Description
This application is divided out of Indian Patent Application No. 3080/KOLNP/2006 dated
25th October 2006, which in turn is the national phase entry of International (PCT)
Application No. PCT/US2005/015856 having an International Filing Date of 5th May 2005.
FIELD OP THE INVENTION
[0002] The present invention relates generally to projection systems and, more
particularly, to multiple source high performance stereo graphic projection systems.
BACKGROUND
[0003] Large format 2D and 3D cinematic projection has been providing audiences with
an immersive theatre experience since the 1970's, and the projection technology is well
established. The large format (70mm) commercial exhibitor benefits from the capability to
present both two-dimensional ("2D") and three-dimensional ("3D") cinematic presentations
from the same projection system. This increases his/her return on investment The operator
would clearly benefit if the projection system functioned efficiently in both the 2D and 3D
operating modes.
[0004] There can be technological differences between standard 35mm and large format
70mm projection equipment. The large film frame dimension offered by the 70mm/15perf
format drives all these differences. The size of the large format film frame is about ten times
that of the standard 35mm film frame. Because of this, almost everything about the large
format projection systems is generally larger, faster, or more powerful than their standard
35mm cousins. A defining feature of the large format technology is the powerful
iurnination system required to iUurninate the horizontally traveling 70mm wide film.
[0005] The mumination system in a projection system represents a significant factor in
the cost of operating the system. The arc lamps have limited lifetimes (1000 hours), and so
must be continually monitored and periodically replaced when they no longer meet
performance requirements. Lamp replacement is a potentially hazardous task that requires a
careful alignment procedure conducted by a trained individual.
[0006] The high power lamps consume significant amounts af electrical power and
generate tremendous amounts of heat. This heat is generally vented from the projection room
and out of the building, and air conditioning must be adequate to cool the small projection

hall. This generates increased utility costs for the exhibitor. Shutting down lamps between
shows to conserve utility costs is often not a viable option. Standard high power arc lamps
generally cannot be extinguished and restarted without significant penalty to the arc lamps
lifetime (1.5 to 2.5 hours per lamp start).
[0007] For 3D projection, the demands on the illumination system may be more than
doubled. In some cases two channels, one for each eye, are projected simultaneously from
two physically separate but synchronized projectors, each with its own film reel. Each
channel may be polarized with a different polarization, and the two polarizations are
orthogonal to each other. In other cases, a single channel is used to project each eye in
sequence. With a single channel 3D projector, the projector may have a polarizer that is
capable of changing for each eye or active LCD glasses are used that are synchronized to the
images being projected. The polarization of the ifiurnination results in a light loss of over
50% as compared to the non-polarized 2D projection, while the screen brightness
requirements remain unchanged. Using active glasses also results in a light loss compared to
2D projection. This results in a significant difference in screen luminance between 3D and
2D presentations. Standard arc lamps can only be operated near their full output power (to
conserve lamp life), so modulating the lamp power to compensate for the varying 2D and 3D
power requirements has not been a viable option with existing systems.
[0008] For long duration 2D projection, there are additional light inefficiencies. Limits to
the physical size of reel units that hold the film demand that these long duration presentations
be split between two distinct reel units. The first part of the presentation is played back
through one channel of the system with a transition to the second channel for the final part of
the presentation. The penalty associated with lamp ignition normally leads to the requirement
that both upper and lower channel lamps remain on during the whole presentation.
[0009] The large film format may demand not only a significantly more powerful
illumination system, but also one that delivers the required uniformity and stability over the
much larger film frame of the 70mm format The performance requirements of the large
format iUurnination system exceed that of the standard 35mm systems.
[0010] Some conventional projection systems have utilized multiple lamps. For example,
U.S. Patent No. 4,916,485 discloses a projection system with side-by-side lamp houses that
can be used for both 3D and 2D projection of large format cinema. While this projector
system uses two lamps, there is only one lamp for each channel, which offers no advantage-
over standard stereographic projection systems. Particularly, there is no way to balance the

light levels between 2D and 3D operating modes without incurring a significant loss in
efficiency. ' -
[0011] U.S. Patent No. 3,914,645 discloses a multiple lamp unit for use with a
photographic projector. The '645 patent provides for a single lamp projector with multiple
"back up" lamps mounted on a turntable that can be rotated so as to move successive lamps
into working position to automatically replace lamps when they fail. In U.S. Patent
Application No. 2003/012S427 a system for employing dual projector lamps is disclosed. It
uses two sources and polarization optics to select between one source and the other, using one
source at a time. U.S. Patent No. 6,545,814 discloses a method for combining multiple arc
lamp sources for a electronic projector using prismatic structures integrated onto an
integrating rod.
[0012] U.S. Patent Application No. 2002/0145708 discloses a dual lamp projector
nlurnination system with a broad spectrum source and a narrow spectrum source. The narrow
spectrum light source is an LED and is used to complement the spectrum of the broad
spectrum source, which has a spectral power deficiency. U.S. Patent No. 5,997,150 discloses
a multiple emitter illumination engine with a holographic diffuser with particular application
to xerographic printers and for iUurninating spatial light modulators with high intensity light.
In U.S. Patent No. 6,341,876, a method for combining two lamps into a light pipe is
disclosed. The '876 patent discloses the use of a parabolic reflector for the arc lamps. The
'876 patent also discloses a method of combining the output of two lamp sources into a light
pipe with two right angle prisms.
[0013] U.S. Patent No. 5,504,544 discloses a method for combining multiple lamps using
a series of Fresnel collecting and focusing elements. U.S. Patent No. 4,372,656 discloses a
single .lamp projector that can be used for 3D as well as 2D projection through the
introduction of a polarization device.
[0014] These prior projection systems do not disclose the balancing of light levels
between the 3D and 2D operating modes of a projection system nor do they address the
optimization of efficiency and reduced operating costs for 2D and 3D operation of these
projection systems.
[0015] Temporal stability of the light output in the frequency range over which the
human visual system is sensitive is an important projection system attribute. Flicker and
shimmer are the product of the frequency dependent sensitivity of the human eye times the
stability of the light output. Flicker is the global fluctuations of light levels at the screen.

