JP2008176185A - Imaging lens - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging lens designed so that its entire length is short, various aberrations are satisfactorily corrected, and brightness is ensured. <P>SOLUTION: An imaging optical system comprises in order from the object side: a first lens 110 of positive refractive power which has convex shapes on both its sides; an aperture diaphragm 120; a second lens 130 of negative refractive power; a third lens 140 of negative refractive power which has a convex face directed toward the object side; and a fourth lens 150 of positive refractive power which has at least one aspherical face and the convex face of which is directed toward the object side. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an imaging lens for a single focus lens used in an imaging apparatus (such as a digital still camera or a mobile phone camera) using an imaging element.

  Year after year, the market for mobile phone cameras is growing, and not only high pixel count but also diversification is required. As for the angle of view, a wide angle is generally used as in Patent Documents 1 to 3, but it is expected that there will be a need for a narrower angle of view due to the development of a camera shake correction function by software. In addition, in mobile phones, downsizing of the imaging device is required in order to reduce the thickness of the terminal itself and to secure a space for mounting multiple functions. As a result, there is an increasing demand for further downsizing the imaging lens mounted on the imaging device.

  In addition to downsizing of image sensors such as CCD (Change Coupled Device) and CMOS (Complementary Mental Oxide Semiconductor), the number of pixels is increasing due to the miniaturization of pixel pitch of the image sensor. High performance has also been demanded for imaging lenses. On the surface of these solid-state imaging devices, a microlens for allowing light to enter efficiently is provided. However, when the exit pupil position approaches the image plane, the off-axis light beam emitted from the imaging lens is incident obliquely on the image plane, and a shading phenomenon occurs. Then, the condensing by the microlens becomes insufficient, and there arises a problem that the brightness of the image changes extremely between the central portion of the image and the peripheral portion of the image. In order to solve this problem, a telecentric optical system with a small emission angle is desirable.

  As described above, an imaging lens that forms an image on an imaging element such as a CCD or CMOS sensor is required to be small first. In addition, it is required to have good imaging performance and distortion characteristics, a sufficient amount of peripheral light, an appropriate back focus, and an exit pupil position as long as possible.

However, as a conventional small-sized narrow-angle imaging lens, although it is small, the imaging performance may become insufficient as the number of pixels increases, or it is not designed as a telephoto lens. It was not a narrow angle of view.
Japanese Patent Laid-Open No. 06-34884 Japanese Unexamined Patent Publication No. 07-311351 JP 2002-350725 A

  The present invention has been made in view of the above points, and an object of the present invention is to appropriately set the shape of the lens, the shape of the aspherical surface, etc. while having high optical performance by the four-lens configuration. It is to provide a small and thin imaging lens.

  In order to achieve the above object, an imaging lens of the present invention includes, in order from the object side, a biconvex first lens having positive refractive power, an aperture stop, and a second lens having negative refractive power. A third lens having a concave surface facing the object side having a negative refractive power, and a fourth lens having a positive refractive power and a convex surface facing the object side having at least one aspheric surface Are arranged to form an imaging optical system. Preferably, the third lens and the fourth lens have a meniscus shape. This makes it possible to shorten the overall length while keeping the exit pupil position appropriate, to correct aberrations well, and to obtain excellent optical characteristics while reducing the size and cost.

Preferably, in the imaging optical system, when the focal length of the lens system is f and the total length of the lens system from the first lens to the image plane is TL, the following conditional expression (1) is satisfied.
1.0 <TL / f <1.5 (1)
This is because if the TL / f is increased while maintaining an appropriate angle of view for a single-focus lens of a digital still camera or a mobile phone camera, the total length becomes longer, and the purpose of compactness is not achieved. This is because if the total length is too short, it becomes difficult to maintain performance and manufacture.

  Preferably, the first to fourth lenses are plastic lenses. This is because the cost can be reduced and the lens system can be reduced in weight in terms of material unit price and aspheric formability compared to the case of forming with a glass material.

