DESCRIPTION
IMAGING LENS AND IMAGING DEVICE
TECHNICAL FIELD
5 The present invention relates to an imaging lens
and an imaging device. More particularly, the present
invention relates to an imaging lens suitable for a
small-sized imaging device such as a digital still camera
or a camera-equipped portable telephone device, which
10 uses a solid-state imaging element such as a CCD (Charge
Coupled Device) or a CMOS (Complementary Metal Oxide
Semiconductor), and an imaging device using the imaging
lens.
15 BACKGROUND ART
There have been generally-known imaging devices
such as camera-equipped portable telephone devices and
digital still cameras that use approximately 3- or 5million
pixel solid-state imaging elements such as CCDs
20 or CMOSs, and have imaging lenses of an aperture Fno of
approximately 2.8 mounted thereon.
Such imaging devices are now required to be even
smaller in size, and the imaging lenses mounted on those
imaging devices are required to have smaller sizes and
25 shorter total optical lengths than ever.
In recent years, in small-sized imaging devices
such as camera-equipped portable telephone devices,
imaging elements have become smaller and become capable
of coping with a larger number of pixels. Models 'with
30 high-pixel imaging elements almost equivalent to digital
still cameras have become popular. Therefore, the
1
imaging lenses mounted on small-sized imaging devices are
required to have high lens performance suitable for such
high-pixel solid-state imaging devices.
Further, there is a demand for lenses with brighter
5 aperture Fno, to prevent image quality degradation due to
noise caused when an image is captured in a dark place.
Each of such small-sized and high-performance imaging
lenses needs to have a four-lens structure or a structure
with more lenses. (see Patent Documents 1 through 5, for
10 example)
CITATION LIST
PATENT DOCUMENTS
Patent Document 1: Japanese Patent Application Laid-Open
15 No. 2004-4566
Patent Document 2: Japanese Patent Application Laid-Open
No. 2002-365530
Patent Document 3: Japanese Patent Application Laid-Open
No. 2006-293324
20 Patent Document 4: Japanese Patent Application Laid-Open
No. 2009-294527
Patent Document 5: Japanese Patent Application Laid-Open
No. 2010-26434
25 SUMMARY OF THE INVENTION
The conventional lens disclosed in Patent Document
1 has a three-lens structure, which is the most
advantageous structure in shortening the total optical
length. In recent years, however, there is a demand for
30 lenses with high resolving power and small chromatic
aberration, as imaging elements involve a large number of
2
pixels. To achieve both of the features, a lens with a
three-lens structure does not have enough lenses to
correct aberration, and it is difficult to achieve
desired optical performance with such a three-lens
5 structure.
The conventional lens disclosed in Patent Document
2 has a four-lens structure. This conventional lens
corrects various aberrations in a preferred manner, but
the total optical length thereof is too long to achieve a
10 small size. Also, in the lens disclosed in Patent
Document 2, the power of the first lens and the power of
the second lens are very strong. Since the power of the
second lens is particularly strong, sensitivity in
manufacture is very high, resulting in a decrease in
15 productivity.
Further, in the lens disclosed in Patent Document
2, there is large adverse influence of spherical
aberrations and coma aberrations that occur when the
aperture Fno is made brighter due to the strong power of
20 the first lens, and it is particularly difficult to
maintain high performance at the peripheral portion.
The conventional lens disclosed in Patent Document
3 has a four-lens structure, and has a high level of
aberration correction capability. However, the total
25 length of the lens is too large to achieve a small size.
Also, in the lens disclosed in Patent Document 3, both
surfaces of the third lens have convex shapes.
Therefore, it is difficult to correct aberrations with
this lens, and sensitivity in manufacture is high.
30 Further, when a peripheral light beam is totallyreflected
by the lens disclosed in Patent Document 3, the
3
•
totally-reflected peripheral light beam is further
reflected by another surface, and enters an imaging
element. As a result, ghosts might be formed and greatly
degrade image quality.
5 The conventional lens disclosed in Patent Document
4 has a five-lens structure, and has a high level of
aberration correction capability. However, the total
length of the lens is also too large to achieve a small
size. This lens disclosed in Patent Document 4 is formed
10 basically by adding a correcting lens to a lens having a
four-lens structure. If the total optical length is
shortened, the power of the first lens becomes too
strong. As a result, aberrations such as spherical
aberrations and coma aberrations that occur in the first
15 lens when the aperture Fno is made brighter cannot be
corrected successfully.
The conventional lens disclosed in Patent Document
5 has a five-lens structure with a high level of
aberration correction capability. However, the power of
20 the first lens relative to the focal length of the entire
system is weak, and effective reductions in size and
height (thickness) are not achieved.
The present invention has been made in view of the
above circumstances, and is to suggest a very small and
25 thin imaging lens that achieves optical performance high
enough for a high-pixel imaging element with 8 million
pixels or more, and an imaging device.
To solve the above problems, an imaging lens of the
present invention includes a first lens having positive
30 refractive power, an aperture stop, a second lens having
positive or negative refractive power, a third lens
4
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. The imaging lens satisfies the following
5 conditional expressions (1), (2), and (3):
(1) 0.80 < fIlf < 1.40
(2) fIllf 3 1 < 1.50
(3) -0.20 < fIlf 2 < 0.90
where
10
15
f: the focal length of the entire lens system,
f 1 : the focal length of the first lens,
f 2 : the focal length of the second lens, and
f 3 : the focal length of the third lens.
Also, in the imaging lens, the following
conditional expression (4) is satisfied:
(4 ) (vd1 + vd2 ) 12 - vd3 > 20
where
vd1 : the Abbe number of the first lens,
vd2 : the Abbe number of the second lens, and
20 vd3 : the Abbe number of the third lens.
In the imaging lens, the relationship between the
focal length of the entire lens system and the focal
length of the fifth lens satisfies the following
conditional expression (5):
25 (5) 0.5 < Ifs/lf < 1.8
where
f: the focal length of the entire lens system, and
f s : the focal length of the fifth lens.
The fundamental characteristics of this imaging
30 lens lie in that the first lens having positive
refractive power, the aperture stop, the second lens
5
•
having positive or negative refractive power, the third
lens having negative refractive power, the fourth lens
having positive refractive power, and the fifth lens
having negative refractive power are provided in this
5 order from the object side, and that positive power is
forward in the entire lens system.
In the imaging lens, if the total optical length is
shortened to reduce the size, the curvature radius of a
first lens having a four-lens structure becomes smaller,
10 and the refractive power increases. As a result,
spherical aberration correction becomes difficult. Also,
in the imaging lens, if the lens aperture is made larger
and Fno is made smaller (brighter) to achieve higher
image quality, coma aberration correction becomes
15 difficult.
To effectively correct spherical aberrations and
coma aberrations that become larger as the size increases
and the aperture becomes larger, the first lens having a
four-lens structure is divided into two in the imaging
20 lens. While the two divisional lenses (the first lens
and the second lens) complement each other with power,
the number of aberration correction planes is increased
by two compared with that prior to the division.
With this arrangement in the imaging lens,
25 spherical and coma aberrations that have occurred in the
first lens are restrained by the second lens, and other
aberrations can also be corrected by the two newly-formed
correction planes.
Although separated in the imaging lens, the first
30 lens and the second lens are located very close to each
other, so that chromatic aberrations that have occurred
6
•
in the first lens and the second lens can be offset by
the third lens.
In the imaging lens, the aperture stop is provided
between the first lens and the second lens that are
5 separated. Accordingly, distortions can be more
efficiently corrected than in a case where the aperture
stop is located closer to the object side than the first
lens is. This also contributes to a decrease in optical
sensitivity, and assembling becomes easier in the
10 manufacturing procedures.
The conditional expression (1) specified for the
imaging lens is a conditional expression for specifying
an appropriate power allocation to the first lens
relative to the power of the entire lens system in such a
15 lens structure.
If the upper limit value defined by the conditional
expression (1) is exceeded, the power of the first lens
becomes too large, and off-axis aberration correction,
particularly astigmatism and field curvature correction,
20 becomes difficult. As a result, easiness of assembling
at the time of manufacture is reduced.
If the lower limit value defined by the conditional
expression (1) is not reached, on the other hand, the
power of the first lens becomes too weak to shorten the
25 total optical length, and compactness might be reduced.
In view of this, satisfying the conditional expression
(1) is an essential condition in shortening the total
optical length in the imaging lens.
The conditional expression (2) specified for this
30 imaging lens concerns appropriate power allocations to
the first lens and the third lens. An absolute value is
7
•
used as the focal length of the third lens, because the
third lens has negative power.
If the lower limit value defined by the conditional
expression (2) is not reached, the power of the first
5 lens becomes too strong. As a result, spherical
aberration and off-axis coma aberration occurrences
increase, and aberration correction becomes difficult.
If the upper limit value defined by the conditional
expression (2) is exceeded, on the other hand, the power
10 of the first lens becomes too weak to allow the first
lens and the third lens to perform appropriate
achromatizing. As a result, optical performance high
enough for high-pixel imaging elements cannot be
maintained. Also, in an imaging environment where a
15 strong power source exists, color bleeding (flare)
occurs, to adversely affect image quality.
Therefore, in the imaging lens, the conditional
expression (2) is satisfied, so that the imaging lens is
made even thinner than a conventional lens, and optical
20 performance high enough for high-pixel imaging elements
can be achieved.
Further, the conditional expression (3) specified
for this imaging lens is a conditional expression that
concerns appropriate power allocations to the first lens
25 and the second lens.
If the lower limit value defined by this
conditional expression (3) is not reached, the power of
the second lens becomes too weak, and a large proportion
of the load is put on the first lens. As a result,
30 spherical aberration and off-axis coma aberration
occurrences increase, and correcting the spherical
8
•
aberration and the off-axis coma aberration becomes
difficult. This also hinders achromatizing with the
third lens, and therefore, optical performance high
enough for high-pixel imaging elements cannot be
5 maintained.
If the upper limit value defined by the conditional
expression (3) is exceeded, on the other hand, the power
of the second lens becomes too strong. As a result,
sensitivity in manufacture becomes higher, and easiness
10 of assembling is reduced at the time of manufacture.
Therefore, in the imaging lens, the conditional
expression (3) is satisfied, so that optical performance
high enough for high-pixel imaging elements can be
achieved while the power allocations to the first lens
15 and the second lens are optimized.
The conditional expression (4) specified for this
imaging lens defines the Abbe numbers of the first
through third lenses at a d-line single wavelength. Such
a glass material that the Abbe number falls within the
20 range defined by the conditional expression (4) is used
for each of the first lens, the second lens, and the
third lens, so that excellent chromatic aberration
correction can be performed without a large increase in
the power of each lens.
25 If the lower limit value defined by the conditional
expression (4) is not reached in the imaging lens, color
bleeding (flare) occurs to adversely affect image
quality. If the conditional expression (4) is satisfied,
the power of each lens does not become very strong.
30 Accordingly, coma aberration and field curvature
occurrences can be restrained in the surrounding area,
9
•
and furthermore, sensitivity in manufacture can be
effectively restrained.
Therefore, in the imaging lens, the conditional
expression (4) is satisfied, so that excellent chromatic
5 aberration correction can be performed, and coma
aberration and field curvature occurrences are restrained
in the surrounding area to lower the sensitivity in
manufacture.
Further, the conditional expression (5) specified
10 for this imaging lens is a conditional expression that
concerns an appropriate power allocation to the fifth
lens relative to the power of the entire lens system.
If the lower limit value defined by the conditional
expression (5) is not reached, the power of the fifth
15 lens becomes too strong. As a result, appropriate field
correction (correction to achieve uniform resolving power
from the axis to the surrounding area) becomes difficult.
Also, optical sensitivity becomes higher, and easiness of
assembling is reduced in manufacture.
20 If the upper limit value defined by the conditional
expression (5) is exceeded, on the other hand, the power
of the fifth lens becomes too weak, and appropriate
aberration correction, particularly field correction
(according to the Petzval's law), becomes difficult.
25 Therefore, in the imaging lens, the conditional
expression (5) is satisfied, so that optical performance
high enough for high-pixel imaging elements can be
achieved while the power allocation to the fifth lens
relative to the entire lens system is optimized.
30 In the imaging lens, the first lens has a convex
surface facing the object side and has positive
10
•
;
5
10
15
20
25
30
refractive power. Accordingly, an achromatizing effect
can be achieved with the first lens, the second lens, and
the third lens, while the refractive power is increased.
In the imaging lens, the third lens has a concave
surface on the imaging plane side. Accordingly, even
when an off-axis light beam is totally-reflected by the
concave surface, the totally-reflected off-axis light
beam diffuses to the lens peripheral portion and is
prevented from directly entering a solid-state imaging
element such as a CCD or CMOS. Thus, formation of ghosts
can be prevented.
