Optical system and imaging device

Abstract

This technology enables weight reduction and a decrease in the amount of movement of the lens group during focusing, providing an optical system with high optical performance. [Solution] The optical system L0 has a first lens group L1 with positive refractive power and a second lens group L2 with negative refractive power. The first lens group does not move during focusing, while the second lens group moves. When the focal length of the optical system is f, the focal length of the second lens group is f2, the Abbe number νdgn1 is the number of the negative lens closest to the object among at least one negative lens included in the first lens group, and SG is the minimum specific gravity of each lens included in the second lens group, the following conditions are satisfied: -8.50 ≤ f2 / f ≤ -1.15, 10.00 ≤ νdgn1 ≤ 31.00, and 0.80 ≤ SG ≤ 2.38.

Description

Technical Field

[0001] The present invention relates to an optical system suitable for imaging.

Background Art

[0002] The optical system disclosed in Patent Document 1 as an optical system used for imaging is composed of, in order from the object side, a first lens group having a positive refractive power that is stationary during focusing, a second lens group having a negative refractive power that moves during focusing, and a third lens group having a positive refractive power that is stationary during focusing.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In an optical system, it is required to reduce the weight and the amount of movement of the lens group that moves during focusing, and further to obtain high optical performance.

Means for Solving the Problems

[0005] The optical system as one aspect of the present invention has a first lens group with a positive refractive power and a second lens group with a negative refractive power, which are arranged in order from the object side to the image side. During focusing, the first lens group does not move, and the second lens group moves. When the focal length of the optical system is f, the focal length of the second lens group is f2, the Abbe number based on the d-line of the most object-side negative lens among at least one negative lens included in the first lens group is νdgn1, and the minimum value of the specific gravity of each of all the lenses included in the second lens group is SG, -8.50 ≦ f2 / f ≦ -1.15 10.00 ≦ νdgn1 ≦ 31.00 0.80 ≦ SG ≦ 2.38 It is characterized by satisfying the following conditions.

[0006] Furthermore, another aspect of the present invention is that the optical system is characterized in that the first lens group has two or more positive lenses. An imaging device equipped with the above optical system also constitutes another aspect of the present invention. [Effects of the Invention]

[0007] According to the present invention, the lens group that moves during focusing can be made lighter. Furthermore, the amount of movement of the lens group can be reduced. In addition, higher optical performance can be obtained. [Brief explanation of the drawing]

[0008] [Figure 1] Cross-sectional view of the optical system of Example 1. [Figure 2] Aberration diagram of the optical system of Example 1 at infinity focus. [Figure 3] Aberration diagram of the optical system of Example 1 in the closest focus state. [Figure 4] Cross-sectional view of the optical system in Example 2. [Figure 5] Aberration diagram of the optical system of Example 2 in the state of infinity focus. [Figure 6] Aberration diagram of the optical system of Example 2 in the closest focus state. [Figure 7] Cross-sectional view of the optical system of Example 3. [Figure 8] Aberration diagram of the optical system of Example 3 at infinity focus. [Figure 9] Aberration diagram of the optical system of Example 3 in the closest focus state. [Figure 10] Cross-sectional view of the optical system of Example 4. [Figure 11] Aberration diagram of the optical system of Example 4 in the state of infinity focus. [Figure 12] Aberration diagram of the optical system of Example 4 at its closest focusing state. [Figure 13] Cross-sectional view of the optical system of Example 5. [Figure 14] Aberration diagram of the optical system of Example 5 in the state of infinity focus. [Figure 15] Aberration diagram in the closest focusing state of the optical system of Example 5. [Figure 16] Cross-sectional view of the optical system of Example 6. [Figure 17] Aberration diagram in the infinity focusing state of the optical system of Example 6. [Figure 18] Aberration diagram in the closest focusing state of the optical system of Example 6. [Figure 19] Cross-sectional view of the optical system of Example 7. [Figure 20] Aberration diagram in the infinity focusing state of the optical system of Example 7. [Figure 21] Aberration diagram in the closest focusing state of the optical system of Example 7. [Figure 22] Cross-sectional view of the optical system of Example 8. [Figure 23] Aberration diagram in the infinity focusing state of the optical system of Example 8. [Figure 24] Aberration diagram in the closest focusing state of the optical system of Example 8. [Figure 25] Diagram showing an imaging device equipped with the optical systems of Examples 1 to 8.

Modes for Carrying Out the Invention

[0009] Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. First, prior to the description of specific Examples 1 to 8, matters common to each example will be described.

[0010] FIG. 1, FIG. 4, FIG. 7, FIG. 10, FIG. 13, FIG. 16, FIG. 19, and FIG. 22 each show a cross-section of the optical system L0 of Examples 1 to 8 in a state of being focused on an object at infinity (hereinafter referred to as the infinity focusing state). The optical system L0 of each example is used in various imaging devices such as digital video cameras, digital still cameras, silver halide film cameras, broadcast cameras, and surveillance cameras.

[0011] In each figure, the left side is the object side (front), and the right side is the image side (rear). The optical system L0 of each embodiment has multiple lens groups. A lens group is a collection of one or more lenses that move together or remain stationary during focusing. That is, in the optical system L0 of each embodiment, the distance between adjacent lens groups changes during focusing. The lens groups may include aperture diaphragms.

[0012] In each diagram, Li represents the i-th lens group (i=1,2,3) counting from the object. Below the lens group that moves during focusing (focus group) in each diagram, an arrow indicates the direction of movement of the focus group when focusing from infinity to near distance.

[0013] SP stands for aperture diaphragm. IP stands for image plane. The image plane IP is where the imaging surface (light-receiving surface) of an image sensor such as a CCD sensor or CMOS sensor, or the film surface (photosensitive surface) of a silver halide film, is located.

[0014] The optical system L0 of each embodiment has a first lens group L1 with positive refractive power and a second lens group L2 with negative refractive power, arranged in order from the object side to the image side. By making the refractive power of the first lens group L1 positive and the refractive power of the second lens group L2 negative, the diameter of the light beam incident on the second lens group L2 is reduced, making it possible to miniaturize and lighten the focusing group.

