JP6695995B2 - Imaging lens system and imaging device - Google Patents

Description

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

  In recent years, a lens corresponding to a wide field of view has been required as an imaging lens system for mounting on an automobile. 2. Description of the Related Art As an imaging lens system for use in an automobile, for example, there is an imaging lens system used for an on-vehicle camera for confirming the front, back, and sides to ensure safety when driving an automobile.

  The imaging lens system of the vehicle-mounted camera is required to have an extremely wide field of view, high resolution, and a bright imaging lens system with an F value of about 2.0. Further, compactness is also required especially in an imaging lens system for an on-vehicle camera.

  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. There is described an imaging lens system including a cemented lens which is made by cementing a fifth lens having a power of 5 and has a positive power as a whole, and a sixth lens which has 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, image pickup lens systems for use in automobiles are required to have a wider field angle of 180 degrees or more. Further, it is necessary to have a wide angle of view, favorably correct aberrations, and secure telecentricity.

  The imaging lens system described in Patent Document 1 has a total angle of view of about 150 degrees even though it is composed of six lenses, and the angle of view is rather narrow for use in a vehicle-mounted camera. Further, there is a problem that the angle of incidence of the principal ray on 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 provides an imaging lens system and an imaging device having a wide field angle of 90 ° or 100 ° or more at a half angle of view, which has good imaging performance and telecentricity. The purpose is to provide.

The imaging lens system of the present invention comprises, in order from the object side, a first lens having a concave shape and a negative power on the image side, a second lens having a concave shape on the image side and having a negative power, and a convex shape on the object side. At the image side, a fourth lens having a negative power at the image side, a fifth lens having a positive power at the object side, and a fifth lens having a positive power at the image side And a sixth lens having a power of, the image-side lens surface of the fourth lens and the object-side lens surface of the fifth lens are cemented together, and the focal length of the sixth lens is f ₆ , When the focal length of the entire lens system is f, it is desirable to satisfy the following conditional expression (1).
1.5 <f ₆ /f<2.5 (1)

When the value goes below the lower limit of conditional expression (1), the power of the sixth lens increases, and it becomes difficult to secure a wide angle of view. If the upper limit of conditional expression (1) is exceeded, the focal length of the sixth lens will become long, and the overall length of the imaging lens system will increase, making it difficult to miniaturize.
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 aspherical 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, which are cemented together, have different shapes from each other, so that the degree of freedom in surface design is increased, which is favorable. Excellent imaging performance can be obtained.

In the present invention, it is preferable that the following conditional expression (2) is satisfied, where f ₄₅ is the combined focal length of the fourth lens and the fifth lens, and f is the focal length of the entire lens system.
-0.1 <f / f ₄₅ <0.1 (2)

If the upper limit of conditional expression (2) is exceeded, the positive combined power of the fourth lens and the fifth lens becomes strong, so the back focus becomes short, and it becomes difficult to arrange the image sensor. Furthermore, since the angle of incidence of the principal ray on the image sensor increases, the amount of light decreases due to shading. When the value goes below the lower limit of the conditional expression (2), the negative combined power of the fourth lens and the fifth lens becomes strong, so that the total length of the imaging lens system increases, and downsizing becomes difficult.
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 , it is desirable to satisfy the following conditional expression (3).
_{-1.2 <f 4 / f 5 <} -0.9 (3)

  When the value goes below the lower limit of conditional expression (3), the power of the fourth lens decreases, so that the chromatic aberration correction is insufficient, and in this case also, the imaging performance deteriorates. When the value exceeds the upper limit of conditional expression (3), the power of the fourth lens increases, so that the correction of chromatic aberration becomes excessive and the imaging performance deteriorates.