In the imaging lens, the third lens has the concave
surface on the imaging plane side, to effectively correct
field curvatures and coma aberrations. Further, in the
imaging lens, the fourth lens has a meniscus shape with
positive power, to effectively correct aberrations,
particularly field curvatures and astigmatisms.
Further, in the imaging lens, the second lens has a
convex surface facing the imaging plane side and has
positive or negative refractive power. Accordingly, an
achromatizing effect can be achieved with the second lens
and the third lens.
In the imaging lens, the above described conditions
are satisfied, so that contrast degradation due to ghosts
and flares can be reduced, and optical performance high
enough for high-pixel imaging elements can be achieved,
while the imaging lens is made very small and thin.
An imaging device of the present invention includes
an imaging lens, and an imaging element that converts an
optical image formed by the imaging lens into an
electrical signal. The imaging lens includes a first
11
Ilens
having positive refractive power, an aperture stop,
a second lens having positive or negative refractive
power, a third lens having negative refractive power, a
fourth lens having positive refractive power, and a fifth
5 lens having negative refractive power in this order from
the object side. The imaging lens satisfies the
following conditional expressions (I), (2), and (3):
(1) 0.80 < fllf < 1.40
(2) fdlf3 1 < 1.50
10 (3) -0.20 < fdf2 < 0.90
where
15
f: the focal length of the entire lens system,
f l : the focal length of the first lens,
f 2 : the focal length of the second lens, and
f 3 : the focal length of the third lens.
The fundamental characteristics of the imaging lens
in this imaging device lie in that the first lens having
25
positive refractive power, the aperture stop, the second
lens having positive or negative refractive power, the
20 third lens having negative refractive power, the fourth
lens having positive refractive power, and the fifth lens
having negative refractive power are provided in this
order from the object side, and that positive power is
forward in the entire lens system.
In the imaging lens, if the total optical length is
shortened to reduce the size, the curvature radius of a
first lens having a four-lens structure becomes smaller,
and the refractive power increases. As a result,
spherical aberration correction becomes difficult. Also,
30 in the imaging lens, if the lens aperture is made larger
and Fno is made smaller (brighter) to achieve higher
12
•
image quality, coma aberration correction becomes
difficult.
To effectively correct spherical aberrations and
coma aberrations that become larger as the size increases
5 and the aperture becomes larger, the first lens having a
four-lens structure is divided into two in the imaging
lens. While the two divisional lenses (the first lens
and the second lens) complement each other with power,
the number of aberration correction planes is increased
10 by two compared with that prior to the division.
With this arrangement in the imaging lens,
spherical and coma aberrations that have occurred in the
first lens are restrained by the second lens, and other
aberrations can also be corrected by the two newly-formed
15 correction planes.
Although separated in the imaging lens, the first
lens and the second lens are located very close to each
other, so that chromatic aberrations that have occurred
in the first lens and the second lens can be offset by
20 the third lens.
In the imaging lens, the aperture stop is provided
between the first lens and the second lens that are
separated. Accordingly, distortions can be more
efficiently corrected than in a case where the aperture
25 stop is located closer to the object side than the first
lens is. This also contributes to a decrease in optical
sensitivity, and assembling becomes easier in the
manufacturing procedures.
The conditional expression (1) specified for the
30 imaging lens is a conditional expression for specifying
an appropriate power allocation to the first lens
13
,
relative to the power of the entire lens system in such a
lens structure.
If the upper limit value defined by the conditional
expression (1) is exceeded, the power of the first lens
5 becomes too large, and off-axis aberration correction,
particularly astigmatism and field curvature correction,
becomes difficult. As a result, easiness of assembling
at the time of manufacture is reduced.
If the lower limit value defined by the conditional
10 expression (1) is not reached, on the other hand, the
power of the first lens becomes too weak to shorten the
total optical length, and compactness might be reduced.
In view of this, satisfying the conditional expression
(1) is an essential condition in shortening the total
15 optical length in the imaging lens.
The conditional expression (2) specified for this
imaging lens concerns appropriate power allocations to
the first lens and the third lens. An absolute value is
used as the focal length of the third lens, because the
20 third lens has negative power.
If the lower limit value defined by the conditional
expression (2) is not reached, the power of the first
lens becomes too strong. As a result, spherical
aberration and off-axis coma aberration occurrences
25 increase, and aberration correction becomes difficult.
If the upper limit value defined by the conditional
expression (2) is exceeded, on the other hand, the power
of the first lens becomes too weak to allow the first
lens and the third lens to perform appropriate
30 achromatizing. As a result, optical performance high
enough for high-pixel imaging elements cannot be
14
t
maintained. Also, in an imaging environment where a
strong power source exists, color bleeding (flare)
occurs, to adversely affect image quality.
Therefore, in the imaging lens, the conditional
5 expression (2) is satisfied, so that the imaging lens is
made even thinner than a conventional lens, and optical
performance high enough for high-pixel imaging elements
can be achieved.
Further, the conditional expression (3) specified
10 for this imaging lens is a conditional expression that
concerns appropriate power allocations to the first lens
and the second lens.
If the lower limit value defined by this
conditional expression (3) is not reached, the power of
15 the second lens becomes too weak, and a large proportion
of the load is put on the first lens. As a result,
spherical aberration and off-axis coma aberration
occurrences increase, and correcting the spherical
aberration and the off-axis coma aberration becomes
20 difficult. This also hinders achromatizing with the
third lens, and therefore, optical performance high
enough for high-pixel imaging elements cannot be
maintained.
If the upper limit value defined by the conditional
25 expression (3) is exceeded, on the other hand, the power
of the second lens becomes too strong. As a result,
sensitivity in manufacture becomes higher, and easiness
of assembling is reduced at the time of manufacture.
Therefore, in the imaging lens, the conditional
30 expression (3) is satisfied, so that optical performance
high enough for high-pixel imaging elements can be
15
t
achieved while the power allocations to the first lens
and the second lens are optimized.
According to the present invention, an imaging lens
includes a first lens having positive refractive power,
5 an aperture stop, a second lens having positive or
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. The
10 imaging lens satisfies the following conditional
expressions (1), (2), and (3):
(1) 0.80 < fllf < 1.40
(2) fdlf3 1 < 1.50
(3) -0.20 < fdf2 < 0.90
15 where
f: the focal length of the entire lens system,
f l : the focal length of the first lens,
f 2 : the focal length of the second lens, and
f 3 : the focal length of the third lens.
20 The fundamental characteristics of this imaging
lens lie in that the first lens having positive
refractive power, the aperture stop, the second lens
having positive or negative refractive power, the third
lens having negative refractive power, the fourth lens
25 having positive refractive power, and the fifth lens
having negative refractive power are provided in this
order from the object side, and that positive power is
forward in the entire lens system.
In the imaging lens, if the total optical length is
30 shortened to reduce the size, the curvature radius of a
first lens having a four-lens structure becomes smaller,
16
and the refractive power increases. As a result,
spherical aberration correction becomes difficult. Also,
in the imaging lens, if the lens aperture is made larger
and Fno is made smaller (brighter) to achieve higher
5 image quality, coma aberration correction becomes
difficult.
To effectively correct spherical aberrations and
coma aberrations that become larger as the size increases
and the aperture becomes larger, the first lens having a
10 four-lens structure is divided into two in the imaging
lens. While the two divisional lenses (the first lens
and the second lens) complement each other with power,
the number of aberration correction planes is increased
by two compared with that prior to the division.
15 With this arrangement in the imaging lens,
spherical and coma aberrations that have occurred in the
first lens are restrained by the second lens, and other
aberrations can also be corrected by the two newly-formed
correction planes.
20 Although separated in the imaging lens, the first
lens and the second lens are located very close to each
other, so that chromatic aberrations that have occurred
in the first lens and the second lens can be offset by
the third lens.
25 In the imaging lens, the aperture stop is provided
between the first lens and the second lens that are
separated. Accordingly, distortions can be more
efficiently corrected than in a case where the aperture
stop is located closer to the object side than the first
30 lens is. This also contributes to a decrease in optical
sensitivity, and assembling becomes easier in the
17
manufacturing procedures.
The conditional expression (1) specified for the
imaging lens is a conditional expression for specifying
an appropriate power allocation to the first lens
5 relative to the power of the entire lens system in such a
lens structure.
If the upper limit value defined by the conditional
expression (1) is exceeded, the power of the first lens
becomes too large, and off-axis aberration correction,
10 particularly astigmatism and field curvature correction,
becomes difficult. As a result, easiness of assembling
at the time of manufacture is reduced.
If the lower limit value defined by the conditional
expression (1) is not reached, on the other hand, the
15 power of the first lens becomes too weak to shorten the
total optical length, and compactness might be reduced.
In view of this, satisfying the conditional expression
(1) is an essential condition in shortening the total
optical length in the imaging lens.
20 The conditional expression (2) specified for this
imaging lens concerns appropriate power allocations to
the first lens and the third lens. An absolute value is
used as the focal length of the third lens, because the
third lens has negative power.
25 If the lower limit value defined by the conditional
expression (2) is not reached, the power of the first
lens becomes too strong. As a result, spherical
aberration and off-axis coma aberration occurrences
increase, and aberration correction becomes difficult.
30 If the upper limit value defined by the conditional
expression (2) is exceeded, on the other hand, the power
18
•
of the first lens becomes too weak to allow the first
lens and the third lens to perform appropriate
achromatizing. As a result, optical performance high
enough for high-pixel imaging elements cannot be
5 maintained. Also, in an imaging environment where a
strong power source exists, color bleeding (flare)
occurs, to adversely affect image quality.
Therefore, in the imaging lens, the conditional
expression (2) is satisfied, so that the imaging lens is
10 made even thinner than a conventional lens, and optical
performance high enough for high-pixel imaging elements
can be achieved.
Further, the conditional expression (3) specified
for this imaging lens is a conditional expression that
15 concerns appropriate power allocations to the first lens
and the second lens.
If the lower limit value defined by this
conditional expression (3) is not reached, the power of
the second lens becomes too weak, and a large proportion
20 of the load is put on the first lens. As a result,
spherical aberration and off-axis coma aberration
occurrences increase, and correcting the spherical
aberration and the off-axis coma aberration becomes
difficult. This also hinders achromatizing with the
25 third lens, and therefore, optical performance high
enough for high-pixel imaging elements cannot be
maintained.
If the upper limit value defined by the conditional
expression (3) is exceeded, on the other hand, the power
30 of the second lens becomes too strong. As a result,
sensitivity in manufacture becomes higher, and easiness
19
•
of assembling is reduced at the time of manufacture.
Therefore, in the imaging lens, the conditional
expression (3) is satisfied, so that optical performance
high enough for high-pixel imaging elements can be
5 achieved while the power allocations to the first lens
and the second lens are optimized.
According to the present invention, an imaging
device includes an imaging lens, and an imaging element
that converts an optical image formed by the imaging lens
10 into an electrical signal. The imaging lens includes a
first lens having positive refractive power, an aperture
stop, a second lens having positive or negative
refractive power, a third lens having negative refractive
power, a fourth lens having positive refractive power,
15 and a fifth lens having negative refractive power in this
order from the object side. The imaging lens satisfies
the following conditional expressions (I), (2), and (3):
(1) 0.80 < fllf < 1.40
(2) f l /lf3 1 < 1.50
20 (3) -0.20 < f l /f2 < 0.90
where
25
f: the focal length of the entire lens system,
f l : the focal length of the first lens,
f 2 : the focal length of the second lens, and
f 3 : the focal length of the third lens.
The fundamental characteristics of the imaging lens
in this imaging device lie in that the first lens having
positive refractive power, the aperture stop, the second
lens having positive or negative refractive power, the
30 third lens having negative refractive power, the fourth
lens having positive refractive power, and the fifth lens
20
•
having negative refractive power are provided in this
order from the object side, and that positive power is
forward in the entire lens system.
The fundamental characteristics of the imaging lens
5 in this imaging device lie in that the first lens having
positive refractive power, the aperture stop, the second
lens having positive or negative refractive power, the
third lens having negative refractive power, the fourth
lens having positive refractive power, and the fifth lens
10 having negative refractive power are provided in this
order from the object side, and that positive power is
forward in the entire lens system.
In the imaging lens, if the total optical length is
shortened to reduce the size, the curvature radius of a
15 first lens having a four-lens structure becomes smaller,
and the refractive power increases. As a result,
spherical aberration correction becomes difficult. Also,
in the imaging lens, if the lens aperture is made larger
and Fno is made smaller (brighter) to achieve higher
20 image quality, coma aberration correction becomes
difficult.
To effectively correct spherical aberrations and
coma aberrations that become larger as the size increases
and the aperture becomes larger, the first lens having a
25 four-lens structure is divided into two in the imaging
lens. While the two divisional lenses (the first lens
and the second lens) complement each other with power,
the number of aberration correction planes is increased
by two compared with that prior to the division.
30 With this arrangement in the imaging lens,
spherical and coma aberrations that have occurred in the
21
•
first lens are restrained by the second lens, and other
aberrations can also be corrected by the two newly-formed
correction planes.
