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

Abstract

An optical glass which has an Abbe's number (νd) of 50 to 59, has the property of not easily reacting with a press mold, a low-temperature softening property, excellent glass stability and high refractivity, and is suitable for precision press-molding. The optical glass comprising BOand SiOas essential components and having a BOand SiOtotal content (BO+SiO) of 45 to 70 by mol % and an SiOcontent/BOcontent molar ratio (SiO/BO) of from 0.1 to 0.5, the optical glass further comprising, by mol %, 5 to 15% of LaO, 0.1 to 8% of GdO, provided that the total content of LaOand GdOis 8% or more, 0 to 10% of YO, 3 to 18% of LiO, provided that the molar ratio of the content of LiO to the total content of BOand SiO[LiO/(BO+SiO)] is over 0 but not more than 0.2, 0.1 to 15% of ZnO, 2 to 20% of CaO, 0 to 5% of BaO, provided that the content of BaO is smaller than the content of ZnO, 0 to 5% of SrO, 0 to 5% of MgO, provided that the molar ratio of the total content of MgO, CaO, SrO and BaO to the total content of BOand SiO[(MgO+CaO+SrO+BaO)/(BO+SiO) is from 0.1 to 0.4, and 0 to 5% of ZrO, and having a refractive index (nd) and an Abbe's number (νd) which satisfy the equation (1),νd≧308.5−150×nd (in which 50≦νd≦59)  (1).