JP2015049453A - Imaging lens and on-vehicle camera - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress ghost generated in an imaging lens.SOLUTION: An imaging lens 100 includes, in order from the object side to the image side: a first lens L1 with negative refractive power having a meniscus shape with a convex surface facing the object side; a second lens L2 with positive refractive power having such a shape that the curvature radius of the image side surface is smaller than that of the object side surface; an aperture stop S; a third lens L3 with positive refractive power having a meniscus shape with a convex surface facing the object side; and a fourth lens L4 with positive refractive power having a meniscus shape with a convex surface facing the image side. At least one surface of the surfaces constituting the third lens L3 and the fourth lens L4 is an aspheric surface.

Description

  The present invention relates to a photographing lens and a vehicle-mounted camera.

  A photographing lens used for an in-vehicle camera has been proposed (see Patent Document 1).

JP 2008-268268 A

  In an in-vehicle camera, there is a problem that headlights and the sun often enter the shooting screen, and a ghost is generated in the screen, resulting in an obstacle to image information acquisition.

(1) The photographic lens described in claim 1 has a meniscus shape having a convex surface facing the object side in order from the object side to the image side, and a first lens having negative refractive power, and a surface on the object side. The image side surface has a small radius of curvature, and has a second lens having a positive refractive power, an aperture stop, a meniscus shape having a convex surface facing the object side, and a third lens having a positive refractive power. A lens and a fourth lens having a meniscus shape with a convex surface facing the image side and having a positive refractive power, and at least one of the surfaces constituting the third lens and the fourth lens is It is aspherical.
(2) An on-vehicle camera according to a seventh aspect includes the photographing lens according to any one of the first to sixth aspects.

  According to the present invention, it is possible to suppress the ghost generated in the photographing lens.

It is a block diagram which shows the structure of a vehicle-mounted camera provided with the imaging lens which concerns on one Embodiment of this invention. It is sectional drawing of the imaging lens which concerns on 1st Example. It is a figure which shows the spherical aberration, astigmatism, and distortion of the photographic lens which concerns on 1st Example. It is a figure which shows the coma aberration of the imaging lens which concerns on 1st Example. It is sectional drawing of the imaging lens which concerns on 2nd Example. It is a figure which shows the spherical aberration, astigmatism, and distortion of the imaging lens which concerns on 2nd Example. It is a figure which shows the coma aberration of the imaging lens which concerns on 2nd Example. It is sectional drawing of the imaging lens which concerns on 3rd Example. It is a figure which shows the spherical aberration, astigmatism, and distortion of the photographic lens which concerns on 3rd Example. It is a figure which shows the coma aberration of the imaging lens which concerns on 3rd Example. It is sectional drawing of the imaging lens which concerns on 4th Example. It is a figure which shows the spherical aberration, astigmatism, and distortion of the photographic lens which concerns on 4th Example. It is a figure which shows the coma aberration of the imaging lens which concerns on 4th Example. It is sectional drawing of the imaging lens which concerns on 5th Example. It is a figure which shows the spherical aberration, astigmatism, and distortion of the photographic lens which concerns on 5th Example. It is a figure which shows the coma aberration of the imaging lens which concerns on 5th Example.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram illustrating a configuration of an in-vehicle camera 10 including a photographing lens 100 according to the present embodiment. The in-vehicle camera 10 is mounted on a car, for example, and is used for photographing the driver and detecting the direction of the driver's face. In addition, the use application of the vehicle-mounted camera 10 is an example, and is not limited thereto. For example, the vehicle-mounted camera 10 may be used for photographing the front of the automobile. The in-vehicle camera 10 includes a photographing lens 100 according to the present embodiment, an image sensor 101, a control unit 102, a storage unit 103, and a near infrared LED 104.

  Near infrared light (for example, wavelength 850 nm to 1000 nm) emitted from the near infrared LED 104 illuminates the driver. The photographing lens 100 forms an image of the driver illuminated with the near infrared light on the image sensor 101. Note that shooting with near-infrared light is intended to enable shooting even in dark conditions such as at night. The image pickup device 101 is an image sensor such as a CMOS image pickup device, for example, picks up an image formed by the photographing lens 100 and outputs the obtained image signal to the control unit 102. The control unit 102 performs predetermined image processing on the image signal acquired from the image sensor 101 to generate image data, and stores the image data in the storage unit 103.

