Abstract:
A focal-plane shutter has a first plate having a first opening, a second plate having a second opening, a shutter blade disposed between the first plate and the second plate, for opening and closing the first opening and the second opening, and a thin plate disposed at a side of the first plate facing the shutter blade and extending in such a direction that the shutter blade travel. A distance between an edge of the first opening and a center of the first opening is greater than that between an edge of the thin plate and the center of the first opening.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to focal-plane shutters. 
         [0003]    2. Description of the Related Art 
         [0004]    Conventionally, referring to Japanese Patent No. 3224786, there has been known a focal-plane shutter as employed in a single-lens reflex camera.  FIGS. 1 and 2  illustrate such a conventional focal-plane shutter.  FIG. 1  is a front view of the conventional focal-plane shutter, and  FIG. 2  is a sectional view showing an essential part of the conventional focal-plane shutter. The conventional focal-plane shutter includes a shutter base plate  10   x , a supporting plate  20   x , a partition plate  30   x , a thin plate  40   x , a leading shutter  50   x , a following shutter  60   x , and a driving mechanism  70   x . A printed circuit board  91   x  is located at the back side of the focal-plane shutter. An image pickup device  90   x  is mounted on the printed circuit board  91   x.    
         [0005]    The shutter base plate  10   x  is located at an object side. The supporting plate  20   x  is located at an image side. A blade chamber which accommodates the leading shutter  50   x  and the following shutter  60   x  is defined by the shutter base plate  10   x  and the supporting plate  20   x . The partition plate  30   x  is located between the leading shutter  50   x  and the following shutter  60   x . The thin plate  40   x  is provided between the shutter base plate  10   x  and the leading shutter  50   x . The thin plate  40   x  prevents the fluttering of distal end of the leading shutter  50   x  or the following shutter  60   x  when the leading shutter  50   x  or the following shutter  60   x  travels. 
         [0006]    The leading shutter  50   x  is connected to arm members  81   x  and  82   x , and actuation of the arm members  81   x  and  82   x  opens and closes an opening  11   x . Likewise, the following shutter  60   x  is connected to arm members  83   x  and  84   x , and actuation of the arm members  83   x  and  84   x  opens and closes the opening  11   x . The driving mechanism  70   x  drives the arm members  81   x  to  84   x.    
         [0007]    A mirror box M is disposed at the object side of the shutter base plate  10   x , and represented by alternate long and short dashed lines in  FIG. 2 . As shown in  FIG. 2 , a sloping surface  12   x  is formed at an edge of the opening  11   x  and inclined upward from the shutter chamber to the object side. 
         [0008]    Incidentally, the focal-plane shutter is also employed in a recent digital camera. As a high pixel density of the digital camera, even if a little dust attaches to the image pickup device, image quality may be adversely affected. 
         [0009]    Therefore, periodical maintenance is required for this camera. For example, brush for sweeping or the like is inserted into the opening of the shutter base plate from the object side, and removing the dust attached to the image pickup device is needed. 
         [0010]    However, in the conventional focal-plane shutter, as shown in  FIG. 2 , the shape of the edge of the opening  11   x  at the object side is not supposed for the insertion of such the cleaning tool. Additionally, in the cases where the shutter base plate or proximity of the opening is made of resin, it is difficult to manufacture the proximity of the opening to be thin. This does not allow the proximity of the opening to be thin, thus reducing a space for insertion of the cleaning tool and making the insertion of the cleaning tool difficult. 
         [0011]    Hence, periodical maintenance is required for maintaining the image quality. Thus, it is preferable that the maintenance operation should be performed with ease. 
       SUMMARY OF THE INVENTION 
       [0012]    It is therefore an object of the present invention to provide a focal-plane shutter for improving the workability of the maintenance operation. 
         [0013]    According to an aspect of the present invention, there is provided a focal-plane shutter having a first plate having a first opening, a second plate having a second opening, a shutter blade disposed between the first plate and the second plate, for opening and closing the first opening and the second opening, and a thin plate disposed at a side of the first plate facing the shutter blade and extending in such a direction that the shutter blade travels, a distance between an edge of the first opening and a center of the first opening being greater than that between an edge of the thin plate and the center of the first opening. 
         [0014]    In the above configuration, the space is obtained in the side of the first plate, thus facilitating the insertion of the cleaning tool at the time of the maintenance operation. This improves the workability of the maintenance operation. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  illustrates a conventional focal-plane shutter. 
           [0016]      FIG. 2  illustrates the conventional focal-plane shutter. 
           [0017]      FIG. 3  is a front view showing a focal-plane shutter in accordance with the present embodiment. 
           [0018]      FIG. 4  is a sectional view showing an essential part of the focal-plane shutter in accordance with the present embodiment. 
           [0019]      FIG. 5  is an enlarged view showing an end of the thin plate. 
