Abstract:
A lens barrel is proposed, in which the optical adjustment of its lens system can be performed easily and at a reduced cost, and also an optical instrument having such a lens barrel is provided. A lens barrel is provided, which comprises: a lens frame for holding a lens; a holding frame for holding the lens frame; and an adjustment mechanism which, while allowing the lens frame to be pressed and fit into the holding frame thereof with a predetermined abutting force resulting from an elastic force, and while retaining its fit-in state, can adjust a position of the lens frame with regard to said holding frame in the directions of an optical axis via a plurality of stepwise stages by rotating said lens frame around its own axis of rotation.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]     This application claims priority from Japanese Priority Application No. 2003-323446, filed on Sep. 16, 2003 with the Japanese Patent Office, the entire content of which is hereby incorporated by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a lens barrel provided with a mechanism to move the lens in the directions of an optical axis, and an optical instrument having the lens barrel thereof.  
         [0004]     2. Description of Related Art  
         [0005]     As a conventional mechanism for adjusting respective gaps between a plurality of lenses for zooming or focusing in a lens barrel in optical instruments such as cameras or the like, generally there are such ones that make a fine adjustment by inserting a spacer in a lens frame, or that move a lens frame in the directions of an optical axis by use of a helicoidal screw.  
         [0006]     However, there are such problems that, in the case of the former, a number of steps are required for removing and reattaching a lens frame in order to select and provide an optimal adjustment spacer, and also, in the latter case, a backlash of the helicoidal screw may affect various functions of the optical instrument.  
         [0007]     In the meantime, there has been proposed a method for adjusting the position of a lens in the directions of an optical axis, comprising the steps of forming a reference plane in a hold frame for supporting a lens frame in a stepwise manner, and rotating the lens frame around its own axis so as to alter the reference plane to adopt as disclosed, for example, in the following.  
         [0008]     Japanese Patent Application Publication No. 2002-350702.  
         [0009]     According to this technique described above, an optimum state of optical adjustment is achieved by abutting a protrusion provided on a rear side of the lens frame against either one of stepwise stages on the holding frame for holding the lens frame. After the optical adjustment having been completed, the lens frame is secured to the holding frame thereof by bonding or the like.  
         [0010]     The aforementioned related art, however, is associated with such a problem that because its lens cannot be secured to any one of the reference planes selected during the optical adjustment, the lens is set afloat during the adjustment. Although it may be considered independently to provide an additional mechanism to press the lens frame against the reference plane, there may result in such drawbacks as of an increased number of parts, an increased cost of manufacture, and an increased space for installation thereof.  
       SUMMARY OF THE INVENTION  
       [0011]     The present invention has been contemplated to solve the aforementioned problems associated with the conventional technology, and an object thereof is to provide a lens barrel in which the optical adjustment of its lens system can be performed easily and performed at a reduced cost, and also to provide an optical instrument having such a lens barrel.  
         [0012]     In order to solve the aforementioned problems associated with the related art, a novel lens barrel is provided according to the present invention, which is characterized by comprising: a lens frame for holding a lens; a holding frame for holding the lens frame; and an adjustment mechanism which, while allowing for the lens frame to be pressed and fit into the holding frame thereof with a predetermined abutting force resulting from an elastic force, and while retaining its fit-in state, can adjust a position of the lens frame within the holding frame in the directions of an optical axis via a plurality of stepwise stages by rotating the lens frame around its own axis of rotation.  
         [0013]     According to this lens barrel according to the present invention, the adjustment mechanism thereof is realized by a unique form and contour of a fit-in section coupling between the holding frame and the lens frame. When the lens frame is rotated around its own axis of rotation, it moves along the contour of the fit-in section, in the directions of the optical axis, and relative to the holding frame. During this operation, because a predetermined abutting force is applied between the holding frame and the lens frame, it is enabled to move the lens frame in the directions of the optical axis while maintaining its fit-in state stably, thereby allowing for the lens frame to stop still stably at any desired position in the optical directions without the help of an external force.  
