Illumination – Light modifier – Refractor
Reexamination Certificate
2001-10-31
2004-02-03
Cariaso, Alan (Department: 2875)
Illumination
Light modifier
Refractor
C362S016000, C362S332000, C362S339000, C359S833000
Reexamination Certificate
active
06685342
ABSTRACT:
This application claims the benefit of Japanese Application No. 2000-338033 filed in Japan on Nov. 6, 2000, the contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an illumination device, or more particularly, an illumination device for radiating illumination light (flashlight) to an object during photography performed by a camera.
2. Description of the Related Art
Conventionally, when a camera is used to perform photography, if the photography is performed at night, indoors, or with an object backlit, an illumination device is used to radiate illumination light (flashlight) to the object.
The illumination device is mounted in a part of a camera body so that illumination light (flashlight) can be radiated to an object while being interlocked with a photographic action of the camera. Photography is thus achieved.
FIG.
22
and
FIG. 23
show sectional views of a conventional illumination device. An illustrated illumination device
10
has a cylindrical flash tube
12
, for example, a xenon (Xe) flash tube placed inside the back
11
a
of a reflector
11
having a radial section. At this time, the flash tube
12
is placed so that the longitudinal direction thereof will be orthogonal to a center axis
13
of the reflector
11
. All that restricts the direction of light emanating from a glowing member of the flash tube
12
is the reflector
11
including the back
11
a
thereof. Light emanating from the glowing member of the flash tube
12
is not reflected from the inner wall of the reflector
11
but radiated directly to the outside of the reflector
11
. Besides, the light is reflected from the inner wall of the reflector
11
and radiated to the outside of the reflector
11
. Besides, the light is reflected from inner wall of the reflector
11
and radiated to the outside of the reflector
11
. Other part of the light (indicated with a mark x) leaks out through a gap between the reflector
11
and flash tube
12
.
FIG. 22
shows numerous light rays emitted at different angles from a center point O in the glowing member of the flash tube
12
.
FIG. 23
shows numerous light rays emitted at different angles from a glowing point A that is off the center point O in the glowing member of the flash tube
12
. Part of the light rays are emitted from the glowing points and radiated directly to outside through the interior of the reflector
11
. Other part of the light rays are reflected from the inner surface of the reflector
11
and radiated to outside. Moreover, still other part of the light rays is directed from the glowing points to the back
11
a
of the reflector. The light rays directed from the glowing points to the back
11
a
of the reflector fall into three parts. That is to say, one part of the light rays is reflected from the inner surface of the back
11
a
of the reflector, propagated through the interior of the reflector
11
, and emitted through an opening
11
b
. Other part of the light rays is reflected from the inner surface of the reflector
11
and then radiated through the opening
11
b
. Still other part of the light rays is radiated to outside through the gap between the reflector
11
and flash tube
12
on both sides without being reflected from the inner surface of the reflector
11
(this part of the light rays does not effectively work on an object).
Each angle written in
FIG. 22
is an angle of radiation (an angle to the center axis of radiation
13
) at which a light ray that passes through the reflector
11
is radiated to an object (upwards in the drawing), which is not shown, through the opening
11
b
that opens radially. An angle of radiation required to distribute light to a relatively narrow area and comparable to an angle of view offered by a photography lens employed shall be, for example, 16°. Light rays indicated with angles that are larger than 16° are radiated to an area outside a desired photographic range in which an object lies. The light rays do not work effectively on the object during photography. The conventional illumination device shown in FIG.
22
and
FIG. 23
has numerous light rays radiated at angles of radiation that exceed an effective range from 0° to 16°, and thus suffers from poor radiation efficiency.
Accordingly, proposals have been made in efforts to improve the radiation efficiency or radiation characteristic of an illumination device.
For example, Japanese Unexamined Patent Application Publication No. 4-138440 describes the structure of an illumination device that radiates light, which diverges from a cylindrically long discharge tube, forwards. Specifically, prisms are placed in front of both the sides of the discharge tube so that light traveling in the longitudinal direction of the discharge tube will be converged forwards.
Moreover, Japanese Unexamined Patent Application Publication No. 10-115853 describes a structure having a plurality of prisms that acts like a light guide located in front of a glowing member, otherwise, one prism is slit in order to draw out the similar effect as that provided by a plurality of light guides.
On the other hand, an illumination device for cameras is required to have an angle of radiation comparable to an angle of view offered by a photography lens employed in a camera (a wide-angle lens, a standard lens, a telephoto lens, etc.).
However, in the structure described in the Japanese Unexamined Patent Application Publication No. 4-138440, only prisms are placed in front of both the sides of a discharge tube. As
FIG. 1A
in the above publication illustrates, light that is emitted from the glowing member of the discharge tube and radiated forwards without being passed through any prism travels rectilinearly but is neither refracted nor reflected in a space between the prisms placed on both the sides of the discharge tube. Therefore, a radiation range of the light is wide. If light must be distributed to a small area, the light cannot be converged efficiently. Moreover, the distance between the prisms placed on both the sides of the discharge tube must be set longer than an arc length of a discharge tube. When a large-energy flash tube characterized by an arc length larger than an arc length made by a discharge tube is used to distribute light to a small area, radiation efficiency is very poor.
Furthermore, the above publication discloses a type of flash tube having a reflecting member placed inside the prisms as illustrated in
FIG. 3A
of the above publication. This type of flash tube has a drawback that the reflecting surface of the reflecting member must be in a complex shape. Besides, even when light must be distributed to a narrow area, the light cannot be converged efficiently.
According to the Japanese Unexamined Patent Application Publication No. 10-115853, a light guide unit is included independently of a housing panel member of a camera body located in front of the light guide unit. This means that a housing panel member must be procured independently of a light guide member. Moreover, light is radiated by merely utilizing total reflection caused by light guides. Light is therefore radiated radially from the emitting surfaces of the light guides opposed to the incidence surfaces thereof. This poses a problem in that light is hard to be efficiently converged on a narrow area.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide an illumination device that is required to distribute light to a relatively narrow area and can allow light to efficiently converge on an object.
According to a first aspect of the present invention, there is provided an illumination device for radiating diverging light, which emanates from a light source, forwards. The illumination device consists mainly of a prism and a reflecting member.
The prism has an incidence surface and a transmitting/totally-reflecting surface. The incidence surface is opposed to the light source so that light emanating from the light source can fall on the incidence surface. The transmitting/tota
Cariaso Alan
Frishauf Holtz Goodman & Chick P.C.
Negron Ismael
Olympus Optical Co,. Ltd.
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