JP2008046385A - Image-pickup apparatus and focus control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image-pickup apparatus which can prevent focus control from being performed on the basis of incorrect information externally measured. <P>SOLUTION: The image-pickup apparatus includes: a first detection means 121 which generates first information corresponding to a contrast state of a picked-up image; a second detection means 141 which receives light from an object to detect second information different from the first information; and a control means 130 which performs the focus control by using the first information and the second information. The control means performs the focus control by using the first information without using the second information when a state that a light-receiving luminance level in the second detection means is lower than a first value is continued longer than a first time. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an imaging apparatus such as a video camera or a digital still camera, and more particularly to focus control in the imaging apparatus.

In autofocus (AF) control of a video camera or the like, an AF evaluation value signal indicating the sharpness (contrast state) of a video signal generated using an image sensor is generated, and a focus lens that maximizes the AF evaluation value signal The TV-AF method for searching for the position of the TV is the mainstream.

  In the AF method, a distance measuring sensor is provided independently of the photographing lens, and the focus lens is calculated from the distance to the subject detected by the distance measuring sensor, and the focus lens is moved there. There is a distance measurement method (external measurement phase difference detection method).

  In the external measurement phase difference detection method, a light beam received from a subject is divided into two, and the two divided light beams are received by a set of light receiving element arrays (line sensors). Then, a shift amount of the image formed on the set of line sensors, that is, a phase difference is detected, a subject distance is obtained from the phase difference using a triangulation method, and a position where the subject distance is focused Move the focus lens to.

Further, there is a hybrid AF method in which these AF methods are combined. In the hybrid AF method, for example, after the focus lens is driven to the vicinity of the focus position by the internal phase difference detection method, the focus lens is driven to the focus position with higher accuracy by the TV-AF method (see, for example, Patent Document 1). ). There is also a hybrid AF method that combines an external measurement phase difference detection method and a TV-AF method (see, for example, Patent Document 2). In the hybrid AF method proposed in Patent Document 2, which method is used for focus control is selected according to the amount of change in each signal in the TV-AF method and the external measurement phase difference detection method.
JP-A-5-64056 (paragraphs 0008 to 0009, FIG. 1 etc.) JP-A-2005-234325 (paragraphs 0037 to 0062, FIG. 3, etc.)

  However, in the hybrid AF using both the TV-AF method and the external distance measuring method, accurate subject distance information cannot be obtained when an obstacle other than the subject exists between the distance measuring sensor and the subject. For example, the distance measuring sensor is generally arranged around the photographing lens in order to avoid parallax between the photographing visual field by the photographing lens and the detection visual field by the distance measuring sensor as much as possible. In this case, there are many cases where the photographer's hand or the like is placed between the distance measuring sensor and the subject and the incidence of light from the subject to the distance measuring sensor is blocked.

  If the light from the subject is blocked from entering the distance measuring sensor, it may take longer to focus or focus may not be achieved. It is impossible to take advantage of the high speed of the focus.

  An object of the present invention is to provide an imaging apparatus and a focus control method that can avoid performing focus control based on erroneous external measurement information.

  An imaging apparatus according to an aspect of the present invention includes a first detection unit that generates first information corresponding to a contrast state of a captured video, and a second detection unit that receives light from a subject and is different from the first information. A second detection unit configured to detect information; and a control unit configured to perform focus control using the first information and the second information. When the state in which the light reception luminance level at the second detection unit is lower than the first value continues for longer than the first time, the control unit uses the first information without using the second information. And focus control is performed.

  According to another aspect of the present invention, there is provided an imaging apparatus including: a first detection unit that generates first information corresponding to a contrast state of a captured image; and at least a pair of light receiving element arrays each having a plurality of light receiving elements. And a second detection means for generating a second information different from the first information by calculating a correlation of signals output from the light receiving element array, and using the first information and the second information Control means for performing focus control. The control means does not use the second information when the state in which the correlation value of the signals output from at least the pair of light receiving element arrays is lower than the first value continues longer than the first time. In addition, focus control is performed using the first information.

  According to another aspect of the present invention, there is provided a focus control method in which first information corresponding to a contrast state of a captured image is acquired, and detection information that receives light from a subject is different from the first information. And a control step of performing focus control using the first information and the second information. Then, in the control step, when the state where the light receiving luminance level at the detection means is lower than the first value continues for longer than the first time, focus is performed using the first information without using the second information. Control is performed.

