JPH05210042A - Automatic focusing device - Google Patents

Abstract

PURPOSE:To fix a photographing lens at a focusing position in a short time and with high accuracy. CONSTITUTION:The moving area of th photographing lens in the case of active system automatic focusing is set. First, active system range-finding using a photodetector(PSD) is executed. Based on the range-finding data thereof, the photographing lens is moved to one end part X of the prescribed moving area B. Next, contrast system automatic focusing is executed. That means, focus voltage data corresponding to the contrast of a video signal is detected in the area B while the photographing lens is moved toward the other end part Y by prescribed amount. When the detection of the focus voltage data is finished to the other end part Y, the maximum value of the focus voltage data is detected and the photographing lens is moved to the position (focusing position F) where the maximum value is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic focus adjusting device which is provided in, for example, an electronic camera and controls a taking lens to a focusing position.

[0002]

2. Description of the Related Art Conventionally, an infrared active method and a contrast detection method are known as automatic focus adjustment for electronic cameras. The infrared active method irradiates infrared rays on a subject and detects the reflected light rays by a position detection element such as PSD, thereby performing distance measurement on the principle of triangulation. In this method, since the magnitude of the output signal of the position detection element such as PSD is divided into several steps to obtain the distance measurement data, the accuracy of this distance measurement data is low, but the area based on this distance measurement data is low. The shooting lens can be extended all at once, and the time required for focusing operation is short. On the other hand, the contrast detection method utilizes the property that the high-frequency component of the video signal is the largest in the in-focus state when shooting one subject. That is, according to this method, the photographing lens is moved little by little to detect the high frequency component of the video signal, and the position of the photographing lens is determined so that the high frequency component is maximized, so that highly accurate focusing is performed.

[0003]

In the infrared active method, the taking lens cannot be accurately set at a predetermined position (for example, the center position of the area) in the selected area due to mechanical error or the like. In that case, if the lens position is largely deviated from the position corresponding to the actual subject distance, there is a possibility that a focused image cannot be obtained.
Further, the contrast detection method detects the in-focus position of the taking lens by the hill climbing method, and it is necessary to compare a lot of data, so especially when the taking lens is at a position far from the in-focus position. There is a problem that it takes time to obtain a focused state. SUMMARY OF THE INVENTION It is an object of the present invention to solve such a problem all at once, and to obtain an automatic focus adjusting device that can set a photographing lens at a focusing position in a short time and with high accuracy.

[0004]

An automatic focusing apparatus according to the present invention measures a distance to an object with a predetermined coarse accuracy and determines a moving area of a photographing lens on the basis of distance measuring data, and the moving means. It is characterized in that it is provided with a means for obtaining the contrast of the video signal while moving the taking lens within the area, and a means for positioning the taking lens at the position where the contrast is maximized.

[0005]

The present invention will be described below with reference to the illustrated embodiments.
FIG. 1 shows a circuit configuration of an automatic focus adjusting device for an electronic camera to which an embodiment of the present invention is applied.

An image of a subject is formed on an image pickup device (CCD) 12 via a taking lens 11. The video signal output from the image sensor 12 is correlated double sampling (CD
S) The signal is processed by the circuit 13 to remove, for example, reset noise when a signal is detected. Thereafter, the video signal is AD-converted by the AD converter 14 and input to the line memory 15 and the digital filter 16, respectively.

The line memory 15 sequentially stores the data of one horizontal scanning line of the video signal and sequentially outputs the data to the process circuit 17. The data of one horizontal scanning line is the process circuit 1
In FIG. 7, γ correction processing is performed, and the recording / reproducing circuit 18 records it on a magnetic disk (not shown). In addition, A
The D converter 14, the line memory 15, the process circuit 17, and the recording / playback circuit 18 are controlled by a control circuit 21 including a microcomputer.

The digital filter 16 acts as a high pass filter, a double wave detection circuit and an integration circuit. That is, the digital filter 16 extracts a high frequency component by differentiating the video signal output from the AD converter 14, and detects positive and negative components of this high frequency component signal in the same direction, and detects the detected signal. Is integrated. As will be described later in detail, the control circuit 21 obtains the in-focus position based on the integrated value and controls the position of the taking lens 11. That is, the digital filter 16 outputs the focus voltage data corresponding to the high frequency component of the video signal used in the automatic focus adjustment of the contrast detection method.

