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.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to focal-plane shutters.

2. Description of the Related Art

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 2illustrate such a conventional focal-plane shutter.FIG. 1is a front view of the conventional focal-plane shutter, andFIG. 2is a sectional view showing an essential part of the conventional focal-plane shutter. The conventional focal-plane shutter includes a shutter base plate10x, a supporting plate20x, a partition plate30x, a thin plate40x, a leading shutter50x, a following shutter60x, and a driving mechanism70x. A printed circuit board91xis located at the back side of the focal-plane shutter. An image pickup device90xis mounted on the printed circuit board91x.

The shutter base plate10xis located at an object side. The supporting plate20xis located at an image side. A blade chamber which accommodates the leading shutter50xand the following shutter60xis defined by the shutter base plate10xand the supporting plate20x. The partition plate30xis located between the leading shutter50xand the following shutter60x. The thin plate40xis provided between the shutter base plate10xand the leading shutter50x. The thin plate40xprevents the fluttering of distal end of the leading shutter50xor the following shutter60xwhen the leading shutter50xor the following shutter60xtravels.

The leading shutter50xis connected to arm members81xand82x, and actuation of the arm members81xand82xopens and closes an opening11x. Likewise, the following shutter60xis connected to arm members83xand84x, and actuation of the arm members83xand84xopens and closes the opening11x. The driving mechanism70xdrives the arm members81xto84x.

A mirror box M is disposed at the object side of the shutter base plate10x, and represented by alternate long and short dashed lines inFIG. 2. As shown inFIG. 2, a sloping surface12xis formed at an edge of the opening11xand inclined upward from the shutter chamber to the object side.

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.

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.

However, in the conventional focal-plane shutter, as shown inFIG. 2, the shape of the edge of the opening11xat 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.

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

It is therefore an object of the present invention to provide a focal-plane shutter for improving the workability of the maintenance operation.

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.

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.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 3is a front view showing a focal-plane shutter in accordance with the present embodiment.FIG. 4is a sectional view showing a part of the focal-plane shutter in accordance with the present embodiment. Moreover,FIG. 3shows that a leading shutter is in a spread state and a following shutter is in an overlapped state.

The focal-plane shutter includes a shutter base plate10, a supporting plate20, a partition plate30, a thin plate40, a leading shutter50, a following shutter60, and a driving mechanism70.

The shutter base plate10is made of resin. The shutter base plate10has a rectangular opening11at a center thereof. As shown inFIGS. 3 and 4, a sloping surface12is formed on an edge of the opening11. The shutter base plate10is disposed at an object side.

The supporting plate20is made of a metal plate. Like the shutter base plate10, the supporting plate20has a rectangular opening21at a center thereof. The supporting plate20is disposed at an image side. A blade chamber which accommodates the leading shutter50and the following shutter60is defined by the shutter base plate10and the supporting plate20. The supporting plate20is disposed at the image side.

The partition plate30is located between the leading shutter50and the following shutter60. The partition plate30prevents the interference of the leading shutter50with the following shutter60. Likewise, the partition plate30has a rectangular opening31.

The leading shutter50is composed of three shutter blades51to53. Likewise, the following shutter60is composed of shutter blades61to63. As shown inFIG. 4, the thin plate40made of metal is located between the shutter base plate10and the leading shutter50.

The leading shutter50is connected to arm members81and82. A parallel linkage is defined by the arm members81and82. Actuation of the arm members81and82converts the overlapped state into the spread state. Specifically, proximal ends of the shutter blades61to53are connected to the arm members81and82with pins.

Like the leading shutter50, the following shutter60is connected to the arm members83and84and the following shutter60is shifted from the overlapped state to the spread state. Proximal ends of the shutter blades61to63are connected to the arm members83and84with pins.

The arm members81to64serve as a driving member causing the leading shutter50and the following shutter60to travel. The leading shutter50and the following shutter60travel between the spread state and the overlapped state, so that the opening11is opened or closed. The driving mechanism70is for driving the arm members81to84.

InFIG. 4, an image pickup device90which receives objective light and forms an image is located at a lower side of the supporting plate20. The image pickup device90is mounted on a printed circuit board91.

A mirror box M is disposed at the object side of the shutter base plate10and is indicated by alternate long and short dashed lines inFIGS. 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.

Primary action of the focal-plane shutter will be described below. As to an initial state shown in FIG.3, the leading shutter50is in the spread state in which each of edges of adjacent shutter blades among the shutter blades51to53is overlapped. The following shutter60is in the overlapped state in which the shutter blades61to63are overlapped one another and opens the opening11. A release button (not shown) is pushed, thus causing the leading shutter50to open the opening11in such a manner that the leading shutter50is the overlapped state. Additionally, the leading shutter50travels in an upper direction inFIG. 3. After the opening11begins to be opened, the following shutter60travels from the overlapped state to the spread state at a time lag corresponding to a suitable exposure time. Then, the opening11is closed. Additionally, the following shutter60travels in the upper direction inFIG. 3.

