Lumicon LumiBrite Star Diagonal - 2 Inch FormatThe Lumicon LumiBrite Dielectric Coated Diagonal reflects 98 percent of the light from the telescope's primary optics directly into your eyepiece. Its single 1/8 wave precision polished surface is superior to the three surfaces of prism diagonals. The Dielectric Coating is smoother and even more durable than an enhanced aluminum coating providing maximum image contrast. Lumicon collimates each and every LumiBrite Star Diagonal with a double-pass collimator ensuring that the light reflected from the diagonal is perfectly perpendicular to the telescope's optical axis. Threaded for use with Lumicon's renowned light pollution blocking filters. Makes eyepiece-changing a breeze while using your Lumicon filter.