| 摘要 |
PURPOSE: To provide a rear foucus type zoom lens capable of reducing the size of the whole of lens system, performing quick focusing, simplifying the mechanical mechanism, and reducing the number of constitutive lenses under a large aperture ratio in spite of having a zoom ratio of a high variable power ratio. CONSTITUTION: This rear focus type zoom lens has, in order from the object side, a first group L1 of positive refractive power, a second group L2 of negative refractive power, a third group L3 of positive refractive power, and a fourth group L4 of positive refractive power. In the zoom lens, the second group L2 is moved to an image surface side to conduct variable power from a wide-angle end to a telephoto-end, an image surface fluctuation accompanying the variable power is corrected by moving the fourth group L4, the fourth group L4 is moved to conduct focusing, the third group L3 is composed of one lens having a diaphragm on the side almost near to an image surface, and having on the object side a convex and aspheric surface on the image surface side.
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