| This ED (extra-low dispersion) glass six-element short focal length (but physically long) parfocal Celestron X-Cel eyepiece is good for medium to medium high magnification viewing with short focal length refractors and fast focal ratio/short focal length reflectors. It also provides about the maximum usable magnification for a typical 8” f/10 Schmidt-Cassegrain. In all cases, its long eye relief and low price make it a good choice for eyeglass wearers, particularly those on a budget. Five-layer full multicoatings provide high contrast that makes it a good choice for splitting close binary stars, for seeing faint low contrast lunar and planetary details, and for ferreting out small planetary nebulas. It generally will only be useful with long focal length refractors, reflectors, or catadioptric scopes under very good or better seeing conditions. Average seeing conditions would limit its usefulness with these scopes. Using it with a 2000mm 8” f/10 Schmidt-Cassegrain, for example, will result in 400x (50x per inch of aperture) and a 0.5mm exit pupil (about 1/50th of an inch across). Both of these are right at the rule of thumb maximum values of magnification per inch of aperture and exit pupil size for usable observing under good to very good seeing conditions for a reasonably experienced observer. 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.
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