Patent ID: 6867157

Claim:
An optical glass having a positive anomalous dispersion comprising, in mass %, SiO 2 40-60% B 2 O 3 3-9% TiO 2 3-15% Nb 2 O 5 0.1-5.0% Al 2 O 3 3-15% WO 3 0.5-5.0% MgO 0-3% CaO 0-3% SrO 0-3% BaO 0-3% K 2 O exceeding 10% and up to 21% Na 2 O 0-10% Sb 2 O 3 0-1% and a fluoride or fluorides of a metal element or elements 3-10%, contained in the above metal oxides, a total amount of F contained in the fluoride or fluorides being free of PbO and As 2 O 3 except for unavoidable mixing of these compounds as impurities, having optical constants of a refractive index (nd) within the range from 1.48 to less than 1.55 and an Abbe number (νd) within the range from 45 to 55, and having an anomalous dispersion (Δθg,F) of +0.0010 or over.