[0015] Furthermore, in the optical system L0 of each embodiment, the second lens group L2, which acts as the focusing group, moves during focusing. This makes it possible to suppress fluctuations in the angle of view that occur during focusing.

[0016] Furthermore, the optical system L0 of each embodiment satisfies at least one of the following conditions (1) to (3).

[0017] -8.50 ≤ f² / f ≤ -1.15 (1) 10.00 ≤ νdgn1 ≤ 31.00 (2) 0.80 ≤ SG ≤ 2.38 (3) In the above equation, f is the focal length of the entire optical system L0, and f2 is the focal length of the second lens group L2. νdgn1 is the Abbe number with reference to the d line of the negative lens Gn1, the negative lens closest to the object (hereinafter referred to as the "negative lens closest to the object") among the at least one negative lens included in the first lens group L1. SG is the minimum specific gravity of each lens included in the second lens group L2. The specific gravity of a lens here is the ratio of its mass to the same volume of water.

[0018] The conditions in equation (1) show an appropriate relationship between the focal length f2 of the second lens group L2, which is the focusing group, and the focal length f of the entire optical system L0. If lenses with high refractive power made of resin material are used in the optical system for weight reduction, aberration fluctuations due to temperature changes will be large. Equation (1) shows the conditions for giving the focusing group an appropriate refractive power while suppressing aberration fluctuations due to temperature changes. If the focal length of the focusing group becomes shorter, i.e., the refractive power of the focusing group becomes larger, so that f2 / f exceeds the upper limit of equation (1), this is undesirable because aberration fluctuations due to temperature changes will be large. If the focal length of the focusing group becomes longer, i.e., the refractive power of the focusing group becomes smaller, so that f2 / f falls below the lower limit of equation (1), this is undesirable because the amount of movement of the focusing group during focusing will be large, and the optical system L0 will become larger.

[0019] Furthermore, it is more preferable to set the lower limit of equation (1) to -8.40, -8.30, -8.20, or -8.10. Also, it is more preferable to set the upper limit of equation (1) to -1.20, -1.25, or -1.29.

[0020] The conditions in equation (2) indicate an appropriate range for the Abbe number of the negative lens Gn1 on the object side. The second lens group L2 uses a material with negative refractive power and a large partial dispersion ratio θgF for the g-line (wavelength 435.8 nm) and F-line (wavelength 486.1 nm), which has a large impact on lateral chromatic aberration. Therefore, it is necessary to suppress lateral chromatic aberration by using a material with a large partial dispersion ratio θgF for the g-line and F-line for the negative lens Gn1 on the object side. The appropriate range for the material of the negative lens Gn1 on the object side in this case is the range in equation (2). If νdgn1 exceeds the upper limit of equation (2), it is advantageous for suppressing axial chromatic aberration, but it is undesirable because it becomes difficult to suppress lateral chromatic aberration. If νdgn1 falls below the lower limit of equation (2), it is advantageous for suppressing lateral chromatic aberration, but it is undesirable because it becomes difficult to suppress axial chromatic aberration.

[0021] Furthermore, it is more preferable to set the lower limit of equation (2) to 12.00, 14.00, 16.00, or 17.00. Also, it is more preferable to set the upper limit of equation (2) to 30.70, 30.40, or 30.10.

[0022] The conditions in equation (3) indicate an appropriate range for the minimum specific gravity of each lens in the second lens group L2. If SG exceeds the upper limit of equation (3), all lenses in the second lens group L2 become glass lenses, increasing the weight of the focusing group, which is undesirable. If SG falls below the lower limit of equation (3), it becomes difficult to create a lens with a refractive power suitable for focusing, which is also undesirable.

[0023] Furthermore, it is more preferable to set the lower limit of equation (3) to 0.85, 0.90, 0.95, or 1.00. Also, it is more preferable to set the upper limit of equation (3) to 2.00, 1.70, 1.50, or 1.30.

[0024] By satisfying the above configuration and the conditions of equations (1) to (3), the optical system L0 of each embodiment can reduce the weight of the focus group, minimize its movement, and achieve high optical performance.

[0025] The optical system L0 of each embodiment preferably satisfies at least one of the following equations (4) to (13).

[0026] 2.00 ≤ TL / f ≤ 7.00 (4) -2.00 ≤ fgn1 / f ≤ -0.50 (5) 15.00 ≤ νdgp1 ≤ 40.00 (6) 1.80 ≤ Ndgn1 ≤ 2.15 (7) -5.00≦(Rn2+Rn1) / (Rn2-Rn1)≦-1.00 (8) 0.70 ≤ f1 / f ≤ 1.20 (9) 0.20 ≤ DF / f ≤ 1.50 (10) 0.14 ≤ SK / TL ≤ 0.30 (11) 0.35 ≤ Db1 / TL ≤ 0.70 (12) 0.00 <Db2 / TL≦0.10 (13) In the above formula, TL is the distance along the optical axis from the lens surface closest to the object in the optical system L0 to the image plane IP, and is the total optical length. fgn1 is the focal length of the negative lens Gn1 closest to the object. νdgp1 is the Abbe number with reference to the d line of the positive lens Gp1 closest to the object (hereinafter referred to as the positive lens closest to the object) among the at least one positive lens included in the first lens group L1. Ndgn1 is the refractive index of the negative lens Gn1 closest to the object at the d line. Rn1 is the radius of curvature of the lens surface on the object side of the negative lens Gn1 closest to the object, and Rn2 is the radius of curvature of the lens surface on the image side of the negative lens Gn1 closest to the object. f1 is the focal length of the first lens group L1. DF is the distance along the optical axis from the lens surface closest to the image in the second lens group L2 in the infinity focus state to the lens surface on the object side of the lens adjacent to the image side in the second lens group L2, or to the image plane IP. SK is the air-equivalent distance from the image-side lens surface to the image plane IP in the optical system L0, and is the back focus. Db1 is the sum of the thicknesses along the optical axis of all lenses included in the first lens group L1. Db2 is the sum of the thicknesses along the optical axis of all lenses included in the second lens group L2.

