WO2011111561A1

WO2011111561A1 - Imaging lens

Info

Publication number: WO2011111561A1
Application number: PCT/JP2011/054518
Authority: WO
Inventors: 久保田洋治; 久保田賢一; 平野整
Original assignee: 株式会社オプトロジック
Priority date: 2010-03-10
Filing date: 2011-02-28
Publication date: 2011-09-15
Also published as: JP2011186297A

Abstract

Disclosed is an imaging lens which can provide satisfactory aberration compensation despite being a wide angle lens. The imaging lens is configured so that four lenses are arranged in the following order from the object side: a first lens (L1) having a planoconcave lens shape with the concave surface facing the imaging plane side; a second lens (L2) having a positive meniscus lens shape with the convex surface facing the object side; a third lens (L3) having a biconvex lens shape; and a fourth lens (L4) which has a negative meniscus lens shape with the convex surface facing the object side. In said configuration, the following condition is satisfied when f12 represents the combined focal length of the first lens (L1) and the second lens (L2), and f34 represents the combined focal length of the third lens (L3) and the fourth lens (L4): -2.0<f12/f34<-0.5.

Description

Imaging lens

The present invention relates to an imaging lens that forms a subject image on an imaging device such as a CCD sensor or a CMOS sensor, and is mounted on a mobile phone, a digital still camera, a portable information terminal, a surveillance camera, an in-vehicle camera, a network camera, and the like. The present invention relates to a suitable imaging lens.

Most cameras are equipped with a camera as standard, and the added value of the mobile phone is improved. One of the ways to use a camera with a mobile phone is so-called selfie. For example, you can take a picture of yourself with a friend with a mobile phone in one hand, or take a picture of yourself against a landscape, and it is widely used mainly by young people. In such a usage, since the photographer himself becomes a subject, an imaging lens of a camera mounted on a cellular phone is required to have an increased shooting angle of view, that is, a wider angle, as well as downsizing.

On the other hand, surveillance cameras and in-vehicle cameras are also required to monitor or visually check the widest possible range of situations. The imaging lens mounted on these cameras is also required to have a wide angle, similar to the imaging lens mounted on the mobile phone camera.

Patent Document 1 discloses a four-lens imaging lens that is relatively small and has a wide angle of view. The imaging lens described in Patent Document 1 includes, in order from the object side, a first lens having a negative refractive power, a second lens having a positive refractive power with a convex surface facing the object side, an aperture, and an image side. And a fourth lens of a positive meniscus lens having a convex surface facing the object side and a fourth lens of a positive meniscus lens having a convex surface facing the object side. In this lens configuration, the refractive power of each of the second to fourth lenses is limited to 1.7 or more, thereby realizing a reduction in size and a wide angle, although the number of lenses is as small as four.

JP 2007-322656 A

In recent years, the resolution of an image sensor has improved dramatically, and it has become necessary to secure sufficient optical performance in accordance with the resolution of the image sensor for an imaging lens mounted on a mobile phone or a surveillance camera. According to the imaging lens described in Patent Document 1, it is possible to widen the angle with a small number of lenses. However, when the first lens is configured with a lens having a negative refractive power as in the imaging lens described in Patent Document 1, the field curvature and chromatic aberration generated by the first lens are positively refracted. It is necessary to correct by a subsequent lens having power. In the imaging lens, correction of field curvature and chromatic aberration is performed with three lenses having positive refractive power, but in this case, there is a tendency that on-axis or off-axis chromatic aberration always remains, which is favorable. It is difficult to obtain aberrations.

Such compatibility between wide-angle and good aberration correction is not a problem specific to the imaging lens mounted on the above mobile phone, surveillance camera, and in-vehicle camera, but is relatively difficult for digital still cameras, personal digital assistants, network cameras, etc. This is a common problem in an imaging lens mounted on a camera that is required to have a wide angle despite its small size.

The present invention has been made in view of the above-described problems of the prior art, and an object of the present invention is to provide an imaging lens capable of correcting aberrations satisfactorily while having a wide angle.

In order to solve the above problems, in the present invention, in order from the object side to the image plane side, a first lens having negative refractive power, a second lens, and a third lens having positive refractive power, A fourth lens is disposed, the first lens is formed in a shape in which the curvature radius of the image side surface is positive, and the second lens is formed with a curvature radius of the object side surface and a curvature radius of the image side surface. And the third lens is formed in a shape in which the radius of curvature of the object side surface is positive and the radius of curvature of the image side surface is negative. In this configuration, the refractive power of the first lens is made stronger than the refractive power of the second lens, the refractive power of the third lens is made stronger than the refractive power of the fourth lens, and the first lens and the second lens are combined. When the focal length is f12, and the combined focal length of the third lens and the fourth lens is f34, the following conditional expression (1) is satisfied.
f12 <0, f34> 0 (1)

According to such a configuration as the imaging lens, the angle of view of the imaging lens is widened (widened) by the negative first lens having a strong refractive power and the positive third lens having a strong refractive power. Various aberrations such as curvature of field and chromatic aberration caused by the above are corrected well by the second lens having a lower refractive power than the first lens and the fourth lens having a lower refractive power than the third lens. In addition, the second lens has a shape in which the curvature radius of the object side surface and the curvature radius of the image side surface are both positive, that is, a meniscus lens having a convex surface facing the object side in the vicinity of the optical axis. Thus, the position of the principal point of the lens system moves to the object side, and the imaging lens can be reduced in size.

In the imaging lens having the above configuration, it is preferable that the following conditional expression (2) is satisfied.
-2.0 <f12 / f34 <-0.5 (2)

Conditional expression (1) is a condition for reducing the focal length of the entire lens system and widening the angle while reducing the size of the imaging lens. At the same time, it is also a condition for suppressing chromatic aberration and distortion occurring with a wide angle within a suitable range. Exceeding the upper limit “−0.5” is effective for widening the angle, but the negative refractive power of the group constituted by the first lens and the second lens becomes relatively strong, and distortion in the negative direction. Will increase. In addition, the position of the best imaging plane for each wavelength is greatly different, and it is difficult to obtain good imaging performance. On the other hand, when the value is below the lower limit “−2.0”, it is effective for correcting distortion, but the chromatic aberration of magnification is overcorrected (short wavelength increases in the positive direction with respect to the reference wavelength), and good results are obtained. It becomes difficult to obtain image performance. In addition, it is difficult to achieve both a reduction in size and a wide angle of the imaging lens.

