Re: [open-phd-guiding] New to guiding and Unable to guide accurately ... please help

[Brian Valente]

Hi Pratul

Can you send a couple pictures of your setup from different angles, make sure to include details on the guide camera/scope setup.

Your main issue is lack of a good calibration. You haven't gotten an acceptable calibration (they are pretty bad, actually), so all guiding is going to be poor until you resolve this. 

For now i would focus on calibration and not look at the guidelogs as any indication other than the calibration is bad. Once you get a good calibration, chances are your guiding will improve in many ways.

Make sure you use the calibration assistant, and follow it with the guiding assistant run. Resolve any issues that the assistants bring up (such as the orthogonality error you already received).

You can also use our baseline guidelog steps (see attached PDF) as a step-by-step to use PHD as a diagnostic tool.

Brian

On Fri, Mar 20, 2026 at 8:10 AM prsharma <pratu...@gmail.com> wrote:

Hello: I am a new to astrophotography and guiding and trying to setup my go to mount with PHD2 but can't get it to work for more than a few minutes. I have watched a lot of youtube videos including all the ones suggested on the PHD2 website and tried to follow all the recommendations. I think my issue is with my mount and have opened a ticket with Sky Watcher as well. They asked me to log an unguided session and submit the PHD2 guide log. I have linked the log file below. I am hoping someone here can take a look at the log file and confirm if it is indeed a mount issue or of I have PHD2 configured incorrectly. 

I have also included a link to log files for my last guided session (Guiding Begins at 2026-03-13 21:38:09) that shows the issue I am having. Please ignore entries after this one. There was another person there that tried, unsuccessfully to make config changes to stabilize guiding. 

Thank you for your help in advance. 

Pratul

My setup:

Mount: Sky Watcher AS-EL55i Pro

Guide camera: ASI676MC

Guide Scope: William Optics Uni-Guide Scope Ultra (200mm)

My process:

1. Rough polar align using "PS Align Pro" app on an iPhone
2. Run PHD2 Calibration Assistant
3. Run PHD2 Drift Alignment
4. Run PHD2 Guiding Assistant and apply recommend changes
5. Start guiding

Link to log files:

Guide log file: https://openphdguiding.org/logs/dl/PHD2_logs_iGvN.zip

Un-guided log file:  https://openphdguiding.org/logs/dl/PHD2_logs_3A6P.zip

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Brian Valente

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[prsharma]

Hello Bruce: Thanks for your reply. 

• I will take a few pictures of the setup tonight and upload them. 
• The first calibration is after doing a rough polar alignment using    "PS Align Pro" app on an iPhone. This one is always bad. (I can't see Polaris from my location and haven't found a better way to do polar alignment.  (I do this first as PHD2 will not let me do a drift alignment without a valid calibration. )
• I then do a drift alignment using PHD2. The one recorded in the submitted logs showed a polar alignment error of 3.1'. Is that not good enough? 
• I follow this with another calibration assistant run. The one in the submitted logs looks like the image below. It shows an orthogonality error of 0.3. 
• I follow this with Guiding assistant and apply recommended changes. 

When using the Calibration assistant, drift alignment and guiding assistant I let PHD2 slew to the location on it's own. 

I believe I am following the steps recommended in the baseline document (Except for the first calibration to be able to do drift alignment).

Please do let me know if I should be doing anything differently. 

Thanks for your help and patience dealing with a clueless newbie 

Thanks!

[Brian Valente]

Pratul

Brian here (not Bruce, but that's okay :) )

Thanks for pointing that out. your guidelogs and calibrations are kind of all over. 

Your guided output showed no good calibrations so the entire guiding in this log is not useful for analysis.

The unguided output showed one bad calibration, followed by a lot of short runs (again, no good for analysis) and then one less-worse calibration at the end

That one calibration you referenced had numerous lost star events (which makes the calibraiton questionable), alerted you to a calibration error (rates), and was not followed by a guiding assistant run. So I think we are still looking for  a valid end-to-end baseline guidelog, that should be your next step in addition to the pictures.

If you had run the guiding assistant after that good calibration, it would have told you 

1. there is substantial dec backlash in your system. fiddling with dec's min move like you did won't help, but enabling dec auto backlash compensation will. The amount of backlash would have been indicated by the GA run, but you can start with 800ms and see how that goes

2. your periodic error for the mount is quite high around +/-24" or about 48" peak to peak. SW should have a spec for their mount but I would guess it's <10"

 

To view this discussion visit https://groups.google.com/d/msgid/open-phd-guiding/7c47ba3f-0f1a-49b9-b48a-d8b2ebd3e77en%40googlegroups.com.

