iOptron CEM60 Equatorial Mount

By Darren Thibodeau

My first view of the CEM60 was at the SIA Astronomy Expo in Southern California. There was clearly something about the physical design of the mount that caught my eye immediately. The interesting aspect of the iOptron CEM 60 is the physical design that places the downward weight of the scope and the counterweight system on opposite sides of the tripod. This design should physically place the overall center of gravity of the system directly over the center of the tripod head, resulting in maximum stability.  

The test sample arrived in a very nicely appointed case that holds the mount, counterweight shaft, handset and all appropriate cables, including a AC power cord with a cigarette lighter adapter. The top of the tripod used two alignment posts on the left and right, relative to the mechanical RA axis that align in radius slots on the mount flange. Once the mount is placed on the top of the tripod, the nuts on the top of these posts sit atop nylon washers and are tightened with a clever tool that is threaded into the side of the mount for safekeeping. The azimuth alignment knobs are mounted at the back of the mount flange and literally push against these posts to pivot the entire mount head on a centering pin on the tripod platform. A very ingenious method for push-pull alignment that is both easy and very convenient when seated behind the mount and viewing through the polar scope. The polar alignment features of the mount are very well thought out, but I’ll delve into that in a bit.

The mount also features some clever design features specifically handy for astro imaging. Like the Paramount MX, the iOptron CEM60 utilizes mount cabling with ports located at the back edge of the saddle plate making those of us wishing to use camera’s and guiders a clean and easy hookup without the need to worry about cable dress. Naturally the appropriate ports to pass from are located on the mount body.

The next notable difference on this mount that is also very much like the paramount MX is the use of magnetic assemblies to engage and disengage the work from the main gear on both axis. In fact, it’s not a clutch at all but rather, turning a small knurled knob on the axis, which completely pulls the worm away from the main gear. Turning the knob in the opposite direction re-engages the worm and the main gear, which is spring loaded in order to engage the gearing, but somewhat allowing the worm to float against the main gear. The mount feels to have little to no backlash using this method, yet it will not bind, even considering some minor machining tolerances in manufacturing of the main gear.

So now let’s give the mount a whirl to see how it functions. In order to test the mount’s stated rating of 60 lbs., I thought it should be solid with an Edge 9.25”. I setup the mount level at my home viewing site and started the polar alignment procedure. Powering up the mount, the internal GPS quickly located the proper coordinates and time for my viewing site. A wonderful feature of the polar alignment system is the handset shows you graphically, in real time, the proper hour angle of Polaris. The polar scope has a magnificent reticle that is marked in hours and minutes. Simply placing Polaris at the correct hour angle on the reticle completes the alignment procedure, yes it’s really THAT SIMPLE. No guessing or matching constellations in the sky, no aligning a second alignment star that you can’t see in suburban skies. Put Polaris where it belongs and you’re done. The only other two systems I’ve seen that are as easy are the Takahashi polar scopes and those from Vixen.

I set the mount up in the manufacturer’s stated home position (counterweight down and OTA pointed to the pole). And started with a simple one star alignment. The mount began to slew and the sound is glorious. It is smooth and very quiet, in fact nearly silent. The first star I had chosen was in the field of view so I centered it and selected a star on the opposite side of the Meridian. The alignment was good as the second star was dead in the middle of the field of my 35mm Panoptic eyepiece and a pretty wide field with the 9.25” Edge. I then cleanly focused the telescope and switched to a 20mm Pentax XW. I then slewed to the next star, again on the opposite side of the meridian at much higher magnification and the GoTo system placed the star just north of the center. GoTo at this level on a mount at this price is much better than average mounts even in similar price ranges. I had no complaints with the mount’s GoTo precision, it was very good.

I did notice however that at the higher magnification, the overall damping time with this OTA was about 15 seconds, which in my opinion was very long, forcing me to question whether or not the weight capacity of the mount is overstated. After all, the manufacturer stated that the mount can carry 60 pounds and my setup was about 30 pounds. Including counterweights, it would be higher. I started to question the tripod. The tripod that iOptron makes for this mount is the same tripod used for their EQ45. The legs use 2” diameter tubing and are not be capable of providing the stability required for the weight capacity the mount can carry. I immediately lowered the tripod legs all the way and embarked upon what one of my best friends refers to as Moroccan Astronomy. To be clear, I was sitting on the ground to look through the scope. I didn’t re-align for this test, I simply pointed the tube in the same direction of the sky and tested the damping. I noticed immediately that the damping was reduced to less than 3 seconds with the same payload.

I am not an astro-imager anymore; therefore I did not run PE curves on the mount. In my experience and from imaging in the past, periodic error is inherent in every mount. As long as the curve is smooth and not erratic and the PE is not ridiculously high, I have no reason to think that this mount cannot be guided to produce fine, long exposure images.  This review is simply written for the astronomer that wants a very well made, reliable, portable platform for observing with a variety of instruments. The IOptron CEM60 provides an excellent platform with easy to use ergonomics and a solid build.

Subscribing to the concept that every product is designed to make the fewest compromises in quality versus price, and that no product is perfect, there are a couple of issues with the mount that I find could be improved. It is important to note that every quality manufacturer needs to consider design compromises in favor of the target price point of the product and the target performance parameters. Specifically, the paint finish on the CEM60 easily chips, therefore one needs to consider this during setup and the mounting of scopes, and other equipment. I noticed the paint under saddle knobs had cracked as well from being tightened. With regard to the tripod, a more stable platform to put this mount on, considering its rated payload capacity will be nice. I can only guess the existing tripod was necessary compromise likely to get it out to market for the many who don’t have heavy equipment. I do hope that iOptron will offer a more stable tripod for this mount for those who WILL need to use the mount closer to the stated capacity.

Overall, I think the folks at iOptron have done a masterful job of creating a mount that nearly anyone will find, performs beautifully, is easy to use and is in fact, a real eye turner at the local star party.

Clear Skies