Optical system, imaging device, and moving object

Abstract

The present invention addresses the problem of providing a compact and high-performance optical system, an imaging device, and a moving object having the imaging device. In order to solve the problem, the optical system according to the present invention comprises, in order from the object side, a front group, a diaphragm, and a rear group, a lens A having a positive refractive power is provided on the object-most side of the front group, a lens B having a negative refractive power is provided on the image-most side of the rear group, and the object-side surface of the lens B has a concave surface on the object side. The optical system satisfies a predetermined conditional expression.

Description

TECHNICAL FIELD

[0001] The present application relates to an optical system, and a interchangeable lens apparatus and an image pickup apparatus each having the optical system, and a mobile body having the optical system. Specifically, for example, the present application relates to a photographic optical system of a digital input / output device such as a digital still camera or a digital video camera, which uses a solid-state image pickup element, a small optical system suitable for a photographic apparatus of a mobile body such as a vehicle or a drone, and a lens apparatus and an image pickup apparatus each having the optical system, and a mobile body having the optical system and the image pickup apparatus. BACKGROUND

[0002] In the past, photographic apparatuses such as digital still cameras and digital video cameras using a solid-state image pickup element have been increasingly popular. Along with high pixelization of the solid-state image pickup element used in these image pickup apparatuses, it is required that the optical system maintain small size and light weight and have high resolution capability. Furthermore, there is a strong demand for small size, large aperture, and low cost of the optical system, and these demands for the optical system have been increasingly strong.

[0003] In order to meet these requirements, for example, a small optical system is proposed, which has 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 which suppresses each aberration (see Patent Literature 1).

[0004] PRIOR ART DOCUMENTS

[0005] PATENT LITERATURE

[0006] Patent Literature 1: Japanese Patent Application Publication No. 2021-189351 SUMMARY

[0007] PROBLEMS TO BE SOLVED BY THE INVENTION

[0008] For the miniaturization of the optical system, it is effective to adopt a telephoto type refractive power configuration having positive refractive power on the object side and negative refractive power on the image side. However, if this refractive power configuration is made stronger, it is difficult to well correct each aberration with a small number of lens pieces. Therefore, in order to balance the miniaturization and the high performance of the optical system, it is necessary to optimize the refractive power or the lens structure of each lens.

[0009] The present application relates to an optical system, and a interchangeable lens apparatus and an image pickup apparatus each having the optical system, and a mobile body having the optical system. Specifically, for example, the present application relates to a photographic optical system of a digital input / output device such as a digital still camera or a digital video camera, which uses a solid-state image pickup element, a small optical system suitable for a photographic apparatus of a mobile body such as a vehicle or a drone, and a lens apparatus and an image pickup apparatus each having the optical system, and a mobile body having the optical system and the image pickup apparatus.

[0010] MEANS FOR SOLVING THE PROBLEMS

[0011] To solve the above problems, an optical system according to the present application is characterized in that it is composed of a front group, a stop, and a rear group in this order from the object side, has a lens A with positive refractive power on the most object side of the front group, has a lens B with negative refractive power on the most image side of the rear group, the object side surface of the lens B has a concave surface on the object side, and satisfies the following conditional expressions.

[0012] 1.59 < NdLB < 2.30 ··· (1)

[0013] 0.20 < fR / f < 0.90 ··· (3-2)

[0014] 25.00 < νdLA < 110.00 ··· (5)

[0015] 0.18 < BF / f < 0.45 ··· (12-1)

[0016] -0.89 < FLB / FLA < -0.20 ··· (15)

[0017] wherein,

[0018] NdLB: refractive index of the lens B at the d line

[0019] fR: focal length of the rear group

[0020] f: focal length of the optical system

[0021] νdLA: Abbe number of the lens A at the d line

[0022] BF: air converted distance from the lens surface on the most image side of the rear group to the image surface

[0023] f: focal length of the optical system

[0024] FLA: focal length of the lens A

[0025] FLB: focal length of the lens B

[0026] Further, to solve the above problems, an optical system according to the present application is characterized in that it is composed of a front group, a stop, and a rear group in this order from the object side, has a lens A with positive refractive power on the most object side of the front group, has a lens B with negative refractive power on the most image side of the rear group, the object side surface of the lens B has a concave surface on the object side, and satisfies the following conditional expressions.

[0027] 1.63 < NdLB < 2.30 ··· (1-1)

[0028] 0.20 < fR / f < 0.90 ··· (3-2)

[0029] -0.83 < FLB / FLA < -0.20 • • • (15-1)

[0030] 0.20 < CRsz / f < 25.00 • • • (13)

[0031] wherein,

[0032] NdLB: refractive index of the lens B at the d line

[0033] fR: focal length of the rear group

[0034] f: focal length of the optical system

[0035] FLA: focal length of the lens A

[0036] FLB: focal length of the lens B

[0037] CRsz: radius of curvature of the lens surface on the image side of the diaphragm

[0038] Further, in order to solve the above problem, the imaging device according to the present application is characterized by comprising the above optical system, and an imaging element that receives an optical image formed by the optical system and converts it into an electric image signal.

[0039] Further, in order to solve the above problem, the mobile body according to the present application is characterized by comprising an imaging device having the above optical system, and an imaging element that receives an optical image formed by the optical system and converts it into an electric image signal.

[0040] Effects of the Invention

[0041] According to the present application, it is possible to provide a small and high-performance optical system, an imaging device, and a mobile body. BRIEF DESCRIPTION OF DRAWINGS

[0042] Figure 1 is a cross-sectional view of the optical system of Embodiment 1 of the present application.

[0043] Figure 2 is a spherical aberration chart, a coma chart, and a distortion aberration chart of the optical system of Embodiment 1 of the present application.

[0044] Figure 3 is a cross-sectional view at the time of photographing an infinite remote subject of the optical system of Embodiment 2 of the present application.

[0045] Figure 4 is a spherical aberration chart, a coma chart, and a distortion aberration chart at the time of photographing an infinite remote subject of the optical system of Embodiment 2 of the present application.

[0046] Figure 5 is a cross-sectional view of the optical system of Embodiment 3 of the present application.

[0047] Figure 6 is a spherical aberration diagram, a coma diagram, and a distortion aberration diagram of the optical system of Embodiment 3 of the present application.

[0048] Figure 7 is a sectional view of the optical system of Embodiment 4 of the present application.

[0049] Figure 8 is a spherical aberration diagram, a coma diagram, and a distortion aberration diagram of the optical system of Embodiment 4 of the present application.

[0050] Figure 9 is a sectional view of the optical system of Embodiment 5 of the present application.

[0051] Figure 10 is a spherical aberration diagram, a coma diagram, and a distortion aberration diagram of the optical system of Embodiment 5 of the present application.

[0052] Explanation of Reference Numerals

[0053] GF • • • front group

[0054] GR • • • rear group

[0055] L1 • • • 1st lens

[0056] L2 • • • 2nd lens

[0057] L3 • • • 3rd lens

[0058] L4 • • • 4th lens

[0059] L5 • • • 5th lens

[0060] L6 • • • 6th lens

[0061] L7 • • • 7th lens

[0062] L8 • • • 8th lens

[0063] S • • • aperture stop

[0064] F • • • focus adjustment group

[0065] CG • • • optical module

[0066] IMG • • • image plane DETAILED DESCRIPTION

[0067] Embodiments of an optical system, an image pickup apparatus, and a moving object to which the present application is applied will be described below.

[0068] 1. Optical system

[0069] 1-1. Optical structure of optical system

[0070] First, the optical structure of the optical system to which the present application is applied will be explained. The optical system of the present embodiment is composed of a front group, a stop, and a rear group in this order from the object side.

[0071] In this optical system, a lens group including at least one lens is provided on the object side and the image side of the stop. By providing the lens group on the object side and the image side of the stop, the aberrations before and after the stop are easily canceled out, and the off-axis coma is easily corrected. Here, the stop means an aperture stop that defines the beam diameter of the optical system, i.e., an aperture stop that defines the Fno of the optical system.

[0072] In this optical system, a lens group including at least one lens is provided on the object side and the image side of the stop. By providing the lens group on the object side and the image side of the stop, the aberrations before and after the stop are easily canceled out, and it is also effective for reducing the number of lens pieces. Thus, it contributes to cost reduction and reduction in the volume of the lens, and to weight reduction of the lens. The total number of lenses having optical power included in the front group and the rear group is preferably 9 or less, which is preferable in terms of cost reduction and weight reduction. The total number of lenses is further preferably 8 or less, and more preferably 7 or less.

