JP2010048996A - Imaging lens - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a small imaging lens of five sheet constitution that includes sufficient brightness of about F2.2 and includes sufficiently corrected aberrations. <P>SOLUTION: The imaging lens forms a subject image on a photoelectric conversion section of a solid imaging element. The imaging lens includes sequentially from an object side: a positive first lens; a negative second lens; a positive third lens; a negative fourth lens; and a negative fifth lens, and establishes the following conditional expression, 45&lt;&nu;4 (1). Here, &nu;4 is Abbe number of the fourth lens. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a small and bright imaging lens using a solid-state imaging device such as a CCD type image sensor or a CMOS type image sensor.

  In recent years, with the widespread use of portable terminals equipped with an imaging device using a solid-state imaging device such as a CCD type image sensor or a CMOS type image sensor, imaging having a high number of pixels so that a higher quality image can be obtained. A device equipped with an imaging device using an element has been supplied to the market. Although the image pickup device having the high number of pixels has been accompanied by an increase in size, in recent years, an increase in the size of pixels has progressed, and the image pickup device has been reduced in size. An imaging lens used for such a high-definition imaging device is required to have a high resolving power, but the resolving power is limited by the F value, and a bright lens with a small F value can obtain a high resolving power. As in the past, with an F value of about F2.8, sufficient performance cannot be obtained. Accordingly, there has been a demand for a bright imaging lens of about F2.2 that is suitable for imaging devices with high pixels, thinning, and miniaturization. As an imaging lens for such applications, an imaging lens having a five-lens configuration is proposed that can have a large aperture ratio and high performance as compared with a lens having three or four lenses.

As a five-lens imaging lens, in order from the object side, a first lens having a positive or negative refractive power, a front group consisting of a second lens having a positive refractive power, an aperture stop, and a third lens having a negative refractive power. An imaging lens configured by a rear group including a lens, a fourth lens having a positive refractive power, and a fifth lens having a negative or positive refractive power is disclosed. (For example, see Patent Documents 1 and 2)
JP 2007-279282 A JP 2006-293042 A

  However, since the imaging lens described in Patent Document 1 is configured with a spherical system in the front group, when the lens is brightened to about F2.2, correction of spherical aberration and coma is insufficient and good performance cannot be ensured. Also, because the front group and rear group have positive refractive power, the main point position of the optical system is on the image side and back focus compared to the configuration of the telephoto type where the rear group has negative refractive power. This is a disadvantageous type for downsizing.

  The imaging lens described in Patent Document 2 has a brightness of about F2.2. However, since both the first lens and the second lens have positive refractive power, color correction in the front group is performed. Is insufficient. Further, as in Patent Document 1, both the front group and the rear group have a positive refractive power, and the final lens is also a positive lens, which is a disadvantageous type for downsizing.

  The present invention has been made in view of such a problem, and has an object to provide a five-lens imaging lens having a small size, sufficient brightness of about F2.2, and various aberrations corrected satisfactorily. To do.

  The object is achieved by the invention described below.

1. An imaging lens for forming a subject image on a photoelectric conversion unit of a solid-state imaging device,
A positive first lens, a negative second lens, a positive third lens, a negative fourth lens, and a negative fifth lens are arranged in order from the object side, and satisfy the following conditional expression: Imaging lens.

45 <ν4 (1)
However,
ν4: Abbe number of the fourth lens 2. The imaging lens according to 1 above, wherein the first lens satisfies the following conditional expression.

1.45 <f / f1 <3.4 (2)
However,
f: focal length of the entire system f1: focal length of the first lens The imaging lens according to 1 or 2, wherein the second lens satisfies the following conditional expression.

−3.0 <f / f2 <−1.1 (3)
However,
f: focal length of the entire system f2: focal length of the second lens The imaging lens according to any one of 1 to 3, wherein the second lens satisfies the following conditional expression.

0.3 <(R3 + R4) / (R3-R4) <1.4 (4)
However,
4. R3: radius of curvature of object side surface of the second lens R4: radius of curvature of image side surface of the second lens The imaging lens according to any one of 1 to 4, wherein the fifth lens satisfies the following conditional expression.

