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 Post Posted: Sun Mar 05, 2017 6:28 pm 

Joined: Tue Feb 21, 2017 8:45 am
Posts: 53
Hi - as a new CMOS camera user, I've been trying to work out what all the various settings do in the X2 driver (as a CCD user, I'm used to temperature, binning and exposure length, and that's about it :D ).

I spent some time taking flats, darks and bias frames, and using the BasicCCDParameters script in PixInsight, I managed to reproduce the gain, read noise and full well capacity for my camera (ASI 1600MC-cooled), which gave me sufficient confidence in the results to draw conclusions.

I then played with the white balance and brightness (offset) controls to try and understand these.

Apologies if this is not quite right, but since I could not find any documentation, I'd post my conclusions in case this helps others.

a) Increasing gain decreases the read noise but also full well capacity. For short exposures, the full well capacity is not a problem, so a high gain is a good choice, but for longer exposures, a reduced gain with a full well capacity may be more useful (I realise this is obvious from the figures on the website, but thought it might be useful for someone even less experienced than me...).

b) The WB_R and WB_B are NOT the same as changing the gain. This seems to be a post processing of the R&B signals to multiply them by these numbers. Like increasing gain, the full well capacity is reduced by increasing these above 50, but the read noise is unchanged. I found that values of WB_B of 53 and WB_R of 97 gave me the same intensity in each channel using my flat light source. So, if achieving a good colour balance in the raw frame is your goal, these are useful parameters to alter. However, for DSO images where colour balance is typically achieved in the post-processing, values of 50 for each are appropriate.

c) The value of brightness (offset) applies a constant value to your signal. This effectively takes up some of the full well capacity, so ideally, you want this to be as low as possible, but making sure that it is high enough so that the signal is not clipped on the low side. This number is dependent on gain - as the gain is increased, the size of the signal is amplified, so there are larger positive and negative swings. I found that a brightness (offset) of 15 worked well at a Gain of zero, but I needed a brightness of 100 for a gain of 200.

I hope this is of some use to others!


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 Post Posted: Thu Sep 07, 2017 12:56 am 
Site Admin

Joined: Fri Jul 25, 2014 2:43 am
Posts: 198
I'll consider your suggestion and update in next version.

ZWO software engineer
Location:lon=120.6 lat=31.3
SuZhou China

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