JMI Dual-Speed Event Horizon Telescope Focuser – Newtonian


Out of stock

Already 8 persons shown interest.

A masterpiece of engineering and workmanship, JMI Dual-Speed Event Horizon Telescope Focuser – Newtonian is a low-profile, friction-drive focuser designed for both the amateur and professional telescope market.


Add to WishlistAdd to Compare

JMI Dual-Speed Event Horizon Telescope Focuser – Newtonian

A masterpiece of engineering and workmanship, JMI Dual-Speed Event Horizon Telescope Focuser – Newtonian is a low-profile, friction-drive focuser designed for both the amateur and professional telescope market.

The highly acclaimed Crayford design uses high pressure on a metal drive shaft pressing against a 3″ 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.  Zero image shift and zero backlash makes this focuser fantastic for visual and photographic work and a must for CCD imaging.  The modular design makes changes and upgrades extremely easy to accomplish.

Featuring a 2″ black-anodized aluminum focuser design with dual-speed drive, pusher bearing, rubber grip gold knobs and two-speed operation.  The focuser lifts up to 8 pounds and its dual-speed manual controls are over 15 times finer (small outer knob) and 1½ times finer (large inner knob) than most rack-and-pinion focusers, with a 9:1 ratio.  Includes a compression ring in the drawtube for holding telescope eyepieces and accessories without scratching the equipment.  The adjusting screw presses against the ring which tightens around the eyepiece or accessory.

Compatible with Newtonian telescopes and mounts on a range of surfaces from a 7.25″ diameter, or larger, tube to a flat surface.

There are no reviews yet.

Only logged in customers who have purchased this product may leave a review.

Package Includes:

  • Dual-Speed EV Focuser – Newtonian

The Event Horizon Focuser (EV) is a low-profile, friction-drive focuser designed for both the amateur and professional market.  The highly acclaimed Crayford design (see below) permits tolerances up to 100 times better than conventional rack-and-pinion focusers.  Zero image shift and zero backlash makes it fantastic for visual and photographic work and a  must for CCD imaging.  The modular design makes changes and upgrades extremely easy to accomplish.  Add the optional variable-speed Motor and Smart Focus or Digital Readout (DRO) for the ultimate focusing system.  The EV is truly a masterpiece of engineering and workmanship that you will be proud to own for years to come.

One of the EV focuser modular bases is designed for Cassegrain telescopes.  The most popular type of Cassegrain telescope is the Schmidt-Cassegrain Telescope (SCT).  These telescopes achieve focus by moving the primary mirror.  This design tends to create image shift which is especially problematic for CCD imaging.  The EV Cassegrain focusers achieve focus by moving the eyepiece, camera or other equipment at the back of the telescope instead of the mirror.

Here are a few key features of the Event Horizon focusers:

  • Modular design makes purchasing and installing options and upgrades a snap

  • Purchase one of our regular models or build a customized focuser by purchasing individual parts.

  • Low profile with no unsightly springs

  • Zero image shift and zero backlash

  • Up to eight (8) pounds of lifting power

  • Brass clamping rings hold eyepieces and equipment without scratching

  • 48mm threads on 1-1/4″ adapters

  • Your choice of plastic or brass locking screw for different locking characteristics

  • Miniature light-weight, high-torque motor the size of an AA battery (motorized version)

  • Small slender hand control (motorized version)

  • Transition between motorized and manual focusing with the twist of a thumbscrew (motorized version)

  • Dual-speed drive with counter (EV-1 model)

  • 16 times finer focus than most rack-and-pinion focusers (EV-1 model)

  • Available with Digital Readout (DRO) hand control

  • Available with Smart Focus for control from your PC (with encoders and positional display)

  • Available with PC Focus Control for control from your PC (without encoders or positional display)

  • Quality construction and just plain beautiful!

Please see the Focuser Comparison Chart.  

Purchasing Hints

Here is a quick overview of the Event Horizon focuser models:

Differences Between Basic 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
EV-2 Pusher Bearing
Rubber-Gripped Gold Knobs
Pusher Bearings give more Lifting Power
EV-3 None Single-Speed Drive, No Pusher Bearing, Knurled-Aluminum Black Knobs
EV-B Varies Features are Based on Options You Choose

Each focuser can be further classified by the type of base (“c” for Cassegrain, “n” for Newtonian or “r” for Refractor) and whether or not it includes a motor.  For example, a motorized EV-1 for an SCT would be model EV-1cM.  You can make even more choices in the specifications of your focuser by purchasing parts to Build-Your-Own model.  You can purchase parts at

The following chart is for those wishing to replace an NGF focuser with the closest match in the Event Horizon series.

