Title: Optical apparatus for a line scanner system with reduced optical total track
Abstract: An optical apparatus for a line scanner system comprises a main lens group, an aspherical field flattener lens and a line sensor arranged sequentially along the same optical axis. The main lens group consists of four rotationally symmetrical lenses for refracting and converging light beams into focus. The field flattener lens is rotationally symmetrical in its optical profile and shapes as a strip oriented along the direction of the line image. The field flattener lens is arranged between the main lens group and the line sensor and closer to the line sensor for refracting the light beam to the line sensor in a relatively wide field angle, and as a result, various aberrations have been corrected while the optical total track also has been reduced. And an image plane is provided in the line sensor for the linear light beam, in which the instantaneous field of view is a line.
Patent Number: 6,894,843 Issued on 05/17/2005 to Chang
| Inventors:
|
Chang; Matthew Tsu-Yang (Fremeont, CA)
|
| Assignee:
|
Foxlink Image Technology Co., Ltd. (Hsinchu, TW)
|
| Appl. No.:
|
443810 |
| Filed:
|
May 23, 2003 |
| Current U.S. Class: |
359/662; 358/494; 359/708 |
| Intern'l Class: |
G02B 003/04; G02B013/18; H04N001/19.1 |
| Field of Search: |
359/196,197,204-207,662,708,710,711,713-717
358/474,482,483,494-497,505
347/244,232,258
|
References Cited [Referenced By]
U.S. Patent Documents
| 4514626 | Apr., 1985 | Tateoka et al.
| |
| 4712884 | Dec., 1987 | Sakuma et al.
| |
| 5113268 | May., 1992 | Yoshida et al.
| |
| 5815301 | Sep., 1998 | Naiki et al.
| |
| 6091532 | Jul., 2000 | Nakanishi et al.
| |
| 6307661 | Oct., 2001 | Fujibayashi et al.
| |
| 6396616 | May., 2002 | Fitzer et al.
| |
| 6507444 | Jan., 2003 | Hayashide et al.
| |
| 6606207 | Aug., 2003 | Tochigi.
| |
| 6633423 | Oct., 2003 | Ishibe.
| |
| 6667822 | Dec., 2003 | Yoshida.
| |
| 2003/0206322 | Nov., 2003 | Atsuumi et al.
| |
Primary Examiner: Sugarman; Scott J.
Assistant Examiner: Raizen; Deborah A.
Attorney, Agent or Firm: Rosenberg, Klein & Lee
Claims
1. An optical apparatus for a line scanner system comprising:
a broadband light source for emitting light beams;
a main lens group for converging said light beams into focus;
at least an aspherical field flattener lens in the shape of a strip for refracting
said light beams; and
an image plane provided for said light beams in which the instantaneous field
of view is a line;
wherein said field flattener lens is arranged between said main lens group and
said image plane.
2. The optical apparatus as claimed in claim 1, wherein said light beams emitted
from said broadband light source can be visible spectrum.
3. The optical apparatus as claimed in claim 1, wherein said broadband light
source, said main lens group, said field flattener lens and said image plane are
arranged sequentially along the same optical axis.
4. The optical apparatus as claimed in claim 1, wherein said main lens group
comprises required amount of rotationally symmetrical lenses.
5. An optical apparatus for a line scanner system comprising:
a main lens group for converging light beams into focus;
at least an aspherical field flattener lens in the shape of a strip for refracting
said light beams, said field flattener lens being rotationally symmetrical; and
an image plane provided for said light beams in which the instantaneous field
of view is a line;
wherein said field flattener lens is arranged between said main lens group and
said image plane.
6. The optical apparatus as claimed in claim 1, wherein said field flattener
lens is positioned closer to said image plane than to said main lens group and
oriented such that the length of the strip aligns with the length of the image.
7. The optical apparatus as claimed in claim 1, wherein said field flattener
lens can be made out of polymer material.
8. The optical apparatus as claimed in claim 7, wherein said field flattener
lens can be replicated using injection molding.
