JP7005209B2 - Image pickup device and its control method - Google Patents

Description

The present invention relates to an image pickup device such as a digital camera or a video camera and a control method thereof, and more particularly to an image pickup device equipped with an image pickup element having a focus detection function and a control method thereof.

An image pickup device such as a digital camera is generally equipped with an image pickup element having an automatic focus detection (AF) function. As a focus detection method, a contrast detection method and a phase difference detection method capable of faster focus detection than the contrast detection method are known, but the phase difference detection method requires a dedicated sensor having a pupil division function. Therefore, it has been used for a relatively large and expensive image pickup device. However, in recent years, an image pickup device has been proposed that can realize focus detection by a phase difference detection method without using a dedicated sensor by adding a pupil division function to the pixels of the image pickup device.

When continuous shooting is performed by the phase difference detection method using the output signal of such an image sensor, it is determined that there is "vignetting" due to the influence of the front frame and the rear frame of the image pickup optical system, especially at a high image height. In this case, a technique for controlling the aperture value to be equal to or higher than a predetermined value has been proposed (Patent Document 1). In this proposal, when it is determined that there is "vignetting", the aperture value is controlled to be equal to or higher than the predetermined value to prevent the focus detection performance from changing due to vignetting and improve the focus detection accuracy. It is said that it can be made to do.

Japanese Unexamined Patent Publication No. 2013-239787

Here, as a result of diligent studies by the present applicant, a baseline determined by conditions such as the exit pupil distance of the lens, the set pupil distance of the image sensor, the aperture value, and the image height, in addition to the influence of vignetting in Patent Document 1 above. It was found that the focus detection performance changes depending on the length. Therefore, in Patent Document 1, there is a limit to performing focus detection while maintaining the focus detection performance above a certain level, and it is necessary to determine the aperture value for focus detection in consideration of the above-mentioned conditions.

The present invention has been made based on such findings, and enables focus detection while maintaining the focus detection performance above a certain level, enabling good focus detection even in small aperture continuous shooting. It is an object of the present invention to provide an image pickup apparatus and a control method thereof.

In order to achieve the above object, the image pickup apparatus of the present invention receives a light beam passing through a first pupil region and a second pupil region different from the first pupil region of the photographing optical system, respectively, for first focus detection. A first focus detection signal is generated based on an image pickup element in which a plurality of pixels and a second focus detection pixel are arranged and a light receiving signal of the first focus detection pixel, and based on the light receiving signal of the second focus detection pixel. The image shift amount is calculated based on the generation means for generating the second focus detection signal, the first focus detection signal, and the second focus detection signal, and the calculated image shift amount is added to the first pupil partial region. A focus detecting means for detecting the amount of defocus by multiplying the baseline length, which is the distance between the center of gravity of the second pupil and the center of gravity of the second pupil portion, and the conversion coefficient according to the set pupil distance of the image pickup element, and the conversion coefficient . Based on the above, a determination means for determining the aperture value at the time of focus detection is provided , and when the conversion coefficient is larger than the threshold value, the aperture value at the time of focus detection is set to the open side of the aperture value for photographing. It is characterized in that it is changed and returned to the aperture value for shooting at the time of shooting .

According to the present invention, it is possible to perform focus detection while maintaining the focus detection performance above a certain level, so that good focus detection can be performed in small aperture continuous shooting.

It is a block diagram which shows the outline of the system configuration example of the digital camera which is 1st Embodiment of the image pickup apparatus of this invention. It is a schematic diagram which shows the arrangement of the image pickup pixel including the focus detection pixel of the image pickup element. (A) is a plan view of one image pickup pixel of the image pickup element as viewed from the light receiving surface side of the image pickup element, and (b) is a sectional view taken along line aa of (a). FIG. 3A is a cross-sectional view taken along the line aa of the pixel structure shown in FIG. 3A and is a schematic view showing an exit pupil surface of the photographing optical system. It is a schematic diagram which shows the correspondence relationship between an image sensor and pupil division. It is a schematic diagram which shows the relationship between the defocus amount of the 1st focus detection signal and the 2nd focus detection signal, and the image shift amount between the 1st focus detection signal and the 2nd focus detection signal. It is a flowchart explaining the focus detection process of the imaging surface phase difference detection method. It is a figure which shows the relationship of the 1st pupil partial region of the 1st focus detection pixel, the 2nd pupil partial region of a 2nd focus detection pixel, and the exit pupil of a photographing optical system in the baseline length, the peripheral image height of an image pickup element. It is a graph which shows the relationship between the conversion coefficient K and the image height for each photographing optical system. It is a graph which shows the image height change of the conversion coefficient for each aperture value of a lens when the lens which the change for each image height of a conversion coefficient is the largest is used. It is a flowchart explaining a series of processing from the start to the end of continuous shooting. It is a flowchart explaining a series of processing from the start to the end of continuous shooting in the digital camera which is the 2nd Embodiment of the image pickup apparatus of this invention.

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

(First Embodiment)
FIG. 1 is a block diagram showing an outline of a system configuration example of a digital camera according to a first embodiment of the image pickup apparatus of the present invention.

