Help Interpret PHD2 log, is my polar alignment good enough?

[John Rightten]

I have a long FL (2000mm) imaging setup installed remotely and I am struggling with long exposures that are hard to guide ( I am using AO as well) so I did multiple tests last night (all in the log) can someone look at it and help me diagnose the issues, starting with Polar alignment (any way to figure out by looking at the log how good it is currently?) any other issues and how to address them?, or what other tests are recommended to zero down on critical things?

https://drive.google.com/file/d/1oA7BL6K7TQOQ4Oem8fQH2_zI3OvcA_5I/view?usp=drive_link

[Brian Valente]

John

That file is inaccessible. Please use the PHD Log Uploader built into the software to send the link to your logs:

https://openphdguiding.org/getting-help/

If you haven't already done so, creating a baseline guidelog is a good diagnostic tool. the steps on how to do this are attached

Brian

On Sun, May 10, 2026 at 4:25 PM John Rightten <johnri...@gmail.com> wrote:

I have a long FL (2000mm) imaging setup installed remotely and I am struggling with long exposures that are hard to guide ( I am using AO as well) so I did multiple tests last night (all in the log) can someone look at it and help me diagnose the issues, starting with Polar alignment (any way to figure out by looking at the log how good it is currently?) any other issues and how to address them?, or what other tests are recommended to zero down on critical things?

https://drive.google.com/file/d/1oA7BL6K7TQOQ4Oem8fQH2_zI3OvcA_5I/view?usp=drive_link

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Brian Valente

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[John Rightten]

I made the link public, please try again. For some reason PHD2 uploader is not working, it just would not connect when i try to upload the log

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[Brian Valente]

John

Can you describe your equipment and configuration? a few pics from different angles would help as well

Some initial thoughts. it looks like you were doing a lot of settings experimentation so results are a bit scattered:

- based on your guiding assistant run at 5:22am, the mount mechanically seems fine (no info on dec backlash), including  polar alignment (measured 5/10  5:22am)

- when you calibrate, you should use the calibration assistant and calibrate at the 0 degrees - many times you are calibrating far from there, and I expect you received warnings about that. This alone may help things considerably

- I'm not sure which guide camera your using or why you are binning it? bin 1 is stil around 0.5" resolution. bin 3 seems unnecessary (and doesn't seem to impact your guidestar SNR) 

- you have not done a dark library, which is highly recommended. some of your guidestars have extremely low SNR

- You didn't specify your exact mount, but assuming it's an ioptron gem of some kind, I don't see any backlash measurement on the GA run? It seems like that may be getting in the way of your dec performance.

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[John Rightten]

Brian, to answer some of your questions, I have the following equip/config:

Mount: iOptron CEM60 installed remotely on the pier with polar alignment performed at least twice by now using sharpCAP

Imaging train:  see attached PDF file

I did a fresh run this night and here is the log: https://openphdguiding.org/logs/dl/PHD2_logs_22Xo.zip

Comments: I did multiple attempts at calibration in different portions of the sky to illustrate some of the issues. A major problem occurs when I calibrate at 0 or 10 deg of DEC, then the following guiding session lasts only for a few minutes and then it abruptly moves in DEC loosing the star completely out FOV of the SC3 and I have to abort it and start over and it happens again only after a few minutes and i have to abort it. I am not sure if this is recorded in the log...this happened on multiple occasions, BUT if I calibrate it near my current target (M101) I have no issues and can guide for hours, there are few other things: following PHD2 guider assistant recommendations on min DEC and RA movement values, did not have a big improvement on the guiding quality and I think the settings that were used for a long session that was successful more or less differ significantly from recommendations. So far I ve been following automated PHD2 instructions after assisted/guiding ot assisted calibration, but I am not sure they improve actual performance....I am not an expert in PHD2 and would greately appreciate your comments/feedback/advice

[John Rightten]

sorry forgot to attach imaging train setup PDF

[Bruce Waddington]

Your picture shows you have a rotator in the optical train ahead of the guide camera - but you don't have the rotator connected to PHD2.  Are you not using the rotator?  If the rotator is being moved by the session manager application, that will invalidate the guide calibration unless you also have PHD2 connected to the rotator.  The new-profile-wizard asks you about this so I don't know why you're trying to operate in this mode.  OTOH, I suspect you didn't run the new-profile-wizard for this configuration which would explain a great deal.

