JPH055927A - Method for combinedly using focal plane shutter and liquid crystal shutter - Google Patents

Abstract

PURPOSE:To enable high-speed synchronism in day light, the simultaneousness of exposure over the whole screen, the accurate shape recording of a moving object, the removal of uneven exposure at the time of high-speed exposure, etc. CONSTITUTION:The liquid crystal (LC) part 11 of an LC shutter 10 is mounted on the front face of a photographing lens 12 of a camera body 1 provided with a focal plane shutter 1a and an LC shutter control part 12 is provided with a releasing button 16 and a shutter dial 17. Voltage is impressed to the LC part 11 by depressing the button 16 to shield the light from a film face, a shutter presheet is traveled, and when an X contact is turned on, the voltage impression is released to make the LC part 11 translucent state, an electronic flash 20 is emitted and the LC part is shielded again prior to the traveling of a shutter post sheet. After traveling the post sheet, the LC part 11 is turned to the translucent state.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a combined use method of a focal plane shutter and a liquid crystal shutter, in which the exposure characteristics can be improved by using the focal plane shutter and the liquid crystal shutter together.

[0002]

2. Description of the Related Art In a focal plane shutter, a shutter front curtain (hereinafter referred to as "first curtain") and a shutter rear curtain (hereinafter referred to as "rear curtain") made of a light-shielding cloth or a metal plate are run in front of a focal plane, The exposure time is controlled by the width of the slit formed between the two curtains and the change in the curtain speed.

In a camera equipped with such a focal plane shutter, the shutter mechanism is entirely on the camera body side and can be arranged independently of the taking lens, and there is no restriction on the aperture of the taking lens. Widely used as shutters for interchangeable lens single-lens reflex cameras and rangefinder linked cameras, from 35 mm format to medium and large format.

On the other hand, liquid crystal shutters include those that utilize the molecular twist effect of liquid crystals and those that utilize the guest-host effect. Among them, a liquid crystal shutter using a nematic liquid crystal having the most general molecular twisting effect forms transparent electrodes on opposite surfaces of a pair of parallel glass substrates, and encloses the nematic liquid crystal between both electrodes,
Polarizing plates whose polarization directions are orthogonal to each other are attached to the outside of both glass substrates.

The molecular axis of the liquid crystal molecule is parallel to the electrode surface and twisted by about 90 ° between the two electrodes. The linearly polarized light passing through one polarizing plate has its polarization plane rotated by 90 ° by the liquid crystal molecule. After passing through the other polarizing plate, the liquid crystal shutter is in a light transmitting state. When a voltage is applied between both electrodes in this state, the molecular axes of the liquid crystal molecules change their directions perpendicular to the respective electrode surfaces, and the liquid crystal shutters are in a light shielding state.

[0006]

However, the above focal plane shutter and liquid crystal shutter have the following problems, respectively.

That is, in the focal plane shutter, the slit formed between the front curtain and the rear curtain travels just before the focal plane to expose the film surface, and the curtain speed is naturally high. Since there is a limit, it takes time for the slit to travel the entire screen in inverse proportion to the curtain speed and in proportion to the length of the screen in the curtain traveling direction. Particularly in the case of a large-medium format camera, since the curtain traveling distance is large, it takes a considerable time to complete the full exposure, and it is impossible to obtain the simultaneity of exposure over the entire screen like a lens shutter.

As a result, when photographing a subject moving at a high speed, there is a disadvantage that the image is distorted and the accurate shape of the subject cannot be reproduced. The distortion varies depending on the relationship between the traveling direction of the subject and the traveling direction of the slit of the focal plane shutter. When the two are in the same direction, the subject is compressed in the traveling direction and in the opposite direction, the subject is expanded. Further, when the traveling direction of the subject and the slit are orthogonal to each other, for example, even if the subject is a rectangle, the distortion is recorded in a parallelogram.

The front and rear curtains of the focal-plane shutter are affected by friction and inertia of the components of the focal-plane shutter, and the curtain speed tends to be low at the beginning of running and fast at the end, so the slit width is set to the screen. The unevenness of the exposure across the entire screen is prevented by making it narrower at one end side and wider at the other end side, but at high speeds, slight slit width and curtain speed errors cause uneven exposure and There is a problem that it is easy to appear.

