Imaging lens system and imaging device

Abstract

To provide an image capturing lens system which is compact and yet offers high imaging performance, higher angular resolution near an axial angle of view and a wide imaging range, and is capable of offering environmental resistance required for in-vehicle applications and low cost and also provide an image capturing device.SOLUTION: An image capturing lens system 11 consists of, in order from the object side to the image side, a first lens L1 having negative power, an aspherical second lens L2 with negative power having a convex surface on the object side and concave surface on the image side, a third lens L3 having positive power, a fourth lens L4 having positive power, a fifth lens L5 having a concave surface on the object side, and a sixth lens L6, where an aperture stop STOP is located somewhere between the second lens and the fifth lens. The second lens has an aspherical object-side surface having local curvatures smaller than that of the center in the periphery.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an imaging lens system and an imaging device, for example, to an imaging lens system and an imaging device for use in a vehicle. [Background technology]

[0002] 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 traveling on a highway.

[0003] On the other hand, in order to detect a wide range of objects around the vehicle, wide-angle performance with a wide angle of view is required.

[0004] 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, allowing for effective use of the limited space in the vehicle and offering cost benefits.

[0005] Such inventions are exemplified by the following prior art documents. 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. 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 strongly generating negative distortion. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 6571840 [Patent Document 2] JP 2019-132967 A Summary of the Invention [Problem to be solved by the invention]

[0007] 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 range, that is, 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.

[0008] Furthermore, 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, posing the issue of insufficient further compactification and cost reduction to make the sensor suitable for in-vehicle use.

[0009] The present invention has been made in consideration of these problems, and aims to provide 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 conventional devices, and a wide imaging range, and can achieve the environmental resistance and low cost required for in-vehicle applications, etc. [Means for solving the problem]

[0010] The imaging lens system of one embodiment is an imaging lens system including, in order from the object side to the image side, a first lens having negative power, a second lens having a convex surface on the object side and a concave surface on the image side, which is an aspheric lens having 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, a sixth lens, and an aperture, the aperture being disposed between the second lens to the fifth lens, and having a local curvature C(h) of When defined by the following formula (1), the object side surface of the second lens is made to have an aspheric shape in which the local curvature at the periphery is smaller than the curvature at the center.

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[0011] According to the present invention, it is possible to provide 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 conventional ones, and a wide imaging range, and that can achieve the environmental resistance and low cost required for in-vehicle applications, etc. [Brief description of the drawings]

