Projector system for video and computer generated information

A projector for use with a light source and including a shutter assembly panel having a multiplicity of pixel light valves overlying an array of interspersed shutter pixels each of which transmits only one of a plurality of colors, and a color filter disposed intermediate the light source and the planar shutter and spaced therefrom and having an array of interspersed filter pixels, each of which only transmits only one of a plurality of colors, wherein the array of interspersed filter pixels is in light and color registration with the array of interspersed shutter pixels, such that generally light of a given color impinges on a shutter area of the same color.

FIELD OF THE INVENTION 
The present invention relates to visual projection and more particularly to 
video and computer generated information projectors and panels useful 
therewith. 
BACKGROUND OF THE INVENTION 
Various types of video and computer generated information projectors are 
known. These include, for example, the SharpVision product line 
commercially available from Sharp Corporation of Japan. Conventional 
projectors of this type have achieved significant market penetration but 
suffer from various disadvantages and limitations. 
One of the significant limitations in liquid crystal panel projectors lies 
in the relatively limited amount of light that can be projected. It may be 
appreciated that the amount of light that can be transmitted through a 
conventional color liquid crystal panel assembly is limited by the amount 
of light that can be absorbed by the liquid crystal panel without 
degradation of its performance and permanent damage thereto inter alia due 
to overheating. Accordingly the brightness of projected images produced by 
such projectors is correspondingly limited. 
Conventional displays also suffer from limitations in contrast due to their 
inability to suppress reflection of ambient light. 
Various types of projection systems are known in the art for a wide range 
of applications using various types of light sources, both coherent and 
non-coherent. Projection systems which employ non-coherent light sources, 
such as incandescent or arc lamps, have been found by the applicants to 
display sometimes unacceptable variations in the intensity of light output 
produced thereby over a projection plane. Such variations may result, 
inter alia, from non-uniformities, asymmetries and imperfections in the 
glass envelope of the light source, as well as shadows produced by the 
light source filament or arc electrodes. 
Halogen lamps, such as Model FLT produced by Thorn Lighting Ltd. of Great 
Britain, are formed with conditioned and segmented reflectors so as to 
direct light from multiple locations on the light source onto each 
location in a projection plane. While such a structure does reduce the 
intensity variation, the reduction is insufficient for certain high 
quality projection applications wherein the projection plane is relatively 
close to the light source. 
SUMMARY OF THE INVENTION 
The present invention seeks to provide an improved projector and projection 
system, and an improved reflector suitable for use therein. 
There is thus provided in accordance with a preferred embodiment of the 
present invention a projector for use with a light source and including: 
a shutter assembly having a multiplicity of pixel light valves; and 
a color separator disposed intermediate the light source and the shutter 
assembly and spaced therefrom and providing a plurality of spatially 
separated differently colored light beams; 
wherein the plurality of spatially separated differently colored light 
beams are in predetermined registration with the multiplicity of pixel 
light valves. 
Additionally in accordance with a preferred embodiment of the present 
invention there is provided a projection system including: 
a projector for use with a light source and including: 
a shutter assembly having a multiplicity of pixel light valves; 
a color separator disposed intermediate the light source and the shutter 
assembly and providing a plurality of spatially separated differently 
colored light beams; and 
a screen arranged in light receiving relationship with the projector and 
including a plurality of light impingement regions having different color 
characteristics, and wherein 
the plurality of spatially separated differently colored light beams are in 
predetermined registration with the multiplicity of pixel light valves, 
and 
the plurality of spatially separated differently colored light beams are 
arranged in predetermined registration with the plurality of light 
impingement regions having different color characteristics. 
In accordance with one embodiment of the present invention, the color 
separator includes a color filter array. 
Preferably, the color separator includes an array of prism/lens 
combinations. 
In accordance with an embodiment of the invention, the color separator 
includes a color filter array and an array of prism/lens combinations. 
Preferably, the array of prism/lens combinations includes an array of 
cylindrical prism/cylindrical lens combinations. 
