JP2010282000A - Imaging lens - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging lens capable of satisfactorily correcting aberration in spite of a reduced size. <P>SOLUTION: The imaging lens is constituted by arranging a diaphragm ST, a positive first lens L1, a negative second lens L2 with a convex surface turned toward an object, a negative third lens L3 with a concave surface turned toward the object, a positive fourth lens L4, and a negative fifth lens L5 in order from the object side. When the focal distance of the overall lens system is f, and the focal distance of the first lens L1 is f1, a condition expression: 0.5<f1/f<1.5 is satisfied. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an imaging lens that forms a subject image on an imaging element such as a CCD sensor or a CMOS sensor, and is relatively small such as a mobile phone, a digital still camera, a portable information terminal, a security camera, an in-vehicle camera, and a network camera. The present invention relates to an imaging lens suitable for being mounted on a camera.

  An imaging lens mounted on the above-described small camera is required to have a high-resolution lens configuration that can cope with a recent imaging device with a high number of pixels as well as a small number of lenses. Conventionally, a three-lens imaging lens has been frequently used as such an imaging lens. However, with the increase in the number of pixels of an imaging element, it has become difficult to obtain sufficient performance with only three lenses. In recent years, adoption of a lens configuration including a four-lens configuration or a five-lens configuration has been sought.

  Among them, the lens configuration consisting of five lenses is expected as a lens configuration adopted for the next generation imaging lens because of its high design freedom. As an imaging lens having a five-lens configuration, for example, an imaging lens described in Patent Document 1 is known. In this imaging lens, in order from the object side, a positive first lens having a convex surface on the object side, a second meniscus second lens having a concave surface facing the image surface, and a convex surface facing the image surface side A positive third meniscus lens, a negative fourth lens having an aspheric surface on both sides and a concave surface on the image plane side in the vicinity of the optical axis, and a positive or negative fifth lens having an aspheric surface on both sides It consists of and. In this configuration, the lower limit value of the Abbe number of the first lens and the upper limit value of the Abbe numbers of the second and fourth lenses are respectively defined to correct axial chromatic aberration and lateral chromatic aberration, thereby improving the performance of the imaging lens. It corresponds to.

JP 2007-264180 A

  According to the imaging lens described in Patent Document 1, it is possible to obtain a relatively good aberration. However, since the total length of the lens system is long, it is difficult to achieve both the downsizing of the imaging lens and good aberration correction.

  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 that can correct aberrations satisfactorily while being small in size.

In order to solve the above problems, in the present invention, in order from the object side to the image surface side, a first lens having a positive refractive power, a second lens having a negative refractive power, and a negative refractive power are obtained. A third lens having a positive refractive power and a fifth lens having a negative refractive power are arranged, the focal length of the entire lens system is f, and the focal length of the first lens is f1. At this time, the following conditional expression (1) was satisfied.
0.5 <f1 / f <1.5 (1)

In the present invention, in order from the object side to the image plane side, a first lens having a positive refractive power, a second lens having a negative refractive power, and a third lens having a positive refractive power; When a fourth lens having a positive refractive power and a fifth lens having a negative refractive power are arranged, the focal length of the entire lens system is f, and the focal length of the first lens is f1, the following conditional expression ( It was configured to satisfy 1).
0.5 <f1 / f <1.5 (1)

  Conditional expression (1) defines the distribution of the refractive power of the first lens in the entire lens system. By setting the refractive power of the first lens within the range of the conditional expression (1), the length (thickness) along the optical axis of the imaging lens is shortened, and on-axis chromatic aberration and off-axis chromatic aberration of magnification. Can be corrected satisfactorily.

  In conditional expression (1), if the upper limit “1.5” is exceeded, the refractive power of the first lens in the entire lens system becomes weak, and it is difficult to reduce the size of the imaging lens. In addition, if the refractive power of the first lens is weak, it is necessary to reduce the refractive power of the second lens having negative refractive power, which causes an increase in astigmatism, and it is difficult to obtain good imaging performance. Become. On the other hand, if the value falls below the lower limit “0.5”, the refractive power of the first lens occupying the entire lens system becomes strong and it becomes easy to reduce the size of the imaging lens, but the axial chromatic aberration is insufficiently corrected ( The short wavelength increases in the negative direction with respect to the reference wavelength). Further, since the off-axis lateral chromatic aberration is insufficiently corrected, it is difficult to match the best imaging plane for each wavelength off-axis. For off-axis light beams, the best image plane with a short wavelength generally increases in the-direction.

  In the imaging lens having the above-described configuration, the second lens is a meniscus having 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, that is, a meniscus having a convex surface facing the object side at least near the optical axis. A third lens having a shape in which the curvature radius of the object side surface and the curvature radius of the image side surface are both negative, that is, a meniscus lens having a concave surface facing the object side at least in the vicinity of the optical axis. It is desirable to have a shape. By adopting such a configuration as the imaging lens, the flatness of the image plane is kept good and the distortion can be corrected well by the symmetry of the second lens and the third lens.

