iOptron ZEQ25 GT equatorial mount review

After releasing a series of interesting altazimuth and equatorial mounts in recent years to cater for a wide range of observing and imaging needs, the new ZEQ25 GT is a departure from iOptron’s usual products.

The mount is finished in the usual attractive off-white and black livery, but the similarities stop there – its design is very different from any of iOptron’s other mounts.

In fact, it’s different from any other mount on the market – so much so that at first glance it’s not obvious quite how it works!

Closer inspection reveals that the design is a variation on the German Equatorial Mount (GEM), but different enough to earn it the moniker ‘Chinese Equatorial Mount’ (CEM).

iOptron should be congratulated for producing such an ingenious design of its own.

The counterbalance bar can be installed in two positions: either in the conventional position parallel to the dec. axis, or at a slight angle outward.

This latter position is useful for locations at low latitude, as it will keep the counterbalance weight out of contact with the tripod legs.

The tripod is a substantial unit with 1.5-inch tubular steel legs and all-metal construction, including the leg-spreader that doubles as a small eyepiece shelf.

A problem often associated with equatorial mounts using a conventional worm gear drive is that of backlash.

Backlash results in a small delay when the gear system changes direction – when guiding, for example – as the slack in the gear mesh is taken up.

iOptron has incorporated a spring-loaded meshing system for the drive to alleviate this problem, so the mount has a rather unusual clutch mechanism.

A small chrome knob with a flat finger bar disconnects the drive, while a second chrome knob with a knurled edge adjusts the mesh tension.

This can be a little fiddly to get right but careful adjustment, avoiding over-tightening the mesh, results in a smooth, backlash-free solution.

The clutch disengages completely, allowing each axis to rotate freely, which makes balancing the telescope easier than on any other mount we have used.

Align and go

An initial problem with poor Go-To slewing was resolved by downloading and installing a complete firmware upgrade.

This upgrade came in three parts, for the hand controller, RA board and dec. board, but each was carried out simply and securely.

Once that was taken care of, we started each session with a four-star alignment to cover a large region of the sky and Go-To accuracy was excellent, with all our chosen deep-sky objects falling comfortably within the field of view of our 17mm eyepiece.

Objects remained centred in the field of view for well over 1.5 hours.

We also sought out Saturn and the planet appeared dead centre of the field of view, so the built-in Solar System computation works well.

Weighty issues

The mount comfortably supported our 72mm refractor, CCD camera and off-axis guider.

Tracking while imaging was generally good but there were some excursions that even our guiding system couldn’t tame and we did lose some sub-frames because of this.

But we suspect this is not the norm, as in-between these occasional outlier excursions, the mount tracked well.

When tracking, the mount was almost silent and you won’t disturb the neighbours as even the slewing was a quiet affair.

We downloaded the iOptron ASCOM driver for the mount and using our own USB-to-serial adaptor we connected our laptop to the mount instantly.

This enabled us to control the Go-To functions of the mount using our free planetarium software, Cartes du Ciel adding to the already huge database of deep-sky and Solar System objects.

Overall this mount performed very well, especially when observing a wide range of objects.

Solidly constructed but light to carry, it would be a good choice for both beginner and intermediate astronomers seeking a portable mount with good payload capacity.

Original gravity

The unusual Z-shaped design of the new iOptron ZEQ25 GT is known as a Chinese Equatorial Mount (CEM) and is currently unique to iOptron.

The company has bravely trodden its own path to come up with a truly novel solution, producing a lightweight, transportable mount with a generous payload of 12.3kg.

The key to this design is keeping the centre of gravity as low as possible and centrally placed above the tripod, so that the system is balanced naturally.

The advantage of this natural balance is that the mount can be made reasonably light while still providing sturdy support for the telescope and any ancillaries like imaging equipment that you may wish to install on the telescope.

The low centre of gravity certainly made the mount feel very solid.

The offset placement of the counterbalance bar and dec. axis makes polar alignment easier than normal – and accessible allthe time, as the view through the supplied polarscope can never be blocked by the declination shaft, as happenson many other designs.

Turnbuckle altitude adjustment

Altitude adjustment is handled by a refreshingly different method using a turnbuckle design. This unique setup makes adjustment of the latitude very quick and simple by turning a single knob. Two different length turnbuckles are supplied: a long one for latitudes of 35° to 60° and a shorter one for latitudes below 35°.

Polarscope

There is an automated polar alignment routine, but we preferred to use the excellent illuminated polarscope, which is dimmable via the hand controller and surprisingly comfortable to view through. The angular position of Polaris is supplied by the hand controller and the star is then simply aligned in the engraved circles of the reticule.

Built-in 32-channel GPS

The built-in GPS receiver automatically updates the hand controller with the date, time, longitude and latitude of your current location. We found that locking onto the GPS satellites often took a long time to and required a very clear outlook, so on several occasions we had to enter this data manually.

Hand controller

The Go2Nova 8408 hand controller supplied with the mount has an excellent four-line display with adjustable brightness. Its comprehensive database contains nearly 59,000 objects chosen from the Solar System, NGC, Messier, Caldwell, Herschel 400, UGC, IC, GCVS and SAO catalogues.

Spring-loaded saddle

The Vixen-compatible saddle is an improvement on basic mounting blocks, as it has two hand bolts and a spring-loaded clamp. This simple design not only ensures that the dovetail bar is securely clamped along the whole 86mm length of the saddle, it also means you won’t mar the finish of the dovetail bar.

This review originally appeared in the October 2013 issue of BBC Sky at Night Magazine.