JP4802742B2 - Focus control device, imaging device, and focus control method - Google Patents

Description

  The present invention relates to a focus control technique in an imaging apparatus.

  Conventionally, as an autofocus (AF) control performed by an imaging apparatus such as a silver salt camera, there are many that employ a so-called phase difference method. However, it is known that this phase difference AF control is not accurate particularly in photographing with a small F number.

  On the other hand, in recent years, with the advent of digital cameras, imaging devices employing so-called contrast type (mountain climbing) AF control have become widespread. In general, it is known that AF control with contrast method (contrast AF control) has higher AF accuracy than AF control with phase difference method (phase difference AF control).

  Therefore, it is conceivable to improve AF accuracy by using both phase difference AF control and contrast AF control.

  However, under a light source such as a fluorescent lamp, fluctuations in the amount of light occur due to so-called flicker, so the peak shape of the evaluation value for evaluating the in-focus state collapses at the timing of acquiring an image in contrast AF control. This leads to a decrease in focusing accuracy.

  In order to solve such a problem, a technique for improving AF accuracy in contrast AF control by sampling (acquiring an image) at a least common multiple of a flicker period and an image reading period has been proposed. (For example, patent document 1).

JP 2001-324670 A

  However, in the technique proposed in Patent Document 1, sampling cannot be performed with a period shorter than the flicker period, and a long time is required for AF control.

  Further, when considering using both phase difference AF control and contrast AF control as described above, the phase difference AF control performs contrast AF control in parallel with this operation in order to move the focus lens at high speed. In this case, AF accuracy cannot be ensured unless sampling is performed with a short period (for example, 200 fps).

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a technique capable of performing high-speed and high-precision focusing control even under illumination in which flicker occurs.

In order to solve the above problems, the invention of claim 1 is directed to a plurality of images based on light from a subject incident through the optical lens while the optical lens is driven along the optical axis. An image acquisition means for acquiring data at a predetermined frame rate; a frequency detection means for detecting a flicker frequency of a light source; and if the flicker frequency L is detected by the frequency detection means, the predetermined frame rate is determined as the flicker frequency. Setting means for setting the frequency L to a value obtained by multiplying n (n is a multiple of 2 which is 4 or more ), and image data for n / 2 frames or more acquired continuously in time by the image acquisition means. Evaluation value calculation means for calculating a plurality of focus evaluation values corresponding to the plurality of image data based on the plurality of image data while calculating one focus evaluation value by using the plurality of image data; It was provided a focusing position detecting means for detecting the focus position of the optical lens based on the focus evaluation value of the number.

The invention according to claim 2 is the focusing control device according to claim 1, wherein the evaluation value calculation means calculates a pixel value of each pixel corresponding to the image data of n / 2 frames or more. generating an addition image data by adding each to calculate the one focus evaluation value based on the added image data.

The invention according to claim 3 is the focusing control device according to claim 1 , wherein the evaluation value calculation means calculates an average pixel value of each corresponding pixel for the image data for n / 2 frames or more. The average image data is generated by calculation, and the one focus evaluation value is calculated based on the average image data.

The invention according to claim 4 is the focusing control apparatus according to claim 1 , wherein the evaluation value calculation means is configured to output the n / 2 frames for the n / 2 frames or more based on the image data for the n / 2 frames or more. After calculating preliminary evaluation values for n / 2 frames respectively corresponding to the above image data, the preliminary evaluation values for n / 2 frames are added to calculate the one in-focus evaluation value.

The invention according to claim 5 is the focusing control apparatus according to claim 1 , wherein the evaluation value calculation means is configured to output the n / 2 frames for the n / 2 frames or more based on the image data for the n / 2 frames or more. after calculating the preliminary evaluation value of n / 2 frames respectively corresponding to the above image data, calculates an average value of the preliminary evaluation value of the n / 2 frames as the one focusing evaluation value.

The invention of claim 6 is the focusing control apparatus according to any one of claims 1 to 5, wherein the n / 2 or more frames of image data is an image data of two frames.

The invention according to claim 7 is the focusing control apparatus according to claim 1, wherein the image data for the n / 2 frames or more is acquired continuously in time by the image acquisition means 3 The evaluation value calculation means calculates the three or more focus evaluation values corresponding to the three or more image data by the interpolation process using the three or more image data. calculating a plurality of focus evaluation value.

Further, the invention of claim 8 is the focusing control apparatus according to claim 7 , wherein the evaluation value calculating means is configured such that the predetermined frame rate is a value obtained by multiplying the flicker frequency L by 4 by the setting means. When the luminance of the second image data among the first, second, and third image data set and continuously acquired in time by the image acquisition means is minimum, the first to while calculating a focus evaluation value for said second image data by interpolation processing using the third image data, and calculates the three focus evaluation values respectively corresponding from the first to the third image data.

The invention according to claim 9 is the focusing control apparatus according to claim 8 , wherein the evaluation value calculation means calculates the first to third preliminary evaluation values for the first to third image data. respectively calculated by the interpolation process based on the first to third pre-evaluation value, and calculates a focus evaluation value for said second image data.

The invention according to claim 10 is the focusing control apparatus according to any one of claims 1 to 9 , wherein the phase difference focusing is performed to detect a focusing position of the optical lens using a phase difference method. detection means, before the detection of the focusing position of the optical lens according to the phase difference in-focus detecting means further includes a detection control unit for controlling to detect the flicker frequency of the light source by the frequency detecting means, said The phase difference focus control using the phase difference focus detection means and the contrast focus control using the focus position detection means are executed in parallel.

The invention of claim 11 is a focusing control device according to claim 1 0, the first directing each light from the object, with respect to the image acquiring means and the phase difference in-focus detecting means and further comprising a second light splitting means for splitting the optical path.

The invention of claim 12 is a focusing control device according to claim 1 0 or Claim 1 1, wherein the contrast focus detection means for performing a contrast focus control, the phase difference in-focus detecting means A focusing surface at an optical position relatively different from the focusing surface according to the above, and the focusing control device starts the contrast focusing control after starting the phase difference focusing control. It further has timing control means for controlling.

The invention of claim 13 is an image pickup apparatus equipped with a focusing control apparatus according to any one of claims 1 to 1 2.

According to a fourteenth aspect of the present invention, there is provided (a) a step of detecting a flicker frequency of a light source, and (b) a frame for acquiring an image in a predetermined imaging means when the flicker frequency L is detected in the step (a). Setting the rate to a value obtained by multiplying the flicker frequency L by n (n is a multiple of 2 which is 4 or more ), and (c) while driving a predetermined optical lens along the optical axis, Acquiring a plurality of image data at a frame rate set in the step (b) based on light from a subject incident through the predetermined optical lens by a predetermined imaging means; and (d) the (c ) While calculating one in-focus evaluation value using image data of n / 2 frames or more acquired continuously in time in the step, a plurality of in-focus evaluation values corresponding to the plurality of image data are calculated. Said compound Calculating on the basis of the image data, and be provided and detecting the focus position of the predetermined optical lens based on focus evaluation value of the plurality of engagement (e).

  Further, the invention of claim 15 is a focusing control method in an imaging apparatus, wherein (a) a step of detecting a flicker frequency of a light source, and (b) a case where a flicker frequency L is detected in the step (a). And (c) driving a predetermined optical lens along the optical axis, setting the flicker frequency L to n (n is a multiple of 2). And acquiring a plurality of image data at the frame rate set in step (b) based on the light from the subject incident via the predetermined optical lens by the predetermined imaging means. , (D) a plurality of in-focus corresponding to the plurality of image data while calculating one in-focus evaluation value using two or more pieces of image data acquired sequentially in the step (c). Comment Calculating on the basis of values to the plurality of image data, characterized by comprising the steps of detecting a focus position of the predetermined optical lens based on focus evaluation value (e) said plurality of engagement.

By the invention of any of claims 1 to 1 2, n times the flicker frequency L a frame rate (n is a multiple of 2 is 4 or more) as well as set to be acquired successively in time While calculating one focus evaluation value using image data of n / 2 frames or more , a plurality of focus evaluation values are calculated, and the focus of the optical lens is calculated based on the plurality of focus evaluation values. By adopting a configuration that detects the position, sampling for contrast AF control can be performed at a cycle shorter than the cycle of flicker, so high-speed and high-precision focusing control can be performed even under illumination where flicker occurs. It can be carried out.

According to the second aspect of the present invention, the frame rate is set to n times the flicker frequency L (n is a multiple of 2 that is 4 or more ), and n / 2 obtained continuously in time. A configuration in which one image data is generated by adding pixel values of corresponding pixels between image data corresponding to frames or more , and one in-focus evaluation value is calculated based on the one image data. By adopting it, it is possible to suppress fluctuations in the focus evaluation value due to fluctuations in the amount of light from the subject due to lighting flicker.

According to the third aspect of the present invention, the frame rate is set to n times the flicker frequency L (n is a multiple of 2 that is 4 or more ), and n / 2 acquired continuously in time. A configuration is adopted in which one image data is generated by calculating an average pixel value of each corresponding pixel for image data for frames or more , and one in-focus evaluation value is calculated based on the one image data. By doing this, it is possible to suppress fluctuations in the focus evaluation value due to fluctuations in the amount of light from the subject due to lighting flicker.

