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Digital Camera Patent Abstract
A digital camera includes a phase difference AF sensor unit, phase
difference AF detection unit, contrast AF detection unit, lens driving
unit which focuses a taking lens, shading determination unit which
determines based on lens information of the taking lens whether
focus detection by the phase difference AF sensor unit is possible,
and an AF control unit. The AF control unit causes the lens driving
unit to focus the taking lens based on a focus detection result
of the phase difference AF detection unit when the shading determination
unit determines that the focus detection by the phase difference
AF sensor unit is possible, and causes the lens driving unit to
focus the taking lens based on a focus detection result of the contrast
AF detection unit when the shading determination unit determines
that the focus detection by the phase difference AF sensor unit
is not possible.
Digital Camera Patent Claims
1. A digital camera, comprising: a taking lens forming an object
image; an imaging device picking up the object image; a first focus
detection unit performing focus detection based on a phase difference
among a plurality of the object images; a second focus detection
unit performing focus detection based on a contrast value of the
object image; a focusing unit focusing the taking lens; a determination
unit determining based on lens information of the taking lens whether
the focus detection by the first focus detection unit is possible;
and a control unit that causes the focusing unit to focus the taking
lens based on a focus detection result of the first focus detection
unit when the determination unit determines that the focus detection
by the first focus detection unit is possible, and causes the focusing
unit to focus the taking lens based on a focus detection result
of the second focus detection unit when the determination unit determines
that the focus detection by the first focus detection unit is not
possible.
2. The digital camera according to claim 1, wherein the determination
unit determines whether the focus detection by the first focus detection
unit is possible by determining based on the lens information whether
a photographing light flux guided from the taking lens to the first
focus detection unit is shaded.
3. The digital camera according to claim 2, wherein the lens information
includes F number information, and the determination unit determines
whether the photographing light flux is shaded based on the F number
information.
4. The digital camera according to claim 2, wherein the lens information
includes lens type information, and the determination unit determines
whether the photographing light flux is shaded based on the lens
type information.
5. The digital camera according to claim 4, wherein the lens type
information includes identification information identifying whether
the taking lens is a reflecting telephoto lens.
6. The digital camera according to claim 2, wherein the taking
lens has an adjustable diaphragm whose diaphragm diameter is adjustable,
the lens information includes diaphragm information showing the
diaphragm diameter of the adjustable diaphragm, and the determination
unit determines whether the photographing light flux is shaded based
on the diaphragm information.
7. The digital camera according to claim 1, wherein the taking
lens has a lens information storage unit in which the lens information
is stored.
8. A digital camera, comprising: a taking lens having an adjustable
diaphragm whose diaphragm diameter is adjustable and forming an
object image; an imaging device picking up the object image; a first
focus detection unit performing focus detection based on a phase
difference among a plurality of the object images; a second focus
detection unit performing focus detection based on a contrast value
of the object image; a focusing unit focusing the taking lens; a
switch; a setting unit setting the adjustable diaphragm to a predetermined
F number in accordance with an input operation with the switch;
a determination unit determining based on the F number set by the
setting unit whether focus detection by the first focus detection
unit is possible; and a control unit that causes the focusing unit
to focus the taking lens based on a focus detection result of the
first focus detection unit when the determination unit determines
that the focus detection by the first focus detection unit is possible,
and causes the focusing unit to focus the taking lens based on a
focus detection result of the second focus detection unit when the
determination unit determines that the focus detection by the first
focus detection unit is not possible.
9. The digital camera according to claim 8, wherein the setting
unit sets the adjustable diaphragm to the predetermined F number
during photographing operation of the digital camera.
Digital Camera Patent Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is based upon and claims the benefit of
priority from Japanese Patent Application No. 2006-071661, filed
Mar. 15, 2006, the entire contents of which are incorporated herein
by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a digital camera provided
with a focusing device that automatically focuses a taking lens
for photographing an object image.
[0004] 2. Description of the Related Art
[0005] Conventionally, a TTL (Through The Lens) phase difference
auto focus (AF) has often been used as an AF mechanism in a lens-interchangeable
single-lens reflex camera using a silver halide film or imaging
device as an image pick-up medium. In the TTL phase difference AF,
a focus detection mechanism is provided in a camera body and, based
on a result of focus detection thereof, a focus is adjusted by driving
a part or whole of a taking lens provided with the interchangeable
lens using a motor mounted inside the interchangeable lens or camera
body.
[0006] In a compact digital camera or camcorder, on the other hand,
an AF mechanism (hereinafter called a contrast AF) adjusting the
focus by driving a taking lens so that, after detecting a contrast
value of an object image using high frequency components of an image
signal obtained by an imaging device, the contrast value becomes
maximum is often used.
[0007] Generally, the TTL phase difference AF and the contrast
AF have different features. For example, the TTL phase difference
AF operates at high speed while the contrast AF can detect the focus
with high accuracy and thus an appropriate AF is used for each purpose.
[0008] In an auto focusing device described in Japanese Patent
Application Laid-Open No. 7-43605, for example, when adjusting the
focus by combining the contrast AF and TTL phase difference AF,
a coarse adjustment is made by the TTL phase difference AF and then
a fine adjustment is made by the contrast AF. Also, in an auto focusing
device described in Japanese Patent Application Laid-Open No. 2003-302571,
if, in focusing processing in which, like Japanese Patent Application
Laid-Open No. 7-43605, a coarse adjustment is made by the TTL phase
difference AF and then a fine adjustment is made by the contrast
AF, a determination is made that focusing can be obtained by the
TTL phase difference AF, a faster focusing operation is implemented
by making the TTL phase difference AF have higher priority to perform
than the contrast AF does.
[0009] The TTL phase difference AF cannot detect the focus accurately
if a light flux for focus detection used for focus detection is
shaded. In a lens-interchangeable single-lens reflex camera or the
like, various kinds of interchangeable lenses can arbitrarily be
attached and, when a lens whose F number (FNO) is large or a special
lens such as a reflecting telephoto lens is attached, a light flux
for focus detection of the TTL phase difference AF may actually
be shaded.
[0010] However, conventional techniques described above do not
mention measure to be taken when a light flux for focus detection
of the TTL phase difference AF is shaded and, if a coarse adjustment
is made by using the TTL phase difference AF, the contrast AF may
be made to perform after moving a taking lens to an incorrect position.
As a result, an amount of deviation from a focusing position increases
and a time required for focusing operation by the contrast AF also
increases.
SUMMARY OF THE INVENTION
[0011] It is an object of the present invention to at least partially
solve the problems.
[0012] A digital camera according to one aspect of the present
invention includes a taking lens forming an object image; an imaging
device picking up the object image; a first focus detection unit
performing focus detection based on a phase difference among a plurality
of the object images; a second focus detection unit performing focus
detection based on a contrast value of the object image; a focusing
unit focusing the taking lens; a determination unit determining
based on lens information of the taking lens whether the focus detection
by the first focus detection unit is possible; and a control unit
that causes the focusing unit to focus the taking lens based on
a focus detection result of the first focus detection unit when
the determination unit determines that the focus detection by the
first focus detection unit is possible, and causes the focusing
unit to focus the taking lens based on a focus detection result
of the second focus detection unit when the determination unit determines
that the focus detection by the first focus detection unit is not
possible.
[0013] A digital camera according to another aspect of the present
invention includes a taking lens having an adjustable diaphragm
whose diaphragm diameter is adjustable and forming an object image;
an imaging device picking up the object image; a first focus detection
unit performing focus detection based on a phase difference among
a plurality of the object images; a second focus detection unit
performing focus detection based on a contrast value of the object
image; a focusing unit focusing the taking lens; a switch; a setting
unit setting the adjustable diaphragm to a predetermined F number
in accordance with an input operation with the switch; a determination
unit determining based on the F number set by the setting unit whether
focus detection by the first focus detection unit is possible; and
a control unit that causes the focusing unit to focus the taking
lens based on a focus detection result of the first focus detection
unit when the determination unit determines that the focus detection
by the first focus detection unit is possible, and causes the focusing
unit to focus the taking lens based on a focus detection result
of the second focus detection unit when the determination unit determines
that the focus detection by the first focus detection unit is not
possible.