Preferably, in the imaging optical system, the following conditional expressions (2) to (5) are satisfied.
0.4 <f1 / f <1.0 (2)
-0.4> f2 / f (3)
-0.82> f3 / f (4)
0.71 <f4 / f (5)
Where f: focal length of the entire system, f1: focal length of the first lens, f2: focal length of the second lens, f3: focal length of the third lens, f4: focal length of the fourth lens is there.
When the focal length of the first lens is shortened and the lower limit value of the conditional expression (2) is exceeded, it becomes difficult to correct distortion and curvature of field, and conversely, the focal length is increased and the upper limit of the conditional expression (2) is reached. Below this value, it is difficult to correct axial chromatic aberration. Further, if the relationship of the focal length of the second lens is not within the range of (3), it is difficult to properly correct the field curvature or astigmatism. If the focal length of the third lens is shortened and exceeds the range of the conditional expression (4), it becomes difficult to correct the aberration while maintaining an appropriate thickness. Further, if the focal length of the fourth lens is shortened and exceeds the range of the conditional expression (5), it becomes difficult to correct curvature of field.

Preferably, the following conditional expression (6) is satisfied.
−1.0 <(R1 + R2) / (R1−R2) <− 0.25 (6)
Where R1: radius of curvature of the object side surface of the first lens and R2: radius of curvature of the image side surface of the first lens.
This is because if the upper limit of the conditional expression is exceeded, the radius of curvature of the object-side surface and the image-side surface of the first lens will be close, and it will be difficult to correct both spherical aberration and distortion.

Preferably, the imaging optical system satisfies the following conditional expression (7).
νd1-νd2> 15.0 (7)
Here, νd1: Abbe number νd of the first lens, νd2: Abbe number νd of the second lens.
This is because the first lens and the second lens arranged before and after the aperture stop have strong positive and negative refracting powers, respectively, and it becomes difficult to correct axial chromatic aberration when the difference in Abbe number becomes small. It is.

  According to the present invention, it is possible to provide a bright imaging lens having a short overall length and excellent correction of various aberrations. As a result, a compact imaging lens that can be mounted on the imaging device can be realized.

The best mode for carrying out the present invention will be described below 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 aperture stop 120, the second lens 130, the third lens 140, the fourth lens 150, a parallel plane glass plate 160, a CCD (Charge Coupled Device) and a CMOS (CMOS) This is a four-lens single-focus lens 100 in which an imaging device 170 such as a complementary mental-oxide semiconductor device) is disposed.

  In the imaging lens embodying the present invention, the four lenses are a biconvex first lens 110 having a positive refractive power in order from the object side, a negative refractive power, and a concave surface directed toward the object side and the image plane side. A biconcave second lens 130, a meniscus third lens 140 having negative refractive power and a concave surface facing the object side, and a meniscus fourth lens having positive refractive power and a convex surface facing the object side They are arranged like lenses 150.

  In the imaging lens 100, the light incident from the object side OBJS is the object side R1 surface 1, the image surface side R2 surface 2, the surface 3 of the aperture stop 120, and the object side R3 surface 4 of the second lens 130. , Image side R4 surface 5, object side R5 surface 6 of third lens 140, image side R6 surface 7, object side R7 surface 8 of fourth lens 150, image side R8 surface 9, object side of cover glass 160 The light passes through the R9 surface 10 and the image surface side R10 surface 11 in order, and is condensed onto the image sensor 170.

  Each lens from the first lens 110 to the fourth lens 150 has an aspheric shape on both sides, and in particular, the aspheric surface of the fourth lens 150 has an inflection point where the direction of curvature changes within the effective diameter range. Formed as follows.

