JP7734014B2 - Optical system and imaging device - Google Patents

Description

The present invention relates to an optical system and an imaging device.

Optical systems used in video cameras, digital still cameras, and mirrorless cameras are required to be small and have high optical performance. Known examples of such optical systems include an optical system consisting 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).

JP 2019-66585 A Japanese Patent Application Laid-Open No. 2017-167327 International Publication No. 2019/073744

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-aperture optical systems, but provide insufficient correction of lateral chromatic aberration. The technology described in Patent Document 3 leaves room for improvement in the arrangement of lenses in the first lens group, and does not adequately achieve both a shorter overall optical length and high performance.

The objective of the present invention is to provide a compact, large-aperture, high-performance optical system and imaging device.

In order to solve the above-described problems, an optical system according to one aspect 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, and 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 satisfies the following formula:
65<νd12max...(1)
-1<(Rr+Rf)/(Rr-Rf)<1...(2)
however,
νd12max: maximum value of Abbe number for 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.

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.

One aspect of the present invention provides a compact, large-aperture, high-performance optical system and imaging device.

FIG. 2 is a diagram illustrating an optical configuration of the optical system of Example 1 when focused at infinity. FIG. 4 is a diagram showing longitudinal aberration of the optical system of Example 1 when focused at infinity. FIG. 10 is a diagram illustrating an optical configuration of the optical system of Example 2 when focused at infinity. FIG. 10 is a diagram showing longitudinal aberration of the optical system of Example 2 when focused at infinity. FIG. 10 is a diagram illustrating an optical configuration of the optical system of Example 3 when focused at infinity. FIG. 10 is a diagram showing longitudinal aberration of the optical system of Example 3 when focused at infinity. FIG. 10 is a diagram illustrating an optical configuration of the optical system of Example 4 when focused at infinity. FIG. 10 is a diagram showing longitudinal aberration of the optical system of Example 4 when focused at infinity. FIG. 12 is a diagram illustrating an optical configuration of the optical system of Example 5 when focused at infinity. FIG. 10 is a diagram showing longitudinal aberration of the optical system of Example 5 when focused at infinity. 1 is a diagram schematically illustrating an example of the configuration of an imaging device according to an embodiment of the present invention.

[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.

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 makes it possible to design an optical system with a large aperture.

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.

In addition, in this specification, a lens group may include a cemented lens. When a lens group includes a cemented lens, the number of lenses includes each cemented lens. An example of a cemented lens is a cemented lens in which multiple lenses are integrated with no 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 with a very thin layer of adhesive that has no substantial optical effect. In this case, the adhesive layer is not counted as a lens.

The lens group may also include a compound lens in which a single lens is integrated with resin. For example, a compound lens in which a single lens is integrated with resin is counted as one lens.

(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.

Moreover, it is more preferable that the first lens and the second lens are negative meniscus lenses with their convex surfaces facing the object side. 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.

It is also preferable that the first lens group includes at least one cemented lens. This configuration is preferable from the perspective of effectively correcting axial chromatic aberration and lateral chromatic aberration that occur throughout the entire optical system. This configuration is also preferable from the perspective of reducing the lens spacing and shortening the overall optical length of the optical system.

(2) Second Lens Group The second lens group is the lens group located in the center 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.

The second lens group is preferably composed of three or fewer lenses. This configuration is preferable from the perspective of miniaturizing the actuator and other driving devices that move the second lens group, thereby miniaturizing the entire lens barrel in the optical system of this embodiment.

Furthermore, in the second lens group, it is preferable that the lens closest to the object side in the second lens group has a concave surface facing the object side. This configuration is preferable from the perspective of effectively correcting image plane fluctuations that occur during focusing.

(3) Third Lens Group The third lens group is the lens group located closest to the image plane among the three lens groups constituting the optical system of this embodiment. The third lens group as a whole has positive refractive power.

The third lens group is preferably composed of three or fewer lenses. This configuration is preferable from the perspective of reducing the number of lenses and shortening the overall optical length. Furthermore, it is preferable that these three or fewer lenses include at least one negative lens, but do not include an aspherical lens. This configuration is preferable from the perspective of excellent correction of chromatic aberration and image plane characteristics.

(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 this embodiment can be achieved.

It is preferable that the optical system has a diaphragm. However, the diaphragm referred to here is the diaphragm that determines the light beam diameter of the optical system, i.e., the diaphragm that determines the F-number of the optical system. From the perspective of making the diaphragm unit more compact, it is preferable that the diaphragm be located between the first lens group and the second lens group.

1-2. Operation During Focusing 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 the focus group allows focusing to be performed by moving only a portion of the lens groups that make up the optical system (only one lens group), making it possible to reduce the size of the entire optical system, including the lens barrel.

