U.S. patent application number 13/429592 was filed with the patent office on 2012-07-19 for camera system, camera body, and interchangeable lens.
This patent application is currently assigned to PANASONIC CORPORATION. Invention is credited to NAOTAKE KITAHIRA, MITSUYOSHI OKAMOTO, KOJI SHIBUNO.
Application Number | 20120183285 13/429592 |
Document ID | / |
Family ID | 41117384 |
Filed Date | 2012-07-19 |
United States Patent
Application |
20120183285 |
Kind Code |
A1 |
SHIBUNO; KOJI ; et
al. |
July 19, 2012 |
CAMERA SYSTEM, CAMERA BODY, AND INTERCHANGEABLE LENS
Abstract
A camera system includes an interchangeable lens and a camera
body. A body controller in the camera body performs control to
transmit a timing signal and a drive information signal to the
interchangeable lens. A lens controller in the interchangeable lens
controls drive of a focus lens based on the drive information
signal and the timing signal which are received from the camera
body. The drive information signal includes information of a
driving time which is a period from a start of driving the focus
lens until an end of driving the focus lens.
Inventors: |
SHIBUNO; KOJI; (Osaka,
JP) ; OKAMOTO; MITSUYOSHI; (Osaka, JP) ;
KITAHIRA; NAOTAKE; (Osaka, JP) |
Assignee: |
PANASONIC CORPORATION
Osaka
JP
|
Family ID: |
41117384 |
Appl. No.: |
13/429592 |
Filed: |
March 26, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12411499 |
Mar 26, 2009 |
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13429592 |
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Current U.S.
Class: |
396/133 |
Current CPC
Class: |
G02B 7/102 20130101;
G03B 13/36 20130101 |
Class at
Publication: |
396/133 |
International
Class: |
G03B 13/36 20060101
G03B013/36 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 28, 2008 |
JP |
2008-086082 |
Claims
1. A camera system comprising an interchangeable lens and a camera
body, the interchangeable lens comprising: a focus lens operable to
move back and forth in an optical axis direction to change a focus
status of a subject image; a driver operable to drive the focus
lens; and a lens controller operable to control an operation of the
interchangeable lens under control of the camera body, the camera
body comprising: an imaging unit operable to image a subject at a
predetermined frame rate to generate image data; a drive signal
transmission unit operable to transmit a drive information signal
for instructing an amount of movement of the focus lens; and a body
controller operable to control an operation of the camera body,
wherein the lens controller controls drive of the focus lens based
on the drive information signal received from the camera body, and
when the focus lens is not moved by the instructed amount of
movement, the lens controller transmits information indicating that
the focus lens is not moved by the instructed amount of movement to
the body controller.
Description
BACKGROUND
[0001] 1. Technical Field
[0002] The technical field relates to a lens-interchangeable camera
system, and more particularly to a camera system capable of
performing an autofocus operation in a contrast detection method
during capture of a moving image.
[0003] 2. Related Art
[0004] JP-A-2003-295047 discloses autofocus control that employs
both a phase-difference detection method and a contrast method. An
imaging apparatus disclosed in JP-A-2003-295047 corrects focus
control information obtained by the phase-difference detection
method, based on focus information obtained by the contrast method.
Specifically, correction information for compensating for
insufficient detection accuracy of the phase-difference detection
which has excellent high-speed performance is obtained based on
information indicating a focus status obtained by using contrast
detection which enables focus determination at high accuracy. This
arrangement can provide focus control by the phase-difference
detection method with higher speed and higher accuracy compared to
the hybrid method, and the like.
[0005] As described above, JP-A-2003-295047 discloses an
improvement in the focus accuracy of a lens-interchangeable camera
system. However, JP-A-2003-295047 discloses an invention for
improving the focus accuracy of the phase-difference detection
method by correcting focus control information obtained by the
phase-difference detection method based on focus information
obtained by the contrast method. It does not disclose an
improvement in the accuracy of focus information itself that is
obtained by the contrast method.
SUMMARY
[0006] An object is therefore to provide a lens-interchangeable
camera system having improved accuracy of an autofocus operation in
a contrast method during capture of a moving image.
[0007] A camera system according to one aspect includes an
interchangeable lens and a camera body. The interchangeable lens
includes a focus lens operable to move back and forth in an optical
axis direction to change a focus status of a subject image; a
driver operable to drive the focus lens, and a lens controller
operable to control an operation of the interchangeable lens under
control of the camera body. The camera body includes an imaging
unit operable to image a subject at a predetermined frame rate to
generate image data, a timing signal generator operable to generate
a predetermined timing signal and transmit the predetermined timing
signal to the interchangeable lens, a drive signal transmission
unit operable to transmit a drive information signal including
information of a driving time which is a period from a start of
driving the focus lens until an end of driving the focus lens, and
a body controller operable to control an operation of the camera
body. The body controller performs control to transmit the timing
signal and the drive information signal to the interchangeable
lens. The lens controller controls drive of the focus lens based on
the drive information signal and the timing signal which are
received from the camera body.
