JP7193362B2 - Imaging lens and imaging device - Google Patents

Description

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

For applications such as in-vehicle cameras and surveillance cameras, there is a demand for compact, low-cost, wide-angle, and high-performance cameras.

As such a lens system, Patent Document 1 describes, in order from the object side, a negative meniscus first lens with a convex surface facing the object side, a negative second lens, a positive third lens, an aperture, and a negative lens. The fourth lens L4 and the fifth lens L5 are cemented together, the cemented surface is convex toward the object side, and the cemented surface is an aspherical surface. It describes an imaging lens that satisfies 1.0<R9/f, where R9 is the radius of curvature and f is the focal length of the entire system.

JP 2014-228570 A

However, in the lens system of Patent Document 1, a luminous flux directed toward the center of the imaging surface (a luminous flux indicated by 2 in FIG. 9 of the patent document) and a luminous flux directed toward the periphery of the imaging surface (a luminous flux indicated by 3 in FIG. 9 of the patent document). overlaps on the object side surface of the third lens, and there is a problem that aberration correction is difficult. For example, the lens system of Patent Document 1 has problems of poor axial chromatic aberration, low central MTF (Modulation Transfer Function), and low peripheral MTF.

The imaging lens system of one embodiment includes, in order from the object side to the image side, a first lens having a negative power and a convex surface facing the object side, a second lens having a negative power and a convex surface facing the object side. a third lens with positive power, an aperture stop, a fourth lens with negative power with a convex surface facing the object side, and a fifth lens with positive power with convex surfaces facing the object and image planes. An imaging lens system,
When the thickness of the third lens at the central optical axis is defined as T3, and the focal length of the entire lens system is defined as f, the following conditional expression (1) is satisfied.
T3/f>2.5 (1)

According to the imaging lens system of one embodiment, the light beams directed toward the center of the image plane and the light beams toward the periphery of the image plane overlap less on the object side surface of the third lens L3. Aberration correction can be performed separately for a ray directed toward the center of the imaging plane and a ray directed toward the periphery of the imaging plane.

According to the present invention, it is possible to provide an imaging lens system and an imaging apparatus that facilitate aberration correction.

2 is a cross-sectional view showing the configuration of the imaging lens system of Example 1. FIG. 4 is a spherical aberration diagram in the imaging lens system of Example 1. FIG. 4 is an astigmatism diagram in the imaging lens system of Example 1. FIG. 4 is a distortion aberration diagram in the imaging lens system of Example 1. FIG. 4 is a diagram of lateral chromatic aberration in the imaging lens system of Example 1. FIG. 4 is an MTF characteristic diagram in the imaging lens system of Example 1. FIG. FIG. 11 is a cross-sectional view showing the configuration of the imaging lens system of Example 2; FIG. 10 is a spherical aberration diagram in the imaging lens system of Example 2; FIG. 10 is an astigmatism diagram in the imaging lens system of Example 2; FIG. 10 is a distortion aberration diagram in the imaging lens system of Example 2; FIG. 10 is a diagram of lateral chromatic aberration in the imaging lens system of Example 2; FIG. 10 is an MTF characteristic diagram in the imaging lens system of Example 2; 10 is a cross-sectional view of an imaging device according to Embodiment 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 having a negative power and a convex surface facing the object side, a second lens having a negative power and a convex surface facing the object side. from a third lens with positive power directed toward, an aperture stop, a fourth lens with negative power with a convex surface facing the object side, and a fifth lens with positive power with convex surfaces directed toward the object and image planes; An imaging lens system that
When the thickness of the third lens at the central optical axis is defined as T3, and the focal length of the entire lens system is defined as f, the following conditional expression (1) is satisfied.
T3/f>2.5 (1)

As described above, according to the imaging lens system of Embodiment 1, the light rays directed toward the center of the imaging plane and the light rays directed toward the periphery of the imaging plane overlap less on the object side surface of the third lens. In the lens, aberration correction can be performed by separating the light beams directed toward the center of the image plane and the light beams toward the periphery of the image plane. As a result, aberration correction is facilitated. Further, according to the imaging lens system of Embodiment 1, it is possible to provide an imaging lens system with good axial chromatic aberration, good central MTF, and good MTF in the direction of 98 degrees (rear) from the central optical axis.

