JP2012242471A - Image pickup lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a compact, lightweight, and inexpensive image pickup lens reducing a focal point shift generated by manufacturing tolerance such as dispersion in shape in metal molds due to consideration to mass productivity of lens units, favorably compensating aberrations, and having an excellent optical performance.SOLUTION: The image pickup lens includes, in order from an object side: a first lens having a negative refractive power in the object side; a second lens having a negative refractive power; a third lens having a positive refractive power; and a fourth lens having an aperture stop and a positive refractive power. When L23 is an interval between central planes of the second lens and the third lens, and TL is a distance from the surface of the first lens in the object side to an image pickup element, the image pickup lens is configured to satisfy an expression: L23/TL≥0.23.

Description

  The present invention relates to an imaging lens used in an imaging apparatus equipped with a solid-state imaging device, such as a monitoring camera or a vehicle-mounted camera, and more particularly to a single-focus wide-angle imaging lens.

  Imaging lenses used for surveillance cameras and in-vehicle cameras are required to have good imaging performance over the entire screen while ensuring a wide angle of view. In addition, since the mounting space is often limited, it is required to be small and lightweight.

  The following Patent Documents 1, 2, and 3 have been proposed as single-focus wide-angle imaging lenses that may be able to meet these demands. However, the single focus lenses described in Patent Documents 1, 2, and 3 do not sufficiently take into account focus shift due to manufacturing tolerances such as lens shape variations between molds. Therefore, an advanced adjustment process is required for manufacturing the imaging module.

JP 2008-268268 A JP 2009-008867 A JP 2010-054646 A

  The present invention has been made in view of the above points, and an object of the present invention is to reduce the focus shift due to manufacturing tolerances, and to reduce the size, weight, and cost of the four-lens configuration while reducing the shape of the lens. It is to provide a wide-angle imaging lens having high optical performance by appropriately setting an aspherical shape and the like.

  In order to achieve the above object, in the present invention, in order from the object side, a first lens having a negative refractive power, a second lens having a negative refractive power, a third lens having a positive refractive power, and an aperture stop And a fourth lens having a positive refractive power, and satisfies the following conditional expression (1).

L23 / TL ≧ 0.23 (1)
However, L23 is the distance between the center planes of the second lens and the third lens, and TL is the distance from the object-side surface of the first lens to the image sensor.

  The imaging lens according to the present invention is a retrofocus system in which negative refractive power is configured before positive refractive power, and L23, which is between negative and positive refractive power with respect to the focal position, plays an important role. However, by satisfying the conditional expression (1), it is possible to weaken the influence of a manufacturing tolerance generated by a certain amount related to the focus shift.

  Preferably, the following conditional expression (2) is satisfied.

L23 / f ≧ 3.7 (2)
Here, f is the focal length of the entire lens system.

  Preferably, the following conditional expression (3) is satisfied.

2W ≧ 130 ° (3)
However, 2W is the total angle of view of light rays incident on the maximum image height position on the imaging plane.

  Preferably, the first lens has a convex surface on the object side, the second lens has a convex surface on the object side, the third lens has a convex surface on the object side, and the fourth lens has a convex surface on the image side. It is characterized by that.

  Preferably, the third lens is formed of a spherical surface.

  Preferably, the first lens and the third lens are made of a glass material, the second lens and the fourth lens are made of a resin material, and the second lens and the fourth lens are not both surfaces. It has a spherical shape.

  Preferably, the material constituting the first lens has an Abbe number of 40 or more with respect to the d line of the material constituting the first lens, and an Abbe number of the material constituting the second lens with respect to the d line of 50 or more. The Abbe number with respect to the d line is set to 40 or less, and the Abbe number with respect to the d line of the material constituting the fourth lens is set to 50 or more.

  More preferably, the following conditional expression (4) is satisfied.

f12 / f <-1.7 (4)
Here, f12 is a combined focal length of the first lens and the second lens, and f is a focal length of the entire lens system.