Although separated in the imaging lens, the first
5 lens and the second lens are located very close to each
other, so that chromatic aberrations that have occurred
in the first lens and the second lens can be offset by
the third lens.
In the imaging lens in the imaging device, the
10 aperture stop is provided between the first lens and the
second lens that are separated. Accordingly, distortions
can be more efficiently corrected than in a case where
the aperture stop is located closer to the object side
than the first lens is. This also contributes to a
15 decrease in optical sensitivity, and assembling becomes
easier in the manufacturing procedures.
The conditional expression (1) specified for the
imaging lens is a conditional expression for specifying
an appropriate power allocation to the first lens
20 relative to the power of the entire lens system in such a
lens structure.
If the upper limit value defined by the conditional
expression (1) is exceeded, the power of the first lens
becomes too large, and off-axis aberration correction,
25 particularly astigmatism and field curvature correction,
becomes difficult. As a result, easiness of assembling
at the time of manufacture is reduced.
If the lower limit value defined by the conditional
expression (1) is not reached, on the other hand, the
30 power of the first lens becomes too weak to shorten the
total optical length, and compactness might be reduced.
22
•
In view of this, satisfying the conditional expression
(1) is an essential condition in shortening the total
optical length in the imaging lens.
The conditional expression (2) specified for this
5 imaging lens concerns appropriate power allocations to
the first lens and the third lens. An absolute value is
used as the focal length of the third lens, because the
third lens has negative power.
If the lower limit value defined by the conditional
10 expression (2) is not reached, the power of the first
lens becomes too strong. As a result, spherical
aberration and off-axis coma aberration occurrences
increase, and aberration correction becomes difficult.
If the upper limit value defined by the conditional
15 expression (2) is exceeded, on the other hand, the power
of the first lens becomes too weak to allow the first
lens and the third lens to perform appropriate
achromatizing. As a result, optical performance high
enough for high-pixel imaging elements cannot be
20 maintained. Also, in an imaging environment where a
strong power source exists, color bleeding (flare)
occurs, to adversely affect image quality.
Therefore, in the imaging lens in the imaging
device, the conditional expression (2) is satisfied, so
25 that the imaging lens is made even thinner than a
conventional lens, and optical performance high enough
for high-pixel imaging elements can be achieved.
Further, the conditional expression (3) specified
for this imaging lens is a conditional expression that
30 concerns appropriate power allocations to the first lens
and the second lens.
23
•
If the lower limit value defined by this
conditional expression (3) is not reached, the power of
the second lens becomes too weak, and a large proportion
of the load is put on the first lens. As a result,
5 spherical aberration and off-axis coma aberration
occurrences increase, and correcting the spherical
aberration and the off-axis coma aberration becomes
difficult. This also hinders achromatizing with the
third lens, and therefore, optical performance high
10 enough for high-pixel imaging elements cannot be
maintained.
If the upper limit value defined by the conditional
expression (3) is exceeded, on the other hand, the power
of the second lens becomes too strong. As a result,
15 sensitivity in manufacture becomes higher, and easiness
of assembling is reduced at the time of manufacture.
Therefore, in the imaging lens in the imaging
device, the conditional expression (3) is satisfied, so
that optical performance high enough for high-pixel
20 imaging elements can be achieved while the power
allocations to the first lens and the second lens are
optimized.
BRIEF DESCRIPTION OF DRAWINGS
25 Fig. 1 is a schematic cross-sectional diagram
showing the structure of an imaging lens in a first
numerical example.
Fig. 2 shows characteristic curves indicating the
aberrations in the first numerical example.
30 Fig. 3 is a schematic cross-sectional diagram
showing the structure of an imaging lens in a second
24
numerical example.
Fig. 4 shows characteristic curves indicating the
aberrations in the second numerical example.
Fig. 5 is a schematic cross-sectional diagram
5 showing the structure of an imaging lens in a third
numerical example.
Fig. 6 shows characteristic curves indicating the
aberrations in the third numerical example.
Fig. 7 is a schematic cross-sectional diagram
10 showing the structure of an imaging lens in a fourth
numerical example.
Fig. 8 shows characteristic curves indicating the
aberrations in the fourth numerical example.
Fig. 9 is a schematic cross-sectional diagram
15 showing the structure of an imaging lens in a fifth
numerical example.
Fig. 10 shows characteristic curves indicating the
aberrations in the fifth numerical example.
Fig. 11 is a schematic cross-sectional diagram
20 showing the structure of an imaging lens in a sixth
numerical example.
Fig. 12 shows characteristic curves indicating the
aberrations in the sixth numerical example.
Fig. 13 is a schematic perspective diagram showing
25 an external appearance of a portable telephone device on
which an imaging device of the present invention is
mounted.
Fig. 14 is a schematic perspective diagram showing
an external appearance of the portable telephone device
30 on which the imaging device of the present invention is
mounted.
25
•
Fig. 15 is a schematic block diagram showing the
circuit configuration of the portable telephone device.
MODES FOR CARRYING OUT THE INVENTION
5 The following is a description of embodiments for
carrying out the invention. Explanation will be made in
the following order.
1. Embodiment
2. Numerical Examples According to the Embodiment (First
10 through Sixth Numerical Examples)
3. Structures of an Imaging Device and a Portable
Telephone Device
4. Other Embodiments
<1. Embodiment>
15 [1-1. Structure of an Imaging Lens]
In an imaging lens of the present invention, a
first lens having positive refractive power, an aperture
stop, a second lens having positive or negative
refractive power, a third lens having negative refractive
20 power, a fourth lens having positive refractive power,
and a fifth lens having negative refractive power are
provided in this order from the object side, and positive
power is forward in the entire lens system.
In this imaging lens, if the total optical length
25 is shortened to reduce the size, the curvature radius of
a first lens having a four-lens structure becomes
smaller, and the refractive power increases. As a
result, spherical aberration correction becomes
difficult. Also, in the imaging lens, if the lens
30 aperture is made larger and Fno is made smaller
(brighter) to achieve higher image quality, coma
26
•
aberration correction becomes difficult.
To effectively correct spherical aberrations and
coma aberrations that become larger as the size increases
and the aperture becomes larger, the first lens having a
5 four-lens structure is divided into two in the imaging
lens. While the two divisional lenses (the first lens
and the second lens) complement each other with power,
the number of aberration correction planes is increased
by two compared with that prior to the division.
10 With this arrangement in the imaging lens,
spherical and coma aberrations that have occurred in the
first lens are restrained by the second lens, and other
aberrations can also be corrected by the two newly-formed
correction planes.
15 Although separated in the imaging lens, the first
lens and the second lens are located very close to each
other, so that chromatic aberrations that have occurred
in the first lens and the second lens can be offset by
the third lens.
20 In the imaging lens, the aperture stop is provided
between the first lens and the second lens that are
separated. Accordingly, distortions can be more
efficiently corrected than in a case where the aperture
stop is located closer to the object side than the first
25 lens is. This also contributes to a decrease in optical
sensitivity, and assembling becomes easier in the
manufacturing procedures.
Also, in this imaging lens, it is preferable to
satisfy the following conditional expressions (1), (2),
30 and (3):
(1) 0.80 20
where
20
vd1 : the Abbe number of the first lens,
vd2 : the Abbe number of the second lens, and
vd3 : the Abbe number of the third lens.
This conditional expression (4 ) defines the Abbe
numbers of the first through third lenses at ad-line
single wavelength. Such a glass material that the Abbe
number falls within the range defined by the conditional
expression (4) is used for each of the first lens, the
25 second lens, and the third lens in the imaging lens, so
that excellent chromatic aberration correction can be
performed without a large increase in the power of each
lens.
If the lower limit value defined by the conditional
30 expression (4) is not reached in the imaging lens, color
bleeding (flare) occurs to adversely affect image
30
•
quality. If the conditional expression (4) is satisfied,
the power of each lens does not become very strong.
Accordingly, coma aberration and field curvature
occurrences can be restrained in the surrounding area,
5 and furthermore, sensitivity in manufacture can be
effectively restrained.
Therefore, in the imaging lens, the conditional
expression (4) is satisfied, so that excellent chromatic
aberration correction can be performed, and coma
10 aberration and field curvature occurrences are restrained
in the surrounding area to lower the sensitivity in
manufacture.
Further, in the imaging lens, the relationship
between the focal length of the entire lens system and
15 the focal length of the fifth lens satisfies the
following conditional expression (5):
(5) 0.5 < Ifsl/f < 1.8
where
f: the focal length of the entire lens system, and
20 f s : the focal length of the fifth lens.
The conditional expression (5) specified for this
imaging lens is a conditional expression that concerns an
appropriate power allocation to the fifth lens relative
to the power of the entire lens system.
25 If the lower limit value defined by the conditional
expression (5) is not reached, the power of the fifth
lens becomes too strong. As a result, appropriate field
correction (correction to achieve uniform resolving power
from the axis to the surrounding area) becomes difficult.
30 Also, optical sensitivity becomes higher, and easiness of
assembling is reduced in manufacture.
31
If the upper limit value defined by the conditional
expression (5) is exceeded, on the other hand, the power
of the fifth lens becomes too weak, and appropriate
aberration correction, particularly field correction
5 (according to the Petzval's law), becomes difficult.
Therefore, in the imaging lens, the conditional
expression (5) is satisfied, so that optical performance
high enough for high-pixel imaging elements can be
achieved while the power allocation to the fifth lens
10 relative to the entire lens system is optimized.
In the imaging lens, the first lens has a convex
surface facing the object side and has positive
refractive power. Accordingly, an achromatizing effect
can be achieved with the first lens, the second lens, and
15 the third lens, while the refractive power is increased.
In the imaging lens, the third lens has a concave
surface on the imaging plane side. Accordingly, even
when an off-axis light beam is totally-reflected by the
concave surface, the totally-reflected off-axis light
20 beam diffuses to the lens peripheral portion and is
prevented from directly entering a solid-state imaging
element such as a CCD or CMOS. Thus, formation of ghosts
can be prevented.
In the imaging lens, the third lens has the concave
25 surface on the imaging plane side, to effectively correct
field curvatures and coma aberrations. Further, in the
imaging lens, the fourth lens has a meniscus shape with
positive power, to effectively correct aberrations,
particularly field curvatures and astigmatisms.
30 Further, in the imaging lens, the second lens has a
convex surface facing the imaging plane side and has
32
•
positive or negative refractive power. Accordingly, an
achromatizing effect can be achieved with the second lens
and the third lens.
Further, in the imaging lens, the fifth lens has
5 negative power in the vicinity of the axis, and
accordingly, is effective in correcting aberrations,
particularly field curvatures. The fifth lens also has a
convex surface at the peripheral portion, and
accordingly, is effective in correcting astigmatisms and
10 distortions.
In the imaging lens, the above described conditions
are satisfied, so that contrast degradation due to ghosts
and flares can be reduced, and optical performance high
enough for high-pixel imaging elements can be achieved,
15 while the imaging lens is made very small and thin.
<2. Numerical Examples According to the Embodiment>
Referring now to the drawings and tables, numerical
examples applying specific numerical values to imaging
lenses of the present invention are described. The
20 meanings of the symbols to be used in the numerical
examples are as follows.
"FNo" represents the F-number, "f" represents the
focal length of the entire lens system, "2m" represents
the full field angle at an opposing corner, "Si"
25 represents the plane number of the ith plane counted from
the object side, "Ri" represents the curvature radius of
the ith plane, "di" represents the on-axis plane interval
between the ith plane and the (i+l) plane counted from
the object side, "ni" represents the refractive index of
30 the ith lens at the d-line (at a wavelength of 587.6 nm),
and "vi" represents the Abbe number of the ith lens at
33
15
•
the d-line (at the wavelength of 587.6 nm). It should be
noted that "00" with respect to a curvature radius
indicates that the subject plane is a flat plane.
Some of the imaging lenses used in the respective
5 numerical examples have aspheric lens surfaces. Where
liZ II represents the depth of the aspheric surface, "y"
represents the height from the optical axis, "R"
represents the curvature radius, "K" represents the conic
constant, and "Ai" represents the aspheric coefficient of
10 the ith (i being an integer of 3 or greater) order, an
aspheric shape is defined by the following mathematical
formula 1:
y2
R
Z= + L Ai· yi ,., ... (1)
I y 2
1+ - (1 + K) [ )
R
[2-1. First Numerical Example]
In Fig. I, reference numeral 1 indicates an entire
imaging lens in a first numerical example. A first lens
Gl having positive refractive power, an aperture stop
STO, a second lens G2 having positive or negative
refractive power, a third lens G3 having negative
20 refractive power, a fourth lens G4 having positive
25
refractive power, and a fifth lens G5 having negative
refractive power are provided in this order from the
object side. Positive power is forward in the entire
lens system.
In the imaging lens I, sealing glass SG for
protecting an imaging plane IMG is provided between the
34
•
fifth lens G5 and the imaging plane IMG of an imaging
element.
