Abstract:
A lens barrel comprises a first cylindrical member having an inner peripheral surface, and a second cylindrical member internally fitted to the first cylindrical member and having an outer peripheral surface. One of the peripheral surfaces has first and second helical parallel axial grooves, and a third groove extending in only a circumferential direction continuously from one side ends of the first and second grooves. The other peripheral surface has first and second protruded portions engaging respectively with the first and second grooves in alignment in the circumferential direction and enabling relative rotations between the cylindrical members and relative movements in the axial direction. When the third groove is reached, the cylindrical members are allowed to make only relative rotations without moving in the axial direction.

Description:
This application claims the benefit of Japanese Patent applications No. 2002-091717 and No. 2002-219461 which are hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a lens barrel structured to extract a straight advancing motion from a rotary motion of a frame member and to perform an operation such as a lens extension, etc. 
     2. Related Background Art 
     In this type of lens barrel, a lens extension-and-reduction mechanism has hitherto been constructed of a multi-thread screw called a helicoid or a cam mechanism configured by cam pins and cam grooves. 
     FIG. 13 is a view showing the helicoid in development in one conventional lens barrel. 
     In this conventional lens barrel, a female helicoid member  10  having a female helicoid includes a first guide groove  10   a  for moving back and forth in the optical-axis directions corresponding to rotations, and a second guide groove  10   b  (a lead-0 portion) defined as a groove formed in a circumferential direction in continuation with the first guide groove  10   a.    
     FIG. 14 is a partially enlarged view of FIG.  9 . 
     A male helicoid member  20  having a male helicoid engaging with the female helicoid of the female helicoid member  10 , has a guide protruded portion  200  configured by surfaces  20   a ,  20   b  facing to the first guide groove  10   a , and surfaces  20   c ,  20   d  facing to the second guide grooves  10   b  (the lead-0 portion). 
     The male helicoid member  20 , when making the relative rotary motion to the female helicoid member  10  by the rotation of the female helicoid member  10 , through engaging with the first guide groove  10   a , moves in the optical-axis direction corresponding to the rotation. In an area of the second guide groove  10   b  (the lead-0 portion), the relative movement in the direction of rotation is made, however, no movement in the optical-axis direction is made. The function of the second guide grove  10   b  is, as disclosed in, for example, Japanese Patent Application Laid-Open No.11-23937, utilized for opening and closing a lens barrier. 
     FIGS. 15 through 17 are views showing a helicoid of another conventional lens barrel in development. 
     In this conventional lens barrel, a female helicoid member  10  having a female helicoid includes a helical groove  10   a  for moving back and forth in the optical-axis directions corresponding to rotations, and a circumferential groove  10   b  defined as a groove formed in the circumferential direction in continuation with the helical guide groove  10   a.    
     A male helicoid member  20 , when making the relative rotary motion to the female helicoid member  10  by the rotation of the female helicoid member  10 , through engaging with the first guide groove  10   a , moves in the optical-axis direction corresponding to the rotation. In the circumferential groove lob, the relative movement in the direction of rotation is made, however, no movement in the optical-axis direction is made. 
     What is required of the conventional lens barrel described above is a contrivance for preventing the operation from becoming unstable due to interference with the helical groove  10   a  when the protruded portion of the male helicoid member  20  passes through the circumferential groove  10   b.    
     Further, it is also required that an incorrect helical engagement with an adjacent groove different from the predetermined position be avoided. 
     For meeting these requests, there has hitherto been adopted a configuration that the number of grooves is restricted, and the grooves are thinned out. 
     Moreover, the helicoid engagement is established by decreasing a length (an angle of rotation) of the circumferential groove  10   b.    
     Accordingly, the helicoid is unable to be disposed along the entire periphery, and an engaging area is reduced, resulting in a drop of engaging force. When receiving an external force, the helicoid might come off the engagement thereof. 
