JP6854619B2 - Focus detection device and method, imaging device, lens unit and imaging system - Google Patents

Description

The present invention relates to a focus detection device and method, an image pickup device, a lens unit, and an image pickup system, and in particular, a focus detection device that performs focus detection based on a signal obtained by photoelectric conversion of light incident through a photographing optical system. And methods, imaging devices, lens units and imaging systems.

Conventionally, the phase difference AF method has been known as a general method for automatic focus detection (AF) of an imaging device. The phase-difference AF method is an AF method often used in video cameras and digital still cameras, and there are some in which an image sensor is used as a focus detection sensor.

In the phase difference AF method, the amount of image shift (phase difference) is detected from the degree of correlation between the pair of image signals by the pair of image signals representing the optical image by the focus detection pixels on the image sensor. Further, the defocus amount is calculated by multiplying the image shift amount by the conversion coefficient, and the focus state is detected. However, since the above AF method performs focus detection using an optical image, an error may occur in the focus detection result due to the aberration of the optical system of the photographing lens.

Therefore, in Patent Document 1, the conversion coefficient is multiplied by a predetermined coefficient according to the detected defocus amount to switch the value of the conversion coefficient, thereby improving the accuracy of the phase difference AF according to the defocus change. The method of planning is disclosed. The change in the conversion coefficient according to the defocus amount is due to the fact that the pair of ranging pupil distributions (the light amount distribution of the pair of focal detection luminous fluxes on the ranging pupil surface) becomes asymmetric with respect to the center of gravity. It is supposed to occur.

Japanese Unexamined Patent Publication No. 2013-054120

However, the configuration of Patent Document 1 has a problem that the focus detection error cannot be sufficiently corrected. Patent Document 1 mentions that the conversion coefficient changes depending on the distance measuring pupil distribution, but does not describe in detail a method of calculating the conversion coefficient according to the aberration of the photographing optical system. That is, when the defocus amount having the same absolute value is detected, that is, in the state of the photographing optical system in which the defocus amount of + X and the defocus amount of −X are detected, the conversion coefficient calculated in Patent Document 1 is The values are the same. However, even if the absolute value is the same defocus amount, the value of the conversion coefficient to be calculated is originally different due to the aberration of the photographing optical system and the like.

The present invention has been made in view of the above problems, and an object of the present invention is to enable more accurate focus adjustment according to aberrations of the photographing optical system and the like.

In order to achieve the above object, the focus detection device of the present invention is obtained from an image pickup device that includes a plurality of photoelectric conversion units for each of the plurality of microlenses and photoelectrically converts light incident through the photographing optical system. Further, the detection means for detecting the signed image shift amount indicating the defocus direction in the optical axis direction based on the correlation amount of the pair of pupil-divided signals, and the signed image shift amount by the conversion coefficient. having conversion means for converting the defocus amount of the optical axis direction, based on the aberration information of the imaging optical system, a calculation unit configured to calculate the transform coefficients corresponding to the image shift amount each signed, the The conversion means uses the conversion coefficient corresponding to the signed image shift amount detected by the detection means for the conversion.

According to the present invention, the focus can be adjusted with higher accuracy according to the aberration of the photographing optical system and the like.

The block diagram which shows the schematic structure of the digital camera in embodiment of this invention. The figure which shows the structural example of the image pickup device in embodiment. The figure which shows the relationship between the photoelectric conversion region and an exit pupil in an embodiment. The figure which shows the example of the focus detection area in an embodiment. The flowchart which shows the AF operation and the calculation method of the conversion coefficient in 1st Embodiment. Explanatory drawing about correlation calculation of a focus detection signal. Explanatory drawing about the correlation amount of a focus detection signal. The figure for demonstrating the calculation method of the conventional conversion coefficient. The figure which shows an example of the pupil division image which does not include the aberration in the position in a different Z direction. The figure which shows an example of the pupil division image which contains the aberration at the position in a different Z direction. The figure which shows an example of the pupil division image after the filter processing in 1st Embodiment. The figure which shows an example of the prediction curve in 1st Embodiment. The figure which shows an example of the conversion coefficient in 1st Embodiment. The flowchart which shows the calculation method of the conversion coefficient in 2nd Embodiment.

Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the accompanying drawings. The embodiment has a specific and specific configuration in order to facilitate understanding and explanation of the invention, but the present invention is not limited to such a specific configuration. For example, although the embodiment in which the present invention is applied to a single-lens reflex type digital camera with interchangeable lenses will be described below, the present invention can also be applied to a digital camera of a non-interchangeable lens type and a video camera. It can also be carried out on any electronic device equipped with a camera, such as a mobile phone, a personal computer (laptop, tablet, desktop type, etc.), a game machine, or the like.

<First Embodiment>
(Explanation of the configuration of the imaging device-lens unit)
FIG. 1 is a block diagram showing a functional configuration example of a digital camera as an example of an imaging device (imaging system) according to an embodiment. As described above, the digital camera of the present embodiment is an interchangeable lens type single-lens reflex camera, and has a lens unit 100 and a camera body 120. The lens unit 100 is attached to the camera body 120 via the mount M shown by the dotted line in the center of the figure.

The lens unit 100 includes an optical system including a first lens group 101, an aperture combined shutter 102, a second lens group 103, a focus lens group 140 (hereinafter, simply referred to as a "focus lens"), and a drive / control system. Has. As described above, the lens unit 100 is a photographing lens including the focus lens 104 and forming an optical image of the subject.

