Optical system and imaging device

Abstract

To provide an optical system capable of ensuring high optical performance over a wide temperature range from low temperature to high temperature, and an image capturing device.SOLUTION: An optical system provided herein consists of a front group, an aperture stop, and a rear group in order from the object side. The front group has at least one lens with negative refractive power. The front group or the rear group has at least one lens with positive refractive power. The lens satisfies given conditional expressions, where a lens Lp in the expressions represents a lens located on the most object side among the lenses having positive refractive power. Also provided is an image capturing device equipped with such optical system and an image sensor.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to an optical system and an imaging device, and more particularly to an optical system and an imaging device suitable for a compact imaging device using a solid-state image sensor or the like. [Background technology]

[0002] Traditionally, imaging devices using solid-state image sensors, such as digital still cameras and digital video cameras, have been widely used. Furthermore, the use of optical systems and imaging devices for specific purposes, such as in-vehicle imaging devices, surveillance imaging devices, and security imaging devices, is also progressing. As the pixel count of solid-state image sensors used in these imaging devices increases, optical systems are increasingly required to maintain a compact and lightweight design while achieving high resolution performance.

[0003] Furthermore, imaging devices such as in-vehicle imaging devices, surveillance imaging devices, and security imaging devices are installed in designated locations and used continuously for long periods, so they are required to be able to capture images even in low-light conditions such as at night. For this reason, bright optical systems, i.e., large-aperture lenses, are required for in-vehicle imaging devices and the like.

[0004] Furthermore, imaging devices such as in-vehicle imaging devices, surveillance imaging devices, and security imaging devices are installed in designated locations and used continuously for long periods, and are therefore greatly affected by the outside air. The interior of a vehicle parked outdoors can experience temperatures ranging from below freezing to over 100 degrees Celsius, so an optical system that exhibits minimal performance degradation over a wide temperature range from low to high temperatures is required. In general, in-vehicle imaging devices often use fixed-focus imaging lenses without actuators for focusing, from the perspective of cost reduction. Therefore, imaging lenses for in-vehicle imaging devices are required to exhibit minimal focus fluctuations even when the ambient temperature changes, and to maintain good imaging performance over long periods not only at room temperature but also in high-temperature and low-temperature environments.

[0005] As an in-vehicle imaging device that exhibits minimal focus shift over a wide temperature range, an optical system has been proposed that comprises, for example, a first lens with negative refractive power, a second lens with positive refractive power, a third lens with negative refractive power, a fourth lens with positive refractive power, and a fifth lens with positive refractive power (see "Patent Document 1"). [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2017-116797 [Overview of the project] [Problems that the invention aims to solve]

[0007] Incidentally, there is a high market demand for optical systems and imaging devices that can ensure high optical performance over a wide temperature range. Although the imaging device disclosed in Patent Document 1 achieves small focus fluctuations over a wide temperature range, the refractive power and glass arrangement disclosed in Patent Document 1 reduce the focus fluctuations in the optical system when temperature changes occur. However, in imaging devices with a long lens barrel, the position change of the image sensor due to temperature changes in the lens barrel becomes large. This results in a discrepancy between the focus fluctuations in the optical system and the position change of the image sensor due to temperature changes in the lens barrel, which is undesirable as it degrades the optical performance.

[0008] The object of this invention is to provide an optical system and imaging device that can ensure good optical performance over a wide temperature range from low to high temperatures. [Means for solving the problem]

[0009] To solve the above problems, the optical system according to the present invention is composed of a front group, an aperture, and a rear group in order from the object side, the front group has at least one lens having negative refractive power, the front group or the rear group has at least one lens having positive refractive power, and the lens Lp is the lens with positive refractive power that is located closest to the object. It is characterized by satisfying the following conditional expressions. 15.00 < νdLp < 31.00 ···(1) -9.0 < dNdtLp × 10 , , , , ,

[0011] , , , , , , , ,

[0012] ,

[0010] , [Figure 6] , [Figure 5] , [Figure 4] , , [Figure 3] , , [Figure 2] , , [Figure 1] , , [Figure 7] < -2.7 ···(2) However, νdLp: Abbe number of the lens Lp with respect to the d-line dNdtLp: Relative refractive index temperature coefficient in air in the temperature range from 0°C to 20°C with respect to the d-line of the lens Lp

[0010] In addition, in order to solve the above problems, the imaging device according to the present invention includes the optical system described above and an imaging element that receives the optical image formed by the optical system and converts it into an electrical image signal.

Effect of the Invention

[0011] According to the present invention, it is possible to provide an optical system and an imaging device capable of ensuring good optical performance in a wide temperature range from low temperature to high temperature.

Brief Description of the Drawings

[0012] [Figure 1] It is a cross-sectional view showing an example of the lens configuration of the optical system of Example 1 of the present invention. [Figure 2] It is a spherical aberration diagram, a coma aberration diagram, and a distortion aberration diagram at the time of taking an image of an infinite object in Example 1 of the present invention. [Figure 3] It is a cross-sectional view showing an example of the lens configuration of the optical system of Example 2 of the present invention. [Figure 4] It is a spherical aberration diagram, a coma aberration diagram, and a distortion aberration diagram at the time of taking an image of an infinite object in Example 2 of the present invention. [[ID=4​​​​​​​​​ [Figure 8] These are spherical aberration diagrams, astigmatism diagrams, and distortion diagrams during infinity object photography in Example 4 of the present invention.

Embodiments for Carrying Out the Invention

[0013] Hereinafter, embodiments of the optical system and imaging device according to the present invention will be described.

[0014] 1. Optical System 1-1. Optical Configuration of the Optical System First, an embodiment of the optical system according to the present invention will be described. The optical system of this embodiment is composed of a front group, an aperture, and a rear group having a positive refractive power, which are arranged in order from the object side.

[0015] The front group has at least one lens having a negative refractive power. Since this optical system is an imaging lens, it has a condensing action. However, in order to correct the image plane property, it is necessary to reduce the Petzval sum. For this purpose, a lens having a negative refractive power is required. Also, a lens having a negative refractive power is required to correct chromatic aberration. By configuring the optical system to include at least one lens having a negative refractive power, as a result, it becomes easy to realize good imaging performance. In addition, by arranging a lens having a negative refractive power in the front group, a diffusion action occurs on the object side of the aperture, so it becomes easy to achieve both wide-angleization and miniaturization of the outer diameter.

[0016] Hereinafter, the optical configuration of the optical system will be described in more detail.

[0017] (1) Front Group The front group is composed of lenses arranged on the object side of the aperture. The refractive power of the entire front group may be positive or negative. By arranging the front group on the object side of the aperture, in the meridional section, the chief ray passes below the optical axis in the front group and above the optical axis in the rear group. As a result, aberration cancellation is likely to occur before and after the aperture, and it becomes easy to correct coma aberration and field curvature. As a result, it becomes easy to realize good imaging performance.

[0018] The specific configuration of the front group is not particularly limited. For example, by dividing the largest air gap within the front group into a subgroup with negative refractive power on the object side and a subgroup with positive refractive power on the image side, a diffusion effect occurs on the object side of the front group, causing the entrance pupil to be on the object side. As a result, it becomes easier to achieve both a wider angle and a smaller outer diameter.

[0019] By placing the lens with the most negative refractive power on the object side of the front group, the object side of the optical system will also have negative refractive power. In this case, diffusion occurs on the object side, and the entrance pupil position will be on the object side. As a result, it becomes easier to achieve both a wide-angle view and a smaller outer diameter.

[0020] By placing the lens with the most positive refractive power on the image side of the front group, the aperture will have a positive refractive power on the object side. In this case, the height of the light rays incident on the aperture will be reduced. As a result, while increasing the aperture size, the amount of aberration caused by manufacturing errors will be reduced, and spherical aberration will be easier to correct. Consequently, it will be easier to achieve both a large aperture and good imaging performance in the optical system.

[0021] By including at least one aspherical surface in the front group of lenses, it becomes easier to achieve good imaging performance with a small number of lenses. Furthermore, by having an aspherical surface on the lens surface with a convex side facing the object, and by using an aspherical shape that weakens the refractive power in the paraxial direction, spherical aberration, field curvature, and coma aberration can be easily corrected. As a result, it becomes easier to achieve good imaging performance in the optical system.

