If you want a high end mirror star diagonal, this GSO 2" Quartz Dielectric Diagonal Mirrors is your best choice. Quartz mirrors offers greater thermal stability, resulting in minimal thermal expansion & contraction.
The feature of Quartz diagonal are:
- 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 over 1/12 wave
Instead of the 2" barrel 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.