The Celestron 1.25” Star Diagonal slides into the focuser (1.25”) of your refractor or catadioptric telescope and accepts standard 1.25” eyepieces, allowing you to view objects more comfortably. A diagonal that is angled at 90º helps avoid neck strain when looking through through the eyepiece. Please note that a 90º diagonal will display images that are right side up, but left to right orientation will be reversed.