[0022] (2) Rear group The rear group consists of lenses positioned on the image side of the aperture. It is preferable that the entire rear group has positive refractive power. By providing a light-gathering effect on the image side of the aperture, it becomes easier to increase the aperture size. If the entire rear group has negative refractive power, it becomes easier to shorten the overall length, which is preferable in terms of miniaturization.

[0023] The specific configuration of the rear group is not particularly limited. For example, if a lens with positive refractive power is placed on the object side of the rear group, that is, a lens with positive refractive power is placed on the image side of the aperture, this has the effect of lowering the height of the light rays within the rear group. This makes it easier to reduce the amount of aberration caused by manufacturing errors within the rear group. As a result, it becomes easier to achieve good imaging performance in the optical system.

[0024] By placing a lens with positive refractive power on the image-side of the rear group, this lens can brighten the optical system. In this case, compared to placing a lens with negative refractive power on the image-side, the combined Fno of the lenses excluding the image-side lens can be increased, making aberration correction easier with fewer lenses. As a result, it becomes easier to achieve a larger aperture while constructing the optical system with fewer lenses, thus reducing costs.

[0025] By placing at least one surface with negative refractive power in the rear group, image field curvature can be easily corrected. As a result, it becomes easier to achieve good imaging performance in the optical system.

[0026] (3) Aperture The aperture (diaphragm) of this optical system is positioned between the front and rear lens groups. By positioning the aperture between the front and rear groups, the principal rays in the meridional cross-section pass below the optical axis in the front group and above the optical axis in the rear group. This facilitates the cancellation of aberrations before and after the aperture, making it easier to correct coma aberration and field curvature. As a result, it becomes easier to achieve good imaging performance. The apex of the image-side surface of the lens positioned closest to the image in the front group may be located on the image side of the aperture plane. Similarly, the apex of the object-side surface of the lens positioned closest to the object in the rear group may be located on the object side of the aperture plane.

[0027] (4) Lens glass It is preferable that all lenses constituting the optical system are glass lenses. Compared to plastic lenses, glass lenses have higher thermal stability and less expansion and contraction with changes in ambient temperature. Therefore, by using glass lenses for all lenses constituting the optical system, changes in focus (focal position) and angle of view can be effectively suppressed even when the ambient temperature changes.

[0028] (5) Number of lens elements While the configuration of the front and rear lens groups is not limited, increasing the number of lens elements increases costs, which is undesirable from a cost-reduction standpoint. Therefore, it is preferable that the total number of lenses in the optical system be seven or less. Here, "substantially composed" means that it is permissible to include lenses that have virtually no refractive power or optical elements other than lenses, such as cover glass. By limiting the number of lenses in the front group to three or less and the number of lenses in the rear group to four or less, it becomes easier to achieve both cost reduction and good imaging performance.

[0029] 1-2. Conditional expression In this optical system, it is preferable to adopt the configuration described above and satisfy the following conditional equation.

[0030] 1-2-1. Conditional expression (1) The optical system preferably satisfies the following condition. 15.00 < νdLp < 31.00 (1) however, νdLp: Abbe number of lens Lp for the d line

[0031] The above conditional equation (1) specifies the Abbe number for the d line (587.56 nm) of the lens Lp located closest to the object among the positive refractive power lenses included in the optical system. In wide-angle lenses, miniaturization is achieved by placing the negative refractive power lens on the object side, which causes the entrance pupil to be on the object side. Furthermore, using glass with a high refractive index for the negative refractive power lens on the object side becomes more effective for miniaturization and correction of image plane quality. Here, if the lens Lp with the positive refractive power closest to the object satisfies conditional equation (1), chromatic aberration with the negative refractive power lens can be easily canceled out, thus achieving an optical system with good chromatic aberration correction.

[0032] Conversely, if the value in the above conditional equation (1) exceeds the upper limit, the lateral chromatic aberration will be undercorrected, which is undesirable in terms of performance. If the value in the above conditional equation (1) falls below the lower limit, the axial chromatic aberration will be overcorrected, which is undesirable in terms of performance.

[0033] To obtain the above effects, the upper limit of the above conditional formula (1) is preferably 30.10, more preferably 29.20, even more preferably 28.50, even more preferably 27.90, and even more preferably 26.60. Also, the lower limit of the above conditional formula (1) is preferably 16.40, more preferably 17.30, even more preferably 17.80, even more preferably 18.60, and even more preferably 19.20.

[0034] 1-2-2. Conditional expression (2) The optical system preferably satisfies the following condition. -9.0 < dNdtLp × 10 6 < -2.7 ···(2) however, dNdtLp: Relative refractive index temperature coefficient in air for the d line of lens Lp in the temperature range of 0°C to 20°C.

[0035] The above conditional equation (2) specifies the relative refractive index temperature coefficient in air for the d line (587.56 nm) in the temperature range from 0°C to 20°C for lens Lp, which is the lens with positive refractive power that is positioned closest to the object among the lenses included in the optical system. The refractive index of the lens glass changes with temperature. Here, the relative refractive index temperature coefficient is the change in refractive index per unit temperature at the d line (587.56 nm) in air (101.325 kPa). As the temperature rises, the lens barrel components expand, so the image plane moves away from the optical system compared to when it is at room temperature. Therefore, the back focus of the optical system needs to be increased when the temperature rises. Also, as the refractive index of a lens with positive refractive power decreases, the light-gathering effect weakens, so the back focus of the optical system increases. Therefore, by using a glass material for a lens with positive refractive power that has a lower refractive index at high temperatures, i.e., a glass material with a negative relative refractive index temperature coefficient, the direction of the image plane change caused by the lens barrel and the direction of the back focus change caused by the optical system coincide, making it easier to correct for focus errors. Here, if the lens Lp, which is the lens with positive refractive power that is closest to the object, satisfies condition (2), the image plane change caused by the lens barrel and the back focus change caused by the optical system easily cancel each other out, thus achieving a high-performance optical system with minimal focus errors.

[0036] Conversely, if the value in the above conditional equation (2) exceeds the upper limit, the change in the back focus of the optical system in response to the image plane change caused by the lens barrel will be under-corrected, resulting in a large focus shift, which is undesirable in terms of performance. If the value in the above conditional equation (2) falls below the lower limit, the change in the back focus of the optical system in response to the image plane change caused by the lens barrel will be over-corrected, resulting in a large focus shift, which is undesirable in terms of performance.

[0037] To obtain the above effect, the upper limit of the above conditional equation (2) is preferably -2.8. Furthermore, the lower limit of the above conditional equation (2) is preferably -7.0, and more preferably -5.0.

[0038] 1-2-3. Conditional expression (3) The optical system preferably has at least one lens with positive refractive power adjacent to the aperture and satisfies the following condition. -12.0 < dNdtpla×10 6 < -0.8 ···(3) however, dNdtpla: Relative refractive index temperature coefficient of a lens with positive refractive power adjacent to the aperture, where the relative refractive index temperature coefficient in air is large in the temperature range of 0°C to 20°C with respect to the d line.

[0039] The above conditional equation (3) defines the relative refractive index temperature coefficient of a lens with a positive refractive power adjacent to the aperture of the optical system, which has a large relative refractive index temperature coefficient in air for the d line (587.56 nm) in the temperature range of 0°C to 20°C. In this optical system, the aperture is located between the front and rear lens groups. In such a configuration, the change in back focus due to the change in refractive index of the lens near the aperture is larger compared to lenses located in other positions. That is, the lens located in this position is more sensitive to changes in focus due to temperature changes compared to lenses located in other positions. Therefore, by using a glass material with a negative relative refractive index temperature coefficient for the positive refractive power lens adjacent to the aperture, it is possible to increase the back focus of the optical system at high temperatures. This allows for correction of the image plane position even when the overall length of the lens barrel is long. When lenses with positive refractive power are adjacent to the object side and image side of the aperture, the lens with the larger relative refractive index temperature coefficient among the two lenses will have a smaller effect on changing the back focus of the optical system. If the lens with the larger relative refractive index temperature coefficient among the two lenses satisfies condition (3), the image plane change caused by the lens barrel and the change in back focus caused by the optical system easily cancel each other out, thus achieving a high-performance optical system with minimal focus shift. If a lens with positive refractive power is adjacent to either the object side or the image side of the aperture, if the relative refractive index temperature coefficient of that lens satisfies condition (3), the image plane change caused by the lens barrel and the change in back focus caused by the optical system easily cancel each other out, thus achieving a high-performance optical system with minimal focus shift.

