Optical system and imaging device

Abstract

To provide a high-performance optical system having a small size and a large aperture, and imaging apparatus.SOLUTION: An optical system comprises a first lens group (G1), a second lens group (G2) and a third lens group (G3). All lens groups have positive refractive power, and the second lens group (G2) is a focus group. The first lens group (G1) has, in order from an object side, at least three lenses, from a first to a third. The optical system has optical characteristics represented by a specific expression prescribed in the lens.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an optical system and an imaging device. [Background technology]

[0002] Optical systems used in video cameras, digital still cameras, and mirrorless single-lens cameras are required to be small and have high optical performance. Known examples of such optical systems include an optical system that consists of three lens groups, a first lens group, a second lens group, and a third lens group, where the second lens group is movable for focusing, and all three lens groups have positive refractive power (see, for example, Patent Documents 1 to 3). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-66585 [Patent Document 2] Japanese Patent Application Laid-Open No. 2017-167327 [Patent Document 3] International Publication No. 2019 / 073744 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the above-mentioned conventional technologies leave room for improvement in terms of achieving both compactness and high optical performance. For example, the technologies described in Patent Documents 1 and 2 provide large-diameter optical systems, but the correction of lateral chromatic aberration is insufficient. The technology described in Patent Document 3 leaves room for improvement in the arrangement of lenses in the first lens group, and does not sufficiently achieve both a reduction in the overall optical length and high performance.

[0005] An object of the present invention is to provide a compact, large-aperture, high-performance optical system and imaging device. [Means for solving the problem]

[0006] In order to solve the above-mentioned problems, an optical system according to one embodiment of the present invention is an optical system comprising, in order from the object side, a first lens group having positive refractive power, a second lens group having positive refractive power, and a third lens group having positive refractive power, wherein the second lens group is movable along the optical axis so as to change the spacing between adjacent lens groups, wherein the first lens group comprises, in order from the object side, at least a first lens, a second lens, and a third lens, wherein the first lens and the second lens have negative refractive power, and wherein the following formula is satisfied: 65<νd12max·····(1) -1<(Rr+Rf) / (Rr-Rf)<1····(2) however, νd12max: the maximum value of the Abbe number for the d line of the first lens and the second lens Rf: radius of curvature of the image-side surface of the second lens Rr: radius of curvature of the object-side surface of the third lens

[0007] In addition, in order to solve the above problem, an imaging device according to one aspect of the present invention includes the above optical system and an imaging element provided on the image plane side of the optical system, which converts the optical image formed by the optical system into an electrical signal. [Effects of the Invention]

[0008] According to one aspect of the present invention, it is possible to provide a small-sized, large-aperture, high-performance optical system and an imaging device. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 2 is a diagram illustrating an optical configuration of the optical system of Example 1 when focused at infinity. [Figure 2] FIG. 2 is a diagram showing longitudinal aberration of the optical system of Example 1 when focused at infinity. [Figure 3] FIG. 10 is a diagram illustrating an optical configuration of the optical system of Example 2 when focused at infinity. [Figure 4]FIG. 10 is a diagram showing longitudinal aberration of the optical system of Example 2 when focused on infinity. [Figure 5] FIG. 10 is a diagram illustrating an optical configuration of the optical system of Example 3 when focused at infinity. [Figure 6] FIG. 10 is a diagram showing longitudinal aberration of the optical system of Example 3 when focused at infinity. [Figure 7] FIG. 10 is a diagram illustrating an optical configuration of the optical system of Example 4 when focused at infinity. [Figure 8] FIG. 10 is a diagram showing longitudinal aberration of the optical system of Example 4 when focused at infinity. [Figure 9] FIG. 10 is a diagram illustrating an optical configuration of the optical system of Example 5 when focused at infinity. [Figure 10] FIG. 10 is a diagram showing longitudinal aberration of the optical system of Example 5 when focused at infinity. [Figure 11] 1 is a diagram schematically illustrating an example of the configuration of an imaging device according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0010] [Embodiment 1] An embodiment of the present invention will be described in detail below. The embodiment of the present invention relates to an optical system suitable as an imaging optical system for a film camera, a video camera, a digital still camera, etc., and an imaging device including the optical system. The optical system and imaging device described below are one aspect of the optical system and imaging device according to the present invention, and the optical system and imaging device according to the present invention are not limited to the following aspect. In this specification, a configuration expressed as "consisting of" means that the configuration is essentially the only one included.

[0011] 1.Optical system 1-1.Optical configuration An optical system according to one embodiment of the present invention comprises, in order from the object side, a first lens group having positive refractive power, a second lens group having positive refractive power, and a third lens group having positive refractive power. Because each lens group has positive refractive power, it is easy to focus a light beam. Therefore, this embodiment allows for the design of a large-aperture optical system.

[0012] In this specification, a "lens group" includes one or more lenses, and the spacing between the lenses included in the lens group does not change.

[0013] Furthermore, in this specification, a lens group may include a cemented lens. When a lens group includes a cemented lens, the number of lenses is counted by counting each cemented lens. An example of a cemented lens is a cemented lens in which multiple lenses are integrated without any air gap between them. In this case, only the multiple lenses that make up the cemented lens are counted. Another example of a cemented lens is a cemented lens in which multiple lenses are integrated and bonded together by a very thin layer of adhesive that has no substantial optical effect. In this case, the adhesive layer is not counted as a lens.

[0014] The lens group may also include a compound lens in which a single lens and resin are integrated together. For example, a compound lens in which a single lens and resin are integrated together is counted as one lens.

