| 摘要 |
PROBLEM TO BE SOLVED: To provide a thin film ND filter which can uniformly attenuate the light quantity in the visible region and has excellent durability. SOLUTION: The ND filter is a thin film type produced by depositing light absorbing films 3, 5 and dielectric films 2, 4, 6 on a transparent substrate 1. The light absorbing films 3, 5 are formed by vapor deposition by using a metal material Ti as the source material and contains oxides TiOx of the metal material produced by introducing a mixture gas containing oxygen during the deposition while keeping a constant vacuum degree in the range from 1×10<-3> Pa to 1×10<-2> Pa. The oxygen proportion in the mixture gas is controlled to <=50%. Preferably, after the light absorbing films 3, 5 and dielectric films 2, 4, 6 are deposited on the transparent substrate 1, the films are heated in an oxygen atmosphere containing >=10% oxygen to saturate changes in the optical characteristics.
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