Ugh... I am going to have to work out my guide scope issues, as 1 minute unguided subs at ~f/14 will not cut it (and I could not pull off 2minute subs). I have imaged this at ~f/4.7 and at f/7, but the C90's long focal length will require much longer subs. Below is my shameful and quick processing of M81, I am not going to waste too much time on the colors and processing, but will share my failure. I don't want to turn this into an imaging thread and to stay on the C90 topic... But the bottom line is the C90 will require a significantly longer exposure than a short focal length refractor. I know this is not the most optimal imaging scope, but this has become a challenge... For reference, here's NASA's Hubble image.
Autosave - M81 C90.jpg
Jaimo!, I don't see why you think this image is so bad, seems to me it just needs
processing in the computer. For a C90 there's an excellent amount of detail. It's
not the Hubble and never will be.