In the imaging lens having the above configuration, it is more desirable to satisfy the following conditional expression (1A).
-1.5 <f12 / f34 <-0.5 (2A)

In the imaging lens according to the present invention, the refractive power of the fourth lens is weaker than the refractive power of the third lens. Therefore, regardless of whether positive or negative is selected as the refractive power of the fourth lens, the aberration is increased while widening the angle. Can be corrected satisfactorily. When negative is selected as the refractive power of the fourth lens, the lens configuration is particularly effective for correcting lateral chromatic aberration and distortion. On the other hand, when positive is selected as the refractive power of the fourth lens, the lens configuration is effective for suppressing the incident angle of the light beam emitted from the imaging lens to the imaging element within a certain range.

In the imaging lens having the above-described configuration, when the refractive power of the fourth lens is negative, when the focal length of the entire lens system is f and the focal length of the third lens is f3, the following conditional expression (3-1) It is desirable to satisfy
0.3 <f3 / f <2.3 (3-1)

On the other hand, in the imaging lens having the above configuration, when the refractive power of the fourth lens is positive, when the focal length of the entire lens system is f and the focal length of the third lens is f3, the following conditional expression (3- It is desirable to satisfy 2).
0.5 <f3 / f <2.5 (3-2)

Conditional expressions (3-1) and (3-2) are conditions for suppressing off-axis coma and field curvature within a favorable range while reducing the size of the imaging lens. If the upper limit is exceeded, the focal length of the third lens having a strong refractive power becomes relatively long, so that it is difficult to reduce the size of the imaging lens. On the other hand, below the lower limit, the refractive power of the third lens becomes relatively strong, which is advantageous for downsizing of the imaging lens, but off-axis internal coma increases, so off-axis optical performance. Will deteriorate. In addition, since the sagittal image plane of the image plane is tilted toward the object side (minus direction), it is difficult to obtain good imaging performance.

In the imaging lens having the above-described configuration, it is desirable that the following conditional expression (4) is satisfied when the focal length of the third lens is f3 and the focal length of the fourth lens is f4.
| F3 / f4 | <1.5 (4)

Conditional expression (4) is a condition for suppressing chromatic aberration within a favorable range. This conditional expression (4) is for suppressing the incident angle of the light beam emitted from the imaging lens at the maximum image height within a certain range and suppressing the curvature of field within a favorable range. It is also a condition. As is well known, a so-called maximum incident angle is provided as a limit on the incident angle of the light beam that can be taken into the image sensor due to the structure of the image sensor. When light rays outside the range of the maximum incident angle are incident on the image sensor, a dark image in the peripheral portion is generated due to the shading phenomenon. Therefore, it is necessary to suppress the incident angle of the light beam emitted from the imaging lens to the imaging element within a certain range.

When the refractive power of the fourth lens is negative, if the upper limit “1.5” is exceeded in the conditional expression (4), the negative refractive power of the fourth lens becomes relatively strong, Off-axis chromatic aberration is overcorrected (short wavelength increases in the positive direction with respect to the reference wavelength), making it difficult to obtain good imaging performance. In addition, since the incident angle of the light beam emitted from the imaging lens to the image sensor increases at the maximum image height, it is difficult to suppress the incident angle of the light beam emitted from the imaging lens to the image sensor within a certain range. It becomes. Further, the field curvature increases in the plus direction, and it is difficult to suppress the field curvature within a favorable range.

If the refractive power of the fourth lens is negative, it is preferable that the following conditional expression (4A) is further satisfied.
| F3 / f4 | <0.8 (4A)

On the other hand, when the refractive power of the fourth lens is positive, if the upper limit “1.5” is exceeded in the conditional expression (4), the positive refractive power of the fourth lens becomes relatively strong and the maximum image becomes larger. Although effective in suppressing the incident angle of the light beam emitted from the imaging lens at a high range within a certain range at high, the on-axis and off-axis chromatic aberration is insufficiently corrected (the short wavelength is minus with respect to the reference wavelength). It is difficult to obtain good imaging performance. In addition, the curvature of field increases in the minus direction, and it is difficult to suppress it within a favorable range.

In the imaging lens having the above-described configuration, when the refractive power of the fourth lens is negative, the focal length of the entire lens system is f, and the optical axis from the object side surface to the image side surface of the second lens is It is desirable to satisfy the following conditional expression (5-1) where d3 is d3.
0.5 <d3 / f <3.0 (5-1)

On the other hand, in the imaging lens configured as described above, when the refractive power of the fourth lens is positive, the focal length of the entire lens system is f, and the optical axis from the object-side surface to the image-side surface of the second lens When the upper distance is d3, it is preferable that the following conditional expression (5-2) is satisfied.
0.5 <d3 / f <2.5 (5-2)

Conditional expressions (5-1) and (5-2) are conditions for suppressing field curvature and chromatic aberration within a favorable range. In this type of wide-angle lens having a wide angle of view, insufficient correction of chromatic aberration that occurs with downsizing is one of the problems. Since it is difficult to improve the MTF value at each image height of the captured image due to the occurrence of chromatic aberration, chromatic aberration is generally corrected by adopting a cemented lens or increasing the number of lens components. However, the adoption of a cemented lens and an increase in the number of lens components cause an increase in the size of the imaging lens and cause an increase in the price of the imaging lens.

Therefore, in the present invention, the flatness of the image plane is reduced by keeping the distance on the optical axis from the object side surface of the second lens to the image side surface, that is, the thickness of the second lens within a certain range. While maintaining, on-axis and off-axis chromatic aberration were suppressed within a favorable range.

