Patent Publication Number: US-2011063586-A1

Title: Projection display device

Description:
This application claims priority under 35 U.S.C. Section 119 of Japanese Patent Application No. 2008-134479 filed May 22, 2008, entitled “PROJECTION DISPLAY DEVICE”. The disclosure of the above application is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to projection display devices that enlarge and project an image in an imager onto a projection plane, and is in particular suitable for use in projection display devices that project light in an oblique direction onto the projection plane. 
     2. Disclosure of Related Art 
     There have been commercialized and widely used projection display devices (hereinafter, referred to as “projectors”) that enlarge and project an image in an imager such as a liquid crystal panel onto a projection plane (a screen or the like). Among this type of projectors, there has been proposed a projector performing oblique projection in which a projection optical system forms a wider angle and a traveling direction of projection light is tilted relative to a light axis of the projection optical system, thereby to shorten a distance between a screen and the projector body. 
     The projector of oblique projection can be realized by using a projection lens unit (refractive optical system) and a mirror (reflective optical system) as a projection optical system, for example. In this configuration, an image in an imager is formed as an intermediate image between the projection lens unit and the mirror, and the intermediate image is enlarged and projected by the mirror. According to this configuration, a wide angle can be realized by a comparatively small curved mirror, thereby suppressing cost increase and upsizing of the projector body. 
     If the foregoing projection optical system is applied to a projector, the projector may be configured as shown in  FIGS. 18A and 18B , for example.  FIG. 18A  shows a projector installed to project an image onto a desktop or a floor surface.  FIG. 18B  shows a projector installed to project an image onto a wall surface or a screen. 
     A casing  1000  contains an optical engine  1100  that generates image light modulated in accordance with an image signal. The generated image light is entered into a refractive optical system  1200 . The image light having passed through the refractive optical system  1200  is reflected and converged by a reflective mirror  1500 . 
     The reflective mirror  1500  has an aspherical or free-form concave reflecting surface, and is shifted opposite to a projection window  1400  from a light axis L of the refractive optical system  1200 . The image light reflected by the reflective mirror  1500  passes through the projection window  14 , and then is projected at a wider angle onto the projection plane. 
     In this configuration, a size of a projected image (hereinafter, referred to as “projection size”) is increased or decreased by changing a distance between the projector and the projection plane. The projection size can be increased by moving the projector away from the projection plane. 
     In the foregoing projector, a distance between a final optical component of the projection optical system (the reflective mirror  1500  in  FIGS. 18A and 18B ) and the projection plane (hereinafter, referred to as “throw distance”) is desirably made short as much as possible, for the following reason as an example. 
     Specifically, the shorter throw distance, the light projected from the projection window  1400  becomes less prone to be cut off by an obstacle, which makes it easy to suppress occurrence of shades on a projected image. In addition, the shorter throw distance with the projector closest to the projection plane (minimum throw distance), a lower limit of the projection size can be further decreased. This widens a range of projection size that can be adjusted by moving the projector closer to or away from the projection plane. 
     However, in the configuration of  FIGS. 18A and 18B , the optical engine  1100 , the refractive optical system  1200 , and the reflective mirror  1500  are arranged in line parallel to a plane on which optical components are mounted in the optical engine  1100 , whereby a size D of the projector body is longer in the direction of arrangement of these three components. Therefore, a throw distance H becomes long even if the projector is made closest to the projection plane, as shown in  FIGS. 18A and 18B . 
     Besides, in the foregoing configuration, an outer shape of the projector body is prolonged in the above-mentioned direction of arrangement, and therefore the projector loses postural stability and is apt to tumble when the projector is installed for projection onto a floor surface, as shown in  FIG. 18A . 
     SUMMARY OF THE INVENTION 
     A projection display device in a first aspect of the present invention includes: an optical engine that emits image light modulated in accordance with an image signal in a direction parallel to a projection plane or in a direction tilted relative to the projection plane at a predetermined angle; a first reflective optical system that reflects the image light in a first direction away from the projection plane; a second reflective optical system that reflects the image light reflected by the first reflective optical system in a second direction away from the optical engine and closer to the projection plane, thereby to enlarge and project image light onto the projection plane; and a refractive optical system that is interposed between the optical engine and the second reflective optical system. Here, the refractive optical system is divided into a first refractive optical system interposed between the optical engine and the first reflective optical system, and a second refractive optical system interposed between the first reflective optical system and the second reflective optical system. In addition, the optical engine is arranged in such a manner that a mounting plane of optical components is almost perpendicular to a plane parallel to both of the first and second directions and is almost parallel to the projection plane. 
     A projection display device in a second aspect of the present invention includes: an optical engine that emits image light modulated in accordance with an image signal in a direction parallel to a projection plane or in a direction tilted relative to the projection plane at a predetermined angle; a first reflective optical system that reflects the image light in a first direction away from the projection plane; a second reflective optical system that reflects the image light reflected by the first reflective optical system in a second direction away from the optical engine and closer to the projection plane, thereby to enlarge and project image light onto the projection plane; and a refractive optical system that is interposed between the optical engine and the second reflective optical system. Here, the refractive optical system is divided into a first refractive optical system interposed between the optical engine and the first reflective optical system, and a second refractive optical system interposed between the first reflective optical system and the second reflective optical system. In addition, optical components constituting the optical engine are scattered in a direction that is almost perpendicular to a plane parallel to both of the first and second directions and is almost parallel to the projection plane. 
     A projection display device in a third aspect of the present invention includes: an optical engine that emits image light modulated by a micro mirror element in accordance with an image signal in a direction parallel to a projection plane; a first reflective optical system that reflects the image light in a first direction away from the projection plane; a second reflective optical system that reflects the image light reflected by the first reflective optical system in a second direction away from the optical engine and closer to the projection plane, thereby to enlarge and project image light onto the projection plane; and a refractive optical system interposed between the optical engine and the second reflective optical system. Here, the refractive optical system is divided into a first refractive optical system that is interposed between the optical engine and the first reflective optical system, and a second refractive optical system that is interposed between the first reflective optical system and the second reflective optical system. In addition, the micro mirror element is arranged such that a longer side thereof is almost perpendicular to a plane parallel to both of the first and second directions and is almost parallel to the projection plane. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and other objects and novel features of the present invention will be more fully understood from the following description of a preferred embodiment when reference is made to the accompanying drawings. 
