” nosepiece to fit into the telescope. You will get better results if you use a flattener instead of a T adapter, and these are designed for specific telescopes, they flatten the field and the distance from sensor to flattener lens is vital to getting a nice flat field and nicely shaped stars into all the corners.

N.B. The Cable supplied is generally not long enough, so I bought myself a USB extension cable, here we go, spending more money, but this is only the beginning.!!!

So what else will you need?

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4. Laptop -

.... and some means of powering it, not a problem at home as you can use mains. If you are out in the field, you’ll need a power pack (this will not last for too long), or a Leisure Battery and an invertor.

You will need power also for your mount, but this generally runs on 12v and comes with it’s own lead. You’ll need a mains to 12V adapter most probably with a cigarette lighter socket on the end. Or you can buy a power cable (which includes a 12V adapter from a reliable Astro-Retailer, I bought mine from

Modern Astronomy and this has a regulated power supply.

Depending on your laptop, and how many USB ports it has, you may need a USB Hub. Always plug the same USB plugs into the same port otherwise it re-installs the drivers and can cause problems. Suggest keeping some sort of template for this, or mark your cables and ports.

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5. Capture software:

I used to use Canon Utility and really like this, but there are several other types of capture software out there which are also good. Canon Utility came with my Canon Camera on a disc so easy to install.

By the way - do install Digital Photo Professional on your laptop (it is part of the EOS Utility suite) as it enables you to view what you have captured see the details and check your histogram on flats (which we will come to later).

APT which I really like as it has many useful tools

http://www.ideiki.com/astro/

Inexpensive and you get a years support. It has some good features and good feedback.

Plus it has a Yahoo Support group

Backyard EOS

I have never used this but I hear it is very good

https://tethertools.com/tethering-software/backyard/

You can also do something called Dithering.

This is a good facility to help reduce noise in images as what it does it move the mount by a few pixels between images so that the noise overlaps so to speak.

You can only do this when the Capture software also connects to your guiding software so it can tell the guiding software (in my case PHD) when you are between subs and when it can “dither”

Nebulosity

Maxim DSLR (I believe this is excellent but expensive)

I am sure there are others and will update as I hear of them.

I will explain my method according to Canon Utility as this was the software I was using at the time I originally wrote this webpage.

Stacking Software

I use Deep Sky Stacker which is a free download.

For Moon and planets I use Registax - also free.

There are other stacking software out there but these are the ones I am familiar with.

Post processing Software:

Photoshop is the software that I use. A bit complicated if you have never used it, but essential, and you can get lots of support on the Forums. Processing is another artform in itself and I will come to that later on. Photoshop is not possible to buy any longer, you can "rent it", or you can also use Photoshop Elements which I gather is a little cheaper.

Pixinsight: which was designed specifically for Astro-imaging, is supposed to be good, but I think there is a steep learning curve and it is fairly mathematical with lots of scripts.

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OK, you have your camera, your telescope and your mount, and a laptop and have installed your software, you’re almost ready to take your first image.

I’m assuming here that you are already familiar with the celestial sphere, how the Earth rotates and how to set up a telescope for a GOTO, but in case you’re not familiar I’ll go into this in a little more detail.

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6. Polar alignment:

This is most important for imaging as you need to orientate your mount so that it is looking at the celestial pole , so that the RA axis of the mount can rotate following the motion of the Earth. If you don’t do this accurately the object with drift out of the FOV and you will get stars trails.

(BTW - I am working from the Northern hemisphere)

You cannot afford to skimp on this.

I am assuming if you have bought your mount brand new that you have checked that your polarscope is aligned correctly within the polarscope shaft. It should explain in your instructions how to do this. Even if it second hand it is worth checking this.

Alternatively this tutorial is very helpful.

http://www.astronomyshed.co.uk/forum/viewtopic.php?f=19&t=4006

1. Place your mount so that the polarscope is pointing towards polaris and so that it is level (having extended the legs to the height that suits you). There is usually a level bubble on the side, but make sure that this is accurate first time you use it with an independent spirit level.

