What gain/exposure time to use with a CMOS camera

[ChrisV (Chris)]

I'm using an ASI071MC-cooled. I realise CMOS cameras are a completely different kettle of fish to CCDs. Read noise, variable gain etc.

I know not many have the ASI071 which I'm using, so if there are ASI1600 or like users who could tell me what gain/exposure times they use and why. What issues should I consider? Or am I trying to make things to complicated for myself (I am a complete noob at this).

The standard ascom interface for the asi071 has:
- zero gain (2.6e-/ADU). Gives full well capacity of 46k e- and read noise ~ 3.3e-.
- unity gain. Gives well capacity ~18k e-. Read noise ~ 2.7e-.
- or higher gain. Say 0.5e-/ADU. So get well capacity of ~ 8ke- and read noise ~ 2.5e-.

My mount will track for up to 10min (that's the most I've tried). So far I have been using unity gain with 5-6min subs or higher gain with 3min subs. I've used these sub lengths because it gives a histogram that peaks at ~ 10-20% though the range.

[glend (Glen)]

Chris, Shiraz did alot of work on this and produced charts for things like optimal exposure time for various f #. His work was all based on the ASI1600MM-C.

I have played around with different gain setting on my 1600, but always come back to Unity. If i am very short of time i will go high gain to complete say some narrowband i am gathering to infill a RGB image.
I never use subs of more than 5 minutes and that is only for narrowband. For broadband your optimal sub length us determined by your sky glow. ADU targets can pin it down, and i assume you can monitor that with SGP or some other tool.
Have a search for Ray's charts. Ok did it for you.

Look here:
http://www.iceinspace.com.au/forum/s...0+exposure+ADU

[ChrisV (Chris)]

Oh wow! That's a load of great info. Thanks heaps - and Shiraz for doing this.

Looks like I might be making my subs way too long. Plus looks like I haven't got my offset high enough either... More reading required.