US007631975B2
`
`(12) United States Patent
`Takaura et a].
`
`(10) Patent N0.:
`(45) Date of Patent:
`
`US 7,631,975 B2
`Dec. 15, 2009
`
`(54) PROJECTION OPTICAL SYSTEM,
`MAGNIFICATION PROJECTION OPTICAL
`SYSTEM, MAGNIFICATION PROJECTION
`APPARATUS, AND IMAGE PROJECTION
`APPARATUS
`
`(75) Inventors: Atsushi Takaura, Tokyo (JP); Kazuhiro
`Fujita, Tokyo (JP); Nobuo Sakuma,
`Tokyo (JP)
`
`(52) US. Cl. ........................... .. 353/99; 353/30; 353/97;
`353/102; 359/449; 359/649; 359/850; 362/297;
`362/299; 362/308
`(58) Field of Classi?cation Search ................. .. 353/30,
`353/31, 34, 37, 69, 70, 77479, 99, 102; 359/449,
`359/648, 650, 6564661, 663, 668, 7264731,
`3 5 9/ 739
`See application ?le for complete search history.
`
`(56)
`
`References Cited
`
`(73) Assignee: Ricoh Company, Ltd., Tokyo (JP)
`
`U.S. PATENT DOCUMENTS
`
`( * ) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 0 days.
`
`(21) Appl.No.: 12/233,653
`
`(22) Filed:
`
`Sep. 19, 2008
`
`(65)
`
`Prior Publication Data
`
`US 2009/0015801A1
`
`Jan. 15,2009
`
`Related US. Application Data
`
`(62) Division of application No. 11/345,493, ?led on Feb.
`2, 2006, noW Pat. No. 7,441,908, Which is a division of
`application No. 10/771,523, ?led on Feb. 5, 2004, noW
`Pat. No. 7,048,388.
`
`(30)
`
`Foreign Application Priority Data
`
`Feb. 6, 2003
`Feb. 6, 2003
`Dec. 8, 2003
`
`(JP)
`(JP)
`(JP)
`
`........................... .. 2003-029595
`2003-029602
`........................... .. 2003-409304
`
`(51) Int. Cl.
`G031; 21/20
`G031; 21/26
`G031; 21/14
`G031; 21/20
`G031; 21/56
`G021; 7/182
`
`(2006.01)
`(2006.01)
`(2006.01)
`(2006.01)
`(2006.01)
`(2006.01)
`
`2,510,080 A
`
`6/1950 Cuneo ...................... .. 352/244
`(Continued)
`FOREIGN PATENT DOCUMENTS
`
`JP
`JP
`JP
`JP
`
`04-107521
`4/1992
`6-91641
`11/1994
`07-013157
`1/1995
`2001-264627
`9/2001
`(Continued)
`Primary ExamineriMelissa J Koval
`(74) Attorney, Agent, or Firm4Oblon, Spivak, McClelland,
`Maier & Neustadt, L.L.P.
`(57)
`ABSTRACT
`A projection optical system for use in an image projection
`apparatus illuminating an image display panel forming an
`image in accordance With a modulating signal With illumina
`tion light from a light source. The projection optical system
`includes ?rst and second optical systems arranged along an
`optical path de?ning an upstream-downstream direction in
`the order described from upstream to downstream on the
`downstream side of the image display panel. The ?rst optical
`system includes at least one dioptric system and has positive
`poWer. The second optical system includes at least one
`re?ecting surface having poWer and has positive poWer. The
`image formed by the image display panel is formed as an
`intermediate image in the optical path, and the intermediate
`image is magni?ed and projected.
`
`6 Claims, 13 Drawing Sheets
`
`L1
`ELLU MJNATIC' N
`L181 11'
`
`
`
` 1
`
`ZEISS 1143
`Zeiss v. Nikon
`IPR2013-00363
`
`

`

`US 7,631,975 B2
`Page 2
`
`US. PATENT DOCUMENTS
`
`2009/0021703 A1
`
`1/2009 Takaura et :11.