  FIG. 2 is a cross-sectional view showing a configuration of the photographic lens 100 according to the present embodiment. The taking lens 100 includes, in order from the object side to the image side, a first lens L1 having a negative refractive power, a second lens L2 having a positive refractive power, an aperture stop S that determines the brightness of the lens, and a positive lens. A third lens L3 having a refractive power of 4 and a fourth lens L4 having a positive refractive power. The first lens L1 has a meniscus shape with a convex surface facing the object side. The second lens L2 has a shape in which the radius of curvature of the image side surface is smaller than the object side surface. The third lens L3 has a meniscus shape with a convex surface facing the object side. The fourth lens L4 has a meniscus shape with a convex surface facing the image side. Of the surfaces constituting the third lens L3 and the fourth lens L4, at least one surface is an aspherical surface.

  In the photographic lens 100, by using the fourth lens L4 as a positive refractive power lens having a meniscus shape with a convex surface facing the image side, the reflected light from the imaging element surface can be diffused, and the ghost intensity can be greatly reduced. it can.

  In the photographing lens 100, at least one of the surfaces constituting the third lens L3 and the fourth lens L4 is aspherical so that spherical aberration, coma aberration, and field curvature are not easily corrected. By arranging the spherical surface, it is possible to ensure good imaging performance with the minimum necessary lens configuration while satisfying desired brightness, angle of view, and size. As a result, the lens surface, which is a ghost generation source, can be configured with the minimum necessary amount, and ghost generation can be suppressed.

  In the photographing lens 100, the first lens L1 is a negative refractive power lens having a meniscus shape with a convex surface facing the object side, and the second lens L2 is a positive lens having a radius of curvature of the image side surface smaller than the object side surface. By using a refractive power lens, the minimum necessary lens configuration and the minimum necessary aspherical lens are achieved. Thereby, low cost is realizable.

  Furthermore, in the photographic lens 100 of the present embodiment, it is desirable that at least one of the surfaces constituting the fourth lens L4 be an aspherical surface. By doing so, the imaging performance of the photographic lens 100 can be kept better.

In the photographing lens 100 of the present embodiment, it is preferable that the following conditional expression (1) is satisfied.
1.5> t ₃ /f>0.4 (1)
However,
f: Focal length of the taking lens 100 t ₃ : Center thickness of the third lens L3

  When the upper limit of conditional expression (1) is exceeded, the center thickness of the third lens L3 becomes too large with respect to the effective diameter of the third lens L3, and the number of manufacturing steps for the third lens L3 increases, resulting in an increase in cost. .

  When the lower limit of conditional expression (1) is exceeded, the balance between spherical aberration and astigmatism correction due to the meniscus shape of the third lens L3 is lost, and the difference between the sagittal image plane and the tangential image plane at the intermediate image height increases. .

In the photographing lens 100 of the present embodiment, it is desirable that the following conditional expressions (2) to (4) are satisfied.
2.0> | f ₁ /f|>1.0 (2)
f ₃ /f>3.0 (3)
f ₂ > f ₄ (4)
However,
f: Focal length of the taking lens 100 f ₁ : Focal length of the first lens L 1 f ₂ : Focal length of the second lens L 2 f ₃ : Focal length of the third lens L 3 f ₄ : Focal length of the fourth lens L 4

  When the upper limit value of conditional expression (2) is exceeded, it is necessary to increase the air gap between the first lens L1 and the second lens L2 in order to ensure a predetermined back focus, and the photographic lens 100 increases in size.

  When the lower limit of conditional expression (2) is exceeded, the refractive power of the first lens L1 becomes strong, and there is a possibility that the photographing lens 100 can be miniaturized, but the distortion becomes large. In order to correct this, it is necessary to use an aspherical surface for the first lens L1, which increases the cost.

  If conditional expression (3) is deviated and the refractive power of the third lens L3 becomes strong, the refractive power of the fourth lens L4 must be weakened to ensure a predetermined focal length in the photographing lens 100. As a result, the exit pupil position of the photographic lens 100 becomes too close, causing a light amount loss around the screen. This can be solved by adjusting the entrance pupil position of the microlens array of the image sensor 101, but in that case, there is a possibility that the microlens array is custom-made and the cost is increased.

