Optical glass, preform for precision press-molding, optical element, and methods for manufacturing the same

Abstract

Provided is an optical glass comprising, denoted as molar percentages: 10 to 20 percent SiO2, 5 to 40 percent B2O3, SiO2+B2O3=15 to 50 percent, 0 to 10 percent Li2O, 12 to 36 percent ZnO, where 3×Li2O+ZnO≧18 percent, 5 to 30 percent La2O3, 0 to 20 percent Gd2O3, 0 to 10 percent Y2O3, La2O3+Gd2O3=10 to 30 percent, La2O3/SIGMA(Σ)RE2O3=0.67 to 0.95 (where SIGMA(Σ)RE2O3=La2O3+Gd2O3+Y2O3+Yb2O3+Sc2O3+Lu2O3), 0.5 to 10 percent ZrO2, 1 to 15 percent Ta2O5, 1 to 20 percent WO3, Ta2O5/WO3≦2.5 (molar ratio), 0 to 8 percent Nb2O5, 0 to 8 percent TiO2; and having a refractive index nd of not less than 1.87 and an Abbé number nu(v)d of not less than 35 but less then 40. A method for manufacturing a preform for precision press molding by separating a glass melt gob from a glass melt obtained by mixing, heating, and melting glass starting materials, and forming a preform in a glass melt gob cooling step, said mixing, heating, and melting of glass starting materials is conducted so as to obtain the above optical glass.

Dependencies are inferred from the claim text.