JP5366314B2 - Imaging lens - Google Patents

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, various lens configurations have been proposed. Among them, a lens configuration including three lenses can correct various aberrations relatively well and is suitable for downsizing. It is used in cameras.

  For example, an imaging lens described in Patent Document 1 is known as a three-lens imaging lens. The imaging lens includes, in order from the object 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. By shortening the focal length of the third lens with respect to the focal length of the entire lens system, that is, by making the refractive power of the third lens relatively strong and making the refractive power of the second lens stronger than that of the first lens, It corrects surface curvature and coma.

JP 2008-76594 A

  In recent years, the downsizing and the increase in the number of pixels of a camera such as a mobile phone are rapidly progressing, and the performance required for the imaging lens is also stricter than before. According to the imaging lens described in Patent Document 1, although aberration is certainly corrected satisfactorily, since the focal length of the entire lens system is relatively long, the light from the object-side surface of the first lens to the image plane It is difficult to shorten the distance on the axis, and there is a limit to achieving both miniaturization 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 plane side, a first lens having a positive refractive power, a second lens having a negative refractive power, and a positive or negative refraction. A third lens having power, and forming the first lens 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 second lens is the object The radius of curvature of the surface on the side is negative, the surface on the object side is concave on the object side near the optical axis and the peripheral portion is convex on the object side, and the radius of curvature of the surface on the image plane is positive And the third lens is formed such that both the radius of curvature of the object-side surface and the radius of curvature of the image-side surface are positive, the image-side surface is convex toward the object side in the vicinity of the optical axis, and The peripheral part is formed in a concave shape on the object side, the focal length of the first lens is f1, the focal length of the second lens is f2, and the third lens Point distance f3, the radius of curvature of the object side surface of the second lens R3, and a radius of curvature of the image-side surface was R4, and configured so as to satisfy the following conditional expressions (1) and (2) .
f1 <| f2 |, f1 <| f3 | (1)
-0.15 <R3 / R4 <0 (2)

  In the imaging lens of the present invention, the focal length of the first lens is made shorter than the focal lengths of the second and third lenses, that is, the refractive power of the second and third lenses is relative to the refractive power of the first lens. The second and third lenses having relatively weak refractive power are used to correct various aberrations. In the imaging lens according to the present invention, the surface of the second lens on the object side has a concave shape on the object side and a peripheral portion is convex on the object side in the vicinity of the optical axis, and the image of the third lens. The surface shape on the surface side is a shape that is convex toward the object side in the vicinity of the optical axis and that the peripheral portion is concave toward the object side. As a result, various aberrations including the correction of the image plane are corrected well by the second and third lenses, and the imaging lens is formed by the surface shape of the second lens on the object side and the surface shape of the third lens on the image plane side. It is possible to suppress the incident angle of the light emitted from the imaging lens to the image plane within a preferable constant range while reducing the size of the imaging lens.

  Here, conditional expression (1) is a condition for shortening the length (thickness) along the optical axis of the imaging lens. According to the present invention, the first lens is formed into 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, that is, a shape that becomes a biconvex lens in the vicinity of the optical axis. The two lenses are 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, that is, a shape that is a biconcave lens in the vicinity of the optical axis. In such a configuration, in the present invention, since the refractive power of the first lens is stronger than the refractive power of the second lens, the distance between the first lens and the second lens is reduced, and the imaging lens is reduced in size, particularly imaging. It is possible to favorably reduce the thickness of the lens.

Conditional expression (2) is a condition for suppressing the aberration within a favorable range while shortening the thickness of the imaging lens. If the upper limit value “0” is exceeded, the position of the principal point of the lens system moves to the image plane side, making it difficult to reduce the size of the imaging lens. On the other hand, if the value falls below the lower limit “−0.15”, the position of the principal point of the lens system moves to the object side, which is effective for downsizing the imaging lens, but the image plane is overcorrected (in the + direction). Increase). Therefore, it is difficult to obtain good imaging performance with corrected aberration. Further, in this case, outward coma increases and correction thereof becomes difficult.

In the imaging lens having the above-described configuration, it is desirable to form the third lens in a shape in which the object side surface is convex toward the object side near the optical axis and the peripheral part is concave toward the object side. By adopting such a surface shape as the third lens, the incident angle of the light emitted from the imaging lens to the image plane can be further suppressed.