`
`3,930,723 A *
`
`1/1976 Holt .......................... .. 353/70
`
`FOREIGN PATENT DOCUMENTS
`
`6,513,935 B2* 2/2003 Ogawa ...................... .. 353/37
`6,631,994 B2* 10/2003 Suzuki et a1.
`353/77
`6,771,427 B1* 8/2004 Matsuo ..................... .. 359/649
`6,873,476 B2
`3/2005 Shafer ...................... .. 359/731
`7,048,388 B2
`5/2006 Takaura e161. .............. .. 353/99
`7,085,075 B2
`8/2006 Mann 6161. ............... .. 359/656
`2001/0048558 A1 12/2001 Lin ............. ..
`.359/555
`2004/0119946 A1
`6/2004 Rudolph e161.
`353/31
`2004/0160666 A1
`8/2004 Hudyma ...... ..
`. 359/359
`2008/0304019 A1 12/2008 Takaura e161. .............. .. 353/38
`2009/0015910 A1
`1/2009 Takaura et a1.
`
`2001_324675
`JP
`20026398
`JP
`200240326
`JP
`2002-57963
`JP
`2002-174853
`JP
`2002-296503
`JP
`2003-75767
`JP
`2004-61959
`JP
`2004-61960
`JP
`2004'61961
`JP
`* cited by examiner
`
`11/2001
`1/2002
`2/2002
`2/2002
`6/2002
`10/2002
`3/2003
`2/2004
`2/2004
`2/2004
`
`2
`
`

`

`US. Patent
`
`Dec. 15, 2009
`
`Sheet 1 0f 13
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`US 7,631,975 B2
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`US. Patent
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`Dec. 15, 2009
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`Sheet 2 0f 13
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`US 7,631,975 B2
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`US. Patent
`US. Patent
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`Dec. 15, 2009
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`US 7,631,975 B2
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`Dec. 15, 2009
`Dec. 15, 2009
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`Sheet 4 0f 13
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`U.S. Patent
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`Dec. 15, 2009
`Dec. 15, 2009
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`Sheet 6 0f 13
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`US 7,631,975 B2
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`Dec. 15, 2009
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`Dec. 15, 2009
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`US 7,631,975 B2
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`U.S. Patent
`US. Patent
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`Dec. 15, 2009
`Dec. 15, 2009
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`Sheet 10 0f 13
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`U.S. Patent
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`Dec. 15, 2009
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`Sheet 11 0f 13
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`US. Patent
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`Dec. 15, 2009
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`US. Patent
`
`Dec. 15, 2009
`
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`US 7,631,975 B2
`
`1
`PROJECTION OPTICAL SYSTEM,
`MAGNIFICATION PROJECTION OPTICAL
`SYSTEM, MAGNIFICATION PROJECTION
`APPARATUS, AND IMAGE PROJECTION
`APPARATUS
`
`CROSS REFERENCE TO RELATED
`APPLICATION
`
`The present application is a Divisional of US. application
`Ser. No. 11/345,493 ?led Feb. 2, 2006, now US. Pat. No.
`7,441,908 Which is a Divisional of US. application Ser. No.
`10/771,523 ?ledon Feb. 5, 2004, now US. Pat. No. 7,048,388
`and in turn claims priority to JP 2003-029595 ?led on Feb. 6,
`2003, JP 2003-029602 ?led on February 6, 2003, and JP
`2003 -409304 ?led on Dec. 8, 2003, the entire contents of each
`of Which are hereby incorporated herein by reference.
`
`10
`
`BACKGROUND OF THE INVENTION
`
`1. Field of the Invention
`The present invention relates to a projection optical system,
`a magni?cation projection optical system, a magni?cation
`projection apparatus, and an image projection apparatus.
`2. Description of the Related Art
`Liquid crystal projectors are Widely knoWn as image pro
`jection apparatuses. In these days, the liquid crystal projec
`tors have employed liquid crystal panels With higher resolu
`tion, have enjoyed improved brightness due to higher
`e?iciencies of light source lamps, and have become less
`expensive.
