Digital Camera Patent Abstract
A digital camera has a half mirror that splits the optical path
from a taking lens to the image-sensing device and an optical viewfinder
that offers the light reflected from the half mirror as a visible
image. Inside the optical viewfinder, a photometric device is disposed.
The amount of light measured by the photometric device is used for
exposure control in ambient-light shooting and for automatic light
adjustment in flash shooting. Digital Camera Patent Claims
What is claimed is:
1. A digital camera comprising: a taking lens; an image-sensing
device for shooting an image by receiving light from the taking
lens; an optical element, disposed retractably in an optical path
from the taking lens to the image-sensing device, for reflecting
part of the light from the taking lens; a photometric device for
measuring an amount of light reflected from the optical element;
a controller that, during shooting, makes an illumination device
start emitting illumination light and then makes the illumination
device stop emitting the illumination light when the amount of light
measured by the photometric device has reached a predetermined value;
a selector that selects either a first mode in which shooting is
performed without emission of the illumination light by the illumination
device and a second mode in which shooting is performed with emission
of the illumination light by the illumination device; and a driver
that retracts the optical element out of the optical path during
shooting when the first mode is selected and that keeps the optical
element in the optical path during shooting when the second mode
is selected.
2. A digital camera as claimed in claim 1, wherein the illumination
device is built in or externally connected to the digital camera.
3. A digital camera as claimed in claim 1, wherein the optical
element is a half mirror.
4. A digital camera as claimed in claim 1, further comprising:
a gain controller that adjusts a gain of an output of the image-sensing
device in such a way that the gain differs between the first and
second modes.
5. A digital camera as claimed in claim 4, wherein the gain controller
sets the gain in the second mode to be approximately equal to the
gain in the first mode multiplied by a reciprocal of a transmittance
of the optical element.
6. A digital camera as claimed in claim 1, further comprising:
a viewfinder that offers a visible image by receiving the light
reflected from the optical element.
7. A method for controlling a digital camera including an optical
element that is disposed retractably in an optical path from a taking
lens to an image-sensing device and that reflects part of the light
from the taking lens, comprising: a step of selecting either a first
mode in which shooting is performed without emission of illumination
light by an illumination device and a second mode in which shooting
is performed with emission of the illumination light by the illumination
device; a step of, when the first mode is selected, retracting the
optical element out of the optical path during shooting; and a step
of, when the second mode is selected, keeping the optical element
in the optical path during shooting, measuring an amount of light
reflected from the optical element, and stopping emission of the
illumination light as soon as the measured amount of light reaches
a predetermined value.
8. A method for controlling a digital camera as claimed in claim
7, further comprising: a step of setting a gain of an output of
the image-sensing device in such a way that the gain differs between
the first and second modes.
Digital Camera Patent Description
This application is based on application No. H11-352984 filed in
Japan on Dec. 13, 1999, the entire contents of which are hereby
incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a digital camera of a single-lens-reflex
type, and more particularly to a digital camera that automatically
adjusts the amount of light in flash shooting.
2. Description of the Prior Art
Generally, a digital camera is equipped with a display device such
as a liquid crystal display device, and this display device is used
both to display a playback of an image shot and stored previously
and to display an image just being shot. This enables the user to
determine picture composition and confirm focus condition while
viewing a "live view", i.e. the image just being shot,
that is displayed on the display device. Thus, the display device
functions as a video viewfinder.
Some digital cameras are additionally equipped with an optical
viewfinder. Digital cameras equipped with an optical viewfinder
divide into a separate type, in which light is introduced to the
viewfinder without being passed through a taking lens, and a single-lens-reflex
(SLR) type, in which the light having passed through a taking lens
is reflected so as to be introduced to the viewfinder. Whereas the
separate type suffers parallax between the viewfinder and the taking
lens, the SLR type has the advantage of intrinsically being free
of parallax.