[0012] [Figure 1] 1 is a cross-sectional view showing a configuration of an imaging lens system according to a first embodiment. [Diagram 2] 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. [Diagram 3] 4A to 4C are diagrams illustrating longitudinal aberration in the imaging lens system of Example 1. [Figure 4] 3 is a diagram showing the curvature of field in the imaging lens system of the first embodiment. FIG. [Diagram 5] 4A to 4C are diagrams illustrating distortion in the imaging lens system of Example 1. [Figure 6] FIG. 11 is a cross-sectional view showing the configuration of an imaging lens system according to a second embodiment. [Figure 7] 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. [Figure 8] 11A to 11C are diagrams illustrating longitudinal aberration in the imaging lens system of Example 2. [Figure 9] FIG. 11 is a diagram showing the curvature of field in the imaging lens system of the second embodiment. [Figure 10] 8A to 8C are diagrams illustrating distortion in the imaging lens system of Example 2. [Figure 11] FIG. 11 is a cross-sectional view showing the configuration of an imaging lens system according to a third embodiment. [Figure 12] 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. [Figure 13] 11A to 11C are diagrams illustrating longitudinal aberration in the imaging lens system of Example 3. [Figure 14] 11 is a diagram showing the curvature of field in the imaging lens system of Example 3. FIG. [Figure 15] 11A to 11C are diagrams illustrating distortion in the imaging lens system of Example 3. [Figure 16] FIG. 11 is a cross-sectional view showing the configuration of an imaging lens system according to a fourth embodiment. [Figure 17] 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. [Figure 18] 13A to 13C are diagrams illustrating longitudinal aberration in the imaging lens system of Example 4. [Figure 19] FIG. 11 is a diagram showing the curvature of field in the imaging lens system of the fourth embodiment. [Figure 20] 11A to 11C are diagrams illustrating distortion in the imaging lens system of Example 4. [Figure 21] FIG. 11 is a cross-sectional view showing the configuration of an imaging lens system according to a fifth embodiment. [Figure 22] 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. [Diagram 23] 13A to 13C are diagrams illustrating longitudinal aberration in the imaging lens system of Example 5. [Figure 24] 13 is a diagram showing the curvature of field in the imaging lens system of Example 5. FIG. [Diagram 25] 13A to 13C are diagrams illustrating distortion in the imaging lens system of Example 5. [Figure 26] FIG. 13 is a cross-sectional view showing the configuration of an imaging lens system according to a sixth embodiment. [Figure 27] 20 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. [Figure 28] 13A to 13C are diagrams showing longitudinal aberration in the imaging lens system of Example 6. [Figure 29] 13 is a diagram showing the curvature of field in the imaging lens system of Example 6. FIG. [Diagram 30] 13 is a diagram illustrating distortion in the imaging lens system of Example 6. FIG. [Diagram 31] FIG. 11 is a cross-sectional view of an imaging device according to a second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] The optical lens and the 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 that includes, in order from the object side to the image side, a first lens having negative power, a second lens having a convex surface on the object side and a concave surface on the image side, which is an aspheric lens having 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, a sixth lens, and an aperture, in which the aperture is disposed between the second lens to the fifth lens, and has a local curvature C(h) of When defined by the following formula (1), the object side surface of the second lens is made to have an aspheric shape in which the local curvature at the periphery is smaller than the curvature at the center.

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[0014] The imaging lens system of the first embodiment is compact (short overall length) yet has high imaging performance, higher angular resolution near the on-axis angle of view than conventional ones, and a wide imaging range, and can achieve the environmental resistance and low cost required for in-vehicle applications, etc.

[0015] In the imaging lens system of embodiment 1, in order to ensure wide-angle performance while ensuring a long back focus relative to the focal length, the front group (first lens L1 / second lens L2) is negative and the rear group (third lens L3 to sixth lens L6) is positive, adopting a retrofocus configuration.

[0016] The object side surface L2R1 of the second lens, where the intersection point of the chief ray of the off-axial angle of view and the lens surface is located relatively far from the optical axis, is made aspheric and its shape is such that the peripheral curvature is smaller than the central curvature, thereby efficiently imparting negative distortion to the light flux at the peripheral angle of view.This makes it possible to ensure a wide shooting angle of view while lengthening the focal length in order to provide high angular resolution to the angle of view near the optical axis.

[0017] Here, by positioning the aperture between the second lens and the fifth lens, the height of the chief ray of the off-axial light beam on 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 light beam at the field of view while suppressing the enlargement of the front group.

[0018] Here, because the first lens L1, which is located closest to the object, is a lens with negative power, the negative power of the front group can be efficiently shared between the first lens L1 and the second lens L2, so that the second lens L2 can be made into a shape that is easy to manufacture while still maintaining the shooting angle of view.

[0019] If the first lens L1 were not present, the object side surface L2R1 of the second lens would be warped or the effective diameter would be large in order to ensure off-axis negative refractive power. For example, when glass molding is performed, air pockets would form in the warped area, making the shape unstable and leading to reduced yields. In addition, a larger effective diameter would result in a larger volume, which would lead to increased costs.

[0020] By making the first lens L1 a negative lens, such a 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, there is no restriction on the concave and convex shape of the surface.

