Need to get better RMS
bw_msgboard
Hi Ali. Your overall guiding RMS is typically below 1 arc-sec so you’re running up against the limitations of the mount’s RA tracking system. You’ve also compounded the problem by screwing around with the RA guiding parameters, adjusting them in exactly the wrong direction. The problem you’re having is the native RA tracking performance, which shows a fair amount (but not unusual) of uncorrected periodic error:
So the RA tracking error is moving around within an envelope of roughly +/- 8 arc-sec. If you make a long Guiding Assistant run, say 16 minutes, you’ll get a clearer view. Most of the error occurs at the frequency of the worm period but there are smaller contributions at various lower frequencies:
So I think your best bet is to try to tame the periodic error. The preferred solution is to get a high-quality periodic error correction programmed into the mount. That can’t be done by hand, it should be done with a specialized app that can measure the error over multiple worm cycles and filter out seeing effects and other anomalies. You can also try using the PHD2 PPEC algorithm in RA, giving it an initial period of 480 sec. This won’t be as effective as doing a real periodic error correction but it will probably help. The best option is to do both. In any case, you need to restore the guiding parameters to their default values and avoid fiddling around with them until you have a very clear understanding of what your mount is doing.
Good luck,
Bruce
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Ali
bw_msgboard
From: open-phd...@googlegroups.com [mailto:open-phd...@googlegroups.com] On Behalf Of Ali
Sent: Thursday, March 18, 2021
4:23 AM
To: Open PHD Guiding
Subject: Re: [open-phd-guiding]
Need to get better RMS
Thanks Bruce for your great support..
I am planning to do PEC correction soon or/and rowan belt mod.
Two things confused me:
1- What is the best pulse guide rate for Ra & Dec to set in ASCOM EQMOD, Some said x0.5 some said to the maximum which is x0.9 ?
2-
What you’re talking about here is the guide speed being used by EQMOD – despite the rather odd labels in the EQMOD UI. Higher numbers, up to 1.0x, will accelerate the completion of guiding commands. This is helpful for clearing Dec backlash and also for settling after dithers. You have to be sure to set the EQMOD parameters using this document:
https://github.com/OpenPHDGuiding/phd2/wiki/EQASCOM-Settings
Notice that the minimum pulse-size should be reduced below the default value. I would say the guide speeds you’re using now are fine for your situation.
3- When performing PEC correction recording in ASCOM EQMOD should I turn PHD2 guiding ON or OFF (just let the mount track alone) ?
This is really an EQMOD question, I think it depends on how you want to do it. A Google search found this guide:
http://eq-mod.source...qmod_vs-pec.pdf
Good luck,
Bruce
To view this discussion on the web visit https://groups.google.com/d/msgid/open-phd-guiding/a07b8368-3cba-41fc-ae53-a8dac9e31b33n%40googlegroups.com.