[0073] In the case where a lens having positive optical power and a lens having negative optical power included in the optical system are joined, the joined lens sometimes breaks in the case where the temperature changes greatly. This is because, if there is a difference in the linear expansion coefficient between the lens having negative optical power and the lens having positive optical power, the shape change due to the temperature change will be different, and the larger the diameter, the greater the shape change, thus leading to breakage of the joined lens. Therefore, when the proportion of the change in the sample length per unit temperature is set as the average linear expansion coefficient a, it is preferable to reduce the difference between the average linear expansion coefficient a1n of the lens having negative optical power and the average linear expansion coefficient a1p of the lens having positive optical power. Further, |a1p - a1n| < 50 x 10 -7 / °C is preferable for preventing breakage of the joined lens having a large diameter.

[0074] Hereinafter, the optical structure of the optical system will be explained in more detail.

[0075] (1) Front Group

[0076] The front group is a lens group disposed on the object side of the stop among the lens groups constituting the optical system. On the object side of the most object-side lens of the front group, an optical element having no optical power or extremely small optical power can also be disposed. As such an optical element, for example, a prism that reflects and bends the optical axis of the lens, a protective filter for protecting the lens from stains or scratches, an ND filter for reducing the amount of incident light, or a PL filter for adjusting the color, and the like can be cited.

[0077] The front group has the lens A with positive refractive power on the most object side. By having converging action on the most object side, it is advantageous for large aperture. Further, in the case of large aperture, it is also possible to avoid the large size of the lens diameter. Thus, it is helpful to reduce the volume of the lens, and to achieve the light weight of the lens.

[0078] The front group has the lens A with positive refractive power on the most object side, and the specific lens structure is not particularly limited. Thus, the front group has at least one lens with positive refractive power. If the front group is configured using a plurality of lenses with positive refractive power, it is easy to correct chromatic aberration or spherical aberration, and thus is preferred.

[0079] The front group has the lens A with positive refractive power on the most object side, and the specific lens structure is not particularly limited. It has converging action on the most object side of the front group, and thus by providing the most image side surface of the front group as a surface with negative refractive power, or providing the most image side of the front group as a lens with negative refractive power, the front group becomes a telescopic structure. By providing such a structure, even if the focal length is extended, it is easy to achieve miniaturization, and in the case of large aperture, it is possible to achieve the miniaturization of the aperture diameter, and is effective for the miniaturization of the optical system.

[0080] The front group has the lens A with positive refractive power on the most object side, and the specific lens structure is not particularly limited. In terms of achieving the miniaturization, light weight, and low cost of the optical system, and achieving high optical performance, the lens with positive refractive power in the front group is preferably composed of 4 or less, and more preferably composed of 3 or less.

[0081] (2) Rear group

[0082] The rear group is a lens group disposed on the image side of the aperture. Among them, on the image side of the most image side lens of the rear group, an optical element having no refractive power or very small refractive power can also be disposed. As such an optical element, for example, a prism that reflects and bends the optical axis of the lens, a protective glass for protecting the imaging element from stains or scratches, a band-pass filter for cutting specific wavelengths, or a low-pass filter for attenuating specific frequencies in order to reduce moire can be cited.

[0083] The rear group has the lens B with negative refractive power on the most image side. By having diverging action on the most image side, it becomes a telescopic structure, and is advantageous for the miniaturization of the overall length direction and the diameter of the image side lens.

[0084] The rear group has the lens B with negative refractive power on the most image side. The object side surface of the lens B has a concave surface on the object side. Thus, it is possible to well correct the off-axis coma, and to achieve high performance.

[0085] The most object side surface of the rear group is preferably convex toward the object side. By having a surface that functions as a converging surface on the most object side of the rear group, the rear group functions as a telescopic structure that functions as a converging surface on the most object side and functions as a diverging surface on the most image side, achieving miniaturization in the overall length direction. In addition, this is effective for correcting spherical aberration, achieving high performance.

[0086] The rear group only needs to have a lens B with negative power on the most image side, and the specific lens structure is not particularly limited. Here, the air lens formed by the image side surface of the lens adjacent to the object side of the lens B and the object side surface of the lens B is preferably convex. By having a convex air lens, i.e., a diverging function, on the object side of the lens B, the radial miniaturization of the lens B is facilitated, achieving miniaturization and light weight.

[0087] The rear group only needs to have a lens B with negative power on the most image side, and the specific lens structure is not particularly limited. In achieving miniaturization, light weight, and low cost of the optical system and achieving high optical performance, the lenses with power in the rear group are preferably composed of 6 or fewer lenses, and more preferably composed of 5 or fewer lenses.

[0088] In the rear group, there is the lens B with negative power on the most image side, and thus there is at least one lens with negative power. The lens with negative power included in the rear group preferably has a high refractive index. Thereby, correction of Petzval is facilitated, field curvature is corrected, and high performance is achieved. The optical system has positive power as a whole, and thus a high refractive index of the lens with negative power in the rear group is preferable for correction of Petzval. The refractive index of the lens with negative power in the rear group is further preferably 1.74 < Ndn, and the lower limit value is more preferably 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, 1.88, in this order.

[0089] (3) Focus Group

[0090] In the optical system, the presence or absence of a focus group is not particularly limited. In the case where a focus group is provided, at least one lens among the lenses constituting the optical system is set as the focus group, and the focus group can be moved in the optical axis direction to focus on a subject at the time of focusing. The position or power of the lens used as the focus group in the optical system is not particularly limited.

[0091] In the case where 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 can be one or a plurality of lenses. However, in terms of suppressing aberration variation occurring at the time of focusing on a close subject, it is preferable that the focus group be composed of a plurality of lenses.

[0092] Further, in order to realize the miniaturization and weight reduction of the focusing group, it is preferable that the focusing group is constituted by one single lens unit. Here, the single lens unit refers to one single lens, or a cemented lens or the like in which a plurality of single lenses are integrated without an air gap. That is, in the case where the single lens unit has a plurality of optical surfaces, only the most object side surface and the most image side surface thereof are in contact with air, and the other surfaces are not in contact with air. Further, in the present specification, the single lens can be either a spherical lens or an aspherical lens. Further, the aspherical lens also includes a so-called compound aspherical lens in which an aspherical film is attached to a surface. In particular, from the viewpoint of suppressing the variation in aberration generated when focusing on a close subject, and realizing the miniaturization and weight reduction of the focusing group, it is preferable that the focusing group is constituted by a plurality of single lenses integrated without an air gap.

[0093] In the case where the focusing group is constituted by the above-described one single lens unit, the focusing group does not include an air gap. Therefore, compared with a structure in which the focusing group is disposed with a plurality of single lenses with an air gap, the focusing group can be miniaturized and reduced in weight. As a result, the focusing drive mechanism (hereinafter referred to as "focus drive mechanism") for moving the focusing group in the optical axis direction at the time of focusing can be miniaturized and reduced in weight, and the entire optical system unit can be miniaturized and reduced in weight. Further, in the optical system unit, in addition to the optical system and the above-described focus drive mechanism, a lens barrel or the like that accommodates the same is provided.

[0094] In the case where the focusing group is provided in the optical system, the configuration of the focusing group is not particularly limited, but it is preferable that one of the lens groups constituting the rear group or a part thereof is provided as the focusing group. The front group has a converging action at the most object side, and is constituted by a lens having a large diameter at the most object side, and therefore, by providing the focusing group in the lens group of the rear group or a part thereof, the focusing group can be easily miniaturized and reduced in weight.

[0095] The focal power of the focusing group can be either positive or negative. In the case where the focal power of the focusing group is positive, the lens group on the object side thereof preferably has a negative focal power. Further, in the case where the focal power of the focusing group is negative, the combined focal power on the object side thereof is preferably positive. Thereby, the lateral magnification of the focusing group can be easily increased, and the focusing sensitivity of the focusing group can be easily improved. As a result, focusing can be performed with a smaller movement amount, and therefore, this is preferable in terms of miniaturization.

[0096] Further, the focusing group included in the optical system is not limited to one, and a plurality of lens groups or a part of a plurality of lens groups can be provided as the focusing group. That is, focusing can also be performed by a floating method. By adopting the floating method, the spherical aberration or the image surface property at the time of close focusing can be made better, and therefore, an optical system having higher optical performance can be realized, and this is preferable.

[0097] (4) Vibration-Isolating Group

[0098] In the optical system, whether or not a vibration-isolating group is not particularly limited. In order to correct image blur due to vibration transmitted to the imaging device or the like at the time of photographing, it is possible to correct by electrically correcting the image or moving the imaging element. In the case where the vibration-isolating group is not provided in the optical system, it is possible to correct the image blur by these methods.

[0099] In the case where the vibration-isolating group is provided in the optical system, it is possible to achieve image shift by eccentricity of at least one lens among the lenses constituting the optical system, and the method thereof is not particularly limited.