If the upper limit value in conditional expressions (5-1) and (5-2) is exceeded, chromatic aberration of magnification will be overcorrected and the sagittal image plane will fall to the object side, making it difficult to obtain good imaging performance. Become. On the other hand, if the value is below the lower limit, it is advantageous for downsizing the imaging lens, but the on-axis and off-axis chromatic aberrations are insufficiently corrected, and it is difficult to improve the MTF value at each image height.

In the imaging lens configured as described above, the following conditional expression (5-1A) is obtained when the refractive power of the fourth lens is negative, and the following conditional expression (5-2A) is obtained when the refractive power of the fourth lens is positive. Satisfaction is more desirable.
1.0 <d3 / f <2.8 (5-1A)
1.0 <d3 / f <2.0 (5-2A)

According to the imaging lens of the present invention, it is possible to provide both a wide angle of the imaging lens and good aberration correction, and provide a small imaging lens in which various aberrations are favorably corrected.

1 is a lens cross-sectional view illustrating a schematic configuration of an imaging lens according to Numerical Example 1 according to a first embodiment of the present invention. FIG. 3 is an aberration diagram illustrating lateral aberration of the imaging lens illustrated in FIG. 1. FIG. 2 is an aberration diagram illustrating spherical aberration, astigmatism, and distortion of the imaging lens illustrated in FIG. 1. FIG. 3 is a lens cross-sectional view illustrating a schematic configuration of an imaging lens according to Numerical Example 2 according to the first embodiment of the present invention. FIG. 5 is an aberration diagram showing lateral aberration of the imaging lens shown in FIG. 4. FIG. 5 is an aberration diagram illustrating spherical aberration, astigmatism, and distortion of the imaging lens illustrated in FIG. 4. FIG. 6 is a lens cross-sectional view illustrating a schematic configuration of an imaging lens according to Numerical Example 3 according to the first embodiment of the present invention. FIG. 8 is an aberration diagram showing lateral aberration of the imaging lens shown in FIG. 7. FIG. 8 is an aberration diagram illustrating spherical aberration, astigmatism, and distortion of the imaging lens illustrated in FIG. 7. FIG. 6 is a lens cross-sectional view illustrating a schematic configuration of an imaging lens according to Numerical Example 4 according to the first embodiment of the present invention. FIG. 11 is an aberration diagram illustrating lateral aberration of the imaging lens illustrated in FIG. 10. FIG. 11 is an aberration diagram illustrating spherical aberration, astigmatism, and distortion of the imaging lens illustrated in FIG. 10. FIG. 10 is a lens cross-sectional view illustrating a schematic configuration of an imaging lens according to Numerical Example 5 regarding the second embodiment of the present invention. FIG. 14 is an aberration diagram illustrating lateral aberration of the imaging lens illustrated in FIG. 13. FIG. 14 is an aberration diagram illustrating spherical aberration, astigmatism, and distortion of the imaging lens illustrated in FIG. 13. FIG. 10 is a lens cross-sectional view illustrating a schematic configuration of an imaging lens according to Numerical Example 6 regarding the second embodiment of the present invention. FIG. 17 is an aberration diagram illustrating lateral aberration of the imaging lens illustrated in FIG. 16. FIG. 17 is an aberration diagram illustrating spherical aberration, astigmatism, and distortion of the imaging lens illustrated in FIG. 16.

(First embodiment)
Hereinafter, a first embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1, FIG. 4, FIG. 7, and FIG. 10 show lens cross-sectional views corresponding to Numerical Examples 1 to 4 of the present embodiment, respectively. Since all the numerical examples have the same basic lens configuration, the lens configuration of the imaging lens according to the present embodiment will be described here with reference to the lens cross-sectional view of the numerical example 1.

As shown in FIG. 1, the imaging lens of the present embodiment includes a first lens L1 having a negative refractive power and a second lens having a positive or negative refractive power in order from the object side to the image plane side. L2, an aperture stop ST, a third lens L3 having a positive refractive power, and a fourth lens L4 having a negative refractive power are arranged. In this configuration, the refractive power of the first lens L1 is stronger than the refractive power of the second lens L2, and the refractive power of the third lens L3 is stronger than the refractive power of the fourth lens L4. A cover glass 10 is disposed between the fourth lens L4 and the image plane. The cover glass 10 can be omitted.

In the imaging lens having the above-described configuration, the first lens L1 is formed in a shape in which the curvature radius R2 of the surface on the image surface side is positive, that is, a shape in which the concave surface is directed to the image surface side. Numerical Example 1 is an example in which the shape of the first lens L1 is a plano-concave lens in the vicinity of the optical axis, and Numerical Examples 2 to 4 have the convex surface facing the object side when the shape of the first lens L1 is in the vicinity of the optical axis. This is an example of a meniscus lens. The shape of the first lens L1 is not limited to the shapes shown in Numerical Examples 1 to 4, but may be a shape that becomes a biconcave lens in the vicinity of the optical axis.

The second lens L2 has a positive curvature radius R3 on the object side surface and a curvature radius R4 on the image side surface, and is formed in a shape that becomes a meniscus lens with a convex surface facing the object side in the vicinity of the optical axis. Yes. Numerical Examples 1 to 3 are examples in which the second lens L2 is a positive meniscus lens having a convex surface facing the object side in the vicinity of the optical axis, and Numerical Example 4 is a case where the second lens L2 is in the vicinity of the optical axis. This is an example of a negative meniscus lens having a convex surface facing the object side. The second lens L2 may be any shape as long as it becomes a meniscus lens having a convex surface facing the object side in the vicinity of the optical axis, and its refractive power may be either positive or negative.

The third lens L3 is formed in a shape in which the curvature radius R5 of the object side surface is positive and the curvature radius R6 of the image side surface is negative, that is, a shape that becomes a biconvex lens in the vicinity of the optical axis. The fourth lens L4 has a positive curvature radius R7 on the object side surface and a curvature radius R8 on the image side surface, and is formed in a shape that becomes a meniscus lens with a convex surface facing the object side in the vicinity of the optical axis. Yes.