The first lens group 101 is arranged at the tip of the lens unit 100 and is movably held in the optical axis direction OA. The aperture combined shutter 102 functions not only as a function of adjusting the amount of light at the time of shooting by adjusting the aperture diameter thereof, but also as a mechanical shutter for controlling the exposure time at the time of shooting a still image. The aperture combined shutter 102 and the second lens group 103 can be integrally moved in the optical axis direction OA, and the zoom function is realized by moving in conjunction with the first lens group 101. Further, the focus lens 104 can also be moved in the optical axis direction OA, and the subject distance (focusing distance) at which the lens unit 100 is focused changes according to the position. By controlling the position of the focus lens 104 in the optical axis direction OA, the focus adjustment for adjusting the focusing distance of the lens unit 100 is performed.

The drive / control system includes a zoom actuator 111, an aperture shutter actuator 112, a focus actuator 113, a zoom drive circuit 114, an aperture shutter drive circuit 115, a focus drive circuit 116, a lens MPU (microprocessor) 117, and a lens memory 118.

The zoom drive circuit 114 drives the zoom actuator 111 according to the zoom operation of the photographer to drive the first lens group 101 to the second lens group 103 in the optical axis direction OA, thereby driving the optical system of the lens unit 100. Control the angle of view of. The aperture shutter drive circuit 115 drives the aperture combined shutter 102 by using the aperture shutter actuator 112, and controls the aperture diameter and the opening / closing operation of the aperture combined shutter 102. The focus drive circuit 116 drives the focus lens 104 in the optical axis direction OA by using the focus actuator 113 to change the focusing distance of the optical system of the lens unit 100. Further, the focus drive circuit 116 detects the current position of the focus lens 104 by using the focus actuator 113.

The lens MPU 117 performs all calculations and controls related to the lens unit 100, and controls the zoom drive circuit 114, the aperture shutter drive circuit 115, and the focus drive circuit 116. Further, the lens MPU 117 is connected to the camera MPU (microprocessor) 125 through the mount M to communicate commands and data. For example, the lens MPU 117 detects the position of the focus lens 104 on the optical axis and notifies the lens position information in response to a request from the camera MPU 125. This lens position information includes the position of the focus lens 104 in the optical axis direction OA, the position and diameter of the exit pupil in the optical axis direction OA when the optical system is not moving, and the optical axis of the lens frame that limits the light beam of the exit pupil. Includes information such as position and diameter in direction OA. Further, the lens MPU 117 controls the zoom drive circuit 114, the aperture shutter drive circuit 115, and the focus drive circuit 116 in response to a request from the camera MPU 125. The lens memory 118 stores in advance optical information necessary for automatic focus detection. The camera MPU 125 controls the operation of the lens unit 100 by, for example, executing a program stored in the built-in non-volatile memory or the lens memory 118.

(Explanation of the configuration of the imaging device-camera body)
The camera body 120 has an optical system including an optical low-pass filter (LPF) 121 and an image sensor 122, and a drive / control system. The first lens group 101 of the lens unit 100, the shutter 102 for both aperture, the second lens group 103, the focus lens 104, and the optical LPF 121 of the camera body 120 constitute a photographing optical system.

The optical LPF 121 reduces false colors and moire of captured images. The image sensor 122 is composed of a CMOS image sensor and peripheral circuits, and a plurality of pixels composed of m pixels in the horizontal direction and n pixels in the vertical direction (n and m are integers of 2 or more) are arranged in a matrix. The image pickup device 122 of the present embodiment has pixels having a pupil division function as described later with reference to FIG. 2, and photoelectrically converts the light incident through the photographing optical system to output an image signal. To do.

The drive / control system includes an image sensor drive circuit 123, an image processing circuit 124, a camera MPU 125, a display 126, an operation switch group 127, a memory 128, and an image pickup surface phase difference focus detection unit 129.

The image sensor drive circuit 123 controls the operation of the image sensor 122, converts the acquired image signal into A / D, and transmits the acquired image signal to the camera MPU 125 and the image processing circuit 124. The image processing circuit 124 performs general image processing performed by a digital camera, such as γ conversion, white balance adjustment processing, color interpolation processing, and compression coding processing, on the image data output from the image sensor 122. Generate image data for display / recording. The image processing circuit 124 also generates focus detection data for phase-difference AF.

The camera MPU 125 performs all calculations and controls related to the camera body 120, and controls the image sensor drive circuit 123, the image processing circuit 124, the display 126, the operation switch group 127, the memory 128, and the image pickup surface phase difference focus detection unit 129. To do. Further, the camera MPU 125 is connected to the lens MPU 117 via the signal line of the mount M, and communicates commands and data with the lens MPU 117. The camera MPU 125 requests the lens MPU 117 to acquire the lens position, the aperture combined shutter 102 with a predetermined drive amount, the focus lens 104, the zoom drive request, the optical information specific to the lens unit 100, and the like. To do. The camera MPU 125 includes a ROM (Read Only Memory) 125a that stores a program that controls camera operation, a RAM (Random Access Memory) 125b that stores variables, and an EEPROM (Electrically Erasable Programmable Read-Only Memory) that stores various parameters. ) 125c is built-in.

The display 126 is composed of an LCD (Liquid Crystal Display) or the like, and displays information on a shooting mode of the camera, a preview image before shooting and a confirmation image after shooting, an in-focus state display image at the time of focus detection, and the like. The operation switch group 127 includes a power switch, a release (shooting trigger) switch, a zoom operation switch, a shooting mode selection switch, and the like. The memory 128 is a detachable flash memory for recording captured images.

