JP2013073159A - Image pickup lens and image pickup apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To implement a compact, inexpensive, wide-angle, and high-performance image pickup lens and eliminate restrictions on an image pickup element to be used.SOLUTION: An image pickup lens 1 comprises substantially six lenses, in order from an object side: a negative first lens L1; a negative second lens L2; a positive third lens L3; a positive fourth lens L4; a negative fifth lens L5; and a positive sixth lens L6. The surface on the object side of the third lens L3 is a recessed surface. When f2 represents the focal length of the second lens L2, f3 represents the focal length of the third lens, and f represents the focal length of the entire system, the image pickup lens satisfies the following conditional expressions (8) and (9): (8) |f2/f|<3.0, and (9) 4.6<f3/f.

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, in applications such as in-vehicle cameras and surveillance cameras, it is required to be compact and can be configured at low cost, and to have a wide angle and high performance.

  The following Patent Documents 1 to 16 disclose a six-lens lens system that can be used for a camera equipped with a small CCD and uses a plastic aspheric lens.

JP-A-2005-221920 JP 2006-171597 A JP 2006-349920 A JP 2007-164079 A JP 2007-249073 A JP 2008-134494 A JP 2010-243709 A Japanese Patent No. 2599312 U.S. Pat. No. 7,023,628 U.S. Pat. No. 7,768,719 U.S. Pat. No. 7,933,078 JP 2010-160479 A JP 2008-76716 A JP 2009-92797 A JP 2009-92798 A JP 2010-009028 A

  By the way, demands for imaging lenses mounted on in-vehicle cameras, surveillance cameras, and the like are becoming stricter year by year, and further downsizing, cost reduction, wide angle, and high performance are desired.

  Here, the lens systems described in Patent Documents 1, 2, 4, 8, 9, and 11 are advantageous in terms of chromatic aberration and sensitivity because of the use of a cemented lens. It is necessary to process, and the cost increases. The lens system described in Patent Document 3 has a half angle of view of 40 ° or less, and the wide angle is insufficient for the wide angle problem as in the present invention. Moreover, since the lens system described in Patent Document 10 is an anamorphic lens, it cannot be manufactured at low cost.

  In view of the circumstances described above, an object of the present invention is to provide an imaging lens that can be reduced in size, cost, wide angle, and high performance, and an imaging apparatus including the imaging lens.

The first imaging lens of the present invention includes, in order from the object side, a negative first lens, a negative second lens, a positive third lens, a positive fourth lens, and a negative fifth lens. Consisting essentially of six lenses with a positive sixth lens,
The object side surface of the third lens is a concave surface;
The following conditional expressions (8) and (9) are satisfied.

| F2 / f | <3.0 (8)
4.6 <f3 / f (9)
However,
f2: focal length of the second lens f3: focal length of the third lens f: focal length of the entire system The second imaging lens of the present invention includes a negative first lens and a negative first lens in order from the object side. It consists essentially of six lenses, two lenses, a positive third lens, a positive fourth lens, a negative fifth lens, and a positive sixth lens,
The object side surface of the third lens is a concave surface;
The fourth lens is a biconvex lens;
The fifth lens is a biconcave lens;
The following conditional expressions (8-1) and (9-1) are satisfied.

| F2 / f | <3.9 (8-1)
4.9 <f3 / f (9-1)
However,
f2: focal length of the second lens f3: focal length of the third lens f: focal length of the entire system The third imaging lens of the present invention includes a negative first lens and a negative first lens in order from the object side. It consists essentially of six lenses, two lenses, a positive third lens, a positive fourth lens, a negative fifth lens, and a positive sixth lens,
The object side surface of the second lens is a convex surface;
The image side surface of the third lens is a convex surface;
The fourth lens is a biconvex lens;
The fifth lens is a biconcave lens;
The following conditional expressions (9) and (10) are satisfied.

4.6 <f3 / f (9)
1.8 <f4 / f (10)
However,
f3: focal length of the third lens f4: focal length of the fourth lens f: focal length of the entire system The fourth imaging lens of the present invention includes a negative first lens and a negative first lens in order from the object side. It consists essentially of six lenses, two lenses, a positive third lens, a positive fourth lens, a negative fifth lens, and a positive sixth lens,
The object side surface of the second lens is a convex surface;
The object side surface of the third lens is a concave surface;
The fourth lens is a biconvex lens;
The fifth lens is a biconcave lens;
The following conditional expressions (9) and (10-1) are satisfied.

4.6 <f3 / f (9)
1.2 <f4 / f (10-1)
However,
f3: focal length of the third lens f4: focal length of the fourth lens f: focal length of the entire system “consisting essentially of six lenses” means substantially power other than six lenses This includes that having a lens without a lens, an optical element other than a lens such as an aperture or a cover glass, a lens flange, a lens barrel, an image sensor, a mechanism portion such as a camera shake correction mechanism, and the like.

  By making the first to fourth imaging lenses of the present invention substantially consist of six lenses, it is possible to obtain good optical performance and to reduce the number of lenses, thereby reducing the size and cost. It becomes possible to suppress.

  In the present invention, the surface shape of a lens such as a convex surface, concave surface, flat surface, biconcave, meniscus, biconvex, plano-convex and plano-concave, and the sign of the refractive power of a lens such as a positive lens and a negative lens are non- Those that contain a spherical surface are considered in the paraxial region unless otherwise noted. In the present invention, 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 first to fourth imaging lenses of the present invention, it is preferable that the following conditional expressions (19) to (23) are satisfied. In addition, as a preferable aspect, what has the structure of any one of following conditional expression (19)-(23) may be sufficient, or it may have the structure which combined arbitrary 2 or more.

1 <(D4 + D5) / f <6 (19)
-1 <f / R5 <1 (20)
-3 <f / R3 <3 (21)
−30 <f23 / f <−3 (22)
2 <f45 / f <25 (23)
However,
D4: Air distance on the optical axis between the second lens and the third lens D5: Center thickness of the third lens f: Focal length of the entire system R5: Curvature radius of the object side surface of the third lens R3: Second lens Radius of curvature f23 of the object side surface: combined focal length of second lens and third lens f45: combined focal length of fourth lens and fifth lens The imaging apparatus of the present invention is the first of the present invention described above. At least one of the fourth imaging lenses is provided.

  According to the first imaging lens of the present invention, in a minimum of six lens systems, the power arrangement in the entire system, the surface shape of the third lens, etc. are suitably set, and the conditional expressions (8) and (9) are satisfied. Therefore, it is possible to achieve downsizing, cost reduction, and wide angle, as well as high optical performance that can correct various aberrations and obtain a good image up to the periphery of the imaging region. A lens can be realized.

  According to the second imaging lens of the present invention, in a minimum of six lens systems, the power arrangement in the entire system, the surface shapes of the third lens, the fourth lens, and the fifth lens are suitably set, and the conditional expression ( Since 8-1) and (9-1) are satisfied, it is possible to achieve downsizing, cost reduction, and widening of the angle, and various aberrations are corrected favorably to the periphery of the imaging region. An imaging lens having high optical performance capable of obtaining an image can be realized.

  According to the third imaging lens of the present invention, in a minimum of six lens systems, the power arrangement in the entire system, the surface shapes of the second lens, the third lens, the fourth lens, and the fifth lens are suitably set. Since the conditional expressions (9) and (10) are satisfied, it is possible to achieve downsizing, cost reduction, and widening of the angle, as well as excellent correction of various aberrations to the periphery of the imaging region. An imaging lens having high optical performance capable of obtaining an image can be realized.

  According to the fourth imaging lens of the present invention, in a minimum of six lens systems, the power arrangement in the entire system, the surface shapes of the second lens, the third lens, the fourth lens, and the fifth lens are suitably set. Since the conditional expressions (9) and (10-1) are satisfied, it is possible to achieve downsizing, cost reduction, and widening of the angle, and various aberrations are corrected well to the periphery of the imaging region. An imaging lens having high optical performance capable of obtaining a good image can be realized.

  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 photographed with a wide angle of view, and a good image with high resolution can be obtained.

The figure which shows the structure and optical path of the imaging lens which concerns on one Embodiment of this invention. The figure for demonstrating the surface shape etc. of a 2nd lens 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. 22A to 22D are graphs showing aberrations of the imaging lens according to Example 1 of the present invention. FIGS. 23A to 23D are aberration diagrams of the image pickup lens of Example 2 of the present invention. FIGS. 24A to 24D are graphs showing aberrations of the imaging lens according to Example 3 of the present invention. 25 (A) to 25 (D) are graphs showing aberrations of the imaging lens according to Example 4 of the present invention. FIGS. 26A to 26D are graphs showing aberrations of the imaging lens according to Example 5 of the present invention. FIGS. 27A to 27D are graphs showing aberrations of the imaging lens according to Example 6 of the present invention. 28A to 28D are diagrams showing aberrations of the imaging lens according to Example 7 of the present invention. FIGS. 29A to 29D are graphs showing aberrations of the imaging lens according to the eighth embodiment of the present invention. 30A to 30D are aberration diagrams of the imaging lens of Example 9 of the present invention. 31 (A) to 31 (D) are graphs showing aberrations of the imaging lens according to Example 10 of the present invention. 32 (A) to 32 (D) are graphs showing aberrations of the imaging lens according to Example 11 of the present invention. 33A to 33D are diagrams showing aberrations of the imaging lens according to the twelfth embodiment of the present invention. 34 (A) to 34 (D) are graphs showing aberrations of the imaging lens according to Example 13 of the present invention. 35 (A) to 35 (D) are graphs showing aberrations of the imaging lens according to Example 14 of the present invention. 36 (A) to 36 (D) are graphs showing aberrations of the image pickup lens of Example 15 of the present invention. 37 (A) to 37 (D) are graphs showing aberrations of the imaging lens according to Example 16 of the present invention. 38 (A) to 36 (D) are graphs showing aberrations of the imaging lens according to Example 17 of the present invention. 39A to 39D are diagrams showing aberrations of the image pickup lens of Example 18 of the present invention. 40A to 40D are aberration diagrams of the imaging lens of Example 19 of the present invention. The figure for demonstrating arrangement | positioning of the vehicle-mounted imaging device which concerns on embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

Embodiment of imaging lens
First, an imaging lens according to an embodiment of the present invention will be described with reference to FIG. FIG. 1 is a diagram illustrating a configuration and an optical path of an imaging lens 1 according to an embodiment of the present invention. The imaging lens 1 shown in FIG. 1 corresponds to an imaging lens according to Example 12 of the present invention described later.

  In FIG. 1, the left side of the drawing is the object side, the right side is the image side, and the axial light beam 2 from an object point at an infinite distance and off-axis light beams 3 and 4 at the full field angle 2ω are also shown. is there. In FIG. 1, the imaging element 5 disposed on the image plane Sim including the image point Pim of the imaging lens 1 is also illustrated in consideration of the case where the imaging lens 1 is applied to the imaging apparatus. 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 a cover glass, a low-pass filter, an infrared cut filter, or the like according to the configuration on the camera side on which the lens is mounted. An example is shown in which an assumed parallel plate-shaped optical member PP is disposed between a lens closest to the image side and the image sensor 5 (image plane Sim).

  First, the configuration of the first embodiment of the present invention will be described. The imaging lens according to the first embodiment of the present invention includes, in order from the object side, a negative first lens L1, a negative second lens L2, a positive third lens L3, and a positive fourth lens L4. , A negative fifth lens L5 and a positive sixth lens L6. In the example shown in FIG. 1, an aperture stop St is disposed between the third lens L3 and the fourth lens L4. Note that the aperture stop St in FIG. 1 does not indicate the shape or size, but indicates the position on the optical axis Z. By disposing the aperture stop St between the third lens L3 and the fourth lens L4, the entire system can be reduced in size. If the aperture stop St is close to the object side, it is easy to reduce the outer diameter of the first lens L1, but if the aperture stop St is too close to the object side, the first lens L1 and the second lens L2 Separation of on-axis rays and off-axis rays becomes difficult, and correction of field curvature becomes difficult. By disposing the aperture stop St between the third lens L3 and the fourth lens L4, it becomes easy to correct the curvature of field while reducing the lens diameter.

  By configuring the imaging lens with a small number of lenses, such as a minimum of six, it is possible to reduce the cost and reduce the total length in the optical axis direction. In addition, the first lens L1 and the second lens L2, which are two lenses disposed on the object side, are both negative lenses, so that it is easy to widen the angle of the entire lens system. Also, by arranging two negative lenses on the most object side, the negative power can be shared by the two lenses, and the incident light from a wide angle of view can be bent step by step. It can be corrected effectively. The positive lens is also composed of the third lens L3, the fourth lens L4, and the sixth lens L6, so that the convergence function for forming an image on the image plane and the correction of each aberration required for the positive lens are performed. Can be shared by the three lenses, and can be corrected effectively.

  By using the third lens L3 as a positive lens, it is possible to favorably correct the curvature of field. By using the fourth lens L4 as a positive lens and the fifth lens L5 as a negative lens, it is possible to satisfactorily correct axial chromatic aberration and lateral chromatic aberration. By using the sixth lens L6 as a positive lens, it is possible to reduce the angle at which peripheral rays are incident on the imaging surface of the imaging lens, and to suppress shading. By using the fourth lens L4 as a positive lens, the fifth lens L5 as a negative lens, and the sixth lens L6 as a positive lens, it is possible to satisfactorily correct spherical aberration and curvature of field. By using negative, negative, positive, positive, negative, and positive power arrangement in order from the object side, a lens system with a small size, wide angle, and good resolution can be obtained even in a lens system with a small F value. Is possible.

  In the imaging lens according to the first embodiment, the object-side surface of the third lens L3 is a concave surface. By making the object side surface of the third lens L3 a concave surface, it is easy to widen the angle, and it is easy to separate the axial ray and the peripheral ray by the first lens L1 and the second lens L2.

  The imaging lens according to the first embodiment of the present invention is configured to satisfy the following conditional expressions (8) and (9).

| F2 / f | <3.0 (8)
4.6 <f3 / f (9)
However,
f2: focal length of the second lens L2 f3: focal length of the third lens L3 f: focal length of the entire system By satisfying the upper limit of the conditional expression (8), it is easy to increase the power of the second lens L2. Accordingly, widening of the angle becomes easy or distortion can be easily corrected. Alternatively, it becomes easy to increase the power of the concave on the object side of the retrofocus type composed of the first lens L1 and the second lens L2, and it is easy to take a long back focus.

  By satisfying the lower limit of conditional expression (9), it is possible to prevent the power of the third lens L3 from becoming too strong, and it becomes easy to ensure the back focus.

  Next, the configuration of the second exemplary embodiment of the present invention will be described. The imaging lens according to the second embodiment of the present invention includes, in order from the object side, a negative first lens L1, a negative second lens L2, a positive third lens L3, and a positive fourth lens L4. , A negative fifth lens L5 and a positive sixth lens L6.

  By configuring the imaging lens with a small number of lenses, such as a minimum of six, it is possible to reduce the cost and reduce the total length in the optical axis direction. In addition, the first lens L1 and the second lens L2, which are two lenses disposed on the object side, are both negative lenses, so that it is easy to widen the angle of the entire lens system. Also, by arranging two negative lenses on the most object side, the negative power can be shared by the two lenses, and the incident light from a wide angle of view can be bent step by step. It can be corrected effectively. The positive lens is also composed of the third lens L3, the fourth lens L4, and the sixth lens L6, so that the convergence function for forming an image on the image plane and the correction of each aberration required for the positive lens are performed. Can be shared by the three lenses, and can be corrected effectively.

  By using the third lens L3 as a positive lens, it is possible to favorably correct the curvature of field. By using the fourth lens L4 as a positive lens and the fifth lens L5 as a negative lens, it is possible to satisfactorily correct axial chromatic aberration and lateral chromatic aberration. By using the sixth lens L6 as a positive lens, it is possible to reduce the angle at which peripheral rays are incident on the imaging surface of the imaging lens, and to suppress shading. By using the fourth lens L4 as a positive lens, the fifth lens L5 as a negative lens, and the sixth lens L6 as a positive lens, it is possible to satisfactorily correct spherical aberration and curvature of field. By using negative, negative, positive, positive, negative, and positive power arrangement in order from the object side, a lens system with a small size, wide angle, and good resolution can be obtained even in a lens system with a small F value. Is possible.

  In the imaging lens according to the second embodiment, the object-side surface of the third lens L3 is a concave surface, the fourth lens L4 is a biconvex lens, and the fifth lens L5 is a biconcave lens. By making the object side surface of the third lens L3 a concave surface, it is easy to widen the angle, and it is easy to separate the axial ray and the peripheral ray by the first lens L1 and the second lens L2. By making the fourth lens L4 a biconvex lens, it becomes easy to increase the power of the fourth lens L4, and it becomes easy to correct axial chromatic aberration and lateral chromatic aberration with the fifth lens L5. By making the fifth lens L5 a biconcave lens, it becomes easy to increase the power of the fifth lens L5, and it becomes easy to correct axial chromatic aberration and lateral chromatic aberration with the fourth lens L4.

  The imaging lens according to the second embodiment of the present invention is configured to satisfy the following conditional expressions (8-1) and (9-1).

| F2 / f | <3.9 (8-1)
4.9 <f3 / f (9-1)
However,
f2: focal length of the second lens L2 f3: focal length of the third lens L3 f: focal length of the entire system By satisfying the upper limit of the conditional expression (8-1), the power of the second lens L2 is increased. This makes it easy to widen the angle or to easily correct the distortion. Alternatively, it becomes easy to increase the power of the concave on the object side of the retrofocus type composed of the first lens L1 and the second lens L2, and it is easy to take a long back focus.

  By satisfying the lower limit of the conditional expression (9-1), it is possible to prevent the power of the third lens L3 from becoming too strong, and it becomes easy to secure the back focus.

  Next, the configuration of the third exemplary embodiment of the present invention will be described. The imaging lens according to the third embodiment of the present invention includes, in order from the object side, a negative first lens L1, a negative second lens L2, a positive third lens L3, and a positive fourth lens L4. , A negative fifth lens L5 and a positive sixth lens L6.

  By configuring the imaging lens with a small number of lenses, such as a minimum of six, it is possible to reduce the cost and reduce the total length in the optical axis direction. In addition, the first lens L1 and the second lens L2, which are two lenses disposed on the object side, are both negative lenses, so that it is easy to widen the angle of the entire lens system. Also, by arranging two negative lenses on the most object side, the negative power can be shared by the two lenses, and the incident light from a wide angle of view can be bent step by step. It can be corrected effectively. The positive lens is also composed of the third lens L3, the fourth lens L4, and the sixth lens L6, so that the convergence function for forming an image on the image plane and the correction of each aberration required for the positive lens are performed. Can be shared by the three lenses, and can be corrected effectively.

  By using the third lens L3 as a positive lens, it is possible to favorably correct the curvature of field. By using the fourth lens L4 as a positive lens and the fifth lens L5 as a negative lens, it is possible to satisfactorily correct axial chromatic aberration and lateral chromatic aberration. By using the sixth lens L6 as a positive lens, it is possible to reduce the angle at which peripheral rays are incident on the imaging surface of the imaging lens, and to suppress shading. By using the fourth lens L4 as a positive lens, the fifth lens L5 as a negative lens, and the sixth lens L6 as a positive lens, it is possible to satisfactorily correct spherical aberration and curvature of field. By using negative, negative, positive, positive, negative, and positive power arrangement in order from the object side, a lens system with a small size, wide angle, and good resolution can be obtained even in a lens system with a small F value. Is possible.

  In the imaging lens according to the third embodiment, the object-side surface of the second lens L2 is a convex surface, the image-side surface of the third lens L3 is a convex surface, and the fourth lens L4 is a biconvex lens. The fifth lens L5 is a biconcave lens. By making the object side surface of the second lens L2 a convex surface, it becomes easy to correct curvature of field and coma. By making the image side surface of the third lens L3 convex, the third lens L3 can have a positive power, and the chromatic aberration of magnification can be corrected well. By making the fourth lens L4 a biconvex lens, it becomes easy to increase the power of the fourth lens L4, and it becomes easy to correct axial chromatic aberration and lateral chromatic aberration with the fifth lens L5. By making the fifth lens L5 a biconcave lens, it becomes easy to increase the power of the fifth lens L5, and it becomes easy to correct axial chromatic aberration and lateral chromatic aberration with the fourth lens L4.

  The imaging lens according to the third embodiment of the present invention is configured to satisfy the following conditional expressions (9) and (10).

4.6 <f3 / f (9)
1.8 <f4 / f (10)
However,
f3: focal length of the third lens L3 f4: focal length of the fourth lens L4 f: focal length of the entire system By satisfying the lower limit of the conditional expression (9), the power of the third lens L3 becomes too strong. Can be prevented, and the back focus can be easily secured.

  By satisfying the lower limit of conditional expression (10), it becomes easy to suppress the power of the fourth lens L4, and it becomes easy to secure the back focus.

  Next, the structure of the 4th Embodiment of this invention is demonstrated. The imaging lens according to the fourth embodiment of the present invention includes, in order from the object side, a negative first lens L1, a negative second lens L2, a positive third lens L3, and a positive fourth lens L4. , A negative fifth lens L5 and a positive sixth lens L6.

  By configuring the imaging lens with a small number of lenses, such as a minimum of six, it is possible to reduce the cost and reduce the total length in the optical axis direction. In addition, the first lens L1 and the second lens L2, which are two lenses disposed on the object side, are both negative lenses, so that it is easy to widen the angle of the entire lens system. Also, by arranging two negative lenses on the most object side, the negative power can be shared by the two lenses, and the incident light from a wide angle of view can be bent step by step. It can be corrected effectively. The positive lens is also composed of the third lens L3, the fourth lens L4, and the sixth lens L6, so that the convergence function for forming an image on the image plane and the correction of each aberration required for the positive lens are performed. Can be shared by the three lenses, and can be corrected effectively.

  By using the third lens L3 as a positive lens, it is possible to favorably correct the curvature of field. By using the fourth lens L4 as a positive lens and the fifth lens L5 as a negative lens, it is possible to satisfactorily correct axial chromatic aberration and lateral chromatic aberration. By using the sixth lens L6 as a positive lens, it is possible to reduce the angle at which peripheral rays are incident on the imaging surface of the imaging lens, and to suppress shading. By using the fourth lens L4 as a positive lens, the fifth lens L5 as a negative lens, and the sixth lens L6 as a positive lens, it is possible to satisfactorily correct spherical aberration and curvature of field. By using negative, negative, positive, positive, negative, and positive power arrangement in order from the object side, a lens system with a small size, wide angle, and good resolution can be obtained even in a lens system with a small F value. Is possible.

  In the imaging lens according to the fourth embodiment, the object-side surface of the second lens L2 is a convex surface, the object-side surface of the third lens L3 is a concave surface, and the fourth lens L4 is a biconvex lens. The fifth lens L5 is a biconcave lens. By making the object side surface of the second lens L2 a convex surface, it becomes easy to correct curvature of field and coma. By making the object side surface of the third lens L3 a concave surface, it is easy to widen the angle, and it is easy to separate the axial ray and the peripheral ray by the first lens L1 and the second lens L2. By making the fourth lens L4 a biconvex lens, it becomes easy to increase the power of the fourth lens L4, and it becomes easy to correct axial chromatic aberration and lateral chromatic aberration with the fifth lens L5. By making the fifth lens L5 a biconcave lens, it becomes easy to increase the power of the fifth lens L5, and it becomes easy to correct axial chromatic aberration and lateral chromatic aberration with the fourth lens L4.

  The imaging lens according to the fourth embodiment of the present invention is configured to satisfy the following conditional expressions (9) and (10-1).

4.6 <f3 / f (9)
1.2 <f4 / f (10-1)
However,
f3: focal length of the third lens L3 f4: focal length of the fourth lens L4 f: focal length of the entire system By satisfying the lower limit of the conditional expression (9), the power of the third lens L3 becomes too strong. Can be prevented, and the back focus can be easily secured.

  By satisfying the lower limit of the conditional expression (10-1), it becomes easy to suppress the power of the fourth lens L4, and it becomes easy to secure the back focus.

  Next, the effects of the imaging lenses according to the first to fourth embodiments of the present invention that are preferably included will be described. In addition, as a preferable aspect, it may have any one of the following configurations, or may have a configuration combining any two or more.

  It is preferable that the following conditional expression (19) is satisfied.

1 <(D4 + D5) / f <6 (19)
However,
D4: Air distance on the optical axis between the second lens L2 and the third lens L3 D5: Center thickness of the third lens L3 f: Focal length of the entire system By satisfying the lower limit of the conditional expression (19), the second The distance between the lens L2 and the third lens L3 and the center thickness of the third lens L3 can be prevented from becoming too small, and the on-axis light beam and the off-axis light beam are separated by the first lens L1 and the second lens L2. This makes it easy to correct field curvature, distortion, and coma. By satisfying the upper limit of the conditional expression (19), it is possible to prevent the distance between the second lens L2 and the third lens L3 and the center thickness of the third lens L3 from becoming too large, and the entire lens can be downsized. Easy to do.

  It is preferable that the following conditional expression (20) is satisfied.

-1 <f / R5 <1 (20)
However,
f: focal length of entire system R5: radius of curvature of object side surface of third lens L3 If the lower limit of conditional expression (20) is not reached, the object side surface of third lens L3 becomes concave toward the object side, and its curvature The radius becomes too small, the power of the third lens L3 becomes weak, and it becomes difficult to correct the chromatic aberration of magnification. If the upper limit of conditional expression (20) is exceeded, the object side surface of the third lens L3 becomes convex toward the object side, the radius of curvature becomes too small, and the power of the third lens L3 becomes too strong. Although chromatic aberration of magnification can be corrected satisfactorily, it is difficult to correct curvature of field and to secure back focus.

  It is preferable that the following conditional expression (21) is satisfied.

-3 <f / R3 <3 (21)
However,
f: focal length of entire system R3: radius of curvature of object side surface of second lens L2 If the lower limit of conditional expression (21) is not reached, the object side surface of second lens L2 becomes concave on the object side, and its curvature Since the radius becomes too small and the light beam is bent sharply on this surface, it becomes difficult to correct the distortion. If the upper limit of conditional expression (21) is exceeded, the object-side surface of the second lens L2 becomes convex and the radius of curvature becomes too small, so that the power of the second lens L2 becomes weak and it becomes difficult to widen the angle. The lens system becomes large.

  It is preferable that the following conditional expression (22) is satisfied.

−30 <f23 / f <−3 (22)
However,
f23: Composite focal length of the second lens L2 and the third lens L3 f: Focal length of the entire system By satisfying the lower limit of the conditional expression (22), it is possible to prevent the power of the second lens L2 from becoming too weak. And widening of the angle becomes easy. By satisfying the upper limit of conditional expression (22), it is possible to prevent the power of the third lens L3 from becoming weak, and it becomes easy to correct the chromatic aberration of magnification, or the power of the second lens L2 becomes too strong. This can be prevented, and the distortion can be easily corrected.

  It is preferable that the following conditional expression (23) is satisfied.

2 <f45 / f <25 (23)
However,
f45: the combined focal length of the fourth lens L4 and the fifth lens L5 f: the focal length of the entire system If the lower limit of the conditional expression (23) is not reached, the combined focal length of the fourth lens L4 and the fifth lens L5 becomes too small. As a result, it is difficult to secure the back focus. If the upper limit of conditional expression (23) is exceeded, the combined focal length of the fourth lens L4 and the fifth lens L5 becomes too large, and it becomes difficult to satisfactorily correct axial chromatic aberration and lateral chromatic aberration.

  It is preferable that the following conditional expression (24) is satisfied.

9 <L / f <20 (24)
However,
L: Distance on the optical axis from the object side surface of the first lens to the image plane (the back focus is the air equivalent length)
f: Focal length of entire system If the upper limit of conditional expression (24) is exceeded, widening of the angle can be easily achieved, but the lens system becomes large. If the lower limit of conditional expression (24) is not reached, the lens system can be miniaturized, but it is difficult to achieve a wide angle.

  It is preferable that the following conditional expression (25) is satisfied.

1 <Bf / f <3 (25)
However,
Bf: Distance on the optical axis from the image side surface of the lens closest to the image side to the image surface (air equivalent length)
f: Focal length of entire system By satisfying the upper limit of conditional expression (25), it is easy to reduce the size of the lens system. Satisfying the lower limit of conditional expression (25) makes it easy to secure the back focus, and makes it easy to dispose various filters, cover glasses, and the like between the lens and the sensor.

  It is preferable that the following conditional expression (26) is satisfied.

1.1 ≦ (R1 + R2) / (R1−R2) ≦ 3.0 (26)
However,
R1: radius of curvature of the object-side surface of the first lens L1 R2: radius of curvature of the image-side surface of the first lens L1 By satisfying conditional expression (26), the convex surface of the first lens L1 faces the object side. Meniscus lens. By using the first lens L1 as a meniscus lens having a convex surface facing the object side, it is possible to capture a wide-angle light beam exceeding 180 ° and to easily correct distortion. By satisfying the upper limit of conditional expression (26), it is possible to prevent the radius of curvature of the object side surface and the image side surface of the first lens L1 from becoming too close, and the power of the first lens L1 is increased. This makes it easy to widen the angle. By satisfying the lower limit of conditional expression (26), it becomes easy to reduce the radius of curvature of the object-side surface of the first lens L1, and distortion can be easily corrected.

  In addition, about each said conditional expression, it is preferable to satisfy what added the upper limit further as follows, or changed the minimum or upper limit. 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. Although the example of a preferable conditional expression change is described below as an example, the example of a change of a conditional expression is not limited to what was described as a formula below, It is good also as what combined the described change value.

  The upper limit of | f2 / f | defined by the conditional expressions (8) and (8-1) is preferably 3.8, which facilitates widening or distortion correction. Further, in order to facilitate the correction of the wide angle or distortion, the upper limit of | f2 / f | is preferably 3.5, more preferably 3.0, and further preferably 2.9. preferable.

  It is preferable to set a lower limit on | f2 / f |. In this case, the lower limit is preferably 1.0, which makes it easy to reduce the diameter of the first lens L1. Furthermore, in order to reduce the diameter of the first lens L1, the lower limit is preferably 2.0, more preferably 2.2, even more preferably 2.73, and 2.75. Even more preferably.

  From the above, it is preferable that the following conditional expressions (8-2) to (8-6) are satisfied, for example.

| F2 / f | <3.8 (8-2)
1.0 <| f2 / f | <3.5 (8-3)
| F2 / f | <2.9 (8-4)
2.0 <| f2 / f | <2.9 (8-5)
2.2 <| f2 / f | <2.9 (8-6)
It is preferable to provide an upper limit for conditional expressions (9) and (9-1). In this case, the upper limit of conditional expressions (9) and (9-1) is preferably set to 13, which makes it easier to correct the curvature of field and the chromatic aberration of magnification. In order to further facilitate correction of field curvature and chromatic aberration of magnification, the upper limit of conditional expressions (9) and (9-1) is preferably 12.5, more preferably 12, and more preferably 10 More preferably, it is more preferably 9.5.

  The lower limit of f3 / f defined by conditional expressions (9) and (9-1) is preferably 4.8, which makes it easy to secure the back focus. In order to make it easier to ensure the back focus, the lower limit of f3 / f is preferably 4.6, more preferably 4.5, even more preferably 4.9. 8 is even more preferable, and 5.3 is even more preferable.

  From the above, it is preferable that the following conditional expressions (9-2) to (9-5) are satisfied, for example.

4.8 <f3 / f <13 (9-2)
4.5 <f3 / f <12 (9-3)
4.8 <f3 / f <10 (9-4)
5.3 <f3 / f <9.5 (9-5)
It is preferable to provide an upper limit to f4 / f defined by conditional expressions (10) and (10-1). In this case, the upper limit is preferably set to 6.0, and thereby the power of the fourth lens L4 is increased. It becomes easy to increase the intensity, and correction of chromatic aberration with the fifth lens L5 is facilitated. Further, in order to facilitate correction of chromatic aberration, the upper limit is preferably 5.0, more preferably 4.0, and even more preferably 3.5.

  The lower limit of f4 / f is preferably 1.2, which makes it easy to secure the back focus. Furthermore, in order to make it easy to ensure the back focus, the lower limit of f4 / f is preferably 1.3, more preferably 1.8, still more preferably 2.0. 7 is even more preferable.

  From the above, it is preferable that the following conditional expressions (10-2) to (10-6) are satisfied, for example.

1.3 <f4 / f (10-2)
2.0 <f4 / f (10-3)
1.8 <f4 / f <5.0 (10-4)
2.0 <f4 / f <4.0 (10-5)
2.7 <f4 / f <3.5 (10-6)
The lower limit of conditional expression (19) is preferably 1.4, which facilitates correction of field curvature, distortion, and coma. In order to further facilitate correction of field curvature, distortion, and coma, the lower limit of conditional expression (19) is preferably 1.7, and more preferably 1.9.

  The upper limit of conditional expression (19) is preferably 5.5, which further facilitates downsizing. In order to further facilitate downsizing, the lower limit of conditional expression (19) is preferably 5.0, and more preferably 4.4.

  From the above, it is preferable that the following conditional expressions (19-1), (19-2), and (19-3) are satisfied, for example.

1.4 <(D4 + D5) / f <5.5 (19-1)
1.7 <(D4 + D5) / f <5.0 (19-2)
1.9 <(D4 + D5) / f <4.4 (19-3)
The lower limit of conditional expression (20) is preferably −0.9, which facilitates correction of chromatic aberration of magnification. In order to further facilitate correction of chromatic aberration of magnification, the lower limit of conditional expression (20) is preferably −0.5, and more preferably −0.2.

  It is preferable to set the upper limit of conditional expression (20) to 0.9, which makes it easier to correct field curvature. In order to further facilitate the correction of the field curvature, the lower limit of conditional expression (20) is preferably 0.5, and more preferably 0.2.

  From the above, it is preferable that the following conditional expressions (20-1), (20-2), and (20-3) are satisfied, for example.

-0.9 <f / R5 <0.9 (20-1)
-0.5 <f / R5 <0.5 (20-2)
-0.2 <f / R5 <0.2 (20-3)
The lower limit of conditional expression (21) is preferably -2.5, which facilitates distortion correction. In order to further easily correct the distortion, the lower limit of the conditional expression (21) is preferably −2.0, and more preferably −1.5.

  It is preferable to set the upper limit of conditional expression (21) to 2.0, which further facilitates widening and downsizing. In order to further facilitate widening and downsizing, the lower limit of conditional expression (21) is preferably 1.5, and more preferably 1.0.

  From the above, it is preferable that the following conditional expressions (21-1), (21-2), and (21-3) are satisfied, for example.

-2.5 <f / R3 <2.0 (21-1)
-2.0 <f / R3 <1.5 (21-2)
-1.5 <f / R3 <1.0 (21-3)
The lower limit of conditional expression (22) is preferably -25, which facilitates widening of the angle. In order to further facilitate the wide angle, the lower limit of conditional expression (22) is preferably −20, and more preferably −19.5.

  It is preferable to set the upper limit of conditional expression (22) to −4, which makes it easier to correct lateral chromatic aberration or distortion. In order to further facilitate correction of chromatic aberration of magnification or distortion, the lower limit of conditional expression (22) is preferably −5, and more preferably −5.5.

  From the above, it is preferable that the following conditional expressions (22-1), (22-2), and (22-3) are satisfied, for example.

−25 <f23 / f <−4 (22-1)
−20 <f23 / f <−5 (22-2)
-19.5 <f23 / f <-5.5 (22-3)
The lower limit of conditional expression (23) is preferably set to 3, which facilitates ensuring the back focus. In order to make it easier to secure the back focus, the lower limit of conditional expression (23) is preferably set to 4, more preferably 4.1.

  The upper limit of conditional expression (23) is preferably set to 22, which makes it easier to correct axial chromatic aberration and lateral chromatic aberration. In order to further easily correct the longitudinal chromatic aberration and the chromatic aberration of magnification, the lower limit of conditional expression (23) is preferably 20 and more preferably 18.

  From the above, it is preferable that the following conditional expressions (23-1), (23-2), and (23-3) are satisfied, for example.

3 <f45 / f <22 (23-1)
4 <f45 / f <20 (23-2)
4.1 <f45 / f <18 (23-3)
The upper limit of conditional expression (24) is preferably 19.8. By setting the upper limit of conditional expression (24) to 19.8, the lens system can be further reduced in size. Furthermore, the upper limit of conditional expression (24) is more preferably 19.3, and even more preferably 19.0.

  The lower limit of conditional expression (24) is preferably 9.5. By setting the lower limit of conditional expression (24) to 9.5, widening of the angle is further facilitated. Furthermore, the lower limit of conditional expression (24) is preferably 10, and more preferably 10.2.

  From the above, it is preferable to satisfy the following conditional expressions (24-1), (24-2), and (24-3), for example.

9.5 <L / f <19.8 (24-1)
10 <L / f <19.3 (24-2)
10.2 <L / f <19.0 (24-3)
The upper limit of conditional expression (25) is preferably 2.95. By setting the upper limit of conditional expression (25) to 2.95, downsizing is further facilitated. For downsizing, the upper limit of conditional expression (25) is more preferably 2.9, more preferably 2.85, and even more preferably 2.3.

  The lower limit of conditional expression (25) is preferably 1.5. By setting the lower limit of conditional expression (25) to 1.5, it becomes easier to secure the back focus. The lower limit of conditional expression (25) is more preferably 1.8, and even more preferably 1.85.

  From the above, it is preferable that the following conditional expressions (25-1) and (25-2) are satisfied, for example.

1.5 <Bf / f <2.95 (25-1)
1.85 <Bf / f <2.85 (25-2)
The upper limit of conditional expression (26) is preferably 2.5, which makes it easier to widen the angle. Further, in order to facilitate widening the angle, the upper limit of conditional expression (26) is preferably 2.0, and more preferably 1.9.

  The lower limit of conditional expression (26) is preferably set to 1.2, which further facilitates distortion correction. Furthermore, the lower limit of conditional expression (26) is preferably 1.3, more preferably 1.4, and even more preferably 1.5.

  From the above, it is preferable that the following conditional expressions (26-1), (26-2), and (26-3) are satisfied, for example.

1.2 ≦ (R1 + R2) / (R1−R2) ≦ 2.5 (26-1)
1.3 ≦ (R1 + R2) / (R1-R2) ≦ 2.0 (26-2)
1.5 ≦ (R1 + R2) / (R1−R2) ≦ 1.9 (26-3)
It is preferable that the aperture stop is disposed between the third lens L3 and the fourth lens L4. By disposing the aperture stop between the third lens L3 and the fourth lens L4, the entire system can be reduced in size. When the aperture stop is close to the object side, it is easy to reduce the outer diameter of the first lens L1, but when the aperture stop is too close to the object side, the first lens L1 and the second lens L2 are on-axis. It becomes difficult to separate the light beam from the off-axis light beam, and it becomes difficult to correct the curvature of field. By disposing the aperture stop between the third lens L3 and the fourth lens L4, it becomes easy to correct the curvature of field while reducing the lens diameter.

  The Abbe number of the material of the first lens L1, the second lens L2, the fourth lens L4, and the sixth lens L6 with respect to the d-line is preferably 40 or more, thereby suppressing the occurrence of chromatic aberration and good resolution performance. Can be obtained. Moreover, it is more preferable to set it as 47 or more.

  It is preferable that the Abbe number of the material of the second lens L2 with respect to the d-line is 50 or more, thereby further suppressing the occurrence of chromatic aberration and obtaining good resolution performance. Moreover, it is more preferable to set it as 52 or more.

  The Abbe number of the material of the sixth lens L6 with respect to the d-line is preferably 50 or more, which can further suppress the occurrence of chromatic aberration and obtain good resolution performance. Moreover, it is more preferable to set it as 52 or more.

  The Abbe number of the material of the third lens L3 with respect to the d-line is preferably 40 or less, which makes it possible to satisfactorily correct lateral chromatic aberration. Further, it is more preferably 30 or less, further preferably 28 or less, and even more preferably 25 or less.

  The Abbe number of the material of the fifth lens L5 with respect to the d-line is preferably 40 or less, which makes it possible to satisfactorily correct lateral chromatic aberration. Further, it is more preferably 30 or less, further preferably 28 or less, still more preferably 25 or less, and even more preferably 20 or less.

  When the Abbe number of the material of the first lens L1 with respect to the d-line is νd1, and the Abbe number of the material of the second lens L2 with respect to the d-line is νd2, νd1 / νd2 is preferably 0.7 or more. Occurrence of chromatic aberration can be suppressed and good resolution performance can be obtained. Furthermore, it is more preferable that it is 0.8 or more. In order to balance the Abbe numbers of the first lens L1 and the second lens L2 and suppress the occurrence of chromatic aberration, νd1 / νd2 is preferably 1.2 or less.

  When the Abbe number of the material of the second lens L2 with respect to the d-line is νd2, and the Abbe number of the material of the third lens L3 with respect to the d-line is νd3, νd2 / νd3 is preferably 2.0 or more. It is possible to satisfactorily correct axial chromatic aberration and lateral chromatic aberration.

  When the Abbe number of the material of the first lens L1 with respect to the d-line is νd1, and the Abbe number of the material of the third lens L3 with respect to the d-line is νd3, νd1 / νd3 is preferably 1.4 or more. It becomes easy to satisfactorily correct axial chromatic aberration and lateral chromatic aberration. Furthermore, in order to satisfactorily correct axial chromatic aberration and lateral chromatic aberration, it is more preferably 1.5 or more.

  When the Abbe number of the material of the first lens L1 with respect to the d-line is νd1, and the Abbe number of the material of the third lens L3 with respect to the d-line is νd3, νd1 / νd3 is preferably 2.5 or less. The Abbe number of the third lens L3 can be prevented from becoming too small, and it becomes easy to make the material of the third lens L3 inexpensive, or the Abbe number of the first lens L1 becomes too large. Therefore, it is easy to increase the refractive index of the first lens L1 to increase the power of the first lens L1, and it is easy to reduce the size of the lens system and correct distortion.

  The refractive index of the material of the first lens L1 with respect to the d-line is preferably 1.90 or less, which makes it easy to make the material of the first lens L1 inexpensive. Furthermore, by using a material having a low refractive index, a material having a large Abbe number can be selected, chromatic aberration can be easily corrected, and good resolution performance can be easily obtained. Further, in order to correct chromatic aberration satisfactorily, it is preferably 1.85 or less.

  The refractive index of the material of the first lens L1 with respect to the d-line is preferably 1.60 or more, which makes it easy to increase the power of the first lens L1, facilitate widening of the angle, and distortion. Correction is easy. Further, in order to facilitate widening and distortion correction, it is more preferably 1.65 or more, and further preferably 1.70 or more.

  The refractive index for the d-line of the material of the second lens L2 is preferably 1.70 or less, which makes it possible to reduce the material of the second lens L2. Furthermore, since the Abbe number becomes small in a material having a high refractive index, chromatic aberration becomes large, and it becomes difficult to obtain good resolution performance. In order to make the material of the second lens L2 inexpensive, it is more preferably 1.65 or less, and further preferably 1.60 or less.

  The refractive index of the material of the second lens L2 with respect to the d-line is preferably set to 1.50 or more, which makes it easy to increase the power of the second lens L2 and easily correct distortion. Moreover, since it becomes easy to increase the power of the second lens L2, it is easy to reduce the size of the lens system.

  The refractive index of the material of the third lens L3 with respect to the d-line is preferably 1.75 or less, which makes it possible to reduce the material of the third lens L3. In order to make the material of the third lens L3 inexpensive, it is more preferably 1.70 or less, further preferably 1.68 or less, and even more preferably 1.65 or less.

  It is preferable that the refractive index of the material of the third lens L3 with respect to the d-line is 1.50 or more, thereby increasing the refractive index of the material of the third lens L3 and increasing the power of the third lens L3. This facilitates correction of chromatic aberration of magnification and curvature of field. In order to increase the refractive index of the third lens L3, it is more preferably 1.55 or more, and further preferably 1.60 or more.

  The refractive index of the fourth lens material with respect to the d-line is preferably 1.80 or less, which makes it possible to reduce the cost of the material of the fourth lens L4. Further, since it becomes easy to select a material having a large Abbe number, it is easy to correct chromatic aberration, and good resolution performance can be obtained.

  It is preferable that the refractive index of the material of the fourth lens L4 with respect to the d-line is 1.50 or more, thereby increasing the refractive index of the material of the fourth lens L4 and increasing the power of the fourth lens L4. It becomes easy. By increasing the power of the fourth lens L4, it becomes easy to correct spherical aberration with the fourth lens L4, and it is easy to bend the light beam greatly with the fourth lens L4, so that the peripheral light beam enters the image sensor. It becomes easy to suppress the angle, and it becomes easy to suppress shading.

  It is preferable that the refractive index of the material of the fifth lens L5 with respect to the d-line is 1.50 or more, thereby increasing the refractive index of the material of the fifth lens L5 and increasing the power of the fifth lens L5. It becomes easy. Further, since it becomes easy to select a material having a large Abbe number, it is easy to correct chromatic aberration, and good resolution performance can be obtained. In order to increase the refractive index of the material of the fifth lens L5, it is more preferably 1.55 or more, further preferably 1.60 or more, still more preferably 1.8 or more, Even more preferably 1.9 or more.

  It is preferable that the refractive index of the material of the sixth lens L6 with respect to the d-line is 1.50 or more, thereby increasing the refractive index of the material of the sixth lens L6 and increasing the power of the sixth lens L6. Therefore, it becomes easy to correct the spherical aberration and to suppress the angle at which the light beam enters the image sensor, and to easily suppress the shading. It is preferable that the refractive index of the material of the sixth lens L6 with respect to the d-line is 1.70 or less. This makes it easy to select a material having a large Abbe number, so that correction of chromatic aberration is facilitated and good resolution is achieved. It becomes easy to obtain performance. In order to correct chromatic aberration, the refractive index of the material of the sixth lens L6 with respect to the d-line is preferably set to 1.60 or less.

  The object-side surface of the second lens L2 is preferably an aspheric surface, which makes it easy to reduce the size and widen the lens system or to easily correct field curvature and distortion. It becomes. In the object side surface of the second lens L2, the center and the effective diameter end both have positive power, and when the positive power between the center and the effective diameter end is compared, the effective diameter end is more positive than the center. It is preferable to use a shape with low power. By forming the object side surface of the second lens L2 in such a shape, it is easy to reduce the lens system and to widen the angle.

  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.

  Further, regarding the aspheric shape, the lens surface i of each lens (i is a symbol representing the corresponding lens surface. For example, when the object side surface of the second lens L2 is represented by 3, the second lens L2 The following description of the object-side surface can be considered as i = 3) When Xi is a certain point on the surface and Pi is the intersection of the normal and the optical axis at that point, the length of Xi-Pi Let (| Xi−Pi |) be the absolute value | RXi | of the radius of curvature at the point Xi, and define Pi as the center of curvature at the point Xi. Further, the intersection of the i-th lens surface and the optical axis is defined as Qi. At this time, the power at the point Xi is defined by whether the point Pi is on the object side or the image side with respect to the point Qi. On the object side surface, the point Pi is located on the image side from the point Qi is defined as positive power, and the case where the point Pi is located on the object side from the point Qi is defined as negative power. On the image side surface, the point Pi is defined as The case where the point is located on the object side from the point Qi is defined as positive power, and the case where the point Pi is located on the image side from the point Qi is defined as negative power.

  When comparing the power of the center and the point Xi, the absolute value of the center radius of curvature (paraxial radius of curvature) is compared with the absolute value of the radius of curvature at the point Xi | RXi | When | RXi | is smaller than the absolute value, it is assumed that the power of the point Xi is stronger than the center. Conversely, when | RXi | is larger than the absolute value of the paraxial radius of curvature, the power at point Xi is weaker than that at the center. This is the same whether the surface is positive power or negative power.

  Here, the shape of the object-side surface of the second lens L2 will be described with reference to FIG. FIG. 2 is an optical path diagram of the imaging lens 1 shown in FIG. In FIG. 2, a point Q3 is the center of the object-side surface of the second lens L2, and is an intersection of the object-side surface of the second lens L2 and the optical axis Z. In FIG. 2, the point X3 on the object side surface of the second lens L2 is at the effective diameter end, and the intersection of the outermost light ray 6 included in the off-axis light beam 3 and the object side surface of the second lens L2. It has become. In FIG. 2, the point X3 is at the effective diameter end, but the point X3 is an arbitrary point on the surface on the second lens object side, and thus can be considered in the same manner at other points.

  At this time, the intersection of the normal of the lens surface at the point X3 and the optical axis Z is a point P3 as shown in FIG. 2, and a line segment X3-P3 connecting the point X3 and the point P3 is a radius of curvature RX3 at the point X3. The length | X3-P3 | of the line segment X3-P3 is defined as the absolute value | RX3 | of the curvature radius RX3. That is, | X3-P3 | = | RX3 |. Further, the radius of curvature at the point Q3, that is, the radius of curvature of the center of the object side surface of the second lens L2 is R3, and its absolute value is | R3 | (not shown in FIG. 2).

  “When both the center and effective diameter end have positive power on the object side surface of the second lens L2 and the positive power between the center and effective diameter end is compared, the effective diameter end is compared with the center. The shape having a weak positive power ”means that when the point X3 is the effective diameter end, the paraxial region including the point Q3 is a convex shape, the point P3 is closer to the image side than the point Q3, and the point X3 This means that the absolute value | RX3 | of the radius of curvature is larger than the absolute value | R3 | of the radius of curvature at the point Q3.

  The object side surface of the second lens L2 may have a shape having positive power at the center and negative power at the effective diameter end. By forming the object side surface of the second lens L2 in such a shape, it is easy to reduce the lens system and to widen the angle.

  The “shape having positive power at the center and negative power at the effective diameter end” of the object side surface of the second lens L2 is shown in FIG. 2 when the point X3 is the effective diameter end. Thus, the paraxial region including the point Q3 has a convex shape, and the point P3 means a shape on the object side of the point Q3.

  It is preferable that the object side surface of the second lens L2 has a negative power at the center and includes a portion having a positive power between the center and the effective diameter end. By forming the object side surface of the second lens L2 in such a shape, the lens system can be reduced in size and widened, and at the same time, the curvature of field can be corrected well.

  “A shape including a portion having a negative power at the center and a positive power between the center and the effective diameter end” of the object side surface of the second lens L2 is a paraxial region including the point Q3. Means a shape in which a point X3 in which the point P3 is closer to the image side than the point Q3 exists between the center and the effective diameter end.

  The object side surface of the second lens L2 may have a shape having a negative power at the center, a portion having a positive power between the center and the effective diameter end, and a negative power at the effective diameter end. . By forming the object side surface of the second lens L2 in such a shape, the lens system can be downsized and widened, and at the same time, the curvature of field and distortion can be corrected well.

  “A shape including a portion having a negative power at the center and a positive power between the center and the effective diameter end” of the object side surface of the second lens L2 is a paraxial region including the point Q3. Means a shape in which a point X3 in which the point P3 is closer to the image side than the point Q3 exists between the center and the effective diameter end. The “shape having negative power at the effective diameter end” of the second lens L2 means a shape in which the point P3 is closer to the object side than the point Q3 when the point X3 is the effective diameter end. .

  The object side surface of the second lens L2 has negative power at both the center and the effective diameter end. When comparing the negative power between the center and the effective diameter end, the effective diameter end is more negative than the center. The shape may be weak. By forming the object side surface of the second lens L2 in such a shape, the lens system can be downsized and widened, and at the same time, the curvature of field can be corrected well.

