Optics: image projectors – Distortion compensation – For projection axis inclined to screen
Reexamination Certificate
2002-11-14
2004-07-13
Dowling, William C. (Department: 2851)
Optics: image projectors
Distortion compensation
For projection axis inclined to screen
C362S268000
Reexamination Certificate
active
06761457
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an optical illumination device used for illuminating an optical spatial modulation element, for example, and a projection display device capable of projecting an optical image formed on the optical spatial modulation element through a projection lens onto a screen.
BACKGROUND ART
Conventionally, as video equipment for a wide screen, projection display devices using various optical spatial modulation elements have been known. For example, these displays have translucent and reflective liquid crystal panels as optical spatial modulation elements, allow a light source to illuminate liquid crystal panels, form optical images on the liquid crystal panels in response to video signals supplied from the outside, and enlarge and project the optical images on screens through projection lenses.
When a projection display device is configured, it is important to achieve large optical output and to provide a bright projected image with high image quality. In order to achieve such a display, it is important to achieve an optical illumination system which can efficiently condense light emitted from a lamp and can evenly illuminate an optical spatial modulation element. Japanese Patent Laid-Open No. 3-111806 and No. 5-346557 disclose an optical illumination device using an optical integrator and a glass rod. Such a device forms a light-emitting surface, which is similar to an optical spatial modulation element in shape, and forms an image of the light-emitting surface on the optical spatial modulation element through a relay lens and so on, thereby achieving high efficiency and highly even illumination.
Meanwhile, regarding an optical illumination system used for a projection display device, for example, in some applications and configurations that include illumination on a reflective optical spatial modulation element and projection with a shifted axis, an illuminating light beam is emitted in a direction having predetermined inclination with respect to the optical spatial modulation element. However, in the case of oblique illumination using the above conventional optical illumination systems, regarding an illuminating light beam formed on an emitted surface, the image-forming condition is maintained near an optical axis but is not maintained at a position away from the optical axis. Hence, it is difficult to efficiently condense light on an effective region on the emitted surface. Further, the problem is that a figure is distorted with respect to the inclining direction of the emitted surface, which results in uneven brightness.
In order to efficiently illuminate a surface inclined with respect to an optical axis, it is necessary to realize an optical illumination system for satisfying an image-forming condition of an inclined object that is referred to as a so-called shine-proof condition. Although the condition rule provides an image-forming condition of two surfaces inclined to each other but does not solve a problem in that a figure is distorted with respect to an inclining direction of an emitted surface and uneven brightness occurs. Such a problem has essentially occurred in oblique illumination.
In response, as a configuration for repeating twice the shine-proof condition, a method for solving the problem of oblique image-formation is disclosed. (e.g., Japanese Patent Laid-Open No. 4-27912).
FIG.
9
(
a
) shows an example of a basic configuration of a conventional projection display device.
The conventional projection display device is constituted by a lamp
121
, a concave mirror
122
, a condenser
123
, a light bulb
124
, a first lens
125
, an intermediate image-forming surface
126
, a reflection mirror
127
, a second lens
128
, and a screen
129
.
Light emitted from the lamp
121
is condensed by the concave mirror
122
, and a single beam of light is formed so as to be almost rotationally symmetric with respect to an optical axis.
The condenser
123
illuminates the entire region of the light bulb
124
by using the single beam of light and condenses light passing through the light bulb
124
near an object-side focus
125
a
of the first lens
125
.
For example, a translucent liquid crystal panel is used as the light bulb
124
and forms an optical image in response to a video signal.
The first lens
125
forms the intermediate image-forming surface
126
using light passing through the light bulb
124
. At the same time, light condensed through the condenser
123
passes near the focus
125
a
of the first lens
125
, so that the light is emitted from the first lens
125
as substantially parallel light which surrounds the intermediate image-forming surface
126
.
The light bulb
124
and the intermediate image-forming surface
126
are inclined to each other with respect to the optical axis
125
b
of the first lens
125
so as to satisfy the shine-proof condition.
The reflection mirror
127
disposed near the intermediate image-forming surface
126
, for example, uses minute reflecting surfaces
127
a
that are arranged in two dimensions as enlarged in FIG.
9
(
b
), so that the reflection mirror
127
allows light emitted from the first lens
125
to efficiently enter the second lens
128
.
The second lens
128
forms an image of the intermediate image-forming surface
126
again on the screen
129
. The intermediate image-forming surface
126
and the screen
129
are inclined to each other with respect to the optical axis
128
b
of the second lens
128
so as to satisfy the shine-proof condition.
According to the above configuration, figure distortion appearing on the first lens
125
can cancel figure distortion appearing on the second lens
126
. Thus, on the screen
129
, it is possible to form an image conjugated to an optical image on the light bulb
123
without distortion. Moreover, since a beam of light emitted from the first lens
125
is substantially parallel light, there brings an advantage in that it is possible to reduce loss of light in an optical path from the first lens
125
to the second lens
128
.
The projection display device of FIG.
9
(a) solves figure distortion caused by inclined image formation and brightness gradient caused by the distortion, and efficiently guides light emitted from the lamp to the screen, so that a bright projected image is obtained without distortion. Therefore, when the above configuration is applied to an optical illumination system, it is possible to efficiently illuminate an optical spatial modulation element inclined with respect to an optical axis. However, the following problem arises.
To be specific, when the shine-proof condition is repeated twice regarding oblique image formation, the optical axes of the first lens and the second lens are largely refracted. Hence, a means of bending an optical path is necessary. In FIG.
9
(b), a minute reflection mirror array having minute reflection mirrors aligned in two dimensions is disposed near the intermediate image-forming surface so as to form the above means. However, since the intermediate image-forming surface has a conjugating relationship with the screen, images of edges and the like of the minute reflection mirrors are formed on the screen.
Namely, in the conventional optical illumination device or projection display device, a problem (first problem) arises in which images of edges and the like of the minute reflection mirrors of the optical path bending means are formed on the screen.
Secondly, since light converged by the condenser illuminates the light bulb in the configuration of FIG.
9
(a), brightness on the light bulb, which is inclined with respect to an optical axis of a light source, has asymmetric distribution with respect to the optical axis. The distribution of brightness on the light bulb is substantially reproduced on the screen by the effect of the above twice image formation, so that an image having brightness distribution asymmetric with respect to the optical axis is formed on the screen.
Namely, in the conventional optical illumination device or projection display device, a problem (second p
Fushimi Yoshimasa
Masumoto Yoshihiro
Wada Mitsuhiro
Dowling William C.
Matsushita Electric - Industrial Co., Ltd.
RatnerPrestia
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