Patent attributes
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<Ndave, 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 Ndave represents the average refractive index for a d-line among all lens elements included in the second lens unit.
