JP6740440B2 - Imaging lens system and imaging device - Google Patents

Description

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

As an optical system for monitoring, there are a lens system for a surveillance camera that secures indoor and outdoor safety, a lens system for a vehicle-mounted camera for surveillance outside and inside the vehicle, and the like. An optical system for surveillance is required to have an extremely wide field of view, a high resolution, and an optical system with an F number as bright as 2.0. Further, compactness is also required particularly in an imaging lens system for an in-vehicle camera.

Patent Document 1 describes an imaging lens system including, in order from the object side, a first lens having negative power, a diaphragm, a second lens having positive power, and a third lens having positive power. According to the imaging lens system including three lenses, it is possible to reduce the size while ensuring a wide angle.

Patent Document 2 describes an imaging lens system including, in order from the object side, a first lens group having negative power, a second lens group that is a meniscus lens having a convex object side, a diaphragm, and a third lens group having positive power. (Optical device) is described. According to this imaging lens system, distortion can be favorably corrected when a lens configuration of 3 to 5 lenses is used.

Patent Document 3 discloses an imaging lens including, in order from the object side, a first lens having negative power, a second lens having negative power, a third lens having positive power, and a fourth lens having positive power. The system is described. According to this imaging lens system composed of four lenses, it is said that the total angle of view exceeds 180 degrees and the size is ultra wide, and the size can be reduced.

Patent Document 4 describes an imaging lens including, in order from the object side, a first lens having negative power, a second lens having negative power, a third lens having positive power, and a fourth lens having positive power. The system is described. According to this imaging lens system, it is said that a four-lens configuration provides an ultra wide angle with a total angle of view of about 140 degrees and can be downsized.

JP, 2007-279547, A JP, 2007-025499, A JP, 2009-003343, A JP, 2006-301222, A

The imaging lens system described in Patent Document 1 is configured with three lenses and has a wide angle, but since it is used in a system for photographing using near infrared rays such as a finger vein authentication system, it cannot be used in the visible region. Have difficulty. The F number is also relatively large at 3.0. As an optical system for monitoring, an imaging lens system that can be used in the visible region, has a smaller F number, and has a high resolution is required.

The image pickup lens system described in Patent Document 2 is brighter and has a wider angle than the image pickup lens system described in Patent Document 1, but the F number is over 2.1, and at least 5 at a wide angle exceeding 180 degrees. It is necessary to have a lens configuration of more than one lens. Therefore, it is difficult to reduce the size of the imaging lens system.

The imaging lens system described in Patent Document 3 can have an ultra wide angle with a relatively small number of lens configurations (four-lens configuration), but has a relatively large F number of 2.8. An imaging lens system having a smaller F number is required as an optical system for monitoring.

The imaging lens system described in Patent Document 4 can have a super wide angle with a relatively small number of lens configurations (four-lens configuration), but has a relatively large F number of 2.8. An imaging lens system having a smaller F number is required as an optical system for monitoring.

The present invention has been made to solve the above problems, and an object of the present invention is to provide an imaging lens system that is small in number, bright in F number of less than 2.1, wide angle, and small in size.

The imaging lens system of the present invention is
An imaging lens system comprising, in order from the object side, a first lens group having negative power, a second lens group having positive power, and a third lens group having positive power,
The first lens group consists of one or two negative lenses,
The second lens group consists of one positive lens,
The third lens group is composed of one final lens which is a positive lens,
The final lens, the image side lens surface is an aspherical surface,
When the radius of curvature near the optical axis of the image-side lens surface of the final lens is sagR and the center thickness of the final lens in the optical axis direction is D, the following conditional expression (1) is satisfied.
4<D/(-sagR)<9 (1)

In the third lens, telecentricity can be ensured by setting the ratio of the radius of curvature near the optical axis on the image side lens surface to the center thickness in the optical axis direction within the range of conditional expression (1). The curvature can be easily corrected. When the value goes below the lower limit of the conditional expression (1), the image surface shifts to an excessive level, and the telecentricity is lost. If the upper limit of conditional expression (1) is exceeded, the image surface will shift slightly to the under side, making it difficult to correct the field curvature.

