U.S. patent application number 15/374157 was filed with the patent office on 2017-12-28 for image reading optical system and image reading apparatus.
This patent application is currently assigned to FUJI XEROX CO., LTD.. The applicant listed for this patent is FUJI XEROX CO., LTD.. Invention is credited to Kiyofumi AIKAWA, Masaki HACHISUGA, Takashi HIRAMATSU.
Application Number | 20170374223 15/374157 |
Document ID | / |
Family ID | 60677760 |
Filed Date | 2017-12-28 |
United States Patent
Application |
20170374223 |
Kind Code |
A1 |
AIKAWA; Kiyofumi ; et
al. |
December 28, 2017 |
IMAGE READING OPTICAL SYSTEM AND IMAGE READING APPARATUS
Abstract
An image reading optical system includes an image reading unit
including plural reading elements that are arranged in a first
direction, a first reflective optical system configured to reflect
reflection light which is irradiation light emitted from a light
source and reflected on an object to be read, a second reflective
optical system configured to condense the reflection light
reflected on the first reflective optical system to the image
reading unit, and an aperture stop including a plate shaped member
formed with an aperture configured to regulate the reflection light
reflected on the first reflective optical system in the first
direction, the plate shaped member including at least one plate
shaped piece bent at a preset angle with respect to the aperture
along a tangent line of the aperture in the first direction.
Inventors: |
AIKAWA; Kiyofumi; (Kanagawa,
JP) ; HACHISUGA; Masaki; (Kanagawa, JP) ;
HIRAMATSU; Takashi; (Kanagawa, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
FUJI XEROX CO., LTD. |
Tokyo |
|
JP |
|
|
Assignee: |
FUJI XEROX CO., LTD.
Tokyo
JP
|
Family ID: |
60677760 |
Appl. No.: |
15/374157 |
Filed: |
December 9, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04N 1/1061 20130101;
H04N 2201/0081 20130101; H04N 1/0289 20130101; H04N 1/02825
20130101 |
International
Class: |
H04N 1/028 20060101
H04N001/028; H04N 1/10 20060101 H04N001/10 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 27, 2016 |
JP |
2016-126397 |
Claims
1. An image reading optical system comprising: an image reading
unit including a plurality of reading elements that are arranged in
a first direction; a first reflective optical system configured to
reflect reflection light which is irradiation light emitted from a
light source and reflected on an object to be read; a second
reflective optical system configured to condense the reflection
light reflected on the first reflective optical system to the image
reading unit; and an aperture stop including a plate shaped member
formed with an aperture configured to regulate the reflection light
reflected on the first reflective optical system in the first
direction, the plate shaped member including at least one plate
shaped piece bent at a preset angle with respect to the aperture
along a tangent line of the aperture in the first direction.
2. The image reading optical system according to claim 1, wherein
the aperture stop regulates the reflection light reflected on the
first reflective optical system in a second direction crossing the
first direction by the plate shaped piece.
3. The image reading optical system according to claim 1, wherein
the plate shaped piece meets one of: a first condition where the
plate shaped piece is bent along a traveling direction of first
turning-back light and disposed between the first reflective
optical system and the second reflective optical system, the first
turning-back light being incident on the first reflective optical
system, and a second condition where the plate shaped piece is bent
along a traveling direction of second turning-back light and
disposed between the first reflective optical system and the second
reflective optical system, the second turning-back light being
reflected on the second reflective optical system.
4. The image reading optical system according to claim 3, wherein
the plate shaped piece meets at least one of: a condition where the
plate shaped piece meets the first condition and is bent in
parallel with the traveling direction of the first turning-back
light, and a condition where the plate shaped piece meets the
second condition and is bent in parallel with the traveling
direction of the second turning-back light.
5. The image reading optical system according to claim 3, wherein
the image reading optical system is provided with both a first
plate shaped piece meeting the first condition and a second plate
shaped piece meeting the second condition.
6. The image reading optical system according to claim 5, wherein
the first plate shaped piece and the second plate shaped piece are
disposed on different planes.
7. An image reading apparatus comprising: a light source that emits
light so that an object to be read is irradiated with the light;
and the image reading optical system of claim 1.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is based on and claims priority under 35
USC 119 from Japanese Patent Application No. 2016-126397 filed Jun.
27, 2016.
BACKGROUND
Technical Field
[0002] The present invention relates to an image reading optical
system and an image reading apparatus.
