Abstract:
A mounting bracket ( 40 ) for suspending a clear aperture of the base face of a prism ( 30 ) has a frame providing a horizontal support surface for allowing light to pass through the clear aperture of the suspended prism ( 30 ). First, second, and third support elements ( 44, 46 ) are spaced apart on the frame for supporting the base face of the prism ( 30 ), suspending the clear aperture. The second and third support elements ( 44 ) are peripheral to the clear aperture. The center of gravity of the prism ( 30 ), vertically projected, lies on or within the triangle formed by the first, second, and third support elements ( 44, 46 ).

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention generally relates to apparatus and methods for mounting a prism in an optical apparatus and more particularly relates to a prism mounting apparatus and method for use in a high-energy illumination subsystem of an electronic color projection system.  
         BACKGROUND OF THE INVENTION  
         [0002]    Initially introduced as small-scale imaging devices for business presentation markets, electronic color projectors have steadily improved in overall imaging capability and light output capacity. In order for electronic motion picture projectors to compete with conventional motion picture film projectors such as those used in theaters, however, a number of significant technical hurdles remain. Among these hurdles is the need for providing sufficient illumination for large-scale image projection applications.  
           [0003]    The overall light path for electronic color projection can be considered as having three basic subsystems: an illumination subsystem for providing red, green and blue color light at sufficient brightness; a modulation subsystem comprising devices such as spatial light modulators for modulating each color light; and a projection subsystem for combining and projecting the modulated light towards a display screen. A key problem that must be resolved in design of the illumination subsystem of an electronic projector is providing sufficiently bright light for modulation and projection components.  
           [0004]    Referring to FIG. 1 a , there is shown an illumination apparatus  10  for providing, from a single white light source  20 , red, green, and blue light for modulation. Light source  20 , typically a xenon lamp or other high intensity white light source, provides light along an optical axis O through uniformizing optics  22 , such as an integrating bar or lenslet array and directed by a lens  24  to a color separator prism  30 . Color separator prism  30  may have the V-cube or V-prism configuration shown in FIG. 1 a , as is disclosed in U.S. Pat. No. 5,944,401 (Murakami et al.) and U.S. Pat. No. 5,357,289 (Konno et al.) Color separator prism  30  may alternately be an X-cube or X-prism, a Philips prism, or similar device. Color separator prism  30  typically uses a set of dichroic coated surfaces on glued-together prism segments, S 1 , S 2 , and S 3  for separating light into its component colors. Red light for modulation is then directed along red optical axis Or, blue light along blue optical axis O b , and green light along green optical axis O g .  
           [0005]    As can be readily appreciated from the block diagram of FIG. 1 a , the role of color separator prism  30  requires handling high intensity light at its input and, therefore, of handling intense heat. Increasing the brightness of individual color channels necessitates increasing the overall brightness of light that must be handled by color separator prism  30 . High-temperature glass sections have suitable coatings and are bonded together with optical adhesives. Mechanical drift and stresses from external mounting components can cause slight angular shifting of the dichroic surfaces within color separator prism  30 , with negative effects such as color shading and light loss. For this reason, support components for mounting color separator prism  30  within a projector chassis must allow for heat-related factors and must be designed to minimize heat build-up and to minimize the effects of thermal expansion due to unwanted thermal containment of the mounting mechanics.  