Converting NGF Part Numbers to the Best Match in the Event Horizon Models
NGF Model EV Model Notes
NGF-DX1(M) EV-1n(M) The EV version includes fast and slow gold rubber-gripped knobs, a position indicator dial and pusher bearings for more lifting power
NGF-DX2(M) EV-2n(M) The EV version includes single-speed gold rubber-gripped knobs and pusher bearings for more lifting power
NGF-DX3(M) EV-3n(M) The EV version Includes single-speed knurled-aluminum Black knobs
Matches the NGF-C with Two-Speed Upgrade (NGF2SPEED)
Matches the NGF-C without Two-Speed Upgrade

JMI Focuser Comparison Chart

JMI Focuser Adapter Comparison Chart

Q. Does JMI sell rack-and-pinion focusers?
A. No.  All of our focusers are based on the superior Crayford design.  They operate with friction between the drive roller and the drawtube created by high pressure.
Q. Can I add a Motor to my Event Horizon focuser at a later date?
A. Yes.  The EV focuser’s modular design makes it simple to add or upgrade any options at a later date.  See EV Focuser Individual Parts.
Q. Can I easily change from motorized focusing to manual focusing?
A. Yes.  You can quickly and easily transition between motorized and manual focusing with the twist of a thumbscrew.
Q. Will an EV focuser work on my Meade Starfinder?
A. Yes.  There are two options available for EV focusers on a Meade Starfinder.  The Starfinder is equipped with a high profile focuser.  EV focusers are low profile.  We have a 4.6 inch drawtube designed for the Starfinder.  Another option is to use an extension tube with our standard low profile drawtubes.  The extension tube option is best if you plan on doing prime-focus photography because it allows you to go back and forth between visual and photographic focus without moving the primary mirror from its normal position.  A longer drawtube may also obstruct the light path inside the optical tube when at minimum height.

Generally, we would make the following recommendations when replacing the Meade Starfinder focuser based on the type of telescope you have:

Equatorial:  The 1.5″ extension tube and two backup plates (optimal for both photographic and visual).
Dobsonian:  The optional 4.6″ drawtube and two backup plates (optimal for visual only).

These two setups will work without relocating the secondary or the focuser positions, however, four new holes must be drilled for mounting the focuser.

NOTE:  Before purchasing, please measure the height of the original focuser when it is fully racked out to insure that the replacement drawtube length is correct.

Q. What is a Backup Plate?
A. A backup plate is a square flat or rounded piece of aluminum that can be bent to conform to the radius of a telescope optical tube.  It is designed to add support for a focuser when attached to a Sonotube (cardboard) or wood constructed optical tube.  Two backup plates are usually recommended for Sonotube mounting, one for the inside and one for the outside of the tube as a base for the focuser.
Q. What are leveling setscrews?
A. Leveling setscrews are installed in the base of EV focusers.  They give you the ability to collimate the focuser with respect to the optical light path.  Correct alignment is critical for optical quality.
Q. What is the difference between the Cassegrain version of the EV focuser and MOTOFOCUS for a Cassegrain telescope?
A. A MOTOFOCUS unit connects to the focusing knob and motorizes the normal focusing motion, which moves the primary mirror in and out.  The Cassegrain version o the EV focuser attaches to the back of the telescope allowing you to focus without moving the mirror, thus eliminating image shift caused by a shifting mirror.  Initial rough focus can be achieved by use of the normal focusing knob (with or without MOTOFOCUS) with fine focus accomplished through the EV focuser.
Q. Will the Cassegrian verison of the EV focuser eliminate the problems I am having with image shift on my SCT?
A. Yes.  The EV-1c, EV-2c, EV-3c or EV-Bc is especially helpful when using a CCD camera.  This focuser is placed on the visual back and does not require the mirror to be moved in order to achieve focus.  Mirror movement in an SCT is what causes most of the image shift.
Q. How much back focus does the EV-1c, EV-2c or EV-3c focuser add to my SCT?
A. It will add 3.0″ at its maximum extension.
Q. How much weight can the EV handle?
A. 8 lbs.  See our focuser comparison chart for more information.
Q. Do I need the Large Format Base with an EV-1c, EV-2c or EV-3c?
A. Large SCTs (10″ or larger) come with an adapter to reduce the large (3.25″ or 4″ diameter) threads on the visual back to standard (2″ diameter) size.  This adapter can be replaced by our Large Format Base to eliminate vignetting (obstructing the light cone).  This is beneficial for large format photography.
Q. What do I do if the radius of the base doesn’t match the curve of my telescope?
A. If your telescope tube has a slightly different radius than the focuser, you can add black foam weather-stripping tape under part of the focuser to block stray light while keeping a professional appearance (see diagram).
Q. Do you have information on how your older NGF focusers and adapters work on SCTs?
A. Yes.  The SCT Accessories Diagram below reflects our NGF DX, Mini and XT focusers and their mounting adapters and output adapters.


