Optical system and imaging device

Abstract

This provides an optical system that suppresses changes in performance and field of view during focusing. [Solution] The optical system L0 is composed of a first lens group L1 with positive refractive power, a second lens group L2 with positive refractive power, and a third lens group L3, arranged in order from the object side to the image side. During focusing, the first and third lens groups do not move, but the second lens group moves, which changes the spacing between adjacent lens groups. The first lens group has a first negative lens and a second negative lens, arranged in order from the object side to the image side. When the focal length of the second lens group is f2, the focal length of the optical system is f, and the focal length of the first lens group is f1, the following conditions are satisfied: 2.70 ≤ f2 / f ≤ 10.00 and 0.50 ≤ f1 / f2 ≤ 2.80.

Description

[Technical Field]

[0001] This invention relates to an optical system suitable for imaging. [Background technology]

[0002] As an optical system as described above, Patent Document 1 discloses one composed of a first lens group with positive refractive power, a second lens group with positive refractive power, and a third lens group with positive refractive power, arranged in order from the object side to the image side. This optical system is an inner-focus type optical system that performs focusing by moving the second lens group. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2023-19073 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] As described above, there is a need for a compact optical system that suppresses changes in the field of view and improves performance during focusing. [Means for solving the problem]

[0005] One aspect of the present invention is an optical system composed of a first lens group with positive refractive power, a second lens group with positive refractive power, and a third lens group, arranged sequentially from the object side to the image side. During focusing, the first and third lens groups do not move, but the second lens group moves, changing the spacing between adjacent lens groups. The first lens group has a first negative lens and a second negative lens, arranged sequentially from the object side to the image side. When the focal length of the second lens group is f2, the focal length of the optical system is f, and the focal length of the first lens group is f1, 2.70 ≤ f² / f ≤ 10.00 0.50 ≤ f1 / f2 ≤ 2.80 It is characterized by satisfying the following conditions. Note that the imaging device equipped with the above optical system also constitutes another aspect of the present invention.

Advantages of the Invention

[0006] According to the present invention, it is possible to provide a small-sized optical system that suppresses changes in performance and angle of view during focusing.

Brief Description of the Drawings

[0007] [Figure 1] Cross-sectional view of the optical system of Example 1. [Figure 2] Longitudinal aberration diagrams of the optical system of Example 1 in the state of focusing on an infinitely distant object (A) and the state of focusing at a distance where the lateral magnification is -0.1 (B). [Figure 3] Cross-sectional view of the optical system of Example 2. [Figure 4] Longitudinal aberration diagrams of the optical system of Example 2 in the state of focusing on an infinitely distant object (A) and the state of focusing at a distance where the lateral magnification is -0.1 (B). [Figure 5] Cross-sectional view of the optical system of Example 3. [Figure 6] Longitudinal aberration diagrams of the optical system of Example 3 in the state of focusing on an infinitely distant object (A) and the state of focusing at a distance where the lateral magnification is -0.1 (B). [Figure 7] Cross-sectional view of the optical system of Example 4. [Figure 8] Longitudinal aberration diagrams of the optical system of Example 4 in the state of focusing on an infinitely distant object (A) and the state of focusing at a distance where the lateral magnification is -0.1 (B). [Figure 9] Cross-sectional view of the optical system of Example 5. [Figure 10] Longitudinal aberration diagrams of the optical system of Example 5 in the state of focusing on an infinitely distant object (A) and the state of focusing at a distance where the lateral magnification is -0.1 (B). [Figure 11] Diagram showing an imaging device equipped with the optical systems of Examples 1 to 5.

Modes for Carrying Out the Invention

[0008] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0009] FIG. 1, FIG. 3, FIG. 5, FIG. 7, and FIG. 9 each show a cross-section of the optical system L0 of Examples 1 to 5 in a state focused on an infinite object (hereinafter referred to as an infinite focus state). The optical system of each example is used as an imaging optical system in an imaging device such as a video camera, a digital still camera, a silver halide film camera, and a TV camera. Note that the optical system of each example can also be used as a projection optical system of an image projection device such as a projector.

[0010] In each cross-sectional view, the left side is the object side (front side), and the right side is the image side (rear side). Also, when the order of the lens groups counted from the object side is i, Li indicates the i-th lens group. A lens group is a collection of one or more lenses that move integrally with respect to the image plane or do not move during focusing, and the interval between adjacent lens groups changes during focusing. The lens group may include an aperture stop.

[0011] Also, in each cross-sectional view, under the second lens group L2 that moves during focusing, the moving direction of the second lens group L2 during focusing from infinity to the nearest distance is indicated by a dashed arrow. In each example, only the second lens group L2 moves toward the object side during focusing from infinity to the nearest distance.

[0012] Furthermore, in each cross-sectional view, SP is an aperture stop that determines (limits) the light beam of the open F-number (Fno). IP is the image plane. On the image plane IP, an imaging surface (light receiving surface) of an imaging element such as a CCD sensor or a CMOS sensor or a film surface (photosensitive surface) of a silver halide film is arranged.

[0013] The characteristic configuration of the optical system L0 in each embodiment will be described below. The optical system L0 in each embodiment is composed of a first lens group L1 with positive refractive power, a second lens group L2 with positive refractive power, and a third lens group L3, which are arranged in order from the object side to the image side. Only the second lens group L2 moves during focusing. The first lens group L1 has a first negative lens and a second negative lens, which are arranged in order from the object side to the image side.

[0014] In the optical system L0 of each embodiment, the light beam focused by the positive first lens group L1 is incident on the positive second lens group L2. With this configuration, it is easy to reduce the lens diameter of the second lens group L2, and the second lens group L2, which moves during focusing, can be made lighter. As a result, it is also easy to make the entire optical system L0 smaller and lighter.

[0015] Furthermore, in wide-angle optical systems, a strong negative refractive force is required on the object side of the optical system to ensure sufficient back focus. For this reason, in the optical system L0 of each embodiment, the first lens group L1 is composed of a first negative lens and a second negative lens, and the strong negative refractive force is shared between these two negative lenses. This makes it possible to reduce the refractive force per negative lens, making it easier to correct barrel distortion and field curvature.

[0016] Furthermore, in the optical system L0 of each embodiment, the third lens group L3 is positioned so that the axial light beam and peripheral light beam on the image side of the second lens group L2, which moves during focusing, are sufficiently separated in a direction perpendicular to the optical axis. This makes it possible to correct astigmatism and distortion while minimizing the impact on spherical aberration correction, thus easily achieving high optical performance across the entire field of view.

[0017] When the focal length of the second lens group L2 is f2, the focal length of the entire optical system L0 is f, and the focal length of the first lens group L1 is f1, it is preferable that the optical system L0 described above satisfies at least one of the following conditions (1) and (2).

[0018] 2.70 ≤ f² / f ≤ 10.00 (1) 0.50 ≤ f1 / f2 ≤ 2.80 (2) The conditions in equation (1) indicate an appropriate relationship between the focal length of the second lens group L2 and the focal length of the entire optical system L0. If the focal length of the second lens group L2 increases so that f2 / f exceeds the upper limit of equation (1), the amount of movement of the second lens group L2 during focusing increases, and the overall length of the optical system L0 increases. This is undesirable because it makes it difficult to make the optical system L0 smaller and lighter. If the focal length of the second lens group L2 decreases so that f2 / f falls below the lower limit of equation (1), the refractive power of the second lens group L2 becomes too strong, making it difficult to suppress spherical aberration, field curvature, and chromatic aberration during focusing, which is also undesirable.

