WO2017170843A1 - Imaging lens, lens unit, and imaging device - Google Patents

Abstract

A low-cost imaging lens is provided which has a long back focus, ensures a wide angle of view, has excellent optical performance while having a large diameter, and has minimal focus shift during environment changes. From the object side, the imaging lens 10 substantially consists of a first lens L1 which is formed from glass, has negative power, and has a concave shape on the image side, a second lens L2 which is formed from glass and has positive power, a third lens L3 which is formed from plastic, has negative power and has at least one aspherical shape, and a fourth lens L4 which is formed from plastic, has positive power and has at least one aspherical shape; this imaging lens satisfies conditional expression (1) relating to the value f12/f, conditional expression (2) relating to the value f3/f4, and conditional expression (3) relating to the value D34/f.

Description

Imaging lens, lens unit, and imaging apparatus

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

In recent years, image sensors such as CCDs and CMOSs have been reduced in size and increased in pixel count. At the same time, an image pickup apparatus body equipped with these image pickup devices has been reduced in size, and an image pickup lens mounted thereon is also required to be reduced in size and performance. Furthermore, lenses mounted on in-vehicle cameras and surveillance cameras are required to have high environmental resistance, low cost and light weight so that they can be used in harsh environments. As an imaging lens having a relatively small number of lenses, which is conventionally known in such a field, for example, those disclosed in Patent Documents 1 and 2 can be cited.

Demands for lenses in the above fields are becoming stricter year by year, and it is required to satisfy a plurality of advanced requirements at the same time. In other words, while having a small configuration with a small number of lenses, it has a long back focus so that a cover glass and a filter can be placed between the lens system and the image sensor, and can be used even in low light conditions such as at night. In particular, there is a demand for an imaging lens that has a large aperture and that has a wide angle of 60 ° or more in all angles of view, but that has been favorably corrected for aberrations. In addition, many in-vehicle cameras and surveillance cameras have a fixed focus that does not have an autofocus function, and defocusing due to environmental changes directly affects the resolution performance. The demand for (characteristics) is getting stronger.

However, with respect to those described in Patent Documents 1 and 2, although the entire system is a simple optical system consisting of four lenses, it satisfies the wide angle and large aperture, and ensuring a long back focus, Since the use of many glass lenses almost eliminates the need for studying the environmental resistance, the structure is contrary to low cost.

JP 2009-14947 A JP 2011-257462 A

In view of the above circumstances, the present invention provides 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 when the environment changes. With the goal.

Another object of the present invention is to provide a lens unit and an image pickup apparatus that include the image pickup lens.

In order to achieve at least one of the above 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 made of glass and having a positive power, a third lens made of plastic, having a negative power and having at least one aspherical shape, and made of plastic, And a fourth lens having at least one 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)
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. The focal length of the lens, and the value D34 is the distance on the optical axis between the third lens and the fourth lens.

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

In order to realize at least one of the above-described objects, an imaging apparatus reflecting one aspect of the present invention includes the above-described lens unit and an imaging element that projects an image by the lens unit.

It is a figure explaining a lens unit provided with an imaging lens of one embodiment of the present invention, and an imaging device. 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. 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. It is a partial expanded sectional view explaining the modification of the 3rd and 4th lens among the imaging lenses shown in FIG.

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

The camera module 30 includes a lens unit 40 that incorporates 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 an imaging lens 10 that is a wide-angle optical system and a lens barrel 41 in which the imaging lens 10 is incorporated. The imaging lens 10 includes first to fourth lenses L1 to L4. The lens barrel 41 is formed of a resin, a metal, a resin mixed with glass fiber, or the like, and stores and holds a lens or the like therein. When the lens barrel 41 is formed of a metal or a resin in which glass fiber is mixed, it is less likely to thermally expand than the resin, and the imaging lens 10 can be stably fixed. The lens barrel 41 has an opening OP through which light from the object side is incident.

