Flats for all of LRGB or just L?

[SkyHiker]

I'm going to put another wrench into this. Your method of casting a headlamp on a wall may be causing more problems. Flat calibration frames have to be completely uniform in illumination. The problem with a headlamp is that the center will be brighter than the edges and that will screw up the flat frame subs. That's why many of us have illuminated flatfield panels.

I don't think so. The FOV of the scope is about 1.5 degrees so the area on the wall that is about 2 m away is roughly the same as the aperture, which is 12". The light beam of my headlamp is spread out about 30 degrees by a lens and covers a 2 m disc that seems pretty uniform. On the relatively small 12" part the nonuniformity will be negligible compared to that caused by vignetting.

Later I found that my Paracorr II causes a lot of vignetting with a sharp edge because its tube is too long for my ASI2600 that has an APS-C sized sensor. Replacing it with the Baader MPCC Mark III fixed the vignetting while still maintaining good coma correction. I found that the angle of the scope during one night taking LRGB in that sequence, had a effect on the light reception from the neighbors flood lights across the street. Adding a light shield, and picking a higher starting, fixed that.

I did reconfirm later that taking L flats is just as good as taking flats for all of LRGB, after eliminating aforementioned angle dependent LP effects.

[Stuart]

Alright then. Whatever works for you.