Optical systems, optical modules and imaging devices

Abstract

An optical system (2, 102, 202, 302), an optical module, and an imaging device (1, 101, 201, 301) capable of reducing thickness include a first lens group (21, 121, 221, 321) and a second lens group (22, 122, 222, 322). The second lens group (22, 122, 222, 322) is arranged closer to the image side than the first lens group (21, 121, 221, 321). When adjusting the focus, the second lens group (22, 122, 222, 322) moves along the optical axis while the first lens group (21, 121, 221, 321) is fixed. Assuming the focal length of the second lens group (22, 122, 222, 322) is "f2", the overall focal length of the combination including the first lens group (21, 121, 221, 321) and the second lens group (22, 122, 222, 322) is "f", and the focus movement amount of the second lens group (22, 122, 222, 322) from an object distance of 20 cm to an object distance of 3 cm is "Fd" (mm), the optical system (2, 102, 202, 302) satisfies "0.8 < f2 / f < 1.3" and "0.2 < Fd < 0.9".

Description

Technical Field

[0001] The present disclosure relates to an optical system, an optical module, and an imaging device. Background Art

[0002] An imaging device including an optical system and an image sensor can form a clear object image on the imaging surface of the image sensor through the optical system, and can obtain a good image signal of the object by adjusting the focus of the optical system. Summary of the Invention

[0003] [Problems to be Solved by the Invention]

[0004] An imaging device can adopt a method of adjusting the focus of the optical system by moving the entire optical system along the optical axis of the optical system. In this case, if the size of the image sensor increases with the demand for a higher number of pixels, the amount of focus movement of the optical system increases, and correspondingly, the thickness of the optical system also increases. If the thickness of the optical system increases, it is difficult to meet the required thickness of the optical system when the optical system is mounted on a thin imaging device.

[0005] The present disclosure is proposed in view of the above problems, and an object of the present disclosure is to provide an optical system, an optical module, and an imaging device capable of reducing the thickness.

[0006] [Means for Solving the Problems]

[0007] To solve the above problems and achieve the object of the present disclosure, according to one aspect of the present disclosure, an optical system includes a first lens group and a second lens group. The second lens group is arranged closer to the image side than the first lens group. When adjusting the focus, the second lens group can move along the optical axis while the first lens group is fixed. Assuming that the focal length of the second lens group is "f2", the overall focal length of the optical system including the first lens group and the second lens group is "f", and the amount of focus movement of the second lens group from an object distance of 20 cm to an object distance of 3 cm is "Fd" (mm), the optical system satisfies "0.8 < f2 / f < 1.3" and "0.2 < Fd < 0.9".

[0008] [Effects of the Invention]

[0009] According to one aspect of the present invention, the thickness of the optical system can be reduced. Brief Description of the Drawings

[0010] Figure 1 is a block diagram showing the configuration of an imaging device including an optical system according to a first embodiment;

[0011] Figure 2 is a schematic diagram showing a focus adjustment operation in the first embodiment;

[0012] Figure 3 is a lens configuration diagram of an optical system according to a first embodiment;

[0013] Figure 4 is a schematic diagram showing paraxial data of a lens configuration of an optical system according to a first embodiment;

[0014] Figure 5 is a schematic diagram showing an aspherical shape of a lens of an optical system according to a first embodiment;

[0015] Figure 6 is a schematic diagram showing aberration characteristics of the optical system according to the first embodiment;

[0016] Figure 7 is a lens configuration diagram of an optical system according to a second embodiment;

[0017] Figure 8 is a schematic diagram showing paraxial data of a lens configuration of an optical system according to a second embodiment;

[0018] Fig. 9 is a schematic diagram showing an aspherical shape of a lens of an optical system according to a second embodiment;

[0019] Fig.10 is a schematic diagram showing aberration characteristics of an optical system according to a second embodiment;

[0020] Fig.11 is a lens configuration diagram of an optical system according to a third embodiment;

[0021] Fig.12 is a schematic diagram showing paraxial data of a lens configuration of an optical system according to a third embodiment;

[0022] Fig.13 is a schematic diagram showing an aspherical shape of a lens of an optical system according to a third embodiment;

[0023] Fig.14 is a schematic diagram showing aberration characteristics of an optical system according to a third embodiment;

[0024] Fig.15 is a lens configuration diagram of an optical system according to a fourth embodiment;

[0025] Fig.16 is a schematic diagram showing paraxial data of a lens configuration of an optical system according to a fourth embodiment;

[0026] Fig.17 is a schematic diagram showing an aspherical shape of a lens of an optical system according to a fourth embodiment; and

[0027] Fig.18: is a schematic diagram showing aberration characteristics of an optical system according to a fourth embodiment. DETAILED DESCRIPTION

[0028] Hereinafter, an optical system according to an embodiment will be described in detail with reference to the accompanying drawings. It should be noted that the present invention is not limited to these embodiments.

[0029] First embodiment

[0030] The optical system according to the first embodiment is mounted on, for example, a thin imaging device and is designed to reduce its thickness. Figure 1 As shown, the optical system 2 is mounted on the imaging device 1 . Figure 1 is a block diagram showing the configuration of an imaging device 1 including an optical system 2. The imaging device 1 may be a portable electronic device suitable for using a thin imaging device. The portable electronic device may be, for example, a smart phone, a tablet computer, a video camera, or a still camera. Alternatively, the imaging device 1 may be a fixed electronic device to which a thin imaging device may be applied. The fixed electronic device may be a vehicle-mounted camera, a surveillance camera, or the like.

[0031] The imaging device 1 includes an optical module 6, an actuator 4 and a controller 5. The optical module 6 includes an optical system 2 and an image sensor 3. The optical system 2 is arranged on the optical axis PA of the image sensor 3 to form an object image on the imaging surface of the image sensor 3. The optical system 2 includes a lens group 21 and a lens group 22. The lens group 21 and the lens group 22 are arranged in sequence along the optical axis PA of the image sensor 3 and intersect with the optical axis PA. The lens group 21 is arranged on the optical axis PA to be closer to the object side than the lens group 22, and is also referred to as the front group. The lens group 22 is arranged on the optical axis PA to be closer to the image side than the lens group 21, and is also referred to as the rear group. The lens group 22 is configured to be movable along the optical axis PA.

[0032] The lens group 21 may have negative refractive power. The lens group 22 may have positive refractive power. Therefore, while correcting aberrations using the lens group 21 and the lens group 22, light can be effectively concentrated on the imaging surface of the image sensor 3, thereby shortening the total track length of the optical system 2.

[0033] The imaging device 1 may be configured to be able to implement an auto focus (AF) function. In the AF function, the controller 5 adjusts the focus of the optical system 2 through the actuator 4. The imaging device 1 can form a clear object image on the imaging surface of the image sensor 3 through the optical system 2, and can obtain an appropriate image signal of the object by adjusting the focus of the optical system 2.

[0034] When viewed from the direction of the optical axis PA (Z direction), the image sensor 3 is configured to be substantially rectangular, and the maximum image height of the imaging surface is approximately half the length of the diagonal line of the imaging surface. Assuming that the focal length of the optical system 2 is "f" and the viewing angle of the optical system 2 is "2θ", the maximum image height "y" of the imaging surface is expressed by the following expression (1).

