Patent ID: 8740394

Claim:
An illumination optical system for use with a projector apparatus in which light emitted from a light source is guided to a TIR prism, light totally reflected by a total reflection surface of the TIR prism is reflected by a DMD having a rectangular surface to perform light modulation, and light transmitted through the total reflection surface after the light modulation is projected on a screen by a projection optical system, wherein: the DMD is disposed such that the rectangular surface of the DMD is parallel to one end face of the TIR prism from which the totally reflected light exits; and the TIR prism is configured such that a projection line, which is a normal to the total reflection surface vertically projected on the surface of the DMD, forms an angle other than 90° with a micromirror turning axis of the DMD, an exit light projection line, which is a principal ray of light beam exits from the total reflection surface vertically projected on the surface of the DMD, forms an angle of 90° with the micromirror turning axis, and an incident light projection line, which is a principal ray of light beam incident on the total reflection surface vertically projected on the surface of the DMD, is located on the same side as the exit light projection line with respect to a straight line passing through an end point of the incident light projection line and extending parallel to a long side of the DMD.