[0027] The conditions in equation (4) indicate an appropriate relationship between the total optical length TL of the optical system L0 and the focal length f of the entire optical system L0. If TL / f exceeds the upper limit of equation (4), the total optical length is not long enough, and the optical system L0 becomes large, which is undesirable. If TL / f falls below the lower limit of equation (4), it is not possible to secure the air gap necessary to suppress various aberrations such as spherical aberration and chromatic aberration, and an increase in weight due to an increase in the number of lenses occurs, which is also undesirable.

[0028] Furthermore, it is more preferable to set the lower limit of equation (4) to 2.10, 2.20, or 2.30. Also, it is more preferable to set the upper limit of equation (4) to 6.80, 6.60, or 6.50.

[0029] The conditions in equation (5) indicate an appropriate relationship between the focal length fgn1 of the negative lens Gn1 on the outermost side and the focal length f of the entire optical system L0. If fgn1 / f exceeds the upper limit of equation (5), the negative refractive power of the negative lens Gn1 on the outermost side becomes too strong, increasing distortion, which is undesirable. If fgn1 / f falls below the lower limit of equation (5), the negative refractive power of the negative lens Gn1 on the outermost side becomes too weak, increasing astigmatism, which is also undesirable.

[0030] Furthermore, it is more preferable to set the lower limit of equation (5) to -1.96, -1.93, or -1.91. Also, it is more preferable to set the upper limit of equation (5) to -0.55, -0.58, or -0.60.

[0031] The conditions in equation (6) indicate an appropriate range for the Abbe number νdgn1 of the closest positive lens Gp1. If νdgn1 exceeds the upper limit of equation (6), it becomes difficult to suppress axial chromatic aberration, which is undesirable. If νdgn1 falls below the lower limit of equation (6), it becomes difficult to suppress lateral chromatic aberration, which is also undesirable.

[0032] Furthermore, it is more preferable to set the lower limit of equation (6) to 17.25, 20.00, or 22.00. Also, it is more preferable to set the upper limit of equation (6) to 38.00, 37.00, or 36.00.

[0033] The conditions in equation (7) indicate an appropriate range for the refractive index Ndgn1 of the negative lens Gn1 on the object side. If Ndgn1 exceeds the upper limit of equation (7), distortion increases, and the partial dispersion ratio θgF for the g-line and F-line becomes large, making it difficult to suppress axial chromatic aberration, which is undesirable. If Ndgn1 falls below the lower limit of equation (7), it becomes difficult to suppress lateral chromatic aberration and field curvature, which is also undesirable.

[0034] Furthermore, it is more preferable to set the lower limit of equation (7) to 1.82, 1.83, or 1.84. Also, it is more preferable to set the upper limit of equation (8) to 2.10, 2.05, or 2.00.

[0035] The conditions in equation (8) indicate an appropriate range for the shape factor (Rn2+Rn1) / (Rn2-Rn1) of the object-side negative lens Gn1. If the shape factor exceeds the upper limit of equation (8), the radius of curvature of the object-side lens surface becomes too small compared to the radius of curvature of the image-side lens surface of the object-side negative lens Gn1, which increases field curvature and is therefore undesirable. If the shape factor falls below the lower limit of equation (8), it is advantageous in suppressing field curvature, but it is undesirable because the lens diameter of the object-side negative lens Gn1 becomes larger, and the optical system L0 becomes larger.

[0036] Furthermore, it is more preferable to set the lower limit of equation (8) to -4.75, -4.60, or -4.50. Also, it is more preferable to set the upper limit of equation (8) to -1.05, -1.08, or -1.10.

[0037] The conditions in equation (9) indicate an appropriate relationship between the focal length f1 of the first lens group L1 and the focal length f of the entire optical system L0. If f1 / f exceeds the upper limit of equation (9), the refractive power of the first lens group L1 becomes too weak, which is undesirable because it increases the overall optical length. If f1 / f falls below the lower limit of equation (9), it is advantageous for miniaturizing the focusing group, but it is undesirable because it increases spherical aberration and axial chromatic aberration.

[0038] Furthermore, it is more preferable to set the lower limit of equation (9) to 0.71, 0.72, or 0.73. Also, it is more preferable to set the upper limit of equation (9) to 1.17, 1.14, or 1.12.

[0039] The conditions in equation (10) indicate an appropriate relationship between the distance DF of the second lens group L2 in the infinity focus state and the focal length f of the optical system L0. If DF / f exceeds the upper limit of equation (10), the overall optical length increases and the optical system L0 becomes larger, which is undesirable. If DF / f falls below the lower limit of equation (10), it becomes impossible to secure the amount of movement of the second lens group L2 necessary for focusing, which is also undesirable.

[0040] Furthermore, it is more preferable to set the lower limit of equation (10) to 0.23, 0.26, 0.30, or 0.32. Also, it is more preferable to set the upper limit of equation (10) to 1.40, 1.30, or 1.20.

[0041] The conditions in equation (11) indicate an appropriate relationship between the back focus SK and the total optical length TL. If SK / TL exceeds the upper limit of equation (11), the spacing between the lenses constituting the optical system L0 becomes too narrow, making it difficult to suppress spherical aberration and chromatic aberration, which is undesirable. If SK / TL falls below the lower limit of equation (11), the back focus SK becomes too short, increasing spherical aberration and coma aberration, which is also undesirable. Furthermore, it is more preferable to set the lower limit of equation (11) to 0.15 or 0.16. Also, it is more preferable to set the upper limit of equation (11) to 0.29, 0.28, or 0.27.

[0042] The conditions in equation (12) indicate an appropriate relationship between the sum of the lens thicknesses Db1 of the first lens group L1 and the total optical length TL. If Db1 / TL exceeds the upper limit of equation (12), the thickness of the first lens group L1 becomes too large, making it unsuitable for weight reduction, which is undesirable. If Db1 / TL falls below the lower limit of equation (12), it becomes difficult to suppress various aberrations, which is also undesirable.

[0043] Furthermore, it is more preferable to set the lower limit of equation (12) to 0.37, 0.39, or 0.40. Also, it is more preferable to set the upper limit of equation (12) to 0.69 or 0.68.