The imaging lens system of the present invention is
An imaging lens system comprising, in order from the object side, a first lens group having negative power, a second lens group having positive power, and a third lens group having positive power,
The first lens group consists of one or two negative lenses,
The second lens group consists of one positive lens,
The third lens group is composed of one final lens which is a positive lens,
The final lens, the image side lens surface is an aspherical surface,
When the radius of curvature near the optical axis of the image side lens surface of the final lens is sagR and the lens effective diameter of the image side lens surface of the final lens is φ, the following conditional expression (2) is satisfied. ..
5<φ/sagR<16 (2)

The range of the lens effective diameter φ is determined to some extent with respect to the size of the image pickup element. In the design of the image pickup lens system, the size of the image pickup element is often predetermined. Therefore, when designing the imaging lens system, the lens effective diameter is not changed significantly. That is, since the lens effective diameter is almost fixed in the design of the imaging lens system, in the conditional expression (2), falling below the lower limit means increasing sagR, and exceeding the upper limit indicates sagR. It means getting smaller. When the value goes below the lower limit of conditional expression (2), sagR becomes large as described above, so that the back focus becomes long and the total length of the imaging lens system increases. On the other hand, when the value exceeds the upper limit of conditional expression (2), sagR becomes small as described above, so that the back focus becomes short and the arrangement of the image sensor becomes difficult.

In the present invention,
It is preferable that the following conditional expression (3) is satisfied.
6<D/(-sagR)<8 (3)

In the present invention,
It is preferable that the following conditional expression (4) is satisfied.
6<φ/sagR<8 (4)

In the present invention,
It is preferable that the F number is less than 2.1.

In the present invention,
The horizontal angle of view is preferably 100 degrees or more.

In the present invention,
It is preferable that the aperture stop is located between the second lens group and the third lens group and closer to the third lens group.

In the imaging lens system, the position of the diaphragm has a great influence on the telecentricity. In an imaging lens system in which the third lens group (final lens) has the above-described characteristics, a diaphragm is arranged between the second lens group and the third lens group and closer to the third lens group. Therefore, it becomes easier to secure telecentricity.

The imaging device of the present invention is
The imaging lens system described above,
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 a wide-angle, bright, and compact imaging lens system.

3 is a cross-sectional view of the imaging device according to the first embodiment. FIG. 3 is a cross-sectional view of the image pickup lens system according to Example 1. FIG. It is a figure explaining the optical axis vicinity curvature radius sagR in a final lens. FIG. 6 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. 9 is an aberration diagram of the image pickup lens system according to Example 2; 6 is a cross-sectional view of the image pickup lens system according to Example 3. FIG. FIG. 9 is an aberration diagram of the image pickup lens system according to Example 3; FIG. 9 is a cross-sectional view of the image pickup lens system according to Example 4; FIG. 9 is an aberration diagram of the image pickup lens system according to Example 4; FIG. 9 is a cross-sectional view of the image pickup lens system according to Example 5; FIG. 9 is an aberration diagram of the image pickup lens system according to Example 5; FIG. 9 is a cross-sectional view of the image pickup lens system according to Example 6; FIG. 16 is an aberration diagram of the image pickup lens system according to Example 6;

Hereinafter, examples of the imaging lens system 101 according to the embodiment of the present invention will be described.

(Example 1)
FIG. 2 is a diagram showing the configuration of the imaging lens system 101 of the first example.
As shown in FIG. 2, the imaging lens system 101 of Example 1 includes, in order from the object side to the image side, a first lens group G1 having negative power and a second lens group G2 having positive power. , A stop STOP, and a third lens group G3 having a positive power. The first lens group G1 includes a lens L11. The second lens group G2 is composed of a lens L21. The third lens group G3 includes a lens L31. The image plane of the image pickup lens system 101 is indicated by IMG. In the imaging lens system 101 of Example 1, the lenses L11, L21, and L31 are plastic lenses.

The lens L11 is an aspherical lens having negative power. The object-side lens surface S1 of the lens L11 is a spherical surface having a negative curvature, and the image-side lens surface S2 is an aspherical surface having a positive curvature. The object-side lens surface S1 has a concave surface facing the object side, and the image-side lens surface S2 has a convex curved surface portion protruding toward the object side.

The lens L21 is an aspherical lens having positive power. The object-side lens surface S3 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, and the image-side lens surface S4 has a convex curved surface portion protruding toward the object side.

The lens L31 is the last lens in the imaging lens system 101, and is an aspherical lens having positive power. The object-side lens surface S6 is an aspherical surface having a negative curvature, and the image-side lens surface S7 is an aspherical surface having a negative curvature. The object-side lens surface S6 has a convex curved surface portion protruding toward the image side, and the image-side lens surface S7 has a convex curved surface portion protruding toward the image side. The lens L31 has a large curvature in the convex curved surface portion projecting toward the image side of the object side lens surface S6, and has a small curvature in the convex curved surface portion projecting toward the image side of the image side lens surface S7. It is the shape of ".

