JP7629272B2 - Imaging lens system and imaging device - Google Patents

Description

The present invention relates to an imaging lens system and an imaging device, for example, an imaging lens system and an imaging device for vehicle use.

For example, in-vehicle sensing devices require telephoto capabilities to capture images of objects with high angular resolution in order to accurately detect distant objects, such as a vehicle ahead while driving on a highway.

On the other hand, wide-angle performance with a wide angle of view is required to detect a wide range of objects around the vehicle.

In response to the above requirements, if a single camera, i.e., a combination of a single image sensor and a single lens, could be equipped with both telephoto and wide-angle capabilities, it would eliminate the need to prepare separate lenses with wide-angle and telephoto capabilities, making it possible to make effective use of the limited space in the vehicle and offering cost benefits.

For example, the following prior art documents exist for such inventions. Patent Document 1 describes an invention that suppresses the amount of decrease in angular resolution that accompanies an increase in the angle of view near the optical axis. Furthermore, Patent Document 2 describes an invention that aims to achieve both a wide angle and ensure resolution at the angle of view near the optical axis by generating strong negative distortion.

Patent No. 6571840 JP 2019-132967 A

However, in the configurations of Patent Documents 1 and 2, if one attempts to further improve the angular resolution near the center while maintaining the shooting angle of view range, in other words, to increase the focal length and generate more negative distortion, various aberrations will occur to a large extent, making it impossible to ensure good imaging performance.

In addition, Patent Document 2 recommends that the overall length be long compared to the focal length, and that all lenses be constructed from glass lenses, which have higher mass production costs than plastic lenses, leaving the problem of insufficient further compactness and cost reduction suitable for in-vehicle use.

The present invention was made in consideration of these problems, and aims to provide an imaging lens system and imaging device that is compact (short overall length) yet has high imaging performance, higher angular resolution near the on-axis angle of view than conventional devices, and a wide imaging range, and can achieve the environmental resistance and low cost required for in-vehicle applications, etc.

ここで，ｈは光軸からのレンズ面の高さ，zは高さｈにおける面頂点から光軸平行方向への変位量，すなわちサグ量である。 An imaging lens system in one embodiment is an imaging lens system comprising, in order from the object side to the image side, a first lens having negative power, a second lens which has a convex surface on the object side and a concave surface on the image side and is aspherical and has negative power, a third lens having positive power, a fourth lens having positive power, a fifth lens which has a concave surface on the object side, a sixth lens, and an aperture, in which the aperture is disposed between the second lens to the fifth lens, and when a local curvature C(h ) is defined by the following equation (1), the object side surface of the second lens has an aspherical shape in which the local curvature on the periphery is smaller than the curvature at the center.

Here, h is the height of the lens surface from the optical axis, and z is the amount of displacement from the apex of the surface at height h in a direction parallel to the optical axis, i.e., the amount of sag.

The present invention provides an imaging lens system and imaging device that are compact (short overall length) yet have high imaging performance, higher angular resolution near the on-axis angle of view than ever before, and a wide imaging range, and can achieve the environmental resistance and low cost required for in-vehicle applications, etc.

1 is a cross-sectional view showing a configuration of an imaging lens system according to a first embodiment. 4 is a graph showing the height and curvature of the lens surface from the optical axis in the second lens of the imaging lens system of Example 1. 4A to 4C are diagrams illustrating longitudinal aberration in the imaging lens system of Example 1. 3 is a diagram showing the curvature of field in the imaging lens system of Example 1. FIG. 4A to 4C are diagrams illustrating distortion in the imaging lens system of Example 1. FIG. 11 is a cross-sectional view showing the configuration of an imaging lens system according to a second embodiment. 11 is a graph showing the height and curvature of the lens surface from the optical axis in the second lens of the imaging lens system of Example 2. 11A to 11C are diagrams illustrating longitudinal aberration in the imaging lens system according to the second embodiment. 11A and 11B are diagrams illustrating curvature of field in the imaging lens system according to the second embodiment. 11A to 11C are diagrams illustrating distortion in the imaging lens system of Example 2. FIG. 11 is a cross-sectional view showing the configuration of an imaging lens system according to a third embodiment. 13 is a graph showing the height and curvature of the lens surface from the optical axis in the second lens of the imaging lens system of Example 3. 13A to 13C are diagrams illustrating longitudinal aberration in the imaging lens system of Example 3. 13A and 13B are diagrams illustrating curvature of field in the imaging lens system according to the third embodiment. 11A to 11C are diagrams illustrating distortion in the imaging lens system of Example 3. FIG. 11 is a cross-sectional view showing the configuration of an imaging lens system according to a fourth embodiment. 13 is a graph showing the height and curvature of the lens surface from the optical axis in the second lens of the imaging lens system of Example 4. 13A to 13C are diagrams illustrating longitudinal aberration in the imaging lens system according to the fourth embodiment. 13A and 13B are diagrams illustrating curvature of field in the imaging lens system according to the fourth embodiment. 13A to 13C are diagrams illustrating distortion in the imaging lens system according to the fourth embodiment. FIG. 13 is a cross-sectional view showing the configuration of an imaging lens system according to a fifth embodiment. 13 is a graph showing the height and curvature of the lens surface from the optical axis in the second lens of the imaging lens system of Example 5. 13A to 13C are diagrams illustrating longitudinal aberration in the imaging lens system according to the fifth embodiment. 13A and 13B are diagrams illustrating curvature of field in the imaging lens system according to the fifth embodiment. 13A to 13C are diagrams illustrating distortion in the imaging lens system according to the fifth embodiment. FIG. 13 is a cross-sectional view showing the configuration of an imaging lens system according to a sixth embodiment. 13 is a graph showing the height and curvature of the lens surface from the optical axis in the second lens of the imaging lens system of Example 6. 13A to 13C are diagrams illustrating longitudinal aberration in the imaging lens system according to the sixth embodiment. 13 is a diagram showing the curvature of field in the imaging lens system of Example 6. FIG. 13A to 13C are diagrams illustrating distortion in the imaging lens system of Example 6. FIG. 11 is a cross-sectional view of an imaging device according to a second embodiment.