[0044] The conditions in equation (13) indicate an appropriate relationship between the sum of the lens thicknesses Db2 of the second lens group L2 and the total optical length TL. If Db2 / TL exceeds the upper limit of equation (13), the thickness of the second lens group L2 becomes too large, resulting in a larger focusing group and making it unsuitable for miniaturizing the optical system L0, which is undesirable. If Db2 / TL falls below the lower limit of equation (13), the thickness of the second lens group L2 is small, but it becomes difficult to mold at least one of the lenses constituting the second lens group L2, which is also undesirable.

[0045] Furthermore, it is more preferable to set the lower limit of formula (13) to 0.005, 0.007, or 0.009. Also, it is more preferable to set the upper limit of formula (13) to 0.09, 0.08, or 0.07.

[0046] Furthermore, it is preferable that the optical system L0 of each embodiment satisfies at least one of the following configurations.

[0047] The lens closest to the image in the optical system L0 preferably has a negative refractive power. This makes it possible to reduce the diameter of the lens closest to the image.

[0048] The first lens group L1 is preferably composed of eight or fewer lenses. This facilitates miniaturization and weight reduction of the entire optical system L0.

[0049] The second lens group L2 is preferably composed of two or fewer lenses. This facilitates weight reduction of the focusing group.

[0050] The optical system L0 is preferably composed of 10 or fewer lenses. This facilitates miniaturization and weight reduction of the optical system L0. Note that if two lenses are joined together to form a single cemented lens, the number of lenses is considered to be 2.

[0051] Next, the optical systems L0 of Examples 1 to 8 will be described in detail. Following the description of Example 8, numerical examples 1 to 8 corresponding to each of Examples 1 to 8 will be shown.

[0052] The optical system L0 of Embodiment 1 shown in Figure 1 and Embodiment 3 shown in Figure 7 consists of a first lens group L1 positioned closest to the object, a second lens group L2 adjacent to the first lens group L1 on the image side, and a third lens group L3 positioned closest to the image. The object-side negative lens Gn1 is positioned closest to the object in the first lens group L1, and the object-side positive lens Gp1 is positioned third from the object side. The first lens group L1 consists of six lenses and includes an aperture diaphragm SP. The focusing group is the second lens group L2, which consists of one resin lens. The optical system L0 of this embodiment consists of nine lenses.

[0053] The optical system L0 of Embodiment 2 shown in Figure 4 consists of a first lens group L1 positioned closest to the object and a second lens group L2 adjacent to the first lens group L1 on the image side (positioned closest to the image). The object-side negative lens Gn1 is positioned closest to the object in the first lens group L1, and the object-side positive lens Gp1 is positioned third from the object side. The first lens group L1 consists of eight lenses and includes an aperture diaphragm SP. The focusing group is the second lens group L2, which consists of one resin lens. The optical system L0 of this embodiment consists of nine lenses.

[0054] The optical system L0 of Embodiment 4 shown in Figure 10 consists of a first lens group L1 positioned closest to the object, a second lens group L2 adjacent to the first lens group L1 on the image side, and a third lens group L3 positioned closest to the image. The object-side negative lens Gn1 is positioned closest to the object in the first lens group L1, and the object-side positive lens Gp1 is positioned third from the object side. The first lens group L1 consists of six lenses and includes an aperture diaphragm SP. The focusing group is the second lens group L2, which consists of two lenses. Of these two lenses, the image-side lens is a resin lens. The optical system L0 of this embodiment consists of ten lenses.

[0055] The optical system L0 of Embodiment 5 shown in Figure 13 consists of a first lens group L1 positioned closest to the object, a second lens group L2 adjacent to the first lens group L1 on the image side, and a third lens group L3 positioned closest to the image. The object-side negative lens Gn1 is positioned closest to the object in the first lens group L1, and the object-side positive lens Gp1 is positioned third from the object side. The first lens group L1 consists of six lenses and includes an aperture diaphragm SP. The focusing group is the second lens group L2, which consists of a cemented lens formed by joining two lenses. The image-side lens of the cemented lens is a resin lens. The optical system L0 of this embodiment consists of 10 lenses.

[0056] The optical system L0 of Embodiment 6 shown in Figure 16, Embodiment 7 shown in Figure 19, and Embodiment 8 shown in Figure 22 consists of a first lens group L1 positioned closest to the object, a second lens group L2 adjacent to the first lens group L1 on the image side, and a third lens group L3 positioned closest to the image. The object-side positive lens Gp1 is positioned closest to the object in the first lens group L1, and the object-side positive lens Gn1 is positioned second from the object side. The first lens group L1 consists of seven lenses and includes an aperture diaphragm SP. The focusing group is the second lens group L2, which consists of one resin lens. The optical system L0 of this embodiment consists of ten lenses.

[0057] Numerical examples 1 to 8 are shown below. In the surface data for each numerical example, the surface number m indicates the order of the surfaces when counted from the object side. r (mm) is the radius of curvature of the m-th surface, and d (mm) represents the lens thickness or air gap on the optical axis between the m-th surface and the (m+1)-th surface. Also, nd is the refractive index of the optical material at the d-line between the m-th surface and the (m+1)-th surface, and νd is the Abbe number of the optical material between the m-th surface and the (m+1)-th surface with respect to the d-line. The Abbe number νd with respect to the d-line is given by Nd, NF, and NC, respectively, when the refractive indices at the d-line (587.56 nm), F-line (486.13 nm), and C-line (656.27 nm) are Nd, NF, and NC, respectively. νd = (Nd-1) / (NF-NC) It is expressed as follows. Furthermore, θgF represents the partial dispersion ratio of the optical material between the m-th plane and the (m+1)-th plane with respect to the g-line (435.84 nm) and the F-line. The partial dispersion ratio θgF is given by, when the refractive index at the g-line is Ng, θgF = (Ng - NF) / (NF - NC) It is represented as follows. Also, sg represents the specific gravity of the optical material between the m-th plane and the (m+1)-th plane.

