Astrophotography diagnosis of IC5070_Askar50P: Periodic error (unguided)

Very favorable conditions. A Bortle 2 sky is the best case for an emission nebula like IC 5070, and the measured background confirms it: only 8% gradient and 0.02 azimuthal anisotropy, so almost nothing to remove. The 82% gibbous Moon is up, true, but only 6.6 deg above the horizon and above all 96.7 deg from the target, which makes its contribution negligible here, all the more so in narrowband on a monochrome camera. You can keep shooting freely that night, and if the Moon climbs later in the session, the angular separation stays your best ally.

A coherent combination. With a 3.36 deg field, IC 5070 and the Pelican surroundings fit comfortably in frame, with margin for the nebulous extensions visible in the DSS. Gain 100 on the ASI585MM and a sensor temperature of -18.5C are healthy settings, dark current under control. Offset 15 holds up: 0% dark clipping, the left tail of the histogram is not truncated. The sky/black-point margin of 2.02 is low in absolute terms, but that is normal behavior for a narrowband monochrome acquisition at 300s, do not chase a higher value at the cost of blown stars. Given the measured elongation, the real headroom is on the mount side, not the settings.