         FIGS. 1A and 1B  are diagrams showing a configuration of a projector in an embodiment of the present invention; 
         FIGS. 2A and 2B  are diagrams showing usage patterns of the projector in the embodiment; 
         FIGS. 3A and 3B  are diagrams for describing that a minimum throw distance H becomes shorter depending on an orientation of a mounting plane of an optical engine in the embodiment; 
         FIGS. 4A and 4B  are diagrams showing a configuration of the projector in a modification example 1; 
         FIGS. 5A and 5B  are diagrams showing a configuration of the projector in a modification example 2; 
         FIGS. 6A and 6B  are diagrams showing a configuration of the projector in a modification example 3; 
         FIGS. 7A and 7B  are diagrams showing a configuration of the projector in a modification example 4; 
         FIGS. 8A and 8B  are diagrams showing an integrated configuration of a refractive optical system and a reflective mirror; 
         FIG. 9  is a diagram showing an integrated configuration of the refractive optical system, the reflective mirror, and a curved mirror; 
         FIGS. 10A ,  10 B, and  10 C are diagrams showing a configuration of a projector in another modification example; 
         FIGS. 11A and 11B  are diagrams showing a configuration of a shift module in another modification example, and a structure of attachment of an imager unit and a projection optical unit to the shift module; 
         FIGS. 12A and 12B  are diagrams showing a configuration of a shift mechanism (a fixing member, a displacement mechanism section, and a linear guide) in another modification example; 
         FIGS. 13A and 13B  are diagrams showing a configuration of the fixing member in another modification example; 
         FIGS. 14A ,  14 B,  14 C, and  14 D are diagrams for describing a shift operation of the shift mechanism in another modification example; 
         FIGS. 15A and 15B  are diagrams for describing transformation examples of the optical engine (configuration examples 1 and 2); 
         FIGS. 16A ,  16 B,  16 C, and  16 D are diagram for describing transformation examples of the optical engine (configuration examples 3 and 4); 
         FIGS. 17A and 17B  are diagrams for describing a transformation example of the optical engine (configuration example 5); and 
         FIGS. 18A and 18B  are diagrams showing a configuration of a projector in a related art. 
     
    
    
     However, the drawings are only for purpose of description, and do not limit the scope of the present invention. 
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     An embodiment of the present invention will be described below with reference to the drawings.  FIGS. 1A and 1B  are diagrams showing an internal structure of a projector  1  in this embodiment.  FIG. 1A  is an internal perspective view of the projector  1  as seen from a side.  FIG. 1B  is an internal perspective view of the projector  1  as seen from the top, which shows mainly a layout of optical components in an optical engine  200 . 
     Referring to  FIGS. 1A and 1B , the projector  1  includes a cabinet  100 . The cabinet  100  has on a front surface  100   a  thereof an image light projection window  101 . The cabinet  100  also has a convex curved surface  100   d  from a back surface  100   b  to an upper surface  100   c  thereof. The convex curved surface  100   d  is provided with a handle  102 . The handle  102  has a grab section  102   a  that is rotatable in an X-Z in-plane direction. The handle  102  is also used as a stand for supporting the cabinet  100  when the projector  1  is installed for “wall projection,” as described later. 
     The cabinet  100  contains the optical engine  200 , a rear refractive optical system  300 , a reflective mirror  400  (equivalent to the first reflective optical system of the present invention), a front refractive optical system  500 , and a curved mirror  600  (equivalent to the second reflective optical system of the present invention). 
     The optical engine  200  is arranged on a bottom surface of the cabinet  100  to generate image light modulated in accordance with an image signal. The optical engine  200  has optical components (liquid crystal panels, a dichroic prism, and the like) arranged in a predetermined layout within a casing thereof. A mounting plane of the optical components is approximately parallel to a bottom surface  100   e  of the cabinet  100 . 
     As shown in  FIG. 1B , the optical engine  200  includes a light source  201 , a light-guiding optical system  202 , three transmissive liquid crystal panels  203 ,  204 , and  205 , and a dichroic prism  206 . 
     The light-guiding optical system  202  separates white light emitted from the light source  201  into a red-waveband light (hereinafter, referred to as “R light”), a green-waveband light (hereinafter, referred to as “G light”), and a blue-waveband light (hereinafter, referred to as “B light”), and then radiates the separated lights to the liquid crystal panels  203 ,  204 , and  205 . The liquid crystal panels  203 ,  204 , and  205  modulate the R, G, and B lights, and then the dichroic prism  206  combines the modulated lights and emits the same as image light. In addition, polarizers (not shown) are disposed on incident sides and output sides of the liquid crystal panels  203 ,  204 , and  205 . 
     Instead of the transmissive liquid crystal panels  203 ,  204 , and  205 , imagers arranged in the optical engine  200  may use reflective liquid crystal panels or MEMS devices. In addition, the optical engine  200  may not be a three-plate optical system including three imagers as described above, but may be a single-plate optical system using one imager and a color wheel, for example. 
     The rear refractive optical system  300  is attached to an image light outgoing window of the optical engine  200 . The rear refractive optical system  300  receives incident image light generated at the optical engine  200 . The rear refractive optical system  300  includes a plurality of lenses. A light axis L 1  of these lenses is parallel to the bottom surface  100   e  (X axis) of the cabinet  100 . As shown in  FIG. 1A , the liquid crystal panels  203 ,  204 , and  205 , and the dichroic prism  206  are shifted in a Z-axis direction (the curved mirror  600  side) from the light axis L 1  of the rear refractive optical system  300 . 
     The reflective mirror  400  is arranged in front of the rear refractive optical system  300 . The reflective mirror  400  is arranged in such a manner as to be perpendicular to an X-Z plane and be tilted at 45 degrees relative to the bottom surface  100   e  of the cabinet  100  (X-Y plane). 
     The front refractive optical system  500  is arranged above the reflective mirror  400 . The front refractive optical system  500  includes a plurality of lenses. A light axis L 2  of these lenses is parallel to a Z axis and also is parallel to an image light outgoing plane of the dichroic prism  206 . In addition, the light axis L 2  of the front refractive optical system  500  is perpendicular to the light axis L 1  of the rear refractive optical system  300  and the bottom surface  100   e  of the cabinet  100 , and intersects the light axis L 1  of the rear refractive optical system  300  on the reflective mirror  400 . That is, the front refractive optical system  500  constitutes one refractive optical system in conjunction with the rear refractive optical system  300 . In this constitution, the light axis of the lens group is converted from a direction perpendicular to the outgoing plane of the dichroic prism  206  to a direction parallel to the same, by the reflective mirror  400  interposed between these two refractive optical systems  300  and  500 . 
     The image light entered into the rear refractive optical system  300  passes through the rear refractive optical system  300 , the reflective mirror  400 , and the front refractive optical system  500 , and then enters the curved mirror  600  arranged above the front refractive optical system  500 . 
     The curved mirror  600  has a concave reflecting surface. The curved mirror  600  includes an effective reflection area on the optical engine  200  side of the light axis L 2  of the front refractive optical system  500 , as shown in  FIG. 1A . The curved mirror  600  may have an aspherical shape, a free-form shape, or a spherical shape. 
     The image light entered into the curved mirror  600  is reflected by the curved mirror  600 , and is enlarged and projected onto the projection plane through the projection window  101 . At that time, the image light is enlarged after being most converged near the projection window  101 . 
       FIGS. 2A and 2B  are diagrams showing usage patterns of the projector  1 .  FIG. 2A  shows a usage pattern for projecting an image onto a desktop or a floor surface, and  FIG. 2B  shows a usage pattern for projecting an image onto a wall surface or a screen. 
     As shown in  FIG. 2A , the projector  1  of this embodiment may be installed with the bottom surface  100   e  of the cabinet  100  on a desktop or a floor surface. This makes it possible to project an image onto the desktop or the floor surface as a projection plane. Hereinafter, this usage pattern will be referred to as “floor projection.” 