Flicker is present when the total luminous flux output from the projector varies with time.
Shimmer is localized spatial fluctuations at the screen. When shimmer is observed, the
illuminance changes locally on the screen despite a constant total luminous flux output from
the projector. Thus a decrease of illuminance in one area on the screen is compensated for by
an increase in iuurninance elsewhere on the screen.
[OOlfi] Arc lamp induced temporal instabilities present a particular challenge to the
illumination system of an arc lamp based projection system. These instabilities can manifest
themselves as flicker and shimmeT of the projected image. Human perception is particularly
sensitive to these fluctuations, and people are able to discern temporal fluctuations as small as
one part in two hundred. This places a far more stringent requirement on the illumination
system than does the requirement for static illurnination uniformity across the screen.
Shimmer and flicker are kept below the human detection threshold in order not to detract
from the presentation.
[0017] Arc lamp instabilities can be caused by modulation of the arc's position and shape
within- the lamp envelope of the lamp. These modulations induce spatial and angular
variations of the illumination signal. Turbulence within the envelope induces other localized
angular deviations as the iflinnination signal propagates through the turbulent regions. These
temporal angular modulations of the fllumination at the lamp are transformed to angular and
spatial fluctuations of the irradiance patterns in subsequent positions of the optical system,
which in turn are perceived as shimmer or flicker by the audience.
[0018] The level of temporal instability of an arc lamp becomes more acute as the power
of the lamp increases and its size decreases. Arc lamp stability is also known to degrade with
lamp age. To meet the illumination requirements of large screens, high power lamps are
employed. To satisfy- the demands of a compact projection system, there is a drive to make
the lamps as small as possible. The higher levels of convection within the envelope of a
compact high power lamp lead to a greater amount of temporal instability.
[0019] Arc lamp output fluctuation is a recognized problem, and there are several
examples of conventional solutions relating to its reduction. These solutions generally
involve modifying or manipulating the electrical power characteristics driving the lamp, for
example, U.S. Patent No. 6,525,491, U.S. Patent No. 6,479,946, and U.S. Patent No.
6,239,556, or modifying the ingredients within the lamp envelope, for example, Japanese
Patent Application No. 02-01-01 01035447, and Japanese Patent Application No. 00-77-76
05151932.

[0020] Optical means to reduce shimmer is also used by some conventional solutions.
Japanese Patent Application No. 03-01-00 00066135 discloses that a number of discrete "half
mirrors" to flatten the light fluctuations caused by the shimmer. In Japanese Patent
Application No. 00-95-76 56149180 a photochromic device is applied with a feedback circuit
to control the transmission of the photochromic device.
[0021] U.S. Patent No. 6,341,876 discloses a method for optically eliminating the effects
of shimmer from the projected images. The '876 patent discloses a condensing lens at the
input of a light pipe with the express intent of eliminating the image of the turbulent region
within the arc lamp at the output of the light pipe.
[0022] In the paper entitled "Design Improvements for Motion Picture Film Projectors,"
C.L. DuMont et al., SMPTE Journal, vol. 110, no. 11, 2001, the authors present results of
their work in applying fly's eye integrators to 35mm cinematic projectors. The paper
discusses the advantages that the fly's eye integrator provides in reducing the lamp-induced
shimmer in the projected image. They also discuss the use of a Cermax sealed beam lamp in
the projection system.
[0023] U.S. Patent Application No. 2003/0142296 discloses a means for monitoring light
levels by using a detector plus integrating box plus mirror assembly located behind a primary
mirror that reflects a large portion of the visible light towards a light imaging device. This
application discloses that it is necessary to sample and integrate 10% to 50% of the light
transmitted by the primary mirror in order to achieve a sufficient signal to noise ratio.
[0024] U.S. Patent No. 5,818,575 discloses a method to detect instability in an arc lamp's
spatial distribution, particularly for use in lithography projection optics. At least two
detectors are placed laterally across the iUurnination field at the wafer plane or conjugate to
the wafer plane. The ratio of the output from the two detectors indicates the stability of the
arc lamp.
[0025] These references do not disclose a light efficient and cost effective means of
suppressing lamp-induced shimmer and flicker in the projected image. As described above,
these modulations may be at a higher magnitude than usual due to die use of compact high
wattage lamps. While fly's eye and light pipe homogenizers reduce these fluctuations,
limitations in the fabrication methods as well as efficiency considerations make sufficient
homogenization impractical and inefficient.
[0026] Additionally, the large physical size of the typical 70mm format projection system
can make them incompatible with standard 35mm projection facilities. The vast majority of

theatre venues are designed for the standard 35mm format projection systems. Theatre
operators considering the installation of modern large format projection equipment must
therefore factor in renovations to convert existing 35mm projection halls. This may increase
the installation costs, disrupt theatre operations, and prolong the installation process. These
factors may all contribute to increased cost of ownership to the theatre operator.
SUMMARY OF INVENTION
[0027] Embodiments of the present invention comprise multiple source high performance
stereographic projection systems. One embodiment of a projection system of the present
invention comprises a first projection channel, a first light source capable of providing light
for the first projection channel, and a second light source capable of providing light for the
first projection channel, wherein when the projection system is in a second presentation mode
the first and second light sources are on, and wherein when the projection system is in a first
presentation mode the first light source is on and the second light source is at a reduced
power. In one embodiment, the first presentation mode is a two-dimensional presentation
mode and the second presentation mode is a three-dimensional presentation mode. In one
embodiment, when the projection system is in two-dimensional presentation mode the second
light source is off. More than two light sources may be used per projection channel.
[0028] The projection system may also have a second projection channel, a third light
source capable of providing light for the second projection channel, and a fourth light source
capable of providing light for the second projection channel, wherein when the projection
system is in the second presentation mode the third and fourth light sources are on, and
wherein when the projection system is in the first presentation mode the third and fourth light
sources are off.
[0029] In another embodiment a system of the present invention comprises a projection
channel, a first light source capable of providing light for the projection channel, a second
light source capable of providing light for the projection channel, a combining device for
combining light produced by the first light source and the second light source into combined
light, and a fly's eye integrator for integrating the combined light.
[0030] These illustrative embodiments are mentioned not to fimit or define the invention,
but to provide one example to aid understanding thereof. Illustrative embodiments are
discussed in the Detailed Description, and further description of the invention is provided

there. Advantages offered by the various embodiments of the present invention may be
further understood by examining this specification.
BRIEF DESCRIPTION OF DRAWINGS
[0031] These and other features, aspects, and advantages of the present invention are
better understood when the following Detailed Description is read with reference to the
accompanying drawings, wherein: .
[0032] Figure 1 shows a schematic of the an illustrative embodiment of an optical system
of a projection system;
[0033] Figure 2 shows the combination of lamps in more detail with one lamp in
operation according to one embodiment of the present invention;
[0034] Figure 3 shows the combination of lamps in more detail with two lamps in
operation according to one embodiment of the present invention;
[0035] Figure 4 shows a method according to one embodiment of the present invention
by which the light distribution at the input to the lens array is transformed to a uniform patch
of light at the image gate with minimal light loss;
[0036] Figure 5 illustrates how the angular and spatial modulations at the primary lamp
focus propagate through to the first lens array according to one embodiment of the present
invention;
[0037] Figure 6 illustrates a diffuser used with a light pipe integrator to reduce shimmer
at the image gate according to one embodiment of the present invention; and
[0038] Figure 7 illustrates a diffuser used with a light pipe integrator to reduce shimmer
at the image gate according to one embodiment of the present invention.
DETAILED DESCRIPTION
Introduction
[0039] Embodiments of the present invention comprise multiple source high performance
stereographic projection systems. There are multiple embodiments of the present invention.
By way of introduction and example, one illustrative embodiment of the present invention
provides a projection system with a compact iHumination system that includes multiple light
sources, such as arc lamps, for each channel, and discloses light source operating strategies to
optimize system efficiency, performance, and operating costs of a projection system with

