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CGEM vs CGEM DX

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#1 dragonslayer1

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Posted 13 October 2013 - 09:12 PM

I have seen where some post or say they have cogging and trackibng issues?? I have also heard that the issues have been addressed in the new mounts being made now? Then have heard that the difference in the motors/gears between the two has the DX with a slight advantage? Any input from users, and regrets over purchase, or thrilled at purchase?? :question: Thank you, Kasey

#2 Stew57

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Posted 13 October 2013 - 09:30 PM

No difference in motors or gears. They both are subject to the cogging effect and 8\3 error equally as these are problems with the servos. Celestron has some beta software working on a fix for the cogging. Not all mounts suffer to a significant degree with either problem.

I have a CGEM. Mine exhits no cogging problem but significant 8\3 error. This error makes PEC useless and guiding at long FL problematic. The software is fantastic. Great pointing accuracy and an easy and accurate ASPA bonus. The price is good also. That said I wish I had spent more on the mount and got something better. I have my hopes on a EQ8 if\when they are released, provided I can get my finances back in shape.

#3 johnd39818

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Posted 15 October 2013 - 12:43 AM

Ive owned my DX for 3 months now with no issues at all. Able to run 10 min subs flawlessly and GOTO's are dead on.

#4 dragonslayer1

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Posted 15 October 2013 - 09:30 AM

Thank you Mark and John,
Thats what am looking to do right now for a while, is run unguided with video cam for about 2 minutes, from things have read and your 10 min (guided subs) sounds pretty good. Am using a 9.25 (deforked) right now on a CG-5. Mark, I checked on that EQ-5, pre-order is about 5K I think. Thats a big step up from 2K for CGEM-DX :bawling:.. I found something on a sale sight that compared the CGEM vs DX and it said there was an upgrade in the motors or something, I will try to find it. Dis you ever consider the Losmandy G-11? Thank you both for your time input and hepl, Kasey

#5 Stew57

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Posted 15 October 2013 - 12:10 PM

I can't see doing 2 min unguided even with a videocam at all. Even with shorter focal lengths the PE is going to be too great. Less than 20 arcseconds is good for a CGEM. PEC won't takeout the 8\3 error, and will in fact make it worse in some areas . A small guider (I use a 50mm finder as guidescope) will sufice for video.

I would be hesitant to buy from someone that advertises different motors or gears in the DX. There was a different MC board for awhile though. It allowed more current flow to the servos. Join teamcelestron and inquire there, or email celestron directly. You may get to discuss with an engineer.

#6 dragonslayer1

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Posted 15 October 2013 - 02:45 PM

Thank you again Mark,
I had seen somewhere that the DX drives the motors a little smoother and better than the CGEM, but that may have been before motor board upgrade. How long have you gone unguided with yours? I have a SSAG set-up from when I had it mounted on the CPC., is all mounted ready to go for over a week now on my CG-5 but as normal the weather has been the pits,,,. I just didn't think most video guys were guiding, I'm VSS+ so am 2 minute max exposures. I have been signed up on Team Celestron for a little while now and have researched the cogging. From all I can get they speak of an upgrade (31.15/31.33) that resolved it?? I cannot find anything about 8/3 error tho. :question:

I did find something interesting tho, the ability to do a tandem mount (like the EQ-45?)? You ever tried tt? ""Tandem support (the ability to turn the Dec axis 90 degrees and mount multiple optical tubes side-by-side) is now available for firmware versions GEM 4.15 and higher for Celestron’s German equatorial mounts."" Thank you again,
Kasey

#7 dmdouglass

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Posted 15 October 2013 - 06:15 PM

Tandem mount...
Yup !! And it works too.

See images at: http://www.az-dahut.net/

[ Or, just look to the left at my avatar... ]

That is my backyard observatory.

Edit (Add): Of course, you do need an accessory from ADM for the "side-by-side" mounting...
http://admaccessorie..._Series_SBS.htm

#8 A. Viegas

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Posted 15 October 2013 - 09:45 PM

CGEM vs. CGEM DX is really a matter of cost and basically $500 when all is said and one, whether you buy new or used... What do you get for the extra $. Basically a better tripod, beefier counterweight bar and i suppose it's debatable if the motor control,board is better in th CGEM DX or not...

For a 9.25" the difference between CGEM or DX is probabl not worth $500... A 11" probably give the edge to the DX, I think 70% I would go with DX with 11"... A 8" is probably 70% better value on the plain CGEM and your 9.25" is more like 50/50 in terms of value proposition to the DX...

If you are planning to really upgrade in 3-5 yrs to an AP or Paramount, then I would say just get the CGEM and with resale value you probably do on... If on the other hand this next mount is close to your final mount purchase, then I would get the DX.

If you plan to guide, then the CGEM + DX are mostly comparable up to 2 mins... Given the savings I would say go for he CGEM ... I chose the CGEM because I bot it at NEAF, got a great deal and best of all saved enough,to buy more gear... I use it with my 8" and C80ED piggybacked...

Al

#9 Stargazer78

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Posted 16 October 2013 - 12:25 AM

You will not be disappointed if you go with the DX. That being said it is a heavy mount but I purchased mine as a final mount. I plan on getting a 10 inch R/C and call it done for my asyrophotography hobby. I have not experienced any issues at all with mine. For the extra payload capacity it a great deal.

#10 dragonslayer1

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Posted 16 October 2013 - 09:19 AM

Thank you all, and yes Al this should be the final mount for me; if I ever upgrade to C11 or the R/C Chris is using, I just want something that can handle it and not worry about weight issues. So would probably be the DX.. I don't figure on any pictures I take gracing the walls at NASA, but would like fairly good quality,,, would be nice to be able to unguided fro a couple minutes...
The Atlas gets good reviews but is only rated to 44 lbs,,, and new handset has ASPA.
I did copy and post a coment on Team Celestron site referencing the Cogging and 8/3 issue
""I can't find anything on the 8/3 anywhere. I own a CPC & CG-5 ASGT. I am looking for a larger mount and asking about the CGEM or DX series. I have seen this more than once but will post a copy of a post concerning the issue, this is the answer I got when asked about the 8/3 issue...
""It's a repeatable non correctable by PEC tracking error caused by the gears from what i understand.
That plus the motor cogging issue made me avoid the CGEM series (including the DX)even if i like them a lot as mounts.
If you give a look on the CGEM yahoogroup you will find a lot of information regarding both issues. ""

Will see what they say, and I knew Stargazer was sold on his DX :jump:,
Kasey

#11 A. Viegas

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Posted 16 October 2013 - 09:29 AM

Kasey

One last bit of advice. If you can wait 6 to 12 months then wait. I suspect celestron will be unveiling a newer CGEM/DX that uses the motor technology of the VX soon. That newer mount probably does not have the 8/3 or cogging risks. Moreover I would not be surprised for a hybrid like alt-az/GEM like the new EQ8. So if you can hold out I would say wait a bit for the new upgrade.

If however you come across a good deal on the used market for a CGEM it may be worth it to upgrade. You can probably go Cgem for a net $500 after you sell your Cg5. So if you really want to jump to a bigger mount now then swap to he CgEM for $500 or so (used) and that probably works for you with the mallincam for the next couple of years. By then the newer celestron mounts will be fully vetted

Al

#12 fetoma

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Posted 16 October 2013 - 11:17 AM

I suspect celestron will be unveiling a newer CGEM/DX that uses the motor technology of the VX soon. That newer mount probably does not have the 8/3 or cogging risks.


Al,

Where did you hear this information and is it from a reliable source?

#13 Steve Cobb

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Posted 16 October 2013 - 01:00 PM

I've got the CGEM-DX and have had some trouble balancing the load and getting regular steady slewing -- there are pauses, noises, even failures to perform the slew. Usually it is okay but nothing's easy with this mount. Sorry to be so ignorant but what is a cogging or 8/3 problem or error?

#14 orlyandico

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Posted 16 October 2013 - 01:11 PM

Cogging - the DEC doesn't respond to small autoguiding corrections, then when the DEC pulses get large enough it jumps. This causes a sawtooth pattern in the DEC guiding graph. The cogging is caused by the cheap Igarashi motor whose armature doesn't have a cogless or reduced-cogging design.

8/3 - it is an irrational periodic error that occurs 8/3 = 2.6666.. times every worm cycle. Because it is irrational, it cannot be corrected with PEC. On some CGEMs and DXs the 8/3 is small, but on others such as the one I had (and Mark's/stew57's) it is huge. On mine it was over 20". With 20" of uncorrectable periodic error happening every 180 seconds, this means you are limited to about 30 seconds unguided with a short focal length (i.e. 400mm range).

Forget about Mallincam with a long-FL SCT as well, as Mark has discovered.

The 8/3 is caused by a harmonic in the cheap Igarashi gearbox used on both the CGEM and DX.

Bottom line, if you're lucky you'll get a decent CGEM or DX that doesn't exhibit cogging or 8/3. If you're unlucky you'll get both, and you'll get something that will bedevil the rest of your days with the mount. One big downside of buying used, is that the seller might be getting rid of it precisely because they're aware of these issues.

I sold my CGEM at a huge loss and I'm glad that boat anchor is gone. I sunk a lot of money and effort into it (Aeroquest high-precision RA worm, ADM dual saddle, replacement high-precision RA worm bearings, hypertuning, etc. etc.) but at the end of the day lipstick on a pig doesn't make it any less of a pig.

In fairness my CGEM pointed very accurately and was a dream to use for visual.

If I were the OP and I had $1500 or so to spend, I'd sit and wait for a used CGE to pop up. Made in the USA, Pittman Lo-Cog motors, same software as the CGEM, etc. etc. It is everything the CGEM and CGEM DX are not.

#15 fetoma

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Posted 17 October 2013 - 11:16 AM

If I were the OP and I had $1500 or so to spend, I'd sit and wait for a used CGE to pop up. Made in the USA, Pittman Lo-Cog motors, same software as the CGEM, etc. etc. It is everything the CGEM and CGEM DX are not.


+1

#16 dragonslayer1

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Posted 17 October 2013 - 12:10 PM

is that the mount that was made by Losmandy before he left? I had heard he made some mounts for celestron, Kasey

#17 fetoma

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Posted 17 October 2013 - 01:13 PM

Yes, it was the CI-700 I believe.

#18 Jason B

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Posted 17 October 2013 - 01:30 PM

All I can say is that we have 3 CGEM/CGEM DX's in our astrophoto group/club and all have worked great for guided long exposure imaging (in focal lengths from 420mm to 2000mm). All are 3 years old or newer.

#19 DaveJ

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Posted 17 October 2013 - 02:34 PM

Yes, it was the CI-700 I believe.


Negative. Losmandy made the original G-11 for Celestron. It was branded "Celestron by Losmandy." I know this because I purchased a CG-11 the first year they became available in September 1992. The CI-700 was Celestron's attempt to duplicate the Losmandy-made G-11 after they (Celestron) decided not to pay for the G-11s any more. Losmandy never "left Celestron" since he didn't work there, Celestron contracted "Hollywood General Machine" to build the G-11 for them. Losmandy's big (now discontinued) GEM was named the "HGM" for Hollywood General Machine.

#20 DaveJ

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Posted 17 October 2013 - 02:59 PM

Losmandy made the original G-11 for Celestron.


It took me a couple minutes, but I found a photo of my 1992 Made-for-Celestron-by-Losmandy G-11

Attached Files



#21 A. Viegas

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Posted 17 October 2013 - 05:27 PM

Hi Frank,


I am purely making a guess in my prediction that Celestron will incorporate the VX gear technology in its next version of CGEM/CGEM DX. I base my prediction on two facts.

1. At NEAF I spoke with Celestron people and I specifically commented on the gap between the VX and CGE-PRO and the issues with the CGEM. I asked them point-blank if they were going to upgrade the CGEM/DX and he said they were working on it. I was buying a CGEM at NEAF so I wanted to know the upgrade cycle. My understanding from the conversation was it 2014/15 at the latest.

2. Given the recent introduction of the EQ8 and Synta's involvement there, it seems logical to expect an entry in the Celestron line-up that will incorporate the concept of dual GEM/Alt-Az like the failed LX-80 and the new Ioptron dual GEM/Alt Az.

Nevertheless, I went ahead and got the CGEM and sold my CG5, because frankly I could not wait. But heck... we are probably 6 months closer now... So if I were in the OP shoes now, I would wait.

Al

#22 bogg

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Posted 17 October 2013 - 05:50 PM

CGEM vs. CGEM DX is really a matter of cost and basically $500 when all is said and one, whether you buy new or used... What do you get for the extra $. Basically a better tripod, beefier counterweight bar and i suppose it's debatable if the motor control,board is better in th CGEM DX or not...

For a 9.25" the difference between CGEM or DX is probabl not worth $500... A 11" probably give the edge to the DX, I think 70% I would go with DX with 11"... A 8" is probably 70% better value on the plain CGEM and your 9.25" is more like 50/50 in terms of value proposition to the DX...

If you are planning to really upgrade in 3-5 yrs to an AP or Paramount, then I would say just get the CGEM and with resale value you probably do on... If on the other hand this next mount is close to your final mount purchase, then I would get the DX.

If you plan to guide, then the CGEM + DX are mostly comparable up to 2 mins... Given the savings I would say go for he CGEM ... I chose the CGEM because I bot it at NEAF, got a great deal and best of all saved enough,to buy more gear... I use it with my 8" and C80ED piggybacked...

Al


I was talking to a Celestron rep at ASTROCATS in Oakville earlier this year. I was asking what the difference was in the two mounts as I was thinking of putting it on a pier mount. The answer I got was I would be better off with the CGEM mount over the DX as on the pier it would have the same performance, including instrument weight as the DX. It really appears the only differences are the counterweight bar, the beefier tripod, and the mount connection between the head and the tripod. Mostly cosmetic. for some the better tripod would be worth it.

#23 dragonslayer1

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Posted 17 October 2013 - 09:13 PM

Hey All, great news from Team Celestron,, I asked about cogging and 8/3 and heres the answer
""The so called "cogging" issue has been corrected in firmware. The public beta has been available for months. I haven't made that public yet becaue I had some checking I needed to do. But that should be done this week. And then I am going public with it.
As for the 8/3 term, as you said, it would require a new gear box like the one we have in the AVX. This might require changing the motor control board as well.""

I just replied back about possibly installing them myself if I ran into the 8/3 so will see. I asked about the cost for one to do it..... and did let him know that many LOVE their mounts and have no problems :jump:
Also Al, they do have the ability to dual mount, there is one that did it on this thread with pictures, and its in the knowledge base also,
Kasey

#24 dragonslayer1

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Posted 17 October 2013 - 09:19 PM

A side note, I have my tri-pod from my CPC after I de-forked it.. I wish was a way to put like a pier mount on it... I am pretty sure is the same as the CPC 11 tri-pod. I am sure it could handle the weight easy, its pretty stout, Kasey

#25 orlyandico

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Posted 17 October 2013 - 10:06 PM

You should be able to reuse the CPC tripod, with some machining. But the CGEM and DX are only sold with tripods, you don't save any money that way. But really why not the tried-and-true Atlas, which has no 8/3.






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