| 摘要 |
PROBLEM TO BE SOLVED: To provide a projection lens for a telephoto type projector which is bright, made relatively small in size, and long in back focus, and has a sufficiently long exit pupil and no variation. SOLUTION: A nearly telecentric telephoto zoom lens which enlarges and projects an image of a display surface on a screen has a 1st lens group L1 with positive refracting power which is fixed during zooming and only adjusts a distance, a 2nd lens group L2 with negative refracting power which is movable during zooming, a 3rd lens group L3 with negative refracting power which is movable during zooming, a 4th lens group L4 with positive refracting power which is movable during zooming, and a 5th lens group L5 with positive refracting power which is fixed during zooming in order from a screen side. Then when the focal length is varied from the focal length at the wide-angle end to the focal length at the telephoto end, the gap between the 2nd lens group L2 and 3rd lens group L3 is shorter at the telephoto end than at the wide-angle end. COPYRIGHT: (C)2006,JPO&NCIPI
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