Patent ID: 6014266
Filing Date: 2000-01-11
Classification: G02B

Abstract:
A method of focusing from an infinite to a close distance, the method comprising the steps of:a) providing a zoom lens comprising a plurality of lens groups, each lens group being axially moveable so as to define a plurality of zoom lens positional states, said zoom lens having an overall focal length that varies as a function of said positional states, said plurality of lens groups comprising in order from an object-side, a first lens group having positive refractive power, a second lens group having positive refractive power and separated from said first lens group by a first air space, and a third lens group having negative refractive power and separated from said second lens group by a second air space, said plurality of zoom lens positional states including an extreme wide-angle positional state and an extreme telephoto positional state and designing said lens groups such that, when zooming from said extreme wide-angle state to said extreme telephoto state, said lens groups move toward the object-side so as to cause said first air space to increase, and said second air space to decrease; andb) focusing by moving each one of said plurality of lens groups such that ratios of amounts by which said lens groups move vary as a function of said overall focal length, including the step of moving said lens groups by respective amounts of movement such that ratios of said respective amounts of movement are a function of said overall focal length, and satisfying the conditions:(1) .DELTA.1>0(2) .DELTA.2>0(3) .DELTA.2W/.DELTA.1W.ltoreq.1.0(4) .DELTA.3T/.DELTA.2T.ltoreq.1.0wherein .DELTA.1 and .DELTA.2 are said amounts of movement for focusing by said first and said second lens groups, respectively, during focusing, .DELTA.1W and .DELTA.2W are said amounts of movement for focusing by said first and said second lens group, respectively, during focusing when said zoom lens is in said extreme wide-angle state, and .DELTA.2T and .DELTA.3T are said amounts of movement for focusing by said second and said third lens groups, respectively, during focusing when said zoom lens is in said extreme telephoto state, and wherein said amounts of movement are positive when toward the object-side.