In the imaging lens having the above-described configuration, the shape of the second lens is an important element in order to achieve both reduction in size and good aberration correction. In order to suppress the thickness of the imaging lens that increases with correction of various aberrations, it is desirable to suppress the thickness of the second lens within a certain range. In the present invention, the distance from the point where the object-side surface of the second lens intersects the optical axis to the point where the tangential plane of the object-side surface intersects the optical axis perpendicularly is H, on the optical axis of the second lens. When the thickness of D is D, the following conditional expression (3) is satisfied.
0.02 <H / D <0.07 (3)

Further, in the imaging lens having the above-described configuration, it is preferable that the following conditional expression (4) is satisfied.
−0.8 <f1 / f2 <−0.3 (4)

  Conditional expression (4) is a condition for suppressing on-axis chromatic aberration, off-axis magnification chromatic aberration, and field curvature within a favorable range while reducing the thickness of the imaging lens. Exceeding the upper limit “−0.3” is effective in reducing the thickness of the imaging lens, but the axial chromatic aberration is undercorrected (short wavelength increases in the − direction with respect to the reference wavelength), and Off-axis lateral chromatic aberration is undercorrected. Further, since the image plane falls to the object side, it is difficult to obtain good imaging performance. On the other hand, below the lower limit “−0.8”, off-axis lateral chromatic aberration is overcorrected (short wavelength increases in the + direction with respect to the reference wavelength). Further, since the image plane falls to the image plane side, it is difficult to obtain good imaging performance in this case.

In the imaging lens having the above configuration, when the distance between the first lens and the second lens is dA and the distance between the second lens and the third lens is dB, the following conditional expression (5) is satisfied. It is desirable.
0.05 <dA / dB <0.5 (5)

  Conditional expression (5) is a condition for suppressing spherical aberration and coma aberration within a favorable range. By disposing the second lens so as to satisfy the conditional expression (5), it is possible to suppress the spherical aberration and the coma aberration within a favorable range. When the upper limit “0.5” is exceeded, spherical aberration is overcorrected, and axial chromatic aberration is undercorrected. In addition, inward coma due to off-axis rays increases, making it difficult to suppress each aberration within a favorable range. On the other hand, if the value falls below the lower limit “0.05”, the spherical aberration becomes insufficiently corrected, and the outward coma aberration due to off-axis rays increases, and in this case as well, it is difficult to suppress each aberration within a favorable range. It becomes.

  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. It is sectional drawing which shows only a 2nd lens among the imaging lenses which concern on the same numerical value Example 1. FIG. 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 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 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 regarding the second 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 a third 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, 5, 8, and 11 are lens cross-sectional views corresponding to Numerical Examples 1 to 4 of the present embodiment, respectively. Since any of the numerical examples has the same basic lens configuration, the lens configuration of the present embodiment will be described with reference to the lens cross-sectional view of Numerical Example 1.

  As shown in FIG. 1, the imaging lens according to the present embodiment includes a first lens L1 having a positive refractive power and a second lens L2 having a negative refractive power in order from the object side to the image plane side. And a third lens L3 having the same negative refractive power is arranged. A cover glass 10 is disposed between the third lens L3 and the image plane of the image sensor. The cover glass 10 can be omitted.

  The first lens L1 is formed in an aspherical 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, that is, a shape that becomes a biconvex lens near the optical axis. The second lens L2 is formed in an aspherical shape in which the radius of curvature of the object side surface is negative and the curvature radius of the image side surface is positive, that is, a shape that is a biconcave lens in the vicinity of the optical axis. The object side surface of the second lens L2 is formed in an aspherical shape in which the vicinity of the optical axis is concave on the object side and the peripheral portion is convex on the object side. The third lens L3 is formed in an aspherical 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 shape that becomes a meniscus lens in the vicinity of the optical axis. In the third lens L3, both the object-side surface and the image-side surface are 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 in the periphery.

  In the present embodiment, the aperture stop is disposed closer to the object side than 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. For example, the aperture stop is located between the apex tangent plane of the object side surface of the first lens L1 and the image surface side surface of the first lens L1. May be arranged.

In the present embodiment, all the lens surfaces of the first lens L1 to the third lens L3 are aspherical. 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 and third embodiments described later).