  When the refractive power of the second lens L2 becomes stronger by deviating from the conditional expression (4), the third lens L3 and the fourth lens L4 are made thin by reducing the center thickness of the third lens L3 in order to ensure a predetermined back focus. It is necessary to reduce the air gap between As a result, it becomes difficult to correct the coma aberration of the peripheral image height, and the exit pupil position of the photographing lens 100 becomes too close.

In the photographing lens 100 of the present embodiment, it is preferable that the following conditional expressions (5) to (7) are satisfied.
−1.2> (r ₂ + r ₁ ) / (r ₂ −r ₁ )> − 2.0 (5)
−0.8> (r ₄ + r ₃ ) / (r ₄ −r ₃ )> − 2.5 (6)
| (R ₇ + r ₆ ) / (r ₇ −r ₆ ) |> 6.0 (7)
However,
r ₁ : radius of curvature of the object side surface of the first lens L 1 r ₂ : radius of curvature of the image side surface of the first lens L 1 r ₃ : radius of curvature of the object side surface of the second lens L 2 r ₄ : second Radius of curvature of the image side surface of the lens L2 r ₆ : radius of curvature of the object side surface of the third lens L3 r ₇ : radius of curvature of the image side surface of the third lens L3

When the upper limit of the conditional expression (5), correction of distortion becomes difficult curvature radius r ₁ of the object-side surface of the first lens L1 becomes too large.

If the lower limit of condition (5), in order to secure the refractive power of the first lens L1, necessary to reduce the radius of curvature r ₂ of the image-side surface of the first lens L1 occurs, the first lens L1 Manufacturing man-hours increase and cost increases.

  When the upper limit of conditional expression (6) is exceeded, the positive refracting power of the object side surface of the second lens L2 becomes too strong, and a predetermined back focus cannot be secured.

  When the lower limit of conditional expression (6) is exceeded, it becomes difficult to balance coma aberration correction and spherical aberration correction.

When the curvature radius r ₆ of the object side surface of the third lens L3 out the conditional expression (7) becomes too smaller than the radius of curvature r ₇ of the image-side surface of the third lens L3, the object of the third lens L3 Since the center of curvature of the side surface and the center of curvature of the image side surface of the third lens L3 are too close, the centering operation of the third lens L3 becomes difficult. When the curvature radius r ₆ of the object side surface of the third lens L3 out of the conditional expression (7) is too larger than the curvature radius r ₇ of the image-side surface of the third lens L3, the peripheral image height It becomes difficult to correct coma aberration.

  In addition, it is desirable that the photographing lens 100 of the present embodiment forms an image of near infrared light having a wavelength in the range of 850 nm to 1000 nm.

-Example-
Hereinafter, each example of the taking lens 100 according to the present embodiment will be described. In the tables described in the following embodiments, OBJ represents an object plane, STO represents an aperture stop, IMG represents an image plane, and a plane with a surface number marked with * represents an aspherical surface. The radius of curvature “INFINITY” indicates a plane or an opening. The refractive index of air is omitted.

但し、
ｚ：レンズ面頂点からの光軸方向のサグ量
ｈ：光軸からの距離
ｃ：曲率（曲率半径の逆数）
Ｋ：コーニック定数
Ａ_ｎ：ｎ次の非球面係数 The aspheric surface used in each embodiment is defined by the following formula (8).

However,
z: Sag amount in the optical axis direction from the apex of the lens surface h: Distance from the optical axis c: Curvature (reciprocal of radius of curvature)
K: Conic constant A _n : n-order aspheric coefficient

<First embodiment>
First, the first embodiment will be described. FIG. 2 is a sectional view of the taking lens 100 according to the first embodiment. Description of the above-described configuration is omitted. In the photographing lens 100 according to the first example, the object-side surface and the image-side surface of the fourth lens L4 are aspheric.

