JP2017009740A - Imaging apparatus, and auto-focusing control method and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an imaging apparatus capable of auto-focusing an object at a greater distance under a low-illuminance environment.SOLUTION: A digital camera 100 includes an AE sensor 17 which measures the brightness of an object, and a system control part 50 which determines whether the imaging is under a low-illuminance environment or not based on the photometric results (S402). When the imaging is determined to be under a low-illuminance environment, an AF auxiliary light emitting part 66 emits AF auxiliary light for auto-focusing by a contrast detection method (S502). When focusing cannot be achieved, a built-in strobe light 65 is pre-flashed for auto-focusing by a phase difference detection method (S506).SELECTED DRAWING: Figure 5

Description

  The present invention relates to an imaging apparatus such as a digital camera or a digital video camera, an autofocus control method in the imaging apparatus, and a program.

  A contrast detection method is mainly used for autofocus (AF) control of a compact digital camera. In the contrast detection method, an AF evaluation value is generated based on the contrast of an image signal generated using an image sensor, and a focus lens position where the generated AF evaluation value is maximized is searched.

  On the other hand, a phase difference detection method is mainly used for AF control of a digital single-lens reflex camera. In the phase difference detection method, a light beam from a subject that has passed through different exit pupil regions of an imaging lens is imaged on a pair of line sensors that constitute an AF sensor. Then, by calculating the relative position of the pair of subject images obtained by the pair of line sensors, the amount of deviation of the focus lens from the in-focus position is detected.

  The phase difference detection method has an advantage that high-speed focusing is possible because the AF operation can be performed without moving the focus lens. However, since the AF sensor is an independent component that is different from the image sensor that outputs the captured image, the focusing accuracy may be reduced due to various factors such as attachment errors of the AF sensor, camera body, lens, etc., and aged deterioration. There is.

  Also, since the AF sensor generally operates on a subject at a predetermined position within the angle of view, the area where AF can be performed is limited. In recent years, an imaging device in which an AF sensor (phase difference detection pixel) is arranged on an imaging element for imaging has been supplied to the market. However, such an imaging device still has this problem. .

  On the other hand, since the contrast detection method performs AF using an image that is actually output, the AF accuracy can be improved. In addition, since AF can be executed at any position on the image, for example, it is advantageous in an imaging mode in which a human face is detected and an AF operation is preferentially performed on the detected face. However, in the contrast detection method, it is necessary to obtain the AF evaluation value while moving the focus lens, and to continue moving the focus lens until it is determined that the obtained AF evaluation value is the maximum as a result. Then, it is inferior to the phase difference detection method.

  Therefore, so-called hybrid AF control is proposed in which a contrast detection method capable of high-precision AF and a phase difference detection method capable of high-speed AF are combined. In the hybrid AF control, for example, after the focus lens is driven to the vicinity of the in-focus position by the phase difference detection method, the focus lens is moved to the optimum in-focus position with higher accuracy by the contrast detection method (for example, , See Patent Document 1).

Japanese Unexamined Patent Publication No. 7-043605

  However, when imaging is performed in a low illuminance environment, any of the above-described AF methods has a problem that AF accuracy is lowered and that it takes time to determine the focus position of the focus lens. In order to avoid such a problem, the main body of the imaging apparatus or the external strobe is often equipped with a light source that emits AF auxiliary light for facilitating AF to the subject. However, since AF auxiliary light generally reaches only a short distance, it is not easy to perform AF on a subject existing at a distance exceeding the AF auxiliary light.

  An object of the present invention is to provide an imaging apparatus that can extend the distance at which AF can be performed in a low illumination environment and can perform AF operation at high speed and with high accuracy.

  An image pickup apparatus according to the present invention includes a strobe light emitting unit that emits strobe light toward a subject, an auxiliary light emitting unit that emits auxiliary light for autofocus toward the subject, and the auxiliary light emitting unit. The first autofocus is performed by the contrast detection method by emitting the auxiliary light, and when the focus cannot be achieved by the first autofocus, the strobe light emitting means is pre-emitted and the second by the phase difference detection method. And a control means for performing auto-focusing.

  According to the present invention, it is possible to extend the distance at which AF can be performed in a low illumination environment, and to perform the AF operation at high speed and with high accuracy.