The total 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 in the direction perpendicular to AX is performed. 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 is fitted into the annular fitting concave portion 10a provided on the flange portion 3b of the third lens L3 so as to be in the optical axis AX direction. In addition, positioning in a direction perpendicular to the optical axis AX is performed. Thus, by adopting a structure in which the third lens L3 and the fourth lens L4 are fitted to the outer periphery, the lens shift error can be suppressed and the collision between the optical surfaces can be avoided because the coaxiality of both the lenses L3 and L4 can be maintained. 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 the solid-state imaging device 51 via the substrate 52. And a sensor holder 53 for holding the sensor. The solid-state image sensor 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 supports the filter F1 so as to face the solid-state image sensor 51 as well as position the solid-state image sensor 51 with respect to the optical axis AX. The lens barrel 41 of the lens unit 40 is fixed in a state of being positioned 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 the imaging surface I, and a signal processing circuit (not shown) is formed in the vicinity thereof. Pixels, that is, photoelectric conversion elements are two-dimensionally arranged in the photoelectric conversion unit 51a. The solid-state imaging device 51 is not limited to the above-described CMOS type image sensor, and may be a device incorporating another imaging device such as a CCD.

It should be noted that a filter or the like can be disposed 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 F <b> 1 is disposed between the fourth lens L <b> 4 of the imaging lens 10 and the solid-state imaging device 51. The filter F1 is a parallel plate assuming an optical low-pass filter, an IR cut filter, a seal glass of the solid-state image sensor 51, and the like. The filter F <b> 1 can be arranged as a separate filter member, but the function can be imparted to any lens surface constituting the imaging lens 10 without being arranged separately. For example, in the case of an infrared cut filter, an infrared cut coat may be applied on the surface of one or a plurality of 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 drive unit 61 outputs YUV and other digital pixel signals to an external circuit (specifically, a circuit associated with the solid-state image sensor 51), a voltage for driving the solid-state image sensor 51 from the control unit 68, The solid-state imaging device 51 is operated by receiving a clock signal. The input unit 62 is a part that accepts user operations, the storage unit 63 is a part 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 for displaying information to be presented to the user, captured images, and the like. The control unit 68 comprehensively controls 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 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 on devices for various uses such as an in-vehicle camera and a surveillance camera.

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

The illustrated imaging lens (wide-angle optical system) 10 has a four-lens configuration having negative, positive, negative, and positive power arrangement in order from the object side. Specifically, the imaging lens 10 is implemented in order from the negative first lens L1, the positive second lens L2, the negative third lens L3, and the positive fourth lens in order from the object side. Become. The first and second lenses L1, L2 are made of glass. The third and fourth lenses L3 and L4 are made of plastic (or resin). About the 1st lens L1 distribute | arranged to the position exposed to external air, the weather resistance is improved by making this into glass. Furthermore, when it is assumed to be used in harsh environments such as in-vehicle cameras and surveillance cameras, the object side surface of the first lens L1 is subjected to treatment for improving strength, scratch resistance, chemical resistance, and antireflection treatment. Is preferred. Furthermore, 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 and 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, but these lenses L1 and L2 each have at least one aspheric shape. You may do it. When the first and second lenses L1 and L2 made of glass have aspheric surfaces, the optical performance is improved although the cost increases. As already described, the third lens L3 and the fourth lens L4 are fitted with each other. A powerful aspheric plastic lens tends to have high eccentricity error sensitivity. Therefore, both the lenses L3 and L4 are not fitted to the lens barrel 41, but only one lens is fitted to the lens barrel 41, and the other lens is directly fitted to the other lens itself. By doing so, the group eccentricity (specifically, the eccentricity between the third and fourth lenses L3 and L4) can be suppressed. The third and fourth lenses L3 and L4 may be cemented lenses. In this case, chromatic aberration can be corrected more favorably. 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 the aperture stop ST as a reference.

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 on the optical axis AX between the third lens L3 and the fourth lens L4.

In the case of a fixed-focus optical system that does not perform automatic focusing (AF), focus deviation due to temperature changes becomes a problem. However, if conditional expressions (1) to (3) are satisfied, the temperature changes while using a plastic lens. It has a configuration that is less likely to be out of focus. 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 first lens L1 The focal length of the optical system is substantially determined by the two lenses L2, and even if the plastic lenses, that is, the third and fourth lenses L3 and L4 are expanded or contracted due to the temperature change, the influence of the accompanying focus deviation is reduced. I have to. Furthermore, when the third lens L3 and the fourth lens L4, which are plastic lenses that are easily affected by temperature changes, satisfy both the conditional expressions (2) and (3), the combined power of the plastic lenses is set to substantially zero. Therefore, it is possible to make the configuration in which the focus shift is less likely 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 at the d-line of the first lens L1, the value vd2 is the Abbe number at the d-line of the second lens L2, and the value vd3 is the Abbe number at the d-line of the third lens L3. The value vd4 is the Abbe number at the d-line of the fourth lens L4.

