JP6285683B2 - Imaging apparatus and control method thereof - Google Patents

Description

  The present invention relates to an imaging apparatus and a control method thereof, and more particularly to an imaging apparatus having an automatic focus adjustment function and a control method thereof.

  As one of focus detection methods performed in the imaging apparatus, there is an imaging plane phase difference method in which focus detection by a phase difference method is performed by focus detection pixels formed on an image sensor.

  Patent Document 1 discloses an imaging apparatus using a two-dimensional imaging element in which one microlens and a plurality of divided photoelectric conversion units are formed for one pixel. The divided photoelectric conversion unit is configured to receive light transmitted through different regions of the exit pupil of the photographing lens through one microlens, and performs pupil division. A phase difference type focus detection is performed by calculating a correlation amount from each focus detection signal output from a pixel (focus detection pixel) having such a divided photoelectric conversion unit and obtaining an image shift amount from the correlation amount. It can be performed. Patent Document 2 discloses that an imaging signal is generated by adding a focus detection signal output from a divided photoelectric conversion unit for each pixel.

  Patent Document 3 discloses an imaging apparatus in which a pair of focus detection pixels is partially arranged on a two-dimensional imaging element composed of a plurality of imaging pixels. The pair of focus detection pixels are configured to receive different regions of the exit pupil of the photographing lens by a light shielding layer having an opening, and perform pupil division. An imaging signal is acquired with imaging pixels arranged in most of the two-dimensional imaging device, a correlation amount is calculated from focus detection signals of focus detection pixels arranged in a part, and an image shift amount is obtained from the correlation amount, It is disclosed to perform phase difference type focus detection.

  In focus detection using the imaging surface phase difference method, it is possible to simultaneously detect the defocus direction and the amount of defocus using focus detection pixels formed on the image sensor, and focus adjustment can be performed at high speed.

US Pat. No. 4,410,804 JP 2001-083407 A JP 2000-156823 A

  However, in the imaging surface phase difference method, the light beam received by the focus detection pixel that performs focus detection differs from the light beam received by the imaging pixel that acquires the captured image, so each aberration (spherical aberration, astigmatism, coma) of the photographic lens is different. The influence of the aberration on the focus detection signal is different from the influence of the imaging signal. For this reason, there is a problem that a difference occurs between the detected in-focus position calculated from the focus detection signal and the best in-focus position of the imaging signal.

  The present invention has been made in view of the above problems, and an object of the present invention is to enable focus detection to be performed with higher accuracy and speed.

In order to achieve the above object, an imaging device of the present invention includes an imaging element having a first focus detection pixel and a second focus detection pixel that respectively receive a pair of light beams that have passed through different pupil partial regions of an imaging optical system. Calculating a correlation amount between the first focus detection signal output from the first focus detection pixel in the focus detection region and the second focus detection signal output from the second focus detection pixel, and calculating the correlation amount Based on the first focus detection means for detecting the first detection defocus amount indicating the difference to the in-focus position, and the first focus detection signal and the second focus detection signal are added while being shifted from each other. A second focus detection unit that calculates a contrast evaluation value for each shift amount from the shift addition signal and detects a second detection defocus amount indicating a difference to the in-focus position based on the contrast evaluation value; The imaging optical system A focus detection correction value for suppressing the difference between the focus position at which the contrast of the signal obtained by the light flux that has passed through the pupil region is maximum and the focus position corresponding to the first detection defocus amount is calculated as the result of the focus detection correction value. A storage unit that stores values corresponding to a zoom position and a focus position of the image optical system, and a focus based on the defocus amount obtained by correcting the first detection defocus amount with the focus detection correction value stored in the storage unit. after the adjusting, possess a focusing means for performing focus point adjusted based on the second detection defocus amount, the focusing means is at least one of the distance to the image height or a subject of the focus detection area If the predetermined condition is satisfied, focus adjustment based on the second detected defocus amount is not performed .

  According to the present invention, focus detection can be performed with higher accuracy and speed.

1 is a schematic configuration diagram of an imaging apparatus according to an embodiment of the present invention. FIG. 3 is a schematic diagram of a pixel arrangement in the embodiment. FIG. 2 is a schematic plan view and a schematic cross-sectional view of a pixel in an embodiment. Schematic explanatory drawing of the pixel structure and pupil division in the embodiment. Schematic explanatory drawing of an image sensor and pupil division in an embodiment. FIG. 6 is a schematic relationship diagram between a defocus amount and an image shift amount of a first focus detection signal and a second focus detection signal in the embodiment. Explanatory drawing of the focus detection area | region in embodiment. The flowchart which shows the process of the 1st focus detection in embodiment. The schematic explanatory drawing of the shading by the pupil shift | offset | difference of the 1st focus detection signal and 2nd focus detection signal in embodiment. The figure which shows an example of the filter frequency band in embodiment. FIG. 5 is a diagram illustrating an example of a first focus detection signal and a second focus detection signal according to the first embodiment. The figure which shows an example of the 1st focus detection signal and 2nd focus detection signal after a 1st filter process in case a focus lens exists in the best focus position. FIG. 5 is a diagram illustrating an example of a first detection defocus amount and a second detection defocus amount according to the first embodiment. FIG. 5 is a schematic explanatory diagram of refocus processing in the embodiment. The flowchart which shows the process of the 2nd focus detection in embodiment. The figure which shows an example of the 1st focus detection signal and 2nd focus detection signal after a 2nd filter process in case a focus lens exists in the best focus position. The figure which shows an example of the shift addition signal of the 1st focus detection signal and the 2nd focus detection signal after the 2nd filter process in embodiment. The figure which shows an example of the contrast evaluation value in embodiment. FIG. 3 is a schematic explanatory diagram of a refocusable range in the embodiment. Explanatory drawing of the focus detection correction value in embodiment. 5 is a flowchart showing a flow of focus detection processing in the first embodiment. 9 is a flowchart showing a flow of focus detection processing in the second embodiment. 10 is a flowchart showing a flow of focus detection processing in the fourth embodiment. Schematic of the pixel arrangement in a 5th embodiment. The schematic plan view and schematic sectional drawing of the pixel in 4th Embodiment.

  The best mode for carrying out the present invention will be described below in detail with reference to the accompanying drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components exemplified in this embodiment should be changed as appropriate according to the configuration of the apparatus to which the present invention is applied and various conditions. However, the present invention is not limited to these examples.

<First Embodiment>
Overall Configuration FIG. 1 shows a schematic configuration of a camera which is an image pickup apparatus having an image pickup device according to an embodiment of the present invention. In FIG. 1, the first lens group 101 is disposed at the tip of the imaging optical system and is held so as to be able to advance and retreat in the optical axis direction. The aperture / shutter 102 adjusts the aperture diameter to adjust the amount of light at the time of shooting, and also has a function as an exposure time adjustment shutter at the time of still image shooting. The second lens group 103 moves forward and backward in the optical axis direction integrally with the diaphragm / shutter 102, and a zooming function (zoom function) can be realized in conjunction with the forward / backward movement of the first lens group 101.

  The third lens group 105 (focus lens) performs focus adjustment by advancing and retreating in the optical axis direction. The optical low-pass filter 106 is an optical element for reducing false colors and moire in the captured image. The image sensor 107 is composed of a two-dimensional CMOS photosensor and its peripheral circuit, and is disposed on the imaging surface of the imaging optical system. The first lens group 101, the diaphragm / shutter 102, the second lens group 103, the third lens group 105, and the optical low-pass filter 106 described above constitute an imaging optical system.

  The zoom actuator 111 rotates a cam cylinder (not shown) to drive the first lens group 101 to the third lens group 103 forward and backward in the optical axis direction, and performs a zooming operation. The aperture shutter actuator 112 controls the aperture diameter of the aperture / shutter 102 to adjust the amount of photographing light, and controls the exposure time during still image photographing. The focus actuator 114 adjusts the focus by driving the third lens group 105 back and forth in the optical axis direction.

  A flash illumination device using a xenon tube is suitable for the electronic flash 115 for illuminating the subject at the time of shooting, but an illumination device including an LED that emits light continuously may be used. The AF auxiliary light emitting unit 116 projects a mask image having a predetermined opening pattern onto the object field via the projection lens, and improves the focus detection capability for a dark subject or a low-contrast subject.

