Hi for the last year I've been running into problems with my LRGB images. I can't get the lights to calibrate properly. I use dark flats for my flats, same temp, gain, etc. Flats are exposed for over 3 sec at 121 gain at 28k ADU. Interestingly enough this procedure works fine for my narrowband image. Just not LRGB. Here's an example and a curious wrinkle. First image is stretched Lum image. See the 'W' gradient image? The stretched Lum flat does not show this image (2nd image). Now what is really weird is that if you look at a stretched image from one of my HA flats, you see the pattern easily. I'm at a real loss as to what's going on here. Appreciate any suggestions/help.
And here's HA flat that shows same pattern. Why isn't it showing up in LUM flat?