In the imaging lens system of Embodiment 1, the Abbe number of the fourth lens may be less than 23.

With this configuration, the effect of correcting chromatic aberration by the fourth lens, which is a concave lens, can be enhanced.

The imaging lens system of Embodiment 1 may satisfy the following conditional expression (2) when the Abbe number of the fourth lens is defined as v4 and the Abbe number of the fifth lens is defined as v5.
v4/v5≦0.4 (2)
With this configuration, chromatic aberration can be easily corrected.

The imaging lens system of Embodiment 1 may satisfy the following conditional expression (3) when the focal length of the fourth lens is defined as f4 and the focal length of the fifth lens is defined as f5.
-2<f4/f5<-1 (3)

With this configuration, the difference in power (reciprocal of the focal length) between the fourth lens, which is a concave lens, and the fifth lens, which is a convex lens, is not so large, which is preferable for correcting aberrations.

Next, an example corresponding to the imaging lens system of Embodiment 1 will be described with reference to the drawings.
(Example 1)
FIG. 1 is a cross-sectional view showing the configuration of the imaging lens system of Example 1. FIG. In FIG. 1, the imaging lens system 11 includes, in order from the object side to the image side, a first lens L1 having a negative power and a convex surface facing the object side, a second lens L2 having a negative power and a lens L2 facing the object side. A third lens L3 with positive power and a convex surface, an aperture stop (STOP), a fourth lens L4 with negative power and a convex surface facing the object side, and positive power with convex surfaces facing the object and image planes. and a fifth lens L5. The imaging plane of the imaging lens system 11 is indicated by IMG.

FIG. 1 also shows a principal ray (axial ray) and a marginal ray (marginal ray) directed toward the screen center, and a principal ray (ray passing through the center of the aperture) and a marginal ray (marginal ray) directed toward the periphery of the screen. there is

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

The second lens L2 is an aspherical plastic lens with negative power. The object-side lens surface S3 of the second lens L2 has a convex curved surface portion. Further, the image-side lens surface S4 of the second lens L2 has a concave curved surface portion.

The third lens L3 is an aspherical plastic lens with positive power. An object-side lens surface S5 of the third lens L3 is convex toward the object side. Further, the image-side lens surface S6 of the third lens L3 is concave toward the object side.

Aperture STOP is an aperture that determines the F value (Fno) of the lens system. A stop STOP is arranged between the third lens L3 and the fourth lens L4.

The fourth lens L4 is an aspherical plastic lens with negative power. An object-side lens surface S8 of the fourth lens L4 is convex toward the object side. The image-side lens surface S9 of the fourth lens L4 is convex toward the image plane side.

The fifth lens L5 is an aspherical plastic lens with positive power. The object-side lens surface S10 of the fifth lens L5 has a convex curved surface portion. The image-side lens surface S11 of the fifth lens L5 is convex toward the image plane side.

The fourth lens L4 and the fifth lens L5 form a cemented lens. That is, the image-side lens surface S9 of the fourth lens L4 and the object-side lens surface S10 of the fifth lens L5 are in contact with each other. For example, the fourth lens L4 and the fifth lens L5 are preferably bonded with an adhesive layer having an axial thickness of 0.02 mm.

The IR cut filter 12 is a filter for cutting light in the infrared region. The IR cut filter 12 is handled integrally with the imaging lens system 11 when the imaging lens system 11 is designed. However, IR cut filter 12 is not an essential component of imaging lens system 11 .

Table 1 shows lens data of each lens surface in the imaging lens system 11 of Example 1. Table 1 presents, as lens data, the radius of curvature of each surface, the surface spacing at the central optical axis, the refractive index for the d-line, and the Abbe number for the d-line. A surface marked with "*" indicates that it is an aspherical surface.

The aspherical shape adopted for the lens surface is 3rd, 4th, 5th, and 6th order, where Z is the amount of sag, C is the reciprocal of the radius of curvature, K is the conic coefficient, and h is the height of the ray from the optical axis Z. Let A3, A4, A5, A6, A7, A8, A10, A12, A14, and A16 be the aspheric coefficients of the next, seventh, eighth, tenth, twelfth, fourteenth, and sixteenth orders, respectively. is represented by the formula

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, "-6.522528E-03" means "-6.522528×10 ^-3 ".