     Further, in an area where the helicoid engagement is attained, it is possible to shield the light that is to leak through a gap between the female helicoid member  10  and the male helicoid member  20 . In an area where the helicoid engagement is not attained, however, a problem arises, wherein the light-shielding can not be performed, and a light shielding means is needed. 
     A further problem is that a non-groove area of the inner periphery of the female helicoid member  10  expands, and, when a beam of light is projected on this area, an intensive reflection occurs to cause a flare. 
     A still further problem is that the helicoid engaging areas can be provided merely in approximately three directions on the circumference because of the configuration of thinning out the helicoid grooves, and ununiform rotations are caused due to sinking in a recessed portion, etc. necessary for a secant relief of a die assembly, which is provided in the inner periphery of the female helicoid member  10 . 
     A yet further problem is that the priority given to establishing the small number of engaging areas conduces to a restraint in terms of design. 
     SUMMARY OF THE INVENTION 
     It is a primary object of the present invention to provide a lens barrel capable of being formed with a multiplicity of grooves, attaining a stable helical engagement, obtaining a high engagement force, exhibiting an excellent light shielding characteristic and making difficult occurrences of the caused-by-stray-light flare, ghost, etc. 
     To accomplish the above object, according to one aspect of the present invention, a lens barrel includes a first cylindrical member having an inner peripheral surface, and a second cylindrical member internally fitted to the first cylindrical member and having an outer peripheral surface that facing in a radial direction to the inner peripheral surface of the first cylindrical member, wherein any one of the inner peripheral surface and the outer peripheral surface is formed with first and second grooves taking a helical shape and extending in an axial direction in parallel with each other, and a third groove extending in only a circumferential direction continuously from one side ends of the first and second grooves, the other of the inner peripheral surface and the outer peripheral surface are formed with first and second protruded portions engaging respectively with the first and second grooves in alignment in the circumferential direction and enabling relative rotations between the first and second cylindrical members and relative movements in the axial direction therebetween, the first and second protruded portions engage respectively with the first and second grooves with the result that the first and second cylindrical members make the relative rotations and the relative movements in the axial direction, and, when reaching the third groove, move through within the third groove, and the first and second cylindrical members are allowed to make only the relative rotations without moving in the axial direction, and the third groove includes a guide portion, formed in continuation from the first groove, for guiding the first protruded portion into the first groove. 
     In the lens barrel according to the present invention, preferably the second groove includes a portion, formed adjacent to the third groove, for inhibiting the first protruded portion from entering. 
     In the lens barrel according to the present invention, preferably a height of the first protruded portion is larger than a height of the second protruded portion, and the entrance inhibiting portion of the second groove has a depth set to permit the second protruded portion to pass through and to inhibit the first protruded portion from passing through. 
     In the lens barrel according to the present invention, preferably the guide portion is a groove bottom portion formed, in the third groove, having a depth set to permit the second protruded portion to pass through and to inhibit the first protruded portion from passing through. 
     In the lens barrel according to the present invention, preferably a length of the first protruded portion in an extending direction of the helical groove is larger than a length of the second protruded portion in the extending direction thereof, and a length of the third groove in the extending direction of the helical groove is larger than the length of the protruded portion on one side of the circumferential direction continuous with the first groove. 
     According to another aspect of the present invention, a lens barrel includes a first helicoid member including a high guide protruded portion provided on an inner surface or an outer surface of a cylinder and a low guide protruded portion lower in height than the high guide protruded portion, and a second helicoid member including a plurality of first guide grooves and a second guide groove that engage with the high guide protruded portion and/or the low guide protruded portion of the first helicoid member, the first guide grooves being formed in a helical shape on an engaging surface of the first helicoid member, the second guide groove being formed continuously with the first guide grooves in a circumferential direction, wherein the second guide groove partially includes a second middle guide groove, for abutting on the high guide protruded portion and guiding the same high guide protruded portion, formed in depth set to permit the low guide protruded portion to pass through and to make the high guide protruded portion unable to pass through so that the engagement between the first helicoid member and the second helicoid member is changed over from the engagement through the second guide groove to the engagement through the first guide grooves. 
