JP2017182096A - Doublet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wide angle lens with angle of view of 65° or more capable of reducing the chief ray incidence angle with respect to an imaging plane while reducing entire length of the lens system.SOLUTION: The wide angle lens includes: a first lens having a concave shape on the lens surface at the image side, which has a negative power; a second lens having a convex shape on the lens surface at the object side, which has a positive power; a third lens having a negative power; a fourth lens having a negative power; and a fifth lens having an inflection point on the lens surface at the image side, which has a positive power, which are disposed from the object side to the image side in order. The focus distance of the first lens with respect to the focus distance of entire lens system is a predetermined ratio.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a small wide-angle lens composed of five lenses and an image pickup apparatus equipped with the wide-angle lens.

  An imaging lens mounted on an information terminal such as a cellular phone or a small digital camera is described in Patent Document 1. The photographic lens of this document is arranged in order from the object side to the image side, the first lens having positive power, the second lens having negative power, the third lens having positive power, and the image side convex. A fourth lens having a meniscus shape and a fifth lens having an aspheric shape with an inflection point on the image side lens surface are provided. The maximum angle of view of the imaging lens of this document is 60 °.

JP 2009-14947 A

  In an imaging lens mounted on a device such as an information terminal or a small digital camera, the angle of view may be widened in consideration of usability. That is, in these small devices, it may be required to replace the imaging lens having a standard angle of view with a wide-angle lens having an angle of view of 60 ° or more.

  Here, in order to replace the standard lens with a wide-angle lens, the overall length of the lens system of the wide-angle lens (the distance from the object-side end of the object-side lens surface of the first lens to the imaging surface) is kept short, and the wide-angle lens is It must be possible to install in the standard lens placement space. Further, in these devices, some image pickup devices arranged at the focal position of the image pickup lens have a characteristic that the sensitivity decreases with respect to light incident obliquely on the sensor surface. The chief ray incident angle with respect to the image forming plane) must be suppressed to be small, and deterioration in image quality must be suppressed.

  In view of such a point, an object of the present invention is to provide a wide-angle lens that can suppress the overall length of the lens system and can suppress the chief ray incident angle with respect to the imaging surface. Another object of the present invention is to provide an imaging apparatus equipped with such a wide-angle lens.

  In order to solve the above problems, a wide-angle lens of the present invention includes a first lens having a negative power, a second lens having a positive power, and a negative power, which are arranged in order from the object side to the image side. A third lens having a negative power, a fourth lens having a negative power, and a fifth lens having a positive power. The image side lens surface of the first lens has a concave shape, and the object side lens surface of the second lens. Has a convex shape, the image side lens surface of the fifth lens is an aspherical surface having an inflection point, the central portion including the optical axis has a concave shape, and the image side lens of the fifth lens When at least two lens surfaces including the surface are aspherical, and the focal length of the entire lens system is f and the focal length of the first lens is f1, “−1.5 ≦ f1 / f ≦ −. It satisfies the conditional expression “0.5”.

  According to the present invention, a negative power lens having a concave shape is disposed on the first lens, and a positive power lens having a convex shape is disposed on the second lens. A lens can be constructed. In addition, since the image side lens surface of the fifth lens is an aspherical surface having an inflection point, it becomes easy to control the direction of the emitted light from the wide-angle lens, and the principal ray incident angle incident on the imaging surface is set. It can be suppressed small. Further, since at least two lens surfaces including the image side lens surface of the fifth lens are aspherical surfaces, it is easy to make the wide-angle lens bright. Furthermore, according to the present invention, it is possible to provide an angle of view of 65 ° or more, which is wider than that of a standard lens. Incidentally, a wide-angle lens generally refers to an imaging lens having an angle of view of 60 ° or more. The chief ray incident angle is the angle at which the light beam incident on the imaging plane intersects the optical axis.

In the present invention, it is desirable that the following conditional expression (1) is satisfied, where f is the focal length of the entire lens system and f2 is the focal length of the second lens.
0.4 ≦ f2 / f ≦ 0.7 (1)

  Conditional expression (1) facilitates the suppression of the total length of the lens system. If the upper limit value of conditional expression (1) is exceeded, the total length of the lens system is increased. If the lower limit value of conditional expression (1) is not reached, it is difficult to ensure the back focus.

In the present invention, it is desirable that the following conditional expression (2) is satisfied when the focal length of the third lens is f3.
−1 ≦ f2 / f3 ≦ −0.25 (2)

  Conditional expression (2) suppresses axial chromatic aberration. That is, the axial chromatic aberration can be suppressed by the second lens 12 having a positive power and the third lens 13 having a negative power arranged adjacent to each other, but the power of the second lens and the power of the third lens can be suppressed. Therefore, when the upper limit value of conditional expression (2) is exceeded, correction of chromatic aberration is insufficient, and when the lower limit value of conditional expression (2) is not reached, excessive correction occurs in chromatic aberration.

In the present invention, when the distance (lens thickness of the lens system) from the object-side end of the object-side lens surface of the first lens to the image-side end of the image-side lens surface of the fifth lens is D, It is desirable to satisfy the conditional expression (3).
1.0 ≦ D / f ≦ 2.0 (3)

  Conditional expression (3) makes it easy to suppress the overall length of the lens system while ensuring back focus. If the upper limit value of conditional expression (3) is exceeded, it will be difficult to secure the back feecus. If the lower limit of conditional expression (3) is not reached, the distance between the lenses will be short, and it will be difficult to place the lenses. That is, the arrangement of the lenses may be difficult due to the center thickness or edge thickness of each lens.

In the present invention, when the focal length of the first lens is f1, the following conditional expression (4) is satisfied.
-1.5 ≤ f1 / f ≤ -0.5 (4)

  Conditional expression (4) facilitates securing the angle of view. If the upper limit value of conditional expression (4) is exceeded, the power of the first lens becomes too large in the lens system, leading to an increase in the overall length. In addition, the power of the first lens becomes too large in the lens system, making it difficult to correct field curvature. If the lower limit value of conditional expression (4) is not reached, it becomes difficult to ensure the angle of view due to a decrease in the power of the first lens.

  In the present invention, the angle of view can be 65 ° or more. That is, a wider angle of view than the standard lens can be provided.

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

  According to the present invention, the overall length of the lens system of the wide-angle lens is kept short. Therefore, the imaging device can be configured to be small. In addition, the wide-angle lens is bright, and the chief ray incident angle with respect to the imaging surface is suppressed to be small. Therefore, even when the image pickup element arranged at the focal position of the image pickup lens has a characteristic that the sensitivity is lowered with respect to light incident obliquely on the sensor surface, deterioration of image quality can be suppressed.

  According to the present invention, it is possible to provide a bright wide-angle lens that suppresses the overall length of the lens system and suppresses the chief ray incident angle with respect to the imaging surface.

