| 摘要 |
An optical glass having high-refractivity and low-dispersion optical properties and having a low glass transition point so that a heat-treating furnace can be operated for a long period of time. The optical glass has a refractive index nd of at least 1.875, an Abbe's number nud of at least 39.5 and a glass transition point Tg of 700° C. or lower, and contains at least one of La2O3, Gd2O3, Y2O3 or Yb2O3 and at least one of ZrO2, Ta2O5 or Nb2O5, with a weight ratio of the total content of La2O3, Gd2O3, Y2O3 and Yb2O3 to the total content of SiO2 and B2O3 of from 3.2 to 5 and the weight ratio of the total content of ZrO2, Ta2O5 and Nb2O5 to the total content of SiO2 and B2O3 is from 1.1 to 1.5.
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