JP6124628B2 - Focus adjustment device and focus adjustment method - Google Patents

Description

  The present invention relates to a focus adjustment device and a focus adjustment method for performing a focus adjustment operation on a subject.

  2. Description of the Related Art Conventionally, a technique is known in which a focus lens is wobbled and automatic focus adjustment is performed by obtaining the contrast of a subject image based on image data acquired by an image sensor. Patent Document 1 discloses AF control using wobbling (hereinafter referred to as wobbling AF). The operation of repeatedly moving the focus lens by a predetermined minute amount (amplitude) in the optical axis direction at a predetermined cycle is generally referred to as wobbling. A method of calculating a focus evaluation value based on image data output from the image sensor during a wobbling operation and detecting the focus is referred to as a wobbling AF method.

JP 2010-271697 A

  In the case of Patent Document 1, by increasing the amplitude of the wobbling operation, it is possible to improve the focus detection performance for a subject with a lower contrast. However, on the other hand, there is a problem that noise noise generated by driving the focus lens is increased, and that the quality of the image when observing the captured image is deteriorated due to fluctuation of the image magnification accompanying the movement of the focus lens. .

  The present invention has been made in view of the above circumstances, and is a focus adjustment device capable of improving the focus detection performance without increasing the driving sound of the focus lens and without degrading the quality of an image to be captured. And to provide a focusing method.

In order to achieve the above object, a focus adjustment apparatus according to a first aspect of the present invention captures a photographic optical system having a focus lens movable in an optical axis direction and a subject image formed by the photographic optical system. An imaging unit, a focus evaluation value calculation unit that calculates a focus evaluation value based on image data generated by the imaging unit, and a focus control unit that performs an AF operation by controlling the focus lens based on the focus evaluation value And the focus control unit uses a second period larger than the first period and the first amplitude in the first signal formed by the first period and the first amplitude. The focus lens is moved based on a signal obtained by superimposing a second signal formed with a second amplitude that is greater than the first, and the focus evaluation value calculation unit calculates the focus evaluation value in synchronization with the movement of the focus lens. Let Run the AF operation based on the out of focus evaluation value,
The focus control unit includes a signal component obtained by superimposing the first signal component and the second signal component in a first period corresponding to a half cycle between the maximum value and the minimum value of the second signal component. The focus lens at a position corresponding to a minimum value of a signal component obtained by superimposing a focus evaluation value when the focus lens is positioned at a position corresponding to the maximum value of the first signal component and the second signal component. A first direction in which the focus lens is in focus is determined based on a difference from a focus evaluation value when the lens is positioned, and a maximum value and a minimum value of the first signal component in the first period A focus evaluation value when the focus lens is positioned at a position corresponding to the maximum value of the first signal component in a second period corresponding to a half cycle between the minimum period and the minimum value of the first signal component The focus lens at a position corresponding to A second direction in which the focus lens is in focus based on a difference in focus evaluation value when the lens is placed, and a direction in which the focus lens is in focus based on the first direction and the second direction It is characterized by determining.

  According to the present invention, it is possible to provide a focus adjustment device and a focus adjustment method capable of improving the focus detection performance without increasing the driving sound of the focus lens and without degrading the quality of an image to be captured. it can.

It is a figure which shows the structure of the imaging device as an example of the focus adjustment apparatus which concerns on embodiment of this invention. It is a figure for demonstrating the state transition of the focus adjustment apparatus which concerns on embodiment of this invention. It is a flowchart which shows the normal wobbling operation | movement of the focus adjustment apparatus which concerns on embodiment of this invention. It is a flowchart shown about search operation | movement of the focus adjustment apparatus which concerns on embodiment of this invention. It is a figure for demonstrating the low frequency wobbling operation | movement of the focus adjustment apparatus which concerns on embodiment of this invention. It is a flowchart shown about to-be-photographed object state determination of the focus adjustment apparatus which concerns on embodiment of this invention. It is a figure for demonstrating in detail the low frequency wobbling operation | movement of the focus adjustment apparatus which concerns on embodiment of this invention. It is a figure for demonstrating the low frequency wobbling operation | movement of the focus adjusting apparatus which concerns on embodiment of this invention. It is a figure for demonstrating in detail the low frequency wobbling operation | movement of the focus adjustment apparatus which concerns on embodiment of this invention. It is a figure for demonstrating the conventional wobbling operation | movement.

  Prior to the description of the present invention, the wobbling operation that is a feature of the present invention will be described with reference to FIGS.

FIG. 10 is a diagram showing two types of wobbling operations with the same amplitude center and period and different amplitudes of the wobbling operation of the focus lens. Here, An indicates the maximum and minimum widths of the wobbling operation, and the amplitude of the wobbling operation is 1 / 2An. Figure 10 includes contrast and normal wobbling operation Wn having an amplitude (1/2) An, a largely amplitude (1/2) Aa than a same cycle amplitude (1/2) An A wobbling operation Wa is shown. Such a wobbling operation Wa has a higher performance than that of the wobbling operation Wn, and thus has a high performance for detecting a change in contrast. However, it is necessary to increase the driving speed of the focus lens in order to set the cycle according to the frame rate of the imaging operation. Increasing the driving speed of the focus lens causes a problem that noise generated from the driving mechanism of the focus lens increases. This is because the noise generated by driving the focus lens is substantially proportional to the driving speed.

