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Digital Camera Patent Abstract
A digital camera is provided with an imaging element including a
plurality of pixels, a shutter unit capable of intercepting light
transmitted from an object to the imaging element, and an optical
low pass filter adapted to allow light with predetermined lower
spatial frequencies to pass therethrough. The optical low pass filter
is embedded in the shutter unit.
Digital Camera Patent Claims
1. A digital camera, comprising: an imaging element including a
plurality of pixels; a shutter unit capable of intercepting light
transmitted from an object to the imaging element; and an optical
low pass filter adapted to allow light with predetermined lower
spatial frequencies to pass therethrough, the optical low pass filter
being embedded in the shutter unit.
2. The digital camera according to claim 1, wherein the shutter
unit includes a shutter panel formed with an aperture portion, and
wherein the aperture portion is formed with the optical low pass
filter.
3. The digital camera according to claim 2, wherein the optical
low pass filter is made of transparent resin, which is integrally
formed with the shutter panel.
4. The digital camera according to claim 3, wherein the optical
low pass filter includes a birefringent element made of transparent
resin.
5. The digital camera according to claim 4, wherein the transparent
resin is made of one of polyethylene, polycarbonate, and polyvinyl
chloride.
6. The digital camera according to claim 4, wherein the optical
low pass filter is configured to split the light transmitted from
the object.
7. The digital camera according to claim 3, wherein the optical
low pass filter includes a diffractive grating made of transparent
resin.
8. The digital camera according to claim 7, wherein the transparent
resin is made of one of polymethyl methacrylate, polycarbonate,
and polystyrene.
9. The digital camera according to claim 8, wherein the optical
low pass filter is configured to split the light transmitted from
the object.
10. The digital camera according to claim 1, wherein the shutter
unit includes a focal-plane shutter and a shutter panel formed with
an aperture portion, and wherein the focal-plane shutter is configured
to open and close the aperture portion, the optical low pass filter
being provided to the aperture portion.
11. A shutter unit for a digital camera adapted to intercept light
transmitted from an object to the imaging element, comprising: an
optical low pass filter adapted to allow light with predetermined
lower spatial frequencies to pass therethrough; the optical low
pass filter being embedded in the shutter unit.
12. The shutter unit according to claim 11, further comprises a
shutter panel formed with an aperture portion, wherein the aperture
portion is formed with the optical low pass filter.
13. The shutter unit according to claim 12, wherein the optical
low pass filter is made of transparent resin, which is integrally
formed with the shutter panel.
14. The shutter unit according to claim 13, wherein the optical
low pass filter includes a birefringent element made of transparent
resin.
15. The shutter unit according to claim 14, wherein the transparent
resin is made of one of polyethylene, polycarbonate, and polyvinyl
chloride.
16. The shutter unit according to claim 14, wherein the optical
low pass filter is configured to split the light transmitted from
the object.
17. The shutter unit according to claim 13, wherein the optical
low pass filter includes a diffractive grating made of transparent
resin.
18. The shutter unit according to claim 17, wherein the transparent
resin is made of one of polymethyl methacrylate, polycarbonate,
and polystyrene.
19. The shutter unit according to claim 18, wherein the optical
low pass filter is configured to split the light transmitted from
the object.
20. The shutter unit according to claim 11, further comprising:
a focal-plane shutter and a shutter panel formed with an aperture
portion, wherein the focal-plane shutter is configured to open and
close the aperture portion, the optical low pass filter being provided
to the aperture portion.
Digital Camera Patent Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a digital camera having
an imaging element such as a CCD (charge-coupled device) and a MOS
(metal oxide semiconductor), and particularly to an SLR (single-lens
reflex) digital camera having a shutter.
[0002] An imaging element used in a digital camera for capturing
an object image such as a CCD and a MOS generally includes a multiplicity
of photo receiving cells (i.e., pixels) that are arranged uniformly
in matrix. Due to the uniformity of the pixels, when an object image
with a pattern is captured by the imaging element, an interference
occurs between the two patterns, and a false color (i.e., moire
fringe) is viewed. To avoid such a false color from occurring, an
optical low pass filter (hereinafter referred to as LPF) is provided
to an image receiving area of the imaging element so as light with
specific higher spatial frequency to cause interferences is blurred.
An example of such technique is disclosed in Japanese Patent Provisional
Publication No. P2004-173139. For such an optical LPF, various types
of materials are used, including a birefringent crystal panel and
a lithium niobate panel. Also, a diffraction grating, which splits
light with a specific wavelength, and a phase filter, which cuts
off light with a specific wavelength, is used.
