Autofocus area of interest - by: schwim

I'm imaging NGC3521 presently. For whatever reason the autofocus auto-star algorithm always picks the core of the galaxy as a focus point rather than the bright stars just off center. This seems like new behavior in the last few months. I seem to recall a strong bias towards the upper left of the image. Now it seems strongly biased toward the center. It's been a few months since I imaged so I'm just getting used to the recent changes....

Focus using the galaxy fails quite frequently presumably due to its fuzziness. So, I choose to manually select a star and this seems to get the job done every time. Problem is, this doesn't seem to work well with automated re-focusing as it seems to forget the star I selected. Jobs fail as a result and the rig sits idle. I tried full field focusing but its too slow and fails more often than I like.

This got me to thinking. Can a pre-determined subframe be set and "full frame" style focusing be run on that? I see you can select percentage of FOV (center, edges) for full frame, but the center is always, uh, the center, and you're still reading in the full frame and its stills slow.

It would be great to speed things up and use a subframe at a definable center point but get the benefit of multiple stars rather than just one that you manually select.