| 摘要 |
PURPOSE:To develop the titled optical glass having small sp.gr., a high refractive index, and low dispersion by adding Nb2O5 and CaO having comparatively small sp.gr. and affording a high refractive index into an optical glass composition. CONSTITUTION:An optical glass is the glass having the following composition. A starting material is melted, homogenized, and annealed to obtain the glass contg. 0-22% SiO2 and 3-30% B2O3 where SiO2+B2O3=20-30%, 18-37% La2O3 and 0-8% Y2O2 where La2O3+Y2O3=18-37%, 8-22% Nb2O5, 1-8% ZrO2, 10-24% CaO and 0-10% MgO where CaO+MgO=10-24%, <10% ZnO, <5% BaO, <8% SrO, <5% PbO, <2% TiO2, <5% Ta2O5, <5% WO3, <5% metallic oxide such as Na2O and K2O, <6% Al2O3, and <6% P2O5. The high-refractive index and low-dispersion optical glass having >=1.78 nud, >=38 nud, and <4.3 sp.gr. can be obtained.
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