Title: Electronic image pick-up apparatus and method of adjusting the focal position thereof
Abstract: An electronic image pick-up apparatus acquires auto-focus data from each of an AF sensor module and an image sensor disposed in conjugate positions in a test mode, stores data on any relative deviation between those items of auto-focus data and drives a photographic lens based on the data of relative deviation of auto-focus in a normal mode.
Patent Number: 6,954,233 Issued on 10/11/2005 to Ito
| Inventors:
|
Ito; Junichi (Hachioji, JP)
|
| Assignee:
|
Olympus Optical (Tokyo, JP)
|
| Appl. No.:
|
547810 |
| Filed:
|
April 11, 2000 |
Foreign Application Priority Data
| Apr 12, 1999[JP] | 11-104486 |
| Current U.S. Class: |
348/350; 348/353 |
| Intern'l Class: |
H04N 005/23.2 |
| Field of Search: |
348/345,349,350,353,188,211.4,211.99,187
250/201.1,201.4,201.7
356/125
346/111,119,133
|
References Cited [Referenced By]
U.S. Patent Documents
Primary Examiner: Garber; Wendy R.
Assistant Examiner: Henn; Timothy J.
Attorney, Agent or Firm: Frishauf, Holtz, Goodman & Chick, P.C.
Claims
1. An electronic camera for electronic photography utilizing an image pick-up
device, comprising:
a focus detection sensor for photoelectrically converting a pair of images of
an object formed by a pair of beams of light which have passed through a photographing
lens respectively;
a first focus detection circuit for measuring an interval between the images
of the object based on an output of the focus detection sensor and for outputting
first information on the state of focusing of the photographing lens based on the interval;
a second focus detection circuit for measuring a peak position of contrast values
of the images of the object from image data output by the image pick-up device
and for outputting second information on the measured state of focusing of the
photographing lens based on the peak position of the contrast values;
an arithmetic circuit for calculating a control parameter for correcting any
relative deviation of the focal position of the photographing lens based on the
first and second information;
a mode setting circuit for setting a normal mode for performing an AF operation
based on a phase difference calculation and a normal electronic photographic operation
using the first focus detection circuit and a test mode for adjusting the focal
position of the image pick-up device using the first focus detection circuit and
the second focus detection circuit; and
a control circuit for controlling the first focus detection circuit and the second
focus detection circuit when the test mode is set by the mode setting circuit and
for controlling only the first focus detection circuit when the normal mode is
set by the mode setting circuit.
2. An electronic camera according to claim 1, wherein the mode setting of the
mode setting circuit is determined according to a communication request from an
external controller provided externally to said electronic camera.
3. An electronic camera according to claim 1, wherein the control parameter is
an interval between images of an object which serves as a reference for calculation
of an amount of defocus.
4. An electronic camera according to claim 1, wherein the control parameter is
a deviation for correcting a driving amount of the photographing lens based on
a calculated amount of defocus.
5. A method for adjusting the focal position of a image pick-up device in an
electronic camera for electronic photography utilizing an image pick-up device,
comprising the steps of:
a first focus detecting step including measuring an interval between images of
an object formed by a pair of beams of light which have been split after passing
through a photographic lens and outputting first information on the measured state
of focusing of the photographic lens based on the interval;
a second focus detecting step including measuring a peak position of contrast
values of images of the object from image data output by the image pick-up device
and outputting second information on the measured state of focusing of the photographic
lens based on the peak position of the contrast values;
adjusting the focal position of the image pick-up device based on the first and
second information;
setting a normal mode for a normal electronic photographic and a test mode; and
controlling the first focus detecting step and the second focus detecting step
when the test mode is set at the mode setting step and controlling only the first
focus detecting step when the normal mode is set at the mode setting step.
6. A method for adjusting the focal position of an image pick-up device of an
electronic camera according to claim 5, further comprising the step of:
calculating a first defocus amount based on an interval between images of an
object obtained by AF based on phase difference calculation during the first focus
detecting step and an interval stored in a storage circuit when the normal mode
is set at the mode setting step.
7. A method for adjusting the focal position of an image pick-up device in an
electronic camera for electronic photography utilizing an image pick-up device
according to claim 5, further comprising the step of:
calculating a second defocus amount based on an interval between images of an
object obtained by AF based on phase difference calculation during said first focus
detecting step and an interval between images of an object resulting from the design
when the normal mode is set at the mode setting step.
8. An electronic camera for electronic photography utilizing an image pick-up
device, comprising:
a focus detection sensor for photoelectrically converting a pair of images of
an object formed by a pair of beams of light which have passed through a photographing
lens respectively;
a first focus detection circuit for measuring an interval between the images
of the object based on an output of the focus detection sensor formed by a pair
of beams of light which have been split after passing through a photographing lens
and for outputting first information on the measured state of focusing of the photographing
lens based on the interval;
a second focus detection circuit for measuring a peak position of contrast values
of images of the object from image data output by the image pick-up device and
for outputting second information on the measured state of focusing of the photographing
lens based on the peak position of the contrast values;
a mode setting circuit for setting a normal mode and a test mode;
an arithmetic circuit for calculating an interval between images of an object
which services as a reference for calculation of an amount of defocus or a deviation
or correcting a driving amount for the photographing lens based on the calculated
amount of defocus, as
a control parameter for correcting any relative deviation of the focal position
of the photographing lens based on the first and second information when the test
mode is set by the mode setting circuit;
a storage circuit for storing the interval or the deviation;
a control circuit for driving the photographing lens to the focal position based
on the control parameter calculated by the arithmetic circuit when the normal mode
is set by the mode setting circuit; and
a first defocus amount calculation circuit for calculating a first defocus amount
based on an interval between images of an object obtained by AF based on phase
difference calculation using the first focus detection circuit and the interval
stored in the storage circuit when the normal mode is set by the mode setting circuit.