As shown in FIG. 1, the digital camera of the present embodiment (hereinafter referred to as a camera) has a first lens group 101 constituting a photographing optical system. The first lens group 101 is arranged on the closest subject side of the photographing optical system, and is held so as to be movable back and forth in the optical axis direction. The aperture combined shutter 102 adjusts the amount of light at the time of shooting by adjusting the aperture diameter thereof, and also functions as a shutter for adjusting the exposure seconds at the time of shooting a still image. The second lens group 103 moves forward and backward in the optical axis direction integrally with the aperture and shutter 102, and performs a zoom operation in conjunction with the forward and backward movement of the first lens group 101.

The third lens group 105 is a focus lens that adjusts the focus by moving forward and backward in the optical axis direction. The optical low-pass filter 106 is an optical element for reducing false color and moire in a captured image. The image sensor 107 is composed of a two-dimensional CMOS photo sensor and a peripheral circuit, and has an image plane on which a subject light flux that has passed through a photographing optical system is imaged.

The zoom actuator 111 moves the first lens group 101 to the second lens group 103 forward and backward in the optical axis direction by rotating a cam cylinder (not shown), and performs a zoom operation. The aperture shutter actuator 112 controls the aperture diameter of the aperture combined shutter 102 to adjust the amount of shooting light, and also controls the exposure time during still image shooting. The focus actuator 114 moves the third lens group 105 forward and backward in the optical axis direction to adjust the focus.

The strobe unit 115 is a light emitting device using a xenon tube, an LED, or the like, and illuminates the subject at the time of shooting. The AF auxiliary light source 116 projects an image of a mask having a predetermined aperture pattern onto the field of view via a projection lens, and improves the focus detection ability for a dark subject or a low-contrast subject.

The system control circuit 121 includes a memory such as ROM and RAM, an A / D converter, a D / A converter, a communication interface circuit, and the like, in addition to a CPU that controls the entire camera. Then, the CPU of the system control circuit 121 drives various circuits of the camera based on a predetermined program stored in the ROM, and executes a series of operations such as AF, imaging, image processing, and recording.

Further, the ROM or the like of the system control circuit 121 stores a correction value calculation coefficient required for focus adjustment using the output signal of the image pickup device 107, which will be described later. The correction value calculation coefficient is the focus state corresponding to the position of the third lens group 105, the zoom state corresponding to the position of the first lens group 101 to the second lens group 103, the F value of the photographing optical system, and the image pickup element 107. Multiple lenses are prepared for each set pupil distance and pixel size.

When adjusting the focus, the optimum correction value calculation coefficient is selected according to the combination of the focus adjustment state (focus state, zoom state) and aperture value of the photographing optical system, the set pupil distance of the image pickup element 107, and the pixel size. .. Then, the correction value is calculated from the selected correction value calculation coefficient and the image height of the image sensor 107.

In the present embodiment, the correction value calculation coefficient is stored in the ROM or the like of the system control circuit 121. For example, in the interchangeable lens type image pickup apparatus, the correction value calculation coefficient is stored in the ROM or the like of the interchangeable lens. You may do so. In this case, the correction value calculation coefficient may be transmitted to the camera according to the focus adjustment state of the photographing optical system.

The strobe control circuit 122 controls lighting of the light emitting unit of the strobe unit 115 in synchronization with the shooting operation. The auxiliary light drive circuit 123 controls the lighting of the AF auxiliary light source 116 in synchronization with the focus detection operation. The image pickup element drive circuit 124 controls the image pickup operation of the image pickup element 107, and A / D-converts the acquired image signal and transmits it to the system control circuit 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 drives and controls the focus actuator 114 based on the focus detection result, and drives the third lens group 105 forward and backward in the optical axis direction to adjust the focus. The aperture shutter drive circuit 128 drives and controls the aperture shutter actuator 112 to control the opening of the aperture combined shutter 102. The zoom drive circuit 129 drives the zoom actuator 111 according to the zoom operation of the photographer.

The display unit 131 is composed of an LCD or the like, and displays information on the shooting mode of the camera, a preview image before shooting and a confirmation image after shooting, a frame of a focus detection area at the time of focus detection, an image in a focused state, 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 recording medium 133 is composed of, for example, a detachable memory card or the like, and records the acquired image.

Next, with reference to FIG. 2, an arrangement of image pickup pixels including focus detection pixels of the image pickup device 107 will be described. FIG. 2 is a schematic diagram showing an array of image pickup pixels of an image pickup device 107 composed of a two-dimensional CMOS sensor in a range of 4 columns × 4 rows (an array of focus detection pixels in a range of 8 columns × 4 rows).

In FIG. 2, in the image pickup pixel group 200 having 2 columns × 2 rows, the image pickup pixel 200R having the spectral sensitivity of R (red) is in the upper left, and the image pickup pixel 200G having the spectral sensitivity of G (green) is in the upper right and the lower left. Image pickup pixels 200B having a spectral sensitivity of B (blue) are arranged at the lower right. Further, each imaging pixel has a first focus detection pixel 201 and a second focus detection pixel 202 arranged in two columns × one row.