[0003] When an imaging element with such an optical LPF is applied
to a digital camera with a shutter, such as an SLR, the optical
LPF is arranged between the shutter and the imaging element. As
seen in an SLR camera illustrated in FIG. 7, for example, on a front
surface of the camera body, a lens mount is provided, to which a
photographing lens unit (not shown) is detachably attached. Light
passed through the photographing lens is reflected by a movable
half mirror (quick return mirror) 11 and forms an image on a focusing
glass 12. The image formed on the focusing glass 12 is further reflected
inside a pentaprism 13 and can be observed through an eyepiece lens
14 Behind the movable half mirror 11 is provided a focal-plane shutter
unit 18. Further behind the shutter unit 18 is provided an imaging
element 20 which captures an object image when a shutter of the
focal-plane shutter unit 18 is opened. Furthermore, an optical LPF
19 is provided in front of the imaging element. It should be noted
that, in a camera, an infra-red cutoff filter is generally provided
to the imaging element in addition to the optical LPF 19, however,
the infra-red cutoff filter in this example is integrated to a protective
glass that is provided to the surface of the imaging element 20.
[0004] It should be noted that such an optical LPF (e.g., the birefringent
crystal panel or the diffraction grating) requires a considerable
thickness, therefore an interspace between the shutter unit 18 and
the imaging element 20 may be large. In that case, the imaging element
20 is required to be arranged in a farther position from the shutter
unit 18. For this reason, the camera should be configured to be
large in the direction of the optical axis.
[0005] In addition, it should be noted that, when dirt and/or dust
adhered to the surface of the optical LPF is removed by a user using
a cleaning tool, the shutter is maintained open. However, if a battery
is exhausted or an AC (alternating current) adapter is unexpectedly
removed from the camera during the cleaning, or a finger of the
user pressing a shutter button to hold the shutter open by a bulb
setting is unintentionally removed, the shutter closes and may be
damaged by the cleaning tool.
SUMMARY OF THE INVENTION
[0006] Aspects of the present invention are advantageous in that
a digital camera downsized in depth is provided. Also, aspects of
the present invention are advantageous in that a digital camera
wherein the dirt and/or dust adhered to the optical LPF thereof
can be effectively and nondestructively removed is provided.
[0007] According to some aspects of the present invention, there
is provided a digital camera having an imaging element including
a plurality of pixels, a shutter unit capable of intercepting light
transmitted from an object to the imaging element, and an optical
low pass filter adapted to allow light with predetermined lower
spatial frequencies to pass therethrough. The optical low pass filter
is embedded in the shutter unit.
[0008] Optionally, the shutter unit may include a shutter panel
formed with an aperture portion. The aperture portion may be formed
with the optical low pass filter.
[0009] Optionally, the optical low pass filter may be made of transparent
resin, which is integrally formed with the shutter panel.
[0010] Optionally, the optical low pass filter may include a birefringent
element made of transparent resin
[0011] Optionally, the transparent resin may be made of one of
polyethylene, polycarbonate, and polyvinyl chloride
[0012] Optionally, the optical low pass filter may be configured
to split the light transmitted from the object.
[0013] Optionally, the optical low pass filter may include a diffractive
grating made of transparent resin.
[0014] Optionally, the transparent resin may be made of one of
polymethyl methacrylate, polycarbonate, and polystyrene.
[0015] Optionally, the shutter unit may include a focal-plane shutter
and a shutter panel formed with an aperture portion. The focal-plane
shutter may be configured to open and close the aperture portion.
The optical low pass filter may be provided to the aperture portion.
[0016] According to another aspects of the present invention, there
is provided a shutter unit for a digital camera. The shutter unit
is capable of intercepting light transmitted from an object to the
imaging element. The shutter unit includes an optical low pass filter
adapted to allow light with predetermined lower spatial frequencies
to pass therethrough. The optical low pass filter is embedded in
the shutter unit.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
[0017] FIG. 1 is a perspective view showing an appearance of a
digital camera according to a first embodiment of the present invention.
[0018] FIG. 2 is a cross-sectional side view of main components
of the digital camera according to the embodiment of the invention.
[0019] FIG. 3 is an exploded perspective view of main components
of the digital camera according to an illustrative embodiment of
the invention.
[0020] FIG. 4 is a cross-sectional side view of main components
of the digital camera taken along a line A-A in FIG. 3 according
to the embodiment of the invention.
[0021] FIG. 5A is a perspective view of a shutter unit made of
a birefringent resin panel according to an illustrative embodiment
of the invention.
[0022] FIG. 5B is a cross-sectional view of the shutter unit with
the birefringent resin panel taken along a line B-B in FIG. 5A according
to an illustrative embodiment of the invention.
[0023] FIG. 6A is a perspective view of a shutter unit with a diffraction
grating resin panel according to a second illustrative embodiment
of the invention.
[0024] FIG. 6B is a cross-sectional view of the shutter unit with
the diffraction grating resin panel taken along a line C-C in FIG.
6A according to the second illustrative embodiment of the invention.
[0025] FIG. 7 is a cross-sectional view of main components of a
known digital camera.
DETAILED DESCRIPTION OF THE EMBODIMENT
First Embodiment
[0026] Referring to the accompanying drawings, a digital camera
according to an embodiment of the invention will be described in
detail.
[0027] FIG. 1 is a perspective view showing an appearance of a
digital camera 1000 according to a first embodiment of the present
invention. The digital camera 1000 is a digital SLR camera employing
interchangeable lens system. As shown in FIG. 1, the camera 1000
has a camera body 1. On a front surface of the camera body 1, a
lens mount 2 is provided, to which a photographing lens unit (not
shown) is detachably attached. On the upper surface of the camera
body 1, a main switch 3 having a rotary lever, a shutter button
4 to be pressed, an LCD (liquid crystal display) 5 for displaying
various information, and a mode dial 6 for setting various photographing
modes are provided. The shutter button 4 functions as a photometry
switch when half-depressed and a release switch when fully depressed.
[0028] FIG. 2 is a cross-sectional side view of main components
of the digital camera 1000. Light from an object is reflected by
a movable half mirror (quick return mirror) 11 and forms an image
on a focusing glass 12. The image formed on the focusing glass 12
is further reflected inside a pentaprism 13, which erects the image,
and can be observed through an eyepiece lens 14. A photometer 15
that evaluates amount of the light is provided in a vicinity of
the eyepiece lens 14. The image passed through the movable half
mirror 11 is further reflected by a second mirror 16 and received
by a known AF (automatic focusing) module 17, which serves as a
distance measuring device to evaluate a distance to the object and
controls focusing. Description in detail of configuration of the
AF module 17 is omitted, as the configuration is known. The image
passed through the movable half mirror 11 is transmitted to a focal-plane
shutter unit 18 (see FIG. 3), and received by an imaging element
20 (when the shutter is opened), which includes, for example, a
CCD or a MOS.
[0029] FIG. 3 is an exploded perspective view of main components
of the digital camera 1000 according to an illustrative embodiment
of the invention. FIG. 4 is cross-sectional view of main components
of the digital camera 1000 taken along the line A-A in FIG. 3 according
to the embodiment of the invention. The shutter unit 18 includes
a shutter panel 181, a shutter blade unit 183, and a known shutter
drive unit 184. The shutter panel 181 is provided with a rectangular
aperture portion 182 wherein the object image from the photographing
lens is transmitted through. The shutter blade unit 183 is fixed
to the shutter panel 181, and includes shutter blades 183a that
are operated to open and close the aperture. The shutter drive unit
184 is fixed to one side of the shutter panel 181 and drives the
shutter blades 183a to open and close.
[0030] It should be noted that a conventional shutter panel is
formed as an opaque panel with a rectangular opening in the center.
The aperture portion 182 is formed with a transparent resin panel
182A, which is the optical LPF, and is formed integrally to the
shutter panel 181. Further, as seen in FIG. 2, an image receiving
area 20S of the imaging element 20 in the present invention is not
provided with a conventional optical LPF. The image receiving area
20S of the imaging element 20 is positioned distinctly close to
a rear area of the shutter unit 18. In this embodiment, a protective
glass is provided in front of the imaging element as a unit, therefore,
the front surface of the protective glass is adjacent to the rear
area of the shutter unit 18.
[0031] FIG. 5A is a perspective view of an aperture unit made of
birefringent resin panel according to an illustrative embodiment
of the invention. FIG. 5B is a cross-sectional side view of the
aperture unit with the birefringent resin panel taken along the
line B-B in FIG. 5A according to an illustrative embodiment of the
invention. The line B-B is inclined at 45 degrees relative to the
horizontal axis of the resin panel 182A. The shutter panel 181 includes
the aperture portion 182 with the transparent resin panel 182A,
and the shutter panel 181 is formed with non-transparent resin,
for example black polycarbonate. The shutter panel 181 and the transparent
resin panel 182A can be formed in a molding method such as coinjection
molding, which is a method to form different materials in one mold
pattern. Certain kinds of resin possess birefringency depending
on the flow orientation of the molding. Therefore, when the shutter
panel 181 is formed, the mold pattern wherein the flow orientation
of the material is in a certain direction is used, so as the resin
is molded with the crystal axis thereof oriented in a predetermined
direction to obtain a desired birefringency. The molded resin panel
182A is thus configured to be an optical LPF with the desired birefringency.
[0032] In this embodiment, as seen in FIG. 5A, the resin panel
182A is configured to have the crystal axis oriented in an angle
.theta. relative to the optical axis, which is substantially perpendicular
to the surface of the resin panel 182A. The light from the object
though the resin panel 182A with a thickness t is refracted as an
ordinary ray Lo and an extraordinary ray Le with different refractive
indexes, each of which forms an image on the image receiving area
20S of the imaging element 20 with a separation distance P therebetween
(see FIG. 5B). The right-hand side of FIG. 5B shows the light transmitted
through the resin panel 182A, which is split into the ordinary ray
Lo and the extraordinary ray Le. The ordinary ray Lo and the extraordinary
ray Le are respectively transmitted to pixels 20a of the imaging
element 20. When the distance P is configured to properly match
the pitch between the pixels 20a, the object image is doubled, and
the output image is slightly blurred. Therefore, the interference
between the uniformity of the pixels 20a and the pattern of the
object image is avoided, and the false color is prevented from occurring
on the output image. Thus the resin panel 182A serves as an optical
LPF.
[0033] When the refractive index of the ordinary ray Lo is represented
by "no" and the refractive index of the extraordinary
ray Le is represented by "ne", P is represented by the
following expression: P=t(ne.sup.2-no.sup.2)sin 2.theta./(no.sup.2
sin.sup.2 .theta.+ne.sup.2 cos.sup.2 .theta.)
[0034] When, for example, P=0.01 mm and t=1 mm, the angle .theta.
is calculated as follows.
[0035] When the material for the resin panel 182A is polyethylene,
no=1.54, ne=1.584, and .theta.=10.6 degrees. When the material is
polycarbonate, no=1.59, ne=1.696, and .theta.=4.75 degrees. Further,
when the material is polyvinyl chloride, no=1.52, ne=1.547, and
.theta.=17.5 degrees.
[0036] The resin panel 182A formed as above is configured to be
the aperture portion 182 of the shutter unit 18 and placed in front
of the image receiving area 20S of the imaging element 20 as the
optical LPF. Therefore, the optical LPF is not required to be positioned
between the shutter and the imaging element in this embodiment,
as the conventional digital camera required This structure allows
the image receiving area 20S of the imaging element 20 to be positioned
distinctly close to the rear area of the shutter unit 18, and the
imaging element 2 to be arranged closer to the shutter unit 18,
and the camera body 1 is downsized in depth.
[0037] Further, it should be noted that in this embodiment the
resin panel 182A is integrally formed with the shutter unit 18 and
not configured independently from the shutter unit 18, therefore
a process to assemble the optical LPF with the imaging element 20
and the camera body 1 can be omitted, which results cost reduction
in manufacturing.
[0038] In addition, when dust adhered to the surface of the resin
panel 182A is removed, the resin panel 182A is exposed through the
opening of the lens mount 2 by moving the movable half mirror 11
to the uplifted position, and the dust can be effectively and nondestructively
removed from the surface of the resin panel 182A. Further, even
when some dust is adhered to the surface of the resin panel 182A,
the dust is positioned closer to the surface of the imaging element
20 for the amount of thickness of the optical LPF 19 compared to
the conventional camera. Therefore, image of the dust is blurred
substantially enough so that the object image captured is not affected
by the image of the dust.
Second Embodiment
[0039] An appearance of a digital camera according to a second
embodiment of the present embodiment is similar to the appearance
of the digital camera 1000 in the first embodiment. The aperture
portion 182 of the shutter panel 181 is formed with a diffraction
grating resin panel 182B in the second embodiment instead of the
birefringent resin panel. FIG. 6A is a perspective view of the shutter
unit 18 with the diffraction grating resin panel according to a
second illustrative embodiment of the invention. FIG. 6B is a cross-sectional
side view of the shutter unit 18 with the diffraction grating resin
panel taken along the line C-C in FIG. 6A according to the second
illustrative embodiment of the invention. In this embodiment, the
configuration corresponding to the configuration of the first embodiment
is referred to by the same reference numbers, and description of
those is omitted. The diffraction grating resin panel 182B is provided
with indented phases on the rear surface thereof. Each phase is
incised in a predetermined angle (i.e., a blaze angle) to the surface
of the aperture portion 182. The light transmitted through the resin
panel 182B is divided into a zero order light, which is parallel
to the normal line, and a primary diffracted light, which is separated
from the zero order light in an angle .beta., each of which forms
an image on the image receiving area 20S of the imaging element
20 with a separation distance P therebetween (see FIG. 6B). When
the distance P is configured to properly match to the pitch between
the pixels 20a, the object image is doubled, and the output image
is slightly blurred. Therefore, the interference between the uniformity
of the pixels 20a and the pattern of the object image is avoided,
and the false color is prevented from occurring on the output image.
Thus the resin panel 182B is served as an optical LPF.
[0040] Here, the relation of a wavelength of the light (represented
by .lamda.), a grating pitch (represented by d), a number of grates
(represented by N), a blaze angle (represented by .theta.B), a refractive
index (represented by n), and order of diffraction (represented
by m), and a distance between the receiving area 20S of the imaging
element 20 and the grating (represented by 1) is expressed in the
following equations: sin .beta.=Nm.lamda.N=1/dnsin .theta.B=sin(.theta.B+.beta.)
.theta. .times. .times. B = tan - 1 ( Nm .times. .times. .lamda.
n - 1 - ( Nm .times. .times. .lamda. ) 2 ) tan .beta.=P/1
[0041] When, for example, P=0.01 mm, 1=5 mm, .lamda.=550 nm, N=3636,
and the material is polymethyl methacrylate, n=1.49 and .theta.B=0.23
degrees. When the material is polycarbonate or polystyrene, for
example, n=1.59 and .theta.B=0.19 degrees.
[0042] The resin panel 182B formed as above is configured to be
the aperture portion 182 of the shutter unit 18 and placed in front
of the image receiving area 20S of the imaging element 20 as the
optical LPF. Therefore, the optical LFP is not required to be positioned
between the shutter and the imaging element in this embodiment,
as the conventional digital camera required. This structure allows
the image receiving area 20S of the imaging element 20 to be positioned
distinctly close to the rear area of the shutter unit 18, and the
imaging element 2 to be arranged closer to the shutter unit 18,
and the camera body 1 is downsized in depth.
[0043] Further, it should be noted that in this embodiment the
resin panel 182B is integrally formed with the shutter unit 18 and
not configured independently from the shutter unit 18, therefore
a process to assemble the optical LFP with the imaging element 20
and the camera body 1 can be omitted, which results cost reduction
in manufacturing.
[0044] In addition, when dust adhered to the surface of the resin
panel 182B is removed, the resin panel 182B is exposed through the
opening of the lens mount 2 by moving the movable half mirror 11
to the uplifted position, and the dust can be effectively and nondestructively
removed from the surface of the resin panel 182B. Further, even
when some dust is adhered to the surface of the resin panel 182B,
the position where the dust is adhered is closer to the surface
of the imaging element 20 for the amount of thickness of the optical
LPF 19 compared to the conventional camera. Therefore, image of
the dust is blurred substantially enough so that the object image
captured is not affected by the image of the dust.
[0045] The resin panel that functions as an optical LPF in the
present invention is not limited to the birefringent resin panel
described in the first embodiment and the diffraction grating resin
panel described in the second embodiment. A transparent resin panel
made of another material may be similarly adapted to function as
an optical LPF. Each of the resin panels described in the first
and second embodiments is formed integrally with the shutter panel.
The shutter panel may have an opening as an aperture, and a resin
panel formed separately may be embedded or adhered to the shutter
panel. It should be noted, however, in this case the resin panel
is required to be produced independently, therefore a process to
assemble the resin panel with the imaging element 20 is required,
which may increases cost in manufacturing.
[0046] In the above described embodiments, the invention is applied
to SLR digital cameras. However, the present invention may be similarly
applied to a digital camera having a shutter in front of an imaging
element.
[0047] The present disclosure relates to the subject matter contained
in Japanese Patent Application No. 2004-335445, filed on Nov. 19,
2004, which is expressly incorporated herein by reference in its
entirety.
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