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

摘要

Provided is an optical glass having high-refractivity low-dispersion properties, having a low glass transition temperature and having the property of being softened at a low temperature so that a preform therefrom is precision press-moldable, and the optical glass comprises, as essential components, B₂O₃, La₂O₃, Gd₂O₃ and ZnO and has a refractive index (nd) of over 1.86, an Abbe's number (nud) of less than 35 and a glass transition temperature (Tg) of 630° C. or lower.