It is a block diagram of the wide angle lens of Example 1 to which the present invention is applied. FIG. 2 is a longitudinal aberration diagram, a lateral aberration diagram, a field curvature diagram, and a distortion diagram of the wide-angle lens in FIG. 1. It is a block diagram of the wide angle lens of Example 2 to which the present invention is applied. FIG. 4 is a longitudinal aberration diagram, a lateral aberration diagram, a field curvature diagram, and a distortion diagram of the wide-angle lens of FIG. 3. It is a block diagram of the wide angle lens of Example 3 to which the present invention is applied. FIG. 6 is a longitudinal aberration diagram, a lateral aberration diagram, a field curvature diagram, and a distortion diagram of the wide-angle lens of FIG. 5. It is a block diagram of the wide angle lens of Example 4 to which this invention is applied. FIG. 8 is a longitudinal aberration diagram, lateral aberration diagram, field curvature diagram, and distortion diagram of the wide-angle lens of FIG. 7. It is a block diagram of the wide angle lens of Example 5 to which the present invention is applied. FIG. 10 is a longitudinal aberration diagram, lateral aberration diagram, field curvature diagram, and distortion diagram of the wide-angle lens of FIG. 9. It is a block diagram of the wide angle lens of Example 6 to which the present invention is applied. FIG. 12 is a longitudinal aberration diagram, lateral aberration diagram, field curvature diagram, and distortion diagram of the wide-angle lens of FIG. 11. It is a block diagram of the wide angle lens of Example 7 to which the present invention is applied. FIG. 14 is a longitudinal aberration diagram, a lateral aberration diagram, a field curvature diagram, and a distortion diagram of the wide-angle lens of FIG. 13. It is explanatory drawing of the imaging device carrying a wide angle lens.

  A wide-angle lens to which the present invention is applied will be described below with reference to the drawings.

Example 1
FIG. 1 is a ray diagram of the wide-angle lens of Example 1. As shown in FIG. 1, the wide-angle lens 10 has a first lens 11 having a negative power, a second lens 12 having a positive power, and a negative power, which are arranged in order from the object side to the image side. It consists of a third lens 13, a fourth lens 14 having negative power, and a fifth lens 15 having positive power. A diaphragm (not shown) is disposed between the first lens 11 and the second lens 12. A cover glass 16 is disposed on the image side of the fifth lens 15. The imaging plane 17 is at a position spaced from the cover glass 16.

  In the first lens 11, each of the object side lens surface 11a and the image side lens surface 11b is an aspherical surface. The object side lens surface 11a has a convex shape, and the image side lens surface 11b has a concave shape. The object-side lens surface 11a has a large curvature radius at the convex lens surface portion and is close to a planar shape.

  In the second lens 12, each of the object side lens surface 12a and the image side lens surface 12b is aspheric. The object side lens surface 12a and the image side lens surface 12b each have a convex shape.

  In the third lens 13, each of the object side lens surface 13a and the image side lens surface 13b is an aspherical surface. The object side lens surface 13a has a convex shape, and the image side lens surface 13b has a concave shape. The object side lens surface 13a has a large radius of curvature of the convex lens surface portion and is close to a planar shape.

  The fourth lens 14 has an object-side lens surface 14a and an image-side lens surface 14b that are aspherical surfaces. The object-side lens surface 14a has a convex shape at the central portion including the optical axis, and the image-side lens surface 14b has a concave shape at the central portion including the optical axis.

  In the fifth lens 15, each of the object side lens surface 15a and the image side lens surface 15b is an aspherical surface. The object side lens surface 15a has a convex shape in the central portion including the optical axis. The image-side lens surface 15b has an inflection point, and has a concave shape in the central portion including the optical axis. Therefore, the image-side lens surface 15b is curved toward the object side from the inflection point toward the inner periphery side, and is curved toward the object side from the inflection point toward the outer periphery side.

The numerical aperture of the wide-angle lens 10 is set to Fno. , The half field angle is ω, L is the total length of the lens system (the distance from the object-side end of the object-side lens surface 11a of the first lens 11 to the imaging surface 17), and the lens thickness of the lens system (first lens) 11 is the distance from the object-side end of the object-side lens surface 11a to the image-side end of the image-side lens surface 15b of the fifth lens 15, and these values are as follows.
Fno. = 2.8
ω = 85.0 °
L = 5.010mm
D = 3.938mm

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 = 2.539
f1 = −3.061
f2 = 1.324
f3 = −2.910
f4 = −3.557
f5 = 2.688

Here, the wide-angle lens 10 of this example satisfies the following conditional expressions (1) to (4).
0.4 ≦ f2 / f ≦ 0.7 (1)
−1 ≦ f2 / f3 = ≦ −0.25 (2)
1.0 ≦ D / f ≦ 2.0 (3)
-1.5 ≤ f1 / f ≤ -0.5 (4)

  That is, f2 / f = 0.521, f2 / f3 = −0.455, D / f = 1.551, and f1 / f = −1.206.

  Since the wide-angle lens 10 satisfies the conditional expression (1), it is easy to suppress the overall length of the lens system and ensure the back focus. That is, exceeding the upper limit value of the conditional expression (1) causes an increase in the total length. If the lower limit value of conditional expression (1) is not reached, it is difficult to ensure the back focus.

  Since the wide-angle lens 10 satisfies the conditional expression (2), axial chromatic aberration is suppressed. That is, axial chromatic aberration can be suppressed by the second lens 12 having a positive power and the third lens 13 having a negative power arranged adjacent to each other. If the power balance of the lens 13 exceeds the upper limit value of the conditional expression (2), the correction of chromatic aberration is insufficient, and if the lower limit value of the conditional expression (2) is not reached, the chromatic aberration is excessively corrected.

  Since the wide-angle lens 10 satisfies the conditional expression (3), it is easy to suppress the entire length of the lens system while ensuring the back focus. That is, when the upper limit value of conditional expression (3) is exceeded, it is difficult to ensure the back focus. If the lower limit value of the conditional expression (3) is not reached, the distance between the lenses becomes short, so that it may be difficult to arrange the lenses depending on the center thickness and edge thickness of each lens.

  Since the wide-angle lens 10 satisfies the conditional expression (4), it is easy to ensure the angle of view. That is, when the upper limit of conditional expression (4) is exceeded, the power of the first lens 11 becomes too large in the lens system, leading to an increase in the total length of the lens system. If the upper limit of conditional expression (4) is exceeded, the power of the first lens 11 becomes too large in the lens system, making it difficult to correct field curvature. On the other hand, if the lower limit value of conditional expression (2) is not reached, it becomes difficult to ensure the angle of view due to a decrease in power of the first lens 11.

The wide-angle lens 10 satisfies the following conditional expressions (5) to (9).
−1.4 ≦ f3 / f ≦ −0.6 (5)
−3 ≦ f4 / f ≦ −1 (6)
0.5 ≦ f5 / f ≦ 1.5 (7)
1.3 ≦ L / f ≦ 2.5 (8)
-2 ≦ f4 / f5 ≦ −1 (9)

  That is, f3 / f = −1.146, f4 / f = −1.401, f5 / f = 1.039, L / f = 1.973, and f4 / f5 = −1. .323.

  Since the wide-angle lens 10 satisfies the conditional expression (5), chromatic aberration can be corrected satisfactorily. That is, when the upper limit value of conditional expression (5) is exceeded, chromatic aberration correction becomes excessive, and when it falls below the lower limit value, chromatic aberration correction becomes insufficient.

  In addition, since the wide-angle lens 10 satisfies the conditional expression (6), the curvature of field can be corrected well. That is, if the upper limit value of conditional expression (6) is exceeded, the correction of field curvature will be excessive, and if it falls below the lower limit value, correction of field curvature will be insufficient.

  Furthermore, the wide-angle lens 10 can reduce the principal ray incident angle incident on the image plane 17 by satisfying conditional expression (7). That is, if the upper limit value of conditional expression (7) is exceeded, the correction of the emission direction of the light beam emitted from the lens system will be insufficient, and if it falls below the lower limit value, the correction of the emission direction will be excessive.

  Furthermore, since the wide-angle lens 10 satisfies the conditional expression (8), it is easier to suppress the total length of the lens system while ensuring the back focus. That is, when the upper limit value of conditional expression (8) is exceeded, it is difficult to ensure the back focus. If the lower limit value of the conditional expression (8) is not reached, the distance between the lenses is shortened, so that it may be difficult to arrange the lenses depending on the center thickness and edge thickness of each lens.

  Further, since the wide-angle lens 10 satisfies the conditional expression (9), the field curvature can be corrected more favorably. That is, when the upper limit value of conditional expression (9) is exceeded, the correction of field curvature becomes excessive, and when it falls below the lower limit value, the correction of field curvature is insufficient.

  Table 1A below shows lens data of each lens surface of the wide-angle lens 10. In Table 1A, each lens surface is specified in the order counted from the object side. In this example, all lens surfaces of each lens are aspheric. In addition, the 11th and 12th surfaces are the glass surfaces of the cover glass 16, and the 13th surface is the imaging surface 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.

  The aspherical shape adopted for the lens surface is 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)
2A to 2D are a longitudinal aberration diagram, a lateral aberration diagram, a field curvature diagram, and a distortion diagram of the wide-angle lens 10. In the longitudinal aberration diagram of FIG. 2A, the horizontal axis indicates the position where the light beam intersects the optical axis L, and the vertical axis indicates the height at which the light beam enters the lens system. In the lateral aberration diagram of FIG. 2B, the horizontal axis indicates the entrance pupil coordinates, and the vertical axis indicates the amount of aberration. 2A and 2B show simulation results for a plurality of visible rays having different wavelengths. In the field curvature diagram of FIG. 2C, the horizontal axis indicates the distance in the optical axis direction, and the vertical axis indicates the height of the image. In FIG. 2C, 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. 2D, the horizontal axis indicates the amount of image distortion, and the vertical axis indicates the height of the image.

  As shown in FIG. 2A, according to the wide-angle lens 10, axial chromatic aberration is corrected well. Further, as shown in FIG. 2B, color bleeding is suppressed. Further, as shown in FIGS. 2C and 2D, the field curvature is corrected well. Therefore, the wide-angle lens 10 has a high resolution.

  In the wide-angle lens 10, a negative power lens having a concave shape is disposed on the first lens 11, and a positive power lens having a convex shape is disposed on the second lens 12. The total length of the lens system having corners can be suppressed to about 5 mm. Furthermore, since the image-side lens surface 15b of the fifth lens 15 is an aspheric surface having an inflection point, it becomes easy to control the direction of the light beam emitted from the wide-angle lens 10 and the main surface incident on the imaging surface 17 can be controlled. The light incident angle can be reduced. In this example, since the lens surface of each lens is an aspherical surface, the wide-angle lens 10 is brightly configured.

(Example 2)
FIG. 3 is a ray diagram of the wide-angle lens of Example 2. As shown in FIG. 3, the wide-angle lens 20 has a first lens 21 having a negative power, a second lens 22 having a positive power, and a negative power, which are arranged in order from the object side to the image side. It consists of a third lens 23, a fourth lens 24 having negative power, and a fifth lens 25 having positive power. A diaphragm (not shown) is disposed between the first lens 21 and the second lens 22. A cover glass 26 is disposed on the image side of the fifth lens 25. The image plane 27 is at a position spaced from the cover glass 26.

  In the first lens 21, each of the object side lens surface 21a and the image side lens surface 21b is aspheric. The object side lens surface 21a has a convex shape, and the image side lens surface 21b has a concave shape. The object side lens surface 21a has a large curvature radius of the convex lens surface portion and is close to a planar shape.

  In the second lens 22, each of the object side lens surface 22a and the image side lens surface 22b is aspheric. The object side lens surface 22a and the image side lens surface 22b each have a convex shape.

  In the third lens 23, each of the object side lens surface 23a and the image side lens surface 23b is aspheric. The object side lens surface 23a has a convex shape, and the image side lens surface 23b has a concave shape. The object side lens surface 23a has a large curvature radius of the convex lens surface portion and is close to a planar shape.

  In the fourth lens 24, each of the object side lens surface 24a and the image side lens surface 24b is aspherical. The object-side lens surface 24a has a convex shape at the central portion including the optical axis, and the image-side lens surface 24b has a concave shape at the central portion including the optical axis.

  In the fifth lens 25, each of the object side lens surface 25a and the image side lens surface 25b is an aspherical surface. The object side lens surface 25a has a convex shape in the central portion including the optical axis. The image side lens surface 25b has an inflection point, and has a concave shape in the central portion including the optical axis. Therefore, the image-side lens surface 25b is curved toward the object side from the inflection point toward the inner periphery, and is curved toward the object side from the inflection point toward the outer periphery.

The numerical aperture of the wide-angle lens 20 is set to Fno. , The half field angle is ω, the entire length of the lens system (the distance from the object-side end of the object-side lens surface 21a of the first lens 21 to the imaging surface 27) is L, and the lens thickness of the lens system (first lens) When the distance from the object side end of the object side lens surface 21a of 21 to the image side end of the image side lens surface 25b of the fifth lens 25 is D, these values are as follows.
Fno. = 2.8
ω = 84.6 °
L = 5.066mm
D = 4.016mm

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 = 2.537
f1 = −3.064
f2 = 1.350
f3 = −2.954
f4 = -3.797
f5 = 2.8776

Here, the wide-angle lens 20 of this example satisfies the following conditional expressions (1) to (4).
0.4 ≦ f2 / f = 0.532 ≦ 0.7 (1)
-1 ≦ f2 / f3 = −0.457 ≦ −0.25 (2)
1.0 ≦ D / f = 1.583 ≦ 2.0 (3)
−1.5 ≦ f1 / f = −1.208 ≦ −0.5 (4)

  Since the wide-angle lens 20 satisfies the conditional expressions (1) to (4), it is easy to suppress the entire length of the lens system and secure the back focus while securing an angle of view of 65 ° or more. In addition, axial chromatic aberration can be suppressed.