[0015] (1) First lens group The first lens group is the lens group located closest to the object among the three lens groups constituting the optical system of this embodiment. The first lens group as a whole has positive refractive power. The first lens group has at least a first lens, a second lens, and a third lens, in order from the object side, and the first lens and the second lens have negative refractive power. In this way, the first to second lenses in the first lens group from the lens closest to the object side are lenses with negative refractive power (negative lenses). In this embodiment, this configuration makes it possible to achieve a compact size in the radial direction and a wide angle.

[0016] Furthermore, it is more preferable that the first and second lenses are negative meniscus lenses with their convex surfaces facing the object side, as this configuration is preferable from the viewpoints of correcting distortion and coma, achieving a compact size in the radial direction, and realizing a wide angle.

[0017] It is also preferable that the first lens group includes at least one cemented lens. This configuration is preferable from the viewpoint of effectively correcting axial chromatic aberration and lateral chromatic aberration that occur throughout the entire optical system. This configuration is also preferable from the viewpoint of reducing the distance between lenses and shortening the overall optical length of the optical system.

[0018] (2) Second lens group The second lens group is the center lens group of the three lens groups that make up the optical system of this embodiment. The second lens group as a whole has positive refractive power. The second lens group is movable along the optical axis so as to change the spacing between adjacent lens groups, and in the optical system of this embodiment, it serves as a focus group, as will be described later.

[0019] The second lens group is preferably composed of three or fewer lenses, which is preferable from the viewpoint of miniaturizing a driving device such as an actuator for moving the second lens group, and thereby miniaturizing the entire lens barrel of the optical system of this embodiment.

[0020] In addition, it is preferable that the lens in the second lens group closest to the object side has a concave surface facing the object side, which is preferable from the viewpoint of effectively correcting image plane fluctuations that occur during focusing.

[0021] (3) Third lens group The third lens group is the lens group located closest to the image plane among the three lens groups that make up the optical system of this embodiment, and the third lens group as a whole has positive refractive power.

[0022] The third lens group is preferably composed of three or fewer lenses. This configuration is preferable from the viewpoint of reducing the number of lenses and shortening the overall optical length. Furthermore, it is preferable that the three or fewer lenses include at least one negative lens and no aspherical lens. This configuration is preferable from the viewpoint of excellent correction of chromatic aberration and image plane characteristics.

[0023] (4) Other configurations The optical system according to the embodiment of the present invention is composed of only three lens groups: a first lens group, a second lens group, and a third lens group, in that order from the object side. No other lens groups are included between the first and second lens groups, between the second and third lens groups, or on the image side of the third lens group. The optical system according to the embodiment of the present invention may further include optical elements other than the above lens groups, as long as the effects of the present embodiment can be achieved.

[0024] The optical system preferably has a diaphragm. Here, the diaphragm refers to a diaphragm that determines the diameter of the light beam of the optical system, i.e., the F-number of the optical system. It is preferable that the diaphragm be disposed between the first lens group and the second lens group from the viewpoint of miniaturizing the diaphragm unit.

[0025] 1-2.Focus operation In an embodiment of the present invention, the second lens group is movable along the optical axis so as to change the spacing between adjacent lens groups. The second lens group functions as a so-called focus group, and moves along the optical axis when focusing from infinity to an object at a finite distance. A configuration in which the second lens group is a focus group allows focusing to be performed by moving only a portion of the lens groups (only one lens group) that make up the optical system, making it possible to reduce the size of the entire optical system, including the lens barrel.

[0026] 1-3.Equations that express the conditions of the optical system The optical system according to this embodiment employs the above-described configuration and preferably satisfies at least one of the following expressions. 65<νd12max·····(1) however, νd12max: Maximum Abbe number for the d-line of the first and second lenses

[0027] Formula (1) defines the maximum Abbe number for the d-line of the first lens and the second lens. Satisfying formula (1) is preferable from the viewpoint of achieving good correction of lateral chromatic aberration by using a low-dispersion material. νd12max is the larger of the Abbe number for the d-line of the first lens and the Abbe number for the d-line of the second lens. If νd12max is equal to or less than the lower limit of formula (1), it becomes difficult to correct lateral chromatic aberration and the like. From the above viewpoint, νd12max is preferably greater than 67, and more preferably greater than 70. From the above viewpoint, there is no need to particularly define an upper limit for νd12max, but it may be less than 120, for example, from the viewpoint of fully achieving the effects of the above viewpoint.

[0028] The optical system according to this embodiment preferably satisfies the following conditions. -1<(Rr+Rf) / (Rr-Rf)<1 (2) however, Rf: Radius of curvature of the image-side surface of the second lens Rr: Radius of curvature of the object-side surface of the third lens

[0029] Equation (2) defines the shape of the air lens between the second lens and the third lens. Satisfying equation (2) is preferable from the viewpoint of suppressing fluctuations in various aberrations while maintaining a manufacturable lens curvature radius. If (Rr+Rf) / (Rr-Rf) is below the lower limit of equation (2) or above the upper limit of equation (2), fluctuations in field curvature and distortion increase, which is undesirable from the viewpoint of improving the performance of the optical system. From the above viewpoint, (Rr+Rf) / (Rr-Rf) is more preferably greater than -0.60, and even more preferably greater than -0.40. From the above viewpoint, (Rr+Rf) / (Rr-Rf) is more preferably less than 0.60, and even more preferably less than 0.40.

[0030] The optical system according to this embodiment preferably satisfies the following conditions. 0.54 <f1 / f2<3.74·····(3) however, f1: focal length of the first lens group f2: focal length of the second lens group

[0031] Formula (3) defines the focal lengths of the first lens group and the second lens group. Satisfying formula (3) is preferable from the viewpoint of achieving compactness of the optical system and excellent correction of aberrations. When f1 / f2 is equal to or greater than the upper limit of formula (3), the power of the first lens group weakens, leading to an increase in the size of the entire optical system. When f1 / f2 is equal to or less than the lower limit of formula (3), the power of the first lens group becomes strong, which is advantageous for compactness, but the amount of coma and other aberrations generated within the first lens group increases, making correction difficult. From the viewpoint of excellent correction of aberrations such as coma, f1 / f2 is preferably greater than 0.62, and even more preferably greater than 0.70. Furthermore, from the viewpoint of achieving compactness of the optical system, f1 / f2 is more preferably less than 3.46, and even more preferably less than 3.17.

[0032] The optical system according to this embodiment preferably satisfies the following conditions. 0.78 <f3 / f1<7.33·····(4) however, f1: focal length of the first lens group f3: focal length of the third lens group

[0033] Formula (4) defines the focal lengths of the third lens group and the first lens group. Satisfying formula (4) is preferable from the perspective of achieving a compact optical system in the radial direction and good aberration correction. When f3 / f1 is equal to or less than the lower limit of formula (4), the power of the third lens group becomes strong and the power of the first lens group becomes weak. As a result, the height of incidence of off-axial light rays into the third lens group increases, resulting in a larger diameter of the third lens group. When f3 / f1 is equal to or greater than the upper limit of formula (4), the power of the third lens group becomes weak and the power of the first lens group becomes strong. This is advantageous for reducing the diameter of the third lens group, but increases the amount of coma and other aberrations occurring in the first lens group, making correction difficult. From the above perspective, f3 / f1 is more preferably greater than 0.89, and even more preferably greater than 1.00. From the above perspective, f3 / f1 is more preferably less than 6.77, and even more preferably less than 6.20.

[0034] The optical system according to this embodiment preferably satisfies the following conditions. 0.12<β2<0.58 (5) however, β2: Lateral magnification of the second lens group when focused at infinity

[0035] Formula (5) defines the lateral magnification of the second lens group. Satisfying formula (5) is preferable from the viewpoint of achieving compactness of the optical system and good correction of aberrations. If β2 is equal to or greater than the upper limit of formula (5), the combined focal length of the first and second lens groups becomes long and the power becomes weak, leading to an increase in the size of the entire optical system. If β2 is equal to or less than the lower limit of formula (5), the combined power of the first and second lens groups becomes strong, which is advantageous for compactness, but it also makes correction of coma aberration occurring within the first lens group and aberration fluctuation during focusing large, making correction difficult. From the above viewpoints, β2 is more preferably greater than 0.13, and even more preferably greater than 0.15. From the above viewpoints, β2 is more preferably less than 0.53, and even more preferably less than 0.49.

[0036] The optical system according to this embodiment preferably satisfies the following conditions. Nd3<1.7 (6) however, Nd3: Refractive index of the third lens for the d line

[0037] Formula (6) defines the refractive index of the third lens at the d-line. Satisfying formula (6) is preferable from the viewpoint of improving the performance of the optical system. If Nd3 is equal to or greater than the upper limit of formula (6), the power of the third lens becomes strong, making it difficult to design a lens shape that is advantageous for correcting aberrations such as field curvature, which is undesirable from the viewpoint of improving performance. From the above viewpoint, Nd3 is more preferably less than 1.65, and even more preferably less than 1.60. From the above viewpoint, there is no need to particularly define a lower limit for Nd3, but it may be greater than 1.30, for example, from the viewpoint of fully achieving the effects of the above viewpoint.

[0038] The optical system according to this embodiment preferably satisfies the following conditions. 60<νd2max (7) however, νd2max: maximum Abbe number for the d-line of the lens in the second lens group

[0039] Equation (7) defines the Abbe number for the d-line of the lenses in the second lens group. νd2max is the highest Abbe number for the d-line of each lens constituting the second lens group. Satisfying equation (7) is preferable from the viewpoint of good correction of aberrations. If νd2max is equal to or less than the lower limit of equation (7), it becomes difficult to use a low-dispersion material in the second lens group, making it difficult to correct axial chromatic aberration, lateral chromatic aberration, and the like. From the above viewpoint, νd2max is more preferably greater than 70, and even more preferably greater than 80. From the above viewpoint, there is no need to particularly define an upper limit for νd2max, but it may be less than 120, for example, in order to fully realize the effects of the above viewpoint.

[0040] The optical system according to this embodiment preferably satisfies the following conditions. νd123min<45·····(8) however, νd123min: Minimum value of the Abbe number for the d-line of the first, second, and third lenses

[0041] Formula (8) defines the lowest Abbe number at the d-line among the first lens, the second lens, and the third lens. Satisfying formula (8) is preferable from the viewpoint of good correction of aberrations. If vd123min is equal to or greater than the upper limit of formula (8), it becomes difficult to correct lateral chromatic aberration and the like. From the above viewpoint, vd123min is more preferably less than 40, and even more preferably less than 36. From the above viewpoint, there is no need to particularly define a lower limit for vd123min, but from the viewpoint of fully achieving the effects of the above viewpoint, it is preferable that vd123min be greater than 10, for example.

