JP2022173832A - Imaging lens system and imaging device - Google Patents

Abstract

To provide an imaging lens system and imaging device which can suppress the occurrence of a ghost even when a plastic lens is used.SOLUTION: An imaging lens system 11 comprises first lens to sixth lens L6 in the order from the object side to the image side, the image side lens surfaces S4, S8 and S14 of the second lens L2, the third lens L3 and the fifth lens L5 have the concave surface shape on the object side, the sixth lens L6 satisfies the following formula (1) and formula (2) when a sag amount at a height H1 in an effective diameter of an object side lens surface S15 is Sg1H and a sag amount at a height H2 in an effective diameter of the image side lens surface is Sg2H, (1) Sg1H/H1<-0.10, (2) Sg2H/H2<-0.10. Here, H1 and H2 are light beam heights at a position through which a light beam that is incident on the outer side of the diagonal length of an imaging element passes.SELECTED DRAWING: Figure 2

Description

The present invention relates to an imaging lens system and an imaging device, and more particularly to an in-vehicle imaging lens system and imaging device.

In recent years, there is a tendency for cameras mounted on vehicles to have a sensing function for purposes such as realizing automatic driving. In order to realize the stability and accuracy of the sensing function, many vehicle-mounted cameras, such as the vehicle-mounted camera described in Japanese Unexamined Patent Application Publication No. 2002-200310, are made entirely of glass lenses.

JP 2019-211598 A

On the other hand, since glass lenses are more expensive than plastic lenses, there is a demand to replace some of the glass lenses with plastic lenses in order to reduce costs. However, there is a drawback that the use of many plastic lenses makes it impossible to ignore the effects of ghosts. Specifically, the AR film (antireflection film) formed on the lens surface of a plastic lens has a reflectance that is about 5 to 10% higher than that of the AR film formed on the lens surface of a glass lens. A camera using a plastic lens is more likely to have a non-negligible ghost effect than a camera configured only with a lens. The ghost affects the imaging performance of the optical system, and when the optical system is used for sensing, the occurrence of the ghost leads to erroneous recognition, and the sensing function of the optical system becomes insufficient.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an imaging lens system and an imaging apparatus capable of suppressing the generation of ghosts even when using a plastic lens.

The imaging lens system of one embodiment comprises, in order from the object side to the image side, a first lens which is a meniscus lens having negative power and a convex surface facing the object side; a second lens that is a meniscus lens with a convex surface facing toward the aperture; a third lens that has positive power and is biconvex; a fourth lens that has negative power and has an image side surface that is convex toward the object side; It has a positive power and consists of a biconvex fifth lens and a sixth lens,
The distance in the direction of the optical axis from the reference plane to the lens surface at the height of the effective diameter of the lens surface when the plane that includes the intersection of the lens surface and the optical axis and is perpendicular to the optical axis is taken as the reference plane. is the amount of sag, and when the direction from the reference plane to the lens surface is positive when the direction is from the object side to the image side,
The sixth lens has the following formula ( 1) and satisfies formula (2),
Sg1H/H1<-0.10 (1)
Sg2H/H2<-0.10 (2)
Here, H1 and H2 are ray heights at positions through which rays incident outside the diagonal length of the imaging element pass. In addition, "outside the diagonal length of the image pickup device" refers to the range of a circle having a diameter equal to the length of the diagonal line of the image pickup device centered on the intersection of the image formation plane and the optical axis on the image formation plane. also means outside. Also, "the height of the effective diameter of the lens surface" means the height from the optical axis of the position within the range of the effective diameter of the lens surface.

According to the present invention, it is possible to provide an imaging lens system and an imaging apparatus that can suppress the occurrence of ghosts even if a plastic lens is used.

FIG. 5 is a cross-sectional view for explaining the amount of sag of a lens; 1 is a cross-sectional view showing the configuration of an imaging device and an imaging lens system according to Example 1. FIG. 4A and 4B are spherical aberration diagrams (longitudinal aberration diagrams), field curvature diagrams, and distortion aberration diagrams in the imaging lens system of Example 1. FIG. FIG. 7 is a cross-sectional view showing the configuration of an imaging device and an imaging lens system according to Example 2; 10A and 10B are spherical aberration diagrams (longitudinal aberration diagrams), field curvature diagrams, and distortion aberration diagrams in the imaging lens system of Example 2. FIG.