According to the invention described in claim 4 , the frame rate is set to n times the flicker frequency L (n is a multiple of 2 which is 4 or more ), and n / 2 obtained continuously in time. based on the image data of the above frame, n / 2 in frames or more of the image data of each evaluation value corresponding n / 2 frames after preliminarily calculating, adding the evaluation values of the n / 2 frames By adopting such a configuration that calculates one in-focus evaluation value, fluctuations in the in-focus evaluation value due to fluctuations in the amount of light from the subject due to illumination flicker can be suppressed. .

According to the fifth aspect of the present invention, the frame rate is set to n times the flicker frequency L (n is a multiple of 2 that is 4 or more ), and n / 2 obtained continuously in time. By adopting a configuration that calculates the average value of preliminary evaluation values for more than one frame as one in-focus evaluation value, it is possible to adjust the alignment caused by fluctuations in the amount of light from the subject due to lighting flicker. Variations in the focus evaluation value can be suppressed.

According to the sixth aspect of the present invention, when the frame rate is set to four times the flicker frequency, one focus evaluation value is obtained using two frames of image data acquired continuously in time. By calculating a plurality of focus evaluation values corresponding to a plurality of image data and detecting a focus position of the optical lens based on the plurality of focus evaluation values Thus, it is possible to suppress fluctuations in the focus evaluation value due to fluctuations in the amount of light from the subject due to lighting flicker.

Further, according to any of the inventions of claims 7 to 9 , when the frame rate is set to n times the flicker frequency (n is a multiple of 2 that is 4 or more ), it is acquired continuously in time. A plurality of focus evaluation values corresponding to a plurality of image data are calculated by calculating three or more focus evaluation values respectively corresponding to the three or more image data by an interpolation process using the three or more image data. With this configuration, it is possible to reduce the influence of fluctuations in the amount of light from the subject caused by illumination flicker, and to achieve highly accurate focusing control.

Further, according to any of the eighth and ninth aspects of the invention, the frame rate is set to four times the flicker frequency, and the first to third image data acquired continuously in time. By adopting a configuration in which the focus evaluation value for the second image data is calculated by the interpolation processing using the first to third image data when the luminance of the second image data is minimum. In addition, since it is possible to calculate a focus evaluation value in consideration of a decrease in the amount of light caused by illumination flicker, high-precision focus control can be realized.

According to the ninth aspect of the invention, the first to third preliminary evaluation values are calculated for the first to third image data, respectively, and the first to third preliminary evaluation values are calculated. By adopting a configuration in which a focus evaluation value for the second image data is calculated by interpolation processing based on the above, a decrease in the evaluation value due to fluctuations in the amount of light from the subject due to lighting flicker is corrected. Therefore, highly accurate focusing control can be realized.

Further, according to the invention described in claim 1 0, before the detection of the focus by the phase difference method the position to detect the flicker frequency of the light source, and a focusing control of the focus control and the contrast method of the phase difference method By adopting a configuration that is implemented in parallel, for example, the optical lens is driven to the vicinity of the in-focus position in a short time by phase difference type focus control, and the focus control is performed by contrast type focus control. Since the accuracy can be ensured, high-speed and high-precision focusing control according to the flicker frequency can be realized.

Further, according to the invention described in claim 1 1, to divide the light from the object into two optical paths, and focusing control of the focus control and the contrast method of the phase difference method using the divided light By carrying out in parallel, high-speed and accurate focusing control becomes possible.

Further, according to the invention described in claim 1 2, the optical position of the focusing plane of the focus detection of the phase difference method and the contrast method mutually made different, after the start of the focusing control of the phase difference method With the configuration in which the contrast-type focus control is started, two focus controls are performed simultaneously. Before the focus state is achieved by the phase-difference focus control, the focus-type contrast control controls the focus lens. Since the lens focus position can be detected, high-speed and high-precision focus control can be realized. Further, for example, since focus control can be performed without moving the focus lens in the reverse direction, it is possible to prevent the occurrence of a backlash problem. Further, for example, the focus feeling can be improved because the subject visually recognized through the finder or the like can smoothly change from a blurred state to a focused state. .

Further, according to the invention described in claims 1 to 3, it is possible to obtain the same effect as the invention according to claims 1 to claim 1 2.

Further, according to the invention described in claims 1 to 4, it is possible to obtain the same effect as the invention described in claim 1.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  In general, when a fluorescent lamp is used as a light source, the fluorescent lamp flickers in a very short cycle, and thus the amount of light emitted from the fluorescent lamp (light quantity) fluctuates (hereinafter also referred to as “flicker”). For example, in Japan, 50 Hz and 60 Hz are adopted as the frequency of the power supply. Therefore, the flicker frequency (hereinafter also referred to as “flicker frequency”) may be 50 Hz or 60 Hz.

  A value (hereinafter referred to as “AF evaluation value” or “focus evaluation value” as appropriate) that evaluates the in-focus state of the subject at a fixed timing when performing contrast autofocus control (hereinafter referred to as “contrast AF control”). ”), The peak shape of the AF evaluation value collapses due to flicker, and the accuracy of AF control decreases.

  In order to solve such a problem, in the imaging device 1 according to the embodiment of the present invention, when a flicker frequency is detected, the image data is sampled at a timing corresponding to the flicker frequency, and a sampling interval is obtained. An AF evaluation value calculation method according to the above is adopted.

<Outline of imaging device>
FIG. 1 is a schematic cross-sectional view illustrating a schematic configuration of an imaging apparatus 1 according to an embodiment of the present invention.

  As illustrated in FIG. 1, the imaging device 1 is configured as a so-called single-lens reflex digital camera, and guides light from a subject to the imaging device main body 300 via a photographing lens unit 2, thereby capturing captured image data relating to the subject. (Captured image) can be obtained. The imaging apparatus main body 300 is equipped with a unit (hereinafter also referred to as “AF control unit” or “focus control apparatus”) 100 for performing autofocus (AF) control in the imaging apparatus 1. The photographing lens unit 2 is provided with a lens group including a plurality of photographing lenses including a lens (focus lens) for realizing AF control on the optical axis L of the photographing lens unit 2.

  FIG. 2 is a schematic diagram focusing on the configuration related to the AF control unit 100 in the configuration of the imaging apparatus 1.

  The AF control unit 100 mainly includes a main mirror 10, a sub mirror 20, a shutter mechanism 4, a C-MOS sensor (hereinafter abbreviated as “C-MOS”) 5 that is an image sensor, and a phase difference AF module 3. Composed.

  The main mirror 10 is constituted by a half mirror, and reflects a part of light from the subject toward the upper part of the imaging apparatus main body 300 to thereby apply reflected light (hereinafter also referred to as “first reflected light”) to the finder optical system. Lead. Specifically, the main mirror 10 projects a subject image on the finder focusing screen 6 by reflecting light from the subject. This subject image is made upright by the pentaprism 7, and the user can check the state of the subject image via the eyepiece 8. The main mirror 10 transmits part of light from the subject toward the sub mirror 20.

  The sub mirror 20 is constituted by a half mirror, and reflects light that has passed through the main mirror 10 (hereinafter also referred to as “first transmitted light”) out of light from the subject toward the lower portion of the imaging apparatus main body 300, Guide to the phase difference AF module 3. On the other hand, the sub mirror 20 transmits a part of the first transmitted light toward the C-MOS 5. That is, the sub mirror 20 divides (branches) the light from the subject into two optical paths that guide the light from the subject to the phase difference AF module 3 and the C-MOS 5 respectively.

  The phase difference AF module 3 is a unit that performs focus detection using a phase difference method. The phase difference AF module 3 includes a condenser lens 3a, a mirror 3b, a separator lens 3c, and a phase difference detection element 3d.

  The condenser lens 3 a guides the light reflected by the sub mirror 20 (hereinafter also referred to as “second reflected light”) into the phase difference AF module 3. The mirror 3b bends the second reflected light toward the separator lens 3c side. The separator lens 3c is a pupil division lens for detecting the phase difference, and divides the second reflected light into the pupil and projects it onto the phase difference detection element 3d.

  3 to 5 are diagrams for explaining the principle of phase difference focusing control. In the phase-difference focusing control, as shown in FIGS. 3 to 5, the light FF emitted from the surface (subject surface) PP of the subject to be focused is used as the photographing lens unit 2, the condenser lens 3a, and the separator. The light is guided to the phase difference detecting element 3d through the lens 3c. At this time, the defocus amount is obtained by measuring the phase difference between the two subject images detected by the phase difference detecting element 3d, that is, the displacement amount of the image interval. Here, the defocus amount is determined so as to be focused on a surface FP equivalent to the imaging surface of the C-MOS 5 set at the imaging home position described later (hereinafter also referred to as “imaging equivalent surface”) FP. That is, the imaging equivalent plane FP is a plane (hereinafter also referred to as “first focusing plane”) on which a focused subject image is formed by phase difference AF control (hereinafter referred to as “phase difference AF control”). Configured as

  For example, when the subject is in focus as shown in FIG. 3, the image interval is a predetermined value determined when the phase difference AF module 3 is designed, but as shown in FIG. If it is a pin, the image interval is narrowed, and as shown in FIG. 5, if it is a rear pin, the image interval is widened.

