CN108885330B

CN108885330B - Imaging lens, lens unit, and imaging device

Info

Publication number: CN108885330B
Application number: CN201780019586.8A
Authority: CN
Inventors: 中村健太郎
Original assignee: Konica Minolta Inc
Current assignee: Konica Minolta Inc
Priority date: 2016-04-01
Filing date: 2017-03-30
Publication date: 2020-11-24
Anticipated expiration: 2037-03-30
Also published as: JPWO2017170843A1; WO2017170843A1; JP6635190B2; CN108885330A

Abstract

The invention provides an inexpensive imaging lens which has a long back focus, a wide angle of view, a large aperture, good optical performance, and a small focus shift under environmental changes. The imaging lens (10) substantially comprises, in order from the object side: a 1 st lens (L1) formed of glass, having a negative refractive power, and having a concave shape on an image side surface; a 2 nd lens (L2) formed of glass and having a positive power; a 3 rd lens (L3) formed of plastic, having a negative power, and having at least 1 aspherical shape; the 4 th lens (L4) is formed of plastic, has positive power, has at least 1 aspherical shape, and satisfies the conditional expression (1) relating to a value f12/f, the conditional expression (2) relating to a value f3/f4, and the conditional expression (3) relating to a value D34/f.

Description

Imaging lens, lens unit, and imaging device

Technical Field

The present invention relates to a wide-angle type imaging lens substantially composed of 4 lenses, and a lens unit and an imaging device including the imaging lens.

Background

In recent years, image pickup devices such as CCDs and CMOSs have been reduced in size and increased in pixel count. Meanwhile, the size reduction of an imaging apparatus main body including these imaging elements is also in progress, and the size reduction and high performance are also required for an imaging lens mounted on the imaging apparatus main body. Further, lenses mounted in vehicle-mounted cameras, surveillance cameras, and the like are required to have high environmental resistance so as to be usable even in severe environments, and are also required to be inexpensive and lightweight. As an imaging lens having a small number of lens sheets, for example, the imaging lenses of patent documents 1 and 2 are known in the art.

The expectations for lenses in the above-mentioned fields are severe year by year, requiring a number of high requirements to be met simultaneously. That is, the following imaging lens is desired: the lens system has a small size with a small number of lenses, has a long back focus such that a cover glass or a filter can be disposed between the lens system and the image pickup element, has a large aperture so as to be usable even under low illuminance conditions such as at night, and is capable of satisfactorily correcting aberrations while ensuring a wide angle of 60 DEG or more in a full view angle. In addition, as an in-vehicle camera, a surveillance camera, or the like, there are many fixed focuses that do not have an autofocus function, and since a focus shift due to an environmental change directly affects resolution performance, a demand for environmental tolerance (particularly, a characteristic against a temperature change) has become stronger.

However, although the contents described in patent documents 1 and 2 satisfy the requirements for ensuring a wide angle, a large diameter, and a long back focal length while the entire system is a simple optical system composed of 4 lenses, glass lenses are widely used, and thus studies on environmental resistance are hardly required, which is contrary to the low cost.

Documents of the prior art

Patent document

Patent document 1: japanese laid-open patent publication No. 2009-14947

Patent document 2: japanese patent laid-open publication No. 2011-257462

Disclosure of Invention

The present invention has been made in view of the above circumstances, and an object thereof is to provide an inexpensive imaging lens having a long back focus, a wide angle of view, a large aperture, good optical performance, and a small focus shift during environmental changes.

Another object of the present invention is to provide a lens unit and an imaging device including the imaging lens.

To achieve at least one of the above objects, an image pickup lens reflecting one aspect of the present invention substantially comprises, in order from an object side: a 1 st lens formed of glass, having a negative refractive power, and having a concave shape on an image side surface; a 2 nd lens formed of glass and having a positive power; a 3 rd lens formed of plastic, having a negative power, and having at least 1 aspherical shape; and a 4 th lens formed of plastic, having a positive power, having at least 1 aspherical shape, and satisfying the following conditional expression.

0.8＜f12/f＜1.2…(1)

-1.65＜f3/f4＜-0.8…(2)

0≤D34/f＜0.04…(3)

Wherein the value f is the focal length of the whole system of the lens, the value f12 is the combined focal length of the 1 st lens and the 2 nd lens, the value f3 is the focal length of the 3 rd lens, the value f4 is the focal length of the 4 th lens, and the value D34 is the interval between the 3 rd lens and the 4 th lens on the optical axis.