  Further, by further enlarging the moving amount of the focus lens, a larger fluctuation in image magnification occurs and the quality of a moving image recorded during the wobbling operation is lowered. The effect of the focus lens wobbling operation on the appearance and quality of the moving image depends on the amount of fluctuation in image magnification per unit time. For example, when a change in image magnification of 0.04% or more is repeated for about 33 ms. It is generally said that observers feel uncomfortable. Therefore, the wobbling operation Wa has a larger amplitude and a larger image magnification fluctuation than the wobbling operation Wn, so that the appearance and quality of the moving image are greatly deteriorated.

  In the present invention, a wobbling operation as shown in FIG. 7 is performed in order to solve the above problem. That is, the wobbling operation Wl is performed by superimposing the lower frequency sine wave amplitude S on the normal wobbling operation Wn. Such a wobbling operation is referred to as a low frequency wobbling operation. With such a low frequency wobbling operation, it is possible to further improve the focus detection performance without degrading the image quality of the moving image with respect to the normal wobbling operation.

  FIG. 8 is a diagram showing improvement in focus detection performance by low-frequency wobbling operation. A curve AFC indicating a change in the focus evaluation value has a shape that peaks at the lens position P0 of the focus lens. Here, when the normal wobbling operation Wn is performed around the lens position P0, the change amount (difference) in the focus evaluation value obtained at the end point of the wobbling amplitude is dn. On the other hand, when the low frequency wobbling operation Wl is performed around the lens position P0, the change amount (difference) in the focus evaluation value obtained at the end point of the wobbling amplitude is dl. As apparent from FIG. 8, since dl> dn, it is shown that the low-frequency wobbling operation Wl has higher in-focus state detection capability than the normal wobbling operation Wn.

  Further, since the speed of the focus lens in the low frequency wobbling operation is the same as the speed in the normal wobbling operation, the magnitude of noise generated by driving the focus lens is the same. When the focus lens moves with respect to the low frequency component (sine wave S component) of the low frequency wobbling operation, for example, when the cycle is about several hundreds of milliseconds, the image magnification fluctuation is hardly recognized visually. Therefore, the low-frequency wobbling operation can improve the focus detection performance without degrading the quality of the moving image. The sine wave signal S has the same effect even if it is a triangular wave signal. The above is the outline of the low frequency wobbling operation that characterizes the present invention. Hereinafter, embodiments of the present invention will be described in detail.

  FIG. 1 is a block diagram mainly showing an electric circuit of an imaging apparatus according to an embodiment of the present invention. An imaging apparatus 100 according to an embodiment of the present invention includes an interchangeable lens 101 and a camera body 102. The interchangeable lens 101 includes a photographing lens 103, a lens CPU 113, a lens storage circuit 114, and a lens driving circuit 115. The photographing lens 103 is composed of a plurality of optical lenses, and the focus state is changed by moving the focus lens in the optical axis direction. The photographing lens 103 is connected to a lens driving circuit 115, and the lens driving circuit 115 moves the photographing lens 103 in the optical axis direction in accordance with a control signal from the lens CPU 113.

  The lens storage circuit 114 is an electrically rewritable nonvolatile memory, and stores various data such as various adjustment values and data unique to the interchangeable lens 101 in addition to the program of the lens CPU 113. Data for wobbling operation such as lens driving parameters described later is also stored in the lens storage circuit 114. The lens CPU 113 reads out necessary data from the lens storage circuit 114 and transmits it to the main body 102 side. Further, the lens CPU 113 causes the lens storage circuit 114 to store the state in the interchangeable lens 101 such as the current position of the focus lens.

  The photographing lens 103 may be a single focus lens or a zoom lens. The interchangeable lens 101 and the camera body 102 can be detachably attached via a lens mount (not shown), and can communicate with each other via a plurality of electrical contacts 112 disposed on the lens mount. It is.

  The camera body 102 includes a shutter 104, an image sensor 105, an image sensor control circuit 107, a shutter control circuit 109, a main body CPU 111, a flash ROM (FROM) 121, a RAM 123, an AF control circuit 125, an AE control circuit 127, an image processing circuit 129, A display circuit 131, a display element 133, an operation switch (SW) detection circuit 135, and an operation unit 137 are included.

  A shutter 104 is disposed on the optical axis of the taking lens 103. The shutter 104 includes a lens shutter, a focal plane shutter, and the like, and opens and closes the subject light flux that has passed through the photographing lens 103. The shutter 104 is connected to a shutter control circuit 109, and the shutter 104 controls the opening / closing time of the subject light flux at a shutter speed according to a control signal from the shutter control circuit 109.

