Optical illumination system and projection apparatus comprising such a system

An illumination system for supplying an optical radiation beam along a principal axis and intended for illuminating an object which, in a plane perpendicular to the principal axis, has a non-round cross-section, said system comprising a radiation source, a concave reflector for concentrating radiation emitted by the radiation source and a lens system arranged in the path of the concentrated radiation, characterized in that the lens system successively comprises a first lens plate provided with a plurality of first lenses which, in a plane perpendicular to the principal axis, have a uniform width in a first direction and a uniform height in a second direction perpendicular to the first direction, a second lens plate provided with a plurality of second lenses whose number is proportional to the number of first lenses and a third lens, the first lens plate dividing a radiation beam incident thereon into a number of sub-beams propositional to the number of first lenses, which sub-beams have their smallest constriction in the plane of the second lenses and whose chief rays are directed towards the centers of the corresponding second lenses, in that the third lens together with the second lens plate images the radiation spots formed on the first lens plate in a superimposed form on the object, and in that the width/height ratio of the first lenses corresponds to said ratio of the object cross-section in that the shape, in the plane of the second lens plate, of each of the second lenses is adapted to the cross-section, in this plane of the sub-beam belonging to the second lens and in that the second lenses are arranged such that the circumference of their total surface in said plane is substantially a circle of minimum diameter.