| 摘要 |
PROBLEM TO BE SOLVED: To properly maintain a back focus without using an spherical lens, while realizing compact type, by inseating a negative lens having a prescribed refracting power at the pre-stage of a front joint lens, applying a gauss type lens constitution, regarding a large-aperture lens for photographing at low illuminance. SOLUTION: This lens is made of a double convex lens L1 , a positive meniscus lens L2 with the concave surface directed toward an object, a negative lens L3 with the concave surface of strong curvature directed toward an image, a positive meniscus lens L4 (jointed to lens L5 ) with the convex surface directed toward the object, a negative meniscus lens L5 with the concave surface directed toward the image, a double concave lens L6 (jointed to lens L7 ) with the surface of strong curvature directed toward the object, double convex lenses L7 and L8 with the surfaces of strong curvature directed toward the image, and a positive meniscus lens L9 with the convex surface directed toward the object, arrayed respectively in order from the object. Also, constitution is so made that a relationship of 0.35<f/|f3|<0.56 is satisfied, where the focal distance of a while system is (f) and the focal distance of the third lens is f3.
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