Table 1 shows lens data of each lens surface of the imaging lens system 101. 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 surface shape used for the lens surface is a first-order, second-order, third-order, fourth-order, where Z is the sag amount, c is the reciprocal of the radius of curvature, k is the conic coefficient, and r is the ray height from the optical axis. When the fifth-order, sixth-order, seventh-order, and eighth-order aspherical coefficients are β1, β2, β3, β4, β5, β6, β7, and β8, respectively, they 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 101 of the first embodiment. In Table 2, for example, “−6.522528E-03” means “−6.522528×10 ⁻³ ”.

In order to secure the telecentricity and facilitate the correction of the field curvature in the image pickup lens system 101 including the first lens group composed of one lens, the inventors of the present invention have the lens L31, which is the final lens, in the optical axis direction. It was found that the ratio of the radius of curvature sagR near the optical axis to the central thickness D (D/(-sagR)) is important. FIG. 3 is a diagram for explaining the radius of curvature sagR near the optical axis in the final lens. As shown in FIG. 3, the radius of curvature sagR near the optical axis in the final lens means two points A and B on the same plane (for example, a tangential surface) at an optical axis height r=0.1 mm from the light ray. And the contact point C between the lens surface and the optical axis is the curvature obtained from the arc connecting the three points in total. In the imaging lens system 101 including one first lens group, by forming the final lens so that 4<D/(-sagR)<9, telecentricity can be ensured and field curvature can be corrected. It will be easier. In the image pickup lens system, it is more preferable to form the final lens so that 6<D/(-sagR)<8.

In addition, the present inventors define the back focus in the imaging lens system 101 including one first lens group, and the light for the lens effective diameter φ (see FIG. 3) in the lens L31 that is the final lens. It has been found that the ratio of the radius of curvature sagR near the axis (φ/sagR) is important. By forming the final lens so that 5<φ/sagR<16 in the image pickup lens system, the back focus can be shortened to the extent that the arrangement of the image pickup element does not become difficult. In the image pickup lens system, it is more preferable to form the final lens so that 6<φ/sagR<8.

Furthermore, the present inventors have found that the following conditional expression is satisfied when the first lens group is composed of one element in the imaging lens system 101.
0.9<f ₃ /f< 1.2
0.9<f _L31R2 /f<1.2
However, f is the focal length of the entire lens system, and f ₃ is the focal length of the third lens group. Further, f _L31R2 is the focal length of the image-side lens surface of the most image-side lens (final lens) forming the third lens group, and is defined by the following formula.
1/f _L31R2 =-(n-1)/R
n: Refractive index of the most image-side lens (final lens) forming the third lens group R: Radius of curvature of the image-side lens surface of the most image-side lens (final lens) forming the third lens group

Table 3 shows the results of calculating the characteristic values of the imaging lens system 101 of Example 1. In the imaging lens system 101, F number is FNo, TL is the distance from the object-side lens surface S1 of the first lens L1 to the image plane IMG of the imaging lens system 101, and f is the focal length of the entire lens system. The focal length of the first lens group G1 is f ₁ , the focal length of the second lens group G2 is f ₂ , the focal length of the third lens group G3 is f ₃ , and the first lens group G1 and the second lens group G2 are combined. The focal length is f ₁₂ , the combined focal length of the second lens group G2 and the third lens group G3 is f ₂₃ , the focal length of the image side lens surface S7 of the lens L31 is f _L31R2 , and the center _{thickness of} the lens L31 in the optical axis direction. Table 3 shows these characteristic values when the thickness is L31_D, the radius of curvature near the optical axis of the image side lens surface S7 of the lens L31 is L31R2_sagR, and the lens effective diameter of the image side lens surface S7 of the lens L31 is L31R2_φ. On the street. The various focal lengths were calculated using light with a wavelength of 587.6 nm.

As described above, the imaging lens system 101 according to the first embodiment includes the first lens group including one lens. From Table 3, the imaging lens system 101 of Example 1 satisfies 4<D/(-sagR)<9. Moreover, the imaging lens system 101 of Example 1 satisfies 5<φ/sagR<16.

