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Equipment Discussions >> Mounts

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rmollise
Postmaster
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Reged: 07/06/07

Re: CG-5 Mount - Polar align, Go-To new [Re: freestar8n]
      #3620302 - 02/12/10 09:24 AM

Quote:

Rod-

He is talking about unsyncing AFTER doing AllStar polar alignment. In order to do AllStar you must sync on the polar alignment star. After you complete AllStar, you are still sync'd to that star. If you then go far from that star, you may be better off unsync'ing to improve GoTo accuracy. If you find your GoTo is still not great, you may choose to replace alignment stars - which requires an unsync anyway.

I think there is a misunderstanding here. You don't need a good polar alignment to have good GoTo - but you do need to do the polar alignment well, and ACHIEVE a good polar alignment, for GoTo to be good immediately after doing AllStar. The alignment should, and must, be good after allstar in order for you to have accurate GoTos without a new alignment - and good GoTos right after doing AllStar is a big advantage of AllStar.

Turning off the mount and starting over would defeat a lot of the purpose of AllStar, but you could do it if you want.

Frank




I'm not misunderstanding anything. If he has a problem with go-to accuracy following a polar alignment, he needs to eliminate problems involving unsyncing stars. Turing the scope off and realigning is how you eliminate that as a troubleshooting measure.


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wsuriano
super member


Reged: 11/13/07

Re: CG-5 Mount - Polar align, Go-To new [Re: rmollise]
      #3620336 - 02/12/10 09:44 AM

I am just wondering why the OP does not use three or more calibration stars before doing his AllStar Polar Alignment. I would not use APA until I got at least 3 calibration stars. I'm with Chris on this one. Once I do my alignment stars and then 3 or 4 calibration stars, followed by the APA, I'm good to go. My GoTos are spot on and I can easily get 5 minute guided subframes. If my GoTos are off after that, as Unk says, I've done something wrong on the front end. I'll shut down and start over making sure that I've got the right alignment and calibration stars in the right part of the sky.

Bill


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mayidunk
Don't Ask...
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Reged: 02/17/10

Loc: Betwixt & Between...
Re: CG-5 Mount - Polar align, Go-To new [Re: wsuriano]
      #3634322 - 02/19/10 10:26 AM

Hi all, I'm new here, so I thought I'd say hello, and impose upon you just a little bit by relating to you my understanding of the CG-5 set-up and alignment procedures, just so I know that I understand what you guys are talking about.

By way of a little background, the only goto scope I'm familiar with is the Celestron Ultima 2000, which I've owned for many years. I also have a Vixen GP GEM that I use with my refractor, so I'm familiar with polar alignment. This mount is manual, so it doesn't have goto capability.

Anyway, after reading through the alignment procedures in the CG-5 User's Manual, I think I understand that there are at least three things that need to be done to insure the mount knows where it is, so that it can then take you where you want to go.

The first one is the mount calibration procedure, which lets the mount know it's datum points (Physical reference points on the mount itself.)

The second one is the set-up procedure, which tells the mount where on Earth it's physically located, and when in time it currently exists. (I'm surmising that, once the coordinates, date, and time have been entered, the mount then uses that data to build a virtual model of your local sky in it's memory, based upon ephemeris data it already has contained within itself.)

And, finally, the two-star alignment procedure, which the mount uses to confirm and refine the model of the sky that it previously built in its memory. Once this procedure is done, the mount should accurately slew to your selected object. However, it will track the object only as accurately as the mount is physically aligned with the Earth's rotational axis.

So, you then use the PA utility to increase the mount's tracking accuracy. It does this by guiding you to physically adjust the angle of the mount's Right Ascension (R.A.) shaft so that it's axis of rotation is parallel with where it thinks the Earth's rotational axis is located. I believe the PA utility does this by first slewing the OTA so that it is parallel with the R.A. shaft, and then allows you to center Polaris in the telescope's field of view by adjusting the R.A. shaft's angular position using the mount's altitude and azimuth adjustment screws.

Of course, if you make these adjustments, you will have then altered the sky model's orientation relative to the mount's physical datum points, because you adjusted the angular position of the R.A. axis in order to bring Polaris's real world position in line with where the mount expected it to be located. So...

You go back and do another two-star alignment, this time to allow the mount to readjust the sky model so that it's back in alignment with the mount. Once this is done, the mount should not only accurately slew to your selected object, it should also accurately track that object.

My question is... do I understand this correctly? Am I in the ball park? out to lunch?... Did you stop reading way before this?

Also, I noticed that the CG-5 doesn't seem to require leveling. My GP mount has a little bulls-eye level built into it. In order to get the best tracking accuracy, the mount must be leveled first, before it's polar aligned. Wouldn't this hold true for the CG-5 as well? Perhaps I missed something, and just glossed right over that part of the set-up procedure?

Thanks for your answers, observations, wisdom, and corrections!

Bob


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mclewis1
Thread Killer
*****

Reged: 02/25/06

Loc: New Brunswick, Canada
Re: CG-5 Mount - Polar align, Go-To new [Re: mayidunk]
      #3634363 - 02/19/10 10:44 AM

Bob, Welcome to CN.

The manual situation is a bit mixed up for the CG-5 because of it's age. It all depends on which firmware level you have loaded in the hand controller. The hardware part of the manual doesn't change but for information about the hand controller (and this includes alignment procedures) then it's probably better to refer to additional manuals.

V3 - Original CG-5 manual
4.10 - Original plus v4 addendum
4.16 - CGEM or CGEPro manual


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anivision
member


Reged: 05/09/09

Loc: Sweden
Re: CG-5 Mount - Polar align, Go-To new [Re: mayidunk]
      #3634515 - 02/19/10 11:44 AM

Quote:

My question is... do I understand this correctly? Am I in the ball park? out to lunch?... Did you stop reading way before this?



I think you got it all pretty well. The difference between the older hand controls and the newer ones is, as mentioned above, the polar alignment procedure. In the older versions you did as you mentioned in your post, aligning to the polaris. It's just that the mount takes in concideration that polaris isn't quit the celestial pole.

In the newer version of the hand control there is a procedure called "all star polar alignment", ASPA, and with this you don't have to align through polaris anymore. You can choose any other bright star of your own desire, but then the procedure is much the same. You can say it slews to the position where your choosen star should have been IF the mount was polar aligned in a correct way.

I hope I didn't messed it up for you again


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