0.06 <t10 / f <0.16 (5)
However,
f: focal length of entire system t10: axial thickness of the fifth lens The image side surface of the fourth lens is formed as an aspheric surface, has a negative refractive power at the center thereof, becomes weaker toward the periphery, and has an inflection point. The imaging lens according to any one of 1 to 5.

  7). 7. The imaging lens according to any one of 1 to 6, wherein the imaging lens is made of a plastic material.

The basic configuration of the present invention for obtaining an imaging lens that is small and has good aberration correction is, in order from the object side, a positive first lens, a negative second lens, a positive third lens, It consists of a negative fourth lens and a negative fifth lens. This so-called telephoto type lens configuration in which a positive lens group including a first lens, a second lens, a third lens, and a fourth lens and a negative fifth lens are arranged in this order from the object side is a compact imaging lens having a total length. This is an advantageous configuration.

  Furthermore, by using three negative lenses in the five-lens configuration, it is possible to easily correct the Petzval sum by increasing the diverging surface, and to obtain an imaging lens that ensures good imaging performance up to the periphery of the screen It becomes possible.

  In particular, when three negative lenses are used and the conditional expression (1) is satisfied, the correction of biased axial chromatic aberration and lateral chromatic aberration is suppressed, and a well-balanced correction effect can be obtained.

Effect of Claim 2 Conditional expression (2) is a conditional expression for appropriately setting the focal length of the first lens and appropriately achieving shortening of the entire length of the imaging lens and correction of aberration. When the value of conditional expression (1) exceeds the lower limit, the focal length of the first lens can be appropriately maintained, and shortening of the total lens length can be achieved. On the other hand, when the value is lower than the upper limit, the focal length of the first lens does not become too small, and generation of higher-order spherical aberration and coma aberration can be suppressed.

  Moreover, the range of the following formula is more desirable.

1.51 <f / f1 <2.5
Effect of Claim 3 Conditional expression (3) is a conditional expression for appropriately setting the focal length of the second lens and appropriately achieving shortening of the entire length of the imaging lens and correction of aberration. When the value of conditional expression (2) exceeds the lower limit, the focal length of the second lens can be appropriately maintained, and shortening of the total lens length can be achieved. On the other hand, when the value is below the upper limit, the absolute value of the focal length of the second lens does not become too large, and generation of higher-order spherical aberration and coma aberration can be suppressed.

  Moreover, the range of the following formula is more desirable.

−2.2 <f / f2 <−1.3
Effect of Claim 4 Conditional expression (4) is a conditional expression for appropriately setting the aberration correction in the second lens and the size in the lens radial direction. When the value of conditional expression (4) exceeds the lower limit, the lens diameter of the second lens can be appropriately maintained, and the size reduction of the entire lens system in the radial direction can be achieved. On the other hand, by being below the upper limit, the aberration correction by the second lens can be corrected in a balanced manner on both sides without being biased toward the image side surface.

  Moreover, the range of the following formula is more desirable.

0.45 <(R3 + R4) / (R3-R4) <1.1
Effect of Claim 5 Conditional expression (5) is a conditional expression for appropriately setting the axial thickness of the fifth lens and appropriately achieving the image surface property of the imaging lens. When the value of conditional expression (5) falls within the range, it is possible to prevent the image plane property of the imaging lens from falling too much toward the over side or the under side.

  Moreover, the range of the following formula is more desirable.

0.09 <t10 / f <0.14
Effect of Claim 6 The image side surface of the fourth lens has a negative refracting power that decreases from the optical axis toward the periphery, and an aspherical shape having an inflection point, so that the telecentric characteristic of the image side light beam is ensured. It becomes easy to do. Further, the image side surface of the third lens does not need to excessively weaken the negative refractive power at the periphery of the lens, and the off-axis aberration can be corrected well.

  Here, the “inflection point” is a point on the aspheric surface where the tangent plane of the aspheric vertex is a plane perpendicular to the optical axis in the curve of the lens cross-sectional shape within the effective radius.

