GSO - 2" 99% Dielectric Quartz Mirror Diagonal CNC for SCT Telescope
 
If you want the high end mirror star diagonal, this GSO 2" Quartz Dielectric Diagonal Mirrors is you best choose. Quartz mirror offers greater thermal stability, resulting in minimal thermal expansion & contraction. 
 
The feature of Quartz diagonal as follow:

* Optical glass Quartz mirror blank
* Reflectivity 99% dielectric coating in the Deluxe star diagonal mirror
* Housing is an all metal CNC construction
* Brass compression rings both for 2" and 1.25"
* The barrel and the 1.25" adaptor both offer a 2" filter thread
* Excellent mirror surface quality

The star diagonal mirror to be used with standard 2" focusers on any refractor telescope. You can attach this diagonal directly to Schmidt-Cassegrain telescopes or most Maksutov-Cassegrains telescope, as long as there is a SC thread on the telescope.

Schmidt-Cassegrain Thread Version
Instead of the 2" barrel with this mirror star diagonal features an SCT thread. You can attach this diagonal directly to Schmidt-Cassegrain telescopes and many Maksutov-Cassegrains, as long as there is a SCT thread on the telescope. Of course both mirror star diagonal come complete with a 1.25" adaptor and brass compression rings for both 2" and 1.25" size.