JP2012032605A - Focus detector and imaging apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a focus detector capable of appropriately detecting a focus state even when luminance of a subject is low and a distance from a light source of an AF auxiliary light to the subject is long.SOLUTION: The focus detector includes: illumination control means 170 which sends out an illumination command for illuminating a subject with illumination light having a predetermined periodic pattern; light-receiving means 161d which receives a pair of luminous fluxes passing through different areas of the pupil of an optical system, and outputs a pair of light-receiving signals; operating means 163 which filter-processes the pair of the light-receiving signals output from the light-receiving means 161d with the use of a differential filter, and performs an arithmetical operation for detecting a focus state of the optical system according to the pair of the filter-processed light-receiving signals; and operation control means 163 which varies an operation method of the operating means 163 according to the periodic pattern of the illumination light.

Description

  The present invention relates to a focus detection apparatus and an imaging apparatus.

  Conventionally, when performing autofocus (AF) for focusing on a subject, when the subject brightness is low or the subject contrast is low, AF assist light having a predetermined pattern is irradiated, and the irradiated AF assist light A method for focusing on a subject by detecting this pattern is known. In such an autofocus method, in order to expand the focus area (multiple points), the AF auxiliary light is branched by a prism or the like, and the pattern of the branched AF auxiliary light is detected to focus on the subject. A technique for matching the two is known (Patent Document 1).

JP 2003-107324 A

  However, the reach distance of the AF auxiliary light (the distance to the subject whose focus state can be appropriately detected when the AF auxiliary light is irradiated) is limited according to the luminance of the light source that emits the AF auxiliary light. When the brightness of the subject is low or the distance from the AF auxiliary light source to the subject is long, the focus state may not be detected properly. In particular, when the AF auxiliary light is branched and irradiated by a prism or the like as in the prior art, the AF auxiliary light reaches a shorter distance than when the AF auxiliary light is irradiated without being branched. It has been difficult to properly detect the focus state.

  The problem to be solved by the present invention is to provide a focus detection device capable of appropriately detecting the focus state even when the luminance of the subject is low or the distance from the AF auxiliary light source to the subject is long. That is.

  The present invention solves the above problems by the following means. In addition, although the code | symbol corresponding to drawing which shows embodiment of this invention is attached | subjected and demonstrated, this code | symbol is only for making an understanding of this invention easy, and is not the meaning which limits this invention.

  [1] The focus detection apparatus according to the present invention passes through illumination control means (170) for sending an illumination command for illuminating a subject with illumination light having a predetermined periodic pattern, and different regions of the pupil of the optical system. A light receiving means (161d) for receiving a pair of light fluxes and outputting a pair of light receiving signals, and filtering the pair of light receiving signals output from the light receiving means using a differential filter, A calculation means (163) for performing calculation for detecting the focus state of the optical system based on the received light signal, and a calculation control means (163) for varying the calculation method of the calculation means according to the periodic pattern of the illumination light. ).

  [2] In the invention related to the focus detection apparatus, the calculation means (163) can be configured to vary the differential filter used for the filter processing according to the periodic pattern of the illumination light.

  [3] In the invention related to the focus detection device, the light receiving means (161d) includes a microlens disposed in the vicinity of the planned focal plane of the optical system, and a photoelectric conversion unit disposed with respect to the microlens. The calculation control means (163) includes a pixel column in which a plurality of pixels having a pixel pattern of the illumination light and the number of pixels constituting the pixel column corresponding to one cycle of the periodic pattern of the illumination light. The differential filter used for the filtering process can be determined.

  [4] In the invention related to the focus detection device, the intensity of the light reception signal from the n-th pixel in the arrangement direction of the pixel row is X (n), and the number of pixels corresponding to one period of the periodic pattern of the illumination light is In the case where W is W, the differential filter f (n) for the light reception signal from the nth pixel in the arrangement direction of the pixel column is expressed as f (n) = 2 × X (n) −X (n−W / 2) −. X (n + W / 2) can be configured.

  [5] In the invention related to the focus detection apparatus, the illumination control means (170) can be configured such that a periodic pattern for illuminating the illumination light can be selected from a plurality of periodic patterns.

  [6] An imaging apparatus according to the present invention includes the focus detection apparatus.

  According to the present invention, the focus state can be appropriately detected even when the luminance of the subject is low or the distance from the AF auxiliary light source to the subject is long.

