Optical system and imaging device

Abstract

[Problem] To provide an optical system that is compact and capable of focusing with suppressed variation in aberration. [Solution] An optical system L0 comprises a positive front lens group Gf, a positive middle lens group Gb, and a rear lens group Gr. The front lens group includes a plurality of positive lenses and an aperture stop SP. The middle lens group moves toward an object during focusing from infinity to close range. When the sum of the thicknesses of all lenses in the middle lens group is TMgl, the distance, in a state of focus on an object at infinity, from a lens surface of the middle lens group closest to the object and a lens surface of the middle lens group closest to an image is TGb, the focal distance of the optical system is f, the air-equivalent distance from a lens surface of the optical system closest to the image to an image surface is skd, the distance on an optical axis from a lens surface of the optical system closest to the object to the image surface is TTL, and the focal distance of the rear lens group is fGr, 0.10 ≤ TMgl / TGb ≤ 0.80, 0.05 ≤ skd / f ≤ 0.33, and 0.01 ≤ |TTL / fGr| < 1.00 are satisfied.

Description

Optical System and Imaging Device

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

[0002] As an optical system used for imaging, Patent Document 1 discloses a so-called inner focus type optical system.

[0003] Japanese Unexamined Patent Application Publication No. 2020-52118

[0004] There is a demand for an inner focus type optical system that can perform focusing with reduced aberration variation while being small in size.

[0005] The optical system as one aspect of the present invention is composed of a front lens group with positive refractive power, an intermediate lens group with positive refractive power, and a rear lens group, which are arranged in order from the object side to the image side. The front lens group includes a plurality of positive lenses and an aperture stop. When focusing from infinity to the closest distance, the front lens group and the rear lens group do not move, and the intermediate lens group moves toward the object side. When the total thickness of all the lenses included in the intermediate lens group on the optical axis is TMg1, the distance on the optical axis from the most object-side lens surface of the intermediate lens group to the most image-side lens surface of the intermediate lens group in the state of being focused on an infinite object is TGb, the focal length of the optical system in the state of being focused on an infinite object is f, the air-equivalent distance on the optical axis from the most image-side lens surface of the optical system to the image plane in the state of being focused on an infinite object is skd, the distance on the optical axis from the most object-side lens surface of the optical system to the image plane in the state of being focused on an infinite object is TTL, and the focal length of the rear lens group in the state of being focused on an infinite object is fGr, it is characterized by satisfying the conditional expressions: 0.10 ≤ TMg1 / TGb ≤ 0.80, 0.05 ≤ skd / f ≤ 0.33, 0.01 ≤ |TTL / fGr| < 1.00. In addition, an imaging device equipped with the above optical system also constitutes another aspect of the present invention.

[0006] Cross-sectional view of the optical system of Example 1 at infinity focus. (A) Longitudinal aberration diagram of the optical system of Example 1 at infinity focus and (B) Longitudinal aberration diagram at closest focus. Cross-sectional view of the optical system of Example 2 at infinity focus. (A) Longitudinal aberration diagram of the optical system of Example 2 at infinity focus and (B) Longitudinal aberration diagram at closest focus. Cross-sectional view of the optical system of Example 3 at infinity focus. (A) Longitudinal aberration diagram of the optical system of Example 3 at infinity focus and (B) Longitudinal aberration diagram at closest focus. Cross-sectional view of the optical system of Example 4 at infinity focus. (A) Longitudinal aberration diagram of the optical system of Example 4 at infinity focus and (B) Longitudinal aberration diagram at closest focus. Cross-sectional view of the optical system of Example 5 at infinity focus. (A) Longitudinal aberration diagram of the optical system of Example 5 at infinity focus and (B) Longitudinal aberration diagram at closest focus. Cross-sectional view of the optical system of Example 6 at infinity focus. (A) Longitudinal aberration diagram of the optical system of Example 6 at infinity focus and (B) Longitudinal aberration diagram at closest focus. Cross-sectional view of the optical system of Example 7 at infinity focus. (A) Longitudinal aberration diagram of the optical system of Example 7 at infinity focus and (B) Longitudinal aberration diagram at closest focus. Cross-sectional view of the optical system of Example 8 at infinity focus. (A) Longitudinal aberration diagram of the optical system of Example 8 at infinity focus and (B) Longitudinal aberration diagram at closest focus. Schematic diagram of an imaging device equipped with the optical systems of Examples 1 to 8.

[0007] The embodiments of the present invention will be described below with reference to the drawings. Before describing the specific embodiments, the matters common to each embodiment will be explained.

[0008] The optical systems of each embodiment are used in various imaging devices and interchangeable lenses such as digital still cameras, video cameras, broadcast cameras, surveillance cameras, and silver halide film cameras. Figures 1, 3, 5, 7, 9, 11, 13, and 15 show cross-sections of the optical systems L0 of Embodiments 1 to 8 in a state where they are in focus on an object at infinity (hereinafter referred to as the infinity focus state). In each figure, the left side is the object side (front side), and the right side is the image side (back side).

[0009] The optical system L0 of each embodiment has multiple lens groups. A lens group is a collection of one or more lenses that move or remain stationary as a whole during zooming between the wide-angle end and the telephoto end, and during focusing between the infinity focus state and the state of focusing on the nearest object (hereinafter referred to as the closest focus state). That is, the distance between adjacent lens groups changes during zooming. A lens group may include an aperture diaphragm.

[0010] In each embodiment, the group of at least one lens positioned on the object side and the image side, respectively, with the widest air gap in the intermediate lens group, is called a sub-lens group.

[0011] Furthermore, the wide-angle end and telephoto end represent the zoom state at which the lens group, which moves during zooming, is positioned at the ends of the range where it is mechanically or controllly movable along the optical axis, resulting in the maximum angle of view (shortest focal length) and minimum angle of view (maximum focal length), respectively.

[0012] In each diagram, SP represents the aperture diaphragm, and IP represents the 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. Furthermore, below the lens group that moves during focusing (focus group), the direction of movement of the focus group when focusing from infinity to close is indicated by an arrow labeled "focus".

[0013] The optical system L0 of each embodiment is composed of multiple lens groups arranged sequentially from the object side to the image side, consisting of a front lens group Gf with positive refractive power, an intermediate lens group Gb with positive refractive power, and a rear lens group Gr. The front lens group Gf, which is closest to the object, has positive refractive power, resulting in a telephoto-type power arrangement. By converging the light rays in the front lens group Gf, the increase in the lens diameter of the intermediate lens group Gb, which is positioned closer to the image side than the front lens group Gf, is suppressed. The front lens group Gf includes multiple positive lenses. This allows for the convergence of light rays without making the refractive power of each positive lens included in the front lens group Gf too strong, thereby suppressing the occurrence of various aberrations such as spherical aberration.