In the imaging lens having the above configuration, it is desirable that the following conditional expression (2) is satisfied when the focal length of the fourth lens is f4.
0.5 <f4 / f <1.5 (2)

  Conditional expression (2) suppresses the incident angle of the light beam emitted from the imaging lens to the imaging element within a certain range, and also suppresses off-axis chromatic aberration and curvature of field within a favorable range. It is a condition. As is well known, a light beam that can be taken into an image sensor has a so-called maximum incident angle as a limit on the incident angle 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.

  In conditional expression (2), when the upper limit value “1.5” is exceeded, the refractive power of the fourth lens becomes weak, and the off-axis lateral chromatic aberration is overcorrected (short wavelength increases in the + direction with respect to the reference wavelength). Become. Further, since the astigmatic difference increases, it becomes difficult to obtain a flat image surface. On the other hand, when the value falls below the lower limit “0.5”, the refractive power of the fourth lens increases, which is advantageous for suppressing the incident angle of the light beam emitted from the imaging lens to the imaging element within a certain range. However, off-axis lateral chromatic aberration is undercorrected (short wavelength increases in the negative direction with respect to the reference wavelength). In addition, since axial chromatic aberration is similarly insufficiently corrected, it is difficult to obtain good imaging performance.

The imaging lens having the above configuration is configured such that the combined focal length of the second lens and the third lens is a negative value, and when the combined focal length of the second lens and the third lens is f23, It is more desirable to satisfy conditional expression (3).
−0.7 <f1 / f23 <−0.2 (3)

  Conditional expression (3) is a condition for reducing the size of the imaging lens and suppressing aberrations such as on-axis and off-axis chromatic aberration, spherical aberration, and astigmatism within a favorable range. If the upper limit value “−0.2” is exceeded, the combined focal length of the second lens and the third lens becomes relatively longer than that of the first lens, that is, the combination of the second lens and the third lens. Although the refractive power is weak, which is advantageous for downsizing the imaging lens, both on-axis and off-axis chromatic aberrations are undercorrected. Moreover, it becomes difficult to obtain the best imaging plane both on-axis and off-axis due to an increase in astigmatism and the influence of spherical aberration.

  On the other hand, when the value is below the lower limit “−0.7”, the combined refractive power of the second lens and the third lens becomes strong, so that it is easy to correct on-axis and off-axis chromatic aberration, but the imaging lens It becomes difficult to reduce the size. In addition, due to the influence of spherical aberration, the best imaging surface outside the axis falls to the image surface side with respect to the best imaging surface on the axis, and it becomes difficult to obtain a flat image surface.

Furthermore, 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 second lens is f2 and the focal length of the third lens is f3.
−0.7 <f2 / f3 <0.7 (4)

  Conditional expression (4) is a condition for suppressing on-axis and off-axis chromatic aberration and curvature of field within a favorable range. If the upper limit “0.7” is exceeded, off-axis lateral chromatic aberration will be overcorrected and the best imaging plane will fall to the image plane side, making it difficult to obtain good imaging performance. On the other hand, if the value falls below the lower limit “−0.7”, the axial chromatic aberration is insufficiently corrected, and the best imaging surface falls to the object side, which makes it difficult to obtain good imaging performance in this case as well. Become. In particular, the sagittal plane is greatly tilted toward the object side, and it is difficult to correct it.

  According to the imaging lens of the present invention, it is possible to provide both a compact imaging lens in which various types of aberrations are favorably corrected while achieving both a reduction in size of the imaging lens and good aberration correction.

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. 6 is an aberration diagram showing lateral aberration of the imaging lens according to Example 1 with the same numerical values. FIG. 6 is an aberration diagram showing spherical aberration, astigmatism, and distortion of the imaging lens according to Example 1 of the same numerical value. FIG. 5 is a lens cross-sectional view illustrating a schematic configuration of an imaging lens according to Numerical Example 2 according to the embodiment of the present invention. FIG. 6 is an aberration diagram showing lateral aberration of the imaging lens according to Numerical Example 2; FIG. 6 is an aberration diagram showing spherical aberration, astigmatism, and distortion of the imaging lens according to Example 2 of the same numerical value. FIG. 10 is a lens cross-sectional view illustrating a schematic configuration of an imaging lens according to Numerical Example 3 according to the embodiment of the present invention. FIG. 10 is an aberration diagram showing lateral aberration of the imaging lens according to Numerical Example 3; FIG. 10 is an aberration diagram showing spherical aberration, astigmatism, and distortion of the imaging lens according to Numerical Example 3; FIG. 10 is a lens cross-sectional view illustrating a schematic configuration of an imaging lens according to Numerical Example 4 regarding the second embodiment of the present invention. FIG. 6 is an aberration diagram showing lateral aberration of the imaging lens according to Numerical Example 4; FIG. 10 is an aberration diagram showing spherical aberration, astigmatism, and distortion of the imaging lens according to Numerical Example 4; FIG. 10 is a lens cross-sectional view illustrating a schematic configuration of an imaging lens according to Numerical Example 5 according to the embodiment of the present invention. FIG. 10 is an aberration diagram illustrating lateral aberration of the imaging lens according to Numerical Example 5; FIG. 10 is an aberration diagram showing spherical aberration, astigmatism, and distortion of the imaging lens according to Numerical Example 5; FIG. 10 is a lens cross-sectional view illustrating a schematic configuration of an imaging lens according to Numerical Example 6 according to the embodiment of the present invention. FIG. 10 is an aberration diagram showing lateral aberration of the imaging lens according to Numerical Example 6; FIG. 10 is an aberration diagram showing spherical aberration, astigmatism, and distortion of the imaging lens according to Numerical Example 6;

