TeleVue Radian

More Information  · Recommended Accessories  · Images of Some Features Price $250.00 List Price $295.00 Field of view 60 ° Eye Relief 20mm Focal Length 3mm Number of optical elements 7 Barrel Size 1.25" Weight 9 oz Warranty 5 years Telescope Eyepiece Formula To calculate the magnification and approximate actual field of view of this eyepiece on your telescope, enter the focal length of your telescope below and press the "Calculate" button. mm

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.