         [0014]     More specifically, the aforementioned adjustment mechanism may be comprised of: a protruding flange strip which is provided on a circumference of either one of the lens frame or the holding frame and the position of which in the directions of an optical axis changes along the circumferential directions thereof; and a pair of grip members which is provided on the other side of the either one of the lens frame or the holding frame, and which grips the flange strip with a predetermined elastic force from the both sides of the flange strip parallel to the direction of the optical axis. At least one of this pair of gripping members which is positioned on either side of the flange strip in the directions of the optical axis has flexibility, and its elastic reaction force applies a predetermined abutting force against the flange strip.  
         [0015]     According to the lens barrel of the present invention, there are such advantages that the lens frame is prevented from floating from the holding frame by an abutting force acting between the lens frame and the holding frame therefor, and that the position of the lens frame in the directions of the optical axis can be varied and adjusted to a plurality of positions by a simple operation of rotating the lens frame. Because this abutting force is provided advantageously by a unique shape and contour of the fit-in coupling between the holding frame and the lens frame, there is no need to provide for any additional part to secure the lens frame during its adjustment. Therefore, it becomes possible easily to carry out an optical adjustment of a lens system in a lens barrel, and also to attain space saving. As a result, it becomes possible to provide for an optical instrument incorporating this lens barrel at a reduced cost. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]      FIG. 1  is an exploded perspective view showing a lens barrel according to a preferred embodiment of the present invention;  
         [0017]      FIG. 2  is a perspective view showing a lens frame for constituting the lens barrel;  
         [0018]      FIG. 3  is a perspective view showing main parts of the lens frame;  
         [0019]      FIG. 4  is a perspective view showing a holding frame for constituting the lens barrel;  
         [0020]      FIG. 5  is a perspective view showing an assembled state of the lens frame and the holding frame; and  
         [0021]      FIG. 6A  to  6 E are schematic diagrams showing a configuration of a mechanism for adjusting the position of the lens and a method of adjustment thereof. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0022]     A preferred embodiment of the present invention will be described in detail by referring to the accompanying drawings. The preferred embodiment of the present invention will be described by way of example as applied to a lens barrel for use in a digital still camera.  FIG. 1  is an exploded perspective view of a lens barrel according to a preferred embodiment of the present invention.  
         [0023]     With reference to  FIG. 1 , the lens barrel according to the preferred embodiment of the present invention is comprised of: a first lens  1 ; a first group lens frame  2 ; a first group holding frame  3 ; a second group unit  4 ; a cam ring  5 ; a forward guide ring  6 ; a stationary ring  7 ; a rotary ring  8 ; a rear barrel  9 ; a second lens  10 ; a third group unit  11  and the like, which are assembled in alignment with an optical axis (shown by dots-and-lines). Because respective usage and functions of these parts and components are well known, detailed descriptions thereof are omitted. By way of example, in the following description, for the sake of convenience, the directions of an optical axis in  FIG. 1  may be used as a reference, and the lower direction in the figure may be referred to as a front side and the upper direction thereof as a rear side.  
         [0024]     In the next, a fit-in coupling structure of a lens frame and a holding frame which constitute a main part of the present invention will be described by way of example based on a relationship between a first group lens frame  2  and a first group holding frame  3 .  FIG. 2  is a perspective view showing a first group lens frame  2  in a state with a first lens  1  mounted thereon.  FIG. 3  is a perspective side view showing a structure of a main portion of the first group lens frame  2 . Further,  FIG. 4  is a perspective view showing a first group holding frame  3 .  
         [0025]     As shown in  FIGS. 2 and 3 , the first group lens frame  2  is made by injection molding (one-piece molding) of a resin material containing a polycarbonate glass by 30%, and it has a cylindrical main body  21  which holds the first lens  1  fit into an inner circumference thereof, and has three pieces of protrusion bars or flange strip (locking member)  22  distributed equidistant from each other on its outer circumference. Each of these flange strips  22  extends circumferentially along a predetermined height on the outer circumference thereof. A slip portion  23  formed between adjoining protruding flange strips  22  provides a passage for a gripping member of a first group holding frame  3  when assembling the first group lens frame  2  into the first group holding frame  3 , which will be described later.  
