JP2013174741A - Photographing lens and imaging device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a compact photographing lens of high resolution that is composed of five elements.SOLUTION: A photographing lens 10 comprises, arranged in order from an object side to an image side: a first lens 11 having positive power; a second lens 12 having negative power; a third lens 13 having positive power or negative power; a fourth lens 14 having positive power; and a fifth lens 15 having negative power. When a focal length of the lens 11 is denoted by f1 and a focal length of the lens 12 is denoted by f2, 1.0≤|f2/f1|≤2.0 is satisfied. Thus, occurrence of chromatic aberration and curvature of field is suppressed and an overall length L of a lens system is suppressed. Further, since all lens surfaces of the fourth lens 14 and fifth lens 15 have an aspherical shape having an inflection point, curvature of field can be well corrected. Furthermore, since all lens surfaces of the fourth lens 14 and fifth lens 15 have an inflection point, a principal light beam incident angle to an image-forming surface 18 can be made small.

Description

  The present invention relates to a high-resolution and compact imaging lens composed of five lenses and an imaging apparatus equipped with the imaging lens.

  An imaging lens used in an imaging apparatus equipped with a CMOS type image sensor or a CCD type image sensor as an imaging element is described in Patent Document 1. The imaging lens of this document includes a first lens having a positive power, a second lens having a negative power, a third lens having a positive power or a negative power, and a positive lens in order from the object side to the image side. It is comprised from the 4th lens provided with power, and the 5th lens provided with negative power.

JP 2010-282000 A

  Due to the demand to mount the imaging device on a small device such as a portable device, the imaging lens is required to be downsized. Further, as the number of pixels of the image sensor mounted on the image pickup apparatus increases, the image pickup lens is required to have a higher resolution. Here, in order to increase the resolution of the imaging lens, it is necessary to suppress the occurrence of chromatic aberration and curvature of field more than in the past.

  In view of such a point, an object of the present invention is to provide a small-sized and high-resolution imaging lens that is configured by five lenses and is suitable for mounting on an imaging device including an imaging element. . Moreover, it is providing the imaging device which mounts such an imaging lens.

In order to solve the above problems, the imaging lens of the present invention is:
In order from the object side to the image side, a first lens having a positive power, a second lens having a negative power, a third lens having a positive power or a negative power, a fourth lens having a positive power, And a fifth lens having negative power,
Each of the fourth lens and the fifth lens has an aspheric shape in which the object side lens surface and the image side lens surface have inflection points,
When the focal length of the first lens is f1 and the focal length of the second lens is f2, the following conditional expression (1) is satisfied.
1.0 ≦ | f2 / f1 | ≦ 2.0 (1)

  According to the imaging lens of the present invention, since conditional expression (1) is satisfied, chromatic aberration and field curvature can be suppressed, and the entire length of the lens system can be reduced. That is, the upper limit value of the conditional expression (1) is for suppressing chromatic aberration, and if the upper limit value of the conditional expression (1) is exceeded, the chromatic aberration increases and it is difficult to correct it. The lower limit value of the conditional expression (1) is for suppressing the occurrence of curvature of field and the increase in the total length of the lens system. If the lower limit value of the conditional expression (1) is exceeded, the first lens and the second lens The balance of power is lost and the curvature of field is increased. Further, when the value of conditional expression (1) is equal to or lower than the lower limit value, the positive power of the first lens becomes weaker than the negative power of the second lens, so that it is difficult to keep the entire length of the lens system short. Furthermore, according to the imaging lens of the present invention, since all the lens surfaces of the fourth lens and the fifth lens are aspherical, curvature of field can be corrected well.

  Further, according to the imaging lens of the present invention, since all of the lens surfaces of the fourth lens and the fifth lens have a shape having an inflection point, the principal ray incident angle with respect to the imaging surface is reduced. Is easy. Therefore, when the image pickup apparatus on which the image pickup lens is mounted has an image pickup element such as a CMOS image sensor or a CCD image sensor, image quality deterioration in the image pickup apparatus can be suppressed. In other words, these image sensors have a characteristic that the sensitivity decreases with respect to light incident obliquely on the sensor surface. Therefore, when the chief ray incident angle is increased, the image quality is deteriorated. In this case, the chief ray incident angle with respect to the imaging surface can be reduced, so that deterioration of image quality due to the incident angle of the light ray on the sensor surface can be suppressed.

