| 摘要 |
PROBLEM TO BE SOLVED: To provide an ND filter having stable spectral properties by suppressing change in spectral properties of a light attenuation film due to oxidation of a metal oxide.SOLUTION: An ND filter is formed by providing on a transparent substrate 21 a light attenuation film comprising AlOfilms 22, which are dielectric layers, and TiOfilms 23, which are light absorption layers, alternately laminated with SiNfilms 24, which act as moisture barrier layers, laminated in between to sandwich the TiOfilms 23; and then providing an ND film on top by forming an MgFfilm 25, which is an anti-reflection film, as an outer most layer. The SiNfilms 24 prevent permeation of moisture or the like, and thus prevent deterioration of the TiOfilms 23, the light absorption layers. |
