JP2013231883A - Imaging device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an imaging device which determines a subject distance according to a used lens, and displays an operating method for obtaining a high accuracy focus correction value, in a focus calibration.SOLUTION: An imaging device includes: focus detecting means 22 for generating an image signal by photoelectrically converting a pair of images formed by light passing through an imaging optical system; focus controlling means 40 for detecting a focus state by a phase difference detection system, and calculating a first focus position for moving a focus lens 10a; calibration means 40 for detecting a second focus position by a contrast detection system, and correcting the first focus position on the basis of difference between the second focus position and the first focus position; and reliability determining means 40 for determining the reliability of the focus state, by using information about the image signal. Before carrying out the contrast detection, an operating method for determining a subject and a subject distance on the basis of a lens optical prescribed position, a focus distance, and the stop position information of the focus lens is displayed in a back surface monitor 43.

Description

  The present invention relates to an imaging apparatus having a focus calibration function for correcting a focus position obtained by a phase difference detection method based on a focus position detected by a contrast detection method.

  In cameras and interchangeable lenses that obtain a focused state by focus control (autofocus: AF) using a phase difference detection method, as the number of times they are used increases, backlash occurs in mechanisms and members related to AF. Focusing accuracy may be reduced. For example, in an interchangeable lens, the focus lens may not be correctly moved to the calculated in-focus position due to backlash generated in a mechanism that moves the focus lens. In the camera, the angle of the mirror that reflects the light from the interchangeable lens toward the AF sensor for detecting the phase difference changes as the number of times the mirror is driven increases. As a result, the manner in which light is incident on the AF sensor changes, and the focus position calculated based on the output from the AF sensor may deviate from the correct focus position. In this case, since the focus lens moves to the in-focus position shifted from the correct in-focus position, the in-focus accuracy is lowered.

  In these cases, in order to return the focusing accuracy to the original good accuracy, the user brings the camera or the interchangeable lens to the service center and requests readjustment of the focusing position, or the imaging disclosed in Patent Document 1 In the test mode, in the test mode, data relating to the focus state is obtained from each of the AF sensor for detecting the phase difference AF and the image sensor (imaging device) for generating the captured image, and the relative deviation amount (difference) between these data is obtained. Remember. In the shooting mode, the focus lens is moved based on the stored relative deviation amount.

  Further, in the imaging apparatus disclosed in Patent Document 2, in the correction value calculation mode, the focus correction is calculated and stored based on the result of the subject state identification unit, and when it is determined that proper correction cannot be performed. Provide information such as warning display.

  In addition, Patent Literature 3 detects subject distance information, displays a graph with the subject image and distance information added, and performs focus change and aperture adjustment by intuitive operation means.

JP 2006-208783 A JP 2007-286438 A JP 2010-93422 A

  However, in the imaging device disclosed in Patent Document 1, when it is determined by the determination of the subject state identification means that proper focus correction cannot be performed, shooting is continued with the focus accuracy remaining low. Alternatively, it is necessary to stop using the camera and bring it into the service center as described above to adjust the focusing accuracy.

  In the imaging apparatus disclosed in Patent Document 2, reliability information is obtained from the difference between the in-focus position calculated by the phase difference detection method and the in-focus position detected by the contrast detection method. For this reason, even when the reliability of the focus position itself obtained by the phase difference detection method is low, there is a possibility that a warning is not output or the difference is used as a correction value for focus calibration.

  The image pickup apparatus disclosed in Patent Document 3 detects and displays distance information to a focused subject during normal shooting, and further performs focus change and aperture adjustment from the above state. There is a possibility that it is not the subject distance with the highest resolution in the lens used for.

  In the focus correction mode by focus calibration, the present invention calculates the subject distance from the lens information to be used, the optical reference distance in lens design, the current focus lens stop position error, etc. An object distance display for obtaining a focus correction value by high-precision focus calibration is provided.

An imaging system (24) that photoelectrically converts an object image formed by the imaging optical system (10) to generate an image signal, and a pair of images formed by light incident from the object through the imaging optical system Focus detection means (22) for converting and generating a pair of image signals;
First focusing is performed by detecting a focus state of the photographing optical system by a phase difference detection method using the pair of image signals and moving a focus lens (10a) included in the photographing optical system according to the focus state. Lens control means (13) for calculating the position;
A second focus position of the focus lens (10a) is detected by a contrast detection method using the image signal, and the second focus position is detected based on the difference between the second focus position and the first focus position. In an imaging apparatus having calibration means (40, 41) for performing focus calibration for correcting one in-focus position and display means (43) for displaying a subject image,
Means (40) for calculating distance information of a subject based on lens information including focal length information and focus distance information from the photographing optical system, and an optical design distance;
The display means (43) determines the stop position of the focus lens (10a) based on the distance information of the subject, and the user changes the distance to the subject while the focus lens is stopped. An image pickup apparatus that displays an operation method for performing focusing.

