JP6635190B2 - Imaging lens, lens unit, and imaging device - Google Patents

Description

  The present invention relates to a wide-angle type imaging lens substantially consisting of four lenses, and a lens unit and an imaging apparatus including the same.

  In recent years, image sensors such as CCDs and CMOSs have been reduced in size and pixels. At the same time, the size of imaging device bodies equipped with these imaging elements has been reduced in size, and the size and performance of imaging lenses mounted on the imaging devices have been demanded. Further, lenses mounted on in-vehicle cameras, surveillance cameras, and the like are required to have high environmental resistance so that they can be used in severe environments, and to be inexpensive and lightweight. Conventionally known imaging lenses having a relatively small number of lenses in such a field include those disclosed in Patent Documents 1 and 2.

  Demands for lenses in the above fields are increasing year by year, and it is required to simultaneously satisfy a plurality of advanced requirements. That is, despite having a small configuration with a small number of lenses, it has a long back focus so that a cover glass or a filter can be arranged between the lens system and the image sensor, and can be used even under low illuminance conditions such as at night. There is a growing demand for an imaging lens which has a large aperture and which has a wide angle of view of 60 ° or more at all angles of view and in which aberrations are well corrected. In addition, many in-vehicle cameras and surveillance cameras have a fixed focus that does not have an auto-focus function, and focus shift due to environmental changes directly affects resolution performance. Demands for characteristics) are becoming stronger.

  However, with respect to those described in Patent Documents 1 and 2, although the entire system is a simple optical system composed of four lenses, the system satisfies securing a wide angle, a large aperture, and a long back focus. Since the use of many glass lenses makes it unnecessary to consider environmental resistance, the configuration is inexpensive.

JP 2009-14947 A JP 2011-257462 A

  The present invention has been made in view of the above circumstances, and provides an inexpensive imaging lens having a long back focus, a wide angle of view, a good optical performance despite a large aperture, and a small focus shift when the environment changes. With the goal.

  Another object of the present invention is to provide a lens unit and an image pickup apparatus having the above-mentioned image pickup lens.

In order to achieve at least one of the above-described objects, an imaging lens reflecting one aspect of the present invention is formed of glass in order from the object side, has negative power, and has a concave shape on the image side surface. One lens, a second lens formed of glass and having a positive power, a third lens formed of plastic, having a negative power and having at least one aspherical shape, and a positive lens formed of plastic; And a fourth lens having at least one aspherical shape, which satisfies the following conditional expression.
0.8 <f12 / f <1.2 (1)
-1.65 <f3 / f4 <-0.8 (2)
0 ≦ D34 / f <0.04 (3)
70 <vd1 <100 (4)
30 <vd2 <50 (5)
20 <vd3 <30 (6)
50 <vd4 <60 (7)
1.3 <D12 / f <2.2 (10)
Here, the value f is the focal length of the entire lens system, the value f12 is the combined focal length of the first lens and the second lens, the value f3 is the focal length of the third lens, and the value f4 is the fourth focal length. The value D34 is the distance between the third lens and the fourth lens on the optical axis , the value vd1 is the Abbe number of the first lens at d-line, and the value vd2 is the focal length of the second lens. The Abbe number at the d-line, the value vd3 is the Abbe number at the d-line of the third lens, the value vd4 is the Abbe number at the d-line of the fourth lens, and the value D12 is The distance on the optical axis with the second lens .

  In order to achieve at least one of the above-described objects, a lens unit according to an aspect of the present invention includes the above-described imaging lens and a lens barrel that holds the imaging lens.

  In order to achieve at least one of the above-described objects, an imaging device according to an aspect of the present invention includes the above-described lens unit and an imaging device that projects an image using the lens unit.

