JP5224455B2 - Imaging lens and imaging apparatus - Google Patents

Description

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

  In recent years, image sensors such as CCDs and CMOSs have been greatly reduced in size and pixels. At the same time, an image pickup apparatus body including these image pickup devices is also downsized, and an image pickup lens mounted thereon is required to be small and light in addition to good optical performance.

  On the other hand, in-vehicle cameras, surveillance cameras, and the like, there is a need for a small, high-performance lens that can be used in a wide temperature range from the outside air in a cold region to the interior of a tropical summer car while having high weather resistance. In particular, a camera that is arranged in a car and monitors the front is required to have a small F number so that it can be used at night and to be usable in a wide wavelength band from the visible range to the infrared range. In addition, when used as an in-vehicle camera, it is also required that the lens portion exposed from a point on the appearance of the car is small.

The present applicant has proposed an imaging lens usable in the above field in Japanese Patent Application No. 2007-132334. Further, as the conventionally known six-lens imaging lens, there are those described in Patent Documents 1 to 4 below. Patent Document 1 describes a lens arrangement in which negative, positive, positive, aperture, negative, positive, and positive lenses are arranged in order from the object side. Patent Document 2 describes a lens arrangement in which negative, positive, positive, aperture, negative, positive, and negative lenses are arranged in order from the object side. Patent Document 3 describes a lens arrangement in which negative, positive, aperture, positive, negative, positive, and positive lenses are arranged in order from the object side. Patent Document 4 describes a lens arrangement of negative, positive, positive, aperture, negative, positive, and positive in order from the object side.
JP 55-45007 A JP 61-90115 A Japanese Patent Laid-Open No. 9-230232 JP 2005-164839 A

  By the way, since an in-vehicle camera, a monitoring camera, and the like can be used at night, an optical system having a small F number is desired. However, those described in Patent Documents 1 and 2 are not preferable because the F number is as large as 3.3 to 4.5, which is a so-called dark optical system. The thing of patent document 4 also has F number 2.5, and since there is room for improvement in this point and using an aspherical lens, it is disadvantageous in cost.

  In addition, what is proposed in Japanese Patent Application No. 2007-132334 has an angle of view of about 27 °, and further widening of the angle is desired for in-vehicle cameras, surveillance cameras, and the like.

  SUMMARY OF THE INVENTION In view of the above circumstances, an object of the present invention is to provide an imaging lens having a wide angle, a small F-number, a low cost, and good optical performance, and an imaging device including the imaging lens. It is.

The imaging lens of the present invention includes, in order from the object side, a first lens having a negative power with a concave surface facing the image side, a second lens having a positive power, a third lens having a positive power, and an aperture from the, a fourth lens having a negative power is a biconcave lens, a fifth lens having a positive power whose convex surface faces the image side, a sixth lens having a positive power whose convex surface faces the object side Thus , the Abbe number of the fourth lens material with respect to the d-line is 30 or less, and the second lens has an absolute value of the radius of curvature of the object-side surface larger than the absolute value of the radius of curvature of the image-side surface. In the lens, the absolute value of the radius of curvature of the object side surface is smaller than the absolute value of the radius of curvature of the image side surface, and in the fifth lens, the absolute value of the radius of curvature of the object side surface is equal to the curvature radius of the image side surface. The absolute value of the radius of curvature of the object side surface of the sixth lens is half the curvature of the image side surface. Absolute value smaller than the focal length of the entire system is f, the composite focal length of the fourth lens to the sixth lens and F456, the curvature radius of the object side surface of the fourth lens and R8, the fourth lens The radius of curvature of the image side surface of the lens is R9, the distance on the optical axis from the object side surface of the most object side lens to the image surface is L, and from the image side surface of the lens of the most image side to the image surface When the distance on the optical axis is Bf and the focal length of the fifth lens is f5 , the following conditional expressions (1) to (4) are satisfied.
1.00 <f456 / f <1.88 (1)
0.30 <| R8 / R9 | <0.90 (2)
0.15 <Bf / (L−Bf) <0.25 (3)
1.20 <f5 / f <1.50 (4)

