Optical system, imaging apparatus, and moving body

Abstract

An object of the present invention is to provide a compact and high-performance optical system, an imaging device, and a moving body having the same.SOLUTION: In order to solve the above problem, an optical system according to the present invention includes, in order from an object side, a front group, a stop, and a rear group, and includes a lens A having a positive refractive power closest to the object side in the front group and a lens B having a negative refractive power closest to an image side in the rear group, in which an object-side surface of the lens B has a concave surface on the object side, a total number of lenses having a refractive power included in the front group and the rear group is eight or less, and a predetermined conditional expression is satisfied.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an optical system, an interchangeable lens device and an imaging device having the optical system, and a mobile object having the optical system. More specifically, the present invention relates to a compact optical system suitable for use in a photographic optical system of a digital input / output device such as a digital still camera or a digital video camera using a solid-state image sensor, or in a photographic device for obtaining external information in a mobile object such as a vehicle or a drone, a lens device and an imaging device having the optical system, and a mobile object having the optical system and the imaging device. [Background technology]

[0002] Image capturing devices using solid-state image sensors, such as digital still cameras and digital video cameras, have become widespread. As the number of pixels in the solid-state image sensors used in these image capturing devices increases, optical systems are being required to have high resolution performance while maintaining a small and lightweight design. Furthermore, there is a strong demand for optical systems that are not only smaller in size but also larger in aperture and lower in cost, and these demands are being placed on optical systems.

[0003] In order to satisfy these requirements, for example, a compact optical system has been proposed that includes a first lens group having positive refractive power, a second lens group having positive refractive power, and a third lens group having negative refractive power, and that suppresses various aberrations (see Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-189351 Summary of the Invention [Problem to be solved by the invention]

[0005] To reduce the size of an optical system, it is effective to adopt a telephoto power arrangement, which has positive refractive power on the object side and negative refractive power on the image side. However, if the power arrangement is strong, it becomes difficult to effectively correct various aberrations with a small number of lenses. Therefore, to achieve both a compact optical system and high performance, it is necessary to optimize the refractive power and lens configuration of each lens.

[0006] An object of the present invention is to provide a small, high-performance optical system, an imaging device, and a mobile object having the same. [Means for solving the problem]

[0007] In order to achieve the above object, the optical system of the present invention comprises, in order from the object side, a front group, a stop, and a rear group, lens A having positive refractive power and located closest to the object side in the front group, and lens B having negative refractive power and located closest to the image side in the rear group, the object-side surface of lens B having a concave surface facing the object side, the front group and the rear group containing a total of eight or less lenses having refractive power, and is characterized by satisfying the following conditional expression: 1.59 < NdLB < 2.30 (1) 1.60 < TLSB / BF < 10.00 (2) 0.20 < fR / f < 1.05 (3) however, NdLB: refractive index of the lens B at the d line TLSB: The distance from the aperture to the image side of lens B BF: Air-equivalent distance from the lens surface closest to the image side of the rear group to the image plane fR: focal length of the rear group f: focal length of the optical system

[0008] In order to solve the above-mentioned problems, an optical system according to the present invention comprises, in order from the object side, a front group, a stop, and a rear group, wherein the optical system comprises a lens A in the front group closest to the object side and having a positive refractive power, and a lens B in the rear group closest to the image side and having a negative refractive power, the object-side surface of lens B having a concave surface facing the object side, the rear group containing a total of five or fewer lenses having refractive power, and wherein the optical system satisfies the following conditional expression: 0.20 < fR / f < 0.92 (3-1) -1.85 < FLB / f < -0.45 (4) 25.00 < νdLA < 110.00 (5) 18.00 < νdLB < 52.00 (6) -1.18 < CRBf / f < -0.20 (7) however, fR: focal length of the rear group f: focal length of the optical system FLB: focal length of lens B νdLA: Abbe number at d line of the lens A νdLB: Abbe number at d line of the lens B CRBf: radius of curvature of the object side surface of lens B

[0009] In addition, in order to solve the above problem, the imaging device of the present invention is characterized by comprising the optical system described above and an imaging element that receives an optical image formed by the optical system and converts it into an electrical image signal.

[0010] In addition, in order to solve the above problem, the moving body of the present invention is characterized by comprising an imaging device having the above-described optical system and an imaging element that receives the optical image formed by the optical system and converts it into an electrical image signal. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide a small-sized and high-performance optical system, an imaging device, and a moving body. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a cross-sectional view of an optical system according to a first embodiment of the present invention. [Figure 2] 2A to 2C are diagrams showing spherical aberration, astigmatism, and distortion of the optical system according to the first embodiment of the present invention. [Figure 3] FIG. 10 is a cross-sectional view of an optical system according to a second embodiment of the present invention when photographing an object at infinity. [Figure 4] 10A to 10C are diagrams showing spherical aberration, astigmatism, and distortion when an object at infinity is photographed using the optical system according to Example 2 of the present invention. [Figure 5] FIG. 10 is a cross-sectional view of an optical system according to a third embodiment of the present invention. [Figure 6] 10A to 10C are diagrams showing spherical aberration, astigmatism, and distortion of the optical system according to Example 3 of the present invention. [Figure 7] FIG. 10 is a cross-sectional view of an optical system according to a fourth embodiment of the present invention. [Figure 8] 10A to 10C are diagrams showing spherical aberration, astigmatism, and distortion of the optical system according to Example 4 of the present invention. [Figure 9] FIG. 10 is a cross-sectional view of an optical system according to a fifth embodiment of the present invention. [Figure 10] 10A to 10C are diagrams showing spherical aberration, astigmatism, and distortion of the optical system according to Example 5 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

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

[0014] 1.Optical system 1-1.Optical configuration of the optical system First, the optical configuration of the optical system according to the present invention will be described. The optical system of this embodiment is composed of, in order from the object side, a front group, a stop, and a rear group.

[0015] The optical system has lens groups including at least one lens on the object side and the image side of the aperture stop. By arranging lens groups on the object side and the image side of the aperture stop, it becomes easier for aberrations to cancel each other out before and after the aperture stop, making it easier to correct off-axis coma. However, the aperture stop referred to here refers to the aperture stop that determines the light beam diameter of the optical system, i.e., the aperture stop that determines the F-number of the optical system.

[0016] This optical system has lens groups including at least one lens on the object side and the image side of the aperture. Arranging lens groups on the object side and the image side of the aperture facilitates cancellation of aberrations before and after the aperture, which is also effective in reducing the number of lenses. This not only reduces costs but also leads to a reduction in the lens volume and weight. From the perspective of reducing costs and weight, it is preferable that the total number of lenses with refractive power included in the front and rear groups be nine or less. It is more preferable that the total number of lenses be eight or less, and even more preferable that the total number be seven or less.

[0017] When a lens having a positive refractive power and a lens having a negative refractive power are cemented together in an optical system, the cemented lens may crack if the temperature changes significantly. This is because a difference in the linear expansion coefficient between the lens having a negative refractive power and the lens having a positive refractive power results in a difference in the shape change due to temperature changes. The larger the diameter, the greater the shape change, leading to cracking of the cemented lens. Therefore, when the average linear expansion coefficient α is the rate of change in the length of the sample per unit temperature, it is preferable to minimize the difference between the average linear expansion coefficient α1n of the lens having a negative refractive power and the average linear expansion coefficient α1p of the lens having a positive refractive power. Furthermore, it is preferable that |α1p - α1n| < 50 × 10-7 / °C in order to prevent cracking of cemented lenses with large diameters.

[0018] The optical configuration of the optical system will be described in more detail below.

[0019] (1) Front group The front group is a lens group that is located closer to the object than the aperture stop among the lens groups that make up the optical system. However, an optical element with no or very little refractive power may be located on the object side of the lens closest to the object in the front group. Examples of such optical elements include a prism that reflects and bends the optical axis of the lens, a protective filter that protects the lens from dirt and scratches, an ND filter used to reduce the amount of incident light, and various filters such as a PL filter for adjusting color.

[0020] The front group has lens A, which has positive refractive power, closest to the object. Having a converging effect closest to the object is advantageous for larger apertures. Even when the aperture is increased, it is possible to avoid an increase in the lens diameter. This leads to a reduction in lens volume, and thus makes the lens lighter.

[0021] The specific lens configuration of the front group is not particularly limited, as long as it has lens A with positive refractive power closest to the object. Therefore, the front group only needs to have at least one lens with positive refractive power. It is preferable to configure the front group using multiple lenses with positive refractive power, as this makes it easier to correct chromatic aberration and spherical aberration.

[0022] The specific lens configuration of the front group is not particularly limited, as long as it has a lens A with positive refractive power closest to the object. Because the front group has a converging effect closest to the object, the front group can be configured as a telephoto lens by having the surface closest to the image side of the front group with negative refractive power, or by having the lens closest to the image side of the front group with negative refractive power. This configuration facilitates compactness even when the focal length is long, and also enables the aperture diameter to be reduced even when the aperture diameter is increased, which is effective in reducing the size of the optical system.

[0023] There are no particular limitations on the specific lens configuration of the front group, as long as it has lens A with positive refractive power closest to the object. In order to achieve high optical performance while reducing the size, weight, and cost of the optical system, it is preferable that the front group be made up of four or fewer lenses with positive refractive power, and more preferably three or fewer lenses.

[0024] (2) Rear group The rear group is a lens group arranged on the image side of the aperture stop. However, an optical element with no refractive power or very little refractive power may be arranged on the image side of the lens closest to the object image in the rear group. Examples of such optical elements include a prism that reflects and bends the optical axis of the lens, a cover glass that protects the image sensor from dirt and scratches, a band-pass filter used to cut off specific wavelengths, and a low-pass filter that attenuates specific frequencies to reduce moiré.

[0025] The rear group has lens B, which has negative refractive power, closest to the image side. Having a diverging effect on the image side creates a telephoto configuration, which is advantageous for reducing the overall length and the diameter of the lens element on the image side.

[0026] The rear group has lens B, which has negative refractive power, closest to the image side. The object-side surface of lens B is concave, which improves off-axis coma correction and achieves high performance.

[0027] It is preferable that the surface of the rear group closest to the object has a convex shape facing the object. By having a converging surface closest to the object in the rear group, the rear group has a telephoto configuration in which the rear group has a converging function closest to the object and a diverging function closest to the image, which allows for a compact overall length. Furthermore, spherical aberration is effectively corrected, resulting in high performance.

[0028] There are no particular limitations on the specific lens configuration of the rear group, so long as it has lens B with negative refractive power closest to the image side. Here, it is preferable that the air lens formed by the image-side surface of the lens adjacent to lens B on the object side and the object-side surface of lens B has a convex shape. Having a convex air lens on the object side of lens B, i.e., having a diverging effect, is advantageous for reducing the radial size of lens B, thereby achieving a reduction in size and weight.

[0029] The specific lens configuration of the rear group is not particularly limited, as long as it has lens B with negative refractive power closest to the image side. In order to achieve high optical performance while reducing the size, weight, and cost of the optical system, it is preferable that the rear group be made up of six or fewer lenses with refractive power, and more preferably five or fewer lenses.

[0030] Since the rear group includes lens B, which has negative refractive power and is closest to the image, it includes at least one lens with negative refractive power. It is preferable that the lens with negative refractive power included in the rear group has a high refractive index. This facilitates Petzval correction, corrects field curvature, and is desirable in terms of high performance. Because the optical system as a whole has positive refractive power, it is preferable for Petzval correction that the lens with negative refractive power in the rear group has a high refractive index. It is more preferable that the refractive index of the lens with negative refractive power in the rear group be 1.74 < Ndn, with the lower limit being 1.75, 1.76, 1.77, 1.78, 1.79, 1.80, 1.81, 1.82, 1.83, 1.84, 1.85, 1.86, 1.87, and 1.88, in that order.

[0031] (3) Focus group In this optical system, there is no particular limitation on whether or not a focus group is included. If a focus group is included, at least one of the lenses constituting the optical system is used as the focus group, and the focus group can be moved in the optical axis direction during focusing to focus on a subject. There are no particular limitations on the position or refractive power of the lens used as the focus group in this optical system.

[0032] When a focus group is provided in the optical system, the number of lenses constituting the focus group is not particularly limited, and the number of lenses constituting the focus group may be one or more. However, in order to suppress aberration fluctuations that occur when focusing on a close subject, it is preferable that the focus group be composed of multiple lenses.

[0033] Furthermore, in order to reduce the size and weight of the focus group, it is preferable that the focus group be composed of a single lens unit. Here, a single lens unit refers to a lens unit such as a single lens or a cemented lens in which multiple single lenses are integrated without any air gap. That is, even if a single lens unit has multiple optical surfaces, only the object-side and image-side surfaces thereof are in contact with air, and the other surfaces are not in contact with air. Furthermore, in this specification, the single lens may be either a spherical lens or an aspherical lens. Furthermore, the term "aspherical lens" also includes so-called composite aspherical lenses with an aspherical film attached to their surfaces. In particular, from the perspective of reducing the size and weight of the focus group while suppressing aberration fluctuations that occur when focusing on a close subject, it is more preferable that the focus group be composed of a cemented lens in which multiple single lenses are integrated without any air gap.

[0034] When the focus group is composed of the single lens unit, there is no air gap between the focus group and the lens barrel. Therefore, compared to a focus group composed of multiple single lenses spaced apart by air, the focus group can be made smaller and lighter. As a result, the mechanical component (hereinafter referred to as the "focus drive mechanism") that moves the focus group along the optical axis during focusing can be made smaller and lighter, thereby reducing the size and weight of the entire optical system unit. The optical system unit includes the optical system, the focus drive mechanism, and the lens barrel that houses these components.

[0035] When a focus group is provided in the optical system, there are no particular limitations on the arrangement of the focus group, but it is preferable that one of the lens groups constituting the rear group, or a part of it, be the focus group. Because the front group has a converging effect closest to the object side and is composed of a lens closest to the object side that has a relatively large diameter, arranging the focus group as the rear lens group or as part of it makes it easy to make the focus group smaller and lighter.

[0036] The refractive power of the focus group may be positive or negative. If the refractive power of the focus group is positive, it is preferable that the lens group on the object side thereof has negative refractive power. Furthermore, if the refractive power of the focus group is negative, it is preferable that the composite refractive power on the object side thereof has positive refractive power. This makes it easy to increase the lateral magnification of the focus group, and to increase the focusing sensitivity of the focus group. As a result, focusing can be achieved with a small amount of movement, which is preferable in terms of compactness.

[0037] The number of focus groups included in the optical system is not limited to one, and multiple lens groups or a portion of multiple lens groups may be used as the focus group. In other words, focusing may be performed using a floating system. By adopting a floating system, spherical aberration and image plane characteristics can be improved at closer focusing, which is preferable because it allows for an optical system with higher optical performance to be realized.

[0038] (4) Anti-vibration group The presence or absence of an image stabilization group in this optical system is not particularly limited. Image blur caused by vibrations transmitted to the imaging device during shooting can be corrected by electrically correcting the image or by moving the imaging element. If the optical system does not have an image stabilization group, image blur can be corrected by these methods.

[0039] When the optical system is provided with a vibration isolation group, the image can be shifted by decentering at least one of the lenses that make up the optical system, and the method for doing so is not particularly limited.

[0040] For example, if at least one of the lenses constituting the optical system is used as an anti-vibration group and the image is shifted by moving the anti-vibration group in a direction approximately perpendicular to the optical axis, the entire optical system unit including the lens barrel can be made smaller, which is preferable in terms of miniaturization.

[0041] When an image stabilization group is provided in the optical system, the location of the image stabilization group is not particularly limited, but it is more preferable to provide the image stabilization group in the rear group. The front group has a converging effect closest to the object and is composed of a lens closest to the object that has a relatively large diameter, so the diameter of the light beam incident on the rear group can be made smaller than the diameter of the light beam incident on the front group. Therefore, by providing the image stabilization group in the rear lens group or in part of it, it is possible to make the image stabilization group smaller and lighter than when the image stabilization group is provided in the front group.

[0042] When the optical system is provided with an image stabilization group, the number of lenses constituting the image stabilization group is not particularly limited. It is preferable to configure the image stabilization group with multiple lenses, as this can suppress aberration fluctuations during image stabilization. In this case, it is preferable that the image stabilization group has at least one lens with negative refractive power and at least one lens with positive refractive power. When the image stabilization group has at least one lens with negative refractive power and at least one lens with positive refractive power, it is possible to suppress the occurrence of chromatic aberrations during image stabilization, thereby realizing an optical system with higher optical performance.

[0043] 1-2.Conditional Expressions In this optical system, it is preferable to employ the above-mentioned configuration and also satisfy the following conditional expression.

[0044] 1-2-1.Conditional Expression (1) It is preferable that the optical system satisfies the following condition: 1.59 < NdLB < 2.30 (1) however, NdLB: refractive index of the lens B at the d line

[0045] Conditional formula (1) above defines the refractive index at the d-line of lens B, the lens closest to the image in the rear group of the optical system. Because the optical system as a whole has a converging effect, the portion closer to the object than lens B, which has the refractive power of the lens closest to the image, has a combined positive refractive power. For light rays incident on lens B, which has a converging effect, it is important from the standpoints of performance and manufacturability to maintain the radius of curvature of the surface closest to the object of lens B within an appropriate range. The refractive power of the surface closest to the object of lens B is determined by the radius of curvature of the surface and the refractive index of the glass material. Therefore, by defining the refractive index within a certain range, it becomes easier to maintain the refractive power of the surface within an appropriate range. Here, satisfying conditional formula (1) enables an optical system with high off-axis performance while keeping costs down. Furthermore, in the case of a so-called composite aspherical lens in which an aspherical film is attached to the surface of lens B closest to the image in the rear group, the refractive index of the base lens is used, not the aspherical film, NdLB.

[0046] On the other hand, if the value of the above conditional expression (1) is above the upper limit, the cost of the glass material becomes too high, which is undesirable from the viewpoint of cost reduction. If the value of the above conditional expression (1) is below the lower limit, it becomes difficult to correct the curvature of field, and it becomes difficult to keep the radius of curvature within an appropriate range, which deteriorates manufacturability. Therefore, it is undesirable from the viewpoint of off-axis performance and manufacturability.

[0047] To obtain the above effects, it is preferable that the upper limit of the conditional expression (1) be 2.20, 2.15, 2.12, 2.08, 2.06, 2.03, 2.01, 1.99, and 1.96, respectively, and it is preferable that the lower limit of the conditional expression (1) be 1.60, 1.61, 1.62, 1.63, 1.64, 1.65, 1.67, and 1.69, respectively.

[0048] 1-2-2.Conditional Expression (2) It is preferable that the optical system satisfies the following condition: 1.60 < TLSB / BF < 10.00 (2) however, TLSB: The distance from the aperture to the image side of lens B BF: Air-equivalent distance from the lens surface closest to the image side of the rear group to the image plane

[0049] The above conditional expression (2) defines the ratio of the distance from the aperture stop to the image side surface of lens B to the air-equivalent distance from the lens surface in the rear group closest to the image to the image plane. In other words, this expression is equivalent to defining the position of lens B in the rear group closest to the image, between the aperture stop and the image plane. When conditional expression (2) is satisfied, the position of lens B is optimized between the aperture stop and the image plane, making it easier to correct coma and achieve high performance.