[0035] y = ftanθ (1)

[0036] The imaging device 1 may adopt a method (whole system focusing method) of adjusting the focus of the optical system 2 by moving the entire optical system 2 along the optical axis PA. In the whole system focusing method, since all lenses in the optical system 2 move together along the optical axis direction when adjusting the focus, the ratio of the focus movement amount to the focal length f of the entire system tends to become large.

[0037] For example, to meet the demand for a higher number of pixels, the size of the image sensor 3 is increased, and the maximum image height y of the imaging surface is increased, so the optical system 2 is also enlarged in a similar manner. In this case, the focal length f of the entire system is increased to achieve a similar viewing angle 2θ in the optical system 2. When the focal length f of the entire system is increased, the amount of focus movement of the optical system 2 during focusing is also increased. When the amount of focus movement during focusing is increased, the thickness of the optical system 2 is increased to ensure a space in which the focus movement can be performed. If the thickness of the optical system 2 is increased, it is difficult to meet the thickness required for the optical system 2 when the optical system 2 is mounted on the thin imaging device 1.

[0038] Therefore, in the imaging device 1, in response to the increase of the maximum image height y of the imaging surface, the optical system 2 can be configured in a post-focusing manner. In the post-focusing manner, as shown in FIG. Figure 2 As shown, since the lens group 22 moves along the optical axis PA while the lens group 21 is fixed when adjusting the focus, the ratio of the focus movement amount to the focal length f of the entire system can be suppressed to a small value. Figure 2 2 is a schematic diagram showing a focus adjustment operation. Hereinafter, a direction along the optical axis PA is referred to as a Z direction, and two directions orthogonal to each other in a plane perpendicular to the Z direction are referred to as an X direction and a Y direction.

[0039] The lens group 21 includes a plurality of lenses 21a and a lens barrel 21b. The plurality of lenses 21a are arranged in sequence along the optical axis PA. The lens barrel 21b is a generally cylindrical component that fixes the plurality of lenses 21a from the outside in the XY directions. The lens group 22 includes a plurality of lenses 22a and a lens barrel 22b. The plurality of lenses 22a are arranged in sequence along the optical axis PA. The lens barrel 22b is a generally cylindrical component that fixes the plurality of lenses 22a from the outside in the XY directions. The actuator 4 is arranged near the lens barrel 21b and can operate the lens barrel 21b in the Z direction according to the control of the controller 5.

[0040] It should be noted that in Figure 2 , for simplicity, the lens 21a included in the lens group 21 and the lens 22a included in the lens group 22 are shown as having similar cross-sectional shapes, but the lens 21a and the lens 22a may have different cross-sectional shapes. The lens group 21 may be configured to have a negative refractive power. The lens group 22 may be configured to have a positive refractive power. In addition, the lens group 21 may include at least one lens 21a having a negative refractive power and at least one lens 21a having a positive refractive power, and the lens group 22 may include at least one lens 22a having a negative refractive power. The number of lenses 21a included in the lens group 21 may be different from the number of lenses 22a included in the lens group 22. The number of lenses 22a included in the lens group 22 may be greater than the number of lenses 21a included in the lens group 21.

[0041] The image sensor 3 has a plurality of pixels that can be arranged on its imaging surface along the XY direction. When the imaging device 1 uses the image plane phase difference detection method to adjust the focus, the plurality of pixels of the image sensor 3 may include imaging pixels and a plurality of pixels for focus detection. The controller 5 obtains the signals of the plurality of pixels for focus detection, and determines the focus position of the optical system 2 by the image plane phase difference detection method based on the phase difference between the plurality of pixel signals. According to the determined focus position, in a state where the lens group 21 is fixed, the controller 5 moves the plurality of lenses included in the lens group 22 as a whole along the direction of the optical axis PA to adjust the focus.

[0042] Assuming that the focal length of the lens group 22 is “f2” and the focal length of the entire system including the lens group 21 and the lens group 22 is “f”, the optical system 2 is configured to satisfy the following expression (2).

[0043] 0.8 < f2 / f < 1.3 (2)

[0044] As shown in expression (2), the optical system 2 is configured so that the focal length f2 of the lens group 22 is in a similar range to the focal length f of the entire system. When f2 / f is 0.8 or less, the focal length f2 of the lens group 22 becomes too small, so it is difficult to perform high-precision focusing by driving the actuator 4. If f2 / f is 1.3 or more, the focus movement amount becomes too large, so it is difficult to reduce the thickness of the optical system 2. By satisfying expression (2), the focus adjustment of the lens group 22 can achieve an operation similar to the focus adjustment of the entire system while reducing the thickness of the optical system 2.

[0045] The focus movement amount Fd (mm) of the lens group 22 is represented by the focus movement amount of the lens group 22 from the object distance OD1 to the object distance OD2. The object distance OD1 corresponds to the distance to a relatively far object assumed in actual use of the imaging device 1. The object distance OD2 corresponds to the distance to a relatively near object assumed in actual use of the imaging device 1. Figure 2 (a) shows the focusing position of the lens group 22 when the object distance OD1 is 20 cm. Figure 2 (b) in FIG. 1 shows the focus position of the lens group 22 when the object distance OD2 is 3 cm. At this time, the focus movement amount Fd of the lens group 22 from the object distance OD1 to the object distance OD2 is as follows: Figure 2 The optical system 2 is configured so that the focus movement amount Fd of the lens group 22 satisfies the following expression (3).

[0046] 0.2 < Fd < 0.9 (3)

[0047] As shown in expression (3), the focus movement amount Fd of the lens group 22 is a movement amount suitable for the small actuator 4, which can be packaged in the main body of the thin imaging device 1. When the focus movement amount Fd is 0.2 mm or less, it is difficult to perform high-precision focusing by driving the actuator 4. When the focus movement amount Fd is 0.9 mm or more, it is difficult to reduce the thickness of the optical system 2 in order to ensure a larger space for focus movement. By satisfying expression (3), the focus adjustment of the lens group 22 can be achieved by utilizing the focus movement amount Fd that can be achieved by the small actuator 4. Therefore, it is easy to compact the space required for focus movement and reduce the thickness of the optical system 2.

[0048] Assuming that the distance on the optical axis from the object-side surface of the lens 21 a closest to the object side in the lens group 21 to the image plane is “Σd”, the optical system 2 is configured to satisfy the following expression (4).

[0049] Σd / f < 4.5 (4)

[0050] According to expression (4), even if the focal length f of the entire system increases, the increase in the total lens length of the optical system 2 relative to the focal length f can be suppressed. If Σd / f reaches 4.5 or more, the total lens length of the optical system 2 increases significantly as the focal length f of the entire system increases, making it difficult to reduce the thickness of the optical system 2. By satisfying expression (4), the thickness of the optical system 2 can be reduced.

[0051] Assuming that the focal length of the lens group 21 is “f1”, the optical system 2 is configured to satisfy the following expression (5).

[0052] -6.0 < f1 / f2 < -1.0 (5)

[0053] As shown in expression (5), the refractive power of lens group 21 and the refractive power of lens group 22 can be balanced within an appropriate range while suppressing the focal length f2 of lens group 22. If f1 / f2 is less than or equal to -6.0, the negative refractive power of lens group 21 is too strong, so it is difficult to correct various aberrations with lens group 22. If f1 / f2 is greater than or equal to -1.0, the positive refractive power of lens group 22 is too strong, so it is difficult to correct various aberrations with lens group 21. By satisfying expression (5), the thickness of optical system 2 can be reduced and the performance degradation of optical system 2 can be suppressed.