  An imaging element 105 is disposed behind the shutter 104 and on the optical axis of the photographing lens 103. The image sensor 105 repeatedly converts the subject image into an image signal at a predetermined cycle and outputs the image signal to the image capture control circuit 107. The image sensor 105 may be an image sensor such as a CCD image sensor or a MOS image sensor.

  The image pickup device 105 is connected to the image pickup control circuit 107, and the image pickup control circuit 107 reads out an image signal from the image pickup device 105 according to control from the main body CPU 111, performs processing such as AD conversion, and then performs processing on the main body CPU 111. Output. The imaging element 105 and the imaging control circuit 107 constitute an imaging unit.

  In addition to the shutter control circuit 109, the imaging control circuit 107, and the lens CPU 113, the main body CPU 111 includes a FROM 121, a RAM 123, an AF control circuit 125, an AE control circuit 127, an image processing circuit 129, a display circuit 131, an operation SW detection circuit 135, and the like. It is connected to the. The main body CPU 111 controls the entire camera according to a program stored in the FROM 121. The main body CPU 111 functions as a focus control unit that determines the moving direction of the photographing optical system (the photographing lens 103) and performs focus adjustment.

  The lens CPU 113 operates in accordance with a program stored in a nonvolatile memory such as a flash ROM, and controls the lens barrel in accordance with a control signal from the main body CPU 111. When performing focus adjustment by contrast AF, the lens driving circuit 115 is controlled in accordance with a control signal from the main body CPU 111 to drive the focus lens in the photographing lens 103 in the optical axis direction. The lens CPU 113 may be omitted, and the main body CPU 111 may directly control the lens driving circuit 115.

  The FROM 121 is an electrically rewritable nonvolatile memory, and stores various data such as various adjustment values in addition to a program for the main body CPU 111. The RAM 123 is an electrically rewritable volatile memory, and temporarily stores various data for calculation of the main body CPU 111 and temporarily stores image data and the like.

  The AF control circuit 125 calculates the contrast (focus evaluation value) of the subject image based on the image signal input from the imaging control circuit 107 by the main body CPU 111. The AF control circuit 125 functions as a focus evaluation value calculation unit. The main body CPU 111 performs drive control of the focus lens of the photographing lens 103 via the lens CPU 113 and the lens drive circuit 115 based on the contrast calculated by the AF control circuit 125.

  The AE control circuit 127 calculates subject luminance based on the image signal input from the imaging control circuit 107 by the main body CPU 111, and the main body CPU 111 calculates an exposure control value such as the shutter speed of the shutter 104 based on the subject luminance. . The calculated shutter speed is output to the shutter control circuit 109, and the shutter speed of the shutter 104 is controlled.

  The image processing circuit 129 performs image processing on the image signal input from the imaging control circuit 107 by the main body CPU 111. As the image processing, various processes such as optical black subtraction processing, white balance correction processing, synchronization processing, gamma / color reproduction processing, color matrix calculation processing, edge enhancement processing, noise reduction processing, and the like are performed. Various processes such as image processing for live view display, image processing for recording on a recording medium, and image processing for reproducing and displaying image data read from the recording medium are also performed.

  The display circuit 131 is connected to the display element 133 and performs display control on the display element 133. As the display element 133, various display elements such as a liquid crystal display element (LCD) and an organic EL element are used. Various displays such as live view display, playback display, and menu screen display are performed on the display element 133.

  The operation switch detection circuit 135 is connected to the operation unit 137 and detects operation states of various operation members in the operation unit 137. The operation members in the operation unit 137 include a power switch, a release button, a playback button, a menu button, a cross button, an OK button, a moving image shooting switch, and the like.

  Next, the operation of the imaging apparatus 100 according to the present embodiment will be described. FIG. 2 is a diagram illustrating the state transition of the autofocus (AF) operation in the moving image shooting mode of the imaging apparatus 100. When the power switch of the operation unit 137 is turned on by the photographer, the main body CPU 111 reads a necessary program code from the FROM 121 and starts operation. When the moving image shooting switch of the operation unit 137 is turned on, the main body CPU 111 recognizes this, sets the moving image shooting mode, starts the moving image shooting operation, and controls the state transition shown in FIG.

  The AF operation in the moving image shooting mode is referred to as moving image AF. When the moving image AF is started, a normal wobbling operation mode (hereinafter referred to as a normal WOB mode) is first executed. The normal wobbling operation is a wobbling operation of a high frequency component different from the low frequency wobbling operation, and means a conventional wobbling operation. In the normal WOB mode, it is determined whether in-focus or out-of-focus. If the in-focus state cannot be maintained, the transition of 1) is performed and the search mode is entered. In the search mode, hill-climbing AF is executed. When hill-climbing AF is executed and the focus state is reached, the transition of 2) is performed and the normal WOB mode is entered.

  Next, when it is determined in the normal WOB mode that focusing or AF is impossible, the transition of 3) is performed to shift to the standby mode. In the standby mode, the focus evaluation value is repeatedly acquired with the position of the focus lens fixed, and it is determined whether or not the focus evaluation value has changed by a predetermined value or more. If it is determined that the focus evaluation value has changed by a predetermined value or more, the transition of 4) is performed to shift to the normal WOB mode. When the change in the focus evaluation value is smaller than the predetermined value, the standby mode is maintained.