Next, aberration will be described with reference to the drawings. FIG. 2 is a spherical aberration diagram in the imaging lens system of Example 1. FIG. In FIG. 2, the horizontal axis indicates the position where the light beam intersects the optical axis Z, and the vertical axis indicates the relative height of the light beam at the pupil diameter. Also, FIG. 2 shows simulation results for light beams with wavelengths of 486 nm, 546 nm and 656 nm. As shown in the spherical aberration diagram of FIG. 2, it can be seen that the axial chromatic aberration in the wavelength range of 486 to 656 nm in Example 1 can be corrected extremely well to 3 μm or less.

FIG. 3 is an astigmatism diagram in the imaging lens system of Example 1. FIG. In FIG. 3, the horizontal axis indicates the distance between the imaging points in the Z direction of the optical axis, and the vertical axis indicates the image height (angle of view). In FIG. 3, Sag indicates astigmatism on the sagittal plane, and Tan indicates astigmatism on the tangential plane. Moreover, FIG. 3 shows a simulation result with a light beam having a wavelength of 546 nm.

FIG. 4 is a distortion aberration diagram in the imaging lens system of Example 1. FIG. FIG. 4 shows the distortion of stereographic projection. In FIG. 4, the horizontal axis indicates the amount of image distortion (%), and the vertical axis indicates the image height (angle of view).

FIG. 5 is a diagram of lateral chromatic aberration in the imaging lens system of Example 1. FIG. In FIG. 5, the vertical axis indicates the image height of the light beam with a wavelength of 546 nm, and the horizontal axis indicates the deviation amount (μm unit) of the image height of the light beam with a wavelength of 486 nm and 656 nm with respect to the image height of the light beam with a wavelength of 546 nm.

As shown in FIG. 2, the imaging lens system 11 of Example 1 has an F number of 2.01. Further, as shown in FIGS. 3 to 5, in the imaging lens system 11 of Example 1, the half angle of view ω is 103°.
As shown in FIGS. 2 to 5, it can be seen that the aberrations are well corrected.

Next, the characteristic values of the lens will be explained. Table 3 shows the results of calculating the characteristic values of the imaging lens system 11 of Example 1. In Table 3, in the imaging lens system 11, f is the focal length of the entire lens system, f ₁ is the focal length of the first lens L1, f ₂ is the focal length of the second lens L2, and f is the focal length of the third lens L3. ₃ , the focal length of the fourth lens L4 is f4, the focal length of the fifth lens L5 is _{f5, the combined focal length of the first lens L1, the second lens L2 and the third lens L3 is f123 ,} and the _fourth lens L4 And f ₄₅ is the combined focal length of the fifth lens L5, T ₁ is the thickness (axial thickness) of the first lens L1 at the center of the optical axis, and T ₂ is the thickness (axial thickness) of the second lens L2 at the center of the optical axis. , T ₃ is the thickness (axial thickness) of the third lens L3 at the center of the optical axis, T 4 is the thickness (axial thickness) of the fourth lens L4 at the center of the optical axis, and T ₄ is the thickness (axial thickness) of the fifth lens L5 at the center of the optical axis ( T ₅ is the axial thickness), d 1 is the distance from the vertex of the image-side surface of the first lens L1 to the vertex of the object-side surface of the second lens L2, and d ₁ is the distance from the vertex of the image-side surface of the second lens L2 to the object of the third lens L3. d2 is the distance to the vertex of the side surface, d3 is the distance from the vertex of the image side surface of the _third lens L3 to the vertex of the object side surface of the _fourth lens L4, and d3 is the distance from the vertex of the image side surface of the fourth lens L4 to the vertex of the fifth lens L5. d ₄ is the distance to the vertex of the object side surface, T ₃ /f is the value obtained by dividing the thickness of the third lens L3 at the center of the optical axis by the focal length of the entire lens system, v ₄ is the Abbe number of the fourth lens L4, The value obtained by dividing the Abbe number of the fourth lens L4 by the Abbe number of the _fifth lens L5 is v4/v5, and the value obtained by dividing the focal length of the _fourth lens L4 by the focal length of the fifth lens L5 is f4/f5. Each characteristic value is shown when Also, the various focal lengths in Table 3 were calculated using light with a wavelength of 546 nm.