[0054] Assume that the radius of curvature at the center of the object side surface of the lens 21a closest to the object side in the lens group 21 is "r 11 ", and the radius of curvature at the center of the image side surface of the lens 21a closest to the object side in the lens group 21 is "r 12 ", the optical system 2 is configured to satisfy the following expression (6).

[0055] 0.5 < (r 11 +r 12 ) / (r 11 -r 12 ) < 3.0 (6)

[0056] As shown in Expression (6), the lens 21a closest to the object side in the lens group 21 may have an appropriate shape. 11 +r 12 ) / (r 11 -r 12 )” is less than or equal to 0.5, it is difficult to reduce the thickness of the optical system 2 because the principal point is close to the image plane. 11 +r 12 ) / (r 11 -r 12)" is greater than or equal to 3.0, it is difficult to correct the aberration in the lens group 21. By satisfying expression (6), the lens 21a closest to the object side in the lens group 21 can have an appropriate shape, the thickness of the optical system 2 can be reduced, and the performance degradation of the optical system 2 can be suppressed.

[0057] The optical system 2 satisfying Expression (2) to Expression (6) may be configured as follows: Figures 3 to 5 shown. Figure 3 2 is a lens configuration diagram of the optical system 2 , and shows a YZ cross-sectional shape of the optical system 2 including the optical axis PA. Figure 4 2 is a schematic diagram showing paraxial data of the lens configuration of the optical system 2 . Figure 5 Schematic diagram showing the aspherical shape of the lens of the optical system 2 .

[0058] Figure 3 The example shows a configuration in which the lens group 21 has two lenses and the lens group 22 has five lenses.

[0059] The lens group 21 includes lens L1, lens L2, and lens stop D1 in order from the object side to the image side. The lens group 22 includes lens L3, lens L4, lens L5, lens L6, lens L7, and filter FL in order from the object side to the image side. The filter FL can perform a filtering process of selectively cutting off light in the infrared (IR) light wavelength region.

[0060] Lenses L1 and L2 in lens group 21 and lenses L3 to L7 in lens group 22 have different cross-sectional shapes containing optical axis PA. Lens group 21 is configured to have negative refractive power. Lens group 22 is configured to have positive refractive power. Lenses L1 to L7 can be made of translucent materials, or can be made of, for example, glass, quartz, translucent plastic or a combination thereof. Lens stop D1 can be made of a light-shielding material, or can be made of any material whose surface is coated with a color suitable for light-shielding (e.g., black).

[0061] In the lens group 21, the effective diameter of the light flux of the image side lens is smaller than the effective diameter of the light flux of the object side lens. For example, the effective diameter of the light flux of the image side lens L2 is smaller than the effective diameter of the light flux of the object side lens L1. In the lens group 22, the effective diameter of the light flux of the image side lens is larger than the effective diameter of the light flux of the object side lens. For example, the effective diameter of the light flux of the image side lens L7 is larger than the effective diameter of the light flux of the object side lens L3.

[0062] The luminous flux effective diameter of the lens L3 closest to the object side in the lens group 22 is smaller than the luminous flux effective diameter of the lens L2 closest to the image side in the lens group 21. The luminous flux effective diameter of the smallest lens L3 in the lens group 22 is smaller than the luminous flux effective diameter of the smallest lens L2 in the lens group 21.

[0063] The lens group 21 may include a meniscus lens or a concave lens located on the object side. The lens group 22 may include a convex lens located on the object side. Figure 3 In the example of FIG. 1 , the object-side lens L1 of the lens group 21 is a concave lens, and the object-side lens L3 of the lens group 22 is a convex lens.

[0064] The lens group 21 may include at least one lens having a negative refractive power and at least one lens having a positive refractive power. The lens having a negative refractive power may be located at a position closest to the object side in the lens group 21. The lens group 22 may include at least one lens having a negative refractive power. The lens having a negative refractive power may be located at a position closest to the image side in the lens group 22. Figure 3 In the example of FIG. 1 , the lens L1 closest to the object side in the lens group 21 has a negative refractive power, and the lens L2 has a positive refractive power. The lens L7 closest to the image side in the lens group 22 has a negative refractive power.

[0065] Figure 4 (a) in FIG. 2 shows that the optical system 2 satisfies all the conditions of Expression (2) to Expression (6). In other words, Figure 4 In (a), by being configured to satisfy all the conditions of expressions (2) to (6), the optical system 2 can set the total lens length (length in the Z direction) to approximately 7.635 mm, can reduce the effective F number to approximately Fno=2.662, and can ensure that the viewing angle is approximately 2θ=87.599[°].

[0066] Figure 4 (b) in FIG. 1 shows the refractive power of lenses L1 to L7 . Figure 4 (b) shows a configuration in which lenses L1, L4 and L7 have negative refractive power, and lenses L2, L3, L5 and L6 have positive refractive power.

[0067] exist Figure 4 (c) Figure 5 (a) and Figure 5 In (b), the surface numbers are assigned as follows:

[0068] Surface number: L1R1: incident surface of lens L1;

[0069] Surface number: L1R2: exit surface of lens L1;

[0070] Surface number: L2R1: incident surface of lens L2;

[0071] Surface number: L2R2: exit surface of lens L2;

[0072] Surface number: L3R1: incident surface of lens L3;

[0073] Surface number: L3R2: exit surface of lens L3;

[0074] Surface number: L4R1: incident surface of lens L4;

[0075] Surface number: L4R2: exit surface of lens L4;

[0076] Surface number: L5R1: incident surface of lens L5;

[0077] Surface number: L5R2: exit surface of lens L5;

[0078] Surface number: L6R1: incident surface of lens L6;

[0079] Surface number: L6R2: exit surface of lens L6;

[0080] Surface numbers: L7R1: incident surface of lens L7; and

[0081] Surface number: L7R2: exit surface of lens L7.

[0082] Figure 4 (c) in FIG. 2 shows the radius of curvature R [mm], the surface distance D [mm], the refractive index Nd and the Abbe number νd for each surface numbered L1R1 to L7R2. The lens configuration is shown with the radius of curvature R. From the image side, the lens group 21 is composed of a concave lens L1 and a positive meniscus lens L2 with the convex surface facing the object side in the paraxial region. The lens group 22 is composed of a convex lens L3, a double concave negative lens L4, a positive meniscus lens L5 with the convex surface facing the object side, a positive meniscus lens L6 with the convex surface facing the image side, and a negative meniscus lens L7 with the convex surface facing the object side. By making the lenses L1 to L7 have different refractive indices Nd and Abbe numbers νd, chromatic aberration can be better corrected.

[0083] Figure 5 (a) and Figure 5 (b) in FIG. 1 shows the aspherical shape of each surface numbered L1R1 to L7R2. Assuming that the Z position (position in the direction of the optical axis PA) is "z", the paraxial curvature (=1 / R, R: radius of curvature) is "C", the XY distance from the optical axis PA is "h", the cone constant is "K", and the n-order aspherical coefficient is "An" (n=3, 4, ..., 20), the aspherical shape is represented by the following expression (7).

