U.S. patent application number 09/797992 was filed with the patent office on 2001-11-08 for focus detecting device, and camera having the focus detecting device.
Invention is credited to Furukawa, Nobuyuki.
Application Number | 20010038751 09/797992 |
Document ID | / |
Family ID | 18582741 |
Filed Date | 2001-11-08 |
United States Patent
Application |
20010038751 |
Kind Code |
A1 |
Furukawa, Nobuyuki |
November 8, 2001 |
Focus detecting device, and camera having the focus detecting
device
Abstract
A focus detecting device includes a light receiving device which
receives reflection light from an object of focus detection, an
auxiliary light device which illuminates the object of focus
detection with auxiliary light, and a control circuit which
controls an illuminating action of the auxiliary light device and
performs focus detection on the basis of a received-light signal
output of the light receiving device. While the auxiliary light
device is in process of being controlled to illuminate the object
of focus detection, the control circuit compares the received-light
signal output of the light receiving device with a prescribed value
and causes the focus detection being made by controlling the
auxiliary light device to stop if the received-light signal output
is less than the prescribed value.
Inventors: |
Furukawa, Nobuyuki;
(Ichikawa-shi, JP) |
Correspondence
Address: |
FITZPATRICK CELLA HARPER & SCINTO
30 ROCKEFELLER PLAZA
NEW YORK
NY
10112
US
|
Family ID: |
18582741 |
Appl. No.: |
09/797992 |
Filed: |
March 5, 2001 |
Current U.S.
Class: |
396/106 |
Current CPC
Class: |
G03B 13/36 20130101;
G02B 7/32 20130101 |
Class at
Publication: |
396/106 |
International
Class: |
G03B 015/02; G03B
013/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 8, 2000 |
JP |
2000-062781 |
Claims
1. A focus detecting device, comprising: a light receiving device
which receives reflection light from an object of focus detection;
an auxiliary light device which illuminates the object of focus
detection with auxiliary light; and a control circuit which
controls an illuminating action of said auxiliary light device and
performs focus detection on the basis of a received-light signal
output of said light receiving device, wherein, while said
auxiliary light device is in process of being controlled to
illuminate the object of focus detection, said control circuit
compares the received-light signal output of said light receiving
device with a prescribed value and causes the focus detection being
made by controlling said auxiliary light device to stop if the
received-light signal output is less than the prescribed value.
2. A focus detecting device according to claim 1, wherein said
light receiving device has a function of outputting a maximum value
of the received-light signal output, and said control circuit
compares the maximum value of the received-light signal output with
the prescribed value and causes the focus detection being made by
controlling said auxiliary light device to stop if the maximum
value is less than the prescribed value.
3. A focus detecting device according to claim 1, wherein said
light receiving device has a function of outputting a maximum value
and a minimum value of the received-light signal output, and said
control circuit compares a difference output indicative of a
difference between the maximum value and the minimum value of the
received-light signal output with the prescribed value and causes
the focus detection being made by controlling said auxiliary light
device to stop if the difference output is less than the prescribed
value.
4. A focus detecting device according to claim 1, wherein said
control circuit causes the focus detection being made by
controlling said auxiliary light device to stop if the
received-light signal output is less than the prescribed value
after said auxiliary light device has performed the illuminating
action just a predetermined number of times.
5. A focus detecting device according to claim 1, wherein said
control circuit causes the focus detection being made by
controlling said auxiliary light device to stop if the
received-light signal output is less than the prescribed value
after said auxiliary light device has performed the illuminating
action just for a predetermined period of time.
6. A focus detecting device according to claim 1, wherein said
auxiliary light device intermittently illuminates the object of
focus detection with the auxiliary light.
7. A focus detecting device according to claim 1, wherein said
auxiliary light device illuminates the object of focus detection
with the auxiliary light in a manner of having a pattern.
8. A focus detecting device according to claim 1, wherein said
auxiliary light device continuously illuminates the object of focus
detection with the auxiliary light.
9. A focus detecting device according to claim 1, wherein said
light receiving device is a pair of sensors.
10. A focus detecting device, comprising: a light receiving device
which receives reflection light from an object of focus detection;
an auxiliary light device which illuminates the object of focus
detection with auxiliary light; and a control circuit which
controls an illuminating action of said auxiliary light device and
performs focus detection on the basis of a received-light signal
output of said light receiving device, wherein, while said
auxiliary light device is in process of being controlled to
illuminate the object of focus detection, said control circuit
compares the received-light signal output of said light receiving
device with a prescribed value and causes the illuminating action
of said auxiliary light device to stop if the received-light signal
output is less than the prescribed value.
11. A focus detecting device according to claim 10, wherein said
light receiving device has a function of outputting a maximum value
of the received-light signal output, and said control circuit
compares the maximum value of the received-light signal output with
the prescribed value and causes the illuminating action of said
auxiliary light device to stop if the maximum value is less than
the prescribed value.
12. A focus detecting device according to claim 10, wherein said
light receiving device has a function of outputting a maximum value
and a minimum value of the received-light signal output, and said
control circuit compares a difference output indicative of a
difference between the maximum value and the minimum value of the
received-light signal output with the prescribed value and causes
the illuminating action of said auxiliary light device to stop if
the difference output is less than the prescribed value.
13. A focus detecting device for a camera, comprising: a light
receiving device which receives reflection light from an object of
photo-taking; an auxiliary light device which illuminates the
object of photo-taking with auxiliary light; and a control circuit
which controls an illuminating action of said auxiliary light
device and performs focus detection on the basis of a
received-light signal output of said light receiving device,
wherein, while said auxiliary light device is in process of being
controlled to illuminate the object of photo-taking, said control
circuit compares the received-light signal output of said light
receiving device with a prescribed value and causes the focus
detection being made by controlling said auxiliary light device to
stop if the received-light signal output is less than the
prescribed value.