[0008] A camera body according to another aspect is a camera body
to which an interchangeable lens having a focus lens capable of
moving back and forth in an optical axis direction to change a
focus status of a subject is mountable. The camera body includes an
imaging unit operable to image a subject at a predetermined frame
rate to generate image data, the subject being formed through the
interchangeable lens, a timing signal generator operable to
generate a predetermined timing signal and transmit the
predetermined timing signal to the interchangeable lens, a drive
signal transmission unit operable to transmit a drive information
signal including information of a driving time which is a period
from a start of driving the focus lens until an end of driving the
focus lens, and a body controller operable to control an operation
of the camera body. The body controller performs control to
transmit the timing signal and the drive information signal to the
interchangeable lens.
[0009] An interchangeable lens according to the other aspect is an
interchangeable lens mountable to a camera body. The
interchangeable lens includes a focus lens operable to move back
and forth in an optical axis direction to change a focus status of
a subject image, a driver operable to drive the focus lens, and a
lens controller operable to control an operation of the
interchangeable lens under control of the camera body. The lens
controller receives, from the camera body, a predetermined timing
signal and a drive information signal including information of a
driving time which is a period from a start of driving the focus
lens until an end of driving the focus lens. The lens controller
controls the drive of the focus lens based on the drive information
signal and the timing signal which are received from the camera
body.
[0010] According to the aforementioned configuration, a drive
information signal including information of driving time which is a
period of time from the start of driving a focus lens to the end of
driving the focus lens is transmitted from a camera body to an
interchangeable lens. The interchangeable lens can recognize
information of the driving time of the focus lens by obtaining the
drive information signal. Accordingly, the drive control of the
focus lens becomes relatively easy. As a result, the accuracy of a
contrast autofocus operation of a lens-interchangeable camera
system during recording a moving image can be improved.
BRIEF DESCRIPTION OF DRAWINGS
[0011] FIG. 1 is a block diagram showing a configuration of a
camera system.
[0012] FIG. 2 is a diagram for describing an imaging preparation
operation of the camera system.
[0013] FIG. 3 is a diagram for describing an autofocus operation in
a contrast method.
[0014] FIGS. 4A and 4B are diagrams for describing a wobbling
control operation.
[0015] FIGS. 5A to 5E are timing charts for describing a wobbling
control operation.
[0016] FIG. 6 is a flowchart for describing a wobbling control
operation.
[0017] FIGS. 7A to 7D are diagrams for describing a wobbling
control operation of a camera system including a MOS image sensor
as an imaging element.
[0018] FIGS. 8A to 8C are diagrams for describing a wobbling
control operation of a camera system including a MOS image sensor
as an imaging element (when using a vertical synchronizing signal
as an exposure synchronizing signal).
DETAIL DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0019] With reference to the accompanied drawings, preferred
embodiments are detailed below.
First Embodiment
[0020] 1-1. Configuration
[0021] 1-1-1. Overview
[0022] FIG. 1 is a block diagram showing a configuration of a
camera system according to embodiments of the present invention. A
camera system 1 includes a camera body 100 and an interchangeable
lens 200 mountable to the camera body 100. The camera system 1 can
perform an autofocus operation in a contrast method, based on image
data generated by a CCD image sensor 110.
[0023] 1-1-2. Configuration of the Camera Body
[0024] The camera body 100 includes the CCD image sensor 110, a
liquid crystal display (LCD) monitor 120, a camera controller 140,
a body mount 150, a power supply 160, and a card slot 170.
[0025] The camera controller 140 controls the entire operation of
the camera system 1 by controlling components such as the CCD image
sensor 110 in response to an instruction from operation members
such as a release button 130. The camera controller 140 transmits a
vertical synchronizing signal to a timing generator 112. In
parallel with this, the camera controller 140 generates an exposure
synchronizing (sync) signal. The camera controller 140 periodically
transmits the generated exposure synchronizing signal to a lens
controller 240 through the body mount 150 and a lens mount 250. The
camera controller 140 uses a DRAM 141 as a work memory when
performing a control operation or image processing operation.
[0026] The CCD image sensor 110 images a subject image that enters
through the interchangeable lens 200 to generate image data.
Specifically, the CCD image sensor 110 is exposed at predetermined
timing to capture a subject image and generate image data. The
generated image data is digitized by an AD converter 111. The
digitized image data is subjected to predetermined image processing
by the camera controller 140. The predetermined image processing
includes, for example, a gamma correction process, a white balance
correction process, a flaw correction process, a YC conversion
process, an electronic zoom process, and a JPEG compression
process.