  Furthermore, the imaging lens system of the present invention comprises, in order from the object side, a first lens having a concave shape and a negative power on the image side, a second lens having a concave shape on the image side and having a negative power, and an object side lens. A convex third lens having positive power, a fourth concave lens having negative power on the image side, a fifth lens convex on the object side having positive power, and a convex lens on the image side And a sixth lens having a positive power, and the image-side lens surface of the fourth lens and the object-side lens surface of the fifth lens are bonded together, and the Abbe number of the fourth lens is less than 21. Is desirable.

  By using the fourth lens having an Abbe number of less than 21 and high dispersion, the chromatic aberration correction capability is enhanced and good imaging performance is obtained.

  Furthermore, the imaging lens system of the present invention is characterized in that the Abbe number of the fifth lens is 55 or more. By using the fifth lens having a low dispersion with an Abbe number of 55 or more, the chromatic aberration correction capability is enhanced and good imaging performance is obtained.

  Further, the fourth lens having a high dispersion of Abbe's number less than 21 and the fifth lens of low dispersion having an Abbe's number of 55 or more further enhances the chromatic aberration correction capability to obtain good imaging performance.

  Furthermore, the imaging lens system of the present invention is characterized in that the Abbe number of the first lens is set to 40.7 or less. By setting the Abbe number of the first lens to 40.7 or less, it becomes easy to correct lateral chromatic aberration in particular, and good imaging performance is obtained in the entire lens system.

  Further, more desirably, by setting the Abbe number of the first lens to less than 36, it becomes easier to correct lateral chromatic aberration, and good imaging performance can be obtained.

  An image pickup apparatus of the present invention is characterized by including the above-mentioned image pickup lens system and an image pickup element arranged at a focal position of the image pickup lens system.

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

3 is a cross-sectional view of the image pickup lens system according to Example 1. FIG. FIG. 4 is an aberration diagram of the imaging lens system according to Example 1. FIG. 4 is an aberration diagram of the imaging lens system according to Example 1. 6 is a cross-sectional view of the image pickup lens system according to Example 2. FIG. FIG. 7 is an aberration diagram of the image pickup lens system according to Example 2; FIG. 7 is an aberration diagram of the image pickup lens system according to Example 2; FIG. 9 is a cross-sectional view of the image pickup lens system according to Example 3; FIG. 6 is an aberration diagram of the image pickup lens system according to Example 3; FIG. 6 is an aberration diagram of the image pickup lens system according to Example 3; It is a sectional view of the imaging device concerning an embodiment.

  Hereinafter, examples of the imaging lens system 11 according to the embodiment of the present invention will be described.

[Example 1]
FIG. 1 is a diagram showing the configuration of the imaging lens system 11 of Example 1. As shown in FIG. 1, the imaging lens system 11 of Example 1 includes a first lens L1 having a concave shape on the image side and a negative power, and a concave shape on the image side in order from the object side to the image side. The second lens L2 having negative power, the third lens L3 having a convex shape on the object side and having a positive power, the diaphragm STOP, the fourth lens L4 having a concave shape on the image side and having a negative power, and the object The fifth lens L5 has a convex shape on the side and has a positive power, and the sixth lens L6 has a convex shape on the image side and has a positive power. The image forming plane of the imaging lens system 11 is indicated by IMG.

  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 aspherical lens having negative power. The object-side lens surface S3 of the second lens L2 is an aspherical surface having a positive curvature, and the image-side lens surface S4 is an aspherical surface having a positive curvature. The object-side lens surface S3 has a convex curved surface portion projecting to the object side in the vicinity of the optical axis Z, and has a concave curved surface portion dented to the object side away from the optical axis, The surface has a so-called inflection point. 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 aspherical 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 that projects toward the object side, and the image-side lens surface S6 has a convex curved surface portion that projects toward the image side near the optical axis Z.

  The first lens L1 and the second lens L2 have a function of gradually converting an incident light ray from a large incident angle into a small angle along the optical axis Z and then passing the stop STOP. The image side lens surfaces of the first lens L1 and the second lens L2 both have a negative curvature and have a concave shape on the image side in order to spread the 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 rays diverged by the first lens L1 and the second lens L2. The above configuration is required to achieve a wide angle, and a total angle of view of 160 ° or more can be achieved.