9. An electronic camera according to claim 8, further comprising:
a second defocus amount calculation circuit for calculating a second defocus
amount based on an interval between images of an object obtained by AF based on
phase difference calculation type using the first focus detection circuit and an
interval between images of an object resulting from the design.
10. An electronic camera according to claim 9, further comprising:
a correction circuit for correcting a driving amount of the photographic lens
based on the second defocus amount calculated by the second defocus amount calculation
circuit by adding the deviation stored in said storage circuit.
11. A focal position adjusting system for adjusting the focal position of an
image pick-up device, comprising:
an electronic image pick-up apparatus for electronic photography utilizing an
image pick-up device including a first focus detection circuit for measuring an
interval between images of an object formed by a pair of beams of light which have
been split after passing through a photographic lens and for outputting first information
on the state of focusing of the photographic lens based on the measured interval,
a second focus detection circuit for measuring contrast values of images of the
object from image data output by the image pick-up device and for outputting second
information on the state of focusing of the photographic lens based on the measured
contrast values, a mode setting circuit for setting a normal mode and a test mode,
an arithmetic circuit for calculating a control parameter for correcting any relative
deviation of the focal position of said photographic lens based on said first and
second information when the test mode is set by the mode setting circuit and a
control circuit for driving the photographic lens to the focal position based on
the control parameter calculated by the arithmetic circuit when the normal mode
is set by the mode setting circuit;
a first chart used for the measurement of the interval with said first focus
detection circuit when the test mode is set by the mode setting circuit and a second
chart used for the measurement of the contrast values with the second focus detection
circuit; and
an external controller connected to the electronic image pick-up apparatus.
12. A focal position adjusting system according to claim 11, wherein the external
controller controls switching between the first chart and the second chart and
makes a communication request to the electronic image pick-up apparatus to determine
the mode setting with the mode setting circuit.
13. A method for adjusting the focal position of an image pick-up device of an
electronic camera for electronic photography, utilizing an image pick-up device
according to claim 11, further comprising the step of:
correcting a driving amount of the photographic lens based on the second defocus
amount calculated during said second defocus amount calculation step by adding
a deviation stored in a storage circuit.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electronic image pick-up apparatus which
performs photographic operations utilizing a solid-state image pick-up device.
2. Related Art Statement
In general, TTL phase difference type focus detection methods have been used
for
single-lens reflex cameras capable of photographing utilizing silver salt films.
However, it is difficult to match a focal position detected by such a phase differential
method with an actual film surface. This is attributable to various factors including
errors that occur when a phase difference type sensor module is attached to a camera
body and dimensional errors of an optical system that makes up the sensor module.
In general, steps for manufacturing a camera include an operation of adjusting
any deviation between a focal position detected using a phase differential method
and a film surface. Such an adjusting operation is carried out during a step provided
near the final step for manufacturing a camera, and adjustment of the photographic
lens is first carried out using an automatic collimator such that an image of an
object at a predetermined distance is formed on a film surface. Next, a phase difference
type focus detecting operation is performed in this state to determine parameters
required for correcting the above-described deviation.
Specifically, rays from an object located equivalently at infinity
are projected upon the photographic lens using the automatic collimator, and a
sensor is temporarily provided to detect the contrast of an image formed by the
photographic lens on the film surface of the camera. The photographic lens is then
retracted to the extremity, and the position of the maximum contrast is thereafter
detected from the sensor output while protruding the photographic lens to use the
amount of protrusion at this time as infinity position information.
In a single-lens reflex camera utilizing a silver salt film, adjustment using
an automatic collimator as described above can be easily carried out because the
exposed surface of the film is exposed by opening the rear cover.
However, an electronic camera has no rear cover because it is loaded with
no film. Therefore, the sensor for detecting contrast can not be temporarily attached.
Further, since an image pick-up device such as a CCD is provided in the
position corresponding to the film surface, it is difficult to perform the adjusting
operation using an automatic collimator.
It has been therefore necessary to perform an adjustment as described above using
a different method in a camera system like an electronic camera in which a surface
corresponding to a film surface is not exposed.
SUMMARY OF THE INVENTION
It is a first object of the invention to provide an electronic image pick-up
apparatus
in which the adjustment of the focal position of the image pick-up can be accurately
and simply carried out.
It is a second object of the invention to provide an electronic image pick-up
apparatus for which a step for adjusting the focal position of the image pick-up
device can be simplified because the adjustment does not involve removal of the
image pick-up device.
It is a third object of the invention to provide an electronic image pick-up
apparatus
in which the adjustment of the focal position can be carried out without any special
device therefor.