1-3. Formulas Representing 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 formulas.
65<νd12max...(1)
however,
νd12max: maximum value of the Abbe number for the d-line of the first lens and the second lens

Equation (1) defines the maximum Abbe number for the d-line of the first lens and the second lens. Satisfying equation (1) is preferable from the perspective 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 equation (1), it becomes difficult to correct lateral chromatic aberration and the like. From the above perspective, νd12max is preferably greater than 67, and more preferably greater than 70. From the above perspective, there is no need to specifically define an upper limit for νd12max, but it may be less than 120, for example, from the perspective of fully demonstrating the effects of the above perspective.

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

Equation (2) defines the shape of the air lens between the second lens and the third lens. Satisfying equation (2) is preferable from the perspective of suppressing fluctuations in various aberrations while maintaining a manufacturable lens radius of curvature. 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 aberrations will increase, which is undesirable from the perspective of improving the performance of the optical system. From the above perspective, it is more preferable that (Rr + Rf)/(Rr - Rf) is greater than -0.60, and even more preferable that it is greater than -0.40. Furthermore, from the above perspective, it is more preferable that (Rr + Rf)/(Rr - Rf) is less than 0.60, and even more preferable that it is less than 0.40.

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

Equation (3) defines the focal lengths of the first and second lens groups. Satisfying equation (3) is preferable from the perspective of achieving compactness and good aberration correction for the optical system. If f1/f2 is equal to or greater than the upper limit of equation (3), the power of the first lens group weakens, leading to an increase in the size of the entire optical system. If f1/f2 is equal to or less than the lower limit of equation (3), the power of the first lens group strengthens, which is advantageous for compactness, but increases the amount of coma and other aberrations generated within the first lens group, making correction difficult. From the perspective of good correction of aberrations such as coma, f1/f2 is more preferably greater than 0.62, and even more preferably greater than 0.70. Furthermore, from the perspective of achieving compactness for the optical system, f1/f2 is more preferably less than 3.46, and even more preferably less than 3.17.

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

Equation (4) defines the focal lengths of the third lens group and the first lens group. Satisfying equation (4) is preferable from the perspective of achieving a compact optical system in the radial direction and good aberration correction. When f3/f1 is below the lower limit of equation (4), the power of the third lens group becomes stronger and the power of the first lens group becomes weaker. As a result, the height of incidence of off-axial light rays on the third lens group increases, increasing the diameter of the third lens group. When f3/f1 is above the upper limit of equation (4), the power of the third lens group becomes weaker and the power of the first lens group becomes stronger. This is advantageous for reducing the diameter of the third lens group, but increases the amount of coma and other aberrations occurring within 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.

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

Equation (5) defines the lateral magnification of the second lens group. Satisfying equation (5) is preferable from the perspective of achieving compactness in the optical system and good aberration correction. If β2 is equal to or greater than the upper limit of equation (5), the combined focal length of the first and second lens groups becomes long and the power becomes weaker, leading to an increase in the size of the entire optical system. If β2 is equal to or less than the lower limit of equation (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 group and aberration fluctuations during focusing large, making correction difficult. From the above perspective, β2 is more preferably greater than 0.13, and even more preferably greater than 0.15. From the above perspective, β2 is more preferably less than 0.53, and even more preferably less than 0.49.

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

Equation (6) defines the refractive index of the third lens at the d-line. Satisfying equation (6) is preferable from the perspective of improving the performance of the optical system. If Nd3 is equal to or greater than the upper limit of equation (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 perspective of improving performance. From the above perspective, Nd3 is more preferably less than 1.65, and even more preferably less than 1.60. From the above perspective, there is no need to specifically define a lower limit for Nd3, but it may be greater than 1.30, for example, from the perspective of fully demonstrating the effects of the above perspective.

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

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

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 lens, the second lens, and the third lens

Equation (8) defines the lowest Abbe number at the d-line among the first, second, and third lenses. Satisfying equation (8) is preferable from the perspective of good correction of aberrations. If νd123min is equal to or greater than the upper limit of equation (8), it becomes difficult to correct lateral chromatic aberration and the like. From the above perspective, νd123min is more preferably less than 40, and even more preferably less than 36. From the above perspective, there is no need to specifically define a lower limit for νd123min, but it is preferable that it be greater than 10, for example, from the perspective of fully demonstrating the effects of the above perspective.

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

Equation (9) defines the highest Abbe number at the d-line of the three lenses included in the third lens group, positioned closest to the image plane. νd321max is the highest Abbe number at the d-line of each of the three lenses positioned closest to the image plane 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 achieving 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 specifically 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.

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

Equation (10) represents 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 viewpoints of compactness of the optical system and good correction of aberrations. When (1-β2 ² )×β3 ² is equal to or less than the lower limit of equation (10), the amount of movement of the second lens group increases, resulting in a long overall optical length. When (1-β2 ² )×β3 ² is equal to or greater than the upper limit of equation (10), this is advantageous for compactness of the focus group (second lens group), but aberration fluctuations during focusing become large, making correction difficult. From the viewpoint of further shortening the overall optical length, (1-β2 ² )×β3 ² is more preferably greater than 0.7, and even more preferably greater than 0.9. Furthermore, 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.

2. Imaging Device Next, an imaging device according to one embodiment of the present invention will be described. The imaging device includes an optical system according to the above embodiment and an imaging element 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.

