Patent Document

BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a light shielding structure of an optical apparatus. 
         [0003]    2. Description of the Related Art 
         [0004]    In an optical apparatus such as a camera, various kinds of light shielding structures have been proposed in order to shield harmful reflected light within an optical path. For example, a light shielding structure in which matte black coating (antireflection coating) is applied, or flock paper is pasted on a reflecting portion has been proposed. Furthermore, Japanese Laid-Open Patent Application Publication No. H11-305098 has disclosed a structure in which a light-shielding member (flare cutter) protruding in the direction orthogonal to the optical axis is provided. 
         [0005]    However, there is a case in which it is difficult to provide the above-described light shielding structure due to structural reasons, or difficult to produce a satisfactory light shielding effect. One example is shown in  FIGS. 1 and 2 , in which first and second relatively-movable members  11  and  12  are relatively moved in an optical axis direction (with respect to each other) to change an overlapped area therebetween.  FIG. 1  shows an operational state of the optical apparatus, and  FIG. 2  shows a non-operational state of the apparatus. In  FIGS. 1 and 2 , OA denotes an optical axis of an optical system, and CF denotes an image surface. 
         [0006]    In the non-operational state shown in  FIG. 2  of the optical apparatus, the first relatively-movable member  11  and the second relatively-movable member  12  overlap each other by almost the entire areas thereof. Whereas, in the operational state shown in  FIG. 1  of the optical apparatus, the first relatively-movable member  11  and the second relatively-movable member  12  are relatively moved to cause a positional relationship such that the mutually overlapped area therebetween is reduced. For example, a lens barrel of a compact camera is a well known optical apparatus which is provided with relatively-movable members having mutually overlapping areas as described above according to whether the apparatus is in an operational state or a non-operational state. Moreover, in the operational state shown in  FIG. 1 , a part of the inner surface  11   a  on the optical axis side of the first relatively-movable member  11  is exposed to the optical path (the optical axis OA), and reflected light by the inner surface  11   a  on the optical axis side enters an image surface CF as shown by an arrowhead in  FIG. 1 , causing an adverse effect. 
         [0007]    In order to control internal reflection by the first relatively-movable member  11 , it is conceivable to, for example, apply antireflection coating onto the inner surface  11   a  on the optical axis side, or paste flock paper on the inner surface  11   a  on the optical axis side. However, when the distance between the first relatively-movable member  11  and the second relatively-movable member  12  is small, there is a possibility that interference occurs between the antireflection coating or the flock paper provided on the inner surface  11   a  on the optical axis side and the second relatively-movable member  12 . When the distance between the first relatively-movable member  11  and the second relatively-movable member  12  is several scores of micrometers because, for example, the flock paper has a thickness of about 100 through 200 micrometers, even if the paper is thin, there is a possibility that a load is applied by repetitive relative movement between the first relatively-movable member  11  and the second relatively-movable member  12 , so that the paper is peeled off or a resistance is caused due to this relative movement. Moreover, control of a film thickness of an antireflection coating is difficult, especially, in the case of a brush coating. Accordingly, such a coating is not appropriate for a light shielding structure for use when the distance between the first relatively-movable member  11  and the second relatively-movable member  12  is small. Furthermore, when light rays enter at a large incident angle in such a way that almost perfect reflection from the inner surface  11   a  on the optical axis side occurs, there is a possibility that a satisfactory light shielding effect may not obtained, even if the antireflection coating is applied. 
         [0008]    Although another method for controlling the internal reflection is possible, wherein a ring-like light shielding member is provided at the rear end portion of the first relatively-movable member  11 , this undesirably causes the whole structure to increase in size and become more complex. Moreover, in some cases, it is not appropriate to provide the light shielding member at the rear end position of the first relatively-movable member  11 , because a normal light which correctly travels along the optical path and an internal reflection light overlap each other to cause a state in which it is difficult to shield only the internal reflection light. Furthermore, when the rear end portion of the first relatively-movable member  11  is a sliding portion, it is difficult to provide the light shielding member at this rear end portion. 
       SUMMARY OF THE INVENTION 
       [0009]    The present invention provides a light shielding structure in an optical apparatus, wherein the structure is a compact structure, and is superior in a shielding performance. 