[0050] On the other hand, if the value of the above conditional expression (2) is equal to or greater than the upper limit, that means the back is too short. In this case, it becomes difficult to arrange optical elements such as a low-pass filter, which is undesirable. In addition, it also leads to an increase in the diameter of the lens B closest to the image, which is undesirable. On the other hand, if the value of the above conditional expression (2) is equal to or less than the lower limit, the aperture and the lens B closest to the image become closer to the back. As a result, the ray height of the off-axial light beams in the lens B does not increase, which reduces the coma aberration correction capability and makes it difficult to achieve high performance, which is undesirable.

[0051] To obtain the above effects, it is preferable that the lower limit of conditional formula (2) be 1.70, 1.80, 1.90, 2.00, 2.10, 2.20, 2.30, 2.40, 2.50, 2.60, 2.70, 2.80, 2.90, and 3.00, respectively, and it is preferable that the upper limit of conditional formula (2) be 9.50, 9.00, 8.50, 8.00, 7.80, 7.60, and 7.40, respectively.

[0052] 1-2-3.Conditional Expression (3) It is preferable that the optical system satisfies the following condition: 0.20 < fR / f < 1.05 (3) however, fR: focal length of the rear group f: focal length of the optical system

[0053] Conditional formula (3) above defines the ratio between the focal length of the rear group and the focal length of the optical system. When conditional formula (3) is satisfied, the rear group has positive refractive power and has a converging effect on the image side of the optical system. This facilitates the optical system having a large aperture. Furthermore, since excessively strong refractive power leads to an increase in the number of lenses and worsening aberrations, there is an appropriate range for achieving both high performance and low cost. By satisfying conditional formula (3), each aberration is corrected within an appropriate range, achieving a large-aperture lens with a small number of lenses.

[0054] On the other hand, when the value of conditional expression (3) exceeds the upper limit, the focal length of the rear group relative to the focal length of the optical system becomes large. In this case, the converging action of the rear group becomes weak, which is undesirable in terms of increasing the aperture. On the other hand, when the value of conditional expression (3) is not greater than the lower limit, the focal length of the rear group relative to the focal length of the optical system becomes small. In this case, the rear group requires excessive aberration correction capability, which is undesirable in terms of high performance, and the number of lenses in the rear group increases, which is undesirable in terms of cost.

[0055] In order to obtain the above effect, it is more preferable that the upper limit value of the above conditional expression (3) is 1.03, 1.01, 0.99, 0.97, 0.95, 0.94, 0.93, 0.92, 0.91, 0.90, 0.89, 0.88, 0.87, 0.86, 0.85, 0.84, 0.83, 0.82, 0.81, 0.80, 0.79, 0.78, 0.77, 0.76, and 0.75, in that order. Furthermore, it is more preferable that the lower limit of the conditional expression (3) be 0.22, 0.24, 0.26, 0.28, 0.30, 0.32, 0.34, 0.36, 0.38, 0.40, 0.42, 0.44, 0.46, 0.48, 0.50, 0.52, 0.54, 0.56, 0.58, and 0.60, in that order.

[0056] 1-2-4.Conditional Expression (4) It is preferable that the optical system satisfies the following condition: -1.85 < FLB / f < -0.45 (4) however, FLB: focal length of lens B f: focal length of the optical system

[0057] Conditional formula (4) above defines the ratio between the focal length of lens B in the rear group closest to the image and the focal length of the optical system. Having negative refractive power closest to the image facilitates a telephoto configuration. However, if the refractive power of the lens closest to the image is too strong, the magnification effect becomes too strong and aberrations occur. Therefore, to achieve both compactness and high performance, it is important to set the refractive power of the lens closest to the image within an appropriate range of refractive power. Satisfying conditional formula (4) makes it possible to achieve both compactness and high performance.

[0058] On the other hand, if the value of conditional expression (4) exceeds the upper limit, the refractive power of the lens B closest to the image becomes too strong, resulting in a large magnification effect. This causes coma and curvature of field, making it difficult to achieve high performance, which is undesirable. Also, if the value of conditional expression (4) falls below the lower limit, the refractive power of the lens B closest to the image becomes too weak, weakening the telephoto power arrangement. This makes it difficult to achieve compact size, which is undesirable.

[0059] To obtain the above effects, it is preferable that the upper limit of conditional expression (4) be −0.46, −0.48, −0.50, −0.52, −0.54, −0.56, −0.58, −0.60, −0.62, −0.64, −0.66, and −0.68, respectively. It is also preferable that the lower limit of conditional expression (4) be −1.70, −1.65, −1.60, −1.55, −1.50, −1.45, −1.40, −1.35, −1.30, −1.25, −1.20, −1.15, −1.10, −1.05, −1.00, and −0.95, respectively.

[0060] 1-2-5.Conditional Expression (5) It is preferable that the optical system satisfies the following condition: 25.00 < νdLA < 110.00 (5) however, νdLA: Abbe number at d line of the lens A

[0061] The above conditional expression (5) defines the Abbe number of the lens A having positive refractive power that is closest to the object in the front group. When conditional expression (5) is satisfied, the axial chromatic aberration of the optical system can be corrected, making it easy to achieve high performance of the optical system.

[0062] On the other hand, if the value of conditional expression (5) is below the lower limit, dispersion increases, making it difficult to correct axial chromatic aberration, which is undesirable. On the other hand, if the value of conditional expression (5) is above the upper limit, dispersion decreases, which is desirable from the perspective of correcting chromatic aberration, but is undesirable from the perspective of cost reduction, since glass with low dispersion is expensive.

[0063] To obtain the above effects, it is preferable that the upper limit of the conditional expression (5) be 100.00, 96.00, 95.00, 92.00, 91.00, 87.00, 83.00, 82.00, 79.00, 78.00, 76.50, 75.60, 75.00, 74.00, 73.00, 72.00, and 70.00, respectively, and it is preferable that the lower limit of the conditional expression (5) be 26.00, 27.00, 28.00, 29.00, 30.00, 32.00, 35.00, 37.00, and 40.00, respectively.

[0064] 1-2-6.Conditional Expression (6) It is preferable that the optical system satisfies the following condition: 18.00 < νdLB < 52.00 (6) however, νdLB: Abbe number at d line of the lens B

[0065] The above conditional expression (6) defines the Abbe number of the lens B having negative refractive power and located closest to the image side in the rear group. When conditional expression (6) is satisfied, chromatic aberration of magnification of the optical system can be corrected, making it easy to achieve high performance of the optical system.

[0066] On the other hand, if the value of conditional expression (6) is below the lower limit, it becomes difficult to correct lateral chromatic aberration at short wavelengths, which is not preferable, and if the value of conditional expression (6) is above the upper limit, it becomes difficult to correct lateral chromatic aberration at long wavelengths, which is also not preferable.

[0067] To obtain the above effects, it is preferable that the upper limit of conditional formula (6) be 51.00, 50.00, 48.00, 47.00, 46.50, 46.00, 45.50, 45.00, 44.00, 43.00, and 42.00, respectively, and it is preferable that the lower limit of conditional formula (6) be 18.20, 18.40, 18.80, 19.20, 19.80, 20.30, 20.80, 21.00, 21.20, and 21.40, respectively.

[0068] 1-2-7.Conditional Expression (7) It is preferable that the optical system satisfies the following condition: -1.18 < CRBf / f < -0.20 (7) however, CRBf: radius of curvature of the object side surface of lens B f: focal length of the optical system

[0069] Conditional formula (7) above defines the shape of the object-side surface of lens B, the lens closest to the image side in the rear group. When the ratio of the radius of curvature of the object-side surface of lens B, the lens closest to the image side in the rear group, to the focal length of the optical system satisfies conditional formula (7), coma can be effectively corrected, and an optical system with high imaging performance can be realized. Furthermore, in the case of a so-called composite aspherical lens in which an aspherical film is attached to the lens unit with positive refractive power located closest to the object, CRBf is the radius of curvature of the base lens, not the radius of curvature of the aspherical film.

[0070] On the other hand, if the value of conditional expression (7) is equal to or less than the lower limit, that is, the radius of curvature of the object-side surface of lens B closest to the image becomes large, and the amount of coma correction becomes small, which is not desirable from the viewpoint of improving performance. Also, if the value of conditional expression (7) is equal to or greater than the upper limit, that is, the radius of curvature of the object-side surface of lens B closest to the image becomes small, and the amount of coma generated becomes large, which is not desirable from the viewpoint of improving performance.

[0071] To obtain the above effect, it is preferable that the lower limit of conditional expression (7) be −1.16, −1.13, −1.10, −1.00, −0.95, −0.90, −0.85, −0.80, −0.75, −0.70, −0.65, and −0.60, in that order. It is also preferable that the upper limit of conditional expression (7) be −0.23, −0.26, −0.28, −0.30, −0.32, −0.34, −0.36, −0.38, −0.40, and −0.42, in that order.

[0072] 1-2-8.Conditional Expression (8) It is preferable that the optical system satisfies the following condition: f / EPD < 2.60 (8) however, f: focal length of the optical system EPD: entrance pupil diameter of the optical system

[0073] The above conditional expression (8) defines the ratio of the entrance pupil diameter of the optical system to the focal length of the optical system. When conditional expression (8) is satisfied, it becomes easy to realize a large aperture of the optical system.

