Transmissive filter for correcting illuminance distribution

A transmissive filter for correcting illuminance distribution, adapted to be positioned between a lens for forming an image of an illuminated original on an image forming surface and the image forming surface, or between said original and said image forming lens, and having transparent areas for passing light therethrough and opaque areas for blocking light, for correcting illuminance irregularities on said image forming surface, said transmissive filter having lowest transmittance around an effective pupil formed by projecting an exit pupil of said lens onto the filter when the filter is disposed between said lens and said image forming surface, or lowest transmittance around an effective pupil formed by projecting an entrance pupil of said lens onto the filter when the filter is disposed between said original and said lens, said transmittance being progressively higher concentrically in a stepwise manner toward an axial center and an outer periphery of the filter, said axial center of said filter being transparent.