Further, an electronic flash (hereinafter referred to as "flash") is attached to the focal plane shutter.
When tuning the
Since it is as short as 4 mS, when the flash is fired while the shutter slit is running, the part exposed by the light is only a part of the screen, and in order to evenly expose the entire screen, a longer exposure than the fully open second of the shutter is required. It is a well-known fact. Especially in medium format cameras using 120/220 film, the exposure time when the shutter is fully opened is, for example, 6 × 7c.
Since it is as long as 1/30 seconds in the case of the m-size camera and 1/60 seconds in the case of the 6 × 4.5 cm format camera, high-speed synchronized shooting such as daytime sync is impossible at all.

For this reason, the present situation is to supply an interchangeable lens with a lens shutter capable of synchronizing the flash at all speeds for high-speed synchro photography while having a focal plane shutter in the camera body. Since it is difficult to provide a synchronizing means between the shutter and the focal-plane shutter on the camera body side, it is often the case that the focal-plane shutter is set to slow speed or a valve to operate the lens shutter during the full opening time. It is not suitable for shooting moving objects etc.
There was difficulty in operability.

Since it is not profitable to prepare two types of lenses for the focal plane shutter and the lens shutter for all of the various types of interchangeable lenses, the type of lens with a lens shutter has a focal length close to that of the standard lens. It has only a relatively small diameter, and is extremely expensive in terms of price.

On the other hand, in liquid crystal shutters, liquid crystal shutter elements used for large-screen displays in recent years have become widespread, and their performance, durability, etc. have greatly improved, and the types thereof have also increased rapidly over time. However, it has not reached the range where it can be used alone as a camera shutter in place of the conventional focal-plane shutter or lens shutter in terms of light-shielding property.

The present invention has been made in view of the above points, and a combined use method of a focal plane shutter and a liquid crystal shutter, in which a liquid crystal shutter is used in combination with the focal plane shutter to solve each of the conventional problems. The purpose is to provide.

[0015]

In order to achieve the above object, the present invention has a liquid crystal shutter disposed on the photographing optical path of a camera equipped with a focal plane shutter, and the liquid crystal shutter is transparent for the full open time of the focal plane shutter. Provided is a combined use method of a focal plane shutter and a liquid crystal shutter in which a liquid crystal shutter is brought into a light state and at least a shutter front curtain and a rear curtain before and after the light curtain travel.

[0016]

According to the combined use method of the focal plane shutter and the liquid crystal shutter according to the present invention, the liquid crystal shutter is already in the light-shielded state when the front curtain starts to run by the release operation of the camera. , While the first curtain is running, the screen is kept almost shielded. When the front curtain has finished running and the shutter has been fully opened, the liquid crystal shutter is also in a state of instantaneous light transmission so that the entire screen is exposed, and then the liquid crystal shutter is again in the light-shielding state while the rear curtain is running.

Therefore, the effective exposure time is only a moment when the shutter is fully opened, and an image without distortion can be obtained even when shooting a high speed moving object. Also, if the flash is fired at the same time as the running of the first curtain, high-speed daytime synchronized shooting becomes possible.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiments of the present invention will be specifically described below with reference to the drawings. Prior to that, the principle of the present invention will be described with reference to FIG. FIG. 2 is a diagram showing the traveling states of the front curtain and the rear curtain at the full-open exposure time of the focal plane shutter. The total exposure amount of the shutter is the start edge of the screen when the front curtain starts traveling by the release operation of the camera. Exposure amount A from the beginning of opening the screen to the end of opening the screen,
It is represented by the sum of the exposure amount B when the screen is in the fully open state and the exposure amount C from when the trailing curtain starts to shield the start edge of the screen to when the rear curtain shields the rear edge of the screen.

Now, for example, in a camera of 6 × 4.5 cm format, the time required for the front curtain and the rear curtain to travel the entire screen is 16 mS, and the time for the screen to be fully opened is 2 mS.
Assuming that, the total exposure time in which a part of the screen is exposed is (16 + 2 + 16) mS (approximately 1/30
Second), effective exposure time is (16 + 2) ms (almost 1 / 60th)
Seconds).

Therefore, if a liquid crystal shutter is arranged on the photographing optical path, the liquid crystal shutter is set in a light-shielding state in an area corresponding to the exposure amounts A and C, and the liquid crystal shutter is set in a light-transmitting state in an area corresponding to the exposure amount B. Assuming that the transmission ratio of the liquid crystal shutter when light is transmitted and when light is shielded is 8, for example, the exposure amount A
And C are amounts corresponding to ⅛ in the figure, that is, the exposure amount equivalent to that of a focal-plane shutter in which the time required for the front curtain and the rear curtain to travel the entire screen is 2 mS, and the effective exposure time is (2 + 2) mS. It is equivalent to a shutter speed of (1/250 second).

