I did some calibration measurements with a flatfield mask. Yet for f4 and slightly above I can’t get rid of some remaining circular residue. Any ideas what I could still try or if there is a way at all to calibrate this lens:
I did some calibration measurements with a flatfield mask. Yet for f4 and slightly above I can’t get rid of some remaining circular residue. Any ideas what I could still try or if there is a way at all to calibrate this lens: