JP5657697B2 - Imaging lens and imaging apparatus - Google Patents

Description

  The present invention relates to an imaging lens and an imaging apparatus, and more particularly, to an in-vehicle camera, a mobile terminal camera, a surveillance camera, and the like using an imaging element such as a charge coupled device (CCD) or a complementary metal oxide semiconductor (CMOS). The present invention relates to an imaging lens suitable for the imaging, and an imaging device including the imaging lens.

  In recent years, image sensors such as CCDs and CMOSs have been greatly reduced in size and pixels. At the same time, an image pickup apparatus body including these image pickup elements is also downsized, and an image pickup lens mounted thereon is required to be downsized in addition to good optical performance. On the other hand, lenses mounted on in-vehicle cameras, surveillance cameras, etc. have a small F, high weather resistance, can be configured at a low cost, and have an F value so that they can be used even under low illumination conditions. It is required to be small.

  Patent Document 1 below describes an imaging lens that can be used for an in-vehicle camera, a surveillance camera, and the like, and the lens closest to the object side is a negative meniscus lens having a convex surface facing the object side, and is composed of five lenses. Yes. Patent Document 2 listed below describes an imaging lens including five lenses that can be used for a camera equipped with a small CCD and includes an aspherical lens.

JP 2008-008960 A JP 11-142730 A JP 2010-107606 A Japanese Patent Application Laid-Open No. 2003-066328 JP 2000-066091 A Japanese Patent Laid-Open No. 10-213742

  By the way, in recent years, combined use with an image pickup device such as a CCD is common, so that the back focus is long so that various filters can be arranged between the lens system and the image pickup device, and imaging of peripheral rays is performed. It is desired that the telecentricity is high and the chromatic aberration is corrected well so that the incident angle to the element is small. And while satisfying these requirements, it has been required to achieve a smaller, cheaper, higher performance, and smaller F-number as in the past or more than in the past.

  Since the lens systems described in Patent Documents 1 and 3 are all composed of spherical lenses, it is possible to produce a lens with good weather resistance at low cost if the lens material is glass, but when an aspherical surface is used. It is thought that further improvement in performance can be expected. Further, it is considered that the cost can be reduced if the lens material is plastic. The lens system described in Patent Document 2 has a large F value of 2.8 or a lens having a small F value, because the lens on the most object side is a plastic lens. Protective means such as glass is required, which increases costs.

  In view of the above circumstances, the present invention includes an imaging lens that can be configured in a small size and at low cost, has high telecentricity, has a long back focus and a small F value, and can realize good optical performance, and the imaging lens. An object of the present invention is to provide an imaging device.

The first imaging lens of the present invention includes, in order from the object side, a negative first lens, a positive second lens, a negative third lens, a positive fourth lens, and a positive fifth lens. And a diaphragm is disposed between the image side surface of the first lens and the object side surface of the third lens, and the refractive index and Abbe number of the third lens material at the d-line are Nd3 and νd3, respectively. The following conditional expressions (1) and (2) are satisfied.
Nd3 <1.75 (1)
νd3 <35 (2)

  According to the first imaging lens of the present invention, in a lens system having a minimum of five lenses, the power arrangement, the aperture position, etc. in the system are suitably set, and the conditional expressions (1) and (2) are satisfied. Since the material of the three lenses is selected, it can be configured small and inexpensive, has high telecentricity, long back focus, small F value, and high optical performance with various aberrations including chromatic aberration corrected well. Easy to do.

  The second imaging lens of the present invention includes, in order from the object side, a negative first lens, a positive second lens, a negative third lens, a positive fourth lens, and a positive fifth lens. A diaphragm is disposed between the image-side surface of the first lens and the object-side surface of the third lens, and at least one lens surface of each of the third lens, the fourth lens, and the fifth lens is aspheric. In addition, the third lens, the fourth lens, and the fifth lens are all made of plastic.

  According to the second imaging lens of the present invention, in the lens system having a minimum of five lenses, the power arrangement, the aperture position, etc. in the system are suitably set, and the aspherical surface and the plastic lens are suitably arranged. Therefore, it is easy to realize high optical performance that has high telecentricity, long back focus, small F value, and various aberrations including chromatic aberration are well corrected.

  The third imaging lens of the present invention includes, in order from the object side, a negative first lens, a positive second lens, a negative third lens, a positive fourth lens, and a positive fifth lens. A diaphragm is disposed between the image-side surface of the first lens and the object-side surface of the third lens, and at least one lens surface of each of the third lens, the fourth lens, and the fifth lens is aspheric. Yes, the image side surface of the third lens has a negative power at the center and is weaker at the effective diameter end than the center, or has a negative power at the center and is positive at the effective diameter end. It is characterized by having the power of

  According to the third imaging lens of the present invention, in a lens system having a minimum of five lenses, the power arrangement in the system, the aperture position, etc. are suitably set, the aspherical lens is suitably arranged, and the surface shape of the third lens Therefore, it is compact and inexpensive, and has high telecentricity, long back focus, small F value, and high optical performance with various aberrations including chromatic aberration corrected well. Becomes easier.

In the first, second, and third imaging lenses of the present invention, when the refractive index at the d-line of the material of the fourth lens is Nd4 and the refractive index at the d-line of the material of the fifth lens is Nd5, It is preferable that conditional expressions (3) and (4) are satisfied.
Nd4 ≦ 1.68 (3)
Nd5 ≦ 1.68 (4)

In the first, second, and third imaging lenses of the present invention, when the focal length of the entire system is f and the distance on the optical axis between the second lens and the third lens is D23, the following conditional expression ( It is preferable to satisfy 5).
0.05 <D23 / f <0.85 (5)

  In the first, second, and third imaging lenses of the present invention, it is preferable that the first lens is a biconcave lens.

In the first, second, and third imaging lenses of the present invention, the following conditional expression (6) is satisfied when the curvature radii of the object side surface and the image side surface of the fifth lens are R10 and R11, respectively. It is preferable to do.
−1.40 <(R10 + R11) / (R10−R11) <− 0.2 (6)

In the first, second, and third imaging lenses of the present invention, when the focal length of the first lens is f1 and the focal length of the second lens is f2, the following conditional expression (7) is satisfied. It is preferable.
−1.30 <f1 / f2 <−0.65 (7)

  In the first, second, and third imaging lenses of the present invention, the object side surface of the third lens has a negative power at the center, and the negative power is weaker than the center at the effective diameter end. It is preferable.

  In the first, second, and third imaging lenses of the present invention, the image-side surface of the fourth lens has a positive power at the center, and the positive power is weaker than the center at the effective diameter end. Alternatively, it is preferable that the center has positive power and has negative power at the effective diameter end.

  In the first, second, and third imaging lenses of the present invention, the image-side surface of the fifth lens has a positive power at the center and is weaker at the effective diameter end than the center. Alternatively, it is preferable that the center has positive power and has negative power at the effective diameter end.

  In the first, second, and third imaging lenses of the present invention, in the case of an aspheric lens, the concave / convex shape of the surface and the sign of refractive power (power) are considered in the paraxial region unless otherwise noted. Shall. The sign of the radius of curvature in the imaging lens of the present invention is positive when the surface shape is convex on the object side and negative when the surface shape is convex on the image side.

  Note that the “effective diameter of the surface” is a circle consisting of the outermost point in the radial direction (the point farthest from the optical axis) when the point where all the rays that contribute to image formation intersect with the lens surface is considered. It means the diameter, and “effective diameter end” means the outermost point. In a rotationally symmetric system with respect to the optical axis, the figure composed of the outermost points is a circle. However, in a system that is not rotationally symmetric, it may not be a circle. The circle diameter may be considered as the effective diameter. For example, when the lens system is used in combination with an image sensor, the effective diameter can be determined based on the size of the imaging surface of the image sensor, and when the image surface is rectangular, for example, 1/2 of the diagonal length thereof. Can be calculated as the maximum image height.

  An image pickup apparatus of the present invention includes the above-described image pickup lens of the present invention.

  According to the imaging lens of the present invention, since the lens configuration, the aperture position, etc. are suitably set in a lens system having a minimum of 5 lenses, it can be configured to be small and inexpensive, high telecentricity, long back focus, and small F And high optical performance with various aberrations including chromatic aberration corrected satisfactorily.

  According to the image pickup apparatus of the present invention, since the image pickup lens of the present invention is provided, the image pickup lens of the present invention can be configured to be small and inexpensive, and can be used even under low-illumination shooting conditions. Can be obtained.

The figure which shows the structure and optical path of the imaging lens concerning one Embodiment of this invention. The figure for demonstrating the aspherical shape of the image side surface of a 3rd lens The figure for demonstrating another aspherical shape of the image side surface of a 3rd lens The figure which shows the structure and optical path of the imaging lens concerning another embodiment of this invention. Sectional drawing which shows the lens structure of the imaging lens of Example 1 of this invention. Sectional drawing which shows the lens structure of the imaging lens of Example 2 of this invention. Sectional drawing which shows the lens structure of the imaging lens of Example 3 of this invention. Sectional drawing which shows the lens structure of the imaging lens of Example 4 of this invention. Sectional drawing which shows the lens structure of the imaging lens of Example 5 of this invention. Sectional drawing which shows the lens structure of the imaging lens of Example 6 of this invention. Sectional drawing which shows the lens structure of the imaging lens of Example 7 of this invention. Sectional drawing which shows the lens structure of the imaging lens of Example 8 of this invention. Sectional drawing which shows the lens structure of the imaging lens of Example 9 of this invention. Sectional drawing which shows the lens structure of the imaging lens of Example 10 of this invention. Sectional drawing which shows the lens structure of the imaging lens of Example 11 of this invention. Sectional drawing which shows the lens structure of the imaging lens of Example 12 of this invention. Sectional drawing which shows the lens structure of the imaging lens of Example 13 of this invention. Sectional drawing which shows the lens structure of the imaging lens of Example 14 of this invention. Sectional drawing which shows the lens structure of the imaging lens of Example 15 of this invention. Sectional drawing which shows the lens structure of the imaging lens of Example 16 of this invention. Sectional drawing which shows the lens structure of the imaging lens of Example 17 of this invention. Sectional drawing which shows the lens structure of the imaging lens of Example 18 of this invention. Sectional drawing which shows the lens structure of the imaging lens of Example 19 of this invention. Sectional drawing which shows the lens structure of the imaging lens of Example 20 of this invention. Sectional drawing which shows the lens structure of the imaging lens of Example 21 of this invention. Sectional drawing which shows the lens structure of the imaging lens of Example 22 of this invention. Sectional drawing which shows the lens structure of the imaging lens of Example 23 of this invention. FIGS. 27A to 27D are graphs showing aberrations of the imaging lens according to Example 1 of the present invention. 28A to 28D are diagrams showing aberrations of the image pickup lens of Example 2 of the present invention. 29A to 29D are aberration diagrams of the imaging lens of Example 3 of the present invention. 30A to 30D are aberration diagrams of the imaging lens of Example 4 of the present invention. 31 (A) to 31 (D) are graphs showing aberrations of the imaging lens of Example 5 of the present invention. 32A to 32D are aberration diagrams of the imaging lens of Example 6 of the present invention. 33A to 33D are diagrams showing aberrations of the imaging lens according to Example 7 of the present invention. 34A to 34D are aberration diagrams of the imaging lens of Example 8 of the present invention. FIGS. 35A to 35D are graphs showing aberrations of the image pickup lens of Example 9 according to the present invention. 36 (A) to 36 (D) are aberration diagrams of the imaging lens of Example 10 of the present invention. FIGS. 37A to 37D are aberration diagrams of the image pickup lens of Example 11 of the present invention. 38 (A) to 38 (D) are graphs showing aberrations of the imaging lens according to Example 12 of the present invention. 39A to 39D are graphs showing aberrations of the imaging lens according to Example 13 of the present invention. 40A to 40D are aberration diagrams of the imaging lens of Example 14 of the present invention. 41 (A) to 41 (D) are graphs showing aberrations of the image pickup lens of Example 15 of the present invention. 42 (A) to 42 (D) are graphs showing aberrations of the imaging lens according to Example 16 of the present invention. 43A to 43D are aberration diagrams of the imaging lens of Example 17 of the present invention. 44 (A) to 44 (D) are graphs showing aberrations of the imaging lens according to Example 18 of the present invention. 45 (A) to 45 (D) are graphs showing aberrations of the image pickup lens of Example 19 according to the present invention. 46A to 46D are aberration diagrams of the imaging lens of Example 20 of the present invention. 47A to 47D are aberration diagrams of the image pickup lens of Example 21 of the present invention. 48 (A) to 48 (D) are graphs showing aberrations of the image pickup lens of Example 22 of the present invention. 49A to 49D are aberration diagrams of the image pickup lens of Example 23 of the present invention. The figure for demonstrating arrangement | positioning of the vehicle-mounted imaging device concerning embodiment of this invention

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. First, an imaging lens according to an embodiment of the present invention will be described with reference to FIG. FIG. 1 shows a lens cross-sectional view of an imaging lens 1 according to an embodiment of the present invention, an axial light beam 2 from an object point at an infinite distance, and off-axis light beams 3 and 4 at a full field angle 2ω. Indicates. The configuration example shown in FIG. 1 corresponds to an imaging lens of Example 1 described later. In FIG. 1, the left side of the figure is the object side, and the right side is the image side.

  In FIG. 1, the imaging element 5 arranged on the image plane Sim of the imaging lens 1 is also illustrated in consideration of the case where the imaging lens 1 is applied to an imaging apparatus. In FIG. 1, the image pickup device is simply illustrated, but actually, the image pickup surface of the image pickup device 5 is arranged so as to coincide with the position of the image plane Sim. The imaging device 5 converts an optical image formed by the imaging lens 1 into an electrical signal, and for example, a CCD image sensor or a CMOS image sensor can be used.

  When the imaging lens 1 is applied to an imaging apparatus, it is preferable to provide various filters such as a cover glass, a low-pass filter, or an infrared cut filter according to the configuration on the camera side on which the lens is mounted. In this example, the parallel plate-like optical member PP assuming these is arranged between the lens closest to the image side and the image sensor 5 (image plane Sim). In particular, when the image pickup lens 1 is used together with the image pickup device 5, a cover glass and various filters are often disposed between the lens system and the image plane Sim, which is sufficient to dispose these in the lens system. Back focus is needed.

  The imaging lens 1 includes a negative first lens L1, a positive second lens L2, a negative third lens L3, a positive fourth lens L4, and a positive lens in order from the object side along the optical axis Z. The fifth lens L5 is provided, and the aperture stop St is disposed between the image-side surface of the first lens L1 and the object-side surface of the third lens L3. These are the basic configurations.

  By disposing the first negative lens L1 closest to the object side and the positive fourth lens L4 and the positive fifth lens L5 on the image side, the lens system can be a retrofocus type lens system. It is easy to widen the angle and the back focus can be made long.

  As in the example shown in FIG. 1, the aperture stop St is arranged between the second lens L2 and the third lens L3, and in order from the object side, negative, positive, aperture stop St, negative, positive, positive power arrangement, In this case, the power on the object side and the image side of the aperture stop St can be made substantially equal, and the field curvature can be easily corrected. By positioning the aperture stop St substantially in the middle of the lens system, the height of the light beam in each lens can be suppressed and the lens diameter can be reduced, which is advantageous for downsizing and cost reduction.

  As shown in an example described later, an aperture stop St is arranged between the first lens L1 and the second lens L2, and in order from the object side, negative, aperture stop St, positive, negative, positive, positive power arrangement and In this case, the light beam height in the first lens L1 can be suppressed, and the lens diameter of the portion exposed to the outside can be reduced, which is advantageous for downsizing. In addition, since the exit pupil position can be brought to the object side, the angle at which the peripheral rays are incident on the image sensor 5 can be suppressed, shading can be suppressed, and the third lens L3 and the fourth lens L4. In the fifth lens L5, the on-axis light beam and the off-axis light beam can be easily separated, and the field curvature can be easily corrected.

  The aperture stop St may be arranged so that the position of the aperture stop St in the optical axis direction is between the object-side surface vertex and the image-side surface vertex of the second lens L2. By arranging in this way, the light beam height in each lens can be suppressed, and the radial direction of the lens system can be made smaller.

  The positive power arranged closest to the image side is divided into two lenses, the fourth lens L4 and the fifth lens L5, so that the spherical aberration can be easily corrected, and even in a lens system having a small F-number. Aberration can be corrected satisfactorily.

  By using the third lens L3 as a negative lens and the fourth lens L4 and the fifth lens L5 as positive lenses, the angle at which peripheral rays enter the image sensor can be reduced while suppressing chromatic aberration, and the telecentricity is good. A lens system can be realized.

  The imaging lens 1 shown in FIG. 1 preferably has a configuration described below as appropriate in accordance with required specifications in addition to the above basic configuration. In addition, as a preferable aspect, it may have any one of the following configurations, or may have a configuration in which any two or more are combined.

When the refractive index and Abbe number at the d-line of the third lens material are Nd3 and νd3, respectively, it is preferable that the following conditional expressions (1) and (2) are satisfied.
Nd3 <1.75 (1)
νd3 <35 (2)

  When the conditional expression (1) is satisfied, the third lens L3 can be manufactured at a low cost, and the cost of the entire lens system can be reduced. Further, by satisfying conditional expression (2), it is possible to satisfactorily correct axial chromatic aberration and lateral chromatic aberration.

For cost reduction, it is preferable to satisfy the following conditional expression (1-2) instead of the conditional expression (1), more preferably to satisfy the following conditional expression (1-3), It is even more preferable that the formula (1-4) is satisfied.
Nd3 <1.70 (1-2)
Nd3 <1.68 (1-3)
Nd3 <1.66 (1-4)

The negative third lens L3 has a function of enhancing telecentricity while suppressing chromatic aberration in cooperation with the positive fourth lens L4 and the fifth lens L5, and thus the third lens L3 and the fourth lens. In order to maintain a good power balance between L4 and the fifth lens L5, it is preferable to satisfy the following conditional expression (1-5), and it is more preferable to satisfy the following conditional expression (1-6).
1.55 <Nd3 (1-5)
1.59 <Nd3 (1-6)

In order to satisfactorily correct the longitudinal chromatic aberration and the chromatic aberration of magnification, it is preferable to satisfy the following conditional expression (2-2) instead of the conditional expression (2), and further to the following conditional expression (2- It is more preferable to satisfy 3), and it is even more preferable to satisfy the following conditional expression (2-4).
νd3 <30 (2-2)
νd3 <27 (2-3)
νd3 <26 (2-4)

In order to reduce the cost, it is preferable to satisfy the following conditional expression (2-5), and it is more preferable to satisfy the following conditional expression (2-6).
15 <νd3 (2-5)
20 <νd3 (2-6)

When the refractive index at the d-line of the material of the fourth lens L4 is Nd4 and the refractive index at the d-line of the material of the fifth lens L5 is Nd5, the following conditional expressions (3) and (4) are preferably satisfied. .
Nd4 ≦ 1.68 (3)
Nd5 ≦ 1.68 (4)

  If the upper limit of conditional expression (3) is exceeded, the power of the fourth lens L4 becomes strong, the power balance with the fifth lens L5 is lost, and it becomes difficult to correct spherical aberration, or the third lens L3, When plastic is used for the material of the fourth lens L4 and the fifth lens L5, the balance between the negative power of the third lens L3 and the positive power of the fourth lens L4 and the fifth lens L5 is lost, and the temperature changes. The amount of focus movement will increase. Alternatively, it becomes difficult to select a material having a large Abbe number from currently available optical materials, and it is difficult to correct chromatic aberration.

  If the upper limit of conditional expression (4) is exceeded, the power of the fifth lens L5 becomes strong, the power balance with the fourth lens L4 is lost, and it becomes difficult to correct spherical aberration, or the third lens L3, When plastic is used for the material of the fourth lens L4 and the fifth lens L5, the balance between the negative power of the third lens L3 and the positive power of the fourth lens L4 and the fifth lens L5 is lost, and the temperature changes. The amount of focus movement will increase. Alternatively, it becomes difficult to select a material having a large Abbe number from currently available optical materials, and it is difficult to correct chromatic aberration.

It is preferable that the following conditional expression (5) is satisfied, where f is the focal length of the entire system and D23 is an air space on the optical axis between the second lens L2, the aperture stop St, and the third lens L3.
0.05 <D23 / f <0.85 (5)

  If the upper limit of conditional expression (5) is exceeded, the distance between the second lens L2 and the third lens L3 becomes too large, making it difficult to reduce the overall length and making it difficult to reduce the first lens L1. . If the lower limit of conditional expression (5) is not reached, the distance between the second lens L2 and the third lens L3 becomes too small, and it becomes difficult to correct field curvature and coma well.

When the radius of curvature of the object side surface of the fifth lens L5 is R10 and the radius of curvature of the image side surface of the fifth lens L5 is R11, it is preferable that the following conditional expression (6) is satisfied.
−1.40 <(R10 + R11) / (R10−R11) <− 0.2 (6)

  If (R10 + R11) / (R10−R11) in the conditional expression (6) is a negative value but exceeds the upper limit of the conditional expression (6), the fifth lens L5 has a radius of curvature between the object side surface and the image side surface. Is a biconvex lens whose absolute value is close (the absolute value of the radius of curvature of the object side surface is smaller than the absolute value of the radius of curvature of the image side surface) or the absolute radius of curvature of the object side surface and the image side surface A biconcave lens having a close value (the absolute value of the radius of curvature of the object side surface is smaller than the absolute value of the radius of curvature of the image side surface). Since the biconcave lens is a negative lens, the fifth lens is contrary to the basic configuration requirement that it is a positive lens. Therefore, the upper limit of conditional expression (6) is exceeded when the fifth lens L5 is a biconvex lens in which the absolute values of the radii of curvature of the object-side surface and the image-side surface are close. If it is a simple shape, it will be difficult to correct spherical aberration.

  The lower limit of conditional expression (6) is below the case where the fifth lens L5 is a negative meniscus lens having a convex surface facing the image side or a positive meniscus lens having a convex surface facing the object side. If the lens L5 is a negative meniscus lens having a convex surface facing the image side, the fifth lens is contrary to the basic configuration requirement of a positive lens. When the fifth lens L5 is a positive meniscus lens having a convex surface facing the object side and falls below the lower limit of the conditional expression (6), the difference in the radius of curvature between the object side surface and the image side surface of the fifth lens L5 becomes small. The power of the fourth lens L4 and the fifth lens L5 becomes poor because the positive power becomes too weak and correction of spherical aberration becomes difficult, or the absolute radius of curvature of the object side surface of the fifth lens L5 becomes difficult. The value becomes too small, making it difficult to correct field curvature and coma.

When the focal length of the first lens L1 is f1, and the focal length of the second lens L2 is f2, it is preferable that the following conditional expression (7) is satisfied.
−1.30 <f1 / f2 <−0.65 (7)

  If the upper limit of conditional expression (7) is exceeded, the negative power of the first lens L1 becomes too strong compared to the positive power of the second lens L2, and it becomes easy to widen the angle. It becomes difficult to correct aberrations. Below the lower limit of conditional expression (7), the positive power of the second lens L2 becomes too strong compared to the negative power of the first lens L1, making it difficult to widen the angle and secure the back focus.

When the focal length of the entire system is f and the focal length of the fourth lens L4 is f4, it is preferable that the following conditional expression (8) is satisfied.
0.5 <f4 / f <2.5 (8)

  If the upper limit of conditional expression (8) is exceeded, the power of the fourth lens L4 becomes too weak, making it difficult to correct chromatic aberration well in cooperation with the third lens, or the power of the fourth lens L4. Becomes too weak, the power balance with the fifth lens L5 becomes poor, and correction of spherical aberration becomes difficult. If the lower limit of conditional expression (8) is not reached, the power of the fourth lens L4 becomes too strong, so that the balance of power with the fifth lens L5 becomes poor, and it becomes difficult to correct spherical aberration.

When the focal length of the entire system is f and the air space on the optical axis of the first lens L1 and the second lens L2 is D2, it is preferable to satisfy the following conditional expression (9).
0.1 <D2 / f <0.6 (9)

  If the upper limit of conditional expression (9) is exceeded, the distance between the first lens L1 and the second lens L2 becomes too large, the diameter of the first lens L1 becomes large, and it becomes difficult to achieve miniaturization. . If the lower limit of conditional expression (9) is not reached, the first lens L1 and the second lens L2 are too close together, making it difficult to increase the back focus.

When the focal length of the entire system is f and the combined focal length of the third lens L3 to the fifth lens L5 is f345, it is preferable that the following conditional expression (10) is satisfied.
1.2 <f345 / f <3.8 (10)

  If the upper limit of conditional expression (10) is exceeded, the power of the fourth lens L4 and the fifth lens L5 becomes too weak, or the power of the third lens L3 becomes too strong, and the lens system moves to the imaging device 5. It becomes difficult to suppress the incident angle, and it becomes difficult to manufacture a lens with good telecentricity. Below the lower limit of conditional expression (10), it becomes difficult to correct field curvature and coma well.

When the combined focal length of the first lens L1 and the second lens L2 is f12 and the combined focal length of the third lens L3 to the fifth lens L5 is f345, it is preferable that the following conditional expression (11) is satisfied.
0.1 <| f12 / f345 | <1.8 (11)

  If the upper limit of conditional expression (11) is exceeded, the total length of the optical system becomes long, and the objective of miniaturization cannot be achieved. Below the lower limit of conditional expression (11), it becomes difficult to correct coma and field curvature.

    When the combined focal length of the first lens L1 and the second lens L2 is f12, it is desirable that f12 be a positive value. By setting f12 to a positive value, it becomes easy to correct field curvature and coma.

When the focal length of the entire system is f and the radius of curvature of the object side surface of the first lens L1 is R1, it is preferable that the following conditional expression (12) is satisfied.
-10.0 <R1 / f <-0.5 (12)

  If the upper limit of conditional expression (12) is exceeded, the absolute value of the radius of curvature of the object-side surface of the first lens L1 becomes too small, and widening is easy, but it is difficult to suppress distortion and curvature of field. It becomes. If the lower limit of conditional expression (12) is not reached, the absolute value of the radius of curvature of the object-side surface of the first lens L1 will increase, making it difficult to correct spherical aberration, or reducing the size of the first lens L1 in the radial direction. It becomes difficult.

When the focal length of the entire system is f and the focal length of the third lens L3 is f3, it is preferable that the following conditional expression (13) is satisfied.
−1.5 <f3 / f <−0.2 (13)

  If the upper limit of conditional expression (13) is exceeded, the power of the third lens L3 becomes too strong, making it difficult to suppress the angle of incidence from the lens system to the image sensor 5 and making a lens with good telecentricity. It becomes difficult. If the lower limit of conditional expression (13) is not reached, the power of the third lens L3 becomes too weak, making it difficult to correct chromatic aberration.

When the focal length of the entire system is f and the distance on the optical axis from the object side surface of the first lens L1 to the image plane Sim is L, it is preferable that the following conditional expression (14) is satisfied. Note that L is the air equivalent length for the back focus.
2.5 <L / f <5.0 (14)

  If the upper limit of conditional expression (14) is exceeded, the lens system will be enlarged. If the lower limit of conditional expression (14) is not reached, downsizing can be easily achieved, but widening becomes insufficient or the overall length becomes too short, making it easy to downsize, but reducing the thickness of each lens. Therefore, it becomes difficult to manufacture or causes an increase in cost.

  Here, L is preferably 22 mm or less. If L exceeds 22 mm, the lens system becomes large, and the objective of size reduction cannot be achieved. L is more preferably 20 mm or less, and L is still more preferably 19 mm or less.

When the focal length of the entire system is f and the focal length of the first lens L1 is f1, it is preferable that the following conditional expression (15) is satisfied.
−1.25 <f1 / f <−0.5 (15)

  If the upper limit of conditional expression (15) is exceeded, the power of the first lens L1 becomes too strong, making it difficult to correct field curvature, and the back focus becomes too long. It becomes difficult. If the lower limit of conditional expression (15) is not reached, the power of the first lens L1 becomes too weak, making it difficult to widen the angle and secure the back focus.

When the focal length of the entire system is f and the focal length of the second lens L2 is f2, it is preferable that the following conditional expression (16) is satisfied.
0.4 <f2 / f <1.5 (16)

  If the upper limit of conditional expression (16) is exceeded, the power of the second lens L2 becomes weak, making it difficult to correct the curvature of field, and the balance of power on the object side and the image side of the aperture stop St is lost. It becomes difficult to correct coma. If the lower limit of conditional expression (16) is not reached, the power of the second lens L2 becomes too strong, and the tolerance for errors related to decentration becomes small, which makes manufacturing difficult or causes an increase in cost.

When the radius of curvature of the object side surface of the first lens L1 is R1, and the radius of curvature of the image side surface of the first lens L1 is R2, it is preferable that the following conditional expression (17) is satisfied.
0.05 <(R1 + R2) / (R1-R2) <0.95 (17)

  In the conditional expression (17), (R1 + R2) / (R1-R2) is a positive value and is 1.0 or less because the first lens L1 is a biconcave lens and the absolute value of the radius of curvature of the object side surface is an image. This is the case where the absolute value of the curvature radius of the side surface is larger than the absolute value of the curvature radius of the object side surface or the absolute value of the curvature radius of the image side surface of the biconvex lens. When the first lens L1 is a biconvex lens, it becomes a positive lens and the first lens L1 is contrary to the basic configuration of a negative lens. This is the case when the absolute value of the radius is larger than the absolute value of the radius of curvature of the image side surface. If the upper limit or lower limit of conditional expression (17) is not satisfied, spherical aberration will be undercorrected or overcorrected, and a good image cannot be obtained. If the upper limit of conditional expression (17) is exceeded, it will be difficult to correct field curvature. If the lower limit of conditional expression (17) is not reached, a biconcave lens in which the difference in absolute value of the radius of curvature between the object side surface and the image side surface of the first lens L1 is small will be difficult to correct spherical aberration and coma. It becomes.

When the focal length of the entire system is f and the focal length of the fifth lens L5 is f5, it is preferable that the following conditional expression (18) is satisfied.
0.99 <f5 / f <2.10 (18)

  If the upper limit or lower limit of conditional expression (18) is not satisfied, the power of the fifth lens L5 becomes too strong or too weak, so that the balance of power between the fourth lens L4 and the fifth lens L5 becomes poor, and the spherical surface It becomes difficult to correct aberrations.

  In addition, about said conditional expression (5)-(18), it is preferable to satisfy what changed the minimum and the upper limit further as follows. Further, as a preferable aspect, a conditional expression configured by combining a lower limit change value and an upper limit change value described below may be satisfied.

  As a change value of the lower limit of conditional expression (5), 0.20 is preferable, 0.25 is more preferable, 0.27 is still more preferable, and 0.30 is still more preferable. As a change value of the upper limit of conditional expression (5), 0.62 is preferable, 0.61 is more preferable, and 0.60 is even more preferable.

  As a lower limit change value of the conditional expression (6), −1.30 is preferable, and −1.20 is more preferable. The upper limit change value of conditional expression (6) is preferably -0.3, more preferably -0.4.

  The lower limit change value of conditional expression (7) is preferably -1.25, more preferably -1.20, and even more preferably -1.15. The upper limit change value of conditional expression (7) is preferably -0.75, more preferably -0.85, and even more preferably -0.90.

  As a change value of the lower limit of conditional expression (8), 0.7 is preferable, 0.8 is more preferable, and 0.9 is even more preferable. As an upper limit change value of conditional expression (8), 1.5 is preferable, 1.25 is more preferable, and 1.20 is even more preferable.

  As a change value of the lower limit of conditional expression (9), 0.2 is preferable. The upper limit change value of conditional expression (9) is preferably 0.51.

  As a change value of the lower limit of conditional expression (10), 1.3 is preferable, and 1.4 is more preferable. The upper limit change value of conditional expression (10) is preferably 2.5, more preferably 2.4, even more preferably 2.3, and even more preferably 2.25.

  As a lower limit change value of conditional expression (11), 0.1 is preferable, 0.2 is more preferable, and 0.3 is even more preferable. As an upper limit change value of conditional expression (11), 1.5 is preferable, 1.3 is more preferable, and 1.2 is even more preferable.

  As a change value of the lower limit of conditional expression (12), −6.0 is preferable, −5.5 is more preferable, and −5.2 is even more preferable. The upper limit change value of conditional expression (12) is preferably −1.0, more preferably −1.5, and even more preferably −1.7.

  As a change value of the lower limit of conditional expression (13), -1.2 is preferable, -1.1 is more preferable, -1.0 is still more preferable, and -0.9 is still more preferable. The upper limit change value of conditional expression (13) is preferably -0.3, more preferably -0.4, and even more preferably -0.45.

  As a change value of the lower limit of conditional expression (14), 2.8 is preferable, 3.0 is more preferable, and 3.4 is even more preferable. As an upper limit change value of conditional expression (14), 4.8 is preferable, 4.6 is more preferable, and 4.5 is even more preferable.

  As a change value of the lower limit of conditional expression (15), −1.20 is preferable, −1.15 is more preferable, and −1.10 is even more preferable. As an upper limit change value of conditional expression (15), -0.55 is preferable, -0.6 is more preferable, and -0.8 is still more preferable.

For example, it is preferable to satisfy the following conditional expression (15-2) instead of the conditional expression (15), and it is more preferable to satisfy the following conditional expression (15-3).
-1.15 <f1 / f <−0.55 (15-2)
−1.10 <f1 / f <−0.60 (15-3)

  As a change value of the lower limit of conditional expression (16), 0.6 is preferable, 0.7 is more preferable, and 0.8 is even more preferable. As an upper limit change value of conditional expression (16), 1.3 is preferable, and 1.2 is more preferable.

  As a change value of the lower limit of conditional expression (17), 0.2 is preferable, 0.4 is more preferable, and 0.6 is even more preferable. The upper limit change value of conditional expression (17) is preferably 0.90, more preferably 0.86, and even more preferably 0.79.

  The change value of the lower limit of conditional expression (18) is preferably 1.00, more preferably 1.20, and even more preferably 1.30. As a change value of the upper limit of conditional expression (18), 2.05 is preferable and 1.98 is more preferable.

  The object side surface of the first lens L1 is preferably a concave surface, which makes it possible to increase the negative power of the first lens L1 and facilitate widening of the angle and long back focus. The first lens L1 is preferably a biconcave lens. According to such a configuration, the negative power of the first lens L1 can be increased, which is advantageous for widening the angle and increasing the back focus. It becomes easy.

  The second lens L2 is preferably a biconvex lens. According to such a configuration, the power of the second lens L2 can be increased, and even when the power of the first lens L1 is increased, the second lens L2 can be increased. It becomes easy to increase the power, and the aberration generated in the first lens L1 of the negative lens can be canceled by the aberration generated in the second lens L2 of the positive lens, and correction of spherical aberration, coma aberration, and field curvature can be performed. It becomes easy.

  The third lens L3 is preferably a biconcave lens. According to such a configuration, the power of the third lens L3 can be increased, and axial chromatic aberration and lateral chromatic aberration can be easily corrected.

  The fourth lens L4 is preferably a biconvex lens. According to such a configuration, the power of the fourth lens L4 can be increased, and chromatic aberration can be favorably corrected in cooperation with the third lens L3. It becomes easy.

  The fifth lens L5 is preferably a lens having a convex surface facing the object side, and according to such a configuration, correction of field curvature is facilitated. When the fifth lens L5 is a biconvex lens, it becomes easy to correct curvature of field. When the fifth lens L5 is a meniscus lens having a convex surface directed toward the object side, it is easy to correct spherical aberration.

  In order to realize high resolution performance with a small number of lenses, it is preferable to use an aspheric surface effectively. For this purpose, at least one side of each of the third lens L3, the fourth lens L4, and the fifth lens L5 is used. The lens surface is preferably an aspherical surface.

  The third lens L3 preferably has a biconcave shape in the paraxial region. With such a configuration, the power of the third lens L3 can be increased, and axial chromatic aberration and lateral chromatic aberration can be easily corrected. Become.

  The third lens L3 preferably has an aspheric surface on at least one of the object side and the image side, whereby it is possible to satisfactorily correct axial chromatic aberration and lateral chromatic aberration as well as spherical aberration and field curvature. It becomes easy.

  In an aspherical surface, the center of each lens surface, that is, the intersection between the surface and the optical axis Z is Ci (i is equivalent to the surface number described in the description of the embodiments described later), and a certain point on the lens surface. Is Xi, and the intersection of the normal of the lens surface at the point Xi and the optical axis Z is Pi, the power at the point Xi indicates whether the point Pi is on the object side or the image side of the point Ci. Defined. When the aspheric surface is an object side surface, the power at the point Xi is positive when the point Pi is closer to the image side than the point Ci, and the point Xi when the point Pi is closer to the object side than the point Ci. Power is defined as negative power. Conversely, when the aspheric surface is an image side surface, the power at the point Xi is positive when the point Pi is closer to the object side than the point Ci, and the point when the point Pi is closer to the image side than the point Ci. The power at Xi is defined as negative power.

  Further, in the aspherical surface, a line segment connecting the point Xi and the point Pi is defined as a radius of curvature RXi at the point Xi, and an absolute value of RXi | RXi | = | Xi−Pi |, where the radius of curvature at the point Ci is When the absolute value is | Ri | and the power at the center is the same as that of the point Xi, the shape where the power is weaker than the center at the point Xi is a shape where | RXi | is larger than | Ri | A shape having a stronger power than the center at the point Xi is a shape in which | RXi | is smaller than | Ri |.

  The general description of the aspheric surface can be applied to any aspheric lens surface of the imaging lens. Ci, Xi, Pi, RXi, and Ri in the above description are symbols used for convenience of description, and are not limited. The point Xi in the above description can be an arbitrary point on the lens surface, and can be considered as, for example, an axial ray diameter end point or an effective diameter end point.

  Note that the “on-axis ray diameter” means the point on the outermost point in the radial direction (the point farthest away from the optical axis) when considering the point where all the rays that contribute to the on-axis image formation intersect the lens surface. ), And the “axial ray diameter end” means the outermost point. The axial ray diameter is determined by the F value of the lens system. For example, the axial ray diameter end includes a point where a ray passing through the periphery of the opening of the aperture stop St intersects the lens surface.

  The image-side surface of the third lens L3 is preferably an aspheric surface, which facilitates correction of spherical aberration and field curvature. The image-side surface of the third lens L3 has a negative power at the center, and has a shape in which the negative power is weaker than the center at the effective diameter end, or has a negative power at the center, and is positive at the effective diameter end. A shape having power is preferable. By making the image side surface of the third lens L3 such a shape, it is easy to correct spherical aberration and curvature of field.

  Here, with reference to FIG. 2A, “the shape having negative power at the center and weaker negative power than the center at the effective diameter end” of the image side surface of the third lens L <b> 3 will be described. To do. FIG. 2A shows a sectional view of the third lens L3 and the light beam 6 that determines the effective diameter end, and illustration of other lenses is omitted in order to avoid complication of the drawing. The light ray 6 that determines the effective diameter end is a light ray that passes through the outermost point (the point farthest from the optical axis) in the radial direction when considering the point where all the light rays that contribute to image formation intersect with the lens surface. . The light beam 6 that determines the effective diameter end should be considered for each lens surface.

  In FIG. 2A, the point C7 is the center of the image side surface of the third lens L3, and is the intersection of the image side surface of the third lens L3 and the optical axis Z. A point X7 in FIG. 2A is an effective diameter end point of the image side surface of the third lens L3, and is an intersection of the light beam 6 that determines the effective diameter end and the image side surface of the third lens L3. Here, the intersection of the normal of the lens surface at the point X7 and the optical axis Z is defined as a point P7 as shown in FIG. 2A.

  At this time, a line segment X7-P7 connecting the point X7 and the point P7 is defined as a curvature radius RX7 at the point X7, and the length | X7-P7 | of the line segment X7-P7 is an absolute value | RX7 | It is defined as The radius of curvature at the point C7, that is, the radius of curvature of the center of the image side surface of the third lens L3 is R7, and the absolute value thereof is | R7 |. That is, when the center of curvature in the paraxial region of the object side surface of the third lens L3 is the point O7, the length of the line segment connecting the point C7 and the point O7 is | R7 |.

  “Having negative power at the center” of the image side surface of the third lens L3 means that the paraxial region including the point C7 is concave. Further, “the shape where the negative power is weaker than the center at the effective diameter end” of the image side surface of the third lens L3 means that the point P7 is closer to the image side than the point C7, and the curvature at the point X7. It means a shape in which the absolute value | RX7 | of the radius is larger than the absolute value | R7 | of the radius of curvature at the point C7.

  In FIG. 2A, in order to help understanding, a circle CC7 centered on a point O7 on the optical axis passes through a point C7 with a radius | R7 |, and is drawn with a two-dot chain line, passes through a point X7 with a radius | RX7 | A circle CX7 centered on the upper point P7 is drawn with a broken line. The circle CX7 is larger than the circle CC7, and it is clearly indicated that | RX7 |> | R7 |.

  Next, with reference to FIG. 2B, the “shape having negative power at the center and positive power at the effective diameter end” of the image side surface of the third lens L3 will be described. FIG. 2B shows a sectional view of the third lens L3 and the light beam 6 that determines the effective diameter end as in FIG. 2A, and the other lenses are not shown in order to avoid complication of the drawing.

  In FIG. 2B, the point C7 'is the center of the image side surface of the third lens L3, and is the intersection of the image side surface of the third lens L3 and the optical axis Z. A point X7 'in FIG. 2B is an effective diameter end point of the image-side surface of the third lens L3, and is an intersection of the light beam 6 that determines the effective diameter end and the image-side surface of the third lens L3. Here, the intersection of the normal of the lens surface at the point X7 'and the optical axis Z is defined as a point P7' as shown in FIG. 2B.

  At this time, a line segment X7′-P7 ′ connecting the point X7 ′ and the point P7 ′ is defined as a curvature radius RX7 ′ at the point X7 ′, and the length | X7-P7 | of the line segment X7-P7 is defined as the curvature radius RX7. Is defined as the absolute value | RX7 ′ |. Further, the radius of curvature at the point C7 ', that is, the radius of curvature of the center of the image-side surface of the third lens L3 is R7', and its absolute value is | R7 '|. That is, when the center of curvature in the paraxial region of the object side surface of the third lens L3 is the point O7 ', the length of the line segment connecting the point C7' and the point O7 'is | R7' |.

  “Having negative power at the center” on the image side surface of the third lens L3 means that the paraxial region including the point C7 'is concave. Further, “the shape having a positive power at the effective diameter end” of the image side surface of the third lens L3 is that the point P7 ′ is closer to the object side than the point C7, and the absolute radius of curvature at the point X7 ′ is absolute. The value | RX7 ′ | means a shape larger than the absolute value | R7 ′ | of the radius of curvature at the point C7 ′.

  In FIG. 2B, to help understanding, a circle CC7 ′ passing through the point C7 ′ with a radius | R7 ′ | and centering on the point O7 ′ on the optical axis is drawn with a two-dot chain line, and a point X7 with a radius | RX7 ′ | A circle CX7 ′ passing through “and centering on the point P7 ′ on the optical axis is drawn with a broken line. The circle CX7 'is larger than the circle CC7', and it is clearly indicated that | RX7 '|> | R7' |.

  Further, the image side surface of the third lens L3 has a negative power at the center, and the negative power is weaker than the center at the axial ray diameter end, or the center has a negative power, and the axial surface It is preferable to have positive power at the end of the beam diameter. By making the image side surface of the third lens L3 such a shape, it is easy to correct spherical aberration and curvature of field.

  The object side surface of the third lens L3 is preferably an aspheric surface, which facilitates correction of spherical aberration and curvature of field. The object side surface of the third lens L3 has a negative radius of curvature at the center, that is, has a negative power at the center, and has a shape in which the negative power is weaker than the center at the effective diameter end. It is preferable. By making the object side surface of the third lens L3 into such a shape, it becomes easy to correct spherical aberration and curvature of field.

  Further, it is preferable that the object side surface of the third lens L3 has a negative power at the center and has a shape in which the negative power is weaker at the axial ray end than at the center. By making the object side surface of the third lens L3 into such a shape, it becomes easy to correct spherical aberration and curvature of field. “The shape where the negative power is weaker than the center at the axial ray end” of the object side surface of the third lens L3 means that the point P6 is the point C6 when the point X6 is the axial ray diameter end. It means a shape that is closer to the object side and has an absolute value | RX6 | of the radius of curvature at the point X6 larger than an absolute value | R6 | of the radius of curvature at the point C6.

  The fourth lens L4 preferably has a convex surface in the paraxial region on the object side surface, whereby the positive power of the fourth lens L4 can be increased and while cooperating with the third lens L3. It becomes easy to correct chromatic aberration satisfactorily. More preferably, the fourth lens L4 has a biconvex shape in the paraxial region, and according to such a configuration, the power of the fourth lens L4 can be made stronger and cooperate with the third lens L3. However, it becomes easy to correct chromatic aberration better.

  The fourth lens L4 preferably has at least one of the object side and the image side as an aspheric surface, so that it can satisfactorily correct axial chromatic aberration and lateral chromatic aberration as well as spherical aberration and field curvature. It becomes easy.

  The object-side surface of the fourth lens L4 is preferably an aspherical surface, which facilitates correction of spherical aberration. It is preferable that the object side surface of the fourth lens L4 has a positive power at the center and a shape with a weak positive power at the effective diameter end as compared with the center. By making the object side surface of the fourth lens L4 in such a shape, it becomes easy to correct spherical aberration and curvature of field.

  It is preferable that the object-side surface of the fourth lens L4 has a positive power at the center and has a weaker positive power at the axial ray end than the center. By making the object side surface of the fourth lens L4 in such a shape, it becomes easy to correct spherical aberration and curvature of field.

  The image-side surface of the fourth lens L4 is preferably an aspheric surface, which facilitates correction of spherical aberration. The image side surface of the fourth lens L4 has a positive power at the center, and has a shape in which the positive power is weaker than the center at the effective diameter end, or has a positive power at the center, and is negative at the effective diameter end. A shape having power is preferable. By making the image side surface of the fourth lens L4 such a shape, it becomes easy to correct spherical aberration and curvature of field.

  The image side surface of the fourth lens L4 has a positive power at the center, and has a shape in which the positive power is weaker than the center at the axial ray end, or has a positive power at the center, and at the axial ray end. A shape having a negative power is preferable. By making the image side surface of the fourth lens L4 such a shape, it becomes easy to correct spherical aberration and curvature of field.

  The fifth lens L5 is preferably a lens having a convex shape facing the object side in the paraxial region, and according to such a configuration, correction of field curvature is facilitated. When the fifth lens L5 has a biconvex shape in the paraxial region, correction of field curvature becomes easy. When the fifth lens L5 has a meniscus shape with a convex surface facing the object side in the paraxial region, it is easy to correct spherical aberration.

  The fifth lens L5 preferably has an aspheric surface on at least one of the object side and the image side. This makes it easy to satisfactorily correct spherical aberration, coma aberration, and field curvature, Telecentricity can be improved.

  The object-side surface of the fifth lens L5 is preferably an aspheric surface, which facilitates correction of coma and field curvature. It is preferable that the object-side surface of the fifth lens L5 has a positive power at the center and a shape with a stronger positive power than the center at the effective diameter end. By making the object-side surface of the fifth lens L5 in this shape, coma and field curvature can be easily corrected and telecentricity can be improved.

  It is preferable that the object-side surface of the fifth lens L5 has a positive power at the center and a shape with a stronger positive power than the center at the axial ray end. By setting the object-side surface of the fifth lens L5 to such a shape, it is easy to correct coma and curvature of field.

  The image-side surface of the fifth lens L5 is preferably an aspherical surface, which facilitates correction of spherical aberration. The image-side surface of the fifth lens L5 has a positive power at the center and has a shape in which the positive power is weaker than the center at the effective diameter end, or has a positive power at the center, and is negative at the effective diameter end. A shape having power is preferable. By making the image side surface of the fifth lens L5 into such a shape, it becomes easy to correct spherical aberration and curvature of field.

  The image side surface of the fifth lens L5 has a positive power at the center, and has a shape in which the positive power is weaker than the center at the axial ray end, or has a positive power at the center, and at the axial ray end. A shape having a negative power is preferable. By making the image side surface of the fifth lens L5 into such a shape, it becomes easy to correct spherical aberration and curvature of field.

  When the Abbe number in the d-line of the material of the first lens L1 is νd1, νd1 is preferably 40 or more, and thereby axial chromatic aberration can be corrected well. In order to correct axial chromatic aberration better, νd1 is more preferably 45 or more, even more preferably 55 or more, and even more preferably 60 or more.

  When the Abbe number of the material of the second lens L2 at the d-line is νd2, νd2 is preferably 35 or more, and thus axial chromatic aberration can be corrected well. In order to correct axial chromatic aberration better, νd2 is more preferably 40 or more, and even more preferably 45 or more.

  In addition, when the Abbe number of the material of the fourth lens L4 on the d-line is νd4, νd4 is preferably 40 or more, and thus axial chromatic aberration can be corrected well. In order to correct axial chromatic aberration better, νd4 is more preferably 45 or more, and even more preferably 52 or more.

  When the Abbe number of the material of the fifth lens L5 on the d-line is νd5, νd5 is preferably 40 or more, and thus axial chromatic aberration can be corrected well. In order to correct axial chromatic aberration better, νd5 is more preferably 45 or more, and even more preferably 52 or more.

  Further, it is preferable that the third lens L3, the fourth lens L4, and the fifth lens L5 are all made of plastic. According to such a configuration, it becomes easy to accurately produce an aspherical shape, and it becomes easy to ensure good optical performance, and it is advantageous for cost reduction and weight reduction.

  Although the plastic lens has a drawback that the amount of movement of the focal position is large when the temperature changes, the third lens L3, the fourth lens L4, and the fifth lens L5 are plastic lenses, so that the positive lens when the temperature changes. Since the amount of movement of the focal position due to the lens and the amount of movement of the focal position due to the negative lens can be offset, performance deterioration due to temperature changes can be suppressed.

  In a system in which the ideal image height when the focal length of the entire system is f and the maximum half angle of view is ω is represented by f × tan (ω), the distortion is preferably ± 10% or less. An image with little distortion can be obtained. In the system in which the imaginary height is represented by f × tan (ω), it is more preferable to set the distortion to ± 5% or less, thereby further suppressing image distortion.

  It is preferable that all lenses constituting the lens system are not cemented. For example, when used as an in-vehicle lens, the lens system is required to have high heat resistance and environmental resistance. When a cemented lens is used, a special cement is used to increase the heat resistance and the environment resistance, and a process for increasing the environment resistance is required, resulting in high costs. Therefore, it is preferable that the first lens L1 to the fifth lens L5 are all single lenses.

  When the imaging lens is used in a harsh environment such as an in-vehicle camera or a surveillance camera, the first lens L1 disposed closest to the object side is resistant to surface deterioration due to wind and rain, temperature change due to direct sunlight, Are required to use materials that are resistant to chemicals such as oils and detergents, that is, materials with high water resistance, weather resistance, acid resistance, chemical resistance, etc. Furthermore, it is required to use materials that are hard and hard to break. Sometimes. These requirements can be satisfied by using glass as the material. Moreover, you may use transparent ceramics as a material of the 1st lens L1. In view of the above circumstances and cost reduction, the first lens L1 is preferably a glass spherical lens, but may be a glass aspherical lens when high optical performance is important.

  It should be noted that a protective means for enhancing the strength, scratch resistance and chemical resistance may be applied to the object side surface of the first lens L1, and in this case, the material of the first lens L1 may be plastic. . Such protective means may be a hard coat or a water repellent coat.

  When the refractive index of the material constituting the first lens L1 is Nd1, Nd1 is preferably 1.80 or less. By setting Nd1 to 1.80 or less, it becomes possible to reduce the cost of the material constituting the first lens L1, and to select a material having a large Abbe number, thereby suppressing the occurrence of chromatic aberration. Therefore, it is possible to manufacture a lens having a wide resolution and a good resolution performance.

