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25 Jul 2018
Glad to announce of release of INDI Library v1.7.4 on 2018-07-25. A few drivers were added in this release as we continue to improve & stabilize existing drivers.
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TOPIC: guide star lost after dither

guide star lost after dither 2 months 1 week ago #28492

  • alacant
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Hi everyone

I'm seeing frequent loss of guiding after a dither. The requested dither is only 3px but the dither itself is much larger than that; the mount seems to be hit far harder than is necessary by the dither pulses e.g 35px for a 2.6px dither request.

Guiding is eventually recovered on another star but never has time to stabilise.

Any ideas what I'm doing wrong?

TIA and clear skies,

Steve

logs: drive.google.com/open?id=1yr-Lw1mF45gOC5YtYV1R9cp3favpKMbc

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ubuntu 18.04
700d, eq6, t7m

guide star lost after dither 2 months 1 week ago #28493

Maybe post this in PHD Google group? Looks like all the requests are sent OK from Ekos side.
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Jasem Mutlaq
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guide star lost after dither 2 months 1 week ago #28495

  • alacant
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ubuntu 18.04
700d, eq6, t7m

guide star lost after dither 2 months 6 days ago #28567

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Hi everyone
Here's Andy's reply:

The dither sizes are ok, but it looks like PHD2 is bouncing around between different guide stars. You are in a rich star field and the dither causes PHD2's search region to shift enough to move a brighter star into the search region and PHD2 switches guide stars. There are a couple things you can do to prevent this from happening.

First I would try changing the size of the search region. You have it set to the default of 15 pixels which is usually ok. Try increasing it to 20-25 pixels. That should allow the brightest star to stay in the search region even when dither causes the search region to move. Alternatively you could decrease the size of the search region to about 10 pixels; that may also work since I think you are just unlucky enough that the there are 2 good guide stars separated by a distance that happens to match the 15-pixel search region size.

The next thing I would try would be to change the dither method to Spiral Dither. This will make the dithers much more predictable. When you change to Spiral you should also reduce your dither size from 3px to something smaller like 1.0 pixel or 0.7 pixel or even less.

If those ideas do not help you you can also try reducing the Star Mass detection tolerance from your current setting of 80% to a lower (more strict) value of perhaps 50-60%. I would be inclined to leave this one alone and only change it as a last resort -- too strict of a tolerance can cause excessive dropped guide frames.


@ Jasem. Andy also mentions this:
On a separate note, I see that some of the dither settles are failing because the settle timeout is too low -- 45 seconds. You should change this to a much higher value, like 180 seconds. The setting is in the Ekos here:

But there's only 2 digit entry. Would it be possible to have 3-digit entry there?

Cheers, HTH other PHD2 guiders and clear skies,
Steve
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ubuntu 18.04
700d, eq6, t7m
Last Edit: by alacant.

guide star lost after dither 2 months 6 days ago #28578

Sure, max value increased to 360 secs.
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Jasem Mutlaq
Support INDI & Ekos; Get StellarMate Astrophotography Gadget.
How to Submit Logs when you have problems?
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