Examples 1-4 according to specific numerical values of the imaging lens are shown below.
<Example 1>
The basic configuration of the lens system in Embodiment 1 is shown in FIG. 2, each numerical data (setting value) is shown in Tables 1 and 2, and aberration diagrams showing spherical aberration, distortion, and astigmatism are shown in FIG. Each is shown.
As shown in FIG. 2, the distance between the R1 surface 1 and the R2 surface 2, which is the thickness of the first lens 110, is D1, the distance between the R2 surface 2 of the first lens 110 and the surface 3 of the diaphragm 120 is D2, The distance between the surface 3 of the portion 120 and the R3 surface 4 of the second lens 130 is D3, the distance between the R3 surface 4 and the R4 surface 5 that is the thickness of the second lens 130 is D4, and the R4 surface 5 of the second lens 130 The distance between the R5 surface 6 of the third lens 140 is D5, the distance between the R5 surface 6 and the R7 surface 8 that is the thickness of the third lens 140 is D6, the R6 surface 7 of the third lens 140 and the R7 of the fourth lens 150. The distance between the surfaces 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 R9 surface 10 of the cover glass 160 is D9. The distance between the R9 surface 10 and the R10 surface 11 that is the thickness of the cover glass 160 And 10.
Table 1 shows the apertures corresponding to the surface numbers of the imaging lens in Example 1, each lens, the radius of curvature (R: mm), the interval (D: mm), the refractive index (N), and the dispersion value of the cover glass. (Ν) is shown.

Table 2 shows aspheric coefficients of predetermined surfaces of the first lens 110, the second lens 130, the third lens 140, and the fourth lens 150 including the aspheric surface in the first embodiment.
The aspherical shape of the lens is as follows when the direction from the object side to the image plane side is positive, k is a conical coefficient, A, B, C, and D are aspherical coefficients, and r is a central radius of curvature. It is represented by h represents the height of the light beam, and c represents the reciprocal of the central radius of curvature. Where Z is the depth from the tangent plane to the surface vertex, A is the fourth-order aspheric coefficient, B is the sixth-order aspheric coefficient, C is the eighth-order aspheric coefficient, and D is the tenth-order aspheric coefficient. Each aspheric coefficient is shown.

  3A and 3B show spherical aberration, FIG. 3B shows astigmatism, and FIG. 3C shows distortion aberration in Example 1, respectively. In FIG. 3B, the solid line M represents the value of the meridional image plane, and the broken line S represents the value of the sagittal image plane. As can be seen from FIG. 3, according to the first embodiment, spherical, distorted, and astigmatism aberrations are satisfactorily corrected, and an imaging lens excellent in imaging performance can be obtained.

In this embodiment, the numerical data of the conditional expressions (1) to (7) are as follows.
(1) TL / f = 1.12
(2) f1 / f = 0.5
(3) f2 / f = −0.59
(4) f3 / f = -1.79
(5) f4 / f = 1.42
(6) (R1 + R2) / (R1-R2) = -0.56
(7) νd1−νd2 = 29.0

<Example 2>
The basic configuration of the lens system in the second embodiment is shown in FIG. 4, each numerical data (setting value) is shown in Tables 3 and 4, and an aberration diagram showing spherical aberration, distortion, and astigmatism is shown in FIG. Each is shown.
Table 3 shows the diaphragm, the lens, the radius of curvature (R: mm), the interval (D: mm), the refractive index (N), and the dispersion value corresponding to each surface number of the imaging lens in Example 2. (Ν) is shown.

Table 4 shows aspherical coefficients of predetermined surfaces of the first lens 110, the second lens 130, the third lens 140, and the fourth lens 150 including the aspherical surface in Example 2. The shape of the aspherical surface of the lens is expressed by the same formula as in the first embodiment.

  FIG. 5 shows spherical aberration, FIG. 5B shows astigmatism, and FIG. 5C shows distortion aberration in Example 2. In FIG. 5B, the solid line M represents the value of the meridional image plane, and the broken line S represents the value of the sagittal image plane. As can be seen from FIG. 5, according to the second embodiment, the spherical lens, the distortion, and the astigmatism are satisfactorily corrected, and an imaging lens excellent in imaging performance can be obtained.

In this embodiment, the numerical data of the conditional expressions (1) to (7) are as follows.
(1) TL / f = 1.07
(2) f1 / f = 0.48
(3) f2 / f = −0.63
(4) f3 / f = −2.75
(5) f4 / f = 4.85
(6) (R1 + R2) / (R1-R2) = -0.60
(7) νd1−νd2 = 29.0

<Example 3>
The basic configuration of the lens system according to Embodiment 2 is shown in FIG. 6, each numerical data (setting value) is shown in Tables 5 and 6, and aberration diagrams showing spherical aberration, distortion, and astigmatism are shown in FIG. Each is shown.
Table 5 shows the diaphragm, lens, radius of curvature (R: mm), interval (D: mm), refractive index (N), and dispersion value corresponding to each surface number of the imaging lens in Example 3. (Ν) is shown.

Table 6 shows aspheric coefficients of predetermined surfaces of the first lens 110, the second lens 130, the third lens 140, and the fourth lens 150 including the aspheric surface in Example 3. The shape of the aspherical surface of the lens is expressed by the same formula as in the first embodiment.

  7A and 7B, in Example 3, FIG. 7A shows spherical aberration, FIG. 7B shows astigmatism, and FIG. 7C shows distortion. In FIG. 7B, the solid line M indicates the value of the meridional image plane, and the broken line S indicates the value of the sagittal image plane. As can be seen from FIG. 7, according to the third embodiment, spherical, distorted, and astigmatism aberrations are satisfactorily corrected, and an imaging lens excellent in imaging performance can be obtained.

In this embodiment, the numerical data of the conditional expressions (1) to (7) are as follows.
(1) TL / f = 1.09
(2) f1 / f = 0.43
(3) f2 / f = −0.48
(4) f3 / f = −1.64
(5) f4 / f = 1.49
(6) (R1 + R2) / (R1−R2) = − 0.39
(7) νd1−νd2 = 29.0

<Example 4>
The basic configuration of the lens system in Embodiment 4 is shown in FIG. 8, 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. Each is shown.
Table 7 shows the aperture corresponding to each surface number of the imaging lens in Example 4, each lens, the radius of curvature (R: mm), the interval (D: mm), the refractive index (N), and the dispersion value of the cover glass. (Ν) is shown.

Table 8 shows aspherical coefficients of predetermined surfaces of the first lens 110, the second lens 130, the third lens 140, and the fourth lens 150 including the aspherical surface in Example 4. The shape of the aspherical surface of the lens is expressed by the same formula as in the first embodiment.

  9A and 9B, in Example 4, FIG. 9A shows spherical aberration, FIG. 9B shows astigmatism, and FIG. 9C shows distortion. In FIG. 9B, the solid line M represents the value of the meridional image plane, and the broken line S represents the value of the sagittal image plane. As can be seen from FIG. 9, according to Example 4, various aberrations of spherical surface, distortion, and astigmatism are satisfactorily corrected, and an imaging lens excellent in imaging performance can be obtained.

In this embodiment, the numerical data of the conditional expressions (1) to (7) are as follows.
(1) TL / f = 1.13
(2) f1 / f = 0.51
(3) f2 / f = −0.67
(4) f3 / f = −1.05
(5) f4 / f = 1.01
(6) (R1 + R2) / (R1-R2) = -0.51
(7) νd1−νd2 = 29.0

<Example 5 (Comparative Example 1)>
The basic configuration of the lens system according to Embodiment 5 is shown in FIG. 10, each numerical data (setting value) is shown in Tables 9 and 10, and the aberration diagram showing spherical aberration, distortion, and astigmatism is shown in FIG. Each is shown.
Table 9 shows the diaphragm, lens, and cover glass radius of curvature (R: mm), spacing (D: mm), refractive index (N), and dispersion value corresponding to each surface number of the imaging lens in Example 5. (Ν) is shown.

Table 10 shows aspherical coefficients of predetermined surfaces of the first lens 110, the second lens 130, the third lens 140, and the fourth lens 150 including the aspherical surface in Example 5.

