Telescope eyepiece focusing mechanism come from simple to very complex.
If you are just doing viewing then a simple rack and pinon type focuser will let you focus easily.
A strait draw tube is hard for the beginner to focus with because you have to hold the telescope still while you push-pull
the eyepiece focuser up and down. You generally loose what you were looking at in the field of view.
Helical type focuser are nice because once you set them they will not shift up and down easily. The usually have coarse
threaded outer helix tube with a fine threaded inner helix tube for fine focusing.
Motorizing your focus mount can be fun to do. But i have found that unless the stepper motor steps are small you
may or may not find best focus.
For CCD focusers you want one that will stay in place after you set it. It will not drift. You can also find some that
have Temperature compensation components so the focus will stay accuretly set day to day.
