Light quantity control device

A light quantity control device includes: a bottom board having an opening; a first blade, a supporting blade, and a second blade linearly moved in opposing directions and controlling the opening to a fully open state, a fully closed state, and a small aperture state; a driving lever connected to the set of blades and driving the set of blades by rotation of the driving lever; and a stopper restricting a rotational range of the driving lever. The set of blades controls the opening to the small aperture state when the driving lever is positioned at one end of the rotational range defined by the stopper.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a light quantity control device for a camera.

2. Description of the Related Art

Conventionally, there has been known a light quantity control device for a camera. In the conventional light quantity control device, at lease two blades are movably supported in opposing directions in a linear manner relative to a bottom board having an opening, a rotational movement of a driving lever connected to these blades is changed to a liner movement, and the liner movement is outputted to the blades, thereby controlling the light quantity passing through the opening (see Japanese Patent Application Publication No. 5-241224).

However, in the conventional light quantity control device, the state of the opening is shifted to a fully open state, and a small aperture state, and a fully closed state in response to the movements of the driving lever. Since the small aperture state is defined when the driving lever is positioned at a partway position of a rotational range of the driving lever, it is difficult to stop the driving lever at an accurate position and maintain the small aperture state. Therefore, it is difficult to assure an accuracy of an opening degree in the small aperture state.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a light quantity control device assuring the accuracy of the opening degree in a small aperture state.

According to an aspect of the present invention, there is provided a light quantity control device characterized by comprising: a bottom board having an opening; a set of blades linearly moved in opposing directions and controlling the opening to a fully open state, a fully closed state, and a small aperture state; a driving lever connected to the set of blades and driving the set of blades by rotation of the driving lever; and a stopper restricting a rotational range of the driving lever, wherein the set of blades controls the opening to the small aperture state when the driving lever is positioned at one end of the rotational range defined by the stopper.

With such a configuration, when the driving lever is positioned at an end of the rotational range defined by the stopper, the set of blades brings the opening to the small aperture state, whereby the opened degree of the opening can be constant in the small aperture state. That is to say, in a light quantity control device that controls the quantity of the light passing through the opening by linearly moving at least two blades relative to the bottom board in the opposing directions, even if the rotational ranges of the misalignment of the driving lever are substantially identical, each blade is greatly misaligned in the moving direction based on the position of the driving lever. The misalignment degree of each blade in the moving direction of each blade is smaller and the opening can be brought to the small aperture state with certainty in cases where the opening is brought to the small aperture state when the driving lever is positioned at one end of the rotational range of the driving lever rather than cases where the opening is brought to the small aperture state when the driving lever is positioned at the partway of the rotational range of the driving lever. Therefore, the small aperture state is maintained.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A description will now be given, with reference to the accompanying drawings, an embodiment of the present invention.

A light quantity control device according to an embodiment of the present invention will be described below with reference to drawings.

FIG. 1is an exploded perspective view of the light quantity control device when viewed from the top.FIG. 2is an exploded perspective view of the light quantity control device when viewed from the bottom.

A light quantity control device1includes: a blade-supporting plate10; a first blade20; a supporting blade30; a plate40; a second blade50; a bottom board60; a driving lever70; and a motor portion80.

The first blade20, the supporting blade30, and the second blade50control a light quantity passing through an opening61formed in the bottom board60by using the movements thereof.

The blade-supporting plate10holds the blades and the like located between the blade-supporting plate10and the bottom board60in an optical axis direction so as to restrict movements of the blades and the like in the optical axis direction.

Additionally, the blade-supporting plate10has an opening11for causing light to reach an image pickup device (not shown).

Further, the blade-supporting plate10has a receiving slot13and a receiving hole12. The receiving slot13is located to face the opening11and has an arc shape so as to receive a first pin71of the of the driving lever70. The receiving hole12for a second pin72of the driving lever70has a semicircular shape.

An opening21, for changing the opening area of the opening61, is formed in the first blade20and shaped in such a manner to spread in the entirety of the middle portion of the first blade20. Additionally, the opening21also serves as a receiving hole for receiving the second pin72formed on the driving lever70.

The first blade20is formed with a slot22, which is engaged with the first pin71formed in the driving lever70, in a widthwise direction of the first blade20. The slot22is a cam having an substantially L-shape bending in the partway thereof.

Further, the first blade20is formed with the guide slot24which is engaged with a guide pin64formed on the bottom board60and which extends in a lengthwise direction of the first blade20.