In this imaging lens I, a first lens (not shown)
having a four-lens structure is divided into two. While
5 the two divisional lenses (the first lens Gl and the
second lens G2) complement each other with power, the
number of aberration correction planes is increased by
two compared with that prior to the division.
With this arrangement in the imaging lens I, the
10 first lens Gl and the second lens G2 complement each
other with power. Accordingly, a decrease in the
curvature radius of the first lens Gl can be restrained,
and an increase in the refractive power can also be
restrained. Thus, spherical aberration correction can be
15 performed. Also, coma aberration correction can be
performed, even if the lens aperture is made larger and
Fno is made smaller (brighter) to achieve higher image
quality.
Although separated in the imaging lens I, the first
20 lens Gl and the second lens G2 are located very close to
each other, so that chromatic aberrations that have
occurred in the first lens Gl and the second lens G2 can
be offset by the third lens G3.
In the imaging lens I, the aperture stop STO is
25 provided between the first lens Gl and the second lens G2
that are separated. Accordingly, distortions can be more
efficiently corrected than in a case where the aperture
stop STO is located closer to the object side than the
first lens Gl is. This also contributes to a decrease in
30 optical sensitivity, and assembling becomes easier in the
manufacturing procedures.
35
•
Further, in the imaging lens 1, the first lens Gl
has a convex surface facing the object side and has
positive refractive power. Accordingly, an achromatizing
effect can be achieved with the first lens Gl, the second
5 lens G2, and the third lens G3, while the refractive
power is increased.
In the imaging lens 1, the third lens G3 has a
concave surface on the imaging plane side. Accordingly,
even when an off-axis light beam is totally-reflected by
10 the concave surface, the totally-reflected off-axis light
beam diffuses to the lens peripheral portion and is
prevented from directly entering the imaging plane IMG of
a solid-state imaging element such as a CCD or CMOS.
Thus, formation of ghosts can be prevented.
15 In the imaging lens 1, the third lens G3 has the
concave surface on the imaging plane side, to effectively
correct field curvatures and coma aberrations. Further,
in the imaging lens 1, the fourth lens G4 has a meniscus
shape with positive power, to effectively correct
20 aberrations, particularly field curvatures and
astigmatisms.
Further, in the imaging lens 1, the second lens G2
has a convex surface facing the imaging plane side and
has positive or negative refractive power. Accordingly,
25 an achromatizing effect can be achieved with the second
lens G2 and the third lens G3.
Further, in the imaging lens 1, the fifth lens G5
has negative power in the vicinity of the axis, and
accordingly, is effective in correcting aberrations,
30 particularly field curvatures. The fifth lens G5 also
has a convex surface at the peripheral portion, and
36
•
accordingly, is effective in correcting astigmatisms and
distortions.
In the following, Table 1 shows the lens data
obtained when specific numerical values were applied to
5 the imaging lens 1 of the first numerical example
according to the embodiment, in conjunction with an Fnumber
FNo, a focal length f of the entire lens system,
and a field angle 2m. In Table 1, each curvature radius
Ri of 00 means that the plane is a flat plane.
FNo=2.4 f=3.8 20)=72.9°
Si Ri Di Ndi vdi
Plane Curvature Plane Refractive Abbe
number radius interval index number
1 2.958 0.442 1. 531 55.9
2 -15.403 0.040 - -
3 (STO) 0() 0.059 - -
4 11. 972 0.483 1.531 55.9
5 -5.476 0.040 - -
6 9.229 0.300 1. 615 25.6
7 1. 985 0.645 - -
8 -2.987 0.745 1. 531 55.9
9 -1.114 0.040 - -
10 1. 795 0.550 1. 531 55.9
11 0.840 0.806 - -
12 0() 0.150 1.518 64.1
13 0() 0.700 - -
10 Table 1 Lens Data in the First Numerical Example
Table 2 shows the third-order, fourth-order, fifthorder,
sixth-order, seventh-order, eighth-order, ninthorder,
tenth-order, eleventh-order, and twelfth-order
15 aspheric coefficients of aspheric planes in the imaging
lens 1 of the first numerical example, in conjunction
with conic constants "K". In Table 2, "E-02" is an
exponential expression using 10 as the base, or
represents "10- 2
". For example, "0.12345E-05" represents
20 "0.12345 x 10-5
".
37
..
FNo=2.4 f=3.8 2<0=72.9°
Si K
Third- Fourth- Fifth- Sixth- Seventh- Eighth- Ninth- Tenth- Eleventh Twelfth-
Plane Conic
order order order order order order order order -order order
number constant
1 -1.06E+Ol - 2.23E-02 - -4.59E-02 - 6.59E-02 - -3.91E-02 - -
2 -1.00E+Ol - -5.51E-02 - 1. 20E-Ol - -1.00E-Ol - 8.49E-03 - -
3
(STO) - - - - - - - - -
4 1. OOE+Ol - -6.04E-02 - 5.97E-02 - -6.82E-02 - -8.21E-02 - -
5 9.30E+00 - -1.94E-Ol - 1.36E-Ol - -9.18E-02 - -4.63E-03 - -
6 1.95E-Ol - -1.90E-Ol - 7.74E-02 - 1. 03E-Ol - -5.83E-02 - -
7 1.35E+00 2.22E-02 -8.66E-02 -2.16E-02 -7.68E-03 8.30E-03 5.30E-02 2.11E-02 -4.57E-02 - -
8 1. 42E+00 2.66E-02 1.27E-Ol -8.08E-02 1. 27E-02 -4.98E-05 4.76E-03 1. 58E-02 -3.09E-02 1. 88E-02 -4.10E-03
9 -5.54E+00 -1.17E-Ol 2.88E-02 8.08E-02 -8.89E-02 4.21E-02 -1. 06E-02 6.03E-03 4.16E-03 -2.44E-03 -8.07E-04
10 -4.21E+00 -1.24E-Ol 1. 25E-Ol 1. 7lE-02 -4.10E-02 2.45E-02 4.l3E-03 -5.72E-03 1. 02E-03 - -
11 -4.82E+00 1.14E-02 -9.49E-02 4.07E-02 -3.21E-03 -1.11E-04 -6.98E-04 -1.82E-04 1.41E-04 - -
Table 2 Aspheric Plane Data in the First Numerical Example
38
"""""'''''''''''~'''---................_---_...._-------_...._---_...._------_..._-----_....-----------------_...._---_...__......_-------_......_-----------------_...
Fig. 2 shows aberrations in the imaging lens 1 of
the first numerical example. In the astigmatism graph,
the solid line indicates values in a sagittal imaging
5 plane, and the dashed line indicates values in a
meridional imaging plane.
As can be seen from the aberration graphs (a
spherical aberration graph, an astigmatism graph, and a
distortion graph) in Fig. 2, aberrations are
10 appropriately corrected, and excellent imaging
performance is achieved by the imaging lens 1 of the
first numerical example.
[2-2. Second Numerical Example]
In Fig. 3, reference numeral 2 indicates an entire
15 imaging lens in a second numerical example. A first lens
G1 having positive refractive power, an aperture stop
STO, a second lens G2 having positive or negative
refractive power, a third lens G3 having negative
refractive power, a fourth lens G4 having positive
20 refractive power, and a fifth lens G5 having negative
refractive power are provided in this order from the
object side. Positive power is forward in the entire
lens system.
In the imaging lens 2, sealing glass SG for
25 protecting an imaging plane IMG is provided between the
fifth lens G5 and the imaging plane IMG of an imaging
element.
In this imaging lens 2, a first lens (not shown)
having a four-lens structure is divided into two. While
30 the two divisional lenses (the first lens G1 and the
second lens G2) complement each other with power, the
39
•
number of aberration correction planes is increased by
two compared with that prior to the division.
With this arrangement in the imaging lens 2, the
first lens Gl and the second lens G2 complement each
5 other with power. Accordingly, a decrease in the
curvature radius of the first lens Gl can be restrained,
and an increase in the refractive power can also be
restrained. Thus, spherical aberration correction can be
performed. Also, coma aberration correction can be
10 performed, even if the lens aperture is made larger and
Fno is made smaller (brighter) to achieve higher image
quality.
Although separated in the imaging lens 2, the first
lens Gl and the second lens G2 are located very close to
15 each other, so that chromatic aberrations that have
occurred in the first lens Gl and the second lens G2 can
be offset by the third lens G3.
In the imaging lens 2, the aperture stop STO is
provided between the first lens Gl and the second lens G2
20 that are separated. Accordingly, distortions can be more
efficiently corrected than in a case where the aperture
stop STO is located closer to the object side than the
first lens Gl is. This also contributes to a decrease in
optical sensitivity, and assembling becomes easier in the
25 manufacturing procedures.
Further, in the imaging lens 2, the first lens Gl
has a convex surface facing the object side and has
positive refractive power. Accordingly, an achromatizing
effect can be achieved with the first lens Gl, the second
30 lens G2, and the third lens G3, while the refractive
power is increased.
40
•
In the imaging lens 2, the third lens G3 has a
concave surface on the imaging plane side. Accordingly,
even when an off-axis light beam is totally-reflected by
the concave surface, the totally-reflected off-axis light
5 beam diffuses to the lens peripheral portion and is
prevented from directly entering the imaging plane IMG of
a solid-state imaging element such as a CCD or CMOS.
Thus, formation of ghosts can be prevented.
In the imaging lens 2, the third lens G3 has the
10 concave surface on the imaging plane side, to effectively
correct field curvatures and coma aberrations. Further,
in the imaging lens 2, the fourth lens G4 has a meniscus
shape with positive power, to effectively correct
aberrations, particularly field curvatures and
15 astigmatisms.
Further, in the imaging lens 2, the second lens G2
has a convex surface facing the imaging plane side and
has positive or negative refractive power. Accordingly,
an achromatizing effect can be achieved with the second
20 lens G2 and the third lens G3.
Further, in the imaging lens 2, the fifth lens G5
has negative power in the vicinity of the axis, and
accordingly, is effective in correcting aberrations,
particularly field curvatures. The fifth lens G5 also
25 has a convex surface at the peripheral portion, and
accordingly, is effective in correcting astigmatisms and
distortions.
In the following, Table 3 shows the lens data
obtained when specific numerical values were applied to
30 the imaging lens 2 of the second numerical example
according to the embodiment, in conjunction with an F-
41
•
number FNo, a focal length f of the entire lens system,
and a field angle 2m. In Table 3, each curvature radius
Ri of 00 means that the plane is a flat plane.
FNo=2.4 f=3.9 20)=71.8°
si Ri Di Ndi
Plane Curvature Plane Refractive vdi
number radius interval index Abbe number
1 2.922 0.447 1. 533 71. 6
2 -14.124 0.040 - -
3 (STO) 00 0.082 - -
4 11.544 0.368 1. 533 71. 6
5 -47.848 0.040 - -
6 3.938 0.300 1.615 25.6
7 2.091 0.796 - -
8 -3.351 0.739 1. 535 56.3
9 -1.275 0.040 - -
10 1. 711 0.556 1. 535 56.3
11 0.854 0.743 - -
12 00 0.150 1.518 64.1
13 00 0.700 - -
5
Table 3 Lens Data in the Second Numerical Example
Table 4 shows the third-order, fourth-order, fifthorder,
sixth-order, seventh-order, eighth-order, ninthorder,
tenth-order, eleventh-order, and twelfth-order
aspheric coefficients of aspheric planes in the imaging
10 lens 2 of the second numerical example, in conjunction
with conic constants "K". In Table 4, "E-02" is an
exponential expression using 10 as the base, or
represents "10-2
". For example, "0.12345E-05" represents
"0.12345 x 10-5
".
15
42
•
FNo=2.4 f=3.9 2<0=71. SO
Si K
Third- Fourth- Fifth- Sixth- Seventh- Eighth- Ninth- Tenth- Eleventh Twelfth-
Plane Conic
number constant
order order order order order order order order -order order
1 -1.06E+01 - 2.23E-02 - -4.93E-02 - 6.S0E-02 - -3.SSE-02 - -
2 -1.41E+01 - -5.2SE-02 - 1.12E-01 - -9.46E-02 - S.39E-03 - -
3 - - - - - - - - - - - (STO)
4 1.00E+01 - -5.S9E-02 - 5.57E-02 - -3.72E-02 - -l.13E-Ol - -
5 9.30E+00 - -1.79E-01 - 1.27E-01 - -1.14E-01 - -3.05E-03 - -
6 1.95E-01 - -1.14E-01 - 5.90E-02 - 5.16E-02 - -2.74E-02 - -
7 1. 35E+00 2.16E-02 -5.1SE-02 -S.36E-03 -2.09E-02 6.0SE-06 5.02E-02 3.2SE-02 -4.10E-02 - -
S 1. 42E+00 2.33E-02 1.20E-01 -S.69E-02 -4.13E-03 -2.20E-03 S.25E-03 1.7SE-02 -3.03E-02 1.79E-02 -6.38E-03
9 -7.32E+00 -1.21E-01 3.52E-02 8.4SE-02 -9.07E-02 3.S4E-02 -1.39E-02 3.93E-03 3.64E-03 -2.27E-03 -1.61E-04
10 -4.21E+00 -1.19E-01 7.23E-03 2.05E-02 -4.12E-02 2.39E-02 4.01E-03 -5.66E-03 1. 03E-03 - -
11 -4.82E+00 2.50E-02 -9.48E-02 3.09E-02 2.16E-03 -5.17E-04 -7.71E-04 -2.43E-04 1.50E-04 - -
Table 4 Aspheric Plane Data in the Second Numerical Example
43
!&.. ",~,,~,.,M~.. ";::: [.lam a «Set k $@M;k$Jwi=WMa_42¥$A"""""'....----------·--·-------·---
•
Fig. 4 shows aberrations in the imaging lens 2 of
the second numerical example. In the astigmatism graph,
the solid line indicates values in a sagittal imaging
5 plane, and the dashed line indicates values in a
meridional imaging plane.
