Optical system and imaging device

Abstract

To provide an optical system that is compact and lightweight, has a long focal length, and enables high-speed focusing and aberration correction.SOLUTION: An optical system comprises a front lens group with positive refractive power, an intermediate group, and a rear lens group. The front lens group includes the largest air space in the optical system. For focusing, the front lens group and the rear lens group do not move. The intermediate group includes two or more focus lens groups that move independently of each other for focusing. When the focus sensitivity B of each focus lens group is defined as B=(1-βf2)βr2, the smallest value among the absolute values of the focus sensitivities B of the two or more focus lens groups is defined as Bab_min, and the open F-number of the optical system is defined as Fno, the condition of 0.10≤Bab_min / Fno≤0.95 is satisfied.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an optical system used for imaging. [Background technology]

[0002] As an imaging optical system with a long focal length, there is a so-called telephoto type in which a lens group with positive refractive power is arranged closest to the object and a lens group with negative refractive power is arranged closer to the image, and Patent Document 1 discloses a single-focus super telephoto lens.

[0003] Generally, for a given F-number, the longer the focal length of an optical system, the larger the maximum effective diameter of the optical system. In this case, when focusing from an object at infinity to a close-up object, a lens group near the aperture stop is often selected as the focus lens group due to mechanical movement constraints and the need to correct various aberrations during close-up imaging. Patent Document 1 discloses an ultra-telephoto lens system that is composed of, arranged in order from the object side to the image side, a first lens group with positive refractive power, a second lens group with positive refractive power that moves during focusing, and a third lens group with negative refractive power overall. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. WO2020 / 217791 Summary of the Invention [Problem to be solved by the invention]

[0005] When a telephoto-type refractive power arrangement is strengthened to reduce the overall length, as in the super-telephoto lens of Patent Document 1, focus sensitivity, which is the sensitivity to the position of the focus lens group in the optical axis direction, tends to increase. This can lead to focus deviations due to variations in the stopping position of the focus lens group, or delays due to refocusing. Furthermore, when the refractive power of the focus lens group is strong, various aberrations tend to increase during close-up imaging.

[0006] The present invention provides an optical system that is small and lightweight, has a long focal length, is capable of high-speed and high-precision focusing, and has various aberrations well corrected. [Means for solving the problem]

[0007] An optical system according to one aspect of the present invention is composed of a front lens group, an intermediate lens group, and a rear lens group, all of which have positive refractive power, arranged in this order from the object side to the image side, and the spacing between adjacent lens groups changes during focusing. The front lens group includes the largest air gap in the optical system. The front and rear lens groups do not move during focusing. The intermediate lens group includes two or more focus lens groups that move independently of each other during focusing. The focus sensitivity B of each focus lens group is expressed as follows: βf is the lateral magnification of the focus lens group, and βr is the combined lateral magnification of all lenses arranged closer to the image side than the focus lens group. B=(1-βf 2 )βr 2 Let Bab_min be the smallest absolute value of the focus sensitivity B of each of the two or more focus lens groups, and Fno be the maximum F-number of the optical system. 0.10≦Bab_min / Fno≦0.95 The optical system is characterized by satisfying the following conditions: An imaging device including the optical system described above also constitutes another aspect of the present invention. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide an optical system that is small and lightweight, has a long focal length, is capable of high-speed and high-precision focusing, and has various aberrations well corrected. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a cross-sectional view of an optical system according to a first embodiment. [Figure 2] 1A and 1B are aberration diagrams of the optical system of Example 1 in a state where the optical system is focused at infinity and a state where the optical system is focused at a close distance, respectively. [Figure 3] FIG. 10 is a cross-sectional view of the optical system of the second embodiment. [Figure 4] 10A and 10B are aberration diagrams of the optical system of Example 2 when focused at infinity and when focused at close range, respectively. [Figure 5] FIG. 10 is a cross-sectional view of the optical system of the third embodiment. [Figure 6] 10A and 10B are aberration diagrams of the optical system of Example 3 in a state where the optical system is focused at infinity and a state where the optical system is focused at a close distance, respectively. [Figure 7] FIG. 10 is a cross-sectional view of an optical system according to a fourth embodiment. [Figure 8] 10A and 10B are aberration diagrams of the optical system of Example 4 when focused at infinity and when focused at close range, respectively. [Figure 9] FIG. 10 is a cross-sectional view of an optical system according to a fifth embodiment. [Figure 10] 10A and 10B are aberration diagrams of the optical system of Example 5 in a state where the optical system is focused at infinity and a state where the optical system is focused at a close distance, respectively. [Figure 11] FIG. 10 is a cross-sectional view of an optical system according to a sixth embodiment. [Figure 12] 13A and 13B are aberration diagrams of the optical system of Example 6 in a state where the optical system is focused at infinity and a state where the optical system is focused at a close distance, respectively. [Figure 13] FIG. 1 is a schematic diagram of an imaging device equipped with the optical system of Examples 1 to 6. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present invention will be described with reference to the drawings. First, before specifically describing the optical systems of Examples 1 to 6, matters common to each of the Examples will be described. The optical systems of each Example are used in various imaging devices such as video cameras, digital cameras, silver halide film cameras, television cameras, surveillance cameras, and vehicle-mounted cameras.

[0011] 1, 3, 5, 7, 9, and 11 respectively show the configurations of the optical systems of Examples 1 to 6. In each figure, the left side is the object side (front side) and the right side is the image side (rear side).

[0012] The optical system of each embodiment is composed of, arranged in order from the object side to the image side, a front lens group Lf with positive refractive power that does not move during focusing, an intermediate group Lm including a focus lens group that moves during focusing, and a rear lens group Lr that does not move during focusing. A lens group is a group of one or more lenses that may or may not move during focusing. In other words, the spacing between adjacent lens groups changes during focusing.

[0013] The front lens group Lf includes the largest air gap in the optical system. Lfa is an object-side partial lens group among the partial lens groups located on the object side and the image side of the front lens group Lf with the largest air gap therebetween.

[0014] The intermediate group Lm includes two or more focus lens groups Lfn (n=1 to 3 from the object side) that move independently of each other. The focus lens groups move independently of each other, meaning that they move in different directions and by different amounts during focusing from infinity to a close distance. In each drawing, an arrow (FOCUSn) below a focus lens group indicates the direction of movement of the focus lens group during focusing from infinity to a close distance. The intermediate group Lm may include a lens group that does not move during focusing, in addition to the focus lens group.

[0015] SP is the aperture stop, which determines the F-number of the optical system. IP is the image plane. The image pickup surface (light receiving surface) of an image sensor such as a CCD sensor or CMOS sensor, or the silver halide film surface (photosensitive surface) is located at the image plane IP. IS is the vibration-proof lens group. For optical vibration-proofing to correct image blur caused by camera shake, etc., the vibration-proof lens group IS is shifted relative to the optical axis.

[0016] In each embodiment, two or more focus lens groups Lfn are provided in the intermediate group Lm, and these groups move by different amounts when focusing at each object distance. This prevents an increase in various aberrations, particularly spherical aberration and coma, during close-range imaging. Furthermore, the amount of deviation from the desired focal position when one focus lens group moves is corrected by moving (feedback control) another focus lens group. This enables high-speed, high-precision focusing that would be difficult with a single focus lens group.

[0017] It is particularly effective to first move one of two or more focus lens groups with a higher absolute value of focus sensitivity, and then auxiliary move the other focus lens group with a lower absolute value of focus sensitivity to correct any focus deviation that occurs during the first movement. Focus sensitivity is the ratio between the amount of movement of the focus lens group and the amount of movement of the image plane, and details will be described later. This makes it possible to suppress a decrease in focusing accuracy and an increase in aberrations during focusing, even if the refractive power of the focus lens group is strengthened, when the refractive power arrangement of the entire optical system, particularly the telephoto arrangement in a telephoto lens, is strengthened to shorten the overall length.

[0018] The optical system of each embodiment satisfies the condition of the following formula (1), where Bab_min is the smallest absolute value of the focus sensitivity of each of the two or more focus lens groups Lfn, and Fno is the maximum F-number of the optical system.

[0019] 0.10≦Bab_min / Fno≦0.95 (1) The focus sensitivity B is defined by the following equation (A) using the lateral magnification βf of the focus lens group and the combined lateral magnification βr of the lens arranged closer to the image side than the focus lens group.

[0020] B=(1-βf 2 )βr 2 (A) The condition of formula (1) indicates the appropriate relationship between the focus sensitivity of the focus lens group with the lowest focus sensitivity and the maximum aperture F-number for high-speed, high-precision focusing. If Bab_min becomes large enough that Bab_min / Fno exceeds the upper limit of formula (1), the focus shift caused by the stopping position error of the focus lens group during focusing becomes significant, which is undesirable. Also, if Fno becomes small enough that Bab_min / Fno exceeds the upper limit of formula (1), the diameter of the front lens group becomes too large, making it difficult to make the optical system compact and lightweight, which is also undesirable.

[0021] When Bab_min is reduced so that Bab_min / Fno falls below the lower limit of equation (1), it is advantageous for correcting focus deviation caused by movement of one focus lens group with the other focus lens group, as described above. However, this is not desirable because it increases the amount of movement of the other focus lens group too much, lengthening the overall length of the optical system. Furthermore, when Fno is increased so that Bab_min / Fno falls below the lower limit of equation (1), it becomes difficult to obtain an optical system with the desired aperture, and further, deterioration of optical performance due to diffraction becomes significant, which is also undesirable.

[0022] By satisfying the above configuration and conditions, it is possible to realize an optical system that is small and lightweight, has a long focal length, is capable of high-speed and high-precision focusing, and has various aberrations well corrected.

[0023] Furthermore, it is preferable that the optical system of each embodiment satisfies at least one of the conditions of the following expressions (2) to (10).

[0024] 0.45≦OTL / f≦1.20 (2) 0.06≦fab_min / f≦0.60 (3) 0.1≦fab_max / f≦2.0 (4) 0.15≦Dmax / OTL≦0.60 (5) 0.2≦f1 / f≦0.8 (6) 0.01≦Df_max / OTL≦0.15 (7) 1.3≦BF / IH≦5.0 (8) 0.5≦Bab_max / Fno≦2.0 (9) 0.2≦f1a / f≦1.0 (10) In equations (2) to (10), OTL is the length on the optical axis from the lens surface closest to the object in the optical system to the image plane (total optical length), f is the focal length of the entire optical system, fab_min is the smallest absolute value of the focal lengths of the two or more focus lens groups, and fab_max is the largest absolute value of the focal lengths of the two or more focus lens groups.

[0025] In each embodiment, the largest air gap in the entire optical system is provided in the front lens group Lf. Since the front lens group Lf accounts for the largest proportion of mass in the entire optical system, it is effective from the perspective of weight reduction to reduce the number of lenses arranged on the object side as much as possible. Dmax is the length on the optical axis of the largest air gap in the front lens group Lf when focused on an object at infinity (hereinafter referred to as the infinity focused state). f1 is the focal length of the front lens group Lf.

