Designed for use with PENTAX brand spotting scopes and with astronomical telescopes with appropriate 1 1/4 or 2 focusers. Ideal for both ground and astronomical observations this eyepiece features fully multi-coated lenses to increase light transmission and color quality high-refraction lanthanum glass elements for high-resolution images with minimal aberrations and JIS Class 4 weatherproof construction for durability. Engineered using advanced computer simulation design technology this high-performance eyepiece provides 20mm eye relief.