  Reference numeral 121 denotes an in-camera CPU that controls various controls of the camera body, and includes a calculation unit, ROM, RAM, A / D converter, D / A converter, communication interface circuit, and the like. The CPU 121 drives various circuits included in the camera based on a predetermined program stored in the ROM, and executes a series of operations such as AF, photographing, image processing, and recording. In the present embodiment, a focus detection correction value corresponding to the state of the imaging optical system is also stored.

  A plurality of focus detection correction values are prepared for each focus state corresponding to the position of the third lens group 105, zoom state corresponding to the position of the first lens group 101, and F number of the imaging optical system. When performing focus adjustment, which will be described later, using the output signal of the image sensor 107, optimum focus detection correction corresponding to the positions and F-numbers of the first lens group 101 and the third lens group 105 of the imaging optical system. A value is selected.

  In the present embodiment, the focus detection correction value is stored in the CPU 121, but the present invention is not limited to this. For example, in an interchangeable lens type imaging apparatus, an interchangeable lens having an imaging optical system may have a nonvolatile memory, and the focus detection correction value described above may be stored in the memory. In this case, the focus detection correction value may be transmitted to the imaging device according to the state of the imaging optical system.

  The electronic flash control circuit 122 controls lighting of the electronic flash 115 in synchronization with the photographing operation. The auxiliary light driving circuit 123 controls the lighting of the AF auxiliary light emitting unit 116 in synchronization with the focus detection operation. The image sensor driving circuit 124 controls the image capturing operation of the image sensor 107, A / D converts the acquired image signal, and transmits it to the CPU 121. The image processing circuit 125 performs processing such as γ conversion, color interpolation, and JPEG compression of the image acquired by the image sensor 107.

  The focus drive circuit 126 controls the focus actuator 114 based on the focus detection result, and adjusts the focus by driving the third lens group 105 back and forth in the optical axis direction. The aperture shutter drive circuit 128 controls the aperture of the aperture / shutter 102 by drivingly controlling the aperture shutter actuator 112. The zoom drive circuit 129 drives the zoom actuator 111 according to the zoom operation of the photographer.

  A display 131 such as an LCD displays information related to the shooting mode of the camera, a preview image before shooting and a confirmation image after shooting, an index of a focus detection area at the time of focus detection, a focus state display image, and the like. The operation switch group 132 includes a power switch, a release (shooting trigger) switch, a zoom operation switch, a shooting mode selection switch, and the like. The detachable flash memory 133 records captured images.

Image Sensor Next, an outline of the arrangement of the imaging pixels and focus detection pixels of the image sensor 107 in the present embodiment is shown in FIG. FIG. 2 shows the pixel (imaging pixel) array of the two-dimensional CMOS sensor (imaging device) of this embodiment in a range of 4 columns × 4 rows and the focus detection pixel array in a range of 8 columns × 4 rows. is there.

  The pixel group 200 includes pixels of 2 rows × 2 columns, a pixel 200R having a spectral sensitivity of R (red) is on the upper left, a pixel 200G having a spectral sensitivity of G (green) is on the upper right and lower left, and B (blue). The pixel 200 </ b> B having the spectral sensitivity is arranged in the lower right. Further, each pixel includes a first focus detection pixel 201 and a second focus detection pixel 202 arranged in 2 columns × 1 row.

  A large number of 4 columns × 4 rows of pixels (8 columns × 4 rows of focus detection pixels) shown in FIG. 2 are arranged on the surface to enable acquisition of a captured image (focus detection signal). In the present embodiment, the pixel period P is 4 μm, the number of pixels N is 5575 columns × 3725 rows = approximately 20.75 million pixels, the column direction cycle PAF of the focus detection pixels is 2 μm, and the focus detection pixel number NAF is 11150 columns × The description will be made assuming that the image sensor has 3725 vertical rows = about 41.5 million pixels.

A plan view of one pixel 200G of the image sensor 107 shown in FIG. 2 as viewed from the light receiving surface side (+ z side) of the image sensor 107 is shown in FIG. 3A, and a cross section taken along the line aa in FIG. FIG. 3B shows a cross-sectional view as seen from the −y side. As shown in FIG. 3, in the pixel 200G of this embodiment, a microlens 305 for condensing incident light is formed on the light receiving side of each pixel, and is divided into _NH (two divisions) in the x direction and in the y direction. N _V division (first division) by photoelectric conversion unit 301 and the photoelectric conversion portion 302 is formed. The photoelectric conversion units 301 and 302 correspond to the first focus detection pixel 201 and the second focus detection pixel 202, respectively. The photoelectric conversion units 301 and 302 may be a pin structure photodiode in which an intrinsic layer is sandwiched between a p-type layer and an n-type layer, or the intrinsic layer may be omitted as necessary to serve as a pn junction photodiode. Also good.

  In each pixel, a color filter 306 is formed between the microlens 305 and the photoelectric conversion units 301 and 302. Further, as necessary, the spectral transmittance of the color filter may be changed for each focus detection pixel, or the color filter may be omitted.

  Light incident on the pixel 200 </ b> G illustrated in FIG. 3 is collected by the microlens 305, dispersed by the color filter 306, and then received by the photoelectric conversion units 301 and 302. In the photoelectric conversion units 301 and 302, a pair of electrons and holes are generated according to the amount of received light and separated by a depletion layer, and then negatively charged electrons are accumulated in an n-type layer (not shown), while holes are constant. The light is discharged outside the image sensor 107 through a p-type layer connected to a voltage source (not shown). Electrons accumulated in n-type layers (not shown) of the photoelectric conversion units 301 and 302 are transferred to a capacitance unit (FD) via a transfer gate, converted into a voltage signal, and output.

  The correspondence relationship between the pixel structure of this embodiment shown in FIG. 3 and pupil division will be described with reference to FIG. FIG. 4 is a cross-sectional view of the pixel structure of the present embodiment shown in FIG. 3A as viewed from the + y side and a view showing an exit pupil plane of the imaging optical system. In FIG. 4, the x-axis and y-axis of the cross-sectional view are inverted with respect to FIG. 3 in order to correspond to the coordinate axis of the exit pupil plane.

  The first pupil partial region 501 of the first focus detection pixel 201 is substantially conjugated by the microlens 305 and the light receiving surface of the photoelectric conversion unit 301 whose center of gravity is decentered in the −x direction. Reference numeral 201 denotes a pupil region that can receive light. The first pupil partial region 501 of the first focus detection pixel 201 has an eccentric center of gravity on the + X side on the pupil plane.

  In addition, the second pupil partial region 502 of the second focus detection pixel 202 is substantially conjugate with the light receiving surface of the photoelectric conversion unit 302 whose center of gravity is decentered in the + x direction and the microlens 305, so that the second focus detection is performed. A pupil region that can be received by the pixel 202 is shown. The second pupil partial region 502 of the second focus detection pixel 202 has an eccentric center of gravity on the −X side on the pupil plane.

  The pupil region 500 is a pupil region that can receive light in the entire pixel 200G when all of the photoelectric conversion units 301 and 302 (the first focus detection pixel 201 and the second focus detection pixel 202) are combined.

  FIG. 5 is a schematic diagram illustrating a correspondence relationship between the image sensor 107 and pupil division according to the present embodiment. A pair of light beams that have passed through the first pupil partial region 501 and the second pupil partial region 502 are incident on the pixels of the image sensor 107 at different angles, and are divided into 2 × 1 first focus detection pixels 201 and Light is received by the second focus detection pixel 202. In the present embodiment, the pupil region is divided into two pupils in the horizontal direction. If necessary, pupil division may be performed in the vertical direction.

  In the above-described example, a plurality of imaging pixels each including the first focus detection pixel and the second focus detection pixel are arranged. However, the present invention is not limited to this. If necessary, the imaging pixel, the first focus detection pixel, and the second focus detection pixel are configured as separate pixels, and the first focus detection pixel and the second focus detection pixel are partially included in a part of the imaging pixel array. It is good also as a structure to arrange.

  In the present embodiment, the first focus detection signal 201 is collected by collecting the light reception signals of the first focus detection pixels 201 of the respective pixels of the image sensor 107, and the second light detection signals of the second focus detection pixels 202 of the respective pixels are collected. A focus detection signal is generated to perform focus detection. Further, by adding the signals of the first focus detection pixel 201 and the second focus detection pixel 202 for each pixel of the imaging element 107, an imaging signal (captured image) having a resolution of N effective pixels is generated.

