JP2012177831A - Imaging lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an imaging lens which allows the distortion aberration to be satisfactorily corrected though being wide-angle.SOLUTION: A first lens L1 which has a biconcave shape in the vicinity of an optical axis X, a second negative lens L2 which has a meniscus shape having a convex on the object side in the vicinity of the optical axis, a third lens L3 which has a biconvex shape in the vicinity of the optical axis, a fourth lens L4 which has a biconcave shape in the vicinity of the optical axis, and a fifth lens L5 having a biconvex shape in the vicinity of the optical axis are arranged in this order from the object side. In this configuration, a surface on the object side of the second lens L2 is formed to such a shape that a more convex surface faces the object side from the optical axis X toward a peripheral edge, and a surface on the image surface side of the fifth lens L5 is formed to an aspherical shape having an inflection point.

Description

  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 security camera, a real projector, a scanner, a network camera, and the like. The present invention relates to a preferable imaging lens.

  With the development of ICT (Information and Communication Technology), sharing of information and knowledge has advanced, and in recent years, ICT devices based on the ICT have appeared. Among them, a real projector, a so-called document camera, capable of enlarging and projecting a planar object such as a textbook or a document to a three-dimensional object, is widely used mainly in educational sites and conference rooms. According to the document camera, the materials and actual objects at hand are enlarged and displayed as they are, so for example, when used in a conference room, the presenter can make a flexible presentation, while one conference participant can understand the contents of the presentation. This makes it easy to grasp the actual object that is the projection target.

  A document camera is usually placed on a desk, so it is desirable that the document camera be small. In addition, it is desirable that more information such as characters and figures be projected or displayed with more detail. For this reason, an imaging lens mounted on a document camera is required to be small in size, to support high resolution, and to widen a shooting angle of view to support a wide shooting range. However, it is difficult to reduce the size while properly correcting various aberrations in order to cope with high resolution, and to widen the shooting angle of view. For example, if the imaging lens is downsized, the refractive power of each lens increases, and it becomes difficult to correct various aberrations satisfactorily. Thus, in actual design of the imaging lens, it is important to satisfy these requirements in a balanced manner.

  As an imaging lens having a wide shooting angle of view, for example, an imaging lens described in Patent Document 1 is known. This imaging lens is configured by arranging, in order from the object side, a front group having a negative refractive power and a rear group having a positive refractive power. The front group includes a biconcave first lens and a meniscus negative second lens having a concave surface facing the object side, and the rear group includes a biconvex third lens and a biconcave shape. It is composed of a fourth lens and a biconvex fifth lens. In this configuration, the ratio of the combined focal length of the front group to the focal length of the entire lens system and the ratio of the combined focal length of the rear group to the focal length of the entire lens system are suppressed within a preferable range. While increasing the angle of view, an increase in distortion due to the widening is suppressed.

JP 2009-134175 A

  An imaging lens mounted on the document camera is strongly required to have an ability to accurately capture the form of the projection target. According to the imaging lens described in Patent Document 1, although the diagonal angle of view is as wide as about 130 °, since the distortion is relatively large, it is difficult to accurately capture the form of the projection target.

  Note that coexistence of widening of the field of view and good correction of distortion is not a problem specific to the imaging lens mounted on the document camera, but is a digital still camera, personal digital assistant, security camera, scanner, network This is also a common problem with imaging lenses mounted on relatively small devices such as cameras.

  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 distortion well 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 a negative refractive power, a second lens having a negative refractive power, and a positive refractive power. A third lens having a negative refracting power and a fifth lens having a positive refracting power are arranged, and the first lens has a positive radius of curvature of the image side surface. And the second lens is formed so that the object side surface has a strong convex surface toward the object side as it goes from the optical axis to the peripheral edge, and the curvature radius of the image side surface 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, and the fourth lens is formed in the object side surface. The fifth lens is formed in a shape in which the curvature radius of the surface is negative and the curvature radius of the image side surface is positive. The radius of curvature is positive, with the radius of curvature of the image surface side is formed in a shape which is negative, the surface of the image surface side, and an aspherical shape having an inflection point.

  According to such a configuration as the imaging lens, a wide angle of field of view can be achieved by the first lens having a negative refractive power and the second lens having the same negative refractive power. Further, the distortion aberration generated in the first lens is preferably corrected by the object-side surface of the second lens and the image-side surface of the fifth lens.

  In the imaging lens having the above-described configuration, it is desirable that the second lens is formed so that its refractive power is weaker than each of the first lens, the third lens, the fourth lens, and the fifth lens. In general, when two lenses having negative refractive power are arranged in order from the object side and the refractive power of the lens arranged on the image plane side is relatively increased while keeping the focal length of the entire lens system constant, the lens Since the position of the principal point of the entire system moves in the direction away from the second lens (image plane side), the back focus becomes long. Such a lens configuration is disadvantageous for downsizing the imaging lens. Therefore, in the present invention, by making the refractive power of the second lens the weakest in the entire lens system, it is possible to reduce the size of the imaging lens while achieving a good balance between widening the shooting angle of view and correcting distortion. ing.