  The imaging lens of the present invention is advantageous for obtaining an optical system having a wide angle, small size, small F-number and good optical performance by suitably selecting the configuration of each lens as described above. Since a configuration without using an aspheric surface is possible, cost reduction can be achieved. Further, the imaging lens of the present invention is advantageous for correcting chromatic aberration by setting the Abbe number of the fourth lens, which is arranged near the stop and can have strong negative power, to 30 or less, and further satisfies the conditional expression (1). With this configuration, it is easy to correct distortion and field curvature, which is advantageous for widening the angle.

In the imaging lens of the present invention, it is preferable that the following conditional expressions (5) and (6) are satisfied. As a preferred embodiment, the following conditional expression (5) may be those satisfying either one of the formulas (6), there have may be one satisfying the set together.
0 . 3 <D6 / D7 <1.2 (5)
0.3 <| f1 / f2 | <1.0 (6)
However ,
f 1: focal length of the first lens f2: focal length of the second lens
D 6: third air gap along the optical axis of the lens and the aperture D7: diaphragm air interval on the optical axis of the fourth lens

  In the case of an aspheric lens, the above “concave surface”, “convex surface”, “biconcave”, and “curvature radius” are considered in the paraxial region.

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

According to the present invention , in the six -lens lens system, the configuration of the shape, power, material, and the like of each lens is suitably set so as to satisfy the conditional expression (1), so that a wide angle can be achieved. It is possible to provide a small imaging lens having a small F-number and capable of obtaining good optical performance at low cost, and an imaging apparatus including the imaging lens.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. First, an embodiment of the imaging lens of the present invention will be described, and then an embodiment of the imaging device will be described.

  FIG. 1 shows a lens cross-sectional view of an imaging lens 1 according to an embodiment of the present invention. 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 maximum field angle are also shown. . Here, the on-axis light beam is a light beam from an object point on the optical axis Z, and the off-axis light beam is a light beam from an object point outside the optical axis Z.

  In FIG. 1, in consideration of a case where the imaging lens 1 is applied to an imaging device, an imaging element 5 disposed on an image plane including the imaging position Pim of the imaging lens 1 is also illustrated. The image pickup device 5 converts an optical image formed by the image pickup lens 1 into an electric signal, and includes, for example, a CCD image sensor.

  In FIG. 1, the parallel plate-shaped optical member PP disposed between the lens system and the image sensor 5 (image plane), and the light shielding disposed on the image side surfaces of the first lens L1 and the second lens L2. Means 11 and 12 are also shown. The optical member PP and the light shielding means 11 and 12 are not essential to the present invention, and the description thereof will be described later.

  The imaging lens 1 includes, in order from the object side, a first lens L1 having a negative power with a concave surface facing the image side, a second lens L2 having a positive power, a third lens L3 having a positive power, An aperture stop St, a fourth lens L4 having negative power, which is a biconcave lens, a fifth lens L5 having positive power with the convex surface facing the image side, and a positive power with the convex surface facing the object side And a sixth lens L6. By configuring the imaging lens 1 with a relatively small number of lenses, that is, a minimum of six, the overall length in the optical axis direction can be reduced. 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.

  The first lens L1 is a lens having a negative power with the concave surface facing the image side, thereby making it possible to widen the angle of the entire system. The first lens L1 is a lens having negative power with the concave surface facing the image side, so that off-axis rays can be refracted in the direction along the optical axis, and the radial direction of the lens system can be reduced in size. Is possible. Also, as in the example shown in FIG. 1, when the first lens L1 is a biconcave lens, the negative power of the first lens L1 can be increased, and the radial direction of the lens system can be reduced. It becomes easier.

  In the first lens L1, it is preferable that the absolute value of the curvature radius of the object-side surface is larger than the absolute value of the curvature radius of the image-side surface. .

  The Abbe number of the material of the first lens L1 with respect to the d-line is preferably 40 or more. This makes it possible to suppress axial chromatic aberration and lateral chromatic aberration.