Here, the imaging element is not limited, and solid-state imaging elements such as CCD (Charge Coupled Device) sensors and CMOS (Complementary Metal Oxide Semiconductor) sensors, as well as silver halide film, can also be used. The imaging device according to this embodiment is suitable for imaging devices that use the above solid-state imaging elements, such as digital cameras and video cameras. The imaging device may also 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 mirrorless single-lens camera.

Figure 11 is a diagram showing a schematic example of the configuration of an imaging device according to this embodiment. As shown in Figure 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 imaging device.

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.

The main body 2 has a cover glass 21 and a CCD sensor 22 as imaging elements. The CCD sensor 22 is positioned within the main body 2 at a position where the optical axis OA of the optical system 30 within the lens barrel 3 attached to the main body 2 is its central axis. Instead of the cover glass 21, the main body 2 may have an optical element with no substantial refractive power, such as an infrared cut filter.

The optical system in the embodiment of the present invention is configured as a compact, high-performance optical system with a short overall length and large aperture by optimizing the power distribution of the optical system and the movable group during focusing. Furthermore, the imaging device in the embodiment of the present invention is equipped with such an optical system, making it suitable for imaging devices that are short in length along the optical axis and require high-performance imaging, such as digital input/output devices such as in-vehicle cameras and drone-mounted cameras.

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.

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, "E-a" represents "×10 ^-a ". While the representations in the figures and tables of Example 1 will be described, the representations in the figures and tables of Example 1 are similar to those in the figures and tables of other examples.

The optical systems of Examples 1 to 5 shown below are composed of, in order from the object side, a first lens group G1 with positive refractive power, a diaphragm S, a second lens group G2 with positive refractive power, and a third lens group G3 with positive refractive power. Furthermore, 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.

[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" denotes a cover glass, and "IMG" denotes 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.

The first lens group is composed of, in order from the object side, a negative meniscus lens with a convex surface facing the object side, a negative meniscus lens with a convex surface facing the object side, a biconcave lens, a biconvex lens, a cemented lens consisting of a biconcave lens and a biconvex lens, and a positive meniscus lens with a convex surface facing the object side.

The second lens group consists of, from the object side, a negative meniscus lens with a concave surface facing the object side, and a biconvex lens.

The third lens group consists of, from the object side, a biconcave lens, a biconvex lens, and a biconvex lens.

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

In the examples, "Surface No." indicates the order of the lens surface when counting from the object side, "R" indicates the radius of curvature of the lens surface, "D" indicates the distance on the optical axis between the lens surfaces, "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 on the optical axis between lens surfaces is a variable distance that changes when focusing. Additionally, "STOP" accompanying the surface number indicates that it is a stop, and "ASPH" indicates that the lens surface is aspherical. Additionally, "0.0000" in the radius of curvature column indicates a flat surface.

[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

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.

[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

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 the 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 nth-order aspherical coefficient.

[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

Figure 2 shows the longitudinal aberration of the optical system of Example 1 when focused at infinity. From the left, Figure 2 shows spherical aberration (mm), astigmatism (mm), and distortion (%).

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).

In the diagram showing astigmatism, the vertical axis represents the half angle of view (°) and the horizontal axis represents defocus. In the diagram 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.

In the graph showing distortion, the vertical axis represents half angle of view (°) and the horizontal axis represents distortion (%).

[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.

[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

[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

[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

[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.

[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

[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

[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

[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.

[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
14STOP 0.0000 0.0000
15 0.0000 D(15)
16ASPH -22.4464 1.1000 1.76802 49.24
17ASPH -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

[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

[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

[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.

[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 0.0000 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

[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

[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

The values calculated using the above formulas and the numerical values used in those formulas in Examples 1 to 5 are shown in Tables 16 and 17.

[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

[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

1. Mirrorless single-lens camera (imaging device)
2 Main body 3 Lens barrel 21 CG cover glass 22 CCD sensor (image pickup element)
30 Optical system 31, G1 First lens group 32, G2 Second lens group 33, G3 Third lens group 34, S Stop IMG Image plane OA Optical axis

Claims (13)

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: the maximum value of the Abbe number for the d line in the first lens and the second lens; Rf: the radius of curvature of the image-side surface of the second lens; Rr: the 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. 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. 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. 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 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. 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. 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 optical system according to claim 1, wherein the first lens and the second lens are both negative meniscus lenses having a convex surface facing the object side. The optical system described in any one of claims 1 to 8, wherein the second lens group is composed of three or fewer lenses. 10. The optical system according to claim 1, wherein the first lens group has at least one cemented lens. The optical system described in any one of claims 1 to 10, wherein the lens closest to the object side in the second lens group has a concave surface facing the object side. 12. The optical system according to claim 1, wherein the third lens group is made up of three or less lenses, includes at least one negative lens, and does not include an aspherical lens. An optical system according to any one of claims 1 to 12;
an image pickup element provided on an image plane side of the optical system, for converting an optical image formed by the optical system into an electrical signal;
An imaging device comprising: