JPH07168241A - Photometry device for camera - Google Patents

Abstract

PURPOSE:To enable photometry without overflowing when an ultra-high luminance object is in a field. CONSTITUTION:The photometry device 30a of a camera is provided with a photometry circuit 12 executing the photometry of the field by a photometric element and outputting a signal corresponding to the luminance of the field, a storage time setting part 15 setting the charge storage time of the photometric element in the photometry circuit 12, an F-number setting part 14 deciding whether an exposure is measured at a full-aperture or a stopped-aperture based on the output of the storage time setting part 15, etc., and an F-number in the exposure measurement at the stopped-aperture, to output this information to a diaphragm 10, etc. When the field is bright, first, the storage time is minimized and only at the time of exceeding the upper limit of the photometry regardless of the fact that the storage time is minimized, the diaphragm 10 is shut. When the field is dark, first, the diaphragm 10 is opened and then, the storage time is made longer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photometric device for a camera which measures the brightness of a field by using a part of a light beam passing through a taking lens.

[0002]

2. Description of the Related Art As a first example of a conventional photometric device for a camera of this type, one disclosed in Japanese Patent Application Laid-Open No. 4-251230 filed by the applicant of the present application is known. The photometric device of this camera divides the luminous flux incident from the taking lens by a plurality of photometric elements (light receiving elements) such as CCDs to obtain proper exposure. As a second example, there is known a photometric device that performs photometry while narrowing down the taking lens. FIG. 10 is a perspective view showing a schematic configuration of an optical system 20 of a camera to which the photometric device of the second example is applied. The optical system 20 of this camera is mainly used in a video camera or the like. The light flux incident from the taking lens 21 passes through the diaphragm 22 and is received by the image pickup device 23 such as CCD, whereby an image of the field is shot. Further, the diaphragm 22 is made of a disk-shaped body having a plurality of openings each having a different size, and the optimum opening is arranged on the optical axis of the lens 21 according to the brightness of the field. Shooting is done.

[0003]

However, the above-described conventional photometric device for a camera has the following problems. In the photometric device of the camera of the first example, the light field incident from the photographing lens is guided to the eyepiece lens to observe the field of view, and the photometric element receives the light beam to perform photometry. The photographic lens aperture is open so that people can easily observe the scene. Therefore, the open metering is performed in which the metering is performed with the diaphragm open. However, in such open metering, when an ultra-high brightness object such as the sun enters the field, the metering element may exceed the metering upper limit (so-called overflow), making metering impossible. In particular, when the photometric element is a charge storage type element, there is a high possibility of overflow.

FIG. 11 is a diagram for explaining the photometric output when the sun is present in the object field in the case where the charge storage type photometric element is used in the first example. When the sun exists in the object field as shown in (a) in the figure, the photometric element in that area exceeds the upper limit of photometry, and as shown in (b) in the figure, the metering in the horizontal area is performed. The electric charge overflows into the element, and an output is obtained as if a long high-intensity object is present horizontally. This phenomenon occurs mainly due to overflow of the register for charge transfer. When electric charge is further supplied to the photometric element, so-called blooming phenomenon occurs in which the electric charge overflows to the photometric element in the region around the sun as shown in FIG. As described above, when a high-intensity object is present in the object scene, electric charge overflows into the surrounding photometric elements, and (b) or (c) in the figure.
The metering output will be as shown in, and accurate metering will not be possible.

In the photometric device of the second example, the diaphragm 22
Since the amount of light incident on the image pickup device 23 is adjusted by the above, there is little possibility of overflow even if the image pickup device 23 is a charge storage type device. However, when a viewfinder that is optically observable is attached and the field of view is observed from this viewfinder, the aperture changes according to the brightness of the field of view, making it difficult for the photographer to observe the field of view. It was impossible to apply it to an SLR camera.

The present invention has been made to solve the above-mentioned problems, and even when an ultra-high brightness object such as the sun exists in the object field, photometry can be performed without overflow. The purpose is to be able to.

