| 摘要 |
A variable focal length optical system is constituted by, in succession from an object side, a first lens unit G1 having a negative refractive power, a second lens unit G2 having a positive refractive power, a third lens unit G3 having a negative refractive power, and a fourth lens unit G4 having a positive refractive power. When the focal length of the entire lens system is changed while maintaining a constant image plane position, the second lens unit G2 moves in the optical axis direction, the third lens unit G3 moves in the optical axis direction to compensate for variations in image plane position upon movement of the second lens unit G2, and the first lens unit G1 and the fourth lens unit G4 are fixed in position in the optical axis direction. An aperture stop is disposed at a position on the object side of a position closest to the image side of the third lens unit G3, or each of the first to fourth lens units G1 to G4 is constituted by two or less lens elements.
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