Patent Publication Number: US-8526108-B2

Title: Image system with diffused imaging screen and method of manufacture

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 61/388,122, filed Sep. 30, 2010, and U.S. Provisional Application No. 61/433,143, filed Jan. 14, 2011, and U.S. Regular Utility Application No. 13/249,847, filed Sep. 30, 2011. 
    
    
     FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     None. 
     TECHNICAL FIELD 
     The present invention relates to diffused but transmissive optical image projection screens and methods of their manufacture, including screens comprising acetal polymers such as polyoxymethylene. Such screens may be used in various applications, including but not limited to image display and control systems adapted to produce high resolution color imagery optically coupled with a biocular. 
     BACKGROUND 
     A biocular is an optical system that produces an image that a user can view with both eyes. Biocular systems have been used as a means to magnify an electronically generated image, such as an image produced by a cathode ray tube (CRT). An example biocular is described in U.S. Pat. No. 5,151,823 to Chen, issued Sep. 29, 1992 (hereafter “Chen”), the entirety of which is incorporated herein by reference as if fully set forth herein. Bioculars have been used in head-up and head-down displays in modern military vehicles such as tanks and other armored vehicles, military and commercial aircraft, flight simulators, microscopes used to inspect semiconductor devices, and medical applications. Various video sources may be used to generate images that are displayed by a biocular, such as thermal imaging systems, day sight video cameras, night vision systems, and computer generated graphics, among others. An advantage of using a biocular eyepiece in a display system, as compared to a monocular eyepiece or a binocular eyepiece, is that the observer is able to freely move her or his head and use both eyes to see essentially the same image at the same light level on the same optical system. However, unconstrained movement between the user and the display can become a problem in tactical applications, where an image may need to be viewed carefully while the user is moving, for instance during combat. 
     Displays that use a biocular can offer the additional advantage of presenting a large virtual image to both eyes of the viewer from a small real image source, such as a very small cathode ray tube (“CRT”). Use of a very small CRT allows the overall package of the system to be compact in size, which is an important attribute in tactical applications such as aircraft, military vehicles and the like, where space is limited. 
     Tactical image display systems typically use a small monochromatic CRT as the active display element. However, small monochrome CRT&#39;s are unable to display color images and are generally limited in resolution and the ability to display high definition video imagery. These deficiencies severely limit the ability of such systems to support applications that require presentation of high quality color imagery. Accordingly, a need exists for an improved image display system, including one that is compact, efficient, reliable, and adapted to produce high-quality and high-resolution color images, and particularly one that is compatible with high definition color video sources, including digital sources. A need also exists for an improved image display system that is specially adapted to be used in tactical applications, where an image may need to be viewed carefully while the user is moving, for instance during combat. 
     In connection with optically coupled magnifying lens cells as discussed above as well as others, a need exists for an improved diffused but transmissive optical image projection screen adapted for use as a small (e.g., 1.62 inch×0.91 inch), yet high resolution (e.g., 1280×768, 1920×1080 or others) screen. 
     One of the biggest challenges facing the development of a small, high-resolution diffused but transmissive optical image projection screen, also known as a rear projection screen, is finding a suitable screen material with optical qualities that work well for this usage. Although there are numerous commercially available optical projection screen materials, most are designed for large projected images. Furthermore, the few materials advertised for use as a small, diffused but transmissive optical image projection screen do not work well at providing a clear, high resolution image without artifacts or other undesirable characteristics when used on a small rear projection image screen. 
     SUMMARY 
     The present invention solves these problems by providing screen materials and methods of manufacture that can be used to form small, diffused but transmissive optical image projection screens that provide clear, high resolution images without artifacts or other undesirable characteristics. It was only after testing numerous commercially available projection screen materials and other choices that the present inventors extended their research to materials not intended for this type of application. This included testing numerous types of plastics, paints, coatings, and liquid crystals. In the course of this research, the inventors unexpectedly discovered that polyoxymethylene and similar acetal materials worked surprisingly well as screen materials for these applications, even though these materials are not designed for this purpose and are typically used as lightweight and strong replacements for metal parts used in mechanical assemblies. Testing of these materials provided surprising, unexpected and unique results that have allowed the inventors to realize their goal of producing an improved diffused but transmissive optical image projection screen that is both small and capable of providing high-resolution color images. 
     Accordingly, provided is a diffused but transmissive optical image projection screen that works very well with small high resolution optical images. 
     In another aspect, provided is the use of a material not originally designed or intended for use as an optical image projection screen. 
     An additional aspect is the use of materials commonly known as Acetal, Polyoxymethylene, Polyacetal or Polyformaldehyde for an optical image projection screen. 
     In further aspects, provided is the use of a copolymer known by the trade name Celcon or a homopolymer known by the trade name Delrin for an optical image projection screen. 