The supporting blade30has an opening31for changing the opening area of the opening61.

A slot32is engaged with the first pin71and linearly extends in the widthwise direction of the supporting blade30. Herein, the first blade20and the supporting blade30are engaged with the first pin71standing on the driving lever70. Further, the supporting blade30overlaps the first blade20, and closes the opening61in conjunction with the first blade20and the second blade50.

The supporting blade30has a receiving hole33for receiving the movement of the second pin72and the receiving hole33has an arc shape.

Further, the supporting blade30has a guide slot34engaged with the guide pin64and the guide slot34extends in the lengthwise direction of the supporting blade30. In response to the moving distance of the supporting blade30, the guide slot34is shorter than the guide slot24formed in the first blade20.

The plate40is accommodated to be sandwiched between the supporting blade30and the second blade50.

Furthermore, the plate40has an opening41for passing through the light to reach the image pickup device.

In addition, the plate40has a receiving hole42for receiving the second pin72and the receiving hole42has an arc shape. The plate40has a receiving hole43for receiving the first pin71and the receiving hole43has a semicircular shape.

The plate40has an engagement hole44fitted onto the guide pin64, whereby the plate40is fixed and is not movable with respect to the bottom board60.

The second blade50has a notch section at its edge and forms a cutout51. The second blade50has a slot52engaged with the second pin72, and the slot52extends in a widthwise direction of the second blade50. The slot52has an substantially L-shape that bents at a partway thereof and also serves as a cam.

The second blade50has a guide slot54engaged with the guide pin64and the guide slot54extends in the moving direction of the second blade50.

The bottom board60has the opening61, and a receiving hole62for receiving the driving lever70. Further, the guide pin64, which is engaged with the guide slots54,34, and24, and which is fitted into the engagement hole44, is formed at the proximity of the opening61. Additionally, guide walls65are partially formed at ends of the bottom board60. The guide pin64and the guide walls65linearly guide the first blade20, the supporting blade30, and the second blade50in the lengthwise direction of the bottom board60.

The driving lever70rotates about the center thereof within a predetermined angular range. The driving lever70has the first pin71and the second pin72at both ends thereof, respectively, and the first pin71and the second pin72protrude to the blades. Additionally, the driving lever70is capable of being stopped in at least of one partway position between one end and the other end of its rotational range. That is to say, the rotation of the driving lever70drives the first blade20, the supporting blade30and the second blade50, so that the light quantity passing through the opening61of the bottom board60is controlled when the driving lever70is stopped at one end, the other end or the partway position.

The motor portion80causes a rotational shaft to be connected to the central position of the driving lever70, and drives the driving lever70.

The following will describe an actions of the blades.

FIGS. 3A to 3Cshow the action states of the blades,FIG. 3Ashows the fully open state,FIG. 3Bshows the fully closed state, andFIG. 3Cshows the small aperture state. Additionally, inFIGS. 3A to 3C, the blade-supporting plate10, the plate40, and the receiving hole62of the bottom board60are omitted. Further, shapes of the first blade20and the supporting blade30are simplify illustrated.

The following will describe the fully open state in reference withFIG. 3A.

The fully open state is maintained in such a manner that the opening61is surrounded by the opening21formed in the first blade20, the opening31formed in the supporting blade30and the cutout51formed in the second blade50.

The driving lever70is positioned to be substantially parallel with a widthwise direction of the light quantity control device1.

The following will describe actions from the fully open state to the fully closed state.

As shown inFIG. 3A, the driving lever70rotates counterclockwise from the fully open state in which the driving lever70is positioned at the other end of the rotational range, so that the first blade20and the supporting blade30are linearly moved in the right hand direction and the second blade50is linearly moved in the left hand direction. That is to say, the first blade20and the supporting blade30, and the second blade50are linearly moved in the opposing directions. The state of the opening61is controlled to be in the fully closed state in which the driving lever70is positioned in the partway of the rotational range thereof. At this time, the fully closed state is maintained in such a manner that the opening61is closed by the first blade20, the supporting blade30, and the second blade50.

The following will describe actions from the fully closed state to the small aperture state.

As shown inFIG. 3B, the driving lever70further rotates counterclockwise from the fully closed state in which the driving lever70is positioned at the partway of the rotational range, so that the first blade20and the supporting blade30are linearly moved in the left hand direction and the second blade50is linearly moved in the right hand direction. As shown inFIG. 3C, the state of the opening61is controlled to the small aperture state in which the driving lever70is positioned in one end of the rotational range. The small aperture state is maintained in such a manner that the opening61is defined by profile of the opening21and that of the cutout51.

