| 摘要 |
PURPOSE:To reduce the size of a lens system by arranging a fixed diaphragm between the 2nd and the 3rd groups of the lens system consisting of four groups. 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 which moves monotonously in the opposite direction from the 2nd group during power variation and has positive refracting power, and the 4th group 34 which performs fixed image forming operation and has positive refracting power, and the fixed diaphragm 35 is arranged between the 2nd and the 3rd groups. Thus, the fixed diaphragm 35 is arranged between the 2nd group 32 and the 3rd group 33 and the 2nd group 32 and the 3rd group 33 are moved monotonously in the opposite directions without any interference to perform zooming, so there is no extra space required. Then, the 2nd group 32 is given power variation effect and the 3rd group 33 is also given power variation effect to obtain a specific power variation ratio effectively. Consequently, the overall length of the whole lens system is shortened and the diameter of the front lens of the 1st group 31 is decreased to reduce the weight of the whole lens system.
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