Hello everyone,
what could be causing this strange gradient (red circular area in the center and green image edges)?
The shot was taken with a Samyang 135mm @ f/4 + Toupteck IMX571 + Askar D2 filter.
This is the master light obtained after 14 hours of integration, calibrated with darks and flats.
📷 D2.jpg
The same target captured with a D1 filter does not show the same gradient.
📷 D1.jpg
I have the same problem with other target
Thanks in advance for your replies.
Not strange, remove the gradient and carry on.
Giuseppe Renna · Jan 3, 2026 at 10:29 PM
Hello everyone,
what could be causing this strange gradient (red circular area in the center and green image edges)?
The shot was taken with a Samyang 135mm @ f/4 + Toupteck IMX571 + Askar D2 filter.
This is the master light obtained after 14 hours of integration, calibrated with darks and flats.
📷 D2.jpg
The same target captured with a D1 filter does not show the same gradient.
📷 D1.jpg
I have the same problem with other target
Thanks in advance for your replies.
Are you sure that your calibration frames were taken with the correct parameters, e.g. temperature and duration?
Reshoot your calibration frames. If this does not fix the issue, then you need to look for light leaks.
Brian Puhl · Jan 4, 2026 at 12:12 AM
Reshoot your calibration frames. If this does not fix the issue, then you need to look for light leaks.
I agree and I also think there may be a light leak as well.
Normal Gradient removal
Nothing else
The gradient is oddly large so calibration frames might be suspect
Normal Gradient removal
Nice work getting most of it out, however; it looks like the right upper and right lower corners may have some sort of light intrusion. To my eye, they seem brighter than the left side corners.
How did you obtain your flats? I had the same problem with my Samyang 135 and ASI6200. When I used a flat device that sat on top of the lens the calibrated lights came out looking just like yours. If I took sky flats, everything calibrated properly. I suspect there was some type of reflection inside the flat device that caused the problem.
Arnie