The smc Zoom eyepiece features a magnification range of 20-60X, an apparent field of view of 38 to 60 degrees, and an eye relief of 20mm. Like all PENTAX eyepieces, it is renowned for its outstanding image reproduction. With its JIS Class 6 rated waterproof and fog proof construction, this Zoom eyepiece is ideal for use with astronomical telescopes.Lens Structure:6 elements, 4 groupsReal Field of View:1.9 - 1 degreesApparent Field of View:38-60 degreesField of View at 1000m:33-17mmField of View at 1000 Yards:108 - 56 ft.Exit Pupil:4-1.3mmEye Relief:20mmRelative Brightness:16-1.7Eyepiece Size:5.7" x 2.7"Lens & Outside Diameter:144 x 69mmWeight:19.2 oz. (550g)Designed for use with PENTAX PF 80 Series Spotting Scopes, provides 20x-60x magnification when used with them. May also be used on other PENTAX PF Series spotting scopes (except PF-63 Spotting Scope) 60 degree apparent field of view Rubber eyepiece ring designed for viewing comfort Also for use with astronomical telescopes with 1.25" focuser Pentax SMC full-surface multi-layer coated optics reduce glare while providing maximum light transmission and color quality High-refraction, low dispersion lanthanum glass to provide high resolution images with minimal aberrations Advanced computer simulation design technology to reduce internal reflections, producing brighter, clearer images Waterproof construction for greater durability.The PENTAX "Worry Free" Warranty is available on all PENTAX Sport Optics products purchased in the United States from an authorized PENTAX dealer. More..