Optical: systems and elements – Single channel simultaneously to or from plural channels – By partial reflection at beam splitting or combining surface
Reexamination Certificate
2000-10-23
2003-01-28
Ben, Loha (Department: 2873)
Optical: systems and elements
Single channel simultaneously to or from plural channels
By partial reflection at beam splitting or combining surface
C359S630000, C359S631000, C359S637000, C359S720000, C359S015000, C359S737000, C345S008000, C250S494100, C353S031000
Reexamination Certificate
active
06512635
ABSTRACT:
BACKGROUND OF THE INVENTION
1) Field of the Invention
The present invention relates to an observation optical system and a photographing optical system. To be specific, it relates to an optical system used in an image display apparatus or a photographing apparatus, such as a camera, that can be held on the head or face of a user and that can be attached to a portable telephone or a portable intelligent terminal.
2) Description of Related Art
In recent years, development has been energetically made for image display apparatuses, specifically for those to be held on the head or face of individuals for entertaining them with a large image. Also, in accordance with recent popularization of portable telephone and portable intelligent terminal, requirements for large view of graphics or text data on these apparatuses have grown. Conventional art has proposed to convert a displayed image on a display surface of an image display device into a virtual image to be viewed by an observer using an optical system constructed of three transmitting or reflecting surfaces each of which assumes rotational asymmetry, as disclosed by Japanese Patent Application Preliminary Publication (KOKAI) Nos. Hei 8-234137, Hei 9-197336 and Hei 9-197337. Also, U.S. Pat. No. 5,959,781 proposes to introduce a displayed image on a display surface of an image display device into a concave mirror via a total-reflection surface or a beam splitter, so as to provide an enlarged virtual image to be viewed by an observer.
However, according to KOKAI Nos. Hei 8-234137, Hei 9-197336 and Hei 9-197337, since the prism is made of a single medium and thus compensating means for compensating the chromatic aberration of magnification is not provided, insufficient compensation of the chromatic aberration of magnification makes it difficult to achieve high resolution. Also, according to KOKAI Nos. Hei 9-197336 and Hei 9-197337, the prism is rendered large in the longitudinal direction (Y direction). According to U.S. Pat. No. 5,959,781, the apparatus is rendered expensive and assembly is complicated because of the large number of parts, as well as a prism medium having extremely poor birefringence property such as glass is employed to result in heavy weight of the apparatus, because a polarization beam splitter is employed as the beam splitter to utilize polarization characteristics, etc. Also, if plastic materials are used for the optical system to solve the problem of heavy weight, the beam splitter has to be a half mirror or the like because a polarization beam splitter cannot be employed. In this case, however, light from an electronic image is attenuated at the half mirror before it reaches the eye of the observer, and thus the visible image becomes dark.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an optical system specifically used in an observation optical system or a photographing optical system, which is compact and lightweight enough to be incorporated into a portable telephone, a portable intelligent terminal, or a virtual image observation system, and which provides bright images with high resolution.
An optical system according to the basic configuration of the present invention comprises, between a pupil surface and an image surface, a first prism and a second prism. The first prism comprises a
1
st
-
1
st
surface which is disposed on the pupil surface side and which has both of the action of transmitting first bundles of rays (defined as bundles of rays travelling along a path between the pupil surface and the image surface via the optical system) and the action of reflecting the first bundles of rays, a
1
st
-
2
nd
surface which is disposed on the opposite side of the pupil surface with respect to the
1
st
-
1
st
surface and which has both of the action of transmitting the first bundles of rays and the action of reflecting the first bundles of rays, and a
1
st
-
3
rd
surface which is disposed on the image surface side and which transmits the first bundles of rays. The second prism comprises a
2
nd
-
1
st
surface which is disposed adjacent to the
1
st
-
2
nd
surface at an air space away and which transmits the first bundles of rays at least twice and a
2
nd
-
2
nd
surface which is disposed on the opposite side of the pupil surface with respect to the
2
nd
-
1
st
surface and which reflects the first bundles of rays. The
1
st
-
1
st
surface is constructed of a prism face of the first prism to which a holographic element is applied. The holographic element is constructed and arranged to transmit the first bundles of rays that are incident thereon at a first incident angle and to reflect by diffraction the first bundles of rays that are incident thereon at a second incident angle, to thereby have both of the action of reflecting the first bundles of rays and the action of transmitting the first bundles of rays. The
1
st
-
2
nd
surface of the first prism is constructed and arranged such that a part of effective rays are incident thereon at angles greater than the critical angle so as to be totally reflected therefrom and a remaining part of the effective rays are incident thereon at angles equal to or smaller than the critical angle so as to be transmitted therethrough, to thereby have both of the action of reflecting the first bundles of rays and the action of transmitting the first bundles of rays.
According to the present invention in general, at least one surface of the first or second prism, specifically a surface having reflecting action, is rotationally asymmetric.
Also, a rotationally asymmetric surface used in the optical system of the present invention may be constructed of an anamorphic surface, a toric surface, a free curved surface that defines only one plane of symmetry. The free curved surface that defines only one plane of symmetry is particularly preferred.
Also, in the optical system according to the present invention, the prism face of the first prism is shaped as a plane base surface and the holographic element is applied to the plane base surface, to form the
1
st
-
1
st
surface.
Alternatively, the prism face of the first prism is shaped as a curved base surface and the holographic element is applied to the curved base surface, to form the
1
st
-
1
st
surface.
In this case, the curved base surface may be shaped as any one of a cylindrical surface, a spherical surface, an aspherical surface, an anamorphic surface, a toric surface, a surface that defines only one plane of symmetry, and a plane-symmetric free curved surface.
Also, according to the present invention, the holographic element applied to the
1
st
-
1
st
surface is constructed of a volume hologram, which preferably has a rotationally asymmetric power.
Also, according to the present invention, the
1
st
-
2
nd
surface of the first prism and the
2
nd
-
1
st
surface of the second prism are congruently shaped so that a path of rays can be formed such that chromatic aberration of the first bundles of rays passing through the air space between the
1
st
-
2
nd
surface and the
2
nd
-
1
st
surface is prevented from being degraded.
In this case, the
1
st
-
2
nd
surface of the first prism and the
2
nd
-
1
st
surface of the second prism may be shaped as plane surfaces or alternatively, as curved surfaces.
In this case, the following Condition (1) is satisfied:
1×10
−3
(mm)<
M<
3 (mm) (1)
where M is the air space between the
1
st
-
2
nd
surface of the first prism and the
2
nd
-
1
st
surface of the second prism.
It is much preferred that the following Condition (2) is satisfied:
1×10
−2
(mm)
<M<
2 (mm) (2)
It is still much preferred that the following Condition (3) is satisfied:
7×10
−1
(mm)
<M<
1.5 (mm) (3)
Also, according to the present invention, a surface having both of the refracting action and the reflecting action, such as the
1
st
-
2
nd
surface, is preferably formed as a rotationally asymmetric surface. However the surface may be formed as a rotationally symmetric surface such as a
Ben Loha
Olympus Optical Co,. Ltd.
Pillsbury & Winthrop LLP
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