Patent ID: 7576020

Claim:
An optical glass which comprises B 2 O 3 , La 2 O 3 and ZnO and is used as a glass material for precision press-molding, the optical glass comprising, by mol %, 20 to 60% of B 2 O 3 , 0 to 20% of SiO 2 , 22 to 42% of ZnO, 5 to 23% of La 2 O 3 , 1 to 19% of Gd 2 O 3 , provided that the total content of La 2 O 3 and Gd 2 O 3 is 10 to 24%, 0 to 10% of ZrO 2 , 0 to 10% of Ta 2 O 5 , 0 to 10% of WO 3 , 0 to 10% of Nb 2 O 5 , 0 to 10% of TiO 2 , 0 to 10% of Bi 2 O 3 , 0 to 10% of GeO 2 , 0 to 10% of Ga 2 O 3 , 0 to 10% of Al 2 O 3 , 0 to 10% of BaO, 0 to 10% of Y 2 O 3 and 0 to 10% of Yb 2 O 3 , having an Abbe's number (νd) of 40 or more but less than 45, a refractive index (nd) of 1.8098 or more and being substantially free of lithium.