| 摘要 |
PURPOSE:To enable focusing to a short distance and to enable macrophotography by introducing a rear focus system which performs focusing by moving a rear group. CONSTITUTION:This rear focus zoom lens consists of a 1st group I which has positive focal length, a 2nd group II which has negative focal length, a 3rd group III which has positive focal length, a 4th group IV which has positive focal length, and a 5th group V which has negative focal length in order from an object side. When zooming operation is performed from the short-focal-length side to the long-focal-length side, the 1st group I moves to the object side and the 2nd group II is stopped; and the 3rd-5th groups III-V move to the object side while varying mutual group gaps while maintaining relations 2f3<f4 and f4>¦f5¦, where f3 is the focal length of the 3rd group III, f4 is the focal length of the 4th group IV, and f5 is the focal length of the 5th group. Further, focusing is performed by displacing the 3rd-5th groups III-V to the image side although their movement quantities are difference. Consequently, macrophotography is possible as the extension of rear focusing and variations of aberrations at the time of close-up photography are small.
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