U.S. patent application number 14/015080 was filed with the patent office on 2014-01-02 for projection optical system and image projecting apparatus.
The applicant listed for this patent is Issei ABE, Kazuhiro Fujita, Atsushi Takaura. Invention is credited to Issei ABE, Kazuhiro Fujita, Atsushi Takaura.
Application Number | 20140002803 14/015080 |
Document ID | / |
Family ID | 39492135 |
Filed Date | 2014-01-02 |
United States Patent
Application |
20140002803 |
Kind Code |
A1 |
ABE; Issei ; et al. |
January 2, 2014 |
PROJECTION OPTICAL SYSTEM AND IMAGE PROJECTING APPARATUS
Abstract
A projection optical system is disclosed. The projection optical
system includes a first optical system configured to form a first
image conjugated with an object and a second optical system
configured to project a second image conjugated with the first
image toward a projection surface. At least one of the first
optical system and second optical system includes at least one
optical element(s) movable relative to the object is provided. An
image distance of the projection optical system is changed and a
size of the second image is changed, by moving at least one of the
optical element(s) relative to the object.
Inventors: |
ABE; Issei; (Kanagawa,
JP) ; Fujita; Kazuhiro; (Tokyo, JP) ; Takaura;
Atsushi; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ABE; Issei
Fujita; Kazuhiro
Takaura; Atsushi |
Kanagawa
Tokyo
Tokyo |
|
JP
JP
JP |
|
|
Family ID: |
39492135 |
Appl. No.: |
14/015080 |
Filed: |
August 30, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12160818 |
Jul 14, 2008 |
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PCT/JP2007/073527 |
Nov 28, 2007 |
|
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14015080 |
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Current U.S.
Class: |
353/97 |
Current CPC
Class: |
G03B 21/28 20130101;
G03B 21/10 20130101; G03B 21/2066 20130101; G02B 17/0852 20130101;
G03B 21/005 20130101; G02B 17/0896 20130101 |
Class at
Publication: |
353/97 |
International
Class: |
G03B 21/20 20060101
G03B021/20 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 4, 2006 |
JP |
2006-327592 |
Oct 10, 2007 |
JP |
2007-264801 |
Claims
1-20. (canceled)
21. An image projection apparatus, comprising: a lens optical
system including a plurality of lenses; a concave mirror disposed
in an outgoing optical path of the lens optical system; and a
housing covering at least the concave mirror and having an aperture
that allows light reflected by the concave mirror to pass through,
wherein an end of the aperture is located closer to a light
entering side of the lens optical system than a closest lens of the
lenses that is closest to the concave mirror.
22. The image projection apparatus as claimed in claim 21, wherein
the closest lens of the lenses faces a reflection surface of the
concave mirror.
23. The image projection apparatus as claimed in claim 22, wherein
another end of the aperture is located between the closest lens and
the concave mirror when seen from a projection plane.
24. An image projection apparatus, comprising: a lens optical
system including a plurality of lenses; a concave mirror disposed
in an outgoing optical path of the lens optical system; and a
housing covering at least the concave mirror and having an aperture
that allows light reflected by the concave mirror to pass through,
wherein a closest lens of the lenses that is closest to the concave
mirror faces a reflection surface of the concave mirror; and an end
of the aperture is located closer to a light entering side of the
lens optical system than the closest lens of the lenses when seen
from a projection plane.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation of U.S. application Ser.
No. 12/160,818 filed Jul. 14, 2008, which is a National Stage of
PCT/JP2007/073527 filed Nov. 28, 2007, and is based upon and claims
the benefit of priority from prior Japanese Patent Application Nos.
2006-327592 and 2007-264801 filed Dec. 4, 2006 and Oct. 10, 2007,
respectively. The entire contents of each of which are incorporated
herein by reference.
TECHNICAL FIELD
[0002] The present invention relates to a projection optical system
and an image projecting apparatus.
BACKGROUND ART
[0003] Projector-type image displaying apparatus are known which
enlarge and project a static image or dynamic image of a character
or picture that is displayed on a compact light valve as a
two-dimensional image, by a projection optical system, so as to
display an image. Recently, attention has also been focused on an
enlargement projection method that uses a display device (referred
to as a light valve, below) which uses a transmission-type or
reflection-type dot matrix liquid crystal, a DMD (Digital
Micro-mirror Device) or the like, enlarges an image displayed on
the light valve and projects it onto a screen so as to show a
large-size image. Furthermore, as for a light valve, recently,
attention is focused on an LCOS (Liquid Crystal on Silicon) that is
excellent in a contrast characteristic, in addition to a
transmission-type liquid crystal panel and a DLP (Digital Light
Processor).
[0004] Practically, an image enlarging projection apparatus (a
projector) has also been utilized widely, at an office, a school
and a home, since no constraint is required for an image size so as
to allow a powerful large image to be obtained.
[0005] As for a projector-type image displaying apparatus, there
are provided a front-projection-type one which enlarges an image on
a light valve and projects it onto a projection surface such as a
reflection-type screen provided away from the apparatus so as to
observe reflected light and a rear-projection-type one with a
transmission-type screen provided in the apparatus as a projection
surface on which an image on a light valve is enlarged and
projected from the side of the back face of the screen so as to
observe an image from the side of the front face of the screen.
[0006] As for an example of optical system, JP-A-2004-258620 is
provided. It is a projection optical system with a configuration
such that an intermediate image is once formed by a lens system and
it is enlarged and projected by a concave mirror, and projection in
a close range has been realized. However, since there is no
mechanism for changing the size of a projected image and projection
with a fixed size is only allowed, there is a possibility of
restricting a use condition on the condition that a projection size
is fixed.
[0007] Therefore, optical systems for changing the size of a
projected image have been suggested, and as an example of a
projection optical system for a front-projection-type one,
JP-A-2003-177320 is provided which requires a telecentric system
composed of four mirrors. The projection optical system disclosed
in JP-A-2003-177320 is composed of four mirror elements arranged
oppositely and is a projection optical system that allows
projection with a variable magnification in a close range by means
of mirror movement.
[0008] However, since a mirror has a sensitivity of performance
degradation to the positional displacement thereof which is
generally higher than that of a lens, it is expected that the
degradation of an image quality due to an error in the position of
a mirror is large when the mirror is moved for projection with a
variable magnification. That is, it is necessary to move a mirror
for variation of magnification but it is expected that the
degradation of an image quality due to an error in the position of
the mirror is large and it is considered that it is necessary to
provide a strict precision of the arrangement of the mirror.
[0009] Also, an optical path on which light rays are repeatedly
reflected between mirrors is adopted and the light rays are high at
the last mirror at the side of enlargement. Accordingly, it is
difficult to reduce the height of such an apparatus and the size of
the apparatus is larger in use. Furthermore, the size of the forth
mirror is also large. In addition, since the mirror is provided
outside a housing of the apparatus, it is considered that the
mirror is easily deteriorated due to an external factor such as
dust, contaminants, and impacts.
[0010] Also, JP-A-2004-295107 discloses a variable magnification
projection optical system in which a first optical system composed
of plural lens systems capable of moving to the side of an object
and a second optical system with a mirror system having a
reflective curved surface at the side of an image are arranged. In
the example of optical system disclosed in JP-A-2004-295107,
variation of magnification is attained by moving a lens part while
a mirror part is fixed. Also, it includes an optical system
composed of lens systems and an optical system composed of plural
curved mirrors and the lens systems form an intermediate image in
the mirror part. The position of the intermediate image is provided
at the enlargement side of the mirror system from the first surface
that is the closest to the lens systems in the mirror system.
[0011] In this system, the image size of the intermediate image is
changed by moving the lens part and the changed intermediate image
is imaged by a second optical system again, whereby variation of
magnification is attained by changing the size of a projected
image. However, since the angle of view is changed for variation of
magnification without a projection distance, it is necessary to
change the (total) focal length of an optical component having an
optical power (a lens part) by a factor of the magnification change
of the size of a projected image, whereby the optical component is
complex and the degree of the movement of a lens part serving to it
is also large.
[0012] Also, plural rotationally asymmetric aspherical mirror is
required in a practical example, in order that an aberration change
caused by a change of the focal length is compensated for by the
mirror part, and it goes without saying that the cost is increased.
Then, the manufacturing assembly is difficult due to the high
tolerance sensitivity and the projection distance, per se, is so
large that it is not suitable for use in a small space like a
projection optical system for a close range.
[0013] Furthermore, a variable magnification optical system in
which the first optical system is composed of a transmission
refractive optical system and the second optical system is composed
of plural mirrors is disclosed and illustrated in JP-A-2004-295107,
but no example of one-mirror configuration is provided. In the
second optical system for repeating reflection by the plural
mirrors, the heights of light rays gradually increase while they
are sequentially reflected from the plural mirrors, and therefore,
it is difficult to bring the height of a mirror system in line with
the height of a lens system and to be configured to a compact one.
As a result, it is difficult to configure an apparatus with a small
height.
[0014] Also, the first optical system is composed of plural movable
lens systems, and if the lens systems are folded and configured to
a compact one, a lens in front or back of folding is moved, whereby
it is considered that the mechanism of a cam is complicated. In the
disclosed figure, all the lens groups of the first optical system
are moved for variation of magnification, and therefore, it is
considered that it is difficult to configure a mechanism for
folding a lens system. Also, since the full length of the part of
mirror system in the second optical system is large, it is
considered that it is difficult to configure the apparatus to a
compact one.
[0015] Furthermore, the variable magnification optical system
disclosed in JP-A-2004-295107 has a function of changing a
projection magnification by changing an angle of view at a
generally identical projection distance, but no function of
changing a projection magnification at the time of changing the
projection distance is disclosed. Also, since the angle of view is
small in the variable magnification optical system, the projection
distance has to be changed drastically if the projection
magnification is changed by changing the projection distance while
the angle of view is kept constant. Since the projection distance
is changed drastically, the degree of focusing also increases.
[0016] FIG. 23 is a schematic diagram showing the configuration of
an optical system disclosed in JP-A-2004-295107.
[0017] Both a first optical system 102 and a second optical system
104 form real images, and therefore, their powers are positive.
Also, the second optical system 104 is composed of a mirror system
but even if it is schematically expressed by a lens, there is no
problem in the following descriptions. In the relation between an
object 101 and an image 105 thereof, the size of an intermediate
image 103 is changed in order to change the size of the image 105
since the second optical system 104 is fixed (see FIG. 2 of
JP-A-2004-295107). Then, the first optical system 102 has to change
the power thereof as well as to move the principal points thereof,
in accordance with the size change of the intermediate image 103.
Practically, the focal length or magnification has to be changed by
a factor of the magnification change of the intermediate image 103
in the paraxial theory. That is, where a factor of the
magnification change of an image size (the value of the maximum
image size divided by the minimum image size) is represented by
.alpha.' and the maximum focal length and minimum focal length of
the first optical system 102 are represented by fa' and fb',
respectively, the following formula (2) is satisfied.
.alpha.'=fa'/fb' (2)
DISCLOSURE OF THE INVENTION
Problems to be Solved by the Invention
[0018] One object of the present invention is to provide a
projection optical system that comprises a first optical system
configured to form a first image conjugated with an object and a
second optical system configured to project a second image
conjugated with the first image toward a projection surface,
wherein an image distance is changed and a size of the second image
is changed.
[0019] Another object of the present invention is to provide an
image projecting apparatus comprising a projection optical system
that comprises a first optical system configured to form a first
image conjugated with an object and a second optical system
configured to project a second image conjugated with the first
image toward a projection surface, wherein an image distance is
changed and a size of the second image is changed.
Means for Solving the Problem
[0020] According to one aspect of the present invention, there is
provided a projection optical system comprising a first optical
system configured to form a first image conjugated with an object
and a second optical system configured to project a second image
conjugated with the first image toward a projection surface, in
which at least one of the first optical system and second optical
system comprises at least one optical element(s) movable relative
to the object, wherein an image distance of the projection optical
system is changed and a size of the second image is changed, by
moving at least one of the optical element(s) relative to the
object.
[0021] According to another aspect of the present invention, there
is provided an image projecting apparatus configured to project an
image onto a projection surface, which comprises the projection
optical system as described above.
Advantageous Effect of the Invention
[0022] According to one aspect of the present invention, there may
be provided a projection optical system that comprises a first
optical system configured to form a first image conjugated with an
object and a second optical system configured to project a second
image conjugated with the first image toward a projection surface,
wherein an image distance is changed and a size of the second image
is changed.
[0023] According to another aspect of the present invention, there
may be provided an image projecting apparatus comprising a
projection optical system that comprises a first optical system
configured to form a first image conjugated with an object and a
second optical system configured to project a second image
conjugated with the first image toward a projection surface,
wherein an image distance is changed and a size of the second image
is changed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] FIG. 1 is a schematic diagram showing a specific example of
an embodiment of the present invention.
[0025] FIG. 2 is a diagram showing a first specific example of an
embodiment of the present invention, which shows a state such that
an 80-inches-diagonal image is projected onto an image plane at a
projection distance of 551 mm.
[0026] FIG. 3 is a diagram showing a first specific example of an
embodiment of the present invention, which shows a state such that
a 60-inches-diagonal image is projected at a projection distance of
438 mm.
[0027] FIG. 4 is a diagram showing a first specific example of an
embodiment of the present invention, which shows a state such that
a 40-inches-diagonal image is projected at a projection distance of
334 mm.
[0028] FIG. 5 is an enlarged view of the optical system of FIG.
2.
[0029] FIG. 6 is an enlarged view of the optical system of FIG.
3.
[0030] FIG. 7 is an enlarged view of the optical system of FIG.
4.
[0031] FIG. 8 is a diagram showing a second specific example of an
embodiment of the present invention, which shows a configuration
for projecting an image onto an 80-inches-diagonal screen.