9. The optical apparatus as claimed in claim 7, wherein said field flattener
lens can be replicated using compression molding.
10. An optical apparatus for a line scanner system comprising:
a main lens group for converging light beams into focus;
at least an aspherical field flattener lens in the shape of a strip for refracting
said light beams, said field flattener lens being rotationally symmetrical; and
an image plane provided for said light beams in which the instantaneous field
of view is a line, said image plane being provided in a line sensor.
11. The optical apparatus as claimed in claim 10, wherein said line sensor can
be a CCD sensor.
12. The optical apparatus as claimed in claim 1, wherein said main lens group
comprises four rotationally symmetrical lenses for converging said light beams
into focus, and the specific values of said optical apparatus are described in
the table below:
1
Plano
3.00
1.516800
64.2
2
Plano
148.02
3
60.960
2.00
1.548140
45.8
4
8.452
1.00
5
12.053
11.18
1.883000
40.8
6
-147.885
0.25
7
Plano
0.25
8
-25.134
1.50
1.922860
20.9
9
35.545
0.50
10
144.650
3.32
1.883000
40.8
11
-13.058
23.18
12
Aspheric
2.00
1.493581
57.5
13
Aspheric
2.00
14
Plano
0.70
1.493581
57.5
15
Plano
wherein, r denotes the radius of curvature, in millimeters, of each individual
lens surface, d is the thickness in millimeters between two adjacent optical surfaces,
N
d is the refractive index at 587.56 nm, and V
d is the Abbe
number; said field flattener lens has rotationally symmetrical optical profiles
and is oriented such that the length thereof aligns with the direction of the line
image, with said aspherical surface profile thereof expressed by:
where, X is the distance by which the coordinates at the point of the aspherical
surface where the height from the optical axis is Y extend from the tangential
plane to the vertex of the aspherical surface C is the curvature (1/r) of the vertex
of the aspheric surface; K is the conic constant; A
4, A
6,
A
8 and A
10 are the aspherical coefficient of the fourth,
sixth, eight and tenth orders respectively; and the respective values of the conic
constants and aspheric coefficients are as follows:
Twelfth surface
Thirteenth surface
C = -0.010000
C = -0.010000
K = -1.000000
K = -1.000000
A4 = -0.190435 × 10-3
A4 = -0.147307 × 10-3
A6 = 0.454775 × 10-6
A6 = 0.262378 × 10-6
A8 = 0.000000
A8 = 0.000000
A10 = 0.000000
A10 = 0.000000
and said image plane is provided in a CCD sensor which has a length of 40.8 mm
with 4-micron pixel size;
the specific values of said optical apparatus in contrast to the conventional
counterpart without any field flattener lens design is shown in the table below:
First embodiment of
Conventional design
this invention
Magnification
0.189×
Operating wavelength
550 nm
Effective focal length
˜37 mm
24.12 mm
F-number
˜7.2
7.25
Half field angle
˜24.5 deg
34.21 deg
Total track
280 mm
200 mm
Improvement
28% reduction on the optical total track
whereby said optical apparatus has 28% reduction on the optical total track compared
with the conventional counterparts.