ここで，ｈは光軸からのレンズ面の高さ，zは高さｈにおける面頂点から光軸平行方向への変位量，すなわちサグ量である。 An optical lens and an imaging device according to the present embodiment will be described below.
(Embodiment 1: Imaging Lens System)
The imaging lens system of the first embodiment is an imaging lens system consisting of, in order from the object side to the image side, a first lens having negative power, a second lens which has a convex surface on the object side and a concave surface on the image side and is aspherical and has negative power, a third lens having positive power, a fourth lens having positive power, a fifth lens which has a concave surface on the object side, a sixth lens, and an aperture, in which the aperture is disposed between the second lens to the fifth lens, and when local curvature C(h ) is defined by the following equation (1), the object side surface of the second lens has an aspherical shape in which the local curvature on the periphery is smaller than the curvature at the center.

Here, h is the height of the lens surface from the optical axis, and z is the amount of displacement from the apex of the surface at height h in a direction parallel to the optical axis, i.e., the amount of sag.

The imaging lens system of the first embodiment is compact (shorter overall length) yet has high imaging performance, higher angular resolution near the on-axis angle of view than ever before, and a wide imaging range, and can achieve the environmental resistance and low cost required for in-vehicle applications, etc.

The imaging lens system of the first embodiment has a retrofocus configuration in which the front group (first lens L1/second lens L2) is negative and the rear group (third lens L3 to sixth lens L6) is positive in order to ensure wide-angle performance while ensuring a long back focus relative to the focal length.

The object side surface L2R1 of the second lens, where the intersection point between the chief ray of the off-axis angle of view and the lens surface is located relatively far from the optical axis, is made aspheric, and its shape has a smaller peripheral curvature than the central curvature, so that negative distortion can be efficiently imparted to the light flux at the peripheral angle of view, and a wide shooting angle of view can be ensured even while increasing the focal length to provide high angular resolution to the angle of view near the optical axis.

Here, by disposing the aperture between the second lens and the fifth lens, the height of the chief ray of the off-axial light beam at the object side surface L2R1 of the second lens can be adjusted to an appropriate height, thereby efficiently imparting negative distortion to the off-axial field angle light beam while suppressing the enlargement of the front group.

Here, the first lens L1, which is located closest to the object, is a lens with negative power, so the negative power of the front group can be efficiently shared between the first lens L1 and the second lens L2, allowing the second lens L2 to have a shape that is easy to manufacture while still ensuring the shooting angle of view.

If the first lens L1 were not present, the object side surface L2R1 of the second lens would tend to curve in order to ensure off-axis negative refractive power, or the effective diameter would tend to become larger. For example, when glass molding is performed, air pockets would form in the curved portion, making the shape unstable and leading to reduced yields. Furthermore, a larger effective diameter would lead to a larger volume, which would lead to increased costs.

By making the first lens L1 a negative lens, this situation can be avoided and the manufacturability of the second lens can be ensured. Note that as long as the first lens L1 is a lens with negative power, it does not matter what the uneven shape of the surface is.

For example, the following characteristics are observed depending on the unevenness.
In the case where the object side surface L1R1 of the first lens is concave toward the object side and the image side surface L1R2 of the first lens is convex toward the image side, when the power of the first lens is fixed, a surface with a strong curvature can be arranged at a high position (L1R1) of the off-axis chief ray, so that it is easy to maximize the difference between the distortion aberration coefficient of the so-called Seidel aberration coefficients and other monochromatic aberration coefficients. Therefore, it is easy to ensure imaging performance (MTF) even when negative distortion is applied.

When the object side surface L1R1 of the first lens is concave toward the object side and the image side surface L1R2 of the first lens is concave toward the image side, when the power of the first lens is fixed, the continuous negative surface makes it easier to ensure refractive power even with a small diameter, which is effective in reducing the diameter.

When the object side surface L1R1 of the first lens is convex toward the object side and the image side surface L1R2 of the first lens is concave toward the image side, the convex shape of the front lens makes it more difficult for water droplets and dust to continue to adhere.

Therefore, the concave and convex shape of the surface of the first lens L1 can be determined based on the required size, cost, angle of view characteristics, etc.

In addition, by configuring the third lens L3 and fourth lens L4, which are close to the aperture and through which a thick light beam passes, as lenses with positive power, the positive power in the rear group can be dispersed, and performance degradation due to spherical aberration and decentering can be suppressed.

In addition, by making the fifth lens L5 a lens with a concave surface facing the object side, it is easier to correct field curvature, spherical aberration, and chromatic aberration.

Furthermore, the sixth lens L6 makes it possible to control the field curvature and distortion of the light beam with a high image height, and the angle of incidence of the chief ray relative to the image surface normal.

The imaging lens system of the first embodiment may be configured to satisfy the following formula (2) when the absolute value of the rate of change of the refractive index of the third lens with respect to temperature is defined as dn3/dt.
|dn3/dt|≦10[ ^10-6 /K]...(2)

According to the imaging lens system of the first embodiment, the absolute value |dn3/dt| of the temperature change rate of the refractive index n3 of the third lens L3, which has positive power in the rear group in the retrofocus configuration, can be set to an upper limit value or less, thereby suppressing performance fluctuations due to temperature changes.