FIG. 1 is a block diagram showing a single-lens reflex digital camera according to the present embodiment. FIG. 2 is a diagram showing the AF auxiliary light emitting unit shown in FIG. FIG. 3 is a diagram showing the focus detection module shown in FIG. FIG. 4 is a diagram illustrating an example of a light reception signal obtained based on AF auxiliary light having a predetermined periodic pattern. FIG. 5 is a flowchart showing the operation of the camera according to the present embodiment. FIG. 6 is a diagram illustrating an example of a correlation amount between a pair of received light signals that have been filtered using the first differential filter. FIG. 7 is a diagram illustrating an example of a correlation amount between a pair of received light signals that have been filtered using the second differential filter.

  In the following, an embodiment in which the present invention is applied to a single-lens reflex digital camera will be described with reference to the drawings. However, the present invention can also be applied to a silver halide film camera, a compact camera, and other imaging devices.

  FIG. 1 is a block diagram showing a single-lens reflex digital camera 1 according to this embodiment. In FIG. 1, the illustration and description of the general configuration of the camera other than those related to the focus detection device and the imaging device of the present invention are partially omitted.

  The single-lens reflex digital camera 1 (hereinafter simply referred to as camera 1) of the present embodiment includes a camera body 100, a lens barrel 200, and a strobe device 300, and the camera body 100 and the lens barrel 200 are detachably coupled. The camera body 100 and the strobe device 300 are also detachably coupled.

  The lens barrel 200 incorporates an imaging optical system including lenses 211, 212, 213 and a diaphragm 220.

  The focus lens 212 is provided so as to be movable along the optical axis L1. The position of the focus lens 212 is adjusted by the focus lens driving motor 230 while the position of the focus lens 212 is detected by the encoder 260. Incidentally, the position information of the focus lens 212 detected by the encoder 260 is sent to the lens drive control unit 165 described later via the lens control unit 250. Then, the drive amount of the focus lens 212 calculated based on this information is sent from the lens drive control unit 165 via the lens control unit 250, and the focus lens drive motor 230 is driven based on this.

  The aperture 220 restricts the amount of light flux that passes through the imaging optical system and reaches the imaging device 110 provided in the camera body 100, and adjusts the amount of blur, so that the aperture diameter around the optical axis L1 is adjusted. It is configured to be possible. For example, information on an appropriate aperture diameter calculated in the automatic exposure mode is sent from the camera control unit 170 to the aperture 220 via the lens control unit 250, and the aperture diameter is adjusted by the aperture 220. The adjustment of the aperture diameter is also performed by inputting information on the aperture diameter set by the manual operation by the operation unit 150 from the camera control unit 170 to the lens control unit 250. The aperture diameter of the aperture 220 is detected by an aperture sensor (not shown), and the lens controller 250 recognizes the current aperture diameter.

  As shown in FIG. 1, the camera 1 includes a strobe device 300. The strobe device 300 is provided with a main light emitting unit 301 and is driven to emit light by a strobe driving unit 302 formed of a light emitting circuit. The light emission amount and light emission timing of the main light emission unit 301 are controlled by a control signal from the camera control unit 170 based on the output of the photometric sensor 137.

  Further, the strobe device 300 is provided with an AF auxiliary light emitting unit 303, which is driven to emit light by an AF auxiliary light driving unit 304 constituted by a light emitting circuit. The emission of the AF auxiliary light is controlled by the camera control unit 170. For example, when the camera control unit 170 determines that the subject has low luminance or the subject has low contrast, AF A control signal for emitting auxiliary light is sent to the AF auxiliary light driving unit 304, and based on this, the AF auxiliary light driving unit 304 performs emission driving of the AF auxiliary light.

  Here, FIG. 2 is a configuration diagram of the AF auxiliary light emitting unit 303 according to the present embodiment. As shown in FIG. 2, the AF auxiliary light emitting unit 303 includes a light source in which two LED light sources 3031 and 3032 having different luminances are arranged, and a prism 3033 provided in the vicinity of the emission side of the AF auxiliary light from the light source. have. The AF auxiliary light emitted from the LED light sources 3031 and 3032 having different luminances is incident on a prism 3033 provided in the vicinity of the AF auxiliary light emission side, and is branched in the direction in which the two LED light sources 3031 and 3032 are arranged. The As a result, the AF auxiliary light has a periodic pattern in which a predetermined contrast is periodically repeated.