Additionally in accordance with a preferred embodiment of the present 
invention there is provided a projector for use with a light source and 
including: 
a shutter assembly having a multiplicity of pixel light valves; and 
a color separator including an array of prism/lens combinations disposed 
intermediate the light source and the shutter assembly and providing a 
plurality of spatially separated differently colored light beams; 
wherein the plurality of spatially separated differently colored light 
beams are in predetermined registration with the multiplicity of pixel 
light valves. 
Additionally in accordance with a preferred embodiment of the invention, 
the projector may also include an upstream selective light absorber 
disposed intermediate the light source and the shutter assembly and spaced 
therefrom. 
Further in accordance with a preferred embodiment of the present invention 
there is provided a projector for use with a light source and including: 
a shutter assembly having a multiplicity of pixel light valves; and 
an upstream selective light absorber disposed intermediate the light source 
and the shutter assembly and spaced therefrom. 
The selective light absorber may be a polarizer and/or a color filter 
array. 
Additionally in accordance with a preferred embodiment of the present 
invention, the projector also includes a downstream selective light 
absorber disposed downstream of the shutter assembly and spaced therefrom. 
Preferably, the shutter assembly includes a liquid crystal display panel 
which may be a black and white liquid crystal display panel but could be a 
color liquid crystal display panel. When a commercially available liquid 
crystal display panel is used, the identical polarizers upstream and 
downstream of the liquid crystal may be separated and distanced therefrom. 
Alternatively, they may be left intact and an additional identical 
upstream polarizer may be provided in spaced relationship therewith to 
provide absorption and dissipation of heat. 
Preferably, the projector also includes a source of collimated light or of 
noncollimated light. 
Preferably, the apparatus of the present invention also includes a 
focussing lens assembly. 
In accordance with one embodiment of the invention, the focussing lens 
assembly and the shutter assembly are tiltably mounted. 
The apparatus of the present invention may be embodied as an overhead 
projection system, a rear projection system, a forward reflective 
projection system, an angled rear projection system or any other suitable 
type of system. 
Further in accordance with a preferred embodiment of the present invention 
there is provided a projection screen including a plurality of differently 
colored light impingement regions. Preferably the differently colored 
light impingement regions include an array of differently colored stripes. 
The projection screen may be used with projectors of the type described 
above or alternatively as a projection screen with any type of projector 
wherein light of different colors appears at different locations on the 
screen. 
Additionally in accordance with a preferred embodiment of the present 
invention there is provided a rear projection display device comprising: 
a projector; 
a light transmissive screen; and 
diverging optics interposed between the projector and the screen for 
directing light from the projector onto the screen. 
In accordance with one embodiment of the invention, the projector is a 
television or video projector and the display device is a rear projection 
television. 
The projector may be any suitable type of projector but preferably is a 
projector of any of the types described hereinabove. 
The diverging optics may comprise a convex mirror, at least one diverging 
lens or a combination thereof. 
There is further provided in accordance with a preferred embodiment of the 
present invention a projector for use with a light source and including a 
shutter assembly panel having a multiplicity of pixel light valves 
overlying an array of interspersed shutter pixels each of which transmits 
only one of a plurality of colors, and a color filter disposed 
intermediate the light source and the planar shutter and spaced therefrom 
and having an array of interspersed filter pixels, each of which only 
transmits only one of a plurality of colors, wherein the array of 
interspersed filter pixels is in light and color registration with the 
array of interspersed shutter pixels, such that generally light of a given 
color impinges on a shutter area of the same color. 
Still further in accordance with a preferred embodiment of the present 
invention the projector also includes a light polarizer associated with 
the color filter. 
Yet further in accordance with a preferred embodiment of the present 
invention the projector also includes a light polarizer disposed 
intermediate the light source and the shutter assembly panel for further 
absorbing energy which would otherwise be absorbed by the shutter assembly 
panel. 
Additionally in accordance with a preferred embodiment of the present 
invention the light source includes a source of collimated light. 
Also in accordance with a preferred embodiment of the present invention the 
array of interspersed shutter pixels and said array of interspersed filter 
pixels are coextensive. 
Further in accordance with a preferred embodiment of the present invention 
the light source includes a source of non-collimated light. 
Still further in accordance with a preferred embodiment of the present 
invention the array of interspersed shutter pixels and said array of 
interspersed filter pixels are non-coextensive. 