[0014] The above and other objects, features, advantages and technical
and industrial significance of this invention will be better understood
by reading the following detailed description of presently preferred
embodiments of the invention, when considered in connection with
the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is a diagram showing a configuration of a digital
camera according to a first embodiment of the present invention;
[0016] FIG. 2 is a diagram showing an internal configuration of
a phase difference AF sensor unit and phase difference AF detecting
unit shown in FIG. 1;
[0017] FIG. 3A is a diagram showing object images detected by the
phase difference AF sensor unit shown in FIG. 2;
[0018] FIG. 3B is a diagram showing a state after shifting one
of the object images detected by the phase difference AF sensor
unit shown in FIG. 2;
[0019] FIG. 3C is a diagram showing a state after shifting one
of the object images detected by the phase difference AF sensor
unit shown in FIG. 2 to superimpose both images;
[0020] FIG. 4 is a diagram showing a calculation example of correlation
function values between the detected object images;
[0021] FIG. 5A is a diagram illustrating vignetting in a taking
lens of a light flux for focus detection;
[0022] FIG. 5B is a front view showing a projected image formation
surface shown in FIG. 5A;
[0023] FIG. 6A is a diagram exemplifying vignetting in the taking
lens of light fluxes for focus detection;
[0024] FIG. 6B is a diagram exemplifying vignetting in the taking
lens of light fluxes for focus detection;
[0025] FIG. 6C is a diagram exemplifying vignetting in the taking
lens of light fluxes for focus detection;
[0026] FIG. 6D is a diagram exemplifying vignetting in the taking
lens of light fluxes for focus detection;
[0027] FIG. 7 is a flowchart showing a processing procedure for
focusing processing according to the first embodiment;
[0028] FIG. 8 is a flowchart showing a processing procedure for
shading determination processing shown in FIG. 7;
[0029] FIG. 9 is a flowchart showing a processing procedure for
contrast AF processing shown in FIG. 7;
[0030] FIG. 10 is a diagram showing the configuration of a digital
camera according to a second embodiment of the present invention;
[0031] FIG. 11 is the internal configuration of a phase difference
AF sensor unit shown in FIG. 10;
[0032] FIG. 12A is a diagram showing a state of light fluxes for
focus detection in an exit pupil of a taking lens;
[0033] FIG. 12B is a diagram showing a state of light fluxes for
focus detection in the exit pupil of the taking lens;
[0034] FIG. 13 is a flowchart showing a processing procedure for
focusing processing according to the second embodiment;
[0035] FIG. 14 is a flowchart showing a processing procedure for
shading determination processing shown in FIG. 13;
[0036] FIG. 15 is a diagram showing the configuration of a digital
camera according to a third embodiment of the present invention;
[0037] FIG. 16A is a diagram showing a state of light fluxes for
focus detection in the exit pupil of the taking lens;
[0038] FIG. 16B is a diagram showing a state of light fluxes for
focus detection in the exit pupil of the taking lens;
[0039] FIG. 17 is a flowchart showing a processing procedure for
focusing processing according to the third embodiment;
[0040] FIG. 18 is a flowchart showing a processing procedure for
shading determination processing shown in FIG. 17;
[0041] FIG. 19 is a diagram showing the configuration of a digital
camera according to a fourth embodiment of the present invention;
[0042] FIG. 20 is a flowchart showing a processing procedure for
focusing processing according to the third embodiment;
[0043] FIG. 21 is a flowchart showing a processing procedure for
shading determination processing shown in FIG. 20; and
[0044] FIG. 22 is a flowchart showing a processing procedure for
focusing processing according to a modification of the fourth embodiment.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0045] Preferred embodiments of digital camera according to the
present invention will be described below with reference to attached
drawings.
[0046] First, a focusing device and digital camera according to
a first embodiment of the present invention will be described. FIG.
1 is a diagram showing a principal part configuration of a digital
camera 100 according to the first embodiment. As shown in FIG. 1,
the digital camera 100 comprises a camera body 1 and interchangeable
lens 2. The interchangeable lens 2 is provided with a taking lens
3, diaphragm 4, lens driving unit 5, lens information storage unit
6, and lens control unit 7. The lens control unit 7 is electrically
connected to the lens driving unit 5 and lens information storage
unit 6.
[0047] The taking lens 3 is configured by using a plurality of
lenses or a group of lenses, and the focus is adjusted by moving
part or all of the lenses thereof in an optical axis direction.
The diaphragm 4 is an adjustable diaphragm provided inside the taking
lens 3 and configured to have an adjustable diaphragm diameter,
and specifies a pupil diameter and FNO of the taking lens 3 and
limits the diameter of a light flux whose image is formed by the
taking lens 3. In FIG. 1, however, the taking lens 3 and diaphragm
4 are shown separately to avoid complication. The lens driving unit
5 performs fore-and-aft driving of the taking lens 3 and open/close
driving of the diaphragm 4 based on instructions from the lens control
unit 7.
[0048] The lens information storage unit 6 stores lens information
showing photographing conditions of the taking lens 3 and the like
as data related to the interchangeable lens 2. The lens information
includes, for example, the pupil diameter of the taking lens 3.
The lens control unit 7 is electrically connected to the camera
body 1 and, based on instructions from the camera body 1, controls
processing and operations of the lens driving unit 5 and lens information
storage unit 6 and outputs lens information obtained from the lens
information storage unit 6 to the camera body 1.
[0049] The camera body 1, on the other hand, comprises a half mirror
8, imaging device 9, image processing unit 10, phase difference
AF sensor unit 11, phase difference AF detection unit 12, contrast
AF detection unit 13, control unit 14, storage unit 15, release
switch 16, LCD panel 17, and finder optical system 18. The control
unit 14 is electrically connected to each component inside the camera
body 1 excluding optical components and the lens control unit 7
of the interchangeable lens 2.
[0050] The half mirror 8 reflects part of a light flux (photographing
light flux) from an object whose image is to be formed on the imaging
device 9 by the taking lens 3 toward the phase difference AF sensor
unit 11. Accordingly, the imaging device 9 and the phase difference
AF sensor unit 11 can receive the photographing light flux simultaneously
for processing. The imaging device 9, which is made of CCD, CMOS,
or the like, picks up an object image formed by the taking lens
3 and outputs an image signal of the formed object image to the
image processing unit 10.
[0051] The image processing unit 10 performs signal processing
of the acquired image signal, calculates a contrast value of the
object image, and also performs various kinds of image processing
such as white balance processing, Y/C processing, and color matrix
processing to generate an image shot and a image for the finder.
The generated image shot is output to the control unit 14 and the
image for the finder is output to the LCD panel 17. The image for
the finder output to the LCD panel 17 is displayed by the LCD panel
17 and observed from outside via the finder optical system 18. The
image processing unit 10 also outputs the calculated contrast value
to the contrast AF detection unit 13.
[0052] The phase difference AF sensor unit 11 and phase difference
AF detection unit 12 are principal parts of the focus detection
mechanism as a TTL phase difference AF and output a focusing position
of the taking lens 3 as a result of focus detection thereof to the
control unit 14. More specifically, the phase difference AF sensor
unit 11 divides a photographing light flux received via the half
mirror 8 into two and forms an image of each of the divided two
light fluxes to form an object image for each and also detects each
object image using separate line sensors.
[0053] The phase difference AF detection unit 12 acquires an image
signal from each line sensor and, after performing predetermined
signal processing, calculates a phase difference corresponding to
a relative interval of each object image. Then, the phase difference
AF detection unit 12 outputs a driven position of the taking lens
3 when the calculated phase difference is within a predetermined
range to the control unit 14 as a focusing position. The phase difference
calculated by the phase difference AF detection unit 12 corresponds
uniquely to an amount of focus deviation of the taking lens 3.
[0054] The contrast AF detection unit 13 is a principal part of
the focus detection mechanism as a contrast AF, and creates a history
of evaluation values based on contrast values of object images acquired
from the image processing unit 10, that is, traces of evaluation
values of object images for the driven positions of the taking lens
3 and also detects the focus by detecting the driven position (peak
position) of the taking lens 3 where the evaluation value takes
a peak value. The contrast AF detection unit 13 outputs the peak
position as a result of focus detection to the control unit 14.
Here, a focus detection area (detection area of objects) by the
contrast AF detection unit 13 is preset so that the focus detection
area matches that by the phase difference AF sensor unit 11.
[0055] The control unit 14 is provided with a shading determination
unit 14a and AF control unit 14b. The shading determination unit
14a determines, based on lens information acquired from the interchangeable
lens 2, whether shading occurs in a light flux for focus detection
of the TTL phase difference AF, that is, two light fluxes received
by the phase difference AF sensor unit 11 after the light flux is
divided. The AF control unit 14b controls processing and operations
of each unit involved in focusing and, particularly when the shading
determination unit 14a determines that shading occurs in two light
fluxes as light fluxes for focus detection, performs a control operation
to cause the contrast AF detection unit 13 to perform focus detection.
[0056] The storage unit 15 comprises ROM in which various processing
programs are stored in advance and RAM in which processing parameters
of various kinds of processing, processing data and the like are
stored. Particularly, the storage unit 15 stores a phase difference
AF pupil area showing a pupil area of the taking lens 3 corresponding
to light fluxes for focus detection detected by the phase difference
AF sensor unit 11 and also lens information of the interchangeable
lens 2 acquired by the AF control unit 14b via the lens control
unit 7, graph showing determination results by the shading determination
unit 14a, image shots processed by the image processing unit 10
and the like when appropriate. Meanwhile, in part of the storage
area in which image shots and the like are stored, portable non-volatile
memory (not shown) or the like is used and configured to be detachable
from the camera body 1.
[0057] The release switch 16 is configured as a switch having a
button unit provided on a surface part of the camera body 1. If
the button unit is halfway depressed, the release switch 16 outputs
AF instruction information instructing execution of focus adjustment
processing to the control unit 14. Also, if the button unit is fully
depressed, the release switch 16 outputs photographing instruction
information instructing execution of photographing processing to
acquire an object image to the control unit 14. While the release
switch 16 is halfway depressed, that is, AF instruction information
is being output, the AF control unit 14b performs a control operation
to repeatedly perform predetermined focusing processing.