In addition, as shown in Table 3, the imaging lens system 101 of Example 1
0.9<f ₃ /f< 1.2
0.9<f _L31R2 /f<1.2
Meets

4A to 4C are a longitudinal aberration diagram, a field curvature diagram, and a distortion aberration diagram of the imaging lens system 101 of the first example. As shown in FIGS. 4A to 4C, in the imaging lens system 101 of Example 1, the half angle of view ω is 80° and the F number is 2.0. In the longitudinal aberration diagram of FIG. 4A, the horizontal axis represents the position where the light beam intersects the optical axis Z, and the vertical axis represents the height at the pupil diameter. In the field curvature diagram of FIG. 4B, the horizontal axis represents the distance in the optical axis Z direction, and the vertical axis represents the image height (angle of view). In FIG. 4B, Sag indicates the field curvature on the sagittal plane, and Tan indicates the field curvature on the tangential plane. In the distortion diagram of FIG. 4C, the horizontal axis represents the image distortion amount (%), and the vertical axis represents the image height (angle of view). 4(a) to 4(c) show simulation results with light having a wavelength of 546 nm.

(Example 2)
FIG. 5 is a diagram showing the configuration of the imaging lens system 101 of Example 2.
As shown in FIG. 5, the imaging lens system 101 of Example 2 includes, in order from the object side to the image side, a first lens group G1 having negative power and a second lens group G2 having positive power. , And a third lens group G3 having a positive power. The first lens group G1 includes a lens L11. The second lens group G2 is composed of a lens L21. The third lens group G3 includes a lens L31. In the imaging lens system 101 of Example 1, the lens L11 is a glass lens, and the lenses L21 and L31 are plastic lenses.

The lens L11 is a spherical meniscus lens having negative power. The object side lens surface S1 of the lens L11 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 and the image-side lens surface S2 are concave on the image side.

The lens L21 is an aspherical lens having positive power. The object-side lens surface S3 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, and the image-side lens surface S4 has a convex curved surface portion protruding toward the object side.

The lens L31 is an aspherical lens having positive power. The object-side lens surface S6 is an aspherical surface having a negative curvature, and the image-side lens surface S7 is an aspherical surface having a negative curvature. The object-side lens surface S6 has a convex curved surface portion protruding toward the image side, and the image-side lens surface S7 has a convex curved surface portion protruding toward the image side.

Table 4 shows lens data of each lens surface of the imaging lens system 101. The surface marked with "*" indicates that it is an aspherical surface.

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 101 of the second embodiment.

Table 6 shows the results of calculating the characteristic values of the imaging lens system 101 of Example 2. Table 6 shows the results of calculation for the same characteristic values as in Table 3.

As described above, in the image pickup lens system 101 of the second embodiment, the first lens group is composed of one element, similarly to the image pickup lens system 101 of the first embodiment. From Table 6, the imaging lens system 101 of Example 2 satisfies 4<D/(-sagR)<9. The imaging lens system 101 of Example 2 satisfies 5<φ/sagR<16.

In addition, as shown in Table 6, the imaging lens system 101 of Example 2
0.9<f ₃ /f< 1.2
0.9<f _L31R2 /f<1.2
Meets

6A to 6C are a longitudinal aberration diagram, a field curvature diagram, and a distortion diagram of the imaging lens system 101 of the second example. As shown in FIGS. 6A to 6C, in the imaging lens system 101 of Example 2, the half angle of view ω is 80° and the F number is 2.0. In the longitudinal aberration diagram of FIG. 6A, the horizontal axis represents the position where the light ray intersects the optical axis Z, and the vertical axis represents the height at the pupil diameter. In the field curvature diagram of FIG. 6B, the horizontal axis indicates the distance in the optical axis Z direction, and the vertical axis indicates the image height (angle of view). In FIG. 6B, Sag indicates the field curvature on the sagittal plane, and Tan indicates the field curvature on the tangential plane. In the distortion diagram of FIG. 6C, the horizontal axis represents the image distortion amount (%), and the vertical axis represents the image height (angle of view). 6(a) to 6(c) show simulation results with light having a wavelength of 546 nm.

(Example 3)
FIG. 7 is a diagram illustrating the configuration of the imaging lens system 101 according to the third embodiment.
The imaging lens system 101 of Example 3 includes, in order from the object side to the image side, a first lens group G1 having negative power, a second lens group G2 having positive power, an aperture stop, and a positive power. And a third lens group G3 having The first lens group G1 includes a lens L11 and a lens L12. The second lens group G2 is composed of a lens L21. The third lens group G3 includes a lens L31. In the imaging lens system 101 of Example 3, the lens L11 is a glass lens, and the lenses L12, L21, and L31 are plastic lenses.