FIG. 1 is a diagram illustrating a lens unit including an imaging lens according to an embodiment of the present invention and an imaging apparatus. FIG. 2A is a cross-sectional view of the imaging lens and the like of Example 1, and FIGS. 2B to 2D are aberration diagrams. FIG. 3A is a cross-sectional view of the imaging lens and the like of Example 2, and FIGS. 3B to 3D are aberration diagrams. FIG. 4A is a cross-sectional view of the imaging lens and the like of Example 3, and FIGS. 4B to 4D are aberration diagrams. FIG. 5A is a cross-sectional view of the imaging lens and the like of Example 4, and FIGS. 5B to 5D are aberration diagrams. FIG. 9 is a partially enlarged cross-sectional view illustrating a modified example of the third and fourth lenses in the imaging lens shown in FIG. 1.

  FIG. 1 is a cross-sectional view illustrating an imaging device 100 according to an embodiment of the present invention. The imaging device 100 includes a camera module 30 for forming an image signal, and a processing unit 60 that performs a function as the imaging device 100 by operating the camera module 30.

  The camera module 30 includes a lens unit 40 containing the imaging lens 10 and a sensor unit 50 that converts a subject image formed by the imaging lens 10 into an image signal.

  The lens unit 40 includes the imaging lens 10 that is a wide-angle optical system, and a lens barrel 41 that incorporates the imaging lens 10. The imaging lens 10 includes first to fourth lenses L1 to L4. The lens barrel 41 is formed of resin, metal, a mixture of glass fiber with resin, or the like, and houses and holds a lens and the like inside. When the lens barrel 41 is formed of a mixture of metal or resin and glass fiber, the lens barrel 41 is less likely to thermally expand than resin, and the imaging lens 10 can be fixed stably. The lens barrel 41 has an opening OP through which light from the object side is incident.

  The full angle of view of the imaging lens 10 is 60 ° or more. The first to fourth lenses L1 to L4 constituting the imaging lens 10 are held directly or indirectly on the inner surface side of the lens barrel 41 at their flange portions or outer peripheral portions, and the optical axis AX direction and the optical axis Positioning is performed in a direction perpendicular to AX. In particular, the fourth lens L4 is supported by the lens barrel 41 via the third lens L3. Specifically, the annular fitting convex portion 10b provided on the flange portion 4b of the fourth lens L4 fits into the annular fitting concave portion 10a provided on the flange portion 3b of the third lens L3, and the optical axis AX direction. Positioning is performed in a direction perpendicular to the optical axis AX. In this way, by adopting a structure in which the third lens L3 and the fourth lens L4 are fitted on the outer periphery, the coaxiality of the two lenses L3 and L4 can be maintained, so that a lens shift error can be suppressed and collision between optical surfaces can be avoided. can do.

  The sensor unit 50 includes a solid-state imaging device 51 that photoelectrically converts a subject image formed by the imaging lens (wide-angle optical system) 10, a substrate 52 that supports the solid-state imaging device 51, and a solid-state imaging device 51 via the substrate 52. And a sensor holder 53 for holding the sensor. The solid-state imaging device 51 is, for example, a CMOS image sensor. The substrate 52 includes wiring for operating the solid-state imaging device 51, peripheral circuits, and the like. The sensor holder 53 is formed of a resin or other material, and not only positions the solid-state imaging device 51 with respect to the optical axis AX, but also supports the filter F1 so as to face the solid-state imaging device 51. The lens barrel 41 of the lens unit 40 is fixed so as to be fitted to the sensor holder 53.

  The solid-state imaging device (imaging device) 51 has a photoelectric conversion unit 51a as an imaging surface I, and a signal processing circuit (not shown) is formed around the photoelectric conversion unit 51a. In the photoelectric conversion unit 51a, pixels, that is, photoelectric conversion elements are two-dimensionally arranged. The solid-state imaging device 51 is not limited to the CMOS image sensor described above, but may be a device incorporating another imaging device such as a CCD.

