Given that the optical train remains the same and that there is no rotation of the fov is it necessary to create a set of master flats for a given filter due to a nightly change in focus due to ambient temperature change particularly in the case of photometry?
Could I take a set for each filter and use them for several nights or weeks?
I take flats, made up of about 50 averaged images, each time something in the optical train changes, like moving the camera or a new blob of dust appears or I use the camera at a different set tempetature. I redo the flats if the season changes but nothing else has changed. However apart from that I keep using the same ones. I’ve experimented and can’t find any decernable improvement if I take flats every time I slightly tweak the focus.
at the end of a nights’s session I can barely keep my eyes open and I have always taken a new set of flats and corresponding darks. I actually have a medical problem of not getting enough sleep which is getting to be a problem. If I was simply imaging I would’t bother, but as I do a lot of photometry the flats may have been an issue. I’ll try experimenting and see if there is any difference. Peter’s experience seems promising.