Abstract:
A photographing lens includes an eccentricity adjusting frame which holds an eccentricity adjusting lens group serving as a part of a photographing optical system of the photographing lens; a lens support frame, an axis of which is coincident with a predetermined optical axis of the photographing optical system, supporting the eccentricity adjusting frame in a manner to allow the eccentricity adjusting frame to move in a plane orthogonal to the predetermined optical axis during an assembly-stage of the photographing lens; and a fixed aperture member having a circular aperture, the fixed aperture member being integrally formed with the lens support frame so that a center of the circular aperture coincides with the axis of the lens support frame.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a photographing lens having an eccentricity adjusting device for adjusting the position of part of the lens groups constituting a photographing optical system in a plane orthogonal to an optical axis, in an adjustment operation during assembly of the photographing lens. 
     2. Description of the Related Art 
     This type of eccentricity adjusting device incorporated in a photographing lens is used to adjust the inclination of an image plane. Specifically, in digital cameras using a CCD image sensor on which object images are formed, it is required to adjust the inclination of the image plane with a higher degree of precision than conventional cameras using silver-salt film due to the characteristics of the CCD image sensor. The first lens group (frontmost lens group) of a photographing lens, which is positioned closest to the object side, is generally adopted as an eccentricity adjusting lens group for adjusting the inclination of the image plane. The inclination of the image plane can be adjusted by decentering the optical axis of the eccentricity adjusting lens group from the predetermined optical axis determined at the design stage of the photographing optical system. 
     However, if an eccentricity adjustment is made on the first lens group (eccentricity adjusting lens group), a problem with the amount of light on the image plane becoming uneven arises. If the brightness on the image plane becomes uneven, shading occurs in digital cameras using an image pickup device (CCD image sensor) on which object images are formed, which is undesirable. 
     SUMMARY OF THE INVENTION 
     The present invention provides a photographing lens having an eccentricity adjusting device which makes it possible to prevent the amount of light on an image plane from varying, specifically prevent the brightness on the image plane from becoming uneven, even if the eccentricity adjustment is made on the eccentricity adjusting lens group. 
     According to an aspect of the present invention, a photographing lens is provided, including an eccentricity adjusting frame which holds an eccentricity adjusting lens group serving as a part of a photographing optical system of the photographing lens; a lens support frame, an axis of which is coincident with a predetermined optical axis of the photographing optical system, supporting the eccentricity adjusting frame in a manner to allow the eccentricity adjusting frame to move in a plane orthogonal to the predetermined optical axis during an assembly-stage of the photographing lens; and a fixed aperture member having a circular aperture, the fixed aperture member being integrally formed with the lens support frame so that a center of the circular aperture coincides with the axis of the lens support frame. 
     It is desirable for the fixed aperture member and the lens support frame to be provided as separate members, and for the fixed aperture member to be fixed to the lens support frame. 
     It is desirable for the fixed aperture member and the lens support frame to be molded in one body. 
     It is desirable for the photographing lens includes a zoom lens, wherein the eccentricity adjusting lens group includes a first lens group of the photographing optical system, and the lens support frame includes a first lens group support frame which supports the first lens group and which moves in the optical axis direction in a zooming operation of the zoom lens. 
     It is desirable for the lens support frame and the eccentricity adjusting frame to include a first orthogonal surface and a second orthogonal surface which face each other in the optical axis direction, respectively, and to be biased in opposite directions to keep the first orthogonal surface and the second orthogonal surface in contact with each other. 
     The photographing lens can include a biasing member, fixed to the lens support frame, for biasing the first orthogonal surface and the second orthogonal surface in the opposite directions. 
     It is desirable for the fixed aperture member to be in the shape of a plate which lies in a plane orthogonal to the optical axis. 
     The photographing lens can include a shutter unit positioned behind the fixed aperture member adjacent thereto. 
     It is desirable for the eccentricity adjusting lens group to be screw-engaged in the eccentricity adjusting frame so that a position of the eccentricity adjusting lens group relative to the eccentricity adjusting frame in the optical axis direction can be adjusted by rotating the eccentricity adjusting lens group relative to the eccentricity adjusting frame in an adjusting operation during assembly of the zoom lens. 
     In an embodiment, a photographing lens is provided, including a lens holder which holds a frontmost lens group of a photographing optical system; a lens-holder support frame which supports the lens holder in a manner to allow the lens holder to move in a plane orthogonal to an optical axis of the photographing optical system during an assembly-stage of the photographing lens, the lens holder and the lens-holder support frame being concentrically arranged; and a fixed aperture member having a circular aperture, the fixed aperture member being integrally formed with the lens-holder support frame so that a center of the circular aperture coincides with an axis of the lens-holder support frame. 