As mentioned above, by the rotation of the driving lever70, the state of the opening61is controlled to the fully closed state from the fully open state, and to the small aperture state from the fully closed state.

The following will describe the position of the driving lever70in detail when the fully closed state is defined.FIGS. 4A to 4Care explanatory views of the position of the driving lever70in the fully closed state.

FIG. 4Ashows the driving lever70at the time when the opening61is controlled to the fully closed state, and a phantom line A passing through the rotational center P of the driving lever70and being parallel in the moving direction of the blades. Moreover, each of α1and α3denote an angular range from the phantom line A to 45 degrees in the clockwise direction with the rotational center P set as a center. Each of α2and α4denote an angular range from the phantom line A to 45 degrees in the counterclockwise direction with the rotational center P set as a center. Additionally, each of β1and β2denote the remaining angular range other than the above angular ranges.

In the fully closed state, the first pin71is positioned within the angular range α3, and the second pin72is positioned within the angular range α1. That is to say, in the fully closed state, the driving lever70is positioned within the angular ranges of 45 degrees in the clockwise direction from the phantom line A.

The following will describe an effect caused by positioning the driving lever70in the position as mentioned above when the opening61is shifted to the fully closed state.

FIG. 4Bshows the driving lever70slightly misaligned counterclockwise from the fully closed state shown inFIG. 4A.FIG. 4Cshows the driving lever70positioned within the rotational range β1, and β2, and slightly misaligned counterclockwise. In addition, the misaligned angles of the driving lever70shown inFIGS. 4B and 4Care substantially identical.

As shown inFIG. 4B, when the driving lever70is slightly misaligned, the center of the second pin72is misaligned by D1in the moving direction of the blades.

On the other hand, as shown inFIG. 4C, when the driving lever70is slightly misaligned, the center of the second pin72is misaligned by D2in the moving direction of the blades.

When D1is compared with D2, the rotational angles caused by misalignment of the driving lever70are substantially identical, however, the misalignment degrees of the blade in the moving directions are greatly different. D1is smaller than D2. Additionally, D1and D2directly indicate the degrees of the misalignment in the moving direction of the blades. That is, even if the rotational range of the misalignment of the driving lever70are substantially identical, each blade is greatly misaligned in the moving direction based on the position of the driving lever70.

As stated heretofore, the driving lever70is positioned within 45 degrees with respect to the phantom line A in the clockwise direction, when the first blade20, the supporting blade30and the second blade50control the state of the opening61to the fully closed state. Therefore, even if when the driving lever70is slightly misaligned from the fully closed state, a displacement of each blade is not greatly affected. Consequently, even if the positional accuracy is roughly set, the fully closed state can be maintained with certainty.

Additionally, even if the second pin72is positioned within α2and the first pin71is positioned within α4at the time when the state of the opening61is controlled to be in the fully closed state, that is to say, even if the driving lever70is positioned within 45 degrees with respect to the phantom line A in the counterclockwise direction, the above effect can be attained. Consequently, by setting the driving lever70to be positioned within 90 degrees with the phantom line A set as a center, the above effect is attained.

Further, by setting the driving lever70to be positioned within the above range at a time when the state of the opening61is in the fully open state or the small aperture state as well as the fully closed state, the above effect is attained.

As well as setting the driving lever70to be positioned within 90 degrees, it may be positioned within 80 or 70 degrees with the phantom line A set as a center. Additionally, the driving lever70may be set to be substantially parallel with the phantom line A.

The following will describe the slots formed on the blades.

FIGS. 5A to 5Care explanatory views of the slots formed on the blades.

In the first blade20, the slot22is formed apart from the opening21and is formed in a region more than a half of the first blade20in a widthwise direction. The slot22is a cam having a shape of a substantially L-shape that bends at the partway, namely, a bending portion22a. In the slot22, the bending portion22ais closer to the opening21.

In the second blade50, the slot52is formed apart from the cutout51and is formed in a region more than a half of the second blade50in a widthwise direction. The slot52is a cam having a shape of a substantially L-shape that bends at the partway, namely, a bending portion52a. In the slot52, the bending portion52ais closer to an opposing side of the cutout51.

