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 Art

[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. Such an optical system includes three lens groups: a first lens group, a second lens group, and a third lens group. The second lens group is movable for focusing, and all three lens groups have positive refractive power. An optical system is known (see, for example, Patent Documents 1 to 3).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the prior art as described above, there is still room for improvement from the perspective of achieving both a reduction in the overall optical length and high optical performance. For example, the technologies described in Patent Documents 1 and 2 are optical systems with a large aperture, but the focal length of the first lens group with respect to the focal length of the entire system and the focal length of the second lens group with respect to the focal length from the object side surface of the first lens group to the lens closest to the image side of the third lens group are not sufficiently optimized. Therefore, it is insufficient to improve the performance while shortening the overall optical length. In addition, in the technology described in Patent Document 3, the focal length of the first lens group with respect to the focal length from the object side surface of the first lens group to the lens closest to the image side of the third lens group is optimized, but the focal length of the second lens group with respect to the focal length from the object side surface of the first lens group to the lens closest to the image side of the third lens group is not sufficiently optimized. Therefore, it is insufficient to improve the performance while shortening the overall optical length.

[0005] An object of the present invention is to provide an optical system and an imaging device that have a short overall optical length and high performance.

Means for Solving the Problems

[0006] To solve the above problems, an optical system according to an aspect of the present invention includes, in order from the object side, a first lens group having a positive refractive power, a second lens group having a positive refractive power, and a third lens group having a positive refractive power. The second lens group is an optical system that is movable along the optical axis so as to change the interval between adjacent lens groups. The first lens group has at least a first lens, a second lens, and a third lens in order from the object side. The first lens and the second lens have a negative refractive power and satisfy the following formula. 1.5 < f1 / f < 7.0 ····· (1) 1.5 < f2 / f < 5.0 ····· (2) However, f: Focal length from the object side surface of the first lens group to the lens closest to the image side of the third lens group when focused at infinity f1: Focal length of the first lens group f2: Focal length of the second lens group

[0007] In order to solve the above problems, an imaging device according to an aspect of the present invention includes the above optical system and an image sensor provided on the image plane side of the optical system for converting an optical image formed by the optical system into an electrical signal.

Advantages of the Invention

[0008] According to an aspect of the present invention, it is possible to provide an optical system and an imaging device with a short overall optical length and high performance.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Modes for Carrying Out the Invention

[0010] 〔Embodiment 1〕 Hereinafter, an embodiment of the present invention will be described in detail. The embodiments of the present invention relate to an optical system suitable as an imaging optical system such as a film camera, a video camera, and a digital still camera, and an imaging device including the optical system. The optical system and the imaging device described below are one aspect of the optical system and the imaging device according to the present invention, and the optical system and the imaging device according to the present invention are not limited to the following aspects. In this specification, a configuration expressed as "consisting of" means that it substantially includes only that configuration.

[0011] 1. Optical System 1-1. Optical Configuration The optical system according to an embodiment of the present invention includes, in order from the object side, a first lens group having a positive refractive power, a second lens group having a positive refractive power, and a third lens group having a positive refractive power. Since each lens group has a positive refractive power, it becomes easy to condense the light beam. Therefore, in this embodiment, it is possible to design an optical system with a large aperture.

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

[0013] Also, in this specification, the lens group may include a cemented lens. When the lens group includes a cemented lens, the number of lens elements is counted by counting the lenses that are cemented together. Examples of the cemented lens include a cemented lens in which a plurality of lenses are integrated without an air gap. In this case, only the plurality of lenses constituting the cemented lens are counted. Another example of the cemented lens is a cemented lens in which a plurality of lenses are integrated by a layer of an adhesive that is very thin and has substantially no optical effect. In this case, the layer of the adhesive is not counted as a lens.

[0014] Further, the lens group may include a composite lens in which one lens and resin are integrated. For example, a composite lens in which one lens and resin are integrated is counted as one lens.