The lens L11 is a spherical meniscus lens having negative power. The object side lens surface S1 of the lens L11 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 and the image-side lens surface S2 are concave on the image side.

The lens L12 is an aspherical lens having negative power. The object side lens surface S3 of the lens L12 is an aspherical surface having a negative 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 image side, and the image-side lens surface S4 has a convex curved surface portion protruding toward the object side.

The lens L21 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 positive 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 object side.

The lens L31 is an aspherical lens having positive power. The object side lens surface S8 is an aspherical surface having a positive curvature, and the image side lens surface S9 is an aspherical surface having a negative curvature. The object-side lens surface S8 has a convex curved surface portion protruding toward the object side, and the image-side lens surface S9 has a convex curved surface portion protruding toward the image side.

Table 7 shows lens data of each lens surface of the imaging lens system 101. The surface marked with "*" indicates that it is an aspherical surface.

The aspherical shapes used for the lens surfaces of the lenses L21 and L31 are represented by the mathematical formulas described in the first embodiment. The aspherical surface shape used for the lens surface of the lens L12 is a fourth order, a sixth order, an eighth 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. When the 10th, 12th, 14th, and 16th aspherical coefficients are α4, α6, α8, α10, α12, α14, and α16, respectively, they are expressed by the following equations.

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 101 of the third example.

In the characteristic table, sagR is the curvature obtained from the three-point arc with the optical axis with the numerical value of Z when the height in the radial direction is r=0.1 mm. And φ indicate the effective diameter of the lens.

In order to secure the telecentricity and facilitate the correction of the field curvature in the image pickup lens system 101 including the first lens group with two lenses, the present inventors consider the lens L31 as the final lens in the optical axis direction. It was found that the ratio of the radius of curvature sagR near the optical axis to the central thickness D (D/(-sagR)) is important. The radius of curvature sagR near the optical axis in the final lens means, as shown in FIG. 3, two points A and B on the same plane (for example, a tangential surface) at an optical axis height r=0.1 mm from the light ray. And the contact point C between the lens surface and the optical axis is the curvature obtained from the arc connecting the three points in total. In the imaging lens system 101 including two first lens groups, by forming the final lens so that 4<D/(-sagR)<9, the telecentricity can be secured and the curvature of field can be corrected. It will be easier.

Further, the present inventors define the back focus in the imaging lens system 101 including the first lens group with two lenses, and in order to define the back focus, the light for the lens effective diameter φ (see FIG. 3) in the lens L31 which is the final lens. It has been found that the ratio of the radius of curvature sagR near the axis (φ/sagR) is important. In an image pickup lens system including two first lens groups, by forming the final lens so that 5<φ/sagR<16, the back focus is shortened to the extent that the arrangement of the image pickup element is not difficult. You can

Furthermore, the present inventors have found that the following conditional expression is satisfied when the first lens group is composed of two lenses in the imaging lens system 101.
1.5<f ₃ /f<2.2
1.5<f _L31R2 /f<2.2
However, f is the focal length of the entire lens system, and f ₃ is the focal length of the third lens group. Further, f _L31R2 is the focal length of the image-side lens surface of the most image-side lens (final lens) forming the third lens group, and is defined by the following formula.
1/f _L31R2 =-(n-1)/R
n: Refractive index of the most image-side lens (final lens) forming the third lens group R: Radius of curvature of the image-side lens surface of the most image-side lens (final lens) forming the third lens group

Table 9 shows the results of calculating the characteristic values of the imaging lens system 101 of Example 3. In the imaging lens system 101, the F number is FNo, the distance (optical total length) from the object side lens surface S1 of the first lens L11 to the image plane IMG of the imaging lens system 101 is TL, and the focal length of the entire lens system is f, The focal length of the first lens group G1 is f ₁ , the focal length of the second lens group G2 is f ₂ , the focal length of the third lens group G3 is f ₃ , the focal length of the lens L11 is f _L11 , and the focal length of the lens L12. _Where f _L12 is the composite focal length of the second lens group G2 and the third lens group G3 is f ₂₃ , and the focal length of the image side lens surface S9 of the lens L31 is f _L31R2 . It is as shown in 9. The various focal lengths were calculated using light with a wavelength of 587.6 nm.

As described above, the imaging lens system 101 of Example 3 includes the first lens group including two lenses. As shown in Table 9, the imaging lens system 101 of Example 3 satisfies 4<D/(-sagR)<9. The imaging lens system 101 of Example 3 satisfies 5<φ/sagR<16.

