Quote:
Originally Posted by Stonius
Working through your example and just going by the graphs, I get 141 at unity (offset 21) and 368 for Gain 200 (offset 50) for a ZWO1600.
On my test images of 47 Tuc I was getting the background around 2800 (16bit values) on Luminance subs of 30 secs at Gain 75, -20 degrees Celsius. I can't remember the offset I think it was 21. Maybe that's all wrong. The brightest parts of the image are at around 32,000. Statistics show the brightest pixels at 65504, just 31 shy of clipping at 65535. I think this was the basis on which I was exposing, TBH - not clipping, rather than skyglow)
It was a heavily light polluted area. Maybe I should have been using gain 200 with shorter exposures.
Markus
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The 1600 has a 12bit ADC so you need to multiply by 16 rather than 4 so your target values should be 4x higher.
Also for the 1600: RN=0.482*Gain (in e-/ADU) + 1.178
At unity with an offset of 21 I get a target value of 777 as the RN is 1.7
A histogram peak at 2800 is quite high so you would get more clipping than if you targetted 700 as per the calculation for 70/21
Don't go higher in gain. 30s subs are already short and you still need the integration time.