U.S. patent application number 09/837357 was filed with the patent office on 2002-01-31 for electronic camera.
This patent application is currently assigned to Olympus Optical Co., Ltd.. Invention is credited to Higuchi, Tatsuji, Kato, Koji.
Application Number | 20020012061 09/837357 |
Document ID | / |
Family ID | 26590671 |
Filed Date | 2002-01-31 |
United States Patent
Application |
20020012061 |
Kind Code |
A1 |
Kato, Koji ; et al. |
January 31, 2002 |
Electronic camera
Abstract
A photographic lens system for forming an object image is placed
in the lens barrel of an electronic camera. In a camera body, a
beam splitter for forming branched optical paths and an image
sensing element for photoelectrically converting the formed object
image are arranged. An optical filter attached to a filter cap is
inserted between the beam splitter and the image sensing element.
The filter cap intimately contacts with the perimeter of the exit
surface of the beam splitter and the perimeter of the image sensing
surface of the image sensing element, thereby forming closed
spaces, between the optical filter and the beam splitter and
between the optical filter and the image sensing element, which
allow incident light to pass through.
Inventors: |
Kato, Koji; (Tama-shi,
JP) ; Higuchi, Tatsuji; (Akiruno-shi, JP) |
Correspondence
Address: |
FRISHAUF, HOLTZ, GOODMAN &
LANGER & CHICK, PC
767 THIRD AVENUE
25TH FLOOR
NEW YORK
NY
10017-2023
US
|
Assignee: |
Olympus Optical Co., Ltd.
43-2, Hatagaya 2-chome Shibuya-ku
Tokyo
JP
|
Family ID: |
26590671 |
Appl. No.: |
09/837357 |
Filed: |
September 13, 2001 |
Current U.S.
Class: |
348/342 ;
348/335; 348/374; 348/E5.027; 348/E5.028; 348/E5.037 |
Current CPC
Class: |
H04N 5/2353 20130101;
H04N 5/2253 20130101; H04N 5/2254 20130101; H04N 5/22521
20180801 |
Class at
Publication: |
348/342 ;
348/335; 348/374 |
International
Class: |
H04N 005/225 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 24, 2000 |
JP |
2000-123102 |
May 1, 2000 |
JP |
2000-132672 |
Claims
What is claimed is:
1. An electronic camera comprising: a photographic lens configure
to form an object image; an image sensing element configured to
photoelectrically convert the formed object image; a light guiding
device configured to guide incident light from an object, which is
incident from the photographic lens, to a first optical path to the
image sensing element and a second optical path different from the
first optical path; an optical filter disposed between the light
guiding device and the image sensing element; and a filter holding
member made of an elastic material to hold the optical filter, the
filter holding member comprising a first portion that surrounds and
holds an outer-diameter portion of the optical filter, and a second
portion that forms a closed space between the optical filter and
the light guiding device, and the second portion being connected to
the first portion and intimately contacting with that surface of
the light guiding device, which faces the optical filter, so as to
surround the first optical path.
2. The camera according to claim 1, wherein the optical filter and
the light guiding device are assembled against an elasticity of the
filter holding member, thereby allowing the second portion of the
filter holding member to intimately contact with the light guiding
device.
3. The camera according to claim 1, wherein the filter holding
member further comprises a third portion that forms a closed space
between the optical filter and the image sensing element, the third
portion being connected to the first portion and intimately
contacting with that surface of the light guiding device, which
faces the optical filter, so as to surround the first optical
path.
4. The camera according to claim 3, wherein the filter holding
member comprises first and second members split in the longitudinal
direction of the optical axis, the second and third portions are
arranged in the first and second members, respectively, and the
first and second members intimately contact with each other.
5. The camera according to claim 1, wherein the light guiding
device comprises a light splitting device configured to split the
incident light to the first and second optical paths.
6. The camera according to claim 5, wherein the light splitting
device comprises a beam splitter.
7. The camera according to claim 1, further comprising: an optical
member disposed on the second optical path in the vicinity of the
light guiding device; and an elastic member configured to form a
closed space between the optical member and the light guiding
device, the elastic member intimately contacting with opposite
surfaces of the optical member and the light guiding device and
surrounding a space between the opposite surfaces so as to surround
the second optical path.
8. An electronic camera comprising: a photographic lens configure
to form an object image; an image sensing element configured to
photoelectrically convert the formed object image; a light guiding
device configured to guide incident light from an object, which is
incident from the photographic lens, to a first optical path to the
image sensing element and a second optical path different from the
first optical path; an optical member disposed on the second
optical path in the vicinity of the light guiding device; and an
elastic member configured to form a closed space between the
optical member and the light guiding device, the elastic member
intimately contacting with opposite surfaces of the optical member
and the light guiding device and surrounding a space between the
opposite surfaces so as to surround the second optical path.
9. The camera according to claim 8, wherein the optical member and
the light guiding device are assembled against an elasticity of the
elastic member, thereby allowing the elastic member to intimately
contact with the optical member and the light guiding device.
10. The camera according to claim 8, wherein the second optical
path comprises an optical path to an optical finder unit configured
to form an image for visual check of an object image.
11. An electronic camera comprising: a photographic lens configure
to form an object image; an image sensing element configured to
photoelectrically convert the formed object image; an optical
filter disposed between the photographic lens and the image sensing
element; a focal-plane shutter disposed between the photographic
lens and the optical filter to mechanically interrupt incident
light to the image sensing element; and a holding frame configured
to surround the image sensing element and the optical filter and to
form a closed space between the image sensing element and the
optical filter.
12. The camera according to claim 11, further comprising a light
guiding device disposed between the photographic lens and the
optical filter to guide incident light from an object, which is
incident from the photographic lens, to a first optical path to the
image sensing element and a second optical path different from the
first optical path.
13. The camera according to claim 12, wherein the light guiding
device comprises a light splitting device configured to split the
incident light to the first and second optical paths.
14. The camera according to claim 13, wherein the light splitting
device comprises a beam splitter.
15. The camera according to claim 12, wherein the light guiding
device comprises an optical path switching device configured to
switch first and second states in which the incident light is
output to the first and second optical paths, respectively.
