Television – Video display – Projection device
Reexamination Certificate
1996-12-17
2001-01-30
Lee, Michael H. (Department: 2714)
Television
Video display
Projection device
C348S781000, C353S077000, C353S098000
Reexamination Certificate
active
06181386
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to projecting images.
2. Description of the Related Art
Referring to
FIG. 1
, light projectors are used, for example, to display images on large surfaces, such as movie or television screens. In a front projection system
20
, an image beam
24
is projected from an image source
21
onto the “front” side of a reflection-type angle transforming screen, which then reflects the light toward a viewer
27
positioned in front of the screen. In a rear projection system, the image beam is projected onto the “rear” side of a transmission-type angle transforming screen
26
and transmitted toward a viewer
29
located in front of the screen.
Due to the physical properties of light, the size of the image beam
24
when it reaches the screen
26
depends upon the magnification rate of the image source
21
and the distance between the screen
26
and the image source
22
. To efficiently utilize the screen
26
, the image beam
24
should just fill the entire height S and width (not shown) of the screen
26
. In
FIG. 1
, the image beam
24
fills the screen
26
when the source
22
is at an appropriate distance D from the screen
26
, i.e., when the center of the image beam
24
follows an optical path
28
of length D. The optical path length D depends upon the screen height S and the magnification rate of the image source. Any non-transparent object placed in the path of the image beam
24
typically will obstruct the image beam
24
and form a shadow on the screen
26
.
Referring to
FIG. 2
, designers have reduced the size of the typical image projection system
30
by “folding” the optical path of the projected image beam to reduce the apparent projection length L of the system
30
. The “folded” system
30
includes one or more mirrors
34
,
36
placed at strategic points along the optical path to redirect the projected image and to form multiple optical subpaths D
1
, D
2
, D
3
. The overall system configuration in this optical system
30
is more rectilinear than the conical system configuration of FIG.
1
.
In the folded image projection system
30
, assuming that the image source
40
and the screen
32
are similar to those in
FIG. 1
, the image
38
fills the screen
32
entirely when the mirrors
34
,
36
are positioned such that the combined length of the optical subpaths D
1
, D
2
, and D
3
equals the optical path length D in
FIG. 1
, even though the apparent projection length L is less than D.
SUMMARY OF THE INVENTION
An “extra-folded” projection display system includes a selectively reflective material (e.g., a linear reflecting polarizer) placed immediately behind the system's imaging screen. The display system includes an image projector that projects an image beam containing light of a predetermined linear polarization toward the imaging screen. The linear reflecting polarizer reflects the light in the image beam away from the screen. The reflected image beam then encounters a ¼-wavelength achromatic retarder which converts the linear polarization to circular polarization. The image beam next hits a mirror that reflects the light back through the ¼-wavelength achromatic retarder, which converts the circular polarization back to linear polarization, with the polarization director rotated 90° from the original polarization director. The linear reflecting polarizer then allows the light to pass through to the image screen.
Embodiments of the invention may include the following features. The system may include a powered optical element to further increase the “folding” of the image beam, change the magnification rate, provide distortion correction, or optimize packaging. The image beam may be folded even further by allowing it to reflect from the mirror twice and to pass through the achromatic retarder four times. The mirror may be positioned between the image source and the imaging screen.
Advantages of the invention may include one or more of the following. An optical element placed immediately behind the screen in a projection imaging system may act as a “mirror” that increases the amount of folding that the light undergoes and therefore may reduce the apparent projection length, or depth, of the system to a greater extent than previously possible. The image source may be placed behind all optical elements in the display system, further reducing the size of the system.
Other advantages and features will become apparent from the following description and from the claims.
REFERENCES:
patent: 4969732 (1990-11-01), Wright
patent: 5172221 (1992-12-01), Ko
patent: 5193015 (1993-03-01), Shanks
patent: 5223869 (1993-06-01), Yanagi
patent: 5467154 (1995-11-01), Gale et al.
patent: 5557343 (1996-09-01), Yamagishi
patent: 5573324 (1996-11-01), De Vaan
patent: 5692820 (1997-12-01), Gale et al.
patent: 5833360 (1998-11-01), Knox et al.
patent: 0 488 590 A1 (1992-03-01), None
patent: 0 657 769 A1 (1995-06-01), None
patent: 3-243932 (1991-10-01), None
European Search Report, May 15, 1997.
Murty et al., “Simple Catadioptic Magnifiers,”Optical Engineering, Jan/Feb., 1983, vol. 22, No. 1, pp. 149-152.
Murty et al., “Catadioptic Magnifiers,”Optical Engineering, Nov./Dec., 1980, vol. 19, No. 6, pp. 915-917.
Murty et al., “Microfiche Reader Using a Plano-Convex Lens,”Centro de Investigaciones en Optica, 1982 Annual Meeting, Opticas Society of America, p. 1827.
Shannon & Wyant, “Applied Optics and Optical Engineering,”Academic Press, Inc., 1983, pp. 244-249.
Duke University
Fleshner & Kim LLP
Lee Michael H.
LandOfFree
Projecting images does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Projecting images, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Projecting images will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2490614