| 摘要 |
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. |