In the imaging lens having the above configuration, it is preferable that the following conditional expression (1) is satisfied, where f is the focal length of the entire lens system and f2 is the focal length of the second lens.
−40 <f2 / f <−5 (1)

  Conditional expression (1) is a condition for more suitably downsizing the imaging lens. If the upper limit “−5” is exceeded, the refractive power of the second lens becomes stronger than the refractive power of the entire lens system, so that the effective diameter of the first lens increases and the imaging lens can be downsized. It becomes difficult. On the other hand, if the value falls below the lower limit “−40”, the refractive power of the second lens becomes weaker than the refractive power of the entire lens system, which is advantageous for downsizing the imaging lens, but the chromatic aberration of magnification is corrected. Insufficient (short wavelength increases in the minus direction with respect to the reference wavelength), it becomes difficult to obtain good imaging performance.

In the imaging lens having the above-described configuration, when the radius of curvature of the image side surface of the first lens is R2 and the radius of curvature of the object side surface of the second lens is R3, the following conditional expression (2) is satisfied. Is desirable.
0.01 <R2 / R3 <0.4 (2)

  Conditional expression (2) is a condition for suppressing astigmatism within a favorable range while suppressing distortion within a favorable range. Exceeding the upper limit “0.4” is effective in correcting barrel-shaped (minus) distortion, but the tangential surface falls in the minus direction (object side) and the astigmatism increases. For this reason, it becomes difficult to suppress astigmatism within a favorable range. On the other hand, below the lower limit “0.01”, barrel distortion increases and the tangential surface falls in the plus direction (image plane side). In this case as well, the astigmatism difference increases, and it is difficult to suppress astigmatism within a favorable range.

In the imaging lens having the above-described configuration, it is desirable that the following conditional expression (3) is satisfied when the focal length of the first lens is f1 and the focal length of the second lens is f2.
0.02 <f1 / f2 <0.8 (3)

  Conditional expression (3) is a condition for suppressing chromatic aberration of magnification within a favorable range while correcting curvature of field. When the upper limit “0.8” is exceeded, the refractive power of the first lens becomes relatively weak compared to the second lens, which is effective for correcting chromatic aberration of magnification, but the image plane is in the minus direction (object It is difficult to obtain good imaging performance. On the other hand, when the value is below the lower limit “0.02,” the refractive power of the first lens becomes relatively stronger than that of the second lens, so that the chromatic aberration of magnification becomes insufficiently corrected. Further, the astigmatic difference increases as the image plane falls in the plus direction (image plane side). Therefore, in this case, it is difficult to obtain good imaging performance.

In the imaging lens having this configuration, it is possible to further suppress distortion and astigmatism within a better range by satisfying the following conditional expression (3A).
0.02 <f1 / f2 <0.5 (3A)

In the imaging lens having the above configuration, it is desirable that the following conditional expression (4) is satisfied, where f is the focal length of the entire lens system and f3 is the focal length of the third lens.
0.5 <f3 / f <1.2 (4)

  Conditional expression (4) is a condition for suppressing astigmatism and curvature of field within a favorable range while suppressing chromatic aberration within a favorable range. When the upper limit “1.2” is exceeded, the refractive power of the third lens becomes weaker than the refractive power of the entire lens system, so that the axial chromatic aberration is overcorrected (short wavelengths are positive in the positive direction relative to the reference wavelength). And the off-axis chromatic aberration is under-corrected. Further, since the image plane falls in the plus direction, it is difficult to suppress the curvature of field within a favorable range. Furthermore, since the astigmatic difference increases, it is difficult to suppress astigmatism within a favorable range. On the other hand, when the value is below the lower limit “0.5”, the refractive power of the third lens becomes stronger than the refractive power of the entire lens system, and the axial chromatic aberration is insufficiently corrected. In addition, astigmatism increases as the image plane tilts in the negative direction. Therefore, in any case, it is difficult to obtain good imaging performance.

In the imaging lens having the above-described configuration, the distance on the optical axis from the image plane side surface of the second lens to the object side plane of the third lens is df, and from the image plane side surface of the third lens to the fourth lens side. When the distance on the optical axis to the object side surface is dr, it is desirable to satisfy the following conditional expression (5).
0.8 <df / dr <2.5 (5)

  Conditional expression (5) is a condition for suppressing chromatic aberration of magnification and distortion within a good range with good balance and for suppressing astigmatism within a good range. If the upper limit value “2.5” is exceeded, the lateral chromatic aberration will be undercorrected and barrel distortion will increase, making it difficult to obtain good imaging performance. On the other hand, when the value is below the lower limit “0.8”, it is effective for correcting chromatic aberration and barrel distortion, but astigmatism increases as the image surface tilts in the negative direction. It becomes difficult to obtain image performance.

In the imaging lens having the above configuration, it is desirable that the following conditional expression (6) is satisfied, where f is the focal length of the entire lens system and f45 is the combined focal length of the fourth lens and the fifth lens.
5 <f45 / f <15 (6)

  Conditional expression (6) is a condition for correcting curvature of field while suppressing the incident angle of the light beam emitted from the imaging lens to the imaging element within a certain range. 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 upper limit “15” is exceeded in conditional expression (6), the combined refractive power of the fourth lens and the fifth lens becomes relatively weak with respect to the refractive power of the entire lens system, and the light emitted from the imaging lens And the incident angle of the light beam emitted from the imaging lens to the image sensor becomes difficult to be controlled within a certain range. In addition, since the image plane is tilted in the plus direction, it is difficult to obtain good imaging performance. On the other hand, below the lower limit “5”, the combined refractive power of the fourth lens and the fifth lens is relatively strong with respect to the refractive power of the entire lens system, and the light is emitted from the imaging lens to the imaging device. However, the astigmatic difference increases as the image plane falls in the negative direction. Therefore, in this case, it is difficult to obtain good imaging performance.