[0014] Furthermore, the front lens group Gf includes an aperture diaphragm SP. By positioning the aperture diaphragm SP closer to the object than the intermediate lens group Gb, the entrance pupil can be positioned closer to the object. This suppresses the increase in the lens diameter of the front lens group Gf, making it easier to miniaturize the lens barrel that holds the optical system L0.

[0015] Furthermore, during focusing, the front lens group Gf and the rear lens group Gr do not move relative to the image plane, while the intermediate lens group Gb, which acts as the focusing group, moves. Specifically, when focusing from infinity to close, the intermediate lens group Gb moves towards the object. Because the intermediate lens group Gb, which has a positive refractive power, moves towards the object when focusing from infinity to close, it becomes easy to position the intermediate lens group Gb on the image side when in focus at infinity. This facilitates good correction of various aberrations such as field curvature and suppresses aberration fluctuations during focusing.

[0016] Furthermore, it is preferable that the optical system L0 of each embodiment satisfies the following conditions of equations (1) to (3). In equations (1) to (3), TMgl is the sum of the thicknesses of all lenses included in the intermediate lens group Gb along the optical axis, and TGb is the distance along the optical axis from the lens surface closest to the object in the intermediate lens group Gb to the lens surface closest to the image in the infinity focus state. f is the focal length of the optical system L0 in the infinity focus state, and skd is the air-equivalent distance along the optical axis from the lens surface closest to the image in the optical system L0 to the image plane IP in the infinity focus state. TTL 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 in the infinity focus state (total optical length), and fGr is the focal length of the rear lens group Gr.

[0017] 0.10 ≤ TMgl / TGb ≤ 0.80 (1) 0.05 ≤ skd / f ≤ 0.33 (2) 0.01 ≤ |TTL / fGr| < 1.00 (3) The conditions in equation (1) show an appropriate relationship between the total thickness of all lenses included in the intermediate lens group Gb and the distance from the lens surface closest to the object in the intermediate lens group Gb to the lens surface closest to the image in the infinity focus state. If TMgl / TGb falls below the lower limit of equation (1), the length of the intermediate lens group Gb in the optical axis direction becomes too large, making it difficult to miniaturize the intermediate lens group Gb and the optical system L0, which is undesirable. If TMgl / TGb exceeds the upper limit of equation (1), the spacing between lenses included in the intermediate lens group Gb becomes too narrow, making it difficult to place some of the lenses in the intermediate lens group Gb on the object side where the on-axial light beam diameter is large, and the other lenses on the image side where the off-axis light rays are located. As a result, it becomes difficult to adequately correct aberrations such as spherical aberration and field curvature, which is undesirable. Furthermore, it becomes difficult to position some of the lenses in the intermediate lens group Gb at a lower position on the aperture side where off-axis rays are located, resulting in the lens diameters of the lenses included in the intermediate lens group Gb becoming too large. As a result, it becomes difficult to reduce the weight of the intermediate lens group Gb, which moves during focusing, which is undesirable.

[0018] Furthermore, it is more preferable to set the lower limit of formula (1) to 0.15, 0.22, 0.27, or 0.29. Also, it is more preferable to set the upper limit of formula (1) to 0.75, 0.70, 0.68, or 0.66.

[0019] The conditions in equation (2) each indicate the appropriate relationship between the focal length of the optical system L0 and the back focus when in focus at infinity. If skd / f exceeds the upper limit of equation (2), the back focus becomes too long, making it difficult to correct aberrations such as field curvature and to miniaturize the optical system L0, which is undesirable. If skd / f falls below the lower limit of equation (2), the lens closest to the image plane IP is positioned near the image plane IP, increasing the diameter of that lens and making it difficult to miniaturize the optical system, which is also undesirable.

[0020] Furthermore, it is more preferable to set the lower limit of formula (2) to 0.06, 0.08, or 0.10. Also, it is more preferable to set the upper limit of formula (2) to 0.31, 0.29, or 0.27.

[0021] The conditions in equation (3) each indicate the appropriate relationship between the total optical length of the optical system L0 and the focal length of the rear lens group Gr when the lens is focused at infinity. If |TTL / fGr| exceeds the upper limit of equation (3), the refractive power of the rear lens group Gr becomes too strong. This is undesirable because it makes it difficult to correct aberrations such as field curvature and astigmatism. If |TTL / fGr| falls below the lower limit of equation (3), it is advantageous for miniaturizing the optical system L0, but the refractive power of each lens group becomes too strong due to the miniaturization, resulting in excessively large amounts of aberrations such as spherical aberration and field curvature. This is undesirable because it makes it difficult to correct these aberrations.

[0022] Furthermore, it is more preferable to set the lower limit of formula (3) to 0.03, 0.06, or 0.08. Also, it is more preferable to set the upper limit of formula (3) to 0.90, 0.85, or 0.82.

[0023] By having the above configuration and satisfying the conditions of equations (1) to (3), it is possible to provide an optical system in which the focus group and the entire optical system are compact and various aberrations are well corrected.

[0024] Furthermore, it is preferable that the optical system L0 of each embodiment satisfies at least one of the following conditions (4) to (12).

[0025] 0.10≦Tbi / TTLg≦0.60 (4) 0.50≦fGf / fGb≦5.00 (5) 0.10≦SFL / SIL≦0.50 (6) -7.50≦(Rb2+Rb1) / (Rb2-Rb1)≦-0.25 (7) 0.01≦|fGb / fGr|≦1.00 (8) 0.01≦|skd / fGr|≦0.20 (9) 0.01≦|fGb2 / fGb1|≦7.00 (10) 0.70≦TTL / f≦1.70 (11) 0.30≦ESGb≦1.50 (12) In equations (4) to (12), TTLg is the distance along the optical axis from the lens surface closest to the object in the optical system L0 to the lens surface closest to the image in the optical system L0 when it is in focus at infinity. Tbi is the distance along the optical axis from the lens surface closest to the object in the intermediate lens group Gb to the lens surface closest to the image in the optical system L0 when it is in focus at infinity.

[0026] Let fGf be the focal length of the front lens group Gf, and fGb be the focal length of the intermediate lens group Gb. Let SFL be the distance along the optical axis from the aperture diaphragm SP to the lens surface closest to the object in the intermediate lens group Gb when in focus at infinity, and SIL be the distance along the optical axis from the aperture diaphragm SP to the image plane IP when in focus at infinity. Let Rb1 be the radius of curvature of the lens surface closest to the object in the lens closest to the image in the intermediate lens group Gb, and Rb2 be the radius of curvature of the lens surface closest to the image in the intermediate lens group Gb. (Rb2 + Rb1) / (Rb2 - Rb1) is the lens shape factor of the lens closest to the image in the intermediate lens group Gb.