SUMMARY
[0003] According to an aspect of the invention, an image reading
optical system includes an image reading unit including plural
reading elements that are arranged in a first direction, a first
reflective optical system configured to reflect reflection light
which is irradiation light emitted from a light source and
reflected on an object to be read, a second reflective optical
system configured to condense the reflection light reflected on the
first reflective optical system to the image reading unit, and an
aperture stop including a plate shaped member formed with an
aperture configured to regulate the reflection light reflected on
the first reflective optical system in the first direction, the
plate shaped member including at least one plate shaped piece bent
at a preset angle with respect to the aperture along a tangent line
of the aperture in the first direction.
BRIEF DESCRIPTION OF THE DRAWINGS
[0004] Exemplary embodiments of the present invention will be
described in detail based on the following figures, wherein:
[0005] FIG. 1 is a schematic sectional view illustrating an
exemplary configuration of an image reading apparatus according to
an exemplary embodiment;
[0006] FIG. 2 is a schematic sectional view illustrating an
exemplary configuration of an image reading optical system
according to an exemplary embodiment;
[0007] FIGS. 3A and 3B are views for explaining a shape of an
aperture stop according to an exemplary embodiment;
[0008] FIGS. 4A and 4B are a side view and a plan view each
illustrating the exemplary configuration of the image reading
optical system according to an exemplary embodiment;
[0009] FIG. 5 is a schematic sectional view illustrating a
modification example of the image reading optical system according
to an exemplary embodiment; and
[0010] FIG. 6 is a schematic sectional view illustrating a
configuration of an image reading optical system according to a
comparative example.
DETAILED DESCRIPTION
[0011] Hereinafter, an exemplary embodiment of the present
invention will be described with reference to the accompanying
drawings.
[0012] An image reading apparatus 12 according to an exemplary
embodiment of the present invention will be described with
reference to FIG. 1. FIG. 1 illustrates an outline configuration of
the image reading apparatus 12. The image reading apparatus 12 is
incidentally installed in, for example, an image forming apparatus
and used to read a document or the like (an object to be read). As
illustrated in FIG. 1, the image reading apparatus 12 includes an
automatic document feeder 50 and an image reading processor 52 that
reads an image formed on a surface of a document.
[0013] The automatic document feeder 50 according to the present
exemplary embodiment includes a document loading stand 60 on which
a document is loaded, a document transport path 61 that transports
a document, and a discharge stand 62 to which a document is
discharged after an image is read.
[0014] The document transport path 61 is formed in a U shape, and a
sheet delivery roller 63, delivery rollers 64, pre-registration
rollers 65, registration rollers 66, a platen roller 67, out
rollers 68, and discharge rollers 69 are provided around the
document transport path 61. The sheet delivery roller 63 moves down
during the transport of a document to pick up the document placed
on the document loading stand 60. The delivery rollers 64 supply
the uppermost document among the documents sent from the sheet
delivery roller 63 to the inside of the automatic document feeder.
The pre-registration rollers 65 temporarily stop the document sent
from the delivery rollers 64 and correct the skew of the document.
The registration rollers 66 temporarily stop the document sent from
the pre-registration rollers 65 and adjust a reading timing. The
platen roller 67 causes the document passing the document transport
path 61 to face a platen glass 70 to be described later. The out
rollers 68 and the discharge rollers 69 discharge the read document
to the discharge stand 62.
[0015] The image reading apparatus 12 has a function to skim the
surface of the document sent by the automatic document feeder 50
from the document loading stand 60, and a function to read the
surface of the document placed on the platen glass 70 as described
later.
[0016] The platen glass 70 is provided on the surface of a housing
75 of the image reading processor 52 which faces the automatic
document feeder 50. A document of which an image is to be read may
be placed on the platen glass 70. The platen glass 70 serve as an
aperture through which the document is irradiated with light when
the automatic document feeder 50 reads the document being
transported. Further, within the housing 75, a reading unit
(carriage) 76 is provided that is movable in the transport
direction (the Y axis direction of FIG. 1) of the document and
reads an image by being stopped at a reading position M of the
platen glass 70 or reads an image while scanning throughout the
entire platen glass 70.
[0017] The reading unit 76 includes an illumination unit 80 (light
source), an image formation unit 87, and a sensor 88 (image
reader). The image reading optical system. 86 according to the
present exemplary embodiment is configured including the image
formation unit 87 and the sensor 88.
