| 摘要 |
A zoom lens system comprises from object side to image side, a front lens unit of a negative refractive power and a rear lens unit of a positive refractive power with a variable air space, which changes in the zooming operation, formed between the front and rear lens units. The rear lens unit consists of a first biconvex lens element, a second biconcave lens element and a third biconvex lens element. Futher, an aperture diaphragm, which is arranged between the front and rear lens units or at the image side next to the rear lens unit, is stationary on the optical axis of the lens system in the zooming operation. In a 2-components zoom lens system having a negative lens unit and a positive lens unit from object side according to the present invention, a zoom ratio of about 2 and a sufficiently long back focal length can be obtained in spite of a small number of lens elements. Moreover, cost reduction, compactness and a high performance in the whole lens system including the aperture diaphragm and a lens barrel are obtainable.
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