[0027] When the intermediate lens group Gb is composed of a first intermediate sub-lens group Gb1 located on the object side of the widest air gap within the intermediate lens group Gb and a second intermediate sub-lens group Gb2 located on the image side of the air gap, the focal length of the first intermediate sub-lens group Gb1 is denoted as fGb1 and the focal length of the second intermediate sub-lens group Gb2 as fGb2. Furthermore, the lateral magnification of the intermediate lens group Gb2 is denoted as βf, and the combined lateral magnification of all lenses positioned on the image side of the intermediate lens group Gb in the optical system L0 is denoted as βR, and the focus sensitivity of the intermediate lens group Gb is given by ESGb = (1 - βf ２ ) × βR ２ Let's assume that.

[0028] The conditions in equation (4) represent the appropriate relationship between the distance from the object-side lens surface to the image-side lens surface of the optical system L0 in the infinity focus state, and the distance from the object-side lens surface of the intermediate lens group Gb to the image-side lens surface of the optical system L0. When Tbi / TTL falls below the lower limit of equation (4), the intermediate lens group Gb is positioned on the image side where the off-axis rays are higher. This is advantageous for correcting field curvature, but it is undesirable because the lens diameter of the intermediate lens group Gb becomes larger, making it difficult to reduce the weight of the intermediate lens group Gb as it moves during focusing. When Tbi / TTL exceeds the upper limit of equation (4), the intermediate lens group Gb is positioned on the object side where the on-axial light beam diameter is larger. This is advantageous for correcting spherical aberration, but it is undesirable because the lens diameter of the intermediate lens group Gb becomes larger, making it difficult to reduce the weight of the intermediate lens group Gb as it moves during focusing.

[0029] Furthermore, it is more preferable to set the lower limit of formula (4) to 0.20, 0.25, or 0.30. Also, it is more preferable to set the upper limit of formula (4) to 0.55, 0.52, or 0.50.

[0030] The conditions in equation (5) indicate an appropriate relationship between the focal lengths of the front lens group Gf and the intermediate lens group Gb. If fGf / fGb falls below the lower limit of equation (5), the refractive power of the front lens group Gf becomes too strong, making it difficult to correct spherical aberration, which is undesirable. If fGf / fGb exceeds the upper limit of equation (5), the refractive power of the intermediate lens group Gb becomes too strong, causing large fluctuations in various aberrations such as spherical aberration and field curvature during focusing, making it difficult to correct them, which is also undesirable.

[0031] Furthermore, it is more preferable to set the lower limit of formula (5) to 0.60, 0.80, or 1.00. Also, it is more preferable to set the upper limit of formula (5) to 4.70, 4.50, or 4.20.

[0032] The conditions in equation (6) represent the appropriate relationship between the distance from the aperture diaphragm SP to the object-side lens surface of the intermediate lens group Gb and the distance from the aperture diaphragm SP to the image plane IP, respectively, when the lens is in focus at infinity. If SFL / SIL falls below the lower limit of equation (6), the aperture diaphragm SP is positioned on the object side where the axial light beam diameter is large. This is undesirable because the aperture diameter becomes large, making it difficult to miniaturize the lens barrel and optical system L0 in the radial direction. If SFL / SIL exceeds the upper limit of equation (6), the intermediate lens group Gb is positioned on the image side where the axial light beam diameter is small. This is undesirable because it makes it difficult to correct spherical aberration.

[0033] Furthermore, it is more preferable to set the lower limit of formula (6) to 0.12, 0.15, or 0.17. Also, it is more preferable to set the upper limit of formula (6) to 0.45, 0.40, or 0.35.

[0034] The conditions in equation (7) indicate the appropriate shape (shape factor) of the image-side lens in the intermediate lens group Gb. If the shape factor falls below the lower limit of equation (7), the image-side lens in the intermediate lens group Gb will have a convex meniscus shape with strong curvature. This is undesirable because it increases the fluctuations of various aberrations such as field curvature during focusing, making correction difficult. If the shape factor exceeds the upper limit of equation (7), the image-side lens in the intermediate lens group Gb will approach a biconvex shape, increasing the volume of that lens. This is undesirable because it makes it difficult to reduce the weight of the intermediate lens group Gb, which moves during focusing.

[0035] Furthermore, it is more preferable to set the lower limit of equation (7) to -7.20, -7.00, or -6.80. Also, it is more preferable to set the upper limit of equation (7) to -0.50, -0.55, or -0.60.

[0036] The conditions in equation (8) indicate an appropriate relationship between the focal lengths of the intermediate lens group Gb and the rear lens group Gr. If |fGb / fGr| falls below the lower limit of equation (8), the refractive power of the intermediate lens group Gb becomes too strong, leading to large fluctuations in various aberrations such as spherical aberration and field curvature during focusing, making correction difficult, which is undesirable. If |fGb / fGr| exceeds the upper limit of equation (8), the refractive power of the intermediate lens group Gb becomes too weak, resulting in a large amount of movement of the intermediate lens group Gb required for focusing on nearby objects. As a result, miniaturization of the optical system L0 becomes difficult, which is undesirable.

[0037] Furthermore, it is more preferable to set the lower limit of formula (8) to 0.06, 0.07, or 0.08. Also, it is more preferable to set the upper limit of formula (8) to 0.80, 0.75, 0.65, or 0.60.

[0038] The conditions in equation (9) indicate an appropriate relationship between the back focus of the optical system L0 and the focal length of the rear lens group Gr. If |skd / fGr| falls below the lower limit of equation (9), the lens closest to the image plane IP is positioned near the image plane IP. As a result, the diameter of the lens closest to the image plane becomes large, making it difficult to miniaturize the optical system, which is undesirable. If |skd / fGr| exceeds the upper limit of equation (9), the refractive power of the rear lens group Gr becomes too strong, making it difficult to correct various aberrations such as field curvature and astigmatism, which is also undesirable.

[0039] Furthermore, it is more preferable to set the lower limit of formula (9) to 0.012, 0.015, or 0.018. Also, it is more preferable to set the upper limit of formula (9) to 0.18, 0.16, or 0.14.

[0040] The conditions in equation (10) indicate an appropriate relationship between the focal lengths of the first intermediate sub-lens group Gb1 and the second intermediate sub-lens group Gb2. If |fGb2 / fGb1| falls below the lower limit of equation (10), the refractive power of the second intermediate sub-lens group Gb2 becomes too strong, causing large fluctuations in various aberrations such as field curvature during focusing, making correction difficult, which is undesirable. Also, if |fGb2 / fGb1| exceeds the upper limit of equation (10), the refractive power of the first intermediate sub-lens group Gb1 becomes too strong, causing large fluctuations in various aberrations such as spherical aberration during focusing, making correction difficult, which is also undesirable.