[0019] Furthermore, it is more preferable to set the lower limit of formula (1) to 2.72, 2.74, 2.76, or 2.77. Also, it is more preferable to set the upper limit of formula (1) to 8.00, 6.00, 5.00, 4.00, or 3.80.

[0020] The conditions in equation (2) indicate an appropriate relationship between the focal length of the first lens group L1 and the focal length of the second lens group L2. If the focal length of the first lens group L1 increases so that f1 / f2 exceeds the upper limit of equation (2), the diameter of the on-axial light beam incident on the second lens group L2 increases, and the second lens group L2 becomes larger. As a result, it becomes difficult to miniaturize the optical system L0, which is undesirable. If the focal length of the first lens group L1 decreases so that f1 / f2 falls below the lower limit of equation (2), the angle of the off-axis light rays incident on the second lens group L2 from the optical axis increases, making it difficult to suppress changes in the angle of view during focusing, which is also undesirable.

[0021] Furthermore, it is more preferable to set the lower limit of equation (2) to 0.55, 0.60, 0.65, or 0.68. Also, it is more preferable to set the upper limit of equation (2) to 2.70, 2.65, or 2.60.

[0022] By satisfying the above configuration and conditions, it becomes possible to realize a compact, lightweight, and wide-angle optical system that has high optical performance across the entire field of view, enables focusing at close range, and suppresses changes in performance and field of view during focusing.

[0023] The optical system L0 of each embodiment preferably satisfies at least one of the following configurations and conditions of equations (3) to (17).

[0024] In the optical system L0 of each embodiment, it is preferable that the first lens group L1 includes an aperture diaphragm SP. This makes it possible to position the aperture diaphragm SP approximately in the center of the optical system L0, thereby reducing the imbalance in lens diameter between the object side and the image side of the optical system L0. As a result, it becomes easier to reduce the overall diameter of the optical system L0.

[0025] In the optical system L0 of each embodiment, it is preferable that at least one of the object-side and image-side lens surfaces of the first negative lens and the second negative lens of the first lens group L1 is aspherical. This facilitates the correction of field curvature and distortion aberrations. Furthermore, it is possible to reduce the number of lenses while suppressing the occurrence of these aberrations, making it easier to miniaturize and lighten the optical system L0.

[0026] In the optical system L0 of each embodiment, the second lens group L2 preferably includes at least two positive lenses and at least two negative lenses. This makes it easier to suppress spherical aberration and field curvature that occur during focusing, while suppressing the occurrence of axial chromatic aberration and lateral chromatic aberration.

[0027] In the optical system L0 of each embodiment, the focal length of the third lens group L3 is f3, the focal length of the subgroup in the first lens group L1 closer to the object than the aperture diaphragm SP is f1A, and the focal length of the subgroup in the first lens group L1 closer to the image than the aperture diaphragm SP is f1B. In the optical system L0, the air-equivalent distance on the optical axis from the lens surface closest to the image to the image plane IP (back focus) is BF, and the distance on the optical axis from the aperture diaphragm SP to the image plane IP is DSI. The lateral magnification of the second lens group L2 in the infinity focus state is β2, and the lateral magnification of the third lens group L3 in the infinity focus state is β3.

[0028] Furthermore, let fGRn be the focal length of the negative lens GRn, the image-side negative lens among the at least one negative lens included in the second lens group L2. Let D23 be the distance along the optical axis from the image-side lens surface of the second lens group L2 to the object-side lens surface of the third lens group L3 when in focus at infinity. Let fG1G2 be the combined focal length of the first negative lens G1 and the second negative lens G2 in the first lens group L1. Let D2Max be the maximum air gap along the optical axis within the second lens group L2.

[0029] Furthermore, let rG1R1 be the paraxial radius of curvature of the object-side lens surface of the first negative lens G1, and rG1R2 be the paraxial radius of curvature of the image-side lens surface of the first negative lens G1. Let rG2R1 be the paraxial radius of curvature of the object-side lens surface of the second negative lens G2, and rG2R2 be the paraxial radius of curvature of the image-side lens surface of the second negative lens G2. Let νdGFn be the Abbe number with respect to the d line of the negative lens GFn closest to the object among the at least one negative lens in the first lens group L that has a lens surface convex to the image side. Let fGFn be the focal length of the negative lens GFn located closest to the object in the first lens group L1 and having a lens surface convex to the image side.

[0030] Furthermore, let fGp be the focal length of the positive lens Gp included in the first lens group L1. Let νdp be the Abbe number of the positive lens Gp included in the first lens group L1 with respect to the d line, and let ΔθgFp be the anomalous partial dispersion of the positive lens Gp on the g line and F line. ΔθgFp is calculated using the Abbe number νdp and the partial dispersion ratio θgFp. ΔθgFp = θgFp - (B3 × νdp 3+B2×νdp 2 (+B1×νdp+B0) B3 = -7.00 × 10 -8 B2 = 1.20 × 10 -4 B1 = -9.90 × 10 -3 B0 = 7.50 × 10 -1 It is expressed as follows. The definitions of the Abbe number νdp and the partial variance ratio θgFp will be explained later.

[0031] 1.00 ≤ f1B / f2 ≤ 9.00 (3) -0.30≦f / f1A≦0.30 (4) 0.10 ≤ BF / DSI ≤ 0.35 (5) -0.30 ≤ f / f3 ≤ 0.30 (6) 0.80 ≤ f / BF ≤ 1.50 (7) 0.50 ≤ (1-β2 2 )×β3 2 ≤1.10 (8) -3.00 ≤ fGRn / f2 ≤ -0.50 (9) 0.01 ≤ D2Max / D23 ≤ 0.60 (10) -4.00≦(rG1R2+rG1R1) / (rG1R2-rG1R1)≦-1.00 (11) -4.00≦(rG2R2+rG2R1) / (rG2R2-rG2R1)≦-1.00 (12) -3.00 ≤ fG1G2 / f ≤ -0.80 (13) 81.0 ≤ νdGFn ≤ 100.0 (14) -6.50 ≤ fGFn / f ≤ -2.00 (15) 0.050 ≤ ΔθgFp ≤ 0.250 (16) 0.020 ≤ f / fGp ≤ 0.090 (17) The conditions in equation (3) indicate an appropriate relationship between the focal length of the subgroup of the first lens group L3 closer to the image than the aperture diaphragm SP and the focal length f2 of the second lens group L2. If f1B increases so that f1B / f2 exceeds the upper limit of equation (3), the diameter of the on-axial light beam incident on the second lens group L2 increases, making it difficult to miniaturize the second lens group L2, which is undesirable. Also, the angle of the off-axis light rays incident on the second lens group L2 from the optical axis increases, making it difficult to suppress changes in the angle of view during focusing, which is undesirable. If f1B decreases so that f1B / f2 falls below the lower limit of equation (3), it becomes difficult to suppress the occurrence of on-axial chromatic aberration, spherical aberration, and coma aberration, which is undesirable.

[0032] Furthermore, it is more preferable to set the lower limit of equation (3) to 1.20, 1.50, 1.60, or 1.70. Also, it is more preferable to set the upper limit of equation (3) to 8.00, 7.50, 7.00, or 6.60.

[0033] The conditions in equation (4) indicate an appropriate relationship between the focal length of the entire optical system L0 and the focal length of the subgroup of the first lens group L1 that is closer to the object than the aperture diaphragm SP. If the positive refractive power of the object-side subgroup becomes strong enough that f / f1A exceeds the upper limit of equation (4), the lens diameter on the image side of the optical system L0 becomes larger, making it difficult to miniaturize the optical system L0, which is undesirable. If the negative refractive power of the object-side subgroup becomes strong enough that f / f1A falls below the lower limit of equation (4), the lens diameters before and after the aperture diaphragm SP become larger, making it difficult to miniaturize the optical system L0, which is also undesirable. Furthermore, on the image side of the aperture diaphragm SP, it becomes difficult to separate the on-axial and off-axial light beams, making it difficult to correct astigmatism, which is also undesirable.

