The iOptron ZEQ25 Mount: The Good, The Bad, and the Ugly--An Owner's Review

The ZEQ25 doing its stuff on a cold night--imaging the Orion Nebula with an 8 inch f/4 astrograph. Note the lovely Christmas rug :)

As an astronomer, I made the unwise choice of buying a home surrounded by dense woodland. As a result, my main scope, a 14 inch Meade ACF, is located at my observatory, about 2 miles away. While that’s much more convenient than my old dark sky site, which was 8 miles away, there are times (especially in winter) when I just want to set up an imaging run and return to the warmth of my living room. I also wanted to have a portable imaging system I could take with me on trips to other dark sky locations.

I do have a reasonable slice of sky available through the treetops if I stand in my driveway, so I decided that a small, easily set up and aligned GEM was “just the ticket” as the basis for a grab n’ go/driveway setup.

My first iOptron mount was the Smart EQ Pro. This little, 11-pound mount was a great performer with my Orion ST-80, 125mm Mak and PST-DS. Gotos were “bang on” accurate, and the scope even managed to keep objects on the imaging chip after a meridian flip! The polar scope ensured good alignment, but it was not the most convenient thing to use, requiring a 90 degree axis declination rotation to access the scope, as well as the unlocking and rotation of the RA axis in order to properly align the polar reticle.

When I decided to upgrade my portable imaging capabilities, adding 2 Mallincam scopes—an 8 inch f/4 newt and a 6 inch Ritchey-Chretien—I also needed a new mount to handle the heavier OTAs. As I had had great success with the EQ Pro, I decided to got with another, inexpensive iOptron product—the ZEQ25, which I picked up from Amazon for around $800.

My first impressions were that this was a significantly more massive mount than the EQ Pro, and with the innovative “Z” design, it was unlike any mount I had ever owned.

Setup and assembly were easy. The polar scope was much easier to use than that on the EQPro as it did not require any axis rotation or reticle alignment. I also discovered a really useful iOS/Android app shows exactly how to position the pole star in the reticle for accurate polar alignment. Using this app, I was able to align the scope in 2 minutes with a accuracy that showed no field drift even after several hours of unguided imaging. The tracking and goto performance of the mount was truly excellent—periodic error appeared to be decent—well within the +/- 10 arcseconds claimed by iOptron, and probably closer to 3-5 arcseconds, though I did not precisely measure it. I was surprised and delighted by the mount’s performance.

The Bad: The ZEQ25 supports PEC training, BUT—it can’t be saved, so the mount has to be retrained every time you use it. For most users, this is unlikely to be an issue, especially as PEC is not too bad on this mount. If it is important for your application, I’d suggest an autoguider, which should pretty much solve the problem. In addition, the 32-channel GPS took several minutes (5-10) to lock onto satellites, but this is a minor inconvenience that can be mitigated by powering up the mount before adding the scope and aligning, By the time you’re finished with these tasks, the GPS usually has a lock.

However, any mount is a compromise, and there was one aspect of this mount I found downright ugly.

The mount uses a spring-loaded, meshing system on both axes to minimize backlash. This is a design used in much more expensive mounts. There’s a small, locking “bar” on each axis, and a chrome knob that adjusts the mesh tension. The manual is vague on the settings for mesh tension, but it varies from scope to scope and iOptron advises that worm wear is minimized if you use the lowest tension you can to support tracking.

Here’s where the ugly comes in: if you set the tension too low (especially in RA), the scope may slip back as the mount slews. The result is “camming”—and permanent damage to the worm and ring gear. This damage is not covered by warranty and fixing it can cost several hundred dollars. The user is caught in a “devil and the deep blue sea” scenario: too little tension and you can “cam” the worm; too much, and you risk excessive wear and neither condition is covered under warranty. In my opinion, the manual needs to be “beefed up” to tell users how to avoid this potential damage.

I would advise the following:

1. Do not move the mount with the axes locked and the gears meshed. At the end of each observing session, with the mount in the zero position, remove the scope and back off the mesh tension by 7 or 8 turns (but do not fully unscrew the knob). Release the axis locking bar. Gently move the axis to ensure it moves smoothly before moving the mount.
2. When setting up, add the counterweights to the unlocked mount. Add the scope and (this is very important) ensure that it is well-balanced. An unbalanced scope can put strain on the gears and can result in slippage and worm damage.
3. Screw down the mesh tension knobs all the way. The degree of “backoff” depends on the weight of the scope, but in practice, I’ve found around 2 turns works.
4. Lock the axis with the locking bar. Very, (and I emphasize, “very”)  gently “rock” the scope to make sure the mount is fully locked. If there is excessive “play” when the mount is locked, contact iOptron or take a look at the excellent ZEQ25 “tuning” videos on YouTube.

Finally, there’s one more “ugly.” The dovetail mounting saddle has a design flaw. On the “knob side,” the adjustment can allow a dovetail to appear to lock when it actually not locked. This problem may have been fixed on newer versions of the mount, but I am not sure on this point. It is important that you visually inspect the dovetail to make sure it is both properly aligned and fully locked. Failure to do so can result in your scope unceremoniously falling out of the dovetail as it slews (especially if the OTA is parallel to the ground).
 

Here's a picture of the front of the saddle:

Here’s my crude sketch of the problem:

The issue is that the two “lips” on the saddle permit unsafe seating of the dovetail. A dovetail secured like this will feel perfectly tight, but if the scope slews parallel to the ground, it will fall out of the saddle. The way to check is to look at the sides of the dovetail from the front to ensure if is seated properly. This step is essential, in my opinion, if you do not modify the mount as follows.

The solution is to use a file to file off the 90-degree angle for the full length of the lips to a 45-degree angle. If you make this easy mod, the dovetail will always slide to it seats and locks in place properly.

Please see this website for a good description of the problem and the fix: https://www.flickr.com/photos/astronewb2011/12245720203/

Conclusion:  Obviously, for $800, you're not going to get an observatory-class mount. What you do get is a mount that performs very well for scopes up to about 8 inches, with accurate gotos and superb tracking. But beware the "uglies" with this mount. A small miscalculation in tension settings could land you with a significant repair bill.