Newton Reflective Telescope D203 F800 Reflective Objective Mirror Main MirrorCaliber: 203mmFocal length: 800mm How to use？Cleaning the mirror surface: first blow off the dust that can be blown off with a blown balloon, then use a good quality absorbent cotton to dip the alcohol and gently wipe the mirror. After drying, look at the light source from the side to see if there is some cotton or Keep the water stains on top, and if necessary, gently wipe them with some good quality mirror cloth (be careful, otherwise it will affect your telescope).Package includes:1PC D203F800 Primary mirror1PC secondary mirror MirrorD203f800 spherical primary mirror and 70mm short axis secondary mirror Spherical mirror, aperture: 203mm, focal length: 800mm, surface aluminized and protective film. The short axis refers to the short side length of the secondary mirror.