  Next, in the normal WOB mode, when it is determined that AF is impossible, a transition of 5) is performed, and a transition is made to a low frequency wobbling operation mode (hereinafter referred to as a low frequency WOB mode), which is a feature of the present invention. If it is determined that focusing or AF is impossible in the low-frequency WOB mode, the transition to 7) is performed to shift to the standby mode. If it is determined that the focus is close to the low frequency WOB mode, the transition to 6) is performed to shift to the normal WOB mode. Further, when it is determined that the in-focus state cannot be maintained in the low-frequency WOB mode and the in-focus state cannot be maintained, the transition of 8) is performed to shift to the search mode. The operation in the low frequency WOB mode will be described later.

  FIG. 3 is a flowchart showing a normal wobbling operation (normal WOB operation) in the normal WOB mode of the imaging apparatus 100. The normal WOB operation is a wobbling operation of a high frequency component different from the low frequency wobbling operation, and means a conventional wobbling operation.

  The main body CPU 111 sets lens driving parameters (hereinafter referred to as LD parameters) in step S100. The LD parameter is data such as the amplitude, period, and driving speed of the wobbling operation.

  In step S102, the focus lens 101 is moved from the infinity side (FAR side) of the wobbling operation to the closest side (NEAR side) position. In step S104, the focus evaluation value at the position on the near side (NEAR side) is acquired and stored in the memory such as the RAM 123 as the near side focus evaluation value. In step S106, the focus lens 101 is moved from the closest side (NEAR side) position of the wobbling operation to the infinite side (FAR side) position based on the set LD parameter. In step S108, the focus lens 101 acquires the focus evaluation value at the position on the infinite side (FAR side) and stores it in the memory as the infinite side focus evaluation value. In this way, the operation for one cycle (one time) of the wobbling operation is performed.

  In step S110, direction determination processing is performed. Specific processing of the direction determination processing is performed as follows. The amount of change (difference) between the focus evaluation value of the near end (NEAR side) end point and the focus evaluation value of the infinite side (FAR side) end point obtained by executing the above wobbling operation and wobbling operation for one period (one time). Calculate more than one. For example, the amount of change is calculated by the following equation (1).

Amount of change δ = (closest focus evaluation value−infinity focus evaluation value) ÷ close focus evaluation value × 100
... (1)
The wobbling operation for a plurality of cycles (for a plurality of times) is repeatedly executed, and a plurality of change amounts δ are calculated based on the acquired plurality of focus evaluation values and stored in the memory. Then, when the signs of the plurality of change amounts δ calculated continuously are positive for a predetermined number of times, the direction determination result is set to the closest side. That is, when the focus evaluation value is continuously increased a predetermined number of times, it is determined that the direction in which the focus lens is focused is the close side. In addition, when the signs of the plurality of change amounts δ calculated continuously are negative for a predetermined number of times, the direction determination result is set to the infinite side. When the focus evaluation value continuously decreases a predetermined number of times, it is determined that the direction in which the focus lens is focused is the infinite side. If the change amount δ does not correspond to both the case where it is positive continuously for a predetermined number of times and the case where it is negative continuously for a predetermined number of times, the direction determination result is undefined.

  Next, in-focus determination processing is performed in step S112. Specifically, in the focus determination process, the following process is performed. If it is determined that the transition of the change amount δ of the focus evaluation value changes stably around 0, it is determined to be in focus. If the transition of the change amount output δ is unstable in the vicinity of 0, it is determined that it is located out of focus of the contrast curve (focus evaluation value change) and is out of focus. Further, when the direction determination process in step S110 determines whether the direction is the closest side or the infinite side, it is determined that the focus is close.

  In step S114, next state processing is executed, and a mode (state) to be changed next is determined. That is, when it is determined that the in-focus state is in-focus, the state transition standby mode is stored as the next state. If it is determined that the in-focus state is located at the bottom of the contrast curve, the state transition search mode is stored as the next state. Further, when it is determined that the focus is in the vicinity, the normal WOB mode is stored as the next state in order to continue the normal WOB operation. Further, when the result of the direction determination process is indefinite in the normal WOB operation and the result of the focus determination process is out of focus, it is determined that the detection is impossible. If it is determined that detection is impossible, the low-frequency WOB mode is stored as the next state.

  Next, in step S116, it is determined whether or not to end the normal WOB processing. Here, if the next state based on the result of the next state determination is the normal WOB mode, it is determined that the normal WOB operation is not terminated, the process returns to step S100, and the normal wobbling process is continued. On the other hand, when the next state is the standby mode, the search mode, or the low frequency WOB mode, it is determined that the normal WOB operation is finished, and the processing of this flowchart is finished.