[0034] Furthermore, it is more preferable to set the lower limit of equation (4) to -0.20, -0.15, -0.10, or -0.08. Also, it is more preferable to set the upper limit of equation (4) to 0.25, 0.20, or 0.17.

[0035] The conditions in equation (5) indicate an appropriate relationship between the back focus of the optical system L0 and the distance from the aperture diaphragm SP to the image plane IP. If the BF increases so that BF / DSI exceeds the upper limit of equation (5), the height of the off-axis light beam incident on the optical system L0 from the optical axis increases, making it difficult to reduce the lens diameter on the object side of the optical system L0, which is undesirable. If the BF decreases so that BF / DSI falls below the lower limit of equation (5), the separation of on-axis and off-axis light beams decreases even near the image plane IP, making it difficult to suppress sagittal coma flare and astigmatism, which is also undesirable.

[0036] Furthermore, it is more preferable to set the lower limit of equation (5) to 0.12, 0.14, or 0.15. Also, it is more preferable to set the upper limit of equation (5) to 0.30, 0.28, or 0.26.

[0037] The conditions in equation (6) indicate an appropriate relationship between the focal length of the entire optical system L0 and the focal length of the third lens group L3. If the positive refractive power of the third lens group L3 becomes strong enough that f / f3 exceeds the upper limit of equation (6), it becomes difficult to suppress the occurrence of barrel distortion, which is undesirable. If the negative refractive power of the third lens group L3 becomes strong enough that f / f3 falls below the lower limit of equation (6), it becomes difficult to suppress the change in the angle of view during focusing, which is also undesirable.

[0038] Furthermore, it is more preferable to set the lower limit of equation (6) to -0.20, -0.15, -0.10, or -0.04. Also, it is more preferable to set the upper limit of equation (6) to 0.25, 0.20, 0.15, or 0.13.

[0039] The conditions in equation (7) indicate an appropriate relationship between the focal length of the entire optical system L0 and the back focus. If f / BF exceeds the upper limit of equation (7), it becomes difficult to suppress field curvature and distortion while ensuring back focus, which is undesirable. If f / BF falls below the lower limit of equation (7), it becomes difficult to reduce the diameter of the object-side lens in a wide-angle optical system, which is also undesirable.

[0040] Furthermore, it is more preferable to set the lower limit of equation (7) to 0.82, 0.85, 0.88, or 0.90. Also, it is more preferable to set the upper limit of equation (7) to 1.45, 1.40, or 1.35.

[0041] The conditions in equation (8) indicate an appropriate range for the focus sensitivity of the second lens group L2 (the ratio of the movement of the image plane IP to the movement of the second lens group L2). If the focus sensitivity exceeds the upper limit of equation (8), the positive refractive power of the second lens group L2 becomes too strong, making it difficult to minimize the change in the angle of view during focusing, which is undesirable. If the focus sensitivity falls below the lower limit of equation (8), the amount of movement of the second lens group L2 becomes large when focusing on close-range subjects, making it difficult to shorten the overall length of the optical system L0, which is also undesirable.

[0042] Furthermore, it is more preferable to set the lower limit of equation (8) to 0.55, 0.60, 0.65, or 0.70. Also, it is more preferable to set the upper limit of equation (8) to 1.00, 0.95, 0.90, or 0.85.

[0043] The conditions in equation (9) indicate an appropriate relationship between the focal length of the negative lens GRn on the image side of the second lens group L2 and the focal length of the second lens group L2. If the negative refractive power of the negative lens GRn becomes strong enough that fGRn / f2 exceeds the upper limit of equation (9), it is undesirable because the Petzval sum for the entire optical system L0 becomes too small, making it difficult to correct field curvature. If the negative refractive power of the negative lens GRn becomes weak enough that fGRn / f2 falls below the lower limit of equation (9), it is undesirable because it becomes difficult to suppress sagittal coma flare.

[0044] Furthermore, it is more preferable to set the lower limit of equation (9) to -2.70, -2.60, -2.55, or -2.50. Also, it is more preferable to set the upper limit of equation (9) to -0.60, -0.65, or -0.70.

[0045] The conditions in equation (10) indicate an appropriate relationship between the maximum air gap within the second lens group L2 and the distance from the image-side lens surface of the second lens group L2 to the object-side lens surface of the third lens group L3 in the infinity focus state. If the thickness of the second lens group L2 on the optical axis increases so that D2Max / D23 exceeds the upper limit of equation (10), it is undesirable because the mechanism driving the second lens group L2 becomes larger, making it difficult to miniaturize and lighten the optical system L0. If D2Max / D23 falls below the lower limit of equation (10), it is undesirable because it becomes difficult to suppress the occurrence of spherical aberration during focusing.

[0046] Furthermore, it is more preferable to set the lower limit of equation (10) to 0.02, 0.03, or 0.04. Also, it is more preferable to set the upper limit of equation (10) to 0.50, 0.45, 0.40, or 0.35.

[0047] The conditions in equation (11) indicate an appropriate range for the shape factor of the first negative lens in the first lens group L1. If the shape factor exceeds the upper limit of equation (11), it becomes difficult to reduce the diameter of the first negative lens while correcting astigmatism, which is undesirable. If the shape factor falls below the lower limit of equation (11), it becomes difficult to suppress the occurrence of barrel distortion, which is also undesirable.

[0048] Furthermore, it is more preferable to set the lower limit of equation (11) to -3.50, -3.00, -2.50, or -2.20. Also, it is more preferable to set the upper limit of equation (11) to -1.04, -1.06, -1.08, or -1.00.

[0049] The conditions in equation (12) indicate an appropriate range for the shape factor of the second negative lens in the first lens group L1. If the shape factor exceeds the upper limit of equation (12), it becomes difficult to correct field curvature, which is undesirable. If the shape factor falls below the lower limit of equation (12), it becomes difficult to suppress distortion and astigmatism, which is also undesirable.

[0050] Furthermore, it is more preferable to set the lower limit of equation (12) to -3.90, -3.80, or -3.70. Also, it is more preferable to set the upper limit of equation (12) to -1.10, -1.20, or -1.30.

[0051] The conditions in equation (13) indicate an appropriate relationship between the combined focal length of the first and second negative lenses in the first lens group L1 and the focal length of the entire optical system L0. If the combined negative refractive power of the first and second negative lenses becomes strong enough that fG1G2 / f exceeds the upper limit of equation (13), it becomes difficult to suppress barrel distortion and chromatic aberration, which is undesirable. If the combined negative refractive power of the first and second negative lenses becomes weak enough that fG1G2 / f falls below the lower limit of equation (13), the Petzval sum for the entire optical system L0 becomes too large, making it difficult to correct field curvature, which is also undesirable. Furthermore, it becomes difficult to reduce the diameter of the object-side lens in the optical system L0, which is also undesirable.

[0052] Furthermore, it is more preferable to set the lower limit of equation (13) to -2.80, -2.50, -2.20, or -2.10. Also, it is more preferable to set the upper limit of equation (13) to -1.00, -1.10, or -1.20.

[0053] The conditions in equation (14) indicate an appropriate range for the Abbe number of the negative lens GFn in the first lens group L1. Having a negative lens with a convex surface facing the image side in the first lens group L1 facilitates higher-order correction of field curvature. If νdGFn exceeds the upper limit of equation (14), the first-order achromatic correction of lateral chromatic aberration becomes overcorrected, which is undesirable. If νdGFn falls below the lower limit of equation (14), it becomes difficult to suppress the occurrence of lateral chromatic aberration, which is also undesirable.