  The second lens L2 and the third lens L3 are positive lenses. Thus, by dispersing the positive power to the two lenses on the object side from the aperture stop St, it is possible to correct spherical aberration well. For example, even if the optical system has an F number of 2.0 or less, it is easy to achieve good optical performance.

  The second lens L2 can correct the curvature of field favorably by making the image side surface convex.

  The second lens L2 can correct spherical aberration and curvature of field satisfactorily by making the absolute value of the radius of curvature of the object side surface larger than the absolute value of the radius of curvature of the image side surface. become.

  The Abbe number of the material of the second lens L2 with respect to the d-line is preferably 25 or more. This makes it possible to suppress the occurrence of axial chromatic aberration and lateral chromatic aberration.

  The third lens L3 can correct the curvature of field favorably by making the object-side surface convex.

  The third lens L3 can correct spherical aberration and curvature of field satisfactorily by making the absolute value of the radius of curvature of the object side surface smaller than the absolute value of the radius of curvature of the image side surface. become.

  The Abbe number of the material of the third lens L3 with respect to the d-line is preferably 40 or more, which makes it possible to suppress the occurrence of axial chromatic aberration and lateral chromatic aberration.

  When the fourth lens L4 is a biconcave lens, strong negative power can be provided.

  When the Abbe number of the material of the fourth lens L4 with respect to the d-line is 30 or less, it is possible to satisfactorily correct axial chromatic aberration and lateral chromatic aberration.

  The fifth lens L5 and the sixth lens L6 are positive lenses. Thus, by dispersing the positive power between the two lenses on the image side with respect to the aperture stop St, it is possible to satisfactorily correct spherical aberration. For example, even if the optical system has an F number of 2.0 or less, good optical performance can be achieved.

  The image side surface of the fifth lens L5 is a convex surface, which makes it possible to favorably correct field curvature.

  The fifth lens L5 can correct spherical aberration and curvature of field satisfactorily by making the absolute value of the radius of curvature of the object side surface larger than the absolute value of the radius of curvature of the image side surface. become.

  The Abbe number of the material of the fifth lens L5 with respect to the d-line is preferably 40 or more, which makes it possible to suppress the occurrence of axial chromatic aberration and lateral chromatic aberration.

  The object side surface of the sixth lens L6 is a convex surface, which makes it possible to favorably correct curvature of field.

  The sixth lens L6 can correct spherical aberration and curvature of field satisfactorily by making the absolute value of the radius of curvature of the object side surface smaller than the absolute value of the radius of curvature of the image side surface. become.

  The Abbe number of the material of the sixth lens L6 with respect to the d-line is preferably 40 or more, which makes it possible to suppress the occurrence of axial chromatic aberration and lateral chromatic aberration.

The imaging lens according to the embodiment of the present invention preferably satisfies the following conditional expressions (1) to (9). In addition, as a preferable aspect, any one of conditional expressions (1) to (9) may be satisfied, or any combination may be satisfied.
1.00 <f456 / f <1.88 (1)
0.30 <| R8 / R9 | <0.90 (2)
0.15 <Bf / (L−Bf) <0.25 (3)
1.20 <f5 / f <1.50 (4)
0.3 <D6 / D7 <1.2 (5)
0.3 <| f1 / f2 | <1.0 (6)
2.0 <ED1 / IH <4.0 (7)
2.0 <L / f <7.0 (8)
0.3 <Bf / f <1.2 (9)
However,
f: focal length of the entire system f1: focal length of the first lens L1 f2: focal length of the second lens L2 f5: focal length of the fifth lens L5 f456: composite focal length from the fourth lens L4 to the sixth lens L6 R8: radius of curvature of the object side surface of the fourth lens L4 R9: radius of curvature of the image side surface of the fourth lens L4 D6: air gap on the optical axis between the third lens L3 and the aperture stop St D7: aperture stop St And air distance L on the optical axis of the fourth lens L4: distance on the optical axis from the object side surface of the first lens L1 to the image plane (the back focus is the air equivalent length)
Bf: distance on the optical axis from the image side surface of the sixth lens L6 to the image surface (corresponding to back focus, air conversion length)
ED1: Maximum ray height IH on the object side surface of the first lens L1: Maximum image height Note that ED1 and IH can be determined by, for example, the specifications of the imaging lens and the specifications of the imaging device to be applied.