[0021] For example, depending on the unevenness, there are the following characteristics. If 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 placed at the high position (L1R1) of the off-axis chief ray, making it easy to maximize the difference between the distortion aberration coefficient of the so-called Seidel aberration coefficient and other monochromatic aberration coefficients. Therefore, it is easy to ensure imaging performance (MTF) even with negative distortion.

[0022] If 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 surfaces make it easier to ensure refractive power even with a small diameter, which is effective in reducing the diameter.

[0023] 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 difficult for water droplets and dust to continue to adhere.

[0024] Therefore, the concave and convex shape of the surface of the first lens L1 may be determined based on the required size, cost, angle of view characteristics, and the like.

[0025] In addition, by configuring the third lens L3 and the 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.

[0026] In addition, by making the fifth lens L5 a lens having a concave surface on the object side, it becomes easier to correct curvature of field, spherical aberration, and chromatic aberration.

[0027] Furthermore, the sixth lens L6 makes it possible to control the field curvature and distortion of a light beam with a high image height, and the angle of incidence of the chief ray with respect to the image surface normal.

[0028] The imaging lens system of the above-mentioned 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)

[0029] According to the imaging lens system of embodiment 1, it is possible to suppress performance fluctuations due to temperature changes by setting 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, to an upper limit value or less.

[0030] 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 like, 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 the 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.

[0031] 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)

[0032] 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 the formula (3), the power of L1 becomes too strong, and it is possible to suppress the occurrence of large 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 the 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 the diameter and deterioration in the manufacturability of L2.

[0033] In the imaging lens system of the first embodiment, the curvature of the first lens on the object side is radius R11, the curvature of the image side of the first lens radius When R12 is defined as R12, the following formula (4) may be satisfied. |R11+R12| / |(R11-R12)|<5 ···(4)

[0034] 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 take similar values. 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 take measures to make each curvature excessively strong in terms of aberration correction. In the imaging lens system of the first embodiment, by satisfying formula (4), it is possible to achieve miniaturization, low cost, and suppression of aberration generation.

[0035] The imaging lens system of the above-mentioned first embodiment may be configured to satisfy the following formula (5), where the inter-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)

[0036] If t12 / f exceeds the upper limit of 0.3, that is, 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.

[0037] According to the imaging lens system of the first embodiment, the lens can be made compact by satisfying the formula (5).

[0038] In the imaging lens system of the first embodiment, the curvature of the object side of the second lens is radius R21, the curvature of the image side of the second lens radius When R22 is defined as R22, the following formula (6) may be satisfied. 1.2<|R21 / R22|<3.2 (6)

[0039] According to the imaging lens system of the first embodiment, it is possible to ensure good manufacturability of the lens elements and good imaging performance.

[0040] If the radius of curvature of the second lens L2 is below the lower limit, the negative power of the second lens L2 becomes 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, and as a result, astigmatism and chromatic aberration of magnification of off-axis rays tend to occur significantly.

[0041] When the radius of curvature of the second lens L2 exceeds the upper limit, that is, the curvature of the object side of the second lens L2 is radius R21 is the curvature of the image side of the second lens radius It's too loose compared to R22.

[0042] In this case, in order to achieve both high angular resolution at the angle of view near the axis and ensuring a wide shooting range, it is necessary for the local curvature of the object-side surface of the second lens to have a shape that changes sharply with change in height from the optical axis, and it is also necessary to increase the effective diameter and the central thickness. This results in increased costs due to increased lens volume, as well as worsening of astigmatism, field curvature, and coma aberration, and reduced performance sensitivity to lens decentering.

[0043] To avoid these situations, it is desirable to configure L2 to satisfy equation (6).

[0044] The imaging lens system of the above-mentioned first embodiment may be configured to satisfy the following formula (7), where t2 is the thickness at the central optical axis of the second lens L2, and f is the focal length of the entire lens system. (t2 / f)>0.2 (7)

[0045] According to the imaging lens system of the first embodiment, off-axis aberration can be corrected satisfactorily while ensuring the imaging angle of view.

