CEM VS GEM

[Johnny Carter]

Hope I don’t bug too much, my last question gave me lots of useful answers, but also brought up more questions. Newbie so trying to understand, especially with the cost of some of these items. It was brought to my attention that I might want to look into an IOPTRON CEM 40 rather than the 26 and 28 we had been looking at, the reason given seemed very valid, and this is within the weight we can work with. As I researched that option I again came up with the enigma (to me ) of CEM vs GEM. I searched on here and found some answers, basically being CEM is center mounted vs weights being set up around the center. To me it seems logical that the CEM would be the better option, however both are still being readily sold. So is one option better for some things over the other, or is this a preference thing? Both types are similar in price ( and oddly the GEM 45 is the same price as GEM 40). Any ideas much appreciated.

[JayTee]

Based on my understanding (which can always be called into question), the CEM - Center weighted equatorial mount places the center of gravity of the mount centered over both axes of motion. This is not true of a GEM. Now is this a marketing gimmick or are there some exclusionary reasons to use a CEM over a GEM. I have yet to hear a compelling one.

Remember in business it's location, location, location. With telescopes, it's all about the mount, the mount, the mount. Choose the largest mount that you can both afford and move and set up as that will give you the most latitude for future growth.

[AstroBee]

Weight. Pure and simple.
I used to own a Celestron CGX (GEM) and it had a payload capacity of 55lbs but the mount weighed 44lbs
I now own an iOptron CEM70 (CEM) and it has a payload capacity of 70lbs but the mount only weighs 30lbs.

[AstroBee]

The new hybrid (HEM) mounts from iOptron are interesting. I haven't read anything on them just yet.
It has a harmonic drive on the RA axis and a standard worm drive on the DEC axis which is why they call it a hybrid. The mount only weighs 8.2lbs with a 29.74lb payload capacity.
Bonus, no counterweights are needed!

[Johnny Carter]

The new hybrid (HEM) mounts from iOptron are interesting. I haven't read anything on them just yet.
It has a harmonic drive on the RA axis and a standard worm drive on the DEC axis which is why they call it a hybrid. The mount only weighs 8.2lbs with a 29.74lb payload capacity.
Bonus, no counterweights are needed!

I saw those too and was curious about them.

[Lady Fraktor]

Then there are the Vixen mounts that use the motors as part of the counterweight making the system lighter with less counterweight needed.

[KathyNS]

In the GEM design, the business end of the mount is cantilevered out beyond the supporting bearing. In the CEM, it is a beam supported between two bearings. A cantilever is less stable and more susceptible to vibration.

That is not to say that the GEM is a bad design. It just means that a CEM can achieve the same stability with less mount weight. CEMs are considerably lighter than GEMs of the same payload capacity.

[Johnny Carter]

Sounds like CEM is the way to go then. I was just wondering if the GEM gave some attribute over the CEM that I was unaware of. With my health, the lighter the better, and the 40/45 is about as high as I can go. Thanx all.