[0084]

[0085] Figure 5 (a) and Figure 5 (b) in FIG. 1 shows the aspheric coefficients A3, A4, ..., A19, and A20 of each of the surfaces with surface numbers L1R1 to L7R2. Figure 5 (a) and Figure 5 Substituting the aspheric coefficients A3 to A20 in (b) into expression (7), and rotating the curve represented by the obtained expression about the optical axis PA, each of the surfaces numbered L1R1 to L7R2 is obtained. Figure 5 (a) and Figure 5 In (b), "Ei" is an exponential notation with base 10. Here, "i" is an integer. By making each surface numbered L1R1 to L7R2 as Figure 5 (a) and Figure 5 The aspherical surface shown in (b) can better correct spherical aberration.

[0086] according to Figures 3 to 5 The optical system 2 configured as shown shows Figure 6 Aberration characteristics shown. Figure 6 Schematic diagram showing aberration characteristics of the optical system 2 .

[0087] Figure 6 (a) in FIG. 1 shows an aberration diagram of spherical aberration relative to the imaging surface (ideal image plane) of the image sensor 3. Here, the vertical axis represents the eye image height, and the horizontal axis represents the focus position. On the horizontal axis, the ideal focus position is represented by 0 [mm], and the deviation of the focus position from the ideal focus position represents the aberration amount. Figure 6 In the aberration diagram of the optical system 2 shown in (a), the aberration amount of the c line (wavelength: 656.28nm) is represented by a dotted line, the aberration amount of the d line (wavelength: 587.56nm) is represented by a solid line, and the aberration amount of the g line (wavelength: 435.84nm) is represented by a dotted line. Figure 6 (a) in FIG. 1 shows a case where the spherical aberration is suppressed within the allowable range.

[0088] Figure 6 (b) in FIG. 1 shows an aberration diagram of astigmatism relative to the imaging surface (ideal image plane) of the image sensor 3. Here, the vertical axis represents the image height, and the horizontal axis represents the focus position. On the horizontal axis, the ideal focus position is represented by 0 [mm], and the deviation of the focus position from the ideal focus position represents the aberration amount. Figure 6 In the aberration diagram of the optical system 2 shown in (b), the aberration amount on the tangential surface is represented by a dotted line, and the aberration amount on the sagittal surface is represented by a solid line. The tangential surface is a surface including the principal ray and the optical axis PA. The sagittal surface is a surface including the principal ray and perpendicular to the tangential surface. Figure 6 (b) in FIG. 1 shows a case where astigmatism is suppressed within an allowable range.

[0089] Figure 6(c) in FIG. 1 shows an aberration diagram of distortion aberration relative to the imaging surface (ideal image plane) of the image sensor 3. Here, the vertical axis represents the image height, and the horizontal axis represents the magnitude of the aberration. Figure 6 In the aberration diagram of the optical system 2 shown in (c), the aberration amount of the d-line (wavelength: 587.56 nm) is indicated by a solid line. Figure 6 (c) in FIG. 1 shows a case where the distortion aberration is suppressed within the allowable range.

[0090] As described above, in the first embodiment, the optical system 2 is configured in a post-focusing manner. In the optical system 2, the ratio of the focal length of the image side lens group 22 to the focal length of the entire system is set to a value greater than 0.8 and less than 1.3. In addition, the focus movement amount Fd of the lens group 22 from the object distance OD1 to the object distance OD2 is set to a value greater than 0.2 (mm) and less than 0.9 (mm). The object distance OD1 corresponds to the distance to a relatively distant object assumed in actual use of the imaging device 1, for example, 20 cm. The object distance OD2 corresponds to the distance to a relatively close object assumed in actual use of the imaging device 1, for example, 3 cm. Therefore, the characteristics of the optical system 2 capable of automatic focusing operation can be improved and its thickness can be reduced.

[0091] It should be noted that in the first embodiment, the optical system 2 may be configured in an inner focusing manner rather than a rear focusing manner. For example, although not shown in the figure, the optical system 2 may further include a lens group 23 that is fixed when adjusting the focus between the lens group 22 and the image sensor 3. Even in this case, the optical system 2 is configured to satisfy Expressions (2) to (6), so that the following can be achieved: Figure 6 This can also achieve improved characteristics and reduced thickness of the optical system 2 capable of automatic focusing operation.

[0092] Second embodiment

[0093] Furthermore, as a second embodiment, the optical system 102 in the imaging device 101 may be configured as follows Figures 7 to 9 shown. Figure 7 1 is a lens arrangement diagram of the optical system 102 , and shows a YZ cross-sectional shape of the optical system 102 including the optical axis PA. Figure 8 1 is a schematic diagram showing paraxial data of the lens configuration of the optical system 102 . Fig. 9 1 is a schematic diagram showing the aspherical shape of the lens of the optical system 102 .

[0094] Figure 7 The example shows a configuration in which the lens group 121 has two lenses and the lens group 122 has five lenses.

[0095] The lens group 121 includes a lens L11, a lens L12, and a lens stop D11 in order from the object side to the image side. The lens group 122 includes a lens L13, a lens L14, a lens L15, a lens L16, a lens L17, and a filter FL in order from the object side to the image side. The filter FL can perform a filtering process of selectively cutting off light in an infrared (IR) light wavelength region.

[0096] Lenses L11 and L12 in lens group 121 and lenses L13 to L17 in lens group 122 have different cross-sectional shapes including optical axis PA. Lens group 121 is configured to have negative refractive power. Lens group 122 is configured to have positive refractive power. Lenses L11 to L17 may be made of translucent materials, such as glass, quartz, translucent plastics, or a combination thereof. Lens stop D11 may be made of a light-shielding material, or may be made of any material whose surface is coated with a color suitable for light-shielding (e.g., black).

[0097] In the lens group 121, the effective diameter of the luminous flux of the image side lens is smaller than the effective diameter of the luminous flux of the object side lens. For example, the effective diameter of the luminous flux of the image side lens L12 is smaller than the effective diameter of the luminous flux of the object side lens L11. In the lens group 122, the effective diameter of the luminous flux of the image side lens is larger than the effective diameter of the luminous flux of the object side lens. For example, the effective diameter of the luminous flux of the image side lens L17 is larger than the effective diameter of the luminous flux of the object side lens L13.

[0098] The luminous flux effective diameter of the lens L13 closest to the object side in the lens group 122 is smaller than the luminous flux effective diameter of the lens L12 closest to the image side in the lens group 121. The luminous flux effective diameter of the smallest lens L13 in the lens group 122 is smaller than the luminous flux effective diameter of the smallest lens L12 in the lens group 121.

[0099] The lens group 121 may include a meniscus lens or a concave lens located on the object side. The lens group 122 may include a convex lens located on the object side. Figure 7 In the example of FIG. 1 , the object-side lens L11 of the lens group 121 is a concave lens, and the object-side lens L13 of the lens group 122 is a convex lens.

[0100] The lens group 121 may include at least one lens having a negative refractive power and at least one lens having a positive refractive power. The lens having a negative refractive power may be located at a position closest to the object side in the lens group 121. The lens group 122 may include at least one lens having a negative refractive power. The lens having a negative refractive power may be located at a position closest to the image side in the lens group 122. Figure 7 In the example of FIG. 1 , the lens L11 closest to the object side in the lens group 121 has a negative refractive power, and the lens L12 has a positive refractive power. The lens L17 closest to the image side in the lens group 122 has a negative refractive power.

