| This very short focal length TeleVue Radian eyepiece is exceptional for high magnification viewing with short focal length refractors and fast focal ratio/short focal length reflectors. Those who must wear eyeglasses when observing will revel in its long eye relief that will let them see a full field of view with no vignetting. Its high contrast makes it an exceptional choice for splitting close binary stars and for seeing faint low contrast lunar and planetary details. It will generally be of marginal utility for regular use with long focal length refractors, reflectors, or catadioptric scopes under average seeing conditions. Using it with a 2000mm 8” f/10 Schmidt-Cassegrain, for example, will result in 500x (63x per inch of aperture) and a 0.4mm exit pupil (about 1/64th of an inch across). Both of these are slightly past the rule of thumb maximum values of 50-60x per inch of aperture and a 0.5mm exit pupil, but are usable by a reasonably experienced observer under very good seeing conditions. Average seeing conditions would generally keep these maximum values from being attainable |
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