JP2009139840A - Imaging device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging device capable of performing multi-point AF in contrast AF with high precision. <P>SOLUTION: This imaging device controls the operation of exposure to light for exposing imaging elements to light sequentially in display frame period of, for example, 1/60 seconds, before actual imaging to display images (live view display) based on the image signals generated by the imaging elements due to exposure to light and detect a focus by a contrast detection system (contrast AF) based on the image signals generated sequentially by the imaging elements while driving a focus lens. When performing the contrast AF in a plurality of AF areas prescribed on an imaging screen of the imaging element, the operation of exposure to light Pa-Pc for different periods of time during the display frame period is sequentially performed at three times by the imaging elements to perform the multi-point AF in a plurality of AF areas based on each image signal generated by the imaging elements by each operation of exposure to light at three times. As a result, the multi-point AF can be performed with high precision in the contrast AF. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an imaging apparatus provided with imaging means for generating an image signal related to a subject.

  A single-lens reflex camera or the like is known in which a multi-point AF is performed by providing a phase-difference AF module capable of performing phase-difference focus detection in each of a plurality of focus detection areas. In this multi-point AF, for example, as disclosed in Patent Document 1, high-precision AF can be realized by adjusting an appropriate exposure time for each focus detection region.

  On the other hand, contrast detection focus detection (hereinafter also referred to as “contrast AF”) based on live view images sequentially acquired by the image sensor in order to display the subject in a moving image mode (live view display) before the actual shooting. There is known a digital camera (imaging device) that performs the above.

Japanese Patent Laid-Open No. 11-2754

  However, when performing multi-point AF by setting a plurality of focus detection areas on the imaging surface in the above contrast AF, a uniform exposure time is set over the entire imaging surface in general exposure control of the imaging device. Therefore, it is impossible to perform phase difference AF by adjusting to an appropriate exposure time for each focus detection area in one exposure as in the above-described phase difference AF module. In this case, a focus detection area with an inappropriate exposure state is generated in a photographing scene having a large luminance difference such as a backlight scene, and it is difficult to perform multipoint AF with high accuracy.

  The present invention has been made in view of the above problems, and an object thereof is to provide an imaging apparatus capable of performing multipoint AF with high accuracy in contrast AF.

  One aspect of the present invention is an imaging apparatus, wherein (a) an imaging unit that generates an image signal related to a subject, and (b) a display unit that can display an image based on the image signal generated by the imaging unit. And (c) a display that performs exposure control for sequentially exposing the image pickup means at a predetermined cycle before the main photographing, and causes the display means to perform image display based on an image signal generated by the image pickup means by the exposure. Control means; (d) drive means for driving a focus lens; and (e) focus detection by contrast detection based on image signals sequentially generated by the imaging means while driving the focus lens by the drive means. A plurality of regions for performing focus detection are defined on the imaging surface of the imaging unit, and the focus detection unit has an exposure value during the predetermined period. Different multiple times Sequentially performed light by the imaging unit, and performs the focus detection by said plurality of regions based on the image signal generated by said imaging means by each of the plurality of times of exposure.

  According to the present invention, a plurality of exposures with different exposure values are sequentially performed by the imaging unit during the exposure cycle for performing image display of the subject before the main shooting, and the imaging unit performs each of the plurality of exposures. Contrast detection focus detection is performed in a plurality of regions defined on the imaging surface of the imaging means based on the generated image signals. As a result, multipoint AF can be performed with high accuracy in contrast AF.

<Appearance configuration of imaging device>
1 and 2 are diagrams showing an external configuration of an imaging apparatus 1 according to the embodiment of the present invention. Here, FIGS. 1 and 2 show a front view and a rear view, respectively.

  The imaging device 1 is configured as, for example, a single-lens reflex digital still camera, and includes a camera body 10 and an interchangeable lens 2 as a photographic lens that can be attached to and detached from the camera body 10.

  In FIG. 1, on the front side of the camera body 10, a mount part 301 to which the interchangeable lens 2 is mounted at the front center and a lens exchange button 302 arranged on the right side of the mount part 301 can be gripped. A grip section 303, a mode setting dial 305 disposed in the upper left portion of the front surface, a control value setting dial 306 disposed in the upper right portion of the front surface, and a shutter button 307 disposed on the upper surface of the grip portion 303 are provided. .

  In FIG. 2, on the rear side of the camera body 10, there are an LCD (Liquid Crystal Display) 311, a setting button group 312 arranged on the left side of the LCD 311, and a cross key 314 arranged on the right side of the LCD 311. And a push button 315 disposed in the center of the cross key 314. On the back side of the camera body 10, an optical finder 316 disposed above the LCD 311, an eye cup 321 surrounding the optical finder 316, and a main switch 317 disposed on the left side of the optical finder 316. An exposure correction button 323 and an AE lock button 324 disposed on the right side of the optical viewfinder 316, and a flash unit 318 and a connection terminal unit 319 disposed above the optical viewfinder 316.

  The mount 301 is provided with a connector Ec (see FIG. 5) for electrical connection with the mounted interchangeable lens 2 and a coupler 75 (see FIG. 5) for mechanical connection.

  The lens exchange button 302 is a button that is pressed when the interchangeable lens 2 attached to the mount unit 301 is removed.

