| 摘要 |
A wide-angle telecentric projection lens system for use in enlarged projection at a magnification of about 15-20, that has a brightness of about FNO 1:7, and which covers a wide field of up to about 25 degrees in terms of the half viewing angle. This is attained by a telecentric projection lens system that comprises, in order from the screen side to the chart side, a first lens group composed of a single positive lens element, a second lens group composed of either a single negative lens element or a positive lens cemented to a negative lens, and a third lens group composed of both a negative lens cemented to a positive lens and two or more positive lens elements, which lens system satisfies the following conditions (1) and (2): (1) -2.5<fI/fII<-0.5 (2) 0.6<fIII/f<0.95 where f: the focal length of the overall lens system fI: the focal length of the first lens group fII: the focal length of the second lens group fIII: the focal length of the third lens group
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