[0058] In each numerical example, the interplanar spacing d (mm), focal length (mm), F-number, and paraxially calculated half-angle of view (°) are all values ​​for the infinity focus state. The back focus SK is, as mentioned above, the air-equivalent distance along the optical axis from the image-side lens surface (final surface) of the optical system L0 to the image plane IP. The total lens length is the distance from the object-side lens surface (first surface) to the final surface of the optical system L0 plus the back focus, and corresponds to the optical total length mentioned above. The asterisk (*) next to the surface number indicates that the surface has an aspherical shape. The aspherical shape is expressed by the following formula, where x is the displacement from the surface vertex in the optical axis direction, h is the height from the optical axis in the direction perpendicular to the optical axis, the direction of light propagation is positive, R is the radius of paraxial curvature, K is the cone constant, and A4, A6, A8, and A10 are aspherical coefficients. The cone constant and aspherical coefficients "e±M" are multiplied by 10⁻¹⁴. ±M It means...

[0059] x=( h 2 / R) / [1+√{1-(1+K)(h / R) 2}] +A4×h 4 +A6×h 6 +A8×h 8 +A10×h 10 Furthermore, Table 1 summarizes the values ​​of the conditions in equations (1) to (13) for optical system L0 in numerical examples 1 to 8. Each numerical example satisfies all the conditions in equations (1) to (13).

