Astrophotography diagnosis of IC 1848: no defect detected

Excellent conditions. Bortle 2 is as good as it gets for IC 1848, and the Moon, waning gibbous at 67%, is below the horizon and 144 degrees from the target: no lunar contribution is possible on this sub. The measured background confirms it, with no significant oriented gradient (plane R2=0.18, plane/radial dominance 0.23). In this context you have no sky background constraint at all, which leaves full freedom to lengthen subs and pile up time. On an emission nebula like this one, narrowband under Bortle 2 is a luxury: the limiting factor will be total integration time alone, not light pollution.

Setup is well matched to the target. At 190 mm focal length, the 3.36 degree field frames IC 1848 entirely with margin on the edges, the right choice for this extended nebula. Sampling at 3.15 arcsec/px is undersampled (stars measure 1.3 to 1.8 px FWHM, so pixel-limited rather than seeing-limited): acceptable on an extended narrowband target, but you will not resolve fine detail. Gain 200 on the ASI585MM is high but consistent for Ha, offset 15 is sufficient (0% dark clipping), and -20C at the sensor is healthy. The 300s sub stays short given the measured background margin: 420 to 600s would be better if tracking holds.