     In the last mentioned lens barrel according to said another aspect of the present invention, preferably among the plurality of first guide grooves, the guide groove with which the low guide protruded portion engages includes a first middle guide groove formed in depth set to make the high guide protruded portion unable to pass through so as to inhibit the high guide protruded portion from entering and to enable the low guide protruded portion to pass through. 
     According to a further aspect of the present invention, a lens barrel includes a first cylindrical member, and a second cylindrical member fitted to the first cylindrical member, the first and second cylindrical members operating so as to consecutively change over a helical movement of moving along an axis of rotation while relatively rotating and a circumferential movement of making relative rotations with no movement in the direction along the axis of rotation, wherein the second cylindrical member includes a first crested portion and a second crested portion, and said first cylindrical member includes a first helical groove engaging with the first crested portion when making the helical movement, and a second helical groove provided adjacent to the first helical groove and engaging with the second crested portion, and the first and second crested portions make relative movements through the circumferential movement to positions to which the adjacent grooves are extended, and the second cylindrical member further includes guide portions for abutting on the first crested portion or the second crested portion and guiding the first and second crested portions so that the first crested portion and the second crested portion advance into the first helical groove and the second helical groove when changing over to the helical movement from the circumferential movement. 
     In the last mentioned lens barrel according to said further aspect of the present invention, preferably the first cylindrical member includes a first circumferential groove through which the first crested portion moves when making the circumferential movement, and a second circumferential groove through which the second crested portion moves when making the circumferential movement, the first crested portion is shorter in length in the direction along the axis of rotation than the second crested portion, and the first circumferential groove is narrower, enough not to permit the second crested portion to pass through, in width in the direction along the axis of rotation than the second circumferential groove. 
     In the last mentioned lens barrel according to said further aspect of the present invention, preferably the first cylindrical member includes a helical movement guide portion, formed in the vicinity of a boundary between the first circumferential groove and the second circumferential groove, for guiding the changeover from the circumferential movement to the helical movement in such a way that the second crested portion abuts thereon. 
     In the last mentioned lens barrel according to said further aspect of the present invention, preferably the first cylindrical member includes a circumferential movement guide portion, formed on the extension of the first helical groove and in the vicinity of the first circumferential groove, for guiding the changeover from the helical movement to the circumferential movement in such a way that the second crested portion abuts thereon. 
     In the last mentioned lens barrel according to said further aspect of the present invention, preferably the first cylindrical member includes a third crested portion formed in a range defined by the first helical groove, the second helical groove and the first circumferential groove, a fourth crested portion formed in a range defined by the first helical groove, the second helical groove and the second circumferential groove, and a fifth crested portion provided in a position facing to the third crested portion with the first circumferential groove interposed therebetween, the circumferential movement guide portion is formed by the fifth crested portion, and the helical movement guide portion is formed by the third crested portion and the fifth crested portion. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a development showing a male helicoid member  2  included in a lens barrel of a first embodiment of the present invention; 
     FIG. 2 is an enlarged perspective view showing the male helicoid member  2  in development; 
     FIG. 3 is a development showing a female helicoid member  1  included in the lens barrel of the present invention; 
     FIG. 4 is an enlarged perspective view showing the female helicoid member  1  in development; 
     FIG. 5 is a sectional view showing a state where the male helicoid member  2  engages with the female helicoid member  1  in a position on the A—A section in FIG. 3; 
     FIG. 6 is a sectional view showing a state where the male helicoid member  2  engages with the female helicoid member  1  in a position on the B—B section in FIG. 3; 
     FIG. 7 is a perspective development showing a state where the male helicoid member  2  engages with the female helicoid member  1  and a state where a high guide protruded portion  2   a  abuts on an inclined surface  1   fa  of a second middle guide groove if; 
     FIG. 8 is a perspective development showing a state where the male helicoid member  2  engages with the female helicoid member  1  and a state where a high guide protruded portion  2   b  exists in a position corresponding to a helical groove  1   c  (a first middle guide groove  1   g ); 
     FIG. 9 is a view showing a second embodiment of the lens barrel of the present invention; 
     FIG. 10 is a development showing the second embodiment of the lens barrel of the present invention; 
     FIG. 11 is a development showing a state when changed over from a helical movement to a circumferential movement; 
     FIG. 12 is a view showing a state when making the circumferential movement; 
     FIG. 13 is a view showing a helicoid of a conventional lens barrel in development; 
     FIG. 14 is a partially enlarged view of FIG. 13; 
     FIG. 15 is a view showing the helicoid of the conventional lens barrel in development; 
     FIG. 16 is a view showing the helicoid of the conventional lens barrel in development; and 
     FIG. 17 is a view showing the helicoid of the conventional lens barrel in development. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiments of the present invention will hereinafter be described with reference to the accompanying drawings. 
