Gain and flat frames

[Somnium]

just wanted to check and see if it is critical to capture flat field and light subs at the same gain settings, i am having a few issues with my data reduction and was wondering if this was the issue.

[Atmos]

With the QHY9, if you change the gain it may change the bias although I would have to double check that.

[Somnium]

Thanks Colin, i will check that out. i took some flats with the original gain settings and it seemed to have worked. although i had 5 ours of the antennae galaxies at too high a gain so as to make obtaining flats impossible. the thing that is really frustrating me now is when i stretch the images i have a gradient from top left to bottom right and i cant figure out what is causing it.

i thought it was an artefact of the shutter on the QHY9 when taking 1 second subs but i managed to take 6 second flats and still had the issue.

there may be some sort of internal reflection, either in the telescope or from the observatory. i will try imaging a different part of the sky tonight and see if that solves the issue ...

[Atmos]

I suppose if you were to take some bias at that higher gain you would be able to correctly calibrate the high gain flats for the corresponding subs.

[multiweb]

Absolutely. Shoot your calibration frames at the same temperature and same gain/offset as when you shot your light frames.

[Somnium]

Thanks, I feel like I am learning everything about this hobby by making every mistake possible

[multiweb]

I lost a whole night at Coonabarabran a couple of years ago because I inadvertently changed the gain of my camera. Lesson learned. There's always one more mistake to discover out there that you haven't done yet. That's the fun part of the hobby. :lol: ... or you do the same again, that comes with age.

[Somnium]

Fair enough , I bet this light gradient issue is going to turn out to be something really stupid too but right now it is showing up in all my images