[0074] On the other hand, if the value of conditional expression (8) is equal to or greater than the upper limit, the entrance pupil diameter relative to the focal length of the optical system becomes small, which is undesirable from the viewpoint of increasing the aperture. Furthermore, although there is no lower limit specified for conditional expression (8), an entrance pupil diameter that is too large leads to an increase in the number of lenses required for aberration correction. Therefore, from the viewpoint of cost, it is preferable to set the lower limit to 0.80 or greater.

[0075] In order to obtain the above effects, it is preferable that the upper limit of conditional expression (8) be 2.55, 2.51, 2.48, 2.45, 2.42, 2.38, 2.33, 2.28, 2.23, 2.18, 2.13, 2.10, 2.08, 2.05, 2.00, 1.96, 1.93, 1.90, 1.88, 1.85, 1.82, 1.79, 1.76, 1.73, 1.70, and 1.68, respectively. It is also preferable that the lower limit of conditional expression (8) be 0.85, 0.90, 0.94, 0.99, 1.05, 1.10, 1.18, 1.25, 1.30, and 1.38, respectively.

[0076] 1-2-9.Conditional Expression (9) It is preferable that the optical system satisfies the following condition: 0.65 < FLA / f < 3.80 (9) however, FLA: focal length of lens A f: focal length of the optical system

[0077] Conditional expression (9) above defines the ratio between the focal length of lens A in the front group closest to the object and the focal length of the optical system. Having positive refractive power on the lens closest to the object facilitates a telephoto configuration. However, if the refractive power of the lens group closest to the object is too strong, the convergence effect becomes too strong, resulting in spherical aberration and curvature of field. Therefore, to achieve both compactness and high performance, it is important to set the refractive power of the lens closest to the object within an appropriate range. Satisfying conditional expression (9) makes it possible to achieve both compactness and high performance.

[0078] On the other hand, if the value of conditional expression (9) is equal to or greater than the upper limit, the refractive power of the lens A closest to the object becomes too small, resulting in a weaker convergence action. This makes it difficult to achieve compactness, which is undesirable. On the other hand, if the value of conditional expression (9) is equal to or less than the lower limit, the refractive power of the lens A closest to the object becomes too large, resulting in a strong convergence action. This causes spherical aberration and curvature of field, making it difficult to achieve high performance, which is undesirable.

[0079] To obtain the above effects, it is preferable that the upper limit of conditional formula (9) be 3.70, 3.60, 3.50, 3.40, and 3.30, in that order, and it is preferable that the lower limit of conditional formula (9) be 0.70, 0.75, 0.80, 0.85, 0.90, 0.95, 1.00, 1.05, 1.10, 1.15, 1.20, 1.25, 1.30, 1.35, and 1.40, in that order.

[0080] 1-2-10.Conditional Expression (10) It is preferable that the optical system satisfies the following condition: -3.20 < (CRBf+CRBr) / (CRBf-CRBr) < -0.53 ···(10) however, CRBf: radius of curvature of the object side surface of lens B CRBr: Radius of curvature of the image side surface of lens B

[0081] Conditional expression (10) above defines the shape of lens B, which is located closest to the image plane. Satisfying the range of conditional expression (10) results in a lens shape with a small absolute value for the radius of curvature of the object-side surface, which is desirable for suppressing the occurrence of coma and improving performance.

[0082] On the other hand, if the value of conditional expression (10) exceeds the upper limit, the negative refractive power of the image-side surface becomes strong, making it difficult to correct coma, which is undesirable from the viewpoint of improving performance. Also, if the value of conditional expression (10) falls below the lower limit, the radius of curvature of the object-side surface becomes large, making it difficult to correct coma. Furthermore, the negative refractive power of lens B becomes weak, making it difficult to reduce the size of the lens both in the overall length and radial directions, which is undesirable.

[0083] In order to obtain the above effects, it is preferable that the upper limit of conditional expression (10) be −0.54, −0.55, −0.56, −0.58, −0.60, −0.62, −0.64, −0.66, −0.68, and −0.70, respectively. It is also preferable that the lower limit of conditional expression (10) be −3.10, −3.00, −2.90, −2.80, −2.70, −2.60, −2.50, −2.40, −2.30, −2.20, −2.10, −2.00, −1.90, −1.80, −1.70, and −1.60, respectively.

[0084] 1-2-11.Conditional Expression (11) It is preferable that the optical system satisfies the following condition: 1.42 < NdLA < 2.30 (11) however, NdLA: refractive index of the lens A at the d line

[0085] The above conditional expression (11) defines the refractive index at the d-line of the lens A, which is closest to the object in the front group. By satisfying conditional expression (11), the amount of spherical aberration generated falls within an appropriate range while the refractive power of the lens A is kept appropriate.

[0086] On the other hand, if the value of conditional expression (11) is below the lower limit, the refractive index becomes small, and the radius of curvature of the surface closest to the object becomes small. In this case, it becomes difficult to correct spherical aberration, which is undesirable. Also, if the value of conditional expression (11) is above the upper limit, the refractive index becomes large. Glass with a high refractive index is expensive, so a refractive index that is too high is undesirable from the perspective of cost reduction. Furthermore, glass with a high refractive index has a high specific gravity, which is undesirable from the perspective of weight reduction.

[0087] In order to obtain the above effect, it is preferable that the lower limit of conditional expression (11) be 1.45, 1.49, 1.50, 1.52, 1.54, 1.56, 1.58, 1.60, 1.62, 1.64, 1.66, 1.68, 1.70, 1.72, 1.74, 1.76, 1.78, and 1.80, respectively. It is also preferable that the upper limit of conditional expression (11) be 2.25, 2.20, 2.18, 2.17, 2.16, 2.15, 2.14, 2.13, 2.12, 2.11, and 2.10, respectively.

[0088] 1-2-12.Conditional Expression (12) It is preferable that the optical system satisfies the following condition: 0.10 < BF / f < 0.55 (12) however, BF: Air-equivalent distance from the lens surface closest to the image side of the rear group to the image plane f: focal length of the optical system

[0089] Conditional expression (12) above defines the ratio of the air-equivalent distance on the optical axis from the side closest to the image side of the optical system to the image plane to the focal length of the optical system. Optical elements such as a low-pass filter and a cover glass must be located between the side closest to the image side of the optical system and the image plane. Therefore, it is important to set the back of the optical system within an optimal range in order to position the optical elements while achieving compactness. When conditional expression (12) is satisfied, the back of the optical system falls within the optimal range, making it easier to achieve compactness.

[0090] On the other hand, if the value of the conditional expression (12) is greater than the upper limit, the total optical length of the optical system increases, and the weight including the mechanical components also increases. This is therefore undesirable from the perspective of achieving compactness and weight reduction. On the other hand, if the value of the conditional expression (12) is less than the lower limit, it becomes difficult to arrange optical elements such as a low-pass filter or a cover glass, which is also undesirable. This is also undesirable because it would result in an increase in the diameter of the lens B, which is the final lens.

[0091] To obtain the above effects, it is preferable that the upper limit of conditional expression (12) be 0.54, 0.52, 0.50, 0.48, 0.46, 0.45, 0.44, 0.43, 0.41, 0.39, 0.37, 0.35, and 0.34, respectively. It is also preferable that the lower limit of conditional expression (6) be 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, and 0.18, respectively.

[0092] 1-2-13.Conditional Expression (13) It is preferable that the optical system satisfies the following condition: 0.20 < CRsz / f < 25.00 (13) however, CRsz: Radius of curvature of the image-side surface of the aperture stop f: focal length of the optical system

[0093] Conditional expression (13) above defines the ratio between the radius of curvature of the image-side surface of the stop, i.e., the radius of curvature of the surface of the rear group closest to the object, and the focal length of the optical system. When conditional expression (13) is satisfied, the surface of the rear group closest to the object will have a convex surface facing the object, and the amount of aberration generated at the surface of the rear group closest to the object can be kept within an appropriate range. This achieves high performance. Furthermore, the convergence action of the rear group at the surface closest to the object facilitates the miniaturization of the optical system.

[0094] On the other hand, if the value of conditional expression (13) is below the lower limit, the radius of curvature of the surface in the rear group closest to the object becomes too small, resulting in spherical aberration and coma, making it difficult to improve performance, which is undesirable. Also, if the value of conditional expression (13) is above the upper limit, the radius of curvature of the surface in the rear group closest to the object becomes too large. This increases the overall optical length, which is undesirable from the perspective of compactness. Furthermore, if the radius of curvature of the surface on the image side of the aperture stop becomes large, harmful light reflected on the image plane re-enters the imaging plane, making it more likely to produce ghosts. Therefore, this is undesirable from the perspective of improving performance.

[0095] In order to obtain the above effects, it is preferable that the upper limit of conditional expression (13) be 20.00, 15.00, 12.00, 10.00, 9.00, 8.00, 7.00, 6.00, 5.50, 5.00, 4.50, 4.00, 3.50, 3.20, 3.00, 2.80, 2.60, 2.40, and 2.20, respectively. It is also preferable that the lower limit of conditional expression (13) be 0.22, 0.24, 0.26, 0.28, 0.30, 0.32, 0.34, 0.36, 0.38, 0.40, 0.42, 0.44, 0.46, 0.48, 0.50, 0.52, 0.54, 0.56, 0.58, and 0.60, respectively.

[0096] 1-2-14.Conditional Expression (14) It is preferable that the optical system satisfies the following condition: 1.90 < |ff| / fR < 1000.00 ····(14) however, ff: focal length of the front group fR: focal length of the rear group

[0097] The above conditional expression (14) defines the ratio of the focal length of the front group to the focal length of the rear group. When conditional expression (14) is satisfied, the power distribution of the front and rear groups becomes appropriate, allowing for a larger aperture and an appropriate number of lens elements. In other words, it becomes easier to achieve both a larger aperture and lower costs.

