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Equipment Discussions >> Mounts

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xcy
sage


Reged: 05/15/06

Loc: Europe
Can't accurately star align CG5-GT
      #3806370 - 05/14/10 10:17 PM

With two align star W of the Meridian and two calibration E and although the procesure is finished succesfully, objects are not in the field of view of a wide angle eyepiece and sometimes the telescope is pointing way off target.

All the required information is entered correctly in the hand control and I am using the latest firmwares. I tried to perform a factory reset without much luck. I am using power from an AC source, so it is not a battery problem either.

Usually the two align stars are in the finder, but the calibration are way off. Any ideas why?

I also noticed that occasioanlly when performing star align the CG5-GT mount will not point to the align star, but under the horizon. The problem is usually solved by switching off and on the power a few times. Is this a known issue?


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David PavlichAdministrator
Transmographied
*****

Reged: 05/18/05

Loc: Mandeville, LA USA
Re: Can't accurately star align CG5-GT new [Re: xcy]
      #3806392 - 05/14/10 10:35 PM

Quick review...mount pointed as close to North as possible? Starting counterweights down? Daylight savings time invoked?

First star fairly far off, but the second star should be at least in the finder, yes? Cal stars...first star should be in the finder, second star closer to the center, third should be there and add a 4th for good measure.

If your last 2 cal stars are on or very close to the center, your gotos should be at least in the FOV of a widefield ep.

So...are your cal stars close, especially the last 2? If so, then your gotos should be good.

David


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Fred1
Carpal Tunnel
*****

Reged: 09/19/07

Loc: Somewhere in the Orion Spur
Re: Can't accurately star align CG5-GT new [Re: David Pavlich]
      #3806455 - 05/14/10 11:20 PM

You didn't mention what scope you're using. Check its orthogonality with the mount. Is the scope pointing in the direction of Polaris when the mount is in "Home" position? If not, check your rings and be sure the dovetail is strait across where it attaches to the rings and not slightly askew.

Also, when you say, "I tried to perform a factory reset without much luck." Do you mean that the factory reset didn't take? Or that it did take but with no improvement in performance?

I just got my 2nd CG5 (I love that mount, the other CG5 is back at Celestron for repair). The new one had similar issues as you described until a few alignment set ups were done. I had at least three separate observing sessions with it before it started behaving like my older one.


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xcy
sage


Reged: 05/15/06

Loc: Europe
Re: Can't accurately star align CG5-GT new [Re: Fred1]
      #3806581 - 05/15/10 02:16 AM

Calibration stars are usually outside the finder. I am using an 8" SCT. When the telescope is at the home position (indexes) and pointing at Polaris I can see the star in the finder. I performed a factory reset succesfully but it did not help.

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rmollise
Postmaster
*****

Reged: 07/06/07

Re: Can't accurately star align CG5-GT new [Re: xcy]
      #3806863 - 05/15/10 09:43 AM

Quote:

Calibration stars are usually outside the finder. I am using an 8" SCT. When the telescope is at the home position (indexes) and pointing at Polaris I can see the star in the finder. I performed a factory reset succesfully but it did not help.




If the cal stars aren't at least close to the center of the finder, you will get nowhere.

Did you keep adding cal stars all the way to four?

It's (usually) best not to get creative with the alignment stars. Just accept those the mount picks unless they are blocked.

Are you sure you are centering all six stars correctly? That is, the correct stars?

Are you doing final centering with the up and right buttons only?

Are you sure your power supply is adequate?

Are you sure all data has been entered _correctly_ in the HC (triple check, referencing the manual).


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David PavlichAdministrator
Transmographied
*****

Reged: 05/18/05

Loc: Mandeville, LA USA
Re: Can't accurately star align CG5-GT new [Re: rmollise]
      #3807225 - 05/15/10 01:50 PM

One more thing and please don't take this as some sort of insult to your knowledge base, but are you sure that the stars you've chosen are the actual stars that you're aligning with? When I align, I use as many of the familiar stars as possible. For example, in the west, Castor and Pollux are good stars and are fairly easy to pick out. In the east, you have Dubhe and Alkaid which are part of the Big Dipper. It's easy to mistake one dimmer star for another. Just a thought.