In the imaging lens according to the present embodiment, when the focal length of the first lens L1 is f1, the focal length of the second lens L2 is f2, and the focal length of the third lens L3 is f3, the following conditional expression (1) And (4) is satisfied.
f1 <| f2 |, f1 <| f3 | (1)
−0.8 <f1 / f2 <−0.3 (4)

  In the imaging lens according to the present embodiment, the amount of protrusion toward the object side at the peripheral portion of the object-side surface of the second lens L2, that is, the vertex of the object-side surface of the second lens L2, The length of the perpendicular when the perpendicular is lowered to a surface that passes through a point (bottom) where the object-side surface and the optical axis intersect and is perpendicular to the optical axis is suppressed within a certain range. In other words, the distance from the point at which the object-side surface of the second lens L2 intersects with the optical axis to the point at which the tangential plane of the object-side surface (through the vertex) and the optical axis intersect perpendicularly is constant. By suppressing within the range, the thickness of the second lens L2 is shortened while performing good aberration correction, and both downsizing of the imaging lens and good aberration correction are achieved.

Specifically, as shown in FIG. 2, in the imaging lens according to the present embodiment, the tangential plane of the object-side surface and the optical axis are from the point where the object-side surface of the second lens L2 intersects with the optical axis. When the distance to the perpendicular intersection is H and the thickness on the optical axis of the second lens L2 is D, the following conditional expression (3) is satisfied.
0.02 <H / D <0.07 (3)

Furthermore, in the imaging lens according to the present embodiment, the radius of curvature of the object-side surface of the second lens L2 is R3, the radius of curvature of the image-side surface of the second lens L2 is R4, and the first lens L1 and the second lens When the distance between the lens L2 is dA and the distance between the second lens L2 and the third lens L3 is dB, the following conditional expressions (2) and (5) are satisfied.
-0.15 <R3 / R4 <0 (2)
0.05 <dA / dB <0.5 (5)

Further, in the imaging lens according to the present embodiment, in order to suppress the axial chromatic aberration and the off-axis chromatic aberration within a certain range, the Abbe number of the second lens L2 is set between the first lens L1 and the third lens L3. The value is set lower than Abbe and is within the range shown below.
Abbe number νd1: νd1> 50 in the d-line of the first lens L1
Abbe number νd2 at the d-line of the second lens L2: νd2 <35
Abbe number νd3 at the d-line of the third lens L3: νd3> 50
νd1−νd2 <32

  In addition, it is not necessary to satisfy all of the conditional expressions (1) to (5), and by obtaining each of the conditional expressions (1) to (5) independently, an effect corresponding to each conditional expression is obtained. Therefore, it is possible to construct a small imaging lens in which aberrations are corrected well compared to a conventional imaging lens.

  Next, numerical examples of 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. An aspheric surface is indicated by adding a symbol of * (asterisk) after the surface number i.

Numerical example 1
Basic lens data is shown below.
f = 2.872mm, Fno = 2.850, ω = 31.36 °
Unit mm
Surface data Surface number i R d Nd νd
(Surface) ∞ ∞
(Aperture) ∞ 0.0101
1 * 1.326 0.4300 1.54420 56.0 (= νd1)
2 * -4.014 0.2189 (= dA)
3 * -2.145 0.2700 1.58500 29.0 (= νd2)
4 * 250.000 0.5201 (= dB)
5 * 1.777 0.4500 1.54420 56.0 (= νd3)
6 * 1.595 0.1400
7 ∞ 0.5000 1.51633 64.2
8 ∞ 0.6997
(Image plane) ∞

Aspherical data first surface k = -2.726960, A ₄ = -3.110338E-02, A ₆ = 2.321001E-01, A ₈ = 1.207622E-01,
A ₁₀ = -3.243233
Second side k = -2.000000E-01, A ₄ = -6.466253E-02, A ₆ = 1.405198, A ₈ = -7.307537E-01,
A ₁₀ = -7.964204
3rd surface k = -8.973423, A ₄ = 1.076485, A ₆ = 7.134322E-01, A ₈ = -3.000000,
A ₁₀ = 1.000000
4th surface k = -5.974132E + 05, A ₄ = 1.034534, A ₆ = 1.966603E-01, A ₈ = 1.002229,
A ₁₀ = -1.685398
5th surface k = -1.772930E + 01, A ₄ = 4.521145E-02, A ₆ = -3.908136E-01, A ₈ = 3.405364E-01,
A ₁₀ = -8.843657E-02
6th surface k = -5.043102, A ₄ = -9.871068E-02, A ₆ = -7.247517E-02, A ₈ = 4.645177E-02,
A ₁₀ = -1.600082E-02