         [0010]    According to an aspect of the present invention, a light shielding structure of an optical apparatus is provided, including first and second relatively-movable members, each having an engaging portion, the engaging portions being engaged with each other and relatively movable to each other so as to change an amount of mutually overlapping area therebetween; and a light shielding member which is provided between the engaging portions of the first and second relatively-movable members. The light shielding member is elastically deformed into a light shielding shape in which the light shielding member inwardly bends toward an optical axis of the optical apparatus to protrude from the engaging portions due to the mutually overlapping area between the engaging portions decreasing, and the light shielding member is elastically deformed into a retracted shape in which the light shielding member is housed between opposing surfaces of the engaging portions due to the mutually overlapping area between the engaging portions increasing, in accordance with a relative movement between the engaging portions. 
         [0011]    It is desirable for the engaging portions of the first and second relatively-movable members to include an inner engaging portion and an outer engaging portion, the outer engaging portion provided on the outer diameter side more distant from the optical axis than the inner engaging portion. The light shielding member includes a fixed portion attached to the outer engaging portion at an inner surface thereof which is opposed to the inner engaging portion; and an elastically-deformable light shielding portion which is configured to protrude from the fixed portion inwardly toward the optical axis in a free state, and to be elastically deformable from the free state toward the outer engaging portion. 
         [0012]    When the mutually overlapping area between the engaging portions of the first and second relatively-movable members is increased, it is desirable for the elastically-deformable light shielding portion to press against the inner engaging portion, and to be elastically deformed in a direction toward the outer engaging portion. 
         [0013]    It is desirable for the elastically-deformable light shielding portion to be curved in a shape of an arc. 
         [0014]    It is desirable for the elastically-deformable light shielding portion to protrude straightly from the fixed portion. 
         [0015]    It is desirable for the first and the second relatively-movable members to be relatively movable to each other in a direction parallel to the optical axis, and for the elastically-deformable light shielding portion of the light shielding member to be inclined so as to gradually protrude from the outer engaging portion inwardly toward the optical axis rearwardly in the optical axis direction. 
         [0016]    In an embodiment, a light shielding structure of an optical apparatus is provided, including a first and a second relatively-movable members, each having an engaging portion, the engaging portions being engaged with each other and relatively movable to each other to as to change an amount of mutually overlapping area therebetween; and a light shielding member which is provided between the engaging portions of the first and second relatively-movable members. The light shielding member is elastically deformed into a retracted state in which the light shielding member is elongated in the relatively moving direction of the first and second relatively-movable members so as to be housed between opposing surfaces of the engaging portions, and the light shielding member is elastically deformed into a light shielding state in which a part of the light shielding member protrudes inwardly toward the optical axis to shield unwanted light rays which are reflected by an inner-surface of the engaging portions toward the image surface. 
         [0017]    According to the present invention, a light shielding structure which is compact, and is superior in a shielding performance can be obtained. 