14. A focus detecting device for a camera, according to claim 13,
wherein said light receiving device has a function of outputting a
maximum value of the received-light signal output, and said control
circuit compares the maximum value of the received-light signal
output with the prescribed value and causes the focus detection
being made by controlling said auxiliary light device to stop if
the maximum value is less than the prescribed value.
15. A focus detecting device for a camera, according to claim 13,
wherein said light receiving device has a function of outputting a
maximum value and a minimum value of the received-light signal
output, and said control circuit compares a difference output
indicative of a difference between the maximum value and the
minimum value of the received-light signal output with the
prescribed value and causes the focus detection being made by
controlling said auxiliary light device to stop if the difference
output is less than the prescribed value.
16. A focus detecting device for a camera, according to claim 13,
wherein said control circuit causes the focus detection being made
by controlling said auxiliary light device to stop if the
received-light signal output is less than the prescribed value
after said auxiliary light device has performed the illuminating
action just a predetermined number of times.
17. A focus detecting device for a camera, according to claim 13,
wherein said control circuit causes the focus detection being made
by controlling said auxiliary light device to stop if the
received-light signal output is less than the prescribed value
after said auxiliary light device has performed the illuminating
action just for a predetermined period of time.
18. A focus detecting device for a camera, according to claim 13,
wherein said auxiliary light device intermittently illuminates the
object of photo-taking with the auxiliary light.
19. A focus detecting device for a camera, according to claim 13,
wherein said auxiliary light device illuminates the object of
photo-taking with the auxiliary light in a manner of having a
pattern.
20. A focus detecting device for a camera, according to claim 13,
wherein said auxiliary light device continuously illuminates the
object of photo-taking with the auxiliary light.
21. A focus detecting device for a camera, according to claim 13,
wherein said auxiliary light device is a flash device incorporated
into said camera.
22. A focus detecting device for a camera, according to claim 13,
wherein said auxiliary light device is a flash device externally
attached to said camera.
23. A focus detecting device for a camera, according to claim 13,
wherein said light receiving device is a pair of sensors.
24. A focus detecting device for a camera, comprising: a light
receiving device which receives reflection light from an object of
photo-taking; an auxiliary light device which illuminates the
object of photo-taking with auxiliary light; and a control circuit
which controls an illuminating action of said auxiliary light
device and performs focus detection on the basis of a
received-light signal output of said light receiving device,
wherein, while said auxiliary light device is in process of being
controlled to illuminate the object of photo-taking, said control
circuit compares the received-light signal output of said light
receiving device with a prescribed value and causes the
illuminating action of said auxiliary light device to stop if the
received-light signal output is less than the prescribed value.
25. A focus detecting device for a camera, according to claim 24,
wherein said light receiving device has a function of outputting a
maximum value of the received-light signal output, and said control
circuit compares the maximum value of the received-light signal
output with the prescribed value and causes the illuminating action
of said auxiliary light device to stop if the maximum value is less
than the prescribed value.
26. A focus detecting device for a camera, according to claim 24,
wherein said light receiving device has a function of outputting a
maximum value and a minimum value of the received-light signal
output, and said control circuit compares a difference output
indicative of a difference between the maximum value and the
minimum value of the received-light signal output with the
prescribed value and causes the illuminating action of said
auxiliary light device to stop if the difference output is less
than the prescribed value.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a focus detecting device
arranged to detect focus by illuminating an object of focus
detection with an auxiliary light of auxiliary light projecting
means and on the basis of an output of light receiving means which
receives reflection light from the object, when the object has a
low luminance in detecting focus, and also to a camera having the
focus detecting device.
[0003] 2. Description of Related Art
[0004] The focus detecting device of a camera or a like
photo-taking apparatus is arranged to detect focus by leading the
light of a photo-taking object incident on an optical system to a
light receiving element. The focus detecting device has been
variously arranged to detect focus, including a phase-difference
(detecting) type. In the case of the phase-difference type, the
focus of a camera or the like is detected, for example, on the
basis of a phase difference between two optical images which are
obtained by splitting incident light of the object into two
images.
[0005] The phase-difference type focus detecting device is
generally arranged to use an integration-type light receiving
element. In the focus detecting device of the phase-difference
type, the light of the object incident on a photo-taking lens is
led to a pair of integration-type light receiving elements arranged
in a secondary image forming system. The pair of light receiving
elements are linearly arranged to accumulate electric charge
according to the amount of incident light and to send out
predetermined outputs as signals according to the accumulated
electric charge. An arithmetic circuit is arranged to receive the
signal outputs and to detect a state of focus (an amount of
defocus) by computing a phase difference between the signal
outputs. The state of focus thus obtained is used for focus
adjustment.
[0006] However, in a case where the photo-taking object is dark,
the arithmetic circuit is unable to obtain the signals with a
sufficient amount of amplitude as the light amount incident on the
light receiving elements is small. Under such a condition, focus
detection cannot be made by the focus detecting device. To solve
the problem, a focus detecting device was disclosed in Japanese
Laid-Open Patent Application No. Sho 59-195605. This focus
detecting device is arranged to detect whether or not the object of
photo-taking has a low luminance and to control the light emitting
action of a light emitting device according to the result of
detection.
[0007] With the focus detecting device arranged in this manner, the
focus detecting device performs a focus detecting action on a focus
detecting area in accordance with the known phase-difference
method.
[0008] FIG. 13 shows the state of signals accumulated by the light
receiving elements (sensor array) with the flash auxiliary light of
a flash device or the like used as the auxiliary light.
