| 摘要 |
Provided is a precision press-molding glass preform, which is formed of a high-refractivity low-dispersion optical glass containing no PbO and which requires none of cutting and polishing of an optical-function surface after the precision press-molding is carried out, the optical glass containing, by mol %, 40 to 60% of B2O3 exclusive of 40%, 5 to 25% of La2O3, 2 to 22% of Gd2O3, 5 to 45% of ZnO and 0 to 10% of SiO2 exclusive of 10% as glass components but containing no PbO, wherein the ratio of the content of B2O3 to the total content of B2O3 and SiO2 (B2O3/(B2O3+SiO2)) is over 0.84 but not more than 1.00, and the ratio of the content of Gd2O3 to the total content of Gd2O3 and Nb2O5 as an optional component (Gd2O3/(Gd2O3+Nb2O5)) is over 0.91 but not more than 1.00, the optical glass having a refractive index (nd) of over 1.80 but not more than 2.00 and an Abbe's number (nud) of 40 to 45 exclusive of 45.
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