Glass lenses are suitable as such glass materials. For example, if the first lens L1 is a glass lens that is resistant to impacts from flying stones and the second lens L2, fourth lens L4, fifth lens L5, and sixth lens L6 are plastic lenses that have a higher absolute value of the temperature change rate of refractive index |dn/dt| than a glass lens and are inexpensive to mass produce, it is possible to configure a low-cost lens while ensuring environmental resistance and temperature stability suitable for in-vehicle use.

The imaging lens system of the above-mentioned first embodiment may be configured to satisfy the following formula (3), where the focal length of the first lens L1 is defined as f1 and the focal length of the entire lens system is defined as f.
1<|f1/f|<10...(3)

According to the imaging lens system of the first embodiment, when the focal length f1 of the first lens L1 is below the lower limit of formula (3), the power of L1 becomes too strong, and it is possible to suppress the occurrence of significant off-axis astigmatism and lateral chromatic aberration in the lower ray. According to the imaging lens system of the first embodiment, when f1 is above the upper limit of formula (3), the amount of negative power shared by the front group of L1 becomes too small, making it difficult to ensure the imaging range, leading to an increase in diameter and deterioration in the manufacturability of L2.

The imaging lens system of the above-mentioned first embodiment may be configured to satisfy the following formula (4), where the radius of curvature of the object side of the first lens is defined as R11 and the radius of curvature of the image side of the first lens is defined as R12.
|R11+R12|/|(R11-R12)|<5...(4)

If the radius of curvature of the first lens L1 falls outside the range of formula (4), the radii of curvature of R1 and R2 will be close to each other. As a result, to ensure the power of the first lens L1 so as to satisfy formula (3), it is necessary to either increase the thickness of the first lens L1 or to make each curvature excessively strong in terms of aberration correction. In the imaging lens system of embodiment 1, by satisfying formula (4), it is possible to achieve compactness, low cost, and suppression of aberration generation.

The imaging lens system of the above-mentioned first embodiment may be configured to satisfy the following formula (5), where the surface-to-surface distance between the first lens L1 and the second lens L2 is defined as t12, and the focal length of the entire lens system is defined as f.
(t12/f)<0.3...(5)

If t12/f exceeds the upper limit of 0.3, i.e. if the L1-L2 inter-surface distance t12 is too large compared to the focal length f, the diameter of L1 will become enlarged, preventing the lens from being made compact.

With the imaging lens system of embodiment 1, the lens can be made compact by satisfying formula (5).

The imaging lens system of the above-mentioned first embodiment may be configured to satisfy the following formula (6), where the radius of curvature of the object side of the second lens is defined as R21 and the radius of curvature of the image side of the second lens is defined as R22.
1.2<|R21/R22|<3.2...(6)

The imaging lens system of the first embodiment can ensure manufacturability of the lens elements and good imaging performance.

If the radius of curvature of the second lens L2 is below the lower limit, the negative power of the second lens L2 will be too weak. In order to ensure the back focus and shooting range, it is necessary to strengthen the negative power of the first lens L1, which results in large astigmatism and chromatic aberration of magnification of off-axis lower rays.

When the radius of curvature of the second lens L2 exceeds the upper limit, that is, the radius of curvature R21 on the object side of the second lens L2 becomes too large compared with the radius of curvature R22 on the image side of the second lens L2.

In this case, in order to achieve both high angular resolution of the near-axis angle of view and a sufficient shooting range, the local curvature of the object side surface of the second lens needs to have a shape that changes sharply with changes in height from the optical axis, and it is necessary to increase the effective diameter and central thickness. This leads to increased costs due to the increase in lens volume, astigmatism, field curvature, and coma aberration, and to a deterioration in performance sensitivity to lens decentering.

To avoid these situations, it is desirable to configure L2 to satisfy equation (6).

The imaging lens system of the above-mentioned first embodiment may be configured to satisfy the following formula (7), where t2 is the thickness of the second lens L2 at the central optical axis, and f is the focal length of the entire lens system.
(t2/f)>0.2...(7)

The imaging lens system of embodiment 1 can effectively correct off-axis aberrations while ensuring a sufficient imaging angle of view.

If t2/f falls below the lower limit, i.e., if the central thickness t2 of the second lens L2 is too thin, then in order to ensure the photographic angle of view, it becomes necessary for the local curvature of the object side surface of the second lens L2 to have a shape that changes abruptly with respect to changes in height from the optical axis. This results in the occurrence of astigmatism, lateral chromatic aberration in off-axis lower rays, and sagittal coma flare. Furthermore, when constructed using a glass molded lens, a shape that changes abruptly makes it difficult to manufacture.

Therefore, it is desirable to satisfy formula (7). By satisfying formula (7), good imaging performance and manufacturability of the lens element can be ensured.

The imaging lens system according to the first embodiment may be configured to satisfy the following formula (8) when the d-line based Abbe number of the second lens L2 is defined as ν2.
ν2>30.0...(8)

In the imaging lens system of embodiment 1, by using a material with an Abbe number of 30.0 or more as the material for the second lens L2, it is possible to suppress the occurrence of chromatic aberration of magnification from the near-axis field angle to off-axis.

The imaging lens system of the first embodiment may be configured to satisfy the following formula (9) when the refractive index of the third lens with respect to the d-line is defined as n3.
n3>1.7...(9)

The third lens L3 with positive power is located closest to the object in the rear group of the retrofocus structure, so marginal rays of the on-axis angle of view pass through a relatively high position.

In the imaging lens system of embodiment 1, by using a high refractive index glass material that satisfies formula (9) for the third lens L3, it is possible to effectively suppress the occurrence of spherical aberration even with a large aperture, and to make the lens resistant to manufacturing errors (decentering).