Also in accordance with a preferred embodiment of the present invention 
there is also included a light transmissive UV & IR blocking filter which 
is interposed between the light source and the color filter. 
Additionally in accordance with a preferred embodiment of the present 
invention the apparatus includes a focussing lens. 
Further in accordance with a preferred embodiment of the present invention 
the shutter assembly panel includes a color liquid crystal shutter 
assembly panel. 
There is provided in accordance with a preferred embodiment of the present 
invention a projector for use with a light source and including a 
polarizing shutter assembly panel having a multiplicity of pixel light 
valves, and a light polarizer disposed intermediate the light source and 
the shutter assembly panel and spaced therefrom for further absorbing 
energy which would otherwise be absorbed by the shutter assembly panel. 
There is also provided in accordance with a preferred embodiment of the 
present invention a radiation reflector for providing generally 
homogeneous illumination in a plane perpendicular to an axis, the 
reflector including a generally curved reflecting surface formed of a 
multiplicity of flat surface units, the multiplicity of flat surface units 
being configured and arranged such that the projection of each of said 
multiplicity of flat surface units onto a plane perpendicular to said axis 
is generally identical. 
Further in accordance with a preferred embodiment of the present invention 
there is provided a compact projection system including: 
a non-homogeneous radiation source; 
a radiation reflector for providing generally homogeneous non-imagewise 
illumination in a plane perpendicular to an axis, the reflector including 
a generally curved reflecting surface receiving radiation from the 
non-homogeneous radiation source, the reflecting surface being formed of a 
multiplicity of flat surface units, the multiplicity of flat surface units 
being configured and arranged such that the projection of each of said 
multiplicity of flat surface units onto a plane perpendicular to said axis 
is generally identical, the radiation reflector being arranged to 
illuminate a light transmissive object in the plane; 
lens apparatus for receiving radiation passing through the light 
transmissive object and imagewise focusing the radiation; and 
a screen for receiving the focused radiation. 
Preferably, the generally curved reflecting surface includes a concave 
surface and includes a surface of rotation. 
In accordance with a preferred embodiment of the present invention, the 
generally curved reflecting surface includes a generally parabolic 
surface. 
In accordance with a preferred embodiment of the present invention, the 
light transmissive object is located at a distance from the facing edge of 
the reflecting surface along the axis which is approximately equal to the 
largest dimension of the opening of the reflecting surface at the facing 
edge. 
Preferably, the generally homogeneous non-imagewise illumination is 
directed generally axially along the axis. 
In accordance with a preferred embodiment of the present invention, the 
maximum dimension of the light transmissive object in the plane is 
approximately equal to the distance of the plane from the light source.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
Reference is now made to FIG. 1A, which illustrates one preferred 
embodiment of the invention, it being understood that the drawing of FIG. 
1A and the remaining drawings herein are drawn not necessarily to scale 
for enhanced clarity and simplicity. 
A collimated light source 10 of relatively high intensity, such as an arc 
lamp having a 1.2 Kilowatt rating, provides a collimated beam of light 
which impinges on a transparent UV & IR blocking filter 12, and then 
preferably, but optionally, passes through a polarizing plate 14. 
The collimated light beam then preferably passes through a light separator, 
in this case a color filter 16 having a multiplicity of color transmissive 
pixels, of different colors. Preferably, the color filter 16 comprises an 
array of interspersed filter pixels, each of which transmits only one of a 
plurality of colors, such as the primary colors, red, green and blue. 
The collimated light from the color filter then impinges on a shutter 
assembly panel 18, such as a liquid crystal shutter assembly panel, spaced 
from the color filter 16, which preferably comprises a multiplicity of 
electrically controlled pixel light valves, employing either active or 
passive matrices, overlying an array of interspersed shutter pixels each 
of which transmits only one of a plurality of colors, such as the primary 
colors red, green and blue. Alternatively any other suitable type of 
shutter assembly panel may be employed. 
When a liquid crystal shutter assembly panel is provided, identical 
polarizers must be provided upstream and downstream of the liquid crystal, 
as can be seen in the embodiment of FIG. 24A. The polarizer 14 is 
preferably spaced from the shutter assembly panel as shown in FIG. 24A, 
but alternatively or additionally may form part of the shutter assembly 
panel 18. 
