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Digital Camera Patent Abstract
In a digital camera system, a lens barrel adapted to a first camera
body can be attached to a second camera body having a flange focal
length which is shorter than that of the first camera body via an
intermediate adapter, and the intermediate adapter is interposed
to thereby set the flange focal length to be equal. Moreover, a
compensating optical device is incorporated in the intermediate
adapter to thereby match an optical distance from a mount surface
to an image capture surface of the first camera body with an optical
distance from a mount surface of the intermediate adapter to an
image capture surface of the second camera body in a state in which
the intermediate adapter is attached.
Digital Camera Patent Claims
1. A digital camera system comprising: a first camera body including
a first image sensor and having a first flange focal length; a first
lens adapted to the first camera body; a first optical device constituted
of a plurality of optical elements arranged between the first lens
and the first image sensor; a second camera body including a second
image sensor and having a second flange focal length which is shorter
than the first flange focal length; a second lens adapted to the
second camera body; a second optical device constituted of a plurality
of optical elements arranged between the second lens and the second
image sensor; and an intermediate adapter having a lens detachable
portion for detachably attaching the first lens on one end of the
intermediate adapter and having a lens detachable portion for detachably
attaching the second camera body on the other end thereof, wherein
the intermediate adapter includes a third optical device; a first
optical equivalent amount .SIGMA.{ti.times.(1-ni)/ni} of the first
optical element is larger than a second optical equivalent amount
.SIGMA.{tj.times.(1-nj)/nj} of the second optical equivalent amount,
in which i and j each is an integer of 1, 2, . . . given to each
optical element of the first and second optical devices from a lens
side, ni is a refractive index of each optical element of the first
optical device, ti is a thickness thereof, nj is a refractive index
of each optical element of the second optical device, and tj is
a thickness thereof; and a sum .SIGMA.{tk.times.(1-nk)/nk}+.SIGMA.{tjx
(1-nj)/nj} of a third optical equivalent amount .SIGMA.{tk.times.(1-nk)/nk}
and the second optical equivalent amount .SIGMA.{tj.times.(1-nj)/nj}
is substantially equal to the first optical equivalent amount .SIGMA.{ti.times.(1-ni)/ni},
in which k is an integer of 1, 2, . . . given to each optical element
of the third optical device from a lens side, nk is a refractive
index of each optical element of the third optical device, and tk
is a thickness thereof.
2. The digital camera system according to claim 1, wherein the
first, second and third optical devices include at least one of
a dustproof glass, a plate constituting an optical low-pass filter
and made of optical crystals, infrared ray absorbing glass and protective
glass for protecting the image sensor.
3. The digital camera system according to claim 1, wherein a pixel
pitch of the first image sensor is larger than that of the second
image sensor.
4. The digital camera system according to claim 1, wherein the
first optical device includes a first optical low-pass filter, and
a thickness of the first optical low-pass filter is larger than
that of a second optical low-pass filter included in the second
optical device.
5. The digital camera system according to claim 1, wherein a maximum
angle formed by a chief ray struck at a diagonal angle of the first
image sensor with an optical axis of the first lens is smaller than
that formed by a chief ray struck at a diagonal angle of the second
image sensor with an optical axis of the second lens.
6. The digital camera system according to claim 1, wherein the
second lens is constituted so as to be prevented from being attached
to the first camera body.
7. An intermediate adapter which adapts a photographing lens adapted
to a first camera body having a first optical device disposed in
a photographing optical path to a second camera body having a second
optical device disposed in the photographing optical path, the second
optical device being configured to have an optical characteristic
which is different from that of the first optical device, wherein
an optical path length compensating optical device is disposed in
order to match an optical distance from an attaching surface of
the photographing lens to an image capture surface of the first
camera body with an optical distance from an attaching surface of
the photographing lens to an image capture surface of the second
camera body in a state in which the intermediate adapter is attached
to the second camera body.
8. The intermediate adapter according to claim 7, wherein the optical
path length compensating optical device does not have any optical
power.
9. A digital camera system comprising: a first camera body in which
a first optical device is disposed in a photographing optical path;
a photographing lens adapted to the first camera body; a second
camera body in which a second optical device having an optical characteristic
different from that of the first optical device is disposed in a
photographing optical path; and an intermediate adapter which adapts
the photographing lens to the second camera body, wherein the intermediate
adapter has an optical path length compensating optical device which
matches an optical distance from a lens attaching surface to an
image capture surface of the first camera body with an optical distance
from a lens attaching surface of the intermediate adapter to an
image capture surface of the second camera body in a state in which
the intermediate adapter is attached to the second camera body.
10. A digital camera system comprising: a first camera body in
which a first optical device is disposed in a photographing optical
path; a photographing lens adapted to the first camera body; a second
camera body in which a second optical device having an optical characteristic
different from that of the first optical device is disposed in a
photographing optical path; an intermediate adapter which attaches
the photographing lens to the second camera body; and an optical
path length compensating optical device disposed between a rear
end portion of the photographing lens and a front end portion of
the second camera body in a state in which the photographing lens
is attached to the second camera body via the intermediate adapter.
Digital Camera Patent Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is based upon and claims the benefit of
priority from prior Japanese Patent Application No. 2005-246606,
filed on Aug. 26, 2005, the entire contents of which are incorporated
herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a digital camera system
in which lenses are interchangeable, and an intermediate adapter
for use in the digital camera system.
[0004] 2. Description of the Related Art
[0005] Heretofore, in a camera system in which lenses are interchangeable,
a distance (flange focal length) from a mount surface of the interchangeable
lens to an image plane is defined, and the interchangeable lens
attachable to the camera is designed based on the defined flange
focal length. Therefore, in a case where the interchangeable lens
designed so as to be applied to a camera having a long flange focal
length is attached to another camera having a short flange focal
length, the flange focal length needs to be adjusted using an intermediate
adapter or the like. As to this type of intermediate adapter, a
large number of proposals are described in Japanese Patent Application
Laid-Open No. 2005-70711.
[0006] In addition, in a conventional digital camera, an optical
low-pass filter (hereinafter referred to as the optical LPF) made
of crystals or the like having birefringent characteristics is disposed
on the front of an image sensor in order to reduce false color and
the like derived from the high-frequency components of a photographed
image. This optical LPF splits an incident luminous flux into normal
light which is not double refracted and abnormal light (birefringent
light), and the split birefringent light is struck on pixels disposed
adjacent to each other in the image sensor. Therefore, to prevent
generation of Moire fringes, a thickness of the optical LPF has
to be appropriately set in accordance with a pixel pitch.
[0007] Moreover, between a photographing lens and the image sensor,
in addition to the optical LPF, flat-plate optical elements are
installed such as a dustproof filter, infrared ray absorbing glass
and protective glass for storing the image sensor in a sealed state.
These optical elements have peculiar optical characteristics (e.g.,
a refractive index, etc.), respectively. Therefore, in the digital
camera in which the lenses are interchangeable, unless the interchangeable
lens is designed in consideration of not only a mechanical distance
(flange focal length) from the mount surface of the interchangeable
lens to the image plane but also a change of an optical distance
(optical path length) attributable to the plurality of optical elements,
a generally high image quality of the digital camera system cannot
be obtained. This also applies to the above intermediate adapter.
[0008] However, in a conventional adapter for adjusting the flange
focal length as described in Japanese Patent Application Laid-Open
No. 2005-70711, only adjustment of the flange focal length is noted.
In Japanese Patent Application Laid-Open No. 2005-70711, there is
not any idea that the optical path length is adapted.
BRIEF SUMMARY OF THE INVENTION
[0009] A digital camera system of the present invention has a first
camera body, an interchangeable lens designed for a second camera
body which is different from the first camera body, and an intermediate
ring attachable to both of the camera body and the interchangeable
lens, and the intermediate ring includes a compensating optical
device.
[0010] The intermediate ring can compensate for a difference in
flange focal length between the first camera body and the second
camera body, and owing to the compensating optical device, an optical
aberration can be minimized.
[0011] One example of a constitution of the digital camera system
of the present invention will hereinafter be described. The system
comprises: a first camera body including a first image sensor and
having a first flange focal length; a first lens adapted to the
first camera body; a first optical device constituted of a plurality
of optical elements arranged between the first lens and the first
image sensor; a second camera body including a second image sensor
and having a second flange focal length which is shorter than the
first flange focal length; a second lens adapted to the second camera
body; a second optical device constituted of a plurality of optical
elements arranged between the second lens and the second image sensor;
and an intermediate adapter having a lens detachable portion for
detachably attaching the first lens on one end of the intermediate
adapter and having a lens detachable portion for detachably attaching
the second camera body on the other end thereof, wherein the intermediate
adapter includes a third optical device; a first optical equivalent
amount .SIGMA.{ti.times.(1-ni)/ni} of the first optical element
is larger than a second optical equivalent amount .SIGMA.{tj.times.(1-nj)/nj}
of the second optical equivalent amount, in which i and j each is
an integer of 1, 2, . . . given to each optical element of the first
and second optical devices from a lens side, ni is a refractive
index of each optical element of the first optical device, ti is
a thickness thereof, nj is a refractive index of each optical element
of the second optical device, and tj is a thickness thereof; and
a sum .SIGMA.{tk.times.(1-nk)/nk}+.SIGMA.{tj.times.(1-nj)/nj} of
a third optical equivalent amount .SIGMA.{tk.times.(1-nk)/nk} and
the second optical equivalent amount .SIGMA.{tj.times.(1-nj)/nj}
is substantially equal to the first optical equivalent amount .SIGMA.{ti.times.(1-ni)/ni},
in which k is an integer of 1, 2, . . . given to each optical element
of the third optical device from a lens side, nk is a refractive
index of each optical element of the third optical device, and tk
is a thickness thereof.
