I was reviewing some dark subs recently and it occurred to me to review the dark frame masters vs a single dark frame.
QHY 168C, Dark frames captured with NINA (previously with APT), stacked in Pixinsight using default in the WBPP script.
30 frames ranging from 1.29sec to 600 seconds.
I was interested to know if the camera being CMOS showed variation in its dark current over the 2 years I have had it.
To my surprise my single dark frame subs were relatively even and clean when STF stretched.
However when viewing the master for each Dark subs there was a definite gradient left to right (left brighter).
I thought oh no I have a light leak or something. However I compared Darks taken over the space of the past 2 years with same camera but different imaging software and either in a cool dark room or just outside at night with lens cap on and no bright lights and in various other connections and environmental conditions.
I noticed the same or at least similar gradient in those dark frames when comparing the master, again the single subs were clean. The issue was more pronounced in shorter exposures.
To rule out an imaging train problem, I pulled the camera off and placed it in a completely dark , cool cupboard and retook all subs cooled to -20c (similar to before), Had the camera connected to its own power supply and it was the only USB3 device connected to the pc. The new library showed essentially identical characteristics to my my other darks taken over the past 2 years. That is the gradient.
Now my understanding was that this camera had no amp glow. My understanding is this would seem some sort of glow however it being worse on short exposures doesn't quite make sense.
I never really looked at master darks because I never saved them preferring to look at individual dark frames and if ok then just stacking them from fresh every-time (I know big waste of time).
My images appear to calibrate out ok with the workflow of flat/dark flats/darks/lights.
Any idea if this expected behaviour or has their been an issue with the camera all along. It seems ok....
The only other conclusion is that somehow the WBPP settings maybe causing a problem, or maybe they might be showing me a problem with the camera.