Looking for a backlash-free Crayford focuser for your SCT or Newtonian? The JMI Event Horizon line is CNC-machined in the USA in manual, dual-speed, and motor-ready versions. Shop all Event Horizon focusers →
JMI Event Horizon Crayford Focusers
Zero backlash. Zero image shift. Built one at a time.
The Event Horizon is a precision Crayford-design focuser engineered for visual observers and astrophotographers who are done fighting their telescope's stock focusing. Available in fully manual, dual-speed, and motor-ready versions for both Cassegrain (SCT, R-C, Maksutov) and Newtonian telescopes — including configurations built to accept your own ZWO EAF or Pegasus FocusCube 3 focus motor.
What Is a Crayford Focuser — And Why It Solves Your Focus Problems
If you've struggled with a stock telescope focuser, the problem usually isn't you — it's the mechanism. The Crayford design fixes the two faults that wreck fine focus.
✗ The Rack-and-Pinion Problem
Traditional rack-and-pinion and SCT mirror-focusing systems drive the optics with meshed gear teeth. That gearing introduces backlash — a dead zone where turning the knob does nothing until the gears re-engage — and image shift, where the image visibly jumps as the mirror flops on its baffle tube. For high-magnification visual work and long-exposure imaging, both are deal-breakers.
✓ The Crayford Solution
A Crayford focuser uses a smooth metal drive shaft pressed directly against a machined metal drawtube, with bearings on the opposing side. This direct, friction-based surface-to-surface contact has no gear teeth to mesh — which eliminates backlash entirely and lets you make impossibly fine adjustments.
- ✓ Zero backlash — every fraction of a turn moves the drawtube immediately
- ✓ Zero image shift — the image stays put while you focus
- ✓ Add fine control to your SCT — use the scope's built-in focuser for rough focus, then the Event Horizon for the critical final adjustment
The Manual Event Horizon Lineup
Three manual models, each in a Cassegrain base (threads to your SCT) or a Newtonian base (configurable drawtube length, for tubes 7.25″ and larger or flat focuser boards). All CNC-machined, individually assembled and tested, and 100% made in the USA.
EV3
Single-speed friction-drive Crayford with a compression ring for secure, mar-free holding of eyepieces and cameras. The straightforward, no-frills way into true zero-backlash focusing. 4 lb load capacity.
EV2
Single-speed friction drive with rubber grip knobs and a higher 8 lb load capacity — built for heavier imaging trains and observers who want a more substantial feel at the knob.
EV1
Our top manual focuser. A dual-speed drive with a 10:1 fine-focus knob for the most precise adjustments possible by hand, plus rubber grip knobs and 8 lb load capacity. The discriminating astronomer's choice.
Motor-Ready: Bring Your Own ZWO or Pegasus Focus Motor
Already own a computerized focus motor? Many astrophotographers buy a ZWO EAF or Pegasus FocusCube and bolt it onto their stock SCT focusing system — only to find it still suffers from backlash and image shift, because the motor is just turning the same flawed mechanism faster. The motor can't fix a problem that lives in the drive train.
The Event Horizon motor-ready versions solve this. We give you the precision Crayford focuser body with a purpose-built mounting adaptation — you supply your own motor, which attaches with a couple of screws using the couplers already included with your motor kit. Now your autofocus routine is driving a true zero-backlash, zero-image-shift mechanism.
✓ EVRZ — for ZWO EAF
Mounts your ZWO EAF focus motor. Control focus from ASIAIR and ASCOM; autofocus with NINA, Sequence Generator Pro, and other popular software. From $380. EVRZ-c (Cassegrain) · EVRZ-n (Newtonian).
✓ EVRP — for Pegasus FocusCube 3
Mounts your Pegasus FocusCube 3 focus motor. Control focus from Pegasus software and ASCOM; autofocus with NINA, SGP, and more. From $380. EVRP-c (Cassegrain) · EVRP-n (Newtonian).
- ✓ True friction-drive Crayford base — zero backlash, zero image shift
- ✓ Works with the autofocus software you already own (ASIAIR, NINA, SGP)
- ✓ Cassegrain version threads to standard SCT rear port; Newtonian version has configurable drawtube length
- ✓ 8 lb load capacity, 1.4 lb focuser weight
- ✓ Individually assembled and tested in our own facility — 100% made in USA
The EVR Fully-Robotic Focuser
For imagers who want a complete turnkey solution, the EVR builds on the Event Horizon base with an integrated high-precision motor and control system — delivering 0.2-micron focus-step precision (roughly ten times finer than comparable focusers) with position feedback. It's ASCOM-compatible out of the box, ships with easy-install drivers, and works with the popular astro-imaging packages you may already own. Available for both Cassegrain and Newtonian telescopes.
Event Horizon Focuser Comparison
| Model | Drive | Motor | Load | Price |
|---|---|---|---|---|
| EV3 | Single-speed friction | Manual | 4 lb | From $315 |
| EV2 | Single-speed, grip knobs | Manual | 8 lb | From $380 |
| EV1 | Dual-speed 10:1 fine focus | Manual | 8 lb | From $499 |
| EVRZ | Friction Crayford | Your ZWO EAF | 8 lb | From $380 |
| EVRP | Friction Crayford | Your Pegasus FocusCube 3 | 8 lb | From $380 |
| EVR | Friction Crayford | Integrated (0.2µm, ASCOM) | 8 lb | Out of production until after summer move |
Every model comes in a Cassegrain base (threads to the standard SCT rear port; 0.565″ / 14.3 mm fine-focus travel; fits all Cassegrain, R-C, and Maksutov scopes with standard SCT rear threads) or a Newtonian base (configurable drawtube length at order; for tubes 7.25″ diameter and larger or flat focuser boards). Focusers ship without optical adapters so you can select only the adapters you need.
Designed, Machined & Tested In-House
The Event Horizon isn't a rebadged import. Every focuser is CNC-machined, individually assembled, and tested in our own facility before it ships.
- ✓ CNC-machined Crayford design — precision metal drive shaft and drawtube, not stamped or cast parts
- ✓ Individually assembled and tested — every unit checked before it leaves the building
- ✓ 100% made in the USA — designed and built by JMI, part of the CXB Astro family
- ✓ Configurable to order — Newtonian drawtube lengths and motor adaptations built to your needs
Fitting Note for Newtonian Owners
Fitting a new focuser onto an existing Newtonian takes careful consideration and engineering — it's not a one-size-fits-all swap. There are many publicly available tools and active community forums to help plan the change. Choose your drawtube length at the time of order to match your optical configuration.
Questions about which Event Horizon fits your setup? Reach our team at support@cxbastro.com.
Find Your Event Horizon Focuser
Manual or motor-ready, Cassegrain or Newtonian — every Event Horizon is a true zero-backlash Crayford, CNC-machined and tested in the USA.
Manual Focusers
EV1 dual-speed, EV2, and EV3 — pure mechanical precision for visual and imaging.
Shop Manual →Motor-Ready Focusers
EVRZ for ZWO EAF and EVRP for Pegasus FocusCube 3 — autofocus on a zero-backlash base.
Shop Motor-Ready →