[neilcreek (Australia)]

Hi!

I'm relatively new to telescopic astrophotography, having purchased a 200mm f4 telescope and kit secondhand a couple of months ago. I'm having quite a bit of success and am really enjoying myself, but the learning curve is very steep and I'm having a few problems which I haven't been able to work out myself yet. First of all I'd like to ask about flat frames.

The attached file shows the problem I'm currently having with my flat frames obviously not doing what they're supposed to. In the past I've done without, or I've shot subjects bright enough that the signal overwhelmed the faint variations in my field. The Pencil Nebula however doesn't give me that luxury and I have to work this out.

The image shows the results of applying bias, darks and flats to 164 minutes of integrated light frames, then applying a background neutralisation and screen stretch in Pixinsight. Obviously the flats aren't working as intended, and seem to be misaligned.

To capture my flats I've been pointing the scope at the ceiling, laying a sheet of white paper over the aperture, positioning and focusing the camera as it was during the image session, and taking shots with a camera flash bouncing off the white ceiling. I've attached a jpeg of my master flat, which was made from 128 subs.

Can anyone tell from looking, where I might be going wrong? I can fill in any missing details if you ask me questions.

Thanks in advance for any help you can offer!