Celestron CGEM Mount Review

Published on 06-02-2012 08:26 AM

http://www.adorama.com/images/large/CNCGEM.JPG

Features:

* CGEM Computerized Equatorial Mount
* Ultra sturdy 2" steel tripod with Accessory Tray
* 40,000 object database with 400 user-definable objects and expanded information on over 200 objects
* Proven NexStar computer control technology
* Flash upgradeable hand control software and motor control units for downloading product updates over the Internet
* New "All-star" Polar alignment uses any bright star for a quick and accurate Polar alignment
* Software Features include: Mount Calibration, Database Filter Limits, Hibernate, five Alignment Procedures, and user-defined slew limits
* Custom database lists of all the most famous deep-sky objects by name and catalog number; the most beautiful double, triple and quadruple stars; variable star; solar systems; objects and asterisms
* Permanent programmable periodic error correction (PEC) - corrects for periodic tracking errors inherent to all worm drives
* Flash upgradeable hand control software and motor control units for downloading product updates over the Internet
* Custom database lists of all the most famous deep-sky objects by name and catalog number; the most beautiful double, triple and quadruple stars; variable star; solar systems; objects and asterisms
* Steel worm gear and 90mm pitch diameter brass worm wheel
* Drive Motors - Low Cog DC Servo motor with integrated optical encoders offer smooth, quiet operation and long life. The motor armatures are skewed to minimize cogging which is required fro low speed tracking.
* Internal Cable wiring for trouble-free setup and transportation
* Designated six-pin RJ-12 modular jack, ST-4 compatible guide port
* Double line, 16-character Liquid Crystal Display Hand Control with backlit LED buttons for easy operation of goto features
* Autoguide port and auxiliary ports located on the electronic pier for long exposure astrophotography
* RS-232 communication port on hand control to control the telescope via a personal computer
* Includes NexRemote telescope control software, for advanced control of your telescope via computer
* GPS-compatible with optional CN16 GPS Accessory

Review-

I ordered this mount for use with a Celestron C6-RGT 6" refractor, after reading numerous positive reviews for the C6-RGT + CG-5 package, all of which raved about the quality of the C6-RGT refractor but complained that the included CG-5 mount was insufficient for the size and weight of the C6-RGT. Based on reviews and specifications, I believed the CGEM would offer the stability necessary for both astrophotography and observation with the C6-RGT, but was much more affordable than the CGE or many of the Losmandy or Vixen mounts. I subsequently purchased the CGEM and this is the subsequent review.

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First impression-

Before even taking it out of the boxes; "Holy smokes, this thing is heavy!"

Packaging-

The mount came packaged in 2 boxes, with the tripod and a single 17lbs counter weight in one box, and the computerized goto and controls in a second box. I'd put each box at around 45lbs. Celestron did a very nice job of packing, and everything was protected very nicely in thick form fitting Styrofoam packaging. The cardboard used was also quite thick. It would take some serious mishandling during shipping to cause any damage to the mount.

Build Quality-

The legs of the mount are quite substantial and weigh enough to almost feel solid, even though you know they aren't. The latches for release of the lower legs are metal rather than plastic as I expected, and the entire tripod oozes quality. Once the accessory tray is in place and tightened down so all legs are braced, this mount feels like it's bolted in place. Very stable!

The goto mount head feels like it is made of cast iron and has a very solid quality feel to it. Everything on this mount is metal, including the declination/ascension locks. Only the dovetail and latitude knobs are plastic, and they are thick heavy gauge textured plastic that almost passes for metal. Dec/Asc movement is tight and precise and the machining tolerances are very impressive.

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Weight of the complete unit is substantial and may be a + or - depending on what you are after. The complete mount with a single counter weight weighs in at 75lbs and as you can see in the photos, the size is substantial. This is a plus for me, as a 6" refractor is no shrinking violet in size and requires a substantial mount for optimum vibration damping. This thing feels like a truck and has great stability. If portability is your primary objective, this likely is not the mount for you, but for astrophotography or just rock solid observation, this mount should serve very well.

Setup-

Tripod setup could not be easier. It literally takes more effort to remove the tripod from the box than it does to get it setup. Setup of the entire unit was very straight forward and only took about 15 minutes, including unpacking everything. I took a quick peek at the instructions just to familiarize myself, but honestly if they forgot to ship the instructions, you could easily set the full mount up without them. It's very self explanatory and very easy to assemble. The goto mount head also has a built in level, so finding level when extending the tripod legs is a breeze as well.