13. The optical apparatus as claimed in claim 1, wherein said main lens group
comprises four rotationally symmetrical lenses for converging said light beams
into focus, and the specific values of said optical apparatus are described in
the table below:
1
Plano
3.00
1.516800
64.1
2
Plano
121.03
3
8.492
2.00
1.487489
70.4
4
2.940
1.35
5
9.871
2.90
1.820168
29.7
6
-28.425
0.10
7
Plano
0.10
8
-10.184
1.50
1.922860
20.9
9
14.556
0.10
10
25.244
2.00
1.787997
47.5
11
-4.961
10.12
12
Aspheric
2.00
1.493581
57.5
13
Aspheric
2.00
14
Plano
0.70
1.493581
57.5
15
Plano
wherein, r denotes the radius of curvature, in millimeters, of each individual
lens surface, d is the thickness in millimeters between two adjacent optical surfaces,
N
d is the refractive index at 587.56 nm, and V
d is the Abbe
number; said field flattener lens has rotationally symmetrical optical profiles
and is oriented such that the length thereof aligns with the direction of the line
image, with said aspherical surface profile thereof expressed by:
where, X is the distance by which the coordinates at the point of the aspherical
surface where the height from the optical axis is Y extend from the tangential
plane to the vertex of the aspherical surface C is the curvature (1/r) of the vertex
of the aspheric surface; K is the conic constant; A
4, A
6,
A
8 and A
10 are the aspherical coefficient of the fourth,
sixth, eight and tenth orders respectively; and the respective values of the conic
constants and aspheric coefficients are as follows:
Twelfth surface
Thirteenth surface
C = -0.010000
C = 0.000000
K = -1.000000
K = -1.000000
A4 = -0.840490 × 10-3
A4 = -0.533770 × 10-3
A6 = 0.101137 × 10-5
A6 = 0.331089 × 10-5
A8 = 0.000000
A8 = 0.000000
A10 = 0.000000
A10 = 0.000000
and said image plane is provided in a CCD sensor which has a length of 20.4 mm
with 4-micron pixel size;
the specific values of said optical apparatus in contrast to the conventional
counterpart without any field flattener lens design is shown in the table below:
Second embodiment of this
Conventional design
invention
Magnification
0.0945×
Operating wavelength
550 nm
Effective focal length
˜14 mm
11.29 mm
F-number
˜6.5
7.25
Half field angle
˜33 deg
40.29 deg
Total track
183 mm
150 mm
Improvement
18% reduction on the optical total track
whereby said optical apparatus has 18% reduction on the optical total track compared
with the conventional counterparts.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an optical apparatus for a line scanner system, and
more particularly, to an optical apparatus which provides a relative wider field
angle resulting in reduced optical total track and high image quality for a line
scanner system.
2. The Related Art
It is well known in the field of optical design that the application of a low
power optical element near or at an image plane is effective in correcting residual
field aberration. Such concept is commonly applied to designs such as projections,
reconnaissance lenses that require high flat field optical performance. Depending
on its effect in the correction of residual field curvature as well as astigmatism
and distortion, a field lens is also commonly known as a field flattener.
Field flatteners were first used in the Petzval type of lenses. The classic
Petzval type lenses are described in U.S. Pat. No. 65,729, German Pat. No. 5761,
Great Britain Pat. No. 4756 and U.S. Pat. No. 1,479,251. The classic Petzval type
lenses suffer from residual astigmatism and field curvature. With the introduction
of a suitably designed field flattener, a much more favorable image performance
can be obtained, without having to resort to a significantly more complex optical
design. Such systems are described in Great Britain Pat. No.127058, U.S. Pat. Nos.
2,076,190, 2,541,484 and 2,649,021. The field flattener lenses in these systems
are of spherical construction in which the profiles of the optical surfaces are
spherical. Further, such field flatteners are positioned between the main converging
lens group and the focal plane and close to the focal plane, thereby accomplishing
the aberration correction requirement.
Without incorporating a field lens, a lens group could be designed to have
similar flat field performance. However such lens group would normally have a more
complex design. More lens elements would be needed to accomplish the same level
of optical aberration correction as in a lens group with a field flattener. The
introduction of a field lens in the optical design is an elegant way of simplifying
a lens group, which would otherwise be a complex design, while maintaining a high
level of optical performance.
An aspherical profile can also be applied to the field flattener with the added
benefit of further improvement in aberration correction. The result is a high performance
optical system. An example of such system is disclosed in U.S. Pat. No. 2,803,997.
In the same patent, a system with relatively wide angle of field of view was disclosed
using the field flattener techniques, indicating that the use of aspherical field
flattener can be advantageous in aberration correction in wide-angle applications.
The aforementioned examples are optical apparatus designs corrected for a sufficiently
broad spectrum, for example, the visible spectrum. There also exists a class of
optical apparatus that incorporates field flatteners in the close proximity of
the image plane, whereby the optical aberration correction are limited to within
a narrow spectrum band. For instance, some lenses each having at least an aspherical
profile can be applied to optical apparatuses in monochromatic laser scanning applications,
as a field flattener with the added benefit of aberration correction. Some typical
examples of such optical apparatus adapted for use in a laser scanning system are
described in U.S. Pat. Nos. 5,179,465 and 6,535,317. In these patents, it is characterized
that a laser light source is utilized to emit a narrow wavelength band light beam
and a rotating polygon mirror is used to reflect and put the light beam into a
sweeping motion in the main scanning plane so that the instantaneous field of view
is a spot. In addition, a lens in the form of a strip having at least an aspherical
surface is arranged for aberration correction as a field flattener. Further, such
optical apparatus has to be designed to realize satisfactory f-theta characteristics
of distortion correction. Typically, the aspherical profile is bi-laterally symmetrical,
following the mathematical description of a toric surface. The overall optical
design is not suitable for broadband imaging applications.
Optical total track is defined as the axial distance from the object plane
to the image plane. This particular optical property has great significance in
a finite conjugate imaging system in which the distance between the object plane
and the lens system is of finite value. In addition, the distance between the lens
and the image plane generally has a finite fixed value. Therefore the optical total
track is generally a fixed value. For first order approximation in optical calculation,
given a fixed object size and magnification ratio, also known as reduction ratio,
the total track is inversely proportional to the tangent of the field angle. A
short optical total track means wide angular field. Generally, for a line-scanning
device, such as a flatbed document scanner, it is desirable to have a short optical
total track, which will afford a compact packaging of the device. This poses a
specific difficulty in the design of the image forming optics. Due to the short
total track requirement, the image forming optics would have to have a wide angular
field of view while providing adequate level of optical aberration correction.
This will inevitably necessitate a complex optical design. However, with the introduction
of a field lens of the proper design, the complexity optical design can be substantially
simplified, affording a system that can be economically produced, while maintaining
a high level of optical performance.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a unique optical apparatus
which has reduced optical total track and high image quality over relatively wider
field angle for a broadband line scanner system.
It is an additional object of the present invention is to provide an optical
apparatus
for a line scanner system in which the instantaneous field of view is a line across
the width of the document and rectilinear distortion can be sufficiently corrected.
It is another object of the present invention is to provide an achromatic optical
apparatus for a line scanner system in which the aberration correction is broad-spectrum.
It is another object of the present invention is also to provide an optical apparatus
for a line scanner system which has a simple and compact construction to achieve
a uniform scan and correct varied aberrations with relatively low cost.
In order to achieve the objects described above, the optical apparatus for a
line
scanner system according to the present invention comprises a main lens group,
an aspherical field flattener lens and a line sensor arranged sequentially along
the same optical axis. The main lens group consists of required number of rotationally
symmetrical lenses for refracting and converging light beams into focus. The field
flattener lens is rotationally symmetrical in its optical profile and shapes as
a strip oriented along the direction of the line image. The field flattener lens
is arranged between the main lens group and the line sensor and closer to the line
sensor for refracting the light beam to the line sensor in a relatively wide field
angle, and as a result, various aberrations have been corrected while the optical
total track also has been reduced. And an image plane is provided in the line sensor
for the linear light beam, in which the instantaneous field of view is a line.
A detailed explanation of the present invention will be given herebelow, with
reference
to the accompanying drawings of the preferred embodiments of the invention, which,
however, should not be taken to be limitative to the present invention, but for
better understanding thereof to those skilled in the art. In the drawings:
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a cross-sectional view showing an optical apparatus of the first embodiment
in accordance with the present invention;
FIG. 2 is a perspective view showing the field flattener lens of the optical
apparatus in accordance with the present invention as shown in FIG. 1;
FIGS. 3A and 3B are diagrams respectively showing astigmatism and distortion
of an optical apparatus of the first embodiment in accordance with the present
invention as shown in FIG. 1;
FIG. 4 is a diagram showing diffraction MTF curves of an optical apparatus of
the first embodiment in accordance with the present invention as shown in FIG. 1;
FIG. 5 is a diagram showing relationship between defocus and spot diameter of
an optical apparatus of the first embodiment in accordance with the present invention
as shown in FIG. 1;
FIG. 6 is a cross-sectional view showing an optical apparatus of the second
embodiment in accordance with the present invention;
FIG. 7 is a perspective view showing the field flattener lens of the optical
apparatus in accordance with the present invention as shown in FIG. 6;
FIGS. 8A and 8B are diagrams respectively showing astigmatism and distortion
of an optical apparatus of the second embodiment in accordance with the present
invention as shown in FIG. 6;
FIG. 9 is a diagram showing diffraction MTF curves of an optical apparatus of
the second embodiment in accordance with the present invention as shown in FIG. 6;
FIG. 10 is a diagram showing relationship between defocus and spot diameter
of an optical apparatus of the second embodiment in accordance with the present
invention as shown in FIG. 6.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
In accordance with the present invention, the optical apparatus for a line scanner
system comprises a broadband light source, a main lens group, a field flattener
lens group and a line sensor arranged sequentially along the same optical axis.
The broadband light source can be selected to emit visible spectrum light beams.
The main lens group consists of required amount of rotationally symmetrical lenses
for refracting and converging the light beams into focus. The field flattener lens
group consists at least an aspherical lens which is rotationally symmetrical in
its optical profile and shapes as a strip oriented along the direction of the line
image. The field flattener lens group is arranged between the main lens group and
the line sensor and closer to the line sensor for refracting the light beam to
the line sensor in a relatively wide field angle, and as a result, various aberrations
have been corrected while the optical total track also has been reduced. And each
field flattener lens is to be made out of polymer material which can be replicated
using conventional high precision optical molding techniques with low cost, such
as injection molding or compression molding. A CCD sensor is usually selected as
the line sensor to provide an image plane for the linear light beam, in which the
instantaneous field of view is a line.
Based on the above-described principal construction of the optical apparatus,
two embodiments with specific values will be described respectively in detail hereinbelow
with reference to the accompanying drawings.
As shown in FIGS. 1 and 2, the optical apparatus of the first embodiment according
to the present invention consists of a broadband light source
20, a main
lens group
30, an aspherical field flattener lens
40 and a CCD sensor
50 arranged sequentially along the optical axis O. The broadband light source
20 emits visible spectrum light beams. The main lens group
30 consists
of four rotationally symmetrical lenses for converging the light beams into a linear
light beam. The specific values of this embodiment will be described in the following
Table 1. In Table 1, r denotes the radius of curvature, in millimeters, of an individual
lens surface, d is the thickness in millimeters between two adjacent optical surfaces,
N
d is the refractive index at 587.56 nm, and V
d is the Abbe number.
| TABLE 1 |
| |
| Surface No. |
R |
D |
Nd |
Vd |
| |
| |
| 1 |
Plano |
3.00 |
1.516800 |
64.2 |
| 2 |
Plano |
148.02 |
| 3 |
60.960 |
2.00 |
1.548140 |
45.8 |
| 4 |
8.452 |
1.00 |
| 5 |
12.053 |
11.18 |
1.883000 |
40.8 |
| 6 |
-147.885 |
0.25 |
| 7 |
Plano |
0.25 |
| 8 |
-25.134 |
1.50 |
1.922860 |
20.9 |
| 9 |
35.545 |
0.50 |
| 10 |
144.650 |
3.32 |
1.883000 |
40.8 |
| 11 |
-13.058 |
23.18 |
| 12 |
Aspheric |
2.00 |
1.493581 |
57.5 |
| 13 |
Aspheric |
2.00 |
| 14 |
Plano |
0.70 |
1.493581 |
57.5 |
| 15 |
Plano |
| |
The field flattener lens
40 is rotationally symmetrical optical profile
in the shape of strip and positioned between the main lens group
30 and
an image plane provided in the CCD sensor
50 and closer to the CCD sensor
50. The field flattener lens
40 is oriented such that the length
thereof aligns with the direction of the line image. The two optical surfaces
12
and
13 of the field flattener lens
40 are aspherical as described
in the above Table 1. The aspherical surface profile can be expressed by:
Where X is the distance by which the coordinates at the point of the aspherical
surface where the height from the optical axis is Y extend from the tangential
plane to the vertex of the aspherical surface C is the curvature (1/r) of the vertex
of the aspheric surface; K is the conic constant; and A
4, A
6,
A
8 and A
10 are the aspherical coefficient of the fourth,
sixth, eight and tenth orders respectively. The respective values of the conic
constants and aspheric coefficients are tabulated in Table 2.