     In addition, as shown in  FIG. 2B , the projector  1  of this embodiment may be installed with the back surface  100   b  of the cabinet  100  on a desktop or a floor surface. This makes it possible to project an image onto a wall surface or a screen. Hereinafter, this usage pattern will be referred to as “wall projection.” In this usage pattern, as shown in  FIG. 2B , the projector  1  may also be installed with the bottom surface  100   e  tightly attached to a wall surface. Accordingly, in wall projection, the projector  1  can be supported on the back side by the grab section  102   a  of the handle  102 , thereby preventing the projector  1  from falling down backward. 
     As shown in  FIG. 2A , the curved mirror  600  and the projection plane are positioned opposite to each other across an axis L 0  that passes through a center of the outgoing plane of the dichroic prism  206  and is perpendicular to the outgoing plane of the dichroic prism  206 . In addition, the outgoing plane of the dichroic prism  206  and the projection plane are perpendicular to each other. 
     In this embodiment, unlike the projector shown in  FIGS. 18A and 18B , the optical engine  200 , the refractive optical systems  300  and  500 , and the curved mirror  600  are not arranged in line in a direction parallel to the mounting plane of the optical components on the optical engine  200 . Specifically, in this embodiment, the optical engine  200 , the refractive optical systems  300  and  500 , and the curved mirror  600  are arranged in an approximately L-shaped form within the cabinet  100 . 
     Accordingly, as shown in  FIGS. 2A and 2B , this embodiment allows the size D of the projector body to be reduced in the direction of the light axis L 2  in which the reflective mirror  400  and the curved mirror  600  are aligned, thereby to shorten the throw distance H (minimum throw distance H) with the projector  1  closest to the projection plane. Therefore, it is easy to prevent that image light projected from the projection window  101  is cut off by an obstacle and that unnecessary shades are cast onto a projected image. In addition, since the lower limit of the projection size can be further decreased, the projection size can be adjusted within an increased range by making the projector  1  closer to or away from the projection plane. 
     In this embodiment, as shown in  FIG. 3A , the optical engine  200  is arranged in such a manner that the mounting plane of the optical components is perpendicular to a plane parallel to both the direction of reflection of image light by the reflective mirror  400  and the direction of reflection of image light by the curved mirror  600 , that is, the mounting plane of the optical components is perpendicular to the X-Z plane in the drawing. Accordingly, a minimum throw distance H 1  of the projector  1  can be readily made shorter without any influence of the width of the mounting plane. Specifically, as shown in  FIG. 3B , if the optical engine  200  is arranged in such a manner the mounting plane of the optical components is parallel to the X-Z plane in the drawing, the minimum throw distance is influenced by a width W of the mounting plane, whereby the dimension of the optical engine  200  under the light axis L 1  of the rear refractive optical system  300  becomes longer than that in this embodiment. Accordingly, a minimum throw distance H 2  in this configuration becomes longer by ΔH than the minimum throw distance Hi of this embodiment. Meanwhile, in this embodiment, as shown in  FIG. 3A , the mounting plane of the optical components is parallel to the X-Y plane in the drawing, which allows the minimum throw distance H 1  of the projector  1  to be shortened without any influence of the width of the mounting plane. 
     Moreover, in this embodiment, the projector body can be formed in an almost cubic shape, which allows the projector  1  to be stably installed in the both usage patterns of floor projection and wall projection. 
     Further, in this embodiment, the reflective mirror  400  is interposed between the rear refractive optical system  300  and the front refractive optical system  500 , thereby preventing a longer back focus of the refractive optical system. 
     Although the embodiment of the present invention is as described above, the embodiment of the present invention may be modified as described below. 
     MODIFICATION EXAMPLE 1 
       FIGS. 4A and 4B  are diagrams showing a configuration of the projector  1  in modification example  1 .  FIG. 4A  shows the projector  1  installed for “floor projection, ” and  FIG. 4B  shows the projector  1  installed for “wall projection.” 
     In the foregoing embodiment, the optical engine  200  and the rear refractive optical system  300  are arranged in parallel to the bottom surface  100   e  of the cabinet  100 . Alternatively, the optical engine  200  and the rear refractive optical system  300  may be slightly tilted relative to the bottom surface  100   e,  as shown in  FIGS. 4A and 4B . In this case, tilt of the reflective mirror  400  relative to the bottom surface  100   e  is made smaller in accordance with the tilt of the rear refractive optical system  300 . 
     In such a configuration, the light axis L 1  of the rear refractive optical system  300  and the light axis L 2  of the front refractive optical system  500  are not perpendicular to each other, and the outgoing plane of the dichroic prism  206  and the projection plane are also not perpendicular to each other. 
     If an angle of the tilt relative to the bottom surface  100   e  is too large, part of the front refractive optical system  500  may interfere with the rear refractive optical system  300  or the optical engine  200 . Therefore, the angle of tilt needs to be set so as not to cause such interference. 
     As described above, the optical engine  200  and the rear refractive optical system  300  may be tilted if necessary in the design of the projector  1 . However, the tilt needs to be set such that part of the front refractive optical system  500  does not interfere with the rear refractive optical system  300  or the optical engine  200 . 
     In the configuration of the modification example 1, as in the foregoing embodiment, it is possible to shorten the minimum throw distance H and install the projector  1  stably in the both usage patterns of floor projection and wall projection. 
     MODIFICATION EXAMPLE 2  
       FIGS. 5A and 5B  are diagrams showing a configuration of the projector  1  in a modification example  2 .  FIG. 5A  shows the projector  1  installed for “floor projection, ” and  FIG. 5B  shows the projector  1  for “wall projection.” 
     In the foregoing embodiment, the refractive optical system is divided into the rear refractive optical system  300  and the front refractive optical system  500 , with the reflective mirror  400  interposed therebetween. 
     Meanwhile, in the configuration of the modification example 2, as shown in  FIG. 5A , the reflective mirror  400  is arranged in front of the optical engine  200 , and a refractive optical system  700 , instead of the rear refractive optical system  300  and the front refractive optical system  500 , is arranged only above the reflective mirror  400 . A light axis L 3  of the refractive optical system  700  is parallel to a Z axis shown in  FIG. 5A , that is, is parallel to the outgoing plane of the dichroic prism  206  and is perpendicular to the axis LO perpendicular to the outgoing plane. In addition, the liquid crystal panels  203 ,  204 ,  205 , and the dichroic prism  206  are arranged above an axis L 5  that is a turn-back of the light axis L 3  from the reflective mirror  400  (the curved mirror  600  side). Image light emitted from the optical engine  200  is reflected by the reflective mirror  400  and is entered into the refractive optical system  700 . 
     In the configuration of the modification example 2, as in the foregoing embodiment, it is possible to shorten the minimum throw distance H and install the projector  1  stably in the both usage patterns of floor projection and wall projection. 
     In addition, in the configuration of the modification example 2, the refractive optical system can be simplified as compared with the configuration where the reflective mirror  400  is interposed between the rear refractive optical system  300  and the front refractive optical system  500 . Nevertheless, in the configuration of the modification example 2, the refractive optical system is distant from the optical engine, thereby prolonging a back focus of the refractive optical system. 