[0040] Conversely, if the value in the above conditional equation (3) exceeds the upper limit, the change in the back focus of the optical system in response to the image plane change caused by the lens barrel will be under-corrected, resulting in a large focus shift, which is undesirable in terms of performance. If the value in the above conditional equation (3) falls below the lower limit, the change in the back focus of the optical system in response to the image plane change caused by the lens barrel will be over-corrected, resulting in a large focus shift, which is undesirable in terms of performance.

[0041] To obtain the above effect, the upper limit of the above conditional equation (3) is preferably -1.2, more preferably -1.6, and even more preferably -2.0. Furthermore, the lower limit of the above conditional equation (3) is preferably -9.0, and more preferably -7.0.

[0042] 1-2-4. Conditional expression (4) The optical system preferably satisfies the following condition. -12.0 < dNdtpmax × 10 6 < -0.2 ···(4) however, dNdtpmax: The relative refractive index temperature coefficient of the lens with the largest relative refractive index temperature coefficient in air in the temperature range of 0°C to 20°C with respect to the d line, among the lenses with positive refractive power included in the front and rear groups.

[0043] The above conditional equation (4) defines the relative refractive index temperature coefficient of the lens with the largest relative refractive index temperature coefficient in air for the d line (587.56 nm) in the temperature range of 0°C to 20°C, among the positive refractive index lenses included in the optical system. As the temperature rises, the lens barrel components expand, causing the image plane to move away from the optical system compared to when it is at room temperature. Therefore, the back focus of the optical system needs to be increased when the temperature rises. Also, as the refractive index of the positive refractive index lenses decreases, the light-gathering effect weakens, so the back focus of the optical system increases. Therefore, by using glass materials that have a smaller refractive index at high temperatures, that is, glass materials with a negative relative refractive index temperature coefficient for all positive refractive index lenses, the direction of the image plane change due to the lens barrel and the change in back focus due to the optical system due to temperature changes coincide, making it easier to correct for focus shifts. By giving the lens with the smallest change in refractive index at high temperatures the effect of increasing the back focus, even in optical systems with long barrel lengths, the direction of the image plane change due to the lens barrel and the direction of the back focus change due to the optical system coincide, making it easy to correct for focus errors. Here, among the positive refractive index lenses included in the optical system, if the lens with the largest relative refractive index temperature coefficient in air for the d line (587.56 nm) in the temperature range from 0°C to 20°C satisfies condition (4), the image plane change due to the lens barrel and the back focus change due to the optical system due to temperature changes easily cancel each other out, thus achieving a high-performance optical system with minimal focus errors.

[0044] Conversely, if the value in the above conditional equation (4) exceeds the upper limit, the change in the back focus of the optical system in response to the image plane change caused by the lens barrel will be under-corrected, resulting in a large focus shift, which is undesirable in terms of performance. If the value in the above conditional equation (4) falls below the lower limit, the change in the back focus of the optical system in response to the image plane change caused by the lens barrel will be over-corrected, resulting in a large focus shift, which is undesirable in terms of performance.

[0045] To obtain the above effect, the upper limit of the above conditional expression (4) is preferably -0.5, more preferably -0.8, even more preferably -1.6, and even more preferably -2.0. Furthermore, the lower limit of the above conditional expression (4) is preferably -9.0, and more preferably -7.0.

[0046] 1-2-5. Conditional expression (5) The optical system preferably satisfies the following condition. 0.2 < dNdtnmin × 10 6 < 15.0 ···(5) however, dNdtnmin: Relative refractive index temperature coefficient of the lens with negative refractive power included in the front and rear groups that has the smallest relative refractive index temperature coefficient in air in the temperature range of 0°C to 20°C with respect to the d line.

[0047] The above conditional equation (5) defines the relative refractive index temperature coefficient of the lens with the smallest relative refractive index temperature coefficient in air for the d line (587.56 nm) in the temperature range of 0°C to 20°C, among the negative refractive index lenses included in the optical system. As the temperature rises, the lens barrel components expand, causing the image plane to move away from the optical system compared to when it is at room temperature. Therefore, the back focus of the optical system needs to be increased when the temperature rises. Also, as the refractive index of a negative refractive index lens increases, the light-gathering effect weakens, so the back focus of the optical system increases. Therefore, by using glass materials that have a high refractive index at high temperatures, i.e., glass materials with a positive relative refractive index temperature coefficient, all negative refractive index lenses can be made to match the direction of the image plane change due to the lens barrel and the change in back focus due to the optical system, making it easier to correct for focus shifts. By giving the back focus a large effect to the negative refractive power lens that exhibits the smallest change in refractive index at high temperatures, even in optical systems with long barrel lengths, the direction of the image plane change due to the lens barrel and the direction of the back focus change due to the optical system coincide, making it easier to correct for focus errors. Here, among the negative refractive power lenses included in the optical system, if the lens with the smallest relative refractive index temperature coefficient in air for the d line (587.56 nm) in the temperature range from 0°C to 20°C satisfies condition (5), the image plane change due to the lens barrel and the back focus change due to the optical system easily cancel each other out, thus achieving a high-performance optical system with minimal focus errors.

[0048] Conversely, if the value in the above conditional equation (5) exceeds the upper limit, the change in the back focus of the optical system in response to the image plane change caused by the lens barrel becomes over-compensated, resulting in a large focus shift, which is undesirable in terms of performance. If the value in the above conditional equation (5) falls below the lower limit, the change in the back focus of the optical system in response to the image plane change caused by the lens barrel becomes under-compensated, resulting in a large focus shift, which is undesirable in terms of performance.

[0049] To obtain the above effect, the upper limit of the above conditional expression (5) is preferably 12.0, more preferably 9.5, even more preferably 8.9, and even more preferably 8.0. Furthermore, the lower limit of the above conditional expression (5) is preferably 0.5.

[0050] 1-2-6. Conditional expression (6) In this optical system, the lens located closest to the object preferably has a negative refractive power and satisfies the following condition. -20.00 < fL1 / f < -0.30 (6) however, fL1: The focal length of the lens closest to the object. f: focal length of the optical system

[0051] The above conditional equation (6) defines the ratio between the focal length of the lens positioned closest to the object in the optical system and the focal length of the optical system itself. When a lens with negative refractive power is positioned closest to the object in the optical system, a diffusion effect occurs on the object side, causing the entrance pupil to be positioned on the object side. As a result, it becomes easier to achieve both a wide-angle view and a smaller outer diameter. When this lens positioned closest to the object satisfies conditional equation (6), the lens falls within an appropriate range, achieving both a smaller diameter and lower costs. Furthermore, good imaging performance is achieved, resulting in a high-performance optical system.

[0052] Conversely, if the value in the above conditional equation (6) exceeds the upper limit, the refractive power of the lens located closest to the object becomes strong, which is desirable for miniaturizing the lens, but it makes it difficult to correct field curvature and coma aberration, which is undesirable in terms of improving the performance of the optical system. On the other hand, if the value in the above conditional equation (6) falls below the lower limit, the refractive power of the lens located closest to the object becomes weak, which is undesirable because it makes it difficult to miniaturize the lens.

[0053] To obtain the above effects, the upper limit of the above conditional formula (6) is preferably -0.50, more preferably -0.70, even more preferably -0.90, even more preferably -1.05, and even more preferably -1.18. Furthermore, the lower limit of the above conditional formula (6) is preferably -10.00, more preferably -5.00, even more preferably -3.00, even more preferably -2.50, and even more preferably -2.00.

[0054] 1-2-7. Conditional expression (7) In this optical system, the lens located closest to the object preferably has a negative refractive power and satisfies the following condition. 0.05 < D12 / f < 2.00 ···(7) however, D12: Distance along the optical axis between the image side of the lens located closest to the object and the object side of the lens positioned on the image side. f: focal length of the optical system

[0055] The above conditional equation (7) defines the ratio of the length of the air gap between the lens located closest to the object and the lens on the image side to the focal length of the optical system. The value of "D12" is the distance on the optical axis between the image side of the first lens, which is the lens located closest to the object in the optical system, and the object side of the second lens, which is positioned on the image side, and corresponds to the thickness of the air lens formed by the first and second lenses. When conditional equation (7) is satisfied, the light beam diverged by the first lens, which has negative refractive power, can be incident on the second lens before the ray height becomes too high. As a result, the amount of aberration caused by manufacturing errors can be reduced, and the optical system can be miniaturized.

