Astromania 1.25" 45-Degree Diagonal Prism Optical Prism Inside Rather Than a Mirror which Makes Your Image Clear and Sharp High quality optical Prism inside rather than a mirror which makes your image clear and sharp. More comfortable viewing orientation as you observe from above, filter thread for any 1.25" filter. Accepts standard 1.25" eyepieces. Protective coating on the mirror to ensure a long life, metal barrel - for secure seating in the focuser. This is a great diagonal for daytime terrestrial use and night time astronomy applications for telescopes or spotting scopes. 1.25" 45-degree mirror star diagonal for any telescope with 1.25" connector (not suitable for Newtonians).