The TPO 2" Deluxe Dieletric Mirror Diagonal features 99% reflectivity, dielectric coatings to maximize light output of your telescope system. Our custom made diagonal uses a BK7 mirror polished to 10th wave accuracy or better for best possible image quality. The TPO 2” dielectric diagonal also features a CNC machined housing. This housing is designed to retain the optimal collimation of the mirror and assure the best optical performance. The CNC machined aluminum housing will provide outstanding results for years of use. This diagonal also includes brass compression rings on both diagonal and the included 2” to 1.25” adapter, assuring gentle treatment of your eyepieces. Some other brands use set screw locking mechanisms that can mar the barrel surface of your favorite eyepieces. Avoid scratches and gouges by using the TPO 2" Deluxe Dieletric Mirror Diagonal. This diagonal is threaded to accept 2" filters.