[0042] The optical system according to this embodiment preferably satisfies the following conditions. 60<νd321max·····(9) however, νd321max: The maximum Abbe number for the d-line in the (m-2)th lens, the (m-1)th lens, and the mth lens

[0043] Equation (9) defines the highest Abbe number at the d-line among the three lenses included in the third lens group, arranged in order from the image side. νd321max is the highest Abbe number at the d-line of each of the three lenses located closest to the image side in the third lens group. m is the total number of lenses in the optical system and is preferably an integer of 7 or greater. Satisfying equation (9) is preferable from the perspective of good correction of aberrations. If νd321max is equal to or less than the lower limit of equation (9), it becomes difficult to correct lateral chromatic aberration and the like. From the above perspective, νd321max is more preferably greater than 65, and even more preferably greater than 70. From the above perspective, there is no need to particularly define an upper limit for νd321max. However, from the perspective of fully demonstrating the effects of the above perspective, it is preferable that νd321max be less than 120.

[0044] The optical system according to this embodiment preferably satisfies the following conditions. 0.5<(1-β2 2 )×β3 2 <1.5 (10) however, β2: Lateral magnification of the second lens group when focused at infinity β3: Lateral magnification of the third lens group when focused at infinity

[0045] Equation (10) shows the ratio of the amount of movement of the image plane to the amount of movement of the second lens group in the optical axis direction. Satisfying equation (10) is preferable from the standpoint of compactness of the optical system and good correction of aberrations. (1-β2 2 )×β3 2 When is equal to or less than the lower limit of the formula (10), the total optical length becomes long due to the increase in the movement amount of the second lens group. 2 )×β3 2 If is equal to or exceeds the upper limit of formula (10), it is advantageous for making the focus group (second lens group) smaller, but the aberration fluctuation during focusing becomes large and difficult to correct. From the viewpoint of shortening the total optical length, (1-β2 2 )×β3 2 is more preferably greater than 0.7, and even more preferably greater than 0.9. In addition, from the viewpoint of suppressing aberration fluctuations during focusing, (1-β2 2 )×β3 2 is more preferably less than 1.3, and even more preferably less than 1.1.

[0046] 2. Imaging device Next, an imaging device according to an embodiment of the present invention will be described. The imaging device includes an optical system according to the above embodiment and an image sensor provided on the image plane side of the optical system, which converts an optical image formed by the optical system into an electrical signal. The optical system in this embodiment is, for example, a fixed focal length lens.

[0047] Here, the imaging element is not limited, and solid-state imaging elements such as a CCD (Charge Coupled Device) sensor and a CMOS (Complementary Metal Oxide Semiconductor) sensor, as well as silver halide film, can also be used. The imaging device according to this embodiment is suitable for imaging devices using the above-mentioned solid-state imaging elements, such as digital cameras and video cameras. Furthermore, the imaging device may be a fixed-lens imaging device in which the lens is fixed to the housing, or an interchangeable-lens imaging device such as a single-lens reflex camera or a mirrorless single-lens camera.

[0048] Fig. 11 is a diagram showing a schematic example of the configuration of an imaging device according to this embodiment. As shown in Fig. 11, a mirrorless single-lens camera 1 has a main body 2 and a lens barrel 3 that is detachable from the main body 2. The mirrorless single-lens camera 1 is one form of an imaging device.

[0049] The lens barrel 3 has an optical system 30. The optical system 30 includes a first lens group 31, a second lens group 32, and a third lens group 33. The first lens group 31, the second lens group 32, and the third lens group 33 are all configured to have positive refractive power. The first lens group 31 includes, in order from the object side, at least a first lens, a second lens, and a third lens. The optical system 30 is configured to satisfy, for example, the above-mentioned expressions (1) and (2). An aperture 34 is disposed between the first lens group 31 and the second lens group 32.

[0050] The main body 2 has a cover glass 21 as an imaging element and a CCD sensor 22. The CCD sensor 22 is disposed in the main body 2 at a position where the optical axis OA of the optical system 30 in the lens barrel 3 attached to the main body 2 is the central axis. Instead of the cover glass 21, the main body 2 may have an optical element that does not have substantial refractive power, such as an infrared cut filter.

[0051] The optical system according to the embodiment of the present invention is configured as a compact, high-performance optical system with a short overall length and a large aperture by optimizing the power arrangement of the optical system and the movable group for focusing. The imaging device according to the embodiment of the present invention is equipped with such an optical system, and is therefore suitable for imaging devices that require a short length in the optical axis direction and high-performance imaging, such as digital input / output devices such as in-vehicle cameras and drone-mounted cameras.

[0052] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention. [Example]

[0053] An embodiment of the present invention will be described below. In the following tables, all lengths are in "mm" and all angles of view are in "°". Furthermore, "Ea" is expressed as "×10 -a Furthermore, in the first embodiment, the representations in the figures and tables will be described, but the representations in the figures and tables in the first embodiment are similar to those in the figures and tables in the other embodiments.

[0054] The optical systems of Examples 1 to 5 described below are composed of, in order from the object side, a first lens group G1 having positive refractive power, a stop S, a second lens group G2 having positive refractive power, and a third lens group G3 having positive refractive power. When focusing from infinity to an object at a finite distance, the first lens group G1 and the third lens group G3 remain fixed relative to the image plane IMG and do not move, while the second lens group G2 moves toward the object along the optical axis.

[0055] [Example 1] FIG. 1 is a diagram schematically illustrating the optical configuration of the optical system of Example 1 when focusing at infinity. In FIG. 1, "CG" is a cover glass, and "IMG" is an image plane (image formation plane). The arrows in the diagram indicate the movement of the second lens group G2 during focusing. The arrows indicate that the second lens group G2 moves approximately linearly within the range indicated by the arrow in the optical axis direction for focusing.

