CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2004-078656, filed Mar. 18, 2004, the entire contents of which are incorporated herein by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a projecting apparatus and a projecting and displaying apparatus which synthesize images formed on a plurality of image forming devices, such as liquid crystal cells, to project and display the synthesized image on a projection surface such as a screen. 
   2. Description of the Related Art 
   A liquid crystal projecting apparatus is known which synthesizes images formed on a plurality of liquid crystal cells to project and display the synthesized image on a projection surface such as a screen. 
     FIG. 6  is a diagram showing the configuration of a conventional liquid crystal projecting apparatus.  FIG. 7  is a diagram illustrating that on-axis chromatic aberration may occur with a conventional liquid crystal projecting apparatus.  FIG. 8  is a diagram illustrating that magnification chromatic aberration may occur with the conventional liquid crystal projecting apparatus. 
   As shown in  FIG. 6 , in this liquid crystal projecting apparatus, a white light source  100  emits white light w. Then, an illuminating optical system  101  and a polarizing optical system  102  adjust the form of a luminous flux and the state of polarization. 
   An interference filter  103  then separates the white light w for which the shape of the luminous flux and the state of polarization have been adjusted, into lights R, G, B in three respective wavelength areas corresponding to red, green, and blue. The red, green, and blue lights R, G, and B are incident on first prisms  104   a  to  104   c  to illuminate liquid crystal cells  105   a  to  105   c  arranged opposite the first prisms  104   a  to  104   c.    
   When the liquid crystal cells  105   a  to  105   c  are illuminated with the lights R, G, and B, images corresponding to the lights R, G, and B are displayed on the liquid crystal cells  105   a  to  105   c,  respectively. The images displayed on the liquid crystal cells  105   a  to  105   c  pass through the first prisms  104   a  to  104   c,  respectively. A second prism  106  then superimposes the images on one another. The resulting image is projected and displayed by a projection lens  107  on a projection surface  108  such as a screen. 
   However, with a liquid crystal projecting apparatus configured as described above, when the lights R, G, and B pass through the projection lens  107 , a difference in wavelength between the lights may cause on-axis chromatic aberration or magnification chromatic aberration, as shown in  FIGS. 7 and 9 . As a result, the image projected on the projection surface  108  may appear blurred. 
   Thus, according to the prior art, the projection lens  107  is composed of a plurality of lenses and the shapes, materials, and arrangement of the lenses are improved so as to correct the on-axis chromatic aberration or the magnification chromatic aberration. 
   However, the projection lens  107  configured as described above is disadvantageous in that for example, the design is complex, is large in size, has a large number of constituent lenses, has a low degree of freedom in selecting the materials of the lenses, and is heavy. This contributes to increasing the size, weight, and cost of the whole apparatus. 
   Thus, a liquid crystal projecting apparatus has been disclosed in which the spacing between each of the liquid crystal cells and the second prism varies (see, for example, Jpn. Pat. Appln. KOKAI Publication No. 2001-5098). According to this liquid crystal projecting apparatus, even with a projection lens not having a function for correcting chromatic aberration, an image on the projection surface can be prevented from undergoing chromatic aberration by arranging the liquid crystal cells so that the optical distances of each type of light between the liquid crystal cells and the projection lens are equal. 
   However, magnification chromatic aberration, which may occur in the image on the projection surface, cannot be corrected even by arranging the liquid crystal cells as previously described. 
   BRIEF SUMMARY OF THE INVENTION 
   In view of the above problems, it is an object of the present invention to provide a projecting apparatus that can correct on-axis chromatic aberration and magnification chromatic aberration which may occur in an image on a projection surface without complicating the design, reducing the degree of freedom in selecting materials, increasing the number of constituent lenses, or increasing the size or weight. 
   To solve the above problems and accomplish this object, a projecting apparatus and a projecting and displaying apparatus are configured as described below. 
   (1) A projecting apparatus comprises a light source which emits a plurality of lights having different wavelength areas, a plurality of image forming devices which are arranged on respective optical paths for the lights emitted by the light source and which are irradiated with the lights to form images via the lights, magnifying devices which process and magnify the respective images formed by the image forming devices to form magnified images, synthesizing devices placed on respective optical paths for the lights via which the magnified images are transmitted, the synthesizing devices superimposing the lights on one another to synthesize the magnified images together to form a synthesized image, and a projection lens placed on an optical path for the light formed by the synthesizing device to project the light. 