In the present invention, the third lens has an aspherical object-side lens surface and an image-side lens surface, and the object-side lens surface of the third lens has a positive curvature. The focal length is longer than the focal length of each of the first lens, the second lens, the fourth lens, and the fifth lens. The focal length of the entire lens system is f, and the focal length of the third lens is f3. It is desirable to satisfy the following conditional expression (2).
| F3 / f | ≧ 10 (2)

  If the conditional expression (2) is satisfied, the power of the third lens is set weaker than the power of other lenses. Accordingly, when correcting the curvature of field by setting the lens surface of the third lens as an aspherical shape, the correction of the curvature of field by the shape of the lens surface of the third lens and the curvature of field by the fourth lens and the fifth lens are corrected. Easy to balance correction. As a result, it becomes easy to satisfactorily correct the curvature of field by the third lens, the fourth lens, and the fifth lens. Here, that the object side lens surface has a positive curvature means that the object side lens surface has a curved surface protruding toward the object side toward the optical axis.

In the present invention, it is preferable that the following conditional expression is satisfied when the focal length of the fourth lens is f4 and the focal length of the fifth lens is f5.
0.5 ≦ | f4 / f5 | ≦ 1.5 (3)

  If the conditional expression (3) is satisfied, the power of the fourth lens and the power of the fifth lens are close to each other. Therefore, the correction of the field curvature due to the shape of the lens surface of the fourth lens and the shape of the lens surface of the fifth lens. It is easy to balance the correction of curvature of field. As a result, it is possible to satisfactorily correct field curvature by the fourth lens and the fifth lens.

In the present invention, in order to reduce the chief ray incident angle, the effective diameter of the fifth lens is φ, and the height from the optical axis to the inflection point on the image side lens surface of the fifth lens is h. In this case, it is desirable to satisfy the following conditional expression (4).
h / φ ≧ 0.4 (4)

In the present invention, when the Abbe number of the second lens is νd2 and the Abbe number of the third lens is νd3, it is preferable that the following conditional expressions (5) and (6) are satisfied.
νd2 ≦ 25 (5)
νd3 ≧ 50 (6)

  If conditional expression (5) and conditional expression (6) are satisfied, a lens made of a high dispersion material and a lens made of a low dispersion material are arranged adjacent to each other, so that chromatic aberration can be corrected well. In addition, since the Abbe number of the third lens having a lower power than that of other lenses is increased, chromatic aberration can be corrected without increasing the field curvature.

  In the present invention, it is preferable that the third lens has a negative power, and the image side lens surface of the third lens has a positive curvature. Here, that the image side lens surface has a positive curvature means that the image side lens surface has a curved surface that is recessed toward the object side toward the optical axis.

  In the present invention, the imaging lens is preferably a wide-angle lens having a half angle of view of 35 ° or more.

  Next, an image pickup apparatus according to the present invention includes the above-described image pickup lens and an image pickup element disposed at a focal position of the image pickup lens.

  According to the present invention, since the imaging lens has a high resolution, an imaging device having a high resolution can be obtained by employing an imaging device having a large number of pixels as the imaging device. In addition, since the entire length of the imaging lens can be shortened, the imaging device can be reduced in size. Furthermore, since the chief ray incident angle incident on the image sensor from the imaging lens can be reduced, deterioration in image quality in the imaging apparatus can be suppressed.

  According to the present invention, since chromatic aberration and curvature of field can be suppressed in the imaging lens, the resolution of the imaging lens can be improved. Moreover, since it can suppress that the full length of an imaging lens becomes long, an imaging lens can be reduced in size. Furthermore, the chief ray incident angle incident on the sensor surface of the image sensor from the imaging lens can be reduced.

