Abstract:
A multiple path stereoscopic projection system is disclosed. The system comprises a polarizing splitting element configured to receive image light energy and split the image light energy received into a primary path and a secondary path, a reflector in the secondary path, and a polarization modulator or polarization modulator arrangement positioned in the primary path and configured to modulate the primary path of light energy. A polarization modulator may be included within the secondary path, a retarder may be used, and optional devices that may be successfully employed in the system include elements to substantially optically superimpose light energy transmission between paths and cleanup polarizers. The projection system can enhance the brightness of stereoscopic images perceived by a viewer. Static polarizer dual projection implementations free of polarization modulators are also provided.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The field of the present invention is the display of stereoscopic motion pictures, and more specifically to increasing image brightness in the projection of stereoscopic images. 
         [0003]    2. Description of the Related Art 
         [0004]    Stereographic moving images are frequently transmitted using projection systems, including but not limited to the ZScreen® product available from Real D and StereoGraphics® Corporation. A primary concern relating to stereoscopic image projection is the low brightness of the image on the screen. The ZScreen and other similar approaches employ at least one absorption sheet polarizer for stereoscopic image selection, and in case, the brightness of the image is reduced by at least fifty per cent. In other words, the stereoscopic image is less than half the brightness of a projected planar image. Since analyzer polarizers are used for image selection, the final brightness results from the losses of two parallel axes polarizers giving considerably less than half the planar brightness. 
         [0005]    One technique that has been employed to decrease the brightness loss due to projection using polarizer image selection is to use high gain projection screens. This method can partially mitigate the loss in brightness, but the fundamental light loss problem associated with absorption polarizers remains because sheet polarizers achieve their function by passing through light polarized along the polarizer&#39;s transmission axis and holding back the remainder of the light. The light held back heats the polarizer instead of providing useful illumination. 
         [0006]    It is therefore beneficial to address and overcome the brightness issue present in previously known stereoscopic image selection techniques for projection, and to provide a stereoscopic projection apparatus or design having improved brightness over devices exhibiting the light loss described herein 
       SUMMARY OF THE INVENTION 
       [0007]    According to a first aspect of the present design, there is provided an apparatus for projecting stereoscopic images. The apparatus comprises a polarizing splitting element configured to receive image light energy and split the image light energy received into a primary path (P path) of light energy along with a secondary path (S path) of light energy. The apparatus further comprises a reflector configured to receive secondary path light energy and direct reflected secondary path light energy toward a projection surface. A first polarization modulator is employed, the first polarization modulator positioned in the primary path and configured to receive the primary path of light energy, modulate the primary path of light energy into primary path light energy, and transmit primary path modulated light energy toward the surface or projection screen. 
         [0008]    A retarder and a secondary polarization modulator may be employed, the retarder configured to receive either the primary or secondary path of light energy and transmit rotated primary or secondary path light energy, and the secondary polarization modulator positioned in the secondary path and configured to receive the secondary path of light energy, modulate the secondary path of light energy into secondary path polarized light energy, and transmit secondary path modulated light energy toward a mirror or reflecting surface and then to the projection surface. 
         [0009]    According to a second aspect of the present design, there is provided a method of projecting stereoscopic images. The method comprises receiving image light energy, splitting the image light energy received into a primary path of light energy transmitted along a primary path and a secondary path of light energy transmitted along a secondary path. The method also comprises receiving secondary path light energy and directing reflected secondary path light energy toward a surface and modulating the primary path of light energy into primary path modulated light energy, and transmitting primary path modulated light energy toward the surface. 
         [0010]    According to a third aspect of the present design, there is provided an apparatus for projecting stereoscopic images. The apparatus comprises a splitter configured to split the image received into a primary path and a secondary path, a reflector positioned in the secondary path configured to reflect secondary path light energy, and a polarization modulator arrangement comprising at least one polarization modulator positioned in the primary path and configured to modulate the primary path of light energy. The polarization modulator arrangement additionally modulates secondary path light energy. 
         [0011]    According to a fourth aspect of the present design, there is provided an apparatus for projecting stereoscopic images. The apparatus comprises a polarizing splitting element configured to receive image light energy and split the image light energy received into a primary path of light energy transmitted along a primary path and a secondary path of light energy transmitted along a secondary path, a reflector configured to receive path light energy from one of primary path energy and secondary path light energy and the path light energy toward a surface, and a static polarizer element configured to rotate one of said primary path light energy and said secondary path light energy. 