[0007]

In order to achieve the above-mentioned object, the first solution of the photometric device for a camera according to the present invention is to provide an object field by optically guiding the light flux passing through the taking lens. In a photometric device of a camera, which has an observable optical system and uses a part of a light flux that has passed through the taking lens to measure the brightness of the field, a photometric element for accumulating electric charges generated by incident light is provided. The photometric device has a photometric device and a light intensity control device for controlling the light intensity of the light beam incident on the photometric device. The photometric device has a plurality of divided photometric regions, and can output for each photometric region. The light amount control means controls the light amount according to the number of the photometric regions where the output is saturated.

A second solving means is the same as the first solving means, wherein the light amount control means is a first light metering setting mode in which the light flux is not dimmed and is incident on the photometric element, and the light flux is dimmed. And a second photometry setting mode in which the light is incident on the photometry element.

A third solving means is the second solving means, wherein the first photometric setting mode is a mode in which an aperture of the photographing lens is opened, and the second photometric setting mode is the photographing lens. The mode is a mode in which the light flux is dimmed by narrowing the diaphragm.

[0010]

In the first solving means, the light quantity control means is
The amount of light incident on the photometric element is controlled according to the number of photometric regions where the output is saturated, and the photometric element measures the object field with the incident light whose light amount is controlled. In the second solving means, the first photometry setting mode and the second photometry setting mode are used together to perform photometry. In the third solution, the aperture of the taking lens controls the amount of light incident on the photometric element. Therefore, it is possible to control the light amount of the light flux incident from the taking lens so that the photometric element does not overflow, and it is possible to expand the photometric dynamic range as compared with the conventional open photometric method. Furthermore, in the third solving means, without newly providing a special mechanism for controlling the amount of light incident on the photometric element,
The amount of light can be controlled.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a photometric device for a camera according to the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a schematic configuration of an optical system of a suitable single-lens reflex camera 30 (hereinafter, simply referred to as “camera 30”) using a photometric device for a camera according to the present invention. FIG. 2 is a block diagram showing an electrical configuration of an embodiment of a photometric device for a camera according to the present invention.

In the camera 30 shown in FIG. 1, the taking lens 1
The light flux incident from the laser beam passes through the quick return mirror 2, the diffusion screen 3, the condenser lens 4, the penta prism 5, and the eyepiece lens 6 and reaches the eye of the photographer. On the other hand, a part of the light flux diffused by the diffusing screen 3 passes through the condenser lens 4, the penta prism 5, the photometric prism 7, and the photometric lens 8 to reach the photometric element 9. The exposure amount on the film surface is adjusted by the diaphragm 10 and the shutter 11.

In FIG. 2, the photometric device 30a of the camera is shown.
Is a photometry circuit 12, an A / D conversion circuit 13, an RO in the lens
An M18 and a microprocessor 19 are provided. Further, the microprocessor 19 includes an aperture setting unit 14, a storage time setting unit 15, a brightness calculation unit 16, and an exposure calculation unit 17.

The photometric circuit 12 is a circuit for photometrically measuring the object field by the photometric element 9 and outputting a signal corresponding to the brightness thereof. The A / D conversion circuit 13 is a circuit that converts the signal from the photometric circuit 12 into a digital value that can be recognized by a computer. The accumulation time setting unit 15 sets the charge accumulation time of the photometric element in the photometric circuit 12. Aperture setting section 1
Reference numeral 4 determines based on the outputs of the accumulation time setting unit 15 and the A / D conversion circuit 13 whether open metering or narrowing metering is to be performed. The information is output to 10.
The in-lens ROM 18 stores information about the photographing lens such as a focal length, an open aperture value, an exit pupil position, and vignetting of ambient light, and outputs these values to the brightness calculation unit 16. The brightness calculation unit 16 includes the A / D conversion circuit 13, the accumulation time setting unit 15, the aperture setting unit 14, and the in-lens RO.
The brightness value is calculated for each of the plurality of photometric regions based on the output from M18. Exposure calculator 17
Is for calculating an appropriate exposure value based on the brightness value calculated by the brightness calculation unit 16. Here, the aperture setting unit 1
The functions of 4, the accumulation time setting unit 15, the brightness calculation unit 16, and the exposure calculation unit 17 can be realized by software in the microprocessor 19 installed in the camera 30.