  “When both the center and effective diameter end have negative power on the object side surface of the second lens L2, and when the negative power between the center and effective diameter end is compared, the effective diameter end is compared with the center. "A shape with weak negative power" means that when the point X3 is the effective diameter end, the paraxial region including the point Q3 is concave, the point P3 is closer to the object side than the point Q3, and the point X3 This means that the absolute value | RX3 | of the radius of curvature is larger than the absolute value | R3 | of the radius of curvature at the point Q3.

  The image-side surface of the second lens L2 is preferably an aspherical surface, so that field curvature and distortion can be corrected well. The image-side surface of the second lens L2 has negative power at both the center and the effective diameter end. When comparing the negative power between the center and the effective diameter end, the effective diameter end is more negative than the center. It is preferable to use a shape with low power. By making the image-side surface of the second lens L2 in such a shape, it is possible to satisfactorily correct field curvature and distortion.

  The shape of the image side surface of the second lens L2 can be considered as follows in the same manner as the shape of the object side surface of the second lens L2 described with reference to FIG. In the lens cross-sectional view, when a certain point on the image side surface of the second lens L2 is X4 and the intersection of the normal at that point and the optical axis Z is a point P4, the point X4 and the point P4 are connected. The segment X4-P4 is defined as the radius of curvature at the point X4, and the length | X4-P4 | of the segment connecting the point X4 and the point P4 is defined as the absolute value | RX4 | of the radius of curvature at the point X4. Therefore, | X4-P4 | = | RX4 |. Further, an intersection of the image side surface of the second lens L2 and the optical axis Z, that is, the center of the image side surface of the second lens L2 is defined as a point Q4. The absolute value of the radius of curvature at the point Q4 is set to | R4 |.

  “When the center and the effective diameter end have negative power on the image side surface of the second lens L2 and when the negative power between the center and the effective diameter end is compared, the effective diameter end is compared with the center. "The shape with weak negative power" means that when the point X4 is the effective diameter end, the shape is concave in the paraxial region including the point Q4, the point P4 is closer to the image side than the point Q4, and the point X4 This means that the absolute value | RX4 | of the radius of curvature at is larger than the absolute value | R4 | of the radius of curvature at the point Q4.

  The object side surface of the third lens L3 is preferably an aspherical surface. The object side surface of the third lens L3 has a negative power at both the center and the effective diameter end, and has a shape in which the negative power is weaker than the center at the effective diameter end, or a negative power at the center. A shape having positive power at the effective diameter end is preferable. By setting the object side surface of the third lens L3 to have such a shape, coma can be favorably corrected.

  The shape of the object side surface of the third lens L3 can be considered as follows in the same manner as the shape of the object side surface of the second lens L2 described with reference to FIG. In the lens cross-sectional view, when a certain point on the object side surface of the third lens L3 is set as X5 and an intersection of the normal line at that point and the optical axis Z is set as a point P5, the point X5 and the point P5 are connected. The line segment X5-P5 is defined as the radius of curvature at the point X5, and the length | X5-P5 | of the line segment connecting the point X5 and the point P5 is defined as the absolute value | RX5 | of the radius of curvature at the point X5. Therefore, | X5-P5 | = | RX5 |. Further, the intersection point between the object side surface of the third lens L3 and the optical axis Z, that is, the center of the object side surface of the third lens L3 is defined as a point Q5. And let the absolute value of the radius of curvature at the point Q5 be | R5 |.

  On the object side surface of the third lens L3, “the center and the effective diameter end both have negative power, and the effective diameter end has a weaker negative power than the center” means that the point X5 is the effective diameter end. Is a concave shape in the paraxial region including the point Q5, the point P5 is closer to the object side than the point Q5, and the absolute value | RX5 | of the radius of curvature at the point X5 is the radius of curvature at the point Q5. Means a shape larger than the absolute value | R5 |.

  In addition, “a shape having a negative power at the center and a positive power at the effective diameter end” is a concave shape in the paraxial region including the point Q5 when the point X5 is the effective diameter end. A shape in which P5 is located on the image side from the point Q5 is meant.

  The object side surface of the third lens L3 has negative power at both the center and the effective diameter end. When comparing the negative power between the center and the effective diameter end, the effective diameter end is negative compared to the center. It is good also as a shape with strong power. By forming the object side surface of the third lens L3 in such a shape, it is easy to widen the angle, and on-axis rays and off-axis rays can be separated by the first lens L1 and the second lens L2. This facilitates correction of field curvature and distortion.

  “When both the center and the effective diameter end have negative power on the object side surface of the third lens L3, and when the negative power between the center and the effective diameter end is compared, the effective diameter end is negative compared to the center. "The shape with strong power" is a concave shape in the paraxial region including the point Q5 when the point X5 is the effective diameter end, the point P5 is closer to the object side than the point Q5, and the point X5 This means that the absolute value | RX5 | of the radius of curvature is smaller than the absolute value | R5 | of the radius of curvature at the point Q5.

  On the object side surface of the third lens L3, the paraxial region may be a flat surface.

  The image side surface of the third lens L3 is preferably an aspherical surface. The image-side surface of the third lens L3 preferably has a shape in which both the center and the effective diameter end have positive power, and the positive power is weaker at the effective diameter end than the center. By forming the third lens L3 in such a shape, it is possible to satisfactorily correct coma due to off-axis rays and improve the image quality at the peripheral portion of the image.

  The shape of the image side surface of the third lens L3 can be considered as follows in the same manner as the shape of the object side surface of the second lens L2 described with reference to FIG. In the lens cross-sectional view, when a certain point on the image side surface of the third lens L3 is X6, and an intersection of the normal line at that point and the optical axis Z is a point P6, the point X6 and the point P6 are connected. The segment X6-P6 is defined as the radius of curvature at the point X6, and the length | X6-P6 | of the segment connecting the point X6 and the point P6 is defined as the absolute value | RX6 | of the radius of curvature at the point X6. Therefore, | X6-P6 | = | RX6 |. Further, the intersection point between the image side surface of the third lens L3 and the optical axis Z, that is, the center of the image side surface of the third lens L3 is defined as a point Q6. And let the absolute value of the radius of curvature at the point Q6 be | R6 |.

  On the image side surface of the third lens L3, “the center and the effective diameter end both have positive power, and the effective diameter end has a weaker positive power than the center” means that the point X6 is the effective diameter end. In the paraxial region including the point Q6, the point P6 is closer to the object side than the point Q6, and the absolute value | RX6 | of the radius of curvature at the point X6 is the radius of curvature at the point Q6. Means a shape larger than the absolute value | R6 |.

  The image-side surface of the third lens L3 may have a shape in which both the center and the effective diameter end have positive power, and the effective diameter end has a stronger positive power than the center. By making the third lens L3 such a shape, it becomes easy to satisfactorily correct spherical aberration and curvature of field.

  On the image side surface of the third lens L3, "the center and the effective diameter end both have positive power, and the effective diameter end has a stronger positive power than the center" means that the point X6 is the effective diameter end. In the paraxial region including the point Q6, the point P6 is closer to the object side than the point Q6, and the absolute value | RX6 | of the radius of curvature at the point X6 is the radius of curvature at the point Q6. Means a shape smaller than the absolute value | R6 |.

  The object side surface of the sixth lens L6 is preferably an aspherical surface. It is preferable that the object-side surface of the sixth lens L6 has a shape in which both the center and the effective diameter end have positive power, and the positive power is weaker at the effective diameter end than the center. By making the object side surface of the sixth lens L6 into such a shape, it becomes easy to favorably correct curvature of field and spherical aberration.

  The above shape of the object side surface of the sixth lens L6 can be considered as follows in the same manner as the shape of the object side surface of the second lens L2 described with reference to FIG. In the lens cross-sectional view, when a certain point on the object-side surface of the sixth lens L6 is X12 and the intersection of the normal line at that point and the optical axis Z is the point P12, the point X12 and the point P12 are connected. The segment X12-P12 is defined as the radius of curvature at the point X12, and the length | X12-P12 | of the segment connecting the point X12 and the point P12 is defined as the absolute value | RX12 | of the radius of curvature at the point X12. Therefore, | X12−P12 | = | RX12 |. Further, an intersection point between the object side surface of the sixth lens L6 and the optical axis Z, that is, the center of the object side surface of the sixth lens L6 is defined as a point Q12. The absolute value of the radius of curvature at the point Q12 is set to | R12 |.

  On the object side surface of the sixth lens L6, “the center and the effective diameter end both have positive power and the effective diameter end has a weaker positive power than the center” means that the point X12 is the effective diameter end. Is a convex shape in the paraxial region including the point Q12, the point P12 is closer to the image side than the point Q12, and the absolute value | RX12 | of the radius of curvature at the point X12 is the radius of curvature at the point Q12. Means a shape larger than the absolute value | R12 |.

  The image side surface of the sixth lens L6 is preferably an aspherical surface. The image side surface of the sixth lens L6 has a positive power at both the center and the effective diameter end, and the effective diameter end has a weaker positive power than the center, or the center has a positive power and is effective. A shape having negative power at the radial end is preferable. By setting the image side surface of the sixth lens L6 to such a shape, it is possible to satisfactorily correct spherical aberration and curvature of field.

  The shape of the image side surface of the sixth lens L6 can be considered as follows in the same manner as the shape of the object side surface of the second lens L2 described with reference to FIG. In the lens cross-sectional view, when a certain point on the image side surface of the sixth lens L6 is X13 and the intersection of the normal at that point and the optical axis Z is a point P13, the point X13 and the point P13 are connected. The line segment X13-P13 is defined as the radius of curvature at the point X13, and the length | X13-P13 | of the line segment connecting the point X13 and the point P13 is defined as the absolute value | RX13 | of the radius of curvature at the point X13. Therefore, | X13−P13 | = | RX13 |. Further, the intersection point between the image side surface of the sixth lens L6 and the optical axis Z, that is, the center of the image side surface of the sixth lens L6 is defined as a point Q13. The absolute value of the radius of curvature at the point Q13 is set to | R13 |.

  The above-mentioned image side surface of the sixth lens L6 has a positive power at both the center and the effective diameter end and a weaker positive power than the center at the effective diameter end. In the case of the radial end, the shape is convex in the paraxial region including the point Q13, the point P13 is closer to the object side than the point Q13, and the absolute value | RX13 | of the radius of curvature at the point X13 is the point Q13 It means a shape larger than the absolute value of curvature radius | R13 |.