[0100] For example, if at least one lens among the lenses constituting the optical system is provided as a vibration-isolating group, and image shift is achieved by moving the vibration-isolating group in a direction substantially orthogonal to the optical axis, it is possible to achieve miniaturization of the entire optical system unit including the lens barrel, and thus is preferable in terms of achieving miniaturization.

[0101] In the case where the vibration-isolating group is provided in the optical system, the configuration of the vibration-isolating group is not particularly limited, but it is more preferable to provide the vibration-isolating group in the rear group. The front group has a converging action at the most object side, and is constituted by a lens having a large diameter at the most object side, and thus it is possible to make the diameter of the incident light beam to the rear group smaller than the diameter of the incident light beam to the front group. Therefore, by providing the vibration-isolating group in the lens group of the rear group or a part thereof, it is possible to achieve miniaturization and lightening of the vibration-isolating group compared to the case where the vibration-isolating group is provided in the front group.

[0102] In the case where the vibration-isolating group is provided in the optical system, the number of lenses constituting the vibration-isolating group is not particularly limited. If the vibration-isolating group is constituted by a plurality of lenses, it is possible to suppress variation in aberration at the time of vibration isolation, and thus is preferable. At this time, the vibration-isolating group preferably has at least one lens having a negative refractive power and at least one lens having a positive refractive power, respectively. In the case where the vibration-isolating group has at least one lens having a negative refractive power and at least one lens having a positive refractive power, respectively, it is possible to suppress chromatic aberration at the time of vibration isolation, and it is possible to achieve an optical system having higher optical performance.

[0103] 1-2. Conditional Expression

[0104] In the optical system, it is preferable to adopt the above-described configuration and satisfy the conditional expression described below.

[0105] 1-2-1. Conditional Expression (1)

[0106] The optical system preferably satisfies the following conditional expression.

[0107] 1.59 < NdLB < 2.30 ··· (1)

[0108] wherein,

[0109] NdLB: refractive index of the lens B at the d-line

[0110] The conditional expression (1) described above is an expression that defines the refractive index of the lens B at the d-line, which is the most image-side lens of the rear group of the optical system. The optical system has a converging action as a whole, and therefore has a positive power in synthesis on the object side than the lens B having a negative power which is the most image-side lens. It is important in terms of performance and manufacturability to suppress the radius of curvature of the most object-side surface of the lens B to an appropriate range with respect to a light ray incident to the lens B having a diverging action. The power of the most object-side surface of the lens B is determined by the radius of curvature of the surface and the refractive index of the glass material, and therefore if the refractive index is defined within a certain range, it is also easy to suppress the power of the surface to an appropriate range. Here, in the case where the conditional expression (1) is satisfied, it is possible to achieve an optical system in which the cost is suppressed and the off-axis performance is high. In addition, in the case where the lens B which is the most image-side lens of the rear group is a so-called complex aspheric lens in which an aspheric film is attached to the surface, NdLB is not the refractive index of the aspheric film, but is set to the refractive index of the base lens.

[0111] In this regard, if the value of the conditional expression (1) described above is equal to or higher than the upper limit, the cost of the glass material is excessively high, and it is not preferable in terms of cost reduction. If the value of the conditional expression (1) described above is lower than the lower limit, it is difficult to correct the field curvature, and it is difficult to suppress the radius of curvature to an appropriate range, and the manufacturability deteriorates. Thus, it is not preferable in terms of off-axis performance and manufacturability.

[0112] In terms of achieving the effects described above, the upper limit value of the conditional expression (1) described above is preferably 2.20, 2.15, 2.12, 2.08, 2.06, 2.03, 2.01, 1.99, 1.96 in this order. In addition, the lower limit value of the conditional expression (1) described above is preferably 1.60, 1.61, 1.62, 1.63, 1.64, 1.65, 1.67, 1.69 in this order.

[0113] 1-2-2. Conditional expression (2)

[0114] The optical system preferably satisfies the following conditional expression.

[0115] 1.60 < TLSB / BF < 10.00... (2)

[0116] wherein,

[0117] TLSB: distance from the stop to the image-side surface of the lens B

[0118] BF: air converted distance from the most image-side lens surface of the rear group to the image surface

[0119] The conditional expression (2) above is an expression for defining the ratio of the distance from the stop to the image side surface of the lens B to the air converted distance from the most image side lens surface of the rear group to the image surface. That is, it is an expression equivalent to defining the position of the most image side lens B of the rear group between the stop and the image surface. In the case where the conditional expression (2) is satisfied, the position of the lens B is optimized between the stop and the image surface, it is easy to correct coma, and it is easy to achieve high performance.

[0120] On the other hand, if the value of the conditional expression (2) above is below the lower limit value, the stop and the most image side lens B become close to the rear portion. Therefore, the ray height of the off-axis rays in the lens B does not become high, and thus the coma correction ability becomes small, it is difficult to achieve high performance, and it is not preferable.

[0121] In terms of achieving the above effects, the lower limit value of the conditional expression (2) is preferably 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, 3.00, in this order. In addition, the upper limit value of the conditional expression (2) above is preferably 9.50, 9.00, 8.50, 8.00, 7.80, 7.60, 7.40, in this order.

[0122] 1-2-3. Conditional expression (3)

[0123] The optical system preferably satisfies the following conditional expression.

[0124] 0.20 < fR / f < 1.05...(3)

[0125] wherein

[0126] fR: focal length of the rear group

[0127] f: focal length of the optical system

[0128] The conditional expression (3) above is an expression for defining the ratio of the focal length of the rear group to the focal length of the optical system. In the case where the conditional expression (3) is satisfied, the rear group has a positive optical power, and has a converging effect on the image side of the optical system. Therefore, it is easy to achieve a large aperture of the optical system. In addition, an excessively strong optical power can result in an increase in the number of lens pieces or deterioration of aberration, and thus there is a range suitable for balancing high performance and low cost. By satisfying the conditional expression (3), each aberration is corrected to be within an appropriate range, and a large aperture lens with a small number of lens pieces is achieved.

[0129] On the other hand, if the value of the conditional expression (3) is below the lower limit value, the focal length of the rear group becomes small with respect to the focal length of the optical system. In this case, excessive aberration correction ability of the rear group is required, and high performance is not preferable, and the number of lens pieces of the rear group increases, and cost is not preferable.

[0130] In terms of obtaining the above-described effects, the upper limit value of the above-described conditional expression (3) is preferably 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, 0.75, in this order. In addition, the lower limit value of the above-described conditional expression (3) is preferably 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, 0.60, in this order.

[0131] 1-2-4. Conditional expression (4)

[0132] The optical system preferably satisfies the following conditional expression.

[0133] -1.85 < FLB / f < -0.45 ··· (4)

[0134] wherein,

[0135] FLB: focal length of the lens B

[0136] f: focal length of the optical system

[0137] The above-described conditional expression (4) is an expression for defining the ratio of the focal length of the lens B, which is the most image side lens of the rear group, to the focal length of the optical system. By having a negative optical power on the most image side, a telescopic structure is easily obtained. However, if the optical power of the most image side lens is too strong, the expansion effect becomes large and aberration occurs. Therefore, in order to balance miniaturization and high performance, it is important to make the optical power of the most image side lens within an appropriate range of optical power. By satisfying the conditional expression (4), it is possible to balance miniaturization and high performance.

[0138] On the other hand, if the value of conditional expression (4) is lower than the lower limit value, the refractive power of the lens B closest to the image side is too small, and thus the refractive power arrangement of the telescope becomes weak. Therefore, it is difficult to achieve miniaturization, and thus it is not preferable.

[0139] In terms of obtaining the above-described effects, the upper limit value of the above-described conditional expression (4) is preferably -0.46, -0.48, -0.50, -0.52, -0.54, -0.56, -0.58, -0.60, -0.62, -0.64, -0.66, -0.68, in this order. In addition, the lower limit value of the above-described conditional expression (4) is preferably -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, -0.95, in this order.

[0140] 1-2-5. Conditional expression (5)

[0141] The optical system preferably satisfies the following conditional expression.

[0142] 25.00 < νdLA < 110.00 ··· (5)

[0143] wherein,

[0144] νdLA: Abbe number of the lens A at d line

[0145] The above-described conditional expression (5) is an expression for defining the Abbe number of the lens A closest to the object side of the front group having a positive refractive power. In the case where the conditional expression (5) is satisfied, the axial chromatic aberration of the optical system can be corrected, and thus it is easy to achieve high performance of the optical system.

[0146] On the other hand, if the value of conditional expression (5) is lower than the lower limit value, the dispersion is too large, and thus it is difficult to correct the axial chromatic aberration, and thus it is not preferable. In addition, if the value of conditional expression (5) is higher than the upper limit value, the dispersion becomes small, and thus it is preferable in terms of correcting chromatic aberration, but the glass having small dispersion is expensive, and thus it is not preferable in terms of reducing costs.

