Control unit, imaging apparatus, control method, program, and storage medium

Abstract

To provide a control unit that can accurately correct a focus detection error caused by aberration of an optical system.SOLUTION: A control unit (100) can execute automatic focus detection in at least either one of a phase difference detection method or a contrast method, and has: storage means (15) that stores a correction value (103) for correcting the position of a focus lens in an optical system (1) in the automatic focus detection; and control means (17) that controls the position of the focus lens by using the correction value. A first wave front aberration of the optical system is measured in a first condition related to a subject distance and an f-value, and the correction value is acquired on the basis of a second wave front aberration of the optical system estimated from the first wave front aberration in a second condition different from the first condition.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to a control device, an imaging device, a control method, a program, and a storage medium. [Background technology]

[0002] In the auto focus detection (AF) of an imaging device, a difference occurs between the best focus position evaluated by the auto focus detection and the best focus position evaluated by the human eye due to the influence of aberrations, etc. Therefore, a process is performed to shift the focus lens from the focus position where the AF evaluation value is maximum to the focus position where the visual best focus position is obtained.

[0003] Patent Document 1 discloses a method of using low-frequency components of spatial frequency included in a subject image as an AF evaluation value of contrast AF and shifting the focus position toward the high-frequency component by a focus correction amount. Patent Document 2 discloses a method of calculating, as a correction value, the difference between a focus lens position obtained by weighting and adding a plurality of pre-stored focus lens positions at which the defocus MTF is maximized by an AF evaluation band and an evaluation band for viewing a captured image. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2015-148707 A [Patent Document 2] JP 2015-222411 A Summary of the Invention [Problem to be solved by the invention]

[0005] In the method disclosed in Patent Document 1, a band-pass filter is used to obtain spatial frequency components contained in a captured image, and a focus correction amount is obtained. However, the band-pass filter also includes signals other than the frequency band that is actually desired to be viewed, so the accuracy of correction is reduced. In the method disclosed in Patent Document 2, no consideration is given to the interpolation of F-numbers other than the adjustment distance, so high-precision correction cannot be performed.

[0006] SUMMARY OF THE PRESENT EMBODIMENTS An object of the present invention is to provide a control device capable of correcting focus detection errors caused by aberrations in an optical system with high accuracy. [Means for solving the problem]

[0007] A control device as one aspect of the present invention is a control device capable of performing autofocus detection using at least one of a phase difference detection method or a contrast method, and has a memory means for storing a correction value for correcting the position of a focus lens of an optical system in the autofocus detection, and a control means for controlling the position of the focus lens using the correction value, wherein the correction value is obtained based on a second wavefront aberration of the optical system under a second condition different from the first condition, the second condition being estimated from a first wavefront aberration of the optical system measured under a first condition related to a subject distance and an F-number.

[0008] Other objects and features of the present invention are illustrated in the following examples. Effect of the Invention

[0009] According to the present invention, it is possible to provide a control device capable of correcting focus detection errors caused by aberrations in an optical system with high accuracy. [Brief description of the drawings]

[0010] [Figure 1] FIG. 2 is a block diagram of an imaging device in each embodiment. [Diagram 2] 4 is a flowchart showing a process of the imaging apparatus in each embodiment. [Diagram 3]FIG. 4 is a diagram showing the defocus MTF of the imaging optical system in each example. [Figure 4] 4 is a flowchart showing the AF process in the first to third embodiments. [Diagram 5] 4 is a flowchart showing a calculation process of a focus correction amount in the first to third embodiments. [Figure 6] FIG. 4 is a characteristic diagram of the subject distance and spherical aberration in each embodiment. [Figure 7] 5 is a characteristic diagram of spherical aberration and focus deviation amount in the first embodiment. FIG. [Figure 8] FIG. 11 is a characteristic diagram of MTF and spherical aberration in the second embodiment. [Figure 9] FIG. 11 is a characteristic diagram of spherical aberration and focus deviation amount in the second embodiment. [Figure 10] FIG. 13 is a characteristic diagram of MTF and focus position for each spatial frequency in the third embodiment. [Figure 11] 13 is a flowchart showing an AF process in the fourth embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0012] Each embodiment has a specific configuration to facilitate understanding and explanation of the present invention, but the present invention is not limited to such a specific configuration. For example, each embodiment describes a digital camera of a type in which the lens cannot be replaced or a single-lens reflex type digital camera of a type in which the lens can be replaced (lens unit detachable type), but each embodiment can also be applied to a video camera. Each embodiment can also be applied to any electronic device equipped with a camera, such as a mobile phone, a personal computer (laptop, tablet, desktop type, etc.), or a game console. EXAMPLES

[0013] Before going into a detailed description of each embodiment, a configuration of an image capture device (control device) 100 such as a digital camera according to all the embodiments of the present invention will be described. The image capture devices 100 have a common configuration as shown in FIG.