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

  1, 4, and 7 are lens cross-sectional views corresponding to Numerical Examples 1 to 3 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 has an aperture stop ST, a first lens L1 having a positive refractive power, and a negative refractive power in order from the object side to the image plane side. The second lens L2, the third lens L3 having negative refractive power, the fourth lens L4 having positive refractive power, and the fifth lens L5 having negative refractive power are arranged. A cover glass 10 is disposed between the fifth lens L5 and the image plane. The cover glass 10 can be omitted. In the present embodiment, the aperture stop is disposed on the object side of the vertex tangent plane of the object side surface of the first lens L1. The position of the aperture stop is not limited to the position in the present embodiment, and may be, for example, between the vertex tangent plane of the object side surface of the first lens L1 and the image surface side surface of the first lens L1.

  In the imaging lens having the above configuration, the first lens L1 has a shape in which the curvature radius R2 of the object side surface is positive and the curvature radius R3 of the image side surface is negative, that is, a biconvex lens in the vicinity of the optical axis. It is formed into a shape. Numerical Example 1 is an example in which the shape of the first lens L1 is a biconvex lens near the optical axis. In Numerical Examples 2 and 3, the shape of the first lens L1 is the radius of curvature of the object-side surface. This is an example of a meniscus lens in which the curvature radius R3 of both the surface R2 and the image surface side is positive, that is, a meniscus lens having a convex surface facing the object side in the vicinity of the optical axis.

  The second lens L2 has a positive curvature radius R4 on the object side surface and a curvature radius R5 on the image surface side, 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. The third lens L3 has a shape in which the curvature radius R6 of the object side surface and the curvature radius R7 of the image surface side are both negative, and a shape that becomes a meniscus lens with a concave surface facing the object side in the vicinity of the optical axis. Is formed.

  The fourth lens L4 has a shape in which the radius of curvature R8 of the object side surface is positive and the radius of curvature R9 of the image side surface is negative, and is formed in a shape that becomes a biconvex lens in the vicinity of the optical axis. The fourth lens L4 may be a lens having a positive refractive power, and may have a shape that becomes a meniscus lens near the optical axis, for example.

  The fifth lens L5 has a shape in which the curvature radius R10 of the object-side surface is negative and the curvature radius R11 of the image-side surface is positive, and is formed into a shape that is a biconcave lens in the vicinity of the optical axis. The image side surface of the fifth lens L5 is formed in an aspherical shape that is convex toward the object side in the vicinity of the optical axis and concave toward the object side at the periphery. With such a shape of the fifth lens L5, the incident angle of the light emitted from the imaging lens to the image plane is suppressed. The fifth lens L5 may be a lens having negative refractive power, and may be a shape that becomes a meniscus lens in the vicinity of the optical axis, for example.

The imaging lens according to the present embodiment is configured to satisfy the following conditional expressions (1) to (4).
0.5 <f1 / f <1.5 (1)
0.5 <f4 / f <1.5 (2)
−0.7 <f1 / f23 <−0.2 (3)
−0.7 <f2 / f3 <0.7 (4)
However,
f: focal length of the entire lens system f1: focal length of the first lens L1 f2: focal length of the second lens L2 f3: focal length of the third lens L3 f4: focal length of the fourth lens L4 f23: second lens L2 Focal length of the lens and the third lens L3

Further, the imaging lens according to the present embodiment satisfies the following conditional expression (5) in addition to the conditional expressions (1) to (4).
−1.5 <f5 / f <−0.5 (5)
However,
f5: focal length of the fifth lens L5

  Conditional expression (5) is a condition for satisfactorily correcting on-axis and off-axis chromatic aberration and field curvature while reducing the size of the imaging lens. If the upper limit “−0.5” is exceeded, the refractive power of the fifth lens becomes strong, which is advantageous for downsizing the imaging lens. However, in order to correct each aberration well, a lens other than the fifth lens can be used. It becomes necessary to increase the refractive power of each lens, and it becomes difficult to satisfactorily correct on-axis and off-axis chromatic aberration and curvature of field. On the other hand, when the value is below the lower limit “−1.5”, the refractive power of the fifth lens becomes weak, and it is difficult to reduce the size of the imaging lens.