Further, as shown in Table 9, the imaging lens system 101 of Example 3 includes
1.5<f ₃ /f<2.2
1.5<f _L31R2 /f<2.2
Meets

8A to 8C are a longitudinal aberration diagram, a field curvature diagram, and a distortion aberration diagram of the imaging lens system 101 of the third example. As shown in FIGS. 8A to 8C, in the imaging lens system 101 of Example 3, the half angle of view ω is 89° and the F number is 2.0. In the longitudinal aberration diagram of FIG. 8A, the horizontal axis represents the position where the light beam intersects the optical axis Z, and the vertical axis represents the height at the pupil diameter. In the field curvature diagram of FIG. 8B, the horizontal axis represents the distance in the optical axis Z direction, and the vertical axis represents the image height (angle of view). In FIG. 8B, Sag indicates the field curvature on the sagittal surface, and Tan indicates the field curvature on the tangential surface. In the distortion diagram of FIG. 8C, the horizontal axis represents the image distortion amount (%), and the vertical axis represents the image height (angle of view). FIG. 8A to FIG. 8C show simulation results with light rays having a wavelength of 546 nm.

(Example 4)
FIG. 9 is a diagram showing the configuration of the imaging lens system 101 of Example 4.
The imaging lens system 101 of Example 4 has, in order from the object side to the image side, a first lens group G1 having negative power, a second lens group G2 having positive power, an aperture stop, and a positive power. And a third lens group G3 having The first lens group G1 includes a lens L11 and a lens L12. The second lens group G2 is composed of a lens L21. The third lens group G3 includes a lens L31. In the imaging lens system 101 of Example 4, the lens L11 is a glass lens, and the lenses L12, L21, and L31 are plastic lenses.

The lens L11 is a spherical meniscus lens having negative power. The object side lens surface S1 of the lens L11 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 and the image-side lens surface S2 are concave on the image side.

The lens L12 is an aspherical lens having negative power. The object side lens surface S3 of the lens L12 is an aspherical surface having a negative 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 image side, and the image-side lens surface S4 has a convex curved surface portion protruding toward the object side.

The lens L21 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 positive 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 object side.

The lens L31 is an aspherical lens having positive power. The object side lens surface S8 is an aspherical surface having a positive curvature, and the image side lens surface S9 is an aspherical surface having a negative curvature. The object-side lens surface S8 has a convex curved surface portion protruding toward the object side, and the image-side lens surface S9 has a convex curved surface portion protruding toward the image side.

Table 10 shows lens data of each lens surface of the imaging lens system 101. The surface marked with "*" indicates that it is an aspherical surface.

Table 11 shows aspherical surface coefficients for defining the aspherical surface shape of the lens surface which is an aspherical surface in the imaging lens system 101 of the fourth embodiment.

Table 12 shows the results of calculating the characteristic values of the imaging lens system 101 of Example 4. Table 12 shows the results of calculation for the same characteristic values as in Table 9.

As described above, in the image pickup lens system 101 of the fourth embodiment, as in the image pickup lens system 101 of the third embodiment, the first lens group includes two lenses. As shown in Table 12, the imaging lens system 101 of Example 4 satisfies 4<D/(-sagR)<9. The imaging lens system 101 of Example 4 satisfies 5<φ/sagR<16.

Further, as shown in Table 12, the imaging lens system 101 of Example 4 is
1.5<f ₃ /f<2.2
1.5<f _L31R2 /f<2.2
Meets

10A to 10C are a longitudinal aberration diagram, a field curvature diagram, and a distortion aberration diagram of the imaging lens system 101 of Example 4. As shown in FIGS. 10A to 10C, in the imaging lens system 101 of Example 4, the half angle of view ω is 89° and the F number is 2.0. In the longitudinal aberration diagram of FIG. 10A, the horizontal axis represents the position where the light beam intersects the optical axis Z, and the vertical axis represents the height at the pupil diameter. In the field curvature diagram of FIG. 10B, the horizontal axis represents the distance in the optical axis Z direction, and the vertical axis represents the image height (angle of view). In FIG. 10B, Sag indicates the field curvature on the sagittal surface, and Tan indicates the field curvature on the tangential surface. In the distortion diagram of FIG. 10C, the horizontal axis represents the image distortion amount (%), and the vertical axis represents the image height (angle of view). 10(a) to 10(c) show simulation results with light rays having a wavelength of 546 nm.