  According to the present invention, focus calibration that obtains a high-accuracy focus correction value is performed by determining a high-precision subject distance with the lens and providing an operation display for focusing at the subject distance. Is possible.

5 is a flowchart illustrating a focus calibration operation of the camera that is Embodiment 1 of the present invention. 7 is a display example of focus setting on the camera display unit of the first embodiment. 6 is a flowchart illustrating phase difference AF focusing control processing of the camera according to the first exemplary embodiment. FIG. 7 is a focus display and subject position diagram in the camera display unit of the first embodiment. 1 is a diagram illustrating a configuration of a camera according to Embodiment 1.

  Embodiments of the present invention will be described below with reference to the drawings.

[Example 1]
FIG. 5 shows a configuration of a camera system that includes a digital single-lens reflex camera 2 that is Embodiment 1 of the present invention and an interchangeable lens 1 that can be interchanged with the camera 2. This camera system performs AF processing by a phase difference detection method (hereinafter referred to as phase difference AF) and has a focus calibration function that is a correction function of phase difference AF using a focus detection result by a contrast detection method.

  A photographing optical system 10 is accommodated in the interchangeable lens 1. The photographing optical system 10 includes a plurality of lens units and a diaphragm. By moving a not-shown zoom lens unit (hereinafter referred to as a zoom lens) among the plurality of lens units in the optical axis direction, zooming can be performed by changing the focal length. Further, focusing can be performed by moving a focus lens unit (hereinafter simply referred to as a focus lens) 10a among the plurality of lens units in the optical axis direction.

  The lens driving unit 11 includes an actuator for moving the zoom lens and the focus lens 10a, a driving circuit for the actuator, and a transmission mechanism for transmitting the driving force of the actuator to each lens. The lens state detection unit 12 can detect the focal length information and the focus distance information by a detection unit in which the positions of the zoom lens and the focus lens 10a are divided into a predetermined number.

  The lens control unit 13 is configured by a CPU or the like, and controls the operation of the interchangeable lens 1 according to a command from a camera control unit 40 described later. The lens control unit 13 is communicably connected to the camera control unit 40 via a communication terminal in the electrical contact 15. The interchangeable lens 1 is supplied with power from the camera 2 through the power terminal of the electrical contact 15. The lens storage unit 14 includes a ROM or the like, and stores various information such as data used for control by the lens control unit 13, identification information of the interchangeable lens 1, and optical information of the photographing optical system 10.

  In the camera 2, the main mirror 20 composed of a half mirror is disposed at a down position in the photographing optical path as shown in the figure when the user observes the subject through the optical viewfinder, and the light from the photographing optical system 10 is shown. Is reflected toward the focus plate 30. Further, the main mirror 20 is retracted from the photographing optical path during live view observation in which an image for an electronic viewfinder (live view image) is displayed on the rear monitor 43 or during photographing for generating a recording image (still image and moving image). Rotates to the up position. Thereby, the light from the photographing optical system 10 travels to the shutter 23 and the image sensor 24.

  The sub mirror 21 rotates together with the main mirror 20 and guides the light transmitted through the main mirror 20 disposed at the down position to the AF sensor 22. When the main mirror 20 is rotated to the up position, the sub mirror 21 is also retracted from the photographing optical path.

  The AF sensor 22 uses the light incident from the subject through the photographing optical system 10 and reflected by the sub-mirror 21 to photograph by a phase difference detection method in a plurality of focus detection areas provided in the photographing range by the camera 2. The focus state of the optical system is detected (focus detection). The AF sensor 22 is an area sensor in which a secondary imaging lens that forms a pair of images (subject images) on the light from each focus detection region and a pair of light receiving element rows that photoelectrically convert the pair of subject images. (CCD or CMOS). The pair of light receiving element rows of the area sensor outputs a pair of image signals, which are photoelectric conversion signals corresponding to the luminance distribution of the pair of subject images, to the camera control unit 40. A plurality of pairs of light receiving element arrays corresponding to a plurality of focus detection areas are two-dimensionally arranged on the area sensor.

  The camera control unit 40 calculates the phase difference between the pair of image signals, and calculates the focus state (defocus amount) of the photographing optical system 10 from the phase difference. Further, the camera control unit 40, based on the detected focus state of the photographing optical system 10, obtains a focusing position (first position) that is a position to move the focus lens 10a to obtain a focusing state of the photographing optical system 10. (Focus position: hereinafter referred to as phase difference in-focus position).