[0046] If t2 / f falls below the lower limit, i.e., if the center thickness t2 of the second lens L2 is too thin, the local curvature of the object side of the second lens L2 must have a shape that changes sharply with respect to the change in height from the optical axis in order to ensure the shooting angle of view. This results in the occurrence of astigmatism, lateral chromatic aberration in off-axis lower rays, and sagittal coma flare. Furthermore, when configured with a glass molded lens, a sharply changing shape makes it difficult to manufacture.

[0047] Therefore, it is desirable to satisfy the formula (7). By satisfying the formula (7), good imaging performance and manufacturability of the lens element can be ensured.

[0048] The imaging lens system of the above-mentioned 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)

[0049] According to the imaging lens system of the first embodiment, by using a material having an Abbe number of 30.0 or more as the material of the second lens L2, it is possible to suppress the occurrence of chromatic aberration of magnification from the field angle near the on-axis to off-axis.

[0050] The imaging lens system of the above-mentioned first embodiment may be configured to satisfy the following formula (9) when the refractive index for the d-line of the third lens is defined as n3. n3>1.7 (9)

[0051] The third lens L3 with positive power, which is located closest to the object in the rear group in the retrofocus configuration, causes marginal rays of the on-axis angle of view to pass through a comparatively high position.

[0052] According to the imaging lens system of embodiment 1, by using a high refractive index glass material that satisfies equation (9) for the third lens L3, it is possible to effectively suppress the occurrence of spherical aberration even at a large aperture, and to make the lens resistant to manufacturing errors (decentering).

[0053] 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)

[0054] 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.

[0055] If f3 / f falls below the lower limit, that is, if the focal length f3 of the third lens is too short, the amount of spherical aberration generated in the third lens L3 and the negative power of the front group will become too large, making it difficult to correct chromatic aberration and ensuring good imaging performance.

[0056] Furthermore, if f3 / f exceeds the upper limit, that is, if the focal length f3 of the third lens is too long, the positive power cannot be appropriately distributed to the positive lens in the rear group, which causes spherical aberration and makes it difficult to correct chromatic aberration.

[0057] Furthermore, for example, if a low-cost hybrid configuration is used in which the fourth lens L4, fifth lens L5, and 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.

[0058] Therefore, according to the imaging lens system of embodiment 1, by keeping the focal length f3 of the third lens within the upper limit of equation (10), the proportion of positive power shared by the rear group of glass lenses with a small temperature change rate of the refractive index dn / dt can be increased, and the temperature change of the back focus can be suppressed.

[0059] The imaging lens system of the above-mentioned embodiment 1 may be configured to satisfy the following equation (11) when the d-line based Abbe number of the fourth lens L4 is defined as ν4 and the d-line based Abbe number of the fifth lens L5 is defined as ν5. ν4-ν5>15 ···(11)

[0060] According to the imaging lens system of the first embodiment, by providing an Abbe number difference in the conditional formula between the fourth lens L4 having positive power and the fifth lens L5 having negative power, it is possible to achieve good chromatic aberration correction.

[0061] The imaging lens system of the above-mentioned embodiment 1 may be configured to satisfy the following equation (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)

[0062] According to the imaging lens system of the first embodiment, if it is configured so as to satisfy the formula (12), the overall length becomes small relative to the focal length.

[0063] The imaging lens system of the above-mentioned embodiment 1 may be configured to satisfy the following equation (13), where IH is the effective diameter of the image circle that represents 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)

[0064] According to the imaging lens system of the first embodiment, it is possible to suppress a decrease in resolution at the periphery of an image while ensuring a wide imaging angle of view, and to recognize a subject that appears at the periphery of an image during sensing or the like.

[0065] 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. 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.

[0066] Next, an example corresponding to the imaging lens system of the first embodiment will be described with reference to the drawings.

[0067] 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 imaging plane of the imaging lens system 11 is indicated by IMG.