     In a further aspect, provided is a diffused but transmissive optical image projection screen comprising commercially available thin film Acetal typically used as a friction reduction surface between mechanical parts. 
     In a further aspect, provided is a diffused but transmissive optical image projection screen comprising commercially available Acetal that has been formed, rolled, and cut in a manner to insure a smooth even surface with consistent thickness and the desired optical light diffusion and transmission properties. 
     In a further aspect, provided is a diffused but transmissive optical image projection screen suitable for use in a variety of applications including but not limited to small optical projection screens. 
     In a further aspect, provided is a diffused but transmissive optical image projection screen suitable for use in applications including but not limited to military display systems utilizing an optically coupled magnifying lens cell. 
     In a further aspect, provided is a diffused but transmissive optical image projection screen suitable for use in a variety of applications including but not limited to a direct view optical projection screen. 
     In a further aspect, provided is a diffused but transmissive optical image projection screen suitable for use in applications including but not limited to automotive and aircraft instrumentation and displays. 
     In a further aspect, provided is a diffused but transmissive optical image projection screen suitable for use in applications including but not limited to simulators and training systems. 
     In a further aspect, provided is a diffused but transmissive optical image projection screen suitable for use in applications including but not limited to commercial, industrial, military, and medical products. 
     In yet a further aspect, provided is an optical light diffusing screen suitable for use in diffused lighting systems including but not limited to area lighting and specialty lamps. 
     In a further aspect, provided is an optical light diffusing screen suitable for use in applications including but not limited to commercial, industrial, military, and medical products. 
     Further details regarding example embodiments of the invention are provided below with reference to the accompanying example figures. Additional aspects, alternatives and variations as would be apparent to persons of skill in the art are also disclosed herein and are specifically contemplated as included as part of the invention, which is limited not by any example but only by the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The following figures illustrate certain aspects of the design and utility of example embodiments of the invention. 
         FIG. 1  is a block diagram showing aspects of an example embodiment of an image system adapted to utilize a diffused imaging screen according to the invention. 
         FIG. 2  is an exploded top plan view of certain components of an example embodiment of an image system adapted to utilize a diffused imaging screen according to the invention. 
         FIG. 3  is an exploded perspective view of certain components of an example embodiment of an image system adapted to utilize a diffused imaging screen according to the invention. 
         FIG. 4  is a right side view of an example embodiment of an image system adapted to utilize a diffused imaging screen according to the invention. 
         FIG. 5  is a top plan section view of the example image system shown in  FIG. 4 , with section lines omitted for clarity. 
         FIG. 6  is a top plan section view of the example microdisplay video projector shown in  FIG. 5 , with section lines omitted for clarity. 
         FIG. 7  is a simplified block diagram showing an example closed-loop electronic control circuit that may be used in connection with image systems adapted to utilize a diffused imaging screen according to the invention. 
         FIG. 8  is a perspective view of an example diffused imaging screen assembly according to the invention, including an image source, a diffused but transmissive optical image projection screen, means to mount the optical image projection screen, and optical light paths. 
         FIG. 9  is an exploded perspective view of the example diffused imaging screen assembly of  FIG. 8 . 
         FIG. 10  is a perspective view of another example diffused imaging screen assembly according to the invention. 
     
    
    
     DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS 
     Example aspects, components and features of various embodiments of image systems  10  adapted to present high resolution color imagery are illustrated in  FIGS. 1 through 10  and are described below. As shown in  FIGS. 1-3 , example image control and display systems  10  may comprise a microdisplay video projector  20  that projects an image onto a diffused but transmissive optical projection screen  70 , which is optically coupled with and may be attached with a biocular  80 , that in certain embodiments is adapted to be mechanically coupled with a user. 
     Example microdisplay video projectors  20 , may comprise one or more microdisplay assemblies  30 , various projector optical components  40 , one or more projector illumination sources  50 , and one or more optical expansion and/or focusing cells  60 . Other microdisplay video projectors  20  suitable for this application may comprise fewer or additional components or elements as appropriate and as would be apparent to persons of skill in the art. 
       FIG. 5  shows the relative scale of certain major components of an example image system  10 , including a microdisplay video projector  20 , diffused but transmissive optical projection screen  70 , and biocular  80 .  FIG. 6  indicates the relative scale of various components of an example microdisplay video projector  20 , including projector illumination source  50 , optical components  40 , and optical expansion and focusing cell  60 . Details regarding these example components and how light travels through them to create high quality color images are provided below. 