[0018] The illumination unit 80 is configured with, for example,
plural white light emitting diodes (LEDs) which are arranged and
serve as a light source. A diffusion/reflection member diffuses and
reflects the light emitted from the illumination unit 80 toward the
document surface. Mirrors 83, 84, and 85 are members that guide the
reflection light L which is obtained from the document surface to
the image reading optical system 86.
[0019] The image formation unit 87 has a function to shape the
light flux of the reflection light L which is obtained from the
document surface (optical image) into a shape suitable for the
light reception in the sensor 88. The image formation unit 87 may
include an image formation lens (not illustrated) that optically
reduces the optical image obtained from the document surface.
Details of the image formation unit 87 will be described later.
[0020] The sensor 88 has a function to photoelectrically convert
the optical image obtained from the image formation unit 87 to
generate signals of a red (R) color, a green (G) color, and a blue
(B) color (image signals). As for the sensor 88, for example,
one-dimensional line sensors extending in the X axis direction and
dedicated for the colors R, G, and B, respectively, are arranged in
three rows in the Z axis direction. As an example, a charge coupled
device (CCD) image sensor is used. In other words, the sensor 88 is
configured such that image capturing elements (reading elements)
are arranged in parallel with each other in the X axis
direction.
[0021] Subsequently, in the image reading apparatus 12 according to
the present exemplary embodiment, the sequence of reading an image
will be described.
[0022] In the image reading apparatus 12, when the document placed
on the platen glass 70 is to be read, a controller (not
illustrated) causes the reading unit 76 to move in the scanning
direction (the direction of the arrow C in FIG. 1). Further, the
controller causes the illumination unit 80 of the reading unit 76
to emit light and the document surface is irradiated with the
light. By this irradiation, the reflection light L from the
document is guided to the image reading optical system 86 through
the mirrors 83, 84, and 85. The light guided to the image reading
optical system. 86 forms an image on the light receiving surface of
the sensor 88. The sensor 88 reads each of the colors R, G, and B
by one line substantially at the same time. When the reading in the
direction of the line is carried out by the scanning throughout the
entire size of the document, the document is read for one page.
[0023] Meanwhile, in the image reading apparatus 12, when the
document placed on the document loading stand 60 is read, the
controller (not illustrated) causes the document placed on the
document loading stand 60 to be transported to the reading position
M of the platen glass 70 along the document transport path 61. In
this case, the reading unit 76 is positioned in a state of being
stopped at the position represented by the solid line in FIG. 1.
The controller causes the illumination unit 80 to emit light and
the document surface is irradiated with the light. Accordingly, the
reflection light L from the document closely contacted with the
platen glass 70 by the platen roller 67 is guided to the image
reading optical system 86 through the mirrors 83, 84, and 85. The
light guided to the image reading optical system. 86 forms an image
on the light receiving surface of the sensor 88. The sensor 88
reads each of the colors R, G, and B by one line substantially at
the same time. Then, when the entire document is caused to pass the
reading position M of the platen glass 70, the document is read for
one page.
[0024] As the optical system in which the reflection light L as
obtained from the document surface is shaped into a shape suitable
for the light reception in the sensor 88, an image reading optical
system in which plural reflective optical systems each having a
power (strength to bend light) in a predetermined direction are
combined with each other may be used. In the image reading optical
system in which plural reflective optical systems are combined with
each other, a turn-back optical path is necessarily generated.
Meanwhile, in the image reading optical system, the aperture stop
is used in order to adjust the light amount, adjust a modulated
transfer function (MTF; a transfer function of an optical system),
increase the focal depth and for other reasons. This aperture stop
is required to regulate light in both the long length direction of
the sensor (the direction in which the image capturing elements are
arranged, that is, the X axis direction of FIG. 1), and the short
length direction of the sensor (the direction perpendicular to the
direction in which the image capturing elements are arranged in
parallel with each other; the Z axis direction of FIG. 1). When two
reflective optical systems are provided, the aperture stop is
generally positioned between the two reflective optical systems. In
addition, a reflective optical systems may be referred to as an
"image formation mirror."
[0025] FIG. 6 illustrates an image reading optical system 200
according to a comparative example as an example of the
above-described image reading optical system. As illustrated in
FIG. 6, the image reading optical system 200 includes an image
formation mirror 100, an image formation mirror 102, an aperture
stop 104, and a sensor 106.