[0054] Furthermore, it is more preferable to set the lower limit of formula (14) to 85.0, 88, 90.0, or 93.0. Also, it is more preferable to set the upper limit of formula (14) to 99.0, 98.0, 97.0, or 96.0.

[0055] The conditions in equation (15) indicate an appropriate relationship between the focal length of the negative lens GFn and the focal length of the entire optical system L0. If the negative refractive power of the negative lens GFn becomes strong enough that fGFn / f exceeds the upper limit of equation (15), it is undesirable because higher-order correction of field curvature becomes difficult. Also, the wavelength dependence of field curvature increases, making it difficult to correct field curvature over a wide wavelength range, which is undesirable. If the negative refractive power of the negative lens GFn becomes weak enough that fGFn / f falls below the lower limit of equation (15), it is undesirable because the correction effect of chromatic aberration becomes small.

[0056] Furthermore, it is more preferable to set the lower limit of equation (15) to -6.00, -5.50, -4.50, or -4.30. Also, it is more preferable to set the upper limit of equation (15) to -2.20, -2.40, -2.50, or -2.60.

[0057] The conditions in equation (16) indicate an appropriate range for the anomalous partial dispersion of the positive lens Gp of the first lens group L1. If ΔθgFp exceeds the upper limit of equation (16), the second-order achromatic correction of axial chromatic aberration becomes overcorrected, which is undesirable. If ΔθgFp falls below the lower limit of equation (16), the second-order achromatic correction of axial chromatic aberration and lateral chromatic aberration becomes undercorrected, which is also undesirable.

[0058] Furthermore, it is more preferable to set the lower limit of formula (16) to 0.080, 0.100, 0.140, or 0.170. Also, it is more preferable to set the upper limit of formula (16) to 0.240, 0.220, 0.200, or 0.185.

[0059] The conditions in equation (17) indicate an appropriate range between the focal length of the positive lens Gp and the focal length of the entire optical system L0. If the positive refractive power of the positive lens Gp weakens so that f / fGp exceeds the upper limit of equation (17), it becomes difficult to suppress axial chromatic aberration, which is undesirable. If the positive refractive power of the positive lens Gp strengthens so that f / fGp falls below the lower limit of equation (17), the wavelength dependence of field curvature increases, making it difficult to correct field curvature over a wide wavelength range, which is also undesirable.

[0060] Furthermore, it is more preferable to set the lower limit of formula (17) to 0.025, 0.030, 0.035, or 0.040. Also, it is more preferable to set the upper limit of formula (17) to 0.080, 0.075, 0.070, 0.065, or 0.060.

[0061] Next, the optical system L0 of each embodiment will be described in detail.

[0062] The optical system L0 of Examples 1, 2, 3, and 4 is composed of a first lens group L1 with positive refractive power, a second lens group L2 with positive refractive power, and a third lens group L3 with positive refractive power. By applying positive refractive power to the third lens group L3, the incident angle of the off-axis light beam incident on the image plane IP can be reduced, making it easier to suppress color unevenness when an image sensor such as a CMOS sensor captures an image of a subject through the optical system L0.

[0063] The optical system L0 of Example 5 is composed of a first lens group L1 with positive refractive power, a second lens group L2 with positive refractive power, and a third lens group L3 with negative refractive power. By applying negative refractive power to the third lens group L3, the Petzval sum is made smaller, and the correction of field curvature becomes easier.

[0064] Furthermore, the angle of incidence of off-axis rays onto the image plane IP can be increased, allowing for a reduction in the lens diameter of the third lens group L3. In addition, since the exit pupil position becomes closer to the image plane IP, the overall length of the lens can be easily shortened.

[0065] In the optical system L0 of Examples 1, 3, 4, and 5, the first negative lens and the second negative lens in the first lens group L1 are aspherical lenses on both sides. In the optical system L0 of Example 2, the first negative lens and the third lens from the object side are aspherical lenses on both sides. This enhances the effectiveness of correcting distortion and astigmatism. By shaping the object-side aspherical lens of these two aspherical lenses so that the absolute value of peripheral curvature is smaller than the absolute value of curvature along the optical axis, the distortion correction effect can be further enhanced. By shaping the image-side aspherical lens of these two aspherical lenses so that the absolute value of peripheral curvature is larger than the absolute value of curvature along the optical axis, the field curvature correction effect can be further enhanced.

[0066] In the optical systems L0 of Examples 1, 2, and 3, the object-side lens surface of the third lens from the object side is concave. This increases the refractive power of the negative air lens formed by the image-side lens surface of the second negative lens and the object-side lens surface of the third lens from the object side. As a result, the Petzval sum is reduced, making it easier to correct field curvature.

[0067] In the optical system L0 of Examples 1, 2, 4, and 5, the positive lens Gp in the first lens group L1 is positioned on the image side of the aperture diaphragm SP and is a positive meniscus lens with its convex surface facing the image side. As a result, the positive lens Gp has a nearly concentric shape with respect to the off-axis light beam incident on it, making it easy to correct both on-axial chromatic aberration and lateral chromatic aberration. Furthermore, the positive lens Gp is ​​a resin lens and is bonded to a biconvex lens on the object side and a biconcave lens on the image side. This enhances environmental resistance.

[0068] In the optical system L0 of each embodiment, the second lens group L2 has three positive lenses and two negative lenses. This makes it possible to reduce the refractive power per lens, and makes it easier to correct spherical aberration and field curvature that occur during focusing, while correcting axial chromatic aberration and lateral chromatic aberration.

[0069] In the optical system L0 of each embodiment, the second lens group L2 includes an aspherical lens in which at least one surface is aspherical. This makes it easier to correct spherical aberration, astigmatism, and coma aberration. By positioning the aspherical lens closer to the image side of the second lens group L2, it becomes easier to correct astigmatism that occurs during focusing.

[0070] In the optical system L0 of each embodiment, the negative lens GRn on the image side of the second lens group L2 has a concave lens surface on the image side. This allows for the generation of a strong negative refractive force on the image side, making it easier to correct sagittal coma flare.

[0071] In the optical system L0 of each embodiment, the third lens group L3 has a cemented lens formed by joining a positive lens and a negative lens. This makes it easy to correct chromatic aberration and astigmatism.

[0072] The following shows numerical examples 1 to 5 corresponding to each of the Examples 1 to 5. In the surface data of each numerical example, the surface number m indicates the order of the optical surfaces when counted from the object. r (mm) is the radius of curvature of the m-th optical surface, and d (mm) is the distance on the optical axis between the m-th surface and the (m+1)-th surface. Also, nd indicates the refractive index of each optical material at the d-line between the m-th surface and the (m+1)-th surface. Furthermore, νd and θgF indicate the Abbe number and partial dispersion ratios at the g-line and F-line of the optical material, respectively, with respect to the d-line. The Abbe number νd with respect to the d-line and the partial dispersion ratios θgF at the g-line and F-line are given by nd, nF, nC, and ng, respectively, when the refractive indices at the Fraunhofer lines d-line (587.6 nm), F-line (486.1 nm), C-line (656.3 nm), and g-line (wavelength 435.8 nm) are nd, nF, nC, and ng, respectively. νd=(nd-1) / (nF-nC) θgF = (ng - nF) / (nF - nC) It is represented as follows.

[0073] In each numerical example, d, focal length (mm), F-number, and half angle of view (°) are all values when the optical system is in an infinitely focused state. The back focus BF is the air-equivalent distance from the lens surface (the final surface) on the image side of the optical system to the image plane, as described above. The overall lens length is the value obtained by adding the back focus to the distance on the optical axis from the lens surface on the object side (the frontmost surface) of the optical system to the final lens surface.