dual 3D/2D presentation modes, and maintaining consistent light levels for both operating
modes. For example, in one embodiment, a stereoscopic projection system has two
projection channels that utilize two light sources per channel. In this embodiment, all four
light sources may be used for 3D presentation mode when both channels are used. In 2D
presentation mode, when a single channel is used, one of the light sources associated with the
channel is not used or the output of both light sources is reduced. The projection system of
the present invention may avoid the high cost of acquiring, installing and operating a high-
resolution steTeographic projection system and is also capable of efficiently projecting high-
resolution 2D presentations. The projection system of the present invention is applicable to
large and 35mm format film and electronic projection systems.
[0040] In one embodiment, the projection system includes polarization components that
. may be automatically inserted and retracted as required for stereographic projection. This
system works in concert with the light source usage protocol to optimize system efficiency,
lower operating costs, simplify operation of the system, and improve the reliability and
quality of the presentations.
[0041] In one embodiment, the projection system provides for the elimination of shimmer
in the image caused by turbulence within the arc lamp's envelope. This is accomplished
through the introduction of a diffusing element that works in concert with "fly's eye" or light
pipe integrating optics. While the fly's eye or light pipe integrating optics reduce these
fluctuations, limitations in the fabrication methods make sufficient integration impractical
and inefficient As described below, a diffusing element is added into the system "that reduces
the residual shimmer to a level significantly below that detectable by the human visual
system. In addition to reducing shimmer, the diffuser also serves to provide more uniform
illumination across the image gate.
[0042] Other aspects of this invention are related to reducing cost and size of the system.
In one embodiment of the projection system, the functions of a cold mirror and mechanical
dowser are combined in the system, thereby reducing part count, system size, and
manufacturing costs. In one embodiment, the projection system uses a compact and light
efficient method to combine the outputs of multiple light sources per channel.
[0043] The above introduction is given to introduce the reader to the general subject
matter of the application. By no means is the invention limited to such subject matter.
Illustrative embodiments are described below.

Illustrative System Description
[0044] Figure 1 shows a schematic of an illustrative embodiment of an optical system of
a projection system. The embodiment of Figure 1 illustrates a system where images are
created on the screen by film transported into the image gate. The present invention applies
equally to electronic projectors utilizing other spatial light modulation techniques at the
image gate, including, but not limited to, micro-electro-mechanical systems (MEMS),
reflective liquid crystal panels (LCOS) and transmissive liquid crystal panels or CRTs.
Figure 1 illustrates a single channel. In some embodiments, the projection system would
have two optical systems 100 within the same housing in order to project 3D content.
[0045] The iUurnination train consists of the two light sources, such as arc lamp
assemblies 1A, IB, each with integrated elliptical reflectors (not shown). The lamps 1 A, IB
direct their iUurnination onto the entrance face of the combining prisms 2. hi one
embodiment, these prisms 2 redirect the lamp illumination by means of total internal
reflection. The light exiting the two combining prisms 2 then enters the integration optics,
which includes the holographic diffuser 3, collimating optics 4, the lens array pair 7A, 7B,
and relay optics 9. The lens array pair 7A, 7B act as a fly's eye integrator. The entrance
pupil of the iUuminatiori system is located at lens array 7B. The relay optics 9 serve to
magnify the images of the lens array to fully iBuminate the image gate 10 and to match the
light to the pupil of the projection lens 11. This light efficient subsystem projects a uniform
light distribution free of perceptible lamp flicker and shimmer onto the image gate. The
desired image is impressed upon this uniform patch of light at the image gate 10 by means of
film (not shown) transported into the image gate 10. The projection lens 11 then projects the
image that is present at the image gate 10 through a removable polarizer 12 onto the screen
(not shown). An ultraviolet filter 6 positioned upstream of the lens array 7A rejects the
damaging short wavelength radiation and prevents it from propagating through the fly's eye
integrator (7A, 7B) and to the image gate 10.
[0046] The hybrid cold mirror/dowser 5 is positioned prior to the lens array pair 7A, 7B.
The cold mirror/dowser 5 has two functions: to filter out the infrared component of the
illumination; and to act as a projector dowser. When flipped OT rotated out of the optical
path, the illumination is transmitted to a beam dump 13 that effectively prevents any
illumination from exiting the projector.
[0047] A second cold mirror 8 reflects the iUurrunation exiting from the lens array pair
7A, 7B and directs it along the optical axis defined by the projection lens 11. It also acts as a

secondary cold minor, filtering out any residual IR radiation left in the illumination. A
detectoT 14 may be placed behind this minor to monitor light levels and temporal
instabilities, such as flicker and shimmer.
[0048] In one embodiment, the illumination system is designed to be compact enough to
allow two separate channels (such as separate left and right eye channels) to be integrated
into a single projection system unit as opposed to a separate projector for each channel. This
can simplify the control electronics for the projection system, reduce the floor space needed
in the projection booth or hallway, and reduce installation time.
Lamps
[0049] The two sealed beam Xenon arc lamps (1A and IB) are aligned -with elliptical
reflectors (not shown) to produce a focused image of the arc. In one embodiment, the
Cermax brand of sealed beam arc lamps are used as the light sources. These lamps,
manufactured and sold by Perkin Elmer, are high intensity discharge lamps (arc lamps) with
several unique characteristics that are exploited to great advantage in the ulumination
architecture presented here. Although Cermax lamps are limited to lower powers than bubble
lamps, multiple Cermax lamps coupled to an efficient illumination system can achieve
equivalent output powers. A number of significant advantages over the single high power
bubble lamp design are also introduced.
[0050] Cermax lamps are significantly more compact than bubble lamps, and even a pair
of Cermax. lamps can have a substantial size advantage over the single bubble lamp design.
This permits the design of a more compact 3D projector system. The importance of a
compact system is driven by the need to fit the projector into existing 35mm hallways, a
capability that can substantially reduce tire cost of installation. Also in cases where two
channels are used for 3D presentation mode, a smaller projector allows the projection points
of left and right images to be closer, which can be a performance advantage. For example,
this can allow better coincidence of images across the screen and reduce differences in light
levels between left and right eye images caused by distinct angles of incidence on a high gain
screen both of which lead to less eye fatigue when viewing a 3D presentation.
[0051] Additionally, compact lamps permit the integration of left and right channels into
a single projector. While mechanically distinct left and right optical trains could lead to a
small separation between projection points, the overall projection system would become
larger and more expensive to manufacture due to higher inventory costs for distinct elements.

