JP2005156737A - Auto focus system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To surely and accurately perform an AF by performing exposure adjustment for the same range as the AF area as an AF object, in a television camera introducing a contrast system auto focus system and provided with imaging elements for AF. <P>SOLUTION: Two imaging elements 26A and 26B for AF, each having a different optical path length, are mounted to a camera main body 10. The automatic focus adjustment is performed based on the video signal in the AF area extracted by gate circuits 52A and 52B among the video signals obtained by the imaging elements 26A and 26B. Besides, the electronic shutter function of the imaging elements 26A and 26B is controlled based on the video signal of the AF area extracted by the gate circuits 52A and 52B, so as to enable the exposure adjustment for the AF area as an object to be performed. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an autofocus system, and more particularly to a contrast-type autofocus system applied for moving image shooting such as a television camera.

A contrast method is generally used as an autofocus (AF) method adopted in a television camera or a video camera. In the contrast method, for example, a high frequency component is extracted from a video signal obtained by photographing a subject using a filter, and the contrast level (sharpness) of the subject image is evaluated based on the high frequency component. Then, the focus (focus lens) of the photographing lens is controlled so that the evaluated value (referred to as a focus evaluation value in this specification) is maximized (maximum). (For example, refer to Patent Document 1.)
JP 2002-365518 A

  By the way, in contrast-type autofocus, in general, a partial area of an imaging range, for example, a central portion is set as a focus area (AF area), and focusing is performed based on a video signal in a range corresponding to the AF area. On the other hand, the exposure adjustment for adjusting the luminance level of the video signal is generally performed in consideration of the entire photographing range. For this reason, if the brightness of the subject outside the AF area differs greatly from the subject within the AF area, the brightness level of the video signal in the AF area will be excessive or insufficient, and an accurate focus evaluation value will not be obtained, and autofocus will not be performed. In some cases, the camera malfunctions or the focus accuracy decreases.

  The present invention has been made in view of such circumstances, and an autofocus system capable of performing exposure adjustment so that the luminance level of the video signal in the AF area is appropriate, and performing focusing by autofocus with certainty and accuracy. The purpose is to provide.

  In order to achieve the above object, the invention according to claim 1 diverges the subject light incident on the photographing lens into an optical path different from an optical path that guides the subject light to an imaging surface of an imaging means for acquiring a video signal for reproducing a moving image. A branching unit that captures the subject light branched by the branching unit, and obtains a video signal for performing autofocus on the photographing lens, and an imaging surface of the AF imaging unit And an AF processing means for performing an autofocus process by a contrast method based on a video signal obtained from a partial AF area of the AF area, and among the imaging surfaces of the AF imaging means, An exposure adjustment hand that detects the luminance of the subject imaged in the AF area and adjusts the exposure only for the AF imaging means based on the detected luminance. It is characterized by having a and.

  The invention described in claim 2 is characterized in that, in the invention described in claim 1, the exposure adjustment means performs exposure adjustment by an electronic shutter function or a gain control function in the AF imaging means.

  According to a third aspect of the present invention, in the first aspect of the present invention, the AF imaging means includes a plurality of imaging surfaces having optical path length differences, and the AF processing means includes an AF area of each imaging surface. The focus of the photographic lens is set to the in-focus position based on a plurality of video signals obtained from the above.

  According to the present invention, since the autofocus AF imaging unit matches the autofocus target range and the exposure adjustment target range, the brightness level of the video signal in the AF area acquired for autofocus is appropriate. Therefore, it is possible to perform focusing by autofocus with certainty and accuracy.

  A preferred embodiment of an autofocus system according to the present invention will be described in detail below with reference to the accompanying drawings.

  FIG. 1 is a diagram showing a schematic configuration of a moving image shooting camera such as a television camera to which the present invention is applied. The camera (television camera) shown in FIG. 1 includes a camera body 10 with interchangeable lenses and a lens device 12 attached to the camera body 10. The lens device 12 electrically controls a photographic lens 14 (optical system) composed of various fixed and movable lens groups and optical components such as an iris, and a movable lens (group) and iris of the photographic lens 14 by electric control. A control device (control system) (not shown) is included.