The imaging lens according to the present embodiment satisfies the following conditional expression. For this reason, according to the imaging lens according to the present embodiment, it is possible to achieve both the widening of the imaging lens and good aberration correction.
f12 <0, f34> 0 (1)
-2.0 <f12 / f34 <-0.5 (2)
0.3 <f3 / f <2.3 (3-1)
| F3 / f4 | <1.5 (4)
0.5 <d3 / f <3.0 (5-1)
However,
f: The focal length of the entire lens system f3: The focal length of the third lens L3 f4: The focal length of the fourth lens L4 f12: The combined focal length of the first lens L1 and the second lens L2 f34: The third lens L3 and the third lens L3 Synthetic focal length with the four lenses L4 d3: Distance (thickness) on the optical axis from the object side surface of the second lens L2 to the image side surface

In addition to the above conditional expressions, the imaging lens according to the present embodiment further satisfies the following conditional expressions in order to more favorably correct curvature of field and chromatic aberration caused by widening the angle.
-1.5 <f12 / f34 <-0.5 (2A)
| F3 / f4 | <0.8 (4A)
1.0 <d3 / f <2.8 (5-1A)

In addition, it is not necessary to satisfy all the conditional expressions described above, and by satisfying each of the conditional expressions alone, it is possible to obtain the effects corresponding to the conditional expressions.

In the present embodiment, the lens surface of each lens is formed as an aspheric surface as necessary. The aspherical shape adopted for these lens surfaces is that the axis in the optical axis direction is Z, the height in the direction perpendicular to the optical axis is H, the conic coefficient is k, and the aspherical coefficients are A ₄ , A ₆ , A ₈ , A ₁₀ , A ₁₂ , A ₁₄ , and A ₁₆ are expressed by the following formulas (the same applies to the second embodiment described later).

Next, numerical examples of the imaging lens according to the present embodiment will be shown. In each numerical example, f represents the focal length of the entire lens system, Fno represents the F number, and ω represents the half angle of view. Further, i indicates a surface number counted from the object side, R indicates a radius of curvature, d indicates a distance (surface interval) between lens surfaces along the optical axis, Nd indicates a refractive index with respect to d-line, and νd Indicates the Abbe number for the d line. The aspherical surface is indicated by adding a symbol of * (asterisk) after the surface number i (the same applies to the second embodiment described later).

Numerical example 1
Basic lens data is shown below.
f = 2.367mm, Fno = 2.550, ω = 44.18 °
Unit mm
Surface data Surface number i R d Nd νd
(Surface) ∞ ∞
1 ∞ 0.5800 1.80420 46.5
2 2.342 0.8000
3 * 4.692 6.0000 1.61420 26.0
4 * 3.270 0.1000
5 * 1.794 1.5317 1.52470 56.2
6 * -1.776 0.1000
7 * 3.623 0.7759 1.61420 26.0
8 * 1.718 1.0000
9 ∞ 0.8000 1.51633 64.1
10 ∞ 1.8628
(Image plane) ∞

f3 = 1.996
f4 = −6.295
f12 = −1.855
f34 = 2.070
d3 = 6.0000

Aspherical data third surface k = 0.000000, A ₄ = -1.028603E-03, A ₆ = 1.099329E-03, A ₈ = -2.322072E-05,
A ₁₀ = -5.273353E-05, A ₁₂ = 1.160232E-05
4th surface k = -2.839900, A ₄ = -7.952640E-03, A ₆ = 3.272493E-02, A ₈ = -2.469437E-02,
A ₁₀ = 2.001948E-02, A ₁₂ = -8.844125E-03
5th surface k = 0.000000, A ₄ = -3.335422E-02, A ₆ = 4.846327E-03, A ₈ = -4.775102E-03,
A ₁₀ = 1.011601E-03, A ₁₂ = 2.596273E-04, A ₁₄ = -1.610992E-03,
A ₁₆ = -6.694518E-04
6th surface k = -6.788322, A ₄ = -4.320767E-02, A ₆ = -2.507905E-04, A ₈ = 4.840310E-03,
A ₁₀ = -6.310766E-03, A ₁₂ = 6.684271E-04, A ₁₄ = 3.579905E-04
7th surface k = -3.311532, A ₄ = 1.756838E-02, A ₆ = -4.721393E-02, A ₈ = 1.182203E-02,
A ₁₀ = -7.257518E-03, A ₁₂ = 5.814087E-03, A ₁₄ = -4.345011E-03
8th surface k = 0.000000, A ₄ = -9.619894E-02, A ₆ = 3.223868E-02, A ₈ = -1.957263E-02,
A ₁₀ = -7.107598E-04, A ₁₂ = 1.006373E-03, A ₁₄ = 3.877688E-04

The value of each conditional expression is shown below.
f12 / f34 = −0.896
f3 / f = 0.743
| F3 / f4 | = 0.317
d3 / f = 2.534

Thus, the imaging lens according to Numerical Example 1 satisfies the conditional expressions. Therefore, according to the imaging lens according to Numerical Example 1, it is possible to correct aberrations satisfactorily while having a wide angle.

FIG. 2 shows the lateral aberration corresponding to the half angle of view ω divided into the tangential direction and the sagittal direction for the imaging lens of Numerical Example 1 (the same applies to FIGS. 5, 8, and 11). . FIG. 3 shows spherical aberration SA (mm), astigmatism AS (mm), and distortion aberration DIST (%) for the imaging lens of Numerical Example 1. In these aberration diagrams, the spherical aberration diagram shows the amount of aberration for each wavelength of 587.56 nm, 435.84 nm, 656.27 nm, 486.13 nm, and 546.07 nm as well as the sine condition violation amount OSC. The aberration diagrams show the aberration amount on the sagittal image plane S and the aberration amount on the tangential image plane T (the same applies to FIGS. 6, 9, and 12). As shown in FIGS. 2 and 3, according to the imaging lens according to Numerical Example 1, various aberrations are favorably corrected.

