LRGB Calibration frames

[E_ri_k]

Quick question, do you need to take flat frames through each RGB filter, or will it do just taking them unfiltered?
Erik

[Peter.M]

You need to do each one to get rid of any dust motes from the filters. You might also find that vignetting changes.

[E_ri_k]

Thanks Peter.
Erik

[RickS]

You may be able to get away with a single set of flats depending on how fast your scope is and how far the filters are from the focal plane. A faster scope will throw dust motes further out of focus as will greater distance from the focal plane.

Try a test... take flats with each of your filters and see how good a correction you get when you apply a master flat from one filter to master flats for the other filters. If you get clean, evenly illuminated results then you don't need separate flats for each filter.