Optics: image projectors – Particular condenser
Reexamination Certificate
1999-10-26
2002-10-15
Dowling, William (Department: 2851)
Optics: image projectors
Particular condenser
C353S038000
Reexamination Certificate
active
06464362
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an illuminating apparatus used in liquid-crystal projectors etc., and a projection type display apparatus using it.
2. Related Background Art
The conventional illuminating devices for projection type display apparatus were usually constructed of a combination of arc tube
1
with parabolic mirror
19
as illustrated in FIG.
10
.
In
FIG. 10
, white light emitted from a light-emitting portion
1
c
of the arc tube
1
(light source) is converted into nearly parallel light by the parabolic mirror
19
and a first lens array
3
forms a light source image of the arc tube
1
at the center of each lens of second lens array
4
. The first lens array
3
and the second lens array
4
have their respective focal lengths approximately equal to each other, and the first lens array
3
and the second lens array
4
are spaced from each other so that the spacing between them is approximately equal to the focal length of the first lens array
3
.
The light condensed by the first lens array
3
is separated into p-polarized light and s-polarized light by a polarization separating layer
5
B of a polarization converting element
5
. The s-polarized light is reflected and is further reflected by an adjacent polarization separating layer
5
B, whereby the light emerges from between half wave plates
5
A arranged in a reed screen pattern on the exit side of the polarization converting element
5
. On the other hand, the p-polarized light passes through the polarization separating layer
5
B and then through the half wave plate
5
A to undergo phase conversion, whereby the direction of the polarization axis thereof is aligned with that of the s-polarized light. Therefore, all the beams emitted from the polarization converting element
5
are the polarized light having the axis of polarization along the same direction. Reference symbol
5
C designates shield plates arranged in a reed screen pattern.
The light emerging from the polarization converting element
5
is condensed by first condenser lens
6
to be deflected onto display regions
8
R,
8
G,
8
B of respective image modulating devices, each device being comprised of a liquid-crystal panel, where the light is modulated in each color of R, G, or B. Among the light emerging from the first condenser lens
6
, red light is reflected by a dichroic mirror DM
1
and the rest green light and blue light is transmitted thereby. The red light reflected by the dichroic mirror DM
1
is guided via reflecting mirror M
1
and second condenser lens
7
R to the display region
8
R of the image modulating device for red. The light transmitted by the dichroic mirror DM
1
is separated into green and blue beams by the dichroic mirror DM
2
. The green light is reflected by the dichroic mirror DM
2
to be guided through the second condenser lens
7
G to the display region
8
G of the image modulating device for green. The blue light transmitted by the dichroic mirror DM
2
is condensed by third condenser lens
11
and reflected by reflecting mirror M
2
to be guided through relay lens
12
and via reflecting mirror M
3
and second condenser lens
7
B to the display region
8
B of the image modulating device for blue. In the drawing, P
1
denotes polarizing plates on the entrance side and P
2
polarizing plates on the exit side. The second condenser lenses
7
R,
7
G,
7
B are placed for condensing the beam emerging from the first condenser lens
6
onto the entrance pupil of projection lens
10
. For color composition, a cross dichroic prism
9
is positioned between the display regions
8
R,
8
G,
8
B of the image modulating devices and the projection lens
10
. The projection lens
10
is designed so as to be telecentric with respect to the display regions
8
R,
8
G,
8
B of the image modulating devices, and angles of incidence at dichroic film surfaces of the cross dichroic prism
9
are arranged so as to be constant everywhere on the dichroic films, thereby preventing chromatic unevenness from occurring due to difference in the angles of incidence on the dichroic films. Beams modulated by the respective display regions
8
R,
8
G,
8
B of the image modulating devices undergo color composition in the cross dichroic prism
9
and combined light is projected at an enlargement ratio onto an unrepresented screen by the projection lens
10
.
In order to further improve the illumination efficiency, the liquid-crystal projector suggested in Japanese Patent Application Laid-Open No. 10-133141 is constructed using a light source device of a combination of an ellipsoidal mirror with a pair of lens arrays, the lens array on the light source side having the concave lens effect. An embodiment disclosed in
FIG. 1
of the official gazette of this Japanese Patent Application Laid-Open No. 10-133141 has a light source section composed of a light source, an ellipsoidal mirror, a first lens array having a concave surface with the concave lens effect on the entrance side, and a second lens array, thereby realizing the smaller size of the lens arrays than those before it.
Incidentally, in the ordinary liquid-crystal projectors as illustrated in
FIG. 10
, it is important in order to improve the illumination efficiency that the eclipse at the shield plates
5
C of the polarization converting element
5
be reduced by improving the parallelism of the beams incident to the first lens array
3
and that the eclipse at the entrance pupil of the projection lens
10
be reduced by decreasing the diameter of the whole light emerging from the polarization converting element
5
.
When the parabolic mirror is used in the light source section, the focal length of the parabolic mirror, however, has to be increased in order to improve the parallelism of the beams emerging from the parabolic mirror. As a result, when a take-in angle of the light emitted from the light source is fixed at the reflector, the exit diameter of the parabolic mirror becomes larger at an increase ratio of the focal length of the parabolic mirror. Conversely, the focal length of the parabolic mirror has to be decreased in order to decrease the exit diameter of the parabolic mirror. The decrease of the focal length will degrade the parallelism of the beams emerging from the parabolic mirror when it is considered that the light source has the finite size.
As described above, the parallelism of the light emerging from the light source section, and the exit diameter are in the relation of tradeoff. With use of the parabolic mirror in the light source section, it was thus impossible to realize the light source section with good parallelism and small exit diameter while assuring a sufficient take-in angle of the light emitted from the light source.
For these reasons, the conventional example described in the aforementioned official gazette employed the ellipsoidal mirror and the concave lens (negative lens) in the light source section in order to improve the illumination efficiency, but optimization of the shape of the concave lens was not enough, though the size reduction of the lens arrays was realized to some extent; therefore, it had the problem that the illumination efficiency was not increased so much.
SUMMARY OF THE INVENTION
The present invention has been accomplished in view of the problems in the above conventional examples, and an object of the present invention is to realize the size reduction of the lens arrays and the increase of the illumination efficiency.
In order to accomplish the above object, an illuminating apparatus according to a first aspect of the present invention is one comprising a light source, a reflector for collecting light emitted from the light source, a negative meniscus lens which is convex on the light source side, a first optical element comprised of a lens array comprising a plurality of lenses, and a second optical element comprised of a lens array comprising a plurality of lenses, wherein the negative meniscus lens is laid between the light source and the first optical element.
In order to acc
Okuyama Atsushi
Sugawara Saburo
Dowling William
Morgan & Finnegan , LLP
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