GB2226648A - Focal plane shutter for a camera with braking means - Google Patents

Description

1 "FOCAL PLANE SHUTTER FOR A CAMEW' This invention relates to a

focal-plane shutter for a camera.

According to the present invention, there is provided a focal plane shutter for a camera comprising fixed structure having a shutter aperture therein; at least one shutter blade means comprising at least one shutter blade plate which is pivotally supported on one side only thereof by a plurality of arms, the arms being pivotally mounted in the fixed structure so that the or each shutter blade plate can be moved relative to the shutter aperture to open and close the latter; and at least one plate-engaging member which is engaged by the opposite side of the respective shutter blade plate or plates so that movement of the latter is braked by the plate-engaging member to cause the respective shutter blade plate to move substantially parallel to itself.

Preferably, the or each shutter blade means comprises two shutter blade plates one of which is a slit-defining plate which is adapted to define a slit with one side of the shutter aperture, and the other of which is a cover plate which is adapted to cover a portion of the shutter aperture not covered by the slit defining plate.

Preferably, the or each of the said slit-defining and cover plates is pivotally dupported by the same arms.

The fixed structure preferably comprises a base plate, the or each plate-engaging member being a planar member which is disposed at an angle to the base plate, the plate-engaging member being spaced from the base plate by a greater distance on the said opposite side of 2 the shutter blade plate or plates than on the said one side thereof.

There may be a plurality of plate-engaging members which are disposed parallel to each other.

The invention also comprises a camera provided with a focal plane shutter as set forth above.

The invention is illustrated, merely by way of example, in the accompanying drawings, in which:- Figure 1 is a side view of part of a focal-plane shutter according to the present invention, showing only one shutter blade means of the shutter; Figure 2 is a side view showing part of a prior shutter known to the Applicants in a similar manner, and Figures 3 and 4 are front views of part of the shutters of either Figure 1 or 2, Figure 3 showing the shutter blade means in a folded-away state in which the shutter aperture is open, and Figure 4 showing the shutter blade means in an extended state in which the shutter aperture 'Is closed.

Terms such as "left" and "right", and "upper" and "lower", as used in the description below, are to be understood to refer to directions as seen in the drawings.

In Figures 2-4 there is shown a prior focal plane shutter for a camera having a base plate 1 which is formed with a shutter aperture la therein. Arms 2, 3 which are capable of pantograph motion are pivotally mounted on the base plate 1 by neans of pivots 4, 5. A slit-defining shutter blade plate 6 is pivotably supported via pivots 7 and 8 by the arms 2 and 3 on the left hand side only thereof so as to be adapted to define a slit with one side 1b of the shutter aperture la when the slit-defining plate 6 is moved relatively to the shutter aperture la to open and close 1 3 the latter. A cover plate 9 is also pivotably supported via pivots 10 and 11 by the arms 2 and 3 so as to be adapted to cover a portion of the shutter aperture la not covered by the slit-defining plate 6. The shutter also comprises a plate 12 of the same shape as that of the base plate 1.

In Figures 2 to 4, there is shown only one of two shutter blade means or assemblies, the other being omitted to simplify the drawings. The latter, however, is identical in configuration with the shutter blade means shown except that its vertical arrangement is inverted.

Figure 3 shows the state in which the shutter blade means is folded up and retracted from over the shutter aperture la so as to open the latter, whereas Figure 4 shows the state in which the shutter blade means is extended so as to cover the shutter aperture la.

When the shutter is used in an exposure action, the shutter blade plates 6, 9 move from the state shown in Figure 3 to the state shown in Figure 4 and vice versa very quickly. This action is caused by the turning of the arms 2 and 3 so that there is upward or downward movement of the slitdefining plate 6 and of the cover plate 9.

Since the slit-defining plate 6 is pivotably supported via the pivots 7 and ' 8 by the arms 2 and 3 on the left hand side of the shutter aperture la, and similarly the cover plate 9 is pivotably supported via the pivots 10 and 11 by the arms 2 and 3, the thickness of the shutter blade means on the left hand side of the shutter aperture la is equal to tl which is the sum of the respective thicknesses of the plates 6, 9 and arms 2, 3. On the contrary, the thickness of the shutter 4 blade means on the right hand shutter aperture is equal to t2 which is the sum of the respective thicknesses of the plates 6, 9 alone. Since the width T1 of the space between the base plate 1 and the plate 12 in which there can be movement of the plates 6, 9 is uniform, the resistance to movement of the shutter blade means differs between the left and right hand sides of the shutter aperture. Accordingly, during the movement of the shutter blade means, due to the inertia of the slit- defining plate 6, its right hand side, which is not supported by the arms 2, 3 moves faster than its left hand side which is so supported and is then momentarily decelerated. Moreover, the cover plate 9 undergoes the contrary phenomenon. As a result, the edge 6a of the slit-defining plate 6 moves while vibrating obliquely with respect to the upper side 1c of the shutter aperture la, so that it does not remain horizontal. Therefore, the exposure time becomes different between the left and right hand sides of the shutter aperture la, making the exposure uneven. Furthermore, since the slit has recently been narrowed to meet the demand for the speedup of the exposure time, this unevenness of exposure has become more serious.

It is therefore an object of the present invention to provide a focal-plane shutter for a camera in which the slit-defining plate 6 is moved substantially parallel to itself so that the exposure time becomes even between the left and righi hand sides of a picture.