     Example Light Path 
     With reference to  FIG. 3 , the path of light through an example image system  10  will now be described. Note that the following description is just an example, however; other examples may use substantially different designs and/or light paths and still fall within the scope of the invention, which is limited not by any examples but only by the claims. Projector illumination source  50  produces light, such as sequential red, green and blue (“RGB”) lighting. RGB light emissions from the projector illumination source  50  may be synchronized with and directed to corresponding presentations of RGB images on reflective microdisplay assembly  30 . This may be accomplished in the following example embodiment as follows. Light from the RGB lighting  51  is collected and concentrated by condensing lens  53  and directed towards scattering screen  54 . After passing through scattering screen  54 , the now concentrated and spatially uniform light source is directed at angled or “folding” mirror  45 . Folding mirror  45  collects light from illumination source  50  and reflects it at an approximately 90 degree angle or other angle appropriate to provide a flat field illumination to collection lens  44  and pre-polarizer  42 A. Collection lens  44  collects and concentrates the light as it passes through to pre-polarizer  42 A. Pre polarizer  42 A polarizes light by blocking or reflecting light having a first polarity and transmitting light having a second polarity. This polarized light then exits pre-polarizer  42 A and enters polarizing beam splitter  41 . 
     Light having a second polarity and entering polarizing beamsplitter  41  from pre-polarizer  42 A is internally reflected and directed towards microdisplay assembly  30  as shown in  FIG. 3 . Specifically, polarizing beamsplitter  41  collects light having a second polarity from pre-polarizer  42 A and reflects it at an approximately 90 degree angle or other angle appropriate to provide a flat field illumination to quarter wave plate  43 . Reflected light having a second polarity thus exits polarizing beamsplitter  41  and its polarity is then conditioned or reinforced by traveling through quarter wave plate  43 . Not all light entering polarizing beamsplitter  41  from illumination source  50  is effectively reflected towards quarter wave plate  43 . Some light from illumination source  50 , passes straight through polarizing beam splitter to strike the surface of color and brightness sensor  55 . 
     Light exiting quarter wave plate  43  then impinges the front surface of microdisplay assembly  30  and is selectively reflected by each pixel of reflective microdisplay  31  to form an image. More specifically, each pixel of reflective microdisplay  31  corresponds to a pixel of the digital image to be presented and is controlled by an array of electrodes (not shown). For example, each pixel of the reflective microdisplay  31  may be controlled to modulate light directed at the surface of the reflective microdisplay  31  to represent the relative intensity of the corresponding pixel of the video image to be displayed. Moreover, in this example embodiment, reflective microdisplay  31  changes the polarity of all the light it reflects so that the reflected light has a new, third polarity (which may or may not be the same as the first polarity) that allows the light to pass straight through polarizing beam splitter  41  without being blocked or reflected. 
     Accordingly, modulated light reflected from microdisplay assembly  30  passes straight back through quarter wave plate  43 , through polarizing beamsplitter  41 , and through post-polarizer  42 B, toward optical expansion and focusing cell  60 . 
     Light entering optical expansion and focusing cell  60  encounters relay lens  61 . Relay lens  61  by way of optical lenses serves to collect and focus light towards a fixed real image focal plane, where the diffused but transmissive optical projection screen  70  is located. Diffused but transmissive optical projection screen  70  provides a real image plane upon which to focus and present the image provided by microdisplay assembly  30  by way of optical components  40  and optical expansion and focusing cell  60 . 
     The image presented on the diffused but transmissive optical projection screen  70  may provide a high resolution color image plane appropriately sized and suitable for use with a biocular  80 . For example, diffused but transmissive optical projection screen  70  can be placed at the input aperture of a biocular  80 . 
     Biocular  80  provides the means to magnify the video image on the diffused but transmissive optical projection screen  70 , and presents this image to both eyes of the user as a large virtual image at infinite focus. 
     Example Projector Illumination Sources 
     With continued reference to  FIG. 3 , example projector illumination sources  50  will now be described. In certain embodiments projector illumination source  50  provides the light used to illuminate reflective microdisplay assembly  30 . Projector illumination source  50  may in various embodiments include, any or all of the following elements: red, green and blue (“RGB”) light emitting diode (“LED”) lighting  51 ; LED lighting control electronics  52 ; one or more condenser lenses  53 ; one or more scattering screens  54 ; and one or more sensors  55 , such as, by way of example and not limitation, RGB color and brightness sensors  55 . 
     Lighting such as RGB LED lighting  51 , may comprise for example one or more solid-state LED corresponding to each RGB color. RGB LED&#39;s may be mounted on a heat conducting and dissipating circuit board or other suitable surface. RGB LED&#39;s may be placed close together to approximate a single point light source. An example of RGB LEDs that may be suitable for use in various embodiments are available from Osram, Sylvania Inc. of Danvers, Mass. as part number LE ATB S2W-JW-1+LBMB-24+G. Although this particular part is a monolithic type device with the RBG LED&#39;s mounted in a single package, other package options may be used and are available, including single color LEDs. For example, a monochromatic spatial light system may be provided by only turning on single color LED&#39;s or by simultaneously turning on all three LED&#39;s to create a substantially white light source. Additionally, adjusting the color and tint of the RGB light source  51  and/or use of special night vision imaging system (“NVIS”) compatible lamps may be employed to provide a NVIS compatible lighting light system. 