         [0012]    These and other objects and advantages of the present invention will become apparent to those skilled in the art from the following detailed description of the invention and the accompanying drawings. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1A  illustrates a previous single path projection system design; 
           [0014]      FIG. 1B  shows the detailed construction and functionality of a polarization modulator usable in the present design, namely the ZScreen; 
           [0015]      FIG. 2  is a dual projection system for projecting stereoscopic images that has been employed for many decades; 
           [0016]      FIG. 3  illustrates the novel dual path projection system of the present design; 
           [0017]      FIG. 4A  represents uncompensated projection of stereoscopic images using the design of  FIG. 3A  having a reflective surface; 
           [0018]      FIG. 4B  shows reflection of a reflective surface; 
           [0019]      FIG. 4C  illustrates compensated projection using an altered, typically curved, reflective surface in the design of  FIG. 3 ; 
           [0020]      FIG. 4D  shows a deformable reflective surface or mirror that may be employed in the design of  FIG. 3  to provide S and P beam transmissions such as is shown in  FIG. 4C ; 
           [0021]      FIG. 5A  represents two dual path projection systems in an arrangement similar to  FIG. 2  but using two instances of the novel dual path projection design presented herein in a circular polarization arrangement employing polarization modulators; 
           [0022]      FIG. 5B  shows a linear polarizer alternative to the design of  FIG. 5A , using no polarizing modulators but operating in a different manner; 
           [0023]      FIG. 6A  is an alternate embodiment including elements to equalize the primary and secondary path lengths of light energy in an embodiment designed to achieve the same ends as those delineated in  FIG. 3 ; 
           [0024]      FIG. 6B  represents a dual projection version of the embodiment of  FIG. 6A ; 
           [0025]      FIG. 6C  shows a linear polarizer alternative to the design of  FIG. 6B , using no polarizing modulators but again operating in a fundamentally different manner; and 
           [0026]      FIG. 7  is a tabular compilation of various static polarizer design alternatives employable using the teachings provided herein. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0027]    The present design seeks to increase overall brightness in a projected stereoscopic image using polarization for image selection. The system creates a dual path arrangement that can greatly increase the brightness of the image perceived by the viewer—in essence almost doubling the amount of light energy projected on the screen. 
         [0028]    A previous stereoscopic projection system is described in  FIG. 1A . The design of  FIG. 1A  uses a single projector having imaging surface  101  and lens  102 . Mounted in front of the projection lens  102  is a ZScreen as manufactured and sold for more than a decade by StereoGraphics Corp. The ZScreen polarization modulator has been described in great detail in Lipton U.S. Pat. No. 4,792,850, which is hereby incorporated by reference. The image is produced using the field-sequential or time-multiplex format for the viewing of stereoscopic computer generated and camera produced images and is well known and understood. Observer  106  wearing polarizing image selection eyewear  105  views the image projected on screen  104  and that screen has polarization conserving characteristics. The ZScreen  103  is described in greater detail in  FIG. 1B  and is used in conjunction with at least one embodiment of this disclosure. The projector produces a stream of alternating left and right image fields and these fields of perspective information are selected for the appropriate eye by means of polarization image selection. The ZScreen electro-optical polarization modulator switches its characteristics of polarization at field rate between left and right handed circularly polarized light and the eyewear worn by the observer  106  use analyzers incorporating left and right handed circular polarizers. 
         [0029]    Note that in  FIG. 1A , as with every drawing presented herein, the drawing is specifically not to scale, either with respect to component sizes or the physical dimensional relationship between components. It is to be appreciated that the drawings are intended to disclose and teach the inventive concepts disclosed herein and the dimensions and relationships between the elements presented are not to scale. 
         [0030]      FIG. 1B  gives the detailed construction and functionality of the ZScreen or as it is also known, push-pull modulator. Ray  107  is representative of a central ray (and all image forming rays) of unpolarized light passing through device or ZScreen  102 . Ray  107  passes through linear polarizer  108  whose axis is given by the double-headed arrowed line  109 . The ZScreen, to properly modulate received light energy, requires the input of linearly polarized light. The ZScreen is made up of two electro-optical cells, or pi-cells, also known as surface mode devices, one shown as pi-cell  111  with axis  110 , and the other as pi-cell  112  with axis  113 . The pi-cells  111  and  112  are phase shifting devices and in this case they are tuned to quarter wave retardation so as to turn the linear polarized light input by polarizer  108  into circularly polarized light that alternates between left and right handedness. In order to perform properly, the orientation of the parts and their axes is as given in the drawing and described herein. The parts are substantially or precisely coplanar and the axes of the pi-cells are orthogonal and bisected by the axis of the polarizer. In other words, the linear polarizer axis is at 45 degrees to the axes of the pi-cells. 
