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More Information Price $39.95 $59.95 SAVE: $20.00 (33%) Field of view 55° Eye Relief 20mm Focal Length 9mm Number of optical elements 7 Barrel Size 1.25" Weight 7 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 also exceptional for medium power viewing with short focal length refractors and fast focal ratio Dobsonian reflectors. The Astro-Tech’s very high contrast makes it an exceptional choice for resolving faint low contrast lunar and planetary details and for seeing subtle detail in planetary nebulas, while its sharpness across the field makes smaller globular clusters vivid and nearly three-dimensional.

It is more or less regularly useful with long focal length scopes, but below average seeing conditions may limit its performance. If so-so seeing is the norm where you observe, its 9mm focal length may represent the maximum practical with a long focal length scope.

Using it with a 2000mm 8" f/10 Schmidt-Cassegrain will result in 222x (about 28x per inch of aperture) and a 0.9mm exit pupil. Both of these are quite close to the values of 30x per inch of aperture that many lunar and planetary observers prefer during nights of average seeing and the 1mm exit pupil that most closely matches the resolving power of your telescope to the resolving power of your eye.