It is a block diagram of the imaging lens of Example 1 to which the present invention is applied. FIG. 2 is a chief ray emission angle diagram of the imaging lens of FIG. 1. FIG. 2 is a longitudinal aberration diagram, a lateral aberration diagram, a field curvature diagram, and a distortion diagram of the imaging lens in FIG. 1. It is a block diagram of the lens unit of Example 2 to which the present invention is applied. FIG. 5 is a chief ray emission angle diagram of the imaging lens of FIG. 4. FIG. 5 is a spherical difference diagram, lateral aberration diagram, field curvature diagram, and distortion diagram of the imaging lens of FIG. 4. It is a block diagram of the lens unit of Example 3 to which the present invention is applied. FIG. 8 is a chief ray emission angle diagram of the imaging lens of FIG. 7. FIG. 8 is a longitudinal aberration diagram, a lateral aberration diagram, a field curvature diagram, and a distortion diagram of the imaging lens in FIG. 7. It is explanatory drawing of the imaging device carrying an imaging lens.

  An imaging lens to which the present invention is applied will be described below with reference to the drawings.

Example 1
FIG. 1 is a configuration diagram (ray diagram) of the imaging lens 10 of the first embodiment. As shown in FIG. 1, the imaging lens 10 of this example includes, in order from the object side to the image side, a first lens 11 having a positive power, a second lens 12 having a negative power, and a negative power. It consists of a third lens 13, a fourth lens 14 with positive power, and a fifth lens 15 with negative power. A diaphragm 16 is disposed on the object side of the first lens 11, and a cover glass 17 is disposed on the image side of the fifth lens 15. The image plane 18 is located at a predetermined distance from the cover glass 17. In this example, each of the third lens 13, the fourth lens 14, and the fifth lens 15 has an aspherical shape on both the object side lens surface and the image side lens surface. In this example, each of the fourth lens 14 and the fifth lens 15 has a shape in which both the object side lens surface and the image side lens surface have inflection points.

In the first lens 11, the object side lens surface 11a has a positive curvature, and the image side lens surface 11b has a negative curvature. Accordingly, the object side lens surface 11a has a convex curved surface portion protruding toward the object side toward the optical axis, and the image side lens surface 11b has a convex curved surface portion protruding toward the image side toward the optical axis. I have. In this example, both the object side lens surface 11a and the image side lens surface 11b of the first lens 11 are aspherical. In the second lens 12, the object side lens surface 12a has a positive curvature, and the image side lens surface 12b has a positive curvature. Accordingly, the object side lens surface 12a has a convex curved surface portion protruding toward the object side toward the optical axis, and the image side lens surface 12b has a concave curved surface portion recessed toward the object side toward the optical axis. Yes. In this example, both the object side lens surface 12a and the image side lens surface 12b of the second lens 12 are aspherical. The first lens 11 and the second lens 12 satisfy the following conditional expression (1) when the focal length of the first lens 11 is f1 and the focal length of the second lens 12 is f2.
1.0 ≦ | f2 / f1 | ≦ 2.0 (1)

  The upper limit value of conditional expression (1) is for suppressing chromatic aberration. If the upper limit of conditional expression (1) is exceeded, chromatic aberration increases and correction thereof becomes difficult. Therefore, to suppress chromatic aberration, 2.0 or less is preferable. The lower limit value of conditional expression (1) is for suppressing the occurrence of field curvature and the increase in the total length of the lens system. When the lower limit value of conditional expression (1) is exceeded, the power balance between the first lens 11 and the second lens 12 is lost, resulting in an increase in field curvature. Further, when the conditional expression (1) is equal to or lower than the lower limit value, the power of the first lens 11 becomes weaker than that of the second lens 12, so that it becomes difficult to keep the entire length of the lens system short. In order to suppress, it is good to set it as 1.0 or more. In this example, | f2 / f1 | = 1.495. Therefore, the occurrence of chromatic aberration and field curvature can be suppressed, and the overall length of the lens system can be suppressed to be short. Regarding conditional expression (1), it is possible to balance chromatic aberration and curvature of field by desirably setting the lower limit value to 1.3 or more and the upper limit value to 1.7 or less.

In the third lens 13, the object side lens surface 13a has a positive curvature, and the image side lens surface 13b has a positive curvature. Therefore, the object side lens surface 13a has a convex curved surface portion protruding toward the object side toward the optical axis, and the image side lens surface 13b has a concave curved surface portion recessed toward the object side toward the optical axis. I have. The third lens 13 satisfies the following conditional expression (2), where f is the focal length of the entire lens system and f3 is the focal length of the third lens 13.
| F3 / f | ≧ 10 (2)

  In this example, | f3 / f | = 78.732. When the conditional expression (2) is satisfied, the power of the third lens 13 is set weaker than the power of other lenses. Therefore, when the curvature of field is corrected by setting the lens surface of the third lens 13 to be aspheric, the correction of curvature of field by the shape of the lens surface of the third lens 13 and the correction by the fourth lens 14 and the fifth lens 15 are performed. It is easy to balance the correction of curvature of field. As a result, the third lens 13, the fourth lens 14, and the fifth lens 15 can favorably correct the field curvature.