         [0031]    The pi-cells are electrically driven out of phase and produce an effect similar or identical to that of a quarter wave retarder rapidly rotated through 90 degrees. In this manner, well known in the art, linearly polarized light is turned into circularly polarized light and because of the effective toggling of the axes of the pi-cells, left and right handed circularly polarized light is produced in synchrony with the field rate and image perspectives as projected. 
         [0032]    As used herein, electro-optical devices such as the ZScreen will be generically referred to as “electro-optical polarization modulators” or simply “polarization modulators.” Polarizers are a constituent component of the polarization modulator providing the required polarized light to enable modulator functionality. The polarization modulators disclosed herein are primarily electro-optical but other non-electro-optical devices may be employed. 
         [0033]    The polarizing device may be linear polarizers, circular polarizers, or a ZScreen and are typically of the sheet polarizer type. Other polarization producing devices may be used. By any one of these sheet polarizers (or polarization modulator devices as shown in  FIG. 5B ) the light of each projector is encoded with a certain specific polarization characteristic that can be analyzed by the eyewear or spectacles  208  such that each eye sees its appropriate perspective view. Each projector projects one of the two perspective views required for a stereoscopic image to be appreciated by observer  209 . The manner of producing and projecting these stereoscopic images is well known in the art, and reference is made to, for example,  Foundations of the Stereoscopic Cinema  by Lipton, published by Van Nostrand Reinhold, New York, 1982, which describes the general method of producing and projecting stereoscopic images, the entirety of which is incorporated herein by reference. Projection in this manner, usually using sheet linear polarizers, is extant in theme parks and location based entertainment venues. 
         [0034]    While the term “circular” is used herein with respect to the polarization, it is to be understood that with respect to polarization modulators such as the ZScreen, polarization is circular at the desired wavelength and may be elliptical at other wavelengths. As used herein, the term “circular” or “circular polarization” or “circularly polarized” is intended to cover any elliptical type of polarization, i.e. polarization at any wavelength under any generally elliptical and non-linear polarization. It is understood by those versed in the art that by relatively simple means, linear and circular polarization states may be managed so as to convert one type into another and nothing in this discussion precludes the use of one type when the other is referred to. 
         [0035]    The traditional method for projecting stereoscopic movies, first discussed more than  100  years ago, is described with the help of  FIG. 2 . Two projectors are used in conjunction with polarizers  205  and  206 , a polarization conserving screen  207 , and audience members  208  wearing analyzing eyewear  209 . The polarizers  205  and  206  shown are known as static polarizers and differ from the polarization modulators or ZScreen embodiments disclosed herein. The projectors are represented, first for the left machine, by image surface  201 , lens  203 , and polarizing device  205 . For the right machine the image surface is given by  202 , the lens by  204 , and the polarizing device by  206 . When projecting stereoscopic images or movies, the device of  FIG. 2  typically transmits images from image surface  201  and  202  at orthogonal axes, thereby producing the stereoscopic effect. 
         [0036]      FIG. 3  illustrates the layout of the present apparatus. The projection system includes an imaging surface  301  inside the projector and the projection lens  302 . Light from a source within the projector (not shown) is modulated by the imaging surface and sent to the projection lens. The light will generally be non-polarized exiting the lens, but in some instances, the light may be polarized to some extent. In a typical system, the light is eventually projected through a polarization modulator (or modulators)  304  and  307  such as the aforementioned ZScreen to a projection surface  309 , typically a projection screen. The system of  FIG. 3  separates the light beam or light energy into two paths, a primary path P and a secondary path S, or more specifically into orthogonal polarization states using a polarizing splitter  303 . Polarizing splitter  303  may be a polarizing beamsplitter such as a glass prism or MacNeille prism, or a wire grid polarizer, or other device able to create P and S beams with substantially orthogonal polarization states. In such a case the P rays  310  project straight through the splitter  303  and have one polarization orientation, along a primary path, and the S rays  311  are reflected along a secondary path with orthogonal polarization to the P rays. 
