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INDI Library v1.9.9 Released (30 Nov 2022)

Bi-monthly INDI Library released with new drivers and bug fixes.

Recommended way to use auto focus during capture sequence

  • Posts: 6
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Hi,
Recently, I tried to use automatic focusing during a capture sequence in EKOS.
I set it up to re-focus every 60 minutes. Then I setup my capturing sequence (exposure time, number of exposures, etc.) and started capturing.

In my focus settings, I had disabled automatic focus-star selection. That's why I focused before starting the sequence.
Also, right at the beginning of the capture sequence, there was a meridian flip.
To make sure that EKOS would have a focus star after the flip, I paused the capture sequence and focused (selecting a focus star manually, focusing automatically).

Then I let the capture sequence run and went to bed.

In the morning, I found that EKOS had aborted the capture sequence, as it wanted to auto-focus, but complained that no focus star was selected. So I missed several hours of exposure :(

My question is: what is the best practice for automatic focusing during capture sequences?
Do I have to enable automatic star selection?
Can I manually select a star before capturing, and will the manual star selection stay valid after a meridian flip?

Also, I think EKOS could have handled the situation better:
It should not allow me to enable focusing every X minutes when the auto focus settings don't allow auto focusing.
It should not abort capturing when it can't focus. I would rather have had some images with slightly imperfect focus, than none at all.

Any ideas?

Best Regards,
Steffen
1 year 6 months ago #72011

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Yes, you must let it auto select the star for auto-focus to work unattended. The error message you suggest seems reasonable...

I also wish that if auto focus failed that it would just return to the original focus setting and continue. It's become a relative non-issue, as I haven't had an aborted auto focus in several weeks.

Ron
Mounts: Sky-Watcher EQ6-R Pro, Meade LX85, Celestron NexStar Evolution Alt/Az
OTAs: Celestron 8" Edge HD w/Hyperstar, Meade 80mm APO Triplet Refractor
Cameras: ASI533MC Pro, ASI183MC Pro, ASI224MC, ASI120MC-S, ZWO ASI290MM
Raspberry Pi 4 with Stellarmate OS, MacBook Pro
1 year 6 months ago #72020

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As Ron says, use auto select stars, and best also full field (SEP).  I use linear algorithm, as I don't trust focuser backlash, and that one takes care of that.  
I'd read through the explanations of step width etc. (tool tips), and verify that the settings you choose give a reliable result (focus curve, is step size reasonable...).
 
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GPDX+EQMOD, CEM60EC, ASI2600/1600/290mini+EFW+EAF
1 year 6 months ago #72029

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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
1 year 6 months ago #72031

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I agree that the user should have the option to continue capturing when focus fails. It might not be pretty though.
Jasem Mutlaq
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1 year 6 months ago #72037

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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
Mounts: Sky-Watcher EQ6-R Pro, Meade LX85, Celestron NexStar Evolution Alt/Az
OTAs: Celestron 8" Edge HD w/Hyperstar, Meade 80mm APO Triplet Refractor
Cameras: ASI533MC Pro, ASI183MC Pro, ASI224MC, ASI120MC-S, ZWO ASI290MM
Raspberry Pi 4 with Stellarmate OS, MacBook Pro
1 year 6 months ago #72047

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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)
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1 year 6 months ago #72067

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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
TSA-120 + FSQ-85 + ONTC 10"F4 Newton (+ epsilon-160 on Japan trip) | Avalon Linear + M-zero | ASI 1600mm pro + 6200mm pro | KStars/INDI on Raspberry Pi 4/Intel NUC
1 year 6 months ago #72069

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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
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1 year 6 months ago #72074

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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).
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1 year 6 months ago #72078

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Auto-Focus flag in a capture sequence should override to auto select star since they are pretty integral to each other.
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1 year 6 months ago #72084

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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.
1 year 6 months ago #72132

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