[0056] Conversely, if the value in the above conditional equation (7) exceeds the upper limit, the air gap between the first lens and the second lens becomes larger relative to the focal length of the optical system, increasing the outer diameter of the second lens and the overall optical length, which is undesirable for miniaturizing the optical system. Furthermore, the increased height of the light rays incident on the second lens increases the amount of aberration caused by manufacturing errors, which is undesirable in terms of performance. On the other hand, if the value in the above conditional equation (7) falls below the lower limit, the air gap between the first lens and the second lens becomes smaller relative to the focal length of the optical system, reducing the aberration correction effect of the air lens formed by the first and second lenses, which is undesirable for improving the performance of the optical system. Furthermore, as the distance between the image side of the first lens and the object side of the second lens decreases, strong aberration cancellation is more likely to occur, increasing the amount of aberration caused by manufacturing errors, which is undesirable for improving the performance of the optical system.

[0057] To obtain the above effects, the upper limit of the above conditional expression (7) is preferably 1.50, more preferably 1.20, even more preferably 0.90, even more preferably 0.70, and even more preferably 0.60. Also, the lower limit of the above conditional expression (7) is preferably 0.10, more preferably 0.15, even more preferably 0.20, even more preferably 0.25, and even more preferably 0.30.

[0058] 1-2-8. Conditional expression (8) The optical system preferably has at least one surface with negative refractive power on the image side of the aperture and satisfies the following condition. 0.05 < fL1 / frn < 3.00 (8) however, fL1: The focal length of the lens closest to the object. frn: The focal length of the surface with the greatest refractive power among the negative refractive surfaces located on the image side of the aperture.

[0059] The above conditional equation (8) defines the ratio of the focal length of the lens located closest to the object to the focal length of the surface with the greatest refractive power among the negative refractive surfaces located on the image side of the aperture. Since this optical system is composed of the front group, aperture, and rear group in that order from the object side, in the meridional cross-section, the principal ray passes below the optical axis in the front group and above the optical axis in the rear group. Here, the aberrations caused by negative refractive power are in opposite directions when the principal ray passes below the optical axis and when it passes above the optical axis, so having refractive powers of the same sign on either side of the aperture makes it easy to cancel out aberrations. Therefore, if there is one negative refractive surface located on the image side of the aperture, the focal length of that surface satisfies conditional equation (8), and if there are multiple negative refractive surfaces located on the image side of the aperture, the focal length of the surface with the greatest refractive power satisfies conditional equation (8), coma aberration can be well corrected, and an optical system with high imaging performance can be achieved.

[0060] Conversely, if the value in the above conditional equation (8) exceeds the upper limit, the focal length of the lens located closest to the object becomes large, making it difficult to miniaturize in the outer diameter direction. Alternatively, the focal length of the negative refractive power surface located on the image side of the aperture becomes too small, making it difficult to correct coma aberration, which is undesirable in terms of performance. On the other hand, if the value in the above conditional equation (8) falls below the lower limit, the focal length of the lens located closest to the object becomes too small, making it difficult to correct coma aberration, and the aberration that occurs when the lens located closest to the object is eccentric becomes large, which is undesirable in terms of performance.

[0061] To obtain the above effects, the upper limit of the above conditional expression (8) is preferably 2.00, more preferably 1.50, even more preferably 1.40, and even more preferably 1.30. Furthermore, the lower limit of the above conditional expression (8) is preferably 0.10, more preferably 0.19, even more preferably 0.25, even more preferably 0.30, and even more preferably 0.40.

[0062] 1-2-9. Conditional expression (9) The optical system preferably has an angle of view of 35 degrees or more for the outermost ray and satisfies the following condition. 0.05 < Dmax / Y < 2.00 (9) however, Dmax: The distance along the optical axis from the object-side plane to the image-side plane that is greatest in terms of air gap. Y: Image height of the outermost ray in the image plane

[0063] The above conditional equation (9) defines the ratio of the distance along the optical axis of the largest air gap in the optical system to the image height of the outermost ray on the image plane. To widen the angle of the optical system, it is preferable to place a negative refractive force on the object side and a positive refractive force on the image side. This makes it easier to achieve both a smaller diameter and a wider angle. Furthermore, widening the distance between the principal points of the negative and positive refractive forces makes it easier to widen the angle. However, widening the distance between the principal points leads to an increase in the overall length, which is undesirable in terms of miniaturization. Therefore, by satisfying conditional equation (9), the maximum air gap becomes within an optimal range, making it easier to achieve both a smaller overall optical length and a wider angle.

[0064] Here, it is preferable for a wide-angle lens to have a field of view of 35 degrees or more for the outermost rays, but in order to satisfy the above condition (9), it is more preferable that the field of view of the outermost rays is 40 degrees or more, even more preferable that it is 45 degrees or more, even more preferable that it is 50 degrees or more, and even more preferable that it is 55 degrees or more.

[0065] Conversely, if the value of the above conditional equation (9) exceeds the upper limit, the length of the largest air gap in the optical system increases, leading to an increase in the overall optical length, which is undesirable in terms of miniaturization. On the other hand, if the value of the above conditional equation (9) falls below the lower limit, the length of the largest air gap in the optical system decreases, which is desirable in terms of miniaturization, but it becomes difficult to widen the principal point spacing, making it difficult to widen the angle of view, and it also leads to an excessively strong refractive force configuration, increasing the amount of aberration caused by manufacturing errors, which is undesirable in terms of improving the performance of the optical system.

[0066] To obtain the above effects, the upper limit of the above conditional expression (9) is preferably 1.50, more preferably 1.20, even more preferably 1.00, even more preferably 0.85, and even more preferably 0.75. Also, the lower limit of the above conditional expression (9) is preferably 0.10, more preferably 0.20, even more preferably 0.25, even more preferably 0.30, and even more preferably 0.40.

[0067] 1-2-10. Conditional expression (10) The optical system preferably satisfies the following condition. 1.50 < OAL / f < 20.00 (10) however, OAL: The distance along the optical axis from the object-side surface to the image plane of the optical system. f: focal length of the optical system

[0068] The above conditional equation (10) defines the ratio of the distance from the object-side surface of the optical system to the image plane to the focal length of the optical system. For example, if the lens barrel of the optical system is made of aluminum, the coefficient of linear expansion is approximately 24.0 × 10 -6 Because the temperature is approximately ( / K), if the total length of the lens barrel is 30 mm and the temperature rises by 100 degrees from the reference temperature, the lens barrel will extend by about 72 μm. As the lens barrel extends, the image plane moves further away from the optical system. Therefore, as the total length increases, the amount of change in back focus in response to temperature changes in the optical system must be increased, otherwise the focus shift will become larger, which is undesirable in terms of performance. Thus, there is an optimal range for the total length of the optical system and the amount of change in back focus in response to temperature changes in the optical system. By satisfying condition (10), the total length of the optical system falls within the optimal range, making it easy to reduce the focus change during temperature changes and enabling the achievement of an optical system with high imaging performance.

[0069] Conversely, if the value in the above conditional equation (10) exceeds the upper limit, the image plane position change due to the lens barrel becomes too large, and the amount of back focus change of the optical system in response to this becomes insufficiently corrected, resulting in a large focus shift, which is undesirable in terms of performance. If the value in the above conditional equation (10) falls below the lower limit, the image plane position change due to the lens barrel becomes too small, and the amount of back focus change of the optical system in response to this becomes overcorrected, resulting in a large focus shift, which is undesirable in terms of performance.

[0070] To obtain the above effects, the upper limit of the above conditional expression (10) is preferably 15.00, more preferably 10.00, even more preferably 8.00, even more preferably 7.50, and even more preferably 7.00. Furthermore, the lower limit of the above conditional expression (10) is preferably 2.00, more preferably 2.50, even more preferably 3.00, even more preferably 3.50, and even more preferably 4.00.

[0071] 1-2-11. Conditional expression (11) The optical system preferably satisfies the following condition. 0.50 < CrL1f / f < 20.00 (11) however, CrL1f: Radius of curvature of the object-side surface of the optical system. f: focal length of the optical system

[0072] The above condition (11) is a formula that defines the ratio of the radius of curvature of the object-side surface of the optical system to the focal length of the optical system. When condition (11) is satisfied, the object-side surface of the optical system is convex toward the object. By satisfying condition (11), the radius of curvature of the object-side surface of the optical system is within an optimal range, making it possible to more effectively prevent light rays incident on the optical system from being reflected at the image plane, and then being re-reflected by the object-side surface of the optical system, and then reaching the image plane again, thereby effectively suppressing the generation of ghost light. In addition, since the object-side surface of the optical system is convex toward the object, it becomes easier to reduce the occurrence of coma aberration and field curvature, and an optical system with high imaging performance can be achieved.