¡In-vehicle cameras and surveillance cameras are expected to be used not only in the daytime but also at night, so it is necessary to support not only visible light but also near-infrared light. Therefore, in a fixed focus optical system, chromatic aberration needs to be corrected from visible light to near infrared light. By using a material satisfying the above conditional expressions (4) to (7), chromatic aberration can be corrected from visible light to near infrared light.

The conditional expressions (4) and (5) are more preferably within 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 conditional expression (8), a small optical system can be obtained while having a long back focus. A sufficient back focus can be secured by exceeding the lower limit of conditional expression (8). On the other hand, by falling below the upper limit of conditional expression (8), the back focus does not become too long, and the imaging lens 10 can be downsized.

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

By satisfying the range of 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 on the optical axis AX between the first lens L1 and the second lens L2.

The imaging lens 10 can be reduced in size by falling below the upper limit of the conditional expression (10). 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 the spherical aberration and the lateral chromatic aberration can be corrected relatively easily.

The conditional expression (10) is more preferably within the range of the following expression.
1.4 <D12 / f <2.1 (10) ′

The imaging lens 10 may further include other optical elements (for example, a lens, a filter member, etc.) that have substantially no power.

In the imaging lens 10 and the like described above, in the wide-angle optical system, the power arrangement is negative, positive, negative, and positive in order from the object side, and the third and fourth lenses L3 and L4 are aspheric plastic lenses. Even with a small number of lenses, aberration can be corrected well even with a large aperture. In addition, by using a plurality of plastic lenses, the cost is reduced as compared with the case where all of them are made of glass lenses.

Such an imaging lens 10 can be suitably used for a fixed-focus camera without a focus function. Specific uses include security cameras such as surveillance cameras, door phone cameras, and authentication cameras, lenses for marketing cameras, lenses for in-vehicle cameras mounted on automobiles and other moving objects, medical endoscopes, and health cameras. Examples include care measurement and medical / industrial optical lenses such as industrial endoscopes. In addition, the imaging lens 10 and the like may be applied to applications that require a wider angle.

In addition, the lens unit 40 and the imaging device 100 incorporate the above-described imaging lens 10 to have a long back focus, a wide angle of view, a good optical performance with a large aperture, and when the environment changes. The focus shift is small and inexpensive.

ただし、
Ａｉ：ｉ次の非球面係数
Ｒ　：曲率半径
Ｋ　：円錐定数 〔Example〕
Examples of the imaging lens and the like of the present invention will be shown below. 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: spacing between upper surface of axis nd: refractive index with respect to d-line of lens material vd: Abbe number of lens material In each example, the surface described with “*” after each surface number has an aspherical shape. The aspherical surface shape is expressed by the following “Equation 1”, where the vertex of the surface is the origin, the X axis is taken in the optical axis direction, and the height in the direction perpendicular to the optical axis is h.

However,
Ai: i-order aspheric 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

Data of the lens surface of the imaging lens of Example 1 is shown in Table 1 below. 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. N R (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

The aspheric coefficients of the lens surfaces of Example 1 are shown in Table 2 below. In the following (including the lens data in the table), a power of 10 (for example, 2.5 × 10 ⁻⁰² ) is expressed by using E (for example, 2.5E-02).
[Table 2]
6th page
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
7th page
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
8th page
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 of the first embodiment. The imaging lens 11 has a negative power, plano-concave first lens L1, a positive power biconvex second lens L2, a negative power bi-concave third lens L3, And a biconvex fourth lens L4 having positive power. The third and fourth lenses L3 and L4 have an aspheric surface as an optical surface. The first and second lenses L1 and L2 are made of glass, and the third and fourth lenses L3 and L4 are made of plastic. An aperture stop ST is disposed 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 image sensor 51. The filter F1 is a parallel plate assuming an optical low-pass filter, an IR cut filter, a seal glass of the solid-state image sensor 51, and the like. Reference numeral I denotes 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 aberration) of the imaging lens 11 of Example 1. FIG.

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

The data of the lens surface of the imaging lens of Example 2 is shown in Table 3 below.
[Table 3]
Surf. N R (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

The aspherical coefficients of the lens surfaces of Example 2 are shown in Table 4 below.
[Table 4]
6th page
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
7th page
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
8th page
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 of the second embodiment. The imaging lens 12 has a negative power and a plano-concave first lens L1, a positive power and a biconvex second lens L2, a negative power and a biconcave third lens L3, And a biconvex fourth lens L4 having positive power. The third and fourth lenses L3 and L4 have an aspheric surface as an optical surface. The first and second lenses L1 and L2 are made of glass, and the third and fourth lenses L3 and L4 are made of plastic. An aperture stop ST is disposed 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 image sensor 51.

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

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

Data of the lens surface of the imaging lens of Example 3 is shown in Table 5 below.
[Table 5]
Surf. N R (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

The aspherical coefficients of the lens surfaces of Example 3 are shown in Table 6 below.
[Table 6]
6th page
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
7th page
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
8th page
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 of the third embodiment. The imaging lens 13 has a negative power and a biconcave first lens L1, a positive power and a biconvex second lens L2, a negative power and a biconcave third lens L3, And a biconvex fourth lens L4 having positive power. The third and fourth lenses L3 and L4 have an aspheric surface as an optical surface. The first and second lenses L1 and L2 are made of glass, and the third and fourth lenses L3 and L4 are made of plastic. An aperture stop ST is disposed 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 image sensor 51.

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

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

Data on the lens surface of the imaging lens of Example 4 is shown in Table 7 below.
[Table 7]
Surf. N R (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

The aspherical coefficients of the lens surfaces of Example 4 are shown in Table 8 below.
[Table 8]
6th page
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
7th page
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
8th page
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 of the fourth embodiment. The imaging lens 14 includes a negative birefringent first lens L1, a positive biconvex second lens L2, a negative power biconcave third lens L3, And a biconvex fourth lens L4 having positive power. The third and fourth lenses L3 and L4 are cemented lenses. The third and fourth lenses L3 and L4 have an aspheric surface as an optical surface. The first and second lenses L1 and L2 are made of glass, and the third and fourth lenses L3 and L4 are made of plastic. An aperture stop ST is disposed 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 image sensor 51.

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

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 mentioned above, although the imaging lens etc. were demonstrated according to embodiment, the imaging lens which concerns on this invention is not restricted to the said embodiment or Example, Various deformation | transformation are possible. For example, in the above embodiment, the third and fourth lenses L3 and L4 in the drawing are not fitted with each other, but are fitted as illustrated in FIG. 1 and FIG. It may be.

Moreover, in the said embodiment, the filter F1 divides | segments the filter F1 into two sheets, and each has another role at the time of imaging with visible light or near-infrared light in uses, such as a vehicle-mounted camera and a surveillance camera. It is also possible to take the configuration as described above.

Claims (9)

From the object side,
A first lens made of glass, having negative power, and having a concave shape on the image side surface;
A second lens made of glass and having a positive power;
A third lens made of plastic, having negative power, and having at least one aspheric shape;
A fourth lens made of plastic, having a positive power and having at least one aspheric shape;
An imaging lens that substantially 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)
here,
f: focal length of the entire lens system f12: combined 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 above Distance on the optical axis with the fourth lens The imaging lens according to claim 1, wherein the materials of the first to fourth lenses satisfy the following conditional expression.
70 <vd1 <100 (4)
30 <vd2 <50 (5)
20 <vd3 <30 (6)
50 <vd4 <60 (7)
here,
vd1: Abbe number at the d-line of the first lens vd2: Abbe number at the d-line of the second lens vd3: Abbe number at the d-line of the third lens vd4: At the d-line of the fourth lens Abbe number 2. The apparatus has a diaphragm disposed between the first lens and the second lens, and satisfies the following conditional expression when the object side is a front group and the image side is a rear group from the diaphragm. The imaging lens according to any one of 1 and 2.
-1.2 <ff / fr <-1.0 (8)
here,
ff: focal length of the front group fr: focal length of the rear group The imaging lens according to any one of claims 1 to 3, wherein the third lens and the fourth lens are fitted with each other. The imaging lens according to any one of claims 1 to 4, wherein the first and second lenses each have at least one aspheric surface. The imaging lens according to any one of claims 1 to 5, which satisfies the following conditional expression.
R2 <| R1 | (9)
here,
R1: radius of curvature of object side surface of the first lens R2: radius of curvature of image side surface of the first lens The imaging lens according to any one of claims 1 to 6, which satisfies the following conditional expression.
1.3 <D12 / f <2.2 (10)
here,
f: focal length of entire system D12: distance on the optical axis between the first lens and the second lens An imaging lens according to any one of claims 1 to 7;
A lens barrel for holding the imaging lens;
A lens unit comprising: The lens unit according to claim 8,
An image sensor for projecting an image by the lens unit;
An imaging apparatus comprising:

Images