JP2008009304A - Illumination device and projection display device using the same - Google Patents

Abstract

[PROBLEMS] To reduce the use efficiency of light and the occurrence of irradiation unevenness due to the shift of the installation position of each part by using an optical fiber, and to illuminate light as compared with the conventional illumination device using an optical fiber. Increase the homogeneity of
A lighting device includes an optical fiber bundle, a red LED, a green LED, and a blue LED. The bundle 10 is configured by bundling a large number of optical fibers 11R, 11G, and 11B. One end of the bundle 10 is bundled to form a converging end 10A. The other end of the bundle 10 is bundled into three to form three branch ends 10R, 10G, and 10B. At the focusing end 10A, the optical fiber 11R at the branch end 10R, the optical fiber 11G at the branch end 10G, and the optical fiber 11B at the branch end 10B are arranged so as to be mixed with each other. Lights from the LEDs 12R, 12G, and 12B enter the branch ends 10R, 10G, and 10B, respectively.
[Selection] Figure 1

Description

  The present invention relates to an illumination device and a projection display device (projector) using the illumination device.

  Conventionally, in a lighting device that forms white light using LEDs of three primary colors, red, blue, and green, a dichroic mirror and a dichroic prism are used to synthesize the light of each color on one optical axis. (Patent Documents 1 and 2 below).

In Patent Document 3 below, three semiconductor lasers (first, second, and third semiconductor lasers) that emit red, blue, and green light, respectively, and three optical fibers that are optically coupled to these semiconductor lasers (first, second, and third semiconductor lasers) An illumination optical system (illumination device) including first, second, and third optical fibers) and a projector using the same have been proposed. In this illumination optical system, the exit ends of the three optical fibers are opposed to one condenser lens, and the light emitted from each optical fiber is incident on the light pipe by the condenser lens.
JP 2000-310742 A JP 2005-88512 A JP 2004-334083 A

  However, in the conventional illumination devices disclosed in Patent Documents 1 and 2, it is difficult to maintain the installation position accuracy between dichroic mirrors or dichroic prisms, and the installation position accuracy between these optical elements and LEDs, If these installation positions are deviated, the light use efficiency is reduced, or irradiation unevenness is caused.

  On the other hand, the conventional illumination device disclosed in Patent Document 3 uses an optical fiber and does not use a dichroic mirror or a dichroic prism. Compared with the illuminating device disclosed in No. 2, it is possible to reduce the decrease in light use efficiency and the occurrence of irradiation unevenness due to the displacement of the installation position.

  However, in the conventional illumination device disclosed in Patent Document 3, since the exit ends of the three optical fibers that guide the light of each color are arranged to face one condenser lens, the illumination light is emitted by the light pipe. Even though the homogeneity of the light was increased, the homogeneity of the illumination light was not so high even after passing through the light pipe.

  The present invention has been made in view of such circumstances, and by using an optical fiber, it is possible to reduce the use efficiency of light and the occurrence of irradiation unevenness due to the displacement of the installation position of each part, and An object of the present invention is to provide an illumination device capable of improving the homogeneity of illumination light and a projection display device using the illumination device, as compared with the conventional illumination device using an optical fiber.

  In order to solve the above-described problem, the illumination device according to the first aspect of the present invention is (i) an optical fiber bundle configured by bundling a plurality of optical fibers, and one end is bundled into a single bundle for focusing. And the other end is bundled into a plurality of bundles to form a plurality of branch ends, and the number of optical fibers at each branch end is two or more. An optical fiber bundle arranged so as to be mixed with each other; and (ii) a plurality of light sources provided corresponding to the plurality of branch ends, each of which is composed of one or more light emitting elements. And. The light emitted from each light source is incident on the branch end corresponding to the light source, and the wavelength of light emitted from at least one light emitting element among all the light emitting elements constituting the plurality of light sources and other The wavelength of light emitted from at least one light emitting element is different.

  The light emitting element may be, for example, an LED (light emitting diode), a laser diode, or an organic EL element.

  When each of the light sources is composed of two or more light emitting elements, it is preferable to use light emitting elements having the same wavelength as these two or more light emitting elements, but it is also possible to use light emitting elements having different wavelengths. is there.

