Optical: systems and elements – Single channel simultaneously to or from plural channels – By partial reflection at beam splitting or combining surface
Reexamination Certificate
2000-03-31
2002-05-28
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
C359S632000, C359S637000, C359S640000
Reexamination Certificate
active
06396639
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a viewing optical system and an image display apparatus using the same. More particularly, the present invention relates to a viewing optical system devised so that a bright image of a display device of the type in which an image is displayed by reflected light, e.g. a reflection type liquid crystal display device, can be observed through an ocular optical system arranged to be compact in size and to minimize the loss of light quality. The present invention also relates to an image display apparatus, e.g. a head-up display, using the viewing optical system.
The present invention also relates to a see-through viewing optical system that allows see-through observation of the outside world or the like in an optical system of an image display apparatus, e.g. a head-up display.
In recent years, with the development of head-up displays and glasses-type displays, compact ocular optical systems have been actively developed. As a result, ocular optical systems using a thin and compact decentered prism have been proposed as disclosed, for example in Japanese Patent Application Unexamined Publication Numbers (hereinafter referred to as “JP(A)”) 7-333551, 8-50256 and 8-234137. These are compact ocular optical systems in which reflecting surfaces have a power and the optical path is folded, and in which rotationally asymmetric decentration aberrations produced by decentered reflecting surfaces with a power are corrected by using an anamorphic reflecting surface or a rotationally asymmetric reflecting surface having one plane of symmetry.
Regarding liquid crystal display devices for displaying an image for observation, reflection type liquid crystal display devices have been developed to form images that are brighter and easier to observe. As a reflection type liquid crystal display device including an illumination structure therefor, JP(A) 10-268306 has been laid open to public.
As an ocular optical system using a reflection type image display device that is brighter than the transmission type, e.g. a reflection type liquid crystal display device, U.S. Pat. No. 5,771,124 is known.
However, the ocular optical system disclosed in U.S. Pat. No. 5,771,124 needs to form all the optical members from glass and is therefore heavy in weight. Regarding the arrangement of the ocular optical system, the number of parts is large, and the structure is large in size. In addition, because illuminating light incident on the reflection type image display device is tilted from the direction perpendicular to the image display surface to a considerable extent, brightness is sacrificed undesirably.
Accordingly, it is conceivable to apply illuminating light from a direction approximately perpendicular to the display surface of the reflection type image display device of the viewing optical system according to JP(A) 10-268306. This is, however, unfavorable for U.S. Pat. No. 5,771,124 because the ocular optical system disclosed therein lacks compactness.
Under these circumstances, it is conceivable to construct a bright and compact viewing optical system by combining together an ocular optical system superior in compactness as proposed, for example, in JP(A) 7-333551, 8-50256 and 8-234137 and the reflection type image display device according to JP(A) 10-268306, in which illuminating light is applied to the display surface approximately perpendicularly.
However, the above-described conventional ocular optical system using a decentered prism is based on the assumption that a transmission type image display device is used. Therefore, the distance between the image display device and the entrance surface of the decentered prism is short. For this reason, it is impossible to ensure a space for placing an optical member for illuminating the display surface of the reflection type image display device between the image display device and the decentered prism. Consequently, it is unavoidably necessary to tilt the reflection type image display device with respect to the optical axis to a considerable extent and to dispose a light source so that illuminating light is applied to the display surface from an oblique direction as in the case of U.S. Pat. No. 5,771,124.
When a reflection type image display device is tilted with respect to the optical axis to a considerable extent, particularly when a reflection type liquid crystal display device is used as the reflection type image display device, the brightness of the reflection type image display device cannot be exhibited satisfactorily owing to the viewing angle dependence. Moreover, because the object plane is tilted with respect to the optical axis, an excessively heavy load is imposed on the ocular optical system to allow the image to be observed perpendicularly to the optical axis without curvature and distortion.
To construct a see-through optical system for see-through observation of the outside world or the like by using a thick prism optical system constituting a conventional ocular optical system as stated above, the common practice is to use surfaces of the same configuration as the eye-side surface and the outside world-side surface and to set the power of the see-through optical path to zero.
However, when the eye-side surface of the prism optical system is not a plane surface, even if the power of the see-through optical path is zero, the angular magnification is not 1. Accordingly, in the case of a head-mounted image display apparatus designed for a single eye, in which the user performs observation with one eye through the prism optical system and the other eye being naked, two images seen with the left and right eyes cannot properly be fused into a single image.
SUMMARY OF THE INVENTION
In view of the above-described problems with the prior art, an object of the present invention is to provide a compact, bright and high-performance viewing optical system using an ocular optical system, which is formed from a decentered prism, and a reflection type image display device, and also provide an image display apparatus using the viewing optical system.
Another object of the present invention is to provide a viewing optical system in which when the outside world or the like is viewed in a see-through manner through an ocular optical system, e.g. a prism optical system, which forms a displayed image of an image display device, the outside world or the like can be seen in the same way as in the case of viewing with the naked eye.
A first viewing optical system according to the present invention provided to attain the first object includes a reflection type image display device for displaying an image by reflecting an illuminating light beam incident from the front side of a display surface for forming an image for observation. The viewing optical system further includes an ocular optical system for leading the image to a pupil position where an observer's eyeball is to be placed.
The image display device has an illuminating device and an illuminating light guide optical device for guiding a light beam emitted from the illuminating device so that the light beam can be applied to the display surface from the front side thereof.
The ocular optical system includes a prism member having an entrance surface through which a display light beam reflected from the reflection type image display device enters the prism member after passing through the illuminating light guide optical device. The prism member further has at least one reflecting surface reflecting the light beam in the prism member, and an exit surface through which the light beam exits from the prism member.
The at least one reflecting surface of the prism member is decentered with respect to an optical axis and has a rotationally asymmetric curved surface configuration that corrects decentration aberrations due to the decentration of the reflecting surface and gives a power to the light beam.
The spacing between the entrance surface of the prism member and the display surface of the reflection type image display device satisfies the following condi
Takeyama Tetsuhide
Togino Takayoshi
Epps Georgia
Olympus Optical Co,. Ltd.
Pillsbury & Winthrop LLP
Seyrafi Saeed
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