WO2013140777A1

WO2013140777A1 - Focus control device and imaging device

Info

Publication number: WO2013140777A1
Application number: PCT/JP2013/001810
Authority: WO
Inventors: 本庄　謙一; 充義岡本; 剛治澁野
Original assignee: パナソニック株式会社
Priority date: 2012-03-21
Filing date: 2013-03-15
Publication date: 2013-09-26
Also published as: JP2015111170A

Abstract

A focus control device equipped with: a focus lens that changes the focused state of an imaging subject; a drive unit for driving the focus lens in the direction of the light axis; a position detection unit that detects the position of the focus lens; an imaging element that carries out exposure with a prescribed timing to generate image data; an AF evaluation value calculation unit that calculates an AF evaluation value from the image data; a focus determination unit that determines the focused state on the basis of the AF evaluation value; and a control unit that controls the drive unit in prescribed control periods on the basis of the determination result from the focus determination unit and the focus lens position detected by the position detection unit. The control unit controls the drive unit such that the focus lens moves with a constant speed for all of the prescribed control periods.

Description

Focus control device and imaging device

The present disclosure relates to a focus control device that continues to focus on a moving subject, and an imaging device equipped with the focus control device.

In the focus control used in a conventional camera, there is a problem that a focus shift occurs with respect to a subject that approaches or moves away from the camera. As a technique for solving the problem of occurrence of defocus as described above, there is a technique disclosed in Patent Document 1. Patent Document 1 discloses a technique for obtaining a focus position of a focus lens using position data of the focus lens and time data corresponding to each position data.

JP 2008-175886 A

The conventional method is based on the premise that the position of the focus lens is fixed at a predetermined time. That is, it is difficult to accurately control the focus lens position from a certain time to the next time after a unit time has elapsed. For this reason, with the conventional method, it is difficult to accurately perform an autofocus operation on a moving subject.

The present disclosure is intended to provide a focus control device and an imaging device capable of improving the accuracy of the autofocus operation even when the subject moves toward or away from the camera.

A focus control device according to the present disclosure includes a focus lens that changes a focus state of a subject image, a drive unit that drives the focus lens in the optical axis direction, a position detection unit that detects the position of the focus lens, An image sensor that generates image data by exposure at timing, an AF evaluation value calculation unit that calculates an AF evaluation value from the image data, a focus determination unit that determines a focus state based on the AF evaluation value, and a focus determination And a control unit that controls the drive unit at predetermined control cycles based on the determination result by the unit and the focus lens position detected by the position detection unit. The control unit controls the drive unit to move the focus lens at a constant speed over the entire predetermined control cycle.

The camera system according to the present disclosure includes a camera body and an interchangeable lens unit that can be attached to the camera body. The camera body is exposed at a predetermined timing to generate an image data, an AF evaluation value calculation unit that calculates an AF evaluation value from the image data, and an in-focus state that determines an in-focus state based on the AF evaluation value A determination unit; and a camera control unit that transmits a command for controlling the operation of the interchangeable lens unit to the interchangeable lens unit based on a determination result of the focus determination unit. The interchangeable lens unit includes a focus lens that changes the focus state of the subject image, a drive unit that drives the focus lens in the optical axis direction, a position detection unit that detects the position of the focus lens, and a command received from the camera body. And a lens control hand unit for controlling the drive unit for each predetermined control cycle based on the focus lens position detected by the position detection unit. The lens control unit controls the drive unit to move the focus lens at a constant speed over the entire predetermined control cycle.

With the configuration of the present disclosure, even when the subject moves toward or away from the camera, the followability of the subject is improved and the accuracy of the autofocus operation can be improved.

The block diagram which shows the structure of the camera system which concerns on embodiment of this invention Signal transmission / reception flowchart for explaining the imaging preparation operation of the camera system according to the embodiment of the present invention Basic operation explanatory diagram of single AF control according to the embodiment of the present invention Explanatory drawing of algorithm for calculating focus position of moving object tracking AF in the embodiment of the present invention Segment range detection principle diagram of moving object tracking AF in the embodiment of the present invention Timing chart for explaining the operation of the moving body tracking method of the camera system according to the embodiment of the present invention The figure which shows the time change of the focus lens position which concerns on embodiment of this invention

Hereinafter, embodiments will be described in detail with reference to the drawings as appropriate. However, more detailed description than necessary may be omitted. For example, detailed descriptions of already well-known matters and repeated descriptions for substantially the same configuration may be omitted. This is to avoid the following description from becoming unnecessarily redundant and to facilitate understanding by those skilled in the art.

The inventor (s) provides the accompanying drawings and the following description in order for those skilled in the art to fully understand the present disclosure, and is intended to limit the subject matter described in the claims. Not what you want.

(Embodiment 1)
Hereinafter, an embodiment in which a focus control apparatus of the present invention is applied to a camera will be described in detail with reference to the drawings.

(1. Configuration)
(1-1. Overview)
FIG. 1 is a block diagram showing a configuration of a camera system according to Embodiment 1 of the present invention. The camera system 1 includes a camera body 100 and an interchangeable lens unit 200 that can be attached to and detached from the camera body 100. The camera system 1 can perform a contrast autofocus operation based on image data generated by the CCD image sensor 110. The present disclosure provides a camera system that performs a contrast autofocus operation with high accuracy.

(1-2. Configuration of camera body)
The camera body 100 includes a CCD image sensor 110, a liquid crystal monitor 120, a camera controller 140, a body mount 150, a power source 160, and a card slot 170.

The camera controller 140 controls the components including the CCD image sensor 110 and the like to control the entire camera body 100 in response to an instruction from an operation member such as the release button 130. The camera controller 140 transmits a vertical synchronization signal to the timing generator 112. In parallel with this, the camera controller 140 generates an exposure synchronization signal based on the vertical synchronization signal. The camera controller 140 transmits the generated exposure synchronization signal as a timing signal to the lens controller 240 via the body mount 150 and the lens mount 250. The camera controller 140 uses the DRAM 141 as a work memory during control operations and image processing operations.

