When we first step in astrophotography, among the first instructions we hear is you CCD needs to be cooled. There are many cameras for lunar, solar and planetary imaging which do fine without cooling because the targets are very bright. But for Deep Space Objects, which are very faint, we need cameras which can be cooled below 0 Celsius.
C14 with SBIG ST9XE CCD Camera
My camera has a regular peltier cooling option and it has an advantage of water cooling as well. These days i am not using water cooling because pipes must be attached and it pulls the scope which in turns troubles the mount in making an accurate pointing model.
I did a test run of my camera to actually see how much Dark Noise it generates at different temperatures. I acquired 60 frames of 60 seconds subs and then BIAS subtracted them and then stacked them. Then i measured the average Pixel Value of the Dark Noise and plotted it with the temperature range from -20C to +35C with 5 degrees increments. The results are interesting.
Figure 1 starts with a lot of Dark Noise in the frame which was captured at +35C and then it ends with a frame at -20C. One can see the dramatic effect of lowering of the noise with lower temperature.
Figure 1. Animation of 12 frames of CCD having temperature of +35C to -20C
The graph (Figure 2) shows it in more detail. Above 0C, the Dark Noise increases rapidly.. kind of exponential growth. At +35C, the average pixel is producing some 10K ADU value. Now this is extremely high and no Deep Space Object can ever be imaged at this temperature with this CCD. Now DSLRs have low noise generating CMOS chips and they do get to have some nice Deep Sky Objects. There are those who install cooling units in their DSLRs to get more faint signal coming from space.
Below 0C, the noise is comparatively very low. Yes cooling gets you to image very faint object but there is not a huge difference of dark electrons generation in sub zero CCD temperatures.
Yes Pros use liquid nitrogen etc.. but that’s quite a different world than our mare mortals’. So yes.. we should be all happy with our sub zero chips. We have bigger enemies than CCD temperature.. we need to kill the clouds first!
Figure 2. Dark Current Vs CCD Temperature