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Equipment Discussions >> Mounts

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Itz marcus
Pooh-Bah
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Reged: 02/12/06

Loc: Brooklyn NY
CG5 question
      #5838245 - 05/03/13 12:14 PM

Hi,
Probably a stupid question but I just got a cg-5 for use with an EON 120. It's the first time I have goto. My previous mount was an SVP. I did a two star align with one calibration star. I asked it to find Saturn and it was in the center of the EP, but when I asked it to goto arcturus it was off (at the edge of the finder scope but not in the ep at all. I didn't polar align but of course I aligned it roughly. (The mount is set at my lat of 40 deg but Polaris isnt off also (not in the finder scope either) what am I doing wrong? I checked and double checked my location. I have this problem with the SVP as well and both sdcope are level and facing North. Even when I get polasris in the scope it wilol move out of view after a few hours so I must be doing something wrong).
Any help would be appreciated.
Thanx
Clear Skies
Itz


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Geo.
Carpal Tunnel
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Reged: 10/01/08

Loc: Upstate NY
Re: CG5 question new [Re: Itz marcus]
      #5838269 - 05/03/13 12:26 PM

Did you run the mount calibration routine?

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Itz marcus
Pooh-Bah
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Reged: 02/12/06

Loc: Brooklyn NY
Re: CG5 question new [Re: Geo.]
      #5838343 - 05/03/13 12:59 PM

I dont have the manual with me but i could've sworn I saw that that was more for ap and not for visual so I didnt but I'll do that. Thanx
Clear Skies
Itz


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Itz marcus
Pooh-Bah
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Reged: 02/12/06

Loc: Brooklyn NY
Re: CG5 question new [Re: Itz marcus]
      #5838475 - 05/03/13 02:17 PM

What abt not getting polaris in the finder scope unless it move alot on the ra axis? Where am i going wrong? Again latitude is correct

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Falcon-
Post Laureate
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Reged: 09/11/09

Loc: Gambier Island, BC, Canada
Re: CG5 question new [Re: Itz marcus]
      #5838501 - 05/03/13 02:35 PM

as far as the go-to to arcturus being off, that may simply be a matter of needing to use more then 2 calibration stars during the initial go-to setup. The CG5 will offer to keep adding stars and I find that aligning on 4-6 stars instead of only 2 stars VASTLY improves the go-to accuracy.

There is also a polar alignment routine built into the hand controller that will let you confirm your "pointed north" is really correct should you need long-term tracking accuracy (or are doing photography).


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RTLR 12
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Reged: 12/04/08

Loc: The Great Pacific NorthWest
Re: CG5 question new [Re: Falcon-]
      #5838521 - 05/03/13 02:45 PM

What Falcon said. You need to add more calibration stars.

Stan


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rmollise
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Reged: 07/06/07

Re: CG5 question new [Re: Itz marcus]
      #5838563 - 05/03/13 03:05 PM

--Do all four calibration stars.
--Make sure you are centering the correct stars.
--Do final centering with up and right buttons only.

Polar alignment will have little or no effect on go-to quality.


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gmartin02
professor emeritus
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Reged: 04/11/05

Loc: Santa Clarita, CA
Re: CG5 question new [Re: Geo.]
      #5838637 - 05/03/13 03:48 PM

Quote:

Did you run the mount calibration routine?




The calibrate mount routine mentioned by George (Utilities -> Calibrate Mount -> RA Switch) will only improve accuracy of the initial slews to the alignment stars. It will not improve the pointing model of the mount once the alignment/calibration stars have been added, so this wont help with the problem Itz reported.

One thing that really helped me get better alignment was to purchase an illuminated reticle eyepiece - something like this: http://agenaastro.com/agena-1-25-wireless-illuminated-reticle-eyepiece-12-5mm...

I know it is an added expense, but it really helps with the pointing accuracy. For visual, once I got the reticle eyepiece, I typically only add one calibration star after the 2 alignment stars and still get pretty good pointing results.

Some responses say to add more calibration stars - this will definitely help, but if you use a reticle eyepiece, you are getting a more accurate position for the first calibration star as well as the 2 alignment stars, so there is less need to add more calibration stars (to get an "average" position for the calibration pointing model). Adding calibration stars will not completely correct for inaccuracies with the 2 alignment stars.

A couple of things Uncle Rod mentioned are really important, perhaps even more important than adding all 4 calibration stars:
--Make sure you are centering the correct stars.
--Do final centering with up and right buttons only.

Greg


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ur7x
sage


Reged: 01/08/12

Re: CG5 question new [Re: rmollise]
      #5838674 - 05/03/13 04:11 PM

Quote:

Do final centering with up and right buttons only.




