Patent ID: 7957071
Filing Date: 2011-06-07
Classification: G02B

Abstract:
1. A focus adjustment method of a zoom lens system for correcting a focal point shift caused by manufacturing error, wherein said zoom lens system comprises three movable lens groups in which at least two of said movable lens groups are moved in an optical axis direction to perform zooming to form an image onto an imaging device; wherein in said zoom lens system, a finite number of focal length positions at which a focus adjustment is performed is provided; wherein said movable lens group which is closest to said imaging device out of said three movable lens groups comprises a focusing lens group; wherein a position of said focusing lens group in the optical axis direction is controlled via pulses of a stepping motor; wherein said focus adjustment method of a zoom lens system comprises the combination of performing said control of said focusing lens group to determine a position of said focusing lens group in the optical axis direction via pulses of said stepping motor and determining an amount of adjustment of said imaging device in the optical axis direction; wherein said performing said control of said focusing lens group and said determining an adjustment amount of said imaging device comprises: a first adjustment in which an amount of adjustment of said imaging device in the optical axis direction is determined based on a traveling distance of said focusing lens group from a standard position to an in-focus position thereof, respectively at the long focal length extremity and the short focal length extremity; and a second adjustment in which said focusing lens group is moved, at at least three distinct focal length positions including the short focal length extremity and the long focal length extremity, to an in-focus position with respect to said imaging device having been adjusted via said first adjustment; at each of the focal length positions, a amount of focus adjustment of said focusing lens group is determined; and said amount of focus adjustment is stored in a memory as a pulse number of said stepping motor.