  The shutter mechanism 4 can open / block the optical path of light transmitted through the sub-mirror 20 (hereinafter also referred to as “second transmitted light”). By opening the optical path, the second transmitted light is transmitted to the C-MOS 5. The object image is projected onto the C-MOS 5.

  The C-MOS 5 obtains an image signal by receiving the second transmitted light of the light from the subject. The image signal obtained by the C-MOS 5 is used to generate the recorded image data for recording, and before the operation for acquiring the recorded image data for recording (main imaging operation), the so-called contrast AF control is performed. It is also used to perform (contrast AF control). The light receiving surface (imaging surface) of the C-MOS 5 is configured as a surface (hereinafter also referred to as “second focusing surface”) on which a focused subject image is formed by contrast AF control.

  Further, since the C-MOS 5 is held so as to be movable with respect to the imaging apparatus main body 300, it can move back and forth along the optical axis L of the second transmitted light. By moving the C-MOS 5 back and forth, the optical position of the second focusing surface is set to be different from the optical position of the first focusing surface.

  Here, “the optical positions are different from each other” means that the subject image is not in focus on the second focus surface when the subject image is in focus on the first focus surface. Furthermore, when the subject image is in focus on the second focus surface, the subject image is not in focus on the first focus surface.

<Functional configuration of imaging device>
FIG. 6 is a block diagram illustrating a functional configuration of the imaging apparatus 1 according to the first embodiment of the invention.

  As shown in FIG. 6, the imaging device 1 includes a photographing lens unit 2, a phase difference AF module 3, a C-MOS 5, a mirror mechanism 10a, a sub mirror mechanism 20a, a control unit 101, a lens position detection unit 201, operating units OP, C. A MOS movement control unit 150, a focus control unit 130, a signal processing circuit 500, an AF circuit 600, and the like are provided.

  The photographic lens unit 2 includes an optical lens (focus lens) 2a and the like for realizing a focused state in which a subject is in a sharp state in an image signal acquired by the C-MOS 5. The focus lens 2a can be moved back and forth along the optical axis of the lens, and the lens position of the focus lens 2a is moved by driving the motor M1 in response to a control signal from the focus control unit 130. The focus control unit 130 generates a control signal based on a signal input from the control unit 101. The position of the focus lens 2a is detected by the lens position detection unit 201, and data indicating the position of the focus lens 2a is sent to the control unit 101.

  The mirror mechanism 10 a is a mechanism including the main mirror 10 that can be retracted from the path of light from the subject (optical path), and is driven by the motor M2 in response to a control signal from the mirror control unit 110, whereby the main mirror 10. Is set in a state of being retracted from the optical path (mirror up state) or in a state of blocking the optical path (mirror down state). The mirror control unit 110 generates a control signal based on the signal input from the control unit 101.

  The sub-mirror mechanism 20a is a mechanism including the sub-mirror 20 that can be retracted from the path of light from the subject, and the sub-mirror 20 is retracted from the optical path by driving the motor M5 in response to a control signal from the sub-mirror control unit 120. It is set to a state (mirror up state) or a state where the optical path is blocked (mirror down state). The sub mirror control unit 120 generates a control signal based on the signal input from the control unit 101.

  The shutter mechanism 4 is a mechanism capable of blocking / opening the path of light from the subject, and the shutter mechanism 4 opens and closes when the motor M3 is driven in response to a control signal from the shutter control unit 140. The shutter control unit 140 generates a control signal based on a signal input from the control unit 101.

  The C-MOS 5 performs imaging (photoelectric conversion) and generates an image signal related to the captured image. In response to the drive control signal (accumulation start signal / accumulation end signal) input from the timing control circuit 170, the C-MOS 5 performs exposure (charge accumulation by photoelectric conversion) of the subject image formed on the light receiving surface. Then, an image signal related to the subject image is generated.

  Further, the C-MOS 5 outputs the image signal to the signal processing unit 51 in response to the read control signal input from the timing control circuit 170.

  The timing control circuit 170 generates various control signals based on signals input from the control unit 101. When the contrast AF control unit 105 (to be described later) recognizes that the light source is a light source (non-flicker light source) that does not cause fluctuation (flicker) in the light amount (light source light amount), and when the flicker frequency is recognized as 50 Hz First, a control signal is output from the timing control circuit 170 to the C-MOS 5 so that an image signal is output from the C-MOS 5 at a first predetermined period (here, 200 fps).

  On the other hand, when the contrast AF control unit 105 recognizes that the light source is a light source causing flicker (flicker light source) and the flicker frequency is 60 Hz, the second predetermined cycle (here) Then, the control signal is output from the timing control circuit 170 to the C-MOS 5 so that the image signal is output at 240 fps.

  A timing signal (synchronization signal) from the timing control circuit 170 is input to the signal processing unit 51 and the A / D conversion circuit 52.

  The C-MOS 5 is moved back and forth along the optical axis of the light from the subject by the C-MOS driving mechanism 5a. The C-MOS drive mechanism 5a is moved by the motor M4 in response to a control signal from the C-MOS movement control unit 150 to move the C-MOS 5 back and forth along the optical axis of light from the subject. . The C-MOS movement control unit 150 generates a control signal based on a signal input from the control unit 101.

  The signal processing unit 51 performs predetermined analog signal processing on the image signal supplied from the C-MOS 5, and the processed image signal is converted into digital image data (image data) by the A / D conversion circuit 52. This image data is input to the signal processing circuit 500 and is also given to the AF circuit 600 in a timely manner for contrast AF control.

  The signal processing circuit 500 performs digital signal processing on the image data input from the A / D conversion circuit 52 to generate image data related to the captured image. Signal processing in the signal processing circuit 500 is performed for each pixel signal constituting the image signal. The signal processing circuit 500 includes a black level correction circuit 53, a white balance (WB) circuit 54, a γ correction circuit 55, and an image memory 56. Of these configurations, the black level correction circuit 53, the white balance (WB) circuit 54, and the γ correction circuit 55 perform digital signal processing.

  The black level correction circuit 53 corrects the black level of each pixel data constituting the image data output from the A / D conversion circuit 52 to a reference black level. The WB circuit 54 performs white balance adjustment of the image. The γ correction circuit 55 performs gradation conversion of the captured image. The image memory 56 is a high-speed accessible image memory for temporarily storing generated image data, and has a capacity capable of storing image data for a plurality of frames.

  When the AF circuit 600 performs contrast AF control, the AF circuit 600 acquires image data relating to a partial area (AF area) of the image data from the A / D conversion circuit 52, and evaluates the focus state of the subject ( AF evaluation value) is calculated.

  When the contrast AF control unit 105 described later detects that the light source is a light source (non-flicker light source) that does not cause fluctuations in the amount of light (non-flicker light source), the AF circuit 600 performs image data related to the AF area between adjacent pixels. The sum of the pixel value differences is calculated as an AF evaluation value.

  On the other hand, when the flicker frequency is detected by the contrast AF control unit 105, the sum of the pixel value differences between adjacent pixels (hereinafter also referred to as “preliminary evaluation value”) is calculated for the image data related to the AF area, and temporally An average value of two preliminary evaluation values calculated in succession is calculated as an AF evaluation value.

  Note that the AF evaluation value calculation method in the AF circuit 600 is switched based on the control of the contrast AF control unit 105. The AF evaluation value calculated by the AF circuit 600 is output to the contrast AF control unit 105.

  The control unit 101 mainly includes a CPU, a memory, a ROM, and the like, and various functions and controls are realized by reading a program stored in the ROM and executing it by the CPU. Specifically, the control unit 101 has a contrast AF control unit 105 as a function for executing contrast AF control, and a phase difference AF control unit 106 as a function for executing phase difference AF control. The overall AF control unit 107 is provided as a function for overall control of the overall AF control.

  The contrast AF control unit 105 recognizes the state of the light source when performing contrast AF control. That is, whether the light source is a non-flicker light source or if the light source is a flicker light source, the flicker frequency is recognized. Then, in accordance with the state of the light source, the acquisition timing (frame rate) of the image signal (image data) in the C-MOS 5 is changed, and the AF evaluation value calculation method is changed.

  Also, the contrast AF control unit 105 sets the lens position of the focus lens 2a at which the AF evaluation value is the maximum for the plurality of AF evaluation values input from the AF circuit 600 (the lens focusing state). (Focus position). Further, the contrast AF control unit 105 outputs a control signal corresponding to the obtained lens focus position to the focus control unit 130, and moves the focus lens 2a to the lens focus position.

  The phase difference AF control unit 106 detects the lens in-focus position of the focus lens 2a based on the detection result in the phase difference AF module 3 when performing the phase difference AF control. Then, the phase difference AF control unit 106 outputs a control signal corresponding to the appropriately obtained lens focusing position to the focus control unit 130, and moves the focus lens 2a to the lens focusing position.

  The overall AF control unit 107 appropriately executes contrast AF control and phase difference AF control.

  The operation unit OP includes a shutter start button (shutter button), various buttons, switches, and the like, and the control unit 101 realizes various operations in response to user input operations on the operation unit OP. The shutter button is a two-stage detection button that can detect two states, a half-pressed state (S1 state) and a fully-pressed state (S2 state). Note that the imaging apparatus 1 performs a preparatory operation for the main photographing operation including AF control when the S1 state is set, and performs the main photographing operation when the S2 state is further set.