  On the other hand, the camera body 100 includes a mirror system 120 for guiding the light flux from the subject to the image sensor 110, the finder 135, the photometric sensor 137, and the focus detection module 161. The mirror system 120 includes a quick return mirror 121 that rotates by a predetermined angle between the observation position and the imaging position of the subject around the rotation axis 123, and the quick return mirror 121 that is pivotally supported by the quick return mirror 121. And a sub mirror 122 that rotates in accordance with the rotation. In FIG. 1, a state where the mirror system 120 is at the observation position of the subject is indicated by a solid line, and a state where the mirror system 120 is at the imaging position of the subject is indicated by a two-dot chain line.

  The mirror system 120 is inserted on the optical path of the optical axis L1 in the state where the subject is at the observation position of the subject, while rotating so as to retract from the optical path of the optical axis L1 in the state where the subject is in the imaging position.

  The quick return mirror 121 is composed of a half mirror, and in a state where the subject is at the observation position, the quick return mirror 121 reflects a part of the light flux (optical axes L2 and L3) from the subject (optical axis L1). Then, the light is guided to the finder 135 and the photometric sensor 137, and a part of the light beam (optical axis L4) is transmitted to the sub mirror 122. On the other hand, the sub mirror 122 is configured by a total reflection mirror, and guides the light beam (optical axis L4) transmitted through the quick return mirror 121 to the focus detection module 161.

  Therefore, when the mirror system 120 is at the observation position, the light flux (optical axis L1) from the subject is guided to the finder 135, the photometric sensor 137, and the focus detection module 161, and the subject is observed by the photographer and exposure calculation is performed. And the focus adjustment state of the focus lens 212 is detected. When the photographer fully presses a release button (not shown), the mirror system 120 is rotated to the photographing position, and all the light flux (optical axis L1) from the subject is guided to the image sensor 110, and the photographed image data is illustrated. Do not save to memory.

  The light flux (optical axis L2) from the subject reflected by the quick return mirror 121 forms an image on a focusing screen 131 disposed on a surface optically equivalent to the image sensor 110, and forms a pentaprism 133 and an eyepiece lens 134. It is possible to observe through. At this time, the transmissive liquid crystal display 132 superimposes and displays a focus detection area mark on the subject image on the focusing screen 131 and relates to shooting such as the shutter speed, aperture value, and number of shots in an area outside the subject image. Display information. As a result, the photographer can observe the subject, its background, and photographing related information through the finder 135 in the photographing preparation state.

  The photometric sensor 137 is composed of a two-dimensional color CCD image sensor or the like, and divides the photographing screen into a plurality of regions and outputs a photometric signal corresponding to the luminance of each region in order to calculate an exposure value at the time of photographing. A signal detected by the photometric sensor 137 is output to the camera control unit 170 and used for automatic exposure control and the like.

  The focus detection module 161 is a focus detection element for executing automatic focusing control by a phase difference detection method using subject light, and the imaging surface of the imaging element 110 of the light beam (optical axis L4) reflected by the sub-mirror 122. It is fixed at an optically equivalent position.

  FIG. 3 is a diagram illustrating a configuration example of the focus detection module 161 illustrated in FIG. 1. The focus detection module 161 of this embodiment includes a condenser lens 161a, a diaphragm mask 161b in which a pair of openings are formed, a pair of re-imaging lenses 161c, and a pair of line sensors 161d. Although not shown, the line sensor 161d of the present embodiment includes a pixel having a microlens disposed in the vicinity of a planned focal plane of the imaging optical system and a photoelectric conversion element disposed with respect to the microlens. A plurality of pixel columns are provided. A pair of light reception signals can be obtained by receiving a pair of light fluxes passing through a pair of regions having different exit pupils of the focus lens 212 by each pixel arranged in the pair of line sensors 161d. And a focus adjustment state can be detected by calculating | requiring the phase shift of a pair of light reception signal acquired with a pair of line sensor 161d by the correlation calculation mentioned later.

  For example, as shown in FIG. 3, when the subject P forms an image on the equivalent surface (scheduled imaging surface) 161e of the image sensor 110, the focused state is achieved, but the focus lens 212 moves in the direction of the optical axis L1 to form a result. When the image point shifts from the equivalent surface 161e toward the subject (referred to as a front pin) or shifts toward the camera body (referred to as a rear pin), a focus shift state occurs.