  The grip part 303 is a part where the user grips the imaging device 1 at the time of photographing, and is provided with surface irregularities that match the finger shape in order to improve fitting properties. Note that a battery storage chamber and a card storage chamber (not shown) are provided inside the grip portion 303. A battery 69B (see FIG. 5) is housed in the battery compartment as a power source for the camera, and a memory card 67 (see FIG. 5) for recording image data of the photographed image is detachably housed in the card compartment. It has come to be. The grip unit 303 may be provided with a grip sensor for detecting whether or not the user has gripped the grip unit 303.

  The mode setting dial 305 and the control value setting dial 306 are made of a substantially disk-shaped member that can rotate in a plane substantially parallel to the upper surface of the camera body 10. The mode setting dial 305 is used for various shootings such as an automatic exposure (AE) control mode, an autofocus (AF) control mode, a still image shooting mode for shooting a single still image, and a continuous shooting mode for continuous shooting. This mode is used to selectively select a mode and a function installed in the imaging apparatus 1, such as a mode and a reproduction mode for reproducing a recorded image. On the other hand, the control value setting dial 306 is for setting control values for various functions installed in the imaging apparatus 1.

  The shutter button 307 is a push switch that can be operated in a “half-pressed state” that is pressed halfway and further operated in a “full-pressed state”. When the shutter button 307 is half-pressed in the still image shooting mode, a preparatory operation (preparation operation for setting an exposure control value, focus detection, etc.) for capturing a still image of the subject is executed, and the shutter button 307 is fully pressed. Then, a photographing operation (a series of operations for exposing the image sensor 101 (see FIG. 3), performing predetermined image processing on the image signal obtained by the exposure, and recording the image signal on a memory card or the like) is performed.

  The LCD 311 includes a color liquid crystal panel capable of displaying an image. The LCD 311 displays an image picked up by the image pickup device 101 (see FIG. 3), reproduces and displays a recorded image, and is mounted on the image pickup apparatus 1. Function and mode setting screen. Note that an organic EL or a plasma display device may be used instead of the LCD 311.

  The setting button group 312 is a button for performing operations on various functions installed in the imaging apparatus 1. The setting button group 312 includes, for example, a selection confirmation switch for confirming the content selected on the menu screen displayed on the LCD 311, a selection cancel switch, a menu display switch for switching the content of the menu screen, a display on / off switch, A display enlargement switch is included.

  The cross key 314 has an annular member having a plurality of pressing portions (triangle marks in the figure) arranged at regular intervals in the circumferential direction, and is not shown and provided corresponding to each pressing portion. The pressing operation of the pressing portion is detected by the contact (switch). The push button 315 is arranged at the center of the cross key 314. The cross key 314 and the push button 315 are used to change the shooting magnification (movement of the zoom lens 212 (see FIG. 5) in the wide direction or the tele direction), frame-by-frame feeding of a recorded image to be reproduced on the LCD 311 and the like, and shooting conditions (aperture value). , Shutter speed, presence / absence of flash emission, etc.) for inputting instructions.

  The optical viewfinder 316 optically displays a range where a subject is photographed. In other words, the subject image from the interchangeable lens 2 is guided to the optical finder 316, and the user can visually recognize the subject actually captured by the image sensor 101 by looking into the optical finder 316. .

  The main switch 317 is a two-contact slide switch that slides to the left and right. When the switch is set to the left, the power of the imaging apparatus 1 is turned on, and when the switch is set to the right, the power is turned off.

  The flash unit 318 is configured as a pop-up built-in flash. On the other hand, when attaching an external flash or the like to the camera body 10, the connection is made using the connection terminal portion 319.

  The eye cup 321 is a “U” -shaped light shielding member that has light shielding properties and suppresses intrusion of external light into the optical viewfinder 316.

  The exposure correction button 323 is a button for manually adjusting an exposure value (aperture value or shutter speed), and the AE lock button 324 is a button for fixing exposure.

  The interchangeable lens 2 functions as a lens window that captures light (light image) from a subject, and also functions as a photographing optical system that guides the subject light to the image sensor 101 disposed inside the camera body 10. It is. The interchangeable lens 2 can be detached from the camera body 10 by depressing the lens interchange button 302 described above.

  The interchangeable lens 2 includes a lens group 21 including a plurality of lenses arranged in series along the optical axis LT (see FIG. 5). The lens group 21 includes a focus lens 211 (see FIG. 5) for adjusting the focal point and a zoom lens 212 (see FIG. 5) for performing zooming. By driving in the direction (see FIG. 3), zooming and focus adjustment are performed. Further, the interchangeable lens 2 is provided with an operation ring that can rotate along the outer peripheral surface of the lens barrel at a suitable position on the outer periphery of the lens barrel. The zoom lens 212 can be operated by manual operation or automatic operation. It moves in the optical axis direction according to the rotation direction and rotation amount of the operation ring, and is set to a zoom magnification (imaging magnification) according to the position of the movement destination.

<Internal Configuration of Imaging Device 1>
Next, the internal configuration of the imaging apparatus 1 will be described. FIG. 3 is a longitudinal sectional view of the imaging apparatus 1. As shown in FIG. 3, the camera body 10 includes an image sensor 101, a finder unit 102 (finder optical system), a mirror unit 103, a phase difference AF module 107, and the like.

