U.S. patent number RE46,034 [Application Number 14/642,942] was granted by the patent office on 2016-06-21 for imaging lens.
This patent grant is currently assigned to KANTATSU CO., LTD., OPTICAL LOGIC INC.. The grantee listed for this patent is KANTATSU CO., LTD., OPTICAL LOGIC INC.. Invention is credited to Yoji Kubota.
United States Patent |
RE46,034 |
Kubota |
June 21, 2016 |
**Please see images for:
( Certificate of Correction ) ** |
Imaging lens
Abstract
An imaging lens includes an aperture stop, a positive first lens
with a biconvex shape, a negative second lens; a negative third
lens, a positive fourth lens, and a negative fifth lens arranged in
this order from an object side. When the whole lens system has a
focal length f, focal lengths and Abbe's numbers of the first and
the second lenses are f1, .nu.d1, f2, and .nu.d2, focal lengths of
the fourth and fifth lenses are f4 and f5, a composite focal length
of the first lens L1 and the second lens L2 is f12, and a distance
from a surface of the first lens L1 on the object side to a surface
of the fifth lens L5 on the image side is .SIGMA.d, the imaging
lens satisfies the following conditional expressions:
0.7<f12/f<1.4 0.2<|f1/f2|<0.6 15<.nu.d1-.nu.d2
0.4<f4/f<1.0 .SIGMA.d/f<1.2 |f5/f|<1.0.
Inventors: |
Kubota; Yoji (Nagano,
JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
OPTICAL LOGIC INC.
KANTATSU CO., LTD. |
Nagano
Tochigi |
N/A
N/A |
JP
JP |
|
|
Assignee: |
OPTICAL LOGIC INC. (Nagano,
JP)
KANTATSU CO., LTD. (Tochigi, JP)
|
Family
ID: |
42287180 |
Appl.
No.: |
14/642,942 |
Filed: |
March 10, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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PCT/JP2009/006799 |
Dec 11, 2009 |
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Reissue of: |
13168145 |
Jun 24, 2011 |
8411376 |
Apr 2, 2013 |
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Foreign Application Priority Data
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Dec 25, 2008 [JP] |
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2008-329285 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G02B
13/0045 (20130101); G02B 9/60 (20130101) |
Current International
Class: |
G02B
9/60 (20060101); G02B 13/18 (20060101); G02B
13/00 (20060101) |
Field of
Search: |
;359/763,764 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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41-006865 |
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Apr 1966 |
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JP |
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60-023814 |
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Feb 1985 |
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JP |
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62-203119 |
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Sep 1987 |
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JP |
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05-127079 |
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May 1993 |
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JP |
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2003-140037 |
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May 2003 |
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JP |
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2007-264180 |
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Oct 2007 |
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JP |
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2008-542821 |
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Nov 2008 |
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JP |
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Other References
Hobbs, P. C. D. Chapter 4: Lenses, Prisms, and Mirrors, in Building
Electro-Optical Systems: Making it all Work, Second Edition, John
Wiley & Sons, Inc., Hoboken, NJ, USA, 2009, pp. 145-179. cited
by examiner .
Office Action for Japanese Patent Application 2008-329285, Oct. 18,
2012, Japan Patent Office. cited by applicant.
|
Primary Examiner: Leung; Christina Y
Attorney, Agent or Firm: Kubotera & Associates, LLC
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
This is a continuation application of the prior PCT application
PCT/JP2009/006799, filed on Dec. 11, 2009, pending, which claims
priority from a Japanese patent application No. 2008-329285, filed
on Dec. 25, 2008, the entire content of which is incorporated
herein by reference.
Claims
What is claimed is:
1. An imaging lens, comprising: a first lens having positive
refractive power; a second lens having negative refractive power; a
third lens having negative refractive power; a fourth lens having
positive refractive power; and a fifth lens having negative
refractive power in this order from an object side to an image
side, wherein .Iadd.said first lens and said second lens are
arranged adjacently to face each other,.Iaddend. said first lens is
a biconvex lens, said second lens has a concave surface facing the
object side, said third lens is a meniscus lens having a concave
surface facing the object side, and said fifth lens is a biconcave
lens.
2. The imaging lens according to claim 1, wherein said first lens
and said second lens have a composite focal length f12 and a whole
lens system has a focal length f so that the following conditional
expression is satisfied: 0.7<f12/f<1.4.
3. The imaging lens according to claim 1, wherein said first lens
has a focal length f1 and said second lens has a focal length f2 so
that the following conditional expression is satisfied:
0.2<f1/f21<0.6.
4. The imaging lens according to claim 1, wherein said first lens
has an Abbe's number .nu.d1 and said second lens has an Abbe's
number .nu.d2 so that the following conditional expression is
satisfied: 15<.nu.d1-.nu.d2.
5. The imaging lens according to claim 1, wherein said fourth lens
has a focal length f4 and a whole lens system has a focal length f
so that the following conditional expression is satisfied:
0.4<f4/f<1.0.
6. The imaging lens according to claim 1, wherein said first lens
and said fifth lens are arranged so that a surface of the first
lens on the object side is away from a surface of the fifth lens on
the image side by a distance .SIGMA.d on an optical axis and a
whole lens system has a focal length f so that the following
conditional expression is satisfied: .SIGMA.d/f<1.2.
7. The imaging lens according to claim 1, wherein said fifth lens
has a focal length f5 and a whole lens system has a focal length f
so that the following conditional expression is satisfied:
|f5/f|<1.0.
8. An imaging lens, comprising: a first lens having positive
refractive power; a second lens having negative refractive power; a
third lens having negative refractive power; a fourth lens having
positive refractive power; and a fifth lens having negative
refractive power in this order from an object side to an image
side, wherein .Iadd.said first lens and said second lens are
arranged adjacently to face each other,.Iaddend. said first lens is
a biconvex lens, said second lens has a concave surface facing the
object side, said third lens is a meniscus lens having a concave
surface facing the object side, and said fourth lens has a focal
length f4 and a whole lens system has a focal length f so that the
following conditional expression is satisfied:
0.4<f4/f<1.0.