           [0020]      FIG. 6  illustrates a circumference of a sloping surface. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0021]    An embodiment of the present invention will be described below with reference to the accompanying drawings. 
         [0022]      FIG. 3  is a front view showing a focal-plane shutter in accordance with the present embodiment.  FIG. 4  is a sectional view showing a part of the focal-plane shutter in accordance with the present embodiment. Moreover,  FIG. 3  shows that a leading shutter is in a spread state and a following shutter is in an overlapped state. 
         [0023]    The focal-plane shutter includes a shutter base plate  10 , a supporting plate  20 , a partition plate  30 , a thin plate  40 , a leading shutter  50 , a following shutter  60 , and a driving mechanism  70 . 
         [0024]    The shutter base plate  10  is made of resin. The shutter base plate  10  has a rectangular opening  11  at a center thereof. As shown in  FIGS. 3 and 4 , a sloping surface  12  is formed on an edge of the opening  11 . The shutter base plate  10  is disposed at an object side. 
         [0025]    The supporting plate  20  is made of a metal plate. Like the shutter base plate  10 , the supporting plate  20  has a rectangular opening  21  at a center thereof. The supporting plate  20  is disposed at an image side. A blade chamber which accommodates the leading shutter  50  and the following shutter  60  is defined by the shutter base plate  10  and the supporting plate  20 . The supporting plate  20  is disposed at the image side. 
         [0026]    The partition plate  30  is located between the leading shutter  50  and the following shutter  60 . The partition plate  30  prevents the interference of the leading shutter  50  with the following shutter  60 . Likewise, the partition plate  30  has a rectangular opening  31 . 
         [0027]    The leading shutter  50  is composed of three shutter blades  51  to  53 . Likewise, the following shutter  60  is composed of shutter blades  61  to  63 . As shown in  FIG. 4 , the thin plate  40  made of metal is located between the shutter base plate  10  and the leading shutter  50 . 
         [0028]    The leading shutter  50  is connected to arm members  81  and  82 . A parallel linkage is defined by the arm members  81  and  82 . Actuation of the arm members  81  and  82  converts the overlapped state into the spread state. Specifically, proximal ends of the shutter blades  61  to  53  are connected to the arm members  81  and  82  with pins. 
         [0029]    Like the leading shutter  50 , the following shutter  60  is connected to the arm members  83  and  84  and the following shutter  60  is shifted from the overlapped state to the spread state. Proximal ends of the shutter blades  61  to  63  are connected to the arm members  83  and  84  with pins. 
         [0030]    The arm members  81  to  64  serve as a driving member causing the leading shutter  50  and the following shutter  60  to travel. The leading shutter  50  and the following shutter  60  travel between the spread state and the overlapped state, so that the opening  11  is opened or closed. The driving mechanism  70  is for driving the arm members  81  to  84 . 
         [0031]    In  FIG. 4 , an image pickup device  90  which receives objective light and forms an image is located at a lower side of the supporting plate  20 . The image pickup device  90  is mounted on a printed circuit board  91 . 
         [0032]    A mirror box M is disposed at the object side of the shutter base plate  10  and is indicated by alternate long and short dashed lines in  FIGS. 3 and 4 . In a typical state, the mirror box M guides the objective light to eyepiece viewed by the user. In a shoot state, the mirror box M drives a mirror, not shown, for guiding the objective light to the image pickup device. 
         [0033]    Primary action of the focal-plane shutter will be described below. As to an initial state shown in FIG.  3 , the leading shutter  50  is in the spread state in which each of edges of adjacent shutter blades among the shutter blades  51  to  53  is overlapped. The following shutter  60  is in the overlapped state in which the shutter blades  61  to  63  are overlapped one another and opens the opening  11 . A release button (not shown) is pushed, thus causing the leading shutter  50  to open the opening  11  in such a manner that the leading shutter  50  is the overlapped state. Additionally, the leading shutter  50  travels in an upper direction in  FIG. 3 . After the opening  11  begins to be opened, the following shutter  60  travels from the overlapped state to the spread state at a time lag corresponding to a suitable exposure time. Then, the opening  11  is closed. Additionally, the following shutter  60  travels in the upper direction in  FIG. 3 . 
         [0034]    The sloping surface  12  will be described below. As shown in  FIGS. 3 and 4 , the sloping surface  12  is formed at an edge of one side of the opening  11 . The sloping surface  12  is declined toward the supporting plate  20  from an outside of the opening  11  to a center of the opening  11 . That is, the thickness of the sloping surface  12  begins to increase as being away from a center of the opening  11 . The position where the sloping surface  12  is provided is apart from the center of the opening  11 , as compared to that of the conventional art as shown in  FIGS. 1 and 2 . The position of an edge  40   a , closer to the opening  11 , of the thin plate  40  as mentioned later is the same as the position of the edge of the conventional opening as shown in  FIGS. 1 and 2 . 