1 is an external perspective view of a camera body constituting a digital camera that is an example of an imaging apparatus according to an embodiment of the present invention. 1 is a block diagram illustrating a schematic configuration of a digital camera that is an example of an imaging apparatus according to an embodiment of the present invention. FIG. 2 is a perspective view showing a state in which a built-in strobe is housed in the camera body and a state in which the camera body pops up from the camera body in the camera body shown in FIG. 1. It is a flowchart of AF control in the digital camera of FIG. 6 is a flowchart of a first example of AF processing in a low-light environment in step S404 in FIG. It is a flowchart of the 2nd example of AF process in the low illumination intensity environment of step S404 of FIG. FIG. 6 is a schematic diagram showing comparison between AF evaluation values when a subject is present at a short distance and when an object is present at a medium distance.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. First, a configuration of a digital camera as an example of an imaging apparatus according to the present invention will be described. In the present embodiment, a camera with an interchangeable lens (lens barrel) attached to the camera body is referred to as a digital camera. In the following description, “AF” is an abbreviation for “autofocus”.

  FIG. 1A is an external perspective view of a camera body 100A constituting a digital camera, which is an example of an imaging apparatus according to an embodiment of the present invention, as viewed from the front side (subject side). FIG. 1B is an external perspective view of the camera body 100A as viewed from the back side.

  The camera body 100 </ b> A includes a communication terminal 10, a quick return mirror 12, an eyepiece finder 16, a display unit 28, a terminal cover 40, an outside finder display unit 43, a mode switch 60 and a shutter button 61. The camera body 100A includes a built-in strobe 65 (strobe light emitting means) and an AF auxiliary light emitting unit 66 (autofocus auxiliary light emitting means). Further, the camera body 100A includes a main electronic dial 71, a power switch 72, a sub electronic dial 73, a cross key 74, a SET button 75, an LV button 76, an enlargement button 77, a reduction button 78, a playback button 79, a grip portion 90, and a lid. 202.

  The display unit 28 provided on the back surface of the camera body 100A is a liquid crystal panel or the like that displays images and various types of information. The outside-finder display unit 43 is a liquid crystal panel or the like provided on the upper surface of the camera body 100A, and various setting values such as a shutter speed and an aperture are displayed on the outside-finder display unit 43. The shutter button 61 is an operation member for giving an imaging instruction. The mode change switch 60 is an operation member for switching various modes. The terminal cover 40 protects a connector (not shown) to which a connection cable or the like for connecting an external device (not shown) and the camera body 100A is connected.

  The main electronic dial 71 is an operation member for changing imaging conditions (setting values) such as a shutter speed and an aperture. The power switch 72 is an operation member that switches on / off the power of the camera body 100A. The sub electronic dial 73 is an operation member for moving a selection frame, feeding an image, and the like. The cross key 74 is an operation member that can be pushed in up, down, left, and right, and performs processing and operations associated with the pushed-in portion. The SET button 75 is an operation member used for determining a selection item (icon) displayed on the display unit 28, for example.

  The LV button 76 is an operation member for switching on / off of live view (hereinafter referred to as “LV”) imaging. When the moving image imaging mode is set, the LV button 76 is used for an instruction to start / stop moving image imaging. . The enlargement button 77 is used to turn on / off an enlargement mode that can be set for an image displayed on the display unit 28 during LV imaging, and to change an enlargement ratio when the enlargement mode is set. It is an operation member. When the camera body 100A is in the playback mode, the playback image can be enlarged by operating the enlargement button 77. The reduction button 78 is an operation member that reduces the enlargement ratio of the reproduction image displayed in an enlarged manner and reduces the displayed image. The playback button 79 is an operation member that switches between the imaging mode and the playback mode. When the playback button 79 is pressed during the imaging mode, the mode is switched to the playback mode, and the latest image among the images stored in the storage medium 200 is displayed on the display unit 28.

  The quick return mirror 12 is raised / down by an actuator (not shown) in accordance with an instruction from a system control unit 50 (see FIG. 2) described later. The communication terminal 10 is a terminal for the camera body 100A to communicate with an interchangeable lens (not shown). When the interchangeable lens is attached to the lens mount of the camera body 100A, the communication terminal 10 is electrically connected to the communication terminal on the interchangeable lens side. Conducted to. The eyepiece finder 16 is a view-type finder. The photographer can confirm the focus and composition of the optical image of the subject obtained through the lens unit 150 by observing the focusing screen 13 (see FIG. 2) through the eyepiece finder 16.