9. The imaging lens according to claim 8, wherein said first lens
and said second lens have a composite focal length f12 and a whole
lens system has a focal length f so that the following conditional
expression is satisfied: 0.7<f12/f<1.4.
10. The imaging lens according to claim 8, wherein said first lens
has a focal length f1 and said second lens has a focal length f2 so
that the following conditional expression is satisfied:
0.2<|f1/f2|<0.6.
11. The imaging lens according to claim 8, wherein said first lens
has an Abbe's number .nu.d1 and said second lens has an Abbe's
number .nu.d2 so that the following conditional expression is
satisfied: 15<.nu.d1-.nu.d2.
12. The imaging lens according to claim 8, wherein said first lens
and said fifth lens are arranged so that a surface of the first
lens on the object side is away from a surface of the fifth lens on
the image side by a distance .SIGMA.d on an optical axis and a
whole lens system has a focal length f so that the following
conditional expression is satisfied: .SIGMA.d/f<1.2.
13. The imaging lens according to claim 8, wherein said fifth lens
has a focal length f5 and a whole lens system has a focal length f
so that the following conditional expression is satisfied:
|f5/f1<1.0.
14. An imaging lens, comprising: a first lens having positive
refractive power; a second lens having negative refractive power; a
third lens having negative refractive power; a fourth lens having
positive refractive power; and a fifth lens having negative
refractive power in this order from an object side to an image
side, wherein .Iadd.said first lens and said second lens are
arranged adjacently to face each other,.Iaddend. said first lens is
a biconvex lens, said second lens has a concave surface facing the
object side, said third lens is a meniscus lens having a concave
surface facing the object side, and said fifth lens has a focal
length f5 and a whole lens system has a focal length f so that the
following conditional expression is satisfied: |f5/f|<1.0.
15. The imaging lens according to claim 14, wherein said first lens
and said second lens have a composite focal length f12 and a whole
lens system has a focal length f so that the following conditional
expression is satisfied: 0.7<f12/f<1.4.
16. The imaging lens according to claim 14, wherein said first lens
has a focal length f1 and said second lens has a focal length f2 so
that the following conditional expression is satisfied:
0.2<|f1/f21<0.6.
17. The imaging lens according to claim 14, wherein said first lens
has an Abbe's number .nu.d1 and said second lens has an Abbe's
number .nu.d2 so that the following conditional expression is
satisfied: 15<.nu.d1-.nu.d2.
18. The imaging lens according to claim 14, wherein said fourth
lens has a focal length f4 and a whole lens system has a focal
length f so that the following conditional expression is satisfied:
0.4<f4/f<1.0.
19. The imaging lens according to claim 14, wherein said first lens
and said fifth lens are arranged so that a surface of the first
lens on the object side is away from a surface of the fifth lens on
the image side by a distance .SIGMA.d on an optical axis and a
whole lens system has a focal length f so that the following
conditional expression is satisfied: .SIGMA.d/f<1.2.
.Iadd.20. An imaging lens, comprising: a first lens having positive
refractive power; a second lens having negative refractive power; a
third lens having negative refractive power; a fourth lens having
positive refractive power; and a fifth lens having negative
refractive power in this order from an object side to an image
side, wherein said first lens and said second lens are arranged
adjacently to face each other, said first lens has a convex surface
facing the object side, said second lens has a concave surface
facing the object side, and said fifth lens has a concave surface
facing the image side..Iaddend.
.Iadd.21. The imaging lens according to claim 20, wherein said
first lens has an Abbe's number .nu.d1 and said second lens has
Abbe's number .nu.d2 so that the following conditional expression
is satisfied: 15<.nu.d1-.nu.d2..Iaddend.
.Iadd.22. The imaging lens according to claim 20, wherein said
fourth lens has a focal length f4 and a whole lens system has a
focal length f so that the following conditional expression is
satisfied: 0.4<f4/f<1.0..Iaddend.
.Iadd.23. The imaging lens according to claim 20, wherein said
first lens and said fifth lens are arranged so that a surface of
the first lens on the object side is away from a surface of the
fifth lens on the image side by a distance .SIGMA.d on an optical
axis and a whole lens system has a focal length f so that the
following conditional expression is satisfied:
.SIGMA.d/f<1.2..Iaddend.
.Iadd.24. The imaging lens according to claim 20, wherein said
fifth lens has a focal length f5 and a whole lens system has a
focal length f so that the following conditional expression is
satisfied: |f5/f|<1.0..Iaddend.
Description
BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT
The present invention relates to an imaging lens for forming an
image on an imaging element such as a CCD sensor and a CMOS sensor.
In particular, the present invention relates to an imaging lens
suitable for mounting in a relatively small camera such as a
cellular phone, a digital still camera, a portable information
terminal, a security camera, an onboard camera, and a network
camera.
An imaging lens to be mounted in a small camera has been required
to have a high resolution lens configuration suitable for a
recently developed imaging element with a high resolution, as well
as to use a fewer number of lenses. Conventionally, a three-lens
imaging lens has been frequently used as such an imaging lens.
However, as an imaging element has higher resolution, it is more
difficult to obtain sufficient performances only with three lenses.
In these years, another lens configuration, a four-lens
configuration or a five-lens configuration, has been applied.
Among the configurations, since a configuration with five lenses
has a higher design flexibility, it may be expected to apply such
lens configuration in a next-generation imaging lens. An imaging
lens disclosed in Patent Reference has been known as an imaging
lens having such a five-lens configuration.
The imaging lens disclosed in Patent Reference includes a positive
first lens having a convex surface on the object side; a second
lens having a negative meniscus shape that directs a concave
surface on the image side; a third lens having a positive meniscus
shape that directs a convex surface on the image side; a negative
fourth lens in which both surfaces have an aspheric shape and a
surface thereof on the image side near an optical axis is concave;
and a positive or negative fifth lens, in which both surfaces are
aspheric shape, in this order from the object side.
In this configuration, when a lower limit of Abbe's number of the
first lens and upper limits of Abbe's numbers of the second and the
fourth lens are respectively assigned, an axial chromatic
aberration and chromatic aberration of magnification are corrected,
so as to compatible with a high performance imaging lens.
