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CGEM vsGM-8

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#1 ScottW

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Posted 18 June 2009 - 12:29 PM

Hi,
Just a thought, which is better? Can the setting circles on the gm-8 do the same job as the goto? Would the gm-11 be better?
Scott

#2 AlexDJ30

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Posted 18 June 2009 - 01:03 PM

well depends on what you want to do.. GM-8 is a great mount but the setting circles is more different than Go to... is more like Push to than Go to.

GM-8 are sell with Go to already..but more pricy, the Gm-11 is the same but it can carry more weight!

The CGEM have go to and i think have a more complete package than GM-8 or GM-11, their handcontroll is more friendly than the GM counterparts (the go to ones) but you should check first how much weight are you goping to use and for what only visual or AP??.

The good thing about the GM mounts are the accesories and parts to repair if something goes wrong, the CGEM if something is not right you would have to send the entire mount to Celestron for repairs...

Just clarefie us for what you want to use the mount..just visual...visual and casual AP...or full AP and how much weight you plan to put in it??

#3 rmollise

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Posted 18 June 2009 - 01:04 PM

Hi,
Just a thought, which is better? Can the setting circles on the gm-8 do the same job as the goto? Would the gm-11 be better?
Scott


The small analog circles of the GM8? If the mount is _precisely_ polar aligned, they will get you in the neighborhood, but "same job"? No way.

The G11? Better for what?

#4 donsinger1

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Posted 18 June 2009 - 10:48 PM

Have had a GM-8 and have a CGEM...both nice mounts; but, the CGEM is hands down better relative to the HC, tracking, pointing and guiding, and polar alignment, is dumb simple and works...love it.

Don

#5 ScottW

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Posted 19 June 2009 - 07:26 AM

Thanks for the advice. I want to use it for visual work only and the weight at the moment is not an issue, 20lbs at the moment and no more than 30lbs, maybe.

#6 RAKing

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Posted 19 June 2009 - 10:06 AM

For fit, finish, and overall quality, the GM-8 is the better of the two by a wide margin.

The Celestron hand paddle is definitely easier to use than the Gemini system on the GM-8.

The CGEM reminds me of my old Atlas and since both mounts are made by Synta, I suspect there are lots of internal similarities. My Atlas was a nice mount and worked quite well, but I wouldn't put it in the class of my GM-8. My little GM-8 could track for hours with just a simple polar alignment.

If you are on a budget, the CGEM is a lot less money.

Those are my impressions. YMMV :),

Ron

#7 Charlie Hein

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Posted 19 June 2009 - 06:41 PM

CGEM is much heavier. Just wanted to throw that in.

#8 Phil Cowell

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Posted 19 June 2009 - 06:54 PM

Get the CGEM. It's Servo based while the Atlas is Stepper based. As to the handcontroller over the G-8, well I think the Celestron is much easier to use and you get the new polar alignment routine Celestron now has. No need to buy a polar alignment scope, another saving.
Phil

#9 Phil Cowell

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Posted 19 June 2009 - 06:56 PM

Hi,
Just a thought, which is better? Can the setting circles on the gm-8 do the same job as the goto? Would the gm-11 be better?
Scott

More like using a slide rule than a goto computerized mount.
Phil

#10 BCB

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Posted 20 June 2009 - 06:49 AM

OK, Tangent question.. ;)

What's the difference between the CGEM's servos, VS. the Atlas's steppers? Better accuracy, noise, what?

#11 Charlie Hein

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Posted 20 June 2009 - 07:24 AM

OK, Tangent question.. ;)

What's the difference between the CGEM's servos, VS. the Atlas's steppers? Better accuracy, noise, what?


At the end of the day, not much really. Servos will have some sort of mechanical encoder installed to determine their position. Steppers do not because their position is determined by counting the number of "steps" they take (or fraction thereof if the stepper is capable of "micro-stepping" as are most that are used in this application). One could say that the encoders give an "actual" position as opposed to a "guess" as to how far the stepper has actually stepped, but in practice this is totally not a consideration.

For example, the Atlas steppers are theoretically capable of positioning the telescope to within a small fraction of an arcsecond depending on the state of the hardware they're attached to. I know from experience that when they're set up right they are deadly accurate pointers. I've heard good things about the CGEM in this regard as well so IMO there's no real advantage either way except for one very small point... from a noise standpoint the buzz right now is that the CGEM is a bit noisier than the Atlas when slewing - but both are very quiet while tracking.

#12 Phil Cowell

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Posted 20 June 2009 - 07:36 AM

Servo's tend to have a small advantage over steppers as they are closed loop. Steppers tend to need sized power wise correctly so as not to miss steps. Mind you servo's can also get bad data back from encoders. At the current state of technology I'd (IMO) still give the servo a slight edge over a stepper but that edge is closing quickly. With some of the new intelligent servos with processors incorporated on them shrinking is size, it's possible the servo might move it's edge back again.
Phil






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