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.
Built by JMI — A World-Renowned Manufacturer
JMI, part of the CXB Astro family, 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 — the kind of engineered precision that defines the Event Horizon line.
Shop Event Horizon Focusers
Each model offers different feature tiers — pick the one that fits your scope and budget.
What Are the Differences Between Event Horizon Models?
| Model | Extra Features | Notes |
|---|---|---|
| EV-1 | Dual-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-2 | Pusher Bearing Rubber-Gripped Gold Knobs |
Pusher Bearings give more Lifting Power (up to 8 lb). |
| EV-3 | None | Single-Speed Drive, Pusher Bearing with 4 lb capacity, Knurled-Aluminum Blue Knobs. |
| EVR | Same as EV-2 with integrated high-precision motor and control system — 8.1×10-6 in. (0.2 micron) focus step precision. Includes USB stick with ASCOM driver and instructions. | 10× finer control than comparable focusers. |
| EVR-Z | Same as EVR with an adaption mechanism to mount the ZWO EAF focus motor on the Crayford focuser. | ZWO EAF motor mounts with two screws using the couplers included with your ZWO focuser. Control focus from ASIAIR. |
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 Adapters Do I Need?
Pair your EV focuser with the right adapter for visual observing, photography, or SCT-threaded accessories.
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ADPT2-1.25T — FOR CAMERA USE
JMI Combination 1.25-inch Eyepiece and T-Thread Adapter
JMI Adapter for mounting a CCD or other camera with a standard T-thread into a 2" drawtube. Also doubles as a 1.25" adapter. A T-adapter holds a CCD camera more securely than a standard 1.25" adapter. Uses a compression ring to secure inserted equipment. Includes standard 48mm filter threads on the focuser-end of the adapter.
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LA1060 — FOR SCT-THREADED ACCESSORIES
Lumicon 2 Inch Male — SCT Male Adapter
Drops into 2″ telescope eyepiece holders and presents male SCT threads (2″ × 24 tpi) for Schmidt-Cassegrain telescope accessory attachment — an SCT diagonal, for example. Includes 2″/48mm filter threads.
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FAV100 — FOR VISUAL OBSERVING
Farpoint 2 Inch Focuser to 1.25 Inch Eyepiece Adapter
A visual 2" to 1.25" eyepiece adapter featuring a non-marring compression ring for precise centering of telescope eyepieces. Threaded for both 2" and 1.25" filters and has a stop to prevent long eyepieces from damaging filters.
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See the EV focuser in action.
Customer Reviews
I just wanted to tell you, I have been an amateur astronomer for 20 years. I just purchased my 8th focuser from you, the EV-2c for SCT telescopes. Your quality machining and general design is truly far superior to all the other focusers I have seen and used. The mega thumbscrew and the ability to have manual or motorized at the turn of a knob is absolutely fantastic. This is the only rotating focuser I have ever used that rotates super smoothly AND actually stays put even with a very heavy imaging train. Thank you so much.
— M.R.
First off the build quality is amazing. I paired it with a Sky-Watcher 180 Maksutov. I included a 2" AstroPhysics barlow, a five-position filter wheel, and a ZWO 290. That’s a significant amount of weight. The focuser holds it fine and locks down very snug. The focus travel is smooth and is a breeze to use. This is a fantastic solution to prevent image shift during focus. It exceeds my expectations. Very highly recommended upgrade.
— Garnett Leary, Canada
Beautiful, quality instrument — much nicer than I expected. Excellent fit and finish, super smooth movement. Huge! I know the dimensions are in the description, but I was not prepared for how large it is. It is going to really top off my humble build.
— Edward Perkins, Colorado