[0032] FIG. 9 is a diagram showing a second specific example of an
embodiment of the present invention, which shows a configuration
for projecting an image onto a 60-inches-diagonal screen.
[0033] FIG. 10 is a diagram showing a third specific example of an
embodiment of the present invention.
[0034] FIG. 11 is a diagram illustrating the curvature of field of
an optical element having a positive power.
[0035] FIG. 12 is a diagram showing a fourth specific example of an
embodiment of the present invention, which shows a configuration
such that an object plane is shifted with respect to the optical
axis of a first optical system.
[0036] FIG. 13 is a diagram showing a fourth specific example of an
embodiment of the present invention, which shows a configuration
for covering an optical system by a housing frame.
[0037] FIGS. 14 (a) and (b) show a fifth specific example of an
embodiment of the present invention.
[0038] FIG. 15 is a diagram showing a spot diagram on an image
plane at a magnification ratio of 127 in numerical practical
example 1.
[0039] FIG. 16 is a diagram showing a spot diagram on an image
plane at a magnification ratio of 95.2 in numerical practical
example 1.
[0040] FIG. 17 is a diagram showing a spot diagram on an image
plane at a magnification ratio of 63.5 in numerical practical
example 1.
[0041] FIG. 18 is a diagram showing correspondence between spots
shown in FIGS. 15, 16 and 17 and the positions thereof on the image
plane.
[0042] FIG. 19 is a diagram showing a TV distortion characteristic
at a projection magnification ratio of 127 in numerical practical
example 1.
[0043] FIG. 20 is a diagram showing a TV distortion characteristic
at a projection magnification ratio of 95.2 in numerical practical
example 1.
[0044] FIG. 21 is a diagram showing a TV distortion characteristic
at a projection magnification ratio of 63.5 in numerical practical
example 1.
[0045] FIG. 22 is a diagram illustrating the movement of an
intermediate image in numerical practical example 1.
[0046] FIG. 23 is a schematic diagram showing the configuration of
an optical system disclosed in JP-A-2004-295107.
[0047] FIG. 24 shows a state such that a 100-inches-diagonal image
is projected at a projection distance of 759 mm in numerical
practical example 2.
[0048] FIG. 25 shows a state such that a 70-inches-diagonal image
is projected at a projection distance of 544 mm in numerical
practical example 2.
[0049] FIG. 26 shows a state such that a 50-inches-diagonal image
is projected at a projection distance of 400 mm in numerical
practical example 2.
[0050] FIG. 27 shows an enlargement of an object plane 1 to a
second optical system 4 in any of FIGS. 24, 25 and 26.
[0051] FIG. 28 is a diagram showing a spot diagram on an image
plane at a magnification ration of 164.7 in numerical practical
example 2.
[0052] FIG. 29 is a diagram showing a spot diagram on an image
plane at a magnification ration of 115.3 in numerical practical
example 2.
[0053] FIG. 30 is a diagram showing a spot diagram on an image
plane at a magnification ration of 82.4 in numerical practical
example 2.
[0054] FIG. 31 is a diagram showing a TV distortion characteristic
at a projection magnification ratio of 164.7 in numerical practical
example 2.
[0055] FIG. 32 is a diagram showing a TV distortion characteristic
at a projection magnification ratio of 115.3 in numerical practical
example 2.
[0056] FIG. 33 is a diagram showing a TV distortion characteristic
at a projection magnification ratio of 82.4 in numerical practical
example 2.
[0057] FIG. 34 is a diagram showing a state such that an
80-inches-diagoinal image is projected at a projection distance of
739 mm in numerical practical example 3.
[0058] FIG. 35 is a diagram showing a state such that a
60-inches-diagoinal image is projected at a projection distance of
571 mm in numerical practical example 3.
[0059] FIG. 36 is a diagram showing a state such that a
40-inches-diagoinal image is projected at a projection distance of
400 mm in numerical practical example 3.
[0060] FIG. 37 shows an enlargement of an object plane 1 to a
second optical system 4 in any of FIGS. 34, 35 and 36.
[0061] FIG. 38 is a diagram showing a spot diagram on an image
plane at a magnification ratio of 131.8 in numerical practical
example 3.
[0062] FIG. 39 is a diagram showing a spot diagram on an image
plane at a magnification ratio of 98.8 in numerical practical
example 3.
[0063] FIG. 40 is a diagram showing a spot diagram on an image
plane at a magnification ratio of 65.9 in numerical practical
example 3.
[0064] FIG. 41 is a diagram showing a TV distortion characteristic
at a projection magnification ratio of 131.8 in numerical practical
example 3.
[0065] FIG. 42 is a diagram showing a TV distortion characteristic
at a projection magnification ratio of 98.8 in numerical practical
example 3.
[0066] FIG. 43 is a diagram showing a TV distortion characteristic
at a projection magnification ratio of 65.9 in numerical practical
example 3.
EXPLANATION OF LETTERS OR NUMERALS
[0067] 1: Object plane [0068] 2: Composite system of a polarization
beam splitter and a cross prism [0069] 3: Plural optical elements
having a refractive power [0070] 3': First optical system [0071] 4:
Reflective curved surface [0072] 5: Image plane [0073] 6:
Intermediate image plane [0074] 7: Folding mirror [0075] 8: Housing
[0076] 9: Aperture [0077] 10: Light source [0078] 11, 12: Cut-off
filter [0079] 13: Polarized light conversion element [0080] 14, 15:
Fly-eye lens array [0081] 16: Condenser lens [0082] 17, 18:
Dichroic mirror [0083] 19, 20, 21: Polarization beam splitter
[0084] 22, 23, 24: Light valve element [0085] 25: Cross prism
[0086] 26: Mirror [0087] 101: Object [0088] 102: First optical
system [0089] 103: Intermediate image [0090] 104: Second optical
system [0091] 105: Image
BEST MODE FOR CARRYING OUT THE INVENTION
[0092] Next, an embodiment(s) of the present invention is/are
described with reference to the drawings.
[0093] The first embodiment of the present invention is a
projection optical system including a first optical system for
forming a first image conjugated with an object and a second
optical system for projecting a second image conjugated with the
first image toward a projection surface, in which at least one of
the first optical system and second optical system includes at
least one optical element(s) movable relative to the object,
wherein the image distance of the projection optical system is
changed and the size of the second image is changed, by moving at
least one of the optical element(s) relative to the object.
[0094] Herein, the projection surface may be a component of the
projection optical system or may not be a component of the
projection optical system. For example, when the projection surface
is a component of the projection optical system, the position of
the projection surface may be brought into identical to the
position of the second image by moving components including the
projection surface relative to the object while an appropriate
well-known mechanism is used. Also, for example, when the
projection surface is not a component of the projection optical
system, the position of the second image may be brought into
identical to the position of the projection surface by moving the
entire projection optical system relative to a housing of the
projection optical system or the like while an appropriate
well-known mechanism is used. Also, for example, when the
projection surface is not a component of the projection optical
system, the position of the second image may be brought into
identical to the position of the projection surface by moving the
entire projection optical system relative to the projection surface
due to artificial means of a user. Additionally, it is only
necessary for the second image to be projected toward the
projection surface and it is not necessarily required to be formed
on the projection surface.
[0095] Also, each of the first image and second image may be an
image containing an aberration. Furthermore, any of well-known
means is allowed to be used for the means for moving relative to
the object the at least one optical element movable relative to an
object.
[0096] Additionally, the image distance of a projection optical
system means a paraxial-optical distance from the principal point
of the entire projection optical system at the side of a second
image to the paraxial-optical position of the second image.
[0097] According to the first embodiment of the present invention,
it may be possible to provide a projection optical system including
a first optical system for forming a first image conjugated with an
object and a second optical system for projecting a second image
conjugated with the first image toward a projection surface,
wherein an image distance is changed and a size of the second image
is changed.
[0098] In the projection optical system according to the first
embodiment of the present invention, preferably, the distance
between the first image and the second optical system is changed by
moving at least one of the optical element(s) relative to the
object.
[0099] Herein, the distance between the first image and the second
image means the distance between the paraxial-optical position of
the first image and one arbitrary position in the second optical
system.
[0100] In this case, it may be possible to provide a projection
optical system in which is allowed to change the image distance of
the projection optical system and to change the size of the second
image comparatively easily by changing the distance between the
first image and the second optical system.
[0101] For example, when the first optical system includes at least
one of the optical element(s) and the second optical system
includes no optical element movable relative to the object, the
distance between the first image and the second optical system may
be changed by moving at least one of the optical element(s)
included in the first optical system relative to the object so that
the first image is moved relative to the object. As a result, it is
allowed to change the image distance of the projection optical
system and to change the size of the second image.
[0102] Also, for example, when the second optical system includes
at least one of the optical element(s) and the first optical system
includes no optical element movable to the object, the distance
between the first image and the second optical system may be
changed by moving at least one of the optical element(s) included
in the second optical system relative to the object so that the
first image is fixed relative to the object and the second optical
system is moved relative to the first image. As a result, it is
allowed to change the image distance of the projection optical
system and to change the size of the second image.
[0103] In the projection optical system according to the first
embodiment of the present invention, preferably, the first optical
system includes at least one of the optical element(s) and the
first image is moved relative to the object by moving at least one
of the optical element(s) included in the first optical system
relative to the object.
[0104] Where the ratio of the paraxial-optical size of the first
image to the paraxial optical size of the object, that is, the
magnification ratio of the first optical system is denoted by m1
(>0) and the ratio of the paraxial-optical size of the second
image to the paraxial-optical size of the first image, that is, the
magnification ratio of the second optical system is denoted by m2
(>0), the ratio of the paraxial-optical size of the second image
to the paraxial-optical size of the object, that is, the
magnification ratio of the projection optical system is
m1.times.m2. Herein, the rate of a change of the paraxial-optical
magnification ratio of the projection optical system to a change
.DELTA.m1 of the magnification ratio of the first optical system is
m2 and the rate of a change of the paraxial-optical magnification
ratio of the projection optical system to a change .DELTA.m2 of the
magnification ratio of the second optical system is m1.
[0105] Hence, for example, in a projection optical system that
satisfies m2>m1, the ratio of a change of the paraxial-optical
magnification ratio of the projection optical system to a change of
the magnification ratio of the first optical system (the
sensitivity of the magnification ratio of the first optical system)
may be larger than the ratio of a change of the paraxial-optical
magnification ratio of the projection optical system to a change of
the magnification ratio of the second optical system (the
sensitivity of the magnification ratio of the second optical
system).
[0106] Therefore, a projection optical system in which the first
optical system includes at least one of the optical element(s) and
the size of the second image is changed by moving at least one of
the optical element(s) included in the first optical system
relative to the object has a sensitivity of magnification ratio
which is higher than that of a projection optical system in which
the second optical system includes at least one of the optical
element(s) and the size of the second image is changed by moving at
least one of the optical element(s) included in the second optical
system relative to the object, and may change the size of the
second image with a less extent of the movement of at least one of
the optical element(s).
[0107] Thus, when the projection optical system satisfies m2>m1,
it may be possible to provide a projection optical system that is
allowed to change the image distance of the projection optical
system and to change the size of the second image more easily.
[0108] In the projection optical system according to the first
embodiment of the present invention, preferably, the second optical
system is fixed relative to the object.
[0109] In this case, it is allowed to change the image distance of
the projection optical system and to change the size of the second
image comparatively easily by only moving at least one of the
optical element(s) included in the first optical system relative to
the object while the second optical system is fixed relative to the
object. As a result, it is allowed to provide a projection optical
system comparatively easily in which the image distance of the
projection optical system is changed and the size of the second
image is changed.
[0110] For example, the projection optical system may be a
projection optical system which projects an enlarged or reduced
image of an object onto an image plane, is capable of changing the
ratio of the size of an image to that of an object, and has a first
optical system provided with a lens unit movable at the time of the
change and having a positive optical power, a second optical system
provided with a reflection curved surface fixed at the time of the
change and having a positive optical power and an intermediate
image provided by generally focusing a light beam emitted from an
object surface between the first optical system and the second
optical system, wherein it is allowed to change the size of the
image by moving the intermediate image by moving the first optical
system at the time of the change and accordingly changing the image
distance.
[0111] In this case, the projection optical system is an optical
system that is capable of an enlarging projection with a high
magnification ratio from a small projection distance and is allowed
to change the projection size. Since the change may be realized by
moving an intermediate image in the optical system so that the
projection distance is changed, a change of the image size may be
realized by a simple configuration such that only the movement of
an optical component(s) for the movement of the intermediate image
is required. Also, since the variation of aberration which is
caused by the movement of the optical component(s) is small, a
mirror optical system for enlarging and projecting an intermediate
image onto an image plane may be realized by a small number of
component(s) and the ease of assembly may be improved
drastically.
[0112] That is, a novel projection optical system may be provided
which is capable of providing enlarging projection at a high
magnification change factor of a projected-image size even if the
projection distance is small, has a simple optical system whereby
the cost of the apparatus is low, and attains the ease of
assembly.
[0113] Also, for example, the projection optical system may be
provided with, at least, a planar object plane, a first optical
system arranged at the side of the image plane, having a refractive
power, involving a movement mechanism in directions of the optical
axis thereof, and including plural optical elements capable of
moving in the directions of the optical axis thereof, and a second
optical system arranged at the side of an image plane and including
a reflection surface, wherein the first optical system forms an
intermediate image at the side of the first optical system from an
optical surface of the second optical system which surface is
closest to the first optical system, and the second optical system
enlarges and projects the intermediate image and the position of
the intermediate image is moved by moving the optical element(s)
included in the first optical system, whereby the projection
distance and the size of an image are changed accordingly.