  The imaging element 101 is arranged in a direction perpendicular to the optical axis LT on the optical axis LT of the lens group included in the interchangeable lens 2 when the interchangeable lens 2 is attached to the camera body 10. . As the image sensor 101, for example, a plurality of pixels configured with photodiodes are two-dimensionally arranged in a matrix, and R (red), G (green), for example, having different spectral characteristics on the light receiving surface of each pixel. , B (blue) color filters are arranged in a ratio of 1: 2: 1, and a Bayer array CMOS color area sensor (CMOS type image sensor) is used. The image sensor 101 converts the light image of the subject formed through the interchangeable lens 2 into analog electrical signals (image signals) of R (red), G (green), and B (blue) color components, and R , G, and B image signals.

  On the optical axis LT, a mirror unit 103 is disposed at a position where subject light is reflected toward the viewfinder unit 102. The subject light that has passed through the interchangeable lens 2 is reflected upward by a mirror unit 103 (a main mirror 1031 described later). Part of the subject light that has passed through the interchangeable lens 2 passes through the mirror unit 103.

  The viewfinder unit 102 includes a pentaprism 105, an eyepiece lens 106, and an optical viewfinder 316. The pentaprism 105 has a pentagonal cross section, and is a prism for converting an object light image incident from the lower surface thereof into an upright image by changing the top and bottom of the light image by internal reflection. The eyepiece 106 guides the subject image that has been made upright by the pentaprism 105 to the outside of the optical viewfinder 316. With such a configuration, the finder unit 102 functions as a finder for confirming the object scene at the time of shooting standby before actual shooting.

  The mirror unit 103 includes a main mirror 1031 and a sub mirror 1032, and is provided on the back side of the main mirror 1031 so that the sub mirror 1032 is tilted toward the back of the main mirror 1031. Part of the subject light transmitted through the main mirror 1031 is reflected by the sub mirror 1032, and the reflected subject light enters the phase difference AF module 107.

  The mirror unit 103 is configured as a so-called quick return mirror, and during exposure (main photographing), as shown in FIG. 4, the mirror unit 103 jumps upward with a rotating shaft 1033 as a rotation fulcrum. At this time, the sub mirror 1032 is folded so as to be substantially parallel to the main mirror 1031 when the mirror unit 103 stops at a position below the pentaprism 105. As a result, the subject light from the interchangeable lens 2 reaches the image sensor 101 without being blocked by the mirror 103, and the image sensor 101 is exposed. When the imaging operation with the imaging element 101 is completed, the mirror unit 103 returns to the original position (position shown in FIG. 3).

  In addition, by setting the mirror unit 103 in the mirror-up state shown in FIG. 4 before the main shooting (shooting for image recording), the imaging device 1 can perform moving image processing based on image signals sequentially generated by the imaging device 101. In this manner, live view (preview) display in which the subject is displayed on the LCD 311 is possible. In other words, in the imaging apparatus 1 before the actual photographing, the composition of the subject can be determined by selecting the electronic viewfinder (live view mode) in which the live view display is performed or the optical viewfinder. Note that switching between the electronic viewfinder and the optical viewfinder is performed by operating the changeover switch 85 shown in FIG.

  The phase difference AF module 107 is configured as a so-called AF sensor including a distance measuring element that detects focus information of a subject. The phase difference AF module 107 is disposed at the bottom of the mirror unit 103 and detects a focus position by phase difference detection type focus detection (hereinafter also referred to as “phase difference AF”). That is, when the user checks the subject with the optical viewfinder 316 during shooting standby, the light from the subject is guided to the phase difference AF module 107 with the main mirror 1031 and the sub mirror 1032 down as shown in FIG. At the same time, the focus lens 211 in the interchangeable lens 2 is driven based on the output from the phase difference AF module 107 to perform focusing. The phase difference AF module 107 can perform so-called multipoint AF (multipoint distance measurement) in order to realize highly accurate phase difference AF.

  A shutter unit 40 is disposed in front of the image sensor 101 in the optical axis direction. The shutter unit 40 includes a curtain body that moves in the vertical direction, and a mechanical focal plane that performs an optical path opening operation and an optical path blocking operation of subject light guided to the image sensor 101 along the optical axis LT by the opening operation and the closing operation. It is configured as a shutter. The shutter unit 40 can be omitted when the image sensor 101 is an image sensor capable of complete electronic shutter.

<Electrical Configuration of Imaging Device 1>
FIG. 5 is a block diagram illustrating an electrical configuration of the imaging apparatus 1. Here, the same members and the like as those in FIGS. 1 to 4 are denoted by the same reference numerals. For convenience of explanation, the electrical configuration of the interchangeable lens 2 will be described first.

  The interchangeable lens 2 includes a lens driving mechanism 24, a lens position detection unit 25, a lens control unit 26, and a diaphragm driving mechanism 27 in addition to the lens group 21 described above.

  In the lens group 21, a focus lens 211 and a zoom lens 212, and a diaphragm 23 for adjusting the amount of light incident on the image sensor 101 provided in the camera body 10 are arranged in the lens barrel 22 with an optical axis LT (FIG. 3). ), And captures an optical image of the subject and forms it on the image sensor 101. In the AF control, focus adjustment is performed by driving the focus lens 211 in the optical axis LT direction by the AF actuator 71M in the interchangeable lens 2.

