Triple-lens type projection display with uniform optical...

Details Triple-lens type projection display with uniform optical... Triple-lens type projection display with uniform optical...

2001-01-05

2002-08-13

Adams, Russell (Department: 2851)

Optics: image projectors

Composite projected image

Plural projection paths with single light source

C353S031000

Reexamination Certificate

active

06431709

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a projection display, more particularly to a triple-lens type projection display with uniform optical path lengths for different color components.
2. Description of the Related Art
Referring to
FIG. 1
, a conventional triple-lens type projection display
1
is shown to comprise a light source
11
, a light filter
12
downstream of the light source
11
for removing ultraviolet rays and infrared rays from a light beam generated by the light source
11
to thereby obtain a white primary beam output, a first expansive lens
141
downstream of the light filter
12
, a first beam splitter
131
downstream of the first expansive lens
141
to split the primary beam output from the first expansive lens
141
into a first color component and a secondary beam output, a second expansive lens
142
downstream of the first beam splitter
131
, a second beam splitter
132
downstream of the second expansive lens
142
to split the secondary beam output from the second expansive lens
142
into second and third color components, and a third expansive lens
143
downstream of the second beam splitter
132
. The first, second and third color components are generally primary color components, such as red, green and blue. The first color component from the first beam splitter
131
passes sequentially through a first focusing lens
151
, a first polarizer
161
, and a light-modulated first light valve
171
before being received by a first projection lens
181
. The second color component from the second beam splitter
132
passes sequentially through a second focusing lens
152
, a second polarizer
162
, and a light-modulated second light valve
172
before being received by a second projection lens
182
. The third color component from the third expansive lens
143
is reflected by a mirror
133
so as to pass sequentially through a third focusing lens
153
, a third polarizer
163
, and a light-modulated third light valve
173
before being received by a third projection lens
183
. The first, second and third projection lenses
181
,
182
,
183
are disposed on a common plane, and project light onto a display screen
19
for showing an image on the latter.
It is noted that, while the distances of the first, second and third projection lenses
181
,
182
,
183
from the respective one of the first and second beam splitters
131
,
132
and the mirror
133
are equal, the distance of the second beam splitter
132
from the light source
11
is longer than that of the first beam splitter
131
, and that the distance of the mirror
133
from the light source is longer than that of the second beam splitter
132
. There is thus a need to install the expansive lenses
141
,
142
,
143
to compensate for the differences in the optical path lengths traveled by the different color components.
However, because three expansive lenses
141
,
142
,
143
are needed for the three focusing lenses
151
,
152
,
153
, the conventional projection display
1
involves a relatively large number of essential components. In addition, the expansive lenses
141
,
142
,
143
can introduce edge distortion to the image
191
shown on the plane of the light valves, as shown in FIG.
2
.
SUMMARY OF THE INVENTION
Therefore, the main object of the present invention is to provide a triple-lens type projection display with uniform optical path lengths for different color components, thereby eliminating the need for expansive lenses as required in the aforesaid prior art.
According to this invention, a triple-lens type projection display comprises:
a source for generating a white primary beam output;
a first beam splitter for splitting the white primary beam output into a first color component and a secondary beam output;
a second beam splitter for splitting the secondary beam output into a second color component and a third color component;
first, second and third light modulators for modulating the first, second and third color components, respectively;
a first projection lens for receiving the first color component from the first light modulator;
a second projection lens for receiving the second color component from the second light modulator; and
a third projection lens for receiving the third color component from the third light modulator.
Each of the first, second and third color components has a respective optical path length that is measured from the first beam splitter to a respective one of the first, second and third light modulators. The optical path lengths of the first, second and third color components are equal.


REFERENCES:
patent: 4690526 (1987-09-01), Ledebuhr
patent: 4864390 (1989-09-01), McKechnie et al.
patent: 5311227 (1994-05-01), Takayasu et al.

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