The wide-angle lens 20 satisfies the following conditional expressions (5) to (9).
−1.4 ≦ f3 / f = −1.164 ≦ −0.6 (5)
−3 ≦ f4 / f = −1.497 ≦ −1 (6)
0.5 ≦ f5 / f = 1.134 ≦ 1.5 (7)
1.3 ≦ L / f = 1.997 ≦ 2.5 (8)
-2 ≦ f4 / f5 = −1.320 ≦ −1 (9)

  Since the wide-angle lens 20 satisfies the conditional expressions (5) to (9), chromatic aberration and curvature of field can be corrected well. In addition, the chief ray incident angle incident on the imaging surface 27 can be reduced. Furthermore, it is easy to suppress the overall length of the lens system while ensuring the back focus.

  Table 2A below shows lens data of each lens surface of the wide-angle lens 20. In Table 2A, each lens surface is specified in the order counted from the object side. In this example, all lens surfaces of each lens are aspheric. In addition, the 11th and 12th surfaces are the glass surfaces of the cover glass 26, and the 13th surface is the imaging surface 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.

(Function and effect)
4A to 4D are longitudinal aberration diagrams, lateral aberration diagrams, field curvature diagrams, and distortion diagrams of the wide-angle lens 20. As shown in FIG. 4A, according to the wide-angle lens 20, axial chromatic aberration is corrected well. Further, as shown in FIG. 4B, color bleeding is suppressed. Further, as shown in FIGS. 4C and 4D, the field curvature is corrected well. Therefore, the wide-angle lens 20 has a high resolution.

  In the wide-angle lens 20, a negative power lens having a concave shape is arranged on the first lens 21, and a lens having a positive power having a convex shape is arranged on the second lens 22. The total length of the lens system having corners can be suppressed to about 5 mm. Furthermore, since the image-side lens surface 25b of the fifth lens 25 is an aspherical surface having an inflection point, it becomes easy to control the direction of the light beam emitted from the wide-angle lens 20, and the main surface incident on the image formation surface 27 is easy to control. The light incident angle can be reduced. In this example, since the lens surface of each lens is an aspherical surface, the wide-angle lens 20 is brightly configured.

(Example 3)
FIG. 5 is a ray diagram of the wide-angle lens of Example 3. As shown in FIG. 5, the wide-angle lens 30 has a first lens 31 having a negative power, a second lens 32 having a positive power, and a negative power, which are arranged in order from the object side to the image side. It consists of a third lens 33, a fourth lens 34 having negative power, and a fifth lens 35 having positive power. A diaphragm (not shown) is disposed between the first lens 31 and the second lens 32. A cover glass 36 is disposed on the image side of the fifth lens 35. The imaging plane 37 is at a position spaced from the cover glass 36.

  In the first lens 31, each of the object side lens surface 31a and the image side lens surface 31b is an aspherical surface. The object side lens surface 31a has a convex shape, and the image side lens surface 31b has a concave shape. The object side lens surface 31a has a large curvature radius of the convex lens surface portion and is close to a planar shape.

  In the second lens 32, each of the object side lens surface 32a and the image side lens surface 32b is aspheric. The object side lens surface 32a and the image side lens surface 32b each have a convex shape.

  In the third lens 33, each of the object side lens surface 33a and the image side lens surface 33b is aspheric. The object side lens surface 33a has a convex shape, and the image side lens surface 33b has a concave shape. The object-side lens surface 33a has a large curvature radius at the convex lens surface portion and is close to a planar shape.

  In the fourth lens 34, each of the object-side lens surface 34a and the image-side lens surface 34b is aspheric. The object-side lens surface 34a has a convex shape at the central portion including the optical axis, and the image-side lens surface 34b has a concave shape at the central portion including the optical axis.

  In the fifth lens 35, each of the object side lens surface 35a and the image side lens surface 35b is aspheric. The object side lens surface 35a has a convex shape in the central portion including the optical axis. The image side lens surface 35b has an inflection point, and has a concave shape in the central portion including the optical axis. Accordingly, the image-side lens surface 35b is curved toward the object side from the inflection point toward the inner periphery, and is curved toward the object side from the inflection point toward the outer periphery.

The numerical aperture of the wide-angle lens 30 is set to Fno. , The half field angle is ω, the full length of the lens system (the distance from the object side end of the object side lens surface 31a of the first lens 31 to the imaging plane 37) is L, and the lens thickness of the lens system (first lens) When the distance from the object-side end of the object-side lens surface 31a of 31 to the image-side end of the image-side lens surface 35b of the fifth lens 35 is D, these values are as follows.
Fno. = 2.8
ω = 85.3 °
L = 5.069mm
D = 4.017mm

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. When the focal length of the fifth lens 35 is f5, these values are as follows.
f = 2.534
f1 = −3.064
f2 = 1.350
f3 = -2.965
f4 = −3.771
f5 = 2.883

Here, the wide-angle lens 30 of this example satisfies the following conditional expressions (1) to (4).
0.4 ≦ f2 / f = 0.533 ≦ 0.7 (1)
−1 ≦ f2 / f3 = −0.455 ≦ −0.25 (2)
1.0 ≦ D / f = 1.585 ≦ 2.0 (3)
−1.5 ≦ f1 / f = −1.209 ≦ −0.5 (4)

  Since the wide-angle lens 30 satisfies the conditional expressions (1) to (4), it is easy to suppress the entire length of the lens system and secure the back focus while securing an angle of view of 65 ° or more. In addition, axial chromatic aberration can be suppressed.

The wide-angle lens 30 satisfies the following conditional expressions (5) to (9).
−1.4 ≦ f3 / f = −1.170 ≦ −0.6 (5)
−3 ≦ f4 / f = −1.488 ≦ −1 (6)
0.5 ≦ f5 / f = 1.138 ≦ 1.5 (7)
1.3 ≦ L / f = 2.000 ≦ 2.5 (8)
-2 ≦ f4 / f5 = −1.308 ≦ −1 (9)

  Since the wide-angle lens 30 satisfies the conditional expressions (5) to (9), chromatic aberration and curvature of field can be corrected well. In addition, the chief ray incident angle incident on the imaging plane 37 can be reduced. Furthermore, it is easy to suppress the overall length of the lens system while ensuring the back focus.

  Table 3A below shows lens data of each lens surface of the wide-angle lens 30. In Table 3A, each lens surface is specified in the order counted from the object side. In this example, all lens surfaces of each lens are aspheric. The 11th and 12th surfaces are the glass surfaces of the cover glass 36, and the 13th surface is an image plane 37. 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.