[0114] The projection optical system may not only have a feature
such that enlarging projection with a high magnification ration is
allowed at a small projection distance but also may conduct the
adjustment of focusing at the time of changing a projection
magnification ratio while a mirror is fixed. That is, the focal
length of the projection optical system may be adjusted by moving
an optical element having a refractive power in the first optical
system so that the adjustment of focusing may be conducted.
Accordingly, no mechanism of mirror movement is required. In a
method for conducting focusing by means of mirror movement, the
cost required for the mechanism of mirror movement is high since
the required precision of mirror movement is high, but the cost may
be reduced by an embodiment of the present invention. It may be
easy to move an optical element having a refractive power in the
directions of the optical axis thereof in the first optical system,
and therefore, a movement mechanism may be provided at low
cost.
[0115] Also, since the angle of view in the projection is large,
the projection magnification ratio may be greatly changed by only
slightly changing the projection distance and therefore the amount
of focusing control may also be small.
[0116] Furthermore, the intermediate image may be enlarged and
projected at a small projection distance by using the reflection
surface on the configuration condition that the first optical
system including an optical element having a refractive power, the
intermediate image, and the reflection surface are arranged in the
order from the object plane (or the intermediate image is between a
mirror system and a lens system).
[0117] Thus, since an optical system for enlarging and projecting
an intermediate image is provided, the mirror may be small. Also,
although the mirror size is small, an image with a high
magnification ration and a less distortion may be obtained and the
cost for manufacturing the mirror may be reduced.
[0118] Also, enlarging projection with a high magnification ratio
is allowed at a small projection distance due to the projection
optical system. In regard to an image projecting apparatus using
the projection optical system, the apparatus may be positioned near
a projection screen. In space for meeting or the like, the
apparatus is not necessarily positioned near a user. That is, the
apparatus may be used even if the distance between a user and it is
large. Also, the apparatus may be used without providing a user
with an influence caused by noise or exhaust gas generated by the
apparatus.
[0119] Then, in the apparatus, a projection image is projected
obliquely, with a predetermined angle with respect to the normal of
a projection screen. In this way, even if a user approaches at the
projection screen, the projected light is not easily shielded and
no shadow may be created. Accordingly, it is easy to use and the
convenience thereof may be improved.
[0120] That is, a novel projection optical system may be provided
which is advantageous in reducing the height of an image displaying
apparatus and downsizing it, has a low apparatus cost for
suppressing the degradation of an image when the projection
magnification ratio is changed, and is capable of conducting
enlarging projection with a high magnification ratio even if the
projection distance is small.
[0121] Furthermore, in the projection optical system, preferably,
in two arbitrary states whose projection magnification ratios are
different from each other, the projection distances from an element
closest to an image plane in the projection optical system to the
image plane are different and the separations between some elements
in the first optical system are different (while the separation(s)
between other elements is/are identical).
[0122] In this case, a mechanism for moving an optical element
constituting the second optical system is not required. The second
optical system includes a reflection mirror. Since a high
precision(s) is/are required for the mechanism for moving a mirror,
the cost required for the mechanism for moving a mirror is high.
According to such a projection optical system, no mechanism for
moving a mirror which has a high cost is required. Then, when the
projection magnification ratio is changed, a stable image quality
may be provided. Also, the cost of an apparatus may be reduced.
Furthermore, the variation of image quality depending on the
apparatus may also be reduced.
[0123] In the projection optical system according to the first
embodiment of the present invention, preferably, when the focal
length of the first optical system is changed from a first focal
length to a second focal length and the size of the second image is
changed from a first size to a second size by moving at least one
of the optical element(s) included in the first optical system
relative to the object, the ratio of the second focal length to the
first focal length is different from the ratio of the second size
to the first size.
[0124] In this case, the size of the second image may be changed
comparatively easily, while the image distance of the projection
optical system is changed, by changing the focal length of the
first optical system from the first focal length to the second
focal length with the ratio of the second focal length to the first
focal length which is different from the ratio of the second image
to the first image when the size of the second image is changed
from the first size to the second size. As a result, it may be
possible to provide a projection optical system comparatively
easily in which the image distance of the projection optical system
is changed and the size of the second image is changed.
[0125] In the projection optical system according to the first
embodiment of the present invention, preferably, when the second
focal length is greater than the first focal length and the second
size is greater than the first size, the ratio of the second size
to the first size is greater than the ratio of the second focal
length to the first focal length.
[0126] In this case, the size of the second image may be changed
comparatively easily while the image distance of the projection
optical system is changed, by changing the focal length of the
first optical system from the first focal length to the second
focal length with the ratio of the second focal length to the first
focal length which is smaller than the ratio of the second size to
the first size when the size of the second image is changed from
the first size to the second size. As a result, it may be possible
to provide a projection optical system comparatively easily in
which the image distance of the projection optical system is
changed and the size of the second image is changed.
[0127] For example, the above-mentioned projection optical system
may be a projection optical system that satisfies the following
conditional formula (1):
.alpha.>fa/fb (1),
wherein .alpha. is a value obtained by dividing the maximum size of
an image by the minimum size of the image, fa is the maximum focal
length of the first optical system, and fb is the minimum focal
length of the first optical system.
[0128] Also, the conditional formula (1) may be expressed by:
1/.alpha.<fb/fa (1)'.
[0129] Also, it can be understood from the conditional formula (1)
or (1)' that the ratio of fa and fb is not equal to the ratio of
the maximum size of an image at fa and the minimum size of the
image at fb (.alpha. or 1/.alpha.), by taking the size of the image
at fa being the maximum size of the image and the size of the image
at fb being the minimum size of the image into consideration.
[0130] In this case, the projection optical system may be an
optical system which is capable of conducting enlarging projection
at a high magnification ratio from a small projection distance and
capable of changing the projection size. Since the magnification
change may be attained by moving an intermediate image created in
the optical system so that the projection distance is changed, only
the movement of an optical component for moving the intermediate
image may be required, whereby the magnification change of the
image size may be attained with a simple configuration. Also, since
the variation of aberration which is caused by moving the optical
component may be small, a mirror optical system for enlarging and
projecting an intermediate image onto an image plane may be
attained with a small number of component(s) whereby the ease of
assembly may be improved drastically.
[0131] In the projection optical system according to the first
embodiment of the present invention, preferably, at least one of
the first optical system and second optical system, which
include(s) at least one of the optical element(s), is a coaxial
optical system.
[0132] In this case, since at least one of the optical element(s)
is included in a coaxial optical system and at least one of the
optical element(s) may be comparatively easily moved relative to
the object along the optical axis of the coaxial optical system, it
may be possible to provide a projection optical system
comparatively easily in which the image distance of the projection
optical system is changed and the size of the second image is
changed.
[0133] In the projection optical system according to the first
embodiment of the present invention, preferably, one of the first
optical system and second optical system includes the at least one
optical element(s) and includes optical element(s) more than an
optical element(s) constituting the other of the first optical
system or second optical system.
[0134] In this case, since the at least one optical element is
included in the (first or second) optical system that includes more
optical components, the degradation of the performance of the
second image may be reduced when at least one of the optical
element(s) is moved. As a result, it may be possible to provide a
projection optical system with a higher optical performance in
which the image distance of the projection optical system is
changed and the size of the second image is changed.
[0135] In the projection optical system according to the first
embodiment of the present invention, preferably, the half angle of
view of a principal ray projected toward the projection surface is
substantially constant while the size of the second image is
changed.
[0136] Herein, the principal ray projected toward the projection
surface means a light ray at the center of a light beam projected
toward a projection surface. Also, the half angle of view of a
principal ray projected toward the projection surface means
90.degree.--(an angle between the normal vector of a projection
surface and the directional vector of a principal ray at a point of
incidence of the principal ray on the projection surface (less
than) 90.degree.)). Furthermore, the half angle of view of a
principal ray projected toward the projection surface being
substantially constant means that the variation of the half angle
of view of a principal ray projected toward the projection surface
is within .+-.2.degree. when the image distance of the projection
optical system is changed and the size of the second image is
changed.
[0137] In this case, it may be possible to provide a projection
optical system which is allowed to change the image distance of the
projection optical system and to change the size of the second
image while the half angle of view of a principal ray projected
toward the projection surface is substantially constant.
[0138] For example, the projection optical system may be a
projection optical system in which the maximum incident angle of a
principal ray incident on an image plane is not substantially
changed at the time of a magnification change.
[0139] In this case, since the size of an image is linearly changed
depending on the projection distance without substantially changing
the maximum incident angle of a principal ray incident on an image
plane, the situation of the magnification change of the image size
may be easily expected, which is easy to use.
[0140] In the projection optical system according to the first
embodiment of the present invention, preferably, the maximum vale
of the half angle of view of a principal ray projected toward the
projection surface is equal to or greater than 60.degree..
[0141] In this case, it may be possible to provide a (super-wide
angle) projection optical system in which the maximum value of the
half angle of view of a principal ray projected toward a projection
surface is equal to or greater than 60.degree. when the image
distance of the projection optical system is changed and the size
of the second image is changed.
[0142] In the projection optical system according to the first
embodiment of the present invention, preferably, the second optical
system includes at least one optical element with a reflection
surface having a positive power.
[0143] In this case, it may be possible to provide a projection
optical system comparatively easily in which the maximum value of
the half angle of view of a principal ray projected toward the
projection surface is large when the image distance of the
projection optical system is changed and the size of the second
image is changed.
[0144] For example, the second optical system in the projection
optical system may have one or more mirrors having a power. Also,
in the projection optical system, one or more mirrors in the second
optical system may have a positive power.
[0145] In this case, an intermediate image is allowed to be
enlarged and projected. When an intermediate image is formed, a
light beam traveling from an object to the intermediate image is
converged and a light beam traveling from the intermediate image to
an image plane is diverged. Then, the diverged light beam is
condensed by one or more mirrors having a power again so as to
obtain an enlarged image. Also, a reflected light beam is guided
onto a predetermined image plane by providing an appropriate power,
so as to provide an image. Furthermore, the distortion of an image
may be reduced.
[0146] As described above, although the light beam traveling from
the intermediate image to the second optical system is diverged, it
may be condensed by a reflection surface having a positive power
again. When the number of reflection surfaces is equal to or
greater than 2, it is only necessary that the total power of the
reflection surfaces is positive, and a reflection surface having a
negative power may be provided. Herein, the power(s) of one or more
reflection surfaces is/are positive. The reflection surface having
a positive power means a so-called concave mirror.
[0147] The light rays reflected from the reflection surface having
a positive power travel on the light path crossing in front of an
image plane and subsequently reaching the image plane. At the
position of the crossing, the width of the light beam is reduced. A
flare component is allowed to be excluded by providing an aperture
at this position. Accordingly, an effect of improving the contrast
of an image may be obtained. The effect may not be obtained in a
not-crossing optical system. The position and shape of the aperture
may be optimized by a design thereof.
[0148] In the projection optical system according to the first
embodiment of the present invention, preferably, at least one of
the reflection surface(s) having a positive power in the at least
one optical element with a reflection surface having a positive
power is a rotationally symmetric aspherical surface.
[0149] Herein, the rotationally symmetric aspherical surface means
that the reflection surface having a positive power has a rotation
axis and the shape of the reflection surface is completely or
substantially axially symmetric around the rotation axis.
Additionally, the substantially axially symmetric one means that it
is axially symmetric in the design thereof and asymmetry caused by
an error in the processing thereof may be present.
[0150] In this case, aberration in the second image may be reduced
comparatively easily by using a rotationally symmetric aspherical
surface. As a result, it may be possible to provide a projection
optical system with a higher optical performance comparatively
easily in which the image distance of the projection optical system
is changed and the size of the second image is changed.
[0151] For example, the rotationally symmetric aspherical surface
may be represented by a well-known formula of aspherical surface
(a):
Z=cr.sup.2/[1+ {1-(1+k)c.sup.2r.sup.2}]+Ar.sup.4+Br.sup.6+Cr.sup.8
(a),
wherein Z is the depth thereof in the directions of the optical
axis thereof, c is the paraxial radius of curvature thereof, r is
the distance thereof from the optical axis in the directions
orthogonal to the optical axis, k is the constant of the cone
thereof, and A, B, C, . . . , etc., are the higher order
coefficients of aspherical surface, and the shape thereof is
specified by substituting specific values for k, A, B, C, . . .
.
[0152] Alternatively, for example, the shape of rotationally
symmetric aspherical surface may be a shape of aspherical surface
which includes an even-ordered term and an odd-ordered term as
coefficients of aspherical surface. The shape of aspherical surface
which includes an even-ordered term and an odd-ordered term is
represented by the following formula (b):
Z(r)=(cr.sup.2)/[1+
{1-(1+K)c.sup.2r.sup.2}]+C1r+C2r.sup.2+C3r.sup.3+C4r.sup.4+
(b),
wherein c is the paraxial curvature thereof, K is the coefficient
of the cone thereof, and Cis (i=1, 2, 3, . . . ) are the
coefficients of aspherical surface.
[0153] Herein, r is the distance thereof from the optical axis
thereof and Z is the depth thereof in the directions of the optical
axis.
[0154] For example, in the projection optical system, at least one
surface in a reflection curved surface(s) of the second optical
system may be a surface having a shape of axially symmetric
aspherical surface. Alternatively, in the projection optical
system, the shape of the mirror may be an axially symmetric
aspherical surface.
[0155] In this case, when the reflection mirror has a shape of
axially symmetric aspherical surface, the freedom of the design may
be increased and the convergence of light rays may be good. Also,
the resolution performance may be improved and the same function
may be reproduced with a small number of a component(s).
Furthermore, both the resolution and the correction of the
distortion may be easily attained by using an aspherical mirror
surface.
[0156] In the projection optical system according to the first
embodiment of the present invention, preferably, at least one of
the reflection surface(s) having a positive power in the at least
one optical element with a reflection surface having a positive
power is a free-form surface.
