JPH0477712A - Dust shadow proofing device for camera - Google Patents

Abstract

PURPOSE:To prevent dust stuck on the emitting face of a lens from being projected onto a film by constituting a transparent sheet, which is arranged between the rear end lens of a photographic optical system and the exposure opening frame of a camera, so as to displace it in a direction intersecting orthogonally with a photographic optical axis during the exposure of a shutter. CONSTITUTION:A transparent sheet 10 is provided on an optical path between the rear end lens of a photographic lens 2 and a film F on the emitting face, and by moving the sheet part area of this transparent sheet 10 to a position covering an aperture 4a of an exposure opening frame 4 in the case of opening a rear lid 3a of the camera, the dust infiltrated into the camera in exchanging the film is prevented from being stuck onto the rear end lens emitting face of the photographic lens 2. Further, in the case of WIDE photographing to generate the degradation of picture quality caused by the dust stuck onto the emitting face of the rear end lens, by displacing this transparent sheet 10 for a prescribed amount during the exposure of the shutter, the influence caused by the shadow of the dust to be projected onto the film F is prevented from standing out on the picture.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a camera dust and shadow prevention device suitable for application to, for example, a camera with a lens shutter capable of variable magnification photography.

[Conventional technology]

For example, when you open the back cover of a camera and perform operations such as changing film, dust floating in the air may enter the camera.

This intrusion of dust into the camera occurs not only when changing the film, but also when winding and rewinding the film. It will adhere to.

However, if this invading dust adheres to the exit surface of the rear end lens of the photographic optical system, the shadow of the adhered dust will be imprinted on the film together with the subject image, causing the film surface and rear end to be Depending on the distance from the exit surface of the lens,
The imprinted dust shadows significantly degrade image quality.

Hereinafter, the phenomenon of deterioration of image quality caused by such dust adhesion will be explained with reference to the diagram illustrating the phenomenon in FIG.

Now, the distance from the exit surface 102 of the rear end lens of the photographic optical system 101 to the film surface 103 (hereinafter also referred to as back focus j) is BF, and the F number FNO of the photographic optical system 101 is φex. Assuming that the effective diameter of the photographing optical system 101 is taken as the effective diameter, the area SP of the axial light beam at the rear end lens exit surface 102 can be determined by the following formula.

It is assumed that dust having an area Sd is attached to the axial light beam on the rear end lens exit surface 102 having such an area Sp.

In this case, the light intensity ratio IP of the on-axis light intensity when no dust is attached to the rear end lens exit surface 102 and the on-axis light intensity when dust is attached is expressed by the following formula. The correlation between BF and the force ρ at this time is as shown in FIG.

As can be seen from this relationship diagram, the light intensity ratio Ip at this time decreases rapidly as the back focus BF becomes smaller. That is, the influence of dust shadows caused by dust adhesion increases significantly as the back focus BF becomes smaller.

Deterioration in image quality caused by this dust adhesion can be easily prevented by constantly cleaning the rear end lens exit surface 1°2 of the photographic optical system 101, so the lens itself can be removed from the camera. This is not a serious problem with removable interchangeable lenses, but with cameras with lens shutters where the lens is permanently attached to the camera, image quality may deteriorate due to dust adhesion. It is necessary to always keep in mind that phenomena will occur.

In other words, in the case of interchangeable lenses, the phenomenon of dust adhesion itself is difficult to occur because lenses are exchanged frequently, and when the lens is removed, the rear lens exit surface 1
02 can be easily cleaned, so no problem arises.

However, in the case of a camera with a lens shutter, since there is no escape route for dust that has entered the camera to the outside, there is a possibility that the dust may adhere to the rear end lens exit surface 102 of the photographing optical system 101. Furthermore, in a camera with a lens shutter, the rear end lens exit surface 102 must be cleaned when the back cover of the camera is opened. This is because there are circumstances in which it is difficult to thoroughly clean the area.

It is thought that the reason why this has not been much of an issue until now is that in the case of conventional cameras with lens shutters, the back focus BF was set relatively long within the film. .

[Problem to be solved by the invention]

However, as there has recently been a demand for high magnification and compact cameras for cameras with 35mm lens shutters, image quality has deteriorated due to dust adhesion. The problem of how to eliminate or prevent deterioration phenomena has become a matter of great concern.

This is because if a camera is designed to satisfy the requirements of high magnification and compactness in variable magnification photography, the back focus BF will inevitably become short.

Therefore, if a camera with a lens shutter is designed by following the conventional structure as it is, it will be extremely difficult to prevent image quality deterioration caused by this dust adhesion.

