Abstract:
The present invention is directed to an improved inner focusing zoom lens barrel that implements a zoom ratio as high as 15×±α and that ensures a well-balanced cam configuration for the smooth zooming and focusing. The inner focusing zoom lens barrel includes a fixed barrel; a focusing cam barrel, a linear shuttle barrel, and a first cam barrel laid one over another in this order inside the fixed barrel; and a zoom linkage ring, a second cam barrel, and a 1st-lens-group sliding barrel laid one over another in this order outside the fixed barrel.

Description:
FIELD OF THE INVENTION 
     The present invention relates to an inner focusing zoom lens barrel, and more particularly, it relates to an inner focusing zoom lens barrel suitable for inner focusing zoom lenses that is capable of attaining a zoom ratio of as high as 15×±α. 
     BACKGROUND ART 
     Inner focusing lenses of high zoom ratio usually have an increased variation rate of a displacement of a focusing lens upon close-up photoshooting at a minimum objective distance from the leading end of the lens to the subject, and an attempt to raise a close-up performance at the minimum objective distance by means of a single focusing cam member causes focus to change greatly in the remaining zooming ranges, resulting in varifocal. Focusing cam curves, which perform a varifocal-zooming conversion, must be deliberately designed for appropriate zooming and focusing parameters. However, this leads to difficulties in ensuring a well-balanced cam configuration for the smooth zooming and focusing, and a curvature of focusing cams must be changed, or some other compensation must be made with the focusing cams. 
     In the prior art high zoom ratio lenses, the focusing lens is simultaneously rotated and displaced forward and backward during either the zooming or the focusing. Typically, guide grooves are defined in the focusing cam barrel to serve as cams along with pins fitted in the guide grooves to slide and trace in the guide grooves of the focusing cam barrel, which permits rotary components to turn for the focusing. During the zooming, the rotary components turn along the focusing cam barrel in bi-directions that determine an operable range of the focusing cams to adjustably obtain an appropriate displacement of the focusing lens (see Patent Document 1 listed below). 
     However, it is still harder to determine the operable range of the focusing cams so as to ensure the appropriate displacement of the focusing lens as well as the further enhanced close-up performance at the minimum objective distance without focal change in the entire zooming range. The zoom lenses of zooming ratio as high as 5×±α are typically of 5-layer configuration where a first cam barrel is inside a fixed barrel while a second cam barrel, a linear shuttle cam barrel, and a third cam barrel are disposed outside the fixed barrel one over another, and with such a configuration, the zoom lenses cannot reduce a diameter any longer. Such zoom lenses do not allow for anti-shake or image stabilization mechanism incorporated therein. 
     Some of the prior art high zoom ratio lenses have focus compensating cams and focusing cams disposed in the same rotary component to attain the desired displacement of the focusing lens (see Patent Document 2 listed below). However, such zoom lenses are typically configured so that the focusing lens is linearly moved during the zooming, and therefore, the zooming operation is simply adjusted by a fixed amount of compensation in any segment of the zooming range, which results in the compensation is insufficient to reduce the objective distance for the close-up photoshooting. In addition, this type of the high zoom ratio lenses encounter a problem that an outer diameters cannot reduce any longer because of their 5-layer configuration having first and second cam barrels, a linear shuttle barrel, and a third cam barrel outside a fixed barrel. This type of the zoom lenses do not allow for anti-shake or image stabilization mechanism incorporated therein. 
     Some other prior art high zoom ratio lenses include, as shown in  FIGS. 10 and 11 , a zoom linkage ring  14  inside a fixed barrel  12 , a first cam barrel  16  inside the zoom linkage ring  14 , a linear shuttle barrel  18  inside the first cam barrel  16 , and a focusing cam barrel  20  inside the linear shuttle barrel  18 . The first cam barrel  16  is engaged with the zoom linkage ring  14  with zoom linkage studs  40  intervening therebetween so that rotation of the zoom ring  30  can be transmitted to the first cam barrel  16 . The first cam barrel  16  has 1st-cam-barrel guide cams with guide studs  39  used to move the first cam barrel along the optical axis, 3rd-lens-group guide cams with 3rd-lens-group guide studs  43  operatively fitted therein, and 4th-lens-group guide cams with 4th-lens-group guide studs  45  operatively fitted therein. The first cam barrel  16  also has 2nd-cam-barrel linkage studs  50  protruding outward at the leading end of the fixed barrel  12  opposite to a lens mount  10 . The 2nd-cam-barrel linkage studs  50  are operatively fitted in longitudinal guide grooves defined in the second cam barrel  22  (see Patent Document 3 listed below). 
