JP5911530B2 - Imaging device - Google Patents

Description

  The present invention relates to a technique for focusing a photographing lens in an imaging apparatus such as a digital still camera or a video camera.

  There are a contrast detection method and a phase difference detection method as a general method using a light beam that has passed through a photographing lens in a camera focus detection and adjustment method. The contrast detection method is a method often used in video cameras and digital still cameras, and an image sensor is used as a focus detection sensor. Focusing on the output signal of the image sensor, particularly information on high-frequency components (contrast information), the position of the photographing lens with the largest evaluation value is used as the in-focus position. However, as it is said to be a hill-climbing method, it is necessary to obtain an evaluation value while moving the focus position of the photographic lens by a small amount, and it is necessary to move until the evaluation value is found to be maximum as a result. It is not suitable for operation.

  On the other hand, phase difference detection type focus detection is often used in single-lens reflex cameras, and is the technology that has contributed most to the practical application of automatic focus detection (Auto Focus: AF) single-lens reflex cameras. For example, in a digital single-lens reflex camera, this phase difference detection type AF is generally constituted by a focus detection means comprising a secondary imaging optical system. The focus detection unit includes a pupil division unit that divides the light beam that has passed through the exit pupil of the photographing lens into two different regions, and the two-divided light beam is second-order through an optical path division optical system disposed in the mirror box. An image is formed on a set of focus detection sensors by an imaging optical system. Then, by detecting the shift amount between the two image signals output from the pair of focus detection sensors, that is, the relative positional shift amount in the pupil division direction, the shift amount in the focusing direction of the photographing lens is directly obtained. is there. Therefore, once the accumulation operation is performed by the focus detection sensor, the amount and direction of the focus shift can be obtained at the same time, and a high-speed focus adjustment operation is possible. Then, at the time of photographing after focus detection, the optical path dividing optical system is retracted out of the photographing light beam, thereby exposing the image sensor to obtain a photographed image.

  On the other hand, a technique has been proposed in which an AF function of a phase difference detection method is added to an image sensor, and high-speed AF is realized even in electronic viewfinder and moving image shooting in which an image is confirmed in real time by a display means such as a rear liquid crystal. . For example, in Patent Document 1, in some of the light receiving elements (pixels) of the image sensor, the pupil division function is provided by decentering the sensitivity region of the light receiving unit with respect to the optical axis of the on-chip microlens. These pixels are used as focus detection pixels, and are arranged at predetermined intervals between the imaging pixel groups, thereby performing phase difference AF. Further, since the location where the focus detection pixels are arranged corresponds to a defective portion of the imaging pixel, image information is generated by interpolation from surrounding imaging pixel information. According to this example, since the phase difference AF can be performed on the imaging surface, high-speed and high-precision focus detection can be performed even in the electronic viewfinder and moving image shooting.

  In each of the two phase difference AFs, focus detection is performed using light beams that pass through two different pupil regions out of light beams that pass through the exit pupil of the photographing lens, and therefore the photographing light beam and the focus detection light beam are different. . As a result, a difference occurs in the best image plane position of the photographing lens between the photographing light flux and the focus detection light flux, and a correction value for correcting this difference is required. Therefore, in the phase difference AF, high-speed and high-precision focus detection is realized by correcting the best image plane position.

JP 2000-156823 A

  However, the camera has the following problems. The correction value of the best image plane position in the phase difference AF is divided into a predetermined number of lens focus positions and zoom positions and held as discrete data for each divided zone due to data capacity constraints. Therefore, if the difference in correction value switching is large when the divided zones are switched, an unnatural focusing movement occurs. Conventionally, when a still image is taken, there is no problem in configuration even if the difference in switching is large. However, during the display with the electronic viewfinder and during moving image shooting, this unnatural movement appears remarkably because the shot image is displayed and shot while adjusting the focus in real time. In addition, in single-lens reflex cameras that use an interchangeable lens system, lenses that were released in the past have a smaller number of divisions due to data capacity constraints at the time, so the difference in correction value switching is large, and unnatural movements occur. There is a problem that stands out.

  The present invention has been made in view of the above problems, and an object of the present invention is to enable natural focusing with high accuracy even when electronic viewfinder display or moving image shooting is performed by phase difference AF. .

In order to solve the above-described problems and achieve the object, an imaging apparatus according to the present invention performs focus detection of the photographing lens by a phase difference method using a pair of light beams that have passed through different pupil regions of the photographing lens. a focus detection unit, the difference between the focus detection result due to the difference between the focus position of the light flux of the pair with the focus position of the light beam having passed through the entire pupil area of the photographing lens, to at least the focus position of the photographing lens On the other hand, when correction is performed by switching correction values that exist discretely, an additional correction value for smoothing the switching between the correction values depends on the difference between the correction value before the switching and the correction value after the switching. set Te, and correcting means for correcting the difference of the focus detection result, the focus detection result of the focus detection unit, or based on the corrected focus detection result of said difference, focusing of the taking lens Characterized in that it comprises a focusing means for performing a.

  According to the present invention, it is possible to perform natural focusing with high accuracy even when electronic viewfinder display or moving image shooting is performed using phase difference AF.

1 is a block diagram illustrating a configuration of a camera system including a camera and a photographing lens according to an embodiment of the present invention. The top view which looked at the light reception pixel in which the to-be-photographed object image of an image pick-up element was seen from the imaging lens side. 3A and 3B illustrate a structure of an imaging pixel. 3A and 3B illustrate a structure of a focus detection pixel. The figure which shows schematically the focus detection structure in an image sensor and an image process part. The figure which shows the signal for a pair of focus detection formed of the synthetic | combination part and a connection part, and sent to AF part. The figure which shows the focus detection area within the imaging | photography range. FIG. 2 is an optical cross-sectional view of the lens and the image sensor in FIG. The figure which shows the focus detection correction value of phase difference type AF by an image sensor. The figure which shows the change of the focus detection amount and focus detection correction value by a focus position. The figure which shows the change of the focus detection correction value and lens drive amount by a focus position. The flowchart which shows actual focus detection operation | movement.