[0058] Next, phase difference focus detection processing as focus
detection processing performed using the phase difference AF sensor
unit 11 and phase difference AF detection unit 12 will be described
with reference to FIG. 2 to FIG. 4. FIG. 2 is a diagram showing
an internal configuration of the phase difference AF sensor unit
11 and phase difference AF detection unit 12 together with the taking
lens 3. In FIG. 2, however, the half mirror 8 arranged on an optical
path between the taking lens 3 and the phase difference AF sensor
unit 11 is left out to avoid complication.
[0059] As shown in FIG. 2, the phase difference AF sensor unit
11 is provided with a visual field mask 21, condensing lens 22,
diaphragm mask 23, secondary image formation optical systems 24A
and 24B, and line sensors 25A and 25B. The phase difference AF detection
unit 12 is provided with an A/D conversion unit 12a and phase difference
calculation unit 12b.
[0060] The visual field mask 21 is arranged near a projected image
formation surface IM, which is a surface on which an object image
is formed by the taking lens 3 and is substantially conjugate with
an imaging surface of the imaging device 9, and limits an imaging
visual field to a predetermined range. The condensing lens 22 condenses
a photographing light flux that has passed through the visual field
mask 23. The diaphragm mask 23 is provided with openings 23a and
23b symmetrically with respect to an optical axis of the condensing
lens 22. Each of the openings 23a and 23b allows part of a photographing
light flux condensed by the condensing lens 22 to pass selectively.
Light fluxes DFA and DFB as light fluxes for focus detection involved
in phase difference focus detection processing are thereby specified
and also pupil areas 3a and 3b of the taking lens 3 corresponding
to these light fluxes DFA and DFB are specified.
[0061] The secondary image formation optical systems 24A and 24B
are arranged near the openings 23a and 23b respectively and condense
the light fluxes DFA and DFB that have passed through the openings
23a and 23b for image reformation. The line sensors 25a and 25b
are imaging devices in which photoelectric conversion elements are
arrayed in a direction connecting the opening 23a and the opening
23b and are arranged so that receiving surfaces thereof coincide
with image reformation surfaces of the secondary image formation
optical systems 24A and 24B respectively. Each of the line sensors
25a and 25b outputs an image signal corresponding to a photographed
object image to the phase difference AF detection unit 12.
[0062] The A/D conversion unit 12a performs A/D-conversion of each
image signal acquired from the line sensors 25A and 25B before the
image signal is output. The phase difference calculation unit 12b
calculates, based on each image signal acquired from the A/D conversion
unit 12a, a phase difference between object images corresponding
to the image signals. Here, the phase difference between object
images shows a relative spatial relationship of each object image
when images corresponding to the two object images are superimposed.
More specifically, the phase difference between object images shows
a relative interval between two object images separated in the direction
connecting the opening 23a and the opening 23b. Images corresponding
to two object images are superimposed so that each intersection
point of each optical axis of the secondary image formation optical
systems 24A and 24B and the line sensors 25a and 25b matches as
a reference point.
[0063] In phase difference focus detection processing performed
using the phase difference AF sensor unit 11 and phase difference
AF detection unit 12 configured as described above, focus detection
is performed by using a fact that a phase difference between two
object images formed by the light fluxes DFA and DFB changes in
accordance with a focusing state of the taking lens 3. The phase
difference between the two object images is determined from a correlation
of each object image.
[0064] More specifically, if two object images IA and IB are obtained
by the phase difference AF sensor unit 11, as shown in FIG. 3A,
the phase difference calculation unit 12b calculates an area (strong
integral value) where each image does not overlap as a correlation
function value of the object images IA and IB. The area is calculated
as a summation of absolute values of intensity difference in pixels
corresponding to the object images IA and IB. Further, as shown
in FIG. 3B, the phase difference calculation unit 12b can also determine
a relationship of an area with respect to an interval between the
object images IA and IB (or a shift amount of the object image IA)
by shifting one pixel (1 bit) of one object image (in this example,
the object image IA) at a time and calculating an area in the same
manner each time one pixel is shifted.
[0065] In the correlation between the interval and area of object
images determined as described above, the area is minimum when the
object image IA and the object image IB match, as shown in FIG.
3C. Therefore, the shift amount of the object image IA until the
area becomes minimum will be a phase difference between the object
images IA and IB to be determined.
[0066] More specifically, the phase difference calculation unit
12b calculates a correlation function value between two object images
in the following manner: based on image signals L(1), L(2), . .
. , L(n) of an object image detected by the line sensor 25A and
on image signals R(1), R(2), . . . , R(n) of an object image detected
by the line sensor 25B, a correlation function value F(i) for a
phase difference i (integral multiple of an image pitch) between
two object images is calculated according to the following equation
(1): F(i)=.SIGMA..sub.j|L(j)-R(j+i)| (1)
[0067] If, as a result of the above calculation, two object images
in the line sensors 25A and 25B are shifted by s pixels, the correlation
function value will be F(s)=0. However, each image signal output
from the line sensors 25A and 25B seldom matches completely due
to noise or the like and the correlation function value will normally
be F(s)>0.
[0068] FIG. 4 is a diagram showing a calculation example of such
correlation function values. In FIG. 4, however, data of discrete
values calculated by using equation (1) is shown as continuous data
for convenience. After determining the minimum value of the correlation
function value F(i), the phase difference calculation unit 12b performs
interpolation calculation using correlation functions values around
the minimum value to improve detection accuracy.
[0069] Next, problems when a light flux for focus detection involved
in phase difference focus detection processing is shaded will be
described. If part of an area (for example, the pupil areas 3a and
3b shown in FIG. 2) occupied by a light flux for focus detection
on a pupil surface of the taking lens 3 is outside the pupil area
of the taking lens 3 or the center of a focus detection area involved
in phase difference focus detection processing is located at a different
position from an intersection point of the optical axis and photographing
area of the taking lens 3, part of the light flux for focus detection
is limited by vignetting in the taking lens 3. Accordingly, image
signals (an A image signal and a B image signal) corresponding to
object images formed by two light fluxes used as the light flux
for focus detection may be unbalanced.
[0070] If the A signal and B signal are unbalanced, the degree
of matching of these two image signals in correlation calculation
will be low, causing an error in the calculated phase difference.
If the A signal and B signal are more markedly unbalanced, the correlation
calculation itself may become impracticable, making focus detection
impossible.
[0071] FIG. 5A is a diagram showing how a light flux for focus
detection involved in phase difference focus detection processing
is limited by vignetting in the taking lens 3. FIG. 5B is a front
view of the projected image formation surface IM shown in FIG. 5A
when viewed from the optical axis direction. The taking lens 3 is
actually comprised of a plurality of lenses, as shown in FIG. 5A,
and the light flux for focus detection is limited, among the plurality
of lenses, by a lens holding frame (back frame) BF of a lens on
a side closest to the projected image formation surface IM and a
lens holding frame (front frame) FF of a lens on a side closest
to objects.
[0072] FIG. 6A to FIG. 6D are diagrams showing states of light
fluxes for focus detection in an exit pupil EP of the taking lens
3. Here, two light fluxes as the light fluxes for focus detection
are shown as light fluxes FA and FB corresponding to the A image
signal and B image signal respectively. FIG. 6A shows a state of
the light fluxes FA and FB that form an image at point O shown in
FIG. 5B. The point O is a point on the optical axis of the taking
lens 3 and the light fluxes FA and FB that form an image at this
point O are not shaded at all.
[0073] FIG. 6B and FIG. 6C show states of the light fluxes FA and
FB that form an image at points k and m deviating from the optical
axis shown in FIG. 5B respectively. The point k is a point that
deviates from the optical axis of the taking lens 3 in a Y direction
(downward direction in FIG. 5B) and the light fluxes FA and FB forming
an image at this point k are almost uniformly shaded in a vertical
direction in FIG. 5B. The point m, on the other hand, is a point
that deviates also from the optical axis of the taking lens 3 in
a X direction (horizontal direction in FIG. 5B) and the light fluxes
FA and FB forming an image at this point m are shaded more intricately.
[0074] Further, FIG. 6D shows a state of the light fluxes FA and
FB that form an image at point O when FNO of the taking lens 3 is
large. In this case, a taking lens pupil area EPA showing an effective
pupil area of the taking lens 3 is smaller than a phase difference
AF pupil area AFA circumscribing each pupil area on the exit pupil
EP corresponding to the light fluxes FA and FB to encircle the pupil
areas. That is, a pupil radius Hg of the taking lens pupil area
EPA is smaller than a pupil radius Hag of the phase difference AF
pupil area AFA. Thus, the light fluxes FA and FB are shaded even
if the light fluxes FA and FB form an image at point O on the optical
axis.
[0075] With light fluxes for focus detection being shaded, as described
above, a relative difference arises between the A image signal and
B image signal and further an interval between centers of gravity
of two object images changes, resulting in an error of the phase
difference to be detected and detection of an incorrect focusing
position in phase difference focus detection processing.