[0014] FIG. 1 is a block diagram of an imaging device 100 in each embodiment. The imaging device 100 has an imaging optical system (optical system) 1 including a lens (lens group) and a diaphragm (aperture stop), a mechanical shutter 2, an imaging element 3, and a CDS unit 4. The imaging element 3 is an image sensor such as a CCD (Charge Coupled Device) or a CMOS (Complementary Metal Oxide Semiconductor). The CDS unit performs analog signal processing. Note that in each embodiment, the imaging optical system 1 is configured integrally with a camera body including the imaging element 3, but is not limited to this and may be configured to be detachable from the camera body.

[0015] The imaging device 100 also has an A / D conversion unit 5 and a timing signal generation unit 6. The A / D conversion unit 5 converts an analog signal into a digital signal. The timing signal generation unit 6 generates signals for operating the imaging element 3, the CDS unit 4, and the A / D conversion unit 5.

[0016] The imaging device 100 also has a drive unit 7, a signal processing unit 8, an image memory 9, and a recording medium 10. The drive unit 7 drives the imaging optical system 1, the mechanical shutter 2, and the image sensor 3. The signal processing unit 8 performs signal processing required for captured image data. The image memory 9 stores the image data that has been signal processed. The recording medium 10 is a memory that is removable from the imaging device 100.

[0017] The imaging device 100 also has a recording control unit 11, an image display unit 12, a display control unit 13, and a system control unit 14. The recording control unit 11 records the signal-processed image data on the recording medium 10. The image display unit 12 displays the signal-processed image data. The display control unit 13 causes the image display unit 12 to display an image. The system control unit 14 controls the entire imaging device 100. The system control unit 14 also has a focus adjustment unit 17. The focus adjustment unit 17 is a control means capable of performing autofocus detection (AF) using at least one of a phase difference detection method or a contrast method.

[0018] The imaging device 100 also has a non-volatile memory (ROM) 15 and a volatile memory (RAM) 16. The non-volatile memory 15 stores a program describing a control method executed by the system control unit 14, control data such as parameters and tables used when executing the program, and correction data such as defect addresses. The volatile memory 16 transfers and stores the program, control data, and correction data stored in the non-volatile memory 15, and is used when the system control unit 14 controls the imaging device 100.

[0019] The following describes the shooting operation using the mechanical shutter 2 in the imaging device 100 configured as described above. Prior to the shooting operation, when the system control unit 14 starts operating, such as when the imaging device 100 is powered on, the necessary programs, control data, and correction data are transferred from the nonvolatile memory 15 to the volatile memory 16 and stored therein. These programs and data are used when the system control unit 14 controls the imaging device 100. If necessary, additional programs and data may be transferred from the nonvolatile memory 15 to the volatile memory 16, or the system control unit 14 may directly read and use the data in the nonvolatile memory 15.

[0020] First, the imaging optical system 1 drives the aperture and the lens in response to a control signal from the system control unit 14 to form an image of the subject set to an appropriate brightness on the imaging element 3. Next, the mechanical shutter 2 is driven to block the imaging element 3 in accordance with the operation of the imaging element 3 in response to a control signal from the system control unit 14 so as to achieve the required exposure time. If the imaging element 3 has an electronic shutter function, it may be used in combination with the mechanical shutter 2 to ensure the required exposure time. The imaging element 3 is driven by a drive pulse based on an operation pulse generated by a timing signal generating unit 6 controlled by the system control unit 14, and converts the subject image into an electrical signal (analog image signal) by photoelectric conversion and outputs the analog image signal. The analog image signal output from the imaging element 3 has clock synchronization noise removed by the CDS unit 4 in response to an operation pulse generated by the timing signal generating unit 6 controlled by the system control unit 14, and is converted into a digital image signal by the A / D conversion unit 5.

[0021] Next, the signal processing unit 8 controlled by the system control unit 14 performs image processing such as color conversion, white balance, and gamma correction, resolution conversion processing, and image compression processing on the digital image signal. The image memory 9 is used to temporarily store the digital image signal undergoing signal processing, or to store image data that is a digital image signal that has been signal-processed. The image data that has been signal-processed by the signal processing unit 8 or the image data stored in the image memory 9 is converted by the recording control unit 11 into data suitable for the recording medium 10 (e.g., file system data having a hierarchical structure) and recorded on the recording medium 10. Alternatively, after the resolution conversion processing is performed by the signal processing unit 8, the display control unit 13 converts the data into a signal suitable for the image display unit 12 (e.g., an analog signal of the NTSC system, etc.) and displays it on the image display unit 12.

[0022] The signal processing unit 8 may output the digital image signal as image data directly to the image memory 9 or the recording control unit 11 without performing signal processing in response to a control signal from the system control unit 14. Furthermore, when requested by the system control unit 14, the signal processing unit 8 outputs information on the digital image signal or image data generated in the signal processing process, or information extracted therefrom, to the system control unit 14. Here, the image data information is, for example, information such as the spatial frequency of the image, the average value of a specified region, or the data amount of a compressed image. When requested by the system control unit 14, the recording control unit 11 outputs information such as the type or free space of the recording medium 10 to the system control unit 14.