[0068] The first lens L1 is a spherical lens having 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.

[0069] The second lens L2 is an aspheric lens having negative power. The object-side lens surface S3 of the second lens L2 faces the convex surface toward the object side. The image-side lens surface S4 of the second lens L2 has a concave curved portion toward the image side.

[0070] The third lens L3 is a spherical lens having a positive power. The object-side lens surface S5 of the third lens L3 faces the convex surface toward the object side. The image-side lens surface S6 of the third lens L3 faces the convex surface toward the image side.

[0071] The aperture STOP is an aperture that determines the F-number (Fno) of the lens system. The aperture STOP is disposed between the third lens L3 and the fourth lens L4.

[0072] The fourth lens L4 is an aspheric plastic lens having a positive power. The object-side lens surface S9 of the fourth lens L4 faces the convex surface toward the object side. The image-side lens surface S10 of the fourth lens L4 faces the convex surface toward the image surface side.

[0073] The fifth lens L5 is an aspheric lens having a negative power. The object-side lens surface S11 of the fifth lens L5 has a concave curved portion. The image-side lens surface S12 of the fifth lens L5 faces the convex surface toward the image surface side.

[0074] 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 that the fourth lens L4 and the fifth lens L5 are cemented together with an adhesive layer having an axial thickness of 0.02 mm.

[0075] The sixth lens L6 is an aspheric lens having a negative power. An object-side lens surface S13 of the sixth lens L6 has a concave curved portion. Also, an image-side lens surface S14 of the sixth lens L6 has a concave curved portion.

[0076] 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.

[0077] 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" corresponds to "-6.522528×10 -3 The same applies to the numerical expressions in the following tables.

[0078] [Table 1]

[0079] The aspheric shape used on 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 4th, 6th, 8th, 10th, 12th, 14th, and 16th orders are A4, A6, A8, A10, A12, A14, and A16, respectively. TIFF0007629272000004.tif12150

[0080] Table 2 shows aspheric coefficients for defining the aspheric shape of the lens surface that is made aspheric in the imaging lens system 11 of the first embodiment.

[0081] [Table 2]

[0082] Fig. 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 Fig. 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.

[0083] Next, aberration will be explained using the drawings. Fig. 3 is a longitudinal aberration diagram in the imaging lens system of Example 1. In Fig. 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. Fig. 3 also shows the results of a simulation using a light ray with a wavelength of 546 nm.

[0084] 4 is a diagram showing the curvature of field in the imaging lens system of the first embodiment. In FIG. 4, the horizontal axis indicates the distance in the optical axis Z direction, and the vertical axis indicates image height In FIG. 4, Sag indicates astigmatism in the sagittal plane, and Tan indicates astigmatism in the tangential plane. FIG. 4 also shows the results of a simulation using light with a wavelength of 546 nm. 。

[0085] 5 is a diagram showing distortion aberration in the imaging lens system of Example 1. In FIG. 6, the horizontal axis shows the amount of image distortion (%), and the vertical axis shows image height Shows.

[0086] As shown in Fig. 3, the imaging lens system 11 of Example 1 has an F-number of 2.0. Also, the half angle of view is 42 degrees. Also, as shown in Figs. 4 and 5, it can be seen that aberrations are well corrected.

