JPH02105120A - camera exposure control device - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an exposure control device for a camera equipped with a built-in flash tube with a small guide number.

[Prior Art] Conventionally, in this type of exposure control device, prior to the exposure operation, an exposure value is calculated based on the photometric output of the subject by a photometer, and the aperture and shutter speed are determined according to the calculated exposure to perform the exposure. is performing an action.

In addition, in the flash flash mode using a flash tube, the shutter speed is usually fixed, and the aperture is determined according to the exposure value calculated based on the photometry output. The camera measures the light reflected from the subject when the flash is emitted, and performs automatic light control that stops the flash when the photometry output reaches a predetermined level, and within the effective distance determined by the flash tube's guide number, only people are photographed. In addition, the background can also be properly exposed.

On the other hand, there are two ways to attach a flash tube to a camera: attaching the flash tube externally and incorporating the flash tube into the camera body.
There is one.

Generally, for external flash tubes, the guide number is 2.
On the other hand, built-in flash tubes have a built-in camera, which limits the installation space, and the effective distance is limited, such as a guide number of 15 or less. A short flash with a small amount of light emission is used.

[Problems to be Solved by the Invention] However, in such conventional exposure control devices, even if the external device with a large guide number is a flash tube,
Even if a built-in flash tube with a small guide number is used, the calculation to determine the exposure value is the same, so if the distance of the subject is long, the amount of flash light will be lower when using the built-in flash tube with a smaller guide number. There was a problem in that the overall photo was likely to be under-lit.

In particular, if you use the built-in flash tube to photograph a person beyond the effective distance in a dimly lit condition with some natural light remaining, such as in the evening, the amount of flash light will be unstable and the person will be underlit. - On the other hand, the background is properly exposed due to the addition of natural light exposure, and there is a problem in that the overall image is under-exposed for a photograph centered on a person.

This problem also applies to daylight photography, which uses the built-in flash tube to photograph people in the shade of trees during the day, and as the subject distance increases, the person becomes under-exposed, making it impossible to obtain proper exposure. There is.

The present invention was made in view of these conventional problems, and provides a camera that can obtain as appropriate exposure as possible even for subjects that exceed the effective distance of the built-in flash tube with a small guide number. The purpose of the present invention is to provide an exposure control device.

[Means for Solving the Problems] First, the present invention includes a built-in flash tube in a camera body, and when the photometric amount of light reflected from a subject due to light emission from the built-in flash tube reaches a predetermined level, the built-in flash tube is activated. Targets cameras with an automatic light control function that stops emitting light.

For such a camera, the present invention includes an exposure value calculation means that calculates an exposure value based on the photometric output of the photographic subject before the start of the exposure operation; Exposure value correction means for correcting the calculated exposure value of the exposure value calculation means to a value on the overexposure side is provided.

In addition, when exposure due to natural light is not expected so that the calculated exposure value is less than a predetermined value, when the film sensitivity is more than a predetermined value, when the shooting aperture is less than a predetermined value that is sufficiently low on the open side, and/or when the subject distance is set as a built-in value. Exposure compensation is not performed when the subject is within the effective distance determined by the guide number of the flash tube.

[Function] In the exposure control device of the present invention having such a configuration, during flash photography using the built-in flash tube, the exposure value calculated from the subject photometry result before the start of the exposure operation is used for exposure. The exposure operation will now be performed by correcting the value to the over side.

For example, the shutter speed for flash photography is 1/125S.
If the exposure value is fixed at eC and the exposure value calculated based on the photometric output is EVO=15, conventionally the exposure value E
The aperture value that satisfies VO=15, for example, F=16, was determined, but in the present invention, the calculated exposure value EVo=
For example, by subtracting a predetermined value α=2 from 15, the exposure value EV=
As a result, the aperture value changes from F=16 to F=
8 and changed to the open side.

Therefore, even if the built-in flash tube does not have enough light for the subject, for example, the subject as a whole, including the person as the main subject, will be extra exposed by natural light in addition to the flash exposure, and the front of the subject will be overexposed. However, it is possible to obtain proper exposure for the main subject, such as a person, and it is possible to reliably prevent the conventional failure of copying, which tends to be underexposed.

[Example] FIG. 1 is a block diagram showing one embodiment of the present invention.

In FIG. 1, reference numeral 1 denotes a control circuit composed of a CPLI or the like, and the control circuit 1 controls various circuit sections and devices for performing an exposure operation. For the control circuit 1, there are a photometry circuit 2, a film sensitivity reading circuit 4, a lens information output circuit 5, an exposure value calculation circuit 6, a flash tube type output circuit 7, an exposure value correction circuit 8, a shutter control device 9, and an aperture control device. 10, TT and automatic dimming circuit 12 are connected.