         [0037]    Polarization of the S rays is, in one embodiment rotated by 90 degrees using a half wave retarder  306 . In an alternative embodiment, the S ray polarization remains non-rotated and the P ray polarization is alternately rotated by placing the half wave retarder in the transmitted beam instead of the reflected beam, or in other words, a half wave retarder is placed after the polarizing splitter  303  or between polarizing splitter  303  and projection screen  309 . 
         [0038]    Rotation of the axes of the polarized beams, either P or S, is required in order to make the axes parallel. As employed herein, to clarify any issues regarding nomenclature, a beam designated as P or S indicates that beam comes from a splitter in that form, and thus while the beam may be altered in form by retarders or other components, the beam originally was either transmitted or reflected in the format identified. In the case of  FIG. 3 , the circular polarization resulting from the polarization modulators&#39; action typically provides a relatively high dynamic range when analyzed provided that the linear components&#39; axes of the polarizers and analyzers are orthogonal, which is relatively straightforward to manage as is known in the art. If the S and P beams have their axes orthogonal, the circularly polarized light outputted by the polarizing modulators or ZScreen will be made up of components of circularly polarized light partially made up of circularly polarized light whose maximum dynamic range may be analyzed at two positions orthogonal to each other. It is not possible to achieve this using the sheet polarizer analyzers currently available. Thus the axes of one beam must be rotated, but it is immaterial which so long as both enter the polarization modulators with axes parallel. 
         [0039]    Polarization beamsplitters may in some circumstances not provide a sufficiently pure linear polarization and can require a “clean-up” polarizer  305 , also referred to herein as a static polarizer. Such a clean-up polarizer  305  is generally known in the art and is optional in the configuration shown or in other configurations. In general practice, the transmitted beam P has a high degree of purity, and the reflected beam S less so. In embodiment of  FIG. 3 , the cleanup polarizer is required only in the reflected (S) or secondary beam path, but may also be placed in the primary path. Further, any clean-up polarizer may be placed in any location after the polarizing beamsplitter or wire grid polarizer  303  in the device shown. For example, while clean-up polarizer  305  is shown between the polarizing beamsplitter or wire grid polarizer  303  and half wave retarder  306  in practice clean-up polarizer  305  may be positioned between  307  and  305 , or in the P path between  303  and  311  or  311  and  304 . 
         [0040]    Once the P and S beams have achieved a high degree of polarization, the beams are then modulated by the polarization modulators or ZScreens  304  and  307  in the manner described in  FIG. 1 . At this point, the device is projecting two beams of light, the primary P beam and reflected beam or secondary S beam, respectively. 
         [0041]    The secondary S beam needs to bend in the direction of the projection screen  309 . A reflective surface such as a mirror  308  (or other reflecting device such as a prism) can be used to do this bending. The mirror  308  is capable of adjusting beam path angles such that the primary and secondary beams may be aligned precisely on the projection screen  309 . At this point the path length to the screen  309  is different for the two beams, and this will result in a difference in magnification and poor resultant image quality since the two images do not precisely overlap. The mirror  308  is therefore preferably deformable to provide optical power, adjust for the difference in magnification of the two beams, and substantially match the magnification of the primary path and secondary path to strike the same position on the projection screen  309 . The deformable mirror or reflective surface may be an essentially planar front surface mirror with a mechanical element  310  capable of pulling or pushing a point such as the center of the surface of the reflective surface to form an approximation of an elliptical surface to provide the required optical power. More than one mechanical element may be employed and any mechanical element employed may be positioned anywhere around the reflective surface. The mirror or reflective surface may also be deformed using other means, including but not limited to fabricating an appropriately optically powered reflective surface having curvature built therein, or deforming or altering the surface using means other than mechanical deformation. In addition a set of mirrors figured with various curvatures may be provided to be interchangeably used in the optical path in place of part  308  so that a mirror of the correct focal length may be chosen from amongst the set to cause the primary and secondary beams&#39; images to have the same magnification. 
         [0042]    While not shown in  FIG. 3  or any specific drawing, a single relatively large polarization modulator or ZScreen may be employed coving both P and S paths rather than the two polarization modulators or ZScreens  304  and  307 . In such an embodiment, the large ZScreen or polarization modulator would be placed in line or parallel to the screen  309  relative to polarization modulator or ZScreen  304  and extend upward to be positioned also between deformable reflective surface or mirror  308  and the screen  309 . One can imagine polarizing modulator  304  being extended upwards to cover the rays reflected by mirror  308 . 
