JMI EV - 3CM motorised focuser review

I purchased one recently to fit on my newly acquired CGE 1100 XLT.

JMI EV - 3cm focuser specifications

The Cassegrain version (EV-3c) 2" is designed for use on 6" to 16" Cassegrain telescopes (e.g. SCT and Mak-Cas) with standard output threads. It includes an SCT threaded output adapter to allow use of standard SCT equipment on the output side of the focuser. The focuser gives 1/2" of travel and is designed for fine focus after rough adjustment with the normal telescope focusing knob. This particular focuser can lift up to 4 lbs of equipment. It will add 3.0" at its maximum extension of back focus. The motorized version (EV-3cm) comes with a hand control unit.

The motorized version (EV-3cm) comes with a hand control unit.

* For Meade owners*

*Although the EV-3cm can be plugged into the telescope's base allowing control from the Meade hand unit, you will have better control with the JMI hand unit. Our hand unit includes an electronic brake (not included in Meade systems), which stops the motor as soon as you quit pressing the keys, and linear voltage control for superior speed control. Also, older LX200 telescopes do not have enough power to properly run the motor on the low setting.* The EV-3c focuser can also be mounted on any 2" drawtube by first inserting the mounting adapter.

This is a very nice crayford style focuser. It has a slight amount of image shift visible at extreme magnification; {the kind of magnification used for planetary imaging} and I do mean slight. Hardly worth mentioning really, and it is of little or no significance even at these ridiculously high magnifications. The 2" - 1 1/4" adapter is of the compression ring type, and on my particular focuser it did not work too well at first. The compression ring was not doing it's job properly & allowing the eyepiece or camera to 'rock' back and forth sideways. I pulled the brass ring out of the adapter and placed another spacer behind it and now it works as it should.

Racking the focuser in and out manually you begin to appreciate the crayford design, it just feels nice and smooth with zero backlash and nice tight tolerances.

I love the simplicity of the motor engagement/disengagement system, allowing both manual and electronic focusing at the turn of a screw. Fantastic. Theres only one thing I think could be improved upon; the options are fast and slow speed on the handcontroller, the fast speed is good to get to focus quickly but the slow speed is not slow enough for my liking. It's quite easy to over run critical focus again and again. I'd love a 3 speed please JMI ;-) I'm sure I'll get the hang of it eventually.

A lovely piece of equipment and worth every cent I paid for it ;-)

by John Earl