The imaging surface phase difference focus detection unit 129 performs focus detection processing (imaging surface phase difference AF) by a phase difference detection method using the focus detection data obtained by the image processing circuit 124. More specifically, the image processing circuit 124 generates a pair of image data formed by the light flux passing through the pair of pupil regions of the photographing optical system as focus detection data, and the imaging surface phase difference focus detection unit 129 The amount of focus shift is detected based on the amount of shift of the pair of image data. As described above, the imaging surface phase difference focus detection unit 129 of the present embodiment performs phase difference AF based on the output of the image sensor 122 without using a dedicated AF sensor. The operation of the imaging surface phase difference focus detection unit 129 will be described in detail later.

(Explanation of focus detection operation: phase difference AF)
Hereinafter, the operation of the imaging surface phase difference focus detection unit 129 will be described in more detail. FIG. 2A is a diagram schematically showing the pixel arrangement of the image sensor 122 in the present embodiment, and covers a range of 6 rows in the vertical direction (Y direction) and 8 columns in the horizontal direction (X direction) of the two-dimensional CMOS area sensor. The state observed from the lens unit 100 side is shown. The image sensor 122 is provided with a Bayer-arranged color filter. The odd-row pixels 211 are alternately green (G) and red (R) color filters from the left, and the even-row pixels 211 are on the left. Blue (B) and green (G) color filters are arranged alternately in order from the beginning. In the pixel 211, the circle 211i represents an on-chip microlens, and the plurality of rectangles 211a and 211b arranged inside the on-chip microlens 211i are photoelectric conversion units, respectively.

In the image sensor 122 of the present embodiment, the photoelectric conversion units of all the pixels 211 are divided into two in the X direction, and the photoelectric conversion signals of the individual photoelectric conversion units and the sum of the photoelectric conversion signals can be read out independently. Further, by subtracting the photoelectric conversion signal of one photoelectric conversion unit from the sum of the photoelectric conversion signals, a signal corresponding to the photoelectric conversion signal of the other photoelectric conversion unit can be obtained. The photoelectric conversion signal in each photoelectric conversion unit can be used as focus detection data for phase difference AF, or can be used to generate a parallax image constituting a 3D (3-Dimensional) image. Further, the sum of the photoelectric conversion signals can be used as normal captured image data.

Here, the pixel signal when performing phase difference AF will be described. As will be described later, in the present embodiment, the emission light flux of the photographing optical system is divided into pupils by the microlens 211i shown in FIG. 2A and the divided photoelectric conversion units 211a and 211b. Then, for a plurality of pixels 211 within a predetermined range arranged in the same pixel row, the outputs of the photoelectric conversion unit 211a are connected and organized, and the AF image A and the outputs of the photoelectric conversion unit 211b are connected and organized. Let the thing be a B image for AF. As the output of the photoelectric conversion units 211a and 211b, a pseudo luminance (Y) signal calculated by adding the outputs of green, red, blue, and green included in the unit array of the color filter is used. However, the AF image A and the AF image B may be organized for each of the red, blue, and green colors.

By detecting the relative image shift amount between the AF A image and the AF B image generated in this way by correlation calculation, it is possible to detect the prediction amount [bit] which is the degree of correlation between the pair of image signals. it can. The camera MPU 125 can be converted into a defocus amount [mm] in a predetermined region by multiplying the prediction amount by a conversion coefficient. In the present embodiment, the sum of the output of one photoelectric conversion unit and the output of all photoelectric conversion units is read from the image sensor 122 from each pixel. For example, when the sum of the output of the photoelectric conversion unit 211a and the output of the photoelectric conversion units 211a and 211b are read, the output of the photoelectric conversion unit 211b is obtained by subtracting the output of the photoelectric conversion unit 211a from the sum. As a result, both the AF image A and the AF image B can be obtained, and phase-difference AF can be realized. Further, the sum of the outputs of the photoelectric conversion unit generally forms one pixel (output pixel) of the output image. Since such an image sensor is known as disclosed in Japanese Patent Application Laid-Open No. 2004-134876, further detailed description thereof will be omitted.

FIG. 2B is a diagram showing a configuration example of a readout circuit of the image pickup device 122 of the present embodiment. Reference numeral 151 is a horizontal scanning circuit, and reference numeral 153 is a vertical scanning circuit. Horizontal scanning lines 152a and 152b and vertical scanning lines 154a and 154b are wired at the boundary of each pixel, and each photoelectric conversion unit reads a signal to the outside via these scanning lines. By control by the vertical scanning circuit 153, the sum of the photoelectric conversion signals can be read out from the photoelectric conversion units 211a and 211b, and a pair of signals of the photoelectric conversion units 211a and 211b can be read out so as to be acquired.

The image sensor of the present embodiment has the following two types of readout modes in addition to the above-mentioned in-pixel readout method. The first readout mode is called an all-pixel readout mode, which is a mode for capturing a high-definition still image. In this case, the signals of all pixels are read out.

The second read mode is called a thinning read mode, which is a mode for recording a moving image or displaying only a preview image. Since the number of pixels required in this case is smaller than that of all pixels, only the pixels thinned out at a predetermined ratio in both the X direction and the Y direction are read out as the pixel group. Also, when it is necessary to read at high speed, the thinning read mode is used in the same manner. When thinning out in the X direction, signals are added to improve S / N, and when thinning out in the Y direction, the signal output of the thinned line is ignored. Phase-difference AF is also usually performed based on the signal read in the second read mode.