     In the above-mentioned high zoom ratio zoom lenses, the zoom linkage ring  14  is attached inside of the fixed barrel  12 , the first cam barrel  16  is disposed inside the zoom linkage ring  14 , and the linear shuttle barrel  18  is disposed inside the first cam barrel  16 . The zoom linkage studs  40  couple the first cam barrel  16  with the zoom linkage ring  14  so as to transmit the rotation of the zoom  30  to the first cam barrel  16 . In order to make the first cam barrel  16  move along the optical axis, the first cam barrel  16  has to be provided with the 1st-cam-barrel guide cams engaged with the 1st-cam-barrel guide studs  30 , the 3rd-lens-group guide cams engaged with the 3rd-lens-group guide studs  43 , and the 4th-lens-guide cams engaged with the 4th-lens-group guide studs  45 . 
     However, the first cam barrel  16  is restricted in its entire extension along the optical axis, and this results in the 1st-cam-barrel guide cams, the 3rd-lens-group guide cams, and the 4th-lens-group guide cams being restricted in their respective entire extensions along the optical axis. Especially, in order to raise a zoom ratio, the third and fourth groups of lenses among others succeeding to the first and the second must respectively be given a greater stroke along the optical axis, but it is hard to accomplish a well-balanced adjustment among the guide cams within the restricted dimension of the first cam barrel  16  extending along the optical axis. In other words, there is no compromised solution in forced arrangement of the guide cams, and if there were, the guide cams are restricted more in their relative configurations and positions without freedom and idleness of design. 
     Moreover, as for an available entire extension of the fixed barrel  12 , a stroke of the linear shuttle barrel  18  is increased as a displacement of the third group of lenses is increased, and this leads to another problem of losing a steady fitting-hold or anchor-hold of the linear shuttle barrel  18  on the fixed barrel  12  during displacing the linear shuttle barrel for the telephoto-shooting to eventually lose the required stability of the lens barrel. Additionally, this type of the zoom lenses do not allow for anti-shake or image stabilization mechanism incorporated therein. 
     On the other hand, at an attempt to configure a lens barrel so that its radial dimensions can be reduced, there has been developed a lens barrel having a shake-compensating unit and a lens frame holding lens pieces both of which are included as at least part of a photoshooting optics, and such a improved lens barrel has a restrictor located in the shake compensating unit so as to restrict rotation of the lens frame (see Patent Document 4). 
     Patent Document 1:
         Japanese Patent Preliminary Publication No. H8-304684       

     Patent Document 2:
         Japanese Patent Preliminary Publication No. 2000-89086       

     Patent Document 3:
         Japanese Patent No. 3689379       

     Patent Document 4:
         Japanese Patent Preliminary Publication No. 2007-79241       

     The present invention is made to overcome the aforementioned disadvantages in the prior art zoom lens barrel, especially, the prior art inner focusing zoom lens barrel, and accordingly, it is an object of the present invention to provide an improved inner focusing zoom lens barrel that implements a zoom ratio as high as 15×±α and that ensures a well-balanced cam configuration for the smooth zooming and focusing and facilitates to incorporate anti-shake mechanism. 
     It is another object of the present invention to provide an inner focusing zoom lens barrel that is capable of attaining a sufficient close-up performance at the minimum objective distance from the leading end of the zoom lens barrel to the subject and of minimizing change in focus throughout the entire zooming range and that is reduced in its outer diameter. 
     It is further another object of the present invention to provide an inner focusing zoom lens barrel that is imposed reduced restrictions on configurations and positions of guide cams and that keeps a steady fitting-hold or anchor-hold of a linear shuttle barrel on a fixed barrel during displacing the linear shuttle barrel for the telephoto-shooting to eventually retain the required stability of the lens barrel. 
     SUMMARY OF THE INVENTION 
     The present invention provides an inner focusing zoom lens barrel that has a fixed barrel; a focusing cam barrel, a linear shuttle barrel, and a first cam barrel laid one over another in this order inside the fixed barrel; and a zoom linkage ring, a second cam barrel, and a 1st-lens-group sliding barrel laid one over another in this order outside the fixed barrel. 
