JP6952830B2 - Imaging lens system - Google Patents

Description

The present invention relates to an image pickup lens system and an image pickup apparatus.

In recent years, a lens compatible with a wide field of view has been required as an image pickup lens system for automobile mounting applications. As an image pickup lens system for automobile mounting applications, for example, there is an image pickup lens system used for an in-vehicle camera for checking the front, back, and sides for ensuring safety when driving a car.

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

Patent Document 1 describes, in order from the object side, a first lens having a negative power, a second lens having a negative power, a third lens having a positive power, an aperture, a fourth lens having a negative power, and a positive lens. Described is an imaging lens system composed of a bonded lens formed by bonding a fifth lens having the power of the above and having a positive power as a whole, and a sixth lens having a positive power. This image pickup 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 automobile mounting applications are required to have a wider angle of view with a total angle of view of 180 degrees or more. Further, it is required that the angle of view is wide, the aberration is corrected well, and the telecentricity is ensured.

Although the image pickup lens system described in Patent Document 1 is composed of 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. Further, there is a problem that the angle of incidence of the main ray on the image sensor is not sufficiently small and the telecentricity is insufficient.

The present invention has been made to solve the above-mentioned problems, and provides an image pickup lens system and an image pickup apparatus having a wide angle of view of 90 ° or 100 ° or more at a half angle of view having good imaging performance and telecentricity. The purpose is to provide.

The imaging lens system of the present invention has a first lens having a concave shape and negative power on the image side, a second lens having a concave shape and negative power on the image side, and a convex shape on the object side in order from the object side. A third lens having a positive power, a fourth lens having a concave shape on the image side and having a negative power, a fifth lens having a convex shape on the object side and having a positive power, and a lens having a convex shape on the image side and having a positive power. of the sixth lens having a power, is composed of the fourth lens are combined image-side lens surface and the object-side lens surface of the fifth lens is attached, and the sixth lens the focal length of f _6, When the focal distance of the entire lens system is f, it is desirable that the following conditional expression (1) is satisfied.
1.5 <f ₆ / f <2.5 (1)

If it falls below the lower limit of the conditional expression (1), the power of the sixth lens increases, so that it becomes difficult to secure a wide angle of view. If the upper limit of the conditional expression (1) is exceeded, the focal length of the sixth lens becomes long, so that the total length of the image pickup lens system increases and miniaturization becomes difficult.
In the image pickup 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 even more 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, and the image-side lens surface of the fourth lens and the object-side lens surface of the fifth lens are aspherical. It is preferable that the spherical coefficients are different.

In the image pickup lens system of the present invention, the degree of freedom in surface design is increased by forming the image-side lens surface of the fourth lens and the object-side lens surface of the fifth lens, which are bonded to each other, into different shapes, which is good. Excellent imaging performance can be obtained.

In the present invention, it is preferable that the following conditional expression (2) is satisfied 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.}
-0.1 <f / f ₄₅ <0.1 (2)

If the upper limit of the conditional expression (2) is exceeded, the positive combined power of the fourth lens and the fifth lens becomes stronger, so that the back focus becomes shorter and it becomes difficult to arrange the image sensor. Further, since the angle of incidence of the main light beam on the image sensor is increased, the amount of light is reduced due to shading. If it falls below the lower limit of the conditional expression (2), the negative combined power of the fourth lens and the fifth lens becomes stronger, which leads to an increase in the overall length of the imaging lens system and makes miniaturization difficult.
In the image pickup lens system of the present invention, it is more preferable that _{0 <f / f 45 <0.1.}

In the present invention, the focal length f ₄ of the fourth _lens, the focal length of the fifth lens when the f _5, it is desirable to satisfy the following conditional expression (3).
-1.2 <f ₄ / f ₅ <-0.9 (3)

If it is less than the lower limit of the conditional expression (3), the power of the fourth lens is reduced, so that the chromatic aberration correction is insufficient, and even in this case, the imaging performance is deteriorated. If the upper limit of the conditional expression (3) is exceeded, the power of the fourth lens increases, so that the correction of chromatic aberration becomes excessive and the imaging performance deteriorates.