  FIG. 1 is a diagram illustrating a configuration of an imaging apparatus according to an embodiment of the present invention, and is a block diagram illustrating a configuration of a camera system including a camera capable of exchanging a plurality of imaging lenses and the imaging lenses. In FIG. 1, the camera system of the present embodiment includes a camera 100 and a photographing lens 300 that is attached to the camera 100 so as to be exchangeable. First, the camera 100 side will be described.

  The camera 100 according to the present embodiment is compatible with a camera system in which a plurality of types of photographing lenses 300 exist, and the same type of lenses having different manufacturing numbers can be attached. Furthermore, a photographic lens 300 having a different focal length or open F-number, or having a zoom function can be mounted, and can be replaced regardless of the same or different photographic lens.

  In the camera 100, the light beam that has passed through the photographing lens 300 passes through the camera mount 106, is reflected upward by the main mirror 130, and enters the optical viewfinder 104. The optical viewfinder 104 can be photographed while the photographer observes the subject as an optical image. In the optical viewfinder 104, some functions of the display unit 54 such as a focus display, a camera shake warning display, a flash charge display, a shutter speed display, an aperture value display, an exposure correction display, and the like are installed.

  The main mirror 130 is composed of a semi-transmissive half mirror, and a part of the light beams incident on the main mirror 130 passes through the half mirror part, is reflected downward by the sub mirror 131, and enters the focus detection device 105. To do. The focus detection device 105 employs a phase difference AF (autofocus) composed of a well-known secondary imaging optical system. The optical image obtained by the focus detection device 105 is converted into an electrical signal and sent to the AF unit 42. .

  The AF unit 42 performs a focus detection calculation from the electric signal, and the system control circuit 50 controls the focus control unit 342 on the photographing lens 300 side, which will be described later, based on the obtained calculation result. I do.

  On the other hand, when the focus adjustment processing of the taking lens 300 is completed and still image shooting, electronic viewfinder display, and moving image shooting are performed, the main mirror 130 and the sub mirror 131 are retracted out of the shooting light beam by a quick return mechanism (not shown). Then, the light beam that has passed through the photographing lens 300 is incident on the image sensor 14 that converts an optical image into an electrical signal via the shutter 12 for controlling the exposure amount. The image sensor 14 is disposed in the vicinity of the scheduled imaging plane of the photographic lens 300. After these photographing operations are completed, the main mirror 130 and the sub mirror 131 return to the positions shown in the figure.

  The electrical signal converted by the image sensor 14 is sent to the A / D converter 16, and the analog signal output is converted into a digital signal (image data). A timing generation circuit 18 supplies a clock signal and a control signal to the image sensor 14, the A / D converter 16, and the D / A converter 26, and is controlled by the memory control circuit 22 and the system control circuit 50.

  The image processing circuit 20 performs predetermined pixel interpolation processing and color conversion processing on the image data from the A / D converter 16 or the image data from the memory control circuit 22. Further, the image processing circuit 20 performs a predetermined calculation process using the image data.

  The imaging device 14 has a part of focus detection means, and can perform phase difference AF even in a state where the main mirror 130 and the sub mirror 131 are retracted out of the imaging light beam by a quick return mechanism (not shown). Of the obtained image data, image data corresponding to focus detection is converted into focus detection image data by the image processing unit 20. Thereafter, the image is sent to the AF unit 42 via the system control unit 50, and the photographing lens 300 is focused by the focus adjusting unit.

  Note that so-called contrast AF is also possible in which the system control circuit 50 causes the focus control unit 342 of the photographing lens 300 to focus based on the calculation result obtained by calculating the image data of the image sensor 14 by the image processing circuit 20. It has become a structure.

  In electronic viewfinder display and moving image shooting, the main mirror 130 and the sub mirror 131 are retracted outside the shooting light beam by a quick return mechanism (not shown), but both phase difference AF and contrast AF can be performed by the image sensor 14. It has become. In particular, since phase difference AF is possible, high-speed focusing is possible.

  As described above, the camera 100 according to the present embodiment uses the phase difference method AF by the focus detection device 105 in the normal still image shooting preparation state in which the main mirror 130 and the sub mirror 131 are in the shooting light beam. Further, the phase difference method AF and the contrast method AF using the image sensor 14 are used during the electronic finder display in which the main mirror 130 and the sub mirror 131 are retracted outside the photographing light beam or during moving image photographing. Therefore, focus detection is possible in any state of still image shooting, electronic viewfinder display, and moving image shooting.

  The memory control circuit 22 controls the A / D converter 16, the timing generation circuit 18, the image processing circuit 20, the image display memory 24, the D / A converter 26, the memory 30, and the compression / decompression circuit 32. Then, the data of the A / D converter 16 is passed through the image processing circuit 20 and the memory control circuit 22, or the data of the A / D converter 16 is passed directly through the memory control circuit 22 to the image display memory 24 or the memory 30. Is written to.

  The image display unit 28 includes a liquid crystal monitor or the like, and displays the display image data written in the image display memory 24 via the D / A converter 26. By sequentially displaying image data captured using the image display unit 28, an electronic viewfinder function can be realized. Further, the image display unit 28 can arbitrarily turn on / off the display according to an instruction from the system control circuit 50. When the display is turned off, the power consumption of the camera 100 can be greatly reduced. .

  As described above, the main mirror 130 and the sub mirror 131 are retracted out of the photographing light beam by the quick return mechanism (not shown) during the electronic finder display or during moving image shooting. Therefore, focus detection by the focus detection device 105 cannot be used at this time. Therefore, the camera 100 according to the present embodiment is configured to perform phase difference AF using the focus detection unit included in the image sensor 14. Therefore, it is possible to detect the focus of the photographing lens 300 in both the optical viewfinder and the electronic viewfinder. Needless to say, contrast detection can be performed during electronic viewfinder display or during moving image shooting.