(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 wide-angle lens 30. FIG. As shown in FIG. 6A, according to the wide-angle lens 30, the axial chromatic aberration is well corrected. 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 wide-angle lens 30 has a high resolution.

  In the wide-angle lens 30, a negative power lens having a concave shape is disposed on the first lens 31 and a positive power lens having a convex shape is disposed on the second lens 32. The total length of the lens system having corners can be suppressed to about 5 mm. Furthermore, since the image-side lens surface 35b of the fifth lens 35 is an aspherical surface having an inflection point, it becomes easy to control the direction of the light beam emitted from the wide-angle lens 30, and the main surface incident on the imaging surface 37 is made. The light incident angle can be reduced. In this example, since the lens surface of each lens is an aspherical surface, the wide-angle lens 30 is configured to be bright.

Example 4
FIG. 7 is a ray diagram of the wide-angle lens of Example 4. As shown in FIG. 7, the wide-angle lens 40 has a first lens 41 having a negative power, a second lens 42 having a positive power, and a negative power, which are arranged in order from the object side to the image side. It consists of a third lens 43, a fourth lens 44 having negative power, and a fifth lens 45 having positive power. A diaphragm (not shown) is disposed between the first lens 41 and the second lens 42. A cover glass 46 is disposed on the image side of the fifth lens 45. The image plane 47 is at a position spaced from the cover glass 46.

  In the first lens 41, each of the object side lens surface 41a and the image side lens surface 41b is aspheric. The object side lens surface 41a has a convex shape, and the image side lens surface 41b has a concave shape. The object side lens surface 41a has a large radius of curvature of the convex lens surface portion and is close to a planar shape.

  In the second lens 42, each of the object side lens surface 42a and the image side lens surface 42b is an aspherical surface. The object side lens surface 42a and the image side lens surface 42b each have a convex shape.

  In the third lens 43, each of the object side lens surface 43a and the image side lens surface 43b is aspheric. The object side lens surface 43a has a convex shape, and the image side lens surface 43b has a concave shape. The object side lens surface 43a has a large curvature radius at the convex lens surface portion and is close to a planar shape.

  In the fourth lens 44, each of the object side lens surface 44a and the image side lens surface 44b is aspherical. The object-side lens surface 44a has a convex shape at the central portion including the optical axis, and the image-side lens surface 44b has a concave shape at the central portion including the optical axis.

  In the fifth lens 45, each of the object side lens surface 45a and the image side lens surface 45b is aspheric. The object side lens surface 45a has a convex shape in the central portion including the optical axis. The image side lens surface 45b has an inflection point, and has a concave shape in the central portion including the optical axis. Accordingly, the image side lens surface 45b is curved toward the object side from the inflection point toward the inner circumference side, and is curved toward the object side from the inflection point toward the outer circumference side.

The numerical aperture of the wide-angle lens 40 is set to Fno. , The half angle of view ω, the full length of the lens system (the distance from the object side end of the object side lens surface 41a of the first lens 41 to the imaging surface 47), and the lens system lens thickness (first lens) Assuming that the distance from the object side end of the object side lens surface 41a of 41 to the image side end of the image side lens surface 45b of the fifth lens 45 is D, these values are as follows.
Fno. = 2.8
ω = 85.6 °
L = 4.238mm
D = 3.184mm

The focal length of the entire lens system is f, the focal length of the first lens 41 is f1, the focal length of the second lens 42 is f2, the focal length of the third lens 43 is f3, and the focal length of the fourth lens 44 is f4. If the focal length of the fifth lens 45 is f5, these values are as follows.
f = 2.535
f1 = −2.398
f2 = 1.154
f3 = −3.057
f4 = −5.852
f5 = 3.463

Here, the wide-angle lens 40 of this example satisfies the following conditional expressions (1) to (4).
0.4 ≦ f2 / f = 0.455 ≦ 0.7 (1)
−1 ≦ f2 / f3 = −0.378 ≦ −0.25 (2)
1.0 ≦ D / f = 1.256 ≦ 2.0 (3)
−1.5 ≦ f1 / f = −0.946 ≦ −0.5 (4)

  Since the wide-angle lens 40 satisfies the conditional expressions (1) to (4), it is easy to suppress the entire length of the lens system and secure the back focus while securing an angle of view of 65 ° or more. In addition, axial chromatic aberration can be suppressed.

The wide-angle lens 40 satisfies the following conditional expressions (5) to (9).
−1.4 ≦ f3 / f = −1.206 ≦ −0.6 (5)
−3 ≦ f4 / f = −2.308 ≦ −1 (6)
0.5 ≦ f5 / f = 1.366 ≦ 1.5 (7)
1.3 ≦ L / f = 1.672 ≦ 2.5 (8)
-2 ≦ f4 / f5 = −1.690 ≦ −1 (9)

  Since the wide-angle lens 40 satisfies the conditional expressions (5) to (9), chromatic aberration and curvature of field can be corrected well. In addition, the chief ray incident angle incident on the imaging surface 47 can be reduced. Furthermore, it is easy to suppress the overall length of the lens system while ensuring the back focus.

  Table 4A below shows lens data of each lens surface of the wide-angle lens 40. In Table 4A, each lens surface is specified in the order counted from the object side. In this example, all lens surfaces of each lens are aspheric. The eleventh and twelfth surfaces are the glass surfaces of the cover glass 46, and the thirteenth surface is the image plane 47. The unit of curvature radius and spacing is millimeters.

  Next, Table 4B and Table 4C show aspherical coefficients for defining the aspherical shape of the aspherical lens surface. In Tables 4B and 4C, the lens surfaces are specified in the order counted from the object side.

(Function and effect)
8A to 8D are longitudinal aberration diagrams, lateral aberration diagrams, field curvature diagrams, and distortion diagrams of the wide-angle lens 40. FIG. As shown in FIG. 8A, according to the wide-angle lens 40, the axial chromatic aberration is corrected well. Further, as shown in FIG. 8B, color bleeding is suppressed. Further, as shown in FIGS. 8C and 8D, the field curvature is corrected well. Therefore, the wide-angle lens 40 has a high resolution.

  In the wide-angle lens 40, a negative power lens having a concave shape is arranged on the first lens 41, and a lens having a positive power having a convex shape is arranged on the second lens 42. The total length of the lens system having corners can be suppressed to 4.3 mm or less. Furthermore, since the image-side lens surface 45b of the fifth lens 45 is an aspherical surface having an inflection point, it becomes easy to control the direction of the light beam emitted from the wide-angle lens 40, and the main surface incident on the imaging surface 47 is made. The light incident angle can be reduced. In this example, since the lens surface of each lens is an aspherical surface, the wide-angle lens 40 is configured to be bright.