[0012] The present invention can also be understood as the invention
of an intermediate ring.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0013] These and other features, aspects, and advantages of the
apparatus and methods of the present invention will become better
understood with regard to the following description, appended claims,
and accompanying drawings where:
[0014] FIG. 1A is a diagram showing a combined state of a camera
body and an interchangeable lens constituting a digital camera system
in one embodiment of the present invention, and an arrangement of
an optical member and an image sensor built in the system, and showing
a combined state of a reference camera body (first camera body)
and a first lens (first lens barrel);
[0015] FIG. 1B is a diagram showing a combined state of a camera
body and an interchangeable lens constituting a digital camera system
in one embodiment of the present invention, and an arrangement of
an optical member and an image sensor built in the system, and showing
a combined state of a non-reference camera body (second camera body)
and a second lens (second lens barrel);
[0016] FIG. 2 is a sectional view of a state in which the first
lens barrel is attached to the second camera body via an intermediate
adapter in the digital camera system of FIGS. 1A and 1B.
[0017] FIG. 3A shows a state of a mount portion of the first lens
barrel viewed from a camera body side, and a mount portion (chain
double-dashed line) of the camera body to be attached in the digital
camera system of FIG. 1A;
[0018] FIG. 3B shows a state of a mount portion of the second lens
barrel viewed from the camera body side, and a mount portion (chain
double-dashed line) of the camera body to be attached in the digital
camera system of FIG. 1B;
[0019] FIG. 4A is a diagram showing ray deviation amounts .DELTA.Hi,
.DELTA.Hj due to oblique incidence at a time when a ray strikes
at an incidence angle X0 on an optical element constituting an optical
device applied to the digital camera system of FIGS. 1A and 1B,
and showing the ray deviation amount .DELTA.Hi with respect to one
optical element (on a first camera body side) having a thickness
ti and a refractive index ni;
[0020] FIG. 4B is a diagram showing the ray deviation amounts .DELTA.Hi,
.DELTA.Hj due to the oblique incidence at a time when the ray strikes
at the incidence angle X0 on the optical element constituting the
optical device applied to the digital camera system of FIGS. 1A
and 1B, and showing the ray deviation amount .DELTA.Hj with respect
to the other optical element (on a second camera body side) having
a different thickness tj and a different refractive index nj;
[0021] FIG. 5 is a graph showing a relation between the incidence
angle X0 and a ray deviation amount ratio .DELTA.Hj/.DELTA.Hi with
respect to the incident ray on conditions that optical equivalent
amounts of the optical elements having different refractive indexes
are set to be equal;
[0022] FIG. 6 is a perspective view (shown in a partially cut section)
showing an inner structure in a state in which the lens barrel is
attached to the camera body of the digital camera system of FIG.
1;
[0023] FIG. 7 is a perspective view (shown in a partially cut section)
showing an inner structure around an image capture unit in the digital
camera system of FIG. 1;
[0024] FIG. 8 is a schematic diagram showing details of an optical
system of the image capture unit applied to the first camera body
in the digital camera system of FIG. 1;
[0025] FIG. 9 is an enlarged vertically sectional view of the image
capture unit applied to the first camera body in the digital camera
system of FIG. 1;
[0026] FIG. 10 is an enlarged vertically sectional view of the
image capture unit applied to the second camera body in the digital
camera system of FIG. 1;
[0027] FIG. 11 is an optical path diagram showing a state of a
change of an image forming position due to the presence of an optical
filter disposed on the front of the image sensor in an image capture
optical system; and
[0028] FIG. 12 is a graph showing a relation between a pixel pitch
of the image sensor or the number of pixels of the image sensor
and thicknesses of optical LPFs (rock crystal and LN device) adapted
to the image sensor.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0029] A preferred embodiment of the invention is described below
with reference to the accompanying drawings.
[0030] Prior to description of the embodiment of the present invention,
there will be described a way to determine a thickness of an optical
LPF in accordance with a pixel pitch of an image sensor and a material
(optical characteristic) of the optical LPF in a digital camera
system in which lenses are interchangeable.
[0031] There are several types of single lens reflex digital cameras
in which the lenses (i.e., lens barrels.) are interchangeable with
respect to camera bodies, and the number of pixels of image sensors
differ from one another. That is, the image sensors having different
pixel pitches are incorporated, and the interchangeable lenses having
the same specifications are attachable to the types of cameras,
respectively.
[0032] In the camera body of the single lens reflex digital camera,
as described above, on the front of the image sensor having the
different pixel pitch, the optical LPF is disposed which has a thickness
in accordance with the pixel pitch.
[0033] A reason why the thickness of the optical LPF is set in
accordance with the pixel pitch of the image sensor as described
above is that a luminous flux transmitted through the optical LPF
is split into normal light which is not double refracted and abnormal
light (birefringent light). On the other hand, to prevent the generation
of the Moire fringes, the split luminous fluxes have to be struck
on the adjacent pixels of the image sensor. Therefore, the thickness
of the optical LPF needs to be determined in accordance with the
pixel pitch.
[0034] In addition, when the optical LPF having the different thickness
is disposed on the front of the image sensor, an image forming position
of the image sensor changes. FIG. 11 is an optical path diagram
showing a state of the change of the image forming position due
to the presence of the optical LPF disposed on the front of the
image sensor in an image capture optical system. Between the interchangeable
lens and the image sensor, flat-plate optical elements are installed
such as a dustproof filter, infrared ray absorbing glass and protective
glass for storing the image sensor in a package in a sealed state.
The image forming position similarly changes with the flat-plate
optical elements.
[0035] In a case where an optical LPF 102 is not disposed in front
of an image capture surface 103 of the image sensor as in FIG. 11,
the center luminous flux transmitted through a lens 101 forms an
image on a point P1 of the image capture surface 103. A peripheral
luminous flux transmitted through the lens 101 forms an image on
a point P2 of the image capture surface 103. However, in a case
where the optical LPF 102 is disposed in front of the image capture
surface 103 of the image sensor, the center luminous flux transmitted
through the lens 101 forms an image on a point P1' behind the image
capture surface 103.
[0036] In a photographing optical system of the digital camera,
a difference in optical path length is usually made between the
luminous flux reaching the center of a photographing screen (the
image is formed on the point P1' of FIG. 11) and the luminous flux
reaching a peripheral portion (the image is formed on a point P2'
of FIG. 11), and a field curvature aberration is generated. To correct
a difference .beta. between the optical path lengths of the center
and the peripheral portion of this photographing screen, in an optical
device constituted of a specific optical element, a photographing
optical system is provided with such an optical characteristic as
to cancel an aberration such as field curvature aberration. In consequence,
aberrations can be corrected such as the field curvature aberration,
a spherical aberration and an astigmatism to form the image on the
image sensor.
[0037] In a case where this way to consider the aberration correction
is applied to the digital camera of the lens interchangeable type,
however, the following problem occurs. That is, there is supposed
a case where in the lens interchangeable type of digital camera
system including a first camera body provided with a first optical
device and an interchangeable lens designed so as to be adapted
to this body, the interchangeable lens is attached to a second camera
body provided with a second optical device. In this case, since
refractive indexes and thicknesses of the optical elements constituting
the first and second optical devices differ, and the specific optical
element is not disposed, the optical path lengths of the camera
bodies differ, and there is generated a problem that an optical
aberration such as the field curvature aberration cannot be appropriately
corrected. More specifically, in a case where the image sensors
having the different pixel pitches are mounted on the first and
second camera bodies, the thicknesses of the optical LPFs need to
be set so as to be adapted to the pixel pitches, respectively. Therefore,
the optical LPFs have different thicknesses, and the above problem
occurs.
[0038] On the other hand, in the conventional lens interchangeable
type of digital camera, as the optical LPF, instead of rock crystal,
there is applied, for example, an LN (LiNbO.sub.3, lithium niobate)
device having a remarkably smaller thickness and a great birefringent
property as compared with rock crystal. To change the number of
the pixels, a size of the image sensor is changed so that the pixel
pitch hardly changes. In a case where the LN device is applied,
since the birefringent property of the device is great, the thickness
of a LPF can be reduced. Therefore, the optical path length of the
luminous flux hardly changes, and the interchangeable lens can be
interchanged even between the bodies of the digital cameras having
different pixel pitches.
[0039] FIG. 12 is a graph showing a relation between the pixel
pitch of an image sensor (or the number of the pixels of an image
sensor) and the thicknesses of the optical LPFs (rock crystal and
LN device) adapted to the image sensor. As shown in FIG. 12, when
the pixel pitch P narrows, the thickness of the adapted optical
LPF is reduced. The thickness of the LN device adapted to an equal
pixel pitch P is about 1/5 to 1/6 of the thickness of rock crystal.
[0040] In consideration of the above contents, an embodiment of
the present invention will be described hereinafter with reference
to the drawings.
[0041] First, there will be described an outline of a constitution
of a digital camera system in a first embodiment of the present
invention with reference to FIGS. 1 to 3.
