Patent ID: 7207681

Claim:
A projection display device for enlarging and projecting an image along a projection optical axis, comprising: a first lens group arranged on the projection optical axis on the enlarging end of the projection display device; a plurality of display elements, each modulating a different one of a plurality of light beams with image information; an optical combiner for receiving from at least two different directions light beams modulated by the different display elements, combining the modulated light beams, and directing the combined modulated light beams along an optical axis to the first lens group; a plurality of second lens groups, each having positive refractive power and each arranged on a separate optical axis so that a different one of the light beams modulated by a different display element is incident on the optical combiner after passing through one of the second lens groups; wherein the following conditions are satisfied by the projection display device for each of the plurality of second lens groups: 1.0< f 2/ f< 8.0 LVD/{ 4·(1−2·tan θ)}< Bf<LVD /(1−2·tan θ′)+ LVD 0.25< d/f 2<1.0 wherein f2 is the focal length of the second lens group; f is the smallest focal length of the combination in optical series of the first lens group and the second lens group; LVD is the diagonal dimension of the display element; Bf is the back focal length of the combination in optical series of the first lens group and the second lens group at the smallest focal length of the combination of the first lens group and the second lens group; θ is the angle for which sin θ=1/(4·F NO ); θ′ is the angle for which sin θ′=1/(2·F NO ); F NO is the f-number at the smallest focal length of the combination in optical series of the first lens group and the second lens group; and d is the air-converted distance along the optical axis, defined by the combination in optical series of the first lens group and each of the second lens groups, between the first lens group and each of the second lens groups at the smallest focal length of the combination in optical series of the first lens group and the second lens group.