Patent ID: 7598193

Claim:
An optical glass essentially free of PbO and comprising at least one of CaO and SrO together with SiO 2 , B 2 O 3 , La 2 O 3 , Nb 2 O 5 , TiO 2 and BaO, having a composition that substantially contains, by weight %, 1 to 18% of SiO 2 , 3 to 24% of B 2 O 3 , provided that the ratio of content of B 2 O 3 to the content of SiO 2 (B 2 O 3 /SiO 2 ) is over 1, 10 to 50% of La 2 O 3 , 1 to 30% of Nb 2 O 5 , 1 to 30% of TiO 2 , over 6% but less than 13% of BaO, less than 7% of CaO, 6% or less of SrO, 0 to 13% of MgO, provided that the total content of BaO, CaO, SrO and MgO is 40% or less, 0 to 15% of ZnO, 0 to 15% of ZrO 2 , 0 to 10% of Al 2 O 3 , 0 to 20% of Gd 2 O 3 , 0% or more but less than 2% of Y 2 O 3 , 0 to 5% of Yb 2 O 3 , 0 to 18% of Ta 2 O 5 , 0 to 20% of Bi 2 O 3 , 0 to 10% of GeO 2 , 0% or more but less than 2% of Sb 2 O 3 , and 0% or more but less than 2% of SnO 2 , and having a refractive index (n d ) of over 1.8, an Abbe's number (ν d ) of 28 to 40 and a density of 4.2 g/cm 3 or more.