70 Apparent Field of View 20mm Eye Relief Weatherproof construction for greater durability Fits Pentax Spotting Scopes The Pentax Eyepiece SMC XW-10 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 scopes. Specifications: LENS STRUCTURE:7 elements, 6 groups FOCAL LENGTH:10mm APPARENT FIELD OF VIEW:70 degrees EYE RELIEF:20mm ATTACHMENT DIAMETER:31.7mm FILTER DIAMETER:28.6mm FIELD STOP DIAMETER:12.4mm EYEPIECE RING:Helicoid type WEIGHT:390