[AdamJL]

Hi all

I've been trying to figure this out for a few weeks now, and I can't for the life of me understand this.

For a long time, my narrowband flats have been showing two abberations.
1. Odd partly circular reflections
2. Edge brightness in one corner.

I have taped up EVERYTHING. Anywhere light can leak, I've plugged it up. I know the issue is from the filter wheel onwards, because if I rotate the filter wheel and camera, the issue rotates as well. I have cleaned and reset my filters multiple times. I have purchased different filter masks made by a different company (first was from Testar, second was from Buckeyestargazer).

I have taped the edges of the filter masks themselves. I have taped any metal inside the filter wheel to minimise reflections.

No matter what I do, I get these abberations.

That said, I do notice that the brightness "centre" for my flats appears to not be in the centre of the frame, suggesting possible tilt in my image train. However, this was an issue before I replaced my focuser as well so I don't know if tilt is the issue that could be causing it.

Something is reflecting inside my filter wheel, and it's showing up in the narrowband flats because they reflect the most light. It's being bounced up into something.

Any ideas?

Only thing I can think of is that my flattener uses an M48 thread, which then opens up into the filter wheel extension that is M54 in size. It would seem odd that this is the cause, because it's QHY's own extensions and if I have the issue, so would many others.

Lastly, I've attached the images below in order of how they are setup in my filter wheel. As you can see, the curved reflection stays the same for the narrowband images. For SII, you can even see the beginning of another curved reflection in the bottom right hand corer.
The other issue: the "corner brightness" shifts between each frame.

Broadband flats look fine.

Any help most appreciated!
Thanks
Adam