The imaging lens system of the above-mentioned first embodiment may be configured to satisfy the following formula (10), where the focal length of the third lens L3 is defined as f3 and the focal length of the entire lens system is defined as f.
0.9<f3/f<1.5...(10)

Equation (10) is a conditional expression for suppressing temperature change in the back focus even in a hybrid configuration that combines glass lenses and plastic lenses while effectively suppressing spherical aberration by appropriately dispersing the positive power of the rear group among the third lens L3 and other lenses.

If f3/f falls below the lower limit, i.e., if the focal length f3 of the third lens is too short, the amount of spherical aberration generated by the third lens L3 and the negative power of the front group become too large, making it difficult to correct chromatic aberration and ensuring good imaging performance.

In addition, if f3/f exceeds the upper limit, i.e., if the focal length f3 of the third lens is too long, the positive power cannot be appropriately shared with the positive lens in the rear group, which causes spherical aberration and makes it difficult to correct chromatic aberration.

In addition, for example, if a low-cost hybrid configuration is used in which the fourth lens L4, the fifth lens L5, and the sixth lens L6 are made of plastic, the power borne by the plastic lenses, which have a large temperature change rate dn/dt of the refractive index, becomes too large, and the temperature change in the back focus is likely to become large.

Therefore, according to the imaging lens system of the first embodiment, by setting the focal length f3 of the third lens to the upper limit of equation (10), it is possible to increase the proportion of the positive power shared by the rear group of glass lenses, which have a small temperature change rate of the refractive index dn/dt, and to suppress the temperature change of the back focus.

The imaging lens system of the first embodiment may be configured to satisfy the following formula (11), where the d-line based Abbe number of the fourth lens L4 is defined as v4 and the d-line based Abbe number of the fifth lens L5 is defined as v5.
ν4−ν5>15 (11)

The imaging lens system of the first embodiment can achieve good chromatic aberration correction by providing an Abbe number difference in the conditional formula between the fourth lens L4, which has positive power, and the fifth lens L5, which has negative power.

The imaging lens system of the above-mentioned first embodiment may be configured to satisfy the following formula (12), where the length on the optical axis from the object-side surface of the first lens to the image plane when the object distance is infinite is defined as TTL, and the focal length of the entire lens system is defined as f.
TTL/f<4.5...(12)

When the imaging lens system of the first embodiment is configured to satisfy formula (12), the overall length is small relative to the focal length.

The imaging lens system of the first embodiment may be configured to satisfy the following formula (13), where IH is the effective diameter of the image circle that indicates the range that can be imaged on the image plane (maximum range that can be photographed), f is the focal length of the entire lens system, and FoV is the angle of view.
0.08<(IH/f×tan(FoV)) ² <0.45...(13)

The imaging lens system of the first embodiment ensures a wide imaging angle while suppressing degradation of resolution at the periphery of the image, making it possible to recognize subjects captured at the periphery of the image during sensing, etc.

If the value of formula (13) is equal to or greater than the upper limit, the amount of distortion will be insufficient, making it difficult to achieve a wide angle of view. On the other hand, if the value of formula (13) is equal to or less than the lower limit, the amount of distortion will be too large, causing the periphery of the image to be compressed. In other words, the resolution of the periphery of the image will decrease. This is undesirable, as it will be difficult to recognize subjects that are captured on the periphery of the image during sensing, etc.

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

The first lens L1 is a spherical lens with negative power. The object-side lens surface S1 of the first lens L1 faces the concave surface toward the object side. The image-side lens surface S2 of the first lens L1 faces the convex surface toward the image side.

The second lens L2 is an aspheric lens with negative power. The object-side lens surface S3 of the second lens L2 faces the convex surface toward the object side. In addition, the image-side lens surface S4 of the second lens L2 has a concave curved portion toward the image side.

The third lens L3 is a spherical lens with positive power. The object-side lens surface S5 of the third lens L3 faces the convex surface toward the object side. In addition, the image-side lens surface S6 of the third lens L3 faces the convex surface toward the image plane side.

The aperture STOP is the aperture that determines the F-number (Fno) of the lens system. The aperture STOP is placed between the third lens L3 and the fourth lens L4.

The fourth lens L4 is an aspheric plastic lens with positive power. The object-side lens surface S9 of the fourth lens L4 faces the convex surface toward the object side. In addition, the image-side lens surface S10 of the fourth lens L4 faces the convex surface toward the image plane side.

The fifth lens L5 is an aspheric lens having negative power. The object-side lens surface S11 of the fifth lens L5 has a concave curved portion. In addition, the image-side lens surface S12 of the fifth lens L5 faces the convex surface toward the image surface side.

The fourth lens L4 and the fifth lens L5 form a cemented lens. That is, the image-side lens surface S10 of the fourth lens L4 and the object-side lens surface S11 of the fifth lens L5 are in contact with each other. For example, it is preferable to cement the fourth lens L4 and the fifth lens L5 with an adhesive layer having an axial thickness of 0.02 mm.

The sixth lens L6 is an aspheric lens having negative power. The object-side lens surface S13 of the sixth lens L6 has a concave curved portion. In addition, the image-side lens surface S14 of the sixth lens L6 has a concave curved portion.

The IR cut filter 12 is a filter for cutting light in the infrared region. When designing the imaging lens system 11, the IR cut filter 12 is treated as an integral part of the imaging lens system 11. However, the IR cut filter 12 is not an essential component of the imaging lens system 11.

Table 1 shows the lens data of each lens surface in the imaging lens system 11 of Example 1. In Table 1, the lens data includes the radius of curvature (mm) of each surface, the surface spacing (mm) at the central optical axis, the refractive index Nd for the d-line, and the Abbe number Vd for the d-line. Surfaces marked with an "*" are aspheric. Also, in Table 1, for example, "-6.522528E-03" means "-6.522528×10 ^-3 ". The numerical expressions in the following tables are similar.

