[AlexN]

Ok, so flats should be taken at the same focals point as light frames, but how do you achieve this when the focuser moves during the course of the night.

I never had dramas with this on a telescope with robofocus however the camera lens im imaging with is very sensitive to focus position changes (and apparently backfocus distance changes too)

So I'm having massive issues getting flat fields to work.

I will post some examples shortly but I get rings, in some images, or the bottom of the frame appears flat fielded but vignetting is still present at the top. I really dunno what to do.

I suffer typical light pollution for someone who is 35km from a major city and 4km from the local Westfield and Costco illuminated carparks.

Any thoughts.