[0026] Here, when it is intended to miniaturize the image reading
optical system 200 by reducing the image reading optical system 200
especially in the short length direction or to improve the
accuracy, that is, when it is intended to reduce the angle .theta.1
or .theta.2 in FIG. 6, the light incident on the image formation
mirror 100, that is, the reflection light L obtained from the
document surface may be blocked by the aperture stop 104 in the
short length direction (see the dashed circle in FIG. 6). This is
caused because the aperture stop 104 is generally manufactured by
forming an aperture such as a circle in a plate shaped member,
which requires a certain size both in the long length direction and
in the short length direction.
[0027] Thus, in this exemplary embodiment, a plate shaped member
having an aperture adapted to regulate the light flux in the long
length direction is provided with a plate shaped piece bent at a
predetermined angle at a tangent line position of the aperture in
the long length direction. Further, suitably, the light flux is
regulated in the short length direction by the plate shaped piece
and an end portion (edge) thereof. Accordingly, since the angle of
the plate shaped piece is set arbitrarily, the aperture stop in the
short length direction is disposed so as not to interfere light
upstream or downstream of the position of the plate shaped member,
in a turn-back optical system such as the image reading optical
system 200. Hence, the image reading optical system is reduced in
the short length direction so that the bending angle of the optical
path becomes small. In the descriptions herein, the terms "regulate
the light flux in the long length direction" indicate regulating
the light flux not to spread in the long length direction.
[0028] The image reading optical system according to the exemplary
embodiment of the present invention will be described with
reference to FIGS. 2 to 4B. FIG. 2 illustrates a schematic
sectional view of the image reading optical system according to the
present exemplary embodiment. As illustrated in FIG. 2, the image
reading optical system 86 includes the image formation unit 87 and
the sensor 88. The image formation unit 87 includes an image
formation mirror 90, an image formation mirror 92, and an aperture
stop 94.
[0029] The image formation mirror 90 according to the present
exemplary embodiment is a reflection mirror (a concave mirror in
the present exemplary embodiment) that condenses the reflection
light L obtained from the document surface, and reflects the light
toward the image formation mirror 92. The image formation mirror 92
according to the present exemplary embodiment is a reflecting
mirror (a concave mirror in the present exemplary embodiment) that
reflects the light reflected by the image formation mirror 90
toward the sensor 88. The aperture stop 94 disposed between the
image formation mirror 90 and the image formation mirror 92
regulates the light flux of the light L reflected by the image
formation mirror 90 in the long length direction and the short
length direction.
[0030] That is, the aperture stop 94 according to the present
exemplary embodiment is provided with an aperture 96 to be
described later and aperture stop pieces 94a and 94b (plate shaped
pieces) so that the single aperture stop regulates the light flux
of the reflection light L in both the long length direction and the
short length direction. Hereinafter, the aperture stop regulating
the light flux of the reflection light L in the long length
direction may be referred to as a "first aperture stop," and the
aperture stop regulating the light flux of the reflection light L
in the short length direction may be referred to as a "second
aperture stop." In addition, each of the light from the light
source to the image formation mirror 90, the light from the image
formation mirror 90 to the image formation mirror 92, and the light
from the image formation mirror 92 to the sensor 88 may be referred
to as "turning-back light."
[0031] The aperture stop 94 according to the present exemplary
embodiment will be described in more detail with reference to FIGS.
3A and 3B. FIG. 3A includes three views of the aperture stop 94
when viewed in three directions. As illustrated in FIG. 3A, the
aperture stop 94 includes an aperture stop plate 94c having the
aperture 96 opened therein, and aperture stop pieces 94a and 94b
formed to be bent in opposite directions with respect to bending
lines S1 and S2 passing the end portions of the aperture 96.
[0032] FIG. 3B is a view for explaining positions for regulating
the light flux of the reflection light L in the long length
direction and the short length direction, in the aperture stop 94
having the configuration of FIG. 3A. As illustrated in FIG. 3B, the
light flux of the reflection light L in the long length direction
is regulated by end portions E1 and E2 of the aperture 96, and the
light flux of the reflection light L in the short length direction
is regulated by end portions E3 and E4 of the aperture 96. That is,
in the aperture stop 94 according to the present exemplary
embodiment, the first aperture stop is formed by the end portions
E1 and E2 of the aperture 96, and the second aperture stop is
formed by the aperture stop piece 94a and the end portion E3 of the
aperture stop piece 94a, and the aperture stop piece 94b and the
end portion E4 of the aperture stop piece 94b.
