Variable magnification optical system

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) 6.0ave, 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_ave represents the average refractive index for a d-line among all lens elements included in the second lens unit.