[0027] The CCD image sensor 110 operates at timing that is
controlled by the timing generator 112. The operations of the CCD
image sensor 110 include a still-image capturing operation, a
through-the-lens image (hereinafter, referred to as a "through
image") capturing operation, and the like. The through image is
mainly a moving image and is displayed on the LCD monitor 120 so
that a user can determine composition for capturing a still
image.
[0028] The LCD monitor 120 displays an image represented by display
image data that is subjected to image processing by the camera
controller 140. The LCD monitor 120 can selectively display both a
moving image and a still image.
[0029] The card slot 170 allows the memory card 171 to be placed
therein, and controls the memory card 171 under control of the
camera controller 140. The memory card 171 can store image data
generated by image processing by the camera controller 140. The
memory card 171 can store, for example, JPEG image files. Image
data or an image file stored in the memory card 171 can be read.
The image data or image file read from the memory card 171 is
subjected to image processing by the camera controller 140. For
example, the camera controller 140 decompresses image data or an
image file obtained from the memory card 171 to generate display
image data.
[0030] The power supply 160 supplies power to be consumed by the
camera system 1. The power supply 160 may be, for example, a dry
battery or rechargeable battery. Alternatively, the power supply
160 may supply power to the camera system 1 from an external source
through a power cable.
[0031] The body mount 150 can be mechanically and electrically
connected to the lens mount 250 of the interchangeable lens 200.
The body mount 150 can transmit and receive data with the
interchangeable lens 200 through the lens mount 250. The body mount
150 transmits an exposure synchronizing signal received from the
camera controller 140 to the lens controller 240 through the lens
mount 250. Also, the body mount 150 transmits other control signals
received from the camera controller 140, to the lens controller 240
through the lens mount 250. Also, the body mount 150 transmits a
signal received from the lens controller 240 through the lens mount
250 to the camera controller 140. Also, the body mount 150 supplies
power received from the power supply 160 to the entire
interchangeable lens 200 through the lens mount 250.
[0032] 1-1-3. Configuration of the Interchangeable Lens
[0033] The interchangeable lens 200 includes an optical system, the
lens controller 240, and the lens mount 250. The optical system
includes a zoom lens 210, an OIS lens 220, and a focus lens
230.
[0034] The zoom lens 210 is a lens for changing the magnification
of a subject image to be formed by the optical system. The zoom
lens 210 includes one or a plurality of lenses. A drive mechanism
211 includes a zoom ring or the like that can be operated by a
user, and transmits an operation of the user to the zoom lens 210
to cause the zoom lens 210 to move along an optical axis direction
of the optical system. A detector 212 detects a moving amount of
the drive mechanism 211. The lens controller 240 can grasp a zoom
magnification of the optical system by receiving a result of the
detection by the detector 212.
[0035] The OIS lens 220 is a lens for correcting shake of a subject
image to be formed by the optical system of the interchangeable
lens 200. The OIS lens 220 moves in a direction to cancel the shake
of the camera system 1, thereby reducing shake of a subject image
on the CCD image sensor 110. The OIS lens 220 includes one or a
plurality of lenses . An actuator 221 drives the OIS lens 220 in a
plane vertical to an optical axis of the optical system, under the
control of an OIS IC 223. The actuator 221 can be implemented by,
for example, a magnet and a planar coil. A position detection
sensor 222 is a sensor for detecting a position of the OIS lens 220
in the plane vertical to the optical axis of the optical system.
The position detection sensor 222 can be implemented by, for
example, a magnet and a Hall element. The OIS IC 223 controls the
actuator 221 based on a detection result obtained by the position
detection sensor 222 and a detection result obtained by a camera
shake detector such as a gyro sensor. The OIS IC 223 obtains a
detection result by the camera shake detector from the lens
controller 240. Also, the OIS IC 223 transmits a signal indicating
a status of an optical image shake correction process to the lens
controller 240.
[0036] The focus lens 230 is a lens for changing a focus status of
a subject image to be formed on the CCD image sensor 110 through
the optical system. The focus lens 230 includes one or a plurality
of lenses.
[0037] A focus motor 233 drives the focus lens 230 to move back and
forth along the optical axis of the optical system under control of
the lens controller 240. By this, the focus status of a subject
image to be formed on the CCD image sensor 110 through the optical
system can be changed. In the present embodiment, as the focus
motor 233, a DC motor can be used. Note, however, that the present
invention is not limited thereto and the focus motor 233 can also
be implemented by a stepping motor, a servo motor, an ultrasonic
motor, and the like.
[0038] Each of a first encoder 231 and a second encoder 232 is a
conventional optical encoder for detecting rotation of the focus
motor 233, which is implemented by, for example, a rotor mounted on
a rotating shaft of the focus motor 233 and a photocoupler. The
lens controller 240 counts detecting signals from the first and
second encoders 231 and 232 with a counter 243 incorporated in the
lens controller 240. The signal from the first encoder 231 is
different in phase from that from the second encoder 232. Thus, it
is possible to detect direction of rotation of the focus motor 233
by counting the detection signal from the first encoder 231 in
combination with the detection signal from the second encoder 232.