[0076] Next, a processing procedure for focusing processing performed
by the digital camera 100 will be described. FIG. 7 is a flowchart
showing the processing procedure for focusing processing. As shown
in FIG. 7, the control unit 14 communicates with the lens control
unit 7 of the interchangeable lens 2 when the digital camera 100
is turned on to perform lens communication processing in which various
kinds of lens information stored in the lens information storage
unit 6 are read and also the lens information read from the lens
information storage unit 6 are recorded in the storage unit 15 (step
S100). Lens information read in the lens communication processing
includes the pupil diameter of the taking lens 3, driving range
of the taking lens 3 in contrast AF processing, various correction
values related to focusing processing and the like.
[0077] Then, the control unit 14 determines whether the release
switch 16 is halfway depressed (step S101) and, if the release switch
16 is not halfway depressed (step S101: No), repeats this determination
processing. The control unit 14 determines that the release switch
16 is halfway depressed by acquiring AF instruction information
from the release switch 16.
[0078] If the release switch 16 is halfway depressed (step S101:
Yes), the shading determination unit 14a performs shading determination
processing to determine whether light fluxes for focus detection
involved in phase difference focus detection processing are shaded
(step S102). Then, based on a determination result of this shading
determination processing, the AF control unit 14b determines whether
light fluxes for focus detection are shaded (step S103) and, if
it is determined that the light fluxes for focus detection are shaded
(step S103: Yes), performs contrast AF processing at step S109.
If, on the other hand, it is determined that the light fluxes for
focus detection are not shaded (step S103: No), the AF control unit
14b performs phase difference focus detection processing of step
S104 and the subsequent steps. At this step S103, the AF control
unit 14b determines whether shading occurs by referring to a shading
determination flag showing a determination result of shading determination
processing. Details of the shading determination processing will
later be described separately.
[0079] At step S104, the AF control unit 14b detects an object
image from light fluxes for focus detection by using the phase difference
AF sensor unit 11 and, based on a signal of the image object, performs
phase difference detection processing in which a phase difference
is calculated by the phase difference AF detection unit 12. Further,
based on the calculated phase difference, the AF control unit 14b
determines whether phase difference detection has been possible,
reliability (degree of reliability) of the phase difference detection
and the like and then records determination result thereof in a
flag or the like.
[0080] After performing processing at step S104, the AF control
unit 14b determines whether phase difference detection has been
possible by referring to the flag or the like where the determination
result at step S104 is recorded (step S105) and, if phase difference
detection has not been possible (step S105: No), performs contrast
AF processing at step S109. If, on the other hand, phase difference
detection has been possible (step S105: Yes), the AF control unit
14b further determines whether the detected phase difference is
within a predetermined range, that is, a focus deviation amount
of the taking lens 3 is within a predetermined range (step S106).
The predetermined range to be a criterion at this step S106 is a
preset range so that, if found to be within this range, focusing
can be performed by contrast AF processing with sufficiently high
accuracy and at high speed.
[0081] If the phase difference is within the predetermined range
(step S106: Yes), the AF control unit 14b performs contrast AF processing
at step S109. If, on the other hand, the phase difference is not
within the predetermined range (step S106: No), the AF control unit
14b calculates, based on the calculated phase difference, a driving
amount of the taking lens 3 required for focusing (step S107) and
drives the taking lens 3 in accordance with the calculated driving
amount (step S108). At this step S108, the AF control unit 14b outputs
the calculated driving amount to the lens control unit 7 so that
the lens control unit 7 is caused to control the lens driving unit
5 to drive the taking lens 3. Then, the AF control unit 14b repeats
processing of step S104 and the subsequent steps, if it is determined
that the phase difference is within the predetermined range at step
S106, and the procedure advances to the contrast AS processing.
[0082] After performing contrast AF processing at step S109 described
later, the AF control unit 14b determines whether it has been possible
to focus the taking lens 3 (step S110) and, if it has been possible
to focus the taking lens 3 (step S110: Yes), causes the LCD panel
17 or the like to display a message of successful focusing (S111).
If, on the other hand, it has not been possible to focus the taking
lens 3 (step S110: No), the AF control unit 14b causes the LCD panel
17 or the like to display a message of focusing failure (S112).
At step S110, the AF control unit 14b makes a determination by referring
to a flag or the like showing a processing result of the contrast
AF processing at step S109.
[0083] Then, the control unit 14 determines whether the release
switch 16 is fully depressed (step S113) and, if the release switch
16 is fully depressed (step S113: Yes), performs normal photographing
processing for photographing an object (step S114) and, after completing
the photographing processing, repeats processing of step S101 the
subsequent steps. If, on the other hand, the release switch 16 is
not fully depressed (step S113: No), the control unit 14 immediately
repeats processing of step S101 the subsequent steps. Such repetition
of processing terminates when a predetermined processing abort instruction
is input, for example, when the digital camera 100 is turned off.
[0084] In the digital camera 100, as described above, a coarse
adjustment of focusing is made by the TTL phase difference AF as
a basic operation and then a fine adjustment of focusing is made
by the contrast AF. In addition, whether light fluxes for focus
detection of the TTL phase difference AF are shaded is determined
and, if it is determined that the light fluxes for focus detection
are shaded, focusing processing by the contrast AF is performed
without performing focusing processing by the TTL phase difference
AF.
[0085] Next, a processing procedure for shading determination processing
shown as step S102 will be described. FIG. 8 is a flowchart showing
the processing procedure for shading determination processing. As
shown in FIG. 8, the shading determination unit 14a first initializes
a shading determination flag by setting "0" to the flag
(step S120) and determines whether a phase difference AF pupil diameter
showing the size of the phase difference AF pupil area AFA is larger
than a taking lens pupil diameter showing the size of the taking
lens pupil area EPA (step S121).
[0086] If the phase difference AF pupil diameter is larger than
the taking lens pupil diameter (step S121: Yes), the shading determination
unit 14a sets "1" to the shading determination flag (step
S122) before returning to step S102. If, on the other hand, the
phase difference AF pupil diameter is not larger than the taking
lens pupil diameter (step S121: No), the shading determination unit
14a immediately returns to step S102.
[0087] In the shading determination processing according to the
first embodiment, as described above, the shading determination
unit 14a compares the size of the phase difference AF pupil diameter
stored in advance in the storage unit 15 in accordance with the
configuration of the phase difference AF sensor unit 11 and that
of the taking lens pupil diameter read as lens information in the
lens communication processing at step S100 and, if the phase difference
AF pupil diameter is larger, determines that light fluxes for focus
detection involved in phase difference focus detection processing
are shaded and records a determination result thereof in the shading
determination flag.
[0088] Next, a processing procedure for contrast AF processing
shown as step S109 will be described. FIG. 9 is a flowchart showing
the processing procedure for contrast AF processing. As shown in
FIG. 9, the AF control unit 14b first refers to a predetermined
flag or the like to determine whether phase difference focus detection
processing has been performed (step S130). Then, if the phase difference
focus detection processing has been performed (step S130: Yes),
the AF control unit 14b sets a scan range to ".+-..DELTA.X"
(step S131) and, if the phase difference focus detection processing
has not been performed (step S130: No), the AF control unit 14b
sets the scan range to a whole range of movement of the taking lens
3, that is, from the closest range to infinity (step S132). If the
focus could not be detected even if the phase difference detection
processing has been performed, that is, the contrast AF is performed
after determining that a phase difference was not detectable at
step S105 shown in FIG. 7, the AF control unit 14b determines that
phase difference focus detection processing has not been performed
at step S130 and the procedure advances to step S132.
[0089] Here, the scan range is a range in which the taking lens
3 is driven when a trace of evaluation values of an object image
with respect to the driven position of the taking lens 3 is determined
by the contrast AF detection unit 13. At step S131, a range .DELTA.X
is set as the scan range to around the center of the current driven
position of the taking lens 3. The range .DELTA.X is a predetermined
range in which a focusing operation by the contrast AF is assumed
to be executable with sufficiently high accuracy and at high speed
and is stored in the lens information storage unit 6 of the interchangeable
lens 2 before being read and used by lens communication processing
at step S100. Various values are preset to the range .DELTA.X in
accordance with a focal length and driven position of the taking
lens 3, the degree of reliability of phase difference focus detection
processing and the like. At step S132, on the other hand, since
phase difference focus detection processing has not been performed
in advance and the taking lens 3 may not be positioned near the
focusing position, the whole range of movement of the taking lens
3 is set as the scan range.
[0090] After setting the scan range, the AF control unit 14b moves
the taking lens 3, of positions at both ends in the scan range,
to the one closer from the current driven position of the taking
lens 3 (step.S133). At this point, the AF control unit 14b moves
the taking lens 3 by outputting the position to which the taking
lens should be moved to the lens control unit 7 to cause the lens
control unit 7 to control the lens driving unit 5.
[0091] Subsequently, the AF control unit 14b calculates an evaluation
value of an object image by using the contrast AF detection unit
13 (step S134) and records the calculated evaluation value and the
drive position of the taking lens 3 as history information of the
evaluation value in the storage unit 15 (step S135). Then, the AF
control unit 14b refers to the history information of the evaluation
value to determine whether the driven position of the taking lens
3 has passed a focusing position, that is, a peak position where
the evaluation value takes a maximum value (step S136).