[0147] In terms of achieving the above effects, the upper limit value of the conditional expression (5) is preferably 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, 70.00, in this order. In addition, the lower limit value of the conditional expression (5) is preferably 26.00, 27.00, 28.00, 29.00, 30.00, 32.00, 35.00, 37.00, 40.00, in this order.

[0148] 1-2-6. Conditional expression (6)

[0149] The optical system preferably satisfies the following conditional expression.

[0150] 18.00 < νdLB < 52.00 ··· (6)

[0151] wherein,

[0152] νdLB: Abbe number of the lens B at the d line

[0153] The conditional expression (6) described above is an expression for defining the Abbe number of the lens B having a negative refractive power, which is the most object side of the rear group. In the case where the conditional expression (6) is satisfied, the magnification chromatic aberration of the optical system can be corrected, and the high performance of the optical system can be easily achieved.

[0154] In relation thereto, if the value of the conditional expression (6) is below the lower limit value, it is difficult to correct the magnification chromatic aberration of the short wavelength, and is not preferable. In addition, if the value of the conditional expression (6) is above the upper limit value, it is difficult to correct the magnification chromatic aberration of the long wavelength, and is not preferable.

[0155] In terms of achieving the above effects, the upper limit value of the conditional expression (6) is preferably 51.00, 50.00, 48.00, 47.00, 46.50, 46.00, 45.50, 45.00, 44.00, 43.00, 42.00, in this order. In addition, the lower limit value of the conditional expression (6) is preferably 18.20, 18.40, 18.80, 19.20, 19.80, 20.30, 20.80, 21.00, 21.20, 21.40, in this order.

[0156] 1-2-7. Conditional expression (7)

[0157] The optical system preferably satisfies the following conditional expression.

[0158] -1.18 < CRBf / f < -0.20 ··· (7)

[0159] wherein,

[0160] CRBf: radius of curvature of the object side surface of the lens B

[0161] f: focal length of the optical system

[0162] The above conditional expression (7) is an expression for defining the shape of the object side surface of the lens B on the most image side of the rear group. In the case where the ratio of the radius of curvature of the object side surface of the lens B on the most image side of the rear group to the focal length of the optical system satisfies the above conditional expression (7), correction of coma can be performed well, and an optical system with high imaging performance can be achieved. In addition, in the case where the lens unit having positive refractive power disposed on the most object side is a so-called complex aspheric lens to which an aspheric film is attached, CRBf is not the radius of curvature of the aspheric film, but is set to the radius of curvature of the base lens.

[0163] In contrast, if the value of conditional expression (7) is below the lower limit value, the radius of curvature of the object side surface of the lens B on the most image side becomes large, and the amount of correction of coma becomes small, and thus it is not preferable in terms of high performance. In addition, if the value of conditional expression (7) is above the upper limit value, the radius of curvature of the object side surface of the lens B on the most image side becomes small, and the amount of generation of coma becomes large, and thus it is not preferable in terms of high performance.

[0164] In terms of obtaining the above effects, the lower limit value of conditional expression (7) is preferably -1.16, -1.13, -1.10, -1.00, -0.95, -0.90, -0.85, -0.80, -0.75, -0.70, -0.65, -0.60, in this order. In addition, the upper limit value of the above conditional expression (7) is preferably -0.23, -0.26, -0.28, -0.30, -0.32, -0.34, -0.36, -0.38, -0.40, -0.42, in this order.

[0165] 1-2-8. Conditional expression (8)

[0166] The optical system preferably satisfies the following conditional expression.

[0167] f / EPD < 2.60 ··· (8)

[0168] wherein,

[0169] f: focal length of the optical system

[0170] EPD: entrance pupil diameter of the optical system

[0171] The above conditional expression (8) is an expression for defining the ratio of the entrance pupil diameter of the optical system to the focal length of the optical system. In the case where conditional expression (8) is satisfied, it is easy to achieve large-diameter of the optical system.

[0172] In this regard, if the value of the above conditional expression (8) is equal to or greater than the upper limit, the entrance pupil diameter becomes small with respect to the focal length of the optical system, and thus it is not preferable in terms of large aperture. In addition, although the lower limit value of the value of the conditional expression (8) is not specified, in the case of an excessively large entrance pupil diameter, the number of lens pieces increases in order to correct aberration. Thus, it is preferable in terms of cost that the lower limit value be equal to or greater than 0.80.

[0173] In terms of obtaining the above effects, the upper limit value of the conditional expression (8) is preferably 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, 1.68, in this order. In addition, the lower limit value of the above conditional expression (8) is preferably 0.85, 0.90, 0.94, 0.99, 1.05, 1.10, 1.18, 1.25, 1.30, 1.38, in this order.

[0174] 1-2-9. Conditional expression (9)

[0175] The optical system preferably satisfies the following conditional expression.

[0176] 0.65 < FLA / f < 3.80 ··· (9)

[0177] wherein,

[0178] FLA: focal length of the lens A

[0179] f: focal length of the optical system

[0180] The above conditional expression (9) is an expression for specifying the ratio of the focal length of the lens A, which is the most object side lens of the front group, to the focal length of the optical system. By having a positive optical power on the most object side, a telescopic structure is easily obtained. However, if the optical power of the lens group on the most object side is excessively strong, the converging action becomes large, and spherical aberration or field curvature is generated. Thus, in order to balance miniaturization and high performance, it is important to make the optical power of the lens on the most object side be within an appropriate range. By satisfying the conditional expression (9), it is possible to balance miniaturization and high performance.

[0181] In this regard, if the value of the conditional expression (9) is equal to or greater than the upper limit value, the optical power of the lens A on the most object side is excessively small, and thus the converging action becomes small. Thus, it is difficult to achieve miniaturization, and thus it is not preferable. In addition, if the value of the conditional expression (9) is less than the lower limit value, the optical power of the lens A on the most object side is excessively large, and thus the converging action becomes large. Thus, spherical aberration or field curvature is generated, and thus it is difficult to achieve high performance, and thus it is not preferable.

[0182] In terms of achieving the above effects, the upper limit value of the conditional expression (9) is preferably 3.70, 3.60, 3.50, 3.40, 3.30, in this order. In addition, the lower limit value of the conditional expression (9) is preferably 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, 1.40, in this order.

[0183] 1-2-10. Conditional expression (10)

[0184] The optical system preferably satisfies the following conditional expression.

[0185] -3.20 < (CRBf + CRBr) / (CRBf - CRBr) < -0.53... (10)

[0186] wherein,

[0187] CRBf: radius of curvature of the object side surface of the lens B

[0188] CRBr: radius of curvature of the image side surface of the lens B

[0189] The conditional expression (10) is an expression for defining the shape of the lens B disposed on the most image side. If the range of the conditional expression (10) is satisfied, the absolute value of the radius of curvature of the object side surface becomes small, the generation of coma is suppressed, and this is preferable in terms of high performance.

[0190] In contrast, if the value of the conditional expression (10) is equal to or more than the upper limit value, the negative refractive power of the image side surface becomes strong, and thus it is difficult to correct the coma, which is not preferable in terms of high performance. In addition, if the value of the conditional expression (10) is less than the lower limit value, the radius of curvature of the object side surface becomes large, and it is difficult to correct the coma. Furthermore, the negative refractive power of the lens B becomes weak, and thus it is difficult to achieve miniaturization in both the overall length direction and the radial direction, which is not preferable.

[0191] In terms of achieving the above effects, the upper limit value of the conditional expression (10) is -0.54, -0.55, -0.56, -0.58, -0.60, -0.62, -0.64, -0.66, -0.68, -0.70, in this order. In addition, the lower limit value of the conditional expression (10) is -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, -1.60, in this order.

[0192] 1-2-11. Conditional expression (11)

[0193] The optical system preferably satisfies the following conditional expression.

[0194] 1.42 < NdLA < 2.30 ··· (11)

[0195] wherein,

[0196] NdLA: refractive index of the lens A at the d line

[0197] The above conditional expression (11) is an expression for specifying the refractive index of the lens A at the d line of the most object side of the front group. By satisfying the conditional expression (11), the power of the lens A is appropriately made, and the amount of generation of spherical aberration becomes within an appropriate range.

[0198] In this regard, if the value of the conditional expression (11) is below the lower limit value, the refractive index becomes small, and the radius of curvature of the most object side surface becomes small. In this case, it is difficult to correct spherical aberration, and it is not preferable. In addition, if the value of the conditional expression (11) is above the upper limit value, the refractive index becomes large. The glass having a high refractive index is high in price, and thus a too high refractive index is not preferable in terms of cost reduction. In addition, the glass having a high refractive index is large in specific gravity, and thus it is also not preferable in terms of weight reduction.

[0199] In terms of obtaining the above effects, the lower limit value of the conditional expression (11) is preferably 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, 1.80, in this order. In addition, the upper limit value of the above conditional expression (11) is preferably 2.25, 2.20, 2.18, 2.17, 2.16, 2.15, 2.14, 2.13, 2.12, 2.11, 2.10, in this order.

[0200] 1-2-12. Conditional expression (12)

[0201] The optical system preferably satisfies the following conditional expression.

[0202] 0.10 < BF / f < 0.55 ··· (12)

[0203] wherein,

[0204] BF: air converted distance from the most image side lens surface of the rear group to the image surface

[0205] f: focal length of the optical system

[0206] The conditional expression (12) is an expression that defines the ratio of the value obtained by air conversion with respect to the distance on the optical axis from the most image-side surface of the optical system to the image surface to the focal length of the optical system. Between the most image-side surface of the optical system and the image surface, an optical element such as a low-pass filter or a protection glass needs to be disposed. Therefore, in order to achieve miniaturization and disposition of the optical element, it is important to make the rear portion of the optical system be within the optimum range. In the case where the conditional expression (12) is satisfied, the rear portion of the optical system is made to be within the optimum range, and thus miniaturization is easily achieved.

[0207] In contrast, if the value of the conditional expression (12) is equal to or greater than the upper limit, the optical total length of the optical system becomes large, and the weight including the mechanism becomes heavy. Thus, it is not preferable in terms of miniaturization and weight reduction. On the other hand, if the value of the conditional expression (12) is equal to or less than the lower limit, it is difficult to dispose an optical element such as a low-pass filter or a protection glass, and thus it is not preferable. In addition, the diameter of the lens B as the final lens becomes large, and thus it is not preferable.

[0208] In terms of achieving the above effects, the upper limit value of the conditional expression (12) is preferably 0.54, 0.52, 0.50, 0.48, 0.46, 0.45, 0.44, 0.43, 0.41, 0.39, 0.37, 0.35, 0.34, in this order. In addition, the lower limit value of the conditional expression (6) is preferably 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, in this order.

[0209] 1-2-13. Conditional expression (13)

[0210] The optical system preferably satisfies the following conditional expression.

[0211] 0.20 < CRsz / f < 25.00 ··· (13)

[0212] wherein,

[0213] CRsz: radius of curvature of the image-side surface of the diaphragm

[0214] f: focal length of the optical system

[0215] The conditional expression (13) is an expression that defines the ratio of the radius of curvature of the image-side surface of the diaphragm, that is, the radius of curvature of the most object-side surface of the rear group, to the focal length of the optical system. In the case where the conditional expression (13) is satisfied, the most object-side surface of the rear group has a convex surface on the object side, and the amount of aberration generation on the most object-side surface of the rear group can be made to be within an appropriate range. Thus, high performance is achieved. In addition, by the converging action of the most object-side surface of the rear group, miniaturization of the optical system is easily achieved.

[0216] In contrast, if the value of conditional expression (13) is below the lower limit value, the curvature radius of the most object side surface of the rear group is too small, and thus spherical aberration or coma is generated, and it is difficult to achieve high performance, and thus is not preferable. In addition, if the value of conditional expression (13) is above the upper limit value, the curvature radius of the most object side surface of the rear group is too large. Thus, the total track length becomes long, and thus is not preferable in terms of miniaturization. In addition, if the curvature radius of the most image side surface becomes large, harmful light reflected on the image surface easily enters the imaging surface again to generate ghosting. Thus, it is not preferable in terms of high performance.

[0217] In terms of achieving the above effects, the upper limit value of conditional expression (13) is preferably 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, 2.20, in this order. In addition, the lower limit value of conditional expression (13) is preferably 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, 0.60, in this order.

[0218] 1-2-14. Conditional expression (14)

[0219] The optical system preferably satisfies the following conditional expression.

[0220] 1.90 < |ff| / fR < 1000.00 ··· (14)

[0221] wherein,

[0222] ff: focal length of the front group

[0223] fR: focal length of the rear group

[0224] The above conditional expression (14) is an expression for defining the ratio of the focal length of the front group to the focal length of the rear group. In the case where conditional expression (14) is satisfied, the power configuration of the front group and the rear group is appropriate, and a large aperture and an appropriate number of lens configuration pieces can be achieved. That is, a large aperture and low cost can be easily balanced.

[0225] In contrast, if the value of conditional expression (14) is above the upper limit value, the power of the rear group is too strong, and thus if the number of lens configuration pieces of the rear group is not increased, it is difficult to correct aberration, and thus is not preferable in terms of balancing low cost and high performance. In addition, if the value of conditional expression (14) is below the lower limit, the power of the rear group is too weak, and thus is not preferable in terms of a large aperture.

[0226] In terms of obtaining the above-described effects, the upper limit value of the conditional expression (14) is preferably 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, 36.00, in this order. In addition, the lower limit value of the conditional expression (14) is preferably 1.95, 2.00, 2.05, 2.10, 2.15, 2.20, 2.25, 2.30, 2.40, 2.45, in this order.

[0227] 1-2-15. Conditional expression (15)

[0228] The optical system preferably satisfies the following conditional expression.

[0229] -0.89 < FLB / FLA < -0.20 ··· (15)

[0230] wherein,

[0231] FLA: focal length of the lens A

[0232] FLB: focal length of the lens B

[0233] The conditional expression (15) is an expression that defines the ratio of the focal length of the lens A to the focal length of the lens B. In the case where the conditional expression (15) is satisfied, a telephoto type power configuration is easily obtained, and thus the miniaturization of the optical system in the optical length direction can be achieved. However, excessive miniaturization makes it difficult to correct aberration and leads to deterioration of error sensitivity. Thus, there is an appropriate range for the ratio of the focal length of the lens A to the focal length of the lens B. Here, in the case where the conditional expression (15) is satisfied, an optical system that balances miniaturization and lightness with high performance can be achieved.

[0234] In contrast, if the value of the conditional expression (15) is equal to or greater than the upper limit, the ratio of the focal length of the lens B to the focal length of the lens A becomes large, and the telephoto type power configuration becomes weak. In this case, the optical length is excessively large with respect to the focal length, and the weight including the mechanical structure becomes heavy, and thus it is not preferable in terms of lightness. If the value of the conditional expression (15) is equal to or less than the lower limit, the ratio of the focal length of the lens B to the focal length of the lens A becomes small, and the magnification effect in the most image-side lens becomes large. In this case, the image-side aberration magnification effect of the optical system becomes large, and thus it is not preferable in terms of high performance.

[0235] In terms of achieving the above-described effects, the upper limit value of the conditional expression (15) is preferably -0.21, -0.22, -0.23, -0.24, -0.25, in this order. In addition, the lower limit value of the conditional expression (15) is preferably -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, -0.55, in this order.

[0236] 1-2-16. Conditional expression (16)

[0237] The optical system preferably satisfies the following conditional expression.

[0238] 0.30 < TLAS / TLSB < 0.92... (16)

[0239] wherein,

[0240] TLAS: distance from the object side surface of the lens A to the stop

[0241] TLSB: distance from the stop to the image side surface of the lens B

[0242] The conditional expression (16) is an expression for defining the ratio of the distance from the object side surface of the lens A to the stop to the distance from the stop to the image side surface of the lens B. In the case where the conditional expression (16) is satisfied, the position of the stop with respect to the lens A on the most object side and the lens B on the most image side is appropriate, and thus the miniaturization of the diameters of the lens A and the lens B is taken into account. Since the enlargement of the diameters of the lenses can be avoided, the volume of the lenses is reduced, and the weight of the lenses is reduced.

[0243] In this regard, if the value of the conditional expression (16) is equal to or greater than the upper limit, the position of the stop with respect to the lens A on the most object side and the lens B on the most image side is close to the lens B. Thus, the diameter of the lens A becomes large, and thus the volume of the lens A becomes large, and not only the weight but also the cost is increased, and thus it is not preferable in terms of weight reduction and cost reduction. If the value of the conditional expression (16) is equal to or less than the lower limit, the position of the stop with respect to the lens A on the most object side and the lens B on the most image side is close to the lens A. Thus, the diameter of the lens B becomes large, and thus the volume of the lens B becomes large, and not only the weight but also the cost is increased, and thus it is not preferable in terms of weight reduction and cost reduction.

[0244] In terms of obtaining the above-described effects, the upper limit value of the conditional expression (16) is preferably 0.91, 0.90, 0.89, 0.88, 0.87, 0.86, 0.85, 0.84, 0.83, 0.82, in this order. In addition, the lower limit value of the conditional expression (16) is preferably 0.31, 0.32, 0.33, 0.34, 0.35, 0.36, 0.37, in this order.