Numerical example 2
Basic lens data is shown below.
f = 2.329mm, Fno = 2.555, ω = 44.01 °
Unit mm
Surface data Surface number i R d Nd νd
(Surface) ∞ ∞
1 11.999 0.5500 1.80420 46.5
2 2.022 1.2567
3 * 4.190 4.2254 1.61420 26.0
4 * 2.997 0.1000
5 * 1.642 0.9099 1.45650 90.3
6 * -1.750 0.1000
7 * 2.000 0.6651 1.52470 56.2
8 * 1.400 1.0000
9 ∞ 0.8000 1.51633 64.1
10 ∞ 1.4732
(Image plane) ∞

f3 = 1.996
f4 = -14.379
f12 = −2.139
f34 = 1.922
d3 = 4.2254

Aspherical data third surface k = 0.000000, A ₄ = -8.212503E-03, A ₆ = 2.061281E-03, A ₈ = -9.059462E-04,
A ₁₀ = 5.715947E-05, A ₁₂ = -5.314974E-06
4th surface k = -2.839900, A ₄ = -2.965113E-02, A ₆ = 3.009807E-02, A ₈ = -2.840842E-02,
A ₁₀ = 1.945366E-02, A ₁₂ = -9.293561E-03
5th surface k = 0.000000, A ₄ = -3.421102E-02, A ₆ = -7.596290E-04, A ₈ = -2.379342E-03,
A ₁₀ = 3.162250E-03, A ₁₂ = -1.246372E-03, A ₁₄ = -5.653149E-03,
A ₁₆ = -2.662851E-03
6th surface k = -6.788322, A ₄ = -4.211138E-02, A ₆ = 1.549686E-02, A ₈ = 6.325562E-03,
A ₁₀ = -8.117420E-03, A ₁₂ = -1.055412E-03, A ₁₄ = -3.586197E-03
7th surface k = -3.311532, A ₄ = 3.054239E-02, A ₆ = -6.575098E-02, A ₈ = 1.958466E-02,
A ₁₀ = -2.832587E-03, A ₁₂ = 3.782635E-03, A ₁₄ = -8.189655E-03
8th surface k = 0.000000, A ₄ = -1.370286E-01, A ₆ = 4.129807E-02, A ₈ = -2.798906E-02,
A ₁₀ = -5.912638E-03, A ₁₂ = 7.861151E-04, A ₁₄ = 1.657199E-03

The value of each conditional expression is shown below.
f12 / f34 = −1.113
f3 / f = 0.870
| F3 / f4 | = 0.141
d3 / f = 1.814

Thus, the imaging lens according to Numerical Example 2 satisfies the conditional expressions. Therefore, the imaging lens according to Numerical Example 2 can correct aberrations satisfactorily while having a wide angle.

FIG. 5 shows lateral aberration corresponding to the half angle of view ω for the imaging lens of Numerical Example 2. FIG. 6 shows spherical aberration SA (mm), astigmatism AS (mm), and distortion. Each aberration DIST (%) is shown. As shown in FIG. 5 and FIG. 6, the imaging lens according to Numerical Example 2 also corrects the image plane well as in Numerical Example 1 and suitably corrects various aberrations.

Numerical Example 3
Basic lens data is shown below.
f = 2.370mm, Fno = 2.550, ω = 44.14 °
Unit mm
Surface data Surface number i R d Nd νd
(Surface) ∞ ∞
1 101.726 0.5500 1.72916 54.7
2 2.289 1.0255
3 * 3.596 3.9447 1.61420 26.0
4 * 2.697 0.2939
5 * 1.667 1.1472 1.49700 81.6
6 * -1.735 0.1000
7 * 2.429 0.6722 1.52470 56.2
8 * 1.423 1.0000
9 ∞ 0.8000 1.51633 64.1
10 ∞ 1.2638
(Image plane) ∞

f3 = 1.926
f4 = −8.504
f12 = -2.308
f34 = 1.927
d3 = 3.9447

Aspheric data 3rd surface k = 0.000000, A ₄ = -7.178337E-03, A ₆ = 1.020357E-03, A ₈ = -3.131979E-04,
A ₁₀ = -8.502021E-05, A ₁₂ = 1.597995E-05
4th surface k = -2.839900, A ₄ = -1.324258E-02, A ₆ = 3.483138E-02, A ₈ = -2.477128E-02,
A ₁₀ = 1.963713E-02, A ₁₂ = -7.004891E-03
5th surface k = 0.000000, A ₄ = -3.530938E-02, A ₆ = 9.556082E-04, A ₈ = -3.815011E-03,
A ₁₀ = 3.825524E-03, A ₁₂ = 1.788855E-03, A ₁₄ = -2.409678E-03,
A ₁₆ = -1.633798E-03
6th surface k = -6.788322, A ₄ = -4.798487E-02, A ₆ = 7.311676E-03, A ₈ = 9.040632E-03,
A ₁₀ = -4.501898E-03, A ₁₂ = 1.247816E-03, A ₁₄ = -1.775255E-03
7th surface k = -3.311532, A ₄ = 2.711627E-02, A ₆ = -5.847770E-02, A ₈ = 1.340630E-02,
A ₁₀ = -3.755744E-03, A ₁₂ = 6.304943E-03, A ₁₄ = -7.236438E-03
8th surface k = 0.000000, A ₄ = -1.179631E-01, A ₆ = 3.466906E-02, A ₈ = -2.498959E-02,
A ₁₀ = -3.755734E-03, A ₁₂ = 9.629862E-04, A ₁₄ = 1.620900E-03

The value of each conditional expression is shown below.
f12 / f34 = -1.198
f3 / f = 0.812
| F3 / f4 | = 0.226
d3 / f = 1.664

Thus, the imaging lens according to Numerical Example 3 satisfies the conditional expressions. Therefore, the imaging lens according to Numerical Example 3 can correct aberrations satisfactorily while having a wide angle.

