Simmons ProSport Compact Porro Prism Binocular (8-17x 25-mm) Magnification x objective: 8-17x 25mm Fully-coated, high-quality optical Glass for bright, sharp, images in full-detail Bk7 prisms for brilliant light transmission Rubber Armor coating for better grip and protection Porro Prism System Multi-coated, high-quality optical glass for bright, sharp, images in full detail BK7 porro prisms Rubber-armored for superior grip and protection 8-17x adjustable magnification and 25mm objective diameter