         [0018]    The present disclosure relates to subject matter contained in Japanese Patent Application No. 2006-138154 (filed on May 17, 2006), which is expressly incorporated herein by reference in its entirety. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]      FIG. 1  is a sectional view showing a prior art example of an internal reflection occurring in an optical apparatus having relatively-movable members; 
           [0020]      FIG. 2  is a sectional view showing a state in which the overlapped area between a first and a second relatively-movable members is large in the optical apparatus shown in  FIG. 1 ; 
           [0021]      FIG. 3  is a perspective view of an disassembled state of a linear movement guide member, a lens holding member and a light shielding piece in a lens barrel to which a light shielding structure according to the present invention is applied; 
           [0022]      FIG. 4  is a perspective view showing a state in which the light shielding piece is attached to the guide key of the linear movement guide member in an disassembled state shown in  FIG. 3 ; 
           [0023]      FIG. 5  is an enlarged perspective view of the light shielding piece and the guide key in an disassembled state shown in  FIG. 3 ; 
           [0024]      FIG. 6  is a enlarged perspective view of the light shielding piece and the guide key in an attached state shown in  FIG. 4 ; 
           [0025]      FIG. 7  is a sectional view of the linear movement guide member (guide key), the lens holding member, and the light shielding piece, illustrating the light shielding function of the light shielding piece in a photographing state of the lens barrel; 
           [0026]      FIG. 8  is a sectional view of the linear movement guide member (guide key), the lens holding member, and the light shielding piece, illustrating an elastic deformation state of the light shielding piece in a retracted state of the lens barrel; and 
           [0027]      FIG. 9  is a sectional view of a linear movement guide member (guide key), a lens holding member, and a light shielding piece, illustrating another embodiment according to the present invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0028]    A linear movement guide member (relatively-movable member)  21  and a lens holding member (relatively-movable member)  22 , which are shown in  FIGS. 3 and 4 , are members of a lens barrel of a compact camera. The linear movement guide member  21  is supported so as not to rotate with respect to the main body of the camera, and the lens holding member  22  holds a part of a plurality of lens groups constituting a photographing optical system (not shown). Three guide grooves (inner engaging portions)  22   a , which are approximately parallel to the optical axis OA of the photographing optical system, are formed on the outer circumferential surface of the lens holding member  22 . In the linear movement guide member  21 , three guide keys (outer engaging portions)  21   a  are provided, and protrude forward from a ring-like portion surrounding the optical axis OA, so that each of the guide keys  21   a  is inserted into the guide grooves  22   a , respectively. The guide keys  21   a  and the guide grooves  22   a  engage with each other in such a way that relative movement of the guide key  21   a  and the guide groove  22   a  is allowed in a linear direction parallel to the optical axis OA, and the relative rotation of the lens holding member  22  and the linear movement guide member  21  is restricted. In other words, the linear movement guide member  21  guides the lens holding member  22  to move linearly in the direction of the optical axis OA. 
         [0029]    A light shielding piece (light shielding member)  23  is provided on the inner surface (optical-axis-side surface)  21   b  of one guide key  21   a  of the linear movement guide member  21 . As shown in  FIG. 5 , the light shielding piece  23  is a thin plate-like member having a rectangular shape and having approximately the same width of the guide key  21   a . The light shielding piece  23  is formed as a molded product separated from the linear movement guide member  21 . 
         [0030]    As shown in  FIGS. 7 and 8 , the plate thickness of the light shielding piece  23  is thinner than the distance between the inner surface (opposing surface)  21   b  of the guide key  21   a  and the bottom surface (opposing surface)  22   b  of the guide groove  22   a . The light shielding piece  23  has a flat plate-like fixed portion  23   a , which is approximately parallel to the inner surface  21   b  of the guide key  21   a , and an inwardly curved portion (elastically-deformable light shielding portion)  23   b  which is bent along an arc over the above fixed portion  23   a . The fixed portion  23   a  is attached to the inner surface  21   b  of the guide key  21   a  under a state in which the inwardly curved portion  23   b  bends (curves) rearwards in the optical axis direction as shown in  FIG. 6 . Appropriate methods using a double-faced tape, bonding, and the like, are used for attaching the fixed portion  23   a.    
         [0031]    In the above-described fixed state, the inwardly curved portion  23   b  of the light shielding piece  23  has a inwardly curved shape toward the rear in the optical axis direction, the inwardly curved portion  23   b  is gradually separated from the inner surface  21   b  of the guide key  21   a  (i.e., approaches the optical axis OA). The inwardly curved portion  23   b  is elastically deformable, and has a inwardly curved shape (light shielding shape) as shown in  FIG. 7  in a free state. When the inwardly curved portion  23   b  is pressed in the outer radial direction as shown in  FIG. 8 , the inwardly curved portion  23   b  elastically deforms in a direction approaching the inner surface  21   b  so as to have an approximately flattened shape (retracted shape). A metal such as stainless steel, a copper alloy, or a synthetic resin are suitable for a material having the above-mentioned elastically deformable characteristics, however, the material of the light shielding piece  23  is not limited thereto. 
         [0032]    Moreover, a dry lubrication grade material having low sliding resistance is used for the surface of the light shielding piece  23 . Furthermore, a matte black coating is applied on the surface of the light shielding piece  23  in order to reduce reflection. 