David


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neptun2
scholastic sledgehammer


Reged: 03/04/07

Loc: Bulgaria
Re: Can't accurately star align CG5-GT new [Re: David Pavlich]
      #3807309 - 05/15/10 02:44 PM

I support David's opinion because i have done this mistake myself. My heq5 pro always puts first of the 3 alignment stars way off and i mean it is not even in the finderscope's field of view. If i do not carry laptop with planetarium program with me it is fairly easy to center the wrong star especially if i select dimmer one. Second and third star are much closer for me so there is no such danger with them but for the first it is definitely a possibility.

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Deetrix
super member


Reged: 09/30/08

Loc: Little Rock, AR
Re: Can't accurately star align CG5-GT new [Re: neptun2]
      #3812202 - 05/18/10 09:07 AM

Guys, also don't forget that one of those indexes is off 180 degrees. XCY, the directions are just plain WRONG. Well, the directions aren't wrong the guys at the factory who have been putting the index sticker in the wrong place are wrong. Take the OTA off, flip the DEC drive around 180 and put the OTA back on and try again. You should know if you have it right b/c that smaller support screw that holds the dovetail will be aimed in a way that it prevents the OTA's dovetail from sliding back due to gravity. I have a feeling you'll be pleasantly surprised.

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Patrick
Postmaster
*****

Reged: 05/16/03

Loc: Franklin, Ohio
Re: Can't accurately star align CG5-GT new [Re: xcy]
      #3812405 - 05/18/10 10:59 AM

Quote:

When the telescope is at the home position (indexes) and pointing at Polaris I can see the star in the finder.




Do not use the index marks. They are notorius for being in the wrong position. As David said, the home position is with the counterweight shaft pointing straight down from the front, and the OTA pointing towards Polaris (make sure your altitude adjustment is set to your latitude). After you get that position, you can remove and place the index marks correctly for future reference.

EDIT: Also, what version of hand controller firmware are you using? I think the latest firmware version is 4.16, IIRC.

Patrick

Edited by Patrick (05/18/10 11:02 AM)


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mclewis1
Thread Killer
*****

Reged: 02/25/06

Loc: New Brunswick, Canada
Re: Can't accurately star align CG5-GT new [Re: Patrick]
      #3812590 - 05/18/10 12:10 PM

The Index marks have no bearing on alignment accuracy (aside from providing a consistent starting point). The mount has no idea where those index marks are ... they can be removed and put anywhere with no effect. The only "index" is where the scope/mount is positioned when it's powered up.

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blb
Post Laureate


Reged: 11/25/05

Loc: Piedmont NC
Re: Can't accurately star align CG5-GT new [Re: Patrick]
      #3812593 - 05/18/10 12:12 PM

Hey! I just learned that my stickers for the home position are located in the wrong position on both my Celestron mounts but they are working fine. I use the three star alignment, except what the controller picks unless I can't see the star and do not add any additional calibration stars. The object I am looking for is almost always in the field of view with a low power eyepiece. NEVER used the two star alignment. I just make sure I can see Polaris through the hole in the RA shaft and do the three star alignment, that's all. Try it. Got in the habit because the two star didn't work that well with my Meade LXD 75 mount either. I had to use a three star with it too.

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Patrick
Postmaster
*****

Reged: 05/16/03

Loc: Franklin, Ohio
Re: Can't accurately star align CG5-GT new [Re: mclewis1]
      #3812889 - 05/18/10 02:17 PM

Quote:

The mount has no idea where those index marks are ...




The hand controller assumes the starting position is the 'home' position when it goes to it's first alignment star. I've tried this many times. When the tripod is level and the counterweight shaft is pointing straight down with the altitude set correctly (essentially with the mount polar aligned..which is the 'home' position and where the index marks SHOULD be), the first goto alignment star will be very close to being in the center of the finder scope. It's not necessarily important that the first star be that close, but I've found it helps if the mount is closer to being accurately polar aligned because the software does not have to deal with as much cone error.

Patrick


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jrcrillyAdministrator
Refractor wienie no more
*****

Reged: 04/30/03

Loc: NE Ohio
Re: Can't accurately star align CG5-GT new [Re: mclewis1]
      #3813220 - 05/18/10 04:42 PM

Quote:

The only "index" is where the scope/mount is positioned when it's powered up.




Regarding the accuracy of the slew to the first alignment star, the index is whatever position was used to begin the last few successful alignments. The mount keeps track of the correction required to center the first star and compensates on future alignments. If you always use the marks, wherever they are, they will become the best initial position (that was Celestron's intent). If you always use CW shaft down instead, or move the marks to some other arbitrary location, then eventually that will become the best position and it will be just as good as if you had used the marks in the first place but no better. If you are inconsistent, then there won't be any best initial position.