2. Turn the Dec axis horizontal so that you can look through the polarscope by removing the circular cap on the top. This requires kneeling down and craning your neck.

N.B. If you polar align without the telescopes etc on the mount, this puts less strain on the adjustment bolts, but don't forget to extend your counterweight bar or this will obscure the view through the polarscope.

If you rotate your RA axis, you’ll see that little circle rotates around and

this is the path that polaris takes around the pole as it is 1 degree away from the true pole.

Some polarscopes will have Ursa Major and Cassiopeia marked as well as a guide.

3. On the body of your mount you will find 2 sets of knobs, the front and back ones are called the Altitude or latitude knobs and these adjust the mount vertically. The smaller ones each side are called the Azimuth bolts or knobs and these turn the mount to left and right.

4. What you need to do now is find out where polaris should be at this time, around that that big circle and rotate the RA axis until the polaris circle is at that position . Then you need to adjust the altitude and azimuth knobs described above until you get polaris into the little circle on the big circle.

There are many methods of doing this., depending on your mount. I don’t intend to go into all these methods, but I will tell a couple of quick ways:

a) You can either rotate the RA until Ursa major/Cassiopeia are positioned as you can see them in the sky (though you won’t see them through the polarscope).

b) or you can use a software called Polarfinder. Provided your laptop has the correct time, this will tell you where polaris should be.

It is best to use Universal time for polar alignment.

If you want to fine tune your polar alignment even further, you can use a software called Alignmaster. There is a very good video on it on Astronomy Shed (also available on You Tube)

http://www.youtube.com/watch?v=dNRFm3LtCrE

You will find a number of useful links and tutorials on the web

Do not skimp on polar alignment, or you will get star trails, rotation, or an imperfect GOTO.

The method I use now and it is brilliant (if costly) is Polemaster. It is a camera fitted to your mount (it will work on a number of mounts including the Skywatcher Star Adventurer. Using software and rotating the mount it works out where polaris should be.

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7. Balancing the Dec and RA.

Home position:

The home position should be with the counterweight bar pointing down to the ground , with the telescopes squarely pointing at polaris.

Balancing:

RA: Before you can proceed any further you need to put on your telescopes and cameras and anything else of any weight and check the balance of the RA, by unlocking the RA lock and rotating the axis. If the camera end is too heavy, move the counterweights down, or add another if necessary. If the counterweights are too heavy, move them up the counterweight shaft. Put the RA axis back to the home position and lock it again.

Dec: Undo the Dec lock and rotate the dec axis. The telescopes should balance each end. If not you may need to move the telescopes up or down, and/ or any hardwear also mounted upon them.

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8. Doing an alignment

The basic way:

Return your Dec axis and RA axis to their starting or home positions.

Put the cap back on the polarscope and put the cover back onto the bottom of the polarscope.

Switch on your mount and enter the location, time and date.

Remember to use the American format mm/dd/yyyy

Don’t forget whether you are using daylight saving in the summer or not in the winter.

Select an alignment method - 1 star, 2 star or 3 star

I must confess these days I only bother with a 1 star alignment as I discovered my set up has cone error. So long as I aim for a star on the same side of the meridian as my target, and then I double check on a bright star or visible object like a cluster close to the target to "sync" the alignment it finds the target just fine.

These days many people do not even bother to do an alignment as they control their mount from the laptop and do plate solving, but that is much more advanced and not for this tutorial. I personally prefer to do it with the handset the old fashioned way.

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9. Connection to the Laptop

It is at this point I switch on my laptop and and DSLR and open up Canon Utility.

I do my alignment on screen and I can also stop on one of my alignment stars and focus as you’ll need a bright star to focus with anyway. I put on my Bahtinov mask and focus.

Once the laptop has recognised that your DSLR has been switched on, the Remote shooting bar brightens up. You can then click on this to open up the control window (see below - Camera settings/Remote shooting is brightened up).

