Patent ID: 7615507

Claim:
An optical glass comprising, as essential components, at least one oxide selected from La 2 O 3 , Gd 2 O 3 , Y 2 O 3 , Yb 2 O 3 , TiO 2 , Nb 2 O 5 and WO 3 , at least one oxide selected from MgO, CaO, SrO and BaO, and B 2 O 3 and optionally containing SiO 2 , wherein on the basis of mass, (a) the total content of B 2 O 3 and SiO 2 is from 1 to 25%, (b) the ratio of the total content of B 2 O 3 and SiO 2 to the total content of La 2 O 3 , Gd 2 O 3 , Y 2 O 3 , Yb 2 O 3 , TiO 2 , Nb 2 O 5 and WO 3 , (B 2 O 3 +SiO 2 )/(La 2 O 3 +Gd 2 O 3 +Y 2 O 3 +Yb 2 O 3 +TiO 2 +Nb 2 O 5 +WO 3 ), is from 0.05 to 0.3, and (c) the ratio of the total content of MgO, CaO, SrO and BaO to the total content of La 2 O 3 , Gd 2 O 3 , Y 2 O 3 , Yb 2 O 3 , TiO 2 , Nb 2 O 5 and WO 3 , (MgO+CaO+SrO+BaO)/(La 2 O 3 +Gd 2 O 3 +Y 2 O 3 +Yb 2 O 3 +TiO 2 +Nb 2 O 5 +WO 3 ), is from 0.1 to 0.4, the optical glass having a refractive index (nd) of 2.000 or more, an Abbe's number (vd) of 27 or less and is substantially free of PbO.