In recent years, for the purpose of downsizing the entire solid-state imaging device, even a solid-state imaging device having the same number of pixels has been developed with a small pixel pitch and consequently a small imaging surface size. In such an imaging lens for a solid-state imaging device having a small imaging surface size, it is necessary to relatively shorten the focal length of the entire system, so that the curvature radius and the outer diameter of each lens are considerably reduced. Therefore, compared to glass lenses manufactured by time-consuming polishing, all lenses are made of plastic lenses manufactured by injection molding, so that even lenses with small radii of curvature and outer diameters are inexpensive. Mass production is possible. In addition, since the plastic lens can lower the press temperature, it is possible to suppress the wear of the molding die, and as a result, the number of replacements and maintenance times of the molding die can be reduced, and the cost can be reduced.

  Examples of the imaging lens of the present invention are shown below. Symbols used in each example are as follows.

f: Focal length of the entire imaging lens fB: Back focus F: F number 2Y: Diagonal length of the imaging surface of the solid-state imaging device R: Radius of curvature D: Spacing on the axis Nd: Refractive index of lens material with respect to d-line νd: Lens material Further, in each example, the surface described with “*” after each surface number is a surface having an aspherical shape, and the aspherical shape has an apex at the surface as the origin and the optical axis direction. Is expressed by the following “Equation 1” where the height in the direction perpendicular to the optical axis is h.

However,
Ai: i-th order aspheric coefficient R: radius of curvature K: conic constant Further, in the aspheric coefficient, a power of 10 (for example, 2.5 × 10 ⁻⁰² ) is used by E (for example, 2.5E-02). It shall represent.
Example 1
The overall specifications are shown below.

f = 5.949mm
fB = 0.500mm
F = 2.2
2Y = 7.2mm
The surface data is shown below.
Surface number R (mm) D (mm) Nd νd
1 (aperture) ∞ 0.000
2 (*) 3.848 1.744 1.5305 55.7
3 (*) -2.939 0.050
4 (*) -84.372 0.786 1.5834 30.2
5 (*) 2.319 0.760
6 (*) -11.368 1.448 1.5305 55.7
7 (*) -1.845 0.100
8 (*) 4.263 0.650 1.5305 55.7
9 (*) 1.739 0.368
10 (*) 7.872 0.650 1.5305 55.7
11 (*) 3.415 0.624
12 ∞ 0.300 1.5168 64.2
13 ∞
All the lenses are made of a plastic material.

The aspheric coefficient is shown below.
Second side
K = -0.59210E + 00, A4 = -0.56653E-02, A6 = 0.15475E-03, A8 = -0.19293E-02, A10 = 0.12381E-03
Third side
K = -0.19350E + 01, A4 = -0.12540E-02, A6 = -0.77825E-02, A8 = 0.27710E-02, A10 = -0.53117E-03
4th page
K = 0.22939E + 04, A4 = -0.29649E-01, A6 = 0.11868E-02, A8 = 0.31394E-02, A10 = -0.58894E-03
5th page
K = -0.24719E + 01, A4 = -0.13764E-01, A6 = 0.47263E-02, A8 = -0.12221E-03,
A10 = 0.21429E-03, A12 = -0.58986E-04
6th page
K = 0.11026E + 02, A4 = 0.26380E-01, A6 = -0.86116E-02, A8 = 0.19403E-02,
A10 = -0.20520E-03, A12 = 0.13618E-04
7th page
K = -0.45605E + 01, A4 = -0.17547E-01, A6 = 0.43663E-02, A8 = -0.87483E-03,
A10 = 0.15770E-03, A12 = -0.10199E-04
8th page
K = -0.34613E + 01, A4 = -0.49284E-01, A6 = 0.56693E-02, A8 = -0.17679E-03,
A10 = -0.18418E-04, A12 = 0.93104E-06
9th page
K = -0.43249E + 01, A4 = -0.23758E-01, A6 = 0.37364E-02, A8 = -0.47059E-03,
A10 = 0.30634E-04, A12 = -0.89096E-06
10th page
K = -0.11231E + 02, A4 = -0.42865E-02, A6 = 0.43380E-04, A8 = 0.17022E-04,
A10 = 0.59641E-06, A12 = -0.48186E-07
11th page
K = -0.14983E + 02, A4 = -0.10336E-01, A6 = 0.67881E-03, A8 = -0.55582E-05,
A10 = -0.47360E-06, A12 = 0.41243E-07
Single lens data is shown below.
Lens Start surface Focal length (mm)
1 2 3.449
2 4 -3.855
3 6 3.943
4 8 -6.078
5 10 -11.978
The values corresponding to each conditional expression are shown below.