  According to the present invention, the focus shift due to manufacturing tolerances is reduced, and the four-lens configuration is compact, lightweight, and inexpensive, but has high optical performance by appropriately setting the shape of the lens, the shape of the aspherical surface, and the like. A wide-angle imaging lens can be provided. As a result, a compact wide-angle imaging lens that can be mounted on a surveillance camera or a vehicle-mounted camera can be realized.

It is a figure which shows the basic composition of the imaging lens of embodiment of this invention. 2 is a diagram illustrating a configuration of an imaging lens employed in Example 1. FIG. In Example 1, it is an aberrational figure which shows spherical aberration, distortion aberration, and astigmatism. 6 is a diagram illustrating a configuration of an imaging lens employed in Example 2. FIG. In Example 2, it is an aberrational figure which shows spherical aberration, distortion aberration, and astigmatism. 6 is a diagram illustrating a configuration of an imaging lens employed in Example 3. FIG. In Example 3, it is an aberrational figure which shows spherical aberration, distortion aberration, and astigmatism. 6 is a diagram illustrating a configuration of an imaging lens employed in Example 4. FIG. In Example 4, it is an aberrational figure which shows spherical aberration, a distortion aberration, and astigmatism. 6 is a diagram illustrating a configuration of an imaging lens employed in Example 5. FIG. FIG. 10 is an aberration diagram showing spherical aberration, distortion, and astigmatism in Example 5. In Example 1 thru | or 5, it is a figure which shows the relationship between L23 / TL and a back focus fluctuation amount.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 shows the lens configuration of the embodiment in an optical section. In these embodiments, in order from the object side, the first lens 110, the second lens 120, the third lens 130, the aperture stop 140, the fourth lens 150, a CCD (Charge Coupled Device) and a CMOS (Complementary Mental-Oxide Semiconductor device). 4 is a single-focus imaging lens 100 having a four-element configuration.

  In the imaging lens embodying the present invention, four lenses are, in order from the object side, a first lens 110 having a negative refractive power, a second lens 120 having a negative refractive power, and a third lens having a positive refractive power. 130, an aperture stop 140, and a fourth lens 150 having a positive refractive power. Moreover, 1 (R1) -9 (R8) of FIG. 1 is a surface number of each component.

  The aperture stop 140 is disposed between the third lens 130 and the fourth lens 150. If the aperture stop 140 is disposed on the image side of the fourth lens 150, it is not preferable because the lens system becomes large, and if it is disposed between the second lens 120 and the third lens 130, the back focus becomes long. It is disadvantageous and not preferable. Therefore, by disposing the lens between the third lens 130 and the fourth lens 150 described above, it is possible to correct various aberrations and make the lens system compact.

  The imaging lens 100 embodying the present invention is preferably configured to satisfy the conditional expression (1).

L23 / TL ≧ 0.23 (1)
However, L23 is the distance between the center planes of the second lens 120 and the third lens 130, and TL is the distance from the object-side surface of the first lens 110 to the image sensor 160.

  The imaging lens 100 is a retrofocus type in which negative refracting power is disposed in front of the lens system, and can take a longer back focus than a symmetric wide-angle lens. Therefore, it is considered that the center plane distance L23 between the first lens 110 and the second lens 120 having a negative refractive power and the third lens 130 and the fourth lens 150 having a positive refractive power greatly affect the focus shift. Therefore, by increasing the ratio between L23 with respect to TL, it becomes possible to alleviate the influence of manufacturing tolerances that are generated by a certain amount.

  Conditional expression (1) relates the ratio of the distance between the center planes of the second lens 120 and the third lens 130 to the distance from the object-side surface of the first lens 110 to the image sensor 160. If the lower limit value of conditional expression (1) is exceeded, the ratio between L23 with respect to TL becomes small, so that it is not preferable because it is greatly affected by manufacturing tolerances generated by a certain amount.

  The imaging lens 100 is preferably configured to satisfy the conditional expression (2).

L23 / f ≧ 3.7 (2)
However, L23 is the center plane space | interval of the 2nd lens 120 and the 3rd lens 130, and f is the focal distance of the whole lens system.

