I’ve been using auto focus now for about six months but mostly using a single star. Recently I’ve started trying the SEP method with full field, multiple stars. What I’ve noticed is that the most obvious stars are not selected. I use an Annulus of 20%-80% and the stars that get selected “could” be actual stars, but they a faint and I’m not sure if they are real or noise. Is there a setting that would have the focus routine select more obvious - bright stars? There was around a dozen that were ignored on my last session.

This does not seem to happen when I use the simulators. I recall turning the gain down, but that didn’t help.

Thanks!

Quick question: What camera do you have? Is it a color one?

I recently got my first OSC, and have seen similar issues with SEP selecting weird/faint stars in AF. Switching to another algorithm for star detection did give much more reasonable selections. You can use multistar also without using SEP. Next thing I want to try is switching the camera to greyscale mode for AF.....

Yes, I have a OSC QHY 183c. I was using linear at the time. I’ll try one of the others. If a change the binning that might help as the QHY cameras turn off the color when set to 2x2.

Thanks for the suggestions.

Ah yes, now that you mention it - I had also tried binning, and that had improved results, too. I wasn't sure if binning for focus is a good idea - but given the pixel size (mine is an ASI183MC - guess that's the same chip as yours?) it's probably safe, at least for my 910mm FL...