This is from my stack of 15 x 180s unguided (phenomenally lucky for 3000 mm FL with only polar scope alignment!) subs from the Bortle-3 Maine Stargazing and Photography Retreat. Not happy with the sharpness and resolution as manifested by the bloated stars and soft detail in the Pillars of Creation. Focus was manual but couldn’t have been far from best achievable.
I have noticed that if I’m close to the tube while it’s tracking, I can hear the tube faintly “singing” at a fixed frequency. I assume that the cogging of the drive servos is resonating with the tube. Could this be causing the spiculated images I see when trying to focus on a bright star and the bloated star images I get from the camera? When I get it set up again back home, I’ll experiment with turning the drive off and see what happens.
Meade 16” SCT w/Optec FF/TC on AP GEM, Nikon D810A, no filter.