  The light emission timing of the light emitting element can be determined as appropriate. For example, all the light emitting elements constituting the plurality of light sources may be driven to emit light at substantially the same timing. In addition, among all the light emitting elements constituting the plurality of light sources, those emitting light of different wavelengths may be driven to emit light at different timings.

  In the illumination device according to the second aspect of the present invention, in the first aspect, the number of the plurality of branch ends is n (n is an integer of 3 or more), and the illumination device is viewed from the optical axis direction of the focusing end. In addition, the plurality of branch ends are located at positions near the apexes of the regular n-gon, and the focusing end is located at a position near the center of the regular n-gon.

  The lighting device according to a third aspect of the present invention is the lighting device according to the first or second aspect, wherein the light source is disposed between at least one branch end of the plurality of branch ends and the corresponding light source. Condensing means for condensing emitted light to the branch end is provided.

  The condensing means is not limited to the one containing the resin described later as in the following fourth and fifth aspects, and may be a single condensing lens, a microlens array, or the like, for example.

  In the illumination device according to a fourth aspect of the present invention, in the third aspect, the light condensing means is filled in the optical path so that no gas exists in the optical path between the light source and the branch end. Resin.

  In the illumination device according to a fifth aspect of the present invention, in the fourth aspect, the refractive index of at least a portion in contact with the branch end in the resin is substantially the same as the refractive index of the core of the optical fiber at the branch end. There is something.

  A projection display device according to a sixth aspect of the present invention is the illumination device according to any one of the first to fifth aspects, a spatial light modulator that modulates light emitted from the focusing end, and the spatial light. A projection optical system for projecting light modulated by the modulator.

  The homogeneity of the illumination light incident on the spatial light modulator also changes depending on the arrangement of the converging ends and the branch ends of the optical fiber bundle. Therefore, the arrangement should be adjusted so that the homogeneity of the illumination light is further increased. Is preferred.

  The projection display device according to a seventh aspect of the present invention is the light guide means for guiding the light emitted from the focusing end to the spatial light modulator in the sixth aspect, and does not have the light guide means. Compared to the case, light guiding means for increasing the light incident on the spatial light modulator and improving the homogeneity of the light incident on the spatial light modulator is provided.

  Examples of the light guide means include a microlens array, a rod mirror, a rod lens, and a light dispersion plate in addition to the light pipe as in the eighth aspect described below.

  A projection display device according to an eighth aspect of the present invention is the projection display device according to the sixth aspect, further comprising a light pipe that guides the light emitted from the focusing end to the spatial light modulator.

  In the projection display device according to a ninth aspect of the present invention, in any of the sixth to eighth aspects, the spatial light modulator is a transmissive spatial light modulator, and the optical axis of the focusing end and the optical axis are The optical axis of the spatial light modulator and the optical axis of the projection optical system are coaxial.

  In the sixth to eighth aspects, a reflective spatial light modulator such as a DMD (digital mirror device) or a reflective liquid crystal panel may be used as the spatial light modulator.

  According to the present invention, by using an optical fiber, it is possible to reduce the use efficiency of light and the occurrence of uneven irradiation due to the shift of the installation position of each part, and the conventional illumination device using the optical fiber. As compared with the above, it is possible to provide an illuminating device capable of enhancing the homogeneity of illumination light and a projection display device using the illuminating device.

  Hereinafter, an illumination device according to the present invention and a projection display device using the same will be described with reference to the drawings.

  FIG. 1 is a schematic configuration diagram schematically showing a projection display device according to an embodiment of the present invention.

  The projection display device according to the present embodiment includes an illumination device 1, a transmissive liquid crystal panel 2 as a spatial light modulator that modulates light emitted from a focusing end 10A of an optical fiber bundle 10 of the illumination device 1, and a focusing device. A light pipe 3 as light guide means for guiding light emitted from the end 10A to the transmissive liquid crystal panel 2 and a projection optical system for projecting light (display image) modulated by the transmissive liquid crystal panel 2 onto the screen 5 A projection lens 4.

  In the present embodiment, the illumination device 1 includes an optical fiber bundle 10, an LED (red LED) 12R that emits red light, an LED (green LED) 12G that emits green light, and an LED (that emits blue light). Blue LED) 12B.

