| This medium focal length 2” Pentax eyepiece is an excellent choice for medium power deep space observing with long focal length refractors, reflectors, or catadioptric scopes that have a 2” focuser or star diagonal. It is a superb low power eyepiece with short focal length refractors and fast focal ratio reflectors. An f/4.5 Dobsonian reflector, for example, will yield a 6.7mm exit pupil, close to the largest usable for bright images of emission nebulas and galaxies. Its sharpness across the wide 70° field makes open star clusters and large nebulas vivid and nearly three-dimensional. The 650mm focal length TMB-105 triplet apo refractor provides 22x, a 6mm exit pupil, and a 3.2-degree field (almost seven times as wide as the Moon). These figures are all virtually perfect for observing open clusters such as the Pleiades; large nebulas such as the Lagoon, Veil, and Orion; large globulars such as M-13 and Omega Centauri; and large galaxies such as M-31 and M-33. All fit easily into the field of view, with a spacious framework of black velvet sky around them to set off their subtleties. The long 20mm eye relief is ideal for those who must wear eyeglasses while observing due to astigmatism. Even those who do not wear glasses will find the long eye relief a comfortable change from the cramped eye relief that is typical of the usual short focal length eyepiece. The substantial 26 oz. weight of the eyepiece may require rebalancing of some Dobsonians if you switch between this 2” eyepiece and a lighter 1.25” eyepiece. |
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