     The present invention also provides an inner focusing zoom lens barrel that has a fixed barrel; a focusing cam barrel, a linear shuttle barrel, and a first cam barrel laid one over another in this order inside the fixed barrel; a zoom linkage ring, a second cam barrel, and a 1st-lens-group sliding barrel laid one over another in this order outside the fixed barrel; and a lens system comprised of a first group of lens pieces of positive refractivity, a second group of lens pieces of negative refractivity serving as a focusing lens, a third group of lens pieces of positive refractivity, and a fourth group of lens pieces of positive refractivity disposed in this order from the closest to the subject where as magnification changes from the wide-angle view to the telephoto view, the first lens group and the second lens group are separated farther from each other, the second lens group and the third lens group are moved closer to each other, and the third lens group and the fourth lens group are also moved closer to each other; the trailing lens pieces in third lens group being moved so as to be perpendicular to the optical axis, thereby enabling compensation for an unstable imaging plane due to a little jerk(s) of the hand(s). 
     In one aspect of the present invention, the inner focusing zoom lens barrel can attain a zoom ratio as high as 15×±α, and has cam configurations well-balanced for the smooth zooming and focusing as well as anti-shake or image-stabilization mechanism easily incorporated therein. 
     In another aspect of the present invention, the inner focusing zoom lens barrel can attain a sufficient close-up performance at the minimum objective distance from the leading end of the zoom lens barrel to the subject and minimize change in focus throughout the entire zooming range, and is reduced in its outer diameter. 
     In still another aspect of the present invention, the inner focusing zoom lens barrel is imposed reduced restrictions on configurations and positions of guide cams and can keep a steady fitting-hold or anchor-hold of a linear shuttle barrel on a fixed barrel during displacing the linear shuttle barrel for the telephoto-shooting to eventually retain the required stability of the lens barrel. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a partial sectional view showing an embodiment of an inner focusing zoom lens upon wide-angle view shooting according to the present invention. 
         FIG. 2  is a partial sectional view showing the embodiment of the inner focusing zoom lens upon telephoto view shooting according to the present invention. 
         FIG. 3  is a view illustrating an exemplary fixed barrel according to the present invention, opened along a diameter and compressed. 
         FIG. 4  is a view illustrating an exemplary first cam barrel according to the present invention, opened along a diameter and compressed. 
         FIG. 5  is a view illustrating an exemplary linear shuttle barrel according to the present invention, opened along a diameter and compressed. 
         FIG. 6  is a view illustrating an exemplary focusing cam barrel according to the present invention, opened along a diameter and compressed. 
         FIG. 7  is a view illustrating an exemplary zoom linkage ring according to the present invention, opened along a diameter and compressed. 
         FIG. 8  is a view illustrating an exemplary second cam barrel according to the present invention, opened along a diameter and compressed. 
         FIG. 9  is a view illustrating an exemplary 1st-lens-group sliding frame according to the present invention, opened along a diameter and compressed. 
         FIG. 10  is a partial sectional view showing a prior art inner focusing zoom lens upon wide-angle view shooting. 
         FIG. 11  is a partial sectional view showing the prior art inner focusing zoom lens upon telephoto view shooting. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A best mode of an inner focusing zoom lens barrel according to the present invention will now be described in conjunction with the drawings. 
     &lt;Lens Barrel Configuration&gt; 
     An inner focusing zoom lens barrel  10  of 18-270 mm focal length includes, as shown in  FIG. 1  and  FIG. 2 , a first group of lens pieces A (focal length+108 mm), a second group of lens pieces B (focal length−13 mm), a third group of lens pieces C (focal length+45 mm), and a fourth group of lens pieces D (focal length+48 mm) attached as a single unit. The third lens group C has the leading lens pieces Cf (focal length+27 mm), and the trailing lens pieces Cr (focal length−40 mm) that are, for the purpose of anti-shake or image stabilizing, shifted so as to be perpendicular to the optical axis. The zoom lens barrel  10  has a fixed barrel  12  integrated with a mount  11  that is used for attachment to a camera body (not shown). 
     The fixed barrel  12  has its inner side overlaid with a focusing cam barrel  20  and a linear shuttle barrel  18 , the latter being inside the former. The linear shuttle barrel  18  has its inner side overlaid with a first cam barrel  16 , and further inside the same, there are a 2nd-lens-group holding frame  2 , a 3rd-lens-group holding frame  3  and a 4th-lens-group holding frame  4  disposed one over another. The 3rd-lens-group holding frame  3  is held by an anti-shake member  114 . The 3rd- and 4th-lens-group holding frames  3 ,  4  are coupled to each other by 4th-lens-group linear guide keys  112  so that they do not rotate about the optical axis relative to each other but can come apart from and close to each other along the optical axis. 