In the supporting blade30, the slot32is formed in the proximity of the receiving hole33. The slot32is formed in a region that occupies more than a half of the supporting blade30in a widthwise direction, and is also formed linearly to slightly tilt in the widthwise direction.

Such slots are formed in the widthwise direction of blades. Therefore, the driving lever70can be positioned within 90 degrees with the phantom line A set as a center.

The following will describe relationships between the shape of the slot and the moving distance of the blade.

FIGS. 6A to 6Care explanatory views of the difference in moving distances of the blades due to a difference in shapes of the slots.

FIG. 6Ashows a change in the position of the slot52in response to the rotation of the second pin72. Additionally, for clearly showing the positions of the second pin72and the slot52in each state, inFIGS. 6A and 6B, the positions of the second pin72and the slot52in the fully open position, the fully closed position, and the small aperture position are indicated by (a), (b), and (c) respectively. Further, the second pin72rotates about the rotational center P within a predetermined range.

In the fully open state (a), the second pin72is positioned at one end of the slot52. At this time, the slot52is positioned in the slightly right side of the rotational center P.

The second pin72rotates counterclockwise from the fully open state (a), so that the second pin72is positioned at the fully closed position (b) in which the second pin72comes closer to the bending portion52aof the slot52. At this time, the slot52is positioned substantially in the left side of the rotational center P (e.g., opening61side). L1indicates the moving distance of the slot52from the fully open position (a) to the fully closed position (b).

Next, the second pin72further rotates counterclockwise from the fully closed position (b) to the small aperture position (c), and is positioned at the other end of the slot52. The slot52is positioned again in the right side (that is, in such a direction as to move away from the opening61) when the second pin72is positioned at the small aperture position (c) form the fully closed position (b).

As mentioned above, when the driving lever70lies within the above 90 degrees, the bending portion52aof the slot52is closer to the rotational center P of the driving lever70. Specifically, the slot52is shaped to protrude relative to a rotational trace of the second pin72.

The following will describe the slot52shaped in a liner shape perpendicular to a moving direction the blade.

FIG. 6Bshows a change in the position of the slot in response to the rotation of the second pin72, if the slot is formed to be vertical with the moving direction of the blades. Additionally, a slot52gdenotes the slot to be linearly shaped. Further,FIG. 6Bshows the slots52g(a),52g(b), and52g(c) corresponding to the above mentioned slots52(a),52(b), and52(c), respectively.

L2indicates the moving distance of the slot52gfrom the position (a) to the position (b).

When the moving distance L1shown inFIG. 6Ais compared with the moving distance L2shown inFIG. 6B, the moving distance L1is longer than the moving distance L2.

FIG. 6Cshows the shape of the slot52. As shown inFIG. 6C, when Δm denotes a distance from the bending portion52ato the end of the slot52in the moving direction, the second blade50greatly moves in the left hand direction by Δm.

As mentioned above, since the slot52is formed such that the bending portion52ais located closer to the rotational center P, when the driving lever70lies in the above range of 90 degrees, the moving distance of the second blade50moved by the rotation of the driving lever70can be increased.

Additionally, likewise, the slot22formed in the first blade20has the similar function of the slot52. This greatly increases the relative moving distances of the first blade20and the second blade50. By greatly increasing the relative moving distances of the first blade20and the second blade50, even if the opening61has a lager size than that of each blade or that of the bottom board60, the state of the opening61can be controlled from the fully open state to the fully closed state. Further, the blades or the bottom board60can be made smaller with the size of the opening61assured. This downsizes the whole light quantity control device.

Additionally, the plate40is sandwiched between the supporting blade30and the second blade50. The moving distance of the supporting blade30is smaller than that of the first blade20, but the supporting blade30moves in the same direction of the first blade20. The plate40has an ability of buffering the movements of the second blade50and the supporting blade30that moves in the opposing direction of the second blade50. This smoothes the movements of the blades, and prevents abrasion thereof.

The following will describe the relationship between the first blade20and the supporting blade30.

FIGS. 7A and 7Bare explanatory views showing the degree of overlapping of the first blade20and the supporting blade30.

FIG. 7Ais an enlarged view of the periphery of the opening61in the fully open state.FIG. 7Bis an enlarged view of the periphery of the opening61in the fully closed state.

