US Patent 7897533 Optical glass composition, preform and optical element

An optical glass composition contains, in % by mole, 14.0% or more and 31.0% or less of SiO2, 19.0% or more and 40.0% or less of B2O3, 0% or more and 5.0% or less of Li2O, 0% or more and 12.0% or less of ZnO, 0% or more and 12.0% or less of ZrO2, 15.0% or more and 26.0% or less of La2O3, 22.0% or more and 38.0% or less of La2O3+ZrO2, 2.0% or more and 5.0% or less of Ta2O5 and 4.0% or more and 16.0% or less of Gd2O3, and has nd of 1.83 or higher and 1.87 or lower and νd of 43 or higher and 47 or lower, and a preform and an optical element are formed from the optical glass composition.