     In the example embodiment shown in  FIG. 3 , light condensing lens  53  is adapted and positioned to collect light from LED lighting  51 , focus it and direct it toward scattering screen  54 . Alternative embodiments may incorporate a light cavity (not shown) or any other suitable structure that concentrates and directs light, such as, for example, internally reflecting materials or light pipes (not shown). 
     A scattering screen  54  may be adapted and positioned to diffuse light from RGB LED lighting  51  to provide more spatially uniform illumination. Scattering screen  54  may be formed of plastic, glass, or any suitable material that provides appropriate light scattering, diffusing, and transmissive properties. One example of a material that is able to provide non-Gaussian intensity distribution with high transmission efficiency is offered by Thorlabs of Newton, N.J. as part number ED1-S20, and is suitable in certain embodiments for use as a light scattering screen or diffuser  54 . 
     Color and brightness sensor  55 , shown in  FIG. 2  may comprise a color and/or brightness sensing device that may be adapted and located anywhere within the path of the illumination source  50  For example, a RGB color and brightness sensor  55  may comprise a photo diode with selective color films and electronic circuitry adapted to convert photo diode current to an electronic signal or digital value that is proportionate to the brightness and chromaticity of light applied to the surface of the sensor. The output of RGB color and brightness sensor  55  may be provided to LED lighting control electronics  52  as part of a control system that regulates color and/or brightness. An example of a digital RGB color and brightness sensor  55  suitable for certain embodiments is available from Taos Inc. of Plano Tex. as part number TCS3414C. 
     LED lighting control electronics  52  may comprise circuitry adapted to provide a voltage and current source to RGB LED lighting  51  as well as circuitry adapted to receive lighting control and timing signals from electronic circuitry and software  32 . Lighting control and timing signals may provide field sequential timing information that synchronizes operation of RGB LED lighting  51  with field sequential video imagery presented on microdisplay  31 . 
     LED lighting control electronics  52  may also receive brightness commands from external controls, whether automatically or by manual adjustment by a user, which may be used to adjust drive current and/or voltage to the RGB LED lighting  51  to brighten or dim the projector illumination source and the resulting image from the microdisplay  31 . LED lighting control electronics  52  may also employ pulse width modulation (“PWM”) to control, for instance, brightness and chromaticity of RGB LED lighting  51 . Brightness, chromaticity, and any other desired properties may be automatically controlled with a closed-loop active electronic control circuit. 
     For example, with reference to  FIG. 7 , a closed loop active electronic control circuit  100  may be provided to adjust and maintain chromaticity according to predetermined values across a range of possible brightness levels. Such an active control circuit may comprise circuitry and firmware that reads values from the RGB color and brightness sensor  55  and compares those to brightness commands provided by external sources, such as a user or another system. The result of this comparison may be used to influence the drive current and/or voltage to the RGB LED lighting  51 , to thereby maintain desired brightness and chromaticity. 
     In the example shown in  FIG. 7 , a closed-loop active electronic control circuit  100  is provided that may be used to adjust and maintain chromaticity according to predetermined values across a range of possible brightness levels. Such an active control circuit may comprise circuitry and firmware capable of reading values provided by RGB color and brightness sensor  55 , brightness commands from external controls  56 , and a myriad of other possible signals or inputs  57 , including but not limited to temperature sensors, external light sensors, communication links, and the like. Microprocessor  52 B and associated firmware may be adapted to provide look-up tables and control algorithms for comparing and correlating values read to predetermined and idealized values for brightness (luminance) and chromaticity (color). The result of this comparison, correlation, and use of preprogrammed look-up tables, algorithms, and control functions may then be used to proportionally influence the control signals provided to the LED drivers  52 C, and thereby maintain the desired brightness and chromaticity of RGB LED lighting  51  over a broad range of operating conditions and requirements. 
     Example Projector Optical Components 
     The description will now turn to various example projector optical components  40 . Projector optical components  40  may include in various example embodiments one or more polarizing beam splitters  41 , one or more pre-polarizers  42 A, one or more post-polarizers  42 B, one or more quarter wave plates  43 , one or more collection lenses  44 , and one or more mirrors  45 , among other elements. 
     Mirror  45  may comprise a silvered or polished surface selected and oriented to reflect visible light from projector illumination source  50 . In the example embodiment shown in  FIG. 3 , mirror  45  is set at an angle to collect light from projector illumination source  50  and redirect it to provide flat field illumination to collection lens  44 . As with the other components, some embodiments with a somewhat different optical path may not require mirror  45 . 
     Collection lens  44  may comprise an optical lens that is adapted to collect and focus light from projector illumination source  50  as reflected by mirror  45 . For example, collection lens  44  may concentrate light from illumination source  50  and direct the concentrated light to pre-polarizer  42 A before the light passes through to a polarizing beam splitter  41 . 