  Furthermore, a focus control method as another aspect of the present invention is a step of acquiring first information corresponding to a contrast state of a captured image, and is output from at least a pair of light receiving element arrays each having a plurality of light receiving elements. By calculating the correlation of the signals, the method includes a step of acquiring second information different from the first information, and a control step of performing focus control using the first information and the second information. Then, in the control step, the second information is not used when the state in which the correlation value of the signals output from at least the pair of light receiving element arrays is lower than the first value continues longer than the first time. In addition, focus control is performed using the first information.

  According to the present invention, when the received light luminance level or the correlation value of the second detection means (or detection means) remains low for a certain period of time, the second information is likely to be incorrect information. Focus control using the first information is performed without performing focus control using the second information. As a result, it is possible to obtain a correct in-focus state while avoiding the focus control using erroneous second information.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 shows the configuration of a video camera (imaging device) that is Embodiment 1 of the present invention. In this embodiment, a video camera will be described, but the present invention can also be applied to other imaging devices such as a digital still camera.

  In the figure, 102 is a fixed lens that is fixed, 103 is a stop, and 104 is a focus lens that moves in the optical axis direction to adjust the focus. The fixed lens 102, the diaphragm 103, and the focus lens 104 constitute an imaging optical system.

  Reference numeral 111 denotes an image sensor as a photoelectric conversion element constituted by a CCD sensor or a CMOS sensor. The light flux from the subject forms an image on the image sensor 111 through the fixed lens 102, the diaphragm 103 and the focus lens 104. The subject image is photoelectrically converted by the image sensor 111, and an image signal is output from the image sensor 111.

  A focus driving circuit 124 drives the focus lens 104 in the optical axis direction. The focus drive circuit 124 includes an actuator such as a stepping motor, a DC motor, a vibration motor, and a voice coil motor, and a drive circuit that drives the actuator.

  A camera signal processing circuit 112 converts an imaging signal output from the imaging device 111 into a standard video signal (video signal) such as NTSC. A recording unit 201 records a video signal output from the camera signal processing circuit 112 on a recording medium such as a magnetic tape, an optical disk, or a semiconductor memory.

  Reference numeral 202 denotes a monitor constituted by an LCD or the like, which displays the video signal output from the camera signal processing circuit 112 as an image.

  Reference numeral 204 denotes a display setting circuit, which outputs a character display signal indicating a character such as a character or graphic prepared in a memory (not shown) of the display setting circuit 204 to the superimposing circuit 205. In this case, video and characters are displayed on the monitor 202 in this case.

  Reference numeral 121 denotes a focus signal detection circuit as a first detection means. The focus signal detection circuit 121 extracts a high frequency component, a luminance difference component generated from the high frequency signal (difference between the maximum value and the minimum value of the luminance level) and the like from the luminance signal component of the video signal output from the camera signal processing circuit 112. Then, an AF evaluation value signal as the first information is generated. The AF evaluation value signal represents the sharpness (contrast state) of the image generated based on the image pickup signal from the image pickup device 111, but the sharpness changes depending on the focus state of the image pickup optical system. The signal represents the focus state of the imaging optical system.

  Reference numeral 131 denotes an AF control circuit, which is configured in a microcomputer (CPU) 130. The microcomputer 130 as a control unit controls the operation of the entire video camera. The AF control circuit 131 controls the focus driving circuit 124 to perform focus control for moving the focus lens 104. The AF control circuit 131 performs focus control in the TV-AF method (hereinafter simply referred to as TV-AF) and focus control in the external distance measurement (external measurement phase difference detection) method (hereinafter simply referred to as external measurement). AF).

  The TV-AF is focus control for obtaining focus by moving the focus lens 104 to monitor a change in the AF evaluation value signal and detecting a focus lens position where the AF evaluation value signal is maximized.

  As the AF evaluation value signal, a high-frequency component extracted by a band-pass filter in a certain band among luminance signal components of a video signal is generally used. This high-frequency component changes as shown in FIG. 5 when a subject at a specific distance is imaged and the focus lens 104 is moved from the closest position to the infinite position. In FIG. 5, the focus lens position where the AF evaluation value is maximized is the focus position (focus point) for the subject.