The focal lengths f1 to f3 of the lenses L1 to L3 and the values of the conditional expressions are shown below.
f1 = 1.85
f2 = -3.634
f3 = −222.45
R3 / R4 = −0.009
H / D = H / d3 = 0.0414
f1 / f2 = −0.519
dA / dB = d2 / d4 = 0.421
νd1−νd2 = 27.0
As described above, the imaging lens according to Numerical Example 1 satisfies the conditional expressions (1) to (5).

  FIG. 3 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 (in FIGS. 6, 9, 12, and 15). the same). FIG. 4 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. 7, 10, 13, and 16).

  As shown in FIGS. 3 and 4, according to the imaging lens according to Numerical Example 1, various aberrations are favorably corrected. In addition, the air-converted distance from the object side surface of the first lens L1 to the image surface is as short as 3.058 mm, and the image pickup lens is also favorably downsized.

Numerical example 2
Basic lens data is shown below.
f = 2.885mm, Fno = 2.850, ω = 31.24 °
Unit mm
Surface data Surface number i R d Nd νd
(Surface) ∞ ∞
(Aperture) ∞ 0.0101
1 * 1.223 0.4300 1.54420 56.0 (= νd1)
2 * -5.389 0.1600 (= dA)
3 * -2.268 0.2700 1.58500 29.0 (= νd2)
4 * 150.000 0.6500 (= dB)
5 * 2.168 0.4500 1.54420 56.0 (= νd3)
6 * 1.904 0.1100
7 ∞ 0.5000 1.51633 64.2
8 ∞ 0.6823
(Image plane) ∞

Aspherical data first surface k = -1.693778, A ₄ = 7.048642E-03, A ₆ = -7.148810E-02, A ₈ = -5.193070E-02,
A ₁₀ = -3.027556E-01
2nd surface k = -2.000000E-01, A ₄ = 7.381654E-02, A ₆ = 9.810826E-01, A ₈ = -1.093289,
A ₁₀ = -3.303644
3rd surface k = -8.973423, A ₄ = 1.076485, A ₆ = 7.134322E-01, A ₈ = -3.000000,
A ₁₀ = 1.000000
4th surface k = 1.491354E + 04, A ₄ = 9.763533E-01, A ₆ = 4.060082E-01, A ₈ = 8.507295E-01,
A ₁₀ = -2.750323
5th surface k = -3.462211E + 01, A ₄ = 9.585375E-02, A ₆ = -4.208477E-01, A ₈ = 3.317266E-01,
A ₁₀ = -8.075152E-02
6th surface k = -1.228985, A ₄ = -1.181057E-01, A ₆ = -8.791890E-02, A ₈ = 5.875926E-02,
A ₁₀ = -1.607393E-02

The focal lengths f1 to f3 of the lenses L1 to L3 and the values of the conditional expressions are shown below.
f1 = 1.875
f2 = -3.817
f3 = −71.957
R3 / R4 = −0.015
H / D = H / d3 = 0.0376
f1 / f2 = −0.491
dA / dB = d2 / d4 = 0.246
νd1−νd2 = 27.0
As described above, the imaging lens according to Numerical Example 2 satisfies the conditional expressions (1) to (5).

  FIG. 6 shows lateral aberration corresponding to the half angle of view ω for the imaging lens of Numerical Example 2. FIG. 7 shows spherical aberration SA (mm), astigmatism AS (mm), and distortion. Each aberration DIST (%) is shown. As shown in FIG. 6 and FIG. 7, various aberrations are satisfactorily corrected by the imaging lens according to Numerical Example 2 as well as Numerical Example 1. In this numerical example, the air-converted distance from the object-side surface of the first lens L1 to the image plane is 3.082 mm, and the image pickup lens is also suitably reduced in size.

