Picking a camera for your telescope, what camera and why?

Picking a camera for your telescope to some is a very easy process, you simply look at what new DSLR you want and pull the trigger. However, once you get into the hobby with any level of depth, you realize that the vast web of information can get overwhelming quickly. Here I’m going to outline pretty much everything I know and some resources I really like to make it a lot easier.

Cooled or no?

This is an easy question, the answer is yes, you should get a cooled camera. The only reason I would say otherwise would be if you live in Canada and only image in the winter. Cooled cameras drastically reduce the noise in your images to a degree that is very noticeable and makes processing way easier. The image below shows the level of noise (dark current) as you increase temperature on the sensor. As you can see there is a very steady decline of noise as your sensor gets colder and I can tell you from direct readouts, your DSLR in the summer is easily sitting above that 30 degree mark if you’re in the northeast US like me. My ZWO ASI1600mm-Cool sits at -15C every imaging session as I’ve found that’s a good balance between cooling performance and not stressing the cooler every imaging session. I would say it probably isn’t best practice to max out the cooler every imaging session as I would assume the life of the cooler decreases under that kind of stress.

Noise level with temperature graph for the ZWO ASI1600mm-Pro. Credit astro-imaging-camera.com

Mono or Color?

This is a bit of a more personal question. The way a camera works is by filtering out light through a bayer matrix and that gives you a color image. Only red wavelengths can pass through the red filter, blue wavelengths through the blue filter etc. What this means is there is a lot of light lost in a color camera as it filters out certain photons. The result is what we see as color noise and a lower effective resolution in your objects. A mono camera does away with this bayer matrix and lets all light in equally. We get color images by then putting a red, green and blue filter in front of a mono sensor and combining the three images later. It is a lot more work and takes longer to do, but the results can be staggering as a result. I’ve personally had both so I have a bit of experience with each workflow. If you don’t get many clear skies per year and don’t want to take days to edit a single picture, color is your way to go. If you’re more like me and are a perfectionist with your images always chasing that little bit more detail, you’ll likely end up frustrated with color results when compared to color images shot on mono. Mono does also cost significantly more to get into though, so tight budgets will also want to stick with color or save up longer and look for a good deal. There are some great cooled color cameras that can be had under $600 on the used market, and I actually prefer color images in many cases when it comes to something like galaxies or other broadband targets due to the way color correction is done on a mono split channel image.

Pixel Size

Pixel size is going to determine the actual resolution your object comes out with once your image is done. You can think about this logically, larger pixels collect more light and therefore result in less noise. However, if you have a fast scope such as a RASA, the extra light gathering of a large pixel probably isn’t worth the tradeoff in resolution since with a larger pixel comes less space for more pixels. Larger pixels will also take up a larger section of the object you’re shooting, so once again if you think about it logically, a smaller pixel will result in more detail being recorded. If you’re pixels are very small on a long focal length telescope though, you won’t increase your detail by getting more megapixels. This is because you’re running into limits with atmospheric interaction with your image and the limits of optical resolution out of your telescope. After all, your telescope will only resolve so much detail before it can’t focus light any finer. So in general, larger pixels work best for longer focal length scopes and smaller pixels work best with shorter focal length scopes, though this rule is malleable to some degree. Something like a ZWO ASI1600MM has a pixel size of 3.8 microns. I’ve used this camera with a scope over 600mm and with my current scope under 400mm and both worked very well. You can also bin your images which basically combines pixels to get an effectively larger pixel. This topic gets very technical and very confusing quickly so I won’t go into too much detail here, maybe in the future I’ll write up something really in depth, but you should have enough here to get going.

I really like this website which allows you to input your camera and telescope and see if your sampling is good or bad on the fly, use this site as your starting point for basically all your camera/scope buying interests. Make sure you switch to imaging mode though.

Link: https://astronomy.tools/calculators/field_of_view/

Software and Brands

Companies producing cameras these days have been getting much better with driver support and customer experience, so it’s not as important as it used to be. Generally today the two biggest players are ZWO and QHY. Both are great options, but the ecosystem for ZWO has more options in terms of equipment outside the camera that works together such as the ASI Air. My default option would be ZWO unless you get a great deal on a QHY or don’t need any other ZWO gear. Beyond these two companies you have your DSLR options such as Canon and Nikon, but honestly their astro focused options are pretty bad value for money. The one I could recommend is a used astro modded T3i or 600D. I got mine for $125 shipped which was an absolute steal and I would do that deal any day of the week if I was a beginner again. Great images for a very low price when paired with a good duo narrowband filter. As you get into the higher end you start to care more about what sensor the camera uses rather than the camera itself. I know a fan favorite is the Kodak KAF8300 sensor, but the pixels are big and the sensor isn’t very high resolution so it just wasn’t for me. For the purposes of this article, there isn’t much more you need to know about brands as beginners really shouldn’t be looking at real scientific focused cameras.

In terms of software, the DSLRs will have the most software available to them, but it isn’t by much at all when compared to the astro focused cameras and it really doesn’t matter anymore. The DSLRs can also hold batteries internally which might be a big plus to some as well. Software like NINA can support all of them equally though and in the end the astro cameras will basically universally perform better.

Some Extra Things To Consider

Nothing here is too much of a concern, but something to consider is that astro cameras will require a bit more in the way of maintenance. My DSLR cleans its sensor automatically, my ZWO won’t. Icing and dew isn’t a problem with my DSLR and yet, because my ZWO is running at -15C, it matters. There is a fan in the astro cameras which means you have a moving part that will eventually break. The cooling systems occasionally fail as well, though that is exceedingly rare these days. These things aren’t exactly huge issues, but they are things you’ll have to retune your brain to think about. I’ve done it without an issue, but I have had to clean my ZWO sensor a couple times due to dust and it is stressful for sure. The important thing is that you do your homework and know what you’re getting into. These things cost a lot money and not understanding how they work could lead to damage or at the very least a very frustrating experience.


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