[0015] (1) First lens group The first lens group is the lens group located closest to the object side among the three lens groups constituting the optical system of the present embodiment. The first lens group has a positive refractive power as a whole. 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 powers. Thus, the lenses from the lens closest to the object side to the second lens in the first lens group are lenses (negative lenses) having negative refractive powers. In the present embodiment, with such a configuration, miniaturization in the radial direction can be achieved, and wide-angleization can also be realized.

[0016] Furthermore, it is more preferable that the first lens and the second lens are negative meniscus lenses with convex surfaces facing the object side. This configuration is preferable from the viewpoints of correcting distortion aberration and coma aberration, achieving miniaturization in the radial direction, and realizing wide-angleization.

[0017] Also, it is preferable to include at least one cemented lens in the first lens group. This configuration is preferable from the viewpoint of favorably correcting axial chromatic aberration and magnification chromatic aberration generated in the entire optical system. Also, this configuration is preferable from the viewpoint of reducing the lens interval and making the overall optical length of the optical system shorter.

[0018] (2) Second lens group The second lens group is the lens group located at the center of the three lens groups constituting the optical system of the present embodiment. The second lens group has a positive refractive power as a whole. The second lens group is movable along the optical axis so as to change the interval between adjacent lens groups, and in the optical system of the present embodiment, it becomes a focus group as will be described later.

[0019] The second lens group is preferably composed of three or fewer lenses. This configuration is preferable from the viewpoint of downsizing a driving device such as an actuator for moving the second lens group, and thus downsizing the entire lens barrel in the optical system of the present embodiment.

[0020] Also, in the second lens group, the lens closest to the object side of the second lens group preferably has a concave surface with respect to the object side. This configuration is preferable from the viewpoint of favorably correcting the image plane fluctuation that occurs during focusing.

[0021] (3) Third lens group The third lens group is the lens group located closest to the image plane side among the three lens groups constituting the optical system of the present embodiment. The third lens group has a positive refractive power as a whole lens group.

[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. And among these three or fewer lenses, it preferably includes at least one negative lens and does not include an aspherical lens. This configuration is preferable from the viewpoint of favorably correcting chromatic aberration and image plane properties.

[0023] (4) Other configurations The optical system of the embodiment of the present invention is composed of only three lens groups, namely, the first lens group, the second lens group, and the third lens group, in order from the object side. There are no other lens groups between the first lens group and the second lens group, between the second lens group and the third lens group, and on the image plane side of the third lens group. The optical system of the embodiment of the present invention may further include other optical elements other than the above lens groups within the range where the effects of the present embodiment can be obtained.

[0024] The optical system preferably has a diaphragm. Here, the diaphragm refers to the diaphragm that defines the light beam diameter of the optical system, that is, the diaphragm that defines the F-number of the optical system. The diaphragm is preferably disposed between the first lens group and the second lens group. This configuration is preferable from the viewpoint of reducing the effective diameters of the lenses on the object side and the image plane side of the diaphragm. Further, this configuration is preferable from the viewpoint of making the effective diameters of both surfaces, i.e., the object side of the positive lens (positive lens) on the object side of the diaphragm and the image plane side of the positive lens on the image plane side of the diaphragm, relatively small with respect to the diaphragm. This configuration is preferable from the viewpoint of suppressing the action of aberration correction by adjacent lenses.

[0025] 1-2. Operation at Focus In an embodiment of the present invention, the second lens group is movable along the optical axis so as to change the interval between adjacent lens groups. The second lens group functions as a so-called focus group and moves in the optical axis direction when focusing from infinity to a finite distance object. The configuration in which the second lens group is a focus group enables miniaturization including the entire lens barrel of the optical system because focusing is performed only by the movement of only a part of the lens groups (only one lens group) constituting the optical system.