(Example 5)
FIG. 9 is a ray diagram of the wide-angle lens of Example 5. As shown in FIG. 9, the wide-angle lens 50 has a first lens 51 having a negative power, a second lens 52 having a positive power, and a negative power, which are arranged in order from the object side to the image side. The third lens 53 includes a fourth lens 54 having a negative power and a fifth lens 55 having a positive power. A diaphragm (not shown) is disposed between the first lens 51 and the second lens 52. A cover glass 56 is disposed on the image side of the fifth lens 55. The image plane 57 is at a position spaced from the cover glass 56.

  In the first lens 51, each of the object side lens surface 51a and the image side lens surface 51b is aspheric. The object side lens surface 51a has a convex shape, and the image side lens surface 51b has a concave shape. The object-side lens surface 51a has a large radius of curvature of the convex lens surface portion and is close to a planar shape.

  In the second lens 52, each of the object-side lens surface 52a and the image-side lens surface 52b is an aspherical surface. The object side lens surface 52a and the image side lens surface 52b each have a convex shape.

  In the third lens 53, each of the object side lens surface 53a and the image side lens surface 53b is aspheric. The object side lens surface 53a has a convex shape, and the image side lens surface 53b has a concave shape. The object-side lens surface 53a has a large curvature radius of a convex lens surface portion and is close to a planar shape.

  In the fourth lens 54, each of the object side lens surface 54a and the image side lens surface 54b is aspheric. The object-side lens surface 54a has a convex shape at the central portion including the optical axis, and the image-side lens surface 54b has a concave shape at the central portion including the optical axis.

  In the fifth lens 55, each of the object side lens surface 55a and the image side lens surface 55b is aspheric. The object side lens surface 55a has a convex shape in the central portion including the optical axis. The image side lens surface 55b has an inflection point, and has a concave shape in the central portion including the optical axis. Accordingly, the image-side lens surface 55b is curved toward the object side from the inflection point toward the inner periphery, and is curved toward the object side from the inflection point toward the outer periphery.

The numerical aperture of the wide-angle lens 50 is set to Fno. , The half field angle is ω, the entire length of the lens system (the distance from the object side end of the object side lens surface 51a of the first lens 51 to the imaging surface 57) is L, and the lens thickness of the lens system (first lens) Assuming that the distance from the object side end of the object side lens surface 51a of 51 to the image side end of the image side lens surface 55b of the fifth lens 55 is D, these values are as follows.
Fno. = 2.8
ω = 85.7 °
L = 4.298mm
D = 3.348mm

The focal length of the entire lens system is f, the focal length of the first lens 51 is f1, the focal length of the second lens 52 is f2, the focal length of the third lens 53 is f3, and the focal length of the fourth lens 54 is f4. When the focal length of the fifth lens 55 is f5, these values are as follows.
f = 2.535
f1 = −2.398
f2 = 1.131
f3 = −2.813
f4 = −4.739
f5 = 3.371

Here, the wide-angle lens 50 of this example satisfies the following conditional expressions (1) to (4).
0.4 ≦ f2 / f = 0.446 ≦ 0.7 (1)
−1 ≦ f2 / f3 = −0.402 ≦ −0.25 (2)
1.0 ≦ D / f = 1.321 ≦ 2.0 (3)
−1.5 ≦ f1 / f = −0.941 ≦ −0.5 (4)

  Since the wide-angle lens 50 satisfies the conditional expressions (1) to (4), it is easy to suppress the entire length of the lens system and secure the back focus while securing an angle of view of 65 ° or more. In addition, axial chromatic aberration can be suppressed.

The wide-angle lens 50 satisfies the following conditional expressions (5) to (9).
-1.4 ≦ f3 / f = −1.110 ≦ −0.6 (5)
−3 ≦ f4 / f = −1.870 ≦ −1 (6)
0.5 ≦ f5 / f = 1.330 ≦ 1.5 (7)
1.3 ≦ L / f = 1.696 ≦ 2.5 (8)
-2 ≦ f4 / f5 = −1.406 ≦ −1 (9)

  Since the wide-angle lens 50 satisfies the conditional expressions (5) to (9), chromatic aberration and curvature of field can be corrected well. In addition, the chief ray incident angle incident on the imaging surface 57 can be reduced. Furthermore, it is easy to suppress the overall length of the lens system while ensuring the back focus.

  Table 5A below shows lens data of each lens surface of the wide-angle lens 50. In Table 5A, each lens surface is specified in the order counted from the object side. In this example, all lens surfaces of each lens are aspheric. The eleventh and twelfth surfaces are the glass surfaces of the cover glass 56, and the thirteenth surface is an image plane 57. The unit of curvature radius and spacing is millimeters.

  Next, Tables 5B and 5C show aspherical coefficients for defining the aspherical shape of the aspherical lens surface. In Tables 5B and 5C, the lens surfaces are specified in the order counted from the object side.

(Function and effect)
10A to 10D are a longitudinal aberration diagram, a lateral aberration diagram, a field curvature diagram, and a distortion diagram of the wide-angle lens 50. FIG. As shown in FIG. 10A, according to the wide-angle lens 50, the axial chromatic aberration is corrected well. Further, as shown in FIG. 10B, color bleeding is suppressed. Further, as shown in FIGS. 10C and 10D, the curvature of field is corrected well. Therefore, the wide-angle lens 50 has a high resolution.

  Further, in the wide-angle lens 50, a negative power lens having a concave shape is disposed on the first lens 51, and a positive power lens having a convex shape is disposed on the second lens 52. The total length of the lens system having corners can be suppressed to 4.3 mm or less. Furthermore, since the image-side lens surface 55b of the fifth lens 55 is an aspherical surface having an inflection point, it becomes easy to control the direction of the light beam emitted from the wide-angle lens 50, and the main surface incident on the imaging surface 57 is obtained. The light incident angle can be reduced. In this example, since the lens surface of each lens is an aspherical surface, the wide-angle lens 50 is brightly configured.

(Example 6)
FIG. 11 is a ray diagram of the wide-angle lens of Example 6. As shown in FIG. 11, the wide-angle lens 60 has a first lens 61 having a negative power, a second lens 62 having a positive power, and a negative power, which are arranged in order from the object side to the image side. It consists of a third lens 63, a fourth lens 64 having negative power, and a fifth lens 65 having positive power. A diaphragm (not shown) is disposed between the first lens 61 and the second lens 62. A cover glass 66 is disposed on the image side of the fifth lens 65. The image plane 67 is at a position spaced from the cover glass 66.

  In the first lens 61, each of the object side lens surface 61a and the image side lens surface 61b is aspherical. The object side lens surface 61a has a convex shape, and the image side lens surface 61b has a concave shape. The object side lens surface 61a has a large radius of curvature of the convex lens surface portion and is close to a planar shape.

  In the second lens 62, each of the object side lens surface 62a and the image side lens surface 62b is aspheric. The object side lens surface 62a and the image side lens surface 62b each have a convex shape.

  In the third lens 63, each of the object side lens surface 63a and the image side lens surface 63b is aspheric. The object side lens surface 63a has a convex shape, and the image side lens surface 63b has a concave shape. The object side lens surface 63a has a large radius of curvature of the convex lens surface portion and is close to a planar shape.

  In the fourth lens 64, each of the object side lens surface 64a and the image side lens surface 64b is aspheric. The object-side lens surface 64a has a convex shape at the central portion including the optical axis, and the image-side lens surface 64b has a concave shape at the central portion including the optical axis.

  In the fifth lens 65, each of the object-side lens surface 65a and the image-side lens surface 65b is aspheric. The object side lens surface 65a has a convex shape in the central portion including the optical axis. The image-side lens surface 65b has an inflection point, and has a concave shape at the center including the optical axis. Accordingly, the image-side lens surface 65b is curved toward the object side from the inflection point toward the inner periphery side, and is curved toward the object side from the inflection point toward the outer periphery side.

The numerical aperture of the wide-angle lens 60 is set to Fno. , The half angle of view ω, the full length of the lens system (the distance from the object side end of the object side lens surface 61a of the first lens 61 to the imaging surface 67), L, and the lens thickness of the lens system (first lens) When the distance from the object-side end of the object-side lens surface 61a of 61 to the image-side end of the image-side lens surface 65b of the fifth lens 65 is D, these values are as follows.
Fno. = 2.8
ω = 84.0 °
L = 4.709mm
D = 3.627mm

The focal length of the entire lens system is f, the focal length of the first lens 61 is f1, the focal length of the second lens 62 is f2, the focal length of the third lens 63 is f3, and the focal length of the fourth lens 64 is f4. If the focal length of the fifth lens 65 is f5, these values are as follows.
f = 2.534
f1 = −2.147
f2 = 1.169
f3 = −2.719
f4 = −5.067
f5 = 3.360

Here, the wide-angle lens 60 of this example satisfies the following conditional expressions (1) to (4).
0.4 ≦ f2 / f = 0.461 ≦ 0.7 (1)
−1 ≦ f2 / f3 = −0.430 ≦ −0.25 (2)
1.0 ≦ D / f = 1.431 ≦ 2.0 (3)
−1.5 ≦ f1 / f = −0.847 ≦ −0.5 (4)

  Since the wide-angle lens 60 satisfies the conditional expressions (1) to (4), it is easy to suppress the entire length of the lens system and secure the back focus while securing an angle of view of 65 ° or more. In addition, axial chromatic aberration can be suppressed.

The wide-angle lens 60 satisfies the following conditional expressions (5) to (9).
-1.4 ≦ f3 / f = −1.073 ≦ −0.6 (5)
−3 ≦ f4 / f = −2.000 ≦ −1 (6)
0.5 ≦ f5 / f = 1.326 ≦ 1.5 (7)
1.3 ≦ L / f = 1.858 ≦ 2.5 (8)
−2 ≦ f4 / f5 = −1.508 ≦ −1 (9)

  Since the wide-angle lens 60 satisfies the conditional expressions (5) to (9), chromatic aberration and curvature of field can be corrected well. In addition, the chief ray incident angle incident on the imaging surface 67 can be reduced. Furthermore, it is easy to suppress the overall length of the lens system while ensuring the back focus.

  Table 6A below shows lens data of each lens surface of the wide-angle lens 60. In Table 6A, each lens surface is specified in the order counted from the object side. In this example, all lens surfaces of each lens are aspheric. The 11th and 12th surfaces are the glass surfaces of the cover glass 66, and the 13th surface is an image forming surface 67. The unit of curvature radius and spacing is millimeters.

  Next, Table 6B and Table 6C show aspherical coefficients for defining the aspherical shape of the lens surface that is aspherical. In Tables 6B and 6C, the lens surfaces are specified in the order counted from the object side.

(Function and effect)
12A to 12D are longitudinal aberration diagrams, lateral aberration diagrams, field curvature diagrams, and distortion diagrams of the wide-angle lens 60. FIG. As shown in FIG. 12A, according to the wide-angle lens 60, the axial chromatic aberration is corrected well. Further, as shown in FIG. 12B, color bleeding is suppressed. Further, as shown in FIGS. 12C and 12D, the curvature of field is corrected well. Therefore, the wide-angle lens 60 has a high resolution.

  In the wide-angle lens 60, a negative power lens having a concave shape is arranged on the first lens 61, and a lens having a positive power having a convex shape is arranged on the second lens 62. The total length of the lens system with corners can be suppressed to 4.8 mm or less. Furthermore, since the image-side lens surface 65b of the fifth lens 65 is an aspherical surface having an inflection point, it becomes easy to control the direction of the light beam emitted from the wide-angle lens 60, and the main surface incident on the imaging surface 67 is obtained. The light incident angle can be reduced. In this example, since the lens surface of each lens is an aspherical surface, the wide-angle lens 60 is brightly configured.

(Example 7)
FIG. 13 is a ray diagram of the wide-angle lens of Example 7. As shown in FIG. 13, the wide-angle lens 70 has a first lens 71 having a negative power, a second lens 72 having a positive power, and a negative power, which are arranged in order from the object side to the image side. It consists of a third lens 73, a fourth lens 74 having negative power, and a fifth lens 75 having positive power. A diaphragm (not shown) is disposed between the first lens 71 and the second lens 72. A cover glass 76 is disposed on the image side of the fifth lens 75. The image plane 77 is at a position spaced from the cover glass 76.

  In the first lens 71, each of the object side lens surface 71a and the image side lens surface 71b is aspheric. The object side lens surface 71a has a convex shape, and the image side lens surface 71b has a concave shape. The object side lens surface 71a has a large radius of curvature of the convex lens surface portion and is close to a planar shape.

  In the second lens 72, each of the object side lens surface 72a and the image side lens surface 72b is aspherical. The object side lens surface 72a and the image side lens surface 72b each have a convex shape.

  In the third lens 73, each of the object side lens surface 73a and the image side lens surface 73b is aspheric. The object side lens surface 73a has a convex shape, and the image side lens surface 73b has a concave shape. The object side lens surface 73a has a large radius of curvature of the convex lens surface portion and is close to a planar shape.

  In the fourth lens 74, each of the object-side lens surface 74a and the image-side lens surface 74b is aspheric. The object-side lens surface 74a has a convex shape at the central portion including the optical axis, and the image-side lens surface 74b has a concave shape at the central portion including the optical axis.

  In the fifth lens 75, each of the object side lens surface 75a and the image side lens surface 75b is aspheric. The object side lens surface 75a has a convex shape in the central portion including the optical axis. The image side lens surface 75b has an inflection point, and has a concave shape in the central portion including the optical axis. Accordingly, the image side lens surface 75b is curved toward the object side from the inflection point toward the inner circumference side, and is curved toward the object side from the inflection point toward the outer circumference side.

