| 摘要 |
PURPOSE:To enable image plane characteristics to be varied optionally by moving three lens groups on an object side among four groups under specific conditions for high-performance floating while aberrational variation is compensated excellently, and moving a 3rd lens group on an optical axis. CONSTITUTION:This photographic lens has four lens groups, i.e. a 1st lens group I with positive refracting power, a 2nd lens group II with positive refracting power, a 3rd lens group III with negative refracting power, and a 4th lens group IV with positive refracting power in order from the object side. When focusing is changed from an infinite-distance body to a short-distance body, floating is performed by moving the 1st-4th lens groups I-IV so that three air gaps formed by the 1st-4th lens groups I-IV all increase. Then when the short-distance body is put in focus, only the 3rd lens group III is moved on the optical axis to vary optical characteristics. Consequently, a stopping-down quantity is reduced at the time of, specially, short-distance photography and image plane characteristics are varied mainly and optionally.
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