Relationship between Defocus Amount and Image Deviation Amount Hereinafter, the relationship between the defocus amount of the first focus detection signal and the second focus detection signal acquired by the image sensor 107 of the present embodiment and the image deviation amount will be described. FIG. 6 is a schematic relationship diagram of the defocus amounts of the first focus detection signal and the second focus detection signal and the image shift amount between the first focus detection signal and the second focus detection signal. As described with reference to FIGS. 4 and 5, the imaging element 107 of the present embodiment is disposed on the imaging surface 800, and the exit pupil of the imaging optical system includes the first pupil partial region 501 and the second pupil partial region. Divided into 502.

  The defocus amount d is a distance | d | from the imaging position of the subject to the imaging surface, and a negative sign (d <0) indicates a front pin state where the imaging position of the subject is on the subject side from the imaging surface. A rear pin state in which the imaging position of the subject is on the opposite side of the subject from the imaging surface is defined as a positive sign (d> 0). An in-focus state where the imaging position of the subject is on the imaging surface (in-focus position) is d = 0. In FIG. 6, the subject 801 shows an example in a focused state (d = 0), and the subject 802 shows an example in a front pin state (d <0). The front pin state (d <0) and the rear pin state (d> 0) are combined to form a defocus state (| d |> 0).

  In the front pin state (d <0), the luminous flux that has passed through the first pupil partial area 501 (second pupil partial area 502) out of the luminous flux from the subject 802 is once condensed and then the gravity center position G1 of the luminous flux. The image spreads in the width Γ 1 (Γ 2) with (G 2) as the center, resulting in a blurred image on the imaging surface 800. The blurred image is received by the first focus detection pixel 201 (second focus detection pixel 202) constituting each pixel arranged in the image sensor 107, and a first focus detection signal (second focus detection signal) is generated. The Therefore, the first focus detection signal (second focus detection signal) is recorded as a subject image in which the subject 802 is blurred by the width Γ1 (Γ2) at the gravity center position G1 (G2) on the imaging surface 800. The blur width Γ1 (Γ2) of the subject image generally increases in proportion to the amount of defocus amount d | d |. Similarly, the magnitude | p | of the object image displacement amount p (= difference G1-G2 in the center of gravity of the light beam) between the first focus detection signal and the second focus detection signal is also the size of the defocus amount d. As | d | increases, it generally increases in proportion. Even in the rear pin state (d> 0), the image shift direction of the subject image between the first focus detection signal and the second focus detection signal is opposite to that in the front pin state, but the same.

  As described above, the first focus detection signal and the second focus detection signal, or the defocus amount of the image pickup signal obtained by adding the first focus detection signal and the second focus detection signal increases. The amount of image shift between the focus detection signal and the second focus detection signal increases.

Focus detection In this embodiment, based on the relationship between the defocus amount and the image shift amount of the first focus detection signal and the second focus detection signal, the first focus detection based on the phase difference method and the refocus principle are used. The second focus detection of the method (hereinafter referred to as “refocus method”) is performed. Further, correction using a focus detection correction value that matches the state of the imaging optical system is also performed. Mainly, focus adjustment is performed from the small defocus state to the vicinity of the best focus position by using the result of the first focus detection corrected by the focus detection correction value in order to adjust the focus from the large defocus state to the small defocus state. Therefore, the second focus detection is performed. Details will be described later.

[Focus detection area]
First, a focus detection area that is an area on the image sensor 107 that acquires the first focus detection signal and the second focus detection signal will be described. FIG. 7 shows the focus detection area in the effective pixel area 1000 of the image sensor 107 and the index indicating the focus detection area displayed on the display 131 at the time of focus detection. In the present embodiment, nine focus detection areas are set, three in the row direction and three in the column direction. The nth focus detection region in the row direction and the mth focus detection region in the column direction is represented as A (n, m), and will be described later using signals from the first focus detection pixel 201 and the second focus detection pixel 202 in this region. First focus detection and second focus detection are performed. Similarly, the index of the nth focus detection region in the row direction and the mth in the column direction is represented as I (n, m).

  In the present embodiment, an example is shown in which three focus detection areas are set in the row direction and three in the column direction. However, in the image sensor that can obtain the first focus detection signal and the second focus detection signal from any pixel in the effective pixel region 1000 like the image sensor 107 described above, the number, position, and size of the focus detection regions are set as appropriate. May be. For example, a predetermined range may be set as the focus detection area around the area designated by the photographer.

[First focus detection of phase difference method]
The phase difference type first focus detection in the first embodiment will be described below. In the first focus detection based on the phase difference method, the first focus detection signal and the second focus detection signal are relatively shifted to calculate a correlation amount (first evaluation value) representing the degree of coincidence of the signals. The image shift amount is detected from the shift amount that improves the degree of coincidence. As the defocus amount of the image pickup signal increases, the image shift amount is determined based on the relationship that the image shift amount increases between the first focus detection signal and the second focus detection signal. Focus detection is performed by converting into a focus amount.

  FIG. 8 shows a schematic diagram of the flow of processing of the first focus detection in the first embodiment. Note that the processing in FIG. 8 is executed by the focus detection signal generation unit, the image sensor 107 as the first focus detection unit, the image processing circuit 125, and the CPU 121 in the first embodiment.

  In S110, a focus detection area is set in the effective pixel area 1000 of the image sensor 107. The focus detection signal generating means generates a first focus detection signal from the light reception signal of the first focus detection pixel 201 in the focus detection area, and detects the second focus from the light reception signal of the second focus detection pixel 202 in the focus detection area. Generate a signal.

  In S120, for each of the first focus detection signal and the second focus detection signal, a three-pixel addition process is performed in the column direction to suppress the signal data amount, and further, the RGB signal is converted into a luminance Y signal. A Bayer (RGB) addition process is performed. These two addition processes are combined into a first pixel addition process.

  In S130, a shading correction process (optical correction process) is performed on the first focus detection signal and the second focus detection signal that have been subjected to the first pixel addition process, respectively. Hereinafter, shading due to pupil shift between the first focus detection signal and the second focus detection signal will be described. FIG. 9 shows the first pupil partial region 501 of the first focus detection pixel 201, the second pupil partial region 502 of the second focus detection pixel 202, and the exit pupil 400 of the imaging optical system at the peripheral image height of the image sensor 107. Show the relationship.

  FIG. 9A shows a case where the exit pupil distance Dl of the imaging optical system and the set pupil distance Ds of the image sensor 107 are the same. In this case, the exit pupil 400 of the imaging optical system is substantially equally divided by the first pupil partial region 501 and the second pupil partial region 502.

  On the other hand, when the exit pupil distance Dl of the imaging optical system shown in FIG. 9B is shorter than the set pupil distance Ds of the image sensor 107, the exit of the imaging optical system is performed at the peripheral image height of the image sensor 107. A pupil shift occurs between the pupil and the entrance pupil of the image sensor 107. Therefore, the exit pupil 400 of the imaging optical system is non-uniformly divided into pupils. Similarly, when the exit pupil distance Dl of the imaging optical system shown in FIG. 9C is longer than the set pupil distance Ds of the imaging device, the imaging pupil and the exit pupil of the imaging optical system are imaged at the peripheral image height of the imaging device 107. A pupil shift of the entrance pupil of the element 107 occurs, and the exit pupil 400 of the imaging optical system is non-uniformly pupil-divided. As pupil division becomes nonuniform at the peripheral image height, the intensity of the first focus detection signal and the second focus detection signal also becomes nonuniform, and one of the first focus detection signal and the second focus detection signal Shading occurs with increasing strength and decreasing the other strength.

  Therefore, in S130, first, according to the image height of the focus detection area, the F value of the imaging lens (imaging optical system), and the exit pupil distance, the first shading correction coefficient of the first focus detection signal, and the second A second shading correction coefficient for the focus detection signal is generated. Then, the first focus detection signal is multiplied by the first focus detection signal, the second shading correction coefficient is multiplied by the second focus detection signal, and shading correction processing (optical) of the first focus detection signal and the second focus detection signal is performed. Correction process).

  In the first focus detection of the phase difference method, the first detection defocus amount is detected based on the correlation (signal coincidence) between the first focus detection signal and the second focus detection signal. When shading due to pupil shift occurs, the correlation between the first focus detection signal and the second focus detection signal may decrease. Therefore, in the first focus detection of the phase difference method, it is desirable to perform shading correction processing in order to improve the correlation between the first focus detection signal and the second focus detection signal and to improve the focus detection performance.