[0098] On the other hand, if the value of conditional expression (14) is equal to or greater than the upper limit, the refractive power of the rear group will be too strong, making it difficult to correct aberrations unless the number of lenses in the rear group is increased, which is undesirable from the viewpoint of achieving both low cost and high performance.Furthermore, if the value of conditional expression (14) is equal to or less than the lower limit, the refractive power of the rear group will be too weak, which is undesirable from the viewpoint of increasing the aperture.

[0099] In order to obtain the above effects, it is preferable that the upper limit of conditional formula (14) be 800.00, 600.00, 400.00, 200.00, 120.00, 100.00, 75.00, 65.00, 50.00, 45.00, 42.00, 40.00, 38.00, and 36.00, respectively. It is also preferable that the lower limit of conditional formula (14) be 1.95, 2.00, 2.05, 2.10, 2.15, 2.20, 2.25, 2.30, 2.40, and 2.45, respectively.

[0100] 1-2-15.Conditional Expression (15) It is preferable that the optical system satisfies the following condition: -0.89 < FLB / FLA < -0.20 (15) however, FLA: focal length of lens A FLB: focal length of lens B

[0101] The above conditional expression (15) defines the ratio of the focal length of lens A to the focal length of lens B. When conditional expression (15) is satisfied, a telephoto power arrangement is easily achieved, which allows the optical system to be made more compact in the overall optical length direction. However, excessive compactness makes it difficult to correct aberrations and leads to increased error sensitivity. For these reasons, there is an appropriate range for the ratio of the focal length of lens A to the focal length of lens B. Here, when conditional expression (15) is satisfied, a compact, lightweight optical system with high performance can be achieved.

[0102] On the other hand, if the value of conditional expression (15) is above the upper limit, the ratio of the focal length of lens B to the focal length of lens A becomes large, weakening the telephoto power arrangement. In this case, the total optical length becomes too long relative to the focal length, and the weight, including the mechanical structure, becomes heavy, which is undesirable from the perspective of weight reduction. If the value of conditional expression (15) is below the lower limit, the ratio of the focal length of lens B to the focal length of lens A becomes small, and the magnification effect of the lens closest to the image side becomes relatively large. In this case, the optical system's aberration magnification effect on the image side becomes large, which is undesirable from the perspective of high performance.

[0103] To obtain the above effect, it is preferable that the upper limit of conditional expression (15) be -0.21, -0.22, -0.23, -0.24, and -0.25, in that order. It is also preferable that the lower limit of conditional expression (15) be -0.87, -0.85, -0.83, -0.81, -0.79, -0.77, -0.75, -0.73, -0.71, -0.69, -0.67, -0.65, -0.63, -0.61, -0.59, -0.57, and -0.55, in that order.

[0104] 1-2-16.Conditional Expression (16) It is preferable that the optical system satisfies the following condition: 0.30 < TLAS / TLSB < 0.92 (16) however, TLAS: the distance from the object side of the lens A to the aperture TLSB: The distance from the aperture to the image side of lens B

[0105] The above conditional expression (16) defines the ratio between the distance from the object-side surface of the lens A to the diaphragm and the distance from the diaphragm to the image-side surface of the lens B. When conditional expression (16) is satisfied, the position of the diaphragm relative to the lens A closest to the object and the lens B closest to the image is appropriate, thereby achieving reductions in the diameters of the lenses A and B. Avoiding an increase in the lens diameter leads to a reduction in the lens volume, thereby achieving a reduction in the weight of the lens.

[0106] On the other hand, if the value of the above conditional expression (16) is equal to or greater than the upper limit, that is, the position of the diaphragm relative to the lens A closest to the object and the lens B closest to the image is closer to the lens B. This increases the diameter of the lens A, which in turn increases the volume of the lens A, which in turn increases the weight and costs, which is undesirable from the perspective of weight reduction and cost reduction. If the value of the above conditional expression (16) is equal to or less than the lower limit, that is, the position of the diaphragm relative to the lens A closest to the object and the lens B closest to the image is closer to the lens A. This increases the diameter of the lens B, which in turn increases the volume of the lens B, which in turn increases the weight and costs, which is undesirable from the perspective of weight reduction and cost reduction.

[0107] To obtain the above effect, it is preferable that the upper limit of conditional expression (16) be 0.91, 0.90, 0.89, 0.88, 0.87, 0.86, 0.85, 0.84, 0.83, and 0.82, respectively. It is also preferable that the lower limit of conditional expression (16) be 0.31, 0.32, 0.33, 0.34, 0.35, 0.36, and 0.37, respectively.

[0108] 1-2-17.Conditional Expression (17) It is preferable that the optical system satisfies the following condition: -4.50 < CRBf / BF < -1.20 (17) however, CRBf: radius of curvature of the object side surface of lens B BF: Air-equivalent distance from the lens surface closest to the image plane in the rear group

[0109] Conditional expression (17) above defines the shape of the object side surface of lens B closest to the image in the rear group. When the ratio of the radius of curvature of the object side surface of lens B closest to the image in the rear group to the air-equivalent distance from the lens surface closest to the image in the rear group satisfies conditional expression (17), coma can be effectively corrected, and an optical system with high imaging performance can be realized. Furthermore, in the case of a so-called composite aspherical lens in which an aspherical film is attached to the lens unit with positive refractive power located closest to the object, CRBf is the radius of curvature of the base lens, not the radius of curvature of the aspherical film.

[0110] On the other hand, if the value of conditional expression (17) is equal to or less than the lower limit, that is, the radius of curvature of the object-side surface of lens B closest to the image becomes large, and the amount of coma correction becomes small, which is not desirable from the viewpoint of improving performance. Also, if the value of conditional expression (17) is equal to or greater than the upper limit, that is, the radius of curvature of the object-side surface of lens B closest to the image becomes small, and the amount of coma generated becomes large, which is not desirable from the viewpoint of improving performance.

[0111] To obtain the above effect, it is preferable that the upper limit of conditional expression (17) be −1.24, −1.26, −1.28, −1.30, −1.32, −1.34, −1.36, −1.38, −1.40, −1.42, −1.44, and −1.46, respectively. It is also preferable that the lower limit of conditional expression (17) be −4.45, −4.40, −4.35, −4.30, −4.25, −4.20, −4.15, −4.10, and −4.05, respectively.

[0112] 1-2-18.Conditional Expression (18) It is preferable that the optical system satisfies the following condition: 0.30 < νdLA / νdLB < 3.00 (18) however, νdLA: Abbe number at d line of the lens A νdLB: Abbe number at d line of the lens B

[0113] The above conditional expression (18) defines the ratio of the Abbe number at the d-line of the lens A to the Abbe number at the d-line of the lens B. When conditional expression (18) is satisfied, both axial chromatic aberration and lateral chromatic aberration are corrected, and high performance is achieved.

[0114] On the other hand, if the value of conditional expression (18) is below the lower limit, i.e., the Abbe number at the d-line of lens A becomes too small, making it difficult to correct axial chromatic aberration, which is not desirable from the viewpoint of improving performance. Also, if the value of conditional expression (18) is above the upper limit, i.e., the Abbe number at the d-line of lens B becomes too small, making it difficult to correct lateral chromatic aberration, which is not desirable from the viewpoint of improving performance.

[0115] In order to obtain the above effects, it is preferable that the upper limit of conditional expression (18) be 2.90, 2.80, 2.70, 2.60, 2.50, 2.40, 2.30, 2.20, 2.10, 2.00, 1.90, and 1.85, in that order. It is also preferable that the lower limit of conditional expression (18) be 0.35, 0.40, 0.45, 0.50, 0.55, 0.60, 0.65, 0.70, 0.75, 0.80, 0.85, 0.90, 0.95, and 0.99, in that order.

[0116] 1-2-19.Conditional Expression (19) It is preferable that the optical system satisfies the following condition: 1.00 < TTL / f < 3.50 (19) however, TTL: The distance from the lens surface closest to the object in the front group to the image plane f: focal length of the optical system

[0117] Conditional expression (19) above defines the ratio of the total optical length to the focal length of the optical system. Making the total optical length smaller relative to the focal length makes it difficult to correct aberrations and increases error sensitivity. Furthermore, making the total optical length too large relative to the focal length increases the weight, including the mechanical structure, so there is an appropriate range for the ratio of total length to focal length. Here, if conditional expression (19) is satisfied, it is possible to achieve both a compact, lightweight optical system with high performance.

[0118] On the other hand, if the value of conditional expression (19) is above the upper limit, the total optical length becomes too long relative to the focal length, and the weight including the mechanical structure becomes heavy, which is undesirable from the perspective of weight reduction. If the value of conditional expression (19) is below the lower limit, the total optical length becomes too short relative to the focal length, and a large number of lenses are required to correct aberrations, which is undesirable from the perspective of cost. Furthermore, this leads to a deterioration in manufacturability, which is undesirable from the perspective of improving performance.

[0119] To obtain the above effect, it is preferable that the upper limit of conditional expression (19) be 3.40, 3.30, 3.20, 3.10, 3.00, 2.90, 2.80, 2.70, 2.60, 2.50, 2.40, 2.30, 2.20, 2.10, and 2.00, respectively, and it is preferable that the lower limit of conditional expression (19) be 1.02, 1.04, 1.06, 1.08, 1.10, 1.12, and 1.13, respectively.

[0120] 2. Imaging device and moving object Next, an 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 described above and an imaging element that receives an optical image formed by the optical system and converts it into an electrical image signal.

