| 摘要 |
The present invention relates to a small zoom lens system for electronic still cameras or video cameras, which has a zoom ratio lying in the range of about 2.5-3.2 and an F-number lying in the range of about 2-2.8, comprises as small as 7 or 8 lenses and is reduced in terms of both the total length and the lens diameter, and which is characterized by comprising, in order from the object side, at least a first lens group having a positive refractive power, a second lens group having a negative refractive power, a stop and a third lens group having a positive refractive power, and in that during zooming the first lens group remains fixed while the second and third lens groups are moved along the optical axis, and the following conditions (1) and (2) are satisfied: 0.9x beta 2T/ beta 2W< beta 3T/ beta 3W<2.0x beta 2T/ beta 2W,(1), and 0.5<f3/¦f2¦<1.5,(2) where beta 2T is the magnification of the second lens group at the telephoto end, beta 2W is the magnification of the second lens group at the wide angle end, beta 3T is the magnification of the third lens group at the telephoto end, beta 3W is the magnification of the third lens group at the wide angle end, f2 is the focal length of the second lens group, and f3 is the focal length of the third lens group.
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