A large number of image pickup pixels of 4 columns × 4 rows (focus detection pixels of 8 columns × 4 rows) are arranged on the surface, and it is possible to acquire an image pickup signal (focus detection signal). In the image pickup device 107 of the present embodiment, the period P of the image pickup pixels is 4 μm, the number of image pickup pixels N is 5575 columns × 3725 rows = about 20.75 million pixels, the column direction period PAF of the focus detection pixels is 2 μm, and the number of focus detection pixels. The NAF is 11150 horizontal columns x 3725 vertical rows = about 41.5 million pixels.

3A is a plan view of one image pickup pixel 200G of the image pickup element 107 from the light receiving surface side (+ z side) of the image pickup element 107, and FIG. 3B is a cross section taken along the line aa of FIG. 3A. It is a cross-sectional view seen from the −y side.

As shown in FIG. 3, in the image pickup pixel 200G, a microlens 305 for condensing incident light is formed on the light receiving side of each image pickup pixel, and NH division (division) in the x direction and NH division (two division) in the y direction. An NV-divided (one-divided) photoelectric conversion unit 301 and a photoelectric conversion unit 302 are formed. The photoelectric conversion unit 301 and the photoelectric conversion unit 302 correspond to the first focus detection pixel 201 and the second focus detection pixel 202, respectively.

The photoelectric conversion unit 301 and the photoelectric conversion unit 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 if necessary, the intrinsic layer is omitted and a pn junction is formed. It may be a photodiode.

A color filter 306 is formed between the microlens 305 and the photoelectric conversion unit 301 and the photoelectric conversion unit 302 in each image pickup pixel. If necessary, the spectral transmittance of the color filter may be changed for each sub-pixel, or the color filter may be omitted. The light incident on the image pickup pixel 200G is collected by the microlens 305, separated by the color filter 306, and then received by the photoelectric conversion unit 301 and the photoelectric conversion unit 302.

In the photoelectric conversion unit 301 and the photoelectric conversion unit 302, electrons and holes are pair-produced according to the amount of light received, and after being separated by the depletion layer, negatively charged electrons are accumulated in the n-type layer (not shown), and the holes are formed. It is discharged to the outside of the image pickup device 107 through a p-type layer connected to a constant voltage source (not shown). The electrons stored in the photoelectric conversion unit 301 and the n-type layer (not shown) of the photoelectric conversion unit 302 are transferred to the capacitance unit (FD) via the transfer gate and converted into a voltage signal.

Next, with reference to FIG. 4, the correspondence between the pixel structure shown in FIG. 3 and the pupil division will be described. FIG. 4 is a cross-sectional view of the aa-line cross section of the pixel structure shown in FIG. 3A as viewed from the + y side, and a schematic view showing the exit pupil surface of the photographing optical system. In FIG. 4, the x-axis and the y-axis are inverted with respect to FIG. 3 (b) in order to correspond to the coordinate axes of the exit pupil surface.

In FIG. 4, the first pupil portion region 501 of the first focus detection pixel 201 has a substantially conjugate relationship with the light receiving surface of the photoelectric conversion unit 301 whose center of gravity is eccentric in the −x direction due to the microlens 305. It represents a pupil region that can receive light from the first focus detection pixel 201. The center of gravity of the first pupil portion region 501 of the first focus detection pixel 201 is eccentric to the + X side on the pupil surface.

On the other hand, the second pupil partial region 502 of the second focus detection pixel 202 has a substantially conjugate relationship with the light receiving surface of the photoelectric conversion unit 302 whose center of gravity is eccentric in the + x direction by the microlens 305, and the second focus detection is performed. The pixel 202 represents a pupil region that can receive light. The center of gravity of the second pupil partial region 502 of the second focus detection pixel 202 is eccentric to the −X side on the pupil surface.

Further, the pupil region 500 is a pupil region in which light can be received by the entire pixel 200G when the photoelectric conversion unit 301 (first focus detection pixel 201) and the photoelectric conversion unit 302 (second focus detection pixel 202) are all combined. The image pickup surface phase-difference AF is affected by diffraction because the pupil is divided using the microlens 305 of the image pickup element 107.

In FIG. 4, the pupil distance to the exit pupil surface is several tens of mm, whereas the diameter of the microlens 305 is several μm. Therefore, the aperture value of the microlens 305 becomes tens of thousands, and diffraction blur of several tens of mm level occurs. Therefore, the image of the light receiving surface of the photoelectric conversion units 301 and 302 does not become a clear pupil region or a pupil portion region, but becomes a pupil intensity distribution (incident angle distribution of the light receiving rate).

FIG. 5 is a schematic view showing the correspondence between the image pickup device 107 and the pupil division. The luminous flux that has passed through the different pupil region regions of the first pupil region 501 and the second pupil region 502 is incident on each image pickup pixel of the image pickup element 107 at a different angle, and is divided into 2 × 1 first. The light is received by the focus detection pixel 201 and the second focus detection pixel 202. In the present embodiment, the pupil region is divided into two in the horizontal direction, but the pupil may be divided in the vertical direction if necessary.