The motor 22 is controlled by the control circuit 21 to move the taking lens 11 in the optical axis direction. The lens position detection circuit 23 detects the position of the taking lens 11 and outputs the detection result to the control circuit 21. The lens focal length detection circuit 24 detects the focal length during zooming operation of the taking lens 11, for example, and the control circuit 21 obtains the depth of field based on the focal length.

The active AF module 31 obtains distance measurement data in infrared active automatic focus adjustment, and outputs this distance measurement data to the control circuit 21. As will be described later, in focusing control, the control circuit 21 moves the taking lens 11 to a predetermined position at once, based on the distance measurement data obtained from the active AF module 31. Then, the control circuit 21 performs the automatic focus adjustment by the contrast detection method, detects the focus voltage data obtained from the contrast of the video signal output from the digital filter 16 while moving the taking lens 11 by a predetermined amount, and the focus voltage The taking lens 11 is set at a position where the data becomes maximum.

FIG. 2 shows the configuration of the active AF module 31. The light receiving element (PSD) 32 is, as is well known,
The distance to the subject is detected by detecting infrared rays emitted from a light emitting element (not shown) and reflected by the subject. That is, the magnitude of the output current ratio of the light receiving element 32 changes linearly depending on the light receiving position of the reflected light beam of the light receiving element 32, and by detecting the value of this current ratio,
Distance measurement is performed according to the principle of triangulation. Light receiving element 32
The output current ratio of is amplified by the head amplifier 33,
It is corrected by the log amplifier 34 so as to be linear with respect to the reciprocal of the distance to the subject. The output signal of the log amplifier 34 is input to the sample hold circuit 36 via the buffer amplifier 35, is held for a certain period of time, and is held by the AD converter 3.
7 is output. The output signal of the AD converter 37 is distributed by the decode latch 38 into a plurality of stages and output. Although three output terminals are shown in the decode latch 38 in the illustrated embodiment, more output terminals are actually provided, and for example, it is configured to output distance measurement data in 32 stages. ing.

FIG. 3 shows an example of the focusing operation in this embodiment, in which the horizontal axis represents time and the vertical axis represents the lens extension amount.

In this embodiment, there are a plurality of types of distance measurement data output from the active AF module 31 as described above, and the lens movement range is divided into a plurality of areas corresponding to the distance measurement data. There is. The taking lens moves from position I corresponding to infinity to position N corresponding to the closest distance.
The size of each area (only area B is shown in FIG. 3) is set in consideration of the performance of the taking lens, the depth of focus, and the like. That is, the lens moving area B is determined so that the depth of focus of the taking lens includes both end portions X and Y of the area when the taking lens is located substantially in the center of this area.

In the example shown in FIG. 3, the taking lens is located at infinity as an initial position. Here, it is assumed that the distance measurement data output from the active AF module 31 corresponds to the area B. In the focusing operation, first, the taking lens is moved to the end X of the area B at once. That is, the region B is defined as the range in which the taking lens moves in the focusing operation based on the active distance measurement data.

Then, a passive focusing operation is performed. That is, in the region B, the focus voltage data corresponding to the contrast of the video signal obtained through the taking lens is detected while moving the taking lens by a predetermined amount. The focus voltage data at each position is the control circuit 2
1 memory. When the detection of the focus voltage data is completed up to the end Y of the region B, the photographing lens is moved to the position corresponding to the maximum value in the data stored in the memory as the focus position F, and the focus lens F is moved to the position. Positioned.

FIG. 4 shows a video signal during the focusing operation of FIG. 3, particularly during the active focusing operation. Long vertical lines X and Y correspond to both ends of the region B in FIG. 3, and a large number of short vertical lines Z show the movement timing of the taking lens. That is, a video signal for one screen is obtained between each vertical line, and the contrast of this video signal is detected as described later.

The image pickup device 12 outputs a video signal, for example, every 1/60 seconds. The CDS circuit 13 performs a predetermined process on this video signal and outputs a video signal as indicated by a symbol K. The waveform of the video signal K changes according to the contrast of the video, and the higher the contrast, the more the high frequency components. The video signal K is AD-converted and then differentiated by the digital filter 16 to extract a high-frequency component. The signal that rises in the positive and negative directions indicated by the symbol L indicates this high frequency component. This high-frequency component signal L is further supplied to the digital filter 16,
The positive and negative components are detected in the same direction. This detected signal is integrated in the digital filter 16 and has a height corresponding to the magnitude of the high frequency component, as indicated by the symbol M. That is, the higher the high frequency component of the video signal K, the higher the height of the signal M.