[0023] Next, a description will be given of a playback operation when image data is recorded on the recording medium 10. The recording control unit 11 reads out image data from the recording medium 10 in response to a control signal from the system control unit 14. The signal processing unit 8 performs image expansion processing when the image data is a compressed image in response to a control signal from the system control unit 14, and stores the image in the image memory 9. The image data stored in the image memory 9 is subjected to resolution conversion processing by the signal processing unit 8, and then converted by the display control unit 13 into a signal suitable for the image display unit 12, and displayed on the image display unit 12.

[0024] Next, the imaging device 100 in each embodiment commonly executes the process shown in Fig. 2. Fig. 2 is a flowchart showing the process of the imaging device 100, and shows the overall flow of the process during shooting. In Fig. 2, each step is mainly executed by the system control unit 14 unless otherwise specified.

[0025] First, in step S301, the system control unit 14 detects the state of a main switch (power switch) (not shown) included in an operation unit (not shown) and determines whether the main switch is on or not. If the main switch is off, step S301 is repeated. On the other hand, if the main switch is on, the process proceeds to step S302.

[0026] In step S302, the system control unit 14 checks the remaining capacity of the attached recording medium 10 and judges whether the remaining capacity is sufficient. If the remaining capacity of the recording medium 10 is sufficient, for example, if it is larger than the captured image data size determined by the image quality setting, the process proceeds to step S304. On the other hand, if it is judged that the remaining capacity of the recording medium 10 is not sufficient, the process proceeds to step S303.

[0027] In step S303, the system control unit 14 issues a warning that the remaining capacity of the recording medium 10 is insufficient, and the process returns to step S301. The warning can be issued, for example, by displaying a message on the image display unit 12, outputting a sound from a sound output unit (not shown), or both.

[0028] In step S304, the system control unit 14 displays the focus detection area on the image display unit 12. That is, the system control unit 14 stores the captured image in the image memory 9, which is a temporary storage unit, and uses the display control unit 13 to generate a display image and display it on the image display unit 12 in a display process that is successively performed, and also displays the focus detection area that was set during normal shooting.

[0029] Next, in step S305, the system control unit 14 determines the state of the release button. If the release button is half-pressed, the process proceeds to step S307. On the other hand, if the release button is not half-pressed, the process proceeds to step S306. In step S306, the system control unit 14 determines the state of the main switch. If the main switch is on, the process returns to step S304. On the other hand, if the main switch is not on, the process returns to step S301.

[0030] In step S307, the system control unit 14 detects the subject brightness using the output signal of the A / D conversion unit 5 (photometry). Then, the system control unit 14 determines the conditions for automatic focus detection (AF) using a program chart based on the detection result, and changes the aperture diameter. Since AF is performed in the open aperture state, the depth of field becomes narrow and the accuracy is improved, AF may be performed in the open aperture even when shooting with the aperture narrowed. In that case, the aperture value (F value) according to the exposure state may differ between AF and shooting. Therefore, in order to correct the difference in the viewing state caused by the aperture during AF and shooting, it is necessary to correct the focus position (the position of the focus lens in the imaging optical system 1).

[0031] Next, in step S308, the system control unit 14 performs automatic focusing processing (AF processing) using the focus adjustment unit 17. If the subject brightness is lower than a predetermined value from the detection result of step S307, an AF auxiliary light is emitted from a light source (not shown) toward the subject for a predetermined time to perform automatic focusing processing. Next, in step S309, in the focused state, the system control unit 14 determines whether or not the release button (not shown) is fully pressed. If the release button is fully pressed, the process proceeds to step S311. On the other hand, if the release button is not fully pressed, the process proceeds to step S310. In step S310, the system control unit 14 determines whether or not the release button is half-pressed. If the release button is half-pressed, the process returns to step S309. On the other hand, if the release button is not half-pressed, the process returns to step S304.

[0032] In step S311, the system control unit 14 starts the photographing process by pressing the release button all the way down. At this time, the system control unit 14 changes the aperture diameter to the aperture diameter for photographing. Next, in step S312, the system control unit 14 judges the remaining capacity of the recording medium 10 in the same manner as in step S302. If the remaining capacity of the recording medium 10 is sufficient, for example, if the remaining capacity is equal to or greater than the remaining capacity required for the next photographing, the process proceeds to step S313. On the other hand, if the remaining capacity of the recording medium 10 is not sufficient, the process proceeds to step S303. In step S313, the system control unit 14 judges whether the release button is fully pressed. If the release button is fully pressed, the process repeats step S313. On the other hand, if the release button is not fully pressed, the process proceeds to step S310.

[0033] This embodiment relates to AF control in the case where the imaging device 100 has a characteristic that a difference occurs between the evaluation frequency (spatial frequency) of a signal used for autofocus detection (AF) and the evaluation frequency (spatial frequency) when viewing a captured image. When capturing a still image, all pixels of the image sensor 3 are read in order to obtain a more highly detailed image to be viewed. On the other hand, during AF, the driving method of the image sensor 3 is switched and pixel addition or thinning processing of the pixels of the image sensor 3 is performed in order to shorten the release time lag. As a result, the spatial frequency evaluated during AF is smaller than the spatial frequency when capturing the captured image to be viewed by the user.