The SLR type requires a prism to be disposed in the optical path
from the taking lens to an image-sensing device so as to reflect
a part and transmit the other part of the light having passed through
the taking lens, and requires also a pentaprism for directing the
reflected light to the eye of the user in such a way as to permit
the user to observe an erect image. In this arrangement, the optical
viewfinder and the video viewfinder can be used at the same time.
However, only part of the light having passed through the taking
lens reaches the image-sensing device, and therefore light is used
inefficiently in shooting.
As is well known, in an SLR-type camera that shoots by exposure
of silver-halide film, it has been customary to dispose a total-reflection
mirror obliquely in the optical path from the taking lens to the
film in such a way that the mirror can be rotated out of the optical
path. Until immediately before shooting, i.e. exposure of film,
the mirror is kept in the optical path so that the incoming light
is reflected toward the pentaprism. Only at the moment of shooting
is the mirror retracted out of the optical path so that the incoming
light is directed to the film, and, immediately after shooting,
the mirror is brought back in the optical path. This type of mirror
is called a quick-return mirror.
Digital cameras equipped with such a quick-return mirror are already
in practical use, producing bright images despite using an optical
viewfinder. However, in this arrangement, while the total-reflection
mirror is placed in the optical path to permit the use of the optical
viewfinder, no light reaches the image-sensing device, and thus
the display device cannot be used as a viewfinder.
To overcome this inconvenience, digital cameras equipped with a
half mirror as a quick-return mirror have been proposed. Whether
the half mirror is placed in or retracted out of the optical path,
the incoming light reaches the image-sensing device, and therefore
both shooting and display are possible at any time. While the half
mirror is placed in the optical path, the optical viewfinder can
be used as well. On the other hand, when an image to be recorded
is shot, the half mirror is retracted out of the optical path so
that all the light from the taking lens is used for shooting.
Generally, irrespective of the type of camera, when shooting is
attempted in so low light that bright images are unlikely to be
obtained, flash is used so that the subject is illuminated to proper
brightness with illumination light emitted from a flash device.
To permit proper adjustment of the amount of illumination light,
some SLR-type cameras that shoot by exposure of silver-halide film
adopt control called automatic light adjustment. Specifically, the
amount of illumination light that reaches the film during shooting
is measured, and emission of the illumination light is stopped when
the measured amount has reached a predetermined value. This control
works excellently to permit the subject to be illuminated to proper
brightness.
Such automatic light adjustment requires the use of a photometric
device, which is usually disposed by the side of the optical path
from the talking lens to the film in such a way as to face the film
obliquely, so that the photometric device measures the amount of
light reflected from the film. Since the film reflects light dispersively,
disposing the photometric device in this way suffices to enable
it to measure the amount of reflected light.
On the other hand, in a digital camera, the image-sensing device
itself outputs a signal representing the amount of light received,
and therefore exposure of the image-sensing device can be controlled
on the basis of that signal. In fact, in ambient-light shooting
involving no emission of illumination light, on the basis of the
output of the image-sensing device, the aperture value and the exposure
time (electronic shutter speed) to be used in succeeding shooting
are determined. However, since it is only after the completion of
shooting of the image of a frame that the image-sensing device outputs
the signal corresponding to that frame, it is impossible to use
the image-sensing device as a photometric device for the purpose
of automatic light adjustment.
For this reason, in a digital camera, first, an image is shot with
preliminarily emitted illumination light and, on the basis of the
result of this shooting, the amount of illumination light to be
emitted is determined. It is only then that an image to be recorded
is shot with emission of the thus determined amount of illumination
light. However, this control has the disadvantage of requiring too
much time after the user has operated the release button to command
recording of an image until the image to be recorded starts to be
shot.
Some might expect that, even in a digital camera, if it is additionally
equipped with a photometric device separate from an image-sensing
device, it would be possible to realize automatic light adjustment
that permits accurate adjustment of the amount of light with quick
response. In reality, however, since the image-sensing device used
in a digital camera hardly reflects light dispersively, it is meaningless
to dispose the photometric device to face the image-sensing device
obliquely. Also meaningless is to dispose the photometric device
to face the image-sensing device squarely, because then the photometric
device obstructs part of the light traveling from the taking lens
to the image-sensing device.