   (2) In the projecting apparatus set forth in (1), an optical distance of each light between each of the plurality of image forming apparatuses and a projection surface can be adjusted. 
   (3) In the projecting apparatus set forth in (1), the light source has a white light source which emits white light and an interference filter which separates the white light emitted by the white light source into red light, green light, and blue light. 
   (4) In the projecting apparatus set forth in (1), the light source has a first monochromatic light source that emits red light, a second monochromatic light source that emits green light, and a third monochromatic light source that emits blue light. 
   (5) In the projecting apparatus set forth in (1), the light source has a first monochromatic light source that emits red light, a second monochromatic light source that emits green light, a third monochromatic light source that emits blue light, a superimposition lens which superimposes the red light, green light, and blue light emitted by the first to third monochromatic light sources to form white light, and an interference filter which separates the white light formed by the superimposition lens into red light, green light, and blue light. 
   (6) In the projecting apparatus set forth in (1), a distance between the image forming device and synthesizing device for each light increases in order of blue, green, and red. 
   (7) In the projecting apparatus set forth in (1), a magnification for the magnifying device present for each color increases in order of blue, green, and red. 
   (8) In the projecting apparatus set forth in (4), each of the first to third monochromatic light sources is a laser, a light emitting diode, or a laser diode. 
   (9) In the projecting apparatus set forth in (5), each of the first to third monochromatic light sources is a laser, a light emitting diode, or a laser diode. 
   (10) A projecting and displaying apparatus comprises a light source which emits a plurality of lights having different wavelength areas, a plurality of image forming devices which are arranged on respective optical paths for the lights emitted by the light source and which are irradiated with the lights to form images via the lights, magnifying devices which process and magnify the respective images formed by the image forming devices to form magnified images, synthesizing devices placed on respective optical paths for the lights via which the magnified images are transmitted, the synthesizing devices superimposing the lights on one another to synthesize the magnified images together to form a synthesized image, a projection lens placed on an optical path for the light formed by the synthesizing device to project the light, and a projection surface which receives the light projected by the projection lens to display the synthesized image. 
   (11) In the projecting and displaying apparatus set forth in (10), an optical distance of each light between each of the plurality of image forming apparatuses and the projection surface can be adjusted. 
   (12) In the projecting and displaying apparatus set forth in (10), the light source has a white light source which emits white light and an interference filter which separates the white light emitted by the white light source into red light, green light, and blue light. 
   (13) In the projecting and displaying apparatus set forth in (10), the light source has a first monochromatic light source that emits red light, a second monochromatic light source that emits green light, and a third monochromatic light source that emits blue light. 
   (14) In the projecting and displaying apparatus set forth in (10), the light source has a first monochromatic light source that emits red light, a second monochromatic light source that emits green light, a third monochromatic light source that emits blue light, a superimposition lens which superimposes the red light, green light, and blue light emitted by the first to third monochromatic light sources to form white light, and an interference filter which separates the white light formed by the superimposition lens into red light, green light, and blue light. 
   (15) In the projecting and displaying apparatus set forth in (10), a distance between the image forming device and synthesizing device for each light increases in order of blue, green, and red. 
   (16) In the projecting and displaying apparatus set forth in (10), a magnification for the magnifying device present for each color increases in order of blue, green, and red. 
   (17) In the projecting and displaying apparatus set forth in (13), each of the first to third monochromatic light sources is a laser, a light emitting diode, or a laser diode. 
   (18) In the projecting and displaying apparatus set forth in (14), each of the first to third monochromatic light sources is a laser, a light emitting diode, or a laser diode. 
   (19) In the projecting and displaying apparatus set forth in (15), each of the first to third monochromatic light sources is a laser, a light emitting diode, or a laser diode. 
   (20) In the projecting and displaying apparatus set forth in (16), each of the first to third monochromatic light sources is a laser, a light emitting diode, or a laser diode. 
   The present invention can correct on-axis chromatic aberration and magnification chromatic aberration which may occur in an image on a projection surface without complicating a design, reducing the degree of freedom in selecting materials, increasing the number of constituent lenses, or increasing the size or weight. 
   Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter. 


   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
     The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention, and together with the general description given above and the detailed description of the embodiments given below, serve to explain the principles of the invention. 
