Optical: systems and elements – Holographic system or element – Head up display
Reexamination Certificate
2000-10-30
2004-11-23
Assaf, Fayez (Department: 2872)
Optical: systems and elements
Holographic system or element
Head up display
C359S014000, C359S015000, C359S630000, C345S008000
Reexamination Certificate
active
06822770
ABSTRACT:
BACKGROUND OF THE INVENTION
1) Field of the Invention
The present invention relates to an observation optical system and a photographing optical system and an apparatus using the same.
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.
As an optical system applicable to such apparatuses, each of FIG. 7(
a
) of Japanese Patent Application Preliminary Publication (KOKAI) No. 7-140414 and Japanese Patent Application Preliminary Publication (KOKAI) No. 9-171151 proposes an optical system in which a half mirror as a tilted mirror for splitting a path is disposed in a prism optical system that includes a concave mirror with a small amount of decentering.
Also, FIG. 9 of U.S. Pat. No. 5,093,567 proposes an optical system in which a first prism including a triangular prism is disposed on the eye side and in which a second prism is disposed at a minute air space away therefrom. Also, each of FIG. 3 of Japanese Patent Application Preliminary Publication (KOKAI) No. 2000-241751 and FIG. 3 of Japanese Patent Application Preliminary Publication (KOKAI) No. 2000-180787 proposes an optical system in which a first prism having a convex lens action is disposed on the eye side and in which a second prism is disposed at a minute air space away therefrom. These optical systems bend the path of light without loss of amount of light by utilizing total reflection phenomenon caused by difference in refractive index between glass and air at the minute air space between the prisms.
Also, U.S. Pat. No. 4,874,214 proposes an observation optical system having hologram elements. This observation optical system uses the hologram elements at the plane surface (2) and the spherical surface (3).
However, in the optical system as disclosed in FIG. 7(
a
) of KOKAI No.7-140414 or in KOKAI No. 9-171151, since the tilted mirror disposed in the prism optical system for splitting the path is constructed of a half mirror, amount of light from the image display element is attenuated to ¼ via twice transmission through the half mirror, to cause dark view of the displayed image. In order to obviate this result, it is necessary to use a bright illumination source, which consumes more power, for illumination of the image display element. If conditions regarding available power consumption, performance of the light source device etc. do not allow a light source to be made bright, observation of the displayed image under bright sunlight could not be made.
Also, in the observation optical system as disclosed in FIG. 9 of U.S. Pat. No. 5,093,567, in FIG. 3 of KOKAI No. 2000-2141751 or in FIG. 3 of KOKAI No. 2000-7180787, since a minute air space is provided between two prisms, alignment of optical axes of these two prisms with each other is required in setting these prisms in place while keeping the air space between, to raise the cost for assembling. Also, impact or vibration applied to an apparatus including such an observation optical system is likely to disorder the alignment of the optical axes.
The optical system proposed in U.S. Pat. No. 4,874,214 is provided with a hologram element that is disposed on the spherical surface
3
and that has the shape of a curved surface.
A hologram element having a shape of a curved surface has two kinds of powers, i. e. an optical power resulting from the shape and a power resulting from the diffraction effect of the hologram element. In reference to the drawings, these two kinds of powers of a hologram element formed on a base member having a spherical surface shape, for example, are explained. The hologram element has a power resulting from difference in interference fringe density such as the pitch of the grating structure in the hologram element as shown in
FIG. 17A
, and has an optical power resulting from its curved surface shape as shown in FIG.
17
B. The optical power of the hologram element depending on its shape is influenced by thickness of the base member also. The power depending on the shape increases as the thickness of the base member increases.
However, in the observation optical system set forth in U.S. Pat. No. 4,874,214, since the space between the plane surface (
2
) and the spherical surface (
3
) is not filled with a medium such as glass or plastic, the optical power resulting from the curved surface shape of the hologram element is small and thus it is difficult to compensate spherical aberration and coma. Furthermore, in this observation optical system, since no optical element is disposed adjacent to the image display element, or in the path between the image surface and the plane surface (
2
), where compensation of distortion could be effectively made, it is difficult to compensate distortion in good condition.
SUMMARY OF THE INVENTION
The present invention has been made to solve the above-mentioned problems involved in the conventional art. An object of the present invention is to provide an observation optical system that allows a displayed image to be bright as observed, is easily assembled, is insusceptible to vibration or impact, is lightweight and compact, and allows, in addition, the displayed image to be observed upon aberrations being compensated in good condition, and to provide an apparatus using the same. Also, upon the travelling direction of light in the path being inverted, such an optical system is applicable to a photographing optical system provided with an imaging optical system which forms an object image, and is applicable to an apparatus using the same.
The observation optical system according to the present invention comprises an observation image forming member which forms an image to be viewed by an observer, and an eyepiece optical member which introduces into an exit pupil formed at the position of the eye of the observer the observation image formed by the observation image forming member. In the observation optical system, the eyepiece optical member includes, at least, a first prism member and a second prism member. The first prism at least includes a first entrance surface through which rays emergent from the observation image enter the first prism, a reflecting surface which reflects the rays inside the first prism, and the first exit surface through which the rays exit out of the first prism. These surfaces are arranged with a first prism medium between. The second prism at least includes a second entrance surface through which the rays emergent from the first prism enter the second prism and a second exit surface through which the rays exit out of the second prism. These surfaces are arranged with a second prism medium between.
Since, in this way, the space inside the eyepiece optical member is filled with glass or plastic material, the optical power depending on the surface shape of each optically operative surface is made large, to compensate aberrations such as spherical aberration and coma in good condition.
Also, the observation optical system according to the present invention is constructed so that, in addition to the above-mentioned configuration, the first prism and the second prism are joined to each other via a hologram element interposed between the first exit surface and the second entrance surface.
The hologram element used as a tilted mirror to split the path achieves diffraction efficiency of nearly 100% in performing reflection by diffraction, and thus can provide bright view of the displayed image without loss of amount of light. Also, since the image display element-side prism and the eye-side prism are joined via a hologram element interposed between, to be an integral member, the assembly process can be free from possible inconsistency of optical axes and complicated works for prism setting, which otherwise would be induced by the ai
Assaf Fayez
Olympus Corporation
Pillsbury & Winthrop LLP
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