[0026] 1-3. Expressions Representing Conditions of the Optical System The optical system according to the present embodiment preferably adopts the above-described configuration and satisfies at least one of the following expressions. 1.5 < f1 / f < 7.0 ····· (1) However, f: Focal length of the optical system at infinity focus f1: Focal length of the first lens group

[0027] Equation (1) defines the focal length of the first lens group and the focal length of the optical system when focused at infinity. Satisfying Equation (1) is preferable from the viewpoint of achieving miniaturization of the optical system and good correction of aberrations. If f1 / f exceeds the upper limit of Equation (1), the power of the first lens group becomes weak, leading to an increase in the size of the entire optical system, which is not preferable. On the other hand, if f1 / f is less than the lower limit of Equation (1), the power of the first lens group becomes strong, which is advantageous for miniaturization. However, the amount of coma aberration and the like generated within the group increases, making correction difficult, which is not preferable. From the above viewpoints, f1 / f is more preferably greater than 1.80, and even more preferably greater than 1.95. Also, from the above viewpoints, f1 / f is more preferably less than 6.50, and even more preferably less than 6.10.

[0028] The optical system according to the present embodiment preferably satisfies the following conditions. 1.5 < f2 / f < 5.0 ····· (2) However, f: Focal length of the optical system when focused at infinity f2: Focal length of the second lens group

[0029] Equation (2) defines the focal length of the second lens group and the focal length of the optical system when focused at infinity. Satisfying Equation (2) is preferable from the viewpoint of achieving miniaturization in the radial direction of the optical system and good correction of aberrations. If f2 / f exceeds the upper limit of Equation (2), the power of the second lens group becomes weak, the movement amount of the focus group increases, and the actuator and the like for moving the focus group become large, which is not preferable. On the other hand, if f2 / f is less than the lower limit of Equation (2), the power of the second lens group becomes strong, which is advantageous for miniaturization of the focus group. However, the aberration variation becomes large during focusing, making correction difficult, which is not preferable. From the above viewpoints, f2 / f is more preferably greater than 1.80, and even more preferably greater than 1.95. Also, from the above viewpoints, f2 / f is more preferably less than 4.00, and even more preferably less than 3.50.

[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] Equation (3) defines the focal length of the first lens group and the focal length of the second lens group. Satisfying Equation (3) is preferable from the viewpoint of realizing miniaturization of the optical system and good correction of aberrations. When f1 / f2 becomes equal to or greater than the upper limit of Equation (3), the power of the first lens group becomes weak, leading to an increase in the size of the entire optical system. When f1 / f2 becomes equal to or less than the lower limit of Equation (3), the power of the first lens group becomes strong, which is advantageous for miniaturization, but the amount of coma aberration and the like generated within the first lens group increases, making correction difficult. From the viewpoint of well-correcting aberrations such as coma aberration, f1 / f2 is more preferably greater than 0.62, and even more preferably greater than 0.70. Also, from the viewpoint of miniaturization 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] Equation (4) defines the focal length of the third lens group and the focal length of the first lens group. Satisfying Equation (4) is preferable from the viewpoint of achieving miniaturization in the radial direction of the optical system and good correction of aberrations. When f3 / f1 is below the lower limit of Equation (4), the power of the third lens group becomes strong and the power of the first lens group becomes weak. For this reason, the incidence height of off-axis rays on the third lens group becomes high, and the diameter of the third lens group becomes large. When f3 / f1 is above the upper limit of Equation (4), the power of the third lens group becomes weak and the power of the first lens group becomes strong. For this reason, it is advantageous for reducing the diameter of the third lens group, but the amount of coma aberration and the like generated within the first lens group increases, making correction difficult. From the above viewpoints, f3 / f1 is more preferably greater than 0.89, and even more preferably greater than 1.00. Also, from the above viewpoints, f3 / f1 is more preferably less than 6.77, and even more preferably less than 6.20.