In this way, the taking lens 11 is located in the area B.
While moving inside from one end X to the other end Y, a video signal K is obtained for each screen every 1/60 seconds.
Then, the integrated value M corresponding to the contrast of each video signal
Are stored in the memory of the control circuit 21. When the detection of the video signal in the area B is completed, the control circuit 21 detects the maximum value from the integrated values M stored in the memory,
The taking lens 11 returns from the end Y toward the end X and is stopped at a position corresponding to this maximum value. In the example of FIG.
The maximum value is indicated by the symbol M1.

As described above, in this embodiment, first, the active lens is used to move the taking lens 11 all the way to the end X of the predetermined area B at a stretch, and then the passive method is used to move the taking lens 11 by a predetermined amount and focus. It is configured to detect voltage data. As described above, in the present embodiment, since the photographing lens 11 is moved in advance to a region close to the in-focus position, the passive-system high-precision focusing operation is performed in the limited region. Will be accurately set to the in-focus position, and an in-focus image will always be obtained. Further, even if the initial position of the taking lens 11 is far from the in-focus position, it does not take time to obtain the in-focus.

Further, in the present embodiment, when the taking lens 11 moves within the area B, the video signal is detected from the end portion X closer to the initial position of the taking lens 11 to the far end Y. After the detection is completed, the taking lens 11 is returned to the position of the maximum value M1. Therefore, the taking lens 11 does not make one round trip within the area B at most, and the moving distance thereof can be minimized.

Further, in this embodiment, the time interval at which the image signal is output from the image pickup device 12 is constant (1/60 seconds). Therefore, when the payout speed of the taking lens 11 is constant, the resolution is high at a short distance where the payout amount is large, and the accuracy of focusing control of the taking lens 11 is improved particularly during macro photography.

As described above, the apparatus according to the present embodiment is capable of performing automatic focus adjustment in a short time and with high accuracy over the entire object distance with a simple structure, as compared with the automatic focus adjusting apparatus having the passive focus control apparatus. You can

The present invention can be applied not only to the electronic still camera but also to a movie camera, and can also be provided in a normal still camera. Further, there is no limitation on the initial position of the taking lens 11, and for example, it may be on the short distance side, or may be a position between infinity and short distance.

[0024]

As described above, according to the present invention, the effect that the photographing lens can be set at the in-focus position in a short time and with high accuracy can be obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing a circuit configuration of an automatic focus adjusting device for an electronic camera to which an embodiment of the present invention is applied.

FIG. 2 is a block diagram showing an active AF module.

FIG. 3 is a diagram showing a focusing operation of the apparatus of the embodiment.

FIG. 4 is a diagram showing a video signal detected in the focusing operation of FIG.

[Explanation of symbols]

 13 CDS circuit B Lens movement area F Focus position

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[Procedure amendment]

[Submission date] April 14, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] 0003

[Correction method] Change

[Correction content]

[0003]

In the infrared active method, the taking lens cannot be accurately set at a predetermined position (for example, the center position of the area) in the selected area due to mechanical error or the like. If the lens position is out of the position corresponding to the actual subject distance,
It may not be possible to obtain a properly focused image. In addition, the contrast detection method uses an image sensor within the range.
The high frequency component of the video signal obtained from the child is extracted and
Detects a large value and sets the corresponding shooting lens position to the in-focus position
Since this is a system in which a large amount of data has to be compared, there is a problem that it takes time to obtain a focused state, especially when the taking lens is located far from the focused position. It is an object of the present invention to solve such problems all at once, and to obtain an automatic focus adjusting device capable of accurately setting a photographing lens at a focus position in a short time.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0008

[Correction method] Change

[Correction content]

The digital filter 16 acts as a high pass filter, a double wave detection circuit and an integration circuit. That is, the digital filter 16 extracts a high frequency component by differentiating the video signal output from the AD converter 14, and detects positive and negative components of this high frequency component signal in the same direction, and detects the detected signal. Is integrated. As will be described later in detail, the control circuit 21 obtains the in-focus position based on the integrated value and controls the position of the taking lens 11. That is , the output from the digital filter 16 is
Focus voltage data corresponding to high frequency components of video signal used in contrast detection type automatic focusing device
Becomes