     Pre-polarizer  42 A may polarize light by blocking or reflecting light having a first polarity and transmitting light having a second polarity. In such an embodiment polarized light exits pre-polarizer  42 A and enters polarizing beam splitter  41  as shown in  FIG. 3 . 
     Polarizing beam splitter  41  may comprise a film (located for instance at the diagonally oriented plane bisecting cube  41 ) having one or more layers, including at least one layer that is an oriented birefringent material. Polarizing beam splitter  41  may further comprise a polarized reflecting element of the same orientation as the pre-polarizer  42 A (located for instance at the same diagonally oriented plane bisecting cube  41 ). Accordingly, in such an embodiment, as shown in  FIG. 3 , nearly all of the incoming light from projector illumination source  50  may be reflected approximately 90 degrees by mirror  45  and another approximately 90 degrees internally within polarizing beam splitter  41 . This light may then be directed out through quarter wave plate  43  toward microdisplay assembly  30 , as shown in  FIG. 3 . An example of a similar polarizing beam splitter  41  is a 20 mm Polarizing Cube Beam Splitter available from Edmund Optics of Barrington, N.J. as part number 48-573. 
     A quarter-wave-retarding wave plate  43  may be provided as shown in  FIG. 3  to correct the incoming and outgoing polarization states of the light incident on the microdisplay  31 , such that the light reflected during the dark (off-state) of the microdisplay  31  is minimized. In particular, the quarter-wave plate  43  may introduce a small phase shift in the polarization state of the light reflected from the microdisplay  31  such that the light that passes through quarter-wave plate  43  is very linearly polarized and will reflect efficiently from the polarizing beam-splitter  41 . An example of a similar achromatic quarter-wave-retarding wave plate is available from Bolder Vision Optik of Boulder, Colo. 
     Like quarter-wave-retarding wave plate  43 , a post-polarizer  42 B may be adapted and oriented to selectively allow only similarly polarized light to pass through to optical expansion and focusing cell  60 . This may improve contrast by helping to block all light except light reflected off microdisplay  31 . 
     Example Microdisplay Assemblies 
     Example aspects of microdisplay assemblies  30  will now be described. Microdisplay assemblies  30  may include one or more liquid crystal on silicon (“LCOS”) reflective microdisplays  31  and corresponding electronic circuitry and software  32 . In one embodiment, the LCOS reflective microdisplay  31  is capable of providing full color images. In alternative embodiments, high resolution color imagery may comprise a video projector  20  comprising two or more microdisplays  30  (for instance, individual ones for displaying red, green, blue, and other light, or combinations thereof), and/or a two or more panel microdisplay assembly  30  (such as a three-panel microdisplay) to provide a full color image. 
     In addition to or instead of using an LCOS reflective microdisplay  31 , microdisplay assembly  30  may use other types of reflective microdisplay technologies including but not limited to such as, for example, digital micro-mirror devices (“DMD”), ferro-electric liquid crystal on silicon devices (“FLCOS”), or any other suitable devices. Alternatively, microdisplay assembly  30  may comprise non-reflective displays, including but not limited to transmissive light valves such as liquid crystal displays (“LCD”), or any other suitable non-reflective displays. 
     Microdisplay assembly  30  may also be described as, or comprise, a spatial light modulator (“SLM”). 
     Alternatively, direct-view display technologies including but not limited to such as LCD type panels and/or emissive organic light emitting diodes (“OLED”) may be used with the biocular  80  if the image plane is sized and located to match the biocular input aperture optics and focal point. This may be accomplished by providing a display properly sized and located relative to the input aperture of the biocular, or by using optical expansion or reduction lenses to adjust the size and location of the image plane, as would be apparent to a person of skill in the art. Such a system could thus be configured to avoid the necessity of using the diffused but transmissive optical projection screen  70 . 
     In the embodiments where microdisplay  31  comprises an LCOS reflective microdisplay  31 , the microdisplay  31  may comprise an array of pixel electrodes (not shown) that are adapted to apply small electrical charges to a medium of liquid crystal material applied to the surface of an optical mirror. The small electrical charges applied to the pixel electrodes control the polarization of the liquid crystal associated with that pixel and operates as a light modulating polarizing medium when a polarized light source is directed to this surface. Accordingly, each pixel of the microdisplay  31  may be controlled to modulate light reflected from the surface of the microdisplay to represent the intensity of the corresponding pixel of the video image to be displayed. 
     An LCOS reflective or other microdisplay  31  may utilize a field sequential system adapted to display color images by sequentially presenting an image using each of the red, green and blue (“RGB”) colors and illuminating the corresponding portions of each sequential image with the appropriate (RGB) color. A spatial light system may also or alternatively be employed by simultaneously turning on all three LED&#39;s to create a substantially white light source. A spatial light system compatible with night vision imaging systems (“NVIS”) may be employed by adjusting the color and tint of the RGB light source and/or by use of lamps specially adapted to be used with NVIS. 