  In addition, a filter or the like can be arranged between the lenses constituting the lens unit 40 or between the lens unit 40 and the sensor unit 50. In the example of FIG. 1, the filter F1 is disposed between the fourth lens L4 of the imaging lens 10 and the solid-state imaging device 51. The filter F1 is a parallel flat plate assuming an optical low-pass filter, an IR cut filter, a seal glass of the solid-state imaging device 51, and the like. The filter F <b> 1 can be disposed as a separate filter member, but the function can be imparted to any of the lens surfaces constituting the imaging lens 10 without being disposed separately. For example, in the case of an infrared cut filter, an infrared cut coat may be applied on the surface of one or more lenses.

  The processing unit 60 includes an element driving unit 61, an input unit 62, a storage unit 63, a display unit 64, and a control unit 68. The element driving unit 61 outputs a YUV or other digital pixel signal to an external circuit (specifically, a circuit attached to the solid-state imaging device 51 or the like), a voltage for driving the solid-state imaging device 51 from the control unit 68, or the like. The solid-state imaging device 51 is operated by receiving supply of a clock signal or the like. The input unit 62 is a unit that receives a user's operation, the storage unit 63 is a unit that stores information necessary for the operation of the imaging apparatus 100, image data acquired by the camera module 30, and the like. This is a part that displays information to be presented to the user, a captured image, and the like. The control unit 68 generally controls the operations of the element driving unit 61, the input unit 62, the storage unit 63, and the like, and can perform various image processing on image data obtained by the camera module 30, for example. .

  Although a detailed description is omitted, the specific functions of the processing unit 60 are appropriately adjusted according to the use of the device in which the imaging device 100 is incorporated. The imaging device 100 can be mounted on devices for various uses such as a vehicle-mounted camera and a surveillance camera.

  Hereinafter, the imaging lens (wide-angle optical system) 10 and the like of the first embodiment will be described with reference to FIG. The imaging lens 10 illustrated in FIG. 1 has substantially the same configuration as an imaging lens 11 according to a first embodiment described later.

  The illustrated imaging lens (wide-angle optical system) 10 has, in order from the object side, a four-lens configuration having a negative, positive, negative, and positive power arrangement. To be more specific, the imaging lens 10 is constructed from a negative first lens L1, a positive second lens L2, a negative third lens L3, and a positive fourth lens in this order from the object side. Become. The first and second lenses L1 and L2 are formed of glass. The third and fourth lenses L3, L4 are formed of plastic (or resin). The first lens L1 disposed at a position exposed to the outside air is made of glass to improve weather resistance. Further, when it is assumed that the first lens L1 is used in a severe environment such as an in-vehicle camera or a surveillance camera, the side surface of the first lens L1 may be subjected to a process for increasing strength, scratch resistance, chemical resistance, or an anti-reflection process. Is preferred. Further, it is preferable to apply a water-repellent coat or a hydrophilic coat to the object side surface of the first lens L1. The first lens L1 has a concave shape on the image side surface. The second lens L2 preferably has a biconvex shape. The third and fourth lenses L3, L4 each have at least one aspherical shape. In the illustrated example, the object side surface and the image side surface of the first and second lenses L1 and L2 have spherical shapes. However, these lenses L1 and L2 each have at least one aspherical shape. It may be. When the first and second lenses L1 and L2 made of glass have an aspherical surface, the cost is increased, but the optical performance is improved. As already described, the third lens L3 and the fourth lens L4 are fitted with each other. Aspheric plastic lenses with strong power tend to have high eccentricity error sensitivity. Therefore, both the lenses L3 and L4 do not fit into the lens barrel 41, but only one of them fits into the lens barrel 41, and the other lens directly fits into the other lens itself. By doing so, group eccentricity (specifically, eccentricity between the third and fourth lenses L3 and L4) can be suppressed. The third and fourth lenses L3, L4 may be cemented lenses. In this case, chromatic aberration can be better corrected. An aperture stop ST is provided between the first lens L1 and the second lens L2. The imaging lens 10 has a configuration in which the object side of the aperture stop ST is a front group Gr1 and the image side is a rear group Gr2 with reference to the aperture stop ST.