Bruce

[John Rightten]

I am not using rotator on those occasions......so this could not explain the behavior...did you have a chance to look at the latest log I provided...what conclusions can you make about mount behavior and polar alignment quality? why do I get the issues I described above? Thanks!

[Bruce Waddington]

Well, yes, I've spent quite a bit of time looking at your data and I'm sorry to say it's quite a mess.  Let's start with my question about the rotator which you seemed to think was irrelevant.  This is a view of two successive PHD2 calibration runs, separated by less than 1 minute of elapsed time with the scope remaining in its original location.  In all graphs here, RA is in red, Dec is in green.  Here's the first one:

Here's the second one:

Can you see there's a dramatic change in the angular orientation of the RA and Dec axes as measured during calibration?  Can you see why I asked about the rotator?  So if the rotator was not being intentionally moved by an app, what is the explanation?  Did it move by itself?  Did the guide camera rotate in the OAG?  Was there a big cable routing problem that interfered with the ability of the mount to rotate the axes as expected?  I can't tell you, you will need to answer that question yourself.  But given that you got two very different results back-back, what confidence can we have that either one is accurate?  

Later in the evening, you got two equally poor results, this time pointing at Dec=54 but still on side-of-pier west. Again the scope wasn't moved between successive calibrations:

More unplanned rotation?

Even when you didn't get these very odd results, the calibration result was inconsistent in terms of the rate of movement.  Here's a calibration done at 23:45:

Look at the huge difference between how RA and Dec responded to equal-sized guide pulses.  You've got a lot of "bunching" in RA - often caused by gear mesh that is too tight - and an inexplicable acceleration of response in Dec.  Of course, all of these things can be caused by problems in the payload such as Dec imbalance or poor cable routing but there's no way for us to distinguish them just from guiding data.

I think the bottom line here is that until you can get repeatable, reasonably accurate calibrations on both sides of the pier, you will continue to get poor results.  The "good" guiding sequences you occasionally see are correlated with situations where nearly all of the corrections are being handled by the AO and there is very little mount bumping.  You need to understand that what we've talked about here are the results of simple measurements - the problems lie with the equipment setup, not PHD2.

Beyond all this, there are many other operational problems that don't necessarily cause these situations but they certainly don't help them:

1.  I continue to suspect that you never really ran the new-profile-wizard for the configuration profile you're using.  I say that because the profile name is !temp!profile!name!~, which is one automatically created by PHD2 when the user refuses to run the new-profile-wizard.  It's very important you do this and it would also give you the opportunity to include the rotator in the PHD2 configuration.

2.  The camera you're using may not have the performance you need for guiding at a long focal length.  The sensor is quite small and you were frequently having to use stars with single-digit SNR values.   This was made worse by your attempts to choose guide stars yourself, your refusal to create a dark library, and your attempt to use very short exposure times.  All of these things are recipes for getting poor results.

Bruce

[John Rightten]

I have another clear night coming tonight and I would like to follow your instructions precisely, so we are on the same page:

1. Run new profile Wizard config

2. Run auto calibration at 0-10 deg DEC on E and W side of the pier (correct?)

3. If it gives me errors should change to recommended values and rerun auto-calibration? I can't do any mechanical adjustments remotely, so I am limited at what I can change.....

4. What to do if auto-calibration can't get satisfactory results?

"I think the bottom line here is that until you can get repeatable, reasonably accurate calibrations on both sides of the pier, you will continue to get poor results. " How do I get them if it keeps saying error and the 3 things it always mentions : Poor polar alignment  (this has been performed already 3 times by the professional staff), large Dec backlash or PE in RA...these are 3 wastly different things, what tests can I run remotely to pinpoint which one it is ?  you also mentioned gear mesh that is too tight...how do I test for it ?

5. As I mentioned in my last post and another user on the forum mentioned the same thing: After running auto-calibration the guiding lasts only for a few minutes then the guider star inexplicably runs away. This does not happen if calibration done near the imaging target.....how to solve this? it happened on multiple nights and I have to redo the calibration near the target to save the night.... 