Table 1 below shows various data of the photographing lens 100 according to the first example. The surface numbers shown in Table 1 correspond to the surface numbers shown in FIG.
[Table 1]
(Overall specifications)
Focal length 3.467 mm
F number 2.4
Maximum image height 2.4 mm
(Lens data)
Surface number Curvature radius Surface spacing Refractive index (d line) Abbe number
OBJ: INFINITY 700.00000
1: 20.68804 1.00000 1.88300 40.76
2: 3.50000 3.00000
3: -47.50922 3.00000 2.00330 28.27
4: -6.81645 0.30000
STO: INFINITY 0.70000
6: 4.41141 2.00000 1.69680 55.53
7: 5.75888 3.00000
* 8: -75.00000 1.50000 1.77030 47.40
* 9: -5.00895 2.94831
IMG: INFINITY

As shown in the lens data in Table 1, the object-side surface (eighth surface) and the image-side surface (ninth surface) of the fourth lens L4 are aspherical surfaces. Table 2 below shows numerical values of the aspheric coefficients in these aspheric surfaces.
[Table 2]
Aspheric coefficient 8th surface 9th surface K 0.000000 0.000000
A ₄ -5.593307E-03 5.306234E-04
A ₆ -1.064014E-03 -8.214012E-04
A ₈ 1.888741E-04 1.452815E-04
A ₁₀ -6.433949E-06 -3.660482E-06
A ₁₂ 0.000000E + 00 0.000000E + 00

In the photographing lens 100 according to the first example, the values related to the conditional expressions (1) to (7) described above are as follows. As described below, the photographic lens 100 according to the first example satisfies the conditional expressions (1) to (7), and thus can obtain the effects described above.
Conditional expression (1) t ₃ / f 0.577
Conditional expression (2) | f ₁ / f | 1.415
Conditional expression (3) f ₃ / f 4.850
Conditional expression (4) f ₂ = 7.650 f ₄ = 6.904
Conditional expression (5) (r ₂ + r ₁ ) / (r ₂ −r ₁ ) −1.407
Conditional expression (6) (r ₄ + r ₃ ) / (r ₄ −r ₃ ) −1.335
Conditional Expression (7) | (r ₇ + r ₆ ) / (r ₇ −r ₆ ) | 7.548

  FIG. 3 shows spherical aberration, astigmatism, and distortion in the photographing lens 100 according to the first example, and FIG. 4 shows coma aberration. 3 and 4, it can be seen that, in the photographic lens 100 according to the first example, each aberration is well corrected and has high optical performance.

  The taking lens 100 according to the first example is designed so that the best imaging performance can be obtained with near infrared light. Therefore, FIGS. 3 and 4 show aberration diagrams with respect to a light beam having a wavelength of 940 nm. However, the back focus and the focal length of the photographing lens 100 shown in Table 1 and the focal length of each lens used for the calculation of the conditional expressions (1) to (7) are defined by the d line.

<Second embodiment>
Next, a second embodiment will be described. FIG. 5 is a cross-sectional view of the taking lens 100 according to the second embodiment. Description of the above-described configuration is omitted. In the photographing lens 100 according to the second example, the object-side surface and the image-side surface of the fourth lens L4 are aspheric. In the second embodiment, two parallel flat plates P1 and P2 are disposed between the fourth lens L4 and the image sensor 101. These parallel flat plates P1 and P2 are a visible light cut filter and a cover glass.

Table 3 below shows various data of the photographing lens 100 according to the second example. The surface numbers shown in Table 3 correspond to the surface numbers shown in FIG.
[Table 3]
(Overall specifications)
Focal length 3.451 mm
F number 2.4
Maximum image height 2.4 mm
(Lens data)
Surface number Curvature radius Surface spacing Refractive index (d line) Abbe number
OBJ: INFINITY 700.00000
1: 15.12306 1.00000 1.88300 40.76
2: 3.50000 3.00000
3: -45.03712 3.00000 2.00330 28.27
4: -7.17844 0.30000
STO: INFINITY 0.60000
6: 5.56624 4.30000 1.65160 58.55
7: 5.56671 1.20000
* 8: -100.00000 1.10000 1.86400 40.58
* 9: -4.55390 1.00000
10: INFINITY 1.10000 1.51680 64.17
11: INFINITY 0.50000
12: INFINITY 0.40000 1.51680 64.17
13: INFINITY 0.84204
IMG: INFINITY