  The fourth lens 14 has an aspherical shape in which the object side lens surface 14a has an inflection point, and has a positive curvature. Therefore, the object side lens surface 14a has a convex shape that protrudes toward the object side toward the optical axis in the lens surface portion on the inner peripheral side of the inflection point. In the object side lens surface 14a, the lens surface portion on the outer peripheral side with respect to the inflection point has a shape protruding toward the object side toward the outer peripheral side. The fourth lens 14 has an aspherical shape in which the image-side lens surface 14b has an inflection point, and has a negative curvature. Therefore, the image side lens surface 14b has a convex shape that protrudes toward the image side toward the optical axis in the lens surface portion on the inner peripheral side with respect to the inflection point. The lens surface portion on the outer peripheral side with respect to the inflection point is curved toward the object side toward the outer peripheral side.

  The fifth lens 15 has an aspherical shape in which the object-side lens surface 15a has an inflection point, and has a positive curvature. Therefore, the object side lens surface 15a has a convex shape that protrudes toward the object side toward the optical axis in the lens surface portion on the inner peripheral side with respect to the inflection point. In the object side lens surface 15a, the lens surface portion on the outer peripheral side with respect to the inflection point has a shape protruding toward the object side toward the outer peripheral side. The fifth lens 15 has an aspherical shape in which the image-side lens surface 15b has an inflection point, and has a positive curvature. Accordingly, the image-side lens surface 15b has a concave shape that is recessed toward the object side toward the optical axis in the lens surface portion on the inner peripheral side with respect to the inflection point. The lens surface portion on the outer peripheral side with respect to the inflection point is curved toward the object side toward the outer peripheral side.

Here, the fourth lens 14 and the fifth lens 15 satisfy the following conditional expression (3) when the focal length of the fourth lens 14 is f4 and the focal length of the fifth lens 15 is f5.
0.5 ≦ | f4 / f5 | ≦ 1.5 (3)

  In this example, | f4 / f5 | = 1.001. When the conditional expression (3) is satisfied, the power of the fourth lens 14 and the power of the fifth lens 15 are close to each other. Therefore, the correction of the field curvature due to the shape of the lens surface of the fourth lens 14 and the fifth lens It is easy to balance the correction of field curvature due to the shape of the 15 lens surfaces. For conditional expression (3), if the upper limit value of 1.5 is exceeded, the field curvature is in the direction of overcorrection, and if the lower limit value of 0.5 is not reached, correction is insufficient. Therefore, when the conditional expression (3) is satisfied, it is possible to satisfactorily correct the field curvature. Regarding conditional expression (3), by setting the lower limit value to 0.8 or more and the upper limit value to 1.2 or less, the correction of curvature of field can be balanced.

Further, for the fifth lens 15, the inflection point ratio when the effective diameter of the fifth lens 15 is φ and the height from the optical axis to the inflection point on the image side lens surface 15b of the fifth lens 15 is h. (H / φ) satisfies the following conditional expression (4).
h / φ ≧ 0.4 (4)

  In this example, the effective diameter φ = 2.470 mm and h = 1.2 mm. Therefore, h / φ = 0.486. Here, there is a correlation between the inflection point ratio (h / φ) and the principal ray exit angle, and the inflection point ratio and the inflection point ratio of the principal ray exit angle are close to each other. Accordingly, by setting the inflection point ratio (h / φ) of the image side lens surface 15b of the fifth lens 15 so as to satisfy the conditional expression (4), the principal ray of the emitted light from the imaging lens 10 is set. It is possible to reduce the incident angle at which the light enters the image plane. FIG. 2 is a chief ray emission angle diagram of the imaging lens 10 of this example. In the chief ray emission angle diagram, the horizontal axis represents the image height, and the vertical axis represents the chief ray incident angle. The chief ray emission angle is an angle formed between the chief ray of the ray emitted from the image-side lens surface of the fifth lens and the optical axis (parallel line parallel to the optical axis). Equivalent to angle.

