Patent ID: 7341357

Claim:
A projection display apparatus comprising: an image forming element; and an imaging optical system comprising a plurality of reflectors for projecting an image formed by said image forming element to provide an enlarged version of the image, wherein at least one of the reflectors in said imaging optical system is movable such that the focus can be adjusted, wherein said movable reflector is movable along a straight line that is non-parallel with a normal line of said image forming element, wherein said plurality of reflectors comprises a first reflector on which light emitted from said image forming element first impinges, a second reflector on which light reflected by said first reflector impinges, a third reflector on which light reflected by said second reflector impinges, and a fourth reflector on which light reflected by said third reflector impinges, wherein said third reflector comprises said movable reflector which is movable for adjusting the focus, and wherein said first reflector comprises a spherical reflective surface, and each of said second reflector, said third reflector, and said fourth reflector comprises an aspherical or a free-form reflective surface.