Astrophotography diagnosis of NGC 7635: Tracking drift

Excellent conditions: Bortle 2 with the Moon below the horizon, so no lunar contribution is possible and the sky background is naturally low, which the measurement confirms (only a 2% gradient with no clear orientation). For an emission target like NGC 7635 this context is ideal: you can afford long exposures without worrying about light pollution gradients, and you could even consider OIII or SII, which are far more demanding on SNR. This is exactly the kind of night to chase faint signal, such as the tenuous extensions around the Bubble or the diffuse nebulosity on the left of the field.

A coherent but heavily undersampled setup: 3.15"/px at 190mm focal length on an ASI585MM, which explains FWHM values around 1.5px, at the low limit of what can be measured. You are in a regime where seeing is no longer the limiting factor, but where spatial detail is capped by the pixel. It is a good trade for covering the 3.36° field and taking in the Bubble, M52 and the neighbouring nebular complex, less so for resolving NGC 7635 on its own. On the settings side, gain 160, offset 15 and -25°C are healthy; the 2.36 e_margin is low but perfectly normal in narrowband, where the background stays dark even at 200s.