iOptron CEM25P portable equatorial mount

The CEM25P mount is the smaller variant of iOptron’s popular CEM 60.

Where the CEM 60 is most often kept in a permanent location because of its size and weight, the CEM25P can be picked up and taken farther afield with ease – it’s a more compact and convenient package aimed at beginner and intermediate astro imagers.

The mount is designed primarily for astrophotography and is an ideal partner for a short focal length refractor, the usual telescopes of choice for deep-sky imaging owing to their large field of view and high-contrast.

Even with the addition of a guidescope, autoguider and other accessories you might need for long-exposure photography, you should remain within the mount’s payload capacity – a not inconsiderable 12.3kg – giving you smooth and unstrained tracking.

The mount’s motors barely whisper when in operation, but are powerful enough to carry relatively large scopes such as long focal length refractors or Schmidt-Cassegrains.

The CEM25P uses the smaller Vixen-type saddle that is common on most small to medium-sized telescopes, therefore no special or extra parts should be needed when mounting your equipment.

The overall construction of the mount is robust, using materials that are well machined and easy to fit together when assembling the setup.

When tested for cone error (where the telescope tube sitting in the tube rings isn’t quite perfectly aligned with the true polar axis of the mount), the accuracy and quality of construction shone through, with negligible error shown.

A colour manual is supplied, and it is clear and concise, making it easy to get to grips with how the mount works.

Setting up is simple and straightforward for an equatorial mount, needing no tools or special equipment.

Even for a novice, it should not prove too difficult to master.

Impressive accuracy

The Go-To system uses the three-star alignment routine that is common with most mounts.

Once the CEM25P has been correctly set up and polar aligned, Go-To and tracking accuracy are quite impressive.

Slewing the telescope from object to object via the handset displayed each target close to or in the centre of the scope’s field of view, even when slewing to locations well apart from each other in the sky.

The slewing motion of the mount itself is extremely smooth and a joy to behold thanks to the synchronous belt drive, accurate stepper motors and large (55mm) RA and dec. ball bearings.

Once the chosen object has been acquired the CEM25’s tracking accuracy is brilliant, with very little in the way of drift from both axes, even if left for long periods – we tested for just over an hour.

This makes taking long-exposure photographs an easier prospect, even if you don’t have an autoguider.

The stability of the mount is also good, with no vibrations visible in the eyepiece during use in normal conditions and a very quick dampening time when we purposefully bumped the tripod to test it.

For those who like to use computer software in place of the supplied handset, the mount is controllable with a computer via the ASCOM software platform.

This is an impressive astrophotography mount for those wishing to take images through a telescope rather than just a DSLR and lens.

It’s portable enough to move to different locations without too much hassle, and has the strength and accuracy needed to achieve good results.

The system is easy enough to use, even for a beginner learning the sometimes complex ways of long-exposure astrophotography, and has the functions and capability to see you through to a more intermediate level of imaging and beyond.

Outstanding feature: The unusual Z of the CEM Design

The overall design of the CEM25P is geared toward having the highest payload capacity in the smallest and lightest package whilst still retaining excellent tracking and stability capabilities.

This mount is a centre-balanced equatorial (CEM) design, a nifty variant of the classic German equatorial mount (GEM) with a Z-shaped mount head that uses two bearings instead of one to improve on tracking accuracy.

A welcome benefit of the CEM is that it will not need as much weight on the counterbalance shaft to correctly balance the payload, giving you less to carry around and a greater neutral stability, due to the centre of gravity being over the mount’s centre point.

There are useful built-in features like the GPS unit and illuminated polarscope, plus the fact that the mount can be polar aligned without Polaris being in view using the Go-To Nova hand controller.

This is great for when your arc of sky is limited or you are in more southerly latitudes.

Combined with low-power motors, you have an excellent mount for remote locations; a perfectly portable performance.

Illuminated reticule Polarscope

Built into the mount head is an accurate and nicely etched polarscope, with a reticule that is illuminated for ease of use.

Unlike in German equatorial mounts, the polarscope of this CEM mount is not blocked by the declination shaft, and so is quickly and easily accessible without having to fiddle around.

Adjustable counterweight shaft

The counterweight shaft is adjustable to accommodate for use at low latitudes.

This eliminates the limitation of the counterweight colliding with the tripod legs, which can be a problem when using other variants of mount on or close to the equator.

As such the CEM25P can be used around the world.

GPS and ports

The CEM25P has a built-in 32-channel Global Positioning System (GPS) that will automatically find and input your location, making setup quicker and more convenient.

There are also ports for the hand controller, iOptron accessories, a dec. connection and ST-4 autoguiding.

Tripod

The included stainless-steel tripod is sturdy, and has adjustable legs and a decent accessory tray.

It strikes a great balance between weight and portability: it’s substantial enough to offer stability without being too cumbersome or weighty, and folds down to a manageable size for ease of transportation

Tension adjustment

The mount has a spring-loaded gear system with large, easily accessible tension adjustment controls located on the housing of each motor.

This allows you to set a custom loading force for each different payload used on the mount, increasing the smoothness and overall performance of the system.

This review originally appeared in the November 2017 issue of BBC Sky at Night Magazine