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

[0035] Equation (5) defines the lateral magnification of the second lens group. Satisfying Equation (5) is preferable from the viewpoint of achieving miniaturization of the optical system and good correction of aberrations. When β2 is above the upper limit of Equation (5), the combined focal length of the first lens group and the second lens group becomes long and the power becomes weak, leading to enlargement of the entire optical system. When β2 is below the lower limit of Equation (5), the combined power of the first lens group and the second lens group becomes strong, which is advantageous for miniaturization, but the aberration variation during correction of coma aberration and focusing within the group increases, making correction difficult. From the above viewpoints, β2 is more preferably greater than 0.13, and even more preferably greater than 0.15. Also, 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 with respect to the d-line

[0037] Equation (6) defines the refractive index of the third lens at the d-line. Satisfying Equation (6) is preferable from the viewpoint of improving the performance of the optical system. When Nd3 exceeds the upper limit of Equation (6), the power of the third lens becomes strong, and it becomes difficult to design a lens shape advantageous for aberration correction such as field curvature, which is not preferable from the viewpoint of performance improvement. From the above viewpoints, Nd3 is more preferably less than 1.65, and even more preferably less than 1.60. According to the above viewpoints, there is no particular need to define a lower limit value for Nd3, but for example, from the viewpoint that the effects of the above viewpoints are sufficiently manifested, it may be more than 1.30.

[0038] The optical system according to this embodiment preferably satisfies the following conditions. 60 < νd2max ····· (7) However, νd2max: Maximum value of the Abbe number with respect to the d-line in the lenses of the second lens group

[0039] Equation (7) defines the Abbe number with respect to the d-line in the lenses of the second lens group. νd2max is the highest value among the Abbe numbers with respect to the d-line of each lens constituting the second lens group. Satisfying Equation (7) is preferable from the viewpoint of good aberration correction. When νd2max is below the lower limit of Equation (7), it becomes difficult to use a low-dispersion material within the second lens group, making it difficult to correct axial chromatic aberration and magnification chromatic aberration. From the above viewpoints, νd2max is more preferably more than 70, and even more preferably more than 80. According to the above viewpoints, there is no particular need to define an upper limit value for νd2max, but for example, from the viewpoint that the effects of the above viewpoints are sufficiently manifested, it may be less than 120.

[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 in the first lens, second lens, and third lens

[0041] Equation (8) defines the Abbe number for the d-line that is the lowest among the first lens, second lens, and third lens. Satisfying Equation (8) is preferable from the perspective of good correction of aberrations. When νd123min exceeds the upper limit of Equation (8), correction of magnification chromatic aberration and the like becomes difficult. From the above perspective, νd123min is more preferably less than 40, and even more preferably less than 36. Although there is no particular need to define a lower limit value for νd123min according to the above perspective, for example, from the perspective that the effects of the above perspective are fully manifested, it is preferably greater than 10.

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

[0043] Equation (9) defines the Abbe number for the d-line that is the highest among the three lenses arranged in order from the image plane side among the lenses included in the third lens group. νd321max is the highest value among the Abbe numbers for the d-line of each of the three lenses located on the most image plane side in the third lens group. Note that m is the total number of lenses in the optical system, and is preferably an integer of 7 or more. Satisfying Equation (9) is preferable from the perspective of good correction of aberrations. When νd321max is below the lower limit of Equation (9), correction of magnification chromatic aberration and the like becomes difficult. From the above perspective, νd321max is more preferably greater than 65, and even more preferably greater than 70. Although there is no particular need to define an upper limit value for νd321max according to the above perspective, for example, from the perspective that the effects of the above perspective are fully manifested, it is preferably 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 at infinity focus of the second lens group β3: Lateral magnification at infinity focus of the third lens group