           [0006]    One conventional solution has been to make color separator prism  30  as large as possible, thereby spreading heat effects over a sizeable mass. However, this coarse approach prevents the design of more compact projection apparatus. Meanwhile, conventional prism mounting techniques for color separator prisms and other heat sensitive prism applications are characterized by mechanical complexity, over-constraint, crowding, and need for precision adjustment and allowance for heat effects. For example:  
           [0007]    U.S. Pat. No. 6,181,490 (Wun et al.) discloses an adjustable optical frame used for a prism in an optical combiner application in which a prism is enclosed within a complex sheet metal frame that provides multiple constraints on prism movement and expansion and has numerous adjustments;  
           [0008]    U.S. Pat. No. 3,848,973 (Merz et al.) discloses a prism holder for use in a light deflection system, in which a compression assembly is employed;  
           [0009]    U.S. Pat. No. 4,571,028 (Ziegler et al.) discloses a prism mount for a prism enclosed in a tube, which would not be well-suited to a high-heat environment due to containment of the prism;  
           [0010]    U.S. Pat. No. 5,749,641 (Brice et al.) discloses a color combiner or separator prism enclosed on five sides within a complex frame structure having multiple sections, with some frame sections used to support mounting of other optical components;  
           [0011]    U.S. Pat. No. 6,141,150 (Ushiyama et al.) discloses a dichroic prism mounting method using oversized components, requiring complex alignment procedures and presenting demanding adhesive requirements; and  
           [0012]    U.S. Pat. No. 6,010,221 (Maki et al.) discloses a prism mount for a projection apparatus, using a diecast holding member that surrounds the prism in an arrangement that would not be optimal for high heat applications and may over-constrain the prism.  
           [0013]    As a rule of thumb, the literature for prism mounting generally recommends using a kinematic configuration, such as mechanical compression, as is discussed in  Handbook of Optomechanical Engineering , Anees Ahmad, Editor, CRC Press, New York, N.Y., 1997, pp. 202-210. However, attempts to provide suitable prism mounting using spring forces, frames, or other mechanical constraints have proved inadequate to the task of providing a stable mount for a color separating prism in a high brightness projection apparatus, primarily due to thermal expansion and the need for cooling. Moreover, any type of mechanical device that applies a constraint or preloading force can obstruct the light path, thereby reducing the available brightness. When mounting a V-prism in the illumination path as a color separator, for example, it is necessary to allow, as far as possible, an unobstructed light path at multiple faces of the prism. In general, it is desirable to minimize the size of a color separator prism while, at the same time, maximizing its effective area for light propagation. Because a V-prism or other type of color separator prism is fabricated as an assembly of glued prism components, mounting schemes should minimize, equalize, or eliminate mechanical stress on glued seams. Unwanted stress birefringence can also occur due to constraining forces applied against any prism surface. These same heat and mounting stress considerations that apply for color separator prisms may also apply for color-combining prisms that combine separate monochrome color modulation paths to form a color output beam for projection, and for prisms used to separate or combine light paths in other applications.  
           [0014]    Thus it can be seen that there is a need for a prism mounting apparatus and method that is particularly well suited for use with a color separator prism or color combiner prism in a high-energy illumination subsystem of an electronic color projection apparatus.  
         SUMMARY OF THE INVENTION  
         [0015]    It is an object of the present invention to provide an apparatus and method for mounting a color separator prism in the illumination path of an electronic color projection apparatus, without requiring a mechanical preload, thereby minimizing or eliminating mechanical stress. With this object in mind, the present invention provides a mounting bracket for suspending a clear aperture of the base face of a prism, the mounting bracket comprising:  
           [0016]    (a) a frame providing a horizontal support surface;  
           [0017]    (b) a first, a second, and a third support element spaced apart on the frame for supporting the base face of the prism, suspending the clear aperture of the prism thereby, the second and third support elements being peripheral to the clear aperture; and  
           [0018]    wherein the center of gravity of the prism, vertically projected, lies on or within the triangle formed by the first, second, and third support elements.  
           [0019]    From another aspect, the present invention provides a mounting bracket for suspending a clear aperture of the base of a prism over an opening, the mounting bracket comprising:  
           [0020]    (a) a frame providing a horizontal support surface and defining the opening for allowing light to pass through the clear aperture;  
           [0021]    (b) a first, a second, and a third support element spaced apart on the frame for supporting the base face of the prism, suspending the clear aperture on the base of the prism over the opening thereby, wherein the second and third support elements are peripheral to the opening and wherein the center of gravity of the prism, vertically projected, lies on or within the triangle formed by the first, second, and third support elements.  