  Conditional expression (2) is a conditional expression in which the ratio of the center plane spacing of the second lens 120 and the third lens 130 to the focal length of the entire lens system is related. If the lower limit value of conditional expression (2) is exceeded, the ratio between L23 with respect to f becomes small, so that it is not preferable because it is greatly affected by manufacturing tolerances generated by a certain amount.

  The imaging lens 100 is preferably configured to satisfy the conditional expression (3).

2W ≧ 130 ° (3)
However, 2W is the total angle of view of light rays incident on the maximum image height position on the imaging plane.

  By setting the numerical value range of the conditional expression (3), it is possible to secure a more preferable shooting range as a monitoring camera or a vehicle-mounted camera.

  The first lens 110 has a convex surface facing the object side, the second lens 120 has a convex surface facing the object side, the third lens 130 has a convex surface facing the object side, and the fourth lens 150 has a convex surface facing the image side. Is preferred.

  Accordingly, the first lens 110 can make light from the object side incident at a wide angle of view by directing the convex surface toward the object side. In the second lens 120, it is possible to reduce the occurrence of ghost flare caused by the light reflected from the object side surface being reflected on the image side surface of the first lens 110 and reaching the imaging surface by directing the convex surface toward the object side. Become. Further, in the third lens 130 and the fourth lens 150 having positive refractive power, the convex surface on the object side and the convex surface on the image side are respectively directed to reduce the sensitivity near the aperture stop 140, thereby making the imaging lens easy to manufacture. 100.

  The imaging lens 100 is a lens that is easy to manufacture because the third lens 130 is formed of a spherical surface.

In the imaging lens 100, the first lens 110 and the third lens 130 are made of a glass material, the second lens 120 and the fourth lens 150 are made of a resin material, and the second lens 120 and the fourth lens 150. It is preferable that both surfaces are configured to be aspherical.
By forming the first lens 110 from a glass material, it is possible to satisfy severe environmental performance such as physical durability and chemical durability applied to a monitoring camera and a vehicle-mounted camera. Further, by forming the third lens 130 from a glass material, a material having a wide dispersion value can be selected, and as a result, it is possible to satisfactorily correct lateral chromatic aberration. Specifically, by using a glass material having a high dispersion value for the third lens 130, an advantageous effect for correcting chromatic aberration generated in the first lens 110 and the second lens 120 is obtained.

  By forming the second lens 120 and the fourth lens 150 from a resin material, weight reduction and cost reduction can be realized and an aspherical shape can be easily manufactured. Each of these lenses is formed with at least one aspherical shape, thereby facilitating correction of aberrations and obtaining good resolution performance while being compact.

  In general, a resin material has a large change in refractive index and shape due to a temperature change as compared with a glass material, and its refractive power is small at a high temperature and large at a low temperature. Therefore, the second lens 120 has a negative refractive power, and the fourth lens 150 has a positive refractive power, so that the variation in refractive power due to the change in shape and refractive index is canceled out, and the focal length in the entire lens system. As a result, desired performance can be obtained even in a wide temperature range.

  It is more preferable that the following conditional expression is satisfied when the focal length of the second lens 120 at the d line is f2 (mm) and the focal length of the fourth lens 150 at the d line is f4 (mm).

0.9 <| f2 / f4 | <1.1
The power ratio (focal length ratio) of the second lens 120 and the fourth lens 150 is set to approximately 1: 1 (within a range of 0.9 to 1.1) by designing so as to satisfy such conditions. Thus, the change accompanying the temperature change is canceled out by the resin lenses.

  In addition, the imaging lens 100 is preferably configured such that the Abbe number of the material constituting the first lens 110 with respect to the d-line is 40 or more, the Abbe number of the material constituting the second lens 120 with respect to the d-line is 50 or more, and the third lens. The Abbe number for the d-line of the material constituting 130 is set to 40 or less, and the Abbe number for the d-line of the material constituting the fourth lens 150 is set to 50 or more.

