Astrophotography diagnosis of IC 1848: Sensor tilt and tracking drift

Near ideal conditions for this target. Bortle 2 with a moon at 0.9% illumination, even 27.7 deg above the horizon and 73.5 deg from the target, amounts to a dark night: no meaningful stray light, confirmed by a very low sky background (median 0.02) and a negligible oriented gradient (5% amplitude, R2 0.15). On IC 1848, an emission nebula, this is the best time to stack deep subs, in broadband as well as Ha. Use this sky to accumulate exposure time rather than to test gear: the conditions explain none of the defects found here, they are all instrumental.

Setup well matched to the target but clearly undersampled. At 190 mm focal length and 2.9 um you are at 3.148 arcsec/px over a 3.36 deg field: IC 1848 fits comfortably in frame with margin, a good framing compromise. However at 3.15 arcsec/px stars are only 1.5 px FWHM at center, right at the measurement limit: any shape defect immediately hurts, and the measured tilt translates directly into resolution loss on the right half. As for settings, gain 160 on an ASI585MM and -20C are healthy, offset 15 clips nothing (0% dark clipping). The e_margin of 2.02 shows a background barely lifted, which is normal in narrowband under this very dark sky, not a sign of underexposure.