According to such a method of using the liquid crystal shutter, it is not necessary to completely shield the liquid crystal shutter, and it is possible to easily prevent, for example, an overexposure during daytime synchronized photographing. However, the time from the actual exposure of the focal plane shutter to the end of the exposure is still 34 mS in the example of FIG. 2, and at a transmission ratio of about 8 the high speed moving object is seen even from the HD curve of a normal film. It is impossible to capture the still image completely.

As a solution to this problem, it is possible to use a liquid crystal having a large transmission ratio between light transmission and light shielding. However, since the liquid crystal shutters available at present have a transmission ratio of about 20 as a limit, the performance is rather stable. It is preferable to use a plurality of liquid crystal shutters having a transmission ratio of about 8 to 10 in series so that their phases are orthogonal to each other, that is, in the same state, the light from the subject passes through all and reaches the film surface. ..
That is, when two sets of liquid crystal shutters having a transmission ratio of 8 are used, the transmission ratio is 64, and when three sets are used, the number is 512, and sufficient light shielding properties can be secured. However, since the amount of transmitted light of the liquid crystal shutter is reduced to 1/2 or less even in the translucent state, it is not preferable to combine the shutters more than necessary.

FIG. 1 shows an example of a concrete structure for carrying out the above method. A camera body 1 of a single-lens reflex camera equipped with a focal plane shutter 1a immediately in front of a film surface 1b is detachably attached with a pentaprism 2 at an upper portion and a taking lens 3 at a front portion. The liquid crystal unit 11 of the liquid crystal shutter 10 is mounted on the front part of the taking lens 3, and the liquid crystal unit 11 is connected to the liquid crystal shutter control unit 12 by a signal line 13.

Further, the liquid crystal shutter control section 12 is connected to the X-contact terminal and the remote-control release terminal of the focal plane shutter 1a provided outside the camera body 1 by the X-contact signal line 14 and the remote release signal line 15 (both shown in the figure). No)) and the electronic flash 2 via the flash signal line 21.
Connect to 0. The liquid crystal shutter control unit 12 itself is provided with a release button 16 for activating the liquid crystal shutter control circuit and for releasing the camera body 1 side, and a shutter dial 17 for setting the shutter speed of the focal plane shutter.

The liquid crystal shutter 10 is shown on the assumption that it is attached and used as an adapter separately from the camera body 1, but it may be built in the camera body 1 or the taking lens 3 from the beginning. This is possible, and by doing so, usability can be further improved in terms of photometry and the like. If the liquid crystal portion 11 can be attached to and detached from the front surface of the taking lens 3 by using a filter screw or the like as in the embodiment shown in FIG. 1, the present invention can be applied to a general camera having a focal plane shutter. Can be easily applied.

In actual photographing, the aperture value of the photographing lens 3 is set based on the guide number of the flash 20 and the transmittance of the liquid crystal shutter 10 in the light transmitting state, and the brightness of the subject, the sensitivity of the film used, and the liquid crystal. An appropriate shutter speed is obtained from the transmittance of the shutter when light is transmitted, and the shutter dial 17 is set. At this time, if the conditions such as the transmission ratio of the liquid crystal shutter and the curtain speed of the focal plane shutter are set in advance, the exposure amount can be automatically corrected. The shutter dial on the camera body 1 side is set to a time slower than the fully open exposure time or a valve.

Next, the operation of the embodiment having the above structure will be described. Release button 16 of liquid crystal control unit 12
When is pressed, a release signal is sent to the camera body 1 side, and a predetermined voltage is applied between both electrodes of the liquid crystal section 11 of the liquid crystal shutter 10 to make the liquid crystal section 11 in a light-shielded state. After that, the front curtain of the focal plane shutter on the camera body 1 side starts to run, and the X contact is turned on when the front curtain has finished running on the screen.

When the X-contact signal of the camera body 1 is input to the liquid crystal shutter control section 12, the voltage applied to the liquid crystal section 11 is released, the liquid crystal section 11 becomes in a light transmitting state, and the film surface is exposed. Is started, and at the same time, the flash 20 emits light. When the predetermined exposure time is over, the liquid crystal part 11 is again applied with a predetermined voltage to be in the light-shielding state, and then the rear curtain of the focal plane shutter 1a on the camera body 1 side runs to close the shutter and to the liquid crystal part. The voltage supply is stopped and the liquid crystal portion 11 is in a light transmitting state.