You then get the control window:

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10. Getting Focus

Use a Bahtinov Mask, it is by far the easiest way to get focus. Some software will let you measure FWHM (full width half maximum which measures the star and the lowest reading is when it is in focus).

The Bahtinov mask splits the light .

When the central spoke is dead centre, then you are in focus. Lock the draw tube and do not move it again.

Remember to remove the Mask afterwards

N.B. You can also use a Hartmann’s mask or a Y mask, but I have found the Bahtinov the most accurate

OK, so you’ve finished your alignment and focussed

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11. Capturing your first image

I am now going to take you through a simple step of capturing an image, but without guiding.

We can add in guiding after we have conquered this step.

Without guiding of course you will not be able to capture a long image before star trails start to appear, but this is good enough for practice purposes.

First of all decide what you want to image and find the object using your usual GOTO method. This is something you will have to learn yourself and live view will only help if there are bright stars in the image. So for this exercise, let us do the Orion nebula M42, as that does indeed have bright enough stars for you to see on live view.

Centre the object as best you can.

Set your settings on the camera.

Many of these can be done on screen.

MANUAL, BULB, 800ISO NB: I have more recently been experimenting with using 400iso and 10 minute subs instead of 5mins with 800 iso, I am finding the results less noisy.

Select RAW files as these give the best quality data (you can select RAW and Large if you want a quick Jpeg to examine.

Daylight white balance (That’s the little Sun in the image)

Make sure you have switched off your noise reduction in the camera as we will deal with this separately.

The timer window (below)

In this case I have set 5 minute subs with a delay of 15 secs before they start, and an interval of 30 secs between the subs, ideally this should be around 45 secs to allow the camera to cool a little between subs, so interval timer shooting is the length of the sub plus the interval time, this trips up a lot of people.

Lastly, how many shots you want to do.

In the case for your first practice shot of Orion nebula, you should try out 30 sec shots (subs) and see how you go.

You can then review your captured images in Digital photo Professional where you can also zoom in.

Remember your single captured images will not look like your stacked final result after processing.

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12. Viewing your first image

If you are using Canon Utility (including Digital Photo Professional - DPP)

You will be able to organise you images as they are taken.

This is a screen shot of my DPP when I was imaging M42 (but at 5mins per frame)

If you look on the left side you can see where I have made sub folders where I drag my subs into for each imaging session having examined them to make sure they are OK, and I can add the appropriate calibration frames to sub folders of those folders to go with each session.

13. Calibration frames (Darks, Flats and Bias)

Lets assume you managed to get say 10 x 30 sec images (subs/light frames) of Orion nebula

The next thing to do is take darks

These are exactly the same images taken again but with the lens cap on.

i.e. Same length, same temperature, same ISO

Darks:

Darks are subtracted from your image to attempt to remove any temperature electrical noise and hot pixels from the image.

You won’t notice the difference this makes with such short subs but it is best to get into the habit of taking them so when you get into longer images you are well used to it. You don't have to have the same number of darks as light frames, but I always try to do about a dozen.

Another tip is to take your darks when the clouds roll in so you don’t waste precious clear sky.

Bias:

You also need to take Bias frames, these remove the “read noise” from the images. These can be done and saved and re-used for a few months as the read noise doesn’t really change much. Bias frames are very short images with the lens cap on (the shortest image your camera will do).

My Bias settings are normally AV 800 ISO, shutter speed 1/4000

You need to research and work out what is right for you.

Flat frames.

These take the vignetting, distortion , gradients to your optical plane and dust particles out of your images, and will make a huge difference to the finished result.

IMPORTANT: You should not move your camera or the focus otherwise the dust will not line up.

There are a number of ways of doing these, but I find the easiest way for me is to do them during the day time, either before I start an imaging session, or the following day.