(Example 5)
FIG. 11 is a diagram showing the configuration of the imaging lens system 101 of Example 5.
The imaging lens system 101 of Example 5 has, in order from the object side to the image side, a first lens group G1 having negative power, a second lens group G2 having positive power, an aperture stop, and a positive power. And a third lens group G3 having The first lens group G1 includes a lens L11 and a lens L12. The second lens group G2 is composed of a lens L21. The third lens group G3 includes a lens L31. In the imaging lens system 101 of Example 5, the lens L11 is a glass lens, and the lenses L12, L21, and L31 are plastic lenses.

The lens L11 is a spherical meniscus lens having negative power. The object side lens surface S1 of the lens L11 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 and the image-side lens surface S2 are concave on the image side.

The lens L12 is an aspherical lens having negative power. The object side lens surface S3 of the lens L12 is an aspherical surface having a negative 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 image side, and the image-side lens surface S4 has a convex curved surface portion protruding toward the object side.

The lens L21 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 positive 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 object side.

The lens L31 is an aspherical lens having positive power. The object-side lens surface S8 is an aspherical surface having a negative curvature, and the image-side lens surface S9 is an aspherical surface having a negative curvature. The object-side lens surface S8 has a convex curved surface portion protruding toward the image side, and the image-side lens surface S9 has a convex curved surface portion protruding toward the image side.

Table 13 shows lens data of each lens surface of the imaging lens system 101. The surface marked with "*" indicates that it is an aspherical surface.

Table 14 shows the aspherical surface coefficients for defining the aspherical surface shape of the lens surface which is an aspherical surface in the imaging lens system 101 of the fifth example.

Table 15 shows the results of calculating the characteristic values of the imaging lens system 101 of Example 5. Table 15 shows the results of calculation for the same characteristic values as in Table 9.

As described above, in the image pickup lens system 101 of the fifth embodiment, as in the image pickup lens system 101 of the third embodiment, the first lens group includes two lenses. As shown in Table 15, the imaging lens system 101 of Example 5 satisfies 4<D/(-sagR)<9. The imaging lens system 101 of Example 5 satisfies 5<φ/sagR<16.

Further, as shown in Table 15, the imaging lens system 101 of Example 5
1.5<f ₃ /f<2.2
1.5<f _L31R2 /f<2.2
Meets

12A to 12C are a longitudinal aberration diagram, a field curvature diagram, and a distortion diagram of the imaging lens system 101 of the fifth example. As shown in FIGS. 12A to 12C, in the imaging lens system 101 of Example 5, the half angle of view ω is 107° and the F number is 2.0. In the vertical aberration diagram of FIG. 12A, the horizontal axis represents the position where the light beam intersects the optical axis Z, and the vertical axis represents the height at the pupil diameter. In the field curvature diagram of FIG. 12B, the horizontal axis represents the distance in the optical axis Z direction, and the vertical axis represents the image height (angle of view). In FIG. 12B, Sag indicates the field curvature on the sagittal surface, and Tan indicates the field curvature on the tangential surface. In the distortion diagram of FIG. 12C, the horizontal axis represents the image distortion amount (%), and the vertical axis represents the image height (angle of view). 12(a) to 12(c) show simulation results with light rays having a wavelength of 546 nm.

(Example 6)
FIG. 13 is a diagram showing the configuration of the imaging lens system 101 of Example 6.
The imaging lens system 101 of Example 6 has, in order from the object side to the image side, a first lens group G1 having negative power, a second lens group G2 having positive power, an aperture stop, and a positive power. And a third lens group G3 having The first lens group G1 includes a lens L11 and a lens L12. The second lens group G2 is composed of a lens L21. The third lens group G3 includes a lens L31. In the imaging lens system 101 of Example 6, the lens L11 is a glass lens, and the lenses L12, L21, and L31 are plastic lenses.

The lens L11 is a spherical meniscus lens having negative power. The object side lens surface S1 of the lens L11 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 and the image-side lens surface S2 are concave on the image side.

The lens L12 is an aspherical lens having negative power. The object side lens surface S3 of the lens L12 is an aspherical surface having a negative 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 image side, and the image-side lens surface S4 has a convex curved surface portion protruding toward the object side.

The lens L21 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 positive 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 object side.

The lens L31 is an aspherical lens having positive power. The object-side lens surface S8 is an aspherical surface having a negative curvature, and the image-side lens surface S9 is an aspherical surface having a negative curvature. The object-side lens surface S8 has a convex curved surface portion protruding toward the image side, and the image-side lens surface S9 has a convex curved surface portion protruding toward the image side.