  11A and 11B, in Example 5, FIG. 11A shows spherical aberration, FIG. 11B shows astigmatism, and FIG. 11C shows distortion. In FIG. 11B, the solid line M represents the value of the meridional image plane, and the broken line S represents the value of the sagittal image plane. As can be seen from FIG. 11, according to the fifth embodiment, the distortion aberration is corrected well, but the spherical surface and the image plane cannot be corrected, and an imaging lens having excellent imaging performance cannot be obtained.

In this embodiment, the numerical data of the conditional expressions (1) to (7) are as follows.
(1) TL / f = 0.98
(2) f1 / f = 0.47
(3) f2 / f = −0.61
(4) f3 / f = −2.49
(5) f4 / f = 11.24
(6) (R1 + R2) / (R1−R2) = − 0.63
(7) νd1−νd2 = 29.0

<Example 6 (Comparative Example 2)>
The basic configuration of the lens system in the sixth embodiment is shown in FIG. 12, each numerical data (setting value) is shown in Tables 11 and 12, and aberration diagrams showing spherical aberration, distortion, and astigmatism are shown in FIG. Each is shown.
Table 11 shows the apertures corresponding to the surface numbers of the imaging lens in Example 6, each lens, the radius of curvature (R: mm), the interval (D: mm), the refractive index (N), and the dispersion value of the cover glass. (Ν) is shown.

Table 12 shows aspheric coefficients of predetermined surfaces of the first lens 110, the second lens 130, the third lens 140, and the fourth lens 150 including the aspheric surface in Example 6.

  FIG. 13 shows spherical aberration, FIG. 13B shows astigmatism, and FIG. 13C shows distortion aberration in Example 6. In FIG. 13B, the solid line M represents the value of the meridional image plane, and the broken line S represents the value of the sagittal image plane. As can be seen from FIG. 13, according to Example 6, various spherical and distorted aberrations are corrected satisfactorily, but an astigmatism is large and an imaging lens excellent in imaging performance cannot be obtained.

In this embodiment, the numerical data of the conditional expressions (1) to (7) are as follows.
(1) TL / f = 1.07
(2) f1 / f = 0.38
(3) f2 / f = −0.39
(4) f3 / f = −1.75
(5) f4 / f = 1.45
(6) (R1 + R2) / (R1-R2) = -0.30
(7) νd1−νd2 = 29.0

<Example 7 (Comparative Example 3)>
The basic configuration of the lens system in the seventh embodiment is shown in FIG. 14, each numerical data (setting value) is shown in Tables 13 and 14, and the aberration diagram showing spherical aberration, distortion, and astigmatism is shown in FIG. Each is shown.
Table 13 shows the diaphragm, lens, radius of curvature (R: mm), interval (D: mm), refractive index (N), and dispersion value corresponding to each surface number of the imaging lens in Example 7. (Ν) is shown.

Table 14 shows aspheric coefficients of predetermined surfaces of the first lens 110, the second lens 130, the third lens 140, and the fourth lens 150 including the aspheric surface in Example 7.

  In FIG. 15, FIG. 15A shows spherical aberration, FIG. 15B shows astigmatism, and FIG. 15C shows distortion aberration in Example 7. In FIG. 15B, the solid line M represents the value of the meridional image plane, and the broken line S represents the value of the sagittal image plane. As can be seen from FIG. 15, according to Example 7, various spherical aberrations, distortions, and astigmatism aberrations are corrected satisfactorily, but an imaging lens having a large axial chromatic aberration and excellent imaging performance can be obtained. Absent.