         [0026]     As clearly shown in  FIG. 3 , these protruding flange strips  22  are formed stepwise so as to allow for the position thereof in the directions of the optical axis to be changeable in three stages. That is, the flange strip  22  is formed to have an introductory portion  40  which initially abuts on the gripping member of the first group holding frame to be described later, then, a first abutting portion  41 , a second abutting portion  42 , and a third abutting portion  43  which are to abut sequentially against the gripping member thereof when the first group lens frame  2  is rotated around its own axis of rotation. Each of the introductory portion  40  and the respective abutting portions has a rectangular shape which has a predetermined breadth in the direction of the optical axis, and abutting planes on the front and the rear sides thereof perpendicular to the optical axis. On a front side abutting plane of respective abutting portions there is provided a notch  44  for catching the grip member of the first group holding frame  3 . Then, from the backward direction to the forward direction of the optical axis, these abutting portions are arranged in the order of the introductory portion  40 , the first abutting portion  41 , the second abutting portion  42  and the third abutting portion  43 . A portion between the introductory portion  40  and its adjacent abutting portion  41 , and also between respective adjoining abutting portions is connected with a bridge portion  45  which is slanting relative to the optical axis.  
         [0027]     Further, on the front side of the main body  21  there are provided adhesive reservoirs  25  each shaped into a groove exposed to an internal circumference thereof, spaced equidistant from each other (separated by 120°) and distributed along the inner circumference thereof. Thereby, after the first lens  1  having been mounted, by supplying adhesive thereto, it is enabled firmly to attach the first lens  1  to the first group lens frame  2  by bonding.  
         [0028]     With reference to  FIG. 4 , a first group holding frame  3  which is formed by injection molding (one-piece molding) of a resin material containing polycarbonate by 30% has a cylindrical main body  31 , and a front wall section  32  thereof is formed into an annulus ring by concentratedly extending a predetermined length from the front end periphery of the main body  31 . An inner end rim of the front wall section  32  forms a circular through-hole  33  which has approximately a similar diameter as the outermost diameter of the first group lens frame  2  including the flange strip  22 . Further, pairs of slits  34  opened toward inside and separated from each pair by 120° are formed in the front wall section  32 , wherein between each pair of slits  34  there is provided a presser arm  35  which extends concentratedly perpendicular to the optical axis. An edge of this presser arm  35  extends into the circular hole  33  by a predetermined length, and is flexible in back-and-forth directions.  
         [0029]     Further, a support section  51  is formed by extending the inner circumferential rim of the front wall section  32  once in the backward direction except for a position corresponding to the presser arm  35  and bending internally to extend concentratedly. On a respective support section  51  and in the vicinity of the slit  34  described above, there is provided an abutting member  52  which protrudes in the forward direction, and the front plane of which forms a reference plane perpendicular to the optical axis. A pair of this abutting member  52  in combination with the presser arm  35  constitutes a grip unit for gripping the first group lens frame  2  while abutting on respective abutting portions of the first group lens frame  2 . Further, a groove of an adhesive reservoir  53  open in the forward direction is provided in the front wall section  32  at a position corresponding to the abutting member  52 . After precisely mounting the first group lens frame  2 , adhesive is supplied thereto, thereby enabling the first group lens frame  2  to be secured firmly by bonding.  
         [0030]     In the next, a method of assembling a lens barrel and a method of adjusting the lens therein according to a preferred embodiment of the present invention will be described by referring to  FIG. 1 . When assembling the lens barrel, at first a second lens  10  is secured by bonding to a rear fixture of the first group lens frame  2 , then the first lens  1  is adjusted to be aligned relative to a reflection center of the second lens  10  used as a reference. According to the preferred embodiment of the present invention, an outer diameter of the first lens  1  is formed smaller approximately by 0.4 mm than an inner diameter of the first group lens frame  2  so as to allow a shifting for alignment adjustment of approximately ±0.2 mm. After completion of the alignment adjustment, the first lens  1  is firmly attached to the first group lens frame  2  by supplying adhesive to the adhesive reservoir  25  therein.  