[0034] The signal processing during AF will be described below. First, the driving method of the image sensor 3 is changed during AF by the operation pulse generated by the timing signal generating unit 6, and the signal of the image sensor 3 that has undergone pixel addition and thinning processing is acquired. After that, the signal is converted into a digital signal by the A / D conversion unit 5, and white balance adjustment is performed to extract an arbitrary color signal according to the color filter of the image sensor 3, and gamma correction is performed to emphasize low luminance components and suppress high luminance components. The gamma-corrected luminance signal is used to calculate an AF evaluation value for each pixel line of the image sensor 3 within the set focus detection area. In this embodiment, the AF evaluation value is calculated for each of the horizontal line direction and the vertical line direction. This allows focus detection to be performed for contrast information of the subject in two orthogonal directions, the horizontal direction and the vertical direction.

[0035] An example of focus correction information will be described with reference to Fig. 3. Fig. 3 is a diagram showing the defocus MTF (Modulation Transfer Function) of the imaging optical system 1. In Fig. 3, the vertical axis indicates the MTF, and the horizontal axis indicates the focus position. Due to the influence of aberration and the like, a difference occurs between the focus position where the MTF (AF evaluation value) of the low-frequency component 102 used in automatic focus detection has a maximum value and the focus position where the MTF of the high-frequency component 101 used in viewing a captured image has a maximum value. Therefore, in order to correct the difference (focus deviation amount) between the peak positions of the low-frequency component 102 and the high-frequency component 101, it is necessary to correct the focus position by the focus correction amount 103.

[0036] Here, the focus correction amount 103 corresponds to a correction value for correcting the focus position of the imaging optical system 1 in automatic focus detection. The focus correction amount 103 is a correction value for reducing the difference between a focus position (first position of the focus lens) which is the peak position of the AF evaluation value and a focus position (second position of the focus lens) which is the peak position of the focus state in shooting. The focus correction amount 103 is stored in a storage means such as the nonvolatile memory 15. The focus adjustment unit 17 uses the focus correction amount 103 to control the focus position.

[0037] Next, the AF process (step S308 in FIG. 2) of the focus adjustment unit 17 will be described with reference to FIG 4. FIG 4 is a flowchart showing the AF process in this embodiment.

[0038] First, in step S401, the focus adjustment unit 17 obtains an AF evaluation value of the low-frequency component 102, and obtains a focus position based on the AF evaluation value. Next, in step S402, the focus adjustment unit 17 determines whether the shooting distance is a macro shooting distance. If the shooting distance is the macro shooting distance, the process proceeds to step S403. On the other hand, if the shooting distance is the normal shooting distance, the process proceeds to step S404.

[0039] In step S403, the focus adjustment unit 17 acquires a focus correction amount corresponding to the focus position acquired in step S401 from a macro shooting distance table. The macro shooting distance table is stored, for example, in the non-volatile memory 15. In step S404, the focus adjustment unit 17 acquires a focus correction amount corresponding to the focus position acquired in step S401 from a normal shooting distance table. The normal shooting distance table is stored, for example, in the non-volatile memory 15.

[0040] Next, in step S405, the focus adjustment unit 17 determines the focus position by shifting the focus position acquired in step S401 by the focus correction amount 103 toward the peak position of the high frequency component 101 (to the left) as shown in Fig. 3. Next, in step S406, the focus adjustment unit 17 causes the image display unit 12 to display a display indicating the focus detection area (auto focus detection frame display) superimposed on, for example, a live view image, and ends this process.

[0041] Next, a calculation process of the focus correction amount 103 in this embodiment will be described with reference to Fig. 5. Fig. 5 is a flowchart showing the calculation process of the focus correction amount 103.

[0042] First, in step S501, the focus adjustment unit 17 uses the design value of the imaging optical system 1 to calculate an arithmetic expression for obtaining the focus correction amount 103 from the spherical aberration. The evaluation frequency band differs depending on the pixel pitch of the imaging element 3. For this reason, it is preferable to prepare a plurality of arithmetic expressions in consideration of a plurality of frequency bands. The method of deriving the arithmetic expression will be described later.

[0043] Next, in step S502, the focus adjustment unit 17 acquires the wavefront aberration (first wavefront aberration) in the infinity focused state and the aperture open state (first condition) of the imaging optical system 1. Here, the wavefront aberration (first wavefront aberration) is measured in advance as the aberration of the imaging optical system 1. Next, in step S503, the focus adjustment unit 17 estimates the wavefront aberration when the aperture is narrowed (wavefront aberration at other F values, second wavefront aberration) using the central aberration information corresponding to the aperture diameter among the measured wavefront aberration (first wavefront aberration). Next, in step S504, the focus adjustment unit 17 acquires the spherical aberration of the imaging optical system 1 using Zernike polynomial approximation (approximation formula) from the wavefront aberration (second wavefront aberration) acquired in step S503. Next, in step S505, the focus adjustment unit 17 estimates the spherical aberration for each F value and subject distance using the design data.