           [0022]    It is a feature of the present invention that it provides a three-point suspension mounting on a single glass section of a V-prism in one embodiment, so that the mount mechanism does not introduce stress to adhesively joined sections.  
           [0023]    It is an advantage of the present invention that it provides minimal obstruction to air flow for cooling the prism.  
           [0024]    It is a further advantage of the present invention that elements of a single-piece mounting bracket is in contact with the prism, thus minimizing mechanical effects due to thermal expansion. The apparatus and method of the present invention provide a non-kinematic mounting solution that is structurally robust and neither imposes mechanical constraints, nor exerts forces such as axial or shear loads upon the prism. The single-piece mounting bracket of the present invention is capable of supporting the weight of a color separator prism sized for the illumination requirements of a large-scale electronic projection apparatus.  
           [0025]    It is a further advantage of the present invention that it provides a mounting solution that does not stress glass seams within the prism.  
           [0026]    It is yet a further advantage of the present invention that it allows straightforward fixturing of a prism into a stable mounting position.  
           [0027]    It is yet a further advantage of the present invention that it provides a solution for suspension mounting of a prism that is relatively low-cost.  
           [0028]    It is a yet further advantage of the present invention that it provides a lens mounting scheme that allows for uniform thermal expansion.  
           [0029]    These and other objects, features, and advantages of the present invention will become apparent to those skilled in the art upon a reading of the following detailed description when taken in conjunction with the drawings wherein there is shown and described an illustrative embodiment of the invention. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0030]    While the specification concludes with claims particularly pointing out and distinctly claiming the subject matter of the present invention, it is believed that the invention will be better understood from the following description when taken in conjunction with the accompanying drawings, wherein:  
         [0031]    [0031]FIG. 1 a  is a schematic block diagram showing the basic components of the illumination path in an electronic projection apparatus;  
         [0032]    [0032]FIG. 1 b  is a perspective view identifying clear apertures of a color separator prism of the V-prism design;  
         [0033]    [0033]FIG. 2 is a perspective view showing a prism mount according to the present invention;  
         [0034]    [0034]FIG. 3 a  is a perspective exploded view showing the mounting bracket with the prism vertically displaced;  
         [0035]    [0035]FIG. 3 b  is a perspective view showing vertical projection of the center of gravity relative to mounting pads, using the method of the present invention;  
         [0036]    [0036]FIG. 4 is a perspective view showing the prism mount of the present invention in an arrangement with color filters and other supporting components in an illumination path;  
         [0037]    [0037]FIG. 5 is a perspective view showing one of a pair of possible locations on the prism where supplemental support may be applied without over-constraint;  
         [0038]    [0038]FIG. 6 is a perspective view showing a prism mount in another embodiment of the present invention; and  
         [0039]    [0039]FIG. 7 is a perspective view showing a fixture for prism alignment within the mounting bracket of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0040]    The present description is directed in particular to elements forming part of, or cooperating more directly with, apparatus in accordance with the invention. It is to be understood that elements not specifically shown or described may take various forms well known to those skilled in the art.  
         [0041]    As is shown in FIG. 1 a , color separator prism  30  has multiple light-transmitting portions. These “optically active” areas are termed the “clear apertures” of the prism. Referring to FIG. 1 b , each of the clear apertures of color separator prism  30  is represented in dotted outline. White light along axis O enters at an input clear aperture AO and is separated into a blue light that exits along axis O b  at a blue clear aperture Ab, a green light that exits along axis O g  at green clear aperture Ag, and a red light that exits along axis O r  at red clear aperture Ar. In order to provide the maximum brightness in each color channel, the ideal mounting solution for color separator prism  30  keeps each of these clear apertures AO, Ab, Ar, and Ag unobstructed. Of particular interest for the purposes of the present invention is red clear aperture Ar at the base of color separator prism  30 . The mounting solution of the present invention keeps red clear aperture Ar unobstructed while, at the same time, supporting color separator prism  30  in a stable mounting arrangement.  