     FIGS. 1 through 8 are explanatory views each showing a lens barrel in a first embodiment of the present invention. 
     The lens barrel in the first embodiment is constructed of, as shown in FIG. 5, a cylindrical female helicoid member  1  having helicoid grooves formed along an inner periphery that will be explained later on, and a male helicoid member  2  fitted in this female helicoid member  1  and including protruded portions so formed along an outer periphery as to be engaged with the helicoid grooves. With a known configuration, the female helicoid member  1  is rotatably provided on a fixing member of the lens barrel, while the male helicoid member  2  capable of only moving straight in optical-axis directions in a way that inhibits its rotations by an unillustrated rotation restriction mechanism. 
     FIG. 1 is a development showing the male helicoid member  2  included in the lens barrel in the first embodiment of the present invention. 
     FIG. 2 is an enlarged perspective view showing the male helicoid member  2  in enlargement. 
     The male helicoid member  2  takes substantially a cylindrical shape and includes totally twelve pieces of high guide protruded portions  2   a ,  2   b  and low guide protruded portions  2   c ,  2   d  lower in height (protruded quantity) than the high guide protruded portions  2   a ,  2   b , wherein these protruded portions are each provided in this sequence by three sets along the outer peripheral portion. The male helicoid member  2  makes helicoid-engagement with the female helicoid member  1  and is this driven as a first helicoid member. 
     FIG. 3 is a development of the female helicoid member  1  included in the lens barrel in the first embodiment of the present invention. 
     Note that the grooves are depicted by one-dotted chain lines in FIG.  3  and developments that will hereinafter be shown. 
     FIG. 4 is an enlarged perspective view illustrating the female helicoid member  1  in enlargement. 
     The female helicoid member  1  is defined as a second helicoid member including first guide grooves ( 1   a  through  1   d ) and a second guide groove  1   e  formed along the inner periphery of the cylinder. 
     The female helicoid member  1  has totally twelve grooves, wherein the first guide grooves ( 1   a  through  1   d ) are each formed by three grooves in the inner periphery of the cylinder thereof. 
     FIG. 5 is a sectional view showing a state where the male helicoid member  2  engages with the female helicoid member  1  in a position on the section A—A in FIG.  3 . 
     Among the first guide grooves ( 1   a  through  1   d ), the helical grooves  1   c ,  1   d  engaging with the low guide protruded portions  2   c ,  2   d  are provided with first middle guide groove portions  1   g ,  1   h  having groove depths so set as to inhibit the high guide protruded portions  2   a ,  2   b  from moving therethrough so that the high guide protruded portions  2   a ,  2   b  do not enter and to permit the low guide protruded portions  2   c ,  2   d  to move therethrough. 
     The second guide groove le is continuous with the first guide grooves ( 1   a  through  1   d ) and is formed in a direction substantially orthogonal to a central axis of rotation of the female helicoid member  1  (the central axis of rotation is substantially coincident with the optical axis in this embodiment). 