[0092] If the taking lens 3 has not passed the peak position (step
S136: No), the AF control unit 14b determines whether the taking
lens 3 is within the scan range (step S137) and, if the taking lens
3 is within the scan range (step S137: Yes), moves the taking lens
3 (step S138) before repeating processing of step S134 and the subsequent
steps. If, on the other hand, the taking lens 3 is not within the
scan range (step S137: No), the AF control unit 14b moves the taking
lens 3 to an initial position of the scan range (step S139) and
records information indicating that no focusing position could be
detected by contrast AF processing in a flag or the like (step S140)
before returning to step S109.
[0093] If the AF control unit 14b determines that the taking lens
3 has passed the peak position at step S136 (step S136: Yes), the
AF control unit 14b moves the taking lens 3 to the peak position
(step S141) and records the peak value of the evaluation value as
a peak evaluation value (step S142) before returning to step S109.
[0094] The digital camera 100 according to the first embodiment
is provided, as described above, with a focus detection mechanism
using the TTL phase difference AF and contrast AF and also a focusing
device that adjusts the focus based on a focus detection result
of each unit of the focus detection mechanism, and the focusing
device is provided with the shading determination unit 14a that
determines whether light fluxes for focus detection involved in
phase difference focus detection processing are shaded based on
lens information of the taking lens 3 and the AF control unit 14b
that performs a control operation to cause the focus detection mechanism
using the contrast AF to detect the focus when the shading determination
unit 14a determines that the light fluxes for focus detection are
shaded. Accordingly, the digital camera 100 and the focus detection
device according to the first embodiment can adjust the focus at
high speed and with high accuracy without being defocused by erroneous
detection even if light fluxes for focus detection involved in phase
difference focus detection processing are shaded.
[0095] Next, a focusing device and digital camera according to
a second embodiment of the present invention will be described.
While the focus detection area of the focus detection mechanism
using the TTL phase difference AF is one point in the above first
embodiment, the detection area is a plurality of points in the second
embodiment and the TTL phase difference AF and contrast AF are controlled
to be used appropriately in accordance with shading conditions of
light fluxes for focus detection for each focus detection area.
[0096] FIG. 10 is a diagram showing the principal part configuration
of a digital camera 200 according to the second embodiment. As shown
in FIG. 10, the digital camera 200 is provided, based on the configuration
of the digital camera 100, with a camera body 31 in place of the
camera body 1. The camera body 31 is provided, based on the configuration
of the camera body 1, with a phase difference AF sensor unit 41,
phase difference AF detection unit 42, and control unit 44 in place
of the phase difference AF sensor unit 11, phase difference AF detection
unit 12, and control unit 14 respectively. Further, the control
unit 44 is provided, based on the configuration of the control unit
14, with a shading determination unit 44a and AF control unit 44b
in place of the shading determination unit 14a and AF control unit
14b.
[0097] FIG. 11 is a diagram showing the internal configuration
of the phase difference AF sensor unit 41 together with the taking
lens 3. In FIG. 11, however, the half mirror 8 arranged on an optical
path between the taking lens 3 and the phase difference AF sensor
unit 41 is left out to avoid complication. As shown in FIG. 11,
the phase difference AF sensor unit 41 is provided with a visual
field mask 51, condensing lenses 52C, 52L, and 52R, diaphragm mask
53, group of image formation lenses as a secondary image formation
optical system, and sensor 55. The secondary image formation optical
system is provided with image formation lenses 54CA, 54CB, 54LA,
54LB, 54RA, and 54RB.
[0098] The phase difference AF sensor unit 41 divides a photographing
light flux in accordance with a plurality of focus detection areas
50C, 50L, and 50R set inside a photographing area 50 of the taking
lens 3 and then detects an object image for each focus detection
area and also outputs an image signal corresponding to each object
image to the phase difference AF detection unit 42.
[0099] Here, the visual field mask 51 is arranged near an image
formation surface of object images by the taking lens 3 and openings
51C, 51L, and 51R formed on the visual field mask 51 allow a photographing
light flux to pass after dividing the photographing light flux in
accordance with the focus detection areas 50C, 50L, and 50R. The
condensing lenses 52C, 52L, and 52R are arranged near the openings
51C, 51L, and 51R respectively to condense a light flux that has
passed through the corresponding opening.
[0100] The diaphragm mask 53 has a pair of openings formed symmetrically
with respect to each optical axis of the condensing lenses 52C,
52L, and 52R and each pair of openings further divides the light
flux from each of corresponding condensing lenses 52C, 52L, and
52R into two light fluxes to allow the light fluxes to pass as light
fluxes for focus detection. More specifically, the diaphragm mask
53 has openings 53Ca and 53Cb formed symmetrically with respect
to the optical axis of the condensing lens 52C. The diaphragm mask
53 also has openings 53La and 53Lb formed symmetrically with respect
to the optical axis of the condensing lens 52L and openings 53Ra
and 53Rb formed symmetrically with respect to the optical axis of
the condensing lens 52R.
[0101] Each image formation lens of the secondary image formation
optical system is arranged near each opening of the diaphragm mask
53 to reform an image by condensing the light fluxes for focus detection
that have passed through the corresponding opening. More specifically,
the image formation lenses 54CA, 54CB, 54LA, 54LB, 54RA, and 54RB
are arranged corresponding to the openings 53Ca, 53Cb, 53La, 53Lb,
53Ra, and 53Rb respectively.
[0102] The sensor 55 is provided with a plurality of line sensors
corresponding to light fluxes for focus detection from each image
formation lens and is arranged in such a way that each receiving
surface matches an image reformation surface of each corresponding
image formation lens. More specifically, the sensor 55 is provided
with line sensors 55CA, 55CB, 55LA, 55LB, 55RA, and 55RB and each
of these line sensors is arranged so that light fluxes for focus
detection reformed by the image formation lenses 54CA, 54CB, 54LA,
54LB, 54RA, and 54RB are detected respectively. Each line sensor
outputs an image signal corresponding to a detected object image
to the phase difference AF detection unit 42.
[0103] The phase difference AF sensor unit 41 can thereby detect
each light flux for focus detection corresponding to the focus detection
areas 50C, 50L, and 50R by the line sensors 55CA and 55CB, line
sensors 55LA and 55LB, and line sensors 55RA and 55RB respectively
and output an image signal for each focus detection area to the
phase difference AF detection unit 42. The phase difference AF detection
unit 42 performs A/D conversion of the image signal acquired from
each line sensor to calculate a phase difference of an object image
for each of the focus detection areas 50C, 50L, and 50R.
[0104] Arrangements of the openings on the visual field mask 51,
condensing lenses 52C, 52L, and 52R, openings on the diaphragm mask
53, image formation lenses in the secondary image formation optical
system, and line sensors on the sensor 55 corresponding to the focus
detection areas 50C, 50L, and 50R respectively are adjusted and
associated with each other in advance in manufacturing processes.
[0105] FIG. 12A and FIG. 12B are diagrams showing states of light
fluxes for focus detection in the exit pupil EP of the taking lens
3. FIG. 12A shows a phase difference AF pupil area AFA-C corresponding
to the focus detection area 50C and light fluxes FA-C and FB-C as
light fluxes for focus detection. FIG. 12B shows a phase difference
AF pupil area AFA-L corresponding to the focus detection area 50L
and light fluxes FA-L and FB-L as light fluxes for focus detection.
A phase difference AF pupil area AFA-R corresponding to the focus
detection area 50R has the same size as the phase difference AF
pupil area AFA-L and thus is shown in FIG. 12B together with light
fluxes FA-R and FB-R as light fluxes for focus detection.
[0106] As shown in FIG. 12A and FIG. 12B, the pupil diameter of
the phase difference AF pupil area corresponding to the focus detection
area 50C and that corresponding to the focus detection areas 50L
and 50R are different and, for example, a pupil radius Hah of the
phase difference AF pupil area AFA-C is larger than a pupil radius
Hav of the phase difference AF pupil areas AFA-L and AFA-R.
[0107] Next, a processing procedure for focusing processing performed
by the digital camera 200 will be described. FIG. 13 is a flowchart
showing the processing procedure for focusing processing. As shown
in FIG. 13, the control unit 44 performs lens communication processing
in the same manner as step S100 shown in FIG. 7 (step S200) when
the digital camera 200 is turned on to determine whether the release
switch 16 is halfway depressed (step S201).
[0108] If the release switch 16 is not halfway depressed (step
S201: No), the control unit 44 repeats this determination processing
and, if the release switch 16 is halfway depressed (step S201: Yes),
the shading determination unit 44a performs shading determination
processing to determine whether light fluxes for focus detection
corresponding to each focus detection area are shaded (step S202).
Details of this shading determination processing will later be described
separately.