FIG. 3 is a diagram in which the division state of the photometric element 9 is compared with the field of view. The photometric element 9 is, for example, CC
A light-receiving element of the charge storage type such as D is used, and photometry is performed by dividing almost the entire field of view into 240 regions of 20 in the horizontal direction and 12 in the vertical direction. Here, the lower left corner is (1,1) and the upper right corner is (20,12) as the address indicating the area.

4 to 7 are flow charts for explaining the program in the microprocessor 19. When the power of the camera is turned on by half-pressing the shutter button (not shown), the main algorithm of FIG. 4 is activated. First, in step 101 of FIG. 4, the charge accumulation time t of the photometric element 9 is set by the charge accumulation time setting unit 15. The accumulation time t is set based on the subroutine flowchart (described later) shown in FIG. Next, in step 102, the aperture setting unit 14 sets the aperture. The aperture setting is performed based on the subroutine flowchart (described later) shown in FIG. next,
In step 103, the photometric element 9 performs photometry of the field based on the accumulation time t set in step 101, and in the next step 104, the brightness value is calculated for each photometric region. This brightness value is calculated by the following equation (Equation 1). (Equation 1) BV (i, j) = log {V (i, j) × k
(F, i, j) / t} / log2 + F Here, BV (i, j) is the luminance value of the address (i, j) shown in FIG. V (i, j) is the A / D converted value of the photometric output at the address (i, j). k (F, i, j) is
It is a photometric correction coefficient for each address, and is determined in advance for each lens type by using the number F of apertures and the addresses i and j of the photometric area as parameters. t is the accumulation time, and F is the number of apertures of the taking lens at the time of photometry. Further, the reason that the luminance value is divided by log2 is that the luminance value is represented by a logarithm with a base of 2.

Next, at step 105, the proper exposure is calculated by a well-known algorithm, and then at step 106, it is judged if the release button (not shown) is fully pressed. In step 106, when the release button is fully pressed, the process proceeds to step 107, and the exposure control is performed based on the proper exposure value. If the release button is not fully pressed in step 106, the process proceeds to step 108. Step 10
At 8, it is determined whether or not the half-press timer in the camera 30 has expired. If the timer has expired, the program is terminated as it is. If the timer has not expired, the process returns to step 101 and the same processing is continued.

FIG. 5 is a flowchart showing an algorithm for setting the accumulation time t by the accumulation time setting unit 15. This algorithm is called and executed by executing step 101 (FIG. 4) of the main algorithm. First, in step 201, it is determined whether or not this algorithm has been executed for the first time, that is, whether or not this is the first photometry after the power is turned on. If it is the first photometry, the process proceeds to step 202, and since the previous photometry data cannot be set, the next accumulation time t cannot be set using the previous photometry data.
Is set to a standard value of 1 mS.

Here, the relationship between the output voltage V of the photometric element 9, the sensitivity S, the illuminance L on the photometric element 9 and the storage time t is as shown in the following equation (Equation 2). (Equation 2) V = S × L × t The standard sensitivity of the photometric element 9 is about 10 V / lx · S, and the saturation voltage and the noise level are 2 V and 16 mV, respectively. Therefore, according to (Equation 2), the photometric range is about 1.6L.
It becomes x-200Lx. When this is converted into a BV value, it is about 2.3 BV to about 9.3 BV, which means that it almost covers the brightness range outdoors during the daytime. Here, the noise level is the total value of the voltages generated by the light receiving element itself, the photometric circuit, etc., and is the lower limit level of photometry when the photometric output falls below this level and is not able to obtain an accurate photometric value due to noise. .