[0033] Returning to FIG. 2, the regulation by the aperture stop 94
in the short length direction will be described in more detail. In
FIG. 2, the uppermost light beam of the light flux of the
reflection light L in the Z axis direction is represented as a
light beam Lu, and the lowermost light beam thereof is represented
as a light beam Ld. As illustrated in FIG. 2, in the image reading
optical system 86 according to the present exemplary embodiment,
the aperture stop piece 94a is disposed substantially in parallel
with the light beam Ld of the light incident on and turning back
from the image formation mirror 90, and the aperture stop piece 94b
is disposed substantially in parallel with the light beam Lu of the
turning-back light between the image formation mirror 92 and the
sensor 88.
[0034] The aperture stop 94 disposed as described above regulates
the light flux of the turning-back light between the image
formation mirror 90 and the image formation mirror 92 in the long
length direction by the end portions E1 and E2 illustrated in FIG.
3B, and regulates the light flux in the short length direction by
the end portions E3 and E4. The regulation in the short length
direction is carried out by regulating a predetermined range of
light flux from the light beam Lu (hereinafter, "upper light flux")
at a position P1 illustrated in FIG. 2, and regulating a
predetermined range of light flux from the light beam Ld
(hereinafter, "lower light flux") at a position P2 illustrated in
FIG. 2.
[0035] The image reading optical system 86 will be described in
more detail with reference to FIGS. 4A and 4B. FIG. 4A is a side
view of the image reading optical system 86 illustrated in FIG. 2
when viewed in the +Y direction, and FIG. 4B is a plan view of the
image reading optical system 86 illustrated in FIG. 2 when viewed
in the -Z direction.
[0036] As illustrated in FIGS. 4A and 4B, the reflection light L is
reflected on the image formation mirror 90, and the light flux of
the reflected turning-back light is regulated in the long length
direction (the X axis direction) by the end portions E1 and E2 in
the aperture 96 of the aperture stop 94. That is, the first
aperture stop is formed by the end portions E1 and E2. Meanwhile,
the turning-back light reflected on the image formation mirror 90
is regulated in the short length direction (the Z axis direction)
by the aperture stop piece 94a of the aperture stop 94 and the end
portion E3 thereof, and the aperture stop piece 94b of the aperture
stop 94 and the end portion E4 thereof. That is, the second
aperture stop is formed by the end portions E3 and E4.
[0037] In the aperture stop 94 according to the present exemplary
embodiment, the aperture stop piece 94a is disposed substantially
in parallel with the light beam Ld, and the aperture stop piece 94b
is disposed substantially in parallel with the light beam Lu.
Hence, as illustrated in FIGS. 4A and 4B, the aperture stop piece
94a does not interfere the light flux of the turning-back light
which is incident on the image formation mirror 90 (hereinafter,
"upstream light flux"), and the aperture stop piece 94b does not
interfere the light flux of the turning-back light between the
image formation mirror 92 and the sensor 88 (hereinafter,
"downstream light flux").
[0038] In other words, the end portions E3 and E4 of the aperture
stop in the short length direction are formed as ends (edges) of
the aperture stop pieces 94a and 94b disposed not to interfere the
upstream light flux and the downstream light flux. In addition, the
aperture stop piece 94a is disposed between the light flux between
the image formation mirrors 90 and 92 (hereinafter, "regulation
target light flux") and the upstream light flux, and the aperture
stop piece 94b is disposed between the regulation target light flux
and the downstream light flux. In this case, the aperture stop
pieces 94a and 94b are disposed on different planes. Accordingly,
the end portions E3 and E4 are disposed to be almost vertical to
the regulation target light flux so that the focal depth becomes
larger.
[0039] Since the aperture stop 94 having the above-described
configuration is largely reduced in the short length direction, the
image reading optical system 86 according to the present exemplary
embodiment is further miniaturized in the short length direction,
as compared to the image reading optical system 200 according to
the comparative example.
[0040] Further, since the aperture stop piece 94a is configured as
a plate shaped piece extending in the X axis direction, the
aperture stop piece 94a suppresses stray light caused from the
upstream light flux from being incident on the regulation target
light flux. That is, the aperture stop piece 94a has a function of
a blocking wall to block the stray light. Likewise, since the
aperture stop piece 94b suppresses stray light caused from the
downstream light flux from being incident on the regulation target
light flux, the aperture stop piece 94b also has the function of
the blocking wall to block the stray light.
[0041] In the present exemplary embodiment, the form of forming
both the aperture stop pieces 94a and 94b of the aperture stop 94
has been described as an example. Without being limited thereto,
however, the form of forming one of the aperture stop pieces 94a
and 94b may be adopted depending on, for example, a state of the
light flux to be regulated.