In the present embodiment, an image pickup device 107 in which a plurality of image pickup pixels having a first focus detection pixel 201 and a second focus detection pixel 202 are arranged is used. The first focus detection pixel 201 receives the light flux passing through the first pupil portion region 501 of the photographing optical system, and the second focus detection pixel 202 is the second pupil portion of the photographing optical system different from the first pupil portion region 501. It receives the light flux passing through the region 502. Further, the image pickup pixel receives a light flux passing through the pupil region including the first pupil portion region 501 and the second pupil portion region 502 of the photographing optical system.

Then, the light-receiving signal of the first focus detection pixel 201 of each image pickup pixel of the image pickup element 107 is collected to generate the first focus detection signal, and the light-receiving signal of the second focus detection pixel 202 of each image pickup pixel is collected to generate the second focus. Generates a detection signal to detect the focus. Further, by adding the light receiving signals of the first focus detection pixel 201 and the second focus detection pixel 202 for each image pickup pixel of the image pickup element 107, an image pickup signal (image pickup image) having a resolution of the number of effective pixels N is generated. ..

In the present embodiment, each image pickup pixel of the image pickup element 107 is composed of the first focus detection pixel 201 and the second focus detection pixel 202, but if necessary, the image pickup pixel and the first focus detection pixel, The second focus detection pixel may be an individual pixel configuration. For example, the first focus detection pixel and the second focus detection pixel may be partially arranged in a part of the array of image pickup pixels.

Next, with reference to FIG. 6, the relationship between the defocus amount and the image shift amount of the first focus detection signal and the second focus detection signal acquired by the image pickup device 107 will be described. FIG. 6 is a schematic diagram showing the relationship between the defocus amount 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.

In FIG. 6, the exit pupil of the photographing optical system is divided into a first pupil portion region 501 and a second pupil portion region 502 as in FIGS. 4 and 5. The defocus amount d is the distance from the image pickup position of the subject to the image pickup surface 800 of the image pickup element 107 as a magnitude | d |, and the front pin state in which the image formation position of the subject is closer to the subject side than the image pickup surface 800 is a minus sign. It is defined as (d <0). Further, the rear pin state in which the imaging position of the subject is on the opposite side of the subject from the imaging surface 800 is defined as a plus sign (d> 0).

The in-focus state in which the image formation position of the subject is on the image pickup surface 800 (focus position) is d = 0. FIG. 5 shows an example in which the subject 801 is in the focused state (d = 0) and the subject 802 is in the front pin state (d <0). The front pin state (d <0) and the rear pin state (d> 0) are combined to obtain a defocus state (| d |> 0).

In the front pin state (d <0), among the luminous fluxes from the subject 802, the luminous flux that has passed through the first pupil portion region 501 (second pupil portion region 502) is once focused and then the center of gravity position G1 of the light flux. It spreads over the width Γ1 (Γ2) around (G2) and becomes 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 image pickup pixel arranged in the image sensor 107, whereby the first focus detection signal (second focus detection signal) is received. ) Is generated.

Therefore, the first focus detection signal (second focus detection signal) is recorded at the center of gravity position G1 (G2) on the image pickup surface 800 as a subject image in which the subject 802 is blurred to the width Γ1 (Γ2). The blur width Γ1 (Γ2) of the subject image increases substantially in proportion as the magnitude | d | of the defocus amount d increases.

Similarly, the magnitude of the image shift amount p (= difference in the position of the center of gravity of the light beam G1-G2) of the subject image between the first focus detection signal and the second focus detection signal | p | is also the magnitude of the defocus amount d. As | d | increases, it increases substantially in proportion. Even in the rear focus 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 focus state, but the same is true.

Therefore, in the present embodiment, as the magnitude of the defocus amount of the first focus detection signal and the second focus detection signal, or the image pickup signal obtained by adding the first focus detection signal and the second focus detection signal increases, the first The magnitude of the image shift amount p between the 1-focus detection signal and the 2nd focus detection signal increases.

In the focus detection of the phase difference detection method of the present embodiment, the correlation amount representing the degree of coincidence of the signals is calculated by relatively shifting the first focus detection signal and the second focus detection signal, and the shift amount that improves the correlation amount. The image shift amount p is detected from. As the magnitude of the defocus amount d of the image pickup signal increases, the magnitude of the image shift amount p between the first focus detection signal and the second focus detection signal increases. Therefore, the image shift amount p is converted into a conversion coefficient. Converts to the detection defocus amount and performs focus detection.

FIG. 7 is a flowchart illustrating the focus detection process of the imaging surface phase difference detection method. Each process of FIG. 7 is executed by expanding the program stored in the ROM or the like of the system control circuit 121 into the RAM and controlling the image processing circuit 125 by the CPU or the like.

In FIG. 7, in step S701, the system control circuit 121 sets a focus detection region centered on the image height (X, Y) for adjusting the focus from the effective pixel region of the image sensor 107, and in step S702. move on. In step S702, the system control circuit 121 generates a first focus detection signal from the light receiving signal of the first focus detection pixel 201 in the focus detection region, and second focus from the light receiving signal of the second focus detection pixel 202 in the focus detection region. A detection signal is generated, and the process proceeds to step S703.