  If the result of the focus determination process is near focus, the normal WOB operation is continued and the following operation is performed. In step S100 of FIG. 3, the amplitude is increased only for the lens driving toward the focus among the lens driving from the near side to the infinity side or the lens driving from the infinity side to the near side. Then, the lens is driven with an amplitude that is increased only for one of steps S102 and S104 and an amplitude that is not increased for the other, thereby performing an operation of gradually moving in the direction toward in-focus. Then, as described above, if it is determined that the change in the change amount of the focus evaluation value is stably changing around 0, the focus is determined to be in focus. When the search operation is performed in the state near the in-focus state, the focus lens moves at a higher speed, which may reduce the appearance. In order to avoid this, control is performed so that the focus is gradually reached by the normal WOB operation without executing the search operation.

  FIG. 4 is a flowchart illustrating a search operation that is a hill-climbing AF operation of the imaging apparatus 100. The search operation is a process executed in the search mode of state transition (FIG. 2). In step S200, the main body CPU 111 drives the focus lens at the set direction and speed to start scan driving. In step S202, the focus evaluation value is acquired during the scanning operation. In step S204, it is determined whether or not the direction determination has been completed. If the direction determination has not been completed yet, the process proceeds to step S206 to execute the direction determination process. The direction determination process is a process for obtaining the driving direction of the focus lens that approaches the in-focus state, and detects a change in the focus evaluation value accompanying the movement of the focus lens and obtains a direction in which the amount of change increases.

  On the other hand, if the direction determination has already been completed, the process proceeds to step S208 to perform peak detection processing. In the peak detection process, the focus evaluation value is repeatedly acquired during the scanning operation, and the position of the focus lens at which the focus evaluation value reaches a peak is obtained. When the peak of the focus evaluation value is detected, the scanning operation is terminated and the focus lens is stopped.

  In step S210, it is determined whether or not the peak detection process has been completed, that is, whether or not the peak has been detected. If it has been completed, the process proceeds to step S212. If it has not been completed, the process returns to step S200 to repeat the peak detection process until a peak can be detected. In step S212, the true focus position is calculated by interpolation processing based on the result of executing the peak detection process, and the focus lens is driven to drive the focus lens to the focus position.

  FIG. 5 is a flowchart illustrating a low-frequency wobbling operation (low-frequency WOB operation) in the low-frequency WOB mode of the imaging apparatus 100. First, in step S300, the main body CPU 111 clears wob-mov-num indicating the number of times wobbling has been executed as an initial setting as will be described later, and moves the focus lens with respect to the low frequency component during the low frequency wobbling operation. Set wob-dir = NEAR2FAR. Next, in step S302, it is determined whether or not wob-mv-num is equal to or greater than a predetermined threshold value WOB_MV. If wob-mv-num is equal to or greater than the number of times of WOB_MV, the process proceeds to step S304, and wob-mv-num is cleared (initialized). On the other hand, if wob-mv-num is smaller than the number of WOB-MVs, the process proceeds to step S310, 1 is added to wob-mv-num, and the process proceeds to step S314.

  When CPU-111 clears wob-mv-num in step S304, main unit CPU 111 proceeds to step S306. In step S306, it is determined whether or not the wob-dir indicating the moving direction of the focus lens regarding the low frequency component during the low frequency wobbling operation is equal to NEAR2FAR indicating the movement from the short distance side to the long distance side. Advances to step S308. In step S308, in order to reverse the driving direction of the focus lens, wob-dir is set to FAR2NEAR, that is, a direction in which the distance lens moves from the far side to the near side.

  On the other hand, if wob-dir is not equal to NEAR2FAR in step S306, that is, if it is a direction to move from the long distance side to the short distance side, the process proceeds to step S312 and wob-dir is changed to NEAR2FAR, that is, the short distance side. Set the direction to move from to the far side. In step S314, LD parameters are set. In the LD parameter setting, the amplitude, period, shift amount, driving speed, etc. of the high frequency wobbling operation are set.

  In step S316, the focus lens is driven from the infinity side to the closest side by the amount of amplitude data based on the set amplitude data of the LD parameter. Thus, the focus lens is positioned at the closest end point in one high-frequency component wobbling operation. In step S318, the focus evaluation value at the focus lens position at the closest end point is acquired. In step S320, the focus lens is driven by the amplitude data from the closest side to the infinity side based on the amplitude data of the set LD parameter. As a result, the focus lens is positioned at the end point on the infinite side in one high frequency component wobbling operation. In step S322, the focus evaluation value is acquired in a state where the focus lens is positioned at the end point on the infinite side in a single high-frequency component wobbling operation.

  Next, in step S324, subject state determination processing is executed. Details of the subject state determination process will be described later. In step S326, a next state determination process is executed based on the result of the subject state determination, and a transition state to be changed next is determined. In step S328, the low-frequency WOB operation is terminated, that is, a normal WOB. When transitioning to the mode, search mode, and standby mode, the processing of this flowchart is completed. On the other hand, when continuing the low frequency WOB operation, the process returns to step S302 and the process is repeated.

  The diagram showing the low-frequency wobbling operation of FIG. 9 will be described with reference to the flowchart of the low-frequency WOB of FIG. As described above, the low-frequency wobbling operation is executed based on the high-frequency component and the low-frequency component, and one cycle of the high-frequency component is HWT and one cycle of the low-frequency component is LWT. Further, the first half cycle of the low-frequency component is LWT1, and the second half cycle is LWT2. In FIG. 9, it is assumed that WOB-MV count = 5 and wob-dir = NEAR2FAR.