The imaging lens (wide-angle optical system) 10 satisfies the following conditional expressions (1) to (3).
0.8 <f12 / f <1.2 (1)
-1.65 <f3 / f4 <-0.8 (2)
0 ≦ D34 / f <0.04 (3)
Here, the value f is the focal length of the entire lens system, the value f12 is the combined focal length of the first lens L1 and the second lens L2, the value f3 is the focal length of the third lens L3, and the value f4 Is the focal length of the fourth lens L4, and the value D34 is the distance between the third lens L3 and the fourth lens L4 on the optical axis AX.

  In the case of a fixed-focus optical system that does not perform automatic focusing (AF), a focus shift due to a temperature change is a problem. However, by satisfying conditional expressions (1) to (3), the temperature change can be performed while using a plastic lens. The configuration is such that defocusing at the time does not easily occur. Specifically, by setting the combined focal length of the glass lenses (specifically, the first and second lenses L1 and L2) so as to satisfy the range of the conditional expression (1), the first lens L1 and the second lens The focal length of the optical system is substantially determined by the two lenses L2, so that even if the plastic lenses, that is, the third and fourth lenses L3 and L4 expand or contract due to a temperature change, the influence of the defocus caused by the expansion or contraction is reduced. I have to. Further, the third lens L3 and the fourth lens L4, which are plastic lenses that are easily affected by a temperature change, satisfy both the conditional expressions (2) and (3), so that the synthetic power of the plastic lens is set to substantially zero. Therefore, it is possible to adopt a configuration in which defocusing is more unlikely to occur.

In the imaging lens 10, the materials of the first to fourth lenses L1 to L4 further satisfy the following conditional expressions (4) to (7).
70 <vd1 <100 (4)
30 <vd2 <50 (5)
20 <vd3 <30 (6)
50 <vd4 <60 (7)
Here, the value vd1 is the Abbe number of the first lens L1 at the d-line, the value vd2 is the Abbe number of the second lens L2 at the d-line, and the value vd3 is the Abbe number of the third lens L3 at the d-line. The value vd4 is the Abbe number of the fourth lens L4 at the d-line.

  In applications for on-vehicle cameras and surveillance cameras, not only daytime use but also nighttime use is assumed, so it is necessary to handle not only visible light but also near-infrared light. Therefore, in a fixed-focus optical system, it is necessary to correct chromatic aberration from visible light to near-infrared light. By using a material that satisfies the ranges of the conditional expressions (4) to (7), it is possible to correct chromatic aberration from visible light to near infrared light.

It is more preferable that the conditional expressions (4) and (5) be in the range of the following expression.
75 <vd1 <85 (4) '
35 <vd2 <45 (5) '

The imaging lens 10 further satisfies the following conditional expression (8).
−1.2 <ff / fr <−1.0 (8)
Here, the value ff is the focal length of the front group Gr1, and the value fr is the focal length of the rear group Gr2.

  By satisfying the range of the conditional expression (8), it is possible to provide a small optical system having a long back focus. By exceeding the lower limit of conditional expression (8), a sufficient back focus can be ensured. On the other hand, when the value is below the upper limit of the conditional expression (8), the back focus does not become too long, and the size of the imaging lens 10 can be reduced.

Further, the imaging lens 10 further satisfies the following conditional expression (9).
R2 <| R1 | (9)
Here, the value R1 is the radius of curvature of the object side surface of the first lens L1, and the value R2 is the radius of curvature of the image side surface of the first lens L1.

  By satisfying the range of the conditional expression (9), it is possible to secure a wide angle of view while suppressing the occurrence of spherical aberration.

The imaging lens 10 further satisfies the following conditional expression (10).
1.3 <D12 / f <2.2 (10)
Here, the value f is the focal length of the entire system, and the value D12 is the distance between the first lens L1 and the second lens L2 on the optical axis AX.

  By falling below the upper limit of conditional expression (10), the size of the imaging lens 10 can be reduced. On the other hand, by exceeding the lower limit of conditional expression (10), it is not necessary to increase the power of the first lens L1, and spherical aberration and lateral chromatic aberration can be corrected relatively easily.

