Dark current of CMOS cameras

[iantaylor2uk]

Some astrophotographers cool their cameras down to -15 C or lower, whereas others only cool to 0 C or -5 C. There seems to be some confusion as to what is best.  

I think this arises becauses manufacturers tend to plot the dark current on a logarithmic vertical scale. As an example, see the graph below (from ZWO) for the 533MC-Pro OSC.

Now it may not be immediately obvious, but the vertical scale is actually logarithmic. The peak dark current, at 30 C, is 0.125, whereas the smallest dark current, 0.00013, at -20, is almost 1000 times less!

I digitized the graph below, using the very useful website https://automeris.io/WebPlotDigitizer/ and replotted the data on a linear scale - this is also shown below too. 

This is why I personally tend to use 0 C or -5 C, and don't tend to go to lower values - I also live in a Bortle 6-7 region, so the light pollution levels will usually far exceed the dark current from the camera.

Hope this is useful. 

[Elp]

I saw this previously. It's true, they also don't uniformly scale the full well depth graph so you can be comparing two cameras and one looks significantly better than the other, but factor in unity gain or HGC modes and that FWD soon drops to lower levels.

I also image with uncooled, after post processing with NR (which you 95pc of the time WILL use on a finished image), there's minimal difference from an uncooled camera to a cooled one, my ambient temps however are usually cool/cold/freezing.

[Clarkey]

Having said this, there is no loss in running at -10 or -20. I have two sets of darks - one for -10 which I can achieve all year regardless of ambient temperature. I also have a set for 0 degrees which I use on battery to reduce the power requirements.

I think sub length is probably more important once below zero, but as I do not want to be producing too many subs, I still run longer than technically necessary. Like most AP, it is a compromise.

[Fegato]

My dark libraries are captured at -10. I would probably choose -5  if I ever get round to replacing them. The impact of dark current at these levels pales into insignificance as far as I can tell, so I'm sure I won't notice any difference. -10 is fine, except for occasional hot summer nights...  I have once or twice had to compromise my subs at slightly less than -10...    I noticed no difference calibrating with -10 darks.

[Martthebass]

I started off using -10C on my 533MCP but moved over to -5C last year and haven't noticed any difference in image quality.

Edited November 7, 2023 by Martthebass

[900SL]

I image at -20c on the 533mc pro, but only because its typically -5 to -15c here in winter

 

In Saudi I imaged at 10C to avoid maxing out the cooling.