  The optical fiber bundle 10 is configured by bundling a large number of optical fibers 11R, 11G, and 11B. One end of the optical fiber bundle 10 is bundled into one bundle to form a focusing end 10A. The other end of the optical fiber bundle 10 is bundled into three bundles to form three branch ends 10R, 10G, and 10B. The number of optical fibers 11R at the branch end 10R (that is, the number of optical fibers 11R bundled at the branch end 10), the number of optical fibers 11G at the branch end 10G, and the number of optical fibers 11B at the branch end 10B are respectively 2 or more.

  In FIG. 1, for convenience of drawing notation, each branch part of the optical fiber bundle 10 is shown as if it is arranged in the same plane as the converging part. As shown in FIG. 2, they are arranged three-dimensionally. FIG. 2 is a schematic perspective view showing an arrangement example of the illumination device 1 in FIG. In the example shown in FIG. 2, when viewed from the direction of the optical axis O of the focusing end 10A, n (n = 3 in this embodiment) branch ends 10R, 10G, and 10B are regular n-gons (this embodiment). In this form, the converging end 10A is located at a position near the center of the regular n-gon. Adopting such an arrangement is preferable because the space in the apparatus can be used effectively, and the footprint of the apparatus (the footprint viewed from the direction of the optical axis O) can be reduced and the size can be reduced. . In addition, when such an arrangement is adopted, the positions of the LEDs 12R, 12G, and 12B can be separated so that they are not affected by the heat generated by each of them. As described above, the use of the arrangement shown in FIG. 2 has a great advantage. However, the present invention is not necessarily limited to such an arrangement, and other three-dimensional arrangements and two-dimensional arrangements are used. It may be adopted.

  In the present embodiment, as shown in FIGS. 1 and 2, one red LED 12R is provided as a light source corresponding to the branch end 10R, the red LED 12R is disposed to face the branch end 10R, and the red LED 12R emits light. The red light thus incident is incident on each optical fiber 11R constituting the branch end 10R. Similarly, one green LED 12G is provided as a light source corresponding to the branch end 10G, the green LED 12G is disposed to face the branch end 10G, and the green light emitted from the green LED 12G constitutes each of the branch ends 10G. The light enters the optical fiber 11G. Similarly, one blue LED 12B is provided as a light source corresponding to the branch end 10B, the blue LED 12B is disposed opposite to the branch end 10B, and the blue light emitted from the blue LED 12B is formed from the branch end 10B. The light enters the optical fiber 11B. In the present embodiment, LEDs 12R, 12G, and 12B with a lens 12a are used.

  In the present embodiment, other light emitting elements such as laser diodes and organic EL elements may be used in place of the LEDs 12R, 12G, and 12B. In the present embodiment, as described above, the light sources corresponding to the branch ends 10R, 10G, and 10B are configured by one LED 12R, 12G, and 12B. The corresponding light source may be composed of two or more LEDs. For example, the light source corresponding to the branch end 10R may be composed of two or more red LEDs, and the light emitted from the two or more red LEDs may enter the branch end 10R. When the light source corresponding to one branch end is constituted by two or more light emitting elements, it is preferable to use light emitting elements having the same color (that is, light having the same wavelength) as the two or more light emitting elements. . However, the present invention is not necessarily limited to this, and it is possible to use light emitting elements having different colors (that is, light having different wavelengths) as the two or more light emitting elements. In this case, the arrangement of the optical fibers at the focusing end 10A may be appropriately determined in accordance with the adoption status of the emission colors of the two or more light emitting elements.

  In the present embodiment, at the focusing end 10A of the optical fiber bundle 10, for example, as shown in FIGS. 3 to 7, the optical fiber 11R at the branch end 10R (that is, the optical fiber 11R having one end bundled with the branch end 10R). The optical fiber 11G at the branch end 10G and the optical fiber 11B at the branch end 10B are arranged so as to be mixed with each other. 3 to 7 are diagrams schematically illustrating examples of arrangement of the optical fibers 11R, 11G, and 11B at the converging end 10A of the optical fiber bundle 10. FIG.

  In the example shown in FIG. 3, the optical fibers 11R, 11G, and 11B form vertical columns, and these columns are sequentially arranged in the horizontal direction, and the optical fibers 11R, 11G, and 11B are mixed only in the horizontal direction.

  In the example shown in FIG. 4, the optical fibers 11R, 11G, and 11B are mixed in the horizontal direction and the vertical direction.