  The focus drive control unit 71A generates a drive control signal for the AF actuator 71M necessary for moving the focus lens 211 to the in-focus position based on the AF control signal given from the main control unit 62 via the lens control unit 26. Is to be generated. The AF actuator 71M is composed of a stepping motor or the like, and applies a lens driving force to the lens driving mechanism 24.

  The lens driving mechanism 24 includes, for example, a helicoid and a gear (not shown) that rotates the helicoid, and receives the driving force from the AF actuator 71M to drive the focus lens 211 and the like in a direction parallel to the optical axis LT. It is. Note that the movement direction and the movement amount of the focus lens 211 are in accordance with the rotation direction and the rotation speed of the AF actuator 71M, respectively.

  The lens position detection unit 25 moves integrally with the lens while being in sliding contact with the encode plate in which a plurality of code patterns are formed at a predetermined pitch in the optical axis LT direction within the movement range of the lens group 21. An encoder brush, and detects the amount of movement of the lens group 21 during focus adjustment. The lens position detected by the lens position detection unit 24 is output as the number of pulses, for example.

  The lens control unit 26 is composed of, for example, a microcomputer having a built-in memory such as a ROM that stores a control program and a flash memory that stores data related to status information.

  The lens control unit 26 has a communication function for performing communication with the main control unit 62 of the camera body 10 via the connector Ec. Thereby, for example, the state information data such as the focal length, the exit pupil position, the aperture value, the focusing distance, and the peripheral light amount state of the lens group 21 and the position information of the focus lens 211 detected by the lens position detection unit 25 are main-controlled. For example, the driving amount data of the focus lens 211 can be received from the main control unit 62.

  The aperture drive mechanism 27 receives the driving force from the aperture drive actuator 76M via the coupler 75 and changes the aperture diameter of the aperture 23.

  Next, the electrical configuration of the camera body 10 will be described. The camera body 10 includes an AFE (analog front end) 5, an image processing unit 61, an image memory 614, a main control unit 62, a flash circuit 63, and an operation unit 64 in addition to the image sensor 101 and the shutter unit 40 described above. , VRAM 65, card I / F 66, memory card 67, communication I / F 68, power supply circuit 69, battery 69B, mirror drive control unit 72A and mirror drive actuator 72M, shutter drive control unit 73A and shutter drive actuator 73M, aperture drive control A portion 76A and a diaphragm drive actuator 76M are provided.

  The image sensor 101 is composed of a CMOS color area sensor as described above, and the timing control circuit 51 described below starts (and ends) the exposure operation of the image sensor 101 and selects the output of each pixel included in the image sensor 101. The imaging operation such as readout of the pixel signal is controlled.

  The AFE 5 gives a timing pulse for causing the image sensor 101 to perform a predetermined operation, performs predetermined signal processing on the image signal output from the image sensor 101, converts the image signal to a digital signal, and outputs the digital signal to the image processing unit 61. To do. The AFE 5 includes a timing control circuit 51, a signal processing unit 52, an A / D conversion unit 53, and the like.

  The timing control circuit 51 generates a predetermined timing pulse (a pulse for generating a vertical scanning pulse φVn, a horizontal scanning pulse φVm, a reset signal φVr, etc.) based on the reference clock output from the main control unit 62, and the imaging device 101. And the imaging operation of the image sensor 101 is controlled. In addition, the operation of the signal processing unit 52 and the A / D conversion unit 53 is controlled by outputting predetermined timing pulses to the signal processing unit 52 and the A / D conversion unit 53, respectively.

  The signal processing unit 52 performs predetermined analog signal processing on the analog image signal output from the image sensor 101, and includes a CDS (correlated double sampling) circuit, an AGC (auto gain control) circuit, a clamp circuit, and the like. It has been. In this AGC circuit, the image signal generated by the image sensor 101 can be amplified in a variable amplification factor (gain), and the ISO sensitivity corresponding to the silver salt film can be changed by changing the gain. In addition, the A / D converter 53 converts the analog R, G, and B image signals output from the signal processor 52 into a plurality of bits (for example, 12) based on the timing pulse output from the timing control circuit 51. Bit) to a digital image signal.

  The image processing unit 61 performs predetermined signal processing on the image data output from the AFE 5 to create an image file, and includes a black level correction circuit 611, a white balance control circuit 612, a gamma correction circuit 613, and the like. Has been. The image data captured by the image processing unit 61 is temporarily written in the image memory 614 in synchronization with the reading of the image sensor 101. Thereafter, the image data written in the image memory 614 is accessed to access the image processing unit. Processing is performed in each of the 61 blocks.

  The black level correction circuit 611 corrects the black level of each of the R, G, and B digital image signals A / D converted by the A / D conversion unit 53 to a reference black level.

  The white balance correction circuit 612 performs level conversion (white balance (WB) adjustment) of digital signals of each color component of R (red), G (green), and B (blue) based on a white reference corresponding to the light source. Is what you do. That is, the white balance control circuit 612 identifies a portion that is originally estimated to be white based on luminance, saturation data, and the like in the photographic subject based on the WB adjustment data provided from the main control unit 62, and R, G of that portion. , B, the average of the respective color components, the G / R ratio and the G / B ratio are obtained, and the levels are corrected as R and B correction gains.

  The gamma correction circuit 613 corrects the gradation characteristics of the image data subjected to WB adjustment. Specifically, the gamma correction circuit 613 performs non-linear conversion and offset adjustment using a gamma correction table set in advance for each color component.