Further, in the imaging lens system of the present invention, in order from the object side, the first lens having a concave shape and negative power on the image side, the second lens having a concave shape and negative power on the image side, and the object side A third lens that is convex and has positive power, a fourth lens that is concave and has negative power on the image side, a fifth lens that is convex and has positive power on the object side, and a convex shape on the image side. It is composed of 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 to each other, and the abbe number of the fourth lens is less than 21. Is desirable.

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

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

Further, the chromatic aberration correction ability is further enhanced and good imaging performance is obtained by configuring the fourth lens having a high dispersion with an Abbe number of less than 21 and the fifth lens having a low dispersion with an Abbe number of 55 or more.

Further, the image pickup lens system of the present invention is characterized in that the Abbe number of the first lens is 40.7 or less. By setting the Abbe number of the first lens to 40.7 or less, it is particularly easy to correct the chromatic aberration of magnification, and good imaging performance is obtained in the entire lens system.

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

The image pickup apparatus of the present invention is characterized by having 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 and an image pickup apparatus having a wide angle of view having good imaging performance and telecentricity.

It is sectional drawing of the image pickup lens system which concerns on Example 1. FIG. It is an aberration diagram of the image pickup lens system which concerns on Example 1. FIG. It is an aberration diagram of the image pickup lens system which concerns on Example 1. FIG. It is sectional drawing of the image pickup lens system which concerns on Example 2. FIG. It is an aberration diagram of the image pickup lens system which concerns on Example 2. FIG. It is an aberration diagram of the image pickup lens system which concerns on Example 2. FIG. It is sectional drawing of the image pickup lens system which concerns on Example 3. FIG. It is an aberration diagram of the image pickup lens system which concerns on Example 3. FIG. It is an aberration diagram of the image pickup lens system which concerns on Example 3. FIG. It is sectional drawing of the image pickup apparatus which concerns on embodiment.

Hereinafter, examples of the image pickup 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 image pickup lens system 11 of the first embodiment. As shown in FIG. 1, the image pickup lens system 11 of the first embodiment has a first lens L1 having a concave shape on the image side and having a negative power, and a concave shape on the image side in order from the object side to the image side. A second lens L2 having a negative power, a third lens L3 having a convex shape on the object side and having a positive power, an aperture STOP, a fourth lens L4 having a concave shape on the image side and having a negative power, and an object. It is composed of a fifth lens L5 having a convex shape on the side and having positive power, and a sixth lens L6 having a convex shape on the image side and having positive power. The image plane of the image pickup lens system 11 is indicated by IMG.

The first lens L1 is a spherical meniscus lens having a 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 that protrudes toward the object side. The image-side lens surface S2 has a concave curved surface portion recessed toward the object side.

The second lens L2 is an aspherical lens having a 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 protruding toward the object side in the vicinity of the optical axis Z, and has a concave curved surface portion dented toward the object side at a distance from the optical axis. It has a surface shape with so-called inflection points. The image-side lens surface S4 has a concave curved surface portion recessed toward the object side.

The third lens L3 is an aspherical lens having a 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 gradually converting an incident light ray from a large incident angle into a small angle along the optical axis Z and then passing the diaphragm STOP. The image-side lens surfaces of the first lens L1 and the second lens L2 both have a negative curvature in order to spread light rays, and have a concave shape on the image side. The third lens L3 is a positive lens having a convex shape toward the object side, and has a function of converging the light rays emitted by the first lens L1 and the second lens L2. The above configuration is required to achieve a wide angle, and an overall angle of view of 160 ° or more can be achieved.

The fourth lens L4 is an aspherical lens having a 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 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 recessed on the object side.