In this embodiment, the numerical data of the conditional expressions (1) to (7) are as follows.
(1) TL / f = 1.14
(2) f1 / f = 1.03
(3) f2 / f = -21.47
(4) f3 / f = -1.98
(5) f4 / f = 5.68
(6) (R1 + R2) / (R1−R2) = − 0.97
(7) νd1−νd2 = 29.0

<Example 8 (Comparative Example 4)>
The basic configuration of the lens system according to Embodiment 8 is shown in FIG. 16, each numerical data (setting value) is shown in Tables 15 and 16, and the aberration diagram showing spherical aberration, distortion, and astigmatism is shown in FIG. Each is shown.
Table 15 shows the apertures corresponding to the surface numbers of the imaging lens in Example 8, each lens, the radius of curvature (R: mm), the interval (D: mm), the refractive index (N), and the dispersion value of the cover glass. (Ν) is shown.

Table 16 shows aspheric coefficients of predetermined surfaces of the first lens 110, the second lens 130, the third lens 140, and the fourth lens 150 including the aspheric surface in Example 8.

  FIG. 17 shows spherical aberration, FIG. 17B shows astigmatism, and FIG. 17C shows distortion aberration in Example 8. In FIG. 17B, the solid line M represents the value of the meridional image plane, and the broken line S represents the value of the sagittal image plane. As can be seen from FIG. 17, according to Example 8, various spherical and distorted aberrations are corrected satisfactorily, but an astigmatism is large and an imaging lens excellent in imaging performance cannot be obtained.

In this embodiment, the numerical data of the conditional expressions (1) to (7) are as follows.
(1) TL / f = 1.08
(2) f1 / f = 0.40
(3) f2 / f = −0.39
(4) f3 / f = -1.95
(5) f4 / f = 1.47
(6) (R1 + R2) / (R1-R2) = -0.32
(7) νd1−νd2 = 29.0

<Example 9 (Comparative Example 5)>
The basic configuration of the lens system according to the ninth embodiment is shown in FIG. 18. Numerical data (setting values) are shown in Tables 17 and 18, and aberration diagrams showing spherical aberration, distortion, and astigmatism are shown in FIG. Each is shown.
Table 17 shows the diaphragm, lens, cover glass radius of curvature (R: mm), distance (D: mm), refractive index (N), and dispersion value corresponding to each surface number of the imaging lens in Example 9. (Ν) is shown.

Table 18 shows aspheric coefficients of predetermined surfaces of the first lens 110, the second lens 130, the third lens 140, and the fourth lens 150 including aspheric surfaces in Example 9.

  FIG. 19 shows spherical aberration, FIG. 19B shows astigmatism, and FIG. 19C shows distortion aberration in Example 9. In FIG. 19B, the solid line M represents the value of the meridional image plane, and the broken line S represents the value of the sagittal image plane. As can be seen from FIG. 19, according to Example 9, various spherical and distorted aberrations are corrected satisfactorily, but an astigmatism is large and an imaging lens with excellent imaging performance cannot be obtained.

In this embodiment, the numerical data of the conditional expressions (1) to (7) are as follows.
(1) TL / f = 1.11
(2) f1 / f = 0.48
(3) f2 / f = −0.71
(4) f3 / f = −0.79
(5) f4 / f = 0.92
(6) (R1 + R2) / (R1−R2) = − 0.42
(7) νd1−νd2 = 29.0

<Example 10 (Comparative Example 6)>
The basic configuration of the lens system in the tenth embodiment is shown in FIG. 20, each numerical data (setting value) is shown in Tables 19 and 20, and the aberration diagram showing spherical aberration, distortion, and astigmatism is shown in FIG. Each is shown.
Table 19 shows the apertures, lenses, and cover glass curvature radii (R: mm), spacing (D: mm), refractive index (N), and dispersion values corresponding to the surface numbers of the imaging lens in Example 10. (Ν) is shown.

Table 20 shows aspheric coefficients of predetermined surfaces of the first lens 110, the second lens 130, the third lens 140, and the fourth lens 150 including the aspheric surface in Example 10.

