JP2013130759A - Focus detector and imaging apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To avoid responsiveness up to focusing from remarkably getting worse, without decreasing accuracy of focus detection.SOLUTION: A focus detector including a first mode in which auxiliary light is projected to an object when detecting a focus and a second mode in which the auxiliary light is not projected to the object when detecting the focus includes control means allowing focus detection processing in the first mode (S401) and then, allowing focus detection processing in the second mode when the detection result in the first mode is reliable (S404), but not allowing focus detection processing in the second mode when the detection result in the first mode is not reliable (NO in S403).

Description

  The present invention relates to a focus detection apparatus and an imaging apparatus having a mode in which auxiliary light is projected onto a subject.

  Conventionally, when the subject brightness is low, focus detection is possible by projecting auxiliary light in a situation where focus detection is severe with natural light. In focus detection, a subject image is acquired as a pair of image waveforms, and a defocus amount is calculated from these image shift amounts. Then, the lens is driven to the focal point based on the defocus amount.

  In addition, in order to improve the reach distance of auxiliary light, the spectral characteristics of auxiliary light can be provided not only in the visible light but also in the infrared light region, and the focus detection sensor can also have spectral sensitivity up to the infrared region. It is common.

  By the way, the focus detection operation of the camera in the interchangeable lens system is performed by a focus detection optical system having a fixed F value (for example, F5.6), and is focused on the reference interchangeable lens (for example, 50 mm / F1.8). The assembly process is adjusted so that the position becomes zero.

  The F value in the interchangeable lens system differs for each interchangeable lens, and the focus position varies depending on the F value. Therefore, each interchangeable lens has a focus difference from the reference interchangeable lens as a correction value.

  In addition, interchangeable lenses are designed with the focus on eliminating various aberrations in the visible light region in a well-balanced manner, and therefore focus on auxiliary light projection due to axial chromatic aberration of visible light and infrared light. The difference is also included as a correction value. These two correction values are different for each interchangeable lens, and the camera performs a focus detection operation so that the focus position becomes zero by electrically communicating the two correction values with the interchangeable lens via the mount.

  That is, the amount of defocus detected by the camera before correction is made is different between when the auxiliary light is projected and when it is not. The auxiliary light correction value is a value when the contribution ratio of the auxiliary light is 100%. Therefore, since the reflected light of the auxiliary light is hardly returned in shooting with mixed auxiliary light and natural light, especially in a distant view, the contribution ratio of natural light is high, and in this case, the defocus amount is not properly corrected and the focus is not adjusted. Correct correction may not be possible. In order to solve this problem, a mechanism has been proposed in which focus detection is performed twice with and without auxiliary light projection, and a more reliable result is selected.

  Further, Patent Document 1 discloses a focus detection device that can reduce the amount of reflected light that reaches even when the auxiliary light is irradiated and stops the irradiation of the invalid auxiliary light when the focus cannot be detected, thereby suppressing waste of energy. Is disclosed.

JP 2001-249269 A

  Although the focus detection operation is performed twice with and without auxiliary light projection as a countermeasure for the above problem, it can be used for focus detection without auxiliary light projection when the brightness is low or when the contrast of the subject is extremely low. It may take time and the responsiveness until focusing may deteriorate.

(Object of invention)
An object of the present invention is to provide a focus detection device and an imaging device capable of avoiding a significant deterioration in responsiveness until focusing without reducing the accuracy of focus detection.

  In order to achieve the above object, the focus detection apparatus of the present invention includes a first mode in which auxiliary light is projected onto the subject during focus detection, and a first mode in which auxiliary light is not projected onto the subject during focus detection. A focus detection apparatus having the second mode, wherein the focus detection process is performed in the first mode, and when the detection result in the first mode is reliable, the focus detection is subsequently performed in the second mode. Control means for performing the process and not performing the focus detection process in the second mode when the detection result in the first mode is unreliable.

  According to the present invention, it is possible to avoid that the responsiveness until focusing is significantly deteriorated without reducing the accuracy of focus detection.

1 is a diagram illustrating an outline of an imaging system including a focus detection apparatus that is Embodiment 1 of the present invention. FIG. It is a block diagram which shows the circuit structure of each part of the imaging system of FIG. It is a flowchart which shows the procedure of the imaging | photography process of the imaging system of FIG. 6 is a flowchart illustrating a procedure of focus detection processing according to the first exemplary embodiment. 10 is a flowchart illustrating a procedure of imaging processing of an imaging system including a focus detection apparatus that is Embodiment 2. 10 is a flowchart illustrating a procedure of focus detection processing according to the second embodiment.

