Quote:
Originally Posted by RickS
If the master flat is scaled wrongly then it will overcorrect an individual flat too, won't it Marc? The flat is no different to any other light apart from probably being brighter overall.
Cheers,
Rick.
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You'd think so. I checked my flats this way when I collect them. Make a master of let's say 10 subs then 20, etc... then flat field a sub to check. They always flat field correctly. If I have the wrong bias which I like to call "dark flat" as opposed to "light flat" then the scaling is all over the place. I never successfully managed to pixel math them to get a proper flat fielding either. As everybody else probably did I've also done a lot of reading in the past trying to figure it out. I know the "maths" say 1/3 or full well, blahblahblah. In practice it never worked for me. It was trial and error until I got the levels I wanted. I don't try to understand why anymore. I just use the exposure times and ADU that work for my camera and scopes. I've found it to be scope dependant and also filter dependant unfortunately. I always flatfield and fully calibrate all my light subs. Always.