JP2016188893A - Imaging lens system and imaging device - Google Patents

Abstract

An object of the present invention is to provide an imaging lens system and imaging apparatus with a wide angle of view and excellent imaging performance and telecentricity. An imaging lens system 11 of the present invention includes, in order from the object side, a first lens L1 having a concave shape on the image side and having negative power, and a second lens L2 having a concave shape on the image side and having negative power. a third lens L3 having a convex shape on the object side and having positive power; a fourth lens L4 having a concave shape on the image side and having negative power; and a fifth lens having a convex shape on the object side and having positive power. L5 and a sixth lens L6 having a convex shape on the image side and having positive power, and the image side lens surface S10 of the fourth lens L4 and the object side lens surface S11 of the fifth lens L5 are cemented together. An imaging lens system that satisfies 1.5<f6/f<2.5, where f6 is the focal length of the sixth lens L6 and f is the focal length of the entire lens system. [Selection drawing] Fig. 1

Description

  The present invention relates to an imaging lens system and an imaging apparatus.

  In recent years, a lens corresponding to a wide field of view is required as an imaging lens system for use in automobiles. As an imaging lens system for use in an automobile, for example, there is an imaging lens system used for an in-vehicle camera for confirming a front, a back, and a side for ensuring safety when driving an automobile.

  An imaging lens system of an in-vehicle camera is required to be a bright imaging lens system having an extremely wide field of view, high resolution, and an F value of about 2.0. In particular, an imaging lens system for a vehicle-mounted camera is also required to be compact.

  In Patent Document 1, in order from the object side, a first lens having negative power, a second lens having negative power, a third lens having positive power, a diaphragm, a fourth lens having negative power, and a positive lens are disclosed. An imaging lens system is described that includes a cemented lens having a positive power as a whole and a sixth lens having a positive power. This imaging lens system has a wide angle, a small F value, and high imaging performance.

Japanese Patent No. 5045300

  In recent years, imaging lens systems for use in automobiles have been required to have a wider field angle of 180 degrees or more. In addition, it is necessary to have a wide angle of view, correct aberration correction, and ensure telecentricity.

  The imaging lens system described in Patent Literature 1 is bright with an F value of 2.0 and has good imaging performance. However, although the imaging lens system described in Patent Document 1 is configured with six lenses, the total angle of view is about 150 degrees, and the angle of view is slightly narrow for use in an in-vehicle camera. Furthermore, there is a problem that the chief ray incident angle to the image sensor is not sufficiently small and the telecentricity is insufficient.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide an imaging lens system and an imaging apparatus with a wide angle of view having good imaging performance and telecentricity.

The imaging lens system of the present invention is
From the object side,
A first lens having a negative shape and a negative power on the image side;
A second lens that is concave on the image side and has negative power;
A third lens having a positive power convex on the object side;
A fourth lens that is concave on the image side and has negative power;
A fifth lens having a positive power convex on the object side;
A sixth lens having a positive shape and a convex shape on the image side,
The image side lens surface of the fourth lens and the object side lens surface of the fifth lens are bonded together,
An imaging lens system that satisfies the following conditional expression (1), where f _{6 is} the focal length of the sixth lens and f is the focal length of the entire lens system.
1.5 <f ₆ /f<2.5 (1)

In the imaging lens system of the present invention, if the lower limit value of conditional expression (1) is not reached, the power of the sixth lens increases, so it is difficult to ensure a wide angle of view. If the upper limit value of conditional expression (1) is exceeded, the focal length of the sixth lens becomes long, so the total length of the imaging lens system increases and it becomes difficult to reduce the size.
In the imaging lens system of the present invention, 2.0 <f ₆ /f<2.5 is more preferable, and 2.3 <f ₆ /f<2.5 is further preferable.

  In the present invention, the image side lens surface of the fourth lens and the object side lens surface of the fifth lens are aspheric surfaces, and the image side lens surface of the fourth lens and the object side lens surface of the fifth lens are non-spherical. It is preferable that the spherical coefficients are different.

  In the imaging lens system of the present invention, the image-side lens surface of the fourth lens and the object-side lens surface of the fifth lens that are bonded to each other have different shapes, so that the degree of freedom in surface design increases. Image performance can be obtained.

