3.58 meter mirror for the New Technology Telescope (NTT)

Early July 1988, the 3.58 meter mirror for the New Technology Telescope (NTT) rests on its active support system during the final tests at the Carl Zeiss (Federal Republic of Germany) works in Oberkochen, FRG. The 6-ton mirror blank is made of Zerodur, a glass ceramic, and was produced by Schott in Mainz, FRG. The polishing of the mirror by Zeiss has taken two years in order to obtain an unsurpassed optical quality. The exceedingly smooth surface has residual errors of no more than 25 nanometers (1 nanometer = 1 millionth of a millimeter).