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Doug6952
Pooh-Bah


Reged: 07/24/08
Posts: 1142
Loc: West Milford, NJ
Polar aligning a side by side
      #3065751 - 04/25/09 07:42 AM

The last 2 nights I've been blessed with clear skies. It was my first time out with my new CGEM and also my first time trying to polar align with a side by side setup. I did the all star align routine and there was no/very little DEC drift, but it slowly drifts west. Every 8 min exposure, it was a bit further west. It didn't cause trailing or odd shaped stars. I have the mount balanced east heavy and Dec axis is balanced.

The 2 scopes that I have set up are a C6 SCT and an EON 72mm. The C6 is closest to center and is the scope I used for the alignment. I wish I could do a drift alignment, but the East and West horizons are blocked by trees. Since neither scope is centered, is it even possible to get a perfect polar alignment?

--------------------
Doug

Sometimes I wonder......."Why is this frisbiee getting bigger" ...... Then it hits me!


Orion EON 72mm
Celestron C6 SCT
ADM SBS rig
CGEM
DSI Pro III
Orion SSAG
Stellarvue F50
Baader LRGB and Ha filters




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HunterofPhotons
scholastic sledgehammer


Reged: 04/26/08
Posts: 856
Loc: Rhode Island, USA
Re: Polar aligning a side by side new [Re: Doug6952]
      #3066098 - 04/25/09 11:28 AM

Quote:

...... I wish I could do a drift alignment, but the East and West horizons are blocked by trees. Since neither scope is centered, is it even possible to get a perfect polar alignment?



Yes.
You're aligning the mount, not the scopes.
As long as you do your alignment with one scope, there should be no problem.
Why not drift align? You only need access to one horizon and you usually avoid the bottom 20-30 degrees anyway. How much of your eastern horizon is blocked?

dan


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DrBuck
professor emeritus


Reged: 12/10/08
Posts: 506
Loc: Susanville, No. Calif.
Re: Polar aligning a side by side new [Re: HunterofPhotons]
      #3066169 - 04/25/09 12:16 PM

Quote:

...... I wish I could do a drift alignment, but the East and West horizons are blocked by trees. Since neither scope is centered, is it even possible to get a perfect polar alignment?


The distance between the two scopes is absolutely unimportant and miniscule. The important thing is to have the main scope square and aligned with the mount as closely as possible, then align the secondary telescope with that. If you absolutely cannot do a drift method alignment, there is another method. Mount and align a green laser pointer so that it is square and pointing exactly at the same distant spot that the telescope is. (Either land object or star) Then do your best polar alignment of the mount. Then Loosen the locks on the mount so that it will swing freely around the polar axis. Then swing the scopes from side to side with the green laser on. carefully observe the far point of the laser and discern whether it is motionless in space or is it moving.?? If it moves, the polar alignment is definitely off. If it appears motionless then the alignment is quite good. Be very specific when aligning the laser with the RA axis of the Mount!!

--------------------
DrBuck

Roll off Roof Observatory,
MI 250 on concrete and steel pier
Takahashi FS 152 apochromatic refractor
Astro-Tech Ritchey Chretien 12 inch
Televue 85MM Apochromatic refractor
Nikon D-90 with 18-200mm AF VR lens
DMK-21
Canon 15x50 IS Binoculars
http://www.flickr.com/photos/697650grr/?saved=1



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Doug6952
Pooh-Bah


Reged: 07/24/08
Posts: 1142
Loc: West Milford, NJ
Re: Polar aligning a side by side new [Re: HunterofPhotons]
      #3066422 - 04/25/09 02:36 PM

Quote:



How much of your eastern horizon is blocked?

dan




East is completely blocked and west I might be able to hit 50° or maybe only 60°. I might try setting up a single scope tonight and see if it's a problem with the mount.

--------------------
Doug

Sometimes I wonder......."Why is this frisbiee getting bigger" ...... Then it hits me!


Orion EON 72mm
Celestron C6 SCT
ADM SBS rig
CGEM
DSI Pro III
Orion SSAG
Stellarvue F50
Baader LRGB and Ha filters




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Doug6952
Pooh-Bah


Reged: 07/24/08
Posts: 1142
Loc: West Milford, NJ
Re: Polar aligning a side by side new [Re: Doug6952]
      #3067549 - 04/26/09 05:39 AM

I managed to do a drift alignment. I set up the mount in a different location so I could get as low in the west as I could. The lowest I could get is somewhere around 40-45°. I've always read that the star in the east or west should be around 20°, but it seems to have worked.

I could do any real imaging due to light clouds, but I did a test shot for 15 min and didn't get any trailing.

Thanks for your help.

--------------------
Doug

Sometimes I wonder......."Why is this frisbiee getting bigger" ...... Then it hits me!


Orion EON 72mm
Celestron C6 SCT
ADM SBS rig
CGEM
DSI Pro III
Orion SSAG
Stellarvue F50
Baader LRGB and Ha filters




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Strgazr27



Reged: 10/04/04
Posts: 7104
Loc: StonyHill Observatory
Re: Polar aligning a side by side new [Re: DrBuck]
      #3067621 - 04/26/09 07:38 AM

Doc,

That method only proves orthogonality of the OTA and not Polar alignment. I could point the scope at any object and do the above but it would not be polar aligned. To be correctly polar aligned you need to have either polaris visible, a good polar scope, software based polar alignment or iterative drift alignment. It does help to have the OTA orthogonal to the mount though.

--------------------
Bobby

http://www.strgazr27.zenfolio.com


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HunterofPhotons
scholastic sledgehammer


Reged: 04/26/08
Posts: 856
Loc: Rhode Island, USA
Re: Polar aligning a side by side new [Re: Doug6952]
      #3068147 - 04/26/09 12:09 PM

Quote:

I managed to do a drift alignment. I set up the mount in a different location so I could get as low in the west as I could. The lowest I could get is somewhere around 40-45°. I've always read that the star in the east or west should be around 20°, but it seems to have worked.....



That's fine, Doug.
They say that it's possible to achieve an accurate alignment using a star up to 50 degrees above the horizon. The problem is that the higher in the sky the star is, the altitude adjustments that you are making are also affecting the previous azimuth adjustment that you made. That means that you need to go back to a meridian star and repeat the azimuth procedure and then a touch-up to the altitude again.

dan


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DrBuck
professor emeritus


Reged: 12/10/08
Posts: 506
Loc: Susanville, No. Calif.
Re: Polar aligning a side by side new [Re: Strgazr27]
      #3068309 - 04/26/09 01:29 PM

Bobby, I see what you mean, I think!! In other words, if I pointed the polar axis of the mount anywhere in the sky and then performed that procedure, it would appear motionless?---that could be possible, I have never done that. The only time I have used that method was with a wedge mounted LX200 12 inch with the laser mounted to the OTA. I have a clear shot at Polaris and other points north. Everytime I performed that procedure, it would only appear motionless when pointed at the NCP, not Polaris. moving the wedge controls one direction or the other would cause the end of the laser to move in an arc. My new cge is correctly polar aligned using celestrons software, but I could test the theory with a smaller GEM that I have.

--------------------
DrBuck

Roll off Roof Observatory,
MI 250 on concrete and steel pier
Takahashi FS 152 apochromatic refractor
Astro-Tech Ritchey Chretien 12 inch
Televue 85MM Apochromatic refractor
Nikon D-90 with 18-200mm AF VR lens
DMK-21
Canon 15x50 IS Binoculars
http://www.flickr.com/photos/697650grr/?saved=1



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