  FIG. 21 shows spherical aberration, FIG. 21B shows astigmatism, and FIG. 21C shows distortion aberration in Example 10. In FIG. 21B, the solid line M represents the value of the meridional image plane, and the broken line S represents the value of the sagittal image plane. As can be seen from FIG. 21, according to Example 10, the distortion aberration is corrected well, but the spherical surface and the image plane cannot be corrected, and an imaging lens with excellent imaging performance cannot be obtained.

In this embodiment, the numerical data of the conditional expressions (1) to (7) are as follows.
(1) TL / f = 1.11
(2) f1 / f = 0.48
(3) f2 / f = −0.54
(4) f3 / f = −0.86
(5) f4 / f = 0.71
(6) (R1 + R2) / (R1-R2) = -0.50
(7) νd1−νd2 = 29.0

<Example 11 (Comparative Example 7)>
The basic configuration of the lens system according to the eleventh embodiment is shown in FIG. 22. Numerical data (setting values) are shown in Table 21 and Table 22, and aberration diagrams showing spherical aberration, distortion, and astigmatism are shown in FIG. Each is shown.
Table 21 shows the apertures corresponding to the respective surface numbers of the imaging lens in Example 11, each lens, the radius of curvature (R: mm), the interval (D: mm), the refractive index (N), and the dispersion value of the cover glass. (Ν) is shown.

Table 22 shows aspherical coefficients of predetermined surfaces of the first lens 110, the second lens 130, the third lens 140, and the fourth lens 150 including the aspherical surface in Example 11.

  23, in Example 11, FIG. 23A shows spherical aberration, FIG. 23B shows astigmatism, and FIG. 23C shows distortion aberration. In FIG. 23B, the solid line M represents the value of the meridional image plane, and the broken line S represents the value of the sagittal image plane. As can be seen from FIG. 23, according to Example 11, spherical, distorted, and astigmatism aberrations are not corrected well, and an imaging lens with excellent imaging performance cannot be obtained.

In this embodiment, the numerical data of the conditional expressions (1) to (7) are as follows.
(1) TL / f = 1.08
(2) f1 / f = 0.40
(3) f2 / f = −0.44
(4) f3 / f = −1.72
(5) f4 / f = 1.47
(6) (R1 + R2) / (R1−R2) = − 0.25
(7) νd1−νd2 = 29.0

<Example 12 (Comparative Example 8)>
The basic configuration of the lens system according to the twelfth embodiment is shown in FIG. 24. Numerical data (setting values) are shown in Tables 23 and 24, and aberration diagrams showing spherical aberration, distortion, and astigmatism are shown in FIG. Each is shown.
Table 23 shows the aperture corresponding to each surface number of the imaging lens in Example 12, each lens, the radius of curvature (R: mm), the interval (D: mm), the refractive index (N), and the dispersion value of the cover glass. (Ν) is shown.

Table 24 shows aspherical coefficients of predetermined surfaces of the first lens 110, the second lens 130, the third lens 140, and the fourth lens 150 including the aspherical surface in Example 12.

  25, in Example 12, FIG. 25A shows spherical aberration, FIG. 25B shows astigmatism, and FIG. 21C shows distortion aberration. In FIG. 25B, the solid line M represents the value of the meridional image plane, and the broken line S represents the value of the sagittal image plane. As can be seen from FIG. 25, according to the twelfth embodiment, various aberrations of spherical surface, distortion, and astigmatism are satisfactorily corrected, but an imaging lens having large axial chromatic aberration and excellent imaging performance can be obtained. Absent.

In this embodiment, the numerical data of the conditional expressions (1) to (7) are as follows.
(1) TL / f = 1.12
(2) f1 / f = 0.56
(3) f2 / f = −0.75
(4) f3 / f = −1.39
(5) f4 / f = 1.21
(6) (R1 + R2) / (R1−R2) = − 0.87
(7) νd1-νd2 = 12.5

  As described above, according to the imaging lens of the present invention, it is possible to provide a bright imaging lens having a short overall length, excellent correction of various aberrations, and brightness.