`Further, small, light-Weight image projection apparatuses
`using a DMD (Digital Micromirror Device) have been Widely
`used not only in o?ices and schools but also at home. Particu
`larly, the portability of front-type projectors has been
`improved so that they are also used in small meetings.
`It is desired that projectors, or image projection appara
`tuses, be able to project a large-screen image. That is, it is
`desired to enlarge a projection screen. Further, it is also
`desired that a projection space required outside a projector be
`reduced as much as possible.
`In order to reduce the outside projection space While
`enlarging the projection screen, it is desirable to incorporate
`the light path of an imaging light beam forming a projected
`image as much as possible in the projector (image projection
`apparatus). The folloWing patent-related documents disclose
`image projection apparatuses employing such technique.
`Japanese Laid-Open Patent Application No. 2002-40326
`(PriorArt 1) discloses an image projection apparatus includ
`ing ?rst through fourth re?ecting mirrors to obtain a Wider
`angle of vieW While preventing an imaging optical system
`from becoming larger in siZe. The ?rst re?ecting mirror has a
`concave shape and each of the second through fourth re?ect
`ing mirrors has a convex shape. The imaging optical system is
`composed of the ?rst through fourth re?ecting mirrors. At
`least one of the ?rst through fourth re?ecting mirrors has a
`free-form surface so as to ensure projection performance.
`Japanese Laid-Open Patent Application No. 2002-174853
`(PriorArt 2) discloses an image projection apparatus that is a
`surface projection type display Whose projection distance to a
`screen is reduced. The surface projection type display
`includes an imaging optical system composed of a pair of a
`concave mirror and a convex mirror having divergence action
`and a projection lens.
`Japanese Examined Patent Application Publication No.
`6-91641 (PriorArt 3) discloses an image projection apparatus
`that is a video projector. The ?rst mirror surface of the imag
`
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`30
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`ing optical system of the video projector has a convex shape
`so as to reduce the thickness of the video projector.
`The image projection methods of PriorArt 1 and 3 perform
`image formation using only one or more re?ecting mirrors to
`magnify and project a single image on a screen. Therefore,
`these image projection methods enjoy the merit of no genera
`tion of chromatic aberration in principle. In the case of dis
`playing images of red, green, and blue separately, using three
`images instead of a single image, and combining the separate
`images on a screen, the intervention of a color combining part
`such as a cross prism or a Philips prism is necessary, thus
`resulting in the generation of chromatic aberration at the time
`of combining colors. HoWever, the imaging optical system
`composed of only re?ecting surfaces cannot correct chro
`matic aberration.
`According to an image projection apparatus disclosed in
`Japanese Laid-Open Patent Application No. 2001-264627
`(PriorArt 4), each light beam from an image display panel is
`guided to a screen successively by the positive-poWer imag
`ing lens system and the re?ection optical system including a
`negative-poWer curved surface mirror of a magni?cation pro
`jection optical system to be focused onto the screen.
`The screen and the imaging lens system are set so that the
`height of the screen is offset from the height of the imaging
`lens system. The light beams are re?ected back from the
`mirror to be guided to the screen. Therefore, the optical path
`length of the imaging light beam differs betWeen the upper
`side and the loWer side of the center part of the magni?ed
`projected image on the screen (corresponding to the center
`part of the image display panel), thus resulting in the genera
`tion of a so-called “trapezoidal distortion.”
`The trapeZoidal distortion is correctable by “keystone cor
`rection,” Which, hoWever, is likely to degrade the quality of
`the magni?ed image on the screen.
`It is Well knoWn to provide a convex mirror betWeen the
`imaging lens system and the screen so that the convex mirror
`is decentered With respect to the optical axis of the imaging
`lens system in order to reduce the trapeZoidal distortion. In
`the case of providing the convex mirror With decentration, the
`convex mirror is provided on the imaging lens side of the
`screen-side focus position of the imaging lens system so as to
`extend the focus position of a projection lens by the negative
`refracting poWer of the convex mirror.
`In order to realiZe a loW-pro?le, large- screen magni?cation
`projection apparatus With the above-described con?guration,
`the negative poWer of the convex mirror may be increased to
`Widen an angle of vieW. This, hoWever, requires stricter shape
`accuracy and stricter assembly tolerance of the convex mirror,
`and also increases distortion.
