Patent ID: 7138348

Claim:
An optical glass comprising: more than 5 to 15 mass % of SiO 2 ; 20 to less than 30 mass % of B 2 O 3 ; a total amount of SiO 2 +B 2 O 3 being more than 25 to 40 mass %; more than 21 to less than 30 mass % of La 2 O 3 ; more than 5 to 15 mass % of Y 2 O 3 ; 0 to less than 10 mass % of Gd 2 O 3 ; 1 to 8 mass % of ZrO 2 ; 0.1 to 5 mass % of Nb 2 O 5 ; more than 5 to 12 mass % of Ta 2 O 5 ; a total amount of ZrO 2 +Nb 2 O 5 +Ta 2 O 5 being 7 to 20 mass %; 0 to 10 mass % of ZnO; 0 to 10 mass % of CaO; 0 to 5 mass % of SrO; 0 to 10 mass % of BaO; a total amount of ZnO+CaO+SrO+BaO being 5 to 15 mass %; 1 to 8 mass % of Li 2 O; 0 to 1 mass % of Sb 2 O 3 ; and 0 to 1 mass % of As 2 O 3 ; wherein the optical glass has optical constants which are a refractive index (nd) in a range of 1.70 to 1.75 and an Abbe number (vd) in a range of 45.0 to 54.0; wherein a glass transformation temperature (Tg) of the optical glass is in a range of 500 to 580° C.; wherein the optical glass is substantially free of Yb 2 O 3 and Al 2 O 3, and devitrification is not generated when the optical glass is kept at a temperature of 920° C. for two hours.