[0101] Figure 8 (a) in FIG. 1 shows that the optical system 102 satisfies all the conditions of Expression (2) to Expression (6). In other words, Figure 8 In (a), by being configured to satisfy all the conditions of expressions (2) to (6), the optical system 102 can set the total lens length (length in the Z direction) to approximately 6.732 mm, can reduce the effective F number to approximately Fno=3.981, and can ensure that the viewing angle is approximately 2θ=69.612[°].

[0102] Figure 8 (b) in FIG. 1 shows the refractive power of lenses L11 to L17 . Figure 8 (b) in FIG. 1 shows a configuration in which lenses L11 , L14 , and L17 have negative refractive power, and lenses L12 , L13 , L15 , and L16 have positive refractive power.

[0103] exist Figure 8 (c) Fig. 9 (a) and Fig. 9 In (b), the surface numbers are assigned as follows:

[0104] Surface number: L11R1: incident surface of lens L11;

[0105] Surface number: L11R2: exit surface of lens L11;

[0106] Surface number: L12R1: incident surface of lens L12;

[0107] Surface number: L12R2: exit surface of lens L12;

[0108] Surface number: L13R1: incident surface of lens L13;

[0109] Surface number: L13R2: exit surface of lens L13;

[0110] Surface number: L14R1: incident surface of lens L14;

[0111] Surface number: L14R2: exit surface of lens L14;

[0112] Surface number: L15R1: incident surface of lens L15;

[0113] Surface number: L15R2: exit surface of lens L15;

[0114] Surface number: L16R1: incident surface of lens L16;

[0115] Surface number: L16R2: exit surface of lens L16;

[0116] Surface number: L17R1: incident surface of lens L17; and

[0117] Surface number: L17R2: exit surface of lens L17.

[0118] Figure 8 (c) in FIG. 1 shows the radius of curvature R [mm], the surface distance D [mm], the refractive index Nd and the Abbe number νd for each surface numbered L11R1 to L17R2. The lens configuration is shown with the radius of curvature R. From the image side, the lens group 121 is composed of a concave lens L11 and a positive meniscus lens L12 with the convex surface facing the object side in the paraxial region. The lens group 122 is composed of a convex lens L13, a double concave negative lens L14, a positive meniscus lens L15 with the convex surface facing the object side, a positive meniscus lens L16 with the convex surface facing the image side, and a negative meniscus lens L17 with the convex surface facing the object side. By making the lenses L11 to L17 have different refractive indices Nd and Abbe numbers νd, chromatic aberration can be better corrected.

[0119] Fig. 9 (a) and Fig. 9 (b) in FIG. 1 shows the aspherical shape of each surface numbered L11R1 to L17R2. Assuming that the Z position (position in the direction of the optical axis PA) is "z", the paraxial curvature (=1 / R, R: radius of curvature) is "C", the XY distance from the optical axis PA is "h", the cone constant is "K", and the n-order aspherical coefficient is "An" (n=3, 4, ..., 20), the aspherical shape is represented by expression (7).

[0120] Fig. 9 (a) and Fig. 9 (b) in FIG. 1 shows the aspheric coefficients A3, A4, ..., A19, and A20 of each of the surface numbers L11R1 to L17R2. Fig. 9 (a) and Fig. 9 Substituting the aspheric coefficients A3 to A20 in (b) into expression (7), and rotating the curve represented by the obtained expression about the optical axis PA, each of the surfaces with surface numbers L11R1 to L17R2 is obtained. It should be noted that Fig. 9 (a) and Fig. 9 In (b), "Ei" is an exponential notation with base 10. Here, "i" is an integer. By making each surface numbered L11R1 to L17R2 as Fig. 9 (a) and Fig. 9 The aspherical surface shown in (b) can better correct spherical aberration.

[0121] according to Figures 7 to 9 The optical system 102 shown in the configuration shown is shown as Fig.10 Aberration characteristics shown. Fig.10 1 is a schematic diagram showing aberration characteristics of the optical system 102 .

[0122] Fig.10 (a) in FIG. 1 shows an aberration diagram of spherical aberration relative to the imaging surface (ideal image plane) of the image sensor 3. Here, the vertical axis represents the eye image height, and the horizontal axis represents the focus position. On the horizontal axis, the ideal focus position is represented by 0 [mm], and the deviation of the focus position from the ideal focus position represents the aberration amount. Fig.10 In the aberration diagram of the optical system 102 shown in (a), the aberration amount of the c-line (wavelength: 656.28nm) is represented by a dotted line, the aberration amount of the d-line (wavelength: 587.56nm) is represented by a solid line, and the aberration amount of the g-line (wavelength: 435.84nm) is represented by a dotted line. Fig.10 (a) in FIG. 1 shows a case where the spherical aberration is suppressed within the allowable range.

[0123] Fig.10 (b) in FIG. 1 shows an aberration diagram of astigmatism relative to the imaging surface (ideal image plane) of the image sensor 3. Here, the vertical axis represents the image height, and the horizontal axis represents the focus position. On the horizontal axis, the ideal focus position is represented by 0 [mm], and the deviation of the focus position from the ideal focus position represents the aberration amount. Fig.10 In the aberration diagram of the optical system 102 shown in (b), the aberration amount on the tangent plane is represented by a dotted line, and the aberration amount on the sagittal plane is represented by a solid line. The tangent plane is a plane including the principal ray and the optical axis PA. The sagittal plane is a plane including the principal ray and perpendicular to the tangent plane. Fig.10 (b) in FIG. 1 shows a case where astigmatism is suppressed within an allowable range.

[0124] Fig.10 (c) in FIG. 1 shows an aberration diagram of distortion aberration relative to the imaging surface (ideal image plane) of the image sensor 3. Here, the vertical axis represents the image height, and the horizontal axis represents the magnitude of the aberration. Fig.10 In the aberration diagram of the optical system 102 shown in (c) in FIG. 1 , the aberration amount of the d-line (wavelength: 587.56 nm) is indicated by a solid line. Fig.10 (c) in FIG. 1 shows a case where the distortion aberration is suppressed within the allowable range.

[0125] Even with such an optical system 102 , improved characteristics of the optical system 102 capable of performing an automatic focusing operation and reduced thickness can be achieved.

[0126] Third embodiment

[0127] Furthermore, as a third embodiment, the optical system 202 in the imaging device 201 may be configured as follows: Figures 11 to 13 shown. Fig.112 is a lens arrangement diagram of the optical system 202 , and shows a YZ cross-sectional shape of the optical system 202 including the optical axis PA. Fig.12 2 is a schematic diagram showing paraxial data of the lens configuration of the optical system 202 . Fig.13 2 is a schematic diagram showing the aspherical shape of the lens of the optical system 202 .

[0128] Fig.11 The example shows a configuration in which lens group 221 has two lenses and lens group 222 has five lenses.

[0129] The lens group 221 includes a lens L21, a lens L22, and a lens stop D21 in order from the object side to the image side. The lens group 222 includes a lens L23, a lens L24, a lens L25, a lens L26, a lens L27, and a filter FL in order from the object side to the image side. The filter FL can perform a filtering process of selectively cutting off light in an infrared (IR) light wavelength region.

[0130] Lenses L21 and L22 in lens group 221 and lenses L23 to L27 in lens group 222 have different cross-sectional shapes containing optical axis PA. Lens group 221 is configured to have negative refractive power. Lens group 222 is configured to have positive refractive power. Lenses L21 to L27 can be made of translucent materials, such as glass, quartz, translucent plastics or a combination thereof. Lens stop D21 can be made of a light-shielding material, or can be made of any material with a surface coated with a color suitable for light-shielding (e.g., black).