  Then, the camera control unit 40 transmits a focus command to the lens control unit 13 so as to move the focus lens 10a to the calculated phase difference in-focus position. The lens control unit 13 moves the focus lens 10a to the phase difference in-focus position via the lens driving unit 11 in accordance with the received focus command. Thereby, the in-focus state of the photographic optical system 10 is obtained.

  In this way, the phase difference AF including the detection of the focus state by the phase difference detection method, the calculation of the phase difference focus position based on the focus state, and the movement of the focus lens 10a to the phase difference focus position is obtained. Done.

  In addition, since the light receiving elements are two-dimensionally arranged in the area sensor of the AF sensor 22, the luminance distribution in the horizontal direction and the vertical direction of the subject is detected for the same field area (for example, the central area) within the imaging range. Focus detection can be performed. This will be described in detail later.

  The shutter 23 is closed during optical viewfinder observation, and is opened during live view observation and moving image shooting, and photoelectric conversion (generation of a live view image and a shooting moving image) by the image sensor 24 of the subject image formed by the shooting optical system 10 is possible. And Further, during still image shooting, the shutter is opened and closed at a set shutter speed, and exposure of the image sensor 24 is controlled.

  The image sensor 24 is composed of a CMOS image sensor or a CCD image sensor and its peripheral circuits, and photoelectrically converts a subject image formed by the photographing optical system 10 and outputs an analog image signal.

  The focus plate 30 is disposed on the primary imaging plane of the photographic optical system 10 that is at a position equivalent to the image sensor 24. A subject image (finder image) is formed on the focus plate 30 during optical viewfinder observation. The pentaprism 31 converts the subject image formed on the focus plate 30 into an erect image. The eyepiece 32 allows the user to observe an erect image. The focus plate 30, the pentaprism 31 and the eyepiece lens 32 constitute an optical finder. Although not shown in FIG. 5, a finder information display unit using a liquid crystal (including a transmission type) device is configured so that various information of the camera can be confirmed while looking through the finder.

  The AE sensor 33 receives light from the focus plate 30 via the pentaprism 31 and measures the luminance of the subject image formed on the focus plate 30. The AE sensor 33 has a plurality of photodiodes, and can measure the luminance in each of a plurality of photometric areas set so as to divide the imaging range of the camera 2.

  The camera control unit 40 is configured by a microcomputer including an MPU and the like, and controls the operation of the entire camera system including the camera 2 and the interchangeable lens 1. The camera control unit 40 functions as a focus control unit as described above, and also functions as a calibration unit and a reliability determination unit as described later.

  The digital control unit 41 converts an analog image pickup signal from the image pickup device 24 into a digital image pickup signal, and further performs various processes on the digital image pickup signal to generate an image signal (image data). The imaging device 24 and the digital control unit 41 constitute an imaging system.

  In addition, the digital control unit 41 extracts a specific frequency component from the image signal and generates a contrast evaluation value indicating the contrast of the image signal. Then, the focus position of the focus lens 10a where the contrast evaluation value is maximized is detected. The operation of detecting the focus position by the contrast detection method in this way (including focusing during live view observation and moving image shooting) is called contrast AF. In addition, the focus position (second focus position) detected by contrast AF is hereinafter referred to as a contrast focus position.

  The camera storage unit 42 stores various data used in the operation of the camera control unit 40 and the digital control unit 41. In addition, the camera storage unit 42 stores the generated recording image. The rear monitor 43 includes a display element such as a liquid crystal panel, and displays a live view image, a recording image, and various types of information.

  Although not shown in FIG. 5, the camera 2 is provided with a release switch.

  When the release switch is pressed halfway, a first switch (SW1) (not shown) is turned on, and AF and photometry are started. When the release switch is fully pressed, a second switch (SW2) (not shown) is turned on and photographing (generation of a recording image) is performed.

  Next, a focus calibration function (hereinafter referred to as AF calibration) that the camera 2 has will be described. AF calibration is a function for correcting the phase difference focus position obtained by the phase difference detection method based on the difference between the phase difference focus position and the contrast focus position obtained by the contrast AF described above. . This AF calibration calculation is mainly performed by the camera control unit 40.

  Further, the camera control unit 40 calculates the reliability of the phase difference AF with respect to the subject that is the target of the phase difference AF, using the information about the pair of image signals from the AF sensor 22 as the reliability unit determination unit, It is determined whether the reliability is high or low. The reliability of the phase difference AF for the subject in the present embodiment is basically the defocus amount (focus state) obtained using a pair of image signals from the AF sensor 22 that receives light from the subject. It is reliability. However, since the phase difference in-focus position is calculated from the defocus amount, it can be said that the phase difference in-focus position is reliable. In the following description, the reliability of the phase difference AF for the subject is also simply referred to as reliability.

  In this embodiment, an S level (SELECT LEVEL) value SL disclosed in Japanese Patent Application Laid-Open No. 2007-052072 is used as an evaluation value indicating the reliability obtained using information relating to a pair of image signals. Use.

  The camera control unit 40 performs AF calibration when the S level value SL is equal to or lower than the threshold value or smaller than the threshold value, that is, when the first level has high reliability. On the other hand, when the S level value SL is greater than or equal to or greater than the threshold, that is, when the reliability is the second level lower than the first level, the AF calibration is limited.

  In this embodiment, a general subject is used for AF calibration. Then, the subject dependency of the phase difference AF can be reduced by using the S level value SL described above as the reliability evaluation value. In other words, if it is determined that the reliability is high (the first level) using the S level value SL, the subject at that time should be able to obtain a highly accurate in-focus state by the phase difference AF. Therefore, by performing AF calibration (calculating a correction value) and correcting the phase difference in-focus position, an original highly accurate in-focus state can be obtained.

  On the other hand, when it is determined that the reliability is low (the second level) using the S level value SL, the subject at that time is a subject for which a good precision in-focus state cannot be obtained by the phase difference AF. There is a high possibility. Therefore, by limiting the AF calibration, it is possible to prevent the erroneous phase difference focus position from being corrected by the AF calibration. Restricting AF calibration means, for example, displaying a warning, not creating a correction value for correcting the phase difference in-focus position, or forcibly redoing AF calibration.

  It should be noted that the reliability can be determined based on the information on the defocus amount and the charge accumulation time in the AF sensor 22 as one of the information related to the pair of image signals (information obtained from the pair of image signals). Good.

  The flowchart of FIG. 1 shows AF calibration processing mainly executed by the camera control unit 40. The camera control unit 40 executes this process and each process described below according to a computer program.

  In step S101, when the focus correction of the phase difference AF by AF calibration is created, the process proceeds to step S102. Otherwise, the normal photographing without newly creating or using the focus correction is performed in step S115.

  In step S102, the process proceeds to step S103 when performing AF calibration using lens information, and proceeds to step S106 when performing focus correction using the existing method.

  In step S103, the focal length information (zoom position information in the case of a zoomable lens), aperture value information, focus lens position information, and the optical design distance of each lens are temporarily calculated from the lens side information. The subject distance is calculated. The temporary subject distance information is a distance for which the optical performance including the resolving power of the lens is guaranteed using the reference distance calculation formula in the lens optical design according to the present embodiment. This is defined as a temporary subject distance when performing. The distance is given by equation (1).

d (m) = (f × k) / 1000 (1)
In this embodiment, an optical reference coefficient k (50 in this embodiment), a temporary subject distance d (m), and a focal length f (mm) of the lens used are used.

  In step S104, switching to focus lens driving by phase difference AF control is performed, and lens driving is performed a predetermined number of times based on the stop position of the focus lens corresponding to the temporary subject distance calculated in step S103, and the stop position error is determined. Is determined OK, the focus lens stop position is determined and stored. When the stop position error of the focus lens is NG determination, the AF calibration is finished, and the process returns to the normal shooting in step S115. The determination of the focus lens stop position error will be described later.

  In step S105, an operation method display for focusing is performed at the focus lens stop position stored in step S104. An example of the display is shown in FIG. 2 in FIG. 2 represents an AF distance measurement point displayed on the rear monitor 43. FIG. 2A shows a case where the display magnification is set to 1. FIG. 2B shows a display magnification set to 5 times. Indicates the display state when The operation method when the display magnification is set to 5 is displayed as 202 in FIG.

  Next, in step S106 in FIG. 1, the position of the camera 401 in FIG. 4A is determined while confirming the focus within the AF distance measurement frame 203 in FIG. 2B with the display magnification set in step S105. The subject is changed as in FIGS. 4A to 402-404, and the subject to be in focus is determined. Further, FIGS. 4B and 4C show display examples in the case where the focus is confirmed in the finder with the phase difference AF. In the finder display 405, when the subject is focused at an arbitrarily selected distance measuring point 406, the stop position of the focus lens 10a is determined by the position of the block display 408 in the camera information display 407 in the finder. To do. If it coincides with the stop position of the focus lens 10a stored in step S104, a block display 408 is displayed just below the triangle mark in the center of the camera information display 407 as shown in FIG. In this case, in conjunction with the stop position of the focus lens, the block display 408 is displayed at any position in the left-right direction (= indicating the distance to the subject + the near-direction) in the camera information display 407. FIG. 4C shows a case where the distance is near the subject distance.