I have heard of some imagers who are unable to leave their kit up until the following day but remove the telescope with camera still in place and take the flats the following day. I even did this myself on one occasion when imaging away from home and just remembered I hadn't done the flats whilst dismantling the rig, I took the scope home with camera still attached and unmoved and took the flats when I got home, and it worked OK.

(Imagers who use a CCD camera and coloured filters have to take separate flats for each filter and need to do them at night, therefore you will hear talk of light boxes etc, but using a DSLR there is no need to go to this trouble, unless you are unable to leave your imaging rig set up until the next day and have forgotten to take them the night before). Leaving up until the next day is best as you may not be exactly sure where focus is the night before).

How to take Flats

I wasn’t doing these properly to start with and the flats were not removing anything from my images. Once I got them right I made a huge leap forward in progress.

What you should do is take an image of an even diffuse light (and nothing else).

Some people use white monitor screens, some use a white T shirt in front of the aperture, or a piece of white typing paper but this has to be kept flat. You can also point the telescope at the sky if it is not too bright, however sometimes there are clouds. I decided to make myself a sort of lens cap, but with a flat piece of white typing paper across the end, this diffuses the light and I point it at the daytime sky (opposite direction to the Sun), and then it doesn’t matter if there are clouds in the sky.

With my 450D I used 100iso & AV and point at the dull daylight sky (just before dusk is best and the mask as described above to even it out, as there is a slight risk of getting bright stars in the flat otherwise), or uneveness from clouds.

However this did notwork when I subsequently bought an 1100D and I had to experiment with different exposures and check the histogram until I got it right.

Demonstration of the effects of not applying a flat frame:

This is an image of the Horsehead Nebula stacked without applying flats and trying to process it. Personally I find it almost impossible to process images without flats. You can see that there is vignetting at the corners, and the middle is brighter, and also it shows dust bunnies.

Back to capturing your images.

Hopefully you will end up with a series of single M42 light subs which look something like this.

A few Tips

Now we have got this far I am going to suggest that you find a way to mark your drawtube so that you know next time approximately where the point of focus is, plus, mark your orientation of the camera in relation to the drawtube and flattener or T piece whichever you are using. This means if you return to the same object at a later date you can orientate it roughly the same.

When you have finished using your mount and want to switch off, always return the mount to the Home position. In EQ6 and CG5 GT this can be found in Utilities, select Home position (or Park Scope) and you have a choice of setting the

Home or Park position or GOTO Home Position.

If you are setting the Park or Home position for the first time, you will manually slew to the Park or Home position and then press “set”. The next time you use the mount, it will remember that position and you can select GOTO

Park/Home Position and it will automatically go there.

This avoids the Mount getting a bit confused which it might do if you switched off anywhere.

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14. Stacking

Use Deep Sky Stacker to start with, most people do and it works pretty well.

Deep Sky stacker has it’s own set of instructions at the bottom left, Deep Sky Stacker Help.

So I don’t intend to go into much detail here.

I just used the defaults when I first started and these should set you off on the right track.

Load your actual images (light frames) in Open Picture files top left.

Load your darks, flats and bias underneath where it says.

You may need to drop down the menu to select RAW files.

DSS will then stack away, subtracting your darks, flats and Bias from your image and will finally produce a stacked Tiff

DSS will do an autosave to file, and will also save a master dark, a master flat and a master bias. My photoshop cannot open these I think they are 64 bit and my Photoshop CS3 will only open 32bit

So I also save picture to file (in the processing box), I can file it where I want to, and it will be a 16bit Tiff. By saving my own file I can name it and place it in a folder of my choice.

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15. Processing

You are now ready to open your image in Photoshop

THIS IS WHERE THE MAGIC BEGINS

This is post processing of a stacked image of the Horsehead Nebula Taken in 5 minute subs using guiding as it is a better demonstration of the power of processing than using the 30sec subs described above.

Post-Processing

This is another artform in itself, can take a long time to learn (I am still learning)

I am just going to take you through a few basics, and give you a few links to useful more advances processing. But these basics will show you what can be done.