The lens controller 240 can recognize an amount of movement and a
position of the focus lens 230 based on the count value of the
counter 243.
[0039] The lens controller 240 controls the focus motor 233 in a
first control mode or a second control mode. In the first control
mode, the lens controller 240 controls the focus motor 233 by only
using a detection signal from the first encoder 231. In the first
control mode, only the detection signal from the first encoder 231
is used, and thus the direction of rotation of the focus motor 233
can not be detected. On the contrary, in the second control mode,
the lens controller 240 controls the focus motor 233 by using the
first and second encoders 231 and 232. In the second control mode,
the lens controller 240 can also detect a direction of driving of
the focus lens 230.
[0040] The lens controller 240 controls the entire interchangeable
lens 200 by controlling the OIS IC 223, the focus motor 233, and
the like, based on control signals from the camera controller 140.
Also, the lens controller 240 receives signals from the detector
212, the OIS IC 223, the first encoder 231, the second encoder 232,
and the like, and transmits the signals to the camera controller
140. Transmission and reception of data between the lens controller
240 and the camera controller 140 is performed through the lens
mount 250 and the body mount 150. The lens controller 240 uses a
DRAM 241 as a work memory when performing control. A flash memory
242 stores programs and parameters to be used for the control by
the lens control 240.
[0041] 1-1-4. Correspondence of Configurations Between the
Embodiments and the Present Invention
[0042] The focus motor 233 is an example of driver. The lens
controller 240 is an example of lens controller. The CCD image
sensor 110 is an example of imaging unit. A configuration including
the camera controller 140 and the body mount 150 is an example of
timing signal transmission unit. A configuration including the
camera controller 140 and the body mount 150 is an example of drive
signal transmission unit. The camera controller 140 is an example
of body controller.
[0043] 1-2. Operation
[0044] 1-2-1. Imaging Preparation Operation
[0045] First, the operation of the camera system 1 for imaging
preparation will be described. FIG. 2 is a diagram showing signal
transmission and reception in an imaging preparation operation of
the camera system 1.
[0046] When a user turns on power to the camera body 100 with the
interchangeable lens 200 mounted on the camera body 100, the power
supply 160 supplies power to the interchangeable lens 200 through
the body mount 150 and the lens mount 250 (S11). Then, the camera
controller 140 requests the lens controller 240 for authentication
information of the interchangeable lens 200 (S12). The
authentication information of the interchangeable lens 200 includes
information on whether the interchangeable lens 200 is mounted and
information on whether accessories are mounted. The lens controller
240 responds to the lens authentication request from the camera
controller 140 (S13).
[0047] Then, the camera controller 140 requests the lens controller
240 to perform an initialization operation (S14). In response to
this, the lens controller 240 performs an initialization operation,
such as reset of an iris and reset of the OIS lens 220. The lens
controller 240 then sends a response indicating that the lens
initialization operation has been completed to the camera
controller 140 (S15).
[0048] Then, the camera controller 140 requests the lens controller
240 for lens data (S16). The lens data is stored in the flash
memory 242. The lens controller 240 reads the lens data from the
flash memory 242 and sends the lens data back to the camera
controller 140 (S17). The lens data includes characteristic values
specific to the interchangeable lens 200, such as a lens name,
F-number, and a focal length.
[0049] When the camera controller 140 grasps the lens data of the
interchangeable lens 200 mounted on the camera body 100, the camera
system 1 goes into a status capable of imaging. In this status, the
camera controller 140 periodically requests the lens controller 240
for lens status data indicating a status of the interchangeable
lens 200 (S18). The lens status data includes, for example,
information of zoom magnification of the zoom lens 210, information
of position of the focus lens 230, and information of aperture
value. In response to the request, the lens controller 240 sends
back the requested lens status data to the camera controller 140
(S19).
[0050] In this status, the camera system 1 can operate in a control
mode in which an image represented by image data generated by the
CCD image sensor 110 is displayed on the LCD monitor 120 as a
through image. This control mode is called "live view mode". In the
live view mode, a through image, which is a moving image, is
displayed on the liquid crystal monitor 120 so that the user can
determine composition for imaging a still image while viewing the
LCD monitor 120. For the method of an autofocus operation in the
live view mode, a contrast method is generally used. This is
because in the live view mode, image data is steadily generated by
the CCD image sensor 110, and thus it is easy to perform a contrast
autofocus operation using the generated image data.
[0051] When performing an autofocus operation in a contrast method,
the camera controller 140 requests the lens controller 240 for data
for contrast AF (S20). The data for contrast AF is data required
for performing an autofocus operation in a contrast method, and
includes, for example, a focus drive speed, the amount of focus
shift, an image magnification, and information indicating whether
contrast AF can be performed.