     According to the present invention, a photographing lens is achieved wherein the brightness of the edge of the image plane does not easily become uneven even if the eccentricity adjustment is made to the eccentricity adjusting lens group and further wherein shading does not easily occur even if the eccentricity adjusting device is used in a digital camera. 
     The present disclosure relates to subject matter contained in Japanese Patent Application No.2004-256335 (filed on Sep. 2, 2004) which is expressly incorporated herein by reference in its entirety. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will be described below in detail with reference to the accompanying drawings in which: 
         FIG. 1  is a longitudinal sectional view of an embodiment of a zoom lens having an eccentricity adjusting device according to the present invention, showing only an upper half of the zoom lens from the optical axis thereof in an accommodated state (fully-retracted state) of the zoom lens; 
         FIG. 2  is a longitudinal sectional view of the zoom lens shown in  FIG. 1 , showing only an upper half of the zoom lens from the optical axis thereof in a state where the zoom lens is set at a shortest focal length thereof; 
         FIG. 3  is a longitudinal sectional view of the zoom lens shown in  FIG. 1 , showing only an upper half of the zoom lens from the optical axis thereof in a state where the zoom lens is set at a longest focal length thereof; 
         FIG. 4  is a developed view of a rotatable cam ring of the zoom lens shown in  FIGS. 1 through 3 ; 
         FIG. 5  is a developed view of a stationary barrel of the zoom lens shown in  FIGS. 1 through 3  in relation to a pinion gear and a cam follower of the rotatable cam ring; and 
         FIG. 6  is a view similar to that of  FIG. 1 , showing another embodiment of the zoom lens having an eccentricity adjusting device according to the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIGS. 1 through 5  show an embodiment of a zoom lens having an eccentricity adjusting device according to the present invention. The overall structure of the zoom lens  10  will be discussed hereinafter. 
     The zoom lens  10  is provided at the back thereof with a main board  11 , and is further provided with a stationary barrel  13  and a CCD substrate  16   a  which are fixed to the main board  11 . The zoom lens  10  is provided in front of the main board  11  with a CCD fixing member  12 . The zoom lens  10  is provided between the CCD substrate  16   a  and the CCD fixing member  12  with a low-pass optical filter  14 , a sealing member  15  and a CCD image sensor  16 , in that order from the front side (left side as shown in  FIGS. 1 through 3 ) of the zoom lens  10 , which are fixed to the CCD substrate  16   a  by the CCD fixing member  12 . All the above described elements of the zoom lens  10  are fixed elements which are immovable during a zooming operation of the zoom lens  10 . 
     The zoom lens  10  is provided with a plurality of ring members (barrel members), and among these ring members the stationary barrel  13  is the radially outermost ring member. The stationary barrel  13  is provided on an inner peripheral surface thereof with a plurality of cam grooves  13   a  (generally three cam grooves  13   a  arranged at equi-angular intervals) and a plurality of linear guide grooves  13   b  (generally three linear guide grooves  13   b  arranged at equi-angular intervals) extending in a direction parallel to a photographing optical axis O. Only one of the plurality of cam grooves  13   a  is shown in  FIG. 5 . The zoom lens  10  is provided radially inside of the stationary barrel  13  with a cam ring  17  positioned coaxially with the stationary barrel  13  to be freely rotatable about the photographing optical axis O. 
     The cam ring  17  is provided on an outer peripheral surface thereof with a plurality of cam followers  17   a  which are engaged in the plurality of cam grooves  13   a  of the stationary barrel  13 , respectively. The cam ring  17  is provided, on an outer peripheral surface thereof in the vicinity of the rear end of the cam ring  17 , with a spur gear  17   b . A pinion gear  18  (see  FIG. 5 ) which is supported by the stationary barrel  13  is in mesh with the spur gear  17   b . The axis  18   a  of the pinion gear  18  extends parallel to the photographing optical axis O. The zoom lens  10  is provided radially inside the cam ring  17  with a linear guide ring  19  (see  FIG. 2 ) which is concentrically connected to the cam ring  17  to move together with the cam ring  17  in the optical axis direction while allowing the cam ring  17  to rotate freely about the optical axis O relative to the linear guide ring  19 . 
     The linear guide ring  19  is provided with a plurality of linear guide projections  18   a which project radially outwards to be engaged in the plurality of linear guide grooves  13   b  of the stationary barrel  13 , respectively. Due to this engagement of the plurality of linear guide projections  19   a with the plurality of linear guide grooves  13   b , rotating the pinion gear  18  forward and reverse cause the cam ring  17  to rotate forward and reverse via the spur gear  17   b , thus causing the cam ring  17  to move forward and rearward in the optical axis direction in accordance with engagement of the plurality of cam followers  17   a  with the plurality of cam grooves  13   a . At the same time, the linear guide ring  19  moves together with the cam ring  17  in the optical axis direction while the cam ring  17  rotates relative to the linear guide ring  19 . 
