Optical system to reduce image to lens distance by polarization control

Claim 1

In an infinity image display system wherein the image is caused to appear at infinity through use of a lens system, apparatus interposed between the real image plane and the lens system to permit compressing the image plane to lens distance comprising: a. a first polarizer disposed on the side of the image plane nearest the lens system; b. a first plane beamsplitter on the side of said first polarizer nearest the lens system at a distance a from said image plane; c. a first quarter waveplate disposed between said lens system said first beamsplitter said waveplate having its fast and slow axes disposed at substantially 45* to the plane of polarization of said first polarizer; d. a second beamsplitter disposed between said first waveplate and said lens system at a distance b from said first beamsplitter. e. a second quarter waveplate disposed on the side of said second beamsplitter nearest the lens system; said second quarter waveplate having its fast and slow axes oriented with respect to the corresponding axes of the first quarter waveplate at angles equal to a first substantially integral multiple of 90*; and f. a second polarizer disposed on the side of said second quarter waveplate nearest the lens system, said second polarizer having its plane of polarization oriented with respect to the plane of polarization of said first polarizer at an angle equal to a second substantially integral multiple of 90*, one of said multiples being even and the other being odd, whereby the distance c of the lens system from said second beam splitter will equal (f - a - 3b) and the total distance from the image plane to the lens will be a+b+c, a reduction of 2b over a system without said apparatus interposed.