As a result, the Abbe relative to the d-line of the material constituting the first lens 110 and the second lens 120 of the negative lens located closer to the object side than the aperture stop 140 and the fourth lens 150 of the positive lens located closer to the image side than the aperture stop 140. The larger the number, the smaller the chromatic aberration of magnification generated in the first lens 110, the second lens 120, and the fourth lens 150. Similarly, the smaller the Abbe number with respect to the d-line of the material constituting the third lens 130 of the positive lens located on the object side than the aperture stop 140, the better the chromatic aberration of magnification can be corrected.
Further, the imaging lens 100 is preferably configured so that the focal length of the entire lens system and the combined focal length of the first lens 110 and the second lens 120 satisfy the following conditional expression (4).

f12 / f <-1.7 (4)
Here, f12 is a combined focal length of the first lens 110 and the second lens 120, and f is a focal length of the entire lens system.

  Conditional expression (4) is a conditional expression relating the ratio of the combined focal length of the first lens 110 and the second lens 120 to the focal length of the entire lens system. The combined focal length of the first lens 110 and the second lens 120 varies the center plane distance L23 that greatly affects the focus shift. In general, when the absolute value of the combined focal length composed of negative refractive power is large, the center plane interval becomes long, and when the absolute value of the combined focal length is small, the center plane interval becomes short. Therefore, if the upper limit value of conditional expression (4) is exceeded, the center plane distance L23 becomes short, which is not preferable.

  The aspherical shape of the lens described in the following numerical examples is positive in the direction from the object side to the image plane side, k is a conical coefficient, A is a fourth-order aspheric coefficient, B Is a 6th-order aspheric coefficient, C is an 8th-order aspheric coefficient, and D is a 10th-order aspheric coefficient. h represents the height of the light beam, c represents the reciprocal of the central radius of curvature, and Z represents the depth from the tangent plane with respect to the surface vertex.

Examples 1 to 5 according to specific numerical values of the imaging lens 100 are shown below. In the numerical examples of Examples 1 to 5, the focal length, F number, field angle, image height, total lens length, back focus (BF), and back focus fluctuation amount (BF fluctuation amount) are as shown in Table 1 below. It is. As the back focus fluctuation amount, the back focus fluctuation amount when L23 is moved by ± 20 μm was calculated from paraxial tracking. Similarly, in the numerical examples of Examples 1 to 5, the numerical data of the conditional expressions (1) to (3) are the values described in Table 2 below.
In Examples 1 to 5, the first lens 110 and the third lens 130 are made of a glass material, and the second lens 120 and the fourth lens 150 are made of a resin material.

<Example 1>
The basic configuration of the imaging lens 100A in Embodiment 1 is shown in FIG. 2, each numerical data (setting value) is shown in Tables 3 and 4, and the aberration diagram showing spherical aberration, distortion aberration, and astigmatism is shown in FIG. Respectively.

  As shown in FIG. 2, the first lens 110 has a meniscus shape with a convex surface facing the object side, the second lens 120 has a meniscus shape with a convex surface facing the object side, and the third lens 130 has a flat surface with the convex surface facing the object side. The fourth lens 150 disposed on the image side of the convex shape and the aperture stop 140 has a meniscus shape with the convex surface facing the image side. Each of the second lens 120 and the fourth lens 150 has an aspheric surface on both sides.

  Further, as shown in FIG. 2, the distance between the R1 surface 1 and the R2 surface 2 that is the thickness of the first lens 110 is D1, and the distance from the R2 surface 2 of the first lens 110 to the R3 surface 3 of the second lens 120. D2, the distance between the R3 surface 3 and the R4 surface 4 that is the thickness of the second lens 120, D3, the distance between the R4 surface 4 of the second lens 120 and the R5 surface 5 of the third lens 130, D4, The distance between the R5 surface 5 and the R6 surface 6 having a thickness of 130 is D5, the distance between the R6 surface 6 of the third lens 130 and the surface 7 of the aperture stop 140 is D6, the surface 7 of the aperture stop 140 and the fourth lens 150. The distance between the R7 surface 8 is D7, the distance between the R7 surface 8 and the R8 surface 9 which is the thickness of the fourth lens 150 is D8, and the distance between the R8 surface 9 of the fourth lens 150 and the imaging element (imaging surface) 160 is The distance is D9. In the following Examples 2 to 5, R1 surface 1 to R8 surface 9 and D1 to D9 mean the same distance.