In order to achieve at least one of the above objects, a lens unit reflecting one aspect of the present invention includes the above-described image pickup lens and a lens barrel holding the image pickup lens.

In order to achieve at least one of the above objects, an imaging device reflecting one aspect of the present invention includes the lens unit and an imaging element that projects an image based on the lens unit.

Drawings

Fig. 1 is a diagram illustrating a lens unit including an imaging lens according to an embodiment of the present invention and an imaging device.

Fig. 2A of fig. 2 is a sectional view of an imaging lens and the like of example 1, and fig. 2B to 2D are aberration diagrams.

Fig. 3A of fig. 3 is a sectional view of an imaging lens and the like of example 2, and fig. 3B to 3D are aberration diagrams.

Fig. 4A of fig. 4 is a sectional view of an imaging lens and the like of example 3, and fig. 4B to 4D are aberration diagrams.

Fig. 5A is a cross-sectional view of an imaging lens and the like of example 4, and fig. 5B to 5D are aberration diagrams.

Fig. 6 is a partially enlarged cross-sectional view illustrating a modification of the 3 rd and 4 th lenses of the imaging lens shown in fig. 1.

Detailed Description

Fig. 1 is a sectional view showing an image pickup apparatus 100 as one 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 functions as the imaging device 100 by operating the camera module 30.

The camera module 30 includes: a lens unit 40 having the imaging lens 10 built therein; and a sensor unit 50 for converting the subject image formed by the imaging lens 10 into an image signal.

The lens unit 40 includes an imaging lens 10 as a wide-angle optical system and a lens barrel 41 in which the imaging lens 10 is incorporated. The imaging lens 10 is composed of 1 st to 4 th lenses L1 to L4. The lens barrel 41 is formed of resin, metal, a material in which glass fiber and resin are mixed, or the like, and accommodates and holds a lens or the like therein. When the lens barrel 41 is formed of a material in which metal or glass fiber is mixed with resin, the lens barrel is less likely to thermally expand than resin, and the imaging lens 10 can be stably fixed. The barrel 41 has an opening OP into which light from the object side enters.

The imaging lens 10 has a total angle of view of 60 ° or more. The 1 st to 4 th lenses L1 to L4 constituting the imaging lens 10 are directly or indirectly held on the inner surface side of the lens barrel 41 at the flange portion or the outer peripheral portion thereof, and are positioned with respect to the optical axis AX direction and the direction perpendicular to the optical axis AX. In particular, the 4 th lens L4 is supported by the lens barrel 41 via the 3 rd lens L3. Specifically, the annular fitting convex portion 10b provided in the flange portion 4b of the 4 th lens L4 is fitted in the annular fitting concave portion 10a provided in the flange portion 3b of the 3 rd lens L3, and is positioned with respect to the optical axis AX direction and the direction perpendicular to the optical axis AX. By adopting the structure in which the 3 rd lens L3 is fitted to the outer periphery of the 4 th lens L4, the coaxiality of the two lenses L3 and L4 can be maintained, and therefore, the lens shift error can be suppressed and the optical surfaces can be prevented from colliding with each other.

The sensor unit 50 includes: a solid-state imaging element 51 that photoelectrically converts an object image formed by the imaging lens (wide-angle optical system) 10; a substrate 52 for supporting the solid-state imaging element 51; the sensor holder 53 holds the solid-state imaging element 51 via the substrate 52. The solid-state imaging element 51 is, for example, a CMOS type image sensor. The substrate 52 includes wiring, a peripheral circuit, and the like for operating the solid-state imaging element 51. The sensor holder 53 is formed of resin or other material, and not only positions the solid-state imaging element 51 with respect to the optical axis AX, but also supports the filter F1 so as to face the solid-state imaging element 51. The lens barrel 41 of the lens unit 40 is fixed in a state of being positioned so as to be fitted into the sensor holder 53.

The solid-state imaging element (imaging element) 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. In the photoelectric conversion portion 51a, pixels, that is, photoelectric conversion elements are arranged in 2 dimensions. The solid-state imaging device 51 is not limited to the CMOS image sensor, and may be incorporated with another imaging device such as a CCD.

