Title: Focal point detection device and camera
Abstract: A camera comprises a spatial modulation optical filter that is disposed in a viewfinder optical system for subject observation at or near a position optically equivalent to an estimated image forming plane of a photographic optical system and modulates a subject light flux entering via the photographic optical system with transmission characteristics to obtain a light flux having a predetermined spatial frequency; a photoelectric conversion device that outputs a signal corresponding to detected light; an optical element that guides the subject light flux having been modulated at the spatial modulation optical filter to the photoelectric conversion device; and a focal adjustment state calculation means that calculates a focal adjustment state of the photographic optical system based upon the signal output from the photoelectric conversion device having received the modulated subject light flux.
Patent Number: 6,975,810 Issued on 12/13/2005 to Iwane
| Inventors:
|
Iwane; Toru (Yokohama, JP)
|
| Assignee:
|
Nikon Corporation (Tokyo, JP)
|
| Appl. No.:
|
808412 |
| Filed:
|
March 25, 2004 |
Foreign Application Priority Data
| Mar 26, 2003[JP] | 2003-086456 |
| Mar 26, 2003[JP] | 2003-086457 |
| Current U.S. Class: |
396/100; 396/111; 396/121; 396/148; 396/271; 348/341; 348/345 |
| Intern'l Class: |
G03B 007/08; G03B 013/36 |
| Field of Search: |
396/100,111,121-123,148,150,152,271
348/341,345
|
References Cited [Referenced By]
U.S. Patent Documents
| 4441798 | Apr., 1984 | Watanabe et al.
| |
| 4488799 | Dec., 1984 | Suzuki et al.
| |
| 6226461 | May., 2001 | Homma et al.
| |
| 6549730 | Apr., 2003 | Hamada.
| |
| 2005/0036779 | Feb., 2005 | Iwane.
| |
| Foreign Patent Documents |
| A 2001-203915 | Jul., 2001 | JP.
| |
Primary Examiner: Perkey; W. B.
Attorney, Agent or Firm: Oliff & Berridge, PLC
Claims
1. A camera comprising:
a spatial modulation optical filter that is disposed in a viewfinder optical
system for subject observation at or near a position optically equivalent to an
estimated image forming plane of a photographic optical system and modulates a
subject light flux entering via the photographic optical system with transmission
characteristics to obtain a light flux having a predetermined spatial frequency;
a photoelectric conversion device that outputs a signal corresponding to detected
light;
an optical element that guides the subject light flux having been modulated at
the spatial modulation optical filter to the photoelectric conversion device; and
a focal adjustment state calculation device that calculates a focal adjustment
state of the photographic optical system based upon the signal output from the
photoelectric conversion device having received the modulated subject light flux.
2. A camera according to claim 1, wherein:
the spatial modulation optical filter modulates a light flux that passes through
at least one of a plurality of divided areas within a photographic image plane
defined by the photographic optical system.
3. A camera according to claim 1, further comprising:
a plurality of the spatial modulation optical filters being disposed along an
optical axis of the photographic optical system, and
a light flux modulation control unit that individually controls modulation of
the subject light flux and detection of the modulated light flux at the photoelectric
conversion device in correspondence to each of the spatial modulation optical filters,
wherein:
the focal adjustment state calculation device calculates the focal adjustment
state of the photographic optical system based upon output signals obtained from
the photoelectric conversion device in correspondence to the individual spatial
modulation optical filters.
4. A camera according to claim 1, wherein:
the focal adjustment state calculation device calculates a light quantity of
the modulated light flux detected at the photoelectric conversion device; and
the camera further comprises:
an autofocus control device that executes a focus operation by moving a focus
lens in the photographic optical system to a target focus position set at a focus
lens position at which the light quantity calculated by the focal adjustment state
calculation device achieves a largest value.
5. A camera according to claim 3, wherein:
the focal adjustment state calculation device calculates a light quantity of
the modulated light flux detected at the photoelectric conversion device; and
the camera further comprises:
an AF calculation unit that calculates a focus lens position at which the light
quantity of the modulated light flux detected at the photoelectric conversion device
achieves the largest value based upon results of a calculation executed by the
focal adjustment state calculation device; and
an autofocus control device that moves a focus lens in the photographic optical
system to the focus lens position calculated by the AF calculation unit.
6. A camera according to claim 3, wherein:
the spatial modulation optical filters are each constituted with a transmission
liquid crystal display panel so as to modulate the subject light flux by using
a display pattern having transmission characteristics with a predetermined spatial
frequency displayed at the liquid crystal display panel.
7. A camera according to claim 6, wherein:
the light flux modulation control unit is capable of implementing control so
as to achieve a first display state in which the display pattern having the transmission
characteristics with the predetermined spatial frequency is displayed and a second
display state in which the subject light flux is allowed to be transmitted; and
the camera further comprises:
a photometric operation unit that executes a photometric operation on the subject
light flux based upon the signal output from the photoelectric conversion device
in the second display state.
8. A camera according to claim 1, wherein:
the spatial frequency at the spatial modulation optical filter is adjustable.
9. A focal point detection device comprising:
a spatial modulation optical filter that is disposed in a viewfinder optical
system for subject observation at or near a position optically equivalent to an
estimated image forming plane of a photographic optical system and can be set in
one of a modulation state in which a subject light flux entering via the photographic
optical system is modulated with transmission characteristics to obtain a light
flux having a predetermined spatial frequency and a transmission state in which
the subject light flux is transmitted through;
a photoelectric conversion device that outputs a signal corresponding to detected
light;
an optical element that guides the subject light flux having been modulated at
the spatial modulation optical filter to a detection surface of the photoelectric
conversion device and guides the subject light flux having been transmitted through
the spatial modulation optical filter to the viewfinder optical system; and
a focal adjustment state calculation device that calculates a focal adjustment
state of the photographic optical system based upon the signal output from the
photoelectric conversion device having received the subject light flux that has
been modulated at the spatial modulation optical filter.
