Patent ID: 7387840

Claim:
A ray cut filter, comprising: a transparent plate; and a multilayer film formed on said transparent plate, wherein: said multilayer film is composed of first thin films made of a high refractive index material and second thin films made of a low refractive index material, said first thin films and said second thin films are alternately layered, said multilayer film is structured so as to form a sharpness preventing means for providing an inflection point at a wavelength, within a change wavelength band in which transmittance changes sharply, which prevents a sharp change in transmittance in a predetermined wavelength band, and said multilayer film is a layered structure composed of a plurality of layers, each of which is composed of said first and second thin films such that optical film thicknesses of said first thin films and said second thin films differ from layer to layer of said plurality of layers such that said layers have thicknesses different from that of each other, wherein said sharpness preventing means comprises optical film thicknesses of each thin film of said first and second thin films having substantially the same optical film thickness in at least one of said plurality of layers, and wherein said first and second thin films have optical film thicknesses which gradually increase between others of said layers with distance from said transparent plate, wherein said sharpness preventing means further comprises adjustment layers provided at at least two locations between said plurality of layers and on both ends of said layered structure, said adjustment layers preventing an amount of change in transmittance from changing sharply between said plurality of layers.