In step S703, the system control circuit 121 performs pixel addition processing on the first focus detection signal and the second focus detection signal, respectively, and proceeds to step S704. Specifically, the first focus detection signal and the second focus detection signal are subjected to three pixel addition processing in the column direction in order to suppress the amount of signal data, respectively, and further, in order to convert the RGB signal into a luminance signal. Performs Bayer (RGB) addition processing. These two addition processes are combined to form a pixel addition process.

In step S704, the system control circuit 121 performs shading correction processing (optical correction processing) on the first focus detection signal and the second focus detection signal, respectively, and proceeds to step S705.

Here, with reference to FIG. 8, the change of the conversion coefficient required for conversion from the image shift amount p due to the pupil shift of the first focus detection signal and the second focus detection signal to the detection defocus amount and the shading correction process will be described. do. FIG. 8 shows the baseline lengths BL0, BL1, BL2, the first pupil region 501 of the first focus detection pixel 201 at the peripheral image height of the image sensor 107, the second pupil region 502 of the second focus detection pixel 202, and the photographing. It is a figure which shows the relationship of the exit pupil 400 of an optical system.

FIG. 8A shows a case where the exit pupil distance Dl of the photographing optical system and the set pupil distance Ds of the image sensor are the same. The set pupil distance Ds of the image pickup element 107 means that when the exit pupil distance Dl is the same as the set pupil distance Ds of the image pickup element 107, the first focus detection signal and the second focus are obtained in any image pickup pixel of the image pickup element 107. This is a parameter in which the strength of the detected signal is substantially the same. This parameter is a value determined by the positional relationship between the photoelectric conversion units 301 and 302 and the microlens 305.

When the exit pupil distance Dl of the photographing optical system and the set pupil distance Ds of the image sensor are the same, the exit pupil 400 of the photographing optical system is substantially evenly divided into pupils by the first pupil portion region 501 and the second pupil portion region 502. Will be done. The baseline length, which is the distance between the center of gravity of the first pupil region 501 and the center of gravity of the second pupil region 502, inside the exit pupil 400 is indicated by BL0. At this time, the conversion coefficient K0 required for conversion from the image shift amount p to the detected defocus amount is obtained by K0 = Ds / BL0.

On the other hand, FIG. 8B shows a case where the exit pupil distance Dl of the photographing optical system is shorter than the set pupil distance Ds of the image pickup device 107. In this case, the peripheral image height of the image pickup element 107 causes a pupil shift between the exit pupil 400 of the image pickup optical system and the entrance pupil of the image pickup element 107, and the exit pupil 400 of the image pickup optical system is unevenly divided into pupils. Therefore, the baseline length becomes BL1 biased to one side, and the conversion coefficient K1 = Ds / BL1 changes accordingly.

FIG. 8C shows a case where the exit pupil distance Dl of the photographing optical system is longer than the set pupil distance Ds of the image pickup device 107. In this case as well, as in FIG. 8B, at the peripheral image height of the image pickup element 107, the exit pupil 400 of the image pickup optical system and the entrance pupil of the image pickup element 107 are displaced from each other, and the exit pupil 400 of the image pickup optical system is affected. The pupil is divided unevenly. Therefore, the baseline length becomes BL2 biased to the opposite side of FIG. 8B, and the conversion coefficient K2 = Ds / BL2 changes accordingly.

Further, as the pupil division becomes non-uniform due to the peripheral image height of the image sensor 107, the intensities of the first focus detection signal and the second focus detection signal also become non-uniform, and the first focus detection signal and the second focus detection become non-uniform. Shading occurs in which the intensity of one of the signals increases and the intensity of the other decreases. Further, it can be seen that the conversion coefficient K and shading change according to the aperture value because the size of the exit pupil 400 in FIG. 8 changes when the aperture value of the photographing optical system changes.

Therefore, the conversion coefficient K from the image shift amount p to the detected defocus amount and the shading depend on the aperture value of the photographing optical system, the exit pupil distance Dl, the pupil intensity distribution (optical characteristics) of the image sensor 107, and the image height. You can see that it changes.

Therefore, the system control circuit 121 has a first shading correction coefficient and a second focus detection of the first focus detection signal according to the image height of the focus detection region of the image sensor 107, the F value of the photographing optical system, and the exit pupil distance Dl. The second shading correction coefficient of the signal is generated respectively. Then, the first shading correction coefficient is multiplied by the first focus detection signal, the second shading correction coefficient is multiplied by the second focus detection signal, and the shading correction processing (optical) of the first focus detection signal and the second focus detection signal is performed. Correction processing) is performed.

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

Here, the exit pupil of the photographing optical system is described as an example in which the set pupil distance Ds of the image sensor 107 is the same and the exit pupil distance Dl of the photographing optical system changes. The same applies when the distance Dl is the same and the set pupil distance Ds of the image pickup element 107 changes. In the focus detection of the image pickup surface phase difference detection method, the luminous flux received by the focus detection pixels (first focus detection pixel, second focus detection pixel) and the image pickup pixel receive light as the set pupil distance Ds of the image pickup element 107 changes. The luminous flux is also changed.

In step S705 of FIG. 7, in order to improve the correlation amount (signal matching degree) and improve the focus detection accuracy, the system control circuit 121 specificly passes through the first focus detection signal and the second focus detection signal. A bandpass filter process having a frequency band is performed, and the process proceeds to step S706. Examples of bandpass filters include differential filters such as (1,0, -1) that cut DC components and perform edge extraction, and additive filters that suppress high-frequency noise components (1,2,1). There is a filter.

