| 摘要 |
PURPOSE:To make a system compact, and to decrease the number of lenses by providing a function for keeping mainly a distance between a copying body surface and an image surface constant, on the first the third groups, and providing mainly a variable power function on the second group, in a copying variable power lens system constituted of three groups. CONSTITUTION:A titled lens system is constituted of the first lens group having a negative focal distance, the second lens group having a positive focal distance, and the third lens group having a negative focal distance, from a copying body side. The first lens group and the third lens group move roughly symmetrically, when the second lens group is based on as a reference, and have a function for keeping mainly a distance between the surface of an object to be photographed and the image surface constant, consist of only one piece of negative lens, and the second lens group has mainly a variable power function, and a biconvex lens, a negative meniscus lens whose concave surface is turned to the center, and a positive meniscus lens whose concave surface is turned to the center are placed in the center, in both its outsides, and also in both its further outside, respectively. In this way, the variable power ratio exceeds three times, the distance between an image and an object is small, the lens system is compact, the number of constitution lenses is small, and an inexpensive copying variable power lens system can be obtained.
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