  The image memory 614 temporarily stores the image data output from the image processing unit 61 in the photographing mode, and is also used as a work area for performing predetermined processing on the image data by the main control unit 62. It is. In the playback mode, the image data read from the memory card 67 is temporarily stored.

  The main control unit 62 is composed of a microcomputer incorporating a storage unit such as a ROM for storing a control program and the like and a RAM for temporarily storing data, and controls the operation of each unit of the imaging apparatus 1. In addition, the main control unit 62 includes a live view control unit 621 and a focus detection unit 622 that are functionally realized by executing, for example, the control program.

  The live view control unit 621 performs exposure control (hereinafter, also referred to as “exposure control for live view display”) that sequentially exposes the image sensor 101 at a period of 1/60 seconds, for example, before the actual shooting. This is a part that causes the LCD 311 to perform image display (live view display) based on image signals periodically generated by the image sensor 101.

  Further, the focus detection unit 622 uses a contrast AF calculation circuit 77 to be described later based on the image signals of the subject sequentially generated by the image sensor 101 while driving the focus lens 211 by the AF actuator 71M in the live view mode. This is a region where focus detection (contrast AF) is performed.

  The flash circuit 63 controls the light emission amount of the external flash connected to the flash unit 318 or the connection terminal unit 319 to the light emission amount set by the main control unit 62 in the flash photographing mode.

  The operation unit 64 includes the mode setting dial 305, the control value setting dial 306, the shutter button 307, the setting button group 312, the cross key 314, the push button 315, the main switch 317, etc., and the operation information is sent to the main control unit 62. It is for input.

  The VRAM 65 has an image signal storage capacity corresponding to the number of pixels of the LCD 311 and is a buffer memory between the main control unit 62 and the LCD 311. The card I / F 66 is an interface for enabling transmission / reception of signals between the memory card 67 and the main control unit 62. The memory card 67 is a recording medium that stores image data generated by the main control unit 62. The communication I / F 68 is an interface for enabling transmission of image data and the like to a personal computer and other external devices.

  The power supply circuit 69 includes, for example, a constant voltage circuit, and generates a voltage for driving the entire imaging apparatus 1 such as a control unit such as the main control unit 62, the imaging element 101, and other various driving units. Note that energization control to the image sensor 101 is performed by a control signal supplied from the main control unit 62 to the power supply circuit 69. The battery 69B includes a primary battery such as an alkaline battery or a secondary battery such as a nickel metal hydride battery, and is a power source that supplies power to the entire imaging apparatus 1.

  The mirror drive control unit 72A generates a drive signal for driving the mirror drive actuator 72M in accordance with the timing of the photographing operation. The mirror drive actuator 72M is an actuator that rotates the mirror unit 103 (quick return mirror) to a horizontal posture or an inclined posture.

  The shutter drive control unit 73A generates a drive control signal for the shutter drive actuator 73M based on a control signal given from the main control unit 62. The shutter drive actuator 73M is an actuator that performs opening / closing driving (opening / closing operation) of the shutter unit 40.

  The diaphragm drive control unit 76A generates a drive control signal for the diaphragm drive actuator 76M based on the control signal given from the main control unit 62. The aperture driving actuator 76M applies a driving force to the aperture driving mechanism 27 via the coupler 75.

  The camera body 10 also includes a contrast AF calculation circuit 77 that calculates an AF evaluation value necessary for contrast AF based on the black level corrected image data output from the black level correction circuit 611. This AF evaluation value is obtained by reading out pixel signals of a pixel group (for example, a pixel group of G pixels) in an AF area Ef (see FIG. 6), which will be described later, set on the imaging surface of the image sensor 101, and the pixel group in the AF area. Is calculated as the sum of absolute values of differences between adjacent pixels.

  Based on the AF evaluation value calculated by the contrast AF calculation circuit 77 and the position information of the focus lens 211 detected by the lens position detection unit 25, the contrast is detected by the focus detection unit 622 of the main control unit 62 during AF control. A process for detecting the in-focus position of the focus lens 211 by AF is executed.

  The contrast AF operation of the imaging apparatus 1 using the contrast AF calculation circuit 77 and the focus detection unit 622 as described above will be described below.

<Contrast AF Operation of Imaging Device 1>
FIG. 6 is a diagram for explaining a plurality of AF areas Ef capable of contrast AF in the imaging apparatus 1.

  A plurality of AF areas (regions) Ef arranged in a matrix are defined on the imaging surface 101 f of the imaging element 101. In each AF area Ef, contrast AF can be performed independently, that is, multipoint AF is possible.

  When performing multi-point AF in the live view mode in such a plurality of AF areas Ef, since the dynamic range of the image sensor 101 is relatively narrow at about 8 EV, an object having a large luminance difference such as a backlight scene (for example, For a subject having a luminance difference of about 20 EV, it is difficult to achieve an appropriate exposure state in all AF areas Ef by one exposure.

  Therefore, the imaging apparatus 1 performs exposure of three patterns with different exposure times in consecutive frames during a display frame period (for example, 1/60 seconds) for live view display, thereby applying an object with various luminances. On the other hand, appropriate exposure data (contrast detection data) can be reliably acquired in each AF area Ef.