[0045] Equation (10) shows the ratio of the movement amount of the imaging surface to the movement amount of the second lens group in the optical axis direction. Satisfying Equation (10) is preferable from the viewpoints of miniaturization of the optical system and good correction of aberrations. (1 - β2 2 ) × β3 2 When it becomes less than or equal to the lower limit of Equation (10), the overall optical length becomes longer due to the increase in the movement amount of the second lens group. (1 - β2 2 ) × β3 2 When it becomes greater than or equal to the upper limit of Equation (10), it is advantageous for miniaturization of the focus group (the second lens group), but the aberration variation becomes large during focusing and correction becomes difficult. From the viewpoint of making the overall optical length shorter, (1 - β2 2 ) × β3 2 is more preferably greater than 0.7, and even more preferably greater than 0.9. Also, from the viewpoint of suppressing aberration variation 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 the optical system according to the above embodiment and an imaging element provided on the image plane side of the optical system that converts the optical image formed by the optical system into an electrical signal. The optical system in this embodiment is, for example, a single-focus lens.

[0047] Here, there is no limitation to the imaging device, and solid-state imaging devices such as CCD (Charge Coupled Device) sensors and CMOS (Complementary Metal Oxide Semiconductor) sensors, silver halide films, infrared cut filters (IRCF), etc. can also be used. The imaging device according to the present embodiment is suitable for imaging devices using the above solid-state imaging devices, such as cameras for FA, digital cameras, and video cameras. Further, the imaging device may be a lens-fixed imaging device in which the lens is fixed to the housing, or may be an interchangeable-lens imaging device such as a single-lens reflex camera or a mirrorless single-lens camera.

[0048] FIG. 11 is a diagram schematically showing an example of the configuration of the imaging device according to the present embodiment. As shown in FIG. 11, the 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 aspect of the 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 a positive refractive power. Further, the first lens group 31 has at least a first lens, a second lens, and a third lens in order from the object side. Furthermore, the optical system 30 is configured to satisfy, for example, the above-described formulas (1) and (2). Note that a diaphragm 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 and a CCD sensor 22 as an imaging device. The CCD sensor 22 is disposed at a position centered on the optical axis OA of the optical system 30 in the lens barrel 3 attached to the main body 2 within the main body 2. The main body 2 may have an optical element having substantially no refractive power, such as an infrared cut filter, instead of the cover glass 21.

[0051] In the embodiment of the present invention, the optical system is configured as a small-sized, large-aperture, and high-performance optical system with a short overall length by appropriately arranging the power of the optical system and the movable group during focusing. And since the imaging device in the embodiment of the present invention includes such an optical system, it is suitable for imaging devices that require high performance with a small length in the optical axis direction, such as in-vehicle cameras and digital input / output devices such as drone-mounted cameras.

[0052] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope shown in 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 example of the present invention will be described below. In the following tables, all units of length are "mm" and all units of the angle of view are "°". Also, "E-a" indicates "×10 -a ". Also, in Example 1, the displays in the figures and tables will be described, and the displays in the figures and tables in Example 1 are the same for the figures and tables in other examples.

[0054] The optical systems of Example 1 to Example 5 shown below are composed of, in order from the object side, a first lens group G1 having a positive refractive power, a diaphragm S, a second lens group G2 having a positive refractive power, and a third lens group G3 having a positive refractive power. Also, when focusing from an infinite distance to a finite-distance object, the first lens group G1 and the third lens group G3 do not move while being fixed with respect to the image plane IMG, and the second lens group G2 moves toward the object side along the optical axis.

[0055] [Example 1] FIG. 1 is a diagram schematically showing an optical configuration at infinity focusing of the optical system of Example 1. "CG" shown in FIG. 1 is a cover glass, and "IMG" is an image plane (imaging plane). The arrow in the figure shows the state of movement of the second lens group G2 during focusing. The arrow indicates that the second lens group G2 moves substantially linearly within the range in the optical axis direction at the arrow for focusing.

[0056] The first lens group is composed of, in order from the object side, a negative meniscus lens having a convex surface with respect to the object side, a negative meniscus lens having a convex surface with respect to the object side, a biconcave lens, a biconvex lens, a cemented lens in which a biconcave lens and a biconvex lens are cemented, and a positive meniscus lens having a convex surface with respect to 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 with respect to 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 the surface data of the optical system of Example 1.