[0044] Here, the relationship between the object distance and the spherical aberration will be described with reference to FIG. 6. FIG. 6 is a characteristic diagram of the object distance and the spherical aberration. In FIG. 6, the vertical axis indicates the spherical aberration, and the horizontal axis indicates the reciprocal of the distance. Design value 201 indicates the design value of the spherical aberration. Simulation value (large spherical aberration) 202 indicates the simulation value when the spherical aberration is large due to a manufacturing error. Simulation value (small spherical aberration) 203 indicates the simulation value when the spherical aberration is small due to a manufacturing error. The individual difference in the spherical aberration does not depend on the change in the focal length, and the change amount of the spherical aberration is constant. Based on this characteristic, an estimated value 204 of the spherical aberration other than the focal length measured in step S502 is obtained.

[0045] 5, the focus adjustment unit 17 applies the appropriate arithmetic expression obtained in step S501 to the spherical aberration obtained in step S505 based on the pixel pitch information of the image sensor 3 to calculate the focus correction amount 103. The focus correction amount 103 is stored in the form of a table (focus correction amount table). The focus correction amount table has correction values ​​for items such as focal length (in the case of zoom), F-number, shooting distance, and temperature of the image pickup device 100. It is preferable to tabulate the changes in each parameter while dividing them into small sections. The focus correction amount table is stored in the non-volatile memory 15. When shooting, an appropriate focus correction amount is obtained from the focus correction amount table based on information such as the focal length (in the case of zoom), F-number, shooting distance, and temperature of the image pickup device 100 during AF.

[0046] When the imaging device 100 has a detachable lens unit, a plurality of focus correction amount tables that take into account pixel pitch information of the imaging element 3 are stored in the lens unit. Then, of the plurality of focus correction amount tables, an appropriate (preferably optimal) focus correction amount table is used based on the pixel pitch information received from the camera body. In addition, a method of calculating a focus correction amount that focuses on the average value of the best MTF in the vertical and horizontal directions using not only spherical aberration but also astigmatism and coma aberration that can be calculated by Zernike polynomial approximation can be considered.

[0047] Next, a method of deriving an arithmetic expression for calculating the focus correction amount 103 from the spherical aberration will be described with reference to FIG. 7. FIG. 7 is a characteristic diagram of spherical aberration and focus deviation amount. In FIG. 7, the vertical axis indicates the focus deviation amount, and the horizontal axis indicates the spherical aberration. There is a correlation between the spherical aberration and the focus deviation amount. The arithmetic expression is derived using this correlation. A polynomial approximation is used to derive an arithmetic expression using the correlation between the spherical aberration and the focus deviation amount. Methods such as the least squares method are considered. When the focus correction amount to be calculated is BP, the spherical aberration is SA, the slope is A, and the intercept is B, the arithmetic expression is expressed as the following equation (1).

[0048] BP = A × SA + B … (1) As described above, the focus correction amount 103 is acquired based on the second wavefront aberration of the imaging optical system 1 under a second condition different from the first condition, which is estimated from the first wavefront aberration of the imaging optical system 1 measured under a first condition related to the subject distance and the F-number. Preferably, the focus adjustment unit 17 estimates the second wavefront aberration using the first wavefront aberration. Also preferably, the non-volatile memory 15 stores the second wavefront aberration. Also preferably, the focus adjustment unit 17 calculates the focus correction amount 103 based on the second wavefront aberration and the spatial frequency for each subject distance. Also preferably, the focus adjustment unit 17 calculates the focus correction amount 103 using the spherical aberration acquired from the second wavefront aberration. More preferably, the focus adjustment unit 17 estimates the spherical aberration by offsetting the data of the design value by the difference between the first wavefront aberration of the imaging optical system 1 and the design value. Also preferably, the focus adjustment unit 17 acquires the focus correction amount 103 based on at least one of the spatial frequency, direction, detected color, focal length, F-number, subject distance, and temperature in automatic focus detection. EXAMPLES

[0049] Next, a second embodiment of the present invention will be described. This embodiment differs from the first embodiment in that the calculation formula for calculating the focus correction amount is divided into a macro shooting distance region and a normal shooting distance region. In the first embodiment, the focus correction amount is calculated by one calculation formula regardless of the subject distance. However, at the macro shooting distance, the amount of spherical aberration increases rapidly, and the amount of focus deviation increases. Therefore, it is preferable to separate the calculation formula for macro shooting and the normal shooting distance. Note that Figs. 1 to 6 described in the first embodiment are also applied to this embodiment.

[0050] This embodiment will be described with reference to Fig. 8 and Fig. 9. Fig. 8 is a characteristic diagram of MTF and spherical aberration in this embodiment. In Fig. 8, the vertical axis indicates MTF, and the horizontal axis indicates spherical aberration. Fig. 9 is a characteristic diagram of spherical aberration and defocus amount in this embodiment. In Fig. 9, the vertical axis indicates defocus amount, and the horizontal axis indicates spherical aberration.

