Celestron Erect Image Prism for Refractor and Schmidt Cassegrain A great accessory for daytime terrestrial viewing with your telescope This 1.25 diagonal produces right side up and left-to-right correct images when used with refractors and catadioptric (Schmidt-Cassegrain) telescopes Inserts into 1.25 focusers or visual backs. Accepts standard 1.25 eyepieces