US008279527B2
`
`(12) Ulllted States Patent
`Lin
`
`(10) Patent N0.:
`(45) Date of Patent:
`
`US 8,279,527 B2
`Oct. 2, 2012
`
`(54) WIDE-ANGLE PROJECTION OPTICAL
`SYSTEM
`
`.
`.
`.
`(75) Inventor: Lal-Chang Lin, Taoyuan Hsien (TW)
`
`(73) Assignee: Delta Electronics, Inc., Taoyuan Hsien
`(TW)
`
`( * ) Notice:
`
`Subject to any disclaimer, the term ofthis
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 238 days.
`
`2/2006 Suzuki et a1.
`6,994,437 B2
`5/2006 Takaura et a1.
`7,048,388 B2
`7,133,084 B2 * 11/2006 Moskovich et a1. ........ .. 348/779
`7,239,452 B2
`7/2007 Kuwa
`7,448,756 B2 110008 Cho et 31‘
`7,529,032 B2
`5/2009 Tak
`t l.
`8,182,097 B2 *
`5/2012 Hirifzteaf ,,,,,,,,,,,,,,,, “ 353/70
`2005/0200974 A1 *
`9/2005 Nishikawa et a1.
`359/691
`
`2006/0132723 A1* 6/2006 Yamagishi . . . . . . . . .
`
`. . . .. 353/98
`
`359/780
`2007/0253076 A1 * ll/2007 Takaura et a1.
`2010/0232038 A1* 9/2010 Kang et a1~ ~~~~~~~~~~~~~~~~~~ ~~ 359/717
`* cited by examiner
`
`(21) Appl. N0.: 12/797,818
`_
`(22) Flled:
`
`Jun‘ 10’ 2010
`
`(65)
`
`Prior Publication Data
`
`US 2010/0315725 A1
`
`Dec. 16, 2010
`
`Related US. Application Data
`(60) Provisional a lication NO 61/187 361 ?led on Jun
`16 2009
`pp
`'
`’
`’
`'
`’
`'
`(51) Int CL
`(200601)
`G02B 9/00
`(200601)
`G02B 17/00
`(200601)
`G02B 13/04
`(52) US. Cl. ....... .. 359/649; 359/648; 359/728; 359/749
`(58) Field of Classi?cation Search ......... .. 359/6494651
`See application ?le for Complete Search history
`
`(56)
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`6,631,994 B2 10/2003 Suzuki et a1.
`6,771,427 B1
`8/2004 Matsuo
`
`Primary Examiner * Jordan Schwartz
`(74) Attorney, Agent, or Firm * Kirton McConkie; Evan R.
`
`Wm
`
`(57)
`
`ABSTRACT
`
`A Wide-angle projection optical system includes a ?rst lens
`set With positive poWer, an aperture stop, a second lens set
`With positive poWer, a third lens set With negative poWer, and
`a negative poWer re?ecting mirror. The ?rst lens set provides
`optical characteristics to match With a light beam coming
`from the object side. The second lens set is arranged behind
`the aperture stop to converge the light beam. The third lens set
`is Con?gured to diverge the light to enlarge 9 full ?eld angle
`The negative POW‘?r re?ecting mirror is Con?gured to funher
`enlarge the full ?eld angle and correct image distortion. The
`?rst lens set, the second lens set, the third lens set and the
`re?ecting mirror have a common optical axis. The optical axis
`is shifted With respect to a center of a micro display.
`
`10 Claims, 6 Drawing Sheets
`
` 1
`
`ZEISS 1144
`Zeiss v. Nikon
`IPR2013-00363
`
`

`
`US. Patent
`
`0a. 2, 2012
`
`Sheet 1 of6
`
`US 8,279,527 B2
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`US. Patent
`U.S. Patent
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`0a. 2, 2012
`Oct. 2, 2012
`
`Sheet 2 of6
`Sheet 2 of6
`
`US 8,279,527 B2
`US 8,279,527 B2
`
`FIG.2
`
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`
`U.S. Patent
`
`Oct. 2, 2012
`
`Sheet 3 of6
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`US 8,279,527 B2
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`Sheet 4 of6
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`US. Patent
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`0a. 2, 2012
`Oct. 2, 2012
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`Sheet 5 of6
`Sheet 5 of6
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`US 8,279,527 B2
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`US. Patent
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`0a. 2, 2012
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`Sheet 6 of6
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`US 8,279,527 B2
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`7
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`

`
`US 8,279,527 B2
`
`1
`WIDE-ANGLE PROJECTION OPTICAL
`SYSTEM
`
`CROSS-REFERENCE TO RELATED
`APPLICATION
`
`This application claims the bene?t of US. Provisional
`Application No. 61/187,361 ?led on Jun. 16, 2009, and
`entitled “WIDE-ANGLE PROJECTION OPTICAL SYS
`TEM AND IMAGE DISPLAY APPARATUS”, the entirety
`of Which is hereby incorporated by reference.