The CCD image sensor 110 captures a subject image incident through the interchangeable lens unit 200 and generates an image signal. The generated image signal is converted into a digital signal by the AD converter 111, and image data is generated. The image data digitized by the AD converter 111 is subjected to various image processing by the camera controller 140. The various image processes referred to here include, for example, gamma correction processing, white balance correction processing, scratch correction processing, YC conversion processing, electronic zoom processing, JPEG compression processing, and the like.

In addition, the camera controller 140 according to the present embodiment uses, for example, an image processing method called segmentation, and performs segmentation using, for example, a person's head and face as a target area, and converts the person's head and face area. The relative size on the liquid crystal monitor 120 can be calculated by extraction. The image processing method called segmentation is a target region from an image as described in the paper “Graph Cut for Image Segmentation by Repeating Smoothing” in the “Image Recognition and Understanding Symposium (MIRU2007)”. This is a known technique for extracting.

The CCD image sensor 110 operates at a timing controlled by the timing generator 112. The CCD image sensor 110 performs a still image capturing operation, a through image capturing operation, and the like. Here, the through image is an image captured by the CCD image sensor 110 and is not recorded on the memory card 171. The through image is mainly a moving image, and is displayed on the liquid crystal monitor 120 in order to determine a composition for capturing a still image.

The liquid crystal monitor 120 displays an image indicated by the image data processed by the camera controller 140. The liquid crystal monitor 120 can selectively display a moving image and a still image.

In the card slot 170, a memory card 171 can be mounted. The card slot 170 controls the memory card 171 based on control from the camera controller 140. The memory card 171 can store image data generated by image processing of the camera controller 140. For example, the memory card 171 can store a JPEG image file. The memory card 171 can output image data or an image file stored therein. The image data or image file output from the memory card 171 is subjected to image processing by the camera controller 140. For example, the camera controller 140 decompresses the image data or image file acquired from the memory card 171 and generates display image data.

The power source 160 supplies power for consumption by the camera system 1. The power source 160 may be, for example, a dry battery or a rechargeable battery. Moreover, the power supplied from the outside by the power cord may be supplied to the camera system 1.

The body mount 150 can be mechanically and electrically connected to the lens mount 250 of the interchangeable lens unit 200. The body mount 150 can transmit and receive data to and from the interchangeable lens unit 200 via the lens mount 250. The body mount 150 transmits the exposure synchronization signal received from the camera controller 140 to the lens controller 240 via the lens mount 250. Further, other control signals received from the camera controller 140 are transmitted to the lens controller 240 via the lens mount 250. The body mount 150 transmits a signal received from the lens controller 240 via the lens mount 250 to the camera controller 140. The body mount 150 supplies the power received from the power supply 160 to the entire interchangeable lens unit 200 via the lens mount 250.

(1-3. Configuration of interchangeable lens unit)
The interchangeable lens unit 200 includes an optical system, a lens controller 240, and a lens mount 250. The optical system of the interchangeable lens unit 200 includes a zoom lens 210, an OIS lens 220, and a focus lens 230.

The zoom lens 210 is a lens for changing the magnification of a subject image formed by the optical system of the interchangeable lens unit 200. The zoom lens 210 is composed of one or a plurality of lenses. The drive mechanism 211 includes a zoom ring or the like that can be operated by the user, transmits the operation by the user to the zoom lens 210, and moves the zoom lens 210 along the optical axis direction of the optical system. The detector 212 detects the drive amount in the drive mechanism 211. The lens controller 240 can grasp the zoom magnification in the optical system by acquiring the detection result in the detector 212.

The OIS lens 220 is a lens for correcting blurring of a subject image formed by the optical system of the interchangeable lens unit 200. The OIS lens 220 moves in a direction that cancels out the blur of the camera system 1, thereby reducing the blur of the subject image on the CCD image sensor 110. The OIS lens 220 is composed of one or a plurality of lenses. The actuator 221 drives the OIS lens 220 in a plane perpendicular to the optical axis of the optical system under the control of the OIS IC 223. The actuator 221 can be realized by a magnet and a flat coil, for example. The position detection sensor 222 is a sensor that detects the position of the OIS lens 220 in a plane perpendicular to the optical axis of the optical system. The position detection sensor 222 can be realized by a magnet and a Hall element, for example. The OIS IC 223 controls the actuator 221 based on the detection result of the position detection sensor 222 and the detection result of a shake detector such as a gyro sensor. The OIS IC 223 obtains the detection result of the shake detector from the lens controller 240. Further, the OIS IC 223 transmits a signal indicating the state of the optical image blur correction process to the lens controller 240.

The focus lens 230 is a lens for changing the focus state of the subject image formed on the CCD image sensor 110 by the optical system. The focus lens 230 is composed of one or a plurality of lenses.

The focus motor 233 drives the focus lens 230 to advance and retract along the optical axis of the optical system based on the control of the lens controller 240. Thereby, the focus state of the subject image formed on the CCD image sensor 110 by the optical system can be changed. In the first embodiment, the focus motor 233 can be a DC motor. However, the focus motor is not limited to this, and can be realized by a stepping motor, a servo motor, an ultrasonic motor, or the like.

The first encoder 231 and the second encoder 232 are encoders that generate signals indicating the driving state of the focus lens 230. The first encoder 231 and the second encoder 232 can be realized by, for example, a rotor and a photocoupler attached to the rotation shaft of the focus motor 233. Here, the rotor is a disk body having holes opened at predetermined intervals. The photocoupler emits detection light from one surface of the rotor and receives light from the other surface. Therefore, when the rotor rotates, the on / off states of the photocouplers are switched to each other. The lens controller 240 includes a counter 243 therein, and the counter 243 counts the number of times the photocoupler is switched on / off. The first encoder 231 and the second encoder 232 are out of phase. Therefore, it is possible to determine the moving direction of the focus lens 230 when the state of the first encoder 231 is switched from off to on. That is, the state of the second encoder 232 when the state of the first encoder 231 is switched from off to on includes an on state and an off state. Therefore, when the state of the first encoder 231 is switched from OFF to ON when the state of the second encoder 232 is ON, the counter 243 determines that this is normal rotation and counts it as “+1”. When the state of the first encoder 231 is switched from OFF to ON while the encoder 232 is OFF, this is determined as reverse rotation and counted as “−1”. By adding this count number, the lens controller 240 can grasp the amount of movement of the focus lens 230.

