Comment by nullc

> slight mis-alignments during polar alignment

For long enough observation there is no such thing as correct polar alignment on earth, thanks to atmospheric lensing. The density of the atmosphere shifts stars up with increasing amounts depending on how low they are.

If your mount can accurately track in dec, then using a more complete pointing model-- the accommodates this lensing along with the major mount orthogonality errors-- generally eliminates the need for a guide camera.