`
`FIELD OF THE INVENTION
`
`The present invention relates to a projection optical system,
`and more particularly to a Wide-angle or an ultra-short throW
`projection optical system.
`
`BACKGROUND OF THE INVENTION
`
`A projection display apparatus is Widely used to produces
`an enlarged image of a small-siZed micro-display through a
`projection optical system (or a projection lens). The small
`siZed micro-display includes for example a high temperature
`liquid crystal display (HTLCD), a digital micro-minor dis
`play (DMD) or a liquid crystal on silicon (LCoS).
`Generally, a Wide-angle projection lens has a large ?eld of
`vieW, or a short effective focal length (EFL). In comparison
`With a conventional projection lens, the projection display
`apparatus With a Wide-angle projection lens is capable of
`producing a certain siZed image at a shorter distance.
`Recently, an integrated system of a projection display
`apparatus and an interactive White board has become very
`useful tool in classrooms, lecture rooms or conference rooms
`in order to provide the interactive functions about education,
`demonstration or entertainment. FIG. 1A is a schematic dia
`gram illustrating an integrated system of a projection display
`apparatus and an interactive White board according to the
`prior art. As shoWn in FIG. 1A, the projection display appa
`ratus 1 0 is usually mounted upside doWn over the White board
`11. The conventional short-throW projection display appara
`tus 10 is usually mounted at a distance of about 1 meter aWay
`from the White board 11. As such, the lecturer With average
`height becomes an obstacle to the light path of the projection
`display apparatus 10 When Writing on the White board 11. In
`addition, the eyes of the lecturer have the potential danger of
`being illuminated by the light from the projection display
`apparatus 10.
`For solving the above problems, as shoWn in FIG. 1B, the
`projection display apparatus 10 needs to be mounted in the
`vicinity of the White board 11. Since the projection distance is
`very short, the projection display apparatus 10 should have a
`Wide-angle projection lens to provide a large full ?eld angle 0
`or a very short focal length. In a case that the projection
`display apparatus 10 With a Wide-angle projection lens is
`mounted over the White board 11, the light ?ux needs to
`incident on the White board 11 at a very steep angle, Which
`incurs a large distortion in the image. Moreover, the projec
`tion lens also needs to have a large offset to avoid the light
`hitting on the main body of the projection display apparatus,
`and avoid the body of re?ecting mirror blocking the top area
`of the White board. In other Words, the Wide-angle or ultra
`short projection lens is very critical for designing the proj ec
`tion display apparatus.
`US. Pat. Nos. 6,631,994 and 6,994,437 disclosed a lens
`design that incorporates negative lenses and a negative
`aspheric mirror to achieve a Wide ?eld ofvieW. In this design,
`
`20
`
`25
`
`30
`
`35
`
`40
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`45
`
`50
`
`55
`
`60
`
`65
`
`2
`negative lenses With moderate poWer are used With the nega
`tive re?ecting mirror. With such an arrangement of optical
`poWer, it is di?icult to simultaneously achieve very large full
`?eld angle and high image quality at the same time.
`US. Pat. No. 7,529,032 disclosed a Wide-angle projection
`optical system. The design uses tWo aspheric plastic lenses,
`one double concave negative lens and a negative aspheric
`re?ecting mirror. The total length of the system is quite long.
`This makes it dif?cult to have a thin projector system. In
`addition, the maximum ?eld angle is on the order of 55
`degree, Which still requires a fairly long projection distance to
`produce an image that is large enough for practical applica
`tions.
