Patent ID: 8163665

Claim:
An optical glass having optical constants of a refractive index (nd) exceeding 1.85 and an Abbe number (νd) of 40 or over and comprising, in mass % calculated on oxide basis, 3-8% SiO 2 , 5-19.5% B 2 O 3 , 15-50% La 2 O 3 , 0.1-25% Gd 2 O 3 , exceeding 10% up to 25% Ta 2 O 5 , 1.5-6% WO 3 , 0-1% TiO 2 , 0.1 or over ZnO and Li 2 O, said optical glass being substantially free of Pb and As, and having glass transition temperature (Tg) of 630° C. or below, wherein the total amount of La 2 O 3 , Gd 2 O 3 , Yb 2 O 3 , ZrO 2 , Ta 2 O 5 , Nb 2 O 5 and WO 3 is 78% or below, log η which is logarithm of viscosity η at liquidus temperature is 0.8 or over, and liquidus temperature is 1100° C. or below.