[0131] In the lens group 221, the effective diameter of the luminous flux of the image side lens is smaller than the effective diameter of the luminous flux of the object side lens. For example, the effective diameter of the luminous flux of the image side lens L22 is smaller than the effective diameter of the luminous flux of the object side lens L21. In the lens group 222, the effective diameter of the luminous flux of the image side lens is larger than the effective diameter of the luminous flux of the object side lens. For example, the effective diameter of the luminous flux of the image side lens L27 is larger than the effective diameter of the luminous flux of the object side lens L23.

[0132] The luminous flux effective diameter of the lens L23 closest to the object side in the lens group 222 is smaller than the luminous flux effective diameter of the lens L22 closest to the image side in the lens group 221. The luminous flux effective diameter of the smallest lens L23 in the lens group 222 is smaller than the luminous flux effective diameter of the smallest lens L22 in the lens group 221.

[0133] Lens group 221 may include a meniscus lens or a concave lens located on the object side. Lens group 222 may include a convex lens located on the object side. Fig.11 In the example, the object side lens L21 of the lens group 221 is a concave lens, and the object side lens L23 of the lens group 222 is a convex lens.

[0134] The lens group 221 may include at least one lens having a negative refractive power and at least one lens having a positive refractive power. The lens having a negative refractive power may be located at a position closest to the object side in the lens group 221. The lens group 222 may include at least one lens having a negative refractive power. The lens having a negative refractive power may be located at a position closest to the image side in the lens group 222. Fig.11 In the example of FIG. 2 , the lens L21 closest to the object side in the lens group 221 has a negative refractive power, and the lens L22 has a positive refractive power. The lens L27 closest to the image side in the lens group 222 has a negative refractive power.

[0135] Fig.12 (a) in FIG. 2 shows that the optical system 202 satisfies all the conditions of Expression (2) to Expression (6). In other words, Fig.12 In (a), by being configured to satisfy all the conditions of expressions (2) to (6), the optical system 202 can set the total lens length (length in the Z direction) to approximately 9.000 mm, can reduce the effective F number to approximately Fno=4.066, and can ensure that the viewing angle is approximately 2θ=78.679[°].

[0136] Fig.12 (b) in FIG. 1 shows the refractive power of lenses L21 to L27. Fig.12 (b) shows a configuration in which lenses L21, L24 and L27 have negative refractive power, and lenses L22, L23, L25 and L26 have positive refractive power.

[0137] exist Fig.12 (c) Fig.13 (a) and Fig.13 In (b), the surface numbers are assigned as follows:

[0138] Surface number: L21R1: incident surface of lens L21;

[0139] Surface number: L21R2: exit surface of lens L21;

[0140] Surface number: L22R1: incident surface of lens L22;

[0141] Surface number: L22R2: exit surface of lens L22;

[0142] Surface number: L23R1: incident surface of lens L23;

[0143] Surface number: L23R2: exit surface of lens L23;

[0144] Surface number: L24R1: incident surface of lens L24;

[0145] Surface number: L24R2: exit surface of lens L24;

[0146] Surface number: L25R1: incident surface of lens L25;

[0147] Surface number: L25R2: exit surface of lens L25;

[0148] Surface number: L26R1: incident surface of lens L26;

[0149] Surface number: L26R2: exit surface of lens L26;

[0150] Surface number: L27R1: incident surface of lens L27; and

[0151] Surface number: L27R2: exit surface of lens L27.

[0152] Fig.12 (c) in FIG. 2 shows the radius of curvature R [mm], the surface distance D [mm], the refractive index Nd and the Abbe number νd for each surface numbered L21R1 to L27R2. The lens configuration is shown with the radius of curvature R. From the image side, the lens group 221 is composed of a concave lens L21 and a positive meniscus lens L22 with the convex surface facing the object side in the paraxial region. The lens group 222 is composed of a convex lens L23, a double concave negative lens L24, a positive meniscus lens L25 with the convex surface facing the object side, a positive meniscus lens L26 with the convex surface facing the image side, and a negative meniscus lens L27 with the convex surface facing the object side. By making the lenses L21 to L27 have different refractive indices Nd and Abbe numbers νd, chromatic aberration can be better corrected.

[0153] Fig.13 (a) and Fig.13 (b) in FIG. 1 shows the aspherical shape of each surface numbered L21R1 to L27R2. Assuming that the Z position (position in the direction of the optical axis PA) is "z", the paraxial curvature (=1 / R, R: radius of curvature) is "C", the XY distance from the optical axis PA is "h", the cone constant is "K", and the n-order aspherical coefficient is "An" (n=3, 4, ..., 20), the aspherical shape is represented by expression (7).

[0154] Fig.13 (a) and Fig.13 (b) in FIG. 1 shows the aspheric coefficients A3, A4, ..., A19, and A20 of each of the surface numbers L21R1 to L27R2. Fig.13 (a) and Fig.13 Substituting the aspheric coefficients A3 to A20 in (b) into expression (7), and rotating the curve represented by the obtained expression about the optical axis PA, each of the surfaces with surface numbers L21R1 to L27R2 is obtained. It should be noted that Fig.13 (a) and Fig.13 In (b), "Ei" is an exponential notation with base 10. Here, "i" is an integer. By making each surface numbered L21R1 to L27R2 as Fig.13 (a) and Fig.13 The aspherical surface shown in (b) can better correct spherical aberration.

[0155] according to Figures 11 to 13 The optical system 202 shown in the configuration shown is shown as Fig.14 Aberration characteristics shown. Fig.14 2 is a schematic diagram showing aberration characteristics of the optical system 202 .

[0156] Fig.14 (a) in FIG. 1 shows an aberration diagram of spherical aberration relative to the imaging surface (ideal image plane) of the image sensor 3. Here, the vertical axis represents the eye image height, and the horizontal axis represents the focus position. On the horizontal axis, the ideal focus position is represented by 0 [mm], and the deviation of the focus position from the ideal focus position represents the aberration amount. Fig.14 In the aberration diagram of the optical system 202 shown in (a), the aberration amount of the c-line (wavelength: 656.28nm) is represented by a dotted line, the aberration amount of the d-line (wavelength: 587.56nm) is represented by a solid line, and the aberration amount of the g-line (wavelength: 435.84nm) is represented by a dotted line. Fig.14 (a) in FIG. 1 shows a case where the spherical aberration is suppressed within the allowable range.

[0157] Fig.14 (b) in FIG. 1 shows an aberration diagram of astigmatism relative to the imaging surface (ideal image plane) of the image sensor 3. Here, the vertical axis represents the image height, and the horizontal axis represents the focus position. On the horizontal axis, the ideal focus position is represented by 0 [mm], and the deviation of the focus position from the ideal focus position represents the aberration amount. Fig.14 In the aberration diagram of the optical system 202 shown in (b), the aberration amount on the tangent plane is represented by a dotted line, and the aberration amount on the sagittal plane is represented by a solid line. The tangent plane is a plane including the principal ray and the optical axis PA. The sagittal plane is a plane including the principal ray and perpendicular to the tangent plane. Fig.14 (b) in FIG. 1 shows a case where astigmatism is suppressed within an allowable range.