  The image data temporarily stored in the image memory 56 is appropriately transferred to the VRAM 102 by the control unit 101 so that an image based on the image data is displayed on the liquid crystal display unit (LCD) 103 disposed on the back surface of the imaging apparatus main body 300. Is done.

  Further, at the time of actual photographing, the image data temporarily stored in the image memory 56 is appropriately subjected to image processing in the control unit 101 and stored in the memory card MC via the card I / F 104.

<Outline of contrast AF control>
FIG. 7 is a diagram illustrating a state in which the peak shape of the AF evaluation value changes due to a change in the AF evaluation value calculation method in contrast AF control. FIG. 7 illustrates an AF evaluation value calculated from each of a plurality of image data acquired at a frame rate of 200 frames / second (fps) when the fluorescent lamp has a light source flicker frequency of 50 Hz. . The vertical axis indicates the AF evaluation value, and the horizontal axis indicates the position of the focus lens 2a.

  Specifically, a black circle indicates that an AF evaluation value is simply calculated from each image data obtained by the C-MOS 5 when the light source is a non-flicker light source (hereinafter also referred to as “normal evaluation value calculation operation”). A plurality of AF evaluation values calculated in the case where is performed. Also, a cross indicates a plurality of AF evaluation values calculated when an AF evaluation value calculation operation (also referred to as “flicker countermeasure evaluation value calculation operation”) is performed when the light source is a flicker light source. Yes.

  When the normal evaluation value calculation operation is performed, the luminance of the image data acquired continuously in time greatly fluctuates due to the flicker of the light source. Then, the AF evaluation value is greatly waved in accordance with the luminance variation. As a result, peaks are detected for a plurality of AF evaluation values indicated by black circles in FIG. 7, and the lens focus position cannot be detected with high accuracy.

  On the other hand, as indicated by the crosses in FIG. 7, the sum of the differences in pixel values between adjacent pixels is evaluated for each image data obtained at a frame rate of 200 fps while moving the focus lens 2a in the optical axis direction. (Hereinafter also referred to as “preliminary evaluation value”) and a flicker countermeasure evaluation value calculation operation for calculating an average value of two preliminary evaluation values calculated successively in time as one AF evaluation value. When executed, the AF evaluation value does not undulate greatly, and the peak shape of the AF evaluation value becomes clear (dashed line in FIG. 7). As a result, the lens focus position can be detected with high accuracy.

  In this way, the principle that the peak shape of a plurality of AF evaluation values becomes clear when the flicker countermeasure evaluation value calculation operation is employed will be described below.

<Principle used by flicker countermeasure evaluation value calculation operation>
8 and 9 are timing charts showing the principle of the flicker countermeasure evaluation value calculation operation. 8 and 9, in order from the top, the exposure timing in the C-MOS 5 (the exposure timing of 200 fps in FIG. 8, the exposure timing of 240 fps in FIG. 9), the fluctuation of the light source amount when the flicker frequency is 50 Hz, It shows the fluctuation of the light amount of the light source when the flicker frequency is 60 Hz.

  As shown in FIG. 8, when the flicker frequency is 50 Hz, each exposure interval (frame acquisition interval) is ½ of the fluctuation period of the light source light amount. The sum of the exposure amounts at the exposure timing is always constant. As a result, if an average value of preliminary evaluation values (that is, two preliminary evaluation values) calculated based on image data acquired at two consecutive (adjacent) exposure timings in time is used as the AF evaluation value. Regardless of the influence of flicker, the peak shapes of a plurality of AF evaluation values become clear.

  However, as shown in FIG. 8, when the flicker frequency is 60 Hz, the fluctuation period of the light source light amount is not twice the frame acquisition interval, and the exposure amount varies greatly at each exposure timing. Therefore, when the flicker frequency is 60 Hz and the frame rate is 200 fps, the average of the preliminary evaluation values respectively calculated based on the image data acquired at two exposure timings that are temporally continuous (adjacent) Even if the value is set as the AF evaluation value, the AF evaluation value is greatly waved, and a clear peak shape of the AF evaluation value cannot be obtained.

  Therefore, in the case where the flicker frequency is 60 Hz, as in the case where the flicker frequency is 50 Hz, when the frame rate is set to 240 fps so that the frame acquisition interval becomes 1/2 of the fluctuation period of the light source light amount, FIG. In this way, the sum of the exposure amounts at two exposure timings that are continuous (adjacent) in time is always constant. As a result, if an average value of preliminary evaluation values (that is, two preliminary evaluation values) calculated based on image data acquired at two consecutive (adjacent) exposure timings in time is used as the AF evaluation value. Regardless of the influence of flicker, the peak shapes of a plurality of AF evaluation values become clear.

  However, as shown in FIG. 9, when the flicker frequency is 50 Hz, the fluctuation period of the light source light amount is not twice the frame acquisition interval, and the exposure amount varies greatly at each exposure timing. Therefore, when the flicker frequency is 50 Hz and the frame rate is 240 fps, the average of the preliminary evaluation values respectively calculated based on the image data acquired at two exposure timings that are temporally continuous (adjacent) Even if the value is set as the AF evaluation value, the AF evaluation value is greatly waved, and a clear peak shape of the AF evaluation value cannot be obtained.

  Therefore, the imaging apparatus 1 detects the state of the light source (the presence or absence of flicker, the flicker frequency) by a method described later, and uses the principle shown in FIGS. 8 and 9 at a frame rate corresponding to the state of the light source. Image data for calculating an AF evaluation value is acquired, and control is performed so that an average value of preliminary evaluation values related to two exposure timings that are temporally continuous (adjacent) is calculated as an AF evaluation value.

<Flicker frequency identification method>
10 and 11 are timing charts for explaining a flicker frequency identifying method, and FIGS. 12 to 15 are diagrams for explaining a flicker frequency identifying method.

  10 and 11, in order from the top, exposure timing in the C-MOS 5 (exposure timing of 100 fps in FIG. 10, exposure timing of 120 fps in FIG. 11), fluctuation of the light source light amount when the flicker frequency is 50 Hz, It shows the fluctuation of the light amount of the light source when the flicker frequency is 60 Hz.

  As shown in FIG. 10, when the frame rate is 100 fps and the flicker frequency is 50 Hz, the frame acquisition interval and the fluctuation period of the light source light quantity coincide with each other, so each image data acquired by the C-MOS 5 There is no variation in pixel value (that is, luminance) between them. On the other hand, when the frame rate is 100 fps and the flicker frequency is 60 Hz, the frame acquisition interval does not match the fluctuation period of the light source light quantity, and therefore, between each image data acquired by the C-MOS 5. Variations in pixel values (ie luminance) occur.

  On the other hand, as shown in FIG. 11, when the frame rate is 120 fps and the flicker frequency is 60 Hz, the frame acquisition interval and the fluctuation period of the light source light quantity coincide with each other. There is no variation in pixel value (ie, luminance) between image data. On the other hand, when the frame rate is 120 fps and the flicker frequency is 50 Hz, the frame acquisition interval does not match the fluctuation period of the light source light amount, and therefore, between each image data acquired by the C-MOS 5. Variations in pixel values (ie luminance) occur.

  In FIG. 12, when the frame rate is 120 fps and the flicker frequency is 60 Hz, a specific example of the average value of pixel values (that is, the average value of luminance) in each image data (each frame) acquired by the C-MOS 5 It is shown. In FIG. 13, when the frame rate is 100 fps and the flicker frequency is 60 Hz, the average value of pixel values (that is, the average value of luminance) of each image data (each frame) acquired by the C-MOS 5 is obtained. Specific examples are shown.

  As shown in FIG. 12, when the frame rate is 120 fps and the flicker frequency is 60 Hz, the luminance average value (luminance average value) hardly varies between the frames.

  On the other hand, as shown in FIG. 13, when the frame rate is 100 fps and the flicker frequency is 60 Hz, the luminance average value fluctuates between the frames, and the luminance average is obtained in a cycle of 5 frames. The value repeats increasing and decreasing.

  FIG. 14 shows a specific example of the fluctuation cycle of the average luminance value of the image data when the frame rate is 100 fps and the flicker frequency is 60 Hz. FIG. 15 shows the flicker with the frame rate of 100 fps. A specific example of the fluctuation cycle of the luminance average value of the image data when the frequency is 50 Hz is shown. In FIGS. 14 and 15, the vertical axis indicates the number of frames between the maximum values in each cycle and the number of frames between the minimum values, that is, the luminance average value variation period when 5 frames are defined as one cycle. The horizontal axis indicates the frame numbers included in each cycle. The diamond marks indicate the number of frames between the maximum values, and the square marks indicate the number of frames between the minimum values.

  As shown in FIG. 14, when the frame rate is 100 fps and the flicker frequency is 60 Hz, the average luminance value fluctuates in approximately 5 frame periods. Therefore, for example, when the frame rate is set to 100 fps, the luminance average value fluctuates in 5 frame periods for 8 or more out of 50 frames, that is, 10 periods (5 frames are defined as 1 period) (situation) In 1), it can be determined that the flicker frequency is 60 Hz.