  Further, in FIG. 1, reference numeral 141 denotes an external distance measuring sensor unit as a second detection unit, which detects a subject distance and inputs subject distance information as second information to the AF control circuit 131. The AF control circuit 131 calculates a position where the in-focus state is obtained with respect to the subject distance according to the input subject distance information, and moves the focus lens 104 to the in-focus position. This is external measurement AF. Here, the “calculation” includes not only calculation using a calculation formula but also reading out data on the in-focus position with respect to the subject distance stored in advance in a memory (not shown).

  Here, the detection principle of the subject distance using the external distance measuring sensor unit 141 will be described. Various methods have been conventionally used as the distance measuring method, and FIGS. 7 and 8 show the principle of distance measurement by the phase difference passive method, which is one of them.

  In the present embodiment, the external distance measuring sensor unit 141 is used as a distance measuring sensor for a so-called passive AF method. The external distance measuring unit 141 is provided separately from the imaging optical system. That is, a light beam from a subject that does not pass through the imaging optical system is incident on the external distance measuring unit 141.

  A configuration example of the external distance measuring sensor unit 141 is shown in FIG. In FIG. 7, 301 is a subject, 331 is a first imaging lens, 341 is a first light receiving element array (line sensor), 332 is a second imaging lens, and 342 is a second light receiving element array (line sensor). ). Each of the first and second line sensors 341 and 342 is configured by arranging a plurality of light receiving elements (pixels) in a line. The first and second line sensors 341 and 342 are spaced apart from each other by the base line length B.

  Of the light from the subject 301, the light passing through the first imaging lens 331 forms an image on the first line sensor 341, and the light passing through the second imaging lens 332 is the second line sensor 342. Image on top.

  Two subject images formed on the line sensors 341 and 342 are photoelectrically converted by the respective line sensors. The signals (image signals) read from the line sensors 341 and 342 are accumulated in the line memories 351 and 352, respectively. FIG. 8 shows an image signal 451 read from one line sensor 341 and accumulated in the line memory 351, and an image signal 452 read from the other line sensor 342 and accumulated in the line memory 352. ing.

  The two image signals accumulated in the line memories 351 and 352 are input to the correlation calculation circuit 361. The correlation calculation circuit 361 calculates a decorrelation value between the two image signals.

  Specifically, first, the light amount (light reception luminance) for each pixel of the line sensor 341 is compared with the light amount for each corresponding pixel in the line sensor 342, and the difference is obtained for each pixel pair. Then, the uncorrelated value is obtained by adding the light amount differences of all the pixel pairs.

  Next, one pixel of the pixel pair for which the light amount difference has been previously obtained is shifted (shifted) by one pixel relative to the other pixel, and the light amount difference and non-correlation are the same as described above. Find the value. In this way, the non-correlation value for each shift amount is calculated while sequentially shifting one pixel of the pixel pair one pixel at a time in the same direction. Similarly, the decorrelation value for each shift amount is calculated while sequentially shifting one pixel of the pixel pair in the opposite direction with respect to the other pixel.

  As a result of the above calculation, the pixel shift amount in the pixel pair having the smallest non-correlation value, that is, the smallest difference in luminance between the pixels among the pixel pairs in which the light amounts are compared becomes the maximum correlation value shift amount. That is, in FIG. 8, when the correlation between the image signals 451 and 452 is obtained, the distance X between the comparison pixels 441 and 442 that minimizes the uncorrelation value is the shift amount X that maximizes the correlation. Further, the shift amount at that time can be obtained by “the number of pixels shifted × pixel size”.

  Next, based on this pixel shift amount, the subject distance calculation circuit 362 obtains the distance L to the subject based on the principle of triangulation.

  When the pixel shift amount is X (see FIG. 7), the base line length is B, and the focal lengths of the imaging lenses 331 and 332 are f, the subject distance L is obtained by the following equation (1).

    L = B · f / X (1).

  In the present invention, not only the passive distance measuring method but also other distance measuring methods can be used. For example, as an active distance measuring method, a method for obtaining a distance by the principle of triangulation by projecting infrared rays may be used. Further, the pixel shift amount X (second information) may be output from an external distance measuring unit, and the subject distance may be obtained based on the X by a microcomputer.

