| 摘要 |
PURPOSE:To make a lens system compact and to reduce its cost by using a lens system of four-group, four-element constitution which meets specific requirements. CONSTITUTION:This lens system consists of a 1st positive meniscus lens which has its convex surface on an object side, a 2nd negative meniscus lens which has its convex surface on the object side, a 3rd negative meniscus lens which is arranged symmetrically with the 2nd lens about a stop, and a 4th positive meniscus lens which is arranged symmetrically with the 1st about the stop and has four-group, four-element constitution meeting the condition of equations (i)-(iv). In the equations, (i)-(iv), N1 is the refractive indexes of the 1st and 4th lenses on (d) lines, N2 the refractive indexes of the 2nd and 3rd lenses on (d) lines, (f) the focal length of the whole lens system for a copying machine, f1 the focal length of the 1st and 4th lenses, f2 the focal length of the 2nd and 3rd lenses, and d3 the core thickness of the 1st and 4th lenses. Consequently, the whole lens system is made compact and reduced in size.
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