FIG. 8 shows lateral aberration corresponding to the half angle of view ω for the imaging lens of Numerical Example 3, and FIG. 9 shows spherical aberration SA (mm), astigmatism AS (mm), and distortion. Each aberration DIST (%) is shown. As shown in FIG. 8 and FIG. 9, the imaging lens according to Numerical Example 3 also corrects the image plane satisfactorily as in Numerical Example 1, and various aberrations are preferably corrected.

Next, Numerical Example 4 of the imaging lens according to the present embodiment will be described.
Numerical Example 4
Basic lens data is shown below.
f = 2.368mm, Fno = 2.400, ω = 45.38 °
Unit mm
Surface data Surface number i R d Nd νd
(Surface) ∞ ∞
1 30.436 0.5800 1.72916 54.7
2 2.064 0.8500
3 * 4.945 3.0000 1.62090 24.0
4 * 3.391 0.5000
5 * 1.794 1.5317 1.52470 56.2
6 * -1.776 0.1000
7 * 3.528 0.7759 1.61420 26.0
8 * 1.697 1.0000
9 ∞ 0.8000 1.51633 64.1
10 ∞ 1.4419
(Image plane) ∞

f3 = 1.996
f4 = −6.347
f12 = −2.192
f34 = 2.062
d3 = 3.0000

Aspheric data 3rd surface k = 0.000000, A ₄ = -8.332297E-03, A ₆ = -4.371098E-04, A ₈ = 2.529433E-04,
A ₁₀ = -1.845956E-04, A ₁₂ = 1.686690E-05
4th surface k = -2.839900, A ₄ = -1.987991E-02, A ₆ = 2.787292E-02, A ₈ = -2.553426E-02,
A ₁₀ = 2.069072E-02, A ₁₂ = -6.790000E-03
5th surface k = 0.000000, A ₄ = -3.177894E-02, A ₆ = 3.819782E-03, A ₈ = -5.912679E-03,
A ₁₀ = 1.013574E-03, A ₁₂ = 1.246839E-03, A ₁₄ = -4.813064E-05,
A ₁₆ = -4.587000E-04
6th surface k = -6.788322, A ₄ = -3.821797E-02, A ₆ = 3.857820E-03, A ₈ = 7.098667E-03,
A ₁₀ = -5.665563E-03, A ₁₂ = 6.366178E-04, A ₁₄ = 3.740255E-04
7th surface k = -3.311532, A ₄ = 1.681047E-02, A ₆ = -4.783746E-02, A ₈ = 1.218450E-02,
A ₁₀ = -7.553507E-03, A ₁₂ = 6.108749E-03, A ₁₄ = -2.858119E-03
8th surface k = 0.000000, A ₄ = -9.096002E-02, A ₆ = 3.420331E-02, A ₈ = -2.111593E-02,
A ₁₀ = -5.339868E-04, A ₁₂ = 1.391608E-03, A ₁₄ = 5.315504E-04

The value of each conditional expression is shown below.
f12 / f34 = −1.063
f3 / f = 0.743
| F3 / f4 | = 0.314
d3 / f = 1.267

Thus, the imaging lens according to Numerical Example 4 satisfies the conditional expressions. Therefore, the imaging lens according to Numerical Example 4 can correct aberrations satisfactorily while having a wide angle.

FIG. 11 shows lateral aberration corresponding to the half angle of view ω for the imaging lens of Numerical Example 4, and FIG. 12 shows spherical aberration SA (mm), astigmatism AS (mm), and distortion. Each aberration DIST (%) is shown. As shown in FIGS. 11 and 12, the imaging lens according to Numerical Example 4 also corrects the image plane satisfactorily as in Numerical Example 1, and various aberrations are preferably corrected.

(Second Embodiment)
Next, a second embodiment of the present invention will be described in detail with reference to the drawings.

FIGS. 13 and 16 are lens cross-sectional views corresponding to Numerical Examples 5 and 6 of the present embodiment. Since all the numerical examples have the same basic lens configuration, the lens configuration of the imaging lens according to the present embodiment will be described here with reference to a lens cross-sectional view of Numerical Example 5.

As shown in FIG. 13, the imaging lens of the present embodiment includes a first lens L1 having a negative refractive power and a second lens having a positive or negative refractive power in order from the object side to the image plane side. L2, an aperture stop ST, a third lens L3 having a positive refractive power, and a fourth lens L4 having a positive refractive power are arranged. In this configuration, the refractive power of the first lens L1 is stronger than the refractive power of the second lens L2, and the refractive power of the third lens L3 is stronger than the refractive power of the fourth lens L4. A cover glass 10 is disposed between the fourth lens L4 and the image plane. The cover glass 10 can be omitted.

In the imaging lens having the above-described configuration, the first lens L1 is formed in a shape in which the curvature radius R2 of the surface on the image surface side is positive, that is, a shape in which the concave surface is directed to the image surface side. Numerical Examples 5 and 6 are examples in which the shape of the first lens L1 is a meniscus lens having a convex surface facing the object side in the vicinity of the optical axis. The shape of the first lens L1 is not limited to the shape shown in Numerical Examples 5 and 6, and may be a shape that becomes a plano-concave lens near the optical axis or a shape that becomes a biconcave lens near the optical axis. .

The second lens L2 has a positive curvature radius R3 on the object side surface and a curvature radius R4 on the image side surface, and is formed in a shape that becomes a meniscus lens with a convex surface facing the object side in the vicinity of the optical axis. Yes. Numerical Example 5 is an example in which the second lens L2 is a positive meniscus lens having a convex surface facing the object side in the vicinity of the optical axis, and Numerical Example 6 is an example in which the second lens L2 is on the object side in the vicinity of the optical axis. This is an example of a negative meniscus lens having a convex surface facing to. The second lens L2 may be any shape as long as it becomes a meniscus lens having a convex surface facing the object side in the vicinity of the optical axis, and its refractive power may be either positive or negative.

