| 摘要 |
PURPOSE:To correct aberration variation at the time of focusing excellently within a wide body-distance range from an infinite-distance body to a short- distance body while employing a rear focus system by providing four lens groups and making the focal lengths of respective groups and the focal length of the whole system meet specific requirements. CONSTITUTION:This lens system has four lens groups, i.e. a 1st group which has at least three positive lenses and a negative lens and positive refracting power on the whole, a 2nd group which has a meniscus lens having it convex surface on an object side and also has negative refracting power on the whole, a 3rd group which has a cemented lens of at least a positive and a negative lens, and a 4th group which has positive refracting power, and this system satisfies inequalities, where fi is the focal length of an i-th group and F is the focal length of the whole system. Thus, the lens constitution is specified to obtain a large-aperture-ratio telephoto lens which has a large aperture ratio and short overall lens length and also has high optical performance is obtained.
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