JMI EV Focusers

A masterpiece of engineering and workmanship, our Event Horizon Telescope Focusers are a low-profile, friction-drive focuser designed for Newtonian and Cassegrain telescopes. The highly acclaimed Crayford design uses high pressure on a metal drive shaft pressing against a metal drawtube which is held by bearings on the opposing side. This direct surface-to-surface drive mechanism eliminates backlash and shifting of the drawtube as seen in other designs, and allows for very fine adjustments. Zero image shift and zero backlash makes this focuser fantastic for visual and photographic work and a must for CCD imaging.

JMI, owned by Optical Structures Incorporated, is a world-renowned manufacturer of astronomical telescopes and after-market accessories for the amateur and professional astronomer. JMI produces a variety of unique products that cannot be found anywhere else.

JMI EV-3c Standard Event Horizon Telescope Focuser - Cassegrain
JMI EV-3c Standard Event Horizon Telescope Focuser - Cassegrain
JMI EV-3c Standard Event Horizon Telescope Focuser - Cassegrain
JMI EV-3c Standard Event Horizon Telescope Focuser - Cassegrain
JMI EV-3c Standard Event Horizon Telescope Focuser - Cassegrain
JMI EV-3c Standard Event Horizon Telescope Focuser - Cassegrain
JMI EV-3c Standard Event Horizon Telescope Focuser - Cassegrain
JMI EV-3c Standard Event Horizon Telescope Focuser - Cassegrain
JMI EV-3c Standard Event Horizon Telescope Focuser - Cassegrain
JMI EV-3c Standard Event Horizon Telescope Focuser - Cassegrain
JMI EV-3c Standard Event Horizon Telescope Focuser - Cassegrain
JMI EV-3c Standard Event Horizon Telescope Focuser - Cassegrain
JMI EV-3c Standard Event Horizon Telescope Focuser - Cassegrain
JMI EV-3c Standard Event Horizon Telescope Focuser - Cassegrain
JMI EV-3c Standard Event Horizon Telescope Focuser - Cassegrain

JMI EV-3c Standard Event Horizon Telescope Focuser - Cassegrain

$253.00
JMI EV-3n Standard Event Horizon Telescope Focuser - Newtonian
JMI EV-3n Standard Event Horizon Telescope Focuser - Newtonian
JMI EV-3n Standard Event Horizon Telescope Focuser - Newtonian
JMI EV-3n Standard Event Horizon Telescope Focuser - Newtonian
JMI EV-3n Standard Event Horizon Telescope Focuser - Newtonian
JMI EV-3n Standard Event Horizon Telescope Focuser - Newtonian
JMI EV-3n Standard Event Horizon Telescope Focuser - Newtonian
JMI EV-3n Standard Event Horizon Telescope Focuser - Newtonian
JMI EV-3n Standard Event Horizon Telescope Focuser - Newtonian
JMI EV-3n Standard Event Horizon Telescope Focuser - Newtonian
JMI EV-3n Standard Event Horizon Telescope Focuser - Newtonian
JMI EV-3n Standard Event Horizon Telescope Focuser - Newtonian

JMI EV-3n Standard Event Horizon Telescope Focuser - Newtonian

$265.10

What are Differences Between Event Horizon Models?

Model  Extra FeaturesNotes
EV-1Dual-Speed Drive
Pusher Bearing
Rubber-Gripped Gold Knobs
Includes a Fast Knob, a Slow Knob, and a Position Indicator Dial
Pusher Bearings give more Lifting Power (up to 8 lb)
EV-2Pusher Bearing
Rubber-Gripped Gold Knobs
Pusher Bearings give more Lifting Power (up to 8 lb)
EV-3NoneSingle-Speed Drive, Pusher Bearing with 4 lb capacity, Knurled-Aluminum Blue Knobs
EVRSame as EV-2 with integrated high precision motor and control system that gives 8.1x10-6 in. (.2 micron) focus step position precision
Comes with a USB stick with the ASCOM driver and instructions
10 times finer control than comparable focusers
EVR-Z Same as EVR with an adaption mechanism to mount the ZWO EAF focus motor on our Crayford FocuserZWO EAF motor mounts with two screws and the couplers already included with your ZWO focuser Control your focus from ASI AIR

Each focuser can be further classified by the type of base ("c" for Cassegrain, "n" for Newtonian.) The Cassegrain base is circular and takes 2" SCT threads, while the Newtonian base mounts with four screws in a 2.75" square pattern.

What is the Crayford Design?

The Crayford Eyepiece Mount (CEM) was invented by John Wall. The Crayford name comes from the Crayford Manor House Astronomical Society (UK) to which he belongs. The Crayford design uses high pressure on a metal drive shaft pressing against a metal drawtube which is held by bearings on the opposing side. This direct surface-to-surface drive mechanism eliminates backlash and shifting of the drawtube as seen in other designs such as the rack-and-pinion focuser and allows for very fine adjustments. JMI recognized the benefits of this design and was the first company to bring it to the amateur market in a commercial product. Mr. Wall, who chose not to patent his idea, continues to design and build Crayford Focusers.

What optical adaptors do I need, if any?

JMI Combination 1.25-inch Eyepiece and T-Thread Adapter, ADPT2-1.25T for camera use. JMI Adapter for mounting a CCD or other camera, with a standard T-thread, into a 2" drawtube. It also doubles as a 1.25" adapter. A T-adapter holds a CCD camera more securely than a standard 1.25" adapter. The adapter uses a compression ring to secure inserted equipment. It includes standard 48mm filter threads on the other end of the adapter (inserted into focuser end). 

Lumicon 2 Inch Male - SCT Male Adapter, LA1060 to attach SCT threaded accessories. Lumicon 2 Inch Male - SCT Male Adapter drops into 2″ telescope eyepiece holders and presents male SCT threads (2″ x 24 tpi) for Schmidt-Cassegrain telescope accessory attachment (SCT diagonal, for example). Includes 2″/48mm filter threads. Select Farpoint 2 Inch Focuser to 1.25 Inch Eyepiece Adapter, FAV100 for a visual 2" to 1.25" eyepiece adapter. Farpoint 2 Inch Focuser to 1.25 Inch Eyepiece Adapter features a non-marring compression ring for precise centering of telescope eyepieces. Threaded for both 2 inch and 1.25 inch filters and has a stop to prevent long eyepieces from damaging filters.

Farpoint 2 Inch Focuser to 1.25 Inch Eyepiece Adapter, FAV100 for a visual 2" to 1.25" eyepiece adapter. Farpoint 2 Inch Focuser to 1.25 Inch Eyepiece Adapter features a non-marring compression ring for precise centering of telescope eyepieces. Threaded for both 2 inch and 1.25 inch filters and has a stop to prevent long eyepieces from damaging filters.

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