It is more desirable that the conditional expression (10) be in the range of the following expression.
1.4 <D12 / f <2.1 (10) '

  The imaging lens 10 may further include another optical element (for example, a lens, a filter member, or the like) having substantially no power.

  In the imaging lens 10 and the like described above, the negative, positive, negative, and positive power arrangements are sequentially performed from the object side, and the third and fourth lenses L3 and L4 are aspheric plastic lenses. Even with a small number of lenses, aberrations can be satisfactorily corrected even with a large aperture. Further, by using a plurality of plastic lenses, the cost can be reduced as compared with the case where all the lenses are made of glass lenses.

  Such an imaging lens 10 can be suitably used for a fixed focus camera having no focus function. Specific applications used include security cameras such as surveillance cameras, door phone cameras, and authentication cameras, lenses for marketing cameras, on-board camera lenses mounted on automobiles and other moving objects, medical endoscopes, and healthcare Examples include care measurement, medical and industrial optical lenses such as industrial endoscopes, and the like. Note that the imaging lens 10 and the like may be applied to applications requiring a wide angle other than these.

  In addition, the lens unit 40 and the imaging device 100 have a long back focus, a wide angle of view, a good optical performance despite a large aperture, and a good Is less expensive and less in focus shift.

ただし、
Ａｉ：ｉ次の非球面係数
Ｒ ：曲率半径
Ｋ ：円錐定数〔Example〕
Hereinafter, examples of the imaging lens and the like of the present invention will be described. The symbols used in each example are as follows.
F: F number w: Maximum full angle of view PD: Defocus when temperature changes by 30 ° C. (considering refractive index and thermal expansion)
R: radius of curvature D: axial upper surface interval nd: refractive index vd of lens material with respect to d-line: Abbe number of lens material In each embodiment, the surface where "*" is described after each surface number has an aspherical shape. The shape of the aspherical surface is represented by the following “Formula 1” where the origin is the vertex of the surface, the X axis is in the optical axis direction, and the height in the direction perpendicular to the optical axis is h.

However,
Ai: i-th order aspherical coefficient R: radius of curvature K: conic constant

(Example 1)
The overall specifications of the imaging lens of Example 1 are shown below.
F: 2.0
w: 96.8 °
PD: 0.0027mm

Table 1 below shows data on the lens surface of the imaging lens of the first embodiment. In Table 1 below, the surface number is represented by “Surf. N”, the aperture stop is represented by “ST”, and the infinity is represented by “INF”.
[Table 1]
Surf.NR (mm) D (mm) nd vd
1 INF 0.500 1.497 81.6
2 3.582 7.781
3 ST INF -0.109
4 14.951 2.077 1.883 40.8
5 -8.087 1.202
6 * -21.376 1.058 1.635 23.9
7 * 2.931 0.120
8 * 3.805 2.644 1.545 56.0
9 * -4.438 4.477
10 INF 0.850 1.517 64.1
11 INF 2.000

Table 2 below shows the aspheric coefficient of the lens surface of Example 1. In the following (including the lens data in the table), a power of 10 (for example, 2.5 × 10 ⁻⁰² ) is represented by E (for example, 2.5E-02).
[Table 2]
Side 6
K = -2.6946E + 00, A4 = -1.2155E-02, A6 = 4.9888E-04, A8 = 9.5137E-05,
A10 = -2.3991E-05, A12 = 1.4888E-06, A14 = 0.0000E + 00
Surface 7
K = -1.1866E + 00, A4 = -9.7766E-03, A6 = -3.8798E-04, A8 = 1.3563E-04,
A10 = -7.1703E-06, A12 = -3.1353E-07, A14 = 0.0000E + 00
Side 8
K = -2.3885E-01, A4 = 4.1911E-05, A6 = -2.3815E-03, A8 = 4.0207E-04,
A10 = -3.3856E-05, A12 = 1.9613E-06, A14 = -8.4247E-08
9th page
K = -2.8858E + 00, A4 = -1.7658E-03, A6 = -9.3635E-04, A8 = 4.3709E-04,
A10 = -8.7673E-05, A12 = 9.0497E-06, A14 = -3.5485E-07

