Check the listing for details. Astronomical Eyepiece 90 Degree Diagonal Erecting Prism 1.25IN O9O0. Condition: New. Listed at 17.59 USD. You can see the upside down but left-right correct with 90 degree erecting prism while upright with 45 degree prism. Just simply insert the erecting prism into 1.25 focuser and enjoy the nature far away: see the birds, deer at the of the forest, the summit on a mountain or a cruise ship far away on the sea…… Feature: Fit for 1.25 focuser stand and eyepiece. Multi-coated BK-7 prism for superior fidelity and clearity. 90 degree erecting prism images upside down but left-right corrected, and 45-degree images uprightly. Work well with refractor, Cassegrain and catadioptric but not recommended for reflector . With dust cover to keep the lens for crisp viewing and long service. Specification: Angle: 45° / 90° (optional) Material: + Metal Size: 1.25inch Weight: 74-88g / 2.6-3.1oz Package weight: 92-106g / 3.2-3.7oz Package size: 10.5 * 7 * 5cm / 4.1 *2.7 *1.9in Package list: 1 * Erecting Prism