[0060] Furthermore, Figures 2, 5, 8, 11, 14, 17, 20, and 23 show the longitudinal aberrations (spherical aberration, astigmatism, distortion, and chromatic aberration) of the optical system L0 for numerical examples 1 to 8 in the infinity focus state, respectively. Figures 3, 6, 9, 12, 15, 18, 21, and 24 show the longitudinal aberrations of the optical system L0 for numerical examples 1 to 8 in the near focus state (close focus state), respectively. In the spherical aberration diagram, Fno is the F number, the solid line shows the spherical aberration at the d line (wavelength 587.6 nm), and the dashed line shows the spherical aberration at the g line (wavelength 435.8 nm). In the astigmatism diagram, the solid line S shows the astigmatism at the sagittal image plane, and the dashed line M shows the astigmatism at the meridional image plane. The distortion diagram shows the distortion at the d-line. The chromatic aberration diagram shows the lateral chromatic aberration at the g-line. ω is the half-angle of view (°) calculated paraxially. [Numerical Example 1] Unit: mm Surface data Face number rd nd νd θgF sg 1 17.757 1.50 1.96300 24.1 0.621 4.20 2 8.341 5.46 3 -50.181 0.90 1.49700 81.5 0.538 3.62 4 10.693 2.15 5 110.017 3.65 2.00069 25.5 0.614 4.73 6 -38.046 4.54 7 57.573 4.14 1.51633 64.1 0.535 2.52 8 -12.938 4.08 9 (aperture) ∞ 4.30 10 3807.287 3.32 1.49700 81.5 0.538 3.62 11 -8.841 0.80 1.96300 24.1 0.621 4.20 12 -13.811 (variable) 13* -100.000 1.00 1.53110 55.9 0.568 1.01 14* 36.390 (variable) 15 34.818 5.74 1.59522 67.7 0.544 4.17 16 -14.251 2.10 17 -12.290 1.00 1.77047 29.7 0.595 3.34 18 -27.581 12.00 Image plane ∞ Aspherical data Page 13 K = 0.00000e+00 A 4= 4.08532e-05 A 6= 1.71506e-06 A 8=-8.77665e-08 A10 = 6.80396e-10 Side 14 K = 0.00000e+00 A 4= 9.15610e-05 A 6=-7.41161e-08 A 8=-2.40331e-08 A10 = 1.01764e-10 Various data Focal length 12.38 F-number 2.83 Half-angle (°): 42.99 Image height 11.54 Lens length 63.50 SK 12.00 Infinity Close d12 1.50 3.39 d14 5.32 3.43 Lens group data Group starting plane focal length 1 1 13.71 2 13 -50.11 3 15 36.09 [Numerical Example 2] Unit: mm Surface data Face number rd nd νd θgF sg 1 22.255 1.50 1.85025 30.1 0.598 4.00 2 7.861 5.53 3 -39.165 0.90 1.49700 81.5 0.538 3.62 4 9.825 2.10 5 139.116 2.40 2.00069 25.5 0.614 4.73 6 -34.774 2.80 7 18.183 4.00 1.51633 64.1 0.535 2.52 8 -13.238 3.32 9 (aperture) ∞ 2.62 10 11449.611 3.48 1.49700 81.5 0.538 3.62 11 -7.196 1.50 2.00069 25.5 0.614 4.73 12 -12.769 0.27 13 29.778 0.95 1.91082 35.3 0.583 4.85 14 14.529 2.46 15 42.415 3.46 1.59522 67.7 0.544 4.17 16 -19.306 (variable) 17* -34.567 1.00 1.53110 55.9 0.568 1.01 18 -100.000 (variable) Image plane ∞ Aspherical data Page 17 K = 0.00000e+00 A 4=-3.55752e-05 A 6= 6.02827e-07 A 8=-1.18983e-08 A10 = 8.48195e-11 Various data Focal length 12.36 F-number 2.83 Half-angle (°): 43.03 Image height 11.54 Lens length: 55.92 SK 15.18 Infinity Close d16 2.46 5.63 d18 15.18 12.00 Lens group data Group starting plane focal length 1 1 10.64 2 17 -100.00 [Numerical Example 3] Unit: mm Surface data Face number rd nd νd θgF sg 1 12.633 2.00 1.92119 24.0 0.620 3.84 2 8.011 6.54 3 -35.859 0.87 1.49700 81.5 0.538 3.62 4 21.118 0.84 5 31.182 2.97 1.91082 35.3 0.583 4.85 6 -29.101 4.14 7 -13.300 2.00 1.49700 81.5 0.538 3.62 8 -10.593 1.49 9 (aperture) ∞ 1.50 10 40.090 4.49 1.49700 81.5 0.538 3.62 11 -12.533 0.79 1.84666 23.8 0.621 3.54 12 -20.783 (variable) 13* 63.007 0.79 1.53110 55.9 0.568 1.01 14 * 14.792 (variable) 15 27.364 3.58 1.59522 67.7 0.544 4.17 16 -100.000 7.17 17 -32.967 1.10 1.73037 32.2 0.590 3.18 18 -77.077 15.32 Image plane ∞ Aspherical data Page 13 K = 0.00000e+00 A 4= 1.13281e-04 A 6=-5.88547e-06 A 8= 1.48510e-07 A10 = -1.37510e-09 Side 14 K = 0.00000e+00 A 4= 1.12815e-04 A 6=-7.18003e-06 A 8= 1.81349e-07 A10 = -1.68669e-09 Various data Focal length 28.17 F-number 2.83 Half-angle (°): 24.14 Image height 12.63 Lens length: 67.03 SK 15.32 Infinity Close d12 1.50 2.45 d14 9.94 8.99 Lens group data Group starting plane focal length 1 1 21.07 2 13 -36.60 3 15 56.24 [Numerical Example 4] Unit: mm Surface data Face number rd nd νd θgF sg 1 20.486 2.00 1.92119 24.0 0.620 3.84 2 8.996 6.43 3 41.199 1.10 1.49700 81.5 0.538 3.62 4 7.684 4.16 5 -88.281 3.50 1.85896 22.7 0.628 3.71 6 -18.346 3.43 7 -14.819 1.74 1.49700 81.5 0.538 3.62 8 -9.242 4.94 9 (aperture) ∞ 3.31 10 22.426 4.29 1.49700 81.5 0.538 3.62 11 -6.240 2.92 2.00100 29.1 0.600 5.12 12 -9.312 (variable) 13 -26.184 1.00 2.00069 25.5 0.614 4.73 14 -91.909 1.35 15 -241.401 1.50 1.53110 55.9 0.568 1.01 16* -60.911 (variable) 17 -40.717 4.16 1.59522 67.7 0.544 4.17 18 -11.874 1.22 19 -10.288 1.00 1.90110 27.1 0.607 3.83 20 -15.449 12.00 Image plane ∞ Aspherical data Page 16 K = 0.00000e+00 A 4= 1.36289e-04 A 6=-1.53262e-07 A 8= 8.38089e-10 A10 = -3.38821e-12 Various data Focal length 10.02 F-number 2.83 Half-angle (°): 48.98 Image height 11.52 Lens length 65.00 SK 12.00 Infinity Close d12 1.50 2.19 d16 3.46 2.77 Lens group data Group starting plane focal length 1 1 7.43 2 13 -50.03 3 17 101.02 [Numerical Example 5] Unit: mm Surface data Face number rd nd νd θgF sg 1 26.940 1.78 1.95906 17.5 0.660 3.59 2 10.423 6.10 3 -47.125 1.80 1.49700 81.5 0.538 3.62 4 12.245 4.73 5 61.049 3.34 2.00069 25.5 0.614 4.73 6 -47.248 4.08 7 2307.926 4.00 1.56732 42.8 0.573 2.57 8 -17.117 4.56 9 (aperture) ∞ 5.21 10 25.369 4.01 1.49700 81.5 0.538 3.62 11 -9.668 1.79 2.00069 25.5 0.614 4.73 12 -14.664 (variable) 13 304.436 0.99 1.92286 18.9 0.650 3.58 14 80.176 0.99 1.63550 23.9 0.636 1.24 15 * 17.278 (variable) 16 62.198 6.64 1.59522 67.7 0.544 4.17 17 -13.016 1.28 18 -13.439 1.00 1.77047 29.7 0.595 3.34 19 -27.491 12.00 Image plane ∞ Aspherical data Page 15 K = 0.00000e+00 A 4= 8.16502e-05 A 6= 4.61430e-09 A 8=-3.40059e-11 A10 = -1.71027e-11 Various data Focal length 12.09 F-number 2.83 Half-angle (°): 43.65 Image height 11.54 Lens length 70.00 SK 12.00 Infinity Close d12 1.49 2.28 d15 4.20 3.41 Lens group data Group starting plane focal length 1 1 9.38 2 13 -26.82 3 16 36.61 [Numerical Example 6] Unit: mm Surface data Face number rd nd νd θgF sg 1 24.873 3.05 1.92119 24.0 0.620 3.84 2 50.889 0.25 3 48.416 1.50 1.96300 24.1 0.621 4.20 4 7.828 5.56 5 -58.456 1.20 1.49700 81.5 0.538 3.62 6 10.399 1.91 7 59.138 3.60 1.96300 24.1 0.621 4.20 8 -47.434 2.31 9 26.837 4.00 1.48749 70.2 0.530 2.46 10 -12.203 3.99 11 (aperture) ∞ 4.60 12 6008.192 3.25 1.49700 81.5 0.538 3.62 13 -7.395 0.85 2.00069 25.5 0.614 4.73 14 -11.072 (variable) 15* -43.192 1.00 1.53110 55.9 0.568 1.01 16* 51.581 (variable) 17 40.612 7.50 1.59522 67.7 0.544 4.17 18 -13.022 0.74 19 -12.286 1.00 1.77047 29.7 0.595 3.34 20 -28.539 12.00 Image plane ∞ Aspherical data Page 15 K = 0.00000e+00 A 4= 2.73879e-05 A 6= 1.68646e-06 A 8=-3.42923e-08 A10=3.47134e-10 Page 16 K = 0.00000e+00 A 4= 9.03920e-05 A 6=-2.94746e-08 A 8= 2.27189e-08 A10 = -3.78789e-10 Various data Focal length 12.36 F-number 2.83 Half-angle (°): 43.03 Image height 11.54 Lens length: 64.43 SK 12.00 Infinity Close d14 1.58 3.04 d16 4.51 3.06 Lens group data Group starting plane focal length 1 1 11.87 2 15 -44.10 3 17 39.28 [Numerical Example 7] Unit: mm Surface data Face number rd nd νd θgF sg 1 66.465 2.53 1.91082 35.3 0.583 4.85 2 789.424 1.00 3 117.037 1.49 1.85025 30.1 0.598 4.00 4 7.035 5.47 5 180.595 1.00 1.49700 81.5 0.538 3.62 6 14.081 0.97 7 56.655 2.09 1.96300 24.1 0.621 4.20 8 -42.392 1.95 9 34.381 4.00 1.49700 81.5 0.538 3.62 10 -11.103 1.48 11 (aperture) ∞ 6.27 12 ∞ 3.51 1.49700 81.5 0.538 3.62 13 -7.990 0.80 2.00069 25.5 0.614 4.73 14 -11.726 (variable) 15* -94.948 1.00 1.53110 55.9 0.568 1.01 16 * 19.217 (variable) 17 41.901 7.10 1.59522 67.7 0.544 4.17 18 -12.965 0.35 19 -12.798 1.38 2.00100 29.1 0.600 5.12 20 -21.646 16.54 Image plane ∞ Aspherical data Page 15 K = 0.00000e+00 A 4=-4.30821e-05 A 6= 8.08773e-07 A 8= 5.42521e-08 A10 = -1.01539e-09 Page 16 K = 0.00000e+00 A 4= 1.10647e-05 A 6=-2.96188e-08 A 8= 6.51392e-08 A10 = -1.01239e-09 Various data Focal length 14.63 F-number 2.83 Half-angle (°): 39.45 Image height 12.04 Lens length: 64.29 SK 16.54 Infinity Close d14 0.52 1.71 d16 4.84 3.65 Lens group data Group starting plane focal length 1 1 12.01 2 15 -30.00 3 17 35.25 [Numerical Example 8] Unit: mm Surface data Face number rd nd νd θgF sg 1 19.278 3.36 1.96300 24.1 0.621 4.20 2 29.448 0.10 3 20.244 1.52 1.95906 17.5 0.660 3.59 4 7.984 7.12 5 -53.297 0.87 1.49700 81.5 0.538 3.62 6 9.891 2.12 7 42.667 3.61 2.00069 25.5 0.614 4.73 8 -46.071 4.12 9 408.385 4.07 1.49700 81.5 0.538 3.62 10 -11.422 1.48 11 (aperture) ∞ 5.66 12 -209.171 3.50 1.49700 81.5 0.538 3.62 13 -9.273 0.99 2.00069 25.5 0.614 4.73 14 -14.029 (variable) 15* -76.849 1.03 1.53110 55.9 0.568 1.01 16 * 129.756 (variable) 17 136.599 6.55 1.59522 67.7 0.544 4.17 18 -14.606 0.40 19 -14.144 1.02 1.77047 29.7 0.595 3.34 20 -40.808 12.17 Image plane ∞ Aspherical data Page 15 K = 0.00000e+00 A 4=-3.28362e-06 A 6= 3.79608e-07 A 8=-1.04343e-09 A10 = 1.08678e-11 Page 16 K = 0.00000e+00 A 4= 1.76211e-05 A 6= 1.49914e-07 A 8= 1.84632e-09 A10 = 1.63421e-11 Various data Focal length 18.13 F-number 2.83 Half-angle (°): 33.83 Image height 12.15 Lens length: 70.71 SK 12.17 Infinity Close d14 1.50 3.30 d16 9.54 7.74 Lens group data Group starting plane focal length 1 1 16.11 2 15 -90.72 3 17 98.62