Motor noise-

The mount has 9 speed settings (1 is slowest, 9 is fastest), and the servo motors on the unit are surprisingly quiet. They were completely inaudible until the 6th setting and then were only whisper audible. Starting with setting 7 the motors became clearly audible and by 9 they were equivalent to say a quiet 9 volt drill on low speed settings. Not at all obnoxious nor anywhere near loud enough to disturb the neighbors during a late night outing, but loud enough you know it's working. So at tracking speeds the motors are completely inaudible and the only time they exhibit sound will be during slewing.

Goto accuracy-

Rather than picking stars for you to align on, the CGEM lets you pick your bright star for alignment, which makes it much more convenient to align. If Polaris is obscured by LP or haze, you can pick another bright star from the list you're familiar with, and there are quite a number of bright stars in the list of alignment stars. Alignment on average takes 5 minutes or less and was very easy and straight forward.

The CGEM uses a minimum 2 bright stars for alignment, but recommends at least 3 for better accuracy and will do up to 4 for greatest accuracy. I only did 3 star alignments and found it very accurate once aligned. Simply point the telescope roughly north and then pick your first bright star, and the CGEM automatically slews to within 1.5 degrees of that star before even being aligned, and after a 3 star alignment, always landed targets in the FOV and usually dead center in the FOV. The CGEM is forgiving but as with most things, you get out what you put in. If you take a moment with each alignment and move in to a high power EP and center with that, rather than just centering in a low magnification wide angle EP, you will have better accuracy later when slewing to a new target. Even with rough alignments simply centering in a wide angle EP, accuracy after alignment was still very good.

Tracking accuracy I found to be stellar. (Pun intended). Once the CGEM has a target in it's sights, it holds it there, period. I was viewing in 3 degree Fahrenheit temperatures and left the mount targeted on the Orion Nebulae while I went and ate some dinner. I came back 35 minutes later and found the scope and mount completely covered in frost, but when I peeked through the EP, Orion was still smack dead center of the FOV.

I also found the motor to be completely noiseless during tracking. The only way you know it's working is your target stays centered. Overall I would rate goto accuracy both in finding, and tracking targets as excellent.

Ease of use-

The controller is fairly straight forward and walks you through everything once you start the mount up. Upon first starting the mount, it will run you through setting up the latitude and longitude and time. If you don't have either the GPS accessory for the mount, or your own GPS to get your coordinates, the CGEM has a list of cities already programmed in that you can choose from that you are close to, and will use those coordinates. I didn't try using a pre-programmed city so I can't say how that would affect accuracy, but I can only assume the more accurate the coordinates you put in, the better accuracy of the goto later. Once you've got your coordinates and time entered, it's on to alignment.

The controller layout is pretty good, with my only complaint being that the up/down commands for scrolling through the menu are on 2 of the number keys. That caused me fits a couple of times when out of natural tendency I went to the up/down arrows on the controller to move up/down through the menu. Those move the telescope rather than scrolling through the menu though, so that took some getting used to. Overall the layout was okay though and that single complaint is probably just a matter of acclimation to the controller. It's easy to use other than that, and easy to figure out. I hate reading instructions and it was intuitive and easy to figure out without having to read them.

The controller has hot keys for planets, stars, Messier objects, NGC objects and Caldwell objects and a tour mode that takes you through a variety of different objects (40,000 plus). It also has a list command, that lets you scroll through lists of those objects. That ended up being the saving grace for the one problem I did run into with the mount controller. When using the "Stars" command to locate stars, the controller asks for the left 3 digits of the SAO number for the particular star you are after. I could not in several tries get it to accept the SAO numbers for several different stars however, and the controller simply kept resetting the numbers after I entered them and would not recognize the SAO number and slew to the new star I was entering. I had to go into the "Lists" command, then "Named Stars" then scroll through the list until I found the desired star and enter it.

In searching the web, I found there is an issue with the original controller firmware that causes a problem with loading stars from the "Stars" command. I found updated firmware for the CGEM controller, that the notes state resolve the problem. The download and install were easy, with exception of the need for an RS-232 cable and adapter to hook the mount up to the computer to install the firmware. That brings me to my only real complaint about the CGEM, that being Celestron chose to use a 45 year old interface technology rather than the now standard USB interface. That seems to be a common issue with most mounts from all vendors though, not just Celestron, so I won't beat the CGEM up too much for that one. Note to telescope manufacturers though, get with the program on modern connectivity standards! I digress though, the point was the issue with the SAO numbers for stars not being recognized by the controller, and the firmware update did resolve the issue and the controller works perfectly now.