  In addition, it is not necessary to satisfy | fill all the said conditional expressions (1)-(5), and each of the said conditional expressions (1)-(5) is satisfy | filled independently, and the effect corresponding to each conditional expression is obtained, respectively. be able to.

In the present embodiment, the lens surface of each lens is formed as an aspherical 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 _{When 10} , A ₁₂ , A ₁₄ , and A ₁₆ , they are expressed by the following formula. In the imaging lens according to the second embodiment to be described later, the lens surfaces of the respective lenses are formed as aspherical surfaces as necessary. The aspherical shape adopted for these lens surfaces is the same as that of the present embodiment. Similar to the form, it is represented by the following formula.

  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. For reference, the sum of the surface intervals from the object-side surface of the first lens L1 to the image-side surface of the fifth lens L5 is shown as Σd.

Numerical example 1
Basic lens data is shown below.
f = 5.295mm, Fno = 2.805, ω = 36.37 °
Unit mm
Surface data Surface number i R d Nd νd
(Surface) ∞ ∞
1 (Aperture) ∞ 0.0100
2 * 2.124 0.8000 1.52470 56.2
3 * -41.020 0.1000
4 * 7.470 0.3500 1.61420 26.0
5 * 2.972 0.9750
6 -1.470 0.4500 1.58500 29.0
7 * -1.700 0.1000
8 * 6.739 1.3297 1.52470 56.2
9 * -4.148 0.5769
10 * -5.137 0.4000 1.58500 29.0
11 * 6.398 0.5500
12 ∞ 0.1500 1.51633 64.12
13 ∞ 0.7017
(Image plane) ∞

f1 = 3.873
f2 = −8.281
f3 = −66.839
f4 = 5.108
f5 = -4.809
f23 = −7.974
Σd = 5.0816

Aspherical data second surface k = -7.644281E-02, A ₄ = 1.288781E-03, A ₆ = -5.380697E-03, A ₈ = 3.543593E-03,
A ₁₀ = -8.350922E-03
3rd surface k = 9.283191E + 02, A ₄ = -4.067445E-03, A ₆ = 6.942289E-03, A ₈ = -1.798149E-02,
A ₁₀ = -7.892011E-03
4th surface k = 1.377968E + 01, A ₄ = -2.526523E-03, A ₆ = -1.690417E-03, A ₈ = 7.698948E-03,
A ₁₀ = -1.244507E-02
5th surface k = 3.181258, A ₄ = -1.196342E-02, A ₆ = 4.560808E-03
7th surface k = -4.235609E-01, A ₄ = -2.327520E-02, A ₆ = 1.492072E-02, A ₈ = -3.063083E-03,
A ₁₀ = 1.358330E-03
8th surface k = -1.254759E + 02, A ₄ = -1.207277E-03, A ₆ = 2.766646E-04
9th surface k = -1.051139, A ₄ = 2.477486E-03, A ₆ = -3.614602E-03, A ₈ = 4.263190E-04
10th surface k = 1.739600, A ₄ = -2.626069E-03, A ₆ = -3.861998E-03, A ₈ = 4.072871E-04
11th surface k = -1.000000, A ₄ = -1.910952E-02, A ₆ = 4.682273E-04, A ₈ = -1.243862E-05,
A ₁₀ = 4.211164E-07

The value of each conditional expression is shown below.
f1 / f = 0.733
f4 / f = 0.965
f1 / f23 = −0.486
f2 / f3 = 0.124
f5 / f = −0.908
As described above, the imaging lens according to Numerical Example 1 satisfies the conditional expressions (1) to (5).

  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 (FIGS. 5, 8, 11, 14, and 14). Same in FIG. 17). 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 surface S and the aberration amount on the tangential image surface T (the same applies to FIGS. 6, 9, 12, 15, and 18). 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 = 3.751mm, Fno = 2.805, ω = 36.25 °
Unit mm
Surface data Surface number i R d Nd νd
(Surface) ∞ ∞
1 (Aperture) ∞ 0.0000
2 * 1.576 0.4200 1.52470 56.2
3 * 15.221 0.1000
4 * 4.890 0.2700 1.61420 26.0
5 * 2.397 0.5000
6 -1.043 0.2900 1.61420 26.0
7 * -1.201 0.2500
8 * 4.824 0.8800 1.52470 56.2
9 * -2.394 0.4300
10 * -3.688 0.3000 1.61420 26.0
11 * 6.041 0.1000
12 ∞ 0.3000 1.51633 64.12
13 ∞ 1.0001
(Image plane) ∞

f1 = 3.315
f2 = −7.984
f3 = −42.796
f4 = 3.183
f5 = -3.685
f23 = −7.224
Σd = 3.4400