`Distortion may be reduced by decreasing the refractive
`poWer of the convex mirror by increasing the distance
`betWeen the imaging lens system and the convex mirror. As
`the distance betWeen the imaging lens system and the convex
`mirror increases, hoWever, the convex mirror becomes larger
`in siZe to increase its cost. Further, the magni?cation proj ec
`tion apparatus is also likely to become larger in siZe.
`According to Japanese Laid-Open Patent Application No.
`2002-296503, a magni?cation projection optical system is
`composed of only re?ecting mirrors. In the case of thus
`obtaining desired optical performance Without using a lens
`optical system, it is necessary to set the surface accuracy and
`position accuracy of each re?ecting surface to extremely high
`
`16
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`

`US 7,631,975 B2
`
`3
`values, thus requiring stricter assembly accuracy of the mag
`ni?cation projection optical system.
`
`SUMMARY OF THE INVENTION
`
`Accordingly, it is a general object of the present invention
`to provide a projection optical system, a magni?cation pro
`jection optical system, a magni?cation projection apparatus,
`and an image projection apparatus in Which the above-de
`scribed disadvantages are eliminated.
`Amore speci?c object of the present invention is to provide
`a projection optical system, a magni?cation projection opti
`cal system, and a magni?cation projection apparatus that can
`increase a projection screen in siZe, employ an imaging opti
`cal system including a re?ecting surface to reduce a projec
`tion space outside a projection apparatus, and at the same
`time, correct chromatic aberration.
`Another more speci?c object of the present invention is to
`provide an image projection apparatus including such a pro
`jection optical system.
`Yet another more speci?c object of the present invention is
`to reduce the thickness of an image projection apparatus and
`perform projection on a large screen Without distortion.
`One or more of the above-described objects of the present
`invention are achieved by a projection optical system for use
`in an image projection apparatus illuminating a light valve
`forming an image in accordance With a modulating signal
`With illumination light from a light source, the projection
`optical system including ?rst and second optical systems
`arranged along an optical path de?ning an upstream-doWn
`stream direction in an order described from upstream to
`downstream on a downstream side of the light valve, Wherein
`the ?rst optical system includes at least one dioptric system
`and has positive poWer; the second optical system includes at
`least one re?ecting surface having positive poWer; and the
`image formed by the light valve is formed as an intermediate
`image in the optical path, and the intermediate image is mag
`ni?ed and projected.
`The above-described projection optical system includes a
`?rst optical system and a second optical system. The image
`formed by the light valve is formed as an intermediate image
`in the optical path of the ?rst and second optical systems, and
`the intermediate image is further magni?ed and projected.
`Accordingly, high projection magni?cation can be realiZed.
`Since the ?rst optical system includes a dioptric system,
`chromatic aberration is correctable using the chromatic dis
`persion characteristic even in the case of employing a color
`composite prism. Further, since the optical path of imaging
`light beams is folded back by a re?ecting surface of the
`second optical system, the projection optical system can be
`made compact.
`One or more of the above objects of the present invention
`are also achieved by an image projection apparatus that illu
`minates a light valve forming an image in accordance With a
`modulating signal With illumination light from a light source,
`the image projection apparatus including: a projection optical
`system, the projection optical system including ?rst and sec
`ond optical systems arranged along an optical path de?ning
`an upstream-doWnstream direction in an order described
`from upstream to doWnstream on a doWnstream side of the
`light valve, Wherein the ?rst optical system includes at least
`one dioptric system and has positive poWer; the second opti
`cal system includes at least one re?ecting surface having
`positive poWer; and the image formed by the light valve is
`formed as an intermediate image in the optical path, and the
`intermediate image is magni?ed and projected by the proj ec
`tion optical system.
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`The above-described image projection apparatus can be
`made compact With a long optical path of image light beams
`being provided in a space in the apparatus. As a result, a
`large-siZe image can be projected and displayed With a
`reduced projection space outside the apparatus.
