摘要 |
A variable magnification optical system for forming an optical image of an object on a light-receiving surface of an image sensor with variable magnification includes: from the object side, at least a first lens unit having a positive optical power, a second lens unit having a negative optical power, a third lens unit having a positive optical power, and a fourth lens unit having a positive optical power. In magnification variation from the wide angle end to the telephoto end, at least the first lens unit moves. Conditional formulae (1) and (2) below are fulfilled: (1) 6.0<fl/fw<20.0 and (2) 1.83<ND<SUB>ave</SUB>, where fl represents the focal length of the first lens unit, fw represents the focal length of the entire system at the wide angle end, and Nd<SUB>ave </SUB>represents the average refractive index for a d-line among all lens elements included in the second lens unit.
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