  The lid 202 is a member that protects a slot that stores the storage medium 200 such as a semiconductor memory card. The grip part 90 is a part for the photographer (operator) to hold the camera body 100A, and is designed to be easily gripped with the right hand when holding the camera body 100A with respect to the subject. The built-in flash 65 and the AF auxiliary light emitting unit 66 will be described later with reference to FIGS. 2 and 3. FIG. 1 shows a state where the built-in flash 65 is housed in the camera body 100A. Yes.

  FIG. 2 is a block diagram illustrating a schematic configuration of the digital camera 100. Of the elements shown in the block diagram of FIG. 2, the same elements as those of the camera body 100A described with reference to FIG.

  The digital camera 100 is configured by attaching a lens unit 150 to a camera body 100A, and the lens unit 150 is detachable from the camera body 100A.

  The lens unit 150 includes a diaphragm 1, a diaphragm driving circuit 2, an AF driving circuit 3, a lens system control circuit 4, a communication terminal 6, and a lens 103. Although the lens 103 is composed of a plurality of lenses, it is simply shown here as a single lens. The communication terminal 6 is electrically connected to the communication terminal 10 provided in the camera main body 100A when the lens unit 150 is attached to the camera main body 100A, and the communication between the lens system control circuit 4 and the system control unit 50 provided in the camera main body 100A. Communication between them. The lens system control circuit 4 controls the aperture driving circuit 2 and the AF driving circuit 3 under the control of the system control unit 50. The aperture driving circuit 2 drives the aperture 1. The AF drive circuit 3 moves the lens 103 in the optical axis direction.

  The camera body 100A includes a focus detection unit 11, a quick return mirror 12, a focusing screen 13, a pentaprism 14, a memory control unit 15, an AE sensor 17, an imaging unit 22, an A / D converter 23, an image processing unit 24, and a display unit. 28 and a system control unit 50. The camera body 100A includes a memory 32, a D / A converter 19, an in-finder display unit 41, an in-finder display unit drive circuit 42, an outside viewfinder display unit 43, an outside viewfinder display unit drive circuit 44, a system memory 52, and a system. A timer 53 and a nonvolatile memory 56 are provided. Further, the camera body 100A includes a mode changeover switch 60, a shutter 101, a shutter button 61, an operation unit 70, a power supply unit 30, a power supply control unit 80, a communication unit 54, a posture detection unit 55, a built-in strobe 65, and an AF auxiliary light emitting unit. 66 and a storage medium I / F 18.

  The AE sensor 17 is a photometric unit that measures the luminance of the subject that has passed through the lens unit 150, and the system control unit 50 determines whether the imaging environment has low illuminance based on the photometric result of the AE sensor 17. it can.

  The focus detection unit 11 is an AF sensor that outputs defocus amount information to the system control unit 50. The system control unit 50 controls the lens unit 150 based on the defocus amount information acquired from the focus detection unit 11 and performs an AF process using a phase difference detection method. The quick return mirror 12 switches the light guide destination of the light beam incident from the lens 103 between the eyepiece finder 16 and the imaging unit 22. The central portion of the quick return mirror 12 is a half mirror that can transmit a part of the light, and a part of the light beam is incident on the focus detection unit 11.

  The photographer can confirm the focus and composition of the optical image of the subject obtained through the lens unit 150 by observing the focusing screen 13 via the pentaprism 14 and the eyepiece finder 16. The shutter 101 is specifically a focal plane shutter, and its operation is controlled by the system control unit 50 to control the exposure time of the imaging unit 22. The imaging unit 22 is an imaging element such as a CCD sensor or a CMOS sensor that converts an optical image of a subject obtained through the lens unit 150 into an electrical signal. The A / D converter 23 converts the analog signal output from the imaging unit 22 into image data that is a digital signal.

  The image processing unit 24 performs resizing processing such as pixel interpolation and reduction, color conversion processing, and the like on the image data transmitted from the A / D converter 23 or the image data transmitted from the memory control unit 15. In addition, predetermined arithmetic processing is performed using the captured image data. The system control unit 50 performs exposure control and distance measurement control based on the calculation result of the image processing unit 24, thereby performing TTL AF processing, AE (automatic exposure) processing, EF (strobe pre-flash) processing, and the like. Done. The image processing unit 24 further performs TTL AWB (auto white balance) processing based on the result of arithmetic processing using the captured image data.