[0060] In the example, "Surface No." is the order of the lens surfaces when counting the lens surfaces of the optical system from the object side, "R" is the radius of curvature of the lens surface, "D" is the interval on the optical axis of the lens surface, "Nd" is the refractive index of the lens with respect to the d-line (wavelength λ = 587.56 nm), and "ABV" represents the Abbe number of the lens with respect to the d-line of the lens. "D(n)" (n is an integer) means that the interval on the optical axis of the lens surface is a variable interval that changes during focusing. Also, "STOP" attached to the surface number indicates that it is a diaphragm, and "ASPH" indicates that the lens surface is an aspherical surface. Also, "0.0000" in the column of the radius of curvature represents a plane.

[0061] [Table 1] Surface No. R D 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 table of the optical system of Example 1. In this specifications table, numerical values of respective optical characteristics at each shooting distance are shown. In this specifications 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 is a table showing the aspherical coefficients of each aspherical surface in the optical system of Example 1. "K, A4, A6, A8, A10, A12" in the table are the coefficients when the aspherical shape of each aspherical surface is defined by the following formula. In the following formula, "Z" is the displacement amount from the reference surface in the optical axis direction, "r" is the paraxial curvature radius, "h" is the height from the optical axis in the direction perpendicular to the optical axis, "K" is the conic coefficient, and "An" is the aspherical coefficient of the n-th order.

[0065]

Equation

[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] Further, FIG. 2 is a diagram showing the longitudinal aberration at infinity focus of the optical system of Example 1. FIG. 2 shows spherical aberration (mm), astigmatism (mm), and distortion (%) in order from the left side toward the drawing.

[0068] In the diagram representing spherical aberration, the vertical axis is the ratio to the open F-number, and the horizontal axis is defocus. In the diagram representing spherical aberration, the solid line indicates the longitudinal aberration at the d-line (wavelength λ = 587.56 nm), the dashed line indicates the longitudinal aberration at the F-line (wavelength λ = 486.13 nm), and the dotted line indicates the longitudinal aberration at the C-line (wavelength λ = 656.28 nm).

[0069] In the diagram representing astigmatism, the vertical axis is the semi-field angle (°), and the horizontal axis is defocus. In the diagram representing astigmatism, the solid line indicates the sagittal image plane (S) for the d-line (wavelength λ = 587.56 nm), and the long dashed dotted line indicates the meridional image plane (T) for the d-line.

[0070] In the diagram representing distortion, the vertical axis is the semi-field angle (°), and the horizontal axis is distortion (%).

[0071] [Example 2] Fig. 3 schematically shows the optical configuration at infinity focus of the optical system of Example 2, and Fig. 4 shows the longitudinal spherical aberration at infinity focus of the optical system of Example 2. Table 4 shows the surface data of the optical system of Example 2, Table 5 shows the specifications table of the optical system of Example 2, and Table 6 shows the aspherical coefficients of each aspherical surface in the optical system of Example 2.

[0072] [Table 4] Surface No. R D 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] Fig. 5 schematically shows the optical configuration at infinity focus of the optical system of Example 3, and Fig. 6 shows the longitudinal spherical aberration at infinity focus of the optical system of Example 3. Further, Table 7 shows the surface data of the optical system of Example 3, Table 8 shows the specification table of the optical system of Example 3, and Table 9 shows the aspherical coefficients of each aspherical surface in the optical system of Example 3.