| |
TABLE 2 |
| |
|
| |
Surface No. 12 |
Surface No. 13 |
| |
|
| |
C = -0.010000 |
C = -0.010000 |
| |
K = -1.000000 |
K = -1.000000 |
| |
A4 = -0.190435 × 10-3 |
A4 = -0.147307 × 10-3 |
| |
A6 = 0.454775 × 10-6 |
A6 = 0.262378 × 10-6 |
| |
A8 = 0.000000 |
A8 = 0.000000 |
| |
A10 = 0.000000 |
A10 = 0.000000 |
| |
|
The CCD sensor
50 has a length of 40.8 mm with 4-micron pixel size. The
specific values of this embodiment in contrast to the conventional counterpart
without any field flattener lens design are shown in the following Table 3.
| TABLE 3 |
| |
| |
|
First embodiment |
| |
Conventional design |
of this invention |
| |
| |
| Magnification |
0.189× |
|
| Operating wavelength |
550 nm |
| Effective focal length |
˜37 mm |
24.12 mm |
| F-number |
˜7.2 |
7.25 |
| Half field angle |
˜24.5 deg |
34.21 deg |
| Total track |
280 mm |
200 mm |
| Improvement |
28% reduction on the optical total track |
| |
As described in Table 3, the optical apparatus of the first embodiment according
to the present invention has 28% reduction on the optical total track by means
of the aspherical field flattener lens
40 providing a relatively wider field
angle compared with the conventional counterparts.
Moreover, FIGS. 3A and 3B show respectively astigmatism and distortions
of the optical apparatus of the first embodiment according to the present invention.
In the FIG. 3A showing astigmatism, a solid line indicates a sagittal image plane
and a broken line indicates a meridional plane. In addition, FIGS. 4 and 5 show
respectively diffraction MTF curves and relationship between defocus and spot diameter
of the optical apparatus of the first embodiment according to this invention. By
the way, the similar symbols used in this embodiment are used in all diagrams showing
aberration of another embodiment. As is apparent from the respective diagrams mentioned
above, excellent correction is made for the varied aberrations and good image quality
is obtained.
With reference to FIGS. 6 and 7, the optical apparatus of the second embodiment
according to the present invention also consists of a broadband light source
20
emitting visible spectrum light beams, a main lens group
30′, an
aspherical field flattener lens
40′ in the shape of strip and a CCD
sensor
50′ arranged sequentially along the optical axis O′.
The main lens group
30′ consists of four rotionally symmetrical lenses
which have different structure and values compared with them in the first embodiment
for converging the light beams into a linear light beam as shown in Table 4. In
Table 4, r denotes the radius of curvature, in millimeters, of an individual lens
surface, d is the thickness between two adjacent optical surfaces, N
d
is the refractive index at 587.56 nm, and V
d is the Abbe number.
