Astrophotography diagnosis of NGC 7000: Astigmatism

Favorable conditions. Bortle 3 is a quality sky for an emission nebula like NGC 7000, and the Moon at 43.6% sits only 1.4 degrees above the horizon, so its contribution to the background is negligible despite a 59 degree separation. The measurements confirm it: no significant oriented gradient (plane amplitude 5%, R squared 0.02), background falloff is purely radial and therefore optical, not atmospheric. With this sky you can stay broadband on this target without penalty and aim for long integration rather than more aggressive exposures. The 4:28 time slot at the end of the night fits a stable sky.

Coherent combination for this target. At 299mm, the 2.17 degree field frames NGC 7000 in full with the Cygnus Wall well placed, which is the right format. Sampling at 2.594 arcsec/px is strictly undersampled, but that is a deliberate trade on wide field and explains a 2 px FWHM, which leaves no margin for judging star shape finely. On settings: gain 100 (unity on the ASI533) and offset 70 are sound, though 1.7% dark clipping suggests you could raise the offset a bit. The background to black point margin of 1.89 shows a weakly sky-limited exposure, logical in Bortle 3 broadband; 300s remains appropriate, no need to lengthen. Sensor at -5C: going to -10C would further reduce dark current.