  In FIG. 1, 136 is a level change time determination circuit. The level change time determination circuit 136 has a luminance component level (hereinafter referred to as a received light luminance level) of an image signal output from the line sensors 341 and 342 of the external ranging sensor unit 141 having a specific luminance level (first luminance level). Value) is determined. Further, it is determined whether or not the state in which the light reception luminance level is lower than the specific luminance level continues for a longer period than the specific time (first time). The specific brightness level and the specific time are stored in advance in a memory (not shown) in the microcomputer 130. The level change time determination circuit 136 transmits the determination result to the AF control circuit 131 in the microcomputer 130.

  Next, AF control by the microcomputer 130 including the AF control circuit 131 in this embodiment will be described with reference to the flowchart shown in FIG. This AF control is executed according to a computer program stored in the microcomputer 130. This is the same in other embodiments described later.

  In step (hereinafter referred to as S) 700, the microcomputer 130 starts AF control. The processing shown in this flow is executed, for example, in the readout cycle of the imaging signal from the imaging device 111 for generating a one-field image.

  In S701, the microcomputer 130 determines whether or not the in-focus state is obtained. If it is determined that it is in focus, the process proceeds to S708. If it is determined that it is not in focus, the process proceeds to S702. The determination of the focus state here can be performed in the same manner as the focus determination process in the TV-AF operation described later.

  In step S <b> 702, it is determined whether or not the focus lens 104 is in focus operation by external measurement AF. If the in-focus operation is being performed, the process proceeds to S708. If the in-focus operation is not being performed, the process proceeds to S703.

  In S703, the TV-AF operation shown in the flowchart of FIG. 6 is executed.

  In FIG. 6, when the focusing process is started in S1001, an AF evaluation value signal is acquired from the focus signal processing circuit 121 in S1002.

  In S1003, the focus flag is confirmed. If the in-focus state is cleared, the process proceeds to S1004. If the in-focus state is set, the process proceeds to S1010.

  In S1004, it is determined whether or not an in-focus determination has been made. The in-focus determination is performed when the number of times the moving direction of the focus lens 104 is alternately reversed in S1006 and S1007, which will be described later, is equal to or greater than a predetermined number. If the in-focus determination is made, the process proceeds to S1008. If the in-focus determination is not made, the process proceeds to S1005.

  In step S1005, it is determined whether the moving direction of the focus lens 102 is correct. For example, if the AF evaluation value acquired in the current routine increases relative to the AF evaluation value acquired in the previous routine, it is determined that the movement direction of the focus lens 104 is correct because it is the direction toward the in-focus position. The process proceeds to S1007. On the other hand, if the AF evaluation value acquired this time has decreased with respect to the previously acquired AF evaluation value, the movement direction of the focus lens 104 is opposite to the in-focus position, so that it is determined as an error and the process proceeds to S1006.

  In S1006, the moving direction of the focus lens 104 is reversed.

  In step S1007, the focus lens 104 is further moved in the same direction as before.

  In step S1008, the focus state is determined, and the movement of the focus lens 104 is stopped to maintain the focus state.

  In S1009, an in-focus flag is set, and the AF evaluation value in the in-focus state is stored in a memory (not shown).

  In S1010, it is determined whether or not the AF evaluation value stored in the previous routine in S1009 differs from the AF evaluation value captured in the current routine by a predetermined value or more. When the AF evaluation value captured this time has decreased by a predetermined value or more with respect to the stored AF evaluation value, the process proceeds to S1011 because it is out of focus. If the amount of decrease of the AF evaluation value captured this time with respect to the stored AF evaluation value is less than the predetermined value, it is determined that the in-focus state is maintained and the process proceeds to S1012.

  In S1011, the focus flag is cleared.

  In S1012, instead of the previously stored AF evaluation value, the currently acquired AF evaluation value is stored in a memory (not shown).

  In S1013, the TV-AF operation is terminated.

  In S704 of FIG. 2, based on the subject distance information obtained from the external distance measuring sensor unit 141, the position of the focus lens 104 at which the focus is obtained with respect to the subject distance (hereinafter referred to as the outer focus position). calculate. Then, the external focus position is compared with the current focus lens 104 position detected by a lens position detector (not shown) to determine whether the current focus lens 104 position is out of the external focus position. Determine whether. If the focus lens 104 is located outside the predetermined range including the outer measurement focus position, the process proceeds to S705. If the focus lens 104 is located within the predetermined range with respect to the outer measurement focus position, the process proceeds to S708.