  A color separation optical system 20 that omits a detailed configuration is disposed in the camera body 10, and subject light that has passed through the photographing lens 14 is red (R), green (G), and so on by the color separation optical system 20. It is decomposed into light of each wavelength band of blue (B). The light separated into each color by the color separation optical system 20 is incident on the image pickup surface of an image pickup device (two-dimensional CCD) corresponding to each color, and is photoelectrically converted by each image pickup device. Then, a broadcast video signal (recording or playback video signal) is generated by a signal processing circuit (not shown). Note that the image pickup device for video is composed of three image pickup devices for R, G, and B, which are equidistant in the optical path length of the subject light. In FIG. It shows with. Further, the camera body 10 may be of a type that captures a color image or a black and white image with a so-called one image sensor, and the image sensor P for video may be understood to indicate that one image sensor. In that case, the color separation optical system 20 is not arranged.

  Further, the color separation optical system 20 is provided with means (not shown) for branching the subject light for focus detection from the subject light incident on the color separation optical system 20, and is separated into, for example, R, G, and B colors. The subject light before the image is branched from the subject light for video as subject light for focus detection (for auto focus (AF)). Note that the autofocus in this system is a contrast method, but as will be described later, it is an autofocus based on an optical path length difference method. Therefore, the subject light for AF is branched.

  The subject light for AF branched from the subject light for video enters, for example, the half mirror surface 24 constituted by two prisms 22A and 22B, and is equally divided into reflected light and transmitted light. The reflected light is incident on the imaging surface of the AF imaging element 26A, and the transmitted light is incident on the imaging surface of the AF imaging element 26B. Subject light incident on the AF image sensors 26A and 26B is photoelectrically converted and output as video signals from the AF image sensors 26A and 26B. It is assumed that the AF imaging elements 26A and 26B both capture black and white images, and the video signals generated by these imaging elements 26A and 26B are luminance signals.

  Here, FIG. 2 shows the image pickup element P for video and the pair of AF image pickup elements 26A and 26B on the same optical axis. As shown in the figure, the optical path length of the subject light incident on the imaging surface of one AF imaging element 26A is shorter than the optical path length of the subject light incident on the imaging surface of the other AF imaging element 26B, The optical path length of the subject light incident on the image pickup surface of the image pickup device P is set to be an intermediate length. That is, the image pickup surfaces of the pair of AF image pickup devices 26A and 26B are arranged at equidistant positions with respect to the image pickup surface of the image pickup device P for video. Accordingly, the subject light incident on the photographic lens 14 is imaged at a position equidistant from the imaging surface of the image pickup device P by the pair of AF image pickup devices 26A and 26B.

  FIG. 3 is a block diagram showing a system configuration mainly related to autofocus in the camera body 10 and the lens device 12. In the lens device 12, the photographic lens 14 includes a focus lens (group) FL driven in the optical axis direction for focusing as a movable lens group, and an optical axis for changing the image magnification (focal length). A zoom lens (group) ZL driven in the direction is disposed. Also, an iris I that is driven to open and close to change the aperture value is arranged. The focus lens FL, the zoom lens ZL, and the iris I are connected to the focus motor FM, the zoom motor ZM, and the iris motor IM, respectively, and are driven by the motors FM, ZM, and IM. Yes.

  The motors FM, ZM, and IM are connected to the focus amplifier FA, the zoom amplifier ZA, and the iris amplifier IA, respectively, and each amplifier is connected from the CPU 30 mounted on the lens device 12 via the D / A converter 32. When a drive signal is given to FA, ZA, IA, a voltage corresponding to the drive signal is applied to each motor FM, ZM, IM, and each motor FM, ZM, IM is driven at a speed corresponding to the applied voltage. It is like that.

  Therefore, the CPU 30 can control the focus lens FL, the zoom lens ZL, and the iris I at a desired operation speed based on the voltage values of the drive signals output to the amplifiers FA, ZA, and IA. Position information indicating the current position of the focus lens FL, the zoom lens ZL, and the iris I is supplied from the potentiometers FP, ZP, and IP to the CPU 30 via the A / D converter 34, respectively. By controlling the operation speed while referring to these current positions, the positions of the focus lens FL, zoom lens ZL, and iris I can also be controlled.

  On the other hand, a lens controller such as a focus demand 36 for manually operating the focus and a zoom demand 38 for manually operating the zoom can be connected to the lens device 12 as a lens accessory (attached device). The focus demand 36 shown in the figure is a digital lens controller. When the focus demand 36 is connected to the lens device 12, the SCI (serial communication interface) 40, 42 is connected between the focus demand 36 and the CPU 30 of the lens device 12. And various signals are exchanged by serial communication. Thereby, for example, a command signal indicating the target position of the focus is given from the focus demand 36 to the CPU 30 based on a manual operation of a predetermined focus operation member (for example, a focus ring). In the manual focus mode, the CPU 30 controls the position of the focus lens FL based on the command signal, and sets the focus to the target position given by the command signal.