[0245] 1-2-17. Conditional expression (17)

[0246] The optical system preferably satisfies the following conditional expression.

[0247] -4.50 < CRBf / BF < -1.20 ··· (17)

[0248] wherein,

[0249] CRBf: radius of curvature of the object side surface of the lens B

[0250] BF: air converted distance from the most object side lens surface of the rear group to the image plane

[0251] The conditional expression (17) is an expression for defining the shape of the object side surface of the lens B on the most image side of the rear group. In the case where the ratio of the radius of curvature of the object side surface of the lens B on the most image side of the rear group to the air converted distance from the most object side lens surface of the rear group to the image plane satisfies the conditional expression (17), correction of coma can be performed well, and an optical system with high imaging performance can be achieved. In addition, in the case where the lens unit having a positive refractive power disposed on the most object side is a so-called complex aspheric lens to which an aspheric thin film is attached, CRBf is not the radius of curvature of the aspheric thin film, but is set to the radius of curvature of the base lens.

[0252] In contrast, if the value of the conditional expression (17) is lower than the lower limit value, the radius of curvature of the object side surface of the lens B on the most image side becomes large, and the amount of correction of coma becomes small, and thus it is not preferable in terms of high performance. In addition, if the value of the conditional expression (17) is higher than the upper limit value, the radius of curvature of the object side surface of the lens B on the most image side becomes small, and the amount of generation of coma becomes large, and thus it is not preferable in terms of high performance.

[0253] In terms of obtaining the above-described effects, the upper limit value of the conditional expression (17) is preferably -1.24, -1.26, -1.28, -1.30, -1.32, -1.34, -1.36, -1.38, -1.40, -1.42, -1.44, -1.46, in this order. In addition, the lower limit value of the conditional expression (17) is preferably -4.45, -4.40, -4.35, -4.30, -4.25, -4.20, -4.15, -4.10, -4.05, in this order.

[0254] 1-2-18. Condition formula (18)

[0255] The optical system preferably satisfies the following condition formula.

[0256] 0.30 < νdLA / νdLB < 3.00 ··· (18)

[0257] wherein,

[0258] νdLA: Abbe number of the lens A at d line

[0259] νdLB: Abbe number of the lens B at d line

[0260] The above condition formula (18) is a formula for defining the ratio of the Abbe number of the lens A at d line to the Abbe number of the lens B at d line. In the case where the condition formula (18) is satisfied, both the axial chromatic aberration and the magnification chromatic aberration are corrected, and high performance is achieved.

[0261] In relation thereto, if the value of the condition formula (18) is below the lower limit value, the Abbe number of the lens A at d line is too small, and thus it is difficult to correct the axial chromatic aberration, and it is not preferable in terms of high performance. In addition, if the value of the condition formula (18) is above the upper limit value, the Abbe number of the lens B at d line is too small, and thus it is difficult to correct the magnification chromatic aberration, and it is not preferable in terms of high performance.

[0262] In terms of obtaining the above effects, the upper limit value of the above condition formula (18) is preferably 2.90, 2.80, 2.70, 2.60, 2.50, 2.40, 2.30, 2.20, 2.10, 2.00, 1.90, 1.85, in this order. In addition, the lower limit value of the above condition formula (18) is preferably 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, 0.99, in this order.

[0263] 1-2-19. Condition formula (19)

[0264] The optical system preferably satisfies the following condition formula.

[0265] 1.00 < TTL / f < 3.50 ··· (19)

[0266] wherein,

[0267] TTL: distance from the most object side lens surface of the front group to the image surface

[0268] f: focal length of the optical system

[0269] The conditional expression (19) described above is an expression that defines the ratio of the total optical length of the optical system to the focal length. If the total optical length is reduced with respect to the focal length, it is difficult to correct aberration and causes deterioration of error sensitivity. In addition, if the total optical length is made excessively large with respect to the focal length, the weight including the mechanical structure becomes heavy, and thus there is an appropriate range for the ratio of the total length to the focal length. Here, in a case where the conditional expression (19) is satisfied, an optical system that balances miniaturization and lightness and high performance can be achieved.

[0270] In this regard, if the value of the conditional expression (19) described above is equal to or more than the upper limit value, the total optical length is made excessively large with respect to the focal length, the weight including the mechanical structure becomes heavy, and thus it is not preferable in terms of lightness. If the value of the conditional expression (19) described above is equal to or less than the lower limit value, the total optical length is made excessively small with respect to the focal length, a large number of lens pieces are required in order to correct aberration, and thus it is not preferable in terms of cost. Furthermore, it causes deterioration of manufacturability, and thus it is not preferable in terms of high performance.

[0271] In terms of obtaining the effects described above, the upper limit value of the conditional expression (19) is preferably 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, 2.00, in this order. In addition, the lower limit value of the conditional expression (19) is preferably 1.02, 1.04, 1.06, 1.08, 1.10, 1.12, 1.13, in this order.

[0272] 2. Imaging device and moving body

[0273] Next, an imaging device according to the present application will be described. The imaging device according to the present application is characterized by including the optical system according to the present application described above, and an imaging element that receives an optical image formed by the optical system and converts the optical image into an electric image signal.

[0274] Here, the imaging element and the like are not particularly limited, and a solid-state imaging element such as a CCD sensor (Charge Coupled Device), a CMOS sensor (Complementary Metal Oxide Semiconductor), or the like can be used. The imaging device according to the present application is suitable as a digital camera, a video camera, a surveillance camera, a vehicle-mounted camera, a camera for a drone, a medical camera, or the like, and these imaging devices that use a solid-state imaging element. In addition, the imaging device can be either a fixed-lens type imaging device in which a lens barrel is fixed to a housing, or a lens exchange type imaging device such as a single-lens reflex camera or a mirrorless single-lens camera. In particular, the optical system according to the present application is small, and thus is suitable for an imaging device that is mounted on a moving body such as a vehicle or a drone.

[0275] The imaging device and the moving body of the present application more preferably have an image processing section that electrically processes the imaging image data acquired by the imaging element to change the shape of the imaging image, or an image correction data holding section that holds image correction data, an image correction program, or the like used to process the imaging image data in the image processing section, and the like. In the case of miniaturizing the optical system, the imaging image shape imaged on the imaging surface is likely to be distorted (aberrated). At this time, it is preferable to have the image correction data holding section hold distortion correction data in advance for correcting the distortion of the imaging image shape, and use the distortion correction data held by the image correction data holding section in the image processing section to correct the distortion of the imaging image shape. According to such an imaging device, further miniaturization of the optical system is possible, a beautiful imaging image can be obtained, and miniaturization of the entire imaging device is possible.

[0276] The imaging device and the moving body of the present application preferably have the image correction data holding section hold magnification chromatic aberration correction data in advance, and use the magnification chromatic aberration correction data held by the image correction data holding section in the image processing section to perform magnification chromatic aberration correction of the imaging image. By having the image processing section correct the aberration of the color, i.e., the magnification chromatic aberration, the number of lens pieces constituting the optical system can be reduced. Therefore, according to such an imaging device, further miniaturization of the optical system is possible, a beautiful imaging image can be obtained, and miniaturization of the entire imaging device is possible.

[0277] Next, an embodiment is shown and the present application is specifically described. However, the present application is not limited to the following embodiment. In each lens sectional view, the left direction toward the drawing is the object side, and the right direction is the image side.

[0278] [Embodiment 1]

[0279] Figure 1 is a lens sectional view showing the configuration of the optical system of Embodiment 1 to which the present application pertains. The optical system is configured by, in order from the object side, a front group GF having a positive refractive power, a diaphragm, and a rear group GR having a positive refractive power.

[0280] The front group GF having a positive refractive power is configured by, in order from the object side, a positive meniscus lens L1 having a convex shape on the object side, a positive meniscus lens L2 having a convex shape on the object side, a positive meniscus lens L3 having a convex shape on the object side, and a negative meniscus lens L4 having a convex shape on the object side. Here, the positive meniscus lens L1 having a convex shape on the object side corresponds to the so-called lens A in the present application.

[0281] The rear group GR having positive refractive power is composed of a lenticular lens L5 having positive refractive power and both the object side surface and the image side surface are convex, and a negative meniscus lens L6 having a concave shape on the object side, in this order from the object side. Here, the negative meniscus lens L6 having a concave shape on the object side corresponds to the lens B in the present invention.

[0282] Further, "IMG" in the figure indicates an image plane. It is an image capturing plane of a solid-state image pickup element such as a CCD sensor, a CMOS sensor, or the like. Light incident from the object side of the optical system is imaged on the image plane. The solid-state image pickup element converts the received optical image into an electric image signal. A digital image corresponding to the image of the subject is generated based on the electric image signal output from the image pickup element by an image processing section (image processing processor, or the like) provided in the image pickup apparatus. The digital image can be recorded in a recording medium such as a hard disk device (HDD), a memory card, an optical disc, a magnetic tape, or the like, for example. Further, the image plane can be a film plane of a silver halide film.