  In S705, it is determined whether or not the received light luminance level at the line sensors 341 and 342 of the external distance measuring sensor unit 141 is lower than a specific luminance level (first value). In this embodiment, it is determined whether or not the light reception luminance level of each line sensor in the pair of line sensors 341 and 342 is lower than a specific luminance level. However, it may be determined whether or not the value obtained by adding the light reception luminance levels of the pair of line sensors 341 and 342 is lower than the specific luminance level.

  Furthermore, in this step, when it is determined that the light reception luminance level is lower than the specific luminance level, it is determined whether or not a state lower than the specific luminance level continues for a longer time than the specific time. If it is longer than the specific time, the process proceeds to S709, and if not, the process proceeds to S706.

  In S706, the direction of the external focus position calculated from the subject distance information obtained by the external distance sensor unit 141 is the same as the focus direction determined in the TV-AF of S703 (S1005 in FIG. 6). It is determined whether or not. If they are in the same direction, the subject distance detection result by the external sensor is assumed to be correct, and the process proceeds to S707. If they are not the same, the process proceeds to S708.

  In step S707, the focus lens 104 is moved to the external measurement focus position. That is, external measurement AF is performed.

  In step S <b> 709, the monitor 202 displays, for example, a character such as “distance sensor information is not used” or a graphic indicating this to the display setting circuit 204.

  In step S708, the AF control process ends.

  Here, a change in the light reception luminance level of the external ranging sensor unit 141 will be described with reference to FIG.

  In the figure, reference numeral 481 is an example of a temporal change in the received light luminance level of the external distance measuring sensor unit 141. The brightness of the light reception brightness level 481 (indicated by the vertical axis) varies with the time indicated by the horizontal axis due to causes such as movement of the subject and camera shake.

  The magnitudes of luminance indicated by ‘a’, ‘b’, ‘c’, ‘d’, ‘e’, ‘f’,... Are the amount of change in luminance per unit time. For example, the light reception luminance level of the external ranging sensor unit 141 (line sensors 341, 342) is sampled at the readout period of the imaging signal, and the difference between the previous sampling value and the current sampling value is taken to obtain a unit per unit time. A luminance change amount can be obtained.

  The figure shows a change in luminance when the front surface of the external ranging sensor unit 141 is covered with an obstacle such as a photographer's hand at the time indicated by 'P'. Since the outer distance measuring sensor unit 141 is covered with an obstacle, light from the subject does not enter the outer distance measuring sensor unit 141, so that the received light intensity level rapidly decreases to a value smaller than the specific luminance level L1. . Further, after the received light luminance level is lowered to a value smaller than the specific luminance level L1, it hardly fluctuates as indicated by 'x'.

  Let t1 be the sampling time immediately after the received light luminance level has decreased from a value greater than the specific luminance level L1 to a smaller value. If the received light luminance level is still lower than the specific luminance level L1 even at the sampling time t2 when the specific time T has elapsed from this time t1, the process proceeds from S705 to S709 in FIG.

  If there is no obstacle covering the outside ranging sensor unit 141 before the specific time T elapses and the light reception luminance level returns to a value larger than the specific luminance level L1, the process proceeds to S706. .

  The specific time T is appropriately set, for example, based on the maximum time required for focus control from the out-of-focus state to the in-focus state when the external ranging sensor unit 141 is not covered with an obstacle.

  As described above, in this embodiment, the subject distance obtained by the external distance measuring sensor unit 141 depending on whether or not the state in which the light receiving luminance level at the external distance measuring sensor unit 141 is lower than the specific luminance level has continued for a specific time. It is determined whether or not to perform external measurement AF using information. When the light receiving luminance level is low for a specific time, TV-AF is performed. This avoids performing external measurement AF using erroneous subject distance information when there is an obstacle such as a photographer's hand in the optical path between the external distance measuring sensor unit 141 and the subject, A correct in-focus state by TV-AF can be obtained.

  Further, according to the present embodiment, since it is determined whether or not the external measurement AF is performed based on the light reception luminance level of both the pair of line sensors 341 and 342, the optical path from the subject to both the line sensors 341 and 342 is determined. Even when is blocked, the above effect can be obtained.

  FIG. 3 shows the configuration of a video camera that is Embodiment 2 of the present invention. In the present embodiment, the same components as those in the first embodiment are denoted by the same reference numerals as those in the first embodiment.

  In the first embodiment, it is determined whether or not the external AF is performed using the light receiving luminance level in the external distance measuring sensor unit 141. In the present embodiment, however, the correlation value of the outputs from the pair of line sensors 341 and 342 is determined. Is used to determine whether or not to perform external measurement AF.