  FIG. 7 is a time chart for explaining three patterns of exposure Pa to Pc having different exposure times. As shown in FIG. 7, when the live view mode is set, the vertical synchronization signal (VD) is generated at a period (1/240 seconds) obtained by dividing the display frame rate of 60 fps into four equal parts.

  In the imaging apparatus 1 set to the live view mode, in response to the AF start by half-pressing the shutter button 307, the entire imaging surface 101f of the imaging element 101, that is, all the AF areas Ef have three different exposure times. Exposure (hereinafter also referred to as “exposure for focus detection”) Pa to Pc is sequentially performed. Then, from the average luminance value of each AF area Ef, an AF evaluation value is calculated by adopting, for example, an image signal obtained from the exposure closest to the appropriate exposure condition among the three exposures Pa to Pc. Thereby, appropriate contrast AF is possible in all the AF areas Ef.

  Specifically, a relatively short exposure assuming a high-luminance subject (for example, a BV value of 8 to 15) in the first (first) frame Tf1 immediately after the shutter button 307 is half-pressed (immediately after the start of AF). Exposure (first exposure) Pa of time (for example, 1/64000 second) is started. Then, the charge signal generated by the image sensor 101 is read out by this first exposure Pa, and the contrast AF calculation circuit 77 performs calculation processing Ma for calculating the AF evaluation value.

  Next, in the second frame Tf2 after the start of AF, exposure Pb is started for an exposure time (for example, 1/1000 second) assuming a medium brightness subject (for example, a BV value of 2 to 9). Then, the charge signal generated by the image sensor 101 is read out by the second exposure Pb, and the contrast AF calculation circuit 77 calculates the AF evaluation value.

  Next, in the third frame Tf3 after the start of AF, exposure Pc is started for an exposure time (for example, 1/240 seconds) assuming a low-luminance subject (for example, a BV value of (−4) to −3). The charge signal generated by the AF pixel 11 f of the image sensor 101 is read out by the third exposure Pc, and the contrast AF calculation circuit 77 calculates the AF evaluation value Mc.

  Finally, exposure Pv for live view display is started in the fourth frame Tf4 after the start of AF. Then, the charge signal generated by the image sensor 101 is read (for example, thinning-out reading) by the fourth exposure Pv, and the live view display Dv is performed on the LCD 311. In the exposure Pv, a predetermined exposure time is not set as in each of the exposure Pa to Pc described above, and exposure is performed with an exposure time obtained by AE control.

  In FIG. 7, the exposures Pa to Pc and Pv are shown as parallelograms, which means that the exposure timing is gradually delayed as the horizontal line of the image sensor 101 is lowered. The exposure timing can be shifted for each horizontal line in this way because of the image sensor 101 (for example, an SMOS sensor) that can arbitrarily set the reset timing and readout timing for each pixel (horizontal line).

  When the exposure Pa to Pc with the exposure time of the three patterns as described above is performed, for example, in the interchangeable lens 2 having Fno of 1.4, ISO sensitivity 100 and exposure time (shutter speed (ss)) 1 / The exposure Pa set to 64000 seconds can deal with a subject having a BV value of 8 to 15 (parallel oblique line portion), and the exposure Pb set to ISO sensitivity 100 and the exposure time (ss) 1/1000 second allows a BV value of 2 to 2. 9 (parallel oblique line) can be handled. In addition, an object having a BV value (−4) to 3 (parallel hatched portion) can be handled by the ISO sensitivity 1600 and the exposure Pc set to the exposure time (ss) of 1/240 seconds. Note that the appropriate (optimum) exposure conditions for each exposure Pa, Pb, and Pc are for subjects with BV values of 13, 7, and 1 (cross-hatched portions), respectively.

  With such three patterns of exposure Pa to Pc, appropriate exposure data (focus detection data) can be obtained even for a subject with a BV value of (−4) to 15 as shown in FIG. Contrast AF can be accurately performed in the area Ef. This will be specifically described with reference to FIG.

  FIG. 9 is a diagram for explaining AF evaluation values obtained by the exposures Pa to Pc. 9A to 9C, the horizontal axis indicates the position of the focus lens 211, and the vertical axis indicates the AF evaluation value calculated by the contrast AF calculation circuit 77. FIGS. 9A to 9C show examples of AF evaluation values obtained in one AF area Ef by the above-described exposure Pa to Pc, respectively.

  The focus lens 211 is moved from the infinity end (∞ end) to the close end at an appropriate exposure of the three patterns Pa to Pc, for example, an exposure Pb with an exposure time of 1/1000 second shown in FIG. 9B. In this case, an AF evaluation value graph Gk having a peak value Pk having a convex shape is obtained. When such AF evaluation value data is obtained, appropriate focus control can be performed by driving the focus lens 211 to the position Fp corresponding to the peak value Pk.

  On the other hand, inappropriate exposure among the three patterns of exposure Pa to Pc, for example, exposure Pa of exposure time 1/64000 seconds and exposure Pc of exposure time 1/240 seconds shown in FIGS. 9 (a) and 9 (c). Then, since the graphs Ga and Gc of the AF evaluation values that make it difficult to determine the peak value are obtained, appropriate contrast AF cannot be performed.

  From the above, an exposure state in which appropriate AF evaluation value data can be obtained in each of the plurality of AF areas Ef (FIG. 6) by repeating the three patterns of focus detection exposures Pa to Pc in the display frame period of the live view. Therefore, it is possible to detect the focus position in each AF area Ef using the AF evaluation value data acquired in the exposure state, and to perform appropriate multi-point AF in contrast AF. It becomes. Here, when the focus positions detected in the respective AF areas Ef are different, the focus position is narrowed down to one by so-called “near priority”, that is, the focus position for the subject closest to the imaging device 1 is finally determined. The AF control is performed as a specific focus position.

  Note that the AF evaluation value data may be acquired by driving the focus lens 211 from the infinity end to the closest end (scanning the entire lens driving range) as shown in FIGS. Although it is good, in order to shorten time until AF completion, you may make it acquire by the following operation | movement.

  FIG. 10 is a diagram for explaining an AF evaluation value data acquisition operation. In FIG. 10, the horizontal axis indicates the position of the focus lens 211, and the vertical axis indicates the AF evaluation value calculated by the contrast AF calculation circuit 77.

  First, AF evaluation value data in each AF area Ef is acquired while driving the focus lens 211 from the infinity end. Then, the focus lens 211 is driven to the closest end side by a predetermined distance Lo from the position Fs of the focus lens 211 corresponding to the peak value Ps detected first in the plurality of AF areas Ef. A peak value Pt closest to the closest end side is obtained from AF evaluation value data in each AF area Ef obtained by driving the focus lens 211 at this distance Lo, and the position of the focus lens 211 corresponding to this peak value Pt. Ft is adopted as the final focusing position. Such an AF evaluation value data acquisition operation eliminates the need for driving Dr of the focus lens 211 up to the closest end, and enables rapid focus control.

  Next, a basic operation of the imaging apparatus 1 that performs the contrast AF operation as described above will be described.

<Basic Operation of Imaging Device 1>
11 and 12 are flowcharts showing the basic operation of the imaging apparatus 1. This operation shows a series of operations from the power-on of the image pickup apparatus 1 to the end of the main photographing, and is executed by the main control unit 62.

  When the user operates the main switch 317 to turn on the power of the imaging apparatus 1, it is determined whether the electronic viewfinder (live view mode) is selected based on the setting state of the changeover switch 85 (step ST1). If the electronic viewfinder is selected, the process proceeds to step ST2, and if the optical viewfinder 316 is selected instead of the electronic viewfinder, the process proceeds to step ST14.

  In step ST2, the mirror drive control unit 72A drives the mirror drive actuator 72M to raise the main mirror 1031 and the sub mirror 1032 in the mirror unit 103 (see FIG. 4).

  In step ST3, the shutter drive control unit 73A drives the shutter drive actuator 73M to open the shutter unit 40.

  In step ST4, the image sensor 101 is activated in the live view mode. As a result, the readout cycle of the image sensor 101 is set to 1/60 seconds, for example, and live view display on the LCD 311 is started.

  In step ST5, it is determined whether or not the optical viewfinder 316 has been switched. Specifically, it is determined whether or not the optical finder 316 has been selected by operating the changeover switch 85 by the user. If the optical finder 316 is switched, the process proceeds to step ST11. If the optical finder 316 is not switched, the process proceeds to step ST6.

  In step ST6, it is determined whether the shutter button 307 has been half-pressed by the user. Here, if half-pressed, the process proceeds to step ST7. If not half-pressed, the process returns to step ST5.

  In step ST7, exposure of three patterns having different exposure times as in exposure Pa to Pc shown in FIG. 7 is performed within the display frame period of the live view, and three types of AF evaluation value data (FIG. 9 (a) to ( c)) is acquired in each AF area Ef, and contrast AF based on data of an appropriate AF evaluation value is performed. Then, for example, a focus position with respect to the subject closest to the imaging apparatus 1 is specified, and the focus lens 211 is driven to that position.

  That is, in step ST7, the image sensor 101 sequentially performs three exposures Pa to Pc with different exposure values during an exposure cycle for live view display (for example, 1/60 seconds), and each of these three exposures. By performing contrast AF in each AF area Ef based on each image signal generated by the image sensor 101, multipoint AF with high accuracy can be performed in contrast AF.

  In step ST8, it is determined whether the shutter button 307 has been fully pressed by the user. Here, if it is fully pressed, the process proceeds to step ST9. If it is not fully pressed, the process returns to step ST5.

  In step ST9, actual photographing is performed. That is, an imaging operation for generating recording image data for recording is performed by the image sensor 101.

  In step ST10, the photographed image data generated by the image sensor 101 by the main photographing in step ST9 is read. The read captured image data can be recorded on the memory card 67 through the processing in the AFE 5 and the image processing unit 61.

  In step ST11, the mirror drive control unit 72A drives the mirror drive actuator 72M to lower the main mirror 1031 and the sub mirror 1032 in the mirror unit 103 (see FIG. 3).

  In step ST12, the shutter drive control unit 73A drives the shutter drive actuator 73M to perform the closing operation of the shutter unit 40.

  In step ST13, since the optical viewfinder is selected, the image sensor 101 and the LCD 311 necessary for the electronic viewfinder are turned off.

  In step ST14, it is determined whether or not the electronic viewfinder has been switched. Specifically, it is determined whether or not the electronic viewfinder has been selected by operating the changeover switch 85 by the user. If the electronic viewfinder is switched, the process returns to step ST2, and if not switched, the process proceeds to step ST15.

