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PHD2 - Mount moving backwards in steps and calibration failed

Astrophotography Software Polar Alignment Beginner Imaging Mount
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16 replies to this topic

#1 Aman Dude

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Posted 25 June 2022 - 03:00 PM

I have the Sky Watcher EQM-35 Pro and I was perfectly polar aligned and level. For some odd reason when I tried to do calibration in phd2, the mount would move back and fourth in steps (I am not on a hot pixel, I am for sure on a star). I have the minimum movement down to 10px and the steps up to 60 and it still failed. For example:

 

Step 1: 0.2px

Step 2: 0.8px

Step 3: 0.3px

Step 4: 1.0px

Step 5: 1.2px

Step 6: 1.0px

Step 7: 0.8px

Step 8: 0.7px

Step 9: 3.0px

Step 10: 1.8px
 

Do any of you know why this could do this? Could the balance be off? Thanks!


Edited by Aman Dude, 25 June 2022 - 03:02 PM.


#2 Tapio

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Posted 25 June 2022 - 03:17 PM

What is your scope and (guide) camera ?

Have you put their relevant values in PHD settings ?

PHD log might be useful info also.



#3 Aman Dude

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Posted 25 June 2022 - 06:05 PM

What is your scope and (guide) camera ?

Have you put their relevant values in PHD settings ?

PHD log might be useful info also.

Yes I have done that.

SVBONY SV305 Pro

SVBONY 30mm Guide Scope



#4 ChrisWhite

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Posted 25 June 2022 - 11:28 PM

Basically it's not even moving. This could be a sign of a gear mesh problem.

#5 rgsalinger

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Posted 25 June 2022 - 11:35 PM

Step size is probably just too small - a duration of 60 millseconds (?) if using a short guide scope might not move it even one pixel.Set it to 300 and see what happens. Chris could be right, though but I'd want to pump up the step size parameter before looking any more deeply as the mount as a starting point. 



#6 Tapio

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Posted 26 June 2022 - 01:09 AM

I agree step size should be bigger.
If you have set guide gear parameters correctly PHD should give you correct step size.
You have 120 mm there for guide scope focal length?

Edited by Tapio, 26 June 2022 - 01:11 AM.


#7 michael8554

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Posted 26 June 2022 - 04:01 AM

Those sub-pixel moves suggest that the mount isn't being guided, it's just tracking.

 

Are you ASCOM or ST-4 guiding ?

 

Ideally post the PHD2 GuideLog that includes the failed Calibrations.

 

You'll find it in the PHD2 folder, check that the date and time in the filename are relevant.

 

As Tapio said, the PHD2 Equipment Wizard will have calculated the correct Calibration Step Size if you have entered the FL as 120, not the 30mm aperture.



#8 colinrm

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Posted 26 June 2022 - 01:43 PM

If using EQMOD, the default guiding rate might be set too low.  You could try turning it up in the EQMOD settings menu, perhaps 0.5x to 0.7x sidereal.



#9 CharLakeAstro

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Posted 26 June 2022 - 10:54 PM

Where in the sky are you calibrating? You should be calibrating near the celestial equator, and for best results, also near the meridian. If you are not pointing near the equatorial, the calculated calibration step size is likely incorrect.

 

1) Calibrate pointed near the equatorial - (think of an arced line where the sun and planets path the sky)

 

2) if (1) is not possible, then increase the Calibration Step size... even go up to 1400msec

 

3) Also (already mentioned) ensure your guidescope focal length is correctly entered, not the guidescope aperture.


Edited by CharLakeAstro, 26 June 2022 - 10:55 PM.


#10 Yerman

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Posted 27 June 2022 - 11:22 AM

I just had this same problem. I believe I have fixed it but due to weather I haven't had a chance to try it out but I'm confident your problem like mine is due to excessive backlash. Most think of worm mesh when you talk about backlash. In my case the backlash was from the belts stretching. I adjusted my belts for now but I am going to get some better grade reinforced belts. As others have said your mount is not moving according to PHD2 the motors may be moving but its not getting to the mount. Run the backlash measurement tool in PHD2 it has a 100 step maximum mine quite at 100 steps saying "insufficient movement" that's what gave it away.



#11 Juzwuz

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Posted 27 June 2022 - 04:49 PM

You might try measuring the guidescope focal length with your camera and image of a starfield using the procedure in:

https://www.lightvor...cal-length.html

 

For my issue with PHD2, I had input 1423mm (using an OAG with my SCT+reducer) but it measured out to be 1472mm. When I had the incorrect value, PHD2 couldn't calibrate. 



#12 michael8554

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Posted 28 June 2022 - 07:35 AM

Beginners often put the guidescope aperture into PHD2 eg 60mm, instead of the FL eg 240mm.

 

Unfortunately even with this huge difference PHD2 Calibrates just fine.

 

But the reported guide figure are totally wrong, which confuses the beginner no end.


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#13 Aman Dude

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Posted 28 June 2022 - 10:18 AM

Beginners often put the guidescope aperture into PHD2 eg 60mm, instead of the FL eg 240mm.

 

Unfortunately even with this huge difference PHD2 Calibrates just fine.

 

But the reported guide figure are totally wrong, which confuses the beginner no end.

No, I put the focal length of my guide scope (120mm). So that is not the issue.



#14 michael8554

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Posted 28 June 2022 - 10:51 AM

Just saying in answer to Juzwuz's post, that a seriously wrong FL doesn't stop PHD2 Calibrating.

 

I wasn't suggesting that is what you did Aman Dude..



#15 Juzwuz

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Posted 28 June 2022 - 11:57 AM

Just saying in answer to Juzwuz's post, that a seriously wrong FL doesn't stop PHD2 Calibrating.

 

I wasn't suggesting that is what you did Aman Dude..

Thanks for the info!  I'm definitely a beginner with PHD2 and guiding in general. I guess instead of saying PHD2 couldn't calibrate, I should have said it was taking a really long time to calibrate and I got impatient and stopped PHD2.  When I had the correct FL, the calibration was relatively quick and painless. 



#16 Yerman

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Posted 01 July 2022 - 01:10 PM

As in my post #10 I had excessive backlash which prevented calibration. After adjusting the belt tension things were much better but it still would not calibrate. This time the issue was seeing conditions. There were lots of bright stars visible but the overall sky condition was a kind of murky brown. This essentially washed out the stars that PHD2 needed to guide on. PHD2 would select a star to guide on but if you watched the FWHM it was jumping around so much that PHD2 could not keep locked on to it. Two nights later in better conditions it calibrated and guided perfectly.



#17 Aman Dude

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Posted 01 July 2022 - 05:30 PM

I fixed it. The mount was not even connected, it was connected to a simulator lol and I just switched to ascom instead of ST-4. Thank you all for your input!


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