[0061] [Table 1]

[0062] [Imaging device] Figure 25 shows a digital still camera (imaging device) using the optical system L0 of Examples 1 to 8 as the imaging optical system.

[0063] 10 is the camera body, and 11 is the imaging optical system composed of one of the optical systems L0 of Examples 1 to 4. 12 is a solid-state image sensor (photoelectric conversion element) such as a CCD sensor or CMOS sensor, which is built into the camera body 10 and captures the optical image (i.e., the subject through the imaging optical system 11) formed by the imaging optical system 11.

[0064] The camera body 10 may be a single-lens reflex camera with a quick-turn mirror, or a mirrorless camera without a quick-turn mirror.

[0065] By applying the optical system L0 of Examples 1 to 10 to an imaging device such as a digital still camera, an imaging device capable of quiet, low-vibration, and high-speed autofocus can be obtained.

[0066] The above embodiments include the following configuration.

[0067] (Composition 1) An optical system having a first lens group with positive refractive power and a second lens group with negative refractive power, arranged in order from the object side to the image side, During focusing, the first lens group does not move, while the second lens group moves. When the focal length of the optical system is f, the focal length of the second lens group is f2, the Abbe number νdgn1 is taken with reference to the d line of the negative lens closest to the object among the at least one negative lens included in the first lens group, and the minimum specific gravity of each lens included in the second lens group is SG, -8.50 ≤ f² / f ≤ -1.15 10.00 ≤ νdgn1 ≤ 31.00 0.80 ≤ SG ≤ 2.38 An optical system characterized by satisfying the following conditions. (Configuration 2) When TL is the distance along the optical axis from the lens surface closest to the object in the aforementioned optical system to the image plane, 2.00 ≤ TL / f ≤ 7.00 The optical system according to configuration 1, characterized by satisfying the following conditions. (Composition 3) When the focal length of the negative lens closest to the object is denoted as fgn1, -2.00 ≤ fgn1 / f ≤ -0.50 The optical system according to configuration 1 or 2, characterized by satisfying the following conditions. (Composition 4) When νdgp1 is the Abbe number with respect to the d line of the positive lens closest to the object among the at least one positive lens included in the first lens group, 15.00 ≤ νdgp1 ≤ 40.00 An optical system according to any one of configurations 1 to 3, characterized by satisfying the following conditions. (Composition 5) When the refractive index at the d-line of the negative lens closest to the object is Ndgn1, 1.80 ≤ Ndgn1 ≤ 2.15 An optical system according to any one of configurations 1 to 4, characterized by satisfying the following conditions. (Composition 6) When Rn1 is the radius of curvature of the object-side lens surface of the negative lens closest to the object, and Rn2 is the radius of curvature of the image-side lens surface of the negative lens closest to the object, -5.00≦(Rn2+Rn1) / (Rn2-Rn1)≦-1.00 An optical system according to any one of configurations 1 to 5, characterized by satisfying the following conditions. (Composition 7) When the focal length of the first lens group is f1, 0.70 ≤ f1 / f ≤ 1.20 An optical system according to any one of configurations 1 to 6, characterized by satisfying the following conditions. (Composition 8) When the lens group is in focus on an object at infinity, let DF be the distance along the optical axis from the image-side lens surface of the second lens group to the object-side lens surface or image surface of the lens adjacent to the second lens group on the image side. 0.20 ≤ DF / f ≤ 1.50 An optical system according to any one of configurations 1 to 7, characterized by satisfying the following conditions. (Composition 9) When SK is the air-equivalent distance along the optical axis from the lens surface closest to the image plane in the aforementioned optical system to the image plane, 0.14 ≤ SK / TL ≤ 0.30 An optical system according to any one of configurations 1 to 8, characterized by satisfying the following conditions. (Composition 10) When Db1 is the sum of the thicknesses of all lenses in the first lens group along the optical axis, 0.35 ≤ Db1 / TL ≤ 0.70 An optical system according to any one of configurations 1 to 9, characterized by satisfying the following conditions. (Composition 11) When Db2 is the sum of the thicknesses of all lenses in the second lens group along the optical axis, 0.00 <Db2 / TL≦0.10 An optical system according to any one of configurations 1 to 10, characterized by satisfying the following conditions. (Composition 12) The optical system according to any one of configurations 1 to 11, characterized in that the lens on the image side of the optical system has a negative refractive power. (Composition 13) The optical system according to any one of configurations 1 to 12, characterized in that the first lens group consists of eight or fewer lenses. (Composition 14) The optical system according to any one of configurations 1 to 13, characterized in that the second lens group consists of two or fewer lenses. (Composition 15) The optical system according to any one of configurations 1 to 14, characterized in that the optical system is composed of 10 or fewer lenses. (Composition 16) The optical system according to any one of configurations 1 to 15, characterized by being composed of the first lens group and the second lens group. (Composition 17) The optical system according to any one of configurations 1 to 15, characterized in that it is composed of the first lens group, the second lens group, and the third lens group having a positive refractive power that does not move during focusing. (Composition 18) An optical system having a first lens group with positive refractive power and a second lens group with negative refractive power, arranged in order from the object side to the image side, During focusing, the first lens group does not move, while the second lens group moves. The optical system is characterized in that the first lens group has two or more positive lenses. (Composition 19) The optical system described in any one of configurations 1 to 18, An imaging device characterized by having an image sensor that captures an image of a subject through the optical system.