[0052] 1-2-2. Contrast Autofocus Operation in Recording a Moving
Image
[0053] Next, an autofocus operation of the camera system 1 in
recording a moving image after the completion of imaging
preparation will be described. Here, an autofocus operation in a
contrast method (hereinafter, referred to as a "contrast AF
operation") will be described.
[0054] FIG. 3 is a diagram explaining the movement of a focus lens
when a contrast AF operation of the camera system 1 according to
the present embodiment is performed. As shown in the diagram, when
the lens is moved from a position away from a focus position, the
contrast value of an image becomes higher as the lens comes closer
to the focus position, and reaches a maximum at the focus position.
In the contrast AF operation according to the present embodiment,
while the focus lens is continuously moved without being stopped,
an image is captured at a timing that synchronizes with an edge
change of an exposure synchronizing signal and position information
of the focus lens at the timing is obtained. Then, a contrast value
is obtained for each captured image. A position of the focus lens
at which the contrast value reaches a maximum is obtained and then
the position is determined to be a focus position. As shown in FIG.
3, a path of contrast values obtained when the focus lens is moved
from a position away from a focus position toward the focus
position represents a mountain shape. In the following description,
an operation of causing the focus lens to move from a position away
from a focus position toward the focus position is called
"mountain-climbing (M/C)".
[0055] In the case of recording a still image, an image captured in
a focus status is finally used as a still image. Thus, even if the
focus lens is moved in a relatively wide range to obtain a maximum
point of a contrast value for determining a focus position, there
is no particular problem. However, in the case of imaging a moving
image, when the focus lens is moved in a wide range, an
out-of-focus moving image is obtained, decreasing image quality.
Thus, wobbling control is generally performed when capturing a
moving image.
[0056] With reference to FIGS. 4A and 4B, wobbling control will be
described. In wobbling control, the focus lens 230 is controlled to
periodically move back and forth by a small distance. Since the
moving distance of the focus lens 230 is small, a change in image
quality is inconspicuous in a moving image, enabling to prevent
degradation in image quality. For example, when, as shown in FIG.
4A, the focus lens 230 is located in position (1), according to
wobbling control, the focus lens 230 moves from the position (1) to
position (2) and thereafter moves from the position (2) to position
(3) . A contrast value of an image is obtained for each of the
positions (1) to (3) to determine a direction in which there is a
focus position. For example, in the case of FIG. 4A, the contrast
value falls when the focus lens 230 moves from the position (1) to
the position (2), and rises when the focus lens 230 moves from the
position (1) to the position (3). From this fact, it can be
estimated that there is a focus position in a direction of the
position (3) as viewed from the position (1). Hence, it can be
recognized that next the focus lens 230 should be moved in a
direction going from the position (1) to the position (3). FIG. 4B
is a diagram showing temporal alteration in lens position when the
focus lens 230 is moved in the manner shown in FIG. 4A, with a
horizontal axis representing time and a vertical axis representing
position of the focus lens 230.
[0057] FIGS. 5A to 5E are timing charts for describing an autofocus
operation of the camera system 1 by wobbling control upon imaging a
moving image. Note that, in the present embodiment, the wording "a
moving image" may refer to a moving image for a through image or a
moving image to be recorded in the memory card 171. In an example
of FIGS. 5A to 5E, it is assumed that the camera controller 140
operates in the live view mode.
[0058] As shown in FIG. 5A, the camera controller 140 periodically
generates a vertical synchronizing signal (VD). Also, as shown in
FIG. 5C, the camera controller 140 generates an exposure
synchronizing (sync) signal from a predetermined point in time
based on the vertical synchronizing signal. The camera controller
140 grasps in advance exposure start timing and exposure end timing
with respect to the vertical synchronizing signal, and thus, can
generate an exposure synchronizing signal. The exposure
synchronizing signal indicates an exposure period of the imaging
element. The camera controller 140 outputs the vertical
synchronizing signal to the timing generator 112 and outputs the
exposure synchronizing signal to the lens controller 240. The lens
controller 240 controls drive of the focus lens 230 in
synchronization with the exposure synchronizing signal. A detail of
this operation will be described later.
[0059] The timing generator 112 periodically generates electronic
shutter drive signals (see FIG. 5B) based on the vertical
synchronizing signal and drives the CCD image sensor 110 based on
the electronic shutter drive signals and a read signal of the CCD
image sensor 110.
[0060] Note that, in the present embodiment, the vertical
synchronizing signal is used as the read signal of the CCD image
sensor 110. However, as the read signal, other signals than the
vertical synchronizing signal can also be used. That is, the read
signal may be shifted in phase from the vertical synchronizing
signal as long as the read signal changes in the same period as the
vertical synchronizing signal. For example, a read signal can be
periodically generated based on a vertical synchronizing signal by
the timing generator 112.