As shown in the lens data of Table 3, the object-side surface (eighth surface) and the image-side surface (ninth surface) of the fourth lens L4 are aspherical surfaces. Table 4 below shows numerical values of the aspheric coefficients in these aspheric surfaces.
[Table 4]
Aspheric coefficient 8th surface 9th surface K 0.000000 0.000000
A ₄ -1.948020E-03 2.815286E-03
A ₆ -2.933776E-03 -2.253020E-03
A ₈ 7.625820E-04 4.607817E-04
A ₁₀ -5.648299E-05 -2.382408E-05
A ₁₂ 0.000000E + 00 0.000000E + 00

In the photographing lens 100 according to the second example, the values related to the conditional expressions (1) to (7) described above are as follows. As described below, the photographic lens 100 according to the second example satisfies the conditional expressions (1) to (7), and thus can obtain the above-described effects.
Conditional expression (1) t ₃ / f 1.246
Conditional expression (2) | f ₁ / f | 1.557
Conditional expression (3) f ₃ / f 8.121
Conditional expression (4) f ₂ = 8.187 f ₄ = 5.493
Conditional expression (5) (r ₂ + r ₁ ) / (r ₂ −r ₁ ) −1.602
Conditional expression (6) (r ₄ + r ₃ ) / (r ₄ −r ₃ ) −1.379
Conditional Expression (7) | (r ₇ + r ₆ ) / (r ₇ −r ₆ ) | 23687.128

  FIG. 6 shows spherical aberration, astigmatism and distortion in the taking lens 100 according to the second example, and FIG. 7 shows coma aberration. 6 and 7, it can be seen that, in the photographic lens 100 according to the second example, each aberration is well corrected and has high optical performance.

  Note that the taking lens 100 according to the second example is designed so as to obtain the best imaging performance with near-infrared light. Therefore, FIGS. 6 and 7 show aberration diagrams with respect to a light beam having a wavelength of 940 nm. However, the back focus and the focal length of the photographing lens 100 shown in Table 3 and the focal length of each lens used for the calculation of the conditional expressions (1) to (7) are defined by the d line.

<Third embodiment>
Next, a third embodiment will be described. FIG. 8 is a sectional view of the taking lens 100 according to the third embodiment. In the photographic lens 100 according to the third example, the object-side surface and the image-side surface of the fourth lens L4 are aspheric. In the third embodiment, two parallel flat plates P1 and P2 are disposed between the fourth lens L4 and the image sensor 101. These parallel flat plates P1 and P2 are a visible light cut filter and a cover glass.

Table 5 below shows various data of the photographing lens 100 according to the third example. The surface numbers shown in Table 5 correspond to the surface numbers shown in FIG.
[Table 5]
(Overall specifications)
Focal length 3.451 mm
F number 2.4
Maximum image height 2.4 mm
(Lens data)
Surface number Curvature radius Surface spacing Refractive index (d line) Abbe number
OBJ: INFINITY 700.00000
1: 14.79079 1.00000 1.88300 40.76
2: 3.50000 3.00000
3: -51.56752 3.00000 2.00330 28.27
4: -7.19699 0.30000
STO: INFINITY 0.60000
6: 5.24325 4.00000 1.65160 58.55
7: 5.02891 1.20000
* 8: -50.00000 1.20000 1.86400 40.58
* 9: -4.32558 1.00000
10: INFINITY 1.10000 1.51680 64.17
11: INFINITY 0.50000
12: INFINITY 0.40000 1.51680 64.17
13: INFINITY 0.81865
IMG: INFINITY

As shown in the lens data in Table 5, the object-side surface (eighth surface) and the image-side surface (ninth surface) of the fourth lens L4 are aspherical surfaces. Table 6 below shows numerical values of the aspheric coefficients in these aspheric surfaces.
[Table 6]
Aspheric coefficient 8th surface 9th surface K 0.000000 0.000000
A ₄ -3.626731E-03 1.638367E-03
A ₆ -2.892586E-03 -2.000042E-03
A ₈ 7.190983E-04 3.852942E-04
A ₁₀ -5.958750E-05 -2.264035E-05
A ₁₂ 0.000000E + 00 0.000000E + 00

