David Bennett replied to the topic 'Auto Focus failures' in the forum. 3 months ago

Hi John,
It is set low because I find the star detection algorithm fails when stars get too far out of focus. With short glimpses when watching auto focus I can see It identifies what is one large star as several smaller stars and returns too low a HFR value for that focus position which throws a wobbly in the best fit parabola estimate. When nearer to focus but star image more of an irregular disk I see a poor HFR estimate. Close to actual focus the star image is good and looks like a fuzzy blob as you would expect and HFR value is OK.
I have tried weights which didn't help. I have tried different combinations of step size and, max travel and multiple out step sizes. The log I sent is just one iteration of different settings I have tried. I will do more testing and I agree with your sound advice of widening the focus motion, I just need to sort out the issue with HFR values being inconsistent. There is almost a pattern that the second point is always too high. Now I you have confirmed how to save the focus images for examination later I can do better testing. I will send you my results when I have had chance after a clear night.
I also need to check out the mechanics of my focuser and optics alignment. I have spent sometime on this already and thought it was good. The focuser is a very solid one and I have 3D printed two brackets to fit the ZWO EAF accurately with no flexure to either the fine or course focus. Currently I am testing on fine focus. I have had the focuser on the bench and there is little backlash which is hard to measure. Backlash is about 40 steps with course and hardly anything with fine. Axial alignment of the focuser and collimation will be checked again as this will contribute to poor star image and then poor HFR estimate.

The other more serious problem is failure in the auto focussing that happens from time to time. (its unpredictable but maybe every 6 to 10 auto focus operations). Auto focussing fails because it fails to capture an image. It looks like a ZWO driver issue to me. This can be seen in the log file around line 176513. Here is the relevant part:
[2022-09-19T02:06:25.614 GMT Summer Time DEBG ][ org.kde.kstars.ekos.focus] - "Focus position reached at 27350, starting capture in 1 seconds."
[2022-09-19T02:06:25.615 GMT Summer Time INFO ][ org.kde.kstars.indi] - ASI EAF : "[INFO] Focuser reached requested position. "
[2022-09-19T02:06:26.615 GMT Summer Time INFO ][ org.kde.kstars.ekos.focus] - "Capturing image..."
[2022-09-19T02:06:26.663 GMT Summer Time DEBG ][ org.kde.kstars.indi] - ZWO CCD ASI120MM Mini : "[DEBUG] StartExposure->setexp : 5.000s "
[2022-09-19T02:06:26.664 GMT Summer Time INFO ][ org.kde.kstars.indi] - ZWO CCD ASI120MM Mini : "[INFO] Taking a 5 seconds frame... "
[2022-09-19T02:06:29.088 GMT Summer Time INFO ][ org.kde.kstars.ekos.guide] - "Exposure timeout. Aborting Autoguide."
[2022-09-19T02:06:29.102 GMT Summer Time DEBG ][ org.kde.kstars.ekos.capture] - Guiding state changed from "Guiding" to "Aborted"
[2022-09-19T02:06:29.103 GMT Summer Time INFO ][ org.kde.kstars.ekos.capture] - "Autoguiding stopped. Aborting..."
[2022-09-19T02:06:29.109 GMT Summer Time INFO ][ org.kde.kstars.ekos.capture] - "CCD capture aborted"
[2022-09-19T02:06:29.115 GMT Summer Time DEBG ][ org.kde.kstars.ekos.guide] - Reset non guiding dithering position
[2022-09-19T02:06:29.116 GMT Summer Time DEBG ][ org.kde.kstars.ekos.focus] - Stopping Focus
[2022-09-19T02:06:29.117 GMT Summer Time DEBG ][ org.kde.kstars.ekos.focus] - State: "Aborted"
[2022-09-19T02:06:29.118 GMT Summer Time DEBG ][ org.kde.kstars.ekos.capture] - Focus State changed from "In Progress" to "Aborted"
[2022-09-19T02:06:29.118 GMT Summer Time INFO ][ org.kde.kstars.ekos.focus] - "Autofocus aborted."
[2022-09-19T02:06:29.129 GMT Summer Time DEBG ][ org.kde.kstars.ekos.capture] - setMeridianFlipStage: "MF_READY"
[2022-09-19T02:06:29.130 GMT Summer Time INFO ][ org.kde.kstars.ekos.guide] - "Autoguiding aborted."
[2022-09-19T02:06:29.132 GMT Summer Time DEBG ][ org.kde.kstars.ekos.guide] - Aborting "Guiding"

The odd thing is that I am using 2 sec exposures for autoguiding and 5 second exposures for auto focus on different cameras of course. At this time it has been running for a couple of hours autoguiding at 2 second exposures then here it changes to 5 seconds! Auto guiding Aborts followed by Auto focussing.

I don't know how developers work and co-ordinate efforts but I see Jasem is often mentioned. Anyway as I say, I have created another forum topic on this particular issue and I can only hope someone picks this up.


P.S.
A minor question. If for simplicity, I set backlash to zero then initial step size to 100, out step multiple to four and Max travel to 200 what happens? Surely Max travel must be >= 4*100.

A thought. If the focus position isn't close to the current position when auto focus starts the resultant parabola is asymmetric, with more points one side of the focus than the other and this adds to the problem of poor HFR values for me. Of course we can't know where the focus position is otherwise no point in auto focus but if computed focus position is near one end of the curve would it be a good idea to do another pass with what is hopefully a computed focus near the centre for improved accuracy?

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