The aspheric shape adopted for the lens surface is expressed by the following equation, where z is the amount of sag, c is the inverse of the radius of curvature, k is the cone coefficient, r is the ray height from the optical axis Z, and the aspheric coefficients of the fourth order, sixth order, eighth order, tenth order, twelfth order, fourteenth order, and sixteenth order are A4, A6, A8, A10, A12, A14, and A16, respectively.

Table 2 shows the aspheric coefficients for defining the aspheric shape of the aspheric lens surface in the imaging lens system 11 of Example 1.

Figure 2 is a graph showing the relationship between the local curvature of the object-side surface of the second lens of the imaging lens system of Example 1 and the height of the lens surface from the optical axis. In Figure 2, C(h) shows the local curvature of the object-side surface of the second lens, and h shows the height of the lens surface from the optical axis.

Next, aberration will be explained using the drawings. Figure 3 is a diagram of longitudinal aberration in the imaging lens system of Example 1. In Figure 3, the horizontal axis indicates the position where the light ray intersects with the optical axis Z, and the vertical axis indicates the height at the pupil diameter. Figure 3 also shows the results of a simulation using light with a wavelength of 546 nm.

Fig. 4 is a diagram of the field curvature in the imaging lens system of Example 1. In Fig. 4, the horizontal axis indicates the distance in the optical axis Z direction, and the vertical axis indicates the image height . In Fig. 4, Sag indicates the astigmatism in the sagittal plane, and Tan indicates the astigmatism in the tangential plane. Fig. 4 also shows the results of a simulation using light with a wavelength of 546 nm .

Fig. 5 is a diagram showing distortion aberration in the imaging lens system of Example 1. In Fig. 6, the horizontal axis indicates the amount of image distortion (%), and the vertical axis indicates the image height .

As shown in Figure 3, the imaging lens system 11 of Example 1 has an F-number of 2.0. The half angle of view is 42 degrees. As shown in Figures 4 and 5, it can be seen that aberrations are well corrected.

Next, the characteristic values of the lenses will be described. Table 3 shows the results of calculating the characteristic values of the imaging lens system 11 of Example 1. In Table 3, the focal length of the first lens L1 is _f1 , the focal length of the second lens L2 is _f2 , the focal length of the third lens L3 is _f3 , the focal length of the fourth lens L4 is _f4 , the focal length of the fifth lens L5 is _f5 , and the focal length of the sixth lens L6 is f6 _. , the focal length of the entire lens system in the imaging lens system 11 is f, the absolute value of the temperature change rate of the refractive index of the third lens is |dn3/dt|, the absolute value of the value obtained by dividing the focal length of the first lens L1 by the focal length of the entire lens system is |f1/f|, the absolute value of the sum of the radius of curvature of the object side of the first lens and the radius of curvature of the image side of the first lens is divided by the absolute value of the value obtained by subtracting the radius of curvature of the image side of the first lens from the radius of curvature of the object side of the first lens is |R11+R12|/|R11-R12|, the absolute value of the value obtained by dividing the absolute value of the surface distance between the first lens L1 and the second lens L2 by the focal length of the entire lens system is |t12|/f, the absolute value of the value obtained by dividing the radius of curvature of the object side of the second lens by the radius of curvature of the image side of the second lens is |R21/R22|, The characteristic values are shown as follows: t2/f is the thickness at the central optical axis of the second lens L2 divided by the focal length of the entire lens system; v2 is the Abbe number of the second lens L2; n3 is the refractive index of the third lens; f3/f is the focal length of the third lens L3 divided by the focal length of the entire lens system; v4-v5 is the Abbe number of the fourth lens L4 subtracted by the Abbe number of the fifth lens L5; TTL/f is the length on the optical axis from the object side surface of the first lens to the image plane when the object distance is infinite divided by the focal length of the entire lens system; and (IH/(f*tan(FoV))) ² is the effective diameter IH of the image circle representing the range that can be imaged on the image plane (maximum range that can be photographed). In Table 3, the units of focal length and central thickness are all mm. Additionally, the various focal lengths in Table 3 were calculated using light with a wavelength of 546 nm.

Example 2
Fig. 6 is a cross-sectional view showing the configuration of the imaging lens system of the second embodiment. In Fig. 6, the imaging lens system 11 is composed of, in order from the object side to the image side, a first lens L1 having a negative power, a second lens L2 having a negative power, a third lens L3 having a positive power, a fourth lens L4 having a positive power, a fifth lens L5 having a positive power, and a sixth lens L6 having a negative power. The imaging plane of the imaging lens system 11 is indicated by IMG. The imaging lens system 11 may also include an IR cut filter 12. The shape and material of each lens are the same as those of the first embodiment.

Table 4 shows the lens data for each lens surface in the imaging lens system 11 of Example 2. In Table 4, the lens data includes the radius of curvature (mm) of each surface, the surface spacing (mm) at the central optical axis, the refractive index Nd for the d-line, and the Abbe number Vd for the d-line. Surfaces marked with an "*" are aspheric.

Table 5 shows the aspheric coefficients for defining the aspheric shape of the lens surface that is made aspheric in the imaging lens system 11 of Example 2. In Table 5, the aspheric shape adopted for the lens surface is expressed by the same formula as in Example 1.

Figure 7 is a graph showing the relationship between the local curvature of the object-side surface of the second lens of the imaging lens system of Example 2 and the height of the lens surface from the optical axis. In Figure 7, C(h) shows the local curvature of the object-side surface of the second lens, and h shows the height of the lens surface from the optical axis.