As can be seen from the aberration graphs (a
spherical aberration graph, an astigmatism graph, and a
distortion graph) in Fig. 4, aberrations are
10 appropriately corrected, and excellent imaging
performance is achieved by the imaging lens 2 of the
second numerical example.
[2-3. Third Numerical Example]
In Fig. 5, reference numeral 3 indicates an entire
15 imaging lens in a third numerical example. A first lens
G1 having positive refractive power, an aperture stop
STO, a second lens G2 having positive or negative
refractive power, a third lens G3 having negative
refractive power, a fourth lens G4 having positive
20 refractive power, and a fifth lens G5 having negative
refractive power are provided in this order from the
object side. positive power is forward in the entire
lens system.
In the imaging lens 3, sealing glass SG for
25 protecting an imaging plane IMG is provided between the
fifth lens G5 and the imaging plane IMG of an imaging
element.
In this imaging lens 3, a first lens (not shown)
having a four-lens structure is divided into two. While
30 the two divisional lenses (the first lens Gl and the
second lens G2) complement each other with power, the
44
•
number of aberration correction planes is increased by
two compared with that prior to the division.
With this arrangement in the imaging lens 3, the
first lens Gl and the second lens G2 complement each
5 other with power. Accordingly, a decrease in the
curvature radius of the first lens Gl can be restrained,
and an increase in the refractive power can also be
restrained. Thus, spherical aberration correction can be
performed. Also, coma aberration correction can be
10 performed, even if the lens aperture is made larger and
Fno is made smaller (brighter) to achieve higher image
quality.
Although separated in the imaging lens 3, the first
lens Gl and the second lens G2 are located very close to
15 each other, so that chromatic aberrations that have
occurred in the first lens Gl and the second lens G2 can
be offset by the third lens G3.
In the imaging lens 3, the aperture stop STO is
provided between the first lens Gl and the second lens G2
20 that are separated. Accordingly, distortions can be more
efficiently corrected than in a case where the aperture
stop STO is located closer to the object side than the
first lens Gl is. This also contributes to a decrease in
optical sensitivity, and assembling becomes easier in the
25 manufacturing procedures.
Further, in the imaging lens 3, the first lens Gl
has a convex surface facing the object side and has
positive refractive power. Accordingly, an achromatizing
effect can be achieved with the first lens Gl, the second
30 lens G2, and the third lens G3, while the refractive
power is increased.
45
•
In the imaging lens 3, the third lens G3 has a
concave surface on the imaging plane side. Accordingly,
even when an off-axis light beam is totally-reflected by
the concave surface, the totally-reflected off-axis light
5 beam diffuses to the lens peripheral portion and is
prevented from directly entering the imaging plane IMG of
a solid-state imaging element such as a CCD or CMOS.
Thus, formation of ghosts can be prevented.
In the imaging lens 3, the third lens G3 has the
10 concave surface on the imaging plane side, to effectively
correct field curvatures and coma aberrations. Further,
in the imaging lens 3, the fourth lens G4 has a meniscus
shape with positive power, to effectively correct
aberrations, particularly field curvatures and
15 astigmatisms.
Further, in the imaging lens 3, the second lens G2
has a convex surface facing the imaging plane side and
has positive or negative refractive power. Accordingly,
an achromatizing effect can be achieved with the second
20 lens G2 and the third lens G3.
Further, in the imaging lens 3, the fifth lens G5
has negative power in the vicinity of the axis, and
accordingly, is effective in correcting aberrations,
particularly field curvatures. The fifth lens G5 also
25 has a convex surface at the peripheral portion, and
accordingly, is effective in correcting astigmatisms and
distortions.
In the following, Table 5 shows the lens data
obtained when specific numerical values were applied to
30 the imaging lens 3 of the third numerical example
according to the embodiment, in conjunction with an F-
46
number FNo, a focal length f of the entire lens system,
and a field angle 200. In Table 5, each curvature radius
Ri of 00 means that the plane is a flat plane.
FNo=2.4 f=3.8 20)=72.6°
Si Ri Di Ndi
Plane Curvature Plane Refractive vdi
number radius interval index Abbe number
1 2.900 0.436 1. 535 56.3
2 -15.623 0.040 - -
3
0.053
(STO) 00 - -
4 14.293 0.448 1. 535 56.3
5 -10.494 0.040 - -
6 4.233 0.300 1. 615 25.6
7 1. 916 0.720 - -
8 -3.106 0.725 1. 535 56.3
9 -1.127 0.040 - -
10 1. 829 0.551 1. 535 56.3
11 0.841 0.798 - -
12 00 0.150 1.518 64.1
13 00 0.700 - -
5
Table 5 Lens Data in the Third Numerical Example
Table 6 shows the third-order, fourth-order, fifthorder,
sixth-order, seventh-order, eighth-order, ninthorder,
tenth-order, eleventh-order, and twelfth-order
aspheric coefficients of aspheric planes in the imaging
10 lens 3 of the third numerical example, in conjunction
with conic constants "K". In Table 6, "E-02" is an
exponential expression using 10 as the base, or
15
represents "10-2
".
"0.12345 X 10-5
".
For example, "0.12345E-05" represents
47
•
FNo=2.4 f=3.8 200 =72.6°
Si K
Plane Conic Third- Fifth- Sixth- Seventh- Eighth- Ninth- Tenth- Eleventh Twelfth-
Fourthnumber
constant
order order order order order order order order -order order
1 -1.06E+Ol - 1.89E-02 - -4.43E-02 - 6.S2E-02 - -3.79E- .. - -
2 -1.S6E+Ol - -S.74E-02 - 1.16E-Ol - -8.83E-02 - 1. 26E- " - -
3(STO) - - - - - - - - - - -
4 1. OOE+Ol - -S.66E-02 - 6.l8E-02 - -6.63E-02 - -7.36E- .. - -
S -1. OSE+Ol - -2.00E-Ol - 1.32E-Ol - -9.36E-02 - S.74E- .. - -
6 1.9SE-Ol - -1.84E-Ol - 6.76E-02 - 9.S3E-02 - -4.76E- .. - -
7 1. 3SE+00 2.0lE-02 -9.2lE-02 -2.63E-02 -1.0SE-02 9.S2E-03 S.34E-02 2.4SE-02 -4.74E- .. - -
8 1. 42E+00 2.l8E-02 1. 22E-Ol -8.0SE-02 1.18E-02 -1.OSE-03 S.12E-03 1.67E-02 -3.03E- .. 1. 89E-02 -4.72E-03
9 -S.64E+00 -l.lSE-Ol 3.3lE-02 7.7SE-02 -9.l0E-02 4.2lE-02 -1.02E-02 6.l7E-03 4.23E- .. -2.48E-03 -8.02E-04
10 -4.2lE+00 -1. 2lE-Ol 1.l2E-02 1. 63E-02 -4.09E-02 2.4SE-02 4.l6E-03 -S.71E-03 1. OlE- .. - -
11 -4.82E+00 1.06E-02 -9.l4E-02 3.91E-02 -3.32E-03 -6.0SE-OS -6.09E-04 -1.94E-04 1. 33E- .. - -
Table 6 Aspheric Plane Data in the Third Numerical Example
48
M£ii"...JQ.JXWiJ 1$..; am &.I(iJJ@f!IJAW .. U",k"U! nuaa tAWt M UA$QUZtiUU t i £1 j ase SiJ.JUU1SZW. U ,&Mil n i.$$1i&P iQiJ\ii.!Ui.';':;·uw ...=;,;® __,:;;Wi"'" " ,,",'''''''''''-_._.
•
Fig. 6 shows aberrations in the imaging lens 3 of
the third numerical example. In the astigmatism graph,
the solid line indicates values in a sagittal imaging
5 plane, and the dashed line indicates values in a
meridional imaging plane.
As can be seen from the aberration graphs (a
spherical aberration graph, an astigmatism graph, and a
distortion graph) in Fig. 6, aberrations are
10 appropriately corrected, and excellent imaging
performance is achieved by the imaging lens 3 of the
third numerical example.
[2-4. Fourth Numerical Example]
In Fig. 7, reference numeral 4 indicates an entire
15 imaging lens in a fourth numerical example. A first lens
Gl having positive refractive power, an aperture stop
STO, a second lens G2 having positive or negative
refractive power, a third lens G3 having negative
refractive power, a fourth lens G4 having positive
20 refractive power, and a fifth lens G5 having negative
refractive power are provided in this order from the
object side. Positive power is forward in the entire
lens system.
In the imaging lens 4, sealing glass SG for
25 protecting an imaging plane IMG is provided between the
fifth lens G5 and the imaging plane IMG of an imaging
element.
In this imaging lens 4, a first lens (not shown)
having a four-lens structure is divided into two. While
30 the two divisional lenses (the first lens Gl and the
second lens G2) complement each other with power, the
49
•
number of aberration correction planes is increased by
two compared with that prior to the division.
With this arrangement in the imaging lens 4, the
first lens Gl and the second lens G2 complement each
5 other with power. Accordingly, a decrease in the
curvature radius of the first lens Gl can be restrained,
and an increase in the refractive power can also be
restrained. Thus, spherical aberration correction can be
performed. Also, coma aberration correction can be
10 performed, even if the lens aperture is made larger and
Fno is made smaller (brighter) to achieve higher image
quality.
Although separated in the imaging lens 4, the first
lens Gl and the second lens G2 are located very close to
15 each other, so that chromatic aberrations that have
occurred in the first lens Gl and the second lens G2 can
be offset by the third lens G3.
In the imaging lens 4, the aperture stop STO is
provided between the first lens Gl and the second lens G2
20 that are separated. Accordingly, distortions can be more
efficiently corrected than in a case where the aperture
stop STO is located closer to the object side than the
first lens Gl is. This also contributes to a decrease in
optical sensitivity, and assembling becomes easier in the
25 manufacturing procedures.
Further, in the imaging lens 4, the first lens Gl
has a convex surface facing the object side and has
positive refractive power. Accordingly, an achromatizing
effect can be achieved with the first lens Gl, the second
30 lens G2, and the third lens G3, while the refractive
power is increased.
50
•
In the imaging lens 4, the third lens G3 has a
concave surface on the imaging plane side. Accordingly,
even when an off-axis light beam is totally-reflected by
the concave surface, the totally-reflected off-axis light
5 beam diffuses to the lens peripheral portion and is
prevented from directly entering the imaging plane IMG of
a solid-state imaging element such as a CCD or CMOS.
Thus, formation of ghosts can be prevented.
In the imaging lens 4, the third lens G3 has the
10 concave surface on the imaging plane side, to effectively
correct field curvatures and coma aberrations. Further,
in the imaging lens 4, the fourth lens G4 has a meniscus
shape with positive power, to effectively correct
aberrations, particularly field curvatures and
15 astigmatisms.
Further, in the imaging lens 4, the second lens G2
has a convex surface facing the imaging plane side and
has positive or negative refractive power. Accordingly,
an achromatizing effect can be achieved with the second
20 lens G2 and the third lens G3.
Further, in the imaging lens 4, the fifth lens G5
has negative power in the vicinity of the axis, and
accordingly, is effective in correcting aberrations,
particularly field curvatures. The fifth lens G5 also
25 has a convex surface at the peripheral portion, and
accordingly, is effective in correcting astigmatisms and
distortions.
In the following, Table 7 shows the lens data
obtained when specific numerical values were applied to
30 the imaging lens 4 of the fourth numerical example
according to the embodiment, in conjunction with an F-
51
..
number FNo, a focal length f of the entire lens system,
and a field angle 2m. In Table 7, each curvature radius
Ri of 00 means that the plane is a flat plane.