Every-one has their own approach, so opinions may vary on this.

MOST IMPORTANT - ALWAYS PROCESS IN 16BIT (OR YOU WILL BE THROWING DATA AWAY).

ALWAYS KEEP A COPY OF YOUR PROCESSED TIFF FILE -

YOU MAY WANT TO GO BACK AND RE-PROCESS THIS AS YOUR PROCESSING SKILLS IMPROVE.

Never convert to Jpeg if you can avoid it, even for E mailing and posting on websites. Normally a PNG file will E mail or post and doesn't lose the data quality like a Jpeg will

When you have finished stacking import the image into Photoshop (lower left "save picture to file")

You will end up with a fairly black image like this.

N.B. this is a long exposure image of 5mins per frame and only really achievable when guiding (see guiding later on).

You will now have a fairly decent finished image:

There are many, many things you can do in photoshop to improve your images, including adding some plugins, but this cannot be learnt all at once, they come with practice and acquisition of new knowledge, take a look at my Video tutorials page.

When I first started I bought myself a DVD by Adam Block of post processing with Photoshop and learnt a lot from it.

Objects with bright cores, need to have two sets of images done on them. Short ones for the core and longer ones to reveal the main galaxy or nebula and these can be combined in Photoshop in a method called layering and masking which I have only just got to grips with myself. There is a thing called High Pass filter which can bring out detail in faint objects, again I have only just learnt.

One important thing to note, is always process in 16 bit as you lose a lot of data when you convert to Jpeg. I always convert to PNG if I want to E Mail or post an image on a Forum, but make sure you always keep a copy of your 16bit file. You can convert in Image/Mode

A good tutorial on DSS stacking and PS Processing

http://www.astronomyshed.co.uk/forum/viewtopic.php?f=19&t=1328

Some useful processing tips

Reducing noise: Filter/noise/despeckle (don't go too mad with this though)

Plug ins: HastaLaVistaGreen (freedownload, takes green out of images)

RCAsto-Gradient Exterminator (does what it says)

I will leave you to experiment with processing as the next stage is I need to do is talk about guiding so that you can capture the data in longer exposures.

Guiding Principles

Even with accurate polar alignment your mount tracking will not be accurate enough to do long exposure without geting star trails. So guiding is simply to correct the tracking.

The idea is that the guide camera looks at a star and keeps it on the crosshairs. If the mount deviates and the star moves then a signal is sent down the cable to the mount and tells it to adjust, and this finely tunes the tracking so that long exposure can be obtained without star trails.

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16. GUIDING

There are different ways of doing guiding.

a) The basic is to mount a 2nd telescope alongside the imaging telescope either side by side or piggy back., so it is looking in the same direction as the imaging scope, and is fixed to the mount so that it moves at the same time as the imaging scope. You need a 2nd camera for this. Both the guide scope and guide camera do not need to be of such high quality as the imaging camera and scope. This is the method I chose.

b) You can adapt your finderscope so it becomes a guidescope, but you still need a guide camera. March 2013 I am using this method now and find it brilliant, you can even use your finderguider as an "on-screen" finderscope (with PHD) saves having to get yourself into awkward positions to see the alignment star.

c) You can use an off axis guider where the guide camera attaches to imaging scope saving the need for a 2nd scope.

d) Some really expensive cameras have the ability to do both imaging and guiding.

e) There are stand alone guide systems, which do not require a PC such as:

SmartGuider, Nexguide, Synguide etc

It is important that the guide scope does not wobble, but also important that you can manipulate it so you can point slightly away from the imaging scope should there not be a suitable guide star in the Field of View (FOV). Though with the finderguider method, the FOV is so wide that it is extremely unlikely that you won't find a guidestar.

The QHY5 guide camera has two cables coming out of it. One cable goes to the laptop, and the other an ST4 cable plugs directly into the autoguide port on the mount.

It is also important that the cables do not trail and wave around when hanging off the back of the guide camera as this can cause minute vibrations and upset the guiding. I tie my cables to the hardware.