In step S706, the system control circuit 121 performs a shift process of relatively shifting the first focus detection signal and the second focus detection signal after the filter processing in the pupil division direction, and calculates the correlation amount indicating the degree of coincidence of the signals. Then, the process proceeds to step S707.

Here, the k-th first focus detection signal after filtering is A (k), the second focus detection signal is B (k), and the range of the number k corresponding to the focus detection region is W. The correlation amount COR is calculated by the following equation (1), where s is the shift amount due to the shift process and Γ is the shift range of the shift amount s.

By the shift processing of the shift amount s, the k-th first focus detection signal A (k) and the k-s-th second focus detection signal B (ks) are associated and subtracted to generate a shift subtraction signal. The absolute value of the generated shift subtraction signal is calculated, the sum of the numbers k is taken within the range W corresponding to the focus detection region, and the correlation amount COR (s) is calculated. If necessary, the correlation amount calculated for each row may be added over a plurality of rows for each shift amount.

In step S707, the system control circuit 121 calculates the shift amount of the real value at which the correlation amount correlation amount COR (s) becomes the minimum value by the sub-pixel calculation from the correlation amount COR (s), and sets it as the image shift amount p. .. Then, the system control circuit 121 detects by multiplying the image shift amount p by the image height in the focal detection region, the F value of the photographing optical system, and the conversion coefficient K corresponding to the exit pupil distance Dl of the photographing optical system. The defocus amount (Def) is detected, and the focus detection process is terminated. After that, the system control circuit 121 drives the lens until the detected defocus amount (Def) becomes a predetermined value or less, and when the detected defocus amount (Def) becomes a predetermined value or less, the exposure amount is calculated and the image pickup operation is performed.

Next, with reference to FIG. 9, the relationship between the conversion coefficient K and the focus detection performance will be described. FIG. 9 is a graph showing the relationship between the conversion coefficient K and the image height for each photographing optical system (photographing lens). As described above, the conversion coefficient K is determined by the relationship between the exit pupil distance D1 of the photographing optical system, the set pupil distance Ds of the image sensor 107, and the image height, and depending on the photographing optical system, the conversion coefficient K is large even at the same image height. May be different. The larger the value of the conversion coefficient K, the lower the focus detection performance tends to be.

As described above, the detected defocus amount (Def) is calculated by multiplying the image shift amount p by the conversion coefficient K, but when an error occurs in the image shift amount p due to the influence of noise or the like, the conversion coefficient By multiplying by K, the error amount is expanded by K times. Therefore, the larger the enlargement ratio, that is, the conversion coefficient K, the lower the focus detection performance. As described above, the conversion coefficient K can be used as an index for the performance at the time of focusing detection.

Next, with reference to FIGS. 9 to 11, focus detection during continuous shooting will be described. When continuous shooting is to be performed in a so-called small aperture state, it is desirable to perform focus detection with an open aperture value that takes as long a baseline length as possible in order to perform focus detection with higher accuracy. In this case, as described above, the conversion coefficient K can be used as an index of the focus detection performance.

With reference to FIG. 9, the lenses A, B, and C, which are optical systems for photographing, have different exit pupil distances D1, and the relationship between the image height, the exit pupil distance Dl, and the set pupil distance Ds of the image sensor 107. Therefore, the conversion coefficient K differs depending on the image height. Since the focus detection accuracy differs depending on the conversion coefficient K, in the present embodiment, in order to keep the focus detection performance above a certain level, the conversion coefficient K is controlled by providing a threshold value Kth.

FIG. 10 is a graph showing, for example, a change in the image height of the conversion coefficient K for each aperture value of the lens A when the lens A in FIG. 9 having the largest change in the conversion coefficient K for each image height is used. Since the conversion coefficient K is derived from the baseline length on the exit pupil surface of the photographing optical system, the conversion coefficient K is determined by the F value. At this time, the smaller the aperture value, the longer the baseline length, and the smaller the value of the conversion coefficient K.

Here, as described above, it is assumed that the threshold value Kth of the conversion coefficient K for keeping the focus detection performance above a certain level is 1. From FIG. 10, in the vicinity of the image height of 0 mm, that is, in the vicinity of the central image height, the conversion coefficient K is equal to or less than the threshold value Kth even in the small aperture state of F11, so that the focus can be detected with good focus detection performance. On the other hand, when the image height exceeds 5 mm, the conversion coefficient K exceeds the threshold value Kth, and the focus detection performance deteriorates. Therefore, it can be seen that it is necessary to perform focus detection at F2.8, which is the maximum aperture.

In this way, by setting a threshold value Kth for the conversion coefficient K and selecting whether to perform focus detection in a small aperture state based on the threshold value Kth or to perform focus detection after opening the aperture to the maximum aperture, the focus is above a certain level. It is possible to perform small aperture continuous shooting while maintaining the detection performance.

FIG. 11 is a flowchart illustrating a series of processes from the start to the end of continuous shooting. Each process of FIG. 11 is executed by the CPU or the like by expanding the program stored in the ROM or the like of the system control circuit 121 into the RAM.

