Many observers prefer to use a good-quality mirror diagonal instead of a prism diagonal with high-end telescope systems. The mirror in these 90-deg diagonals are meticulously polished to yield maximum performance. Housings are made of black-anodized aluminum. Barrels are internally blackened. Each 2" diagonal accepts both 2" and 1.25" eyepieces (with included adapter). The 2" eyepiece holder as two locking setscrews for maximum eyepiece security. These diagonals render images that are right-side up and reversed left to right (therefore, not recommended for terrestrial observing). Diagonals are not recommended for use in reflector telescopes.