`One or more of the above objects of the present invention
`are also achieved by a magni?cation projection optical sys
`tem that guides a light beam from an image display panel to a
`screen in an upstream-doWnstream direction, projects the
`light beam from a direction inclined to a normal of the screen,
`and forms on the screen a magni?ed version of an image
`displayed on the image display panel, the magni?cation pro
`jection optical system including: a re?ection optical system;
`and a transmission optical system, Wherein the re?ection
`optical system includes a plurality of re?ecting surfaces hav
`ing poWer and includes at least one rotationally asymmetric
`re?ecting surface; and the transmission optical system
`includes a transmitting surface having refractive poWer and
`includes at least one aspheric surface.
`One or more of the above objects of the present invention
`are also achieved by a magni?cation projection optical sys
`tem that guides a light beam from an image display panel to a
`screen in an upstream-doWnstream direction, projects the
`light beam from a direction inclined to a normal of the screen,
`and forms on the screen a magni?ed version of an image
`displayed on the image display panel, the magni?cation pro
`jection optical system including: a transmission optical sys
`tem including a plurality of transmitting surfaces; a re?ection
`optical system including a plurality of re?ecting surfaces; and
`a diaphragm, Wherein one of the re?ecting surfaces, on Which
`a light beam pas sing through the diaphragm is made incident
`?rst, has negative poWer.
`One or more of the above objects of the present invention
`are also achieved by a magni?cation projection optical sys
`tem that guides a light beam from an image display panel to a
`screen in an upstream-doWnstream direction, projects the
`light beam from a direction inclined to a normal of the screen,
`and forms on the screen a magni?ed version of an image
`displayed on the image display panel, Wherein a position and
`a shape of an intermediate image of the image display panel
`formed With negative magni?cation by light beams traveling
`from the image display panel to the screen are substantially
`identical to a position and a shape, respectively, of an inter
`mediate image of the screen formed With negative magni?
`cation by light beams traveling from the screen to the image
`display panel.
`The above-described magni?cation projection optical sys
`tems can project the image on the image display panel as a
`large screen With little distortion.
`One or more of the above objects of the present invention
`are also achieved by a magni?cation projection apparatus
`that: displays an image on an image display panel; illuminates
`the image display panel With light from a light source; and by
`a magni?cation projection optical system, guides a light beam
`from the image display panel to a screen in an upstream
`doWnstream direction, projects the light beam from a direc
`tion inclined to a normal of the screen, and forms on the
`screen a magni?ed version of the image displayed on the
`image display panel, Wherein: the magni?cation projection
`optical system comprises a re?ection optical system and a
`transmission optical system; the re?ection optical system
`includes a plurality of re?ecting surfaces having poWer and
`includes at least one rotationally asymmetric re?ecting sur
`face; and the transmission optical system includes a transmit
`ting surface having refractive poWer and includes at least one
`aspheric surface.
`
`17
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`

`

`US 7,631,975 B2
`
`5
`One or more of the above objects of the present invention
`are also achieved by a magni?cation projection apparatus
`that: displays an image on an image display panel; illuminates
`the image display panel With light from a light source; and by
`a magni?cation projection optical system, guides a light beam
`from the image display panel to a screen in an upstream
`doWnstream direction, projects the light beam from a direc
`tion inclined to a normal of the screen, and forms on the
`screen a magni?ed version of the image displayed on the
`image display panel, Wherein: the magni?cation projection
`optical system comprises: a transmission optical system
`including a plurality of transmitting surfaces; a re?ection
`optical system including a plurality of re?ecting surfaces; and
`a diaphragm; and one of the re?ecting surfaces, on Which a
`light beam passing through the diaphragm is made incident
`?rst, has negative poWer.
`One or more of the above objects of the present invention
`are also achieved by a magni?cation projection apparatus
`that: displays an image on an image display panel; illuminates
`the image display panel With light from a light source; and by
`a magni?cation projection optical system, guides a light beam
`from the image display panel to a screen in an upstream
`doWnstream direction, projects the light beam from a direc
`tion inclined to a normal of the screen, and forms on the
`screen a magni?ed version of the image displayed on the
`image display panel, Wherein a position and a shape of an
`intermediate image of the image display panel formed With
`negative magni?cation by light beams traveling from the
`image display panel to the screen are substantially identical to
`a position and a shape, respectively, of an intermediate image
`of the screen formed With negative magni?cation by light
`beams traveling from the screen to the image display panel.