[0051] As shown in FIG. 8, in an area where the spherical aberration is low, the MTF is high and the amount of focus deviation is small. However, as the spherical aberration increases, the MTF decreases. As a result, as shown in FIG. 9, the ratio of the change in the amount of focus deviation to the change in the spherical aberration changes at a certain MTF. For this reason, it is preferable to use different calculation formulas for the macro shooting distance area and the normal shooting distance area. For example, a method can be used in which the MTF at the change point of the correlation between the MTF and the amount of focus deviation is used as a threshold value, the approximation range is divided into an area where the MTF is high and an area where the MTF is low, and the least squares method is used to find the respective values.

[0052] The focus correction amount to be calculated is BP, the spherical aberration is SA, the slope in the high MTF region is MTFH_A, the intercept is MTFH_B, the slope in the low MTF region is MTFL_A, and the intercept is MTFL_B. In this case, the calculation formula is expressed as the following formulas (2a) and (2b).

[0053] (Area with high MTF) BP = MTFH_A × SA + MTFH_B … (2a) (Area with low MTF) BP = MTFL_A × SA + MTFL_B … (2b) As described above, in this embodiment, the focus correction amount 103 includes a first focus correction amount (first correction value) and a second focus correction amount (second correction value) different from the first focus correction amount. When the focus adjustment unit 17 determines that the shooting distance is the macro shooting distance, it controls the focus position using the first correction value. On the other hand, when the focus adjustment unit 17 determines that the shooting distance is not the macro shooting distance, it controls the focus position using the second correction value. EXAMPLES

[0054] Next, a third embodiment of the present invention will be described. This embodiment differs from the first and second embodiments in that the spatial frequency to be evaluated is changed according to the subject distance. Note that Figs. 1 to 6 described in the first embodiment are also applied to this embodiment.

[0055] The spatial frequency evaluated in this embodiment will be described with reference to FIG. 10. FIG. 10 is a characteristic diagram of the MTF and the focus position for each spatial frequency. In FIG. 10, the vertical axis indicates the MTF, and the horizontal axis indicates the focus position. In the high frequency 601, the depth of field 603 is narrower than that in the low frequency 602. In the macro region, the spherical aberration is large, which deteriorates the image quality, and it may not be possible to evaluate the amount of focus deviation at a predetermined spatial frequency. For this reason, in the macro shooting distance region where the evaluation frequency when viewing the captured image is not resolved due to problems such as lens performance, the evaluation is performed using a spatial frequency having a depth of field equivalent to the depth of field 603 of the MTF resolved at the distance of the macro shooting distance region where the image is resolved. EXAMPLES

[0056] Next, a fourth embodiment of the present invention will be described. This embodiment differs from the first to third embodiments in that it holds aberration information in addition to a focus correction amount table, and performs aberration estimation processing and correction value calculation processing.

[0057] In the first embodiment, the correction value table holds focus correction amounts for items such as focal length (in the case of zooming), F-number, shooting distance, and temperature of the imaging device 100. On the other hand, in this embodiment, by estimating aberration and calculating the focus correction amount during AF processing, it is possible to reduce the storage capacity of the correction value table. If the imaging device 100 has a detachable lens unit, the lens unit may hold the aberration estimation process, aberration information, and correction value calculation process. Here, the aberration information refers to the aberration of the imaging optical system 1 at the design reference temperature. The aberration information is stored in the non-volatile memory 15. Note that Figs. 1 to 3 and Fig. 6 described in the first embodiment are also applied to this embodiment.

[0058] The AF process (step S308 in FIG. 2) of the focus adjustment unit 17 will be described with reference to FIG 11. FIG 11 is a flowchart showing the AF process in this embodiment.

[0059] First, in step S701, the focus adjustment unit 17 obtains an AF evaluation value of the low-frequency component 102, and obtains a focus position based on the AF evaluation value. Then, in step S702, the focus adjustment unit 17 determines whether or not a conversion lens is connected. If a conversion lens is connected, the process proceeds to step S703. On the other hand, if a conversion lens is not connected, the process proceeds to step S704.

[0060] In step S703, the focus adjustment unit 17 acquires aberration information of the conversion lens, and estimates the aberration when the conversion lens is connected from the design data together with information on the focal length, F-number, and subject distance during AF. Here, the aberration information of the conversion lens may be acquired in advance at the timing when the imaging device 100 detects the connection of the conversion lens. In step S704, the focus adjustment unit 17 estimates the aberration using the design data based on the information on the focal length, F-number, and subject distance during AF (normal aberration estimation).

[0061] Next, in step S705, the focus adjustment unit 17 determines whether the temperature (current temperature) of the image capture device 100 is room temperature, for example, whether the difference (temperature difference) between the current temperature of the image capture device 100 and the design reference temperature is within a predetermined value range. If the temperature is room temperature, the process proceeds to step S707. On the other hand, if the temperature is not room temperature, the process proceeds to step S706. In step S706, the focus adjustment unit 17 estimates the aberration when the temperature changes (under the current temperature).