  In S140, a first filter process is performed on the first focus detection signal and the second focus detection signal subjected to the shading correction process. An example of a pass band of the first filter processing of the first embodiment is indicated by a solid line 901 in FIG. In the first embodiment, since the focus detection in the large defocus state is performed by the first focus detection of the phase difference method, the pass band of the first filter processing is configured to include the low frequency band. When the focus adjustment is performed from the large defocus state to the small defocus state as necessary, the pass band of the first filter processing at the time of the first focus detection according to the defocus state is indicated by a one-dot chain line in FIG. In this way, the frequency may be adjusted to a higher frequency band.

  Next, in S150, a first shift process that relatively shifts the first focus detection signal and the second focus detection signal after the first filter process in the pupil division direction is performed, and a correlation amount (a first amount indicating the degree of coincidence of the signals) 1 evaluation value) is calculated.

  The k-th first focus detection signal after the first filter processing is A (k), the second focus detection signal is B (k), and the range of the number k corresponding to the focus detection area is W. Further, assuming that the shift amount by the first shift process is s1 and the shift range of the shift amount s1 is Γ1, the correlation amount (first evaluation value) COR is calculated by Expression (1).

シフト量ｓ１の第１シフト処理により、ｋ番目の第１焦点検出信号Ａ（ｋ）とｋ−ｓ１番目の第２焦点検出信号Ｂ（ｋ−ｓ１）を対応させ減算し、シフト減算信号を生成する。生成されたシフト減算信号の絶対値を計算し、焦点検出領域に対応する範囲Ｗ内で番号ｋの和を取り、相関量（第１評価値）ＣＯＲ（ｓ１）を算出する。必要に応じて、各行毎に算出された相関量（第１評価値）を、各シフト量毎に、複数行に渡って加算しても良い。

By the first shift process of the shift amount s1, the k-th first focus detection signal A (k) and the k-s1st second focus detection signal B (k-s1) are subtracted in correspondence to generate a shift subtraction signal. To do. The absolute value of the generated shift subtraction signal is calculated, the number k is summed within the range W corresponding to the focus detection area, and the correlation amount (first evaluation value) COR (s1) is calculated. If necessary, the correlation amount (first evaluation value) calculated for each row may be added over a plurality of rows for each shift amount.

  In S160, from the correlation amount (first evaluation value), a real-valued shift amount at which the correlation amount is the minimum value is calculated by subpixel calculation, and is set as the image shift amount p1. Then, the calculated image shift amount p1 is multiplied by the image height of the focus detection region, the F value of the imaging lens (imaging optical system), and the first conversion coefficient K1 corresponding to the exit pupil distance, thereby the first detection defocus. The amount (Def1) is detected.

  As described above, in the first focus detection of the phase difference method in the present embodiment, the first filter processing and the first shift processing are performed on the first focus detection signal and the second focus detection signal, the correlation amount is calculated, and the correlation is calculated. The first detection defocus amount is detected from the amount.

  In the image sensor 107 of the present embodiment, the light beam received by the first focus detection pixel and the second focus detection pixel is different from the light beam received by the image pickup pixel, and each aberration (spherical aberration, astigmatism, The influence on the focus detection pixel and the influence on the imaging signal are different. The difference becomes larger when the aperture value of the imaging optical system is small and the aperture is large (the subject is dark). Therefore, when the aperture value of the imaging optical system is small and the aperture is large, the detection focus position (position where the first detection defocus amount is 0) calculated by the first focus detection of the phase difference method, for example, There may be a difference between the best focus position such as the MTF peak position of the imaging signal. In particular, when the aperture value of the imaging optical system is equal to or less than a predetermined aperture value, the focus detection accuracy of the first focus detection of the phase difference method may be lowered.

  FIG. 11 shows the first focus detection signal (broken line) and the second focus detection signal (solid line) at the peripheral image height of the image sensor 107 of the first embodiment when the third lens group 105 is in the best focus position. An example of Here, an example is shown in which the first focus detection signal and the second focus detection signal are different in signal shape due to the influence of each aberration of the imaging optical system, although it is in the best focus position. FIG. 12 also shows the first focus detection signal (broken line) and the second focus detection signal (solid line) at the peripheral image height after the shading correction process and the first filter process when the third lens group 105 is at the best focus position. ). Although the third lens group 105 is in the best focus position, the image shift amount p1 between the first focus detection signal and the second focus detection signal is not zero. As described above, there is a difference between the detection focus position calculated by the first focus detection of the phase difference method and the best focus position of the imaging signal.

  FIG. 13 shows an example of the first detected defocus amount (broken line) obtained by the first focus detection of the phase difference method in the first embodiment. The horizontal axis is the set defocus amount with the best focus position being the defocus amount 0 [mm], and the vertical axis is the detected defocus amount obtained by the first focus detection of the phase difference method. Note that the first focus detection signal and the second focus detection signal shown in FIG. 11 are the first focus detection signal and the second focus detection signal at the set defocus amount of 0 [mm] in FIG. At the best focus position where the set defocus amount is 0 [mm], since the first detection defocus amount is offset by about 50 μm to the rear pin side, detection calculated by the best focus position and the first focus detection It can be seen that there is a difference of about 50 μm from the in-focus position.

  In the present embodiment, the difference between the detected focus position calculated from the focus detection signal and the best focus position that can be obtained from the imaging signal is suppressed, thereby realizing highly accurate focus detection. Therefore, in addition to the first focus detection using the phase difference method, correction using a focus detection correction value that matches the state of the imaging optical system, and high-precision focus detection near the best focus position of the imaging optical system The second focus detection of the refocusing method that can be performed is performed in combination according to the situation at the time of focus detection.

[Refocus second focus detection]
Hereinafter, the refocus second focus detection in the first embodiment will be described.

  In the second focus detection of the refocus method of the first embodiment, the first focus detection signal and the second focus detection signal are relatively shifted and added to generate a shift addition signal (refocus signal). Then, the contrast evaluation value of the generated shift addition signal (refocus signal) is calculated, the MTF peak position of the imaging signal is estimated from the contrast evaluation value, and the second detection defocus amount is detected.

  A schematic explanatory diagram of a refocus process in a one-dimensional direction (column direction, horizontal direction) by the first focus detection signal and the second focus detection signal acquired by the image sensor 107 of the first embodiment with reference to FIG. explain. The imaging surface 800 in FIG. 14 corresponds to the imaging surface 800 illustrated in FIGS. 5 and 6. In FIG. 14, i is an integer, and the first focus detection signal of the i-th pixel in the column direction of the image sensor 107 arranged on the imaging surface 800 is schematically represented as Ai, and the second focus detection signal as Bi. The first focus detection signal Ai indicates a light reception signal of a light beam that has passed through the pupil partial region 501 and has entered the i-th pixel at the principal ray angle θa. Similarly, the second focus detection signal Bi indicates a light reception signal of a light beam that has passed through the pupil partial region 502 and has entered the i-th pixel at the principal ray angle θb.

  The first focus detection signal Ai and the second focus detection signal Bi have not only light intensity distribution information but also incident angle information. Therefore, the first focus detection signal Ai is translated along the angle θa to the virtual imaging plane 810, and the second focus detection signal Bi is translated along the angle θb to the virtual imaging plane 810 and added. A refocus signal at the virtual imaging plane 810 can be generated. Translating the first focus detection signal Ai along the angle θa to the virtual imaging plane 810 corresponds to shifting +0.5 pixels in the column direction. Further, translating the second focus detection signal Bi along the angle θb to the virtual imaging plane 810 corresponds to shifting by −0.5 pixel in the column direction. Therefore, the first focus detection signal Ai and the second focus detection signal Bi are relatively shifted by +1 pixel, and Ai and Bi + 1 are added in correspondence with each other, thereby generating a refocus signal on the virtual imaging plane 810. Similarly, by shifting the first focus detection signal Ai and the second focus detection signal Bi by an integer pixel and adding them, a shift addition signal (refocus signal) on each virtual imaging plane corresponding to the integer shift amount is added. Can be generated.

  The contrast evaluation value of the generated shift addition signal (refocus signal) is calculated, and the MTF peak position of the imaging signal is estimated from the calculated contrast evaluation value, thereby performing the second focus detection of the refocus method.

  FIG. 15 is a schematic diagram showing the flow of the second focus detection process in the first embodiment. The processing in FIG. 15 is executed by the focus detection signal generation unit, the image sensor 107 as the second focus detection unit, the image processing circuit 125, and the CPU 121 in the first embodiment.