Next, the MTF characteristics of lenses will be described. FIG. 6 is an MTF characteristic diagram in the imaging lens system of Example 1. FIG. In FIG. 6, the horizontal axis indicates the angle of incident light with respect to the central optical axis Z, and the vertical axis indicates the MTF value. FIG. 6 shows MTF characteristics at a spatial frequency of 60 lines/mm. In FIG. 6, the solid line T1 indicates the MTF value in the tangential direction, and the dotted line S1 indicates the MTF value in the sagittal direction.

As shown in FIG. 6, it has good MTF values of 68% or more in both the sagittal and tangential directions from 0 to 96 degrees of view. Also, the MTF value of 58% can be maintained even at the outermost periphery with an angle of view of 103 degrees.

(Example 2)
FIG. 7 is a cross-sectional view showing the configuration of the imaging lens system of Example 2. FIG. In FIG. 7, in order from the object side to the image side, a first lens L1 having negative power with a convex surface facing the object side, a second lens L2 having negative power, and a positive lens L2 with a convex surface facing the object side. A third lens L3 having power, an aperture stop (STOP), a fourth lens L4 having negative power and having a convex surface facing the object side, and a fifth lens L5 having positive power and having convex surfaces facing the object and image planes. consists of The imaging plane of the imaging lens system 11 is indicated by IMG. The imaging lens system 11 also includes an IR cut filter 12 .

Table 4 shows lens data of each lens surface in the imaging lens system 11 of Example 2. Table 1 presents, as lens data, the radius of curvature of each surface, the surface spacing at the central optical axis, the refractive index for the d-line, and the Abbe number for the d-line. A surface marked with "*" indicates that it is an aspherical surface.

Table 5 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 5, the aspheric shape adopted for the lens surface is represented by the same formula as in the first embodiment.

Next, aberration will be described with reference to the drawings. FIG. 8 is a spherical aberration diagram in the imaging lens system of Example 2. FIG. In FIG. 8, the horizontal axis indicates the position where the light beam intersects the optical axis Z, and the vertical axis indicates the relative height of the light beam at the pupil diameter. Also, FIG. 8 shows simulation results with light beams having wavelengths of 486 nm, 546 nm and 656 nm. As shown in the spherical aberration diagram of FIG. 8, it can be seen that the axial chromatic aberration at 486 to 656 nm in Example 2 can be corrected extremely well to 2 μm or less.

FIG. 9 is an astigmatism diagram in the imaging lens system of Example 2. FIG. In FIG. 9, the horizontal axis indicates the distance between the imaging points in the Z direction of the optical axis, and the vertical axis indicates the image height (angle of view). In FIG. 9, Sag indicates astigmatism on the sagittal plane, and Tan indicates astigmatism on the tangential plane. Moreover, FIG. 9 shows a simulation result with a light beam having a wavelength of 546 nm.

FIG. 10 is a distortion aberration diagram in the imaging lens system of Example 2. FIG. FIG. 10 shows the distortion of stereographic projection. In FIG. 10, the horizontal axis indicates the amount of image distortion (%), and the vertical axis indicates the image height (angle of view).

FIG. 11 is a diagram of lateral chromatic aberration in the imaging lens system of Example 2. FIG. In FIG. 11, the vertical axis indicates the image height of the light beam with a wavelength of 546 nm, and the horizontal axis indicates the shift amount (μm unit) of the image height of the light beam with a wavelength of 486 nm and 656 nm with respect to the image height of the light beam with a wavelength of 546 nm.

As shown in FIG. 8, the imaging lens system 11 of Example 2 has an F number of 2.02. Further, as shown in FIGS. 9 to 11, in the imaging lens system 11 of Example 2, the half angle of view ω is 103°.
As shown in FIGS. 8 to 11, it can be seen that the aberrations are well corrected.