  The fourth lens L4 is an aspherical lens having negative power. The object side lens surface S9 of the fourth lens L4 is an aspherical surface having a positive curvature, and the image side lens surface S10 is an aspherical surface having a positive curvature. The object-side lens surface S9 has a convex curved surface portion protruding 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 aspherical lens having positive power. The object-side lens surface S11 of the fifth lens L5 is an aspherical surface having a positive curvature, and the image-side lens surface S12 is an aspherical surface having a negative curvature. The object-side lens surface S11 has a convex curved surface protruding toward the object. The image side lens surface S12 has a convex curved surface portion protruding toward the object side. The image-side lens surface S10 of the fourth lens L4 and the object-side lens surface S11 of the fifth lens L5 have different shapes from each other, and are bonded together with an adhesive.

  The sixth lens L6 is an aspherical lens having positive power. The object side lens surface S13 of the sixth lens L6 is an aspherical surface having a positive curvature, and the image side lens surface S14 is an aspherical surface having a negative curvature. The object side lens surface S13 has a convex curved surface portion protruding toward the object side. The image side lens surface S14 has a convex curved surface portion protruding toward the image side.

  The fourth lens L4 is a lens having a negative power and a large dispersion with an Abbe number of 20.3. The fifth lens L5 is a lens having a positive power and an Abbe number of 56.2 and a small dispersion. The first lens is a lens having a relatively large dispersion with an Abbe number of 35.3. Therefore, the axial chromatic aberration and the lateral chromatic aberration can be corrected by combining the fourth lens L4 and the fifth lens L5 and further combining the first lens L1.

  In the sixth lens L6, the image-side lens surface S14 has a large positive power to converge the light rays. This ensures the telecentricity of the imaging lens system 11 and maintains the brightness of the entire lens system.

  In the imaging lens system 11 of the first embodiment, 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, and the focus when a temperature change occurs. Movement is canceled between plastic lenses to reduce the amount of focus movement.

  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 treated integrally with the imaging lens system 11 when the imaging lens system 11 is designed.

  Table 1 shows lens data of each lens surface of the imaging lens system 11. As lens data, the radius of curvature of each surface, the surface spacing, the refractive index, and the Abbe number are listed. The surface marked with "*" indicates that it is an aspherical surface.

  The aspherical shape used for the lens surface is a fourth order, a sixth order, an eighth order, a tenth order, where z is a sag amount, c is a reciprocal of a radius of curvature, k is a conic coefficient, and r is a ray height from the optical axis. , 12th, 14th, and 16th aspherical coefficients are α4, α6, α8, α10, α12, α14, and α16, respectively, and are expressed by the following equations.

Table 2 shows the aspherical surface coefficients for defining the aspherical surface shape of the lens surface that is an aspherical surface in the imaging lens system 11 of the first embodiment. In Table 2, for example, “−4.323344E-03” means “−4.323344 × 10 ⁻³ ”.

  2A and 2B are a longitudinal aberration diagram and a field curvature diagram of the imaging lens system 11 of Example 1, respectively. As shown in FIGS. 2A and 2B, in the imaging lens system 11 of Example 1, the half angle of view ω is 113 ° and the F value is 2.0. In the longitudinal aberration diagram of FIG. 2A, the horizontal axis represents the position where the light ray intersects the optical axis Z, and the left end of the horizontal axis of the graph is −0.05 mm and the right end is 0.05 mm, and the vertical axis represents the height at the pupil diameter. Show. In the field curvature diagram of FIG. 2B, the horizontal axis represents the distance in the optical axis Z direction, the left end of the graph horizontal axis is −0.10 mm and the right end is 0.10 mm, and the vertical axis represents the image height (angle of view). . In FIG. 2B, S represents the field curvature in the sagittal plane, and T represents the field curvature in the tangential plane. 2A and 2B show simulation results with a light beam having a wavelength of 546 nm.