     FIG. 6 is a sectional view showing a state where the male helicoid member  2  engages with the female helicoid member  1  in a position on the section B—B in FIG.  3 . 
     The second guide groove  1   e  partially has a second middle guide groove  1   f , having a depth so set as to permit the low guide protruded portions  2   c ,  2   d  to move therethrough and to inhibit the high guide protruded portions  2   a ,  2   b  from moving therethrough, so the second middle guide groove  1   f  abuts on the high guide protruded portion  2   a  and guide the male helicoid member  2  so that the protruded portions  2   a  through  2   d  are changed over to the engagements with the first guide grooves ( 1   a  through  1   d ) from the engagement with the second guide groove  1   e . For this purpose, the second middle guide groove if is formed with an inclined surface  1   fa  continuous with an inclined surface  1   aa  of the helical groove  1   a.    
     When the male helicoid member  2  makes the helicoid-engagement (at the first guide grooves ( 1   a  through  1   d )) with the female helicoid member  1 , the male helicoid member  2  moves in the axial directions with the mutual rotations. Further, when engaging with the second guide groove le, the position in the axial direction remains unchanged even if the mutual rotations occur. 
     The high guide protruded portions  2   a ,  2   b  and the low guide protruded portions  2   c ,  2   d  of the male helicoid member  2  continuously move between the first guide grooves ( 1   a  through  1   d ) and the second guide groove le of the female helicoid member  1 . At this time, the first middle guide grooves  1   g ,  1   h  and the second middle guide groove if function effectively. This point will hereinafter be discussed. 
     FIG. 7 is a perspective development showing a state the male helicoid member  2  engages with the female helicoid member  1 . The high guide protruded portion  2   a  of the male helicoid member  2  abuts on the inclined surface  1   fa  of the second middle guide groove  1   f  of the female helicoid member  1 . 
     The male helicoid member  2  moves in an arrow direction C, and, as in the state shown in FIG. 7, the high guide protruded portion  2   a  abuts on the inclined surface  1   fa  of the second middle guide groove  1   f . Thereupon, the male helicoid member  2  is unable to rotate directly in the arrow direction C but is guided by the inclined surface  1   fa . Then, a crested portion of the guide protruded portion  2   a  moves forward along the inclined surface  1   fa , and the guide protruded portions  2   a  through  2   d  respectively move to the first guide grooves. At this time, the portions with which the low guide protruded portions  2   c ,  2   d  engage are formed with the first middle guide grooves  1   g ,  1   h , however, the heights thereof are so set as to enable them to pass through each other, and hence these portions can enter directly. 
     FIG. 8 is a perspective development illustrating a state where the male helicoid member  2  engages with the female helicoid member  1  and also a state where the high guide protruded portion  2   b  exists in a position corresponding to the helical groove  1   c  (the first middle guide groove  1   g ). 
     At this time, the high guide protruded portion  2   b  abuts on the first middle guide groove  1   g  and is unable to enter this helical groove  1   c . Accordingly, the male helicoid member  2  moves to the position shown in FIG.  7  and comes to engage with predetermined grooves. 
     In the second guide groove le, the low guide protruded portions  2   c ,  2   d  do not interfere with the second middle guide groove if, and therefore the configuration described above can be adopted. 
     According to the first embodiment, the number of the helicoid grooves can be increased, whereby the helical engagement state can be stabilized and a binding force can be enhanced. 
     Further, the female helicoid member  1  and the male helicoid member  2  engage with each other substantially over the entire periphery of the cylinder, thereby making it possible to improve a light shielding characteristic against the light entering from between the cylinders. 
     Further, the flat area of the inner periphery of the female helicoid member  1  is reduced with the result that an amount of reflection of the light reflected from the flat area, and a flare and a ghost can be reduced. 
     The first embodiment has exemplified the helicoid, however, a so-called cam mechanism based on engagement between a cam pin and a cam groove is also available without being limited to the helicoid. 
     Next, a second embodiment of the present invention will be explained in greater detail. 