The lens controller 240 controls the entire interchangeable lens unit 200 such as the OIS IC 223 and the focus motor 233 based on the control signal from the camera controller 140. In addition, signals are received from the detector 212, the OIS IC 223, the first encoder 231, the second encoder 232, and the like, and transmitted to the camera controller 140. The lens controller 240 performs the transmission / reception with the camera controller 140 via the lens mount 250 and the body mount 150. The lens controller 240 uses the DRAM 241 as a work memory at the time of control. The flash memory 242 stores programs and parameters used when the lens controller 240 is controlled.

The focus motor 233 is an example of a drive unit. The configuration including the first encoder 231, the second encoder 232, and the counter 243 is an example of a position detection unit. The CCD image sensor 110 is an example of an image sensor. The camera controller 140 is an example of an AF evaluation value calculation unit, a focus determination unit, and a movement determination unit. The lens controller 240 is an example of a lens control unit. The camera system 1 is an example of an imaging device.

(2. Operation)
(2-1. Imaging preparation operation)
First, the operation of the camera system 1 for imaging preparation will be described. FIG. 2 is a sequence diagram for explaining the imaging preparation operation of the camera system 1.

When the user turns on the power of the camera body 100 with the interchangeable lens unit 200 mounted on the camera body 100, the power supply 160 supplies power to the interchangeable lens unit 200 via the body mount 150 and the lens mount 250. (S11). Next, the camera controller 140 requests authentication information of the interchangeable lens unit 200 from the lens controller 240 (S12). Here, the authentication information of the interchangeable lens unit 200 includes information regarding whether or not the interchangeable lens unit 200 is mounted and information regarding whether or not an accessory is mounted. The lens controller 240 responds to the lens authentication request from the camera controller 140 (S13).

Next, the camera controller 140 requests the lens controller 240 to perform an initialization operation (S14). In response to this, the lens controller 240 performs initialization operations such as resetting the aperture and resetting the OIS lens 220. Then, the lens controller 240 returns to the camera controller 140 that the lens initialization operation has been completed (S15).

Next, the camera controller 140 requests lens data from the lens controller 240 (S16). The lens data is stored in the flash memory 242. Therefore, the lens controller 240 reads the lens data from the flash memory 242 and sends it back to the camera controller 140 (S17). Here, the lens data is characteristic values unique to the interchangeable lens unit 200 such as a lens name, F number, focal length, focus lens drive speed upper limit value, and focus image plane movement amount.

When the camera controller 140 grasps the lens data of the interchangeable lens unit 200 attached to the camera body 100, the camera controller 140 is ready for imaging. In this state, the camera controller 140 periodically requests lens state data indicating the state of the interchangeable lens unit 200 from the lens controller 240 (S18). The lens state data includes, for example, zoom magnification information by the zoom lens 210, position information of the focus lens 230, aperture value information, and the like. In response to this request, the lens controller 240 returns the requested lens state data to the camera controller 140 (S19).

In this state, the camera system 1 can operate in a control mode in which an image indicated by image data generated by the CCD image sensor 110 is displayed on the liquid crystal monitor 120 as a through image. This control mode is called “live view mode”. In the live view mode, the through image is displayed as a moving image on the liquid crystal monitor 120, so that the user can determine the composition for capturing a still image while viewing the liquid crystal monitor 120. The user can select whether to set the live view mode. In addition to the live view mode, there is also a control mode for guiding the subject image from the interchangeable lens unit 200 to an optical viewfinder (not shown) as a control mode that can be selected by the user. In order to realize this control mode, a movable mirror or the like for guiding a subject image to an optical viewfinder (not shown) is required. A contrast method is suitable as a method of autofocus operation in the live view mode. This is because in the live view mode, the image data is constantly generated by the CCD image sensor 110, so that it is easy to perform a contrast autofocus operation using the image data.

When performing the contrast autofocus operation, the camera controller 140 requests contrast AF data from the lens controller 240 (S20). The contrast AF data is necessary for the contrast autofocus operation, and includes, for example, the communication cycle between the camera body and the lens, the focus drive speed, the focus shift amount, the image magnification, and the contrast AF availability information. .

(2-2. Contrast autofocus operation)
Next, the contrast AF control operation will be described. FIG. 3 is a diagram for explaining the basic operation of the single AF control according to the present embodiment. The camera controller 140 receives a user half-press operation of the release button 130 and executes a single AF control operation.

The focus motor 233 continues to drive the focus lens 230 in one direction from the infinite end or the closest end. The camera controller 140 instructs the lens controller 240 to drive the focus lens 230 through the body mount 150 and the lens mount 250 and continues to calculate the AF evaluation value periodically in accordance with the drive of the focus lens 230. As a method for calculating the AF evaluation value, a method is known in which a luminance signal is obtained from image data generated by the CCD image sensor 110 and a high frequency component in the screen of the luminance signal is integrated.

The camera controller 140 instructs the lens controller 240 to continue driving the focus lens 230 in one direction as long as the AF evaluation value continues to rise. When the AF evaluation value stops increasing and starts decreasing, the camera controller 140 determines that the in-focus position has passed. Then, the camera controller 140 instructs the lens controller 240 to rotate the focus motor 233 in the reverse direction, and drives the focus lens 230 in the reverse direction so far to move it to the in-focus position. When the movement of the focus lens 230 to the in-focus position is completed, the camera controller 140 instructs the lens controller 240 to fix the focus lens 230 at the in-focus position.

(2-3. Basic Principle of Moving Object Tracking AF Control)
The basic principle of the moving body tracking AF control operation in this embodiment will be described. The moving body tracking AF control operation is a control operation that continuously detects the movement of the subject and continuously adjusts the focus lens 230 so that the movement is focused on the detected subject. The user can set which subject in the image is detected for tracking. As an example, the moving body tracking AF control operation is performed when the user presses the release button 130 halfway. This operation mode is controlled and recognized by the camera controller 140. It should be noted that the operation may be performed continuously before the user presses the release button 130 halfway.

