Strange gradient with Askar D2 filter causing red center and green edges

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?

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.

wsg · Jan 4, 2026 at 01:10 AM

Normal Gradient removalNothing else

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.