[0073] Conversely, if the value of the above conditional equation (11) exceeds the upper limit, the radius of curvature of the object-side surface of the optical system becomes close to a plane, and light rays reflected from the image plane are re-reflected from the object-side surface of the optical system and re-imaged at the image plane, resulting in a conjugate relationship that makes it difficult to effectively suppress the occurrence of ghosting. On the other hand, if the value of the above conditional equation (11) falls below the lower limit, the radius of curvature of the object-side surface of the optical system becomes too small, increasing coma aberration and field curvature, which is undesirable in terms of performance.

[0074] To obtain the above effects, the upper limit of the above conditional expression (11) is preferably 10.00, more preferably 8.00, even more preferably 6.00, even more preferably 4.00, and even more preferably 3.00. Furthermore, the lower limit of the above conditional expression (11) is preferably 0.60, more preferably 0.70, even more preferably 0.80, and even more preferably 0.90.

[0075] 1-2-12. Conditional expression (12) In this optical system, the lens located closest to the image has a positive refractive power and preferably satisfies the following condition. 1.20 < fe / f < 5.00 ···(12) however, fe: Focal length of the lens located closest to the image. f: focal length of the optical system

[0076] The above conditional equation (12) defines the ratio of the focal length of the lens located closest to the image in the optical system to the focal length of the optical system. By satisfying conditional equation (12), the focal length of the lens located closest to the image in the optical system becomes within an optimal range, making it easier to reduce costs and miniaturize the system. Placing a lens with positive refractive power closest to the image allows this lens to brighten the optical system. In this case, compared to placing a lens with negative refractive power closest to the image, the combined Fno of the lenses excluding the lens closest to the image can be increased, making it easier to correct aberrations with fewer lenses. As a result, it becomes easier to achieve a large aperture while constructing the optical system with fewer lenses, thus reducing costs. Furthermore, placing a lens with positive refractive power closest to the image moves the exit pupil further from the image plane. As the exit pupil moves further from the image plane, the effective diameter of the final lens increases, so miniaturization is achieved by setting the focal length of the lens closest to the image within an optimal range.

[0077] Conversely, if the value in the above conditional equation (12) exceeds the upper limit, the effect of the lens located closest to the image on brightening the optical system becomes smaller, requiring a reduction in the combined Fno of the lenses excluding this closest-to-image lens, resulting in insufficient aberration correction. Alternatively, a large number of lenses may be required for higher performance, making it difficult to achieve cost reduction, which is undesirable. On the other hand, if the value in the above conditional equation (12) falls below the lower limit, the focal length of the lens with the most positive refractive power on the closest-to-image side becomes too short, causing the exit pupil to move further away from the image plane. As a result, the effective diameter of the final lens becomes larger, making it difficult to miniaturize the optical system, which is undesirable.

[0078] To obtain the above effects, the upper limit of the above conditional expression (12) is preferably 4.60, more preferably 4.40, even more preferably 4.10, even more preferably 3.90, and even more preferably 3.70. Also, the lower limit of the above conditional expression (12) is preferably 1.40, more preferably 1.60, even more preferably 1.80, even more preferably 2.00, and even more preferably 2.20.

[0079] 1-2-13. Conditional expression (13) The optical system preferably satisfies the following condition. 0.00 < |f / fGf| < 1.00 ···(13) however, f: focal length of the optical system fGf: Focal length of the front group

[0080] The above conditional equation (13) defines the ratio of the focal length of the optical system to the focal length of the front group. Since the optical system consists of the front group, aperture, and rear group in that order from the object side, the value of conditional equation (13) corresponds to the lateral magnification of the rear group. By satisfying conditional equation (13), the lateral magnification of the rear group is within an optimal range, making it easy to correct various aberrations well without increasing the number of lenses while increasing the aperture size.

[0081] Conversely, if the value of the above conditional equation (13) is not satisfied, that is, if the magnification of the rear group increases, the aberrations generated in the optical system will be amplified by the magnification of the rear group, making it difficult to correct spherical aberration, coma aberration, etc., which is undesirable in terms of high performance. Alternatively, a large number of lenses will be required to achieve high performance, making it difficult to achieve cost reduction, which is also undesirable.

[0082] In order to obtain the above effect, the upper limit of the above conditional expression (13) is preferably 0.95, more preferably 0.92, even more preferably 0.89, even more preferably 0.87, and even more preferably 0.86.

[0083] 2. Imaging device Next, the imaging device according to the present invention will be described. The imaging device according to the present invention is characterized by comprising the optical system according to the present invention and an image sensor that receives the optical image formed by the optical system and converts it into an electrical image signal.

[0084] Here, there are no particular limitations on the image sensor, and solid-state image sensors such as CCD sensors (Charge Coupled Devices) and CMOS sensors (Complementary Metal Oxide Semiconductors) can also be used. The imaging device according to the present invention is suitable for imaging devices using such solid-state image sensors, such as digital cameras, video cameras, surveillance cameras, and in-vehicle cameras. Furthermore, the imaging device may be a fixed-lens type imaging device in which the lens is fixed to the housing, or it may be an interchangeable-lens type imaging device such as an SLR camera or a mirrorless interchangeable-lens camera.

[0085] Herein, the imaging device according to the present invention can be used not only as a general imaging device used to image a subject for viewing purposes, but also as a fixed imaging device that is installed and fixed to a vehicle or building, such as an in-vehicle imaging device or a surveillance imaging device, and used for specific purposes such as surveillance or sensing. The imaging lens according to the present invention is small, has a large aperture, and has high imaging performance. Furthermore, it has high imaging performance over a wide temperature range, making it suitable for imaging devices used in situations where the temperature changes. In particular, it is especially suitable for sensing cameras that are mounted on various mobile bodies (land mobile bodies, air mobile bodies, sea mobile bodies) and used to detect or recognize objects in front of and around the direction of travel of each mobile body. The above-mentioned mobile bodies include vehicles such as automobiles, airplanes, and ships, as well as unmanned aerial vehicles (drones, etc.) or unmanned submersibles, and various mobile bodies such as robots with autonomous mobility functions, such as autonomous bipedal walking robots (including cleaning robots, etc.). Furthermore, it is particularly suitable for surveillance imaging devices that are installed and fixed to buildings and other structures, and can be used not only in visible light but also in wavelength ranges other than visible light wavelengths, such as infrared.

[0086] Furthermore, the following inventions can be considered as alternative inventions that apply the present invention. It consists of a front group, an aperture, and a rear group, in that order from the object side, and the front group or the rear group has at least one lens with negative refractive power and at least one lens with positive refractive power. An optical system characterized by satisfying the following conditional equation. -12.0 < dNdtpmax × 10 6 < -0.8 ···(4)' 0.2 < dNdtnmin × 10 6 < 15.0 ···(5) however, dNdtpmax: Relative refractive index temperature coefficient of the lens with the largest relative refractive index temperature coefficient in air in the temperature range of 0°C to 20°C with respect to the d line, among the lenses with positive refractive power included in the front group and the rear group. dNdtnmin: Relative refractive index temperature coefficient of the lens with negative refractive power included in the front group and the rear group that has the smallest relative refractive index temperature coefficient in air in the temperature range of 0°C to 20°C with respect to the d line.

[0087] Next, the present invention will be specifically described with reference to examples. However, the present invention is not limited to the following examples. Also, in each lens cross-sectional view, the left side is the object side and the right side is the image side. [Examples]

[0088] (1) Lens configuration of the optical system Figure 1 is a cross-sectional view of a lens showing the configuration of an optical system of Embodiment 1 according to the present invention. The optical system is composed of a front group Gf having negative refractive power, an aperture S, and a rear group Gr having positive refractive power, in that order from the object side. The front group Gf is composed of a first lens L1 having a convex surface on the object side and negative refractive power, and a second lens L2 having a concave surface on the object side and positive refractive power, in that order from the object side. The rear group Gr is composed of a third lens L3 having positive refractive power, a fourth lens L4 having a concave surface on the image plane side and negative refractive power, and a fifth lens L5 having positive refractive power, in that order from the object side. The aperture aperture S is located on the image side of the second lens L2. Both sides of the first lens L1 and both sides of the third lens L3 are aspherical.

