Patent ID: 7947618

Claim:
An optical glass comprising, based on a total weight of the optical glass: 22 to 29 weight percent of SiO 2 ; 15 to 38 weight percent of B 2 O 3 ; 0.1 to 8 weight percent of Al 2 O 3 ; 2 to 10 weight percent of Li 2 O; 1 to 9 weight percent of BaO; 5 to 20 weight percent of La 2 O 3 ; 0.5 to 4 weight percent of Nb 2 O 5 ; 0 to 5 weight percent of Na 2 O; 0 to 5 weight percent of K 2 O; 0 to 10 weight percent of CaO; 0 to 5 weight percent of SrO; 0 to 2 weight percent of ZnO; 0 to 5 weight percent of ZrO 2 ; 0 to 5 weight percent of WO 3 ; 0 to 5 weight percent of Ta 2 O 5 ; 0 to 10 weight percent of Yb 2 O 3 ; and 0 to 1 weight percent of Sb 2 O 3 , wherein a weight ratio of SiO 2 and B 2 O 3 (SiO 2 /B 2 O 3 ) is in a range of 0.8 to 1.2, the optical glass has a refractive index nd in a range of 1.56 to 1.63, where the refractive index nd is a refractive index for helium d line (wavelength of 587.56 nm), an Abbe number vd in a range of 56 to 63, a specific gravity not larger than 2.9, an average thermal expansion coefficient a not larger than 87×10 −7 /K at a temperature in a range of 100° C. to 300° C., and a liquid phase temperature TL satisfying T L <T (30P) and T (5P) ≦1200° C. where T (30P) is a temperature at which the optical glass has a viscosity of 30 poises and T (5P) is a temperature at which the optical glass has a viscosity of 5 poises.