FIG. 4 is a diagram for explaining an in-focus position calculation algorithm of moving object tracking AF in the present embodiment. In the figure, a subject, a focus lens 230, and a CCD image sensor 110 are schematically shown. When the subject S approaches the camera 1, the state shown in FIG. 4 (a) is changed to the state shown in FIG. 4 (b). FIG. 4D and FIG. 4E show the subject S displayed on the liquid crystal display 170 in the respective states of FIG. 4A and FIG. The state is also shown. Further, it is assumed that the transition time from the state of FIG. 4A to the state of FIG. 4B is T [s]. FIG. 4C will be described later.

In order to explain the principle more concretely, explanation will be made using specific values indicated by the following conditions (1) to (4).
Condition (1) Use of a lens with a focal length f = 150 mm and an aperture value F = 5.6 Note that the zoom lens 210 is omitted because it is not operated.
Condition (2) The vertical size of the CCD image sensor is 13 mm.
Condition (3) In FIG. 4A, the subject is captured within a range of 1 m above and below. Condition (4) The subject is moving at 7 m / s.

Under these conditions, if the distance from the subject to the focus lens 230 is a0 and the distance from the focus lens 230 to the CCD image sensor is b0, the following equation is established.
a0: b0 = 1000: 13
The following formula is obtained from the focal length f = 150 [mm] and the general formula 1 / f = 1 / a0 + 1 / b0.
a0 = f · (1 + 1000/13) = 11688.46154 [mm]
b0 = 151.95 [mm]
If the time T = 1/30 [s] has elapsed from the state of FIG. 4A to the state of FIG. 4B, the following equation is obtained.
Δa = 7000/30 = 233.3 [mm]
Δb = − (b0 ² / a0 ² ) · Δa
∵Δ (1 / b0) = Δ (1 / f-1 / a0)

Therefore, the following formula is obtained.
Δb = 39.4 [μm]

Therefore, for a subject coming at 7 m / s, the in-focus state can be maintained by driving the focus lens 230 at a speed of 39.4 [μm] at 1/30 [s]. That is, the distance b1 from the focus lens 230 to the CCD image sensor is obtained as follows.
b1 = b0 + Δb = 151.9894 [μm]

At this time, the distance a1 from the subject to the focus lens 230 is obtained as follows.
a1 = a0 + b0−b1 = 11168.42214 [mm]

At this time, if the unit movement amount of the focus lens 230 in the optical axis direction is equal to the focus position movement amount (image plane movement amount) to the CCD image sensor, the image plane movement amount at 1/30 [s]. Corresponds to 0.42 [Fδ] (where δ = 16.7 [μm]).

FIG. 5 is a diagram for explaining the principle of detecting the segment range of the moving object tracking AF in the present embodiment. 4D to 4F show the state of the subject S displayed on the liquid crystal monitor 120. FIG. 5 (a) to 5 (c) show the detailed states of FIGS. 4 (d) to 4 (f) and explain the principle of detecting the segment of the head of the subject S and calculating the segment range. ing. FIG. 5A shows a state in which the subject is in focus, as in FIG. FIG. 5B shows a state in which the subject is focused on the subject while approaching the camera by Δa, as in FIG. 4B.

In FIG. 5A, the size (vertical direction) of the head of the subject S recognized using segmentation is detected as the segment range h0 with respect to the vertical imaging range L of the liquid crystal monitor 120. It shows a state. The ratio of the segment range h0 to the imaging range L can be expressed as k0 = h0 / L. FIG. 5B shows a state in which the subject S is focused as in FIG. 4B, and segmentation is used for the vertical imaging range L of the liquid crystal monitor 120. The state of detecting the size (vertical direction) of the head of the subject S recognized as the segment range h1 is shown. The ratio of the segment range h1 to the imaging range L can be expressed as k1 = h1 / L. Here, the relationship between k0 and k1 can be expressed by the following equation.
k1 = k0 · (a0 / a1) · (b1 / b0)

As described above, the camera controller 140 recognizes the values a0, a1, b0, and b1. K0 and k1 are also segment range ratios using segmentation, and are similarly known values in the camera controller 140. Therefore, the above relational expression holds in any of FIGS. 4A, 5A, 4B, and 5B as long as the subject is in focus.

Here, a state where the subject S is not focused in the state of the focus lens position shown in FIG. FIG. 4C shows a state where the subject is not focused in the state of the focus lens position shown in FIG. FIG. 4F shows a state of the subject S displayed on the liquid crystal display 170 in the case of FIG. In FIG. 4C, if the distance between the subject S and the focus lens 230 is a2 (a2> a1, that is, the approached subject is smaller than Δa), the ratio k2 of the segment range h2 in FIG. It can be expressed by a formula.
k2 = k0. (a0 / a2). (b1 / b0)

The camera controller 140 recognizes the values of k0, a0, a1, b0, and b1. k2 can be expressed as k2 = h2 / L by detecting the segment range h2 as shown in FIG. Therefore, the unknown in the above equation is the distance a2 between the subject and the focus lens 230. However, since a2 can be expressed by all known numerical values, a2 can be accurately obtained.
a2 = (a0 / k2) · (b1 / b0)

By bringing the focus lens 230 close to the CCD image sensor 110 side by Δb1 obtained from the following formula, the subject can be focused.
Δb1 = − (b1 ² / a1 ² ) · Δa1
Here, Δa1 = a2−a1.

As described above, in the present embodiment, the size of the subject is detected using segmentation or the like, and the size of the subject captured in the past by the CCD image sensor and the current CCD image sensor are captured. Compare the size of the subject. This makes it possible to determine whether the subject is in focus or not in focus. In the out-of-focus state, the camera controller 140 can calculate the amount of movement of the focus lens 230 for focusing.

As described above, in the present embodiment, it is possible to calculate the amount of movement of the focus lens for maintaining the in-focus state with respect to the subject moving in the camera direction. By performing drive control of the focus lens using the calculated movement amount, it is possible to perform a moving body tracking AF control operation that maintains a focused state for a subject moving in the camera direction.