Patent Reference Japanese Patent Application Publication No.
2007-264180
According to the imaging lens disclosed in Patent Reference, it is
possible to obtain relatively satisfactory aberrations. Since the
total length of the lens system is long, however, it is difficult
to attain both miniaturization of an imaging lens and satisfactory
aberration correction.
In view of the problems of the conventional techniques described
above, an object of the present invention is to provide an imaging
lens with a small size capable of properly correcting
aberration.
SUMMARY OF THE INVENTION
In order to attain the object described above, according to the
present invention, an imaging lens includes a first lens having
positive refractive power; a second lens having negative refractive
power; a third lens having negative refractive power; a fourth lens
having positive refractive power; and a fifth lens having negative
refractive power in this order from the object side to the image
side. The first lens is shaped to form a biconvex lens and the
second lens is shaped to form a lens that directs a concave surface
on the object side.
According to the invention, the first lens is shaped to form a
biconvex lens. Therefore, it is possible to set the refractive
power of the first lens relatively strong, so that it is possible
to suitably attain miniaturization of an imaging lens. On the other
hand, with this first lens having positive refractive power, there
remains a concern of generation of field curvature. For this
reason, according to the invention, disposing on the image side of
the first lens the second lens having negative refractive power so
as to direct the concave surface on the object side, it is possible
to reduce worsening of the field curvature generated at the first
lens. Therefore, according to the imaging lens of this invention,
despite the small size, it is possible to satisfactorily correct
the aberrations.
Here, for a shape of the third lens, for example, it may be
possible to choose a shape of a meniscus lens that directs a
concave surface on the object side. In addition, as a shape of the
fourth lens, for example, it may be possible to choose a shape of a
biconvex lens.
According to the imaging lens with the above-described
configuration, when the whole lens system has a focal length f and
a composite focal length of the first lens and the second lens is
f12, it is preferred to satisfy the following conditional
expression (1): 0.7<f12/f<1.4 (1)
When the above conditional expression (1) is satisfied, it is
possible to keep the total length of the imaging lens short and
also the field curvature and coma aberration stable. When the value
exceeds the upper limit "1.4", the focal length of the first lens
increases, so that it is difficult to attain a small-sized imaging
lens. On the other hand, if it is below the lower limit "0.7", the
refractive power of the first lens is too strong, so that it is
difficult to secure the back focal length. In order to secure a
certain back focal length, it is necessary to increase the
refractive power of the third lens. When the value is below the
lower limit "0.7", even if it is possible to attain a small-sized
imaging lens, it is difficult to correct the field curvature and
correct coma aberration, so that it is difficult to attain both a
small-sized imaging lens and satisfactory aberration
correction.
Furthermore, according to the imaging lens with the aforementioned
configuration, when the first lens has a focal length f1 and the
second lens has a focal length f2, it is preferred to satisfy the
following conditional expression (2): 0.2<|f1/f2|<0.6 (2)
When the above conditional expression (2) is satisfied, it is
possible to keep the axial chromatic aberration and spherical
aberration stable. When the value exceeds the upper limit "0.6",
since the refractive power of the second lens increases, the axial
chromatic aberration is in the plus direction in relative to that
of a reference wavelength and is excessively corrected. In
addition, the spherical aberration is in the plus direction at a
ring zone section and is excessively corrected.
As a result, it is difficult to keep the axial chromatic aberration
and spherical aberration stable. On the other hand, when the value
is below the lower limit "0.2", since the refractive power of the
second lens decreases, the axial chromatic aberration is in the
minus direction in relative to that of the reference wavelength and
is insufficiently corrected. In addition, even the spherical
aberration is in the minus direction at the ring zone section and
is similarly insufficiently corrected. Therefore, even in this
case, it is difficult to keep the axial chromatic aberration and
spherical aberration stable, and it is difficult to obtain
satisfactory imaging performance.
Moreover, in case of the imaging lens with the aforementioned
configuration, when Abbe's number of the first lens is .nu.d1 and
Abbe's number of the second lens is .nu.d2, it is more preferred to
satisfy the following conditional expression (3):
15<.nu.d1-.nu.d2 (3)
When the above conditional expression (3) is satisfied, it is
possible to keep the axial chromatic aberration and off-axis
chromatic aberration stable while satisfactorily correcting those
chromatic aberrations. If the conditional expression (3) is not
satisfied, the axial chromatic aberrations at short wavelengths
increase in the minus direction in relative to that of the
reference wavelength, and the aberration is insufficiently
corrected.
When the Abbe's number of the third lens is set to a small value in
order to improve such insufficient correction of chromatic
aberration, the axial chromatic aberration is satisfactorily
corrected, but the off-axis chromatic aberration of magnification
is excessively corrected and worsened.
Further, in case of the imaging lens with the aforementioned
configuration, when the whole lens system has a focal length f and
the fourth lens has a focal length f4, it is more preferred to
satisfy the following conditional expression (4):
0.4<f4/f<1.0 (4)
In case of an imaging element such as a CCD sensor and a CMOS
sensor, there is a limit in an acceptance angle of an incoming
light beam due to its structure. Generally speaking, this limit in
the acceptance angle of an incoming light beam is provided as
certain range around principal light beam (e.g. .+-.25.degree. of
the principal light beam).
When an angle of emergence of the off-axis principal light beam is
outside the limitation range, since a sensor does not take a light
beam outside the range therein, a resultant image taken through the
imaging lens has a periphery that is dark in comparison with a
center part. In other words, a shading phenomenon occurs.
When the aforementioned conditional expression (4) is satisfied, it
is possible to keep the maximum angle of emergence of the off-axis
principal light beam small while keeping each aberration stable.
When the value exceeds the upper limit "1.0", since the refractive
power of the fourth lens decreases, while it is easy to correct the
coma aberration and the chromatic aberration of magnification, the
maximum angle of emergence of the off-axis principal light beam
becomes large and a shading phenomenon more easily occurs. On the
other hand, when the value is below the lower limit "0.4", since
the refractive power of the fourth lens increases, although it is
possible to reduce the maximum angle of emergence of the off-axis
principal light beam, it is difficult to correct the field
curvature and the distortion.