In the imaging lens having the above-described configuration, it is preferable that the following conditional expression (7) is satisfied when the Abbe number of the fourth lens is νd4 and the Abbe number of the fifth lens is νd5.
νd4 <35 and 45 <νd5 <80 (7)

  Conditional expression (7) is a condition for suppressing chromatic aberration within a favorable range. Outside the range of conditional expression (7), chromatic aberration is undercorrected both on and off the axis, making it difficult to obtain good imaging performance.

In the imaging lens having the above configuration, when the Abbe number of the first lens is νd1, the Abbe number of the second lens is νd2, and the Abbe number of the third lens is νd3, the following conditional expression (8) is further satisfied. It is desirable.
45 <νd1 <80, 45 <νd2 <80, and 45 <νd3 <80 (8)

  Conditional expression (8) is a condition for suppressing chromatic aberration within a better range. Outside the range of conditional expression (8), chromatic aberration is undercorrected both on and off the axis, making it difficult to obtain good imaging performance.

In the imaging lens having the above-described configuration, it is desirable that the following conditional expression (9) is satisfied when the focal length of the fourth lens is f4 and the focal length of the fifth lens is f5.
−1.5 <f4 / f5 <−0.5 (9)

  Conditional expression (9) is a condition for suppressing chromatic aberration and astigmatism within a favorable range. When the upper limit “−0.5” is exceeded, chromatic aberration is overcorrected. In addition, the astigmatic difference increases as the tangential surface falls in the positive direction. For this reason, it is difficult to obtain good imaging performance. On the other hand, below the lower limit “−1.5”, the chromatic aberration is insufficiently corrected. In addition, the tangential surface falls in the negative direction, and the astigmatic difference also increases. Therefore, in this case, it is difficult to obtain good imaging performance.

  According to the imaging lens of the present invention, it is possible to provide an imaging lens in which distortion is favorably corrected while having a wide angle.

1 is a lens cross-sectional view illustrating a schematic configuration of an imaging lens according to Numerical Example 1 according to an 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. 4 is a lens cross-sectional view illustrating a schematic configuration of an imaging lens according to Numerical Example 2 in the embodiment. FIG. 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. 5 is a lens cross-sectional view illustrating a schematic configuration of an imaging lens according to Numerical Example 3 in the embodiment. FIG. 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. 6 is a lens cross-sectional view illustrating a schematic configuration of an imaging lens according to Numerical Example 4 in the embodiment. FIG. 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. 6 is a lens cross-sectional view illustrating a schematic configuration of an imaging lens according to Numerical Example 5 in the embodiment. FIG. 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.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

  1, 4, 7, 10, and 13 are lens cross-sectional views corresponding to Numerical Examples 1 to 5 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 L2 having a negative refractive power in order from the object side to the image plane side. A third lens L3 having a positive refractive power, a fourth lens L4 having a negative refractive power, and a fifth lens L5 having a positive refractive power are arranged. A filter 10 is disposed between the fifth lens L5 and the image plane IM. This filter 10 can be omitted. In the imaging lens according to the present embodiment, an aperture stop is provided on the image side surface of the third lens L3.

  In the imaging lens having the above-described configuration, the first lens L1 has a shape in which the curvature radius R1 of the object-side surface is negative and the curvature radius R2 of the image-side surface is positive, that is, a biconcave lens in the vicinity of the optical axis X. Is formed into a shape. The object side surface of the first lens L1 according to the present embodiment is formed in an aspherical shape having an inflection point. That is, the object-side surface of the first lens L1 has a shape with a concave surface facing the object side in the vicinity of the optical axis X, and a shape with a convex surface facing the object side at the periphery. In the present embodiment, an inflection point is provided in the vicinity of 50% of the maximum effective diameter of the first lens L1. Note that the shape of the first lens L1 is not limited to the shape according to the present embodiment. The shape of the first lens L1 may be any shape as long as the curvature radius R2 of the surface on the image plane side is positive. The first curvature L1 and the curvature radius R2 are both positive, that is, in the vicinity of the optical axis X. The shape may be a meniscus lens having a convex surface facing the object side.

  The second lens L2 has a shape in which the curvature radius R3 of the object side surface and the curvature radius R4 of the image side surface are both positive, that is, a shape that becomes a meniscus lens having a convex surface facing the object side in the vicinity of the optical axis X. Formed. The object-side surface of the second lens L2 according to the present embodiment is an aspherical surface, and is formed to have a shape with a strong convex surface facing the object side from the optical axis X toward the periphery. That is, the object-side surface of the second lens L2 is formed in an aspherical shape in which the curve becomes tighter from the optical axis X toward the lens periphery. Note that the shape of the second lens L2 is not limited to the shape according to the present embodiment. The shape of the second lens L2 may be any shape as long as the curvature radius R4 of the surface on the image plane side is positive. The curvature radius R3 is negative and the curvature radius R4 is positive, that is, the optical axis X. The shape may be a biconcave lens in the vicinity of.