Each focuser or accessory in the diagram above is labeled with its part number.  To see photos of each adapter, go to the Adapter Comparison Chart.

Generally, a medium SCT (Schmidt Cassegrain Telescope) is one with a 10″ to 14″ aperture.  A large SCT is one with a 16″ or larger aperture (e.g. Meade LX200 16″).  Although we refer to these accessories as SCT accessories, they will work on any Cassegrain telescope (e.g. Maksutov-Cassegrain) of the correct size with standard output threads.  Six of the mounting adapters (ADPT2SCT(L), ADPT3SCT(L), ADPT4SCT(L)) are for mounting the two NGF focusers (1.25″ NGFMINC, 2″ NGFC) specifically designed for Cassegrain telescopes.  Two of the mounting adapters (ADPT3XT, ADPT4XT) are for mounting the 3″ EV-XTc focuser on a large SCT with mounting threads of 3″ and 4″ diameter respectively.

Most medium size SCTs come with an adapter that reduces the larger output threads to the smaller output threads found on the small SCTs.  These adapters usually cut into the light cone.  We designed the Large Format mounting Adapters (ADPT3SCT(L), ADPT4SCT(L)) to overcome this problem.  The larger version (ADPT4SCT(L)) is designed for the 4″ threads on the Meade 16″ LX200.  There are two more adapters (ADPT3XT, ADPT4XT) which are designed specifically for mounting the EV-XTc focuser.  All these adapters are non-vignetting.  In other words, they do not reduce the amount of light that gets to the eyepiece.

An “L” on the end of the part number indicates that a light shield is built in to the adapter.  The light shield portion of the adapter is shown in a light gray color in the chart above.  A light shield blocks any stray light coming through the bearing cavities and is normally not necessary unless you are using a CCD camera.  (The EV-XT design does not require any light shield.)

The threaded output adapter (ADPT2THREAD) duplicates the standard threads found on a small SCT.  The large threaded output adapter (ADPT3THREAD) duplicates the large threads found on the Meade LX200 16″ telescope.  This allows you to use your standard SCT accessories on the back side of an EV/NGF focuser.  We have a standard 1.25″ eyepiece adapter (ADPT2-1.25) to allow the use of 1.25″ eyepieces in a 2″ diameter drawtube.  The combination 1.25″ eyepiece and T-thread adapter (ADPT2-1.25T) also works as a 1.25″ eyepiece adapter but is designed for mounting cameras having a standard T-thread (including CCD cameras) into a 2″ drawtube.

Future products for the EV-XTc may include special 1.25″ eyepiece adapters to fit in the 2″ eyepiece adapter (ADPT3-2).

“I just received the EV3N.  Wow, what a beauty.”  (D. C.  12/20/2016)

“I now have a dilemma, whether to fit the EV-2cM to my Takahashi Mewlon 180 or should I place it in a glass case on the mantelshelf as a contemporary display of fine American design, engineering and manufacturing.  It is so heartening to see that there are still some organizations producing such elegant, quality, functional and cost effective products after the shocking excesses of the financial institutions of Wall Street and other global financial centres.  If only they had kept the customer in focus as JMI does…”  (D. S.  04/14/2014)

“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.  07/2013)

“Thanks for turning out superb products, especially your Event Horizon focusers.”  (S. S.)

“I am a retired Tool & Die Maker (28 yrs) and I am accustomed to making precision machines, etc.  The focuser which I bought from you is superb in all areas of fit and finish.  Keep up the great work!  (T. C.)

“Just received your Event Horizon Focuser – WOW – fit and finish were astronomical!!  Words can’t describe how happy I am with your product.  I MEAN that!  Anyone who spends $$$ more on _______ is foolish.  THANK YOU all for a stellar product!  God Bless.”  (K. C.)

“Product Report [on the EV-3r]:  Superb focuser fellas!  No doubt the best value in a refractor Crayford out there.  I’m so glad I didn’t go for the import to save a paltry $30!  Solid, smooth, nice to look at, no slop.  Tech support with installation questions first rate.  Keep up the fine craftsmanship, ingenuity and value that JMI stands for.”  (J. M.)

“I received my EV-3r focuser Saturday and am wholly impressed with it.  Thank you for the lovely engineering and attention to detail.  I’m absolutely convinced this focuser is the finest available, especially for the price – bar none!  (I’ve owned Moonlite, Feathertouch and GSO crayfords so I’m speaking from experience.)”  (J. M.)

