If you already have a good collection of lenses (500mm f/6 apo
) then why not just shoot from the hip, so to speak. You could get a reasonably priced HEQ5 (pretty good value atm apparently) or second hand Polaris with motors and a small scope to help you to polar align and you would be away. For short FL (<100mm) if your alignment is good you could mount the camera directly to the mount and not worry about having to guide the mount for shots of 3-5 min.