Table 3 shows the results of calculating the characteristic values of the imaging lens system 11 of Example 1. In the imaging lens system 11, the F number is “FNo”, the distance from the object-side lens surface S1 of the first lens L1 to the image plane IMG of the imaging lens system 11 is “optical length”, and the focal length of the entire lens system is “ Whole system f ”, focal length of first lens L1 is“ f ₁ ”, focal length of second lens L2 is“ f ₂ ”, focal length of third lens L3 is“ f ₃ ”, focal point of fourth lens L4 distance _{"f 4",} the focal length of the fifth lens L5 _{"f 5",} the _{"f 6"} the focal length of the sixth lens L6, a first lens L1 of the composite focal length of the second lens L2 "f ₁₂ ", a second lens L2 of the composite focal length of the third lens L3" _{f 23} ", and the third lens L3 to composite focal length of the fourth lens L4" _{f 34} ", and the fourth lens L4 fifth the composite focal length of the lens L5 "f _45", indicating the fifth lens L5 composite focal distance "f _56," these characteristic values are displayed as the sixth lens L6. These various focal lengths were calculated using a light beam with a wavelength of 546 nm. (Note that the display items of each characteristic value are also followed in Table 6 (Example 2) and Table 9 (Example 3)).
The axial chromatic aberration at the wavelength of 436 nm to 656 nm in Example 1 is 0.040 mm.

[Example 2]
FIG. 3 is a diagram illustrating the configuration of the imaging lens system 11 according to the second 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 aspherical surface coefficients for defining the aspherical surface shape of the lens surface that is an aspherical surface in the imaging lens system 11 of Example 2.

  4A and 4B are a longitudinal aberration diagram and a field curvature diagram of the imaging lens system 11 of Example 2, respectively. In the longitudinal aberration diagram of FIG. 4A, the horizontal axis represents the position where the light ray intersects the optical axis Z, and the left end of the horizontal axis of the graph is −0.05 mm and the right end is 0.05 mm, and the vertical axis represents the height at the pupil diameter. Show. In the field curvature diagram of FIG. 4B, the horizontal axis indicates the distance in the optical axis Z direction, the left end of the graph horizontal axis is −0.10 mm, and the right end is 0.10 mm. As shown in FIGS. 4A and 4B, In the imaging lens system 11 of Example 2, the half angle of view ω is 108 ° and the F value is 2.0.

Table 6 shows the results of calculating the characteristic values of the imaging lens system 11 of Example 2.
The axial chromatic aberration at the wavelength of 436 nm to 656 nm in Example 2 is 0.040 mm.

[Example 3]
FIG. 5 is a diagram showing the configuration of the imaging lens system 11 of Example 3.

  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 the aspherical surface coefficients for defining the aspherical surface shape of the lens surface that is an aspherical surface in the imaging lens system 11 of Example 3.

6A and 6B are a longitudinal aberration diagram and a field curvature diagram of the imaging lens system 11 of Example 3.
In the longitudinal aberration diagram of FIG. 6A, the horizontal axis represents the position where the light beam intersects the optical axis Z, and the left end of the graph horizontal axis is −0.05 mm and the right end is 0.05 mm, and the vertical axis represents the height at the pupil diameter. Show. In the field curvature diagram of FIG. 6B, the horizontal axis represents the distance in the optical axis Z direction, the left end of the graph horizontal axis is −0.05 mm, the right end is 0.05 mm, and the vertical axis represents the image height (angle of view). .. As shown in FIGS. 6A and 6B, in the imaging lens system 11 of Example 3, the half angle of view ω is 110 ° 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. The axial chromatic aberration at a wavelength of 436 nm to 656 nm in Example 3 is 0.022 mm.

[Summary of conditional expressions]
Table 10 shows the results of calculating the parameters of the conditional expressions (1), (2) and (3) in the imaging lens system 11 of Examples 1 to 4.

