Patent ID: 8728963

Claim:
An optical glass that is an oxide glass and that comprises, by cationic %, 0 to 30% of Si 4+ , 10 to 55% of B 3+ , less than 5% of total of Li + , Na + and K + , less than 5% of total of Mg 2+ , Ca 2+ and Sr 2+ , 0 to 8% of Ba 2+ , 0.1 to 15% of Zn 2+ , 10 to 50% of La 3+ , 0 to 20% of Gd 3+ , 0.25 to 15% of Y 3+ , 0 to 10% of Yb 3+ , 0 to 20% of Zr 4+ , 0.1 to 22% of Ti 4+ , 0 to 20% of Nb 5+ , 0 to 8% of Ta 5+ , 0 to 5% of W 6+ , 0 to 8% of Ge 4+ , 0 to 10% of Bi 3+ , and 0 to 10% of Al 3+ , the cationic ratio of the content of Si 4+ to the content of B 3+ , Si 4+ /B 3+ , being less than 1.0, the total content of Nb 2 O 5 and Ta 2 O 5 as oxides being determined so as to achieve a liquidus temperature of 1,220° or lower, the optical glass having a refractive index nd of 1.930 to 2.2, an Abbe's number νd of 25 to 45 and a glass transition temperature Tg of 630° C. or higher.