Optical: systems and elements – Lens – With light limiting or controlling means
Reexamination Certificate
2001-02-23
2002-06-18
Epps, Georgia (Department: 2873)
Optical: systems and elements
Lens
With light limiting or controlling means
C359S224200, C359S291000, C359S833000, C359S739000
Reexamination Certificate
active
06407871
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to an optical device for eliminating the stray light, and particularly to an optical device diverting the original transmitting path of the stray light beam to improve the quality of the output image and the luminance projected on a screen.
DESCRIPTION OF THE RELATED ART
FIG. 1
is a schematic diagram of an conventional optical system employing a “digital micromirror device” (DMD) or a “reflecting type liquid crystal on silicon” (LCOS).
FIG. 2
is an enlarged schematic diagram of a conventional chromatic halo generated by a stop of a projection lens with an aperture angle greater than 10 degree in coordination with the DMD chip with 10 degree turning angle. As shown in FIG.
1
and
FIG. 2
, the conventional optical system, using the DMD chip or the LCOS consists of a light source
10
, a integration rod
12
, a stop
20
of an illuminating system, a reflecting panel (DMD or LCOS)
30
, a stop
40
of a projection lens, and a screen
50
for display.
By means of apparatus mentioned above, the light beam is transmitted from the light source
10
into the stop
20
of the illuminating system through the integration rod
12
. Then, the light beam is transmitted into the stop
40
of the projection lens after being reflected form the reflecting panel
30
in order to project the image on the screen
50
.
When the DMD chips with 10 degree turning angle is used for projection, the optical system only allows the light beam with an aperture angle of approximate 10 degree to enter the stop
40
of the projection lens for achieving the best luminance and contrast ratio of the image. And, that is due to the inherent characteristics of optics of the DMD
30
currently used. Despite of above mentioned, we could use a method to improve the luminance up to a certain level. Such method is implemented by using a stop of the projection lens with an aperture angle greater than 10 degree in coordination with the DMD chip
30
with 10 degree turning angle. However, on the other hand, the area A near the periphery of the stop of the projection lens with an aperture angle greater than 10 degree receives the additional light beam transmitted from the area B near the periphery of the stop
20
of the illuminating system. Such additional light beam is reflected from the DMD
30
, and is transmitted into the stop
40
of the projection lens, and then is projected on the screen
50
that results in the chromatic halo
60
. Such chromatic halo
60
always exists in any image so that it affects the quality of the output image. Especially when a black image is projected, since the existence of the chromatic halo results in an imperfect black image, the contrast ratio of the optical system is therefore affected. The chromatic halo
60
is resulted from the area A near the periphery of the stop of the projection lens with an aperture angle greater than 10 degree, and the area A is conjugated to the area B near the periphery of the stop
20
of the illuminating system. Thus, for any image being projected, the light beam at the area B is always projected by the projection lens through the DMD chip
30
(whether DMD is on or off) so as to generate the chromatic halo that causes flaws in the image projection. Furthermore, the second light source of point form at such area contributes a certain level in terms of the lumina output by the optical system. Therefore, if the light beam at this area is completely covered, the amount of lumina output by the optical system is greatly affected.
SUMMARY OF THE INVENTION
In view of the conventional flaws caused by the chromatic halo
60
in the image projection mentioned above, a small-sized reflecting mirror (with a flat surface or a curved surface) or a small-sized prism is provided at the area B according to the invention. Wherein, either a stop of a projection lens with an aperture angle greater than 10 degree is employed in coordination with a DMD chip
30
with 10 degree turning angle, or a stop of a projection lens with an aperture angle greater than 12 degree is employed in coordination with a DMD chip
30
with 12 degree turning angle. Thus, the light beam from the light source at this area is reflected by the reflecting mirror or is refracted by the prism so as to divert the original transmitting path of the light beam. Then, the light beam is reflected from the DMD
30
and is uniformly transmitted into the stop of the projection lens so as to increase the contrast ratio of the projection system and to improve the luminance output by the optical system. Such small-sized reflecting mirror or prism is installed near the periphery of the stop or the second light source of point form of the illuminating system so as to enhance the output lumina and to increase the contrast ratio of the optical system. The illuminating system, in which a stop of a projection lens with an aperture angle greater than 10 degree is used in coordination with a DMD chip
30
with 10 degree turning angle, or a stop of a projection lens with an aperture angle greater than 12 degree is used in coordination with a DMD chip
30
with 12 degree turning angle, and any design uses an aperture angle greater than that angle limited by the DMD chip, is implemented by the invention. Thereby, the luminance of the optical system is improved, and the best contrast ratio and the quality of image are achieved.
In order to achieve the object mentioned above, an optical device for eliminating the stray light (“stray light” is the common name for above mentioned chromatic halo
60
) is provided according to the invention. The optical device is provided at a stop
20
of a illuminating system in an optical system of the “digital light processing” (DLP) that consists of the stop
20
of the illuminating system, a DMD
30
, a stop
40
of a projection lens, and a screen
50
. And, the stray light is the chromatic halo
60
at the peripheral area on the screen. Wherein, the optical device includes a reflecting mirror designed of an adjustable angle and installed at the area B near the periphery of the stop of the illuminating system. And, the chromatic halo generated by the light beam at the area B near the periphery of the stop of the illuminating system is reflected from the DMD and is transmitted into the stop of the projection lens, and then is projected on the screen
50
. And, the reflecting mirror is used to reflect the light beam at the area B near the periphery of the stop of the illuminating system so as to divert the original transmitting path of the light beam. Thus, the light beam at area B is reflected from the DMD and is uniformly transmitted into the stop of the projection lens. Thereby, the contrast ratio of the optical system is increased, and the quality of the output image is improved, and the efficiency of the DLP system is enhanced, and the luminance projected on the screen
50
is improved.
These and other objects, features and advantages of the invention will become apparent with reference to the following description and accompanying drawings as follow.
REFERENCES:
patent: 5428408 (1995-06-01), Stanton
patent: 5604624 (1997-02-01), Magarill
patent: 6215547 (2001-04-01), Ramanujan et al.
Coretronic Corporation
Epps Georgia
Hsu Winston
Thompson Timothy
LandOfFree
Optical device for eliminating stray light does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Optical device for eliminating stray light, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Optical device for eliminating stray light will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2958724