Abstract: An optical glass having a refractive index (nd) and an Abbe number (vd) which are within an area surrounded by the straight lines which are drawn by connecting point A (nd=1.835, vd=46.5), point B (nd=1.90, vd=40.0), point C (nd=1.90, vd=35.0) and point D (nd=1.835, vd=38.0) in a sequence of A, B, C, D and A as border lines in x-y coordinates shown in FIG. 1, in which X-axis is the Abbe number (vd) and Y-axis is the refractive index (nd), the area including the border line. The optical glass has low glass transition temperature (Tg), and suitable for precision mold pressing.

Abstract: An optical glass having a refractive index (nd) and an Abbe number (vd) which are within an area surrounded by the straight lines which are drawn by connecting point A (nd=1.835, vd=46.5), point B (nd=1.90, vd=40.0), point C, (nd=1.90, vd=35.0) and point D (nd=1.835, vd=38.0) in a sequence of A, B, C, D and A as border lines in x-y coordinates shown in FIG. 1, in which X-axis is the Abbe number (vd) and Y-axis is the refractive index (nd), the area including the border line. The optical glass has low glass transition temperature (Tg), and suitable for precision mold pressing. The optical glass which has the refractive index (nd) and Abbe number (vd) within the above-described area, where the area includes the border lines, has the composition of SiO2—B2O3—La2O3—Gd2O3—Li2O—F system, the transition temperature (Tg) of 550 to 650° C., and is free from lead, cadmium, thorium, Y2O3, P2O5 and TeO2.

Abstract: An optical glass having a refractive index (nd) and an Abbe number (?d) which are within an area surrounded by the straight lines which are drawn by connecting point A (nd=1.835, ?d=46.5), point B (nd=1.90, ?d=40.0), point C, (nd=1.90, ?d=35.0) and point D (nd=1.835, ?d=38.0) in a sequence of A, B, C, D and A as border lines in x-y coordinates shown in FIG. 1, in which X-axis is the Abbe number (?d) and Y-axis is the refractive index (nd), the area including the border line. The optical glass has low glass transition temperature (Tg), and suitable for precision mold pressing.

Abstract: An optical glass which is free of PbO which causes environmental pollution and also is free of expensive Ta2O5 and Nb2O5 comprises, in mass %, SiO2 40-60% B2O3 1 to less than 5% Al2O3 0-3% TiO2 15.5-19%?? ZrO2 0-1% WO3 0-5% ZnO 0-5% CaO 0-4% SrO 0-10% BaO 10.5-20%?? Na2O + K2O 11-20% in which Na2O 0-9% and K2O ?6-20% a refining agent 0-1% and has optical constants of a refractive index (nd) within a range from 1.55 to less than 1.67 and an Abbe number (?d) within a range from 30 to 45.

Abstract: An optical glass having a refractive index (nd) and an Abbe number (vd) which are within an area surrounded by the straight lines which are drawn by connecting point A (nd=1.835, vd=46.5), point B (nd=1.90, vd=40.0), point C, (nd=1.90, vd=35.0) and point D (nd=1.835, vd=38.0) in a sequence of A, B, C, D and A as border lines in x-y coordinates shown in FIG. 1, in which X-axis is the Abbe number (vd) and Y-axis is the refractive index (nd), the area including the border line. The optical glass has low glass transition temperature (Tg), and suitable for precision mold pressing. The optical glass which has the refractive index (nd) and Abbe number (vd) within the above-described area, where the area includes the border lines, has the composition of SiO2—B2O3—La2O3—Gd2O3—Li2O—F system, the transition temperature (Tg) of 550 to 650° C., and is free from lead, cadmium, thorium, Y2O3, P2O5 and TeO2.

Abstract: An optical glass which is free of PbO which causes environmental pollution and also is free of expensive Ta2O5 and Nb2O5 comprises, in mass %, 1 SiO2 40-60% B2O3 1 to less than 5% Al2O3 0-3% TiO2 15.5-19%   ZrO2 0-1% WO3 0-5% ZnO 0-5% CaO 0-4% SrO 0-10% BaO 10.