ND FILTER FOR APERTURE DEVICE AND APERTURE DEVICE COMPRISING ND FILTER

Abstract

This invention decreases deformation of a plastic substrate caused by thermal expansion and contraction in an evaporation process of forming a multi-layered film of an ND filter, thus arising of wrinkles is prevented. The plastic substrate serving as the base of the ND filter is made of a polyimide-based plastic material having a glass transition temperature of 200° C. or more, and has a total transmittance of light of 90% or more and has a haze factor, which represents the haze of 0.5% or less. As the multi-layered film, Al2O3 films for reduction of the reflectance and TiOx films for reduction of the transmittance are alternately formed on the substrate. An MgF2 film made of a low-refraction material is formed as the uppermost layer to further reduce the reflection. In the evaporation process, even when the temperature of the plastic substrate reaches almost 200° C., the sufficiently high glass transition temperature of the plastic material can suppress arising of wrinkles on that portion of the plastic substrate where the multi-layered film is formed.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing the arrangement of a photographing optical system;

FIG. 2 is a view showing the arrangement in the chamber of a vacuum evaporation machine;

FIG. 3 is a perspective view of a substrate jig;

FIG. 4 is a schematic sectional view of an ND filter according to the first embodiment;

FIG. 5 is a graph of the transmittance characteristics of the ND filter according to the first embodiment;

FIG. 6 is a graph of the reflectance characteristics of the ND filter according to the first embodiment;

FIG. 7 is a plan view of an ND filter according to the second embodiment;

FIG. 8 is a sectional view of the ND filter according to the second embodiment; and

FIG. 9 is a plan view of an ND filter according to the third embodiment.

Claims

1. An ND filter for an aperture device, wherein at least one multi-layered thin film which reduces a quantity of transmitted light is formed by an evaporation method on a plastic substrate made of a plastic material, and a glass transition temperature of said plastic material is not less than 200° C.

2. The ND filter according to claim 1, wherein total transmittance of light of said plastic substrate is not less than 90% and a haze factor of said plastic substrate is not more than 0.5%.

3. The ND filter according to claim 1, wherein said plastic substrate is made of a polyimide-based plastic material.

4. The ND filter according to claim 1, including a density profile in which a quantity of transmitted light changes stepwise in accordance with a position where the light is transmitted.

5. The ND filter according to claim 1, including a density profile in which a quantity of transmitted light changes continuously in accordance with a position where the light is transmitted.

6. An aperture device comprising at least one ND filter, wherein said ND filter, which is manufactured by forming a multi-layered film to reduce a quantity of transmitted light on a plastic substrate made of a plastic material with a glass transition temperature of not less than 200° C., is attached to an aperture blade, and said ND filter reduces the quantity of light passing through an aperture that said aperture blade forms.

7. A camera comprising an optical system which includes an aperture device according to claim 6, and a solid-state image pickup element which photographs an image that said optical system forms.