  The zoom demand 38 is an analog lens controller. When the zoom demand 38 is connected to the lens device 12, for example, a command signal indicating a target speed of zoom based on a manual operation of a zoom operation member is sent to the A / D converter 34. Is given to the CPU 30 via The CPU 30 controls the operating speed of the zoom lens ZL based on the command signal, and moves the zoom at the target speed given by the command signal.

  In addition, the lens device 12 is provided with an AF switch S1 for switching between a manual focus mode and an autofocus mode. The CPU 30 executes a manual focus process when the AF switch S1 is off, and executes an autofocus process when the AF switch S1 is turned on. In the manual focus mode, the focus lens FL is controlled based on the command signal from the focus demand 36 as described above.

  On the other hand, in the autofocus mode, serial communication is performed with the CPU 50 of the camera body 10 using the SCIs 44 and 46, and focus information is acquired from the camera body 10 as will be described in detail later. Based on the focus information, the focus lens FL is controlled to perform automatic focus adjustment.

  The camera body 10 includes processing circuits 52A to 58A, 52B to 58B, and the like for generating focus evaluation values indicating the level of contrast of images captured by the AF imaging elements 26A and 26B described above as focus information. Has been. Since the processing circuits 52A to 58A and 52B to 58B are configured similarly for both the AF imaging elements 26A and 26B, the processing circuits 52A to 58A configured for the AF imaging element 26A will be described. To do.

  As shown in the figure, a video signal (luminance signal) output from the AF image sensor 26A is first input to the gate circuit 52A, and only a signal within a predetermined AF area is extracted from the video signal. . AF rear indicates the target range of the subject to be focused by AF on the imaging surface (shooting range) of the AF image sensor 26A. For example, the AF area setting unit 60 allows the operator to change the position and size of the AF area. It can be specified. It is assumed that the shooting range of the AF image sensors 26A and 26B and the shooting range of the video image sensor P are substantially the same. As a method for designating the AF area, for example, the size and shape of the AF area are determined, and the center position of the AF area is designated while looking at a viewfinder (not shown) with a direction indicator switch such as a joystick. Any method may be used, such as a method of touching and specifying a touch panel installed on the viewfinder. The size and shape of the AF area can be specified by a predetermined procedure using the same operation means. The CPU 50 recognizes the position and size of the AF area designated by the operator from the AF area control signal given from the AF area setting unit 60, and sends an AF area setting signal for setting the AF area to the gate circuit 52A. give.

  The video signal extracted from the range of the AF area by the gate circuit 52A is then cut off by the high pass filter (HPF) 54A, and only the high frequency component is extracted. The video signal of the high frequency component extracted by the HPF 54A is converted into a digital signal by the A / D converter 56A.

  The video signal output as a digital signal by the A / D converter 56A is then input to the adder circuit 58A and integrated by the adder circuit 58A for each image (one field in the interlace video signal). The signal obtained by the integration of the adder circuit 58A is a value indicating the degree of focus on the subject in the AF area (contrast level), and the value obtained by the adder circuit 58A is sequentially read by the CPU 50 as a focus evaluation value. It is done. The focus evaluation value obtained from the video signal from the AF image sensor 26A in this way is referred to as the focus evaluation value of the channel (ch) A, and similarly the focus evaluation obtained from the video signal from the AF image sensor 26B. The value is referred to as a chB focus evaluation value.

  The CPU 50 of the camera body 10 transmits the chA and chB focus evaluation values obtained in this way to the CPU 30 of the lens device 12 as focus information. The maximum luminance detection circuit 62 and the shutter control circuit 64 in the camera body 10 shown in FIG.

  Next, an outline of AF processing in the CPU 30 of the lens apparatus 12 will be described. Based on the chA and chB focus evaluation values acquired from the CPU 50 of the camera body 10 as described above, the current focus state of the photographic lens 14 with respect to the imaging surface of the imaging device P for video can be detected.