  In S210, a focus detection area is set in the effective pixel area 1000 of the image sensor 107. The focus detection signal generating means generates a first focus detection signal from the light reception signal of the first focus detection pixel 201 in the focus detection area, and detects the second focus from the light reception signal of the second focus detection pixel 202 in the focus detection area. Generate a signal.

  In S220, for each of the first focus detection signal and the second focus detection signal, a three-pixel addition process is performed in the column direction to suppress the signal data amount, and further, the RGB signal is converted into a luminance Y signal. A Bayer (RGB) addition process is performed. These two addition processes are combined into a second pixel addition process. If necessary, one or both of the three-pixel addition processing and the Bayer (RGB) addition processing may be omitted.

  In S230, the second filter processing is performed on the first focus detection signal and the second focus detection signal subjected to the second pixel addition processing. An example of a pass band of the second filter processing of the first embodiment is indicated by a broken line 903 and a dotted line 904 in FIG. In the first embodiment, focus detection is performed from the small defocus state to the vicinity of the best focus position by the second focus detection of the refocus method. Therefore, the pass band of the second filter process is configured to include a higher frequency band than the pass band of the first filter process. If necessary, a second filter processing is performed using a Laplacian type (second-order differential type) [1, -2, 1] filter that performs edge extraction of the subject signal, as indicated by a dotted line 904 in FIG. The pass band of processing may be adjusted to a higher frequency band. By extracting the high frequency component of the subject and performing the second focus detection, the focus detection accuracy can be further improved.

  In S240, a second shift process for relatively shifting the first focus detection signal and the second focus detection signal after the second filter process in the pupil division direction is performed and added to generate a shift addition signal (refocus signal). To do. In S240, a contrast evaluation value (second evaluation value) is further calculated from the generated shift addition signal.

The k-th first focus detection signal after the first filter processing is A (k), the second focus detection signal is B (k), and the range of the number k corresponding to the focus detection area is W. The contrast evaluation value (second evaluation value) RFCON is calculated by Expression (2), where s _{2 is} the shift amount by the second shift process and Γ2 is the shift range of the shift amount s ₂ .

By the second shift process of the shift amount s ₂ , the kth first focus detection signal A (k) and the k−s2nd second focus detection signal B (k−s ₂ ) are added in correspondence with each other, and shift addition is performed. Generate a signal. Then, the absolute value of the shift addition signal is calculated, the maximum value in the range of the focus detection area W is taken, and the contrast evaluation value (second evaluation value) RFCON (s ₂ ) is calculated. If necessary, the contrast evaluation value (second evaluation value) calculated for each row may be added over a plurality of rows for each shift amount.

  In S250, from the contrast evaluation value (second evaluation value), a real-value shift amount at which the contrast evaluation value becomes the maximum value is calculated by subpixel calculation, and is set as the peak shift amount p2. The second detection defocus amount (Def2) is obtained by multiplying the peak shift amount p2 by the image height of the focus detection area, the F value of the imaging lens (imaging optical system), and the second conversion coefficient K2 corresponding to the exit pupil distance. Is detected. If necessary, the first conversion coefficient K1 and the second conversion coefficient K2 may be the same value.

  As described above, in the second focus detection of the refocus method in the present embodiment, the second focus processing signal and the second focus detection signal are subjected to the second filter processing and the second shift processing, and are added to obtain the shift addition signal. And the contrast evaluation value is calculated from the shift addition signal. Further, the second detection defocus amount is detected from the contrast evaluation value.

  In the image sensor 107 of the first embodiment, as shown in FIGS. 4 and 5, an image obtained by adding the light beam received by the first focus detection pixel 201 and the light beam received by the second focus detection pixel 202 is captured. It becomes a light beam received by the pixel. In the second focus detection of the refocus method, unlike the first focus detection of the phase difference method, focus detection is performed by a shift addition signal (refocus signal) of the first focus detection signal and the second focus detection signal. Therefore, since the light beam corresponding to the shift addition signal used in the second focus detection and the light beam corresponding to the imaging signal substantially coincide with each other, each aberration of the imaging optical system (spherical aberration, astigmatism, coma aberration, etc.) The influence on the shift addition signal and the influence on the imaging signal are substantially the same. Therefore, the detection focus position (position where the second detection defocus amount is 0) calculated by the refocus second focus detection and the best focus position of the imaging signal (MTF peak position of the imaging signal) are approximately Therefore, the focus detection can be performed with higher accuracy than the first focus detection using the phase difference method.

  An example of the first focus detection signal (broken line) and the second focus detection signal (solid line) at the best focus position of the image pickup signal at the peripheral image height of the image pickup device of the first embodiment shown in FIG. FIG. 16 shows the first focus detection signal (broken line) and the second focus detection signal (solid line) after the filtering process. In addition, the first focus detection signal (broken line) and the second focus detection signal (solid line) after the second filter processing are relatively shifted by -2, -1, 0, 1, 2, and shifted to add. An example of the addition signal (refocus signal) is shown in FIG. It can be seen that the peak value of the shift addition signal changes as the shift amount changes. An example of the contrast evaluation value (second evaluation value) calculated from each shift addition signal is shown in FIG.

  FIG. 13 shows an example of the second detected defocus amount (solid line) obtained by the second focus detection of the refocus method in the first embodiment. The horizontal axis is the set defocus amount with the best focus position being the defocus amount of 0 [mm], and the vertical axis is the detected defocus amount obtained by the second focus detection of the refocus method. It can be seen that at the best in-focus position where the set defocus amount is 0 [mm], the second detection defocus amount is suppressed to be smaller than the first detection defocus amount by the first focus detection, and the focus detection can be performed with high accuracy.

  As described above, in the present embodiment, in the vicinity of the best focus position where the set defocus amount of the imaging optical system is 0 [mm], the second focus detection of the refocus method is the first focus of the phase difference method. Focus detection can be performed with higher accuracy than detection.

[Refocusable range]
On the other hand, since there is a limit to the refocusable range, the range of the defocus amount that can be detected with high accuracy by the refocus second focus detection is limited.

A schematic explanatory diagram of a refocusable range in the first embodiment is shown in FIG. If the allowable circle of confusion is δ and the aperture value of the imaging optical system is F, the depth of field at the aperture value F is ± Fδ. On the other hand, the effective aperture value F ₀₁ (or F ₀₂ ) in the horizontal direction of the pupil partial region 501 (or 502) that is narrowed by N _H × N _V (2 × 1) is F ₀₁ = N _H It becomes dark with F. The effective depth of field for each first focus detection signal (or second focus detection signal) becomes _NH Fδ and N _H times deeper, and the focus range is extended N _H times. Within the range of effective depth of field ± N _H Fδ, a focused subject image is acquired for each first focus detection signal (or second focus detection signal). Accordingly, the refocusing process of moving the first focus detection signal (or second focus detection signal) along the principal ray angle θa (or θb) shown in FIG. Refocus). Therefore, the defocus amount d from the imaging surface where the focus position can be readjusted (refocused) after shooting is limited, and the refocusable range of the defocus amount d is approximately the range of Expression (3). .

許容錯乱円δは、δ＝２ΔＸ（画素周期ΔＸのナイキスト周波数１／（２ΔＸ）の逆数）などで規定される。必要に応じて、第２画素加算処理後の第１焦点検出信号（第２焦点検出信号）の周期ΔＸ_ＡＦ（＝６ΔＸ：６画素加算の場合）のナイキスト周波数１／（２ΔＸＡＦ）の逆数を許容錯乱円δ＝２ΔＸ_ＡＦとしても用いても良い。

The permissible circle of confusion δ is defined by δ = 2ΔX (the reciprocal of the Nyquist frequency 1 / (2ΔX) of the pixel period ΔX). If necessary, the reciprocal of the Nyquist frequency 1 / (2ΔXAF) of the period ΔX _AF (= 6ΔX: in the case of 6 pixel addition) of the first focus detection signal (second focus detection signal) after the second pixel addition processing is allowed. The circle of confusion δ = 2ΔX may be used as _AF .