  Also, as shown in FIG. 15, when the frame rate is 100 fps and the flicker frequency is 50 Hz, the luminance average value does not vary. Therefore, for example, when the frame rate is set to 100 fps and the luminance average value does not fluctuate in 5 frame periods (situation 2) in 50 frames, that is, 10 periods (5 frames as 1 period), the flicker frequency Can be determined to be 50 Hz.

  Similarly to the above method, the flicker frequency can be detected with the frame rate set to 120 fps.

  Specifically, when the frame rate is 120 fps and the flicker frequency is 50 Hz, the luminance average value fluctuates in approximately 6 frame periods. Therefore, for example, when the frame rate is set to 120 fps, the luminance average value fluctuates in 6 frame periods for 8 or more out of 60 frames, that is, 10 periods (6 frames are defined as 1 period). In 3), it can be determined that the flicker frequency is 50 Hz.

  When the frame rate is 120 fps and the flicker frequency is 60 Hz, the luminance average value does not vary for most image data, and the luminance average value does not vary for 6 frame periods. Therefore, for example, when the frame rate is set to 120 fps and the luminance average value does not fluctuate in 6 frame periods (situation 4) in 60 frames, that is, 10 periods (6 frames as 1 period), the flicker frequency Can be determined to be 60 Hz.

  Using the above principle, in the contrast AF control unit 105 of the imaging apparatus 1, i) in 60 frames acquired at a frame rate of 120 fps, i.e., situation 1 is established in 50 frames acquired at a frame rate of 100 fps. When the situation 4 is established, it is determined that the flicker frequency is 60 Hz. On the other hand, if situation 2 is established in 50 frames acquired at a frame rate of 100 fps and situation 3 is established in 60 frames obtained at a frame rate of 120 fps, it is determined that the flicker frequency is 50 Hz. To do. In cases other than i) and ii), it is determined that the light source is not a flicker light source.

<Shooting operation>
FIGS. 16 to 19 are flowcharts illustrating the shooting operation flow in the imaging apparatus 1. This operation flow is realized by the control of the control unit 101. 20 and 21 are diagrams illustrating timing charts of AF control in the imaging apparatus 1.

  20 and 21, the horizontal axis indicates the time elapsed from the state S1. In FIG. 20, in order from the top, the motor rotation speed of the motor M1, the number of pulses (PI number) input to the motor M1, the image plane movement speed corresponding to the movement speed of the focus lens 2a, the activation of the AF microcomputer, the position The timing of phase difference AF measurement and the driving timing of the C-MOS 5 are shown. Furthermore, an example of the relationship between the exposure timing in the C-MOS 5 for obtaining the AF evaluation value in the contrast AF control and the position of the focus lens 2a and the AF evaluation value is shown in the lower part of FIG.

  In FIG. 21, a broken line LL indicating the position (ie, movement) of the focus lens 2a and a broken line LS indicating the position (ie, movement) of the imaging surface (ie, the second focusing surface) of the C-MOS 5 are shown. . Note that, in the vertical axis direction of FIG. 21, the numerical value corresponding to the position of the broken line LL is omitted, but the numerical value (500 μm or the like) corresponding to the position of the broken line LS is given. Furthermore, in FIG. 21, a mark (short vertical line segment) indicating a lens position corresponding to the exposure timing for obtaining the AF evaluation value is attached to the broken line LL, and corresponds to the processing step of FIG. Step numbers (for example, step S34 etc.) are given to the parts to be performed.

  Hereinafter, the photographing operation flow will be described with reference to FIGS. 20 and 21 as appropriate. When the shooting operation flow is started, the C-MOS 5 is set to a predetermined reference position (also referred to as “imaging home position”) where the actual shooting operation is actually performed, and the first and second focusing surfaces are set. Are set to the same optical position.

  Here, when the imaging apparatus 1 is set to a mode for capturing a still image (still image capturing mode) by appropriately operating various buttons included in the operation unit OP, the process proceeds to step S1 in FIG.

  In step S1, the C-MOS 5 is energized, the C-MOS 5 is activated, and the shutter mechanism 4 is opened. Note that the shutter mechanism 4 is in a closed state before the still image shooting mode is set.

  In step S2, the frame rate at which the C-MOS 5 acquires image signals is set to 100 fps. Specifically, the timing control circuit 170 outputs a control signal in response to a signal from the control unit 101, so that the C-MOS 5 starts reading a charge signal of 100 fps.

  In step S3, while reading out the image data for 50 frames at 100 fps, the average luminance value (the average luminance value of 100 fps) is calculated for the image data for 50 frames. The 50 luminance average values are temporarily stored in the memory in the control unit 101.

  In step S4, the frame rate at which the C-MOS 5 acquires image signals is set to 120 fps. Specifically, the timing control circuit 170 outputs a control signal in response to a signal from the control unit 101, and the C-MOS 5 starts reading a charge signal of 120 fps.

  In step S5, the image data for 60 frames is read out at 120 fps, and the luminance average value (120 fps luminance average value) is calculated for the image data for 60 frames. The 60 luminance average values are temporarily stored in the memory in the control unit 101.

  In step S6, it is determined whether or not the luminance average value of 100 fps calculated in step S3 has a periodic variation. Specifically, if a situation (situation 1) in which the luminance average value fluctuates in 5 frame periods is recognized for 8 periods or more out of 50 frames, that is, 10 periods (5 frames as 1 period), 100 fps is recognized. It is determined that there is a periodic variation in the average luminance value. In step S6, if it is determined that there is a periodic variation, the process proceeds to step S7. If it is determined that there is no periodic variation, the process proceeds to step S12.

  In step S7, it is determined whether or not the 120 fps luminance average value calculated in step S5 has no periodic fluctuation. Specifically, if a situation (situation 3) in which the luminance average value fluctuates in 6 frame periods is recognized for 8 periods or more of 60 frames, that is, 10 periods (6 frames as 1 period), 120 fps is recognized. It is determined that there is a periodic variation in the average luminance value. If it is determined in step S7 that there is a periodic variation, the process proceeds to step S8. If it is determined that there is no periodic variation, the process proceeds to step S10.

  In step S8, the light source is recognized as a non-flicker light source. Here, since periodic fluctuations were observed in both the luminance average values according to 100 fps and 120 fps, it is impossible to determine whether the flicker frequency of the light source is 50 Hz or 60 Hz, and therefore, the light source is recognized as a non-flicker light source.

  In step S9, the frame rate is set to a default value of 200 fps in accordance with the non-flicker light source recognized in step S8, and the process proceeds to step S21 in FIG.

  In step S10, the light source is recognized as a fluorescent lamp having a flicker frequency of 60 Hz.

  In step S11, the frame rate is set to 240 fps in accordance with the flicker frequency (60 Hz) recognized in step S10, and the process proceeds to step S21 in FIG.

  In step S12, it is determined whether or not there is a periodic variation in the 120 fps luminance average value calculated in step S5. Specifically, if a situation (situation 3) in which the luminance average value fluctuates in 6 frame periods is recognized for 8 periods or more of 60 frames, that is, 10 periods (6 frames as 1 period), 120 fps is recognized. It is determined that there is a periodic variation in the average luminance value. If it is determined in step S12 that there is a periodic variation, the process proceeds to step S13. If it is determined that there is no periodic variation, the process proceeds to step S15.

  In step S13, the light source is recognized as a fluorescent lamp with a flicker frequency of 50 Hz.

  In step S14, the frame rate is set to 200 fps in accordance with the flicker frequency (50 Hz) recognized in step S13, and the process proceeds to step S21 in FIG.

  In step S15, the light source is recognized as a non-flicker light source. Here, since no periodic fluctuation was observed in both the luminance average values according to 100 fps and 120 fps, it is recognized that the light source is a non-flicker light source.

  In step S16, the frame rate is set to a default value of 200 fps in accordance with the non-flicker light source recognized in step S15, and the process proceeds to step S21 in FIG.

  In step S21, it is determined whether or not the shutter button is half-pressed in the S1 state. Here, the determination in step S21 is repeated until the S1 state is reached, and when the S1 state is reached, the process proceeds to step S22. At this time, all AF related functions of the AF microcomputer, that is, the contrast AF control unit 105, the phase difference AF control unit 106, and the AF overall control unit 107 as functions of the control unit 101 are activated (0 to 50 ms in FIG. 20). .

  In step S22, the phase difference AF module 3 and the phase difference AF control unit 106 perform distance measurement by phase difference AF control (50 to 100 ms in FIG. 20).

  In step S23, the overall AF control unit 107 determines the amount of deviation between the current position of the focus lens 2a and the lens in-focus position based on the distance measurement result in step S3. If the absolute value of the deviation amount is less than a first predetermined value (for example, 30 μm), it is determined that the in-focus state of the subject has already been realized, and the process proceeds to step S41 in FIG. That is, the present shooting operation is performed without performing AF control. If the absolute value of the deviation amount is greater than or equal to a second predetermined value (for example, 1000 μm), the deviation amount is sufficient and the process proceeds to step S31 in FIG. Further, if the absolute value of the deviation amount is equal to or greater than the first predetermined value and less than the second predetermined value, it is determined that the deviation amount is insufficient and the process proceeds to step S24.