Table 3 shows the stop corresponding to each surface number of the imaging lens 100A in Example 1, the radius of curvature R, the interval D, the refractive index Nd, and the dispersion value νd of each lens. In Table 3, the surface with * in the surface number indicates an aspherical shape. Table 4 shows the aspheric coefficient of the predetermined surface.
Numerical example 1

  3A shows a spherical aberration (435.8 nm, 486.1 nm, 546.1 nm, 587.6 nm, 656.3 nm from the left) and FIG. 3B shows an astigmatism (solid line: left) in Example 1. 35.8nm, 486.1nm, 546.1nm, 587.6nm, 656.3nm sagittal rays, dotted line: 435.8nm, 486.1nm, 546.1nm, 587.6nm, 656.3nm tangential rays from the left), Figure 3 (C) Distortion aberrations (435.8 nm, 486.1 nm, 546.1 nm, 587.6 nm, and 656.3 nm overlap) are shown. 3B and 3C, the vertical axis represents the half field angle ω. In FIG. 3B, the solid line S represents the sagittal image plane value, and the broken line T represents the tangential image plane value. (The same applies to FIGS. 5, 7, 9, and 11). As can be seen from FIG. 3, according to the first embodiment, the imaging lens 100 </ b> A having excellent imaging performance can be obtained in which various spherical, distorted, and astigmatism aberrations are satisfactorily corrected.

<Example 2>
The basic configuration of the imaging lens 100B in Embodiment 2 is shown in FIG. 4, each numerical data (setting value) is shown in Tables 5 and 6, and the aberration diagram showing spherical aberration, distortion aberration, and astigmatism is shown in FIG. Respectively.

  The imaging lens 100B according to the second embodiment is designed for the purpose of further reducing L23 of the first embodiment, reducing the focus shift due to manufacturing tolerances, and reducing the cost.

  As shown in FIG. 4, the first lens 110 has a meniscus shape with a convex surface facing the object side, the second lens 120 has a meniscus shape with a convex surface facing the object side, and the third lens 130 has a flat surface with the convex surface facing the object side. The fourth lens 150 disposed on the image side of the convex shape and the aperture stop 140 has a meniscus shape with the convex surface facing the image side. Each of the second lens 120 and the fourth lens 150 has an aspheric surface on both sides.

Table 5 shows the stop corresponding to each surface number of the imaging lens 100B in Example 2, the radius of curvature R, the interval D, the refractive index Nd, and the dispersion value νd of each lens. In Table 5, the surface numbered with * indicates that the surface is aspherical. Table 6 shows the aspheric coefficient of the predetermined surface.
Numerical example 2

  5A is a spherical aberration (435.8 nm, 486.1 nm, 546.1 nm, 587.6 nm, 656.3 nm from the left) and FIG. 5B is an astigmatism (solid line: left) in Example 2. (5) to 435.8nm, 486.1nm, 546.1nm, 587.6nm, 656.3nm sagittal rays, dotted line: 435.8nm, 486.1nm, 546.1nm, 587.6nm, 656.3nm tangential rays from the left). Distortion aberrations (435.8 nm, 486.1 nm, 546.1 nm, 587.6 nm, and 656.3 nm overlap) are shown. As can be seen from FIG. 5, according to the second embodiment, the spherical lens, distortion, and astigmatism aberrations are corrected favorably, and an imaging lens 100B having excellent imaging performance can be obtained.

<Example 3>
The basic configuration of the imaging lens 100C according to the third embodiment is shown in FIG. 6, each numerical data (setting value) is shown in Tables 7 and 8, and the aberration diagram showing spherical aberration, distortion, and astigmatism is shown in FIG. Respectively.

  The imaging lens 100C in the third embodiment is designed for the purpose of further reducing the length of L23 in the second embodiment, reducing the focus shift due to manufacturing tolerances, and reducing the cost.