Here, in the second lens 12 and the third lens 13, when the Abbe number of the second lens 12 is νd2 and the Abbe number of the third lens 13 is νd3, the following conditional expressions (5) and (6) Is satisfied.
νd2 ≦ 25 (5)
νd3 ≧ 50 (6)

  In this example, νd2 = 23.42, and νd3 = 56.04. As a result, in the imaging lens 10, the lens made of a high dispersion material (second lens 12) and the lens made of a low dispersion material (third lens 13) are arranged adjacent to each other, so that chromatic aberration is corrected well. it can. In addition, since the Abbe number of the third lens 13 having a lower power than that of other lenses is increased, chromatic aberration can be corrected without increasing the curvature of field.

The F number of the imaging lens 10 of this example is set to Fno. When the half angle of view is ω and the total length of the lens system is L, these values are as follows.
Fno. = 2.4
ω = 38 °
L = 4.613mm

The focal length of the entire lens system is f, the focal length of the first lens 11 is f1, the focal length of the second lens 12 is f2, the focal length of the third lens 13 is f3, and the focal length of the fourth lens 14 is f4. Assuming that the focal length of the fifth lens 15 is f5, these values are as follows.
f = 3.77 mm
f1 = 3.069mm
f2 = −4.587mm
f3 = -296.84mm
f4 = 2.874 mm
f5 = −2.891 mm

  Next, Table 1A shows lens data of each lens surface of the imaging lens 10. In Table 1A, each lens surface is specified in the order counted from the object side. The lens surface marked with an asterisk is aspheric. The 11th and 12th surfaces are the glass surfaces of the cover glass 17. The unit of curvature radius and spacing is millimeters.

Next, Tables 1B and 1C show aspherical coefficients for defining the aspherical shape of the aspherical lens surface. In Tables 1B and 1C, the lens surfaces are specified in the order counted from the object side. Table 1B shows aspheric coefficients of the lens surfaces of the first lens 11 and the second lens 12, and Table 1C shows aspheric coefficients of the lens surfaces of the third lens 13, the fourth lens 14, and the fifth lens 15. Show.

  The aspherical shape adopted for the lens surface is such that Y is the sag amount, c is the reciprocal of the radius of curvature, K is the cone coefficient, h is the ray height, 4th order, 6th order, 8th order, 10th order, 12th order, If the 14th and 16th aspherical coefficients are A4, A6, A8, A10, A12, A14, and A16, respectively, they are expressed by the following equations.

(Function and effect)
3A to 3D are a longitudinal aberration diagram, a lateral aberration diagram, a field curvature diagram, and a distortion diagram of the imaging lens 10. In the longitudinal aberration diagram of FIG. 3A, the horizontal axis indicates the position where the light beam intersects the optical axis, and the vertical axis indicates the height of the light beam. In the lateral aberration diagram of FIG. 3B, the horizontal axis indicates the entrance pupil coordinates, and the vertical axis indicates the amount of aberration. 3A and 3B show simulation results for a plurality of light beams having different wavelengths. In the field curvature diagram of FIG. 3C, the horizontal axis indicates the distance in the optical axis direction, and the vertical axis indicates the height of the image. In FIG. 3C, S represents the field curvature aberration on the sagittal surface, and T represents the field curvature aberration on the tangential surface. In the distortion diagram of FIG. 3D, the horizontal axis indicates the amount of image distortion, and the vertical axis indicates the height of the image.

  As shown in FIG. 3A, according to the imaging lens 10 of this example, the axial chromatic aberration is corrected well. Further, as shown in FIG. 3B, color bleeding is suppressed. Further, as shown in FIGS. 3C and 3D, the curvature of field is well corrected. Therefore, the imaging lens 10 has a high resolution. Further, according to this example, the total length L of the lens system is suppressed to be as short as about 4.6 mm.

  Furthermore, in this example, since the inflection point ratio (h / φ) of the image side lens surface 15b of the fifth lens 15 is set to be larger than 0.4, the chief ray incident angle can be kept small, and the image Side telecentricity is improved.