[0041] Incidentally, it is more preferable that the lower limit of the formula (10) is 0.012, 0.015 or 0.018. Further, it is more preferable that the upper limit of the formula (10) is 6.50, 6.20 or 6.00.

[0042] The conditions of the formula (11) respectively show an appropriate relationship between the overall optical length of the optical system L0 in the infinity focus state and the focal length of the optical system L0. When TTL / f is less than the lower limit of the formula (11), the refractive power of each lens group becomes too strong in order to shorten the overall optical length. As a result, various aberrations such as spherical aberration and field curvature increase, and it becomes difficult to correct them, which is not preferable. When TTL / f exceeds the upper limit of the formula (11), the overall optical length becomes too large, and it becomes difficult to miniaturize the optical system L0, which is not preferable.

[0043] Incidentally, it is more preferable that the lower limit of the formula (11) is 0.80, 0.90 or 1.00. Further, it is more preferable that the upper limit of the formula (11) is 1.60, 1.50 or 1.45.

[0044] The conditions of the formula (12) show an appropriate focus sensitivity ESGb of the intermediate lens group Gb. When ESGb is less than the lower limit of the formula (12), the focus sensitivity of the intermediate lens group Gb becomes too weak, and the movement amount of the intermediate lens group Gb for focusing on a close object becomes large, making it difficult to miniaturize the optical system L0, which is not preferable. When ESGb exceeds the upper limit of the formula (12), the focus sensitivity becomes too strong, and the optical path of off-axis rays varies greatly depending on the object distance. As a result, it becomes difficult to correct field curvature, which is not preferable.

[0045] Incidentally, it is more preferable that the lower limit of the formula (12) is 0.35, 0.40 or 0.42. Further, it is more preferable that the upper limit of the formula (12) is 1.25, 1.20 or 1.10.

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

[0047] It is preferable that the entire intermediate lens group Gb moves as a single unit during focusing. This simplifies the focusing mechanism that drives the intermediate lens group Gb and reduces the space required for the focusing mechanism.

[0048] Preferably, the intermediate lens group Gb is composed of a first intermediate sub-lens group Gb1 and a second intermediate sub-lens group Gb2, which move during focusing. This allows the two lens groups to move during focusing, making it easier to correct various aberrations such as spherical aberration and field curvature during focusing.

[0049] The intermediate lens group Gb is preferably composed of five or fewer lenses. This makes it easier to reduce the weight of the intermediate lens group Gb, which moves during focusing.

[0050] The rear lens group Gr preferably has a negative refractive power. This results in a telephoto-type lens configuration for the optical system L0, making it easy to shorten the overall optical length.

[0051] Preferably, the lens closest to the object in the front lens group Gf has a positive refractive power. This allows the light rays to converge at the positive lens closest to the object in the front lens group Gf, making it easier to miniaturize the lenses positioned on the image side of the positive lens and the intermediate lens group Gb that moves during focusing.

[0052] It is preferable that the lens closest to the object in the intermediate lens group Gb has a positive refractive power. This allows the light rays to converge at the positive lens closest to the object in the intermediate lens group Gb, making it easier to miniaturize and lighten the lenses in the intermediate lens group Gb that are positioned on the image side of the positive lens.

[0053] It is preferable that the lens closest to the image in the intermediate lens group Gb has a positive refractive power. This allows the lens closest to the image to have a small on-axial beam diameter and off-axis rays positioned at a high location, thereby suppressing the occurrence of spherical aberration and facilitating correction of field curvature.

[0054] Next, the optical system L0 of Examples 1 to 8 will be described in detail. After Example 8, numerical examples 1 to 8 corresponding to each of Examples 1 to 8 are shown.

[0055] The optical system L0 of Embodiment 1 (Numerical Example 1) shown in Figure 1 is composed of a front lens group Gf with positive refractive power, an intermediate lens group Gb with positive refractive power, and a rear lens group Gr with negative refractive power, arranged in order from the object side to the image side.

[0056] The front lens group Gf consists of three positive lenses, three negative lenses, and an aperture diaphragm SP.

[0057] The intermediate lens group Gb consists of a first intermediate sub-lens group Gb1 with negative refractive power and a second intermediate sub-lens group Gb2 with positive refractive power, arranged in order from the object side to the image side, separated by the widest air gap within the intermediate lens group Gb. The first intermediate sub-lens group Gb1 and the second intermediate sub-lens group Gb2 are composed of two lenses and one lens, respectively. When focusing from infinity to the nearest focus, the intermediate lens group Gb (first intermediate sub-lens group Gb1 and second intermediate sub-lens group Gb2) moves together toward the object.

[0058] Figure 2(A) shows the longitudinal aberrations (spherical aberration, astigmatism, distortion, and chromatic aberration) in the optical system L0 of Numerical Example 1 at infinity focus. In the spherical aberration diagram, Fno indicates 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 (°). The above explanations for the aberration diagrams are the same for the other aberration diagrams. Figure 2(B) shows the longitudinal aberration in the optical system L0 of Numerical Example 1 when it is focused on an object located 800 mm away from the image plane IP along the optical axis.

[0059] The optical system L0 of Embodiment 2 (Numerical Example 2) shown in Figure 3 is composed of a front lens group Gf with positive refractive power, an intermediate lens group Gb with positive refractive power, and a rear lens group Gr with positive refractive power, arranged in order from the object side to the image side.

[0060] The front lens group Gf consists of three positive lenses, three negative lenses, and an aperture diaphragm SP.

[0061] The intermediate lens group Gb consists of a first intermediate sub-lens group Gb1 with positive refractive power and a second intermediate sub-lens group Gb2 with positive refractive power, arranged in order from the object side to the image side, separated by the widest air gap within the intermediate lens group Gb. The first intermediate sub-lens group Gb1 and the second intermediate sub-lens group Gb2 are composed of two lenses and one lens, respectively. When focusing from infinity to close, the first intermediate sub-lens group Gb1 and the second intermediate sub-lens group Gb2 move toward the object side, each tracing a different trajectory.

[0062] Figure 4(A) shows the longitudinal aberration in the optical system L0 of numerical example 2 when it is in focus at infinity. Figure 4(B) shows the longitudinal aberration in the optical system L0 of numerical example 2 when it is in focus on an object located 850 mm away from the image plane IP along the optical axis.

[0063] The optical system L0 of Embodiment 3 (Numerical Example 3) shown in Figure 5 is composed of a front lens group Gf with positive refractive power, an intermediate lens group Gb with positive refractive power, and a rear lens group Gr with negative refractive power, arranged in order from the object side to the image side.

[0064] The front lens group Gf consists of three positive lenses, one negative lens, and an aperture diaphragm SP.