[0061] The CCD image sensor 110 reads, according to the read
signal, pixel data generated by numbers of photoelectric conversion
elements (not shown) in the CCD image sensor 110, out to a vertical
transferring unit (not shown).
[0062] Also, the CCD image sensor 110 performs an electronic
shutter operation according to the electronic shutter drive signal.
The electronic shutter operation can sweep out unnecessary
charges.
[0063] The CCD image sensor 110 sweeps out charges by electronic
shutter drive signals and reads pixel data with a read signal out
to the vertical transferring unit. It means that an exposure
operation for image data for a through image is performed during a
period from the last one of a group of electronic shutter drive
signals to a vertical synchronizing signal. The exposure
synchronizing signal is a signal that indicates the exposure period
and that rises at a rise of the last one of electronic shutter
drive signals and falls at a rise of the vertical synchronizing
signal (see FIG. 5C).
[0064] 1-2-2-1. Processing Flow
[0065] The flow of a contrast AF operation of the camera system 1
according to the first embodiment will be described with reference
to a flowchart of FIG. 6.
[0066] When a user selects a moving image recording mode, the
camera controller 140 transmits a drive information signal to the
lens controller 240 (S30 and time t1 in FIGS. 5A to 5E). The drive
information signal is a signal instructing start of wobbling
control, and includes the following information concerning wobbling
control:
[0067] 1) a period of time from the start of driving the focus lens
230 to the end of driving the focus lens 230 (hereinafter, referred
to as "driving time");
[0068] 2) information on a moving direction of the focus lens 230;
and
[0069] 3) information on an amount of movement from the start of
driving the focus lens 230.
[0070] Note that the drive information signal does not necessarily
need to have such a configuration. For example, the drive
information signal may include only information on driving time of
the focus lens 230. Alternatively, the drive information signal may
include only information on driving time of the focus lens 230 and
information on a moving direction of the focus lens 230.
[0071] When receiving the drive information signal, the lens
controller 240 determines whether an exposure synchronizing signal
(falling edge) has been received from the camera controller 140
(S31).
[0072] If it is determined that an exposure synchronizing signal
(falling edge) has been received, then the lens controller 240
controls the focus motor 233 to cause the focus lens 230 to start
to move (S32 and time t2 in FIGS. 5A to 5E) . At this time, the
focus motor 233 moves the focus lens 230 in a moving direction of
the focus lens 230 indicated by the drive information signal and by
an amount of movement of the focus lens 230 indicated by the drive
information signal. The interchangeable lens 200 (lens controller
240) can recognize information on the moving direction, amount of
movement, and driving time of the focus lens 230 in the wobbling
control, from the drive information signal, and accordingly, drive
control of the focus lens 230 in the wobbling control is
facilitated. Note that the focus lens 230 is controlled to move at
a constant or substantially constant predetermined speed during a
period of time from the start of driving the focus lens 230 until
the driving time indicated by the drive information signal
elapses.
[0073] After the start of movement of the focus lens 230, the lens
controller 240 determines whether the time of moving lens which
elapses from the start of the movement of the focus lens 230 has
exceeded the driving time for the wobbling control (S33) . In this
example, the driving time is set to a period of time required for
one frame of a moving image which is being captured. Thus, the
driving time is determined according to the frame rate of a moving
image being captured. For example, when the frame rate of a moving
image being captured is 60 frames/second, the driving time is set
to 1/60 second. In the present embodiment, as long as the frame
rate of a moving image being captured is constant, the driving time
is constant. As such, since the driving time is always constant,
the lens control becomes relatively easy. Note that the camera
controller 140 should not set the driving time to be smaller than a
minimum value of driving time of the focus lens 230 controllable in
the interchangeable lens 220. This is because the control is
impossible in the interchangeable lens 220 with such a smaller
driving time.
[0074] Although, in the present embodiment, the driving time is a
period of time required for one frame of a moving image being
captured, the driving time may be a period of time required for two
or three frames. That is, the driving time should be an integral
multiple of a period of time required for one frame. Setting an
upper limit of the driving time in a frame unit allows the focus
lens 230 to be driven and stopped in a frame unit. Also, control of
the drive and stop of the focus lens 230 in a frame unit causes the
focus lens 230 to be kept stopping while an image for an evaluation
in autofocus is exposed.
[0075] If the elapsing time has not exceeded the driving time, then
the lens controller 240 determines whether the focus lens 230 has
moved by a predetermined amount (S34). Here, the predetermined
amount is an amount of movement of the focus lens 230 indicated by
the drive information signal.
[0076] If it is determined that the focus lens 230 has not moved by
a predetermined amount, then the lens controller 240 returns to
step S33 again to determine whether the elapsing time has exceeded
the driving time.