6. Perform auto-guiding session (~ 5 min) on E and W side of the pier? should I use the auto-calibration star near meridian or I can the star near my target?

7. I will connect the rotator to PHD2 profile, I plan to use it tonight

8. what tests do I need to run to address the quality of polar alignment specifically? Remote observatory is asking this because they can re-align the mount, they just need to know the test results...

Any other recommendations?

[Bruce Waddington]

I think you need to come to terms with the likelihood that you have mechanical problems with the current setup and until you can isolate and identify what they are, you can't know whether the fixes will be hard or easy or whether the on-site staff will be able to repair them.  Your only goal for now should be to figure out why you can't get decent calibrations.  To start doing that, you should do the following:

1.  Run the new-profile-wizard to create a profile only for testing, being careful to input the parameters correctly.  At this point, it's ok to include the rotator in the configuration but do NOT include the AO device.  At this point the AO is only masking the problems you need to be looking at.

2.  Have someone make sure all the fittings on the back of the scope are completely tight and that nothing can rotate or move on its own under the pull of gravity.  Also make sure the azimuth/altitude adjustment tools on the mount are completely tight.

3.  Expect to spend significant time only doing testing and diagnosis, not imaging.  So, do NOT try to use a session manager app like NINA or do actual imaging - conduct all the tests just running PHD2 by itself.  You are basically using PHD2 as a measurement tool to understand what's going on.

4.  Use the Calibration Assistant for doing calibrations and do what it tells you.  Despite what you think, it is there to help you.  When you complete a calibration, use the Tools/Review Calibration menu item to explicitly look at the results of the calibration.  You should be seeing reasonably straight lines whose orientation remains constant until you change the side-of-pier.

5.  Since your most serious problems happen on side-of-pier west, start working there.  It's ok to move the scope around between calibrations to see if pointing position affects results - but keep the location between 0 and 20 degrees Dec. In the Calibration Assistant window, you don't have to click on 'Slew' first, you can just tell it to calibration in-place by clicking on the 'Calibrate' button.

6.  If you continue to get whacky results, run the Star Cross tool (Tools/Star-cross Test) in PHD2 and save the resulting image.

7.  If you do get an acceptable calibration, go ahead and let PHD2 guide for 15 minutes in-place and don't ever try to tweak any of the guiding parameters.

8. Repeat the calibration tests from side-of-pier east and see if the results differ.

Depending on the outcome of the tests, you may need to have the site review all the cable routing that's been done.  Site operators can get overly enthusiastic with fasteners and cable tautness and these mistakes can create situations where the mount can't move freely in all locations.  Conversely, they may have left some cables dangling such that they can snag or drag on stationary parts of the setup. Testing this by slewing means nothing - the amount of energy pumped into the drive systems for slewing is typically several hundred times higher than what is used for guiding - so slewing can often just "blow through" certain kinds of problems that interfere with guiding.  With regard to most of your questions, virtually nothing can be done to distinguish one problem source from another until you have a calibration that is reliable.  

None of this is going to be fun or rewarding, but provisioning a large telescope setup at a remote location is not an easy business.  Many of us dealt with this by doing all this sort of debugging at a reachable location before moving the entire rig to a remote location.  But, there are some remote site operators who are very skilled in these things and can sort them out for you, in which case you might be fortunate and get a relatively quick resolution.

Bruce

[Bruce Waddington]

One other thing - for these tests, use exposure times of 1-2 seconds.  It's important to avoid lost-star problems because those just interfere with the testing.  To be on the safe side, start with 2-sec exposures and let Auto-Find do its thing.

Bruce

[Brian Valente]

John

Bruce provided extensive detail, but i want to make sure the bigger picture is clear: the mount itself seems to have mechanical issues (or mount-related, such as cabling, etc.). Testing without the AO will allow you to see the raw mount performance.

AO can certainly help improving things, but it can't compensate for all performance issues. Once you get the mount performing well on its own, you can return the AO to the mix and tune from there.

Sorry if that's redundant but just want to make sure the picture is clear. 

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