Bullet-proof auto focus with platesolving

What I have done for autofocus on targets with few stars in the field is to find an area near the target with a good number of stars and create a sequence using the Faming and Mosaic wizard. I then slew to and center on this target and run my initial autofocus. You can then set it as the focus position. I had great success with my SCT to autofocus for each filter (wide and narrowband) on an open star cluster. After setting the focus, I then slew and center on the target, set the camera rotation, and then calibrate PHD2 on a guide star. With target and focus positions set, then autofocus will work flawlessly for me. After initial focus on the star cluster or area with enough stars, good focus is achieved and refocusing on the target is usually successful, provided the transparency and seeing are sufficient, even with few stars and with Ha or Sii filters. No plate solving needed other than for recentering.

To automate the sequence, you can move the focusing sequence to the top of the list, set the camera rotation to that of the target, do the autofocus and let the camera reach set point, take one exposure to save the HFR on the imaging binning setting, then move on to the first imaging target.

Mark W

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Has autofocus been enhanced so it no longer picks up double stars, small galaxies and other non-star objects that throw off the HFR calculation as discussed in this thread?

I didn’t see this mentioned in recent release notes.

Not that I am aware. By measuring multiple stars, however, single anomalies have little impact on the result.
The one thing it really doesn’t like is globulars. It confuses the calculation.
Mark’s prior comment echos one of mine from a while back. There is a focus target feature in SGP but it seems to have been forgotten about over the years. Mark’s idea is what I expected the focus target to implement. I should make it an official feature request.

ISTM that the ability for the user to specify the focus stars to use would answer most of the questions and issues raised here; I could click on 10 or so things that I know to be single stars, and only they would be used for autofocus.
Or alternatively, allow the user to specify an area (probably a polygon) inside of which it should NOT use any objects. That would let you (for example) draw a box around M42 and make it only use objects outside the box.

This can be 100% automated with platesolving and outlier rejection logic.

Probably, but making that logic work for everyone is not a trivial task.