[0026] Df_max is the distance on the optical axis to the lens surface on the aperture stop side of the focus lens group farthest from the aperture stop among two or more focus lens groups. BF is the air-equivalent length on the optical axis from the lens surface closest to the image side of the optical system to the image plane (back focus). IH is the maximum image height, and Bab_max is the largest absolute value of the focus sensitivity of each of two or more focus lens groups. f1a is the focal length of the object-side partial lens group Lfa.

[0027] The condition of formula (2) indicates an appropriate range for the ratio (telephoto ratio) between the total optical length OTL and the focal length f in order to achieve both a reduction in the overall length of the optical system and the suppression of various aberrations. If the total optical length OTL is increased so that OTL / f exceeds the upper limit of formula (2), the overall length becomes too long, making compactness difficult, which is undesirable. Also, if the focal length f is shortened so that OTL / f exceeds the upper limit of formula (2), an optical system with an appropriate telephoto focal length cannot be obtained, which is undesirable. On the other hand, if the total optical length OTL is reduced so that OTL / f falls below the lower limit of formula (2), this is good from the perspective of reducing the overall length, but is undesirable because the telephoto refractive power arrangement becomes stronger, increasing various aberrations, particularly spherical aberration, chromatic aberration, and curvature of field. Also, if the focal length f is increased so that OTL / f falls below the lower limit of formula (2), it becomes difficult to sufficiently correct chromatic aberration while maintaining the optical system's light weight, which is undesirable.

[0028] The condition of Equation (3) indicates the appropriate relationship between the absolute value of the smallest focal length, fab_min, of two or more focus lens groups and the focal length, f, of the entire optical system, in order to achieve good aberration correction even in close-range imaging. If the minimum focal length, fab_min, of the focus lens group becomes small so that fab_min / f exceeds the upper limit of Equation (3), the refractive power of the focus lens group becomes too strong, increasing various aberrations, particularly spherical aberration and curvature of field, when focusing on a close object, which is undesirable. Also, if the focal length, f, of the entire system becomes small so that fab_min / f exceeds the upper limit of Equation (3), it is undesirable because an appropriate telephoto focal length cannot be obtained. On the other hand, if the minimum focal length, fab_min, of the focus lens group becomes large so that fab_min / f falls below the lower limit of Equation (3), various aberrations when focusing on a close object can be suppressed, but the amount of movement of the focus lens group increases, undesirably lengthening the overall length of the optical system. Furthermore, if the focal length f of the entire system becomes so large that fab_min / f falls below the lower limit of equation (3), it becomes difficult to sufficiently correct chromatic aberration while maintaining the light weight of the optical system, which is undesirable.

[0029] The condition of equation (4) indicates the appropriate relationship between the absolute value fab_max of the longest focal length among two or more focus lens groups and the focal length f of the entire optical system, in order to achieve both good aberration correction in close-up imaging and a shortened overall length of the optical system. Increasing the maximum focal length fab_max of a focus lens group so that fab_max / f exceeds the upper limit of equation (4) is advantageous for correcting focus errors that occur when the other focus lens group moves, but is undesirable because it increases the amount of movement of the focus lens group with the longest focal length during focusing, making it difficult to shorten the overall length of the optical system. Furthermore, reducing the focal length f of the entire system so that fab_max / f exceeds the upper limit of equation (4) is undesirable because it makes it impossible to obtain an appropriate telephoto focal length. On the other hand, reducing the maximum focal length fab_max of a focus lens group so that fab_max / f falls below the lower limit of equation (4) is undesirable because the refractive power of that focus lens group becomes too strong, increasing spherical aberration and field curvature during close-up focusing. Furthermore, if the focal length f of the entire system becomes large so that fab_max / f falls below the lower limit of equation (4), an appropriate telephoto focal length can be obtained, but it becomes difficult to perform good aberration correction while miniaturizing the optical system, which is not desirable.

[0030] The condition of formula (5) indicates an appropriate relationship between the maximum air gap length Dmax in the front lens group Lf and the total optical length OTL in order to achieve both a reduction in the weight and the overall length of the optical system. If the maximum air gap length Dmax is increased so that Dmax / OTL exceeds the upper limit of formula (5), the weight of the optical system can be reduced, but the axial ray height in the image-side partial lens group adjacent to the maximum air gap becomes too small, making it difficult to perform sufficient spherical aberration correction, which is undesirable. Furthermore, if the total optical length OTL is shortened so that Dmax / OTL exceeds the upper limit of formula (5), the overall length can be shortened, but the telephoto arrangement at the telephoto focal length becomes extremely strong, making it difficult to suppress various aberrations, particularly spherical aberration and field curvature, which is undesirable. If the maximum air gap length Dmax becomes small so that Dmax / OTL falls below the lower limit of formula (5), the lenses will be arranged together in a portion of the front lens group Lf with a large diameter, which is advantageous from the viewpoint of aberration correction, but it becomes difficult to reduce the weight, which is undesirable.Furthermore, if the total optical length OTL becomes large so that Dmax / OTL falls below the lower limit of formula (5), it becomes difficult to reduce the size of the optical system, which is undesirable.