  The mode for carrying out the invention is as described in Examples 1 and 2 below.

  FIG. 1 is a configuration diagram illustrating an outline of an imaging system including a focus detection apparatus that is Embodiment 1 of the present invention. In FIG. 1, reference numeral 100 denotes an imaging apparatus, which has the following members 101 to 116.

  Reference numeral 101 denotes an erect image optical system constituting the finder optical system, and reference numeral 102 denotes an eyepiece. Reference numeral 103 denotes a finder screen, and reference numeral 104 denotes a main mirror that deflects a part of the imaging light flux to the finder optical system. Reference numeral 105 denotes a sub-mirror that deflects the imaging light flux that has passed through the main mirror 104 with respect to a focus detection unit described later. Reference numeral 106 denotes an image pickup element that controls the image pickup of the image pickup apparatus 100, 107 denotes a shutter that shields the image pickup element 106, and 108 denotes a built-in flash housed inside the image pickup apparatus 100. The image sensor 106 receives the light beam from the subject that has passed through the interchangeable lens 200 and outputs an electrical signal. Reference numeral 109 denotes a focus detection unit that includes a plurality of focus detection sensors including a plurality of light receiving units and includes a focus detection optical system for performing focus detection by a phase difference detection method. Specifically, the light beam that has passed through the exit pupil of the focus lens included in the interchangeable lens 200 is divided into two, and the two divided light beams are received by a set of line sensors. Then, a defocus amount of the focus lens is obtained by detecting a shift amount of a signal output according to the received light amount, that is, an imaging control circuit described later, which is a relative positional shift amount in the beam splitting direction. Therefore, once the accumulation operation is performed by the focus detection sensor, the amount and direction in which the focus lens should be moved can be obtained, and the lens can be driven.

  110 is a photometric unit that measures the exposure of the imaging apparatus 100, 111 is a lens that forms an image of a subject light beam on the photometric unit 110, and 112 is an imaging control circuit that controls the imaging apparatus 100 (also referred to as a microprocessor). Reference numeral 113 denotes an accessory shoe for mounting an external strobe described later. Reference numeral 114 denotes a Fresnel lens of the built-in flash 108, 115 a finder display unit that displays information superimposed on an optical finder provided in the imaging apparatus 100, and 116 an external display unit that displays various types of information outside the imaging apparatus 100. It is. The focus detection unit 109 and the imaging control circuit 112 constitute a focus detection apparatus of the present invention.

  Reference numeral 200 denotes an interchangeable lens that is an imaging optical system, and includes the following members 201 to 203. Reference numeral 201 denotes a lens control circuit (also referred to as a microprocessor) that communicates with the communication unit of the imaging apparatus 100, 202 denotes a lens (imaging optical system) for imaging, and 203 denotes an aperture that adjusts the amount of light. The lens 202 includes a focus lens.

  Reference numeral 300 denotes an external strobe that is an illumination unit, and includes the following members 301 to 306. Reference numeral 301 denotes an external strobe control circuit (also referred to as a microprocessor) that controls the external strobe 300, 302 a light emitting unit, and 303 a reflector that reflects the light flux of the light emitting unit 302 toward the object side. Reference numeral 304 denotes a strobe panel for controlling the light distribution of the light beam reflected by the reflector 303, reference numeral 305 denotes an attaching portion for attaching to the accessory shoe 113 of the image pickup apparatus 100, and reference numeral 306 denotes an auxiliary light portion provided in the external strobe 300. is there.

  FIG. 2 is a block diagram illustrating a circuit configuration of each unit (the imaging device 100, the interchangeable lens 200, and the external strobe 300) of the imaging system. In FIG. 2, the imaging device 100 includes the components 112 and the following components 1 to 13.