`The above-described magni?cation projection apparatuses
`can be realiZed With a loW-pro?le con?guration.
`One or more of the above objects of the present invention
`are also achieved by a projection optical system, including: a
`?rst optical system including at least one dioptric system and
`having positive poWer; and a second optical system including
`one or more re?ecting surfaces having poWer, the second
`optical system having positive poWer as a Whole, Wherein the
`?rst and second optical systems are arranged along an optical
`path de?ning an upstream-doWnstream direction in an order
`described from upstream to doWnstream on a doWnstream
`side of an object surface; an object image is temporarily
`formed as an intermediate image, and thereafter, is formed as
`a normal image; and With respect to an optical axis of an
`optical element positioned at a furthest upstream end of the
`?rst optical system and having refractive poWer, at least one
`of other optical elements is shifted or tilted.
`One or more of the above objects of the present invention
`are also achieved by a projection optical system, including: a
`?rst optical system including at least one dioptric system and
`having positive poWer; and a second optical system including
`one or more re?ecting surfaces having poWer, the second
`optical system having positive poWer as a Whole, Wherein the
`?rst and second optical systems are arranged along an optical
`path de?ning an upstream-doWnstream direction in an order
`described from upstream to doWnstream on a doWnstream
`side of an object surface; an object image is temporarily
`formed as an intermediate image, and thereafter, is formed as
`a normal image; and in the ?rst optical system, With respect to
`an optical axis of one of optical elements of the ?rst optical
`system, Which one is positioned at a furthest upstream end of
`the ?rst optical system and has refractive poWer, the other
`optical elements are prevented from being tilted.
`According to the above-described projection optical sys
`tems, the ?rst optical system forms an intermediate image,
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`and the second optical system magni?es and projects the
`intermediate image, thereby increasing the (enlarging) mag
`ni?cation of the composition of the optical systems. Since the
`?rst optical system includes a dioptric system, chromatic
`aberration is correctable using the chromatic dispersion char
`acteristic even in the case of employing a color composite
`prism. Further, by causing lens elements forming the dioptric
`system to be shifted or tilted, reverse distortion can be gen
`erated effectively in the intermediate image so as to prevent
`distortion from occurring in the projected image.
`One or more of the above objects of the present invention
`are also achieved by an image projection apparatus that, by a
`projection optical system, guides a light beam from an image
`display panel to a screen and forms on the screen a normal
`version of the image displayed on the image display panel,
`Wherein: the projection optical system includes: a ?rst optical
`system including at least one dioptric system and having
`positive poWer; and a second optical system including one or
`more re?ecting surfaces having poWer, the second optical
`system having positive poWer as a Whole; the ?rst and second
`optical systems are arranged along an optical path de?ning an
`upstream-downstream direction in an order described from
`upstream to doWnstream on a doWnstream side of an object
`surface; an object image is temporarily formed as an inter
`mediate image, and thereafter, is formed as a normal image;
`and With respect to an optical axis of an optical element
`positioned at a furthest upstream end of the ?rst optical sys
`tem and having refractive poWer, at least one of other optical
`elements is shifted or tilted.
`One or more of the above objects of the present invention
`are also achieved by an image projection apparatus that, by a
`projection optical system, guides a light beam from an image
`display panel to a screen and forms on the screen a normal
`version of the image displayed on the image display panel,
`Wherein: the projection optical system includes: a ?rst optical
`system including at least one dioptric system and having
`positive poWer; and a second optical system including one or
`more re?ecting surfaces having poWer, the second optical
`system having positive poWer as a Whole; the ?rst and second
`optical systems are arranged along an optical path de?ning an
`upstream-downstream direction in an order described from
`upstream to doWnstream on a doWnstream end of an object
`surface; an object image is temporarily formed as an inter
`mediate image, and thereafter, is formed as a normal image;
`and in the ?rst optical system, With respect to an optical axis
`of one of optical elements of the ?rst optical system, Which
`one is positioned at a furthest upstream end of the ?rst optical
`system and has refractive poWer, the other optical elements
`are prevented from being tilted.
