I have some doubts regarding the Synscan Polar Alignment "refinement" procedure.
After choosing a star, the mounts move a little and then asks you to re-center the star using only the Altitude screws.
However I find myself in a situation similar to the sketch below: using only ALT screws I can move the star along a line that does not cross (or pass close to) the centre of the frame. The same happens with the second step involving the Az screws.
I found tutorials showing that the star does not go EXACTLY back to the centre, but my offset is rather significant.
This happens even if my errors are often below 30 seconds. What should I do? Should I just bring the start to the closest point (eg. point P in the sketch above)? Or should I do something else?
PS: a little unrelated question: for 2-5' subs, how good is good enough with a 500mm focal? And with a 2000mm focal? Would you even bother going below 30 seconds or would you call it a match?
PPS: of course I do use a driving scope afterwards!