         [0031]     Subsequently, respective parts of the first group holding frame  3 , a second group unit  4 , a cam ring  5 , a forward guide ring  6 , a stationary ring  7 , a rotary ring  8 , a rear barrel  9  and a third group unit  11  are assembled to complete a barrel portion except for units to be accommodated into the first group lens frame  2 . After then, the first group lens frame  2  is assembled and secured to the first group holding frame  3 .  
         [0032]     In the next, a fixture mechanism and a method of securing the first group lens frame  2  to the first group holding frame  3  will be described.  FIG. 5  is a perspective view showing an assembled state of the first group lens frame  2  and the first group holding frame  3 .  FIG. 6A  to  6 E are schematic diagrams showing a configuration of the adjustment mechanism for adjusting a lens position, and a method of adjustment thereof. By way of example, in  FIG. 6A  to  6 E, the upper direction corresponds to the forward direction, and the lower direction corresponds to the backward direction, respectively.  
         [0033]     When assembling the first group lens frame  2  into the first group holding frame  3 , the position of the slit  23  in the first group lens frame  2  is aligned with the position of the presser arm  35  in the first group holding frame  3 , then the first group lens frame  2  is pressed into the first group holding frame  3 . When a rear abutting plane of the flange strip  22  of the first group lens frame  2  comes into abutment against the reference plane of the abutting member  52  of the first group holding frame  3 , the first group lens frame  2  is rotated around the optical axis in a clockwise direction with reference to  FIG. 5 .  
         [0034]     At this instant, as shown in  FIG. 6A , the introductory portion  40  of the flange strip  22  of the first group lens frame  2  comes into contact with the presser arm  35  of the holding frame  3 , and when the lens frame  2  is further rotated clock-wise, the presser arm  35  climbs up to a first abutting portion  41  thereof via a bridge portion  45  as shown in  FIG. 6B , as a result, gripping the flange strip  22  between the presser arm  35  and the abutting member  52  which constitute the gripping pair. In this operation, the first group lens frame  2  moves in the backward direction of the optical axis relative to the first group holding frame  3 .  
         [0035]     When the first group lens frame  2  is further rotated clockwise from the state of  FIG. 6B , the presser arm  35  climbs up to a second abutting portion  42  via a bridge portion  45  as shown in  FIG. 6C , and when the first group lens frame  2  is still further rotated, the presser arm  35  climbs up to a third abutting portion  43  via a bridge portion  45  as shown in  FIG. 6D . During this operation, the first group lens frame  2  moves backward sequentially in the directions of the optical axis relative to the first group holding frame  3 .  
         [0036]     By carrying out an inverse operation of the above, it is also enabled sequentially to move the first group lens frame  2  in the forward direction of the optical axis relative to the first group holding frame  3 . As described above, the position of the first group lens frame  2  relative to the first group holding frame  3  can be adjusted to reside on any position desired. As a result, the position of the first lens  1  within the lens barrel can be adjusted appropriately and precisely. According to a preferred embodiment of the present invention, the case of  FIG. 6E  in which a portion thereof gripped between the presser arm  35  and the abutting member  52  lies in the center of the flange strip  22  (that is, a state thereof straddling both the first and the second abutting portions  41 ,  42 ) is specified to be a normal position (0) of adjustment as designed. If the position of the first group lens frame  2  deviates from the normal position due to errors in assembling or the like, the first group lens frame  2  is allowed to move in the forward direction (+) or in the backward direction (−) along the optical axis by its rotation.  
         [0037]     By way of example, the flange strip  22  is formed to have a constant breadth in the directions of the optical axis. As shown in  FIG. 6E , a respective distance between the front plane of the first abutting portion  41  and the rear plane of the introductory portion  40 , between the front plane of the second abutting portion  42  and the rear plane of the first abutting portion  41 , and between the front plane of the third abutting portion  43  and the rear plane of the second abutting portion  42  is retained at a constant value h. On the other hand, a gap between the presser arm  35  and the abutting member  52  is formed slightly smaller than the distance h described above under application of no external force. Therefore, during the movement of the first group lens frame  2  in the directions of the optical axis while the flange strip  22  thereof is inserted and seized between the presser arm  35  and the abutting member  52 , the presser arm  35  is elastically deformed by a predetermined quantity in the direction of the optical axis. By use of a reaction force thereof (abutting force), the flange strip  22  is secured without being affected by unstableness. Further, because the distance h is formed always to be constant, a pushing force of the presser arm  35  against the first group lens frame  2  will not change substantially. Therefore, even if a quantity of adjustment of the position becomes large, the flexure of the presser arm  35  will not affect a precision of adjustment.  
