| This very short focal length TeleVue Radian eyepiece is superb for high magnification viewing with short focal length refractors and fast focal ratio/short focal length reflectors. Its very high contrast makes it an exceptional choice for splitting close binary stars and for seeing faint low contrast lunar and planetary details. It is very probably too short a focal length for use with long focal length refractors, reflectors, or catadioptric scopes under anything less than absolutely perfect (and accordingly very, very rare) seeing conditions. For example, using it with a 2000mm 8” f/10 Schmidt-Cassegrain will result in 667x (83x per inch of aperture) and a 0.3mm exit pupil (about 1/75th of an inch across). Both of these far exceed the rule of thumb maximum values of 50-60x per inch of aperture and a 0.5mm exit pupil for usable observing under good to very good seeing conditions, even for a reasonably experienced observer. |
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