Patent ID: 7138349

Claim:
An optical glass having: a refractive index (n d ) and an Abbe number (v d ) which are within an area surrounded by straight lines that are drawn by connecting point A (n d =1.835, v d =46.5), point B (n d =1.90, v d =40.0), point C, (n d =1.90, v d =35.0) and point D (n d =1.835, v d =38.0) in a sequence of A, B, C, D and A as border lines in x-y orthogonal coordinates shown in FIG. 1 , in which X-axis is the Abbe number (v d ) and Y-axis is the refractive index (n d ), the area including the border lines; the optical glass comprising: 0.1 to 8 mass % of SiO 2 ; 5 to less than 20 mass % of B 2 O 3 ; 15 to 50 mass % of La 2 O 3 ; 0.1 to 30 mass % Gd 2 O 3 , 0 to 10 mass % of GeO 2 and 0 to 8 mass % of Nb 2 O 5 , where a total content of Gd 2 O 3 , GeO 2 and Nb 2 O 5 is more than 10 mass % to 30 mass %; 0 to 5 mass % of Yb 2 O 3 ; 0 to 1 mass % of TiO 2 ; 0 to 8 mass % of ZrO 2 ; more than 19 to 25 mass % of Ta 2 O 5 ; 0 to 10 mass % of WO 3 ; 0 to 15 mass % of ZnO; 0 to 5 mass % of RO, where RO is one or more kinds of oxides selected from CaO, SrO and BaO; more than 0.5 to less than 3 mass % of Li 2 O; 0 to 1 mass % of Sb 2 O 3 ; and 0.1 to 6 mass % in a the total content of fluorides of above-described metal elements as F element with which a part or all of one or more kinds of oxides of above-described metal elements are substituted; wherein the optical glass is free from cadmium, thorium, Y 2 O 3 , P 2 O 5 , and TeO 2 , and the optical glass has a transition temperature (Tg) of 550 to 650° C.