  Further, “a shape having a positive power at the center and a negative power at the effective diameter end” is a convex shape in the paraxial region including the point Q13 when the point X13 is the effective diameter end. It means a shape in which P13 is on the image side with respect to the point Q13.

  Each surface from the object-side surface of the second lens L2 to the image-side surface of the sixth lens L6 has an aspherical shape as described above, so that distortion is added in addition to spherical aberration, field curvature, and coma. Can be corrected well.

  The first lens L1 is preferably a meniscus lens having a convex surface directed toward the object side, which makes it possible to produce a wide-angle lens exceeding 180 degrees, for example. When the first lens L1 is a biconcave lens, it is easy to increase the power of the first lens L1, and thus widening the angle is easy. However, since the light rays are suddenly bent by the first lens L1, distortion is caused. Correction becomes difficult. If the object-side surface is concave, the incident angle when the peripheral ray is incident on the lens surface increases, and the reflection loss at the time of incidence on the surface increases, so that the peripheral portion becomes dark. In addition, a light beam having an incident angle exceeding 180 degrees cannot be incident. Therefore, in order to facilitate distortion correction while having a wide angle, the first lens L1 is preferably a positive meniscus lens having a convex surface facing the object side.

  The second lens L2 is preferably a biconcave lens, which facilitates widening of the angle and facilitates correction of field curvature, distortion, and spherical aberration.

  The second lens L2 may be a meniscus lens having a convex surface directed toward the object side. This makes it easy to widen the angle and corrects distortion and curvature of field well.

  The object-side surface of the third lens L3 is preferably a concave surface or a flat surface, which facilitates widening of the angle and separates the on-axis light beam and the peripheral light beam with the first lens L1 and the second lens L2. This makes it easy to correct field curvature and coma.

  The image-side surface of the third lens L3 is preferably a convex surface, whereby the power of the third lens L3 can be made positive and the chromatic aberration of magnification can be corrected well. It becomes.

  The third lens L3 is preferably a meniscus shape with a concave surface facing the object side or a plano-convex lens with a plane surface facing the object side. This makes it easy to reduce the lens system direction and reduce the image. It becomes possible to correct surface curvature and coma well.

  The fourth lens L4 is preferably a biconvex lens, which makes it possible to satisfactorily correct spherical aberration and field curvature. Further, by increasing the power of the fourth lens L4, it becomes easy to correct chromatic aberration with the fifth lens L5.

  The fifth lens L5 is preferably a biconcave lens or a plano-convex lens having a flat surface facing the image side, which makes it possible to favorably correct field curvature. Furthermore, it becomes easy to increase the power of the fifth lens L5, and it becomes easy to correct chromatic aberration with the fourth lens L4.

  The fifth lens L5 may be a negative meniscus lens having a convex surface facing the image side, or a plano-concave lens having a flat surface facing the image side. This makes it easy to favorably correct coma and curvature of field. .

  The sixth lens L6 is preferably a biconvex lens, which makes it possible to suppress the angle at which light rays are incident on the image sensor and facilitate shading.

  The sixth lens L6 may be a meniscus lens having a convex surface directed to the image side, which facilitates good correction of field curvature.

  The material of the first lens L1 is preferably glass. 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, Is 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., and materials that are hard and hard to break are required. 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. Further, as the material of the first lens L1, a material having a Knoop hardness of 550 or more may be used. In addition, as the material of the first lens L1, the powder acid resistance is preferably class 4 or higher and the powder water resistance is class 3 or higher in the powder acid resistance and powder water resistance tests established by the Japan Optical Glass Industry Association. Is preferred. The higher the class, the better. Moreover, it is preferable that it is a class 3 or more in the detergent resistance of an ISO regulation. The surface method weather resistance is preferably Class 3 or higher. In addition, for example, in-vehicle cameras and surveillance camera lenses are exposed to ultraviolet rays from the sun for a long period of time. Therefore, it is preferable to use materials that are resistant to ultraviolet rays as the materials used for these lenses.

  One or both surfaces of the first lens L1 may be aspheric. By making the first lens L1 a glass aspheric lens, various aberrations can be corrected more satisfactorily.

  Note that a protective means for enhancing 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.

  In any one of the second lens L2, the third lens L3, and the sixth lens L6, or any combination of these, it is preferable that the material is plastic. By using plastic as the material, it is possible to configure the lens system at a low cost and light weight, and when an aspheric surface is provided, the aspherical shape can be accurately produced, so that a good performance can be obtained. A lens can be manufactured.

  The material of at least one of the fourth lens L4 and the fifth lens L5 may be plastic. By using plastic as the material, it is possible to configure the lens system at a low cost and light weight, and when an aspheric surface is provided, the aspherical shape can be accurately produced, so that a good performance can be obtained. A lens can be manufactured.

  The material of the second lens L2 and the sixth lens L6 is preferably polyolefin. Polyolefin has a low water absorption, a high transparency, a low birefringence, and a material with a large Abbe number. By using polyolefin as the material of the second lens L2 and the sixth lens L6, it becomes possible to produce a lens with a small shape change due to water absorption, a high transmittance, and a small birefringence. Furthermore, since a material with a large Abbe number can be used, it is possible to suppress the occurrence of axial chromatic aberration and lateral chromatic aberration, and it is possible to manufacture a lens with high environmental resistance and good resolution performance.

  The material of the third lens L3 is preferably polycarbonate. Polycarbonate is characterized by a small Abbe number. By using polycarbonate for the third lens L3, it is possible to satisfactorily correct lateral chromatic aberration.

  The material of the second lens L2 and the sixth lens L6 may be acrylic. Since acrylic is inexpensive, it is possible to make the lens system inexpensive by using acrylic.

  When a plastic material is used for at least one of the second lens L2, the third lens L3, the fourth lens L4, the fifth lens L5, and the sixth lens L6, the plastic is smaller than the wavelength of light. A so-called nanocomposite material in which particles are mixed may be used.

  The material of the second lens L2, the third lens L3, and the sixth lens L6, or any combination of these may be glass. By using glass as the material, it is possible to suppress performance deterioration due to temperature changes.

  It is preferable that at least one of the fourth lens L4 and the fifth lens L5 is made of glass. By using glass as the material of the fourth lens L4, it is possible to suppress performance deterioration due to temperature changes. In addition, since the fifth lens L5 is made of glass, it is easy to select a material having a small Abbe number, and thus correction of chromatic aberration is facilitated.

  As a material for at least one of the first lens L1, the second lens L2, the third lens L3, the fourth lens L4, the fifth lens L5, and the sixth lens L6, a glass transition temperature (Tg) of 145 ° C. or higher is used. It is preferable to use, more preferably 150 ° C. or higher. By using a material having a glass transition temperature of 150 ° C. or higher, a lens having good heat resistance can be manufactured.

  Depending on the application of the imaging lens 1, a filter that cuts blue light from ultraviolet light or an IR (InfraRed) cut filter that cuts infrared light is inserted between the lens system and the imaging device 5. May be. A coat having the same characteristics as the 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 is arranged between the lens system and the image sensor 5. Instead, these various filters are arranged between the lenses. Also good. Or you may give the coat | court which has the effect | action similar to various filters to the lens surface of either lens which an imaging lens has.

  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 the light beam that becomes stray light to serve as the light shielding means. 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 and 12 are provided outside the effective diameters of the image-side surfaces of the first lens L1 and the second lens L2. 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.

  Further, a member such as a diaphragm that blocks the peripheral light beam may be disposed between the lenses in a range where 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 disposing the member that blocks the peripheral light in this way, the image quality in the periphery of the imaging region can be improved. Moreover, it becomes possible to reduce a ghost by interrupting | blocking the light which generates a ghost with this member.

  In the imaging lenses according to the first to fourth embodiments, the lens system includes the first lens L1, the second lens L2, the third lens L3, the fourth lens L4, the fifth lens L5, and the sixth lens L6. It is preferable to configure so that it consists of only 6 sheets. By configuring the lens system with only six lenses, the lens system can be made inexpensive.

  Since the imaging apparatus according to the present embodiment includes the imaging lens according to the present embodiment, the imaging apparatus can be configured to be small and inexpensive, have a sufficiently wide angle of view, and obtain a good image with high resolution using the imaging element. be able to.

  In addition, you may make it display the image image | photographed with the imaging device provided with the imaging lens which concerns on 1st-4th embodiment on a mobile telephone. For example, an imaging device including the imaging lens according to the present embodiment may be mounted on a vehicle as an in-vehicle camera, the back and the periphery of the vehicle may be captured by the in-vehicle camera, and an image acquired by the imaging may be displayed on the display device. In such a case, in a car equipped with a car navigation system (hereinafter referred to as a car navigation system), the captured image may be displayed on the display device of the car navigation system. It is necessary to install a dedicated display device in the car. However, the display device is expensive. On the other hand, mobile phones in recent years are equipped with high-performance display devices such as being able to browse videos and Web. By using a mobile phone as a display device for a vehicle-mounted camera, it is not necessary to mount a dedicated display device even for a car that is not equipped with a car navigation system. As a result, a vehicle-mounted camera can be mounted at a low cost. .

  Here, the image captured by the in-vehicle camera may be transmitted to the mobile phone by cable using a cable or the like, or may be transmitted to the mobile phone by radio such as infrared communication. In addition, the mobile phone and the operating state of the car are linked so that when the car's gear enters the back or the winker is taken out, the image of the in-vehicle camera is automatically displayed on the display device of the mobile phone. May be.

  The display device for displaying the image of the in-vehicle camera is not limited to a mobile phone, but may be a portable information terminal such as a PDA, a small personal computer, or a portable car navigation system.

[Numerical example of imaging lens]
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 19 are shown in FIGS. 3 to 21, the left side of the figure is the object side, and the right side is the image side. Similarly to FIG. 1, the aperture stop St, the optical member PP, and the image sensor 5 disposed on the image plane Sim are also illustrated. Yes. 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.

  The imaging lens according to the first embodiment of the present invention is in Examples 1 to 4, 6 to 19, and the imaging lens according to the second embodiment of the present invention is in Examples 1 to 3 and 6 to 19. The imaging lens according to the third embodiment of the present invention corresponds to Examples 6 and 11 to 18, and the imaging lens according to the fourth embodiment of the present invention corresponds to Examples 6 and 11 to 18.

  Tables 1 to 19 show lens data of the imaging lenses of Examples 1 to 19, 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 increases sequentially toward the image side with the object-side surface of the most object-side component as the first. , Ri column indicates the radius of curvature of the i-th surface, and Di column indicates the surface spacing 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 “St” is also written in the surface number column of the surface corresponding to the aperture stop St.