  If the upper limit of conditional expression (1) is exceeded, the combined power of the three lenses on the image side from the aperture stop St becomes weak, and it becomes difficult to widen the angle while correcting distortion well. If the lower limit of conditional expression (1) is not reached, the combined power of the three lenses on the image side from the aperture stop St becomes strong, making it difficult to correct the curvature of field, and the back focus is shortened. It is difficult to dispose various filters, cover glasses, and the like between the image sensors disposed on the surface.

  If the upper limit of conditional expression (2) is exceeded, it will be difficult to correct field curvature well. If the lower limit of conditional expression (2) is not reached, the absolute value of the radius of curvature of the object-side surface of the fourth lens L4 becomes too small, making processing difficult.

  If the upper limit of conditional expression (3) is exceeded, the entire system becomes large. If the lower limit of conditional expression (3) is not reached, the back focus is shortened, and it is difficult to dispose various filters and cover glasses between the lens system and the image sensor disposed on the image plane.

  If the upper limit of conditional expression (4) is exceeded, it will be difficult to correct field curvature well. If the lower limit of conditional expression (4) is not reached, the power of the fifth lens L5 becomes too strong, and the tolerance of manufacturing and assembly errors with respect to decentration is reduced, making assembly difficult or increasing costs. End up.

  If the upper limit of conditional expression (5) is exceeded, the aperture stop St will move closer to the fourth lens L4, and the lens diameter of the object side lens will become larger than the aperture stop St. If the lower limit of conditional expression (5) is not reached, the aperture stop St is too close to the third lens L3, so that the lens diameter of the lens on the image side becomes larger than the aperture stop St.

  If the upper limit of conditional expression (6) is exceeded, the power of the first lens L1 will become weak and it will be difficult to widen the angle, or it will be difficult to obtain a long back focus. If the lower limit of conditional expression (6) is not reached, it will be difficult to satisfactorily correct field curvature and distortion.

  If the upper limit of conditional expression (7) is exceeded, the effective diameter of the first lens L1 becomes too large, and it becomes difficult to downsize the portion of the lens exposed to the outside. For example, when this imaging lens is mounted on a vehicle-mounted camera, it is desirable that the portion of the lens exposed to the outside is small so as not to impair the appearance of the vehicle, and therefore satisfies the upper limit of conditional expression (7). It is preferable to configure as described above. If the lower limit of conditional expression (7) is not reached, it is possible to reduce the size of the part exposed to the outside, but it becomes difficult to separate the on-axis light beam and the off-axis light beam with the optical system closer to the object than the aperture stop St. It becomes difficult to correct the curvature of field well.

  If the upper limit of conditional expression (8) is exceeded, the total length in the optical axis direction becomes long and the lens system becomes large or it becomes difficult to widen the angle. If the lower limit of conditional expression (8) is not reached, the total length becomes too short, each lens becomes thin, and it becomes difficult to process and assemble the lens.

  If the upper limit of conditional expression (9) is exceeded, the back focus becomes too long, resulting in an increase in the size of the entire system. If the lower limit of conditional expression (9) is not reached, the back focus is too short and it is difficult to dispose various filters, cover glasses, etc. between the lens system and the image sensor disposed on the image plane. Further, a ghost caused by the return light from the image sensor to the lens system is also likely to occur.

Furthermore, the imaging lens of the present embodiment has the following conditional expressions (1-1), (2-1), (6-1), (7-1), (8-1), and (9-1). It is more preferable to satisfy.
1.1 <f456 / f <1.88 (1-1)
0.4 <| R8 / R9 | <0.90 (2-1)
0.4 <| f1 / f2 | <0.8 (6-1)
3.0 <ED1 / IH <4.0 (7-1)
2.0 <L / f <4.0 (8-1)
0.5 <Bf / f <1.0 (9-1)

  Satisfying the conditional expression (1-1) makes it easier to correct curvature of field and secure a back focus for arranging various filters, cover glasses, and the like.

