BOROSILICATE OPTICAL CROWN GLASS WITH ANOMALOUS PARTIAL DISPERSIONS WITH NEGATIVE DELTAVE DISPERSION VALUES

摘要

1,141,627. Optical glass compositions. ERNST LEITZ G.m.b.H. 9 March, 1967 [3 May, 1966], No. 11117/67. Heading C1M. Optical crown glass having anomalous partial dispersion is melted from a mix comprising in Mol (wt.) percentages: SiO 2 24-52 (17-50); B 2 O 3 24À2-35 (24-35); oxide of at least one alkali metal 10À2-25À6 (6-18); Al 2 O 3 2-9 (3-13); oxide of Ta or Nb or both 0À4-7 (2-20À8) and not more than 10 of the oxides of Zn, Cd, Pb, the balance, if any, consisting of other compatible constituents and impurities. Lithium is the preferred alkali metal. A total of up to 15 mol per cent of the oxides of Zr, La and W may be included. A large number of examples are given.