First, the photometry circuit 2 outputs photometry information based on the light reception output of subject light incident on the photometry light receiving element 3. A film sensitivity reading circuit 4 reads the DX code provided on the film cartridge and outputs film sensitivity information. The lens information output circuit 5 outputs the aperture F of the i-shadow lens installed in the camera.
Outputs lens information such as value and focal length. The exposure value calculation circuit 6 calculates and outputs an exposure value based on the photometry information from the photometry circuit 2 obtained via the control circuit 1 and the lens information from the lens information output circuit 5.

The flash tube type output circuit 7 determines whether or not it is a strobe photography mode using a built-in flash tube and outputs the result. The photographing mode using the built-in flash tube is set manually by the photographer, such as by popping up the built-in flash tube, or by setting an automatic strobe mode when the brightness of the subject falls below a predetermined value.

The exposure value correction circuit 8 adjusts the exposure value calculated by the exposure value calculation circuit 6 to a value on the overexposure side when the flash tube type output circuit 7 outputs that the mode is a shooting mode using the built-in flash tube. A correction calculation is performed and a corrected exposure value is output. Of course, when the flash tube type output circuit 7 determines that the type is not a built-in flash tube, the exposure value correction circuit 8 does not work, and the exposure value calculated by the exposure value calculation circuit 6 is used as is.

When the flash tube type output circuit 7 determines that the built-in flash tube is not in the shooting mode, the shutter control device 9 and the aperture control device 10 adjust the shutter speed and aperture based on the exposure value calculated by the exposure value calculation circuit 6. control,
On the other hand, when the flash tube type output circuit 7 determines that the built-in flash tube is used, the shutter speed and aperture are controlled to be based on the corrected exposure value calculated by the exposure value correction circuit 8.

For the TTL automatic light control circuit 12, there is a light emitting circuit 11 that controls the built-in flash tube to emit light, and a TTL that receives the object light that has passed through the photographic lens from the object light by emitting light from the built-in flash tube.
A light receiving element 13 is provided.

That is, the light emitting circuit 11 causes the built-in flash tube to start emitting light when an unillustrated X contact closes in response to a release signal.゛When the built-in flash tube starts emitting light, T
The amount of reflected light from the subject that is incident on the TL light receiving element 13 is determined by the TTL automatic light control circuit 12, and when the amount of reflected light reaches a preset level, a light emission stop signal is output to the light emitting circuit 11. Stops the built-in flash tube from emitting light.

Next, exposure control in the embodiment shown in FIG. 1 will be explained with reference to the flowchart shown in FIG.

The photographer presses the shutter release button shown halfway
Then, the half-press switch is turned on, and power is supplied to each circuit section including the control circuit 1 shown in FIG.
is activated, and photometric information is output to the control circuit 1 based on the light receiving output of the object light received by the light receiving element 3 at that time. At the same time, the film sensitivity reading circuit 4 and lens information output circuit 5 output film sensitivity information and lens information, and as a result, the control circuit 1 outputs photometry information, film sensitivity information, and lens information to the exposure value calculation circuit 6, and The value calculation circuit 6 calculates the exposure value EVO as shown in step S1 in FIG.

Subsequently, in step S2, it is determined whether or not photography is to be performed using the built-in flash tube.

At this time, if the photographer has set the shooting mode using the built-in flash tube by pop-up operation or manual setting operation of the built-in flash tube, the pattern using the built-in flash tube is determined in step S2. Proceed to step S3,
The exposure value EVo calculated in step S1 is corrected.

That is, in this embodiment, the exposure value correction circuit 8 calculates the corrected exposure value EV as follows: EV=EVO-α. As a result, there is a relationship of EV<EVO between the exposure value EVO calculated in step S1 and the corrected exposure value EV calculated in step S3, and from this correction calculation, the calculated exposure value EVO is on the overexposed side. It will be corrected to the value EV.

Subsequently, in step S4, the shutter speed and aperture are set in the shutter control circuit 9 and the aperture control device 10 based on the corrected exposure value EV calculated in step S3, and the release switch is turned on by pressing the release button deeply. Exposure operation accompanied by flash emission from the built-in flash tube begins to take place.

On the other hand, if it is determined in step S2 that the shooting is not using the built-in flash tube, the process proceeds to step 85, where the calculated exposure value EVo is used as the corrected exposure value EV, that is, the process proceeds to step S4 without performing exposure compensation. The shutter speed and aperture are controlled, and the exposure operation is performed after waiting for a release signal accompanying a deep press operation of the release button.

FIG. 3 is an explanatory diagram showing three exposure value correction characteristics as a specific example of the exposure correction process shown in step S3 of FIG.

