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Sharpcap polar alignment error.

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#1 acrh2

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Posted 22 June 2021 - 08:07 PM

I do rough polar alignment first using the polar scope.

Then in Sharpcap, when I rotate RA axis clockwise, I am within 1-2 arcmin before adjusting elevation and azimuth of the mount. When I rotate counter clockwise, I am within 10 arcmin.

Then I adjust the knobs to within 5 arcsec per Sharpcap.

 

Judging by errors in PHD2, the first alignment is much better than the second one - there are far fewer corrections required, and the total error is better by 0.2-0.5 arcsec.

 

The Sharpcap manual says flexure - loose telescope/camera/cables. There isn't much I can do about telescope/guide scope and cameras - they are as strong as they will be. But the cables are indeed loose.

 

Here's a picture of the setup, just imagine a refractor/flattener/back focus adapters and rings/and ASI533MC Pro instead.

 

51100970010_e7dac12953_b.jpg

 

How would I even go about securing cables? Where do you attach them to minimize flexure? Do I need some kind of Velcro ties to fix them to the base of the telescope?

 

Thanks.

 

Edit: also, can I rotate the declination saddle 180 degrees, so the knobs that secure the telescope are on the opposite side? Does that do anything?


Edited by acrh2, 22 June 2021 - 08:11 PM.


#2 Dynan

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Posted 22 June 2021 - 08:18 PM

Uneven mount leveling will show different PA's on either side of pier. That's why I do both sides, repeatedly until they agree.

 

Even on my pier, leveled as best I can, the PA readings are different until both are adjusted. It usually takes two repetitions (two each side) to get them to agree.

Adding to this difficulty is any mirror movement. (I have a refractor.)

 

Patience is the key to success.



#3 AhBok

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Posted 22 June 2021 - 08:20 PM

Loop your cables and tie them to a point close to the saddle or to the DEC axis. You can turn the saddle around. Your mount can be synced from either position.

#4 acrh2

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Posted 22 June 2021 - 08:31 PM

Loop your cables and tie them to a point close to the saddle or to the DEC axis. You can turn the saddle around. Your mount can be synced from either position.

Thank you. Can you recommend some equipment from Amazon or popular AP vendor sites? Or do I just use duct tape or something?laugh.gif



#5 acrh2

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Posted 22 June 2021 - 08:36 PM

Uneven mount leveling will show different PA's on either side of pier. That's why I do both sides, repeatedly until they agree.

 

Even on my pier, leveled as best I can, the PA readings are different until both are adjusted. It usually takes two repetitions (two each side) to get them to agree.

Adding to this difficulty is any mirror movement. (I have a refractor.)

 

Patience is the key to success.

Thank you. I'm not sure I understand though. When you say leveling, do you mean leveling of the actual mount head/tripod? Or do you mean balancing the telescope and the counter weight?

I was under the impression that the Sharpcap polar alignment didn't care about the mount leveling.

Also, I tried to repeatedly polar align rotating left and right and left and right and so on. But the results didn't converge - one side was always 10 arcmin different from the other.



#6 Dynan

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Posted 22 June 2021 - 08:42 PM

Leveling the mount. In fact, I believe this is the best indication of mount leveling, since we can see down to seconds of a degree.

 

If you never get them to agree, something else is flexing, flopping, moving...


Edited by Dynan, 22 June 2021 - 08:43 PM.



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