very bad quiding during last sesions /Ioptron CEM70/

[Krzysztof]

During recent sessions, which I haven't had many of due to the weather, the guiding has deteriorated significantly, mainly in the RA axis. The mount is good balanced on both sides, the PA is accurate, calibration was recently performed with result- good, the cables were checked, and no wind.Guiding assistance performed .

My total RMS error was always  0.6- 0.9.

I'd appreciate any suggestions on what might be causing this.

Could this indicate a mechanical problem, looseness in the mount?

Log attached.

https://openphdguiding.org/logs/dl/PHD2_logs_iKc9.zip

many thanks for your support,

Krzysztof

[Bruce Waddington]

This is a sample of your mount's RA tracking, which is obviously poor:

This could certainly be a problem with the RA drive mechanics and it's certainly not a guiding problem.  But all of the short guiding sequences you sent - even the GA run - were done while pointing at Dec=69.  This isn't useful for diagnostics for a number of reasons and it's also a pointing position that is quite likely to expose problems in cable routing.  In order for us to give you any more insight, we would need to see logs with the following:

1.  A fresh run of the Calibration Assistant near Dec=0 with a calibration result that is at least 'acceptable.'

2.  15-20 minute guiding sessions on each side of the meridian while also pointing near Dec=0.

3.  If no problems appear in step 2, then repeat the guiding sessions at Dec=69.

I looked again at the logs you sent us in January where you were also having serious problems with the RA tracking.  How did you get those resolved?  If you've already spent time making changes and adjustments to the RA drive system, then you can look at that stuff again.  My guess is that an over-mesh somewhere in the system could cause this pattern of slow-response to guide corrections followed by quick over-shoot.  But I think you should do the testing at Dec=0 first to be sure the problem isn't coming from something on the mount payload.

Bruce

[Krzysztof]

Hello Bruce,

Thank you for all recomendations. 

I will check all of them.

My problem from Jan last year was solved by replacing the worm gear after check by local Ioptron's service.

Since then it has worked very well.

Regards,krzysztof

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[Krzysztof]

Hello Bruce,
I checked my mount very carefully, screw by screw, cable by cable.

And it turned out that the dovetail wasn't properly attached to the
telescope. I tightened each mounting screw by 1/4 or even half a turn.
This was the cause of the peaks in the RA axis, in my opinion.

After this operation, the guiding was normal.

All recommendations were followed and the log is attached.

My error in the RA axis is still twice as large as in the DEC axis.

Can I ask for any recommendations in this case after the analysis?

Is there anything I can improve, or am I doing something wrong?

https://openphdguiding.org/logs/dl/PHD2_logs_itub.zip
thank you and regards,krzysztof

czw., 2 kwi 2026 o 18:22 Krzysztof <krzyszto...@gmail.com> napisał(a):
>
> Hello Bruce,
>
> Thank you for all recomendations.
> I will check all of them.
> My problem from Jan last year was solved by replacing the worm gear after check by local Ioptron's service.
> Since then it has worked very well.
> Regards,krzysztof
>
> czw., 2 kwi 2026, 17:13 użytkownik Bruce Waddington <bw_m...@earthlink.net> napisał:
>>
>> This is a sample of your mount's RA tracking, which is obviously poor:
>>
>>

[Bruce Waddington]

Well, as before you're sending data from sessions where you're pointing at Dec=69 degrees so our analysis is hampered.  This is what a typical guiding session looked like at that sky location:

You can see the residual periodic error here which is coming from a tracking error component of about 20 arc-sec peak-peak, recurring at an interval of about 360 seconds:

So you could try using PPEC for the RA algorithm, setting a period length of 360 seconds and un-checking the auto-adjust option.  As it is, this guiding session had an RA rms of 0.68 arc-sec and a total rms of 0.75 arc-sec, so PHD2 has done a pretty good job of correcting for the tracking error.

I think you need to ask yourself whether this current guiding performance is actually interfering with your final imaging results. Are you getting consistently elongated stars because of the difference between RA and Dec guiding results?   If so, I think you will need to invest time in systematically testing and measuring the mount's performance as opposed to doing automated imaging and hoping for the best.  When you are pointing at Dec=69, the magnitude of the RA tracking error is reduced by 65% simply as a consequence of the spherical geometry of the sky.  That's why we always want diagnostic guiding to be done close to Dec=0.  You should also learn to use the PHD LogViewer app so you can evaluate these results yourself.  It's not difficult to do, and identifying periodic error like we're talking about here is pretty straightforward.

https://openphdguiding.org/phd2-log-viewer/

Regards,

Bruce