[0109] Then, based on a determination result of the shading determination
processing, the AF control unit 44b determines whether shading occurs
in all focus detection areas (step S203) and, if it is determined
that shading occurs in all focus detection areas (step S203: Yes),
performs contrast AF processing at step S217. If, on the other hand,
it is determined that shading occurs not in all focus detection
areas (step S203: No), the AF control unit 44b performs phase difference
detection processing for focus detection area(s) where no shading
occurs (step S204). At step S203, the AF control unit 44b determines
whether shading occurs by referring to the shading determination
flag showing a determination result of the shading determination
processing.
[0110] At step S204, the AF control unit 44b detects an object
image from light fluxes for focus detection by the phase difference
AF sensor unit 41 for each focus detection area 50C, 50L, and 50R
and, based on a signal of the object image, performs phase difference
detection processing in which a phase difference is calculated using
the phase difference AF detection unit 42. Further, the AF control
unit 44b determines, based on the calculated phase difference, whether
phase difference detection has been possible, reliability (degree
of reliability) of phase difference detection and the like for each
focus detection area 50C, 50L, and 50R and then records determination
results thereof in flags.
[0111] After performing processing at step S204, the AF control
unit 44b determines whether phase difference detection has been
impossible in all focus detection areas where no shading occurs
by referring to the flags in which the determination results at
step S204 are recorded (step S205). Then, if phase difference detection
has been impossible in all focus detection areas (step S205: Yes),
the AF control unit 44b performs contrast AF processing at step
S217 and, if there is any focus detection area where phase difference
detection has not been impossible (step S205: No), selects a focus
detection area (closest range focus detection area) whose focus
deviation amount is closest to the back pin from among focus detection
areas where phase difference detection is possible and no shading
occurs in light fluxes for focus detection (step S206).
[0112] Subsequently, the AF control unit 44b determines whether
the detected phase difference in the closest range focus detection
area is within a predetermined range, that is, the focus deviation
amount of the taking lens 3 is within the predetermined range (step
S207) and, if it is determined that the phase difference is within
the predetermined range (step S207: Yes), performs contrast AF processing
at step S211. If, on the other hand, it is determined that the phase
difference is not within the predetermined range (step S207: No),
the AF control unit 44b calculates a driving amount of the taking
lens 3 to bring the taking lens 3 into focus based on the calculated
phase difference (step S208) and drives the taking lens 3 in accordance
with the calculated driving amount (step S209).
[0113] The predetermined range to be a criterion at step S207 is
a preset range so that, if found to be within this range, focusing
can be performed by contrast AF processing with sufficiently high
accuracy and at high speed. At step S209, the AF control unit 44b
outputs the calculated driving amount to the lens control unit 7
so that the lens control unit 7 is caused to control the lens driving
unit 5 to drive the taking lens 3.
[0114] After driving the taking lens 3, the AF control unit 44b
performs phase difference detection processing again for the closest
range focus detection area selected at step S206 (step S210) and,
if it is determined that, by repeating processing of step S207 and
the subsequent steps, a phase difference is within the predetermined
range of step S207 and the subsequent steps, and the procedure advances
to contrast AF processing at step S211.
[0115] Processing of subsequent step S211 to S216 is performed
in the same manner as that of step S109 to S214 shown in FIG. 7.
In contrast AF processing at step S217, on the other hand, the AF
control unit 44b performs contrast AF processing for all focus detection
areas to calculate a peak value of the evaluation value for each
focus detection area and a driven position of the taking lens 3
corresponding to the peak value. Then, the AF control unit 44b performs
closest range selection processing in which the taking lens 3 is
driven to a driven position corresponding to a focus detection area
whose focus deviation amount is closest to the back pin. Subsequently,
the AF control unit 44b performs processing of step S212 and the
subsequent steps.
[0116] In the digital camera 200, as described above, a coarse
adjustment of focusing is made by the TTL phase difference AF as
a basic operation and then a fine adjustment of focusing is made
by the contrast AF. In addition, whether light fluxes for focus
detection are shaded is determined for each of a plurality of focus
detection areas of the TTL phase difference AF and, if it is determined
that the light fluxes for focus detection are shaded in all focus
detection areas, focusing processing by the contrast AF is performed
without performing focusing processing by the TTL phase difference
AF.
[0117] At steps S206 and S207, a focus detection area whose focus
deviation amount closest to the back pin is selected in the above
description, but such selection processing is not limited to this
selection and, for example, a focus detection area may be selected
based on selection information after acquiring the selection information
of the focus detection areas from outside via an operation unit
(not shown) of the digital camera 200.
[0118] Next, a processing procedure for shading determination processing
shown as step S202 will be described. FIG. 14 is a flowchart showing
the processing procedure for shading determination processing. As
shown in FIG. 14, the shading determination unit 44a first initializes
shading determination flags "a" to "c" by setting
"0" to each flag (step S220) and determines whether a
phase difference AF pupil diameter showing the size of the phase
difference AF pupil area AFA-C corresponding to the focus detection
area 50C in the center is larger than a taking lens pupil diameter
showing the size of the taking lens pupil area EPA (step S221).
[0119] If the phase difference AF pupil diameter is larger than
the taking lens pupil diameter (step S221: Yes), the shading determination
unit 44a sets "1" to the shading determination flag "a"
(step S222) before advancing to step S223. If, on the other hand,
the phase difference AF pupil diameter corresponding to the focus
detection area 50C is not larger than the taking lens pupil diameter
(step S221: No), the shading determination unit 44a immediately
advances to step S223.
[0120] At step S223, the shading determination unit 44a determines
whether the phase difference AF pupil diameter showing the size
of the phase difference AF pupil area AFA-R corresponding to the
focus detection area 50R on a right side is larger than the taking
lens pupil diameter and, if it is determined that the phase difference
AF pupil diameter is larger than the taking lens pupil diameter
(step S223: Yes), sets "1" to the shading determination
flag "b" (step S224) before advancing to step S225. If,
on the other hand, it is determined that the phase difference AF
pupil diameter corresponding to the focus detection area 50R is
not larger than the taking lens pupil diameter (step S223: No),
the shading determination unit 44a immediately advances to step
S225.
[0121] At step S225, the shading determination unit 44a determines
whether the phase difference AF pupil diameter showing the size
of the phase difference AF pupil area AFA-L corresponding to the
focus detection area 50L on a left side is larger than the taking
lens pupil diameter and, if it is determined that the phase difference
AF pupil diameter is larger than the taking lens pupil diameter
(step S225: Yes), sets "1" to the shading determination
flag "c" (step S226) before returning to step S202. If,
on the other hand, it is determined that the phase difference AF
pupil diameter corresponding to the focus detection area 50L is
not larger than the taking lens pupil diameter (step S225: No),
the shading determination unit 44a immediately returns to step S202.
[0122] In the shading determination processing according to the
second embodiment, as described above, the shading determination
unit 44a compares each phase difference AF pupil diameter stored
in the storage unit 15 in advance corresponding to the focus detection
areas 50C, 50L, and 50R and the size of the taking lens pupil diameter
read as lens information in the lens communication processing at
step S200 and, if the phase difference AF pupil diameter is larger,
determines that light fluxes for focus detection involved in phase
difference focus detection processing are shaded and performs processing
to record a determination result in each shading determination flag
for each focus detection area.
[0123] In the digital camera 200 and the focusing device according
to the second embodiment, as described above, even if there are
a plurality of focus detection areas involved in phase difference
focus detection processing, whether light fluxes for focus detection
corresponding to each focus detection area are shaded can be determined
and, if it is determined that shading occurs, the focus detection
mechanism using the contrast AF is caused to perform focus detection
and therefore, the focus can be adjusted at high speed and with
high accuracy without being defocused by erroneous detection.
[0124] Next, a focusing device and digital camera according to
a third embodiment of the present invention will be described. While
the first and second embodiments described above are provided with
an interchangeable lens having a taking lens of a general dioptric
system, the third embodiment is provided with an interchangeable
lens having a reflecting telephoto lens as a catadioptric system.
[0125] FIG. 15 is a diagram showing the principal part configuration
of a digital camera 300 according to the second embodiment. As shown
in FIG. 15, the digital camera 300 comprises a cameral body 61 and
interchangeable lens 62. The cameral body 61 is provided, based
on the configuration of the camera body 1, with a control unit 74
in place of the control unit 14. The control unit 74 is provided,
based on the configuration of the control unit 14, with a shading
determination unit 74a and AF control unit 74b in place of the shading
determination unit 14a and AF control unit 14b. The interchangeable
lens 62 is provided, based on the configuration of the interchangeable
lens 2, with a taking lens 63 and lens information storage unit
66 in place of the taking lens 3 and lens information storage unit
6.
[0126] The taking lens 63 is a reflecting telephoto lens comprising
two reflectors and, for example, a reflecting telephoto lens disclosed
in Japanese Patent Application Laid-Open No. 1-344736 may be used.
Such a reflecting telephoto lens has advantages that a lens barrel
can be made shorter than that of a telephoto lens as a dioptric
system and also an overall weight of the lens can be made lighter.
In FIG. 15, however, the taking lens 63 is shown as an integral
lens to avoid complication. Moreover, the diaphragm 4 is actually
provided inside the taking lens 63, but is shown separately from
the taking lens 63 for convenience.