ν4 = 55.7
f / f1 = 1.725
f / f2 = −1.543
(R3 + R4) / (R3-R4) = 0.947
t10 / f = 0.109
1 is a cross-sectional view of the imaging lens of Example 1. FIG. In the figure, L1 is a first lens, L2 is a second lens, L3 is a third lens, L4 is a fourth lens, L5 is a fifth lens, S is an aperture stop, and I is an imaging surface. F is a parallel plate that assumes an optical low-pass filter, an IR cut filter, a seal glass of a solid-state image sensor, and the like. FIG. 2 is an aberration diagram (spherical aberration, astigmatism, distortion) of the imaging lens of Example 1.
(Example 2)
The overall specifications are shown below.

f = 5.629 mm
fB = 0.500mm
F = 2.2
2Y = 7.2mm
The surface data is shown below.
Surface number R (mm) D (mm) Nd νd
1 (aperture) ∞ 0.000
2 (*) 4.487 1.733 1.5305 55.7
3 (*) -2.892 0.100
4 (*) -27.229 0.953 1.5834 30.2
5 (*) 2.590 0.659
6 (*) -16.884 1.436 1.5305 55.7
7 (*) -2.414 0.100
8 (*) 3.142 0.600 1.5305 55.7
9 (*) 1.762 0.334
10 (*) 2.462 0.600 1.5305 55.7
11 (*) 1.994 0.685
12 ∞ 0.300 1.5168 64.2
13 ∞
All the lenses are made of a plastic material.

The aspheric coefficient is shown below.
Second side
K = -0.14770E + 01, A4 = -0.57769E-02, A6 = -0.15662E-02, A8 = -0.83629E-03,
A10 = -0.11239E-03
Third side
K = -0.13531E + 01, A4 = -0.27407E-02, A6 = -0.49698E-02, A8 = 0.13375E-02, A10 = -0.27696E-03
4th page
K = 0.30000E + 02, A4 = -0.22845E-01, A6 = 0.65590E-03, A8 = 0.16894E-02, A10 = -0.23691E-03
5th page
K = -0.25176E + 01, A4 = -0.97960E-02, A6 = 0.27368E-02, A8 = -0.24306E-03,
A10 = 0.91554E-04, A12 = -0.12528E-04
6th page
K = -0.61130E + 01, A4 = 0.21094E-01, A6 = -0.52670E-02, A8 = 0.10117E-02,
A10 = -0.83043E-04, A12 = 0.55844E-05
7th page
K = -0.34732E + 01, A4 = -0.11227E-01, A6 = 0.28221E-02, A8 = -0.43003E-03,
A10 = 0.79132E-04, A12 = -0.79038E-06
8th page
K = -0.43887E + 01, A4 = -0.36756E-01, A6 = 0.34840E-02, A8 = -0.12406E-03,
A10 = -0.10210E-04, A12 = 0.82727E-06
9th page
K = -0.39343E + 01, A4 = -0.19770E-01, A6 = 0.20377E-02, A8 = -0.23156E-03,
A10 = 0.13159E-04, A12 = -0.26279E-06
10th page
K = -0.10236E + 02, A4 = -0.13594E-01, A6 = 0.44884E-03, A8 = 0.36946E-04,
A10 = 0.70507E-06, A12 = -0.13431E-06
11th page
K = -0.62333E + 01, A4 = -0.13741E-01, A6 = 0.32070E-03, A8 = 0.31411E-04, A10 = 0.50738E-06,
A12 = -0.10341E-06
Single lens data is shown below.
Lens Start surface Focal length (mm)
1 2 3.609
2 4 -4.007
3 6 5.134
4 8 -8.902
5 10 -35.597
The values corresponding to each conditional expression are shown below.

