RolandWooster I found it very difficult to accurately focus the guide camera using only the looping image.
The easiest way to focus a guide scope is to use a Bahtinov mask, which provides accurate focus information even when the star is wobbling due to atmospheric tubulence. Even the star size in the Guide window is not that reliable.
If you don't want to make you own mask, many small telescopes that people use as guide scopes have threaded dew shields, and you can buy pre-made masks that are already mounted in photography filter threads. One of my guide scopes is a Borg 55FL, and its dew shield has a 58mm thread. You can get various step up rings to match an off the shelf Bahtinov thread to your guide scope.
The downside of a Bahtinov mask is that you need bright stars and dark backgrounds to get enough contrast -- so you can't really use them until at least dusk.
To adjust focus, you can use the Focus Mode in ASIAIR, where it has a decent frame rate once you zoom in to a smaller ROI.
Another way is to use the Detect Star tools in the Tools menu in the Preview window. The tool will read out the average HFD, but it is laborious and slow. The Bahtinov mask way is much faster (and much more reliable when there is lots of atmospheric turbulence -- it is hard to judge wobbly star size, but the angles of the diffraction spikes from a Bahtinov mask stay pretty constant even when it is wobbling).
Chen