[0121] Here, the imaging element is not particularly limited, and solid-state imaging elements such as a CCD sensor (Charge Coupled Device) or a CMOS sensor (Complementary Metal Oxide Semiconductor) can also be used. The imaging device of the present invention is suitable for imaging devices using these solid-state imaging elements, such as digital cameras, video cameras, surveillance cameras, in-vehicle cameras, drone cameras, and medical cameras. The imaging device may be a fixed-lens imaging device in which the lens is fixed to the housing, or an interchangeable-lens imaging device such as a single-lens reflex camera or a mirrorless single-lens camera. In particular, the optical system of the present invention is compact, making it suitable for imaging devices mounted on moving objects such as vehicles and drones.

[0122] The imaging device and moving object of the present invention preferably include an image processing unit that electrically processes captured image data acquired by the imaging element to change the shape of the captured image, and an image correction data storage unit that stores image correction data, an image correction program, etc., used to process the captured image data in the image processing unit. When the optical system is miniaturized, distortion (curvature) of the captured image formed on the imaging plane is likely to occur. In this case, it is preferable to store distortion correction data for correcting the distortion of the captured image shape in advance in the image correction data storage unit, and for the image processing unit to correct the distortion of the captured image shape using the distortion correction data stored in the image correction data storage unit. Such an imaging device allows for a further miniaturization of the optical system, resulting in a clearer captured image and a smaller overall imaging device.

[0123] In the imaging device and moving object of the present invention, it is preferable that the image correction data storage unit stores magnification chromatic aberration correction data in advance, and the image processing unit corrects the magnification chromatic aberration of the captured image using the magnification chromatic aberration correction data stored in the image correction data storage unit. By correcting the magnification chromatic aberration, i.e., chromatic distortion, using the image processing unit, it is possible to reduce the number of lenses constituting the optical system. Therefore, with such an imaging device, it is possible to further miniaturize the optical system, obtain beautiful captured images, and miniaturize the entire imaging device.

[0124] Next, the present invention will be described in detail with reference to examples. However, the present invention is not limited to the following examples. In each lens cross-sectional view, the left side is the object side and the right side is the image side. [Example]

[0125] 1 is a cross-sectional view of a lens system according to Example 1 of the present invention, which is composed of, in order from the object side, a front group GF having positive refractive power, a stop, and a rear group GR having positive refractive power.

[0126] The front group GF, which has positive refractive power, is composed of, in order from the object side, a positive meniscus lens L1 with a convex shape facing the object side, a positive meniscus lens L2 with a convex shape facing the object side, a positive meniscus lens L3 with a convex shape facing the object side, and a negative meniscus lens L4 with a convex shape facing the object side. Here, the positive meniscus lens L1 with a convex shape facing the object side corresponds to the lens A referred to in the present invention.

[0127] The rear group GR, which has positive refractive power, is composed of, in order from the object side, a biconvex lens L5, which has positive refractive power and is convex on both the object-side and image-side surfaces, and a negative meniscus lens L6, which is concave toward the object side. Here, the negative meniscus lens L6, which is concave toward the object side, corresponds to the lens B referred to in the present invention.

[0128] Note that "IMG" in the diagram indicates the image plane. This is the imaging surface of a solid-state imaging element such as a CCD sensor or CMOS sensor as described above. Light incident from the object side of the optical system is focused on the image plane. The solid-state imaging element converts the received optical image into an electrical image signal. An image processing unit (image processing processor, etc.) provided in the imaging device, etc., generates a digital image corresponding to the image of the subject based on the electrical image signal output from the imaging element. This digital image can be recorded on a recording medium such as an HDD (Hard Disk Device), memory card, optical disk, or magnetic tape. Note that the image plane may also be the film surface of a silver halide film.

[0129] The "CG" in the figure indicates the image plane. It is an optical block. The optical block CG is composed of optical filters, cover glass, crystal low-pass filters, infrared cut filters, etc. These symbols (IMG, CG) indicate the same things in the drawings shown in other embodiments, so explanations will be omitted below. [Example]

[0130] 3 is a cross-sectional view of a lens system according to Example 2 of the present invention, which is composed of, in order from the object side, a front group GF having positive refractive power, a stop, and a rear group GR having positive refractive power.

[0131] The front group GF, which has positive refractive power, is composed of, in order from the object side, a positive meniscus lens L1 with a convex surface facing the object side, a positive meniscus lens L2 with a convex surface facing the object side, and a biconcave lens L3 with negative refractive power and both its object-side and image-side surfaces being concave. Here, the positive meniscus lens L1 with a convex surface facing the object side corresponds to the lens A referred to in the present invention.

[0132] The rear group GR, which has positive refractive power, is composed of, in order from the object side, a positive meniscus lens L4 with a convex surface facing the object side, a biconcave lens L5 with negative refractive power and both concave surfaces on the object side and image side, a cemented lens consisting of a biconvex lens L6 with positive refractive power and both convex surfaces on the object side and image side and a negative meniscus lens L7 with a concave surface facing the object side, and a negative meniscus lens L8 with a concave surface facing the object side. Here, the negative meniscus lens L8 with a concave surface facing the object side corresponds to the lens B referred to in the present invention.

[0133] Here, the biconcave lens L5, which has negative refractive power and has concave surfaces on both the object side and image side, corresponds to a focusing group that moves from an object at infinity to an object at a finite distance toward the image side. [Example]

[0134] 5 is a cross-sectional view of an optical system according to Example 3 of the present invention, which is composed of, in order from the object side, a front group GF having negative refractive power, a stop, and a rear group GR having positive refractive power.

[0135] The front group GF, which has negative refractive power, is composed of, in order from the object side, a positive meniscus lens L1 with a convex shape facing the object side, a positive meniscus lens L2 with a convex shape facing the object side, and a biconcave lens L3 with negative refractive power and both the object side and image side surfaces being concave. Here, the positive meniscus lens L1 with a convex shape facing the object side corresponds to the lens A referred to in the present invention.

[0136] The rear group GR, which has positive refractive power, is composed of, from the object side, a biconvex lens L4, which has positive refractive power and both convex surfaces on the object side and image side, a cemented lens consisting of a biconvex lens L5, which has positive refractive power and both convex surfaces on the object side and image side, and a negative meniscus lens L6, which has a concave surface on the object side, and a biconcave lens L7, which has negative refractive power and both concave surfaces on the object side and image side. Here, the biconcave lens L7, which has negative refractive power and both concave surfaces on the object side and image side, corresponds to the lens B referred to in the present invention. [Example]

[0137] 7 is a cross-sectional view of an optical system according to Example 4 of the present invention, which is composed of, in order from the object side, a front group GF having positive refractive power, a stop, and a rear group GR having positive refractive power.

[0138] The front group GF, which has positive refractive power, is composed of, in order from the object side, a biconvex lens L1, which has positive refractive power and both its object-side and image-side surfaces are convex, a positive meniscus lens L2, which has a convex shape toward the object side, and a biconcave lens L3, which has negative refractive power and both its object-side and image-side surfaces are concave. Here, the biconvex lens L1, which has positive refractive power and both its object-side and image-side surfaces is the lens A referred to in the present invention.

[0139] The rear group GR, which has positive refractive power, is composed of, in order from the object side, a biconvex lens L4, which has positive refractive power and both its object-side and image-side surfaces are convex, a cemented lens consisting of a biconvex lens L5, which has positive refractive power and both its object-side and image-side surfaces, cemented together with a negative meniscus lens L6, which has a concave object-side surface, and a negative meniscus lens L7, which has a concave object-side surface. Here, the negative meniscus lens L7, which has a concave object-side surface, corresponds to the lens B referred to in the present invention. [Example]

[0140] 9 is a cross-sectional view of a lens system according to a fifth embodiment of the present invention, which is composed of, in order from the object side, a front group GF having negative refractive power, a stop, and a rear group GR having positive refractive power.

[0141] The front group GF, which has negative refractive power, is composed of, in order from the object side, a positive meniscus lens L1 with a convex shape facing the object side, a positive meniscus lens L2 with a convex shape facing the object side, and a biconcave lens L3 with negative refractive power and both the object side and image side surfaces being concave. Here, the positive meniscus lens L1 with a convex shape facing the object side corresponds to the lens A referred to in the present invention.

[0142] The rear group GR, which has positive refractive power, is composed of, in order from the object side, a biconvex lens L4, which has positive refractive power and both its object-side and image-side surfaces are convex, a cemented lens consisting of a biconvex lens L5, which has positive refractive power and both its object-side and image-side surfaces, cemented together with a negative meniscus lens L6, which has a concave object-side surface, and a negative meniscus lens L7, which has a concave object-side surface. Here, the negative meniscus lens L7, which has a concave object-side surface, corresponds to the lens B referred to in the present invention.

[0143] This shows a longitudinal aberration diagram of the optical system when focused at infinity. The longitudinal aberration diagram, from left to right, shows spherical aberration (mm), astigmatism (mm), and distortion (%). In the diagram showing spherical aberration, the vertical axis represents the maximum aperture (Fno). The solid line represents spherical aberration at the d-line (wavelength 587.56 nm), the dotted line represents spherical aberration at the C-line (wavelength 656.27 nm), and the dash-dot line represents spherical aberration at the g-line (wavelength 435.84 nm). In the diagram showing astigmatism, the vertical axis represents image height (mm). The solid line represents the sagittal direction at the d-line (wavelength 587.56 nm), and the dotted line represents the meridional direction at the d-line. In the diagram showing distortion, the vertical axis represents image height (mm) and shows distortion (%) at the d-line (wavelength 587.56 nm).

