Projector

Details Projector Projector

1999-06-08

2001-11-13

Dowling, William (Department: 2851)

Optics: image projectors

Miscellaneous

C353S038000

Reexamination Certificate

active

06315417

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a projection display device in which a light beam emitted from a light source is modulated by a light valve using a liquid crystal panel or the like, and the modulated light beam is enlarged and projected via a projection optical system.
2. Description of Related Art
A projection display device has been known in which a light beam emitted from an illumination optical system is converted into a modulated beam corresponding to image information by using a liquid crystal light valve, and the modulated beam is enlarged and projected onto a screen (projection plane) via a projection optical system.
FIG. 6
shows an optical system in such a projection display device. As this figure shows, a projection display device
1000
comprises an illumination optical system
80
including a light source
81
and a uniform illumination optical system
82
, a liquid crystal light valve l
00
A to be irradiated with light by the illumination optical system
80
, and a projection optical system
60
A for enlarging and projecting emergent light from the liquid crystal light valve
100
A onto a screen
900
.
In the projection display device
1000
having such a conventional configuration, the f-numbers F
L
and F
P
of the illumination optical system
80
and the projection optical system
60
A are designed to be nearly equal to each other.
In general, the projection optical system
60
A is frequently represented by a single lens element, as shown in
FIG. 6
, whereas it is normally composed of a plurality of lens elements. This means that a plurality of lens elements can be replaced by a single lens element having a function equivalent to that of those lens elements. It is assumed that the f-number F
P
of the projection optical system refers to the f-number of the single lens element thus replaced, that is to say, a value 1
P
/d
P
that is obtained by dividing a focal distance
1
P
of the single lens element by a diameter d
P
of the lens.
Furthermore, it is assumed that the f-number F
L
of the illumination optical system refers to the f-number of a lens element disposed on the most downstream side of the optical path, that is, closest to the liquid crystal light valve
100
A, which is an object to be illuminated, among a plurality of lens elements included in the illumination optical system. When the lens element disposed on the most downstream side of the optical path is a lens array composed of a plurality of small lenses, as shown in
FIG. 6
, the f-number F
L
of the illumination optical system does not refer to the f-number of each small lens, but to a value 1
L
/d
L
obtained by dividing a distance 1
L
from the lens array to an object to be illuminated by the maximum diameter d
L
of the lens array (e.g., the diameter in the case of a circular lens array, the length of the diagonal line in the case of a rectangular lens array).
On the other hand, projection display devices have recently been required to display high-definition images. In order to display a high-definition image, it is necessary to increase the number of pixels in a liquid crystal light valve. In a liquid crystal light valve in which pixels are arranged in a matrix, the peripheries of the pixels are shielded from light by a light-shielding layer called a black matrix. Therefore, as the number of pixels in the liquid crystal light valve increases, the region occupied by the black matrix enlarges, and conversely, the area of pixel apertures decreases. That is to say, the amount of light emitted from the liquid crystal light valve decreases as the definition of the liquid crystal light valve increases, and therefore, a projection image produced by the projection display device becomes dark as the definition of an image to be projected increases.
In order to avoid such harmful effects, a liquid crystal light valve has been proposed which is provided with a microlens array composed of a plurality of microlenses so that light is efficiently guided to corresponding pixel apertures by the microlenses.
While incident light can be efficiently guided to the pixel apertures in the liquid crystal light valve provided with the microlens array, emergent light from the liquid crystal light valve, however, is diffused by the lensing action of the microlens array. For this reason, the inclination angle of emergent light from the liquid crystal light valve having microlenses is greater than that of emergent light from a liquid crystal light valve that does not have microlenses.
Therefore, if a liquid crystal light valve having microlenses is incorporated in the conventional projection display device
1000
in which the f-numbers of the illumination optical system
80
and the projection optical system
60
A are designed to be nearly equal, there is a fear that a part of emergent light from the liquid crystal light valve will not be drawn into the projection optical system
60
A. As a result, light utilization efficiency is lowered, and an image projected on the screen becomes dark.
SUMMARY OF THE INVENTION
In view of the above-described problems, an object of the present invention is to provide a projection display device having a light valve with microlenses incorporated therein, wherein a bright projection image can be obtained by preventing light utilization efficiency from being deteriorated due to light diffusion by the microlenses.
In order to solve the above problems, the present invention provides a projection display device comprising a light valve for modulating a light beam emitted from an illumination optical system, the light valve including pixels arranged in a matrix, and a microlens array having a plurality of microlenses for collecting incident light to the pixels; and a projection optical system for enlarging and projecting the light beam modulated by the light valve, wherein the f-number of the projection optical system is less than the f-number of the illumination optical system.
In the projection display device of the present invention, the f-number of the projection optical system is set to be less than that of the illumination optical system so that emergent light from the liquid crystal light valve diffused by the microlenses is efficiently drawn into the projection optical system. For this reason, it is possible to prevent light utilization efficiency from being deteriorated due to light diffusion by the microlenses, and to obtain a sufficient effect of forming the microlenses in the liquid crystal light valve. That is to say, it is possible to cause a large amount of light guided to pixel apertures by the microlenses to efficiently reach a projection plane, and to obtain a bright projection image in a projection display device in which a liquid crystal light valve having microlenses is incorporated.
In order to make almost all emergent light from the liquid crystal light valve, which is diffused by the microlenses, to be drawn into the projection optical system, the f-number F
P
of the projection optical system is set to satisfy the following equation:
F
P
≦[tan{tan
−1
(2×F
M
)+tan
−1
(2×F
L
)−90°}]/2
where the F-numbers of the projection optical system, the illumination optical system, and the microlenses are F
P
, F
L
, and F
M
, respectively.
The illumination optical system to be adopted may include a light source, and a uniform illumination optical system for splitting a light beam emitted from the light source into a plurality of partial beams, and superimposing the partial beams onto the light valve. The adoption of such an illumination optical system makes it possible to uniformly illuminate the liquid crystal light valve, and to thereby obtain a high-contrast projection image.
When the illumination optical system to be adopted includes a light source, a first lens plate having a plurality of rectangular lenses for splitting emergent light from the light source into a plurality of intermediate beams, and a second lens plate having a plurality of rectangular lenses

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