[0009] Referring to FIG. 13, the amount of light emission increases
and an accumulation voltage which is accumulated at the light
receiving elements rises as long as the object is illuminated with
the flash auxiliary light. A maximum image signal shown in FIG. 13
represents the value of output of a cell which gives the largest
image signal output among other cells included in a sensor array
which is composed of a plurality of cells. A minimum image signal
shown in FIG. 13 represents the output value of a cell which gives
the smallest image signal output among other cells included in the
sensor array composed of the plurality of sensors. As shown in FIG.
13, both the maximum image signal and the minimum image signal rise
every time the illuminating flash light is projected. In the case
of FIG. 13, a difference between the maximum image signal and the
minimum image signal comes to exceed a predetermined decision value
POS when the flash light emission is made for the eighth time, thus
indicating that the accumulation of electric charge has come to an
end . The decision value POS is a value at which the output image
signals are sufficiently obtained to obtain a correlation to be
used for a focus detecting arithmetic operation, because the
difference between the maximum image signal and the minimum image
signal is large enough to give a sufficient image signal
amplitude.
[0010] However, the amount of auxiliary light emission for
illumination is limited. Hence, the conventional art has been found
requiring further improvement in respect of the following
points.
[0011] In taking pictures at night, the auxiliary light often fails
to reach objects due to far distances, etc.
[0012] FIG. 14 shows, for example, a case where the object of
photo-taking is located at such a far distance that the flash
auxiliary light emitted from the camera hardly can reach the
object. In this case, the luminance of the object is low despite of
the flash auxiliary light emission which is made eight times.
Therefore, the value of a signal from the light receiving element
indicating a difference between the maximum image signal and the
minimum image signal hardly becomes larger. The amplitude of the
output image signals is too small to be used for focus detection.
Thus, the focus detecting arithmetic operation is hardly
possible.
[0013] In this respect, a focus detecting arrangement has been
developed to increase the amount of auxiliary light emission for
illumination in cases where the auxiliary light emission amount is
too small, as disclosed in Japanese Laid-Open Patent Application
No. Hei 6-289281. However, since there is also a limit to the
increase of the amount of light emission, the flash auxiliary light
still fails to reach the object in some cases.
[0014] FIG. 15 shows another case where the photo-taking object is
something like a wall having a uniform reflection factor. In such a
case, the focus detecting arithmetic operation cannot be performed
as it is impossible to obtain a difference signal indicative of a
difference between the maximum image signal and the minimum image
signal.
[0015] In these cases, the arrangement of the conventional art
cited above is meaninglessly illuminating the object with the
auxiliary light despite of the impossibility of focus detection and
is thus hardly considered to be efficiently using energy. Besides,
the number of cameras of the kind having a built-in flash device
and using its flash light as the auxiliary light is increasing
these days. Since the electric energy of a battery is rapidly
consumed by the built-in flash device, the conventional arrangement
of focus detecting devices must be improved also in respect of the
service life of the battery.
BRIEF SUMMARY OF THE INVENTION
[0016] One aspect of the invention lies in the provision of a focus
detecting device having control means arranged to cause an
auxiliary light device to illuminate an object of focus detection
with auxiliary light, if the luminance of the object of focus
detection is low at the time of focus detection, by performing
control in the following manner. If the output of a light receiving
device for receiving reflection light from the object of focus
detection is found to be lower than a prescribed value, the control
means stops focus detection being made by controlling the auxiliary
light device. Therefore, waste of energy can be minimized by
stopping useless illumination in a case where the reflection light
cannot be obtained in sufficient amount by illuminating the object
of focus detection with the auxiliary light of the auxiliary light
device.
[0017] Another aspect of the invention lies in the provision of a
focus detecting device for a camera, having control means arranged
to cause an auxiliary light device to illuminate the object of
photo-taking with auxiliary light, if the luminance of the object
of photo-taking is low at the time of focus detection, by
performing control in the following manner. If the output of a
light receiving device for receiving reflection light from the
object of photo-taking is found to be lower than a prescribed
value, the control means stops focus detection being made by
controlling the auxiliary light device. Therefore, waste of energy
can be minimized by stopping useless illumination in a case where
the reflection light cannot be obtained in sufficient amount by
illuminating the object of photo-taking with the auxiliary light of
the auxiliary light device.
[0018] The above and other objects and features of the invention
will become apparent from the following detailed description of
preferred embodiments thereof taken in connection with the
accompanying drawings.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0019] FIG. 1 is a block diagram showing in outline the electrical
arrangement of a camera according to a first embodiment of the
invention.
[0020] FIG. 2 is a block diagram showing communication to be
conducted between a microcomputer and a focus detecting sensor
shown in FIG. 1.
[0021] FIG. 3 is a diagram showing sensor cells arranged within the
focus detecting sensor shown in Fig. 1.
[0022] FIG. 4 is a diagram showing the signal output of the focus
detecting sensor shown in FIG. 1.
[0023] FIG. 5 is a flow chart showing the AF control operation of
the camera according to the first embodiment.
[0024] FIG. 6 is a flow chart showing the details of step S400
shown in FIG. 5.
[0025] FIG. 7 is a diagram showing by way of example an
illumination light amount obtained by illuminating an object with
auxiliary light in relation to the output of the focus detecting
device in the first embodiment.
[0026] FIG. 8 is a diagram showing another example of the
illumination light amount obtained in illuminating an object with
the auxiliary light in relation to the output of the focus
detecting device in the first embodiment.
[0027] FIG. 9 is a flow chart showing the AF control operation of a
camera according to a second embodiment of the invention.
[0028] FIG. 10 is a diagram showing by way of example an
illumination light amount obtained in illuminating an object with
auxiliary light in relation to the output of the focus detecting
device in the second embodiment.
[0029] FIG. 11 is a flow chart showing the AF control operation of
a camera according to a third embodiment of the invention.
[0030] FIG. 12 is a diagram showing by way of example an
illumination light amount obtained in illuminating an object with
auxiliary light in relation to the output of the focus detecting
device in the third embodiment.