10. A focal point detection device according to claim 9, wherein:
the spatial modulation optical filter modulates a light flux that passes through
at least one of a plurality of divided areas within a photographic image plane
defined by the photographic optical system.
11. A focal point detection device according to claim 9, wherein:
the optical element is an element, optical anisotropic characteristics of which
change in correspondence to an electrical field applied to the element; and
the focal point detection device further comprises:
an optical element control device that controls the electrical field applied
to the optical element so as to guide the subject light flux having been modulated
at the spatial modulation optical filter to the detection surface of the photoelectric
conversion device and to guide the subject light flux having been transmitted through
the spatial modulation optical filter to the viewfinder optical system.
12. A focal point detection device according to claim 9, wherein:
a viewfinder screen of a camera is to be disposed at a position optically equivalent
to the estimated image forming plane of the photographic optical system.
13. A focal point detection device according to claim 11, wherein:
the optical element is a polymer dispersion liquid crystal constituted of an
isotropic polymer and an optically anisotropic liquid crystal achieving refractive
indices substantially equal to each other for refracting the subject light flux
when the electrical field is applied, which includes a diffraction grating having
layers constituted of the isotropic polymer and layers constituted of the liquid
crystal disposed in regular order at least in a focal point detection area; and
the optical element control device controls the electrical field applied to the
diffraction grating so as to guide the subject light flux having been modulated
at the spatial modulation optical filter to the detection surface of the photoelectric
conversion device and to guide the subject light flux having been transmitted through
the spatial modulation optical filter to the viewfinder optical system.
14. A focal point detection device according to claim 13, wherein:
the isotropic polymer layers and the liquid crystal layers that together function
as the diffraction grating are constituted as a hologram formed as a result of
interference occurring between parallel light entering the optical element at a
right angle to the optical element and a light flux radiated from a point light
source provided at a position at which the photoelectric conversion device is to
be located.
15. A focal point detection device comprising:
a photoelectric conversion device that outputs a signal corresponding to a light
quantity of detected light;
a polymer dispersion liquid crystal panel that is disposed in a viewfinder optical
system for subject light flux observation at or near a position optically equivalent
to an estimated image forming plane of a photographic optical system and is constituted
with an isotropic polymer and an optically anisotropic liquid crystal achieving
refractive indices substantially equal to each other for refracting a subject light
flux when an electrical field is applied;
a diffraction grating disposed at least at a focal point detection area of the
polymer dispersion liquid crystal panel, which includes layers constituted of the
isotropic polymer and layers constituted of the liquid crystal disposed in regular
order and condenses the subject light flux entering the focal point detection area
onto the photoelectric conversion device;
a liquid crystal panel control device that forms at the diffraction grating a
diffraction pattern with which the subject light flux entering to the diffraction
pattern is modulated with transmission characteristics to obtain a light flux having
a predetermined spatial frequency by applying an electrical field with a specific
pattern to the diffraction grating; and
a focal adjustment state calculation device that calculates a focal adjustment
state of the photographic optical system based upon the signal output from the
photoelectric conversion device.
16. A focal point detection device according to claim 15, wherein:
the liquid crystal panel control device can be set in one of an application mode
in which the electrical field with the specific pattern is applied to the diffraction
grating and an application OFF mode in which application of the electrical field
to the diffraction grating is stopped; and
the focal point detection device further comprises:
a photometric operation unit that executes a photometric operation on the subject
light flux based upon the signal output from the photoelectric conversion device
in the application OFF mode.
17. A focal point detection device according to claim 15, further comprising:
a spatial modulation optical filter that is disposed further toward a subject
relative to the polymer dispersion liquid crystal panel and can be set in one of
a modulation state in which the subject light flux in the focal point detection
area is modulated with transmission characteristics to obtain a light flux having
a predetermined spatial frequency and a transmission state in which the subject
light flux is transmitted through, wherein:
the liquid crystal panel control device can be set in one of an application mode
in which the electrical field achieving the specific pattern is applied to the
diffraction grating in the transmission state and an application OFF mode in which
application of the electrical field to the diffraction grating is stopped in the
modulation state; and
the focal adjustment state calculation device calculates the focal adjustment
state in the photographic optical system based upon the signal output from the
photoelectric conversion device in the application mode and the signal output from
the photoelectric conversion device in the application OFF mode.
18. A camera comprising:
a spatial modulation optical filter that is disposed in a viewfinder optical
system for subject observation at or near a position optically equivalent to an
estimated image forming plane of a photographic optical system and modulates a
subject light flux entering via the photographic optical system with transmission
characteristics to obtain a light flux having a predetermined spatial frequency;
a photoelectric conversion device that outputs a singal corresponding to detected
light;
an optical element that guides the subject light flux having been modulated at
the spatial modulation filter to the photoelectric conversion device; and
a focal adjustment state calculation means that calculates a focal adjustment
state of the photographic system based upon the signal output from the photoelectric
conversion device having received the modulated subject light flux.
