Stacking frames from a non-flat field

[JamesF]

I have a load of data collected with my Photoline 72.  Unfortunately the field isn't particularly flat and it shows, particularly on a sensor the size of the 174.  I believe for this reason the image won't stack in DSS.

It struck me this evening that as the object in the image only occupies the centre of the frame, I could possibly convert the FITS images to TIFF and crop off, say, the outer third of the frame, then try stacking again.

Does this sound like a plausible way forward, or is there something else I should try?

(I do actually have a reducer/flattener for the OTA, but haven't fitted it yet as I didn't have the right spacers.  In fact, as the focal length is only 432mm to start with, I'm not actually sure I want to reduce it at all so I might just have a look to see if there's a pure flattener that will work with it.)

James

[tooth_dr]

I would try stacking it in a different software, eg APP. I’ve had quite a few fails with DSS, but none with APP.