[0062] Next, in step S707, the focus adjustment unit 17 determines whether the shooting distance is the macro shooting distance. If the shooting distance is the macro shooting distance, the process proceeds to step S708. On the other hand, if the shooting distance is the normal shooting distance, the process proceeds to step S709.

[0063] In step S708, the focus adjustment unit 17 acquires pixel pitch information of the image sensor 3, and determines a spatial frequency to be evaluated based on the acquired pixel pitch information to derive a macro photography arithmetic equation. Here, the macro photography arithmetic equation is an equation for calculating a focus correction amount for correcting a focus deviation amount due to a temperature difference or aberration, using the estimated aberration information or the temperature difference acquired in step S705. Then, the focus adjustment unit 17 applies the macro photography arithmetic equation to the estimated aberration information to calculate a focus correction amount (macro focus correction amount). If the image pickup device 100 has a detachable lens unit, the arithmetic equation derivation process may be performed at the timing when it is detected that the lens unit is connected to the camera body. In addition, when the lens unit is connected, wavefront aberration estimation, arithmetic equation derivation process, and focus correction amount calculation may be performed, and stored in advance as a table in a storage unit such as the non-volatile memory 15.

[0064] In step S709, the focus adjustment unit 17 acquires pixel pitch information of the image sensor 3. Based on the acquired pixel pitch information, the focus adjustment unit 17 determines a spatial frequency to be evaluated and derives an arithmetic expression for normal shooting distance. The arithmetic expression for normal shooting distance is an expression for calculating a focus correction amount for correcting a focus deviation amount due to a temperature difference or aberration, using the estimated aberration information or the temperature difference acquired in step S705. The focus adjustment unit 17 then applies the arithmetic expression for normal shooting distance to the estimated aberration information to calculate a focus correction amount (normal focus correction amount). If the image pickup device 100 has a detachable lens unit, the arithmetic expression derivation process may be performed at the timing when it is detected that the lens unit is connected to the camera body.

[0065] Next, in step S710, the focus adjustment unit 17 determines the focus position acquired in step S701 by shifting the focus position by the focus correction amount 103 toward the peak position of the high frequency component 101 (to the left) as shown in Fig. 3. Next, in step S711, the focus adjustment unit 17 causes the image display unit 12 to display a display indicating the focus detection area (auto focus detection frame display) superimposed on, for example, a live view image, and ends this process.

[0066] (Other Examples) The present invention can also be realized by a process in which a program for implementing one or more of the functions of the above-mentioned embodiments is supplied to a system or device via a network or a storage medium, and one or more processors in a computer of the system or device read and execute the program. It can also be realized by a circuit (e.g., ASIC) that implements one or more of the functions.

[0067] Each embodiment uses wavefront measurement to measure wavefront aberration including aberrations such as spherical aberration or astigmatism of the optical system. As a result, each embodiment provides a control device, an imaging device, a control method, a program, and a storage medium that are capable of correcting focus detection errors caused by aberrations of the optical system with high accuracy.

[0068] The disclosure of each embodiment includes the following configurations and methods. (Configuration 1) A control device capable of performing automatic focus detection using at least one of a phase difference detection method and a contrast method, a storage unit that stores a correction value for correcting a position of a focus lens of an optical system in the automatic focus detection; a control unit that controls the position of the focus lens by using the correction value; a control device characterized in that the correction value is acquired based on a second wavefront aberration of the optical system under a second condition different from the first condition, the second condition being estimated from a first wavefront aberration of the optical system measured under a first condition related to an object distance and an F-number. (Configuration 2) 2. The control device according to configuration 1, wherein the control means estimates the second wavefront aberration using the first wavefront aberration. (Configuration 3) 3. The control device according to configuration 1 or 2, wherein the storage means stores the second wavefront aberration. (Configuration 4) 4. The control device according to any one of configurations 1 to 3, wherein the control means calculates the correction value based on the second wavefront aberration and a spatial frequency for each subject distance. (Configuration 5) 5. The control device according to any one of configurations 1 to 4, wherein the control means calculates the correction value by using a spherical aberration obtained from the second wavefront aberration. (Configuration 6) The control device according to configuration 5, wherein the control means estimates the spherical aberration by offsetting data of the design value by a difference between the first wavefront aberration of the optical system and a design value. (Configuration 7) The control device according to any one of configurations 1 to 6, characterized in that the control means acquires the correction value based on at least one of the spatial frequency, direction, detected color, focal length, the F-number, the subject distance, or temperature in the automatic focus detection. (Configuration 8) The control device according to any one of configurations 1 to 7, wherein the control means estimates the second wavefront aberration when the aperture is narrowed down by using aberration information corresponding to a diameter of an aperture among the first wavefront aberration of the optical system. (Configuration 9) The control device described in any one of configurations 1 to 8, characterized in that the correction value is a correction value for reducing the difference between a first position of the focus lens, which is a peak position of an evaluation value in the automatic focus detection, and a second position of the focus lens, which is a peak position of a focus state in shooting. (Configuration 10) the correction value includes a first correction value and a second correction value different from the first correction value, The control means when it is determined that the shooting distance is a macro shooting distance, the position of the focus lens is controlled using the first correction value; 10. The control device according to any one of configurations 1 to 9, wherein when it is determined that the shooting distance is not the macro shooting distance, the control device controls the position of the focus lens using the second correction value. (Configuration 11) 11. An imaging device comprising the control device according to any one of configurations 1 to 10 and an imaging element. (Method 1) A control method for controlling execution of auto focus detection using at least one of a phase difference detection method and a contrast method, comprising: storing a correction value for correcting a position of a focus lens of an optical system in the automatic focus detection; and controlling the position of the focus lens using the correction value, a control method characterized in that the correction value is acquired based on a second wavefront aberration of the optical system under a second condition different from the first condition, the second condition being estimated from a first wavefront aberration of the optical system measured under a first condition related to an object distance and an F-number. (Method 2) A control method for controlling execution of auto focus detection using at least one of a phase difference detection method and a contrast method, comprising: Measuring wavefront aberration of the optical system; calculating a correction value for correcting a difference between the result of the automatic focus detection calculated from the wavefront aberration and a focus state of a viewed image; and storing the correction value. (Configuration 12) A program for causing a computer to execute the control method according to Method 1 or 2. (Configuration 13) A computer-readable storage medium storing the program according to claim 12.