  When the imaging point of the subject P is shifted from the equivalent surface 161e toward the subject, the interval w between the pair of light reception signals detected by the pair of line sensors 161d becomes shorter than the interval w in the focused state, and vice versa. If the imaging point of the subject P is shifted to the camera body 100 side, the interval w between the pair of light reception signals detected by the pair of line sensors 161d becomes longer than the interval w in the focused state.

  That is, the light reception signal detected by the pair of line sensors 161d overlaps with the center of each line sensor 161d in the focused state, but the light reception signal shifts with respect to the center of the line sensor 161d in the out-of-focus state, That is, since a phase difference occurs, it is possible to focus by moving the focus lens 212 by an amount corresponding to this phase difference (deviation amount).

  Here, FIG. 4 is a diagram illustrating an example of a light reception signal obtained by the line sensor 161d when the AF auxiliary light emitting unit 303 emits AF auxiliary light. In FIG. 4, the vertical axis indicates the intensity of the received light signal, and the horizontal axis indicates the pixel number of each pixel constituting the pixel row arranged in the line sensor 161d. In this pixel number, the pixel number of the pixel located at the left end in the arrangement direction is set to No. 1, the pixel number of the pixel adjacent to the right is set to No. 2, and similarly, the pixel number increases toward the right side in the arrangement direction. Thus, pixel numbers are assigned. In the example illustrated in FIG. 4, the light reception signals obtained from the 20th pixel to the 60th pixel among the pixels configuring the pixel column arranged in the line sensor 161 d are illustrated.

  As described above, the AF auxiliary light emitting unit 303 of the present embodiment includes the two LED light sources 3031 and 3032 that emit AF auxiliary light having different luminances, as shown in FIG. Therefore, in the light reception signal obtained when the AF auxiliary light is irradiated, as shown in FIG. 4, the peak a based on the output waveform A having a relatively high intensity corresponding to the LED light source 3031 having a relatively high luminance and the luminance are A peak b based on the output waveform B having a relatively small intensity corresponding to the relatively low LED light source 3032 appears. In the AF auxiliary light emitting unit 303 of the present embodiment, the AF auxiliary light emitted from the two LED light sources 3031 and 3032 is incident on a prism 3033 provided near the emission side of the AF auxiliary light of the light source. Is branched in the direction in which the LED light sources 3031 and 3032 are arranged. Therefore, in the light reception signal obtained when the AF auxiliary light is irradiated, as shown in FIG. 4, the peak a based on the output waveform A having a relatively high intensity corresponding to the LED light source 3031 having a relatively high luminance and the luminance are The peak b based on the output waveform B having a relatively small intensity corresponding to the relatively low LED light source 3032 repeatedly appears alternately in the direction in which the LED light sources 3031 and 3032 are arranged. As described above, the AF auxiliary light emitted from the AF auxiliary light emitting unit 303 has a periodic pattern in which the peak of the output waveform A and the peak of the output waveform B repeat every one period (minimum period unit). Become. In the example shown in FIG. 4, the periodic pattern of AF auxiliary light is repeated with 12 pixels per period.

  Returning to FIG. 1, the AF-CCD control unit 162 controls the accumulation conditions such as the gain and accumulation time of the pair of line sensors 161 d of the focus detection module 161 in the autofocus mode, and is provided in the focus detection area 161. The pair of received light signals detected by the pair of line sensors 161 d read out, and the read out received light signals are output to the defocus calculation unit 163.

  The defocus calculation unit 163 performs filter processing described later on the pair of light reception signals sent from the AF-CCD control unit 162. In addition, the defocus calculation unit 163 performs a correlation calculation on the pair of light reception signals that have been subjected to the filter processing, and calculates a defocus amount. The calculated defocus amount is output to the lens driving amount calculation unit 164.

  Based on the defocus amount df sent from the defocus calculation unit 163, the lens drive amount calculation unit 164 calculates a lens drive amount Δd corresponding to the defocus amount df, and supplies this to the lens drive control unit 165. Output.

  The lens drive controller 165 drives the focus lens drive motor 230 based on the lens drive amount Δd sent from the lens drive amount calculator 164 and adjusts the position of the focus lens 212.

  The image sensor 110 is provided on the optical axis L1 of the light beam from the subject of the camera body 100 and at a position that is a planned focal plane of the imaging optical system including the lens groups 211, 212, and 213, and a shutter is provided in front of the image sensor 110. 111 is provided. The image sensor 110 is a two-dimensional array of a plurality of photoelectric conversion elements, and can be constituted by a two-dimensional CCD image sensor, a MOS sensor, a CID, or the like. The electrical image signal photoelectrically converted by the image sensor 110 is subjected to image processing by the camera control unit 170 and then stored in a memory (not shown). Note that the memory for storing the captured image can be configured by a built-in memory or a card-type memory.