Next, aberration will be explained using drawings. Figure 8 is a diagram of longitudinal aberration in the imaging lens system of Example 2. In Figure 8, the horizontal axis indicates the position where the light ray intersects with the optical axis Z, and the vertical axis indicates the height at the pupil diameter. Figure 8 also shows the results of a simulation using light with a wavelength of 546 nm.

Fig. 9 is a diagram of the field curvature in the imaging lens system of Example 2. In Fig. 9, the horizontal axis indicates the distance in the optical axis Z direction, and the vertical axis indicates the image height . In Fig. 9, Sag indicates the astigmatism in the sagittal plane, and Tan indicates the astigmatism in the tangential plane. Fig. 9 also shows the results of a simulation using light with a wavelength of 546 nm .

Fig. 10 is a diagram showing distortion aberration in the imaging lens system of Example 2. In Fig. 10, the horizontal axis indicates the amount of image distortion (%), and the vertical axis indicates the image height .

As shown in Figure 8, the imaging lens system 11 of Example 1 has an F-number of 2.0. The half angle of view is 55 degrees. As shown in Figures 8 to 10, it can be seen that aberrations are well corrected.

Next, the characteristic values of the lenses will be explained. Table 6 shows the results of calculating the characteristic values of the imaging lens system 11 of Example 2. Each item in Table 6 shows the same characteristic values as in Table 3. In addition, the various focal lengths in Table 6 were calculated using light with a wavelength of 546 nm.

Example 3
Fig. 11 is a cross-sectional view showing the configuration of an imaging lens system of Example 3. In Fig. 11, the imaging lens system 11 is composed of, in order from the object side to the image side, a first lens L1 having negative power, a second lens L2 having negative power, a third lens L3 having positive power, a fourth lens L4 having positive power, a fifth lens L5 having negative power, and a sixth lens L6 having negative power. The imaging plane of the imaging lens system 11 is indicated by IMG. The imaging lens system 11 may also include an IR cut filter 12. The shape and material of each lens are the same as those of Example 1.

Table 7 shows the lens data for each lens surface in the imaging lens system 11 of Example 3. In Table 7, the lens data includes the radius of curvature (mm) of each surface, the surface spacing (mm) at the central optical axis, the refractive index Nd for the d-line, and the Abbe number Vd for the d-line. Surfaces marked with an "*" are aspheric.

Table 8 shows the aspheric coefficients for defining the aspheric shape of the lens surface that is made aspheric in the imaging lens system 11 of Example 3. In Table 8, the aspheric shape adopted for the lens surface is expressed by the same formula as in Example 1.

Figure 12 is a graph showing the relationship between the local curvature of the object-side surface of the second lens of the imaging lens system of Example 3 and the height of the lens surface from the optical axis. In Figure 12, C(h) shows the local curvature of the object-side surface of the second lens, and h shows the height of the lens surface from the optical axis.

Next, aberration will be explained using the drawings. Figure 13 is a diagram of longitudinal aberration in the imaging lens system of Example 3. In Figure 13, the horizontal axis indicates the position where the light ray intersects with the optical axis Z, and the vertical axis indicates the height at the pupil diameter. Figure 13 also shows the results of a simulation using light with a wavelength of 546 nm.

Fig. 14 is a diagram of the field curvature in the imaging lens system of Example 3. In Fig. 14, the horizontal axis indicates the distance in the optical axis Z direction, and the vertical axis indicates the image height . In Fig. 14, Sag indicates the astigmatism in the sagittal plane, and Tan indicates the astigmatism in the tangential plane. Fig. 14 also shows the results of a simulation using light with a wavelength of 546 nm .

Fig. 15 is a diagram showing distortion aberration in the imaging lens system of Example 3. In Fig. 15, the horizontal axis indicates the amount of image distortion (%), and the vertical axis indicates the image height .

As shown in Figure 13, the imaging lens system 11 of Example 1 has an F-number of 2.0. The half angle of view is 46 degrees. As shown in Figures 13 to 15, it can be seen that aberrations are well corrected.

Next, the characteristic values of the lenses will be explained. Table 9 shows the results of calculating the characteristic values of the imaging lens system 11 of Example 3. Each item in Table 9 shows the same characteristic values as in Table 3. In addition, the various focal lengths in Table 9 were calculated using light with a wavelength of 546 nm.

Example 4
Fig. 16 is a cross-sectional view showing the configuration of the imaging lens system of Example 4. In Fig. 16, the imaging lens system 11 is composed of, in order from the object side to the image side, a first lens L1 having negative power, a second lens L2 having negative power, a third lens L3 having positive power, a fourth lens L4 having positive power, a fifth lens L5 having negative power, and a sixth lens L6 having negative power. The imaging plane of the imaging lens system 11 is indicated by IMG. The imaging lens system 11 may also include an IR cut filter 12. The shape and material of each lens are the same as those of Example 1.

Table 10 shows the lens data for each lens surface in the imaging lens system 11 of Example 4. In Table 10, the lens data includes the radius of curvature (mm) of each surface, the surface spacing (mm) at the central optical axis, the refractive index Nd for the d-line, and the Abbe number Vd for the d-line. Surfaces marked with an "*" are aspheric.

Table 11 shows the aspheric coefficients for defining the aspheric shape of the lens surface that is made aspheric in the imaging lens system 11 of Example 4. In Table 11, the aspheric shape adopted for the lens surface is expressed by the same formula as in Example 1.

Figure 17 is a graph showing the relationship between the local curvature of the object-side surface of the second lens of the imaging lens system of Example 4 and the height of the lens surface from the optical axis. In Figure 17, C(h) shows the local curvature of the object-side surface of the second lens, and h shows the height of the lens surface from the optical axis.