[0031] FIG. 13 is a diagram showing by way of example an
illumination light amount obtained in illuminating an object with
auxiliary light in relation to the output of a focus detecting
device arranged in a conventional manner.
[0032] FIG. 14 shows another example of the illumination light
amount obtained in illuminating an object with auxiliary light in
relation to the output of the conventional focus detecting
device.
[0033] FIG. 15 shows a further example of the illumination light
amount obtained in illuminating an object with auxiliary light in
relation to the output of the conventional focus detecting
device.
DETAILED DESCRIPTION OF THE INVENTION
[0034] Hereinafter, preferred embodiments of the invention will be
described in detail with reference to the drawings.
[0035] (First Embodiment)
[0036] FIG. 1 shows in a block diagram the electrical arrangement
of a camera according to a first embodiment of the invention.
Referring to FIG. 1, a microcomputer 1 is arranged to control the
whole camera. A RAM 2 is externally attached to the microcomputer
1. An EEPROM 3, which is a nonvolatile memory, is externally
attached to the microcomputer 1. A focus detecting sensor 4 is
connected to the microcomputer 1. A sensor driving control circuit
5 is included in the focus detecting sensor 4. A sensor part 6 is
arranged within the focus detecting sensor 4 to be driven and
controlled by the sensor driving control circuit 5. The sensor part
6 includes a part SNS-A and another part SNS-B each of which is
composed of a plurality of sensor cells, and are arranged in pair
to form a focus detecting area in one line (hereinafter will be
referred to as an AF point). In a case where the camera has a
plurality of AF (automatic focusing) points, the focus detecting
sensor 4 includes a number of pairs of these parts corresponding to
the plurality of AF points. However, for simplification's sake, the
first embodiment is described by way of example here on the
assumption that the camera has only one AF point. The focus
detecting sensor 4 further includes a sensor signal processing
circuit 7 which is arranged to perform a signal processing action,
according to a signal from the sensor driving control circuit 5, on
the signal accumulated at the sensor part 6 and to send the result
of the signal processing action to the microcomputer 1.
[0037] A light measuring circuit 8 is connected to the
microcomputer 1 and is arranged to measure the luminance of a
photo-taking object. A lens control circuit 9 is also connected to
the microcomputer 1 and is arranged to control an electronic
circuit disposed within an interchangeable lens 10 which is
detachably mounted on the body of the camera. The interchangeable
lens 10, which is connected to the lens control circuit 9 and
detachably mounted on the camera body, includes the electronic
circuit. The electronic circuit of the interchangeable lens 10 is
arranged to control an AF lens in accordance with a control signal
coming from the lens control circuit 9. A display circuit 11 is
connected to the microcomputer 1 and is provided for displaying a
shutter speed, an aperture value, various setting values of the
camera, etc. A display part 12 is connected to the display circuit
11 and is arranged to make displays of varied kinds.
[0038] A switch 13 (or switch SW1) is connected to the
microcomputer 1 for causing the commencement of a light measuring
action and a focus detecting action. A switch 14 (or switch SW2) is
connected to the microcomputer 1 for the commencement of an
exposure. These switches 13 (SW1) and 14 (SW2) are formed into one
release switch of the two-step structure. The switch 13 (SW1) is
arranged to be turned on by the first stroke of the release switch.
The switch 14 (SW2) is arranged to be turned on by the second
stroke of the release switch with the switch 13 (SW1) turned on. A
dial detecting circuit 16 is connected to the microcomputer 1 and
is arranged to detect various setting operations on dials (not
shown) which are provided on the camera.
[0039] The camera body (not shown) is loaded with a film 18. A film
detecting circuit 19 is arranged for detecting the position of the
film 18 under the control of the microcomputer 1. A photo-sensor 20
is arranged to be driven by the film detecting circuit 19 to detect
the position of the film 18. A film transport circuit 21 is
arranged for winding and rewinding the film 18 under the control of
the microcomputer 1. A film transport motor 22 is arranged to be
controlled and driven by the film transport circuit 21 to transport
the film 18.
[0040] A shutter control circuit 23 is arranged for control over a
shutter 24 for making an exposure under the control of the
microcomputer 1. A flash-device control circuit 25 is arranged to
control a built-in flash device 26. The flash device 26 is arranged
to emit light in a amount according to a control value computed by
the flash-device control circuit 25. An auxiliary light circuit 27
is arranged to be caused by the microcomputer 1 to act when the
luminance of the object is low at the time of focus detection. An
auxiliary light projecting lamp 28 is arranged to be lighted up by
the auxiliary light circuit 27. The shape of the auxiliary light
projecting lamp 28 varies with the cameras. In some cases, the
auxiliary light projecting lamp 28 is arranged to project light in
a pattern. In a case where flash auxiliary light is to be used as
the auxiliary light, the built-in flash device 26 is used in place
of the auxiliary light projecting lamp 28.
[0041] FIG. 2 shows the relation of the microcomputer 1 to the
focus detecting sensor 4.
[0042] Referring to FIG. 2, for control over the focus detecting
sensor 4, commands of varied kinds are sent to the focus detecting
sensor 4 from the microcomputer 1. On the other hand, the focus
detecting sensor 4 is arranged to send information on its state to
the microcomputer 1. Further, the focus detecting sensor 4 is
arranged to send to the A/D converter of the microcomputer 1,
through the sensor signal processing circuit 7, an analog signal
which is obtained by processing signals accumulated at the sensor
part 6, in accordance with a clock signal received from the
microcomputer 1.
[0043] FIG. 3 shows in detail the arrangement of sensor cells of
the sensor part 6 of the focus detecting sensor 4.
