My RA error tends to be ~2x my DEC error. Is this something to be tuned?

[Ryan Haveson]

It is very consistent that my RA error is higher than my DEC error.  Usually around 2x.

I am also getting the RA OSC (though am told it is a useless statistic) number showing red in the display and the graph does seem to show the RA is oscillating. 

Any ideas?

Link to logfile: https://openphdguiding.org/logs/dl/PHD2_logs_usPX.zip

Link to previous night where I ran GA/Calibration (scope is semi-permanent setup so didn't move): https://openphdguiding.org/logs/dl/PHD2_logs_8HVd.zip

--Ryan

[Brian Valente]

Hi Ryan

thanks for uploading all those logs

Your issue with RA can be shown pretty clearly when looking at all the RA (blue line) compared with DEC (red) - you can see the regular oscillations that are much larger:

'

Specifically you have larger periodic errors at 348 seconds and at 116 seconds (both around 3.8")

the limiting factor to your guiding appears to be the 116 sec error, here you can see residual tracking (i.e., what cannot be guided out):

This is probably an adjustment in your mount somewhere. You may here from someone who owns youare Ioptron mount, or better to check with an ioptron user group or with the manufacturer directly

Brian

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Brian Valente

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[Ryan Haveson]

Thanks so much for the analysis.  I am following up with iOptron.  I'll also poke around on the mount forum on CN and see if anyone has anything helpful to say.

One question.  I thought that PPEC would take care of this, do I understand that wrong?

(also now that I am mentioning that, I realize that I do not have PPEC enabled, maybe that setting changed when I upgraded to 2.6.10?)  But either way, do you think that is worth trying or is this not the sort of thing that PPEC addresses?

--Ryan

[Brian Valente]

Hi Ryan

you can definitely give PPEC a try, it certainly can't hurt and will likely improve things. The question is will it be enough? the residual error is quite high, > 1". PPEC will help but i'm not sure it will be enough, and you would definitely want to investigate this anyways.

make sure you set PPEC period for exactly the length you want (116 seconds) and disable auto adjust period

You will also probably want a faster exposure time, like 1-1.5 seconds

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[bw_msgboard]

Hi Ryan.  As Brian said, the periodic errors in RA tracking are dominating your guiding results.  I don't know the story on whether iOptron mounts handle periodic error correction in a sensible way.  One other thing you can try is to use shorter guide camera exposures, like 1-second.  If you can use multi-star guiding and are a bit careful about the min-move setting, shorter exposures would let PHD2 guide more aggressively and perhaps reduce the error until you can get a mechanical improvement.  To do this, you might have to consider binning the guide camera - which you can afford to do - and/or increase the camera gain in order to get adequate SNR.

 

Good luck,

Bruce

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From: open-phd...@googlegroups.com [mailto:open-phd...@googlegroups.com] On Behalf Of Ryan Haveson
Sent: Wednesday, August 25, 2021 9:47 AM
To: Open PHD Guiding
Subject: Re: [open-phd-guiding] My RA error tends to be ~2x my DEC error. Is this something to be tuned?

To view this discussion on the web visit https://groups.google.com/d/msgid/open-phd-guiding/f18d1685-c132-43d3-8961-1ac59f784764n%40googlegroups.com.

[Ryan Haveson]

Thanks for all the input friends!  

In case anyone is interested I am posting an update here (TL;DR it got better).

- logs: https://openphdguiding.org/logs/dl/PHD2_logs_xADe.zip

Last night I made the following changes:

- 1 Sec guiding

- Enabled PPEC

- Set PPEC Period to 116 (though it looks like I forgot to disable auto-adjust so it adjusted itself to 348, so I'll address that tonight)

This made the guiding much better than the previous night.  The RA error is still higher but now it is more like 30% higher instead of double.  And total error was for the most part < 0.5".

@Bruce, when you say "adequate SNR" what would be the adequate range?  In looking at the logs I was right around 26-27 SNR.

@Brian, how did you get that graph / determine that the period was 116sec?

For next steps, since I forgot to disable the auto-adjust Ill have another go at it tonight with that corrected.

Depending on what happens there I may then try to enable the iOptron PEC to see what that does.  For the training, I think I should switch the RA guiding algorithim back to Histeresys, is that correct?

I do also have a thread out on CN and also with the manufacturer to look into the mechanical adjustment options.

--Ryan