| 摘要 |
PURPOSE:To sufficiently correct aberrations even if a rear conversion lens system is set to a large-aperture telephoto lens, by specifying conditions of five lenses. CONSTITUTION:This lens system consists of five lenses, namely, a first negative lens L1 which has a powerful concave directed to the image side, a second positive double convex lens L2, a third negative lens L3, a fourth negative lens L4 which has a powerful concave directed to the object side, and a fifth positive lens L5 in order from the object side. These lenses satisfy inequalities I-VI where fW, f123, f45, T3, R2-2, N1, and nu4 are the focal length of the whole of the rear conversion lens system, the resultant focal length of first - third lenses, the resultant focal length of fourth and fifth lenses, the air interval between second and third lenses, the radius of curvature of the image-side surface of the second lens L2, the refractive index of the first lens L1, and the Abbe's number of the fourth lens L4 respectively. Thus, the settable object range of the lens system is extended, and aberrations are satisfactorily corrected, and the lens system can be applied to a large-aperture telephoto lens.
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