  Nd1 is more preferably 1.65 or less, and further preferably 1.60 or less. Nd1 is preferably 1.46 or more. If Nd1 is smaller than 1.46, it is possible to select a material with a large Abbe number and suppress the occurrence of chromatic aberration. However, since the material has a high degree of wear and becomes a soft material, for example, in-vehicle When used as a camera lens or a surveillance camera lens, the weather resistance is insufficient. Nd1 is more preferably 1.50 or more.

  The material of the second lens L2 is preferably glass. By using the second lens L2 as a glass lens, the range of selection of the refractive index of the second lens L2 is widened, and the refractive index of the second lens L2 can be increased. By increasing the refractive index of the second lens L2, it is easy to increase the power of the second lens L2, and it becomes easy to correct field curvature.

  When the refractive index of the material constituting the second lens L2 is Nd2, Nd2 is preferably 1.72 or more, more preferably 1.75 or more, and even more preferably 1.80 or more. preferable.

  Depending on the specifications, the material of the second lens L2 may be plastic. By making the second lens L2 plastic, it becomes possible to produce a lens system at low cost. In addition, when an aspheric surface is used for the second lens L2, it is easy to accurately reproduce the aspheric shape, and a high-performance lens can be manufactured.

  When the imaging lens is used as, for example, an in-vehicle camera, it is desired that the imaging lens can be used in a wide temperature range from the outside air in a cold region to the interior of a summer car in a tropical region. For example, under such severe conditions, all lenses may be made of glass. By using the third lens L3, the fourth lens L4, and the fifth lens L5 as glass lenses, a lens system with high heat resistance can be realized.

  Depending on the use of the imaging lens 1, light in a specific wavelength region such as a UV (Ultra Violet) cut filter or an IR (InfraRed) cut filter is blocked, transmitted, or reflected between the lens system and the image sensor 5. Various filters may be inserted. Alternatively, a coat having the same function as such a filter may be applied to the lens surface. Alternatively, a material that absorbs ultraviolet light, blue light, infrared light, or the like may be used as a material of any lens.

  FIG. 1 shows an example in which the optical member PP assuming various filters and the like is arranged between the lens system and the image sensor 5. Instead, these various filters are arranged between the lenses. May be.

  It is desirable that the lens system is composed of only five lenses of the first lens L1, the second lens L2, the third lens L3, the fourth lens L4, and the fifth lens L5. This makes it possible to reduce the cost of the lens system while maintaining good optical performance.

  Note that the light flux that passes outside the effective diameter between the lenses reaches the image plane as stray light and may become a ghost. Therefore, if necessary, it is preferable to provide a light shielding unit that shields the stray light. As the light shielding means, for example, an opaque paint may be applied to a portion outside the effective diameter of the lens, or an opaque plate material may be provided. Alternatively, an opaque plate material may be provided in the optical path of a light beam that becomes stray light to serve as a light shielding unit. Alternatively, a hood that blocks stray light may be disposed further on the object side of the most object side lens. As an example, FIG. 1 shows an example in which the light shielding means 11 is provided outside the effective diameter of the image side surface of the first lens L1. The location where the light shielding means is provided is not limited to the example shown in FIG. 1, and may be arranged between other lenses or between the lenses. For example, in the lens system as shown in FIG. 1, it is preferable to provide a light shielding means for shielding light passing outside the effective diameter between the fourth lens L4 and the fifth lens L5, thereby preventing ghosting. Can do.

  Further, a member such as a diaphragm that blocks the peripheral light beam may be disposed between the lenses so long as the peripheral light amount ratio has no practical problem. A peripheral ray is a ray that passes through a peripheral portion of the entrance pupil of the optical system among rays from an object point outside the optical axis Z. By arranging the member that blocks the peripheral light in this way, the image quality in the periphery of the imaging region can be improved. In addition, it is possible to reduce the ghost by blocking the stray light that generates the ghost with this member. As an example, FIG. 1 shows an example in which a light blocking unit 12 that blocks peripheral rays and stray light is provided on the object side surface of the fifth lens L5. Here, the light shielding means 12 functions as a vignetting diaphragm that performs vignetting.

  Note that the imaging lens of the present invention does not necessarily require the light shielding member that shields the peripheral light as described above. For example, as shown in the configuration diagram of the imaging lens 10 in FIG. A configuration without using a member is also possible, and good optical performance can be obtained even with such a configuration. The imaging lens 10 shown in FIG. 3 corresponds to Example 11 described later.

  Next, numerical examples of the imaging lens of the present invention will be described. Lens cross-sectional views of the imaging lenses of Examples 1 to 23 are shown in FIGS. 4 to 26, respectively. 4 to 26, the left side of the figure is the object side, the right side is the image side, and the aperture stop St and the optical member PP are also illustrated. The aperture stop St in each figure does not indicate the shape or size, but indicates the position on the optical axis Z. In each embodiment, symbols Ri and Di (i = 1, 2, 3,...) In the lens cross-sectional view correspond to Ri and Di of lens data described below.

  Tables 1 to 23 show lens data of the imaging lenses of Examples 1 to 23, respectively. In each table, (A) shows basic lens data, (B) shows various data, and (C) shows aspherical data.

  In the basic lens data, the column of Si indicates the i-th (i = 1, 2, 3,...) Surface number that sequentially increases toward the image side with the surface of the component closest to the object side as the first. The column indicates the radius of curvature of the i-th surface, and the column Di indicates the surface interval on the optical axis Z between the i-th surface and the i + 1-th surface. The sign of the radius of curvature is positive when the surface shape is convex on the object side and negative when the surface shape is convex on the image side. In the column of Ndj, the refractive index with respect to the d-line (wavelength: 587.6 nm) of the j-th (j = 1, 2, 3,...) Optical element that sequentially increases toward the image side with the most object-side lens as the first. The column of νdj indicates the Abbe number for the d-line of the jth optical element. The basic lens data includes the aperture stop St and the optical member PP, and the word “aperture stop” is also described in the column of the radius of curvature of the surface corresponding to the aperture stop St. .

  In various data, L (in Air) is the distance on the optical axis Z from the object-side surface of the first lens L1 to the image plane Sim (the back focus is the air equivalent length), and Bf (in Air) is the most image side. The distance on the optical axis Z from the image side surface of the lens to the image plane Sim (corresponding to back focus, air conversion length), f is the focal length of the entire system, f1 is the focal length of the first lens L1, and f2 is The focal length of the second lens L2, f3 is the focal length of the third lens L3, f4 is the focal length of the fourth lens L4, f5 is the focal length of the fifth lens L5, and f12 is the distance between the first lens L1 and the second lens L2. A combined focal length, f345, is a combined focal length from the third lens L3 to the fifth lens L5.

  The imaging lenses of Examples 1, 3, 6, 7, and 23 are designed assuming that a vignetting diaphragm that is a light shielding unit that shields ambient light and stray light is provided. The surface number and the radius are provided as the vignetting surface number and the vignetting aperture diameter, respectively.

Ｚｄ：非球面深さ（高さＹの非球面上の点から、非球面頂点が接する光軸に垂直な平面に 下ろした垂線の長さ）
Ｙ：高さ（光軸からのレンズ面までの距離）
Ｃ：近軸曲率
ＫＡ、ＲＢｍ：非球面係数（ｍ＝３、４、５、…１０）In the basic lens data, the surface number of the aspheric surface is marked with *, and the value of the paraxial curvature radius (center curvature radius) is shown as the curvature radius of the aspheric surface. The aspheric data shows the surface number of the aspheric surface and the aspheric coefficient for each aspheric surface. The numerical value “E−n” (n: integer) of the aspheric surface data means “× 10 ⁻ⁿ ”, and “E + n” means “× 10 ⁿ ”. The aspheric coefficient is a value of each coefficient KA, RBm (m = 3, 4, 5,... 20) in the aspheric expression represented by the following expression.

Zd: Depth of aspheric surface (length of perpendicular drawn from a point on the aspherical surface of height Y to a plane perpendicular to the optical axis where the aspherical vertex contacts)
Y: Height (distance from the optical axis to the lens surface)
C: paraxial curvature KA, RBm: aspheric coefficient (m = 3, 4, 5,... 10)

  In the table of this specification, numerical values rounded by a predetermined digit are described. As the unit of each numerical value, “mm” is used for the length, but this is an example, and the optical system can be used even with proportional enlargement or reduction, so other appropriate units may be used. it can.

  In all the imaging lenses of Examples 1 to 23, the first lens L1 and the second lens L2 are glass spherical lenses, and the third lens L3, the fourth lens L4, and the fifth lens L5 are plastic aspheric lenses.

  Table 24 shows values corresponding to the conditional expressions (1) to (18) in the imaging lenses of Examples 1 to 23. In Examples 1 to 23, the d-line is used as a reference wavelength, and Table 24 shows values at this reference wavelength.