As shown inFIG. 7A, the first blade20and the supporting blade30are held by the bottom board60with the opening61opened. Additionally, the first blade20and the supporting blade30are held such that a predetermined region of the first blade20and that of the second blade30, covering the opening61when the fully closed state is defined, are held within a space S. The space S indicates a distance from the left edge of the opening61to the left end of the bottom board60.

L indicates a distance in which the first blade20and the supporting blade30are overlapped with each other.

When shifted to the fully closed state, as shown inFIG. 7B, the first blade20and the supporting blade30covers the opening61such a way to reduce the degree of overlapping of the first blade20and the supporting blade30. When ΔL denotes a misalignment degree of overlapping of the first blade20and the supporting blade30, a distance of an area, in which the opening61is covered with the first blade20and the supporting blade30, can be expressed by L+ΔL.

As mentioned heretofore, the first blade20and the supporting blade30are overlapped with each other so as to bring the opening61to the fully open state. Next, the degree of overlapping of the first blade20and the supporting blade30is reduced, as if the first blade20and the supporting blade30extended, then the first blade20, the supporting blade30, and the second blade50bring the opening61to the fully closed state. Therefore, the space in which the first blade20and the supporting blade30are held can be reduced. This also downsizes the light quantity control device.

The following will describe the misalignment degree of the first blade20and the supporting blade30based on the shape differences of the first blade20and the supporting blade30.

FIG. 8is an explanatory view of the misalignment degree of the first blade20and the supporting blade30based on the shape differences between the first blade20and the supporting blade30. Additionally, to clearly show positions of the first pin71and the slot32in each state,32(a) and32(b) respectively denote the slot32in the fully open position and the fully closed position. Likewise,71(a) and71(b) respectively denote the first pin71in the fully open position and the fully closed position. Also, how the slot32and the first pin71are changed is shown on the basis of the slot22.

As shown inFIG. 8, the slot32is positioned on the right side of the slot22in the fully open position (a) of the first pin71. Additionally, the first pin71is positioned at the lower ends of the slots22and32.

The first pin71rotates counterclockwise from the fully open position (a), and is positioned in the fully closed position (b) near the bending portion22aof the slot22. The position of the slot32with the first pin71positioned in the fully closed position (b) is misaligned and shifted to the left side from the position of the slot32with the first pin71positioned in the fully open position (a). The misalignment degree at this time is represented by ΔL. This misalignment shown inFIGS. 7A and 7Bcaused by moving the first blade20and the supporting blade30, because the slot22and the slot32are differ in the shape from each other. With such a configuration, the overlapping degree of the first blade20and the supporting blade30can be changed between the time when the opening61is brought to the fully closed state and the time when the opening61is brought to the fully open state.

The following will describe the position of the driving lever70defining the small aperture state.

FIG. 9is an explanatory view of a position of the driving lever defining the small aperture state.

FIG. 9shows the receiving hole62formed in the bottom board60and the driving lever70when the small aperture state is defined.

The receiving hole62is shaped into a substantially circular shape, and is formed with stopper portions63such that an inner profile of the receiving hole62are partially curved to project to a center thereof. The stopper portions63are located at respective two positions in a symmetric manner with respect to the center of the receiving hole62.

When the small aperture state is defined, the driving lever70is restricted to rotate counterclockwise by abutting the first pin71and the second pin72with the stopper portions63.

Therefore, when the driving lever70is positioned at an end of the rotational range defined by the stopper portions63, each blade brings the opening61to the small aperture state, whereby the opened degree can be constant in the small aperture state. Consequently, the small aperture state is defined with high accuracy.

Further, the stopper portions63are integrally formed with the bottom board60. With such a configuration, the rotational range of the driving lever70can be restricted by a simple structure.

Additionally, the first blade20, the supporting blade30, and the second blade50bring the opening61to the fully open state when the driving lever70is positioned at the other end of the rotational range thereof, and bring the opening61to the fully closed state when the driving lever70is positioned at a partway of the rotational range thereof. This configuration maintains the fully open state, the fully closed state, and the small aperture state in the opening61.

Further, the first blade20, the supporting blade30and the second blade50are configured such that the moving directions thereof while the driving lever70rotates from one end of the rotational range to the partway position thereof are respectively opposite to those while the driving lever70rotates from the above partway position to the other end thereof. Therefore, while the driving lever70rotates from one end of the rotational range to the partway position thereof, each of the above blades is shifted from the small aperture position to the fully closed position. While the driving lever70rotate from the partway position of the rotational range to the other end thereof, each of the above blade is shifted from the fully closed position to the fully open position.

