| 摘要 |
Disclosed is 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 present invention provides an optical glass having a refractive index nd of at least 1.875, an Abbe's numberνd of at least 39.5 and a glass transition point Tg of 700° C. or lower, an optical glass which is a borosilicate glass comprising at least one selected from La2O3, Gd2O3, Y2O3 or Yb2O3 and at least one selected from ZrO2, Ta2O5 or Nb2O5, wherein the ratio (weight ratio) of the total content of La2O3, Gd2O3, Y2O3 and Yb2O3 to the total content of SiO2 and B2O3 is from 3.2 to 5 and the ratio (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, and which has a refractive index nd of at least 1.875 and an Abbe's numberνd of at least 39.5, and the like.
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