Table 16 shows lens data of each lens surface of the imaging lens system 101. The surface marked with "*" indicates that it is an aspherical surface.

Table 17 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 101 of the sixth example.

Table 18 shows the results of calculating the characteristic values of the imaging lens system 101 of Example 6. Table 18 shows the results of calculation for the same characteristic values as in Table 9.

As described above, in the image pickup lens system 101 of Example 6, as in the image pickup lens system 101 of Example 3, the first lens group includes two lenses. As shown in Table 18, the imaging lens system 101 of Example 6 satisfies 4<D/(-sagR)<9. The imaging lens system 101 of Example 6 satisfies 5<φ/sagR<16.

Further, as shown in Table 18, the imaging lens system 101 of Example 6
1.5<f ₃ /f<2.2
1.5<f _L31R2 /f<2.2
Meets

14A to 14C are a longitudinal aberration diagram, a field curvature diagram, and a distortion aberration diagram of the imaging lens system 101 of the sixth example. As shown in FIGS. 14A to 14C, in the imaging lens system 101 of Example 6, the half angle of view ω is 109° and the F number is 2.0. In the longitudinal aberration diagram of FIG. 14A, the horizontal axis represents the position where the light beam intersects the optical axis Z, and the vertical axis represents the height at the pupil diameter. In the field curvature diagram of FIG. 14B, the horizontal axis represents the distance in the optical axis Z direction, and the vertical axis represents the image height (angle of view). In FIG. 14B, Sag indicates the field curvature on the sagittal surface, and Tan indicates the field curvature on the tangential surface. In the distortion diagram of FIG. 14C, the horizontal axis represents the image distortion amount (%) and the vertical axis represents the image height (angle of view). 14(a) to 14(c) show simulation results with light rays having a wavelength of 546 nm.

Table 19 shows a summary of the parameter D/(-sagR) related to the conditional expression (1) and the parameter φ/sagR related to the conditional expression (2) in the imaging lens system 101 of Examples 1 to 6.

(Application example to imaging device)
FIG. 1 is a diagram showing a configuration of an image pickup apparatus 100 using an image pickup lens system 101. The image pickup apparatus 100 includes an image pickup lens system 101, a cover glass 102, and an image pickup element 103. The image pickup lens system 101, the cover glass 102, and the image pickup element 103 are housed in a housing (not shown).

The image sensor 103 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 103 is arranged at the image forming position (focal point position) of the image pickup lens system 101. The horizontal angle of view is an angle of view corresponding to the horizontal direction of the image sensor 103.

The cover glass 102 is provided on the image sensor 103 in order to protect the image sensor 103 from foreign matter.

The present invention is not limited to the above-mentioned embodiment, and can be modified as appropriate without departing from the spirit of the present invention. For example, the use of the imaging lens system 101 of the present invention is not limited to an in-vehicle camera or a surveillance camera, but it can be used for other uses such as mounting on a small electronic device such as a mobile phone.

100 image pickup apparatus 101 image pickup lens system 102 cover glass 103 image pickup elements G1 to G3 first lens group to third lens group L11 to L31 lens

Claims (7)

An imaging lens system comprising, in order from the object side, a first lens group having negative power, a second lens group having positive power, and a third lens group having positive power,
The first lens group consists of one or two negative lenses,
The second lens group consists of one positive lens,
The third lens group is composed of one final lens which is a positive lens,
The final lens, the image side lens surface is an aspherical surface,
When the radius of curvature near the optical axis of the image side lens surface of the final lens is sagR and the central thickness in the optical axis direction of the final lens is D, the following conditional expression (1) is satisfied, and the diaphragm is An image pickup lens system, which is located between the second lens group and the third lens group and is closer to the third lens group.
4<D/(-sagR)<9 (1)
However, the radius of curvature sagR in the vicinity of the optical axis is defined by two points A and B on the same plane at the optical axis height r=0.1 mm from the light ray and a contact point C between the lens surface and the optical axis. It is the curvature obtained from the arc connecting the three points in total. The imaging lens system according to claim 1, wherein the following conditional expression (3) is satisfied: 6<D/(-sagR)<8 (3) The imaging lens system according to claim 1, wherein the first lens group is composed of one negative lens. The imaging lens system according to claim 1, wherein the first lens group is composed of two negative lenses. The imaging lens system according to claim 1, wherein the F number is less than 2.1. The imaging lens system according to claim 1, wherein the horizontal angle of view is 100 degrees 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.

Images