In Figure 1 there is therefore shown a focal plane shutter for a camera according to the present invention, Figure I showing a section at the right hand end of Figure 4. Parts of the Figure 1 construction which correspond to those of Figures 2-4 are given the same reference symbols.

m In Figures 1(1) and (2), the spaces through which the two shutter blade means can move are defined by the base plate 1 and by the plate 12. Thus the spaces A, B through which the two shutter blade means can respectively move are defined by planar partition boards 13a, 13b and 13c.

In the embodiment of Figure 2, when the plates 6 and 9 are in the Figure 4 position in which they close the shutter aperture la, the spaces A and B are defined by the partition boards 13a, 13b and 13c as shown in Figure 2 where they approach each other on the left hand side of the shutter aperture la, whereas in the embodiment of Figure 1(1) they approach each other on the right hand side of the shutter aperture la.

That is, in the embodiment of Figure 1(1), the space A is progressively narrowed towards the right hand side of the shutter aperture la because of the angle between the partition board 13a and the base plate 1.

Therefore, when the arms 2 and 3 are actuated from the positions shown in Figure 4 in order to open the shutter aperture la, the plates 6 and 9 are moved by means of the pivots 7, 8, 10 and 12 toward the right hand side of the space A. At this time, since the unsupported right hand side of the plates are quickly moved rightward from the static state, by virtue of inertia, it would normally have a tendency to be accelerated more than the suppgrted left hand side thereof. However, since the partition board 13a slopes rightward, the right hand sides of the plates 9 and 6 are progressively friction-braked by the partition board 13a and are prevented from such relative movement with respect to the left hand sides thereof. Accordingly, they maintain a substantially parallel condition with respect to the upper and lower sides lc, 1b of the i 0 6 shutter aperture Ia.

Figure 1(2) shows a second embodiment of the present invention in which the space A slopes rightward but its extent is uniform, the partition boards 13a, 13b, 13c being parallel to each other.

The operational effect exerted on the movement of the plates 6 and 9 in the Figure 1(2) embodiment is identical with that of Figure 1(1), and thus, no detailed description is given here.

It should be noted that the other shutter blade means is similarly shaped and disposed.

Some modifications to the foregoing embodiments are possible. For example, the partition board 13b in Figure 1(1) is shown as being parallel to the base plate 1 but it can be inclined, e.g. in the direction opposite to that of the partition board 13a or upwards towards the right.

In the embodiments of Figures 1(1) and 1(2) the space through which the unsupported portion of the plates 6, 9 move is less than that of the space through which the supported portion of the plates move so as to impose an increasing resistance on the unsupported portion of the plates as they move ahead so that the plates move parallel to themselves. Thus, the possibility of the so-called unevenness of exposure, meaning that the exposure time differs between the left and right hand sides of a picture, is lessened. The present invention is particularly effective for a camera demanding a high-speed shutter or whose slit width is narrow. Further, the present invention is effective also in preventing the so-called rebounding of the blades that would be caused by reaction after the completion of the movement of the blades.

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Claims (9)

1. A focal plane shutter for a camera comprising fixed structure having a shutter aperture therein; at least one shutter blade means comprising at least one shutter blade plate which is pivotally supported on one side only thereof by a plurality of arms, the arms being pivotally mounted in the fixed structure so that the or each shutter blade plate can be moved relative to the shutter aperture to open and close the latter; and at least one plate-engaging member which is engaged by the opposite side of the respective shutter blade plate or plates so that movement of the latter is braked by the p late-engaging member to cause the respective shutter blade plate to move substantially parallel to itself.

2. A shutter as claimed in claim 1 in which the or each shutter blade means comprises two shutter blade plates one of which is a slit-defining plate which is adapted to define a slit with one side of the shutter aperture, and the other of which is a cover plate which is adapted to cover a portion of the shutter aperture not covered by the slit-defining plate.

3. A shutter as claimed in claim 2 in which each of the said slit-defining and aover plates is pivotally supported by the same arms.

4. A shutter as claimed in any preceding claim in which the fixed structure comprises a base plate, the or each plate-engaging member being a planar member which is disposed at an angle to the base plate, the plate-engaging member being spaced from the base plate 8 g by a greater distance on the said opposite side of the shutter blade plate or plates than on the said one side thereof.

5. A shutter as claimed in claim 4 in which there are a plurality of plate-engaging members which are disposed parallel to each other.

6. A focal plane shutter for a camera substantially as hereinbefore described with reference to and as shown in Figure I(l) or Figure 1(2) of the accompanying drawings.

7. A camera provided with a focal plane shutter as claimed in any preceding claim.

8. A focal-plane shutter for cameras comprising two shutter blades, each shutter blade including a plurality of thin opaque plates and being configured so that at least one of said plates for forming a slit is supported at two points by two arms as being capable of pantograph motion, characterized in that a partition board is provided to slope a working plane on which a point portion of said plate runs with respect to another working plane on which a supporting portion, supported by said arms, of said plate runs, in the direction of braking said plate increasingly with the progressive running of said plate.

9. Any novel integer or step, or combination of integers or steps, hereinbefore described and/or shown in the accompanying drawings, irrespective of whether the present claim is within the scope of, or relates to the same or a different invention from that of, the preceding claims.

hed 199D atThe Patent Onice, State House, 66171 High Holoom. TAndon WC1R 4TP. Further copies maybe obtainedfrom The PatentOffice. Wes Branch, St Mary Cray, Orpington. Kent BR5 3RD. Printed by Multijlex techniques Itd, St Mary Cray, Kent. Con 1/87 1 Z