         [0043]    Further, while not specifically shown in  FIG. 3 , an alternate arrangement may be employed wherein the P beam from the polarizing splitter  303  contacts a reflective surface and the S beam proceeds toward the screen  309  without contacting a reflective surface or mirror. Such an arrangement may be achieved if the imaging surface  301  and projection lens  302  are, for example, pointing in a direction 90 degrees offset from the screen  309  rather than directly at the screen  309 . The key is for the S and P light energy paths to substantially coincide at the screen  309  using reflective surfaces where required in order to achieve increased brightness. An embodiment using different components and altering the S and P paths is shown in  FIG. 6  described below. 
         [0044]    The representation of  FIG. 3  contemplates circular polarization with respect to various components shown, including but not limited to polarization modulators  604  and  607 . However, it should be noted that linear polarization may also be employed, replacing the circularly polarized or polarizing elements of  FIG. 3  with linearly polarized elements. 
         [0045]    As noted, the optical path lengths of the P-polarization and S-polarization states, as given in  FIG. 3 , are of unequal length. The S path is longer. Hence its image will be larger than the image formed by the P path. Albeit this is a small path difference compared with the throw from projector to projection screen but it is long enough to create a significant difference in magnification between the two beams. Both images must substantially coincide and be of the same magnification to within a fine tolerance. The resultant images, uncompensated, are shown in  FIG. 4A , wherein the S image is larger than the P image and should be brought into coincidence as shown in  FIG. 4C . 
         [0046]    Bringing images into coincidence is achieved using the deformable mirror  308  shown in  FIG. 3  and as additionally shown in  FIGS. 4B and 4D . The reflective surface or mirror  408  in its flat state or non-deformed state is shown at  403 . Mirror  408  is shown with a concave curve in  404 . Note that light rays  405  and  405 ′ originating from the extreme edges of the image are divergent compared to the light rays shown at  406  and  406 ′. The slight curvature required, exaggerated here from actual practice for didactic purposes, is provided by deforming the relatively thin mirror  408  by a minute amount by pulling on its center or a point on the rear of the mirror  308  as shown conceptually by element  310 . The mechanical means for achieving this are generally understood in the art and employed in various optical devices such as telescopes. In setting up the design, a technician adjusting the light enhancer or mirror  308  observes the screen  309 , possibly with a telescope from the projection booth, and by means of employing the proper target can make adjustments to element  310  and mirror  308 &#39;s curvature to bring the S and P images into coincidence. 
         [0047]    The present design may be employed not only for single projector projection as shown in  FIG. 3  for use with a polarization modulator such as a ZScreen or similar polarization switching device, but it may also be used for dual projection systems as described in  FIG. 2 .  FIG. 5A  shows a nearly identical arrangement of parts with the exception that the polarization device is replaced by the present design. All parts in  FIG. 5A  are shown mirror image as an illustration convenience. In  FIG. 5A , imaging surface  501  is an imaging surface associated with the left projector and lens  502  is the corresponding lens. Device  507  is the present dual path device placed in the optical path. The screen, surface, or polarization conserving screen  505  receives light energy and audience member  506  wears analyzing spectacles or eyewear  509 .The right projector imaging surface  503  includes corresponding lens  504  and dual path device  508 . 
         [0048]    The dual projection apparatus shown in  FIG. 5A  may be used for several approaches to projection. In every case described herein the P and S combiner operates as described above and polarization modulators such as the ZScreens are provided such as is shown in  FIG. 5A . One category of projection uses the ZScreen electro-optical polarization modulators such as polarizing modulators/ZScreens  5057  and  5077  employed in the steady-state mode as described in co-pending U.S. patent application Ser. No. 11/367,617, entitled “Steady State Surface Mode Device for Stereoscopic Projection,” inventor Lenny Lipton, filed Mar. 3, 2006, which is hereby incorporated by reference. Such polarization modulators serve to supply circularly polarizer light of left-handedness for one projector and right-handedness for the other. It is immaterial which projector provides left or right handed circularly polarized light. The modulators are not used to switch between polarization states as depicted, for example, in  FIGS. 3 and 6A  or in detail with respect to  FIG. 1B . Rather, each modulator is run as a tunable quarter wave plate so as to optimize its wavelength setting and substantially match the characteristics of the analyzers in the selection device eyewear. 
