| 摘要 |
PURPOSE:To shorten the overall length of a lens system consisting of four lens groups and to reduce the weight by arranging a fixed stop between the 2nd and the 3rd groups and satisfying a specific condition between the on-axis gap between the 2nd and the 3rd groups at a wide-angle zoom end and the on-axis gap between the 2nd group and stop. CONSTITUTION:The lens system consists of the 1st group 31 for focusing which has positive refracting power, the 2nd group 32 which moves monotonously during power variation and has negative refracting power, the 3rd group 33 which moves monotonously in the opposite direction from the 2nd group 32 during power variation and has positive refracting power, and the 4th group 34 which performs fixed image forming operation and has positive refracting power successively fro an object side and when the fixed stop 35 is arranged between the 2nd and the 3rd groups, an inequality holds, where 1w is the on-axis gap between the 2nd and the 3rd groups at the wide-angle zoom end and 1s is the on-axis gap between the 2nd group and stop. Then, the 2nd group, the 3rd group, and the stop are so arranged as to satisfy the inequality to realize high power variable power without mechanical interference between both groups and the stop. Consequently, the overall length of the lens system is shortened and the diameter of the front lens of the 1st group 31 is decreased to reduce the size of the whole lens system.
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