     The fixed barrel  12  has its outer side overlaid with a zoom linkage ring  14 , a second cam barrel  22 , and a 1st-lens-group sliding frame  24  disposed one over another in this order. Outside the 1st-lens-group sliding frame  24 , an outer armor barrel  26 , a zooming ring  30 , and a focusing ring  28  are exposed. The fixed barrel  12  is further superposed with an intermediate lens barrel  29  integrated with it, and a focus linkage plate  102  secured to the focusing ring  28 . The focus linkage plate  102  has its leading end (i.e., opposite to the mount  11 ) provided with focus linkage studs  83  that pass through clearances or through-holes  104  defined in the fixed barrel  12  so as to fit in focus cam grooves  106 . 
       FIG. 3  depicts the fixed barrel  12  having the clearances or through-holes  104  which the focus linkage studs  83  implanted in the focus linkage plate  102  extend through. The fixed barrel  12  has linear guide grooves  47  defined in its inner surface so that guide studs  100  implanted in the linear shuttle barrel  18  are operatively fitted in the guide grooves  47 . Also, the fixed barrel  12  has 1st-cam-barrel guide studs  39  implanted in its outer surface. 
     The focusing cam barrel  20  has, as shown in  FIG. 4 , focus cams  27  in which 2nd-lens-group focus studs  96  are operatively fitted, focus cams  79  in which 2nd-lens-group focus studs  74  are operatively fitted, both of the cams being to shift the second lens group for the focusing, and focus cam grooves  106  in which the focus linkage studs  83  are operatively fitted. 
     The linear shuttle barrel  18  has, as shown in  FIG. 5 , 2nd-lens-group guide cams  80  in which the 2nd-lens-group guide studs  74  are operatively fitted, 2nd-lens-group guide cams  81  in which the 2nd-lens-group focus studs  96  are operatively fitted, and 1st-cam barrel grooves  88  in which 1st-cam-barrel guide studs  86  implanted in the first cam barrel  16  are operatively fitted to rotate the first cam barrel. The linear shuttle barrel  18 , which has the guide studs  100  implanted therein to guide it, is further provided with second longitudinal guide grooves  61  in which 3rd-lens-group guide studs  43  implanted in the 3rd-lens-group holding frame  3  are operatively fitted. The linear shuttle barrel  18  has studs  66  at its leading end to fit in lateral guide grooves  62  defined in the second cam barrel  22  and to slide the first lens group. 
     As shown in  FIG. 6 , the first cam barrel  16 , which has the 1st-cam-barrel guide studs  86  to rotate the first cam barrel, has 3rd-lens-group guide cams  44  in which the 3rd-lens-group guide studs  43  are operatively fitted, 4th-lens-group guide cams  46  in which 4th-lens-group guide studs  45  are operatively fitted, and third longitudinal guide grooves  48  in which the 2nd-lens-group guide studs  74  are operatively fitted. 
     The zoom linkage ring  14  has, as shown in  FIG. 7 , guide cams  42  in which the 1st-cam-barrel guide studs  30  implanted in the fixed barrel  12  are operatively fitted so as to guide the zoom linkage ring  14 . Also, the zoom linkage ring  14  has first bores  57  in which guide studs  50  are implanted to guide the zoom linkage ring  14 . In addition, the zoom linkage ring  14  has second bores  75  in which the 2nd-lens-guide studs  75  are implanted to guide the second lens group. The zoom linkage ring  14  further has zoom linkage posts  31  protruding toward the imaging field to which zoom linkage studs  40  are attached. 
     The second cam barrel  22  has, as shown in  FIG. 8 , 1st-lens-group guide cams  77  in which 1st-lens-group guide studs  70  are operatively fitted, first longitudinal guide grooves  60  in which the guide studs  50  are operatively fitted to guide the zoom linkage ring  14 , and lateral guide grooves  62  in which the studs  66  are fitted in to slide the first lens group. 
     As can be seen in  FIG. 9 , the 1st-lens-group sliding frame  24  has its inner surface provided with third longitudinal guide grooves  64  in which the studs  66  are operatively fitted, and the 1st-lens-group guide studs  70  operatively fitted in the 1st-lens-group guide cams  77  defined in the second cam barrel  22 . 