     An example of an LCOS reflective microdisplay  31  suitable for certain embodiments is the Aurora (OVT) full color sequential HED-5216 LCOS microdisplay with a resolution of 1280×768. This product is available at the time of writing from Holoeye Corporation, located at 3132 Tiger Run Court, Suite 112, Carlsbad, Calif. 92010. 
     An example embodiment of the electronic circuit and software  32  in the microdisplay assembly  30  will now be described. Input signals, including video input signals, may be provided to the electronic circuit and software  32  from any suitable source, including thermal imaging systems, day sight video cameras, night vision systems, and computer generated graphics, among others (not shown). When an active video input signal comprising encoded video image information is transmitted to electronic circuit and software  32 , electronic circuit and software  32  may translate and convert this signal to a digital representation of the encoded video image. This digital image is then converted to electrical control signals used to manipulate individual pixels of the microdisplay  31 , which may comprise an LCOS reflective microdisplay. Electronic circuit and software  32  may also decode video signal timing information from the active video input signal and use that information to generate and deliver synchronization signals to other video projector electronics, such as the projector illumination source  50 . 
     Electronic circuitry and software  32  may in certain example embodiments comprise a printed circuit board (shown in  FIG. 3  at  32 ) upon which LCOS reflective microdisplay  31  may be attached. In certain alternative embodiments, LCOS reflective microdisplay  31  may be connected with the printed circuit board of electronic circuitry and software  32 , via a flex cable or any other suitable interconnection system (not shown). Electronic circuitry and software  32  may further comprise multiple LSIC&#39;s (Large Scale Integrated Circuits), FPGA&#39;s (Field Programmable Gate Arrays), and other complex active electronics. Electronic circuitry and software  32  may also comprise software and firmware that include algorithms and control logic adapted to operate microdisplay  31 . Electronic circuitry and software  32  may additionally generate and deliver lighting control and timing signals to LED lighting control electronics  52  to synchronize operation of RGB LED lighting  51 . The underlying technical details regarding electronic circuit and software  32  that may be desired in various embodiments will be apparent to persons of skill in the art and are not repeated here in order to maintain the focus of this description on the overall system  10 . 
     Example Optical Expansion And Focusing Cells 
     Optical expansion and focusing cells  60  will now be described. In certain embodiments an optical expansion and focusing cell  60  may comprise one or more relay lenses  61 . A relay lens  61  may be a fixed lens or other optical element adapted to project an optical image to the real image plane of a diffused but transmissive optical projection screen  70 , where the optical image was projected from microdisplay assembly  30  and through projector optical components  40 . 
     In certain example embodiments, optical expansion and focusing cell  60 , when coupled with the other elements of microdisplay video projector  20 , may provide an image to the real image plane of a diffused but transmissive optical projection screen  70 , in a number of formats including but not limited to: 
     (A) 1.412″×0.794″, 1.620″ Diagonal, 2.945 Magnification; 
     (B) 1.575″×0.886″, 1.807″ Diagonal, 3.286 Magnification; 
     (C) 1.620″×0.911″, 1.859″ Diagonal, 3.379 Magnification; and 
     (D) 1.760″×0.990″, 2.019″ Diagonal, 3.672 Magnification. 
     An example of a similar optical expansion and focusing cell  60 , with a 25 mm compact-fixed-focal-length lens is available from Edmund Optics of Barrington, N.J. as part number NT59-871. 
     Example Bioculars 
     Turning to biocular  80 , in certain embodiments biocular  80 , may comprise one or more lenses or other structures that magnify the video image on the diffused but transmissive optical projection screen  70 , and presents this image to both eyes of the user as a large virtual image at infinite focus. For example, biocular  80  may comprise diffractive optical components, magnifying lenses, prismatic lenses, and other optical elements adapted to generate a large virtual image of the image presented on the diffused but transmissive optical projection screen  70 , described below. 
     A similar biocular has been described in U.S. Pat. No. 5,151,823 to Chen. An embodiment in Chen may be suitable for adaptation and use in certain embodiments, namely the embodiment shown in FIG. 2 of Chen, which is described as a biocular having a three-element biocular eyepiece system, including a first optical element having at least one diffractive surface, a second optical element having a refracting convex surface and a refracting concave surface, and a third optical element having a refracting convex surface. 
     In certain embodiments image control and display systems  10  are adapted to be coupled with the head of a user so that the user&#39;s head will move with and stay in relatively fixed alignment with biocular  80 , so that the user can readily maintain a steady view of biocular  80 , even during movements of a structure that biocular  80  may be attached to, such as a vehicle, aircraft, or the like (not shown). This may be accomplished by providing compliant material, such as low durometer elastomer, positioned between the biocular  80  and the head of a user (not shown) viewing an image presented by the biocular. 