In the present invention, when the combined focal length of the fourth lens and the fifth lens is f ₄₅ and the focal length of the entire lens system is f, the following conditional expression (2) is satisfied: The imaging lens system according to claim 1 or 2.
−0.1 <f / f ₄₅ <0.1 (2)

If the upper limit value of conditional expression (2) is exceeded, the positive combined power of the fourth lens and the fifth lens becomes strong, so that the back focus is shortened and it is difficult to arrange the image sensor. Furthermore, since the chief ray incident angle to the image sensor increases, the amount of light decreases due to shading. If the lower limit value of conditional expression (2) is not reached, the negative combined power of the fourth lens and the fifth lens becomes strong, leading to an increase in the overall length of the imaging lens system, making it difficult to reduce the size.
In the imaging lens system of the present invention, it is more preferable that 0 <f / f ₄₅ <0.1.

In the present invention, when the focal length of the fourth lens is f ₄ and the focal length of the fifth lens is f ₅ , the following conditional expression (3) is satisfied: The imaging lens system according to any one of the above.
−1.2 <f ₄ / f ₅ <−0.9 (3)

  If the lower limit value of conditional expression (3) is not reached, the power of the fourth lens decreases, so that chromatic aberration correction is insufficient, and in this case as well, the imaging performance is deteriorated. If the upper limit value of conditional expression (3) is exceeded, the power of the fourth lens will increase, so that correction of chromatic aberration will be excessive and image formation performance will be degraded.

The imaging apparatus of the present invention
The imaging lens system described above;
And an image pickup device disposed at a focal position of the image pickup lens system.

  According to the present invention, it is possible to provide an imaging lens system and an imaging apparatus with a wide angle of view having good imaging performance and telecentricity.

1 is a cross-sectional view of an imaging lens system according to Example 1. FIG. FIG. 4 is an aberration diagram of the imaging lens system according to Example 1. 6 is a cross-sectional view of an imaging lens system according to Example 2. FIG. 6 is an aberration diagram of the imaging lens system according to Example 2. FIG. 6 is a cross-sectional view of an imaging lens system according to Example 3. FIG. FIG. 6 is an aberration diagram of the imaging lens system according to Example 3. 6 is a cross-sectional view of an imaging lens system according to Example 4. FIG. FIG. 10 is an aberration diagram of the imaging lens system according to Example 4. It is sectional drawing of the imaging device which concerns on embodiment.

  Examples of the imaging lens system 11 according to the embodiment of the present invention will be described below.

[Example 1]
FIG. 1 is a diagram illustrating a configuration of the imaging lens system 11 according to the first embodiment. As shown in FIG. 1, the imaging lens system 11 of Example 1 has a first lens L1 having a negative shape and a negative power on the image side, and a concave shape on the image side, in order from the object side to the image side. A second lens L2 having negative power, a third lens L3 having a positive shape and a positive power on the object side, a stop STOP, a fourth lens L4 having a negative shape and a negative power on the image side, and an object The fifth lens L5 is convex on the side and has positive power, and the sixth lens L6 is convex on the image side and has positive power. The imaging plane of the imaging lens system 11 is indicated by IMG. In the imaging lens system 11 of Example 1, the second lens L2 to the fifth lens L5 are plastic lenses, and the first lens L1 and the sixth lens L6 are glass lenses.

  The first lens L1 is a spherical meniscus lens having negative power. The object side lens surface S1 of the first lens L1 is a spherical surface having a positive curvature, and the image side lens surface S2 is a spherical surface having a positive curvature. The object side lens surface S1 has a convex curved surface portion protruding toward the object side. The image side lens surface S2 has a concave curved surface portion that is recessed toward the object side.

  The second lens L2 is an aspheric lens having negative power. The object side lens surface S3 of the second lens L2 is an aspheric surface having a positive curvature, and the image side lens surface S4 is an aspheric surface having a positive curvature. The object side lens surface S3 has a convex curved surface portion projecting toward the object side in the vicinity of the optical axis Z. The image side lens surface S4 has a concave curved surface portion that is recessed toward the object side.