     FIG. 9 is a schematic view showing the second embodiment of the lens barrel of the present invention. 
     The lens barrel in the second embodiment operates in such a way that a female helicoid member (a first cylindrical member)  101  is combined with a male helicoid member (a second cylindrical member)  102 , and the female helicoid member  101  thus rotates, whereby the male helicoid member  102  continuously changes over, as will be explained later on, between a helical movement relative to the female helicoid member  101  (which is, i.e., a rectilinear movement in the optical-axis direction as the center of rotation) and a circumferential movement. 
     FIG. 10 is a development showing the lens barrel in the second embodiment. 
     The female helicoid member  101  includes a third crested portion  101   a , a fourth crested portion  101   b , a fifth crested portion  10   c , a first helical groove  101   d , a second helical groove  101   e , a first circumferential groove  101   g  and a second circumferential groove  10   f.    
     The male helicoid member  102  has a first crested portion  102   a  and a second crested portion  102   b , and is so provided as to be capable of moving straight only with its rotation regulated by an unillustrated straight movement guide mechanism. 
     A first helical groove  101   d  of the female helicoid member  101  is engaged with the first crested portion  102   a  of the male helicoid member  102 . A second helical groove  101   e  of the female helicoid member  101  is engaged with the second crested portion  102   b  of the male helicoid member  102 . With these helicoid engagements, the female helicoid member  101  and the male helicoid member  102  make relative rotations, and the male helicoid member  102  rectilinearly moves in a direction along the center of rotation (which will hereinafter be termed a straight moving direction). 
     On the inner peripheral surface of the female helicoid member  101 , a crested portion formed between the first helical groove  101   d  and the second helical groove  101   e  includes two types of crested portions, i.e., a third crested portion  101   a  formed in a range defined by the first helical groove  101   d , the second helical groove  101   e  and a first circumferential groove  101   g , and a fourth crested portion  101   b  formed in a range defined by the first helical groove  101   d , the second helical groove  101   e  and a second circumferential groove  101   f.    
     The first circumferential groove  101   g  of the female helicoid member  101  corresponds to the first crested portion  102   a  of the male helicoid member  102 . The second circumferential groove  101   f  corresponds to the second crested portion  102   b . A width of the first circumferential groove  101   g  in the straight moving direction is an engagement dimension corresponding to a width of the first crested portion  101   a  in the straight moving direction. Accordingly, when the first circumferential groove  101   g  engages with the first crested portion  102   a , the female helicoid member  101  and the male helicoid member  102  can not move relatively in the straight moving direction and therefore make the relative rotational movements (circumferential movements). Namely, even when the female helicoid member  101  is rotated, the male helicoid member  102  does not move. Note that a width of the second circumferential groove  101   f  in the straight moving direction is well larger than a width of the second crested portion  102   b  in the straight moving direction. 
     The first crested portion  102   a  is shorter in the straight moving direction than the second crested portion  102   b . Further, the first circumferential groove  101   g  is narrower in width in the straight moving direction than the second circumferential groove  10   f . Hence, the second crested portion  102   b  is unable to pass through the first circumferential groove  101   g.    
     According to the second embodiment, the first crested portion  102   a  and the second crested portion  102   b  of the male helicoid member  102  make the relative movements up to positions to which the adjacent helicoid grooves extend through the circumferential movements. For this purpose, the first circumferential groove  101   g  and the second circumferential groove  101   f  are formed on the extensions of the third crested portion  101   a  and the fourth crested portion  101   b  of the male helicoid member  101 . A fifth crested portion  101   c  is formed substantially on the extension of the third crested portion  101   a . The first circumferential groove  101   g  is formed in a position interposed between the third crested portion  101   a  and the fifth crested portion  101   c.    
     Next, an operation of the lens barrel in the second embodiment will be discussed. 