Aspherical data second surface k = 1.136990, A ₄ = -8.153389E-03, A ₆ = -3.769255E-02, A ₈ = 2.690469E-02,
A ₁₀ = -2.357625E-01
3rd surface k = -1.242099E + 03, A ₄ = 1.540398E-02, A ₆ = 1.762106E-02, A ₈ = -1.451009E-01,
A ₁₀ = -2.893807E-01
4th surface k = -1.790884E + 01, A ₄ = -2.010434E-02, A ₆ = 2.345432E-03, A ₈ = 1.296707E-01,
A ₁₀ = -4.940520E-01
5th surface k = -7.021443E-01, A ₄ = 1.111750E-02, A ₆ = 5.082258E-02
7th surface k = -4.453865E-01, A ₄ = -8.294035E-02, A ₆ = 3.994330E-02, A ₈ = -2.448183E-03,
A ₁₀ = -2.105226E-02
8th surface k = -1.404949E + 02, A ₄ = 2.270077E-03, A ₆ = 4.091082E-03
9th surface k = -7.090167E-01, A ₄ = 4.424760E-03, A ₆ = 3.984416E-03, A ₈ = 1.586669E-03
10th surface k = -3.140993, A ₄ = -3.055203E-02, A ₆ = -1.164968E-02
11th surface k = 0, A ₄ = -4.126709E-02, A ₆ = -2.432407E-03

The value of each conditional expression is shown below.
f1 / f = 0.484
f4 / f = 0.849
f1 / f23 = −0.458
f2 / f3 = 0.187
f5 / f = −0.982
As described above, the imaging lens according to Numerical Example 2 satisfies the conditional expressions (1) to (5).

  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 and corrects various aberrations as well as Numerical Example 1.

Numerical Example 3
Basic lens data is shown below.
f = 3.700mm, Fno = 2.805, ω = 31.30 °
Unit mm
Surface data Surface number i R d Nd νd
(Surface) ∞ ∞
1 (Aperture) ∞ 0.0000
2 * 1.689 0.4200 1.61800 63.4
3 * 9.481 0.1000
4 * 1.663 0.2700 1.58500 29.0
5 * 1.221 0.5000
6 -1.500 0.2700 1.58500 29.0
7 * -1.850 0.2000
8 * 11.648 0.8000 1.52470 56.2
9 * -1.581 0.3000
10 * -2.144 0.3000 1.58500 29.0
11 * 11.545 0.1000
12 ∞ 0.5000 1.51633 64.12
13 ∞ 0.7507
(Image plane) ∞

f1 = 3.258
f2 = -10.139
f3 = −18.948
f4 = 2.709
f5 = −3.066
f23 = −6.871
Σd = 3.1600

Aspherical data second surface k = 1.224714, A ₄ = -1.936434E-02, A ₆ = -4.196981E-02, A ₈ = -1.539555E-02,
A ₁₀ = -7.269246E-02
3rd surface k = -8.459881E + 01, A ₄ = 2.348368E-02, A ₆ = -1.807915E-02, A ₈ = -4.707691E-02,
A ₁₀ = -8.009570E-02
4th surface k = -4.227424E-01, A ₄ = 7.415721E-03, A ₆ = 1.230385E-02, A ₈ = -2.979599E-03,
A ₁₀ = -5.131533E-02
5th surface k = -1.573689E-01, A ₄ = -9.847234E-03, A ₆ = 3.687548E-02
7th surface k = -8.912540E-01, A ₄ = -1.510988E-02, A ₆ = 3.875740E-03, A ₈ = 3.088671E-02,
A ₁₀ = 1.799942E-02
8th surface k = -2.497553E + 02, A ₄ = -9.567089E-03, A ₆ = 4.999140E-03
9th surface k = -2.732886, A ₄ = 8.290396E-03, A ₆ = 1.647650E-03, A ₈ = -3.071388E-03
10th surface k = -4.687485E-02, A ₄ = -1.381541E-02, A ₆ = -1.291757E-02
11th surface k = 0, A ₄ = -8.046678E-02, A ₆ = 2.912423E-03

The value of each conditional expression is shown below.
f1 / f = 0.811
f4 / f = 0.732
f1 / f23 = −0.474
f2 / f3 = 0.535
f5 / f = −0.829
Thus, the imaging lens according to Numerical Example 3 satisfies the conditional expressions (1) to (5).

  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 well and various aberrations as well as Numerical Example 1.

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

  FIGS. 10, 13, and 16 are lens cross-sectional views corresponding to Numerical Examples 4 to 6 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 a lens cross-sectional view of Numerical Example 4.