         [0042]    Referring to FIGS. 2 and 3 a , there is shown a mounting bracket  40  for suspension mounting of color separator prism  30 , a V-prism in a preferred embodiment, on its base face B. Mounting bracket  40  provides a horizontal support surface and frames an opening  42  that allows an unobstructed light path through the red clear aperture Ar, that is, through the light-transmitting portion, of base B of color separator prism  30 . As is shown by the cross-section of light cone L in FIG. 3 a , indicated by dotted lines, the unobstructed light path is through a portion of opening  42  in the embodiment shown. Light cone L is represented as generally circular in FIG. 3 a ; in practice, however, light cone L can have the cross-sectional shape of a rounded rectangle. At a minimum, opening  42  should allow passage of light from light cone L into the clear aperture Ar or “working portion” of base B of color separator prism  30 . With the V-prism of the preferred embodiment, the clear aperture Ar of base B of color separator prism  30  is that portion of base B that lies below prism segment S 1 , as shown in FIGS. 1 a ,  1   b , and  2 . Opening  42  can be expanded further, beyond the area needed for light cone L, as is shown most clearly in FIG. 3 a , to allow more substantial air flow from below color separator prism  30  when in its suspended mounting position. A three-point seating is provided for base B of color separator prism  30 , with two rear mounting pads  44  and a front mounting pad  46  serving as support elements. For stable suspension of color separator prism  30 , allowing for some thermal expansion without imposing over-constraint, rear mounting pads  44  can be substantially aligned with the center of gravity C grav  of color separator prism  30 , as shown in FIGS. 3 a  and  3   b.    
         [0043]    Because the structure of color separator  30  is essentially homogeneous, the center of gravity C v coincides with its centroid of volume. For homogeneous 3-dimensional devices in general, using conventional x, y, and z axis coordinates, the center of gravity C grav  is the point ({overscore (X)}, {overscore (Y)}, {overscore (Z)}) where each coordinate is found by solving for the following, respectively:  
         {overscore (X)}ΣV=Σ{overscore (x)}V  
         {overscore (Y)}ΣV=Σ{overscore (y)}V  
         {overscore (Z)}ΣV=Σ{overscore (z)}V  
         [0044]    where V represents the volume. With the V-prism used as color separator prism  30  in FIGS. 2 and 3 a , its three planes of symmetry intersect at the centroid of its volume, that is, at the center of gravity C grav . Methods for computing the center of gravity for a homogeneous structure are well known in the mechanical arts and can be found in standard engineering texts.  
         [0045]    For stable suspension of color separator prism  30  over opening  42 , rear mounting pads  44  and front mounting pad  46  must be properly positioned with respect to the center of gravity C grav  of color separator prism  30 . Referring to FIG. 3 b , there is shown how this relationship is defined. Front and rear mounting pads  46  and  44  define a triangle T along the horizontal surface defined by mounting bracket  40 . The vertical projection of center of gravity C grav  of color separator prism  30  must lie on or within the bounds of triangle T. Otherwise, the mounting for prism  30  would be unstable and cause stress at adhesion points on front and rear mounting pads  46  and  44 . In a preferred embodiment, center of gravity C grav  of color separator prism  30  lies on the line between rear mounting pads  44 ; this arrangement maximizes the relative allowable size of the clear aperture of color separator prism  30  that is suspended over opening  42 .  