Additionally, the slots22and52are shaped into a cam shape in the widthwise direction of each blade. With such a configuration, each blade is easily moved to the small aperture position, the fully closed position, and the fully open position in response to the rotational position of the driving lever70.

The following will describe a modification of the light quantity control device.

A second blade50A, according to a modification of the light quantity control device, has a ND filter at the cutout51.FIG. 10is an exemplary view of the second blade50A having the ND filter. The ND filter51A is provided to cover the opening61when the driving lever70is positioned at one end of the rotational range, that is to say, when each blade is positioned at the small aperture position.

In this manner, at least one of the blades may be provided with the ND filter.

While the preferred embodiment of the present invention has been illustrated in detail, the present invention is not limited to the above-mentioned embodiment, and other embodiments, variations and modifications may be made without departing from the scope of the present invention.

In the above embodiment, as shown inFIGS. 3A to 3C, the rotation of the driving lever in one direction allow the fully open state to be shifted to the fully closed state, and the fully closed state to be shifted to the small aperture state. However, the present invention is limited to the configuration, for example, the fully closed state may be shifted to the fully open state, and the fully open state may be shifted to the small aperture state.

Additionally, although the number of stop positions of the driving lever is three in the embodiment, and the stop positions may be two including one end and the other end. In this case, the driving lever70rotates within 90 degrees with a phantom line set as center, the phantom line passing through the rotational center of the driving lever70and being parallel with moving direction of blades.

Movements of the first blade20, the supporting blade30, and the second blade50may allow the quantity of the light passing through the opening41, which is smaller than the opening61formed on the bottom board60, formed on the plate40.

Only the first blade20and the second blade50may control the quantity of the light passing through the opening61without the provision of the supporting blade30. Additionally, in this case, the plate40is arranged between the first blade20and the second blade50, thereby buffering the sliding of both blades.

Finally, several aspects of the present invention are summarized as follows.

According to an aspect of the present invention, there is provided a light quantity control device characterized by comprising: a bottom board having an opening; a set of blades linearly moved in opposing directions and controlling the opening to a fully open state, a fully closed state, and a small aperture state; a driving lever connected to the set of blades and driving the set of blades by rotation of the driving lever; and a stopper restricting a rotational range of the driving lever, wherein the set of blades controls the opening to the small aperture state when the driving lever is positioned at one end of the rotational range defined by the stopper.

With such a configuration, when the driving lever is positioned at an end of the rotational range defined by the stopper, the set of blades brings the opening to the small aperture state, whereby the opened degree of the opening can be constant in the small aperture state. That is to say, in a light quantity control device that controls the quantity of the light passing through the opening by linearly moving at least two blades relative to the bottom board in the opposing directions, even if the rotational ranges of the misalignment of the driving lever are substantially identical, each blade is greatly misaligned in the moving direction based on the position of the driving lever. The misalignment degree of each blade in the moving direction of each blade is smaller and the opening can be brought to the small aperture state with certainty in cases where the opening is brought to the small aperture state when the driving lever is positioned at one end of the rotational range of the driving lever rather than cases where the opening is brought to the small aperture state when the driving lever is positioned at the partway of the rotational range of the driving lever. Therefore, the small aperture state is maintained.

Additionally, the set of blades may control the opening to the fully open state or the fully closed state when the driving lever is positioned at the other end or a partway position of the rotational range.

With such a configuration, the state of the opening is brought to the fully open state, the fully closed state, and the small aperture state with certainty.

Further, the moving directions of the set of blades while the driving lever moves from the one end of the rotational range to the partway position may be opposite to those of the set of blades while the driving lever moves form the partway position to the other end.

With such a configuration, for example, while the driving lever rotates from one end of the rotational range to the partway position thereof, each of the blades is shifted from the small aperture position to the fully closed position, and while the driving lever rotate from the partway position of the rotational range to other end thereof, each of the blades is shifted from the fully closed position to the fully open position.

Furthermore, the set of blades each may have a slot engaged with a pin provided in the driving lever, and at least one of the slots may be formed in widthwise directions of the set of blades.

With such a configuration, since the slots are formed in widthwise directions of the set of blades, each blade is easily moved to the small aperture position, the fully closed position, and the fully open position in response to the rotational position of the driving lever.

Furthermore, the stopper may be integrally formed with the bottom board.

With such a configuration, the rotational range of the driving lever can be restricted by a simple structure.