[0031] The condition of formula (6) indicates an appropriate relationship between the focal length f1 of the front lens group Lf and the focal length f of the entire optical system in order to achieve both compactness and lightweight design and aberration correction. If the focal length f1 of the front lens group Lf increases so that f1 / f exceeds the upper limit of formula (6), the telephoto arrangement cannot be strengthened, making it difficult to shorten the overall length of the optical system, which is undesirable. Also, if the focal length f of the entire system decreases so that f1 / f exceeds the upper limit of formula (6), it becomes difficult to obtain an appropriate telephoto focal length, which is undesirable. On the other hand, if the focal length f1 of the front lens group Lf decreases so that f1 / f falls below the lower limit of formula (6), this is advantageous for shortening the overall length, but it becomes difficult to adequately correct spherical aberration and coma aberration generated in the front lens group Lf with the subsequent lens groups, which is undesirable. Furthermore, if the focal length f of the entire system becomes so large that f1 / f falls below the lower limit of equation (6), it becomes difficult to sufficiently correct chromatic aberration while maintaining the light weight of the optical system, which is undesirable.

[0032] The condition of equation (7) indicates the appropriate relationship between the total optical length OTL and the distance Df_max from the aperture diaphragm SP to the focus lens group farthest from the aperture diaphragm SP among the two focus lens groups, in order to provide sufficient aberration correction during focusing from infinity to close distances. If the distance Df_max increases so that |Df_max| / OTL exceeds the upper limit of equation (7), the distance from the aperture diaphragm SP to the focus lens group becomes too great, making it difficult to sufficiently suppress field curvature aberration during close focusing, which is undesirable. In particular, if the focus lens group is farther away from the aperture diaphragm SP toward the object side, this is undesirable from the perspective of reducing the weight of the focus lens group. Furthermore, if the total optical length OTL decreases so that |Df_max| / OTL exceeds the upper limit of equation (7), this is advantageous for shortening the overall length of the optical system, but it is undesirable because it makes it difficult to sufficiently suppress spherical aberration and coma aberration. On the other hand, if the distance Df_max becomes small so that |Df_max| / OTL falls below the lower limit of equation (7), two or more focus lens groups will be arranged close together near the aperture stop SP, making it difficult to secure the arrangement space, which is undesirable.Furthermore, if the total optical length OTL becomes large so that |Df_max| / OTL falls below the lower limit of equation (7), it will be difficult to shorten the total length of the optical system, which is also undesirable.

[0033] The condition of formula (8) indicates the appropriate relationship between the back focal length BF and the maximum image height IH. If BF / IH exceeds the upper limit of formula (8), the overall length of the optical system becomes too long, increasing the weight of the components, such as the lens barrel, that hold the optical system. This makes weight reduction difficult, which is undesirable. On the other hand, if BF / IH falls below the lower limit of formula (8), the back focal length becomes too short. In this case, the diameter of the lens (final lens) located closest to the image side of the optical system becomes too large, which increases the diameter of the mount for attaching the interchangeable optical system to the imaging device. This makes it difficult to construct a compact and lightweight optical system and imaging device, which is undesirable. On the other hand, if the back focal length is reduced and the diameter of the final lens of the optical system is reduced so that BF / IH falls below the lower limit of formula (8), the angle of incidence of light rays on the imaging element in the imaging device increases. This is undesirable, as it tends to degrade image quality, especially in the peripheral areas of the image.

[0034] The condition in equation (9) indicates the appropriate relationship between the maximum absolute value of the focus sensitivity of each of two or more focus lens groups, Bab_max, and the maximum F-number, Fno. If Bab_max / Fno exceeds the upper limit of equation (9), the focus lens group with the larger Bab_max will experience excessive focus deviation due to a shift in the stop position. This is undesirable because it takes a long time to correct the focus deviation using the other focus group. If Bab_max / Fno falls below the lower limit of equation (9), a long space must be secured along the optical axis for focusing, which is undesirable from the perspective of shortening the overall length.

[0035] The condition of formula (10) indicates an appropriate relationship between the focal length f1a of the object-side partial lens unit Lfa of the front lens unit Lf and the focal length f of the entire optical system in order to achieve both a reduction in the overall length of the optical system and suppression of aberrations. If the focal length f1a of the object-side lens unit becomes large so that f1a / f exceeds the upper limit of formula (10), it becomes difficult to reduce the overall length of the optical system, which is undesirable. Also, if the focal length f of the entire system becomes small so that f1a / f exceeds the upper limit of formula (10), it becomes difficult to obtain an appropriate telephoto focal length, which is undesirable. On the other hand, if the focal length f1a of the object-side partial lens unit Lfa becomes small so that f1a / f falls below the lower limit of formula (10), it becomes difficult to suppress spherical aberrations and chromatic aberrations generated in the object-side partial lens unit Lfa with the subsequent lens units, which is undesirable. Furthermore, if the focal length f of the entire system becomes so large that f1a / f falls below the lower limit of equation (10), it becomes difficult to sufficiently correct chromatic aberration while maintaining the light weight of the optical system, which is undesirable.

