GSO’s 2″ refractor diagonal features dielectric coatings with 99% reflectivity across the visible spectrum and a 1/12 wave BK7 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.