[rogerg (Roger)]

I have always figured it logical that if I am to accurately autoguide a photograph, I need to be guiding at the same or higher image resolution as the imaging chip.

That is, if I am imaging at 1.04 arcsec/pixel, I need to be guiding at 1.04 arcsec/pixel (or 0.86 if I felt like it, but 1.04 is already asking for trouble).

Practically, this implies that the guide scope would usually need a longer focal length than the imaging scope. You could of course have a shorter focal length scope and smaller pixel size on the camera, but practically, you really need a longer focal length for the guider.

As an example, there would be no point guiding a scope that has a focal length of 2160mm with a scope that has a focal length of 900mm, when both scopes have cameras of the same (or near) pixel size.

Correct?