It is a figure which shows the basic composition of the imaging lens of this embodiment. In this embodiment, it is a figure which shows the surface number provided with respect to the aperture part of an imaging lens, each lens, and the cover glass which comprises an imaging part. 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. It is a figure which shows the structure of the imaging lens employ | adopted in Example 5 (comparative example 1). In Example 5 (comparative example 1), it is an aberrational figure which shows spherical aberration, a distortion aberration, and astigmatism. It is a figure which shows the structure of the imaging lens employ | adopted in Example 6 (comparative example 2). In Example 6 (comparative example 2), it is an aberrational figure which shows a spherical aberration, a distortion aberration, and an astigmatism. It is a figure which shows the structure of the imaging lens employ | adopted in Example 7 (comparative example 3). In Example 7 (comparative example 3), it is an aberrational figure which shows a spherical aberration, a distortion aberration, and an astigmatism. It is a figure which shows the structure of the imaging lens employ | adopted in Example 8 (comparative example 4). FIG. 10 is an aberration diagram showing spherical aberration, distortion, and astigmatism in Example 8 (Comparative Example 4). It is a figure which shows the structure of the imaging lens employ | adopted in Example 9 (comparative example 5). FIG. 10 is an aberration diagram showing spherical aberration, distortion, and astigmatism in Example 9 (Comparative Example 5). It is a figure which shows the structure of the imaging lens employ | adopted in Example 10 (comparative example 6). FIG. 10 is an aberration diagram showing spherical aberration, distortion, and astigmatism in Example 10 (Comparative Example 6). It is a figure which shows the structure of the imaging lens employ | adopted in Example 11 (comparative example 7). FIG. 10 is an aberration diagram showing spherical aberration, distortion, and astigmatism in Example 11 (Comparative Example 7). It is a figure which shows the structure of the imaging lens employ | adopted in Example 12 (comparative example 8). In Example 12 (comparative example 8), it is an aberrational figure which shows a spherical aberration, a distortion aberration, and an astigmatism.

Explanation of symbols

100, 100A to 100L: imaging lens 110: first lens
120: Aperture stop 130: Second lens
140: Third lens 150: Fourth lens
160: Parallel plane plate made of glass (cover glass)
170: Imaging surface

Claims (7)

  In order from the object side, a concave surface is directed to the object side having a negative refractive power, and a biconvex first lens having a positive refractive power, an aperture stop, a second lens having a negative refractive power, and the negative lens side. A third lens and a fourth lens having a positive refractive power and having a convex surface facing the object side and having at least one aspheric surface form an imaging optical system. An imaging lens.   The imaging lens according to claim 1, wherein the third lens and the fourth lens have a meniscus shape. The imaging optical system satisfies the following conditional expression (1), where f is a focal length of the lens system and TL is a total length of the lens system from the first lens to the image plane. The imaging lens according to 1 or 2.
1.0 <TL / f <1.5 (1)   The imaging lens according to any one of claims 1 to 3, wherein the first lens to the fourth lens are plastic lenses. The imaging lens according to any one of claims 1 to 4, wherein the imaging optical system satisfies the following conditional expressions (2) to (5).
0.4 <f1 / f <1.0 (2)
-0.4> f2 / f (3)
-0.82> f3 / f (4)
0.71 <f4 / f (5)
However,
f: focal length of the entire system,
f1: Focal length of the first lens
f2: Focal length of the second lens
f3: Focal length of the third lens
f4: the focal length of the fourth lens. The imaging lens according to claim 1, wherein the imaging optical system satisfies the following conditional expression (6).
−1.0 <(R1 + R2) / (R1−R2) <− 0.25 (6)
However,
R1: radius of curvature of the object side surface of the first lens
R2: radius of curvature of the image side surface of the first lens. The imaging lens according to any one of claims 1 to 6, wherein the imaging optical system satisfies the following conditional expression (7).
νd1-νd2> 15.0 (7)
However,
νd1: Abbe number of the first lens νd
νd2: Abbe number of the second lens νd
It is.

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