| 摘要 |
A four-group zoom lens includes, in succession from the object side, a first group having a positive refractive power and movable on the optical axis for focusing, a second group having a negative refractive power and movable on the optical axis to vary the total focal length of the entire system, a third group having a positive refractive power and movable on the optical axis to keep the image plane at a predetermined position, and a fourth group as a relay lens system having a positive refractive power. The second group has a cemented lens component comprising three negative, positive and negative lenses cemented together and having a composite negative refractive power, and a negative lens component.
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