Moreover, in the imaging lens with the aforementioned
configuration, when the whole lens system has a focal length f and
a distance on the optical axis from a surface of the first lens on
the object side to a surface of the fifth lens on the image side is
.SIGMA.d, it is preferred to satisfy the following conditional
expression (5) also in view of miniaturization of an imaging lens:
.SIGMA.d/f<1.2 (5)
In addition, in the imaging lens with the aforementioned
configuration, when the whole lens system has a focal length f and
the fifth lens has a focal length f5, it is preferred to satisfy
the following conditional expression (6): |f5/f|<1.0 (6)
As well known, as an effective means to attain miniaturization of
an imaging lens, it may be possible to reduce a focal length of a
lens. Actually, this approach has been employed in designing many
imaging lenses. However, when a focal length decreases while
keeping an ideal image height constant, the angle of emergence of
the off-axis light beam increases, and it is more difficult to
balance among aberrations including a spherical aberration, a
chromatic aberration, distortion, and a field curvature. Therefore,
it is necessary to attain miniaturization of an imaging lens while
keeping the focal length long.
When the imaging lens has a configuration that satisfies the
conditional expression (6), a position of a principal point of the
optical system moves towards the object side, so that it is
possible to attain miniaturization of an imaging lens while keeping
the focal length long. Here, it is effective to satisfy the
conditional expression (5) also as a means to supplement
insufficient correction of axial chromatic aberration.
According to the imaging lens of the invention, it is possible to
both reduce the size of the imaging lens and correct the aberration
properly, thereby making it possible to provide the imaging lens
with the small size capable of correcting aberrations properly.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic sectional view showing a configuration of an
imaging lens in Numerical Data Example 1;
FIG. 2 is an aberration diagram showing a lateral aberration of the
imaging lens in Numerical Data Example 1;
FIG. 3 is an aberration diagram showing a spherical aberration, an
astigmatism, and a distortion of the imaging lens in Numerical Data
Example 1;
FIG. 4 is a schematic sectional view showing a configuration of an
imaging lens in Numerical Data Example 2;
FIG. 5 is an aberration diagram showing a lateral aberration of the
imaging lens in Numerical Data Example 2;
FIG. 6 is an aberration diagram showing a spherical aberration, an
astigmatism, and a distortion of the imaging lens in Numerical Data
Example 2;
FIG. 7 is a schematic sectional view showing a configuration of an
imaging lens in Numerical Data Example 3;
FIG. 8 is an aberration diagram showing a lateral aberration of the
imaging lens in Numerical Data Example 3;
FIG. 9 is an aberration diagram showing a spherical aberration, an
astigmatism, and a distortion of the imaging lens in Numerical Data
Example 3;
FIG. 10 is a schematic sectional view showing a configuration of an
imaging lens in Numerical Data Example 4;
FIG. 11 is an aberration diagram showing a lateral aberration of
the imaging lens in Numerical Data Example 4;
FIG. 12 is an aberration diagram showing a spherical aberration, an
astigmatism, and a distortion of the imaging lens in Numerical Data
Example 4;
FIG. 13 is a schematic sectional view showing a configuration of an
imaging lens in Numerical Data Example 5;
FIG. 14 is an aberration diagram showing a lateral aberration of
the imaging lens in Numerical Data Example 5; and
FIG. 15 is an aberration diagram showing a spherical aberration, an
astigmatism, and a distortion of the imaging lens in Numerical Data
Example 5.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
First Embodiment
Hereunder, referring to the accompanying drawings, a first
embodiment of the present invention will be fully described.
FIGS. 1, 4, and 7, and 10 are schematic sectional views showing
image lenses in Numerical Data Examples 1 to 4 according to the
embodiment, respectively. Since a basic lens configuration is the
same among the Numerical Data Examples 1 to 4, the lens
configuration of the embodiments will be described with reference
to the lens sectional view of Numerical Data Example 1.
As shown in FIG. 1, the imaging lens of the embodiment includes an
aperture stop ST; a first lens L1 having positive refractive power;
a second lens L2 having negative refractive power; a third lens L3
having negative refractive power; a fourth lens L4 having positive
refractive power; and a fifth lens L5 having negative refractive
power, which are arranged in this order from an object side to an
image side of the imaging lens. A cover glass 10 is provided
between the fifth lens L5 and the image plane of an imaging
element. It is noted that the cover glass 10 may be optionally
omitted.
In the imaging lens with the above-described configuration, the
first lens L1 is a biconvex lens, and the second lens L2 is a
meniscus lens that directs a concave surface on the object side.
These first lens L1 and the second lens L2 satisfy the following
conditional expressions (1) to (3): 0.7<f12/f<1.4 (1)
0.2<|f1/f2|<0.6 (2) 15<.nu.d1-.nu.d2 (3)
In the above conditional expressions,
f: Focal length of the whole lens system
f1: Focal length of the first lens L1
f2: Focal length of the second lens L2
f12: Composite focal length of the first lens L1 and the second
lens L2
.nu.d1: Abbe's number of the first lens L1
.nu.d2: Abbe's number of the second lens L2
When the conditional expressions (1) to (3) are satisfied, it is
possible to obtain the following effects respectively. When the
conditional expression (1) is satisfied, it is possible to keep the
field curvature and coma aberration stable while keeping the whole
length of the imaging lens short. In addition, when the conditional
expression (2) is satisfied, it is possible to keep the axial
chromatic aberration and spherical aberration stable. Furthermore,
when the conditional expression (3) is satisfied, it is possible to
keep the axial chromatic aberration and off-axis chromatic
aberration stable while properly correcting those chromatic
aberrations.
In such configuration, according to this embodiment, the third lens
L3 is shaped to form a meniscus lens that directs a concave surface
on the object side and the fourth lens L4 is shaped to form a
biconvex lens.
The fifth lens L5 is shaped to form a biconcave lens. In this fifth
lens L5, a surface thereof on the image side is shaped to form an
aspheric shape, which is concaved on the image side near the
optical axis and is convex on the image side at the periphery, i.e.
aspheric shape having an inflection point. Because of this, an
incident angle of a light beam emitted from the fifth lens L5 to an
image plane is restrained.