16. The camera according to claim 15, wherein the optical path
switching device comprises a movable mirror.
17. The camera according to claim 11, further comprising: a stop
device configured to limit the amount of light beam incident on the
image sensing element; a stop controller configured to form a set
value of the aperture area of the stop device; a shutter controller
configured to form a set value of the shutter speed of the
focal-plane shutter; and an exposure controller configured to
operate the focal-plane shutter in different modes in accordance
with the set value of the aperture area of the stop, even when the
set value of the shutter speed remains the same, thereby obtaining
a predetermined exposure time.
18. An electronic camera comprising: a photographic lens configure
to form an object image; an image sensing element configured to
photoelectrically convert the formed object image; an optical
filter disposed between the photographic lens and the image sensing
element; a light guiding device disposed between the photographic
lens and the optical filter to guide incident light from an object,
which is incident from the photographic lens, to a first optical
path to the image sensing element and a second optical path
different from the first optical path; a focal-plane shutter
disposed between the photographic lens and the light guiding device
to mechanically interrupt incident light to the image sensing
element; and a holding frame configured to surround the image
sensing element and the optical filter and to form a closed space
between the image sensing element and the optical filter.
19. The camera according to claim 18, further comprising: a stop
device configured to limit the amount of light beam incident on the
image sensing element; a stop controller configured to form a set
value of the aperture area of the stop device; a shutter controller
configured to form a set value of the shutter speed of the
focal-plane shutter; and an exposure controller configured to
operate the focal-plane shutter in different modes in accordance
with the set value of the aperture area of the stop, even when the
set value of the shutter speed remains the same, thereby obtaining
a predetermined exposure time.
20. The camera according to claim 18, wherein the light guiding
device comprises a light splitting device configured to split the
incident light to the first and second optical paths.
21. The camera according to claim 18, wherein the light guiding
device comprises an optical path switching device configured to
switch first and second states in which the incident light is
output to the first and second optical paths, respectively.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is based upon and claims the benefit of
priority from the prior Japanese Patent Applications No.
2000-123102, Apr. 24, 2000; and 2000-132672, May 1, 2000, the
entire contents of both of which are incorporated herein by
reference.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to an electronic camera and,
more particularly, to an electronic camera capable of preventing
deterioration of the picture quality and deterioration of the
quality of a finder image caused by adhesion of dust, and at the
same time allowing easy replacement/disassembly of optical
members.
[0003] In an electronic camera, if dust adheres to an optical
member through which incident light to an image sensing element
passes, a photographed picture is influenced by the dust. When this
is the case, it is highly likely that even rubbish of a very small
size, i.e., dust, which is not a problem in a silver halide camera,
appears as a black dot on a photographed frame and deteriorates the
picture quality. This is mainly because the size of the image
sensing surface of an image sensing element is smaller than that of
a silver halide film used in a silver halide camera. Adhesion of
dust to optical members is particularly a big problem for an image
sensing element having a high pixel density (multiple pixels),
because such an image sensing element is required to have a high
picture quality.
[0004] In addition, the zoom magnification at the focusing plane of
an optical finder of an electronic camera is larger than that of a
silver halide camera. Therefore, even rubbish of a very small size,
i.e., dust, which is of no problem in a silver halide camera is
highly likely to appear as a black dot in a finder field and
deteriorate the quality of a finder image.
[0005] To solve these problems, in a digital still camera disclosed
in Jpn. Pat. Appln. KOKAI Publication No. 11-109203, a lens and an
optical filter are fixed in a sealed state in a cylindrical sealing
member, and this cylindrical sealing member is attached to a
substrate for mounting an image sensing element so as to cover this
image sensing element tightly. That is, in this camera, a closed
space is formed between the lens and the optical filter through
which incident light to the image sensing element passes, and
around the image sensing element. This prevents deterioration of
the picture quality caused by adhesion of dust.
[0006] In this digital still camera disclosed in Jpn. Pat. Appln.
KOKAI Publication No. 11-109203, however, once a unit including the
components in the cylindrical sealing member is assembled, it is
not easy to disassemble the unit in order to replace the parts in
the cylindrical sealing member. That is, this conventional
structure in which the optical members in the vicinity of the image
sensing element are covered with the sealing member to thereby
prevent invasion and adhesion of dust still has antinomic problems:
improving the picture quality and facilitating
replacement/disassembly of optical members.
[0007] Also, a camera containing a focal-plane shutter having front
and rear curtains is known as a silver halide camera (a camera
using a silver halide film). Since the film surface must be
shielded except during exposure in a silver halide camera, this
focal-plane shutter operates as follows.
[0008] Before exposure, the front curtain is always in a shielding
position, and the rear curtain is in a retraction position. By a
release operation, the front curtain moves to a retraction position
to uncover the film surface, and the film surface is exposed to
light. After a predetermined time has elapsed, the rear curtain in
the retraction position moves to shield the film surface and
complete the exposure. That is, the operation timings of the front
and rear curtains determine the shutter speed. When the shutter
speed is low (e.g., 1/500 SEC or more), the rear curtain moves
after the front curtain retracts. When the shutter speed is high,
the rear curtain begins to move while the front curtain is moving.
In this case, the exposure time is determined by the width (size)
of a slit gap between the trailing end of the front curtain and the
leading end of the rear curtain (slit shutter mode).
[0009] In an electronic camera, on the other hand, a time
corresponding to the exposure time in a silver halide camera can be
set by an element shutter which is defined by turn on/off of an
image sensing element for photoelectric conversion, e.g., a CCD.
However, even an electronic camera uses a mechanical shutter for
the following reasons. First, an interlace CCD requires the
operation of a mechanical shutter at the end of exposure. Second, a
progressive CCD must be shielded by a mechanical shutter
immediately after exposure is completed by an element shutter, in
order to prevent smear (therefore, exposure is preferably
terminated by a mechanical shutter).
[0010] For example, Jpn. Pat. Appln. KOKAI Publication No.
11-122542 disclosed an electronic camera containing a focal-plane
shutter having only one of front and rear curtains. Also, Jpn. Pat.
Appln. KOKAI Publication No. 11-218838 disclosed an electronic
camera containing a focal-plane shutter having a large number of
sectors functioning as a shutter which also serves as a stop. The
latter publication also describes that a focal-plane shutter having
front and rear curtains is also usable.
[0011] In an electronic camera containing the conventional
focal-plane shutter, e.g., in each of the electronic cameras
disclosed in the above two publications, the shutter is placed
closely in front of a CCD. This is so because the role of the
focal-plane shutter is to shield the image sensing surface of the
CCD. This similarly holds for a silver halide camera.
[0012] The focal-plane shutter operates a considerable number of
times at high speed. Therefore, wear caused by contact of the
sectors produces wear dust. In a silver halide camera,
deterioration of the picture quality caused by this wear dust is
hardly a problem because the size of a silver halide film is large.
However, as described previously, if wear dust adheres to the cover
glass of a CCD in an electronic camera, this adhered wear dust
appears as a black dot in a photographed frame and deteriorates the
picture quality. The reasons are, for example, that the image
sensing surface of a CCD is much smaller than a silver halide film,
and the cover glass is very close to the image sensing surface.
BRIEF SUMMARY OF THE INVENTION
[0013] The present invention has been made in consideration of
these problems of the prior art, and has as its object to provide
an electronic camera capable of preventing deterioration of the
picture quality caused by adhesion of dust to optical members
through which incident light to an image sensing element passes,
and at the same time allowing easy replacement/disassembly of these
optical members.
[0014] It is another object of the present invention to provide an
electronic camera capable of preventing deterioration of the
quality of a finder image or the like caused by adhesion of dust to
optical members through which incident light to an optical finder
unit or the like passes, and at the same time allowing easy
replacement/disassembly of these optical members.
[0015] It is still another object of the present invention to
prevent deterioration of the picture quality caused by wear dust
produced by a focal-plane shutter, in an electronic camera
containing the focal-plane shutter.
[0016] According to a first aspect of the present invention, there
is provided an electronic camera comprising
[0017] a photographic lens configure to form an object image,
[0018] an image sensing element configured to photoelectrically
convert the formed object image,
[0019] a light guiding device configured to guide incident light
from an object, which is incident from the photographic lens, to a
first optical path to the image sensing element and a second
optical path different from the first optical path,
[0020] an optical filter disposed between the light guiding device
and the image sensing element, and
[0021] a filter holding member made of an elastic material to hold
the optical filter, the filter holding member comprising a first
portion that surrounds and holds an outer-diameter portion of the
optical filter, and a second portion that forms a closed space
between the optical filter and the light guiding device, and the
second portion being connected to the first portion and intimately
contacting with that surface of the light guiding device, which
faces the optical filter, so as to surround the first optical
path.
[0022] According to a second aspect of the present invention, there
is provided an electronic camera comprising
[0023] a photographic lens configure to form an object image,
[0024] an image sensing element configured to photoelectrically
convert the formed object image,
[0025] a light guiding device configured to guide incident light
from an object, which is incident from the photographic lens, to a
first optical path to the image sensing element and a second
optical path different from the first optical path,
[0026] an optical member disposed on the second optical path in the
vicinity of the light guiding device, and
[0027] an elastic member configured to form a closed space between
the optical member and the light guiding device, the elastic member
intimately contacting with opposite surfaces of the optical member
and the light guiding device and surrounding a space between the
opposite surfaces so as to surround the second optical path.
[0028] According to a third aspect of the present invention, there
is provided an electronic camera comprising
[0029] a photographic lens configure to form an object image,
[0030] an image sensing element configured to photoelectrically
convert the formed object image,
[0031] an optical filter disposed between the photographic lens and
the image sensing element,
[0032] a focal-plane shutter disposed between the photographic lens
and the optical filter to mechanically interrupt incident light to
the image sensing element, and
[0033] a holding frame configured to surround the image sensing
element and the optical filter and to form a closed space between
the image sensing element and the optical filter.
[0034] According to a fourth aspect of the present invention, there
is provided an electronic camera comprising
[0035] a photographic lens configure to form an object image,
[0036] an image sensing element configured to photoelectrically
convert the formed object image,
[0037] an optical filter disposed between the photographic lens and
the image sensing element,
[0038] a light guiding device disposed between the photographic
lens and the optical filter to guide incident light from an object,
which is incident from the photographic lens, to a first optical
path to the image sensing element and a second optical path
different from the first optical path,
[0039] a focal-plane shutter disposed between the photographic lens
and the light guiding device to mechanically interrupt incident
light to the image sensing element, and
[0040] a holding frame configured to surround the image sensing
element and the optical filter and to form a closed space between
the image sensing element and the optical filter.
[0041] Additional objects and advantages of the invention will be
set forth in the description which follows, and in part will be
obvious from the description, or may be learned by practice of the
invention. The objects and advantages of the invention may be
realized and obtained by means of the instrumentalities and
combinations particularly pointed out hereinafter.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
[0042] The accompanying drawings, which are incorporated in and
constitute a part of the specification, illustrate presently
preferred embodiments of the invention and, together with the
general description given above and the detailed description of the
preferred embodiments given below, serve to explain the principles
of the invention.
[0043] FIG. 1 is a perspective view showing the external appearance
of an electronic camera according to an embodiment of the present
invention;
[0044] FIG. 2 is a sectional view showing the internal structure of
the electronic camera shown in FIG. 1;
[0045] FIG. 3 is an enlarged sectional view showing the main parts
of the structure shown in FIG. 2;
[0046] FIGS. 4A and 4B are perspective views showing the assembled
state and disassembled state, respectively, of a casing used in a
camera body of the electronic camera shown in FIG. 1;
[0047] FIG. 5 is a perspective view showing the disassembled state
of a holding frame structure used in the electronic camera shown in
FIG. 1;
[0048] FIG. 6 is a perspective view showing the relationship
between a front plate of the holding frame structure, a lens
barrel, and a front cover of the casing in the electronic camera
shown in FIG. 1;
[0049] FIG. 7 is a sectional view showing the internal structure of
an electronic camera according to another embodiment of the present
invention;
[0050] FIG. 8 is a block diagram showing the whole configuration,
particularly, circuits in the electronic camera shown in FIG.
7;
[0051] FIG. 9 is a timing chart showing the operation sequence of a
shutter at a low shutter speed in the electronic camera shown in
FIG. 7;
[0052] FIG. 10 is a timing chart showing the operation timing of
the shutter at a high shutter speed in the electronic camera shown
in FIG. 7;
[0053] FIGS. 11A and 11B are views showing the relationship between
front and rear curtains and the image sensing surface of an image
sensing element in a setup state and a ready state, respectively,
common to low and high shutter speeds in the electronic camera
shown in FIG. 7;
[0054] FIGS. 12A and 12B are views showing the relationship between
the front and rear curtains and the image sensing surface of the
image sensing element when the shutter speed is high in the
electronic camera shown in FIG. 7;
[0055] FIG. 13 is a view for explaining the relationship between
the aperture diameter of a stop and the exposure time;
[0056] FIG. 14 is a view showing the state in which optical parts
shown in FIG. 7 are arranged in accordance with the structure of a
conventional electronic camera:
[0057] FIG. 15 is a view showing the arrangement of the optical
parts of the electronic camera shown in FIG. 7;
[0058] FIG. 16 is a view showing the arrangement of optical parts
of an electronic camera according to still another embodiment of
the present invention; and
[0059] FIG. 17 is a view showing the arrangement of electronic
parts of an electronic camera according to still another embodiment
of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0060] Embodiments of the present invention will be described below
with reference to the accompanying drawings. In the following
explanation, the same reference numerals denote components having
substantially the same functions and configurations, and a
duplicate explanation will be made only where necessary.
[0061] FIG. 1 is a perspective view showing the outer appearance of
an electronic camera according to an embodiment of the present
invention. FIG. 2 is a sectional view showing the internal
structure of the electronic camera. FIG. 3 is an enlarged sectional
view showing the main parts of the electronic camera. As shown in
FIG. 1, this electronic camera 10 includes a camera body 12, and a
lens barrel 14 detachably attached to the front surface of a casing
13 of the body 12. FIG. 1 also shows a two-step release switch 15
for starting photographing, and a release terminal 16 and a strobe
terminal 17 for connecting lines for remotely controlling release
and strobe operations.
[0062] In the lens barrel 14, zoom lenses 21a and 21b, a stop 22,
and a focusing lens 23 are arranged in this order from the incident
light side. The zoom lenses 21a and 21b and the focusing lens 23
construct a photographic lens system for forming an object image
(in FIG. 2, the arrangement of these lenses is schematically
shown).
[0063] At the entrance of the camera body 12, a beam splitter 24
(light guiding device or light splitting device) for splitting an
incident optical image from the photographic lens system toward a
CCD image sensing element 30 and an optical finder unit 40 is
placed. This beam splitter 24 is formed by combining two prisms,
i.e., lower and upper prisms 25 and 26. The CCD image sensing
element (photoelectric conversion element) 30 photoelectrically
converts the incident object image formed on the image sensing
surface, and outputs it as an electrical signal.
[0064] Two optical filters 28 and 29 are inserted between the beam
splitter 24 and the image sensing element 30. The filter 28 is an
IR cut filter for cutting infrared radiation, which is formed by
deposition on a glass surface. The filter 29 is a low-pass filter
for preventing moire, which is formed by stacking two or more
quartz plates. These filters 28 and 29 are integrated by
adhesion.
[0065] The beam splitter 24, the optical filters 28 and 29, and the
image sensing element 30 are installed in a form to be described
later in the camera body 12 by a holding frame structure 32. A
first printed circuit board 33 is placed at the back of this
holding frame structure 32, and the image sensing element 30 is
connected to this first printed circuit board 33. In addition, a
second printed circuit board 34 is placed below the holding frame
structure 32 so as to form a right angle to the first printed
circuit board 33.
[0066] An optical finder unit 40 is attached to the holding frame
structure 32 in accordance with the optical path branched upward by
the beam splitter 24. This optical finder unit 40 includes a finder
frame 41 bent at a right angle. A focusing plate 42 for focusing
and a field frame plate 43 are attached to that side of the finder
frame 41, which faces the beam splitter 24. In this finder frame
41, a plurality of lenses 44 and 45 and a mirror 46 are arranged
(the lens arrangement is schematically shown in FIG. 2). The light
beam split toward the optical finder unit 40 by the beam splitter
24 is guided to a finder window at the back of the camera body 12
via these optical members.
[0067] An image display LCD 18 is placed in the middle of the back
surface of the camera body 12. This image display LCD 18 is used as
a photographic finder in recording mode and as a monitor for
reproducing a recorded photographed picture in playback mode.
[0068] FIG. 4A is a perspective view showing the assembled state of
the casing 13 of the camera body 12. FIG. 4B is a perspective view
showing the disassembled state of the casing 13. As shown in FIGS.
4A and 4B, this casing 13 is composed of a front cover 51, a rear
cover 52, and an upper cover 53, all of which are metal products
having a high thermal conductivity, e.g., aluminum diecast
products. These covers 51, 52, and 53 are joined by using known
screw members (not shown). The covers 51, 52, and 53 are thermally
connected as their contact surfaces intimately contact with each
other, thereby constructing an integrated heat-radiating casing
having large thermal capacity, i.e., the casing 13, for radiating
heat to the outside of the camera.
[0069] FIG. 5 is a perspective view showing the disassembled state
of the holding frame structure 32. As shown in FIGS. 3 and 5, this
holding frame structure 32 includes a prism frame (heat-transfer
frame member) 61, a bottom plate 62, and a rear plate 63, all of
which are metal products having a high thermal conductivity, e.g.,
aluminum diecast products. The holding frame structure 32 also
includes filter caps 66 and 67 and a sealing member 68 assembled
inside the prism frame 61. All of the filter caps 66 and 67 and the
sealing member 68 are products made from highly elastic materials,
e.g., synthetic rubber molded products.
[0070] The prism frame 61 is so constructed as to insert the beam
splitter 24 from the lower opening of this prism frame 61. The
bottom plate 62 is fastened to the prism frame 61 by using known
screw members (not shown) so as to close this lower opening. The
prism frame 61 and the bottom plate 62 are thermally connected as
their contact surfaces intimately contact with each other, thereby
constructing an integrated heat-transfer frame member having large
thermal capacity.
[0071] On the bottom surface 62, a leaf spring 65 for pressing the
beam splitter 24 in a biased state at a predetermined position is
disposed. The lower prism 25 is positioned by the biasing force of
this leaf spring 65. In this state, those contact surfaces 25a and
25b at the upper and lower edges of the reference oblique surface
of the lower prism 25, which protrude from the upper prism 26,
contact with corresponding stop surfaces 61a and 61b, respectively,
formed on the prism frame 61. The upper prism 26 is positioned as
it is pushed against the reference oblique surface of the lower
prism 25 by the sealing member 68.
[0072] The rear plate 63 is much larger than the image sensing
element 30 and intimately contacts with the rear surface of the
image sensing element 30. This rear plate 63 is fastened to the
prism frame 61 by using known screw members (not shown) so as to
close the rear opening of the prism frame 61. The rear plate 63 is
thermally connected to the prism frame 61 as their contact surfaces
intimately contact with each other, thereby forming a thick
heat-transfer path from the rear plate 63 to the prism frame 61. A
pair of slits 63a are formed in this rear plate 63. A lead frame 35
for electrically connecting the image sensing element 30 and the
printed circuit board 33 is disposed through these slits 63a.
[0073] As shown in FIGS. 3 and 6, the holding frame structure 32
further includes a front plate 71 placed on the front side of the
prism frame 61. This front plate 71 is a metal product having a
high mechanical strength and a high thermal conductivity, e.g., a
steel plate product. FIG. 6 is a perspective view showing the
relationship between the front plate 71 of the holding frame
structure 32, the lens barrel 14, and the front cover 51 of the
casing 13.
[0074] The prism frame 61 is fastened to the front plate 71 by
using known screw members (not shown). This prism frame 61 is
thermally connected to the front plate 71 as their contact surfaces
intimately contact with each other, thereby forming a thick
heat-transfer path from the prism frame 61 to the front plate 71.
Furthermore, the front plate 71 is fastened to the front cover 51
of the casing 13 by using known screw members (some screw members
are shown in FIG. 6). This front plate 71 is thermally connected to
the front cover 51 as their contact surfaces intimately contact
with each other, thereby forming a thick heat-transfer path from
the front plate 71 to the front cover 51.
[0075] Also, a portion of the lens barrel 14 constructs a
heat-radiating barrel 72 for radiating heat to the outside of the
camera. This heat-radiating barrel 72 is made of a thermally
conductive material, e.g., aluminum. The rest of the lens barrel 14
is formed with a synthetic resin. The heat-radiating barrel 72 is
fastened to the front plate 71 by using known screw members (not
shown). This lens barrel 72 is thermally connected to the front
plate 71 as their contact surfaces intimately contact with each
other, thereby forming a thick heat-transfer path from the front
plate 71 to the heat-radiating barrel 72.
[0076] As described above, a thick heat-transfer path is formed
from the image sensing element 30 to the casing 13 of the camera
body 12 and to the heat-radiating barrel 72 of the lens barrel 14,
both having large thermal capacity, via the holding frame structure
32 which includes, e.g., the prism frame 61 having large thermal
capacity. Since the heat generated by the image sensing element 30
is rapidly released to the outside of the camera through this
heat-transfer path, it is possible to prevent a rise of the
temperature of the image sensing element 30 and thereby prevent
deterioration of the picture quality. In particular, the lens
barrel 14 has a large exposure area to the outside and hence has a
high heat-radiating effect. Note that the members such as the prism
frame 61 of the holding frame structure 32 forming the
heat-transfer path and the casing 13 and the heat-radiating barrel
72 for radiating heat to the outside of the camera are all
originally necessary members. Therefore, the internal structure of
the apparatus can be flexibly made compact without adding any extra
members.
[0077] Referring back to FIG. 5, the filter caps 66 and 67
assembled inside the prism frame 61 are separately molded products
and fastened to the front and rear sides, respectively, of the
integrated filters 28 and 29. These filter caps 66 and 67 are
inserted, as they hold the filters 28 and 29, into the prism frame
61 from its rear opening, before the rear plate 63 is attached to
the prism frame 61. The filter cap 66 is positioned by abutting it
against the exit surface of the beam splitter 24. The filter cap 67
is positioned by abutting it against an internal stop surface 61c
of the prism frame 61.
[0078] As shown in FIG. 3, the filter cap 66 has as its main
portion a surrounding portion 66a for holding the filter 28 by
surrounding it. In addition, this filter cap 66 has an extended
portion 66b which intimately contacts with the perimeter of the
exit surface of the beam splitter 24 by elastic deformation,
thereby forming, between the filter 28 and the beam splitter 24, a
substantially closed space through which incident light to the
image sensing element 30 passes. Similarly, the filter cap 67 has
as its main portion a surrounding portion 67a for holding the
filter 29 by surrounding it. This filter cap 67 also has an
extended portion 67b which intimately contacts with the perimeter
of the image sensing surface of the image sensing element 30 by
elastic deformation, thereby forming, between the filter 29 and the
image sensing element 30, a substantially closed space through
which incident light to the image sensing element 30 passes.
[0079] The beam splitter 24, the filters 28 and 29, and the image
sensing element 30 are assembled against the elasticity of the
filter caps 66 and 67. Consequently, the surrounding portions 66a
and 67a intimately contact with the beam splitter 24 and the image
sensing element 30, respectively.
[0080] Since the filter caps 66 and 67 surround the whole
perimeters of the filters 28 and 29, it is possible to reliably
prevent damage to the edges of these filters 28 and 29 and thereby
prevent the generation of particles. Also, since the filter caps 66
and 67 form a substantially closed space surrounding the optical
path between the beam splitter 24 and the image sensing element 30,
deterioration of the picture quality caused by invasion and
adhesion of dust can be prevented. Furthermore, the filter caps 66
and 67 and the sealing member 68 intimately contact only with the
beam splitter 24 and the image sensing element 30. This facilitates
disassembling the beam splitter 24, the filters 28 and 29, and the
image sensing element 30, when any of these components is to be
replaced. Although the filter caps 66 and 67 are separate members
in this embodiment, they can also be an integrated member.
[0081] The sealing member 68 is attached to the upper opening of
the prism frame 61 which opens to the optical finder unit 40. This
sealing member 68 has a flange portion 68a in its upper portion.
The sealing member 68 is positioned by clamping this flange portion
68a in an intimate contact state between the prism frame 61 and the
finder frame 41. The sealing member 68 also has a cylindrical
portion 68b which intimately contacts with the perimeter of the
exit surface of the beam splitter 24 by elastic deformation,
thereby forming, between the focusing plate 42 and the beam
splitter 24, a substantially closed space through which incident
light to the optical finder unit 40 passes.
[0082] The beam splitter 24 and the finder frame 41 are assembled
against the elasticity of the sealing member 68. Consequently, the
sealing member 68 intimately contacts with the beam splitter 24 and
the finder frame 41.
[0083] That is, a substantially closed space is also formed for the
optical finder unit 40, in the vicinity of the focusing plate 42,
by the sealing member 68. Therefore, deterioration of the quality
of a finder image caused by invasion and adhesion of dust can be
prevented. Additionally, since the sealing member 68 intimately
contacts only with the beam splitter 24, disassembly of the parts
around this beam splitter 24 is not interfered with.
[0084] In the above embodiment, aluminum is used as the material of
the front cover 51, the rear cover 52, and the upper cover 53 of
the casing 13 and the prism frame (heat-transfer frame member) 61,
the bottom plate 62, and the rear plate 63 of the holding frame
structure 32, from the viewpoint of thermal conductivity and light
weight. However, similar effects can be obtained even when zinc or
magnesium is used as the material of these parts.
[0085] FIG. 7 is a sectional view showing the internal structure of
an electronic camera according to another embodiment of the present
invention. As shown in FIG. 7, this electronic camera 110 includes
a camera body 112, and a lens barrel 114 detachably attached to the
front surface of a casing 113 of the body 112.
[0086] In the lens barrel 114, two zoom lenses 121, a stop 122, and
a focusing lens 123 are arranged along an optical path L1 in this
order from the incident light side. The two zoom lenses 121 and the
focusing lens 123 construct a photographic lens system for forming
an object image.
[0087] At the entrance of the camera body 112, a beam splitter 124
(light guiding device or light splitting device) for splitting an
incident object image from the photographic lens system toward a
CCD image sensing element 130 (an optical path L2) and an optical
finder unit 150 (an optical path L3) is placed. Between this beam
splitter 124 and the image sensing element 130, a shutter 125 and
two types of optical filters 128 and 129 are arranged along the
optical path L2.
[0088] The shutter 125 is a focal-plane shutter having a front
curtain 126 and a rear curtain 127 to be opened and closed in a way
to be described later. The filter 128 is an IR cut filter for
cutting infrared radiation. The filter 129 is a low-pass filter for
preventing the generation of moire. The CCD image sensing element
(photoelectric conversion element) 130 photoelectrically converts
an incident object image formed on an image sensing surface 130a
and outputs it as an electrical signal.
[0089] The beam splitter 124 and the shutter 125 are held in a
first holding frame 142. This holding frame 142 is mounted on and
fixed to a mounting frame 141 which is fastened to the casing 113
of the body 112. The filters 128 and 129 are held in a second
holding frame 143. This second holding frame 143 forms a
substantially closed space for preventing invasion of dust and the
like, between the filter 129 and the image sensing element 130. The
second holding frame 143 is mounted on and fixed to the first
holding frame 142.
[0090] A first printed circuit board 144 is disposed at the end
portion of the second holding frame 143. The image sensing element
130 is mounted on this first printed circuit board 144. In
addition, a second printed circuit board 145 is disposed below the
holding frames 142 and 143 so as to form a right angle to the first
printed circuit board 144.
[0091] The optical finder unit 150 is mounted on the first holding
frame 143 along the optical path L3 branched from the optical path
L2 by the beam splitter 124. This optical finder unit 150 has a
lens 152 and an eyepiece 154 placed at the two ends of a finder
frame 151 bent at a right angle, and a mirror 153 placed in the
bent portion of the finder frame 151. A light beam separated by the
beam splitter 124 is guided to a finder window 155 at the back of
the camera body 112 via these optical members 152, 153, and
154.
[0092] An image display LCD 115 is placed in the middle of the back
surface of the camera body 112. This image display LCD 115 is used
as a photographic finder in recording mode and as a monitor for
reproducing a recorded photographed picture in playback mode.
[0093] As described earlier, the focal-plane shutter 125 operates a
considerable number of times at high speed, so wear by contact of
the sectors (the front curtain 126 and the rear curtain 127)
produces wear dust. In the electronic camera 110 according to this
embodiment, therefore, the shutter 125 is placed away from the
image sensing element 130 and closer to the incident light side
than the filters 128 and 129. In addition, the second holding frame
143 forms a substantially closed space for preventing invasion of
dust and the like, between the filter 129 and the image sensing
element 130. Hence, adhesion of wear dust to the cover glass of the
image sensing element 130 can be prevented. Accordingly, it is
possible to avoid phenomenon in which adhered wear dust appears as
a black dot on the frame to deteriorate the picture quality.
[0094] FIG. 8 is a block diagram showing the overall configuration,
particularly, circuits in the electronic camera 110.
[0095] An optical image of an object to be photographed is input
via the photographic lens systems 121 and 123 and formed on the CCD
image sensing element 130. During this image formation, in
accordance with the set conditions and the photographing
environment, the zoom lenses 121, the stop 122, and the focusing
lens 123 are driven by a zoom motor 132, a stop actuator 133, and
an AF (Automatic Focusing) motor 134, respectively, under the
control of a driving controller 131. Also, the front curtain 126
and the rear curtain 127 of the shutter 125 are driven by a front
curtain actuator 136 and a rear curtain actuator 137, respectively,
under the control of a driving controller 135. Each of these
actuators 133, 136, and 137 is a combination of a motor and
solenoid.
[0096] The image sensing element 130 photoelectrically converts the
incident object image formed on the image sensing surface 130a, and
outputs it as an electrical signal. The signal from the image
sensing element 130 is input to an A/D (analog/digital) converter
164 via an image sensing circuit 163 for signal processing. The
signal from the A/D converter 164 is input to a system controller
161 via an AE (Automatic Exposure)/AF (Automatic Focusing) circuit
165, and to an internal memory 166 via a bus 162.
[0097] The internal memory 166 is connected to the system
controller 161 via the bus 162. The image data stored in this
internal memory 166 is compressed and recorded in a memory card 168
in a card slot via the bus 162 and an I/F (interface) 169. That is,
the input image data is converted into a signal recordable in the
memory card 168, under the control of the system controller
161.
[0098] The image display LCD 115 is connected to the bus 162 via a
VRAM (Video RAM) 171 and a driving controller 172. The image data
supplied from the image sensing element 130 or the memory card 168
and stored in the internal memory 166 is transferred to the image
display LCD 115 via the driving controller 172, and displayed as an
image.
[0099] An operation unit 173 is also connected to the system
controller 161. This operation unit 173 includes various operation
buttons and operation keys. An operation command is input to the
system controller 161 via the operation unit 173 to set the
operation of this electronic camera.
[0100] Furthermore, a strobe emission unit 174 including, e.g., a
strobe, strobe controller, and strobe capacitor is connected to the
system controller 161.
[0101] The operation of the shutter 125 performed in photographing
mode of the electronic camera 110 under the control of the shutter
driving controller 135 and the system controller 161 will be
described in detail below. FIGS. 9 and 110 are timing charts
showing the operation sequences of the shutter 125 at a low shutter
speed (e.g., 1/500 msec or more) and a high shutter speed (e.g.,
less than 1/500 msec), respectively. FIGS. 11A and 11B are views
showing the relationship between the front curtain 126, the rear
curtain 127, and the image sensing surface 130a of the image
sensing element 130 in a setup state and ready state common to the
low and high shutter speeds. FIGS. 12A and 12B are views showing
the relationship between the front curtain 126, the rear curtain
127, and the image sensing surface 130a of the image sensing
element 130 at the high shutter speed.
[0102] The upper ends of the front curtain 126 and the rear curtain
127 are taken up by rolls which are driven by the motors of the
actuators 136 and 137, respectively. The lower ends of these front
and rear curtains 126 and 127 are taken up by rolls which are
driven by springs. The front and rear curtains 126 and 127 are
charged when taken up by the rollers on the motor side. When the
solenoids of the actuators 136 and 137 are turned off, the front
and rear curtains 126 and 127 are released and taken up by the
rolls on the spring side at high speed.
[0103] In the charged state, the front curtain 126 is closed to
shield the image sensing surface 130a of the image sensing element
130, and the rear curtain 127 is opened to uncover the image
sensing surface 130a. In the released state, the front curtain 126
is opened to uncover the image sensing surface 130a of the image
sensing element 130, and the rear curtain 127 is closed to shield
the image sensing surface 130a. That is, the opening/closure of the
front curtain 126 is exactly opposite to that of the rear curtain
127 in each of the charged and released states.
[0104] FIG. 11A shows the setup state initially set in
photographing mode. In this state, both the front and rear curtains
126 and 127 are opened to uncover the image sensing surface 130a
(the front curtain 126 is released, and the rear curtain 127 is
charged). In this state, the image sensing element 130 is used to
monitor the object on the image display LCD 115 or perform
photometry for AE (Automatic Exposure)/AF (Automatic Focusing).
FIG. 11B shows the ready state immediately before a release SW
(switch) is turned on. In this state, the front curtain 126 is
closed to shield the image sensing surface 130a, and the rear
curtain 127 is opened to uncover the image sensing surface 130a
(both the front and rear curtains 126 and 127 are charged).
[0105] As shown in FIG. 9, when the release SW is turned on from
the ready state shown in FIG. 11B at the low shutter speed, the
front curtain 126 is first released to uncover the image sensing
surface 130a. In substantially synchronism with this, an element
shutter (defined by turn on/off of the image sensing element 130)
is turned on to start image sensing. When a predetermined certain
image sensing time has elapsed, the rear curtain 127 is released to
shield the image sensing surface 130a. After that, the signal from
the image sensing element 130 is transferred and read out. That is,
a time (to be referred to as an exposure time hereinafter)
corresponding to the exposure time of a silver halide camera is
determined by the period from the ON of the element shutter to the
shielding by the mechanical shutter 125.
[0106] On the other hand, as shown in FIG. 10, when the shutter
speed is high, the element shutter is already ON in the ready state
shown in FIG. 11B. When the release SW is turned on from this ready
state, the front curtain 126 is first released, and the rear
curtain 127 is then released to start moving while the front
curtain 126 is moving. In other words, the front and rear curtains
126 and 127 are released with a certain time lag between them and
expose the image sensing surface 130a to light while running
parallel to each other (FIG. 12A). When the rear curtain 127
shields the image sensing surface 130a (FIG. 12B), the exposure is
complete. After that, the signal from the image sensing element 130
is transferred and read out. That is, a time (to be referred to as
an exposure time hereinafter) corresponding to the exposure time of
a silver halide camera is determined by the width (size) of a slit
gap 125a between the trailing end of the front curtain 126 and the
leading end of the rear curtain 127 (slit shutter mode).
[0107] In the electronic camera according to this embodiment, the
shutter 125 is positioned away from the image sensing surface 130a
of the image sensing element 130, compared to the conventional
electronic camera. For example, the arrangement of the optical
parts of the electronic camera 110 of this embodiment is as shown
in FIG. 15. However, when these optical parts are arranged in
accordance with the structure of the conventional electronic
camera, the arrangement is as shown in FIG. 14. Hence, the camera
is influenced by the aperture area (aperture diameter) of the stop
122 more strongly than in the conventional structure. That is, in
slit shutter mode when the shutter speed is high, the exposure time
of the image sensing surface largely changes in accordance with the
aperture diameter of the stop 122 for the same shutter speed. This
will be explained below.
[0108] FIG. 13 is a view for explaining the relationship between
the aperture diameter of the stop and the exposure time. Referring
to FIG. 13, a position P1 closely in front of the image sensing
surface 130a of the image sensing element 130 indicates the
position of the shutter 125 in the conventional structure shown in
FIG. 14. A position P2 away from the image sensing surface 130a
indicates the position of the shutter 125 in this embodiment shown
in FIG. 15.
[0109] In slit shutter mode when the shutter speed is high, an
exposure time T of the image sensing surface 130a is calculated
by
T=(S+d)/v (1)
[0110] where S is the width of the slit 125a, v is the shutter
speed (the running speeds of the front and rear curtains 126 and
127, and the speeds of the two curtains are equal), and d is the
diameter of a light beam at the shutter 125 (the position P1 or
P2).
[0111] The diameter d of the light beam is calculated by
d=(f-x)D/f (2)
[0112] where f is the focal length of the zoom lens 121 (the
distance from the zoom lens 121 to the image sensing surface 130a),
x is the distance from the zoom lens 121 to the shutter 125 (the
position P1 or P2), and D is the aperture diameter of the stop
122.
[0113] When the shutter 125 is in the position P1 closely in front
of the image sensing surface 130a as in the conventional structure
shown in FIG. 14, the distance x has a value close to the focal
length f in equation (2), so the diameter d of the light beam at
the shutter 125 has a very small value regardless of the value of
the aperture diameter D of the stop 122. When this is the case, the
diameter d of the light beam is much smaller than the width S of
the slit 125a. Accordingly, the width S of the slit 125a and the
shutter speed v are dominant as elements for determining the
exposure time T. That is, this exposure time T is not largely
influenced by the aperture diameter D of the stop 122.
[0114] By contrast, when the shutter 125 is in the position P2 away
from the image sensing surface 130a as in the structure of this
embodiment shown in FIG. 15, the value of the distance x is smaller
than that of the focal length f, so the diameter d of the light
beam at the shutter 125 has a relatively large value. In this case,
the diameter d of the light beam has a value not small when
compared to the width S of the slit 125a in equation (1). In
addition, the diameter d of the light beam greatly changes in
accordance with a change in the aperture diameter D of the stop
122. This increases the influence of the diameter d of the light
beam as an element for determining the exposure time T. That is,
the exposure time T is largely influenced by the aperture diameter
D of the stop 122.
[0115] For example, the right-hand side of FIG. 13 exaggeratively
indicates the relationship between diameters d2 and d4 of the light
beam at the position P2 and the width S of the slit 125a when the
aperture diameter of the stop 122 is set to F2 and F4. As shown in
FIG. 13, if the diameters d2 and d4 of the light beam are about
four and two times, respectively, the width S of the slit 125a,
exposure times T2 and T4 of the image sensing surface 130a when the
aperture diameter of the stop 122 is set to F2 and F4 have a ratio
of 5:3 from equation (1), i.e., they are largely different from
each other, even for the same shutter speed v.
[0116] To solve this problem, in the electronic camera 110
according to this embodiment, the shutter driving controller 135
controls driving of the front and rear curtains 126 and 127 in
accordance with the set value of the aperture area of the stop 122
formed by the system controller 161 and with the set value of the
shutter speed of the shutter 125, such that the exposure time of
the image sensing surface 130a is equal to a predetermined exposure
time to be obtained by the set value of the shutter speed. That is,
even when the set value of the shutter speed remains the same, the
shutter driving controller 135 operates the front and rear curtains
126 and 127 in different modes in accordance with the set value of
the aperture area of the stop 122, thereby obtaining a
predetermined exposure time. As described above, this can eliminate
the problem posed when the shutter 125 is placed in the position
away from the image sensing surface 130a of the image sensing
element 130 compared to the conventional electronic camera.
[0117] FIGS. 16 and 17 are views showing the arrangements of
optical parts of electronic cameras according to still other
embodiments of the present invention.
[0118] In the embodiment shown in FIG. 16, a shutter 125 is placed
closer to the incident light side than a beam splitter 124. In the
embodiment shown in FIG. 17, a click return mirror (optical path
switching device) 180 is disposed, instead of a beam splitter 124,
as a light guiding device for forming a branched optical path to an
optical finder. The beam splitter 124 can be moved between a
position Pr at which the direction of a light beam passing through
a photographic lens system is changed toward the optical finder and
a position Ps at which this light beam is passed toward an image
sensing element 130.
[0119] In the embodiments shown in FIGS. 16 and 17, the shutter 125
is similarly disposed away from the image sensing element 130 and
closer to the incident light side than filters 128 and 129.
Therefore, it is possible to prevent adhesion of wear dust from the
focal-plane shutter 125 to the image sensing surface of the image
sensing element 130, and thereby avoid deterioration of the picture
quality. In these embodiments, as in the embodiment shown in FIG.
7, it is desirable to form a substantially closed space for
preventing invasion of dust and the like, between the image sensing
element 130 and the optical member (in this case, the filter 129)
closely in front of the image sensing element 130, by using an
appropriate holding frame.
[0120] In each of the above embodiments, the focal-plane shutter
125 is the shutter 125 having the front and rear curtains 126 and
127. However, the present invention is also applicable to a
focal-plane shutter having only one curtain (sector) or a large
number of sectors.
[0121] Additional advantages and modifications will readily occur
to those skilled in the art. Therefore, the invention in its
broader aspects is not limited to the specific details and
representative embodiments shown and described herein. Accordingly,
various modifications may be made without departing from the spirit
or scope of the general inventive concept as defined by the
appended claims and their equivalents.
* * * * *