In the photographing lens 100 according to the third example, the values related to the conditional expressions (1) to (7) described above are as follows. As will be described below, the taking lens 100 according to the third example satisfies the conditional expressions (1) to (7), and thus can obtain the above-described effects.
Conditional expression (1) t ₃ / f 1.159
Conditional expression (2) | f ₁ / f | 1.570
Conditional expression (3) f ₃ / f 8.599
Conditional expression (4) f ₂ = 8.064 f ₄ = 5.415
Conditional expression (5) (r ₂ + r ₁ ) / (r ₂ −r ₁ ) −1.620
Conditional expression (6) (r ₄ + r ₃ ) / (r ₄ −r ₃ ) −1.324
Conditional Expression (7) | (r ₇ + r ₆ ) / (r ₇ −r ₆ ) | 47.925

  FIG. 9 shows spherical aberration, astigmatism and distortion in the taking lens 100 according to the third example, and FIG. 10 shows coma aberration. 9 and 10, it can be seen that in the photographic lens 100 according to the third example, each aberration is well corrected and has high optical performance.

  The taking lens 100 according to the third example is designed so that the best imaging performance can be obtained with near infrared light. Therefore, FIGS. 9 and 10 show aberration diagrams with respect to a light beam having a wavelength of 940 nm. However, the back focus and the focal length of the photographing lens 100 shown in Table 5 and the focal length of each lens used for the calculation of the conditional expressions (1) to (7) are defined by the d line.

<Fourth embodiment>
Next, a fourth embodiment will be described. FIG. 11 is a cross-sectional view of the taking lens 100 according to the fourth embodiment. In the photographing lens 100 according to the fourth example, only the object-side surface of the fourth lens L4 is an aspherical surface. In the fourth embodiment, two parallel flat plates P1 and P2 are arranged between the fourth lens L4 and the image sensor 101. These parallel flat plates P1 and P2 are a visible light cut filter and a cover glass.

Table 7 below shows various data of the photographing lens 100 according to the fourth example. The surface numbers shown in Table 7 correspond to the surface numbers shown in FIG.
[Table 7]
(Overall specifications)
Focal length 3.452 mm
F number 2.4
Maximum image height 2.4 mm
(Lens data)
Surface number Curvature radius Surface spacing Refractive index (d line) Abbe number
OBJ: INFINITY 700.00000
1: 11.60670 1.00000 1.88300 40.76
2: 3.50000 3.00000
3: -21.00000 2.90000 2.00330 28.27
4: -7.08842 0.30000
STO: INFINITY 0.70000
6: 4.73871 4.00000 1.58913 61.14
7: 5.26428 1.00000
* 8: -200.00000 1.40000 1.85400 40.39
9: -4.54691 1.00000
10: INFINITY 1.10000 1.51680 64.17
11: INFINITY 0.50000
12: INFINITY 0.40000 1.51680 64.17
13: INFINITY 0.93805
IMG: INFINITY

Further, as shown in the lens data of Table 7, the object side surface (eighth surface) of the fourth lens L4 is an aspherical surface. Table 8 below shows numerical values of the aspheric coefficients in this aspheric surface.
[Table 8]
Aspheric coefficient 8th surface K 0.000000
A ₄ -5.545826E-03
A ₆ 5.950405E-04
A ₈ -2.683160E-04
A ₁₀ 2.873463E-05
A ₁₂ 0.000000E + 00

In the photographing lens 100 according to the fourth example, the values related to the conditional expressions (1) to (7) described above are as follows. As will be described below, the photographic lens 100 according to the fourth example satisfies the conditional expressions (1) to (7), and thus can obtain the effects described above.
Conditional expression (1) t ₃ / f 1.159
Conditional expression (2) | f ₁ / f | 1.745
Conditional expression (3) f ₃ / f 6.107
Conditional expression (4) f ₂ = 9.657 f ₄ = 5.430
Conditional expression (5) (r ₂ + r ₁ ) / (r ₂ −r ₁ ) −1.863
Conditional expression (6) (r ₄ + r ₃ ) / (r ₄ −r ₃ ) −2.019
Conditional Expression (7) | (r ₇ + r ₆ ) / (r ₇ −r ₆ ) | 19.032

  FIG. 12 shows spherical aberration, astigmatism and distortion in the photographing lens 100 according to the fourth example, and FIG. 13 shows coma aberration. 12 and 13, it can be seen that, in the photographic lens 100 according to the fourth example, each aberration is well corrected and has high optical performance.

