JP2003029313A - Camera - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a simplification of the internal function of a camera, a reduction of the cost and a miniaturization of the camera by providing a photometric means for performing accurate exposure control with a simple constitution. SOLUTION: This camera is provided with a light projecting means (light projecting lens 2, a light emitting diode 2a and a driver 2b) for projecting light for range-finding to a subject, a light receiving means (a light receiving lens 3 and a PSD 3a) for receiving reflection signal light reflected from the subject, a separation means (a hold amplifier 6) for separating an output photoelectric current from the light receiving means to the component of the reflection signal light and the component of the normal light, and an integration circuit 15 for integrating a current signal based on the separated reflection signal light. The focusing on the subject is performed according to the output signal of the circuit 15 during activation of the separation means, and the exposure control for the subject is performed according to the output signal of the circuit 15 during non-activation of the separation means.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a camera.

[0002]

2. Description of the Related Art Since a photometric circuit of a camera measures light in a wide luminance range, a device such as a logarithmic compression circuit is used to suppress the voltage change range in response to a large dynamic range of the output current of a light receiving element. Was being done.

[0003]

However, when a logarithmic compression circuit or the like is used, there is a drawback that the configuration becomes complicated.

There is also a proposal such as Japanese Patent Application No. 2001-63937 in which a distance measuring circuit is applied to simplify a circuit in a camera. However, particularly at low luminance, sufficient photometric characteristics cannot be obtained, and particularly in an indoor environment. There was room for improvement in the exposure at.

The present invention has been made in view of these problems, and an object thereof is to provide a photometric means for performing highly accurate exposure control with a simple structure, and to simplify the structure of the camera. Downsizing and simplification, downsizing of the camera,
It is to provide a camera that can achieve cost reduction.

[0006]

In order to achieve the above object, a camera according to a first aspect of the present invention comprises a light projecting means for projecting distance measuring light onto a subject, and a reflection reflected from the subject. Light receiving means for receiving signal light, separating means for separating the output photocurrent of the light receiving means into the reflected signal light component and the stationary light component, and a current signal based on the reflected signal light component separated by the separating means And integrating means for integrating, and performing focusing on the subject based on the output signal of the integrating means during operation of the separating means,
Exposure control of the subject is performed based on the output signal of the integrating means when the separating means is not operating.

According to a second aspect of the present invention, in the camera according to the first aspect, the camera has photometric means, and the camera is based on the output of the photometric means and the output of the integrating means when the separating means is inactive. Switch the exposure control.

According to a third aspect of the present invention, in the camera according to the first aspect, the camera has a detecting means for detecting the stationary light component separated by the separating means, and cannot be detected by the detecting means. At this time, the separation means is deactivated, and the exposure control is performed based on the output signal of the integration means.

A fourth aspect of the present invention is a camera having photometric means for determining exposure based on the output of the photometric means, wherein the photometric means is generated by flowing a photocurrent during photometry through an impedance component. A first photometric mode for determining exposure based on a voltage signal, and a second photometric mode for determining exposure based on a signal generated by integrating a signal dependent on photocurrent during photometry, The first photometry mode and the second photometry mode are switched according to the distance measurement result in the first photometry mode.

[0010]

DETAILED DESCRIPTION OF THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings.

(First Embodiment) FIG. 1 is a diagram showing a main part of an electric circuit of a camera to which the present embodiment is applied. A CPU (arithmetic control unit) 1 composed of a one-chip microcomputer or the like for controlling the sequence of the entire camera receives a sequence of exposure and focusing and a timing signal for switching operation of each circuit via a timing control circuit 19 including a decoder circuit and the like. Form.

For exposure control, the output of the photometric sensor 17a is input to the CPU 1 through the photometric circuit 17, and the exposure control means 2
0 and strobe control means 18 are controlled. On the other hand, in focusing, the driver 2b is controlled to cause the light emitting diode (LED) 2a to emit light, and the reflected light of the light focused and projected on the subject by the light projecting lens 2 is transmitted to the PSD (light position) via the light receiving lens 3. Light is received by the detection element 3a, the incident position and the amount of light are determined, and the focusing unit 21 is controlled.

FIG. 2A is an external view of such a camera. On the front surface of the camera 30, in addition to the taking lens 32, the stroboscopic light emitting unit 18-1, the viewfinder objective window 33, the light projecting lens 2, the light receiving lens 3, and the photometric sensor 17a are arranged. By operating the release button 31, the CPU 1 automatically performs focusing and exposure control so that anyone can take a beautiful photograph.

FIG. 2B is a diagram for explaining the principle of distance measurement of the distance measuring means at the time of focusing. As described above, the light projecting lens 2 and the light receiving lens 3 provided on the front surface of the camera are arranged apart from each other by a predetermined base line length S, and L
The distance measuring light projected by the ED 2a is reflected from the subject 40 and enters the PSD 3a. The incident position x has a relationship of x = (S · f) / L (f: focal length of the light receiving lens 3) with the focusing distance L, and therefore the incident position x is detected by
The focusing distance L is obtained. In addition to the reflected signal light, sunlight or artificial illumination light that illuminates the subject constantly enters the PSD 3a. Therefore, a complicated circuit or control is required to separate these components and the signal light. I need.

Due to its photovoltaic effect and the photocurrent shunting effect in the resistance layer, the PSD 3a has two electrodes,
It outputs two output current signals (photocurrents) Ia and Ib. If this signal is separated from the stationary light component and the ratio is obtained, a signal depending on x can be obtained. Also, Ia, I
Since both b increase with the intensity of the incident light, the focusing distance L can be obtained also by these magnitudes. Highly accurate focusing is performed by properly using the calculation result of the ratio and the magnitude of this photocurrent depending on the case.

In addition, the light projection for distance measurement is not performed, and the PS
Using the output of D3a makes it possible to perform exposure control with higher accuracy. That is, in the indoor scene as shown in FIG. 3, the scenery 34 outside the background window is too bright, and the background 3 is detected in the photometric range (average photometry) 35 by the photometric sensor 17a.
Even if the proper exposure was obtained for the image No. 4, the image for the person 40 tended to be an under photograph. However, PSD3
Since a monitors a very narrow range 36,
It is possible to accurately determine the brightness of the person 40, which is the main subject, and to lengthen the exposure time or to make the strobe emit light so that the person 40 can be properly exposed.

Therefore, if the output of the PSD 3a is selectively used for distance measurement or photometry and the shooting control of the camera is performed according to the result, more sophisticated scene analysis can be performed without preparing a special sensor or circuit. It is possible to provide a fully automatic camera with no failed photos in a simpler way.

Now, returning to FIG. 1, a circuit for processing the output current signal (photocurrent) Ia from the PSD 3a will be described.

The photocurrent Ia flows into the base of the amplifying transistor 14 due to the effect of the preamplifier 5 and then into the compression diode 12a by the current mirror circuit 13. The compression diode 12a is biased by bias current sources 11a and 11b, which are minute current sources, together with a pair of compression diodes 12b.
Amplifier that compares these compression potentials (hold amplifier)
The voltages are compared by 6. When the above-mentioned amplified signal of photocurrent is added in this state, the balance of these compression voltages is lost, and the output of the hold amplifier 6 changes to the + side. This operation continues until all the photocurrent Ia is absorbed as the collector current of the hold transistor 7. Therefore, when the hold amplifier 6 is operating, the photocurrent does not enter the base of the amplifying transistor 14. Becomes

In this state, since all the light input to the PSD 3a is constantly flowing to the hold transistor 7, the voltage VH generated at the emitter resistor 8 is guided to the A / D conversion circuit 1a of the CPU 1 by the buffer 10. For example, it is possible to detect a signal corresponding to the brightness of the portion 36 in FIG. 3 (first photometric mode).

In this state, the LED 2a is caused to emit light, and the bias current source 11a is synchronized with the B. When it is turned off by the C signal and the operation of the hold amplifier 6 is stopped by the HOLD signal from the timing control circuit 19, the hold transistor 7
Since the base potential of is fixed by the hold capacitor 9, the stationary light component always flows into the hold transistor 7, and only the newly added signal photocurrent component is input to the base of the amplification transistor 14 and amplified. What was done is poured into the compression diode 12a.

At this time, the voltage generated in the compression diode 12a depends on the magnitude of the signal light current. Therefore, if this result is input to the integrating circuit 15, the output VIN depending on the light quantity is obtained.
T is formed.

Further, if the difference between the outputs of the compression diodes 12a is obtained in the ratio calculation unit 16, the ratio of the photocurrents Ia and Ib is obtained, and the signal depending on the incident position x is obtained. In this integration operation, if the LED 2a emits light repeatedly, the noise component is canceled and the accuracy is improved.

FIG. 4 shows a timing chart at this time. When the hold amplifier 6 is turned on before the IRED emission, the voltage VH of the emitter resistor 8 rises according to the stationary light component. When the bias cut (BC), the hold (HOLD) off, and the IRED light emission ON are repeated, the integrated voltage VINT rises each time, and the accurate light amount component can be detected.

FIG. 5 is a diagram showing a detailed circuit configuration of the integrating circuit 15. As mentioned above, I from PSD3a
Two output current signals (photocurrent) of a and Ib are output. The block 4a is a signal processing block for the optical signal Ia, while the block 4b is a signal processing block for the optical signal Ib. Therefore, a compression diode corresponding to the compression diode 12a in the block 4a is also present in the block 4b. This compression diode is shown as 12c in FIG.

Therefore, if the voltages of the compression diodes 12a and 12c are input to the bases of the transistors 22a and 22b via the buffers 23a and 23b, respectively, the collector currents of these transistors 22a and 22b are photocurrents Ia and Ib, respectively. Will depend on. Therefore, if these currents are added in the current mirror circuit 25 and flowed into the integrating capacitor 27, an integrated voltage VINT with the reference voltage Vref as a reference is generated, which corresponds to the total amount of light incident on the PSD 3a. Become.

Here, prior to integration, the integration capacitor 2
Both ends of 7 are reset by the reset switch 28, and the operation of the integration switch 26 is controlled by the timing control circuit 19 so that the current mirror circuit 25 is turned on only at the time of integration. The integrated voltage VINT may be read by the A / D conversion circuit 1a of the CPU 1 or the second integrated current source 2
Alternatively, the integrated charge may be released at 9 and converted into a time signal by the so-called double integration principle for reading.

By using such an integrating circuit 15, it is possible to perform photometry up to a lower luminance than when the output voltage VH of the hold resistor is used. That is, if the hold amplifier 6 is turned off without causing the LED 2a to emit light, all the stationary photocurrent flows into the compression diode 12a via the amplification transistor 14 and the current mirror circuit 13, so the bias current source 11a is turned off. Then, the compressed voltage becomes the luminance signal of the subject as it is.

When the hold amplifier 6 is off and the bias current is off, timing control as shown in FIG. 6 is performed. That is, when the integration switch 26 is turned off for a predetermined integration time tINT, the current mirror circuit 25 charges the integration capacitor 27 and VINT is generated. After that, when the second integrated current source 29 is turned on, the brightness determination within the range of 36 in FIG. 3 can be performed by counting the time t2nd until it returns to the integration reference level.

That is, when VINT is large (brightness is high), t2nd is long, and when VINT is small (brightness is low), t2nd is short. Further, the longer the integration time tINT, the smaller the photocurrent, that is, the lower the brightness can be detected (the second photometry mode).

The photometry modes and principles in the two modes (first photometry mode and second photometry mode) using VH and VINT have been described above. The photometry characteristics are shown in FIG. It is a graph of a) -FIG.7 (c). If the voltage range that can be detected by the A / D conversion circuit 1a of the CPU 1 is between VTH1 and VTH2, as shown in FIG.
Brightness lower than BV1 cannot be determined by photometry by the voltage drop VH of the hold resistor. For example, if it is OK outdoors, photometry cannot be performed indoors, and it is difficult to perform sufficient brightness determination in an indoor scene as shown in FIG.

However, in the method of integrating the photocurrent over time, it is possible to make a determination up to even lower brightness. Further, if the integration time t is lengthened as described above, V = I · t / C (C:
By using the relationship between capacity and I: photocurrent), even a small photocurrent I can be determined with a large voltage V, so that determination with even lower luminance can be performed.

FIGS. 7B and 7C are diagrams for explaining this. FIG. 7B shows VINT obtained in the integral photometry mode when the integration time is t1.
(C) is VINT obtained when the integration time is t2.
Is. In the case of FIG. 7B, BV2 lower than BV1
In the case of FIG. 7C, the brightness of B is even lower.
It is possible to obtain the brightness up to V3. However,
In these photometric methods, A / D is used when the brightness is higher than BV1.
Since it exceeds the dynamic range of, effective photometry is not possible.

FIG. 8 is a flow chart showing the photographing operation of this embodiment in consideration of the above characteristics. If the CPU 1 controls the camera according to the flow shown in the figure, it is possible to take a picture with correct exposure without adding a special sensor or circuit.

Steps S1 to S5 are a sequence at the time of distance measurement, and show the same operation as the operation of FIG. 4 already described. First, the hold amplifier (steady light separating means) 6 is turned on.
N to store the stationary light (step S1), then project the distance measuring light (step S2), and obtain the focusing distance L from the light incident position signal obtained by the ratio calculator 16 (step S3). ). It is determined whether or not this result is a long distance (step S4), and if it is a long distance, the reflected signal light amount is small,
Assuming that the value is not reliable, the integrated light quantity result V
Using INT, obtain the focusing distance L (step S
5).

Thereafter, the photometric sensor 17a is used to perform average photometry (the portion 35 in FIG. 3), and this signal is BVAV.
(Step S6). If the distance is not long in step S4, step S6 is immediately executed.

Next, at the time of distance measurement, the potential VH depending on the voltage in which the stationary light is stored is detected, and the spot photometry result of the portion 36 in FIG. 3 is set to BVsp (step S7). Then this B
It is judged whether Vsp is lower in brightness than BV1 (step S8). If BVsp is lower in brightness than BV1 (FIG. 7A), it is unreliable, so the hold amplifier (steady light separating means) 6 is turned off (step S9). ) And then step S10
In, the integration is performed for the time of t1 and the spot photometry result BVsp is obtained from the obtained result (see FIGS. 7B and 6).

Next, the spot photometry result BVsp is BV2.
It is determined whether the brightness is lower than that (step S11), and B
If Vsp is lower in brightness than BV2, the integration time is 2 × t1
To re-integrate and perform spot metering (step S
12). After that, focusing is performed (step S1).
3). If NO in step S8 or step S11, step S13 is immediately executed.

In the next step S14, the finally obtained spot photometric signal BVsp and the average photometric result BVAV
And when the central brightness is too low, step S
In the scene as shown in FIG. 3, the main flash is prevented from being underexposed in the scene shown in FIG. If there is no great difference in the comparison in step S14, the exposure control by average photometry (BVAV) is performed (step S15).

As described above, according to this embodiment,
You can get beautifully printed photos for difficult scenes with difficult exposure control, such as backlighting, without adding special sensors or circuits.

Further, in the above-described embodiment, the method (steps S8, S11, etc.) in which the photometric method is sequentially changed when spot photometry is not successful is adopted, but as shown in FIG. 9, average photometry is performed ( In step S20), depending on whether the result is larger than BV1 or BV2 (steps S21 and S23), a spot metering mode suitable for use (steps S24, S25 and S3).
If 1) is selected, it is possible to reduce the number of times of re-doing the photometry and realize high speed.

That is, in step S21, step S
It is determined whether or not the average photometric result BVAV at 20 is larger than BV1, and if it is determined to be larger, the hold amplifier 6 (separation means) is turned on (step S30),
At the time of distance measurement, the potential VH depending on the voltage in which the stationary light is stored is detected, and the spot photometry result of the portion 36 in FIG. 3 is set to BVsp (step S31).

When it is determined in step S21 that BVAV is smaller than BV1, the hold amplifier 6
After turning off (separation means) (step S22), BVAV
Is greater than BV2 (step S2
3) If it is determined to be large, the integration time is set to t1 (step S25), integration is performed for the time of this t1 and the spot photometry result BVsp is obtained from the obtained result (step S26).

When it is determined in step S23 that BVAV is smaller than BV2, the integration time is set to 2 × t1 (step S24), integration is performed for the time of 2 × t1, and the spot is obtained from the obtained result. A photometric result BVsp is obtained (step S26).

(Second Embodiment) In the above embodiment, the spot metering of only the central portion of the screen has been described, but in consideration of the scene shown in FIG.
The same concept can be applied to a multi-AF camera having a plurality of distance measuring points 36L, 36C, and 36R to perform appropriate exposure control for the person 40.

Such a multi-AF camera is shown in FIG.
As shown in (b), it has a sensor 3a for monitoring, for example, three directions. The photometric flow in this case is shown in FIG.
It becomes something like (c). First, after performing the multi-AF (step S40), it is determined which one of the three positions is the main subject position (step S41).
If the position of the screen 35 of 0 (a) is measured by the conventional average photometry (step S42), the above-described spot photometry is performed by the sensor that measures the distance to the main subject (step S43).
Even in a backlight scene such as that shown in FIG.
The exposure of can be controlled correctly.