  As shown in FIG. 10, the imaging lens according to the present embodiment has an aperture stop ST, a first lens L1 having a positive refractive power, and a negative refractive power in order from the object side to the image plane side. The second lens L2, the third lens L3 having positive refractive power, the fourth lens L4 having positive refractive power, and the fifth lens L5 having negative refractive power are arranged. A cover glass 10 is disposed between the fifth lens L5 and the image plane.

  Thus, in the imaging lens according to the present embodiment, unlike the imaging lens according to the first embodiment, the third lens L3 is configured as a lens having a positive refractive power. In this embodiment as well, the aperture stop is arranged on the object side with respect to the vertex tangent plane of the object side surface of the first lens L1, and the position of the aperture stop is the same as that in the first embodiment. Similarly, the position is not limited to the position in the present embodiment.

  In the imaging lens having the above configuration, the first lens L1 has a shape in which the curvature radius R2 of the object side surface is positive and the curvature radius R3 of the image side surface is negative, that is, a biconvex lens in the vicinity of the optical axis. It is formed into a shape. The first lens L1 may be a lens having a positive refractive power, and may have a shape that becomes a meniscus lens near the optical axis, for example.

  The second lens L2 has a positive curvature radius R4 on the object side surface and a curvature radius R5 on the image surface side, 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. The third lens L3 has a shape in which the curvature radius R6 of the object side surface and the curvature radius R7 of the image surface side are both negative, and a shape that becomes a meniscus lens with a concave surface facing the object side in the vicinity of the optical axis. Is formed.

  The fourth lens L4 has a shape in which the radius of curvature R8 of the object side surface is positive and the radius of curvature R9 of the image side surface is negative, and is formed in a shape that becomes a biconvex lens in the vicinity of the optical axis. The fourth lens L4 may be a lens having a positive refractive power as in the first embodiment, and may have a shape that becomes a meniscus lens near the optical axis, for example.

  The fifth lens L5 has a shape in which the curvature radius R10 of the object-side surface is negative and the curvature radius R11 of the image-side surface is positive, and is formed into a shape that is a biconcave lens in the vicinity of the optical axis. The surface on the image plane side of the fifth lens L5 is formed in an aspherical shape that is convex toward the object side in the vicinity of the optical axis and concave toward the object side at the periphery. As in the first embodiment, the fifth lens L5 may be a lens having a negative refractive power, and may be a shape that becomes a meniscus lens near the optical axis, for example.

The imaging lens according to the present embodiment is configured to satisfy the following conditional expressions (1) to (4).
0.5 <f1 / f <1.5 (1)
0.5 <f4 / f <1.5 (2)
−0.7 <f1 / f23 <−0.2 (3)
−0.7 <f2 / f3 <0.7 (4)
However,
f: focal length of the entire lens system f1: focal length of the first lens L1 f2: focal length of the second lens L2 f3: focal length of the third lens L3 f4: focal length of the fourth lens L4 f23: second lens L2 Focal length of the lens and the third lens L3

In addition to the conditional expressions (1) to (4), the imaging lens according to the present embodiment satisfies the following conditional expression (5) as in the first embodiment.
−1.5 <f5 / f <−0.5 (5)
However,
f5: focal length of the fifth lens L5

  In addition, it is not necessary to satisfy | fill all the said conditional expressions (1)-(5), and each of the said conditional expressions (1)-(5) is satisfy | filled independently, and the effect corresponding to each conditional expression is obtained, respectively. be able to.

  Next, numerical examples of the imaging lens according to the present embodiment will be shown. In this 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. Here, for reference, the sum of the surface intervals from the object-side surface of the first lens L1 to the image-side surface of the fifth lens L5 is shown as Σd.

Numerical Example 4
Basic lens data is shown below.
f = 5.297mm, Fno = 2.805, ω = 36.36 °
Unit mm
Surface data Surface number i R d Nd νd
(Surface) ∞ ∞
1 (Aperture) ∞ 0.1500
2 * 2.188 0.8000 1.49700 81.6
3 * -123.000 0.1000
4 * 7.865 0.3500 1.58500 29.0
5 * 2.963 1.0000
6 -1.720 0.3500 1.61420 26.0
7 * -1.670 0.1000
8 * 7.494 1.3000 1.52470 56.2
9 * -4.200 0.6000
10 * -4.760 0.4000 1.58500 29.0
11 * 5.370 0.5500
12 ∞ 0.1500 1.51633 64.12
13 ∞ 0.8178
(Image plane) ∞

f1 = 4.335
f2 = −8.346
f3 = 25.531
f4 = 5.334
f5 = −4.251
f23 = -14.916
Σd = 5.000

