Celestron CGEM Review- Part 1

This is the first of a series of reviews planned for my new Celestron CGEM mount. I had my eye on the CGEM ever since it was first announced by Celestron. Some of the attractive features were its payload, Permanent Periodic Error Correction (PEC), new All-star polar alignment, and its ability to track well past the meridian before the scope needed to be flipped. I received the CGEM on Monday of this week (9/14/09) and had it fully assembled within an hour. Part 1 of this series is my review of the ordering process through the final assembly. I hope you find my CGEM review useful! Please feel free to add comments or questions at the bottom of the page (“Leave a Reply” section). Note that registration is not necessary to leave a comment.

Ordering the CGEM

I bought my CGEM through a long-time favorite dealer- Orion Telescopes and Binoculars. This is where I bought my first serious telescope about 20 years ago! Although they have their own line of telescopes and equipment, they also sell many Celestron products including the CGEM. I chose the 9.25″ SCT version due to its popularity as a great optical platform for planetary imaging.

The entire ordering process was a breeze. I found that their system was quite sophisticated and I was comfortable making such a large purchase online. Here is the telescope I ordered: Celestron CGEM-925 Computerized 9.25″ Cassegrain Telescope.

Receiving the CGEM

CGEM Review- Telescope CartonsI had been tracking the shipping and delivery status through my account on Orion’s website. The packages were delivered on they day that they specified. There were five boxes total. One each for the optical tube, CGEM, tripod, extra counterweight, and the AC adapter. Note that if you are going to buy the CGEM, the AC adapter is optional. It only comes with the 12-volt adapter. You can purchase the adapter from Amazon quite reasonably though: CGEM AC Adapter here.

All of the boxes were in great shape with the exception of the tripod box which had some minor damage to the the cardboard flap. But there was no damage to the tripod and accessory tray since they were packed in their own double-wall cardboard boxes. In fact, everything was very well protected with heavy cardboard and foam. The CGEM mount was even packed in triple-wall cardboard! Here are some photos of the packages:

Assembling the CGEM

With the help of my dog Sirius (very fitting name, eh) watching over everything, I assembled the entire telescope in about an hour. First, I set up the tripod. It comes fully assembled so it’s just a matter of spreading the legs apart and raising them to the desired height.

Then the CGEM mount was installed next. The azimuth adjustment knobs had to be attached first and then the mount was set onto the tripod. It was secured by the knob on the underside of the tripod. The accessory tray and counterweight system were installed next. Here is the CGEM up to this point:

CGEM Review- Assembled Mount

I want to note that any pictures that I have seen (including my own in this review) do not do this mount justice! It is MUCH beefier than it looks in photos. It’s really an impressive-looking piece of equipment in person. I noticed how substantial the CGEM was when I pulled it out of the box. It is heavy! I owned a Celestron CG5 a couple of years ago but it pales in comparison to the CGEM.

Some have questioned whether the CGEM’s housing is plastic. It may look like that in pictures, but it is definitely made of metal. It has a nicely textured finish and very cool-looking metallic orange parts. Yeah, the CGEM is a beautiful mount!

The last part is mounting the optical tube. The CGEM has a nice wide and sturdy mounting platform for the dovetail bar. It is a much better system than my CG5 was. There are two mounting screws with knobs that open both sections of the mounting platform and the dovetail bar slides in smoothly and locks firmly in place.

The visual back came already installed. I finished up the assembly by adding the viewfinder, star diagonal, and eyepiece that came with the 9.25″ optical tube. And last, I plugged in the hand controller. Here is a photo of the final assembly with me standing there (ugh!) for visual reference to the size of the CGEM.


Playing with the CGEM!

I spent the rest of the evening familiarizing myself with the CGEM. It goes without saying that it was a cloudy night. This is expected with every new telescope. All astronomers know this. It’s a well documented curse. But that didn’t stop me from using it! So I plugged it in and set up my local time and location and did some slewing. The mount is very smooth and is fairly quite at most slew rates. There are nine speeds total to choose from. The highest rate (9) is somewhat loud but I don’t think it’s an issue. Here is a video of me slewing the CGEM in RA and DEC. Note that the slew rate is at its highest setting of 9. Be sure to turn up the sound to hear what it sounds like:

All Pros and No Cons?

Not exactly. No matter how much you spend on a telescope, there is always something that isn’t quite right. With my CGEM, there were a couple of things that were a bit of a concern (although not major). For instance, the hand controller cord seems too short in some instances. I have seen other reports of this. Fortunately you can order an extension cable for the CGEM hand controller here at AstroPhotography Tonight.