  By the way, in the present embodiment, the second lens L2 is formed so that its refractive power is weaker than each of the first lens L1, the third lens L3, the fourth lens L4, and the fifth lens L5. As a result, the widening of the shooting angle of view and the correction of distortion aberration can be achieved in a well-balanced manner, and at the same time, the imaging lens can be reduced in size.

  The third lens L3 has 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, and is a shape that becomes a biconvex lens in the vicinity of the optical axis X. The

  The fourth lens L4 has a shape in which the curvature radius R7 of the object side surface is negative and the curvature radius R8 of the image side surface is positive, and is formed into a shape that becomes a biconcave lens in the vicinity of the optical axis X. . The fifth lens L5 has a shape in which the curvature radius R9 of the object side surface is positive and the curvature radius R10 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 X. Is done. In the present embodiment, the image side surface of the fifth lens L5 is formed in an aspheric shape having an inflection point. That is, the surface on the image plane side of the fifth lens L5 has a shape in which the convex surface is directed to the image plane side in the vicinity of the optical axis X, and has a shape in which the concave surface is directed to the image plane side in the peripheral portion. . In the present embodiment, an inflection point is provided in the vicinity of 60% of the maximum effective diameter of the fifth lens L5. Such a shape of the image-side surface of the fifth lens L5 corrects distortion aberrations together with the shape of the object-side surface of the first lens L1 and the shape of the object-side surface of the second lens L2. To contribute to. Specifically, off-axis rays incident on the first lens L1 sequentially pass through the object-side surface of the first lens L1, the object-side surface of the second lens L2, and the image-side surface of the fifth lens L5. By passing, the optical path is corrected. As a result, distortion is suppressed within a good range. Further, such a shape of the fifth lens L5 suppresses the incident angle of the light beam emitted from the fifth lens L5 to the image plane IM within a certain range.

The imaging lens according to the present embodiment satisfies the following conditional expressions (1) to (9). For this reason, according to the imaging lens according to the present embodiment, both widening of the imaging lens and good aberration correction can be achieved.
−40 <f2 / f <−5 (1)
0.01 <R2 / R3 <0.4 (2)
0.02 <f1 / f2 <0.8 (3)
0.5 <f3 / f <1.2 (4)
0.8 <df / dr <2.5 (5)
5 <f45 / f <15 (6)
νd4 <35, 45 <νd5 <80 (7)
45 <νd1 <80, 45 <νd2 <80, 45 <νd3 <80 (8)
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 f45: combined focal length of the fourth lens L4 and the fifth lens L5 R2: radius of curvature of the image side surface of the first lens L1 R3: radius of curvature of the object side surface of the second lens L2 df: from the image side surface of the second lens L2 to the object side of the third lens L3 Distance on the optical axis to the surface dr: Distance on the optical axis from the image side surface of the third lens L3 to the object side surface of the fourth lens L4 νd1: Abbe number of the first lens L1 νd2: Second Abbe number of lens L2 νd3: Abbe number of third lens L3 νd4: Abbe number of fourth lens L4 νd5: Abbe number of fifth lens L5

In the imaging lens according to the present embodiment, the following conditional expression (3A) is satisfied in order to suppress distortion and astigmatism within a better range.
0.02 <f1 / f2 <0.5 (3A)

In the imaging lens according to the present embodiment, when the focal length of the fourth lens is f4 and the focal length of the fifth lens is f5, the following conditional expression (9) is satisfied.
−1.5 <f4 / f5 <−0.5 (9)

  In addition, it is not necessary to satisfy all of the conditional expressions (1) to (9) (including conditional expression (3A); the same applies hereinafter), and by satisfying each of them independently, the effects corresponding to the conditional expressions are achieved. Each can be obtained.

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 _{When 10} , A ₁₂ , and A ₁₄ , they are expressed 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.

Numerical example 1
Basic lens data is shown below.
f = 2.84mm, Fno = 2.44, ω = 46.9 °
Unit mm
Surface data Surface number i R d Nd νd
(Object) ∞ 250
1 * -12.79 0.45 1.53 56.0
2 * 2.24 0.68
3 * 6.18 0.45 1.53 56.0
4 * 5.40 1.24 (= df)
5 * 2.57 1.06 1.53 56.0
6 * (aperture) -2.32 0.72 (= dr)
7 * -5.06 0.40 1.61 26.0
8 * 2.33 0.15
9 * 8.25 1.03 1.53 56.0
10 * -1.92 0.50
11 ∞ 0.50 1.52 64.1
12 ∞ 2.81
(Image plane) ∞