FIG. 3 is a diagram illustrating a conjugate relationship between the exit pupil surface of the photographing optical system and the photoelectric conversion units 211a and 211b of the image pickup element 122 arranged near the center of the image plane, that is, the image height is zero in the image pickup apparatus of the present embodiment. Is. The photoelectric conversion units 211a and 211b in the image sensor 122 and the exit pupil surface of the photographing optical system are designed to have a conjugate relationship by the on-chip microlens 211i. Generally, the exit pupil of the photographic optical system substantially coincides with the surface on which the iris diaphragm for adjusting the amount of light is placed, but the photographic optical system of the present embodiment includes a zoom lens having a scaling function, and depending on the optical type. , The distance and size of the exit pupil from the image plane change when the magnification operation is performed. FIG. 3A shows a state in which the focal length of the lens unit 100 is at the center of the wide-angle end and the telephoto end. With the exit pupil distance Zep in this state as a standard value, the optimum design of the eccentricity parameter according to the shape of the on-chip microlens 211i and the image height (X, Y coordinates) is made.

In FIG. 3A, 101 is a first lens group, 101b is a lens barrel member that holds the first lens group, 104 is a focus lens, and 104b is a lens barrel member that holds the focus lens 104. 102 is a shutter that also serves as a diaphragm, 102a is an opening plate that defines the aperture diameter when the diaphragm is open, and 102b is a diaphragm blade for adjusting the aperture diameter when the diaphragm is opened. Note that 101b, 102a, 102b, and 104b, which act as limiting members for the light flux passing through the photographing optical system, show an optical virtual image when observed from the image plane. Further, the synthetic aperture in the vicinity of the diaphragm and shutter 102 is defined as the exit pupil of the lens, and the distance from the image plane is Zep as described above.

The pixel 211 is arranged near the center of the image plane, and is referred to as a center pixel in the present embodiment. From the bottom layer, the central pixel 211 is composed of photoelectric conversion units 211a and 211b, wiring layers 211e to 211g, color filters 211h, and on-chip microlens 211i. Then, the two photoelectric conversion units 211a and 211b are projected onto the exit pupil surface of the photographing optical system by the on-chip microlens 211i. In other words, the exit pupil of the photographing optical system is projected onto the surface of the photoelectric conversion unit via the on-chip microlens 211i.

FIG. 3B shows the projected images of the photoelectric conversion units 211a and 211b on the exit pupil surface of the photographing optical system, and the projected images on the photoelectric conversion units 211a and 211b are EP1a and EP1b, respectively. Further, in the present embodiment, the image sensor 122 has a pixel capable of obtaining the output of either one of the two photoelectric conversion units 211a and 211b and the output of the sum of both. The output of the sum of both is the photoelectric conversion of the luminous flux that has passed through both the projected images EP1a and EP1b, which are almost the entire pupil region of the photographing optical system. Therefore, the TL and the projected image in FIG. 3 (b) are obtained. A value corresponding to the luminous flux corresponding to the area where EP1a and EP1b overlap is output.

When performing phase-difference AF, the camera MPU 125 controls the image sensor drive circuit 123 so as to read the above-mentioned two types of outputs from the image sensor 122. Then, the camera MPU 125 gives information on the focus detection region to the image processing circuit 124, generates data of the AF image A and the AF B image from the output of the pixels included in the focus detection region, and generates the image plane position. It is instructed to supply to the phase difference focus detection unit 129. The image processing circuit 124 generates data for the AF image A and the AF image B according to this command and outputs the data to the imaging surface phase difference focus detection unit 129.

Although the configuration in which the exit pupil is divided into two in the horizontal direction has been described here as an example, a configuration in which the exit pupil is divided into two in the vertical direction may be used for some pixels of the image sensor 122. Further, the exit pupil may be divided in both the horizontal and vertical directions. By providing pixels that divide the exit pupil in the vertical direction, phase-difference AF corresponding to the contrast of the subject in the vertical direction as well as the horizontal direction becomes possible.

(Explanation of focus detection area)
FIG. 4 is a diagram showing an example of a focus detection region within the photographing range. As described above, the phase difference AF is performed based on the signal obtained from the pixels included in the focus detection region. In FIG. 4, the rectangle shown by the dotted line indicates the focus detection region 219 within the imaging range of the image sensor 122. In the example of FIG. 4, the pixels of afH (horizontal) × afV (vertical) [pix] are included. In FIG. 4, an example in which the focus detection area is set by performing face detection is shown, but the focus detection area may be set so as to include the main subject 220, or the focus detection area preset by the user may be used. .. The number, position and size are not limited to those shown.

(Explanation of the flow of focus detection processing)
Next, the automatic focus detection (AF) operation in the digital camera of the present embodiment will be described with reference to FIG. The following AF processing operations are mainly executed by the camera MPU 125, unless another subject is specified. Further, when the camera MPU 125 drives or controls the lens unit 100 by transmitting a command or the like to the lens MPU 117, the operating subject may be described as the camera MPU 125 for the sake of brevity.

First, in S1, the camera MPU 125 sets the focus detection region. As shown in FIG. 4, the focus detection area 219 set here may be determined by the main subject 220 or may be a preset focus detection area. Here, the coordinates (x, y) representing the focus detection area 219 are set with respect to the focus detection area. The representative coordinates (x, y) at this time may be, for example, the position of the center of gravity with respect to the focus detection region 219.

Next, in S2, the focus detection data is read out. By using the signals read from the pixels in the focus detection area 219 set in S1 by the method described above, the signals of the AF image A and the AF image B are generated.