         [0049]    In the present design, the polarization modulator device is similar in functionality to that which is shown in  FIG. 5B  insofar as it resembles traditional devices used to project stereoscopic images with each projector assigned to the task of providing one and only one perspective view. 
         [0050]    In a second category of projection, the ZScreen electro-optical polarization modulator can be used in either one of two ways described in a co-pending application being concurrently filed, entitled “Dual ZScreen Projection,” inventors Matt Cowan, Lenny Lipton, and Josh Greer, the entirety of which is incorporated herein by reference. In the first sub-category the modulators are run in synchrony with each projector providing one perspective view. In other words, each projector provides a specific perspective view. 
         [0051]    In the second sub-category the left and right images are mixed for both left and right images to be projected by the left projector and both left and right images to be projected by the right projector. Such a design may be employed as the polarization modulators described herein with possible slight changes to the components described. 
         [0052]      FIG. 5B  removes the electro-optical polarization modulators from the design. From  FIG. 5B , the projection system includes an imaging surfaces  5001  and  5003  inside the projector (not shown) and projection lenses  5002  and  5004 . Light from a light source within the projector is sent to the corresponding projection lens. The system of  FIG. 5B  separates each light beam into two paths, a primary path P and a secondary path S, or more specifically into orthogonal polarization states using polarizing splitter  5058  and  5078 . Polarizing splitter  5058  and  5078  may be a polarizing beamsplitter such as a glass prism or MacNeille prism, or a wire grid polarizer, or other device able to create separate orthogonal polarization in the P and S beams. In such a case the polarized P rays  5020  and  5030  project straight through the splitter  5058  and  5078 , along a primary path, and the polarized S rays  5021  and  5031  are reflected along a secondary path. 
         [0053]    The polarized S ray is, in one embodiment rotated by 90 degrees using a half wave retarder  5054  and  5074 . In an alternative embodiment, the polarized S ray remains non-rotated and the polarized P ray is alternately rotated by placing the half wave retarder in the transmitted beam instead of the reflected beam, or in other words, a half wave retarder is placed after the polarizing splitter  5058 / 5078  or between polarizing splitter  5058 / 5078  and projection screen  5005 . 
         [0054]    Static polarizers  5055 / 5075  and  5057 / 5077  of opposite polarity are provided to provide the proper polarization for the light energy received. Any clean-up polarizer may be placed in any location after the polarizing splitter or wire grid polarizer  5058 / 5078  in the device shown. 
         [0055]    At this point, the device is projecting two beams of light, the primary P beam and reflected beam or secondary S beam, respectively. The secondary S beam needs to bend in the direction of the projection screen  5005 . A reflective surface such as a mirror  5051  or  5071  (or other reflecting device such as a prism) can be used to do this bending. The mirrors  5051  and  5071  adjust beam path angles such that the primary and secondary beams may be aligned precisely on the projection screen  5005 . The mirror  5051  or  5071  is therefore preferably deformable to provide optical power, adjust for the difference in magnification of the two beams, and substantially match the magnification of the primary path and secondary path to strike the same position on the projection screen  5005 . The deformable mirror or reflective surface  5051  or  5071  again may be an essentially planar front surface mirror with a mechanical element  5052  or  5072  capable of pulling or pushing a point such as the center of the surface of the reflective surface to form an approximation of an elliptical surface to provide the required optical power. As with  FIG. 3 , more than one mechanical element may be employed and any mechanical element employed may be positioned anywhere around the reflective surface. The mirror or reflective surface may also be deformed using other means. 
         [0056]    Two projectors having static polarizers are provided in the design of  FIG. 5B . The purpose of  FIG. 5B  as opposed to  FIG. 5A  is to provide a simple static polarizer design (linear or circular) that obviates the need for polarization modulators. Operation of the two embodiments of  FIGS. 5A and 5B  are fundamentally different. Rather than having a uniform circularly polarized pair of projection devices wherein the modulators produce alternating polarization states ( FIG. 5A ), the dual projection system of  FIG. 5B  produces images having orthogonal projection axes thereby producing the desired stereoscopic effect, and thus different images are projected by imaging surfaces  5001  and  5003 . 
