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Problem with AVX Polar Scope mechanical alignment

Polar Alignment Mount
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#1 vtaDan

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Posted 28 September 2022 - 05:33 PM

I'm fairly new to astronomy and bought my first real (non-department store) setup a few months ago. It included a Celestron AVX mount. I had been having trouble getting a good polar alignment using the polar scope so I attempted to align it's reticle and discovered something unexpected. As I rotated the RA axis, the reticle rotated and moved through an arc as expected but I also noticed the image of the object I was aimed at was sweeping through an arc as well. So is there a misalignment between the polar scope and the RA axis of the mount?

 

I imagine some small error is unavoidable but this seems significant. The arc the image made was maybe 0.15 degree radius. Is this typical?

Is this most likely an issue with the mount (loose RA bearing? polar scope mounting threads cut wrong?) or with the polar scope itself?

Any ideas on how to figure out the root issue and correct it?

 

I searched Celestron's page and the forums here and couldn't find discussion on this problem anywhere. Any help is appreciated!


Edited by vtaDan, 29 September 2022 - 01:27 PM.


#2 TelescopeGreg

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Posted 28 September 2022 - 06:15 PM

Yes, expected.  One needs to align the polar scope to your particular mount before it's accurate.  As shipped from the factory, mine was way off.

 

There should have been instructions on how to align it somewhere in the packaging, if purchased new.  Otherwise I would hope Celestron has the info on their website someplace.  Basically there are 3 little (really little) hex screws that you need to adjust such that the center of the reticle (middle of the big "+") stays on a distant stationary target as the mount is rotated in RA.  The screws interact as you adjust them - pull one out a bit, and push another in - but remembering which screw results in what change of direction will fry your mind.  Work slowly.  It's tedious, but you should only have to do it once.  At least it's something you do during the day.


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#3 vtaDan

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Posted 28 September 2022 - 06:29 PM

Yes, expected.  One needs to align the polar scope to your particular mount before it's accurate.  As shipped from the factory, mine was way off.

 

There should have been instructions on how to align it somewhere in the packaging, if purchased new.  Otherwise I would hope Celestron has the info on their website someplace.  Basically there are 3 little (really little) hex screws that you need to adjust such that the center of the reticle (middle of the big "+") stays on a distant stationary target as the mount is rotated in RA.  The screws interact as you adjust them - pull one out a bit, and push another in - but remembering which screw results in what change of direction will fry your mind.  Work slowly.  It's tedious, but you should only have to do it once.  At least it's something you do during the day.

I was actually doing the alignment you described when I noticed this issue. I was expecting the reticle itself to rotate and move in an arc as I turned the RA axis but the image of what I was pointing at in the distance was also moving in an arc, thus my assumption that there is an issue of the polar scope itself (not just the reticle) being misaligned with the RA axis. Sorry if that wasn't clear in my initial description. 



#4 TelescopeGreg

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Posted 28 September 2022 - 10:10 PM

The reticle should spin, but the image of the distant target as seen in the polar scope's eyepiece should only shift position.  What you're looking for is minimum (ideally zero) movement.  It will be inverted, of course.

 

I forget how much movement mine had, but it was very apparent.



#5 RTLR 12

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Posted 28 September 2022 - 10:21 PM

Here are Celestron’s instructions.

https://s3.amazonaws...raxixfinder.pdf

#6 vtaDan

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Posted 29 September 2022 - 01:24 PM

The reticle should spin, but the image of the distant target as seen in the polar scope's eyepiece should only shift position.  What you're looking for is minimum (ideally zero) movement.  It will be inverted, of course.

 

I forget how much movement mine had, but it was very apparent.

Ok, that's exactly what I was seeing. I wasn't expecting the image of the target to move. 

I did a few more iterations of reticle adjustment after reading your post. Got everything lined up and the image no longer moves when the I turn the RA axis.

I don't understand how the reticle being off would also cause the target image to be off but I guess that's the fun of diving deeper into this hobby: lots more to learn!

Thanks for the help!



#7 vtaDan

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Posted 29 September 2022 - 01:24 PM

Here are Celestron’s instructions.

https://s3.amazonaws...raxixfinder.pdf

Thank you!




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