In accordance with a preferred embodiment of the invention, the array of 
interspersed filter pixels is in light and color registration with the 
array of interspersed shutter pixels, such that generally light of a given 
color impinges on a shutter area of the same color. 
In the embodiment of FIG. 1A, where collimated light is used, the array of 
interspersed filter pixels is in one-to-one registration with the array of 
interspersed shutter pixels. 
Light modulated by the shutter assembly panel 18 is focussed by a lens 20 
downstream thereof or at any other suitable location. 
Reference is now made to FIG. 24A which illustrates a further preferred 
embodiment of the projector of FIG. 1A. The projector of FIG. 24A is 
similar to the projector of FIG. 1A except in that light modulated by the 
shutter assembly panel 18, and passing through another polarizer plate 14, 
identical to the polarizer plate 14 upstream of filter 16, is focussed by 
a lens assembly 619 downstream thereof or at any other suitable location. 
Preferably, lens assembly 619 includes a Fresnel lens 620 and a compound 
lens 621. 
Reference is now made to FIG. 1B which illustrates another preferred 
embodiment of the invention. 
A non-collimated light source 30 of relatively high intensity provides a 
non-collimated beam of light which impinges on a transparent UV & IR 
blocking filter 32 and then preferably but optionally passes through a 
polarizing plate 34. 
The non-collimated light beam preferably then passes through a light 
separator, such as a color filter 36, preferably spaced from the 
polarizing plate and having a multiplicity of color transmissive pixels, 
of different colors. Preferably, the color filter 36 comprises an array of 
interspersed filter pixels, each of which transmits only one of a 
plurality of colors, such as the primary colors, red, green and blue. 
The non-collimated light from the color filter then impinges on a shutter 
assembly panel 38, such as a liquid crystal shutter assembly panel, spaced 
from the color filter 36, which preferably comprises a multiplicity of 
electrically controlled pixel light valves overlying an array of 
interspersed shutter pixels each of which transmits only one of a 
plurality of colors, such as the primary colors red, green and blue. When 
a liquid crystal shutter assembly panel is provided, a polarizer must be 
provided, as can be seen in the embodiment of FIG. 24B. The polarizer 34 
is preferably spaced from the shutter assembly panel as shown in FIG. 1B, 
but alternatively or additionally may form part of the shutter assembly 
panel 38. 
In accordance with a preferred embodiment of the invention, the array of 
interspersed filter pixels is in light and color registration with the 
array of interspersed shutter pixels, such that generally light of a given 
color impinges on a shutter area of the same color. 
In the embodiment of FIG. 1B, where non-collimated light is used, the array 
of interspersed filter pixels is not in one-to-one registration with the 
array of interspersed shutter pixels. 
Light modulated by the shutter assembly panel 38 is focussed by a lens 40 
downstream thereof. 
Reference is now made to FIG. 24B, which illustrates a projector 
constructed and operative in accordance with yet another preferred 
embodiment of the present invention. The projector of FIG. 24B is similar 
to the projector of FIG. 1B except in that light modulated by the shutter 
assembly panel 38, and passing through another polarizer plate 34, 
identical to the polarizer plate 34 upstream of filter 36, is focussed by 
a lens assembly 639 downstream thereof or at any other suitable location. 
Preferably, lens assembly 639 includes a Fresnel lens 640 and a compound 
lens 641. 
FIG. 2A illustrates in simplified schematic form an array 50 of 
interspersed filter pixels forming part of a shutter assembly panel such 
as assembly 18 (FIG. 1A) or assembly 38 (FIG. 1B). A controller 52 
controls the opening or closing of the pixel light valves (not shown) 
which govern whether light is permitted to pass through each of the 
individual colored pixels of the assembly. 
FIG. 2B illustrates another example of an array 60 of interspersed filter 
pixels forming part of a shutter assembly panel such as assembly 18 (FIG. 
1A) or assembly 38 (FIG. 1B). A controller 62 controls the opening or 
closing of the pixel light valves (not shown) which govern whether light 
is permitted to pass through each of the individual colored pixels of the 
assembly. 