  As shown in FIG. 6, the first lens 110 has a meniscus shape with a convex surface facing the object side, the second lens 120 has a meniscus shape with a convex surface facing the object side, and the third lens 130 has a flat surface with the convex surface facing the object side. The fourth lens 150 disposed on the image side of the convex shape and the aperture stop 140 has a meniscus shape with the convex surface facing the image side. Each of the second lens 120 and the fourth lens 150 has an aspheric surface on both sides.

Table 7 shows the stop corresponding to each surface number of the imaging lens 100C in Example 3, the radius of curvature R, the interval D, the refractive index Nd, and the dispersion value νd of each lens. In Table 7, the surface numbered with * indicates that the surface is aspherical. Table 8 shows the aspheric coefficient of the predetermined surface.
Numerical Example 3

  7A is a spherical aberration (435.8 nm, 486.1 nm, 546.1 nm, 587.6 nm, 656.3 nm from the left), and FIG. 7B is an astigmatism (solid line: solid line) in Example 3. Sagittal rays of 435.8nm, 486.1nm, 546.1nm, 587.6nm, 656.3nm from the left, dotted line: tangential rays of 435.8nm, 486.1nm, 546.1nm, 587.6nm, 656.3nm from the left), Fig. 7 (C) Shows distortion aberrations (435.8 nm, 486.1 nm, 546.1 nm, 587.6 nm, and 656.3 nm overlapping), respectively. As can be seen from FIG. 7, according to the third embodiment, the spherical lens, distortion, and various astigmatism aberrations are corrected well, and the imaging lens 100C having excellent imaging performance can be obtained.

<Example 4>
The basic configuration of the imaging lens 100D according to the fourth embodiment is shown in FIG. 8. Each numerical data (setting value) is shown in Tables 9 and 10, and the aberration diagrams showing spherical aberration, distortion, and astigmatism are shown in FIG. Respectively.

  The imaging lens 100D in the fourth embodiment is designed for the purpose of further reducing L23 of the third embodiment, reducing the focus shift due to manufacturing tolerances, and reducing the cost.

  As shown in FIG. 8, the first lens 110 has a meniscus shape with a convex surface facing the object side, the second lens 120 has a meniscus shape with a convex surface facing the object side, and the third lens 130 has a flat surface with the convex surface facing the object side. The fourth lens 150 disposed on the image side of the convex shape and the aperture stop 140 has a meniscus shape with the convex surface facing the image side. Each of the second lens 120 and the fourth lens 150 has an aspheric surface on both sides.

Table 9 shows the stop corresponding to each surface number of the imaging lens 100D in Example 4, the radius of curvature R, the interval D, the refractive index Nd, and the dispersion value νd of each lens. In Table 9, the surface numbered with * indicates that the surface is aspherical. Table 10 shows the aspheric coefficient of the predetermined surface.
Numerical Example 4

  FIG. 9 shows the spherical aberration (435.8 nm, 486.1 nm, 546.1 nm, 587.6 nm, 656.3 nm from the left) and FIG. 9B shows the astigmatism (solid line: solid line) in Example 4. Sagittal rays of 435.8nm, 486.1nm, 546.1nm, 587.6nm, 656.3nm from the left, dotted lines: 435.8nm, 486.1nm, 546.1nm, 587.6nm, 656.3nm tangential rays from the left), Fig. 9 (C) Shows distortion aberrations (435.8 nm, 486.1 nm, 546.1 nm, 587.6 nm, and 656.3 nm overlapping), respectively. As can be seen from FIG. 9, according to the fourth embodiment, the spherical lens, distortion, and various astigmatism aberrations are corrected well, and the imaging lens 100D having excellent imaging performance can be obtained.

<Example 5>
The basic configuration of the imaging lens 100E according to Embodiment 5 is shown in FIG. 10, each numerical data (setting value) is shown in Tables 11 and 12, and the aberration diagram showing spherical aberration, distortion, and astigmatism is shown in FIG. Respectively.

