Optical glass for precision press molding, preform for precission press molding, and process for the production thereof

An optical glass for precision press molding, comprising B2O3, SiO2, La2O3, Gd2O3, ZnO, Li2O, ZrO2 and Ta2O5 as essential components, containing 0 to 1 mol % of Sb2O3 as an optional component, substantially containing none of PbO and Lu2O3, having a glass transition temperature of 630° C. or lower, and having a refractive index nd of greater than 1.85 and an Abbe's number νd of greater than 35.

An optical glass comprising, as essential components and by mol %, 15 to 40% of B2O3, 3 to 25% of SiO2, 5 to 20% of La2O3, 5 to 20% of Gd2O3, 2 to 35% of ZnO, 0.5 to 15% of Li2O, 0.5 to 15% of ZrO2 and 0.2 to 10% of Ta2O5, containing 0 to 15% of WO3, 0 to 8% of Y2O3, O to 8% of Yb2O3 and 0 to 1% of Sb2O3 as optional components, and further containing Nb2O5, BaO and GeO2 as optional components, the total content of the above components being at least 95%, the optical glass substantially containing none of PbO and Lu2O3, having a glass transition temperature of 630° C. or lower, and having a refractive index nd and an Abbe's number νd which satisfy all of the following relational expressions,

• 1.80<nd≦1.90
• 35<νd≦50, and
• nd≧2.025−(0.005×νd).