Color projector

Details Color projector Color projector

2000-06-05

2002-08-27

Mahoney, Christopher (Department: 2851)

Optics: image projectors

Composite projected image

Multicolor picture

C353S034000, C353S037000, C353S101000, C349S007000, C349S058000, C348S745000, C348S806000

Reexamination Certificate

active

06439724

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a color projector adopting three display devices, and more particularly, to a color projector in which the size or position of display devices with respect to each color is changed so that chromatism can be compensated for.
2. Description of the Related Art
In a typical color projector, an image formed by a display device such as an LCD panel is projected onto a screen by using an additional light source. The color projector is divided into a transmission type and a reflection type according to the type of display device.
FIG. 1
is a view showing the optical arrangement of a conventional transmission type color projector. Referring to the drawing, the conventional transmission type color projector includes a light source
10
, first and second dichromatic mirrors DM
1
and DM
2
for splitting the light ray emitted from the light source
10
into red (R), blue (B) and green (G) colors, a plurality of total reflection mirrors M
1
, M
2
and M
3
for allowing the light rays split by the first and second dichromatic mirrors DM
1
and DM
2
to proceed along three different paths, first through third LCD panels
21
,
23
and
25
, arranged on the proceeding path of each of the split light rays, a color prism
30
for synthesizing images according to the respective colors formed by the first through third LCD panels
21
,
23
and
25
, and a projection lens unit
40
for projecting the synthesized color image formed while passing through the color prism
30
toward a screen
50
by magnifying the same.
Each of the first through third LCD panels
21
,
23
and
25
is formed of a plurality of pixels arranged on a plane. Each pixel independently driven polarization-modulates an incident light according to input video signals and also makes light rays of a polarization component proceed toward the color prism
30
. The first LCD panel
21
forms an image of an input red (R) light which is reflected by the first dichromatic mirror DM
1
and passes through the second dichromatic mirror DM
2
; the second LCD panel
23
forms an image of an input green (G) light which is reflected by the first and second dichromatic mirrors DM
1
and DM
2
; and the third LCD panel
25
forms an image of an input blue (B) light passing through the first dichromatic mirror DM
1
.
The color prism
30
has first through third incident surfaces
31
,
33
and
35
disposed to face the first through third LCD panels
21
,
23
and
25
, respectively, and a single exhaust surface
37
facing the projection lens unit
40
. The color prism
30
also has a first mirror surface
30
a
for reflecting the light input through the first incident surface
31
and passing the light input through the second and third incident surfaces
33
and
35
, and a second mirror surface
30
b
for reflecting the light input though the third incident surface
35
and passing the light input through the first and second incident surfaces
31
and
33
. The projection lens unit
40
projects the image, which is formed by the first through third LCD panels
21
,
23
and
25
, synthesized by passing through the color prism
30
and output through the exhaust surface
37
, toward the screen
50
by magnifying the same.
In the conventional transmission type projector having the above structure, the first through third LCD panels
21
,
23
and
25
have the same specifications. That is, the sides of the first through third LCD panels
21
,
23
and
25
facing one another have the same length h. Also, the first through third LCD panels
21
,
23
and
25
each are arranged to be separated the same distance from the projection lens unit
40
. When the optical distances from the respective first through third incident surfaces
31
,
33
and
35
of the color prism
30
to an incident surface
41
a
of a first lens
41
forming the projection lens unit
40
are the same, the first through third LCD panels
21
,
23
and
25
are installed to be separated the same distance d from the first through third incident surfaces
31
,
33
and
35
, respectively.
A typical lens exhibits chromatism which is an aberration depending on the wavelength of an input light. Referring to
FIG. 2
, the light input parallel to a convex lens
60
is theoretically focused at a focal point f. Actually, of the input light, a red (R) light which has a relatively long wavelength focuses at a focal point F
R
which is a position farther than the focal point f of the convex lens
60
, while a blue (B) light which has a relatively short wavelength focuses at a focal point F
B
which is a position closer than the focal point f of the convex lens
60
.
Thus, due to the chromatism, the color images with respect to red, green and blue colors formed by the first through third LCD panels
21
,
23
and
25
of
FIG. 1
focus on the screen
50
at different sizes. Also, as the difference in magnification is generated with respect to red, green and blue colors, a degree of mismatch of the red, green and blue color images increases at the periphery of the screen
50
, thereby deteriorating the quality of image. Therefore, as the projection lens unit
40
necessarily has an additional optical structure to compensate for the above chromatism, the structure of the projector becomes complicated.
Further, the projection lens unit
40
should be designed considering distortion and field curvature of an image formed on the screen
50
. Here, the projection lens unit
40
is not able to perfectly correct both distortion and chromatism. Thus, when the projection lens unit
40
is mainly adjusted to correct the distortion that is easily noticeable to a viewer, an additional lens to correct chromatism is needed. In this case, however, it is a drawback that only a limited correction of chromatism is possible.
SUMMARY OF THE INVENTION
To solve the above problems, it is an objective of the present invention to provide a color projector which can compensate for chromatism by changing the size and/or position of a display device with respect to each color to improve image quality and also a compact design of the projection lens unit is possible.
Accordingly, to achieve the above objective, there is provided a color projector comprising a light source, a splitting device for splitting the light emitted from the light source to proceed along first through third optical paths according to the wavelength thereof, first through third display devices, arranged on the first through third optical paths, for forming an image from an input light of a predetermined wavelength, a synthesizing means for synthesizing lights of different colors to proceed along one path by selectively transmitting or reflecting input lights passing through the first through third display devices according to the wavelength thereof, and a projection lens unit for magnifying and projecting a color image synthesized by the synthesizing device toward a screen, in which two or more display devices selected from the first through third display devices have the different sizes of effective areas where an image is formed such that chromatism generated while lights of different colors synthesized by the synthesizing device pass the projection lens unit can be corrected.
Also, to achieve the above objective, there is provided a color projector comprising a light source, a splitting device for splitting the light emitted from the light source to proceed along first through third optical paths according to the wavelength thereof, first through third display devices, arranged on the first through third optical paths, for forming an image from an input light of a predetermined wavelength, a synthesizing means for synthesizing lights of different colors to proceed along one path by selectively transmitting or reflecting input lights passing through the first through third display devices according to the wavelength thereof, and a projection lens unit for magnifying and projecting a color image synthesized by the synthesizing device toward a screen, in

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