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Equipment Discussions >> Mounts

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rmollise
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Reged: 07/06/07

Re: CGEM vs CGEM DX new [Re: Stew57]
      #6145738 - 10/18/13 10:28 PM

Quote:

I have watched NSN and asked around and have found very few. I have tried my self with a couple of CGEMs. 2 min unguided at long FL is a dream for a CGEM. Video is forgiving but not that forgiving. If you have some raw screen shots I would love to see them.




Our experiences differ. Anyhow, the CGEM's unguided performance is very comparable to the other mounts in its price range AND to those in the tier above including the G11.


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dragonslayer1
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Reged: 02/25/12

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Re: CGEM vs CGEM DX new [Re: rmollise]
      #6145778 - 10/18/13 10:50 PM

Thank you Rod, and you are probably already aware of them possibly addressing the 8/3, but I have a question on it posted on Team Celestron Misc web page... I seems that the 8/3 is maybe hit and miss or real mild and a few can be real severe,,, guess is the luck of the draw,,,,,I guess if you get a bad one cn always exchange it,,,
Thank you, Kasey


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Stew57
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Re: CGEM vs CGEM DX new [Re: rmollise]
      #6145785 - 10/18/13 10:54 PM

Raw PE of the competing mounts are all similar which would be the limiting factor in uunguided use. To reduce this inherent problem PEC is used. The 8/3 error in the CGEM/DX, depending upon the severity of the error, makes the PEC on the CGEM work less optimally than the others, Iin fact in some cases depending on the PE curve and 8/3 error, PEC can make things worse. When unguided quality PEC is invaluable, and may not be working on a lot of CGEMs. None of this matters for guiding.

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orlyandico
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Re: CGEM vs CGEM DX new [Re: Stew57]
      #6145949 - 10/19/13 01:00 AM

I'm not sure if a large 8/3 is considered grounds for return. I had similar PM's with Derik, he said that the 8/3 is under 8" p-p for most people (but for me it was over 20" p-p) and that only 1% of imagers needed that performance. Same story as Mark.

If you can buy the CGEM or DX at a local store, and be able to return it if you get one with huge 8/3 (spare yourself the shipping headaches) then I'd say it's worth the risk.

Otherwise, the Atlas is a safer bet. As Rod points out, all of these mounts have comparable periodic error. The difference is, the 8/3 can't be corrected by PEC, so long-duration unguided is out. An Atlas with a good PEC training should be able to get under 5" corrected. Very few CGEM's would be able to achieve that (even Derik's best case of 8" of 8/3 means you can't get less than 8" after PEC).


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dragonslayer1
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Reged: 02/25/12

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Re: CGEM vs CGEM DX new [Re: orlyandico]
      #6146160 - 10/19/13 07:57 AM

Man oh man, decisions, things to digest, ponder weight capabilities, craving 2 minute unguided (I like the Alt/AZ of Atlas and CGEM & DX).. It seems from what I could gather that the servo motors seem like would be better just for normal viewing, tracking, not considering guiding into the formula. I gather that they have a constant source of "power" applied to the motors?? But yet Atlas always seems to get good reviews... I just wish it was rated for more weight (6lb), alt/az could almost be a c-6,,, I know Celestron has excellent customer service, how is Orion? Then have 1 year warranty vs 2 year.. And Celestron just seems to be trying new things, Kasey

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Mike X.
scholastic sledgehammer


Reged: 06/28/10

Loc: Greece-Athens and Rome-Italy
Re: CGEM vs CGEM DX new [Re: dragonslayer1]
      #6146196 - 10/19/13 08:26 AM

If it is of help i was on the same dilemma you are now, i waited as long as i could for a solution for the CGEM...and i finally found it on the new AZEQ6...I never looked back and i'm really happy with the results.
PS: I do guided immaging , and i have far better results than the CG5 CG5 even with guiding.
In the past i used to do unguided 1 minute exposures at 945mm and 1500mm with the CG5)
Here is an example with the cg5 at 1500mm unguided


I can't immagine why the Atlas or the Atlas AZ can'd do any better,specially at lower focal lenghts.

Edited by Mike X. (10/19/13 08:39 AM)


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rmollise
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Re: CGEM vs CGEM DX new [Re: dragonslayer1]
      #6146217 - 10/19/13 08:40 AM

Quote:

Thank you Rod, and you are probably already aware of them possibly addressing the 8/3, but I have a question on it posted on Team Celestron Misc web page... I seems that the 8/3 is maybe hit and miss or real mild and a few can be real severe,,, guess is the luck of the draw,,,,,I guess if you get a bad one cn always exchange it,,,
Thank you, Kasey




I would spend exactly zero time worrying about "8/3," especially if I were doing video.


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Mike X.
scholastic sledgehammer


Reged: 06/28/10

Loc: Greece-Athens and Rome-Italy
Re: CGEM vs CGEM DX new [Re: rmollise]
      #6146220 - 10/19/13 08:46 AM

Video?!? Wow sorry i must have missread, i agree with Rod,no need to worry about that then, choose the mount you like most

Edited by Mike X. (10/19/13 08:46 AM)


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Phil Cowell
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Re: CGEM vs CGEM DX new [Re: Stew57]
      #6146258 - 10/19/13 09:14 AM

Quote:

The G11 is in another class.




And another complete class of issues. Research well before you drop your coin on one.