Numerical Example 3
Basic lens data is shown below.
f = 2.876mm, Fno = 2.856, ω = 31.32 °
Unit mm
Surface data Surface number i R d Nd νd
(Surface) ∞ ∞
(Aperture) ∞ 0.0101
1 * 1.200 0.4300 1.54420 56.0 (= νd1)
2 * -5.461 0.1100 (= dA)
3 * -2.414 0.2700 1.58500 29.0 (= νd2)
4 * 41.076 0.7000 (= dB)
5 * 2.458 0.4500 1.54420 56.0 (= νd3)
6 * 2.123 0.1100
7 ∞ 0.5000 1.51633 64.2
8 ∞ 0.6886
(Image plane) ∞

Aspherical data first surface k = -1.901343, A ₄ = -1.077516E-02, A ₆ = -2.466574E-01, A ₈ = -3.848209E-01,
A ₁₀ = 7.850272E-01
Second surface k = -2.000000E-01, A ₄ = 2.295499E-02, A ₆ = 7.989374E-01, A ₈ = -1.419015,
A ₁₀ = -1.851361
3rd surface k = -8.973423, A ₄ = 1.076485, A ₆ = 7.134322E-01, A ₈ = -3.000000,
A ₁₀ = 1.000000
4th surface k = 5.704117E + 02, A ₄ = 9.930533E-01, A ₆ = 4.351151E-01, A ₈ = 8.434294E-01,
A ₁₀ = -2.636398
5th surface k = -6.462274E + 01, A ₄ = 1.126729E-01, A ₆ = -4.225992E-01, A ₈ = 3.293896E-01,
A ₁₀ = -8.061301E-02
6th surface k = -9.384260E-01, A ₄ = -1.029261E-01, A ₆ = -9.007869E-02, A ₈ = 5.891562E-02,
A ₁₀ = -1.563757E-02

The focal lengths f1 to f3 of the lenses L1 to L3 and the values of the conditional expressions are shown below.
f1 = 1.850
f2 = −3.889
f3 = −54.355
R3 / R4 = −0.059
H / D = H / d3 = 0.0335
f1 / f2 = −0.476
dA / dB = d2 / d4 = 0.157
νd1−νd2 = 27.0
Thus, the imaging lens according to Numerical Example 3 satisfies the conditional expressions (1) to (5).

  FIG. 9 shows lateral aberration corresponding to the half angle of view ω for the imaging lens of Numerical Example 3, and FIG. 10 shows spherical aberration SA (mm), astigmatism AS (mm), and distortion. Each aberration DIST (%) is shown. As shown in FIGS. 9 and 10, various aberrations are satisfactorily corrected by the imaging lens according to Numerical Example 3 as well as Numerical Example 1. In this numerical example, the air-converted distance from the object side surface of the first lens L1 to the image plane is 3.088 mm, and the imaging lens is also favorably miniaturized.

Numerical Example 4
Basic lens data is shown below.
f = 2.883mm, Fno = 2.850, ω = 31.35 °
Unit mm
Surface data Surface number i R d Nd νd
(Surface) ∞ ∞
(Aperture) ∞ 0.0101
1 * 1.200 0.4300 1.54420 56.0 (= νd1)
2 * -6.181 0.1600 (= dA)
3 * -2.245 0.2700 1.58500 29.0 (= νd2)
4 * 500.000 0.6000 (= dB)
5 * 1.942 0.4300 1.54420 56.0 (= νd3)
6 * 1.727 0.1500
7 ∞ 0.5000 1.51633 64.2
8 ∞ 0.6927
(Image plane) ∞

Aspherical data first surface k = -1.682257, A ₄ = 1.008400E-02, A ₆ = -6.309280E-03, A ₈ = -1.376137E-01,
A ₁₀ = -2.072613
Second side k = -2.000000E-01, A ₄ = 6.713812E-02, A ₆ = 9.984905E-01, A ₈ = -1.315973,
A ₁₀ = -5.712717
3rd surface k = -8.973423, A ₄ = 1.076485, A ₆ = 7.134322E-01, A ₈ = -3.000000,
A ₁₀ = 1.000000
4th surface k = 4.509810E + 05, A ₄ = 1.005785, A ₆ = 2.811773E-01, A ₈ = 9.059264E-01,
A ₁₀ = -5.675254E-01
5th surface k = -2.421189E + 01, A ₄ = 9.692854E-02, A ₆ = -4.169404E-01, A ₈ = 3.322301E-01,
A ₁₀ = -8.234996E-02
6th surface k = -1.874003, A ₄ = -1.270593E-01, A ₆ = -7.749536E-02, A ₈ = 5.824229E-02,
A ₁₀ = -1.750529E-02

The focal lengths f1 to f3 of the lenses L1 to L3 and the values of the conditional expressions are shown below.
f1 = 1.85
f2 = −3.820
f3 = −97.112
R3 / R4 = −0.004
H / D = H / d3 = 0.0383
f1 / f2 = −0.493
dA / dB = d2 / d4 = 0.267
νd1−νd2 = 27.0
As described above, the imaging lens according to Numerical Example 4 satisfies the conditional expressions (1) to (5).

