Patent ID: 7157159

Claim:
An infrared ray cut filter comprising: a transparent substrate; and a multilayer membrane including multiple high-refractive index thin membranes of a high-refractive index material and multiple low-refractive index thin membranes of a low-refractive index material, which are laid on said transparent substrate in an alternating fashion, said multilayer membrane having thin membrane layers of no less than 16 but no more than 32, wherein: a design wavelength λ for the thin membrane layers is 750 nm, a first layer of said multilayer membrane from a side of said transparent substrate is one of said high-refractive index thin membranes and is formed to have an optical thickness of no less than λ/4; a second layer of said multilayer membrane is formed to have an optical thickness of no less than λ/4; each layer from a third layer through a prescribed layer of said multilayer membrane is formed to have an optical thickness of no more than λ/4; each layer sandwiched in between said prescribed layer and a last layer of said multilayer membrane is formed to have an optical thickness of no less than λ/4; and said last layer is one of said low-refractive index thin membranes and is formed to have an optical thickness of no more than λ/4.