On the other hand, in an SLR-type digital camera, as described
above, the optical path is split by a semi-transmissive optical
element such as a prism or half-mirror so that the light reflected
from that optical element is directed to the optical viewfinder.
However, no arrangement has conventionally been known that uses
this reflected light for any other purpose than to offer a viewfinder
image.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an SLR-type digital
camera that can automatically adjust the amount of light in flash
shooting.
To achieve the above object, according to one aspect of the present
invention, a digital camera is provided with: a taking lens; an
image-sensing device for shooting an image by receiving light from
the taking lens; an optical element, disposed retractably in the
optical path from the taking lens to the image-sensing device, for
reflecting part of the light from the taking lens; a photometric
device for measuring the amount of light reflected from the optical
element; a controller that, during shooting, makes an illumination
device start emitting illumination light and then makes the illumination
device stop emitting the illumination light when the amount of light
measured by the photometric device has reached a predetermined value;
a selector that selects either a first mode in which shooting is
performed without emission of the illumination light by the illumination
device and a second mode in which shooting is performed with emission
of the illumination light by the illumination device; and a driver
that retracts the optical element out of the optical path during
shooting when the first mode is selected and that keeps the optical
element in the optical path during shooting when the second mode
is selected.
This digital camera performs shooting without emission of the illumination
light in the first mode, and performs shooting with flash, i.e.
with emission of the illumination light, and with automatic light
adjustment as well in the second mode. The photometric device used
for automatic light adjustment is disposed in the optical path of
the light reflected from the optical element, and thus it never
obstructs the light having passed through the optical element and
traveling toward the image sensing device. Moreover, since there
is no need to measure the amount of light reflected from the image-sensing
device, no consideration needs to be given to the fact that the
image-sensing device does not reflect light dispersively, and thus
the photometric device can be disposed at any convenient position
in the optical path of the light reflected from the optical element.
Furthermore, in the first mode, the optical element is retracted
out of the optical path during shooting, and therefore all the light
having passed through the taking lens can be used for shooting.
The illumination device may be built into the digital camera, or
may be, as a separate unit, externally connected to the digital
camera.
The gain of the output of the image-sensing device may be made
variable so that the gain is set to differ between in the first
and second modes. Here, it is preferable that the gain in the second
mode be approximately equal to the gain in the first mode multiplied
by the reciprocal of the transmittance of the optical element. In
flash shooting, keeping the optical element in the optical path
causes the amount of light reaching the image-sensing device to
lower according to the transmittance of the optical element. Therefore,
if the predetermined value that determines when to stop the emission
of the illumination light is determined on the basis of the total
amount of light passing through the taking lens, the actually shot
image will be dimmer than it should be. This can be solved by enhancing
the sensitivity of the image-sensing device by a factor of the reciprocal
of the transmittance of the optical element when flash shooting
is performed with the optical element kept in the optical path,
because then, even if the predetermined value is determined on the
basis of the total amount of light passing through the taking lens,
proper automatic light adjustment is possible without fail.
This digital camera may be additionally equipped with a viewfinder
that offers a visible image by receiving the light reflected from
the optical element. This makes it possible to present an optical
image identical with the image shot by the image-sensing device
without parallax.
BRIEF DESCRIPTION OF THE DRAWINGS
This and other objects and features of the present invention will
become clear from the following description, taken in conjunction
with the preferred embodiments with reference to the accompanying
drawings in which:
FIG. 1 is a sectional view showing the optical construction of
a digital camera embodying the invention;
FIG. 2 is a rear view of the digital camera shown in FIG. 1;
FIG. 3 is a block diagram showing the circuit configuration of
the digital camera shown in FIG. 1;
FIGS. 4A to 4D are sectional views of the digital camera shown
in FIG. 1, as observed during shooting in the ambient-light mode;
and
FIGS. 5A to 5D are sectional views of the digital camera shown
in FIG. 1, as observed during shooting in the flash mode;
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Hereinafter, an embodiment of the present invention will be described
with reference to the drawings. FIG. 1 and FIG. 2 are a sectional
view and a rear view, respectively, of a digital camera 1 embodying
the invention.