Aspherical data second surface k = 7.816470E-03, A ₄ = 2.245317E-03, A ₆ = -1.449120E-03, A ₈ = 3.477430E-04,
A ₁₀ = -4.407501E-03
3rd surface k = 2.185177E + 03, A ₄ = -2.920200E-03, A ₆ = 6.171094E-03, A ₈ = -1.021987E-02,
A ₁₀ = -6.938202E-03
4th surface k = -2.830204, A ₄ = -8.437785E-03, A ₆ = -2.914928E-03, A ₈ = 3.626528E-03,
A ₁₀ = -7.454739E-03
5th surface k = 2.608311, A ₄ = -1.040970E-02, A ₆ = 3.139623E-04
7th surface k = -3.294938E-01, A ₄ = -2.653472E-02, A ₆ = 1.343421E-02, A ₈ = -3.259187E-03,
A ₁₀ = 8.215336E-04
8th surface k = -1.760978E + 02, A ₄ = -2.170199E-03, A ₆ = 1.571859E-04
9th surface k = -2.059658, A ₄ = 3.729424E-03, A ₆ = -3.498959E-03, A ₈ = 2.999830E-04
10th surface k = 1.739600, A ₄ = -2.626069E-03, A ₆ = -3.861998E-03, A ₈ = 4.072871E-04
11th surface k = -1.000000, A ₄ = -1.910952E-02, A ₆ = 4.682273E-04, A ₈ = -1.243862E-05,
A ₁₀ = 4.211164E-07

The value of each conditional expression is shown below.
f1 / f = 0.818
f4 / f = 1.007
f1 / f23 = −0.291
f2 / f3 = −0.327
f5 / f = −0.803
As described above, the imaging lens according to Numerical Example 4 satisfies the conditional expressions (1) to (5).

  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, according to the imaging lens according to Numerical Example 4, various aberrations are favorably corrected.

Numerical Example 5
Basic lens data is shown below.
f = 5.307mm, Fno = 2.805, ω = 36.31 °
Unit mm
Surface data Surface number i R d Nd νd
(Surface) ∞ ∞
1 (Aperture) ∞ 0.0100
2 * 2.172 0.8000 1.52470 56.2
3 * -73.266 0.1000
4 * 7.339 0.3500 1.61420 26.0
5 * 2.911 0.9884
6 -1.515 0.4500 1.58500 29.0
7 * -1.611 0.1000
8 * 8.402 1.3065 1.52470 56.2
9 * -3.960 0.6007
10 * -4.893 0.4000 1.58500 29.0
11 * 6.444 0.5500
12 ∞ 0.1500 1.51633 64.12
13 ∞ 0.7848
(Image plane) ∞

f1 = 4.035
f2 = −8.099
f3 = 59.526
f4 = 5.332
f5 = −4.693
f23 = -10.847
Σd = 5.0956

Aspheric data second surface k = -2.254152E-02, A ₄ = 1.940950E-03, A ₆ = -3.155615E-03, A ₈ = 3.832048E-03,
A ₁₀ = -7.265498E-03
Third surface k = -1.615339E + 02, A ₄ = -1.769518E-03, A ₆ = 7.854194E-03, A ₈ = -1.506243E-02,
A ₁₀ = -6.486282E-03
4th surface k = 8.726061, A ₄ = -4.392010E-03, A ₆ = -2.142554E-03, A ₈ = 7.346625E-03,
A ₁₀ = -1.016687E-02
5th surface k = 2.891833, A ₄ = -1.247630E-02, A ₆ = 2.750535E-03
7th surface k = -3.960595E-01, A ₄ = -2.204086E-02, A ₆ = 1.436825E-02, A ₈ = -3.192608E-03,
A ₁₀ = 1.091071E-03
8th surface k = -2.339065E + 02, A ₄ = -1.474389E-03, A ₆ = 2.570016E-04
9th surface k = -1.146943, A ₄ = 2.353065E-03, A ₆ = -3.693389E-03, A ₈ = 4.183601E-04
10th surface k = 1.739600, A ₄ = -2.626069E-03, A ₆ = -3.861998E-03, A ₈ = 4.072871E-04
11th surface k = -1.000000, A ₄ = -1.910952E-02, A ₆ = 4.682273E-04, A ₈ = -1.243862E-05,
A ₁₀ = 4.211164E-07

The value of each conditional expression is shown below.
f1 / f = 0.760
f4 / f = 1.003
f1 / f23 = −0.372
f2 / f3 = −0.136
f5 / f = −0.884
As described above, the imaging lens according to Numerical Example 5 satisfies the conditional expressions (1) to (5).

  FIG. 14 shows lateral aberration corresponding to the half angle of view ω for the imaging lens of Numerical Example 5, and FIG. 15 shows spherical aberration SA (mm), astigmatism AS (mm), and distortion. Each aberration DIST (%) is shown. As shown in FIG. 14 and FIG. 15, the imaging lens according to Numerical Example 5 also corrects the image plane well and corrects various aberrations as well as Numerical Example 4.