`The above-described image projection apparatuses can
`perform extremely close range projection With a desired (en
`larging) magni?cation.
`One or more of the above objects of the present invention
`are also achieved by a projection optical system guiding and
`projecting a light beam from a projected object surface onto a
`projection surface in an upstream-downstream direction
`through a transmission dioptric system and a re?ection diop
`tric system of one or tWo re?ecting mirrors, Wherein: the
`transmission dioptric system includes a plurality of transmis
`sion refractive elements; substantial telecentricity is provided
`from the projected object surface up to a ?rst surface of the
`transmission dioptric system; an intermediate image surface
`of the projected object surface is positioned closer to the
`re?ection dioptric system than to the transmission dioptric
`system, and an intermediate image on the intermediate image
`surface is formed as a normal image on the projection surface
`via the re?ecting mirrors; the re?ecting mirrors include at
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`US 7,631,975 B2
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`7
`least one anamorphic polynomial free-form surface having
`different vertical and lateral powers; a light beam from the
`re?ection dioptric system to the projection surface is guided
`at an angle to a normal of the projection surface; and the
`transmission dioptric system is decentered With respect to a
`normal of the projected object surface, and the transmission
`refractive elements of the transmission dioptric system are
`prevented from being decentered With respect to each other.
`One or more of the above objects of the present invention
`are also achieved by a projection optical system guiding and
`projecting a light beam from a projected object surface onto a
`projection surface in an upstream-doWnstream direction
`through a transmission dioptric system and a re?ection diop
`tric system of one or tWo re?ecting mirrors, Wherein: the
`transmission dioptric system includes a plurality of transmis
`sion refractive elements; substantial telecentricity is provided
`from the projected object surface up to a ?rst surface of the
`transmission dioptric system; an intermediate image surface
`of the projected object surface is positioned closer to the
`re?ection dioptric system than to the transmission dioptric
`system, and an intermediate image on the intermediate image
`surface is formed as a normal image on the projection surface
`via the re?ecting mirrors; the re?ecting mirrors include at
`least one anamorphic polynomial free-form surface having
`different vertical and lateral poWers; a light beam from the
`re?ection dioptric system to the projection surface is guided
`at an angle to a normal of the projection surface; and the
`transmission dioptric system is decentered With respect to a
`normal of the projected object surface, and the transmission
`refractive elements of the transmission dioptric system are
`prevented from being decentered With respect to each other at
`a group unit level.
`The above-described projection optical systems can
`project a large screen Without distortion.
`One or more of the above objects of the present invention
`are also achieved by an image projection apparatus magnify
`ing an image displayed on a projected object surface and
`projecting the magni?ed image on a projection surface by a
`projection optical system, Wherein: the projection optical sys
`tem guides and projects a light beam from the projected object
`surface onto the projection surface in an upstream-doWn
`stream direction through a transmission dioptric system and a
`re?ection dioptric system of one or tWo re?ecting mirrors; the
`transmission dioptric system includes a plurality of transmis
`sion refractive elements; substantial telecentricity is provided
`from the projected object surface up to a ?rst surface of the
`transmission dioptric system; an intermediate image surface
`of the projected object surface is positioned closer to the
`re?ection dioptric system than to the transmission dioptric
`system, and an intermediate image on the intermediate image
`surface is formed as a normal image on the projection surface
`via the re?ecting mirrors; the re?ecting mirrors include at
`least one anamorphic polynomial free-form surface having
`different vertical and lateral poWers; a light beam from the
`re?ection dioptric system to the projection surface is guided
`at an angle to a normal of the projection surface; and the
`transmission dioptric system is decentered With respect to a
`normal of the projected object surface, and the transmission
`refractive elements of the transmission dioptric system are
`prevented from being decentered With respect to each other.
`One or more of the above objects of the present invention
`are further achieved by an image projection apparatus