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| This short focal length Pentax eyepiece is designed primarily for high resolution/high contrast lunar, planetary, and binary star observing using the unobstructed optics of premium quality refractors. Its low level of internally scattered light will also reveal subtle lunar rilles and low contrast lunar domes that are often masked by the internal glare in lesser eyepieces. Splitting tightly spaced binary star components is also easier, due to the tighter stellar discs and cleaner diffraction rings provided by its high resolution and contrast. The eyepiece uses five lenses in three groups to provide outstanding high magnification, particularly with the unobstructed light paths of short focal length refractors. One of the elements is an ED (Extra-low Dispersion) lens made with rare earth lanthanum glass for excellent color accuracy and contrast. Using it with an 820mm 4" f/8 Takahashi FS-102 fluorite refractor will result in 161x (40x per inch of aperture) and a 0.64mm exit pupil. Both of these figures are well within the generally accepted maximum values of magnification per inch of aperture and exit pupil size for usable observing under good seeing conditions. Using it with the longer focal length of a 2000mm 8" f/10 Schmidt-Cassegrain will result in 392x (49x per inch of aperture) and a 0.51mm exit pupil (about 1/50th of an inch across). Operating successfully in this range generally requires very good to excellent seeing conditions and an experienced observer. The lower contrast of the telescope’s obstructed optical system will limit the eyepiece’s performance compared with its images with an unobstructed refractor. The eyepiece’s limited eye relief will also restrict its use for observers who must wear eyeglasses due to severe astigmatism.
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Terms of Sale | PRIVACY POLICY 7/1/2004 | Fine Print
Toll-Free Telephone Astronomics: 800-422-7876; Christophers, Ltd.: 800-356-6603
Alternate Telephone: 405-364-0858 24 Hour Fax Line: 405-447-3337
Telephone Hours: Monday 8 AM - 6 PM CST
Tuesday-Friday 8 AM - 8 PM CST
Saturday Noon - 5 PM CST
Store Hours: Monday-Friday 9 AM - 5 PM CST
Saturday Noon - 5 PM CST
Astronomics / Christophers, Ltd.
680 S.W. 24th Ave.
Norman, OK, 73069
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