f1 = −3.53 mm
f2 = -100.00mm
f3 = 2.47mm
f4 = −2.55 mm
f5 = 3.02mm
f45 = 24.28mm

Aspherical data first surface k = 0.000, A ₄ = 3.446E-02, A ₆ = -3.599E-03, A ₈ = -8.291E-05,
A ₁₀ = 1.543E-05
Second surface k = 0.000, A ₄ = 1.750E-02, A ₆ = -1.105E-02, A ₈ = 3.441E-02,
A ₁₀ = -1.719E-02, A ₁₂ = 3.262E-03
3rd surface k = 0.000, A ₄ = -3.026E-02, A ₆ = 3.233E-02, A ₈ = -1.004E-02,
A ₁₀ = 2.042E-03
4th surface k = 0.000, A ₄ = 3.205E-02, A ₆ = -3.662E-03, A ₈ = 8.714E-03,
A ₁₀ = -2.056E-03
Fifth surface _{k = 0.000, A 4 = 2.103E} -02, A 6 = -3.153E-02, A 8 = 3.669E-02,
A ₁₀ = -2.507E-02, A ₁₂ = 5.415E-03
6th surface k = -6.021, A ₄ = -2.650E-02, A ₆ = 1.713E-03, A ₈ = 1.064E-02,
A ₁₀ = -1.641E-02, A ₁₂ = 6.241E-03
7th surface k = 0.000, A ₄ = -1.003E-01, A ₆ = 2.765E-03, A ₈ = -5.120E-02,
A ₁₀ = 9.268E-02, A ₁₂ = -4.181E-02
8th surface k = 0.000, A ₄ = -6.169E-02, A ₆ = -2.045E-02, A ₈ = 1.781E-02,
A ₁₀ = -3.303E-03, A ₁₂ = -2.295E-04
9th surface k = 0.000, A ₄ = 6.242E-02, A ₆ = -1.454E-02, A ₈ = -6.595E-03,
A ₁₀ = 6.315E-03, A ₁₂ = -1.348E-03
10th surface k = 0.000, A ₄ = 3.200E-02, A ₆ = 1.686E-03, A ₈ = 1.200E-02,
A ₁₀ = 1.294E-03, A ₁₂ = -1.979E-03, A ₁₄ = 2.615E-04

The value of each conditional expression is shown below.
f2 / f = −35.21
R2 / R3 = 0.36
f1 / f2 = 0.035
f3 / f = 0.87
df / dr = 1.72
f45 / f = 8.55
f4 / f5 = −0.84
Thus, the imaging lens according to Numerical Example 1 satisfies the conditional expressions (1) to (9). Further, the distance (air conversion length) on the optical axis X from the object side surface of the first lens L1 to the image plane IM is 9.82 mm, and the imaging lens is downsized.

  FIG. 2 illustrates the lateral aberration corresponding to the ratio H of each image height to the maximum image height (hereinafter referred to as “image height ratio H”) in the tangential direction and the sagittal direction for the imaging lens of Numerical Example 1. (It is the same in FIG. 5, FIG. 8, FIG. 11, and FIG. 14). FIG. 3 shows spherical aberration (mm), astigmatism (mm), and distortion (%) for the imaging lens of Numerical Example 1. Among these aberration diagrams, the spherical aberration diagram includes g-line (435.84 nm), F-line (486.13 nm), e-line (546.07 nm), d-line (587.56 nm), C-line (656.27 nm). The astigmatism diagram shows the aberration amount on the sagittal image plane S and the aberration amount on the tangential image plane T (in FIGS. 6, 9, 12, and 15). the same). As shown in FIG. 2 and FIG. 3, according to the imaging lens according to Numerical Example 1, the image plane is corrected well, and various aberrations are preferably corrected.

Numerical example 2
Basic lens data is shown below.
f = 2.84mm, Fno = 2.46, ω = 46.9 °
Unit mm
Surface data Surface number i R d Nd νd
(Object) ∞ 250
1 * -11.64 0.45 1.53 56.0
2 * 2.24 0.68
3 * 6.26 0.45 1.53 56.0
4 * 5.40 1.15 (= df)
5 * 2.75 1.23 1.53 56.0
6 * (aperture) -2.17 0.72 (= dr)
7 * -7.88 0.40 1.61 26.0
8 * 2.02 0.15
9 * 7.17 0.99 1.53 56.0
10 * -1.99 0.50
11 ∞ 0.50 1.52 64.1
12 ∞ 2.77
(Image plane) ∞

f1 = −3.47 mm
f2 = −90.04 mm
f3 = 2.48mm
f4 = −2.58 mm
f5 = 3.03mm
f45 = 28.01 mm

Aspherical data first surface k = 0.000, A ₄ = 3.517E-02, A ₆ = -3.879E-03, A ₈ = -4.207E-05,
A ₁₀ = 1.425E-05
Second surface k = 0.000, A ₄ = 1.750E-02, A ₆ = -1.105E-02, A ₈ = 3.441E-02,
A ₁₀ = -1.719E-02, A ₁₂ = 3.262E-03
3rd surface k = 0.000, A ₄ = -3.105E-02, A ₆ = 3.378E-02, A ₈ = -1.052E-02,
A ₁₀ = 2.170E-03
4th surface k = 0.000, A ₄ = 3.205E-02, A ₆ = -3.662E-03, A ₈ = 8.714E-03,
A ₁₀ = -2.056E-03
Fifth surface k = 0.000, A ₄ = 5.577E-03, A ₆ = -8.975E-03, A ₈ = -1.789E-04,
A ₁₀ = -8.581E-05, A ₁₂ = -1.741E-03
6th surface k = -4.450, A ₄ = -3.024E-02, A ₆ = 1.075E-02, A ₈ = -2.034E-02,
A ₁₀ = 1.403E-02, A ₁₂ = -4.934E-03
7th surface k = 0.000, A ₄ = -1.075E-01, A ₆ = -2.729E-02, A ₈ = 4.481E-02,
A ₁₀ = -3.235E-03, A ₁₂ = -7.411E-03
8th surface k = 0.000, A ₄ = -1.039E-01, A ₆ = 1.145E-02, A ₈ = 1.077E-03,
A ₁₀ = -1.078E-04, A ₁₂ = -2.254E-04
9th surface k = 0.000, A ₄ = 5.538E-02, A ₆ = -5.087E-03, A ₈ = -1.266E-02,
A ₁₀ = 8.470E-03, A ₁₂ = -1.670E-03
10th surface k = 0.000, A ₄ = 3.103E-02, A ₆ = 5.686E-03, A ₈ = 9.425E-03,
A ₁₀ = 3.140E-03, A ₁₂ = -2.706E-03, A ₁₄ = 3.394E-04