An optical lens and an imaging device according to this embodiment will be described below.
(Embodiment 1: Imaging lens system)
The imaging lens system of Embodiment 1 includes, in order from the object side to the image side, a first lens which is a meniscus lens having negative power and a convex surface facing the object side, a first lens having positive power, and an image. a second lens that is a meniscus lens with a convex surface facing the object side, an aperture, a third lens that has positive power and is biconvex, and a fourth lens that has negative power and has an image side convex surface facing the object side. , has a positive power, and consists of a biconvex fifth lens and a sixth lens.
In the imaging lens system of Embodiment 1, the sixth lens has a sag amount of Sg1H at the height H1 of the effective diameter of the object-side lens surface, and a sag amount of Sg1H at the height H2 of the effective diameter of the image-side lens surface. is Sg2H, the following equations (1) and (2) are satisfied.
Sg1H/H1<-0.10 (1)
Sg2H/H2<-0.10 (2)

Here, the lens sag amount will be described with reference to FIG. As shown in FIG. 1, when the plane PO that includes the intersection of the object-side lens surface SO of the lens L and the optical axis Z and is orthogonal to the optical axis is taken as a reference plane, the effective diameter of the object-side lens surface SO is The distance in the optical axis Z direction from the reference plane PO at the height H1 to the object-side lens surface SO is defined as a sag amount Sg1H. Similarly, when the plane PI that includes the intersection of the image-side lens surface SI of the lens L and the optical axis Z and is orthogonal to the optical axis is taken as a reference plane, the height H2 at the effective diameter of the image-side lens surface SI is The distance in the optical axis Z direction from the reference plane PI to the image-side lens surface SI is defined as a sag amount Sg2H. Moreover, it is positive when the direction from the reference planes PO and PI to the lens surfaces SO and SI is from the object side to the image side. That is, when the object-side lens surface SO is convex at the height H1, the sag amount Sg1H is a positive value. Further, when the image-side lens surface SI has a convex shape at the position of height H2, the sag amount Sg2H becomes a negative value.

Heights H1 and H2 are heights of light rays at positions through which light rays incident outside the diagonal length of the image sensor pass. In addition, "outside the diagonal length of the image pickup device" refers to the range of a circle having a diameter equal to the length of the diagonal line of the image pickup device centered on the intersection of the image formation plane and the optical axis on the image formation plane. also means outside. It should be noted that "outside the diagonal length of the image sensor" is because the shape of the position on the lens surface through which the light rays that should enter the image sensor pass is designed based on the imaging performance. Therefore, the purpose is to exclude this part.
Also, "the height of the effective diameter of the lens surface" means the height from the optical axis of the position within the range of the effective diameter of the lens surface.
That is, the heights H1 and H2 are the heights from the optical axis at positions within the range of the effective diameter of the lens surface and through which light rays incident outside the diagonal length of the image sensor pass. is.

As a result, it is possible to suppress the occurrence of ghosts even if a plastic lens is used.
Specifically, the ghost is generated when the light reflected by the lens surfaces of the lenses constituting the optical system enters the imaging device. In particular, when the light reflected by the image-side lens surface of the lens is incident on the imaging device, a strong ghost is generated. However, in the imaging lens system according to Embodiment 1, the image-side lens surfaces of the second lens, the third lens, and the fifth lens have a concave surface shape toward the object side, and the second lens, the third lens, and the The reflected light is reflected in the direction of divergence (the direction away from the optical axis Z) on the image-side lens surfaces of the lens and the fifth lens, and can be suppressed from entering the imaging device. Further, the sag amount Sg1H at a position through which a light ray incident outside the diagonal length of the imaging device on the object-side lens surface of the sixth lens passes, satisfies the above formula (1). Therefore, the overall shape of the object-side lens surface of the sixth lens is concave toward the object side, and light reflected at that position can be suppressed from entering the image sensor. Further, the sag amount Sg2H at a position through which a light ray incident outside the diagonal length of the imaging device on the image-side lens surface of the sixth lens passes, satisfies the above formula (2). Therefore, the overall shape of the image-side lens surface of the sixth lens is concave toward the object side, and light reflected at that position can be suppressed from entering the image sensor.
Therefore, in the imaging lens system according to Embodiment 1, it is possible to suppress the incidence of reflected light from the lens surface into the imaging device, thereby suppressing the occurrence of ghosts.

In addition, since the sixth lens closest to the imaging element in the imaging lens system has an aspherical shape that makes the optical axis and the principal ray parallel, the angle of incidence of the sensor on the imaging plane of the imaging element is reduced. can do. As a result, a sufficient amount of peripheral light is ensured, and an imaging lens system having an excellent sensing function can be realized.