[0044] As shown in FIG. 3, in the sensor part 6, the sensor cells
are laterally aligned in a row composed of the two parts SNS-A and
SNS-B for the purpose of carrying out the focus detection in
accordance with the known phase difference method. The part SNS-A
is composed of a total of 32 sensor cells, i.e., sensor cells
SNS-Al to SNS-A32. The other part SNS-B is also composed of a total
of 32 sensor cells, i.e., SNS-Bl to SNS-B32.
[0045] FIG. 4 shows an image signal outputted from the focus
detecting sensor 4.
[0046] Referring to FIG. 4, the focus detecting sensor 4 outputs an
analog image signal in accordance with a reading clock signal
outputted from the microcomputer 1. The image signal is composed of
a property signal section which indicates the property of the image
signal, and an image signal section which corresponds to the actual
outputs of the sensor cells.
[0047] In the property signal section, a Dark signal which is a
signal from such a sensor cell that is blocked from light, a Bottom
signal which is a signal from a sensor cell giving the smallest
output among the sensor cells SNS-Al to SNS-B32, a Peak signal
which is a signal from a sensor cell giving the largest output
among the sensor cells SNS-Al to SNS-B32, and a P-B signal which
indicates a difference value obtained by subtracting the Bottom
signal from the Peak signal and thus represents the contrast of the
image, are serially outputted in this order.
[0048] In the image signal section of the image signal of the focus
detecting sensor 4, output signals of the sensor cells SNS-Al to
SNS-B32 are serially outputted.
[0049] FIG. 5 is a flow chart showing in outline a control
operation to be performed by the microcomputer 1 in carrying out an
AF control by using auxiliary light in a case where a photo-taking
object has a low luminance. When the switch 13 (SW1) shown in FIG.
1 turns on, the flow of operation begins at step S100 of FIG. 5.
The flow then proceeds from the step S100 to step S200.
[0050] At the step S200, a focus detecting process is performed in
an ordinary manner without using any auxiliary light to illuminate
the object. At the next step S300, a check is made to find if the
focus detection has been possible without auxiliary light. If so,
the flow proceeds from the step S300 to step S500. If not, the flow
proceeds to step S400. At the step S400, a focus detecting process
is performed by illuminating the object with auxiliary light in a
manner as will be described in detail later with reference to FIG.
6. In a case where the focus detecting process has been possible
with the auxiliary light being used, the flow proceeds from the
step S400 to the step S500. If the focus detection with the
auxiliary light is found at the step S400 to be impossible, the
flow proceeds from the step S400 to step S800. At the step S800,
the display part 12 is caused through the display circuit 11 to
make a display indicating that the focus detection is impossible.
The flow then returns to a main routine (not shown).
[0051] At the step S500, a focus detecting arithmetic operation is
performed to obtain an amount of driving the AF lens, i.e., a
defocus amount, by using the signal supplied from the focus
detecting sensor 4. At the next step S600, the result of the
arithmetic operation performed at the step S500 is examined by
comparing the defocus amount with a predetermined value for the
necessity of driving the AF lens. If the defocus amount is found to
be less than the predetermined value, the AF control process is
terminated, and the flow returns to the main routine (not shown).
If the defocus amount is found to be larger than the predetermined
value, the flow proceeds from the step S600 to step S700. At the
step S700, the AF lens is driven on the basis of the result of the
arithmetic operation obtained at the step S500. After the step
S700, the flow returns to the step S200 to repeat the above-stated
steps in the same manner.
[0052] Procedures for executing the step S400 of FIG. 5 which is
provided for focus detection by illuminating the object of focus
detection with auxiliary light are next described referring to the
flow chart of FIG. 6 as follows.
[0053] In the case of the first embodiment, the auxiliary light is
of a flash auxiliary light type using the flash light of the
built-in flash device 26 for illuminating the object. However, the
invention is not limited to the use of the flash auxiliary light
type but applies also to a case where an ordinary lamp or a lamp
light having some pattern such as the auxiliary light projecting
lamp 28 shown in FIG. 1. Only it must be noted that, while
illumination is intermittently made in the case of the flash
auxiliary light, the illumination is continuous in a case where the
ordinary lamp or the like is used. In the latter case, the concept
of use of a counter "i" which is described below is likely replaced
with control by time.
[0054] At step S402 of FIG. 6, the counter "i" is set at "1". The
counter "i" is arranged to store information on the number of times
of illuminating or projecting the flash auxiliary light. At the
next step S403, the built-in flash device 26 is driven through the
flash-device control circuit 25 to emit flash light toward the
object. At step S404, after illuminating the object with the flash
light, the P-B signal is read from the focus detecting sensor 4.
The P-B value indicated by the P-B signal is checked to find if the
P-B value is equal to or larger than the predetermined value POS.
If so, the probability that the focus detecting arithmetic
operation is possible is sufficiently high and, therefore, the flow
proceeds from the step S404 to step S409. If not, the flow proceeds
from the step S404 to step S405.
[0055] At the step S405, a check is made to find if the count value
of the counter "i" has reached a predetermined number of times "n".
If so, the flow proceeds to step S406. If not, the flow proceeds
from the step S405 to step S407. At the step S406, a value obtained
by dividing the P-B value by the count value "i" is compared with a
halfway decision value A. If the value is found to be less than the
halfway decision value A, focus detection is decided to be
impossible, and the flow proceeds to step S411 to stop the
auxiliary light from being projected. If the value obtained by
dividing the P-B value by the count value "i" is found to be equal
to or larger than the value A, there still remains the possibility
of the focus detecting arithmetic operation and, therefore, the
flow proceeds from the step S406 to step S408 to continue
illuminating the object with the flash auxiliary light. At the step
S408, the count value of the counter "i" is incremented by one (1).
With regard to the halfway decision value A, it is considered to be
theoretically adequate to obtain the value A by dividing the
predetermined value POS by a prescribed value "imax" that
corresponds to the maximum count value of the counter "i". In
actuality, however, the value A is decided through experiments by
taking into consideration such noises that likely enter the
circuits and the focus detecting sensor of the camera.