The value of each conditional expression is shown below.
f2 / f = −31.70
R2 / R3 = 0.36
f1 / f2 = 0.039
f3 / f = 0.87
df / dr = 1.60
f45 / f = 9.86
f4 / f5 = −0.84
Thus, the imaging lens according to Numerical Example 2 satisfies the conditional expressions (1) to (9). Further, the distance (air conversion length) on the optical axis X from the object side surface of the first lens L1 to the image plane IM is 9.82 mm, and the imaging lens is downsized.

  FIG. 5 shows lateral aberration corresponding to the image height ratio H for the imaging lens of Numerical Example 2. FIG. 6 shows spherical aberration (mm), astigmatism (mm), and distortion ( %). As shown in FIGS. 5 and 6, the image pickup lens according to Numerical Example 2 also corrects the image plane well and various aberrations are preferably corrected similarly to Numerical Example 1.

Numerical Example 3
Basic lens data is shown below.
f = 2.88mm, Fno = 2.39, ω = 46.5 °
Unit mm
Surface data Surface number i R d Nd νd
(Object) ∞ 250
1 * -15.21 0.45 1.53 56.0
2 * 2.37 0.61
3 * 41.52 0.40 1.53 56.0
4 * 10.64 1.19 (= df)
5 * 2.71 1.24 1.53 56.0
6 * (aperture) -2.17 0.74 (= dr)
7 * -6.86 0.40 1.61 26.0
8 * 2.00 0.15
9 * 6.28 1.02 1.53 56.0
10 * -1.98 0.50
11 ∞ 0.50 1.52 64.1
12 ∞ 2.78
(Image plane) ∞

f1 = -3.80 mm
f2 = −26.87 mm
f3 = 2.47mm
f4 = -2.48mm
f5 = 2.94mm
f45 = 26.61mm

Aspherical data first surface k = 0.000, A ₄ = 3.686E-02, A ₆ = -5.745E-03, A ₈ = 1.870E-04,
A ₁₀ = 5.956E-06
Second surface k = 0.000, A ₄ = 1.751E-02, A ₆ = -1.104E-02, A ₈ = 3.441E-02,
A ₁₀ = -1.719E-02, A ₁₂ = 3.262E-03
3rd surface k = 0.000, A ₄ = -9.374E-03, A ₆ = 6.269E-02, A ₈ = -2.628E-02,
A ₁₀ = 4.905E-03
4th surface k = 0.000, A ₄ = 5.912E-02, A ₆ = 3.630E-02, A ₈ = -1.591E-02,
A ₁₀ = 1.982E-03
5th surface k = 0.000, A ₄ = 1.531E-02, A ₆ = -1.525E-02, A ₈ = 1.315E-02,
A ₁₀ = -9.891E-03, A ₁₂ = 1.540E-03
6th surface k = -4.370, A ₄ = -1.958E-02, A ₆ = 3.714E-03, A ₈ = -5.359E-03,
A ₁₀ = 3.662E-04, A ₁₂ = 7.524E-06
7th surface k = 0.000, A ₄ = -1.051E-01, A ₆ = -1.030E-02, A ₈ = 2.021E-02,
A ₁₀ = 6.272E-03, A ₁₂ = -9.737E-03
8th surface k = 0.000, A ₄ = -1.045E-01, A ₆ = 1.099E-02, A ₈ = 2.017E-03,
A ₁₀ = -2.032E-03, A ₁₂ = 2.975E-04
9th surface k = 0.000, A ₄ = 5.185E-02, A ₆ = -1.019E-02, A ₈ = -7.167E-03,
A ₁₀ = 5.543E-03, A ₁₂ = -1.096E-03
10th surface k = 0.000, A ₄ = 3.369E-02, A ₆ = 3.097E-03, A ₈ = 1.059E-02,
A ₁₀ = 1.521E-03, A ₁₂ = -2.110E-03, A ₁₄ = 2.993E-04

The value of each conditional expression is shown below.
f2 / f = −9.33
R2 / R3 = 0.057
f1 / f2 = 0.14
f3 / f = 0.86
df / dr = 1.61
f45 / f = 9.24
f4 / f5 = −0.84
Thus, the imaging lens according to Numerical Example 3 satisfies the conditional expressions (1) to (9). Further, the distance (air conversion length) on the optical axis X from the object side surface of the first lens L1 to the image plane IM is 9.81 mm, and the imaging lens is downsized.

  FIG. 8 shows lateral aberration corresponding to the image height ratio H for the imaging lens of Numerical Example 3, and FIG. 9 shows spherical aberration (mm), astigmatism (mm), and distortion ( %). As shown in FIGS. 8 and 9, the imaging lens according to Numerical Example 3 also corrects the image plane well and various aberrations as well as Numerical Example 1.