  12 shows lateral aberration corresponding to the half angle of view ω for the imaging lens of Numerical Example 4, and FIG. 13 shows spherical aberration SA (mm), astigmatism AS (mm), and distortion. Each aberration DIST (%) is shown. As shown in FIGS. 12 and 13, the imaging lens according to Numerical Example 4 also corrects various aberrations in the same manner as Numerical Example 1. In this numerical example, the air conversion distance from the object side surface of the first lens L1 to the image surface is 3.062 mm, and the imaging lens is also favorably miniaturized.

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

  FIG. 14 shows a lens cross-sectional view of Numerical Example 5 corresponding to the present embodiment.

  As shown in FIG. 14, the imaging lens according to the present embodiment includes a first lens L1 having a positive refractive power and a second lens L2 having a negative refractive power in order from the object side to the image plane side. And a third lens L3 having a positive refractive power are arranged. A cover glass 10 is disposed between the third lens L3 and the image plane of the image sensor. The cover glass 10 can be omitted.

  The first lens L1 is formed in an aspherical 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, that is, a shape that becomes a biconvex lens near the optical axis. The second lens L2 is formed in an aspherical shape in which the radius of curvature of the object side surface is negative and the curvature radius of the image side surface is positive, that is, a shape that is a biconcave lens in the vicinity of the optical axis. The object side surface of the second lens L2 is formed in an aspherical shape in which the vicinity of the optical axis is concave on the object side and the peripheral portion is convex on the object side. The third lens L3 is formed in an aspherical 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 shape that becomes a meniscus lens in the vicinity of the optical axis. In the third lens L3, both the object-side surface and the image-side surface are 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 in the periphery.

  Also in the present embodiment, the aperture stop is disposed closer to the object side than the vertex tangent plane of the object side surface of the first lens L1. The position of the aperture stop 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.

Also in the imaging lens according to the present embodiment, the focal length of the first lens L1 is f1, the focal length of the second lens L2 is f2, the radius of curvature of the object side surface of the second lens L2 is R3, and the second lens L2. The radius of curvature of the surface on the image plane side is R4, the distance between the first lens L1 and the second lens L2 is dA, the distance between the second lens L2 and the third lens L3 is dB, and the second lens L2 The distance from the point where the object-side surface and the optical axis intersect to the point where the tangential plane of the object-side surface and the optical axis intersect perpendicularly is H, and the thickness of the second lens L2 on the optical axis is D When satisfied, the following conditional expressions (1) to (5) are satisfied.
f1 <| f2 |, f1 <| f3 | (1)
-0.15 <R3 / R4 <0 (2)
0.02 <H / D <0.07 (3)
−0.8 <f1 / f2 <−0.3 (4)
0.05 <dA / dB <0.5 (5)

Further, in order to suppress the on-axis chromatic aberration and the off-axis chromatic aberration within a certain range, also in the imaging lens according to the present embodiment, the Abbe numbers νd1 to νd3 of the lenses L1 to L3 are within the following ranges. Is in the range.
νd1> 50
νd2 <35
νd3> 50
νd1−νd2 <32

  In the present embodiment, it is not necessary to satisfy all of the conditional expressions (1) to (5). By satisfying each of the conditional expressions (1) to (5) independently, each conditional expression can be handled. Thus, it is possible to obtain a small-sized imaging lens in which aberrations are favorably corrected as compared with a conventional imaging lens.

  Next, numerical examples of 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. An aspheric surface is indicated by adding a symbol of * (asterisk) after the surface number i.