  In the example shown in FIG. 5, although the optical fibers 11R, 11G, and 11B are mixed in the horizontal direction and the vertical direction, the number of the green optical fibers 11G is changed to the red optical fibers 11R and the blue optical fibers. This is an example in comparison with 11B. In this case, when the output of the green LED is lower than the output of the red LED and the output of the blue LED, the luminance of each color can be made uniform. In this case, for example, the number of optical fibers of each branch end 10R, 10G, 10B may be changed without increasing the branch ends, or the branch ends are increased by one to four, and the added branch ends are A green LED may be arranged separately from the green LED 12G for the branch end 10G, and the optical fiber at the branch end may be regarded as the optical fiber 11G at the branch end 10G as shown in FIG.

  In the example shown in FIG. 6, the optical fibers 11R, 11G, and 11B form horizontal rows, and these rows are sequentially arranged in the vertical direction, and the optical fibers 11R, 11G, and 11B are mixed only in the vertical direction.

  In the example shown in FIGS. 3 to 6, each optical fiber is arranged so as to be positioned at the grid, whereas in the example shown in FIG. 7, each optical fiber is in a close-packed state. Is arranged. The example shown in FIG. 7 is obtained by changing the arrangement shown in FIG. 3 to the close-packed state, but each example shown in FIGS. 4 to 6 may be changed to the close-packed state.

  In the present embodiment, the optical fibers 11R, 11G, and 11B are arranged at the focusing end 10A so as to form a rectangular shape that matches the rectangular shape of the display screen as shown in FIGS. .

  FIG. 8 is an enlarged view of the vicinity of the light pipe 3 in FIG. 1, and also shows the state of light emitted from the focusing end 10A. In the present embodiment, the light pipe 3 is a cylindrical member having an inner reflection surface that is rectangular in cross section perpendicular to the optical axis O. The light pipe 3 emits light emitted from the converging end 10A so as to increase the light incident on the transmissive liquid crystal panel 2 and to increase the homogeneity of the light incident on the transmissive liquid crystal panel 2 as compared with the case without this. To the transmissive liquid crystal panel 2. Instead of the light pipe 3, for example, a micro lens array, a rod mirror, a rod lens, a light dispersion plate, or the like may be used. Thus, although it is preferable to provide light guide means such as the light pipe 3, it is not always necessary to provide such light guide means in the present invention.

  In this embodiment, as shown in FIGS. 1 and 8, the optical axis of the converging end 10A of the optical fiber bundle 10, the optical axis of the light pipe 3, the optical axis of the transmissive liquid crystal panel 2, and the light of the projection lens 4 are used. The axis is coaxial O. Therefore, the apparatus can be remarkably reduced in size. However, the present invention is not limited to this. For example, instead of the transmissive liquid crystal panel 2, a reflective spatial light modulator such as a DMD or a reflective liquid crystal panel is used, and each optical axis is bent appropriately. May be.

  By the way, as the transmissive liquid crystal panel 2, a color panel having a color filter of each color for each pixel may be used, or a panel having no color filter for each pixel may be used. In the former case, the LEDs 12R, 12G, and 12B may be driven to emit light at the same timing. In the latter case, the LEDs 12R, 12G, and 12B may be driven so as to sequentially emit light at different timings. In this case, the transmissive liquid crystal panel 2 is driven so as to perform spatial light modulation with the image signal of the color being emitted.

  In the lighting device 1 used in the present embodiment, optical fibers 11R, 11G, and 11B are used, and no dichroic mirror or dichroic prism is used. Compared with the conventional illumination devices disclosed in Documents 1 and 2, it is possible to reduce the decrease in light use efficiency and the occurrence of uneven irradiation due to the displacement of the installation position.

  Moreover, in the illuminating device 1 used in this embodiment, the light of each color of red, green, and blue is not guided by one total of three optical fibers, but three branch ends 10R, 10G, 10B. The optical fibers 11R, 11G, and 11B of the branch ends 10R, 10G, and 10B are combined at the converging end 10A to synthesize light of each color. Therefore, according to this illuminating device 1, compared with the conventional illuminating device disclosed by patent document 3, the homogeneity of illumination light can be improved.

  Therefore, according to the present embodiment, it is possible to easily attach, position adjust, and replace the light source and improve the image quality of the display image.