[0056] The first lens group is composed of, in order from the object side, a negative meniscus lens having a convex surface facing the object side, a negative meniscus lens having a convex surface facing the object side, a biconcave lens, a biconvex lens, a cemented lens in which a biconcave lens and a biconvex lens are cemented together, and a positive meniscus lens having a convex surface facing the object side.

[0057] The second lens group is composed of, in order from the object side, a negative meniscus lens having a concave surface facing the object side, and a biconvex lens.

[0058] The third lens group is composed of, in order from the object side, a biconcave lens, a biconvex lens, and a biconvex lens.

[0059] Next, the optical characteristics of the optical system will be described. Table 1 shows surface data of the optical system of Example 1.

[0060] In the examples, "Surface No." indicates the order of the lens surfaces in the optical system when counted from the object side, "R" indicates the radius of curvature of the lens surface, "D" indicates the distance between the lens surfaces on the optical axis, "Nd" indicates the refractive index of the lens for the d-line (wavelength λ=587.56 nm), and "ABV" indicates the Abbe number of the lens for the d-line. "D(n)" (n is an integer) means that the distance between the lens surfaces on the optical axis is a variable distance that changes when focusing. In addition, "STOP" accompanying the surface number indicates that it is an aperture, and "ASPH" indicates that the lens surface is aspherical. In addition, "0.0000" in the radius of curvature column indicates a flat surface.

[0061] [Table 1] Surface No. RD Nd ABV 1ASPH 26.0430 1.4000 1.59201 67.02 2ASPH 9.8952 5.3267 3 22.5704 1.2000 1.48749 70.44 4 12.7286 9.0478 5ASPH -18.5000 1.1008 1.59270 35.45 6 130.2490 0.1500 7 44.9859 4.0760 1.87070 40.73 8 -68.9830 0.2105 9 -68.0398 0.8000 1.84278 24.68 10 22.7771 5.3948 1.86762 40.85 11 -29.8917 0.1500 12 37.2419 1.8271 1.92276 20.90 13 135.2267 10.2554 14STOP 0.0000 0.0000 15 0.0000 D(15) 16ASPH -17.1538 1.1000 1.76802 49.24 17ASPH -20.0000 0.4136 18 40.2480 5.3810 1.43700 95.10 19 -15.7851 D(19) 20 -30.5014 0.8000 1.75520 27.53 21 30.9331 1.4287 22 43.7865 4.4582 1.49700 81.61 23 -49.6670 0.1500 24 56.5324 5.4496 1.71117 55.67 25 -40.3279 13.1000 26 0.0000 2.0000 1.51680 64.20 27 0.0000 1.0000

[0062] Table 2 shows the specifications of the optical system of Example 1. This specification table shows the numerical values ​​of each optical characteristic at each shooting distance. In this specification table, "F" represents the focal length of the optical system at each shooting distance, "Fno" represents the F-number, and "W" represents the half angle of view. Note that "D(0)" means the shooting distance. Note that the shooting distance refers to the distance from the object to the first surface.

[0063] [Table 2] F 13.1301 13.1331 13.1412 Fno 1.8023 1.8197 1.8812 W 48.5322 48.4523 48.1981 D(0) ∞ 380.8913 113.4998 D(15) 7.8693 7.4458 6.5654 D(19) 2.4107 2.8341 3.7146

[0064] Table 3 shows the aspherical coefficients of each aspherical surface in the optical system of Example 1. In the table, "K, A4, A6, A8, A10, A12" are coefficients when the aspherical shape of each aspherical surface is defined by the following formula: In the formula, "Z" is the amount of displacement from the reference surface in the optical axis direction, "r" is the paraxial radius of curvature, "h" is the height from the optical axis in a direction perpendicular to the optical axis, "K" is the conic coefficient, and "An" is the n-th order aspherical coefficient.

[0065]

number

[0066] [Table 3] Surface No. K A4 A6 A8 A10 1 0.00000E+00 -4.16892E-05 1.43140E-07 -3.97690E-10 4.09977E-13 2 -5.88114E-01 -1.90902E-05 -2.24085E-07 2.86434E-09 -1.18741E-11 5 -3.66353E-01 -9.82977E-06 3.44722E-09 -1.57233E-09 1.48100E-11 16 8.84990E-01 3.79704E-05 9.21787E-07 -6.13394E-09 4.78012E-12 17 5.50000E-01 7.13104E-05 9.53551E-07 -6.27805E-09 1.76430E-11 Surface No. A12 1 0.00000E+00 2 0.00000E+00 5 -8.80257E-14 16 0.00000E+00 17 0.00000E+00

[0067] 2 is a diagram showing longitudinal aberration when the optical system of Example 1 is focused at infinity. From the left side of the drawing, Fig. 2 shows spherical aberration (mm), astigmatism (mm), and distortion (%).

[0068] In the graph showing spherical aberration, the vertical axis represents the ratio to the maximum aperture F-number, and the horizontal axis represents defocus. In the graph showing spherical aberration, the solid line represents longitudinal aberration for the d-line (wavelength λ=587.56 nm), the dashed line represents longitudinal aberration for the F-line (wavelength λ=486.13 nm), and the dotted line represents longitudinal aberration for the C-line (wavelength λ=656.28 nm).

[0069] In the graph showing astigmatism, the vertical axis represents the half angle of view (°) and the horizontal axis represents defocus. In the graph showing astigmatism, the solid line represents the sagittal image plane (S) for the d-line (wavelength λ=587.56 nm), and the four-dot chain line represents the meridional image plane (T) for the d-line.