  The image data output from the A / D converter 23 is written into the memory 32 via the image processing unit 24 and the memory control unit 15 or only through the memory control unit 15. The memory 32 stores image data output from the A / D converter 23 and image data to be displayed on the display unit 28. The memory 32 also serves as an image display memory (video memory).

  The D / A converter 19 converts the image display data stored in the memory 32 into an analog signal and supplies it to the display unit 28, whereby an image is displayed on the display unit 28. The digital signal once A / D converted by the A / D converter 23 and stored in the memory 32 at the time of imaging is converted into an analog signal by the D / A converter 19 and sequentially transferred to the display unit 28, whereby LV display is performed. It can be carried out.

  In the finder display unit 41, the finder display unit driving circuit 42 displays an AF frame (a frame indicating the AF target AF point), icons indicating the setting states of the camera body 100A and the lens unit 150, and the like. . The outside-finder display unit driving circuit 44 drives the outside-finder display unit 43. The nonvolatile memory 56 is an electrically erasable / storable memory, and for example, an EEPROM or the like is used. The nonvolatile memory 56 stores (stores) constants for operation of the system control unit 50, programs for realizing various processes and operations executed by the digital camera 100, and the like.

  The system control unit 50 performs overall control of the digital camera 100 by reading a program stored in the nonvolatile memory 56 to the system memory 52. The system memory 52 is specifically a RAM, and constants and variables for operation of the system control unit 50, programs read from the nonvolatile memory 56, and the like are expanded in the system memory 52. The system control unit 50 performs display control by controlling the memory 32, the D / A converter 19, the display unit 28, and the like. The system timer 53 supplies time used by the system control unit 50 for various controls, and measures the time of a built-in clock.

  The mode switch 60, the shutter button 61, and the operation unit 70 are operation means for inputting various operation instructions to the system control unit 50. The mode switch 60 switches the operation mode of the system control unit 50 between, for example, a still image capturing mode, a moving image capturing mode, and a playback mode. Still image capturing modes include an auto image capturing mode, a manual mode, an aperture priority mode (Av mode), a shutter speed priority mode (Tv mode), and various scene-specific image capturing modes.

  The shutter button 61 has a first shutter switch SW1 and a second shutter switch SW2. The first shutter switch SW1 is turned on during the operation of the shutter button 61 provided in the camera body 100A (half-pressed state), whereby the system control unit 50 performs AF processing, AE processing, AWB processing, EF processing, and the like. The imaging preparation operation is started. The second shutter switch SW2 is turned on when the operation of the shutter button 61 is completed (fully pressed), whereby the system control unit 50 performs the process from reading the signal from the imaging unit 22 to writing the imaging data to the storage medium 200. A series of imaging processing operations are performed.

  The built-in strobe 65 is composed of a xenon tube or the like, and emits light during AF processing or EF processing based on an instruction from the system control unit 50. 3A is a perspective view showing a state in which the built-in strobe 65 is housed in the camera body 100A, and FIG. 3B is a perspective view showing a state in which the built-in strobe 65 pops up from the camera body 100A. is there. The built-in flash 65 is normally housed in the camera body 100A as shown in FIG. When the system control unit 50 determines that strobe light emission is necessary based on the signals output from the AE sensor 17 and the image processing unit 24, the system control unit 50 shows the built-in strobe 65 in FIG. As shown in FIG. The AF auxiliary light emitting unit 66 includes an LED or the like, and emits light based on an instruction from the system control unit 50 during AF processing.

  The operation unit 70 includes the main electronic dial 71, the power switch 72, the sub electronic dial 73, the cross key 74, the SET button 75, the LV button 76, the enlarge button 77, the reduce button 78, and the play button 79 described with reference to FIG. including.

  The power supply control unit 80 includes a battery detection circuit, a DC-DC converter, a switch circuit for switching an energization block, and the like, and detects whether or not a battery is installed, the type of battery installed, and the remaining battery level. Further, the power control unit 80 controls the DC-DC converter based on the detection result and an instruction from the system control unit 50, and supplies a necessary voltage to each unit including the storage medium 200 for a necessary period. The power supply unit 30 is a primary battery such as an alkaline battery or a lithium battery, a secondary battery such as a NiCd battery, a NiMH battery, or a lithium ion battery, or an AC adapter.

  The storage medium I / F 18 is an interface that enables communication between the storage medium 200 such as a semiconductor memory card and a hard disk and the system control unit 50. The communication unit 54 enables communication between an external device (not shown) and the system control unit 50 by wireless or wired cable. As a result, video signals and audio signals can be transmitted and received between the external device and the digital camera 100.