[0068] The embodiments described above are merely representative examples, and various modifications and changes can be made to each embodiment when implementing the present invention. [Explanation of Symbols]

[0069] L0 optical system L1 First lens group L2 Second lens group L3 Third lens group Gn1 Negative lens on the object side SP aperture diaphragm IP image plane

Claims

1. An optical system having a first lens group with positive refractive power and a second lens group with negative refractive power, arranged in order from the object side to the image side, During focusing, the first lens group does not move, while the second lens group moves. When the focal length of the optical system is f, the focal length of the second lens group is f2, the Abbe number with respect to the d line of the negative lens closest to the object among the at least one negative lens included in the first lens group is νdgn1, and the minimum specific gravity of each lens included in the second lens group is SG, -8.50 ≤ f² / f ≤ -1.15 10.00 ≤ νdgn1 ≤ 31.00 0.80 ≤ SG ≤ 2.38 An optical system characterized by satisfying the following conditions.

2. When TL is the distance along the optical axis from the lens surface closest to the object in the aforementioned optical system to the image plane, 2.00 ≤ TL / f ≤ 7.00 The optical system according to claim 1, characterized in that it satisfies the following conditions.

3. When the focal length of the negative lens closest to the object is denoted as fgn1, -2.00 ≤ fgn1 / f ≤ -0.50 The optical system according to claim 1, characterized in that it satisfies the following conditions.

4. When νdgp1 is the Abbe number with respect to the d line of the positive lens closest to the object among the at least one positive lens included in the first lens group, 15.00 ≤ νdgp1 ≤ 40.00 The optical system according to claim 1, characterized in that it satisfies the following conditions.

5. When the refractive index at the d-line of the negative lens closest to the object is Ndgn1, 1.80 ≤ Ndgn1 ≤ 2.15 The optical system according to claim 1, characterized in that it satisfies the following conditions.

6. When Rn1 is the radius of curvature of the object-side lens surface of the negative lens closest to the object, and Rn2 is the radius of curvature of the image-side lens surface of the negative lens closest to the object, -5.00≦(Rn2+Rn1) / (Rn2-Rn1)≦-1.00 The optical system according to claim 1, characterized in that it satisfies the following conditions.

7. When the focal length of the first lens group is f1, 0.70 ≤ f1 / f ≤ 1.20 The optical system according to claim 1, characterized in that it satisfies the following conditions.

8. When the lens group is in focus on an object at infinity, let DF be the distance along the optical axis from the image-side lens surface of the second lens group to the object-side lens surface or image surface of the lens adjacent to the second lens group on the image side. 0.20 ≤ DF / f ≤ 1.50 The optical system according to claim 1, characterized in that it satisfies the following conditions.

9. When SK is the air-equivalent distance along the optical axis from the lens surface closest to the image plane of the aforementioned optical system to the image plane, 0.14 ≤ SK / TL ≤ 0.30 The optical system according to claim 1, characterized in that it satisfies the following conditions.

10. When Db1 is the sum of the thicknesses of all lenses in the first lens group along the optical axis, 0.35 ≤ Db1 / TL ≤ 0.70 The optical system according to claim 1, characterized in that it satisfies the following conditions.

11. When Db2 is the sum of the thicknesses of all lenses in the second lens group along the optical axis, 0.00<Db2 / TL≦0.10 The optical system according to claim 1, characterized in that it satisfies the following conditions.

12. The optical system according to claim 1, characterized in that the lens on the image side of the optical system has a negative refractive power.

13. The optical system according to claim 1, characterized in that the first lens group consists of eight or fewer lenses.

14. The optical system according to claim 1, characterized in that the second lens group is composed of two or fewer lenses.

15. The optical system according to claim 1, characterized in that the optical system is composed of 10 or fewer lenses.

16. The optical system according to claim 1, characterized in that it is composed of the first lens group and the second lens group.

17. The optical system according to claim 1, characterized in that it comprises the first lens group, the second lens group, and the third lens group having a positive refractive power that does not move during focusing.

18. An optical system having a first lens group with positive refractive power and a second lens group with negative refractive power, arranged in order from the object side to the image side, During focusing, the first lens group does not move, while the second lens group moves. The optical system is characterized in that the first lens group has two or more positive lenses.

19. An optical system according to any one of claims 1 to 18, An imaging device characterized by having an image sensor that captures an image of a subject through the optical system.

Images