Patent ID: 6860607

Claim:
An integrator type illumination optical system comprising: a first lens array consisting of a plurality of lens cells arranged into a matrix in a column direction and a line direction, wherein the first lens array is constituted by three column groups consisting a left column group, a center column group and a right column group, the thickness of the lens cells included in the center column group is thinner than that of the lens cells included in other column groups, the lens cells included in the left column group and the right column group are formed such that the thickness of the lens cells in each column group increases gradually from the innermost column to the outermost column in each group, respective lens cells of a second lens array have shapes that are capable of forming images of the respective lens cells of the first lens array on the object to be illuminated, and the first and the second lens arrays are formed in such a manner that the adjacent lens cells constituting the first and the second lens arrays are in contact with each other on their surfaces of curvature.