| 摘要 |
PURPOSE:To attain a high optical performance even if a rear converter lens is set to a main lens system having a large aperture, by adopting the rear converter method and specifying the lens shape of each lens group so as to satisfactorily correct various aberrations. CONSTITUTION:A 1st lens group consists of a 11th lens which has the convex directed to the object side and has a negative refracting power and the 12th double-convex lens, and the 2nd lens group consists of a 21st lens which has the convex directed to the image surface side and has a positive refracting power, a 22nd double-concave lens, and a 23rd double-convex lens. A 3rd lens group consists of a 31st lens which has the convex directed to the image surface side and has a positive refracting power and a 32nd double-concave lens, and the conditions of inequalities I-V are satisfied where rij is the radius of curvature of the j-th lens surface in the i-th lens group and dij is the j-th lens thickness or air interval and li is the air interval between the j-th lens group and the (i+1)th lens group and F is the focal length of the whole of the rear converter lens system. Thus, various aberrations are satisfactorily corrected, and an excellent image forming capacity is obtained even in case of a large aperture.
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