19. A focal point detection device comprising:
a spatial modulation optical filter that is disposed in a viewfinder optical
system for subject observation at or near a position optically equivalent to an
estimated image forming plane of a photographic optical system and can be set in
one of a modulation state in which a subject light flux entering via the photographic
optical system is modulated with transmission characteristics to obtain a light
flux having a predetermined spatial frequency and a transmission state in which
the subject light flux is transmitted through;
a photoelectric conversion device that outputs a signal corresponding to detected
light;
an optical element that guides the subject light flux having been modulated at
the spatial modulation optical filter to a detection surface of the photoelectric
conversion device and guide the subject light flux having been transmitted through
the spatial modulation optical filter to the viewfinder optical system; and
a focal adjustment state calculation means that calculates a focal adjustment
state of the photographic optical system based upon the signal output from the
photoelectric conversion device having received the subject light flux that has
been modulated at the spatial modulation optical fiber.
20. A focal point detection device comprising:
a photoelectric conversion device that outputs a signal corresponding to a light
quantity of detected light;
a polymer dispersion liquid crystal panel that is disposed in a viewfinder optical
system for subject light flux observation at or near a position optically equivalent
to an estimated image forming plane of a photographic optical system and is constituted
with an isotropic polymer and and optically anisotropic liquid crystal achieving
refractive indices substantially equal to each other for refracting a subject light
flux when an electrical field is applied;
a diffraction grating disposed at least at a focal point detection area of the
polymer dispersion liquid crystal panel, which includes layers constituted of the
isotropic polymer and layers constituted of the liquid crystal disposed in regular
order and condenses the subject light flux entering the focal point detection area
onto the photoelectric conversion device;
a liquid crystal panel control means that forms at the diffraction grating a
diffraction pattern with which the subject light flux entering to the diffraction
pattern is modulated with transmission characteristics to obtain a light flux having
a predetermined spatial frequency by applying an electrical field with a specific
pattern to the diffraction grating; and
a focal adjustment state conclusion means that calculates a focal adjustment
state of the photographic optical system based upon the signal output from the
photoelectric conversion device.
Description
INCORPORATION BY REFERENCE
The disclosures of the following priority applications are herein incorporated
by reference:
Japanese Patent Application No. 2003-86456 filed Mar. 26, 2003
Japanese Patent Application No. 2003-86457 filed Mar. 26, 2003
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a focal point detection device adopting a contrast
method and a camera having the focal point detection device.
2. Description of the Related Art
Camera AF (autofocus) systems in the related art include the phase difference
system adopted mostly in single lens reflex cameras, the external light infrared
active system generally adopted in compact cameras and the contrast system adopted
in digital compact cameras. The specific AF system used in a given camera is determined
primarily in correspondence to the camera type.
While an AF operation in a digital compact camera is executed by using image
signals generated at an image-capturing element provided to photograph images,
an image cannot always be obtained at an image-capturing element in a single lens
reflex digital camera having a main mirror disposed to the front of the image-capturing
surface. For this reason, an AF operation is normally executed in the single lens
reflex digital camera in the phase difference method by providing an AF sensor
in addition to the image-capturing element (see, for instance, Japanese Lain Open
Patent Publication No. 2001-203915).
In the phase difference method, the parallax of a light flux passing through
two
virtual pupils set at an objective lens is detected by a light receiving element
such as a CCD and the image plane distance to the focused position and the lens
drive distance are calculated based upon the detection results. For this reason,
the phase difference method has an advantage in that the focal point detection
operation can be executed speedily. In addition, the external light method has
an advantage in that the distance to the subject can be ascertained even in darkness
since light is emitted from the camera. The contrast method is advantageous in
that since data of a captured image are used, the focal point detection can be
executed without having to provide a special mechanism and in that the focal point
detection can be executed without any adjustment error by directly monitoring the
state of the light receiving surface.
However, a single lens reflex camera adopting the phase difference method
houses an internal AF detection device, and thus such a camera cannot be provided
as a compact unit. In addition, since the state of the light receiving surface
is not directly monitored, there is always the potential for an adjustment error.
SUMMARY OF THE INVENTION
A camera according to the present invention comprises a spatial modulation optical
filter that is disposed in a viewfinder optical system for subject observation
at or near a position optically equivalent to an estimated image forming plane
of a photographic optical system and modulates a subject light flux entering via
the photographic optical system with transmission characteristics to obtain a light
flux having a predetermined spatial frequency; a photoelectric conversion device
that outputs a signal corresponding to detected light; an optical element that
guides the subject light flux having been modulated at the spatial modulation optical
filter to the photoelectric conversion device; and a focal adjustment state calculation
means that calculates a focal adjustment state of the photographic optical system
based upon the signal output from the photoelectric conversion device having received
the modulated subject light flux.
The spatial modulation optical filter modulates a light flux that passes through
at least one of a plurality of divided areas within a photographic image plane
defined by the photographic optical system.
It is also possible to further provide a plurality of the spatial modulation
optical
filters being disposed along an optical axis of the photographic optical system,
and a light flux modulation control unit that individually controls modulation
of the subject light flux and detection of the modulated light flux at the photoelectric
conversion device in correspondence to each of the spatial modulation optical filters.
The focal adjustment state calculation means may calculate the focal adjustment
state of the photographic optical system based upon output signals obtained from
the photoelectric conversion device in correspondence to the individual spatial
modulation optical filters.
The focal adjustment state calculation means may calculate a light quantity of
the modulated light flux detected at the photoelectric conversion device; and it
is also possible to provide an autofocus control means that executes a focus operation
by moving a focus lens in the photographic optical system to a target focus position
set at a focus lens position at which the light quantity calculated by the focal
adjustment state calculation means achieves a largest value.
The focal adjustment state calculation means may calculate a light quantity of
the modulated light flux detected at the photoelectric conversion device; and it
is also possible to further provide an AF calculation unit that calculates a focus
lens position at which the light quantity of the modulated light flux detected
at the photoelectric conversion device achieves the largest value based upon results
of a calculation executed by the focal adjustment state calculation means; and
an autofocus control means that moves a focus lens in the photographic optical
system to the focus lens position calculated by the AF calculation unit.