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EdTheEdge
Carpal Tunnel


Reged: 04/10/09

Loc: Lomita, CA
Re: Can't accurately star align CG5-GT new [Re: jrcrilly]
      #3813236 - 05/18/10 04:51 PM

I regularly SYNCH to the objects that I am observing. That seems to help GoTos or is it just my imagination????

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Patrick
Postmaster
*****

Reged: 05/16/03

Loc: Franklin, Ohio
Re: Can't accurately star align CG5-GT new [Re: jrcrilly]
      #3813823 - 05/18/10 10:00 PM

Quote:

Regarding the accuracy of the slew to the first alignment star, the index is whatever position was used to begin the last few successful alignments. The mount keeps track of the correction required to center the first star and compensates on future alignments. If you always use the marks, wherever they are, they will become the best initial position (that was Celestron's intent). If you always use CW shaft down instead, or move the marks to some other arbitrary location, then eventually that will become the best position and it will be just as good as if you had used the marks in the first place but no better. If you are inconsistent, then there won't be any best initial position.




Interesting John...I never knew the hand controller was storing that kind of data.

Patrick


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jrcrillyAdministrator
Refractor wienie no more
*****

Reged: 04/30/03

Loc: NE Ohio
Re: Can't accurately star align CG5-GT new [Re: Patrick]
      #3813838 - 05/18/10 10:06 PM

Quote:

.I never knew the hand controller was toring that kind of data.

Patrick




Hi, Patrick!

I never heard of another mount doing it but it was present from the beginning of the CG5-GT model; pretty neat trick.


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rmollise
Postmaster
*****

Reged: 07/06/07

Re: Can't accurately star align CG5-GT new [Re: Patrick]
      #3814509 - 05/19/10 07:59 AM

Quote:

Quote:

When the telescope is at the home position (indexes) and pointing at Polaris I can see the star in the finder.




Do not use the index marks. They are notorius for being in the wrong position. As David said, the home position is with the counterweight shaft pointing straight down from the front, and the OTA pointing towards Polaris (make sure your altitude adjustment is set to your latitude). After you get that position, you can remove and place the index marks correctly for future reference.

EDIT: Also, what version of hand controller firmware are you using? I think the latest firmware version is 4.16, IIRC.

Patrick




It really doesn't matter where they are. The important thing is that you start from the same position _every time_.


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Eddgie
Postmaster
*****

Reged: 02/01/06

Re: Can't accurately star align CG5-GT new [Re: xcy]
      #3815467 - 05/19/10 03:05 PM

Sometimes these mounts have some slop in the gears.. The aligment routing is supposed to accomodate it, but I have owned several LXD-55s and CG5s, and some pointed with good consistency, while others did not.

You did not say what kind of scope you have, but if it is a C8, don't expect targets to be in the center of the field of a "Low Power" eyepiece, though they should usually be somewhere in the field. For a small refractor, they should always be in the field.

In every case where the mount did NOT point with good accuracy, the problem was resolved by removing the slop in the gears.

Lock the RA clutch, then try wiggling the bottom of the counterweigth shaft East and West. If it moves more than a little bit, your worm gear may have some slop in it. Same for the DEC axis.

Again, the alignment routine is supposed to account for this slop, but in my own case, I have owned several mounts where the play was bad enough that pointing was sloppy.

Also, check that the mount is tight. If ANYTHING is shifting because of loose screws, this will also kill your pointing.

Good luck.

Ed


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ZMass
sage


Reged: 11/07/07

Re: Can't accurately star align CG5-GT new [Re: Eddgie]
      #3815716 - 05/19/10 04:58 PM

I didn't see mention already - scope pointing below the horizon is a tell-tale sign of power issues. If you haven't already, try a known good power supply. The mile-long cigarette lighter plug is one of the weak links.

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magnus
professor emeritus


Reged: 03/17/04

Loc: Visby, Sweden
Re: Can't accurately star align CG5-GT new [Re: ZMass]
      #3821999 - 05/22/10 03:05 PM

Rod!
Thanks for your advice: "Are you doing the final centering with up and rights buttons only?"
I had missed that detail and at last my 8"f/6 Newt find it`s targets on my CG-5GT. Had just given up hope that my Newt could work on the CG-5GT but now it sure does!

All the best,
Magnus


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