Patent ID: 8089696

Claim:
An illumination optical system comprising: a condenser that converges light emerging from a light source so that convergent light emerges from the condenser; a first lens array that converts convergent light emerging from the condenser into a plurality of parallel bundles of light in a first cross sectional plane that contains an optical axis of the illumination optical system; a second lens array that converts a plurality of convergent bundles of light emerging from the first lens array into a plurality of parallel bundles of light in a second cross sectional plane that contains the optical axis of the illumination optical system and perpendicular to the first cross sectional plane; and a polarized beam splitting surface that guides the plurality of bundles of light emerging from the second lens array to an illuminated surface, wherein light incident on the condenser is compressed by the condenser, the first lens array, and the second lens array, the second cross sectional plane is parallel to the normal of the polarized beam splitting surface; let L 0 be a distance on the optical axis of the illumination optical system between the surface of a lens cell in the first lens array and the surface of a lens cell in the second lens array, and let L 1 be the distance between the surface of an outermost lens cell in a direction perpendicular to the optical axis, among lens cells in the first lens array and the surface of an outermost lens cell in the direction perpendicular to the optical axis, among lens cells in the second lens array, in the first cross sectional plane, a value obtained by dividing the longer one of distances L 0 and L 1 by the shorter one of distances L 0 and L 1 is larger than 1 and smaller than 1.2.