ND FILTER

Abstract

Provided is an ND filter including an alternating layer which is composed of two films being alternately stacked and formed on a transparent substrate, the two films having different refractive indexes, wherein the alternating layer has a substrate-side reflected light attenuating multi-layered film and a transmittance adjusting multi-layered film formed on the transparent substrate in the stated order from the transparent substrate side, and the light absorption amount of the substrate-side reflected light attenuating multi-layered film is set to be 20% or more and 30% or less. Thus, an ND filter having satisfactory front surface reflection characteristics and rear surface reflection characteristics can be stably obtained while the transmittance of 4% or more and 11% or less is maintained with respect to the entire visible region (400 nm or more and 700 nm or less).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of an ND filter according to the present invention.

FIG. 2 is a cross-sectional view of a conventional ND filter.

FIG. 3 is a cross-sectional view of the ND filter according to the present invention.

FIG. 4 is a spectral characteristics diagram of the ND filter according to the present invention.

FIG. 5 is a table showing a film configuration of an ND filter according to Example 1 of the present invention.

FIG. 6 is a spectral characteristics diagram of the ND filter according to Example 1 of the present invention.

FIG. 7 is a table showing a film configuration of an ND filter according to Example 2 of the present invention.

FIG. 8 is a spectral characteristics diagram of the ND filter according to Example 2 of the present invention.

FIG. 9 is a table showing a film configuration of an ND filter according to Example 3 of the present invention.

FIG. 10 is a spectral characteristics diagram of the ND filter according to Example 3 of the present invention.

FIG. 11 is a table showing a film configuration of an ND filter according to Comparative Example 1 of the present invention.

FIG. 12 is a spectral characteristics diagram of the ND filter according to Comparative Example 1 of the present invention.

FIG. 13 is a table showing a film configuration of an ND filter formed of a multi-layered film of NbO_x and SiO₂.

FIG. 14 is a spectral characteristics diagram of the ND filter formed of the multi-layered film of NbO_x and SiO₂.

Claims

1. An ND filter, comprising: a transparent substrate; andan alternating layer composed of two films being alternately stacked and formed on the transparent substrate, the two films having different refractive indexes,wherein the alternating layer has a substrate-side reflected light attenuating multi-layered film and a transmittance adjusting multi-layered film formed on the transparent substrate in stated order from a side of the substrate, and a light absorption amount of the substrate-side reflected light attenuating multi-layered film is 20% or more and 30% or less.

2. An ND filter according to claim 1, wherein the alternating layer is composed of a dielectric film and a metal oxide film.

3. An ND filter according to claim 2, wherein the dielectric film comprises one film formed of one selected from Al2O3, SiO2 and MgF2, and the metal oxide film comprises one film formed of one selected from TiOx and NbOx.

4. An ND filter according to claim 3, wherein a thickness of the dielectric film in the substrate-side reflected light attenuating multi-layered film is larger than a thickness of the dielectric film in the transmittance adjusting multi-layered film.

5. An ND filter according to claim 1, wherein the ND filter has a transmittance of 4% or more and 11% or less, and a front surface reflectance and a rear surface reflectance of 3% or less, in an entire visible region of 400 nm or more and 700 nm or less.

6. An ND filter, comprising: a transparent substrate; andan alternating layer composed of two films being alternately stacked and formed on the transparent substrate, the two films having different refractive indexes,wherein the alternating layer has a substrate-side reflected light attenuating multi-layered film, a transmittance adjusting multi-layered film, and a front-surface side reflected light attenuating multi-layered film formed on the transparent substrate in stated order from a side of the transparent substrate, and a light absorption amount of the substrate-side reflected light attenuating multi-layered film is 20% or more and 30% or less.

7. An ND filter according to claim 6, wherein the alternating layer is composed of a dielectric film and a metal oxide film.

8. An ND filter according to claim 7, wherein the dielectric film comprises one film formed of one selected from Al2O3, SiO2 and MgF2, and the metal oxide film comprises one film formed of one selected from TiOx and NbOx.

9. An ND filter according to claim 8, wherein a thickness of the dielectric film in the substrate-side reflected light attenuating multi-layered film is larger than a thickness of the dielectric film in the transmittance adjusting multi-layered film.

10. An ND filter according to claim 6, wherein the ND filter has a transmittance of 4% or more and 11% or less, and a front surface reflectance and a rear surface reflectance of 3% or less, in an entire visible region of 400 nm or more and 700 nm or less.