[0036] It is more preferable that the numerical ranges of the formulas (2) to (10) are as follows:

[0037] 0.20≦Bab_min / Fno≦0.93 (1a) 0.55≦OTL / f≦1.10 (2a) 0.08≦fab_min / f≦0.55 (3a) 0.13≦fab_max / f≦1.90 (4a) 0.25≦Dmax / OTL≦0.60 (5a) 0.25≦f1 / f≦0.75 (6a) 0.015≦Df_max / OTL≦0.120 (7a) 1.5≦BF / IH≦4.0 (8a) 0.7≦Bab_max / Fno≦1.9 (9a) 0.30≦f1a / f≦0.95 (10a) Furthermore, it is more preferable to set the numerical ranges of the formulas (2) to (10) as follows:

[0038] 0.22≦Bab_min / Fno≦0.91 (1b) 0.6≦OTL / f≦1.0 (2b) 0.10≦fab_min / f≦0.35 (3b) 0.18≦fab_max / f≦1.75 (4b) 0.35≦Dmax / OTL≦0.55 (5b) 0.31≦f1 / f≦0.55 (6b) 0.025≦Df_max / OTL≦0.085 (7b) 1.7≦BF / IH≦2.5 (8b) 0.9≦Bab_max / Fno≦1.8 (9b) 0.40≦f1a / f≦0.88 (10b) In each embodiment, in order to obtain good imaging performance (suppress aberration fluctuations) even during optical image stabilization, it is preferable that the image stabilization lens group IS be composed of three or more lenses, including a positive lens and a negative lens. Note that in the case of a cemented lens in which two or more lenses, n in number, are cemented together, the number of lenses is counted as n.

[0039] In each embodiment, it is preferable that the vibration-reduction lens group IS be formed from at least a part of the rear lens group Lr, which is closer to the image than the focus lens group, thereby enabling good optical vibration reduction with a small and lightweight vibration-reduction lens group.

[0040] In each embodiment, it is preferable that the focus lens group be located closer to the image side than the aperture stop SP. Furthermore, it is preferable that all of the focus lens groups have negative refractive power and move toward the image side during focusing from infinity to close range, from the viewpoint of efficiently arranging a focus drive mechanism that drives the focus lens groups.

[0041] In each embodiment, it is preferable from the viewpoint of weight reduction that the object-side partial lens unit Lfa, which is located closer to the object than the maximum air gap in the front lens unit Lf, be composed of one or two positive lenses.

[0042] By satisfying the above conditions and configuration, an optical system can be obtained that has a long telephoto focal length, excellent correction of various aberrations, and a small and lightweight focus lens group.

[0043] Next, the optical system of each embodiment will be specifically described. [Example]

[0044] The optical system of Example 1 shown in Figure 1 has an intermediate lens unit Lm located closer to the image side than the aperture stop SP. The intermediate lens unit Lm is composed of two adjacent focus lens units Lf1 and Lf2, each having negative refractive power. During focusing from infinity to a close distance, the focus lens units Lf1 and Lf2 move toward the image side as indicated by the arrows in the figure, increasing the distance between them.

[0045] The object-side partial lens unit Lfa of the front lens unit Lf is made up of two positive lenses.

[0046] The vibration-reduction lens group ISf, which is a partial lens group formed by the third to fifth lenses counting from the object side in the rear lens group Lr, shifts with respect to the optical axis for optical vibration reduction. [Example]

[0047] The optical system of Example 2 shown in FIG. 3 has the same configuration as the optical system of Example 1, except that a partial lens unit EXT is inserted in the rear lens unit Lr.

[0048] The partial lens group EXT is inserted into and removed from the space between the final lens in the rear lens group Lr and the lens immediately preceding it toward the object side by an insertion / removal mechanism (not shown). The partial lens group EXT has negative refractive power and functions as an extender that increases the focal length of the entire optical system by approximately 1.4 times. [Example]

[0049] The optical system of Example 3 shown in Figure 5 has an intermediate lens unit Lm located closer to the image side than the aperture stop SP. The intermediate lens unit Lm is composed of two adjacent focus lens units Lf1 and Lf2, each having negative refractive power. During focusing from infinity to a close distance, the focus lens units Lf1 and Lf2 move toward the image side as indicated by the arrows in the figure, narrowing the distance between them.

[0050] The object-side partial lens unit Lfa of the front lens unit Lf is composed of one positive lens whose object-side surface is aspherical.

[0051] The vibration-reduction lens group ISf, which is a partial lens group formed by the third to fifth lenses counting from the object side in the rear lens group Lr, shifts with respect to the optical axis for optical vibration reduction. [Example]

[0052] In the optical system of Example 4 shown in Figure 7, the intermediate unit Lm is composed of, arranged in order from the object side to the image side, a focus lens unit Lf1 with positive refractive power, an aperture stop SP, a focus lens unit Lf2 with negative refractive power, and a focus lens unit Lf3 with negative refractive power. During focusing from infinity to a close distance, the focus lens unit Lf1 moves toward the object side, and the focus lens units Lf2 and Lf3 move toward the image side so that the distance between them decreases. The aperture stop SP does not move during focusing.

[0053] The object-side partial lens unit Lfa of the front lens unit Lf is made up of two positive lenses.

[0054] The vibration-reduction lens group ISf, which is a partial lens group formed by the third to fifth lenses counting from the object side in the rear lens group Lr, shifts with respect to the optical axis for optical vibration reduction. [Example]

[0055] The optical system of Example 5 shown in Figure 9 has an intermediate lens unit Lm located closer to the image side than the aperture stop SP. The intermediate lens unit Lm is composed of, arranged in order from the object side to the image side, a focus lens unit Lf1 with negative refractive power, a positive lens that does not move during focusing, and a focus lens unit Lf2 with negative refractive power. During focusing from infinity to a close distance, the focus lens units Lf1 and Lf2 move toward the image side so that the distance between them increases.

[0056] The object-side partial lens unit Lfa of the front lens unit Lf is composed of one positive lens whose object-side surface is aspherical.