  The memory 30 is for storing captured still images and moving images, and has a storage capacity sufficient to store a predetermined number of still images and a predetermined time of moving images. Thereby, even in the case of continuous shooting or panoramic shooting in which a plurality of still images are continuously shot, it is possible to write a large amount of images to the memory 30 at high speed. The memory 30 can also be used as a work area for the system control circuit 50.

  The compression / decompression circuit 32 has a function of compressing / decompressing image data by adaptive discrete cosine transform (ADCT) or the like, reads an image stored in the memory 30, performs compression processing or decompression processing, and finishes the processed image data Is written into the memory 30.

  The shutter control unit 36 controls the shutter 12 based on the photometry information from the photometry unit 46 in cooperation with the aperture control unit 344 that controls the aperture 312 on the photographing lens 300 side.

  The interface unit 38 and the connector 122 electrically connect the camera 100 and the photographing lens 300. These have functions of transmitting control signals, status signals, data signals, and the like between the camera 100 and the photographing lens 300 and supplying currents of various voltages. Moreover, it is good also as a structure which transmits not only electrical communication but optical communication, audio | voice communication, etc.

  The photometry unit 46 performs AE processing. The exposure state of the image can be measured by causing the light beam that has passed through the photographing lens 300 to enter the photometry unit 46 via the camera mount 106, the main mirror 130, and a photometry lens (not shown). The photometry unit 46 also has an EF processing function in cooperation with the flash 48. The system control circuit 50 can also perform AE control on the shutter control unit 36 and the aperture control unit 344 of the photographing lens 300 based on the calculation result obtained by calculating the image data of the image sensor 14 by the image processing circuit 20. It is.

  The flash 48 also has an AF auxiliary light projecting function and a flash light control function. The system control circuit 50 controls the entire camera 100, and the memory 52 stores constants, variables, programs, and the like for operation of the system control circuit 50.

  The display unit 54 is a liquid crystal display device that displays an operation state, a message, and the like using characters, images, sounds, and the like in accordance with execution of a program in the system control circuit 50. The display unit 54 is installed at a single or a plurality of positions near the operation unit of the camera 100 where it can be easily seen, and is configured by a combination of, for example, an LCD and an LED.

  Among the display contents of the display unit 54, what is displayed on the LCD or the like includes information on the number of shots such as the number of recorded sheets and the number of remaining shots, information on shooting conditions such as shutter speed, aperture value, exposure correction, and flash. There is. In addition, the remaining battery level, date / time, and the like are also displayed. In addition, as described above, a part of the display unit 54 is installed in the optical viewfinder 104. The nonvolatile memory 56 is an electrically erasable / recordable memory, and for example, an EEPROM or the like is used.

  Reference numerals 60, 62, 64, 66, 68, and 70 denote operation units for inputting various operation instructions of the system control circuit 50. A single unit such as a switch, a dial, a touch panel, a pointing by gaze detection, a voice recognition device, or the like Consists of multiple combinations.

  The mode dial switch 60 can switch and set each function mode such as power off, auto shooting mode, manual shooting mode, panoramic shooting mode, macro shooting mode, playback mode, multi-screen playback / erase mode, and PC connection mode. .

  A shutter switch SW1 62 is turned on when a shutter button (not shown) is half-pressed, and instructs to start operations such as AF processing, AE processing, AWB processing, and EF processing. The shutter switch SW2 64 is turned on when a shutter button (not shown) is fully pressed, and instructs the start of a series of processing related to photographing. The processing related to photographing is exposure processing, development processing, recording processing, and the like. In the exposure process, the signal read from the image sensor 14 is written into the memory 30 via the A / D converter 16 and the memory control circuit 22. In the development processing, development is performed using computations in the image processing circuit 20 and the memory control circuit 22. In the recording process, image data is read from the memory 30, compressed by the compression / decompression circuit 32, and written to the recording medium 200 or 210.

  The image display ON / OFF switch 66 can set ON / OFF of the image display unit 28. With this function, when photographing is performed using the optical viewfinder 104, it is possible to save power by cutting off the current supply to the image display unit including a liquid crystal monitor or the like.

  The quick review ON / OFF switch 68 sets a quick review function for automatically reproducing image data taken immediately after photographing. The operation unit 70 includes various buttons and a touch panel. The various buttons include a menu button, a flash setting button, a single shooting / continuous shooting / self-timer switching button, a selection moving button, a shooting image quality selection button, an exposure correction button, a date / time setting button, and the like.

  The power supply control unit 80 is configured by a battery detection circuit, a DC / DC converter, a switch circuit that switches blocks to be energized, and the like. The presence / absence of the battery, the type of battery, and the remaining battery level are detected, and the DC / DC converter is controlled based on the detection result and the instruction of the system control circuit 50. Supply to each part.

  The connectors 82 and 84 connect the camera 100 with a power supply unit 86 including a primary battery such as an alkaline battery or a lithium battery, a secondary battery such as a NiCd battery, a NiMH battery, or a Li ion battery, or an AC adapter.

  The interfaces 90 and 94 have a connection function with a recording medium such as a memory card or a hard disk, and the connectors 92 and 96 perform physical connection with a recording medium such as a memory card or a hard disk. The recording medium attachment / detachment detection unit 98 detects whether or not the recording medium is attached to the connector 92 or 96.

  In the present embodiment, it is assumed that there are two systems of interfaces and connectors for attaching a recording medium. Of course, the interface and the connector for attaching the recording medium may have a single or a plurality of systems, any number of systems. Moreover, it is good also as a structure provided with combining the interface and connector of a different standard. Further, the interface and the connector may be configured using a PCMCIA card, a CF (Compact Flash (registered trademark)) card, an SD card, or the like that conforms to a standard.