Numerical Example 4
Basic lens data is shown below.
f = 2.89mm, Fno = 2.41, ω = 46.3 °
Unit mm
Surface data Surface number i R d Nd νd
(Object) ∞ 250
1 * -14.22 0.45 1.53 56.0
2 * 2.32 0.62
3 * 80.52 0.40 1.53 56.0
4 * 14.80 1.21 (= df)
5 * 2.69 1.24 1.53 56.0
6 * (aperture) -2.15 0.74 (= dr)
7 * -6.55 0.40 1.61 26.0
8 * 1.99 0.14
9 * 6.23 1.00 1.53 56.0
10 * -2.01 0.50
11 ∞ 0.50 1.52 64.1
12 ∞ 2.76
(Image plane) ∞

f1 = -3.69 mm
f2 = −34.00 mm
f3 = 2.45mm
f4 = −2.44 mm
f5 = 2.97mm
f45 = 39.98mm

Aspherical data first surface k = 0.000, A ₄ = 3.687E-02, A ₆ = -5.740E-03, A ₈ = 1.887E-04,
A ₁₀ = 6.376E-06
Second side k = 0.000, A ₄ = 1.756E-02, A ₆ = -1.098E-02, A ₈ = 3.442E-02,
A ₁₀ = -1.719E-02, A ₁₂ = 3.263E-03
3rd surface k = 0.000, A ₄ = -9.178E-03, A ₆ = 6.269E-02, A ₈ = -2.629E-02,
A ₁₀ = 4.902E-03
4th surface k = 0.000, A ₄ = 5.879E-02, A ₆ = 3.639E-02, A ₈ = -1.581E-02,
A ₁₀ = 2.045E-03
5th surface k = 0.000, A ₄ = 1.545E-02, A ₆ = -1.530E-02, A ₈ = 1.306E-02,
A ₁₀ = -9.959E-03, A ₁₂ = 1.505E-03
6th surface k = -4.363, A ₄ = -1.962E-02, A ₆ = 3.683E-03, A ₈ = -5.399E-03,
A ₁₀ = 3.216E-04, A ₁₂ = -3.783E-05
7th surface k = 0.000, A ₄ = -1.044E-01, A ₆ = -1.076E-02, A ₈ = 1.963E-02,
A ₁₀ = 5.953E-03, A ₁₂ = -9.788E-03
8th surface k = 0.000, A ₄ = -1.044E-01, A ₆ = 1.120E-02, A ₈ = 2.062E-03,
A ₁₀ = -2.045E-03, A ₁₂ = 2.817E-04
9th surface k = 0.000, A ₄ = 5.193E-02, A ₆ = -1.016E-02, A ₈ = -7.135E-03,
A ₁₀ = 5.560E-03, A ₁₂ = -1.092E-03
10th surface k = 0.000, A ₄ = 3.354E-02, A ₆ = 3.112E-03, A ₈ = 1.059E-02,
A ₁₀ = 1.515E-03, A ₁₂ = -2.114E-03, A ₁₄ = 2.978E-04

The value of each conditional expression is shown below.
f2 / f = -11.76
R2 / R3 = 0.029
f1 / f2 = 0.11
f3 / f = 0.85
df / dr = 1.64
f45 / f = 13.83
f4 / f5 = −0.82
Thus, the imaging lens according to Numerical Example 4 satisfies the conditional expressions (1) to (9). Further, the distance (air conversion length) on the optical axis X from the object side surface of the first lens L1 to the image plane IM is 9.79 mm, and the imaging lens is downsized.

  FIG. 11 shows lateral aberration corresponding to the image height ratio H for the imaging lens of Numerical Example 4. FIG. 12 shows spherical aberration (mm), astigmatism (mm), and distortion ( %). 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.

Numerical Example 5
Basic lens data is shown below.
f = 2.82mm, Fno = 2.32, ω = 47.3 °
Unit mm
Surface data Surface number i R d Nd νd
(Object) ∞ 250
1 * -23.04 0.45 1.53 56.0
2 * 2.59 0.59
3 * 159.31 0.47 1.53 56.0
4 * 7.27 1.20 (= df)
5 * 2.68 1.21 1.53 56.0
6 * (aperture) -2.16 0.70 (= dr)
7 * -7.50 0.40 1.61 26.0
8 * 2.00 0.16
9 * 6.12 1.04 1.53 56.0
10 * -1.96 0.50
11 ∞ 0.50 1.52 64.1
12 ∞ 2.72
(Image plane) ∞

f1 = −4.33 mm
f2 = -14.26 mm
f3 = 2.45mm
f4 = −2.53 mm
f5 = 2.91mm
f45 = 20.23mm

Aspherical data first surface k = 0.000, A ₄ = 3.691E-02, A ₆ = -5.744E-03, A ₈ = 1.841E-04,
A ₁₀ = 5.497E-06
2nd surface k = 0.000, A ₄ = 1.960E-02, A ₆ = -1.117E-02, A ₈ = 3.437E-02,
A ₁₀ = -1.717E-02, A ₁₂ = 3.276E-03
3rd surface k = 0.000, A ₄ = -9.616E-03, A ₆ = 6.246E-02, A ₈ = -2.636E-02,
A ₁₀ = 4.911E-03
4th surface k = 0.000, A ₄ = 6.008E-02, A ₆ = 3.682E-02, A ₈ = -1.586E-02,
A ₁₀ = 1.863E-03
Fifth surface k = 0.000, A ₄ = 1.473E-02, A ₆ = -1.537E-02, A ₈ = 1.323E-02,
A ₁₀ = -9.785E-03, A ₁₂ = 1.598E-03
6th surface k = -4.383, A ₄ = -1.953E-02, A ₆ = 3.724E-03, A ₈ = -5.307E-03,
A ₁₀ = 4.546E-04, A ₁₂ = 1.197E-04
7th surface k = 0.000, A ₄ = -1.046E-01, A ₆ = -9.770E-03, A ₈ = 2.043E-02,
A ₁₀ = 6.342E-03, A ₁₂ = -9.673E-03
8th surface k = 0.000, A ₄ = -1.043E-01, A ₆ = 1.088E-02, A ₈ = 1.922E-03,
A ₁₀ = -2.088E-03, A ₁₂ = 2.659E-04
9th surface k = 0.000, A ₄ = 5.180E-02, A ₆ = -1.019E-02, A ₈ = -7.184E-03,
A ₁₀ = 5.529E-03, A ₁₂ = -1.105E-03
10th surface k = 0.000, A ₄ = 3.427E-02, A ₆ = 3.179E-03, A ₈ = 1.061E-02,
A ₁₀ = 1.529E-03, A ₁₂ = -2.108E-03, A ₁₄ = 2.997E-04

The value of each conditional expression is shown below.
f2 / f = −5.06
R2 / R3 = 0.016
f1 / f2 = 0.30
f3 / f = 0.87
df / dr = 1.71
f45 / f = 7.17
f4 / f5 = −0.87
Thus, the imaging lens according to Numerical Example 5 satisfies the conditional expressions (1) to (9). Further, the distance on the optical axis X from the object-side surface of the first lens L1 to the image plane IM (equivalent air length) is 9.77 mm, and the imaging lens is downsized.

  FIG. 14 shows lateral aberration corresponding to the image height ratio H for the imaging lens of Numerical Example 5. FIG. 15 shows spherical aberration (mm), astigmatism (mm), and distortion ( %). As shown in FIG. 14 and FIG. 15, the imaging lens according to Numerical Example 5 also corrects the image plane well as in Numerical Example 1, and various aberrations are preferably corrected.

  Therefore, when the imaging lens according to the above embodiment is applied to an imaging optical system mounted on a mobile phone, a digital still camera, a portable information terminal, a security camera, an actual projector, a scanner, a network camera, etc. Both high functionality and downsizing can be achieved.

  INDUSTRIAL APPLICABILITY The present invention can be applied to an imaging lens mounted on a device that is required to have a small distortion, a wide angle, and a good distortion correction capability, such as a document camera or a scanner.

L1 1st lens L2 2nd lens L3 3rd lens L4 4th lens L5 5th lens 10 Filter

Claims (10)

In order from the object side to the image plane side, the first lens having negative refractive power, the second lens having negative refractive power, the third lens having positive refractive power, and the negative refractive power A fourth lens and a fifth lens having a positive refractive power are arranged;
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 such that the object-side surface has a shape with a strong convex surface facing the object side from the optical axis toward the peripheral edge, and the curvature radius of the image-side surface becomes positive. Formed into a shape,
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 fourth lens is formed in a shape in which the curvature radius of the object side surface is negative and the curvature radius of the image side surface is positive.
The fifth 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, and the aspherical surface has an inflection point on the image side surface. Formed into,
An imaging lens characterized by the above.   The said 2nd lens is formed so that refractive power may become weaker than each of a said 1st lens, a said 3rd lens, a said 4th lens, and a said 5th lens. Imaging lens. When the focal length of the entire lens system is f and the focal length of the second lens is f2,
−40 <f2 / f <−5
The imaging lens according to claim 1, wherein: When the radius of curvature of the image side surface of the first lens is R2, and the radius of curvature of the object side surface of the second lens is R3,
0.01 <R2 / R3 <0.4
The imaging lens according to claim 1, wherein the imaging lens is satisfied. When the focal length of the first lens is f1, and the focal length of the second lens is f2,
0.02 <f1 / f2 <0.8
The imaging lens according to claim 1, wherein the imaging lens is satisfied. 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 <1.2
The imaging lens according to claim 1, wherein the imaging lens is satisfied. The distance on the optical axis from the image side surface of the second lens to the object side surface of the third lens is df, and the object side surface of the fourth lens from the image side surface of the third lens When the distance on the optical axis to is dr
0.8 <df / dr <2.5
The imaging lens according to any one of claims 1 to 6, wherein: When the focal length of the entire lens system is f, and the combined focal length of the fourth lens and the fifth lens is f45,
5 <f45 / f <15
The imaging lens according to claim 1, wherein the imaging lens is satisfied. When the Abbe number of the fourth lens is νd4 and the Abbe number of the fifth lens is νd5,
νd4 <35
45 <νd5 <80
The imaging lens according to claim 1, wherein the imaging lens is satisfied. When the Abbe number of the first lens is νd1, the Abbe number of the second lens is νd2, and the Abbe number of the third lens is νd3,
45 <νd1 <80
45 <νd2 <80
45 <νd3 <80
The imaging lens according to claim 9, wherein:

Images