The Pentax Eyepiece SMC XW-3.5 Tube of/ers a 70 degree field of view for easier viewing. All of our eyepieces are constructed with a high-refraction, low-dispersion lanthanum glass that consistently delivers bright, high-resolution images with minimal distortion. In addition, all XW series eyepieces are built to JIS Class 4 weather-proof standards which increases their durability in less than ideal conditions. Designed for use with a wide range of telescopes and PENTAX spotting scopes, the XW series eyepieces are a clear choice for ground and astronomical applications.This Eyepiece is Compatible with the PF-65 and PF-65 ED II series spotting scopes, PF-80 series spotting scopes, PF-100 series spotting scopesSpecifications:- : Pentax- LENS STRUCTURE: 8 elements, 5 groups- FOCAL LENGTH: 3.5mm- APPARENT FIELD OF VIEW: 70 degrees- EYE RELIEF: 20mm- ATTACHMENT DIAMETER: 31.7mm- FILTER DIAMETER: 28.6mm- FIELD STOP DIAMETER: 4.3mm- EYEPIECE RING: Helicoid type- DIMENSIONS: 61 x 137mm (W X H)- WEIGHT: 405g