[0076] [Table 7] Surface No. R D Nd ABV 1 ASPH 22.9749 1.4000 1.69350 53.20 2 ASPH 9.9172 6.5857 3 31.0739 1.2000 1.48749 70.44 4 16.6992 10.0647 5 ASPH -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 14 STOP 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 at infinity focus of the optical system of Example 4 is schematically shown in FIG. 7, and the longitudinal aberration at infinity focus of the optical system of Example 4 is shown in FIG. 8. Also, the surface data of the optical system of Example 4 is shown in Table 10, the 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. R D 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 0.1500 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 4.7492 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 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 at infinity focus of the optical system of Example 5 is schematically shown in Fig. 9, and the longitudinal aberration at infinity focus of the optical system of Example 5 is shown in Fig. 10. Also, the surface data of the optical system of Example 5 is shown in Table 13, the 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. R D Nd ABV 1 ASPH 24.3621 1.4000 1.61881 63.85 2 ASPH 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 0.0000 D(15) 16ASPH -17.4108 1.1000 1.76802 49.24 17ASPH -20.0000 0.3438 18 39.7191 5.3491 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] 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] In addition, the calculated values according to the above 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 f 13.13, 13.13, 13.13, 13.13, 13.13 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

[0089] [Table 17] Example 1, Example 2, Example 3, Example 4, Example 5 (1) f1 / f 3.08, 6.00, 2.00, 2.42, 3.31 (2) f2 / f 2.25, 2.08, 2.59, 2.50, 2.25 (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 Body 3 Lens barrel 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 Diaphragm IMG Image Plane OA Optical Axis

Claims

1. An optical system comprising, in order from the object side, a first lens group having a positive refractive power, a second lens group having a positive refractive power, and a third lens group having a positive refractive power, wherein the second lens group is movable along the optical axis so as to change the distance between adjacent lens groups at the time of focusing. 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 powers. The third lens group has at least the (m - 2)th lens, the (m - 1)th lens, and the mth lens when the total number of lenses in the optical system is m. An optical system that satisfies the following formula. 1.5 < f1 / f < 7.0 ······ (1) 1.5 < f2 / f < 5.0 ······ (2) 60 < νd321max ········ (9) However, f: The focal length of the optical system at infinity focus f1: The focal length of the first lens group f2: The focal length of the second lens group νd321max: The maximum value of the Abbe number with respect to the d-line in the (m - 2)th lens, the (m - 1)th lens, and the mth lens

2. The optical system according to claim 1, which satisfies the following formula. 0.54 < f1 / f2 < 3.74 ······ (3)

3. The optical system according to claim 1 or 2, which satisfies the following formula. 0.78 < f3 / f1 < 7.33 ······ (4) However, f3: The focal length of the third lens group

4. The optical system according to any one of claims 1 to 3, which satisfies the following formula. ０．１２＜β２＜０．５８・・・・・（５） However, β2: The lateral magnification of the second lens group at infinity focus

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

6. The optical system according to any one of claims 1 to 5, which satisfies the following formula. 60 < νd2max ······ (7) However, νd2max: The maximum value of the Abbe number with respect to the d-line in the lenses of the second lens group

7. The optical system according to any one of claims 1 to 6, which satisfies the following formula. νd123min < 45 ······ (8) However, νd123min: The minimum value of the Abbe number with respect to the d-line in the first lens, the second lens, and the third lens

8. The optical system according to any one of claims 1 to 7, which satisfies the following formula. ０．５＜（１－β２ ２ ）×β３ ２ ＜１．５・・・・・（１０） However, β3: The lateral magnification of the third lens group at infinity focus

9. The optical system according to any one of claims 1 to 8, wherein both the first lens and the second lens are negative meniscus lenses having convex surfaces facing the object side.

10. The optical system according to any one of claims 1 to 9, wherein the second lens group is composed of three or fewer lenses.

11. The optical system according to any one of claims 1 to 10, wherein the first lens group has at least one cemented lens.

12. The optical system according to any one of claims 1 to 11, wherein the lens closest to the object side in the second lens group has a concave surface facing the object side.

13. The optical system according to any one of claims 1 to 12, wherein the third lens group is composed of three or fewer lenses, includes at least one negative lens, and does not include an aspherical lens.

14. An imaging device comprising: the optical system according to any one of claims 1 to 13; and an imaging element provided on the image plane side of the optical system and configured to convert an optical image formed by the optical system into an electrical signal.

Images