| 摘要 |
PURPOSE:To improve the lens performance when a lens is stopped down by moving a stop to an object side independently from the 1st lens group in the stage of focusing. CONSTITUTION:The lens constitution in the stage of the unmagnification from an infinite object is shown in (a), (b). The hatched part in the figure is an off axial luminous flux. The lens consists of the 1st lens group of a positive focal length and the 2nd lens group of the negative focal length and is disposed with the stop between both lens groups. The lens performance is not deteriorated even if the stop is stopped down when the lens is focused to the infinite object in the case of the stop fixed to the 2nd lens group but only the marginal luminous flux remains and the peripheral performance is deteriorated when the stop is stopped down by focusing the lens to the point such as unmagnification where the magnification is large. The stop is therefore made independently movable and the stop is also moved to the object side independently from the 1st lens group in the stage of extending mainly the 1st lens group to the object side and focusing the lens in the high magnification direction, by which the adverse influence of the stop to be generated in the high magnification stage is eliminated.
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