  The method of calculating the decorrelation value and the method of calculating the subject distance in the external distance measuring sensor unit 141 are as described in the first embodiment. That is, the two image signals read from the line sensors 341 and 342 shown in FIG. 7 and accumulated in the line memories 351 and 352 are input to the correlation calculation circuit 361, where the uncorrelated values of the two image signals are obtained. Is calculated. In addition, the subject distance is calculated by the subject distance calculation calculation circuit 362 based on the shift amount between the light quantity comparison pixels having the smallest uncorrelation value (maximum correlation value) among the pixels on the line sensors 341 and 342. Is done.

  In FIG. 3, reference numeral 137 denotes a correlation value change time determination circuit, which determines whether or not the correlation value of two image signals read from the pair of line sensors 341 and 342 is lower than a specific value (first value). To do.

  Furthermore, the correlation value change time determination circuit 137 determines whether or not the state where the correlation value is lower than the specific value continues longer than the specific time (first time). The specific value and the specific time are stored in advance in a memory (not shown) in the microcomputer 130. The correlation value change time determination circuit 137 transmits the determination result to the AF control circuit 131 in the microcomputer 130.

  Here, the correlation value will be described with reference to FIG. In FIG. 9, 451 ′ is an image signal read from one line sensor 341 and accumulated in the line memory 351, and 452 ′ is an image signal read from the other line sensor 342 and accumulated in the line memory 352. is there. In FIG. 9, the image signals 451 ′ and 452 ′ are shown superimposed in a state where they are shifted by the shift amount X so that their correlation values are maximized.

  Reference numerals 454 and 455 indicate maximum shift amounts when a correlation value is obtained in a predetermined correlation comparison area. Generally, the correlation value can be obtained with high accuracy by setting the maximum shift amount to a shift amount corresponding to 1/2 or more of the length of the line sensor.

  A portion 453 indicated by hatching corresponds to the decorrelation value of the two image signals described in the first embodiment. The smaller the decorrelation value 453, that is, the greater (higher) the correlation value, the more accurately the subject distance can be obtained.

  Next, AF control by the microcomputer 130 including the AF control circuit 131 will be described using the flowchart of FIG.

  In S400, the microcomputer 130 starts AF control. The processing shown in this flow is executed, for example, in the readout cycle of the imaging signal from the imaging device 111 for generating a one-field image.

  In S401, the microcomputer 130 determines whether or not the in-focus state is obtained. If it is determined that it is in focus, the process proceeds to S408, and if it is determined that it is not in focus, the process proceeds to S402. The determination of the focus state here can be performed in the same manner as the focus determination process in the TV-AF operation described later.

  In S402, it is determined whether or not the focus lens 104 is in focus operation by external measurement AF. If the focusing operation is being performed, the process proceeds to S408, and if the focusing operation is not being performed, the process proceeds to S403.

  In S403, the TV-AF operation shown in the flowchart of FIG. 6 is executed.

  In S404, based on the subject distance information obtained from the external distance measuring sensor unit 141, the outer focus position of the focus lens 104 that can be focused on the subject distance is calculated. Then, the outer focus position is compared with the current focus lens 104 position to determine whether or not the current focus lens 104 position is out of the outer focus position. If the focus lens 104 is located outside the predetermined range including the outer measurement focus position, the process proceeds to S405. If the focus lens 104 is located within the predetermined range with respect to the outer measurement focus position, the process proceeds to S408.

  In S405, it is determined whether or not the correlation value of the image signals on the line sensors 341 and 342 obtained from the external distance measuring sensor unit 141 is lower than a specific value.

  Further, in this step, when it is determined that the correlation value is lower than the specific value, it is determined whether or not a state lower than the specific value continues for a longer time than the specific time. If it has continued for a longer time than the specific time, the process proceeds to S408, and if not, the process proceeds to S406.

  In S406, it is determined whether or not the direction of the out-of-focus position relative to the current position of the focus lens 104 is the same as the correct movement direction of the focus lens 104 determined in the TV-AF process (S1005 in FIG. 6) in S403. judge. If they are the same, the external measurement focus position (or subject distance information) is correct and the process proceeds to S407, and if they are not the same, the process proceeds to S408.

  In step S407, the focus lens 104 is moved to the external measurement focus position. That is, external measurement AF is performed.