| TABLE 4 |
| |
| Surface No. |
R |
D |
Nd |
Vd |
| |
| |
| 1 |
Plano |
3.00 |
1.516800 |
64.1 |
| 2 |
Plano |
121.03 |
| 3 |
8.492 |
2.00 |
1.487489 |
70.4 |
| 4 |
2.940 |
1.35 |
| 5 |
9.871 |
2.90 |
1.820168 |
29.7 |
| 6 |
-28.425 |
0.10 |
| 7 |
Plano |
0.10 |
| 8 |
-10.184 |
1.50 |
1.922860 |
20.9 |
| 9 |
14.556 |
0.10 |
| 10 |
25.244 |
2.00 |
1.787997 |
47.5 |
| 11 |
-4.961 |
10.12 |
| 12 |
Aspheric |
2.00 |
1.493581 |
57.5 |
| 13 |
Aspheric |
2.00 |
| 14 |
Plano |
0.70 |
1.493581 |
57.5 |
| 15 |
Plano |
| |
The field flattener lens
40′ also has different structure and values
compared with that in the first embodiment. The two optical surfaces
12
and
13 of the field flattener lens
40 are aspherical as described
in the above Table 4. The aspherical surface profile can be expressed by:
Where X is the distance by which the coordinates at the point of the aspherical
surface where the height from the optical axis is Y extend from the tangential
plane to the vertex of the aspherical surface C is the curvature (1/r) of the vertex
of the aspheric surface; K is the conic constant; and A
4, A
6,
A
8 and A
10 are the aspherical coefficient of the fourth,
sixth, eight and tenth orders respectively. The respective values of the conic
constant and aspheric coefficients are tabulated in Table 5.
| |
TABLE 5 |
| |
|
| |
Surface No. 12 |
Surface No. 13 |
| |
|
| |
C = -0.010000 |
C = 0.000000 |
| |
K = -1.000000 |
K = -1.000000 |
| |
A4 = -0.840490 × 10-3 |
A4 = -0.533770 × 10-3 |
| |
A6 = 0.101137 × 10-5 |
A6 = 0.331089 × 10-5 |
| |
A8 = 0.000000 |
A8 = 0.000000 |
| |
A10 = 0.000000 |
A10 = 0.000000 |
| |
|
The CCD sensor
50′ in this embodiment has a length of 20.4 mm with
4-micron pixel size. The specific values of this embodiment in contrast to the
conventional counterpart without any field flattener lens design are shown in the
following Table 6.
| TABLE 6 |
| |
| |
|
Second embodiment |
| |
Conventional design |
of this invention |
| |
| |
| Magnification |
0.0945× |
|
| Operating wavelength |
550 nm |
| Effective focal length |
˜14 mm |
11.29 mm |
| F-number |
˜6.5 |
7.25 |
| Half field angle |
˜33 deg |
40.29 deg |
| Total track |
183 mm |
150 mm |
| Improvement |
18% reduction on the optical total track |
| |
As described in Table 6, the optical apparatus of the second embodiment according
to the present invention has 18% reduction on the optical total track by means
of the aspherical field flattener lens
40′ providing a relatively
wider field angle compared with the conventional counterparts.
Furthermore, FIGS. 8A and 8B show respectively astigmatism and distortions
of the optical apparatus of the second embodiment according to this invention.
In addition, FIGS. 9 and 10 show respectively diffraction MTF curves and relationship
between defocus and spot diameter of the optical apparatus of this embodiment.
As is apparent from the respective diagrams mentioned above, excellent correction
is made for the varied aberrations and good image quality is obtained.
As mentioned above, the aspherical field flattener lens
40 and
40′
in the shape of strip is utilized to achieve the purpose of the optical total track
reduction and aberration correction over relatively wider field angle, and hence,
the optical apparatus for a line scanner system according to the present invention
can be more compact with high image quality. Particularly, rectilinear distortion
can be sufficiently corrected by means of the strip-shaped aspherical field flattener
lens
40 and
40′ in the achromatic optical apparatus according
the present invention.
While the present invention has been described with respect to what are presently
considered to be the preferred embodiments, it is to be understood that the invention
is not limited to the disclosed embodiments. Contrarily, the present invention
is intended to cover various modifications and equivalent arrangements that may
be resorted to within the spirit and scope of the claims thereof.
*