  In step S24, the focus lens 2a is retracted by driving the motor M1 based on the control signal from the focus control unit 130 under the control of the AF overall control unit 107. Here, in order to prevent a problem such that the peak of the AF evaluation value in the contrast AF control passes due to the movement of the second focal plane described later if the amount of deviation is insufficient, a sufficient amount of deviation is secured. The retraction drive for moving the lens position of the focus lens 2a is performed. In this retraction drive, for example, the focus lens 2a is moved to one end of the movable range of the focus lens 2a.

  In step S31, based on the result of distance measurement in step S22, an operation of moving the C-MOS 5 to the far side (feeding side) or the near side (feeding side) is started (90 ms in FIG. 20). Here, if the subject is farther than the current focus position (the place where the focus is in focus) with reference to the imaging apparatus 1 according to the distance measurement value that is the detection result by the phase difference AF module 3, C -Move the MOS 5 in a direction away from the subject. On the other hand, if the subject is nearer than the current focus position (the place where the focus is in focus), the C-MOS 5 is moved in a direction closer to the subject. The movement of the C-MOS 5 is performed at a speed of about 20 to 30 mm / sec, for example.

  In step S32, it is determined whether or not the movement of the C-MOS 5 started in step S31 is completed. Here, the determination in step S32 is repeated until the C-MOS 5 moves by a predetermined distance (for example, 500 μm), and when the C-MOS 5 moves by a predetermined distance, the movement of the C-MOS 5 is terminated (90 in FIGS. 20 and 21). ~ 100 ms).

  Note that the predetermined distance is appropriately set depending on the optical design of the imaging apparatus 1. Further, the lens focal length of the photographing lens unit 2 (the longer the lens focal length is, the longer the predetermined distance), and the movement ratio of the focus lens 2a (when the movement amount of the focus lens 2a is longer than the rotation speed of the focus motor M1). (The predetermined distance is long).

  As described above, in steps S31 to S32, the optical position of the second focusing surface is moved to a position that is relatively different from the first focusing surface. Specifically, according to the detection result by the phase difference AF module 3, AF is performed while moving the position of the focus lens 2a from the state where the optical positions of the first and second focusing surfaces are set to be the same. When the control is performed, the state is changed to a state in which the focused state of the subject is realized on the second focused surface earlier than the first focused surface. That is, it is set so that the in-focus state of the subject is detected by the contrast AF control before the focus is reached by the phase difference AF control.

  In step S33, the motor M1 is started and the movement of the focus lens 2a is started (100 to 130 ms in FIG. 20). The movement of the focus lens 2a follows the phase difference AF control.

  In step S34, contrast AF control is started under the control of the AF overall control unit 107, and an operation for acquiring an AF evaluation value at a timing according to the frame rate setting (200 fps or 240 fps) is started (FIGS. 20 and 20). 21 of 145 ms). Here, the operation of acquiring the AF evaluation value is performed at the time when the image plane moving speed has slowed to a certain extent of 110 μm / 10 ms.

  In step S34, when the light source is a non-flicker light source, each AF evaluation value is calculated from each image data acquired by the C-MOS 5. Further, when the light source is a flicker light source, two preliminary evaluation values are calculated from two image data sequentially acquired by the C-MOS 5 in time, and an average value of the two preliminary evaluation values is calculated. Is calculated as one AF evaluation value. Note that this contrast AF control is executed, for example, with the aperture opened.

  In step S35, the contrast AF control unit 105 determines whether a peak of the AF evaluation value has been found. Here, if the AF evaluation value peak is found, the process proceeds to step S36, and if the AF evaluation value peak is not found, the process proceeds to step S39 (145 to 200 ms in FIGS. 20 and 21). 20 and 21 show a case where an AF evaluation value peak is found as an example.

  In step S36, the focus position of the focus lens 2a is obtained (200 ms in FIG. 20).

  Here, as shown in FIG. 20, first, when the AF evaluation value starts to increase and then decreases, data of three points of the AF evaluation value maximum value Yn and the AF evaluation values Yn−1 and Yn + 1 before and after the AF evaluation value are used. Thus, the lens focus position P of the focus lens 2a at which the AF evaluation value reaches the peak is calculated by the quadratic interpolation approximation calculation shown in the following equation (1).

  The timing at which the lens in-focus position P is calculated by such calculation includes a certain amount of time for reading the charge signal from the C-MOS 5, calculating the AF evaluation value, and calculating according to the above equation (1). Therefore, for example, as shown in FIG. 20, after the exposure timing related to the maximum value Yn of the AF evaluation value, the exposure timing at which a charge signal in which the AF evaluation value decreases continuously several times is obtained.

  The lens in-focus position P obtained as described above is a lens in-focus position with respect to the imaging surface in which the C-MOS 5 is shifted by a predetermined distance, that is, by a predetermined distance. Therefore, a value in consideration of an image plane difference of a predetermined distance (for example, 500 μm) at the lens focusing position P is obtained as the lens focusing position Q with respect to the imaging home position where the actual shooting operation is actually performed.

  In this way, the lens focus position Q can be obtained before the movement of the focus lens 2a by the phase difference AF control is completed.

  In step S37, the C-MOS 5 moves so as to return to the imaging home position (210 to 220 ms in FIGS. 20 and 21).

  In step S38, the movement of the focus lens 2a is stopped at the lens in-focus position Q (235 ms in FIGS. 20 and 21).

  In step S39, it is determined whether or not the phase difference AF control is finished. If the phase difference AF control has not been completed, the process returns to step S35. If the phase difference AF control has been completed, the process proceeds to step S40. In the case where the process proceeds from step S39 to step S40, the movement of the focus lens 2a is stopped with the end of the phase difference AF control.

  In step S40, the C-MOS 5 moves so as to return to the imaging home position.

  In step S41, the shutter mechanism 4 is closed.

  In step S42, the charge is accumulated by discharging the charge accumulated in the C-MOS 5.

  In step S43, it is determined whether the S1 state has been released. Here, for example, when the S1 state is canceled by the user operating the operation unit OP, the operation flow is terminated, and if the S1 state is not canceled, the process proceeds to step S51 in FIG.

In step S51, it is determined whether or not the S2 state has been reached. Here, it waits, repeating determination of step S43 and step S51 until it will be in S2 state. And S
In the second state, it is determined that an instruction for the main photographing operation has been issued, and the process proceeds to step S52.

  In step S52, the main mirror 10 and the sub mirror 20 are in the mirror-up state, and the shutter mechanism 4 is in the open state.

  In step S53, the C-MOS 5 performs imaging, that is, exposure for the main photographing operation.

  In step S54, the shutter mechanism 4 is closed.

  In step S55, the main mirror 10 and the sub-mirror 20 are in the mirror-down state, the charge signal is read from the C-MOS 5 and the image data is stored in the memory card MC, and the operation flow is finished. To do.

  As described above, in the imaging device 1 according to the embodiment of the present invention, when the flicker frequency (50 Hz or 60 Hz) is detected before performing the AF control, the frame rate is four times the flicker frequency (200 fps or 240 fps). Set to. Thereafter, a plurality of AF evaluation values are calculated by calculating one AF evaluation value using two pieces of image data acquired successively in time. Then, the focus position of the focus lens 2a is detected based on the plurality of AF evaluation values. By adopting such a configuration, it is possible to perform contrast AF control sampling at a cycle shorter than the flicker cycle, so that high-speed and high-precision focus control can be performed even under illumination where flicker occurs. it can.

  In particular, since one AF evaluation value is calculated using two frames of image data acquired continuously in time, the influence of fluctuations in the amount of light from the subject caused by illumination flicker, which is a light source, is affected. It is possible to realize a focus control with high accuracy. Specifically, a plurality of AF evaluation values are calculated by calculating an average value of preliminary evaluation values for two frames acquired continuously in time as one AF evaluation value, and the plurality of AF evaluation values are calculated. Based on the value, the focus position of the focus lens 2a is detected. For this reason, fluctuations in the AF evaluation value due to fluctuations in the amount of light from the subject due to lighting flicker that is a light source can be suppressed.

  Further, before detecting the in-focus position by the phase difference AF control, the flicker frequency of the light source is detected, and the phase difference AF control and the contrast AF control are performed in parallel. By adopting such a configuration, for example, the focus lens 2a is driven to the vicinity of the lens in-focus position by phase difference AF control in a short time, and focusing accuracy is ensured by contrast AF control, while corresponding to the flicker frequency. can do. For this reason, high-speed and high-precision focusing control according to the flicker frequency can be realized.

  Further, the light from the subject is divided into two optical paths, and the phase difference AF control and the contrast AF control are performed in parallel using each of the divided lights. By adopting such a configuration, high-speed and high-precision focusing control is possible.

  In addition, the contrast AF control is started after the phase difference AF control is started by changing the optical positions of the in-focus surfaces related to the focus detection in the phase difference AF control and the contrast AF control. With such a configuration, two in-focus controls are performed at the same time, and the focus position of the focus lens 2a can be detected by the contrast AF control before the in-focus state by the phase difference AF control is realized. For this reason, high-speed and high-precision focusing control can be realized. Further, for example, since focus control can be performed without moving the focus lens 2a in the reverse direction, it is possible to prevent the occurrence of a backlash problem. Further, for example, the focus feeling can be improved because the subject visually recognized through the finder or the like can smoothly change from a blurred state to a focused state. .

