Tracking /Guiding issues half way through an Imaging session.

dayglow · Apr 27, 2026, 07:05 PM

I suggest using PHD LogViewer to examine the PHD2 log file for events at the time tracking was lost.

Check to see if PHD was actually guiding and that the SNR reported for the guide star(s) was decent.

Thanks just had a look and it lost the star at 1:38am and never recovered I have set a trigger to restart guiding in NINA too. The seestar managed fine a few dropped frames but nothing drastic.

Sean

dayglow · Apr 27, 2026, 07:33 PM

Remember to slew back to the target before restarting guiding.

I have a trigger set up to recentre on drift too, I assumed that would cover it.

Recenter on drift won’t work because the smeared subs can’t be solved, so the software has no idea where it’s pointing.

If you have good guiding for awhile after the meridian flip (> just a min. or two) than it’s not a reverse after flip issue. The PHD2 logs are where I suspect you’ll find your answer. If it keeps loosing lock than the most likely culprits are clouds or a cable pull. The fact that the SeeStar also lost frames at the same time is telling. I would check your cable management and have another run, stay up and observe the system.

That would point then to something in the way your NINA script is written. The “Restore Guiding” command must be in the triggers section so that it checks guiding with every loop.

I would say PHD2 is not configured to rotate the calibration data after a meridian flip, as a result, you’re you’re getting good guiding up until the meridian, then the scope flips, and every guide correction being sent to the mount is the opposite of what’s required, thus, it’s pushing you constantly away from the guide star.

Sorry, Tony, but I disagree. If one’s mount tracks well and is well polar aligned, there should be no drift and therefore no DEC corrections. I personally have seen this exact behavior with my mount. It can go for quite some time before any DEC corrections are made, and then it goes crazy.

It’s easy to test. Calibrate PHD2 on one side of the meridian, then try to guide on something on the other side. All the better if the polar alignment is a little out. Let it run long enough to see several DEC corrections and see if they go in the correct direction. If not, then the tick box needs to be toggled.

There’s alot of speculation in here, but we’re beating around the bush a bit. If you drop a PHD log in here, I can tell you exactly what happened and steps to fix it.

Tony Gondola · Apr 29, 2026, 03:33 AM

Ron · Apr 29, 2026, 12:43 AM

Sorry, Tony, but I disagree. If one’s mount tracks well and is well polar aligned, there should be no drift and therefore no DEC corrections. I personally have seen this exact behavior with my mount. It can go for quite some time before any DEC corrections are made, and then it goes crazy.

It’s easy to test. Calibrate PHD2 on one side of the meridian, then try to guide on something on the other side. All the better if the polar alignment is a little out. Let it run long enough to see several DEC corrections and see if they go in the correct direction. If not, then the tick box needs to be toggled.

All I can say is no matter how good my PA gets, I have never seen a case when there are no DEC corrections, both + and -. Maybe it’s possible but I’ve never seen it.

Ron is correct, to a fault. Seeing can, and will affect the declination corrections. Your consistant back and forth corrections are just your mount chasing the seeing conditions. In a perfect world, if seeing was perfect and polar alignment was perfect, you would never see any declination corrections. I have seen plenty of nights where I can go for quite awhile without seeing dec corrections, but it’s rare as well. If I was using a high end mount and longer guide exposures, I’d probably never see them.

Now the other half of that story is if you do see a constant correction in one direction on declination, or when the majority of the corrections are on one side, this is high indicative of bad polar alignment. Generally speaking most mounts can guide through this, but at the end of the night you’ll find alot of field rotation in your images.