         [0035]    That is to say, the edge  40   a  of the thin plate  40  partially defines an opening for shooting. Since the thin plate  40  may be formed to be thinner than the shutter base plate  10  made of resin, light is hardly reflected by the edge  40   a . This rarely causes the flare, as compared to cases where the opening for shooting is defined by only the shutter base plate  10 . Edges of the opening  11  other than the edge in which the sloping surface  12  is formed are formed vertically. 
         [0036]    Such a configuration of the sloping surface  12  facilitates the insertion of the cleaning tool, such as a brush for cleaning, into the opening  11 . This improves the workability of removing the dust attached to the image pickup device  90  disposed at the back side of the supporting plate  20 . This is, even if the cleaning tool is inserted into the opening  11  from the object side of the sloping surface  12 , the sloping surface  12  can guide the cleaning tool to the center of the opening  11  with facility, because the sloping surface  12  is inclined downward. This arrangement improves the workability of the maintenance operation. 
         [0037]    Even if the sloping surface  12  is not provided, the enlargement of the opening  11  may improve the workability of the maintenance operation. However, the enlarged opening  11  may lead to an increased size of the focal-plane shutter. Therefore, the provision of the sloping surface  12  prevents the upsizing of the focal-plane shutter and improves the workability of the maintenance. 
         [0038]    Furthermore, the sloping surface  12  has a function for preventing a secondary light reflected by the mirror box M from reaching the image pickup device  90 . This will be described below with reference to  FIG. 6 . The same portions as in  FIG. 4  are given the same reference numerals and a description thereof will be omitted. If it is attempted to merely facilitate the insertion of the cleaning tool, a sloping surface  12 Y may be formed at the edge of the opening  11  of the shutter base plate  10  disposed at the object side, as shown in  FIG. 4 . However, if the sloping surface  12 Y is formed at the edge of the opening of the shutter base plate  10  disposed at the object side, a partial reflected light by the mirror box M may be further reflected by the sloping surface  12 Y and entered to the image pickup device. This is undesirable because of the cause of the flare. 
         [0039]    Consequently, as shown in  FIG. 4 , the sloping surface  12  is extended to an outside of the mirror box M. with such a configuration, the reflected light by the mirror box M is incident to the sloping surface  12  at a smaller incident angle. For this reason, the reflection angle of the light reflected by the sloping surface  12  becomes smaller, so that the reflected light hardly directs toward the image pickup device  90 . Therefore, the focal-plane shutter is configured such that the cleaning tool is guided to the opening  11  and the flare is prevented. 
         [0040]    The thin plate  40  will be described below. The thin plate  40  is mounted on the image side of the shutter base plate  10 . The thin plate  40  is located between the shutter base plate  10  and distal end of the leading shutter  50 . As shown in  FIG. 3 , the thin plate  40  extends in such a direction in which the leading shutter  50  and the following shutter  60  travel. Further, a distance between the edge  40   a  of the thin plate  40  and the center of the opening  11  is shorter than that between the sloping surface  12 , which defines one side of the opening for shooting, and the center of the opening  11 . Namely, the thin plate  40  broadly covers the distal end of the leading shutter  50 . With such a configuration, the thin plate  40  prevents deflection of the leading shutter  50  and the flattering of the distal end of the leading shutter  50  in conjunction with the traveling of the leading shutter  50 . 
         [0041]      FIG. 5  is an enlarged view showing an end of the thin plate  40 . The edge, close to the opening, of the thin plate  40  is disposed to be exposed through the opening  11 . That is, as shown in  FIG. 2 , the thin plate  40  is disposed to project toward the center of the opening relative to the edges of the openings  11 ,  21  and  31 . The thin plate  40  thus arranged functions to define an optical path for shooting. 
         [0042]    With such a configuration, as shown in  FIG. 5 , the space as large as the region S is obtained, as compared to the conventional art as shown in  FIGS. 1 and 2 , thus facilitating the insertion of the cleaning tool for the space. Consequently, the thin plate  40  has multiple functions, thereby preventing the number of parts from increasing. 
         [0043]    While the preferred embodiments of the present invention have been illustrated in detail, the present invention is not limited to the above-mentioned embodiments, and other embodiments, variations and modifications may be made without departing from the scope of the present invention. 
         [0044]    In the above embodiment, the sloping surface  12  is formed at the edge of one side of the opening  11 . Multiple sloping surfaces  12  may be formed at multiple sides of the opening  11 , respectively. In the above embodiment, the shutter base plate  10  is disposed at the object side and the supporting plate  20  is disposed at the image side. The positional relationship of the shutter base plate  19  and the supporting plate  20  may be reversed so that the shutter base plate  10  is disposed at the image side and the supporting plate  20  is disposed at the object side. The supporting plate  20  may be made of resin. 
         [0045]    The present application is based on Japanese Patent Application No. 2007-082060 filed Mar. 27, 2007, the entire disclosure of which is hereby incorporated by reference.