[0283] In addition, "CG" in the figure indicates an image plane. It is an optical module. The optical module CG corresponds to a filter, a protection glass, a crystal low-pass filter, an infrared cut filter, or the like. These marks (IMG, CG) are the same in each of the drawings shown in other embodiments, and thus the explanation is omitted below.

[0284] [Embodiment 2]

[0285] Figure 3 is a lens sectional view showing the configuration of the optical system according to Embodiment 2 of the present invention. The optical system is composed of a front group GF having positive refractive power, a diaphragm, and a rear group GR having positive refractive power, in this order from the object side.

[0286] The front group GF having positive refractive power is composed of a positive meniscus lens LI having a convex shape on the object side, a positive meniscus lens L2 having a convex shape on the object side, and a biconcave lens L3 having negative refractive power and both the object side surface and the image side surface are concave, in this order from the object side. Here, the positive meniscus lens LI having a convex shape on the object side corresponds to the lens A in the present invention.

[0287] The rear group GR having positive refractive power is composed of a positive meniscus lens L4 having a convex shape on the object side, a biconcave lens L5 having negative refractive power and both the object side surface and the image side surface are concave, a lenticular lens L6 having positive refractive power and both the object side surface and the image side surface are convex, a joint lens composed of a negative meniscus lens L7 having a concave shape on the object side and a negative meniscus lens L8 having a concave shape on the object side, and the negative meniscus lens L8 having a concave shape on the object side, in this order from the object side. Here, the negative meniscus lens L8 having a concave shape on the object side corresponds to the lens B in the present invention.

[0288] Here, the double-concave lens L5 having a negative refractive power and having both the object side surface and the image side surface concave corresponds to a focus adjusting group which performs focusing from an infinite distance object to a finite distance object by moving toward the image side.

[0289] [Example 3]

[0290] Figure 5 is a lens sectional view showing the configuration of the optical system of Example 3 to which the present application is applied. The optical system is configured by, in order from the object side, a front group GF having a negative refractive power, a diaphragm, and a rear group GR having a positive refractive power.

[0291] The front group GF having a negative refractive power is configured by, in order from the object side, a positive meniscus lens LI having a convex object side surface, a positive meniscus lens L2 having a convex object side surface, and a double-concave lens L3 having a negative refractive power and having both the object side surface and the image side surface concave. Here, the positive meniscus lens LI having a convex object side surface corresponds to the so-called lens A in the present application.

[0292] The rear group GR having a positive refractive power is configured by, in order from the object side, a double-convex lens L4 having a positive refractive power and having both the object side surface and the image side surface convex, a cemented lens of a double-convex lens L5 having a positive refractive power and having both the object side surface and the image side surface convex and a negative meniscus lens L6 having a concave object side surface, and a double-concave lens L7 having a negative refractive power and having both the object side surface and the image side surface concave. Here, the double-concave lens L7 having a negative refractive power and having both the object side surface and the image side surface concave corresponds to the so-called lens B in the present application.

[0293] [Example 4]

[0294] Figure 7 is a lens sectional view showing the configuration of the optical system of Example 4 to which the present application is applied. The optical system is configured by, in order from the object side, a front group GF having a positive refractive power, a diaphragm, and a rear group GR having a positive refractive power.

[0295] The front group GF having a positive refractive power is configured by, in order from the object side, a double-convex lens LI having a positive refractive power and having both the object side surface and the image side surface convex, a positive meniscus lens L2 having a convex object side surface, and a double-concave lens L3 having a negative refractive power and having both the object side surface and the image side surface concave. Here, the double-convex lens LI having a positive refractive power and having both the object side surface and the image side surface convex corresponds to the so-called lens A in the present application.

[0296] The rear group GR having positive refractive power is composed of, in order from the object side, a lenticular lens L4 having positive refractive power and having both the object side surface and the image side surface in convex shape, a lenticular lens L5 having positive refractive power and having both the object side surface and the image side surface in convex shape, a cemented lens of a negative meniscus lens L6 having the object side in concave shape and a lenticular lens L7 having the object side in concave shape. Here, the negative meniscus lens L7 having the object side in concave shape corresponds to the so-called lens B in the present application.

[0297] [Embodiment 5]

[0298] Figure 9 is a lens sectional view showing the constitution of the optical system of Embodiment 5 to which the present application is applied. The optical system 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.

[0299] The front group GF having negative refractive power is composed of, in order from the object side, a positive meniscus lens Ll having the object side in convex shape, a positive meniscus lens L2 having the object side in convex shape, and a double concave lens L3 having negative refractive power and having both the object side surface and the image side surface in concave shape. Here, the positive meniscus lens Ll having the object side in convex shape corresponds to the so-called lens A in the present application.

[0300] The rear group GR having positive refractive power is composed of, in order from the object side, a lenticular lens L4 having positive refractive power and having both the object side surface and the image side surface in convex shape, a lenticular lens L5 having positive refractive power and having both the object side surface and the image side surface in convex shape, a cemented lens of a negative meniscus lens L6 having the object side in concave shape and a lenticular lens L7 having the object side in concave shape. Here, the negative meniscus lens L7 having the object side in concave shape corresponds to the so-called lens B in the present application.

[0301] A longitudinal aberration diagram at the time of focusing on infinity of the optical system is shown. The longitudinal aberration diagram is, in order from the left side when facing the drawing, the spherical aberration (mm), the coma (mm), the distortion aberration (%). In the graph showing the spherical aberration, the longitudinal axis shows the opening F value (Fno). The solid line shows the spherical aberration at the d line (wavelength 587.56 nm), the dotted line shows the spherical aberration at the C line (wavelength 656.27 nm), and the one-dot chain line shows the spherical aberration at the g line (wavelength 435.84 nm). In the graph showing the coma, the longitudinal axis shows the image height (mm). 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 graph showing the distortion aberration, the longitudinal axis is the image height (mm), and shows the distortion aberration (%) at the d line (wavelength 587.56 nm).

[0302] The following shows numerical examples 1 to 5 corresponding to examples 1 to 5, respectively. In the surface data of each numerical example, "surface No." indicates the number of the lens surface counted from the object side, "r" indicates the radius of curvature (mm) of the lens surface (where the value of r is 0.0000, the surface is a plane), "d" indicates the interval on the optical axis (mm) between the i-th (i is a natural number) lens surface from the object side and the (i+1)-th lens surface, "Nd" indicates the refractive index corresponding to the d-line (wavelength λ = 587.56 nm), "νd" indicates the Abbe number corresponding to the d-line, and "h" indicates the effective radius (mm).

[0303] Further, in each numerical example, the focal length (mm), the F value (Fno), the half field angle (°), the image height (mm), the total track length (mm), and the back focus (BF (in air)) (mm) of the imaging lens are shown. Here, the total track length is the distance on the optical axis from the object side surface of the 1st lens to the image plane. In addition, the back focus is a value obtained by air conversion of the distance on the optical axis from the image side surface of the n-th lens disposed closest to the image side to the image plane.

[0304] In the case where the optical surface is an aspheric surface, a mark * is added to the right side of the surface number. The aspheric shape and the aspheric coefficients can be expressed by the following aspheric equation, taking the displacement amount Z in the optical axis direction at a position having a height h with respect to the optical axis as the surface vertex reference.

[0305] Z = ch 2 / [1 + {1 - (1 + k)c 2 h 2} 1 / 2 ]+ A4h 4 + A6h 6 + A8h 8 + A10h 10 + ···

[0306] where c is the curvature (1 / r), h is the height with respect to the optical axis, k is the conic constant, A4, A6, A8, A10, ··· are the aspheric coefficients of each order. In addition, the mark "E±m" (m indicates an integer) in the numerical value of the aspheric coefficients and the conic constant means "×10±m".

[0307] Regarding the aperture stop, a mark S is added to the right side of the surface number.

[0308] Regarding the interval that changes in focusing, a mark d is added to the left side of the interval number. The interval data indicates the variable interval of the optical system.

[0309] In addition, the lens focal length indicates the focal length of each lens constituting the optical system.

[0310] Further, the lens group focal length indicates a focal length of each lens group constituting the optical system.