[0074] The "*" attached to the surface number means that the surface has an aspherical shape. The aspherical shape is represented by the following formula when X is the displacement amount from the surface vertex in the optical axis direction, h is the height from the optical axis in the direction orthogonal to the optical axis, the light traveling direction is positive, R is the paraxial curvature radius, K is the conic constant, and A4, A6, A8, A10, A12, A14 are the aspherical coefficients of each order.

[0075] X=(h 2 / R) / [1+{1-(1+K)(h / R) 2} 1 / 2 +A4×h 4 +A6×h 6 +A8×h 8 +A10×h 10 +A12×h 12 +A14×h 14 Note that "e±XX" in the conic constant and aspherical coefficients means "×10 ±XX ". [Numerical Example 1] Unit: mm Surface Data Surface Number r d nd νd θgF 1* 72.028 2.80 1.58313 59.4 2* 16.266 13.91 3* 230.372 2.50 1.85400 40.4 4* 36.824 5.96 5 -52.544 1.70 1.49700 81.7 6 227.055 3.25 2.00100 29.1 ​7 -66.875 4.72 8 -19.936 1.20 1.43387 95.1 9 -174.771 1.15 10 666.926 7.95 1.75500 52.3 11 -19.196 1.20 1.90366 31.3 12 -37.194 0.30 13 366.220 4.19 2.00100 29.1 14 -49.913 0.88 15 -452.541 1.30 1.85478 24.8 16 126.230 4.59 17 (aperture) ∞ 1.99 18 51.465 6.73 1.74320 49.3 19 -64.595 0.70 1.57060 20.1 0.7782 20 -47.173 1.10 1.66565 35.6 21 52.870 (Variable) 22 102.903 7.91 1.59282 68.6 23 -18.997 0.90 1.85478 24.8 24 104.859 0.26 25 40.761 5.64 1.53775 74.7 26 -40.761 0.30 27 80.536 4.90 1.92286 20.9 28 -52.817 0.24 29* -451.581 2.60 1.85400 40.4 30 52.550 (variable) 31 1258.224 9.47 1.59282 68.6 32 -19.963 1.10 2.00100 29.1 33 -38.825 13.43 Image plane ∞ Aspherical data Front page K = 0.00000e+00 A 4= 2.85263e-06 A 6=-1.06525e-09 A 8= 6.56552e-12 A10=-1.19824e-14 A12= 1.27858e-17 A14=-5.74533e-21 2nd side K =-7.63673e-01 A 4= 3.24368e-07 A 6= 1.38290e-08 A 8=-2.16651e-10 A10= 1.03526e-12 A12=-2.85465e-15 A14= 2.51224e-18 3rd page K = 0.00000e+00 A 4=-1.93330e-05 A 6= 5.99502e-08 A 8= 2.63193e-11 A10 = -1.91446e-13 Side 4 K = 0.00000e+00 A 4=-1.26314e-06 A 6= 8.53091e-08 A 8= 3.29375e-10 A10=-1.43389e-12 A12= 6.79219e-15 Page 29 K = 0.00000e+00 A 4=-1.36198e-05 A 6=-5.53900e-09 A 8= 2.76263e-11 A10=-2.94829e-13 A12= 7.25340e-16 Various data Focal length 14.42 F-number 1.45 Half-angle (°): 52.40 Image height 18.73 Lens length: 127.50 BF 13.43 When focused at infinity When focused on an object at a horizontal magnification of -0.1x Object plane to image plane: Infinity 254.067 d21 5.67 3.89 d30 6.98 8.76 Lens group data Group starting plane focal length 1 1 60.70 2 22 45.36 3 31 164.62 Single lens data Lens starting plane, focal length 1 1 -36.71 2 3 -51.63 3 5 -85.68 4 6 51.89 5 8 -51.99 6 10 24.84 7 11 -45.33 8 13 44.10 9 15 -115.35 10 18 39.52 11 19 302.13 12 20 -37.29 13 22 27.72 14 23 -18.75 15 25 38.84 16 27 35.18 17 29 -54.99 18 31 33.24 19 32 -42.29 [Numerical Example 2] Unit: mm Surface data Face number rd nd νd θgF 1* 68.228 2.80 1.58313 59.4 2* 22.023 6.02 3 48.678 1.30 1.49700 81.7 4 19.877 10.23 5* -65.000 2.10 1.85400 40.4 6* 98.359 0.58 7 27.484 2.58 1.77047 29.7 8 41.872 7.80 9 -17.377 0.90 1.43875 94.7 10 -50.987 0.15 11 -661.523 9.33 1.72916 54.7 12 -17.758 1.00 1.84666 23.8 13 -39.714 0.20 14 317.043 3.77 2.00100 29.1 15 -49.175 0.30 16 40.000 1.20 1.54814 45.8 17 29.455 8.25 18 (aperture) ∞ 1.66 19 52.664 3.98 1.91082 35.2 20 -300.000 0.70 1.57060 20.1 0.7782 21 -107.199 1.00 1.54072 47.2 22 57.316 (Variable) 23 210.839 6.03 1.43875 94.7 24 -21.633 0.90 1.85478 24.8 25 -757.038 0.80 26* 49.445 8.55 1.49700 81.7 27* -25.759 0.35 28 36.498 4.10 1.92286 20.9 29 213.891 0.50 30 47.520 0.85 1.85478 24.8 31 22.781 (Variable) 32 437.990 11.25 1.53775 74.7 33 -17.377 0.90 2.00069 25.5 34 -34.119 11.00 Image plane ∞ Aspherical data Front page K = 0.00000e+00 A 4= 8.40179e-06 A 6=-2.16752e-08 A 8= 3.89602e-11 A10=-3.74428e-14 A12= 2.56441e-17 A14=-1.04282e-20 2nd side K =-1.18258e+00 A 4= 2.25254e-06 A 6= 1.42326e-10 A 8=-2.60579e-10 A10= 9.49508e-13 A12=-1.35856e-15 A14= 7.06455e-19 5th page K = 0.00000e+00 A 4=-5.00917e-05 A 6= 4.73233e-07 A 8=-1.46028e-09 A10 = 1.74157e-12 Side 6 K = 0.00000e+00 A 4=-2.12787e-05 A 6= 4.86543e-07 A 8=-1.14039e-09 A10= 9.67632e-13 A12= 2.88212e-15 Page 26 K = 0.00000e+00 A 4=-8.60844e-06 A 6= 6.93515e-09 A 8= 8.60818e-11 A10=-4.00880e-13 A12= 9.42337e-18 Page 27 K = 0.00000e+00 A 4= 1.07871e-05 A 6= 1.27312e-08 A 8=-2.42671e-10 A10= 1.62259e-12 A12=-3.95572e-15 Various data Focal length 14.42 F-number 1.46 Half-angle (°): 51.59 Image height 18.18 Lens length: 123.63 BF 11.00 When focused at infinity When focused on an object at a horizontal magnification of -0.1x Object plane to image plane infinity 247.931 d22 6.08 4.21 d31 6.47 8.34 Lens group data Group starting plane focal length 1 1 36.62 2 23 51.76 3 32 236.68 Single lens data Lens starting plane, focal length 1 1 -57.04 2 3 -68.62 3 5 -45.56 4 7 96.30 5 9 -60.58 6 11 24.87 7 12 -38.75 8 14 42.75 9 16 -212.39 10 19 49.45 11 20 291.94 12 21 -68.92 13 23 45.07 14 24 -26.07 15 26 35.41 16 28 47.16 17 30 -52.02 18 32 31.35 19 33 -36.37 [Numerical Example 3] Unit: mm Surface data Face number rd nd νd θgF 1* 267.177 2.80 1.58313 59.4 2* 14.498 11.53 3* 67.327 2.40 1.80400 46.5 4* 34.774 4.61 5 -183.000 1.50 1.43875 94.7 6 54.102 0.35 7 53.453 2.72 1.85478 24.8 8 309.000 4.98 9 -19.293 1.20 1.43387 95.1 10 -408.469 0.29 11 666.691 8.34 1.83400 37.2 12 -14.076 1.00 2.00100 29.1 13 -42.469 0.30 14 147.148 4.68 2.00100 29.1 15 -39.771 0.35 16 -499.877 1.20 1.80518 25.4 17 177.463 3.75 18 (aperture) ∞ 1.00 19 34.242 4.06 1.48749 70.2 20 -196.366 1.10 1.85478 24.8 21 92.200 (Variable) 22 526.322 6.70 1.59282 68.6 23 -17.821 0.90 1.85478 24.8 24 81.915 0.20 25 33.276 6.09 1.49700 81.5 26 -36.575 1.28 27 40.274 5.42 1.92286 20.9 28 -70.437 1.13 29* -719.648 2.30 1.85400 40.4 30 * 39.887 (variable) 31 96.515 10.92 1.59282 68.6 32 -18.249 1.10 2.00069 25.5 33 -45.803 10.97 Image plane ∞ Aspherical data Front page K = 0.00000e+00 A 4= 1.69844e-05 A 6=-3.17085e-08 A 8= 5.48951e-11 A10=-5.97168e-14 A12= 3.72776e-17 A14=-1.00928e-20 2nd side K =-7.19651e-01 A 4=-1.30351e-05 A 6= 1.09004e-07 A 8=-8.61665e-10 A10= 3.58174e-12 A12=-1.00862e-14 A14= 1.07411e-17 3rd page K = 0.00000e+00 A 4=-9.08937e-05 A 6= 5.19871e-07 A 8=-1.25801e-09 A10 = 1.16180e-12 Side 4 K = 0.00000e+00 A 4=-6.59571e-05 A 6= 6.18490e-07 A 8=-1.77781e-09 A10=5.74121e-12 A12=-8.19795e-15 Page 29 K = 0.00000e+00 A 4=-2.36034e-05 A 6=-3.46142e-09 A 8=-2.04769e-11 A10=6.75972e-14 A12=-2.13753e-16 Page 30 K = 0.00000e+00 A 4= 7.67496e-09 A 6=-1.56427e-10 A 8= 1.21761e-12 A10 = -3.19667e-15 Various data Focal length 12.37 F-number 1.45 Half-angle (°): 56.52 Image height 18.70 Lens length: 113.78 BF 10.97 When focused at infinity When focused on an object at a horizontal magnification of -0.1x Object plane to image plane: Infinity 222.953 d21 4.31 2.64 d30 4.33 6.00 Lens group data Group starting plane focal length 1 1 43.78 2 22 45.33 3 31 171.13 Single lens data Lens starting plane, focal length 1 1 -26.40 2 3 -92.49 3 5 -94.99 4 7 75.24 5 9 -46.71 6 11 16.62 7 12 -21.41 8 14 31.67 9 16 -162.53 10 19 60.16 11 20 -73.27 12 22 29.21 13 23 -17.05 14 25 36.10 15 27 28.43 16 29 -44.19 17 31 26.84 18 32 -30.93 [Numerical Example 4] Unit: mm Surface data Face number rd nd νd θgF 1* 51.539 2.80 1.58313 59.4 2* 15.371 13.33 3* 61.291 2.50 1.85400 40.4 4* 35.039 3.91 5 649.855 1.70 1.49700 81.7 6 31.302 2.27 2.00069 25.5 7 44.812 7.68 8 -20.849 1.20 1.43387 95.1 9 -141.674 0.55 10 150.414 6.39 1.87070 40.7 11 -23.249 1.20 1.84666 23.8 12 -86.168 0.30 13 96.682 3.91 2.00100 29.1 14 -79.582 0.29 15 29.031 1.30 1.85478 24.8 16 23.995 5.91 17 (aperture) ∞ 1.00 18 45.666 3.98 1.74320 49.3 19 -1500.170 0.70 1.57060 20.1 0.7782 20 -146.486 1.10 1.62205 41.1 21 56.157 (Variable) 22 326.489 7.19 1.59282 68.6 23 -19.321 0.90 1.85478 24.8 24 -164.893 0.29 25 43.177 6.25 1.53775 74.7 26 -49.914 0.30 27 4710.975 3.65 1.92286 20.9 28 -58.311 0.92 29* 151.547 2.60 1.85400 40.4 30 54.632 (Variable) 31 -317.076 9.73 1.59282 68.6 32 -20.352 1.10 2.00100 29.1 33 -34.529 16.85 Image plane ∞ Aspherical data Front page K = 0.00000e+00 A 4= 1.43080e-07 A 6=-3.60971e-09 A 8= 3.90689e-11 A10=-9.24067e-14 A12= 1.02941e-16 A14=-4.56015e-20 2nd side K =-1.26528e+00 A 4= 2.03157e-05 A 6= 8.32472e-10 A 8=-2.79434e-10 A10= 2.15327e-12 A12=-6.81150e-15 A14= 6.54481e-18 3rd page K = 0.00000e+00 A 4=-1.26561e-05 A 6=-8.36736e-08 A 8= 6.18279e-10 A10 = -9.98654e-13 Side 4 K = 0.00000e+00 A 4= 5.66918e-07 A 6=-6.27596e-08 A 8= 9.66481e-10 A10=-2.52364e-12 A12= 9.09062e-15 Page 29 K = 0.00000e+00 A 4=-1.25691e-05 A 6=-8.33507e-09 A 8= 8.92018e-12 A10=-5.45463e-14 A12= 7.21573e-17 Various data Focal length 15.42 F-number 1.45 Half-angle (°): 51.98 Image height 19.72 Lens length: 123.21 BF 16.85 When focused at infinity When focused on an object at a horizontal magnification of -0.1x From object plane to image plane: Infinity 259.830 d21 6.08 4.13 d30 5.34 7.29 Lens group data Group starting plane focal length 1 1 111.42 2 22 43.02 3 31 132.99 Single lens data Lens starting plane, focal length 1 1 -38.66 2 3 -100.19 3 5 -66.23 4 6 95.72 5 8 -56.52 6 10 23.53 7 11 -37.94 8 13 44.10 9 15 -183.70 10 18 59.70 11 19 284.45 12 20 -65.12 13 22 31.01 14 23 -25.68 15 25 44.09 16 27 62.44 17 29 -101.28 18 31 36.24 19 32 -51.52 [Numerical Example 5] Unit: mm Surface data Face number rd nd νd θgF 1* 122.242 2.80 1.58313 59.4 2* 17.150 9.08 3* 66.939 2.50 1.80400 46.5 4* 36.194 1.00 5 23.223 2.15 2.00069 25.5 6 26.658 9.63 7 -18.851 1.20 1.43387 95.1 8 -126.534 0.52 9 224.310 10.54 1.75500 52.3 10 -15.919 1.20 1.90366 31.3 11 -43.505 0.30 12 147.913 5.07 2.00100 29.1 13 -51.304 0.29 14 220.281 1.30 1.85478 24.8 15 65.807 3.74 16 (aperture) ∞ 1.26 17 65.974 4.77 1.74320 49.3 18 -73.394 0.70 1.57060 20.1 0.7782 19 -54.080 1.10 1.66565 35.6 20 332.302 (variable) 21 -33.574 5.51 1.59282 68.6 22 -17.442 0.90 1.85478 24.8 23 -32.738 1.21 24 31.427 7.48 1.49700 81.5 25 -47.785 0.30 26 163.838 3.56 1.92286 20.9 27 -75.076 0.21 28* -659.596 2.50 1.85400 40.4 29 37.848 (Variable) 30 153.035 8.15 1.49700 81.5 31 -22.527 1.10 1.85478 24.8 32 -75.301 14.44 Image plane ∞ Aspherical data Front page K = 0.00000e+00 A 4= 1.15340e-05 A 6=-1.13219e-08 A 8= 1.18913e-11 A10=-2.17324e-14 A12= 4.61433e-17 A14=-3.54334e-20 2nd side K =-9.44856e-01 A 4= 5.33008e-06 A 6= 3.05029e-08 A 8=-1.69870e-10 A10= 7.70192e-13 A12=-4.56971e-15 A14= 6.57283e-18 3rd page K = 0.00000e+00 A 4=-1.17437e-05 A 6= 2.75779e-08 A 8=-7.15484e-11 A10 = 1.10546e-13 Side 4 K = 0.00000e+00 A 4= 8.18047e-06 A 6= 5.13359e-08 A 8=-8.15633e-11 A10= 8.86408e-13 A12= 1.13719e-16 Page 28 K = 0.00000e+00 A 4=-1.66207e-05 A 6=-6.95908e-09 A 8=-6.03052e-12 A10=7.91456e-14 A12=-9.83138e-17 Various data Focal length 18.53 F-number 1.45 Half-angle (°): 47.16 Image height 19.98 Lens length: 118.22 BF 14.44 When focused at infinity When focused on an object at a horizontal magnification of -0.1x Object plane to image plane infinity 286.039 d20 8.88 6.66 d29 4.83 7.05 Lens group data Group starting plane focal length 1 1 41.83 2 21 54.70 3 30 -892.86 Single lens data Lens starting plane, focal length 1 1 -34.55 2 3 -101.70 3 5 137.18 4 7 -51.23 5 9 20.07 6 10 -28.37 7 12 38.54 8 14 -110.21 9 17 47.44 10 18 355.47 11 19 -69.79 12 21 54.32 13 22 -44.89 14 24 39.38 15 26 56.19 16 28 -41.84 17 30 40.13 18 31 -37.97 The values ​​for equations (1) to (17) in each numerical example are summarized in Table 1 below. The optical systems in each numerical example satisfy all the conditions of equations (1) to (17).

