Bright circle in my images

Acquisition Deep Sky Artifacts
3 replies•180 views
Menelaos avatar
Menelaos avatar
Hello good people.

I created a topic a couple days ago about flat frames and i uploaded some images when it was pointed out to me that my images have a bright circle in them and that it might be a problem within the imaging tube with reflections. I don’t know where to begin with this. I am using a skywatcher 150/750 pds Newtonian with a ts maxfield coma corrector (which I recently bought). I am just hoping that the coma corrector is not defective because it is giving me quite a lot of vignette as well to be honest. How do i go fixing this if it really is a problem? Can i work around this with flats? My flats seem to have the bright circle too. And just to be clear i am not talking about vignetting there seems to be a bright ring.
here is an image to see what it looks like and i have marked the ring.
thanks.
andrea tasselli avatar
andrea tasselli avatar
You have a light leak, either during the light exposures or during the acquisition of flats. Incidentally, it isn't the corrector that is vignetting it is the secondary that is undersized.
Helpful Insightful Concise
Brian Puhl avatar
Brian Puhl avatar
Did you try longer exposures on your flats and bias?   Multiple folks suggested this.    I'm not sure why you needed to create an additional post for the same exact issue.
Well Written
Oscar H. avatar
Oscar H. avatar
The bright circle is the good part, the black is the vignetting and the issue you need to resolve. I see a multi ring pattern in the bright area though, I don't know if that's just the way it looks here on the AB thread, but if it's still there when you stretch it and increase the black point then it's a tough issue to fix. And yes, your flats should remove the vignetting, I think.

(my opinion)

messierman3000


EDIT: If your flats are overexposed, then they wont remove the vignetting. This has happened to me; my flats were totally white (I used a white shirt with a flashlight FYI) and they visibly didn't help when I compared a flat calibrated light master with a non-flat-calibrated light master.
Related discussions
Flat acquisition no longer sufficient for broadband only
I can't seem to fix this problem, but all my broadband stacks are coming out like this now, flats are no longer fully correcting them. Not a problem with narrowband at all. I have been imaging for over a year, and this just started happening. It ...
Flat frames not fully correcting vignetting issues in stacked broadband images.
Jun 10, 2025
extreme offset vignetting in flats and lights
This issue has persisted for a while now through at least 3 set ups and I honestly cannot for the life of me figure out what is causing this. Here is an image of one of my flats which displays the extreme offset in vignetting in my imaging train whic...
Extreme vignetting in flats and lights across multiple equipment setups.
Nov 9, 2025
Flats undercorrecting vignetting
Hello all! I'm facing issues trying to calibrate my light frames with flats, they seem to be undercorrecting the vignetting on the frame: The equipment I'm using is the following: - Modificated Sky-Watcher Quattro 250P OTA - Sharpstar 1x GPU ...
Flat frames undercorrecting vignetting during light frame calibration process.
Aug 6, 2025