Moreover, it is preferable that an infrared cut filter is arranged between the third lens and the fourth lens. As a result, it is possible to prevent reflected light from the infrared cut filter from entering the imaging device, and to further suppress the occurrence of ghosts.
Specifically, since an infrared cut filter is more expensive than a lens, the lens system is usually designed without an infrared cut filter, and finally, an infrared filter is placed closest to the image side of the lens system. A cut filter is placed. However, the light reflected by the object-side surface of the infrared cut filter is re-reflected by, for example, the object-side lens surface of the second lens and enters the imaging device, causing a ghost. However, in the imaging lens system according to the first embodiment, since the infrared cut filter is arranged between the third lens and the fourth lens, the light reflected by the object-side surface of the infrared cut filter cuts the infrared rays. Even if the light is re-reflected by the lens surface of the lens located closer to the object side than the filter, it is less likely to enter the imaging device. This can prevent reflected light from the infrared cut filter from entering the imaging device.

Moreover, it is preferable that the fourth lens and the fifth lens form a cemented lens. Chromatic aberration can be suitably corrected by configuring the cemented lens with the fourth lens and the fifth lens.

In addition, it is preferable that at least the object-side and image-side lens surfaces of the second lens, the third lens, and the sixth lens have an aspherical shape. This makes it possible to suitably correct spherical aberration, curvature of field, and distortion, and realize an imaging lens system with excellent imaging performance.

Next, an example corresponding to the imaging lens system of Embodiment 1 will be described with reference to the drawings.
(Example 1)
FIG. 2 is a cross-sectional view showing the configuration of the imaging device 10 of Example 1. As shown in FIG. Specifically, the imaging device 10 includes an imaging lens system 11 and an imaging device 12 . The imaging lens system 11 and the imaging element 12 are housed in a housing (not shown).

The imaging element 12 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 imaging element 12 is arranged at an imaging position (focus position) of the imaging lens system 11 .

The imaging lens system 11 according to Example 1 includes, in order from the object side to the image side, a first lens L1, a second lens L2, an aperture stop (STOP), a third lens L3, a fourth lens L4, and an infrared cut filter. (IRCF), fifth lens L5, and sixth lens L6. The imaging plane of the imaging lens system 11 is indicated by IMG.

The first lens L1 is a glass lens with negative power. The object-side lens surface S1 of the first lens L1 has a spherical shape that is convex toward the object side. The image-side lens surface S2 of the first lens L1 has a spherical shape that is convex toward the object side.

The second lens L2 is a plastic lens with positive power. The object-side lens surface S3 of the second lens L2 has an aspheric shape concave to the object side. In addition, the image-side lens surface S4 of the second lens L2 has an aspheric shape concave toward the object side.

Aperture STOP is an aperture that determines the F value (F number, Fno) of the lens system. A stop STOP is arranged between the second lens L2 and the third lens L3.

The third lens L3 is a glass lens with positive power. The object-side lens surface S7 of the third lens L3 has an aspheric shape convex to the object side. Further, the image-side lens surface S8 of the third lens L3 has an aspheric shape concave to the object side.

An infrared cut filter (IRCF) is a filter for cutting light in the infrared region. The infrared cut filter is handled integrally with the imaging lens system 11 when the imaging lens system 11 is designed. However, the infrared cut filter is not an essential component of the imaging lens system 11 . An infrared cut filter is arranged between the third lens L3 and the fourth lens L4.

The fourth lens L4 is a plastic lens with negative power. The object-side lens surface S11 of the fourth lens L4 has an aspheric shape that is convex toward the object side. Further, the image-side lens surface S12 of the fourth lens L4 has an aspheric shape that is convex toward the object side.

The fifth lens L5 is a plastic lens with positive power. The object-side lens surface S13 of the fifth lens L5 has an aspheric shape that is convex toward the object side. Further, the image-side lens surface S14 of the fifth lens L5 has an aspheric shape concave to the object side.

The fourth lens L4 and the fifth lens L5 constitute a cemented lens. That is, the image-side lens surface S12 of the fourth lens L4 and the object-side lens surface S13 of the fifth lens L5 are in contact with each other. The fourth lens L4 and the fifth lens L5 are joined with an adhesive layer having an axial thickness of 0.020 mm.

The sixth lens L6 is a plastic lens with negative power. The object-side lens surface S15 of the sixth lens L6 has an overall aspheric shape concave toward the object side. Further, the image-side lens surface S16 of the sixth lens L6 has an aspherical shape that is concave toward the object side as a whole.

Table 1 shows lens data of each lens surface in the imaging lens system 11 of Example 1. In Table 1, the lens data includes the glass material, the refractive index Nd for the d-line, the Abbe number Vd for the d-line, the curvature of each surface, the radius of curvature of each surface (mm), the surface interval (mm) at the central optical axis, and the effective The diameter (mm) is presented. The refractive index for the d-line and the Abbe number for the d-line shown in Table 1 are values when the environmental temperature t (° C.), which is the temperature around the imaging lens system 11, is 25 (° C.). Also, in Table 1, the surfaces marked with "*" are aspheric surfaces.

