Zoom lens system adapted for use in a digital still camera

摘要

A zoom lens system particularly suited for use with an electronic image sensor includes a first positive lens element group located at a fixed position during a zooming operation, a second moveable negative lens element group, and a third moveable positive lens element group that provides the majority of the magnification change during the zooming operation. The diameter of the first lens element group is relatively large and therefore the surfaces of its glass elements are only spherical. The second and third lens element groups are made of molded plastic lens elements and both contain weak lens elements with aspherical surfaces that primarily correct for aberrations. A conventional aperture stop is positioned between the second lens element group and the third lens element group. Drive mechanisms are used to move the second and third lens element groups back and forth along the optical axis in order to perform a zoom operation. The first and third lens element groups are movable to focus an image of the object on a CCD. The aperture stop is normally positioned at a fixed location along the optical axis during a wide angle-to-normal portion of the zooming operation, and is moveable along the optical axis with the third lens element group during a remainder portion of the zooming operation.