       FIG. 1  is a diagram showing the configuration of a liquid crystal projecting apparatus according to an embodiment of the present invention; 
       FIG. 2  is a diagram illustrating that the liquid crystal projecting apparatus according to the embodiment has corrected on-axis chromatic aberration; 
       FIG. 3  is a diagram illustrating that the liquid crystal projecting apparatus according to the embodiment has corrected magnification chromatic aberration; 
       FIG. 4  is a diagram showing the configuration of a liquid crystal projecting apparatus according to a first variation of the embodiment; 
       FIG. 5  is a diagram showing the configuration of a liquid crystal projecting apparatus according to a second variation of the embodiment; 
       FIG. 6  is a diagram showing the configuration of a conventional liquid crystal projecting apparatus; 
       FIG. 7  is a diagram illustrating that on-axis chromatic aberration may occur with a conventional liquid crystal projecting apparatus; and 
       FIG. 8  is a diagram illustrating that magnification chromatic aberration may occur with the conventional liquid crystal projecting apparatus. 
   


   DETAILED DESCRIPTION OF THE INVENTION 
   With reference to the drawings, description will be given below of the best mode for carrying out the present invention. 
     FIG. 1  is a diagram showing the configuration of a liquid crystal projecting apparatus (projecting and displaying apparatus) according to an embodiment of the present invention. 
   In  FIG. 1 , reference numerals  1 ,  2 ,  3 ,  4 , and  5  denote a white light source, a fly eye lens, and a polarizing optical element, an superimposition lens and an interference filter, respectively. Reference numerals  6   a,    6   b,  and  6   c  denote prisms. Reference numeral  7  denotes a cross dichroic prism (synthesizing device). References  8   a  and  8   c  denote first reflectors. Reference numerals  9   a,    9   b,  and  9   c  denote half wave-length plates. Reference numerals  10   a,    10   b,    10   c,  and  10   d  denote quarter wavelength plates. Reference numeral  11  denotes a second reflector. Reference numerals  12   a,    12   b,  and  12   c  denote liquid crystal cells (image forming devices). Reference numerals  13 ,  14 , and  15  denote an image processing device (magnifying device), a projection lens, and a screen (projection surface), respectively. 
   The white light source  1 , the fly eye lens  2 , the polarizing optical element  3 , the superimposition lens  4 , the interference filter  5 , the cross dichroic prism  7 , the projection lens  14 , and the screen  15  are arranged in parallel on an axis O. 
   The cross dichroic prism  7  is formed substantially cubic. The cross dichroic prism  7  is placed so that the center of its first surface  7   a  and the axis O cross at substantially right angles. 
   The prisms  6   a  and  6   c  are arranged opposite a second surface  7   b  and a third surface  7   c  of the cross dichroic prism  7  which are parallel with each other and which cross the first surface  7   a.  The prism  6   b  is placed opposite the first surface  7   a  of the cross dichroic prism  7 . 
   The liquid crystal cells  12   a,    12   b,  and  12   c  are arranged so that the spacings between the prisms  6   a,    6   b,  and  6   c  and the corresponding liquid crystal cells  12   a,    12   b,  and  12   c  have predetermined values La, Lb, and Lc, respectively. 
   La, Lb, and Lc can be set so that after passing through the liquid crystal cells  12   a,    12   b,  and  12   c,  lights R, G, and B (described later) travel an equal optical distance before being projected on the screen  15 . La&gt;Lb&gt;Lc is satisfied. 
   The white light source  1  is an incandescent lamp, a cold cathode tube, a halogen lamp, a mercury lamp, a high pressure mercury lamp, a white light emitting diode, or the like. 
   In this liquid crystal projecting apparatus, white light w emitted by the white light source  1  passes through the fly eye lens  2 , the polarizing optical element  3 , and the superimposition lens  4 . The white light w is incident on the interference filter  5 . In this case, when the white light w passes through the fly eye lens  2  and superimposition lens  4 , the shape of its luminous flux is adjusted. When the white light w passes through the polarizing optical element  3 , the state of its polarization is adjusted. 
   After entering the interference filter  5 , the white light w is separated into lights R, G, and B (red light, green light, and blue light) having wavelength areas corresponding to red, green, and blue. The lights R, G, and B travel along optical paths  30 ,  40 , and  50 , respectively. The lights R and B, which travel along the optical paths  30  and  50 , are reflected by the first reflectors  8   a  and  8   c,  respectively. The lights R and B then enter the prisms  6   a  and  6   c.  On the other hand, the light G, which travels along the optical path  40 , is incident on the prism  6   b.    
   After entering the prisms  6   a  and  6   c,  the lights R and B are reflected by an internal refracting interface in a substantially perpendicular direction. To enhance the reflectance of the prisms to a maximum, the lights  6   a  and  6   c  may be applied to internal refracting interface at an angle other than 45. The lights R and B then pass through the quarter wavelength plates  10   a  and  10   c.  The lights R and B then enter the liquid crystal cells  12   a  and  12   c,  respectively. Thus, images corresponding to the lights R and B are formed on the liquid crystal cells  12   a  and  12   c,  respectively. 
   On the other hand, after entering the prism  6   b,  the light G is reflected by an internal refracting interface in a substantially perpendicular direction. To enhance the reflectance of the prism  6   b  to a maximum, the light G may be applied to internal refracting interface at an angle other than 45. The light G then passes through the quarter wavelength plate  10   d.  The light G is then reflected by the reflector  11  in the opposite direction. The light G reflected by the second reflector  11  passes through the quarter wavelength plate  10   d.  The light G then enters the prism  6   b  again. 
   Since the light G passes through the quarter wavelength plate  10   d  twice, its phase is shifted by π/2[rad]. Accordingly, the light G is transmitted without being reflected by the refracting interface of the prism  6   b.  After being transmitted through the refracting interface, the light G passes through the quarter wavelength plate  10   b.  The light G then enters the liquid crystal cell  12   b.  Thus, an image corresponding to the light G is formed on the liquid crystal cell  12   b.    
   The images formed on the liquid crystal cells  12   a,    12   b,  and  12   c  are magnified by the image processing device  13  using magnifications Ga, Gb, and Gc (Ga&gt;Gb&gt;Gc is satisfied) for the lights R, G, and B. The resulting magnified images are displayed on the respective liquid cells  12   a,    12   b,  and  12   c.  After passing through the liquid crystal cells  12   a,    12   b,  and  12   c,  the lights R, G, and B have sectional shapes corresponding to the magnified images. 
   The magnifications Ga, Gb, and Gc are set so that when the lights R, G, and B having passed through the liquid cells  12   a,    12   b,  and  12   c  are projected on the screen  15 , the images obtained have an equal size. For example, if the image corresponding to the light G formed on the liquid crystal cell  12   b  is used as a reference (Gb=1), the image corresponding to the light R formed on the liquid crystal cell  12   a  is magnified using Ga&gt;1. The image corresponding to the light B formed on the liquid crystal cell  12   c  is magnified using Gc&lt;1. The reference for magnification may be the image corresponding to the light R or B instead of the image corresponding to the light G. 
   After passing through the liquid crystal cells  12   a  and  12   c,  the lights R and B pass through the quarter wavelength plates  10   a  and  10   c,  respectively. The lights R and B then enter the prisms  6   a  and  6   c,  respectively. Since the lights R and B pass through the quarter wavelength plates  10   a  and  10   c  twice, their phases are shifted by π/2[rad]. Accordingly, the lights R and B are transmitted without being reflected by the refracting interfaces of the prisms  6   a  and  6   c.  After being transmitted through the refracting interfaces, the lights R and B pass through the quarter wavelength plates  9   a  and  9   c,  respectively. The lights R and B then enter the cross dichroic prism  7 . 
   On the other hand, after passing through the liquid crystal cell  12   b,  the light G passes through the quarter wavelength plate  10   b.  The light G then enters the prism  6   b.  Since the light G passes through the quarter wavelength plate  10   b  twice, its phase is shifted by π/2[rad]. Accordingly, the light G is reflected by the refracting interface of the prism  6   b  in a substantially perpendicular direction. To enhance the reflectance of the prism  6   b  to a maximum, the light G may be applied to internal refracting interface at an angle other than 45. After being reflected by the refracting surface, the light G passes through the half wavelength plate  9   b.  The light G then enters the cross dichroic prism  7 . 
   The cross dichroic prism  7  superimposes the incident lights R, G, and B on one another to synthesize the magnified images corresponding images corresponding to the lights R, G, and B. One synthesized image is thus formed. The light R+G+B obtained by the superimposition through the dichroic prism  7  has a sectional shape corresponding to the synthesized image. 
   The light R+G+B from the cross dichroic prism  7  passes through the projection lens  14  and is then projected on the screen  15 . Thus, the synthesized image is displayed on the screen  15  in color. 
   With the liquid crystal projecting apparatus according to the present embodiment, the spacings (La, Lb, and Lc) between the prisms  6   a,    6   b,  and  6   c  and the corresponding liquid crystal cells  12   a,    12   b,  and  12   c  are adjusted so that after passing through the liquid crystal cells  12   a,    12   b,  and  12   c,  the lights R, G, and B travel an equal optical distance before being projected on the screen  15 . 
   This serves to correct possible on-axis chromatic aberration resulting from a difference in wavelength between the lights R and G and B. Therefore, a clear image can be projected on the screen. 
     FIG. 2  is a diagram illustrating that the liquid crystal projecting apparatus according to the embodiment has corrected on-axis chromatic aberration.  FIG. 2  indicates that all the focuses of the lights R, G, and B on the optical axis are located on the screen. This indicates that the on-axis chromatic aberration has been corrected. 
   Further, the images formed on the liquid crystal cells  12   a,    12   b,  and  12   c  are magnified by the image processing device  13  using the magnifications corresponding to the lights R, G, and B. 
   This serves to correct possible on-axis chromatic aberration resulting from a difference in wavelength between the lights R and G and B. Therefore, a clearer image can be projected on the screen. 
     FIG. 3  is a diagram illustrating that the liquid crystal projecting apparatus according to the embodiment has corrected magnification chromatic aberration. In  FIG. 3 , points P and Q on the image displayed on the liquid crystal cell  12   a  are the same as those on the image displayed on the liquid crystal cells  12   c.  The point P corresponds to the image after magnification. The point Q corresponds to the image before magnification. Further, solid lines indicate optical paths for the lights R, G, and B emitted from the point P. Dotted lines indicate optical paths for the lights R, G, and B emitted from the point Q. That is, as shown in  FIG. 3 , the liquid crystal cell  12   a  magnifies the image so that p/q (=Ga) &gt;1. The liquid crystal cell  12   b  magnifies the image so that p/q (=Gb)=1. The liquid crystal cell  12   c  magnifies the image so that p/q (=Gc) &lt;1. 
     FIG. 3  shows that the same part of the images is formed at the same position on the screen  15 . This indicates that magnification chromatic aberration has been corrected. 
   The present invention is not limited to the above embodiment. In implementation, the present invention can be embodied by varying the components of the embodiment without departing from the spirit of the invention. Further, various inventions can be formed by appropriately combining a plurality of the components disclosed in the embodiment. 
   For example, as shown in  FIG. 4 , it is possible to use, in place of the white light source  1 , a first to third monochromatic light sources  71   a,    71   b,  and  71   c  having wavelength areas for red, green, and blue, which are the three primary colors of light. 
   In this case, a fly eye lens  72   a,    72   b,  or  72   c,  a polarizing optical element  73   a,    73   b,  or  73   c,  and a superimposition lens  74   a,    74   b,  or  74   c  must be arranged on an optical path for each of the lights R, G, and B emitted from the first to third monochromatic light sources  71   a,    71   b,  and  71   c.  Each of the first to third monochromatic light sources  71   a,    71   b,  and  71   c  is a laser, laser diode, a light emitting diode, or the like. 
   Further, it is also possible to use, in place of the white light source  1 , the first to third monochromatic light sources  71   a,    71   b,  and  71   c  having the wavelength areas for red, green, and blue, which are the three primary colors of light, as shown in  FIG. 5 . In this case, a superimposition lens  75  is used to superimpose the lights R, G, and B emitted by the first to third monochromatic light sources  71   a,    71   b,  and  71   c,  on one another to form white light w. Then, the white like w is separated into red, green, and blue lights R, G, and B again. Each of the first to third monochromatic light sources  71   a,    71   b,  and  71   c  is a laser, laser diode, a light emitting diode, or the like. 
   Further, the present invention is not limited to the projector that projects and displays images on the screen  15  as previously described. The present invention may be used as, for example, a projecting apparatus that displays images on a television screen. 
   According to the present embodiment, the liquid crystal cells  12   a,    12   b,  and  12   c  are used as image forming device. However, the type of the image forming devices is not particularly limited provided that the devices are configured to display an image by allowing light from a light source such as a backlight to pass through, as in the case of liquid crystal display devices. 
   Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.
The present invention includes a light source which emits a plurality of lights having different wavelength areas, a plurality of image forming devices which are arranged on respective optical paths for the lights emitted by the light source and which are irradiated with the lights to form images via the lights, magnifying devices which process and magnify the respective images formed by the image forming devices to form magnified images, synthesizing devices placed on respective optical paths for the lights via which the magnified images are transmitted, the synthesizing devices superimposing the lights on one another to synthesize the magnified images together to form a synthesized image, and a projection lens placed on an optical path for the light formed by the synthesizing device to project the light.