  When the low frequency wobbling operation is started, since wob-mv-num = 0 is set (S300), wob-mv-num <WOB-MV times (S302: NO), and 1 in wob-mv-num. And wob-mv-num = 1 is set (S310). Next, the amplitude, period, shift amount, etc., of the high frequency component operation, which are LD parameters, are set (S314), and the focus lens is moved to the position L1N of the closest end point (S316). Then, the focus evaluation value H1N is acquired in the state N1 at time T1N and stored in the memory (S318). Next, the focus lens is moved to the position L1F of the end point on the infinite side according to the settings of amplitude, shift amount, period, etc. (S320), and the focus evaluation value H1F is acquired in the state F1 at time T1F and stored in the memory (S322). ). Also, the change amount δ related to the difference between the focus evaluation values H1N and H1F is calculated based on the equation (1) and stored in the memory as δ [1].

  Here, as an example, the amplitude and shift amount, which are LD parameters, are set as amplitude = 3 pulses and shift amount = 4 pulses in units of drive pulses of the stepping motor that drives the focus lens. Therefore, the amount of movement of the focus lens from the closest side to the infinite side is 3 + 4 = 7 pulses (amplitude + shift amount), and the amount of movement from the infinite side to the closest side is 3 pulses (= amplitude). Further, the period of the high-frequency component wobbling operation is set to a value corresponding to twice (T1F-T1N) in FIG.

  The operation (HWT) for one cycle corresponding to such a high frequency component is repeatedly executed. When the operation corresponding to such a high frequency component is repeated five times, wob-mv-num = 5 is obtained (S302: YES), and since wob-dir = NEAR2FAR (S306: YES), wob-dir = FAR2NEAR. It is set (S308). At time T5N, the focus lens position L5N is moved and positioned (S316). In this state N5, the focus evaluation value H5N is acquired and stored in the memory (S318). At time T5F, the focus lens is moved to position L5F (S320), and in this state F5, the focus evaluation value H5F is acquired and stored in the memory (S322). Further, a change amount δ related to the difference between the focus evaluation values H5N and H5F is calculated based on the equation (1), and is stored in the memory as δ [5].

  Thereafter, since wob-dir = FAR2NEAR is set, the operation proceeds to the operation of the second half cycle (LWT2) of the low frequency component, and in step S314, the LD parameter corresponding to the second half cycle is set to the high frequency component. The corresponding operation is performed a predetermined number of times. In the above example, the wobbling operation corresponding to the high frequency component is set as the LD parameter with amplitude = 3 pulses and shift amount = 4 pulses. Accordingly, the amount of movement of the focus lens from the infinite side to the close side is 3 + 4 = 7 pulses (amplitude + shift amount), and the amount of movement from the close side to the infinite side is 3 pulses (= amplitude). Note that one cycle LWT of this low frequency wobbling operation may be repeated a plurality of times. Further, LD parameters such as amplitude may be changed according to the detection result of the focus evaluation value.

  FIG. 6 is a flowchart showing the operation of the subject state determination process executed in step S324 of the low frequency WOB operation (FIG. 5) of the imaging apparatus 100. In the subject state determination processing, two types of processing, mainly direction determination processing based on a high frequency component and direction determination processing based on a low frequency component, are performed, and each result is stored in a memory.

  First, the main body CPU 111 executes a stability determination operation in step S400. In the stability determination operation, it is determined whether or not the amount of change in the plurality of focus evaluation values acquired by the low-frequency WOB operation changes stably and has a sine wave shape. The amount of change calculated at time T [1] when the low frequency component of the low frequency WOB operation reaches one end point is δ [1], and is calculated at time T [N] when the opposite end point is reached. Let the amount of change be δ [N]. Also, let δ [2] to δ [N−1] be the amount of change calculated from one end point to the opposite end point. And it is judged that it is stable when the following equation (2) is satisfied.

ABS (δ [1] −δ [N]) × coefficient A ≦ (ABS (δ [1] −δ [2]) + ABS (δ [2] −δ [3]) +... + ABS (δ [N−1] ] −δ [N])) (2)
The coefficient A is a predetermined fixed value.

  For example, in the case of FIG. 9, the expression (2) is expressed by the following expression.

ABS (δ [1] −δ [5]) × coefficient A ≦ (ABS (δ [1] −δ [2]) + ABS (δ [2] −δ [3]) + ABS ([δ [3] −δ [4]] + ABS (δ [4] −δ [5]))
However, the change amounts δ [1],..., Δ [5] are expressed as follows.