[prsharma]

Brian: My sincere apologies! I hate it when people do that to me and even more when I do it myself. Sorry!

The periodic error is what I was concerned about. Thanks for confirming. 

I am going to do another test tonight. Hopefully it will be a lot cleaner. The short runs are mostly from the drift alignment. Still trying to get a hang of it 🥴

I will do the following:

1. Rough polar align using "PS Align Pro" app on an iPhone
2. Run PHD2 Calibration Assistant 
3. Run PHD2 Drift Alignment
4. Run PHD2 Guiding Assistant and apply recommend changes
5. Run PHD2 Calibration Assistant

1. Run unguided for 20 - 30 minutes (To capture mount behaviour)
2. Run guided for 20 - 30 minutes

Thanks for your help and apologies again for messing the name. 

Pratul

To view this discussion visit https://groups.google.com/d/msgid/open-phd-guiding/CAJa45i5wAVP54W7kHzQajt%3DN10ZyzDcWnd0SwcYdDPVeDXuOaQ%40mail.gmail.com.

[Brian Valente]

perfect

I can't really comment on polar alignment but based on your description, it sounds like you are taking the right approach there. 

To view this discussion visit https://groups.google.com/d/msgid/open-phd-guiding/CAMMLnGMyDRF-p-M2V6k%3DgfmF44iQOFo0_02jPVdR5BM17FUnng%40mail.gmail.com.

[prsharma]

Brian:

I ran the test last night but couldn't get consistent calibrations. During the entire process, I did not touch the mount or the camera and there was nothing blocking movement. 

I have also attached a few pictures of my setup below.

Sky Watcher is insisting that the mount is working fine and they don't see any issues. However, with the large periodic error we are seeing, the large Dec backlash which is causing the guiding assistant test to fail and the inconsistent calibration runs, I am not convinced. 

Thanks for your help!

Link to log file: https://openphdguiding.org/logs/dl/PHD2_logs_W6Mh.zip

Step 1:

I started with doing a polar alignment using N.I.N.A

Step 2:

Ran Calibration Assistant (at 21:00:08 in the logs, did not get any errors)

Step 3:

Ran Guiding Assistant (at 21:03:25 in the logs)

I read the output of the guiding assistant as:

• • my polar alignment was good
  • My periodic errors are high
  • Have issues with Dec backlash

I applied all the recommended changes

Step 4:

Ran calibration assistant (at 21:16:24 in the logs)

Got a warning that this calibration was significantly different from the previous run

Step 5:

to rule out any issues, I restart the mount and all the applications and used N.I.N.A to confirm polar alignment:

Step 6:

Reran calibration assistant (at 21:40:37 in the logs)

Again got the warning that this was significantly different than the last calibration

Step 7:

Ran Guiding Assistant (at 21:43:47 in the logs)

Just like the previous time, dec backlash test failed to complete. 

Step 8:

Although I did not get a clean calibration run, still went ahead to capture an unguided session (at 22:00:22 in the logs)

This again showed the large Periodic error. Actually worse than before. 

Step 9:

Captures a guided session (at 22:13:26 in the logs)

Guiding assistant updated the Dec backlash compensation to 1000 mSec. 

Pictures of my setup:

Leveled:

balanced:

Guide scope mounting setup:

[Bryan]

Pratul

If you have followed this forum, then you may recall the issue of differential flexure (DF).  This is an equipment setup where the guide scope moves independently from the imaging scope.  This movement prevents calibration and guiding, because PHD2 will control adjustments, based on the images from the guiding optics, not matching what the imaging camera is capturing.  The differential movement can impact this even at a few microns, which you cannot detect by hand testing the setup.

Typically, guide scopes are mounted close to the imaging scope, e.g. piggyback.  Even this does not prevent DF.  I think your setup has a few factors that could lead to DF.

Side-by-side mounting with several inches between scopes. Given you are using a camera lens as the imaging scope (nice lens, by the way!), I can understand why piggyback is a challenge.  

Guide scope mounted with a single point of attach leaving a long moment arm in front.

Just my perspective. Others may have more insight.

Bryan

[prsharma]

Thanks for your reply Bryan. I did read about differential flexure but didn't realize having the guide scope and imaging scope like I do would make it worse. A few follow up questions:

• Can my setup cause the high periodic error that I am seeing?
• Can the setup be the cause for guiding assistant Dec backlash test to fail? 

Do you have any suggestions on how I can improve my setup? Will mounting the guide camera on a cheese plate where it is secured both at the front and the back help? Not sure How I can bring them closer. I looked for ways to install the guide scope on to of the lens but haven't found a solution yet.

Tonight I'll try to run a test with the guide scope mounted directly on the mount. 

Thank you!