  It should be noted that the flicker frequency of the light source is detected before the phase difference AF control is started in the imaging apparatus 1 due to the high-speed movement of the focus lens 2a when the phase difference AF control is started. This is because the average luminance value of the image data acquired continuously fluctuates, resulting in a decrease in flicker frequency detection accuracy.

<Modification>
As mentioned above, although embodiment of this invention was described, this invention is not limited to the thing of the content demonstrated above.

  For example, in the above embodiment, in contrast AF control, the frame rate is set to four times the flicker frequency, and one AF evaluation value is calculated using two image data acquired sequentially in time. Not limited to this. For example, when the frame rate is set to 6 times the flicker frequency, the period in which the amount of light from the light source fluctuates is 3 times the frame acquisition interval. One AF evaluation value may be calculated from one image data.

  Furthermore, when the frame rate is set to n times the flicker frequency (n is a natural number that is a multiple of 2), the period in which the light amount of the light source fluctuates coincides with n / 2 times the frame acquisition interval. , One AF evaluation value is calculated using a plurality of pieces of image data corresponding to a natural number (1, 2, 3,...) Times n / 2, which is obtained in succession by the C-MOS 5. May be. Even if such a configuration is adopted, the contrast AF control sampling can be performed at a cycle shorter than the flicker cycle, so that high-speed and high-precision focus control can be performed even under illumination where flicker occurs. it can.

  More specifically, when the frame rate is set to n times the flicker frequency (n is a natural number that is a multiple of 2), the cycle in which the amount of light from the light source fluctuates matches the frame rate n / 2 times. Therefore, one AF evaluation value may be calculated using image data for n / 2 frames acquired continuously in time by the C-MOS 5. By adopting such a configuration, it is possible to reduce the influence of fluctuations in the amount of light from the subject caused by illumination flicker, and to realize highly accurate focus control.

  Further, when the flicker frequency L is detected, the frame rate is set to n times the flicker frequency L (n is a natural number that is a multiple of 2), and images for n / 2 frames acquired continuously in time. A configuration is adopted in which one image data is generated by adding pixel values of corresponding pixels between data, and one AF evaluation value is calculated based on the one image data. Also good. Even if such a configuration is adopted, it is possible to suppress the variation in the AF evaluation value due to the variation in the amount of light from the subject due to the flicker of illumination.

  Further, when the flicker frequency L is detected, the frame rate is set to n times the flicker frequency L (n is a natural number that is a multiple of 2), and images for n / 2 frames acquired continuously in time. One image data may be generated by calculating an average pixel value of each pixel corresponding to the data, and one AF evaluation value may be calculated based on the one image data. Even if such a configuration is adopted, it is possible to suppress the variation in the AF evaluation value due to the variation in the amount of light from the subject due to the flicker of illumination.

  In the above embodiment, when the light source is a flicker light source, two preliminary evaluations corresponding to the image data for two frames based on the image data for two frames acquired continuously in time. After calculating the respective values, the average value of the two preliminary evaluation values was calculated as one AF evaluation value. However, the present invention is not limited to this. For example, the image data for two frames acquired continuously in time is used. Based on this, two preliminary evaluation values corresponding to image data for two frames may be calculated, and the two preliminary evaluation values may be simply added to calculate one AF evaluation value.

  More generally, when the light source is a flicker light source, the frame rate is set to n times the flicker frequency L (n is a natural number that is a multiple of 2), and n / 2 frames acquired continuously in time. After calculating preliminary evaluation values for n / 2 frames corresponding to image data for n / 2 frames based on the image data for minutes, 1 is obtained by adding the preliminary evaluation values for n / 2 frames. Two AF evaluation values may be calculated. Even if such a configuration is adopted, it is possible to suppress the variation in the AF evaluation value due to the variation in the amount of light from the subject due to the flicker of the illumination that is the light source.

  In the above embodiment, when the light source is a flicker light source, for example, one AF evaluation value is calculated based on two pieces of image data acquired sequentially in time. Although the AF evaluation value is calculated, the present invention is not limited to this. For example, when the frame rate is set to four times the flicker frequency, 3 corresponding to each of the three or more image data by interpolation processing using three or more image data acquired continuously in time. A plurality of AF evaluation values may be calculated by calculating the above AF evaluation values.

  Hereinafter, an interpolation process using three or more image data will be described.

  FIG. 22 is a diagram illustrating an interpolation process using three image data. In FIG. 22, the horizontal axis indicates the lens position of the focus lens 2a, the vertical axis indicates the AF evaluation value, and the black circle indicates that the frame rate is set to four times the flicker frequency before performing AF control. An evaluation value (preliminary evaluation value) calculated from each image data is shown.

  As shown in FIG. 22, relatively high preliminary evaluation values (high preliminary evaluation values) and low preliminary evaluation values (low preliminary evaluation values) are alternately calculated due to fluctuations in the amount of light by the flicker light source.

  At this time, the low preliminary evaluation value is obtained by interpolating the three consecutive high preliminary evaluation values, the low preliminary evaluation value, and the high preliminary evaluation value calculated from the three pieces of image data acquired sequentially in time. Instead of this, a value that matches the high preliminary evaluation value indicated by the black triangle mark is obtained.

  For example, as shown in FIG. 22, the high preliminary evaluation value indicated by a black triangle mark instead of the low preliminary evaluation value V2 by interpolation processing for the high preliminary evaluation value V1, the low preliminary evaluation value V2, and the high preliminary evaluation value V3. A value (interpolation evaluation value) Vm that matches the value is obtained.

  Specific interpolation processing methods include, for example, the rate of change between the high preliminary evaluation value V1 and the low preliminary evaluation value V2, and the value between the low preliminary evaluation value V2 and the high preliminary evaluation value V3. There is a method of calculating the interpolation evaluation value Vm by extrapolation using the high preliminary evaluation value (V1 or V3) as a reference, using an average value (average change rate) with the change rate.

  When the interpolation evaluation value and the high preliminary evaluation value obtained by such interpolation processing are adopted as the AF evaluation value, the peak shape of the AF evaluation value becomes clear as shown by the broken line in FIG. As a result, the lens in-focus position can be detected with high accuracy using the same method as in the above embodiment.

  In other words, when the frame rate is set to four times the flicker frequency and the luminance of the second image data among the first to third image data acquired continuously in time is the minimum. The first to third preliminary evaluation values are calculated for the first to third image data, respectively, and the interpolation processing based on the first to third preliminary evaluation values, that is, the first to third image data is calculated. A configuration in which an AF evaluation value for the second image data is calculated by the interpolation processing used can be employed.

  By adopting such a configuration, it is possible to calculate an evaluation value in consideration of a decrease in the evaluation value caused by illumination flicker, so that highly accurate focusing control can be realized.

  Further, here, the interpolation evaluation value is calculated using the three preliminary evaluation values and is simply adopted as the AF evaluation value. However, the present invention is not limited to this. For example, the temporal evaluation includes three preliminary evaluation values used for the interpolation processing. If a plurality of AF evaluation values are obtained by performing a general smoothing process on five or more preliminary evaluation values obtained continuously, the peak shape of the AF evaluation values becomes clearer. Even if such a configuration is adopted, it is possible to reduce the influence of fluctuations in the amount of light from the subject due to lighting flicker, and to achieve highly accurate focusing control.

  Here, the interpolation evaluation value that is consistent with the high preliminary evaluation value is calculated instead of the low preliminary evaluation value by the interpolation process, but conversely, it is consistent with the low preliminary evaluation value instead of the high preliminary evaluation value by the interpolation process. It is conceivable to calculate the interpolation evaluation value to be used, but in such a method, the peak of the AF evaluation value is low and unclear, and as a result, the focusing accuracy is lowered. It is preferable to calculate an interpolation evaluation value consistent with the high preliminary evaluation value instead of the low preliminary evaluation value by the processing.

  In the above embodiment, image data for contrast AF control is acquired by the C-MOS 5. However, the present invention is not limited to this. For example, a dedicated image sensor for acquiring image data for contrast AF control is provided. Also good.

  In the above embodiment, the time required for the AF control is shortened by executing the phase difference AF control and the contrast AF control in parallel. However, the present invention is not limited to this. Even if contrast AF control is performed after the completion, since the sampling interval in contrast AF control can be set shorter than in the conventional technique, high-speed and high-precision focusing control can be realized.

  In the above embodiment, the AF control unit 100 as shown in FIG. 2 is employed, but the present invention is not limited to this, and other AF control unit configurations may be employed. Hereinafter, an AF control unit 100A will be described as an example of the configuration of another AF control unit.

  FIG. 23 is a diagram schematically illustrating a configuration related to the AF control unit 100A included in the imaging apparatus 1A according to the modification.

  In the imaging apparatus 1 according to the above-described embodiment, the main mirror 10 is configured to include a half mirror. However, as illustrated in FIG. 23, in the imaging apparatus 1A according to the modification, the main mirror 10 adopts a pellicle mirror as the half mirror. A mirror 10A is used.