         [0046]    It is instructive to note that, given a V-prism configuration for color separator prism  30  and its arrangement within mounting bracket  40  as shown in FIGS. 2 and 3 a , conventional design practices would suggest using mounting pads or elements located at alternative mount points  51 ,  52 , and  53 , as labeled in FIG. 3 a . However, it can be seen that providing a mounting feature at alternative mount point  53  requires either of two compromises: (i) enlargement of color separator prism  30  or (ii) partial obstruction of light cone L. By design, however, color separator prism  30 , is designed to equalize optical path lengths for each color; thus, enlarging one leg of color separator prism  30  requires compensatory resizing of other components, adding bulk and weight. Obstruction of light cone L has undesirable effects, reducing the light available through opening  42  and therefore through the clear aperture of color separator prism  30  for the corresponding color path (the red light path in the embodiment of FIG. 1 a ). While an additional mounting feature at  50  may reduce sensitivity to vibration and lift, the need for such additional support is minimized by careful alignment of rear mounting pads  44  with respect to the center of gravity C grav  of color separator prism  30 , as was described with respect to FIG. 3 b.    
         [0047]    When seated as shown in FIG. 2, color separator prism  30  is adhesively fixed to mounting pads  44  and  46 . This three-point seating arrangement, following the rule for positioning mounting pads  44  and  46  relative to center of gravity C grav  of color separator prism  30 , thus provides sufficient mechanical constraint for color separator prism  30 , without redundancy and without the need for an adjustment or alignment mechanism integrated into mounting bracket  40 . In a preferred embodiment, an adhesive of an epoxy type is used for front mounting pad  46  adhesion, while a more flexible adhesive, such as an adhesive of an RTV type, is used for both rear mounting pads. Use of this combination of adhesives allows fixing contact firmly at front mounting pad  46  while allowing some slight flexibility for attachment at rear mounting points  44 , minimizing over-constraint at adhesion points, thereby minimizing or eliminating a possible cause of stress birefringence. Other adhesive types and combinations of adhesive types could be employed for adhesively fixing color separator prism  30  to mounting pads  44  and  46 , as is well known in the opto-mechanical arts.  
         [0048]    To support the mass of color separator prism  30 , which can easily weigh more than 1 lb. (0.5 kg or more), mounting bracket  40  must be structurally robust. In a preferred embodiment, mounting bracket  40  is a single piece of cast or machined aluminum. By comparison, prior art solutions using sheet metal structures, such as those disclosed in U.S. Pat. No. 5,749,641, for example, would require additional support features in order to adequately handle the weight requirement for color separator prism  30 . Additionally, sheet metal frame structures could be subject to objectionable levels of thermal shift.  
         [0049]    Front and rear mounting pads  44  and  46  are stainless steel pads in a preferred embodiment. Alternately, one or more mounting pads  44  or  46  could be an integral structural feature, cast as part of or machined into mounting bracket  40 .  
         [0050]    Unlike prior art solutions that house a prism within a frame, mounting bracket  40  allows unobstructed air flow over and around the surface of color separator prism  30 , with a minimum of obstruction of air flow at base B of mounting bracket  40  due to opening  42 . With this arrangement, potential hot-spots are eliminated or minimized.  
         [0051]    Mounting bracket  40  provides a generally vertical mounting surface  48  for attachment to a chassis structure within the color projection apparatus. Referring to FIG. 4, there is shown a compact arrangement of supporting optical components in a projection apparatus using mounting bracket  40 . Optical axis designations are the same as were shown in FIGS. 1 a  and  1   b . White light, provided along optical axis O, is directed through lens  24  toward color separator prism  30  by a mirror  38 . Color separator prism  30  provides blue light along axis Ob, upward in the configuration of FIG. 4. A blue color filter  34   b  is provided for improving the spectral characteristics of the blue light that has been reflected from an internal dichroic surface (not shown) within color separator  30  and out Ob. Green light is provided along axis Og, to the left in the configuration shown in FIG. 3. A green color filter  34   g  conditions the green light output along Og. Red light is provided along axis Or, downward in the configuration of FIG. 3, and is redirected by mirror  38 . A red color filter  34   r  is provided for the red illumination path; red color filter  34   r  is supported within-opening  42  of mounting bracket  40 , as is also shown in FIG. 2.  
