Patent ID: 6940658
Filing Date: 2005-09-06
Classification: G02B

Abstract:
1. A step-zoom lens which changes a variable focal length thereof stepwise, comprising: two movable lens groups; a lens group support unit which supports said two movable lens groups, said lens group support unit being linearly guided along an optical axis to perform zooming and focusing operations, wherein a distance between said two movable lens groups is changed, in said lens group support unit, between a first distance in a wide-angle range which ranges from a short focal length extremity to an intermediate focal length, and a second distance in a telephoto range which ranges from said intermediate focal length to a long focal length extremity; and a cam ring having at least one cam groove, a rotation of said cam ring causing said lens group support unit to move linearly along said optical axis according to said cam groove; wherein said cam groove comprises a finite number of focal-length steps for each of said wide-angle range and said telephoto range, said focal-length steps being determined so as to follow a reference cam diagram for moving said two movable lens groups to perform said zooming operation when focused at infinity, said cam groove being determined to perform said focusing operation between an infinite photographing position and a closest photographing position at each of said focal-length steps by rotation of said cam ring; wherein said cam groove comprises a wide-angle mode section for defining said wide-angle range, a telephoto mode section for defining said telephoto range, and a mode switching section for switching between said wide-angle mode section and said telephoto mode section; wherein said closest photographing positions in two adjacent said focal-length steps are adjacent to each other, and said infinite photographing positions in two adjacent said focal-length steps are adjacent to each other; and wherein one of said focal-length steps of said infinite photographing position at a longest focal length in said wide-angle mode section is provided at one end of said mode switching section, and another of said focal-length steps of said infinite photographing position at a shortest focal length in said telephoto mode section is provided at the other end of said mode switching section.