[0157] Herein, the free-form surface means any of the spherical
surfaces except rotationally symmetric aspherical surfaces.
[0158] In this case, aberration in the second image may be reduced
better by using a free-form surface. As a result, it may be
possible to provide a projection optical system with a higher
optical performance in which the image distance of the projection
optical system is changed and the size of the second image is
changed.
[0159] For example, an anamorphic polynomial free-form surface may
be a shape represented by:
Z=X2x.sup.2+Y2y.sup.2+X2Yx.sup.2y+Y3y.sup.3+X4x.sup.4+X2Y2x.sup.2y.sup.2-
+Y4y.sup.4+X4Yx.sup.4y+X2Y3x.sup.2y.sup.3+Y5y.sup.5+X6x.sup.6+X4Y2x.sup.4y-
.sup.2+X2Y4x.sup.2y.sup.4+Y6y.sup.6+ (c),
wherein the Y-directions are short axis directions, the
X-directions are long axis directions, the Z-directions are in the
directions of the depth of the curved surface, and X2, Y, X2Y, Y3,
X2Y2, etc., are the coefficients thereof, with respect to a
projected image as a reference.
[0160] For example, in the projection optical system, at least one
surface in the reflection curved surface in the second optical
system may be a surface having a shape of free-form surface.
Alternatively, in the projection optical system, the shape of one
or more mirrors as described above is a free-form surface.
[0161] When the reflection mirror has a shape of axially symmetric
aspherical surface or a shape of free-form surface, the freedom of
the design may be increased and the convergence of light rays may
be good. Also, the resolution performance may be improved and the
same function may be reproduced with a small number of a
component(s).
[0162] Furthermore, both the resolution and the correction of the
distortion may be not only easily attained by using a free-form
surface but also a configuration such that a mirror is arranged
near the optical axis may be attained. Accordingly, the thickness
of the apparatus may be reduced. Also, the size of a mirror may be
reduced. Accordingly, the cost of the mirror may be reduced. The
cost of the apparatus may also be reduced. The downsizing and cost
reduction of the apparatus may be attained simultaneously.
[0163] In the projection optical system according to the first
embodiment of the present invention, preferably, the number of the
at least one optical element with a reflection surface having a
positive power, included in the second optical system is one.
[0164] In this ease, since the configuration of the second optical
system may be simpler, it may be possible to provide a projection
optical system with a simpler configuration in which the image
distance of the projection optical system is changed and the size
of the second image is changed.
[0165] For example, the number of a reflection curved surface of
the second optical system may be one in the projection optical
system.
[0166] In this case, when the number of a mirror(s) is one, not
only the cost of the whole of the second optical system may be
reduced but also the productibity may be improved since the
assembly of a mirror system with a high tolerance sensitivity is
completed at once. Also, when the optical system is included in a
housing, the size thereof is small, leading to the downsizing.
[0167] In the projection optical system according to the first
embodiment of the present invention, preferably, at least one
folding mirror for folding an optical path from the object to the
second image is included in the optical path.
[0168] In this case, the optical path from the object to the second
image is folded whereby it may be possible to provide a more
compact projection optical system in which the image distance of
the projection optical system is changed and the size of the second
image is changed.
[0169] For example, in the projection optical system, the optical
path thereof may be folded by arranging a folding mirror between
the object plane and the image plane. Alternatively, in the
projection optical system, the first optical system may be
configured to fold the optical path.
[0170] In this case, when a folding mirror is arranged to fold the
optical path, the occupation surface area of the optical system may
be reduced and the size of a housing may be reduced. Alternatively,
the first optical system may be included in a compact housing. That
is, a housing of the apparatus may be configured to be compact.
Accordingly, the portability of the apparatus and the ease of
positioning thereof may be improved.
[0171] In the projection optical system according to the first
embodiment of the present invention, preferably, the at least one
optical element(s) movable relative to the object is arranged at a
side of the object or at a side of the second image relative to the
at least one folding mirror.
[0172] In this case, the at least one optical element movable
relative to the object may be moved relative to the object more
easily (or with a simpler mechanism) such that the image distance
of the projection optical system is changed and the size of the
second image is changed. As a result, it may be possible to provide
a projection optical system with a simpler configuration in which
the image distance of the projection optical system is changed and
the size of the second image is changed.
[0173] For example, in the projection optical system, only an
optical element at the side of either one of the object or the
image may be moved relative to the position of folding in the first
optical system.
[0174] Commonly, a mechanism for cooperatively moving both optical
elements in front and back of the folding configuration is
complicated and tends to increase the cost thereof. However,
according to the projection optical system, the complication of
such a cam mechanism may be avoided so that the cost of the cam is
reduced and the cost of the apparatus is reduced. Also, since the
optical system is arranged to be folded, the apparatus may be
compact.
[0175] In the projection optical system according to the first
embodiment of the present invention, preferably, the at least one
folding mirror is arranged between the object and the first
image.
[0176] In this case, since the position of the first image may be
prevented from overlapping with the position of the at least one
folding mirror, the influence of the at least one folding mirror on
the first image, that is, the influence of the at least one folding
mirror on the second image, may be reduced. As a result, it may be
possible to provide a projection optical system with a better
optical performance in which the image distance of the projection
optical system is changed and the size of the second image is
changed.
[0177] For example, in the projection optical system, the folding
mirror may be arranged in the first optical system.
[0178] In this case, the optical axis of the first optical system
extends in the directions perpendicular to a screen but the first
optical system may be compact by folding the optical path thereof
as described above. Also, an intermediate image between the first
optical system and the second optical system may be prevented from
overlapping with a folding mirror, by folding not between the first
optical system and the second optical system but in the first
optical system, that is, in a lens unit thereof. Additionally, a
light beam emitted from one point on the object is generally
converged at the intermediate image again so that the diameter of
the light beam is small, and therefore, if a tiny dust or the like
adheres to the folding mirror, the ratio of the size of the dust to
the diameter of the light beam may be large so that the influence
thereof on an image on a subsequent image plane tends to be large.
Therefore, it is preferable to prevent the intermediate image from
overlapping with the folding mirror.
[0179] In the projection optical system according to the first
embodiment of the present invention, preferably, the first optical
system includes an optical element fixed relative to the object and
being closest to the first image.
[0180] In this case, even if the first optical system includes at
least one optical element movable relative to the object, the at
least one optical element movable relative to the object is
arranged between an object and an optical element fixed relative to
the object and being closest to the first image, and therefore, at
least one of the optical element(s) may be moved relative to the
object more easily. As a result, it may be possible to provide a
projection optical system with a simpler configuration in which the
image distance of the projection optical system is changed and the
size of the second image is changed.
[0181] For example, in the projection optical system, the lens unit
of the first optical system which is closest to the side of an
image may be fixed at the time of a magnification change.
[0182] In this case, since the unit of the first optical system
which is closest to the side of an image is provided at the
location at which a light beam emitted from each point on an object
is most separated, the diameter of the lens is large and the weight
thereof is high. However, when the lens unit is fixed, a variable
mechanism for a body tube thereof may be small and may be a
mechanism that is easy to operate. Also, in regard to an effect of
the folding mirror in combination with the effect of the
configuration of the arrangement thereof in the first optical
system, when a folding mirror fixed just in front of a lens unit at
the side of an object is arranged, it is only necessary to move
only a lens unit between the object and the folding mirror, whereby
the design of a body tube thereof may be easy or simple. On the
contrary, if the unit is also variable, lens units whose optical
axis is folded by a folding mirror in front and back of the mirror
have to be moved simultaneously and linearly, and therefore, it may
be very complicated to design a variable mechanism for a body tube
thereof.
[0183] In the projection optical system according to the first
embodiment of the present invention, preferably, the first image
has a curvature of field which curves toward a side of the
object.
[0184] In this case, the curvature of field of the first image that
is curved toward the side of the object may be reduced more easily
by using at least one optical component with a reflection surface
having a positive power. As a result, it may be possible to provide
a projection optical system with a higher optical performance
comparatively easily in which the image distance of the projection
optical system is changed and the size of the second image is
changed.
[0185] For example, in the projection optical system, the
intermediate image may have a characteristic of a curvature of
field at the under side. Herein, the under side of an image refers
to the direction in which the more the coordinate in an plane
perpendicular to an optical axis is separated from the optical
axis, the more it approaches to the side of an object, and the over
side of an object refers to the direction in which the more the
coordinate in an plane perpendicular to an optical axis is
separated from the optical axis, the more it departs from the side
of an image.
[0186] Thus, when the intermediate image is provided with a
characteristic of a curvature of field at the under side, it may be
easy to correct the inclination of an image in combination with a
mirror having a positive power. The characteristic of a curvature
of field at the under side refers to a state such that the larger
the distance from the optical axis is, the smaller the distance
between the intermediate image and the first optical system is. If
the intermediate image is considered as an object plane for the
second optical system, the object plane is inclined to the
direction of the over side. That is, the larger the distance of a
position from the optical axis is, the larger the distance from the
intermediate image to the mirror is. In such a condition, it may be
easy to correct the image inclination of a secondary image of the
intermediate image which secondary image is obtained by a mirror
having a positive power. Additionally, the secondary image of the
intermediate image corresponds to an image for the projection
optical system.
[0187] Also, when an image of an object is obtained by an optical
element having a positive power, the image plane tends to incline
to the under side on the condition that the object is not inclined.
Herein, the amount of inclination of an image plane inclining to
the under side may be reduced with inclining an object plane to the
over side. Commonly, the inclination is not linear but is curved.
Meanwhile, it is commonly difficult to curve an object plane in a
curved shape. The object plane is planar in many practical
examples. For example, the object plane may be on a light valve
element in a projector optical system and an image on the light
valve element is formed into a planar shape. For a light valve
element, a DMD (Digital Mirror Device), an LCoS (Liquid Crystal on
Silicon), a transmission-type liquid crystal light valve, and the
like are provided. Any of them has a planar shape. Therefore, a
high cost may be required for making it into a curved shape.
However, according to an embodiment of the present invention, since
the object plane is an intermediate image, a different situation is
provided. That is, it may be possible to provide an intermediate
image with a shape curving to the under side due to a design of the
first optical system and an additional cost required for
implementation may be low. Then, there may be provided an effect
such that the inclination of an image plane for the projection
optical system may be easily corrected by providing an intermediate
image curving to the under side.
[0188] In the projection optical system according to the first
embodiment of the present invention, preferably, the first optical
system is a coaxial optical system and the object is decentered
relative to the optical axis of the first optical system.
[0189] In this case, the object is decentered relative to optical
axis of the first optical system whereby it may be possible to
provide a projection optical system in which the first optical
system and the second optical system are arranged more
appropriately while the image distance of the projection optical
system is changed and the size of the second image is changed.
[0190] For example, the projection optical system may be a
projection optical system such that the center of an object plane
is arranged to be decentered relative to the optical axis of the
first optical system and the height of a light ray incident on the
mirror is lower than the optical axis of the first optical
system.
[0191] In the projection optical system, the center of an object
plane is arranged to be decentered relative to the optical axis of
the first optical system. Herein, a Cartesian coordinate system is
defined such that the Z-axis is in the directions of the optical
axis and the X-axis and Y-axis are in one of the directions
orthogonal to the optical axis and in the other, respectively. When
the object plane is shifted to the direction of +Y, the
intermediate image is formed to the direction of -Y based on the
imaging principle of optics. When a mirror of the second optical
system is arranged at the side of enlargement with respect to the
intermediate image, the mirror may be arranged in a region of -Y so
as to reflect light. If the direction of +Y is taken in the
directions of the height of the apparatus, a mirror may be arranged
not to project from the upper side of the apparatus. Accordingly,
the mirror may be included in a housing of the apparatus. Then, a
user does not contact the mirror. Also, since the mirror is covered
by a housing, dust does not easily adhere to it. If the dust is
scorched by heat, the reflectance of the mirror may be reduced, or
the image quality of a projected image may be degraded while it
functions as a scattering source. Then, the reduction of the
reflectance may reduce the brightness. The scattering may reduce
the contrast. However, such situations may be prevented. Also,
damages such as generation of breakage or warping caused by
contacting a mirror may also be prevented.
[0192] The second embodiment of the present invention is an image
projecting apparatus for projecting an image onto a projection
surface, which includes the projection optical system according to
the first embodiment of the present invention.
[0193] According to the second embodiment of the present invention,
it may be possible to provide an image projecting apparatus that
includes a projection optical system which includes a first optical
system for forming a first image conjugated with an object and a
second optical system for projecting a second image conjugated with
the first image toward a projection surface wherein the image
distance thereof is changed and the size of the second image is
changed.
[0194] For example, the image projecting apparatus may be an image
displaying apparatus having at least one image forming element, an
illumination optical system for illuminating the image forming
element, and a projection optical system for enlarging or reducing
a light image signal modulated by the image forming element,
wherein the projection optical system is any of the projection
optical systems described above.
[0195] In this case, an image displaying apparatus using a novel
projection optical system may be attained which is capable of
enlarging and projecting a projection image with a size at a high
magnification ratio even if the projection distance is small, has a
low apparatus cost due to a simple optical system and attains an
ease of assembly.
[0196] Also, the image projecting apparatus, for example, may be an
image displaying apparatus having t least one light valve element,
an illumination optical system for illuminating the light valve,
and a projection optical system for enlarging and projecting a
light image signal modulated by the light valve, wherein the
projection optical system is any of the projection optical systems
described above.