  The operation unit 150 is a shutter relays button, a zoom button, and input switches for a photographer to set various operation modes of the camera 1, and a release button switch is a first switch that is turned on when the button is half-pressed. SW1 and a second switch SW2 that is turned on when the button is fully pressed are included. Various modes set by the operation unit 150 are transmitted to the camera control unit 170, and the operation of the entire camera is controlled by the camera control unit 170.

  The camera body 100 is provided with a camera control unit 170. The camera control unit 170 includes a microprocessor and peripheral components such as a memory, is electrically connected to the lens control unit 250, receives lens information from the lens control unit 250, and defocuses to the lens control unit 250. Send information such as volume and aperture control signal. In addition, as described above, the camera control unit 170 outputs a control signal for emitting AF auxiliary light when it is determined that the subject has low brightness or the contrast of the subject is low. By sending the light to the auxiliary light driving unit 304, the AF auxiliary light emitting unit 303 emits AF auxiliary light. Further, the camera control unit 170 also controls the entire camera 1 such as correction of captured image information and detection of a focus adjustment state, an aperture adjustment state, and the like of the lens barrel 200.

  Next, an operation example of the camera 1 according to this embodiment will be described. FIG. 5 is a flowchart showing the operation of the camera 1 according to this embodiment.

  First, in step S101, the camera control unit 170 determines whether or not the release button is half-pressed (the first switch SW1 is turned on). If the release button is half pressed (the first switch SW1 is turned on), the process proceeds to step S102. On the other hand, if the release button is not half pressed (the first switch SW1 is turned on), the process waits in step S101.

  In step S102, the camera control unit 170 determines the luminance of the subject. The method for determining the luminance of the subject is not particularly limited. For example, based on the output of the photometric sensor 137, it is determined whether or not the gain for the received light signal obtained in a predetermined accumulation time is equal to or greater than a predetermined value. When the gain with respect to the light reception signal obtained at the predetermined accumulation time is equal to or greater than the predetermined value, the subject can be determined to have low brightness, and conversely, with respect to the light reception signal obtained at the predetermined accumulation time. If the gain is less than the predetermined value, it can be determined that the subject has high brightness.

  In step S103, the camera control unit 170 determines whether or not AF auxiliary light needs to be emitted based on the result of the luminance determination of the subject in step S102. If it is determined in step S102 that the subject has low brightness, it is determined that AF auxiliary light needs to be emitted, and the process proceeds to step S104 in order to emit AF auxiliary light. On the other hand, if it is determined in step S102 that the subject has high luminance, it is determined that the AF auxiliary light is not required, and the process proceeds to step S113.

  In step S104, since it is determined in step S103 that the AF auxiliary light needs to be emitted, the camera control unit 170 sends a control signal for emitting the AF auxiliary light to the AF auxiliary light driving unit 304. The Thereby, the AF auxiliary light driving unit 304 performs the driving of AF auxiliary light, and the AF auxiliary light emitting unit 303 emits AF auxiliary light having a predetermined periodic pattern.

  Subsequently, in step S105, the light flux from the subject is received by the pair of line sensors 161d. Then, charges are accumulated according to the intensity of the received light by each pixel constituting the pixel row arranged in the pair of line sensors 161d, and the accumulated pair of received light signals are converted into the AF-CCD control unit 162. Is output to the defocus calculation unit 163.

  Next, in step S106, the defocus calculation unit 163 performs a filtering process on the pair of light reception signals read in step S105 using the first differential filter corresponding to the AF auxiliary light periodic pattern. Is called. In the filtering process in step S106, first, the defocus calculation unit 163 obtains the number of pixels W corresponding to one period of the periodic pattern of the AF auxiliary light. The method for calculating the number of pixels W corresponding to one period of the AF auxiliary light periodic pattern is not particularly limited. For example, one period of the AF auxiliary light periodic pattern depends on the configuration of the prism 3033 that branches the AF auxiliary light. If the pixel number W corresponding to is predetermined, information on the pixel number W may be acquired. In the example illustrated in FIG. 4, the defocus calculation unit 163 acquires the number of pixels W corresponding to one period of the periodic pattern of the AF auxiliary light as 12 pixels.