  In S408, the AF control process is terminated.

  As described above, in this embodiment, the subject distance obtained by the sensor unit 141 according to whether or not the state in which the correlation value of the image signal obtained by the external distance measuring sensor unit 141 is lower than the specific value has continued for a specific time. It is determined whether or not to perform external measurement AF using information. Then, when the state where the correlation value is low continues for a specific time, TV-AF is performed. This avoids performing external measurement AF using erroneous subject distance information when there is an obstacle such as a photographer's hand in the optical path between the external distance measuring sensor unit 141 and the subject, A correct in-focus state by TV-AF can be obtained.

1 is a block diagram showing a configuration of a video camera that is Embodiment 1 of the present invention. 3 is a flowchart illustrating an AF control procedure according to the first embodiment. The block diagram which shows the structure of the video camera which is Example 2 of this invention. 9 is a flowchart illustrating an AF control procedure according to the second embodiment. The figure which shows the principle of TV-AF in an Example. The flowchart which shows the control procedure of TV-AF in an Example. The figure which shows the ranging method in an Example. The figure which shows the waveform of the image signal used for the correlation calculation in an Example. The conceptual diagram of the correlation calculation in Example 2. FIG. FIG. 6 is a diagram illustrating an example of a change in received light luminance level of the external ranging sensor unit according to the first embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 104 Focus lens 111 Image pick-up element 121 Focus signal detection circuit 130 Microcomputer 131 AF control circuit 136 Level change time determination circuit 137 Correlation value change time determination circuit 141 External distance measuring sensor unit

Claims (9)

First detection means for generating first information corresponding to a contrast state of a captured image;
Second detection means for detecting second information different from the first information in response to light from a subject;
Control means for performing focus control using the first information and the second information,
When the light receiving luminance level at the second detection means is lower than the first value for a longer time than the first time, the control means does not use the second information and does not use the second information. An image pickup apparatus that performs focus control using information. The second detection means has a plurality of light receiving sensors,
The control means does not use the second information when the light receiving luminance level of each light receiving sensor is lower than the first value for a longer time than the first time. The image pickup apparatus according to claim 1, wherein focus control is performed using an image sensor. The second detection means has a plurality of light receiving sensors,
When the state where the sum of the received light intensity levels of the respective light receiving sensors is lower than the first value continues for a longer time than the first time, the control means does not use the second information and does not use the first information. The imaging apparatus according to claim 1, wherein focus control is performed using the information.   The control means is a case where the received light luminance level at the second detection means is higher than the first value, and the direction of the focus position of the focus lens obtained based on the second information is the first value. 4. The imaging apparatus according to claim 1, wherein focus control is performed using the second information when the direction is obtained based on the information of 1. 5. First detection means for generating first information corresponding to a contrast state of a captured image;
A second light-receiving element array that has at least a pair of light-receiving element arrays each having a plurality of light-receiving elements, calculates a correlation of signals output from the light-receiving element arrays, and generates second information different from the first information Detection means;
Control means for performing focus control using the first information and the second information,
When the state in which the correlation value of the signals output from the at least one pair of light receiving element arrays is lower than the first value continues for a longer time than the first time, the control means outputs the second information. An image pickup apparatus that performs focus control using the first information without using the first information.   The control means obtains the direction of the focus position of the focus lens obtained based on the second information based on the first information when the correlation value is higher than the first value. The imaging apparatus according to claim 5, wherein focus control is performed using the second information when the direction coincides with the direction.   The imaging apparatus according to claim 1, wherein the second detection unit detects the second information corresponding to a distance to a subject. Obtaining first information corresponding to a contrast state of a captured image;
Obtaining second information different from the first information by detecting means for receiving light from a subject;
A control step of performing focus control using the first information and the second information,
In the control step, the first information is used without using the second information when a state in which the light reception luminance level at the detection unit is lower than the first value continues for a longer time than the first time. Focus control method characterized by performing focus control. Obtaining first information corresponding to a contrast state of a captured image;
Obtaining second information different from the first information by calculating a correlation between signals output from at least a pair of light receiving element arrays each having a plurality of light receiving elements;
A control step of performing focus control using the first information and the second information,
In the control step, the second information is used when a state in which the correlation value of the signals output from the at least one pair of light receiving element arrays is lower than the first value continues longer than the first time. A focus control method, wherein focus control is performed using the first information.