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

  The image sensor 14 is an element that converts received light into an electric signal, and for example, a CCD image sensor or a CMOS image sensor is used. The image pickup element 14 is arranged at the focal position of the image pickup 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 matter.

  The present invention is not limited to the above-mentioned embodiments, but can be modified 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 an in-vehicle camera, but can be used for other purposes such as a surveillance camera and a camera mounted on a small electronic device such as a mobile phone.

   This application claims the priority on the basis of Japanese application Japanese Patent Application No. 2016-197128 for which it applied on October 5, 2016, and takes in those the indications of all here.

10 Imaging Device 11 Imaging Lens 12 IR Cut Filter 13 Cover Glass 14 Imaging Elements L1 to L6 First Lens to Sixth Lens

Claims (11)

From the object side,
A first lens having a concave image side surface and negative power,
A second lens having a concave image side surface and negative power;
A third lens having a convex surface on the object side and having a positive power;
A fourth lens having a negative power, in which the object side surface is convex and the image side surface is concave;
A fifth lens having a positive power whose object side surface is convex and whose image side surface is concave;
And a sixth lens having a convex power on the image side and having a positive power,
The image side lens surface of the fourth lens and the object side lens surface of the fifth lens are bonded together ,
When the focal length of the sixth lens is f6 and the focal length of the entire lens system is f,
An imaging lens system satisfying the following conditional expression (1).
1.5 <f6 / f <2.5 (1) From the object side,
A first lens having a concave image side surface and negative power,
A second lens having a concave image side surface and negative power;
A third lens having a convex surface on the object side and having a positive power;
A fourth lens having a negative power, in which the object side surface is convex and the image side surface is concave;
A fifth lens having a positive power whose object side surface is convex and whose image side surface is concave;
A sixth lens having a convex power on the image side and having a positive power, and an image side lens surface of the fourth lens and an object side lens surface of the fifth lens are bonded together ,
An imaging lens system, wherein the Abbe number of the first lens is less than 41. From the object side,
A first lens having a concave image side surface and negative power,
A second lens having a concave image side surface and negative power;
A third lens having a convex surface on the object side and having a positive power;
A fourth lens having a negative power, in which the object side surface is convex and the image side surface is concave;
A fifth lens having a positive power whose object side surface is convex and whose image side surface is concave;
A sixth lens having a convex power on the image side and having a positive power, and an image side lens surface of the fourth lens and an object side lens surface of the fifth lens are bonded together ,
An imaging lens system, wherein the Abbe number of the fourth lens is less than 21, and the Abbe number of the fifth lens is 55 or more. The image side surface of the fourth lens and the object side surface of the fifth lens are both aspherical surfaces, and the image side surface of the fourth lens and the object side surface of the fifth lens are different from each other. Item 4. The imaging lens system according to any one of items 1 to 3. The combined focal length of the fourth lens and the fifth lens is f ₄₅ The imaging lens system according to any one of claims 1 to 3, wherein the following conditional expression (2) is satisfied, where f is the focal length of the entire lens system.
-0.2 <f / f ₄₅ <0.1 (2) The focal length of the fourth lens is f _Four , The focal length of the fifth lens is f ₅ When satisfy | filling, the following conditional expression (3) is satisfy | filled, The imaging lens system in any one of Claim 1 to 3 characterized by the above-mentioned.
-1.2 <f _Four / F ₅ <-0.9 (3) The image pickup lens system according to any one of claims 1 to 3, wherein the half angle of view is 90 ° or more. The image pickup lens system according to claim 1, wherein the half angle of view is 100 ° or more. The imaging lens system according to claim 2, wherein the Abbe number of the first lens is less than 36. The image pickup lens system according to claim 2, wherein the Abbe number of the fourth lens is less than 21, and the Abbe number of the fifth lens is 55 or more. An image pickup apparatus comprising: the image pickup lens system according to claim 1; and an image pickup element arranged at a focal position of the image pickup lens system.

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