As described above, according to the present embodiment, there are several photometric modes, and the scene brightness determination is performed in an appropriate photometric mode according to the situation, so that a beautiful print can be obtained by correct exposure control. You can take a picture. In addition, photometry can be performed especially in difficult situations such as a backlit scene.

(Appendix) 1. In a camera having photometric means and determining exposure based on the output of the photometric means, the photometric means determines the exposure based on a voltage signal generated by flowing a photocurrent during photometry through an impedance component. And a second photometric mode for determining exposure based on a signal generated by integrating a signal depending on the photocurrent during photometry, and according to the result of the first photometric mode, A camera characterized by switching between the first photometry mode and the second photometry mode.

2. When the photometric result of the first photometric mode is low luminance, exposure control is performed according to the photometric result of the second photometric mode. The camera described in.

3. 1. A control means for switching and controlling the first photometric mode and the second photometric mode by a third photometric mode using a photometric means different from the photometric means. The camera described in.

[0051]

According to the present invention, there is provided a photometric means for controlling exposure with high precision with a simple structure, the structure inside the camera is simplified and simplified, and the size and cost of the camera are reduced. Can be achieved.

[Brief description of drawings]

FIG. 1 is a diagram showing a main part of an electric circuit of a camera to which a first embodiment of the present invention has been applied.

FIG. 2A is an external view of a camera, and FIG. 2B is a diagram for explaining the principle of distance measurement of distance measuring means during focusing.

FIG. 3 is a diagram showing an example of a shooting scene in the present embodiment.

FIG. 4 is a timing chart for explaining an integration operation of this embodiment.

5 is a diagram showing a detailed circuit configuration of an integrating circuit 15. FIG.

FIG. 6 is a diagram for explaining timing control of an integrating circuit.

FIG. 7 is a diagram for explaining photometric characteristics by a photometric operation according to the present embodiment.

FIG. 8 is a flowchart showing a shooting operation of this embodiment.

FIG. 9 is a flowchart for explaining a photometric operation of this embodiment.

FIG. 10 is a diagram for explaining the second embodiment of the present invention.

[Explanation of symbols]

1 Arithmetic control means (CPU) 1a A / D conversion circuit 2 Projection lens 2a Light emitting diode (LED) 2b driver 3 Light receiving lens 3a Optical position detector (PSD) 5 preamplifier 6 Hold amplifier 7 Hold transistor 8 Emitter resistance 9 Hold capacitor 10 buffers 11a, 11b Bias current source 12a compression diode 12b compression diode 12c compression diode 13 Current mirror circuit 14 Transistor for amplification 15 Integrator circuit 16 Ratio calculator 17 Photometric circuit 17a Photometric sensor 18 Strobe control means 18-1 Strobe emission part 19 Timing control circuit 20 Exposure control means 21 Focusing section 22a, 22b transistors 23a, 23b buffer 25 Current mirror circuit 26 Integral switch 27 Integrating capacitor 28 Reset switch 29 Second integrated current source 30 cameras 31 Release button 32 shooting lens 33 Viewfinder objective window 34 landscape 35 Metering range 36 Narrow range 40 subjects

Claims (4)

[Claims] 1. A light projecting means for projecting distance measuring light to a subject, a light receiving means for receiving reflected signal light reflected from the subject, and an output photocurrent of the light receiving means for the reflected signal light component. And a stationary light component, and an integrating means for integrating a current signal based on the reflected signal light component separated by the separating means, and an output of the integrating means when the separating means operates. A camera, wherein the subject is focused on the basis of a signal, and the exposure of the subject is controlled on the basis of the output signal of the integrating means when the separating means is inactive. 2. The camera according to claim 1, wherein the camera has a photometric means, and the exposure control is switched based on the output of the photometric means and the output of the integrating means when the separating means is inactive. camera. 3. The camera has a detecting means for detecting the stationary light component separated by the separating means, and when the detecting means cannot detect the stationary light component, the separating means is deactivated and the integrating means is operated. The camera according to claim 1, wherein the exposure control is performed based on an output signal. 4. A camera having photometric means for determining exposure based on the output of the photometric means, wherein the photometric means is exposed based on a voltage signal generated by flowing a photocurrent during photometry through an impedance component. First to judge
And a second photometry mode for determining exposure based on a signal generated by integrating a signal dependent on the photocurrent during photometry, according to the distance measurement result in the first photometry mode. , Above first
And a second photometry mode described above.