[0076] [Table 1]

[0077] Figures 2, 4, 6, 8, and 10 show the longitudinal aberrations (spherical aberration, astigmatism, distortion, and chromatic aberration) of the optical system L0 for numerical examples 1 to 5, respectively. In each figure, (A) shows the longitudinal aberration at infinity focus, and (B) shows the longitudinal aberration at a distance where the lateral magnification is -0.1x.

[0078] In the spherical aberration diagram, Fno indicates the F number, the solid line shows spherical aberration at the d line (wavelength 587.6 nm), and the dashed line shows spherical aberration at the g line (wavelength 435.8 nm). In the astigmatism diagram, the solid line S shows astigmatism at the sagittal image plane, and the dashed line M shows astigmatism at the meridional image plane. The distortion diagram shows distortion at the d line. The chromatic aberration diagram shows lateral chromatic aberration at the g line. ω is the half-angle of view (°).

[0079] [Imaging device] Figure 11 shows a digital still camera (imaging device) 10 using the optical system L0 of Examples 1 to 5 as the imaging optical system. In Figure 11, 13 is the camera body. 11 is the imaging optical system composed of any of the optical systems L0 of Examples 1 to 5, and is detachably attached to or integrated with the camera body 13. 12 is an image sensor such as a CCD sensor or CMOS sensor, which is built into the camera body 13 and performs photoelectric conversion of the optical image formed by the imaging optical system 11 (imaging the subject through the optical system).

[0080] The camera body 13 may be a single-lens reflex camera with a quick-turn mirror, or a mirrorless camera without a quick-turn mirror.

[0081] By using the optical system L0 of each embodiment as the imaging optical system, it is possible to acquire images with a wide field of view and good image quality while maintaining a small size and light weight.

[0082] Furthermore, the optical system L0 in each of the above embodiments may be used in an imaging device that has an image processing function to correct aberrations (distortion aberration and chromatic aberration).

[0083] The above embodiments include the following configuration.

[0084] (Composition 1) It is composed of a first lens group with positive refractive power, a second lens group with positive refractive power, and a third lens group, arranged in order from the object side to the image side. During focusing, the first and third lens groups do not move, but the second lens group moves, which changes the spacing between adjacent lens groups. The first lens group has a first negative lens and a second negative lens arranged in order from the object side to the image side, When the focal length of the second lens group is f2, the focal length of the optical system is f, and the focal length of the first lens group is f1, 2.70 ≤ f² / f ≤ 10.00 0.50 ≤ f1 / f2 ≤ 2.80 An optical system characterized by satisfying the following conditions. (Configuration 2) The optical system according to configuration 1, characterized in that the first lens group includes an aperture diaphragm. (Composition 3) When the focal length of the subgroup of the first lens group that is closer to the image than the aperture diaphragm is set to f1B, 1.00 ≤ f1B / f2 ≤ 9.00 The optical system according to configuration 2, characterized by satisfying the following conditions. (Composition 4) When the focal length of the subgroup of the first lens group that is closer to the object than the aperture diaphragm is denoted as f1A, -0.30≦f / f1A≦0.30 The optical system according to configuration 2 or 3, characterized by satisfying the following conditions. (Composition 5) When BF is the air-equivalent distance along the optical axis from the lens surface closest to the image plane of the optical system to the image plane, and DSI is the distance along the optical axis from the aperture diaphragm to the image plane, 0.10 ≤ BF / DSI ≤ 0.35 An optical system according to any one of configurations 2 to 4, characterized by satisfying the following conditions. (Composition 6) When the focal length of the third lens group is f3, -0.30 ≤ f / f3 ≤ 0.30 An optical system according to any one of configurations 1 to 5, characterized by satisfying the following conditions. (Composition 7) When BF 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, 0.80 ≤ f / BF ≤ 1.50 An optical system according to any one of configurations 1 to 6, characterized by satisfying the following conditions. (Composition 8) When the lateral magnification of the second lens group is in focus on an object at infinity, let β2 be the lateral magnification of the third lens group in the same state, 0.50 ≤ (1-β2 2 )×β3 2 ≤1.10 An optical system according to any one of configurations 1 to 7, characterized by satisfying the following conditions. (Composition 9) When the focal length of the negative lens closest to the image among the at least one negative lens included in the second lens group is fGRn, -3.00 ≤ fGRn / f2 ≤ -0.50 An optical system according to any one of configurations 1 to 8, characterized by satisfying the following conditions. (Composition 10) When D2Max is the maximum air gap along the optical axis within the second lens group, and D23 is the distance along the optical axis from the image-side lens surface of the second lens group to the object-side lens surface of the third lens group when focused on an object at infinity, 0.01 ≤ D2Max / D23 ≤ 0.60 An optical system according to any one of configurations 1 to 9, characterized by satisfying the following conditions. (Composition 11) When the paraxial radius of curvature of the object-side lens surface of the first negative lens is rG1R1 and the paraxial radius of curvature of the image-side lens surface of the first negative lens is rG1R2, -4.00≦(rG1R2+rG1R1) / (rG1R2-rG1R1)≦-1.00 The optical system according to any one of Configurations 1 to 10, characterized by satisfying the following conditions. (Configuration 12) When the paraxial curvature radius of the object-side lens surface of the second negative lens is rG2R1 and the paraxial curvature radius of the image-side lens surface of the second negative lens is rG2R2, -4.00 ≦ (rG2R2 + rG2R1) / (rG2R2 - rG2R1) ≦ -1.00 The optical system according to any one of Configurations 1 to 11, characterized by satisfying the following conditions. (Configuration 13) When the combined focal length of the first negative lens and the second negative lens is fG1G2, -3.00 ≦ fG1G2 / f ≦ -0.80 The optical system according to any one of Configurations 1 to 12, characterized by satisfying the following conditions. (Configuration 14) The first lens group has at least one negative lens having a convex lens surface on the image side, When the Abbe number based on the d-line of the most object-side negative lens among the at least one negative lens is νdGFn, 81.0 ≦ νdGFn ≦ 100.0 The optical system according to any one of Configurations 1 to 13, characterized by satisfying the following conditions. (Configuration 15) When the focal length of the most object-side negative lens is fGFn, -6.50 ≦ fGFn / f ≦ -2.00 The optical system according to Configuration 14, characterized by satisfying the following conditions. (Configuration 16) When the anomalous partial dispersion of the positive lens in the g-line and F-line is ΔθgFp for the first lens group, 0.050 ≦ ΔθgFp ≦ 0.250 The optical system according to any one of Configurations 1 to 15, characterized by including a positive lens that satisfies the following conditions. (Configuration 17) When the focal length of the positive lens is fGp, 0.020 ≦ f / fGp ≦ 0.090 The optical system according to configuration 16, characterized by satisfying the following conditions. (Composition 18) The optical system according to any one of configurations 1 to 17, characterized in that the first negative lens and the second negative lens each have an aspherical lens surface on at least one of the object side and the image side. (Composition 19) The optical system according to any one of configurations 1 to 18, characterized in that the second lens group has at least two positive lenses and at least two negative lenses. (Composition 20) It is composed of a first lens group with positive refractive power, a second lens group with positive refractive power, and a third lens group, arranged in order from the object side to the image side. During focusing, the distance between adjacent lens groups changes. The optical system is characterized in that the first lens group has a negative meniscus lens with a convex surface facing the object. (Composition 21) The optical system described in any one of configurations 1 to 20, An imaging device characterized by having an image sensor that captures an image of a subject through the optical system.