[0197] According to such an image projecting apparatus, it may be
possible to provide a configuration such that a mirror is included
in a housing without increasing the height and/or thickness of the
housing. Thereby, an effect of the projection optical system may be
obtained in which the center of the image plane is arranged to be
decentered with respect to the optical axis of the first optical
system and the height of a light ray incident on the mirror is
lower than the optical axis of the first optical system. Also, the
image shape of the intermediate image may be controlled by the
design of the first optical system with a low cost. Thereby, an
image plane that is focused well without inclination thereof may be
obtained. Also, since the object plane is shifted, oblique
projection may be provided with a predetermined angle with respect
to the normal line of an image plane, and therefore, enlarging
projection may be provided at a small projection distance.
Furthermore, even if the projection magnification ratio is changed,
focusing may be provided without moving a mirror. No mechanism for
moving a mirror which may require a high precision and may cause a
cost increase is required. Also, since the mirror may be configured
to be small, the cost of the mirror may be low. Furthermore, since
the mirror may be configured to be small and have even a shape of
free-form surface except shapes of aspheircal surfaces, a high
image aberration correcting effect may be obtained by the free-form
surface while the cost is suppressed, whereby an image quality may
be improved. Although elements having a refractive power which are
represented by lenses are arranged in the first optical system,
focusing may be controlled by only moving them in the directions of
the optical axis thereof, and therefore, no special movement
mechanism is required. Also, a housing may be configured to be
compact by taking a configuration such that the first optical
system is folded. Although it is preferable that the folding
direction be generally a folding in an XY-plane, the spirit of the
present invention is not lost even if a folding angle component in
an XZ-plane may be present according to need. Also, it may be
possible to attain a configuration such that a mechanism for moving
an optical element is not complicated even if folding is
applied.
[0198] That is, it may be possible to provide an image displaying
apparatus using a novel projection optical system which is
advantageous in reducing the height of the image displaying
apparatus to be compact, has a low apparatus cost for suppressing
the degradation of an image at the time of changing the projection
magnification ratio, and is capable of providing enlarging
projection with a high magnification ratio even if the projection
distance is small.
[0199] Next, specific examples of embodiments of the present
invention are described with reference to the drawings.
[0200] FIG. 1 is a schematic diagram showing a specific example of
an embodiment of the present invention.
[0201] Similarly to FIG. 23, both a first optical system 102 and a
second optical system 104 have positive powers thereof, and
although the second optical system 104 is composed of a mirror
system, no problem is provided to the descriptions even if it is
schematically shown as a lens. Since the second optical system 104
is fixed, the position of an intermediate image 103 is moved so as
to change the image distance as shown in FIG. 1, whereby the size
of an image 105 is changed. Herein, since the second optical system
104 greatly enlarges the intermediate image 103, the positive power
thereof is large. Therefore, even if the position of the
intermediate image 103 is slightly changed, the image distance is
greatly changed according to the relationship of a longitudinal
magnification and the size of the image 105 is also changed
greatly. That is, the size of the image 105 may be greatly changed
by slightly changing the position of the intermediate image 103.
Then, the first optical system 102 has a fixed focus thereof but
moves the position of a principal point thereof, whereby the
position of the intermediate image 103 is slightly moved. In
practice, the focal length of the first optical system 102 is
changed for aberration correction, no change of the focal length is
required which change corresponds to the image size change as
represented by the above formula (2) (.alpha.'=fa'/fb'). That is,
the above formula (1) (.alpha.>fa/fb) is satisfied, wherein
.alpha. is the magnification ratio of the image size (a value
obtained by dividing the maximum image size by the minimum image
size) and fa and fb are the maximum focal length and minimum focal
length of the first optical system 102, respectively. Since the
change of the focal length of the first optical system 102 is
allowed to be small, the configuration of the magnification change
may be simple. Also, since an aberration change in the entire
optical system is small, an aberration change that should be
absorbed by the second optical system 104 may be small and the
second optical system 104 may be simple. Furthermore, the maximum
incident angle of a principal ray incident on the image plane is
slightly changed by slightly changing the position of the
intermediate image 103 in order to absorb the aberration change,
but is configured not substantially to change in the paraxial
theory.
[0202] FIGS. 2, 3 and 4 are diagrams showing the first example of
an embodiment of the present invention.
[0203] In FIGS. 2, 3 and 4, numerical reference 1 denotes a surface
of an object in imaging of a projection optical system. In
practice, it is, for example, "an image displaying surface of a
light valve", and "an image displaying surface of a reflection-type
light valve" is supposed in the specific example of the embodiment.
Additionally, it is not limited to the reflection-type one but may
be an image displaying surface of a transmission-type light valve.
In the specific example of the embodiment, a color image display
that uses three reflection-type light valves is supposed, and since
the three light valves are arranged at equivalent positions with
respect to a projection optical system, an object plane 1
represents three object planes.
[0204] Numerical reference 2 denotes "a combination system of a
polarization beam splitter for guiding light from a light source to
each light valve and a cross prism for combining light beams
reflected from the respective light valves" as a transparent plate
having an optical path length equivalent thereto.
[0205] Numerical reference 3 denotes "plural optical elements
having a refractive power". In the specific example of the
embodiment, although they are composed of ten lens elements and a
stop, the number of the lens elements is not limited to ten. Also,
the position of the stop is not limited to the position shown
therein.
[0206] Numerical reference 4 denotes "a non-movable reflection
curved surface". In the embodiment, the second optical system is
composed of only the non-movable reflection curved surface 4.
[0207] FIG. 2 is a diagram showing the first specific example of an
embodiment of the present invention and shows a state such that an
80-inches-diagonal image is projected onto an image plane at a
projection distance of 551 mm.
[0208] FIG. 3 is a diagram showing the first specific example of an
embodiment of the present invention and shows a state such that a
60-inches-diagonal image is projected at a projection distance of
438 mm.
[0209] FIG. 4 is a diagram showing the first specific example of an
embodiment of the present invention and shows a state such that a
40-inches-diagonal image is projected at a projection distance of
334 mm.
[0210] In FIGS. 2, 3 and 4, the light valve element is a
0.6-inches-diagonal one and has an aspect ratio of 3:4.
[0211] In FIGS. 2, 3 and 4, all the optical paths of five light
beams emitted from the object plane 1 is shown. These are enlarged
and focused on an image plane 5.
[0212] FIGS. 5, 6 and 7 show enlargements of the object plane 1 to
the second optical system 4 in FIGS. 2, 3 and 4, respectively.
[0213] FIG. 5 shows an enlarged view of the optical system in FIG.
2.
[0214] FIG. 6 shows an enlarged view of the optical system in FIG.
3.
[0215] FIG. 7 shows an enlarged view of the optical system in FIG.
4.
[0216] In FIGS. 5, 6 and 7, numerical reference 6 denotes an
intermediate image of an object point on the object plane 1.
Strictly, a light beam of each angle of view may not be focused on
one point at the intermediate image and may have aberration.
[0217] In FIGS. 5, 6 and 7, countless light beams are emitted from
the object plane 1 in practice but not all of them are shown. A
dashed line 6 schematically shows an intermediate image obtained by
these light beams. As shown in the figures, the intermediate image
is curved to the under side in the specific example of the
embodiment. In the optical system according to an embodiment of the
present invention, an intermediate image that is curved to the
under side is shown as a typical example.
[0218] In FIGS. 5, 6 and 7, the first optical system forms an
intermediate image at the side of the first optical system with
respect to the optical surface that is closest to the first optical
system in the second optical system.
[0219] Then, the intermediate image is enlarged and projected by a
mirror of the second optical system.
[0220] Herein, when FIG. 5, FIG. 6 and FIG. 7 are referred to, only
the elements of the first optical system are moved and the mirror
of the second optical system is not moved.
[0221] Also, lenses L8, L9 and L10 are not moved in the first
optical system.
[0222] The second optical system is composed of one concave mirror
4 and the concave mirror has a power. Also, the power is positive.
In this practical example, the concave mirror 4 has a free-form
surface. The formula for defining the free-form surface is
expressed by the formula (c) of anamorphic polynomial free-form
surface as described above.
[0223] The formula (2) can be applied to the reflection curved
surface 4 by taking a coordinate system as shown in FIG. 2. In this
case, the reflection curves surface has a symmetric shape with
respect to the position of X=0 in the directions of positive X and
negative X in a typical example of an embodiment of the present
invention.
[0224] The reflection curved surface 4 may be a free-form surface
in the embodiment, and otherwise, may be, for example, an axially
symmetric aspheric surface represented by the above formula (b) or
(c). Furthermore, the axially symmetric aspherical surface may
include an odd-ordered aspherical surface as represented by the
above formula (c).
[0225] FIG. 8 and FIG. 9 show the second specific example of an
embodiment of the present invention.
[0226] FIG. 8 is a diagram showing the second specific example of
an embodiment of the present invention and shows a configuration
for projecting an image onto an 80-inches-diagonal screen. FIG. 9
is a diagram showing the second specific example of an embodiment
of the present invention and shows a configuration for projecting
an image onto a 60-inches-diagonal screen.
[0227] A configuration such that a folding mirror 7 is provided
between a lens L7 and a lens L8 in the first optical system is
shown in FIG. 8. Projection is applied on an 80-inches-diagonal
screen in the configuration of FIG. 8. In the configuration of FIG.
9, projection is applied on a 60-inches-diagonal screen. In FIGS. 8
and 9, since lenses L8, L9 and L10 are not moved in a first optical
system 3', it is only necessary to provide a cam at the side of
reduction with respect to a folding mirror. Also, a mirror 4 of the
second optical system is not moved in FIGS. 8 and 9. Furthermore,
the folding mirror is not moved. Herein, although lenses of the
first optical system 3' are fixed and a cam is provided only at the
side of reduction with respect to the folding mirror in the
specific example, otherwise, lenses at the side of reduction with
respect to a folding mirror are fixed and a cam may be provided at
the side of the second optical system so as to move lenses at the
side of the second optical system, as shown in FIG. 27.
[0228] FIGS. 10 and 11 show the third specific example of an
embodiment of the present invention.
[0229] FIG. 10 is a diagram showing the third specific example of
an embodiment of the present invention. FIG. 11 is a diagram
illustrating the curvature of field of an optical element having a
positive power.
[0230] In FIG. 10, an intermediate image formed by the first
optical system is shown by a dashed line. The intermediate image is
curved to the under side.
[0231] When the intermediate image is provided with the
characteristic of a curvature of field to the under side, the
inclination of the image may be easily corrected in combination
with a mirror having a positive power. The characteristic of a
curvature of field to the under side refers to a state such that
the larger the distance from an optical axis is, the smaller the
distance between the intermediate image and the first optical
system is. Herein, the optical axis is expressed by O-O' in FIG.
10.
[0232] From a different viewpoint, when the intermediate image 6 is
considered as an object plane for the second optical system, the
object plane is inclined to the over direction. That is, the larger
the distance of a position from the optical axis O-O' is, the
larger the distance from the intermediate image 6 to the mirror 4
is. In such a situation, the image inclination of the secondary
image of the intermediate image may be easily corrected which
secondary image is obtained by a mirror having a positive power.
Herein, the secondary image of the intermediate image corresponds
to an image plane for the projection optical system.
[0233] When an image of an object is obtained by an optical element
having a positive power, the image plane tends to incline to the
under side on the condition of no inclination of the object. FIG.
11 schematically shows the situation.
[0234] Herein, when the object plane gets inclined to the over
side, the inclination of the image plane inclining to the under
side may be reduced.
[0235] Commonly, the inclination is not linear but is curved.
Meanwhile, it is commonly difficult to curve the object plane into
a curved shape. The object plane is planar in many practical
examples. For example, the object plane is on a light valve element
in a projector optical system and a planar image is formed on a
light valve element. For the light valve element, a DMD (Digital
Mirror Device), an LCoS (Liquid Crystal on Silicon), a
transmission-type liquid crystal light valve and the like are
provided. Any of these has a planar shape. Therefore, high cost is
required for forming it into a curved shape.
[0236] Meanwhile, a different situation is provided according to an
embodiment of the present invention since the object plane
corresponds to the intermediate image. That is, it is possible to
form the intermediate image into a shape curving to the under side
by a design of the first optical system and an additional cost
required for implementation thereof is low. Then, an effect is
obtained such that the inclination of an image plane for the
projection optical system is easily corrected by curving the
intermediate image to the under side.
[0237] FIG. 12 and FIG. 13 show the fourth specific example of an
embodiment of the present invention. FIG. 12 is a diagram showing
the fourth specific example of an embodiment of the present
invention and shows a configuration such that the object plane is
shifted with respect to the optical axis of the first optical
system. FIG. 13 is a diagram showing the fourth specific example of
an embodiment of the present invention and shows a configuration
such that the optical system is covered by a housing.
[0238] In FIG. 10, the optical axis of the first optical system is
shown by a straight line O-O'. The object plane is arranged to
shift to the side of +Y with respect to the optical axis. Then, the
intermediate image formed by the first optical system is shown by a
dashed line MM'. The intermediate image is formed at the side of -Y
from the optical axis. Also, the figure shows that the concave
mirror of the second optical system may be arranged at the side of
-Y from the optical axis. FIG. 12 is a general view of the optical
system shown in FIG. 10 and also shows the position of an image
plane. There is provided a configuration such that light rays
reflected from a mirror passes through the optical axis and reaches
an image plane at the opposite side. The maximum distance from the
optical axis to the mirror is denoted by H1. When the optical
system is covered by a housing, only a thickness of approximately
H1+H2 (wherein H2 is the outer diameter of a lens L19) is needed.
Herein, a configuration such that reflection is not repeated by
curved mirrors several times is different from the configuration
shown in the diagram of the conventional example. Accordingly, the
increase of the thickness of an optical system which is caused by
repeated reflection is not caused.