`US. Pat. No. 7,239,452 disclosed a Wide-angle projection
`lens Which uses aspheric lenses and re?ecting mirror. HoW
`ever, one ?at mirror is disposed betWeen the negative lens
`group and the negative aspheric mirror. This type of optical
`path layout makes it suitable mostly for rear projection appli
`cation, not convenient for front projection applications.
`US. Pat. No. 6,771,427 disclosed a Wide angle projection
`lens design that incorporates regular negative lens group and
`an aspheric re?ecting mirror on the image side of the lens
`layout. Due to the use of regular spherical lenses, the full ?eld
`angle of this design is quite small, and multiple ?at re?ecting
`mirrors are needed to achieve thin pro?le.
`US. Pat. No. 7,048,388 disclosed a Wide-angle projection
`lens design that incorporates a ?at mirror and a positive
`aspheric re?ecting mirror. Again, this type of layout tends to
`make the projector bulky and inconvenient to use With a White
`board.
`US. Pat. No. 7,448,756 disclosed a Wide-angle lens design
`that consists of a series of negative lenses and a negative
`re?ecting mirror. In this design, an intermediate real image
`With a speci?c distortion is formed in the light path and is then
`re-imaged on to the screen by the rest of the optical system.
`Due to the formation of an intermediate real image, the opti
`cal path of this design tends to be long and complicated,
`Which make it di?icult to have a compact and thin display
`system.
`
`SUMMARY OF THE INVENTION
`
`It is an object of the present invention to provide a Wide
`angle or an ultra-short throW projection optical system With a
`full ?eld angle larger than :70 degrees.
`An object of the present invention provides a Wide-angle or
`an ultra-short throW projection optical system having a large
`full ?eld angle, a short effective focal length, thin pro?le, loW
`distortion, and high image quality.
`In accordance With an aspect of the present invention, there
`is provided a Wide-angle projection optical system. From an
`object side to an image side, the Wide-angle projection optical
`system includes a ?rst lens set With positive poWer, an aper
`ture stop, a second lens set With positive poWer, a third lens set
`With negative poWer, and a negative poWer re?ecting mirror.
`The ?rst lens set is con?gured to provide optical characteris
`tics to match With a light beam coming from the object side.
`The second lens set is arranged behind the aperture stop, and
`con?gured to converge the light beam. The third lens set is
`con?gured to diverge the light to enlarge a full ?eld angle. The
`negative poWer re?ecting mirror is closer to the image side
`than the ?rst lens set, the second lens set and the third lens set,
`and con?gured to further enlarge the full ?eld angle and
`correct image distortion. The ?rst lens set, the second lens set,
`the third lens set and the re?ecting mirror have a common
`optical axis. The optical axis is shifted With respect to a center
`of a micro display.
`
`8
`
`

`
`US 8,279,527 B2
`
`3
`In accordance With another aspect of the present invention,
`there is provided a Wide-angle projection optical system.
`From an object side to an image the, the Wide-angle projec
`tion optical system includes a ?rst lens set, an aperture stop, a
`second lens set, a third lens set With negative poWer, and a
`negative poWer re?ecting mirror. The ?rst lens set is con?g
`ured to provide optical characteristics to match With a light
`beam coming from the object side. The second lens set is
`arranged behind the aperture stop, and con?gured to converge
`the light beam. The third lens set is con?gured to diverge the
`light to enlarge a full ?eld angle. The third lens set comprises
`at least three convex-concave lenses, and both surfaces of
`each of at least tWo lenses of the third lens set are aspheric.
`The negative poWer re?ecting mirror is arranged in the vicin
`ity of the image side, and con?gured to further enlarge the full
`?eld angle and correct image distortion.
`The above contents of the present invention Will become
`more readily apparent to those ordinarily skilled in the art
`after revieWing the folloWing detailed description and accom
`panying draWings, in Which:
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1A is a schematic diagram illustrating an integrated
`system of a projection display apparatus and an interactive
`White board according to the prior art;
`FIG. 1B is a schematic diagram illustrating an integrated
`system of a Wide-angle projection display apparatus and an
`interactive White board according to the prior art;
`FIG. 2 is a schematic diagram illustrating an exemplary
`reversed telephoto con?guration used in the Wide-angle pro
`jection optical system of the present invention;
`FIG. 3 is a schematic diagram illustrating the architecture
`of a Wide-angle projection optical system according to the
`present invention;
`FIG. 4 is a schematic diagram illustrating modulation
`transfer function (MTF) characteristics in the image side by
`the Wide-angle projection optical system of the present inven
`tion;
`FIG. 5 is a schematic diagram illustrating grid distortion in
`the image side by the Wide-angle projection optical system of
`the present invention; and
`FIG. 6 is a schematic diagram illustrating lateral color in
`the image side by the Wide-angle projection optical system of
`the present invention.
