| 摘要 |
PROBLEM TO BE SOLVED: To secure specified back focus and the position of an exit pupil and to obtain excellent image-formation performance with little ghost by constituting the lens of a front group having negative refractive power, an aperture diaphragm and a rear group having positive refractive power in order from the side of an object and making focal length, distance and the radius of curvature satisfy specified conditions. SOLUTION: This lens is composed of the front group constituted of a positive lens and a negative meniscus lens whose strong concave surface faces to the side of an image, the aperture diaphragm and the rear group whose surface on the side nearest to the object is the concave surface facing to the side of the object and which has the positive refractive power in order from the side of the object. The condition (I)|DS1 +fRF|/f<0.22 and the condition (II) 0.5< f1 B-(D12 +R21 )}/f<2.7 are satisfied. Provided that (f) means the focal length of an entire system, DS1 means the distance between the aperture diaphragm and the surface of the rear group on the side nearest to the object, fRF means the front side focal position of the rear group, f1 B means the rear side focal position of the positive lens of the front group, D12 means the distance between the positive lens of the front group and the negative meniscus lens of the front group, and R21 means the radius of curvature of the surface of the negative meniscus lens of the front group on the side of the object.
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