Trailed stars captured in SGP with PHD2.6.2


Dear SGP developer,

I got trailed stars last night after I upgraded to PHD2 release version 2.6.2. This was not happened before, and I am not sure if it is related to the spiral dither option just for RA I chose, having an integration issue with SGP.

It looks to me, when I saw the guiding curve onsite, I saw a jump in DEC, PHD2 tried to reduce the DEC drift and may be there was also a huge correction in RA which is not seen in the guide curve, but result in a long trail of stars.

It did not happen in every frame.

Could the exposure happen when the dithering is still running? I just want to ensure there is nothing wrong in SGP.

I attach the logs of that portion (00:57-01:01) of the frame for investigation: Logs and FITS

I also reported the issue to PHD2.

Thank you.



Dear SGP developer,

Can you help to take a look on this issue?

I reported to PHD2 development, and they mentioned, as according to the logs, SGP started the exposure too soon before the dithering is settled.

Please help, as this problem ruined a number of frames with severely trailed stars.

Thank you.



I looked into this earlier today. Nothing sticks out immediately. Will require more investigation.



Hi Jared,

Does it look like the exposure started at 12:57:36, but the dither only settled until 12:58:15 causing the trail?



Hi Jared,

Just to see if there is something wrong you found in the log, or it is not an issue of SGP but in PHD2?



This sounds similar to my problem and Marco as well!
See my other thread …



The issue was not there in my last imaging session back in Feb, when SGP and PHD2.6.1 were used.

The problem is severe as it looks this latest release together with PHD2 gave trailed stars, when clear night is rare at my location.

I need to test whether I have to revert back to SGP2.5.0.10 or the PHD to 2.6.1, but the sky nor time permit me to do so.

I hope Jared will take a look soon to figure out the issue and resolution.


Have you tried guiding and doing single frame shots? I’m betting you’re not going to get good images regardless and it isn’t related to SGP at all.


3 reports of the issue on SGP/PHD firing to soon, and yet it’s user error hmmm …



I used it on Friday and it seemed to work.

So what is PHD2 doing on its own?


No. It was a sequence run.

The logs are an extract of one the issue frame.


May I ask if this issue will be followed up?

Since PHD2 people mentioned it is a SGP issue, I want to double confirm whether I should revert to an earlier version of SGP to work with.

Having frames trailed is an very annoying issue.

Thank you.


It has not. I haven’t been able to duplicate this in my tests with the simulator. Maybe something was introduced in the .16/.17 fix. If you want to revert I’d go back to



Thanks Jared.


BTW, the issue happened 5 times out of the 16 subs I took that night.


Have you tried tightening up your ‘settling’ requirements? I still don’t see how SGP can cause trailing stars. Keep posting logs, Jared/Ken can find something if they have the data.


The settling parameter remains unchanged when the SGP version were upgraded.

It is unticked, with value 0 second.


Why don’t use settling?


Hi Jared,

I revert to and wait for a clear sky.

The weather here is no good for many months which I need a stable version to work on when there is chance to image.

I found beta is released. May I ask if the dithering control coding in this beta is kept at, or



Some update on this issue, I had last night under the full Moon 2 hours with the sky opened for test.

With PHD2.6.2 dev 3, it gave an erratic guiding, I uninstalled and reinstalled PHD2.6.1, the problem did not come up then.

I tried both SGP2.5.1.15 and, and so far there is no issue with dithering.

So, I suspect this is an issue with PHD2.6.2 or some integration matter with SGP.

I shall stay with SGP and PHD2.6.1 until the root cause is found with PHD2.