Also, the manual refers to index marks on the RA and DEC axis that you line up before starting your alignment procedure. Oddly, on the DEC axis, one index mark is on the back side of the mount and the other is on the front! I wonder if they decided to place the index marks on the back (so you can see both RA and DEC marks on same side of scope) but accidentally placed the one on the front out of habit. It looks to me that the collar can be spun around 180 degrees and it will correct that. I will probably try it! But even if it doesn’t, it should not be a problem because there is a screw hole located below the front index mark that will serve as a reference.  As you’ll see in Part 2 of my CGEM review, this didn’t phase my alignment because the goto was spot on! I was very impressed with my CGEM’s performance on the first night out!


My first impression of the Celestron CGEM was a good one. It is a very solid and sophisticated mount. I still have much more to learn about it and I look forward to exploring its capabilities in astrophotography (planetary and deep space).

Part 2 of my CGEM review will cover my first night out with it. Keep checking back here on AstroPhotography Tonight for further coverage of the CGEM. As mentioned earlier, if you have any questions or comments, please post them in the “Leave a Reply” section below. Also, I have added a survey below to find out if this review was helpful to you.

Clear Skies! Ray Shore

This review of the Celestron CGEM was:

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  1. AstroPhotography Tonight

    Feel free to leave any questions or comments regarding Ray’s review of the CGEM.

  2. I am also in the process of getting this scope and mount so will be very interested in your next review. For the first time I can see the scale of it.


  3. Ray – I have to thank you ever so much for posting the video clip of the noise at high speed. I’ve owned my CGEM for about six hours now, and I have to admit I was concerned with the amount of noise. Knowing that at least one other mount sounds like mine, makes me feel a lot better!

  4. John- you are very welcome. I think I was used to that amount of noise with my LX200. Congrats on your new CGEM, you’re going to enjoy it! Ray

  5. Fabrice Pierre

    Ray-I have to admit that I am a bit concerned by the level of noise. How does it sound at lower speed?
    one of my pleasures in astronomy is to be out in the silent night.
    I have never owned an motorized mount before and plan to buy one soon. Is it that noisy when tracking objects??
    thanks in advance.

  6. Fabrice- I can’t hear the CGEM at all when it is in “tracking” mode. It is very quite. The noise in the video is when it is “slewing” at it’s maximum rate of 9. So you will only hear the CGEM when it slews from one object to another. If I remember correctly, it slews at a rate of 9 when in goto mode and cannot be adjusted (would be nice if I’m wrong!). But if you want to slew in non-goto mode, you can select a slower rate that doesn’t make as much noise. Maybe I’ll get a chance to record another video this weekend that records the noise level difference at each rate of slew. I’m not sure how well the video would represent the noise as if you were operating the CGEM in person, but you will be able to hear the difference at each level. Would this be helpful? Thanks, Ray

  7. Fabrice Pierre

    thanks for your answer. I feel relieved by the silent tracking mode. A bit of noise when moving t between objects is perfectly fine.
    I am hesitating right now between a 925 ”regular”OTA and an 800 edge HD. They are only $300 away from each other, and I rather trade “latest technology” for a bigger aperture.
    Are you satisfied with your 925 optics? is portability still OK? is the new edge HD worth sacrifying some aperture?

  8. Fabrice,
    You’re very welcome. I thought very seriously about the Edge HD as well. I was looking at both the 8″ and the 9.25″. I’ve been wanting to try a 9.25″ SCT for some time due to the reports of it being an ideal size for planetary astrophotography. But I didn’t want to wait until after the first of the year for the 9.25″ HD to be available so I went ahead with the standard 9.25″. I might trade in my OTA for the HD someday.

    So far, I’m very satisfied with the 9.25″ optics. I had some very sharp views of Jupiter awhile back when the seeing was good. There was a shadow transit occuring (before I could get my camera setup) and it was razor sharp through the eyepiece. I still need to put these optics to the test with more astrophotography.

    One of the attractions of the HD for me was the mirror locks that Celestron incorporated. These should help minimize mirror flop that occurs with SCT’s.

    I have done a lot of imaging with an 8″ Celestron SCT and I thought the results were pretty good. I wanted to move up one size to the 9.25″ this time though. I’m having troubles providing advice when it comes to choosing the 8″ Edge HD or the standard 9.25″. I wonder what others think?

