| 摘要 |
PROBLEM TO BE SOLVED: To obtain a retrofocus wide-angle lens having seven-lens constitution where a negative front group and a positive rear group are arrayed from an object side, satisfying a specified conditional expression so that it may be compact, have a wide-angle and large-aperture such as an F-number of <=1.4 while maintaining excellent optical performance, and suitable for a monitor camera. SOLUTION: In this lens, a negative 1st lens group G1 constituted by arraying a 1st lens L1 consisting of a negative meniscus lens whose convex surface faces to the object side, a 2nd lens L2 consisting of a biconvex lens and a 3rd lens L3 consisting of a negative meniscus lens whose convex surface faces to the object side, a diaphragm 1, a positive 2nd lens group G2, an aperture diaphragm 2, a positive 3rd lens group G3 and a filter part 3 are arranged from the object side, and an image is formed at an image-forming position P. Then, the lens satisfies the conditional expressions (1) 0.6<f'/I<0.85 and (2) 0.45<|f'G1/DG1-2|<0.88 (Provided that f' means the focal distance of an entire system, (I) means the length of the diagonal of an effective image plane, f'G1 means the focal distance of the 1st lens group G1, DD1-2 means a distance from the surface of the 1st lens L1 on the object side to the surface of the 4th lens L4 on an image forming surface side).
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