[0089] Here, the aperture diaphragm S is positioned closer to the object than the top of the image surface of the second lens L2, but since it is positioned closer to the image than the object surface of the second lens L2, this corresponds to the second lens L2 being positioned closer to the object than the aperture diaphragm S. Physically, the lenses are also arranged in the order of second lens L2 and aperture diaphragm S. The lens Lp that is furthest from the object among the lenses with positive refractive power in this optical system is the second lens L2. The lenses with positive refractive power adjacent to the aperture diaphragm S are the second lens L2 and the third lens L3, and of these, the lens with the largest relative refractive index temperature coefficient is the third lens L3. Furthermore, among the surfaces with negative refractive power included in the rear group, the surface with the greatest refractive power is the image surface of the fourth lens L4.

[0090] In the diagram, "IMG" indicates the image plane. This is the image plane of a solid-state image sensor, such as a CCD sensor or CMOS sensor, as described above. Light incident from the object side of the optical system forms an image on the image plane. The solid-state image sensor converts the received optical image into an electrical image signal. An image processing unit (image processing processor, etc.) in the imaging device generates a digital image corresponding to the image of the subject based on the electrical image signal output from the image sensor. This digital image can be recorded on a recording medium such as an HDD (Hard Disk Device), memory card, optical disc, or magnetic tape. The image plane may also be the film surface of a silver halide film.

[0091] Also, "CG" in the figure is an optical block. The optical block CG corresponds to an optical filter, a faceplate, a crystal low-pass filter, an infrared cut filter, etc. Since these reference numerals (IMG, CG) indicate the same components in each figure shown in other embodiments, the description thereof will be omitted hereinafter.

[0092] (2) Numerical Examples A numerical example applying the specific numerical values of the optical system employed in Example 1 will be described. Table 1 shows the lens data of the imaging lens. In Table 1, "surface number" is the number of the lens surface counted from the object side, "r" is the radius of curvature of the lens surface (mm) (however, a surface with an "r" value of INF indicates that the surface is a plane), "d" is the distance (mm) on the optical axis between the i-th (i is a natural number) lens surface counted from the object side and the (i + 1)-th lens surface, "Nd" is the refractive index with respect to the d-line (wavelength λ = 587.56 nm), "νd" is the Abbe number with respect to the d-line, "h" is the effective radius (mm), and "dNdt" is the relative refractive index temperature coefficient (10 -6 / K) in air in the temperature range from 0°C to 20°C with respect to the d-line. However, when the lens surface is an aspherical surface, "ASP" is attached beside the surface number in the table. Also, in the case of an aspherical surface, the paraxial radius of curvature is shown in the column of "r".

[0093] Table 2 shows various data of the optical system. Specifically, it shows the focal length (mm), F-number (F value), semi-field angle (°), image height (mm), total lens length (mm), and back focus (BF (in air)) (mm) of the imaging lens. Here, the total lens length is the distance on the optical axis from the object-side surface of the first lens to the image plane. Also, the back focus is the value obtained by converting the distance on the optical axis from the image-side surface of the n-th lens arranged closest to the image side to the image plane into air.

[0094] Table 3 shows the aspherical data. For the aspherical data shown in Table 1, the aspherical coefficient is given when the shape is defined by the following formula. The aspherical coefficient can be expressed by the following aspherical formula, using the displacement in the optical axis direction at a height h from the optical axis, with the surface vertex as the reference.

[0095] z=ch 2 / [1+{1-(1+k)c 2 h 2} 1 / 2 ]+A4h 4 +A6h 6 +A8h 8 +··· However, c is the curvature (1 / r), h is the height from the optical axis, k is the conicity coefficient (conic constant), and A4, A6, A8, ... are the aspherical coefficients of each order. Also, the notation "E±m" (where m is an integer) in the numerical values ​​of the aspherical coefficients and conic constants means "×10 ±m It means "...".

[0096] Table 4 shows the focal lengths of each lens that make up the optical system.

[0097] Table 5 shows the focal lengths of each lens group that constitutes the optical system.

[0098] Table 21 also shows the numerical values ​​for each conditional expression of the optical system. The details of these tables are the same as those shown in the tables of other embodiments, so their explanation is omitted below.

[0099] Figure 2 shows the longitudinal aberration diagram of the optical system when focused at infinity. The longitudinal aberration diagram in Figure 2 shows, from left to right, spherical aberration (mm), astigmatism (mm), and distortion (%). In the diagram showing spherical aberration, the vertical axis represents the aperture value (Fno). The solid line shows spherical aberration at the d line (wavelength 587.56 nm), the dotted line shows spherical aberration at the C line (wavelength 656.27 nm), and the dashed line shows spherical aberration at the g line (wavelength 435.84 nm). In the diagram showing astigmatism, the vertical axis represents the field of view (°). The solid line shows the sagittal direction at the d line (wavelength 587.56 nm), and the dotted line shows the meridional direction at the d line. In the diagram showing distortion, the vertical axis is the field of view (°), and the distortion (%) at the d line (wavelength 587.56 nm) is shown. Since the same applies to the longitudinal aberration diagrams shown in other embodiments, the explanation will be omitted below.

[0100] [Table 1] Face number rd Nd vd h dN / dt 1 ASP 10.2009 1.000 1.84820 39.96 3.615 7.4 2 ASP 3.8218 1.870 2.662 3 -7.3960 5.080 1.77830 23.91 2.430 -4.1 4 -7.2032 -0.480 2.678 5 S INF 2.460 2.670 6 ASP 6.6895 2.933 1.61881 63.85 2.935 -2.8 7 ASP -10.3776 0.250 2.750 8 14.5970 0.710 1.94595 17.98 2.788 3.9 9 5.6855 1.550 2.707 10 16.7923 2.190 1.49700 81.61 3.255 -5.9 11 -8.2925 2.541 3.488 12 INF 0.500 1.51680 64.20 3.797 13 INF 3.000 3.827

[0101] [Table 2] Focal length 4.776 F-number 1.714 Half-angle 60,000 Image height 4.105 Lens length: 23.604 BF (in air) 5.870

[0102] [Table 3] Page numbers 1 2 6 7 k 0.00000 -0.63390 0.00000 0.00000 A4 -2.06923E-03 -4.57214E-04 -6.35264E-04 7.73837E-04 A6 -2.11059E-04 -5.93838E-04 3.26309E-05 -5.17980E-05 A8 3.97350E-05 1.13518E-04 -1.32886E-05 4.48147E-06 A10 -2.45518E-06 -3.50124E-06 1.52698E-06 -2.71503E-07 A12 5.35794E-08 -1.67513E-07 -6.66821E-08 2.34497E-10

[0103] [Table 4] Lens surface number Focal length L1 1-2 -7.764 L2 3-4 28.330 L3 6-7 7.035 L4 8-9 -10.242 L5 10-11 11.503

[0104] [Table 5] Group Surface number Focal length Gf 1-4 -21.352 Gr 6-11 8.343 [Examples]

[0105] (1) Lens configuration of the optical system Figure 3 is a cross-sectional view of the lens configuration of Embodiment 2 of the present invention. The optical system is composed of a front group Gf having negative refractive power, an aperture S, and a rear group Gr having positive refractive power, in that order from the object side. The front group Gf is composed of a first lens L1 having a convex surface on the object side and negative refractive power, a second lens L2 having a concave surface on the object side and negative refractive power, and a third lens L3 having positive refractive power, in that order from the object side. The rear group Gr is composed of a fourth lens L4 having positive refractive power, a cemented lens formed by joining a fifth lens L5 having positive refractive power and a sixth lens L6 having negative refractive power, and a seventh lens L7 having positive refractive power, in that order from the object side. Both sides of the first lens L1 and both sides of the fourth lens L4 are aspherical.

[0106] Here, the lens Lp that is closest to the object among the lenses with positive refractive power in this optical system is the third lens L3. Also, the lenses with positive refractive power adjacent to the aperture diaphragm S are the third lens L3 and the fourth lens L4, and of these, the lens with the largest relative refractive index temperature coefficient is the fourth lens L4. Furthermore, among the surfaces with negative refractive power included in the rear group, the surface with the largest refractive power is the image surface of the sixth lens L6.

[0107] (2) Numerical Examples Next, we will describe a numerical example in which the specific numerical values ​​of the optical system adopted in Example 2 are applied. Tables 6 to 10 show the lens data, various data of the optical system, aspherical data, focal length of each lens, and focal length of each lens group, respectively. Figure 4 shows the longitudinal aberration diagram of the optical system when it is in focus at infinity.