The fifth lens L5 is an aspherical lens having a 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 portion that protrudes toward the object side. The image-side lens surface S12 has a convex curved surface portion that protrudes 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 and are bonded by an adhesive.

The sixth lens L6 is an aspherical lens having a 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 that protrudes 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 having a large Abbe number of 20.3 and a large dispersion. The fifth lens L5 is a lens having a positive power and having a small Abbe number of 56.2 and a small dispersion. The first lens has a relatively large dispersion of 35.3 Abbe numbers. Therefore, by combining the fourth lens L4 and the fifth lens L5, and further combining the first lens L1, axial chromatic aberration and magnifying chromatic aberration can be corrected.

In the sixth lens L6, the light beam is converged by giving a large positive power to the image side lens surface S14. As a result, the telecentricity of the image pickup lens system 11 is ensured, and the brightness of the entire lens system is maintained.

In the image pickup 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, so that the focus is when a temperature change occurs. About movement The amount of focus movement is reduced by canceling between plastic lenses.

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 image pickup lens system 11 at the time of designing the image pickup lens system 11.

Table 1 shows the lens data of each lens surface of the image pickup lens system 11. The lens data includes the radius of curvature of each surface, the distance between the surfaces, the refractive index, and the Abbe number. The surface marked with "*" indicates that it is an aspherical surface.

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 conical coefficient, and r is the ray height from the optical axis. , 12th, 14th, and 16th order aspherical coefficients are α4, α6, α8, α10, α12, α14, and α16, respectively, and are expressed by the following equations.

Table 2 shows the aspherical coefficient for defining the aspherical shape of the lens surface which is the aspherical surface in the image pickup lens system 11 of the first embodiment. In Table 2, for example, "-4.3323344E-03" means "-4.3323344 × 10 ^-3 ".

2A and 2B are a longitudinal aberration diagram and an curvature of field diagram of the image pickup lens system 11 of the first embodiment, respectively. As shown in FIGS. 2A and 2B, in the image pickup lens system 11 of the first embodiment, 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 indicates the position where the light ray intersects the optical axis Z, 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 height at the pupil diameter. show. In the curvature of field diagram of FIG. 2B, the horizontal axis indicates the distance in the optical axis Z direction, the left end of the graph horizontal axis is −0.10 mm, the right end is 0.10 mm, and the vertical axis indicates the image height (angle of view). .. In FIG. 2B, S indicates curvature of field on the sagittal surface and T indicates curvature of field on the tangential surface. 2A and 2B show simulation results with light rays having a wavelength of 546 nm.

Table 3 shows the results of calculating the characteristic values of the image pickup lens system 11 of Example 1. In the image pickup lens system 11, the F value is "FNo", the distance from the object-side lens surface S1 of the first lens L1 to the image formation surface IMG of the image pickup lens system 11 is "optical length", and the focal distance of the entire lens system is ". The whole system f ”, the focal distance of the first lens L1 is“ f ₁ ”, the focal distance of the second lens L2 is“ f ₂ ”, the focal distance of the third lens L3 is“ f ₃ ”, and the focal point of the fourth lens L4. The distance is "f ₄ ", the focal distance of the fifth lens L5 is "f ₅ ", the focal distance of the sixth lens L6 is "f ₆ ", and the combined focal distance of the first lens L1 and the second lens L2 is "f". ₁₂ ”, the combined focal distance between the second lens L2 and the third lens L3 is“ f ₂₃ ”, the combined focal distance between the third lens L3 and the fourth lens L4 is“ f ₃₄ ”, the fourth lens L4 and the fifth lens The combined focal distance with the lens L5 is indicated as "f ₄₅ ", and the combined focal distance between the fifth lens L5 and the sixth lens L6 is indicated as "f ₅₆ ," and these characteristic values are shown. These various focal lengths were calculated using light rays 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) below.)
The axial chromatic aberration at a wavelength of 436 nm to 656 nm in Example 1 is 0.040 mm.