FIG. 3 illustrates in greater detail the apparatus of the embodiment of 
FIG. 1A and shows the configuration of the color filter 16 which includes 
an array of interspersed filter pixels, each of which transmits only one 
of a plurality of colors, such as red, green and blue. 
The one-to-one registration of the array of interspersed filter pixels of 
filter 16 and the array of interspersed shutter pixels of shutter assembly 
panel 18 is clearly shown. 
The aforesaid color and light registration thus minimizes the absorption of 
light by the shutter assembly panel and enables relatively high intensity 
light sources to be employed without overheating and thus damaging the 
shutter assembly panel. 
According to the present invention, only light of a given spectral content 
is allowed to impinge on a shutter area which transmits light of that 
spectral content. 
Reference is now made to FIG. 25 which is similar to the embodiment of FIG. 
3 except in that a polarizer is disposed in spaced relationship upstream 
of the shutter in order to absorb and dissipate heat which would otherwise 
impinge thereon. 
Reference is now made to FIG. 4, which illustrates an overhead projector 
constructed and operative in accordance with a preferred embodiment of the 
present invention. The overhead projector comprises a housing 70 in which 
is disposed a conventional, high intensity light source 72. Disposed in 
light receiving relationship with light source 72 is a Fresnel lens 74. 
A polarizer 76 is disposed in spaced relationship above Fresnel lens 74 and 
a shutter assembly panel 78, which may be similar in all relevant respects 
to shutter assembly panel described above, is disposed in spaced 
relationship above polarizer 76. The shutter assembly panel 78 defines a 
selectable image which is reflected via a mirror 80 onto a screen or other 
suitable surface 82. 
Reference is now made to FIGS. 5 and 6, which illustrate the use of a 
prism/lens combination to provide color separation of white light into R,G 
and B spectral portions. FIG. 5 shows an ordinary prism 90 associated with 
a cylindrical lens 92 receiving a collimated beam of white light and 
providing respective angled R,G and B beams. FIG. 5 indicates that this 
combination reduces the width of the R,G and B beams produced, in the 
illustrated embodiment, such that the total width of all of the beams is 
less than the width of the beam of white light impinging on the prism 90. 
FIG. 6 illustrates an arrangement constructed and operative in accordance 
with a preferred embodiment of the present invention wherein light passes 
first through a polarizer 93 and thence through an array 94 of 
prism/cylindrical lens combinations, which break the light into 
individually colored beams, each of which then impinges on a suitably 
colored portion of a color filter 96 in registration therewith. The light 
beams passing through the individually colored portions of the color 
filter 96 impinge on portions of a shutter assembly panel 98, preferably 
an LCD, which are selected to correspond to the colored light impinging 
thereon. 
Array 94 and filter 96 are preferably spaced from each other and from the 
polarizing plate 93. 
It is appreciated that filter 96 and panel 98 may be attached together, 
such as in a commercially available color LCD panel. Alternatively, and 
preferably, a black and white LCD panel 98 may be employed and color 
filter 96 may be separate and spaced therefrom. 
The structure of FIG. 6 is particularly suitable for use as a projector 
plate which can be employed with any suitable conventional overhead 
projector. 
FIG. 7 is a pictorial illustration of an elongate prism/lens combination 
array 100 which is useful in the present invention, as shown in FIG. 6. 
FIG. 8 illustrates array 100 in combination with a shutter assembly panel 
102, which may be similar to panel 18 or 98, described above. It is seen 
that each of the R, G and B spectral components is directed through a 
corresponding shutter pixel 104 of panel 102. 
Reference is now made to FIG. 9, which is a simplified illustration of a 
projector of the type shown in FIG. 24A employing the prism/lens 
combination of FIG. 8. 
A collimated light source 110 of relatively high intensity, such as an arc 
lamp having a 1.2 Kilowatt rating provides a collimated beam of light 
which impinges on a transparent UV & IR blocking filter 112, and then 
preferably but optionally passes through a polarizing plate 114. 