     MODIFICATION EXAMPLE 3  
       FIGS. 6A and 6B  are diagrams showing a configuration of the projector  1  in a modification example  3 .  FIG. 6A  shows the projector  1  installed for “floor projection,” and  FIG. 6B  shows the projector  1  for “wall projection.” 
     In the configuration of the modification example 3, unlike the foregoing embodiment, a refractive optical system  800 , instead of the rear refractive optical system  300  and the front refractive optical system  500 , is arranged only in front of the optical engine  200  and only a curved mirror  600  is arranged above the reflective mirror  400 . A light axis L 4  of the refractive optical system  800  is perpendicular to the outgoing plane of the dichroic prism  206  and is parallel to the axis L 0  perpendicular to the outgoing plane. 
     In the configuration of the modification example 3, as in the foregoing embodiment, it is possible to shorten the minimum throw distance H and install the projector  1  stably in the both usage patterns of floor projection and wall projection. 
     In addition, in the configuration of the modification example 3, no refractive optical system is interposed between the reflective mirror  400  and the curved mirror  600 , which allows the minimum throw distance H to be shorter than that in the foregoing embodiment. Nevertheless, in the configuration of the modification example 3, the dimension of the projector body is larger in the direction of the light axis L 4  of the refractive optical system  800 . Therefore, the projector  1  may be installed in a slightly less stable manner for wall projection as compared with the case in the foregoing embodiment, as shown in  FIG. 6B . 
     MODIFICATION EXAMPLE 4 
       FIGS. 7A and 7B  are diagrams showing a configuration of the projector  1  in a modification example  4 .  FIG. 7A  shows the projector  1  installed for “floor projection,” and  FIG. 7B  shows the projector  1  for “wall projection.” 
     In the configuration of the modification example 4, a curved mirror  900  having a convex reflecting surface (equivalent to the second reflective optical system of the present invention) is arranged instead of the curved mirror  600 . The curved mirror  900  includes an effective reflection area on the front surface  100   a  side of the light axis L 2  of the front refractive optical system  500 . The curved mirror  900  may have an aspherical shape, a free-form shape, or a spherical shape. 
     The liquid crystal panels  203 ,  204 ,  205 , and the dichroic prism  206  are shifted from the light axis L 1  of the rear refractive optical system  300  toward the bottom surface  100   e  of the cabinet  100 . 
     Image light emitted from the optical engine  200  passes through the rear refractive optical system  300 , the reflective mirror  400 , and the front refractive optical system  500 , and then enters the curved mirror  900 . Then, the image light is reflected by the curved mirror  900 , and is enlarged and projected onto the projection plane through the projection window  101 . 
     In the configuration of the modification example 4, as in the foregoing embodiment, it is possible to shorten the minimum throw distance H and install the projector  1  stably in the both usage patterns of floor projection and wall projection. 
     However, in the configuration of the modification example 4, the image light is enlarged immediately after being reflected by the curved mirror  900 , and therefore an opening area of the projection window  101  is larger than that in the foregoing embodiment. Since the projection window  101  is generally covered with a window plate made of glass or the like, the larger opening area requires a larger-sized window plate. 
     Others 
     The foregoing embodiment and the modification examples 1 to 4 use the reflective mirror  400 , but this is not a definitive arrangement. For example, a reflective prism may be used instead. 
     In addition, in the foregoing embodiment and modification examples 1 and 4, the rear refractive optical system  300 , the front refractive optical system  500 , and the reflective mirror  400  are separated from each other. Alternatively, the three components may be integrated with a mirror frame  150  as shown in  FIGS. 8A and 8B , for example. In such a configuration, it is easy to assemble the rear refractive optical system  300 , the front refractive optical system  500 , and the reflective mirror  400  into the cabinet  100 . 
     Further, the curved mirror  600  ( 900 ), the refractive optical systems  300  and  500  ( 700  and  800 ), and the reflective mirror  400  may be integrated with a mirror frame  160 , as shown in  FIG. 9 . 
     In such a configuration, it is easy to assemble the curved mirror  600  ( 900 ), the refractive optical systems  300  and  500  ( 700  and  800 ), and the reflective mirror  400  into the cabinet  100 . 
     Another Modification Example 
       FIGS. 10A ,  10 B, and  10 C are diagrams showing a configuration of a projector in another modification example.  FIG. 10A  is a perspective view of an outer appearance of the projector,  FIG. 10B  is a perspective view of an internal structure of the projector as seen from a side, and  FIG. 10C  is a lateral view of a configuration of a projection optical unit U. 
     In the projector of this modification example, a position of an image projected onto a projection plane can be adjusted by shifting imagers (liquid crystal panels) vertically. For example, if an image is projected onto a surface on which the projector is installed (floor surface or desktop), the position of the projected image can be adjusted in the front-back direction. For this purpose, the projector has on a side thereof a knob  84  for use in position adjustment as shown in  FIG. 10A . 
     As shown in  FIG. 10B , the projector of this modification example includes a casing  10 . The casing  10  has a convex curved shape from rear to upper sides thereof. The casing  10  contains an optical engine  20 , a refractive optical unit  30 , a curved mirror  40  (equivalent to the second reflective optical system of the present invention), and a housing  50 . 
     The optical engine  20  has the same configuration as that of the optical engine  200  in the foregoing embodiment, and also includes an imager unit  21 . The imager unit  21  is a component into which three liquid crystal panels for R, G, and B lights and a dichroic prism are integrated. 
     The refractive optical unit  30  includes a rear refractive optical system  31 , a reflective mirror  32  (equivalent to the first reflective optical system of the present invention), and a front refractive optical system  33 . The reflective mirror  32  is housed in a mirror case  34 . The rear refractive optical system  31 , the mirror case  34 , and the front refractive optical system  33  are integrated. 
     The refractive optical unit  30  and the curved mirror  40  are assembled into the housing  50 . As shown in  FIG. 10C , the refractive optical unit  30  is assembled into the housing  50  in such a manner that the front refractive optical system  33  is housed within the housing  50 , and that the mirror case  34  and the rear refractive optical system  31  are exposed downward. In addition, the curved mirror  40  is assembled into an upper end of the housing  50 . The housing  50  has flanges  51  on both sides of a lower part thereof. When the refractive optical unit  30  and the curved mirror  40  are assembled into the housing  50 , the projection optical unit U is completed. 
     Configurations and positions of the rear refractive optical system  31 , the reflective mirror  32 , the front refractive optical system  33 , and the curved mirror  40  are identical to those of the rear refractive optical system  300 , the reflective mirror  400 , the front refractive optical system  500 , and the curved mirror  600  in the foregoing embodiment, respectively. 
     In addition, in the optical engine  20 , a mounting plane of optical components is perpendicular to a plane parallel to both the direction of reflection of image light by the reflective mirror  32  and the direction of reflection of image light by the curved mirror  40  (that is, a plane perpendicular to an X-Z plane in the drawing). Here, the mounting plane is parallel to a projection plane of image light. Accordingly, the optical components are scattered in a direction parallel to the projection plane. 
     The imager unit  21  is held by a shift module M so as to be displaceable in an up-down direction (in a direction perpendicular to the light axis L 1 ). In addition, the projection optical unit U is attached to a base member (described later) constituting the shift module M. 
       FIGS. 11A and 11B  are diagrams showing a configuration of the shift module M, and a structure of attachment of the imager unit  21  and the projection optical unit U to the shift module M.  FIG. 11A  is a side view of the projection optical unit U attached to a base member  60 .  FIG. 11B  is a perspective view of a configuration of the base member  60 . 
     As shown in  FIG. 11A , the shift module M includes the base member  60 , a fixing member  70 , a displacement mechanism section  80 , and a linear guide  90 . The fixing member  70 , the displacement mechanism section  80 , and the linear guide  90  constitute a shift mechanism for shifting the imager unit  21 . The shift mechanism with the imager unit  21  and the projection optical unit U are attached together to the base member  60 . 
     As shown in  FIG. 11B , the base member  60  includes a pedestal  61 , a supporting plate  62  extending vertically (upward) relative to the pedestal  61 , and an attachment stand  63  arranged in front of the supporting plate  62 . 
     The pedestal  61  has attachment holes  61   a  at a rear end on right and left sides thereof. The attachment holes  61   a  are used to screw the base member  60  into a predetermined position of the casing  10 . 
     The attachment stand  63  is a member separated from the pedestal  61 , and is fixed to the pedestal  61  with screws or the like. Alternatively, the attachment stand  63  may be integral with the pedestal  61 . 
     The attachment stand  63  includes a pair of legs  64  and  65 . When the projection optical unit U is attached to the base member  60 , the rear refractive optical system  31  and the mirror case  34  are housed between the legs  64  and  65 . 
     The legs  64  and  65  have on upper ends thereof holding sections  66  and  67  and flanges  68  and  69 , respectively. The holding sections  66  and  67  are lowered in height, to house the bottom portion of the housing  50  by one level than the flanges  68  and  69 . In addition, the flanges  68  and  69  have three each screw holes  68   a  and  69   a,  respectively. 
     As shown in  FIG. 11A , the projection optical unit U is placed on the attachment stand  63 , and is fixed to the attachment stand  63  by tightening the flanges  51  and the flanges  68  and  69 . At that time, a leading end of the rear refractive optical system  31  is inserted into an opening  62   a  of the supporting plate  62 . 
       FIGS. 12A and 12B  are diagrams showing a configuration of the shift mechanism (the fixing member  70 , the displacement mechanism section  80 , and the linear guide  90 ) attached to the base member  60 .  FIG. 12A  is a perspective view of the shift mechanism, and  FIG. 12B  is a diagram for describing a configuration of the linear guide  90 , which is a cross-section view of  FIG. 12A  taken along A-A′. 
     The fixing member  70  is attached to the back side of the supporting plate  62  via right and left linear guides  90  (only the right guide is shown in the drawing). 
     Each of the linear guides  90  includes a rail section  91  vertically extending and a stage section  92  that engages with the rail section  91  to move vertically along the rail section  91 . The rail section  91  has a plurality of ball bearings  93  vertically arranged at predetermined intervals, so that the stage section  92  can move smoothly over the rail section  91 . The rail section  91  is fixed to the supporting plate  62 , and the stage section  92  is fixed to the fixing member  70 . 
     In this manner, the fixing member  70  is supported by the supporting plate  62  in such a manner as to be displaceable vertically along the right and left linear guides  90 . 
       FIGS. 13A and 13B  are diagrams showing a configuration of the fixing member  70 .  FIG. 13A  shows a configuration of the fixing member  70  in this modification example, and  FIG. 13B  shows a transformation example of the fixing member  70 . 
     As shown in  FIG. 13A , the fixing member  70  includes a flat plate  71  that is arranged in line with the supporting plate  62 . The flat plate  71  has an opening  71   a  through which image light from the imager unit  21  passes. In addition, the flat plate  71  is integral with a placement section  72  on which the imager unit  21  is placed. A placement surface of the placement section  72  is perpendicular to the flat plate  71  and the supporting plate  62 . 
     The placement section  72  has a receiving part  72   a  at a base of a back surface thereof. The receiving part  72   a  is integral with the placement section  72  and the flat plate  71  so as to connect the placement section  72  and the flat plate  71 , thereby increasing the base of the placement section  72  in strength. In addition, the placement section  72  has on the back surface thereof an attachment boss  72   b  for screwing the imager unit  21  at a leading end thereof. Further, the placement section  72  has on the back surface thereof a reinforcement rib  72   c  connecting the receiving part  72   a  and the attachment boss  72   b.  Moreover, the placement section  72  has on the back surface thereof two reinforcement ribs  72   d  connecting to the receiving part  72   a  on the both sides of the reinforcement rib  72   c.  The reinforcement ribs  72   c  and  72   d  are formed along a direction in which the placement section  72  projects from the flat plate  71 . 
     In this manner, the placement section  72  is reinforced with the receiving part  72   a,  the attachment boss  72   b,  and the reinforcement ribs  72   c  and  72   d.  This prevents that the leading end of the placement section  72  is weighted down with the imager unit  21 . In addition, the imager unit  21  generates high heat due to irradiated light. Accordingly, the placement section  72  is prone to reach a high temperature, but the foregoing reinforcements can prevent thermal deformation of the placement section  72 . 
     As shown in  FIG. 13B , the flat plate  71  may have a vertically extending reinforcement rib  72   e.  This prevents the flat plate  71  from being deformed with an upper part inclined frontward or backward due to weight or heat generation of the imager unit  21 . In this transformation example, the flat plate  71  has two each reinforcement ribs  72   e  on right and left ends. 
     Returning to  FIGS. 12A and 12B , the imager unit  21  is placed on the placement section  72  of the fixing member  70 . The imager unit  21  is formed by integrating three liquid crystal panels  21   a,    21   b,  and  21   c  and a dichroic prism  21   d,  as described above. 
     The fixing member  70  is shifted by the displacement mechanism section  80  in an up-down direction, that is, in a direction perpendicular to the light axis L 1  of the rear refractive optical system  31 . 
     The displacement mechanism section  80  is constituted by a shaft  81 , an eccentric cam  82 , a displacement member  83 , and the knob  84 , and two shaft bearings  85  and  86 . 
     The eccentric cam  82  is fixed to the shaft  81  with two screws  82   a.  The shaft  81  is rotatably supported by the shaft bearings  85  and  86  on both sides of the eccentric cam  82 . The shaft bearings  85  and  86  are fixed to an upper end of the supporting section  62  with two screws  85   a  and  86   a,  respectively. 
     The eccentric cam  82  is inserted into a cam hole  83   a  of the displacement member  83 . The eccentric cam  82  is formed in such a manner as to obtain a desired displacement amount of the imager unit  21 . The displacement member  83  is fixed to an upper end of the flat plate  71  with two screws  83   b.    
     The shaft bearings  85  and  86  may be integral with the supporting plate  62 . In addition, the displacement member  83  may be integral with the flat plate  71 . 
     The knob  84  is attached to one end of the shaft  81 . The knob  84  is exposed on an outer surface of the casing  10  (refer to  FIG. 10A ) such that a user can turn the knob  84 . 