δ [1] = (H1N−H1F) / H1N × 100
...
δ [5] = (H5N−H5F) / H5N × 100
Next, in step S402, based on the result of the stability determination operation, it is determined whether or not it is stable. If stable, the process proceeds to step S404. On the other hand, if it is not stable, it is determined that the detection is impossible, and the flow of the subject state determination process ends. In step S404, a direction determination operation based on the result of the low frequency WOB operation is executed. The focus evaluation values H5F and H1N acquired at the infinite side end point (L5F in FIG. 9) and the near side end point (L1N in FIG. 9) of the low frequency WOB operation are compared. If the focus evaluation value H1N on the near side is larger than the focus evaluation value H5F on the infinite side, it is determined that the direction determination result is the close side, that is, the direction in which the focus lens is in focus is the close side. Conversely, when the infinite focus evaluation value H5F is larger than the close focus evaluation value H1N, the direction determination result is determined to be infinite, that is, the direction in which the focus lens is in focus is determined to be infinite. .

  Next, in step S406, direction determination based on a plurality of change amounts δ (equation (1)) sequentially stored in the memory by the low frequency WOB operation, that is, direction determination based on the high frequency component is performed. When the signs of the plurality of change amounts δ are positive a predetermined number of times in succession in the time series, it is determined that the closest side. On the other hand, when the signs of the plurality of change amounts δ are negative for a predetermined number of times in a time series, it is determined that the number is infinite. When these are not satisfied, it is determined that the direction cannot be determined.

  And based on the direction determination result based on the low frequency component by the low frequency WOB operation and the direction determination result based on the high frequency component, the final direction determination operation is executed as follows. When the direction determination results of both the low frequency component and the high frequency component are close to each other, the final direction determination result is set to the close side. Further, when both the direction determination results of the low frequency component and the high frequency component are on the infinite side, the final direction determination result is set to the infinite side. Further, when the direction determination results of the low frequency component and the low frequency component are different, the final direction determination result is the same as the final direction determination result of the high frequency component. Then, the final direction determination result is stored in the memory.

  The reason why the direction determination result of the high frequency component is adopted when the direction determination result of the low frequency component and the direction determination result of the high frequency component are different is as follows. This is because the direction determination of the high frequency component is less susceptible to noise due to the passage of time, and is considered to be more reliable. In order to determine the direction of the low frequency component, a time corresponding to a half cycle of the low frequency WOB operation is required. For example, if wob-mv-num = 5 and the frame rate is 30 fps, the time for a half cycle of the low-frequency WOB operation is about 166 ms (= 1/30 (S) × 5 (times)). On the other hand, the direction determination of the high frequency component is considered to be more reliable because the direction determination results for five times are accumulated in about 1/5 of the above time to obtain a comprehensive direction determination result.

  In step S408, focus determination is executed as follows. If the transition of the change amount obtained by the low-frequency WOB operation is a state in which a sine wave is stably drawn with 0 as the center, it is determined that the focus is achieved. Further, when all the transitions of the change amounts are positive (or negative), it is determined that the focus is near. Furthermore, when the transition of the change amount is unstable in the vicinity of 0, it is determined that it is in the out-of-focus state and is located at the base of the contrast curve. The result of the above in-focus determination is stored in the memory, and the subject state determination process is terminated.

  The final direction determination result and the focus determination result made in the subject state determination process determine the next state to be changed in the next state determination in step S326 of the low frequency WOB operation. That is, the final direction determination result is operated by adopting the final direction determination result in the normal WOB operation after the transition to the normal WOB mode. If it is determined that the subject is in focus, the mode is changed to the standby mode. If it is determined that the subject is in the vicinity of the in-focus state, the mode is changed to the normal WOB mode. Set to transition to.

  Therefore, even if it is determined that AF is impossible in the normal WOB mode, the focus, near focus, and out of focus are determined by performing the low frequency WOB operation with higher detection capability in the low frequency WOB mode. It becomes possible. Then, it is possible to focus by moving to the normal WOB mode or the search mode and executing the normal WOB operation or the search operation, respectively.

  As described above, imaging is performed without increasing the driving sound of the focus lens by performing a low frequency wobbling operation in which a lower frequency sinusoidal amplitude component is superimposed on a wobbling operation having a high frequency amplitude component. Therefore, it is possible to improve the focus detection performance without degrading the quality of the image to be performed.

  Modification examples of the present invention will be described below.

  The stability determination operation shown in step S400 of the subject state determination process shown in FIG. 6 may be performed by the following method. Based on the shape of the predetermined sine wave, the correlation between the acquired transition data of the plurality of changes and the predetermined sine wave is performed, and when it is determined that the degree of correlation is greater than the predetermined threshold, It is determined that The amplitude and period of the predetermined sine wave may be set according to the LD parameter of the low frequency wobbling operation.

  Furthermore, as another modification, the following method may be employed for the stability determination operation. An approximate expression by the least square method is calculated for the obtained transition data of a plurality of change amounts, and if it can be determined that this approximate expression indicates a sine wave, it is determined that it is stable. For example, the correlation between the calculated approximate expression and a sine wave having a predetermined amplitude and period is calculated, and when it is determined that the degree of correlation is greater than a predetermined threshold, it may be determined that the correlation is stable.