[0065] The intermediate lens group Gb consists of a first intermediate sub-lens group Gb1 with negative refractive power and a second intermediate sub-lens group Gb2 with positive refractive power, arranged in order from the object side to the image side, separated by the widest air gap within the intermediate lens group Gb. The first intermediate sub-lens group Gb1 and the second intermediate sub-lens group Gb2 are composed of two lenses and one lens, respectively. When focusing from infinity to close, the intermediate lens group Gb (first intermediate sub-lens group Gb1 and second intermediate sub-lens group Gb2) moves together toward the object.

[0066] Figure 6(A) shows the longitudinal aberration in the optical system L0 of numerical example 3 when it is in focus at infinity. Figure 6(B) shows the longitudinal aberration in the optical system L0 of numerical example 3 when it is in focus on an object located 800 mm away from the image plane IP along the optical axis.

[0067] The optical system L0 of Embodiment 4 (Numerical Example 4) shown in Figure 7 is composed of a front lens group Gf with positive refractive power, an intermediate lens group Gb with positive refractive power, and a rear lens group Gr with negative refractive power, arranged in order from the object side to the image side.

[0068] The front lens group Gf consists of three positive lenses, three negative lenses, and an aperture diaphragm SP.

[0069] The intermediate lens group Gb consists of a first intermediate sub-lens group Gb1 with negative refractive power and a second intermediate sub-lens group Gb2 with positive refractive power, arranged in order from the object side to the image side, separated by the widest air gap within the intermediate lens group Gb. Each of the first and second intermediate sub-lens groups Gb1 and Gb2 consists of a single lens. When focusing from infinity to near, the intermediate lens group Gb (first intermediate sub-lens group Gb1 and second intermediate sub-lens group Gb2) moves together toward the object.

[0070] Figure 8(A) shows the longitudinal aberration in the optical system L0 of numerical example 4 when it is in focus at infinity. Figure 8(B) shows the longitudinal aberration in the optical system L0 of numerical example 4 when it is in focus on an object located 900 mm away from the image plane IP along the optical axis.

[0071] The optical system L0 of Embodiment 5 (Numerical Example 5) shown in Figure 9 is composed of a front lens group Gf with positive refractive power, an intermediate lens group Gb with positive refractive power, and a rear lens group Gr with negative refractive power, arranged in order from the object side to the image side.

[0072] The front lens group Gf consists of three positive lenses, three negative lenses, and an aperture diaphragm SP.

[0073] The intermediate lens group Gb consists of a first intermediate sub-lens group Gb1 with negative refractive power and a second intermediate sub-lens group Gb2 with positive refractive power, arranged in order from the object side to the image side, separated by the widest air gap within the intermediate lens group Gb. The first intermediate sub-lens group Gb1 and the second intermediate sub-lens group Gb2 are composed of two lenses and one lens, respectively. When focusing from infinity to close, the first intermediate sub-lens group Gb1 and the second intermediate sub-lens group Gb2 move toward the object side, each tracing a different trajectory.

[0074] Figure 10(A) shows the longitudinal aberration in the optical system L0 of numerical example 5 when it is in focus at infinity. Figure 10(B) shows the longitudinal aberration in the optical system L0 of numerical example 5 when it is in focus on an object located 1000 mm away from the image plane IP along the optical axis.

[0075] The optical system L0 of Embodiment 6 (Numerical Example 6) shown in Figure 11 is composed of a front lens group Gf with positive refractive power, an intermediate lens group Gb with positive refractive power, and a rear lens group Gr with positive refractive power, arranged in order from the object side to the image side.

[0076] The front lens group Gf consists of three positive lenses, two negative lenses, and an aperture diaphragm SP.

[0077] The intermediate lens group Gb consists of a first intermediate sub-lens group Gb1 with positive refractive power and a second intermediate sub-lens group Gb2 with positive refractive power, arranged in order from the object side to the image side, separated by the widest air gap within the intermediate lens group Gb. The first intermediate sub-lens group Gb1 and the second intermediate sub-lens group Gb2 are composed of two lenses and one lens, respectively. When focusing from infinity to close, the intermediate lens group Gb (first intermediate sub-lens group Gb1 and second intermediate sub-lens group Gb2) moves together toward the object.

[0078] Figure 12(A) shows the longitudinal aberration in the optical system L0 of numerical example 6 when it is in focus at infinity. Figure 12(B) shows the longitudinal aberration in the optical system L0 of numerical example 6 when it is in focus on an object located 850 mm away from the image plane IP along the optical axis.

[0079] The optical system L0 of Embodiment 7 (Numerical Example 7) shown in Figure 13 is composed of a front lens group Gf with positive refractive power, an intermediate lens group Gb with positive refractive power, and a rear lens group Gr with positive refractive power, arranged in order from the object side to the image side. The front lens group Gf is composed of three positive lenses, two negative lenses, and an aperture diaphragm SP.

[0080] The intermediate lens group Gb consists of a first intermediate sub-lens group Gb1 with negative refractive power and a second intermediate sub-lens group Gb2 with positive refractive power, arranged in order from the object side to the image side, separated by the widest air gap within the intermediate lens group Gb. The first intermediate sub-lens group Gb1 and the second intermediate sub-lens group Gb2 are composed of two lenses and one lens, respectively. When focusing from infinity to close, the intermediate lens group Gb (first intermediate sub-lens group Gb1 and second intermediate sub-lens group Gb2) moves together toward the object.

[0081] Figure 14(A) shows the longitudinal aberration in the optical system L0 of numerical example 7 when it is in focus at infinity. Figure 14(B) shows the longitudinal aberration in the optical system L0 of numerical example 7 when it is in focus on an object located 800 mm away from the image plane IP along the optical axis.

[0082] The optical system L0 of Embodiment 8 (Numerical Example 8) shown in Figure 15 is composed of a front lens group Gf with positive refractive power, an intermediate lens group Gb with positive refractive power, and a rear lens group Gr with negative refractive power, arranged in order from the object side to the image side.

[0083] The front lens group Gf consists of three positive lenses, one negative lens, and an aperture diaphragm SP.

[0084] The intermediate lens group Gb consists of a first intermediate sub-lens group Gb1 with negative refractive power and a second intermediate sub-lens group Gb2 with positive refractive power, arranged in order from the object side to the image side, separated by the widest air gap within the intermediate lens group Gb. The first intermediate sub-lens group Gb1 and the second intermediate sub-lens group Gb2 are composed of two lenses and one lens, respectively. When focusing from infinity to close, the intermediate lens group Gb (first intermediate sub-lens group Gb1 and second intermediate sub-lens group Gb2) moves together toward the object.

[0085] Figure 16(A) shows the longitudinal aberration in the optical system L0 of numerical example 8 when it is in focus at infinity. Figure 16(B) shows the longitudinal aberration in the optical system L0 of numerical example 8 when it is in focus on an object located 800 mm away from the image plane IP on the optical axis.