  In addition, by connecting various communication cards such as LAN cards and modem cards to the interface and connector, image data and management information attached to the image data can be transferred to and from other peripheral devices such as computers and printers. I can do it.

  The communication unit 110 has various communication functions such as RS232C, USB, IEEE1394, P1284, SCSI, modem, LAN, and wireless communication. The connector 112 connects the camera 100 to other devices via the communication unit 110, and is an antenna in the case of wireless communication.

  The recording media 200 and 210 are memory cards, hard disks, and the like. The recording media 200 and 210 include recording units 202 and 212 configured by a semiconductor memory, a magnetic disk, and the like, interfaces 204 and 214 with the camera 100, and connectors 206 and 216 for connecting with the camera 100.

  Next, the photographing lens 300 side will be described. The taking lens 300 is configured to be detachable from the camera 100. The lens mount 306 mechanically couples the taking lens 300 with the camera 100 and is exchangeably attached to the camera 100 via the camera mount 106. The camera mount 106 and the lens mount 306 include functions of a connector 122 and a connector 322 that electrically connect the photographing lens 300 to the camera 100. The lens 311 includes a focus lens that focuses the subject, and the diaphragm 312 is a diaphragm that controls the amount of light of the photographing light beam.

  The connector 322 and the interface 338 electrically connect the taking lens 300 to the connector 122 of the camera 100. The connector 322 has a function of transmitting a control signal, a status signal, a data signal, and the like between the camera 100 and the photographing lens 300 and supplying currents of various voltages. The connector 322 may be configured to transmit not only electrical communication but also optical communication, voice communication, and the like.

  The zoom control unit 340 controls zooming of the lens 311, and the focus control unit 342 controls the operation of the focus lens of the lens 311. If the photographing lens 300 is a single focus lens type without a zoom function, the zoom control unit 340 may be omitted.

  The aperture control unit 344 controls the aperture 312 in cooperation with the shutter control unit 36 that controls the shutter 12 based on the photometry information from the photometry unit 46. The lens system control unit 346 controls the entire taking lens 300. The lens system control unit 346 has a memory function for storing constants, variables, programs, and the like for photographing lens operation.

  The nonvolatile memory 348 stores identification information such as a number unique to the photographing lens, management information, function information such as an open aperture value, a minimum aperture value, and a focal length, and current and past setting values. In the present embodiment, a focus detection correction value corresponding to the state of the photographic lens 300 is also stored.

  A plurality of focus detection correction values are prepared corresponding to the focus position and zoom position of the lens 311. When the camera 100 performs focus detection using the focus detection means, an optimum focus detection correction value corresponding to the focus position and zoom position of the lens 311 is selected.

  Note that since the photographing light flux of the photographing lens 300 and the focus detection light flux by the focus detection means have different pupil regions, the best image plane position of the photographing light flux and the best image plane position of the focus detection light flux are shifted from each other. The focus detection correction value is for correcting this. Accordingly, different types of photographing lenses having different focal lengths, open F-numbers, focus, zoom, and the like, that is, different optical configurations, have different focus detection correction values. Also, even when the same type of photographing lens has a different manufacturing number, the focus detection correction value may be different in consideration of manufacturing errors.

  The above is the configuration of the camera system including the camera 100 and the photographing lens 300 in the present embodiment.

  Next, the focus detection unit of the present embodiment including the image sensor 14 will be described. The focus detection unit of this embodiment employs phase difference AF as in the focus detection apparatus 105, and the configuration thereof will be described.

  FIG. 2 is a plan view of a light receiving pixel on which a subject image is formed in the image pickup device 14 in the camera system block diagram of FIG. Reference numeral 400 denotes an imaging range including the entire pixels formed by m pixels in the horizontal direction and n pixels in the vertical direction on the image sensor 14, and 401 indicates one of the pixel portions. In each pixel portion, an on-chip Bayer array primary color filter is formed and arranged in a 4-pixel cycle of 2 rows × 2 columns. In FIG. 2, only 10 pixels × 10 pixels on the upper left are displayed as the pixel portion in order to eliminate complexity, and other pixel portions are omitted.

  3 and 4 are diagrams for explaining the structures of the imaging pixel and the focus detection pixel in the pixel portion in FIG. 2, and are optical cross-sectional views of the lens 311 and the imaging element 14 in FIG. 1 viewed from the optical finder 104 side. is there. Note that members unnecessary for the description are omitted. In this embodiment, out of 4 pixels of 2 rows × 2 columns, pixels having a spectral sensitivity of G (green) are arranged in 2 diagonal pixels, and R (red) and B (blue) are arranged in the other 2 pixels. A Bayer arrangement in which one pixel having spectral sensitivity is arranged is employed. A focus detection pixel having a structure to be described later is arranged between the Bayer arrays.

  FIG. 3 shows the arrangement and structure of the imaging pixels. FIG. 3A is a plan view of 2 × 2 imaging pixels. As is well known, in the Bayer array, G pixels are arranged diagonally, and R and B pixels are arranged in the other two pixels. A structure of 2 rows × 2 columns is repeatedly arranged. The imaging pixels receive the light flux that has passed through the entire pupil region of the photographic lens 300.

  FIG. 3B is a cross-sectional view taken along the line AA in FIG. ML is an on-chip microlens disposed on the forefront of each pixel, CFR is an R (red) color filter, and CFG is a G (green) color filter. PD (Photo Diode) schematically shows a photoelectric conversion element of a CMOS image sensor. CL (Contact Layer) is a wiring layer for forming signal lines for transmitting various signals in the CMOS image sensor. FIG. 3 is a diagram showing a pixel structure near the center of the image sensor 14, that is, a pixel structure near the axis of the photographing lens 300.