In FIG. 11, in step S1101, the system control circuit 121 determines the exposure condition for focus detection, and proceeds to step S1102. In step S1102, the system control circuit 121 acquires the conversion coefficient K when performing focus detection, and proceeds to step S1103.

The conversion coefficient K acquired here is a conversion coefficient table in which the image height, the F value, the exit pupil distance D1 of the photographing optical system, the set pupil distance Ds of the image sensor 107, and the like are calculated in advance according to the optical conditions. It is saved in the ROM or the like of the circuit 121. Alternatively, in the system control circuit 121, the conversion coefficient may be calculated and used from the optical conditions such as the image height, the F value, the exit pupil distance D1, and the set pupil distance Ds of the image pickup device 107 each time.

Further, information on so-called frame vignetting by the front frame and the rear frame of the lens, which is the photographing optical system, may be used. For example, the conversion coefficient K is calculated from the optical conditions such as the exit pupil distance D1, the set pupil distance Ds of the image sensor 107, and the image height, and the conversion coefficient at the peripheral image height is calculated by using the frame vignetting information for each lens. Can be corrected to calculate a more accurate conversion coefficient K. Further, the switching of the aperture drive by the conversion coefficient K can be made more accurate.

In step S1103, the system control circuit 121 determines whether or not the conversion coefficient K is equal to or less than the threshold value Kth (below the threshold value), and if the conversion coefficient K is equal to or less than the threshold value Kth, the process proceeds to step S1104 and the conversion coefficient K is the threshold value Kth. If it exceeds, the process proceeds to step S1108. Since it can be said that the focus detection performance is sufficient in step S1104, the system control circuit 121 performs focus detection with the aperture value as it is, and proceeds to step S1105.

Since the in-focus state is already good in this state, the system control circuit 121 performs an imaging operation in step S1106, determines whether or not continuous shooting is completed in step S1107, and if so, ends the process. If it is not completed, the process returns to step S1101.

On the other hand, in step S1108, the system control circuit 121 sets the aperture value of the conversion coefficient K to or less than the threshold value Kth or the open aperture value, and proceeds to step S1109. By setting the aperture value to the open aperture value, the conversion coefficient K can be lowered as much as possible, and good focus detection performance can be obtained.

In step S1 1 09, the system control circuit 121 determines the exposure condition at the aperture value set in step S1 108 , and proceeds to step S1 1 10. Then, the system control circuit 121 detects the focus in step S1 10 and drives the lens in step S1 11 and then takes a picture of the aperture value set in step S1 1 08 in step S1 1 12. The aperture value is returned to the aperture value for, and imaging is performed in step S1106.

As described above, in the present embodiment, since focus detection can be performed while maintaining the focus detection performance above a certain level, good focus detection can be performed even in small aperture continuous shooting, and during continuous shooting. It is possible to obtain an image in a good in-focus state.

(Second embodiment)
Next, with reference to FIG. 12, a digital camera according to a second embodiment of the image pickup apparatus of the present invention will be described. Regarding the parts that overlap with the first embodiment, the differences will be mainly described while diverting the figures and the reference numerals.

In the first embodiment, the aperture value at the time of focus detection is determined according to the comparison result of the conversion coefficient K and the threshold value Kth in step S1103 of FIG. 11, but the present invention is not limited to this. For example, the aperture value for the next focus detection may be determined in consideration of the defocus amount detected each time the focus is detected. In the focus detection by the imaging surface phase difference detection method, the larger the aperture value, the less blurred the image is and the clearer the image is, so that the focus detection performance is improved when the defocus amount is large.

FIG. 12 is a flowchart illustrating a series of processes from the start to the end of continuous shooting. Each process of FIG. 12 is executed by the CPU or the like by expanding the program stored in the ROM or the like of the system control circuit 121 into the RAM. Since the processing of steps S1201 to S1212 in FIG. 12 is the same as the processing of steps S1101 to S1102 of FIG. 11 of the first embodiment, step S1203a will be described.

In step S1203, even if the conversion coefficient K exceeds the threshold value Kth, if the detection defocus amount Def detected at that time or immediately before it exceeds the threshold value Dth, focus detection is performed with a small aperture. It is more accurate to go.

The smaller the conversion coefficient K is, the better it is to show high detection performance in the vicinity of focusing, but this is not always the case when the detected defocus amount Def is large.

Therefore, in step S1203a, if the detected defocus amount Def exceeds the threshold value Dth, the system control circuit 121 proceeds to step S1204 to perform focus detection with a small aperture, and if it is equal to or less than the threshold value Dth, the system control circuit 121 goes to step S1208. move on. By determining the aperture value for focus detection in this way, it is possible to perform good focus detection in any defocus state. Other configurations and effects are the same as those in the first embodiment.

The present invention is not limited to those exemplified in each of the above embodiments, and can be appropriately modified without departing from the gist of the present invention.

