Orion 8727 2-Inch Dielectric Mirror Star Diagonal 90 degrees 2" mirror diagonal features sophisticated, lab-tested dielectric coatings that provide an astounding 99% reflectivity Dielectric mirror coatings are more durable than enhanced aluminum coatings and provide higher reflectivity for maximum view brightness Machined and anodized aluminum housing features machine-threaded glare baffles for high contrast Nosepiece barrel is threaded to accept 2" Orion filters, a 2"-1.25" step-down adapter is included The diagonal is a great way to make nighttime viewing orientations through a refractor telescope more comfortable