Patent ID: 8039408

Claim:
An optical glass having a refractive index n d of 1.70 or greater and an Abbé number of 51 or greater, and, given as mole percentages, comprising: B 2 O 3 20 to 80 percent, SiO 2 0 to 30 percent, Li 2 O 1 to 25 percent; ZnO 0 to 20 percent, La 2 O 3 4 to 30 percent, Gd 2 O 3 1 to 25 percent, Y 2 O 3 0 to 20 percent, ZrO 2 0 to 5 percent, MgO 0 to 25 percent, CaO 0 to 15 percent, and SrO 0 to 10 percent, wherein the combined quantity of the above components being 97 percent or greater; wherein the molar ratio of {ZnO/(La 2 O 3 +Gd 2 O 3 +Y 2 O 3 )} being 0.8 or less and the molar ratio of {(CaO+SrO+BaO)/(La 2 O 3 +Gd 2 O 3 +Y 2 O 3 )} being 0.8 or less; wherein the molar ratio, La 2 O 3 /Gd 2 O 3 , is in the range of equal to or higher than 1.166; wherein Ta 2 O 5 may be incorporated at 0-1 percent and the molar ratio {(ZrO 2 +Ta 2 O 5 )/(La 2 O 3 +Gd 2 O 3 +Y 2 O 3 )} is 0.4 or less, and wherein the glass comprises no fluorine.