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 “× 10n”. 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,... 20)
In various data, L 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-converted length), and Bf is from the image-side surface of the most image-side lens. The distance on the optical axis Z to the image plane Sim (corresponding to back focus, equivalent air 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, f6 is the focal length of the sixth lens L6, and f23 is the second lens L2 and the third lens. The combined focal length between L3 and f45 is the combined focal length between the fourth lens L4 and the fifth lens L5.

  Tables 20 and 21 collectively show values corresponding to the conditional expressions of the respective examples. Conditional expression (1) is (R8 + R9) / (R8-R9), conditional expression (2) is D9 / f, conditional expression (3) is (R5 + R6) / (R5-R6), and conditional expression (4) is (R10 + R11) / (R10-R11), conditional expression (5) is D4 / f, conditional expression (6) is νd3 + νd5, conditional expression (7) is | f1 / f |, and conditional expression (8) is | f2 / f. |, Conditional expression (9) is f3 / f, conditional expression (10) is f4 / f, conditional expression (11) is R2 / f, conditional expression (12) is R9 / f, conditional expression (13) is R1 / f, conditional expression (14) is f6 / f, conditional expression (15) is R13 / f, conditional expression (16) is f5 / f, conditional expression (17) is R4 / f, conditional expression (18) is R10 / f. f, conditional expression (19) is (D4 + D5) / f, conditional expression (20) is f / R5, conditional expression (21) is f / R3, conditional expression (22) is f23 / f, condition Expression (23) is f45 / f, conditional expression (24) is L / f, conditional expression (25) is Bf / f, and conditional expression (26) is (R1 + R2) / (R1-R2).

However,
R1: radius of curvature of the object side surface of the first lens L1 R2: radius of curvature of the image side surface of the first lens L1 R3: radius of curvature of the object side surface of the second lens L2 R4: image of the second lens L2 Radius of curvature R5: curvature radius of the third lens object side surface R6: curvature radius of the third lens image side surface R8: curvature radius of the object side surface of the fourth lens L4 R9: fourth lens L4 Radius of curvature R10 of the image side surface: radius of curvature R11 of the object side surface of the fifth lens L5: radius of curvature R13 of the image side surface of the fifth lens L5: radius of curvature of the image side surface of the sixth lens L6 D4: Air distance on the optical axis between the second lens L2 and the third lens L3 D5: Center thickness of the third lens L3 D9: Air distance on the optical axis between the fourth lens L4 and the fifth lens L5 νd3: First Abbe number νd5 for the d-line of the material of the third lens L3: d-line of the material of the fifth lens L5 Abbe number f: total system focal length f1: first lens L1 focal length f2: second lens L2 focal length f3: third lens L3 focal length f4: fourth lens L4 focal length f5: fifth Focal length f6 of lens L5: Focal length f23 of sixth lens L6: Combined focal length f45 of second lens L2 and third lens L3: Combined focal length L of fourth lens L4 and fifth lens L5: First lens Distance on the optical axis from the object-side surface to the image plane (back focus is air equivalent length)
Bf: Distance on the optical axis from the image side surface of the lens closest to the image side to the image surface (air equivalent length)
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 the imaging lenses of Examples 1 to 19, the first lens L1, the fourth lens L4, and the fifth lens L5 are glass spherical lenses, and the second lens L2, the third lens L3, and the sixth lens L6 are plastic aspheric surfaces. It is a lens.

  The aberration diagrams of the imaging lenses according to Examples 1 to 19 are shown in FIGS. 22 (A) to 22 (D), FIGS. 23 (A) to 23 (D), and FIGS. D), FIGS. 25 (A) to 25 (D), FIGS. 26 (A) to 26 (D), FIGS. 27 (A) to 27 (D), and FIGS. 28 (A) to 28 (D). 29 (A) to 29 (D), 30 (A) to 30 (D), 31 (A) to 31 (D), 32 (A) to 32 (D), FIG. 33 (A) to 33 (D), FIG. 34 (A) to FIG. 34 (D), FIG. 35 (A) to FIG. 35 (D), FIG. 36 (A) to FIG. 36 (D), FIG. A) to FIG. 37 (D), FIG. 38 (A) to FIG. 38 (D), FIG. 39 (A) to FIG. 39 (D), and FIG. 40 (A) to FIG.

  Here, the aberration diagram of Example 1 will be described as an example, but the same applies to the aberration diagrams of other Examples. 22 (A), 22 (B), 22 (C), and 22 (D) are spherical aberration, astigmatism, distortion (distortion aberration), and lateral chromatic aberration (magnification aberration) of the imaging lens according to Example 1, respectively. The aberration diagram of chromatic aberration of magnification) is shown. F in the 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 of 2f × tan (φ / 2) using the focal length f and the angle of view φ (variable treatment, 0 ≦ φ ≦ ω) of the entire system. Each aberration diagram shows aberration with d-line (587.56 nm) as a reference wavelength, but spherical aberration diagram shows F-line (wavelength 486.13 nm), C-line (wavelength 656.27 nm), and sine condition violation The aberration for the quantity (denoted as SNC) is also shown, and the chromatic aberration diagram for the magnification shows the aberration for the F-line and C-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 19 are configured with a small number of lenses, such as six, and can be manufactured in a small size and at a low cost, and the total angle of view is about 178 to 208 degrees. A wide angle of view is achieved, the F-number is as small as 2.0, each aberration is corrected well, and the optical performance is good. These imaging lenses can be suitably used for surveillance cameras, in-vehicle cameras for taking images of the front, side, rear, etc. of automobiles.

[Embodiment of Imaging Device]
As a usage example, FIG. 41 shows a state in which an imaging apparatus including the imaging lens of the present embodiment is mounted on the automobile 100. In FIG. 41, 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 embodiments of the present invention, and convert an imaging lens according to an embodiment of the present invention and an optical image formed by the imaging lens into an electrical signal. An image pickup device.

  Since the imaging lens according to the embodiment of the present invention has the above-described advantages, the outside cameras 101 and 102 and the inside camera 103 can also be configured to be small and inexpensive, have a wide angle of view, and have an imaging region peripheral portion. A good image can be obtained.

  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, and the Abbe number of each lens component are not limited to the values shown in the above numerical examples, and can take other values.

  In the above-described embodiments, all the lenses are made of a homogeneous material, but a gradient index lens may be used. In the above-described embodiments, there are lenses in which the second lens L2 to the sixth lens L6 are constituted by refractive lenses provided with aspherical surfaces, but a diffractive optical element is formed on one surface or a plurality of surfaces. May be.

  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.

DESCRIPTION OF SYMBOLS 1 Imaging lens 2 On-axis light beam 3, 4 Off-axis light beam 5 Imaging element 6 Light beam 11, 12 Light-shielding means 100 Car 101, 102 Outside camera 103 In-vehicle camera Pim Imaging position L1 1st lens L2 2nd lens L3 3rd lens L4 Fourth lens L5 Fifth lens L6 Sixth lens PP Optical member Sim Image surface St Aperture stop Z Optical axis

Claims (11)

In order from the object side, a negative first lens, a negative second lens, a positive third lens, a positive fourth lens, a negative fifth lens, and a positive sixth lens are substantially provided. It consists of 6 lenses,
The object side surface of the third lens is a concave surface;
An imaging lens satisfying the following conditional expressions (8) and (9):
| F2 / f | <3.0 (8)
4.6 <f3 / f (9)
However,
f2: focal length of the second lens f3: focal length of the third lens f: focal length of the entire system In order from the object side, a negative first lens, a negative second lens, a positive third lens, a positive fourth lens, a negative fifth lens, and a positive sixth lens are substantially provided. It consists of 6 lenses,
The object side surface of the third lens is a concave surface;
The fourth lens is a biconvex lens;
The fifth lens is a biconcave lens;
An imaging lens satisfying the following conditional expressions (8-1) and (9-1):
| F2 / f | <3.9 (8-1)
4.9 <f3 / f (9-1)
However,
f2: focal length of the second lens f3: focal length of the third lens f: focal length of the entire system In order from the object side, a negative first lens, a negative second lens, a positive third lens, a positive fourth lens, a negative fifth lens, and a positive sixth lens are substantially provided. It consists of 6 lenses,
The object side surface of the second lens is a convex surface;
The image side surface of the third lens is a convex surface;
The fourth lens is a biconvex lens;
The fifth lens is a biconcave lens;
An imaging lens satisfying the following conditional expressions (9) and (10):
4.6 <f3 / f (9)
1.8 <f4 / f (10)
However,
f3: focal length of the third lens f4: focal length of the fourth lens f: focal length of the entire system In order from the object side, a negative first lens, a negative second lens, a positive third lens, a positive fourth lens, a negative fifth lens, and a positive sixth lens are substantially provided. It consists of 6 lenses,
The object side surface of the second lens is a convex surface;
The object side surface of the third lens is a concave surface;
The fourth lens is a biconvex lens;
The fifth lens is a biconcave lens;
An imaging lens satisfying the following conditional expressions (9) and (10-1):
4.6 <f3 / f (9)
1.2 <f4 / f (10-1)
However,
f3: focal length of the third lens f4: focal length of the fourth lens f: focal length of the entire system The imaging lens according to any one of claims 1 to 4, wherein the following conditional expression (19) is satisfied.
1 <(D4 + D5) / f <6 (19)
However,
D4: air space on the optical axis between the second lens and the third lens D5: center thickness of the third lens f: focal length of the entire system The imaging lens according to claim 1, wherein the following conditional expression (20) is satisfied.
-1 <f / R5 <1 (20)
However,
f: focal length of the entire system R5: radius of curvature of the object side surface of the third lens The imaging lens according to claim 1, wherein the following conditional expression (21) is satisfied.
-3 <f / R3 <3 (21)
However,
f: focal length of entire system R3: radius of curvature of object side surface of the second lens The imaging lens according to claim 1, wherein the following conditional expression (22) is satisfied.
−30 <f23 / f <−3 (22)
However,
f23: the combined focal length of the second lens and the third lens f: the focal length of the entire system The imaging lens according to claim 1, wherein the following conditional expression (23) is satisfied.
2 <f45 / f <25 (23)
However,
f45: combined focal length of the fourth lens and the fifth lens f: focal length of the entire system   The imaging lens according to any one of claims 1 to 9, wherein a diaphragm is disposed between the third lens and the fourth lens.   The imaging device carrying the imaging lens of any one of Claim 1 to 10.