[0052] Ceimax lamps are fabricated with an integrated reflector pre-aligned with the arc
gap defined by the cathode and anode at the time of manufacture. External datum features
facilitate accurate alignment between the arc lamp and an optical system. The etendue of the
light emitted by the Ceimax lamp is smaller than the portion of the etendue of the film gate
seen by each lamp. This characteristic is exploited in a number of ways in embodiments of
the present invention. When coupled with an appropriately designed illumination system
such as the one described below, the accuracy to which the lamp needs to be positioned to
achieve consistent uniform screen iUuminance is easily met by inexpensive machining
tolerances. This may eliminate the need for a skilled projectionist or technician to perform
lamp alignment, a task that requires training, skill and patience. This advantage can reduce
the cost of operating the projection system, and ensure a more consistent and reliable
illumination quality.
[0053] The Cermax lamp can be operated over a broad range of power levels, unlike
standard arc lamps, which are generally used at or near full power in order to achieve stable
operation and maximum lifetime. Furthermore, operating a Cermax lamp at lower power
significantly extends the life of the lamp. Unlike standard bubble lamps, Cermax lamps can
be extinguished and restarted with little penalty to lamp life. These capabilities can be
exploited to significantly improve system efficiency through the application of lamp
operating strategies for combined 3D/2D illumination systems.
[0054] For 3D presentation mode utilizing a two-channel system, each channel may be
polarized with a linear polarizer. Resulting polarization losses in each channel are typically
greater than 50%. The polarizer is not required for 2D presentation mode, and therefore there
is no polarization loss incurred for 2D presentation mode if the polarizer is removed,
Similarly, if active glasses are used with a 3D projection system illumination losses also
occur. With the projection system of the present invention, a lamp utilization strategy maybe
employed to optimize operating costs for the projection system. For 3D presentation mode,
two lamps are operated for each channel in a two-channel system (or for a single channel in a
single channel system) to provide high ihuminatioiL power to overcome polarization or other
illumination losses, such as losses incurred when using time sequential 3D. The two lamps
may be operated at levels significantly less than uieir full power to extend their life. Sensors,
such as detector 14 shown in Figure 1, connected to a feedback or control system can monitor
each lamp's output. Increasing the drive current to the lamp can compensate for decreasing
output levels as the lamp ages.

[0055] Electronic projectors that output polarized light (e.g. LCOS and LC projectors)
can be configured to present 3D images with only a small brightness loss compared to 2D
presentations. In these systems there is not a need to overcome polarization losses.
However, light levels may need to be reduced due to ghosting in 3D presentations. Ghosting
is a double image that the viewer sees when light enters the incorrect eye. In 3D
presentations there is a tradeoff between perceived ghosting and brightness. Specifically, the
perceived ghosting is reduced as the brightness is decreased. In this situation it may be
desirable to operate the lamps in a fashion that is opposite to what is described above. Here
more light output is required for 2D presentations leading to the requirement that both lamps
are turned on. Less light output is required for 3D presentations allowing for either single
lamp operation or two lamp operation at reduced power levels.
[0056] For 2D presentation mode in a two-channel system, only one of the projection
channels may need to be operated. If the first channel is elected, its polarizer is retracted and
one of the lamps in the first channel can be operated at a reduced power, such as zero power
so that it is extinguished. Both lamps in the second channel are extinguished as well. This
leaves one of four lamps in the system operating, reducing rctrical power requirements for
illumination to 25% of that required for 3D presentation mode. Further efficiencies are
gained through reduced cooling requirements, reduced load on projection room ventilation
and air conditioning, and increased lamp life. The lamp used can be alternated for each 2D
projection event in order to maintain similar lamp lifetimes across the two lamps. In case of
failure of one of the lamps, the second lamp provides an immediate backup, thereby
providing redundancy for the 2D presentation mode of operation. Yet another strategy for
2D presentation mode is to operate both lamps associated with a projection channel
simultaneously at significantly reduced power (but greater than zero), which can extend the
lifetime of each lamp. In one embodiment, the projection system may allow for the change of
presentation mode during a single presentation, such as changing between a two-dimension
presentation mode and a three-dimensional presentation mode. For example, a 3D
presentation preview trailer may be shown before a 2D presentation and a 3D sequence may
be shown within a 2D presentation.
]0057] While Cermax lamps are the preferred light source for this system, it will be clear
to one of skill in the art that other light sources may be used in the system. Integrated
modules with a bubble lamp pre-aligned to a reflector are readily available from a number of
different suppliers. There are other suppliers of sealed beam arc lamps as well. Other lamps

with small etendue, such as high-pressure mercury lamps and metal halide, may also be used
in the present invention to great advantage.
[0058] Lamps with parabolic reflectors may also be used provided their output is focused
into the combining prisms through the use of a lens. While the embodiments described above
utilize two lamps per channel, alternative embodiments may combine more than two lamps
per channel.
Combining prisms
[0059] In one embodiment, each combining prism 2, shown in Figure 1, uses total
internal reflection (TIR) to reflect the lamp ilhrrnmation into a common optical padi. The
TIR mechanism precludes the use of damage-prone reflective coatings, and provides 100%
reflectivity from the TIE. surface of the prism. Prism material is typically but not limited to
quartz, which has a high tolerance to heat absorbed from the radiation and from components
in contact with the prisms. Anti-reflection coatings can be applied to the input and exit faces
of the prisms. It will be apparent to those skilled in the art that while prisms are used in one
embodiment for lamp combining, other methods of combination including polished
aluminum mirrors and dichroic mirrors could be used. It will also be apparent to those
skilled in the art that the prisms are used as needed to combine the output of multiple lamps.
For example, one method to combine three lamps would be to separate the two prisms 2
allowing the light output from a third lamp to pass without deviation between the two prisms.
[0060] Figure 2 shows the combination of lamps 1A, IB in more detail with a few select
rays from one of the two lamps IB shown. (For illustrative purposes, the dowser is not
shown in this figure and a point source is assumed for the arc of the lamp.) Note that the
lamp focus 16 is offset from the optical axis of the collimating optics 4 that follows. The
orientation of the prisms about this optical axis is dictated by the Lagrangian formed by the
image gate 10 and projection lens 11 as depicted in Figure 1. This Lagrangian at the image
gate 10 may be used to determine the aperture 15 size at the output of the prisms into which
light must travel to pass through the system and onto the screen. The aperture 15 is normally
rectangular in shape due to a rectangular image gate coupled with a non-anamorphic
projection lens. To minimize loss, the offset of the lamp focus 16 should coincide with the
long dimension of the rectangular aperture 15. The aperture 15 depicted in Figure 2 shows
the extent of the larger of the two dimensions of the rectangular aperture 15. Light from each
lamp 1A, IB sees one half of the full aperture 15. The offset of the lamp focus 16 from
optical axis is chosen such that the illuminance distribution is centered within the half of the

aperture used by that lamp. As the lamp ages and the illuminance distributio'n at the lamp
focus 16 increases in size, the light output will remain constant until the edge of the light is
vignetted by the boundaries formedby the aperture 15 and the apex of the prism 2 nearest the
lamp focus 16.
[0061] Figure 3 shows the combination of lamps with rays from both lamps 1A, IB
turned on. (For illustrative purposes, the dowser is not shown in this figure and a point source
is assumed for the arc of the lamp.) Note that the output light is collimated for each of the
two lamps 1A, IB but skewed at an angle relative to the optical axis due to the offset of the
lamp foci from the optical axis. The prisms 2, in this case, are tilted slightly about an axis
perpendicular to the plane of reflection in order to modify the characteristics of the reflected
illumination beams. This tilt can aid in reducing the keystone distortion of the illumination at
the image gate 10, caused by the offset of the images of the arc 16 and is designed to match
the illumination light to the entrance pupil of the illumination system (located at lens array
7B) for improved efficiency. This matching is illustrated by the convergence of light from
the two lamps into a single patch of light onto the lens array 7 A.
[0062] Figures 2 and 3 show the collimating optics 4 as single lens. Those skilled in the
art know that collimation can be performed by multiple lenses if necessary to reduce
aberrations.
[0063] While Figure 3 shows an illustrative embodiment for lamp combination that is
, compact, those skilled in the art would realize that there are alternatives. For example, if the
lamp assembly was fabricated with parabolic reflectors, the collimated output of the lamps
can be combined by tilting their output relative to the optical axis such that the light beams
superimpose at the lens array. This method may not be as compact as that shown in the
illustrative embodiment of Figures 2 and 3 and can suffer from an increase in etendue present
at the lens array compared to that of the lamp due to the distance between the lamp and the
lens array. Optics can be added into the system to eliminate this inefficiency, but this may
further increase the size of the system.
Beam Integrator
[0064] Figure 4 shows a method by which the light distribution at the input to the lens
array 7A, 7B is transformed to a uniform patch of light at the image gate with minimal light
loss. The two lens arrays 7A, 7B may be identical, and aligned so that each element of the
first array 7A shares a common optical axis with its corresponding element on the second
array 7B. The apertures of the array elements are chosen to match the geometrical shape of

the image gate 10 to be illuminated. The lens array pair 7A, 7B and the relay optics 9
function to create a uniform illumination distribution on the image gate 10.'
[0065] Sometimes referred to as a "fly's eye" "beam homogenizer, these components may
function as follows. The two lens arrays 7 A and 7B are nominally separated by a distance
equal to the focal length of the individual elements making up the arrays. Each lens element
(or lenslet) of the first lens array 7 A creates an image of the source(s) within the aperture and
at the plane of the corresponding lens in the second array 7B.
[0066] Each element of the second lens array 7B then forms an image of the aperture of
the corresponding element of the first lens array 7A. These sub-images are projected to
infinity by the lenses of the second array 7B. The relay optics 9 serves to superimpose the
sub-images onto the film gate 10 with a slight overfilling of the aperture to allow for optical
and assembly tolerances. To illustrate the combination of images, Figure 4 shows solid lines
representing two chief rays and an axial ray 17 from two specific lenslets in the array. These
are shown to superimpose upon one another at 22 at the image gate 10. The dimensions in
Figure 4 are not intended to indicate relative scale.
[0067] Light from each lenslet in lens array 7A iUuminates the entire image gate 10.
Referring back to Figure 3, each lamp 1A, IB is responsible for iUuminatmg the entire image
gate 10.
[006S] The etendue limit of the optical system is dictated by the area of the image gate 10
and the numerical aperture of the projection lens 11. Using the principle of etendue
conservation, the focal length of the relay lens 9 is selected to balance the competing
objectives of compactness of the system, constraining the size of the lens array 7 A, 7B to
accommodate fabrication limitations, and providing sufficient area to support a large array of
lenses.
[0069] The fly's eye beam-integrator system operates by superimposing numerous
• sub-images at the image gate, resulting in an iUumination distribution that is the (incoherent)
sum of the illumination distributions across each individual aperture of the first lens array 7A.
The uniformity is a function of the number of array elements and the individual distributions.
As the number of array elements increases, the uniformity of the resulting superimposed sum
of sub-images will improve. The individual lens size can be chosen as a balance between the
degree of homogenization and light efficiency of the system. Smaller lenses can lead to a
lower fill-factor (Hie ratio of the clear aperture of a lens to the size of the lens) and increased

scattering thus lowering system efficiency. This is a result of finite sized transition regions
between lenslets, a feature that is limited by fabrication technology.
[0070] There are a number of factors that limit the density of lenses in the lens array 7A
and 7B. The magnification of the input lens array 7A to the image plane 10 is given by the
ratio of focal length of the relay optics 9 to the focal length of the lens array. As stated
previously, the focal length of the relay optics fixes the overall size of the array. As the
lenses in the array get smaller, care must be made to ensure the resulting radius of curvature
of the lenslets, due to the smaller focal length, remains 'within manufacturing tolerance limits
of this molded optical element. Also, it can be appreciated that smaller lenslets will require
better lateral and rotational precision in order to maintain the relative alignment between the
two arrays thus increasing manufacturing cost.
[0071] The relay optics 9 shown in Figures 1 and 4 is drawn as a single element for
illustrative purposes. It will be apparent to those skilled in the art that relay optics satisfying
the requirements given above may consist of multiple lenses to reduce aberrations. It will
also be apparent to those skilled in the art that the type of modulator used at the image gate
will affect the design of the relay optics 9. For example, spatial light modulators including,
but not limited to, MEMS, LCOS and transmissive liquid crystal panels, will require color
separation and color recombination optics which in turn place back focal length and
telecentric requirements on the design of the relay optics.
[0072] In one embodiment, the combined etendue of the light sources combined into one
channel is less than the etendue defined by the image plane. This ensures that the second lens
array remains under filled and insensitive to the exact mechanical placement of the light
source and to the tolerances involved in creating the integrated light source and reflector
assembly. Lamps may then be replaced without the need for alignment to achieve peak
performance. A characteristic of DC arc lamps, CERMAX lamps included; is that the
cathode bums back as the lamp ages. This increase in electrode separation leads to an
increase in etendue. Provided the resultant etendue is less than the etendue of the optical
system that follows, the light output remains constant as the lamp ages.

Shimmer and the Holographic Diffiiser
[0073] Axe lamps are generally subject to a continuous spatial modulation of the arc
location within the arc lamp envelope. This modulation is caused by gas turbulence within
the envelope of the arc lamp. In addition, as the lamp ages, it is common for the electrodes to
become worn and pitted leading to a fluctuation in the attachment point of the arc. The
resulting light output from the arc is further modulated by the density dependent fluctuations
of the gas within the envelope of the lamp. The modulation of the position of the arc,
combined with density fluctuations in the gas, lead to a modulation of the angular intensity
distribution from the reflector. This yields a primary lamp focus 16 that is modulated both in
space and in angle.
[0074] Figure 5 illustrates how the angular and spatial modulations at the primary lamp
focus 16 propagate through to the first lens array 7A. The collimating lens 4 acts to convert
the angular modulation at the primary focus 16 to a spatial modulation first lens array 7A.
Likewise the spatial modulation at the focus 16 is converted to an angular modulation at the
first lens array 7A.
[0075] If one is limited by the etendue of the light source, the first order effect of the
angular modulation at the lens array 7 A can be to modulate the over fill of light present at the
second lens array 7B. This introduces a time dependent loss in the system resulting in flicker
at the image gate. Standard closed loop feedback mechanisms can be used to eliminate this
global modulation. For example, a detector monitoring the light output from the projector
can signal to the lamp's current control to reduce the global modulation.
[0076] In one embodiment, where the combined etendue of the light sources is less than
the etendue defined by the image gate and the projection lens, the angular modulation at the
lens array does not affect the stability of the light at the image gate 10 due to the fact that the
second lens array 7B is under filled.
[0077] The spatial modulation at the first lens array 7A, caused by the angular
modulation at the lamp focus becomes a local spatial modulation or equivalentiy shimmer at
the image gate 10. This is true regardless of whether the lamp or the optical system limits the ■
etendue. Unlike flicker, a standard closed loop feedback system will not reduce the shimmer.
The magnitude of the modulation at the image gate 10 is generally less than that at any single
lens within array 7A because the modulation is normally random from lens to lens and the
light from multiple lenses is superimposed at the film plane. The resulting temporal noise at
the film plane is roughly reduced by the square root of the number of lenses illuminated. As

stated earlier, manufactiirability of the lens array and a negative impact on lignt efficiency
place a limit on the number of lenses that can be used in the array 7 A and 7B.
[0078] There is a desire to reduce these spatially dependent temporal fluctuations further
than what can be done by increasing the number of lenses. Reducing flicker to levels below
visual detection threshold when the lamp is new is a primary requirement There is a
secondary requirement to reduce the flicker levels so that as the lamp ages, greater
instabilities in the arc do not translate to perceived flicker. This secondary requirement may
become important in a system such as this one. Whereas the normal lamp failure mechanism
is due to the increased arc gap and the increased etendue and light loss that it incurs, the
Cermax's small etendue offers far more change in arc gap size before its etendue degrades
the system's performance. In one embodiment, the lifetime of the Cermax lamps is also
extended by operating at less than their full output power. As a result, it is expected that in
projection systems designed in accordance with the present invention, lamp life may become
limited by stability, not increase in etendue. Improving the shimmer reduction can increase
lamp life yet further again, leading to savings in lamp cost and maintenance requirements.
[0079] It is the function of the diffuser 3 to further reduce the spatial fluctuations and
extend the life of the arc lamps without placing more stringent demands on the fly's eye
integrator. The schematic depicted in Figure 5 discloses the operating principle of the diffuser
3 when used in concert with the fly's eye integrator for shimmer reduction. The integrated
lamp assembly 1 focuses its output to the nominal focal plane 16, where an image of the arc
is formed. The converging cone of rays defines the nominal envelope conlaining the lamp's
output.
[0080] The angular modulations at the reflector's focal plane 16 are transformed by the
collimating lens 4 to spatial fluctuations at the first lens array 7A. Because of the limited
angular excursion of the perturbations of the illumination at the focal plane 16, there is a
limited spatial extent of the induced irradiance fluctuations at the first lens array 7A This is
indicated in Figure 5 by the dashed lines showing envelope of the maximum deviation cone
propagating from the focal plane to the first lens amy 7A. The area defined by the projection
of the cone on the lens array surface defines the region over which the flickeT may extend.
[0081] By inserting an engineered diffuser 3 at OT near the focal plane 16 of the lamp 1,
and designing the diffuser 3 so that it diffuses the light over a range of angles dictated by the
angular perturbation cone from the lamp 1, the perceived shimmer can be eliminated. Each
and every elemental illumination contribution from the focal point, whether nominal or

perturbed, is diffused, or "blurred" to illuminate a larger region at the lens array. This is
equivalent to convolving the instantaneous irradiance distribution over the entrance of the
lens array pair 7A, 7B by the response of the diffuser 3. The irradiance distribution at any
point on the first lens array 7 A is then seen to be averaged with the irradiance of the
neighboring points on the surface, with the averaging region having a size and extent defined
by the diffusion angle of the diffuser 3. Table 1 below shows the reduction of shimmer as a
function of the magnitude of angular perturbation relative to the magnitude of diffusion.
Results are shown for the simple case of a diffuser with a Gaussian scattering profile with full
width half maximum (FWHM) of W. The effectiveness of the diffuser 3 to remove shimmer
improves as the angulaT perturbation decreases, ha practice, it has been found that with
2.4kW CERMAX lamps as the light source, a Gaussian diffuser with FHWM equal to 1
degree removed 80% of the existing shimmer, which in this case left fluctuations well below
the visual detection threshold. Table 1 indicates that the primary source of lamp
perturbations were less than 1.5 degrees.

[00S2] As the lamp ages and instabilities increase, the amount of diffusion required to
eliminate perceived flicker becomes greater. The etendue of the light source as viewed from
the output from the diffuser may be calculated by including the effects of lamp fluctuations
and the amount of angular scattering introduced by the diffuser. Provided the combined
etendue from all these light sources directing their output into the single channel remains less
than the etendue defined by the projection lens and image gate, the system may be designed
to allow the addition of the diffuser without any loss of light efficiency.
[0083] In one embodiment, a holographic diffuser is used because backscattering is
negligible and it represents a compact cost effective solution. The diffusing power of a
holographic diffuser can also be made asymmetric to better smear the angular perturbations

from the lamp which may themselves not be symmetric. This will optimize the illumination
throughput while reducing flicker to well "below the limit of human perception. Those skilled
in the art will realize that other means of diffusing light may he employed, including, but not
limited to, standard diffusers, lens arrays, diffractive gratings, and scattering introduced by
the movement of an element at a rate such that the scatter is not perceived by the human
visual system.
[0084] In one embodiment, the light diffusion is engineered to be anisotropic. One
reason to make the diffhser anisotropic is to overcome variations in the lamp output that are
more pronounced for some angles compared to others. Another reason to engineer an
anisotropic diffuser is to optimize overall system performance when anisotropic behavior
within other parts of the system exists. To illustrate this point, consider the case of electronic
projectors that use spatial light modulators to create an image on the screen. The modulators
themselves generally have a performance that is dependent upon the angle of light incident
upon them. For example, the off axis iUumination of a DMD modulator yields an
asymmetry in its scattering and diffraction characteristics. This anisotropic scattering and
diffraction from the modulator, relative to the optical axis of the system, leads to a
degradation in projection system contrast and efficiency. Another example is that of
projectors that employ LCD and LCOS modulators. Those modulators rely on polarized
light to achieve high contrast. Here contrast can be compromised by the angle dependent
leakage of light as skew rays propagate through the system. In either of these cases,
designing the characteristics of a diffuser with the knowledge of anisotropics that exist
elsewhere in the system allows one to optimize the projection system performance. Those
skilled in the art will realize that there are other examples of anisotropics existent in
projection systems and to which this embodiment applies.
[0085] The position in one embodiment of the diffuser 3 is near the focus 16 of the
lamps. However, other locations that are sufficiently distant from lens array 7A to minimize
loss from scattering may be used. la one embodiment, the diffuser 3 is placed near the pupil
of the illumination system (at lens array 7B) or any conjugate plane to that pupil, rn a one
embodiment, the diffuser 3 is placed near the output of the combining prisms 2 where the
lamp light is focused. Other possible conjugate planes to lens array 7B include those that are
formed through the addition of relays in the system.
[0086] A light pipe (also commonly known as an integrating bar, a light bar, or a
kaleidoscope), with appropriate optics, can be used in place of the fly's eye integrator to

achieve similar advantages when applied to the present invention. While the system size and
cost may be greater for a light pipe integrator, the multi-lamp method for light balancing and
improving operating efficiencies is just as applicable with this technology. As shown below,
the mixing properties of the light pipe will also benefit from the addition of a diffuser in front
of the light pipe's entrance to eliminate shimmer.
[0087] Figures 6 and 7 illustrate how the diffuser may be used with a light pipe integrator
to reduce shimmer at the image gate 10 and therefore at the screen. The diffuser 3 is
positioned in front of a light pipe, such as an integrating bar 18. Figure 6 shows how the
homogenized illuminance distribution, including any temporal modulations, located at the
output of the integrating bai 1S is imaged to the image gate 10 with appropriate magnification
to allow a slight over fill of the gate. The relay 19 that images the light to the image gate 10
also serves to couple the light to the pupil of a projection lens that follows. The pupil of the
relay 19 is shown as 20 in Figure 6.
[00SS] Figure 7 illustrates how light propagates from the lamp 1 to the output of the light
pipe, sueh as an integrator bar IS, according to one embodiment of the present invention. In
this illustration, the light pipe is illuminated by a single lamp 1. The light travels to the
output of the light pipe by total internal reflection for a solid light pipe, or reflection for a
hollow light pipe. The dashed lines in Figure 7 represent the envelope of the maximum
deviation cone caused by angular fluctuations from the lamp 1. The degree of
homogenization increases as the light pipe length is increased relative to its cross-section.
This is due to an increased number of reflections along the length of the light pipe. As the
light pipe is lengthened, the illumination system becomes less compact, manufacturing costs
increase and the efficiency of the system drops due to bulk and surface scattering through the
light pipe. The designer is therefore penalized by increasing the homogenizing performance
of the light pipe to address the added demands of shimmer reduction.
[0089] As with the fly's eye integrator, an alternative method is desired to eliminate
fluctuations that result in perceived sliimmer when the lamp is new and as it ages. The
addition of an engineered diffuser working in concert with the light pipe serves to reduce this
shimmer below the human visual system detection threshold. Figure 7 shows one
embodiment with the diffuser 3 placed near or at the input surface of the integrating bar 18.
The spatially dependent flicker is eliminated when the angular scattering is equal to or
exceeds the angular modulations from the lamp.

[0090] If the system is not limited by the etendue of the light output from the diffuser, the
system may be designed to ensure no light is lost through the introduction of the diffuser.
The dashed lines in Figure 6 show the increase in numerical aperture due to diffusion while
the solid lines show the chief and marginal rays corresponding to the output of the lamp
without a diffuser present. Should the image gate and or projection lens not be capable of
accepting light of the increased numerical aperture introduced by the diffuser, vignetting may
cause light loss through the system and can also result in contrast degradation. There are a
variety of ways to redesign the system to eliminate this problem. For example, a change in
the lamp reflector could be made to iUuminate the input of the light pipe with light of slightly
lower numerical aperture. This would lead directly to a reduction in the cone angle output
from the light pipe. The spot size at the entrance to the light pipe would increase but not
result in any loss because the system is not limited by the etendue of the lamp. Another way
to reduce the cone angle output from the light pipe would be to introduce a slight taper in the
light pipe. Here, the output cross-section would remain the same and the input cross section
of the light pipe would be decreased once again without incurring any efficiency penalties.
Shimmer Detection
[0091] An effective indicator of illumination system performance can be constructed
within the illumination system to ensure that performance is maintained to the end of the life
of the lamp. Such a system can automatically signal a warning to the operator that the lamps
require replacement before the audiences can perceive reduced performance. In addition, a
controller can be used to manage lamps oased on their performance. This includes the
possibility of switching to another lamp within a presentation or judiciously choosing which
lamp is to run at lower power to maximize presentation quality. By using two or more
sensors within the illumination system, the spatial/temporal modulations can be. monitored.
Signal processing meuiods, such as differencing the signal from these detectors, would give a
direct measure of the stability of the source. The active area of the sensors and tiieir spacing
would he designed to optimize sensitivity to fluctuations, allowing early warning of lamp
problems before they compromise the theatre experience.
[0092] As shown in Figure 1, in the preferred embodiment, the sensors, such as detectors
14, are placed behind the upper cold mirror 8 to detect the leakage of visible light or sample
the infrared light that is present in this location. In one embodiment, the detectors 14 are
positioned behind a lens so that modulations detected are directly proportional to modulations
seen at the input lens array 7A. The lens in front of the detector 14 acts as a telay so that the

detectors 14 lie in a plane conjugate to lens array 7A and die image gate 10. Thus each
detector 14 samples light that corresponds to a distinct location at the image gate 10. There
are advantages to limiting the aperture of the detector's relay lens so that the detector
monitors light from a subset of lenslets in lens array 7. First, limiting the aperture of the
detector's relay lens reduces the detection system size and cost. Second, the lateral position
of the detector assembly behind the upper cold mirror 8 can be judiciously chosen to observe
shimmer from a subset of lenslets.
[0093] The selection of a subset of lenslets maps directly back to a portion of the angular
intensity distribution output from the lamp and thus allows one to look at the shimmer
contribution from different positions on the reflector of the lamp. This ability to select a
region on the reflector is particularly advantageous when combined with the knowledge of
convective patterns present within the lamp. Multiple detector assemblies can be
incorporated to yield sMrnrner contributions from a variety of positions on the lamp. To
reduce the cost of such an implementation, a lens array can be used in front of the detectors
rather than using discrete lenses. Analysis of the signal from these detectors can allow the
extraction of data well correlated with the shimmer at the film plane. Those skilled in the art
will realize that this sampling of the light is not limited to this location.
Automated Retraction and Insertion
[0094] A stereoscopic projection system encodes the light so that left and right eye
images received by a viewer enter the proper eye with minimal light entering the wrong eye.
Light may be encoded by polarization, time multiplexing, color or direction plus any
combination diereof. In one embodiment, an automated controller of the projection system
inserts the encoder in the correct orientation automatically, eliminating an error prone and
tedious task for the projectionist. If left to the projectionist, the repetitive nature of the task
and limited time between presentations can lead to incorrect placement .of encoders. This
includes but is not limited to mixing up right eye and left eye encoders and inserting encoders
■ in the wrong orientation. These gross errors lead to unwatchable 3D presentations. If the
separation between left and right eye images is based on linearly polarized light, there exists a
strict requirement for die orientation of the linear polarizers to minimize ghosting. It can be
difficult to maintain this requirement when polarizers are manually inserted leading to sub-
optimum system performance. For a 2D presentation mode, the encoder or encoders are
automatically retracted. This overcomes the error of accidentally leaving the encoder or
encoders in place leading to a degradation in 2D presentations. FOT example, if the encoder is