(2-4. Moving object tracking AF control operation)
Details of the moving body tracking AF control operation in the present embodiment will be described with reference to FIGS. 6 and 7.

FIG. 6 is a timing chart for explaining the operation of the moving object tracking method of the camera system 1 according to the present embodiment. FIG. 7 is a graph showing temporal changes in the focus lens position in the camera system 1 according to the present embodiment. The control period T is a communication period between the camera body 100 and the interchangeable lens unit 200, and is equal to the period of the exposure synchronization signal. That is, the elapsed time from time t0 to time t1, the elapsed time from time t1 to time t2,..., The elapsed time from time t8 to time t9 is T. In FIG. 7, a solid line X is an actual drive profile of the focus lens 230 when driven according to the moving body tracking AF control of the present embodiment, and a broken line Y is the focus lens 230 for maintaining the in-focus state. It is an ideal drive profile indicating the position.

Suppose that the camera controller 140 is operating in the live view mode. In this state, the camera controller 140 periodically generates a CCDVD signal (hereinafter referred to as “vertical synchronization signal”) as shown in FIG. 6A. In parallel with this, the camera controller 140 generates an exposure synchronization signal based on the vertical synchronization signal as shown in FIG. 6C. Since the camera controller 140 knows in advance the exposure start timing and the exposure end timing on the basis of the vertical synchronization signal, the camera controller 140 can generate the exposure synchronization signal. The camera controller 140 outputs a vertical synchronization signal to the timing generator 112 and outputs an exposure synchronization signal to the lens controller 240. The lens controller 240 acquires position information of the focus lens 230 in synchronization with the exposure synchronization signal. This operation will be described later.

The timing generator 112 periodically generates a readout signal (not shown) of the CCD image sensor 110 and an electronic shutter drive signal as shown in FIG. 6B based on the vertical synchronization signal. The timing generator 112 drives the CCD image sensor 110 based on the readout signal and the electronic shutter drive signal. That is, the CCD image sensor 110 reads out pixel data generated by a large number of photoelectric conversion elements (not shown) in the CCD image sensor 110 to a vertical transfer unit (not shown) according to the read signal. In the present embodiment, the read signal and the vertical synchronization signal coincide with each other, but this is not an essential matter in implementing the present invention. That is, the vertical synchronization signal and the readout signal may be shifted. In short, it is only necessary that the vertical synchronization signal and the readout signal are synchronized.

Also, the CCD image sensor 110 performs an electronic shutter operation in accordance with the electronic shutter drive signal. Thereby, the CCD image sensor 110 can sweep out unnecessary charges to the outside. The electronic shutter drive signal is composed of a plurality of signal groups that are periodically transmitted within a short time. For example, the electronic shutter drive signal transmits five signals as a group. The CCD image sensor 110 performs one electronic shutter operation on one signal while a group of electronic shutter drive signals are being transmitted. Increasing the number of signals included in the group of electronic shutter drive signals can surely sweep out the charges accumulated in the CCD image sensor 110, but the drive method of the CCD image sensor 110 becomes complicated.

Therefore, the CCD image sensor 110 sweeps out the electric charge by the electronic shutter drive signal, and reads the pixel data to the vertical transfer unit (not shown) by the read signal. Therefore, during the period from the last signal of the group of electronic shutter drive signals to the vertical synchronization signal, the exposure operation is performed for the image data for the through image (see FIG. 6C).

In the above state, the camera controller 140 monitors whether or not the release button 130 is half-pressed. In FIG. 6, it is assumed that the release button 130 is half-pressed at time t0. Then, the camera controller 140 sends an AF start command to the lens controller 240 as shown in FIG. 6D. The AF start command is a command indicating that the contrast autofocus operation is started, and at the same time, is a command indicating that the moving body tracking AF control operation is started in the present embodiment.

The camera controller 140 transmits a linear drive start command to the lens controller 240 as shown in FIG. 6E. Here, the linear drive start command is such that the focus lens 230 reaches the target position just after the arrival time specified by the target position specifying command (described later) has elapsed since the start of driving the focus lens 230. Is a command for setting the mode to drive at a constant speed (linear drive). Upon receiving this linear drive start command, the lens controller 240 prepares to drive the focus lens 230 linearly (linearly) during the control period T.

The camera controller 140 periodically transmits a lens position acquisition command to the lens controller 240 as shown in FIG. 6H. In response to this, as shown in FIG. 6G, the lens controller 240 transmits the number of pulses (position information of the focus lens 230) stored in the DRAM 241 to the camera controller 140 in a state associated with the exposure synchronization signal. The camera controller 140 stores the number of pulses corresponding to the position information of the focus lens 230 in the DRAM 241. While the focus motor 233 is driven in accordance with an instruction from the camera controller 140, the number of pulses of the counter 243 at the time when the exposure synchronization signal is switched from off to on and the exposure synchronization signal is switched from on to off. The number of pulses of the counter 243 at the time is sequentially stored in the DRAM 241.

Next, the image data generated by exposure during the exposure period by the CCD image sensor 110 and then converted by the AD converter 111 is transmitted to the camera controller 140. The camera controller 140 calculates an AF evaluation value for autofocus operation based on the received image data. The calculated AF evaluation value is stored in the DRAM 141 in a state associated with the exposure synchronization signal. The lens position information acquired from the lens controller 240 is also associated with the exposure synchronization signal. Therefore, the camera controller 140 can store the AF evaluation value in association with the lens position information. The camera controller 140 calculates the segment range of the subject by segmentation based on the received image data. Therefore, as shown in FIG. 6J, the exposure synchronization signal, the lens position information acquired from the lens controller 240, the AF evaluation value acquired from the CCD image sensor 110, and the segment range information are associated with each other and stored in the DRAM 141.

