Quote:
Originally Posted by Nikolas
55mm backfocus from the camera sensor to the field flattener glass, my bet is that your backfocus is not correct
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It isn't a back-focus problem (the stars in the image are in focus), it is a problem with the spacing between the flattener and the sensor. Too long and you get tangential elongation at the edge of the field of view, too short and you get radial elongation. Only the flattener manufacturer can tell you what the correct spacing is, unless you want to work it out by trial and error.