[0311] [Numeral Example 1]

[0312] Surface data

[0313] Face No. r d Nd Lens 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

[0314]

[0315]

[0316] Lens focal length

[0317] Face No. Focal length Group 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

[0318] Lens group focal length

[0319] Face No. Focal length GF GR 1-8 52.719 Focal length 10-13 14.974

[0320] [Numeral Example 2] Surface data

[0321]

[0322]

[0323] Aspherical surface data

[0324]

[0325]

[0326] F value 75.907 Half field angle 1.476 Image height 16.098 Overall length 21.630 BF 113.557 INF 21.268

[0327] Variable interval data

[0328] d0 Group 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

[0329] Lens focal length

[0330]

[0331]

[0332] Lens group focal length

[0333] Face No. Focal length GF GR 1-6 291.249 Focal length 8-17 60.239

[0334] [Numeral Example 3] Surface data

[0335]

[0336]

[0337] F value 15.393 Half field angle 1.624 Image height 17.000 Overall length 4.702 BF 27.856 Group 2.125

[0338] lens focal length

[0339]

[0340] lens group focal length

[0341] Face No. Focal length GF GR 1-6 -218.480 Focal length 8-14 10.836

[0342] [Numeral example 4] Surface data

[0343]

[0344]

[0345] F value 15.372 Half field angle 1.648 Image height 17.500 Overall length 4.847 BF 28.534 Lens 2.566

[0346] lens focal length

[0347] Face No. Focal length Group 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

[0348] lens group focal length

[0349] Face No. Focal length GF GR 1-6 388.055 Focal length 8-14 11.464

[0350] [Numeral example 5] Surface data

[0351]

[0352]

[0353] F value 15.400 Half field angle 1.600 Image height 17.500 Overall length 4.856 BF 29.499 Group 4.785

[0354] lens focal length

[0355]

[0356] lens group focal length

[0357] Face No. Focal length GF GR 1-6 -18.815 ​ 8-14 7.619

[0358] In the following Table 1, the corresponding values of the conditional expressions (1) to (19) in Examples 1 to 5 and each numeral are described.

[0359] [Table 1]

[0360]

[0361]

[0362]

[0363]

[0364]

[0365]

[0366] The above describes preferred embodiments of the present application, but the present application is not limited to these embodiments, and various modifications and changes can be made within the scope of the gist thereof.

[0367] Further, as another application of the present application, the following application can be conceived. In order to solve the above problem, an optical system according to the present application is composed of, in order from the object side, a front group, a stop, and a rear group, has a lens A with positive refractive power on the most object- side of the front group, has a lens B with negative refractive power on the most image- side of the rear group, has a concave surface on the object side of the object side surface of the lens B, and satisfies the following conditional expression.

[0368] 1.59 < NdLB < 2.30...(1)

[0369] 0.10 < BF / f < 0.55...(12)

[0370] wherein,

[0371] NdLB: refractive index of the lens B at the d line

[0372] BF: air converted distance from the lens surface on the most image- side of the rear group to the image plane

[0373] f: focal length of the optical system

[0374] Further, as another application of the present application, the following application can be conceived. In order to solve the above problem, an optical system according to the present application is composed of, in order from the object side, a front group, a stop, and a rear group, has a lens A with positive refractive power on the most object- side of the front group, has a lens B with negative refractive power on the most image- side of the rear group, has a concave surface on the object side of the object side surface of the lens B, and satisfies the following conditional expression.

[0375] 1.59 < NdLB < 2.30...(1)

[0376] 1.00 < TTL / f < 3.50...(19)

[0377] wherein,

[0378] NdLB: refractive index of the lens B at the d line

[0379] TTL: distance from the lens surface on the most object- side of the front group to the image plane

[0380] f: focal length of the optical system

[0381] Industrial applicability

[0382] According to the present application, a small and high-performance optical system, an imaging device, and a moving body can be provided.

Claims

1. An optical system composed of, in order from the object side, a front group, a stop, and a rear group, provided with a lens A having a positive refractive power on the most object side of the front group, and provided with a lens B having a negative refractive power on the most image side of the rear group, the object side surface of the lens B having a concave surface on the object side, the optical system satisfying the following conditional expressions: 1.59 < NdLB < 2.30 ••• (1) 0.20 < fR / f < 0.90 ••• (3-2) 25.00 < vdLA < 110.00 ••• (5) 0.18 < BF / f < 0.45 ••• (12-1) -0.89 < FLB / FLA < -0.20 ••• (15) wherein, NdLB: the refractive index of the lens B at the d line fR: the focal length of the rear group f: the focal length of the optical system vdLA: the Abbe number of the lens A at the d line BF: the air converted distance from the lens surface on the most image side of the rear group to the image surface f: the focal length of the optical system FLA: the focal length of the lens A FLB: the focal length of the lens B.

2. An optical system composed of, in order from the object side, a front group, a stop, and a rear group, provided with a lens A having a positive refractive power on the most object side of the front group, and provided with a lens B having a negative refractive power on the most image side of the rear group, the object side surface of the lens B having a concave surface on the object side, the optical system satisfying the following conditional expressions: 1.63 < NdLB < 2.30 ••• (1-1) 0.20 < fR / f < 0.90 ••• (3-2) -0.83 < FLB / FLA < -0.20 ••• (15-1) 0.20 < CRsz / f < 25.00 ••• (13) wherein, NdLB: the refractive index of the lens B at the d line fR: the focal length of the rear group f: the focal length of the optical system FLA: the focal length of the lens A FLB: the focal length of the lens B CRsz: the radius of curvature of the lens surface on the image side of the stop.

3. The optical system of claim 1, wherein, The following conditional expression is satisfied: 0.20 < CRsz / f < 25.00 ••• (13) wherein, CRsz: the radius of curvature of the surface on the image side of the stop.

4. The optical system of claim 2, wherein, The following conditional expression is satisfied: 25.00 < vdLA < 110.00 ••• (5) wherein, vdLA: the Abbe number of the lens A at the d line.

5. The optical system of claim 2, wherein, The following conditional expression is satisfied: 0.10 < BF / f < 0.55 ••• (12) wherein, BF: the air converted distance from the lens surface on the most image side of the rear group to the image surface.

6. The optical system of claim 1 or 2, wherein The following conditional expression is satisfied: 1.60 < TLSB / BF < 10.00 ••• (2) wherein, TLSB: the distance from the stop to the image side surface of the lens B BF: the air converted distance from the lens surface on the most image side of the rear group to the image surface.

7. The optical system of claim 1 or 2, wherein The following conditional expression is satisfied: -1.85 < FLB / f < -0.45 ••• (4) wherein, FLB: the focal length of the lens B.

8. The optical system of claim 1 or 2, wherein, The following conditional expression is satisfied: 18.00 < vdLB < 52.00 ••• (6) wherein, νdLB: Abbe number of the lens B at the d line.

9. The optical system of claim 1 or 2, wherein, The following conditional expression is satisfied: -1.18 < CRBf / f < -0.20 ··· (7) where, CRBf: radius of curvature of the object side surface of the lens B.

10. The optical system of claim 1 or 2, wherein, The following conditional expression is satisfied: f / EPD < 2.60 ··· (8) where, EPD: entrance pupil diameter of the optical system.

11. The optical system of claim 1 or 2, wherein, The following conditional expression is satisfied: 0.65 < FLA / f < 3.80 ··· (9) where, FLA: focal length of the lens A.

12. The optical system of claim 1 or 2, wherein, The following conditional expression is satisfied: -3.20 < (CRBf + CRBr) / (CRBf - CRBr) < -0.53 ··· (10) where, 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.

13. The optical system of claim 1 or 2, wherein, The following conditional expression is satisfied: 1.42 < NdLA < 2.30 ··· (11) where, NdLA: refractive index of the lens A at the d line.

14. The optical system of claim 1 or 2, wherein, The following conditional expression is satisfied: 1.90 < |ff| / fR < 1000.00 ··· (14) where, ff: focal length of the front group fR: focal length of the rear group.

15. The optical system of claim 1 or 2, wherein, The following conditional expression is satisfied: 0.30 < TLAS / TLSB < 0.92 ··· (16) where, TLAS: distance from the object side surface of the lens A to the stop TLSB: distance from the stop to the image side surface of the lens B.

16. The optical system of claim 1, wherein, The following conditional expression is satisfied: -4.50 < CRBf / BF < -1.20 ··· (17) where, CRBf: radius of curvature of the object side surface of the lens B BF: air converted distance from the most image side lens surface of the rear group to the image surface.

17. The optical system of claim 1 or 2, wherein, The following conditional expression is satisfied: 0.30 < νdLA / νdLB < 3.00 ··· (18) where, νdLA: Abbe number of the lens A at the d line νdLB: Abbe number of the lens B at the d line.

18. The optical system of claim 1 or 2, wherein, The following conditional expression is satisfied: 1.00 < TTL / f < 3.50 ··· (19) where, TTL: distance from the most object side lens surface of the front group to the image surface.

19. An imaging device characterized by comprising: on the image side of the optical system according to claim 1 or 2, an imaging element that converts an optical image formed by the optical system into an electric signal.

20. A mobile body characterized by comprising: comprising the imaging device according to claim 19.

Images