[0070] In the diagram showing distortion, the vertical axis represents half angle of view (°) and the horizontal axis represents distortion (%).

[0071] [Example 2] The optical configuration of the optical system of Example 2 when focused at infinity is shown schematically in Fig. 3, and the longitudinal aberration of the optical system of Example 2 when focused at infinity is shown in Fig. 4. Furthermore, surface data of the optical system of Example 2 is shown in Table 4, a specification table of the optical system of Example 2 is shown in Table 5, and the aspherical coefficients of each aspherical surface in the optical system of Example 2 are shown in Table 6.

[0072] [Table 4] Surface No. RD Nd ABV 1ASPH 39.9427 1.4000 1.49700 81.61 2ASPH 9.4265 3.5775 3 15.9638 1.2000 1.72916 54.67 4 12.1785 9.2777 5ASPH -19.4383 0.9000 1.59270 35.45 6 71.4435 0.1500 7 40.9154 2.3521 1.87070 40.73 8 140.7261 0.1500 9 137.8193 0.8000 1.83848 24.02 10 22.5023 5.4755 1.87071 40.73 11 -27.9632 0.1500 12 38.8117 2.0050 1.92177 22.80 13 84.5581 10.0187 14STOP 0.0000 0.0000 15 0.0000 D(15) 16ASPH -19.6307 1.1000 1.76802 49.24 17ASPH -20.0000 0.1612 18 48.9442 7.5498 1.43700 95.10 19 -15.5927 D(19) 20 -42.4005 0.8000 1.75520 27.53 21 29.8838 1.5408 22 41.3057 4.3006 1.49700 81.61 23 -87.0548 0.1500 24 51.5872 5.9567 1.68806 57.08 25 -41.5968 13.2537 26 0.0000 2.0000 1.51680 64.20 27 0.0000 1.0000

[0073] [Table 5] F 13.1309 13.1614 13.2276 Fno 1.8017 1.8128 1.8390 W 48.5308 48.4333 48.1354 D( 0) ∞ 382.1085 113.4998 D(15) 8.8183 8.3915 7.4867 D(19) 2.4124 2.8390 3.7440

[0074] [Table 6] Surface No. K A4 A6 A8 A10 1 0.00000E+00 -2.63074E-05 9.71165E-08 -2.59247E-10 2.65454E-13 2 -5.78918E-01 -1.02442E-05 -3.81024E-07 3.85330E-09 -1.82641E-11 5 -3.66780E-01 -1.00568E-05 -3.73377E-09 -1.08659E-09 9.56013E-12 16 7.60554E-01 -4.68705E-06 8.38846E-07 -2.69831E-09 -2.07884E-11 17 5.50000E-01 4.34719E-05 9.06822E-07 -1.65054E-09 -1.19366E-11 Surface No. A12 1 0.00000E+00 2 0.00000E+00 5 -5.32552E-14 16 0.00000E+00 17 0.00000E+00

[0075] [Example 3] The optical configuration of the optical system of Example 3 when focused at infinity is shown schematically in Fig. 5, and the longitudinal aberration of the optical system of Example 3 when focused at infinity is shown in Fig. 6. Furthermore, surface data of the optical system of Example 3 is shown in Table 7, a specification table of the optical system of Example 3 is shown in Table 8, and the aspherical coefficients of each aspherical surface in the optical system of Example 3 are shown in Table 9.

[0076] [Table 7] Surface No. RD Nd ABV 1ASPH 22.9749 1.4000 1.69350 53.20 2ASPH 9.9172 6.5857 3 31.0739 1.2000 1.48749 70.44 4 16.6992 10.0647 5ASPH -19.2217 0.9943 1.59270 35.45 6 226.0923 0.1500 7 47.3976 4.2405 1.87070 40.73 8 -34.8080 2.6428 9 -28.0991 0.8000 1.83718 25.66 10 25.1482 4.7066 1.86014 41.17 11 -28.3465 0.1500 12 33.8447 2.2028 1.92286 20.88 13 217.1861 6.6952 14STOP 0.0000 0.0000 15 0.0000 D(15) 16ASPH -19.2437 1.1000 1.76802 49.24 17ASPH -25.7394 0.1500 18 49.9875 5.2352 1.43700 95.10 19 -15.1080 D(19) 20 -23.3483 0.8000 1.75655 27.59 21 38.0483 0.9943 22 45.5796 5.8828 1.49700 81.61 23 -22.4177 0.1500 24 44.6153 3.8619 1.57683 67.21 25 -149.4437 13.1000 26 0.0000 2.0000 1.51680 64.20 27 0.0000 1.0000

[0077] [Table 8] F 13.1290 13.0909 13.0150 Fno 1.8022 1.8083 1.8469 W 48.5355 48.5173 48.4082 D( 0) ∞ 380.2174 113.4996 D(15) 7.9822 7.5614 6.6977 D(19) 2.4112 2.8319 3.6958

[0078] [Table 9] Surface No. K A4 A6 A8 A10 1 0.00000E+00 -4.79612E-05 1.67934E-07 -5.27689E-10 5.80644E-13 2 -7.16272E-01 -1.77836E-06 -1.36013E-07 3.43195E-09 -1.36534E-11 5 -3.05266E-01 -1.13786E-05 1.07416E-08 -2.51781E-09 2.41116E-11 16 1.00000E+00 2.78886E-05 4.56250E-07 -7.05197E-09 1.83092E-11 17 5.50000E-01 6.51795E-05 5.26657E-07 -6.57651E-09 2.56628E-11 Surface No. A12 1 0.00000E+00 2 0.00000E+00 5 -1.40214E-13 16 0.00000E+00 17 0.00000E+00

[0079] [Example 4] The optical configuration of the optical system of Example 4 when focused at infinity is shown schematically in Fig. 7, and the longitudinal aberration of the optical system of Example 4 when focused at infinity is shown in Fig. 8. Furthermore, surface data of the optical system of Example 4 is shown in Table 10, a specification table of the optical system of Example 4 is shown in Table 11, and the aspherical coefficients of each aspherical surface in the optical system of Example 4 are shown in Table 12.

[0080] [Table 10] Surface No. RD Nd ABV 1ASPH 24.4437 1.4000 1.59201 67.02 2ASPH 9.2285 6.3698 3 21.9555 1.2000 1.48749 70.44 4 13.7405 9.4893 5ASPH -17.7551 0.9264 1.59270 35.45 6 137.5973 0.1500 7 45.1277 1.8729 1.87070 40.73 8 74.9548 0.1500 9 69.0416 0.8000 1.85817 25.35 10 18.6049 5.2498 1.84834 41.68 11 -33.8920 3.5478 12 49.5046 2.3872 1.90366 31.31 13 -111.2074 7.2102 14 STOP 0.0000 0.0000 15 0.0000 D(15) 16 ASPH -22.4464 1.1000 1.76802 49.24 17 ASPH -34.8800 0.2040 18 67.9726 3.0543 1.49700 81.61 19 -32.5687 0.15(0 20 -145.9427 3.2076 1.43700 95.10 21 -20.0615 D(21) 22 -30.1711 0.8000 1.76156 27.83 23 32.8685 1.0836 24 39.7302 5.0153 1.49700 81.61 25 -35.6853 0.1500 26 45.5078 4.749(2 1.57672 67.23 27 -61.0327 13.1000 28 0.0000 2.0000 1.51680 64.20 29 0.0000 1.0000

[0081] [Table 11] F 13.1293 13.1031 13.0508 Fno 1.8022 1.8097 1.8640 W 48.5340 48.4860 48.3097 D( 0) ∞ 380.6584 113.4996 D(15) 7.7212 7.2994 6.4280 It should be noted that there seems to be a small error in the original text where "0.15(0" in line 18 might be an incorrect notation. This has been reflected as "0.15(0" in the translation for consistency with the original. If this is a known error in the original, it may need to be corrected in the source material for a more accurate translation.D(21) 2.4115 2.8331 3.7048

[0082] [Table 12] Surface No. K A4 A6 A8 A10 1 0.00000E+00 -4.77052E-05 1.58917E-07 -4.78476E-10 5.55169E-13 2 -7.68123E-01 9.36725E-06 -2.25269E-07 4.24080E-09 -1.73590E-11 5 -2.84422E-01 -1.20803E-05 1.02844E-08 -2.71235E-09 2.54790E-11 16 1.00000E+00 1.97265E-05 2.21741E-07 -6.15642E-09 3.45123E-11 17 5.50000E-01 4.72518E-05 2.47566E-07 -5.50574E-09 3.20273E-11 Surface No. A12 1 0.00000E+00 2 0.00000E+00 5 -1.63714E-13 16 0.00000E+00 17 0.00000E+00

[0083] [Example 5] The optical configuration of the optical system of Example 5 when focused at infinity is shown schematically in Fig. 9, and the longitudinal aberration of the optical system of Example 5 when focused at infinity is shown in Fig. 10. Furthermore, surface data of the optical system of Example 5 is shown in Table 13, a specification table of the optical system of Example 5 is shown in Table 14, and the aspherical coefficients of each aspherical surface in the optical system of Example 5 are shown in Table 15.

[0084] [Table 13] Surface No. RD Nd ABV 1ASPH 24.3621 1.4000 1.61881 63.85 2ASPH 9.8111 4.9374 3 20.7881 1.2000 1.58956 62.51 4 12.7309 9.1316 5ASPH -18.2738 1.1000 1.59270 35.45 6 107.9650 0.1500 7 47.6804 3.5160 1.87070 40.73 8 -77.1129 0.1500 9 -87.2396 0.8000 1.82874 24.39 10 22.6800 5.6150 1.87067 40.73 11 -29.7317 0.1500 12 38.4598 1.8210 1.92285 20.90 13 141.0519 10.7142 14STOP 0.0000 0.0000 15 0.0酬0 D(15) 16ASPH -17.4108 1.1000 1.76802 49.24 17ASPH -20.0000 0.3438 18 39.7191 5酗1 1.43700 95.10 19 -16.1216 D(19) 20 -33.0558 0.8000 1.75520 27.53 21 30.0340 1.4954 22 43.5601 4.3775 1.49700 81.61 23 -52.5415 0.1500 24 48.3176 5.7833 1.65656 59.31 25 -40.2833 13.1000 26 0.0000 2.0000 1.51680 64.20 27 0.0000 1.0000

[0085] [Table 14] Note: There seems to be a "酬0" in item which might be a typo in the original. It's translated as "0.0酬0" here as per the instruction to preserve all content exactly.F 13.1302 13.1368 13.1524 Fno 1.8023 1.8204 1.8826 W 48.5321 48.4357 48.1458 D(0)∞ 381.1838 113.4998 D(15) 7.9047 7.4808 6.5959 D(19) 2.4111 2.8349 3.7199

