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Acceptable DEC and RA Drift and Polar Alignment Error

Astrophotography
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#1 pemongillo

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Posted 26 September 2021 - 08:44 AM

I am learning to the intricacies of PHD guiding reports. I am not sure what are acceptable numbers for these items. Here are the numbers I got from my last night out: RA Drift +2.72/min or +.91 px/min, DEC Drift -.96/min or -.32 px/min, Polar Alignment Error 3.7'. Thanks for any advice you might have. I have an Asiair, but have decided to use PHD2 until I understand how the full version of PHD2 works before returning the the Asiair. 



#2 Tapio

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Posted 26 September 2021 - 08:55 AM

That PA error certainly is acceptable.

#3 daveco2

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Posted 26 September 2021 - 08:57 AM

It would be useful to use the AsiAir polar alignment and guiding utilities, note its readouts to find acceptable limits of PA error and guiding error, take some frames to see how that translates into star shape; and then with that information firmly established, if you still feel inclined, jump into the dark waters of PHD2 - or just continue to make subs of your favorite targets before they go out of view with the next season.



#4 pemongillo

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Posted 26 September 2021 - 09:07 AM

It would be useful to use the AsiAir polar alignment and guiding utilities, note its readouts to find acceptable limits of PA error and guiding error, take some frames to see how that translates into star shape; and then with that information firmly established, if you still feel inclined, jump into the dark waters of PHD2 - or just continue to make subs of your favorite targets before they go out of view with the next season.

As I said, I am using PHD2 for guiding and think that will be helpful to me when using Asiair guiding. I do PA with Asiair.



#5 DJL

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Posted 26 September 2021 - 09:12 AM

ASIAIR guiding is a version of PHD2.



#6 pemongillo

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Posted 26 September 2021 - 09:14 AM

ASIAIR guiding is a version of PHD2.

I understand that.  I think it is helpful to learn the more complex version before going off the grid with my Asiair. Are the results I posted acceptable?



#7 Alex McConahay

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Posted 26 September 2021 - 09:26 AM

What is acceptable to you is the real issue here. You can judge acceptability by whether you get tight round stars or they are elongated (and the elongation is caused by polar alignment and not some other thing.). 

 

If you are doing short exposures, with a wide field (not much focal length), you can get by with a pretty poor polar alignment. If you are doing longer exposures, and more focal length, you will have a problem. Where your target is in the sky will also have some effect on how good a polar alignment you need. 

 

In most cases the results you posted will not present a problem.....

 

If you want to explore further, go here:

 

http://www.celestial...rErrorCalc.html

 

 

 

>>>>>I think it is helpful to learn the more complex version before going off the grid with my Asiair.

Always good to play around with it all before taking it out on the road. 

 

Alex


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#8 michael8554

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Posted 27 September 2021 - 05:50 AM

RA Drift +2.72/min or +.91 px/min,

DEC Drift -.96/min or -.32 px/min,

Polar Alignment Error 3.7'

 

PAE of 3.7Arcmins is easily guided out by PHD2.

 

I think that ultimately PHD2 Guide Errors in arcsecs will dictate your star shapes, not long-term drift figures due to PE and PAE.

 

If the RA and Dec errors are similar, then round stars should result.

 

Large similar RA and Dec figures will result in round but bloated stars.

 

The acceptable error depends on the image scale, but most people aspire to 1 arcsec or less.




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