The aspherical shape adopted for the lens surface is 4th, 6th, 8th, 10 When the aspheric coefficients of the next, 12th, 14th and 16th orders are A4, A6, A8, A10, A12, A14 and A16, respectively, they are represented by the following equations.

Table 2 shows the aspherical 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, "-2.119E-03" means "-2.119×10 ^-3 ". Numerical expressions are the same for the following tables.

Next, aberration will be described with reference to the drawings. FIG. 3 shows a spherical aberration diagram (longitudinal aberration diagram), a field curvature diagram, and a distortion aberration diagram in the imaging lens system 11 of Example 1. FIG. As shown in FIG. 3, the imaging lens system 11 of Example 1 has a pupil radius of 0.7303 and a half angle of view of 47.228°. Also, the F number is 2.8.
In the longitudinal aberration diagram of FIG. 3A, the horizontal axis indicates the position where the light beam intersects the optical axis Z, and the vertical axis indicates the height in the pupil diameter. Also, FIG. 3A shows simulation results for light beams of 408 nm, 538 nm, 600 nm, and 668 nm.
In the curvature of field diagram of FIG. 3B, the horizontal axis indicates the distance in the Z direction of the optical axis, and the vertical axis indicates the image height (angle of view). In the curvature of field diagram of FIG. 3B, Sag indicates the curvature of field on the sagittal plane, and Tan indicates the curvature of field on the tangential plane. Further, FIG. 3B shows the simulation result with a light beam having a wavelength of 538 nm.
In the distortion diagram of FIG. 3C, the horizontal axis indicates the amount of image distortion (%), and the vertical axis indicates the image height (angle of view). Also, FIG. 3C shows a simulation result with a light beam having a wavelength of 538 nm.
FIG. 3 shows a spherical aberration diagram (longitudinal aberration diagram), a field curvature diagram, and a distortion aberration diagram when the environmental temperature t (° C.) is 25 (° C.).

(Example 2)
FIG. 4 is a cross-sectional view showing the imaging lens system 11 according to Example 2. As shown in FIG. As in Example 1, the imaging lens system 11 according to Example 2 includes a first lens L1, a second lens L2, an aperture stop (STOP), a third lens L3, a third It consists of four lenses L4, an infrared cut filter (IRCF), a fifth lens L5, and a sixth lens L6. In the imaging lens system 11 according to Example 2, the second lens L2 has negative power, the sixth lens L6 has positive power, and the object-side lens surface S11 and the image-side lens surface S11 of the fourth lens L4 This embodiment differs from the first embodiment in that S12 has a spherical shape, and the object-side lens surface S13 and the image-side lens surface S14 of the fifth lens L5 have spherical shapes. Characteristic data of the imaging lens system 11 according to Example 2 will be described below.

Table 3 shows lens data of each lens surface of the imaging lens system 11 according to the second embodiment. Since the items shown in Table 3 are the same as those in Table 1, the description thereof is omitted.

Table 4 shows the aspherical coefficients for defining the aspherical shape of the aspherical lens surface in the imaging lens system 11 of Example 2. In Table 4, the aspheric shape adopted for the lens surface is represented by the same formula as in the first embodiment.

FIG. 5 shows a spherical aberration diagram (longitudinal aberration diagram), a field curvature diagram, and a distortion aberration diagram in the imaging lens system 11 of Example 2. FIG. Since the explanation of each aberration diagram shown in FIG. 5 is the same as that of FIG. 3, the explanation thereof is omitted.

Table 5 shows the total length TL of the optical system of the imaging lens system 11, the focal length f1 of the first lens L1, the focal length f2 of the second lens L2, the focal length f3 of the third lens L3, and the focal length f4 of the fourth lens L4. , the focal length f5 of the fifth lens L5, the focal length f6 of the sixth lens L6, the combined focal length f45 of the fourth lens L4 to the fifth lens L5, the focal length F of the entire optical system of the imaging lens system 11, f1/F ~ f6/F value, f45/F value, height H1 at effective diameter of object-side lens surface S15 of sixth lens L6, sag amount Sg1H of object-side lens surface S15 of sixth lens L6, sixth lens The height H2 at the effective diameter of the image-side lens surface S16 of L6 and the sag amount Sg2H of the object-side lens surface S16 of the sixth lens L6 are shown. In Table 5, the unit of total length, focal length, height and sag amount is mm. Also, the focal length, height, and sag shown in Table 5 were calculated using light with a wavelength of 538 nm.

