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Equipment Discussions >> Mounts

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JMac85X
super member


Reged: 09/13/12

Loc: California
Re: cgem or cgem dx? new [Re: EFT]
      #5519058 - 11/14/12 04:48 AM

So if I want to do wide field imaging with an 80mm on my DX I'm screwed? Or couldn't I just piggyback it on my 11 HD which I believe is 27lbs. Or I make sure the refractor isn't too light? And what about using the fastar, anyone have good success with that? I'm just wondering because I've mine for about two months and I've had balancing issues. When I think it's balanced and slew it the motors will struggle and kind of jump so I bring the counterweight down and that solves my problem

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EFT
Vendor - Deep Space Products
*****

Reged: 05/07/07

Loc: Phoenix, AZ
Re: cgem or cgem dx? new [Re: JMac85X]
      #5519186 - 11/14/12 08:44 AM

Quote:

So if I want to do wide field imaging with an 80mm on my DX I'm screwed? Or couldn't I just piggyback it on my 11 HD which I believe is 27lbs. Or I make sure the refractor isn't too light? And what about using the fastar, anyone have good success with that? I'm just wondering because I've mine for about two months and I've had balancing issues. When I think it's balanced and slew it the motors will struggle and kind of jump so I bring the counterweight down and that solves my problem




Yes. By piggy backing or using a heavier OTA you are adding more weight to the saddle end of the axis which overcomes the issue. Again, the problem is that people don't generally expect this to be an issue in the first place. Personally, this is the only mount that I know of that has this issue (although I expect there are other mounts that are specifically designed for heavy loads only).

If the axes are stiff when the clutches are released, balancing will be difficult if possible at all.


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esthel
journeyman


Reged: 06/21/12

Re: cgem or cgem dx? new [Re: EFT]
      #5521240 - 11/15/12 01:33 PM

I'm thinking about buying a CGEM DX and use a 8" sct with it. Will I be able to balance this with a 11lb weight?

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EFT
Vendor - Deep Space Products
*****

Reged: 05/07/07

Loc: Phoenix, AZ
Re: cgem or cgem dx? new [Re: esthel]
      #5521395 - 11/15/12 03:06 PM

Quote:

I'm thinking about buying a CGEM DX and use a 8" sct with it. Will I be able to balance this with a 11lb weight?




It should balance with an 11 pound wieght.


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fetoma
Carpal Tunnel
*****

Reged: 09/26/06

Loc: Southern New Jersey
Re: cgem or cgem dx? new [Re: EFT]
      #5522938 - 11/16/12 01:38 PM

Hi Ed,

You should add an aluminum counterweight shaft for the DX to your offerings, or an adapter to use the CGEM counterweight shaft.


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neilson
professor emeritus


Reged: 08/22/10

Re: cgem or cgem dx? new [Re: fetoma]
      #5523195 - 11/16/12 04:59 PM

Hi Ed,
A 10lbs counter weight for the CGEM DX would be nice.


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LateViewer
Pooh-Bah
*****

Reged: 11/17/05

Loc: Manhattan
Re: cgem or cgem dx? new [Re: neilson]
      #5523449 - 11/16/12 08:51 PM

Good thread. I have been wondering about the difference between these two mounts for a while.

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Stew57
Carpal Tunnel
*****

Reged: 05/03/09

Loc: Silsbee Texas
Re: cgem or cgem dx? new [Re: LateViewer]
      #5523497 - 11/16/12 09:35 PM

The tracking ability of each mount is equivalent. There will be as much deviation amoung units of the same set as units from opposite sets. The big difference is the weight of the tripod. If you are going to pier mount or carry your unit out nightly skip the DX. If you set up for extended times or plan on using some type of wheeled dolly, then go for the DX. don't expect better or worse results either visually or when doing AP with either mount despite the differing wheight capacities.

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neilson
professor emeritus


Reged: 08/22/10

Re: cgem or cgem dx? new [Re: Stew57]
      #5523545 - 11/16/12 10:17 PM

Hi, I had read that the periodic error should be around 15 to 25 arcseconds before you Hypertune or use PEC. Is that about right, and wouldn't the thicker weight bar and heavier tripod make the DX's lower? Or do they not make a difference.
And what should the error be after PEC is applied?

Neilson


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EFT
Vendor - Deep Space Products
*****

Reged: 05/07/07

Loc: Phoenix, AZ
Re: cgem or cgem dx? new [Re: neilson]
      #5523789 - 11/17/12 02:00 AM

Quote:

Hi, I had read that the periodic error should be around 15 to 25 arcseconds before you Hypertune or use PEC. Is that about right, and wouldn't the thicker weight bar and heavier tripod make the DX's lower? Or do they not make a difference.
And what should the error be after PEC is applied?

Neilson




For the most part, these things are unrelated. It is not necessarily the magnitude of the PE that determines the need for tuning. More important is the shape of the PE and the amount of random error. HyperTuning's greatest benefit is in smoothing the curve and decreasing random error so that the mount can be easily guided. While some reduction in periodic error may accompany that, the only way to significantly reduce PE is to change the gears to higher precision gears since that is where the majority of the PE comes from.

The heavier counterwieght bar and tripod have nothing to do with PE at all. They might have some effect on random error, but not much.

PEC is problematic because the current programming cannot cover the error (which is large in some cases) that comes from the motor gearbox. In a system with very well behaved PE, mount indexing, and robust PEC programming, PE would ideally substantially reduces, if not eliminated, PE. However, this is not such a system, so the results of PEC can vary significantly. In addition, the use of PEC and guiding seems to often be problematic.


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neilson
professor emeritus


Reged: 08/22/10

Re: cgem or cgem dx? new [Re: EFT]
      #5523825 - 11/17/12 03:22 AM

Hi Ed,
Thank you for clearing that up for me.


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Stew57
Carpal Tunnel
*****

Reged: 05/03/09

Loc: Silsbee Texas
Re: cgem or cgem dx? new [Re: neilson]
      #5524075 - 11/17/12 10:21 AM

A real good sample will be in the 15 to 25 arc seconds. I think a median sample will be closer to 40 to 50 arc seconds. But like Ed said a 60 arc second PE that is easily guided is much better than a 15 arc second that can not. You will have to guided either one for AP anyway. keep your fingers crossed for some real updates coming sometime early next year.

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Tom Godsey
member


Reged: 02/17/12

Re: cgem or cgem dx? new [Re: EFT]
      #5532495 - 11/21/12 03:30 PM

Hi, I have a cgem-dx mount for my 132mm FLT refractor....its a great combination. last year was in the bigbend,tx and the winds kick up to about 45 mph that cgems-dx did not move.

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