[0239] In FIG. 10, a panel surface 1 is arranged to shift to a
direction orthogonal to the optical axis of the first optical
system. The amount of shifting in this embodiment is 6.8 mm. As
shown in FIGS. 10 and 12, an effect may be obtained such that the
height of a reflection curved surface of the second optical system
is arranged not to be high to the direction of +Y by arranging the
panel to shift, since the optical path after emitting from the
first optical system is directed to the direction of -Y with
respect to the optical axis. Also, as described below, since the
size of the reflection curved surface may be configured to be
compact, the reflection curved surface may be prevented from being
too low to the direction of -Y. Due to these effects, when such an
optical system is included in a housing, the reflection curved
surface may be easily included in the housing and the height of the
housing in the Y-directions may be small.
[0240] A configuration such that an optical system including a
mirror part is covered by a housing is schematically shown in FIG.
13. In the configuration of FIG. 13, a user does not contact the
mirror. Also, since the mirror is covered by a housing 8, dust does
not easily adhere to it. These effects similarly apply to the first
optical system.
[0241] If the dust is scorched by heat, the reflectance of the
mirror may be reduced or it may be a scattering source so that the
image quality of a projected image is degraded. The reduction of
the reflectance reduces the brightness. The scattering reduces the
contrast. In this practical example, such situations are prevented.
Also, damages such as generation of breakage or warping caused by
contacting a mirror are also prevented.
[0242] Additionally, an aperture 9 is provided on a part of the
apparatus housing 8 in FIG. 13 so that light rays pass out of the
housing 8.
[0243] Also, although the optical path in the first optical system
is not folded in the example of FIG. 13, a folding configuration as
shown in FIGS. 8 and 9 is, of course, possible. The length of the
apparatus in the Z-directions may be reduced by the folding
thereof.
[0244] FIGS. 14 (a) and (b) shows the fifth specific example of an
embodiment of the present invention.
[0245] An image displaying apparatus may be configured by using the
projection optical system described above. An example of the
configuration is schematically shown in FIGS. 14 (a) and (b).
[0246] A lamp light source is shown as a light source 10. For the
lamp light source, a xenon lamp, a halogen lamp, a metal halide
lamp, a super-high pressure mercury lamp and the like may be used.
Alternatively, a solid light source such as an LED, an LD and a
laser may be used.
[0247] The light from the light source may include a UV component
and an IR component but they may be cut out by cut filters 11 and
12 so that the degradation of an optical element is suppressed.
[0248] A polarized light converting element 13 is allowed to
convert the light polarization characteristic of a light ray to a
linearly polarized light so that the efficiency of light
utilization may be improved.
[0249] A pair of fly-eye lens arrays 14 and 15 are allowed to
homogenize the distribution of illumination light quantity.
[0250] A condenser lens 16 is allowed to adjust the illumination
angle and illumination area for the light valve.
[0251] A light beam emitted from the fly-eye lens 15 in FIG. 14(a)
reaches a dichroic mirror 17 in FIG. 14(b).
[0252] The dichroic mirror 17 selects and reflects a
blue-wavelength component so as to separate the optical path of
blue illumination from the optical path of multi-color
illumination. The light transmitting through the dichroic mirror 17
(the light including a green-wavelength component and a
red-wavelength component) is reflected from a mirror 26 and enters
a dichroic mirror 18.
[0253] The dichroic mirror 18 selects and reflects a
green-wavelength component so as to separate the optical paths of
green illumination and red illumination.
[0254] The light reflected from the dichroic mirror 17 transmits
through a polarization beam splitter 19 so as to illuminate a light
valve element 22.
[0255] The light reflected from the dichroic mirror 18 transmits
through a polarization beam splitter 20 so as to illuminate a light
valve element 23.
[0256] The light transmitting through the dichroic mirror 18
transmits through a polarization beam splitter 21 so as to
illuminate a light valve element 24.
[0257] The light valve elements 22, 23 and 24 shown here are
reflection-type light valve elements.
[0258] The illumination light for the light valve element 22 is
modulated by the light valve element 22 so as to provide an image
signal of the blue-wavelength component.
[0259] The illumination light for the light valve element 23 is
modulated by the light valve element 23 so as to provide an image
signal of the green-wavelength component.
[0260] The illumination light for the light valve element 24 is
modulated by the light valve element 24 so as to provide an image
signal of the red-wavelength component.
[0261] The reflected light modulated by the light valve element 22
is reflected from the polarization beam splitter 19 and combined
with reflected light with other colors by a cross prism 25.
[0262] The reflected light modulated by the light valve element 23
is reflected from the polarization beam splitter 20 and combined
with reflected light with other colors by the cross prism.
[0263] The reflected light modulated by the light valve element 24
is reflected from the polarization beam splitter 21 and combined
with reflected light with other colors by the cross prism.
[0264] The reflected light combined by the dichroic prism 25 forms
an intermediate image by the first optical system of the projection
optical system.
[0265] The intermediate image is enlarged and projected by the
second optical system.
[0266] The projection optical system is configured such that the
light valve elements 22, 23 and 24 are object planes 1 for the
projection optical system.
[0267] According to the configuration example described above, a
three-plate-type enlarged image displaying apparatus may be
provided. The effect that has already been described may be
obtained by using a projection optical system according to an
embodiment of the present invention.
[0268] Additionally, the projection optical system according to an
embodiment of the present invention may also be applied to an image
displaying apparatus in which a transmission-type light valve
element is used, without a problem.
[0269] Alternatively, the projection optical system according to an
embodiment of the present invention may also be applied to an image
displaying apparatus in which an image is field-sequentially
displayed by one light valve element.
[0270] Next, numerical practical example 1 of a projection optical
system according to an embodiment of the present invention is shown
below, with reference to FIGS. 15-22.
[0271] The numerical values of a surface number, radius of
curvature, surface distance, refractive index and Abbe number for a
projection optical system in the practical example are shown in
TABLE 1.
TABLE-US-00001 TABLE 1 Radius of Surface Surface curvature distance
Refractive Abbe Note Note number (mm) (mm) index number 1 2 Object
0.000 4.200 1 0.000 1.100 1.517 64.2 2 0.000 4.010 3 0.000 24.900
1.517 64.2 4 0.000 6.567 5 -352.269 6.496 1.497 81.6 6 -32.778
2.465 7 87.501 2.946 1.834 37.3 8 30.729 9.454 1.497 81.6 9 -34.470
3.839 10 -20.746 1.800 1.517 64.2 11 -362.003 6.492 1.497 81.6 12
-23.226 26.066 Stop 0.000 2.224 14 26.708 2.597 1.511 56
.largecircle. 15 19.023 9.979 .largecircle. 16 69.143 4.990 1.569
71.3 17 -99.499 77.949 .largecircle. 18 -62.400 9.835 1.713 53.9 19
-32.800 3.190 1.487 70.4 20 62.528 23.041 21 -33.721 5.539 1.531 56
.largecircle. 22 -35.600 30.000 .largecircle. 23 0.000 100.566 24
0.000 -535.393 .largecircle. .largecircle. Image 0.000 0.000 Note
1: An aspherical surface is indicated by a ".largecircle." mark.
(Herein, however, the 24th surface is a free-form surface.) Note 2:
A reflection surface is indicated by a ".largecircle." mark.
[0272] In TABLE 1, an aspherical surface is indicated by a
".smallcircle." mark in the column of Note 1. The 14th, 15th, 17th,
21th, and 22th surfaces are rotationally symmetric aspherical
surfaces and the 24th surface is an anamorphic polynomial free-form
surface.
[0273] In TABLE 1, a reflection surface is also indicated by a
".smallcircle." mark in the column of Note 2. That is, the 24th
surface is a mirror surface.
[0274] In TABLE 1, the values of surface distance which are changed
depending on the projection magnification ratio are shown in the
italic format.
[0275] An optical path length equivalent to that of the case where
a cross prism or a polarization beam splitter is provided is
provided between an object and the 5th surface.
[0276] The coefficients of aspherical surface are shown in TABLES
2-6.
TABLE-US-00002 TABLE 2 Surface number 14 K 0 A -0.00010 B -1.64E-08
C 6.26E-10 D -1.95E-13 E -2.80E-14 F 8.91E-17
TABLE-US-00003 TABLE 3 Surface number 15 K 0 A -0.00014 B -3.66E-08
C 1.34E-09 D -8.64E-12 E 1.74E-14 F -4.50E-18
TABLE-US-00004 TABLE 4 Surface number 17 K 0 A -0.00014 B -3.66E-08
C 1.34E-09 D -8.64E-12 E 1.74E-14 F -4.50E-18
TABLE-US-00005 TABLE 5 Surface number 21 K 0 A 5.23E-06 B -6.84E-08
C 1.10E-10 D 2.68E-15 E -7.52E-17 F 3.35E-20
TABLE-US-00006 TABLE 6 Surface number 22 K 0 A 3.12E-06 B -4.29E-08
C 6.31E-11 D -4.01E-14 E 3.49E-17 F -1.62E-20
TABLE-US-00007 TABLE 7 4th order coefficient A 6th order
coefficient B 8th order coefficient C 10th order coefficient D 12th
order coefficient E 14th order coefficient F
[0277] The relation between the orders of the coefficients provided
in the above formula (a) and the symbols of the coefficients are
summarized in TABLE 7.
[0278] The coefficients of free-form surface of the 24th surface
are shown in TABLE 8. The coefficients of free-form surface of the
24th surface are the coefficients provided in the above formula
(b).
TABLE-US-00008 TABLE 8 Surface number 24 X 2 -0.0057697 Y 2
-3.44E-03 X 2Y -4.09E-05 Y 3 -1.92E-05 X 4 -1.79E-08 X 2Y 2
-4.25E-07 Y 4 -2.15E-07 X 4Y 5.78E-10 X 2Y 3 -2.26E-09 Y 5
-2.25E-09 X 6 -8.76E-13 X 4Y 2 -9.06E-13 X 2Y 4 -8.10E-12 Y 6
-2.90E-11 X 6Y 1.47E-14 X 4Y 3 -1.15E-13 X 2Y 5 -2.12E-13 Y 7
-3.89E-14 X 8 -1.48E-15 X 6Y 2 2.05E-15 X 4Y 4 -9.37E-16 X 2Y 6
-5.66E-15 Y 8 7.05E-15 X 8Y -1.84E-17 X 6Y 3 5.49E-18 X 4Y 5
3.85E-17 X 2Y 7 -6.43E-17 Y 9 1.06E-16 X 10 2.27E-19 X 8Y 2
-4.02E-19 X 6Y 4 -2.97E-21 X 4Y 6 4.72E-19 X 2Y 8 -3.17E-19 Y 10
4.88E-19
[0279] The degree of decentering of the 24th surface is shown in
TABLE 9.
TABLE-US-00009 TABLE 9 Shift in an X direction (mm) -48.22 Rotation
in a YZ plane (.degree.) -33.66
[0280] The numerical aperture (NA) of the optical system at the
side of an object in numerical practical example 1 is 0.25.
[0281] In numerical practical example 1, the center of an image
plane is arranged to be shifted to a +Y direction by 6.46 mm with
respect to the optical axis of the first optical system.
[0282] Additionally, the magnification ratio of numerical practical
example 1 in TABLE 1 is 127. Herein, the magnification ratio is
approximately a ratio of the size of an image to the size of an
object.
[0283] Also, the values of the surface distance in the states of
different magnification ratios in numerical practical example 1 are
shown in TABLE 10.
[0284] In TABLE 10, for example, surface distance d10 means the
surface distance between the surface of number 10 and the surface
of number 11.
TABLE-US-00010 TABLE 10 Magnification 126.99 95.20 63.49 d4 6.57
7.59 8.52 d6 2.46 1.97 5.53 d9 3.84 6.15 7.69 d12 26.07 23.08 19.20
d13 2.22 9.04 18.13 d17 77.95 71.23 60.00 d24 -535.39 -424.89
-321.62
[0285] FIG. 15 is a diagram showing a spot diagram on an image
plane at a magnification ratio of 127 in numerical practical
example 1. Similarly, FIG. 16 is a diagram showing a spot diagram
on an image plane at a magnification ratio of 95.2 in numerical
practical example 1. Furthermore, FIG. 17 is a diagram showing a
spot diagram on an image plane at a magnification ratio of 63.5 in
numerical practical example 1.
[0286] FIG. 18 is a diagram showing the correspondence between
spots shown in FIGS. 15, 16 and 17 and the positions thereof on the
image plane. In regard to an area of X.ltoreq.0 on an image plane
in an XY plane, nine lattice points obtained by equally dividing it
in the X-directions into three parts and equally dividing it in the
Y-directions into three parts are shown in FIG. 18. These lattice
points are indicated by [0287] {circle around (1)}.about.{circle
around (9)} and the spot diagrams of them are shown in FIGS. 15, 16
and 17.
[0288] Additionally, in numerical practical example 1, the image
plane is in an XY plane and only the positions of spots at the side
of +X are shown in FIG. 18 since the spot characteristics on the
image plane should be symmetric spot characteristics with respect
to the Y-axis in the .+-.X-directions.
[0289] As shown in FIGS. 15, 16 and 17, the light spots are
condensed well in any of the projection magnification ratios. In
numerical practical example 1, an XGA class of resolution can be
obtained.
[0290] In regard to an XGA resolution frequency, the obtained
performance that is the value of a white modulation transfer
function (MTF) is 50% or greater all over the area of a screen.
[0291] FIG. 19 is a diagram showing a TV distortion characteristic
at a projection magnification ratio of 127. FIG. 20 is a diagram
showing a TV distortion characteristic at a projection
magnification ratio of 95.2. FIG. 21 is a diagram showing a TV
distortion characteristic at a projection magnification ratio of
63.5.