  This embodiment may be modified as shown in FIGS. 9 to 12, for example.

  FIG. 9 is an enlarged view of a main part showing a first modification, and also shows a state of light emitted from the green LED 12G and incident on the branch end 10G. In the first modification, in the embodiment, the green LED 12G that does not have the lens 12a is used, and the condenser lens 21 is disposed between the green LED 12G and the branch end 10G of the optical fiber bundle 10, The light emitted from the green LED is condensed by the condenser lens 21 and enters the branch end 10G. In addition, in FIG. 9, 12b has shown typically the light emission part of LED12G (this point is the same also about FIG. 10 thru | or FIG. 12 mentioned later). In addition, you may deform | transform similarly between FIG. 9 between the red LED 12R and the branch end 10R, and between the blue LED 12B and the branch end 10B.

  FIG. 10 is an enlarged view of a main part showing a second modification, and also shows a state of light emitted from the green LED 12G and incident on the branch end 10G. In the second modification, in the above-described embodiment, the green LED 12G that does not have the lens 12a is used, so that no gas exists in the optical path between the green LED 12G and the branch end 10G of the optical fiber bundle 10. The optical path is filled with resins 22a and 22b. The refractive index of the resin 22a on the green LED 12G side is higher than the refractive index of the resin 22b, and the resin 22a forms a convex lens. In this modification, the resins 22a and 22b constitute a condensing unit that condenses the light emitted from the green LED 12G onto the branch end 10G.

  As shown in FIG. 10, the light emitted from the green LED 12G is collected relatively weakly by the convex lens 22a, and then passes through the resin 22b and enters the branch end 10G as it is, or is totally reflected by the side surface of the resin 22b. Then, the light enters the branch end 10G. Therefore, in the modification shown in FIG. 10, the light emitted from the green LED 12G can be incident on the branch end 10G with low loss. The refractive index of the resin 22b on the branch end 10G side is preferably substantially the same as the refractive index of the core of the optical fiber 11G. In this case, since reflection at the end face of the core of the optical fiber 11G is reduced, light emitted from the green LED 12G can be incident on the branch end 10G with lower loss.

  In addition, you may deform | transform similarly between FIG. 10 between red LED12R and the branch end 10R, and between blue LED12B and the branch end 10B.

  FIG. 11 is an enlarged view of a main part showing a third modification, and also shows a state of light emitted from the green LED 12G and incident on the branch end 10G. In the third modification, in the above-described embodiment, the green LED 12G that does not have the lens 12a is used, so that no gas exists in the optical path between the green LED 12G and the branch end 10G of the optical fiber bundle 10. The resin 23 is filled in the optical path. In this modification, the resin 23 constitutes a condensing unit that condenses the light emitted from the green LED 12G onto the branch end 10G.

  As shown in FIG. 11, the light emitted from the green LED 12G passes through the resin 22b and enters the branch end 10G as it is, or is totally reflected by the side surface of the resin 23 and then enters the branch end 10G. Therefore, in the modification shown in FIG. 11, the light emitted from the green LED 12G can be incident on the branch end 10G with low loss. The refractive index of the resin 23 is preferably substantially the same as the refractive index of the core of the optical fiber 11G. In this case, since reflection at the end face of the core of the optical fiber 11G is reduced, light emitted from the green LED 12G can be incident on the branch end 10G with lower loss.

  In addition, between red LED 12R and branch end 10R, and between blue LED 12B and branch end 10B, you may deform | transform similarly to FIG.

  FIG. 12 is an enlarged view of a main part showing a fourth modified example, and also shows a state of light emitted from the green LED 12G and incident on the branch end 10G. In the fourth modification, the light pipe 24 connects the green LED 12G with the lens 12a and the branch end 10G of the optical fiber bundle 10 in the above embodiment. In this modification, the degree of light collection by the lens 12a is relatively weak. In this modification, the light pipe 24 constitutes a condensing unit that condenses the light emitted from the green LED 12G onto the branch end 10G.

  As shown in FIG. 12, the light emitted from the green LED 12G is collected relatively weakly by the lens 12a and then enters the branch end 10G as it is or is reflected by the inner surface (reflection surface) of the light pipe 24. The light enters the branch end 10G. Therefore, in the modification shown in FIG. 12, the light emitted from the green LED 12G can be incident on the branch end 10G with low loss. The red LED 12R and the branch end 10R and the blue LED 12B and the branch end 10B may be modified in the same manner as in FIG.