[0056] At the step S407, a check is made to find if the number of
times "i" of illuminating with the flash auxiliary light has come
to exceed the prescribed value "imax". If so, the flow proceeds
from the step S407 to step S411. The result of the check at the
step S407 indicates that the P-B signal cannot be obtained in a
sufficient amount even by illuminating the object with the
auxiliary light the prescribed number of times "imax". Such a
result of check is rarely obtained with the flow of operation
arranged to compare the P-B value with the predetermined value POS
halfway in process of illuminating and to stop illuminating with
the auxiliary light according to the result of the halfway check,
as in the present embodiment. The step S407 is provided against
some unexpected occasion.
[0057] In a case where the flow proceeds to the step S409, a check
is made for the end of the process of accumulation. If the process
is found to be finished thus indicating that the focus detection is
possible, the flow proceeds to step S410. At the step S410, since
the focus detection is possible, the flow proceeds to the step S500
of FIG. 5. At the step S411, since the focus detection is found to
be impossible, the flow is allowed to proceed to the step S800 of
FIG. 5 to let the user know that the focus detection is
impossible.
[0058] FIG. 7 shows a case where illumination with the auxiliary
light is stopped halfway as the object of photo-taking is dark and
located at a far distance.
[0059] The camera described here is arranged to have the prescribed
value "imax" which corresponds to the maximum count value of the
counter "i" set at "8" and a predetermined number of times "n" of
comparing the P-B value with the predetermined value POS set at
"3". If the predetermined number of times "n" is at a small value,
a great energy saving effect can be attained in the event of
stopping the illuminating process halfway, because the decision can
be made when the amount of the illuminating light emitted from the
built-in flash device 26 is still small. On the other hand, the
results of tests indicate that, if the number of times "n" is
small, the signal cannot be obtained in sufficient amount for
accurate decision due to the adverse effect of noises. Therefore,
in designing the camera, the number of times "n" should be decided
on the basis of experience according to the purpose for which the
camera is adapted.
[0060] With the flash auxiliary light emitted three times from the
built-in flash device 26, if the P-B value is found at the step
S404 to be less than the predetermined value POS, the flow proceeds
to the step S405. Then, since i=n, the flow proceeds from the step
S405 to the step S406. At the step S406, a value obtained by
dividing the P-B signal by the value "i" (3) is compared with the
halfway decision value A. If the value is found to be less than the
halfway decision value A, it is judged that the P-B signal would
not reach the value POS even if the illumination with the auxiliary
light is repeated further up to the prescribed number of times
"imax" (8). The focus detection is thus decided to be impossible,
and the flow proceeds to the step S411 to stop illuminating the
object with the auxiliary light any further.
[0061] FIG. 8 shows a case where the object of photo-taking is
something like a wall having a uniform reflection factor. In the
case of such an object, even if the object is illuminated with the
flash auxiliary light, both the Peak value and the Bottom value
would rise alike to make it impossible to obtain a sufficiently
large P-B signal. In this case, the flow of operation proceeds from
the step S405 to the step S406 when the count value of the counter
"i" is at "3". At the step S406, where a check is made for the P-B
value, focus detection is judged (decided) to be impossible,
because the P-B signal would not reach the predetermined value POS
even if the illumination with the auxiliary light is repeated
further up to the prescribed number of times "imax" (8). The flow
then proceeds from the step S406 to the step S411 to stop
illuminating with the auxiliary light any further.
[0062] (Second Embodiment)
[0063] The following description describes the actions of essential
parts of a camera according to a second embodiment of the
invention. The structural arrangement of the camera is the same as
that of the first embodiment described above.
[0064] FIG. 9 is a flow chart showing the flow of the AF control
operation of the second embodiment performed with auxiliary light
being used because of a low luminance of the object of
photo-taking. In a case where the auxiliary light used for
illuminating the object has a pattern, which herein means light
projected in approximately perpendicular stripes with respect to
the sensor array, the Bottom value does not rise following the Peak
value even in the event of such an object that has a uniform
reflection factor like a wall. Therefore, unlike in the case of
FIG. 8, the P-B signal can be obtained in a sufficient amount
because the Peak value of the signal saliently rises as compared
with the Bottom value as long as the auxiliary light reaches the
object. Hence, the decision as to the possibility of focus
detection can be made by comparing only the Peak signal with the
predetermined value POS with the object illuminated with the
pattern of auxiliary light. The second embodiment is, therefore,
arranged to decide whether the illumination with the auxiliary
light should be continued or to be discontinued halfway, by
comparing only the Peak signal. With the exception of this point,
the second embodiment is arranged in the same manner as the first
embodiment. Although the arrangement of the second embodiment is
applicable also to the use of flash light as the auxiliary light,
the following describes the second embodiment on the assumption
that intermittent patterned auxiliary light is used.
[0065] When focus detection is decided to be impossible without
auxiliary light at the step S300 of FIG. 5, the flow of operation
proceeds to step S421 of FIG. 9 to start focus detection with
auxiliary light from step S422.
[0066] At the step S422, the counter "i" is set at "1". The counter
"i" is arranged to store information on the number of times of
illuminating or projecting the patterned auxiliary light. At the
next step S423, the auxiliary light projecting lamp 28 is driven
through the auxiliary light circuit 27 to emit the patterned
auxiliary light toward the object. At step S424, after illuminating
the object with the patterned auxiliary light, the Peak signal is
read from the focus detecting sensor 4. The Peak value which
represents the magnitude of the Peak signal is checked to find if
the Peak value is equal to or larger than the prescribed value POS.
If so, the possibility that the focus detecting arithmetic
operation is possible is sufficiently high and, therefore, the flow
proceeds from the step S424 to step S429. If not, the flow proceeds
from the step S424 to step S425.