[0057] The vibration-reduction lens group ISf, which is a partial lens group formed by the third to fifth lenses counting from the object side in the rear lens group Lr, shifts with respect to the optical axis for optical vibration reduction. [Example]

[0058] The optical system of Example 6 shown in Figure 11 has an intermediate lens unit Lm located closer to the image side than the aperture stop SP. The intermediate lens unit Lm is composed of two adjacent focus lens units Lf1 and Lf2, each having negative refractive power. During focusing from infinity to a close distance, the focus lens units Lf1 and Lf2 move toward the image side as indicated by the arrows in the figure, narrowing the distance between them.

[0059] The object-side partial lens unit Lfa of the front lens unit Lf is composed of one positive lens whose object-side and image-side surfaces are aspherical.

[0060] The vibration-reduction lens group ISf, which is a partial lens group formed by the third to fifth lenses counting from the object side in the rear lens group Lr, shifts with respect to the optical axis for optical vibration reduction.

[0061] Numerical Examples 1 to 6 corresponding to Examples 1 to 6 are shown below. In each numerical example, surface number i indicates the order of the surface when counted from the object side. r is the radius of curvature (mm) of the ith surface from the object side, d is the lens thickness or air gap (mm) on the optical axis between the ith and (i+1)th surfaces, and nd is the refractive index at the d-line of the optical material between the ith and (i+1)th surfaces. νd is the Abbe number based on the d-line of the optical material between the ith and (i+1)th surfaces. The Abbe number νd based on the d-line is expressed as νd=(Nd-1) / (NF-NC), where Nd, NF, and NC are the refractive indices at the Fraunhofer d-line (587.6 nm), F-line (486.1 nm), and C-line (656.3 nm).

[0062] In each numerical example, d, focal length (mm), F-number, and half angle of view (°) are all values ​​when focused at infinity. BF represents back focus (mm). Back focus is the distance on the optical axis from the lens surface closest to the image (final surface) of the optical system to the paraxial image plane, expressed as an air-equivalent length. The total lens length is the distance on the optical axis from the lens surface closest to the object to the final surface of the optical system plus the back focus, and corresponds to the total optical length OTL in equation (2).

[0063] An asterisk (*) next to a surface number indicates that the surface has an aspherical shape. When x is the displacement from the vertex of the surface in the optical axis direction, h is the height from the optical axis in a direction perpendicular to the optical axis, R is the paraxial radius of curvature, k is the conic constant, and A4, A6, A8, A10, and A12 are aspherical coefficients of each order, the aspherical shape is expressed as follows: 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 In addition, "e±XX" in the conic constant and aspherical coefficient is expressed as "×10± XX " means.

[0064] The values ​​of the above-mentioned formulas (1) to (10) for each numerical example are summarized in Table 1. The optical system of each numerical example satisfies all of the conditions of formulas (1) to (10).

[0065] 2(A), 4(A), 6(A), 8(A), 10(A), and 12(A) respectively show longitudinal aberrations (spherical aberration, astigmatism, distortion, and chromatic aberration) when the optical systems of Numerical Examples 1 to 6 are focused at infinity. FIG. 2(B), 4(B), 6(B), 8(B), 10(B), and 12(B) respectively show longitudinal aberrations when the optical systems of Numerical Examples 1 to 6 are focused at close range.