The collimated light beam then preferably passes through a prism/lens 
combination array 116, such as that shown in FIG. 7. The color separated 
beams produced by array 116 may then pass through a color filter 117, 
similar to color filter 16 (FIG. 1A) and defining a plurality of color 
transmissive pixels of different colors. Preferably, the color filter 117 
comprises an array of interspersed filter pixels, each of which transmits 
only one of a plurality of colors, such as the primary colors, red, green 
and blue. Use of the color filter 117 is optional. When a liquid crystal 
shutter assembly panel is provided, a polarizer must be provided. The 
polarizer is preferably spaced from the shutter assembly panel as shown at 
reference numeral 114 in FIG. 9, but additionally or alternatively may 
form part of the shutter assembly panel 118. 
The collimated light from the color filter 117 or directly from array 116 
then impinges on a shutter assembly panel 118, such as a liquid crystal 
shutter assembly panel, spaced from the color filter 117, which preferably 
comprises a multiplicity of electrically controlled pixel light valves, 
employing either active or passive matrices, overlying an array of 
interspersed shutter pixels each of which transmits only one of a 
plurality of colors, such as the primary colors red, green and blue. 
Alternatively any other suitable type of shutter assembly panel may be 
employed. 
In accordance with a preferred embodiment of the invention, the array of 
color separated light beams from array 116 is in light and color 
registration with the array of interspersed shutter pixels, such that 
generally light of a given color impinges on a shutter area of the same 
color. 
In the embodiment of FIG. 9, where collimated light is used, the array of 
color separated light beams is in one-to-one registration with the array 
of interspersed shutter pixels. 
Light modulated by the shutter assembly panel 118 may pass through a 
further polarizer 114, which may be identical to polarizer 114 upstream of 
panel 118, and is then focussed by a focusing lens assembly 119 downstream 
thereof or at any other suitable location. Focusing lens assembly 119 
preferably includes a Fresnel lens 120 and a compound lens 121. 
Reference is now made to FIG. 10, which is a simplified illustration of a 
projector of the type shown in FIG. 24B employing the prism/lens 
combination of FIG. 8. 
A non-collimated light source 130 of relatively high intensity provides a 
non-collimated beam of light which impinges on a transparent UV & IR 
blocking filter 132 and then preferably but optionally passes through a 
polarizing plate 134. 
The non-collimated light beam preferably then passes through a prism/lens 
combination array 136, such as that shown in FIG. 7. The color separated 
beams produced by array 136 may then pass through a color filter 137, 
similar to color filter 16 (FIG. 1b) and defining a plurality of color 
transmissive pixels of different colors. Preferably, the color filter 137 
comprises an array of interspersed filter pixels, each of which transmits 
only one of a plurality of colors, such as the primary colors, red, green 
and blue. Use of the color filter 137 is optional. 
Array 136 and filter 137 are preferably spaced from each other and the 
polarizing plate 134 and have a multiplicity of color transmissive pixels, 
of different colors. 
The non-collimated light from the color filter 137 or directly from array 
136 then impinges on a shutter assembly panel 138, such as a liquid 
crystal shutter assembly panel, spaced from the color filter 137 and array 
136 and which preferably comprises a multiplicity of electrically 
controlled pixel light valves overlying an array of interspersed shutter 
pixels each of which transmits only one of a plurality of colors, such as 
the primary colors red, green and blue. 
In accordance with a preferred embodiment of the invention, the array of 
color separated light beams from array 136 is in light and color 
registration with the array of interspersed shutter pixels, such that 
generally light of a given color impinges on a shutter area of the same 
color. 
In the embodiment of FIG. 10, where non-collimated light is used, the array 
of color separated light beams is not in one-to-one registration with the 
array of interspersed shutter pixels. 
Light modulated by the shutter assembly panel 138, and passing through 
another polarizer plate 134, identical to the polarizer plate 134 upstream 
of separator 136, is focussed by a lens assembly 139 downstream thereof or 
at any other suitable location. Preferably, lens assembly 139 includes a 
Fresnel lens 140 and a compound lens 141. 
Reference is now made to FIGS. 11A and 11B which are respectively a 
simplified illustration of a projector 150 and an illustration of an image 
152 projected thereby onto a screen 154 or other surface. The projector 
may be a projector constructed and operative in accordance with any of the 
above-described embodiments, particularly that of FIG. 24A. The projected 
image 152 is seen to have a trapezoidal shape due to the non-perpendicular 
angle between the optical axis 155 of the projector 150 and the screen 
154. 
