Soft focus lens systems

Abstract

A soft-focus zoom lens system including a positive front lens group, a negative intermediate lens group, and a positive rear lens group, in this order from the object. Zooming is performed by varying axial distances among the front, intermediate and rear lens groups. The zoom lens system satisfies the following conditions: SAU/fw<−0.10  (1) 0.30<D23w/fw  (2) 0.25<D12t/ft  (3) wherein: SAU designates the amount of spherical aberration at an open aperture, with respect to a focal length at which the amount of spherical aberration, upon zooming, becomes the smallest; fw designates the focal length of the entire lens system at the short focal length extremity; D23w designates the axial distance, at the short focal length extremity, between the most image-side surface of the intermediate lens group and the most object-side surface of the rear lens group; D12t designates the axial distance, at the long focal length extremity, between the most image-side surface of the front lens group and the most object-side surface of the intermediate lens group; and ft designates the focal length of the entire zoom lens system at the long focal length extremity.

Dependencies are inferred from the claim text.