“Based on the price, weight capacity and feedback from others, I decided to order the JMI…”  Online Cloudy Nights Telescope Reviews — JMI EV-1r Focuser  (Barry Etter)

“I got two great nights out with the scope and new [EV-2nM] focuser.  The difference is astounding.  It makes observing a real treat when you don’t take so much time achieving a great, sharp view.  Also, it is nice to know the focuser feels the same no matter how low the temperatures get.  Thanks for your assistance.”  (R. G.)

“The EV-2nM and enhanced extension tube are a fantastic upgrade from the stock focuser on my [telescope].  I had troubles getting the stock focuser to achieve a crisp focus because of image shift, backlash and vibration.  Those issues are all eliminated with this fine piece of equipment.  [I] only wish I had done the upgrade when I first got the telescope.  I’d have spent much more time observing and less frustration with trying to get the image focused.  [This is] a truly fine product and [your are] great people to deal with.”

My experience with your company has, to say the least, been outstanding.  I contacted you on Monday and spoke with helpful staff who conveyed a sense of both understanding my requirements and reaspsuring me that the item would arrive within the timeframe I needed.  A follow up call made to check progress was treated in the same friendly, knowledgeable way.  While I have not used the focuser outside yet (storms tonight), it mounted easily and took my accessories with ease.  I will be going to our clubs dark site this weekend and will put the unit through its paces.  Many thanks for upholding excellent customer care and providing the hobby with first class instruments.  Thanks.  (S. P.)

“[The EV focuser] is a thing of beauty!!  A wonderful addition to my SN 8″.  Makes the scope look like a million bucks!  Thank you very much!  It has been a pleasure doing business with you!  And I plan to do business with you in the future.  A long time customer of JMI, Roger…”  (R. S.)

“I bought my EV-3n with a check, so I expected a delay but the focuser arrived well before I expected it.  The packing was great, the finish was beautiful, but there was a tiny “hitch” in the focuser movement that synched with the rotation of the knobs.  I called the office and was immediately put in touch with knowledgeable support (I work in support also – yours is top rate!) who gave me a suggestion to try and permitted me to undo the shaft box to inspect the shaft for more clues.  I found two tiny coincident gouges on either side of center, which had left two tiny scrims of metal on the shaft – not more than a few thousandths of an inch.  It may have been caused during shipping, although there wasn’t any obvious damage to the box.  A little 1000 grit sandpaper on a flat stick and the problem is gone – I can’t even tell where it was. Now the focuser works as well as it looks.  (T. F.)

“The EV-1n 2-inch motorized focuser I purchased from you was better than I had expected.  The ease of use was refreshing in these days of over complication.  I would certainly recommend this item to anyone considering the purchase of a motorized focuser.”  (R. A. S.)

“I received my EV-2c focuser from you yesterday and immediately installed it on my C8 and took it outside for a test.  I must say that I am very pleased with its performance.  I think that this it the first time I have ever had my C8 in perfect focus.  Everything works to more than my expectations.  Thanks.”  (R. G.)

“I got the focuser on Saturday and I have to tell you it is simply a work of art!  It installed easily and so far it seems to work great.  I have yet to get to try it out under dark skies but I am sure it is going to do the job.  One thing that impressed me was the absolute zero image shift while focusing.  I have never been able to get a real good collimation on this scope using my laser collimator.  As I rack the stock focuser in and out the laser dot moves quite a bit.  Not with the EV thought, it is rock steady.  The laser dot stays in one spot and doesn’t move at all.  Great work!”  (D. C.)

“The quality of the workmanship on my new EV Focuser astonished me and was excellent.  It is so nice to get a piece of equipment made here and not in China.”  (J. V. C.)

“I recently purchased a JMI EV [motorized focuser] for my [scope]…  The stock focuser is so sloppy and toy-like that precise focus really is not possible.  Hold the two in each of your hands (the EV and the stock focuser) and the difference is striking.  This is, hands down, the best upgrade I have made.  It makes a good scope great.”  (R. G.)

“The EV-3n came in faster than I expected.  My first word when I opened the box was, WOW!  The quality and craftsmanship was far better than I expected.  Thank you JMI for building such quality gear for our telescopes.  I will be buying from you guys again.”  (K. B.)

I…note with pleasure that someone at last is manufacturing the Crayford Eyepiece Mount commercially.  I had no intentions of doing this myself…  I write to say, good luck in your venture and what better use could the new CEM be put than to grace your splendid range of well designed telescopes.”  (J. Wall, Inventor of the C.E.M.)