In the embodiment, the lens surfaces of all lenses are formed to be
an aspheric surface as necessary.
When the aspheric surface applied to the lens surfaces have an axis
Z in the optical axis direction, a height H in a direction
perpendicular to the optical axis, a conical coefficient k, and the
aspheric coefficients A.sub.4, A.sub.6, A.sub.8, and A.sub.10, the
aspheric surfaces of the lens surfaces may be expressed as follows.
Here, even in case of an imaging lens according to a second
embodiment, which will be described later, the lens surfaces of all
lenses are formed to be an aspheric surface as necessary, and
aspheric surface shapes applied in theses lens surfaces are
expressed by the following formula similarly to this
embodiment:
.times..times..times..times..times..times..times. ##EQU00001## The
imaging lens according to this embodiment satisfies the following
conditional expressions (4) to (6) in addition to the
aforementioned conditional expressions (1) to (3):
0.4<f4/f<1.0 (4) .SIGMA.d/f<1.2 (5) |f5/f|<1.0 (6)
In the above conditional expressions,
f: Focal length of the whole lens system
f4: Focal length of the fourth lens L4
f5: Focal length of the fifth lens L5
.SIGMA.d: Distance on the optical axis from a surface of the first
lens L1 on the object side to a surface of the fifth lens L5 on the
image side.
When the conditional expressions (4) to (6) are satisfied, it is
possible to obtain the following effects respectively. When the
conditional expression (4) is satisfied, it is possible to keep the
maximum angle of emergence of the off-axis principal light beam
small, while keeping each aberration stable. In addition, when the
conditional expression (5) is satisfied, it is possible to attain
miniaturization of the imaging lens. Furthermore, when the
conditional expression (6) is satisfied, it is possible to attain
miniaturization of the imaging lens while keeping the focal length
long.
Here, it is not necessary to satisfy all of the above conditional
expressions (1) to (6). When any single one of the conditional
expressions (1) to (6) is individually satisfied, it is possible to
obtain an effect corresponding to the respective conditional
expression.
Next, Numerical Data Examples of the embodiment will be described.
In each of Numerical Data Examples, f represents a focal length of
a whole lens system, Fno represents an F number, and .omega.
represents a half angle of view, respectively. In addition, i
represents a surface number counted from the object side, R
represents a curvature radius, d represents a distance between lens
surfaces (an on-axis surface spacing) along the optical axis, Nd
represents a refractive index for a d line, and .nu.d represents
Abbe's number at the d line. Here, the aspheric surfaces are
indicated with surface numbers affixed with * (asterisk).
Numerical Data Example 1
TABLE-US-00001 Basic lens data are shown below. f = 3.903 mm, Fno =
2.805, w = 31.59.degree. Unit: mm Surface Data Surface Number i R d
Nd .nu.d (Object) .infin. .infin. 1 (Stop) .infin. 0 2* 1.571
0.5500 1.52470 56.2 (=.nu.d1) 3* -7.132 0.1500 4 -3.521 0.3000
1.61420 26.0 (=.nu.d2) 5* -19.595 0.2800 6* -1.823 0.2800 1.58500
29.0 7* -5.912 0.3600 8* 3.357 0.8500 1.52470 56.2 9* -1.613 0.3000
10* -2.617 0.3300 1.52470 56.2 11* 3.067 0.3000 12 .infin. 0.1500
1.51633 64.12 13 .infin. 0.8823 (Image plane) .infin. f1 = 2.508 f2
= -7.038 f12 = 3.573 f4 = 2.206 f5 = -2.639 .SIGMA.d = 3.400
Aspheric Surface Data Second Surface k = -1.544427E-01, A.sub.4 =
1.976046E-02, A.sub.6 = -1.793809E-02 Third Surface k = 1.063940,
A.sub.4 = 4.713006E-03, A.sub.6 = -2.945120E-02 Fifth Surface k =
1.415349E+02, A.sub.4 = -2.371673E-02, A.sub.6 = 1.311554E-02 Sixth
Surface k = -2.723790, A.sub.4 = -1.147380E-02, A.sub.6 =
-4.130846E-02, A.sub.8 = -3.948624E-03, A.sub.10 = 5.021037E-02
Seventh Surface k = -9.933691, A.sub.4 = 3.758781E-03, A.sub.6 =
1.719515E-02, A.sub.8 = 1.736953E-02, A.sub.10 = 1.092378E-02
Eighth Surface k = -2.241293E+01, A.sub.4 = -2.578027E-02, A.sub.6
= -7.694008E-03, A.sub.8 = -1.375408E-03, A.sub.10 = 6.496087E-04
Ninth Surface k = 6.248352E-02, A.sub.4 = 1.165596E-01, A.sub.6 =
-3. 911326E-02 , A.sub.8 = 1.261679E-02, A.sub.10 = 1.134638E-04
Tenth Surface k = 1.999301, A.sub.4 = 3.503592E-02, A.sub.6 =
-3.907364E-02, A.sub.8 = 1.551177E-02, A.sub.10 = -3.231912E-03
Eleventh Surface k = 2.223974E-01, A.sub.4 = -9.602329E-02, A.sub.6
= 7.338596E-03, A.sub.8 = -1.181135E-03, A.sub.10 = -3.315528E-04
Values of the conditional expressions (1) to (6) are as follows:
f12/f = 0.915 |f1/f2| = 0.356 .nu.d1 - .nu.d2 = 30.2 f4/f = 0.565
.SIGMA.d/f = 0.871 |f5/f| = 0.676
Accordingly, the imaging lens of Numerical Data Example 1 satisfies
the conditional expressions (1) to (6). FIG. 2 shows the lateral
aberration that corresponds to the half angle of view .omega. in
the imaging lens of Numerical Data Example 1 by dividing into a
tangential direction and sagittal direction (which is also the same
in FIGS. 5, 8, and 11). Furthermore, FIG. 3 shows a spherical
aberration SA (mm), an astigmatism AS (mm), and a distortion DIST
(%), respectively. In the aberration diagrams, the Offence against
the Sine Condition (OSC) is also indicated for the spherical
aberration diagram in addition to the aberrations at the respective
wavelengths of 587.56 nm, 435.84 nm, 656.27 nm, 486.13 nm, and
546.07 nm. Further, in the astigmatism diagram, the aberration on
the sagittal image surface S and the aberration on the tangential
image surface T are respectively indicated (which are the same in
FIGS. 6, 9, and 12).
