JP3140491B2 - Automatic focusing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic focusing device,
In particular, the present invention relates to an automatic focusing device for a camera that performs photographing with a release time lag reduced for a subject in a dynamic state.

[0002]

2. Description of the Related Art As various functions of a camera are being automated, a technique of focusing on a subject of a camera has been developed in a direction to overcome a subject which is considered to be weak. However, conventionally, the following two subjects have been dealt with. That is, a subject existing outside the center of the screen,
It is a moving subject, and it is required that these subjects not be out of focus (out of focus).

[0003]

Heretofore, techniques for preventing out-of-focus for these subjects include the following (i) for example, a screen disclosed in JP-A-63-159817. Multi-AF technology for sequentially measuring a plurality of points in a camera, (ii) Japanese Patent Application Laid-Open No. 62-2327
No. 571, a moving object ranging technique for determining the speed of a subject in accordance with a plurality of ranging results obtained by shifting the distance at different times, thereby preventing defocus due to subject movement occurring during a release time lag. , There were two.

[0004] However, a problem with both of the above two technologies is that the time required for ranging is lengthened.
Regarding (i), the more distance measuring points, the more
The time required for the distance measurement becomes longer. As for (ii), as described above, it is necessary to perform distance measurement many times at different times. For this reason, in any of (i) and (ii), the release time lag is sacrificed. In other words, a mere combination of these technologies results in a camera that cannot capture a photo opportunity.

The present invention has been made in view of the above-mentioned problems, and when a subject is a moving object, even if the number of light projections is increased to improve the distance measurement accuracy, a time lag is longer for the moving subject. It is another object of the present invention to provide an automatic focusing apparatus that can perform high-speed processing and obtain good focus on a moving object.

[0006]

Means for Solving the Problems] That is the present invention, shooting
A moving object detecting means for outputting information depending on the moving speed of the subject along the optical axis direction of the photographing lens for the central part of the shadow screen, and a first means for measuring the distance of the subject at the central part in the photographing screen.
It is determined that the subject is moving on the basis of information dependent on the moving speed of the moving object detecting means, the second ranging means for measuring the distance of the peripheral object in the shooting screen, In this case, the distance measurement by the second distance measuring means is prohibited, the focus of the photographing lens is adjusted based on the output of the first distance measuring means, and it is determined that the subject is stationary. In this case, a focus adjusting means for adjusting the focus of the photographing lens based on the output of the first distance measuring means and the second distance measuring means is provided. According to another aspect of the present invention, there is provided an automatic focusing apparatus including a distance measuring unit capable of measuring a plurality of distance measuring points in a shooting screen, and a focus adjusting unit for adjusting a focus of a photographing lens based on an output of the distance measuring unit. Has moving object detection means for outputting information depending on the moving speed of the subject along the optical axis direction of the taking lens, the focus adjustment means,
Based on the information depending on the moving speed of the moving body detecting means,
When it is determined that the object is moving, only the distance measuring means for one distance measuring point is operated, the focus of the photographing lens is adjusted based on the output, and it is determined that the object is stationary. In this case, the distance measuring means for a plurality of distance measuring points is operated, and the focus of the photographing lens is adjusted based on the output.

[0007]

In the automatic focusing apparatus according to the present invention, the subject is
Even if it is a moving object, the time lag does not increase and high-speed processing is performed.
Possible to obtain an autofocusing device that provides good focus.
As well as drop out when the subject is stationary.
An automatic focusing device that gives a good focus
You.

[0008]

First, the effect of the time lag will be described with reference to FIG.

FIG. 2A shows a photograph of a composition assumed by a photographer of the camera. The release operation is performed in this composition state. However, if the distance between a plurality of points is measured after the release and the time lag until photographing is long, the subject moves during the distance measurement. For this reason, the actually photographed photograph has a different composition as shown in FIG. 3B, and the distance changes every moment during the distance measurement.
As a result , an out-of-focus photograph is created.

Therefore, in the present invention, the camera is pointed at the subject, and the release button is pressed halfway in the state shown in FIG. 2C to make the camera detect whether or not the subject is a moving object. Then, after that, when the release button is pressed in the composition as shown in FIG.
Then, since the photographing is performed with a short time lag, the photograph as shown in FIG. That is, FIG.
As shown in (d), the composition is almost the same as that of FIG. 2 (a), and a photograph with good composition and almost the intended focus is obtained.

Next, an embodiment of the present invention will be described.

