| 摘要 |
An optical glass which is a SiO2-Nb2O5-R'2O (R' being an alkali metal element)-F system of a specific composition range exhibits optical constants of a refractive index (Nd) of about 1.60 or below and an Abbe number ( nu d) of about 57-40, is free of PbO and has an improved light transmissivity.
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