Numerical Example 6
Basic lens data is shown below.
f = 6.104mm, Fno = 2.805, ω = 33.24 °
Unit mm
Surface data Surface number i R d Nd νd
(Surface) ∞ ∞
1 (Aperture) ∞ 0.0200
2 * 2.237 0.9230 1.52470 56.2
3 * -38.360 0.1150
4 10.434 0.4000 1.61420 26.0
5 3.497 1.0400
6 -1.748 0.5200 1.58500 29.0
7 * -1.905 0.1150
8 * 12.278 1.4750 1.52470 56.2
9 * -7.254 0.4600
10 * -11.422 0.4600 1.58500 29.0
11 * 6.409 0.6300
12 ∞ 0.1700 1.51633 64.12
13 ∞ 0.8728
(Image plane) ∞

f1 = 4.060
f2 = −8.756
f3 = 162.987
f4 = 8.992
f5 = −6.952
f23 = -10.424
Σd = 5.5080

Aspherical data second surface k = -1.643371E-01, A ₄ = 1.917724E-04, A ₆ = -6.667749E-03, A ₈ = 9.037175E-03,
A ₁₀ = -4.219264E-03, A ₁₂ = -1.978097E-04, A ₁₄ = -5.307641E-05, A ₁₆ = 3.196725E-05
Third surface k = 0, A ₄ = -8.194940E-03, A ₆ = 8.073323E-03, A ₈ = -1.722615E-03, A ₁₀ = -3.530646E-03
7th surface k = -7.267883E-01, A ₄ = -1.208723E-02, A ₆ = 1.204065E-02, A ₈ = -1.696226E-03,
A ₁₀ = 1.010631E-03, A ₁₂ = -9.991592E-06, A ₁₄ = -3.138679E-07, A ₁₆ = 4.287207E-06
8th surface k = -5.582484E + 02, A ₄ = -5.779034E-03, A ₆ = 2.393445E-05
9th surface k = 4.602461, A ₄ = -2.388356E-03, A ₆ = -1.396139E-03, A ₈ = 7.261183E-05,
A ₁₀ = -4.630012E-06, A ₁₂ = 0, A ₁₄ = -4.759863E-08, A ₁₆ = -1.538876E-09
10th surface k = 1.739600, A ₄ = -1.708790E-03, A ₆ = -1.887048E-03, A ₈ = 1.494376E-04
11th surface k = -1.000000, A ₄ = -1.325283E-02, A ₆ = 3.704832E-04, A ₈ = -1.375953E-06,
A ₁₀ = 9.552826E-09, A ₁₂ = -1.589930E-08, A ₁₄ = -1.123242E-09, A ₁₆ = -5.806715E-11

The value of each conditional expression is shown below.
f1 / f = 0.665
f4 / f = 1.462
f1 / f23 = −0.389
f2 / f3 = −0.054
f5 / f = −1.139
As described above, the imaging lens according to Numerical Example 6 satisfies the conditional expressions (1) to (5).

  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 FIG. 17 and FIG. 18, the imaging lens according to Numerical Example 6 also corrects the image plane well and corrects various aberrations as well as Numerical Example 4.

  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 security camera, an in-vehicle camera, a network camera, and the like, Both miniaturization can be achieved.

  The present invention can be applied to an imaging lens mounted on a device that is required to have a small aberration as well as a good aberration correction capability, such as a mobile phone or a digital still camera.

ST Aperture L1 1st lens L2 2nd lens L3 3rd lens L4 4th lens L5 5th lens 10 Cover glass

Claims (6)

A first lens having a positive refractive power, a second lens having a negative refractive power, a third lens having a negative refractive power, and a positive refractive power in order from the object side to the image plane side. It is composed of a fourth lens and a fifth lens having negative refractive power,
When the focal length of the entire lens system is f and the focal length of the first lens is f1,
0.5 <f1 / f <1.5
An imaging lens characterized by satisfying In the second lens, the radius of curvature of the object side surface and the radius of curvature of the image side surface are both positive,
In the third lens, both the radius of curvature of the object side surface and the radius of curvature of the image side surface are negative.
The imaging lens according to claim 1. A first lens having a positive refractive power, a second lens having a negative refractive power, a third lens having a positive refractive power, and a positive refractive power in order from the object side to the image plane side. It is composed of a fourth lens and a fifth lens having negative refractive power,
When the focal length of the entire lens system is f and the focal length of the first lens is f1,
0.5 <f1 / f <1.5
An imaging lens characterized by satisfying When the focal length of the fourth lens is f4,
0.5 <f4 / f <1.5
The imaging lens according to claim 1, wherein: When the combined focal length of the second lens and the third lens is negative and the combined focal length of the second lens and the third lens is f23,
−0.7 <f1 / f23 <−0.2
The imaging lens according to claim 1, wherein the imaging lens is satisfied. When the focal length of the second lens is f2, and the focal length of the third lens is f3,
-0.7 <f2 / f3 <0.7
An imaging lens characterized by satisfying