US Patent 7287865 Display optical system

A projection type display optical system is provided to resolve problems of keystone distortion, and to improve illumination efficiency and contrast uniformity of an image. The projection type display optical system includes: a light source; DMD as an image display means to which an emitting light ray from the light source is irradiated; and an illumination unit installed in between the light source and the image display means, and comprising: a rod lens operating as an optical device for unifying the brightness distribution of an incident light ray from the light source and emitting the brightness unified light ray; a first lens for transmitting the emitted light ray by the rod lens; a second lens on which the transmitted light ray from the first lens incidents; and a projection part for magnifying and projecting an image formed on the image display means onto a screen, wherein the first and second lenses are set in such a manner that an optical axis of the second lens and an optical axis of the first lens do not coincide with each other, whereby a surface image that is formed when an emitted surface of the rod lens transmits the first and second lens groups is not inclined to the surface of the image display means.