  The aberration diagrams of the imaging lenses according to Examples 1 to 23 are shown in FIGS. 27 (A) to 27 (D), 28 (A) to 28 (D), and FIG. 29 (A) to FIG. D), FIG. 30 (A) to FIG. 30 (D), FIG. 31 (A) to FIG. 31 (D), FIG. 32 (A) to FIG. 32 (D), FIG. 33 (A) to FIG. 34 (A) to 34 (D), 35 (A) to 35 (D), 36 (A) to 36 (D), 37 (A) to 37 (D), FIG. 38 (A) to FIG. 38 (D), FIG. 39 (A) to FIG. 39 (D), FIG. 40 (A) to FIG. 40 (D), FIG. 41 (A) to FIG. 41 (D), FIG. A) to FIG. 42D, FIG. 43A to FIG. 43D, FIG. 44A to FIG. 44D, FIG. 45A to FIG. 45D, and FIG. FIG. 46 (D), FIG. 47 (A) to FIG. 47 (D), FIG. 48 (A) to FIG. D), shown in FIG. 49 (A) ~ FIG 49 (D).

  Here, the aberration diagram of Example 1 will be described as an example, but the same applies to the aberration diagrams of other Examples. 27 (A), 27 (B), 27 (C), and 27 (D) are respectively spherical aberration, astigmatism, distortion (distortion aberration), and lateral chromatic aberration (for the imaging lens according to Example 1). The aberration diagram of chromatic aberration of magnification) is shown. Fno. Of spherical aberration diagram. Means F value, and ω in other aberration diagrams means half angle of view. The distortion diagram shows the amount of deviation from the ideal image height f × tan (φ) using the focal length f and the angle of view φ (variable treatment, 0 ≦ φ ≦ ω) of the entire system. Each aberration diagram shows aberrations with the d-line (587.56 nm) as the reference wavelength, while the spherical aberration diagram shows the F-line (wavelength 486.13 nm), C-line (wavelength 656.27 nm), and s-line ( The aberration for the sine condition violation amount (denoted as SNC) is also shown, and the magnification chromatic aberration diagram shows the aberration for the F-line, C-line, and s-line. Since the line type of the chromatic aberration diagram of magnification is the same as that of the spherical aberration diagram, the description is omitted.

  As can be seen from the above data, the imaging lenses of Examples 1 to 23 are small and inexpensive, have a small F number of 1.60 to 2.00, and a total angle of view of 45.0 ° to 65.4. It has a sufficiently long back focus, various aberrations are well corrected, and good optical performance. These imaging lenses can be suitably used for surveillance cameras, in-vehicle cameras for taking images of the front, side, rear, etc. of automobiles.

  As an example of use, FIG. 50 illustrates a state in which an imaging apparatus including the imaging lens of the present embodiment is mounted on the automobile 100. In FIG. 50, an automobile 100 includes an on-vehicle camera 101 for imaging a blind spot range on the side surface on the passenger seat side, an on-vehicle camera 102 for imaging a blind spot range on the rear side of the automobile 100, and a rear surface of a rearview mirror. An in-vehicle camera 103 is attached and is used for photographing the same field of view as the driver. The vehicle exterior camera 101, the vehicle exterior camera 102, and the vehicle interior camera 103 are imaging devices according to the embodiment of the present invention. An imaging lens according to the embodiment of the present invention and an optical image formed by the imaging lens are used as electrical signals. An image sensor for conversion.

  Since the imaging lens according to the embodiment of the present invention has the above-described advantages, the exterior cameras 101 and 102 and the interior camera 103 do not impair the appearance of the vehicle, can be configured to be small and inexpensive, and have low illuminance. It can be used even under the above photographing conditions, and a good image with high resolution can be obtained by using the image sensor.

  The present invention has been described with reference to the embodiments and examples. However, the present invention is not limited to the above embodiments and examples, and various modifications can be made. For example, the values of the radius of curvature, the surface interval, the refractive index, the Abbe number, and the aspheric coefficient of each lens component are not limited to the values shown in the above numerical examples, and can take other values.

  Further, in the embodiment of the imaging apparatus, the example in which the present invention is applied to a vehicle-mounted camera has been described with reference to the drawings. However, the present invention is not limited to this application, and for example, a mobile terminal camera or a surveillance camera The present invention can also be applied.

Claims (19)

In order from the object side, a negative first lens, a positive second lens, a negative third lens, a positive fourth lens, and a positive fifth lens,
An aperture is disposed between the image-side surface of the first lens and the object-side surface of the third lens;
An image pickup lens satisfying the following conditional expressions (1) and (2-4), where Nd3 and νd3 are the refractive index and Abbe number at the d-line of the third lens material, respectively.
Nd3 <1.75 (1)
νd3 <26 (2-4) In order from the object side, a negative first lens, a positive second lens, a negative third lens, a positive fourth lens, and a positive fifth lens,
An aperture is disposed between the image-side surface of the first lens and the object-side surface of the third lens;
The first lens is a biconcave lens;
An imaging lens satisfying the following conditional expressions (1) and (2) when the refractive index and Abbe number of the third lens material at the d-line are Nd3 and νd3, respectively.
Nd3 <1.75 (1)
νd3 <35 (2) In order from the object side, a negative first lens, a positive second lens, a negative third lens, a positive fourth lens, and a positive fifth lens,
An aperture is disposed between the image-side surface of the first lens and the object-side surface of the third lens;
When the refractive index and Abbe number at the d-line of the third lens material are Nd3 and νd3, the focal length of the entire system is f, and the air space on the optical axis of the first lens and the second lens is D2. An imaging lens that satisfies the following conditional expressions (1-2), (2), and (9):
Nd3 <1.70 (1-2)
νd3 <35 (2)
0.1 <D2 / f <0.6 (9)   At least one lens surface of each of the third lens, the fourth lens, and the fifth lens is an aspherical surface, and the third lens, the fourth lens, and the fifth lens are all made of plastic. The imaging lens according to any one of claims 1 to 3, characterized in that: At least one lens surface of each of the third lens, the fourth lens, and the fifth lens is an aspheric surface,
The image-side surface of the third lens has a negative power at the center, and the negative power is weaker than the center at the effective diameter end, or the center has a negative power and is positive at the effective diameter end. The imaging lens according to claim 1, wherein the imaging lens has power. When the refractive index at the d-line of the material of the fourth lens is Nd4 and the refractive index at the d-line of the material of the fifth lens is Nd5, the following conditional expressions (3) and (4) are satisfied. The imaging lens according to any one of claims 1 to 5.
Nd4 ≦ 1.68 (3)
Nd5 ≦ 1.68 (4) The following conditional expression (5) is satisfied, where f is the focal length of the entire system and D23 is the distance on the optical axis between the second lens and the third lens. The imaging lens according to claim 1.
0.05 <D23 / f <0.85 (5)   The imaging lens according to claim 1, wherein the first lens is a biconcave lens. The following conditional expression (6) is satisfied, where the curvature radii of the object side surface and the image side surface of the fifth lens are R10 and R11, respectively. Imaging lens.
−1.40 <(R10 + R11) / (R10−R11) <− 0.2 (6) The following conditional expression (7) is satisfied, where f1 is a focal length of the first lens and f2 is a focal length of the second lens. Imaging lens.
−1.30 <f1 / f2 <−0.65 (7)   11. The imaging according to claim 1, wherein the object-side surface of the third lens has a negative power at the center, and a negative power is weaker at the effective diameter end than at the center. lens.   The image side surface of the fourth lens has a positive power at the center and is weaker at the effective diameter end than the center, or has a positive power at the center and is negative at the effective diameter end. The imaging lens according to claim 1, wherein the imaging lens has power.   The image side surface of the fifth lens has a positive power at the center and is weaker at the effective diameter end than at the center, or has a positive power at the center and negative at the effective diameter end. The imaging lens according to claim 1, wherein the imaging lens has power. 14. The imaging lens according to claim 1, wherein the following conditional expression (1-4) is satisfied, where Nd3 is a refractive index of the third lens material at d-line.
Nd3 <1.66 (1-4) The imaging lens according to any one of claims 1 to 14, wherein the following conditional expression (2-4) is satisfied, where νd3 is an Abbe number of the third lens material in the d-line.
νd3 <26 (2-4) The following conditional expression (5-1) is satisfied, where f is the focal length of the entire system and D23 is the distance between the second lens and the third lens on the optical axis. The imaging lens according to any one of 1 to 15.
0.30 <D23 / f <0.60 (5-1) The following conditional expression (6-1) is satisfied, where the curvature radii of the object side surface and the image side surface of the fifth lens are R10 and R11, respectively. The imaging lens described.
−1.20 <(R10 + R11) / (R10−R11) <− 0.4 (6-1) The following conditional expression (7-1) is satisfied, where f1 is a focal length of the first lens and f2 is a focal length of the second lens. The imaging lens described.
-1.15 <f1 / f2 <-0.90 (7-1)   An imaging apparatus comprising the imaging lens according to claim 1.

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