| 摘要 |
A zoom lens system for use in microfilm projection apparatus in which the image projection is conducted in a condition of a definite object-image distance, the system comprising from the enlargement side to the reduction side, an aperture stop disposed fixedly, a first lens group of a positive refractive power located near the aperture stop at the longest focal length side, a second lens group of a negative refractive power, and a third lens group of a positive refractive power, wherein the first to third lens groups are moved along the optical axis while increasing a distance between the first and second lens groups and decreasing a distance between the second and third lens groups in an operation of zooming from the longest focal length side to the shortest focal length side.
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