In the moving body tracking AF control operation, the camera controller 140 instructs the lens controller 240 to perform drive control of the focus lens 230 so as to maintain an in-focus state with respect to a subject that approaches or moves away from the camera system 1. Specifically, the camera controller 140 uses the position information of the focus lens 230, the AF evaluation value, and the segment range information to maintain the focused state for the moving subject by the target position designation command shown in FIG. 6F. Thus, the drive of the focus lens 230 is controlled. The target position designation command is a command for notifying the interchangeable lens unit 200 of a target position (or movement amount) for moving the focus lens 230 and a time (arrival time) until the focus lens 230 reaches the target position. is there. The interchangeable lens unit 200 drives the focus lens 230 at a constant speed (linear drive) so that the focus lens 230 reaches the target position when the designated movement time has elapsed from the start of driving the focus lens 230. In the present embodiment, the arrival time designated by the target position designation command is a period of the control cycle T.

An example of the moving object tracking AF control operation will be described with reference to FIG. For example, consider a state in which focus is achieved at time t0 by the single AF control described above. As shown in the description of the focus position calculation algorithm of the moving object tracking AF, using the segment range information of the subject calculated using the image data exposed in each of the periods a and b shown in FIG. 6C. In this way, the camera controller 140 calculates the amount of movement of the focus lens 230. As shown in FIG. 6F, at time t2, a target position designation command for designating the focus lens position p4 as a target position is transmitted from the camera controller 140 to the lens controller 240. The lens controller 240 linearly moves the focus lens 230 from the position p0 to the position p4 during the period T according to the position p4 designated by the target position designation command transmitted from the camera controller 140 at time t3 (at a constant speed). (See the solid line X in FIG. 7 (period from t3 to t4)). That is, the focus lens 230 is driven at a constant speed v expressed by the following equation.
v = (p4-p0) / T

Here, during transmission from the camera controller 140 to the lens controller 240 at the position p4 of the focus lens 230, the focus lens 230 is moved so as to maintain the focused state at the time t4 from the focused state at the time t0. There is a need. Therefore, from the segment range information of the subject calculated from the period a and the period b shown in FIG. 6C, the amount of movement of the subject in the period T (corresponding to Δa in the above description) and the subject for focusing on the period T The amount of movement of the focus lens 230 (corresponding to Δb in the above description) is determined. At time t4, since 4 · T minutes have elapsed from time t0 in the in-focus state, the amount of movement of the subject is 4 · Δa. Therefore, the amount of movement of the focus lens 230 that can be focused at time t4 is 4 · Δb, and the position p4 of the focus lens 230 at time t4 is given by the following equation.
p4 = p0 + 4 · Δb

Next, the camera controller 140 calculates the movement amount of the focus lens 230 using the segment range information of the subject calculated using the image data exposed in each of the periods b and c shown in FIG. 6C. To do. As shown in FIG. 6F, a target position designation command for designating the focus lens position p5 is transmitted from the camera controller 140 to the lens controller 240. The lens controller 240 linearly drives the focus lens 230 from the position p4 to the position p5 during the period T according to the focus lens position p5 designated by the target position designation command received from the camera controller 140 (solid line X in FIG. 7). (Refer to the period from t4 to t5). That is, the focus lens 230 is driven at a constant speed v shown by the following equation.
v = (p5-p4) / T

Here, when the target position designation command for designating the position p5 of the focus lens 230 is transmitted from the camera controller 140 to the lens controller 240, the in-focus state is maintained at the time t5 from the in-focus state at the time t4. It is necessary to move the focus lens 230. From the segment range information of the subject calculated in the period b and the period c shown in FIG. 6C, the amount of movement of the subject during the period T (corresponding to Δa in the above description) and the subject during the period T are matched. A moving amount of the focus lens 230 for focusing (corresponding to Δb in the above description) is determined. At time t5, since T minutes have elapsed from the focused time t4, the amount of movement of the subject is Δa. Therefore, the amount of movement of the focus lens 230 that can be focused at time t5 is Δb, and the position p5 of the focus lens 230 at time t5 is given by the following equation.
p5 = p4 + Δb = p0 + 5 · Δb

Thereafter, similarly, the position of the focus lens 230 is moved to p9 by transmitting a target position designation command from the camera controller 140 to the lens controller 240 every control cycle T. FIG. 7 shows an example of a change in the lens position when the focus lens 230 is linearly driven every period T in this way.

As described with reference to FIG. 7, the focus lens 230 is linearly driven every period T, so that the in-focus state is always maintained for a subject that approaches or moves away from the camera system 1 after time t4. In addition, the focus lens 230 can be driven and controlled. Therefore, even in continuous shooting operation, after time t4, it is possible to acquire image data that maintains the in-focus state even if the subject that approaches or moves away from the digital camera is exposed at an arbitrary timing. . For this reason, it is possible to acquire image data in which a focused state is always maintained in moving image shooting.

Note that the exposure time by the CCD image sensor 110, the time until the camera controller 140 calculates and obtains an evaluation value such as segment range information, the time for transmitting a command from the camera controller 140 to the lens controller 240, the lens controller The position of the focus lens 230 that maintains the in-focus position may be obtained in consideration of each time required to drive the focus lens 230 at 240. Such control can further improve the focusing accuracy in the moving object tracking AF control according to the present embodiment.

In addition, as described with reference to FIG. 4C, when the focus lens 230 is out of focus and is out of focus, the movement amount of the focus lens 230 may be corrected by the shift. In this embodiment, even when the speed of the subject that approaches or moves away from the camera system 1 is changed by such control, it is possible to automatically perform correction so as to maintain the in-focus state. is there.

In the present embodiment, the autofocus operation is started after half-pressing the release button 130, but the trigger for starting the autofocus operation is not limited to this. The concept of this embodiment can be applied to a configuration in which an autofocus operation is always performed on a subject regardless of the operation of the release button 130.

(3. Effect, etc.)
As described above, the camera body 100 according to the present embodiment can be mounted with an interchangeable lens unit including a focus lens and a drive unit that drives the focus lens. The camera body 100 includes a CCD image sensor 110 that performs exposure at a predetermined timing to generate image data, and a camera controller 140 that calculates an AF evaluation value from the image data and determines an in-focus state based on the AF evaluation value. Prepare. The camera controller 140 transmits a command for controlling the focus motor 233 of the interchangeable lens unit 200 every predetermined control period (T) based on the determination result of the in-focus state and the position of the focus lens. The command includes a linear drive start command that instructs the interchangeable lens unit 200 to move the focus lens 230 at a constant speed over a predetermined control period.

The interchangeable lens unit 200 of the present embodiment includes a focus lens 230 that changes the focus state of the subject image, a focus motor 233 that drives the focus lens 230 in the optical axis direction, and an encoder that detects the position of the focus lens 230 ( Position detection units) 231, 232, a lens mount 250 that receives a command for driving the focus lens 230 from the camera body 100, a command received from the camera body 100, and a focus lens position detected by the position detection unit And a lens controller 240 for controlling the focus motor 233 every predetermined control period (T). The lens controller 240 controls the focus motor 233 so as to move the focus lens 230 at a constant speed over the entire predetermined control cycle.

With the above configuration, the focus lens 230 can be driven at a constant speed over the entire control period (T), and the focus lens 230 can be moved linearly as shown by the solid line X in FIG. Accordingly, the focus lens 230 can be moved along an ideal driving profile (dashed line Y) that gives a focused state, and a focused state can be more accurately obtained for a subject that approaches or moves away from the camera system 1. Can be maintained.

In the above embodiment, the focus control device detects the position of the focus lens 230 that changes the focus state of the subject image, the focus motor 233 that drives the focus lens 230 in the optical axis direction, and the position of the focus lens 230.

Encoders

231 and 232 that perform exposure, CCD image sensor 110 that generates image data by exposure at a predetermined timing, AF evaluation values are calculated from the image data, an in-focus state is determined based on the AF evaluation values, and the determination result And a focus controller 230 that controls the focus motor 233 every predetermined control period (T) based on the focus lens position and the focus lens 230 so as to move at a constant speed over the entire predetermined control period. With the lens controller 240 that controls the motor 233 It can be formed.

(Other embodiments)
As described above, the first embodiment has been described as an example of the technique disclosed in the present application. However, the technology in the present disclosure is not limited to this, and can also be applied to an embodiment in which changes, replacements, additions, omissions, and the like are appropriately performed. Moreover, it is also possible to combine each component demonstrated in the said Embodiment 1, and it can also be set as a new embodiment. Therefore, other embodiments will be exemplified below.

In the above-described embodiment, the configuration including the zoom lens 210 and the OIS lens 220 is illustrated, but these are not essential components for the idea of the present disclosure. That is, the idea of the present disclosure can be applied to a camera system equipped with a single focus lens that does not have a zoom function. The idea of the present disclosure can also be applied to a camera system equipped with an interchangeable lens that does not have a camera shake correction function.

In the above embodiment, the camera body that does not include the movable mirror is exemplified, but the configuration of the camera body is not limited to this. For example, the camera body may include a movable mirror or a prism for separating the subject image. Further, the movable mirror may be provided not in the camera body but in various adapters mounted between the camera body and the lens.

In the above-described embodiment, the lens-interchangeable camera system has been described. However, the idea of the present disclosure can be applied to a camera in which a camera body and a lens are integrated. In the case of an integrated camera, the functions of the lens controller and the camera controller described above may be realized by a single controller.

In the above embodiment, the position of the focus lens 230 is not detected directly, but is detected indirectly by detecting the rotation angle of the rotation shaft of the focus motor 233. The position of the focus lens 230 may be detected directly or indirectly by detecting the position of a mechanism member that is linked to the focus lens 230. For example, it is possible to detect the position of the focus lens 230 by managing how many pulses of the drive output of the focus motor 233 are sent by software or a dedicated IC. In short, in the present disclosure, the detection of the focus lens position only needs to be able to identify the position of the focus lens as a result, and includes both the direct detection of the lens position and the indirect detection of the lens position.

In the above embodiment, a camera system not equipped with a phase difference detection sensor is exemplified. However, the idea of the present disclosure is not limited to such an embodiment. A phase difference detection sensor may be provided in the camera system, and the camera controller 140 may determine an in-focus state based on an output from the phase difference detection sensor and execute an autofocus operation. In this case, a phase difference autofocus operation and a contrast autofocus operation may be selectively executed. In this case, the concept of the present disclosure can be applied when performing a contrast-type autofocus operation.

In the above embodiment, the exposure synchronization signal of the CCD image sensor 110 is used as the timing signal transmitted from the camera controller 140 to the lens controller 240. However, the timing signal is not limited to the exposure synchronization signal. For example, the timing signal may be a signal correlated with the exposure synchronization signal (for example, a signal having the same period and shifted phase). Alternatively, the vertical synchronization signal and the electronic shutter drive signal for the CCD image sensor 110 may be transmitted to the lens controller 240 as timing signals. Thereby, since the camera controller 140 does not need to transmit an exposure synchronization signal, the control can be facilitated. However, in this case, it is necessary to notify the lens controller 240 of the specifications of the electronic shutter drive signal (such as the transmission interval and the number of transmissions within one group of the electronic shutter drive signal) in advance. The lens controller 240 reads the pulse value of the counter 243 based on the electronic shutter drive signal and the vertical synchronization signal according to the notified specification.

In the embodiment of the present invention, the focus lens 230 is described as a single lens, but the focus lens may be composed of a plurality of lenses. Further, it may be configured as a focus lens group that is independently driven by a plurality of motors. Furthermore, the amount of movement of the focus lens 230 in the optical axis direction corresponds to the amount of movement of the in-focus position to the CCD image sensor 110. However, the moving amount of the in-focus position to the CCD image sensor 110 may be increased or decreased with respect to the unit moving amount of the focus lens 230 in the optical axis direction. In this case, information regarding the amount of movement of the in-focus position of the CCD image sensor 110 with respect to the unit movement amount of the focus lens 230 may be notified in advance from the lens controller 240 to the camera controller 140.