[0069] Although the preferred embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and various modifications and changes are possible within the scope of the gist of the present invention. [Explanation of symbols]

[0070] 1 Imaging optical system (optical system) 15 Non-volatile memory (storage means) 17 Focus adjustment unit (control means) 100 Imaging device (control device) 103 Focus correction amount (correction value)

Claims

1. A control device capable of performing automatic focus detection using at least one of a phase difference detection method and a contrast method, a storage unit that stores a correction value for correcting a position of a focus lens of an optical system in the automatic focus detection; a control unit that controls the position of the focus lens by using the correction value; The control device is characterized in that the correction value is acquired based on a second wavefront aberration of the optical system under a second condition different from the first condition, the second condition being estimated from a first wavefront aberration of the optical system measured under a first condition related to a subject distance and an F-number.

2. 2. The control device according to claim 1, wherein the control means estimates the second wavefront aberration using the first wavefront aberration.

3. 2. The control device according to claim 1, wherein the storage means stores the second wavefront aberration.

4. 2. The control device according to claim 1, wherein the control means calculates the correction value based on the second wavefront aberration and a spatial frequency for each subject distance.

5. The control device according to claim 1 , wherein the control unit calculates the correction value by using a spherical aberration obtained from the second wavefront aberration.

6. 6. The control device according to claim 5, wherein the control means estimates the spherical aberration by offsetting data of the design value by a difference between the first wavefront aberration of the optical system and a design value.

7. The control device according to claim 1 , wherein the control means acquires the correction value based on at least one of a spatial frequency, a direction, a detected color, a focal length, the F-number, the subject distance, or a temperature in the automatic focus detection.

8. 2. The control device according to claim 1, wherein the control means estimates the second wavefront aberration when the aperture is narrowed by using aberration information corresponding to a diameter of an aperture, among the first wavefront aberration of the optical system.

9. The control device according to claim 1, characterized in that the correction value is a correction value for reducing the difference between a first position of the focus lens, which is a peak position of the evaluation value in the automatic focus detection, and a second position of the focus lens, which is a peak position of the focus state in shooting.

10. the correction value includes a first correction value and a second correction value different from the first correction value, The control means When it is determined that the shooting distance is a macro shooting distance, the position of the focus lens is controlled using the first correction value; 2 . The control device according to claim 1 , wherein when it is determined that the shooting distance is not the macro shooting distance, the position of the focus lens is controlled using the second correction value.

11. An imaging device comprising: the control device according to claim 1 ; and an imaging element.

12. A control method for controlling execution of auto focus detection using at least one of a phase difference detection method and a contrast method, comprising: storing a correction value for correcting a position of a focus lens of an optical system in the automatic focus detection; and controlling the position of the focus lens using the correction value, A control method characterized in that the correction value is obtained based on a second wavefront aberration of the optical system under a second condition different from the first condition, the second condition being estimated from a first wavefront aberration of the optical system measured under a first condition related to a subject distance and an F-number.

13. A control method for controlling execution of auto focus detection using at least one of a phase difference detection method and a contrast method, comprising: Measuring wavefront aberration of the optical system; calculating a correction value for correcting a difference between the result of the automatic focus detection calculated from the wavefront aberration and a focus state of an image to be viewed; and storing the correction value.

14. A program for causing a computer to execute the control method according to claim 12 or 13.

15. A computer-readable storage medium storing the program according to claim 14.

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