In Examples 1 and 2, the image-side lens surfaces S4, S8, and S14 of the second lens L2, the third lens L3, and the fifth lens L5 have concave surface shapes toward the object side. Reflected light is reflected in the direction of divergence (direction away from the optical axis Z) on the image side lens surfaces S4, S8, and S14 of the third lens L3 and the fifth lens L5, and can be suppressed from entering the image sensor 12. can. Further, as shown in Table 5, in Examples 1 and 2, the value of Sg1H/H1 satisfies the above formula (1), and the value of Sg2H/H2 satisfies the above formula (2). As a result, in the imaging lens systems 11 according to Examples 1 and 2, it is possible to suppress the reflected light from the object-side lens surface S15 and the image-side lens surface S16 of the sixth lens L6 from entering the imaging device 12 . As a result, the imaging lens systems 11 according to Examples 1 and 2 can suppress the occurrence of ghosts, have excellent imaging performance, and achieve high resolution. In fact, as shown in FIGS. 3 and 5, the imaging lens systems 11 according to Examples 1 and 2 can suitably reduce various aberrations, have excellent imaging performance, and achieve high resolution.

In addition, in Examples 1 and 2, since the sixth lens L6 located closest to the image sensor 12 has an aspherical shape such that the optical axis and the principal ray are parallel to each other, the imaging plane IMG of the image sensor 12 can reduce the angle of incidence of the sensor on the As a result, it is possible to realize the imaging lens system 11 in which a sufficient amount of peripheral light is ensured and which has an excellent sensing function.

An infrared cut filter IRCF is arranged between the third lens L3 and the fourth lens L4. This can prevent the reflected light originating from the infrared cut filter IRCF from entering the imaging element 12, and can further suppress the occurrence of ghosts.

Further, since the fourth lens L4 and the fifth lens L5 constitute a cemented lens, chromatic aberration can be corrected favorably.

At least the object side lens surfaces S3, S7 and S15 and the image side lens surfaces S4, S8 and S16 of the second lens L2, the third lens L3 and the sixth lens L6 preferably have an aspheric shape. Accordingly, it is possible to appropriately correct spherical aberration, curvature of field, and distortion, and realize the imaging lens system 11 having excellent imaging performance.

Further, according to the image pickup apparatus 10, by providing the image pickup lens system 11, it is possible to provide an image pickup apparatus that suppresses the occurrence of ghosts at a level necessary for image recognition in automatic driving and has excellent imaging performance.

It should be noted that the present invention is not limited to the above embodiments, and can be modified as appropriate without departing from the scope of the invention. For example, the application of the imaging lens system of the present invention is not limited to vehicle-mounted cameras and surveillance cameras, but can also be used for other applications such as being mounted on small electronic devices such as mobile phones.

10 Imaging device 11 Imaging lens system 12 Imaging device L1 First lens L2 Second lens L3 Third lens L4 Fourth lens L5 Fifth lens L6 Sixth lens STOP Aperture IRCF Infrared cut filter IMG Imaging plane Z Optical axis

Claims (6)

In order from the object side to the image side, the first lens is a meniscus lens having negative power and a convex surface facing the object side, and the meniscus lens having positive power and a convex surface facing the image side. a second lens, an aperture, a third lens having positive power and being biconvex, a fourth lens having negative power and having an image side surface convex toward the object side, a fourth lens having positive power and being biconvex consists of a fifth lens and a sixth lens of
The distance in the optical axis direction from the reference plane to the lens surface at the height of the effective diameter of the lens surface when a plane that includes the intersection of the lens surface and the optical axis and is perpendicular to the optical axis is taken as the reference plane. is the amount of sag, and when the direction from the reference plane to the lens surface is positive when the direction is from the object side to the image side,
The sixth lens has the following formula ( 1) and satisfies formula (2),
Sg1H/H1<-0.10 (1)
Sg2H/H2<-0.10 (2)
Here, H1 and H2 are the heights of light rays at positions through which light rays incident outside the diagonal length of the image pickup element pass. 2. The imaging lens system according to claim 1, wherein said sixth lens is a meniscus lens. 3. The imaging lens system according to claim 1, wherein an infrared cut filter is arranged between said third lens and said fourth lens. 4. The imaging lens system according to claim 1, wherein said fourth lens and said fifth lens constitute a cemented lens. 5. The imaging lens system according to claim 1, wherein at least object-side and image-side lens surfaces of said second lens, said third lens, and said sixth lens have an aspheric shape. an imaging lens system according to any one of claims 1 to 5;
and an imaging device arranged at a focal position of the imaging lens system.

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