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 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 NGF 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 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. The NGF-XTcm 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 NGF-XTcm "Extreme" Focuser The NGF-XTcm is a motorized 3" black-anodized aluminum "Extreme" focuser designed for use on large (10" to 16") Cassegrain Telescopes with standard output threads. It includes a 3" to 2" adapter to allow the use of 2" accessories. The manual version of the NGF-XT lifts up to 12 pounds and the motorized version up to 18 pounds. Manual "Nano Drive" control is approximately 13 times finer than most rack-and-pinion focusers.
The NGF-XTcm is a motorized 3" black-anodized aluminum "Extreme" focuser designed for use on large (10" to 16") Cassegrain Telescopes with standard output threads. It includes a 3" to 2" adapter to allow the use of 2" accessories. The manual version of the NGF-XT lifts up to 12 pounds and the motorized version up to 18 pounds. Manual "Nano Drive" control is approximately 13 times finer than most rack-and-pinion focusers. The motor, gear box and drive train of every NGF motorized focuser is warranted by JMI Telescopes (Jim's Mobile, Inc.) to be free from defects in material and workmanship for a period of five years from the date of original purchase. JMI will repair or replace a part found to be defective, provided the defective part is returned to JMI freight prepaid with proof of purchase.