Numerical Example 5
Basic lens data is shown below.
f = 2.835mm, Fno = 2.850, ω = 31.69 °
Unit mm
Surface data Surface number i R d Nd νd
(Surface) ∞ ∞
(Aperture) ∞ 0.0101
1 * 1.228 0.4300 1.54420 56.0 (= νd1)
2 * -5.109 0.1100 (= dA)
3 * -2.261 0.2700 1.58500 29.0 (= νd2)
4 * 234.916 0.7000 (= dB)
5 * 2.400 0.4500 1.54420 56.0 (= νd3)
6 * 2.400 0.1100
7 ∞ 0.5000 1.51633 64.2
8 ∞ 0.7120
(Image plane) ∞

Aspherical data first surface k = -1.786122, A ₄ = -1.604778E-03, A ₆ = -1.685937E-01, A ₈ = -3.792832E-01,
A ₁₀ = -8.140890E-01
Second surface k = -2.000000E-01, A ₄ = 7.189249E-02, A ₆ = 9.062164E-01, A ₈ = -1.692214,
A ₁₀ = -4.033243
3rd surface k = -8.973423, A ₄ = 1.076485, A ₆ = 7.134322E-01, A ₈ = -3.000000,
A ₁₀ = 1.000000
4th surface k = -3.024910E + 07, A ₄ = 9.588657E-01, A ₆ = 4.023783E-01, A ₈ = 9.849866E-01,
A ₁₀ = -1.800379
5th surface k = -7.413000E + 01, A ₄ = 1.246003E-01, A ₆ = -4.185439E-01, A ₈ = 3.296663E-01,
A ₁₀ = -8.119929E-02
6th surface k = -2.441679E-01, A ₄ = -9.905229E-02, A ₆ = -9.880606E-02, A ₈ = 6.025187E-02,
A ₁₀ = -1.335594E-02

The focal lengths f1 to f3 of the lenses L1 to L3 and the values of the conditional expressions are shown below.
f1 = 1.864
f2 = −3.827
f3 = 66.742
R3 / R4 = −0.010
H / D = H / d3 = 0.0378
f1 / f2 = −0.487
dA / dB = d2 / d4 = 0.157
νd1−νd2 = 27.0
As described above, the imaging lens according to Numerical Example 5 satisfies the conditional expressions (1) to (5).

  FIG. 15 shows lateral aberration corresponding to the half angle of view ω for the imaging lens of Numerical Example 5, and FIG. 16 shows spherical aberration SA (mm), astigmatism AS (mm), and distortion. Each aberration DIST (%) is shown. As shown in FIG. 15 and FIG. 16, various aberrations are satisfactorily corrected by the imaging lens according to Numerical Example 5 as well as Numerical Example 1. In this numerical example, the air conversion distance from the object-side surface of the first lens L1 to the image plane is 3.112 mm, and the imaging lens is also favorably miniaturized.

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

  FIG. 17 shows a lens cross-sectional view of Numerical Example 6 corresponding to the present embodiment.

  The basic configuration of the imaging lens according to the present embodiment is the same as that of the imaging lens according to the second embodiment. However, the imaging lens according to the present embodiment differs from the second embodiment in the shape of the object-side surface of the third lens L3.

  In the second embodiment, both the object side surface and the image surface side surface of the third lens L3 are convex on the object side in the vicinity of the optical axis and concave on the object side in the periphery. It is formed into a shape. On the other hand, in the present embodiment, as shown in FIG. 17, only the image side surface of the third lens L3 has a convex shape on the object side in the vicinity of the optical axis and a concave shape on the object side in the peripheral portion. It is formed into an aspherical shape. Even if such a shape is adopted as the third lens L3, it is possible to achieve both reduction in size of the imaging lens and good aberration correction.

Numerical Example 6
Basic lens data is shown below.
f = 2.821mm, Fno = 2.856, ω = 31.81 °
Unit mm
Surface data Surface number i R d Nd νd
(Surface) ∞ ∞
(Aperture) ∞ 0.0101
1 * 0.988 0.3399 1.54420 56.0 (= νd1)
2 * 52.040 0.1022 (= dA)
3 * -2.164 0.2700 1.58500 29.0 (= νd2)
4 * 500.000 0.7000 (= dB)
5 * 2.322 0.5000 1.54420 56.0 (= νd3)
6 * 2.380 0.5000
7 ∞ 0.3000 1.51633 64.2
8 ∞ 0.4351
(Image plane) ∞