The present invention was made in view of the above circumstances, and even if dust in the air enters the camera and adheres to the exit surface of the rear end lens of the photographic optical system, the film will not be damaged. An object of the present invention is to provide a new camera layer prevention device capable of making the shadow of dust imprinted on the top inconspicuous.

[Means to solve the problem]

In order to achieve the above object, the invention of claim 1 is characterized in that a transparent sheet that can be displaced in a direction perpendicular to the photographing optical axis is connected to the rear end lens of the photographing optical system and the exposure aperture frame of the camera. This is because the transparent sheet is disposed between the two and can be displaced by a predetermined amount in a direction perpendicular to the photographing optical axis during shutter exposure.

Further, the invention according to claim 2 is characterized in that the transparent sheet is configured as a member having two regions: a transparent partial region that can cover the exposure aperture frame and an opening region that can expose the exposure aperture frame. However, when the rear end lens is at a close position within a predetermined distance from the exposure aperture frame, the rear end lens is arranged so that the transparent portion of the transparent sheet faces a position that can cover the exposure aperture frame, and the rear end lens is close to the exposure aperture frame. The transparent sheet is configured such that the aperture area of the transparent sheet faces the position of the exposure aperture frame when the transparent sheet is located at a position beyond the predetermined distance from the transparent sheet.

Further, the invention according to claim 3 is characterized in that the transparent sheet includes two regions: a transparent partial region that can cover the exposure aperture frame and an opening region that can expose the exposure aperture frame, and at least When the back cover of the camera is opened, the transparent portion of the transparent sheet faces a position where it can cover the exposure aperture frame.

[For production]

The layer formation prevention device for a camera configured as described above includes a transparent sheet provided on the optical path between the rear end lens exit surface of the photographing lens and the film, and a sheet area of the transparent sheet placed on the back cover of the camera. By moving the exposure aperture frame to a position that covers the aperture when it is opened, it is possible to prevent dust that has entered the camera when changing film from adhering to the rear end lens exit surface of the photographing lens. During WIDE shooting, where image quality deterioration occurs due to dust adhering to the exit surface, by displacing this transparent sheet by a predetermined amount during shutter exposure, the effect of dust shadows imprinted on the film can be reduced. The reason is that it is made to be less noticeable on the screen.

In addition, when shooting at E, where image quality deterioration due to attached dust does not occur, the shooting light beam is
By guiding the light to the film without passing through a partial area, the quality of photographed images can be further improved.

〔Example〕

Hereinafter, the layer formation prevention device for a camera according to the present invention will be explained in detail based on the illustrated embodiment. Prior to that, the principle of layer formation prevention used in the present invention will be explained with reference to FIGS. 3 and 4. I will explain.

Now, a plane-parallel plate 1゜4 with few optical aberration problems is placed on the optical path between the rear end lens exit surface 102 of the photographing optical system 101 and the film surface 103, and the plane-parallel plate 1.
It is assumed that a disk-shaped dust 105 with a diameter φd centered on the optical axis ○ is attached to the image field side surface of the lens 04.

Under such conditions, the exit pupil 1 of the photographing optical system 101
It is assumed that the axially emitted light beam from 01a passes through a circular region with a diameter φP set on the image field side surface of the plane-parallel plate 104.

In this case, if φP>φd, then the light intensity ratio I
p becomes the value expressed by φP, and if φp≦φd, then IP=○
...(4).

Now, as shown in FIG. 4, from this state, the parallel plane plate 1
04 is displaced by Y in the direction perpendicular to the optical axis O, the on-axis light intensity ratio IP' after the displacement becomes larger than IP when . After this displacement, the axial light intensity ratio Ip/
increases monotonically until the value of Y satisfies the equation (6), at which time it becomes the value Ip'=1.

This means that when the plane-parallel plate 104 is displaced to a position that satisfies equation (6), the average light intensity ratio on the axis becomes larger than when the plane-parallel plate 104 is stopped, and the image is not reflected on the film. This means that the influence of the shadow of the included dust 105 is reduced.

On the other hand, the circular area φP set on the surface of the parallel plane plate 104 on the image field side is expressed by the formula NO, and the diameter φd of the dust is determined by the aperture diagonal length of the exposure aperture frame of the camera (from the bottom surface of the camera). When D is the angular length), it can be hypothetically expressed by the following formula. Therefore, in the present invention, the displacement Y of the parallel plane plate 104 is calculated as Y2O,0029XD... under these conditions. ...(
It is desirable to set the value to a value that satisfies the equation 9).

According to the principle of layer formation prevention used in the present invention, a transparent sheet (transparent film) corresponding to the parallel plane plate 104 is displaced by this amount of displacement Y in a direction perpendicular to the optical axis O during the shutter opening time. This makes the shadow of the dust 105 imprinted on the film less noticeable in terms of image quality.

Next, a specific example utilizing this principle of layer formation prevention will be described.

FIG. 1 is a schematic perspective view showing a specific embodiment of the layer formation prevention device for a camera according to the present invention. Indicates if it is set.

In FIG. 1, reference numeral 1 denotes a camera with a lens shutter equipped with a layer prevention device according to the present invention, and is composed of a variable focus type photographing lens 2 and a camera body 3 whose back cover can be opened and closed.

In this case, the variable focus type photographing lens 2 is composed of a zoom optical system configured in a positive/negative arrangement or a negative/positive/negative arrangement, for example, in order to shorten the total length of the lens itself. The distance between the rear lens exit surface of the lens 2 and the film surface is designed to be the smallest at the WIDE end and largest at the E end.

On the other hand, the camera body 3 includes a back cover 3 which is known per se.
a, a film winding mechanism (not shown), a film rewinding mechanism and a shirt release mechanism (not shown) are provided.

4 is the exposure aperture frame of the camera installed on the photographing optical axis 0,
For example, the aperture 4a is set to 36 llff1l×24 mm.

5 is a film F such as a 35mm roll film, for example.
This film cartridge has a built-in film cartridge, and is removably connected to the film rewinding mechanism described above through appropriate means, similar to known ones.

A winding shaft 6 is connected to the film winding mechanism described above via a winding gear 7 provided at its lower end.

Reference numeral 10 denotes a transparent sheet having a shape in which two areas 11 and 12 are continuous in the horizontal direction and can cover the front surface of the aperture 4a of the exposure aperture frame 4, respectively, and the sheet covers the rear end lens exit surface of the photographing lens 2 and the exposure aperture frame. 4, so as to cross this optical path and to be movable in the lateral direction.

In this case, one region 11 is W as shown in FIG.
As the WIDE area used during IDE photography, the entire area is formed of a transparent sheet part, and the other area 12 is
As shown in FIG. 2, the entire area is opened as a position-E area used for position-E photography.

Note that it is desirable that the transparent sheet 10 be provided at a position closer to the exposure aperture frame 4.

A transparent sheet winding shaft 13 holds one end of the transparent sheet 10, and is provided outside one side of the exposure aperture frame 4 so as to be rotatable in forward and reverse directions.

Reference numeral 14 denotes a transparent sheet rewinding shaft that holds the other end of the transparent sheet 10, and is provided outside the other side of the exposure aperture frame 4 so as to be rotatable in forward and reverse directions.

The transparent sheet winding shaft 13 and the transparent sheet unwinding shaft 14
is configured to be rotated synchronously by the drive control unit 15 so as to prevent slack from occurring.

The drive control section 15 moves the transparent sheet in the following manner based on the opening signal from the camera back 3a, the WIDE-position E multiplication signal from the photographic lens 2, and the shutter speed signal from the shutter speed setting section 16. The winding shaft 13 and the transparent sheet unwinding shaft 14 are configured to be controlled. Namely.

(a) WIDE signal from the photographing lens 2, or
When the opening signal from the back cover 3a is transmitted, the transparent sheet is moved so that the WIDE area 11 of the transparent sheet 10 moves to a position W (the position shown in FIG. 1) to cover the aperture 4a and stops at that position. The rewinding shaft 14 is rotated.

At this time, the transparent sheet winding shaft 13 is set in a state that allows the transparent sheet 10 to be rewound by the transparent sheet unwinding shaft 14.

(b) When the shirt release operation is performed while the WIDE signal from the photographic lens 2 is being transmitted,
After confirming that the transparent sheet 10 has moved to a position covering the aperture 4a, the transparent sheet 10 is moved to a position where the amount of displacement Y≧0.0029 The transparent sheet rewinding shaft 14 is rotated so as to be displaced in a predetermined direction.

In this case, the transparent sheet winding shaft 13 may be rotated instead of the transparent sheet unwinding shaft 14, and regardless of which shaft 14.13 is rotated, the displacement operation speed of the transparent sheet 10 and The number of repetitions of displacement is set to an appropriate value depending on the length of the shutter time at that time.

(c) When the position E magnification signal is transmitted from the photographing lens 2, the position E area 12 (opening area) of the transparent sheet 10 moves to the position facing the aperture ¥48 (the position shown in Figure 2) and remains at that position. Turn the transparent sheet winding shaft 1 so as to stop it.
Rotate 3.

At this time, the transparent sheet unwinding shaft 14 is set in a state that allows the transparent sheet winding shaft 13 to wind up the transparent sheet 10 .