[0158] Fig.14 (c) in FIG. 1 shows an aberration diagram of distortion aberration relative to the imaging surface (ideal image plane) of the image sensor 3. Here, the vertical axis represents the image height, and the horizontal axis represents the magnitude of the aberration. Fig.14 In the aberration diagram of the optical system 202 shown in (c) in FIG. 1 , the aberration amount of the d-line (wavelength: 587.56 nm) is indicated by a solid line. Fig.14 (c) in FIG. 1 shows a case where the distortion aberration is suppressed within the allowable range.

[0159] Even with such an optical system 202 , improved characteristics of the optical system 202 capable of performing an automatic focusing operation and reduced thickness can be achieved.

[0160] Fourth embodiment

[0161] Furthermore, as a fourth embodiment, the optical system 302 in the imaging device 301 may be configured as follows Figures 15 to 17 shown. Fig.15 2 is a lens arrangement diagram of the optical system 302 , and shows a YZ cross-sectional shape of the optical system 302 including the optical axis PA. Fig.16 3 is a schematic diagram showing paraxial data of the lens configuration of the optical system 302 . Fig.17 3 is a schematic diagram showing the aspherical shape of the lens of the optical system 302 .

[0162] Fig.15 The example shows a configuration in which lens group 321 has two lenses and lens group 322 has five lenses.

[0163] The lens group 321 includes a lens L31, a lens L32, and a lens stop D31 in order from the object side to the image side. The lens group 322 includes a lens L33, a lens L34, a lens L35, a lens L36, a lens L37, and a filter FL in order from the object side to the image side. The filter FL can perform a filtering process of selectively cutting off light in an infrared (IR) light wavelength region.

[0164] The lenses L31 and L32 in the lens group 321 and the lenses L33 to L37 in the lens group 322 have different cross-sectional shapes including the optical axis PA. The lens group 321 is configured to have a negative refractive power. The lens group 322 is configured to have a positive refractive power. The lenses L31 to L37 can be made of a translucent material, for example, glass, quartz, translucent plastic or a combination thereof. The lens aperture D31 can be made of a light-shielding material, or can be made of any material whose surface is coated with a color suitable for light-shielding (for example, black).

[0165] In the lens group 321, the effective diameter of the luminous flux of the image side lens is smaller than the effective diameter of the luminous flux of the object side lens. For example, the effective diameter of the luminous flux of the image side lens L32 is smaller than the effective diameter of the luminous flux of the object side lens L31. In the lens group 322, the effective diameter of the luminous flux of the image side lens is larger than the effective diameter of the luminous flux of the object side lens. For example, the effective diameter of the luminous flux of the image side lens L37 is larger than the effective diameter of the luminous flux of the object side lens L33.

[0166] The luminous flux effective diameter of the lens L33 closest to the object side in the lens group 322 is smaller than the luminous flux effective diameter of the lens L32 closest to the image side in the lens group 321. The luminous flux effective diameter of the smallest lens L33 in the lens group 322 is smaller than the luminous flux effective diameter of the smallest lens L32 in the lens group 321.

[0167] Lens group 321 may include a meniscus lens or a concave lens located on the object side. Lens group 322 may include a convex lens located on the object side. Fig.15 In the example, the object side lens L31 of the lens group 321 is a concave lens, and the object side lens L33 of the lens group 322 is a convex lens.

[0168] Lens group 321 may include at least one lens having negative refractive power and at least one lens having positive refractive power. The lens having negative refractive power may be located at a position closest to the object side in lens group 321. Lens group 322 may include at least one lens having negative refractive power. The lens having negative refractive power may be located at a position closest to the image side in lens group 322. Fig.15 In the example of FIG. 3 , the lens L31 closest to the object side in the lens group 321 has a negative refractive power, and the lens L32 has a positive refractive power. The lens L37 closest to the image side in the lens group 322 has a negative refractive power.

[0169] Fig.16 (a) in FIG. 3 shows that the optical system 302 satisfies all the conditions of Expression (2) to Expression (6). In other words, Fig.16 In (a), by being configured to satisfy all the conditions of expressions (2) to (6), the optical system 302 can set the total lens length (length in the Z direction) to approximately 7.257 mm, can reduce the effective F number to approximately Fno=3.888, and can ensure that the viewing angle is approximately 2θ=94.384[°].

[0170] Fig.16 (b) in FIG. 1 shows the refractive power of lenses L31 to L37. Fig.16 (b) shows a configuration in which lenses L31, L34 and L37 have negative refractive power, and lenses L32, L33, L35 and L36 have positive refractive power.

[0171] exist Fig.16 (c) Fig.17 (a) and Fig.17 In (b), the surface numbers are assigned as follows:

[0172] Surface number: L31R1: incident surface of lens L31;

[0173] Surface number: L31R2: exit surface of lens L31;

[0174] Surface number: L32R1: incident surface of lens L32;

[0175] Surface number: L32R2: exit surface of lens L32;

[0176] Surface number: L33R1: incident surface of lens L33;

[0177] Surface number: L33R2: exit surface of lens L33;

[0178] Surface number: L34R1: incident surface of lens L34;

[0179] Surface number: L34R2: exit surface of lens L34;

[0180] Surface number: L35R1: incident surface of lens L35;

[0181] Surface number: L35R2: exit surface of lens L35;

[0182] Surface number: L36R1: incident surface of lens L36;

[0183] Surface number: L36R2: exit surface of lens L36;

[0184] Surface number: L37R1: incident surface of lens L37; and

[0185] Surface number: L37R2: exit surface of lens L37.

[0186] Fig.16 (c) in FIG. 3 shows the radius of curvature R [mm], the surface distance D [mm], the refractive index Nd and the Abbe number νd for each surface numbered L31R1 to L37R2. The lens configuration is shown with the radius of curvature R. From the image side, the lens group 321 is composed of a concave lens L31 and a positive meniscus lens L32 with the convex surface facing the object side in the paraxial region. The lens group 322 is composed of a convex lens L33, a biconcave negative lens L34, a convex lens L35, a positive meniscus lens L36 with the convex surface facing the image side, and a negative meniscus lens L37 with the convex surface facing the object side. By making the lenses L31 to L37 have different refractive indices Nd and Abbe numbers νd, chromatic aberration can be better corrected.

[0187] Fig.17 (a) and Fig.17(b) in FIG. 1 shows the aspherical shape of each surface numbered L31R1 to L37R2. Assuming that the Z position (position in the direction of the optical axis PA) is "z", the paraxial curvature (=1 / R, R: radius of curvature) is "C", the XY distance from the optical axis PA is "h", the cone constant is "K", and the n-order aspherical coefficient is "An" (n=3, 4, ..., 20), the aspherical shape is represented by expression (7).

[0188] Fig.17 (a) and Fig.17 (b) in FIG. 1 shows the aspheric coefficients A3, A4, ..., A19, and A20 of each of the surfaces with surface numbers L31R1 to L37R2. Fig.17 (a) and Fig.17 Substituting the aspheric coefficients A3 to A20 in (b) into expression (7), and rotating the curve represented by the obtained expression about the optical axis PA, each of the surfaces with surface numbers L31R1 to L37R2 is obtained. It should be noted that Fig.17 (a) and Fig.17 In (b), "Ei" is an exponential notation with base 10. Here, "i" is an integer. By making each surface numbered L31R1 to L37R2 as Fig.17 (a) and Fig.17 The aspherical surface shown in (b) can better correct spherical aberration.