Aspherical data first surface k = -1.324165, A ₄ = 3.629701E-02, A ₆ = -1.689376E-01, A ₈ = -4.823010E-01,
A ₁₀ = -2.706396, A ₁₂ = -1.678278, A ₁₄ = -7.824178, A ₁₆ = -2.359938E + 01
Second surface k = -2.000000E-01, A ₄ = 3.891946E-03, A ₆ = 5.654417E-01, A ₈ = -2.489689,
A ₁₀ = -8.388261, A ₁₂ = -4.566875, A ₁₄ = -2.054143
Third surface k = −8.973423, A ₄ = 1.027423, A ₆ = 4.637295E-01, A ₈ = −4.049567, A ₁₀ = −2.165919,
A ₁₂ = -7.131607, A ₁₄ = -1.418408E + 01
4th surface k = -3.641872E + 08, A ₄ = 1.157415, A ₆ = 2.676480E-01, A ₈ = -7.084293E-01,
A ₁₀ = -7.781085E-01, A ₁₂ = 1.468836, A ₁₄ = -2.749283, A ₁₆ = -7.179977E + 01
5th surface k = -1.322595E + 01
6th surface k = -2.317301, A ₄ = -4.757656E-02, A ₆ = -3.815292E-02, A ₈ = 3.725375E-02,
A ₁₀ = -1.672389E-02, A ₁₂ = 2.143275E-03, A ₁₄ = 5.171325E-04, A ₁₆ = -1.445483E-04

The focal lengths f1 to f3 of the lenses L1 to L3 and the values of the conditional expressions are shown below.
f1 = 1.847
f2 = -3.682
f3 = 43.359
R3 / R4 = −0.004
H / D = H / d3 = 0.0441
f1 / f2 = −0.501
dA / dB = d2 / d4 = 0.146
νd1−νd2 = 27.0
As described above, the imaging lens according to Numerical Example 6 satisfies the conditional expressions (1) to (5).

  FIG. 18 shows lateral aberration corresponding to the half angle of view ω for the imaging lens of Numerical Example 6, and FIG. 19 shows spherical aberration SA (mm), astigmatism AS (mm), and distortion. Each aberration DIST (%) is shown. As shown in FIGS. 18 and 19, various aberrations are favorably corrected by the imaging lens according to Numerical Example 6 as well as Numerical Example 1. In this numerical example, the air-converted distance from the object-side surface of the first lens L1 to the image plane is 3.045 mm, and the imaging lens is also favorably downsized.

  Therefore, when the imaging lens according to the present embodiment 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, and a network camera, the camera and the like have high functionality and small size. Can be achieved simultaneously.

  The imaging lens according to the present invention is not limited to the above embodiments. In the above embodiment, all the surfaces of the first lens L1 to the third lens L3 are aspherical surfaces, but it is not always necessary to make all the surfaces aspherical.

  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.

L1 1st lens L2 2nd lens L3 3rd lens 10 Cover glass

Claims (5)

In order from the object side to the image plane side, the first lens having a positive refractive power, the second lens having a negative refractive power, and a third lens having a positive or negative refractive power,
The first 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 second lens has a negative radius of curvature of the object side surface, the object side surface is concave on the object side in the vicinity of the optical axis, and the peripheral part is convex on the object side, and the image side surface Is formed in a shape with a positive curvature radius,
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 positive, the image-side surface is convex near the optical axis, and the peripheral portion is an object. It is formed in a concave shape on the side,
The focal length of the first lens is f1, the focal length of the second lens is f2, the focal length of the third lens is f3 , the radius of curvature of the object side surface of the second lens is R3, and the surface on the image plane side When the radius of curvature is R4 ,
f1 <| f2 |, f1 <| f3 |
-0.15 <R3 / R4 <0
An imaging lens characterized by satisfying The third lens is formed in a shape in which the object-side surface is convex toward the object side in the vicinity of the optical axis and the peripheral portion is concave toward the object side.
The imaging lens according to claim 1. The distance from the point at which the object side surface of the second lens intersects with the optical axis to the point at which the tangent plane of the object side surface of the second lens intersects perpendicularly with the optical axis is H, the light of the second lens When the thickness on the shaft is D,
0.02 <H / D <0.07
The imaging lens according to claim 1, wherein: −0.8 <f1 / f2 <−0.3
The imaging lens according to claim 1, wherein the imaging lens is satisfied. When the distance between the first lens and the second lens is dA, and the distance between the second lens and the third lens is dB,
0.05 <dA / dB <0.5
The imaging lens according to claim 1, wherein the imaging lens is satisfied.