ν4 = 55.7
f / f1 = 1.560
f / f2 = −1.405
(R3 + R4) / (R3-R4) = 0.826
t10 / f = 0.107
FIG. 3 is a cross-sectional view of the imaging lens of the second embodiment. In the figure, L1 is a first lens, L2 is a second lens, L3 is a third lens, L4 is a fourth lens, L5 is a fifth lens, S is an aperture stop, and I is an imaging surface. F is a parallel plate that assumes an optical low-pass filter, an IR cut filter, a seal glass of a solid-state image sensor, and the like. FIG. 4 is an aberration diagram (spherical aberration, astigmatism, distortion) of the imaging lens of Example 2.
(Example 3)
The overall specifications are shown below.

f = 5.200mm
fB = 0.500mm
F = 2.2
2Y = 7.2mm
The surface data is shown below.
Surface number R (mm) D (mm) Nd νd
1 (aperture) ∞ 0.000
2 (*) 3.818 1.619 1.5305 55.7
3 (*) -2.685 0.062
4 (*) -9.830 0.837 1.5834 30.2
5 (*) 2.844 0.680
6 (*) -6.511 1.261 1.5305 55.7
7 (*) -1.953 0.050
8 (*) 2.847 0.600 1.5305 55.7
9 (*) 1.728 0.247
10 (*) 2.504 0.600 1.5305 55.7
11 (*) 1.862 0.740
12 ∞ 0.300 1.5168 64.2
13 ∞
All the lenses are made of a plastic material.

The aspheric coefficient is shown below.
Second side
K = -0.10256E + 01, A4 = -0.48351E-02, A6 = -0.27601E-02, A8 = -0.41626E-03,
A10 = -0.62403E-03
Third side
K = -0.96216E + 00, A4 = -0.42254E-02, A6 = -0.59181E-02, A8 = 0.17037E-02, A10 = -0.46446E-03
4th page
K = 0.20443E + 02, A4 = -0.30036E-01, A6 = 0.24382E-02, A8 = 0.18604E-02, A10 = -0.12427E-03
5th page
K = -0.35691E + 01, A4 = -0.90071E-02, A6 = 0.31872E-02, A8 = -0.38993E-03,
A10 = 0.88658E-04, A12 = -0.51420E-05
6th page
K = -0.30269E + 01, A4 = 0.23636E-01, A6 = -0.75619E-02, A8 = 0.11000E-02,
A10 = -0.30408E-04, A12 = -0.11264E-04
7th page
K = -0.21070E + 01, A4 = -0.82588E-02, A6 = 0.23338E-02, A8 = -0.74860E-03,
A10 = 0.13866E-03, A12 = -0.31432E-06
8th page
K = -0.44235E + 01, A4 = -0.37339E-01, A6 = 0.35759E-02, A8 = -0.84348E-04,
A10 = -0.83679E-05, A12 = 0.45025E-06
9th page
K = -0.39589E + 01, A4 = -0.20259E-01, A6 = 0.21464E-02, A8 = -0.23547E-03,
A10 = 0.13610E-04, A12 = -0.31509E-06
10th page
K = -0.13150E + 02, A4 = -0.84996E-02, A6 = 0.61261E-03, A8 = -0.15591E-04,
A10 = 0.58399E-06, A12 = 0.10743E-07
11th page
K = -0.65023E + 01, A4 = -0.13867E-01, A6 = 0.93903E-03, A8 = -0.96760E-05,
A10 = -0.20072E-05, A12 = 0.11702E-06
Single lens data is shown below.
Lens Start surface Focal length (mm)
1 2 3.252
2 4 -3.691
3 6 4.800
4 8 -10.179
5 10 -20.246
The values corresponding to each conditional expression are shown below.