     For example, as shown in  FIG. 3 , a brow pad  90  or other head or face support structure  91  formed at least in part from compliant material and adapted to support at least a portion of the head of a user (not shown) may be provided. The brow pad  90  or other head or face support structure  91  may be connected with the image display and control system  10  by being connected directly to the biocular  80  or to another nearby structure that moves with the biocular  80  during use. For example, in certain embodiments a brow pad  90  may be provided on the hull of a vehicle to which the biocular is connected, such that the user may rest their forehead on the brow pad  90  while viewing the image presented by biocular  80 . Alternatively or additionally, compliant material may be provided near the viewing portion of the biocular  80  for the user to rest their face while viewing the image presented by the biocular  80 , as shown by the face support pad  91  in  FIG. 3 . Any combination of brow pads  90 , face support pad  91 , or similar compliant material may be used to adapt image control and display systems  10  so that the biocular  80  is mechanically coupled with a user during use, so that the user&#39;s head and biocular  80  move together in a synchronized fashion during use. When used in this sense, “mechanically coupled” does not necessarily mean rigidly fixed, but means sufficiently connected to prevent excessive relative movement between the user&#39;s head and biocular  80 , such as when a user rests their forehead on a brow pad  90  affixed to structure connected with biocular  80 . This can be especially useful in tactical environments such as military applications, where a user may need to carefully view a display while the vehicle moves and engages in combat. Furthermore this adaptation to provide a stabilized viewing image while a vehicle is in motion may also reduce the likelihood of the user experiencing motion sickness or other undesired effects due to unsynchronized movement of the user and display during viewing. 
     Example Diffused But Transmissive Optical Projection Screens 
     Next, examples of diffused but transmissive optical projection screens  70  will be described. Diffused but transmissive optical projection screens  70  may comprise a polarization-independent scattering screen with optical qualities optimized to present video imagery to a biocular  80  from a microdisplay video projector  20 . Example optical qualities that may be considered for optimization include but are not limited to lambertian dispersion, light transmission, and low distortion. 
     Diffused but transmissive optical projection screens  70  may be formed from any materials that provide the diffused but transmissive qualities required to present high resolution video imagery to the biocular. In certain embodiments transmissive optical projection screens  70  may be formed from any or all of polymers, polytetrafluoroethylene (PTFE), acetal copolymer films, polymer dispersed liquid crystal, glass, or any other suitable material. Various materials for diffused but transmissive optical projection screens  70  may be manufactured and formed using heating, cooling, pressing, extrusion, adhesive bonding, and the like. 
     With reference to  FIG. 5 , diffused but transmissive optical projection screen  70  may in certain embodiments be sized to be as large as or larger than the input aperture of the biocular  80 . Diffused but transmissive optical projection screen  70  may in various embodiments be bonded, laminated, or otherwise mounted to glass, plastic, or any other suitable substrate, to provide a mounting structure adapted to be attached to or aligned with the input aperture of biocular  80 . 
     For example, with reference to  FIGS. 8 and 9 , shown is an example embodiment of an optical image projection system comprising an image source  130 , a diffused but transmissive optical image projection screen  70  comprising a thin sheet of Acetal  110  positioned between layers  120 ,  121  of optical glass or plastic substrate. Example optical light paths  140  are shown projecting from the image source  130  to the diffused but transmissive optical image projection screen  70 , which then projects optical light paths  141 . 
     With reference to  FIGS. 8 and 9 , optical image projection screen  110  may comprise a thin sheet of Acetal polymer, for instance approximately 0.001 inch to 0.020 inch thick, sized to accommodate the desired optical image size projected from image source  130 . Optical glass or plastic substrate  120  and  121  may provide a planar or other supporting surface to which the optical image projection screen  110  may be attached or sandwiched between. Optical light paths  140  and  141  represent the light path from projected image source  130 , through optical glass or plastic substrate  120 , on to a proximate side of optical image projection screen  110 , away from a distal side of optical image projection screen  110 , and out through optical glass or plastic substrate  121 . 
     Optical glass or plastic substrate  120  and  121  may comprise ultraviolet (UV), anti-reflecting (AR), and optical light filters or coatings to improve optical performance and reduce potentially damaging effects of UV and other radiation on optical image projection screen  110 . 
     Optical glass or plastic substrate  120  may not be required, for instance in applications where optical image projection screen  110  is bonded directly to optical glass or plastic substrate  121 . Optical glass or plastic substrate  120  and  121  may also not be required in applications where optical image projection screen  110  is manufactured to provide a thicker outer edge allowing independent mounting. Optical glass or plastic substrate  120  and  121  may likewise not be required in applications where optical image projection screen  110  is mounted by means other than with use of an optical glass or plastic substrate. 