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`DETAILED DESCRIPTION OF THE PREFERRED
`EMBODIMENT
`
`The present invention Will noW be described more speci?
`cally With reference to the folloWing embodiments. It is to be
`noted that the folloWing descriptions of preferred embodi
`ments of this invention are presented herein for purpose of
`illustration and description only. It is not intended to be
`exhaustive or to be limited to the precise form disclosed.
`The present invention provides a Wide-angle projection
`optical system. The Wide-angle projection optical system is
`applied to a projection display apparatus. The Wide-angle
`projection optical system is used to produce an enlarged
`image of a small-siZed micro-display (i.e. an object side) on a
`projection screen (i.e. an image side). The small-siZed micro
`display includes for example a high temperature liquid crystal
`display (HTLCD), a digital micro-minor display (DMD) or a
`liquid crystal on silicon (LCoS). In the Wide-angle projection
`optical system of the present invention, the optical con?gu
`ration of a projection lens is in the form of a reversed tele
`photo (or retro-focus) con?guration. This type of optical con
`
`50
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`55
`
`60
`
`65
`
`4
`?guration provides a back focal length (BFL) that is longer
`than the effective focal length (EFL). The long back focal
`length may provide space for the integration of illumination
`optics, micro display, and projection lens.
`FIG. 2 is a schematic diagram illustrating an exemplary
`reversed telephoto con?guration used in the Wide-angle pro
`jection optical system of the present invention. From the
`image side B to the object side A, the reversed telephoto
`con?guration comprises a negative front lens group 21 and a
`rear positive lens group 22. The rear positive lens group 22
`provides a proper Working distance or back focal length
`(BFL). The rear positive lens group 22 also sets up the optical
`characteristics to match With the illumination optics. The
`negative front lens group 21 and the rear positive lens group
`22 cooperate With each other to correct the aberrations,
`thereby creating a Well-focused and undistorted image on the
`screen. The negative front lens group 21 is used for bend the
`chief ray L to provide the required magni?cation of the
`image. The effective focal length (EFL) of a reversed tele
`photo lens is given by the equation (I) beloW:
`
`Where, Fa is a focal length of the negative front lens group 21,
`and D is the distance betWeen the negative front lens group 21
`and the rear positive lens group 22.
`By using a ?rst-order ray trace formula, the full ?eld angle
`6 of the chief ray L or the full ?eld of vieW could be deduced
`from equation (2) beloW:
`
`Where, h is the height of the micro display.
`For a projection display apparatus capable of completely
`avoiding shining lights on the lecturer Who Writes on a White
`board, the full ?eld angle should be larger than :70 degrees.
`For a projection display apparatus With a 0.65" 16:10 aspect
`ratio micro display at 120% offset, the effective focal length
`(EFL) of the projection lens is in the order of a feW millime
`ters. Obviously, from equations (1) and (2), it is found that to
`achieve such a large full ?eld angle, Fa needs to be very short,
`or the front lens group 21 needs to have a very large negative
`poWer. Because of the large negative poWer required in the
`front lens group 21, the design of the rear positive lens group
`22 and the distribution of poWer among the lenses in the front
`lens group 21 are very critical in achieving high quality and
`loW distortion images.
`FIG. 3 is a schematic diagram illustrating the architecture
`of a Wide-angle projection optical system according to the
`present invention. Please refer to FIGS. 2 and 3. From the
`object side A to the image side B, the Wide-angle projection
`optical system 2 comprises a rear positive lens group 22, a
`negative front lens group 21 and a negative poWer re?ecting
`mirror 23. The rear positive lens group 22 comprises at least
`tWo lens sets. The ?rst lens set 221 of the rear positive lens
`group 22 sets up proper Working space and pupil position to
`match With the illumination optical system. The second lens
`set 222 of the rear positive lens group 22 is a loW poWer
`positive lens for helping the correction of spherical and astig
`matic aberrations. In some embodiments, the ?rst lens set 221
`of the Wide-angle projection optical system 2 has an effective
`focal length (EFL) of 32 mm, Which is about 7 to 12 times of
`that of the system EFL. The second lens set 222 has an
`effective focal length (EFL) of 65 mm, Which is about 15 to 25
`times of that of the system EFL.