[0066] In the spherical aberration diagram, Fno indicates the F-number, the solid line indicates spherical aberration for the d-line (wavelength 587.6 nm), and the two-dot chain line indicates spherical aberration for the g-line (wavelength 435.8 nm). In the astigmatism diagram, the solid line ΔS indicates astigmatism on the sagittal image plane, and the dashed line ΔM indicates astigmatism on 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 (°). [Numerical example 1] Unit: mm Surface Data Surface number rd nd νd 1 361.590 8.96 1.48749 70.2 2 -23384.147 0.30 3 165.569 12.81 1.43387 95.1 4 622.689 132.44 5 87.354 12.05 1.43875 94.7 6 -239.145 2.50 1.80610 33.3 7 57.954 0.18 8 56.866 12.48 1.43387 95.1 9 -360.152 0.20 10 76.054 7.94 1.43387 95.1 11 814.525 2.12 12 -268.908 2.00 1.61340 44.3 13 59.417 10.11 1.66382 27.4 14 -194.105 4.41 15 (Aperture) ∞ (Variable) 16 25372.899 1.70 1.59522 67.7 17 71.961 (variable) 18 119.836 1.70 1.59522 67.7 19 58.499 (variable) 20 196.399 1.50 1.98612 16.5 21 116.011 3.12 1.73800 32.3 22 -606.051 2.33 23 -179.127 3.48 1.80000 29.8 24 -60.919 1.50 1.57144 71.6 25 86.488 1.47 26 855.808 1.50 1.80400 46.5 27 119.682 7.35 28 -42.017 2.00 1.49700 81.5 29 -49.197 2.00 30 146.161 6.69 1.85026 32.3 31 -56.569 1.60 1.98612 16.5 32 -95.361 56.03 33 -3569.656 2.00 1.72825 28.5 34 ∞ (variable) Image plane ∞ Various data Focal length 387.98 F-number 2.91 Half angle of view (°) 3.19 Image height 21.64 Lens total length 372.01 BF 38.28 (When object distance is infinite) d15 3.44 d17 5.07 d19 20.74 d34 38.28 (When object distance is -2.5m) d15 18.74 d17 5.34 d19 5.17 d34 38.28 Lens group data Group starting plane focal length 1 1 172.37 2 16 -121.24 3 18 -194.02 4 20 207.60 [Numerical example 2] Unit: mm Surface Data Surface number rd nd νd 1 361.590 8.96 1.48749 70.2 2 -23384.147 0.30 3 165.569 12.81 1.43387 95.1 4 622.689 132.44 5 87.354 12.05 1.43875 94.7 6 -239.145 2.50 1.80610 33.3 7 57.954 0.18 8 56.866 12.48 1.43387 95.1 9 -360.152 0.20 10 76.054 7.94 1.43387 95.1 11 814.525 2.12 12 -268.908 2.00 1.61340 44.3 13 59.417 10.11 1.66382 27.4 14 -194.105 4.41 15 (Aperture) ∞ (Variable) 16 25372.899 1.70 1.59522 67.7 17 71.961 (variable) 18 119.836 1.70 1.59522 67.7 19 58.499 (variable) 20 196.399 1.50 1.98612 16.5 21 116.011 3.12 1.73800 32.3 22 -606.051 2.33 23 -179.127 3.48 1.80000 29.8 24 -60.919 1.50 1.57144 71.6 25 86.488 1.47 26 855.808 1.50 1.80400 46.5 27 119.682 7.35 28 -42.017 2.00 1.49700 81.5 29 -49.197 2.00 30 146.161 6.69 1.85026 32.3 31 -56.569 1.60 1.98612 16.5 32 -95.361 2.48 33 22.976 8.53 1.48749 70.2 34 167.264 0.17 35 51.442 3.74 1.57501 41.5 36 121.848 1.00 1.90525 35.0 37 27.926 10.16 38 -672.196 0.95 1.72916 54.7 39 14.961 14.43 1.59270 35.3 40 -15.436 0.95 1.81600 46.6 41 75.686 0.65 42 31.712 9.96 1.60342 38.0 43 -22.105 1.05 2.00100 29.1 44 -102.267 1.99 45 -3569.656 2.00 1.72825 28.5 46 ∞ (variable) Image plane ∞ Various data Focal length 543.19 F-number 4.12 Half angle of view (°) 2.28 Image height 21.64 Lens total length 372.05 BF 38.30 (When object distance is infinite) d15 3.44 d17 5.07 d19 20.74 d46 38.30 (When object distance is -2.5m) d15 18.74 d17 5.34 d19 5.17 d46 38.30 Lens group data Group starting plane focal length 1 1 172.37 2 16 -121.24 3 18 -194.02 4 20 -186.53 [Numerical example 3] Unit: mm Surface Data Surface number rd nd νd 1* 248.151 14.18 1.59349 67.0 2 -824.380 150.33 3 60.269 12.75 1.43387 95.1 4 -18936.039 0.20 5 285.198 1.80 1.77047 29.7 6 43.002 11.78 1.43875 94.7 7 442.854 9.59 8 86.585 5.94 1.43387 95.1 9 -482.598 0.86 10 -208.293 2.00 1.67300 38.1 11 34.591 10.05 1.71338 26.0 12 -413.575 4.41 13 (Aperture) ∞ (Variable) 14 202.953 1.50 1.88300 40.8 15 78.905 (variable) 16 176.134 1.40 1.80400 46.6 17 45.961 (variable) 18 178.052 1.50 1.98612 16.5 19 56.107 4.65 1.85478 24.8 20 -148.672 1.00 21 194.147 5.31 1.59270 35.3 22 -46.710 1.50 1.53775 74.7 23 35.018 6.15 24 -54.008 1.20 1.49700 81.5 25 156.911 1.06 26 69.234 4.44 1.73037 32.2 27 -280.157 18.01 28* 96.272 7.70 1.73037 32.2 29 -73.401 1.60 1.98612 16.5 30 -238.443 (variable) Image plane ∞ Aspheric data Front page K = 0.00000e+00 A 4=-1.52594e-08 A 6=-3.05283e-13 A 8= 1.96693e-17 A10=-4.31090e-21 A12= 3.32591e-25 A14=-2.92022e-30 Page 28 K = 0.00000e+00 A 4= 2.91447e-07 A 6= 2.37934e-10 A 8=-2.19986e-13 A10= 1.97198e-16 Various data Focal length 387.76 F-number 2.91 Half angle of view (°) 3.19 Image height 