  The taking lens 100 according to the fourth example is designed so that the best imaging performance can be obtained with near-infrared light. Therefore, FIGS. 12 and 13 show aberration diagrams for a light beam having a wavelength of 940 nm. However, the back focus and the focal length of the taking lens 100 shown in Table 7 and the focal length of each lens used for the calculation of the conditional expressions (1) to (7) are defined by the d line.

<Fifth embodiment>
Next, a fifth embodiment will be described. FIG. 14 is a sectional view of the taking lens 100 according to the fifth embodiment. In the photographing lens 100 according to the fifth example, only the image side surface of the third lens L3 is aspheric. In the fifth embodiment, two parallel flat plates P1 and P2 are arranged between the fourth lens L4 and the image sensor 101. These parallel flat plates P1 and P2 are a visible light cut filter and a cover glass.

Table 9 below shows various data of the photographing lens 100 according to the fifth example. The surface numbers shown in Table 9 correspond to the surface numbers shown in FIG.
[Table 9]
(Overall specifications)
Focal length 3.440 mm
F number 2.4
Maximum image height 2.4 mm
(Lens data)
Surface number Curvature radius Surface spacing Refractive index (d line) Abbe number
OBJ: INFINITY 700.00000
1: 28.69721 1.00000 1.833300 40.76
2: 3.50000 3.00000
3: 100.00000 2.90000 2.00330 28.27
4: -7.95414 0.30000
STO: INFINITY 0.70000
6: 8.42804 5.00000 1.65160 58.55
* 7: 9.62735 0.50000
8: -25.00000 1.40000 1.86400 40.58
9: -4.49098 1.00000
10: INFINITY 1.10000 1.51680 64.17
11: INFINITY 0.50000
12: INFINITY 0.40000 1.51680 64.17
13: INFINITY 1.74427
IMG: INFINITY

Further, as shown in the lens data of Table 9, the image side surface (seventh surface) of the third lens L3 is an aspherical surface. Table 10 below shows numerical values of the aspheric coefficients in this aspheric surface.
[Table 10]
Aspheric coefficient 7th surface K 0.000000
A ₄ 6.459051E-03
A ₆ -6.621031E-04
A ₈ 9.826798E-05
A ₁₀ -8.707881E-06
A ₁₂ 0.000000E + 00

In the photographing lens 100 according to the fifth example, the values related to the conditional expressions (1) to (7) described above are as follows. As will be described below, the photographic lens 100 according to the fifth example satisfies the conditional expressions (1) to (7), and thus can obtain the effects described above.
Conditional expression (1) t ₃ / f 1.454
Conditional expression (2) | f ₁ / f | 1.337
Conditional expression (3) f ₃ / f 11.413
Conditional expression (4) f ₂ = 7.444 f ₄ = 6.142
Conditional expression (5) (r ₂ + r ₁ ) / (r ₂ −r ₁ ) −1.278
Conditional expression (6) (r ₄ + r ₃ ) / (r ₄ −r ₃ ) −0.853
Conditional Expression (7) | (r ₇ + r ₆ ) / (r ₇ −r ₆ ) | 15.055

  FIG. 15 shows spherical aberration, astigmatism and distortion in the taking lens 100 according to the fourth example, and FIG. 16 shows coma aberration. 15 and 16, it can be seen that in the photographic lens 100 according to the fifth example, each aberration is well corrected and has high optical performance.

  The taking lens 100 according to the fifth example is designed so that the best imaging performance can be obtained with near-infrared light. Therefore, FIGS. 15 and 16 show aberration diagrams with respect to a light beam having a wavelength of 940 nm. However, the back focus and the focal length of the photographing lens 100 shown in Table 9 and the focal length of each lens used for the calculation of the conditional expressions (1) to (7) are defined by the d line.