  The imaging lens 100E according to the fifth embodiment is designed for the purpose of further reducing the length L23 of the fourth embodiment, reducing the focus shift due to manufacturing tolerances, and reducing the cost.

  As shown in FIG. 10, the first lens 110 has a meniscus shape with a convex surface facing the object side, the second lens 120 has a meniscus shape with a convex surface facing the object side, and the third lens 130 has a flat surface with the convex surface facing the object side. The fourth lens 150 disposed on the image side of the convex shape and the aperture stop 140 has a meniscus shape with the convex surface facing the image side. Each of the second lens 120 and the fourth lens 150 has an aspheric surface on both sides.

Table 11 shows the stop corresponding to each surface number of the imaging lens 100E in Example 5, the radius of curvature R, the interval D, the refractive index Nd, and the dispersion value νd of each lens. In Table 11, a surface numbered with * indicates that it has an aspherical shape. Table 12 shows the aspheric coefficient of the predetermined surface.
Numerical Example 5

  11A is a spherical aberration (435.8 nm, 486.1 nm, 546.1 nm, 587.6 nm, 656.3 nm from the left), and FIG. 11B is an astigmatism (solid line: left) in Example 5. 115.8C, 486.1nm, 546.1nm, 587.6nm, 656.3nm sagittal rays, dotted line: 435.8nm, 486.1nm, 546.1nm, 587.6nm, 656.3nm tangential rays from the left), Figure 11 (C) Distortion aberrations (435.8 nm, 486.1 nm, 546.1 nm, 587.6 nm, and 656.3 nm overlap) are shown. As can be seen from FIG. 11, according to the fifth embodiment, the imaging lens 100 </ b> E excellent in imaging performance can be obtained in which various spherical, distortion, and astigmatism aberrations are satisfactorily corrected.

  FIG. 12 shows the relationship between L23 / TL and the back focus fluctuation amount in the first to fifth embodiments. As can be seen from FIG. 12, the back focus fluctuation amount can be reduced as L23 / TL increases.

100, 100A to 100E: imaging lens 110: first lens 120: second lens 130: third lens 140: aperture stop 150: fourth lens 160: imaging element (imaging plane)

Claims (8)

In order from the object side, a first lens having a negative refractive power, a second lens having a negative refractive power, a third lens having a positive refractive power, an aperture stop, and a fourth lens having a positive refractive power. An imaging lens comprising a lens and satisfying the following conditional expression (1):
L23 / TL ≧ 0.23 (1)
However, L23 is the distance between the center planes of the second lens and the third lens, and TL is the distance from the object-side surface of the first lens to the image sensor. The imaging lens according to claim 1, wherein the following conditional expression (2) is satisfied.
L23 / f ≧ 3.7 (2)
Here, f is the focal length of the entire lens system. The imaging lens according to claim 1, wherein the following conditional expression (3) is satisfied.
2W ≧ 130 ° (3)
However, 2W is the total angle of view of light rays incident on the maximum image height position on the imaging plane.   The first lens has a convex surface facing the object side, the second lens has a convex surface facing the object side, the third lens has a convex surface facing the object side, and the fourth lens has a convex surface facing the image side. The imaging lens according to any one of claims 1 to 3.   The imaging lens according to claim 1, wherein the third lens is formed of a spherical surface. The first lens and the third lens are made of a glass material, and the second lens and the fourth lens are made of a resin material,
The imaging lens according to claim 1, wherein the second lens and the fourth lens have both aspherical surfaces.   The Abbe number for the d-line of the material constituting the first lens is 40 or more, the Abbe number for the d-line of the material constituting the second lens is 50 or more, and the d-line of the material constituting the third lens is The imaging lens according to claim 1, wherein the Abbe number is set to 40 or less, and the Abbe number for the d-line of the material constituting the fourth lens is set to 50 or more. The imaging lens according to claim 1, wherein the following conditional expression (4) is satisfied.
f12 / f <-1.7 (4)
Here, f12 is a combined focal length of the first lens and the second lens, and f is a focal length of the entire lens system.

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