The liquid crystal unit 1 is released after the voltage application to the liquid crystal unit 11 is released by turning on the X contact of the focal plane shutter.
Since there is a slight time lag until 1 becomes the translucent state, if the value is large and the opening time of the liquid crystal shutter deviates from the full opening time of the screen, the shutter front curtain is moved to the camera body 1 side at the same time. An FP contact that turns on is provided, and when the FP contact turns on, voltage application to the liquid crystal unit 11 is stopped,
The flash 20 may be made to emit light when the X contact is turned on.

Alternatively, the liquid crystal part of the liquid crystal part is made into two layers, a transparent intermediate electrode is provided in the middle part thereof, and a voltage is applied to one side of the liquid crystal part to change the liquid crystal part from the light-transmitting state to the light-shielding state, and the both sides are It is also possible to reduce the time lag by applying a voltage at the same time to change the light-shielding state to the light-transmitting state.

Unlike the mechanical shutter, the liquid crystal portion 11 of the above liquid crystal shutter does not change the shape of the opening even during operation, so that it can be installed at any position on the optical path for photographing. That is, as shown in FIG. 3, in addition to (a) the front surface of the taking lens 3 which is orthogonal to the taking lens optical axis L as shown in the embodiment of FIG. Alternatively, the rear surface, (c) the inside of the converter 4, (d) the rear of the mirror 5 of the single-lens reflex camera, and the front of the curtain surface of the focal plane shutter 1a can be considered.

In particular, when the liquid crystal part 11 is arranged at the position (d), the viewfinder surface is not affected by the liquid crystal shutter, so that the viewfinder surface can always be kept at the maximum brightness and the liquid crystal shutter is always on. Can be kept in a light-shielding state, and only when the focal-plane shutter is fully opened is in a light-transmitting state, so that the control of the liquid crystal shutter becomes extremely simple.

As described above, in a camera having a focal-plane shutter, shooting is performed using the built-in focal-plane shutter during normal shooting, and a moving object must be recorded without distortion of shape or high-speed daytime synchronized shooting. In some cases, if you use a combination of a focal-plane shutter and a liquid crystal shutter, you can perform extra operations on images that are free from subject blurring and distortion due to exposure only when the shutter is open, and are not affected by exposure when the shutter curtain is running. It is easy to obtain without the need and has excellent operability.

In the above embodiments, the case where the liquid crystal shutter is combined with the focal plane shutter has been described. However, the shutter element to be combined is not necessarily limited to the liquid crystal, and the same effect can be obtained by using a photochromic element or the like. It is possible to obtain.

[0035]

As described above, in the combined use method of the focal plane shutter and the liquid crystal shutter according to the present invention, the liquid crystal shutter is arranged on the photographing optical path of the camera having the focal plane shutter, and the full open time of the focal plane shutter is set. Only the liquid crystal shutter is in the light-transmitting state, and at least the front and rear curtains before and after that are in the light-shielding state, so simultaneous exposure can be obtained over the entire screen by an extremely simple method, and image distortion and It is possible to eliminate uneven exposure during high-speed exposure, and it is also possible to increase the speed during synchronized synchronization.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of the present invention.

FIG. 2 is a curtain travel diagram of a focal plane shutter for explaining the principle of the present invention.

FIG. 3 is an explanatory diagram showing various arrangement examples of a liquid crystal section of a liquid crystal shutter.

[Explanation of symbols]

1 Camera body 1a Focal plane shutter 2 Penta prism 3 Photographing lens 4 Converter 5 Mirror 10 Liquid crystal shutter 11 Liquid crystal part 12 Liquid crystal control part 16 Release button 17 Shutter dial 20 Electronic flash

Claims (1)

Claim: What is claimed is: 1. A liquid crystal shutter is arranged on a photographing optical path of a camera having a focal plane shutter, and the liquid crystal shutter is kept in a light-transmitting state for a full open time of the focal plane shutter, and at least shutters before and after the shutter are provided. A combined use method of a focal plane shutter and a liquid crystal shutter, characterized in that the liquid crystal shutter is set in a light blocking state when the front curtain and the rear curtain are running.