Then, based on the number of pixels W corresponding to one period of the AF auxiliary light periodic pattern, the defocus calculation unit 163 receives the light received when the AF auxiliary light is irradiated as shown in the following formula (1). A first differential filter f (n) for filtering the signal is determined.
f (n) = 2 × X (n) −X (n−W / 2) −X (n + W / 2) (1)
In the above formula (1), X (n) is the intensity of the received light signal obtained from the nth pixel in the arrangement direction of the pixel column. In the above formula (1), the number of pixels (W / 2) corresponding to the half cycle of the periodic pattern of the AF auxiliary light is processed to be an integer. That is, when the number of pixels W corresponding to one period of the periodic pattern of the AF auxiliary light is an odd number, the decimal point portion of the number of pixels (W / 2) is set so that the number of pixels (W / 2) is an integer. , Rounded off, rounded down, rounded up, etc. For example, when the number of pixels W corresponding to one period of the periodic pattern of AF auxiliary light is an odd number of five pixels, the number of pixels (W / 2) corresponding to the half period of the periodic pattern of AF auxiliary light is 5 / 2 pixel, that is, the decimal point of 2.5 pixels is rounded off to obtain 3 pixels.

In the example shown in FIG. 4, since the number of pixels W corresponding to one period of the AF auxiliary light periodic pattern is 12 pixels, the number of pixels corresponding to the half period of the AF auxiliary light pattern (W / 2) is 6 pixels. It becomes. Therefore, in the example shown in FIG. 4, the first differential filter can be obtained as shown in the following formula (2).
f (n) = 2 × X (n) −X (n−6) −X (n + 6) (2)
Then, the filter processing of the pair of received light signals is performed by the first differential filter thus obtained.

For example, in the example shown in FIG. 4, the light reception signal output from the 27th pixel in the arrangement direction corresponding to the peak a based on the output waveform A having a relatively high intensity corresponding to the LED light source 3031 having a relatively high luminance is Filter processing is performed using the first differential filter shown in Equation (2) as shown in Equation (3) below.
X (27) = 2 × X (27) −X (21) −X (33) (3)
In addition, the filter processing is performed in the other pixels constituting the pixel row as in the above formula (3).

  In step S107, the defocus calculation unit 163 calculates the correlation amount C (k) based on the pair of received light signals that have been filtered using the first differential filter expressed by the above formula (1).

Specifically, the defocus calculation unit 163 performs a pair of light reception when the intensities of the pair of light reception signals after the filter processing obtained from the nth pixel in the arrangement direction are α (n) and β (n). The correlation amount C (k) of the signal is obtained by the correlation calculation shown in the following formula (4).
C (k) = Σ | α (n) −β (n + k) | (4)
In the above equation (4), Σ operation indicates a cumulative operation (phase sum operation) for n, and is limited to a range in which data of α (n) and β (n + k) exists according to the image shift amount k. The The image shift amount k is an integer, and is a shift amount in units of the pixel interval of the pixel column arranged in the line sensor 161d.

  Here, FIG. 6 shows an example of the correlation amount C (k) based on the pair of light reception signals obtained by filtering the pair of light reception signals obtained when the AF auxiliary light is irradiated using the first differential filter. It is a graph. In FIG. 6, the vertical axis represents the correlation amount C (k), and the horizontal axis represents the shift amount in units of the pixel interval of the pixel column. The smaller the value of the correlation amount C (k), the higher the degree of correlation between the pair of received light signals (the smaller the shift amount), and when the correlation amount C (k) is minimal, the correlation between the pair of received light signals. The degree is the highest.

  In step S108, the defocus calculation unit 163 calculates the defocus amount df based on the correlation amount C (k) calculated in step S107 by, for example, three-point interpolation.

  In step S109, the camera control unit 170 performs in-focus determination. In the present embodiment, for example, when the defocus amount df calculated in step S108 is equal to or less than a predetermined value, it is determined that the focus is achieved, and the process proceeds to step S110. On the other hand, if the defocus amount df exceeds a predetermined value and is not determined to be in focus, the process proceeds to step S112.

  In step S110, the camera control unit 170 determines whether or not the release button has been fully pressed (second switch SW2 is turned on). If it is determined that the release button has been fully pressed, the process proceeds to step S111. An image is captured. On the other hand, if it is determined in step S110 that the release button has not been fully pressed (the second switch SW2 is turned on), the process returns to step S101 and the focus adjustment operation is performed again.