Reference is now made to FIGS. 12A, 12B and 12C, which are respectively a 
simplified illustration of a projector 160, an illustration of the image 
162 produced thereby as seen along arrow B and an illustration of an image 
164 projected thereby as seen along arrow C. 
It is seen that whereas in the projector 150 of FIG. 11A, the shutter 
assembly panel 156 and focussing lens 158 are generally parallel, in the 
projector 160, the corresponding shutter assembly panel 166 and focussing 
lens assembly 167, including Fresnel lens 168 and a compound lens 169, are 
tilted towards each other. This creates a distortion in the image 162 
which is opposite to the distortion produced by the non-perpendicular 
angular relationship between the optical axis 165 of projector 160 and the 
screen 170. The result is a desired rectangular projected image 164. 
Reference is now made to FIG. 13, which is a simplified illustration of a 
projector of the type shown in FIG. 9 employing the prism/lens combination 
of FIG. 8 and employing tiltable optical components. The optical 
components may be identical to those shown in FIG. 9. Here, however, the 
shutter assembly panel 218 and the focusing lens assembly 219 including 
Fresnel lens 220 and compound lens 221 are tiltably mounted by any 
suitable mounting mechanism, so as to enable a selected distortion to be 
provided to the image produced thereby. This selected distortion is chosen 
to be identical but opposite to the distortion resulting from arrangement 
of the projector such that its optical axis is non-perpendicular with 
respect to a screen or other projection surface. It is appreciated that 
either or both of lenses 220 and 221 may be tilted as appropriate. 
Reference is now made to FIGS. 14 and 15, which are respective simplified 
schematic and partially cut away pictorial illustrations of a projection 
system constructed and operative in accordance with a preferred embodiment 
of the present invention. Here a projector 230 is arranged with its 
optical axis 232 at a non-perpendicular angle with respect to a mirror 234 
which directs the image projected by the projector 230 onto a screen 236. 
Preferably, the projector 230 is of the type illustrated in FIG. 13 and 
described hereinabove. 
Reference is now made to FIGS. 16 and 17, which are simplified schematic 
illustrations of front and rear projection systems employing a filtered 
screen and a projector constructed and operative in accordance with a 
preferred embodiment of the present invention. 
In the embodiment of FIG. 16, the projector 248 may be a projector 
according to any of the embodiments of the invention described hereinabove 
other than that of FIG. 2B, and the resulting colored light beams are 
spatially aligned with an array 250 of colored filter strips associated 
with a projection screen 252, such that each color separation beam falls 
on a filter strip of generally the same color. It is assumed that the 
number and size of the strips making up array 250 may be such that the 
individual strips cannot be discerned by the unaided human eye from a 
normal viewing distance. 
FIG. 16 illustrates a rear projection system, while FIG. 17 illustrates the 
equivalent front projection system, employing a projector 268, an array 
280 and an associated screen 282. 
The projection systems illustrated in FIGS. 16 and 17 have been found to 
demonstrate greatly enhanced contrast, clarity and brightness as compared 
with conventional projection systems. 
Reference is now made to FIG. 18, which illustrates a projection screen 
constructed and operative in accordance with a preferred embodiment of the 
present invention. The projection screen comprises any suitable pattern, 
such as strips 300, of transparent material in the three basic colors. 
Preferably the maximum width of the strip or other pattern is less than 
the resolution limit of the human eye during normal viewing. 
The projection screen of FIG. 18 can be used with any rear projection 
system wherein a light transmissive screen is required and wherein light 
of different colors impinges at different locations on the screen. It is 
not limited in applicability to use with a projector of the type described 
hereinabove in connection with any of FIGS. 1-17 and 24A-25. It has the 
effect of significantly increasing the contrast of the displayed image 
with respect to the ambient, but does reduce brightness of the displayed 
image. The screen of FIG. 18 may also be used for front projection, when a 
reflective or emissive substrate is disposed therebehind. 