         [0038]     Then, a flange-back test for inspecting whether or not a gap between the first lens  1  and the second lens  10  is as specified is carried out in the state as shown in  FIG. 5  with the first group lens frame  2  being assembled into the first group holding frame  3 . If the inspection is passed, adhesive is filled into the adhesive reservoir  53  so as to secure the first group lens frame  2  to the first group holding frame  3  by bonding. If not passed, the position of the first group lens frame  2  relative to the first group holding frame  3  in the directions of the optical axis is readjusted in the manner as described above.  
         [0039]     As described hereinabove, according to the lens barrel according to the preferred embodiment of the present invention, it is enabled for the position of the first group lens frame  2  relative to the first group holding frame  3  to be adjusted in the direction of the optical axis sequentially in the three stages merely by rotating the first group lens frame  2 , without causing the unstableness by use of the abutting force exerting between the gripping pair of the presser arm  35  in combination with the abutting member  52  and the protrusion flange strip  22 . Because this abutting force is obtained from the unique shape of the fit-in coupling arrangement between the first group lens frame  2  and the first group holding frame  3 , without the need of provision of any additional part for holding the first group lens frame  2 , the optical adjustment of the first lens  1  in the lens barrel can be carried out easily, and also space saving can be achieved. Further, because no other additional parts are required, it is possible to manufacture an optical instrument incorporating the lens barrel described above at a reduced cost. Still further, because a quantity of flexure of the presser arm  35  remains constant, the flexure thereof is unlikely to cause any problem during the adjustment operation of the position of the first group lens frame  2 .  
         [0040]     Although the invention has been described in its preferred form with a certain degree of particularity, obviously many changes, variations and combinations are possible herein. It is therefore to be understood that any modification will be practiced otherwise than as specifically described herein without departing from the scope of the present invention.  
         [0041]     For example, in the above description of the preferred embodiment of the present invention, the position of adjustment for the first group lens frame  2  relative to the first group holding frame  3  has been described to be movable along the three stages, however, it is not limited thereto, and any number of stages, e.g. two stages, four stages or more stages may be adopted therefor. Furthermore, although the invention has been described by way of example in which the flange strip  22  is formed to have a stepwise sequential shape so that the position thereof in the directions of the optical axis changes along plural stages, however, it is not limited thereto, and the flange strip  22  may be formed discontinuously as well provided that the gripping operation by the presser arm  35  and the abutting member  52  is not impaired.  
         [0042]     Still further, instead of the stepwise contour, the flange strip  22  may be formed into a continuous slope so that the position thereof in the directions of the optical axis can be changed smoothly. Thereby, the position of the first group lens frame  2  in the directions of the optical axis can be adjusted more precisely.  
         [0043]     Furthermore, although the invention has been described by way of example in which the flange strip  22  is provided on the first group lens frame  2  and the gripping pair of the presser arm  35  and the abutting member  52  are provided on the first group holding frame  3 , however, it is not limited thereto, and it may be arranged vice versa such that the flange strip  22  is provided on the first group holding frame  3  and the gripping pair of the presser arm  35  and the abutting plate  52  are provided on the first group lens frame  2 .  
         [0044]     Still further, although the lens barrel according to the preferred embodiment of the present invention has been described specifically as applied to a relation between the first group lens frame  2  and the first group holding frame  3 , however, it should be understood that this is also applicable to any other lens group comprising a lens frame and its holding frame.  
         [0045]     Furthermore, the lens barrel according to the present invention is applicable not only to the digital still camera described above but also to any other types of cameras, imaging equipment, and to observation equipment such as a microscope or the like.  
         [0046]     The present invention is applicable to any optical equipment which requires a positional adjustment in the directions of the optical axis while movably holding the lens frame relative to the holding frame therefor.