  On the other hand, if it is not determined to be in focus in step S109, the process proceeds to step S112. In step S112, the lens drive amount calculation unit 164 calculates the lens drive amount Δd based on the defocus amount df calculated in step S108. Then, the calculated lens drive amount Δd is output from the lens drive amount calculation unit 164 to the lens drive control unit 165, and the lens drive control unit 165 via the lens control unit 250 drives a drive command based on the lens drive amount Δd. Is sent to the focus lens drive motor 230. As a result, the focus lens drive motor 230 moves the focus lens 212 in accordance with a drive command based on the lens drive amount Δd. After step S112, the process returns to step S101, and the focus adjustment operation is performed again.

  If it is determined in step S103 that the luminance of the subject is high and it is not necessary to emit AF auxiliary light, the process proceeds to step S113. In step S113, the light beams from the subject are received by the pixels arranged in the pair of line sensors 161d without emitting AF auxiliary light. Thereby, in each pixel arranged in the pair of line sensors 161d, charges are accumulated according to the intensity of the received light, and the accumulated pair of received light signals are output to the defocus calculation unit 163. .

In the subsequent step S114, the defocus calculation unit 163 performs a filtering process on the pair of light reception signals acquired in step S113, using the second differential filter that does not consider the AF auxiliary light periodic pattern. As such a second differential filter, for example, a second differential filter f (n) represented by the following formula (5) can be used.
f (n) = 2 × X (n) −X (n−2) −X (n + 2) (5)
The second differential filter used in step S114 is not limited to the differential filter shown in the above formula (5), and may be, for example, a differential filter that does not consider the AF auxiliary light periodic pattern unlike the first differential filter. For example, it may be set arbitrarily, or may be configured not to perform the filter processing.

  After the filtering process is performed using the second differential filter in step S114, the process proceeds to step S107, and the correlation amount is calculated based on the pair of received light signals filtered in step S114 (step S107). A defocus amount df is calculated based on the calculated correlation amount (step S108). Then, it is determined that the in-focus state is obtained by the in-focus determination (step S109 = YES), and when the release button is fully pressed (step S110 = YES), an image is captured (step S111).

  As described above, in the present embodiment, when irradiating AF auxiliary light, a pair of light reception signals is filtered using the first differential filter corresponding to the periodic pattern of the AF auxiliary light. Then, the focus state is detected based on the pair of light reception signals filtered using the first differential filter. Here, FIG. 7 shows a differential filter that does not take into account the periodic pattern of the AF auxiliary light (for example, the second differential filter shown in the above formula (5)) from the received light signal obtained when the AF auxiliary light is irradiated. It is a graph which shows an example of the correlation amount C (k) at the time of performing a filter process using. When the received light signal obtained when the AF auxiliary light is irradiated is filtered using the first differential filter (FIG. 6) and the second differential filter. In comparison with the correlation amount graph (FIG. 7), the correlation amount (when the shift amount (horizontal axis) is between −10 and −5 and between the shift amount between 5 and 10 is In the graph shown in FIG. 6, the minimum value C (x) with respect to the continuous correlation amount C (k) is a value close to 0 in the graph shown in FIG. On the other hand, in the graph shown in FIG. 7, the minimum value C (x) with respect to the correlation amount is a value close to 0.5. When the amount of change ΔC of the correlation amount C (k) based on the received light signal obtained when the AF auxiliary light is irradiated is compared, the correlation amount C when the first differential filter is used (graph shown in FIG. 6). The amount of change ΔC in (k) is larger than the amount of change ΔC in the amount of correlation C (k) when the second differential filter is used (graph shown in FIG. 7). That is, in the present embodiment, the AF auxiliary light is obtained by performing the filter process using the first differential filter corresponding to the periodic pattern of the AF auxiliary light with respect to the light reception signal obtained when the AF auxiliary light is irradiated. A higher correlation amount C (k) can be obtained as compared with the case where the filter process is performed using the second differential filter that does not consider the periodic pattern. As a result, according to the present embodiment, the focus state is appropriately adjusted without changing the luminance of the light source even when the luminance of the subject is low or the distance from the AF auxiliary light source to the subject is long. Can be detected.

