| 摘要 |
The invention provides a lens system especially adapted for use with photocopying machines, phototypesetters, etc. whose magnifying power may be varied continuously within a range near the unity magnification for example between 0.7 and 1.4. The lens system comprises lenses and lens groups symmetrically arranged with respect to a center stop in such a manner that the outermost lenses (the front and rear lenses) and/or the lens next to the outermost lenses may be shifted toward and away from the stop while maintaining said symmetrical relation. In an embodiment, the magnification is unity when the overall length of the lens system is the longest while the magnification is greater or smaller than unit when the overall length is shorter than the longest one. Aberrations including chromatic aberration are well corrected.
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