     The cam ring  17  is provided on an inner peripheral surface thereof with a plurality of first-lens-group driving cam grooves  17   c   1  (generally three first-lens-group driving cam grooves  17   c   1  arranged at equi-angular intervals; only one of them is shown in  FIG. 4 ) and a plurality of second-lens-group driving cam grooves  17   c   2  (generally three second-lens-group driving cam grooves  17   c   2  arranged at equi-angular intervals; only one of them is shown in  FIG. 4 ). The zoom lens  10  is provided between the cam ring  17  and the linear guide ring  19  with a cylindrical first lens group support frame (lens support frame)  20  which indirectly supports a first lens group L 1 . The first lens group support frame  20  is guided linearly in the optical axis direction by linear guide elements  19   b  and  20   a  of a linear guide mechanism provided between the linear guide ring  19  and the first lens group support frame  20 . The first lens group support frame  20  is provided on an outer peripheral surface thereof with a plurality of cam followers  20   b  which are engaged in the plurality of first-lens-group driving cam grooves  17   c   1  of the cam ring  17 , respectively. Forward and reverse rotations of the cam ring  17  cause the first lens group support frame  20  to move forward and rearward linearly in the optical axis direction, respectively, in accordance with contours of the plurality of first-lens-group driving cam grooves  17   c   1 . The zoom lens  10  is provided around the first lens group L 1  with an eccentricity adjusting frame  21  which supports the first lens group L 1 . The first lens group L 1  serves as an eccentricity adjusting lens group for adjusting the inclination of an image plane. 
     The zoom lens  10  is provided radially inside the linear guide ring  19  with a second lens group support frame  22  which supports a second lens group L 2 . The linear guide ring  19  is provided on an inner peripheral surface thereof with a plurality of linear guide grooves  19   c  extending parallel to the optical axis O, and the second lens group support frame  22  is slidably engaged in the plurality of linear guide grooves  19   c  to be guided linearly in the optical axis direction. The zoom lens  10  is provided with a shutter unit  23 , and both the second lens group L 2  and the shutter unit  23  are fixed to the second lens group support frame  22 . The second lens group support frame  22  is provided on an outer peripheral surface thereof with a plurality of cam followers  22   a  which are engaged in the plurality of second-lens-group driving cam grooves  17   c   2  of the cam ring  17 , respectively. Forward and reverse rotations of the cam ring  17  cause the second lens group support frame  22  to move forward and rearward linearly in the optical axis direction, respectively, in accordance with contours of the plurality of second-lens-group driving cam grooves  17   c   2 . The zoom lens  10  is provided between the first lens group support frame  20  and the second lens group support frame  22  with a compression coil spring  24  having a truncated conical shape which biases the first lens group support frame  20  and the second lens group support frame  22  in directions away from each other in the optical axis direction to remove backlash between the plurality of second-lens-group driving cam grooves  17   c   2  and the plurality of cam followers  22   a.    
     A third lens group L 3 , which is positioned behind the second lens group L 2 , serves as a focusing lens group which is driven in the optical axis direction by a drive mechanism (not shown) to perform a focusing operation in accordance with object distance information. 
     In the zoom lens  10  that has the above described structure, driving the pinion gear  18  forward and reverse cause the cam ring  17  to move forward and rearward in the optical axis direction while rotating, respectively, which in turn cause the first lens group support frame  20  (the first lens group L 1 ) and the second lens group support frame  22  (the second lens group L 2 ) to move forward and rearward in the optical axis direction, respectively, to perform a zooming operation or a zoom lens retracting operation. The contours of the plurality of cam grooves  13   a  of the cam ring  13  are determined so as to provide a smooth zooming operation and a smooth zoom lens retracting operation while taking into consideration the contours of the plurality of first-lens-group driving cam grooves  17   c   1  and the plurality of second-lens-group driving cam grooves  17   c   2 . 
     The above described concentrically arranged ring members of the zoom lens  10 , i.e., the stationary barrel  13 , the cam ring  17 , the first lens group support frame  20 , the linear guide ring  19  and the second lens group support frame  22  have a common axis coincident with a predetermined optical axis determined at the design stage (the photographing optical axis O) of the photographing optical system of the zoom lens  10 . 