  In this embodiment, the low frequency wobbling operation is performed by superimposing the lower frequency sinusoidal amplitude component on the normal wobbling operation, but the lower frequency triangular wave amplitude component is superimposed. The same effect can be obtained even when the low frequency wobbling operation is performed.

  Although the present invention has been described above based on the embodiments, the present invention is not limited to the above-described embodiments, and various modifications and applications are naturally possible within the scope of the gist of the present invention. Further, in the description of the operation described above, the operation is described using “first”, “next”, and the like for convenience. However, it does not mean that the operation is essential in this order.

  Further, the above-described embodiments include various stages of the invention, and various inventions can be extracted by appropriately combining a plurality of disclosed constituent elements. For example, even if some configuration requirements are deleted from all the configuration requirements shown in the embodiment, the above-described problem can be solved, and this configuration requirement is deleted when the above-described effects can be obtained. The configuration can also be extracted as an invention.

  DESCRIPTION OF SYMBOLS 100 ... Imaging device, 101 ... Interchangeable lens, 102 ... Camera body, 103 ... Imaging optical system, 104 ... Shutter, 105 ... Imaging element, 107 ... Imaging control circuit, 109 ... Shutter control circuit, 111 ... Main body CPU, 112 ... Electricity 113 ... lens CPU, 114 ... lens storage circuit, 115 ... lens drive circuit, 121 ... FROM, 123 ... RAM, 125 ... AF control circuit, 126 ... AE control circuit, 129 ... image processing circuit, 131 ... display circuit DESCRIPTION OF SYMBOLS 133 ... Display element, 135 ... Operation SW detection circuit, 137 ... Operation part

Claims (4)

A photographing optical system having a focus lens movable in the optical axis direction;
An imaging unit for imaging a subject image formed by the imaging optical system;
A focus evaluation value calculation unit that calculates a focus evaluation value based on image data generated by the imaging unit;
A focus control unit for controlling the focus lens based on the focus evaluation value to execute an AF operation;
Comprising
The focus control unit generates a second signal larger than the first period and a second amplitude larger than the first amplitude in the first signal formed by the first period and the first amplitude. The focus lens is moved based on a signal formed by superimposing the second signal formed by the above, and the focus evaluation value is calculated by the focus evaluation value calculation unit in synchronization with the movement of the focus lens. An AF operation is executed based on the evaluation value,
The focus control unit includes a signal component obtained by superimposing the first signal component and the second signal component in a first period corresponding to a half cycle between the maximum value and the minimum value of the second signal component. The focus lens at a position corresponding to a minimum value of a signal component obtained by superimposing a focus evaluation value when the focus lens is positioned at a position corresponding to the maximum value of the first signal component and the second signal component. Determining a first direction in which the focus lens is in focus based on a difference from a focus evaluation value when
The focus is set to a position corresponding to the maximum value of the first signal component in a second period corresponding to a half cycle between the maximum value and the minimum value of the first signal component in the first period. The focus lens is in focus based on the difference between the focus evaluation value when the lens is positioned and the focus evaluation value when the focus lens is positioned at a position corresponding to the minimum value of the first signal component. Judging the direction of 2,
Determining a direction in which the focus lens is in focus based on the first direction and the second direction;
A focusing device characterized by that.   The focus control unit determines the second direction for each period of the first signal component in the first period, and the same direction is determined when the same direction is determined a predetermined number of times consecutively in time series. The focus adjustment apparatus according to claim 1, wherein the direction determined as the direction is determined as the second direction.   The focus control unit determines the direction determined to be the same when the first direction and the second direction are the same as the direction in which the focus lens is in focus, and determines the second direction when they are different from each other. The focus adjustment apparatus according to claim 1, wherein the focus lens is determined as a direction in which the focus lens is in focus. In a focus adjustment method of an imaging apparatus comprising: an imaging optical system having a focus lens movable in the optical axis direction; and an imaging unit that images a subject image formed by the imaging optical system;
The first signal formed by the first period and the first amplitude is the second signal formed by the second period larger than the first period and the second amplitude larger than the first amplitude. The focus lens is moved based on a signal obtained by superimposing the signal, and the focus evaluation value is calculated based on the output of the imaging unit by performing imaging of the imaging unit in synchronization with the movement of the focus lens.
Corresponding to the maximum value of the signal component obtained by superimposing the first signal component and the second signal component in a first period corresponding to a half cycle between the maximum value and the minimum value of the second signal component. The focus evaluation value when the focus lens is located at the position and the focus when the focus lens is located at a position corresponding to the minimum value of the signal component obtained by superimposing the first signal component and the second signal component Determining a first direction in which the focus lens is in focus based on a difference from the evaluation value;
The focus is set to a position corresponding to the maximum value of the first signal component in a second period corresponding to a half cycle between the maximum value and the minimum value of the first signal component in the first period. The focus lens is in focus based on the difference between the focus evaluation value when the lens is positioned and the focus evaluation value when the focus lens is positioned at a position corresponding to the minimum value of the first signal component. Judging the direction of 2,
Determining a direction in which the focus lens is in focus based on the first direction and the second direction;
Focus adjustment method characterized by the above.

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