FNo=2.4 f=4.1 200=69.2°
Si Ri Di Ndi
Plane Curvature Plane Refractive vdi
number radius interval index Abbe number
1 2.442 0.517 1. 535 56.3
2 -7.985 0.040 - -
3
00 0.050 - -
(STO)
4 36.736 0.350 1. 535 56.3
5 47.420 0.040 - -
6 4.213 0.300 1.615 25.6
7 2.003 0.759 - -
8 -3.547 0.696 1. 535 56.3
9 -1. 476 0.111 - -
10 1.797 0.550 1. 535 56.3
11 0.976 0.738 - -
12 00 0.150 1.518 64.1
13 00 0.700 - -
5
Table 7 Lens Data in the Fourth Numerical Example
Table 8 shows the third-order, fourth-order, fifthorder,
sixth-order, seventh-order, eighth-order, ninthorder,
tenth-order, eleventh-order, and twelfth-order
aspheric coefficients of aspheric planes in the imaging
10 lens 4 of the fourth numerical example, in conjunction
with conic constants "K". In Table 8, "E-02" is an
exponential expression using 10 as the base, or
represents "10-2
". For example, "0.12345E-05" represents
"0.12345 X 10-5
".
15
52
•
FNo=2.4 f=4.1 20)=69.2°
Si K
Third- Fourth- Fifth- Sixth- Seventh- Eighth- Ninth- Tenth- Eleventh Twelfth-
Plane Conic
order order order order order order order order -order order
number constant
1 -1.06E+Ol - 6.13E-02 - -8.07E-02 - 6.18E-02 - -3.32E-02 - -
2 -1.00E+Ol - -3.80E-02 - 9.57E-02 - -1.31E-Ol - 4.50E-02 - -
3 (STO) - - - - - - - - - - -
4 1. OOE+Ol - -2.37E-02 - 6.15E-02 - -9.03E-02 - -5.12E-03 - -
5 9.30E+00 - -1.90E-Ol - 1. 67E-Ol - -9.84E-02 - 7.36E-03 - -
6 1. 95E-Ol - -1.56E-Ol - 8.37E-02 - 1.14E-Ol - -8.38E-02 - -
7 1. 35E+00 2.78E-02 -7.89E-02 -8.99E-03 -8.35E-04 1. 42E-02 5.12E-02 2.66E-02 -5.55E-02 - -
8 1. 42E+OO 1.59E-02 1.24E-Ol -9.15E-02 2.91E-03 -3.96E-03 5.80E-03 1. 78E-02 -2.99E-02 1. 85E-02 -5.71E-03
9 -8.07E+OO -1.33E-Ol 5.98E-02 7.90E-02 -9.71E-02 3.74E-02 -1. 23E-02 5.49E-03 4.13E-03 -2.27E-03 -5.54E-04
10 -4.21E+OO -1. 44E-Ol 2.02E-02 1.97E-02 -4.11E-02 2.40E-02 3.94E-03 -5.74E-03 1.06E-03 - -
11 -4.82E+OO -5.53E-03 -8.35E-02 3.74E-02 -2.01E-03 -4.23E-04 -7.93E-04 -1. 85E-04 1.59E-04 - -
Table 8 Aspheric Plane Data in the Fourth Numerical Example
53
~~<',~A ·-aMP U '0KCH ZiP ,·r ), .• OM ·¥X Ukt" ;;;m. "~_._.
Fig. 8 shows aberrations in the imaging lens 4 of
the fourth numerical example. In the astigmatism graph,
the solid line indicates values in a sagittal imaging
5 plane, and the dashed line indicates values in a
meridional imaging plane.
As can be seen from the aberration graphs (a
spherical aberration graph, an astigmatism graph, and a
distortion graph) in Fig. 8, aberrations are
10 appropriately corrected, and excellent imaging
performance is achieved by the imaging lens 4 of the
fourth numerical example.
[2-5. Fifth Numerical Example]
In Fig. 9, reference numeralS indicates an entire
15 imaging lens in a fifth numerical example. A first lens
Gl having positive refractive power, an aperture stop
STO, a second lens G2 having positive or negative
refractive power, a third lens G3 having negative
refractive power, a fourth lens G4 having positive
20 refractive power, and a fifth lens G5 having negative
refractive power are provided in this order from the
object side. Positive power is forward in the entire
lens system.
In the imaging lens 5, sealing glass SG for
25 protecting an imaging plane IMG is provided between the
fifth lens G5 and the imaging plane IMG of an imaging
element.
In this imaging lens 5, a first lens (not shown)
having a four-lens structure is divided into two. While
30 the two divisional lenses (the first lens Gl and the
second lens G2) complement each other with power, the
54
number of aberration correction planes is increased by
two compared with that prior to the division.
With this arrangement in the imaging lens 5, the
first lens Gl and the second lens G2 complement each
5 other with power. Accordingly, a decrease in the
curvature radius of the first lens Gl can be restrained,
and an increase in the refractive power can also be
restrained. Thus, spherical aberration correction can be
performed. Also, coma aberration correction can be
10 performed, even if the lens aperture is made larger and
Fno is made smaller (brighter) to achieve higher image
quality.
Although separated in the imaging lens 5, the first
lens Gl and the second lens G2 are located very close to
15 each other, so that chromatic aberrations that have
occurred in the first lens Gl and the second lens G2 can
be offset by the third lens G3.
In the imaging lens 5, the aperture stop STO is
provided between the first lens Gl and the second lens G2
20 that are separated. Accordingly, distortions can be more
efficiently corrected than in a case where the aperture
stop STO is located closer to the object side than the
first lens Gl is. This also contributes to a decrease in
optical sensitivity, and assembling becomes easier in the
25 manufacturing procedures.
Further, in the imaging lens 5, the first lens Gl
has a convex surface facing the object side and has
positive refractive power. Accordingly, an achromatizing
effect can be achieved with the first lens Gl, the second
30 lens G2, and the third lens G3, while the refractive
power is increased.
55
In the imaging lens 5, the third lens G3 has a
concave surface on the imaging plane side. Accordingly,
even when an off-axis light beam is totally-reflected by
the concave surface, the totally-reflected off-axis light
5 beam diffuses to the lens peripheral portion and is
prevented from directly entering the imaging plane IMG of
a solid-state imaging element such as a CCD or CMOS.
Thus, formation of ghosts can be prevented.
In the imaging lens 5, the third lens G3 has the
10 concave surface on the imaging plane side, to effectively
correct field curvatures and coma aberrations. Further,
in the imaging lens 5, the fourth lens G4 has a meniscus
shape with positive power, to effectively correct
aberrations, particularly field curvatures and
15 astigmatisms.
Further, in the imaging lens 5, the second lens G2
has a convex surface facing the imaging plane side and
has positive or negative refractive power. Accordingly,
an achromatizing effect can be achieved with the second
20 lens G2 and the third lens G3.
Further, in the imaging lens 5, the fifth lens G5
has negative power in the vicinity of the axis, and
accordingly, is effective in correcting aberrations,
particularly field curvatures. The fifth lens G5 also
25 has a convex surface at the peripheral portion, and
accordingly, is effective in correcting astigmatisms and
distortions.
In the following, Table 9 shows the lens data
obtained when specific numerical values were applied to
30 the imaging lens 5 of the fifth numerical example
according to the embodiment, in conjunction with an F-
56
number FNo, a focal length f of the entire lens system,
and a field angle 200. In Table 9, each curvature radius
Ri of 00 means that the plane is a flat plane.
FNo=2.4 f=3.8 200=72.6°
. si Ri Di Ndi
Plane Curvature Plane Refractive vdi
number radius interval index Abbe number
1 2.895 0.445 1.535 56.3
2 -14.800 0.040 - -
3 (STO) 00 0.053 - -
4 11.139 0.476 1.535 56.3
5 -4.713 0.040 - -
6 13.787 0.300 1. 615 25.6
7 1. 991 0.635 - -
8 -3.105 0.758 1. 535 56.3
9 -1.144 0.040 - -
10 1. 775 0.550 1. 535 56.3
11 0.848 0.813 - -
12 00 0.150 1. 518 64.1
13 00 0.700 - -
5
Table 9 Lens Data in the Fifth Numerical Example
Table 10 shows the third-order, fourth-order,
fifth-order, sixth-order, seventh-order, eighth-order,
ninth-order, tenth-order, eleventh-order, and twelfthorder
aspheric coefficients of aspheric planes in the
10 imaging lens 5 of the fifth numerical example, in
conjunction with conic constants "K". In Table 10, "E02"
is an exponential expression using 10 as the base, or
represents "10-2
". For example, "0.12345E-05" represents
"0.12345 X 10-5
".
15
57
•
FNo=2.4 £=3.8 2ro=72.6°
Si K Third- Fourth- Fifth- Sixth- Seventh- Eighth- Ninth- Tenth- Eleventh Twelfth-
Plane Conic
number constant
order order order order order order order order -order order
1 -1.06E+01 - 2.60E-02 - -4.70E-02 - 6.66E-02 - -4.10E-02 - -
2 -1. 00E+01 - -5.46E-02 - 1. 22E-01 - -1.06E-01 - 1.10E-02 - -
3 (STO) - - - - - - - - - - -
4 1. 00E+01 - -6.72E-02 - 5.67E-02 - -7.18E-02 - -7.57E-02 - -
5 9.30E+00 - -1.84E-01 - 1. 44E-01 - -9.14E-02 - -7.72E-03 - -
6 1.95E-01 - -1.70E-01 - 8.69E-02 - 1.06E-01 - -7.10E-02 - -
7 1. 35E+00 1.98E-02 -7.99E-02 -1. 82E-02 -9.51E-03 8.59E-03 5.56E-02 2.57E-02 -5.32E-02 - -
8 1. 42E+00 2.47E-02 1.28E-01 -8.51E-02 1. 24E-02 1.76E-04 4.68E-03 1. 54E-02 -3.11E-02 1. 89E-02 -3.71E-03
9 -5.77E+00 -1.22E-01 3.17E-02 8.22E-02 -9.01E-02 4.07E-02 -1.11E-02 5.89E-03 4.26E-03 -2.31E-03 -7.26E-04
10 -4.21E+00 -1.27E-01 1. 40E-02 1.70E-02 -4.08E-02 2.44E-02 4.11E-03 -5.74E-03 1.03E-03 - -
11 -4.82E+00 1. 27E-02 -9.99E-02 4.40E-02 -3.54E-03 -2.50E-04 -7.38E-04 -1.82E-04 1.51E-04 - -
Table 10 Aspheric Plane Data in the Fifth Numerical Example
58
•
Fig. 10 shows aberrations in the imaging lens 5 of
the fifth numerical example. In the astigmatism graph,
the solid line indicates values in a sagittal imaging
5 plane, and the dashed line indicates values in a
meridional imaging plane.
As can be seen from the aberration graphs (a
spherical aberration graph, an astigmatism graph, and a
distortion graph) in Fig. 10, aberrations are
10 appropriately corrected, and excellent imaging
performance is achieved by the imaging lens 5 of the
fifth numerical example.
[2-6. Sixth Numerical Example]
In Fig. 11, reference numeral 6 indicates an entire
15 imaging lens in a sixth numerical example. A first lens
G1 having positive refractive power, an aperture stop
STO, a second lens G2 having positive or negative
refractive power, a third lens G3 having negative
refractive power, a fourth lens G4 having positive
20 refractive power, and a fifth lens G5 having negative
refractive power are provided in this order from the
object side. Positive power is forward in the entire
lens system.
In the imaging lens 6, sealing glass SG for
25 protecting an imaging plane IMG is provided between the
fifth lens G5 and the imaging plane IMG of an imaging
element.
In this imaging lens 6, a first lens (not shown)
having a four-lens structure is divided into two. While
30 the two divisional lenses (the first lens G1 and the
second lens G2) complement each other with power, the
59
•
number of aberration correction planes is increased by
two compared with that prior to the division.
With this arrangement in the imaging lens 6, the
first lens Gl and the second lens G2 complement each
5 other with power. Accordingly, a decrease in the
curvature radius of the first lens Gl can be restrained,
and an increase in the refractive power can also be
restrained. Thus, spherical aberration correction can be
performed. Also, coma aberration correction can be
10 performed, even if the lens aperture is made larger and
Fno is made smaller (brighter) to achieve higher image
quality.
Although separated in the imaging lens 6, the first
lens Gl and the second lens G2 are located very close to
15 each other, so that chromatic aberrations that have
occurred in the first lens Gl and the second lens G2 can
be offset by the third lens G3.
In the imaging lens 6, the aperture stop STO is
provided between the first lens Gl and the second lens G2
20 that are separated. Accordingly, distortions can be more
efficiently corrected than in a case where the aperture
stop STO is located closer to the object side than the
first lens Gl is. This also contributes to a decrease in
optical sensitivity, and assembling becomes easier in the
25 manufacturing procedures.
Further, in the imaging lens 6, the first lens Gl
has a convex surface facing the object side and has
positive refractive power. Accordingly, an achromatizing
effect can be achieved with the first lens Gl, the second
30 lens G2, and the third lens G3, while the refractive
power is increased.
60
In the imaging lens 6, the third lens G3 has a
concave surface on the imaging plane side. Accordingly,
even when an off-axis light beam is totally-reflected by
the concave surface, the totally-reflected off-axis light
5 beam diffuses to the lens peripheral portion and is
prevented from directly entering the imaging plane IMG of
a solid-state imaging element such as a CCD or CMOS.
Thus, formation of ghosts can be prevented.
In the imaging lens 6, the third lens G3 has the
10 concave surface on the imaging plane side, to effectively
correct field curvatures and coma aberrations. Further,
in the imaging lens I, the fourth lens G4 has a meniscus
shape with positive power, to effectively correct
aberrations, particularly field curvatures and
15 astigmatisms.
Further, in the imaging lens 6, the second lens G2
has a convex surface facing the imaging plane side and
has positive or negative refractive power. Accordingly,
an achromatizing effect can be achieved with the second
20 lens G2 and the third lens G3.
Further, in the imaging lens 6, the fifth lens G5
has negative power in the vicinity of the axis, and
accordingly, is effective in correcting aberrations,
particularly field curvatures. The fifth lens G5 also
25 has a convex surface at the peripheral portion, and
accordingly, is effective in correcting astigmatisms and
distortions.
In the following, Table 11 shows the lens data
obtained when specific numerical values were applied to
30 the imaging lens 6 of the sixth numerical example
according to the embodiment, in conjunction with an F-
61
number FNo, a focal length f of the entire lens system,
and a field angle 2m. In Table 12, each curvature radius
Ri of 00 means that the plane is a flat plane.
FNo=2.4 f=3.8 200=72.4°
Si Ri Di Ndi
Plane Curvature Plane Refractive vdi
number radius interval index Abbe number
1 2.859 0.438 1. 535 56.3
2 -21.025 0.064 - -
3 (STO) 00 0.100 - -
4 15.053 0.425 1. 535 56.3
5 10.644 0.204 - -
6 3.562 0.300 1.615 25.6
7 3.142 0.621 - -
8 -2.398 0.707 1.535 56.3
9 -1.000 0.137 - -
10 2.565 0.550 1. 535 56.3
11 0.866 0.605 - -
12 00 0.150 1. 518 64.1
13 00 0.700 - -
5
Table 11 Lens Data in the Sixth Numerical Example
Table 12 shows the third-order, fourth-order,
fifth-order, sixth-order, seventh-order, eighth-order,
ninth-order, and tenth-order aspheric coefficients of
aspheric planes in the imaging lens 6 of the sixth
10 numerical example, in conjunction with conic constants
"K". In Table 12, "E-02" is an exponential expression
using 10 as the base, or represents "10-2
". For example,
"0.12345E-05" represents "0.12345 x 10-5
".
62
•
FNo=2.4 f=3.8 20)=72.4°
Si K
Third- Fourth- Fifth- Sixth- Seventh- Eighth- Ninth- Tenth- Eleventh Twelfth-
Plane Conic
number constant
order order order order order order order order -order order
1 -1.06E+Ol - 3.27E-02 - -4.S4E-02 - S.74E-02 - -3.73E-02 - -
2 -1.00E+Ol - -2.99E-02 - S.78E-02 - -3.36E-02 - -2.13E-02 - -
3 (STO) - - - - - - - - - - -
4 1. OOE+Ol - -S.S2E-02 - S.60E-02 - -3.22E-02 - -8.67E-02 - -
5 9.30E+00 - -2 .11E- 01 - 1.20E-Ol - -8.30E-02 - -6.76E-03 - -
6 1. 9SE-Ol - -2.00E-Ol - S.03E-02 - 9.S9E-02 - -4.41E-02 - -
7 1.3SE+00 7.3SE-03 -8.12E-02 -S.63E-03 3.60E-03 1. 06E-02 4.I0E-02 1. 71E-02 -2.3SE-02 - -
8 1.42E+00 1. 78E-02 S.S8E-02 -7.0IE-02 2.84E-02 -1.2SE-02 -1. 72E-02 1.0IE-02 -1. 30E-02 3.32E-02 -2.16E-02
9 -4.3SE+00 -1.12E-Ol -3.40E-02 8.30E-02 -7.74E-02 4.46E-02 -1. 62E-02 -7.20E-04 S.28E-04 -1.S7E-03 3.10E-03
10 -4.21E+00 -1. 73E-Ol 1. 68E-02 2.70E-02 -3.92E-02 2.34E-02 3.6SE-03 -S.80E-03 1.I0E-03 - -
11 -4.82E+00 -6.62E-02 -1. 74E-02 1.I9E-02 -1.I7E-03 4.I9E-06 -1. 68E-04 -2.0SE-04 8.62E-OS - -
Table 12 Aspheric Plane Data in the Sixth Numerical Example
63
Fig. 12 shows aberrations in the imaging lens 6 of
the sixth numerical example. In the astigmatism graph,
the solid line indicates values in a sagittal imaging
5 plane, and the dashed line indicates values in a
meridional imaging plane.
As can be seen from the aberration graphs (a
spherical aberration graph, an astigmatism graph, and a
distortion graph) in Fig. 12, aberrations are
10 appropriately corrected, and excellent imaging
performance is achieved by the imaging lens 6 of the
sixth numerical example.
[2-7. Numerical Values According to the Respective
Conditional Expressions]
15 Table 13 shows respective numerical values
according to the conditional expressions (1) through (4)
for the imaging lenses 1 through 6 described in the first
through sixth numerical examples, and Table 14 shows the
respective numerical values that support those
20 conditional expressions in the first through sixth
numerical examples.
64
First Second Third Fourth Fifth Sixth
Conditional expression numerical numerical numerical numerical numerical numerical
example example example example example example
(1) 0.8020 26.00 46.07 30.71 30.71 30.71 46.07
(4) 0.50-'"QW:WJ! ,KX ¥ifLQ
As can be seen from Table 13, "fl/f" according to
the conditional expression (1) has a minimum value of
"0.87" and a maximum value of "1.30", which fall within
5 the numerical range, 0.8 < fl/f < 1.40, defined as the
conditional expression (1).
Also, as can be seen from Table 13, "fl /lf3 1"
according to the conditional expression (2) has a maximum
value of "1.20", which falls within the numerical range,
10 f l /lf3 1 < 1.50, defined as the conditional expression
(2) .
Further, as can be seen from Table 13, "fdf2 "
according to the conditional expression (3) has a minimum
value of "-0.07" and a maximum value of "0.66", which
15 fall within the numerical range, -0.20 < f l /f2 < 0.90,
defined as the conditional expression (3).
Further, as can be seen from Table 13, "(vdl +
vd2)/2 - vd3 " according to the conditional expression (4)
has a minimum value of "26.00", which falls within the
20 numerical range, (vdl + vd2)/2 - vd3 > 20, defined as the
conditional expression (4).
Further, as can be seen from Table 13, "Ifsl/f"
according to the conditional expression (5) has a minimum
value of "0.72" and a maximum value of "1.28", which fall
25 within the numerical range, 0.5 < Ifsl/f < 1.80, defined
as the conditional expression (5).
Accordingly, in the imaging lenses 1 through 6 in
the first through sixth numerical examples, all the above
mentioned conditional expressions (1) through (5) are
30 satisfied, and, as shown in the respective aberration
graphs, the respective aberrations of spherical
66
aberrations, astigmatisms, and distortions can be
corrected in a balanced manner.
<3. Structures of an Imaging Device and a Portable
Telephone Device>
5 [3-1. Structure of an Imaging Device]
The following is a description of an imaging device
formed by combining an imaging lens of the present
invention and an imaging element such as a CCD (Charge
Coupled Device) sensor or a CMOS (Complementary Metal
10 Oxide Semiconductor) sensor for converting an optical
image formed by the imaging lens into an electrical
signal.
In the following explanation, the imaging lens 1 of
the above described first numerical example is applied to
15 the imaging device. However, any of the imaging lenses 2
through 6 of the above described second through sixth
numerical examples can also be applied to the imaging
device.
In the imaging lens 1 (Fig. 1) provided in this
20 imaging device, a first lens Gl having positive
refractive power, an aperture stop STO, a second lens G2
having positive or negative refractive power, a third
lens G3 having negative refractive power, a fourth lens
G4 having positive refractive power, and a fifth lens G5
25 having negative refractive power are provided in this
order from the object side, and positive power is forward
in the entire lens system.
In this imaging lens I, if the total optical length
is shortened to reduce the size, the curvature radius of
30 a first lens (not shown) having a four-lens structure
becomes smaller, and the refractive power increases. As
67
a result, spherical aberration correction becomes
difficult. Also, in the imaging lens, if the lens
aperture is made larger and Fno is made smaller
(brighter) to achieve higher image quality, coma
5 aberration correction becomes difficult.
To effectively correct spherical aberrations and
coma aberrations that become larger as the size increases
and the aperture becomes larger, the first lens having a
four-lens structure is divided into two in the imaging
10 lens 1. While the two divisional lenses (the first lens
Gl and the second lens G2) complement each other with
power, the number of aberration correction planes is
increased by two compared with that prior to the
division.
15 With this arrangement in the imaging lens 1,
spherical and coma aberrations that have occurred in the
first lens Gl are restrained by the second lens G2, and
other aberrations can also be corrected by the two newlyformed
correction planes.
20 Although separated in the imaging lens 1, the first
lens Gl and the second lens G2 are located very close to
each other, so that chromatic aberrations that have
occurred in the first lens Gl and the second lens G2 can
be offset by the third lens G3.
25 In the imaging lens 1, the aperture stop STO is
provided between the first lens Gl and the second lens G2
that are separated. Accordingly, distortions can be more
efficiently corrected than in a case where the aperture
stop STO is located closer to the object side than the
30 first lens Gl is. This also contributes to a decrease in
optical sensitivity, and assembling becomes easier in the
68
manufacturing procedures.
Also, in this imaging lens I, it is preferable to
satisfy the following conditional expressions (I), (2),
and (3):
5
10
(1 ) 0.80 < fdf < 1.40,
(2 ) fll I f 3 1 < 1. 50, and
(3) -0.20 < fdf2 < 0.90,
where
f: the focal length of the entire lens system,
f l : the focal length of the first lens,
f 2 : the focal length of the second lens, and
f 3 : the focal length of the third lens.
The conditional expression (1) specified for the
imaging lens 1 is a conditional expression for specifying
15 an appropriate power allocation to the first lens Gl
relative to the power of the entire lens system in such a
lens structure.
If the upper limit value defined by the conditional
expression (1) is exceeded, the power of the first lens
20 Gl becomes too large, and off-axis aberration correction,
particularly astigmatism and field curvature correction,
becomes difficult. As a result, easiness of assembling
at the time of manufacture is reduced.
If the lower limit value defined by the conditional
25 expression (1) is not reached, on the other hand, the
power of the first lens Gl becomes too weak to shorten
the total optical length, and compactness might be
reduced. In view of this, satisfying the conditional
expression (1) is an essential condition in shortening
30 the total optical length in the imaging lens 1.
The conditional expression (2) specified for this
69
imaging lens 1 concerns appropriate power allocations to
the first lens Gl and the third lens G3. An absolute
value is used as the focal length of the third lens G3,
because the third lens G3 has negative power.
5 If the lower limit value defined by the conditional
expression (2) is not reached, the power of the first
lens Gl becomes too strong. As a result, spherical
aberration and off-axis coma aberration occurrences
increase, and aberration correction becomes difficult.
10 If the upper limit value defined by the conditional
expression (2) is exceeded, on the other hand, the power
of the first lens Gl becomes too weak to allow the first
lens Gl and the third lens G3 to perform appropriate
achromatizing. As a result, optical performance high
15 enough for high-pixel imaging elements cannot be
maintained. Also, in an imaging environment where a
strong power source exists, color bleeding (flare)
occurs, to adversely affect image quality.
Therefore, in the imaging lens I, the conditional
20 expression (2) is satisfied, so that the imaging lens is
made even thinner than a conventional lens, and optical
performance high enough for high-pixel imaging elements
can be achieved.
Further, the conditional expression (3) specified
25 for this imaging lens 1 is a conditional expression that
concerns appropriate power allocations to the first lens
Gl and the second lens G2.
If the lower limit value defined by this
conditional expression (3) is not reached, the power of
30 the second lens G2 becomes too weak, and a large
proportion of the load is put on the first lens Gl. As a
70
result, spherical aberration and off-axis coma aberration
occurrences increase, and correcting the spherical
aberration and the off-axis coma aberration becomes
difficult. This also hinders achromatizing with the
5 third lens G3, and therefore, optical performance high
enough for high-pixel imaging elements cannot be
maintained.
If the upper limit value defined by the conditional
expression (3) is exceeded, on the other hand, the power
10 of the second lens G2 becomes too strong. As a result,
sensitivity in manufacture becomes higher, and easiness
of assembling is reduced at the time of manufacture.
