Maybe someone can offer a possible explanation for the dark bar that I get at the bottom edge of my calibrated, stacked image of the flying bat?
Some background info on the picture: WO Star 71 with Atik 383L, Atik OAG and Atik EFW, Baader 36 mm Ha 8nm filter, 35x 300 sec subframes, properly calibrated with bias, darks and flats. Processed using PI with drizzle integration. I am imaging in a Bortle 9 area ;-(
I tried to process without flats, and got the same result.
I tried to move up the pick up prism of the OAG a bit, same result.
The attached picture is a boosted stretch of the integrated image.
I find it very difficult to remove the sharp gradient at the bottom in PI with ABE or DBE.
Any suggestions on where this might come from and/or how to remedy in processing?
Thanks in advance for your reply.