Problems with RA guiding on HEQ5

[Henny]

Hi,

I have a new HEQ5 Pro and noticed my stars are elongated in the east-west direction, even in 30s unguided exposures. I started guiding using PHD2 but I run into the problem that my RMS in RA is always 4-5x higher than in DEC. Therefore I keep having elongated stars, even with guiding. I tried to follow the PHD2 Best Practices presentation and tested a lot with different settings on the Hysteresis algorithm and some short tests with the PPEC algorithm. I also ran the Guiding Assistant every time for about 10 minutes and accepted the provided advice. The scope is balanced slightly east heavy and camera heavy. However, nothing seems to resolve the issue. The best RMS values I seem to get are mostly above 2" on RA and <0.5" on DEC.

To further try to resolve the issue, I tried to record a PEC curve in EQMOD using AutoPEC. My hope was this would make life easier on the guider. However, the PEC seems to vary every time I record it over multiple worm periods. Therefore, today I recorded a guide log without guide output to the mount and tried to use PECPrep to analyse the resulting curve. Before recording, I calibrated PHD2 near the equator and meridian as specified in the best practices. Looking at the curve of over 1 hour, it seems to me that there is no clear regular PEC pattern. Or at least, there is a large random fluctuation making it difficult to see. I assume that is why the AutoPEC result varies all the time.

I am running a bit out of ideas at the moment. I wonder if there is anything else I can try with PHD2 or whether there might be something wrong with the mount that I cannot resolve myself... Especially the fact that I cannot seem to get a proper PEC curve worries me a lot. Hope someone can help me out on this. The guide and debug logs can be found here:

https://openphdguiding.org/logs/dl/PHD2_logs_xkGt.zip

I hope this is a sufficient description. Otherwise, please let me know!

Thank you in advance,

Henny

Equipment list:

Skywatcher HEQ5-Pro

William Optics Zenitstar 73

William Optics 73A flattener

ZWO ASI533MC Pro

William Optics 50mm guide scope

ZWO ASI120mm mini mono guide camera

[jksi...@gmail.com]

Hi Henry

I used PHD2LogViewer to check your guide log. In the first guide period of 56 minutes, something obviously happened around the 10 minute mark but a frequency analysis of the remaining 46 minutes does indicate the typical worm period and harmonics for the HEQ5 Pro mount: e.g. there's a 3.5" peak around 670 seconds vs the mount period of 638 seconds - I think a longer run would define these peaks and periods more clearly. There's also a sharp peak at 13.6s. In the second guide period of 35 minutes the long periods are hardly present but again there is a very sharp peak of over 2" at 13.6 seconds. PHD will easily correct for the long periods but it cannot cope well with that very short period oscillation and it accounts for most, if not all, of your RA RMS. I read (in the PECPrep mount parameters) that this 13.6s period corresponds to the "gear mesh period" of the HEQ5. I think you have to get some expert advice on that mount - if it is still under warranty the vendor can surely help if that oscillation is out of spec, or else you may have to make some adjustments yourself to tune it up. I would not do any PEC or use PHD's PPEC until that issue has been resolved.

Good luck

John

[Henny]

Hi John,

Thank you so much for taking the time to look at my guide log, I really appreciate it! I had another look using PHD2LogViewer and with your explanation in mind it is a lot clearer to me :-) Really good to see that the guiding does handle the longer periods! Looking at the guided section, the 13.6s is indeed standing out. It starts to make sense now. I will give it another try once the weather clears up so I can get some more time/periods to get more defined peaks. But before I attempt any further PEC recordings, I will follow your advice and first look into the 13.6s. The mount is still under warranty so I hope the reseller is willing to help me out with this! Again, thank you very much for helping me with the analysis of the guide log!

Regards,

Henny

Op zaterdag 22 augustus 2020 om 03:36:29 UTC+2 schreef jksi...@gmail.com: