Optical: systems and elements – Single channel simultaneously to or from plural channels – By partial reflection at beam splitting or combining surface
Reexamination Certificate
2001-07-27
2004-02-24
Epps, Georgia (Department: 2873)
Optical: systems and elements
Single channel simultaneously to or from plural channels
By partial reflection at beam splitting or combining surface
C359S638000
Reexamination Certificate
active
06697200
ABSTRACT:
BACKGROUND OF THE INVENTION
1) Field of the Invention
The present invention relates to an image display apparatus having an observation optical system.
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 wide-screen image. Conventionally, as head-mount image display apparatuses, there are known a type in which an image on an image display element such as a CRT is transmitted via an image transmitting element to an object surface, where the image is projected in the air by a toric reflecting surface (U.S. Pat. No. 4,026,641), and a type in which an image displayed on a liquid crystal display device (LCD) is once imaged in the air via a refraction-type relay optical system and then is introduced into an eye of an observer via an eyepiece optical system composed of a concave mirror arranged in a decentered manner (Japanese Patent Application Preliminary Publication (KOKAI) No. Hei 6-294943).
However, these types of the head-mount image display apparatus are not suitable for long-time use as being held on the head or face, because their optical systems are large and heavy. Therefore, it is desired to reduce the weight of the apparatus while maintaining good image quality.
Also, in accordance with recent popularization of cellular phone and portable intelligent terminal, requirements for wide-screen view, via an image display apparatus, of graphics or text data on a cellular phone or portable intelligent terminal have grown. For application to a cellular phone or the like also, it is desired to reduce weight of the apparatus while maintaining good image quality because users would personally carry the cellular phones or the like with them in their pockets or bags.
As conventional resolution examples for achieving weight reduction, observation optical systems that are constituted with a combination of thin platelike optical members (Japanese Patent Application Preliminary Publication (KOKAI) No. Hei 8-234137, Japanese patent Application Preliminary Publication (KOKAI) No. 8-240773) are known.
Although such an observation optical system is allowed to have a lightweight structure, it involves a problem in having difficulty in providing good image quality, because dust is easily caught on reflecting surfaces thereof to cause flare or the like.
In reference to
FIGS. 29-30
, this problem is explained. Each of observation optical systems shown in
FIGS. 29
,
30
is configured to reflect bundles of rays emergent from an image display element
1
such as LCD at a reflecting surface
2
1
of an optical member
2
. Since the observation optical system as shown in
FIG. 29
uses a prism, there is no chance that dust or flaws would damage the reflecting surface
2
1
during assembling or transportation. In contrast, since the observation optical system as shown in
FIG. 30
is constituted with a combination of thin platelike optical members for the purpose of weight reduction, the reflecting surface
2
1
is apt to be damaged with dust or flaws and thus assembling and transportation is difficult.
SUMMARY OF THE INVENTION
Therefore, an object of the present invention is to achieve weight reduction while maintaining good image quality in an image display apparatus that is used for magnifying observation of an image formed on a display element.
An image display apparatus according to the first aspect of the present invention includes an image display element and an observation optical system which forms an exit pupil for observation of an image displayed on the image display element, wherein the observation optical system has at least one surface having a lens function, and the following condition (1) is satisfied:
0.1<
P·PD·ZD<
5 (1)
where P is a pixel pitch (in &mgr;m) of the image display element, PD is a diameter (in mm) of the exit pupil, and ZD is a distance (in mm) from the display surface of the image display element to a first surface having a lens function.
For example, in the optical system provided with an optical member similar to that shown in
FIG. 30
, it is desirable that Condition (1) is satisfied for the purpose of obtaining good image quality with optical performance being little affected by dust or flaws that would damage the reflecting surface during assembling or transportation. In
FIG. 1
, the reference numeral
1
represents an image display element such as a LCD, the reference
2
represents a first optical member, the reference numeral
2
1
represents a first reflecting surface, and the reference numeral
4
represents an exit pupil.
Light emergent from the image display element
1
has a relatively small beam diameter as it is incident on the first reflecting surface
2
1
, and the beam diameter is widened after the light is reflected from the reflecting surface
2
1
. Therefore, if dust is caught on the first reflecting surface
2
1
, a blurred image of the dust is projected on the pupil as enlarged for observation, to degrade image quality.
In this case, under the condition where a dust particle with the same size is caught on the reflecting surface
2
1
, a finer pixel pitch of the image display element
1
causes the blurred image of the dust particle to be more conspicuous because resolution of the image is finer, while a coarser pixel pitch makes the image of the dust particle to be less conspicuous because resolution over the entire image is coarser. Also, a larger diameter of the exit pupil
3
, or a larger value of NA causes a larger beam diameter at the first reflecting surface, and thus the dust particle is projected relatively small to be less conspicuous. Also, a longer distance from the display surface of the image display element
1
to the first surface having a lens function causes a larger beam diameter at the first reflecting surface, and thus the dust particle is projected relatively small to be less conspicuous.
Considering the discussions set forth above collectively, the applicant has revealed that satisfaction of Condition (1) is desirable in the image display apparatus according to the first aspect.
If Condition (1) is satisfied, it is possible to achieve good image quality because dust, which would be caught on the reflecting surface during fabrication, is inconspicuous as observed.
Failing to reach the lower limit value, 0.1 of Condition (1) is not preferable, because it degrades image quality with dust caught on the reflecting surface being conspicuous as a large image. Exceeding the upper limit value, 5 of Condition (1) is not preferable, because such a configuration is impractical with bulkiness of the optical system or with degraded image quality over the entire field.
Also, an image display apparatus according to the second aspect of the present invention includes an image display element and an observation optical system which forms an exit pupil for observation of an image displayed on the image display element, wherein the observation optical system includes at least one diffraction element which is given a lens function by diffraction effect, and an optical element satisfying the following condition (2) is used in observation:
a<90 (2)
where a is a transmittance (in %) for a wavelength range of 500 nm-650 nm.
As measures to achieve weight reduction of the observation optical system, use of a diffraction element, which has a lens function in spite of its thin structure, is known. As a reflection type- or transmission type-diffraction element, a relief hologram or a volume hologram is available. However, a diffraction element involves a problem of flare caused by undesired order rays. Therefore, if light from bright light source such as the sun or an electric lamp is incident on a diffraction element, for example, flare caused at the diffraction element prevents a good image from being formed.
Therefore, in the image display apparatus according to the second aspect, an optical member which satisfies Condition (2) is used for the purpose o
Epps Georgia
Harrington Alicia M
Olympus Optical Co,. Ltd.
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