  Specifically, the attitude detection unit 55 is an acceleration sensor, a gyro sensor, or the like, and detects the attitude of the digital camera 100 with respect to the direction of gravity. Based on the attitude detected by the attitude detection unit 55, the system control unit 50 is an image captured by the imaging unit 22 that is captured by holding the digital camera 100 horizontally or captured vertically. Determine whether it is. The system control unit 50 adds posture information corresponding to the posture detected by the posture detection unit 55 to the image data of the captured image, or rotates the captured image according to the posture detected by the posture detection unit 55. Store in the storage medium 200.

  Next, an autofocus control method executed by the digital camera 100 will be described. FIG. 4 is a flowchart of AF control by the digital camera 100. Each process shown in the flowchart of FIG. 4 is realized by the system control unit 50 reading a program stored in the nonvolatile memory 56 to the system memory 52 and controlling the operation of each unit constituting the digital camera 100.

  When the photographer detects that the first shutter switch SW1 is turned on by half-pressing the shutter button 61, the system control unit 50 starts an imaging preparation operation in step S401. In step S401, AE processing is performed as one of the imaging preparation operations.

  In subsequent step S402, based on the result of the AE process in step S401 (based on the image signal output from the AE sensor 17 or the image processing unit 24), the system control unit 50 is in a low illumination environment (the imaging environment is low). Illuminance). For example, when the luminance detected by the AE sensor 17 is equal to or lower than a predetermined threshold or when the ratio of pixels equal to or lower than a predetermined pixel value in the image signal output from the image processing unit 24 is equal to or higher than a predetermined value, It can be determined that Note that when LV imaging is performed by the digital camera 100, the order of step S401 and step S402 may be reversed. If the system control unit 50 is not in a low illumination environment (NO in S402), the process proceeds to step S403. If the system control unit 50 is in a low illumination environment (YES in S402), the process proceeds to step S404.

  In step S403, the system control unit 50 performs normal AF processing. Note that a known contrast detection method or phase difference detection method can be used for normal AF processing, and is not particularly limited. On the other hand, in step S404, the system control unit 50 performs AF processing in a low illuminance environment. Details of the AF process in the low illumination environment in step S404 will be described later with reference to the flowchart of FIG.

  When the subject is brought into focus in step S403 or step S404, the photographer can either fully press the shutter button 61 or change the subject by returning the shutter button 61 and then press the shutter button 61 halfway again. is expected. Therefore, in the present embodiment, in step S405 following steps S403 and S404, the system control unit 50 determines whether or not the second shutter switch SW2 is turned on. If the second shutter switch SW2 is turned on (YES in S405), the system control unit 50 advances the process to step S406, and if the second shutter switch SW2 is not turned on even after a predetermined time has passed (NO in S405), The process returns to step S401.

  In step S <b> 406, the system control unit 50 performs a series of imaging processing operations from reading a signal from the imaging unit 22 to writing image data into the storage medium 200. This process ends when the imaging process ends.

  FIG. 5 is a flowchart of a first example of AF processing in a low illumination environment in step S404. In step S <b> 501, the system control unit 50 transmits a light emission command to the AF auxiliary light emitting unit 66. Thereby, the AF auxiliary light emitting unit 66 emits AF auxiliary light. Note that the AF auxiliary light is continuously emitted until an extinction instruction is issued in step S503.

  In subsequent step S502, the system control unit 50 performs AF processing (first autofocus) by a contrast detection method. A well-known method can be used as the contrast detection method. In general, the image processing unit 24 calculates contrast information from the captured image data while changing the position of the lens 103, and uses the system control unit as an AF evaluation value. 50. Then, the system control unit 50 identifies the position of the lens 103 that maximizes the AF evaluation value received from the image processing unit 24, and sets the position as the in-focus position. Subsequently, in step S <b> 503, the system control unit 50 transmits an extinction command to the AF auxiliary light emitting unit 66. Thereby, the AF auxiliary light emitting unit 66 extinguishes the AF auxiliary light.

  Next, in step S504, the system control unit 50 determines whether or not the in-focus position has been specified in step S502. If the in-focus position can be specified (YES in S504), the system control unit 50 ends this process. As a result, the process proceeds to step S405. The case where the determination result in step S504 is “YES” is that the subject is present at a position closer than the reachable distance of the AF auxiliary light and the subject can be sufficiently irradiated with light. This is a case where the AF processing by the contrast detection method is successful.

