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I’m being lazy here but a quick search seems to suggest the target mean ADU value for a ZWO ASI1600MM-Pro should be around 850 (with a gain of 139) and this should be measured from an uncalibrated sub. So, converting to 16-bit values I have means around 1000 (value drops as the Rosette gets higher in the sky). From this it would seem I need slightly shorter Ha subs, especially when shooting nearer the horizon. The calibrated subs have a mean value of 700 to 750. My Horsehead uncalibrated subs (300s) have a mean value of around 600 in less moon affected skies and a mean value of 1300 in moon affected skies. So it would seem to be a case of really monitoring as you go with certain expectations when the moon/cloud/dust are about. The other factor in this is the stability of the mount (guided Heq5 that is setup on each imaging session) and I guess shorter subs will assist in dealing with its roughness: so while the target ADU could be kept in mind there is perhaps a point where other limitations apply.
Does all this seem correct in theory and practice?
Extra info: the mean values I’m getting are for the entire image. Should I really be getting these values from the background sky only?
Last edited by Benjamin; 13-12-2018 at 11:25 PM.
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