       FIGS. 14A ,  14 B,  14 C, and  14 D are diagrams for describing a shift operation by the shift mechanism. 
     For example, when a user turns the knob  84  in an intermediate position shown in  FIG. 14B  clockwise (in the direction of solid arrow), a wide section  82   b  of the eccentric cam  82  (refer to  FIG. 14D ) moves upward to displace the displacement member  83  upward, thereby displacing the flat plate  71  (fixing member  70 ) upward, as shown in  FIG. 14C . Accordingly, the imager unit  21  on the placement section  72  shifts upward. 
     Meanwhile, when a user turns the knob  84  in the intermediate position counterclockwise (in the direction of dashed arrow), the wide section  82   b  of the eccentric cam  82  moves downward to displace the displacement member  83  downward, thereby displacing the flat plate  71  (fixing member  70 ) downward. Accordingly, the imager unit  21  on the placement section  72  shifts downward. 
     The displacement mechanism section  80  is provided with a lock device (not shown) for locking the knob  84  so as not to turn. After shifting the imager unit  21  to a desired position, a user locks the knob  84  with the lock device. This allows the imager unit  21  to be fixed at an arbitrary position. Alternatively, the lock device may be configured to lock any component other than the knob  84 , for example, the shaft  81  or the fixing plate  70 . In addition, the shaft  81  may be electrically driven by a motor or the like, instead of being turned by manual operation of the knob  84 . 
     Spot sizes of R, G, and B lights radiated to the liquid crystal panels  21   a,    21   b,  and  21   c  are set wider than the effective display planes of the liquid crystal panels, so that the liquid crystal panels can be entirely irradiated with light even when the imager unit  21  is vertically displaced. 
     Accordingly, as shown in  FIG. 10B , the image light generated at the optical engine  20  passes through the rear refractive optical system  31 , the reflective mirror  32 , and the front refractive optical system  33 , and then is entered into the curved mirror  40 . Then, the image light is reflected by the curved mirror  40 , and is enlarged and projected onto a floor surface through the projection window  11 . 
     At that time, the position of the projected image can be adjusted by shifting the imager unit  21 . For example, when the knob  84  is turned to shift the imager unit  21  from top down, the imager unit  21  comes closer to the light axis L 1 . Accordingly, a key light position of upper and lower ends of the image light emitted from the front refractive optical system  33  (hereinafter, “key light position of upper and lower ends” will be referred to as “light position”) changes from a light position shown by a dashed line to a light position shown by a solid line in the drawing. Specifically, the light position of the image light from the front refractive optical system  33  comes closer to the light axis L 2 , and therefore an incident position of the image light on the curved mirror  40  is shifted forward. Accordingly, the light position of the image light reflected by the curved mirror  40  and traveling toward the floor surface is shifted toward the projector (Image A shifts to Image B as shown in the drawing). 
     According to this modification example, as the foregoing, it is possible to shorten the minimum throw distance, and it is also possible to install the projector stably in the both usage patterns of floor projection and wall projection, as in the foregoing embodiment. 
     In addition, according to this modification example, the position of a projected image can be adjusted simply by shifting the imager unit  21  without having to move the projector. 
     Modification Example of the Optical Engine 
     In the foregoing embodiment, the optical engine  200  uses the transmissive liquid crystal panels  203 ,  204 , and  205  as imagers. Alternatively, the optical engine  200  may use liquid crystals on silicon (LCOSs) that is reflective liquid crystal panels or digital micro mirror devices (DMDs) that is MEMS devices as imagers, as shown in configuration examples 1 to 5 described below. In addition, the projectors in the foregoing modification examples 1 to 4 and another modification example may use the imagers in the configuration examples 1 to 5. 
     CONFIGURATION EXAMPLE 1 
       FIG. 15A  is a diagram showing a configuration of an optical engine  220  in the configuration example 1. This configuration example uses LCOSs as imagers. 
     The optical engine  220  includes a light source  221 , two mirrors  222 ,  223  and two dichroic mirrors  224 ,  225  constituting a light-guiding optical system, and an imager unit  235  modulating and combining light from the light-guiding optical system. 
     The imager unit  235  is formed by integrating three polarized beam splitters (PBSs)  226 ,  227 ,  228 , three LCOSs  229 ,  230 ,  231 , and two λ/2 plates  232 ,  233 , a dichroic prism  234 , and polarizers (not shown) arranged on incident planes of the PBSs  226 ,  227 ,  228 . 
     The light source  221  includes a lamp, a fly-eye lens, a PBS array, and a condenser lens. Light emitted from the light source  221  is uniformed in a direction of polarization by the PBS array. 
     The light emitted from the light source  221  is reflected by the mirror  222  and entered into the dichroic mirror  224 . Out of the entered light, the dichroic mirror  224  reflects R and G lights and lets a B light pass through. 
     The R and G lights reflected by the dichroic mirror  224  are reflected by the mirror  223  and entered into a dichroic mirror  225 . The dichroic mirror  225  reflects the G light and lets the R light pass through. 
     The R light having passed through the dichroic mirror  225  is cleared of an unnecessary P polarization component by the polarizer (not shown), and is set as S polarized light with respect to the PBS  226 . The R light is then reflected by the PBS  226  and is radiated to the LCOS  229 . The LCOS  229  modulates and reflects the R light in accordance with an image signal. Specifically, the LCOS  229  turns the direction of polarization of the R light for each of pixels constituting an effective display plane of the LCOS  229 . 
     Accordingly, the modulated R light passes through the PBS  226  according to the polarization direction thereof, and passes through the λ/2 plate  232 , as a result, the polarization direction of the modulated R light turns, and then the modulated R light enters the dichroic prism  234 . 
     In addition, the G light reflected by the dichroic mirror  225  is cleared of an unnecessary P polarization component by the polarizer (not shown), and is set as S polarized light with respect to the PBS  227 . The G light is then reflected by the PBS  227  and is radiated to the LCOS  230 . The LCOS  230  modulates and reflects the G light in accordance with an image signal. 
     Accordingly, the modulated G light passes through the PBS  227  in the direction of polarization, and enters the dichroic prism  234 . 
     Meanwhile, the B light having passed through the dichroic mirror  224  is cleared of an unnecessary P polarization component by a polarizer (not shown), and is set as S polarized light with respect to the PBS  228 . The B light is then reflected by the PBS  228  and is radiated to the LCOS  231 . The LCOS  231  modulates and reflects the B light in accordance with an image signal. 
     Accordingly, the modulated B light passes through the PBS  228  in accordance with the polarization direction, and passes through the λ/2 plate  233 , as a result, the polarization direction of the modulated B light turns, and then the modulated B light enters the dichroic prism  234 . 
     When the R and B lights are reflected by the dichroic prism  234  and the G light passes through the dichroic prism  234 , these three lights are combined and entered as image light into the rear refractive optical system  300 . 
     The R, G, and B lights that have been modulated by the LCOSs  229 ,  230 , and  231  and have passed through the PBSs  226 ,  227 , and  228 , are each set as P polarized light with respect to the dichroic prism  234 . In this case, S polarized light is higher in reflection rate in a wider wavelength band due to characteristics of a dielectric multilayer film of the dichroic prism  234 . Therefore, in the dichroic prism  234 , the G light is high in transmission efficiency, but the R and B lights are low in reflection efficiency if the R and B lights remain P polarized lights. Therefore, the optical engine  220  of  FIG. 15A  lets the R and B lights pass through the λ/2 plates  232  and  233  so as to turn into S polarized lights, thereby enhancing reflection efficiencies of the R and B lights on the dichroic prism  234 . 