It is a fourth object of the invention to provide an electronic image pick-up
apparatus in which the focal position and a photographic surface can be matched
more accurately.
Briefly, an electronic image pick-up apparatus according to the invention includes:
- first focus detection means for photoelectrically converting a pair
of images formed by a pair of respective rays which have passed through a photographic
lens and for detecting an interval between the pair of images to output first auto-focus
data associated with the focal condition of the photographic lens;
- second focus detection means for outputting an image signal obtained
by photoelectrically converting the images formed by rays which have passed through
the photographic lens and for evaluating contrast of the image signal to output
second auto-focus data associated with the focal condition of the photographic lens;
- mode setting means for setting a normal mode and a test mode; and
- control means for controlling the first and second focus detection means
to store data on relative deviation between the first and second auto-focus data
in the test mode and for driving the photographic lens based on the first auto-focus
data and the stored data on relative deviation.
The objects and advantages of the present invention will become further apparent
from the following detailed explanation.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram showing a configuration of an electronic camera which
is a first embodiment of the invention.
FIG. 2 is a perspective view of major parts of a photographic lens and a lens
driving mechanism of the electronic camera of the first embodiment of the invention.
FIG. 3 is a sectional view of major parts of the photographic lens, the lens
driving mechanism and a camera body of the electronic camera of the first embodiment
of the invention.
FIG. 4 is an exploded perspective view of a major part of an AF sensor module
of the electronic camera of the first embodiment of the invention showing a configuration
of the same.
FIG. 5 is a flow chart showing a main routine executed by a system controller
of the electronic camera of the first embodiment of the invention.
FIG. 6 is a flow chart showing a first portion of a subroutine "test mode" of
the electronic camera of the first embodiment of the invention.
FIG. 7 is a flow chart showing the remaining portion of the remaining portion
of the subroutine "test mode" of the electronic camera of the first embodiment
of the invention.
FIG. 8 is an illustration of an image pick-up device of the electronic camera
of the first embodiment of the invention and pixel areas whose contrast is calculated.
FIG. 9 is a graph showing an example of a plot of contrast values obtained from
the output of the image pick-up device of the electronic camera of the first embodiment
wherein the number of operations is plotted on the horizontal axis and the contrast
values are plotted on the vertical axis.
FIG. 10 is an illustration of a method for approximating a maximum contrast
value in the third focus area shown in FIG. 10.
FIGS. 11A, 11B and 11C are of a principle behind the detection
of a defocus amount.
FIG. 12 is another illustration of a principle behind the detection of a defocus amount.
FIG. 13 is an illustration of an example of the execution of a reference image
interval measuring mode in the electronic camera of the first embodiment of the invention.
FIG. 14 is a flow chart showing a method for matching a focal position and a
photographic surface in an electronic camera according to a second embodiment of
the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Preferred embodiments of the present invention will now be described with
reference to the drawings.
FIG. 1 is a block diagram showing a configuration of an electronic camera which
is a first embodiment of the invention.
Referring to FIG. 1, in an electronic camera
100 of the present
embodiment, rays of photographic light from an object image (not shown) are guided
to a quick return mirror
3 rotatable in the direction of the arrow in the
figure through a photographic lens
1 and a diaphragm
2 which is exposure
means for adjusting the quantity of light. A half mirror is defined in a central
region of the quick return mirror
3 to transmit a part of the rays when
the quick return mirror
3 is directed downward. The transmitted rays are
reflected by a secondary mirror
4 provided on the quick return mirror
3
to be guided to an AF sensor module
5.
Rays of photographic light reflected by the quick return mirror
3 travel
to an eye of the photographer through a penta-prism
6 and an eyepiece
7.
When the quick return mirror
3 is directed upward, rays from the photographic
lens
1 travel through a filter
9 and a focal plane shutter
10
which is a mechanical shutter to reach an image sensor
11 as an image pick-up
device which is typically a CCD. The filter
9 has two functions, i.e., a
function of guiding only visible rays of light to the image sensor
11 by
cutting infrared and another function as an optical low-pass filter. The focal
plane shutter
10 has front and rear screens and serves as shading means
for controlling transmission and shading of rays from the photographic lens
1.
The secondary mirror
4 is folded when the quick return mirror
3
is directed upward.
The electronic camera
100 of the present embodiment has a system controller
15 constituted by a CPU for controlling the electronic camera as a whole
and appropriately controls the operation of each part to be described later.
Connected to the system controller
15 are a lens control circuit
39 for controlling a lens driving mechanism
16 which moves the photographic
lens
1 in the direction of the optical axis thereof for focusing, a stop
driving mechanism
17 for driving the diaphragm
2, a mirror driving
mechanism
18 for driving the quick return mirror
3 upward and downward,
a shutter charge mechanism
19 for controlling a shutter charge of the focal
plane shutter
10, a shutter control circuit
20 for controlling the
travel of the front and rear screens of the focal plane shutter
10, a photometric
circuit
22 connected to a photometric sensor disposed in the vicinity of
the eyepiece
7, a line-of-sight detection circuit
21 connected to
a line-of-sight detecting portion
8 provided in the vicinity of the eyepiece
7 for detecting the line of sight of a photographer
300, an EEPROM
23 for storing parameters which must be adjusted in order to control the
electronic camera
100 and the like.
