| 摘要 |
PROBLEM TO BE SOLVED: To secure back focus, to suppress the generation of color shading, and to obtain excellent optical performance with an about 38 deg. field angle of photography and an F value of about 1.4 by composing an image pickup lens of two groups across a stop as a retrofocus type wide-angle lens and satisfying specific conditional expressions. SOLUTION: This lens is constituted by arranging a front group with negative refractive power, a stop 3, and a rear group with positive refractive power in this order from the object side; and the front group is constituted by arranging a positive lens L1 and two negative lenses L2 and L3 and the rear group is formed by arranging a positive lens L4 , two pairs of cemented lenses L5 to L8 , and a positive lens L9 . Here, 0.85<|fF/fR|<1.4, 2.6<|f1 /f23|<4.4, 1.8<DFR/f<3.8, and 70.0<νd , where f1 is the focal length of the 1st lens, fF the focal length of the front group, fR the focal length of the rear group, f23 the composite focal length of the 2nd and 3rd lenses, DFR the air gap between the groups, f the focal length of the whole system,νd the mean value of the Abbe's numbers of the positive lenses in the rear group.
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