  FIG. 2A is a cross-sectional view of the imaging lens 11 and the like according to the first embodiment. The imaging lens 11 has a first lens L1 having a negative power and a plano-concave, a second lens L2 having a positive power and a bi-convex, a third lens L3 having a negative power and a bi-concave, And a biconvex fourth lens L4 having a positive power. The third and fourth lenses L3 and L4 have aspherical surfaces as optical surfaces. The first and second lenses L1 and L2 are formed of glass, and the third and fourth lenses L3 and L4 are formed of plastic. An aperture stop ST is arranged between the first lens L1 and the second lens L2. A filter F1 having an appropriate thickness is arranged between the fourth lens L4 and the solid-state imaging device 51. The filter F1 is a parallel flat plate assuming an optical low-pass filter, an IR cut filter, a seal glass of the solid-state imaging device 51, and the like. Reference symbol I indicates an imaging surface that is a projection surface of the solid-state imaging device 51. Note that the symbols F1 and I are the same in the following embodiments.

  2B to 2D show aberration diagrams (spherical aberration, astigmatism, and distortion) of the imaging lens 11 of Example 1.

(Example 2)
The overall specifications of the imaging lens of Example 2 are shown below.
F: 2.0
w: 97.4 °
PD: 0.0013mm

Table 3 below shows data on the lens surface of the imaging lens of the second embodiment.
[Table 3]
Surf.NR (mm) D (mm) nd vd
1 INF 0.500 1.497 81.6
2 3.680 7.827
3 ST INF 0.657
4 9.700 1.730 1.834 37.3
5 -8.050 0.918
6 * -6.054 0.600 1.635 23.9
7 * 3.854 0.050
8 * 3.798 2.568 1.531 56.0
9 * -4.491 4.899
10 INF 0.850 1.517 64.1
11 INF 2.000

Table 4 below shows the aspheric coefficient of the lens surface of the second embodiment.
[Table 4]
Side 6
K = -2.5360E + 01, A4 = -1.6838E-02, A6 = 2.9078E-03, A8 = -5.2744E-04,
A10 = 5.9126E-05, A12 = -2.9430E-06, A14 = 2.1701E-08
Surface 7
K = -7.6637E-01, A4 = 1.9638E-03, A6 = -3.0325E-03, A8 = 5.0220E-04,
A10 = -2.9478E-05, A12 = -6.8946E-07, A14 = 9.0652E-08
Side 8
K = 4.7842E-01, A4 = 1.5608E-03, A6 = -4.1509E-03, A8 = 8.3052E-04,
A10 = -9.8822E-05, A12 = 7.0248E-06, A14 = -2.6726E-07
9th page
K = -1.2941E + 00, A4 = -9.9983E-05, A6 = -6.0676E-04, A8 = 2.5408E-04
A10 = -4.9160E-05, A12 = 4.9743E-06, A14 = -1.8050E-07

  FIG. 3A is a cross-sectional view of the imaging lens 12 and the like according to the second embodiment. The imaging lens 12 has a plano-concave first lens L1 having a negative power, a biconvex second lens L2 having a positive power, a biconcave third lens L3 having a negative power, And a biconvex fourth lens L4 having a positive power. The third and fourth lenses L3 and L4 have aspherical surfaces as optical surfaces. The first and second lenses L1 and L2 are formed of glass, and the third and fourth lenses L3 and L4 are formed of plastic. An aperture stop ST is arranged between the first lens L1 and the second lens L2. A filter F1 having an appropriate thickness is arranged between the fourth lens L4 and the solid-state imaging device 51.

  3B to 3D show aberration diagrams (spherical aberration, astigmatism, and distortion) of the imaging lens 12 of Example 2.

(Example 3)
The overall specifications of the imaging lens of the third embodiment are shown below.
F: 2.0
w: 97.4 °
PD: -0.0006mm

Table 5 below shows data on the lens surface of the imaging lens of the third embodiment.
[Table 5]
Surf.NR (mm) D (mm) nd vd
1 -150.00 1.000 1.497 81.6
2 3.590 7.206
3 ST INF 0.642
4 8.700 1.720 1.835 42.7
5 -8.700 1.050
6 * -6.720 0.800 1.635 23.9
7 * 4.100 0.075
8 * 4.117 2.500 1.531 56.0
9 * -4.598 4.436
10 INF 0.850 1.517 64.1
11 INF 2.000

Table 6 below shows the aspheric coefficient of the lens surface of the third embodiment.
[Table 6]
Side 6
K = -2.9216E + 01, A4 = -1.3523E-02, A6 = 1.5786E-03, A8 = -2.0423E-04,
A10 = 1.9139E-05, A12 = -7.2649E-07, A14 = -1.9568E-08
Surface 7
K = -5.1186E-01, A4 = 3.7984E-03, A6 = -3.9837E-03, A8 = 7.8640E-04,
A10 = -7.3726E-05, A12 = 3.1569E-06, A14 = -5.4749E-08
Side 8
K = 6.2445E-01, A4 = 2.5481E-03, A6 = -3.9968E-03, A8 = 7.6921E-04,
A10 = -8.3782E-05, A12 = 5.3296E-06, A14 = -1.7574E-07
9th page
K = -1.4447E + 00, A4 = -4.0836E-05, A6 = -7.0313E-04, A8 = 2.8062E-04,
A10 = -5.1193E-05, A12 = 4.4993E-06, A14 = -1.2974E-07

  FIG. 4A is a cross-sectional view of the imaging lens 13 and the like according to the third embodiment. The imaging lens 13 has a bi-concave first lens L1 having a negative power, a bi-convex second lens L2 having a positive power, a bi-concave third lens L3 having a negative power, And a biconvex fourth lens L4 having a positive power. The third and fourth lenses L3 and L4 have aspherical surfaces as optical surfaces. The first and second lenses L1 and L2 are formed of glass, and the third and fourth lenses L3 and L4 are formed of plastic. An aperture stop ST is arranged between the first lens L1 and the second lens L2. A filter F1 having an appropriate thickness is arranged between the fourth lens L4 and the solid-state imaging device 51.

  4B to 4D show aberration diagrams (spherical aberration, astigmatism, and distortion) of the imaging lens 13 of the third embodiment.

(Example 4)
The overall specifications of the imaging lens of the fourth embodiment are shown below.
F: 2.0
w: 128 °
PD: 0.0029mm

Table 7 below shows data on the lens surface of the imaging lens of the fourth embodiment.
[Table 7]
Surf.NR (mm) D (mm) nd vd
1 -69.00 1.720 1.497 81.6
2 2.950 4.630
3 ST INF 0.540
4 21.400 3.110 1.911 35.2
5 -5.040 0.320
6 * -7.968 1.850 1.635 23.9
7 * 2.676 2.870 1.531 56.0
8 * -3.980 2.540
9 INF 0.700 1.517 64.1
10 INF 3.200

Table 8 below shows the aspheric coefficient of the lens surface of the fourth embodiment.
[Table 8]
Side 6
K = -1.8561E + 01, A4 = -1.1239E-02, A6 = 6.7090E-04, A8 = -8.8165E-05,
A10 = 3.0806E-06, A12 = 0.0000E + 00, A14 = 0.0000E + 00
Surface 7
K = -3.7073E + 00, A4 = -1.1593E-03, A6 = 6.2674E-04, A8 = -2.4716E-04,
A10 = 3.4931E-05, A12 = -1.9241E-06, A14 = 0.0000E + 00
Side 8
K = -1.6695E + 00, A4 = -2.2794E-03, A6 = -1.6762E-05, A8 = -2.4037E-06,
A10 = 3.6577E-07, A12 = 0.0000E + 00, A14 = 0.0000E + 00

  FIG. 5A is a cross-sectional view of the imaging lens 14 and the like according to the fourth embodiment. The imaging lens 14 has a bi-concave first lens L1 having a negative power, a bi-convex second lens L2 having a positive power, a bi-concave third lens L3 having a negative power, And a biconvex fourth lens L4 having a positive power. The third and fourth lenses L3, L4 are cemented lenses. The third and fourth lenses L3 and L4 have aspherical surfaces as optical surfaces. The first and second lenses L1 and L2 are formed of glass, and the third and fourth lenses L3 and L4 are formed of plastic. An aperture stop ST is arranged between the first lens L1 and the second lens L2. A filter F1 having an appropriate thickness is arranged between the fourth lens L4 and the solid-state imaging device 51.

  5B to 5D show aberration diagrams (spherical aberration, astigmatism, and distortion) of the imaging lens 14 of Example 4.

Table 9 below summarizes the values of Examples 1 to 4 corresponding to the conditional expressions (1) to (8) and (10) for reference.
[Table 9]

  As described above, the imaging lens and the like have been described according to the embodiments. However, the imaging lens according to the present invention is not limited to the above embodiments or examples, and various modifications are possible. For example, in the above-described embodiment, the third and fourth lenses L3 and L4 in the drawings show examples in which the lenses are not fitted with each other. However, as shown in FIGS. May be.

  Further, in the above-described embodiment, the filter F1 is divided into two parts so that the filter F1 has a different role when capturing an image with visible light or near-infrared light in an application such as a vehicle-mounted camera or a surveillance camera. It is also possible to take such a configuration.

Claims (7)

In order from the object side,
A first lens formed of glass, having negative power, and having a concave shape on the image side surface;
A second lens formed of glass and having a positive power;
A third lens formed of plastic, having negative power, and having at least one aspherical shape;
A fourth lens formed of plastic, having a positive power, and having at least one aspherical shape;
And an imaging lens substantially satisfying the following conditional expressions.
0.8 <f12 / f <1.2 (1)
-1.65 <f3 / f4 <-0.8 (2)
0 ≦ D34 / f <0.04 (3)
70 <vd1 <100 (4)
30 <vd2 <50 (5)
20 <vd3 <30 (6)
50 <vd4 <60 (7)
1.3 <D12 / f <2.2 (10)
here,
f: focal length of the entire lens system f12: composite focal length of the first lens and the second lens f3: focal length of the third lens f4: focal length of the fourth lens D34: the third lens and the Distance on the optical axis with the fourth lens
vd1: Abbe number of the first lens at d-line
vd2: Abbe number of the second lens at d-line
vd3: Abbe number of the third lens at d-line
vd4: Abbe number of the fourth lens at d-line
D12: distance on the optical axis between the first lens and the second lens Wherein the first lens has a diaphragm that is disposed between the second lens, the front group of the object side of the stop, when the rear group to the image side, the following conditional expression is satisfied, according to claim 1 the imaging lens according to.
−1.2 <ff / fr <−1.0 (8)
here,
ff: focal length of the front group fr: focal length of the rear group Wherein the third lens and the fourth lens is fitted in the lens between the imaging lens according to any one of claims 1 and 2. The imaging lens according to any one of claims 1 to 3 , wherein the first and second lenses each have at least one aspheric surface. Satisfies the following conditional expression, the imaging lens according to any one of claims 1-4.
R2 <| R1 | (9)
here,
R1: radius of curvature of the object side surface of the first lens R2: radius of curvature of the image side surface of the first lens An imaging lens according to any one of claims 1 to 5 ,
A lens barrel holding the imaging lens,
A lens unit comprising: A lens unit according to claim 6 ,
An imaging element that projects an image by the lens unit;
An imaging device comprising:

Images