The sloping surface12will be described below. As shown inFIGS. 3 and 4, the sloping surface12is formed at an edge of one side of the opening11. The sloping surface12is declined toward the supporting plate20from an outside of the opening11to a center of the opening11. That is, the thickness of the sloping surface12begins to increase as being away from a center of the opening11. The position where the sloping surface12is provided is apart from the center of the opening11, as compared to that of the conventional art as shown inFIGS. 1 and 2. The position of an edge40a, closer to the opening11, of the thin plate40as mentioned later is the same as the position of the edge of the conventional opening as shown inFIGS. 1 and 2.

That is to say, the edge40aof the thin plate40partially defines an opening for shooting. Since the thin plate40may be formed to be thinner than the shutter base plate10made of resin, light is hardly reflected by the edge40a. This rarely causes the flare, as compared to cases where the opening for shooting is defined by only the shutter base plate10. Edges of the opening11other than the edge in which the sloping surface12is formed are formed vertically.

Such a configuration of the sloping surface12facilitates the insertion of the cleaning tool, such as a brush for cleaning, into the opening11. This improves the workability of removing the dust attached to the image pickup device90disposed at the back side of the supporting plate20. This is, even if the cleaning tool is inserted into the opening11from the object side of the sloping surface12, the sloping surface12can guide the cleaning tool to the center of the opening11with facility, because the sloping surface12is inclined downward. This arrangement improves the workability of the maintenance operation.

Even if the sloping surface12is not provided, the enlargement of the opening11may improve the workability of the maintenance operation. However, the enlarged opening11may lead to an increased size of the focal-plane shutter. Therefore, the provision of the sloping surface12prevents the upsizing of the focal-plane shutter and improves the workability of the maintenance.

Furthermore, the sloping surface12has a function for preventing a secondary light reflected by the mirror box M from reaching the image pickup device90. This will be described below with reference toFIG. 6. The same portions as inFIG. 4are 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 surface12Y may be formed at the edge of the opening11of the shutter base plate10disposed at the object side, as shown inFIG. 4. However, if the sloping surface12Y is formed at the edge of the opening of the shutter base plate10disposed at the object side, a partial reflected light by the mirror box M may be further reflected by the sloping surface12Y and entered to the image pickup device. This is undesirable because of the cause of the flare.

Consequently, as shown inFIG. 4, the sloping surface12is 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 surface12at a smaller incident angle. For this reason, the reflection angle of the light reflected by the sloping surface12becomes smaller, so that the reflected light hardly directs toward the image pickup device90. Therefore, the focal-plane shutter is configured such that the cleaning tool is guided to the opening11and the flare is prevented.

The thin plate40will be described below. The thin plate40is mounted on the image side of the shutter base plate10. The thin plate40is located between the shutter base plate10and distal end of the leading shutter50. As shown inFIG. 3, the thin plate40extends in such a direction in which the leading shutter50and the following shutter60travel. Further, a distance between the edge40aof the thin plate40and the center of the opening11is shorter than that between the sloping surface12, which defines one side of the opening for shooting, and the center of the opening11. Namely, the thin plate40broadly covers the distal end of the leading shutter50. With such a configuration, the thin plate40prevents deflection of the leading shutter50and the flattering of the distal end of the leading shutter50in conjunction with the traveling of the leading shutter50.

FIG. 5is an enlarged view showing an end of the thin plate40. The edge, close to the opening, of the thin plate40is disposed to be exposed through the opening11. That is, as shown inFIG. 2, the thin plate40is disposed to project toward the center of the opening relative to the edges of the openings11,21and31. The thin plate40thus arranged functions to define an optical path for shooting.

With such a configuration, as shown inFIG. 5, the space as large as the region S is obtained, as compared to the conventional art as shown inFIGS. 1 and 2, thus facilitating the insertion of the cleaning tool for the space. Consequently, the thin plate40has multiple functions, thereby preventing the number of parts from increasing.

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.

In the above embodiment, the sloping surface12is formed at the edge of one side of the opening11. Multiple sloping surfaces12may be formed at multiple sides of the opening11, respectively. In the above embodiment, the shutter base plate10is disposed at the object side and the supporting plate20is disposed at the image side. The positional relationship of the shutter base plate19and the supporting plate20may be reversed so that the shutter base plate10is disposed at the image side and the supporting plate20is disposed at the object side. The supporting plate20may be made of resin.

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.