As shown in FIGS. 2 and 3, in the imaging lens of Numerical Data
Example 1, the respective aberrations are satisfactorily corrected.
Especially, as shown in the astigmatism diagram, the astigmatic
difference is very small, the image surface is satisfactorily
corrected, and the distortion is also small.
Numerical Data Example 2
TABLE-US-00002 Basic lens data are shown below. f = 3.899 mm, Fno =
2.800, w = 32.67.degree. Unit: mm Surface data Surface Number i R d
Nd .nu.d (Object) .infin. .infin. 1 (Stop) .infin. 0 2* 1.604
0.5500 1.52470 56.2 (=.nu.d1) 3* -8.437 0.1500 4 -3.456 0.3000
1.61420 26.0 ( =.nu.d2) 5* -18.051 0.2800 6* -1.948 0.2800 1.58500
29.0 7* -4.589 0.3000 8* 3.916 0.8000 1.52470 56.2 9* -1.597 0.2500
10* -2.618 0.3300 1.52470 56.2 11* 3.256 0.3000 12 .infin. 0.1500
1.51633 64.12 13 .infin. 1.0397 (Image plane) .infin. f1 = 2.618 f2
= -7.014 f12 = 3.817 f4 = 2.276 f5 = -2.713 .SIGMA.d = 3.240
Aspheric Surface Data Second Surface k = -1.439472E-01, A.sub.4 =
2.032875E-02, A.sub.6 = -1.399217E-02 Third Surface k = 1.913498,
A.sub.4 = 4.854973E-03, A.sub.6 = -1.585207E-02 Fifth Surface k =
2.521344E+02, A.sub.4 = -2.591410E-02, A.sub.6 = 3.798179E-03 Sixth
Surface k = -3.165513, A.sub.4 = -7.669636E-03, A.sub.6 =
-4.014852E-02, A.sub.8 = 5.980691E-03, A.sub.10 = 3.235352E-02
Seventh Surface k = -3.803800, A.sub.4 = 1.097028E-03, A.sub.6 =
1.770991E-02, A.sub.8 = 1.736123E-02, A.sub.10 = 1.453023E-02
Eighth Surface k = -5.618736E+01, A.sub.4 = -3.829839E-02, A.sub.6
= -1.530875E-02, A.sub.8 = -3.059261E-03, A.sub.10 = 4.242948E-04
Ninth Surface k = 8.069668E-02, A.sub.4 = 1.050962E-01, A.sub.6 =
-4.000834E-02, A.sub.8 = 1.262215E-02, A.sub.10 = -9.911318E-05
Tenth Surface k = 2.019736, A.sub.4 = 4.417573E-02, A.sub.6 =
-3.888932E-02, A.sub.8 = 1.333875E-02, A.sub.10 = -4.117009E-03
Eleventh Surface k = 8.429077E-01, A.sub.4 = -9.283294E-02, A.sub.6
= 9.981823E-03, A.sub.8 = -1.869262E-03, A.sub.10 = -4.558872E-04
Values of each conditional expression are as follows: f12/f = 0.979
|f1/f2| = 0.373 .nu.d1 - .nu.d2 = 30.2 f4/f= 0.584 .SIGMA.d/f =
0.831 |f5/f| = 0.696
Accordingly, the imaging lens of Numerical Data Example 2 satisfies
the conditional expressions (1) to (6). FIG. 5 shows the lateral
aberration that corresponds to the half angle of view .omega. in
the imaging lens of Numerical Data Example 2, and FIG. 6 shows the
spherical aberration SA (mm), the astigmatism AS (mm), and the
distortion DIST (%), respectively. As shown in FIGS. 5 and 6, in
the imaging lens of Numerical Data Example 2, the image surface is
satisfactorily corrected, and the respective aberrations are
satisfactorily corrected similarly to Numerical Data Example 1.
Numerical Data Example 3
TABLE-US-00003 Basic lens data are shown below. f = 3.907 mm, Fno =
2.805, w = 32.64.degree. Unit: mm Surface Data Surface Number i R d
Nd .nu.d (Object) .infin. .infin. 1 (Stop) .infin. 0 2* 1.575
0.5500 1.52470 56.2 (=.nu.d1) 3* -7.276 0.1500 4 -3.502 0.3000
1.61420 26.0 (=.nu.d2) 5* -19.883 0.2800 6* -1.831 0.2800 1.58500
29.0 7* -5.761 0.3600 8* 3.400 0.8500 1.52470 56.2 9* -1.611 0.3000
10* -2.619 0.3300 1.52470 56.2 11* 3.153 0.3000 12 .infin. 0.1500
1.51633 64.12 13 .infin. 0.9013 (Image plane) .infin. f1 = 2.521 f2
= -6.969 f12 = 3.615 f4 = 2.212 f5 = -2.674 .SIGMA.d = 3.400
Aspheric Surface Data Second Surface k = -1.709914E-01, A.sub.4 =
1.904787E-02, A.sub.6 = -1.792465E-02 Third Surface k = 7.046181,
A.sub.4 = 2.542724E-03, A.sub.6 = -2.853682E-02 Fifth Surface k =
1.341757E+02, A.sub.4 = -2.342623E-02 A.sub.6 = 1.151604E-02 Sixth
Surface k = -2.664785, A.sub.4 = -1.221495E-02, A.sub.6 =
-4.161820E-02, A.sub.8 = -3.480280E-03, A.sub.10 = 4.712500E-02
Seventh Surface k = -1.007092E+01, A.sub.4 = 3.857254E-03, A.sub.6
= 1.729519E-02, A.sub.8 = 1.721151E-02, A.sub.10 = 1.079714E-02
Eighth Surface k = -2.440426E+01, A.sub.4 = -2.565446E-02, A.sub.6
= -8.232621E-03, A.sub.8 = -1.561612E-03, A.sub.10 = 6.144595E-03
Ninth Surface k = 6.497601E-02, A.sub.4 = 1.149186E-01, A.sub.6 =
-3.897702E-02, A.sub.8 = 1.270717E-02, A.sub.10 = 1.210040E-04
Tenth Surface k = 1.994817, A.sub.4 = 3.657337E-02, A.sub.6 =
-3.934563E-02, A.sub.8 = 1.507533E-02, A.sub.10 = -3.504426E-03
Eleventh Surface k = 3.526177E-02, A.sub.4 = -9.652400E-02, A.sub.6
= 7.275239E-03, A.sub.8 = -1.425736E-03, A.sub.10 = -3.842309E-04
Values of the conditional expressions (1) to (6) are as follows:
f12/f = 0.925 |f1/f2| = 0.362 .nu.d1 - .nu.d2 = 30.2 f4/f = 0.566
.SIGMA.d/f = 0.870 |f5/f| = 0.684
Accordingly, the imaging lens of Numerical Data Example 3 satisfies
the conditional expressions (1) to (6). FIG. 8 shows the lateral
aberration that corresponds to the half angle of view .omega. in
the imaging lens of Numerical Data Example 3, and FIG. 9 shows the
spherical aberration SA (mm), the astigmatism AS (mm), and the
distortion DIST (%), respectively. As shown in FIGS. 8 and 9, in
the imaging lens of Numerical Data Example 3, the image surface is
satisfactorily corrected, and the respective aberrations are
satisfactorily corrected similarly to Numerical Data Example 1.