  The defocus amount range in which the refocus second focus detection can detect the focus with high accuracy is generally limited to the range of the expression (3), and the defocus range in which the focus detection can be performed with high accuracy by the second focus detection is as follows. The range is equal to or smaller than the defocus range in which the first focus detection of the phase difference method can be performed. As shown in FIG. 6, the relative shift amount and the defocus amount in the horizontal direction between the first focus detection signal and the second focus detection signal are substantially proportional. Therefore, in the first embodiment, the shift range of the second shift process of the second focus detection of the refocus method is configured to be equal to or less than the shift range of the first shift process of the first focus detection of the phase difference method. The

  In the focus detection in the first embodiment, the first focus detection is performed to adjust the focus from the large defocus state to the small defocus state of the imaging optical system, and the best focus is achieved from the small defocus state of the imaging optical system. Second focus detection is performed to adjust the focus to near the position. Therefore, it is desirable that the pass band of the second filter processing of the second focus detection includes a higher frequency band than the pass band of the first filter processing of the first focus detection. In addition, it is desirable that the pixel addition number in the second pixel addition process for the second focus detection is equal to or less than the pixel addition number in the first pixel addition process for the first focus detection.

  As described above, when the aperture value of the imaging optical system is equal to or smaller than the predetermined aperture value, the focus detection accuracy of the first focus detection of the phase difference method may be lowered. Therefore, if necessary, when the aperture value of the imaging optical system is equal to or smaller than the predetermined aperture value, the second detection defocus amount is obtained by the refocus second focus detection in addition to the phase difference first focus detection. Therefore, it is desirable to detect focus and to perform highly accurate focus detection.

  In the first embodiment, since the pupil region is divided into two pupils in the horizontal direction, the horizontal MTF peak position of the imaging signal can be detected. If necessary, the difference between the horizontal MTF peak position of the imaging signal and the MTF peak position of the imaging signal (the average of the MTF peak positions in the horizontal and vertical directions of the imaging signal) is held as a correction value, and the second detection defocus is performed. The amount may be corrected.

  As described above, since the second detection defocus amount is detected by using the first focus detection signal and the second focus detection signal, the detection defocus amount is affected by the subject condition, the manufacturing error of the imaging optical system, and the like. It is hard to receive. On the other hand, the range in which the second detection defocus amount can be detected is limited, or the detection may be impossible depending on the state of the subject such as low contrast and low illuminance. Even when such a second detected defocus amount cannot be detected, in this embodiment, the first detection defocus amount is corrected using the focus detection correction value in order to perform highly accurate focus adjustment.

[Focus detection correction value]
Hereinafter, correction by the focus detection correction value performed for the first focus detection of the phase difference method in the first embodiment will be described.

  As described above, there is a difference between the detection focus position indicated by the first detection defocus amount calculated from the focus detection signal and the best focus position of the imaging signal. In the first embodiment, as a method for suppressing the difference, in addition to the above-described second focus detection, correction using a focus detection correction value can be performed.

  FIG. 20 shows an example of the correction value of the first detection defocus amount calculated by the first focus detection stored in the CPU 121. FIG. 20 shows focus detection correction values corresponding to the focus detection area A (2, 2) in FIG. Similarly, focus detection correction values are stored for the other eight focus detection areas. However, the design focus detection correction values are equal for the focus detection regions that are symmetrical with respect to the optical axis of the imaging optical system. Therefore, it suffices to store a table of four focus detection correction values for nine focus detection areas.

  In FIG. 20, the zoom position and the focus position of the imaging optical system are divided into eight zones, and focus detection correction values BP111 to BP188 are provided for each of the divided zones. Accordingly, a highly accurate focus detection correction value can be obtained according to the positions of the third lens group 105 and the first lens group 101 of the imaging optical system.

  In the first embodiment, the focus detection correction value is stored as table data for each focus detection area as shown in FIG. 20, but the method of storing the focus detection correction value is not limited to this. For example, coordinates are set with the intersection of the optical axis of the imaging device and the imaging optical system as the origin and the horizontal and vertical directions of the imaging device as the X axis and the Y axis, and the correction value at the center coordinate of the focus detection area is set as X You may obtain | require with the function of Y. In this case, the amount of information to be stored as the focus detection correction value can be reduced.

Focus Detection Process Flow Next, the focus detection process flow in the first embodiment will be described with reference to the flowchart of FIG. In the first embodiment, after performing the first focus detection of the phase difference method until the absolute value of the defocus amount of the imaging optical system becomes equal to or less than the threshold value Th1, the focus detection correction is performed on the first detected defocus amount. The lens is driven by correcting the value. Thereby, the focus adjustment is performed from the large defocus state to the small defocus state of the imaging optical system. Thereafter, until the absolute value of the defocus amount of the imaging optical system becomes equal to or less than the threshold value Th2 (<threshold Th1), the second focus detection of the refocusing method is performed to drive the lens, and the small focus state of the imaging optical system is Adjust the focus to near the best focus position.

  In S100, the first detection defocus amount (Def1) is detected by the first focus detection by the phase difference method. Thereafter, in S101, the first detected defocus amount is corrected, and the corrected first detected defocus amount (Def1 ′) is calculated. As described above, the correction performed here is performed using the stored correction value according to the state of the imaging optical system. If the magnitude | Def1 '| of the corrected first defocus amount (Def1') is larger than the threshold Th1 (NO in S102), the lens is determined in S103 according to the corrected first detected defocus amount (Def1 '). Drive is performed, and the process returns to S100. If the corrected first detected defocus amount (Def1 ′) | Def1 ′ | is equal to or smaller than the threshold Th1 (YES in S102), the process proceeds to S200.

  In S200, the second detection defocus amount (Def2) is detected by the second focus detection by the refocus method. If the detected magnitude | Def2 | of the second defocus amount (Def2) is larger than the threshold Th2 (<threshold Th1) (NO in S201), the lens is determined in S202 according to the second defocus amount (Def2). Drive is performed, and the process returns to S200. When the detected magnitude | Def2 | of the second defocus amount (Def2) is equal to or smaller than the threshold Th2 (YES in S201), the focus adjustment operation is terminated.

  In the first embodiment, the first detection defocus amount detected by the first focus detection is corrected using the correction value stored in accordance with the state of the imaging optical system, and the correction value is calculated. Used to drive the lens to near the in-focus position. Thereby, even when the second focus detection cannot be performed because the subject has a low contrast or the illuminance is low, the focus adjustment can be performed with high accuracy.

  Further, since the lens is driven to near the in-focus position using the corrected first detection defocus amount, the second focus detection can be performed near the in-focus position as compared with the case where the correction is not performed. Thereby, it is possible to secure a wider defocus range in which focus detection is possible in the second focus detection.

  In the first embodiment, since the second focus detection is performed after the lens is driven based on the corrected first detection defocus amount, the focus detection with high accuracy is possible. However, since the two focus detection processes are performed continuously, the focus detection time interval becomes longer and the detection accuracy becomes longer during continuous AF in which focus detection is continued for a subject moving in the optical axis direction of the imaging optical system. May lead to deterioration. In such a continuous AF or when continuous shooting is repeated with continuous AF, the second focus detection may be omitted. In the present invention, since continuous AF can be performed as a result of correcting the first detection defocus amount by the focus detection correction value, a highly accurate focus adjustment state can be maintained.

  In the first embodiment, the reason why the threshold value Th1 is larger than the threshold value Th2 is to perform focus detection with higher accuracy by the second focus detection. In the first focus detection, the focus adjustment may be performed up to the defocus range in which the second focus detection is possible, and therefore the threshold value Th1 may be larger than the threshold value Th2. Thereby, it is possible to shift from the first focus detection to the second focus detection at a higher speed. However, when the second focus detection is omitted, the threshold value Th1 may be reduced and set equal to the threshold value Th2. This is because high-precision focus adjustment can be realized even when the focus detection process is finished based on the corrected first detection defocus amount.

  With the above configuration, the difference between the detection focus position calculated from the focus detection signal and the best focus position of the imaging signal is suppressed, and high-precision focus detection is possible.

<Second Embodiment>
Next, a second embodiment of the present invention will be described. FIG. 22 is a flowchart showing the flow of focus detection processing in the second embodiment. In the second embodiment, whether or not to perform the second focus detection is switched depending on the condition, and the case where the focus detection is performed at high speed when the second focus detection process is not performed will be described. Since other processes and the configuration of the imaging apparatus are the same as those described in the first embodiment, description thereof is omitted.

  In S100 of FIG. 22, the first detection defocus amount (Def1) is detected by the first focus detection by the phase difference method. Thereafter, in S101, the first detected defocus amount is corrected, and the corrected first detected defocus amount (Def1 ′) is calculated. The correction performed here is performed using the correction value stored in accordance with the state of the imaging optical system as described above. If the magnitude | Def1 '| of the corrected first defocus amount (Def1') is larger than the threshold Th1 (NO in S102), the lens is determined in S103 according to the corrected first detected defocus amount (Def1 '). Drive is performed, and the process returns to S100.