[0042] FIGS. 1A, 1B and 2 are sectional views showing a combined
state of a camera body and an interchangeable lens constituting
the digital camera system of the first embodiment of the present
invention, and an arrangement of an optical member and an image
sensor built in the system. FIG. 1A shows a combined state of a
reference camera body (first camera body) and a first lens, and
FIG. 1B shows a combined state of a non-reference camera body (second
camera body) and a second lens. FIG. 2 is a sectional view of a
state in which the first lens is attached to the second camera body
via an intermediate adapter.
[0043] FIGS. 3A, 3B show a state of a mount portion of the lens
viewed from a camera body side, and a mount portion (chain double-dashed
line) of the camera body to be attached in the digital camera system
of the present embodiment. FIG. 3A shows the mount portion of the
first lens, and FIG. 3B shows the-mount portion of the second lens.
[0044] The digital camera system of the present embodiment includes
a digital camera 1 and a digital camera 2 shown in FIGS. 1A, 1B
and a digital camera 30 shown in FIG. 2 as described above.
[0045] The digital camera 1 has a first camera body 11A which is
the reference camera body, and an interchangeable lens barrel (hereinafter
referred to as the lens barrel) 12A as the first lens detachably
attached to the camera body 11A.
[0046] The digital camera 2 has a second camera body 11B and an
interchangeable lens barrel (hereinafter referred to as the lens
barrel) 12B, the second camera body is a non-reference camera body
having a physical distance from a mount surface to an image capture
surface of the image sensor, that is, a flange focal length which
is shorter than that of the first camera body 11A, and the lens
barrel is a second lens detachably attached to the camera body 11B
and having a short back focal length.
[0047] The digital camera 30 has the second camera body 11B and
the lens barrel 12A attached to the camera body 11B via an intermediate
adapter 31.
[0048] As shown in FIG. 3A, a body-side mount portion 3A of the
first camera body 11A is provided with three body-side mount pawls
3Ab and three cutout portions 3Ac. A lens-side mount portion 4A
of the lens barrel 12A is provided with three lens-side mount pawls
4Ab.
[0049] In a case where the lens barrel 12A is attached to the first
camera body 11A, an operator inserts the lens-side mount pawls 4Ab
into the cutout portions 3Ac (shown by the chain double-dashed line
in FIG. 3A) of the body-side mount portion 3A of the first camera
body in an optical axis O direction. Thereafter, the lens barrel
12A is rotated around the optical axis O of the first camera body
11A to engage the lens-side mount pawls 4Ab with the body-side mount
pawls 3Ab (shown by a dotted line in the drawing), thereby obtaining
an attached state. In this lens barrel attached state, a mount surface
3Aa which is a lens attaching surface of the front of the mount
portion 3A of the first camera body 11A abuts on a mount surface
4Aa of the mount portion 3A of the lens barrel 12A, and both of
the surfaces are brought into close contact with each other to define
relative positions of the surfaces in the optical axis direction.
It is to be noted that a first flange focal length of the first
camera body 11A is a distance between the mount surface 3Aa and
a photoelectric conversion surface (image capture surface) 5Aa of
an image sensor 5A.
[0050] As shown in FIG. 3B, a mount portion 3B of the second camera
body 11B is provided with four body-side mount pawls 3Bb and four
cutout portions 3Bc. A lens-side mount portion 4B of the lens barrel
12B is provided with four lens-side mount pawls 4Bb. Moreover, a
mount diameter of the second camera body 11B is smaller than that
of the first camera body 11A.
[0051] In a case where the lens barrel 12B is attached to the second
camera body 11B, the operator inserts the lens-side mount pawls
4Bb into the cutout portions 3Bc (shown by the chain double-dashed
line in FIG. 3B) of the body-side mount portion 3B of the second
camera body in the optical axis O direction. Thereafter, the lens
barrel 12B is rotated around the optical axis O of the second camera
body 11B to engage the lens-side mount pawls 4Bb with the body-side
mount pawls 3Bb (shown by a dotted line in the drawing).
[0052] In the above lens barrel attached state, a mount surface
3Ba which is a lens attaching surface of the front of the mount
portion 3B of the second camera body 11B abuts on a mount surface
4Ba of the mount portion 3B of the lens barrel 12B, and both of
the surfaces are brought into close contact with each other to define
relative positions of the surfaces in the optical axis direction.
It is to be noted that a second flange focal length of the second
camera body 11B is a distance between the mount surface 3Ba and
a photoelectric conversion surface (image capture surface) 5Ba of
an image sensor 5B, and shorter than the first flange focal length
of the first camera body 11A.
[0053] As described above, the lens barrel 12A is different from
the lens barrel 12B in mount diameter. Moreover, since the number
of engagement pawls also differs, the lens barrel 12A cannot be
directly attached to the second camera body 11B, and the lens barrel
12B cannot be attached to the first camera body 11A.
[0054] In the first camera body 11A to which the lens barrel 12A
is detachably attached, as shown in FIG. 1A, there are built: the
image sensor 5A as a first image sensor constituted of a CCD (or
a CMOS type image sensor) or the like having a protective glass
6A; an optical LPF 8A as a first optical low-pass filter including
an infrared ray absorbing glass 8Ab disposed on the front of the
image sensor; and a dustproof filter 21A which protects the image
sensor and the optical LPF from dust. The first camera body 11A
has the body-side mount portion 3A having the body-side mount surface
3Aa which can abut on the lens-side mount surface 4Aa as described
above. It is to be noted that the dustproof filter 21A, the optical
LPF 8A and the protective glass 6A built in the first camera body
11A constitute a first optical device.
[0055] The image sensor 5A is, for example, a 4/3 [four thirds.RTM.]
type of image sensor having a predetermined reference pixel pitch
.delta.0 which is a first pixel pitch (the corresponding reference
pixel number is S0), and a subject image formed on the photoelectric
conversion surface 5Aa which is an image forming surface of the
image sensor 5A is converted into an electric image capture signal.
[0056] The optical LPF 8A has such a predetermined thickness as
to split a ray in accordance with the reference pixel pitch .delta.0
of the image sensor 5A in order to prevent generation of the Moire
fringes, is formed of crystal plates 8Aa, 8Ac and 8Ad having birefringent
characteristics in a predetermined direction, and further includes
the infrared ray absorbing glass 8Ab.
[0057] In a case where the reference pixel pitch .delta.0=7 .mu.m
is set, to form the optical LPF 8A for tetragonal four-point splitting
(the incident ray is split into four points passing through corners
of a square with side length of the pixel pitch), a thickness and
a rotation angle of each crystal plate are set as follows. That
is, the crystal plate 8Aa has a rotation angle=45.degree. with a
thickness t2=0.84 mm, the crystal plate 8Ac has a rotation angle=45.degree.
with a thickness t4=0.84 mm, and the crystal plate 8Ad has a rotation
angle=0.degree. with a thickness t5=1.19 mm. At this time, refractive
indexes of rock crystal are n2, 4 and 5=1.544. This optical LPF
8A has a total crystal plate thickness of 2.87 mm.
[0058] The infrared ray absorbing glass 8Ab is made of phosphate
glass or fluoric phosphate glass, and a thickness t3=0.5 mm is set
with a refractive index n3=1.542. There is not any restriction on
a material or a thickness of the dustproof filter 21A, but here
the filter is an optical glass having a refractive index n1=1.52
with a thickness t1=1 mm. Furthermore, the protective glass 6A is
an optical glass having a refractive index n6=1.52 with a thickness
t6=0.6 mm.
[0059] The optical LPF 8A is disposed between the body-side mount
portion 3A and the image sensor 5A, and the filter is the thickest
even as compared with the optical LPF 8B of the second camera body
11B described later, and other optical LPF applied to another non-reference
camera body detachably attached to the same lens barrel 12A.
[0060] This lens barrel 12A contains a photographing optical system
12Aa constituted of a plurality of photographing lens units, and
can directly be attached to the first camera body 11A as described
above. Furthermore, the lens barrel 12A can detachably be attached
to the second camera body 11B via the intermediate adapter 31 (FIG.
2) described later. This lens barrel 12A corresponds to one of a
plurality of interchangeable lenses such as interchangeable lenses
having different focal lengths, zoom lenses and macro lenses.
[0061] In a state in which the photographing optical system 12Aa
of the lens barrel 12A is attached to the first camera body 11A,
a taken subject luminous flux passes through the dustproof filter
21A and the optical LPF 8A to form an image on the photoelectric
conversion surface 5Aa of the image sensor 5A. The photographing
optical system 12Aa is designed and produced so as to form the image
on the photoelectric conversion surface 5Aa without generating a
field curvature aberration, a spherical aberration, an astigmatism
or the like in a state in which an effective optical path length
is changed in accordance with the refractive index and the thickness
of the optical LPF 8A or the like. That is, the system is designed
and produced so as to obtain a non-aberration state in which the
image forming point P1' formed by the center luminous flux and the
image forming point P2' by the peripheral luminous flux shown in
FIG. 11 are both positioned on the photoelectric conversion surface
5Aa of the image sensor 5A.