  When the conditional expression (2-1) is satisfied, the configuration is more advantageous for processing.

  Satisfying the upper limit of conditional expression (6-1) makes it easier to realize a wide angle or a long back focus. Satisfying the lower limit of conditional expression (6-1) is advantageous in favor of correction of curvature of field and distortion.

  Satisfying the conditional expression (7-1) is advantageous for good correction of field curvature.

  When the conditional expression (8-1) is satisfied, the lens system can be further reduced in size.

  By satisfying conditional expression (9-1), the effect obtained when conditional expression (9) is satisfied can be further improved.

  When the imaging lens 1 is used in a harsh environment such as an in-vehicle 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, It is preferable to use materials that are resistant to chemicals such as fats and oils, that is, materials having high water resistance, weather resistance, acid resistance, chemical resistance, and the like. In addition, as the material of the first lens L1 disposed on the most object side, it is preferable to use a material that is hard and difficult to break. From the above, as the material of the first lens L1, specifically, glass is preferably used, or transparent ceramics may be used. Ceramics have properties of higher strength and higher heat resistance than ordinary glass.

  The center thickness of the first lens L1 is preferably 0.5 mm or more. For example, when applied to an in-vehicle camera, the lens system is required to have strength against various impacts. Therefore, by setting the center thickness of the first lens L1 to 0.5 mm or more, it is possible to make the first lens L1 difficult to break.

  In addition, when the imaging lens 1 is applied to, for example, a vehicle-mounted camera, it is required that the imaging lens 1 can be used in a wide temperature range from the outside air in a cold region to the interior of a tropical summer vehicle. When used in a wide temperature range, it is preferable to use a lens having a small linear expansion coefficient. When it is required to be usable even in a wide temperature range, such as in-vehicle camera applications, it is preferable that the material of all lenses is glass.

  In addition, the first lens L1 may be provided with a waterproof structure so as to block the flow of air from the outside so that clouding does not occur inside due to severe temperature changes and humidity changes. The waterproof structure may be a sealed structure by bonding the first lens L1 and the lens frame, or may be a sealed structure by inserting an airtight member such as an O-ring between the first lens L1 and the lens frame. .

  Further, when the lens system is used under a severe temperature environment or humidity environment, it is desirable not to use a cemented lens in the lens system. For example, when applied to an in-vehicle camera, it is necessary to be usable in a wide temperature range from the outside air in a cold region to the interior of a summer car in a tropical region. When a cemented lens is used, a special cementing agent must be used for use in a wide temperature range, resulting in an increase in cost.

  In order to manufacture lenses at low cost, it is preferable that all the lenses are spherical lenses. Alternatively, an aspheric lens may be used to correct each aberration better when performance is important. In order to form the aspherical surface accurately and at low cost, plastic may be used as the lens material.

  When the imaging lens 1 is applied to the 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 of the camera side on which the lens is mounted. It is assumed. For example, when the imaging lens 1 is used in a vehicle-mounted camera and used as a night vision camera for night vision assistance, blue light is cut from ultraviolet light between the lens system and the imaging device. A filter may be inserted.

  Alternatively, instead of disposing a low-pass filter or various filters that cut a specific wavelength region between the lens system and the image sensor 5, these various filters may be disposed between the lenses. Or you may give the coat | court which has the effect | action similar to various filters to the lens surface of either lens which the imaging lens 1 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 a light beam that becomes stray light to serve as a light shielding unit. Alternatively, a hood that blocks stray light may be disposed further on the object side of the most object side lens. As an example, FIG. 1 shows an example in which the light shielding means 11 and 12 are provided on the image-side surfaces of the first lens L1 and the second lens L2, respectively. It is not limited, You may arrange | position to another lens and between lenses.