Next, in S3, the camera MPU detects the relative image shift amount of the AF A image and the AF B image obtained in S2 by the correlation calculation, so that the image shift is a prediction amount [bit]. The quantity P [bit] is detected. Here, an example of the method of correlation calculation will be described with reference to FIG. It is assumed that in S2, the AF A image (hereinafter, A image) and AF B image (hereinafter, B image) signals as shown in FIG. 6A are read from the focus detection pixels. The camera MPU 125 first performs digital filter processing on the A image and the B image in order to reduce noise. The waveform after the filter processing of FIG. 6 (a) is shown in FIG. 6 (b). Then, as shown in FIGS. 6 (b) to 6 (e), the camera MPU 125 calculates the correlation amount COR at that time while bit-shifting either or both of the A image and the B image. The correlation amount COR at this time may be the area when the A image and the B image are overlapped, the area of the A image-the area of the B image, or any value as long as it is a calculated value representing the degree of correlation. ..

FIG. 7 illustrates the relationship between the shift amount [bit] and the correlation amount COR (here, the difference between the area of the A image and the area of the B image) when the A image and the B image shown in FIG. 6 are correlated. Is. When the A image and the B image match, the overlap between the A image and the B image becomes large, so that the correlation is the highest and the correlation amount COR becomes small. Here, since the shift amount [bit] when the correlation amount COR takes the minimum value is the image shift amount P, the image shift amount P = 2.6 [bit] is calculated by interpolation interpolation calculation or the like.

Next, in S4, the conversion coefficient K, which is a value for obtaining the defocus amount DEF, is obtained by multiplying the image shift amount P. The calculation method of the conversion coefficient K will be described in detail later.

Next, the camera MPU calculates the defocus amount DEF [mm] in S5 by the following calculation formula (1).
DEF = P × K… (1)

Next, in S6, the camera MPU 125 calculates the drive amount M [lensmm] of the focus lens 104 by the following equation (2) based on the defocus amount DEF obtained in S5, and drives the focus lens 104. ..
M = DEF / FS ... (2)

FS is a coefficient for converting the defocus amount DEF [mm] into the lens drive amount [lensmm], and is a value obtained from the lens MPU 117. The camera MPU 125 drives the focus lens 104 in the optical axis direction by the amount of the lens drive amount M to obtain a focus image suitable for the user's intention.
Next, the calculation method of the conversion coefficient K in the first embodiment will be described in detail with reference to FIGS. 5 (b) and 8. In S11, first, the state (calculation state) of the image pickup apparatus used for calculating the conversion coefficient K is acquired. The calculation states include the zoom position of the photographing optical system, the F value, the focus lens position, and the coordinates (x, y) of the focus detection area 219 set in S1 when AF detection is performed in FIG. 5 (a). The image shift amount P detected in S3 is stored or acquired from the lens MPU 117.

Next, in S12, the aberration information corresponding to the calculation state acquired by the camera MPU 125 in S11 is acquired from the lens MPU 117. Here, the reason why aberration information is required when calculating the conversion coefficient K will be described.

First, a conventional method of obtaining the conversion coefficient K will be described with reference to FIG. The Z-direction axis in FIG. 8 indicates the optical axis direction of the photographing optical system, and Z = 0 indicates the image sensor surface. Zep indicates the exit pupil distance described above. The pupil intensity distribution PI_A and the pupil intensity distribution PI_B, which are the light intensity distributions of the focal detection light fluxes of the A image and the B image on Z = Zep, are taken from the photoelectric conversion units 211a and 211b arranged on the matrix as shown in FIG. This is a projected image of the output focus detection signal projected onto the exit pupil surface. PI_A and PI_B in FIG. 8 show a one-dimensional pupil intensity distribution. PI_AB is a value obtained by adding the intensity distributions of PI_A and PI_B for each x-coordinate, and represents the pupil intensity distribution which is the light intensity distribution of the luminous flux of the output pixel (A + B image). In other words, the pupil intensity distribution PI_AB is divided into a pupil intensity distribution PI_A and a pupil intensity distribution PI_B.

Assuming that the distance between the center of gravity of PI_A and PI_B at this time is the baseline length BL, the amount of change [mm] in the optical axis direction with respect to the unit lateral displacement amount [bit] of the A image and the B image in the ratio of the exit pupil distance Zep and the baseline length BL ] Can be obtained. Therefore, the conversion coefficient K can be expressed by the following equation (3).
Conversion coefficient K [mm / bit] = Zep / BL ... (3)

In the above equation (3), the A image and the B image which are assumed to be detected at the positions in each Z direction have similar shapes of the pupil intensity distributions PI_A and PI_B. For example, as shown in FIG. 9, the pupil separation images at the Z = Z5 position are P_A (Z5) and P_B (Z5), and the pupil separation images at the Z = Z-5 position are P_A (Z-5), It is P_B (Z-5). On the image sensor surface with Z = 0, like P_A (0) and P_B (0), the luminous flux becomes a pulse shape and the luminous flux converges at one point, and the pupil separation images A and B completely match, but other than that. At the position in the Z direction, the pupil separation image has a similar shape to the pupil intensity distribution. Therefore, the conversion coefficient K calculated by the equation (3) converts the image shift amount P of the A image and the B image in the X direction into the defocus amount DEF in the optical axis direction.

However, at each position in the Z direction (for example, Z = Z5, 0, Z-5 in FIG. 9), the A image and the B image detected by the focus detection pixels are received through the photographing optical system. Actually, the characteristics including the aberration of the photographing optical system are received by the focus detection pixel. The aberration information of the photographing optical system at each position in the Z direction (Z = Z5, 0, Z-5 in FIG. 9) is shown in FIG. In FIG. 10, the line image intensity distribution of the photographing optical system is shown as an example of the aberration information.