[0087] Next, the characteristic values ​​of the lenses 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, 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, 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 focal length of the first lens L1 divided by the focal length of the entire lens system is |f1 / f|, the curvature of the object side of the first lens is |f1 / f|, the absolute value of the refractive index of the third lens is |f2 / f|, the absolute value of the refractive index of the first lens L1 divided by the focal length of the entire lens system is |f1 / f|, the curvature of the object side of the first lens is |f2 / f|, the absolute value of the refractive index of the third lens is |f3 / f|, the absolute value of the refractive index of the third lens is |f4 / f|, the absolute value of the refractive index of the third lens is |f5 / f|, the absolute value of the refractive index of the first lens L1 divided by the focal length of the entire lens system is |f6 / f|, the absolute value of the refractive index of the third lens is |f1 / f|, the absolute value of the refractive index of the third lens is |f2 ... radius and the curvature of the image side of the first lens radius The absolute value of the sum of these is the curvature of the object side of the first lens. radius to the curvature of the image side of the first lens radius The absolute value of the distance between the first lens L1 and the second lens L2 divided by the focal length of the entire lens system is |t12| / f, and the curvature of the object side of the second lens is |t12| / f. radius is the curvature of the image side of the second lens. radius The absolute value of the value obtained by dividing by is |R21 / R22|, the value obtained by dividing the thickness at the central optical axis of the second lens L2 by the focal length of the entire lens system is t2 / f, the Abbe number of the second lens L2 is ν2, the refractive index of the third lens is n3, the value obtained by dividing the focal length of the third lens L3 by the focal length of the entire lens system is f3 / f, the value obtained by subtracting the Abbe number of the fourth lens L4 by the Abbe number of the fifth lens L5 is ν4-ν5, the value obtained by dividing 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 by the focal length of the entire lens system is TTL / f, and the value obtained by dividing the effective diameter IH of the image circle, which indicates the range that can be imaged on the image plane (maximum range that can be photographed), by the focal length f of the entire lens system multiplied by the tangent of the angle of view FoV is (IH / (f*tan(FoV))). 2 The characteristic values ​​are shown when the focal length and center thickness are set as above. In Table 3, the units of focal length and center thickness are all mm. The focal lengths in Table 3 were calculated using light with a wavelength of 546 nm.

[0088] [Table 3]

[0089] 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 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 the first embodiment.

[0090] Table 4 shows the lens data of 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.

[0091] [Table 4]

[0092] Table 5 shows 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.

[0093] [Table 5]

[0094] Fig. 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 Fig. 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.

[0095] Next, aberration will be explained using the drawings. Fig. 8 is a longitudinal aberration diagram in the imaging lens system of Example 2. In Fig. 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. Fig. 8 also shows the results of a simulation using a light ray with a wavelength of 546 nm.

[0096] 9 is a diagram showing the curvature of field in the imaging lens system of the second embodiment. In FIG. 9, the horizontal axis indicates the distance in the optical axis Z direction, and the vertical axis indicates image height In FIG. 9, Sag indicates astigmatism in the sagittal plane, and Tan indicates astigmatism in the tangential plane. FIG. 9 also shows the results of a simulation using light with a wavelength of 546 nm. 。

[0097] 10 is a diagram showing distortion aberration in the imaging lens system of Example 2. In FIG. 10, the horizontal axis shows the amount of image distortion (%), and the vertical axis shows image height Shows.

[0098] As shown in Fig. 8, the imaging lens system 11 of Example 1 has an F-number of 2.0. Also, the half angle of view is 55 degrees. Also, as shown in Figs. 8 to 10, it can be seen that aberrations are well corrected.

[0099] 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.

[0100] [Table 6]

[0101] 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.

[0102] Table 7 shows the lens data of 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.

[0103] [Table 7]

[0104] Table 8 shows 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.

[0105] [Table 8]

[0106] Fig. 12 is a graph showing the relationship between the local curvature of the object-side surface of the second lens and the height of the lens surface from the optical axis in the imaging lens system of Example 3. In Fig. 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.

[0107] Next, aberration will be explained using the drawings. Fig. 13 is a longitudinal aberration diagram in the imaging lens system of Example 3. In Fig. 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. Fig. 13 also shows the results of a simulation using a light ray with a wavelength of 546 nm.

