Abstract: An optical glass for precision press molding that has desired optical constants, a low glass transformation point (Tg), and a devitrification temperature that is lower than a temperature of a glass melt, at which a viscosity suitable for forming of a preform material is obtained, is provided. The optical glass for precision press molding has a lanthanum borosilicate system glass having optical constants of refractive index (nd) within a range from 1.65 to 1.73 and Abbe number (&ngr;d) within a range from 50 to 60, a Tg within a range of 480-580° C. The optical glass for precision press molding has a devitrification temperature that is lower than a temperature of the glass melt when the glass melt has a viscosity &eegr; (poise) of log &eegr;=2.5. The optical glass for precision press molding has a specific composition range of SiO2—B2O3—La2O3—Y2O3—Ta2O5—CaO—Li2O system composition.

Abstract: An optical glass comprises, in mass percent, 15-35% of P2O5, 40-60% of Nb2O5, 0.5% to less than 15% of Na2O and 3% to less than 25% of BaO, has a ratio in mass % of (BaO+Nb2O5)/{(TiO2+WO3)×3+Bi2O3+Nb2O5}>1.0; is free of Pb and As; and has a refractive index (nd) within a range from 1.78 to 1.90 and an Abbe number (&ngr;d) within a range from 18 to 27.

Abstract: An optical glass having a positive anomalous dispersion comprises, in mass %, 1 SiO2 40-60% B2O3 3-9% TiO2  3-15% Nb2O5 0.1-5.0% Al2O3  3-15% WO3 0.5-5.

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.

Abstract: An optical glass includes SiO2; PbO; B2O3; not less than 0.1 mass % of TeO2; and not less than 0.4 mass % of Li2O.

Abstract: An optical glass has a large negative anomalous dispersion value and optical constants of refractive index (nd) within a range of 1.65-1.80 and Abbe number (.nu.d) within a range of 28-42. The optical glass includes, as its essential ingredients, in weight percent, 20-50% SiO.sub.2, 6-20% B.sub.2 O.sub.3 where SiO.sub.2 /B.sub.2 O.sub.3 .ltoreq.6, 0.5-15% ZrO.sub.2 and 31-50% Nb.sub.2 O.sub.5.

Abstract: An optical glass having optical constants of a refractive index (Nd) from 1.50 to 1.60 and an Abbe number (.nu.d) ranging from 62 to 73, a transformation temperature (Tg) of 550.degree. C. or below, and barely cracks or sticks to metal molds when the glass is subjected to mold pressing, maintains excellent chemical durability, and having softening capability at a low temperature which can be obtained by restricting the composition of the glass in weight percents within a specific range of a SiO.sub.2 --Al.sub.2 O.sub.3 --P.sub.2 O.sub.5 --R.sub.2 O system.

Abstract: An optical glass including as its main ingredients in weight percent 25-50% SiO.sub.2, 16-40% B.sub.2 O.sub.3, 5-25% SrO and 1-10% Li.sub.2 O has optical constants of refractive index (Nd) of 1.55-1.65 and Abbe number (.nu.d) of 55-63 and a yield point (At) below 600.degree. C. which is suited for mold pressing.