The characteristic diagrams in FIG. 3 (a>(b) and (c) show the calculated exposure value EVO on the horizontal axis and the corrected exposure value EV on the vertical axis. In either case, the calculated exposure value EVO is EVO= Exposure correction calculation having the characteristics shown in the figure is performed in the range of 8 or more, that is, when the built-in flash tube is used at nine shadows in a brightness higher than the dark state in the evening.

First, in Fig. 3(a), when shooting without using the built-in flash tube, the calculated exposure value EVO is used as the corrected exposure value EV as shown by the broken line, but when the built-in flash tube is used,
In shadows, if EVo=8 or higher, the corrected exposure value EV that determines the actual shutter speed and aperture is EV=8.
to be fixed.

Fig. 3(b) shows a correction where the corrected exposure value EV is set to EV=EVo-α when the calculated exposure value EVO=8 or more, and is basically the same as the exposure correction shown in step S3 of Fig. 2. become.

Furthermore, in FIG. 3, the corrected exposure value EV is calculated so that it has a predetermined reduction rate when the calculated exposure value EVO=8 or more.

No matter which of the three exposure value correction characteristics shown in Fig. 3 is used, the calculated exposure value EVo will be corrected to a value on the overexposure side when using the built-in flash tube @ in the shadow. Become.

Next, the effect of the exposure value correction during photographing using the flash tube of the present invention will be explained using the exposure value correction characteristic shown in FIG. 3(a) as an example.

First, when taking pictures using an external flash tube with a large guide number and when using the built-in flash tube of the present invention with a small guide number, exposure value correction according to the characteristics shown in Figure 3 (a) is required. The following table shows the photographic results without and with exposure value correction.

In addition, in this table, the main subject is a person, and the main subject is within the effective distance of the external flash tube with a large guide number, but the internal flash tube with a small guide number is within the effective distance. As an example, the case where there is no distance is taken as an example, and the brightness of the subject is taken at the time of 900, when the calculated exposure value is EVO=8 or more, or during daylight photography when photographing a person in the shade of a tree.

First, when exposure value correction is not performed, as shown in the upper part of the table, when photographing with an external flash tube with a large guide number, proper exposure can be obtained for both the person and the background. On the other hand, in the case of shadows caused by the use of a built-in flash tube with a small guide number and no person within the effective distance,
The background will be properly exposed, but the person will be underexposed due to insufficient flash output from the built-in flash tube.

Next, when the calculated exposure value EVo = 8 or more is corrected to the overexposure side by fixing the exposure value to EV = 8 as shown in Figure 3 (a), the external device with a large guide number is used for shooting with a flash tube. In this case, the person is properly exposed, but the background is overexposed because it is exposed by natural light in addition to the reflected light a from the flash light emission.

This point is the same when using a built-in flash tube with a small guide number; the exposure value is corrected to the over side, and the background becomes overexposed due to the additional exposure due to natural light; For a person who was previously underexposed, even if the amount of flash light is insufficient, proper exposure can be obtained by adding exposure from natural light.

As a result, there is no need for the exposure value correction of the present invention for external flash tubes with large guide numbers, but when shooting with built-in flash tubes with small guide numbers,
By performing exposure correction when photographing a main subject, for example, a person, the background will be overexposed, but the person itself can be properly exposed, and as a result, the photograph intended by the photographer can be obtained.

FIG. 4 is a flowchart showing another embodiment of the present invention. In this embodiment, even if a built-in flash tube with a small guide number is used, if a high-sensitivity film is used, underexposure will occur due to insufficient light intensity. Because it can compensate for
It is characterized by adding film sensitivity conditions to the exposure compensation judgment when taking pictures using the built-in flash tube.

That is, in FIG. 4, the exposure value EVo is calculated in step S1, and when it is determined in step S2 that the built-in flash tube is used for photography, the process proceeds to step S4, where the film sensitivity AsΔ is determined. =400 or more, do not perform exposure compensation in step S4 and proceed to step $6.
The process proceeds to Step S4, where the corrected exposure value EV is directly used as the calculated exposure value EVo, and only when a film sensitivity smaller than film sensitivity ASA=400 is detected in Step S3.
Perform exposure compensation.

FIG. 5 is a flowchart showing an embodiment of the present invention. In this embodiment, when the aperture during shooting is small, sufficient exposure can be obtained even with the built-in flash tube with a small guide number. Therefore, the present invention is characterized in that a judgment condition based on the photographing aperture is added to the exposure correction.

