There are many different dedicated astrophotography cameras available on the market. They can have very different characteristics, and even different architectures such as CCD or CMOS style chips. At first glance, they may seem like they are not as good as a DSLR: astro-cams often have fewer megapixels, they can't be used as "normal" cameras, and many of them are monochrome, not even giving you a color image! (though in astrophotography, there are quite a few advantages to imaging in monochrome, a topic for a different blog post)
While all of that may be true, there are a class of cameras that have a huge advantage over DSLRs when it comes to deep-sky astrophotography: any camera that has a cooler, or regulated temperature control, is excellent for our special purposes.
The most important part of the astrophotography game is maximizing our Signal to Noise Ratio (SNR) in our images. There are many sources of noise that make it into our frames, and a significant contributor can be dark noise, as well as dark current. Both of these things are unwanted and contribute to a worse final SNR in our images. They are also both temperature dependent: the warmer your sensor, the more noise and dark current will accumulate.
For a more in-depth discussion about this aspect of astrophotography, you can check out the blog series Astrophotography, Pixel by Pixel: Part 6.
What all this means is that a colder camera will produce far less dark current and dark noise, and will therefore improve our image's SNR. The colder the better! Dedicated astro-cams can commonly get to -15° or -20°C, which when compared to DSLRs that can often run about 18° or 23°C for long exposures makes a huge difference. On average, an increase of 6°C will double the dark current, so conversely, decreasing the temperature of the sensor by each increment of 6°C will halve the dark current.
Another way to think about this, is that if you cool a camera sensor by 40°C, you cut the amount of dark current that accumulates by over a factor of 6! (that's to be read as excitement, not as a factorial)
The other advantage provided by cooled cameras is that the temperature can most often be regulated. When taking calibration frames, the best results come from matching your dark frames in exposure duration, Gain/ISO, and you guessed it: temperature. Cameras that have regulated cooling can keep the temperature at a particular setting you choose. This allows perfect temperature matching between your imaging session and your dark, flat, bias, and flat-dark calibration frames, which further improves the final SNR in your images.
Cooled cameras are better than bad; they're good!
Thank you for your very informative articles
If I understood you correctly, cooling by 6 degrees halves the dark current, so cooling by 40 degrees should decrease the dark current by one half to the power of 40/6 or about 100 to 1! (Again, that’s excitement, not one factorial)