When it is determined in step 201 that the photometry is not the first photometry, that is, the photometry is the second or subsequent photometry, the process proceeds to step 203, and the previous photometry data remains in the memory in the microprocessor 19. The next accumulation time t is set with reference to the photometric data. In step 203, it is judged whether or not the number F of stop stages of the photographing lens is 0, that is, whether or not the diaphragm 10 is in the open state. If F = 0 is not satisfied here, the routine proceeds to step 204, where the next accumulation time t is set to the minimum accumulation time of 10 μS. This is because only if the upper limit of photometry is exceeded even if the accumulation time t is minimized, the aperture 1
This is because 0 is narrowed down. That is, when the field gradually becomes brighter, the accumulation time is first minimized, and then the diaphragm 10 of the lens is narrowed down. When the field becomes darker, the diaphragm 1 is stopped first.
0 is released and then the accumulation time becomes longer.

When F = 0 in step 203,
The process proceeds to step 205 and the average value AD of the previous photometric data
The mean is calculated. Next, in step 206, A
It is determined whether Dmean is less than 16 mV, that is, less than the noise level. When ADmean is less than 16 mV, the routine proceeds to step 207, where the next accumulation time t is given a value 128 times the previous accumulation time t as shown in the following equation (Equation 3). (Equation 3) t = t × 128 By setting the next accumulation time t in this way,
The subject that was just around the noise level in the previous photometry will enter the photometric range in the next photometry.

In step 206, ADmean is 1
If it is not less than 6 mV, proceed to step 208 and set to A
It is determined whether Dmean is 2 V or higher, that is, the saturation level or higher. When ADmean is 2 V or more, the routine proceeds to step 209, where the next accumulation time t is given a value that is 1/128 of the previous accumulation time t as shown in the following equation (Equation 4). (Equation 4) t = t / 128 By setting the next accumulation time t in this way,
The subject that was just around the saturation level in the previous photometry will enter the photometric range in the next photometry.

In step 208, ADmean is 2
When it is not V or more, the routine proceeds to step 210, where the brightness distribution in the field is most efficiently within the photometric range at the next photometry, that is, ADmean is in the vicinity of about 180 mV. The following formula (Equation 5)
Then, the next accumulation time t is calculated. (Equation 5) t = t × 180 / ADmean If the luminance distribution state of the object field does not change compared to the previous time of photometry, the accumulation time t obtained by (Equation 5) is used. When the next metering is performed, the center value of the metering data is the center of the logarithmic value of the metering dynamic range 1
Since it is 80 mV and the photometric dynamic range can be maximized, efficiency is good.

Next, the routine proceeds to step 211, where it is judged if the next accumulation time t is shorter than the minimum accumulation time of 10 μS. If it is shorter, the routine proceeds to step 212 where the accumulation time t is set to 10 μS and accumulation is performed. Time t is 10μ
When it is S or more, the process proceeds to step 213. In step 213, it is determined whether or not the accumulation time t is longer than 100 mS, and when it is longer, the routine proceeds to step 214, where the accumulation time t is set to 100 mS. With the above, the flow of step 101 in FIG. 4 ends, and the process proceeds to step 102 in FIG.

FIG. 6 is a flowchart showing an algorithm for setting the aperture by the aperture setting unit 14. This algorithm is called and executed by executing step 102 (FIG. 4) of the main algorithm. First, in step 301, it is determined whether or not the present algorithm has been executed for the first time. If it is the first time, the process proceeds to step 302, and since the previous photometric data does not remain, it is not possible to set the aperture reduction number using the previous photometric data. Therefore, F = 0, that is, the aperture 10 is set to open. To be done.

When it is determined in step 201 that the photometry is not the first photometry, that is, the photometry is the second or subsequent photometry, the previous photometry data remains in the memory in the microprocessor 19. The diaphragm 10 is set. Therefore, first step 3
In step 03, it is determined whether or not the accumulation time t at the previous photometry is the shortest accumulation time tmin (= 10 μS). When the accumulation time t is not tmin, the routine proceeds to step 302, where F = 0, that is, the aperture 10 is set to open.
When the accumulation time t is tmin in step 303, the process proceeds to step 304, and the number of saturated regions (the number of regions where the previous photometric output was 2 V or more) Nov is calculated from the previous photometric output. .