         [0057]      FIG. 6A  shows an alternative embodiment of the system for enhanced stereoscopic projection. The implementation of  FIG. 6A  seeks to equalize the optical path lengths of the P and S beams. As in  FIG. 3 , the image is sent from the projector in the form of light energy provided from imaging surface  621  through a projection lens  601  and enters the splitter, or polarizing splitter  602 . Again, the polarizing splitter  602  may be any appropriate polarizing beamsplitter such as a glass prism or MacNeille prism, or a wire grid polarizer, or other device able to create separate P and S polarized beams. The P beam is polarized  612  when transmitted straight through the polarizing splitter  602  along a primary path and the S beam is polarized  611  when reflected from the splitter along a secondary path in the direction shown. The reflected beam or secondary path beam is reflected toward the projection screen  608  using a prism or front surface planar mirror  605 . The path length from the projector lens  601  to the projection screen  608  is increased by the length of the offset beam. The primary beam, P, has its polarization state rotated using a half wave retarder  604  so that its polarization is coincident with the polarization of the secondary S beam. Note that a retarder may be placed in either the transmitted or reflected beam path. 
         [0058]    A pair of prisms  605  and  620  or front surface mirrors is used to increase the path length of the transmitted beam in order to match the path length of the reflected beam. The purity of polarization of the reflected and transmitted beams may be inadequate, and thus the system may benefit from an optional clean-up polarizer  609 ,  610  on one or both of the beams, again position independent but positioned depending on circumstances that may be determined empirically. The beams are then modulated as described with respect to  FIG. 1  using the polarization modulators  606 ,  607 , such as ZScreens, and the light projected to the projection screen  608 . The arrangement of  FIG. 6  serves to substantially optically superimpose light energy transmission between the second path and the first path. 
         [0059]      FIG. 6B  illustrates essentially a dual projector setup that comprises two of the arrangement of  FIG. 6A . The image is sent from each projector in the form of light energy provided from imaging surface  6001 / 6051  through a projection lens  6002 / 6052  and enters the splitter, or polarizing splitter  6003 / 6053 . Again, the polarizing splitter  6003 / 6053  may be any appropriate polarizing beamsplitter such as a glass prism or MacNeille prism, or a wire grid polarizer, or other device able to create separate P and S polarized beams. The P beam  6020 / 6030  becomes polarized when transmitted straight through the polarizing splitter  6003 / 6053  along a primary path and the S beam becomes polarized  6021 / 6031  as it is reflected from the splitter along a secondary path in the direction shown. The reflected beam or secondary path beam is reflected toward the projection screen  608  using a prism or front surface planar mirror  6004 / 6054 . The path length from the projector lens  6001 / 6051  to the projection screen  608  is increased by the length of the offset beam. The polarization of the primary beam, P, is rotated using a half wave retarder  6007 / 6057  so that its polarization is coincident with the polarization of the secondary S beam. Note that a retarder  6007 / 6057  may be placed in either the transmitted or reflected beam path. 
         [0060]    A pair of prisms  6008 / 6058  and  6009 / 6059  or front surface mirrors is used to increase the path length of the transmitted beam in order to match the path length of the reflected beam. The purity of polarization of the reflected and transmitted beams may be inadequate, and thus the system may benefit from an optional clean-up polarizer  6005 / 6055 ,  6010 / 6060  on one or both of the beams, again position independent but positioned depending on circumstances. The beams are then modulated using the polarization modulators  6006 / 6056 ,  6010 / 6060  such as ZScreens, and the light projected to the projection screen  608 . 
         [0061]      FIG. 6C  is a similar design to that of  FIG. 6A  that omits the polarizing modulators, and in that regard resembles  FIG. 5B . As with  FIG. 5B , the purpose of  FIG. 6C  as opposed to  FIG. 6B  is to provide a simple static linear or circular polarizer design that obviates the need for polarization modulators. Operation of the two embodiments of  FIGS. 6B and 6C  are fundamentally different. Rather than having a uniform circularly polarized pair of projection devices wherein the modulators produce specific images ( FIG. 6B ), the dual projection system of  FIG. 6C  produces images having orthogonal projection axes thereby producing the desired stereoscopic effect, and thus different images are projected by imaging surfaces  6101  and  6151 . 
