CGEM 925: Personal review

[Gem]

Hi from (finally) clear Canberra!
Knowing how much I have been helped by reading firsthand reviews of scopes by others, here is my own review of my first impressions of the CGEM 925. I grew up in and around astro societies and had many years experience with a 4" SCT, an 80mm refractor and a 10" dob, but this is my first experience of an equatorial mount...

After much research, I recently purchased a CGEM 925 - which is a Celestron 9.25" Schmitt-Cassegrain OTA (optical tube assembly) on a Celestron german equatorial mount (CGEM). I was trying to get a scope that was a "jack of all trades": something that could be portable, nice visually, and able to image down the track. Some people go for two (or more!!) scopes, but I was trying to get something that could do it all.

I ordered through Andrews - who were very helpful. Most of my previous experiences in ordering telescopes has been through BINTEL. Bintel's service has been great, but I was happy to save a couple of hundred dollars with Andrews. Andrews were also very helpful. The CGEM mount was out of stock and I had to wait a couple of weeks for it to arrive and have everything shipped to Canberra.

It all arrived safely (with clouds for free!!) and I assembled the scope as per the more than adequate manual. It was really easy. Everything looks nice and feels nice too. It has a quality feel!

The scope is easily portable and easy to assemble with only one person. I use the scope in the backyard (we have a small tiled backyard) just a few metres outside a large screen down. For ease of use, I move the mount, then the counterweight, and then the OTA. It all takes only a few minutes. The dovetail for the OTA is quite easy and, again, has a quality feel to it. Even with star alignment for the GOTO, I am fully set up in around 10 minutes.

I approximately put the mount facing roughly south the first night. I found the controller is easy to use, but has a limited cord. It would be nicer to have a longer cord! The CGEM has different options for alignment for the GOTO - I usually choose the two star alignment with two extra calibration stars. It uses a large list of named stars that are up for you to choose from. The GOTO is then very accurate - the middle of a low power eyepiece or near the middle of a medium power.

The CGEM comes with a "all star polar alignment" feature. In this mode, the scope points to where any selected star should be IF the mount was polar aligned properly. You then MANUALLY move the tripod and manual fine tuning controls (plus the latitude fine tuner) on the tripod head to align the finderscope then eyepiece to the selected star. In others words, you polar align the scope to any star your desire from the list. Once this was done the first time, I then black permanent marker on the tiles where the legs were. The next time I brought the scope out I put the scope on the same marks and found it was with about quarter of a finderscope being aligned when I put the first star into the two star goto alignment. Not bad for plonking a scope on three black dots on tiles! I have not polar alignment more yet, since I am moving the scope every night and not imaging yet.

The scope has lots of nifty features - precise goto when you line up with a brighter nearby object and let the scope then find the fainter object from that calibrated starting point; an identify mode for when you see something you don't recognise; information mode that gives the mag, type, and other info on each object; etc...

The optics of the 9.25" SCT only got a real work out once the weather improved a week or two later. I have managed to view mag 13 galaxies in the backyard in suburban Canberra - so I am not missing the 10" dob. The OTA seems to take a long time to fully cool down (thanks Logan for pointing this out!). In addition, achieving good focus seems more difficult than it did on the ol' reflector. I have not had sufficient use of other similar sized SCT to compare.

The mount more than handles for the weight of the 9.25". I was toying with the 11", but decided on the 9.25" so that it would be well under the max weight for imaging down the track. I am happy with my choice. 9.25" is also easier to be putting on and off the mount each night.

I have been using an Orion dew heater, which has been good. I made the mistake of getting an Orion flexishield which doesn't fit well. The dovetail goes too close to the end of the OTA. I will need to mod it in the future.

The 25mm plossl it came with is adequate - better than my Sirius 25mm plossl, but not in the same league as a Televie plossl (I have a 32mm TV). I bought a new Celestron Axiom 15mm eyepiece recently (FOV 82) for around $180 including freight - this has provided good views! A cheaper alternative to Naglers.

In short, so far, so good. It is keeping me happy in all areas: portability, features, optics, etc... the only one left to try is imaging but that will have to wait for the camera... :)

[lepton3]

I agree, it's good to have this information from users out there. I have the C11 on the CGEM, so please allow me to add a few remarks to your (excellent) review.

I can endorse the good words about the Polar Alignment routine -- it is a quick way to get a polar alignment good enough for 3-minute images, and a good starting point for drift alignment, when you are setting up on the lawn.

While the C11 OTA is only 2.5kg heavier than a C9.25, you do feel it when you have to lift the scope onto the saddle plate and hold it with one hand while you tighten the clamps! I would not recommend it for someone who is not strong or fit.

There are a couple of quibbles -- you mentioned the short cord on the handset (it is insane!), but also, the knobs on the dovetail clamp seem to be shaped to be as difficult as possible to use with gloves on.

The screw in power connector is a big improvement, and the whole thing feels very solid and robust. Pointing is very accurate, easily putting objects in the FOV of a CCD.

-Ivan

[Marke]

Thanks for the review I have had mine 2yrs now and still np .
As for knobs etc try here
http://www.admaccessories.com/Miscellaneous_CGEM.htm
I replaced all mine early on :D

[Gem]

Thanks for confirming my suspicions! I was agonising over whether to go with the 9.25 or the 11. In the end I thought the 9.25 would be big enough for regular setting up and taking down, as well as a bit lighter for adding on imaging equipment. I am please with my choice. The 9.25 doesn't make me wish for my old 10" dob - it is a fine view.
I surprises me how few people seem to use the CGEM on this forum - it is a nice mount! Maybe we are just quieter than heq5 and eq6 users.. :)

[The_bluester]

I will add one thing about the mount having bought the CPC925 instead. I think the only real things that seperate the CPC and CGEM for visual use is that the CPC is more "Idiot proof" to set up and align, and it is cheaper. I agonised for quite a while between the CPC and CGEM, I could not say with any certainty that I was ever likely to do much imaging, so the CPC got the nod with plans for a wedge later if I felt the need.

Another possible advantage of the CPC is that the EP is always accessible! Even pointed at the Zenith, where it is between the fork arms, you can still get an eye to it easily enough, where I felt that it could end up in some awkward places on the CGEM.

There must be something about buying a Celestron 9.25, I have had far fewer clear nights than I recall since I bought it! I probably only need to install a pier to complete the set and ensure clouds forever!

Interesting that yours came with a 25mm Plossl, mine came with a 40mm, I have been thinking about a 2" upgrade to get a real wide field view as the field stop in the 40mm looks about as big as you could get in a 1.25" EP. I am just leery about spending money on a top line EP without having had the advantage of looking through one in my scope (Or another 9.25) first to see how they match up.

[Gem]

The CGEM 1100 came with a 40mm I believe, but the 9.25 came with a 25mm. I have a Bintel 40mm plossl, but haven't tried it yet in the 9.25. I have been usually using a 32mm TV plossl (great!) or a Celestron 15mm Axiom. For Saturn I have tried an older 12.5mm Celestron plossl and (for fun!) a 4.8mm Nagler. 4.8mm with a f/10 is really pushing it!!! I got the 4.8mm years ago for use on the moon with the 10" dob.
I would consider the 2" diagonal in the future. If anyone has tried it - let us know how it goes!
I haven't found the viewing awkward, provided I extend the legs of the tripod a bit.
I hope CGEM users get more active in imaging - I think we all want to see the results!! It will be another 12 months before my budget allows for a decent camera though...

[The_bluester]

The highest I have pushed mine has been to about 430X via an 11mm Nagler and 2X Televue Barlow. There have been select (Very few) times when I thought it could handle a bit more, times when the Cassini division just jumped out of the EP when looking at Saturn. I think I will gain better value out of something really wide field, but I am just not sure how wide I will be able to go before I just end up with mangled looking things at the edge of the FOV, I don't know how wide you can push the 9.25 before it falls to bits. As per some previous discussion on the site, I wonder about a 24mm Panoptic, which would give me at least the TFOV of the 40mm Celestron Plossl but at higher mag, it would probably obsolete at least two of my current set (The 40mm Celestron and a 25mm TV Plossl) But I would really like to go wider to be able to get wider views of the likes of the Orion nebula, Tarantula ETC.

I am just leery about committing hundreds of dollars to an EP without being able to see how one performs in my own scope (Or someone elses 9.25) first, I took a leap with the 11mm Nagler, but can't afford to do that very often, if I end up with a dud that does not work well in my scope, the frowns from the other side of the bed are likely not to be nice!

[Gem]

If you want 82 degree FOV (ie nagler) but for a fraction of the price, try a Celestron axiom. I bought a 15mm axiom new via ebay for $170 including freight. It isn't quite a TV nagler, but it is quite ok. I would get a 24mm but it is a 2" eyepiece and I would need a new diagonal...

[toc]

The main reason is probably the cost - the initial prices for the CGEM were quite ludicrous :eyepop: Once it got closer to the $2000 mark, it started to become a lot more interesting to me :)

[g__day]

A few comments on the C9.25 - having owned one for a few years now.

1. The finderscope that came with mine was poor - a $100 GSO one from Andrews was brilliant in comparision.
2. Originally mounted on a CG5 - the 2" dovetail was flimsy junk, I replaced it with the Losmandy D dovetail asap - great choice!
3. Collimination is essential - Bob's knobs and a trial version of CCD Inspector are your friends!
4. A Bhatinov masks makes focusing this thing child's play.
5. The focuser causes a huge amount of mirror shift, replace it asap with a Feathertouch Microfocuser instead and you won't regret it.
6. For Astro imaging - add maybe a Meade motorfocuser (into JMI Meade motorfocuser -> USB converter) and a Lumicon Off Axis Guider and IDAS light pollution filter.

I bought the Carbon Fibre model - has brilliant focal length stability during large thermal changes. I think the scope is a very good all round performer (on the right mount). Hope you get years of enjoyment out of yours!