As shown in FIG. 1, the digital camera 1 has a taking lens 11,
a charge-coupled device (CCD) 12 serving as an image-sensing device,
a liquid crystal display (LCD) 13, a half mirror 14 serving as a
semi-transmissive optical element, and an optical viewfinder 15.
The taking lens 11 images the light from a subject on the light-receiving
surface of the CCD 12. The CCD 12 is disposed perpendicularly to
the optical axis Ax of the taking lens 11, and serves to shoot an
image by converting the light from the taking lens 11 into an electric
signal. The shooting of an image by the CCD 12 is performed repeatedly
at substantially regular time intervals. The LCD 13 is disposed
on the back of the digital camera 1, and serves to display the image
shot by the CCD 12 and messages to the user.
The half mirror 14 is disposed between the taking lens 11 and the
CCD 12. The half mirror 14 has, at the upper end thereof, a rotation
axis, which lies perpendicular to the optical axis Ax of the taking
lens 11 and about which the half mirror 14 rotates between an intercepting
position, in which the half mirror 14 crosses the optical path from
the talking lens 11 to the CCD 12, and a retracted position, in
which the half mirror 14 is retracted out of the optical path. The
half mirror 14, when in the intercepting position, crosses the optical
axis Ax at 45.degree. and, when in the retracted position, lies
parallel to the optical axis Ax. The half mirror 14 is designed
to have a transmittance of approximately 60%. The half mirror 14
is driven by an actuator 16 provided near the upper end thereof.
The optical viewfinder 15 is composed of a focusing screen 15a,
a pentaprism 15b, and an eyepiece lens 15c. The screen 15a is disposed
parallel to the optical axis Ax of the taking lens 11, and serves
to image the light reflected from the half mirror 14 when the half
mirror 14 is in the intercepting position. The distance from the
intersection between the optical axis Ax and the half mirror 14
to the imaging surface of the screen 15a is made equal to the distance
from the same intersection to the light-receiving surface of the
CCD 12. Thus, these two surfaces are located at optically equivalent
positions. By observing the image formed on the screen 15a through
the eyepiece lens 15c and the pentaprism 15b, the user can observe
an erect image equivalent to the image formed on the CCD 12.
Immediately in front of the CCD 12, a focal-plane shutter 17 is
disposed that switches between a state in which light is allowed
to reach the CCD 12 and a state in which light is shut off therefrom.
Between the half mirror 14 and the shutter 17, a low-pass filter
18 is disposed that eliminates high-frequency components. Inside
the optical viewfinder 15, a photometry device 19 is disposed that
measures the amount of light from the prism 15b. The amount of light
measured by the photometry device 19 is used to control the exposure
of the CCD 12, and, in flash shooting, it is used also to achieve
automatic light adjustment. Near the pupil of the taking lens 11,
an aperture stop 20 is disposed that restricts the diameter of the
light beam and thereby controls the exposure of the CCD 12.
As shown in FIG. 2, on the back of the digital camera 1 are arranged,
in addition to the LCD 13, a number of switches including two slide-type
switches 21 and 22 and a push-type switch 23. On the top of the
digital camera 1 are arranged a release button 26, a dial 27, and
a receptacle 28 that permits a flash device 2 (see FIG. 3) to be
attached thereto. On each of the flash device 2 and the receptacle
28, electric contacts are provided so that the flash device 2, when
attached to the receptacle 28, is electrically connected to the
digital camera 1.
The switch 21 is used to turn on and off the supply of electric
power and to set the operation mode. The digital camera 1 operates
in a shooting mode, in which an image is shot by the CCD 12 and
the shot image is recorded on a recording medium as requested by
the user, or in a playback mode, in which a previously recorded
image is reproduced and displayed on the LCD 13. In the shooting
mode, the shooting of an image and the display of the shot image
on the LCD 13 may be repeated at regular time intervals (for example,
1/30 seconds). This makes it possible to offer a "live view"
display capability whereby the target subject is displayed in a
form much like a moving video picture.