  The third lens L3 is an aspheric lens having positive power. The object side lens surface S5 is an aspherical surface having a positive curvature, and the image side lens surface S6 is an aspherical surface having a negative curvature. The object side lens surface S5 has a convex curved surface portion protruding toward the object side, and the image side lens surface S6 has a convex curved surface portion protruding toward the image side in the vicinity of the optical axis Z.

  The first lens L1 and the second lens L2 have a function of converting incident light from a large incident angle little by little to a small angle along the optical axis Z before passing through the stop STOP. The image side lens surfaces of the first lens L1 and the second lens L2 both have negative curvatures in order to spread light rays. The third lens L3 is a positive lens having a convex shape on the object side, and has a function of converging the light beams diverged by the first lens L1 and the second lens L2. The above-described configuration is necessary to achieve a wide angle, and a full angle of view of 160 degrees or more can be achieved.

  The fourth lens L4 is an aspheric lens having negative power. The object side lens surface S9 of the fourth lens L4 is an aspheric surface having a positive curvature, and the image side lens surface S10 is an aspheric surface having a positive curvature. The object-side lens surface S9 has a convex curved surface portion that protrudes toward the object side in the vicinity of the optical axis Z. The image side lens surface S10 has a concave curved surface portion that is recessed toward the object side.

  The fifth lens L5 is an aspheric lens having positive power. The object side lens surface S11 of the fifth lens L5 is an aspheric surface having a positive curvature, and the image side lens surface S12 is an aspheric surface having a negative curvature. The object side lens surface S11 has a convex curved surface portion protruding toward the object side. The image side lens surface S12 has a convex curved surface portion that protrudes toward the image side in the vicinity of the optical axis Z. The image side lens surface S10 of the fourth lens L4 and the object side lens surface S11 of the fifth lens L5 are bonded together with an adhesive.

  The sixth lens L6 is an aspheric lens having positive power. The object side lens surface S13 of the sixth lens L6 is an aspheric surface having a positive curvature, and the image side lens surface S14 is an aspheric surface having a negative curvature. The object side lens surface S13 has a convex curved surface portion projecting toward the object side in the vicinity of the optical axis Z. The image side lens surface S14 has a convex curved surface portion protruding toward the image side.

  The fourth lens L4 is a highly dispersed lens having negative power. The fifth lens L5 is a lens with positive power and small dispersion. Therefore, by combining the fourth lens L4 and the fifth lens L5, axial chromatic aberration and lateral chromatic aberration can be corrected.

  In the sixth lens L6, the image side lens surface S14 has a large positive power to converge the light rays. Thereby, the telecentricity of the imaging lens system 11 is ensured, and the brightness of the entire lens system is maintained.

  The IR cut filter 12 is a filter for cutting light in the infrared region. The cover glass 13 is a glass plate for protecting the image sensor. The IR cut filter 12 and the cover glass 13 are handled as an integral part of the imaging lens system 11 when the imaging lens system 11 is designed. However, the IR cut filter 12 and the cover glass 13 are not essential components of the imaging lens system 11.

  Table 1 shows lens data of each lens surface of the imaging lens system 11. The lens data includes the radius of curvature, surface spacing, refractive index, and Abbe number of each surface. A surface marked with “*” indicates an aspherical surface. The eighth surface in Table 1 is a dummy surface used during design.

  The aspherical shape adopted for the lens surface is 4th, 6th, 8th, 10th, where z is the sag amount, c is the reciprocal of the radius of curvature, k is the cone coefficient, and r is the height of the light beam from the optical axis. The 12th, 14th, and 16th aspherical coefficients are expressed by the following equations when α4, α6, α8, α10, α12, α14, and α16, respectively.

Table 2 shows the aspheric coefficients for defining the aspherical shape of the aspherical lens surface in the imaging lens system 11 of Example 1. In Table 2, for example, “−3.055534E-03” means “−3.055534 × 10 ⁻³ ”.

