I've been struggling with a strange ring artifact in my images and thought it was due to my neighbors shining a light on my telescope all night long. I was planning to create a light shield, but after some digging tonight I think the problem may be something else. The ring even shows up in my flats if I stretch and prod them enough. Here is the research.
First, a stack of uncalibrated images with a simple dynamic background extraction:
Then, my flat with a background extraction and some stretching to bring out the details:
And finally, a stack of calibrated images with a simple dynamic background extraction:
This ring is a nightmare to try and get out of my images. I need to run dynamic background extraction multiple times with dozens of sample points to try and get rid of it. Any ideas on what it could be?
Has anyone seen anything like this? It's present in all my filters except narrowband. My best guess is internal tube reflections. The inside of my tube is coated with a matte black paint, but it's not flocked or baffled. I have a lot of ambient light in my normal imaging area (did I mention my neighbors?). Showing up in the flats makes sense too as I sit an led tracing tablet on the end of the scope to take my flats. Some of the light would bounce off the inside tube walls.