Next, in step 305, Nov = 0
Is determined. When Nov = 0, the routine proceeds to step 306, where it is judged if F = 0. F =
When it is 0, the aperture 10 for the next time may be open, so
The process proceeds to step 312 without changing the number of narrowing steps.

If F = 0 is not found in step 306,
Proceeding to step 307, it is determined whether ADmean is smaller than 16 mV. When ADmean is smaller than 16 mV, the process proceeds to step 308, and the aperture 10 is overly narrowed, and the photometric output is small. Therefore, the aperture 10 is opened one step in the next photometry, and the process proceeds to step 312. When ADmean is 16 mV or more in step 307, the process proceeds to step 312 without changing the number of narrowing stages.

When Nov = 0 is not satisfied at step 305, the routine proceeds to step 309, where it is judged if there are less than 40 Novs. When the number of Novs is less than 40, the process proceeds to step 310, and the diaphragm 10 is set in the direction of narrowing by 0.5 steps. When the number of Novs is 40 or more, the process proceeds to step 311 and the diaphragm 10 is set in the direction of narrowing by one step.

Next, the routine proceeds to step 312, where it is judged if F is smaller than 0. If it is smaller than 0, the aperture 10 cannot be opened beyond the open state, so the routine proceeds to step 313 and F = 0, That is, the diaphragm 10 is set to open. Further, when F is 0 or more in step 312, the process proceeds to step 314, and it is determined whether or not F is larger than the maximum narrowing stage number Fmax. F is Fmax
If it is larger, the process proceeds to step 315, and the aperture 10
Cannot be narrowed down to more than Fmax, so F = F
set to max. Then, in step 316, the aperture 10 is controlled to the set F. With the above, the flow of step 102 of FIG. 4 is completed, and step 103 of FIG.
Proceed to.

FIG. 7 is a flow chart showing the main part of the second embodiment of the aperture setting shown in FIG. The flowchart shown in FIG. 7 includes steps 309 to 31 in FIG.
It corresponds to 1. That is, step 30 in FIG.
When Nov is not 0 in step 5, the process proceeds to step 401,
It is determined whether the number of Novs is less than 20, and when the number of Novs is less than 20, the process proceeds to step 402, and the number of narrowing stages F is narrowed down by 0.5. Similarly, step 40
3, 405, 407, 409, and 411, the number range of Nov is determined, and steps 404 and 40 are performed so that the diaphragms are suitable for photometry according to the number range of Nov.
6, 408, 410, 412, the narrowing down step number F is narrowed down by a predetermined step number. By doing so, it is possible to set a more appropriate number of narrowing stages F. Further, even with photometry after overflow, there is a high probability that it will be successful once.

Next, the aperture 10 is calculated by the above-mentioned algorithm.
The case where is set will be described with reference to FIG. When a high-intensity object such as the sun exists in the object scene, the object scene observed from the viewfinder becomes slightly dark as a whole as shown in FIG. 8A, but at the same time, the sun also becomes dark. Further, the photometric element 9 does not cause an overflow or blooming phenomenon, can obtain a photometric output as shown in FIG. 8B, and can properly perform photometry on the object field. Note that when there is no high-luminance object such as the sun in the field, photometry is performed with the diaphragm 10 open, and therefore the field observed from the viewfinder does not become dark.

Although one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment,
Various modifications are possible without departing from the spirit of the invention. For example, the unit of the number of aperture steps F varies depending on the aperture correction capability of the camera to which this photometric device is applied, and is not limited to the embodiment of the present invention. Further, the number range of Novs for setting the number of narrowing steps F differs depending on the number of photometric regions of the photometric element 9 and the like, and is not limited to the embodiment of the present invention.

Further, in the embodiment, the diaphragm 1 of the taking lens 1
Although the amount of light incident on the photometric element 9 is controlled by using 0, it is also possible to use a neutral density filter 10a including a plurality of light transmissive bodies having different light transmissivities as shown in FIG. 9, for example. The neutral density filter 10a is arranged between the photometric prism 7 and the photometric lens 8 in FIG. 1 so that light passes through the neutral density filter 10a and enters the photometric element 9, and enters the photometric element 9. The amount of light to be emitted may be controlled. In this way, the field of view can be observed from the viewfinder with the diaphragm 10 always open.

[0035]

According to the photometric device for a camera of the present invention, when a high-luminance object is present in the object field, the light amount of the luminous flux incident from the taking lens is controlled so that the photometric element does not overflow. Accurate photometry is possible.
As a result, as compared with the conventional open metering system, it is possible to measure even higher brightness, and it is possible to expand the dynamic metering range. Further, according to claim 3, the light amount can be controlled without newly providing a special mechanism or the like for controlling the light amount incident on the photometric element, and the camera of the present invention can be provided without particularly increasing the cost. It is possible to provide the photometric device.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration of an optical system of a single-lens reflex camera 30, which is suitable for using a photometric device for a camera according to the present invention.

FIG. 2 is a block diagram showing an electrical configuration of an embodiment of a photometric device for a camera according to the present invention.

FIG. 3 is a diagram in which the division state of the photometric element 9 is compared with the field of view.

FIG. 4 is a flowchart illustrating a program in the microprocessor 19.

5 is a flowchart showing a flow of setting a storage time t by a storage time setting unit 15. FIG.

FIG. 6 is a flowchart showing the flow of aperture setting by the aperture setting unit.

FIG. 7 is a flowchart showing a main part of a second embodiment of aperture setting shown in FIG.

FIG. 8 is a diagram illustrating photometric output when the sun is present in the object field in the present invention.

FIG. 9 is a diagram showing an embodiment of a neutral density filter of a photometric device for a camera according to the present invention.

FIG. 10 is a perspective view showing a schematic configuration of an optical system 20 of a camera to which a conventional photometric device of a second example is applied.

FIG. 11 is a diagram illustrating a photometric output when the sun is present in the object field in the first conventional example.

[Explanation of symbols]

 1 Photographic lens 2 Quick return mirror 3 Diffusing screen 4 Condenser lens 5 Penta prism 6 Eyepiece lens 7 Photometric prism 8 Photometric lens 9 Photometric element 10 Aperture 10a Dimming filter 11 Shutter 12 Photometric circuit 13 A / D conversion circuit 14 Aperture setting Part 15 Storage time setting part 16 Luminance calculation part 17 Exposure calculation part 18 ROM in lens 19 Microprocessor 30 Single-lens reflex camera 30a Photometric device

Claims (3)

[Claims] 1. An optical system capable of observing an object scene by optically guiding a light flux that has passed through a taking lens, and using a part of the light flux that has passed through the taking lens, the brightness of the object scene. In a photometric device for a camera that measures light intensity, the photometric device includes a photometric device that has a photometric device that accumulates charges generated by incident light, and a light amount control device that controls the light amount of a light beam that enters the photometric device. , Has a plurality of divided photometric regions, and is capable of outputting for each photometric region, and the light amount control means controls the light amount according to the number of the photometric regions in which the output is saturated. A photometric device for a camera characterized in that 2. The photometric device for a camera according to claim 1, wherein the light amount control means is a first photometric setting mode in which the light flux is not dimmed and is incident on the photometric element, and the light flux is dimmed. A photometric device for a camera, comprising: a second photometric setting mode for entering a photometric element. 3. The photometric device for a camera according to claim 2, wherein the first photometric setting mode is a mode in which an aperture of the taking lens is opened, and the second photometric setting mode is the taking lens. A photometric device for a camera, which is in a mode in which a light beam is dimmed by narrowing the diaphragm.