The spatial modulation optical filters may be each constituted with a transmission
liquid crystal display panel so as to modulate the subject light flux by using
a display pattern having transmission characteristics with a predetermined spatial
frequency displayed at the liquid crystal display panel.
Furthermore, the light flux modulation control unit may be capable of
implementing control so as to achieve a first display state in which the display
pattern having the transmission characteristics with the predetermined spatial
frequency is displayed and a second display state in which the subject light flux
is allowed to be transmitted; and it is possible to further provide a photometric
operation unit that executes a photometric operation on the subject light flux
based upon the signal output from the photoelectric conversion device in the second
display state.
The spatial frequency at the spatial modulation optical filter may be adjustable.
A focal point detection device according to the present invention comprises a
spatial
modulation optical filter that is disposed in a viewfinder optical system for subject
observation at or near a position optically equivalent to an estimated image forming
plane of a photographic optical system and can be set in one of a modulation state
in which a subject light flux entering via the photographic optical system is modulated
with transmission characteristics to obtain a light flux having a predetermined
spatial frequency and a transmission state in which the subject light flux is transmitted
through; a photoelectric conversion device that outputs a signal corresponding
to detected light; an optical element that guides the subject light flux having
been modulated at the spatial modulation optical filter to a detection surface
of the photoelectric conversion device and guides the subject light flux having
been transmitted through the spatial modulation optical filter to the viewfinder
optical system; and a focal adjustment state calculation means that calculates
a focal adjustment state of the photographic optical system based upon the signal
output from the photoelectric conversion device having received the subject light
flux that has been modulated at the spatial modulation optical filter.
The spatial modulation optical filter modulates a light flux that passes through
at least one of a plurality of divided areas within a photographic image plane
defined by the photographic optical system.
The optical element is an element, optical anisotropic characteristics of which
change in correspondence to an electrical field applied to the element; and it
is also possible to provide an optical element control means that controls the
electrical field applied to the optical element so as to guide the subject light
flux having been modulated at the spatial modulation optical filter to the detection
surface of the photoelectric conversion device and to guide the subject light flux
having been transmitted through the spatial modulation optical filter to the viewfinder
optical system.
A viewfinder screen of a camera may be disposed at a position optically equivalent
to the estimated image forming plane of the photographic optical system.
The optical element is a polymer dispersion liquid crystal constituted of an
isotropic polymer and an optically anisotropic liquid crystal achieving refractive
indices substantially equal to each other for refracting the subject light flux
when the electrical field is applied, which includes a diffraction grating having
layers constituted of the isotropic polymer and layers constituted of the liquid
crystal disposed in regular order at least in a focal point detection area; and
the optical element control means may control the electrical field applied to the
diffraction grating so as to guide the subject light flux having been modulated
at the spatial modulation optical filter to the detection surface of the photoelectric
conversion device and to guide the subject light flux having been transmitted through
the spatial modulation optical filter to the viewfinder optical system.
The isotropic polymer layers and the liquid crystal layers that together function
as the diffraction grating may be constituted as a hologram formed as a result
of interference occurring between parallel light entering the optical element at
a right angle to the optical element and a light flux radiated from a point light
source provided at a position at which the photoelectric conversion element is
to be located.
A focal point detection device according to the present invention comprises a
photoelectric
conversion device that outputs a signal corresponding to a light quantity of detected
light; a polymer dispersion liquid crystal panel that is disposed in a viewfinder
optical system for subject light flux observation at or near a position optically
equivalent to an estimated image forming plane of a photographic optical system
and is constituted with an isotropic polymer and an optically anisotropic liquid
crystal achieving refractive indices substantially equal to each other for refracting
a subject light flux when an electrical field is applied; a diffraction grating
disposed at least at a focal point detection area of the polymer dispersion liquid
crystal panel, which includes layers constituted of the isotropic polymer and layers
constituted of the liquid crystal disposed in regular order and condenses the subject
light flux entering the focal point detection area onto the photoelectric conversion
device; a liquid crystal panel control means that forms at the diffraction grating
a diffraction pattern with which the subject light flux entering to the diffraction
pattern is modulated with transmission characteristics to obtain a light flux having
a predetermined spatial frequency by applying an electrical field with a specific
pattern to the diffraction grating; and a focal adjustment state calculation means
that calculates a focal adjustment state of the photographic optical system based
upon the signal output from the photoelectric conversion device.
The liquid crystal panel control means can be set in one of an application mode
in which the electrical field with the specific pattern is applied to the diffraction
grating and an application OFF mode in which application of the electrical field
to the diffraction grating is stopped; and it is also possible to provide a photometric
operation unit that executes a photometric operation on the subject light flux
based upon the signal output from the photoelectric conversion device in the application
OFF mode.