According to the embodiment described above, the following operational effects can be obtained.
The taking lens 100 has a meniscus shape with a convex surface facing the object side in the order from the object side to the image side, a first lens L1 having negative refractive power, and the curvature of the image side surface relative to the object side surface. A second lens L2 having a small radius and having a positive refractive power; an aperture stop S; a third lens L3 having a meniscus shape having a convex surface facing the object side and having a positive refractive power; A fourth lens L4 having a meniscus shape with a convex surface facing the side and having a positive refractive power, and at least one of the surfaces constituting the third lens L3 and the fourth lens L4 is non- It was made to be spherical. With such a configuration, it is possible to suppress a ghost generated in the photographing lens 100 and to make the ghost inconspicuous even when a high-luminance object such as a headlight enters the photographing screen. In particular, the light reflected from the imaging element surface is reflected by the lens surface of the photographing lens 100 and returns to the imaging element surface, and the reflectance of the imaging element surface is high. -A ghost that is tens of times brighter than a strike. On the other hand, in the photographing lens 100 of the present embodiment, the reflected light from the imaging element surface can be diffused by the fourth lens L4, so that the ghost intensity can be reduced. Further, in the photographing lens 100 of the present embodiment, at least one of the surfaces constituting the third lens L3 and the fourth lens L4 is aspherical, so that the lens surface that is a ghost generation source is minimized. Therefore, it is possible to suppress the occurrence of ghosts.

-Modification-
In the above-described embodiment, the example in which the photographing lens 100 is used for photographing with near-infrared light has been described. However, the present invention is not limited to this, and the photographing lens 100 may be used for photographing with visible light. In this case, the photographing lens may be designed so as to have the best imaging performance with visible light.

  Although various embodiments have been described above, the present invention is not limited to these contents. Other embodiments conceivable within the scope of the technical idea of the present invention are also included in the scope of the present invention.

DESCRIPTION OF SYMBOLS 10 ... Car-mounted camera, 100 ... Shooting lens, 101 ... Imaging element, L1 ... 1st lens, L2 ... 2nd lens, L3 ... 3rd lens, L4 ... 4th lens, S ... Aperture stop

Claims (7)

From the object side to the image side,
A first lens having a meniscus shape with a convex surface facing the object side and having negative refractive power;
A second lens having a shape in which the radius of curvature of the image side surface is smaller than the object side surface and having a positive refractive power;
An aperture stop,
A third lens having a meniscus shape with a convex surface facing the object side and having a positive refractive power;
A fourth lens having a meniscus shape with a convex surface facing the image side and having a positive refractive power;
Consisting of
A photographic lens, wherein at least one of the surfaces constituting the third lens and the fourth lens is an aspherical surface. The photographic lens according to claim 1,
A photographing lens, wherein at least one of the surfaces constituting the fourth lens is an aspherical surface. The photographic lens according to claim 1 or 2,
A photographic lens characterized by satisfying the following conditional expression (1):
1.5> t ₃ /f>0.4 (1)
However,
f: Focal length of the taking lens t ₃ : Center thickness of the third lens In the photographic lens according to any one of claims 1 to 3,
A photographic lens characterized by satisfying the following conditional expressions (2) to (4):
2.0> | f ₁ /f|>1.0 (2)
f ₃ /f>3.0 (3)
f ₂ > f ₄ (4)
However,
f: focal length of the taking lens f ₁ : focal length of the first lens f ₂ : focal length of the second lens f ₃ : focal length of the third lens f ₄ : focal length of the fourth lens The photographic lens according to claim 4,
A photographic lens characterized by satisfying the following conditional expressions (5) to (7):
−1.2> (r ₂ + r ₁ ) / (r ₂ −r ₁ )> − 2.0 (5)
−0.8> (r ₄ + r ₃ ) / (r ₄ −r ₃ )> − 2.5 (6)
| (R ₇ + r ₆ ) / (r ₇ −r ₆ ) |> 6.0 (7)
However,
r ₁ : radius of curvature of the object side surface of the first lens r ₂ : radius of curvature of the image side surface of the first lens r ₃ : radius of curvature of the object side surface of the second lens r ₄ : the first Radius of curvature of the image side surface of the two lenses r ₆ : radius of curvature of the object side surface of the third lens r ₇ : radius of curvature of the image side surface of the third lens In the photographing lens according to any one of claims 1 to 5,
An imaging lens, wherein near-infrared light having a wavelength in the range of 850 nm to 1000 nm is imaged.   An in-vehicle camera comprising the photographing lens according to any one of claims 1 to 6.

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