     In this configuration example, as in the foregoing embodiment the optical components of the optical engine  220  such as the imager unit  235  are arranged in a predetermined layout on the mounting plane of the optical component shown in  FIG. 1A . Accordingly, the optical components are scattered in a direction parallel to the projection plane (X-Y plane) shown in  FIG. 2A . 
     Accordingly, as in the foregoing embodiment, it is possible to shorten the minimum throw distance even if the optical engine  200  in the foregoing embodiment is replaced by the optical engine  220  in this configuration example. In addition, it is possible to install the projector stably in the both usage patterns of floor projection and wall projection. 
     CONFIGURATION EXAMPLE 2 
       FIG. 15B  is a diagram showing a configuration of an optical engine  240  in the configuration example 2. In this configuration example, LCOSs are used as imagers as in the configuration example 1. 
     The optical engine  240  includes a light source  241  and an imager unit  247  modulating and combining light from the light source. 
     The imager unit  247  is formed by integrating a polarized beam splitter (PBS)  242 , a dichroic prism  243 , three LCOSs  244 ,  245 , and  246 , and a polarizer (not shown) arranged on an incident plane of the PBS  242 . 
     The light source  241  includes a lamp, a fly-eye lens, a PBS array, and a condenser lens. Light emitted from the light source  241  is uniformed in a direction of polarization by the PBS array. 
     The light emitted from the light source  241  is cleared of an unnecessary P polarization component by the polarizer (not shown), and is set as S polarized light with respect to the PBS  242 . The light is then reflected by the PBS  242  and is entered into the dichroic prism  243 . Out of the light entered into the dichroic prism  243 , R and B lights are reflected by the dichroic prism  243  and radiated to the LCOSs  244  and  246 , respectively. Meanwhile, a G light passes through the dichroic prism  243  and is radiated to the LCOS  245 . 
     The R, G, and B lights that have been modulated by the LCOSs  244 ,  245 , and  246 , are entered again into the dichroic prism  243  and combined. After that, the combined light passes through the PBS  242  in the direction of polarization, and then enters as image light into the rear refractive optical system  300 . 
     In this configuration example, the optical components of the optical engine  240  such as the imager unit  247  are arranged in a predetermined layout on the mounting plane shown in  FIG. 1A . Accordingly, the optical components are scattered in a direction parallel to the projection plane (X-Y plane) shown in  FIG. 2A . 
     Accordingly, as in the foregoing embodiment, it is possible to shorten the minimum throw distance even if the optical engine  200  in the foregoing embodiment is replaced by the optical engine  240  in this configuration example. In addition, it is possible to install the projector stably in the both usage patterns of floor projection and wall projection. 
     CONFIGURATION EXAMPLE 3 
       FIG. 16A  is a diagram showing a configuration of an optical engine  260  in the configuration example  3 .  FIG. 16B  is a diagram showing a mounting state of an imager unit  267  on a mounting plane, as seen in the direction of arrow P in  FIG. 16A . In this configuration example, a single-plate DMD is used as an imager. 
     The optical engine  260  includes a light source  261 , a rod integrator  262 , a color wheel  263 , a relay lens group  264 , and an imager unit  267 . The rod integrator  262 , the color wheel  263 , and the relay lens group  264  constitute a light-guiding optical system. The imager unit  267  modulates and combines light from the light-guiding optical system. 
     The imager unit  267  is formed by integrating a total internal reflection (TIR) prism  265  and a single-plate DMD  266 . 
     Light emitted from the light source  261  is unified in illumination distribution by the rod integrator  262 , and is entered into the color wheel  263 . The color wheel  263  includes red, green, and blue filters that are switched in turn in a short time. The red filter lets only a R light pass through, the green filter lets only a G light pass through, and the blue filter lets only a B light pass through. 
     The color wheel may also include white, yellow, cyan, and magenta filters as well as red, green, and blue ones. 
     The R, G, and B lights having passes through the color wheel  263  with time differences, pass through the relay lens group  264 , and then are reflected by the TIR prism  265  and radiated to the DMD  266 . Then, after being modulated by the DMD  266 , the lights pass through the TIR prism  265  and enter the rear refractive optical system  300 . 
     Since the filters in the color wheel  263  are switched at a high speed, images of the R, G, and B lights are combined and projected as one image onto a screen. 
     In this configuration example, as in the foregoing embodiment, optical components of the optical engine  260  such as the imager unit  267  are mounted in a predetermined layout on the mounting plane of the optical components shown in  FIG. 1A . Accordingly, the optical components are scattered in a direction parallel to the projection plane (X-Y plane) shown in  FIG. 2A . 
     As shown in  FIG. 16B , the imager unit  267  is held on the mounting plane by a holding section  268  in such a manner that a longer side of the DMD  266  is parallel to the mounting plane and the TIR prism  265  is tilted relative to the mounting plane in the direction of Y axis. The TIR prism  265  is tilted because it is needed to irradiate light onto the DMD  266  in an oblique direction due to a structure of a micro mirror (moving mirror) constituting the DMD  266 . In accordance with the tilt of the TIR prism  265 , other optical components such as the light source  261  may be tilted as appropriate relative to the mounting plane. However, even if the TIR prism  265  and the like are held so as to be tilted, the mounting plane of the optical components is unchangeably perpendicular to the X-Z plane of  FIG. 1 . 
     Accordingly, it is possible to shorten the minimum throw distance as in the foregoing embodiment, even if the optical engine  200  of the foregoing embodiment is replaced by the optical engine  260  of this configuration example. In addition, it is possible to install the projector stably in the both usage patterns of floor projection and wall projection. 
     Alternatively, it is conceivable that the mounting plane of the optical components is tilted in accordance with the tilt of the TIR prism  265  and other optical components. Even in this case, however, the optical components are scattered within the projector in a direction parallel to the projection plane. Therefore, it is possible to install the projector stably in the both usage patterns of floor projection and wall projection. 
     CONFIGURATION EXAMPLE 4 
       FIGS. 16C and 16D  are diagrams showing a configuration of an optical engine  270  in the configuration example 4.  FIG. 16C  is a top view, and  FIG. 16D  is a side view as seen in the direction of arrow P in  FIG. 16C . In  FIG. 16D , an arrangement of the light source  271  to the relay lens group  274  is omitted. 
     In this configuration example, a single-plate DMD is used as an imager as in the configuration example 3. 
     The optical engine  270  includes a light source  271 , a color wheel  272 , a rod integrator  273 , a relay lens group  274 , a plane mirror  275 , a concave mirror  276 , and a single-plate DMD  277 . 
     Light emitted from the light source  271  is entered into the color wheel  272 . The color wheel  272  includes red, green, and blue filters that are switched in turn in a short time, as in the color wheel  263  of the configuration example 3. 