  In step ST15, it is determined whether the shutter button 307 has been half-pressed by the user. Here, if half-pressed, the process proceeds to step ST16. If not half-pressed, the process returns to step ST14.

  In step ST16, phase difference AF is performed by the phase difference AF module 107. Here, highly accurate phase difference AF is possible by the multipoint AF described above.

  In step ST17, it is determined whether the shutter button 307 has been fully pressed by the user. Here, if it is fully pressed, the process proceeds to step ST18. If it is not fully pressed, the process returns to step ST14.

  In step ST18, the mirror drive control unit 72A drives the mirror drive actuator 72M to raise the main mirror 1031 and the sub mirror 1032 in the mirror unit 103 (see FIG. 4).

  In step ST19, actual photographing is performed. That is, an imaging operation for generating recording image data for recording is performed by the image sensor 101.

  In step ST20, the captured image data generated by the image sensor 101 by the actual imaging in step ST19 is read, and the mirror drive actuator 72M is driven by the mirror drive control unit 72A to drive the main mirror 1031 and the sub mirror 1032 in the mirror unit 103. Bring down.

  With the operation of the imaging apparatus 1 described above, the three patterns of focus detection exposures Pa to Pc having different exposure values are performed within the live view display frame period, so that multipoint AF can be performed with high accuracy in contrast AF.

<Modification>
In the above embodiment, it is not essential to change the exposure time to realize exposure Pa to Pc (FIG. 7) with different exposure values, and change only the ISO sensitivity to realize exposure with different exposure values. You may do it. That is, in multiple exposures, the exposure value can be changed by changing the ISO sensitivity and / or the exposure time. Thereby, exposure with different exposure values can be realized.

  In the above embodiment, it is not essential to distinguish exposure for live view display from exposure for focus detection, and exposure for live view display may be used as exposure for focus detection. For example, live view display may be performed on the LCD 311 using an image signal obtained by the imaging device by exposure with a relatively good exposure state among the three exposures Pa to Pc (FIG. 7) having different exposure times. Thereby, the exposure for live view display can be omitted, and the exposure cycle for focus detection can be lengthened. That is, by including exposure by exposure control for live view display in a plurality of exposures for focus detection, a relatively long exposure time can be set in focus detection exposure.

  In the above embodiment, it is not essential to perform the focus detection exposure three times during the live view display frame period, and the focus detection exposure may be performed twice or four times or more. good.

  In the above embodiment, it is not essential to use an image sensor (for example, a CMOS type image sensor) that can arbitrarily set the reset timing and readout timing for each pixel, and the reset timing and readout timing for each pixel are arbitrary. An image sensor that cannot be set to (for example, a CCD-type image sensor) may be used.

1 is a diagram illustrating an external configuration of an imaging apparatus 1 according to an embodiment of the present invention. 1 is a diagram illustrating an external configuration of an imaging apparatus 1. FIG. 1 is a longitudinal sectional view of an imaging apparatus 1. FIG. It is a figure which shows the state of the mirror up in the mirror part. 2 is a block diagram illustrating an electrical configuration of the imaging apparatus 1. FIG. 6 is a diagram for explaining a plurality of AF areas Ef capable of contrast AF in the imaging apparatus 1. FIG. It is a time chart for demonstrating 3 patterns exposure Pa-Pc from which exposure time differs. It is a figure for demonstrating 3 patterns exposure Pa-Pc. It is a figure for demonstrating AF evaluation value obtained by each exposure Pa-Pc. It is a figure for demonstrating the data acquisition operation | movement of AF evaluation value. 3 is a flowchart showing a basic operation of the imaging apparatus 1. 3 is a flowchart showing a basic operation of the imaging apparatus 1.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Imaging device 2 Interchangeable lens 10 Camera body 62 Main control part 77 Contrast AF calculating circuit 85 Changeover switch 101 Image pick-up element 101f Imaging surface 103 Mirror part 107 Phase difference AF module 211 Focus lens 307 Shutter button 311 LCD
316 Optical viewfinder 622 Focus detection unit Ef AF areas Pa to Pc Focus detection exposure Pv Live view display exposure

Claims (3)

An imaging device,
(a) imaging means for generating an image signal related to the subject;
(b) display means capable of displaying an image based on an image signal generated by the imaging means;
(c) Display control means for performing exposure control for sequentially exposing the image pickup means at a predetermined cycle before the main photographing, and causing the display means to perform image display based on an image signal generated by the image pickup means by the exposure. When,
(d) driving means for driving the focus lens;
(e) a focus detection unit that performs focus detection of a contrast detection method based on image signals sequentially generated by the imaging unit while driving the focus lens by the driving unit;
With
A plurality of areas for performing the focus detection are defined on the imaging surface of the imaging means.
The focus detection unit sequentially performs a plurality of exposures with different exposure values during the predetermined period by the imaging unit, and based on each image signal generated by the imaging unit by each of the plurality of exposures. An image pickup apparatus that performs the focus detection in a plurality of regions. The imaging apparatus according to claim 1,
(f) Amplifying means for amplifying the image signal generated by the imaging means in a variable amplification factor,
Further comprising
An imaging apparatus characterized in that, in the plurality of exposures, the exposure value is changed by changing an amplification factor and / or an exposure time of the amplification means. The imaging apparatus according to claim 1,
The imaging apparatus according to claim 1, wherein the plurality of exposures include exposure by the exposure control.

Images