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0010

[Correction method] Change

[Correction content]

The active AF module 31 obtains distance measurement data in infrared active automatic focus adjustment, and outputs this distance measurement data to the control circuit 21. As will be described later, in focusing control, the control circuit 21 moves the taking lens 11 to a predetermined position at once, based on the distance measurement data obtained from the active AF module 31. Then, the control circuit 21 performs the automatic focus adjustment of the contrast detection method, and detects the focus voltage data obtained from the high frequency component of the video signal output from the digital filter 16 while moving the taking lens 11 by a predetermined amount. Then, the taking lens 11 is set at a position where the focus voltage data becomes maximum.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0015

[Correction method] Change

[Correction content]

Then, a contrast type focusing operation is performed. That is, in the region B, the focus voltage data corresponding to the high frequency component of the video signal obtained via the photographing lens is detected while moving the photographing lens by a predetermined amount. The focus voltage data at each position is the control circuit 2
1 memory. When the detection of the focus voltage data is completed up to the end Y of the region B, the photographing lens is moved to the position corresponding to the maximum value in the data stored in the memory as the focus position F, and the focus lens F is moved to the position. Positioned.

[Procedure Amendment 5]

[Document name to be amended] Statement

[Correction target item name] 0016

[Correction method] Change

[Correction content]

FIG. 4 shows a video signal during the focusing operation of FIG. 3, particularly during the active focusing operation. Long vertical lines X and Y correspond to both ends of the region B in FIG. 3, and a large number of short vertical lines Z show the movement timing of the taking lens. That is, a video signal for one screen is obtained between each vertical line, and the focus voltage data is detected for this video signal as described later.

[Procedure correction 6]

[Document name to be amended] Statement

[Correction target item name] 0018

[Correction method] Change

[Correction content]

In this way, the taking lens 11 is located in the area B.
While moving inside from one end X to the other end Y, a video signal K is obtained for each screen every 1/60 seconds.
Then, the integrated value M corresponding to the high frequency component of each video signal is stored in the memory of the control circuit 21. When the detection of the video signal in the area B is completed, the control circuit 21 detects the maximum value from the integrated values M stored in the memory, and the taking lens 11 moves from the end Y to the end X. Video signal
Return without getting data and stop at the position corresponding to this maximum value. In the example of FIG. 4, the maximum value is shown by the code M1.

[Procedure Amendment 7]

[Document name to be amended] Statement

[Name of item to be corrected] 0019

[Correction method] Change

[Correction content]

As described above, in this embodiment, first, the active lens is used to move the taking lens 11 all the way to the end X of the predetermined area B at a stretch, and then the contrast method is used to move the taking lens 11 by a predetermined amount and focus. It is configured to detect voltage data. As described above, in the present embodiment, after moving the taking lens 11 in advance to the area close to the in-focus position, the contrast is reduced within the limited area.
Since it performs high-precision focusing operation by
The shooting lens will be accurately set to the in-focus position,
You will always get a focused image. Also,
Even if the initial position of the taking lens 11 is far from the in-focus position, it does not take time to obtain in-focus.

[Procedure Amendment 8]

[Document name to be amended] Statement

[Correction target item name] 0020

[Correction method] Change

[Correction content]

Further, in this embodiment, when the taking lens 11 moves within the area B, the focus voltage data is detected from the end X closer to the initial position of the taking lens 11 to the end Y on the far side. After the detection of (1) is completed, the taking lens 11 is returned to the position of the maximum value M1 without detecting the focus voltage data . Therefore, the taking lens 11
Does not make one round trip within the area B at most, and its moving distance can be minimized.

[Procedure Amendment 9]

[Document name to be amended] Statement

[Name of item to be corrected] 0022

[Correction method] Change

[Correction content]

As described above, the apparatus according to the present embodiment is different from the automatic focus adjusting apparatus having the contrast type focus control apparatus in that
With a simple configuration, it is possible to perform automatic focus adjustment in a short time and with high accuracy over the entire subject distance.

Claims (1)

[Claims] 1. A means for performing distance measurement on a subject with a predetermined coarse accuracy, and means for determining a moving area of a photographing lens based on distance measuring data, and a contrast of a video signal while moving the photographing lens within the moving area. An automatic focus adjustment device comprising: a means for obtaining the contrast and a means for positioning the taking lens at a position where the contrast is maximized.