(Example 2)
FIG. 4 is a configuration diagram (ray diagram) of the imaging lens of the second embodiment. As illustrated in FIG. 4, the imaging lens 20 includes a first lens 21 having a positive power, a second lens 22 having a negative power, and a third lens having a negative power in order from the object side to the image side. 23, a fourth lens 24 having a positive power, and a fifth lens 25 having a negative power. A diaphragm 26 is disposed on the object side of the first lens 21, and a cover glass 27 is disposed on the image side of the fifth lens 25. The image plane 28 is located at a predetermined distance from the cover glass 27.

  Also in this example, each of the third lens 23, the fourth lens 24, and the fifth lens 25 has an aspherical shape on both the object side lens surfaces 23a, 24a, 25a and the image side lens surfaces 23b, 24b, 25b. ing. Also in this example, each of the fourth lens 24 and the fifth lens 25 has a shape in which both the object side lens surfaces 24a and 25a and the image side lens surfaces 24b and 25b have inflection points. In addition, since the shape of the lens surfaces 21a to 25a and 21b to 25b of each lens of the imaging lens 20 is the same as the shape of the lens surface of each lens corresponding to the imaging lens 10, the description thereof is omitted.

The F number of the imaging lens 10 of this example is set to Fno. When the half angle of view is ω and the total length of the lens system is L, these values are as follows.
Fno. = 2.4
ω = 37.7 °
L = 4.662mm

The focal length of the entire lens system is f, the focal length of the first lens 21 is f1, the focal length of the second lens 22 is f2, the focal length of the third lens 23 is f3, and the focal length of the fourth lens 24 is f4. Assuming that the focal length of the fifth lens 25 is f5, these values are as follows.
f = 3.805 mm
f1 = 2.832mm
f2 = −4.041mm
f3 = −151.84 mm
f4 = 2.852 mm
f5 = −2.887 mm

Further, assuming that the effective diameter of the image side lens surface 25b of the fifth lens 25 is φ and the height from the optical axis to the inflection point on the image side lens surface 15b of the fifth lens 15 is h, these values are as follows: It is as follows. FIG. 5 is a principal ray emission angle diagram of the imaging lens 20 of this example.
φ = 2.545
h = 1.2

Moreover, the values of the conditional expressions (1) to (6) shown in the description of the first embodiment are as follows, and any conditional expressions (1) to (6) are satisfied.
1.0 ≦ | f2 / f1 | = 1.427 ≦ 2.0
| F3 / f | = 39.91 ≧ 10
0.5 ≦ | f4 / f5 | = 0.987 ≦ 1.5
h / φ = 0.471 ≧ 0.4
νd2 = 23.42 ≦ 25
νd3 = 56.04 ≧ 50

  Next, Table 2A shows lens data of the lens surfaces 21 a to 25 a and 21 b to 25 b of the lenses 21 to 25 of the imaging lens 20. In Table 2A, each lens surface is specified in the order counted from the object side. The lens surface marked with an asterisk is aspheric. The 11th and 12th surfaces are the glass surfaces of the cover glass 27. The unit of curvature radius and spacing is millimeters.

  Next, Table 2B and Table 2C show aspheric coefficients for defining the aspherical shape of the aspherical lens surface. In Tables 2B and 2C, the lens surfaces are specified in the order counted from the object side. Table 2B shows aspheric coefficients of the lens surfaces of the first lens 21 and the second lens 22, and Table 2C shows aspheric coefficients of the lens surfaces of the third lens 23, the fourth lens 24, and the fifth lens 25. Show.

(Function and effect)
6A to 6D are a longitudinal aberration diagram, a lateral aberration diagram, a field curvature diagram, and a distortion diagram of the imaging lens 20, respectively. As shown in FIG. 6A, according to the imaging lens 20 of this example, the axial chromatic aberration is corrected well. Further, as shown in FIG. 6B, color bleeding is suppressed. Further, as shown in FIGS. 6C and 6D, the field curvature is corrected well. Therefore, the imaging lens 20 has a high resolution. Further, according to this example, the total length L of the lens system is suppressed to be as short as about 4.6 mm.

  Furthermore, in this example, since the inflection point ratio (h / φ) of the image side lens surface 25b of the fifth lens 25 is set to be larger than 0.4, the chief ray incident angle can be suppressed to be small, and the image side telecentricity is achieved. Improved.

