| 摘要 |
A zoom lens system comprising, in order from an enlargement side, a first lens unit of a positive power, a second lens unit of a positive power, a third lens unit of a negative power, and a fourth lens unit of a positive power. During a magnification varying operation from a longest focal length condition to a shortest focal length condition, the first lens unit, the third lens unit and the fourth lens unit are movable simply from the enlargement side to a reduction side. The second lens unit is closest to the third lens unit in the longest focal length condition, and closest to the first lens unit in the shortest focal length condition. This zoom lens system satisfies the following conditions: 42=<fL/fI=<5 4=<fL/¦fIII¦=<13 where fL is a focal length of the entire system in the longest focal length condition, fI is a focal length of the first lens unit, and fIII is a focal length of the third lens unit.
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