  On the other hand, if the in-focus position cannot be specified (NO in S504), the system control unit 50 advances the process to step S505. When the determination result in step S504 is “NO”, since the subject exists at a position farther than the reachable distance of the AF auxiliary light, the subject cannot be sufficiently irradiated with light, and AF by contrast detection is used. This is a case where the process has failed. Therefore, in step S505, the system control unit 50 transmits a light emission command to the built-in strobe 65, and causes the built-in strobe 65 to perform pre-light emission (preliminary light emission before the main light emission at the time of actual imaging). In step S506, the system control unit 50 performs AF processing (second autofocus) using a phase difference detection method.

  Thereafter, in step S507, the system control unit 50 transmits an extinction command to the built-in flash 65. As a result, the built-in flash 65 is extinguished. Note that since the flash time is short in strobe pre-flash, the calculation of the defocus amount information by the focus detection unit 11 in the AF processing by the phase difference detection method and the strobe pre-flash is performed by the system control unit 50 in synchronization. . This process ends by the process of step S507.

  By the way, AF processing may fail in both step S502 and step S506. In this case, the subject exists at a position farther than the reachable distance between the AF auxiliary light and the strobe light, and the subject is sufficiently light. It is considered that AF processing cannot be performed because of no irradiation. In this case, a display such as “impossible focus” may be displayed on the display unit 28, for example.

  As described above, in the first example of the AF processing in the low illumination environment, even if the subject exists at a distance where the AF auxiliary light does not reach in the low illumination environment, the subject is detected by the flash pre-flash. The AF process can be performed with bright illumination. This is because the strobe light generally uses the characteristic that it can reach farther than the AF auxiliary light. In addition, since the contrast detection method is preferentially performed, there is no difference in processing time when an object is present at a short distance compared to AF processing by a normal contrast detection method. In other words, there is no time lag. Furthermore, as already described, the contrast detection method can specify the in-focus position of the lens 103 with high accuracy. In the first example, since the contrast detection method is preferentially performed, the subject is located at a short distance. If there exists, stable and highly accurate AF processing becomes possible.

  In addition, when the strobe pre-flash is performed in step S404, the phase difference detection method is used instead of the contrast detection method. The influence of can be suppressed. The reason is as follows. In other words, when performing AF processing using a contrast detection method by emitting strobe light, continuous strobe light emission is required for each repeated imaging while changing the lens position. Here, in order to perform strobe light emission, it is necessary to charge an electric charge, and if strobe pre-light emission is performed continuously, a time lag occurs due to the charging time and a light emission amount is reduced, which affects pre-light emission and main light emission. . On the other hand, since the phase difference detection method can perform AF processing with one focus detection, such a problem hardly occurs. Therefore, a necessary and sufficient amount of light emission can be ensured without causing a time lag during the main light emission.

  In addition, since the AF auxiliary light emitted from the LED is given priority over the strobe light emitted from the xenon tube, an effect of power saving can be obtained. Further, if a strobe light with a large amount of light is irradiated for AF processing when there is a subject such as a human at a short distance, the human will feel unpleasant glare. However, in the first example, strobe pre-emission is performed when the subject is not at a short distance, so occurrence of such a problem can be avoided.

  Next, a second example of the AF process in the low illuminance environment in step S404 will be described. FIG. 6 is a flowchart of a second example of the AF process in the low illumination environment in step S404. Steps S602 to S605 and S607 to S609 in FIG. 6 are the same processes as steps S501 to S504 and S505 to 507 in FIG. 5, respectively, so that the description thereof will be omitted and the processing contents of steps S601 and S606 will be described below. Explained.

  In step S601, the system control unit 50 controls the lens unit 150, and changes the position of the lens 103 so that the focus position (the position where the focus is achieved) becomes the maximum point where the AF auxiliary light reaches. As a result, the focus position after the change in step S601 becomes the AF process start position (initial position) by the contrast detection method in the subsequent step S603. Therefore, in step S603, the system control unit 50 gradually moves the focus position closer to the camera body 100A side from the initial position set in step S601, and acquires an AF evaluation value. The reason for performing such processing will be described with reference to FIG.