         [0052]    Unlike conventional, complex sheet metal mounts having multiple adjustments and constraints, single-piece mounting bracket  40  provides a gravity-assisted three-point mount. A three point mount allows a minimum of contact between color separator prism  30  and its mounting bracket  40 , yet still provides a highly stable support arrangement. With the non-kinematic mounting solution provided by mounting bracket  40 , there are no external loading forces applied to color separator prism  30 , so that there is minimum stress on glued surfaces within color separator prism  30 . Advantageously, the use of a V-prism as color separator prism  30  places all three mounting pads  44  and  46  in contact with a single glass surface (the base of section S 2 , as shown in FIG. 2), causing no counteracting stresses on glued prism surfaces.  
         [0053]    Alignment of Color Separator Prism  30   
         [0054]    Using mounting bracket  40  of the present invention, color separator prism  30  does not require sensitive adjustments or alignment for seating and adhesion. Notably, no datum surface for color separator prism  30  alignment need be provided within mounting bracket  40  itself. Using conventional methods, a vertical datum surface or datum points could be provided on mounting bracket  40 , aligned with or parallel to mounting surface  48  as shown in FIG. 2. Color separator prism  30  would then be aligned against such a datum surface during assembly into mounting bracket  40 . It can be appreciated by those skilled in the opto-mechanical arts that a built-in datum surface, such as would be conventionally provided, introduces additional constraints, possibly causing asymmetric thermal expansion, and may introduce added mechanical stresses to color separator prism  30  glued surfaces.  
         [0055]    External fixturing can be provided for precision mounting of color separator prism  30  within mounting bracket  40  in a straightforward manner, simplifying mechanical alignment during adhesive curing time, for example. In a conventional fixturing scheme, mounting bracket  40  is temporarily mounted to a surface provided by the fixture. Then, color separator  30  is aligned in position on mounting bracket  40 , using mechanical datum points provided by the fixture, employing alignment techniques well known in the optical component assembly art.  
         [0056]    [0056]FIG. 7 shows one example of an alignment fixture  50  for use with mounting bracket  40 . Mounting fixture  40  is itself attached to alignment fixture  50  during alignment and curing. Using the reference set of x, y, z coordinate axes shown in FIG. 7, datum points  54  and  55  fix the position of color separator prism  30  in the y-direction. Datum point  56  then fixes the position of color separator prism  30  in the x-direction. Mounting pads  44  and  46 , on mounting bracket  40  itself, fix the position of color separator prism in the z-direction. It can be readily appreciated that it would be possible to build datum points  54  and  55  into mounting bracket  40  if desired.  
         [0057]    Use of Additional Support Elements  
         [0058]    As noted in the background section above, conventional design practices suggest prism mounting using kinematic techniques. The apparatus and methods of the present invention provide prism mounting with minimal constraints and unobstructed light paths for input white light and output monochromatic light; however, additional elements can be added to mounting bracket  40  in some cases, without obstructing the light path and without adding constraints that are unduly excessive. For example, where vibration levels pose a problem or a high degree of portability is needed for a projection apparatus using mounting bracket  40 , the application of additional support forces may be justified, even if this risks some slight amount of overconstraint. Referring to FIG. 5, there is shown one optional contact point area R, which would be paired with a corresponding, symmetric point area R′ (shown dotted) on the opposite face of color separating prism  30 . Applying a slight amount of kinematic force between point areas R and R′ may provide additional stability, without obstructing the light paths. As FIG. 5 indicates, the best position for point areas R and R′ would be at the center of prism segment S 2 . Alternate points of contact could be used; however, the best arrangement for minimizing stress on glued joints of color separator prism  30  would be to use contact points on prism segment S 2  only, for a V-prism in the configuration shown. At the points of contact, a flexible adhesive such as an adhesive of an RTV type can be used. (Direct metal-to-glass contact at both point areas R and R′ would not be recommended.) It must be emphasized that use of the optional contact point areas R and R′ shown in FIG. 5 is described by way of example only; other conventional methods could be used to add stability to the prism mount when required by the application. Additional support must be designed according to the specific loads applied, within the elastic region of the constraint. Key principles that should be followed in any case include maintaining unobstructed clear apertures for color separator prism  30 , maximizing open space around color separator prism  30  to allow air flow for cooling, and minimizing undue stress upon color separator prism  30 .  