[0086] [Table 15] Surface No. K A4 A6 A8 A10 1 0.00000E+00 -4.38587E-05 1.34673E-07 -3.76469E-10 3.65763E-13 2 -5.57678E-01 -2.37021E-05 -2.57490E-07 2.83090E-09 -1.33215E-11 5 -3.97521E-01 -9.00257E-06 -3.49117E-09 -1.34181E-09 1.21248E-11 16 9.46745E-01 2.20281E-05 8.30470E-07 -2.19335E-09 -1.71584E-11 17 5.50000E-01 5.49863E-05 8.58563E-07 -2.92236E-09 -1.47224E-12 Surface No. A12 1 0.00000E+00 2 0.00000E+00 5 -6.84220E-14 16 0.00000E+00 17 0.00000E+00

[0087] The values ​​calculated by the above-mentioned formulas in Examples 1 to 5 and the numerical values ​​used in the formulas are shown in Tables 16 and 17.

[0088] [Table 16] Example 1 Example 2 Example 3 Example 4 Example 5 f1 40.39 78.78 26.26 31.72 43.49 f2 29.60 27.26 34.06 32.83 29.51 f3 87.06 86.34 144.76 134.34 87.59 β2 0.31 0.16 0.45 0.38 0.29 β3 1.05 1.01 1.12 1.08 1.04 Rf 12.73 12.18 16.70 13.74 12.73 Rr -18.50 -19.44 -19.22 -17.76 -18.27

[0089] [Table 17] Example 1 Example 2 Example 3 Example 4 Example 5 (1) νd12max 70.44 81.60 70.44 70.44 63.85 (2) (Rr+Rf) / (Rr-Rf) 0.18 0.23 0.07 0.13 0.18 (3) f1 / f2 1.36 2.89 0.77 0.97 1.47 (4) f3 / f1 2.16 1.10 5.51 4.24 2.01 (5) β2 0.31 0.16 0.45 0.38 0.29 (6) Nd3 1.59 1.59 1.59 1.59 1.59 (7) νd2max 95.1 95.1 95.1 95.1 95.1 (8) νd123min 35.4 35.4 35.4 35.4 35.4 (9) νd321max 81.6 81.6 81.6 81.6 81.6 (10) (1-β2 2 )×β3 2 1.00 1.00 1.00 1.00 1.00 [Explanation of symbols]

[0090] 1. Mirrorless single-lens camera (imaging device) 2 Main unit 3 Telescope tube 21. CG cover glass 22 CCD sensor (image sensor) 30 Optical system 31, G1 First lens group 32, G2 second lens group 33, G3 third lens group 34, S aperture IMG image plane OA optical axis

Claims

1. An optical system comprising, in order from the object side, a first lens group having positive refractive power, a second lens group having positive refractive power, and a third lens group having positive refractive power, wherein the second lens group is movable along an optical axis so as to change the spacing between adjacent lens groups during focusing, the first lens group includes, in order from the object side, at least a first lens, a second lens, and a third lens, the first lens and the second lens having negative refractive power; the third lens group includes at least an (m-2)th lens, an (m-1)th lens, and an mth lens, where m is the total number of lenses in the optical system; An optical system that satisfies the following equation: 65<νd12max...(1) -1<(Rr+Rf) / (Rr-Rf)<1...(2) 60<νd321max...(9) ０．５＜（１－β２ ２ ）×β３ ２ ＜１．５・・・・・（１０） however, νd12max: Abbe number for the d line of the first lens and the second lens Maximum value of Rf: radius of curvature of the image-side surface of the second lens Rr: radius of curvature of the object-side surface of the third lens νd321max: the maximum value of the Abbe number for the d line in the (m−2) lens, the (m−1) lens, and the m lens β2: lateral magnification of the second lens group when focused at infinity β3: lateral magnification of the third lens group when focused at infinity

2. 2. The optical system of claim 1, wherein the following formula is satisfied: 0.54<f1 / f2<3.74 (3) however, f1: focal length of the first lens group f2: focal length of the second lens group

3. 3. The optical system according to claim 1, wherein the following formula is satisfied: 0.78<f3 / f1<7.33...(4) however, f1: focal length of the first lens group f3: focal length of the third lens group

4. 4. The optical system according to claim 1, wherein the following formula is satisfied: ０．１２＜β２＜０．５８・・・・・（５） however, β2: lateral magnification of the second lens group when focused at infinity

5. The optical system according to any one of claims 1 to 4, which satisfies the following formula: Nd3<1.7...(6) however, Nd3: refractive index of the third lens with respect to the d line

6. 6. The optical system according to claim 1, wherein the following formula is satisfied: 60<νd2max...(7) however, νd2max: the maximum value of the Abbe number for the d-line of the lens in the second lens group

7. 7. The optical system according to claim 1, wherein the following formula is satisfied: νd123min<45...(8) however, νd123min: d in the first lens, the second lens, and the third lens Minimum Abbe number for a line

8. The first lens and the second lens are both negative lenses having a convex surface facing the object side. The optical system according to any one of claims 1 to 7, which is a squint lens.

9. 9. The optical system according to claim 1, wherein the second lens group is made up of three or less lenses.

10. 10. The first lens group according to claim 1, wherein the first lens group has at least one cemented lens. The optical system according to claim 1.

11. 11. The optical system according to claim 1, wherein the lens in the second lens group closest to the object side has a concave surface facing the object side.

12. The third lens group is composed of three or less lenses, and at least one negative lens and no aspherical lens.

13. An optical system according to any one of claims 1 to 12; An optical image formed by the optical system is converted into an electrical signal. an imaging element that converts An imaging device comprising:

Images