This is the best tip that anyone can consider who is struggling with near miss goto's. If you final align in the same direction that the mount does its final approach... also called the "right up" rule. Your goto's will get considerably better.

That and in my back yard I found the better the location you can give the mount the better, having the time of day right is also a help. First time I used my CG5 I got the month/day backwards which caused all kinds of confusion... and of course getting the star that you think is the right star in the cross-hairs is a big plus too..


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Eddgie
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Reged: 02/01/06

Re: CG5 question new [Re: Itz marcus]
      #5839150 - 05/03/13 09:56 PM

Quote:

Even when I get polasris in the scope it wilol move out of view after a few hours so I must be doing something wrong).





No amount of calibration or anything else will fix this.

The GG5 does not track in Declination... Only Right Ascension. In fact most "Go-To" mounts behave the exact same way.. They will slew to a star, but if the mount is not in exact polar alignment, the star will drift out of the field in time.

There is no fix for this. Autoguider programs will of course drive the Dec axis, but the computers that come with the scope do not drive the Dec axis except on initial slew,

Again, no amount of alignment stars or calibration routines will fix this. For long term tracking, you have to autoguide or do an accurate polar alignment.

And a tip. Find the Losmandy G11 or GM8 User's Guide and take the time to shim your scope for Cone Error. This will improve your pointing and your tracking. It is easy to do.

Edited by Eddgie (05/03/13 10:00 PM)


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DaveJ
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Reged: 01/07/05

Loc: NE Ohio
Re: CG5 question new [Re: Eddgie]
      #5840067 - 05/04/13 12:43 PM

Quote:

And a tip. Find the Losmandy G11 or GM8 User's Guide and take the time to shim your scope for Cone Error. This will improve your pointing and your tracking. It is easy to do.




While it might be easy to do, with the Celestron GEMs it is totally unnecessary since the 2+4 alignment successfully calculates the cone error and completely takes it out of the go-to equation. I've intentionally introduced cone-error on my CGE and CGEM DX and experimented. The NexStar firmware's 2+4 alignment successfully calculated the cone-error and all go-tos were accomplished successfully.


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Eddgie
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Reged: 02/01/06

Re: CG5 question new [Re: DaveJ]
      #5840522 - 05/04/13 06:01 PM

I don't think doing cone error is essential, but at the same time, I found that my own initial slews seemed to be more accurate, and overall, my pointing accuracy seemed to improve. I often had slews (especially with the CGE) that would fail to put objects into the center of the field.

I felt that removing the cone error helped.

I agree though that it is not essential.

The bigger issue here though is that these calibrations will not fix the OPs problem. You can calibrate until the cows come home, but if the polar alignment is not accurate, the target will still drift out of the field.

No matter how perfect the stars were centered and how many calibration stars you do, if the mount is not accurately polar aligned, stars will drift out because these mounts don't track in Declination. They only drive in RA.

The declination motor only runs when slewing, when being controlled by an autoguider, or by manually adjusting it using the control pad.

At least this is the way My CGE, CG5, LXD-55, and LXD 750 mounts all worked.


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Itz marcus
Pooh-Bah
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Reged: 02/12/06

Loc: Brooklyn NY
Re: CG5 question new [Re: Eddgie]
      #5840926 - 05/04/13 11:29 PM

Hi,
Thanx for all the replies! I used for calibration stars and it works yay! I still can't see much deep space from my light polluted area but I'll be upstate new York for July and August. There's light pollution there too but not nearly as bad!
Are there any galaxies that can be readily seen in a 120 scope in ny city?
Clear Skies
Itz


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pjensen
super member


Reged: 04/08/12

Loc: Highland Village, Tx
Re: CG5 question new [Re: Eddgie]
      #5841364 - 05/05/13 09:51 AM

Quote:

The GG5 does not track in Declination... Only Right Ascension. In fact most "Go-To" mounts behave the exact same way.. They will slew to a star, but if the mount is not in exact polar alignment, the star will drift out of the field in time.

There is no fix for this. Autoguider programs will of course drive the Dec axis, but the computers that come with the scope do not drive the Dec axis except on initial slew,




This explains why my initial GoTos are dead center at the beginning of the evening, but seem to drift off later on in the evening (but still within the eyepiece field of 0.30 degrees). So my polar alignment is not quite dead on (yet).

Quote:

Find the Losmandy G11 or GM8 User's Guide and take the time to shim your scope for Cone Error. This will improve your pointing and your tracking. It is easy to do.




Looked at both these manuals (on the Losmandy website) and did not see how to reduce cone error. Maybe there is another (more detailed) manual?

Thanks,

Paul


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