[0042] In the present exemplary embodiment, the form of forming the
aperture stop pieces 94a and 94b by bending the plate shaped member
along the bending lines S1 and S2 consistent with the end portions
of the aperture 96 has been described as an example. Without being
limited thereto, however, the aperture stop pieces 94a and 94b may
be formed by bending the plate shaped member along bending lines
positioned in further inner portions of the aperture 96, that is,
the bending lines S3 and S4 illustrated in FIG. 3A.
[0043] In the present exemplary embodiment, as illustrated in FIG.
2, the form of disposing the aperture stop 94 to make the aperture
stop plate 94c substantially vertical to the optical axis of the
regulation target light flux has been described as an example.
Without being limited thereto, however, the aperture stop 94 may be
disposed to make the aperture stop plate 94c inclined with respect
to the optical axis of the regulation target light flux. FIG. 5
represents an example of an image reading optical system 86A and an
image formation unit 87A in which the aperture stop 94 illustrated
in FIG. 2 is disposed to be inclined at an angle .theta.. In FIG.
5, since the aperture stop 94 is inclined, the aperture stop piece
94a is not in parallel with the upstream light flux, and the
aperture stop piece 94b is not in parallel with the downstream
light flux. However, in order to implement the parallel
relationship, the angles of the aperture stop pieces 94a and 94b
with respect to the aperture stop plate 94c may be changed.
[0044] In the present exemplary embodiment, the aperture stop 94
having the substantially rectangular aperture 96 has been described
as an example. Without being limited thereto, however, the shape of
the aperture may be a circle, an ellipse, a triangle or others in
consideration of, for example, the sectional shape of the light
flux to be regulated. In this case, the positions of the bending
lines S1 and S2 may be positions of tangent lines with respect to
the aperture in the long length direction (the X axis
direction).
[0045] In the present exemplary embodiment, the form of using the
image formation mirrors 90 and 92 (the concave mirrors in the
present exemplary embodiment) each having a power in a
predetermined direction as the reflection mirrors constituting the
image reading optical system has been described as an example.
Without being limited thereto however, for example, a plane mirror
may be used. For example, when a plane mirror is disposed between
the image formation mirrors 90 and 92, the optical path is turned
back so that the length of the image reading optical system 86 in
the Y axis direction is reduced, and the image reading optical
system 86 is further miniaturized.
[0046] When the image formation mirrors 90 and 92 each having a
power in a predetermined direction are used as the reflection
mirrors constituting the image reading optical system, the
direction of the power of each of the image formation mirrors 90
and 92 may be the long length direction or the short length
direction. In addition, both of the image formation mirrors 90 and
92 may have the power, or only one thereof may have the power.
[0047] In the present exemplary embodiment, the form of using two
image formation mirrors (the image formation mirrors 90 and 92) has
been described as an example. Without being limited thereto,
however, three or more image formation mirrors may be used. For
example, one or more image formation mirrors may be additionally
disposed between the mirror 85 and the image formation mirror 90 or
between the image formation mirror 92 and the sensor 88 to cause
the traveling light to be turned back.
[0048] Mirrors each having a positive power (a condensing optical
system) are required before and behind the aperture stop,
respectively, and a negative power (a magnifying optical system)
may exist therebetween. It is obvious to a person understanding the
existing aperture stop technology in the art that what is required
is merely that an optical system or an optical system group having
a total positive power is positioned in front of the aperture stop
(the upstream side on the optical path), and an optical system or
an optical system group having a total positive power is disposed
behind the aperture stop (the downstream side on the optical path).
Accordingly, in implementing exemplary embodiments of the present
invention, the order of arrangement of the mirrors is arbitrary and
whether the power of each of the plural mirrors is positive or
negative is also arbitrary. It is easily understood by a person
skilled in the art that the present invention may be smoothly
implemented, for example, even when a mirror having a negative
power exists immediately before the aperture stop.
[0049] The foregoing description of the exemplary embodiments of
the present invention has been provided for the purposes of
illustration and description. It is not intended to be exhaustive
or to limit the invention to the precise forms disclosed.
Obviously, many modifications and variations will be apparent to
practitioners skilled in the art. The embodiments were chosen and
described in order to best explain the principles of the invention
and its practical applications, thereby enabling others skilled in
the art to understand the invention for various embodiments and
with the various modifications as are suited to the particular use
contemplated. It is intended that the scope of the invention be
defined by the following claims and their equivalents.
* * * * *