[0067] At the step S425, a check is made to find if the count value
of the counter "i" has reached a predetermined number of times "n".
If so, the flow proceeds to step S426. If not, the flow proceeds
from the step S425 to step S427. At the step S426, a value obtained
by dividing the value of the Peak signal by the count value "i" is
compared with a halfway decision value A2. If the value is found to
be less than the halfway decision value A2, focus detection is
judged to be impossible, and the flow proceeds to step S431 to stop
projecting the auxiliary light. If the value obtained by dividing
the value of the Peak signal by the count value "i" is found to be
equal to or larger than the halfway decision value A2, there still
remains some possibility of focus detection and, therefore, the
flow proceeds from the step S426 to step S428 to continue
illuminating the object with the patterned auxiliary light. At the
step S428, the count value of the counter "i" is incremented by one
(1). With regard to the halfway decision value A2, it is considered
to be theoretically adequate to obtain the halfway decision value
A2 by dividing the value POS by a prescribed value "imax" that
corresponds to the maximum count value of the counter "i". In
actuality, however, the halfway decision value A2 is decided
through experiments by taking into consideration such noises that
likely enter the circuits and the focus detecting sensor of the
camera and also a drift portion of a Dark signal component. Hence,
the halfway decision value A2 in the second embodiment is generally
larger than the halfway decision value A in the first
embodiment.
[0068] At the step S427, a check is made to find if the number of
times "i" of illuminating with the patterned auxiliary light has
come to exceed the prescribed value "imax". If so, the flow
proceeds from the step S427 to step S431. The result of the check
at the step S427 indicates that the Peak signal cannot be obtained
in a sufficient amount even with the object illuminated with the
auxiliary light the prescribed number of times "imax". Such a
result of check is rarely obtained with the flow of operation
arranged to compare the Peak value with the predetermined value POS
halfway in process of illuminating and to stop illuminating with
the auxiliary light according to the result of the halfway check,
as in the second embodiment. However, the step S427 is provided
against some unexpected occasion.
[0069] In a case where the flow proceeds to the step S429, a check
is made for the end of the process of accumulation. If the process
is found to be finished thus indicating that the focus detection is
possible, the flow proceeds to step S430. At the step S430, since
the focus detection is possible, the flow proceeds to the step S500
of FIG. 5. At the step S431, since the focus detection is found to
be impossible, the flow is allowed to proceed to the step S800 of
FIG. 5 to let the user know that the focus detection is
impossible.
[0070] FIG. 10 shows a case where illumination with the auxiliary
light is stopped halfway as the object of photo-taking is dark and
located at a far distance.
[0071] The camera described here is arranged to have the prescribed
value "imax" which corresponds to the maximum count value of the
counter "i" set at "8"while the predetermined number of times "n"
of comparing the Peak value with the predetermined value POS is set
at "3". If the predetermined number of times "n" is a small value,
a great energy saving effect can be attained in the event of
stopping the illuminating process halfway, because the decision can
be made while the amount of the illuminating light is still small.
On the other hand, the results of tests indicate that, if the
number of times "n" is small, the signal cannot be obtained in
sufficient amount to make accurate decision due to the adverse
effect of noises. Therefore, the number of times "n" should be
decided on the basis of experience in designing the camera
according to the purpose for which the camera is adapted.
[0072] With the auxiliary light projected three times, if the Peak
value is found at the step S424 to be less than the predetermined
value POS, the flow proceeds to the step S425. Then, since i=n, the
flow proceeds from the step S425 to the step S426. At the step
S426, a value obtained by dividing the Peak signal by the value "i"
(3) is compared with the halfway decision value A2. If the value is
found to be less than the halfway decision value A2, it is judged
that the Peak signal would not reach the value POS even if the
illumination with the auxiliary light is repeated further up to the
prescribed number of times "imax"(8). The focus detection is thus
decided to be impossible, and the flow proceeds to the step S431 to
stop illuminating with the auxiliary light any further.
[0073] (Third Embodiment)
[0074] The first and second embodiments described above are
arranged to intermittently project the light of the flash device or
the patterned auxiliary light. A third embodiment of the invention
is arranged, on the other hand, to continuously project the light
of the auxiliary light projecting lamp 28 instead of intermittently
projecting the auxiliary light. The circuit arrangement and the AF
control of the third embodiment are the same as those of the first
embodiment. The third embodiment operates as follows.
[0075] When the focus detection is found impossible without
auxiliary light at the step S300 of FIG. 5, the flow of operation
proceeds to step S461 of FIG. 11 to start performing focus
detection from step S462.
[0076] At the step S462, a timer "t" is reset and is allowed to
start a time count. The timer "t" is arranged to be used for
control over the length of time of illuminating an object with the
auxiliary light. At the next step S463, the auxiliary light
projecting lamp 28 is driven through the auxiliary light circuit 27
to project the auxiliary light toward the object of photo-taking.
At step S464, the P-B signal is read out from the focus detecting
sensor 4. A check is made to find if the P-B value is equal to or
larger than the predetermined value POS. If so, the probability
that a focus detecting arithmetic operation is possible is
sufficiently high, and the flow proceeds from the step S464 to step
S469. If not, the flow proceeds from the step S464 to step
S465.
[0077] At the step S465, a check is made to find if the count value
of the timer "t" has reached a predetermined length of time
"taban". If so, the flow proceeds to step S466. In actually, a
certain period of time is required for execution of the loop of the
processing steps "S464-S465 -S467-S464", depending on the
processing capability of the microcomputer 1. Therefore, a
predetermined time "t" to be used for comparison with the count
time of the timer "t" is set to include the processing time
required by the microcomputer 1. If the count value of the timer
"t" is not close to the predetermined time "t", the flow proceeds
from the step S465 to step S467.