The numerical aperture of the wide-angle lens 70 is set to Fno. , The half field angle is ω, L is the total length of the lens system (the distance from the object-side end of the object-side lens surface 71a of the first lens 71 to the imaging surface 77), and the lens thickness of the lens system (first lens) When the distance from the object side end of the object side lens surface 71a of 71 to the image side end of the image side lens surface 75b of the fifth lens 75 is D, these values are as follows.
Fno. = 2.8
ω = 84.6 °
L = 4.786mm
D = 3.742mm

The focal length of the entire lens system is f, the focal length of the first lens 71 is f1, the focal length of the second lens 72 is f2, the focal length of the third lens 73 is f3, and the focal length of the fourth lens 74 is f4. If the focal length of the fifth lens 75 is f5, these values are as follows.
f = 2.565
f1 = -1.944
f2 = 1.151
f3 = -2.800
f4 = −5.197
f5 = 3.381

Here, the wide-angle lens 70 of this example satisfies the following conditional expressions (1) to (4).
0.4 ≦ f2 / f = 0.449 ≦ 0.7 (1)
−1 ≦ f2 / f3 = −0.411 ≦ −0.25 (2)
1.0 ≦ D / f = 1.659 ≦ 2.0 (3)
−1.5 ≦ f1 / f = −0.758 ≦ −0.5 (4)

  Since the wide-angle lens 70 satisfies the conditional expressions (1) to (4), it is easy to suppress the entire length of the lens system and secure the back focus while securing an angle of view of 65 ° or more. In addition, axial chromatic aberration can be suppressed.

The wide-angle lens 70 satisfies the following conditional expressions (5) to (9).
−1.4 ≦ f3 / f = −1.092 ≦ −0.6 (5)
−3 ≦ f4 / f = −2.026 ≦ −1 (6)
0.5 ≦ f5 / f = 1.318 ≦ 1.5 (7)
1.3 ≦ L / f = 1.866 ≦ 2.5 (8)
-2 ≦ f4 / f5 = −1.537 ≦ −1 (9)

  Since the wide-angle lens 70 satisfies the conditional expressions (5) to (9), chromatic aberration and curvature of field can be corrected well. In addition, the chief ray incident angle incident on the imaging plane 77 can be reduced. Furthermore, it is easy to suppress the overall length of the lens system while ensuring the back focus.

  Table 7A below shows lens data of each lens surface of the wide-angle lens 70. In Table 7A, each lens surface is specified in the order counted from the object side. In this example, all lens surfaces of each lens are aspheric. The 11th and 12th surfaces are the glass surfaces of the cover glass 76, and the 13th surface is an image plane 77. The unit of curvature radius and spacing is millimeters.

  Next, Table 7B and Table 7C show aspherical coefficients for defining the aspherical shape of the aspherical lens surface. In Tables 7B and 7C, the lens surfaces are specified in the order counted from the object side.

(Function and effect)
14A to 14D are a longitudinal aberration diagram, a lateral aberration diagram, a field curvature diagram, and a distortion diagram of the wide-angle lens 70. FIG. As shown in FIG. 14A, according to the wide-angle lens 70, the axial chromatic aberration is corrected well. Further, as shown in FIG. 14B, color bleeding is suppressed. Further, as shown in FIGS. 14C and 14D, the field curvature is corrected well. Therefore, the wide-angle lens 70 has a high resolution.

  In the wide-angle lens 70, a negative power lens having a concave shape is disposed on the first lens 71, and a positive power lens having a convex shape is disposed on the second lens 72. The total length of the lens system with corners can be suppressed to 4.8 mm or less. Furthermore, since the image-side lens surface 75b of the fifth lens 75 is an aspheric surface having an inflection point, the direction of the light beam emitted from the wide-angle lens 70 can be easily controlled, and the main surface incident on the imaging surface 77 can be controlled. The light incident angle can be reduced. In this example, since the lens surface of each lens is an aspherical surface, the wide-angle lens 70 is configured to be bright.

(Imaging device)
FIG. 15 is an explanatory diagram of an imaging apparatus 100 equipped with the wide angle lens 10 of the present invention. As shown in FIG. 15, the imaging apparatus 100 includes an imaging element 101 in which a sensor surface 101 a is arranged on the imaging surface 17 (focal position) of the wide-angle lens 10. The image sensor 101 is a CCD sensor or a CMOS sensor.

  According to this example, since the overall length L of the lens system of the wide-angle lens 10 is short, the imaging device 100 can be reduced in size. Furthermore, since the chief ray incident angle incident on the image sensor 101 from the wide-angle lens 10 can be suppressed to be small, deterioration of image quality in the image pickup apparatus 100 can be suppressed. That is, these imaging elements 101 have a characteristic that sensitivity is lowered with respect to light incident on the sensor surface 101a 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. In addition, since the resolution of the wide-angle lens 10 is high, the imaging device 100 can have a high resolution by adopting the imaging device 101 having a large number of pixels as the imaging device 101. In addition, the wide-angle lenses 20 to 70 can be mounted on the imaging apparatus 100 in the same manner as the wide-angle lens 10, and the same effect can be obtained in this case.

  In the above example, all the lens surfaces are aspherical. However, if at least two lens surfaces including the image side lens surface of the fifth lens are aspherical, the wide-angle lens can be made bright. It becomes easy.

10, 20, 30, 40, 50, 60, 70 ... Wide-angle lenses 11, 21, 31, 41, 51, 61, 71 ... First lenses 12, 22, 32, 42, 52, 62, 72 ... Second lens 13, 23, 33, 43, 53, 63, 73 ... Third lens 14, 24, 34, 44, 54, 64, 74 ... Fourth lens 15, 25, 35, 45 · 55 · 65 · 75 · · · fifth lens 15b · 25b · 35b · 45b · 55b · 65b · 75b · · · object side lens surface 16 · 26 · 36 · 46 · 56 · 66 · 76 of the fifth lens ... Cover glass 17, 27, 37, 47, 57, 67, 77 ... Imaging surface 100 ... Imaging device 101 ... Imaging element 101a ... Sensor surface D of imaging element ... Lens System lens thickness L ... Overall length of the lens system

Claims (2)

A first lens having negative power, a second lens having positive power, a third lens having negative power, a fourth lens having negative power, arranged in order from the object side to the image side; A fifth lens having positive power,
The image side lens surface of the first lens has a concave shape,
The object side lens surface of the second lens has a convex shape,
The image side lens surface of the fifth lens is an aspherical surface having an inflection point, and the central portion including the optical axis has a concave shape,
At least two lens surfaces including the image-side lens surface of the fifth lens are aspheric surfaces;
A wide-angle lens satisfying the following conditional expression, where f is the focal length of the entire lens system, and f1 is the focal length of the first lens.
-1.5 ≤ f1 / f ≤ -0.5   The wide-angle lens according to claim 1, wherein the angle of view is 65 ° or more.

Images