  Here, the on-chip microlens ML and the photoelectric conversion element PD of the imaging pixel are configured to capture the light flux that has passed through the photographing lens 300 as effectively as possible. In other words, the exit pupil of the photographing lens 300 and the photoelectric conversion element PD are in a conjugate relationship by the microlens ML, and the effective area of the photoelectric conversion element is designed to be large. A light beam 410 in FIG. 3 shows the state, and the entire area of the exit pupil 411 is taken into the photoelectric conversion element PD. As described above, in this embodiment, the exit pupil position of the photographing lens 300 is the stop 312, and thus the exit pupil 411 corresponds to the opening of the stop 312. In FIG. 3B, the incident light beam of the R pixel has been described, but the G pixel and the B (blue) pixel have the same structure. Further, the members around the microlens ML are enlarged and displayed for easy understanding of the explanation, but the actual shape is in the order of microns.

  FIG. 4 shows the arrangement and structure of focus detection pixels for pupil division in the horizontal direction (lateral direction) of the photographic lens 300. Here, the horizontal direction indicates the longitudinal direction of the image sensor 14 shown in FIG. FIG. 4A is a plan view of pixels of 2 rows × 2 columns including focus detection pixels. When obtaining an image signal for recording or viewing, the main component of luminance information is acquired by G pixels. Since human image recognition characteristics are sensitive to luminance information, image quality degradation is easily recognized when G pixels are lost. On the other hand, the R pixel or the B pixel is a pixel that acquires color information (color difference information). However, since human visual characteristics are insensitive to color information, the pixel that acquires color information has some defects. However, image quality degradation is difficult to recognize. Therefore, in the present embodiment, among the pixels of 2 rows × 2 columns, the G pixel is left as an imaging pixel, and the R pixel and the B pixel are replaced with focus detection pixels. The focus detection pixels are denoted as SHA and SHB in FIG.

  FIG. 4B is a cross-sectional view taken along the line AA in FIG. The microlens ML and the photoelectric conversion element PD have the same structure as the imaging pixel shown in FIG. 2 is a diagram illustrating a pixel structure in the vicinity of the center of the imaging element 14, that is, a pixel structure in the vicinity of the on-axis of the photographing lens 300.

  In the present embodiment, since the signal of the focus detection pixel is not used for image generation, a transparent film CFW (white) is disposed instead of the color separation color filter. Further, since the exit pupil 411 is divided by the image sensor, the opening of the wiring layer CL is eccentric in one direction with respect to the center line of the microlens ML. Specifically, since the opening OPHA of the pixel SHA is decentered by 421HA on the right side with respect to the center line of the microlens ML, the light beam 420HA that has passed through the left exit pupil region 422HA across the optical axis L of the lens 311. Is received. Similarly, since the opening OPHB of the pixel SHB is decentered by 421HB to the left with respect to the center line of the microlens ML, the light beam 420HB that has passed through the right exit pupil region 422HB across the optical axis L of the lens 311 is received. To do. As is apparent from FIG. 4, the eccentric amount 421HA is equal to the eccentric amount 421HB. As described above, the light beam 420 passing through different pupil regions of the photographing lens 300 can be extracted by the eccentricity of the micro lens ML and the opening OP.

  With the configuration as described above, a plurality of pixels SHA are arranged in the horizontal direction, and a subject image acquired by these pixel groups is defined as an A image. The pixels SHB are also arranged in the horizontal direction, and the subject image acquired by these pixel groups is defined as a B image. Then, by detecting the relative position between the A image and the B image, the amount of defocus (defocus amount) of the subject image can be detected. Therefore, the imaging device 14 has a function as a second focus detection unit, and also includes a second pupil division unit.

  4 illustrates the focus detection pixel in the vicinity of the center of the image sensor 14. However, except for the center, the openings OPHA and OPHB of the microlens ML and the wiring layer CL are different from those in FIG. The exit pupil 411 can be divided by decentering with. Specifically, the opening OPHA will be described as an example. By decentering the spherical core of the microlens ML made of a substantially spherical shape on the line connecting the center of the opening OPHA and the center of the exit pupil region 411, Even in the periphery of the image sensor 14, pupil division can be performed substantially equivalent to the focus detection pixels near the center shown in FIG. Detailed description is omitted.

  By the way, in the pixels SHA and SHB, focus detection is possible for an object having a luminance distribution in the horizontal direction of the photographing screen, for example, a vertical line, but focus detection is not possible for a horizontal line having a luminance distribution in the vertical direction. For this purpose, it is only necessary to provide a pixel that performs pupil division in the vertical direction (longitudinal direction) of the photographing lens. In this embodiment, the pixel structure for focus detection is provided in both vertical and horizontal directions.

  Further, since the focus detection pixel does not have original color information, a signal is created by performing interpolation calculation from pixel signals in the peripheral portion when forming a captured image. Accordingly, the image quality of the captured image is not reduced by arranging the focus detection pixels on the image sensor 14 discretely rather than continuously.

  As described above with reference to FIGS. 2, 3, and 4, the image sensor 14 has not only a function of only imaging but also a function as a focus detection unit. In addition, as a focus detection method, since a focus detection pixel that receives a light beam obtained by dividing the exit pupil 411 is provided, phase difference AF can be performed.

  FIG. 5 is a diagram schematically illustrating a focus detection configuration in the image sensor 14 and the image processing unit 20. In the description of the camera system block diagram of FIG. 1, the image data obtained by the image sensor 14 is sent to the image processing unit 20 via the A / D converter 16, but FIG. The A / D converter 16 is omitted.

  The imaging device 14 includes a plurality of focus detection units 901 including pupil detection pixels 901a and 901b divided into pupils. The focus detection unit 901 corresponds to FIG. 4A, and the focus detection pixel 901a corresponds to the pixel SHA, and the focus detection pixel 901b corresponds to the pixel SHB. The imaging element 14 includes a plurality of imaging pixels for photoelectrically converting a subject image formed by the photographing lens.

