PHD2 drifting

[TheMan]

Phd2 is acting really weird lately. I started guiding and all looked fine (My polar alignment is practically perfect). But a few hours later I saw my target slowly drifted across the FoV! I tried everything in my power but could not do anything. Does anyone know how to fix this? Any help is appreciated

Edited April 7, 2019 by TheMan

[Dr_Ju_ju]

Any cable snags ?  seeing conditions, especially for the selected star ? have you got your settings too aggressive, so its overshooting ?   myriad of possibilities....

[TheMan]

Everything was running as usual, seeing conditions were great, I used the guiding assistant. The image drifts very slowly over the night, but the guide star is still in the frame! My guide setup has a very small FoV so the star should be out of the frame if it drifts slowly throughout the night...

[Dr_Ju_ju]

if the guide star is drifting over the night, I'd suggest your polar alignment is out, maybe not by much, but.... 

[almcl]

Alternatively, and without knowing what scope, guide camera, mount and guidescope you have it's difficult to give specific advice, it could be differential flexure? 

[TheMan]

2 minutes ago, almcl said:

without knowing what scope, guide camera, mount

Sorry about that. I use a Az-Gti in eq mode, a knock off asi120mc as a guide camera, astro modified nikon d5000, f/5.6 72mm doublet refractor and a 300mm focal length guidescope.

[almcl]

OK, in which case check to see if there's any possibility of movement between the guidescope and the imaging scope. 

Do you have the guiding logs for the session in question? 

[TheMan]

I believe these are the right ones. And here are 2 images from the same night not even 2 hrs apart from each other. Guiding was around 1 arc second. Hope this helps

PHD2_DebugLog_2019-04-06_200717.txt PHD2_DebugLog_2019-04-06_210751.txt PHD2_GuideLog_2019-04-06_210751.txt

[almcl]

Unfortunately the guide log only shows two minutes of guiding, which isn't really long enough to make a judgement although PHD2 has reported an issue with guide rates in the calibration, but the images certainly look like flex between guider and imager.  

Try taking an image of the PHD2 screen at the start of a run (the 'Save image' function on the file menu can do this) and at the end of the run and then compare the two images.  If the guide star hasn't moved, it's likely to be flexure.

[TheMan]

3 minutes ago, almcl said:

Try taking an image of the PHD2 screen at the start of a run (the 'Save image' function on the file menu can do this) and at the end of the run and then compare the two images.  If the guide star hasn't moved, it's likely to be flexure.

That sounds like a plan. But if it is flexure what can I do other than those expensive looking solutions in that website?PHD2_DebugLog_2019-04-07_020729.txt

Also I uploaded the wrong log files... sorry 

PHD2_GuideLog_2019-04-06_220030.txt PHD2_GuideLog_2019-04-07_020729.txt PHD2_DebugLog_2019-04-06_220030.txt PHD2_DebugLog_2019-04-07_020729.txt

[almcl]

I cured a similar problem by switching to an OAG.  This might be overkill for a ~500 mm focal length imaging rig, but getting rid of any plastic tipped screw mounting guidescope rings and just clamping with solid rings may help?

[newbie alert]

Don't look like it's drifting by much but maybe dither??

[TheMan]

4 minutes ago, newbie alert said:

maybe dither??

I did not have dither on.

44 minutes ago, almcl said:

clamping with solid rings may help?

That seems like a good solution I'll try that out.

[bobequus]

Hope I'm not too late to the party.  I just ran into the same problem last night.  While imaging M101, my image slowly moved out of the center of the frame and moved roughly south over about two hours.  Sorry about the tiny PNG's.
Great guiding from PHD2 with less than .4 error in RA and DEC.  PHD2 told me polar align was off by 8.1'  Guide star was round and un saturated with a 12-14 SNR.  Guide time was around 4 seconds.  Other than a lot of images with meteor streaks (Lyrid shower), stars are round and small.  Scope is a Vixen 825mm AX103 on a SXP mount. Well cabled; no snags. Guide camera is a Touptek on an Orion OAG.  Main camera is an ASI183 Pro Cooled.  I started the night using APT with PHD2's dithering, but after about the fifth image, it hung up so I restarted without dither. One weird thing that occurred was when I decided to try a different star in the guide frame, my calibration did not work.  After about ten seconds the graph lines would shoot off the chart.  I re-calibrated and all was fine after that.
I've been wracking my tiny brain and the only thing that I can come up with is that I was not using a star for the guide but something else that moves differently.  Comet?  I think it would have moved faster and I doubt I would have gotten a good round star.  Asteroid?  Are there any that you can see in high light pollution suburb?  Geo stationary satellite?  Maybe, but none showed up anywhere near that area when I checked Stellarium.  On top of all that; what are the chances of using something that is not a star (or a hot pixel) for guiding?  Gotta be a million to one.  Any thoughts or ideas greatly appreciated.

Bobby Sapovits (new to the list, and a former resident of the "other" Telford in Pennsylvania, USA)
 

[michael8554]

Is it me ? I can't see any similarity between those 2 images ?

If you post your PHD2 Guide Log there might be some clues.

Michael 

[bobequus]

Whoops, one was turned. Log attached.  Thanks.

PHD2_GuideLog_2019-04-22_215509.txt

[michael8554]

Hi  Bobby 

Apologies, away from home so can  only look at the text of your log file, nothing stands out but Log Viewer always shows more.

In the same fov as image 1 in image 2 I can see more stars, but that might be due to better seeing.

Your PA of 8.1 arcmins might be enough to explain the drift.

Michael