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Configurable timeout for dithering


1DegreeN

Question

When dithering via PHD2, BYEOS waits for around 90 seconds for PHD2 to report that the guide star has returned to within the settle distance from the lock position. Is this 90 second timeout set by BYEOS and could it be made a configurable parameter via Settings? 

I am using an Astrotrac mount which only guides in RA. I'm using PHD2's drift alignment to try to get the best Polar Alignment I can but even a tiny PA error results in Dec drift that accumulates over the session and of course can't be guided out. When PHD2 dithers and it reports the distance from the lock position back to BYEOS, it is the absolute dec drift from the start of the guiding session that is measured and not the relative dec drift before and after dithering. Even though the dec drift during each sub is small and my subs have nice round stars, after a few subs the absolute dec drift has grown to the point where PHD2 will never report a small enough settle distance to trigger BYEOS to begin the next sub - and then I have to wait for the 90 second timeout to elapse. 

I do have a manual workaround: about 15 seconds before the end of a sub I switch to PHD2 and quickly stop guiding, auto-select the guidestar again and resume guiding - this resets the lock position. My experience so far shows that my Astrotrac mount typically takes 15-30 seconds for RA to return to lock after dithering; if the timeout could be configured then I would set it to around 30  seconds. 

Thanks!

John

 

 

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I suspect that your problem is because PHD2 is unable to reacquire the lock position because it can't adjust the mount in Dec.  It is really a PHD/mount issue and not a BYE issue. I may be wrong, but I believe that the timeout is on the PHD side.

You should post your issue to PHD2 support.  You may be able to ease things by allowing PHD to look further away to reacquire the guide star. I think that the default is 15 pixels, but it is changeable.

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The issue is not that PHD fails to re-acquire the guide star after the dither, it is that the monotonic increase in dec drift eventually prevents PHD reporting a post-dither distance less than the Settle distance specified by the client. I don't think PHD is doing anything wrong - it's measuring the distance relative to the lock position at the start of the guiding session; it's just unfortunate for anyone with an RA-only tracking mount such as my Astrotrac. Clearly I should put more effort into getting a better PA via drift alignment! 

Re the timeout: in the PHD2 API the timeout is in the Settle parameter of the dither command issued by the client. However I saw a comment that BYE may use the PHDv1 API and I haven't found the documentation for that yet so the timeout could be a PHD controlled parameter rather than a BYE parameter.

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You have control of the "Dither Settle-At" parameter in BYE - a larger value will allow larger PHD2 Guide Star Offset values.

You also have control - in PHD2 - of the "Dither in RA-Only" setting.

And, you can define a "Pause per Image" in the BYE Imaging Plan.

However, your Best Option would be to fine tune your PHD2 Usage such that you can perform Full Multi-Axis Guiding and Dithering.

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This is actually not possible.  This is because PHD is doing the dithering, not BYE/BYN.  Once BYE/BYN sends to command to PHD to dither BYE/BYN is there for the ride only and must wait for PHD to be done.  The way you choose how close to the new location you are comfortable with is by setting the "Settle Dither At".  This is your only way out... so increase it as much as you can where you do no see any residual effect in your images.  This is a trial and error process.  If you are imaging a low focal length you may get away with a higher number, say 0.50 to 0.60.  If you are imaging at high focal length you may need to keep it down to 0.20 to 0.30.  Again this is a trial and error process.

You may also try a less aggressive dither setting, which will have PHD move less further from the start point and therefore be faster to get to the new location and resume guiding successfully.

Hope this helps.

Regards,

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