  Reference numeral 112 denotes a microprocessor (imaging control circuit) that controls the image pickup apparatus 100, and reference numeral 1 denotes a motor drive circuit for driving a movable part of the image pickup apparatus 100. 2 is a photometric unit (including the photometric unit 110 in FIG. 1) for measuring the luminance of the subject, and 3 is a focus detecting unit (including the focus detecting unit 109 in FIG. 1) for detecting the focus state of the interchangeable lens 200. . Reference numeral 4 denotes a shutter control circuit that controls the exposure amount of the imaging apparatus 100, and is included in the shutter 107 in FIG. Reference numeral 5 denotes an aperture control circuit that controls the light beam taken into the imaging apparatus 100, and controls the aperture 203 in FIG. Reference numeral 6 denotes a display unit that displays the state of the imaging apparatus 100, and includes the finder display unit 115 and the external display unit 116 of FIG. A strobe control circuit 7 controls the built-in strobe 108 shown in FIG. 8 is a storage circuit for storing the setting state of the imaging apparatus 100, 9 is an imaging circuit for performing imaging processing, 10 is a lens communication circuit for communicating with the interchangeable lens 200 attached to the imaging apparatus 100, 11 Is a communication circuit for communicating with the external strobe 300. 12 (SW1) is a switch for starting an imaging preparation operation, and 13 (SW2) is a switch for starting imaging. The built-in strobe 108 not only illuminates the subject when taking an image without the external strobe 300 attached, but also has a function as auxiliary light for irradiating the subject at the time of focus detection.

  The interchangeable lens 200 includes 201 and the following 21 to 26 components. Reference numeral 201 denotes a microprocessor (lens control circuit) that controls the interchangeable lens 200, and reference numeral 21 denotes a lens drive circuit that drives the interchangeable lens 200. Reference numeral 22 denotes a lens position detection circuit that detects the position of the interchangeable lens 200, and reference numeral 23 denotes a lens focal length detection circuit that detects the set focal length of the interchangeable lens 200. Reference numeral 24 denotes a storage circuit that holds a set value of the interchangeable lens 200. Reference numeral 25 denotes an aperture driving circuit that is included in the aperture 203 of FIG. 1 and drives the aperture. Reference numeral 26 denotes a lens communication circuit for performing communication with the imaging apparatus 100.

  The external strobe 300 includes 301 and the following 31 to 39 components. Reference numeral 301 denotes a microprocessor (external strobe control circuit) that controls the external strobe, reference numeral 31 denotes a communication circuit for performing communication with the imaging apparatus 100, and reference numeral 32 denotes a storage circuit that holds setting values of the external strobe 300. Reference numeral 33 denotes an irradiation angle changing unit that changes the flash irradiation range in accordance with the state of the imaging device 100 and the interchangeable lens 200 to which the external flash 300 is attached. Reference numeral 34 denotes a flash irradiation angle detection unit that detects a setting value of the flash irradiation range. is there. Reference numeral 35 denotes a light emission amount monitor unit that directly monitors the light emission amount of the external strobe 300, 36 denotes a strobe charging circuit that performs strobe charging, and 37 denotes a light emission amount control circuit that controls the strobe light emission amount. Reference numeral 38 denotes a display unit for displaying the setting state of the external strobe 300, 39 denotes a setting unit for setting the state of the external strobe 300, and 306 denotes an auxiliary light unit built in the external strobe 300.

  FIG. 3 is a flowchart illustrating a procedure of imaging processing of the imaging system including the focus detection apparatus according to the first embodiment.

  First, if the switch 12 (SW1) of the imaging apparatus 100 is on in S301, the process proceeds to S302, and if not, the operation of S301 is performed again. This operation is repeated until the switch 12 is turned on. Subsequently, in S302, the focus detection unit 109 and the focus detection unit 3 perform focus detection processing. Details of the focus detection process will be described later. In step S303, the focus lens is driven through the lens communication circuit 10 and the lens communication circuit 26 based on the defocus amount calculated by the focus detection process in step S302.

  Next, if the switch 13 (SW2) is on in S304, the process proceeds to S305, and if not, the process proceeds to S307. If the current focus position is at the in-focus position by driving the focus lens in S303 in S305, the process proceeds to S306, and if not, the process proceeds to S307. In S306, the shutter control circuit 4 prepares for shooting, and in S308, the imaging circuit 9 performs recording processing. If the switch 12 is on in step S307, the process proceeds to step S302 to perform focus detection again. If not, the process ends.

  Next, FIG. 4 is a flowchart illustrating a procedure of focus detection processing according to the first embodiment.