(d) When the E magnification signal is transmitted from the photographing lens 2, the transparent sheet 1o is held stopped at a position covering the aperture 4a even when the shirt release operation is performed.

The drive control section 15 performs the control as described above.

Note that the criteria for determining WIDE and position E are set based on whether or not the shadow of dust attached to the surface of the WIDE area 11 of the transparent sheet 10 is in a state where the quality of the photographed image is degraded.

Next, the operation of the layered prevention device of the illustrated embodiment constructed in this way will be explained.

When the back cover 3a is open, the WIDE area 11 of the transparent sheet 10 covers the rear end lens exit surface of the photographic lens 2. Therefore, if any dust enters through the open portion of the back cover 3a when replacing the film, that dust will adhere to the surface of the WIDE area 11 of the transparent sheet 10.

However, since the transparent sheet 10 can be placed closer to the exposure aperture frame 4, it is possible to use WIDE even when the back cover is open, which makes cleaning difficult.
Dust attached to the surface of the storage area 11 can be easily cleaned.

Now, when shooting is performed regardless of whether dust is attached to the WIDE area 11 of the transparent sheet 10, if it is WIDE shooting, the transparent sheet 10 is controlled as follows. That will happen.

That is, when the photographic lens 2 is set to the WIDE photographing state, the photographic lens 2 is
Since the WIDE signal is outputted to the drive control section 15, the drive control section 15 issues a rotation command to the transparent sheet rewinding shaft 14, and performs the above-mentioned control procedures (a) and (b). ) will be executed.

In this case, immediately after the film F is loaded and the back cover 3a is closed, the control in section (b) of the control procedure will be executed immediately since the control in section (a) of the control procedure has already been completed. Become.

In addition, if the photographing lens 2 is changed from the position E photographing state to the WIDE ID state, first the control procedure (a
) term control will be executed.

In either case, when the control in section (a) of the control procedure is completed, the WIDE area 11 of the transparent sheet 10 is stopped at a position covering the aperture 4a, so the control procedure in section (b) of the control procedure is completed. When the control is executed, the transparent sheet 10 is displaced from the stop position by an amount Y (≧○, O
○29・D) will be displaced in the predetermined direction.

As a result, the shadow of the dust imprinted on the film F becomes so-called "out of focus" and becomes less noticeable on the screen.

On the other hand, when the photographing lens 2 is changed from the WIDE photographing state to the position E photographing state, the position E multiplication signal from the photographing lens 2 is output to the drive control unit 15 in conjunction with the changing operation. The control unit 15 issues a rotation command to the transparent sheet winding shaft 13 to execute control according to items (c) and (cl) of the control procedure described above.

That is, when the control in section (c) of the control procedure is executed,
The transparent sheet 1-winding shaft 13 rotates to move the WIDE area 11 that has been covering the aperture 4a outward from that position, and also moves the WIDE area 11 that has covered the aperture 4a to the outside from that position, and also moves the WIDE area 11 that has covered the aperture 4a to the outside from that position.
Place the transparent sheet 1 so that it faces the position covering the aperture 4a.
0 will be moved and stopped at that position.

Then, shutter exposure will be performed after the transparent sheet 10 has stopped, but at this time, the transparent sheet 10 is maintained at that position according to the control in section (d) of the control instructions, so that the image is taken. The light flux emitted from the rear end lens exit surface of the lens 2 does not pass through the sheet portion of the transparent sheet 10, that is, it reaches the film F as it is via the opening area.

Therefore, in this case, the movement of displacing the transparent sheet 10 to prevent image quality deterioration due to shadows of dust is not performed, but at the time of position E, the rear end lens exit surface of the photographing lens 2 and the film F are Since the distance between the transparent sheets 10 and 10 is long, there will be no deterioration in image quality due to the shadows of the imprinted dust, and the operation of displacing the transparent sheet 10 can be omitted.

Therefore, in the case of position E photography, the image quality is improved by the fact that the sheet portion of the transparent sheet 10 is not interposed in the photographing optical path.

Of course, when performing position E photography, it is also possible to perform photography while displacing the transparent sheet 10 with the sheet partial region of the transparent sheet 10 covering the aperture 4a, as in the case of WIDE photography. It is.

As explained above, in the camera layer formation prevention device according to the above embodiment, the transparent sheet 10 is provided on the optical path between the rear end lens exit surface of the photographing lens 2 and the film F, and the sheet portion of this transparent sheet 10 is By moving the area to a position where it covers the aperture 4a of the exposure aperture frame 4 when the camera back cover 3a is opened, dust that has entered the camera during film exchange can be prevented from adhering to the rear lens exit surface of the photographic lens 2. Furthermore, image quality deterioration caused by dust adhering to the exit surface of the rear lens occurs.
During IDE photography, by displacing this transparent sheet 10 by a predetermined amount during shutter exposure, the effect of the shadow of dust imprinted on the film F is made less noticeable on the screen, so that the shadow of dust is It has become possible to obtain images of good quality regardless of the presence or absence.

Moreover, when shooting with a camera in which the image quality does not deteriorate due to attached dust, the shooting image quality can be further improved by guiding the shooting light flux to the film F without passing through the sheet area of the transparent sheet 10. It has also become possible to improve the

Although one embodiment has been described above, the present invention is not limited to this, and can be modified in various ways without changing the gist thereof.

For example, the present invention can be applied even when the photographic lens is not limited to a zoom lens, but is a bifocal lens or a varifocal lens.

〔Effect of the invention〕

As described above, when using the present invention, even if dust in the air enters the camera and adheres to the exit surface of the rear end lens of the photographic optical system, the image will not be captured on the film. It becomes possible to realize a new anti-glare device for a camera that can make the shadows of the included dust inconspicuous.

[BRIEF DESCRIPTION OF THE DRAWINGS] FIGS. 1 and 2 are schematic perspective views showing the configuration of a specific embodiment of the anti-glare device for a camera according to the present invention. If the lid is open, or
FIG. 2 shows a case where the focal length of the zoom optical system is set to the WIDE state, and FIG. 2 shows a case where the focal length of the zoom optical system is set to the WIDE state. FIG. 3 and FIG. 4 are both principle explanatory views for explaining the principle of preventing glare used in the camera glare preventing device according to the present invention. Figure 5 is a phenomenon explanatory diagram for explaining the phenomenon of deterioration of image quality caused by dust attached to the exit surface of the rear end lens of the photographing optical system, and Figure 6 is the exit surface of the rear end lens of the photographing optical system. FIG. 3 is a relational diagram showing a light intensity ratio IP between the light intensity on the axis when no dust is attached to the light intensity and the light intensity on the axis when dust is attached. 1...Camera with lens shutter, 2...
・Photography lens. 3...Camera body 3a...Back cover, 4...Exposure aperture frame, 4a...Aperture. 5... Film cartridge, 6... Winding shaft, 7... Winding gear, 10... Transparent sheet, 11... WIDE area, 12... ... Area for placing E 13 ... Transparent sheet winding shaft, 14 ... Transparent sheet rewinding shaft, 15 ...
・Drive control section, 16...Shutter time setting section, 1, 01...
... Photographing optical system, 101, a... Exit pupil, 102... Rear end lens exit surface, 103...
・Film surface, 104...Parallel plane plate, 105...Dust, ○...Photographing optical axis, F...Film, BF...Back focus, FNO ...F number φex of the photographing optical system...
...Effective diameter of the photographing optical system, φp...Circular area on the image field side of the plane-parallel plate, φd...Diameter of dust, ...Axis at the exit surface of the rear end lens Area of the upper luminous flux.・・・・・・Area of dust on the exit surface of the rear end lens, ・Light intensity ratio.・・・・・・Axis light intensity ratio after displacement, ・・Displacement amount of parallel plane plate. 9 calm;

Claims (3)

[Claims] (1) A transparent sheet that can be displaced in a direction perpendicular to the photographing optical axis is disposed between the rear end lens of the photographing optical system and the exposure aperture frame of the camera, and the transparent sheet is used to control the photographic light during shutter exposure. A dust shadow prevention device for a camera, characterized in that it is configured to be able to be displaced by a predetermined amount in a direction perpendicular to an axis. (2) The transparent sheet includes two regions: a transparent partial region that can cover the exposure aperture frame and an aperture region that can expose the exposure aperture frame, and the rear end lens is located within a predetermined distance from the exposure aperture frame. When the transparent sheet is in the approach position, the transparent portion of the transparent sheet faces a position where it can cover the exposure aperture frame, and when the rear end lens is in a position away from the exposure aperture frame by more than the predetermined distance, the transparent sheet is 2. The dust and shadow prevention device for a camera according to claim 1, wherein control is performed so that the aperture area of the sheet faces the position of the exposure aperture frame. (3) The transparent sheet has two regions: a transparent partial region that can cover the exposure aperture frame and an opening region that can expose the exposure aperture frame, and at least when the back cover of the camera is open, 3. The dust and shadow prevention device for a camera according to claim 1, wherein the transparent partial area of the transparent sheet faces a position where it can cover an exposure aperture frame.