[0085] 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]

[0086] L0 optical system L1 First lens group L2 Second lens group L3 Third lens group SP aperture diaphragm IP image plane

Claims

1. It is composed of a first lens group with positive refractive power, a second lens group with positive refractive power, and a third lens group, arranged in order from the object side to the image side. During focusing, the first and third lens groups do not move, but the second lens group moves, which changes the spacing between adjacent lens groups. The first lens group comprises a first negative lens and a second negative lens arranged in order from the object side to the image side, When the focal length of the second lens group is f2, the focal length of the optical system is f, and the focal length of the first lens group is f1, 2.70 ≤ f² / f ≤ 10.00 0.50 ≤ f1 / f2 ≤ 2.80 An optical system characterized by satisfying the following conditions.

2. The optical system according to claim 1, characterized in that the first lens group includes an aperture diaphragm.

3. When the focal length of the subgroup of the first lens group that is closer to the image than the aperture diaphragm is set to f1B, 1.00 ≤ f1B / f2 ≤ 9.00 The optical system according to claim 2, characterized in that it satisfies the following conditions.

4. When the focal length of the subgroup of the first lens group that is closer to the object than the aperture diaphragm is denoted as f1A, -0.30 ≤ f / f1A ≤ 0.30 The optical system according to claim 2, characterized in that it satisfies the following conditions.

5. When BF is the air-equivalent distance along the optical axis from the lens surface closest to the image plane of the optical system to the image plane, and DSI is the distance along the optical axis from the aperture diaphragm to the image plane, 0.10 ≤ BF / DSI ≤ 0.35 The optical system according to claim 2, characterized in that it satisfies the following conditions.

6. When the focal length of the third lens group is f3, -0.30 ≤ f / f3 ≤ 0.30 The optical system according to claim 1, characterized in that it satisfies the following conditions.

7. When BF 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, 0.80 ≤ f / BF ≤ 1.50 The optical system according to claim 1, characterized in that it satisfies the following conditions.

8. When the lateral magnification of the second lens group in the state where it is focused on an object at infinity is β2, and the lateral magnification of the third lens group in the same state is β3, ０．５０≦（１－β２ ２ ）×β３ ２ ≦１．１０ The optical system according to claim 1, characterized in that it satisfies the following conditions.

9. When the focal length of the negative lens closest to the image among the at least one negative lens included in the second lens group is fGRn, -3.00 ≤ fGRn / f2 ≤ -0.50 The optical system according to claim 1, characterized in that it satisfies the following conditions.

10. When the maximum air gap on the optical axis within the second lens group is D2Max, and the distance on the optical axis from the image-side lens surface of the second lens group to the object-side lens surface of the third lens group when focused on an object at infinity is D23, 0.01 ≤ D2Max / D23 ≤ 0.60 The optical system according to claim 1, characterized in that it satisfies the following conditions.

11. When the paraxial radius of curvature of the object-side lens surface of the first negative lens is rG1R1 and the paraxial radius of curvature of the image-side lens surface of the first negative lens is rG1R2, -4.00≦(rG1R2+rG1R1) / (rG1R2-rG1R1)≦-1.00 The optical system according to claim 1, characterized in that it satisfies the following conditions.

12. When the paraxial radius of curvature of the object-side lens surface of the second negative lens is rG2R1 and the paraxial radius of curvature of the image-side lens surface of the second negative lens is rG2R2, -4.00≦(rG2R2+rG2R1) / (rG2R2-rG2R1)≦-1.00 The optical system according to claim 1, characterized in that it satisfies the following conditions.

13. When the combined focal length of the first negative lens and the second negative lens is fG1G2, -3.00 ≤ fG1G2 / f ≤ -0.80 The optical system according to claim 1, characterized in that it satisfies the following conditions.

14. The first lens group includes at least one negative lens having a lens surface that is convex on the image side, When the Abbe number with reference to the d-line of the negative lens closest to the object among the at least one negative lens is νdGFn, 81.0 ≤ νdGFn ≤ 100.0 The optical system according to claim 1, characterized in that it satisfies the following conditions.

15. When the focal length of the negative lens closest to the object is fGFn, -6.50 ≤ fGFn / f ≤ -2.00 The optical system according to claim 14, characterized in that it satisfies the following conditions.

16. When the anomalous partial dispersion of the positive lens in the g-line and F-line of the first lens group is ΔθgFp, 0.050 ≤ ΔθgFp ≤ 0.250 The optical system according to claim 1, characterized by including a positive lens that satisfies the following conditions.

17. When the focal length of the positive lens is fGp, 0.020 ≤ f / fGp ≤ 0.090 The optical system according to claim 16, characterized in that it satisfies the following conditions.

18. The optical system according to claim 1, characterized in that the first negative lens and the second negative lens each have an aspherical lens surface on at least one of the object side and the image side.

19. The optical system according to claim 1, characterized in that the second lens group has at least two positive lenses and at least two negative lenses.

20. It is composed of a first lens group with positive refractive power, a second lens group with positive refractive power, and a third lens group, arranged in order from the object side to the image side. During focusing, the distance between adjacent lens groups changes. The optical system is characterized in that the first lens group has a negative meniscus lens with a convex surface facing the object.

21. An optical system according to any one of claims 1 to 20, An imaging device characterized by having an image sensor that captures an image of a subject through the optical system.

Images