ν4 = 55.7
f / f1 = 1.599
f / f2 = -1.409
(R3 + R4) / (R3-R4) = 0.551
t10 / f = 0.115
FIG. 5 is a cross-sectional view of the imaging lens of the third embodiment. In the figure, L1 is a first lens, L2 is a second lens, L3 is a third lens, L4 is a fourth lens, L5 is a fifth lens, S is an aperture stop, and I is an imaging surface. F is a parallel plate that assumes an optical low-pass filter, an IR cut filter, a seal glass of a solid-state image sensor, and the like. FIG. 6 is an aberration diagram (spherical aberration, astigmatism, distortion) of the imaging lens of Example 3.
Example 4
The overall specifications are shown below.

f = 4.800mm
fB = 0.500mm
F = 2.2
2Y = 7.2mm
The surface data is shown below.
Surface number R (mm) D (mm) Nd νd
1 (aperture) ∞ 0.000
2 (*) 5.042 1.619 1.5305 55.7
3 (*) -2.107 0.050
4 (*) -9.768 0.887 1.5834 30.2
5 (*) 2.373 0.428
6 (*) -15.724 1.572 1.5305 55.7
7 (*) -1.791 0.050
8 (*) 5.773 0.600 1.5305 55.7
9 (*) 2.127 0.050
10 (*) 1.813 0.600 1.5305 55.7
11 (*) 1.483 0.865
12 ∞ 0.300 1.5168 64.2
13 ∞
All the lenses are made of a plastic material.

The aspheric coefficient is shown below.
Second side
K = -0.34623E + 01, A4 = -0.72868E-02, A6 = -0.26917E-02, A8 = -0.17267E-02,
A10 = -0.26025E-03
Third side
K = -0.18608E + 01, A4 = 0.17507E-02, A6 = -0.93875E-02, A8 = 0.17788E-02, A10 = -0.30151E-03
4th page
K = 0.30000E + 02, A4 = -0.32528E-01, A6 = 0.92324E-02, A8 = -0.16155E-02, A10 = 0.63142E-03
5th page
K = -0.56742E + 01, A4 = -0.26156E-02, A6 = 0.29424E-02, A8 = -0.10067E-02,
A10 = 0.21960E-03, A12 = -0.18639E-04
6th page
K = -0.30000E + 02, A4 = 0.29410E-01, A6 = -0.57243E-02, A8 = 0.98623E-03,
A10 = -0.55392E-04, A12 = -0.24518E-05
7th page
K = -0.18950E + 01, A4 = -0.21965E-02, A6 = 0.12653E-02, A8 = -0.46558E-03,
A10 = 0.12542E-03, A12 = -0.31432E-06
8th page
K = -0.44235E + 01, A4 = -0.37339E-01, A6 = 0.35759E-02, A8 = -0.84348E-04,
A10 = -0.33832E-04, A12 = 0.45025E-06
9th page
K = -0.52362E + 01, A4 = -0.20259E-01, A6 = 0.20932E-02, A8 = -0.23547E-03,
A10 = 0.13610E-04, A12 = -0.31509E-06
10th page
K = -0.63617E + 01, A4 = -0.84996E-02, A6 = -0.75293E-03, A8 = 0.73259E-04,
A10 = 0.58399E-06, A12 = 0.10743E-07
11th page
K = -0.45386E + 01, A4 = -0.14863E-01, A6 = 0.16385E-02, A8 = -0.24424E-03,
A10 = 0.15782E-04, A12 = -0.26624E-06
Single lens data is shown below.
Lens Start surface Focal length (mm)
1 2 3.040
2 4 -3.187
3 6 3.667
4 8 -6.730
5 10 -41.501
The values corresponding to each conditional expression are shown below.

ν4 = 55.7
f / f1 = 1.579
f / f2 = -1.506
(R3 + R4) / (R3-R4) = 0.609
t10 / f = 0.125
FIG. 7 is a sectional view of the imaging lens of Example 4. In the figure, L1 is a first lens, L2 is a second lens, L3 is a third lens, L4 is a fourth lens, L5 is a fifth lens, S is an aperture stop, and I is an imaging surface. F is a parallel plate that assumes an optical low-pass filter, an IR cut filter, a seal glass of a solid-state image sensor, and the like. FIG. 8 is an aberration diagram (spherical aberration, astigmatism, distortion) of the imaging lens of Example 4.
(Example 5)
The overall specifications are shown below.