[Example 2]
FIG. 3 is a diagram showing the configuration of the image pickup lens system 11 of the second embodiment. In the image pickup lens system 11 of the second 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.

Table 4 shows the lens data of each lens surface of the image pickup lens system 11 of the second embodiment.

Table 5 shows the aspherical coefficient for defining the aspherical shape of the lens surface which is the aspherical surface in the image pickup lens system 11 of the second embodiment.

4A and 4B are a longitudinal aberration diagram and an curvature of field diagram of the image pickup lens system 11 of the second embodiment, respectively. In the longitudinal aberration diagram of FIG. 4A, the horizontal axis indicates the position where the light ray intersects the optical axis Z, 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 height at the pupil diameter. show. In the curvature of field 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, and as shown in FIGS. 4A and 4B, this is carried out. In the image pickup 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 image pickup lens system 11 of Example 2.
The axial chromatic aberration at a 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 image pickup lens system 11 of the third embodiment.

In the image pickup lens system 11 of the third 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.

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

Table 8 shows the aspherical coefficient for defining the aspherical shape of the lens surface which is the aspherical surface in the image pickup lens system 11 of the third embodiment.

6A and 6B are a longitudinal aberration diagram and an image plane curvature diagram of the image pickup lens system 11 of the third embodiment.
In the longitudinal aberration diagram of FIG. 6A, the horizontal axis indicates the position where the light ray intersects the optical axis Z, 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 height at the pupil diameter. show. In the curvature of field diagram of FIG. 6B, the horizontal axis indicates 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 indicates the image height (angle of view). .. As shown in FIGS. 6A and 6B, in the image pickup lens system 11 of the third embodiment, 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 image pickup 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 image pickup lens system 11 of Examples 1 to 4.

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

The image pickup device 14 is an element that converts the received light into an electric signal, and for example, a CCD image sensor or a CMOS image sensor is used. The image pickup device 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 pickup element 14 in order to protect the image pickup element 14 from foreign matter.

The present invention is not limited to the above embodiment, and can be appropriately modified without departing from the spirit.

For example, the application of the image pickup lens system 11 of the present invention is not limited to an in-vehicle camera, and can be used for other applications such as a surveillance camera and a camera mounted on a small electronic device such as a mobile phone.

This application claims priority on the basis of Japanese application Japanese Patent Application No. 2016-197128 filed on October 5, 2016, and incorporates all of its disclosures herein.

10 Imaging device 11 Imaging lens 12 IR cut filter 13 Cover glass 14 Imaging elements L1 to L6 1st to 6th lenses

Claims (6)

From the object side,
The first lens, which is concave on the image side and has negative power,
A second lens that is concave on the image side and has negative power,
A third lens that is convex toward the object and has positive power,
A fourth lens that is concave on the image side and has negative power,
A fifth lens that is convex on the object side and concave on the image side and has positive power,
It is composed of a sixth lens that is convex on the image side and has positive power.
The image-side lens surface of the fourth lens and the object-side lens surface of the fifth lens are bonded to each other.
An imaging lens system characterized in that the Abbe number of the fourth lens is less than 21, and the Abbe number of the fifth lens is 55 or more. Wherein the focal length of the fourth lens f _4, a focal length of the fifth lens when the f _5, the imaging lens system according to claim 1, characterized by satisfying the following conditional expression (3).
-1.2 <f ₄ / f ₅ <-0.9 (3) The first aspect of claim 1 , wherein the following conditional expression (4) is satisfied 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. Imaging lens system.
-0.2 <f / f ₄₅ <0.1 (4) The imaging lens system according to claim 1, wherein both the image side surface of the fourth lens and the object side surface of the fifth lens are aspherical surfaces. The imaging lens system according to claim 1, wherein the shape of the image side surface of the fourth lens and the shape of the object side surface of the fifth lens are different from each other. The imaging lens system according to claim 1, wherein both the fourth lens and the fifth lens are plastic lenses.

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