[0144] Below are shown Numerical Examples 1 to 5 corresponding to Examples 1 to 5, respectively. In the surface data of each Numerical Example, "surface number" is the number of the lens surface counted from the object side, "r" is the radius of curvature (mm) of the lens surface (however, a surface with an r value of 0.0000 indicates that the surface is flat), "d" is the distance (mm) on the optical axis between the ith lens surface (i is a natural number) and the (i+1)th lens surface counted from the object side, "Nd" is the refractive index for the d-line (wavelength λ=587.56 nm), "νd" is the Abbe number for the d-line, and "h" is the effective radius (mm).

[0145] In each numerical example, the focal length (mm), F-number (F value), half angle of view (°), image height (mm), total lens length (mm), and back focus (BF (in air)) (mm) of the imaging lens are shown. 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. The back focus is the air-equivalent value of the distance on the optical axis from the image-side surface of the nth lens, which is arranged closest to the image, to the image plane.

[0146] If the optical surface is aspherical, an * symbol is added to the right of the surface number. The aspherical shape can be expressed by the following aspherical formula, where the aspherical coefficient is determined by the displacement Z in the optical axis direction at a position of height h from the optical axis, as the surface vertex reference: Z=ch 2 / [1+{1-(1+k)c 2 h 2} 1 / 2 ]+A4h 4 +A6h 6 +A8h 8 +A10h 10 +··· where c is the curvature (1 / r), h is the height from the optical axis, k is the conic coefficient (conic constant), and A4, A6, A8, A10, ... are the aspheric coefficients of each order. Also, the notation "E±m" (m is an integer) in the numerical values ​​of the aspheric coefficients and conic constants means "×10±m."

[0147] The aperture stop is indicated by the letter S to the right of the surface number.

[0148] The intervals that change during focusing are marked with the symbol d to the left of the interval number. The interval data indicates the variable interval of the optical system.

[0149] The lens focal length indicates the focal length of each lens that constitutes the optical system.

[0150] The lens group focal length indicates the focal length of each lens group that constitutes the optical system.

[0151] [Numerical Example 1] Surface Data Surface number rd Nd vd h 1 11.8115 1.163 1.76250 51.90 4.750 2 34.7231 0.100 4.652 3 9.3481 1.410 1.49700 81.61 4.420 4 22.7879 0.170 4.183 5 6.7710 1.688 1.49700 81.61 3.789 6 18.0838 0.657 3.384 7 34.5707 0.490 1.90366 31.31 3.074 8 4.5480 1.666 2.650 9S 0.0000 4.115 2.600 10 14.2002 2.240 1.75666 43.30 3.200 11 -9.6258 2.195 3.353 12 -7.7717 0.520 1.80610 33.27 3.210 13 -63.4644 2.641 3.391 14 0.0000 1.000 1.51680 64.20 4.081 15 0.0000 1.006 4.244 Focal length 18.441 F-value 1.976 Half angle of view 13.604 Image height 4.500 Total length 21.055 BF 4.300 Lens focal length Lens Surface Number Focal Length L1 1-2 22.972 L2 3-4 30.819 L3 5-6 20.750 L4 7-8 -5.841 L5 10-11 7.902 L6 11-12 -11.032 Lens group focal length Group Surface number Focal length GF 1-8 52.719 GR 10-13 14.974 [Numerical Example 2] Surface Data Surface number rd Nd vd h 1 67.9170 8.400 1.90109 42.85 26.500 2 605.0464 0.626 25.719 3 57.7434 5.238 1.75002 58.39 23.682 4 123.4468 6.739 22.741 5 -911.5790 1.800 1.84666 23.78 20.068 6 41.5245 9.001 18.368 7S 0.0000 2.508 18.000 8 57.6803 5.163 1.80420 46.50 18.432 9 8704.3538 d9 18.296 10 -941.887 1.297 1.48749 70.44 16.500 11* 35.8899 d11 16.500 12 0.0000 4.570 17.000 13 66.3026 14.412 1.99680 42.77 21.030 14 -40.6808 1.700 1.59270 35.45 21.234 15 -97.2186 4.313 20.645 16* -42.8945 1.850 1.84666 23.78 20.500 17 -197.4151 18.619 20.553 18 0.0000 2.500 1.51633 64.15 21.582 19 0.0000 d19 21.668 Aspheric data Face number 11 16 k 0.00000E+00 0.00000E+00 A4 3.24697E-07 -5.10314E-07 A6 -3.57689E-09 6.84468E-09 A8 1.79819E-11 -1.48313E-11 A10 -2.44845E-14 1.23711E-14 Focal length 75.907 F-value 1.476 Half angle of view 16.098 Image height 21.630 Total length 113.557 BF 21.268 Variable Interval Data d0 INF 2400.433 636.565 d9 3.684 6.673 15.990 d11 20.137 17.148 7.833 d19 1.025 1.034 1.163 Lens focal length Lens Surface Number Focal Length L1 1-2 84.278 L2 3-4 139.872 L3 5-6 -46.868 L4 8-9 72.183 L5 10-11 -70.889 L6 13-14 27.116 L7 14-15 -119.358 L8 16-17 -65.084 Lens group focal length Group Surface number Focal length GF 1-6 291.249 GR 8-17 60.239 [Numerical Example 3] Surface Data Surface number rd Nd vd h 1 14.9283 2.000 1.80420 46.50 5.327 2 37.4558 0.200 4.873 3 14.8826 1.560 1.80100 49.35 4.555 4 25.9267 1.600 4.226 5 -74.7966 0.600 1.66083 25.44 3.819 6 9.0588 1.090 3.588 7S 0.0000 4.823 3.600 8 11.8228 3.698 1.84796 42.67 5.155 9 -95.0613 3.030 5.109 10 18.2705 3.990 1.74443 49.26 4.798 11 -6.8304 1.000 1.85451 25.15 4.535 12 -40.6708 1.541 4.308 13 -8.5200 0.600 1.71048 32.52 4.115 14 1001.8088 0.380 4.258 15 0.0000 0.500 1.56883 56.04 4.314 16 0.0000 1.000 4.361 17 0.0000 0.500 1.56883 56.04 4.512 18 0.0000 0.112 4.559 Focal length 15.393 F-value 1.624 Half angle of view 17,000 Image height 4.702 Total length 27.856 BF 2.125 Lens focal length Lens Surface Number Focal Length L1 1-2 29.442 L2 3-4 40.714 L3 5-6 -12.012 L4 8-9 12.490 L5 10-11 7.112 L6 11-12 -9.595 L7 13-14 -11.750 Lens group focal length Group Surface number Focal length GF 1-6 -218.480 GR 8-14 10.836 [Numerical Example 4] Surface Data Surface number rd Nd vd h 1 42.0621 1.533 1.80420 46.50 5.296 2 -1655.6058 0.220 5.024 3 11.1051 1.897 1.77250 49.62 4.500 4 33.3982 2.069 4.201 5 -88.8186 0.600 1.69895 30.05 3.627 6 8.6361 1.108 3.393 7S 0.0000 5.017 3.394 8 11.5135 3.987 1.61800 63.39 4.450 9 -32.7094 0.220 4.671 10 23.7072 5.000 1.88100 40.14 4.714 11 -10.3589 1.794 1.75211 25.05 4.457 12 -840.8044 1.583 4.133 13 -7.4582 0.600 1.59270 35.45 4.050 14 -152.2476 0.300 4.253 15 0.0000 0.500 1.51680 64.20 4.314 16 0.0000 1.000 4.370 17 0.0000 0.500 1.51680 64.20 4.541 18 0.0000 0.607 4.596 Focal length 15.372 F-value 1.648 Half angle of view 17.500 Image height 4.847 Total length 28.534 BF 2.566 Lens focal length Lens Surface Number Focal Length L1 1-2 50.613 L2 3-4 20.605 L3 5-6 -11.092 L4 8-9 14.188 L5 10-11 8.707 L6 11-12 -13.749 L7 13-14 -13.111 Lens group focal length Group Surface number Focal length GF 1-6 388.055 GR 8-14 11.464 [Numerical Example 5] Surface Data Surface number rd Nd vd h 1 24.1852 1.602 1.81080 46.50 5.434 2 65.0858 0.200 5.106 3 11.3761 1.560 1.89126 40.80 4.650 4 13.9166 1.420 4.287 5 -17.5996 0.600 1.73902 32.23 4.226 6 10.4013 1.474 4.202 7S 0.0000 1.566 4.415 8 15.1455 3.464 1.89126 40.80 5.400 9 -26.1438 0.885 5.573 10 17.0821 4.450 1.62172 63.39 5.529 11 -7.4849 2.500 1.86746 25.15 5.348 12 -14.3048 3.833 5.429 13 -7.0976 0.797 1.69804 31.14 4.143 14 -25.4844 0.500 4.349 15 0.0000 0.500 1.51680 64.20 4.417 16 0.0000 2.572 4.442 17 0.0000 0.500 1.51680 64.20 4.642 18 0.0000 1.077 4.667 Focal length 15.400 F-number 1.600 Half angle of view 17.500 Image height 4.856 Total length 29.499 BF 4.785 Lens focal length Lens Surface Number Focal Length L1 1-2 46.649 L2 3-4 54.231 L3 5-6 -8.767 L4 8-9 11.203 L5 10-11 8.996 L6 11-12 -21.812 L7 13-14 -14.349 Lens group focal length Group Surface number Focal length GF 1-6 -18.815 GR 8-14 7.619

[0152] The corresponding values ​​of conditional expressions (1) to (19) and various numerical values ​​in Examples 1 to 5 are shown in Table 1 below. [Table 1] (1) NdLB (2) TLSB / BF (3) fR / f (4) FLB / f (5) νdLA (6) νdLB (7) CRBf / f (8) f / EPD (9) FLA / f (10) (CRBf + CRBr) / (CRBf - CRBr) (11) NdLA (12) BF / f (13) CRsz / f (14) |ff| / fR (15) FLB / FLA (16) TLAS / TLSB (17) CRBf / BF (18) νdLA / νdLB (19) TTL / f Example 1 Example 2 Example 3 Example 4 Example 5 (1) 1.806 1.847 1.719 1.599 1.698 (2) 2.109 2.804 8.792 7.092 3.656 (3) 0.812 0.794 0.705 0.746 0.495 (4) -0.598 -0.857 -0.764 -0.854 -0.932 (5) 51.903 42.849 46.502 46.502 46.502 (6) 33.269 23.784 32.520 35.445 31.138 (7) -0.421 -0.565 -0.554 -0.486 -0.461 (8) 1.976 1.476 1.621 1.600 1.600 (9) 1.246 1.110 1.914 3.295 3.029 (10) -1.279 -1.555 -0.983 -1.103 -1.772 (11) 1.763 1.901 1.811 1.811 1.811 (12) 0.232 0.280 0.138 0.167 0.311 (13) 0.770 0.760 0.769 0.750 0.983 (14) 3.521 4.835 20.163 33.851 2.470 (15) -0.480 -0.772 -0.399 -0.259 -0.308 (16) 0.810 0.533 0.377 0.408 0.392 (17) -1.807 -2.017 -4.010 -2.906 -1.483 (18) 1.560 1.802 1.430 1.312 1.493 (19) 1.142 1.496 1.834 1.857 1.915 TLSB 9.070 59.634 18.681 18.201 17.494 BF 4.300 21.268 2.125 2.566 4.785 fR 14.974 60.239 10.836 11.464 7.619 f 18.441 75.907 15.380 15.361 15.400 FLB -11.032 -65.084 -11.750 -13.111 -14.348 CRBf -7.772 -42.895 -8.520 -7.458 -7.098 EPD 9.334 51.432 9.491 9.600 9.625 FLA 22.972 84.278 29.442 50.613 46.649 CRBr -63.464 -197.415 1001.809 -152.248 -25.484 CRsz 14.200 57.680 11.823 11.513 15.146 ff 52.719 291.249 -218.480 388.055 -18.815 TLAS 7.344 31.804 7.050 7.427 6.856 TTL 21.055 113.557 28.211 28.527 29.499

[0153] Although the preferred embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and various modifications and changes are possible within the scope of the gist of the present invention.

[0154] Another invention that applies the present invention is as follows: In order to solve the above problem, an optical system according to the present invention is composed of, in order from the object side, a front group, a stop, and a rear group, and includes a lens A in the front group closest to the object and having positive refractive power, and a lens B in the rear group closest to the image side and having negative refractive power, the object-side surface of lens B having a concave surface facing the object side, and satisfying the following conditional expression: 1.59 < NdLB < 2.30 (1) 0.10 < BF / f < 0.55 (12) however, NdLB: refractive index of the lens B at the d line BF: Air-equivalent distance from the lens surface closest to the image side of the rear group to the image plane f: focal length of the optical system

[0155] Another invention that applies the present invention is as follows: In order to solve the above problem, an optical system according to the present invention is composed of, in order from the object side, a front group, a stop, and a rear group, and includes a lens A in the front group closest to the object and having positive refractive power, and a lens B in the rear group closest to the image side and having negative refractive power, the object-side surface of lens B having a concave surface facing the object side, and satisfying the following conditional expression: 1.59 < NdLB < 2.30 (1) 1.00 < TTL / f < 3.50 (19) however, NdLB: refractive index of the lens B at the d line TTL: The distance from the lens surface closest to the object in the front group to the image plane f: focal length of the optical system [Industrial Applicability]

[0156] According to the present invention, it is possible to provide a small-sized and high-performance optical system, an imaging device, and a moving body. [Explanation of symbols]

[0157] GF... Front group GR... Rear group L1: First lens L2: Second lens L3: Third lens L4: Fourth lens L5: Fifth lens element L6: Sixth lens element L7: Seventh lens element L8: Eighth lens element S Aperture stop F ··· focus group CG ··· Optical Block IMG... Image plane

Claims

1. An optical system comprising, in order from the object side, a front group, a stop, and a rear group, lens A having positive refractive power and located closest to the object side of the front group, and lens B having negative refractive power and located closest to the image side of the rear group, wherein the object side surface of lens B has a concave surface facing the object side, the front group and the rear group contain a total of eight or less lenses having refractive power, and the optical system satisfies the following conditional expression: 1.59 < NdLB < 2.30 (1) 1.60 < TLSB / BF < 10.00 (2) 0.20 < fR / f < 1.05...(3) however, NdLB: refractive index of the lens B at the d line TLSB: distance from the aperture to the image side of the lens B BF: air-equivalent distance from the lens surface of the rear group closest to the image plane fR: focal length of the rear group f: focal length of the optical system

2. An optical system comprising, in order from the object side, a front group, a stop, and a rear group, lens A having positive refractive power and located closest to the object side of the front group, and lens B having negative refractive power and located closest to the image side of the rear group, wherein the object-side surface of lens B has a concave surface facing the object side, the rear group includes five or fewer lenses having refractive power in total, and the optical system satisfies the following conditional expression: 0.20 < fR / f < 0.92 (3-1) -1.85 < FLB / f < -0.45 (4) 25.00 < νdLA < 110.00 (5) 18.00 < νdLB < 52.00 (6) -1.18 < CRBf / f < -0.20 (7) however, fR: focal length of the rear group f: focal length of the optical system FLB: focal length of lens B νdLA: Abbe number of the lens A at the d line νdLB: Abbe number at d line of the lens B CRBf: radius of curvature of the object side surface of the lens B

3. 2. The optical system according to claim 1, wherein the following condition is satisfied: -1.85 < FLB / f < -0.45 (4) however, FLB: focal length of lens B

4. 2. The optical system according to claim 1, wherein the following condition is satisfied: 25.00 < νdLA < 110.00 (5) however, νdLA: Abbe number of the lens A at the d line

5. 2. The optical system according to claim 1, wherein the following condition is satisfied: 18.00 < νdLB < 52.00 (6) however, νdLB: Abbe number at d line of the lens B

6. 2. The optical system according to claim 1, wherein the following condition is satisfied: -1.18 < CRBf / f < -0.20 (7) however, CRBf: radius of curvature of the object side surface of the lens B

7. 3. The optical system according to claim 2, wherein the following condition is satisfied: 1.59 < NdLB < 2.30 (1) however, NdLB: refractive index of the lens B at the d line

8. 3. The optical system according to claim 2, wherein the following condition is satisfied: 1.60 < TLSB / BF < 10.00 (2) however, TLSB: distance from the aperture to the image side of the lens B BF: air-equivalent distance from the lens surface of the rear group closest to the image plane

9. 3. The optical system according to claim 1, wherein the following condition is satisfied: f / EPD < 2.60 (8) however, EPD: entrance pupil diameter of the optical system

10. 3. The optical system according to claim 1, wherein the following condition is satisfied: 0.65 < FLA / f < 3.80 (9) however, FLA: focal length of lens A

11. 3. The optical system according to claim 1, wherein the following condition is satisfied: -3.20< (CRBf+CRBr) / (CRBf-CRBr)<-0.53...(10) however, CRBf: radius of curvature of the object side surface of the lens B CRBr: radius of curvature of the image side surface of the lens B

12. 3. The optical system according to claim 1, wherein the following condition is satisfied: 1.42 < NdLA < 2.30 (11) however, NdLA: refractive index of the lens A at the d line

13. 3. The optical system according to claim 1, wherein the following condition is satisfied: 0.10 < BF / f < 0.55 (12) however, BF: air-equivalent distance from the lens surface of the rear group closest to the image plane

14. 3. The optical system according to claim 1, wherein the following condition is satisfied: 0.20 < CRsz / f < 25.00 (13) however, CRsz: radius of curvature of the image-side surface of the aperture

15. 3. The optical system according to claim 1, wherein the following condition is satisfied: 1.90 < |ff| / fR < 1000.00 (14) however, ff: focal length of the front group fR: focal length of the rear group

16. 3. The optical system according to claim 1, wherein the following condition is satisfied: -0.89 < FLB / FLA < -0.20 (15) however, FLA: focal length of lens A FLB: focal length of lens B

17. 3. The optical system according to claim 1, wherein the following condition is satisfied: 0.30 < TLAS / TLSB < 0.92 (16) however, TLAS: the distance from the object side of the lens A to the aperture TLSB: distance from the aperture to the image side of the lens B

18. 2. The optical system according to claim 1, wherein the following condition is satisfied: -4.50 < CRBf / BF < -1.20 (17) however, CRBf: radius of curvature of the object side surface of the lens B BF: air-equivalent distance from the lens surface of the rear group closest to the image plane

19. 3. The optical system according to claim 1, wherein the following condition is satisfied: 0.30 < νdLA / νdLB < 3.00 (18) however, νdLA: Abbe number of the lens A at the d line νdLB: Abbe number at d line of the lens B

20. 3. The optical system according to claim 1, wherein the following condition is satisfied: 1.00 < TTL / f < 3.50 (19) however, TTL: the distance from the lens surface in the front group closest to the object to the image plane

21. 3. An imaging apparatus comprising: an imaging element, on an image side of the optical system according to claim 1, for converting an optical image formed by the optical system into an electrical signal.

22. A moving body comprising the imaging device according to claim 21.

Images