[0086] Numerical examples 1 to 8 are shown below. In the surface data, surface number i indicates the order of the surfaces when counted from the object side. r is the radius of curvature (mm) of the i-th surface from the object side, d is the lens thickness or air gap on the optical axis between the i-th and (i+1)-th surfaces (mm), and nd is the refractive index of the optical material at the d-line between the i-th and (i+1)-th surfaces. νd is the Abbe number with respect to the d-line of the optical material between the i-th and (i+1)-th surfaces. The Abbe number νd with respect to the d-line is expressed as νd = (Nd-1) / (NF-NC), where Nd, NF, and NC are the refractive indices at the d-line (587.6 nm), F-line (486.1 nm), and C-line (656.3 nm). In each numerical example, d, focal length (mm), F-number, and half-angle of view (°) are all values ​​in the infinity focus state.

[0087] The back focus BF is the air-equivalent value of the distance along the optical axis from the image-side lens surface (final surface) of the optical system to the paraxial image plane, and corresponds to skd in equations (2) and (9). The total lens length is the length obtained by adding the back focus to the distance along the optical axis from the object-side lens surface (frontmost surface) of the optical system to the final surface, and corresponds to the total optical length TTL in equations (3) and (11).

[0088] 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, with the direction of light propagation being positive, R is the radius of paraxial curvature, K is the cone constant, and A4, A6, A8, A10, and A12 are aspherical coefficients. The cone constant and aspherical coefficients "e±M" are "×10 ±Ｍ It means "...".

[0089]

[0090] Furthermore, the object distance at which the object is in focus in each numerical example represents the distance along the optical axis from the image plane IP to the object.