    Ray Shore

  9. I think the benefits of mirror lock along with a nice flat field to the edge would definetly favor a few hundred extra for the HD OTA. The 9.25″ OTA seems like a great portable setup and good weight for the CGEM. I had the 800HD edge ota on order but have backed out waiting for some reviews. Will be looking at OTA in beginning of 2010 for my CGEM mount. I may stick to the 800 but my gut instinct tells me to go with the 9.25HD ota. Then again I have heard some great reviews on the Explore Scientific 127mm. I still have my 12″ LX-200GPS and since buying my Meade 80mm ED 5000 apo refractor(guide and widefield scope) I have been starting to lean towards a nice size refractor for imaging, the Explore Scientific looks like a great option. Too many decisions., but if I were to decide on the Celestron for a few hundred more I would definetly go for the HD ota if I was thinking of imaging.

  10. The EdgeHD looks to be a great OTA. I’ll have to try one someday! I think the Explore Scientific refractor is a good idea too. It’s tough to make a decision on this stuff!!


  11. Fabrice Pierre

    FYI, I finally chose to buy the 925XLT CGEM. You seem to be very satisfied with yours and I just can’t wait for the edgeHD to be available. I also found very good reviews on the 925 XLT OTA on cloudy nights which support your comments.
    In addition Celestron has just started to lower the XLT price by $300, probably because of the new HD line . This allow me to stay within my budget with a higher aperture than originally planned (8″).

    I currently own a 90 mm refractor (konus 90) on equatorial mount, it’s going to be a big jump for me!
    I am planning to use the new one for observation first, and then gradually move to planetary imaging and deep sky photography.
    Thanks for your very interesting web site which came at the perfect time for me (this is my 40th birthday gift!). I am looking forward to sharing my impressions with you and your readers.

  12. Fabrice,

    Good to hear that you can get the bigger aperature within your budget. And what a nice birthday gift!!! The CGEM 9.25″ should serve you well. Do you plan to keep the Konus 90?

    Thanks for your offer to share your experience. It is well appreciated!

    Ray Shore

  13. Hi,
    This is one of the most useful review I’ve ever read, It’s very well organized.

    I planed to bye Celestron CGEM 1100 HD, 11″ EdgeHD which looks very good optically and more interesting with this “Rock mount”.

    Thank you very much


  14. Hi Algady,

    Thanks for the nice feedback! Good choice on the EdgeHD CGEM. I wouldn’t mind hearing about your experience with it!

    Ray Shore

  15. Buddy Atwood

    Ray, I have been reading and enjoying your reviews. That, plus the opinions of a couple trusted friends has prompted me to buy myself a 9.25 CGEM. As you so wisely observed, the weather sucks. I got on my 73rd birthday this week and I am waiting to take a look. Thanks for your valuable review.

    Buddy Atwood

  16. Buddy, thanks for the feedback on my CGEM review! I think it’s a great scope in its class. With all the bad weather we’ve been having, I may have to relearn how to use it!! I may have to shovel out an area in my yard so I can setup. Anyway, congrats on getting a CGEM! I think you will be happy with it!

  17. Ray,

    I had to chuckle reading your con about the index marks. I too noted the upper index mark was on the opposite side of the mount head for DEC when I got my CGEM. I thought it was goofy for a moment too and was about to start cussing Chinese workmanship…, until I realized all I had to do was take the OTA off, release the DEC lock and turn the mount head around (then put the OTA back on again) and they would line up. 😉

    B.J. Koho

  18. Jeff Turner


    Was reading the remarks also about index marks. With my side to side setup they do not matter anyways. I have to start scope with the dovetail turned 90 degrees. One of the features in the utilities is for use of the side by side setup. You simply have to tell the mount to start 90 East or 90 West in my case for the OTA orientation.

    The new Edge 800 OTA on my setup looks beautiful.


    Jeff Turner

  19. I thought about turning the mount head around too but that made the saddle plate release knobs on the opposite side of where the user guide showed them. Not that it matters though, it just seemed odd and was not the intention of Celestron. I’ve gotten used to the knobs being on the same side as shown in the user guide so probably won’t change anything now. 🙂 I still haven’t tried to spin the collar around to see if it corrects it. Ray Shore

  20. Hi Ray, Thanks for the great review I am just sorry that the CGEM Computerized mount is no longer available The CGEM will be my best option now.Wishing you clear skies. John Potgieter

  21. Ray Hi there,
    Ray its my fault is should be CGE Computerized once again thank you and tons wish you clear skies.
    John> South Africa

  22. Ray Shore

    Hello John,

    No problem…I thought you might have meant another mount. Yeah, the CGE did get discontinued since it was replaced by the CGE Pro. I probably would have gotten a CGE when the prices came down if it didn’t have that early limit for the meridian flip.