Stability-

I found the mount to be rock solid, with vibration being very minimal. I noted no vibration during observation unless I bumped the telescope, and when I did vibration was minimal and settled down almost immediately. Vibration during focusing was also very slight and again stopped almost immediately upon letting go of the focuser. Overall I found the mount to be very stable, despite the 40lbs long weight (nearly 4.5 feet) of the C6-RGT.

Final thoughts-

I think Celestron has hit the sweet spot with the CGEM mount, offering stability and performance of much more expensive mounts, without the substantial price increase. The goto accuracy is very good and tracking accuracy is excellent. Despite some niggles with the controller, it's also very easy to use. This is a high quality mount that should serve well for both viewing and astrophotography, and I'm sure I will be happy with it for years to come. Add in the peace of mind of Celestron's 2 year warranty and they have a winner on their hands.

Stability- 9
Build Quality - 9
Price - 9
Features- 8
Portability - 6
Ease of use - 8
Goto accuracy - 9
Tracking accuracy - 10

(Scale of 1-10, 10 being the best)

http://hphotos-snc3.fbcdn.net/hs048...._4370391_n.jpg
CGEM mount with C6 Refractor

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_{This article was originally published in forum thread:

Celestron CGEM Mount - Full Review
started by
Ghostryderflyby} _{View original post}

Categories:
Telescope Mount Reviews

24 Comments

admin - 06-02-2012, 08:31 AM
- Reply
test article comment

satcomsta - 06-08-2012, 05:56 PM
- Reply
Very insightful and detailed article. Lots of information and very clear. Thank you for such a refined first light!

CygnusX-1 - 08-05-2012, 10:33 PM
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do you think the dx is worth the extra $

Ghostryderflyby - 08-06-2012, 09:39 AM
- Reply
Originally Posted by CygnusX-1

do you think the dx is worth the extra $

For the 10lbs extra load capacity and more stable tripod, with the gear weight I have, I would say yes. I think the DX is probably a very good compromise between load, stability and price. You get 50lbs load capacity, great visual tracking, good with some tweaks AP tracking, and a rock solid tripod, without even getting close to the $5000 or better price tag for a CGE Pro or other higher end mounts. If the DX had been available when I bought my CGEM, I definitely would have gotten the CGEM DX rather than the plane jane CGEM.

I'd say it depends on your gear though. If you are running a 9.5" or smaller SCT, or a 120mm or smaller refractor, the plane jane CGEM would be more than adequate to the task. I have a 150mm refractor and it does well, but I'm definitely pushing the weight limit once I get all of my AP gear attached. Anything larger than a 150mm refractor or an 11" SCT, and you're asking too much from a plane jane CGEM. Even with an 11" SCT, if you start adding a bunch of AP gear you're probably asking too much from it, and a CGEM DX would be a better choice.

Hope that helps!

Clear skies!

Stew57 - 08-06-2012, 12:14 PM
- Reply
The internal differences are minimal. Just a motor control chip that allows more current to the servo motors(mot neccessarily a good thing though it does allow for swining a heavier load). The real differenc in the tripod and counter weight shaft. If you are going to pier mount don't bother with the DX, if you are going to set up portable and can handle the extra weight the DX is the way to go. Of course for a little more there is the.... you can little more yourself until you own the hubble.

Ghostryderflyby - 09-18-2012, 08:48 PM
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Well a sad update to this review, which dampens the experience and my score. At 2 years and 9 months old, and after maybe 20 outings, my CGEM has encountered a serious issue. I took it up to Bruneau for the Idaho Star Party last weekend, and upon setting it up to start my first night of observing, I found that I had no movement at the DEC axis. I could hear the click as the motor took out the backlash, but it did not have enough oomph to do anything more than that. I tried some trouble shooting out there, with a different hand controller from another CGEM, a different power cord, a different power supply etc, but no dice.

I called Celestron tech support today, and I'll give them a huge kudos for having U.S. tech support staff that are in and from the U.S. so you can understand them. The gentlemen I spoke with was also very friendly and knowledgeable. I told him the problem and he had me try a factory reset and try changing some backlash settings just to trouble shoot. When that didn't work, he confirmed that the DEC motor probably was tango uniform. He gave me the RMA information and said he was going to have them check both the DEC and RA motors, as well as the gear backlash while they had it.