[0292] Herein, the TV distortion is a numerical value for
evaluating the distortion of an image in the directions of a long
side thereof when the image is projected on a TV monitor and is
defined by Dh=.DELTA.h/2 h.times.100%, wherein Dh represents the TV
distortion, h represents the length between the center of the image
and an end of the image in the directions of a short side thereof,
and .DELTA.h represents the distance from a straight line extending
in the directions of a long side of the image and passing through
an apex of the image to a straight line extending in the directions
of a long side of the image and passing through an end of the image
in the directions of a short side of the image.
[0293] The TV distortion is 1% or less and the distortion is
corrected well in any of the cases.
[0294] Also, the maximum distances between the image plane and the
mirror at projection magnification ratios of 127, 95.2, and 63.5
are 535.4 mm, 424.9 mm, and 321.6 mm, respectively. Thus, the
distance from the mirror to the image plane is small and the
practical example may attain a performance such that enlarging
projection with a high magnification ratio in a close range may be
allowed.
[0295] Also, the maximum value of a half angle of view of a
principal ray projected toward a projection surface is
approximately 74.degree. in the projection optical system in
numerical practical example 1.
[0296] Additionally, in the projection optical system in numerical
practical example 1, an intermediate image is moved when the
projection distance and the projection magnification ratio are
changed.
[0297] FIG. 22 is a diagram illustrating the movement of an
intermediate image in numerical practical example 1. A concave
mirror (having the 24th surface) and a lens (having the 21th and
22th surfaces) which is closest to the concave mirror are shown in
FIG. 22. As shown in FIG. 22, "a" is the optical path length of a
principal ray from the intermediate image to the impingement
thereof on the concave mirror which ray is the uppermost one
reaching a portion of a screen in an axis connecting the optical
axis of the lens and the center of the screen (the Y-axis, the
directions of a short axis of the screen).
TABLE-US-00011 TABLE 11 Image plane size a 80 inches 112.3 mm 40
inches 117.6 mm
[0298] As shown in TABLE 11, the optical path length "a" between an
intermediate image and a concave mirror in an 80-inches one whose
projection distance is large is small and the optical path length
"a" between an intermediate image and a concave mirror in a
40-inches one whose projection distance is small is large. Thus,
when the projection distance is changed, that is, the projection
magnification ratio is changed, from for 80 inches to for 40 inches
in numerical practical example 1, it may be confirmed that the
intermediate image is moved.
[0299] Next, numerical practical example 2 of a projection optical
system according to an embodiment of the present invention is shown
below, with reference to FIGS. 24-33.
[0300] The numerical values of a surface number, radius of
curvature, surface distance, refractive index and Abbe number for a
projection optical system in the practical example are shown in
TABLE 12.
TABLE-US-00012 TABLE 12 Radius of Surface Surface curvature
distance Refractive Abbe Note Note number (mm) (mm) index number 1
2 Object 0.000 4.000 1 0.000 1.800 1.517 64.2 2 0.000 0.400 1.517
64.2 3 0.000 20.560 1.589 61.3 4 0.000 3.250 1.589 61.3 5 0.000
25.000 1.517 64.2 6 0.000 5.000 7 49.502 6.228 1.497 81.6 8 -57.839
0.100 9 73.010 1.600 1.835 43.0 10 18.571 8.910 1.497 81.6 11
-62.839 11.303 12 279.254 6.379 1.567 42.8 13 -201.777 3.891 14
-26.570 2.839 1.581 40.9 15 -22.006 12.388 16 0.000 3.755 17
-73.296 1.300 1.806 40.7 18 43.180 1.500 19 51.386 3.920 1.723 38.0
20 -93.574 1.000 21 0.000 78.501 22 41.833 10.000 1.533 56.7
.largecircle. 23 47.189 20.022 .largecircle. 24 55.093 16.606 1.488
70.4 25 -353.432 3.273 26 -166.099 9.000 1.786 43.9 27 -1582.630
8.796 28 -936.901 6.442 1.713 53.9 29 50.387 26.257 30 -83.019
8.000 1.533 56.7 .largecircle. 31 -62.823 12.000 .largecircle. 32
0.000 100.000 33 0.000 -703.095 .largecircle. .largecircle. Image
0.000 0.000 Note 1: An aspherical surface is indicated by a
".largecircle." mark. (Herein, however, the 33th surface is a
free-form surface.) Note 2: A reflection surface is indicated by a
".largecircle." mark.
[0301] In TABLE 12, an aspherical surface is indicated by a
".smallcircle." mark in the column of Note 1. The 22th, 23th, 30th,
and 31th surfaces are rotationally symmetric aspherical surfaces
and the 33th surface is an anamorphic polynomial free-form
surface.
[0302] In TABLE 12, a reflection surface is also indicated by a "o"
mark in the column of Note 2. That is, the 33th surface is a mirror
surface.
[0303] In TABLE 12, the values of surface distance which are
changed depending on the projection magnification ratio are shown
in the italic format.
[0304] An optical path length equivalent to that of the case where
a cross prism or a polarization beam splitter is provided is
provided between an object and the 7th surface.
[0305] The coefficients of asnherical surface are shown in TABLES
13-16.
TABLE-US-00013 TABLE 13 Surface number 22 K 0 A -6.22E-06 B
-5.72E-10 C 1.13E-12 D -9.50E-16 E 1.92E-19 F -5.59E-23 G
-5.45E-27
TABLE-US-00014 TABLE 14 Surface number 23 K 0 A -8.09E-06 B
1.39E-09 C -7.92E-14 D -1.41E-16 E -1.37E-19 F 1.22E-23 G
2.53E-26
TABLE-US-00015 TABLE 15 Surface number 30 K 0 A -1.23E-05 B
1.42E-08 C -2.88E-11 D 2.74E-14 E -9.84E-18 F 1.33E-21 G
-8.38E-26
TABLE-US-00016 TABLE 16 Surface number 31 K 0 A -9.30E-06 B
9.38E-09 C -1.51E-11 D 1.14E-14 E -4.21E-18 F 1.98E-21 G
-5.82E-25
TABLE-US-00017 TABLE 17 4th order coefficient A 6th order
coefficient B 8th order coefficient C 10th order coefficient D 12th
order coefficient E 14th order coefficient F 16th order coefficient
G
[0306] The relation between the orders of the coefficients provided
in the above formula (a) and the symbols of the coefficients are
summarized in TABLE 17.
[0307] The coefficients of free-form surface of the 33th surface
are shown in TABLE 18. The coefficients of free-form surface of the
33th surface are the coefficients provided in the above formula
(c).
TABLE-US-00018 TABLE 18 Surface number 33 X 2 -0.0038697 Y 2
-0.0017467 X 2Y -1.09E-05 Y 3 -1.87E-05 X 4 -2.48E-08 X 2Y 2
-3.35E-07 Y 4 7.79E-07 X 4Y -8.55E-10 X 2Y 3 9.47E-09 Y 5 -2.07E-08
X 6 -4.53E-12 X 4Y 2 4.18E-11 X 2Y 4 -3.29E-10 Y 6 3.08E-10 X 6Y
4.80E-14 X 4Y 3 -1.32E-12 X 2Y 5 6.54E-12 Y 7 -2.61E-12 X 8
9.46E-16 X 6Y 2 -3.83E-15 X 4Y 4 1.35E-14 X 2Y 6 -8.68E-14 Y 8
9.33E-15 X 8Y 2.71E-18 X 6Y 3 1.09E-16 X 4Y 5 2.78E-18 X 2Y 7
6.43E-16 Y 9 1.16E-17 X 10 -1.13E-19 X 8Y 2 -8.22E-20 X 6Y 4
-1.00E-18 X 4Y 6 -4.92E-19 X 2Y 8 -2.06E-18 Y 10 -1.45E-19
[0308] The degree of decentering of the 33th surface is shown in
TABLE 19.
TABLE-US-00019 TABLE 19 Shift in a Y direction (mm) -97.18 Rotation
in a YZ plane (.degree. ) -48.46
[0309] The numerical aperture (NA) of the optical system at the
side of an object in numerical practical example 2 is 0.22.
[0310] In numerical practical example 2, the center of an image
plane is arranged to be shifted to a +Y direction by 5.57 mm with
respect to the optical axis of the first optical system.
[0311] Additionally, the magnification ratio of numerical practical
example 2 in TABLE 12 is 164.7.
[0312] Also, the values of the surface distance in the states of
different magnification ratios in numerical practical example 2 are
shown in TABLE 20.
[0313] In TABLE 20, for example, surface distance d21 means the
surface distance between the surface of number 21 and the surface
of number 22.
TABLE-US-00020 TABLE 20 Magnification 164.72 115.30 82.36 d21
78.501 80.012 82.289 d23 20.022 12.258 1.500 d27 8.796 9.984 11.545
d29 26.257 31.322 38.242 d33 -703.095 -487.617 -343.987
[0314] FIG. 24 shows a state such that a 100-inches-diagonal image
is projected at a projection distance of 759 mm in numerical
practical example 2. FIG. 25 shows a state such that a
70-inches-diagonal image is projected at a projection distance of
544 mm in numerical practical example 2. FIG. 26 shows a state such
that a 50-inches-diagonal image is projected at a projection
distance of 400 mm in numerical practical example 2.
[0315] In FIGS. 24, 25 and 26, the light-valve element is a
0.16-inches-diagonal one and the aspect ratio thereof is 9:16.
[0316] FIG. 27 shows the object plane 1 to the second optical
system 4 in any of FIGS. 24, 25 and 26.
[0317] Similarly to FIGS. 5, 6 and 7, an intermediate image is
provided and the image plane of the intermediate image is curved to
the under side.
[0318] Herein, although folding of the optical path of the first
optical system by a folding mirror as shown in FIGS. 8 and 9 is not
provided in FIG. 27, space for arranging a folding mirror 7 to
conduct such folding is sufficiently retained, and although the
optical path is schematically drawn in a straight one, the optical
path is allowed to be folded by the folding mirror 7.
[0319] Whereas a lens at the side of reduction, that is, at the
side of an object plane is moved with respect to the folding mirror
7 in numerical practical example 1, a lens at the side of
enlargement, that is, between the folding mirror and the second
optical system 4 is moved with respect to the folding mirror 7 in
numerical practical example 2. Thus, a cam mechanism for moving a
lens may be a lens group at the side of reduction with respect to
the folding mirror 7 or may be a lens group at the side of
enlargement.
[0320] FIG. 28 is a diagram showing a spot diagram on an image
plane at a magnification ratio of 164.7 in numerical practical
example 2. Similarly, FIG. 29 is a diagram showing a spot diagram
on an image plane at a magnification ratio of 115.3 in numerical
practical example 2. Furthermore, FIG. 30 is a diagram showing a
spot diagram on an image plane at a magnification ratio of 82.4 in
numerical practical example 2.
[0321] Herein, FIGS. 28, 29 and 30 show spot diagrams on nine
lattice points as shown in FIG. 18, similarly to FIGS. 15, 16 and
17.
[0322] Additionally, also in numerical practical example 2, the
image plane is in an XY plane and only the positions of spots at
the side of +X are shown in FIG. 18 since the spot characteristics
on the image plane should be symmetric spot characteristics with
respect to the Y-axis in the .+-.X-directions.
[0323] As shown in FIGS. 28, 29 and 30, the light spots are
condensed well in any of the projection magnification ratios. In
numerical practical example 2, a full-high-definition-television
class of resolution (1920.times.1080) can be obtained.
[0324] FIG. 31 is a diagram showing a TV distortion characteristic
at a projection magnification ratio of 164.7. FIG. 32 is a diagram
showing a TV distortion characteristic at a projection
magnification ratio of 115.3. FIG. 33 is a diagram showing a TV
distortion characteristic at a projection magnification ratio of
82.4. The TV distortion is 1% or less and the distortion is
corrected well in any of the cases.
[0325] Also, the maximum distances between the image plane and the
mirror at projection magnification ratios of 164.7, 115.3, and 82.4
are 759 mm, 544 mm, and 400 mm, respectively. Thus, the distance
from the mirror to the image plane is small and the practical
example may attain a performance such that enlarging projection
with a high magnification ratio in a close range may be allowed.
Also, the maximum value of a half angle of view of a principal ray
projected toward a projection surface is approximately 71.9.degree.
in the projection optical system in numerical practical example
2.
[0326] Furthermore, similarly to numerical practical example 1,
where "a" is the optical path length of a principal ray from the
intermediate image to the impingement thereof on the concave mirror
which ray is the uppermost one reaching a portion of a screen in an
axis connecting the optical axis of the lens and the center of the
screen (the Y-axis, the directions of a short axis of the screen),
the optical path length "a" between an intermediate image and a
concave mirror in an 100-inches one whose projection distance is
large is small and the optical path length "a" between an
intermediate image and a concave mirror in a 50-inches one whose
projection distance is small is large, as shown in TABLE 21.
TABLE-US-00021 TABLE 21 Image plane size a 100 inches 113.5 mm 50
inches 121.1 mm
[0327] Thus, when the projection distance is changed, that is, the
projection magnification ratio is changed, from for 100 inches to
for 50 inches in numerical practical example 2, it may be confirmed
that the intermediate image is moved.
[0328] Next, numerical practical example 3 of a projection optical
system according to an embodiment of the present invention is shown
below, with reference to FIGS. 34-43.
[0329] The numerical values of a surface number, radius of
curvature, surface distance, refractive index and Abbe number for a
projection optical system in the practical example are shown in
TABLE 22.