         [0062]    From  FIG. 6C , orthogonal images may be sent from each projector in the form of light energy provided from imaging surface  6001 / 6151  through a projection lens  6102 / 6152  and enters the splitter, or polarizing splitter  6103 / 6153 . Again, the polarizing splitter  6103 / 6153  may be any appropriate polarizing beamsplitter such as a glass prism or MacNeille prism, or a wire grid polarizer, or other device able to create separate P and S polarized beams. The P beam becomes polarized  6120 / 6130  when transmitted straight through the polarizing splitter  6103 / 6153  along a primary path and the S beam becomes polarized  6121 / 6131  when it is reflected from the splitter along a secondary path in the direction shown. The reflected beam or secondary path beam is reflected toward the projection screen  608  using a prism or front surface planar mirror  6104 / 6154 . The path length from the projector lens  6101 / 6151  to the projection screen  608  is increased by the length of the offset beam. The polarized primary beam P on one projector is rotated using a retarder  6107 . On the opposite projector, the opposite beam must be rotated, and in this case the secondary beam S is rotated using a retarder  6157 . Note that a retarder  6107 / 6157  may be placed in either the transmitted or reflected beam path. 
         [0063]    A pair of prisms  6108 / 6158  and  6109 / 6159  or front surface mirrors is used to increase the path length of the transmitted beam in order to match the path length of the reflected beam. The system also includes, as with  FIG. 5B , two static sheet polarizers of opposite polarity  6105 / 6155 ,  6110 / 6160 . Again, clean-up polarizers beyond the elements illustrated may be provided, positioned depending on circumstances. 
         [0064]    As may be appreciated from the foregoing description, different components may be employed in accordance with the current design, including different components placed in different relative orientations. To that end,  FIG. 7  is presented to show a general array of possible static polarizer designs in accordance with the current teachings. From  FIG. 7 , line  701  represents the element number from  FIG. 3  as a general reference to the element being discussed. As shown in  FIG. 7 , the first projector transmits a primary beam and a secondary beam, while the second projector also transmits a primary beam and secondary beam. Each beam for each projector includes a retarder and a clean up (linear) polarizer. Reading down the left column of the table of  FIG. 7 , group  702  is for a linear polarizer having a polarizing beam splitter assembly in symmetrical orientation, wherein one channel needs rotation. Group  703  is for a linear polarizer with one projector&#39;s polarizing beam splitter rotated 90 degrees about an optical axis. Group  704  is for a polarizing beam splitter arranged symmetrically on the left and right projectors, and group  705  is for one polarizing beam splitter oriented or rotated 90 degrees from the other. As may be appreciated from the next column, polarization may be linear for groups  702  and  703  and circular for groups  704  and  705 . 
         [0065]    Taking as a first example the third entry in group  702 , the polarization is linear, and for the first projector, the retarder for the primary beam is a half wave retarder, and no clean-up polarizer, corresponding to clean-up polarizer  311 , is required. For the secondary beam, no retarder, corresponding to retarder  306 , is required and no clean-up polarizer, corresponding to clean-up polarizer  305 , is required. For the second projector, the retarder for the primary beam is not required, and no clean-up polarizer, corresponding to clean-up polarizer  311 , is required, For the secondary beam, a half wave retarder, corresponding to retarder  306 , is necessary, but no clean-up polarizer, corresponding to clean-up polarizer  305 , is required. 
         [0066]    Taking as a second example the third entry in group  705 , the polarization is circular, and for the first projector, the retarder for the primary beam is a quarter left retarder, and no clean-up polarizer, corresponding to clean-up polarizer  311 , is required. For the secondary beam, a quarter right retarder is required, corresponding to retarder  306 , is required, and a linear clean-up polarizer, corresponding to clean-up polarizer  305 , is required. For the second projector, the retarder for the primary beam is a quarter left retarder, and again no clean-up polarizer, corresponding to clean-up polarizer  311 , is required. For the secondary beam, a quarter right retarder is necessary, corresponding to retarder  306 , and a linear clean-up polarizer, corresponding to clean-up polarizer  305 , is also required. The result is a polarizing beam splitter rotated 90 degrees from the other. 
         [0067]    The design presented herein and the specific aspects illustrated are meant not to be limiting, but may include alternate components while still incorporating the teachings and benefits of the invention, namely the dual path stereoscopic projection system disclosed and claimed herein. As noted, none of the drawings presented are to scale. While the invention has thus been described in connection with specific embodiments thereof, it will be understood that the invention is capable of further modifications. This application is intended to cover any variations, uses or adaptations of the invention following, in general, the principles of the invention, and including such departures from the present disclosure as come within known and customary practice within the art to which the invention pertains.