First, in S401, the first phase difference detection process is performed. In this phase difference detection process, the defocus amount is calculated, the reliability indicating the accuracy of the phase difference detection result, and the accumulation time required for the process are calculated. Further, it is determined whether or not auxiliary light is required to be projected. If necessary, auxiliary light is emitted and phase difference detection is performed. A mode in which auxiliary light is projected onto the subject at the time of focus detection is defined as a first mode. On the other hand, the mode in which the auxiliary light is not projected on the subject at the time of focus detection is set to the second mode. In the next step S402, was the auxiliary light projected at the time of the first phase difference detection process of S401? That is, it is determined whether the mode is the first mode or the second mode, and the subsequent processing is branched with or without auxiliary light projection. In the case of the first mode in which the auxiliary light is projected, the process proceeds to S403. In the second mode in which the auxiliary light is not projected, the phase difference detection result in S401 is used as the current focus detection result, and the process proceeds to S407. In S403, it is further determined whether or not the detection result calculated in S401 is reliable. If reliable, the process proceeds to S404. Otherwise, the detection result in S401 is used as the result of the current focus detection, and the process proceeds to S407. In step S404, the second phase difference detection process is performed. Here, the phase difference detection processing in the second mode in which auxiliary light is not necessarily projected is performed. In step S405, it is determined whether the detection result calculated in step S404 is reliable. If reliable, the process proceeds to S406, and if not, the process proceeds to S407. In S406, the storage time and reliability calculated in S401 and S404 are compared as evaluation values, and finally, which detection result is used as the current focus detection result is selected.

  Finally, in S407, the defocus amount of the finally selected detection result is converted so that the focus lens can be driven.

  As described above, in the first embodiment, it can be confirmed that the auxiliary light is projected in the first phase difference detection process of S401, and when the reliability of the phase difference detection result is poor, the auxiliary light of S404 is projected. The phase difference detection process is not performed when there is no light. Thereby, the processing time for focus detection can be shortened.

  FIG. 5 is a flowchart illustrating a procedure of imaging processing of an imaging system including a focus detection apparatus that is Embodiment 2 of the present invention. The processing from S301 to S308 is the same as that shown in FIG.

  First, in S501, the skip flag is turned off. This skip flag is a (second) phase difference detection in the second mode in which the auxiliary light is not projected when the (first) phase difference detection process is performed in the first mode in which the auxiliary light is projected. This is a flag indicating whether processing is required. Further, since this process is performed only once before entering the focus detection process, once the skip flag is turned on, it is not changed until the switch 12 (SW1) is turned off.

  FIG. 6 is a flowchart showing the procedure of focus detection processing according to the second embodiment. The processing from S401 to S407 is the same as that shown in FIG.

  First, in S601, if the skip flag is off, the process proceeds to S403, and if it is on, the phase difference detection processing in the second mode in which auxiliary light is not projected is not performed, and the first mode in S401 is not performed. The first detection result is used as the current focus detection result, and the process proceeds to S407. In step S403, the reliability of the phase difference detection result in step S401 is determined. In step S404, phase difference detection processing is performed when no auxiliary light is projected (second mode). Subsequently, when the reliability of the detection result in S404 is poor in S405, the process proceeds to S602.

  In step S602, the skip flag is turned on. By turning on this skip flag, it is possible to skip the phase difference detection process when the auxiliary light is not projected (second mode) when the auxiliary light is projected in the subsequent focus detection process. Become.

  As described above, in Example 2, when the auxiliary light is not projected in S405 (second mode) and the detection result is unreliable, the subsequent auxiliary light is projected by turning on the skip flag. Phase difference detection processing is not performed when light is not emitted (second mode). Thereby, the processing time for focus detection can be shortened.

108 Built-in flash 109 Focus detection unit 112 Imaging control circuit 306 Auxiliary light unit

Claims (4)

A focus detection apparatus including a first mode in which auxiliary light is projected onto a subject during focus detection and a second mode in which auxiliary light is not projected onto the subject during focus detection,
When the focus detection process is performed in the first mode and the detection result in the first mode is reliable, the focus detection process is subsequently performed in the second mode, and the detection result in the first mode And a control means for preventing the focus detection process in the second mode from being performed when the camera is not reliable.   The control means compares the detection result in the first mode and the detection result in the second mode using an accumulation time or reliability as an evaluation value, and determines one of the detection results as a current focus detection. The focus detection device according to claim 1, wherein the focus detection device is selected as a result.   When the detection result in the first mode is reliable and the detection result in the second mode is unreliable, the control means thereafter performs focus detection processing in the second mode until the photographing process is completed. The focus detection device according to claim 1, wherein the focus detection device is not performed.   An imaging apparatus comprising the focus detection apparatus according to claim 1.

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