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Abstract

An illumination system for illuminating an illumination region having a difference in size along a first direction and a second direction perpendicular to the first direction. The illumination system includes an optical integrator having elements with different refractive powers with respect to the first and second directions as the optical integrator is viewed in an optical axis direction, the elements also having the same pitch with respect to the first and second directions, and an optical device for directing light from a light source upon the optical integrator at different largest incidence angles with respect to the first and second directions, so as to satisfy a relation 0.8<[(tan .theta..sub.1 /tan .theta..sub.2)/(.o slashed..sub.1 /.o slashed..sub.2)]<1.2 where .o slashed..sub.1 and .o slashed..sub.2 are largest incidence angles of the light incident on the optical integrator with respect to the first and second directions, and .o slashed..sub.1 and .o slashed..sub.2 are refractive powers of the optical integrator with respect to the first and second directions.

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