     &lt;Zooming Operation&gt; 
     With reference to  FIG. 1  and  FIG. 2 , the zoom ring  30  is revolved for the zooming in and out. Rotation of the zoom ring  30  is transmitted to the zoom linkage ring  14  via the zoom linkage studs  40  fitted and sliding in the linear grooves (not shown) in parallel with the optical axis of the zoom ring  30  and via the zoom linkage posts  31 . 
     When the zoom linkage ring  14  is revolved, the 1st-cam-barrel guide studs  39  implanted in the fixed barrel  12  fit and slide in the 1st-cam-barrel guide cams  42  to permit the zoom linkage ring  14  to move along the optical axis and rotate about the same. 
     The 2nd-lens-group guide studs  74  implanted inside the zoom linkage ring  14  fit and slide in the 2nd-lens-group focus cams  79  defined in the focus cam barrel  20 , the 2nd-lens-group guide cams  80  in the linear shuttle barrel  18 , and the third longitudinal guide grooves  48  in the first cam barrel  16 . This permits the focus cam barrel  20  to move along the optical axis and rotate about it, the linear shuttle barrel  18  to linearly move along the optical axis, and the first cam barrel  16  to rotate. 
     The guide studs  50  implanted outside the zoom linkage ring  14  fit and slide the first longitudinal guide grooves  60  defined in the second cam barrel, which permits rotation of the zoom linkage ring  14  to be transmitted to the second cam barrel  22 . 
     As for motions of the first lens group A during the zooming, the 1st-lens-group studs  66  fitted and sliding in the lateral guide grooves  62  enable the movement of the linear shuttle barrel  18  along the optical axis to be transmitted to the second cam barrel  22 , and although the second cam barrel  22  itself is prevented from revolving, the 1st-lens-group guide studs  70  fitted and sliding in the  1  st-lens-guide cams  77  defined in the second cam barrel  22  permit the 1st-lens-group sliding frame  24  to move along the optical axis over the second cam barrel  22 . 
     As to motions of the second lens group B during he zooming, the second lens group B move along the optical axis and rotate about it as the 2nd-lens-group focus studs  96  of the 2nd-lens-group holding frame  2  do. 
     In order to implement the desired motions of the third lens group C during the zooming, the 3rd-lens-group guide studs  43  implanted in the 3rd-lens-group holding frame  3  fit and slide in the second longitudinal guide grooves  61  in the linear shuttle barrel  18  and the 3rd-lens-group guide cams  44  in the first cam barrel  16 , and thus, permit the third lens group C to move along the optical axis. 
     As to motions of the fourth lens group D during the zooming, the 4th-lens-group guide studs  45  implanted in the 4th-lens-group holding frame  4  fit and slide the 4th-lens-group guide cams  46  defined in the first cam barrel  16 , and the 4th-lens-group linear guide keys  112  are engaged with rotation stopper grooves (not shown) defined in the 4th-lens-group holding frame  4  in parallel with the optical axis, which permits the fourth lens group D to move along the optical axis. 
     &lt;Focusing Operation&gt; 
     With reference to  FIG. 1  and  FIG. 2 , rotation of the focusing ring  28  is transmitted to the focus cam barrel  20  via a focus gear ring  94  and the focus linkage plate  102 . Rotation of the focus cam barrel  20  is supported by the stationary 2nd-lens-group guide studs  74 . Specifically, the 2nd-lens-group guide studs  74  fit and slide in the 2nd-lens-group focus cams  79  and the 2nd-lens-group guide cams  80  defined in the linear shuttle barrel  18  while the 2nd-lens-group focus studs  96  of the 2nd-lens-group holding frame  2  fit and slide in the 2nd-lens-group focus cams  27  and the 2nd-lens-group guide cams  81  defined in the linear shuttle barrel  18 , which enables the focusing lens or the second lens group to move along the optical axis. 
     &lt;Modified Version&gt; 
     In the aforementioned preferred embodiment, the rotation of the 4th-lens-group holding frame  4  is restricted by the 4th-lens-group linear guide keys  112 . The 4th-lens-group linear guide keys  112  may be replaced with a configuration where the linear shuttle barrel  18  is extended toward the imaging field so as to be engaged with the rotation stop grooves defined in the 4th-lens-group holding frame  4  in parallel with the optical axis.