  Further, in the present embodiment, a filter process is performed using the first differential filter corresponding to the periodic pattern of the AF auxiliary light, so that the portion of the received light signal having a relatively high intensity (for example, based on the output waveform A in FIG. 4). At peak a), the intensity of the received light signal can be increased, while at the portion where the intensity of the received light signal is relatively small (for example, peak b based on the output waveform B in FIG. 4), the intensity of the received light signal. Can be made smaller. Therefore, according to the present embodiment, it is possible to more appropriately detect the in-focus state by obtaining the correlation amount between the pair of light reception signals based on the pair of light reception signals filtered using the first differential filter. In addition, it is possible to effectively prevent false focusing. In particular, conventionally, for example, in the example shown in FIG. 4, it may be erroneously determined that the output waveform A and the output waveform B are in focus at a position where they overlap, and false focus may occur. On the other hand, in the present embodiment, by filtering the light reception signal using the first differential filter corresponding to the AF auxiliary light pattern, the intensity of the light reception signal in a portion where the light reception signal intensity is relatively large. On the other hand, in the portion where the intensity of the light reception signal is relatively small, the intensity of the light reception signal can be further reduced, so that false focusing can be effectively prevented.

  The embodiment described above is described for facilitating understanding of the present invention, and is not described for limiting the present invention. Therefore, each element disclosed in the above embodiment is intended to include all design changes and equivalents belonging to the technical scope of the present invention.

  For example, in the above-described embodiment, the AF auxiliary light emitting unit 303 illuminates AF auxiliary light having a single periodic pattern. However, the present invention is not limited to this, and for example, a plurality of AF auxiliary having different periodic patterns. A configuration may be adopted in which AF auxiliary light having one of the periodic patterns is selected from the light and irradiated. In this case, according to the selected AF auxiliary light periodic pattern, the number of pixels W corresponding to one period of the periodic pattern is calculated, and the focus state is detected using a differential filter that takes into account the calculated number of pixels W can do. Therefore, even when the periodic pattern of AF auxiliary light can be selected from a plurality of periodic patterns, the focus state can be appropriately detected.

DESCRIPTION OF SYMBOLS 1 ... Single-lens reflex digital camera 100 ... Camera body 110 ... Image pick-up element 150 ... Operation part 161 ... Focus detection module 161a ... Condenser lens 161b ... Aperture mask 161c ... Re-imaging lens 161d ... Line sensor 162 ... AF-CCD control part 163 ... Defocus calculation unit 164 ... Lens drive amount calculation unit 165 ... Lens drive amount control unit 170 ... Camera control unit 200 ... Lens barrel 212 ... Focus lens 230 ... Focus lens drive motor 250 ... Lens control unit 300 ... Strobe device 301 ... Main Light emitting unit 302 ... Strobe driving unit 303 ... AF auxiliary light emitting unit 304 ... AF auxiliary light driving unit

Claims (6)

Illumination control means for transmitting an illumination command for illuminating the subject with illumination light having a predetermined periodic pattern;
A light receiving means for receiving a pair of light beams passing through different regions of the pupil of the optical system and outputting a pair of light reception signals;
An arithmetic means for performing a calculation for detecting the focus state of the optical system based on the pair of received light signals obtained by filtering the pair of received light signals output from the light receiving means using a differential filter. When,
A focus detection apparatus comprising: a calculation control unit that changes a calculation method of the calculation unit according to a periodic pattern of the illumination light. The focus detection apparatus according to claim 1,
The focus detection apparatus according to claim 1, wherein the calculation unit varies a differential filter used for the filter processing according to a periodic pattern of the illumination light. The focus detection apparatus according to claim 2,
The light receiving means includes a pixel row in which a plurality of pixels having a microlens arranged in the vicinity of the planned focal plane of the optical system and a photoelectric conversion unit arranged with respect to the microlens are arranged,
The focus detection characterized in that the arithmetic control means determines a differential filter used for the filter processing based on the number of pixels constituting the pixel column corresponding to one period of the periodic pattern of the illumination light. apparatus. The focus detection apparatus according to claim 3,
The arrangement direction of the pixel column when the intensity of the received light signal from the nth pixel in the arrangement direction of the pixel column is X (n) and the number of pixels corresponding to one period of the periodic pattern of the illumination light is W The differential filter f (n) for the received light signal from the nth pixel is f (n) = 2 × X (n) −X (n−W / 2) −X (n + W / 2). Focus detection device. In the focus detection apparatus according to any one of claims 1 to 4,
The focus detection apparatus, wherein the illumination control means can select a periodic pattern for illuminating the illumination light from a plurality of periodic patterns.   An imaging device provided with the focus detection apparatus of any one of Claims 1-5.

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