FIG. 1 is a block diagram schematically showing a basic configuration of the present invention. In FIG. 1, an arithmetic control circuit (CPU) 1 composed of a one-chip microcomputer or the like includes a central distance measuring unit 2 for measuring a distance of a central portion of a screen in a finder.
A peripheral distance measuring unit 4 for measuring the distance around the screen in the viewfinder via a prohibiting unit 3 and a moving object detecting unit 5 for detecting whether or not the subject is a moving object are connected. The CPU 1 has:
A switch SW1 that closes when the release button is half-pressed;
A switch SW2 that is closed by pressing the release button is connected.

Now, press the release button halfway to switch S
When W1 is closed, the moving body detection unit 5 operates to detect whether the subject is a moving body. As a result, when it is determined that the subject is a moving object, the center distance measuring unit 2 measures the distance at the center of the screen in the finder at the same time when the switch SW2 is pressed. In this case, the prohibition unit 3 controls the peripheral distance measurement unit 4
Is not performed, and exposure is performed after the focusing operation.

On the other hand, when the subject is not a moving object, the central distance measuring section 2 and the peripheral distance measuring section 4 are sequentially activated at the same time when the switch SW2 is pressed, and the closest distance among the distance measurement results is output. The object is focused and the exposure operation is started. Note that these sequence controls are performed by the CPU 1.

FIG. 3 is a block diagram of an automatic focusing apparatus according to the present invention employing a known active triangulation. In the figure, an infrared light emitting diode (IRED)
The AF signal light from the lens 11 is projected onto a subject (not shown) via the projection lens 12. Then, the reflected light from the subject is received by the light position detecting element (PSD) 14 via the light receiving lens 13, and the distance is obtained based on the incident position.

However, the IRED 11 and the PSD 14 are divided not only into the center but also into three parts to measure the left and right distances.
Shown as 4S, 14L, 14R.

That is, the A projected from the IRED 11L
The F light is projected at an angle θ from the optical axes of the light projecting and light receiving lenses 12 and 13 and the photographing lens (not shown), as indicated by l _L1 . When the subject is located at the light projection position, the light is incident on the light receiving lens 13 through an optical path of l _L2 .

The angle of incidence of l _L2 has an inclination depending on the subject distance with respect to the direction connecting the principal points of the light projecting and receiving lenses 12 and 13 (base line length direction). Therefore, the position of the signal light spot incident on the PSD 14 is different in the base line length direction of the PSD 14 depending on the subject distance. That is, the object distance can be obtained by detecting the incident position of the signal light on the PSD.

The PSD 14 is an element for outputting a light incident position in the form of two output currents. When the signal light is incident on the center of the PSD in the longitudinal direction (vertical direction in FIG. 3), the PSD 14 is used.
Becomes 1: 1. When a signal light is incident on a point where the PSD is internally divided in the length direction of 3: 1, the current signal ratio becomes 3: 1.

In this embodiment, the ratio is calculated using a compression / expansion circuit known in analog circuit technology.

The output of the PSD 14S is
5 and 16 are supplied to compression circuits 19 and 20. The outputs of the PSDs 14L and 14R are supplied to compression circuits 21 and 22 via preamplifiers 17 and 18. Then, these compression circuits 19, 20, 21, 2
The output of 2 is supplied to the expansion / integration circuit 27 via the buffers 23, 24, 25 and 26.

The CPU 29 receives the signal from the expansion / integration circuit 27 via the output terminal 28 and controls the driver 10, the decoder 30, the direction switching circuit 31, and the reset circuit 32.

FIG. 4 shows the compression circuits 19-2 shown in FIG.
2, a specific configuration example of buffers 23 to 26, expansion / integration circuit 27, output terminal 28, direction switching circuit 31, and reset circuit 32 is shown. Assuming that the currents obtained by amplifying the two signals of the PSD are I ₁ and I ₂ , the compression diode 3
The voltages generated at 3 and 34 are as shown in Equations 1 and 2, respectively.

[0024]

(Equation 1)

[0025]

(Equation 2) Here, I _S is the reverse saturation current of the diode, and V S
_T represents thermal voltage.

Further, after passing through the buffers 35 and 36,
In the figure, the difference between V _A and V _{B is} as shown in Equation 3 because the emitters of the transistors 37 and 38 are common.

[0027]

(Equation 3) Therefore, Equation 4 is obtained.

[0028]

(Equation 4) On the other hand, Equation 6 is obtained from the relation of Equation 5.

[0029]

(Equation 5)

[0030]

(Equation 6) Therefore, I _OUT is as shown in Expression 7.

[0031]

(Equation 7) Here, I ₀ is a current flowing from the current source 39, _IX is a current flowing to the diode 40, and I _OUT is a current flowing to the collector of the transistor 38.

Further, since I ₁ + I ₂ is proportional to the total photocurrent incident on the PSD, I _OUT is a current signal that depends only on the subject distance without regard to the reflectivity of the subject.