[0091] Furthermore, the values ​​relating to the conditions of equations (1) to (12) mentioned above in numerical examples 1 to 8 are summarized in Tables 1 and 2. The optical system L0 in numerical examples 1 to 8 satisfies all the conditions of equations (1) to (12). [Numerical Example 1] Unit: mm Surface Data Surface Number rd nd νd 1 42.507 6.40 1.95375 32.3 2 165.495 0.20 3 29.040 8.42 1.49700 81.5 4 204.426 1.10 1.77047 29.7 5 23.266 6.32 6 -205.960 1.00 1.77047 29.7 7 91.154 1.75 8 60.903 1.00 1.84666 23.8 9 37.136 0.35 10 38.995 4.11 1.80400 46.5 11 825.511 2.40 12 (aperture) ∞ (variable) 13 46.521 3.00 1.90043 37.4 14 314.092 1.36 15 -55.403 0.91 1.63980 34.5 16 46.531 6.80 17 624.380 3.76 1.90043 37.4 18 -50.908 (Variable) 19 -35.800 1.00 1.69680 55.5 20 102.768 0.20 21 66.850 9.62 1.83400 37.2 22 -37.256 4.00 23 -33.635 1.00 1.84666 23.8 24 -66.939 15.33 Image plane ∞ Various data Zoom ratio 1.00 Focal length 82.50 F-number 1.85 Half angle of view (°) 14.69 Image height 21.64 Lens length 97.83 BF 15.33 Object distance Infinity Closest d12 14.81 2.01 d18 3.01 15.81 Lens group data group Starting plane Focal length 1 1 108.64 2 13 84.18 3 19 -442.41 [Numerical example 2] Unit mm Plane data plane number rd nd νd 1 54.044 7.64 1.95375 32.3 2 181.616 0.48 3 35.157 11.19 1.49700 81.7 4 225.104 1.10 1.77047 29.7 5 27.331 8.74 6 -287.552 1.00 1.77047 29.7 7 113.045 4.34 8 82.906 1.00 1.84666 23.8 9 41.128 0.41 10 42.995 5.76 1.89190 37.1 11 -4036.502 1.75 12 (aperture) ∞ (variable) 13 -37.317 1.00 1.57501 41.5 14 25.956 7.84 1.80400 46.5 15 -60.027 (variable) 16* -100.618 2.17 1.53160 55.8 17* -72.254 (variable) 18 -52.759 1.00 1.54814 45.8 19 83.017 0.20 20 65.888 7.92 1.89190 37.1 21 -57.508 6.66 22 -38.966 1.00 1.76182 26.5 23 -82.881 16.00 Image plane ∞ Aspherical data 16th plane K = 0.00000e+00 A 4=-7.41308e-06 A 6=-3.48477e-08 A 8= 9.84703e-11 17th plane K = 0.00000e+00 A 4=-4.09620e-07 A 6=-3.20576e-08 A 8= 1.23371e-10 Various data Zoom ratio 1.00 Focal length 83.17 F number 1.46 Half angle of view (°) 14.58 Image height 21.64 Lens total length 118.00 BF 16.00 Object distance Infinity Closest d12 22.74 5.64 d15 5.93 5.01 d17 2.12 20.14 Lens group data group Starting plane Focal length 1 1 136.87 2 13 135.08 3 16 469.72 4 18 356.43 [Numerical example 3] Unit mm Plane data plane number rd nd νd 1 41.645 5.16 1.95375 32.3 2 89.467 0.20 3 38.177 4.50 1.49700 81.5 4 70.832 0.20 5 26.804 8.34 1.49700 81.5 6 86.850 1.10 1.85478 24.8 7 19.368 7.71 8 (aperture) ∞ (variable) 9 43.264 2.61 1.59522 67.7 10 -243.832 1.00 11 -45.422 0.90 1.61340 44.3 12 63.063 4.82 13 -5714.263 3.13 1.91082 35.2 14 -49.431 (variable) 15 -50.804 1.00 1.90043 37.4 16 178.623 2.16 17* -91.256 2.00 1.53160 55.8 18* -613.260 0.20 19 61.240 8.57 2.00100 29.1 20 -44.075 4.42 21 -29.435 1.00 1.92286 20.9 22 -65.113 15.33 Image plane ∞ Aspherical data 17th plane K = 0.00000e+00 A 4 = 7.12357e-06 A 6 = 4.93973e-08 A 8 = -2.71779e-10 A10 = 1.30969e-13 A12 = 8.25459e-18 18th plane K = 0.00000e+00 A 4 = 6.17244e-06 A 6 = 2.60982e-08 A 8 = -2.20431e-10 A10 = 3.35762e-13 A12 = -4.99816e-16 Various data Zoom ratio 1.00 Focal length 82.50 F number 1.85 Half angle of view (°) 14.69 Image height 21.64 Lens length 89.55 BF 15.33 Object distance Infinity Closest d 8 13.71 1.51 d14 1.50 13.70 Lens group data group Starting plane Focal length 1 1 106.42 2 9 82.71 3 15 -427.79 [Numerical example 4] Unit mm Surface data plane number rd nd νd 1 44.839 6.40 1.91082 35.3 2 164.225 2.68 3 28.322 8.57 1.49700 81.7 4 174.045 1.10 1.72825 28.5 5 22.614 6.84 6 -167.155 1.00 1.65412 39.7 7 71.324 3.28 8 60.577 1.00 1.76182 26.5 9 37.566 0.44 10 40.779 4.01 1.80400 46.5 11 923.222 1.86 12 (aperture) ∞ (variable) 13* 52.357 1.48 1.53160 55.8 14* 50.599 13.28 15 -198.710 4.21 1.69680 55.5 16 -42.588 (variable) 17 -51.033 1.75 1.60311 60.6 18 70.518 0.68 19 55.356 8.87 1.85150 40.8 20 -43.481 2.91 21 -36.265 1.27 1.59270 35.3 22 210.724 16.85 Image plane ∞ Aspherical data 13th plane K = 0.00000e+00 A 4=-3.51464e-05 A 6=-6.43678e-08 A 8= 1.10181e-10 14th surface K = 0.00000e+00 A 4 = -3.10669e-05 A 6 = -6.56585e-08 A 8 = 1.51465e-10 Various data Zoom ratio 1.00 Focal length 85.80 F-number 1.85 Half angle of view (°) 14.15 Image height 21.64 Lens length 103.90 BF 16.85 Object distance Infinity Closest d12 13.83 2.00 d16 1.60 13.44 Lens group data group Starting surface Focal length 1 1 122.93 2 13 78.91 3 17 -297.92 [Numerical example 5] Unit mm Surface data surface number rd nd νd 1 54.333 10.12 1.84666 23.8 2 252.593 0.20 3 39.870 12.32 1.49700 81.5 4 638.720 1.10 1.85478 24.8 5 32.891 8.79 6 -334.880 1.00 1.85478 24.8 7 169.170 1.75 8 54.387 1.00 1.96300 24.1 9 39.127 0.50 10 40.975 6.73 1.67790 55.3 11 1161.945 12.26 12 (aperture) ∞ (variable) 13 -44.847 1.00 1.53172 48.8 14 30.265 4.32 1.76385 48.5 15 -457.425 (variable) 16* 4994.436 3.75 1.58313 59.4 17* -48.503 (variable) 18 -79.824 1.00 1.60300 65.4 19 226.628 8.45 20 -59.458 1.00 1.49700 81.5 21 63.982 5.98 1.85478 24.8 22 -135.157 16.29 Image plane ∞ Aspherical data 16th plane K = 0.00000e+00 A 4=-9.65570e-06 A 6= 6.19989e-09 A 8=-1.53393e-10 A10= 4.35024e-13 A12=-1.42556e-15 17th plane K = 0.00000e+00 A 4=-4.06002e-06 A 6= 5.41239e-09 A 8=-1.81497e-10 A10= 8.41890e-13 A12=-2.38809e-15 Various data Zoom ratio 1.00 Focal length 131.00 F-number 2.06 Half-angle of view (°) 9.38 Image height 21.64 Lens length 135.06 BF 16.29 Object distance Infinity Closest d12 26.06 4.92 d15 5.65 6.79 d17 5.79 25.79 Lens group data group Starting plane Focal length 1 1 141.29 2 13 -411.99 3 16 82.40 4 18 -168.83 [Numerical example 6] Unit mm Surface data plane number rd nd νd 1 39.344 3.22 1.84666 23.8 2 97.554 0.20 3 23.445 5.51 1.80400 46.5 4 89.704 1.10 1.85478 24.8 5 18.284 6.58 6 -115.365 1.00 1.78880 28.4 7 25.646 4.32 1.89190 37.1 8 -145.326 1.10 9 (aperture) ∞ (variable) 10 -22.358 1.00 1.54072 47.2 11 33.864 5.76 1.81600 46.6 12 -31.950 4.72 13* -100.384 2.00 1.53160 55.8 14* -74.062 (variable) 15 -35.373 1.00 1.65412 39.7 16 157.296 0.20 17 76.224 8.79 1.89190 37.1 18 -33.792 4.12 19 -28.212 1.00 1.80809 22.7 20 -64.699 14.00 Image plane ∞ Aspherical data 13th plane K = 0.00000e+00 A 4 = -2.36904e-05 A 6 = -6.98504e-08 A 8 = -6.94731e-11 14th surface K = 0.00000e+00 A 4 = -1.14124e-05 A 6 = -6.90682e-08 A 8 = 5.79708e-11 Various data: Zoom ratio 1.00, Focal length 55.08, F-number 1.85, Half-angle of view (°) 21.44, Image height 21.64, Lens length 78.50, BF 14.00, Object distance Infinity Closest d 9 10.68 4.12 d14 2.20 8.76 Lens group data group: Starting surface Focal length 1 1 84.52 2 10 76.02 3 15 749.92 [Numerical Example 7] Unit: mm Surface Data Surface Number rd nd νd 1 43.230 6.61 1.90043 37.4 2 210.713 0.21 3 28.156 9.43 1.49700 81.7 4 1197.212 1.10 1.72047 34.7 5 20.982 6.31 6 -282.826 1.00 1.85478 24.8 7 60.087 2.98 1.90043 37.4 8 510.579 1.94 9 (Aperture) ∞ (Variable) 10 50.112 2.42 1.90043 37.4 11 947.195 1.01 12 -73.240 2.85 1.69895 30.1 13 57.366 7.31 14 4483.889 3.39 1.90043 37.4 15 -60.849 (variable) 16 -44.796 1.00 1.51633 64.1 17 78.960 0.20 18 55.150 9.54 1.76200 40.1 19 -44.572 5.94 20 -35.979 1.00 1.85478 24.8 21 -78.438 16.00 Image plane ∞ Various data Zoom ratio 1.00 Focal length 82.50 F-number 1.85 Half angle of view (°) 14.69 Image height 21.64 Lens length 100.36 BF 16.00 Object distance Infinity Closest d 9 17.36 2.00 d15 2.75 18.11 Lens group data Group Starting plane Focal length 1 1 143.69 2 10 90.61 3 16 755.82 [Numerical Example 8] Unit: mm Surface Data Surface Number rd nd νd 1 39.299 6.00 1.66382 27.4 2 94.672 0.20 3 48.464 4.00 1.85150 40.8 4 98.172 0.20 5 28.622 8.05 1.49700 81.5 6 254.446 1.10 1.85478 24.8 7 21.112 12.71 8 (Aperture) ∞ 1.50 9 85.082 1.80 1.74077 27.8 10 49.273 (Variable) 11 41.299 3.01 1.83481 42.7 12 -205.573 1.24 13 -42.506 0.90 1.74077 27.8 14 57.926 8.96 15 215.877 4.45 2.00100 29.1 16 -49.923 (Variable) 17 -85.393 1.00 1.67790 55.3 18 61.428 0.20 19 52.646 8.43 1.76200 40.1 20 -48.455 6.67 21 -37.962 1.00 2.00069 25.5 22 -179.890 16.00 Image plane ∞ Various data Zoom ratio 1.00 Focal length 82.50 F-number 1.85 Half angle of view (°) 14.69 Image height 21.64 mm, Lens length 100.16 mm, BF 16.00 mm, Object distance (infinity, close): d10 10.75 2.00, d16 2.00 10.75 mm. Lens group data: Starting plane, Focal length 1 1 204.22 2 11 50.49 3 17 -125.26