TABLE-US-00022 TABLE 22 Radius of Surface Surface curvature
distance Refractive Abbe Note Note number (mm) (mm) index number 1
2 Object 0.000 22.100 1 0.000 12.000 1.835 43.0 2 0.000 27.300
1.517 64.2 3 0.000 6.050 4 164.630 4.792 1.488 70.4 5 -84.820 0.300
6 31.675 6.548 1.488 70.4 7 158.047 0.300 8 56.577 1.600 1.804 35.1
9 26.874 7.546 1.488 70.4 10 -365.882 0.300 11 -665.123 1.600 1.762
32.2 12 22.955 10.471 1.497 81.6 13 -31.691 0.395 14 -30.477 1.700
1.808 40.3 15 26.927 8.552 1.785 25.7 16 -53.271 24.826 17 0.000
5.000 18 -52.415 1.896 1.534 58.1 .largecircle. 19 -44.013 67.772
.largecircle. 20 35.540 14.290 1.506 73.7 21 439.032 15.735 22
-147.851 10.790 1.835 43.0 .largecircle. 23 52.844 37.629
.largecircle. 24 82.003 13.000 1.608 39.3 25 -96.520 1.827 26
-95.986 10.000 1.835 43.0 27 90.174 25.217 28 -85.919 7.423 1.550
51.8 .largecircle. 29 -62.856 154.802 .largecircle. 30 -74.638
-738.910 .largecircle. .largecircle. Image 0.000 0.000 Note 1: An
aspherical surface is indicated by a ".largecircle." mark. Note 2:
A reflection surface is indicated by a ".largecircle." mark.
[0330] In TABLE 22, an aspherical surface is indicated by a
".smallcircle." mark in the column of Note 1. The 18th, 19th, 22th,
23th, 28th, 29th, and 30th surfaces are rotationally symmetric
aspherical surfaces.
[0331] In TABLE 22, a reflection surface is also indicated by a
".smallcircle." mark in the column of Note 2. That is, the 30th
surface is a mirror surface. Against numerical practical examples 1
and 2, the minor surface of the second optical system is a
rotationally symmetric aspherical surface in numerical practical
example 3. In TABLE 22, the values of surface distance which are
changed depending on the projection magnification ratio are shown
in the italic format.
[0332] An optical path length equivalent to that of the case where
a cross prism or a polarization beam splitter is provided is
provided between an object and the 4th surface.
[0333] The coefficients of aspherical surface are shown in TABLES
23-29.
TABLE-US-00023 TABLE 23 Surface number 18 K 0 A 1.84E-06 B
-6.61E-09 C 6.08E-11 D -1.13E-13
TABLE-US-00024 TABLE 24 Surface number 19 K 0 A 1.71E-06 B
-7.40E-09 C 5.89E-11 D -1.07E-13
TABLE-US-00025 TABLE 25 Surface number 22 K 0 A -1.18E-05 B
1.67E-08 C -1.30E-11 D 3.94E-16 E 2.64E-17 F -2.74E-20
TABLE-US-00026 TABLE 26 Surface number 23 K -10.1056 A -3.89E-06 B
1.37E-08 C -1.49E-11 D 1.32E-14 E 6.37E-18 F -5.72E-21
TABLE-US-00027 TABLE 27 Surface number 28 K 0 A -5.36E-06 B
-1.27E-08 C 2.26E-11 D -1.89E-14
TABLE-US-00028 TABLE 28 Surface number 29 K 0 A -3.53E-06 B
-1.26E-08 C 2.57E-11 D -3.21E-14 E 2.09E-17 F -8.00E-21
TABLE-US-00029 TABLE 29 Surface number 30 K -2.2565 A -1.44E-07 B
7.94E-12 C -4.34E-16 D -1.95E-20 E 3.69E-24 F -1.41E-28
TABLE-US-00030 TABLE 30 4th order coefficient A 6th order
coefficient B 8th order coefficient C 10th order coefficient D 12th
order coefficient E 14th order coefficient F
[0334] The relation between the orders of the coefficients provided
in the above formula (a) and the symbols of the coefficients are
summarized in TABLE 30.
[0335] The numerical aperture (NA) of the optical system at the
side of an object in numerical practical example 3 is 0.20.
[0336] In numerical practical example 3, the center of an image
plane is arranged to be shifted to a +Y direction by 5.80 mm with
respect to the optical axis of the first optical system.
[0337] Additionally, the magnification ratio of numerical practical
example 3 in TABLE 22 is 131.8.
[0338] Also, the values of the surface distance in the states of
different magnification ratios in numerical practical example 3 are
shown in TABLE 31.
[0339] In TABLE 31, for example, surface distance d19 means the
surface distance between the surface of number 19 and the surface
of number 20.
TABLE-US-00031 TABLE 31 Magnification 131.77 98.83 65.89 d19 67.772
69.026 71.398 d23 37.629 30.428 13.482 d25 1.827 2.278 3.183 d27
25.217 30.713 44.381 d30 -738.910 -570.890 -400.000
[0340] FIG. 34 shows a state such that an 80-inches-diagonal image
is projected at a projection distance of 739 mm in numerical
practical example 3.
[0341] FIG. 35 shows a state such that a 60-inches-diagonal image
is projected at a projection distance of 571 mm in numerical
practical example 3.
[0342] FIG. 36 shows a state such that a 40-inches-diagonal image
is projected at a projection distance of 400 mm in numerical
practical example 3.
[0343] In FIGS. 34, 35 and 36, the light-valve element is a
0.16-inches-diagonal one and the aspect ratio thereof is 9:16.
[0344] FIG. 37 shows the object plane 1 to the second optical
system 4 in any of FIGS. 34, 35 and 36.
[0345] Similarly to FIGS. 5, 6 and 7, an intermediate image is
provided and the image plane of the intermediate image is curved to
the under side.
[0346] Herein, although folding of the optical path of the first
optical system by a folding mirror as shown in FIGS. 8 and 9 is not
provided in FIG. 37, space for arranging a folding mirror 7 to
conduct such folding is sufficiently retained, and although the
optical path is schematically drawn in a straight one, the optical
path is allowed to be folded by the folding mirror 7.
[0347] Similarly to numerical practical example 2, a lens at the
side of enlargement, that is, between the folding mirror and the
second optical system 4 is moved with respect to the folding mirror
7.
[0348] FIG. 38 is a diagram showing a spot diagram on an image
plane at a magnification ratio of 131.8 in numerical practical
example 3. Similarly, FIG. 39 is a diagram showing a spot diagram
on an image plane at a magnification ratio of 98.8 in numerical
practical example 3. Furthermore, FIG. 40 is a diagram showing a
spot diagram on an image plane at a magnification ratio of 65.9 in
numerical practical example 3.
[0349] Herein, FIGS. 38, 39 and 40 show spot diagrams on nine
lattice points as shown in FIG. 18, similarly to FIGS. 15, 16 and
17.
[0350] Additionally, also in numerical practical example 3, the
image plane is in an XY plane and only the positions of spots at
the side of +X are shown in FIG. 18 since the spot characteristics
on the image plane should be symmetric spot characteristics with
respect to the Y-axis in the .+-.X-directions.
[0351] As shown in FIGS. 38, 39 and 40, the light spots are
condensed well in any of the projection magnification ratios. In
numerical practical example 3, a full-high-definition-television
class of resolution (1920.times.1080) can be obtained.
[0352] FIG. 41 is a diagram showing a TV distortion characteristic
at a projection magnification ratio of 131.8. FIG. 42 is a diagram
showing a TV distortion characteristic at a projection
magnification ratio of 98.8. FIG. 43 is a diagram showing a TV
distortion characteristic at a projection magnification ratio of
65.9. The TV distortion is 1% or less and the distortion is
corrected well in any of the cases.
[0353] Also, the maximum distances between the image plane and the
mirror at projection magnification ratios of 131.8, 98.8, and 65.9
are 739 mm, 571 mm, and 400 mm, respectively. Thus, the distance
from the mirror to the image plane is small and the practical
example may attain a performance such that enlarging projection
with a high magnification ratio in a close range may be
allowed.
[0354] Also, the maximum value of a half angle of view of a
principal ray projected toward a projection surface is
approximately 67.7.degree. in the projection optical system in
numerical practical example 3.
[0355] Furthermore, similarly to numerical practical example 1,
where "a" is the optical path length of a principal ray from the
intermediate image to the impingement thereof on the concave mirror
which ray is the uppermost one reaching a portion of a screen in an
axis connecting the optical axis of the lens and the center of the
screen (the Y-axis, the directions of a short axis of the screen),
the optical path length "a" between an intermediate image and a
concave mirror in an 80-inches one whose projection distance is
large is small and the optical path length "a" between an
intermediate image and a concave mirror in a 40-inches one whose
projection distance is small is large, as shown in TABLE 32.
TABLE-US-00032 TABLE 32 Image plane size a 80 inches 106.2 mm 40
inches 111.2 mm
[0356] Thus, when the projection distance is changed, that is, the
projection magnification ratio is changed, from for 80 inches to
for 40 inches in numerical practical example 3, it may be confirmed
that the intermediate image is moved.
[0357] Although an embodiment(s) and/or a practical example(s) of
the present invention has/have been specifically described above,
the present invention is not limited to the embodiment(s) and/or
practical example(s) and the embodiment(s) and/or practical
example(s) may be altered or modified without departing from the
spirit and scope of the present invention.
[0358] [Appendix]
[0359] Typical embodiments (1) to (20) of the present invention are
provided below.
[0360] Embodiment (1) is a projection optical system comprising a
first optical system configured to form a first image conjugated
with an object and a second optical system configured to project a
second image conjugated with the first image toward a projection
surface, in which at least one of the first optical system and
second optical system comprises at least one optical element(s)
movable relative to the object, characterized in that an image
distance of the projection optical system is changed and a size of
the second image is changed, by moving at least one of the optical
element(s) relative to the object.
[0361] Embodiment (2) is the projection optical system as described
in embodiment (1) above, characterized in that a distance between
the first image and the second optical system is changed by moving
at least one of the optical element(s) relative to the object.
[0362] Embodiment (3) is the projection optical system as described
in embodiment (1) or (2) above, characterized in that the first
optical system comprises at least one of the optical element(s) and
the first image is moved relative to the object by moving at least
one of the optical element(s) comprised in the first optical system
relative to the object.
[0363] Embodiment (4) is the projection optical system as described
in embodiment (3) above, characterized in that the second optical
system is fixed relative to the object.
[0364] Embodiment (5) is the projection optical system as described
in embodiment (4) above, characterized in that when a focal length
of the first optical system is changed from a first focal length to
a second focal length and a size of the second image is changed
from a first size to a second size by moving at least one of the
optical element(s) comprised in the first optical system relative
to the object, a ratio of the second focal length to the first
focal length is different from a ratio of the second size to the
first size.
[0365] Embodiment (6) is the projection optical system as described
in embodiment (5) above, characterized in that when the second
focal length is greater than the first focal length and the second
size is greater than the first size, a ratio of the second size to
the first size is greater than a ratio of the second focal length
to the first focal length.
[0366] Embodiment (7) is the projection optical system as described
in any of embodiments (1) to (6) above, characterized in that at
least one of the first optical system and second optical system,
which comprise(s) at least one of the optical element(s), is a
coaxial optical system.
[0367] Embodiment (8) is the projection optical system as described
in any of embodiments (1) to (7) above, characterized in that one
of the first optical system and second optical system comprises the
at least one optical element(s) and comprises optical element(s)
more than an optical element(s) constituting the other of the first
optical system or second optical system.
[0368] Embodiment (9) is the projection optical system as described
in any of embodiments (1) to (8) above, characterized in that a
half angle of view of a principal ray projected toward the
projection surface is substantially constant while a size of the
second image is changed.
[0369] Embodiment (10) is the projection optical system as
described in embodiment (9) above, characterized in that a maximum
vale of a half angle of view of a principal ray projected toward
the projection surface is equal to or greater than 60.degree..
[0370] Embodiment (11) is the projection optical system as
described in any of embodiments (1) to (10) above, characterized in
that the second optical system comprises at least one optical
element with a reflection surface having a positive power.
[0371] Embodiment (12) is the projection optical system as
described in embodiment (11) above, characterized in that at least
one of the reflection surface(s) having a positive power in the at
least one optical element with a reflection surface having a
positive power is a rotationally symmetric aspherical surface.
[0372] Embodiment (13) is the projection optical system as
described in embodiment (11) above, characterized in that at least
one of the reflection surface(s) having a positive power in the at
least one optical element with a reflection surface having a
positive power is a free-form surface.
[0373] Embodiment (14) is the projection optical system as
described in any of embodiments (11) to (13) above, characterized
in that a number of the at least one optical element with a
reflection surface having a positive power, comprised in the second
optical system is one.
[0374] Embodiment (15) is the projection optical system as
described in any of embodiments (1) to (14) above, characterized in
that at least one folding mirror configured to fold an optical path
from the object to the second image is comprised in the optical
path.
[0375] Embodiment (16) is the projection optical system as
described in embodiment (15) above, characterized in that the at
least one optical element(s) movable relative to the object is
arranged at a side of the object or at a side of the second image
relative to the at least one folding mirror.
[0376] Embodiment (17) is the projection optical system as
described in embodiment (15) or (16) above, characterized in that
the at least one folding mirror is arranged between the object and
the first image.
[0377] Embodiment (18) is the projection optical system as
described in any of embodiments (1) to (17) above, characterized in
that the first image has a curvature of field which curves toward a
side of the object.
[0378] Embodiment (19) is the projection optical system as
described in any of embodiments (1) to (18) above, characterized in
that the first optical system is a coaxial optical system and the
object is decentered relative to an optical axis of the first
optical system.
[0379] Embodiment (20) is an image projecting apparatus configured
to project an image onto a projection surface, characterized by
comprising the projection optical system as described in any of
embodiments (1) to (19) above.
INDUSTRIAL APPLICABILITY
[0380] An embodiment of the present invention may be applied to a
projection optical system, an enlargement projection optical
system, a variable magnification projection optical system and an
image displaying apparatus such as a projector. For example, an
embodiment of the present invention may be applied to a projection
optical system of an image projecting apparatus such as a
projection apparatus, and in particular, may be applied to a
projection optical system for attaining projection in a close range
in a front projector.
* * * * *