  FIG. 4 is a diagram illustrating the state of the focus evaluation value with respect to the focus position when a certain subject is photographed, with the horizontal axis indicating the position (focus position) of the focus lens FL of the photographing lens and the vertical axis indicating the focus evaluation value. . A curve C indicated by a dotted line in the figure indicates a focus evaluation value when it is assumed that a focus evaluation value is obtained from a video signal from a video image sensor (or an image sensor arranged at a conjugate position with the video image sensor). The curves A and B indicated by the solid lines in the figure indicate the focus evaluation values of chA and chB obtained from the AF image sensors 26A and 26B, respectively, with respect to the focus position. is there. In the figure, the position F3 at which the focus evaluation value of the curve C is maximum (maximum) is the in-focus position.

When the focus position of the photographic lens 14 is set to F1 in the figure, the chA focus evaluation value V _A1 is a value corresponding to the position F1 of the curve A, and the chB focus evaluation value V _B1 is the position of the curve B. The value corresponds to F1. In this case, the chA focus evaluation value V _A1 is larger than the chB focus evaluation value V _B1 , and therefore, the focus position is set closer to the in-focus position (F3). That is, it can be seen that this is the state of the front pin.

On the other hand, when the focus position of the photographic lens 14 is set to F2 in the figure, the chA focus evaluation value V _A2 is a value corresponding to the position F2 of the curve A, and the chB focus evaluation value V _B2 is the curve B The value corresponds to the position F2. In this case, the chA focus evaluation value V _A2 is smaller than the chB focus evaluation value V _B2 , and therefore, the focus position is set on the infinity side of the focus position (F3). It can be seen that the state is the state of the rear pin.

On the other hand, when the focus position of the photographing lens 14 is set to F3, that is, the in-focus position, the chA focus evaluation value V _A3 is a value corresponding to the position F3 of the curve A, and the chB focus evaluation value V _B3 is a value corresponding to the position F3 of the curve B. At this time, the chA focus evaluation value V _A3 is equal to the chB focus evaluation value V _{B3, which} indicates that the focus position is set to the in-focus position (F3).

  In this way, it is possible to detect whether the current focus state of the photographing lens 14 is the front pin, the rear pin, or the in-focus state based on the focus evaluation values of chA and chB. Therefore, the CPU 30 of the lens device 12 controls the position of the focus lens FL based on the chA and chB focus evaluation values acquired from the CPU 50 of the camera body 10 and moves the focus lens FL to the in-focus position. That is, when the focus evaluation values of chA and chB are determined to be the front pins, the focus lens FL is moved in the infinity direction, and when the focus evaluation values are determined to be the rear pins, When the focus lens FL is moved in the closest direction and the focus lens FL is determined to be in focus, the focus lens FL is set at the focus position by stopping the focus lens FL at that position.

  Next, AF exposure adjustment in the camera body 10 in this system will be described. The exposure adjustment for AF is a process for adjusting the brightness level (the level of the brightness signal) of the video signal obtained from the AF image sensors 26A and 26B to an appropriate level and obtaining an accurate focus evaluation value. 5 and 6 are diagrams comparing the levels of the high frequency components of the luminance signal when the luminance signal level is appropriate and when it is inappropriate. FIG. 5 shows a case where the level of the luminance signal is appropriate. FIG. 5A shows the luminance signal for the subject at the center of the screen when the focus of the photographic lens 14 is in focus on the subject at the center of the screen. The signal of the high frequency component is shown, and FIG. 5B shows the subject at the center of the screen when the focus of the photographing lens 14 is not in focus with respect to the same subject as FIG. A luminance signal and a signal of a high frequency component thereof for the same subject as in A) are shown. In this case, the image of the subject at the center of the screen is blurred in the out-of-focus state as compared to the in-focus state, and the signal of the high frequency component becomes small. Accordingly, the focus evaluation value in this case is maximized when the focus of the photographic lens 14 is in focus, and an appropriate result is obtained.

  On the other hand, FIG. 6 shows a case where the level of the luminance signal is too large and inappropriate, and FIG. 6A shows the center of the screen when the focus of the photographic lens 14 is in focus on the subject at the center of the screen. The luminance signal for the subject and the signal of the high-frequency component thereof are shown, and FIG. 8B shows the center of the screen when the focus of the photographic lens 14 is not in focus with respect to the same subject as FIG. The luminance signal for the subject and the signal of its high frequency component are shown. In this case, the image of the subject at the center of the screen is blurred in the out-of-focus state as compared to the in-focus state, but since the level of the luminance signal is in a saturated state, the signal of the high frequency component does not become small. Rather, since the image becomes larger in both the horizontal direction and the vertical direction, the high-frequency component increases in the out-of-focus state than in the in-focus state, and the focus evaluation value may become maximum in the out-of-focus state. Therefore, autofocus may malfunction unless exposure adjustment is performed so that the luminance signal is at an appropriate level.