[0108] [Table 6] Face number rd Nd vd h dN / dt 1 ASP 4.6832 0.955 1.84820 39.96 3.664 7.4 2 ASP 2.5191 1.828 2.612 3 -18.5247 0.730 1.80610 33.27 2.370 4.7 4 14.5773 0.469 2.426 5 98.1584 3.834 1.77830 23.91 2.501 -4.1 6 -10.8910 0.000 2.931 7 S INF 1.624 2.935 8 ASP 15.8014 3.206 1.61881 63.85 3.514 -2.8 9 ASP -7.0469 0.133 3.668 10 8.1806 2.373 1.61800 63.40 3.390 -2.2 11 -13.3078 0.010 1.56732 42.84 3.303 12 -13.3078 0.592 1.80518 25.46 3.303 0.7 13 6.5443 1.739 3.234 14 7.8428 2.346 1.61800 63.40 4.353 -2.2 15 -85.2297 1.276 4.336 16 INF 0.500 1.51680 64.20 4.248 17 INF 3.000 4.227

[0109] [Table 7] Focal length 4.718 F-number 1.540 Half-angle 70,000 Image height 4.037 Lens length: 24.614 BF (in air) 4.605

[0110] [Table 8] Page numbers 1 2 8 9 k -1.82840 -1.54720 0.00000 0.00000 A4 -3.97516E-03 1.59533E-04 -1.56485E-04 2.99638E-04 A6 2.49029E-05 2.54074E-05 8.99537E-06 1.01627E-05 A8 5.03314E-06 8.23749E-06 -6.37180E-07 -3.72450E-07 A10 -1.63389E-07 5.39589E-07 3.19681E-08 2.31576E-08 A12 0.00000E+00 0.00000E+00 0.00000E+00 0.00000E+00

[0111] [Table 9] Lens surface number Focal length L1 1-2 -8.059 L2 3-4 -10.021 L3 5-6 12.793 L4 8-9 8.322 L5 10-11 8.559 L6 12-13 -5.377 L7 14-15 11.734

[0112] [Table 10] Group Surface number Focal length Gf 1-6 -9.988 Gr 8-15 7.100 [Examples]

[0113] (1) Lens configuration of the optical system Figure 5 is a cross-sectional view of the lens configuration of Embodiment 3 according to the present invention. The optical system consists of a front group Gf having negative refractive power, an aperture S, and a rear group Gr having positive refractive power, in that order from the object side. The front group Gf consists of a first lens L1 having a convex surface on the object side and negative refractive power, and a second lens L2 having a concave surface on the object side and positive refractive power, in that order from the object side. The rear group Gr consists of a third lens L3 having positive refractive power, a cemented lens formed by joining a fourth lens L4 having positive refractive power and a fifth lens L5 having negative refractive power, and a sixth lens L6 having positive refractive power, in that order from the object side. Both sides of the first lens L1 and both sides of the third lens L3 are aspherical.

[0114] Here, the lens Lp that is closest to the object among the lenses with positive refractive power in this optical system is the second lens L2. Also, the lenses with positive refractive power adjacent to the aperture diaphragm S are the second lens L2 and the third lens L3, and of these, the lens with the largest relative refractive index temperature coefficient is the third lens L3. Furthermore, among the surfaces with negative refractive power included in the rear group, the surface with the largest refractive power is the image surface of the fifth lens L5.

[0115] (2) Numerical Examples Next, we will describe a numerical example in which the specific numerical values ​​of the optical system adopted in Example 3 are applied. Tables 11 to 15 show the lens data, various data of the optical system, aspherical data, focal length of each lens, and focal length of each lens group, respectively. Figure 6 shows the longitudinal aberration diagram of the optical system when it is in focus at infinity.

[0116] [Table 11] Face number rd Nd vd h dN / dt 1 ASP 5.7395 1.000 1.84819 39.96 3.549 7.4 2 ASP 2.6436 1.817 2.609 3 -11.5121 5.031 1.77829 23.91 2.470 -4.1 4 -9.9198 0.000 3.093 5 S INF 1.893 3.088 6 ASP 14.4595 3.480 1.61880 63.85 3.713 -2.8 7 ASP -7.4589 0.250 3.881 8 11.7828 2.522 1.61800 63.40 3.560 -2.2 9 -11.9307 0.010 1.56732 42.84 3.480 10 -11.9307 0.626 1.85450 25.15 3.479 2.6 11 9.1892 1.737 3.464 12 8.4295 2.542 1.61800 63.40 4.331 -2.2 13 -1061.5265 1.536 4.289 14 INF 0.500 1.51680 64.20 4.207 15 INF 2.000 4.189

[0117] [Table 12] Focal length 5.077 F-number 1.587 Half-angle 60,000 Image height 4.022 Lens length: 25.943 BF (in air) 4.866

[0118] [Table 13] Page numbers 1 2 6 7 k -2.29952 -1.69223 0.00000 0.00068 A4 -5.32894E-03 -1.23061E-03 -1.42697E-04 3.27942E-04 A6 1.92822E-04 2.50316E-04 -2.52694E-08 2.32251E-06 A8 -2.51105E-06 -6.12977E-06 2.15506E-07 2.18147E-07 A10 -3.67698E-08 7.70490E-07 1.35070E-10 1.59564E-09 A12 0.00000E+00 0.00000E+00 0.00000E+00 0.00000E+00

[0119] [Table 14] Lens surface number Focal length L1 1-2 -6.784 L2 3-4 38.672 L3 6-7 8.466 L4 8-9 9.999 L5 10-11 -5.993 L6 12-13 13.545

[0120] [Table 15] Group Surface number Focal length Gf 1-4 -11.909 Gr 6-13 7.801 [Examples]

[0121] (1) Lens configuration of the optical system Figure 7 is a cross-sectional view of the lens configuration of Embodiment 4 according to the present invention. The optical system consists of a front group Gf having positive refractive power, an aperture S, and a rear group Gr having positive refractive power, in that order from the object side. The front group Gf consists of a first lens L1 having a convex surface on the object side and negative refractive power, a second lens L2 having a concave surface on the object side and positive refractive power, and a third lens L3 having positive refractive power, in that order from the object side. The rear group Gr consists of a cemented lens formed by joining a fourth lens L4 having positive refractive power and a fifth lens L5 having negative refractive power, and a sixth lens L6 having positive refractive power, in that order from the object side. Both sides of the first lens L1 and both sides of the third lens L3 are aspherical.

[0122] Here, the lens Lp that is closest to the object among the lenses with positive refractive power in this optical system is the second lens L2. The lenses with positive refractive power adjacent to the aperture diaphragm S are the third lens L3 and the fourth lens L4, of which the lens with the largest relative refractive index temperature coefficient is the fourth lens L4. Furthermore, among the surfaces with negative refractive power included in the rear group, the surface with the largest refractive power is the image surface of the fifth lens L5.

[0123] (2) Numerical Examples Next, we will describe a numerical example in which the specific numerical values ​​of the optical system adopted in Example 4 are applied. Tables 16 to 20 show the lens data, various data of the optical system, aspherical data, focal length of each lens, and focal length of each lens group, respectively. Figure 8 shows the longitudinal aberration diagram of the optical system when it is in focus at infinity.