[0127] The lens information storage unit 66 stores a type of the
taking lens 63, that is, a lens ID indicating a reflecting telephoto
lens as lens information, in addition to the pupil diameter of the
taking lens 63. The lens control unit 7 is electrically connected
to the control unit 74 and, based on instructions from the control
unit 74, controls processing and operations of the lens driving
unit 5 and lens information storage unit 66 and also outputs lens
information acquired from the lens information storage unit 66 to
the control unit 74.
[0128] Meanwhile, the taking lens 63 as a reflecting telephoto
lens reflects a light flux from an object inside the lens to turn
back the reflected light flux to a focal plane and therefore one
of reflectors is arranged inside the light flux. For this reason,
a central part of the light flux is shaded and, as shown in FIG.
16A, the light flux is limited even in the central part of the pupil.
Here, FIG. 16A shows that a circular pupil shading area SHA is formed
by a reflector inside the taking lens pupil area EPA of the taking
lens 63. Inner parts of the light fluxes FA and FB as light fluxes
for focus detection are partially limited by the pupil shading area
SHA.
[0129] Because of the above circumstances, it is not possible to
correctly determine whether light fluxes for focus detection are
shaded for the taking lens 63 solely based on the pupil diameter
(pupil external diameter) or full-aperture FNO like shading determination
processing in the first and second embodiments. Thus, in the third
embodiment, whether light fluxes for focus detection are shaded
is correctly determined by referring to a pupil external diameter
and pupil internal diameter as pupil diameters of the taking lens
pupil area in the taking lens 63 and comparing these pupil diameters
with the size of the phase difference AF pupil area.
[0130] In FIG. 16A, the pupil internal diameter of the taking lens
pupil area EPA is equal to a shading diameter of the pupil shading
area SHA and the radius thereof is shown as a pupil internal radius
Hn. If a pupil shading area SHA' is small as shown in FIG. 16B,
the light fluxes FA and FB are not shaded by the pupil shading area
SHA' even for a reflecting telephoto lens.
[0131] Next, a processing procedure for focusing processing performed
by the digital camera 300 will be described. FIG. 17 is a flowchart
showing the processing procedure for focusing processing. As shown
in FIG. 17, the control unit 74 communicates with the lens control
unit 7 of the interchangeable lens 62 when the digital camera 300
is turned on to perform lens communication processing in which various
kinds of lens information stored in the lens information storage
unit 66 are read and also the lens information read from the lens
information storage unit 66 is recorded in the storage unit 15 (step
S300). Lens information read in the lens communication processing
includes the pupil external diameter and pupil internal diameter
of the taking lens 63, lens ID of the taking lens 63, driving range
of the taking lens 63 in contrast AF processing, various correction
values related to focusing processing and the like.
[0132] Subsequently, the control unit 74 determines whether the
release switch 16 is halfway depressed (step S301) and, if the release
switch 16 is not halfway depressed (step S301: No), repeats this
determination processing. If, on the other hand, the release switch
16 is halfway depressed (step S301: Yes), the shading determination
unit 74a refers to the lens ID to determine whether the taking lens
63 is a reflecting telephoto lens (step S302).
[0133] Then, if the taking lens 63 is not a reflecting telephoto
lens (step S302: No), the shading determination unit 74a performs
first shading determination processing (step S303) and, if the taking
lens 63 is a reflecting telephoto lens (step S302: Yes), performs
second shading determination processing (step S304). At step S303,
the shading determination unit 74a determines whether light fluxes
for focus detection are shaded by a processing procedure similar
to the shading determination processing shown in FIG. 8. At step
S304, the shading determination unit 74a refers to the pupil external
diameter and pupil internal diameter of the taking lens 63 to determine
whether light fluxes for focus detection are shaded. Details of
the second shading determination processing will be described later
separately.
[0134] Then, based on determination results of the first and second
shading determination processing, the AF control unit 74b determines
whether light fluxes for focus detection are shaded (step S305)
and, if it is determined that light fluxes for focus detection are
shaded (step S305: Yes), performs contrast AF processing at step
S311. If, on the other hand, it is determined that light fluxes
for focus detection are not shaded (step S305: No), the AF control
unit 74b performs phase difference focus detection processing of
step S306 and the subsequent steps. At step S305, the AF control
unit 74b determines whether light fluxes for focus detection are
shaded by referring to determination results of the first and second
shading determination processing.
[0135] Subsequently, the control unit 74 performs processing of
steps S306 to S316 in the same manner as steps 104 to S114 shown
in FIG. 7 and also repeats processing of step S301 and the subsequent
steps until a predetermined processing abort instruction such as
power-off of the digital camera 300 is input.
[0136] In the digital camera 300, as described above, a coarse
adjustment of focusing is made by the TTL phase difference AF as
a basic operation and then a fine adjustment of focusing is made
by the contrast AF. In addition, whether light fluxes for focus
detection of the TTL phase difference AF are shaded is determined
based on the first and second shading determination processing as
shading determination processing in accordance with the lens ID
of the taking lens 63 and, if it is determined that the light fluxes
for focus detection are shaded, focusing processing by the contrast
AF is performed without performing focusing processing by the TTL
phase difference AF.
[0137] Next, a processing procedure for the second shading determination
processing shown as step S304 will be described. FIG. 18 is a flowchart
showing the processing procedure for second shading determination
processing. As shown in FIG. 18, the shading determination unit
74a first initializes the shading determination flag by setting
"0" to the flag (step S320) and determines whether a phase
difference AF pupil external diameter showing the external diameter
of the phase difference AF pupil area is larger than a taking lens
pupil external diameter showing the external diameter of the taking
lens pupil area (step S321).
[0138] If the phase difference AF pupil external diameter is larger
than the taking lens pupil external diameter (step S321: Yes), the
shading determination unit 74a sets "1" to the shading
determination flag (step S322) before returning to step S304. If,
on the other hand, the phase difference AF pupil external diameter
is not larger than the taking lens pupil external diameter (step
S321: No), the shading determination unit 74a determines whether
a phase difference AF pupil internal diameter showing the internal
diameter of the phase difference AF pupil area is smaller than a
taking lens pupil internal diameter showing the internal diameter
of the taking lens pupil area (step S323). That is, at step 323,
the shading determination unit 74a determines whether a pupil internal
radius Han in the phase difference AF pupil area shown in FIG. 16A
is smaller than the pupil internal radius Hn in the taking lens
pupil area.
[0139] If the phase difference AF pupil internal diameter is smaller
than the taking lens pupil internal diameter (step S323: Yes), the
shading determination unit 74a sets "1" to the shading
determination flag (step S324) before returning to step S304. If,
on the other hand, the phase difference AF pupil internal diameter
is not smaller than the taking lens pupil internal diameter (step
S323: No), the shading determination unit 74a immediately returns
to step S304.
[0140] In the second shading determination processing, as described
above, the shading determination unit 74a compares the pupil external
diameter and pupil internal diameter of the phase difference AF
pupil area stored in advance in the storage unit 15 in accordance
with the configuration of the phase difference AF sensor unit 11
and those of the taking lens pupil area read as lens information
in the lens communication processing at step S300 to determine whether
light fluxes for focus detection involved in phase difference focus
detection processing will be shaded and records a determination
result thereof in the shading determination flag.
[0141] In the digital camera 300 and the focusing device according
to the third embodiment, as described above, whether the taking
lens 63 is a reflecting telephoto lens is determined based on the
lens ID as lens information and then, in accordance with this determination
result, whether light fluxes for focus detection are shaded can
be determined and, if it is determined that the light fluxes for
focus detection are shaded, the focus detection mechanism using
the contrast AF is caused to perform focus detection and therefore,
the focus can be adjusted at high speed and with high accuracy without
being defocused by erroneous detection even if a reflecting telephoto
lens is used as a taking lens.
[0142] Next, a focusing device and digital camera according to
a fourth embodiment of the present invention will be described.
While, in the above first to third embodiments, whether light fluxes
for focus detection involved in phase difference focus detection
processing are shaded is determined based on the size of the taking
lens pupil area when the diaphragm 4 is maximum, whether light fluxes
for focus detection are shaded is determined in the fourth embodiment
by also considering the pupil size of the taking lens when the diaphragm
4 is reduced.
[0143] FIG. 19 is a diagram showing the principal part configuration
of a digital camera 400 according to the fourth embodiment. As shown
in FIG. 19, the digital camera 400 is provided, based on the configuration
of the digital camera 100, with a camera body 81 in place of the
camera body 1. The camera body 81 is provided, based on the configuration
of the camera body. 1, with a control unit 94 in place of the control
unit 14 and further with a preview switch 99. The control unit 94
is provided, based on the configuration of the control unit 14,
with a shading determination unit 94a and AF control unit 94b in
place of the shading determination unit 14a and AF control unit
14b.
[0144] The preview switch 99 is configured as a switch having a
button unit mounted on the surface of the camera body 81. When the
button unit is depressed, the preview switch 99 outputs preview
instruction information to perform preview processing to the control
unit 94. In this case, the control unit 94 performs a control operation
to reduce the diaphragm 4 to an F number preset as the F number
equal to that during photographing to make preview processing to
be performed so as to enable observation of a field equivalent to
that during photographing through a finder and, based on the F number,
to make shading determination processing to be performed in which
whether light fluxes for focus detection are shaded is determined.
