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More Information  · Recommended Accessories Price $67.95 List Price $102.95 Field of view 55° Eye Relief 20mm Focal Length 2.3mm Number of optical elements 6 Barrel Size 1.25" Weight 8 oz Warranty 2 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 generally 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 870x (109x per inch of aperture) and a 0.23mm exit pupil (about 1/100th 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 excellent seeing conditions, even for experienced observers.

For eyeglass wearers, its long eye relief makes this parfocal eyepiece an obvious choice for comfortable very high power observing. A soft rubber eyecup shields the eye from ambient light and rolls down for more comfortable eyeglass use. Two knurled rubber rings on the barrel provides a secure grip when changing eyepieces in cold weather. At a price only about 30% the cost of other premium ED glass eyepieces of similar focal lengths, it's a bargain indeed.