Focal length of tracking scope vs imaging scope

[KISA]

Hi,


I'm looking into the appropriate focal length for a tracking scope verses the focal length of the imaging scope.
I had originally thought a tracking scope would need a higher focal length than the imaging scope to ensure deviations were picked up in the tracking scope before the imaging scope.
But from what I've read when controlling by eye you can use a tracking scope with 1/3 the focal length and when using software 1/10 the focal length.
I'm struggling to understand how tracking with significantly less magnification can pick up drifting before the imaging scope with a higher magnification, and therefore cause unwanted blur in the image.


Can someone please explain why this is so :question:?


Thanks,


Markus

[that_guy]

Usually, the guide camera is a smaller sensor than the imaging camera. So it's more imaging scale you're looking for rather than the focal length alone.

[KISA]

Ahhh, that makes sense now, thanks for explaining that, didn't think of the sensor pixel size :).