Next, aberration will be explained using the drawings. Figure 18 is a diagram of longitudinal aberration in the imaging lens system of Example 4. In Figure 18, the horizontal axis indicates the position where the light ray intersects with the optical axis Z, and the vertical axis indicates the height at the pupil diameter. Figure 18 also shows the results of a simulation using light with a wavelength of 546 nm.

Fig. 19 is a diagram of the field curvature in the imaging lens system of Example 4. In Fig. 19, the horizontal axis indicates the distance in the optical axis Z direction, and the vertical axis indicates the image height . In Fig. 19, Sag indicates the astigmatism in the sagittal plane, and Tan indicates the astigmatism in the tangential plane. Fig. 19 also shows the results of a simulation using a light beam with a wavelength of 546 nm .

Fig. 20 is a diagram showing distortion aberration in the imaging lens system of Example 4. In Fig. 20, the horizontal axis indicates the amount of image distortion (%), and the vertical axis indicates the image height .

As shown in Figure 18, the imaging lens system 11 of Example 1 has an F-number of 2.0. The half angle of view is 48 degrees. As shown in Figures 18 to 20, it can be seen that aberrations are well corrected.

Next, the characteristic values of the lenses will be explained. Table 12 shows the results of calculating the characteristic values of the imaging lens system 11 of Example 4. Each item in Table 12 shows the same characteristic values as in Table 3. In addition, the various focal lengths in Table 12 were calculated using light with a wavelength of 546 nm.

Example 5
Fig. 21 is a cross-sectional view showing the configuration of the imaging lens system of Example 5. In Fig. 21, the imaging lens system 11 is composed of, in order from the object side to the image side, a first lens L1 having negative power, a second lens L2 having negative power, a third lens L3 having positive power, a fourth lens L4 having positive power, a fifth lens L5 having negative power, and a sixth lens L6 having positive power. The imaging plane of the imaging lens system 11 is indicated by IMG. The imaging lens system 11 may also include an IR cut filter 12. The shape and material of each lens are the same as those of Example 1.

Table 13 shows the lens data for each lens surface in the imaging lens system 11 of Example 5. In Table 13, the lens data includes the radius of curvature (mm) of each surface, the surface spacing (mm) at the central optical axis, the refractive index Nd for the d-line, and the Abbe number Vd for the d-line. Surfaces marked with an "*" are aspheric.

Table 14 shows the aspheric coefficients for defining the aspheric shape of the lens surface that is made aspheric in the imaging lens system 11 of Example 5. In Table 14, the aspheric shape adopted for the lens surface is expressed by the same formula as in Example 1.

Figure 22 is a graph showing the relationship between the local curvature of the object-side surface of the second lens of the imaging lens system of Example 5 and the height of the lens surface from the optical axis. In Figure 22, C(h) shows the local curvature of the object-side surface of the second lens, and h shows the height of the lens surface from the optical axis.

Next, aberration will be explained using drawings. Figure 23 is a diagram of longitudinal aberration in the imaging lens system of Example 5. In Figure 23, the horizontal axis indicates the position where the light ray intersects with the optical axis Z, and the vertical axis indicates the height at the pupil diameter. Figure 23 also shows the results of a simulation using light with a wavelength of 546 nm.

Fig. 24 is a diagram of the field curvature in the imaging lens system of Example 5. In Fig. 24, the horizontal axis indicates the distance in the optical axis Z direction, and the vertical axis indicates the image height . In Fig. 24, Sag indicates the astigmatism in the sagittal plane, and Tan indicates the astigmatism in the tangential plane. Fig. 24 also shows the results of a simulation using a light beam with a wavelength of 546 nm .

Fig. 25 is a diagram showing distortion aberration in the imaging lens system of Example 5. In Fig. 25, the horizontal axis indicates the amount of image distortion (%), and the vertical axis indicates the image height .

As shown in Figure 23, the imaging lens system 11 of Example 1 has an F-number of 2.0. The half angle of view is 42 degrees. As shown in Figures 23 to 25, it can be seen that aberrations are well corrected.

Next, the characteristic values of the lenses will be explained. Table 15 shows the results of calculating the characteristic values of the imaging lens system 11 of Example 5. Each item in Table 15 shows the same characteristic values as in Table 3. In addition, the various focal lengths in Table 15 were calculated using light with a wavelength of 546 nm.

Example 6
Fig. 26 is a cross-sectional view showing the configuration of an imaging lens system of Example 6. In Fig. 26, the imaging lens system 11 is composed of, in order from the object side to the image side, a first lens L1 having negative power, a second lens L2 having negative power, a third lens L3 having positive power, a fourth lens L4 having positive power, a fifth lens L5 having positive power, and a sixth lens L6 having negative power. The imaging plane of the imaging lens system 11 is indicated by IMG. The imaging lens system 11 may also include an IR cut filter 12. The shape and material of each lens are the same as those of Example 1.

Table 16 shows the lens data for each lens surface in the imaging lens system 11 of Example 6. In Table 16, the lens data includes the radius of curvature (mm) of each surface, the surface spacing (mm) at the central optical axis, the refractive index Nd for the d-line, and the Abbe number Vd for the d-line. Surfaces marked with an "*" are aspheric.

Table 17 shows the aspheric coefficients for defining the aspheric shape of the lens surface that is made aspheric in the imaging lens system 11 of Example 6. In Table 17, the aspheric shape adopted for the lens surface is expressed by the same formula as in Example 1.

Figure 27 is a graph showing the relationship between the local curvature of the object-side surface of the second lens of the imaging lens system of Example 6 and the height of the lens surface from the optical axis. In Figure 27, C(h) shows the local curvature of the object-side surface of the second lens, and h shows the height of the lens surface from the optical axis.