The line image intensity distribution LSF_AB in FIG. 10 (a) shows the line image intensity distribution in the state where the pupils are not separated (A + B image), and the line image intensity distributions LSF_A and LSF_B in FIG. 10 (b) are pupils. The line image intensity distribution of the A image and the B image in the divided state is shown. Further, the A image and the B image actually received by the focus detection pixel have the line image intensity distributions LSF_A and LSF_B at the positions in each Z direction (Z = Z5, 0, Z-5 in FIG. 10) and the subject signal. It is a convoluted signal. Since the subject signal does not change according to the amount of defocus, the conversion coefficient K [mm / bit], which is the amount of change [mm] in the optical axis direction with respect to the unit lateral displacement amount [bit] of the A image and the B image, is the photographing optics. It is a value to be determined by the line image intensity distribution including the aberration information of the system.

As shown in the example of FIG. 9, the conversion coefficient K of the pupil separation image changes only by exchanging the P_A image and the P_B image depending on the sign of the position in the Z direction (Z = Z5, Z-5 in FIG. 9). No, that is, it had a symmetrical shape. On the other hand, as shown in the example of FIG. 10, since the shape of the line image intensity distribution differs depending on the code of the position in the Z direction (Z = Z5, Z-5 in FIG. 10), the conversion also differs depending on this code. You have to get the coefficient. That is, the absolute values of Z = Z5 and Z = Z-5 are the same at 5, but the line image intensity distribution shape is different between the positive Z = Z5 and the negative Z = Z-5.

Further, the larger the aberration of the photographing optical system, the more the value of the line image intensity distribution becomes an asymmetrical shape depending on the position and the sign in the Z direction. Therefore, in the present embodiment, in S12, the line image intensity distribution of FIG. 10B, which is the aberration information in the calculated state acquired in S11, is acquired. The position and the number of points in the Z direction for acquiring the aberration information are arbitrary, but it is desirable to acquire the aberration information in the prediction amount and the defocus range that covers the image shift amount P that can be calculated in S3. However, in view of the large amount of calculation, for example, the acquisition range of the aberration information may be changed according to the sign of the image shift amount P. Further, the aberration information is expressed as a function expressing the shape of the line image intensity distribution and may be stored in the camera ROM, or a typical parameter representing the shape (half width or the center of gravity of the A image and the B image). Interval) may be expressed.

Next, in S13, aberration information is converted for the line image intensity distributions LSF_A and LSF_B of the A image and the B image acquired in S12. Here, digital filter processing and correlation calculation are performed. The digital filter processing here applies the same digital filter as that used at the time of the correlation calculation in S3. This is because the frequency fluctuation of the line image intensity distribution that changes due to optical aberration is correctly detected according to the digital filter band, and the conversion coefficient K is calculated. When the line image intensity distribution of FIG. 10B is filtered, d_LSF_A and d_LSF_B are obtained as shown in FIG.

Further, at each position in the Z direction (Z = Z5, 0, Z-5), the waveform of the obtained aberration information (line image intensity distribution) after the digital filter is subjected to the correlation calculation processing by the method described above. , The correlation amount LSF_P for each position in the Z direction is calculated. The result is shown in FIG. FIG. 12 is a diagram showing a curve (hereinafter, referred to as “prediction curve”) when the calculated prediction amount Pred [bit] is plotted on the horizontal axis and the defocus amount def [mm] is plotted on the vertical axis. is there. The graph Cuv1 shown by the dotted line shows the prediction curve when there is no aberration in the photographing optical system (when the pupil separation image shown in FIG. 9 is the A image and the B image). The graph Cuv2 shown by the solid line shows the prediction curve when there is an aberration in the photographing optical system (when the line image intensity distribution obtained in S12 is an A image and a B image). Here, for example, the correlation amount LSF_P (5) = 3 at the position Z = Z5 (def = 5 mm) in the Z direction, and the correlation amount LSF_P (5) = 3 at the position Z = Z-5 (def = -5 mm) in the Z direction. The prediction curve Cuv2 when it is −3.5 is shown in the figure.

As described above, due to the aberration of the photographing optical system, the slope of the prediction curve changes depending on the sign of the position in the Z direction (the Pred differs between def = 5 mm and def = -5 mm), and the position in the Z direction. The slope of the prediction curve also differs depending on the type. Since the shape of the prediction curve Cuv2 shown in FIG. 12 differs depending on the photographing optical system, the zoom position of the photographing optical system, the F value, the focus lens position, and the digital filter band, the calculation state acquired in S11 and the digital filter used are used. Calculate for each. Here, it is assumed that the line image intensity distribution, which is the aberration information, is acquired in the range of the defocus amount ± 7 mm in 1 mm increments, and the prediction curve is calculated. Then, the plot points of the black circles as shown in FIG. 12 are obtained, and the prediction curve Cuv2 can be obtained by interpolation calculation and fitting.

Further, as the aberration information, the line image intensity distribution may be held in the state of the prediction curve as shown in FIG. 12 which has been filtered in advance. In that case, a plurality of prediction curves that change depending on the band of the digital filter are held, and the camera MPU 125 selects the prediction curve that matches the detection band of the digital filter.

Further, in general, as the defocus amount increases, the prediction curve Cuv2 gradually approaches the prediction curve Cuv1. Therefore, the number of acquisition points of the line image intensity distribution, which is aberration information, may become coarser as the defocus range increases. Further, in the calculation state acquired in S11, in general, the higher the image height (that is, the farther away from the central image height), the larger the aberration of the photographing optical system. It is also possible to increase the number of acquisition points of a certain line image intensity distribution. Further, in the calculation state acquired in S11, generally, when the F value is small, the aberration of the photographing optical system becomes large, so the number of acquisition points of the line image intensity distribution which is the aberration information is determined according to the F value. You can increase it.

Next, in S14, the conversion coefficient K is calculated. Here, the conversion coefficient K corresponding to the image shift amount P obtained in S3 is calculated from the prediction curve obtained in S13. Now, since the correlation amount obtained in S3 is P = 2.6 [bit], the defocus amount def [mm] corresponding to Pred [bit] = 2.6 [bit] in FIG. 12 is calculated. .. The interpolation calculation method may be obtained from the fitting function of the prediction curve Cuv2, or may be a method of interpolation of two neighboring points (interpolation from two points of def = + 4, + 5 in FIG. 12). Here, it is assumed that the defocus amount def [mm] = 4.2 [mm] corresponding to Pred [bit] = 2.6 [bit] is acquired as shown in FIG. Then, the conversion coefficient K is K [mm / bit] = 4.2 / 2.6≈1.6 ... (4)

Can be obtained as. Then, as shown in FIG. 13, the value of the conversion coefficient K in each Pred [bit] is calculated and stored in advance based on the prediction curve of FIG. 12, and the process is completed. Then, in S4, the corresponding conversion coefficient is selected from the image shift amount P detected in S3. The conversion coefficient K described above may be calculated each time AF is performed. In that case, since the defocus amount corresponding to the image shift amount P can be directly obtained from the prediction curve, it is possible to avoid performing the above equations (4) and (3).
As described above, according to the first embodiment, since it is possible to change the conversion coefficient according to the aberration information of the photographing optical system, it is possible to correct the focus detection more according to the user's intention.

Further, in the above description, the calculation of the correction value is mainly performed by the camera MPU 125, but the present invention is not limited to this. For example, the correction value may be calculated by the lens MPU 117. In that case, aberration information is transmitted from the camera MPU 125 to the lens MPU 117, and the conversion coefficient K is calculated in the lens MPU 117. In that case, the lens MPU 117 may correct the in-focus position transmitted from the camera MPU 125 to drive the lens.

<Second embodiment>
Next, a second embodiment of the present invention will be described. The second embodiment is different from the first embodiment in that the calculation method of the conversion coefficient K is switched depending on the magnitude of the aberration. Since the configuration and operation of the image pickup apparatus are the same as those described in the first embodiment except for the calculation method of the conversion coefficient K, the description thereof will be omitted as appropriate.

The method of calculating the conversion coefficient K in the second embodiment will be described with reference to FIG. In FIG. 14, the same reference numbers as those in FIG. 5 (b) are attached to the steps of performing the same process as the process in FIG. 5 (b) described in the first embodiment.

In S11, the calculation state is acquired by the method described above. Next, in S21, it is determined whether or not the calculation state for obtaining the conversion coefficient K acquired in S11 is a lens state having a large aberration. In an interchangeable lens type camera, if the above-mentioned calculation of the conversion coefficient K in the first embodiment is performed in all the lenses and the calculation state, the calculation load and the storage capacity of the camera will increase. Therefore, it is conceivable to switch whether or not to calculate the conversion coefficient K depending on the lens ID and the calculation state acquired in S11.

The determination flag of the magnitude of the aberration may be added to the lens information in advance and transmitted from the lens MPU 117 to the camera MPU 125, or the determination flag may be prepared for each state acquired in S11. Further, it may be switched depending on the presence or absence of the deviation amount (= best focus correction amount (hereinafter, BP correction amount)) between the best image plane and the AF detection result caused by the aberration of the photographing optical system. Since the method of generating the BP correction amount and the method of correction are known as disclosed in Japanese Patent Application Laid-Open No. 2009-128843, detailed description here will be omitted. Further, there are a plurality of types of aberrations, for example, spherical aberration, non-point aberration, chromatic aberration, coma, etc., but the lens has a size discrimination flag for each aberration factor, for example, the shape of the most line image intensity distribution. It is also possible to discriminate S21 based on the aberration factor that affects the above.

Similarly, in an interchangeable lens camera, if BP correction is applied to all lenses, the calculation load and storage capacity of the camera will increase. Therefore, whether or not to perform BP correction is determined by the lens ID and S11. It is conceivable to switch depending on the acquired calculation state. Further, in general, a lens having a large BP correction value is often subjected to BP correction. Since the BP correction value is mainly caused by the aberration of the photographing optical system, the lens to which the BP correction is applied often has a large aberration of the photographing optical system. Here, in order to reduce the calculation load of the calculation process of the conversion coefficient K described above, a conversion coefficient K prepared in advance is used for the lens having a small aberration (that is, the aberration of the photographing optical system is small) and the calculation state. Apply.

In this way, the magnitude of the aberration is determined in S21, and if the lens has a large aberration or the calculation state, the process proceeds to S12, and the same processing as in the first embodiment is performed in S12 to S14. On the other hand, if the lens is not in the calculation state and the lens has a large aberration in S21, the process proceeds to S22.

In S22, the conversion coefficient K obtained from the pupil separation image is acquired. When the aberration of the photographing optical system is small, as shown in FIG. 9, the A image and the B image which are supposed to be output from the photoelectric conversion units 211a and 211b have similar shapes of the pupil intensity distributions PI_A and PI_B. .. Therefore, in S22, the conversion coefficient K is
Conversion coefficient K [mm / bit] = Zep / BL ... (3)

Can be obtained at. In S22, the conversion coefficient K is stored as the value obtained by the equation (3), and the process ends.
As described above, according to the second embodiment, the magnitude of the aberration of the photographing optical system can be easily determined based on the magnitude of the aberration of the photographing optical system, and the conversion coefficient can be changed. The calculation load can be reduced.

<Other Embodiments>
The present invention may be applied to a system composed of a plurality of devices or a device composed of one device.

The present invention also supplies a program that realizes one or more functions of the above-described embodiment to a system or device via a network or storage medium, and one or more processors in the computer of the system or device implement the program. It can also be realized by the process of reading and executing. It can also be realized by a circuit (for example, ASIC) that realizes one or more functions.

100: Lens unit, 104: Focus lens, 113: Focus actuator, 117: Lens MPU, 118: Lens memory, 120: Camera body, 122: Imaging element, 125: Camera MPU, 129: Imaging surface phase difference detector

Claims (15)

Based on the correlation amount of a pair of pupil-divided signals obtained from an imaging element that has a plurality of photoelectric conversion units for each of the plurality of microlenses and photoelectrically converts light incident through the photographing optical system. A detection means for detecting a signed image shift amount indicating the defocus direction in the optical axis direction, and
The image shift amount with the code, the conversion factor, conversion means for converting the defocus amount of the optical axis direction,
It has a calculation means for calculating the conversion coefficient corresponding to each signed image shift amount based on the aberration information of the photographing optical system.
The conversion means is a focus detection device that uses the conversion coefficient corresponding to the signed image shift amount detected by the detection means for the conversion. The calculation means calculates the conversion coefficient for a plurality of different signed image shift amounts, stores the calculated conversion coefficient in the storage means, and stores the calculated conversion coefficient in the storage means.
The focus detection device according to claim 1, wherein the conversion means reads out a conversion coefficient corresponding to the signed image shift amount detected by the detection means from the storage means and uses it for the conversion. .. The calculation means calculates a conversion coefficient according to the signed image shift amount detected by the detection means.
The focus detection device according to claim 1, wherein the conversion means uses the calculated conversion coefficient for the conversion. The focus detection device according to claim 1, wherein the calculation means acquires the aberration information that differs depending on the photographing optical system, the zoom position, the F value, and the focus lens position. The focus detection device according to any one of claims 1 to 4, wherein the calculation means digitally filters the aberration information and calculates the conversion coefficient using the digitally filtered aberration information. .. The focus detection device according to any one of claims 1 to 5, wherein the aberration information is a line image intensity distribution of the pair of image signals. The focus detection device according to claim 6, wherein the line image intensity distribution of the pair of image signals has an asymmetrical shape. Claim 1 is characterized in that when the aberration of the photographing optical system is smaller than the predetermined aberration, the conversion means uses a predetermined conversion coefficient that does not change according to the amount of image shift for the conversion. 7. The focus detection device according to any one of 7. The conversion means calculates the conversion coefficient by the calculation means when there is a deviation between the best image plane and the image plane obtained from the defocus amount caused by the aberration of the photographing optical system. The invention according to any one of claims 1 to 7, wherein a predetermined conversion coefficient which is used for the conversion and does not change according to the amount of image deviation when the deviation does not occur is used for the conversion. Focus detector. An image pickup element that has a plurality of photoelectric conversion units for each of the plurality of microlenses and photoelectrically converts the light incident through the photographing optical system.
A reading means for retrievably reading a pair of pupil-divided signals from the image sensor.
An imaging device comprising the focus detection device according to any one of claims 1 to 9. The image shift amount with a code indicating the defocus direction of the detected direction of the optical axis based on the correlation of a pair of signals based on the light having passed through different pupil regions of the photographing optical system, the conversion coefficient, the optical axis direction Conversion means to convert to the amount of defocus of
A calculation means for calculating the conversion coefficient corresponding to each signed image shift amount based on the aberration information of the photographing optical system, and
It has a focusing means for adjusting the focus by driving the lens based on the converted defocus amount.
The conversion means is a lens unit characterized in that the conversion coefficient corresponding to the detected signed image shift amount is used for the conversion. An imaging system that includes an imaging device and a lens unit.
The image pickup device
An image pickup element that has a plurality of photoelectric conversion units for each of the plurality of microlenses and photoelectrically converts the light incident through the photographing optical system.
A reading means for retrievably reading a pair of pupil-divided signals from the image sensor.
It has a detecting means for detecting a signed image shift amount indicating a defocus direction in the optical axis direction based on a correlation amount of the pair of signals.
The lens unit
The image shift amount with the code, the conversion factor, conversion means for converting the defocus amount of the optical axis direction,
A calculation means for calculating the conversion coefficient corresponding to each signed image shift amount based on the aberration information of the photographing optical system, and
It has a focusing means for adjusting the focus by driving the lens based on the converted defocus amount.
The conversion means is an imaging system characterized in that the conversion coefficient corresponding to the signed image shift amount detected by the detection means is used for the conversion. The readout means includes a plurality of photoelectric conversion units for each of the plurality of microlenses, and reads out a pair of pupil-divided signals from an image sensor that photoelectrically converts the light incident through the photographing optical system. Process and
A detection step in which the detection means detects a signed image shift amount indicating a defocus direction in the optical axis direction based on the correlation amount of the pair of signals.
Conversion means, a conversion step of converting the image shift amount with the code, the conversion factor, the defocus amount of the optical axis direction,
The calculation means includes a calculation step of calculating the conversion coefficient corresponding to each of the signed image shift amounts based on the aberration information of the photographing optical system.
In the conversion step, the focus detection method is characterized in that the conversion coefficient corresponding to the signed image shift amount detected in the detection step is used for the conversion. A program for causing a computer to execute each step of the focus detection method according to claim 13. A computer-readable storage medium that stores the program according to claim 14.

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