If you want a high-end mirror diagonal for your refractor telescope, this ASC 2″ Quartz Dielectric Diagonal Mirror is an excellent choice. ASC’s 2″ refractor 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. Diagonals with comparable quality and specifications often sell for $200 or more in today’s astronomy market.
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.
The 2″ chrome barrel of this diagonal on the telescope end is threaded to accept standard 2″ filters. 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 46.6mm.