  Further, a member that blocks the peripheral light may be disposed between the lenses. 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 blocking the peripheral rays in the range where the peripheral light amount ratio has no practical problem, 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.

  Next, specific numerical examples of the imaging lens according to the present invention will be described.

<Example 1>
FIG. 2 shows a lens configuration diagram of the imaging lens according to Example 1, and Table 1 shows lens data and various data.

  In the lens data of Table 1, the surface number indicates the i-th (i = 1, 2, 3,...) Surface number that sequentially increases toward the image side with the surface of the component closest to the object side as the first. The lens data in Table 1 includes the aperture stop St and the optical member PP.

  In Table 1, Ri represents the radius of curvature of the i-th (i = 1, 2, 3,...) Surface, and Di represents the i-th surface between the i (i = 1, 2, 3,...) Surface and the i + 1-th surface. The surface interval on the optical axis Z is shown. Ndj represents the refractive index with respect to the d-line of the j-th (j = 1, 2, 3,...) Optical element that increases sequentially toward the image side with the most optical element on the object side being first, and νdj is j The Abbe number for the d-line of the th optical element is shown. In Table 1, the radius of curvature is positive when convex on the object side and negative when convex on the image side.

  In the various data in Table 1, Fno. Is the F number, 2ω is the full field angle, L is the distance on the optical axis Z from the object side surface of the first lens L1 to the image plane (the back focus is the air equivalent length), and Bf is the image side of the sixth lens. The distance from the image surface to the image surface (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, f2 is the focal length of the second lens L2, and f3 is the first 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 f456 is from the fourth lens L4 to the sixth lens L6. (The combined focal length of the fourth lens L4, the fifth lens L5, and the sixth lens L6), IH is the maximum image height on the image plane, and ED1 is the maximum ray on the object side surface of the first lens L1. Is high.

  In the various data in Table 1, the unit of 2ω is degrees. Here, “mm” is used as the unit of the radius of curvature and the surface interval in Table 1, and the units of L, Bf, focal length, combined focal length, IH, and ED1 in Table 1. However, since the same optical performance can be obtained even if the optical system is proportionally enlarged or reduced, the unit is not limited to “mm”, and other appropriate units can also be used.

  In FIG. 2, the left side of the figure is the object side, and the right side is the image side. The aperture stop St shown in FIG. 2 does not indicate the shape or size, but indicates the position on the optical axis Z. The symbols Ri and Di (i = 1, 2, 3,...) In FIG. 2 correspond to Ri and Di in Table 1.

  The meaning of the symbols in Table 1 in the above description and the method of drawing the lens configuration diagram are basically the same for the examples described later.

  The imaging lens of Example 1 includes, in order from the object side, a first lens L1 as a biconcave lens, a second lens L2 as a biconvex lens, a third lens L3 as a biconvex lens, an aperture stop St, a fourth lens L4 as a biconcave lens, and both. It is composed of a fifth lens L5 that is a convex lens and a sixth lens L6 that is a biconvex lens.

<Example 2>
A lens configuration diagram of the imaging lens according to Example 2 is shown in FIG. 3, and lens data and various data are shown in Table 2. The imaging lens of Example 2 includes, in order from the object side, a first lens L1 that is a biconcave lens, a second lens L2 that is a positive meniscus lens having a convex surface facing the image side, a third lens L3 that is a biconvex lens, an aperture stop St, and both The lens includes a fourth lens L4 that is a concave lens, a fifth lens L5 that is a biconvex lens, and a sixth lens L6 that is a biconvex lens.

<Example 3>
FIG. 4 shows a lens configuration diagram of the imaging lens according to Example 3, and Table 3 shows lens data and various data. The imaging lens of Example 3 includes, in order from the object side, a first lens L1 that is a biconcave lens, a second lens L2 that is a positive meniscus lens having a convex surface facing the image side, a third lens L3 that is a biconvex lens, an aperture stop St, and both The lens includes a fourth lens L4 that is a concave lens, a fifth lens L5 that is a positive meniscus lens having a convex surface facing the image side, and a sixth lens L6 that is a positive meniscus lens having a convex surface facing the object side.

