| 摘要 |
PURPOSE:To make a lens systems small-sized by satisfying prescribed conditions in the lens system which is provided with the first and the second lens groups arranged in order from the light source side and is constituted of three lenses of two group as prescribed. CONSTITUTION:Two lens groups, namely, the first and the second lens groups I and II arranged in order from the incidence side of a luminous flux constitute the lens system. The lens system is constituted of three lenses of two groups, that is, the first lens group I consists of a cemented lens of the first concave meniscus lens L1 whose convex is directed to the incidence side and the second convex lens L2 and the second lens group II consists of the third concave meniscus lens L3 whose convex is directed to the incidence side and these lenses are arranged in order from the incidence side. This lens system is constituted to satisfy conditions of formulas I and II where (f), f12, f3 are the focal length of the whole of the system, that of the first lens group I, and that of the second lens group II respectively and r3 is the radius of curvature of the condensing-side surface of the third lens L3.
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