This is a 2" 90-degree mirror star diagonal for Schmidt-Cassegrain telescopes (SCTs) which screws directly to the visual back of any SCT on the market (all Meade and Celestron). Includes a 1.25" to 2" eyepiece adapter. With end cap and plug. Get the best possible views through your SCT with this superb accessory - all-metal (black-paited and anodised aluminium) construction gives the whole unit a lovely quality feel. Excellent mirror quality with protective coating - the reflectance efficiency is in excess of 98%.