a polarizer and it is left in, the 2D presentations become unacceptably dim. If the encoder is
a color filter then the 2D presentation is both dim and has unacceptable color. As seen in
Figure 1, a polarizer 12 is used to encode the light and is located in front of the projection
lens 11. OtheT locations within the projector are possible. The encoder or encoders may be,
for example, a linear polarizer, a circular polarizer, an elliptical polarizer, a shutter, a color
filter, or an active polarizer, such as a Z-screen. A variety of mechanical systems to retract
and insert the encoder or encoders into the optical path may be used including systems that
achieve the requirements through a means of translation or rotation.
[0095] When the projection system is used for 3D presentations, light that is lost
compared to output levels for 2D presentations may be partially recovered by automatic
removal of elements in the projection system. In one embodiment, an element or elements
that are normally needed to boost the quality of 2D presentations are automatically removed
to improve light levels. Such elements include, for example, masks for boosting the contrast
and color filters for improving the color quality of 2D presentations. To achieve optimum
overall performance such elements are removed in an automated fashion for 3D presentations
and inserted back in the system for 2D presentations. Masks are normally employed at or
near the pupil of a relay in the illumination chain. As well, a mask may be employed at or
near the pupil of the projection lens. This is to reduce previously disclosed anisotropic
unwanted light in specific directions that leaks through the system due to, for example,
scattering, diffraction, or polarization effects. A color filter may be a notch filter or filters to
increase color separation between color components.
Cold Mirror/Dowser
[0096] In one embodiment, a substantial component of the infrared (JR.) radiation from
the lamp illumination is removed by virtue of a dichroic coating on the cold mirror/dowser 5
shown in Figure 1. The IR radiation is transmitted through to the beam stop 13, while the
visible component of the lamps' radiation spectrum is reflected through to the lens arrays 7A,
7B. The cold mirror/dowser 5 protects the film and other downstream components from being
exposed to the excessive heat that would be generated by the DR. radiation were it not
removed from the optical path.
[0097] By mounting the cold mirror/dowser 5 on a hinge or other rotating or translating
mechanism, the cold mirror/dowser 5 can be moved completely out of the optical path. In
this position, all of the illumination light is directed to the beam stop, and no light is
permitted to escape from the projector's lens at all. Thus the projection system can be

darkened without extinguishing the lamp(s). The hybrid cold mirror/dowser 5 eliminates a
mechanical component typically found in projection systems, thereby reducing part count,
simplifying the design, and reducing size. It also allows the same single heat sink, such as
beam trap 13, that is used for the ER. light to be used for the visible light thus reducing
components again and simplifying thermal management allowing more compact system.
Cooling
[0098] Cooling die illumination is critical for stable operation and reliable performance.
The effectiveness of the cold mirrors in removing the fR from the illumination significantly
reduces the heat load on the second stage of the optical system, i.e. those parts of the system
downstream of the first cold mirror 5 shown in Figure 1. The second stage of the optical
system can be sealed and therefore protected from the surrounding environment This may
eliminate the requirement for cleaning and maintaining this stage of the optical system.
[0099] The first stage can also be maintained within a sealed enclosure with a filtered
forced air-cooling system providing the required ventilation. The filtered air can be pulled
from behind the beam stops through to the lamps. By filtering the cooling air prior to pulling
it into the enclosed environment of the illumination system, the cleanliness of the optics can
be assured. This reduces maintenance, increases reliability, and once again reduces operating
costs.
General
[00100] While the above description contains many specifics, these specifics should not be
construed as limitations on die scope of the invention, but merely as exemplifications of the
disclosed embodiments. Those skilled in the art will envision any other possible variations
that are within the scope of the invention. For example, the present invention is equally
applicable to large format film projections systems, 35mm film projection systems, and
electronic projection systems.

CLAIMS:
1. A shimmer-reducing projection system, comprising:
a) at least one light source (1);
b) a proj ection lens (11);
c) a shimmer-reducing diffuser (3) located between the light source (1)
and the projection lens (11)
characterised in that:
the diffuser (3) is located:
I) at or near a focal plane (16) of the light source (1); or,
II) near a pupil of the projection system (100) or any conjugate plane to
that pupil; or,
III) substantially at the focus point of light from a combining device where
light from the light source is focused.
1. The projection system of claim 1, wherein integrating optics (18) are located
between the projection lens (11) and the at least one light source (1).
3. The projection system of claim 2 wherein the integrating optics comprise a
fly's eye integrator (7A, 7B).
4. The projection system of claim2, wherein the integrating optics comprise an
integrating bar (18) and the diffuser is (3) located between the light source (1)
and the integrating bar.
5. The projection system of claim 2, wherein the integrating optics comprise an
integrating bar (18) and the diffuser (3) is located near the input to the
integrating bar.
6. The projection system of claim 5, wherein the diffuser (3) is located near the
pupil of an illumination relay (9) or any conjugate plane to the pupil of the
illumination relay.

7. The projection system of any of claims 1 to 6, wherein the diffuser (3) is a
holographic diffuser or a light scattering element or a diffractive element or a
moving element and/or is anisotropic.
8. The projection system of any of claims 1 to 6, comprising an engineered
diffuser (3) at or near the focal plane (16) of the light source (1), the diffuser
being designed so that it diffuses light from the light source over a range of
angles dictated by the angular perturbation cone of the light source.
9. The projection system of claim 8, wherein the light source (1) is a 2.4kW .
CERMAX lamps and the diffuser (3) has a Gaussian scattering profile with
full width half maximum (FWHM) equal to 1 degree thereby to remove 80%
of the existing shimmer to leave fluctuations well below the visual detection
threshold.

A shimmer-reducing projection system, comprising:
a) at least one light source (1);
b) a projection lens (11);
c) a shimmer-reducing diffuser (3) located between the light source (1)
and the projection lens (11)
characterised in that:
the diffuser (3) is located:
I) at or near a focal plane (16) of the light source (1): or,
II) near a pupil of the projection system (100) or any conjugate plane to
that pupil; or,
III) substantially at the focus point of light from a combining device where
light from the light source is focused.