Mirror making thumb|left|200px|Grinding a mirror using an abrasive and a smaller tool over mirror ("ATM Korenica 2006", in Korenica, Croatia) Since the Newtonian reflector is the most common telescope built by amateur telescope makers, large sections of the literature on the subject are devoted to fabrication of the primary mirror. The mirrors start as a flat disk of glass, typically plate glass or borosilicate glass (Pyrex).Gary Seronik, Four Infamous Telescope Myths, skyandtelescope.com, July 28, 2006 The disk is carefully ground, polished and figured to an extremely accurate shape, usually a paraboloid. Telescopes with high focal ratios may use spherical mirrors since the difference in the two shapes is insignificant at those ratios. The tools used to achieve this shape can be simple, consisting of a similarly sized glass tool, a series of finer abrasives, and a polishing pitch lap made from a type of tree sap. Through a whole series of random strokes the mirror naturally tends to become spherical in shape. At that point, a variation in polishing strokes is typically used to create and perfect the desired paraboloidal shape.
Mirror making thumb|left|200px|Grinding a mirror using an abrasive and a smaller tool over mirror ("ATM Korenica 2006", in Korenica, Croatia) Since the Newtonian reflector is the most common telescope built by amateur telescope makers, large sections of the literature on the subject are devoted to fabrication of the primary mirror The mirrors start as a flat disk of glass, typically plate glass or borosilicate glass (Pyrex).Gary Seronik, Four Infamous Telescope Myths, skyandtelescope.com, July 28, 2006 The disk is carefully ground, polished and figured to an extremely accurate shape, usually a paraboloid. Telescopes with high focal ratios may use spherical mirrors since the difference in the two shapes is insignificant at those ratios. The tools used to achieve this shape can be simple, consisting of a similarly sized glass tool, a series of finer abrasives, and a polishing pitch lap made from a type of tree sap. Through a whole series of random strokes the mirror naturally tends to become spherical in shape. At that point, a variation in polishing strokes is typically used to create and perfect the desired paraboloidal shape.