By the way, in recent years, an increasing number of cameras allow the photographer to select whether to emphasize focusing accuracy or continuous shooting speed when performing continuous shooting. Therefore, when the photographer emphasizes focusing accuracy, when the conversion coefficient K exceeds the threshold value Kth, the aperture value is changed to the aperture value equal to or less than the threshold value Kth, and when the continuous shooting speed is emphasized, the aperture drive itself is desired to be omitted. Therefore, the aperture may be used for shooting by performing focus detection with the aperture value for shooting. As a result, when the photographer places importance on focusing accuracy or continuous shooting speed, the aperture drive suitable for each is performed, and continuous shooting with a balance between focusing accuracy and continuous shooting speed is performed. Is possible.

Further, in each of the above embodiments, the method of determining the aperture value of the focus detection when performing continuous shooting has been described, but the method is not limited to continuous shooting, and a single shooting of only one image may be performed.

Further, the scope of application of the present invention can be applied to all of an image pickup device for shooting a still image, an image pickup device for shooting a moving image, and an image pickup device for shooting both of them. For example, it can be applied to an image pickup device for image blur correction such as a general single-lens reflex camera, a compact camera, a video camera, or a surveillance camera.

The present invention is also realized by executing the following processing. That is, the present invention 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 reads the program. It can also be realized by the processing to be executed. It can also be realized by a circuit (for example, ASIC) that realizes one or more functions.

101 1st lens group 102 Aperture combined shutter 103 2nd lens 105 3rd lens 107 Image sensor 112 Aperture shutter actuator 121 System control circuit 124 Image sensor drive circuit 125 Image processing circuit 128 Aperture shutter drive circuit

Claims (11)

An image sensor in which a plurality of first focus detection pixels and second focus detection pixels that receive light flux passing through a first pupil region and a second pupil region different from the first pupil region of the photographing optical system are arranged. When,
A generation means for generating a first focus detection signal based on the light receiving signal of the first focus detection pixel and generating a second focus detection signal based on the light receiving signal of the second focus detection pixel.
The image shift amount is calculated based on the first focus detection signal and the second focus detection signal, and the calculated image shift amount includes the center of gravity of the first pupil portion region and the center of gravity of the second pupil portion region. A focus detection means for detecting the amount of defocus by multiplying the baseline length, which is the interval between the above, and the conversion coefficient according to the set pupil distance of the image pickup element .
A determination means for determining the aperture value at the time of focus detection based on the conversion coefficient is provided .
When the conversion coefficient is larger than the threshold value, the aperture value at the time of focusing detection is changed to the open side of the aperture value for photography, and the aperture value for photography is returned to the aperture value at the time of photography. Imaging device. The imaging device according to claim 1 , wherein the conversion coefficient is a value corresponding to the optical conditions of the photographing optical system at the time of photographing. The image pickup apparatus according to claim 1 , wherein the conversion coefficient is selected from a conversion coefficient table previously recorded in a memory according to the optical conditions of the photographing optical system at the time of photographing. The imaging device according to claim 2 or 3 , wherein the optical conditions of the photographing optical system include at least the exit pupil distance of the photographing optical system. The image pickup apparatus according to any one of claims 2 to 4 , wherein the optical conditions of the photographing optical system include at least frame vignetting information of the photographing optical system. The image pickup apparatus according to any one of claims 2 to 5 , wherein the optical conditions of the image pickup element include at least a set pupil distance of the image pickup element. The image pickup apparatus according to any one of claims 1 to 6 , further comprising a selection means for the photographer to select an aperture value at the time of focus detection. Claims 1 to 6 are characterized in that, when the conversion coefficient exceeds the threshold value, the determination means sets the aperture value at the time of focus detection to a diaphragm value such that the conversion coefficient is equal to or less than the threshold value. The image pickup apparatus according to any one of the above. When the conversion coefficient exceeds the threshold value and the detected defocus amount is equal to or less than the threshold value, the determination means sets the aperture value at the time of the focus detection to be the aperture value such that the conversion coefficient is equal to or less than the threshold value. The image pickup apparatus according to any one of claims 1 to 6 , wherein the image pickup apparatus is set to. It also has a control means for controlling the aperture diameter of the aperture to adjust the amount of shooting light.
The image pickup apparatus according to any one of claims 1 to 9 , wherein the control means controls the aperture diameter of the diaphragm based on the diaphragm value determined by the determination means. An image sensor in which a plurality of first focus detection pixels and second focus detection pixels that receive light flux passing through a first pupil region and a second pupil region different from the first pupil region of the photographing optical system are arranged. It is a control method of an image pickup device provided with
A generation step of generating a first focus detection signal based on the light receiving signal of the first focus detection pixel and generating a second focus detection signal based on the light receiving signal of the second focus detection pixel.
The image shift amount is calculated based on the first focus detection signal and the second focus detection signal, and the calculated image shift amount includes the center of gravity of the first pupil portion region and the center of gravity of the second pupil portion region. A focus detection step for detecting the amount of defocus by multiplying the baseline length, which is the interval between the above, and the conversion coefficient according to the set pupil distance of the image pickup element .
A determination step for determining the aperture value at the time of focus detection based on the conversion coefficient is provided .
When the conversion coefficient is larger than the threshold value, the aperture value at the time of focusing detection is changed to the open side of the aperture value for photography, and the aperture value for photography is returned to the aperture value at the time of photography. Control method of the image pickup device.

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