JMI EV-XTc 3" Extreme Focuser for Cassegrains
JMI EV-XTc 3" Extreme Focuser for Cassegrain Telescopes
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 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 EV is truly a masterpiece of engineering and workmanship that you will be proud to own for years to come.
What is a Crayford Focuser?
The Crayford Eyepiece Mount (CEM) was invented by John ("Jack") 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.
The EV-XTc is specifically 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. This focuser achieves focus by moving the eyepiece, camera or other equipment at the back of the telescope instead of the mirror.
The EV-XTc "Extreme" Focuser
The EV-XTc is a 3" black-anodized aluminum "Extreme" focuser designed for use on large (10" to 16") Cassegrain Telescopes with standard output threads, and includes a 3" to 2" Adapter. The manual version of the EV-XT lifts up to 8 pounds and the motorized version up to 12 pounds. Manual "Nano Drive" control is approximately 13 times finer than most rack-and-pinion focusers.
Customer Note: The EV-XT requires a special modified 1.25" eyepiece adapter. The included 2" adapter does not accept the thumbscrew in a normal 1.25" eyepiece adapter.
Focuser Or Mask Size3" Drawtube