Next, aberration will be explained using drawings. Figure 28 shows the longitudinal aberration diagram for the imaging lens system of Example 6. In Figure 28, the horizontal axis indicates the position where the light ray intersects with the optical axis Z, and the vertical axis indicates the height at the pupil diameter. Figure 28 also shows the results of a simulation using light with a wavelength of 546 nm.

Fig. 29 is a diagram of the field curvature in the imaging lens system of Example 6. In Fig. 29, the horizontal axis indicates the distance in the optical axis Z direction, and the vertical axis indicates the image height . In Fig. 29, Sag indicates the astigmatism in the sagittal plane, and Tan indicates the astigmatism in the tangential plane. Fig. 29 also shows the results of a simulation using a light beam with a wavelength of 546 nm .

Fig. 30 is a diagram showing distortion aberration in the imaging lens system of Example 6. In Fig. 30, the horizontal axis indicates the amount of image distortion (%), and the vertical axis indicates the image height .

As shown in Figure 28, the imaging lens system 11 of Example 1 has an F-number of 2.0. The half angle of view is 46 degrees. As shown in Figures 28 to 30, it can be seen that aberrations are well corrected.

Next, the lens characteristic values will be explained. Table 18 shows the results of calculating the characteristic values of the imaging lens system 11 of Example 6. Each item in Table 18 shows the same characteristic values as in Table 3. In addition, the various focal lengths in Table 18 were calculated using light with a wavelength of 546 nm.

(Embodiment 2: Example of application to an imaging device)
47, an imaging device 21 includes an imaging lens system 11 and an imaging element 22. The imaging lens system 11 and the imaging element 22 are housed in a housing (not shown). The imaging lens system 11 is the imaging lens system 11 described in the above-mentioned first embodiment.

The image sensor 22 is an element that converts the received light into an electrical signal, and may be, for example, a CCD image sensor or a CMOS image sensor. The image sensor 22 is disposed at the imaging position of the imaging lens system 11.

In this way, the imaging device of the second embodiment is compact (shorter overall length) yet has high imaging performance, higher angular resolution near the on-axis angle of view than ever before, and a wide imaging range, and can achieve the environmental resistance and low cost required for in-vehicle applications, etc.

The present invention is not limited to the above-mentioned embodiments, and can be modified as appropriate without departing from the spirit of the invention. For example, embodiment 2 may be applied to embodiments 1 to 6. For example, the applications of the imaging lens system of the present invention are not limited to vehicle-mounted cameras and surveillance cameras, and can also be used for other applications, such as being mounted on small electronic devices such as mobile phones.

11 imaging lens system 12 IR cut filter 21 imaging device 22 imaging element L1 first lens L2 second lens L3 third lens L4 fourth lens L5 fifth lens L6 sixth lens STOP aperture IMG imaging surface

Claims (10)

an imaging lens system including, in order from the object side to the image side, a first lens having negative power, a second lens which is an aspheric lens having a convex surface on the object side and a concave surface on the image side and which has negative power, a third lens having positive power, a fourth lens having positive power, a fifth lens having a concave surface on the object side, and a sixth lens, wherein a diaphragm is disposed between the second lens and the fifth lens, and when a local curvature C(h) is defined by the following formula (1), the object side surface of the second lens has an aspheric shape in which a local curvature on a periphery is smaller than a curvature at a center, the object side surface of the second lens has an inflection point, and when the Abbe number of the second lens is defined as v2, the refractive index of the third lens is defined as n3 , the focal length of the third lens is defined as f3, and the focal length of the entire lens system is defined as f , the imaging lens system satisfies the following formulas (8), (9 ), and (10) .

ν2>30.0...(8)
n3>1.7...(9)
Here, h is the height of the lens surface from the optical axis, and z is the amount of displacement from the apex of the surface at height h in a direction parallel to the optical axis, i.e., the amount of sag.
0.9<f3/f<1.5...(10) 2. The imaging lens system according to claim 1, wherein when an absolute value of a rate of change of a refractive index of the third lens with respect to temperature is defined as dn3/dt, the following formula (2) is satisfied:
|dn3/dt|≦10[ ^10-6 /K]...(2) 3. The imaging lens system according to claim 1, wherein the following formula (3) is satisfied, where f1 is a focal length of the first lens and f is a focal length of the entire lens system:
1<|f1/f|<10...(3) 4. The imaging lens system according to claim 1, wherein when a radius of curvature on an object side of the first lens is defined as R11 and a radius of curvature on an image side of the first lens is defined as R12, the following formula (4) is satisfied:
|R11+R12|/|(R11-R12)|<5...(4) 5. The imaging lens system according to claim 1, wherein the following formula (5) is satisfied when a surface-to-surface distance between the first lens and the second lens is defined as t12 and a focal length of the entire lens system is defined as f:
(t12/f)<0.3...(5) 6. The imaging lens system according to claim 1, wherein when a radius of curvature on an object side of the second lens is defined as R21 and a radius of curvature on an image side of the second lens is defined as R22, the following formula (6) is satisfied:
1.2<|R21/R22|<3.2...(6) 7. The imaging lens system according to claim 1, wherein when a thickness of the second lens L2 at a central optical axis is defined as t2 and a focal length of the entire lens system is defined as f, the following formula (7) is satisfied:
(t2/f)>0.2...(7) 8. The imaging lens system according to claim 1 , wherein when 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 formula (11) is satisfied:
ν4−ν5>15 (11) 9. The imaging lens system according to claim 1, wherein the following formula (12) is satisfied when a length on the optical axis from an object-side surface of the first lens to an image plane when an object distance is infinite is defined as TTL, and a focal length of the entire lens system is defined as f:
TTL/f<4.5...(12) An imaging lens system according to any one of claims 1 to 9 ;
an imaging element disposed at a focal position of the imaging lens system.

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