  The pellicle mirror is characterized in that it is very thin (for example, about 100 μm) compared to a general half mirror. Since this pellicle mirror is extremely thin, it is not suitable for mirror-up driving. Therefore, the imaging apparatus 1A is configured such that the main mirror 10A does not mirror up and the sub-mirror 20A is retracted downward from the optical path of the light from the subject during the main photographing.

  Other configurations are the same as those of the imaging device 1 according to the above-described embodiment. With regard to functions and operations, etc., instead of both the main mirror 10 and the sub mirror 20 being in the retracted / blocked state with respect to the optical path, Since only the sub mirror 20A is different from the optical path in the retracted state / blocked state, the other functions and operations are substantially the same, and thus the description thereof is omitted.

  Hereinafter, advantages of using a pellicle mirror as the half mirror of the main mirror 10A will be described.

  In the imaging apparatus 1 according to the above embodiment, when the refractive index Nd of a general half mirror is about 1.5 and the thicknesses of the main mirror 10 and the sub mirror 20 are a and b, respectively, the mirror up state and the mirror down state Therefore, the focal position is shifted to the user side (right side in FIG. 2) by about 0.5 (a + b).

  When the phase difference AF control and the contrast AF control are used in combination, the second focusing is performed earlier than the first focusing surface when realizing the in-focus state of the subject while moving the position of the focus lens 2a. It is necessary to make the optical positions of the first and second focusing surfaces different from each other so that the in-focus state of the subject is realized on the surface. Therefore, at this time, the C-MOS 5 must be moved along the optical axis L from the imaging home position in view of the focal position shift (about 0.5 (a + b)) by the half mirror.

  With respect to such a problem, by using an extremely thin pellicle mirror, it is possible to suppress the shift of the focal position by the half mirror to about 0.5b. That is, the amount of shift of the focal position caused by the main mirror 10 can be suppressed. As a result, since the amount of movement of the C-MOS 5 for correcting the amount of deviation is small, the configuration for moving the C-MOS 5 can be simplified.

  In the above embodiment, the fluctuation of the amount of light (light quantity) emitted from the light source due to the flickering of the fluorescent lamp is referred to as “flicker”, and the frequency of the fluctuation is referred to as “flicker frequency”. For example, the fluctuation of the amount (light quantity) of light emitted from a light source other than a fluorescent lamp may be generally referred to as “flicker”, and the frequency of the fluctuation may be referred to as “flicker frequency”.

It is a cross-sectional schematic diagram which shows schematic structure of the imaging device which concerns on embodiment of this invention. It is a figure which illustrates typically composition concerning an in-focus control unit. It is a figure for demonstrating the principle of focusing control of a phase difference system. It is a figure for demonstrating the principle of focusing control of a phase difference system. It is a figure for demonstrating the principle of focusing control of a phase difference system. FIG. 25 is a block diagram illustrating a functional configuration of an imaging apparatus. It is a figure which illustrates the change of the peak shape of AF evaluation value based on the change of the calculation method of AF evaluation value. It is a timing chart which shows the principle of flicker countermeasure evaluation value calculation operation. It is a timing chart which shows the principle of flicker countermeasure evaluation value calculation operation. It is a timing chart explaining the identification method of a flicker frequency. It is a timing chart explaining the identification method of a flicker frequency. It is a figure explaining the identification method of a flicker frequency. It is a figure explaining the identification method of a flicker frequency. It is a figure explaining the identification method of a flicker frequency. It is a figure explaining the identification method of a flicker frequency. It is a flowchart which shows an imaging | photography operation | movement flow. It is a flowchart which shows an imaging | photography operation | movement flow. It is a flowchart which shows an imaging | photography operation | movement flow. It is a flowchart which shows an imaging | photography operation | movement flow. It is a figure which illustrates the timing chart of AF control. It is a figure which illustrates the timing chart of AF control. It is a figure explaining the interpolation process using three image data. It is a figure which shows the AF control unit which concerns on a modification.

Explanation of symbols

1, 1A Imaging device 2a Focus lens 3 Phase difference AF module 5 C-MOS
5a C-MOS drive mechanism 10, 10A main mirror 10a mirror mechanism 20, 20A sub mirror 20a sub mirror mechanism 100, 100A AF control unit 101 control unit 105 contrast AF control unit 106 phase difference AF control unit 107 AF overall control unit 130 focus control unit 150 Movement control unit OP operation unit V1, V3 High preliminary evaluation value V2 Low preliminary evaluation value Vm Interpolation evaluation value

Claims (14)

Image acquisition means for acquiring a plurality of image data at a predetermined frame rate based on light from a subject incident through the optical lens while the optical lens is driven along the optical axis;
Frequency detection means for detecting the flicker frequency of the light source;
Setting means for setting the predetermined frame rate to a value obtained by multiplying the flicker frequency L by n (n is a multiple of 2 which is 4 or more ) when the flicker frequency L is detected by the frequency detection means;
A plurality of focus evaluations corresponding to the plurality of image data while calculating one focus evaluation value using image data of n / 2 frames or more acquired continuously in time by the image acquisition means. Evaluation value calculation means for calculating a value based on the plurality of image data;
A focus position detecting means for detecting a focus position of the optical lens based on the plurality of focus evaluation values;
A focusing control device. The focusing control device according to claim 1 ,
The evaluation value calculating means is
If said n / 2 or more frames of pixels corresponding between image data pixel value to generate an added image data by adding each to calculate a focus evaluation value the one case on the basis of the addition image data Focus control device. The focusing control device according to claim 1 ,
The evaluation value calculating means is
Focusing said n / 2 to produce an average image data by calculating an average pixel value of each pixel corresponding the frame or image data, and calculates a focus evaluation value the one case on the basis of the average image data Control device. The focusing control device according to claim 1 ,
The evaluation value calculating means is
Based on the n / 2 or more frames of image data, the after calculating the respective preliminary evaluation value of the corresponding n / 2 frames into n / 2 or more frames of image data, the n / 2 frames spare A focus control device that calculates the one focus evaluation value by adding the evaluation values. The focusing control device according to claim 1 ,
The evaluation value calculating means is
Based on the n / 2 or more frames of image data, the after calculating the respective preliminary evaluation value of the corresponding n / 2 frames into n / 2 or more frames of image data, the n / 2 frames spare A focus control apparatus that calculates an average value of evaluation values as the one focus evaluation value. A focusing control device according to any one of claims 1 to 5 ,
The image data for n / 2 frames or more is
A focusing control device that is image data of two frames. The focusing control device according to claim 1,
The image data for n / 2 frames or more is
Three or more pieces of image data acquired continuously in time by the image acquisition means,
The evaluation value calculating means is
A focus control apparatus that calculates the plurality of focus evaluation values by calculating three or more focus evaluation values corresponding to the three or more image data by an interpolation process using the three or more image data. The in-focus control device according to claim 7 ,
The evaluation value calculating means is
The predetermined frame rate is set to a value obtained by multiplying the flicker frequency L by 4 by the setting means, and the first, second, and third image data obtained in succession in time by the image obtaining means. When the brightness of the second image data is minimum, the focus evaluation value for the second image data is calculated by the interpolation process using the first to third image data, and the first image data is calculated. third focus control device which calculates the corresponding three focus evaluation values respectively to the image data of. The focus control device according to claim 8 ,
The evaluation value calculating means is
Focus evaluation for the second image data is performed by calculating first to third preliminary evaluation values for the first to third image data, respectively, and performing interpolation processing based on the first to third preliminary evaluation values. Focus control device that calculates the value. The focusing control device according to any one of claims 1 to 9 ,
A phase difference focus detection means for detecting a focus position of the optical lens using a phase difference method;
Prior to detection of the focusing position of the optical lens according to the phase difference in-focus detecting means further includes a detection control unit for controlling to detect the flicker frequency of the light source by the frequency detection means,
A focus control device in which phase difference focus control using the phase difference focus detection means and contrast focus control using the focus position detection means are executed in parallel. A focusing control apparatus according to claim 1 0,
A focusing control apparatus further comprising: a light splitting unit that splits light from the subject into first and second optical paths that guide the light from the subject to the image acquisition unit and the phase difference focus detection unit, respectively. A focusing control apparatus according to claim 1 0 or Claim 1 1,
Contrast focus detection means for performing the contrast focus control,
Having a focusing surface at an optical position relatively different from the focusing surface according to the phase difference focusing detection means,
The focusing control device is
A focus control device further comprising timing control means for controlling the contrast focus control to start after the phase difference focus control is started. An imaging device equipped with a focusing control apparatus according to any one of claims 1 to 1 2. (a) detecting the flicker frequency of the light source;
(b) When the flicker frequency L is detected in the step (a), the flicker frequency L is multiplied by n (n is a multiple of 2 which is 4 or more ) by the frame rate of image acquisition in a predetermined imaging means. A step to set the value,
(c) While driving a predetermined optical lens along the optical axis, a plurality of pieces of image data based on light from a subject incident through the predetermined optical lens by the predetermined imaging unit obtaining at the frame rate set in (b);
(d) A plurality of image data corresponding to the plurality of image data while calculating one in-focus evaluation value using image data of n / 2 frames or more acquired continuously in time in the step (c). Calculating an in-focus evaluation value based on the plurality of image data;
(e) detecting a focus position of the predetermined optical lens based on the plurality of focus evaluation values;
A focus control method.

Images