         [0059]    It can be seen that the apparatus and method of the present invention provide, for color separator prism  30 , a suspension mounting solution that allows prism  30  to have minimum size while, at the same time, providing maximum allowable light path for each clear aperture of the prism.  
         [0060]    Alternative Embodiments  
         [0061]    In the embodiments of FIGS. 2, 3 a , and  3   b , mounting bracket  40  defines opening  42  for light passage through the suspended clear aperture of base B of color separator prism  30 . As is noted hereinabove with reference to FIG. 4, it is advantageous for opening  42  to be defined in this way, since mounting bracket  40  conveniently provides a suitable housing for color filter  34   r . However, in an alternative embodiment, the clear aperture Ar of base B of color separator prism  30  may be suspended without an opening  42  specifically defined. Referring to FIG. 6, there is shown an alternate mounting bracket  40 ′ for suspension mounting of color separator prism  30  in this way. Using the same basic principles described with respect to the first embodiment of FIGS. 2 through 5, alternate mounting bracket  40 ′ in FIG. 6 provides front and rear mounting pads  44  and  46  for seating color separator prism  30 . The alternative configuration of FIG. 6 uses the same relationship of mounting pads  44  and  46  with the center of gravity C grav  of color separator prism  30  that is described above with reference to FIG. 3 b.    
         [0062]    The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the scope of the invention as described above, and as noted in the appended claims, by a person of ordinary skill in the art without departing from the scope of the invention. While the embodiment described is for suspension mounting of a prism used as a color separator, the apparatus and method of the present invention could be more broadly applied to prism components in other applications, particularly where high-temperature conditions apply. For example, in some types of electronic color projector design, a color combining prism having the same overall V-structure of color separator prism  30  may be used. For a color combining prism, monochromatic and white light would travel in opposite directions from that shown in FIGS. 1 a  and  1   b , with red, green, and blue light provided as input to the prism, and synthesized white light as output for projection.  
         [0063]    Mounting bracket  40  allows the stable suspension of a prism over an opening while imposing minimal or no obstruction of light paths above, below, and to each side of the prism. Thus, mounting bracket  40  could be used with a wide range of prism designs in addition to the V prism configuration described hereinabove.  
         [0064]    Thus, what is provided is an apparatus and method for suspension mounting of a prism within an electronic color projection system.  
       Parts List  
       [0065]    [0065] 10  Illumination apparatus  
         [0066]    [0066] 20  Light source  
         [0067]    [0067] 22  Uniformizing optics  
         [0068]    [0068] 24  Lens  
         [0069]    [0069] 30  Color separator prism  
         [0070]    [0070] 34   r  Color filter, red  
         [0071]    [0071] 34   g  Color filter, green  
         [0072]    [0072] 34   b  Color filter, blue  
         [0073]    [0073] 38  Mirror  
         [0074]    [0074] 40  Mounting bracket  
         [0075]    [0075] 40 ′ Alternate mounting bracket  
         [0076]    [0076] 42  Opening  
         [0077]    [0077] 44  Rear mounting pads  
         [0078]    [0078] 46  Front mounting pad  
         [0079]    [0079] 48  Mounting surface  
         [0080]    [0080] 50  Alignment fixture  
         [0081]    [0081] 51  Alternative mount point  
         [0082]    [0082] 52  Alternative mount point  
         [0083]    [0083] 53  Alternative mount point  
         [0084]    [0084] 54  Datum points  
         [0085]    [0085] 55  Datum points  
         [0086]    [0086] 56  Datum points