The transistors 42 and 43 forming a current mirror circuit are connected to the collector of the transistor 38 via switches 41 and 44, respectively. The switch 44 is connected to an integrating capacitor 45 for charging I _OUT, and is controlled by a CPU (not shown) via an inverter 46. Reset circuit 47, the output V _a and V _b described later integration capacitor 4
5 is provided for resetting before being charged. Reference numeral 48 denotes an output terminal.

The above-described compression diode and buffer are used for either central distance measurement or peripheral distance measurement. Actually, two sets of buffers have the same output. Be composed.

In such a configuration, the current source 39 (FIG. 4) is turned on / off in synchronization with the light emission of the IRED, and
_The integration effect is obtained by charging _OUT to the integration capacitor 45.

FIG. 5 shows the IR of the circuit thus constructed.
The operation of ED emission and integration is shown.

First, FIG. 5A shows an operation at the time of a normal distance measuring operation, and C represents the direction switching shown in FIG.
The HANGE signal is at the high level (H) at this time. Therefore, the switch 41 is turned on, and the switch 44 is turned off by the inversion of the inverter, so that current flows into the integration capacitor 45. Therefore, when the INT signal for integration is turned on / off in synchronization with the light emission of the IRED, the integrated waveform output to the output terminal 48 has a stepped shape as shown in the figure. Then, the output V _a after a predetermined number of times light emission of IRED is, C as the subject distance information
It is input to PU29.

Here, the reason why the IRED emits light a plurality of times is that even if the distance measurement data includes noise, if the data is random noise, averaging can be performed to achieve more accurate distance measurement. Because it becomes. In other words, the greater the number of times of distance measurement, the more the above-mentioned random noise is canceled out. In this case, in order to process this in an analog manner, the distance measurement results are sequentially added using the integrating capacitor 45. I have. Averaging can be performed by normalizing the integration result with a predetermined number of distance measurements. This is performed by the CPU 29.

By applying this integration circuit to switch the integration direction in the first half of the IRED emission and the integration direction in the second half of the IRED emission, FIG.
When the integration as shown in (b) is performed and the subject is not moving, the first half integration result and the second half integration result have the same amount, and _Vb in the figure becomes zero. (Coincides with _Vref )
However, if the subject is moving, the distance measurement result changes every time, so that _Vb takes a certain voltage value with respect to _Vref as shown in FIG. The control in the integration direction is performed by controlling the CHANGE signal of FIG. 4 by the CPU. In the example of FIG.
The GE signal has a high level (H) during the first half of the IRED emission and a low level (L) during the second half. In the first half, the switch 41 is turned on and the switch 44 is turned off, and the signal current I _OUT is integrated in the positive direction by the current mirror circuits 42 and 43. In the latter half, the switch 41 is turned off and the switch 44 is turned on, and the signal current I _OUT is turned on. _OUT is integrated in the negative direction.

Next, returning to FIG. 3, a switching method for measuring the distance of three points in the photographing screen will be described.

The CPU 29 controls the IR
The ED 11 that emits light in a predetermined direction is selected and driven. Then, the light of the IRED 11 is reflected on the subject and is incident on the corresponding PSD 14. The output current of the PSD 14 is absorbed by the preamplifiers 15, 16, 17, and 18 with low input impedance, and after being amplified,
It flows into the compression circuits 19, 20, 21, 22 described above.

These compression circuits 19, 20, 21, 22
The buffers 23, 24, 25, and 26 guide the compressed output of the above to the expansion / integration circuit 27. These buffers 23,
24, 25, and 26 are selected and switched by the operation of the decoder 30 according to the distance measurement points in the shooting screen. The switching table is shown in Table 1.

[0043]

[Table 1] The reason why the PSDs 14L and 14R use a common preamplifier is to simplify the circuit, while the 14S is connected to an independent preamplifier to reduce the noise incident on the PSD as much as possible and to increase the accuracy. It is.

Here, as shown in Table 1, when the IRED 11L for left distance measurement emits light, the buffers 25 and 26 are operated, and the buffers 23 and 24 are turned off. When three points are measured continuously, the IRE should be
D, and while switching the buffer, the ranging sequence described in FIG. 5 (a), CPU 29 inputs a sequential V _a.

Next, referring to the flowchart of FIG.
An operation when the above-described automatic focusing device is applied to a camera will be described.

First, in step S1, the CPU 29 detects a half-pressed state of the release button of the camera. If it is half-pressed, the process proceeds to step S2 to perform the above-described moving object detection operation, reset the output value by the reset circuit 32, and then input the output _Vb .

Next, at step S3, the timing of pressing the release button is detected. In this step S3, the moving object detection operation is repeated until the release button is pressed, and _Vb is updated. Then, when detecting the pushing of the release button, the routine proceeds to step S4, measures the distance of the subject in the center of the screen as described above, determine the distance l _S from the output V _a.