         [0033]      FIG. 7  is a sectional view showing a relative positional relationship between the guide key  21   a  and the guide groove  22   a  in a photographing state of the lens barrel, and  FIG. 8  is a sectional view showing a relative positional relationship between the guide key  21   a  and the guide groove  22   a  in a retracted (non photographing) state of the lens barrel. When the lens barrel is moved from the photographing state to the retracted state, and vice versa, the linear movement guide member  21  and the lens holding member  22  are relatively moved in a direction parallel to the optical axis OA. In the retracted state of the lens barrel shown in  FIG. 8 , the mutually overlapped area between the guide key  21   a  and the guide groove  22   a  is increased, and in the photographing state shown in  FIG. 7 , the overlapped area therebetween is decreased. 
         [0034]    In the photographing state shown in  FIG. 7 , the guide groove  22   a  is relatively moved forward (toward the object side) to the guide key  21   a  to cause the light shielding piece  23  to cover the exposed portion of the inner surface  21   b  of the guide key  21   a . At this time, the inwardly curved portion  23   b  does not contact the lens holding member  22 , and is maintained in a free state in which the inwardly curved portion  23   b  curves inwards toward the optical axis OA. In the inwardly curved state of the inwardly curved portion  23   b , light traveling toward the inner surface  21   b  of the guide key  21   a  is cut (shielded/intercepted) by the inwardly curved portion  23   b  in such a way that this unwanted light does not travel toward the image surface side, as shown by an arrowhead in  FIG. 7 . In other words, the inwardly curved portion  23   b  functions as a light shielding wall preventing internal reflection of light rays via the guide key  21   a . The inward protruding distance h (see  FIG. 7 ) of the inwardly curved portion  23   b  from the inner surface  21   b  in the above light shielding state is determined so that light rays which correctly travel through the photographing optical path are not eclipsed. Note that, since the light shielding piece  23  is ultra thin, and the inwardly curved portion  23   b  extends toward rearward inward position, substantially no light rays are reflected toward the image surface from the end surface  23   c  of the inwardly curved portion  23   b , and substantial no adverse influence on the image quality occurs. 
         [0035]    When the lens barrel is moved from the photographing state shown in  FIG. 7  to the retracted state shown in  FIG. 8 , the inwardly curved portion  23   b  presses against the bottom surface  22   b  of the guide groove  22   a , and is elastically deformed in the radial direction toward the inner surface  21   b  of the guide key  21   a  to be housed between the inner surface  21   b  of the guide key  21   a  and the bottom surface  22   b  of the guide groove  22   a . Although elastic stress occurs while the inwardly curved portion  23   b  returns to a free state thereof, a load applied to a relative movement between the guide key  21   a  and the guide groove  22   a  by the light shielding piece  23  (the inwardly curved portion  23   b ) can be suppressed down to an extremely small amount by, for example, forming the light shielding piece  23  so as to be ultra thin, providing excellent lubricating properties for the light shielding piece  23  (i.e., provided an extremity low sliding resistance therefor), and forming the inwardly curved portion  23   b  so as to have a shape which is gradually curved inward in the rearward direction. 
         [0036]    On the other hand, when the lens barrel is moved from the retracted state shown in  FIG. 8  to the photographing state shown in  FIG. 7 , the shape of the inwardly curved portion  23   b  naturally (elastically) returns to the initial inwardly curved state to achieve the above-described light shielding function because the guide groove  22   a  is moved forward relative to the guide key  21   a  in the optical axis direction to release restriction on the inwardly curved portion  23   b.    
         [0037]    According to the above-described light shielding structure of the present embodiment, the light shielding piece  23  is provided between the guide key  21   a  and the guide groove  22   a , the inwardly curved portion  23   b  of the light shielding piece  23  curves (bends) inwardly toward of the optical axis OA to shield internally reflected light via the guide key  21   a  in the photographing state in which the overlapped area between the guide key  21   a  and the guide groove  22   a  is small, and the inwardly curved portion  23   b  is elastically deformed so that the inwardly curved portion  23   b  has an approximately flat shape so that the entire light shielding piece  23  is housed in between the guide key  21   a  and the guide groove  22   a  in the retracted state in which the overlapped area between the guide key  21   a  and the guide groove  22   a  is increased. The light shielding piece  23  can be formed thinner than flock paper, and the thickness of the light shielding piece  23  can be set more accurately in comparison with antireflection coating applied by hand, since it is difficult to control the film thickness thereof. Accordingly, the light shielding piece  23  can be easily provided in a narrow space between the guide key  21   a  and the guide groove  22   a  without causing interference with the linear movement guide member  21  and the lens holding member  22 . 