`In this embodiment, the negative front lens group 21 com
`prises a third lens set 211, Which consists of three convex
`concave lenses. The effective optical poWer of the third lens
`set 211 is properly distributed, so that the bending of chief ray
`
`9
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`

`
`US 8,279,527 B2
`
`10
`
`5
`is gradually achieved as it traverses through the second lens
`set 222 toWard the re?ecting mirror 23. The three convex
`concave lenses of the third lens set 211 closest to the image
`side B have meniscus-shaped convex surfaces relative to the
`image side B. In this embodiment, the ?rst convex-concave 5
`lens 21111 of the third lens set 211 is either a regular spherical
`lens or a lens With aspheric surfaces. The second convex
`concave lens 211!) and the convex-concave lens 2110 are
`aspheric lenses, Wherein both surfaces of each lens are
`aspheric.
`The negative poWer re?ecting mirror 23 also has an
`aspheric shape. The negative poWer re?ecting mirror 23 is
`used for correct the aberration and distortion. The negative
`poWer re?ecting mirror 23 may also change the optical path,
`so that the projection lens and hence the main body of the 15
`projection display apparatus are located in the space betWeen
`the re?ecting mirror and the screen to achieve a thin and
`compact projecting system.
`In the Wide-angle projection optical system 2, the lenses of
`the lens sets 221, 222 and 211 and the negative poWer re?ect- 20
`ing mirror 23 have a common optical axis. Especially, the
`lenses of the lens sets 221, 222 and 211 and the negative
`poWer re?ecting mirror 23 are circularly symmetric With
`respect to the common optical axis. Moreover, the axis of
`symmetry (i.e. the optical axis) is shifted With respect to the 25
`center of the micro display. As such, When the image is
`projected on the screen, a proper offset is provided.
`Please refer to FIG. 3 again. The Wide-angle projection
`optical system 2 of the present invention is applied to a pro
`jection display apparatus including a micro display. The 30
`micro display includes plural light valves. Each light valve
`has an object surface 3. The object surface 3 is an image
`display surface of the light valve. The object surface 3 is
`arranged at the object side of the Wide-angle projection opti
`cal system 2. The projection display apparatus further com- 35
`prises a polarization beam splitter 4 for guiding a light from a
`light source to the object side. In addition, the light re?ected
`by the object side is transmitted through the polarization
`beam splitter 4 and guided to the Wide-angle projection opti
`cal system 2.
`Moreover, the ?rst lens set 221 of the Wide-angle projec
`tion optical system 2 comprises plural refractive type lenses
`having positive effective optical poWer in order to provide the
`telecentricity to the object space and also converge the light
`emitted from micro display toWard an aperture stop 223. The 45
`aperture stop 223 is arranged betWeen the ?rst lens set 221
`and the second lens set 222.
`
`40
`
`6
`The negative poWer re?ecting mirror 23 further diverges
`the light beam and re?ects the light toWard the screen. The
`re?ecting mirror 23 has an aspheric surface to effectively
`correct the distortion.
`Table 1 shoWs the prescription data of the projection lens.
`In Table 1, “No.” is a surface number from the object side to
`the image side. For example, “No. 0” indicates the object
`surface, “No. 1”, “No. 2”, “No. 3” and “No. 4” indicate all
`surfaces of the polariZation beam splitter 4, “No. 15” indi
`cates the surface of the aperture stop 223, and “No. 24”
`indicates the mirror surface of the re?ecting mirror 23. In
`addition, “R” indicates radius of curvature, “D” indicates a
`space betWeen surfaces, “Nd” indicates a refractive index,
`and “vd” indicates an Abbe number. The front and rear sur
`faces of the lenses 211a, 2111) and 2110 of the third lens set
`211 (No. 20, No. 21, No. 22, and No. 23) are all aspheric. The
`mirror surface of the re?ecting mirror 23 is also aspheric (No.
