SharpCap Forums

Hi Brian,

Hah! That's great to hear about the reduction in dark current! Proof of concept for cooling I suppose

Yes I had it enabled and yes, I realise you're the responsible party for that implementation! In my mind, I've always felt compelled to keep the data as raw as possible for post-processing, even if it does "look" darker in the post-calibration/stacking result. I'm happy to hear and accept arguments against this for astrophotography though..

Let me know how the rest of the data analysis goes!

Cheers
Minos

Minos,

Here are the results. It's pretty much base 10 logarithmic but for clarity I'm scaling it linearly here. I gotta get me one!

Thanks, Minos. Wouldn't it be nice if manufacturers provided this information? It seems like something that lends itself to automation. A good summer project for an intern.

By the way, your value at +20C matches almost precisely my value at +68F for my Altair 290M (uncooled).

Brian

Brian, wonderful, thanks for the analysis!

Looks like there is not a big reduction in dark current for -20°C vs -10°C and since I'm powering the camera with a portable lithium battery, it may be better for power conservation to keep the camera at -10°C, so as to last longer.

Cheers
Minos

Minos, I agree with you if you are running off a battery pack but if you are running off of mains I would go down to -20C. The benefits look small due to the linear scaling of the vertical axis. Perhaps Robin can add to this discussion since it is a little out of my realm of experience.

Brian

Good points Brian!

Hi folks,

the dark noise plot above looks fairly typical in shape (you can find similar plots online). The choice of how far to cool basically comes down to the sky background brightness.

If you are imaging with light pollution with no filters and your sky brightness is 1 e/pixel/s (or higher) then there's really not much point in going beyond about +10C - total noise is going to be 1 e/pixel/s from the sky and a bit over 0.1 from the sensor, so maybe 1.12 e/pixel/s. Cool it down to -20 and you still get about 1.01 or so, which is only a 10% improvement - not really worth it.

Change to a dark site or go to narrowband with sky brightness of 0.1e/pixel/s or lower and it's now worth cooling as far as you can, since the drop from 0.12 to ~0.01 is worth it compared to the smaller sky brightness.

hope this helps,

Robin

Thanks Robin, makes sense.

Minos

Hi guys,

I am a bit confused how to interpret SCap gain values while using ASI...
Lets say, I set up Unity Gain on ASI driver (139),
and how SC treats that gain number? =139 also? or 0? or 100?

A bit confusing...

Hi,

the gain value displayed in SharpCap for the ZWO cameras will match the values shown on their sense of charts on the ZWO website. So if you're looking for unity gain at a value of 139 then just set the SharpCap gain value to 139. ZW0 cameras measure the gain in tenths of the decibel above the minimum camera again, so a value of 139 means that the actual gain is 13.9 dB above the minimum value.

Hope this helps, Robin