In the above embodiment, a linear drive start command for instructing linear drive of the focus lens 230 is transmitted from the camera body 100 to the interchangeable lens unit 200. However, the linear drive start command is not always necessary. Instead of the linear drive start command, information for instructing linear drive of the focus lens 230 may be transmitted from the camera body 100 to the interchangeable lens unit 200. For example, a flag for instructing linear drive of the focus lens 230 may be designated in the target position designation command. In this case, the lens controller 240 refers to the flag of the target position designation command and determines whether or not the focus lens 230 is linearly driven.

Also, in the target position designation command, the target position and information regarding the driving speed of the focus lens may be designated. In this case, the lens controller 240 performs linear drive of the focus lens 230 at a speed based on information related to the drive speed designated by the target position designation command. Note that the information regarding the driving speed specified by the target position specifying command may be the value of the driving speed itself, or information that can calculate the driving speed.

In the above embodiment, a CCD image sensor is shown as an example of an image sensor, but the image sensor is not limited to this. Other imaging sensors such as a CMOS image sensor can be used.

The idea of the present disclosure can be applied not only to the above-described camera system but also to various imaging devices having an autofocus function, such as a digital still camera and a movie.

As described above, the embodiments have been described as examples of the technology in the present disclosure. For this purpose, the accompanying drawings and detailed description are provided.

Accordingly, among the components described in the accompanying drawings and the detailed description, not only the components essential for solving the problem, but also the components not essential for solving the problem in order to illustrate the above technique. May also be included. Therefore, it should not be immediately recognized that these non-essential components are essential as those non-essential components are described in the accompanying drawings and detailed description.

In addition, since the above-described embodiments are for illustrating the technique in the present disclosure, various modifications, replacements, additions, omissions, and the like can be made within the scope of the claims and the equivalents thereof.

The present disclosure can be applied to an imaging apparatus having an autofocus function, such as a digital still camera or a movie.

Claims

A focus lens that changes the focus state of the subject image;
A drive unit for driving the focus lens in the optical axis direction;
A position detector for detecting the position of the focus lens;
An image sensor that generates image data by exposing at a predetermined timing;
An AF evaluation value calculation unit for calculating an AF evaluation value from the image data;
A focus determination unit that determines a focus state based on the AF evaluation value;
A control unit that controls the drive unit at predetermined control cycles based on the determination result by the focus determination unit and the focus lens position detected by the position detection unit;
The control unit controls the driving unit to move the focus lens at a constant speed over the entire predetermined control cycle.
Focus control device.
A movement determination unit for determining whether the subject is approaching or moving away based on a change in size of the predetermined area in the image data;
The control unit controls the drive unit based on the AF evaluation value, the position of the focus lens, and the determination result of the movement determination unit.
The focus control apparatus according to claim 1.
The AF evaluation value calculation unit calculates the AF evaluation value based on a contrast of a subject image included in the image data;
The focus control apparatus according to claim 1.
A phase difference detection unit for detecting a phase difference of the subject image;
The focus control apparatus according to claim 1, wherein the focus determination unit determines a focus state based on the phase difference.
A camera system comprising a camera body and an interchangeable lens unit attachable to the camera body,
The camera body is
An image sensor that generates image data by exposing at a predetermined timing;
An AF evaluation value calculation unit for calculating an AF evaluation value from the image data;
A focus determination unit that determines a focus state based on the AF evaluation value;
A camera control unit that transmits a command for controlling the operation of the interchangeable lens unit to the interchangeable lens unit based on a determination result of the focus determination unit;
With
The interchangeable lens unit is
A focus lens that changes the focus state of the subject image;
A drive unit for driving the focus lens in the optical axis direction;
A position detector for detecting the position of the focus lens;
A lens control hand that controls the drive unit at predetermined control intervals based on a command received from the camera body and a focus lens position detected by the position detection unit;
The lens control unit controls the drive unit to move the focus lens at a constant speed over the predetermined control period;
Camera system.
A movement determination unit that determines whether the subject is approaching or moving away based on a change in the size of the predetermined area in the image data;
The camera system according to claim 5, wherein the lens control unit controls the drive unit based on the command, the focus lens position, and a determination result of the movement determination unit.
6. The camera system according to claim 5, wherein the AF evaluation value calculation unit calculates an AF evaluation value based on a contrast of a subject image included in the image data.
A phase difference detection unit for detecting a phase difference of the subject image in the image data;
The camera system according to claim 5, wherein the focus determination unit determines a focus state based on the phase difference.
A camera body capable of mounting an interchangeable lens unit having a focus lens and a drive unit for driving the focus lens,
An image sensor that generates image data by exposing at a predetermined timing;
An AF evaluation value calculation unit for calculating an AF evaluation value from the image data;
A focus determination unit that determines a focus state based on the AF evaluation value;
A control unit that transmits a command for controlling the drive unit of the interchangeable lens unit at predetermined control cycles based on the determination result of the focus determination unit and the position of the focus lens;
The command includes a command for instructing the interchangeable lens unit to move the focus lens at a constant speed over the predetermined control period.
The camera body.
The camera body according to claim 9, wherein the AF evaluation value calculation unit calculates an AF evaluation value based on a contrast of a subject image included in the image data.
A movement determination unit for determining whether the subject is approaching or moving away based on whether the predetermined region of the image data is larger or smaller than the predetermined region of the image data captured previously;
The control unit according to claim 9, wherein the control unit controls the drive unit of the interchangeable lens unit based on a determination result of the focus determination unit, a position of the focus lens, and a determination result of the movement determination unit. The camera body.
A phase difference detection unit for detecting a phase difference of the subject image in the image data;
The camera body according to claim 9, wherein the focus determination unit determines a focus state based on the phase difference.
An interchangeable lens unit that can be attached to the camera body,
A focus lens that changes the focus state of the subject image;
A drive unit for driving the focus lens in the optical axis direction;
A position detector for detecting the position of the focus lens;
A receiver for receiving a command for driving the focus lens from the camera body;
A lens control unit that controls the drive unit at predetermined control cycles based on a command received from the camera body and a focus lens position detected by the position detection unit;
The lens control unit controls the drive unit to move the focus lens at a constant speed over the predetermined control period;
Interchangeable lens unit.
An imaging device comprising the focus control device according to any one of claims 1 to 4.