(Example 3)
FIG. 7 is a configuration diagram (ray diagram) of the imaging lens 30 of the third embodiment. The imaging lens 30 of this example includes a first lens 31 having a positive power, a second lens 32 having a negative power, a third lens 33 having a positive power, and a positive lens in order from the object side to the image side. It consists of a fourth lens 34 having power and a fifth lens 35 having negative power. A diaphragm 36 is disposed on the object side of the first lens 31, and a cover glass 37 is disposed on the image side of the fifth lens 35. The image plane 38 is located at a predetermined distance from the cover glass 37.

  Also in this example, each of the third lens 33, the fourth lens 34, and the fifth lens 35 has an aspherical shape on both the object side lens surfaces 33a, 34a, 35a and the image side lens surfaces 33b, 34b, 35b. ing. In this example, each of the fourth lens 34 and the fifth lens 35 has a shape in which the object side lens surfaces 34a and 35a and the image side lens surfaces 34b and 35b have inflection points.

  Here, the shape of each of the lenses 31 to 35 of the imaging lens 30 is the same as the shape of each of the corresponding lenses of the imaging lens 10 except for the third lens 33, and thus the description other than the third lens 33 is omitted. In the third lens 33, the object side lens surface 33a has a positive curvature, and the image side lens surface 33b has a negative curvature. Accordingly, the object side lens surface 33a has a convex curved surface portion protruding toward the object side toward the optical axis, and the image side lens surface 33b has a convex curved surface portion protruding toward the image side toward the optical axis. I have.

The F number of the imaging lens 30 of this example is set to Fno. When the half angle of view is ω and the total length of the lens system is L, these values are as follows.
Fno. = 2.4
ω = 37.3 °
L = 4.645mm

The focal length of the entire lens system is f, the focal length of the first lens 31 is f1, the focal length of the second lens 32 is f2, the focal length of the third lens 33 is f3, and the focal length of the fourth lens 34 is f4. Assuming that the focal length of the fifth lens 35 is f5, these values are as follows.
f = 3.808 mm
f1 = 2.731mm
f2 = −4.050mm
f3 = 45.96mm
f4 = 3.050mm
f5 = −2.625 mm

Further, assuming that the effective diameter of the image side lens surface 35b of the fifth lens 35 is φ and the height from the optical axis to the inflection point on the image side lens surface 35b of the fifth lens 15 is h, these values are as follows: It is as follows. FIG. 8 is a chief ray emission angle diagram of the imaging lens 30 of this example.
φ = 2.570
h = 1.3

Moreover, the values of the conditional expressions (1) to (6) shown in the description of the first embodiment are as follows, and any conditional expressions (1) to (6) are satisfied.
1.0 ≦ | f2 / f1 | = 1.383 ≦ 2.0
| F3 / f | = 12.069 ≧ 10
0.5 ≦ | f4 / f5 | = 1.161 ≦ 1.5
h / φ = 0.506 ≧ 0.4
νd2 = 23.42 ≦ 25
νd3 = 56.04 ≧ 50

  Next, Table 3A shows lens data of the lens surfaces 31 a to 35 a and 31 b to 35 b of the lenses 31 to 35 of the imaging lens 30. In Table 3A, each lens surface is specified in the order counted from the object side. The surface marked with an asterisk is aspheric. The 11th and 12th surfaces are the glass surfaces of the cover glass 27. The unit of curvature radius and spacing is millimeters.

  Next, Tables 3B and 3C show aspheric coefficients for defining the aspherical shape of the aspheric lens surface. In Tables 3B and 3C, the lens surfaces are specified in the order counted from the object side. Table 3B shows aspheric coefficients of the lens surfaces of the first lens 31 and the second lens 32, and Table 3C shows aspheric coefficients of the lens surfaces of the third lens 33, the fourth lens 34, and the fifth lens 35. Show.

(Function and effect)
9A to 9D are a longitudinal aberration diagram, a lateral aberration diagram, a field curvature diagram, and a distortion diagram of the imaging lens 30. FIG. As shown in FIG. 9A, according to the imaging lens 30 of this example, the axial chromatic aberration is corrected well. Further, as shown in FIG. 9B, color bleeding is suppressed. Further, as shown in FIGS. 9C and 9D, the curvature of field is corrected well. Therefore, the imaging lens 30 has a high resolution. Further, according to this example, the total length L of the lens system is suppressed to be as short as about 4.6 mm.

