CMOS basics and 294C

[kasism]

Hey so switching from using ccd cameras since an ST6 in 93 (ST4, ST6, ST2k, STL11000, STT 8300, STF8300C) so this is all new territory in CMOS.  Just got the 294C, and  I am testing the camera out on a AT92. @ f5.5 in a heavy light polluted area.  Imaging using The SKYX with Ascom drivers.

Starting test, gain 1600, offset 35, exposure 15?

Initial tests stars had black centers (in focus), is this the effect with over saturation in CMOS?

Tried 1600 gain @ 25, 35, 45 offset, tried 60?, 30?, 10?, 3? exposures. At 3? 1600 gain, 45 offset, black centers went away. 
What is ?unity? on this camera, is it 1500?   Is offset equivalent of the ?pedestal? in ccd?

Your great graphs in this forum seem to show that a gain of 1500, gives best noise and at -15c beat read noise balance.   

But what is the offset?   

Is there an algorithm to define what is unity gain & offset?

Again very beginner CMOS questions, but this CMOS imaging is all new to me, I have been a CCD follower, and TheSkyX user for a very long time!

Keith

[eseavey]

Welcome to the CMOS world! It is a different world than the CCD.  In general, because the wells are relatively small, you need to use unity gain as a starting point.  Offset needs to be set to be able to subtract things like ampglow.  With your camera, 20 or 40 offset is fine, check the histogram.  Sharpcap pro has a tool to analyze your camera and can give you the optimum settings for a given scope/sky: https://www.sharpcap.co.uk/sharpcap/features/smart-histogram
Once I used that, I got really good images with my cameras.

[kasism]

Hey thanks for the information.  Have gotten some very good working level understanding, it was all based on a video done by the creator of SharpCap - https://www.youtube.com/watch?v=3RH93UvP358

The lights came on, and now I have a much better understanding.   I change my settings based on where I am shooting and have realized that the CCD maxum of longer is better is wrong.   So I got a terabyte ssd, and now understand stacking a lot is my new push.   

What are others using?  I have mostly used gain of 1601, and exposures of 240 sec at -5C for reasonable skies. 

A fun camera so far now, just a learners curve that was like driving on the other side of the road ...
keith