| 摘要 |
The invention provides a zoom lens system much more reduced in size and cost than ever before and best-suited for use on portable information terminals of small size. The zoom lens system comprises, in order from an object side thereof, a first lens group G 1 having positive refracting power and designed to be fixed during zooming, a second lens group G 2 having negative refracting power and designed to move from the object side to an image plane side of the system for zooming from a wide-angle end to a telephoto end of the system, a third lens group having refracting power and designed to move from the image plane side to the object side for zooming from the wide-angle end to the telephoto end, and a fourth lens group G 4 having positive refracting power and designed to be movable during zooming. Condition (1) with respect to the power of the third lens group G 3, condition (2) with respect to the amount of zooming movement of the third lens group G 3 or condition (3) with respect to the composite power of the third and fourth lens groups G 3 and G 4 and condition (10) with respect to the actual value of the back focus are satisfied.
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