This is my current guide scope and camera (2014)

You can see the guide camera (QHY5) in the back of the finderscope. A dew heater wrapped around the front to stop it dewing up.

I purchased some very small guide rings from America (couldn't find any that small in the UK), to hold the finderscope as I was finding I was getting flexure using the Skywatcher mounting bracket. Flexure means some small movement between the imaging scope and the guidescope.

I use PHD software on the laptop - this is free and is excellent for guiding. You need to install the drivers for your Guide Camera and then select the camera and the mount on PHD. Once both are connected click on "capture" and this will show what stars are available for guiding with. If you cannot see any stars then you could be out of focus, or there is not a suitable star in the FOV.

To find focus the first time, try pointing at something bright like the Moon and get focus, then mark the drawtube so you know where to find focus again. It is possible you might need an extension tube to reach focus.

If you’ve checked your focus and still cannot find a star, then you need to adjust your guide rings in order to find one.

The above is PHD1 which was the standard when I made this tutorial, there is PHD2 now days which is a slightly more technical, but to be honest I have never bothered to change from PHD1 since it does the job perfectly fine. I have it on an installation disc which came with my QHY5, so unless that dies on me and I am forced to move to PHD2 I will stick with it.

I will see if I can get hold of some PHD2 examples to post up here.

N.B. There are lots of tweaks, and nuances to do with controlling PHD (in the "brain") which I do not plan to go into here as I am just explaining the basics.

You need to recalibrate if you move to a different part of the sky.

You can examine your subs as you do them and see if the stars are round, you will learn over time that some of the slight movement in the graph, is just the mount doing adjustments, but if they get too big, you will see mishapen stars. You can also see how a simple thing like slightly touching the mount or moving or drag on a cable can cause big peaks in the graph.

I have been told that you should weight your mount just slightly heavier to the East of the Meridian which gives the drive train a constant load to work against. If the scope is “perfectly” balanced so as to have no bias east or west, up or down, the OTA can oscillate slightly .

So if you are imaging East of the meridian, the counterweights should be slightly heavier. If you are imaging West of the Meridian the cameras should be slightly heavier.

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17. Modifying your DSLR for Astro-Imaging

To Mod or not to Mod?

There is a lot of discussion about whether or not to Modify your DSLR.

Modifying the DSLR removes the IR filter from the camera so you can capture the red Hydrogen Alpha in images.

Some people are reluctant to do this because you will get pinkish coloured photos for daytime use. However this can by overcome by doing a custom white balance with a white sheet of paper. I have never done it, but have seen it done and it works fine. Alternatively depending on your day time camera lens you can replace this with a clip in IR filter, or lastly there is a replacement IR filter which goes over the lens, but currently is only available n the US via the internet. I had my camera Modded around 2011 and since that time the data I have captured not only now includes the Ha, but also I am generally capturing much more data and my imaging has taken a big leap forward, I don’t think this is just due to my own progression as an imager.

The IR filter can be replaced with plain glass, or a Baader filter. I gather there are focusing problems if used with a daytime lens if the filter is not replaced at all, so I had a Baader filter put in. It is not cheap to have the camera modified, but if you are clever with electronics you can do it yourself if you are handy with this sort of thing.

There are two places I know where you can get this done. This is where I got mine done, Andy at Astronomiser - I believe he still does it.

http://www.astronomiser.co.uk/

Juan at Cheap Astrophotography, who sells already modified DSLRs and also will modify your own. I have never personally had any dealings with him, but I know many have and have been very happy with his work.

https://www.cheapastrophotography.com/

One final tip

The more images you do the less noise will be apparent because of the slight overlapping of subs. This can be made better still by dithering in guiding where the guiding moves a couple of pixels between subs.

Below is an example of the Rosette nebula with varying subs

This is about as far as I plan to go, as this is really a simple

introduction to get you started.

I suggest joining some of the imaging forums on the web, for more

in-depth and specific questions.