LBT mirror. Researcher Roger Angel with the mirror for the Large Binocular Telescope (LBT). This 8.4- metre telescope mirror is the largest ever cast. The mirror's borosilicate glass has a honeycomb design which makes it strong but light. It was cast by a process of melting, moulding & spinning in a rotating oven. The mirror is then finely polished. Two identical mirrors will be placed on a common mount in the LBT constructed on Mount Graham in Arizona, USA. Together they will have the light-collecting power and image sharpness of a much larger single mirror. Roger Angel is director of the University of Arizona Mirror Laboratory in Tucson, USA. Photographed in 1997.