Patent ID: 8437084

Claim:
An optical low-pass filter, comprising: a base material; and a coating layer formed to the base material on a light-entering-surface side, the coating layer including a plurality of high-refractive layers and a plurality of low-refractive layers sequentially disposed alternately on one on the other for reflecting or passing through a light of a specific wavelength range, wherein at least one high-refractive layer of the plurality of high-refractive layers is made of a transparent conductive material, different from a material of which the remaining high-refractive layers of the plurality high-refractive layers are made, to prevent attachment of dirt and dust to a surface of the coating layer, the at least one high-refractive layer has a greater layer thickness than a total layer thickness of refractive layers positioned to the light-entering-surface side of the at least one high-refractive layer, and a layer thickness of a low-refractive layer in contact with the at least one high-refractive layer on the opposite side of the light-entering-surface side is in a range of 140 to 220 nm.