Therefore, in the imaging lens 1, the conditional
expression (3) is satisfied, so that optical performance
15 high enough for high-pixel imaging elements can be
achieved while the power allocations to the first lens G1
and the second lens G2 are optimized.
Further, in this imaging lens 1, it is preferable
to satisfy the following conditional expression (4):
20 (4) (vd1 + vd2 ) /2 - vd3 > 20
where
vd1 : the Abbe number of the first lens,
vd2 : the Abbe number of the second lens, and
vd3 : the Abbe number of the third lens.
25 This conditional expression (4) defines the Abbe
numbers of the first through third lenses G1 through G3
at a d-line single wavelength. Such a glass material
that the Abbe number falls within the range defined by
the conditional expression (4) is used for each of the
30 first lens G1, the second lens G2, and the third lens G3
in the imaging lens 1, so that excellent chromatic
71
•
aberration correction can be performed without a large
increase in the power of each lens.
If the lower limit value defined by the conditional
expression (4) is not reached in the imaging lens I,
5 color bleeding (flare) occurs to adversely affect image
quality. If the conditional expression (4) is satisfied,
the power of each lens does not become very strong.
Accordingly, coma aberration and field curvature
occurrences can be restrained in the surrounding area,
10 and furthermore, sensitivity in manufacture can be
effectively restrained.
Therefore, in the imaging lens I, the conditional
expression (4) is satisfied, so that excellent chromatic
aberration correction can be performed, and coma
15 aberration and field curvature occurrences are restrained
in the surrounding area to lower the sensitivity in
manufacture.
Further, in the imaging lens I, the relationship
between the focal length of the entire lens system and
20 the focal length of the fifth lens G5 satisfies the
following conditional expression (5):
(5) 0.5 < Ifsl/f < 1.8
where
f: the focal length of the entire lens system, and
25 f s : the focal length of the fifth lens.
The conditional expression (5) specified for this
imaging lens 1 is a conditional expression that concerns
an appropriate power allocation to the fifth lens G5
relative to the power of the entire lens system.
30 If the lower limit value defined by the conditional
expression (5) is not reached, the power of the fifth
72
lens G5 becomes too strong. As a result, appropriate
field correction (correction to achieve uniform resolving
power from the axis to the surrounding area) becomes
difficult. Also, optical sensitivity becomes higher, and
5 easiness of assembling is reduced in manufacture.
If the upper limit value defined by the conditional
expression (5) is exceeded, on the other hand, the power
of the fifth lens G5 becomes too weak, and appropriate
aberration correction, particularly field correction
10 (according to the Petzval's law), becomes difficult.
Therefore, in the imaging lens I, the conditional
expression (5) is satisfied, so that optical performance
high enough for high-pixel imaging elements can be
achieved while the power allocation to the fifth lens G5
15 relative to the entire lens system is optimized.
Also, in the imaging lens I, the first lens Gl has
a convex surface facing the object side and has positive
refractive power. Accordingly, an achromatizing effect
can be achieved with the first lens Gl, the second lens
20 G2, and the third lens G3, while the refractive power is
increased.
In the imaging lens I, the third lens G3 has a
concave surface on the imaging plane side. Accordingly,
even when an off-axis light beam is totally-reflected by
25 the concave surface, the totally-reflected off-axis light
beam diffuses to the lens peripheral portion and is
prevented from directly entering a solid-state imaging
element such as a CCD or CMOS. Thus, formation of ghosts
can be prevented.
30 In the imaging lens I, the third lens G3 has the
concave surface on the imaging plane side, to effectively
73
correct field curvatures and coma aberrations. Further,
in the imaging lens 1, the fourth lens G4 has a meniscus
shape with positive power, to effectively correct
aberrations, particularly field curvatures and
5 astigmatisms.
Further, in the imaging lens 1, the second lens G2
has a convex surface facing the imaging plane side and
has positive or negative refractive power. Accordingly,
an achromatizing effect can be achieved with the second
10 lens G2 and the third lens G3.
Further, in the imaging lens 1, the fifth lens G5
has negative power in the vicinity of the axis, and
accordingly, is effective in correcting aberrations,
particularly field curvatures. At the same time, the
15 fifth lens G5 also has a convex surface at the peripheral
portion, and accordingly, is effective in correcting
astigmatisms and distortions.
In the imaging lens 1, the above described
conditions are satisfied, so that contrast degradation
20 due to ghosts and flares can be reduced, and optical
performance high enough for high-pixel imaging elements
can be achieved, while the imaging lens is made very
small and thin.
[3-2. Structure of a Portable Telephone Device Having an
25 Imaging Device Mounted Thereon]
Next, a portable telephone device having an imaging
device of the present invention mounted thereon is
described.
As shown in Figs. 13 and 14, a portable telephone
30 device 100 has a display unit 101 and a main body unit
102 foldably connected to each other via a hinge unit
74
•
103. When being carried around, the display unit 101 and
the main body unit 102 are in a folded state (Fig. 13).
During a call, the display unit 101 and the main body
unit 102 are in an opened state (Fig. 14).
5 A liquid crystal display panel 111 is provided on
one of the surfaces of the display unit 101, and a
speaker 112 is provided above the liquid crystal display
panel 111. An imaging device 107 is incorporated into
the display unit 101, and an infrared communication unit
10 104 for performing infrared wireless communication is
provided at the top end of the imaging device 107.
Also, a cover lens 105 located on the object side
of the first lens in the imaging device 107 is provided
on the other surface of the display unit 101.
15 Various operation keys 113 such as numeric keys and
a power key are provided on one of the surfaces of the
main body unit 102, and a microphone 114 is provided at
the lower end of the main body unit 102. A memory card
slot 106 is formed in a side surface of the main body
20 unit 102, so that a memory card 120 can be inserted and
detached to and from the memory card slot 106.
As shown in Fig. 13, the portable telephone device
100 includes a CPU (Central processing Unit) 130, so that
a control program stored in a ROM (Read Only Memory) 131
25 is loaded into a RAM (Random Access Memory) 132, and the
entire portable telephone device 100 is integrally
controlled via a bus 133.
The portable telephone device 100 includes a camera
control unit 140, and controls the imaging device 107 via
30 the camera control unit 140, to capture still images or
moving images.
75
The camera control unit 140 performs a compression
process compliant with JPEG (Joint Photographic Experts
Group) or MPEG (Moving Picture Expert Group) on image
data obtained by capturing images through the imaging
5 device 107. The resultant image data is transmitted to
the CPU 130, a display control unit 134, a communication
control unit 160, a memory card interface 170, or an
infrared interface 135 via the bus 133.
This imaging device 107 is formed by combining one
10 of the imaging lenses 1 through 6 of the first through
sixth numerical examples and an imaging element SS formed
with a CCD sensor, a CMOS sensor, or the like.
In the portable telephone device 100, the CPU 130
temporarily stores image data supplied from the camera
15 control unit 140 into the RAM 132, or stores the image
data into the memory card 120 via the memory card
interface 170 where necessary, or outputs the image data
to the liquid crystal display panel 111 via the display
control unit 134.
20 Also, in the portable telephone device 100, audio
data recorded through the microphone 114 at the same time
as image capturing is temporarily stored into the RAM 132
via an audio codec 150, or is stored into the memory card
120 through the memory card interface 170 where
25 necessary, or is output from the speaker 112 via the
audio codec 150 at the same time as displaying of an
image on the liquid crystal display panel 111.
The portable telephone device 100 is designed to
output image data and audio data to the outside via the
30 infrared interface 135 and the infrared communication
unit 104, and transmit the image data and the audio data
76
to another electronic device having an infrared
communication function, such as a portable telephone
device, a personal computer, or a PDA (Personal Digital
Assistant) .
5 In a case where a moving image or a still image is
to be displayed on the liquid crystal display panel 111
based on image data stored in the RAM 132 or the memory
card 120 in the portable telephone device 100, the image
data is decoded or decompressed by the camera control
10 unit 140, and is then output to the liquid crystal
display panel 111 via the display control unit 134.
The communication control unit 160 is designed to
transmit and receive radio waves to and from base
stations via an antenna (not shown), and, in a voice
15 communication mode, perform predetermined processing on
received audio data and then output the audio data to the
speaker 112 via the audio codec 150.
The communication control unit 160 is also designed
to perform predetermined processing on audio signals
20 collected by the microphone 114 via the audio codec 150,
and then transmit the audio signals through the antenna
(not shown).
In this imaging device 107, the incorporated one of
the imaging lenses 1 through 6 can have a smaller size
25 and a larger aperture while shortening the total optical
length as described above. Accordingly, this imaging
device 107 is advantageous when mounted on an electronic
device required to be smaller in size, such as a portable
telephone device.
30 <4. Other Embodiments>
It should be noted that the specific shapes,
77
structures, and numerical values mentioned in the above
described embodiments and the first through sixth
numerical examples are merely examples for carrying out
the present invention, and do not limit the technical
5 scope of the invention.
In the above described embodiments, the specific
numerical values shown in Table 13 are used based on the
first through sixth numerical examples. However, the
present invention is not limited to those embodiments,
10 and other various specific shapes, structures, and
numerical values may be used within the range satisfying
the conditional expressions (.1) through (5).
Also, in the above described embodiments, the
imaging lens has the above described power layout, and is
15 designed to satisfy the conditional expressions (1)
through (5). However, the present invention is not
limited to that, and the imaging lens may have the above
described power layout and satisfy only the conditional
expressions (1), (2), (3), and (5).
20 Further, in the above described embodiments, the
first lens used in the imaging lens has a convex surface
facing the object side, and has positive refractive
power. However, the present invention is not limited to
that, and a first lens that has a concave surface facing
25 the object side and has positive refractive power may be
used.
Further, in the above described embodiment, the
portable telephone device 100 has been described as an
example of an electronic device having an imaging lens
30 mounted thereon. However, specific examples of imaging
devices are not limited to that, and the present
78
invention can be applied to other various electronic
devices such as digital still cameras, digital video
cameras, personal computers equipped with cameras, and
PDAs having cameras incorporated thereinto.
5
REFERENCE SIGNS LIST
1, 2, 3, 4, 5, 6 ... Imaging lens, G1 First lens,
G2 Second lens, G3 Third lens, G4 Fourth lens,
G5 Fifth lens, SG Sealing glass, IMG ... Imaging plane,
10 100 Portable telephone device, 101 ... Display unit,
102 Main body unit, 103 Hinge unit, 104 Infrared
communication unit, 105 Cover lens, 106 Memory card
slot, 107 Imaging device, 111 ... Liquid crystal display
panel, 112 Speaker, 113 ... Operation keys,
15 114 Microphone, 120 ... Memory card, 130 ... CPU,
131 ROM, 132 ... RAM, 134 ... Display control unit,
135 Infrared interface, 140 ... Camera control unit,
150 Audio codec, 160 ... Communication control unit,
170 Memory card interface

CLAIMS
1. An imaging lens comprising, in order from an object
side, a first lens having positive refractive power, an
5 aperture stop, a second lens having positive or 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, the
imaging lens satisfying the following conditional
10 expressions (I), (2), and (3) :
(1) 0.80 < fl/f < 1.40,
(2) fl/lf31 < 1.50, and
(3) -0.20 < fl/f2 < 0.90,
where
15 f represents a focal length of the entire lens system,
fl represents a focal length of the first lens,
f2 represents a focal length of the second lens, and
f3 represents a focal length of the third lens.
20 2. The imaging lens according to claim 1, wherein the
following conditional expression (4) is satisfied:
(4) (vdl + vd2)/2 - vd3 > 20
where
vdl represents an Abbe number of the first lens,
25 vd2 represents an Abbe number of the second lens, and
vd3 represents an Abbe number of the third lens.
3. The imaging lens according to claim 1 or 2, wherein
a relationship between the focal length of the entire
30 lens system and a focal length of the fifth lens
satisfies the following conditional expression (5) :
(5) 0.5 < (f51/f < 1.8,
where
f represents the focal length of the entire lens system,
and
5 f, represents the focal length of the fifth lens.
4. The imaging lens according to any of claims 1 to 3,
wherein the first lens has a convex surface facing the
object side.
10
5. The imaging lens according to any of claims 1 to 3,
wherein the third lens has a concave surface facing an
imaging plane side.
15 6. The imaging lens according to any of claims 1 to 3,
wherein the second lens has a convex surface facing an
imaging plane side.
7. An imaging device comprising an imaging lens, and
20 an imaging element configured to convert an optical image
formed by the imaging lens into an electrical signal,
wherein the imaging lens comprises, in order from
an object side, a first lens having positive refractive
power, an aperture stop, a second lens having positive or
25 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, the imaging lens satisfying the
following conditional expressions (I), (2), and (3):
30 (1) 0.80 < fl/f < 1.40,
(2) fl/lf31 < 1.50, and
where > 8
i
f represents a focal-length of an entire . lens system, -
f, represents a focal length,of the first lens,
5 f2 represents a focal length of the second lens, and
f3 represents a focal length of the third lens.