f = 5.950mm
fB = 0.500mm
F = 2.2
2Y = 7.2mm
The surface data is shown below.
Surface number R (mm) D (mm) Nd νd
1 (aperture) ∞ 0.000
2 (*) 3.836 1.894 1.5305 55.7
3 (*) -2.959 0.050
4 (*) -96.943 0.740 1.5834 30.2
5 (*) 2.379 0.727
6 (*) -8.928 1.377 1.5305 55.7
7 (*) -1.782 0.100
8 (*) 4.446 0.650 1.5305 55.7
9 (*) 1.749 0.403
10 (*) 7.452 0.650 1.5305 55.7
11 (*) 3.306 0.608
12 ∞ 0.300 1.5168 64.2
13 ∞
All the lenses are made of a plastic material.

The aspheric coefficient is shown below.
Second side
K = -0.41347E + 00, A4 = -0.52824E-02, A6 = 0.52405E-03, A8 = -0.15226E-02, A10 = 0.83977E-04
Third side
K = -0.23712E + 01, A4 = -0.32100E-03, A6 = -0.79654E-02, A8 = 0.27564E-02, A10 = -0.45081E-03
4th page
K = 0.27446E + 04, A4 = -0.30176E-01, A6 = 0.74490E-03, A8 = 0.31270E-02, A10 = -0.56314E-03
5th page
K = -0.26815E + 01, A4 = -0.14226E-01, A6 = 0.46278E-02, A8 = -0.17638E-03,
A10 = 0.21144E-03, A12 = -0.51014E-04
6th page
K = 0.90448E + 01, A4 = 0.27613E-01, A6 = -0.86836E-02, A8 = 0.19101E-02,
A10 = -0.20342E-03, A12 = 0.17303E-04
7th page
K = -0.43827E + 01, A4 = -0.19366E-01, A6 = 0.44588E-02, A8 = -0.86555E-03,
A10 = 0.15756E-03, A12 = -0.10791E-04
8th page
K = -0.22525E + 01, A4 = -0.49664E-01, A6 = 0.55412E-02, A8 = -0.17798E-03,
A10 = -0.19699E-04, A12 = 0.34330E-06
9th page
K = -0.45423E + 01, A4 = -0.24632E-01, A6 = 0.38320E-02, A8 = -0.48017E-03,
A10 = 0.30175E-04, A12 = -0.82044E-06
10th page
K = -0.33332E + 02, A4 = -0.50707E-02, A6 = 0.87549E-04, A8 = 0.20687E-04,
A10 = 0.74982E-06, A12 = -0.45919E-07
11th page
K = -0.14958E + 02, A4 = -0.11428E-01, A6 = 0.68932E-03, A8 = -0.57292E-05,
A10 = -0.41947E-06, A12 = 0.58520E-07
Single lens data is shown below.
Lens Start surface Focal length (mm)
1 2 3.486
2 4 -3.969
3 6 3.935
4 8 -5.933
5 10 -11.845
The values corresponding to each conditional expression are shown below.

ν4 = 55.7
f / f1 = 1.707
f / f2 = −1.499
(R3 + R4) / (R3-R4) = 0.952
t10 / f = 0.109
FIG. 9 is a sectional view of the imaging lens of Example 5. In the figure, L1 is a first lens, L2 is a second lens, L3 is a third lens, L4 is a fourth lens, L5 is a fifth lens, S is an aperture stop, and I is an imaging surface. F is a parallel plate that assumes an optical low-pass filter, an IR cut filter, a seal glass of a solid-state image sensor, and the like. FIG. 10 is an aberration diagram (spherical aberration, astigmatism, distortion) of the imaging lens of Example 5.

  Here, since the plastic material has a large refractive index change when the temperature changes, if all of the first lens to the fifth lens are made of plastic lenses, the image point position of the entire imaging lens system changes when the ambient temperature changes. I have the problem of fluctuating.