[0124] [Table 16] Face number rd Nd vd h dN / dt 1 ASP 5.9137 1.000 1.84819 39.96 3.563 7.4 2 ASP 2.6606 1.815 2.619 3 -12.4278 5.038 1.79019 23.95 2.480 -2.9 4 -9.9235 1.872 3.000 5 ASP 14.8803 3.464 1.61880 63.85 3.458 -2.8 6 ASP -7.3917 0.000 3.496 7 S INF 0.291 3.260 8 13.6355 2.451 1.61800 63.40 3.353 -2.2 9 -10.1740 0.010 1.56732 42.84 3.326 10 -10.1740 0.620 1.80517 25.46 3.326 0.7 11 9.3870 1.723 3.361 12 8.3272 2.636 1.61800 63.40 4.273 -2.2 13 -6053.2688 1.546 4.236 14 INF 0.575 1.51680 64.20 4.173 15 INF 3.000 4.158

[0125] [Table 17] Focal length 5.074 F-number 1.601 Half-angle 60.032 Image height 4.032 Lens length: 26.041 BF (in air) 4.925

[0126] [Table 18] Page numbers 1 2 5 6 k -2.34806 -1.76418 0.00000 0.10686 A4 -5.42841E-03 -8.47910E-04 -1.67464E-04 3.43212E-04 A6 2.16645E-04 2.47583E-04 5.41689E-06 7.27314E-06 A8 -4.22130E-06 -8.35849E-06 -3.02412E-07 -1.59041E-07 A10 8.01257E-09 8.46602E-07 1.67118E-08 1.35237E-08 A12 0.00000E+00 0.00000E+00 0.00000E+00 0.00000E+00

[0127] [Table 19] Lens surface number Focal length L1 1-2 -6.639 L2 3-4 33.011 L3 5-6 8.485 L4 8-9 9.814 L5 10-11 -5.979 L6 12-13 13.458

[0128] [Table 20] Group Surface number Focal length Gf 1-6 5.964 Gr 8-13 41.424

[0129] [Table 21] Example 1 Example 2 Example 3 Example 4 Conditional expression (1) νdLp 23.912 23.912 23.912 23.949 Conditional expression (2) dNdtLp × 10 6 -4.100 -4.100 -4.100 -2.900 Conditional expression (3) dNdtpla × 10 6 -2.800 -2.800 -2.800 -2.200 Conditional expression (4) dNdtpmax × 10 6 -2.800 -2.200 -2.200 -2.200 Conditional equation (5) dNdtnmin × 10 6 3.900 0.700 2.600 0.700 Conditional expression (6) fL1 / f -1.626 -1.708 -1.336 -1.308 Conditional expression (7) D12 / f 0.392 0.388 0.358 0.358 Conditional expression (8) fL1 / frn 1.292 0.992 0.631 0.569 Conditional expression (9) Dmax / Y 0.482 0.453 0.470 0.464 Conditional expression (10) OAL / f 4.942 5.217 5.110 5.132 Conditional expression (11) CrL1f / f 2.136 0.993 1.130 1.165 Conditional expression (12) fe / f 2.408 2.487 2.668 2.652 Conditional expression (13) |f / fGf| 0.224 0.472 0.426 0.851 f 4.776 4.718 5.077 5.074 fL1 -7.764 -8.059 -6.784 -6.639 D12 1.870 1.828 1.817 1.815 frn -6.010 -8.128 -10.754 -11.658 CrL1f 10.201 4.683 5.740 5.914 Dmax 1.980 1.828 1.893 1.872 Y 4.105 4.037 4.022 4.032 OAL 23.604 24.614 25.943 26.041 fe 11.503 11.734 13.545 13.458 fGf -21.352 -9.988 -11.909 5.964 [Industrial applicability]

[0130] According to the present invention, it is possible to provide an optical system and imaging device that can ensure good optical performance over a wide temperature range from low to high temperatures. Therefore, it is suitable for imaging devices mounted on various mobile vehicles (land vehicles, air vehicles, sea vehicles), surveillance imaging devices, security imaging devices, and imaging devices that are installed and fixed to various buildings, etc. [Explanation of Symbols]

[0131] Gf...front group Gr... Rear group L1 ··· First lens L2 ··· Second lens L3 ··· Third lens L4 ··· 4th lens L5 ··· 5th lens L6 ··· 6th lens L7 ··· 7th lens S ··· Aperture diaphragm CG ··· Optical Block IMG... Image plane

Claims

1. The lens is composed of a front group, an aperture, and a rear group, in that order from the object side, and the front group contains at least one lens with negative refractive power, and the front group contains at least one lens with positive refractive power, and the lens with positive refractive power that is located closest to the object is called lens Lp. An optical system characterized by satisfying the following conditional equation. 15.00 < νdLp < 31.00 (1) -7.0 < dNdtLp×10 ６ < -2.8 ・・・(2) however, νdLp: Abbe number of the lens Lp with respect to the d line dNdtLp: Relative refractive index temperature coefficient in air for the d line of the lens Lp in the temperature range of 0°C to 20°C.

2. The lens is composed of a front group, an aperture, and a rear group, in that order from the object side, and the front group contains at least one lens with negative refractive power, and the front group contains at least one lens with positive refractive power, and the lens with positive refractive power that is located closest to the object is called lens Lp. An optical system characterized by satisfying the following conditional equation. 15.00 < νdLp < 31.00 (1) -7.0 < dNdtLp×10 ６ < -2.7 ・・・(2) -12.0 < dNdtpmax×10 ６ < -0.8 ・・・(4) however, νdLp: Abbe number of the lens Lp with respect to the d line dNdtLp: Relative refractive index temperature coefficient in air for the d line of the lens Lp in the temperature range of 0°C to 20°C. dNdtpmax: Relative refractive index temperature coefficient of the lens with the largest relative refractive index temperature coefficient in air in the temperature range of 0°C to 20°C with respect to the d line, among the lenses with positive refractive power included in the front group and the rear group.

3. The optical system according to claim 1 or claim 2, having a lens adjacent to the aperture having a positive refractive power, and satisfying the following conditional expression. -12.0 < dNdtpla×10 ６ < -0.8 ・・・(3) however, dNdtpla: Relative refractive index temperature coefficient of a lens with positive refractive power adjacent to the aperture, which has a large relative refractive index temperature coefficient in air in the temperature range of 0°C to 20°C with respect to the d line.

4. The optical system according to claim 1 or claim 3, satisfying the following conditional expression. -12.0 < dNdtpmax×10 ６ < -0.2 ・・・(4) however, dNdtpmax: Relative refractive index temperature coefficient of the lens with the largest relative refractive index temperature coefficient in air in the temperature range of 0°C to 20°C with respect to the d line, among the lenses with positive refractive power included in the front group and the rear group.

5. An optical system according to any one of claims 1 to 4, satisfying the following conditional expression. 0.2 < dNdtnmin×10 ６ < 15.0 ・・・(5) however, dNdtnmin: The relative refractive index temperature coefficient of the lens with the smallest relative refractive index temperature coefficient in air in the temperature range of 0°C to 20°C with respect to the d line, among the lenses with negative refractive power included in the front group and the rear group.

6. The optical system according to any one of claims 1 to 5, wherein the lens located closest to the object has a negative refractive power.

7. The optical system according to claim 6, satisfying the following conditional expression. -20.00 < fL1 / f < -0.30 (6) however, fL1: The focal length of the lens located closest to the object. f: Focal length of the optical system

8. The optical system according to claim 6 or claim 7, satisfying the following conditional expression. 0.05 < D12 / f < 2.00 (7) however, D12: Distance along the optical axis between the image side of the lens located closest to the object and the object side of the lens positioned on the image side. f: Focal length of the optical system

9. The optical system according to any one of claims 6 to 8, having at least one surface having negative refractive power on the image side of the aperture, and satisfying the following conditional expression. 0.05 < fL1 / frn < 3.00 (8) however, fL1: The focal length of the lens located closest to the object. frn: The focal length of the surface with the greatest refractive power among the negative refractive surfaces located on the image side of the aperture.

10. The angle of view of the outermost rays is 35 degrees or more. An optical system according to any one of claims 1 to 9 that satisfies the following conditional expression. 0.05 < Dmax / Y < 2.00 (9) however, Dmax: The distance along the optical axis from the object-side surface to the image-side surface that has the largest air gap. Y: Image height of the outermost ray in the image plane

11. An optical system according to any one of claims 1 to 10 that satisfies the following conditional expression. 1.50 < OAL / f < 20.00 (10) however, OAL: The distance along the optical axis from the object-side surface of the optical system to the image plane. f: Focal length of the optical system

12. An optical system according to any one of claims 1 to 11 that satisfies the following conditional expression. 0.50 < CrL1f / f < 20.00 (11) however, CrL1f: Radius of curvature of the object-side surface of the optical system. f: Focal length of the optical system

13. The optical system according to any one of claims 1 to 12, wherein the lens located closest to the image has a positive refractive power.

14. The optical system according to claim 13, satisfying the following conditional expression. 1.20 < fe / f < 5.00 (12) however, fe: The focal length of the lens located closest to the image. f: Focal length of the optical system

15. An optical system according to any one of claims 1 to 14 that satisfies the following conditional expression. 0.00 < |f / fGf| < 1.00...(13) however, f: Focal length of the optical system fGf: Focal length of the front group

16. An imaging device comprising an optical system according to any one of claims 1 to 15, and an image sensor that receives an optical image formed by the optical system and converts it into an electrical image signal.

Images