The third lens L3 is formed in a shape in which the curvature radius R5 of the object side surface is positive and the curvature radius R6 of the image side surface is negative, that is, a shape that becomes a biconvex lens in the vicinity of the optical axis. The fourth lens L4 is formed in a shape in which the radius of curvature R7 of the object side surface is positive and the radius of curvature R8 of the image side surface is negative, that is, a shape that becomes a biconvex lens in the vicinity of the optical axis. The shape of the fourth lens L4 is not limited to a shape that becomes a biconvex lens in the vicinity of the optical axis. The shape of the fourth lens L4 may be any shape as long as its refractive power is positive, and may be a shape that becomes a meniscus lens having a convex surface facing the object side in the vicinity of the optical axis. Numerical Example 6 is an example in which the shape of the fourth lens L4 is a meniscus lens having a convex surface facing the object side in the vicinity of the optical axis.

The imaging lens according to the present embodiment satisfies the following conditional expression. For this reason, according to the imaging lens according to the present embodiment, it is possible to achieve both the widening of the imaging lens and good aberration correction.
f12 <0, f34> 0 (1)
-2.0 <f12 / f34 <-0.5 (2)
0.5 <f3 / f <2.5 (3-2)
| F3 / f4 | <1.5 (4)
0.5 <d3 / f <2.5 (5-2)
However,
f: The focal length of the entire lens system f3: The focal length of the third lens L3 f4: The focal length of the fourth lens L4 f12: The combined focal length of the first lens L1 and the second lens L2 f34: The third lens L3 and the third lens L3 Synthetic focal length with the four lenses L4 d3: Distance (thickness) on the optical axis from the object side surface of the second lens L2 to the image side surface

In addition to the above conditional expressions, the imaging lens according to the present embodiment further satisfies the following conditional expressions in order to more favorably correct curvature of field and chromatic aberration caused by widening the angle.
-1.5 <f12 / f34 <-0.5 (2A)
1.0 <d3 / f <2.0 (5-2A)

It should be noted that it is not necessary to satisfy all the conditional expressions described above, and by satisfying each of the conditional expressions alone, the operational effects corresponding to the conditional expressions can be obtained.

Next, numerical examples of the imaging lens according to the present embodiment will be shown.

Numerical Example 5
Basic lens data is shown below.
f = 2.361mm, Fno = 2.555, ω = 43.62 °
Unit mm
Surface data Surface number i R d Nd νd
(Surface) ∞ ∞
1 6.538 0.5500 1.80420 46.5
2 1.773 1.0994
3 * 5.500 4.1400 1.61420 26.0
4 * 4.050 0.1000
5 * 12.655 0.7000 1.45650 90.3
6 * -2.445 0.1000
7 * 3.257 0.7000 1.45650 90.3
8 * -5.524 1.0000
9 ∞ 0.8000 1.51633 64.1
10 ∞ 2.7828
(Image plane) ∞

f3 = 4.555
f4 = 4.603
f12 = −2.320
f34 = 2.384
d3 = 4.1400

Aspheric data third surface k = 0.000000, A ₄ = -8.983318E-03, A ₆ = 3.017054E-03, A ₈ = -1.400843E-03,
A ₁₀ = 1.654081E-04, A ₁₂ = -6.912875E-05
4th surface k = -2.839900, A ₄ = -3.272938E-02, A ₆ = 1.334859E-02, A ₈ = -4.608573E-02,
A ₁₀ = 9.106202E-03, A ₁₂ = -4.692913E-03
5th surface k = 0.000000, A ₄ = -1.675862E-02, A ₆ = 1.254982E-02, A ₈ = -9.637673E-03,
A ₁₀ = -1.641580E-02, A ₁₂ = -1.886303E-02, A ₁₄ = -8.281361E-03,
A ₁₆ = 2.046571E-02
6th surface k = -6.788322, A ₄ = -1.918057E-02, A ₆ = 1.023597E-02, A ₈ = 1.223965E-02,
A ₁₀ = 6.050601E-03, A ₁₂ = 9.323315E-03, A ₁₄ = -9.622720E-03
7th surface k = -3.311532, A ₄ = 1.254705E-02, A ₆ = -2.682482E-02, A ₈ = 2.304837E-02,
A ₁₀ = -1.087836E-02, A ₁₂ = 3.007239E-03, A ₁₄ = 1.573687E-03
8th surface k = 0.000000, A ₄ = -3.214158E-02, A ₆ = 1.923961E-02, A ₈ = -2.092446E-02,
A ₁₀ = 3.990970E-03, A ₁₂ = 3.900573E-03, A ₁₄ = -3.216035E-04

The value of each conditional expression is shown below.
f12 / f34 = −0.973
f3 / f = 1.929
| F3 / f4 | = 0.990
d3 / f = 1.753

Thus, the imaging lens according to Numerical Example 5 satisfies the conditional expressions. Therefore, the imaging lens according to Numerical Example 5 can correct aberrations satisfactorily while having a wide angle.

FIG. 14 shows the lateral aberration corresponding to the half angle of view ω divided into the tangential direction and the sagittal direction for the imaging lens of Numerical Example 5 (the same applies to FIG. 17). FIG. 15 shows spherical aberration SA (mm), astigmatism AS (mm), and distortion aberration DIST (%) for the imaging lens of Numerical Example 5. In these aberration diagrams, the spherical aberration diagram shows the amount of aberration for each wavelength of 587.56 nm, 435.84 nm, 656.27 nm, 486.13 nm, and 546.07 nm as well as the sine condition violation amount OSC. In the aberration diagram, the amount of aberration on the sagittal image surface S and the amount of aberration on the tangential image surface T are shown (same in FIG. 18). As shown in FIGS. 14 and 15, according to the imaging lens according to Numerical Example 5, various aberrations are favorably corrected.