Therefore, recently, it has been found that inorganic fine particles can be mixed in a plastic material to reduce the temperature change of the plastic material. More specifically, mixing fine particles with a transparent plastic material generally causes light scattering and lowers the transmittance, so it was difficult to use as an optical material. By making it smaller than the wavelength, it is possible to substantially prevent scattering. The refractive index of the plastic material decreases with increasing temperature, but the refractive index of inorganic particles increases with increasing temperature. Therefore, it is possible to make almost no change in the refractive index by using these temperature dependencies so as to cancel each other. Specifically, by dispersing inorganic particles having a maximum length of 20 nanometers or less in a plastic material as a base material, a plastic material with extremely low temperature dependency of the refractive index is obtained. For example, by dispersing fine particles of niobium oxide (Nb ₂ O ₅ ) in acrylic, the refractive index change due to temperature change can be reduced. In the present invention, a plastic material in which such inorganic particles are dispersed is used for the positive lenses (L1, L3) or all the lenses (L1 to L5) having a relatively large refractive power. It is possible to suppress the image point position fluctuation at the time of temperature change to be small.

  In the present embodiment, the chief ray incident angle of the light beam incident on the imaging surface of the solid-state imaging device is not necessarily designed to be sufficiently small at the periphery of the imaging surface. However, recent techniques have made it possible to reduce shading by reviewing the arrangement of the color filters of the solid-state imaging device and the on-chip microlens array. Specifically, if the pitch of the arrangement of the color filters and the on-chip microlens array is set slightly smaller than the pixel pitch of the image pickup surface of the image pickup device, the color filter or Since the on-chip microlens array is shifted to the optical axis side of the imaging lens, the obliquely incident light beam can be efficiently guided to the light receiving portion of each pixel. Thereby, the shading which generate | occur | produces with a solid-state image sensor can be suppressed small. The present embodiment is a design example aiming at further miniaturization with respect to the portion where the requirement is relaxed.

2 is a cross-sectional view of an imaging lens of Example 1. FIG. FIG. 3 is an aberration diagram of the imaging lens of Example 1. 6 is a cross-sectional view of an imaging lens of Example 2. FIG. 6 is an aberration diagram of the imaging lens of Example 2. FIG. 6 is a cross-sectional view of an imaging lens of Example 3. FIG. 6 is an aberration diagram of the imaging lens of Example 3. FIG. 6 is a cross-sectional view of an imaging lens of Example 4. FIG. FIG. 6 is an aberration diagram of the imaging lens of Example 4. 6 is a cross-sectional view of an imaging lens of Example 5. FIG. 10 is an aberration diagram of the imaging lens of Example 5. FIG.

Explanation of symbols

L1 1st lens L2 2nd lens L3 3rd lens L4 4th lens L5 5th lens S Aperture stop I Imaging surface F Parallel flat plate

Claims (7)

An imaging lens for forming a subject image on a photoelectric conversion unit of a solid-state imaging device,
A positive first lens, a negative second lens, a positive third lens, a negative fourth lens, and a negative fifth lens are arranged in order from the object side, and satisfy the following conditional expression: Imaging lens.
45 <ν4
However,
ν4: Abbe number of the fourth lens The imaging lens according to claim 1, wherein the first lens satisfies the following conditional expression.
1.45 <f / f1 <3.4
However,
f: focal length of the entire system f1: focal length of the first lens The imaging lens according to claim 1, wherein the second lens satisfies the following conditional expression.
−3.0 <f / f2 <−1.1
However,
f: focal length of the entire system f2: focal length of the second lens The imaging lens according to claim 1, wherein the second lens satisfies the following conditional expression.
0.3 <(R3 + R4) / (R3-R4) <1.4
However,
R3: radius of curvature of the object side surface of the second lens R4: radius of curvature of the image side surface of the second lens The imaging lens according to claim 1, wherein the fifth lens satisfies the following conditional expression.
0.06 <t10 / f <0.16
However,
f: focal length of entire system t10: axial thickness of the fifth lens The image side surface of the fourth lens is formed as an aspheric surface, has a negative refractive power at the center thereof, and the negative refractive power becomes weaker toward the periphery, and has an inflection point. Item 6. The imaging lens according to any one of Items 1 to 5. The imaging lens according to claim 1, wherein the imaging lens is entirely made of a plastic material.

Images