  When the magnitude | Def1 ′ | of the corrected first detection defocus amount (Def1 ′) is equal to or smaller than the threshold Th1 (YES in S102), the image height of the focus detection area is larger than the threshold Th3 (first threshold). Whether or not it is small is determined. If it is small (YES in S110), the focus adjustment operation is terminated. The image height of the focus detection area is calculated by the distance between the centers of the nine focus detection areas exemplified in FIG. 7 and the center of the effective pixel area 1000 (imaging range). In general, the closer the image height of the focus detection area is to 0, the smaller the individual variation of each aberration of the imaging optical system. Therefore, sufficiently high-precision focus detection can be performed by the correction using the focus detection correction value without performing the second focus detection. Therefore, in the second embodiment, when the image height of the focus detection area is smaller than the threshold Th3, focus detection can be performed at high speed by not performing the second focus detection.

  On the other hand, if the image height of the focus detection area is greater than or equal to the threshold Th3 (NO in S110), it is determined in S111 whether or not the subject distance is farther than the threshold Th4 (second threshold). If the subject distance is longer than the threshold Th4 (YES in S111), the focus adjustment operation is terminated. The subject distance is stored in the CPU 121 in association with the position of the third lens group 105 of the imaging optical system, so that the subject distance is calculated based on the position of the third lens group 105 and the first detected defocus amount. be able to. In general, the farther the subject distance, the smaller the amount of each aberration of the imaging optical system and the smaller the individual variation. Therefore, sufficiently high-precision focus detection can be performed by the correction using the focus detection correction value without performing the second focus detection. In the second embodiment, when the subject distance is farther than the threshold Th4, focus detection can be performed at high speed by not performing the second focus detection.

  If the subject distance is equal to or smaller than the threshold Th4 (NO in S111), the process proceeds to S200 as in the first embodiment. Since the processing after S200 is the same as the processing described with reference to FIG. 21 in the first embodiment, description thereof is omitted here.

  In the second embodiment, when the individual variation of each aberration of the imaging optical system is expected to be small, the focus detection can be performed with sufficiently high accuracy by the correction using the focus detection correction value. By omitting, focus detection can be performed at high speed. In the second embodiment, the likelihood of the individual variation of each aberration of the imaging optical system is determined using both the image height of the focus detection area and the subject distance, but either one is used. May be determined.

  Further, the method for determining the magnitude of individual variation of each aberration of the imaging optical system is not limited to the above method. For example, it is conceivable to determine whether or not to perform the second focus detection based on the F number of the imaging optical system. When the F number is small, the amount of each aberration of the imaging optical system is large, and thus individual variation is large. Therefore, when the F number is larger than a predetermined value, it is conceivable to omit the second focus detection.

  As another method, whether the second focus detection is performed depending on whether or not the correction value stored as the focus detection correction value is a value including individual variation (individual difference) of the imaging optical system. It is conceivable to determine whether or not. When the focus detection correction value is measured and stored for each individual at the time of manufacturing the imaging device, the focus detection correction value includes individual variation, and thus it is conceivable to omit the second focus detection. In particular, if there is an interchangeable lens type imaging device with an interchangeable imaging optical system, the focus detection correction value may or may not include individual variations in the imaging optical system, depending on the interchangeable lens. Whether or not to perform the second focus detection may be switched by the interchangeable lens.

  As another method, corresponding to the astigmatism of the imaging optical system, the focus detection correction value is made independent of the correction value in the radial direction and the correction value in the concentric direction with respect to the optical axis of the imaging optical system. It is possible to memorize it. In this case, the focus detection correction value exemplified in FIG. 20 is set to the radiation direction with respect to the optical axis of the imaging optical system for focus detection regions other than the central focus detection region A (2, 2). Two types of concentric directions are stored. In the configuration of the second embodiment, the first focus detection and the second focus detection perform focus detection in one horizontal direction. For this reason, when there is a large difference between the focus detection correction values in the radiation direction and the concentric direction, high-precision focus detection cannot be performed even if the second focus detection is performed on a subject having a contrast other than the horizontal direction. For this reason, it is conceivable to omit the second focus detection when there is a large difference between the focus detection correction values in the radiation direction and the concentric direction.

  In the second embodiment, the threshold value Th1 is set to a larger value than the threshold value Th2 because the focus detection is performed with higher accuracy by the second focus detection. In the first focus detection, the focus adjustment may be performed up to the defocus range in which the second focus detection is possible, and therefore the threshold value Th1 may be larger than the threshold value Th2. Thereby, it is possible to shift from the first focus detection to the second focus detection at a higher speed. However, when the second focus detection is omitted, the threshold value Th1 may be reduced and set equal to the threshold value Th2. This is because high-precision focus adjustment can be realized even when the focus detection process is finished based on the corrected first detection defocus amount.

  As described above, according to the second embodiment, the difference between the detection focus position calculated from the focus detection signal and the best focus position of the imaging signal is suppressed, and high-precision focus detection is possible.

<Third Embodiment>
Next, a third embodiment of the present invention will be described. In the third embodiment, the focus detection correction value for correcting the first detection defocus amount is an angle formed by the horizontal direction, which is the direction of shift processing performed in the first focus detection, and the radiation direction of the imaging optical system. To change. As a result, a more accurate focus detection correction value can be calculated. Since other processes and the configuration of the imaging apparatus are the same as those described in the first embodiment, description thereof is omitted.

  In the third embodiment, the focus detection correction value is stored independently of the correction value in the radial direction and the correction value in the concentric direction with respect to the optical axis of the imaging optical system. In this case, the focus detection correction values exemplified in FIG. 20 of the first embodiment are set to 2 in the concentric direction and the radiation direction for the focus detection areas other than the central focus detection area A (2, 2). Remember the type.

When the correction value in the radiation direction in the state where the imaging optical system is present is BPm, the correction value in the concentric circle direction is BPs, and the angle between the straight line connecting the center of the focus detection area and the center of the effective pixel area 1000 and the horizontal direction is θ. The focus detection correction value BP to be used is calculated by the following equation (4).
BP = BPm x cosθ + BPs x (1-cosθ) (4)
The first detection defocus amount is corrected using the focus detection correction value calculated by Expression (4). As a result, the lens can be driven to near the in-focus position with higher accuracy, so even when the second focus detection cannot be performed under conditions such as low contrast of the subject or low illuminance, high-precision focus adjustment is possible. It can be carried out.

  In addition, in order to perform correction with higher accuracy, the second focus detection can be performed near the in-focus state. Thereby, it is possible to secure a wider defocus range in which focus detection is possible in the second focus detection.

<Fourth Embodiment>
Next, a fourth embodiment of the present invention will be described. FIG. 23 is a flowchart illustrating a flow of focus detection processing according to the fourth embodiment. In the fourth embodiment, the detection of the first detection defocus amount by the first focus detection of the phase difference method and the detection of the second detection defocus amount by the second focus detection of the refocus method are processed in parallel, and high speed processing is performed. An example of performing focus detection will be described. In addition, the same step number is attached | subjected to the process similar to the process demonstrated with reference to FIG. 22 in 2nd Embodiment. Since other processes and the configuration of the imaging apparatus are the same as those described in the first embodiment, description thereof is omitted.

  In S100 of FIG. 23, the first detection defocus amount (Def1) is detected by the first focus detection by the phase difference method. In S101, the first detection defocus amount is corrected, and the corrected first detection defocus amount is detected. A focus amount (Def1 ′) is calculated. In parallel, in S200, the second detection defocus amount (Def2) is detected by the second focus detection by the refocus method.

  Next, in S300, when the second detection defocus amount (Def2) is detected within the shift range of the second shift process, the process proceeds to S301, and the second detection defocus amount (Def2) is third detected. A defocus amount (Def3) is assumed. When not detected, it progresses to S302 and makes 1st detection defocus amount (Def1 ') after correction | amendment 3rd detection defocus amount (Def3). In the next S303, if the magnitude | Def3 | of the third defocus amount (Def3) is larger than the threshold Th2, the lens is driven in S304 according to the third defocus amount (Def3), and S100 and S200 are performed. Return. When the magnitude | Def3 | of the third defocus amount (Def3) is equal to or smaller than the threshold value Th2, the focus adjustment operation is terminated.

  As described above, according to the fourth embodiment, the difference between the detection focus position calculated from the focus detection signal and the best focus position of the imaging signal is suppressed, and high-precision focus detection is possible.

<Fifth Embodiment>
Next, a fifth embodiment of the present invention will be described. In the fifth embodiment, the configuration of the width pixels of the image sensor 107 is different from that shown in FIG. Since other processes and the configuration of the imaging apparatus are the same as those described in the first embodiment, description thereof is omitted.

  FIG. 24 shows the pixel (imaging pixel) array of the image sensor 107 (two-dimensional CMOS sensor) in the fifth embodiment in a range of 4 columns × 4 rows, and the sub-pixel array in a range of 8 columns × 8 rows. Is. In the configuration shown in FIG. 2, each pixel is divided into sub-pixels of 2 columns × 1 row, whereas in the configuration shown in FIG. 24, each pixel is sub-pixelated from sub-pixels 241 of 2 columns × 2 rows. The place where the pixel 244 is configured is different.

  A large number of 4 columns × 4 rows of pixels (8 columns × 8 rows of sub-pixels) shown in FIG. 24 are arranged on the surface, and a captured image (sub-pixel signal) can be acquired. In the fifth embodiment, the pixel period P is 4 μm, the pixel number N is 5575 columns × 3725 rows = approximately 20.75 million pixels, the subpixel cycle PSUB is 2 μm, and the subpixel number NSUB is 11150 columns × 7450 pixels. The description will be made assuming that the image sensor having a row = about 83 million pixels.

FIG. 25A shows a plan view of one pixel 200G of the image sensor 107 shown in FIG. 24 as viewed from the light receiving surface side (+ z side) of the image sensor 107, and a cross section taken along the line aa in FIG. FIG. 25 (b) shows a cross-sectional view as seen from the −y side. As shown in FIG. 25, in the pixel 200G of the fifth embodiment, a microlens 305 for condensing incident light is formed on the light receiving side of each pixel, and is divided into _{NH in} the x direction (two divisions), y the photoelectric conversion unit 304 from N _V division (2 divided) photoelectric conversion unit 301 is formed in the direction. Photoelectric converters 301 to 304 correspond to subpixels 241 to 204, respectively.

  In the fifth embodiment, an image signal (captured image) having a resolution of N effective pixels is generated by adding the signals of the sub-pixels 241 to 204 for each pixel of the image sensor 107.

  In the fifth embodiment, the first focus detection signal is generated by adding the signals of the sub-pixel 241 and the sub-pixel 243 for each pixel, and the signals of the sub-pixel 242 and the sub-pixel 204 are added together. A bifocal detection signal can be generated. By these addition processes, the first focus detection signal and the second focus detection signal corresponding to the pupil division in the horizontal direction can be acquired, and the first focus detection of the phase difference method and the second focus detection of the refocus method can be performed. it can. That is, in this case, the subpixel 241 and the subpixel 243 correspond to the first focus detection pixel, and the subpixel 242 and the subpixel 244 correspond to the second focus detection pixel.

  Similarly, in the fifth embodiment, for each pixel, the signals of the subpixel 241 and the subpixel 242 are added to generate a first focus detection signal, and the signals of the subpixel 243 and the subpixel 244 are added. A second focus detection signal can be generated. By these addition processes, the first focus detection signal and the second focus detection signal corresponding to the pupil division in the vertical direction can be acquired, and the first focus detection of the phase difference method and the second focus detection of the refocus method can be performed. it can. That is, in this case, the subpixel 241 and the subpixel 242 correspond to the first focus detection pixel, and the subpixel 243 and the subpixel 244 correspond to the second focus detection pixel.

  As described above, according to the fifth embodiment, the detected in-focus position calculated from the focus detection signal and the imaging signal, regardless of whether the subject has a high frequency component in either the horizontal direction or the vertical direction. It is possible to suppress a difference from the best in-focus position and to detect a focus with high accuracy.

  Needless to say, the image sensor 107 according to the fifth embodiment can be used as the image sensor 107 according to the first to fourth embodiments.

Claims (8)

An imaging device having a first focus detection pixel and a second focus detection pixel that respectively receive a pair of light beams that have passed through different pupil partial regions of the imaging optical system;
A correlation amount between the first focus detection signal output from the first focus detection pixel in the focus detection region and the second focus detection signal output from the second focus detection pixel is calculated, and based on the correlation amount First focus detection means for detecting a first detection defocus amount indicating a difference to the in-focus position;
A contrast evaluation value for each shift amount is calculated from a shift addition signal obtained by adding the first focus detection signal and the second focus detection signal while shifting each other, and based on the contrast evaluation value, the contrast evaluation value is calculated. Second focus detection means for detecting a second detection defocus amount indicating a difference to the focal position;
Focus detection for suppressing the difference between the focus position at which the contrast of the signal obtained by the light beam that has passed through the pupil region of the imaging optical system is maximum and the focus position corresponding to the first detection defocus amount Storage means for storing a correction value as a value corresponding to a zoom position and a focus position of the imaging optical system;
After the focus adjustment based on the defocus amount corrected by said stored focus detection correction value in the storage means the first detecting defocus amount, the adjusted focal point based on the second detection defocus amount It possesses a focus adjustment means for performing,
The focus adjusting unit does not perform focus adjustment based on the second detected defocus amount when at least one of an image height of the focus detection area or a distance to a subject satisfies a predetermined condition. Imaging device. The focus adjustment unit does not perform focus adjustment based on the second detected defocus amount when the focus adjustment by the focus adjustment unit is continuously performed in order to keep the focused state. The imaging device according to claim 1 . If the image height is less than the first threshold value determined in advance, the focal point adjusting means, according to claim 1 or 2, characterized in that does not perform focus adjustment based on the second detection defocus amount Imaging device. It further has an acquisition means for acquiring information related to the distance to the subject,
Distance to the subject is, is larger than a second threshold previously determined, the focusing means to claim 1, characterized in that not adversely line focus adjustment based on the second detection defocus amount 4. The imaging device according to any one of 3 . The imaging optical system is replaceable, and it is selected whether or not to perform focus adjustment based on the second detection defocus amount based on individual variation of the mounted imaging optical system. The imaging device according to any one of claims 1 to 4 . If third greater than the threshold value F-number of the imaging optical system is predetermined, said focusing means, claims, characterized in that not adversely line focus adjustment based on the second detection defocus amount The imaging device according to any one of 1 to 5 . The focus detection correction value includes a focus detection correction value in a radial direction and a focus detection correction value in a concentric direction with respect to the optical axis of the imaging optical system,
The focus detection correction value in the radiation direction and the focus detection correction value in the concentric direction according to the angle formed by the deviation direction between the radiation direction or the concentric circle direction and the first focus detection signal and the second focus detection signal. with focus detection correction value calculated by weight the imaging apparatus according to any one of claims 1 to 6, characterized in that to correct the first detection defocus amount. A method for controlling an imaging apparatus having an imaging element having a first focus detection pixel and a second focus detection pixel that respectively receive a pair of light beams that have passed through different pupil partial regions of an imaging optical system,
The first focus detection means calculates a correlation amount between the first focus detection signal output from the first focus detection pixel in the focus detection area and the second focus detection signal output from the second focus detection pixel. A first focus detection step of detecting a first detection defocus amount indicating a difference to the in-focus position based on the correlation amount;
The correction unit suppresses a difference between a focus position at which a contrast of a signal obtained by the light beam that has passed through the pupil region of the imaging optical system is maximum and a focus position corresponding to the first detection defocus amount. A focus detection correction value corresponding to the first detection defocus amount is read out from a storage unit that stores a focus detection correction value for the focus as a zoom position and a focus position of the imaging optical system. A correction step of correcting the first detection defocus amount using a detection correction value;
A second focus detection unit calculates a contrast evaluation value for each shift amount from a shift addition signal obtained by adding the first focus detection signal and the second focus detection signal while shifting each other, and the contrast A second focus detection step of detecting a second detection defocus amount indicating a difference to the in-focus position based on the evaluation value;
The focus adjustment unit performs focus adjustment based on the defocus amount obtained by correcting the first detection defocus amount with the focus detection correction value stored in the storage unit, and then based on the second detection defocus amount. focus Te point adjustment possess a focusing step of performing,
In the focus adjustment step, focus adjustment based on the second detection defocus amount is not performed when at least one of the image height of the focus detection region and the distance to the subject satisfies a predetermined condition. Control method of imaging apparatus.

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