[0108] 14 is a diagram showing the curvature of field in the imaging lens system of the third embodiment. In FIG. 14, the horizontal axis indicates the distance in the optical axis Z direction, and the vertical axis indicates image height In FIG. 14, Sag indicates astigmatism in the sagittal plane, and Tan indicates astigmatism in the tangential plane. FIG. 14 also shows the results of a simulation using light with a wavelength of 546 nm. 。

[0109] 15 is a diagram showing distortion aberration in the imaging lens system of Example 3. In FIG. 15, the horizontal axis shows the amount of image distortion (%), and the vertical axis shows image height Shows.

[0110] As shown in Fig. 13, the imaging lens system 11 of Example 1 has an F-number of 2.0. Also, the half angle of view is 46 degrees. Also, as shown in Figs. 13 to 15, it can be seen that aberrations are well corrected.

[0111] 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.

[0112] [Table 9]

[0113] 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.

[0114] Table 10 shows the lens data of 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.

[0115] [Table 10]

[0116] Table 11 shows 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.

[0117] [Table 11]

[0118] Fig. 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 Fig. 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.

[0119] Next, aberration will be explained using the drawings. Fig. 18 is a longitudinal aberration diagram in the imaging lens system of Example 4. In Fig. 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. Fig. 18 also shows the results of a simulation using a light ray with a wavelength of 546 nm.

[0120] 19 is a diagram showing the curvature of field 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 image height In FIG. 19, Sag indicates astigmatism in the sagittal plane, and Tan indicates astigmatism in the tangential plane. FIG. 19 also shows the results of a simulation using light with a wavelength of 546 nm. 。

[0121] 20 is a diagram showing distortion aberration in the imaging lens system of Example 4. In FIG. 20, the horizontal axis shows the amount of image distortion (%), and the vertical axis shows image height Shows.

[0122] As shown in Fig. 18, the imaging lens system 11 of Example 1 has an F-number of 2.0. Also, the half angle of view is 48 degrees. Also, as shown in Figs. 18 to 20, it can be seen that aberrations are well corrected.

[0123] 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.

[0124] [Table 12]

[0125] 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.

[0126] Table 13 shows the lens data of 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.

[0127] [Table 13]

[0128] Table 14 shows 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.

[0129] [Table 14]

[0130] Fig. 22 is a graph showing the relationship between the local curvature of the object-side surface of the second lens and the height of the lens surface from the optical axis in the imaging lens system of Example 5. In Fig. 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.

[0131] Next, aberration will be explained using the drawings. Fig. 23 is a longitudinal aberration diagram in the imaging lens system of Example 5. In Fig. 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. Fig. 23 also shows the results of a simulation using a light ray with a wavelength of 546 nm.

[0132] 24 is a diagram showing the curvature of field in the imaging lens system of the fifth embodiment. In FIG. 24, the horizontal axis indicates the distance in the optical axis Z direction, and the vertical axis indicates image height In FIG. 24, Sag indicates astigmatism in the sagittal plane, and Tan indicates astigmatism in the tangential plane. FIG. 24 also shows the results of a simulation using light with a wavelength of 546 nm. 。

[0133] 25 is a diagram showing distortion aberration in the imaging lens system of Example 5. In FIG. 25, the horizontal axis shows the amount of image distortion (%), and the vertical axis shows image height Shows.

[0134] As shown in Fig. 23, the imaging lens system 11 of Example 1 has an F-number of 2.0. Also, the half angle of view is 42 degrees. Also, as shown in Figs. 23 to 25, it is clear that aberrations are well corrected.

[0135] 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.

[0136] [Table 15]

[0137] 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.

[0138] Table 16 shows the lens data of 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.

[0139] [Table 16]

[0140] Table 17 shows 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.

[0141] [Table 17]

[0142] Fig. 27 is a graph showing the relationship between the local curvature of the object-side surface of the second lens and the height of the lens surface from the optical axis in the imaging lens system of Example 6. In Fig. 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.

[0143] Next, aberration will be explained using the drawings. Fig. 28 is a longitudinal aberration diagram in the imaging lens system of Example 6. In Fig. 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. Fig. 28 also shows the results of a simulation using a light ray with a wavelength of 546 nm.