  As mentioned above, although one Embodiment of this invention and each modification were demonstrated, this invention is not limited to these.

  For example, when full-color display is performed using four colors, an optical fiber bundle 10 having four branch ends may be used, and light of each color may be incident on each branch end. Similarly, when performing color display with two colors, an optical fiber bundle 10 having two branch ends may be used, and light of each color may be incident on each branch end.

  The application of the illumination device according to the present invention is not limited to the projection display device, and can be used in various applications such as a light source for a scanner, a light source for a portable display, and a light source for a microscope.

It is a schematic block diagram which shows typically the projection type display apparatus by one embodiment of this invention. It is a schematic perspective view which shows the example of arrangement | positioning of the illuminating device in FIG. It is a figure which shows typically the example of 1 arrangement | positioning of the optical fiber in the condensing end of an optical fiber bundle. It is a figure which shows typically the other example of arrangement | positioning of the optical fiber in the condensing end of an optical fiber bundle. It is a figure which shows typically the further example of arrangement | positioning of the optical fiber in the condensing end of an optical fiber bundle. It is a figure which shows typically the further example of arrangement | positioning of the optical fiber in the condensing end of an optical fiber bundle. It is a figure which shows typically the further example of arrangement | positioning of the optical fiber in the condensing end of an optical fiber bundle. It is an enlarged view of the vicinity of the light pipe in FIG. It is a principal part enlarged view which shows a 1st modification. It is a principal part enlarged view which shows the 2nd modification. It is a principal part enlarged view which shows the 3rd modification. It is a principal part enlarged view which shows the 4th modification.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Illuminating device 2 Transmission type liquid crystal panel 3 Light pipe 4 Projection lens 10 Optical fiber bundle 10A Focusing end 10R, 10G, 10B Branching end 11R, 11G, 11B Optical fiber 12R, 12G, 12B LED

Claims (9)

An optical fiber bundle configured by bundling a plurality of optical fibers, wherein one end is bundled into one bundle to form a focusing end and the other end is bundled into a plurality of bundles to form a plurality of branch ends, The number of optical fibers at each branch end is two or more, and an optical fiber bundle disposed so that the optical fibers at the branch ends are mixed with each other at the focusing end;
A plurality of light sources provided corresponding to the plurality of branch ends, each of which is composed of one or more light emitting elements;
With
The light emitted from each light source is incident on the branch end corresponding to the light source,
An illumination apparatus, wherein a wavelength of light emitted from at least one light emitting element among all the light emitting elements constituting the plurality of light sources is different from a wavelength of light emitted from at least one other light emitting element.   The number of the plurality of branch ends is n (n is an integer of 3 or more), and when viewed from the optical axis direction of the converging end, the plurality of branch ends are located at positions near each vertex of the regular n-gon. The lighting device according to claim 1, wherein the illuminating device is located at a position near the center of the regular n-gon.   Condensing means for condensing light emitted from the light source to the branch end is provided between at least one branch end of the plurality of branch ends and the light source corresponding to the branch end. The lighting device according to claim 1.   4. The illumination device according to claim 3, wherein the condensing unit includes a resin filled in the optical path so that no gas exists in the optical path between the light source and the branch end.   5. The lighting device according to claim 4, wherein a refractive index of at least a portion of the resin in contact with the branch end is substantially the same as a refractive index of a core of the optical fiber at the branch end. A lighting device according to any one of claims 1 to 5;
A spatial light modulator for modulating light emitted from the focusing end;
A projection optical system for projecting light modulated by the spatial light modulator;
A projection type display device comprising:   Light guiding means for guiding light emitted from the focusing end to the spatial light modulator, which increases light incident on the spatial light modulator and increases the spatial light as compared to the case without the light guiding means. 7. A projection type display device according to claim 6, further comprising a light guide means for improving the homogeneity of light incident on the modulator.   The projection display device according to claim 6, further comprising a light pipe that guides light emitted from the focusing end to the spatial light modulator. The spatial light modulator is a transmissive spatial light modulator;
9. The projection display device according to claim 6, wherein an optical axis of the focusing end, an optical axis of the spatial light modulator, and an optical axis of the projection optical system are coaxial.

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