  Therefore, in this system, AF exposure adjustment is performed, but AF exposure adjustment in this system is not intended for the entire photographing range, but is performed for the range of the AF area. That is, even if there is an extremely high or low luminance subject outside the AF area, the luminance signal level corresponding to the AF area is not affected thereby, and the luminance signal in the AF area becomes an appropriate level. The exposure is adjusted.

  Exposure adjustment for AF is performed by a maximum luminance detection circuit 62 and a shutter control circuit 64 shown on the camera body 10 side in FIG. The maximum luminance detection circuit 62 acquires the luminance signal of the AF area output by the gate circuit 52A, and detects the maximum value of the luminance signal obtained within a period of one field for each field, for example. Note that the maximum value of the luminance signal output from the gate circuit 52B may be detected.

  The maximum value detected by the maximum luminance detection circuit 62 is given to the shutter control circuit 64, and the shutter control circuit 64 sets the electronic shutter time (charge) in the AF image sensors 26A and 26B so that the maximum value is not saturated. (Accumulation time) is controlled. Thereby, the luminance signal in the AF area is adjusted to an appropriate level. In this system, the position of the AF area can be changed on the shooting screen, but the exposure adjustment range can be changed so that the AF area and the exposure adjustment target range (exposure adjustment range) match as shown in FIG. Therefore, the luminance signal in area A is adjusted to an appropriate level.

  The exposure adjustment for AF is not based on the electronic shutter function, but the brightness signal in the AF area may be adjusted to an appropriate level by using a gain control function for adjusting the gain for the brightness signal. It may be adjusted by a simple diaphragm (a diaphragm arranged at a position that does not affect the subject light incident on the image pickup device P).

  As described above, in the above-described embodiment, the system using the so-called optical path length difference autofocus using the two AF image sensors 26A and 26B has been described. However, the present invention is different from the image sensor for video. The present invention can be applied to a system that includes an image sensor and performs autofocus processing based on a video signal obtained by the AF image sensor.

FIG. 1 is a diagram showing a schematic configuration of a moving image shooting camera such as a television camera to which the present invention is applied. FIG. 2 is a diagram illustrating the image pickup device and the pair of AF image pickup devices on the same optical axis. FIG. 3 is a block diagram illustrating a system configuration mainly related to autofocus in the camera body and the lens apparatus. FIG. 4 is an explanatory diagram used for explaining the principle of detecting the focus state. FIG. 5 is an explanatory diagram used for explaining the AF exposure adjustment. FIG. 6 is an explanatory diagram used for explaining AF exposure adjustment. FIG. 7 is an explanatory diagram used for explaining AF exposure adjustment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Camera body, 12 ... Lens apparatus, 14 ... Shooting lens, 20 ... Color separation optical system, P ... Image sensor for image, 26A, 26B ... Image sensor for AF, FL ... Focus lens (group), FM ... For focus Motor, 30, 50 ... CPU, S1 ... AF switch, 52A, 52B ... Gate circuit, 54A, 54B ... High pass filter (HPF), 56A, 56B ... A / D converter, 58A, 58B ... Adder circuit, 60 ... AF Area setting section, 62 ... maximum luminance detection circuit, 64 ... shutter control circuit

Claims (3)

Branching means for branching the subject light incident on the photographing lens to an optical path different from the optical path leading to the imaging surface of the imaging means for video for acquiring video signals for moving image reproduction, and imaging the subject light branched by the branching means An AF imaging means for obtaining a video signal for performing autofocusing on the photographing lens, and a video signal obtained from an AF area in a partial area of the imaging surface of the AF imaging means. In an autofocus system comprising AF processing means for executing autofocus processing by a contrast method,
An exposure adjustment unit that detects the luminance of a subject imaged in the AF area on the imaging surface of the AF imaging unit, and performs exposure adjustment only on the AF imaging unit based on the detected luminance;
An autofocus system characterized by comprising 2. The autofocus system according to claim 1, wherein the exposure adjustment unit performs exposure adjustment by an electronic shutter function or a gain control function in the AF imaging unit. The AF imaging means includes a plurality of imaging surfaces having optical path length differences, and the AF processing means focuses the photographing lens at a focus position based on a plurality of video signals obtained from the AF areas of the imaging surfaces. The autofocus system according to claim 1, wherein the autofocus system is set.

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