While I'm sorely disappointed that the CGEM went kaput on me after only 2 years and 9 months of use, I'm at least impressed with the support staff for Celestron. Hopefully when I get the mount head back in 10 weeks (estimated turn around), I'm as impressed with the repair technicians. *crossing my fingers*

Based on my own experience with reliability with my CGEM, and some other reports I've heard of similar issues, particularly with the DEC motor and gears, I think I'd have to drop my overall score to a 6.9. It's still a great mount when it's working properly, but reliability is apparently an issue and that drags the score down significantly.

Stew57 - 09-18-2012, 10:06 PM
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Did they give you an idea of cost for the repair?

Ghostryderflyby - 09-19-2012, 09:18 AM
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Originally Posted by Stew57

Did they give you an idea of cost for the repair?

Unfortunately no. I asked about an estimate but they said they couldn't give one without knowing what is wrong and how in depth the repair will be. While I understand not wanting to give blind estimates, it does leave me with no idea at all what I'm looking at for repair cost.

DaltonSkyGazer - 09-19-2012, 09:25 AM
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Sorry to hear of the dec motor issue, do hope they get you back up at reasonable cost.

Star Rider - 10-20-2012, 01:47 PM
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Any up-dates on the repair? I seem to be having some issues when slewing the Dec Motor as well when on a low setting. I have to go up to at least #6 to make an adjustment, but it still trackes very well. What are your backlash settings (all of them)? I'm not sure I have them set correctly in my mount.

Dalton/Jeff - What are your mount settings for backlash?

Clear Skies,
Bob

Ghostryderflyby - 10-21-2012, 10:04 AM
- Reply
Originally Posted by Star Rider

Any up-dates on the repair? I seem to be having some issues when slewing the Dec Motor as well when on a low setting. I have to go up to at least #6 to make an adjustment, but it still trackes very well. What are your backlash settings (all of them)? I'm not sure I have them set correctly in my mount.

Dalton/Jeff - What are your mount settings for backlash?
Clear Skies,
Bob

The RA motor on the CGEM is actually fine, the gears for the RA axis just got bound up somehow. That is good news since that is substantially less expensive than a new RA motor. They are cleaning and re-greasing the gears, adjusting both axis, flashing the firmware for the mount and HC to the new version that just came out 2 weeks ago, then sending her back. It cost me $70 for shipping and another $130 for their service of it, but it's better than $1500 for a replacement mount since mine is out of warranty.

Can't remember what I had my backlash set at now. Since they will be flashing the firmware, I won't know what it was set at either. Sorry, not much help there. It wasn't too aggressive though. Bumped it up by maybe 2 or 3 settings on the RA axis if memory serves.

At least Vader (that's what I named my new 10" Dob) is keeping me observing in the interim. No AP for me for now, but at least I can still get some good visual observation in. I just hope it doesn't take Celestron the full 8 weeks they said it could be before they finish the service and ship it. I would like to get some AP in before it's -0f temps out!

laser314 - 10-28-2012, 08:39 AM
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Do you think this gear problem could be related to transporting the scope? My brother is about to buy a 9 1/2" on a SGEM and it will be pier mounted permanently .

Ghostryderflyby - 10-29-2012, 11:29 AM
- Reply
Originally Posted by laser314

Do you think this gear problem could be related to transporting the scope? My brother is about to buy a 9 1/2" on a SGEM and it will be pier mounted permanently .

I can't rule it out. I left the mount on the tripod, and the entire setup on my scopebuggy, and used load straps to secure the entire rig to the floor of my buddy's toy hauler to take it to the Idaho Star Party. It had worked fine the last outing at home 6 weeks prior or so to the trip, and wouldn't work on the first outing after transport, so it is a possibility.

In the past when I have transported it, I've taken it apart and laid it down on the bed in the toy hauler. This time I tried leaving it all intact (minus the OTA) on the scopebuggy since I had the room with no 4 wheelers in the toy hauler this time. I have considered that maybe leaving it upright for transport was the problem. I had the clutches locked, thinking that was better, but in hind sight the vibration with the clutches locked might have induced the problem. It might have been okay vertical on the scopebuggy if I'd unlocked the clutches.

At this point it's all conjecture, but I won't leave the mount head on the tripod if I haul it that way again. I'll at least remove it and lay it on the bed, as it has been fine several times after transporting it that way.

AlbertP - 10-29-2012, 03:29 PM
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Originally Posted by Ghostryderflyby

..... but in hind sight the vibration with the clutches locked might have induced the problem. It might have been okay vertical on the scopebuggy if I'd unlocked the clutches.
.