It is also possible to provide a spatial modulation optical filter that is disposed
further toward a subject relative to the polymer dispersion liquid crystal panel
and can be set in one of a modulation state in which the subject light flux in
the focal point detection area is modulated with transmission characteristics to
obtain a light flux having a predetermined spatial frequency and a transmission
state in which the subject light flux is transmitted through. The liquid crystal
panel control means may be set in one of an application mode in which the electrical
field achieving the specific pattern is applied to the diffraction grating in the
transmission state and an application OFF mode in which application of the electrical
field to the diffraction grating is stopped in the modulation state; and the focal
adjustment state calculation means may calculate the focal adjustment state in
the photographic optical system based upon the signal output from the photoelectric
conversion device in the application mode and the signal output from the photoelectric
conversion device in the application OFF mode.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a camera achieved in an embodiment of the present invention;
FIG. 2 is a sectional view of a liquid crystal optical member 6;
FIG. 3 is a plan view of the liquid crystal optical member 6;
FIG. 4 is a sectional view of a condenser optical element 14, taken along
II—II in FIG. 3;
FIG. 5 is a block diagram of the AF system in the camera 1;
FIG. 6 is provided to facilitate an explanation of a defocus quantity x;
FIG. 7 shows the change in I occurring relative to the defocus quantity x;
FIG. 8 shows a shaded stripe pattern with a cosine-wave pattern transmittance;
FIG. 9 presents an example of a rectangular wave pattern display;
FIG. 10A presents an example of a display at filters F1 and F2
that may be adopted to execute a focusing state detection by displaying a stripe
pattern at the filter F2;
FIG. 10B presents an example of a display at the filters F1 and F2
that may be adopted to execute a focussing state detection by displaying a stripe
pattern at the filter F1;
FIG. 11 shows a light intensity curve Z;
FIG. 12 shows the light intensity I in correspondence to different spatial wavelengths R;
FIG. 13 presents an example of display at the filters F1 and F2
that may be adopted during a photo metering operation;
FIG. 14 shows a pattern of focus lens movement when executing focus adjustment
in hill-climbing method;
FIG. 15 illustrates the principle of a 3-point interpolation calculation;
FIG. 16 is a sectional view of the liquid crystal optical member 6 having
a viewfinder screen 50 which is formed separately;
FIG. 17 is a sectional view of the liquid crystal optical member 6 having
filters F1 and F2 constituted of TN liquid crystal or STN liquid crystal;
FIG. 18 is a sectional view of a detection area 285 at a condenser optical
element 140;
FIG. 19 illustrates the operation of the hologram in a schematic partial sectional
view of a polymer dispersion liquid crystal member 145 with no voltage applied
to the electrode at the detection area 285;
FIG. 20 illustrates the operation of the hologram in a schematic partial sectional
view of the polymer dispersion liquid crystal member 145 with a voltage
applied to the electrode at the detection area 285;
FIG. 21 indicates the direction along which the subject light flux advances
when no voltage is applied to the electrode at the detection area 285;
FIG. 22 indicates the direction along which the subject light flux advances
when a voltage is applied to the electrode at the detection area 285;
FIG. 23 shows the method adopted to form the condenser optical element 140;
FIG. 24 is a block diagram of the AF system achieved in a second embodiment;
FIG. 25A presents an example of display at the filters F1 and F2
that may be adopted to execute a focusing state detection by displaying a stripe
pattern at the filter F2;
FIG. 25B presents an example of display at the filters F1 and F2
that may be adopted to execute a focusing state detection by displaying a stripe
pattern at the filter F1;
FIG. 26 is a block diagram of the AF system achieved in a third embodiment;
FIG. 27 is a sectional view of a liquid crystal optical member 60;
FIG. 28 is a plan view of the liquid crystal optical member 60;
FIG. 29 is a sectional view taken along IV—IV in FIG. 28, with a stripe
pattern formed at the detection area 285 of the filter F12 and the
detection area 285 of the filter F1 set in a transmission state;
FIG. 30 is a sectional view taken along IV—IV in FIG. 28, with a stripe
pattern formed at the detection area 285 of the filter F1;
FIG. 31 is a sectional view taken along IV—IV in FIG. 28 of a liquid crystal
optical member which includes filters F11 and F12 when the high frequency
component is obtained at the filter F12; and
FIG. 32 is a sectional view taken along IV—IV in FIG. 28 of the liquid
crystal optical member which includes the filters F11 and F12 when
the high frequency component is obtained at the filter F11.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The following is an explanation of the embodiments of the present invention,
given in reference to the drawings.
First Embodiment
FIG. 1 shows a camera achieved in an embodiment of the present invention in
a schematic sectional view of a single lens reflex digital camera. A lens barrel
3 is mounted at a lens mount
2 of the camera
1. Subject light
having passed through a photographic optical system
4 disposed in the lens
barrel
3 is reflected at a quick return mirror
5 and forms an image
on a liquid crystal optical member
6. The liquid crystal optical member
6 is disposed at a position optically equivalent to an estimated image forming
plane of the photographic optical system
4, in the vicinity of a position
at which a view finder screen should be set. In this embodiment, an image-capturing
element
11 is disposed at the estimated image forming plane of the photographic
optical system
4, and the liquid crystal optical member
6 also functions
as the viewfinder screen. The image-capturing element
11 is a two-dimensional
image-capturing device which maybe a CCD-type, a MOS-type or a CID-type device.
The subject image formed on the liquid crystal optical member
6 can be
observed through a viewfinder eyepiece window
9 via a pentaprism
7
and an eyepiece lens
8. In addition, part of the light guided to the pentaprism
7 is further guided to a photo metering sensor
10. A shutter
15
is provided between the quick return mirror
5 and the image-capturing element
11.
A focus area is set within a photographic image plane defined by the photographic
optical system
4, and a light flux having passed through the focus area
is condensed onto a photoelectric conversion element
13 by a condenser optical
element
14 provided at the top of the liquid crystal optical member
6.
The photoelectric conversion element
13 is disposed at the pentaprism
7
on its surface that is not used to reflect the viewfinder light flux, i.e., on
a first surface. The photoelectric conversion element
13, which may be constituted
of a photodiode, a CdS or the like, is capable of detecting the quantity of the
light condensed by the condenser optical element
14.
In the sectional view of the liquid crystal optical member
6 presented
in FIG. 2, the subject light enters from the lower side in the figure. Reference
numerals
21 to
23 each indicate a transparent substrate such as a
glass substrate. At a lower surface
21a of the transparent substrate
21, the viewfinder screen is formed. In the embodiment, the viewfinder screen
21a and the image-capturing surface of the image-capturing element
11 (see FIG. 1) are positioned so that they are optically equivalent to
each other relative to the photographic optical system
4.
Reference numerals
26a,
26b,
27a
and
27b indicate transparent conductive films (ITOs) formed at
the surfaces of the transparent substrates
21,
22 and
23 each
facing opposite the next surface and the transparent conductive films each form
a specific electrode pattern. A liquid crystal
24 is sealed in between the
transparent conductive film
26a and the transparent conductive film
26b, whereas a liquid crystal
25 is sealed in between the
transparent conductive from
27a and the transparent conductive film
27b. The condenser optical element
14 is pasted on the upper
surface of the transparent substrate
23.
In the embodiment, the liquid crystal layers
24 and
25 are polymer
dispersion crystals such as NCAP crystals or PN crystals. In polymer dispersion
NCAP crystal, extremely small liquid crystal particles are dispersed within an
isotropic high molecule polymer. As a voltage is applied, liquid crystal molecules
inside the individual micro particles become aligned with the electric field, and
thus, as long as the constant refractive index of the crystal is set equal to the
refractive index of the high molecule polymer, incident light does not become scattered
and a transparent state is achieved.
However, when no voltage is applied, the liquid crystal molecules take on
a random arrangement and thus, incident light is scattered and the liquid crystal
becomes non-transparent. The arrangement of the liquid crystal molecules is affected
by the voltage level, and thus, by controlling the level of the voltage that is
applied, the liquid crystal can be set in a transparent or non-transparent state.
It is to be noted that the liquid crystal layers
24 and
25 are positioned
over a predetermined distance d
2 from each other, and a distance between
the liquid crystal layer
24 and the viewfinder screen
21a is
set to d
1.
FIG. 3 is a plan view of the liquid crystal optical member
6, showing
its focus areas used in an AF operation. In the example presented in FIG. 3, a
total of 9 rectangular detection areas
281 to
289 (three disposed
along the vertical direction by three disposed along the horizontal direction),
are provided as focus areas. In the embodiment, the electrode patterns formed at
the transparent conductive films
26a,
26b,
27a
and
27b (see FIG. 2) in the detection areas
281 to
289
are dot matrix patterns.
By controlling the voltages applied to the electrode patterns in the detection
areas
281 to
289, the states of the liquid crystal layers
24
and
25 can be altered so as to set the liquid crystals over the entirety
of a given area in a transparent state or a non-transparent state or to form a
stripe pattern having transparent and non-transparent vertical stripes alternating
as shown in FIG.
3. The spatial frequency that defines the reiterating cycle
of the stripe pattern does not need to be fixed and instead, it may be variable.
In addition, a horizontal stripe pattern instead of a vertical stripe pattern may
be formed. It is to be noted that the electrode patterns in the detection areas
281 to
289 may be striped electrode patterns instead of dot matrix patterns.
The condenser optical element
14 disposed at the liquid crystal optical
member
6 is an optical element that imparts refracting power only within
the detection areas
281 to
289. For instance, such an optical element
may be achieved by forming lens surface areas of a lens
29 indicated by
a dotted-line in FIG. 3, which is decentered from the optical axis corresponding
to the detection areas
281 to
289 on the condenser optical element
14 areas of which correspond to the detection areas
281 to
289.
FIG. 4 shows the condenser optical element
14 in a sectional view taken
along II—II in FIG.
3. Above the condenser optical element
14,
the lens
29 is also shown in a sectional view in correspondence to the condenser
optical element
14. Reference numerals
29A,
29B and
29C
indicate lens surface areas of the lens
29 corresponding to the detection
areas
282,
285 and
288 respectively. Surface areas
14A,
14B and
14C are formed in shapes identical to those of the surface
areas
29A,
29B and
29C at the detection areas
282,
285 and
288 of the condenser optical element
14, respectively.
It is to be noted that the condenser optical element
14 may be achieved
as a diffraction grating such as a hologram instead of by forming the surface areas
29A,
29B and
29C at the decentered lens
29.
(AF System)
FIG. 5 is a block diagram of the AF system in the camera
1. FIG. 5 does
not include an illustration of the transparent substrates
21 to
23
(see FIG. 2) at the liquid crystal optical member
6. The liquid crystal
layers
24 and
25 at the liquid crystal optical member
6 each
function as a filter that executes a Fourier conversion on the subject light, with
a filter F
1 constituted with the liquid crystal layer
24 and the
transparent conductive films
26a and
26b used to alter
the state of the liquid crystal layer
24 and a filter F
2 constituted
of the liquid crystal layer
25 and the transparent conductive films
27a
and
27b. The voltage applied to the transparent conductive films
26a and
26b is controlled by a filter control unit
31, whereas the voltage applied to the transparent conductive films
27a
and
27b is controlled by a filter control unit
32.
As described earlier, the viewfinder screen
21a of the liquid crystal
optical member
6 is disposed at a position optically equivalent to the estimated
image forming plane of the photographic optical system
4, and as a focused
subject image is formed on the image-capturing element
11 in FIG. 1, a focused
subject image is also formed at the viewfinder screen
21a. Reference
numeral
33 indicates a lens drive device that controls the drive of the
focus lens (not shown) in the photographic optical system
4. As the focus
lens in the photographic optical system
4 is driven by the lens drive device
33, the image forming position moves to the left/right in the figure. The
lens drive device
33 and the filter control units
31 and
32
mentioned earlier are controlled by a control device
34 of the camera
1.
Light having been transmitted through the detection areas
281 to
289
(see FIG. 3) at the filters F
1 and F
2 is condensed onto a detection
surface of the photoelectric conversion element
13 by the condenser optical
element
14. The output from the photoelectric conversion element
13
is first amplified at an amplifier
35, and then an A/D converter
36
converts the amplified output to a digital signal which is then input to the control
device
34. Based upon the signals input thereto, an arithmetic unit
34a
of the control device
34 calculates the focal adjustment state at the
photographic optical system
4. The control device
34 implements autofocus
control under which the lens drive device
33 is engaged in autofocus operation,
as well as controlling the filter control units
31 and
32.
(Focal Adjustment Operation)
(Acquisition of the Spatial Frequency Component)
In the embodiment, a spatial frequency component in the high-frequency range
of
the subject light is obtained by displaying stripe patterns to be detailed later
at the filters F
1 and F
2. Then, the focal point is adjusted by moving
the focus lens in the photographic optical system
4 to the lens position
at which the spatial frequency component indicates a peak value. An explanation
is given first on how the spatial frequency component is obtained at the filters
F
1 and F
2.
The following explanation is given on an example in which a focal point
40
of the photographic optical system
4 is present at a position x to the right
of the filter F
2, as shown in FIG.
6. While FIG. 6 shows both the
filter F
1 and the filter F
2, the explanation is given in reference
to the filter F
2 alone. The extent to which the subject image loses sharpness
at the position x can be represented by the diameter r of a plane across which
a circular cone
41 having its vertex at the focal point
40 is cut
by the filter F
2. With θ representing the angle formed by the optical
axis and the generating line of the circular cone, the diameter r may be expressed
as in (1) below.
Since tan θ is the product of the reciprocal of the F value (=focal length/aperture)
of the lens and ½ in this system, the extent of loss of sharpness r is expressed
as in (2) below.
r may be regarded as the attenuation wavelength at the primary filter. Accordingly,
the attenuation f of the subject image resulting from the loss of sharpness at
the spatial wavelength R can be expressed as in (3) below.
I in expression (4) below is the absolute value of f and indicates the attenuation
of the spatial frequency component at the wavelength R attributable to the defocus
quantity x.
I indicates a quantity corresponding to the intensity of the light detected by
the photoelectric conversion element
13. In the following explanation, I
is referred to as the light intensity.
A curve L
1 in FIG. 7 indicates the change occurring in I relative to the
defocus quantity x. When x=0, i.e., when the filter F
2 is set at the focal
point position
40, I=1 and the value of I decreases as the absolute value
of x becomes larger. Expression (4) indicates that the attenuation of the spatial
frequency component of the wavelength R is defined by the defocus quantity x. This,
in turn, implies that once the spatial frequency component at a specific wavelength
R at a specific position on the optical axis is ascertained, the defocus quantity
x can be estimated.
The spatial frequency component at the wavelength R at the specific position
may be ascertained through a Fourier conversion of the light flux at the position.
When shaded stripes with a transmittance achieving a cosine wave form such as that
shown in FIG. 8 are displayed at the detection areas
281 to
289 (see
FIG. 3) of the filter F
2, a light flux undergoes a Fourier cosine conversion
as it is transmitted through the filter F
2. Assuming that the spatial wavelength
of the shaded stripes in FIG. 8 is R, the intensity of the light flux advancing
toward the photoelectric conversion element
13 can be expressed as in (5) below.
In the expression given above, I
0 represents the intensity of the
light
flux transmitted when the filter F
2 is set in a full transmission state,
i.e., a state in which the shaded stripe filter pattern is not inserted in the
optical path. In addition, cosθ
f indicates the Fourier cosine conversion.
θ
f in expression (5) represents the spatial
frequency when the spatial wavelength is R, and I
θ represents
the spatial frequency component at the spatial wave length R. It is to be noted
that if a shaded stripe pattern with a transmittance corresponding to a Fourier
sine wave is displayed at the filter F
2, I
θ corresponding
to the Fourier sine conversion is obtained. Either conversion may be adopted to
calculate the focal point position.
As the light flux having been modulated at the filter F
2 as described
above
is received at the photoelectric conversion element
13, the output from
the photoelectric conversion element
13 achieves the level of intensity
having undergone the Fourier conversion in hardware. If the wavelength R of the
shaded or variable-density stripe pattern is altered, the Fourier conversion is
executed in correspondence to the adjusted wavelength R. For this reason, the output
data measured at different positions x and plotted on the x-I plane in FIG. 7 achieve
a curve having a profile identical to that of the curve L
1 in FIG.
7.
This means that the contrast of the subject image becomes highest and a focus
match is achieved at the position x=0 at which the curve L
1 peaks. Thus,
the focus lens needs to be moved to the lens position at which the peak position
of the curve L
1, i.e., the focal point position corresponds to the viewfinder
screen
21a.
In the example described above, a uniform cosine-wave pattern or sine-wave pattern
is displayed at the detection areas
281 to
289 at the filter F
2.
As an alternative, a rectangular wave pattern with alternating transmission and
non-transmission areas may be displayed. FIG. 9 presents an example of rectangular
wave pattern display, with a full transmission vertical stripe area
42 and
a full light blocking vertical stripe area
43 alternately reiterating along
the horizontal direction. While the rectangular wave pattern is not as desirable
as the uniform sine-wave pattern or cosine-wave pattern, the rectangular wave pattern
can still be used in a practical application without any problem. Considering the
difficulty in achieving a gradation display with a liquid crystal, the rectangular
wave pattern, which is simpler, may be easier to handle than the sine-wave pattern
or the cosine-wave pattern.
It is to be noted that the output from the photoelectric conversion element
13
will indicate extremely small values if the vertical stripe pattern is used when
there is hardly any contrast change along the horizontal direction in the subject,
and thus, a horizontal stripe pattern should be formed in such a case. In addition,
instead of a vertical stripe pattern or a horizontal stripe pattern, a diagonal
stripe pattern may be used. A diagonal stripe pattern can be used in the spatial
frequency component extraction either when there is no contrast change along the
vertical direction in the subject or when there is no contrast change along the
horizontal direction.
(Focal Adjustment Operation)
Next, the displays at the filters F
1 and F
2 used to obtain the
spatial frequency components are explained. As shown in FIG. 3, focal adjustment
information, i.e., the spatial frequency component, can be obtained at each of
the nine detection areas
281 to
289 within the photographic range
in the camera achieved in the embodiment. An explanation is given here on a focal
adjustment executed based upon the spatial frequency components obtained in the
central detection area
285. Exactly the same principle applies to the focal
adjustment executed based upon the spatial frequency component obtained in the
other detection areas as that of the focal adjustment executed based upon the spatial
frequency component obtained in the detection area
285.
When obtaining the spatial frequency component at the filter F
2, displays
such as those shown in FIG. 10A are achieved at the filters F
1 and F
2.
At the filter F
1, the detection area
285 is set in a full transmission
state and the areas other than the detection area
285 are set in a full
light blocking state. At the filter F
2, a stripe pattern with a predetermined
spatial frequency is displayed in the detection area
285 and the areas other
than the detection area
285 are set in a full light blocking state.
Next, in order to obtain the spatial frequency component at the filter F
1,
displays such as those shown in FIG. 10B are achieved at the filters F
1
and F
2. Namely, a display similar to the display at the filter F
2
in FIG. 10A is achieved at the filter F
1 and a display similar to the display
at the filter F
1 in FIG. 10A is achieved at the filter F
2. It is
to be noted that as long as in the areas other than the detection area
285
at least one of the filters F
1 and F
2 is in a full light blocking
state, the corresponding areas at the other filter do not need to be in a full
light blocking state (they may be set, for instance, in a full transmission state).
However, it is more desirable to set the areas other than the detection area
285
at both the filters F
1 and F
2 in a full light blocking state in order
to cut off the light flux in the areas other than the detection areas
285
with a high degree of efficiency.
By obtaining output values from the photoelectric conversion element
13
in the two display states shown in FIGS. 10A and 10B, two types of data taken at
different positions on the optical axis can be obtained with regard a single subject
image. In the embodiment, the viewfinder screen
21a is set at a position
optically equivalent to the estimated image forming plane, with the filter F disposed
at a position set over a distance d1 from the viewfinder screen
21a and
the filter F
2 disposed at a position set over a distance (d
1+d
2)
from the viewfinder screen
21a.
With y representing the distance from the focal point
40 to the viewfinder
screen
21a, as shown in FIG. 6, the distances from the focal point
40 to the filters F
1 and F
2 are respectively expressed as
(y-d1) and (y-(d
1+d
2)). Thus, the light intensity Za detected in
the state illustrated in FIG. 10A is expressed as in (6) below, whereas the light
intensity Zb detected in the display state shown in FIG. 10B is expressed as in
(7) below.
It is to be noted that a in expressions (6) and (7) represents the light intensity
detected when the light flux is not attenuated. By using expressions (6) and (7),
the distance y to the viewfinder screen
21a and the light intensity
"a" when there is no attenuation can be calculated. However, when Za=Zb, the filters
F
1 and F
2 can be assumed to be located over distances equal to each
other from the focal point position
40 with the focal point
40 present
halfway between them and thus, the focal point
40 is assumed to be at the
halfway position between the filters F
1 and F
2, i.e. at (y-(d
1+d
2)/2).
FIG. 11 shows a curve Z=a/(1+(y/RF)
2)
1/2, with y indicating
the distance from the image forming position (focal point
40) of the photographic
optical system
4. When the distance between the image forming position and
the viewfinder screen
21a is y′, the positions of the filters
F
1 and F
2 are (y′-d
1) and (y′-d
1-d
2)
respectively, and thus, the light intensity levels Za and Zb are indicated by the
values of Z at points P
11 and P
12 on the curve Z. Namely, when
the light intensity levels Za and Zb take such values, a focused match state can
be achieved by adjusting the focus lens position with the lens drive device
33
and moving the image forming position over the distance y′ towards the viewfinder
screen
21a.
When a focal point detection operation is not being executed, the liquid crystal
layers
24 and
25 including their detection areas
281 to
289
are set in a full transmission state. It is to be noted that by setting the detection
areas used in the AF operation in a light blocking state over a predetermined length
of time following a focus match, the exact position of the subject at which the
focus match has been achieved may be visually checked through the viewfinder.
(Filter Pattern)
Expression (4) explained earlier indicates that the light intensity I
has dependency upon the spatial wavelength R (or the spatial frequency) at the
filters F
1 and F
2. Curves L
11 to L
13 in FIG. 12 indicate
the light intensity level I corresponding to different spatial wavelengths R. The
curve L
11 indicates the light intensity corresponding to a wavelength R
1,
the curve L
12 indicates the light intensity corresponding to the wavelength
R
2=R
1/2 and the curve L
13 indicates the light intensity corresponding
to the wavelength R
3=R
1/4. As FIG. 12 indicates, the curve peaks
more sharply as the wavelength R of the stripe pattern is