Further, a filter or the like may be disposed between 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 4 th lens L4 of the imaging lens 10 and the solid-state imaging element 51. The filter F1 is a parallel flat plate assumed to be an optical low-pass filter, an IR cut filter, a seal glass of the solid-state imaging element 51, or the like. The filter F1 may be disposed as an independent filter member, but may be disposed not independently but may be provided with this function on an arbitrary lens surface constituting the imaging lens 10. For example, in the case of an infrared cut filter, an infrared cut coating layer may be applied to the surface of 1 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 device driving unit 61 operates the solid-state imaging device 51 by outputting YUV and other digital pixel signals to an external circuit (specifically, a circuit attached to the solid-state imaging device 51, or the like), or by receiving a voltage for driving the solid-state imaging device 51 and a clock signal from the control unit 68. The input unit 62 is a unit that receives an operation by a user, 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, and the display unit 64 is a unit that displays information to be presented to the user, an image obtained by shooting, and the like. The control unit 68 can control the operations of the element driving unit 61, the input unit 62, the storage unit 63, and the like in a lump, and can perform various image processing on image data obtained by the camera module 30, for example.

Although detailed description is omitted, the specific function of the processing unit 60 is appropriately adjusted according to the application of the device in which the imaging apparatus 100 is incorporated. The imaging device 100 can be mounted in various devices for use such as an in-vehicle camera and a monitoring camera.

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

The illustrated image pickup lens (wide-angle optical system) 10 has a 4-lens structure having a negative, positive, negative, and positive power arrangement in order from the object side. Specifically, the imaging lens 10 substantially includes, in order from the object side: a negative 1 st lens L1, a positive 2 nd lens L2, a negative 3 rd lens L3, and a positive 4 th lens. The 1 st and 2 nd lenses L1 and L2 are made of glass. The 3 rd and 4 th lenses L3 and L4 are made of plastic (or resin). The 1 st lens L1 disposed at a position exposed to the outside air is made of glass to improve weather resistance. Further, when use in a severe environment such as an in-vehicle camera or a surveillance camera is assumed, it is preferable to perform treatment for improving strength, scratch resistance, chemical resistance, and antireflection treatment on the object side surface of the 1 st lens L1. Further, it is preferable to apply a hydrophobic coating or a hydrophilic coating to the object side surface of the 1 st lens L1. The 1 st lens L1 has a concave shape on the image side surface. The 2 nd lens L2 preferably has a biconvex shape. The 3 rd and 4 th lenses L3 and L4 each have at least 1 aspherical shape. In the illustrated example, the object-side surface and the image-side surface of the 1 st and 2 nd lenses L1 and L2 have spherical shapes, but the lenses L1 and L2 may have at least 1 aspherical shape. When the glass 1 st and 2 nd lenses L1 and L2 have aspherical surfaces, the cost increases, but the optical performance improves. As described above, the 3 rd lens L3 and the 4 th lens L4 are fitted to each other. The decentering error sensitivity of the aspherical plastic lens having a strong power tends to become high. Therefore, by configuring such that only one of the two lenses L3 and L4 is fitted to the lens barrel 41 and the other lens is directly fitted to the other lens without fitting both lenses to the lens barrel 41, group decentration (specifically, decentration between the 3 rd and 4 th lenses L3 and L4) can be suppressed. The 3 rd and 4 th lenses L3 and L4 may be cemented lenses. In this case, the chromatic aberration can be corrected more favorably. An aperture stop ST is provided between the 1 ST lens L1 and the 2 nd lens L2. The imaging lens 10 has the following structure: with the aperture stop ST as a reference, the object side of the aperture stop ST is a front group Gr1, and the image side is a rear group Gr 2.

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)

The value f is the focal length of the entire lens system, the value f12 is the combined focal length of the 1 st lens L1 and the 2 nd lens L2, the value f3 is the focal length of the 3 rd lens L3, the value f4 is the focal length of the 4 th lens L4, and the value D34 is the distance between the 3 rd lens L3 and the 4 th lens L4 on the optical axis AX.

In the case of a fixed-focus optical system that does not perform Automatic Focusing (AF), although defocusing due to temperature changes is a problem, the configuration is such that defocusing is less likely to occur during temperature changes using plastic lenses by satisfying conditional expressions (1) to (3). Specifically, by setting the combined focal length of the glass lenses (specifically, the 1 st and 2 nd lenses L1, L2) so as to satisfy the range of the conditional expression (1), the focal length of the optical system is substantially determined by the 1 st lens L1 and the 2 nd lens L2, and even if the plastic lenses, that is, the 3 rd and 4 th lenses L3, L4 expand or contract due to a temperature change, the influence of defocus associated therewith is reduced. Further, the 3 rd lens L3 and the 4 th lens L4, which are plastic lenses susceptible to temperature changes, satisfy both the conditional expressions (2) and (3), and the combined refractive power of the plastic lenses can be set to substantially 0, so that a structure in which defocus is less likely to occur can be obtained.