Numerical Data Example 4
TABLE-US-00004 Basic lens data are shown below. f = 3.848 mm, Fno =
2.805, w = 30.32.degree. Unit: mm Surface Data Surface Number i R d
Nd .nu.d (Object) .infin. .infin. 1 (Stop) .infin. 0 2* 1.566
0.5500 1.52470 56.2 (=.nu.d1) 3* -7.023 0.1500 4 -3.536 0.3000
1.61420 26.0 (=.nu.d2) 5* -19.676 0.2800 6* -1.837 0.2800 1.52470
56.2 7* -6.033 0.3600 8* 3.302 0.8500 1.52470 56.2 9* -1.614 0.3000
10* -2.639 0.3300 1.58500 29.0 11* 2.922 0.3000 12 .infin. 0.5000
1.51633 64.12 13 .infin. 0.5310 (Image plane) .infin. f1 = 2.495 f2
= -7.068 f12 = 3.539 f4 = 2.197 f5 = -2.320 .SIGMA.d = 3.400
Aspheric Surface Data Second Surface k = -1.514551E-01, A.sub.4 =
2.041462E-02, A.sub.6 = -2.332746E-02 Third Surface k =
4.107515E-02, A.sub.4 = 5.196393E-03, A.sub.6 = -3.559135E-02 Fifth
Surface k = 8.917948E+01, A.sub.4 = -2.298304E-02, A.sub.6 =
1.782019E-02 Sixth Surface k = -2.682345, A.sub.4 = -1.244876E-02,
A.sub.6 = -4.412886E-02, A.sub.8 = -8.375465E-03, A.sub.10 =
5.365573E-02 Seventh Surface k = -1.211874E+01, A.sub.4 =
4.641584E-03, A.sub.6 = 1.781682E-02, A.sub.8 = 1.808663E-02,
A.sub.10 = 1.095189E-02 Eighth Surface k = -1.915006E+01, A.sub.4 =
-2.420006E-02, A.sub.6 = -6.347979E-03, A.sub.8 = -8.744578E-04,
A.sub.10 = 8.120666E-04 Ninth Surface k = 6.472730E-02, A.sub.4 =
1.202224E-01, A.sub.6 = -3.910233E-02, A.sub.8 = 1.241952E-02,
A.sub.10 = 4.587975E-05 Tenth Surface k = 1.948054, A.sub.4 =
3.123665E-02, A.sub.6 = -3.881734E-02, A.sub.8 = 1.645138E-02,
A.sub.10 = -2.866062E-03 Eleventh Surface k = 1.218782, A.sub.4 =
-9.899569E-02, A.sub.6 = 7.341671E-03, A.sub.8 = -9.793363E-04,
A.sub.10 = -3.286655E-04 Values of the conditional expressions (1)
to (6) are as follows: f12/f = 0.920 |f1/f2| = 0.353 .nu.d1 -
.nu.d2 = 30.2 f4/f= 0.571 .SIGMA.d/f = 0.884 |f5/f| = 0.603
Accordingly, the imaging lens of Numerical Data Example 4 satisfies
the conditional expressions (1) to (6). FIG. 11 shows the lateral
aberration that corresponds to the half angle of view .omega. in
the imaging lens of Numerical Data Example 4, and FIG. 12 shows the
spherical aberration SA (mm), the astigmatism AS (mm), and the
distortion DIST (%), respectively. As shown in FIGS. 11 and 12, in
the imaging lens of Numerical Data Example 4, the image surface is
satisfactorily corrected, and the respective aberrations are
satisfactorily corrected similarly to Numerical Data Example 1.
Second Embodiment
Hereunder, referring to the accompanying drawings, a second
embodiment of the invention will be described. Similarly to the
imaging lens of the first embodiment, the imaging lens of this
embodiment includes an aperture stop ST; a first lens L1 having
positive refractive power; a second lens L2 having negative
refractive power; a third lens L3 having negative refractive power;
a fourth lens L4 having positive refractive power; and a fifth lens
L5 having negative refractive power, which are arranged in this
order from the object side towards the image side of an imaging
lens. A cover glass 10 is provided between the fifth lens L5 and
the image plane.
According to the imaging lens of this embodiment, however, the
second lens L2 is a biconcave lens, the first lens L1 and the
second lens L2 are combined as shown in FIG. 13. With the lens
configuration like this, it is possible to more suitably correct
chromatic aberration.