  Further, in this example, since the inflection point ratio (h / φ) of the image side lens surface 35b of the fifth lens 35 is set to be larger than 0.4, the chief ray incident angle can be suppressed to be small, and the image side telecentricity is achieved. Improved.

(Imaging device)
FIG. 10 is an explanatory diagram of an imaging apparatus 50 equipped with the imaging lens 10 of the present invention. As shown in FIG. 10, the imaging device 50 includes an imaging element 51 in which a sensor surface 51 a is arranged on the imaging plane 18 (focal position) of the imaging lens 10. The image sensor 51 is a CCD sensor or a CMOS sensor.

  According to this example, since the resolution of the imaging lens 10 is high, the imaging device 50 can have a high resolution by adopting the imaging device 51 having a large number of pixels as the imaging device 51. Moreover, since the total length L of the lens system of the imaging lens 10 is short, the imaging device 50 can be reduced in size. Furthermore, since the chief ray incident angle incident on the image sensor 51 from the imaging lens 10 is kept small, deterioration in image quality in the imaging device 50 can be suppressed. That is, these imaging elements 51 have a characteristic that sensitivity is lowered with respect to light incident on the sensor surface 51a from an oblique direction. Therefore, when the chief ray incident angle is increased, the image quality is deteriorated. 10 makes it possible to reduce the chief ray incident angle with respect to the image forming plane, so that deterioration of image quality due to the incident angle of the ray on the sensor surface can be suppressed. The imaging device 50 can be equipped with the imaging lenses 20 and 30 in the same manner as the imaging lens 10, and the same effect can be obtained in this case.

10, 20, 30, imaging lens 11, 21, 31, first lens 12, 22, 32, second lens 13, 23, 33, third lens 14, 24, 34, fourth lens 15 .25.35..Fifth lens 16, 26.36..Aperture 17, 27.37..Cover glass 18..28.38..Image plane 50..Image pickup device 51..Image sensor 51a..Sensor surface

Claims (8)

In order from the object side to the image side, a first lens having a positive power, a second lens having a negative power, a third lens having a positive power or a negative power, a fourth lens having a positive power, And a fifth lens having negative power,
Each of the fourth lens and the fifth lens has an aspheric shape in which the object side lens surface and the image side lens surface have inflection points,
An imaging lens satisfying the following conditional expression (1), where f1 is a focal length of the first lens and f2 is a focal length of the second lens.
1.0 ≦ | f2 / f1 | ≦ 2.0 (1) In claim 1,
In the third lens, the object side lens surface and the image side lens surface are aspherical,
The object side lens surface of the third lens has a positive curvature,
The focal length of the third lens is longer than the focal length of each of the first lens, the second lens, the fourth lens, and the fifth lens.
An imaging lens satisfying the following conditional expression (2), where f is a focal length of the entire lens system and f3 is a focal length of the third lens.
| F3 / f | ≧ 10 (2) In claim 1 or 2,
An imaging lens satisfying the following conditional expression when the focal length of the fourth lens is f4 and the focal length of the fifth lens is f5.
0.5 ≦ | f4 / f5 | ≦ 1.5 (3) In any one of claims 1 to 3,
When the effective diameter of the fifth lens is φ and the height from the optical axis to the inflection point on the image side lens surface of the fifth lens is h, the following conditional expression (4) is satisfied. A characteristic imaging lens.
h / φ ≧ 0.4 (4) Regarding any one of claims 1 to 4,
An imaging lens satisfying the following conditional expression (5) and conditional expression (6) when the Abbe number of the second lens is νd2 and the Abbe number of the third lens is νd3:
νd2 ≦ 25 (5)
νd3 ≧ 50 (6) In any one of claims 1 to 5,
The third lens has negative power;
The imaging lens, wherein the image side lens surface of the third lens has a positive curvature. In any one of claims 1 to 6,
An imaging lens having a half angle of view of 35 ° or more. The imaging lens according to any one of claims 1 to 7,
An imaging apparatus comprising: an imaging element disposed at a focal position of the imaging lens.