         [0038]    Moreover, the inwardly curved portion  23   b  in the light shielding piece  23  is elastically deformed according to the changes in the mutually overlapping area between the guide key  21   a  and the guide groove  22   a , the inwardly curved portion  23   b  is housed in the space between the linear movement guide member  21  and the lens holding member  22  in the retracted state, and the inwardly curved portion  23   b  bends radially inwards as required, only in the photographing state which requires the light shielding function. According to this configuration, superior space efficiency can be achieved. 
         [0039]    Moreover, since the inwardly curved portion  23   b  is easily deformable, a resistance applied to the relative movement between the linear movement guide member  21  and the lens holding member  22  can be suppressed down to an extremely small amount. 
         [0040]    Furthermore, since the inwardly curved portion  23   b  of the light shielding piece  23  has a inwardly curved shape in the light shielding state, wherein the inwardly curved portion  23   b  protrudes toward the optical axis OA, unfavorable internal reflection can be reliably prevented so as to attain high light shielding performance even when light rays enter onto the inner surface  21   b  of the guide key  21   a  at a large incident angle. 
         [0041]    Moreover, since the light shielding piece  23  is configured to be attached to the guide key  21   a  after being formed separately from the linear movement guide member  21 , the productivity of the light shielding piece  23  is higher in comparison with that of an antireflection coating requiring processes for the applying and the drying thereof. The light shielding piece  23  itself has a simple shape which is easily molded. 
         [0042]    Furthermore, since the inwardly curved portion  23   b  in the light shielding piece  23  curved in a shape of an arc, stress is not concentrated on a specific location when elastically deformed so as to advantageously reduce aged deterioration thereof. 
         [0043]    The inward protruding distance h of the inwardly curved portion  23   b  of the light shielding piece  23  in a light shielding state (an inward angle with respect to the fixed portion  23   a , and a length from the fixed portion  23   a  to the end portion  23   c ) may be arbitrarily configured according to required light shielding function within a range in which the light rays which correctly travel through the photographing optical path are not eclipsed. 
         [0044]      FIG. 9  shows another embodiment according to the present invention. A light shielding piece (light shielding member)  33  shown in  FIG. 9  has a fixed portion  33   a  with a flat-plate shape attached to an inner surface  21   b  of a guide key  21   a , and a inwardly bent portion (elastically-deformable light shielding portion)  33   b  which is formed to protrude straightly from the fixed portion  33   a  at a bending portion  33   c . In other words, the inwardly bent portion  33   b  is formed in a straight line (flat plate) shape and is not curved, unlike the inwardly curved portion  23   b  of the previous embodiment. Similar to the inwardly curved portion  23   b , the inwardly bent portion  33   b  functions as a light shielding wall preventing reflection light on the inner surface  21   b  of the guide key  21   a  from reaching the image surface in a photographing state ( FIG. 9 ). Though not shown, in the retracted state, the inwardly bent portion  33   b  presses against the bottom surface  22   b  of a guide groove  22   a , and is elastically deformed in the direction approaching the inner surface  21   b  to cause a state in which the inwardly bent portion  33   b  is housed between a linear movement guide member  21  (the inner surface  21   b ) and a lens holding member  22  (the bottom surface  22   b ) in a similar manner to that of the inwardly curved portion  23   b  shown in  FIG. 8 . 
         [0045]    Although the light shielding structure according to the present invention has been described by referring to the embodiments shown in the drawings, however, the present invention is not limited thereto. Though the embodiment has been applied to a structure for preventing internal reflection in the members forming the lens barrel, a light shielding structure according to the present invention may be also applied to, for example, an optical apparatus other than a lens-barrel. 
         [0046]    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.

Technology Category: g