The electronic camera
100 can be connected to an external controller
200
which is typically a personal computer (PC), and the personal computer
200
and the system controller
15 can communicate with each other through a communication
interface circuit
40.
The photometric sensor connected to the photometric circuit
22 is a sensor
for measuring the luminance of an object which is not shown, and the output of
the same is supplied to the system controller
15 through the photometric
circuit
22.
The line-of-sight detection circuit
21 receives information from the line-of-sight
detecting portion
8 for detecting the line-of-sight of the photographer
300 and transmits the result of detection to the system controller
15.
The system controller
15 selects a particular area from among a plurality
of focus areas based on the result of detection.
The system controller
15 controls the lens driving mechanism
16
to form an image of the object on the image sensor
11. The system controller
15 further controls the stop driving mechanism
17 for driving the
diaphragm
2 based on a preset Av value and outputs a control signal to the
shutter control circuit
20 based on a preset Tv value.
Driving sources for the front and rear screens of the focal plane shutter
10 are constituted by springs, and a spring charge is required for an operation
following a shutter movement. The shutter charge mechanism
19 controls this
spring charge.
An image data controller
25 is connected to the system controller
15.
The image data controller
25 is correction data sampling means and correction
means constituted by a DSP (digital signal processor) for controlling the image
sensor
11 and correcting and processing image data input from the image
sensor
11 based on instructions from the system controller
15.
Connected to the image data controller
25 are a timing pulse generation
circuit
27 for outputting a pulse signal required for driving the image
sensor
11, an A-D converter
28 for receiving a timing pulse generated
by the timing pulse generation circuit
27 along with the output of the image
sensor
11 and for converting an analog signal associated with an object
image output by the image sensor
11 into a digital signal, a DRAM
29
for temporarily storing the resultant image data (digital data), a D-A converter
30 and an image compression circuit
31.
The DRAM
29 is used as storage means for temporarily storing image data
before it is processed or subjected to data conversion into a predetermined format.
An image display circuit
32 is connected to the D-A converter
30
through an encoder circuit
31. Further, an image data recording medium
34
is connected to the image compression circuit
33.
The image display circuit
32 is a circuit for displaying image data obtained
by the image sensor
11 and is generally constituted by a color liquid crystal
display device.
The image data controller
25 causes the D-A converter
30 to convert
the image data in the DRAM
29 into an analog signal which is in turn output
to the encoder circuit
31. The encoder circuit
31 converts the output
of the D-A converter
30 into a video signal (e.g., an NTSC signal) required
for driving the image display circuit
32.
The image compression circuit
33 is a circuit for performing compression
and conversion (e.g., JPEG) of the image data stored in the DRAM
29. The
converted image data are stored in the image data recording medium
34. A
hard disk, flash memory, floppy disk or the like is used as the recording medium.
Further, an operation display circuit
36 for displaying information
of the operation mode of the electronic camera and exposure information (shutter
time in seconds, stop value and the like) and a multiplicity of operation switches
37 operated by a user to cause the electronic camera to perform desired
operations are connected to the system controller
15.
A detailed description will be made with reference to FIGS. 2 and 3 on the photographic
lens
1 and lens driving mechanism
16.
FIG. 2 is an external perspective view of major parts of the photographic lens
and lens driving mechanism of the electronic camera of the first embodiment of
the invention. FIG. 3 is a sectional view showing parts of the photographic lens,
lens driving mechanism and camera body of the electronic camera.
As shown in FIG. 2, the photographic lens
1 is held in a focusing frame
52, and a focusing frame gear
53 is disposed integrally with one
end of the focusing frame
52 and is engaged with a power transmission mechanism
46 to be described later. Further, a helicoid
54 is formed at the
periphery of the focusing frame
52.
The lens driving mechanism
16 for driving the photographic lens
1
is formed by a motor
41 which is a driving source, a power transmission
mechanism
46 constituted by a pinion gear
42 provided on an output
shaft of the motor
41 and gears
43,
44 and
45 which
are sequentially engaged with the same, a rotary slit
47 disposed coaxially
with the gear
43 and rotated at the same speed and a photo-interrupter
48
for the rotary slit
47.
The final stage of the power transmission mechanism
46 is engaged with
the focusing frame gear
53. Therefore, the rotary force of the motor
41
is transmitted to the focusing frame gear
53 through the power transmission
mechanism
46 to rotate the focusing frame
52.
Pulse signals output by the photo-interrupter
48 are input to the system
controller
15 through the lens control circuit
39, and the system
controller
15 counts the pulse signals to detect the amount of protrusion
of the photographic lens
1.
As shown in FIG. 3, the photographic lens
1 (focusing frame
52)
and lens driving mechanism
16 are disposed in a mirror frame
56 which
is integrally secured to a part
55 of the camera body. A fixed frame
57
is secured to the forward end of the mirror frame
56 at a flange portion
thereof. A helicoid
57a is formed on an inner circumferential surface
of a frame portion of the fixed frame
57 to be engaged with the helicoid
54 provided on the focusing frame
52.
While the focusing frame
52 is thus engaged with the fixed frame
57
and is included in the mirror frame
56, the lens driving mechanism
16,
i.e., the motor
41, power transmission mechanism
46 and the like
are disposed in a space defined between the focusing frame
52 and mirror
frame
56.
With such configurations of the focusing frame
52 and lens driving mechanism
16, when the motor
41 rotates CCW in response to a CCW direction
signal (originating from an instruction of the system controller
1), the
focusing frame
52 moves such that it protrudes from the fixed frame
57.
The protruding movement can continue until a rear end
53b of the
focusing frame gear
53 abuts a rear end face
57b of the fixed
frame
57.
When the motor rotates CW in response to a CW direction signal, the focusing
frame
52 moves such that it is retracted into the fixed frame
57.
The retracting movement can continue until a rear end face
53a of
the focusing gear frame
53 abuts a part
55a of the camera body.
A detailed description will now be made on the AF sensor module
5 with
reference
to FIG. 4.
As shown in FIG. 4, a major part of the AF sensor module
5 is formed by
a field mask
62, a group of condenser lenses
64, a group of separator
lenses
65, a stop mask
63, a group of line sensors
66 and
the like. It is a sensor for dividing rays from objects
61a through
61c with eye-division optical systems associated with focus areas
FA
1, FA
2 and FA
3 and for forming images of the same on the
group of line sensors
66 which are one-dimensional CCDs to perform focus
detection according to the phase differential method.
Specifically, object rays in the focus areas FA
1, FA
2
and FA
3 in a photographed area
61 associated with objects
61a,
61b and
61c are transmitted by the photographic lens
1, passed through the field mask
62 which eliminates stray rays,
and incident upon respective ones of the group of condenser lenses
64 (condenser
lenses CL
1, CL
2 and CL
3).
The object rays are projected by the group of condenser lenses
64 upon
respective open eye positions of the stop mask
63. The group of paired separator
lenses
65 (separator lenses SL
1a/SL
1b, SL
2a/SL
2b
and SL
3a/SL
3b) are disposed at the openings of
the stop mask
63. Rays from exit eyes of the photographic lens
1
defined by the condenser lenses CL
1 through CL
3 and the openings
of the stop mask
63 are projected by the respective separator lenses SL
1a/SL
1b,
SL
2a/SL
2b and SL
3a/SL
3b upon
respective line sensors S
1, S
2 and S
3 of the group of line
sensors
66 to form images thereon.
Each of the line sensors S
1 through S
3 is constituted by a pair
of groups, i.e., groups a and b, and two images formed by a pair of separator lenses
are projected upon sensors for respective images. By detecting an interval between
the pair of images on each of the line sensors S
1 through S
3, the
amounts of defocus (i.e., deviations from the focal position of the photographic
lens) of the objects
61a through
61c in the focus areas
FA
1 through FA
3 associated with the sensors relative to the film
surface can be found. The amounts of defocus can be obtained according to a publicly
known phase differential calculation.
The output ends of the line sensors S
1 through S
3 are connected
to the system controller
15. Referring to the supply of the output of the
line sensors S
1 through S
3, the output is first input to an interface
circuit in the focus detection circuit
38. The output is then integrated
by a line sensor control circuit provided in the interface circuit. When the output
of integration reaches an adequate level, it is converted by an A-D converter into
a digital value which is in turn transferred to the system controller
15.
A main routine executed by the system controller
15 will now be described
with reference to FIG. 5.
When a power switch which is one of the operation switches
37 is turned
on, power is supplied to the system to cause the system controller
15 to
start operating. The system controller
15 first performs initialization
(step S
100). Specifically, operations are performed including initialization
of memories, I/O ports and each circuit connected to the system controller
1
(CPU) and activation of the image data controller
25 (DSP).
Next, at step S
101, the system controller
15 determines whether
there is any communication request from the external controller (personal computer)
200 through the communication interface circuit
40. If there is a
communication request, the process proceeds to step S
102 at which a subroutine
"test mode" is executed. If there is no communication request, the process proceeds
to step S
103.
The test mode includes an adjusting operation required for the steps for manufacturing
the camera and an operation of reading image data stored by a user in the camera.
At step S
103, information on the luminance of an object is input to the
system controller
15 from the photometric circuit
22. Based on the
luminance information, it determines the shutter time that represents the integration
time of the image sensor
11 (CDC) and a preset stop value. At step S
104,
it outputs data indicating the operating condition of the camera, the shutter time
and the preset stop value to the operation display circuit
36.
At step S
105, the system controller
15 detects the state of a release
switch which is one of the operation switches
37. The process proceeds to
step S
108 if the switch is on and proceeds to step S
106 if it is off.
At step
106, the system controller
15 detects the state of the
power
switch. If the power switch is off, the system operation must be terminated. Therefore,
the process proceeds from step S
106 to step S
107 where a process
for system termination is carried out, and the system controller
15 thereafter
stops operating. If the power switch is on, the process proceeds to step S
103
from which the camera operation is continued.
When the process proceeds from step S
105 to step S
108, the system
controller
15 selects one of the three focus areas (FA
1, FA
2
and FA
3 in FIG. 4) based on the output of the line-of-sight detection circuit
21. At step S
109, it instructs the focus detection circuit
38
to integrate the line sensors
66 associated with the selected area.
At step S
110, the system controller
15 waits for the completion
of the integration of the selected line sensors
66.
When the integration of the line sensors
66 is completed, the focus detection
circuit
38 performs A-D conversion of the output of each of elements that
make up the line sensors
66 and outputs the result to the system controller
15. The data obtained by the conversion are input to the system controller
15 at step S
111.
At step S
112, the system controller
15 calculates the distance
between
two images formed on the line sensors
66 by a pair of separator lenses
65
(image interval). The calculation is carried out using a known method which will
not be described here.
At step S
113, the system controller
15 reads a reference image
interval
from the EEPROM
23. The reference image interval is the distance between
two images formed on the line sensors
66 when an image of an object is formed
on the image pick-up device by the photographic lens
1. This image interval
is measured in the subroutine "test mode".
Thereafter, at step S
114, the system controller
15 calculates
a defocus amount from the difference between the current image interval obtained
at step S
112 and the reference image interval.
Table 1 shows reference image intervals stored in the EEPROM
23.
| |
TABLE 1 |
| |
|
| |
Focus Area |
Reference Image Interval |
| |
|
| |
| |
FA1 |
67.50 |
(elements) |
| |
FA2 |
70.20 |
| |
FA3 |
68.90 |
| |
|
In the present embodiment, a reference image interval is stored for each of the
three focus areas (FA
1, FA
2 and FA
3) in particular addresses
defined on the EEPROM
23. The best imaging point varies depending on the
position of focus detection because of the astigmatism of the photographic lens
1. Therefore, a reference image interval must be stored for each of the
three focus areas.
While the electronic camera of the present embodiment employs a single-focus
lens, the astigmatism changes depending on the focal length when a zoom lens is
used. In such a case, reference image intervals in accordance with focal lengths
are stored.
A principle behind the detection of a defocus amount will now be described with
reference to FIGS. 11 and 12.
As illustrated, the image interval on the line sensors have a certain value when
the image pick-up device is in focus. Such a value can be determined during designing.
In practice, the design value may not be achieved because of dimensional variation
of parts and assembly-related errors. In practice, it is therefore difficult to
identify the image interval (reference image interval Lo) without performing measurement.
As apparent from FIG. 11, an image interval smaller than the reference image interval
Lo indicates a front-focus, and an image interval greater than the reference image
interval indicates a back-focus.
FIG. 12 illustrates a model in which the condenser lenses are deleted from the
optical system of the AF sensor module
5.
As illustrated, a defocus amount L can be expressed by the following expression:
where θ represents the angle of the principal ray; β represents
the magnification of the separator lenses; ΔL and ΔL′ represent
amounts of movement of images; and β tan θ is a parameter which is
determined when the AF sensor module
5 is designed.
ΔL′ can be identified from the reference image interval
Lo and the current image interval Lt.
Referring again to FIG. 5, at step S
115, the system controller
15
determines whether focusing has been properly achieved or not from the defocus
amount thus identified. If it determines that focusing has been achieved, the process
proceeds to step S
116.
At step S
116, the image pick-up device is integrated according to conditions
determined at step S
103 to fetch the image data. The image data are converted
into a predetermined format and are thereafter stored in the image data recording medium.
When it is determined at step S
115 that focusing has not been achieved,
the process proceeds to step S
117. At step S
117, the defocus amount
is converted into a lens driving amount (Px: the number of pulses of the photo-interrupter).
The process proceeds from step S
118 to step S
119 in the front-focus
state to rotate the motor
41 CW. As a result, the photographic lens
1
is retracted. The driving of the photographic lens
1 is continued until
the counted number of pulses generated by the photo-interrupter
48 reaches Px.
When the counted number reaches Px, the system controller
15 proceeds
from step S
121 to step S
122 where it brakes the motor
41 to
stop the movement of the photographic lens
1. It proceeds to step S
109
to perform the focus detecting operation again.
When the defocusing direction represents a back-focus state, the system controller
15 proceeds from step S
118 to step S
120 to drive the photographic
lens
1 in the protruding direction.
The subroutine "test mode" will now be described with reference to FIGS. 6 and
7. The following description of an operation will be made basically on an assumption
that the operation is performed by the system controller
15.
At step S
200, data indicating an operation mode is input to the system
controller
15 from the external controller
200. It is determined
at step S
201 whether the operation mode is a reference image interval measurement
mode. If it is the reference image interval measurement mode, the process proceeds
to step S
203 and, if not, the process proceeds to step S
202. When
the reference image interval measurement mode is executed, the electronic camera
100 is secured in advance to a bench as shown in FIG. 13. Black and white
stripes are used as the chart (A) in FIG. 13. The pitch P of the stripes and the
distance M from the electronic camera
100 to the chart are set at appropriate
values taking the resolution of the photographic lens
1 and the pitch of
the pixels forming the image pick-up device into consideration.
At step S
203, the system controller
15 clears an operation counter.
At step S
204, it outputs a driving signal to cause the motor
41 to
rotate CW to the lens control circuit
39. As a result, the focusing frame
52 starts moving in the retracting direction.
The motor
41 continues rotating until a part
53a of the
focusing frame gear
53 abuts the part
55a of the camera body,
and the photo-interrupter
48 continues outputting the pulse signals as long
as the motor
41 rotates. Thereafter, the pulse signals disappear when the
part
53a of the focusing frame gear
53 abuts the part
55a
of the camera body to stop the motor
41.
At step S
205, the system controller
15 detects the pulse signals
and stands by until the pulse signals disappear. When the pulse signals disappear,
it proceeds from step S
205 to step S
206 to output a brake signal
to the lens control circuit
39. This stops the motor
41. At this
time, the focusing frame gear
52 is stopped in the position of maximum retraction.
Further, the system controller
15 drives the quick return mirror
3 upward at step S
207 in order to guide rays from the photographic
lens
1 to the image sensor
11.
At step S
208, the system controller
15 drives the diaphragm
2
to a predetermined position. At this time, the diaphragm
2 is driven to
a value at which the detection of maximum contrast is likely to occur at the image
sensor
11. In general, a value that results in the maximum opening of the
diaphragm
2 may be employed, although such a value of opening does not necessarily
provide the best result.
At step S
209, the system controller
15 controls each part such
that
the focal plane shutter
10 is opened. At step S
210, it instructs
the image data controller
25 (DSP) to perform an operation of integrating
the line sensors
66. At step S
2101, it stands by for a predetermined
time. When the integration time passes, the process proceeds to step S
211
where the focal plane shutter
10 is closed.
At step S
212, the system controller
15 charges the focal plane
shutter
10 in preparation for the next operation. At step S
213, it instructs
the image data controller
25 to fetch image data from the image sensor
11.
At step S
214, information on the positions of focus areas is output to the
image data controller
25.
The image data controller
25 calculates contrast values from image data
associated with the three focus areas and stores them in the DRAM
29 through
the system controller
15.
FIG. 8 is an illustration showing the positional relationship between the image
sensor
11 and pixel areas where contrast calculation is to be carried out.
For example, contrast calculation is carried out according to the following expression.
##EQU1##
where Sadd represents the address of the memory in which the starting pixel
data of an area to be calculated is stored; Eadd represents the address of the
memory in which the pixel data at the end of the area to be calculated is stored;
and Xn represents the output value of each of the pixels that make up the image
sensor
11.
When contrast calculation in the image data controller
25 is completed,
the system controller
15 determines whether the count value in the operation
counter has reached a predetermined number of times (Nx) at step S
215. If
the value in the operation counter is not Nx, the process proceeds from step S
215
to step S
216.
At step S
216, the system controller
15 increments the operation
counter. At step S
217, it outputs a driving signal to the lens control circuit
39 to rotate the motor
41 CCW. This causes the focusing frame
52
to start moving in the protruding direction.
At step S
218, the system controller
15 stands by until the number
of the pulse signals generated by the photo-interrupter
48 equals a predetermined
value PΔ. When the pulse count value reaches PΔ, the process proceeds
from step S
218 to step S
219. At step S
219, the motor
41
is braked to stop the movement of the photographic lens
1. The process then
proceeds to step S
209 to calculate contrast from the output value of the
image sensor
11 again.
The operations of calculating contrast and protruding the photographic lens
1
by a predetermined amount are repeated until the number of operations reaches Nx.
When the number of operations reaches Nx, the process proceeds from step S
215
to step S
220. At step S
220, the system controller
15 returns
the diaphragm
2 to the open position.
At step S
221, the system controller
15 returns the quick return
mirror
3 to the downward position. At step S
222, contrast values
calculated based on image data are input from the image data controller
25.
FIG. 9 is a plot of contrast values obtained from the output of the image sensor
11 in which the horizontal axis represents the number of operations and
the vertical axis represents the contrast values.
At step S
223, the system controller
15 finds the operation which
has resulted in the maximum contrast value. The number of operations which has
resulted in the maximum contrast is then multiplied with PΔ. The result of
this calculation is data of the position of peak contrast (Ppeak).
As apparent from FIG. 9, the first focus area FA
1 has the maximum contrast
value at the tenth operation. Let us assume that PΔis 10 pulses. Then, the
peak position data for the first focus area FA
1 is 100 (tenth×10) pulses.
That is, the contrast peaks when the photographic lens
1 is protruded in
an amount corresponding to 100 pulses from the position of the maximum retraction,
and an image of the chart is formed on the image pick-up device.
Peak position data for the second focus area FA
2 can be similarly calculated
at 80 pulses.
In the case of the third focus area FA
3 in which the maximum contrast
value
appears between the ninth and tenth operations, the position of the maximum value
between the ninth and tenth operations can be calculated using the method shown
in FIG. 10. Specifically, the left side of the peak of the contrast curve is linearly
approximated (line 1) using contrast values C
8 and C
9 at the eighth
and ninth operations. Similarly, the right side of the peak of the contrast curve
is linearly approximated (line 2) using C
10 and C
11. Then, the position
of the maximum contrast value can be identified by finding the point of intersection
between the two lines.
If the resultant value is 9.4-th operation, the peak position data for the third
focus area FA
3 is 94 pulses. Peak position data for the three focus areas
can be summarized as shown in Table 2.
| |
TABLE 2 |
| |
|
| |
Focus Area |
Peak Contrast Position |
| |
|
| |
| |
FA1 |
100 |
(pulses) |
| |
FA2 |
80 |
| |
FA3 |
94 |
| |
|
The number (Nx) of contrast detecting operations and the amount (PΔ) of
lens protrusion must be determined in consideration of parameters including the
optical characteristics of the photographic lens
1, the conversion ratio
for the conversion of the speed of the motor
41 into the movement of the
lens
1 and dimensional variations of the frame that supports the photographic
lens
1.
Those parameters can not be fixed uniformly, and unexpected changes may be
required for such parameters. In the present embodiment, the quantities Nx and
PΔ are stored in the EEPROM
23 taking such a situation into consideration.
This makes it possible to set optimum values as required.
The system controller
15 then stands by at step S
2231 until the
personal computer
200 changes the chart. This is because the chart for detecting
the positions of peak contrast is not suitable for focus detection with a phase
difference type AF sensor.
At step S
224, the system controller
15 sets "1" in the selection
counter. The value of the selection counter indicates a focus area.
The operations at subsequent steps S
225 through S
227 are the same
as the operations at steps S
204 through S
206. Specifically, the system
controller
15 moves the photographic lens
1 to the position of maximum
retraction. Peak contrast position data are data measured using the position of
maximum retraction of the photographic lens
1 as a reference. Therefore,
the processes at steps S
225 through S
227 are required to move the
photographic lens
1 to a position of peak contrast (focus position).
At step S
2271, the system controller
15 reads the peak position
data for the focus area corresponding to the value in the selection counter from
a memory in the system controller
15. For example, when the value in the
selection counter is "1", the peak position data (Ppeak) for the first focus area
is read. As shown in Table 2, the Ppeak is "100".
At steps S
228 through S
230, the system controller
15 protrudes
the photographic lens
1 until the counted number of pulses from the photo-interrupter
48 reaches Ppeak. At this time, the object image formed on the region of
the line sensor
66 corresponding to the focus area FA
1 is in focus.
An interval between two images formed on the line sensor
66 of the AF sensor
module
5 at this time must be found.
At step S
231, the system controller
15 instructs the focus detection
circuit
38 to perform integration of the line sensor
66 associated
with the focus area FA
1. At step S
232, it stands by until the integration
of the line sensor
66 is completed. When the integration is completed, the
output of the line sensor
66 is subjected to A-D conversion and then output
to the system controller
15.
The data output by the line sensor
66 are read into the system controller
15 at step S
233. At step S
234, the system controller
15
calculates an image interval associated with the focus area FA
1 from the
data. The image interval data calculated here is reference image interval data
for the focus area FA
1. This data is stored in a predetermined address of
the EEPROM
23 at step S
235.
At step S
236, the system controller
15 determines whether the value
in the selection counter is "3". If it is not "3", the process proceeds to step
S
237 to increment the selection counter. The process then proceeds to step
S
225 to obtain reference image interval data for the next focus area.
When the calculation of reference image interval data for the three focus areas
is completed, the value in the selection counter is "3", and the process returns
from step S
236 to the main routine.
As described above, adjusting steps can be simplified for the electronic camera
according to the first embodiment of the invention because there is no need for
removing the image pick-up device to adjust the focal position of the image pick-up device.
The adjustment is possible without any special device such as an automatic collimator.
That is, accurate adjustment can be achieved even at service centers and the like
having only simple equipment.
A second embodiment of the present invention will now be described.
In the first embodiment, a reference image interval is determined based on the
position of the photographic lens at which images of an object are formed on the
image pick-up device. A design reference image interval is determined when the
AF sensor module
5 is designed. It is therefore possible to calculate an
amount of defocus using the design reference image interval. An amount of lens
movement (number of pulses) can be calculated from the defocus amount to form an
image of the object in a design focal position by moving the lens by the amount.
However, when the image pick-up device is not mounted on the camera body
in accordance with design values, the design focal position can deviate from the
photographic surface of the image pick-up device. In consideration of variation
of accuracy and the like that occur during the manufacture of the AF sensor module
5, measures must be taken further to match the design focal position and
the photographic surface of the image pick-up device with higher accuracy.
An electronic camera according to the second embodiment of the invention has
been
conceived taking such a situation into consideration, and it is possible to match
the design focal position and the photographic surface of the image pick-up device
with higher accuracy.
Since the configuration of the electronic camera of the present embodiment
as represented by the block diagram of FIG. 14 is similar to that of the first
embodiment shown in FIG. 1, no detailed description will be made on the same except
for differences from the first embodiment.
FIG. 14 is a flow chart showing a method for matching the focal position and
photographic surface of the electronic camera of the second embodiment and primarily
showing operations of the system controller
15.
When initialization and the like are carried out similarly to the first embodiment
after the activation of the electronic camera, the system controller
15
determines whether the test mode has been enabled at step S
300. If not,
the process proceeds to step S
320.
At step S
320, the state of the release switch is detected. If the release
switch is on, the process proceeds from step S
320 to step S
321. At
step S
321, the AF sensor module
5 performs integration similarly
to that described above. The operation is controlled by the focus detection circuit
38 under the control of the system controller
15.
When the
