Patent ID: 7932952

Claim:
A light quantity adjusting device which comprises a diaphragm for forming an aperture and a filter member for attenuating a quantity of light passing through the aperture and in which a cover ratio of the aperture by the filter member is changed, wherein the filter member includes a plurality of regions having different transmittances, wherein in a state in which the aperture is completely covered with the filter member, each of the plurality of regions of the filter member is configured so that a phase difference between lights with a predetermined wavelength λ, which pass through the respective regions of the filter member inside the aperture, is within one of the following three ranges: (−1/5)λ to (1/5)λ; (1−1/5)λ to (1+1/5)λ; and (2−1/5)λ to (2+1/5)λ, wherein the filter member comprises: a substrate; a first region which is formed on a first surface of the substrate and does not have an ND layer; a second region which is formed on a region different from the first region on the first surface of the substrate and has an ND layer having a predetermined transmittance; a third region which is formed on a second surface of the substrate and has an ND layer having the predetermined transmittance; and a fourth region which is formed on a region different from the third region on the second surface of the substrate and has an ND layer having a transmittance smaller than the predetermined transmittance, wherein the second region and the fourth region are different from each other in area, wherein the second surface is located on a side of the substrate facing an opposite direction as compared to the first surface, wherein the first region includes a base coat layer and an AR coat layer provided on the base coat layer, wherein the second region includes the respective ND layer having the predetermined transmittance and an AR coat layer provided on the respective ND layer having the predetermined transmittance, wherein the third region includes a base coat layer, the respective ND layer which is provided on the base coat layer and has the predetermined transmittance, and an AR coat layer provided on the respective ND filter having the predetermined transmittance, wherein the fourth region includes the ND layer having a transmittance smaller than the predetermined transmittance, and an AR coat layer provided on the ND layer having the transmittance smaller than the predetermined transmittance, and wherein each of the base coat layers is configured to have a film thickness that causes the phase difference to be within one of the three ranges.