That is, in FIG. 5, the exposure value EVO is calculated in step S1, and if it is determined in step S2 that the photograph is taken using the built-in flash tube, the process proceeds to step S3, where the photographing aperture f is larger than f=2, for example. Determine whether or not. When the photographic aperture is smaller than f=2, that is, when it is on the open side of f=2, sufficient exposure can be obtained, so step S4 is performed.
The process proceeds to step S6 without performing exposure correction, and the aperture and shutter speed are determined by using the calculated exposure 1-direction EVO as the corrected exposure value EV.

On the other hand, if the photographing aperture is larger than f=2 in step S3, the process advances to step S4 and exposure compensation is performed.

Furthermore, FIG. 6 is a flowchart showing another embodiment of the present invention, and this embodiment is characterized in that the subject distance is added to the judgment of exposure compensation when shooting using the built-in flash tube. do. In other words, since the distance at which flash photography can be effectively performed is determined based on the guide number of the built-in flash tube, it is determined whether the subject distance is within the effective distance of the built-in flash tube, and if it is within the effective distance, the exposure is It is characterized in that no correction is performed, but on the other hand, if the distance exceeds the effective distance, exposure correction is performed.

That is, in FIG. 6, the exposure value EVo is calculated in step S1, and when it is determined in step S2 that the photograph is taken using the built-in flash tube, the process proceeds to step S3, where the exposure value EVo is calculated based on the subject distance and the guide number of the built-in flash tube. Determined effective distance L
Compare with O. If the subject distance is shorter than the effective distance LO, a sufficient amount of light reflected from the subject can be obtained by the flash of the built-in flash tube, so the process proceeds to step S6 and the calculated exposure value EVO is directly used as the corrected exposure value without performing exposure compensation. Performs aperture and shutter control.

On the other hand, if the subject distance is longer than the effective distance LO of the built-in flash tube in step S3, the process proceeds to step S4 where exposure compensation is performed and the aperture and shutter speed are controlled in accordance with the corrected exposure value.

It goes without saying that other embodiments of the present invention may be a combination of FIGS. 4, 5, and 6.

Furthermore, the exposure value correction of the present invention is not limited to the three types shown in FIG. Alternatively, the corrected exposure value EV may be determined based on the calculated exposure value EVo as a combination thereof.

Furthermore, when using the built-in flash tube for decoy photography, the shutter speed is usually fixed according to the camera shake limit and only aperture control is performed to obtain the aperture according to the corrected exposure value, but if the shutter speed is longer than the camera shake limit, Of course, when is set, both the shutter speed and the aperture may be controlled based on the corrected exposure value.

Furthermore, when the exposure compensation of the present invention is performed, the background side will be overexposed, so if the shooting aperture is set to f<2.8, for example,
It is also possible to set a limit such that the brightness is high.

Furthermore, although the above embodiments take as an example the control of the amount of flash light emitted by TTL automatic light control, it goes without saying that an external automatic light control method may be used.

[Effects of the Invention] As explained above, according to the present invention, even if the built-in flash tube with a small guide number is used to fully fire the built-in flash tube at the time of shadowing, the light reflected from the subject due to the flash light emission is insufficient. Even if the copying conditions result in underexposure, by correcting the calculated exposure value to an overexposure value, you can obtain more exposure with natural light.
When photographing people at dusk or during daylight copying of a person in the shade of a tree during the day, it ensures that the copying fails due to the person as the main subject being undershot due to insufficient flash light intensity. can be prevented.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention; FIG. 2 is a flowchart showing exposure control according to the embodiment of FIG. 1; FIG. 3 is a characteristic diagram of exposure compensation according to the present invention; 5.6
The figure is a flowchart showing exposure control according to another embodiment of the present invention. 1: Control circuit 2: Photometry circuit 3: Photometry light receiving element 4: Film sensitivity reading circuit 5: Lens information output circuit 6: Exposure value calculation circuit 7: Flash tube type output circuit 8: Exposure value correction circuit 9: Shutter control device 10: Aperture control device 11: Light emitting circuit 12: TTL automatic light control circuit 13: TTL light receiving element

Claims (2)

[Claims] (1) A camera that has a flash tube built into the camera body and performs automatic light adjustment control that stops the light emission of the built-in flash tube when the photometric amount of light reflected from the subject due to light emission between the built-in flashes reaches a predetermined level. an exposure value calculation means for calculating an exposure value based on the photometric output of the photographic subject before the start of the exposure operation; and when a flash photography mode using the built-in flash tube is set;
An exposure control device for a camera, comprising: exposure value correction means for correcting the calculated exposure value of the exposure value calculation means to a value on the overexposure side. (2) The exposure value correction means is configured to operate when the calculated exposure value is below a predetermined value, when the film sensitivity is above a predetermined value, when the shooting aperture is below a predetermined value, and/or when the subject distance is 2. The camera exposure control device according to claim 1, wherein the calculated exposure value is not corrected when the calculated exposure value is within the distance.