Phil


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dragonslayer1
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Reged: 02/25/12

Loc: SLC, UT
Re: CGEM vs CGEM DX new [Re: Phil Cowell]
      #6146285 - 10/19/13 09:40 AM

Thank you all, yes am seeing the G-11 is another class/world it seems. Nice pic Mike; yes am doing video now but started out DSLR on a 4SE/ then CPC9.25/ then some minor CCD,,, I would like to try some more down the road, just at this time my time is limited somewhat and video offers the best option for viewing under time constraints, (even if not under constraints is a real gas), Kasey,,

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dragonslayer1
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Re: CGEM vs CGEM DX new [Re: dragonslayer1]
      #6146290 - 10/19/13 09:41 AM

PS now am using C9.25 on CG-5; this is to be travel mount,
Kasey


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Stew57
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Re: CGEM vs CGEM DX new [Re: dragonslayer1]
      #6146326 - 10/19/13 10:10 AM

It is true that in the past those doing astrovideo had lower expectations. It seems that they are becoming more demanding. The chip does not care if it is in a dedicated ccd camera or a video camera. The error is the same.

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Raginar
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Re: CGEM vs CGEM DX new [Re: Stew57]
      #6146363 - 10/19/13 10:30 AM

The G11 is just fine. It probably has as many issues from people tinkering with it as legitimate problems. Somewhat similar to a CGEM. The new G11s certainly don't have the work gear issues like the old ones. There was a bad batch in 2012.

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rmollise
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Re: CGEM vs CGEM DX new [Re: Stew57]
      #6146699 - 10/19/13 01:21 PM

Quote:

It is true that in the past those doing astrovideo had lower expectations. It seems that they are becoming more demanding. The chip does not care if it is in a dedicated ccd camera or a video camera. The error is the same.




Most video users are still not doing long exposures, however--it's not necessary--and most CGEM users have had better luck with their mounts than you have. I'm sorry you have had trouble, but, frankly, you experience is not typical.


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Stew57
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Re: CGEM vs CGEM DX new [Re: dragonslayer1]
      #6146902 - 10/19/13 03:29 PM

The servos in the CGEM and DX are pulse driven. They are operated like steppers that use encoders rather than count steps. The advantage you list for servos does not exist for the CGEM\DX.

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dragonslayer1
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Re: CGEM vs CGEM DX new [Re: Stew57]
      #6146919 - 10/19/13 03:40 PM

OK, so trying to see if I understand this right, if they were "servo" driven, there would not be a pulse but more like a potentiometer or reostat controlling a steady source of voltage or current?? The "encoders" would have to be changed to run them like servos rather thanpulse driven?? Am I even close to getting it??? , Kasey

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Stew57
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Re: CGEM vs CGEM DX new [Re: dragonslayer1]
      #6147059 - 10/19/13 05:08 PM

If you are polar aligned only the RA would be driven. There would be a constant current only varied as the encoder relied being ahead or behind the correct position. The servos in the CGEM are given pulses of curret that drive the RA. There is nothing wrong being pulse driven. Servos being better than high resolution steppers is a red herring in my opinion.

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orlyandico
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Re: CGEM vs CGEM DX new [Re: Stew57]
      #6147657 - 10/19/13 11:43 PM

No, no, no.. all servo motors are driven using PWM (pulse wide modulation). Nobody drives servos with constant current, it would be too inefficient.

Servos still have advantages over steppers - more torque at low speeds (no need to micro-step) and a larger dynamic range, i.e. they can run at both low speeds and high speeds very well. With steppers you have to decide whether you want very fine low-speed performance (in which case the maximum speed is compromised).

That said, a not-so-good servo implementation results in... cogging.

Kasey, you are over-analyzing this. As Rod has said, there isn't much difference between all the mounts in this class. And your concern about the Atlas having 6lb less capacity? that's irrelevant. The weight ratings Celestron and Orion throw out are optimistic anyway. I would go with the Atlas, for reasons already previously stated.


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A. Viegas
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Re: CGEM vs CGEM DX new [Re: dragonslayer1]
      #6147986 - 10/20/13 08:23 AM

Kasey-

So early this morning I tried using my C8 on the CGEM with my Mallincam Extreme and I did not guide. Conclusion is you can probably get 60s - 90s without too much trouble if you bother to decently polar align. My PEC training apparently sucks because it messed up a few of the pics, so maybe if you are not a total doob like me and you can figure out PEC maybe that gets to about 2mins?

For my test run I ran the following:

CGEM with 1 17# and 1 11# counterweight
C8 with C80ED refractor piggybacked + 50mm finder +MCX and Orion SSPIAG guider. So probably 27 # I am guessing total weight.

There was a full moon and I did not use any filters. For the Mallincam I used ONLY the MFR3 rear element which according to my astro-aid APP and Astrometry.net is basically F8 so ~1600mm FL - a decent test I think.

Ok here are the images. Easy one first

M42 - MCX in CCD Mode (NO AGC) - C8 @ F8 --35 seconds

[image]http://www.cloudynights.com/photopost/showphoto.php?photo=28474&password=&sort=7&thecat=500[/image]


M42 - MCX in CCD Mode (NO AGC) - C8 @ F8 --50 seconds

[image]http://www.cloudynights.com/photopost/showphoto.php?photo=28473&password=&sort=7&thecat=500[/image]

NGC1514 - MCX in CCD Mode (NO AGC) - C8 @ F8 --90 seconds

[image]http://www.cloudynights.com/photopost/showphoto.php?photo=28472&password=&sort=7&thecat=500[/image]

-Note this last one was close to the moon and i found out later a leaf had fallen on the corrector making that mark in the upper right corner.

As you can see at 90 seconds I was starting to get trailing.

--Hope this helps

Al


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Stew57
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Re: CGEM vs CGEM DX new [Re: orlyandico]
      #6148050 - 10/20/13 09:17 AM

I stand corrected. Thanks
There is one advantage to a stepper often over looked. When overloaded a stepper will just sit and try and step with no ill efects. The servor will draw more current until something spills it's magic blue smoke, unless there is some type of overload protection built in the circuit.


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