Guiding Issue

[Matt Brown]

I have used PHD2 successfully several times but last night was different. I would start guiding and it looked good for about 15 seconds and then both RA and DEC would veer off  zero a large amount and never correct. It seemed that the mount was ignoring the correction commands. I had made no changes to the guiding parameters. After a couple of attempts I did an update of my Ascom drivers to v7.1.1, but that made no difference. I ran guiding assistant and it recommended that I improve polar alignment, and gave the usual min move recommendations, but nothing out of the ordinary. I later found that PA error was 10 arc-min but did not correct at that time. Dec backlash was very low.

Here is the link to my log file.

https://openphdguiding.org/logs/dl/PHD2_logs_RByB.zip

Thanks in advance for any guidance you can offer.

Matt Brown

[Michael Waring]

Hi Matt

If I were a betting man, I'd say you needed to recalibrate.

As something in the rig seems to have moved since the last Cal on 12/10/2025 8:22:38 PM.

From GA run "Recommendation: Consider re-doing your calibration"

[Brian Valente]

Matt

As Michael suggested, I would start with recalibrating. It looks like the mount is not responding. you have a number of mount move fails, but the guide pulses are being sent. In addition, you have a rotator and I can see it's being moved, so I would avoid using that for now until you can sort out the guiding.

The mount move fails may be a result ofthe calibration being invalid, but after a calibration you can also do a start cross test to confirm your mount is responding properly

Brian

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Brian Valente

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[Matt Brown]

I would not have thought recalibration necessary for two reasons:

--PHD2 said I have good calibration and issued no warning alerts.

--The previous night I imaged NGC1499 for five hours using 6-minute sub exposure times, without any issues. Below is the link to that guiding session.

https://openphdguiding.org/logs/dl/PHD2_logs_89uw.zip

Matt

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From: open-phd...@googlegroups.com <open-phd...@googlegroups.com> on behalf of Brian Valente <bval...@gmail.com>
Sent: Tuesday, December 16, 2025 10:15 AM
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Subject: Re: [open-phd-guiding] Guiding Issue

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[Brian Valente]

PHD said your prior calibration had no issues, not that it remains good

in fact, when you ran the guiding assistant, it reported that you should re-do the calibration. It also said that your polar alignment error was >10arcmin. This could also happen if your rotator invalidated the calibration

So recalibrating is a good place to start. 

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[Bruce Waddington]

Like Brian, I think you need to isolate the rotator behavior from the equation.  On the previous night, the rotator was at 180 degrees which is where the calibration was done.  But last night it had been rotated to 56 degrees.  Do you know for sure that this has worked in the past when the rotator was being moved?  Have you already gone through the procedure to determine whether you need to use the 'Reverse angle' property in PHD2 for the rotator configuration?  For the next session, you could put the rotator back to 180 degrees and see if the guiding behaves - without doing a new calibration.  If it works correctly, then you know there's an issue with the rotator configuration.  Here's the recommended procedure for figuring that out:

https://openphdguiding.org/man-dev/Basic_use.htm#Rotator_Selection

Good luck,

Bruce

[Matt Brown]

It certainly is an easy place to start. I'll do it first the next time I have clear skies.

Thanks for the advice.

Matt

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From: open-phd...@googlegroups.com <open-phd...@googlegroups.com> on behalf of Brian Valente <bval...@gmail.com>

Sent: Tuesday, December 16, 2025 10:39 AM

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[Matt Brown]

I think you hit on it. I did not re-cal before imaging at a different angle from the previous session. The previous three or so sessions were all done at 180 degrees I believe.

I need to check the box labeled "Force Calibration" in the sequence instruction for starting guiding in NINA software, at least to force me to acknowledge the possible need to re-cal as a result of shifting the angle.

Thanks,

Matt

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Sent: Tuesday, December 16, 2025 10:42 AM
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[Brian Valente]

Is this an automated rotator? You can connect it to PHD to automatically compensate, but it needs to be correctly configured. 

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[Matt Brown]

It is a ZWO CAA camera angle adjuster, automated via NINA. What is involved in making it "correctly configured"?

Bruce pointed out that I did not perform a re-cal when changing the angle from the value used on the previous night, and that is necessary.

Matt

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From: open-phd...@googlegroups.com <open-phd...@googlegroups.com> on behalf of Brian Valente <bval...@gmail.com>

Sent: Tuesday, December 16, 2025 11:04 AM

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[Brian Valente]

>>> Bruce pointed out that I did not perform a re-cal when changing the angle from the value used on the previous night, and that is necessary.

again, you can automate this in PHD as many of us have done. Recalibrating while using a rotator is not required when it's setup properly.

start by making sure it's working correctly in NINA

then follow the steps in PHD documentation: https://openphdguiding.org/man/Basic_use.htm#AO_Selection

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