     In contrast to these concentrically arranged ring members, the position of the eccentricity adjusting frame  21  that supports the first lens group L 1  can be adjusted on a plane orthogonal to the predetermined optical axis (the photographing optical axis O) in an adjustment operation during assembly of the zoom lens  10 . Specifically, the first lens group support frame  20  and the eccentricity adjusting frame  21  are provided with a first orthogonal surface  20   f  and a second orthogonal surface  21   f  which face each other in the optical axis direction, respectively, and are biased by an annular leaf spring  25  in opposite directions to keep the first orthogonal surface  20   f  and the second orthogonal surface  21   f  in contact with each other. The annular leaf spring  25  is supported by the first lens group support frame  20 . A slight radial clearance is provided between the first lens group support frame  20  and the eccentricity adjusting frame  21  so that the position of the eccentricity adjusting frame  21  can be adjusted to some extent relative to the first lens group support frame  20  in a plane orthogonal to the photographing optical axis O with the first orthogonal surface  20   f  and the second orthogonal surface  21   f  remaining in contact with each other. The zoom lens  10  is provided behind the eccentricity adjusting frame  21  (the first lens group L 1 ) with a fixed aperture plate (fixed aperture member)  26  which is formed as an independent member separate from the eccentricity adjusting frame  21 . The fixed aperture plate  26  is bonded to the first lens group support frame  20 . The fixed aperture plate  26  is provided at a center thereof with a circular aperture  26   a  having its center on the predetermined optical axis (the photographing optical axis O) of the photographing optical system of the zoom lens  10 . The circular aperture  26   a  restricts the cross sectional shape of an optical path of the photographing optical system of the zoom lens  10  to a circular cross sectional shape having its center on the predetermined optical axis (the photographing optical axis O) of the photographing optical system of the zoom lens  10  regardless of any adjustment made to the position of the eccentricity adjusting frame  21  (the first lens group L 1 ). 
     Accordingly, in the zoom lens  10  that incorporates the above described eccentricity adjusting device, the inclination of an image plane can be adjusted by adjusting the position of the eccentricity adjusting frame  21  (the first lens group L 1 /eccentricity adjusting lens group) in a plane orthogonal to the photographing optical axis O with the first orthogonal surface  20   f  and the second orthogonal surface  21   f  remaining in contact with each other while the inclination of the image plane is adjusted. 
     In conventional zoom lenses having an eccentricity adjusting device, as a result of such an eccentricity adjusting operation, the center of a light bundle passing through the first lens group L 1  becomes eccentric to the predetermined optical axis (the photographing optical axis O) of the photographing optical system of the zoom lens  10 , which may cause the brightness of the edge of the image plane to become uneven. However, in the present embodiment of the zoom lens, the brightness of the edge of the image plane can be prevented from becoming uneven while shading can be prevented from occurring on the CCD image sensor  16  because the fixed aperture plate  26 , which restricts the cross sectional shape of an optical path of the photographing optical system of the zoom lens  10  to a circular cross sectional shape having its center on the predetermined optical axis (the photographing optical axis O) of the photographing optical system of the zoom lens  10  without regard to an adjustment made to the position of the eccentricity adjusting frame  21  (the first lens group L 1 ), is fixed to the first lens group support frame  20 . 
     In the above illustrated embodiment of the zoom lens, the first lens group L 1  (a fixing frame thereof) and the eccentricity adjusting frame  21  are provided on outer and inner peripheral surfaces thereof with male and female screw threads  21   a , respectively, which are engaged with each other so that the position of the first lens group L 1  relative to the eccentricity adjusting frame  21  in the optical axis direction can be adjusted by rotating the first lens group L 1  relative to the eccentricity adjusting frame  21  in an adjusting operation during assembly of the zoom lens. This adjusting operation (assembly-stage focus adjustment operation) is performed to prevent the focal point from changing during a zooming operation. Upon completion of the eccentricity adjusting operation, the eccentricity adjusting frame  21  and the first lens group support frame  20  are fixed to each other by, e.g., an adhesive. Upon completion of the assembly-stage focus adjustment operation, the male and female screw threads  21   a  of the first lens group L 1  and the eccentricity adjusting frame  21  are bonded to each other. 
     Although the first lens group support frame  20  and the fixed aperture plate  26  are separate members in the above illustrated embodiment of the zoom lens, it is possible that the first lens group support frame  20  and the fixed aperture plate  26  be molded of synthetic resin to have a single-piece construction as shown in  FIG. 6 . 
     Although the above described embodiment of the photographing lens is a zoom lens, the present invention can also be applied to a photographing lens other than zoom lens. Moreover, the present invention can be applied to a different type of photographing lens in which a lens group of a photographing optical system other than the first lens group serves as an eccentricity adjusting lens group. 
     Obvious changes may be made in the specific embodiments of the present invention described herein, such modifications being within the spirit and scope of the invention claimed. It is indicated that all matter contained herein is illustrative and does not limit the scope of the present invention.