In the imaging lens 10, the materials of the 1 st to 4 th lenses L1 to L4 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 1 st lens L1 at d-line, the value vd2 is the abbe number of the 2 nd lens L2 at d-line, the value vd3 is the abbe number of the 3 rd lens L3 at d-line, and the value vd4 is the abbe number of the 4 th lens L4 at d-line.

In the use of an in-vehicle camera or a monitoring camera, not only daytime use but also night use is assumed, and therefore, it is necessary to cope with imaging not only in visible light but also in near infrared light. Therefore, in a fixed-focus optical system, it is necessary to correct chromatic aberration in the range of visible light to near-infrared light. By using a material satisfying the ranges of the conditional expressions (4) to (7), chromatic aberration can be corrected in the range of visible light to near-infrared light.

The conditional expressions (4) and (5) are more preferably in the range of the following expressions.

75＜vd1＜85…(4)′

35＜vd2＜45…(5)′

The imaging lens 10 also satisfies the following conditional expression (8).

-1.2＜ff/fr＜-1.0…(8)

Where the value ff is the focal length of the front group Gr1 and the value fr is the focal length of the back group Gr 2.

By satisfying the range of conditional expression (8), a compact optical system can be achieved while having a long back focus. When the lower limit of the conditional expression (8) is exceeded, a sufficient back focus can be secured. On the other hand, by being lower than the upper limit of conditional expression (8), the back focal length is not excessively long, and the imaging lens 10 can be downsized.

The imaging lens 10 also satisfies the following conditional expression (9).

R2＜|R1|…(9)

The value R1 is the radius of curvature of the object-side surface of the 1 st lens L1, and the value R2 is the radius of curvature of the image-side surface of the 1 st lens L1.

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

The imaging lens 10 also satisfies the following conditional expression (10).

1.3＜D12/f＜2.2…(10)

Where the value f is the focal length of the entire system, and the value D12 is the interval on the optical axis AX of the 1 st lens L1 and the 2 nd lens L2.

By being lower than the upper limit of the conditional expression (10), the imaging lens 10 can be downsized. On the other hand, exceeding the lower limit of conditional expression (10) makes it possible to relatively easily correct spherical aberration and chromatic aberration of magnification without increasing the power of the 1 st lens L1.

The conditional expression (10) is more preferably in the range of the following expression.

1.4＜D12/f＜2.1…(10)′

The imaging lens 10 may further include other optical elements (e.g., a lens, a filter member, etc.) having substantially no optical power.

In the imaging lens 10 and the like described above, the arrangement of the negative, positive, negative, and positive powers in order from the object side is made, and the 3 rd and 4 th lenses L3 and L4 are made as aspherical plastic lenses, whereby the aberration can be corrected favorably even with a large aperture while the number of lenses is small in a wide-angle optical system. Further, by using a plurality of plastic lenses, cost reduction is achieved as compared with the case where all of the plastic lenses are made of glass lenses.

Such an imaging lens 10 can be applied to a camera for fixing a focus without a focusing function. Specific applications to be used include security cameras such as surveillance cameras, door phone cameras, and authentication cameras, lenses for marketing cameras, lenses for vehicle-mounted cameras mounted on automobiles and other moving bodies, medical and industrial optical lenses such as medical endoscopes, health care measurements, and industrial endoscopes. The imaging lens 10 and the like can be applied to applications requiring a wide angle, in addition to these applications.

Further, by incorporating the imaging lens 10, the lens unit 40 and the imaging apparatus 100 have a long back focus, a wide angle of view is ensured, a large aperture, good optical performance, and a low-cost configuration with a small focus shift during environmental changes.

[ example ]

Hereinafter, examples of the imaging lens and the like of the present invention will be described. The symbols used in the embodiments are as follows.

F: f number

w: maximum full viewing angle

PD: defocusing at 30 ℃ change (taking into account refractive index and thermal expansion)

R: radius of curvature

D: axial upper surface spacing

nd: refractive index of lens material with respect to d-line

vd: abbe number of lens material

In each of the embodiments, a surface having an aspherical shape whose origin is the vertex of the surface and whose height in the direction perpendicular to the optical axis is h using the X axis as the optical axis direction is represented by "expression 1" below.

[ formula 1]

Wherein the content of the first and second substances,

ai: aspheric coefficient of order i

R: radius of curvature

K: constant of cone

(example 1)

The following shows the overall elements of the imaging lens of example 1.

F：2.0

w：96.8°

PD：0.0027mm

Table 1 below shows data of the lens surface of the imaging lens of example 1. In table 1 and the like below, the surface number is represented by "surf.n", the aperture stop is represented by "ST", and the infinite is represented by "INF".

[ Table 1]

Table 2 below shows aspherical coefficients of the lens surface of example 1. Further, hereinafter (including lens data of the table), E (e.g., 2.5E-02) is used to represent a power of 10 (e.g., 2.5 × 10)^-02)。

[ Table 2 ]

The 6 th plane

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

The 7 th plane

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

The 8 th plane

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

The 9 th plane

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 sectional view of the imaging lens 11 and the like of example 1. The imaging lens 11 includes a plano-concave 1 st lens L1 having negative refractive power, a biconvex 2 nd lens L2 having positive refractive power, a biconcave 3 rd lens L3 having negative refractive power, and a biconvex 4 th lens L4 having positive refractive power. The 3 rd and 4 th lenses L3 and L4 have aspherical surfaces as optical surfaces. The 1 st and 2 nd lenses L1 and L2 are formed of glass, and the 3 rd and 4 th lenses L3 and L4 are formed of plastic. An aperture stop ST is disposed between the 1 ST lens L1 and the 2 nd lens L2. A filter F1 having an appropriate thickness is disposed between the 4 th lens L4 and the solid-state imaging element 51. The filter F1 is a parallel flat plate assumed to have an optical low-pass filter, an IR cut filter, a sealing glass of the solid-state imaging element 51, and the like. Reference numeral I denotes an imaging surface which is a projected surface of the solid-state imaging element 51. The same applies to reference numerals F1 and I in the following embodiments.

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

(example 2)

The following shows the overall elements of the imaging lens of example 2.

F：2.0

w：97.4°

PD：0.0013mm

Table 3 below shows data of the lens surface of the imaging lens in example 2.

[ Table 3 ]

Table 4 below shows aspherical coefficients of the lens surface of example 2.

[ Table 4 ]

The 6 th plane

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

The 7 th plane

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

The 8 th plane

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

The 9 th plane

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 sectional view of the imaging lens 12 and the like of example 2. The imaging lens 12 includes a plano-concave 1 st lens L1 having negative refractive power, a biconvex 2 nd lens L2 having positive refractive power, a biconcave 3 rd lens L3 having negative refractive power, and a biconvex 4 th lens L4 having positive refractive power. The 3 rd and 4 th lenses L3 and L4 have aspherical surfaces as optical surfaces. The 1 st and 2 nd lenses L1 and L2 are formed of glass, and the 3 rd and 4 th lenses L3 and L4 are formed of plastic. An aperture stop ST is disposed between the 1 ST lens L1 and the 2 nd lens L2. A filter F1 having an appropriate thickness is disposed between the 4 th lens L4 and the solid-state imaging element 51.

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

(example 3)

The following shows the overall elements of the imaging lens of example 3.

F：2.0

w：97.4°

PD：-0.0006mm

Table 5 below shows data of the lens surface of the imaging lens of example 3.

[ Table 5 ]

Table 6 below shows aspherical coefficients of the lens surface of example 3.

[ Table 6 ]

The 6 th plane

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

The 7 th plane

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

The 8 th plane

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

The 9 th plane

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 sectional view of the imaging lens 13 and the like of example 3. The imaging lens 13 includes a biconcave 1 st lens L1 having negative refractive power, a biconvex 2 nd lens L2 having positive refractive power, a biconcave 3 rd lens L3 having negative refractive power, and a biconvex 4 th lens L4 having positive refractive power. The 3 rd and 4 th lenses L3 and L4 have aspherical surfaces as optical surfaces. The 1 st and 2 nd lenses L1 and L2 are formed of glass, and the 3 rd and 4 th lenses L3 and L4 are formed of plastic. An aperture stop ST is disposed between the 1 ST lens L1 and the 2 nd lens L2. A filter F1 having an appropriate thickness is disposed between the 4 th lens L4 and the solid-state imaging element 51.

Fig. 4B to 4D show aberration diagrams (spherical aberration, astigmatism, and distortion aberration) of the imaging lens 13 of example 3.

(example 4)

The following shows the overall elements of the imaging lens of example 4.

F：2.0

w：128°

PD：0.0029mm

Table 7 below shows data of the lens surface of the imaging lens of example 4.

[ Table 7 ]

Table 8 below shows aspherical coefficients of the lens surface of example 4.

[ Table 8 ]

The 6 th plane

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

The 7 th plane

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

The 8 th plane

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 sectional view of the imaging lens 14 and the like of example 4. The imaging lens 14 includes a biconcave 1 st lens L1 having negative refractive power, a biconvex 2 nd lens L2 having positive refractive power, a biconcave 3 rd lens L3 having negative refractive power, and a biconvex 4 th lens L4 having positive refractive power. The 3 rd and 4 th lenses L3 and L4 are cemented lenses. The 3 rd and 4 th lenses L3 and L4 have aspherical surfaces as optical surfaces. The 1 st and 2 nd lenses L1 and L2 are formed of glass, and the 3 rd and 4 th lenses L3 and L4 are formed of plastic. An aperture stop ST is disposed between the 1 ST lens L1 and the 2 nd lens L2. A filter F1 having an appropriate thickness is disposed between the 4 th lens L4 and the solid-state imaging element 51.

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

For reference, table 9 below summarizes the values of examples 1 to 4 corresponding to conditional expressions (1) to (8) and (10).

[ Table 9 ]

The imaging lens and the like have been described above with reference to the embodiments, but the imaging lens of the present invention is not limited to the above embodiments or examples, and various modifications are possible. For example, in the above embodiment, the 3 rd and 4 th lenses L3 and L4 are not shown as examples in which the lenses are fitted to each other, but may be fitted as illustrated in fig. 1 and 6.

In the above embodiment, the filter F1 may be configured to have two separate filters F1 and to have different functions when capturing images under visible light or near infrared light in applications such as in-vehicle cameras and surveillance cameras.

Claims

1. An image pickup lens substantially comprising, in order from an object side:

a 1 st lens formed of glass, having a negative refractive power, and having a concave shape on an image side surface;

a 2 nd lens formed of glass and having a positive power;

a 3 rd lens formed of plastic, having a negative power, and having at least 1 aspherical shape; and

a 4 th lens formed of plastic, having a positive power, having at least 1 aspherical shape,

the following conditional expression is satisfied,

0.8<f12/f<1.2… (1)

－1.65<f3/f4<－0.8… (2)

0≤D34/f<0.04… (3)

1.3<D12/f<2.2… (10)

wherein the content of the first and second substances,

f: focal length of the whole lens system

f 12: a combined focal length of the 1 st lens and the 2 nd lens

f 3: focal length of the 3 rd lens

f 4: focal length of the 4 th lens

D34: a spacing on an optical axis of the 3 rd lens and the 4 th lens,

d12: a distance on an optical axis between the 1 st lens and the 2 nd lens.

2. The imaging lens according to claim 1,

the materials of the 1 st to 4 th lenses satisfy the following conditional expressions,

70<vd1<100… (4)

30<vd2<50… (5)

20<vd3<30… (6)

50<vd4<60… (7)

wherein the content of the first and second substances,

vd 1: abbe number under d-line of the 1 st lens

vd 2: abbe number under d-line of the 2 nd lens

vd 3: abbe number under d-line of the 3 rd lens

vd 4: abbe number under d-line of the 4 th lens.

3. The imaging lens according to claim 1 or 2,

the imaging lens has an aperture stop disposed between the 1 st lens and the 2 nd lens, and satisfies the following conditional expression when the aperture stop is a front group on an object side and a rear group on an image side,

－1.2<ff/fr<－1.0… (8)

wherein the content of the first and second substances,

ff: focal length of the front group

fr: the focal length of the back group.

4. The imaging lens according to claim 1 or 2,

the 3 rd lens and the 4 th lens are fitted with each other.

5. The imaging lens according to claim 1 or 2,

the 1 st and 2 nd lenses have at least 1 aspherical surface, respectively.

6. The imaging lens according to claim 1 or 2,

the imaging lens satisfies the following conditional expression,

R2<|R1|… (9)

wherein the content of the first and second substances,

r1: radius of curvature of object side surface of the 1 st lens

R2: a radius of curvature of an image-side surface of the 1 st lens.

7. A lens unit includes:

the imaging lens according to any one of claims 1 to 6; and

a lens barrel that holds the imaging lens.

8. An imaging device is provided with:

the lens unit of claim 7; and

and an image pickup element that projects an image based on the lens unit.