<Example 4>
FIG. 5 shows a lens configuration diagram of the imaging lens according to Example 4, and Table 4 shows lens data and various data. The imaging lens of Example 4 includes, in order from the object side, a first lens L1 that is a biconcave lens, a second lens L2 that is a positive meniscus lens having a convex surface facing the image side, a third lens L3 that is a biconvex lens, an aperture stop St, and both The lens includes a fourth lens L4 that is a concave lens, a fifth lens L5 that is a biconvex lens, and a sixth lens L6 that is a biconvex lens.

<Example 5>
FIG. 6 shows a lens configuration diagram of the imaging lens according to Example 5, and Table 5 shows lens data and various data. The imaging lens of Example 5 includes, in order from the object side, a first lens L1 as a biconcave lens, a second lens L2 as a biconvex lens, a third lens L3 as a biconvex lens, an aperture stop St, a fourth lens L4 as a biconcave lens, and an image. It is composed of a fifth lens L5 of a positive meniscus lens having a convex surface facing the side, and a sixth lens L6 of a biconvex lens.

Table 6 shows values corresponding to the conditional expressions (1) to (9) in the imaging lenses of Examples 1 to 5. In Examples 1 to 5, the d-line is used as a reference wavelength, and Table 6 shows values at this reference wavelength. As can be seen from Table 6, Examples 1 to 5 satisfy all conditional expressions (1) to (9).

  Aberration diagrams of spherical aberration, astigmatism, distortion (distortion aberration), and lateral chromatic aberration (chromatic aberration of magnification) of the imaging lens according to Example 1 are shown in FIGS. 7A, 7B, and 7C, respectively. As shown in FIG. Each aberration diagram shows the aberration with the d-line (587.56 nm) as the reference wavelength, but the spherical aberration diagram and the lateral chromatic aberration diagram show the F-line (wavelength 486.13 nm) and the C-line (wavelength 656.27 nm). , Aberrations for the s-line (852.11 nm) are also shown. In addition, the spherical aberration diagram also shows the amount of violation of the sine condition (Offset against the Sine Condition) as the OSC. Fno. Of spherical aberration diagram. Is an F number, and ω in other aberration diagrams represents a half angle of view. The distortion diagram shows the amount of deviation from the ideal image height f × tanφ using the focal length f and the angle of view φ (variable treatment, 0 ≦ φ ≦ ω) of the entire system.

  Similarly, the aberration diagrams of spherical aberration, astigmatism, distortion (distortion aberration), and lateral chromatic aberration of the imaging lenses according to Examples 2, 3, 4, and 5 are shown in FIGS. 8A to 8D, respectively. 9 (A) to 9 (D), FIG. 10 (A) to FIG. 10 (D), and FIG. 11 (A) to FIG. 11 (D). As can be seen from the respective aberration diagrams, in the first to fifth embodiments, each aberration is well corrected from the visible region to the near infrared region.

  The imaging lenses of Examples 1 to 5 can be manufactured at low cost because they are all composed of spherical lenses in the six-lens configuration and are all composed of a single lens without using any cemented lens. In addition, the imaging lenses of Examples 1 to 5 are compact and have a wide angle, have good optical performance, have an F number as small as 2.0, and are well corrected for aberrations from the visible range to the near infrared range. Therefore, it can be suitably used for a surveillance camera, a vehicle-mounted camera for taking images of the front, side, rear, etc. of an automobile.

  As a usage example, FIG. 12 illustrates a state in which an imaging apparatus including the imaging lens of the present embodiment is mounted on the automobile 100. In FIG. 12, an automobile 100 includes an outside camera 101 for imaging a blind spot range on the side surface on the passenger seat side, an outside 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 an embodiment of the present invention. The imaging lens of the embodiment of the present invention and an optical image formed by the imaging lens are converted into electrical signals. 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 in-vehicle camera 103 can be configured to be small and inexpensive, and the imaging surface of the imaging element is favorable. An image can be formed.