     The color wheel may also include white, yellow, cyan, and magenta filters as well as red, green, and blue ones. 
     The R, G, and B lights having passes through the color wheel  272  with time differences are unified in illumination distribution by the rod integrator  273 , and then are emitted from the relay lens  274 . 
     As shown in  FIG. 16D , the DMD  277  is shifted upward with respect to the light axis L 1  of the rear refractive optical system  300 . The plane mirror  275  is tilted relative to a light axis of the light source  271  so that light from the light source  271  enters the DMD  277  at a predetermined incident angle. In addition, the concave mirror  276  is tilted relative to the light axis of the light source  271  and the light axis L 1  of the rear refractive optical system  300 , so that light from the light source  271  enters the DMD  277  at a predetermined incident angle, and the concave mirror  276  is eccentrically arranged. 
     The light (R, G, and B lights) emitted from the relay lens group  274  is reflected by the plain mirror  275 , and then is reflected by the concave mirror  276  and radiated to the DMD  277 . Then, after being modulated by the DMD  277 , the light is entered into the rear refractive optical system  300 . 
     Since the filters in the color wheel  272  are switched at a high speed, images of the R, G, and B lights are combined and projected as one image onto a screen. 
     In this configuration example, as in the foregoing embodiment, optical components of the optical engine  270  such as the DMD  277  are mounted in a predetermined layout on the mounting plane of the optical components shown in  FIG. 1A . Accordingly, the optical components are scattered in a direction parallel to the projection plane (X-Y plane) shown in  FIG. 2A . 
     Some of the optical components such as the concave mirror  276  are tilted relative to the mounting plane. However, even if the concave mirror  276  and the like are held so as to be tilted, the mounting plane of the optical components is unchangeably perpendicular to the X-Z plane of  FIG. 1 . 
     Accordingly, it is possible to shorten the minimum throw distance as in the foregoing embodiment, even if the optical engine  200  of the foregoing embodiment is replaced by the optical engine  270  of this configuration example. In addition, it is possible to install the projector stably in the both usage patterns of floor projection and wall projection. 
     CONFIGURATION EXAMPLE 5 
       FIG. 17A  is a diagram showing a configuration of an optical engine  280  in the configuration example 5.  FIG. 17B  is a diagram showing a mounting state of an imager unit  288  on the mounting plane, as seen in the direction of arrow P in  FIG. 17A . This configuration example uses a three-plate DMD. 
       FIGS. 17A and 17B  are conceptual diagrams for describing light paths of color lights in the optical engine using a three-plate DMD. Therefore, it is to be noted that a three-dimensional layout of a light source  281 , a rod integrator  282 , a relay lens group  283 , a three-DMD color separating/combining prism  284 , and a TIR prism  284   a  is actually different from that shown in  FIGS. 17A and 17B . 
     The optical engine  280  includes a light source  281 , a rod integrator  282  and a relay lens group  283  constituting a light-guiding optical system, and an imager unit  288  modulating/combining light from the light-guiding optical system. 
     The imager unit  288  is formed by integrating the color separating/combining prism  284  for three-digital micro-mirror device (DMD), and a three-plate DMD  285 ,  286 , and  287 . 
     Light emitted from the light source  281  is unified in illumination distribution by the rod integrator  282 , and then is entered into the TIR prism  284   a  of the three-DMD color separating/combining prism  284  via the relay lens group  283 . The details of a configuration of the three-DMD color separating/combining prism  284  are described in JP 2006-79080 A, for example. 
     The light entered into the three-DMD color separating/combining prism  284  is separated by dichroic films  284   b  and  284   c  constituting the three-DMD color separating/combining prism  284 . The R light enters an R light DMD  285 , the G light enters a G light DMD  286 , and the B light enters a B light DMD  287 . The R, G, and B lights modulated by the DMDs  285 ,  286 , and  287  are unified in light path by the three-DMD color separating/combining prism  284 , and image light with a combination of the color lights is entered from the TIR prism  284   a  into the rear refractive optical system  300 . 
     In this configuration example, as in the foregoing embodiment, optical components of the optical engine  280  such as the imager unit  288  are mounted in a predetermined layout on the mounting plane of the optical components shown in  FIG. 1A . Accordingly, the optical components are scattered in a direction parallel to the projection plane (X-Y plane) shown in  FIG. 2A . 
     As shown in  FIG. 17B , the imager unit  288  is held on the mounting plane by a holding section  289  in such a manner that the G light DMD  286  is parallel to the mounting plane and the three-DMD color separating/combining prism  284  is tilted relative to the mounting plane in the Y-axis direction. The R light DMD  285  and the B light DMD  287  are integrated with the three-DMD color separating/combining prism  284  in such a manner as to have a predetermined amount of tilt relative to the three-DMD color separating/combining prism  284 . This is for the purpose of allowing light to be radiated in an oblique direction relative to micro mirrors of the DMDs  285 ,  286 , and  287 , as in the configuration example 3. 
     Further, in accordance with the tilt of the three-DMD color separating/combining prism  284 , other optical components such as the light source  281  may be tilted relative to the mounting plane at a predetermined angle to the three-DMD color separating/combining prism  284 , by mounting a folding mirror as appropriate. However, if the three-DMD color separating/combining prism  284  and the like are held so as to be tilted, the mounting plane is unchangeably perpendicular to the X-Z plane in  FIGS. 1A and 1B . 
     Accordingly, it is possible to shorten the minimum throw distance as in the foregoing embodiment, even if the optical engine  200  of the foregoing embodiment is replaced by the optical engine  280  of this configuration example. In addition, it is possible to install the projector stably in the both usage patterns of floor projection and wall projection. 
     In this configuration example, the mounting plane of the optical components may be tilted in accordance with the tilt of the three-DMD color separating/combining prism  284  and other optical components, as in the configuration example 3. However, the optical components are unchangeably scattered within the projector in a direction parallel to the projection plane. Even in this case, it is possible to install the projector stably in the both usage patterns of floor projection and wall projection. 
     Others 
     If the optical engines in the configuration examples 1 to 5 are applied to the projector in another modification example shown in  FIGS. 10A to 14D , the imager units  235 ,  247 ,  267 , and  288  in the configuration examples 1 to 3 and 5 are each placed on the placement section  72  of the fixing member  70  and are shifted vertically by the shift mechanism. In the configuration example 4, the DMD  277  is placed on the placement section  72  and is shifted vertically by the shift mechanism. In addition, as in another modification example, the spot sizes of R, G, and B lights radiated to the imagers (LCOSs or DMDs) are set larger than effective display planes of the imagers so that light can be radiated to the effective display planes even when the imager modules or the like in the configuration examples move vertically. 
     In addition, the foregoing embodiment and modification examples use a lamp light source having a reflector as a light source. However, the light source is not limited to this and may be LEDs or laser diodes instead. In this case, in the optical engines with a single-plate DMD in the configuration examples 3 and 4, LEDs or laser diodes as a light source may be illuminated on for each color in a time-division manner, instead of using a color wheel. 
     Although the embodiment and modification examples of the present invention are described above, the present invention is not limited to by these embodiment and examples. Besides, the embodiment of the present invention can be further modified in various manners within the scope of technical ideas shown in the claims.