I have been imaging using a Celestron 11” XLT with a .63 focal reducer and L-Extreme filter, ASI294MC on a CGX mount using an off-axis guider/ASI224MC. I’m in a severely light polluted city and would like to invest in a mono camera and narrowband filters to help deal with the light pollution.
My issue is that even with the off-axis guider, I am not able to get exposures longer than about 3 minutes without getting some wonky looking stars. However, from what I read about narrowband, most people are getting their best results with longer exposure times of 5+ min.
I am getting “excellent” alignment using All Star Polar Align, and PHD2 is typically indicating guiding errors of about .65. I am starting to think that 3 minute subs is just the best I am going to be able to pull off at a 1,750 mm focal length given my current equipment. If anyone has experience with this type of setup that proves me wrong, please do share, but I am not looking to upgrade my mount at this time.
My question is, would I likely benefit by switching to a shorter focal length scope, APO or reflector, which in theory would be more forgiving and allow longer exposure times?
I know that it all “depends” and that there are mathematical formulas that can calculate ideal exposure times. But I am not that sophisticated and am just looking for those who can perhaps share some general real-world experience.