When the switch 21 is in a position marked "OFF", no
power is supplied, and thus the digital camera 1 remains out of
operation. With the switch 21 in a position marked "PLAY",
the digital camera 1 operates in the playback mode. With the switch
21 in a position marked "LIVE VIEW", the digital camera
1 operates in the shooting mode with a live view, and, with the
switch 21 in a position marked "CAM", the digital camera
1 operates in the shooting mode without a live view.
In addition, the digital camera 1 operates in a flash mode, in
which illumination light is emitted from the flash device 2 when
an image to be recorded is shot, or in an ambient-light mode, in
which no illumination light is emitted. The switch 22 is used to
switch between these two modes. When the switch 22 is in a position
marked "ON", the digital camera 1 operates in the flash
mode, and, when the switch 22 is in a position marked "OFF",
the digital camera 1 operates in the ambient-light mode.
In the ambient-light mode, the half mirror 14 is operated as a
quick-return mirror. That is, in this mode, until there is a request
to record an image, shooting is performed with the half mirror 14
kept in the intercepting position. As soon as there is a request
to record an image, the half mirror 14 is moved to the retracted
position, then an image to be recorded is shot on completion of
the retraction of the half mirror 14, and then, on completion of
the shooting of this image, the half mirror 14 is moved back to
the intercepting position. In the flash mode, irrespective of whether
there is a request to record an image or not, shooting is performed
with the half mirror 14 kept in the intercepting position all the
time, and, as soon as there is a request to record an image, illumination
light is emitted from the flash device 2.
The release button 26, when pressed halfway, produces a signal
S1, and, when pressed fully, additionally produces a signal S2.
The digital camera 1 adopts automatic focusing whereby the focus
of the taking lens 11 is adjusted on the basis of the image shot
by the CCD 12. The signal S1 requests starting of automatic focusing.
The signal S1 also requests starting of calculation of the aperture
value of the aperture stop 20 and the photoelectric conversion time
(electronic shutter speed) of the CCD 12 on the basis of the output
of the photometric device 19 in order to control the exposure of
the CCD 12.
The signal S2 requests recording of the image being shot. When
the signal S2 is issued, first, the aperture value and the electronic
shutter speed are set at the values that have been calculated previously.
In addition, in the ambient-light mode, the half mirror 14 is driven
to the retracted position. Then, the image shot on completion of
these operations is recorded.
The digital camera 1 uses as an image recording medium a removable
memory card. An image may or may not be compressed before being
recorded. The switch 23 is used to switch between compressed and
non-compressed recording of images. Exposure can be controlled in
an aperture-priority, shutter-priority, or program mode. The dial
27 is used to select among these modes.
FIG. 3 schematically shows the circuit configuration of the digital
camera 1. The digital camera 1 has a CPU 31, a CCD driver circuit
32, a mirror driver circuit 33, an aperture driver circuit 34, a
photometric calculation circuit 35, a flash control circuit 36,
an operation portion 37, a CDS (correlative double sampling) circuit
41, an AGC (automatic gain control) circuit 42, an A/D converter
43, a CPU 44, an image memory 45, a video encoder 46, and a card
interface 47.
The CPU 31 controls the operation of the entire digital camera
1. Hereinafter, the CPU 31 is called the control CPU. The CCD driver
circuit 32 produces a clock that is used as the basis of operation
timing, and feeds it to the CCD 12 so as to control the operation
of the CCD 12 by instructing it to start photoelectric conversion,
output the electric charges accumulated by photoelectric conversion,
and the like. The mirror driver circuit 33 instructs the actuator
16 to control the movement of the half mirror 14. The aperture driver
circuit 34 controls, through a driving mechanism (not shown), the
aperture value (aperture diameter) of the aperture stop 20. These
are controlled according to commands from the control CPU 31.