  In step S107, the mode is switched to the TVAF focusing mode in the state of the subject and subject distance determined in step S106.

  In step S108, the lens drive control is changed so that the in-focus position is detected by contrast AF.

  In step S109, the lens drive control changed in step S108 is performed, and if a contrast peak is detected, the process proceeds to step S110. If no peak can be detected, the process returns to step S108 and the contrast peak detection is repeated a specified number of times. .

  In step S110, the focus lens where the contrast peak was detected in step S109 is stopped and stored.

  In step S111, distance measurement is performed with phase difference AF, and the stop position of the focus lens is stored.

  In step S112, the difference between the stop positions of the focus lens in step S110 and step S111 is calculated, and the focus correction value at the time of phase difference AF distance measurement is calculated.

  In step S113, a display of the focus correction value calculated in step S112 and an operation display for inputting the focus correction value are displayed on the rear monitor 43.

  In step S114, the focus correction value input in the focus correction value input display in step S113 is stored in the camera storage unit. At this time, the temperature information affecting the focus accuracy and the GPS position information for effectively using the focus correction value may be stored at the same time.

  Next, the stop position error determination of the focus lens 10a in step S104 will be described with reference to FIG.

  In step S301, based on the temporary subject distance calculated in step S103, the stop position of the focus lens 10a is detected from a pre-divided focus pulse signal, and the focus lens 10a is driven and stopped at the subject distance in focus. Let

  In step S302, the focus pulse position at which the lens stopped in step S301 is stored.

  Next, in step S303, each of the position from the closest end and the position from the infinite end to the position of the focus lens 10a is controlled by lens drive control from the camera with reference to the position of the focus lens 10a temporarily stored in step S302. The lens is driven and stopped twice.

  In step S304, it is determined whether or not the stop position of the focus lens 10a in step S303 matches the focus pulse position stored in step S302. If OK, the process proceeds to step S305. If NO, the process proceeds to step S306. . In step S306, it is determined whether to perform normal AF calibration. If so, the process proceeds to determination of the subject in step S107. If NO, the process proceeds to normal shooting in step S115.

  In step S305, the operation is stopped at the position of the focus lens 10a that is OK in step S304.

  According to the present embodiment, since the focus lens stop position error of the used lens and the optical design distance of the lens are taken into consideration, the lens has the best shooting resolution, so the contrast peak detection It is possible to avoid performing the AF calibration operation a plurality of times due to the inability, and it is possible to obtain a focus correction value by highly accurate AF calibration.

  As mentioned above, although preferable embodiment of this invention was described, this invention is not limited to these embodiment, A various deformation | transformation and change are possible within the range of the summary.

  According to the present invention, it is possible to provide an imaging apparatus capable of performing focus calibration with high reliability.

DESCRIPTION OF SYMBOLS 10 Shooting optical system 10a Focus lens 13 Lens control part 22 AF sensor 24 Image sensor 40 Camera control part 41 Digital control part 43 Rear monitor

Claims (4)

An imaging system (24) that photoelectrically converts an object image formed by the imaging optical system (10) to generate an image signal, and a pair of images formed by light incident from the object through the imaging optical system Focus detection means (22) for converting and generating a pair of image signals;
First focusing is performed by detecting a focus state of the photographing optical system by a phase difference detection method using the pair of image signals and moving a focus lens (10a) included in the photographing optical system according to the focus state. Lens control means (13) for calculating the position;
A second focus position of the focus lens (10a) is detected by a contrast detection method using the image signal, and the second focus position is detected based on the difference between the second focus position and the first focus position. In an imaging apparatus having calibration means (40, 41) for performing focus calibration for correcting one in-focus position and display means (43) for displaying a subject image,
Means (40) for calculating distance information of a subject based on lens information including focal length information and focus distance information from the photographing optical system, and an optical design distance;
The display means (43) determines the stop position of the focus lens (10a) based on the distance information of the subject, and the user changes the distance to the subject while the focus lens is stopped. An image pickup apparatus that displays an operation method for performing focusing.   The imaging apparatus according to claim 1, wherein the display unit (43) controls a display magnification when the subject is in focus.   The imaging apparatus according to claim 1, further comprising means (40) for detecting a stop position error of the focus lens (10a) when determining a stop position of the focus lens (10a) at the subject distance.   The imaging apparatus according to claim 1, wherein various information obtained in the imaging apparatus can be stored in a focus correction value by focus calibration at the subject distance.