    Ray Shore

  23. Becky Johnson

    Hi Ray. Thanks for the great review. I have the exact set-up and the same two issues. The cable to the hand-controller is too short, and the markings on the Dec assembly are messed up. If you align the Dec and RA marks as instructed, then the OTA lockdowns and the Dec release are on the left side of the OTA; in the manual they are on the right side. I went in to OPT and asked the sales guy who sold it to me about this. He said to line up the RA and Dec marks as instructed and don’t worry about the picture in the instruction manual. He said the picture is wrong – not the markings. I find it really annoying to have the RA controls on the right and the Dec controls on the left, but it does work. I started using a polar scope for polar alignment and it goes-to and tracks beautifully. What made you so sure right away that the marlins were wrong? Was it because the OTA lockdowns are on the right side in the manual? BTW, the Guy from POT (who is a really good astro-imager and a great guy) said that it actually should not matter which way you turn the OTA platform. That doesn’t make a lot of sense, but I guess it is true since both of our assembly methods seem to be working.

    1. AstroPhotography Tonight

      Hi Becky,

      Thanks for your input. I realized that the index marks were wrong by comparing my CGEM to the manual in the same orientation (OTA and DEC locks on the left side in the photo). I actually think that the picture is showing the original location of the index marks but they decided to move them to the back of the scope so that they are on the same side as the RA index marks. The DEC marks should line up but they don’t. Fortunately you can line up the index mark with the screw hole on the front. Not sure what the guy from OPT meant when he said that it doesn’t matter which way you turn the OTA platform. I assume that you need to have the index marks lined up prior to alignment so the scope can automatically slew close to your first alignment star based on the original position (lined up with the marks). Like you say though, it seems to be ok because our methods are working.

      The short hand controller cable was a surprise too. We have made extension cables available here on AstroPhotography Tonight: http://www.astrophotography-tonight.com/hand-controller-extension-cable-cgem. I’ve been using the 7′ version for quite some time and it works great.

      Thanks again for your input and let us know how things go with your CGEM! Ray Shore

  24. Thanks,Ray. I”ll buy the extension for the hand control. Sorry for the typos, too (…the “guy from POT”? … and “marlins” = markings ) Typing on a phone . Thanks again.

    1. AstroPhotography Tonight

      Thanks Becky! I realized what you meant…i have the same problem when I type on my phone! Just too spoiled with spell check! Ray Shore

  25. I had two reservations about this scope before I read your review. I thought that the mount was better suited for just an 8″ OTA, instead of the 9.25. Also I was under the impression that the slewing was slow.
    I now have thrown both of these reservations out the window. It slews fine, and that CGEM mount is a beauty.
    Nice review.

    1. AstroPhotography Tonight

      Hello Grant,

      Thanks for the feedback. So far my CGEM is working well for me. Last night I did a goto alignment and it put the objects almost perfectly in the center. And then I did a couple of 4 minute expsoures on M31 (using the Orion Autoguider) and it worked perfect. Now if I could just get my computer to work ok. It kept locking up on me so I didn’t get to capture a full set of frames :-(. Hopefully all will go well tonight. Thanks, Ray Shore

  26. Hello,

    In the specs of this mount, one can read:

    “Latitude Range : 15° to 70°”

    This means, I suppose, that I couldn’t use this mount here in Venezuela (Lat. ~10º N).

    Any suggestion?

  27. Hi Ray,

    very informative review.

    I have just purchase the CGEM dx 11 inch HD Edge which, if looks are anything to go by, appears to be well worth the cash although since I purchased it last week, I’m suffering from ‘New’ scope curse and not had a clear night sky since.

    Any way I have the same problem as you with the dec index marks being out by 180 degrees if the dove-tail mount is orientated as the picture on the front cover of the instructions ie with the OTA locking bolts facing towards you on the same side as the HC aux ports. Also you can’t point a tripod leg towards north as then the trpiod head lug will not position over the leg. From you review way back in 2009 it seems that Celestron still haven’t addressed this.

    What did you do leave as is and continue to work arond the problem?



  28. I recently got a CGEM 1100 mount, and so far, things are going great, really enjoy using it, and learning things as I go. I have one small problem, I don’t know how to get the mount to track when looking at a planet or nebula, etc. I have read something in the manual about tracking, but I’m really not having much luck at getting things set up to work. Is thier an easy way to get the tracking mode set up. I would be very appreciative if you would be able to help me with this problem.
    Tom Reid

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