[0077] If it is determined that the focus lens 230 has moved by a
predetermined amount, then the lens controller 240 controls the
focus motor 233 to stop drive of the focus lens 230 (S35) and then
determines whether the elapsing time of the focus lens 230 from the
start of the drive of the focus lens 230 has exceeded the driving
time (S36).
[0078] If it is determined that the elapsing time has exceeded the
driving time, then the camera controller 140 calculates an
evaluation value for an autofocus operation (hereinafter, referred
to as an "AF evaluation value"), based on image data obtained from
the CCD image sensor 110 (S38). At this time, the image data for
calculating an AF evaluation value is image data generated several
frames before and is image data generated in a frame in which the
focus lens 230 is stopped. For an AF evaluation value calculation
method, for example, it is generally known to obtain luminance
signals from image data generated by the CCD image sensor 110 and
add up high frequency components of the luminance signals in a
screen so as to determine an AF evaluation value. With this method,
an AF evaluation value for a lens position in which the focus lens
230 is stopped can be obtained.
[0079] On the other hand, if it is determined at step S33 that the
elapsing time has exceeded the driving time, then the lens
controller 240 controls the focus motor 233 to stop the drive of
the focus lens 230 (S37 and time t3 in FIGS. 5A to 5E).
Accordingly, when the elapsing time has exceeded the driving time,
even if the focus lens 230 has not moved by the amount of movement
indicated by the drive information signal, drive of the focus lens
230 is forcedly stopped. The driving time is set to a period of
time required for a frame and accordingly the drive of the focus
lens 230 can be controlled in a frame unit. Note that when the
elapsing time has exceeded the driving time and thus the focus lens
230 has not been able to move by an instructed amount of movement,
the lens controller 240 sets a predetermined flag (referred to as
"focus drive nonattainment flag") indicating that the focus lens
230 has not been able to move by an instructed amount of movement
to "1". A focus drive nonattainment flag is stored in the DRAM 141.
The camera controller 240 can recognize that the focus lens 230 has
not been able to move by an instructed amount of movement with
reference to the focus drive nonattainment flag.
[0080] After drive of the focus lens 230 is stopped (S37), the
camera controller 140 calculates an AF evaluation value based on
image data obtained from the CCD image sensor 110 (S38). The
calculated AF evaluation value is stored in the DRAM 141 in a state
that the calculated AF evaluation value is associated with position
information of the focus lens 230. In FIGS. 5A to 5E, an AF
evaluation value is calculated between times t3 and t5.
[0081] After the calculation of an AF evaluation value, the camera
controller 140 determines whether a predetermined number of AF
evaluation values have been stored in the DRAM 141 (S39). The
predetermined number is three in the present example but it may be
two or more.
[0082] If it is determined that a predetermined number (three) of
AF evaluation values have not been stored in the DRAM 141, then the
camera controller 140 transmits a drive information signal to the
lens controller 240 again so as to repeat drive/stop of the focus
lens 230 and calculation of an AF evaluation value (S30 to S39) in
the aforementioned manner.
[0083] If it is determined that a predetermined number (three) of
AF evaluation values have been stored in the DRAM 141, then the
camera controller 140 determines a drive method for the focus lens
230 based on the predetermined number of AF evaluation values
stored in the DRAM 141 (S40). Here, the drive method includes the
moving direction, amount of movement, and so on of the focus lens
230.
[0084] When a drive method for the focus lens 230 is determined,
the camera controller 140 sends out a drive information signal
again to the lens controller 240 to repeat the same process (S30 to
S40). Here, the drive information signal includes information
related to the determined drive method for the focus lens 230.
[0085] An autofocus operation with such wobbling control is
performed upon capturing a moving image in the camera system 1
according to the present embodiment to always maintain a certain
degree of a focus state with simple lens control.
Other Embodiments
[0086] Although the first embodiment is described above, the
embodiment is not limited thereto. Other embodiments will be
summarized in this section.
[0087] Although the first embodiment exemplifies as the second
control mode a control mode using the first encoder 231 and the
second encoder 232, the second control mode is not limited thereto.
For example, the second control mode may use one encoder and a
linear position detection sensor. The linear position detection
sensor is, for example, a position sensor implemented by a linear
resistor whose length is same as that of a drive range of the focus
lens 230 and a contact that moves in contact with and on the
resistor in conjunction with drive of the focus lens 230. In other
words, the second control mode should be such a control mode that
is relatively superior to the first control mode in accuracy of the
position detection of a reversal of the drive direction of the
focus lens 230 that is not intended by the lens controller 240. The
first control mode does not necessarily need to be provided and
only the second control mode may be provided.
[0088] Although the first embodiment exemplifies a configuration
having the zoom lens 210 and the OIS lens 220, such lenses are not
essential. That is, the idea of the first embodiment can also be
applied to a camera system having a single-vision lens with no zoom
function. Alternatively, the idea of the first embodiment can also
be applied to a camera system having an interchangeable lens with
no camera shake correction function.