Yes, I am thinking that could very likely be the problem. I always try to remember (and sometimes forget) to unlock the clutches whenever I move my CGEM, even if it's across the yard. I am glad it didn't cost you an arm and a leg though, because, someday, all of us who own CGEMs, if we are lucky enough to wear out the worm gears through normal use, will need this service!

Ghostryderflyby - 10-30-2012, 11:31 AM
- Reply
Originally Posted by AlbertP

Yes, I am thinking that could very likely be the problem. I always try to remember (and sometimes forget) to unlock the clutches whenever I move my CGEM, even if it's across the yard. I am glad it didn't cost you an arm and a leg though, because, someday, all of us who own CGEMs, if we are lucky enough to wear out the worm gears through normal use, will need this service!

Considering it probably was my error by leaving the clutches locked while transporting it vertically in a travel trailer, I will kick my score back up too. The 6.9 overall was probably a bit knee jerk from frustration thinking the mount had failed me. Now that I think I probably failed the mount instead, I'll stick with most of my original scores. It has been a good mount aside from this issue. I would bring the tracking accuracy down to an 8 from the 10 I originally listed though. For visual observation the tracking is outstanding, definitely a 10, but AP tracking is a bit more troublesome so I can only give it an 8 for overall tracking.

AlbertP - 10-30-2012, 02:24 PM
- Reply
[QUOTE= I would bring the tracking accuracy down to an 8 from the 10 I originally listed though. For visual observation the tracking is outstanding, definitely a 10, but AP tracking is a bit more troublesome so I can only give it an 8 for overall tracking.[/QUOTE]

I have had a different experience with the AP tracking.. but then I looked at what you are running on the mount, and I am not surprised.

With the 80mm guidescope, rings, etc, along with the camera, you must be pushing something about 30 lbs total. When I was using my SW120 and the ST80, ADM dovetail rings, finder, cameras, etc, my total weight was a five lbs or so less than your total weight, and the CGEM tracked "ok" but not great. Switching to the Mini-50 Guider helped quite a bit, kept it about 20lbs, and now that my primary AP scope is the ED80T CF, I have dropped an additional 5 lbs or so, and the mount tracks beautifully. With a single-star drift alignment, it will keep a star within the small box on the dual-cross hair IR ep for between 25 and 30 minutes pretty consistently, using tracking alone. I don't know what this translates to in actual accuracy, but without the motors on, the star drifts through the box in a bit under two seconds. I think a lot of it might have to do with the length of the OTA, and not just the weight. I am positive that if I put your yard-canon on my CGEM, along with the AP stuff, that I would have results similar to yours!

hrgreen - 12-14-2012, 11:05 AM
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I was on the verge of buying a LX200ACF, but after reading more, it seems that if I want to do AP down the road and care about warranty and service, I might do better to get a CGEM 800 HD. It seems a little worrisome from owner comments that the GOTO mounts of both competitors might not be too reliable over the long term. Should the standard CGEM (all the weight I want to heft) be able to handle an autoguider and camera with the 8" OTA?

AlbertP - 12-14-2012, 05:01 PM
- Reply
Originally Posted by hrgreen

I was on the verge of buying a LX200ACF, but after reading more, it seems that if I want to do AP down the road and care about warranty and service, I might do better to get a CGEM 800 HD. It seems a little worrisome from owner comments that the GOTO mounts of both competitors might not be too reliable over the long term. Should the standard CGEM (all the weight I want to heft) be able to handle an autoguider and camera with the 8" OTA?

If you mean the 8" Orion Astrograph (about 17 lbs), yes, if you utilize something like the Mini-50 Autoguider and a camera which doesn't weigh a ton . That would put you somewhere around 25 lbs with adapters, coma-corrector, doodads and whatever, which, from my experience, works well, if a bit finicky on balancing, for long-exposure AP. The 8" is fairly short (compared to my 120mm refractor), so that should help, as well.

hrgreen - 12-15-2012, 08:18 AM
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No, I meant the complete CGEM 800 HD. That OTA is specified as 14 lb.

I did decide to order one yesterday, and just hope it's not made on a Monday or a Friday. It'll take me awhile to get up to speed on it, but will report what success I have.

AlbertP - 12-15-2012, 03:13 PM
- Reply
Originally Posted by hrgreen

No, I meant the complete CGEM 800 HD. That OTA is specified as 14 lb.

I did decide to order one yesterday, and just hope it's not made on a Monday or a Friday. It'll take me awhile to get up to speed on it, but will report what success I have.

\

That should work just dandy! Please give us a first light report.. and congratulations!!