Reference is now made to FIGS. 19 and 20, which are simplified 
illustrations of two versions of a rear projection television system 
constructed and operative in accordance with a preferred embodiment of the 
present invention. 
Whereas prior art rear projection television systems involve severe 
limitations on ability to reduce the depth thereof, the present invention 
overcomes this limitation by using optics having optical power in place of 
a conventional flat folding mirror just before the screen. 
In the embodiment of FIG. 19, there is provided a projector 305, which may 
be any suitable projector and is preferably a projector of the type 
described hereinabove in connection with any of FIGS. 1-17 and 24A-25. The 
projector 305 typically receives a generally collimated beam of light from 
a light source 310, typically via a folding mirror 312 and typically 
includes a filter and shutter assembly 314. 
Modulated light from filter and shutter assembly 314 is supplied via an 
objective lens 316 and a folding mirror 318 to a diverging lens 320 which 
projects the light modulated by the filter and shutter assembly 314 onto a 
screen 322, which can be any suitable screen, producing a real image at 
the screen. 
In the embodiment of FIG. 20, there is provided a projector 325, which may 
be any suitable projector and is preferably a projector of the type 
described hereinabove in connection with any of FIGS. 1-17 and 24A-25. The 
projector 325 typically receives a generally collimated beam of light from 
a light source 330, typically via a folding mirror 332 and typically 
includes a filter and shutter assembly 334. 
Modulated light from filter and shutter assembly 334 is supplied via an 
objective lens 336 to a diverging mirror 338 which projects the light 
modulated by filter and shutter assembly 334 onto a screen 340, which can 
be any suitable screen, producing a real image on the screen. 
In order to correct optical distortions, the diverging optics employed in 
the apparatus of FIGS. 19 and 20 should include aspheric elements or other 
means of correction. The use of lens 320 adds additional chromatic 
distortions, which are a disadvantage in comparison with the preferred 
version, shown in FIG. 20. 
Reference is now made to FIGS. 21-23, which illustrate a projection system 
constructed and operative in accordance with a preferred embodiment of the 
present invention. The projection system comprises a light source 410, 
preferably a high intensity incandescent light source such as a halogen 
lamp. Preferably the light source is a metal Halide arc lamp, such as a 
Philips MSR series lamp. The light source 410 is at least partially 
surrounded by a concave reflector 412 which is constructed and operative 
in accordance with a preferred embodiment of the present invention. 
Concave reflector 412 may be made of any suitable substrate such as metal, 
glass and plastic and may have a reflective surface made of any suitable 
material such as metal or one or more dielectric coating layers, and is 
preferably symmetrical about a reflector axis 414. In accordance with a 
preferred embodiment of the present invention, the reflector is 
characterized in being formed of a multiplicity of flat reflector surface 
units 415, the multiplicity of flat surface units being configured and 
arranged such that the projection of each of the multiplicity of flat 
surface units onto a plane perpendicular to the axis is generally 
identical, as illustrated in FIG. 23. 
It may be appreciated from a consideration of FIG. 22, that the two 
dimensional and three-dimensional configuration of each of the reflector 
surface units 415 varies as a function of its distance from axis 414 along 
the reflector surface. 
It is a particular feature of the present invention that the reflector is 
operative to reflect onto every location within a projection region in a 
projection plane extending perpendicular to axis 414 in front of the 
reflector, light from various locations on the light source, so as to 
produce a generally homogeneous, non-imagewise reflection from the light 
source to the projection plane. 
In accordance with a preferred embodiment of the present invention a light 
transmissive object 420, such as a liquid crystal transparency panel or 
film transparency to be projected is located in a projection plane which 
is relatively close to the light source and to the reflector. Preferably, 
the distance D of the object 420 from the facing edge 422 of the 
reflecting surface 412 parallel to axis 414 is approximately equal to the 
largest dimension L of the opening of the reflecting surface 412 at the 
facing edge 422. 
The present invention is particularly useful for compact-wide screen 
projection apparatus, such as projection television, where the depth of 
the unit is sought to be minimized. 
It will be appreciated by persons skilled in the art that the present 
invention is not limited by what has been particularly shown and described 
hereinabove. Rather the scope of the present invention is intended to 
include also modifications and variations within the scope of the claims 
which follow: