GSO – 2″ Mirror Diagonal 99% Dielectric SCT-Quartz

If you want a high-end mirror diagonal for your Schmidt-Cassegrain telescope, this GSO 2″ Quartz Dielectric Diagonal Mirror is an excellent choice. GSO’s 2″ SCT diagonal features dielectric coatings with 99% reflectivity across the visible spectrum and a 1/12 wave quartz mirror. The all metal diagonal body is CNC machined. The combined result is a superb diagonal offering excellent mechanical and optical quality at a great price. Dielectric coatings are more durable than regular or enhanced aluminum coatings, so you will enjoy years of excellent performance from this product.

High quality diagonal mirrors are usually made of BK7 glass. Quartz glass goes a notch higher – it offers greater thermal stability, resulting in minimal thermal expansion and contraction as compared to other glass types. The result is a minimal, if any, shift in focus due to temperature changes over long observation sessions, making this quartz diagonal ideal for photographic and imaging applications.

You can attach this diagonal directly to Schmidt-Cassegrain telescopes and many Maksutov-Cassegrain telescopes, as long as there is a SCT male thread on the telescope. The standard SCT thread is a 2″x24 tpi thread.

A 1.25″-2″ adapter is included so you can use this diagonal with 1.25″ or 2″ eyepieces. The 1.25″ and 2″ holders both feature a brass compression ring, so your eyepiece barrels will not be scratched by the set screw. The 1.25″-2″ adapter is also threaded to accept 2″ filters. The clear aperture is 38.2mm. The diagonal comes in a very nice foam-fitted storage box and includes 2 end caps. Weight = 1lb-4oz. (with 1.25″ adapter); 1lb-1oz. (without 1.25″ adapter). Made in Taiwan.

Please note: Even though the eyepiece holder and the SCT adapter of this diagonal have standard SCT (2″x24TPI) threads that will work with other SCT threaded items, the threads on the body of the diagonal are NOT standard SCT threads. The thread diameter on the diagonal body is 2″ but the thread pitch is very slightly different (not 24TPI) and has not been specified. GSO ensures that these components that they machine fit together, but SCT-threaded adapters from other brands will not thread on properly or at all to GSO’s 2″ diagonal bodies in most cases due to this marginally different thread pitch.