  The image processing unit 20 includes a combining unit 902 and a connecting unit 903. In addition, the image processing unit 20 assigns a plurality of sections (regions) CST to the imaging surface of the imaging device 14 so as to include a plurality of focus detection units 901. Then, the image processing unit 20 can appropriately change the size, arrangement, number, and the like of the section CST. The synthesizing unit 902 performs a process of synthesizing the output signals from the focus detection pixels 901a to obtain a first synthesized signal of one pixel in each of the plurality of sections CST assigned to the image sensor 14. The combining unit 902 also performs processing for combining each output signal from the focus detection pixel 901b to obtain a second combined signal of one pixel in each section CST. In the plurality of sections CST, the connecting unit 903 connects the pixels that are the first combined signal to obtain the first connected signal, and connects the second combined signal to obtain the second connected signal. Process. In this way, a connection signal in which pixels of the number of sections are connected to each of the focus detection pixels 901a and 901b is obtained. A calculation unit 904 in the AF unit 42 calculates the amount of defocus of the photographing lens 300 based on the first connection signal and the second connection signal. In this way, since the output signals of the focus detection pixels in the same pupil division direction arranged in the section are synthesized, even if the brightness of each focus detection unit is small, the brightness distribution of the subject is Sufficient detection is possible.

  FIG. 6 shows a pair of focus detection signals that are formed by the focus detection unit 901, the synthesis unit 902, and the connection unit 903 in FIG. 5 and are sent to the AF unit 42. In FIG. 6, the horizontal axis indicates the pixel arrangement direction of the connected signals, and the vertical axis indicates the signal intensity. The focus detection signal 430a is a signal formed by the focus detection pixel 901a, and the focus detection signal 430b is a signal formed by the focus detection pixel 901b. Since the photographing lens 300 is defocused with respect to the image sensor 14, the focus detection signal 430a is shifted to the left side and the focus detection signal 430b is shifted to the right side.

  Since the AF unit 42 calculates the amount of deviation of the focus detection signals 430a and 430b by a known correlation calculation or the like, it is possible to know how much the photographing lens 100 is defocused. It is possible to perform matching.

  FIG. 7 is a diagram showing a focus detection area in the imaging range, and phase difference AF by the image sensor 14 is performed in this focus detection area. In FIG. 7, a rectangle 217 indicated by a dotted line indicates an imaging range in which pixels of the imaging element 14 are formed. Three vertical and horizontal focus detection areas 218ah, 218bh, 218ch, 218av, 218bv, and 218cv are formed in the imaging range. The vertical and horizontal focus detection areas are arranged so as to intersect with each other, forming a so-called cross-type focus detection area. In the present embodiment, the cross-type focus detection areas are configured to be provided at a total of three locations, that is, the central portion of the imaging range 217 and the two left and right as shown in the figure.

  In the present embodiment, the phase difference AF is realized by the image sensor 14 in the present embodiment. However, in the phase difference AF, focus detection is performed using a light beam that passes through two different regions of the light beam that passes through the exit pupil 411 of the photographing lens 300, so the photographing light beam and the focus detection light beam are different. As a result, a difference occurs in the best image plane position of the photographing lens between the photographing light beam and the focus detection light beam, and a focus detection correction value for correcting this difference is required. Details will be described below.

  FIG. 8 is an optical cross-sectional view of the lens 311 and the image sensor 14 in the camera system block diagram of FIG. 1 as viewed from the optical viewfinder 104 side. It is a figure which shows the focus detection light beam. Note that members unnecessary for the explanation other than the lens 311 and the image sensor 14 are omitted.

  In FIG. 8, a light beam 401 indicated by a dotted line is a photographing light beam that passes through the lens 311 of the photographing lens 300 and the stop 312 and forms an image near the center of the light receiving surface of the image sensor 14. On the other hand, a pair of light beams 440a and 440b indicated by hatching in the figure forms an image near the center of the light receiving surface of the image sensor 14 among the focus detection light beams received by the focus detection pixels 901a and 901b in FIG. It is a focus detection light beam.

  Here, the best image plane positions (focusing positions) of the focus detection light beams 440a and 440b and the photographing light beam 401 are shifted because the light beams are different. FIG. 8 shows a case where the focus of the photographic lens 300 is adjusted by the focus detection means. In this case, the best image plane position of the photographic light beam 401 is on the front pin side with respect to the image sensor 14. Such deviation of the best image plane position between the photographing light beam and the focus detection light beam is caused by various aberrations such as spherical aberration of the photographing lens 300. BP in the figure indicates the amount of deviation, and even if the focus detection unit 300 adjusts the focus of the photographic lens 300, the BP will be out of focus. Therefore, BP is prepared in advance as a focus detection correction value, and this problem is solved by adding to the focus detection result.

  FIGS. 9A, 9 </ b> B, and 9 </ b> C show focus detection correction values of phase difference AF by the image sensor 14 stored in the nonvolatile memory 348 in the photographing lens 300. 9A shows focus detection correction values corresponding to the focus detection areas 218ah and 218av in FIG. 7, FIG. 9B shows focus detection correction values corresponding to the focus detection areas 218bh and 218ch in FIG. (C) shows focus detection correction values corresponding to the focus detection areas 218bv and 218cv in FIG. The focus detection areas 218ah and 218av, the focus detection areas 218bh and 218ch, and the focus detection areas 218bv and 218cv are optically symmetrical about the optical axis L, respectively. The positional deviation is the same. Therefore, the three focus detection correction values are shared by the six focus detection areas.

  9A, in this embodiment, the zoom position and the focus position of the photographing lens 300 are divided into eight zones, and focus detection correction values BP111 to BP188 are provided for each of the divided zones. Therefore, the correction can be performed with higher accuracy in accordance with the zoom position and the focus position of the photographic lens 300. The same applies to FIGS. 9B and 9C.

