Importance

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Abstract

An illumination optical system includes a fly's eye lens, having a plurality of small lens elements, for forming secondary light sources by use of light from a light source, an optical device for illuminating a surface to be illuminated, with light from the secondary light sources, wherein the optical device is arranged to assure that the secondary light sources as seen from points on the surface illuminated have substantially the same numerical aperture, an optical filter for restricting, at an entrance side of the fly's eye lens, a quantity of light entering a desired small lens element of the plurality of small lens elements constituting the fly's eye lens, and a driver for driving the optical filter.

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First Claim