[0144] Fig. 29 is a diagram showing the curvature of field 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 image height In FIG. 29, Sag indicates astigmatism in the sagittal plane, and Tan indicates astigmatism in the tangential plane. FIG. 29 also shows the results of a simulation using light with a wavelength of 546 nm. 。

[0145] 30 is a diagram showing distortion aberration in the imaging lens system of Example 6. In FIG. 30, the horizontal axis shows the amount of image distortion (%), and the vertical axis shows image height Shows.

[0146] As shown in Fig. 28, the imaging lens system 11 of Example 1 has an F-number of 2.0. Also, the half angle of view is 46 degrees. Also, as shown in Figs. 28 to 30, it can be seen that aberrations are well corrected.

[0147] Next, the characteristic values ​​of the lenses 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.

[0148] [Table 18]

[0149] (Embodiment 2: Application example to imaging device) 47, imaging device 21 includes imaging lens system 11 and imaging element 22. Imaging lens system 11 and imaging element 22 are housed in a housing (not shown). Imaging lens system 11 is the imaging lens system 11 described in the above-mentioned first embodiment.

[0150] The imaging element 22 is an element that converts received light into an electrical signal, and is, for example, a CCD image sensor or a CMOS image sensor. The imaging element 22 is disposed at an imaging position of the imaging lens system 11.

[0151] Thus, the imaging device of embodiment 2 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.

[0152] The present invention is not limited to the above-mentioned embodiments, and can be modified as appropriate without departing from the spirit of the present invention. For example, the embodiment 2 may be applied to the embodiments 1 to 6. For example, the use of the imaging lens system of the present invention is not limited to vehicle-mounted cameras and surveillance cameras, and can be used for other purposes such as being mounted on small electronic devices such as mobile phones. [Explanation of symbols]

[0153] 11 Imaging lens system 12 IR cut filter 21 Imaging device 22 Image sensor L1 First lens L2 Second lens L3 Third lens L4 4th lens L5 5th lens L6 6th lens STOP Squeeze IMG Image plane

Claims

1. 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 equation (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 equations (8), (9), and (10). [0010] 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. An imaging lens system as described in claim 1, which satisfies the following formula (2) when the absolute value of the temperature change rate of the refractive index of the third lens is defined as dn3 / dt. |dn3 / dt|≦10[10 －６ / K] ・・・(2)

3. An imaging lens system as described in claim 1 or 2, which satisfies the following formula (3) when the focal length of the first lens is defined as f1 and the focal length of the entire lens system is defined as f. 1<|f1 / f|<10...(3)

4. An imaging lens system described in any of claims 1 to 3, which satisfies the following formula (4) when the radius of curvature on the object side of the first lens is defined as R11 and the radius of curvature on the image side of the first lens is defined as R12. |R11+R12| / |(R11-R12)|<5...(4)

5. An imaging lens system described in any of claims 1 to 4, which satisfies the following equation (5) when the inter-surface distance between the first lens and the second lens is defined as t12 and the focal length of the entire lens system is defined as f. (t12 / f)<0.3...(5)

6. An imaging lens system described in any of claims 1 to 5, which satisfies the following formula (6) when the radius of curvature on the object side of the second lens is defined as R21 and the radius of curvature on the image side of the second lens is defined as R22. 1.2<|R21 / R22|<3.2...(6)

7. An imaging lens system described in any one of claims 1 to 6, which satisfies the following formula (7) when the thickness of the second lens L2 at the central optical axis is defined as t2 and the focal length of the entire lens system is defined as f. (t2 / f)>0.2...(7)

8. An imaging lens system as described in any one of claims 1 to 7, which satisfies the following formula (11) when the Abbe number of the fourth lens is defined as ν4 and the Abbe number of the fifth lens is defined as ν5. ν4−ν5>15 (11)

9. 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)

10. 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.

Images