[0189] according to Figures 15 to 17 The optical system 302 shown in the configuration shown is shown as Fig.18 Aberration characteristics shown. Fig.18 302 is a schematic diagram showing aberration characteristics of the optical system 302 .

[0190] Fig.18 (a) in FIG. 1 shows an aberration diagram of spherical aberration relative to the imaging surface (ideal image plane) of the image sensor 3. Here, the vertical axis represents the eye image height, and the horizontal axis represents the focus position. On the horizontal axis, the ideal focus position is represented by 0 [mm], and the deviation of the focus position from the ideal focus position represents the aberration amount. Fig.18 In the aberration diagram of the optical system 302 shown in (a), the aberration amount of the c-line (wavelength: 656.28nm) is represented by a dotted line, the aberration amount of the d-line (wavelength: 587.56nm) is represented by a solid line, and the aberration amount of the g-line (wavelength: 435.84nm) is represented by a dotted line. Fig.18 (a) in FIG. 1 shows a case where the spherical aberration is suppressed within the allowable range.

[0191] Fig.18(b) in FIG. 1 shows an aberration diagram of astigmatism relative to the imaging surface (ideal image plane) of the image sensor 3. Here, the vertical axis represents the image height, and the horizontal axis represents the focus position. On the horizontal axis, the ideal focus position is represented by 0 [mm], and the deviation of the focus position from the ideal focus position represents the aberration amount. Fig.18 In the aberration diagram of the optical system 302 shown in (b), the aberration amount on the tangent plane is represented by a dotted line, and the aberration amount on the sagittal plane is represented by a solid line. The tangent plane is a plane including the principal ray and the optical axis PA. The sagittal plane is a plane including the principal ray and perpendicular to the tangent plane. Fig.18 (b) in FIG. 1 shows a case where astigmatism is suppressed within an allowable range.

[0192] Fig.18 (c) in FIG. 1 shows an aberration diagram of distortion aberration relative to the imaging surface (ideal image plane) of the image sensor 3. Here, the vertical axis represents the image height, and the horizontal axis represents the magnitude of the aberration. Fig.18 In the aberration diagram of the optical system 302 shown in (c) in FIG. 1 , the aberration amount of the d-line (wavelength: 587.56 nm) is indicated by a solid line. Fig.18 (c) in FIG. 1 shows a case where the distortion aberration is suppressed within the allowable range.

[0193] Even with such an optical system 302 , improved characteristics of the optical system 302 capable of performing an automatic focusing operation and reduced thickness can be achieved.

[0194] Although certain embodiments have been described, these embodiments are given by way of example only and are not intended to limit the scope of the invention. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions, and changes may be made to the forms of the embodiments described herein without departing from the spirit of the invention. The appended claims and their equivalents are intended to cover such forms or modifications that fall within the scope and spirit of the invention.

[0195] [Explanation of letters or numbers]

[0196] 1, 101, 201, 301: Imaging equipment

[0197] 2, 102, 202, 302: Optical system

[0198] 3: Image Sensor

[0199] 4: Actuator

[0200] 5: Controller

[0201] 21, 121, 221, 321: lens group

[0202] 22, 122, 222, 322: lens group

[0203] D1, D11, D21: lens aperture

[0204] FL: Light filter

[0205] L1 to L7, L11 to L17, L21 to L27, L31 to L37: Lens

Claims

1. An optical system, comprising: A first lens group; as well as a second lens group, the second lens group being arranged closer to the image side than the first lens group, wherein when adjusting the focus, the second lens group moves along the optical axis in a state where the first lens group is fixed, and Assuming that the focal length of the second lens group is "f2", the focal length of the entirety of the first lens group and the second lens group is "f", and the focal length of the second lens group from the first object distance to the second object distance is "Fd" mm, the optical system satisfies: "0.8<f2 / f<1.3"; and "0.2<Fd<0.9".

2. The optical system according to claim 1, wherein: The first object distance is 20 cm, and The second object distance is 3 cm.

3. The optical system according to claim 1, wherein: Assuming that the distance from the object-side surface of the lens closest to the object side in the first lens group to the image plane on the optical axis is "Σd", the optical system satisfies: "Σd / f<4.5".

4. The optical system according to claim 1, wherein: Assuming that the focal length of the first lens group is "f1", the optical system satisfies: "-6.0<f1 / f2<-1.0".

5. The optical system according to claim 1, wherein: Assume that the radius of curvature at the center of the object side surface of the lens closest to the object side in the first lens group is "r 11 ", and the radius of curvature at the center of the image side surface of the lens closest to the object side in the first lens group is "r 12 ", then the optical system satisfies: "0.5＜(r 11 +r 12 ) / (r 11 -r 12 )＜3.0”。 6. The optical system according to claim 1, wherein: The first lens group has negative refractive power, and the second lens group has positive refractive power.

7. The optical system of claim 6, wherein: In the first lens group, the luminous flux effective diameter of the image side lens is smaller than the luminous flux effective diameter of the object side lens, and In the second lens group, a luminous flux effective diameter of the image side lens is larger than a luminous flux effective diameter of the object side lens.

8. The optical system according to claim 6, wherein: The luminous flux effective diameter of the lens closest to the object side in the second lens group is smaller than the luminous flux effective diameter of the lens closest to the image side in the first lens group.

9. The optical system according to claim 6, wherein: The luminous flux effective diameter of the smallest lens in the second lens group is smaller than the luminous flux effective diameter of the smallest lens in the first lens group.

10. The optical system of claim 6, wherein: The first lens group includes a meniscus lens or a concave lens located on the object side, and The second lens group includes a convex lens located on the object side.

11. The optical system according to claim 6, wherein: The number of lenses included in the second lens group is greater than the number of lenses included in the first lens group.

12. The optical system of claim 1, wherein: The first lens group comprises: at least one first lens having negative refractive power; and at least one second lens having positive refractive power, and The second lens group includes at least one third lens having negative refractive power.

13. The optical system according to claim 12, wherein: The first lens is located at a position closest to the object side in the first lens group.

14. The optical system according to claim 13, wherein: Assuming that the distance from the object side surface of the first lens to the image plane on the optical axis is "Σd", the optical system satisfies: "Σd / f<4.5".

15. The optical system according to claim 13, wherein: Assume that the radius of curvature at the center of the object side surface of the first lens is "r 11 ", and the radius of curvature at the center of the image side surface of the first lens is "r 12 ", then the optical system satisfies: "0.5＜(r 11 +r 12 ) / (r 11 -r 12 )＜3.0”。 16. The optical system according to claim 13, wherein: The third lens is located closest to the image side in the second lens group.

17. The optical system according to claim 16, wherein: An image-side surface of the third lens is concave near the optical axis.

18. The optical system of claim 13, wherein: The third lens is made of a material including at least one of glass, quartz and translucent plastic.

19. An optical module, comprising: Image sensor; as well as The optical system according to claim 1, wherein the optical system forms an image of an object on an imaging surface of the image sensor.

20. An imaging device comprising: Image sensor; The optical system according to claim 1, comprising a first lens group and a second lens group, the second lens group being arranged closer to the image sensor than the first lens group; and A controller is configured to integrally move the plurality of lenses included in the second lens group along an optical axis direction to adjust a focus in a state where the first lens group is fixed.

Images