Numerical Example 6
Basic lens data is shown below.
f = 2.355mm, Fno = 2.555, ω = 43.69 °
Unit mm
Surface data Surface number i R d Nd νd
(Surface) ∞ ∞
1 8.314 0.5500 1.80420 46.5
2 1.882 0.9720
3 * 5.290 4.1601 1.61420 26.0
4 * 3.521 0.1000
5 * 2.166 1.0020 1.45650 90.3
6 * -2.029 0.1000
7 * 1.800 0.4000 1.52470 56.2
8 * 2.000 1.0000
9 ∞ 0.8000 1.51633 64.1
10 ∞ 2.1895
(Image plane) ∞

f3 = 2.481
f4 = 20.320
f12 = −2.133
f34 = 2.123
d3 = 4.1601

Aspherical data third surface k = 0.000000, A ₄ = -1.268173E-02, A ₆ = 3.441824E-03, A ₈ = -1.513992E-03,
A ₁₀ = -3.511395E-05, A ₁₂ = -2.215871E-05
4th surface k = -2.839900, A ₄ = -4.256199E-02, A ₆ = 2.417970E-02, A ₈ = -3.572356E-02,
A ₁₀ = 1.410330E-02, A ₁₂ = -2.052114E-03
Fifth surface k = 0.000000, A ₄ = -1.615025E-02, A ₆ = -2.318088E-03, A ₈ = -7.877264E-03,
A ₁₀ = -8.244710E-04, A ₁₂ = -2.237993E-03, A ₁₄ = -3.615144E-03,
A ₁₆ = 1.485079E-03
6th surface k = -6.788322, A ₄ = -2.730842E-02, A ₆ = 1.514906E-02, A ₈ = 6.267446E-03,
A ₁₀ = -7.120737E-03, A ₁₂ = -1.439232E-04, A ₁₄ = -3.952609E-03
7th surface k = -3.311532, A ₄ = 2.603641E-02, A ₆ = -3.812154E-02, A ₈ = 1.969940E-02,
A ₁₀ = -1.073969E-02, A ₁₂ = 2.216594E-03, A ₁₄ = -1.250410E-03
8th surface k = 0.000000, A ₄ = -9.118051E-02, A ₆ = 3.149749E-02, A ₈ = -2.109894E-02,
A ₁₀ = 7.808130E-04, A ₁₂ = 2.076978E-03, A ₁₄ = -8.885547E-04

The value of each conditional expression is shown below.
f12 / f34 = −1.005
f3 / f = 1.504
| F3 / f4 | = 0.122
d3 / f = 1.766

Thus, the imaging lens according to Numerical Example 6 satisfies the conditional expressions. Therefore, the imaging lens according to Numerical Example 6 can correct aberrations satisfactorily while having a wide angle.

FIG. 17 shows lateral aberration corresponding to the half angle of view ω for the imaging lens of Numerical Example 6, and FIG. 18 shows spherical aberration SA (mm), astigmatism AS (mm), and distortion. Each aberration DIST (%) is shown. As shown in FIGS. 17 and 18, the image pickup lens according to Numerical Example 6 also corrects the image plane well as in Numerical Example 5, and various aberrations are preferably corrected.

Therefore, when the imaging lens according to each of the above embodiments is applied to an imaging optical system such as a mobile phone, a digital still camera, a portable information terminal, a surveillance camera, an in-vehicle camera, a network camera, etc., the imaging angle of view is wide. Nevertheless, it is possible to provide a small camera in which aberrations are corrected satisfactorily.

The present invention can be applied to an imaging lens mounted on a device that requires a wide angle of view and good aberration correction capability, such as a mobile phone, a surveillance camera, and an in-vehicle camera.

ST Aperture L1 1st lens L2 2nd lens L3 3rd lens L4 4th lens 10 Cover glass

Claims

A first lens having a negative refractive power, a second lens, a third lens having a positive refractive power, and a fourth lens are arranged in order from the object side to the image plane side.
The first lens is formed in a shape in which the radius of curvature of the image side surface is positive,
The second lens is formed in a shape in which both the radius of curvature of the object side surface and the radius of curvature of the image side surface are positive,
The third lens is formed in a shape in which the curvature radius of the object side surface is positive and the curvature radius of the image side surface is negative.
The refractive power of the first lens is stronger than the refractive power of the second lens,
The refractive power of the third lens is stronger than the refractive power of the fourth lens,
When the combined focal length of the first lens and the second lens is f12, and the combined focal length of the third lens and the fourth lens is f34,
f12 <0, f34> 0
An imaging lens characterized by satisfying
When the combined focal length of the first lens and the second lens is f12, and the combined focal length of the third lens and the fourth lens is f34,
-2.0 <f12 / f34 <-0.5
The imaging lens according to claim 1, wherein:
The fourth lens has negative refractive power;
The imaging lens according to claim 1, wherein:
When the focal length of the entire lens system is f and the focal length of the third lens is f3,
0.3 <f3 / f <2.3
The imaging lens according to claim 3, wherein:
When the focal length of the third lens is f3 and the focal length of the fourth lens is f4,
| F3 / f4 | <1.5
The imaging lens according to claim 3 or 4, wherein:
When the focal length of the entire lens system is f, and the distance on the optical axis from the object side surface to the image side surface of the second lens is d3,
0.5 <d3 / f <3.0
The imaging lens according to any one of claims 3 to 5, wherein:
The fourth lens has a positive refractive power;
The imaging lens according to claim 1, wherein:
When the focal length of the entire lens system is f and the focal length of the third lens is f3,
0.5 <f3 / f <2.5
The imaging lens according to claim 7, wherein:
When the focal length of the third lens is f3 and the focal length of the fourth lens is f4,
| F3 / f4 | <1.5
The imaging lens according to claim 7 or 8, wherein:
When the focal length of the entire lens system is f, and the distance on the optical axis from the object side surface to the image side surface of the second lens is d3,
0.5 <d3 / f <2.5
The imaging lens according to any one of claims 7 to 9, wherein: