This is an iOptron 1.25" Dielectric Coated Mirror Star Diagonal. This diagonal uses a mirror to fold the beam from your telescope. This mirror is extremely flat and is coated with a dielectric material for high transmission of light. The diagonal eyepiece barrel is made to accept 1.25" standard astronomical eyepieces.

NOTE: The photo shows a generic iOptron star diagonal; your product may look slightly different due to continuing upgrades and improved designs from iOptron.