AP1150AE / PHD2 / NINA dither settle failures despite normal guiding

[John Hague]

Logs uploaded:  https://openphdguiding.org/logs/dl/PHD2_logs_A8Ej.zip

I am using an Astro-Physics AP1150GTO AE with absolute encoders, EdgeHD 1100 at f/7, OAG-L, ASI174MM Mini guide camera, ASI2600MC imaging camera, NINA 3.2, and PHD2 2.6.14.

Normal guiding appears acceptable when left alone, often around 0.35–0.50 arcsec RMS. The problem is specifically around dithering and settling. After dither events from NINA/PHD2, the settle distance starts much larger than expected and decays slowly, often timing out. In one case, the selected dither vector appears very small, but the settle distance is still several pixels. The guide star does not appear to be lost during the main dither failures; PHD2 seems to remain locked and issue corrections, but it does not satisfy settle. Later in the night, guide-star loss did occur, likely from clouds/haze, but that appears separate from the earlier dither-settle problem.

Current relevant settings:

• Guide camera: ASI174MM Mini through OAG
• Guide exposure: 4s
• MultiStar: on
• Fast Recenter: was off for this log, but I plan to turn it back on
• RA algorithm: Lowpass2
• DEC algorithm: Lowpass2
• RA/DEC aggression: 50
• RA/DEC min-move: 0.37 px
• Dither amount from NINA: 2
• Settle: 2 px for 3 sec, 60 sec timeout
• StarMinSNR: 20
• Absolute encoder mount profile/settings enabled

Questions:

1. How do I change my settings so the guiding will settle.  Right now it is not converging.
2. Does the debug log show that PHD2 is interpreting the NINA dither command correctly?
3. Why would a small selected dither vector produce a much larger settle distance?
4. Are there recommended settings for AP absolute-encoder mounts during dithering/settling, especially short delay / variable exposure delay / Fast Recenter / DEC algorithm?
5. Should I loosen settle tolerance to 4 px, reduce dither amount to 1, or change short-delay behavior for this type of mount?
6. Is MultiStar ever known to cause a reference jump after dithering with an OAG?

I have uploaded the PHD2 logs for the last two nights.  Both nights had similar issues.  If you want the NINA logs, I can upload those as well.

Thanks for any help.

[Brian Valente]

Hi John

I think the main issue is your polar alignment appears quite far off. The dither/settle seem to be okay, but it never completes seetling because your Dec will never get back to lock position. Here's an example showing Dec (and RA for that matter) offset from the lock position:

Try redoing your polar alignment, recalibrate using the calibration assistant, and run the guiding assistant to measure your polar alignment.

Brian

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Brian 

Brian Valente

astronomy portfolio https://www.astrobin.com/users/bvalente/ 

[jhag...@gmail.com]

Thanks, Brian.  Appreciate you looking into this.  I will do that.  However, in TPPA in Nina it showed was within ten seconds on both axes when I completed the PA three days prior and the mount has not moved.  However, I will recheck.  That was my planned next step as well (whenever the clouds leave again!).  Good idea to use the Guiding Assistant to doublecheck TPPA.

 

What you show is exactly what I was seeing.  The DEC never converges back to the new settle position after dither and upon startup.  However, the normal guiding is just fine (.4s and .5s RMS mostly) and the calibration had an ortho error of .4% so it seemed pretty good.  Weird that it would guide just fine but not settle well.

 

All the best,

 

John

 

From: open-phd...@googlegroups.com <open-phd...@googlegroups.com> On Behalf Of Brian Valente
Sent: Monday, July 13, 2026 9:54 AM
To: open-phd...@googlegroups.com
Subject: Re: [open-phd-guiding] AP1150AE / PHD2 / NINA dither settle failures despite normal guiding

 

Hi John

 

I think the main issue is your polar alignment appears quite far off. The dither/settle seem to be okay, but it never completes seetling because your Dec will never get back to lock position. Here's an example showing Dec (and RA for that matter) offset from the lock position:

 

Try redoing your polar alignment, recalibrate using the calibration assistant, and run the guiding assistant to measure your polar alignment.

 

Brian

 

To view this discussion visit https://groups.google.com/d/msgid/open-phd-guiding/CAJa45i7fRR2EdapSJe%3DWGrv5yjebfdd4Bmw4sjTtOqfR4uEsFw%40mail.gmail.com.

[Brian Valente]

John

I am just the messenger for what your data shows, and that's what it shows. TPPA results can be inaccurate, i've seen it many times (not intended to diminish TPPA). Drift measurements and alignment are more reliable.

To view this discussion visit https://groups.google.com/d/msgid/open-phd-guiding/01b401dd12e1%24f18cc8e0%24d4a65aa0%24%40gmail.com.

[jhag...@gmail.com]

Perfect, Brian.  I am sure you are on the right track.  Thank you sooo much for your help on this!

To view this discussion visit https://groups.google.com/d/msgid/open-phd-guiding/CAJa45i55dmSBgwQ0VQuXrgCTt8qbZfYj3%2BOsBKreKxnfZhcL5g%40mail.gmail.com.

[Brian Valente]

The good news is if this is the issue, it's easily fixed. The guiding assistant run will measure the PA (let it run for 5-10 minutes). For the 1150 disable measure backlash, no need for that.

To view this discussion visit https://groups.google.com/d/msgid/open-phd-guiding/021501dd12ec%24159c9cb0%2440d5d610%24%40gmail.com.