[0062] On the other hand, in the second camera body 11B to which
the lens barrel 12B is detachably attached, as shown in FIG. 1B,
there are built: the image sensor 5B as a second image sensor constituted
of a CCD (MOS type image sensor) or the like having a protective
glass 6B; an optical LPF 8B as a second optical low-pass filter
including an infrared ray absorbing glass 8Bb disposed on the front
of the image sensor; and a dustproof filter 21B which protects the
image sensor and the optical LPF from dust. The second camera body
has the body-side mount portion 3B having the body-side mount surface
3Ba which can engage with the lens-side mount surface 4Ba as described
above. It is to be noted that the dustproof filter 21B, the optical
LPF 8B and the protective glass 6B built in the second camera body
11B constitute a second optical device.
[0063] The image sensor 5B is a 4/3 [four thirds.RTM.] type of
image sensor in the same manner as in the region image sensor 5A,
but has a pixel pitch .delta.1 as a second pixel pitch having a
value which is smaller than that of the reference pixel pitch .delta.0.
A subject image formed on the photoelectric conversion surface 5Ba
which is an image forming surface of this image sensor 5B is converted
into an electric image capture signal in the same manner as in the
image sensor 5A.
[0064] The optical LPF 8B corresponds to the pixel pitch .delta.1
of the image sensor 5B. In a case where this optical LPF is formed
of a crystal plate having the same constitution as that of the optical
LPF 8A, a thickness becomes different from that of the optical LPF
8A.
[0065] In a case where, for example, a pixel pitch .delta.1=5 .mu.m
is set, to form the optical LPF 8B for tetragonal four-point splitting
(in detail, the incident ray is split into four points passing through
corners of a square having the pixel pitch as one side) in the same
manner as in the optical LPF 8A, a thickness and a rotation angle
of each crystal plate are set as follows. That is, a crystal plate
8Ba has a rotation angle of 45.degree. with a thickness t2=0.60
mm, a crystal plate 8Bc has a rotation angle of -45.degree. with
a thickness t4=0.60 mm, and the crystal plate 8Bd has a rotation
angle=0.degree. with a thickness t5=0.85 mm. As compared with a
case where the reference pixel pitch .delta.0=7 .mu.m is set, the
above optical LPF 8B has a total crystal plate thickness of 2.05
mm, and becomes thinner as much as 0.82 mm. The refractive indexes
of rock crystal are n2, 4 and 5=1.544.
[0066] The infrared ray absorbing glass 8Bb is made of phosphate
glass or fluoric phosphate glass, and a thickness t3=0.5 mm is set
with a refractive index n3=1.542. There is not any restriction on
a material or a thickness of the dustproof filter 21B, but here
the filter is an optical glass having a refractive index n1=1.52
with a thickness t1=1 mm. Furthermore, the protective glass 6B is
an optical glass having a refractive index n6=1.52 with a thickness
t6=0.6 mm. These specifications of the optical elements are the
same as those of the infrared ray absorbing glass 8Ab, the dustproof
filter 21A and the protective glass 6A built in the first camera
body 11A.
[0067] The digital camera 2 is designed and produced so as to form
the image on the photoelectric conversion surface 5Ba without generating
the field curvature aberration, the spherical aberration, the astigmatism
or the like in a state in which the effective optical path length
changes in accordance with the refractive index and the thickness
of the optical LPF 8B or the like.
[0068] In the above state, since the crystal plates have the different
thicknesses, the optical path length of the optical device disposed
between the lens barrel 12B and the image sensor 5B is shorter than
that of the optical device of the first camera body 11A.
[0069] Therefore, it is possible to reduce a thickness of the second
camera body 11B in the optical axis direction. The closer to the
image sensor the ray from the interchangeable lens is, the smaller
the distance from the optical axis becomes. Therefore, an outer
shape of the camera body can be reduced even in a direction crossing
the optical axis at right angles.
[0070] On the other hand, the lens barrel 12B has the lens-side
mount portion 4B provided with the lens-side mount surface 4Ba which
can abut on the mount surface 3Ba on the side of the second camera
body, and contains a photographing optical system 12Ba constituted
of a plurality of photographing lens units. This lens barrel 12B
has a short back focal length as compared with the lens barrel 12A.
In other words, as compared with the maximum angle formed, with
the optical axis O, by a chief ray which has struck at a diagonal
angle of the image sensor 5A in the lens barrel 12A, the maximum
angle is larger which is formed, with the optical axis O, by a chief
ray struck at a diagonal angle of the image sensor 5B in the lens
barrel 12B. The interchangeable lens itself also becomes short in
the optical axis direction. The closer to a focal surface the ray
is, the smaller the breadth becomes. Therefore, the diameter of
the lens is reduced, and the interchangeable lens can be miniaturized.
[0071] It is to be noted that this lens barrel 12B has a short
back focal length. Therefore, if the mount is constituted so that
the lens barrel can be attached to the first camera body 11A, the
photographing lens interferes with a constituting member (e.g.,
a quick return mirror for a TTL optical finder) of the camera body
11A, thereby causing a problem. To avoid the problem, in the present
embodiment, as described above, the mount of the digital camera
1 is constituted to be different from that of the digital camera
2, and the lens barrel 12B cannot be directly attached to the first
camera body 11A each other (see FIGS. 3A and 3B). The optical aberration
of the lens barrel 12B is designed to be small in accordance with
the thickness of the optical device of the second camera body 11B.
As described later, even when the lens barrel 12A is attached to
the second camera body 11B via the intermediate adapter 31, the
optical aberration of the lens barrel can be minimized.
[0072] The above digital camera 30 is constituted of the second
camera body 11B and the lens barrel 12A as the first lens attached
to the second camera body 11B via the intermediate adapter 31 (FIG.
2).
[0073] The intermediate adapter 31 has: a front mount portion 33
which is a lens detachable portion disposed on one end of the adapter
on a lens side; a rear mount portion 34 which is a lens detachable
portion disposed on the other end of the adapter on a camera body
side; and an intermediate cylinder 32 fixedly sandwiched between
the front mount portion and the rear mount portion.
[0074] In the intermediate cylinder 32, a correction optical device
32a is disposed as a third optical device (optical device for compensating
the optical path length). This correction optical device 32a is
constituted of a glass plate which does not have any optical power.
[0075] Moreover, a state in which the correction optical device
32a is combined with the second optical device constituted of the
optical LPF 8B built in the second camera body 11B and the like
is optically equivalent (in other words, an optical equivalent amount
is set to be equal) to a state of the first optical device constituted
of the optical LPF 8A built in the first camera body 11A and the
like. This respect will be described later.
[0076] The front mount portion 33 has the same shape as that of
the mount portion 3A of the first camera body 11A, and can be engaged
with and attached to the mount portion 4A of the lens barrel 12A.
[0077] The rear mount portion 34 has the same shape as that of
the mount portion 4B of the lens barrel 12B, and can be engaged
with and attached to the mount portion 3B of the second camera body
11B.
[0078] When the mount portion 34 of the intermediate adapter 31
is engaged with the mount portion 3B of the second camera body 11B,
and the mount portion 33 of the intermediate adapter 31 is engaged
with the mount portion 4A of the lens barrel 12A, the lens barrel
12A can be attached to the second camera body 11B via the intermediate
adapter 31.
[0079] In the above attached state, a mount surface 33a of the
front mount portion 33 closely abuts on the mount surface 4Aa of
the lens barrel 12A. Furthermore, a mount surface 34a of the rear
mount portion 34 closely abuts on the mount surface 3Ba of the second
camera body 11B, and relative positions of the lens barrel 12A,
the intermediate adapter 31 and the second camera body 11B are defined
in the optical axis O direction.
[0080] In the present embodiment, a distance between the front
mount surface 33a and the rear mount surface 34a of the intermediate
adapter 31 is a distance which compensates for shortness of the
flange focal length of the second camera body 11B with respect to
the flange focal length of the first camera body 11A. Therefore,
the optical flange focal length of the second camera body 11B having
the intermediate adapter 31 attached thereto is equal to that of
the first camera body 11A.
[0081] However, the first optical device adapted to the lens barrel
12A is different from the second optical device adapted to the lens
barrel 12B of the second camera body 11B. Therefore, even when the
lens barrel 12A is focused, the optical aberration of the lens barrel
cannot be minimized. To solve the problem, as described above, the
present embodiment is constituted by incorporating the correction
optical device 32a in the intermediate cylinder 32 of the intermediate
adapter 31 and combining the correction optical device 32a with
the second optical device so that the second optical device optically
becomes equivalent to the optical device disposed in the first camera
body.
[0082] To be more specific, as described above, the total crystal
plate thickness of the optical LPF 8A (the only crystal plates excluding
the infrared ray absorbing glass) built in the first camera body
11A is 2.87 mm, and the total crystal plate thickness of the optical
LPF 8B (the only crystal plates excluding the infrared ray absorbing
glass) built in the second camera body 11B is 2.05 mm. The infrared
ray absorbing glasses 8Ab and 8Bb, the dustproof filters 21A and
21B and the protective glasses 6A and 6B constituting the first
and second optical devices except the crystal plates are made of
the same material having an equal thickness.
[0083] Therefore, to set the total thickness of the first optical
device to be equal to the total thickness obtained by adding the
thickness of the correction optical device 32a to the total thickness
of the second optical device, the thickness corresponding to shortness
of the total crystal plate thickness of the optical LPF 8B with
respect to that of the optical LPF 8A may be set to the thickness
of the correction optical device 32a on the side of the intermediate
adapter 31. The thickness corresponding to the deficiency is 0.82
mm. Even when the correction optical device 32a having a physical
thickness of 0.82 mm is applied to the intermediate adapter 31,
however, the optical aberration cannot be minimized.
[0084] To solve the problem, in the present embodiment, to set
the optical equivalent amount of the second optical device and the
correction optical device 32a to be equal to that of the first optical
device, it is possible to minimize the optical aberration at a time
when the intermediate adapter 31 is used.
[0085] In other words, by providing the correction optical device
32a within the intermediate adapter 31, an optical distance from
the mount surface (lens attaching surface) 3Aa of the first camera
body 11A to the image capture surface and an optical distance from
the mount surface (lens attaching surface) 33a of the intermediate
adapter 31 to the image capture surface of the second camera body
11B are set to be equal in a state in which the intermediate adapter
31 is attached to the second camera body 11B. In consequence, even
with a combination of the lens barrel 12A and the second camera
body 11B, the optical aberration can be minimized.
[0086] The optical equivalent-amount corresponds to an equivalent
amount of a change of the effective optical path length in the optical
axis direction including a deviation of an oblique ray in a magnification
direction, and is given by .SIGMA.{optical element thickness+(1-optical
element refractive index)/optical element refractive index}. When
this value is set to be equal in the optical device having the different
constitution, the photoelectric conversion surface of the image
sensor is focused, and the aberration can be minimized in both of
the camera.
[0087] In the first camera body 11A (in a case where the reference
pixel pitch .delta.0 of the image sensor=7 .mu.m), a first optical
equivalent amount of the first optical device constituted of optical
elements is as follows:.SIGMA.{ti.times.(1-ni)/ni} =1.00.times.(1-1.52)/1.52
+0.84.times.(1-1.544)/1.544+0.5(1-1.542)/1.542 +0.84.times.(1-1.544)/1.544+1.19.times.(1-1.544)/1.544
+0.6.times.(1-1.52)/1.52=-1.734, wherein i is an integer of 1, 2,
. . . given to each optical element constituting the first optical
device from a lens side, ni is a refractive index of each optical
element, and ti is a thickness thereof
[0088] In the second camera body 11B (in a case where the pixel
pitch .delta.1 of the image sensor=5 .mu.m), a second optical equivalent
amount of the second optical device constituted of optical elements
is smaller than the first optical equivalent amount as follows:.SIGMA.{tj.times.(1-nj)/nj}
=1.00.times.(1 1.52)/1.52 +0.6.times.(1-1.554)/1.544+0.5(1-1.542)/1.542
+0.6.times.(1-1.544)/1.544+0.85.times.(1-1.544)/1.544 +0.6.times.(1-1.52)/1.52
=-1.445, wherein j is an integer of 1, 2, . . . given to each optical
element constituting the second optical device from the lens side,
nj is a refractive index of each optical element, and tj is a thickness
thereof.
[0089] Moreover, the correction optical device 32a built in the
intermediate adapter 31 may be an optical device having a difference
between the first optical equivalent amount and the second optical
equivalent amount, that is, a third optical equivalent amount given
by the following:.SIGMA.{ti.times.(1-ni)/ni}-.SIGMA.{tj.times.(1-nj)/nj}=(-1-
.734)-(-1.445)=-0.289.
[0090] For example, in a case where the device is made of glass
having a refractive index n=1.5, the third optical equivalent amount
is th.times.(1-1.5)/1.5, wherein th is a thickness of glass. Therefore,
the thickness is as follows:th=-0.289.times.1.5/(1-1.5)=0.867 mm.
That is, when the optical glass plate having a thickness of th=0.867
mm is applied as the correction optical device 32a, a sum of the
second optical equivalent amount and the third optical equivalent
amount equals the first optical equivalent amount, and the above
conditions can be satisfied.
[0091] In the present embodiment, the correction optical device
32a is used for correcting the optical equivalent amount, but may
be provided with an effect of an infrared ray cutting filter or
a visible light cutting filter, or may, needless to say, be provided
with an effect of an optical low-pass filter to provide a secondary
optical effect such as the optical low-pass filter effect different
from an inherent effect. In a case where such a secondary effect
is imparted to the correction optical device 32a, when the correction
optical device is detachably attached to the intermediate adapter,
a user can use the digital camera while freely changing the above
secondary effect.
[0092] Moreover, the above correction optical device 32a itself
does not have to be necessarily disposed in the intermediate adapter
31. For example, in a state in which the lens barrel 12A is attached
to the second camera body 11B via the intermediate adapter 31, the
correction optical device 32a may be inserted between a rear end
portion of the lens barrel 12A and a front end portion of the second
camera body 11B, or may be attached to the rear end portion of the
lens barrel 12A or the front end portion of the second camera body
11B.
[0093] It is to be noted that in a case where the correction optical
device of the third optical device is constituted of a plurality
of optical elements, the third optical equivalent amount of the
correction optical device is given by .SIGMA.{tk.times.(1-nk)/nk},
wherein k is an integer of 1, 2, . . . given to each optical element
constituting the correction optical device from the lens side, nk
is the refractive index of each optical element and tk is the thickness
thereof. Moreover, the first optical equivalent amount .SIGMA.{ti.times.(1-ni)/ni}
of the first optical device may equal the sum of the second optical
equivalent amount .SIGMA.{tj.times.(1-nj)/nj} of the second optical
device and the third optical equivalent amount .SIGMA.{tk.times.(1-nk)/nk}
of the correction optical device.
[0094] As described above, the distance between the front mount
surface 33a and the rear mount surface 34a in the intermediate adapter
31 of the present embodiment is set so that the flange focal length
on the side of the second camera body 11B having the intermediate
adapter 31 attached thereto equals the flange focal length of the
first camera body 11A. However, even in a case where there is a
slight excess or deficiency in the distance, with respect to the
first optical equivalent amount, the value of the sum of the second
optical equivalent amount and the third optical equivalent amount
is set to such a value as to compensate for the excess or the deficiency
of the distance. Accordingly, in a state in which the lens barrel
12A is attached to the second camera body 11B via the intermediate
adapter, a subject can be focused. Moreover, it is possible to take
in a subject image having less optical aberration.
[0095] FIGS. 4A, 4B are diagrams showing ray deviation amounts
.DELTA.Hi, .DELTA.Hj due to oblique incidence at a time when the
ray strikes at an incidence angle X0 on two types of optical elements
having different thicknesses and refractive indexes. FIG. 4A shows
the ray deviation amount .DELTA.Hi with respect to one optical element
(on a first optical device side) having a thickness ti and a refractive
index ni. FIG. 4B shows the ray deviation amount .DELTA.Hj with
respect to the other optical element (on a second optical device
side) having a different thickness tj and a different refractive
index nj. It is to be noted that in the drawing, each of Hi and
Hj denotes a height to a position where the incident ray is extended,
each of Hi' and Hj' denotes a height to an emission point of a refracted
ray, and the ray deviation amounts .DELTA.Hi, .DELTA.Hj are given
by differences between Hi and Hj and between Hi' and Hj , respectively.
[0096] In a case where the aberration of the photographing lens
in the magnification direction is considered, when the ray deviation
amount .DELTA.Hi equals .DELTA.Hj, the aberration is equal. That
is, a ray deviation amount ratio .DELTA.Hj/.DELTA.Hi may be 1. It
is to be noted that the optical equivalent amount with respect to
the optical device constituted of the above optical elements corresponds
to a value obtained by adding the ray deviation amount .DELTA.Hi
or .DELTA.Hj of each optical element.
[0097] FIG. 5 is a graph showing a relation between the incidence
angle X0 and the ray deviation amount ratio .DELTA.Hj/.DELTA.Hi
on conditions that optical equivalent amounts of the optical elements
having different refractive indexes are set to be equal. In the
drawing, as the ray deviation amount .DELTA.Hi, a value at a time
when the optical element having a refractive index ni=1.5 is applied.
The ray deviation amount .DELTA.Hj indicates a value of the optical
element in which the refractive index nj changes to 1.4, 1.8, 2,
2.2 or 2.4.
[0098] As shown in FIG. 5, in a general optical material (the refractive
index at a wavelength of 587.6 nm is 1.4 to 2), when the incidence
angle is 15.degree. or less, an optical deviation amount ratio is
approximately 1 (error is 1% or less), and does not influence the
optical aberration. The refractive index of 2.4 indicates a case
where the LN device for use in the optical low-pass filter is used
as the material. Even when a special material having a high refractive
index, such as this LN device, is used, the optical deviation amount
ratio can be close to 1. In this graph, the refractive index of
light having a wavelength of 587.6 nm has been considered. Even
as to another light having a wavelength of, for example, 486.1 nm
to 626.3 nm, when the optical material is selected so that the ray
deviation amount ratio is close to 1, it is possible to suppress
an aberration change of even a chromatic aberration. In the digital
camera, subject light having a wavelength in the vicinity of 420
nm to 650 nm is dominant in forming the image. Therefore, when the
ray deviation amount ratio is set to approximately 1 in this wavelength
range, an influence on the image of the chromatic aberration can
be reduced.
[0099] Next, there will be described an inner structure of the
digital camera 1 or 2 in the digital camera system of the present
embodiment with reference to FIGS. 6 to 10.
[0100] FIG. 6 is a perspective view (shown in a partially cut section)
showing the inner structure in a state in which the interchangeable
lens barrels 12A, 12B are attached to the camera bodies 11A, 11B
in the digital cameras 1, 2, respectively. FIG. 7 is a perspective
view (shown in a partially cut section) showing an inner structure
around an image capture unit 15A, 15B in the digital camera 1, 2.
[0101] As shown in FIG. 6, the digital camera 1 includes: the lens
barrel 12A; and the first camera body 11A which is a reference camera
body detachably attached to the lens barrel 12A, or the digital
camera 2 includes the lens barrel 12B; and the second camera body
11B which is a non-reference camera body detachably attached to
the lens barrel 12B.
[0102] The first camera body 11A is different from the second camera
body 11B in the image sensor of the contained image capture unit,
the optical LPF, and the flange focal length, but the other constitution
is the same.
[0103] The lens barrel 12A or 12B is constituted to hold therein
the photographing optical system 12Aa or 12Ba constituted of a plurality
of lenses, respectively. Moreover, this photographing optical system
12Aa or 12Ba is constituted of, for example, a plurality of optical
lenses and the like so that a luminous flux from a subject is transmitted
to form an image of the subject by the subject luminous flux in
a predetermined position (on the photoelectric conversion surface
of the image sensor 5A, 5B of FIG. 7) in a state in which there
is not any optical aberration such as the field curvature aberration.
That is, the photographing optical system is designed so as to eliminate
the field curvature aberration generated by the optical LPF disposed
on the front of the image sensor.
[0104] It is to be noted that here the state in which there is
not any aberration includes a state in which there is the aberration
to such an extent that there is not any practical problem during
actual use. In other words, the photographing optical system 12Aa
or 12Ba is designed so that various aberrations are optimum in consideration
of the optical LPF disposed on the front of the image sensor and
the like.
[0105] The camera body 11A or 11B includes various types of constituting
members and the like in a main body portion 11Aa or 11Ba, and the
body-side mount portion 3A or 3B is disposed in the front of the
main body portion so that the lens barrel 12A or 12B holding the
photographing optical system 12Aa, 12Ba is detachably attached.
In this manner, the camera body 11A or 11B is a so-called "single
lens reflex type" camera body. That is, substantially in the
center of the front of the camera main body portion 11Aa, 11Ba,
there is formed an aperture for exposure having a predetermined
aperture size so as to guide the subject luminous flux into the
camera main body portion 11Aa, 11Ba, and the body-side mount portion
3A or 3B is formed on a peripheral edge of this aperture for exposure.
[0106] There will be described in detail an inner constitution
of the camera body 11A or 11B of the first or second digital camera.
[0107] First, in a predetermined position such as the top portion
or the back of the camera main body portion 11Aa, 11Ba, there are
disposed various types of operation members for operating the camera
body 11A or 11B, for example, a release button 17 for generating
an instructing signal or the like to start a photographing operation.
[0108] In each of the camera main body portions 11Aa and 11Ba,
as shown in FIG. 6, various types of constituting members are arranged
in predetermined positions, respectively: for example, a finder
unit 13; a shutter portion 14; the image capture unit 15A (for the
first camera body) or 15B (for second camera body); and a plurality
of circuit substrates including a main circuit substrate 16A (for
the first camera body) or 16B (for the second camera body).
[0109] The finder unit 13 is disposed in order to form a desired
subject image taken by the photographing optical system 12Aa or
12Ba in a predetermined position different from a position on the
photoelectric conversion surface of the image sensor 5A or 5B (FIG.
7), thereby forming a so-called observation optical system. The
shutter portion 14 includes a shutter mechanism and the like which
controls an irradiation time or the like with the subject luminous
flux onto the photoelectric conversion surface of the image sensor
5A or 5B. The image capture unit 15A, 15B includes the image sensor,
and obtains a subject image signal based on the subject luminous
flux transmitted through the photographing optical system 12Aa,
12Ba. On the main circuit substrate 16A, 16B, various types of electric
members are mounted which constitute an electric circuit such as
an image signal processing circuit for subjecting the image signal
acquired by the image sensor 5A or 5B to various types of signal
processing. On the front of the image capture unit 15A, 15B, the
dustproof filter 21A or 21B is disposed which prevents dust and
the like from being attached to the photoelectric conversion surface
of the image sensor.
[0110] The finder unit 13 is constituted of a reflective mirror
13b, a penta prism 13a, an eyepiece lens 13c and the like. The reflective
mirror 13b bends the optical axis of the subject luminous flux transmitted
through the photographing optical system 12Aa or 12Ba to guide the
flux toward the observation optical system. The penta prism 13a
receives the luminous flux emitted from this reflective mirror 13b
to form a normal image. The eyepiece lens 13c enlarges the subject
image via this penta prism 13a to observe the image.
[0111] The reflective mirror 13b is constituted movably between
a position set back from the optical axis of the photographing optical
system 12Aa or 12Ba and a predetermined position on the optical
axis. The reflective mirror 13b in a usual state is disposed at
a predetermined angle of, for example, 45.degree. along the optical
axis of the photographing optical system 12Aa or 12Ba. Accordingly,
while the camera 1 or 2 is in the usual state, the optical axis
of the subject luminous flux transmitted through the photographing
optical system 12Aa or 12Ba is bent by the reflective mirror 13b,
and the flux is reflected toward the penta prism 13a disposed above
the reflective mirror 13b.
[0112] In an exposure operation during the photographing of the
digital camera 1 or 2, the reflective mirror 13b moves to a predetermined
position set back from the optical path of the photographing optical
system 12Aa, 12Ba. Accordingly, the subject luminous flux is guided
toward the image sensor to irradiate the photoelectric conversion
surface of the image sensor.
[0113] The shutter portion 14 similar to a shutter portion for
general utilization in a conventional camera or the like is applied,
the portion including, for example, a focal plane type of shutter
mechanism, a driving circuit for controlling an operation of this
shutter mechanism and the like.
[0114] The image capture unit 15A for the first camera body is
different from the image capture unit 15B for the second camera
body in the contained image sensor and optical LPF only, and the
other constitution is substantially the same. First, the image capture
unit 15A for the first camera body will be described.
[0115] As shown in FIG. 7, the image capture unit 15A is constituted
of: the image sensor 5A; an image sensor fixing plate 28; the optical
LPF 8A; a low-pass filter receiving member 26; an image sensor storage
case member 24 (hereinafter referred to as the CCD case 24); a dustproof
filter receiving member 23; the dustproof filter 21A; a piezoelectric
device 22; a pressing member 20 and the like.
[0116] The image sensor 5A is constituted of a CCD or the like
which obtains an image signal corresponding to light transmitted
through the photographing optical system 12Aa to irradiate the photoelectric
conversion surface of the system. The image sensor fixing plate
28 is constituted of a thin-plate-like member which fixedly supports
this image sensor 5A. The optical LPF 8A is disposed on the photoelectric
conversion surface of the image sensor 5A, and formed so as to remove
high-frequency components from the subject luminous flux transmitted
through the photographing optical system 12Aa to irradiate the photoelectric
conversion surface of the system. The low-pass filter receiving
member 26 is disposed in a peripheral edge between this optical
LPF 8A and the image sensor 5A, and is formed of an elastic member
substantially having a frame shape or the like. The CCD case 24
stores and fixedly holds the image sensor 5A. Moreover, the optical
LPF 8A is brought into close contact with a peripheral edge portion
of the CCD case or the vicinity of the portion, and supported. A
predetermined portion of the CCD case is brought into close contact
with the dustproof filter receiving member 23 described later. As
to the dustproof filter receiving member 23, the dustproof filter
21A disposed on the front of this CCD case 24 is brought into close
contact with a peripheral edge portion of the dustproof filter receiving
member or the vicinity of the portion, and supported. The dustproof
filter 21A is a dustproof member supported by this dustproof filter
receiving member 23 and disposed to face a predetermined position
having a predetermined interval from the optical LPF 8A on the front
of the optical LPF 8A on the photoelectric conversion surface of
the image sensor 5A. The piezoelectric device 22 is disposed on
the peripheral edge portion of this dustproof filter 21A, and applies
a predetermined vibration to the dustproof filter 21A to remove
the dust from the filter. The pressing member 20 is constituted
of an elastic material which attaches the dustproof filter 21A to
the dustproof filter receiving member 23 in an airtight manner to
fixedly hold the filter.
[0117] The image sensor 5A receives the subject luminous flux transmitted
through the photographing optical system 12Aa by the photoelectric
conversion surface 5Aa (FIG. 1A) of the system to subject the flux
to photoelectric conversion processing, thereby acquiring an image
signal corresponding to the subject image formed on the photoelectric
conversion surface. As the image sensor 5A, there is applied, for
example, a 4/3 [four thirds.RTM.] type of charge coupled device
having a reference pixel pitch .delta.0 of approximately 7 .mu.m
as a first pixel pitch.
[0118] This image sensor 5A is mounted on a predetermined position
of the main circuit substrate 16A via the image sensor fixing plate
28. On this main circuit substrate 16A, both of an image signal
processing circuit and a work memory (not shown) are mounted, and
an output signal from the image sensor 5A, that is, an image signal
obtained by the photoelectric conversion processing is transmitted
to the image signal processing circuit or the like. The protective
glass 6A (FIG. 7) is disposed in front of the photoelectric conversion
surface of the image sensor 5A.
[0119] As signal processing in the image signal processing circuit,
there are various types of signal processing such as processing
to convert, into a signal adapted to a recording mode, the image
output signal of the image sensor 5A corresponding to the image
formed on the photoelectric conversion surface of the image sensor
5A by the photographing optical system 12Aa of the lens barrel 12A.
Such signal processing is similar to processing usually performed
in a general digital camera or the like constituted so as to handle
an electronic image signal.
[0120] On the front of the image sensor 5A, the optical LPF 8A
is disposed with the low-pass filter receiving member 26 being held
between the sensor and the optical LPF. The optical LPF 8A is made
of rock crystal of an optical element having a birefringent characteristic,
and has a thickness ts0 corresponding to the pixel pitch .delta.0
(approximately 7 .mu.m) of the image sensor 5A as described later.
It is to be noted that as described later, the infrared ray absorbing
glass is inserted into the optical LPF 8A.
[0121] Moreover, the CCD case 24 is disposed so as to cover the
optical LPF 8A. Substantially in the center of this CCD case 24,
a rectangular aperture is disposed, and in this aperture, the optical
LPF 8A and the image sensor 5A are disposed from behind the aperture.
On an inner peripheral edge portion behind this aperture, a stepped
portion 24a having a substantially L-shaped section is formed which
abuts on the front of the optical LPF 8A.
[0122] As described above, between the optical LPF 8A and the image
sensor 5A, the low-pass filter receiving member 26 is disposed which
is constituted of an elastic member or the like. This low-pass filter
receiving member 26 is disposed in a position which avoids an effective
region of the photoelectric conversion surface in the peripheral
edge portion of the front of the image sensor 5A, and abuts on the
vicinity of the peripheral edge portion of the back of the optical
LPF 8A. Moreover, airtightness is substantially held between the
optical LPF 8A and the image sensor 5A. Accordingly, an elastic
force of the low-pass filter receiving member 26 acts on the optical
LPF 8A in the optical axis direction.
[0123] Moreover, the peripheral edge portion of the front of the
optical LPF 8A is brought into contact with the 24a of the CCD case
24 in a substantially airtight manner. Accordingly, the position
of the optical LPF 8A in the optical axis direction is regulated
against the elastic force of the low-pass filter receiving member
26 which is to displace the optical LPF 8A in the optical axis direction
of the LPF.
[0124] In other words, when the optical LPF 8A is inserted into
the aperture of the CCD case 24 from the backside, the position
of the LPF in the optical axis direction is regulated by the stepped
portion 24a. Accordingly, the optical LPF 8A is directed toward
the front of the CCD case 24 so as to be prevented from being extracted
outwardly.
[0125] After the optical LPF 8A is inserted into the aperture of
the CCD case 24 from the backside in this manner, the image sensor
5A is disposed on the back of the optical LPF 8A. The low-pass filter
receiving member 26 is held between the peripheral edge portions
of the optical LPF 8A an dh image sensor 5A.
[0126] Moreover, the image sensor 5A is mounted on the main circuit
substrate 16A with the image sensor fixing plate 28 being held therebetween
as described above. Moreover, the image sensor fixing plate 28 is
fixed to a screw hole 24e by a screw 28b from the backside of the
CCD case 24 via a spacer 28a. Moreover, the main circuit substrate
16A is fixed to the image sensor fixing plate 28 by a screw 16d
via a spacer 16c.
[0127] On the front of the CCD case 24, the dustproof filter receiving
member 23 is fixed to a screw hole 24b of the CCD case 24 by a screw
23b. A peripheral groove 24d is formed into a substantially annular
state in a predetermined position on the peripheral edge of the
front of the CCD case 24. On the other hand, in a predetermined
position of the peripheral edge of the backside of the dustproof
filter receiving member 23, an annular convex portion 23d corresponding
to the peripheral groove 24d of the CCD case 24 is substantially
annularly formed over the whole periphery. Therefore, the annular
convex portion 23d is fitted into the peripheral groove 24d to thereby
fit the CCD case 24 into the dustproof filter receiving member 23
in an annular region, that is, a region where the peripheral groove
24d and the annular convex portion 23d are formed in the substantially
airtight manner.
[0128] The dustproof filter 21A is made of glass, and entirely
forms a circular or polygonal plate shape. At least a region of
the filter having a predetermined breadth from the center of the
filter in a radial direction forms a transparent portion, and this
transparent portion is disposed to face the front of the optical
LPF 8A at a predetermined interval.
[0129] Moreover, to the peripheral edge portion of one surface
of the dustproof filter 21A, the piezoelectric device 22 is integrally
disposed by bonding means such as an adhesive or the like. The piezoelectric
device is a predetermined vibrating member for applying a vibration
to the dustproof filter 21A, and is formed of an electromechanical
conversion device or the like. This piezoelectric device 22 is constituted
so that a predetermined driving voltage can be applied to the device
from the outside to generate a predetermined vibration in the dustproof
filter 21A.
[0130] Furthermore, the dustproof filter 21A is fixedly held by
the pressing member 20 constituted of an elastic material such as
a leaf spring so that the filter is bonded to the dustproof filter
receiving member 23 in the airtight manner.
[0131] Substantially in the vicinity of the center of the dustproof
filter receiving member 23, a circular or polygonal aperture is
disposed. This aperture is set so as to have a sufficient size for
transmitting the subject luminous flux transmitted through the photographing
optical system 12Aa to irradiate the photoelectric conversion surface
of the image sensor 5A disposed rearwards with the luminous flux.
[0132] In the peripheral edge portion of this aperture, a wall
portion 23e protruding toward the front is substantially annularly
formed, and in a distant end of this wall portion 23e, a receiving
portion 23c is formed so as to further protrude toward the front.
[0133] On the other hand, in the vicinity of an outer peripheral
edge portion of the front of the dustproof filter receiving member
23, a plurality of (three in the present embodiment) protruding
portions 23a are formed in predetermined positions so as to protrude
toward the front. The protruding portions 23a are formed to fixedly
dispose the pressing member 20 which fixedly holds the dustproof
filter 21A, and the pressing member 20 is fixed to distant end portions
of the protruding portions 23a by fastening means such as a screw
20a.
[0134] The pressing member 20 is formed of an elastic material
such as the leaf spring as described above, a proximal end portion
of the member is fixed to the protruding portions 23a, and a free
end portion of the member abuts on the outer peripheral edge portion
of the dustproof filter 21A. Accordingly, the member presses the
dustproof filter 21A toward the dustproof filter receiving member
23, that is, in the optical axis direction.
[0135] In this case, a predetermined portion of the piezoelectric
device 22 disposed on the outer peripheral edge portion of the backside
of the dustproof filter 21A abuts on the receiving portion 23c to
thereby regulate the positions of the dustproof filter 21A and the
piezoelectric device 22 in the optical axis direction. Therefore,
the dustproof filter 21A is fixedly held by the piezoelectric device
22 so that the filter is bonded to the dustproof filter receiving
member 23 in the airtight manner.
[0136] In other words, the dustproof filter receiving member 23
is bonded to the dustproof filter 21A via the piezoelectric device
22 by an urging force of the pressing member 20 in the airtight
manner.
[0137] In addition, as described above, in the dustproof filter
receiving member 23 and the CCD case 24, the annular convex portion
23d is fitted into the peripheral groove 24d in the substantially
airtight manner. Moreover, the dustproof filter receiving member
23 is bonded to the dustproof filter 21A via the piezoelectric device
22 by the urging force of the pressing member 20 in the airtight
manner. The optical LPF 8A is disposed in the CCD case 24 so that
there is substantially the airtightness between the peripheral edge
portion of the front of the optical LPF 8A and the stepped portion
24a of the CCD case 24. Furthermore, on the backside of the optical
LPF 8A, the image sensor 5A is disposed via the low-pass filter
receiving member 26, and the airtightness is substantially held
between the optical LPF 8A and the image sensor 5A.
[0138] Therefore, in a space where the optical LPF 8A faces the
dustproof filter 21A, a predetermined gap portion 51a is formed.
In the peripheral edge of the optical LPF 8A, the CCD case 24, the
dustproof filter receiving member 23 and the dustproof filter 21A
form a space portion 51b. This space portion 51b is a sealed space
formed so as to protrude outwardly from the optical LPF 8A.
[0139] Moreover, this space portion 51b is set as a space broader
than the gap portion 51a. Moreover, the space formed by the gap
portion 51a and the space portion 51b is a sealed space 51 sealed
with the CCD case 24, the dustproof filter receiving member 23,
the dustproof filter 21A and the optical LPF 8A in the substantially
airtight manner as described above.
[0140] FIG. 8 is a schematic diagram showing details of an optical
system of the image capture unit 15A in the first camera body 11A,
and FIG. 9 is an enlarged vertically sectional view of the image
capture unit 15A.
[0141] As shown in FIG. 8, the protective glass 6A is disposed
as the first optical device on the front of the image sensor 5A,
and in front of the protective glass, the optical LPF 8A and the
dustproof filter 21A are arranged.
[0142] As already described with reference to FIG. 1A, the optical
LPF 8A is constituted by superimposing, from the front side, the
crystal plate 8Aa having a birefringent direction (rotation angle)
of -45.degree., the infrared ray absorbing glass 8Ab, the crystal
plate 8Ac having a birefringent direction (rotation angle) of +45.degree.
and the crystal plate 8Ad having the birefringent direction (rotation
angle) of 0.degree..
[0143] Each of the crystal plates 8Aa and 8Ac has a thickness corresponding
to the pixel pitch .delta.0 (approximately 7 .mu.) of the image
sensor 5A shown in FIG. 12. The crystal plate 8Ad has a thickness
of square root times to that of the crystal plate 8Aa, 8Ab. Therefore,
when the subject luminous flux struck via the lens barrel 12A forms
the image on the photoelectric conversion surface 5Aa of the image
sensor 5A, the Moire fringes are prevented from being generated.
[0144] Moreover, each of the crystal plates 8Aa, 8Ac and 8Ad and
the infrared ray absorbing glass 8Ab has a refractive index close
to that of glass, and a total thickness of the crystal plates and
the infrared ray absorbing glass 8Ab is ts0. Moreover, the photoelectric
conversion surface 5Aa of the image sensor 5A is positioned in the
image forming position of the subject luminous flux based on the
effective optical path length corresponding to the refractive index
and the thickness ts0 of each of the crystal plates 8Aa, 8Ac and
8Ad and the infrared ray. absorbing glass 8Ab. Therefore, the subject
luminous flux taken in by the lens barrel 12A is correctly formed
into the image on the photoelectric conversion surface 5Aa of the
image sensor 5A in the state in which there is not any field curvature
aberration. Strictly, the thicknesses of the protective glass 6A
and the dustproof filter 21A also contribute to the change of the
effective optical path length.
[0145] It is to be noted that the thicknesses of the protective
glass 6A for the first camera body 11A and the dustproof filter
21A are equal to those of the protective glass 6B for the second
camera body 11B and the dustproof filter 21B (FIG. 1B), respectively.
Therefore, there is not any difference in effective optical path
length between the protective glasses 6A and 6B and between the
dustproof filters 21A and 21B in the first camera body 11A and the
second camera body 11B.
[0146] Moreover, in a case where the thickness and/or the material
of the protective glass 6A or the dustproof filter 21A is changed
for the first camera body 11A and the second camera body 11B, the
thickness or the material of the compensating optical device needs
to be changed so as to compensate for the change of the effective
optical path length accompanying the change, thereby correcting
optical aberrations such as the field curvature aberration, the
spherical aberration and the astigmatism.
[0147] On the other hand, instead of the image sensor 5A and the
optical LPF 8A of the image capture unit 15A of the first camera
body 11A, the second camera body 11B contains the image sensor 5B
and the optical LPF 8B of the image capture unit 15B. The other
constitution of the second camera body 11B is the same as that of
the first camera body 11A, and a different respect will be described
hereinafter. FIG. 10 is an enlarged vertically sectional view of
the image capture unit 15B in the second camera body 11B.
[0148] The size of the image sensor 5B of the image capture unit
15B contained in the second camera body 11B is of the 4/3 [four
thirds.RTM.] type in the same manner as in the image sensor 5A,
but the image sensor 5B has, for example, a pixel pitch .delta.1
as the second pixel pitch which is different from the reference
pixel pitch .delta.0 (approximately 7 .mu.).
[0149] As already described with reference to FIG. 1B, the optical
LPF 8B disposed in front of the image sensor 5B is an optical device
member constituted by superimposing the crystal plate 8Ba, the infrared
ray absorbing glass 8Bb, the crystal plate 8Bc and the crystal plate
8Bd to secure them with an optical adhesive. The crystal plates
8Ba, 8Bc and 8Bd have such thicknesses to double refract the subject
luminous flux in accordance with the pixel pitch of the image sensor
5B, and the thickness of this optical LPF 8B is ts1. The infrared
ray absorbing glass 8Bb is formed of the same material as that of
the infrared ray absorbing glass 8Ab applied to the first camera
body 11A, and has an equal thickness and refractive index.
[0150] It is to be noted that the crystal plate may be replaced
with the LN device as described later in accordance with the pixel
pitch of the image sensor.
[0151] In a case where the pixel pitch .delta.1 of the image sensor
5B of the second camera body 11B is smaller than the reference pixel
pitch .delta.0=7 .mu.m, and is 5 .mu.m, that is, the number of the
pixels of the image sensor 5B is larger than that of the image sensor
5A, the thickness ts1 of the optical LPF 8B of the second camera
body 11B is smaller than the thickness ts0 of the optical LPF 8A
(FIG. 12).
[0152] Moreover, the dustproof filter 21B and the protective glass
6B are disposed on front portions of the optical LPF 8B and the
image sensor 5B, respectively, but as described above, they have
thicknesses and refractive indexes which are equal to those of the
dustproof filter 21A and the protective glass 6A in the first camera
body 11A, respectively, as described above.
[0153] According to the above image capture unit 15B, the subject
luminous flux taken via the attached lens barrel 12B is correctly
formed into the image on the photoelectric conversion surface 5Ba
of the image sensor 5B without any image forming positional deviation
in a state in which there is not any field curvature aberration,
spherical aberration, astigmatism or the like.
[0154] In the present embodiment, the reference pixel pitch .delta.0
of the image sensor on the side of the reference first camera body
11A is set to 7 .mu.. A method of setting this reference pixel pitch
will be described hereinafter.
[0155] As described above, the thickness of the optical LPF (optical
low-pass filter) is determined in accordance with the pixel pitch
of the image sensor. Even when the pixel pitch is equal, however,
the thickness of the filter changes in accordance with the material
of the optical LPF. As shown in FIG. 12, in a case where, for example,
rock crystal is used as a first material, and a case where the LN
device is used as a second material, the thickness completely differs.
It is to be noted that the number of the pixels shown in FIG. 12
indicates an example of the 3/4[four thirds.RTM.] type image sensor.
[0156] On the other hand, to miniaturize the camera, it is preferable
to use a thinner optical LPF, but an excessively thin filter is
not preferable because it is difficult to manufacture the optical
LPF itself, and the filter might be broken. The example of the LN
device will be described. In the present situation, as shown in
FIG. 12, the thickness of each LN device constituting the optical
LPF in accordance with the image sensor having a pixel pitch which
is smaller than about 7 to 6 .mu.m is about 0.1 mm or less, and
it becomes difficult to manufacture the optical LPF.
[0157] To solve the problem, the pixel pitch which is not less
than a pixel pitch capable of coping with the minimum thickness
formed by the LN device as the second material is set as the reference
pixel pitch. Moreover, when the optical LPF is made of rock crystal
as the first material in accordance with this reference pixel pitch,
the minimum thickness of the optical LPF can be set with respect
to the camera body having any pixel pitch.
[0158] That is, with respect to the camera body having the image
sensor with the pixel pitch which is smaller than the reference
pixel pitch, as seen from FIG. 12, the optical LPF which is thinner
than that made of rock crystal in accordance with the reference
pixel pitch can be formed of rock crystal which is the same material
as that of the optical LPF in accordance with the reference pixel
pitch. Since the thickness of the optical LPF can be set to be smaller
than that of the optical LPF corresponding to the reference pixel
pitch in this manner, the effective optical path length can be compensated
by the compensating optical device.
[0159] Moreover, the number of the pixels of the image sensor of
the digital camera is set to, for example, three million pixels,
four million pixels and five million pixels in a stepwise manner
in many cases. Therefore, the reference pixel pitch may be slightly
smaller than the pixel pitch which can be coped with by the optical
LPF formable of the second material and having the minimum thickness.
That is, the optical LPF corresponding to the pixel pitch of the
image sensor having a smaller pixel number (larger pixel pitch)
as compared with the reference camera body may be formed of the
second material. When the reference pixel pitch is set in this manner,
the thickness of the optical LPF can further be reduced.
[0160] Furthermore, reference pixel pitch data set as described
above are references for design of the lens barrel (interchangeable
lens) and design of the finder unit 13 for use in attaching this
lens barrel to the camera body 11B having a short flange focal length.
[0161] As described above, according to the digital camera system
of the present embodiment, in the digital camera system constituted
of the first camera body 11A having a long flange focal length and
the first lens barrel 12A attachable to the camera body, the second
camera body 11B having a short flange focal length and the lens
barrel 12B attachable to the camera body, and the intermediate adapter
31, the second camera body 11B can further be miniaturized and lightened.
Furthermore, the lens barrel 12A can be attached to the second camera
body 11B via the intermediate adapter 31, and high-quality image
capture can be performed even in the attached state.
[0162] This invention is not limited to the above embodiments,
and additionally in an implementing stage, various modifications
can be carried out without departing from the scope. Furthermore,
the above embodiments include various stages of inventions, and
various inventions can be extracted by an appropriate combination
of a plurality of disclosed constituting requirements.
[0163] According to the digital camera system of the present invention,
in the digital camera system constituted of the first and second
camera bodies having different flange focal lengths and the first
and second lenses attachable to the camera bodies, and the intermediate
adapter, the second camera body having a short flange focal length
can be miniaturized and lightened. Furthermore, the system can be
utilized as a digital camera system in which the first lens can
be attached to the second camera body via the intermediate adapter,
and high-quality image capture can be performed even in the attached
state.
[0164] While there has been shown and described what are considered
to be preferred embodiments of the invention, it will, of course,
be understood that various modifications and changes in form or
detail could readily be made without departing from the spirit of
the invention. It is therefore intended that the invention not be
limited to the exact forms described and illustrated, but constructed
to cover all modifications that may fall within the scope of the
appended claims.
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