Next, in step S5, the determination of the motion detection result is performed by comparing the absolute value of the V _b with a predetermined voltage. That is, _if the absolute value of _Vb is equal to or less than the predetermined value, it is determined that the subject is not moving, and the process proceeds to step S6. In this step S6, the CPU 29
The combination of 1 and the buffer is selected according to Table 1 described above, and the distances l _L and l _R of the objects existing on the left and right sides of the shooting screen are measured while switching. Then, in step S7, the closest distance is selected from the above l _S , l _L , l _{R and} is set as the focusing distance.

On the other hand, if it is determined in step S5 that the object is a moving object, the process proceeds to step S8. Then, in step S8, the l _S as focusing distance l _X, the process proceeds to step S9.

[0050] In step S9, performs focusing against focusing distance l _X. Here, when the operations in steps S6 and S7 are performed, the distance measurement is performed on the left and right sides in the photographing screen, so that the so-called hollow phenomenon is eliminated. On the other hand, when the operation of step S8 is performed, the distance measurement is not performed on the left and right in the shooting screen, so that the time lag is reduced.

Thereafter, in step S10, exposure is performed.

In the above-described embodiment, it is assumed that the moving object is detected by the IRED and the PSD at the center. However, the present invention is not limited to this. Good thing.

[0053]

As described above, according to the present invention, when the subject is a moving object, if the time lag is long for the moving subject even if the number of projections is increased to improve the distance measurement accuracy. It is possible to provide an automatic focusing device that can perform high-speed processing and obtain good focus on moving objects without moving objects, even for moving objects that are not good at conventional autofocus cameras. A camera with a simple configuration that can take a composition that the photographer intends and can take a picture with good focus, and can take a picture with better focus without stopping for a still subject Can be realized.

[Brief description of the drawings]

FIG. 1 is a block diagram schematically showing a basic configuration of the present invention.

FIG. 2 is a diagram showing a composition in a state in which a subject is moving so that a photographer of the camera takes a picture.

FIG. 3 is a block diagram of the automatic focusing apparatus of the present invention employing a known active triangulation.

FIG. 4 is a diagram showing a specific configuration example of a compression circuit, a buffer, a decompression / integration circuit, an output terminal, a direction switching circuit, and a reset circuit of FIG. 3;

5A is a timing chart of an IRED light emission and an integration operation during a normal distance measurement operation, and FIG.
6 is a timing chart of RED light emission, direction switching, and integration.

FIG. 6 is a flowchart illustrating an operation when the automatic focusing apparatus of the present invention is applied to a camera.

[Explanation of symbols]

1, 29: arithmetic control circuit (CPU), 2: central distance measuring unit,
3 ... prohibition section, 4 ... peripheral distance measurement section, 5 ... moving body detection section, 10 ...
Driver, 11, 11L, 11R, 11S: infrared light emitting diode (IRED), 12: light projecting lens, 13: light receiving lens, 14, 14L, 14R, 14S: light position detecting element (PSD), 15-18 ... Preamplifier, 19-2
2. Compression circuit, 23 to 26 buffer, 27 expansion / integration circuit, 28 output terminal, 30 decoder, 31 direction switching circuit, 32 reset circuit.

Claims (2)

(57) [Claims] 1. A moving object detecting means for outputting information depending on a moving speed of a subject along a direction of an optical axis of a photographing lens in a central portion of a photographing screen, and measuring a distance of the subject in the central portion of the photographing screen. A first distance measuring means, a second distance measuring means for measuring a distance of a peripheral object in a photographing screen, and information based on a moving speed of the moving object detecting means.
If it is determined that the subject is moving, the second
The distance measurement by the distance measuring means is prohibited, the focus of the photographing lens is adjusted based on the output of the first distance measuring means, and when it is determined that the subject is stationary, the first An automatic focusing device comprising: a distance measuring means; and a focus adjusting means for adjusting a focus of the photographing lens based on an output of the second distance measuring means. 2. An automatic focusing apparatus comprising: a distance measuring means capable of measuring a plurality of distance measuring points in a photographing screen; and a focus adjusting means for adjusting a focus of a photographing lens based on an output of the distance measuring means. In the above, moving object detecting means for outputting information dependent on the moving speed of the subject along the optical axis direction of the photographing lens, the focus adjusting means, based on the information dependent on the moving speed of the moving object detecting means When it is determined that the subject is moving, only the distance measuring means for one distance measuring point is used.
Is operated, the focus of the photographing lens is adjusted based on the output, and when it is determined that the subject is stationary, the distance measuring means for a plurality of distance measuring points is operated,
An automatic focusing device wherein the focus of the photographing lens is adjusted based on the output.