`24). The aspheric coef?cients (C, A2, A4, A6, A8, A10) of
`these surfaces are listed in Table 2. As a consequence, Wide
`angle projection optical system 2 of the present invention can
`achieve a full ?eld angle larger than :70 degrees.
`
`TABLE 1
`
`No.
`
`R
`
`D
`
`Nd
`
`vd
`
`0
`1
`2
`3
`4
`5
`6
`7
`8
`9
`10
`11
`12
`13
`14
`15
`16
`17
`18
`19
`20
`21
`22
`23
`24
`
`In?nity
`In?nity
`In?nity
`In?nity
`In?nity
`48.38458
`—46.68644
`44.96219
`20.03234
`—106.3374
`32.06727
`276.2004
`41.61152
`155.7021
`—96.46147
`In?nity
`91.89713
`—120.2314
`—24.02027
`—36.99214
`—28.54044
`—31.05977
`—16.82069
`—53.66645
`67.36121
`
`0.5
`3
`2.5
`20
`5
`8.22
`4.73
`2.43
`7.57
`0.2
`4.4
`2
`8.03
`7.11
`6.4
`14.75
`9
`33.77
`2.24
`34.3
`8
`31.9
`7.2
`51.3
`—350
`
`1.51
`
`1.52
`
`1.5
`
`1.79
`1.5
`
`1.5
`
`1.72
`1.5
`
`61.2
`
`64.1
`
`81.5
`
`26.3
`81.5
`
`81.5
`
`56.4
`81.5
`
`1.83
`
`42.7
`
`1.5
`
`1.53
`
`1.53
`
`—1
`
`81.5
`
`56
`
`56
`
`0
`
`24
`
`—5.095365
`
`—1.9417E—08
`
`3.3877-13
`
`3.1988E-18
`
`—1.4407E—22
`
`55
`
`The second lens set 222 comprises at least one lens 222a
`having positive poWer (eg a convex lens). The lens 22211 is
`arranged behind the aperture stop 223. The second lens group
`can further converge the light beam. The third lens set 221
`comprises at least three negative poWer lenses 211a, 2111) and
`2110 for diverging the light beam to provide enlargement
`effect. In the third lens set 221, the front and rear surfaces of 60
`at least tWo lenses (eg 21119 and 2110) are aspheric surfaces
`in order to correct aberration and distortion. In some embodi
`ments, these tWo lenses 21119 and 2110 are manufactured by a
`plastic molding process. The effective optical poWer of the 65
`lens sets is properly distributed among the lenses in order to
`loWer the sensitivity to mechanical tolerances.
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`FIG. 4 is a schematic diagram illustrating modulation
`transfer function (MTF) characteristics in the image side by
`the Wide-angle projection optical system of the present inven
`tion. The horiZontal axis indicates spatial frequency (cycles/
`mm) and the vertical axis of ordinates indicates modulation
`values. The spatial frequency indicates the number of sine
`Waves per millimeter. The maximum value 1 in the vertical
`axis indicates that the MTF is 100%. As shoWn in FIG. 4, the
`MTF ratio does not obviously decrease, so that sharpness,
`contrast and recognition of the image are enhanced in achiev
`ing high quality. FIG. 5 is a schematic diagram illustrating
`grid distortion in the image side by the Wide-angle projection
`optical system of the present invention. As shoWn in FIG. 5,
`the image distortion or grid distortion can be effectively cor
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`rected. FIG. 6 is a schematic diagram illustrating lateral color
`in the image side by the Wide-angle projection optical system
`of the present invention. As shoWn in FIG. 6, the chromatic
`aberration is also effectively corrected. From the above draW
`ings, the Wide-angle projection optical system 2 of the present
`invention has a large full ?eld angle, loW image aberration or
`distortion, good optical characteristics and high image qual
`ity.
`From the above description, the Wide-angle or an ultra
`short throW projection optical system of the present invention
`is capable of providing a large full ?eld angle. The Wide-angle
`projection optical system comprises a ?rst lens set With posi
`tive poWer, a second lens set With positive poWer, a third lens
`set With negative poWer, and a re?ecting mirror With negative
`poWer. The Wide-angle projection optical system may pro
`vide a full ?eld angle larger than :70 degrees, a very short
`effective focal length, loW image distortion and high image
`quality. The use of the Wide-angle projection optical system
`makes the compact and thin display system possible. More
`over, by means of the Wide-angle projection optical system,
`the projection display apparatus may be installed over the
`White board or the display screen.