[0078] At the step S466, a value obtained by dividing the value of
the P-B signal by the time count value of the timer "t" is compared
with a halfway decision value A3. If the value is found to be less
than the halfway decision value A3, focus detection is considered
to be impossible, and the flow proceeds to step S471 to stop the
auxiliary light from being projected. If the value obtained by
dividing the value of the P-B signal by the time count value "t" is
found to be equal to or larger than the halfway decision value A3,
there still remains some probability that the focus detection is
possible and, therefore, the flow proceeds from the step S466 to
step S464 to continue the process of illuminating the object with
the auxiliary light. With regard to the halfway decision value A3,
it is considered to be theoretically adequate to obtain the halfway
decision value A3 by dividing the predetermined value POS by a
prescribed value that corresponds to the maximum time count value
"tmax" of the timer "t". In actuality, however, the halfway
decision value A3 is decided through experiments by taking into
consideration such noises that likely enter the circuits and the
focus detecting sensor of the camera.
[0079] At the step S467, a check is made to find if the length of
time of illuminating the object with the auxiliary light has come
to exceed the prescribed value "tmax". If so, the flow proceeds
from the step S467 to step S471. The result of the check at the
step S467 indicates that the P-B signal would not be obtained in a
sufficient amount even by illuminating the object with the
auxiliary light for the prescribed length of time "tmax". Such a
result of check is rarely obtained with the flow of operation
arranged to compare the P-B value with the predetermined value POS
halfway in process of illuminating the object with the auxiliary
light and to stop illuminating according to the result of the
halfway check, as in the third embodiment. However, the step S467
is provided against some unexpected occasion.
[0080] In a case where the flow proceeds to the step S469, a check
is made for the end of the process of accumulation. If the process
is found to be finished thus indicating that the focus detection is
possible, the illumination with the auxiliary light is brought to a
stop, and the flow proceeds to step S470. At the step S470, since
the focus detection is possible, the flow proceeds to the step S500
of FIG. 5. At the step S471, since the focus detection is found to
be impossible, the illumination with the auxiliary light is brought
to a stop, and the flow is allowed to proceed to the step S800 of
FIG. 5 to let the user know that the focus detection is
impossible.
[0081] FIG. 12 shows a case where illumination with the auxiliary
light is stopped halfway as the object of photo-taking is dark and
located at a far distance.
[0082] The camera described here is arranged to have the prescribed
(maximum time) value "tmax" which corresponds to the maximum count
value of the timer "t" set at 160 ms, while the predetermined time
"taban" of comparing the P-B value with the predetermined value POS
is set at 75 ms. The length of time required by the processing
capability of the microcomputer 1 in executing the loop of steps
S464-S465-S467-S464 is set at 5 ms. If the predetermined length of
time "taban" is short, a great energy saving effect can be attained
in the event of stopping the illuminating process halfway, because
the decision can be made while the amount of illuminating light
projected is still small. On the other hand, the results of tests
indicate that, if the time value "taban" is short, the signal
cannot be obtained in sufficient amount for making accurate
decision due to the adverse effect of noises, etc. Therefore, the
predetermined time "taban" should be decided on the basis of
experience in designing the camera according to the purpose for
which the camera is adapted.
[0083] With the auxiliary light projected only for the
predetermined time "taban", which is 75 ms, if the P-B value is
found at the step S464 to be less than the predetermined value POS,
the flow proceeds to the step S465. Then, since t=taban, the flow
proceeds from the step S465 to the step S466. At the step S466,
with a value obtained by dividing the P-B signal by the value "t"
(3) found to be less the halfway decision value A3, it is judged
that the P-B signal would not reach the value POS even if the
illumination with the auxiliary light is allowed to continue
further for the maximum time "tmax". The focus detection is thus
decided to be impossible, and the flow proceeds to the step S471 to
stop illuminating the object with the auxiliary light any further.
In this instance, however, the illumination with the auxiliary
light is terminated after the lapse of time "t=80 ms" by taking
into consideration the arithmetic operation time required by the
processing capability of the microcomputer 1.
[0084] According to the arrangement of each of the embodiments
described above, the process of illuminating the object with the
auxiliary light can be brought to an end halfway of the process
when the illumination with the auxiliary light is found to be not
effective. Therefore, in cases where focus detection is impossible,
waste of energy due to ineffective and useless illumination with
the auxiliary light can be minimized. The battery energy capacity
required for a portable apparatus such as a camera arranged to be
driven with a battery, therefore, can be lessened for reduction in
size of the apparatus.
[0085] It is another advantage of the invention that, since the
flash auxiliary light is annoyingly perceivable by human eyes and
thus gives a disagreeable impression to people around the camera,
the minimization of use of the flash auxiliary light enhances the
quality of the camera or the like.
[0086] (Modification Examples)
[0087] In each of the embodiments described above, the invention is
applied by way of example to the focus detecting device for a
camera. However, the invention is applicable also to focus
detecting devices for apparatuses other than cameras.
[0088] Further, while the focus detecting device in each embodiment
has been described as arranged to have one AF (automatic focusing)
point, the invention is likewise applicable to a focus detecting
device having a plurality of AF points.
[0089] Further, while, in each of the embodiments described above,
the built-in flash device 26 or the built-in auxiliary light
projecting lamp 28 is used as an auxiliary light means, an
externally-attached flash device or an externally-attached
auxiliary light projecting lamp may be used.
[0090] According to the arrangement of each of the first, second
and third embodiments of the invention described above, a focus
detecting device or a focus detecting device for a camera can be
arranged to bring the process of illuminating the object with the
auxiliary light to a stop halfway of the process in cases where the
amount of reflection light obtainable by illuminating the object
with the auxiliary light is small, or where the contrast of the
object is too low for focus detection, so that waste of energy by
the ineffective use of auxiliary light can be minimized.
* * * * *