Next, the characteristic values of the lens will be explained. Table 6 shows the results of calculating the characteristic values of the imaging lens system 11 of Example 2. The definition of each characteristic value in Table 6 is the same as in Table 3. The various focal lengths in Table 6 were calculated using light with a wavelength of 546 nm.

Next, the MTF characteristics of lenses will be described. FIG. 12 is an MTF characteristic diagram in the imaging lens system of Example 2. FIG. In FIG. 12, the horizontal axis indicates the angle of incident light with respect to the central optical axis Z, and the vertical axis indicates the MTF value. FIG. 12 shows MTF characteristics at a spatial frequency of 60 lines/mm. In FIG. 12, the solid line T1 indicates the MTF value in the tangential direction, and the dotted line S1 indicates the MTF value in the sagittal direction.

As shown in FIG. 12, it has good MTF values of 68% or more in both the sagittal and tangential directions from 0 to 96 degrees of view. Also, the MTF value of 58% can be maintained even at the outermost periphery with an angle of view of 103 degrees.

(Embodiment 2: Application example to imaging device)
13 is a cross-sectional view of an imaging device according to Embodiment 2. FIG. The imaging device 21 includes an imaging lens system 11 , a cover glass 22 and an imaging element 23 . The imaging lens system 11, the cover glass 22, and the imaging element 23 are housed in a housing (not shown).

The imaging element 23 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 device 23 is arranged at an imaging position of the imaging lens system 11 . Note that the horizontal angle of view is the angle of view corresponding to the horizontal direction of the imaging device 23 .

A cover glass 22 is provided on the imaging element 23 to protect the imaging element 23 from foreign matter.

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.

11 Imaging lens system 12 Cut filter 21 Imaging device 22 Cover glass 23 Imaging element L1 First lens L2 Second lens L3 Third lens L4 Fourth lens L5 Fifth lens STOP Aperture IMG Imaging plane

Claims (8)

In order from the object side to the image side, a first lens having a convex surface facing the object side and having negative power, a second lens having negative power, and a third lens having a positive power and having a convex surface facing the object side. , an aperture diaphragm, a fourth lens having a negative power with a convex surface facing the object side, and a fifth lens having a positive power with a convex surface facing the object surface and the image surface, comprising:
When the thickness of the third lens at the center optical axis is defined as T3 and the focal length of the entire lens system is defined as f, the following conditional expression (1) is satisfied,
T3/f>2.5 (1)
The imaging lens system, wherein the Abbe number of the fourth lens is less than 23. 2. The imaging lens system according to claim 1 , wherein the following conditional expression (2) is satisfied when the Abbe number of the fourth lens is defined as v4 and the Abbe number of the fifth lens is defined as v5.
v4/v5≦0.4 (2) 3. The imaging lens system according to claim 1 , wherein the following conditional expression (3) is satisfied when the focal length of the fourth lens is defined as f4 and the focal length of the fifth lens is defined as f5.
-2<f4/f5<-1 (3) an imaging lens system according to any one of claims 1 to 3 ;
and an imaging device arranged at a focal position of the imaging lens system. In order from the object side to the image side, a first lens having a convex surface facing the object side and having negative power, a second lens having negative power, and a third lens having a positive power and having a convex surface facing the object side. , an aperture diaphragm, a fourth lens having a negative power with a convex surface facing the object side, and a fifth lens having a positive power with a convex surface facing the object surface and the image surface, comprising:
When the thickness of the third lens at the central optical axis is defined as T3, the focal length of the entire lens system is defined as f, the Abbe number of the fourth lens is defined as v4, and the Abbe number of the fifth lens is defined as v5, the following An imaging lens system that satisfies conditional expressions (1) and (2).
T3/f>2.5 (1)
v4/v5≦0.4 (2) 6. The imaging lens system according to claim 5, wherein the fourth lens has an Abbe number of less than 23. 7. The imaging lens system according to claim 5, wherein the following conditional expression (3) is satisfied when the focal length of the fourth lens is defined as f4 and the focal length of the fifth lens is defined as f5.
-2<f4/f5<-1 (3) an imaging lens system according to any one of claims 5 to 7;
and an imaging device arranged at a focal position of the imaging lens system.

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