  FIG. 7 is a schematic diagram showing comparison between AF evaluation values when the subject is present at a short distance from the camera body 100A and when the subject is present at an intermediate distance. Since the AF evaluation value is maximized at the position where the subject is in focus (becomes in focus), the contrast detection method calculates the AF evaluation value while changing the focus position, and calculates the AF evaluation value. Search for the maximum point. For this reason, when the number of searches increases, it takes a long time to focus. Therefore, in the second example, the speed of AF processing is increased by reducing the number of searches for the focus position where the AF evaluation value is maximized.

  The upper part of FIG. 7 shows the AF evaluation value when the subject is in a short distance, that is, within the reachable distance of the AF auxiliary light. Below that, AF evaluation values are shown when the distance is within the reach of the intermediate distance, that is, the reachable distance of the strobe pre-light emission and outside the reachable distance of the AF auxiliary light.

  The section using the contrast detection method is within the reachable range of the AF auxiliary light. Therefore, the maximum reaching point of the AF auxiliary light is set to the initial position S for starting the search for the focus position by the contrast detection method.

  When the subject is present at a short distance, the AF evaluation value tends to increase as the focus position is moved from the initial position S toward the camera body 100A. However, when the subject is not at a short distance but at a medium distance, the AF evaluation value tends to decrease or become substantially constant as the focus position is moved closer to the camera body 100A from the initial position S. Therefore, based on these tendencies, it is possible to determine whether or not the subject exists at a short distance by performing several searches within a certain range from the initial position S.

  Therefore, in the second example, the system control unit 50 terminates the search when it is determined that there is no subject at a short distance and that focusing cannot be performed, and the process of step S603 is ended. Therefore, since a redundant search is not performed, the AF process can be speeded up. It should be noted that the determination method for determining whether or not the subject exists at a short distance is not a short distance if h1> h2>... When the AF evaluation values of several points from the initial position S are h1, h2,. Can be determined. On the other hand, if a predetermined sufficiently small threshold value k is set and h1, h2,. The determination method is not limited to these examples, and any method may be used as long as it can be determined whether or not the subject exists within the reachable range of the AF auxiliary light from a plurality of AF evaluation values. .

  Next, the process of step S606 will be described. In step S606, the system control unit 50 sets the initial position for starting the search for the focus position by the phase difference detection method in the subsequent step S608 within the reachable distance of the strobe pre-flash and the arrival of the AF auxiliary light. Set out of range of possible distance.

  The settable range of the initial position in step S606 is indicated by a range L in FIG. 7, and the reason for setting the initial position in step S606 in this way is as follows. That is, in general, when AF processing is performed using the phase difference detection method, if the focus position is greatly deviated from the subject (so-called out-of-focus state), the reliability of the AF processing decreases. Here, in steps S601 to S605, since it is known that the subject exists within the range L or at a longer distance, setting the focus position within the range L prevents the image from being greatly out of focus, and AF processing Can improve the reliability.

  The initial position set in step S606 may be anywhere as long as it is within the range L, but is preferably the midpoint of the range L. However, the present invention is not limited to this, and the focus position may be determined from the AF evaluation value obtained in step S603. For example, if the subject is on the camera body 100A side within the range L, it is estimated that the AF evaluation value tends to decrease from the initial position S set in step S601. On the other hand, if the subject is on the far side in the range L, the AF evaluation value is estimated to be substantially constant from the initial position S. That is, the existence probability of the subject position can be estimated based on whether or not several AF evaluation values are substantially constant, and a more preferable initial position can be set based on the result.

  As described above, in the second example of AF processing in a low illumination environment, the search time in the contrast detection method can be reduced, and the reliability in the phase difference detection method can be increased.

  The reachable distances of the AF auxiliary light and the strobe light can be measured by, for example, the following method. Specifically, a gray plate having a predetermined reflectance (for example, a standard reflector having a reflectance of 18%) is used as a subject, and imaging using AF auxiliary light or strobe light emission is performed while gradually moving away from the digital camera 100, The distance between the camera and the plate when the reflected light has a predetermined luminance is defined as the reaching distance. Here, the predetermined luminance is the lowest luminance that can accurately execute each AF method. The method of measuring the reaching distance is not limited to this, and any method may be used as long as the distance between the subject and the digital camera 100 that can secure sufficient brightness that enables AF processing can be determined. The reachable distances of the AF auxiliary light and the strobe light determined in this way can be stored in the system memory 52, for example.