[0089] Although the first embodiment exemplifies a camera body with
no movable mirror, the first embodiment is not limited thereto. For
example, a movable mirror may be included in a camera body or a
prism for splitting a subject image may be included. Alternatively,
a movable mirror may be included in an adapter instead of in a
camera body.
[0090] In the first embodiment, a position of the focus lens 230 is
not directly detected but indirectly detected by detecting an angle
of rotation of the rotating shaft of the focus motor 233. As such,
in the present invention, a position of the focus lens 230 may be
directly detected or may be indirectly detected by detecting a
position of a mechanical member that operates in conjunction with
the focus lens 230. That is, detection can be performed in any
manner as long as a position of the focus lens 230 can be
identified eventually.
[0091] The first embodiment exemplifies a camera system that does
not incorporate a phase-difference detection sensor. However, a
camera system may incorporate a phase-difference detection sensor
so that a phase-difference autofocus operation and a contrast
autofocus operation can be selectively performed. In this case, the
idea of the first embodiment is applicable when a contrast
autofocus operation is performed.
[0092] Although the first embodiment exemplifies the CCD image
sensor 110 as an imaging element, the imaging element is not
limited thereto. The imaging element may be configured by a CMOS
image sensor or NMOS image sensor. This enables a further reduction
in power consumption and noise.
[0093] As described above, in a MOS image sensor, unlike a CCD
image sensor, an exposure timing varies with the area of an imaging
plane. Specifically, an exposure timing in a lower part of the
imaging plane is delayed more than that in an upper part. Thus, as
shown in FIG. 7B, exposure for one frame by a MOS image sensor is
not completed within one vertical synchronizing period
(hereinafter, referred to as a "1 VD period"). Accordingly, even if
stop and drive of a focus lens are repeated every 1 VD period, a
problem is caused in that an appropriate AF evaluation value cannot
be obtained because the focus lens moves while exposure of a frame
for calculating an AF evaluation value is performed.
[0094] In the first embodiment, the driving time of the focus lens
230 is transmitted from the camera body 100 to the interchangeable
lens 200, and this configuration can solve the aforementioned
problem arising from a MOS image sensor. For example, it is assumed
that the length of a 1 VD period is "a", as shown in FIG. 7A, and
the time required for exposing one frame is "1.5 a", as shown in
FIG. 7B. An exposure synchronizing signal is set to a signal which
rises up at the end of the exposure period, as shown in FIG. 7C. In
this case, the camera controller 140 transmits the driving time
indicating 0.5 a to the interchangeable lens 200. Hence, as shown
in FIGS. 7A to 7D, the camera controller 140 can drive the focus
lens 230 only for a period between time t11 and time t12 and
subsequently stop the lens 230 for a period of 1.5 a, thereby
ensuring a stop period of 1.5 a which is required for exposing one
frame. This configuration allows the focus lens 230 to stop during
a period (period of 1.5 a in FIG. 7B) for capturing a frame for
calculating an AF evaluation value and to move slightly back and
forth at the other timing. As a result, the focus lens 230 can be
stopped during exposure of a frame for calculating an AF evaluation
value, enabling to obtain an appropriate AF evaluation value based
on an image captured when the focus lens 230 stops.
[0095] Note that the vertical synchronizing signal (see FIG. 8A)
may be used, as an exposure synchronizing signal, for driving the
lens during the wobbling control operation. In this case, a delay
time D with respect to an exposure synchronizing signal may be set
as shown in FIG. 8C, and information of the delay time D may be
included in the drive information signal and transmitted to the
lens controller 240. The lens controller 240 may start the lens
driving operation at a timing made by delaying the exposure
synchronizing signal by the delay time D.
[0096] Even when the imaging element is a CCD image sensor,
information of the delay time to the exposure synchronizing signal
may be included in the drive information signal and transmitted to
the lens controller 240 which may start the lens driving operation
at a timing made by delaying the exposure synchronizing signal by
the delay time D. This is advantageous to wobbling control using a
lens having bad response. That is, in the wobbling control using a
lens having bad response, delaying of start timing of the lens
drive by a predetermined time according to the lens response
achieves exposure at a timing the lens is moved at an appropriate
position.
INDUSTRIAL APPLICABILITY
[0097] The aforementioned embodiments can be applied to
lens-interchangeable camera systems. Specifically, the
aforementioned embodiments can be applied to digital still cameras,
digital movie cameras, and so on.
[0098] Although the aforementioned description has been provided in
connection with specified embodiments thereof, many other
modifications, corrections and applications are apparent to those
skilled in the art. Therefore, the embodiments are not limited by
the disclosure provided herein. The present disclosure relates to
subject matter contained in Japanese Patent Application No.
2008-086082, filed on Mar. 28, 2008, which is expressly
incorporated herein by reference in its entirety.
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