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

摘要

A high-refractivity high-dispersion optical glass for producing an optical element, which requires no machining, such as polishing or lapping, of an optical-function surface after precision press molding, containing 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 (1) having a refractive index nd and an Abbe's number νd which satisfy all of the following relational expressions, 1.80nd≦1.90, 35νd≦50, and nd≧2.025−(0.005×νd) or (2) having an nd of greater than 1.85 and a νd of greater than 35.