  However, since the focus detection correction value is discrete data, if the difference in switching of the focus detection correction value is large when the divided zones are switched, an unnatural focusing movement occurs. Conventionally, when a still image is taken, there is no problem in configuration even if the difference in switching is large. However, during the electronic viewfinder display or during moving image shooting, the captured image is displayed and shot in real time, so this unnatural movement appears remarkably. Therefore, in the present embodiment, when the change of the focus detection correction value is detected during the electronic viewfinder display or the moving image shooting by the change detection means for detecting the change of the focus detection correction value in advance, the focus detection before the change is detected. An additional correction value calculating unit that calculates an additional correction value for continuously changing the focus detection correction value from the correction value toward the focus detection correction value after switching is configured. Details will be described below.

  FIG. 10A is a diagram showing a state in which a moving subject is followed for a predetermined time in focus detection areas 218ah and 218av at the center of the shooting screen. In FIG. 10A, the horizontal axis indicates time, the vertical axis indicates the focus detection amount, and the straight line 450 indicates the focus detection result in the graphs of the vertical axis and the horizontal axis. The focus detection amount changes as time passes, and the subject moves at substantially constant speed, so 450 is a straight line.

  FIG. 10B is a diagram in which the horizontal axis in FIG. 10A is changed to the focus position of the photographic lens 300. A straight line 451 indicates that the focus position fluctuates with a change in the focus detection amount, as in the case of FIG. Here, the focus position is divided into three ranges 452, 453, and 454 as shown in the figure. Each range is obtained when the zoom position is 1 and the focus position is 1 to 3 in FIG. It shall be supported. That is, the range 452 corresponds to the focus position 1, the range 453 corresponds to the focus position 2, and the range 454 corresponds to the focus position 3, respectively.

  FIG. 10C is a diagram illustrating the relationship between the focus detection correction amount and the focus position. Similarly to FIG. 10B, ranges 452, 453, and 454 indicated by arrows correspond to the focus positions 1, 2, and 3 in FIG. 9A, respectively. The focus detection correction values at that time are BP111, BP121, and BP131, respectively, and it can be seen that they change stepwise. A curve 455 indicated by an alternate long and short dash line in the figure indicates an ideal focus detection correction value due to focus position fluctuation, and is a smooth curve. The curve 454 is approximated by discrete focus detection correction values BP111, BP121, and BP131.

  FIG. 10D is a diagram illustrating a lens driving amount by the focus control unit 342 obtained by adding the focus detection correction amount of FIG. 10C to the focus detection amount of FIG. 10B. Similarly to FIG. 10B, ranges 452, 453, and 454 indicated by arrows correspond to the focus positions 1, 2, and 3 in FIG. 9A, respectively. The lens driving amount is affected by the focus detection correction amount and is stepped at the focus range switching position. A curve 456 corresponds to the case where the focus detection correction amount is the curve 455, and shows an ideal lens driving amount.

  As described above, if the discrete focus detection correction values are used as they are, the range of the focus position is changed stepwise, resulting in an unnatural image during electronic viewfinder display or moving image shooting. Therefore, in the present embodiment, a switching detection unit that detects in advance the switching of the focus detection correction value is provided, and the focus detection correction value is continuously changed from the focus detection correction value before switching to the focus detection correction value after switching. Additional correction value calculating means for calculating an additional correction value for causing the correction to occur.

  FIG. 11A shows the relationship between the focus detection correction amount and the focus position, and corresponds to FIG. The focus detection correction amount is continuously switched from BP111 to BP121 between the focus positions Fb111 and Fa121 near the switching of the focus ranges 452 and 453. Similarly, the focus detection correction amount is continuously switched from the BP 121 to the BP 131 between the focus positions Fb121 and Fa131 near the switching between the ranges 453 and 454. Therefore, the focus detection correction amount according to FIG. 11A is closer to the curve 455 indicating the ideal focus detection correction value than that of FIG. 10C.

  FIG. 11B is a diagram illustrating a lens driving amount by the focus control unit 342 in which the focus detection correction amount of FIG. 11A is added to the focus detection amount of FIG. 10B. Compared to FIG. 10D, the step shape at the switching position of the focus ranges 452, 453, and 454 is relaxed, and approaches the curve 456 that is an ideal lens driving amount. Then, the lens driving amount that is stepped in FIG. 10D is improved so as to continuously change in the vicinity of the switching of the focus ranges 452, 453, and 454.

  That is, it is detected whether the current focus position of the photographic lens 300 exists between the focus positions Fb111 and Fa121 and between the focus positions Fb121 and Fa131 shown in FIG. This is the switching detection means. Then, when it is detected that it exists, an additional correction value is calculated so as to continuously change the focus detection correction value. When this additional correction value is BP ′, the additional correction value is calculated by the following equation (1).

BP '= (BPn + 1-BPn). (F'-Fbn) / (Fan + 1-Fbn) (1)
Here, the focus detection correction value before BPn is switched, the focus detection correction value after BPn + 1 is switched, and F ′ represents an arbitrary focus position corresponding to the additional correction value BP ′. Fbn and Fan + 1 are focus positions within a range in which the focus detection correction value is continuously changed, and correspond to Fbn before switching and after Fan + 1 switching. This corresponds to the additional correction value calculation means, and the lens of the photographic lens 300 is driven by adding the calculation result obtained by Expression (1) to the focus detection correction value. The actual Fbn and Fan + 1 may be determined from the difference between the focus detection correction values BPn and BPn + 1 before and after switching. That is, when the difference is large, relatively large values are set for Fbn and Fan + 1, and conversely, when the difference is small, Fbn and Fan + 1 may be set to small values. Further, when the difference between the focus detection correction values BPn and BPn + 1 before and after switching is smaller than a predetermined level, the speed can be increased by performing normal lens driving without performing the additional correction.