  Although the present invention has been described in detail based on preferred embodiments thereof, the present invention is not limited to these specific embodiments, and various forms within the scope of the present invention are also included in the present invention. included. Furthermore, each embodiment mentioned above shows only one embodiment of this invention, and it is also possible to combine each embodiment suitably.

  For example, in the above-described embodiment, the digital camera 100 is taken up as the imaging device. However, the present invention is not limited to this, and a digital video camera, a camera function (an imaging function that acquires an image using an imaging device), and an AF auxiliary light emission function Various electronic devices having the above may be used.

  In the block diagram of FIG. 2, the digital camera 100 arranges the focus detection unit 11 at a position different from the imaging unit 22, but the focus detection unit 11 may be incorporated in the imaging unit 22. . As a result, it is not necessary to have an independent focus detection unit 11, and the digital camera 100 can be downsized. Also, so-called image plane phase difference detection AF processing can be performed, and the AF processing during LV imaging can be speeded up.

  Furthermore, in the above embodiment, the AF auxiliary light emitting unit 66 built in the camera main body 100A emits AF auxiliary light to perform AF processing by the contrast detection method, and the built-in strobe 65 is pre-flashed to detect the phase difference. AF processing by the method was performed. Alternatively, an external strobe may be attached to the camera main body 100A, and the AF process may be similarly performed using the external strobe and the AF auxiliary light emitting unit attached to the external strobe. In general, since the external light source emits a larger amount of light than the light source built in the camera body 100A, using an external strobe makes it possible to perform AF processing on a farther subject.

  The present invention supplies a program that realizes one or more functions of the above-described embodiments to a system or apparatus via a network or a storage medium, and one or more processors in a computer of the system or apparatus read and execute the program. It can also be realized by processing. It can also be realized by a circuit (for example, ASIC) that realizes one or more functions.

DESCRIPTION OF SYMBOLS 4 Lens system control circuit 11 Focus detection part 17 AE sensor 22 Imaging part 24 Image processing part 50 System control part 65 Built-in flash 66 AF auxiliary light emission part 100 Digital camera 100A Camera main body 103 Lens 150 Lens unit

Claims (7)

Strobe light emitting means for emitting strobe light toward the subject;
Auxiliary light emitting means for emitting auxiliary light for autofocus toward the subject;
The auxiliary light emitting means emits the auxiliary light to perform first autofocus by a contrast detection method, and when the first autofocus cannot be focused, the strobe light emitting means is pre-lighted. An image pickup apparatus comprising: control means for performing second autofocus by a phase difference detection method. A metering means for metering the brightness of the subject;
Determination means for determining whether or not the image is taken in a low illuminance environment based on a photometric result by the photometric means,
The control unit performs the first autofocus when the determination unit determines that the imaging is performed in the low illumination environment, and performs the first autofocus when the focus cannot be achieved with the first autofocus. The image pickup apparatus according to claim 1, wherein autofocus of 2 is performed.   The control means sets an initial position of a focus position for starting the first autofocus as a maximum reaching point of the auxiliary light, and moves the focus position from the initial position toward the imaging device. The first autofocus is performed, and the first autofocus is terminated when it is determined that focusing is impossible within a certain range from the initial position based on the evaluation value calculated by the contrast detection method. The imaging device according to claim 1 or 2.   The control means sets an initial position of a focus position for starting the second autofocus within the range of the strobe light reachable by the pre-flash, and sets the reachable distance of the strobe light by the pre-flash. The imaging apparatus according to claim 1, wherein the second autofocus is performed within a range.   The control means sets an initial position of a focus position for starting the second autofocus within the reachable distance range of the auxiliary light and within the reachable distance range of the strobe light by the pre-flash. The imaging apparatus according to claim 4, wherein the imaging apparatus is set. An autofocus control method executed by an imaging apparatus including a strobe light emitting unit that emits strobe light toward a subject and an auxiliary light emitting unit that emits auxiliary light for autofocus toward the subject,
A metering step for metering the brightness of the subject;
A determination step for determining whether or not the image is taken in a low illuminance environment based on the photometric result of the photometric step;
A first autofocus that performs a first autofocus by a contrast detection method by causing the auxiliary light emitting means to emit the auxiliary light when it is determined in the determination step that the image is taken in the low illumination environment; Steps,
A second autofocus step for performing second autofocus by a phase difference detection method by pre-flashing the strobe light emitting means when focusing cannot be achieved in the first autofocus step. A characteristic autofocus control method.   A program for causing a computer to execute each step of the autofocus control method according to claim 6.

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