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Open PHD Guide 2 and Polar Alignment Accuracy Display

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#1 Jim Waters

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Posted 21 April 2017 - 01:51 AM

I used my QHY PoleMaster to align my CGEM tonight and recorded the RMS Error as reported by PHD.  I later went back and rechecked the CGEM using the PoleMaster and alignment was off some in ALT but not much.  I believe things shifted during slewing.

 

How can I determine how far my polar alignment was off from the information below?  Should both RA and DEC RMS Error be zero for 'perfect' alignment?

 

RMS Error:

  • RA     0.33
  • DEC  0.35
  • Tot     0.48

Guide Stats:

  • RA    (RMS) 0.33   (Peak) 0.90
  • DEC (RMS) 0.35   (Peak) 1.18
  • Total  0.48
  • RA Osc  0.35
  • RA Limited    0 (0%)
  • DEC Limited 0 (0%)


#2 baron555

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Posted 21 April 2017 - 06:37 AM

I can't answer your question exactly but your theory is correct....that something changed as you slewed your system around.

 

Another way to check this theory is to keep Polemaster running, at the end where you line up the box and circle.....keep that screen on and running and then slew your system around.  If they move from each other you will know how much "flex" you have.  I guess one could slew to a position that you will be imaging from and re-align the PA at that point.



#3 pedxing

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Posted 21 April 2017 - 07:12 AM

The PHD RMS error isn't necessarily directly related to polar alignment error.

 

If you want to cross-check your PA in PHD, you need to either use its drift alignment tool or run an analysis tool like PHDLab against your full guiding session.



#4 cfosterstars

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Posted 21 April 2017 - 11:10 AM

Also run the guiding assistant in PhD2 for 2-3 minutes. It reports the net polar alignment error, but it is noisy unless you run it for a while. Some recommend even runing for 10 minutes, but that a bit excessive.



#5 Jim Waters

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Posted 21 April 2017 - 02:01 PM

Thanks all.  I will run 'Guiding Assistant' during my next run and also download the manual for PHD Log Viewer.



#6 Alex McConahay

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Posted 21 April 2017 - 03:15 PM

I havew never gotten perfectly consistent results from any polar alignment program, including Phd2 an Pempro. I can run them once, even waiting ten to fifteen minutes on the run, and get one answer. And then immediately run again, and get a slightly different answer. Don't sweat the results of the program. Check out your images. If the stars are round enough, get on with your imaging. What "round enough" means depends on your standards, your audience,  on how you plan to display, and your processing skills, among other things.

 

Alex


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#7 erictheastrojunkie

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Posted 21 April 2017 - 03:54 PM

Also run the guiding assistant in PhD2 for 2-3 minutes. It reports the net polar alignment error, but it is noisy unless you run it for a while. Some recommend even runing for 10 minutes, but that a bit excessive.

The reason people recommend 10 minutes is because that is generally one-cycle of the worm gear for most mounts, that's why you should run it that long, to know the total polar alignment error over one entire cycle of the worm gear. 



#8 Jim Waters

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Posted 21 April 2017 - 05:07 PM

 

Also run the guiding assistant in PhD2 for 2-3 minutes. It reports the net polar alignment error, but it is noisy unless you run it for a while. Some recommend even runing for 10 minutes, but that a bit excessive.

The reason people recommend 10 minutes is because that is generally one-cycle of the worm gear for most mounts, that's why you should run it that long, to know the total polar alignment error over one entire cycle of the worm gear. 

 

Good point about running it for one worm cycle.  Thx



#9 Darrenlh

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Posted 24 April 2017 - 01:22 PM

Should you ever expect any system to have "zero" error? With the guiding corrections based somewhat on atmospheric turbulence, periodic error alone, mount orientation and balance..etc, even if zero is reported...is it real? 




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