There are few telescope accessories that work as hard or are as important as a diagonal. As an integral part of the optical chain, a good diagonal can make a significant difference in the quality of the displayed image. If you want to use 2-inch eyepieces while observing with your telescope, a 2-inch diagonal is required. With the larger 2-inch tube, you can see a greater percentage of the telescope's light cone, which works wonders when capturing faint deep-sky objects with low surface brightness. The Celestron 2-inch mirror diagonal is designed for outstanding performance. The housing is machined with precision instruments to ensure that the optics remain perfectly aligned. The mirror of the diagonal is tested with an interferometer and is guaranteed to have a 1/10 wave or better. The surface of the mirror is coated with the same powerful XLT coatings used on Celestron's best telescopes. The result is a sharp, bright image that satisfies even the most demanding amateur astronomers. This 2-inch diagonal securely attaches to the rear cell of standard Schmidt-Cassegrain telescopes. To take advantage of the additional light transmission of the XLT diagonal, insert a 2-inch eyepiece into the tube. If you want to use 1.25-inch eyepieces, slide the included 2-inch to 1.25-inch adapter into the eyepiece tube and secure it with the thumbscrew. When not in use, store your diagonal for protection in the included aluminum case.