JMI NGF-XT Focuser (Cassegrain) A 3" black-anodized (gold-anodized optional) aluminum "Extreme" focuser designed for use on large (10" to 16") Cassegrain Telescopes (NGF-XTc) with standard output threads and Newtonian Telescopes (NGF-XTn). A 2" Eyepiece Adapter is included. The Newtonian version includes a removable combination base (works on 10" radius up to a flat surface). The manual version of the NGF-XT lifts up to 8+ pounds and the motorized version up to 18 pounds. Manual "Nano Drive" control is approximately 13 times finer than most rack-and-pinion focusers. Regular motorized versions include a standard hand unit.What is a Next Generation Focuser?The Next Generation Focuser (NGF) 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. Add the optional variable-speed Motor and Smart Focus, Digital Read Out (DRO) or Digital Focus Counter (DFC), for the ultimate focusing system. The NGF is truly a masterpiece of engineering and workmanship that you will be proud to own for years to come.
The NGF-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. The NGF-XTc achieves focus by moving the eyepiece, camera or other equipment at the back of the telescope instead of the mirror.