More specifically, in the imaging lens of this embodiment, the
first lens L1 is biconvex lens, the second lens L2 is a biconcave
lens, and those lenses are combined. The third lens L3 is a
meniscus lens that directs a concave surface on the is object side,
and the fourth lens L4 is a biconvex lens. The fifth lens L5 is a
biconcave lens, and a surface thereof on the image side is formed
to be an aspheric shape having an inflection point.
Even in this embodiment, the imaging lens is configured to satisfy
the following conditional expressions (1) to (6) similarly to the
first embodiment. 0.7<f12/f<1.4 (1) 0.2<|f1/f2|<0.6 (2)
15<.nu.d1-.nu.d2 (3) 0.4<f4/f<1.0 (4) .SIGMA.d/f<1.2
(5) |f5/f|<1.0 (6)
In the above conditional expressions,
f: Focal length of the whole lens system
f1: Focal length of the first lens L1
f2: Focal length of the second lens L2
f12: Composite focal length of the first lens L1 and the second
lens L2
.nu.d1: Abbe's number of the first lens L1
.nu.d2: Abbe's number of the second lens L2
f4: Focal length of the fourth lens L4
f5: Focal length of the fifth lens L5
.SIGMA.d: Distance on the optical axis from a surface of the first
lens L1 on the object side to a surface of the fifth lens L5 on the
image side.
Next, Numerical Data Examples of the imaging lens according to this
embodiment are shown. In this Numerical Data Example, f is a focal
length of the whole lens system, Fno represents an F number, and
.omega. represents a half angle of view, respectively. Moreover, i
represents a surface number counted from the object side, R
represents a curvature radius, d is a distance between lens
surfaces, Nd on the optical axis is refractive index for a d line,
and .nu.d is Abbe's number at a d line, respectively. Here, the
aspheric surfaces are indicated with surface numbers affixed with *
(asterisk).
Numerical Data Example 5
TABLE-US-00005 Basic lens data are shown below. f = 3.871 mm, Fno =
2.800, w = 30.17.degree. Unit: mm Surface Data Surface Number i R d
Nd .nu.d (Object) .infin. .infin. 1 (Stop) .infin. 0 2* 2.393
0.5000 1.67790 55.5 (=.nu.d1) 3 -3.334 0.3000 1.66446 36.0
(=.nu.d2) 4 41.657 0.4272 5* -1.904 0.2640 1.58500 29.0 6* -4.245
0.6695 7* 4.525 0.8798 1.52470 56.2 8* -1.707 0.4993 9* -2.515
0.3234 1.58500 29.0 10* 3.495 0.1000 11 .infin. 0.5000 1.51633
64.12 12 .infin. 0.5945 (Image plane) .infin. f1 = 2.130 f2 =
-4.633 f12 = 3.660 f4 = 2.483 f5 = -2.451 .SIGMA.d = 3.863 Aspheric
Surface Data Second Surface k = 2.191111, A.sub.4 = -9.435404E-03,
A.sub.6 = -3.285189E-02, A.sub.8 = 3.672070E-02, A.sub.10 =
-3.270308E-02 Fifth Surface k = -1.984333, A.sub.4 = -1.805977E-02,
A.sub.6 = -2.675334E-02, A.sub.8 = 7.933052E-04, A.sub.10 =
1.631158E-02 Sixth Surface k = -5.661022E-01, A.sub.4 =
-1.709355E-02, A.sub.6 = -1.717627E-03, A.sub.8 = -5.550278E-03,
A.sub.10 = 4.049249E-03 Seventh Surface k = -4.220498, A.sub.4 =
-8.6408444E-03, A.sub.6 = -8.170485E-04, A.sub.8 = -6.511240E-05,
A.sub.10 = 2.033590E-05 Eighth Surface k = 3.300032E-02, A.sub.4 =
1.125967E-01, A.sub.6 = -3.672376E-02, A.sub.8 = 1.170047E-02,
A.sub.10 = 3.409990E-04 Ninth Surface k = 1.781895, A.sub.4 =
6.458725E-03, A.sub.6 = -5.275346E-02, A.sub.8 = 1.858108E-02,
A.sub.10 = -1.882214E-03 Tenth Surface k = -5.273886E-01, A.sub.4 =
-9.506179E-02, A.sub.6 = 6.538888E-03, A.sub.8 = -7.519095E-04,
A.sub.10 = 1.760657E-05 Values of each conditional expression are
as follows: f12/f = 0.945 |f1/f2| = 0.460 .nu.d1 - .nu.d2 = 19.5
f4/f= 0.641 .SIGMA.d/f = 0.998 |f5/f| = 0.633
Accordingly, the imaging lens of Numerical Data Example 5 satisfies
the conditional expressions (1) to (6).
FIG. 14 shows the lateral aberration that corresponds to the half
angle of view .omega. in the imaging lens of Numerical Data Example
5, and FIG. 15 shows the spherical aberration SA (mm), the
astigmatism AS (mm), and the distortion DIST (%), respectively. As
shown in FIGS. 14 and 15, in the imaging lens of Numerical Data
Example 5, the image surface is satisfactorily corrected, and the
respective aberrations are satisfactorily corrected similarly to
Numerical Data Example 1 to 4.
Accordingly, when the imaging lens of the respective embodiments is
applied to an imaging optical system of a cellular phone, a digital
still camera, a portable information terminal, a security camera,
an onboard camera, a network camera, and the like, it is possible
to obtain the high performance and the small size for the camera or
the like.
Here, it is noted that the imaging lens of the invention shall not
be limited to the above-described embodiments. For example, in the
above embodiments, the fifth lens L5 is configured to have an
inflection point so as to restrain the incident angle of a light
beam into an imaging element. However, if there is some allowance
in the incident angle of a light beam into the imaging element and
it is not necessary to provide an inflection point to the fifth
lens L5, a lens surface of the fifth lens L5 may be formed in a
aspheric shape that does not have an inflection point, or one
surface or both surfaces of the fifth lens L5 may be formed with a
spherical surface(s).
The invention may be applicable to the imaging lens of a device
that is required to have a small size and satisfactory aberration
correction ability, e.g., the imaging lenses used in the cellular
phones, the digital still cameras, and the like.
* * * * *