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Equipment Discussions >> Mounts

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Fred1
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Reged: 09/19/07

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Re: (Sorry) Another Q on the CGEM Polar Align sequence new [Re: freestar8n]
      #3617879 - 02/11/10 12:11 AM

Frank is right. Celestron has come up with a great program for Polar Alignment. Note that the $5000 CGE Pro has no accommodation for a polar axis scope. The Celestron rep at an expo I was at in October told me it was because the PA program is so accurate it negates the polar axis scope altogether. Also, I've read that the CGEM will be the last Celestron mount to have a bore hole for the polar axis scope option.

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David PavlichAdministrator
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Reged: 05/18/05

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Re: (Sorry) Another Q on the CGEM Polar Align sequence new [Re: freestar8n]
      #3618291 - 02/11/10 09:18 AM

Thanks, Frank! I wondered if the mount compensated for the adjusments made when polar aligning.

David


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gatsbyiv
sage


Reged: 03/29/09

Loc: Whitehouse Station, NJ
Re: (Sorry) Another Q on the CGEM Polar Align sequence new [Re: David Pavlich]
      #3619625 - 02/11/10 09:16 PM

Interesting. Thanks, Frank. I was just following the manual instructions, which state to Undo Sync, then replace the alignment stars after Polar Align. But if I don't have to do this, well then, that is that much more time inside (where it is warm)!

Also, I figured out my Caph/Hamal problem described above. I was *manually* slewing over to the next star I wanted to replace. If I ask the mount to do the slewing by selecting the star from the Named Star list, the replacement works fine. Frankly, it's faster for me to manually slew, but it looks like the whole step is unnecessary anyway.


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freestar8n
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Re: (Sorry) Another Q on the CGEM Polar Align sequence new [Re: gatsbyiv]
      #3619851 - 02/11/10 11:21 PM

Hi-

I just re-read the cgem manual to see how they describe it. They say:

"After polar alignment it's a good idea to check the pointing accuracy of the telescope to see how much it may have been affected by moving the mount. Since the polar alignment process requires you to "sync" the telescope on a bright star before you begin, it will be necessary to undo the sync before re-aligning."

This is somewhat loaded, but it says you MAY need to re-align, but check the goto accuracy and see if it is needed. Although the mount does move during polar alignment, as long as the mount moves as it should to polar align, the GoTo accuracy should still be ok.

So - I'd just do the polar alignment carefully and then see how good the GoTo is. If it is accurate near the polar alignment star, but it gets worse farther away, try unsyncing. If it is still bad, try replacing 1 or 2 alignment stars.

So - mainly I'd say just to try things and see what is needed for your mount. But make sure the mount is calibrated before you do the All-Star, or the polar alignment won't be as accurate as it could be, and the pointing accuracy immediately after the polar align also won't be as good as it could be.

Frank


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David PavlichAdministrator
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Re: (Sorry) Another Q on the CGEM Polar Align sequence new [Re: freestar8n]
      #3620299 - 02/12/10 09:21 AM

Quote:

Hi-

This is somewhat loaded, but it says you MAY need to re-align, but check the goto accuracy and see if it is needed. Although the mount does move during polar alignment, as long as the mount moves as it should to polar align, the GoTo accuracy should still be ok.

Frank




This is the part that puzzles me, especially if you're using an SC. With its narrow FOV, even a little bit of movement of the Alt and Az adjustments will move an object out of the FOV. I don't know how the gotos would be accurate unless you were lucky enough to have everything polar aligned before you started the PA routine.

That's why I asked the question earlier. If this is the case, then the mount doesn't compensate for the manual movement in Alt/Az. Or am I missing something?

David


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freestar8n
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Re: (Sorry) Another Q on the CGEM Polar Align sequence new [Re: David Pavlich]
      #3620329 - 02/12/10 09:41 AM

Quote:

That's why I asked the question earlier. If this is the case, then the mount doesn't compensate for the manual movement in Alt/Az. Or am I missing something?





Hi-

There is a related discussion ongoing in a similar thread - but basically AllStar knows how far off the polar alignment is (just use Align/Polar Alignment/Display to see the error in Alt Az) but the hc has no ability to physically move the mount in alt/az - which is what is needed to become physically polar aligned.

So - it intentionally aims 'off' from the alignment star and asks a human to move the mount until the star is centered - at which point it assumes it is perfectly aligned.

As long as the mount has been moved cleanly in alt/az motions of the correct distance, AllStar knows how the mount is now aligned against the sky and can do GoTo's directly.

If there were big motors to move the equatorial head in alt/az, the hc could do it all by itself - but it uses a human instead.

After the alignment, the displayed polar alignment error is 0,0 - since it assumes it is now perfectly polar aligned and it has no other information to go by unless someone replaces alignment stars - at which point those errors will show as non-zero, but hopefully small values.

Frank


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David PavlichAdministrator
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Reged: 05/18/05

Loc: Mandeville, LA USA
Re: (Sorry) Another Q on the CGEM Polar Align sequence new [Re: freestar8n]
      #3620456 - 02/12/10 10:47 AM

Quote:

Quote:

That's why I asked the question earlier. If this is the case, then the mount doesn't compensate for the manual movement in Alt/Az. Or am I missing something?





Hi-

There is a related discussion ongoing in a similar thread - but basically AllStar knows how far off the polar alignment is (just use Align/Polar Alignment/Display to see the error in Alt Az) but the hc has no ability to physically move the mount in alt/az - which is what is needed to become physically polar aligned.

So - it intentionally aims 'off' from the alignment star and asks a human to move the mount until the star is centered - at which point it assumes it is perfectly aligned.

As long as the mount has been moved cleanly in alt/az motions of the correct distance, AllStar knows how the mount is now aligned against the sky and can do GoTo's directly.

If there were big motors to move the equatorial head in alt/az, the hc could do it all by itself - but it uses a human instead.

After the alignment, the displayed polar alignment error is 0,0 - since it assumes it is now perfectly polar aligned and it has no other information to go by unless someone replaces alignment stars - at which point those errors will show as non-zero, but hopefully small values.

Frank




Got it. Thanks, Frank!

David


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SanDiegoPaul
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Reged: 07/22/05

Loc: San Diego
Re: (Sorry) Another Q on the CGEM Polar Align sequence [Re: David Pavlich]
      #3620598 - 02/12/10 11:50 AM

Frank thanks for answering my & David's questions so well. Hopefully we'll get under some stars this weekend to re test what you're saying.

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