| 摘要 |
PURPOSE:To continuously vary projection power within a specific range and to hold an F number effective by composing a lens system of an aperture stop, a 1st positive lens group, and a 2nd negative lens group, and moving the groups to a reduction side at the time of zooming while increasing the interval between the groups. CONSTITUTION:The aperture stop S, the positive lens group I, and the 2nd lens group II are arranged in order from an enlargement side and the groups are moved to the reduction side at the time of zooming from the longest focal length end to the shortest focal length end while the interval alpha10 between the groups is widened. The group I is composed of a positive, a biconcave, a positive, a negative lens and aberrations are compensated excellently; and the group II is composed of a positive meniscus lens having its concave surface on the enlargement side and a negative lens and various aberrations at the time of zooming are compensated. Thus, the groups are moved to the reduction side while the interval between the groups is widened to hold the distance between object images constant, so projection power can be varied freely and continuously within a range of about 28-38 and the effective F number of the compact lens system on the enlargement side is held within a range where there is no practical problem.
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