     (Helical Movement) 
     FIG. 10 illustrates a state the crested portions  102   a ,  102   b  of the male helicoid member  102  make helical movements with respect to the female helicoid member  101 . When making the helical movements, the first crested portion  102   a  is engaged with the first helical groove  110   d  while the second crested portion  102   b  is engaged with the second helical groove  101   e , and the male helicoid member  102  moves in the straight moving direction while rotating relatively to the female helicoid member  101 . 
     (Changeover from Helical Movement to Circumferential Movement) 
     FIG. 11 is a development showing a state when the helical movement is changed over to the circumferential movement. 
     When moved to the state shown in FIG. 11 from the state in FIG. 10, the first crested portion  102   a  disengages from the first helical groove  101   d , and the second crested portion  102   b  disengages from the second helical groove  10   e . Further, simultaneously when disengaging therefrom, the first crested portion  102   a  abuts on the fifth crested portion  10   c , and it follows that the male helicoid member  102  makes only the rotational movement relatively to the female helicoid member  101 . In this case, the fifth crested portion  101   c  functions as a circumferential movement guide portion for guiding the changeover from the helical movement to the circumferential movement. 
     (Circumferential Movement) 
     FIG. 12 is a view showing a state when making the circumferential movement. 
     When moving the circumferential movement illustrated in FIG. 12, the first crested portion  102   a  engages with the first circumferential groove  101   g , thus regulating a relative position in the straight moving direction. The second crested portion  102   b  exists on the second circumferential groove  101   f  when making the circumferential movement but has a gap from the fourth crested portion  101   b  configuring the second circumferential groove  10   f.    
     (Changeover from Circumferential Movement to Helical Movement) 
     A state of the changeover from the circumferential movement to the helical movement is the state illustrated in FIG. 11, wherein the direction of the relative rotation is reversed. In this case, the first crested portion  102   a  and the second crested portion  102   b  disengage from the first circumferential groove  101   g  and the second circumferential groove  101   f , and simultaneously the second crested portion  102   b  abuts on the third crested portion  101   a  and on the fifth crested portion  101   c , thus changing over to the helical movement. In this case, the third crested portion  101   a  and the fifth crested portion  101   c  function as helical movement guide portions for guiding the changeover from the circumferential movement to the helical movement. 
     Thus, according to the second embodiment, even if the first crested portion  102   a  and the second crested portion  102   b  are structured to make the relative movements to the positions to which the adjacent grooves are extended through the circumferential movements, both of the changeover from the helical movement to the circumferential movement and the changeover from the circumferential movement to the helical movement, can be surely performed. Accordingly, the first circumferential groove  101   g  and the second circumferential groove  101   f  can be formed on the extensions of the third crested portion  101   a  and of the fourth crested portion  101   b , whereby the number of grooves can be increased. With this contrivance, it is possible to obtain the lens barrel capable of attaining the stable helical engagement with a high accuracy, exhibiting an excellent light shielding characteristic and making difficult occurrences of the caused-by-stray-light flare, ghost, etc. 
     The second embodiment has exemplified the case in which the female helicoid member  101  rotates, thereby driving the male helicoid member  102  in the straight moving direction, however, without being limited to this, for example, the female helicoid member may be driven in the straight moving direction by rotating the male helicoid member. 
     As described in depth, according to the present invention, the multiplicity of grooves can be formed, thereby making it possible to attain the stable helical engagement, exhibit the excellent light shielding characteristic and to make difficult the occurrences of the caused-by-stray-light flare, ghost, etc. 
     In the above embodiments of the present invention, the first and second guide protruded portions can be prevented from entering the incorrect guide grooves, and, even when forming the multiplicity of guide grooves, the stable operation can be attained. 
     In the above embodiments of the present invention, the multiplicity of cam grooves can be formed, thereby making it possible to attain the stable helical engagement, exhibit the excellent light shielding characteristic and to make difficult the occurrences of the caused-by-stray-light flare, ghost, etc. 
     In the above embodiments of the present invention, even when the multiplicity of helical grooves are formed, the stable operation can be attained.