  The present invention has been described with reference to the embodiment and examples. However, the present invention is not limited to the above embodiment and example, 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.

  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.

1 is an optical path diagram of an imaging lens according to an embodiment of the present invention. Sectional drawing which shows the lens structure of the imaging lens concerning Example 1 of this invention. Sectional drawing which shows the lens structure of the imaging lens concerning Example 2 of this invention. Sectional drawing which shows the lens structure of the imaging lens concerning Example 3 of this invention. Sectional drawing which shows the lens structure of the imaging lens concerning Example 4 of this invention. Sectional drawing which shows the lens structure of the imaging lens concerning Example 5 of this invention. 7A to 7D are aberration diagrams of the imaging lens according to Example 1 of the present invention. 8A to 8D are aberration diagrams of the imaging lens according to Example 2 of the present invention. 9A to 9D are aberration diagrams of the imaging lens according to Example 3 of the present invention. 10A to 10D are aberration diagrams of the imaging lens according to Example 4 of the present invention. FIGS. 11A to 11D are graphs showing aberrations of the imaging lens according to Example 5 of the present invention. The figure for demonstrating arrangement | positioning of the vehicle-mounted imaging device concerning embodiment of this invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Imaging lens 2 On-axis light beam 3, 4 Off-axis light beam 5 Imaging element 11, 12 Light-shielding means 100 Car 101, 102 Outside camera 103 In-vehicle camera Di (i = 1, 2, 3, ...) i-th surface and i + 1th Surface Pim on the Optical Axis Pim Imaging Position L1 First Lens L2 Second Lens L3 Third Lens L4 Fourth Lens L5 Fifth Lens L6 Sixth Lens PP Optical Member Ri (i = 1, 2, 3) , ...) Radius of curvature of i-th surface St Aperture stop Z Optical axis

Claims (4)

In order from the object side, a first lens having a negative power with a concave surface facing the image side, a second lens having a positive power, a third lens having a positive power, a stop, and a negative that is a biconcave lens consists of a fourth lens having a power, and a fifth lens having a positive power whose convex surface faces the image side, a sixth lens having a positive power whose convex surface faces the object side,
The Abbe number with respect to the d-line of the material of the fourth lens is 30 or less,
The absolute value of the radius of curvature of the object side surface of the second lens is larger than the absolute value of the radius of curvature of the image side surface,
The absolute value of the radius of curvature of the object side surface of the third lens is smaller than the absolute value of the radius of curvature of the image side surface,
In the fifth lens, the absolute value of the radius of curvature of the object side surface is larger than the absolute value of the radius of curvature of the image side surface,
The absolute value of the curvature radius of the object side surface of the sixth lens is smaller than the absolute value of the curvature radius of the image side surface;
The focal length of the entire system is f, the combined focal length from the fourth lens to the sixth lens is f456, the radius of curvature of the object side surface of the fourth lens is R8, and the image side of the fourth lens The radius of curvature of the surface of the lens is R9, the distance on the optical axis from the object side surface of the lens closest to the object side to the image plane is L, and the optical axis from the image side surface of the lens closest to the image side to the image plane An imaging lens satisfying the following conditional expressions (1) to (4) , where Bf is an upper distance and f5 is a focal length of the fifth lens.
1.00 <f456 / f <1.88 (1)
0.30 <| R8 / R9 | <0.90 (2)
0.15 <Bf / (L−Bf) <0.25 (3)
1.20 <f5 / f <1.50 (4) When the air gap on the optical axis of the third lens and the diaphragm is D6 and the air gap on the optical axis of the diaphragm and the fourth lens is D7, the following conditional expression (5) is satisfied. claim 1 Symbol placement of the imaging lens is.
0.3 <D6 / D7 <1.2 (5) The imaging lens according to claim 1 or 2 , wherein when the focal length of the first lens is f1 and the focal length of the second lens is f2, the following conditional expression (6) is satisfied.
0.3 <| f1 / f2 | <1.0 (6) Imaging apparatus characterized by including an imaging lens of any one of claims 1 to 3.

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