  Note that although the expression (1) is an expression for linearly changing the focus detection correction value, it may be an expression corresponding to a curve in order to drive the lens more smoothly. In the present embodiment, a straight line equation is used in consideration of the dullness of the edge due to the calculation load and the actual response of the focus lens. Further, although the above description has been given taking the focus position as an example, the same applies to switching of the zoom position, and detailed description thereof is omitted.

  Next, an actual operation in the camera 100 will be described. FIG. 12 is a flowchart showing an actual focus detection operation stored in the system control unit 50. In this flowchart, the main mirror 130 and the sub-mirror 131 are retracted out of the photographing light beam, and the focus detection operation is performed during electronic viewfinder display that performs phase difference AF using the image sensor 14 or during moving image shooting.

  First, in S501, it is detected whether or not the focus detection start instruction button is turned on by an operation of the SW1 or the operation unit 70, and if it is turned on, the process proceeds to S502.

  In step S <b> 502, a pair of focus detection signals is generated by the combining unit 902 and the connecting unit 903 of the image processing unit 20 from the sequentially read image data. Then, the focus detection signal is sent to the AF unit 42, and the process proceeds to S503. In the present embodiment, since focus detection is performed by the image sensor 14 during electronic viewfinder display or during moving image shooting, the focus detection pixels 901a and 901b have a discrete arrangement corresponding to thinning readout.

  In step S503, the AF unit 42 calculates a shift amount of the pair of focus detection signals using a known correlation calculation, and converts it to a defocus amount. In S504, as described with reference to FIG. 9, various lens data such as the current focus position of the photographing lens 300 and the corresponding focus detection correction value are acquired via the interface units 38 and 338 and the connectors 122 and 322. In this embodiment, since the additional correction value BP ′ is calculated as described above, information such as the focus detection correction value before and after the current position and the switching position of the focus position is also acquired.

  In step S505, the switching detection unit detects whether the current focus position is within a range in which the focus detection correction value is continuously changed. If it is within the range, the process proceeds to S506, and if it is not within the range, two steps are skipped and the process proceeds to S508.

  In S506, it is determined whether or not the difference between the focus detection correction values before and after switching is equal to or greater than a predetermined threshold value. If it is equal to or greater than the threshold value, the process proceeds to S507. If it is equal to or less than the threshold value, one step is skipped and the process proceeds to S508. Here, the threshold value may be determined from the focal depth of the photographing lens. As is well known, the depth of focus Fd can be calculated by the following equation (2) using the F number Fn of the photographing lens and the allowable circle of confusion δ.

Fd = Fn × δ (2)
As the allowable circle of confusion δ, an optimal value is set in accordance with each of the electronic finder display and the moving image shooting. This is because the permissible circle of confusion δ can be determined by the pixel pitch of the image sensor 14 and the thinning-out readout interval, and therefore has a different value in accordance with each photographing state. In the present embodiment, the permissible circle of confusion δ for each shooting mode is provided in advance in the nonvolatile memory 56, and is selected according to the shooting mode.

  In step S507, the additional correction value BP ′ is calculated by the additional correction value calculation unit using Expression (1).

  In S508, the lens driving amount of the photographic lens 300 is calculated based on the defocus amount calculated in S503, the focus detection correction value acquired in S504, and the additional correction value calculated in S507.

  In S509, the lens driving amount is sent to the focus control unit 342 of the photographing lens 300 via the interface units 38 and 338 and the connectors 122 and 322, and the focus lens is driven to adjust the focus of the photographing lens 300.

  The above is the focus detection operation of the camera 100 of the present embodiment. Note that the description with the follow chart of FIG. 12 has been described by taking the focus position as an example, but the same applies to switching of the zoom position, and detailed description thereof is omitted.

  As described above, in the present embodiment, the change detection unit detects the change in the focus detection correction value, and when the difference in focus detection correction value before and after the change is equal to or greater than the predetermined threshold, the additional correction value calculation unit adds the additional correction value. Is calculated so that the focus detection correction value is continuously switched. Therefore, high-precision and natural focusing can be performed even when the electronic viewfinder is displayed or when moving images are taken.

  In the above embodiment, the phase difference AF using the image sensor 14 has been described as an example. However, the present invention can also be applied to the phase difference AF using the focus detection device 105. Further, the present invention can be applied not only to electronic viewfinder and moving image shooting but also to still image shooting.

  In the above embodiment, an example in which focusing is performed by driving the focus lens of the photographing lens 300 has been described. However, the imaging element 14 is configured to be able to advance and retract in the optical axis direction of the photographing lens 300, and the imaging element 14. Focus adjustment may be performed by driving. In particular, when an imaging lens that is not good at minute amount driving or low-speed driving is attached to the camera 100, smooth focusing can be performed by driving the image sensor 14.

Claims (3)

A focus detection means for detecting the focus of the photographing lens in a phase difference method using a pair of light beams that have passed through different pupil regions of the photographing lens;
The difference of the focus detection result due to the difference between the focus position of the light beam focusing position and the pair of the light flux passing through the entire pupil area of the photographing lens, discretely with respect to at least the focus position of the photographing lens When correcting by changing an existing correction value, an additional correction value for smoothing the switching between the correction values is set according to the difference between the correction value before the switching and the correction value after the switching, Correction means for correcting the difference between the focus detection results;
Focus detection result of the focus detection unit, or based on the corrected focus detection result of said difference, a focusing means for performing focusing of the photographing lens,
An imaging apparatus comprising:   When the difference between the correction value before switching and the correction value after switching is equal to or greater than a predetermined threshold, the focus adjustment unit adds the additional correction value to the focus detection result and the correction value. The imaging apparatus according to claim 1, wherein the lens is focused.   The image pickup device further includes an image pickup device disposed in the vicinity of a predetermined imaging plane of the photographing lens, and the focus adjustment unit performs focusing by controlling a focus position of the photographing lens and a relative position of the image pickup device. The imaging apparatus according to claim 1 or 2.

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