Thanks Ron and DerPit for your replies and help.
Now I know that I have to let EKOS auto select the focus star, that's fine.

I had already tried focusing with full field. But in my experience it didn't work as good as single star. I think that EKOS was picking up a different set of stars each time, and therefore the average HFR value was very noisy and did not result in a smooth V-curve. With single star focusing, I get a nice V-curve, and together with the linear algorithm, focusing works nicely. Maybe I have to tweak the star detection settings.

One thing to improve:
When the user starts capturing (pressing "Play" on the sequence queue of the capture module) and has automatic re-focusing enabled while automatic focusing is not possible, please show a warning message! The user can then decide to skip auto re-focusing, or change the auto-focus settings.

Regards,
Steffen

I agree that the user should have the option to continue capturing when focus fails. It might not be pretty though.

Jasem, I agree... but often I find my focus wasn't that bad before the re-focus. Would rather revert back to the original focus setting than eliminate capturing the remainder of the night.

Ron

In my opinion, these are two different problems, and yes, solving both would be great

1. don't abort capture when focusing fails, especially when the focuser was not touched at all
2. don't allow a user to start capturing with auto-focus enabled when auto-focus is not possible because of focus settings
   It's better to get an error message right away, than after one hour (or whenever focusing would be scheduled)

Hi Steffen,
I use the autofocus feature quite often. To avoid the problem with a focus star selection, I use the "Full field" option and set the Annulus to 20%-100%. It's slightly slower since it always needs to download a full frame, but it is reliable.

Wolfgang

I consider that starting an autofocus with the automatic star selection unset is a bug. Are there any use cases with that flag cleared?

-Eric

If you mean unattended AF then yes, that wouldn't make much sense. For "manual" AF it has it's use case of course.
So I guess it would be task of the capture/scheduler module to enable this on the fly (or at least issue a warning on start).

Auto-Focus flag in a capture sequence should override to auto select star since they are pretty integral to each other.

I agree, I used to use the "refocus if delta T " feature but half of the time it failed to refocus and stopped for the rest of the night. It would be great if it can go back to previous position and just keep on shooting.

Also I used SEP with all star profile and linear algorithm, I believe the star extraction is not very reliable as it often picks noise instead of slightly off-focused star.

You can edit the SEP profile and adjust it until it's reliable enough. The thing about SEP is that it requires fine-tuning for some setups and you have a GUI editor to select the parameters, it's trial and error to get the results you want. If you have a profile which works consistently, please share it and let us know so we can check it out.

Is there any way tune it on images saved to disk? So I can tune it during a day?

EDIT: nevermind found in CCD simulator->Simulator Config->Use Directory to enable load images from provided directory

Good question. It is possible, go to Settings --> Configure KStars --> FITS , and you can see HFR SEP Profile. Select one then you open FITS image --> Mark Stars.

Then you can go back and "edit" the select SEP profile and change settings as you see fit.