`While the invention has been described in terms of What is
`presently considered to be the most practical and preferred
`embodiments, it is to be understood that the invention needs
`not be limited to the disclosed embodiment. On the contrary,
`it is intended to cover various modi?cations and similar
`arrangements included Within the spirit and scope of the
`appended claims Which are to be accorded With the broadest
`interpretation so as to encompass all such modi?cations and
`similar structures.
`What is claimed is:
`1. A Wide-angle projection optical system, from an object
`side to an image side, said Wide-angle projection optical
`system comprising:
`a ?rst lens set comprising one or more lenses, having posi
`tive poWer, and converging a light beam coming from
`said object side;
`an aperture stop;
`a second lens set comprising one or more lenses, having
`positive poWer, arranged behind said aperture stop, and
`con?gured to converge said light beam;
`a third lens set With negative poWer, and con?gured to
`diverge said light to enlarge a full ?eld angle, Wherein
`said third lens set comprises at least three meniscus
`lenses, the most image side lens being convex to the
`image at an optical axis, and both surfaces of each of at
`least tWo lenses of said third lens set are aspheric;
`a negative poWer re?ecting minor closer to said image side
`than said ?rst lens set, said second lens set and said third
`lens set, and con?gured to further enlarge said full ?eld
`angle and correct image distortion; and a micro display,
`Wherein said ?rst lens set, said second lens set, said third
`lens set and said re?ecting minor have a common sub
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`stantially collinear optical axis, and said optical axis is
`shifted With respect to a center of said micro display.
`2. The Wide-angle projection optical system according to
`claim 1 Wherein said three meniscus lenses closest to said
`image side have meniscus-shaped convex surfaces relative to
`said image side.
`3. The Wide-angle projection optical system according to
`claim 2 Wherein both surfaces of each of at least tWo lenses
`closest to the image side of said third lens set are aspheric.
`4. The Wide-angle projection optical system according to
`claim 2 Wherein at least tWo lenses of said third lens set are
`manufactured by a plastic molding process.
`5. The Wide-angle projection optical system according to
`claim 2 Wherein from said object side to said image side, said
`third lens set comprises a ?rst meniscus lens, a second menis
`cus lens and a third meniscus lens, Wherein said ?rst meniscus
`lens is either a regular spherical lens or an aspheric lens, both
`surfaces of said second meniscus lens are aspheric, and both
`surfaces of said third meniscus lens are aspheric.
`6. The Wide-angle projection optical system according to
`claim 1 Wherein said re?ecting mirror has an aspheric shape.
`7. The Wide-angle projection optical system according to
`claim 1 Wherein said full ?eld angle is larger than :70
`degrees.
`8. A Wide-angle projection optical system, from an object
`side to an image side, said Wide-angle projection optical
`system comprising:
`a ?rst lens set comprising one or more lenses and refracting
`a light beam coming from said object side;
`an aperture stop;
`a second lens set comprising one or more lenses, arranged
`behind said aperture stop, and con?gured to converge
`said light beam;
`a third lens set having negative poWer, and con?gured to
`diverge said light to enlarge a full ?eld angle, Wherein
`said third lens set comprises at least three meniscus
`lenses, the most image side lens being convex to the
`image side at an optical axis, andboth surfaces of each of
`at least tWo lenses of said third lens set are aspheric; and
`a negative poWer re?ecting minor arranged in the vicinity
`of said image side, and con?gured to further enlarge said
`full ?eld angle and correct image distortion,
`Wherein said ?rst lens set, said second lens set, said third
`lens set and said re?ecting mirror have a common sub
`stantially collinear optical axis.
`9. The Wide-angle projection optical system according to
`claim 8 Wherein said ?rst lens set and said second lens set
`have positive poWer.
`10. The Wide-angle projection optical system according to
`claim 8 Wherein said Wide-angle projection optical system
`further comprise a micro display and Wherein said optical
`axis is shifted With respect to a center of said micro display.
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