     With reference to  FIG. 10 , shown is an example embodiment of an alternative diffused lighting system consisting of light source  130 , optical light diffusing screen  70  made from an Acetal material  110 , and optical light path  140  and  141 . With reference to  FIG. 10 , light source  130  may be any number or type of light sources including but not limited incandescent, fluorescent, halogen or others as is known in the art. Optical light diffusing screen  70  may comprise a sheet or fabricated part made of an Acetal type polymer of an appropriate thickness to provide the desired optical diffusion and transmission properties suitable for the particular application. Diffused optical light paths  140  and  141  represent the light path of the light source  130 , entering through a proximate side  140  of the light diffusing screen  70 , and exiting through a distal side  141  of the diffused lighting system. 
     Suitable Acetal polymers for optical light diffusing screen  70  may include Polyoxymethylene (commonly referred to as POM and also known as polyacetal or polyformaldehyde), an engineering thermoplastic typically used in precision parts that require high stiffness, low friction and excellent dimensional stability. POM is available from Ticona Hostaform under the trademark Celcon, from DuPont under the trademark Delrin, from Polyplastic under the trademark Duracon, from Korea Engineering Plastics under the trademark Kepital, from Mitsubishi under the trademark Jupital, and from BASF under the trademark Ultraform. 
     POM is characterized by its high strength, hardness and rigidity to −40° Celsius. POM is intrinsically opaque white, due to its high crystalline composition, but it is available in all colors. POM has a density of ρ=1.410-1.420 g/cm3. POM homopolymer is typically a semi-crystalline polymer (75-85% crystalline) with a melting point of 175° Celsius. The POM copolymer typically has a slightly lower melting point of about 162-173° Celsius. POM is a tough material with a very low coefficient of friction. However, it is susceptible to polymer degradation catalyzed by acids, which is why both polymer types are stabilized. Both homopolymer and copolymer have chain end groups (introduced via end capping) which resist depolymerization. With the copolymer, the second unit normally is a C2 (ethylene glycol) or C4 (1,4-butanediol) unit, which is introduced via its cyclic acetal (which can be made from the diol and formaldehyde) or cyclic ether (e.g. ethylene oxide). These units resist chain cleavage, because the O-linkage is then no longer an acetal group, but an ether linkage, which is stable to hydrolysis. POM is sensitive to oxidation, and an anti-oxidant is normally added to molding grades of the material. Typical characteristics of POM include: high abrasion resistance; low coefficient of friction; high heat resistance; good electrical and dielectric properties; and low water absorption. 
     Different manufacturing processes may be used to produce the homopolymer and copolymer versions of POM. To make polyoxymethylene homopolymer, anhydrous formaldehyde must be generated. The principal method is by reaction of the aqueous formaldehyde with an alcohol to create a hemiformal, dehydration of the hemiformal/water mixture (either by extraction or vacuum distillation) and release of the formaldehyde by heating the hemiformal. The formaldehyde is then polymerized by anionic catalysis and the resulting polymer stabilized by reaction with acetic anhydride. A typical example polyoxymethylene homopolymer is DuPont&#39;s Delrin. 
     To make polyoxymethylene copolymer, formaldehyde is generally converted to trioxane. This is done by acid catalysis (either sulfuric acid or acidic ion exchange resins) followed by purification of the trioxane by distillation and/or extraction to remove water and other active hydrogen containing impurities. Typical copolymers are Hostaform from Ticona and Ultraform from BASF. 
     The co-monomer is typically dioxolane but ethylene oxide can also be used. Dioxolane is formed by reaction of ethylene glycol with aqueous formaldehyde over an acid catalyst. Other diols can also be used. Trioxane and Dioxolane are polymerized using an acid catalyst, often boron trifluoride etherate, BF3 OEt2. The polymerization can take place in a non-polar solvent (in which case the polymer forms as a slurry) or in neat trioxane (e.g. in an extruder). After polymerization, the acidic catalyst must be deactivated and the polymer stabilized by melt or solution hydrolysis in order to remove the unstable end groups. Stable polymer is melt compounded, adding thermal and oxidative stabilizers and optionally lubricants and miscellaneous fillers. 
     While POM is described in detail above as an example, any suitable Acetal material may be used for optical light diffusing screen  70 . 
     Although exemplary embodiments and applications of the invention have been described herein, there is no intention that the invention be limited to these exemplary embodiments and applications or to the manner in which the exemplary embodiments and applications operate or are described herein. Indeed, many variations and modifications to the exemplary embodiments are possible, as will be apparent to persons of skill in the art. Accordingly, the invention is limited only by the scope of the claims. Unless otherwise specified, the phrase “adapted to” indicates characteristics of structure, namely that that the structure comprises the necessary characteristics as disclosed or suggested herein and therefore has been particularly adapted as stated. Accordingly, unless otherwise specified, the phrase “adapted to” does not indicate a method or steps.