Optics: image projectors – Distortion compensation
Reexamination Certificate
2001-03-08
2003-09-30
Adams, Russell (Department: 2851)
Optics: image projectors
Distortion compensation
C353S070000, C353S098000, C353S099000, C359S364000, C359S858000, C359S859000
Reexamination Certificate
active
06626541
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a projection optical system and a projection type displaying apparatus using the same, and in suitable for an optical apparatus such as a liquid crystal projector (projection) for directing a beam light-modulated by an image displaying panel such as a liquid crystal display element (liquid crystal panel) or a digital micromirror device to a screen or a wall, and forming image information.
2. Related Background Art
There have heretofore been proposed various passive type projectors for illuminating an image displaying panel such as a liquid crystal panel by a beam from a light source, enlarging and projecting it onto a screen or a wall by a projection lens by the use of transmitted light or reflected light light-modulated by the image displaying panel and forming an image.
There have been proposed various projection optical systems for use for projection capable of effecting oblique projection onto a screen to shorten the distance between the screen and the apparatus.
FIG. 15
of the accompanying drawings is a schematic view of an embodiment of a projection optical system disclosed in Japanese Patent Application Laid-Open No. 05-100312. In
FIG. 15
, L designates an illumination system, and LV denotes a light valve using transmission or reflection type dot matrix liquid crystal or the like. An image based on the light valve LV is enlarged and projected onto a screen S by a projection optical system PL, and is displayed on the screen S. In the invention of this publication, a wide angle lens having a great angle of field is used as the projection optical system PL, and the light valve LV and the screen S are shifted and disposed relative to the optical axis La of the projection optical system PL, and projection is effected by the use of the end portion of the angle of field to thereby constitute an oblique projection optical system.
FIG. 16
of the accompanying drawings is a schematic view of an embodiment of a projection optical system disclosed in Japanese Patent Application Laid-Open No. 05-080418. In
FIG. 16
, L designates an illumination system, and LV denotes a light valve using transmission or reflection type dot matrix liquid crystal or the like. An image based on the light valve LV is projected by a first projection optical system PL
1
to thereby form an intermediate image, which in turn is enlarged and projected onto a screen S by a second projection optical system PL
2
. In the invention of this publication, the optical axes of the first and second projection optical systems are appropriately inclined to thereby project the image obliquely onto the screen.
Also, in republished Patent No. WO 97/01787, there is disclosed a projection optical system for projecting an image from an oblique direction by the use of a plurality of reflecting surfaces.
On the other hand, recently, there have been proposed various imaging systems utilizing a non-coaxial optical system to achieve the downsizing of the entire optical system. In the non-coaxial optical system, the concept of the reference axis is introduced and a constituent surface is made into an asymmetrical aspherical surface, whereby it is possible to construct an optical system in which aberrations are sufficiently corrected, and a designing method therefor is shown, for example, in Japanese Patent Application Laid-Open No. 9-5650, and examples of the design thereof are shown in Japanese Patent Application Laid-Open No. 8-292371 and Japanese Patent Application Laid-Open No. 8-292372.
Such a non-coaxial optical system is called an off-axial optical system (when supposing a reference axis along a ray passing through the center of an image and the center of a pupil, an optical system defined as an optical system including a curved surface (off-axial curved surface) in which a plane normal at the point of intersection between the constituent surface and the reference axis is not on the reference axis, and at this time, the reference axis is of a bent shape). In this off-axial optical system, the constituent surface is generally non-coaxial and eclipse does not occur even in a reflecting surface and therefore, it is easy to construct an optical system using a reflecting surface. The off-axial optical system also has the feature that it is easy to make an integral type optical system by a technique of integrally molding the constituent surface whereby an optical path can be relatively freely designed.
In Japanese Patent Application Laid-Open No. 05-100312, use is made of a projection optical system in which a light valve and a screen are shifted relative to an optical axis, and in this case, as shown in
FIG. 11
of the accompanying drawings, the magnitude of the angle of field of the projection optical system used is &thgr;
2
. However, a lens system of a high angle of field having a considerably great angle of field (&thgr;
1
) is required as the projection optical system used. Also, in an ordinary lens system, the quantity of light decreases as the angle of field becomes greater from the optical axis La. Therefore, if a lens system of a higher angle of field is used, a difference will come out in brightness particularly in the vertical direction of a screen S. Also, when design is made such that the optical axis La goes toward the center of the screen S (
FIG. 12
of the accompanying drawings), an image is not formed on the screen S but is formed on a plane S′ perpendicular to the optical axis La in the ordinary lens system. When such design is made, as is well known, the projected image is distorted into a trapezoid and the focus deviates in the vertical direction of the screen S. When the inclination of this image plane is to be corrected, the difference between the optical path L
1
of a ray passing through the upper portion of the screen S and the optical path L
2
of a ray passing through the lower portion of the screen S must be negated. When this difference is to be corrected, if it can be corrected near the imaging plane, the difference between the optical path L
1
and the optical path L
2
will be reduced and therefore the amount of correction may be small. On the other hand, when the difference is to be corrected on the optical surface of the screen side on which the projected image is enlarged, the difference between the optical path L
1
and the optical path L
2
directly affects.
Also, in an apparatus disclosed in Japanese Patent Application Laid-Open No. 05-080418, a lens system is only tilted and therefore it is difficult to incline the image plane sufficiently.
Also, if the amount of tilt is too great, it will become difficult to secure optical performance.
In a projection optical system in a reflection type displaying apparatus disclosed in republished Patent No. WO 97/01787, a coaxial system is comprised of a concave mirror and one or two convex mirrors, and an image is projected from an oblique direction by the use of some of the reflecting surfaces of the concave mirror and the convex mirrors. Because of the coaxial system, aberration correction is difficult and it is difficult to make the reflecting optical system bright (to make F number small).
Also, the projection optical system uses a construction in which a stop is disposed between the reflecting members. A beam passed through the stop is incident on the convex mirror, and a divergent beam from this convex mirror is incident on the next convex mirror. Therefore, the effective diameter of the second convex mirror has tended to increase. Also, at this time, the two convex mirrors form the virtual image of the stop.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a projection optical system and a projection type displaying apparatus using the same.
It is also an object of the present invention to provide a bright projection optical system and a projection type displaying apparatus using the same.
To achieve the above object, the projection optical system of the present invention is a projection optical system for guiding a beam from an
Canon Kabushiki Kaisha
Koval Melissa J
Morgan & Finnegan , LLP
LandOfFree
Projection optical system and projection type displaying... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Projection optical system and projection type displaying..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Projection optical system and projection type displaying... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3079336