[0092]

[0093]

[0094] [Imaging Device] Figure 17 shows a digital still camera as an imaging device using the optical system L0 of Examples 1 to 8 as the imaging optical system. In Figure 17, 13 is the camera body, and 11 is the imaging optical system composed of any of the optical systems L0 of Examples 1 to 8. 12 is an image sensor (photoelectric conversion element) such as a CCD sensor or CMOS sensor, which is built into the camera body 13 and converts the subject image as an optical image formed by the imaging optical system 11 into a photoelectric image (that is, it images the subject through the imaging optical system 11).

[0095] 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.

[0096] By applying the optical system L0 of Examples 1 to 8 to the imaging device, it is possible to provide an imaging device that is compact, yet suppresses fluctuations in optical performance during focusing, and has a compact and lightweight focus group suitable for high-speed focusing.

[0097] The embodiments described above are merely representative examples, and various modifications and changes can be made to each embodiment when implementing the present invention.

Claims

1. An optical system comprising a front lens group with positive refractive power, an intermediate lens group with positive refractive power, and a rear lens group, arranged in order from the object side to the image side, wherein the front lens group includes a plurality of positive lenses and an aperture diaphragm, and when focusing from infinity to near, the front lens group and the rear lens group do not move, but the intermediate lens group moves toward the object side, and when TMgl is the sum of the thicknesses of all lenses included in the intermediate lens group along the optical axis, TGb is the distance along the optical axis from the lens surface closest to the object of the intermediate lens group to the lens surface closest to the image of the intermediate lens group when focused on an object at infinity, f is the focal length of the optical system when focused on an object at infinity, skd is the air-equivalent distance along the optical axis from the lens surface closest to the image of the optical system to the image plane when focused on an object at infinity, TTL is the distance along the optical axis from the lens surface closest to the object of the optical system to the image plane when focused on an object at infinity, and fGr is the focal length of the rear lens group, An optical system characterized by satisfying the following conditions: 0.10 ≤ TMgl / TGb ≤ 0.80, 0.05 ≤ skd / f ≤ 0.33, and 0.01 ≤ |TTL / fGr| < 1.

00.

2. The optical system according to claim 1, wherein when the optical system is in focus on an object at infinity, TTLg is the distance along the optical axis from the lens surface closest to the object to the lens surface closest to the image to the optical system, and Tbi is the distance along the optical axis from the lens surface closest to the object to the intermediate lens group to the lens surface closest to the image to the optical system, and the condition 0.10 ≤ Tbi / TTLg ≤ 0.60 is satisfied.

3. The optical system according to claim 1 or 2, characterized in that, when the focal length of the front lens group is fGf and the focal length of the intermediate lens group is fGb, the condition 0.50 ≤ fGf / fGb ≤ 5.00 is satisfied.

4. The optical system according to any one of claims 1 to 3, characterized in that, when SFL is the distance along the optical axis from the aperture diaphragm to the lens surface of the intermediate lens group closest to the object when the system is in focus on an object at infinity, and SIL is the distance along the optical axis from the aperture diaphragm to the image plane when the system is in focus on an object at infinity, the condition 0.10 ≤ SFL / SIL ≤ 0.50 is satisfied.

5. The optical system according to any one of claims 1 to 4, characterized in that the lens closest to the image in the intermediate lens group has a positive refractive power.

6. The optical system according to any one of claims 1 to 5, characterized in that, when Rb1 is the radius of curvature of the object-side lens surface of the lens closest to the image in the intermediate lens group, and Rb2 is the radius of curvature of the image-side lens surface of the lens closest to the image in the intermediate lens group, the condition -7.50 ≤ (Rb2 + Rb1) / (Rb2 - Rb1) ≤ -0.25 is satisfied.

7. The optical system according to any one of claims 1 to 6, characterized in that when the focal length of the intermediate lens group is fGb, the condition 0.01 ≤ |fGb / fGr| ≤ 1.00 is satisfied.

8. The optical system according to any one of claims 1 to 7, characterized in that it satisfies the condition 0.01 ≤ |skd / fGr| ≤ 0.

20.

9. The optical system according to any one of claims 1 to 8, wherein the intermediate lens group is composed of a first intermediate sub-lens group positioned on the object side of the widest air gap in the intermediate lens group, and a second intermediate sub-lens group positioned on the image side of the air gap, and when the focal length of the first intermediate sub-lens group is fGb1 and the focal length of the second intermediate sub-lens group is fGb2, the condition 0.01 ≤ |fGb2 / fGb1| ≤ 7.00 is satisfied.

10. The optical system according to any one of claims 1 to 9, characterized in that it satisfies the condition 0.70 ≤ TTL / f ≤ 1.

70.

11. Let βf be the lateral magnification of the intermediate lens group, and βR be the combined lateral magnification of all lenses positioned closer to the image than the intermediate lens group in the optical system, then ESGb = (1 - βf ２ ) × βR ２ The optical system according to any one of claims 1 to 10, characterized in that it satisfies the condition 0.30 ≤ ESGb ≤ 1.

50.

12. The optical system according to any one of claims 1 to 11, characterized in that the entire intermediate lens group moves together as a single unit during focusing.

13. The optical system according to any one of claims 1 to 12, characterized in that the intermediate lens group is composed of a first intermediate sub-lens group and a second intermediate sub-lens group, which move integrally with each other during focusing.

14. The optical system according to any one of claims 1 to 13, characterized in that the intermediate lens group is composed of five or fewer lenses.

15. The optical system according to any one of claims 1 to 14, characterized in that the rear lens group has a negative refractive power.

16. The optical system according to any one of claims 1 to 15, characterized in that the lens closest to the object in the front lens group has a positive refractive power.

17. The optical system according to any one of claims 1 to 16, characterized in that the lens closest to the object in the intermediate lens group has a positive refractive power.

18. An optical system comprising a front lens group with positive refractive power, an intermediate lens group with positive refractive power, and a rear lens group, arranged in order from the object side to the image side, wherein the front lens group includes a plurality of positive lenses and an aperture diaphragm, and the front lens group and the rear lens group do not move when focusing from infinity to near, while the intermediate lens group moves toward the object side.

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

Images