The photometric calculation circuit 35, in the ambient-light mode,
feeds a signal representing the amount of light measured by the
photometric device 19 to the control CPU 31. On the basis of this
signal, the control CPU 31 calculates the aperture value of the
aperture stop 20 and the electronic shutter speed of the CCD 12
at which they are to be set. The photometric calculation circuit
35, in flash mode, compares the amount of light measured by the
photometric device 19 with a predetermined value stored in itself,
and, as soon as the measured amount of light reaches the predetermined
value, feeds the control CPU 31 with a signal (hereinafter called
the light adjustment signal) notifying it of that fact. The predetermined
value is determined on the basis of the value observed when the
light having passed through the taking lens 11 directly reaches
the CCD 12 without passing through the half mirror 14.
The flash control circuit 36 controls the operation of the flash
device 2 by feeding it with signals that instruct it to charge electric
power for light emission, start light emission, and stop light emission.
When the flash mode is established, the control CPU 31 instructs
the flash control circuit 36 to start charging electric power. When
the signal S2 is issued, the control CPU 31 feeds the CCD drive
circuit 32 with a signal that instructs it to start shooting an
image to be recorded, and simultaneously feeds the flash control
circuit 36 and the photometric calculation circuit 35 with signals
that instruct them to start light emission and start photometry,
respectively. Thereafter, on receiving the light adjustment signal
from the photometric calculation circuit 35, the control CPU 31
immediately feeds the flash control circuit 36 with a signal that
instructs it to stop light emission. In this way, automatic light
adjustment is achieved in flash shooting.
The operation portion 37 includes various operation members such
as the switches 21 to 23, the release button 26, and the dial 27,
and serves to transmit the operation performed by the user to the
control CPU 31.
The CDS circuit 41 reduces the noise in the analog signal output
from the CCD 12, and the AGC circuit 42 adjusts, according to the
gain thereof, the levels of all the signals from the CDS circuit
41. The A/D converter 43 converts the analog signal from the AGC
circuit 42 into 10-bit digital signals.
The gain of the AGC circuit 42 is set by the control CPU 31. The
control CPU 31 sets the gain of the AGC circuit 42 for periods in
which an image to be recorded is processed in flash shooting to
be equal to the gain of the AGC circuit 42 for the other periods
multiplied by the reciprocal of the transmittance of the half mirror
14. That is, if the gain when shooting is performed without passing
light though the half mirror 14 is G, and the transmittance of the
half mirror 14 is T, then the gain Gf when flash shooting is performed
is given by Gf=G/T. This compensates the sensitivity of the CCD
12 that receives a reduced amount of light when light is passed
through the half mirror 14, and thereby makes proper automatic light
adjustment possible. The control CPU 31 has a ROM 31a having the
transmittance T or its reciprocal 1/T stored therein.
The CPU 44 processes the obtained digital signals so as to produce
image data representing an image. Hereinafter, the CPU 44 is called
the image CPU. The signals output from the A/D converter 43 are
stored in the image memory 45 for a while. The image CPU 44 reads
these signals from the image memory 45, and performs pixel interpolation,
color balance adjustment, and gamma correction so as to produce
image data.
Pixel interpolation 44a is performed to interpolate the signals
from the three-color, i.e. R, G, and B, pixels arranged alternately
on the CCD 12. Color balance adjustment 44b is performed to correct
individually the gains of the interpolated three-color signals and
thereby achieve correct reproduction of the colors of the subject.
Gamma correction 44c is performed to subject the gain-adjusted signals
to non-linear conversion and thereby obtain gradation fit for the
LCD 13. The image CPU 44 stores as image data the signals having
undergone these operations once again in the image memory 45.
The image CPU 44 reads the image data from the image memory 45
and feeds it to the video encoder 46. The video encoder 46 then
encodes the received image data into a format complying with the
NTSC system, and feeds the encoded image data to the LCD 13 to display
it as an image thereon.
The memory card 48 stores the image data. The card interface 47
writes data to and reads data from the memory card 48. On receiving
an instruction from the control CPU 31 in response to the signal
S2, the image CPU 44 reads the image data from the image memory
45, and feeds it to the card interface 47 to record it on the memory
card 48. If the control CPU 31 is requesting data compression, before
the image data is recorded on the memory card 48, the image CPU
44 performs data compression 44d on the image data by a method complying
with JPEG.
In the playback mode, in response to an instruction from the control
CPU 31, the image CPU 44 reads the image data stored on the memory
card 48 through the card interface 47, decompresses the image data
if necessary, and stores it in the image memory 45. Then, the image
CPU 44 reads this image data, and feeds it to the video encoder
46 to display it on the LCD 13.
FIGS. 4A to 4D show sectional views of the digital camera 1 as
observed during shooting in the ambient-light mode. FIG. 4A shows
the state when the signal S1 alone is being issued. Here, the half
mirror 14 is in the intercepting position, and the photometric device
19 is performing photometry. The aperture stop 20 is fully open.
FIG. 4B shows the state when the signal S2 has just been issued
to request recording of an image. At this point, the half mirror
14 is in the intercepting position, but subsequently it moves to
the retracted position. The photometric device 19 suspends photometry.
FIG. 4C shows the state when an image to be recorded is being shot.
Here, the half mirror 14 is in the retracted position. The aperture
stop 20 is stopped down according to the result of photometry performed
in the state shown in FIG. 4A. FIG. 4D shows the state when the
signal S1 is still present after completion of the shooting of the
image to the recorded. Here, the half mirror 14 has moved back to
the intercepting position, the photometric device 19 has restarted
photometry, and the aperture stop 20 is fully open.
FIGS. 5A to 5D show sectional views of the digital camera 1 as
observed during shooting in the flash mode. FIG. 5A shows the state
when the signal S1 alone is being issued. FIG. 5B shows the state
when the signal S2 has just been issued to request recording of
an image. FIG. 5C shows the state when an image to be recorded is
being shot with emission of illumination light. FIG. 5D shows the
state when the signal S1 is still present after completion of the
shooting of the image to the recorded. In this mode, the half mirror
14 is kept in the intercepting position all the time. The photometric
device 19 suspends photometry when, as shown in FIG. 5B, the signal
S2 is issued, and thereafter restarts photometry as soon as, as
shown in FIG. 5C, an image to be recorded starts being shot. Thus,
the photometric device 19 is used for light adjustment.
In this way, in shooting in the flash mode, keeping the half mirror
14 in the optical path eliminates the need to move the half mirror
14 to the retracted position. This makes it possible to shoot quickly
an image to be recorded in response to the signal S2. On the other
hand, in ambient-light shooting, moving the half mirror 14 to the
retracted position makes it possible to use all the light having
passed through the taking lens 11 for the shooting of an image to
be recorded.
The embodiment described specifically above uses a half mirror
as a semi-transmissive optical element, and operates it as a quick-return
mirror. However, the present invention, according to which a photometric
device for light adjustment is disposed in the optical path of the
light reflected from that optical element, applies also in arrangements
in which a prism serving as a semi-transmissive optical element
is disposed in a fixed position. The photometric device may be disposed
anywhere in the optical path of the light reflected from the semi-transmissive
optical element. However, it is preferable that, as in the embodiment
described specifically above, the photometric device be disposed
at a position where it receives light after being imaged on the
focusing screen. This makes it easy to prevent the viewfinder image
from being obstructed by the photometric device, and in addition
permits effective use of light that does not eventually reach the
user's eye.
The embodiment described specifically above uses a flash device
of a type that is detachably attached to the digital camera. However,
the flash device may be of a type that is built in the digital camera.
It is also possible to use a flash device that is placed away from
the digital camera and connected thereto with a cable or the like.
Obviously, many modifications and variations of the present invention
are possible in light of the above teachings. It is therefore to
be understood that within the scope of the appended claims, the
invention may be practiced other than as specifically described.
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