  2A to 2C are a longitudinal aberration diagram, a field curvature diagram, and a distortion diagram of the imaging lens system 11 of Example 1. FIG. As shown in FIGS. 2A to 2C, in the imaging lens system 11 of Example 1, the half angle of view ω is 102 ° and the F value is 2.0. In the longitudinal aberration diagram of FIG. 2A, the horizontal axis indicates the position where the light beam intersects the optical axis Z, and the vertical axis indicates the height at the pupil diameter. In the field curvature diagram of FIG. 2B, the horizontal axis indicates the distance in the optical axis Z direction, and the vertical axis indicates the image height (field angle). In FIG. 2B, Sag indicates the field curvature in the sagittal plane, and Tan indicates the field curvature in the tangential plane. In the distortion diagram of FIG. 2C, the horizontal axis represents the amount of image distortion (%), and the vertical axis represents the image height (field angle). FIG. 2A to FIG. 2C show simulation results using light rays having a wavelength of 546 nm.

Table 3 shows the result of calculating the characteristic value of the imaging lens system 11 of Example 1. In the imaging lens system 11, the F value is FNo, the distance from the object side lens surface S1 of the first lens L1 to the imaging plane IMG of the imaging lens system 11 is “optical total length”, the focal length of the entire lens system is f, focal length _{f 1} of the first lens L1, the focal distance _{f 2} of the second lens L2, the focal length of the third lens L3 _{f 3,} a focal length of the fourth lens L4 _{f 4,} a focal length of the fifth lens L5 F ₅ , the focal length of the sixth lens L 6 is f ₆ , the combined focal length of the first lens L 1 and the second lens L 2 is f ₁₂ , and the combined focal length of the second lens L 2 and the third lens L 3 is f _23. The combined focal length of the third lens L3 and the fourth lens L4 is f ₃₄ , the combined focal length of the fourth lens L4 and the fifth lens L5 is f ₄₅ , and the combined focal length of the fifth lens L5 and the sixth lens L6. When the distance is f ₅₆ , these The characteristic values are as shown in Table 3. Various focal lengths were calculated using light rays with a wavelength of 546 nm.

[Example 2]
FIG. 3 is a diagram illustrating a configuration of the imaging lens system 11 according to the second embodiment. As shown in FIG. 3, the first lens L <b> 1 to the sixth lens L <b> 6 have the same shape as in the first embodiment. In the imaging lens system 11 of Example 2, the second lens L2 to the fifth lens L5 are plastic lenses, and the first lens L1 and the sixth lens L6 are glass lenses.

  Table 4 shows lens data of each lens surface of the imaging lens system 11 of Example 2.

  Table 5 shows the aspheric coefficients for defining the aspherical shape of the aspherical lens surface in the imaging lens system 11 of Example 2.

  4A to 4C are a longitudinal aberration diagram, a field curvature diagram, and a distortion diagram of the imaging lens system 11 of Example 2. FIG. As shown in FIGS. 4A to 4C, in the imaging lens system 11 of Example 2, the half angle of view ω is 102 ° and the F value is 2.0.

  Table 6 shows the result of calculating the characteristic value of the imaging lens system 11 of Example 2.

[Example 3]
FIG. 5 is a diagram illustrating a configuration of the imaging lens system 11 according to the third embodiment. The first lens L1 to the fifth lens L5 have the same shape as in the first embodiment. The shape of the sixth lens L6 is different from that of the first embodiment.

  The sixth lens L6 is an aspheric lens having positive power. The object side lens surface S13 of the sixth lens L6 is an aspheric surface having a negative curvature, and the image side lens surface S14 is an aspheric surface having a negative curvature. The object-side lens surface S13 has a concave curved surface portion that is recessed toward the image side in the vicinity of the optical axis Z. The image side lens surface S14 has a convex curved surface portion protruding toward the image side.

  In the imaging lens system 11 of Example 3, the second lens L2 to the fifth lens L5 are plastic lenses, and the first lens L1 and the sixth lens L6 are glass lenses.

  Table 7 shows lens data of each lens surface of the imaging lens system 11 of Example 3.

  Table 8 shows aspherical coefficients for defining the aspherical shape of the aspherical lens surface in the imaging lens system 11 of Example 3.

  6A to 6C are a longitudinal aberration diagram, a field curvature diagram, and a distortion diagram of the imaging lens system 11 of Example 3. FIG. As shown in FIGS. 6A to 6C, in the imaging lens system 11 of Example 3, the half angle of view ω is 102 ° and the F value is 2.0.