The F number to which the diaphragm 4 is reduced in preview processing
is stored in advance in the storage unit 15.
[0145] Here, a processing procedure for focusing processing performed
by the digital camera 400 will be described. FIG. 20 is a flowchart
showing the processing procedure for focusing processing. As shown
in FIG. 20, the control unit 94 performs lens communication processing
in the same manner as step S100 shown in FIG. 7 when the digital
camera 400 is turned on (step S400) before determining whether the
release switch 16 is halfway depressed (step S401).
[0146] If the release switch 16 is not halfway depressed (step
S401: No), the control unit 94 further determines whether the preview
switch 99 is depressed (step S402) and, if the preview switch 99
is not depressed (step S402: No), repeats processing of step S401
and the subsequent steps. If the preview switch 99 is depressed
(step S402: Yes), the control unit 94 performs preview processing
(step S403). The control unit 94 determines that the preview switch
99 is depressed by acquiring preview instruction information from
the preview switch 99.
[0147] After performing step S403 or if it is determined at step
S401 that the release switch 16 is halfway depressed (step S401:
Yes), the shading determination unit 94a performs shading determination
processing in which whether light fluxes for focus detection are
shaded is determined based on the F number of the diaphragm 4, that
is, FNO of the taking lens 3 (step S404). Details of the shading
determination processing will be described later separately.
[0148] Then, based on a determination result of the shading determination
processing, the AF control unit 94b determines whether light fluxes
for focus detection are shaded (step S405) and, if it is determined
that shading occurs (step S405: Yes), performs contrast AF processing
at step S411. If, on the other hand, it is determined that no shading
occurs (step S405: No), the AF control unit 94b performs phase difference
focus detection processing of step S406 and the subsequent steps.
At step S405, the AF control unit 94b determines whether shading
occurs by referring to the shading determination flag showing a
determination result of the shading determination processing.
[0149] Then, after performing processing of steps S406 to S414
in the same manner as steps 104 to S112 shown in FIG. 7, the control
unit 94 determines whether the preview switch 99 is depressed (step
S415) and, if the preview switch 99 is depressed (step S415: Yes),
performs steps S416 and S417 in the same manner as steps S113 and
S114 and then repeats processing of step S401 and the subsequent
steps. If, on the other hand, the preview switch 99 is not depressed
(step S415: No), the control unit 94 immediately repeats processing
of step S401 and the subsequent steps. Such repeated processing
terminates when a predetermined processing abort instruction such
as power-off of the digital camera 400 is input.
[0150] In the digital camera 400, as described above, a coarse
adjustment of focusing is made by the TTL phase difference AF as
a basic operation and then a fine adjustment of focusing is made
by the contrast AF. In addition, whether light fluxes for focus
detection of the TTL phase difference AF are shaded is determined
based on whether the preview switch 99 is depressed, that is, whether
the diaphragm 4 is reduced and, if it is determined that shading
occurs, focusing processing by the contrast AF is performed without
performing focusing processing by the TTL phase difference AF.
[0151] Next, a processing procedure for shading determination processing
shown as step S404 will be described. FIG. 21 is a flowchart showing
the processing procedure for shading determination processing. As
shown in FIG. 21, the shading determination unit 94a first initializes
the shading determination flag by setting "0" to the flag
(step S420) and determines whether the preview switch 99 is depressed
(step S421).
[0152] If the preview switch 99 is not depressed (step S421: No),
the shading determination unit 94a determines whether a phase difference
AF pupil FNO corresponding to the phase difference AF pupil area
is larger than a taking lens pupil full-aperture FNO showing the
FNO of the taking lens 3 corresponding to a case in which the diaphragm
4 is maximum (step S422). Then, if it is determined that the phase
difference AF pupil FNO is larger than the taking lens pupil full-aperture
FNO (step S422: Yes), the shading determination unit 94a sets "1"
to the shading determination flag (step S424) before returning to
step S404 and, if it is determined that the phase difference AF
pupil FNO is not larger than the taking lens pupil full-aperture
FNO (step S422: No), immediately returns to step S404.
[0153] If, on the other hand, the preview switch 99 is depressed
at step S421 (step S421: Yes), the shading determination unit 94a
determines whether the phase difference AF pupil FNO is larger than
a taking lens pupil reduced FNO showing the FNO of the taking lens
3 corresponding to the F number of the diaphragm 4 (step S423).
Then, if it is determined that the phase difference AF pupil FNO
is larger than the taking lens pupil reduced FNO (step S423: Yes),
the shading determination unit 94a sets "1" to the shading
determination flag (step S424) before returning to step S404 and,
if it is determined that the phase difference AF pupil FNO is not
larger than the taking lens pupil reduced FNO (step S423: No), immediately
returns to step S404.
[0154] In the shading determination processing according to the
fourth embodiment, as described above, the shading determination
unit 94a determines whether light fluxes for focus detection involved
in phase difference focus detection processing are shaded is determined
by comparing the phase difference AF pupil FNO stored in the storage
unit 15 in advance in accordance with the configuration of the phase
difference AF sensor unit 11 and, depending on whether the preview
switch 99 is depressed, the pupil diameter (pupil FNO) of the taking
lens read as lens information in the lens communication processing
at step S400 or the F number of the diaphragm 4 preset corresponding
to preview processing and then records a determination result thereof
in the shading determination flag.
[0155] In the digital camera 400 and the focusing device according
to the fourth embodiment, as described above, whether light fluxes
for focus detection are shaded can be determined based on the F
number of the diaphragm 4 and, if it is determined that shading
occurs, the focus detection mechanism using the contrast AF is caused
to perform focus detection and therefore, the focus can be adjusted
at high speed and with high accuracy without being defocused by
erroneous detection even if the diaphragm 4 is reduced in preview
processing.
[0156] The shading determination processing according to the fourth
embodiment has been described that, if a F number is changed in
accordance with preview processing, whether light fluxes for focus
detection are shaded is determined based on the F number. However,
determination whether light fluxes for focus detection are shaded
can also be made based on the F number when the diaphragm 4 is manipulated
by other processing than preview processing.
[0157] Meanwhile, preview processing is normally performed when
an amount of diaphragm reduction is large and thus when preview
processing is performed, it is highly probable that focus detection
cannot be performed correctly by phase difference focus detection
processing. Therefore, in this case, focus detection processing
can be made to perform more reliably by not relying on shading determination
and performing focus detection processing by the contrast AF without
performing focus detection processing by the TTL phase difference
AF.
[0158] FIG. 22 is a flowchart showing a processing procedure when
such focusing processing is performed in the digital camera 400.
In this case, the control unit 94 performs lens communication processing
in the same manner as step S400 (step S430) to determine whether
the release switch 16 is halfway depressed (step S431). Then, if
it is determined that the release switch 16 is not halfway depressed
(step S431: No), whether the preview switch 99 is depressed is further
determined (step S432). If the preview switch 99 is not depressed
(step S432: No), the control unit 94 repeats processing of step
S431 and the subsequent steps. If, on the other hand, the preview
switch 99 is depressed (step S402: Yes), the control unit 94 performs
preview processing (step S433) and then performs contrast AF processing
at step S441.
[0159] If it is determined that the release switch 16 is halfway
depressed at step S431 (step S431: Yes), the shading determination
unit 94a performs shading determination processing in the same manner
as the processing procedure shown in FIG. 8. Then, based on a determination
result of the shading determination processing, the AF control unit
94b determines whether light fluxes for focus detection are shaded
(step 435) and, if it is determined that the light fluxes for focus
detection are shaded (step 435: Yes), performs contrast processing
at step S441. If, on the other hand, it is determined that the light
fluxes for focus detection are not shaded (step 435: No), the AF
control unit 94b performs phase difference focus detection processing
of step 436 and the subsequent steps.
[0160] Subsequently, the control unit 94 performs processing at
steps S436 to S447 in the same manner as steps 406 to S417 shown
in FIG. 20 and repeats processing of step S431 and the subsequent
steps until a predetermined processing abort instruction is input.
[0161] In the digital camera 400 according to the present modification,
as described above, a coarse adjustment of focusing is made by the
TTL phase difference AF as a basic operation and then a fine adjustment
of focusing is made by the contrast AF. In addition, whether the
preview switch 99 is depressed is determined and, if the preview
switch 99 is depressed, focus detection processing by the contrast
AF is immediately performed and, if the preview switch 99 is not
depressed, whether light fluxes for focus detection of the TTL phase
difference AF are shaded is further determined. If it is determined
that shading occurs, focusing processing by the contrast AF is performed
without performing focusing processing by the TTL phase difference
AF. Accordingly, the digital camera 400 and the focus detection
device according to the present modification can adjust the focus
at high speed and with high accuracy when preview processing is
performed.
[0162] Additional advantages and modifications will readily occur
to those skilled in the art. Therefore, the invention in its broader
aspects is not limited to the specific details and representative
embodiments shown and described herein. Accordingly, various modifications
may be made without departing from the spirit or scope of the general
inventive concept as defined by the appended claims and their equivalents. |