  Table 9 shows the results of calculating the characteristic values of the imaging lens system 11 of Example 3.

[Example 4]
FIG. 7 is a diagram illustrating a configuration of the imaging lens system 11 according to the fourth embodiment. As shown in FIG. 7, the first lens L1 to the sixth lens L6 have the same shape as in the third embodiment. In the imaging lens system 11 of Example 4, the second lens L2 to the fifth lens L5 are plastic lenses, and the first lens L1 and the sixth lens L6 are glass lenses.

  Table 10 shows lens data of each lens surface of the imaging lens system 11 of Example 4.

  Table 11 shows aspherical coefficients for defining the aspherical shape of the aspherical lens surface in the imaging lens system 11 of Example 4.

  8A to 8C are a longitudinal aberration diagram, a field curvature diagram, and a distortion diagram of the imaging lens system 11 of Example 4. FIG. As shown in FIGS. 8A to 8C, in the imaging lens system 11 of Example 2, the half angle of view ω is 102 ° and the F value is 2.0.

  Table 12 shows the result of calculating the characteristic value of the imaging lens system 11 of Example 4.

[Summary of conditional expressions]
Table 13 shows the results of calculating the parameters of conditional expressions (1), (2), and (3) in the imaging lens systems 11 of Examples 1 to 4.

[Application example to imaging device]
FIG. 9 is a diagram illustrating a configuration of the imaging apparatus 10 using the imaging lens system 11. The imaging device 10 includes an imaging lens system 11, an IR cut filter 12, a cover glass 13, and an imaging element 14. The imaging lens system 11, the IR cut filter 12, the cover glass 13, and the imaging element 14 are accommodated in a housing (not shown).

  The imaging element 14 is an element that converts received light into an electrical signal, and for example, a CCD image sensor or a CMOS image sensor is used. The imaging element 14 is disposed at the focal position of the imaging lens system 11. The horizontal angle of view is an angle of view corresponding to the horizontal direction of the image sensor 14.

  The IR cut filter 12 is a filter for cutting light in the infrared region. Only visible light passes through the IR cut filter 12 and enters the image sensor 14. The cover glass 13 is provided on the image sensor 14 in order to protect the image sensor 14 from foreign substances.

  Note that the present invention is not limited to the above-described embodiment, and can be changed as appropriate without departing from the spirit of the present invention. For example, the use of the imaging lens system 11 of the present invention is not limited to the in-vehicle camera, but can be used for other uses such as a surveillance camera and a camera mounted on a small electronic device such as a mobile phone.

DESCRIPTION OF SYMBOLS 10 Imaging device 11 Imaging lens 12 IR cut filter 13 Cover glass 14 Imaging element L1-L6 1st lens-6th lens

Claims (5)

From the object side,
A first lens having a negative shape and a negative power on the image side;
A second lens that is concave on the image side and has negative power;
A third lens having a positive power convex on the object side;
A fourth lens that is concave on the image side and has negative power;
A fifth lens having a positive power convex on the object side;
A sixth lens having a positive shape and a convex shape on the image side,
The image side lens surface of the fourth lens and the object side lens surface of the fifth lens are bonded together,
An imaging lens system that satisfies the following conditional expression (1), where f _{6 is} the focal length of the sixth lens and f is the focal length of the entire lens system.
1.5 <f ₆ /f<2.5 (1)   The image side lens surface of the fourth lens and the object side lens surface of the fifth lens are aspheric surfaces, and the aspheric coefficients of the image side lens surface of the fourth lens and the object side lens surface of the fifth lens are different. The imaging lens system according to claim 1, wherein: The following conditional expression (2) is satisfied, where f ₄₅ is a combined focal length of the fourth lens and the fifth lens, and f is a focal length of the entire lens system. The imaging lens system according to 2.
−0.1 <f / f ₄₅ <0.1 (2) Focal length f ₄ of the fourth _lens, the focal length of the fifth lens when the f _5, any one of claims 1, characterized by satisfying the following conditional expression (3) 3 1 The imaging lens system according to item.
−1.2 <f ₄ / f ₅ <−0.9 (3) An imaging lens system according to any one of claims 1 to 4,
An image pickup device disposed at a focal position of the image pickup lens system.