21.64 Lens total length 350.09 BF 37.64 (When object distance is infinite) d13 2.83 d15 4.48 d17 24.22 d30 37.64 (When object distance is -2.5m) d13 16.77 d15 3.01 d17 11.75 d30 37.64 Lens group data Group starting plane focal length 1 1 162.66 2 14 -147.04 3 16 -77.72 4 18 129.95 [Numerical example 4] Unit: mm Surface Data Surface number rd nd νd 1 214.815 8.20 1.48749 70.2 2 2858.165 0.30 3 131.160 8.11 1.43387 95.1 4 296.511 108.02 5 59.061 9.22 1.43875 94.7 6 -834.931 2.50 1.80610 33.3 7 40.320 0.07 8 39.698 9.97 1.43387 95.1 9 -1108.152 0.20 10 55.009 5.51 1.43387 95.1 11 281.223 1.75 12 -248.383 2.00 1.61340 44.3 13 48.570 7.01 1.66382 27.4 14 -259.456 (variable) 15 -267.876 1.77 1.84961 24.1 16 -164.795 (variable) 17 (Aperture) ∞ (Variable) 18 144.973 1.00 1.62580 64.2 19 33.451 (variable) 20 -2938.396 1.00 1.67744 59.1 21 52.065 (variable) 22 47.624 1.50 1.98612 16.5 23 34.404 3.72 1.73800 32.3 24 521.716 2.19 25 -193.942 2.79 1.80000 29.8 26 -54.832 1.50 1.57144 71.6 27 45.569 2.28 28 -272.462 1.50 1.80400 46.5 29 348.000 2.61 30 73.446 2.00 1.49700 81.5 31 243.232 2.00 32 105.943 4.54 1.85026 32.3 33 -97.352 1.60 1.98612 16.5 34 -264.722 14.92 35 227.342 2.00 1.84499 25.4 36 ∞ (variable) Image plane ∞ Various data Focal length 293.93 F-number 2.91 Half angle of view (°) 4.21 Image height 21.64 Lens total length 280.10 BF 37.92 (When object distance is infinite) d14 9.58 d16 2.56 d17 3.65 d19 5.45 d21 9.19 d36 37.92 (When object distance is -2.5m) d14 8.72 d16 3.41 d17 12.44 d19 2.91 d21 2.94 d36 37.92 Lens group data Group starting plane focal length 1 1 146.25 2 15 500.10 3 17 ∞ 4 18 -69.73 5 20 -75.51 6 22 79.53 [Numerical example 5] Unit: mm Surface Data Surface number rd nd νd 1* 181.780 11.26 1.59349 67.0 2 -792.802 104.82 3 63.151 10.08 1.43387 95.1 4 -435.065 1.41 5 1995.530 1.80 1.77047 29.7 6 44.839 9.19 1.43875 94.7 7 -1540.104 0.19 8 120.168 4.99 1.43387 95.1 9 -289.132 0.79 10 -166.118 2.00 1.67300 38.1 11 41.233 6.87 1.71338 26.0 12 440.009 4.41 13 (Aperture) ∞ (Variable) 14 460.813 1.50 1.57501 41.5 15 58.113 (variable) 16 67.515 4.34 1.90525 35.0 17 -322.866 (variable) 18 345.625 1.00 1.72916 54.7 19 37.967 (variable) 20 123.777 1.50 1.98612 16.5 21 90.228 2.69 1.75700 47.8 22 -1251.283 1.00 23 151.227 4.12 1.59270 35.3 24 -71.341 1.50 1.53775 74.7 25 40.675 4.39 26 -67.989 1.20 1.49700 81.5 27 74.403 1.53 28 54.472 3.33 1.73037 32.2 29 223.241 20.60 30* 84.345 8.46 1.73037 32.2 31 -66.019 1.60 1.98612 16.5 32 -174.334 (variable) Image plane ∞ Aspheric data Front page K = 0.00000e+00 A 4=-2.98031e-08 A 6=-9.51752e-13 A 8= 2.44412e-17 A10=-1.21721e-20 A12= 3.32864e-25 A14= 2.70525e-28 Page 30 K = 0.00000e+00 A 4=-4.54498e-08 A 6= 1.16669e-10 A 8=-3.19123e-13 A10= 1.36316e-16 Various data Focal length 293.91 F-number 2.91 Half angle of view (°) 4.21 Image height 21.64 Lens total length 285.03 BF 38.50 (When object distance is infinite) d13 3.10 d15 10.65 d17 2.93 d19 13.28 d32 38.50 (When object distance is -2.5m) d13 10.10 d15 3.65 d17 11.50 d19 4.71 d32 38.50 Lens group data Group starting plane focal length 1 1 184.74 2 14 -115.81 3 16 62.01 4 18 -58.58 5 20 163.52 [Numerical example 6] Unit: mm Surface Data Surface number rd nd νd 1* 99.578 11.66 1.59349 67.0 2* -11291.333 83.80 3 52.203 6.93 1.43387 95.1 4 -84.555 0.20 5 -93.456 1.40 1.77047 29.7 6 32.199 5.28 1.43875 94.7 7 163.008 12.64 8 35.431 5.99 1.43387 95.1 9 -78.480 0.20 10 -118.489 1.50 1.83481 42.7 11 23.489 6.42 1.71338 26.0 12 -101.816 4.41 13 (Aperture) ∞ (Variable) 14 82.241 1.00 1.88300 40.8 15 27.039 (variable) 16 -40.745 1.00 1.77250 49.6 17 -156.365 (variable) 18 111.289 1.20 1.98612 16.5 19 34.955 4.51 1.85478 24.8 20 -62.278 1.00 21 79.965 4.67 1.59270 35.3 22 -34.368 1.00 1.53775 74.7 23 26.859 5.23 24 -31.176 1.20 1.49700 81.5 25 238.025 0.87 26 53.994 3.85 1.77047 29.7 27 -178.142 14.51 28* -190.776 5.30 1.73037 32.2 29 -31.556 1.60 1.98612 16.5 30 -58.924 (variable) Image plane ∞ Aspheric data Front page K = 0.00000e+00 A 4=-8.08909e-08 A 6=-4.40701e-12 A 8=-2.96813e-15 A10=-1.45875e-18 A12= 3.22851e-25 A14=-9.74246e-27 2nd side K = 0.00000e+00 A 4=-3.06763e-08 A 6= 7.18030e-12 A 8=-6.27380e-15 Page 28 K = 0.00000e+00 A 4=-1.16736e-07 A 6=-1.17777e-09 A 8= 3.18931e-12 A10=-4.92448e-15 Various data Focal length 387.52 F-number 4.60 Half angle of view (°) 3.20 Image height 21.64 Lens total length 250.40 BF 41.80 (When object distance is infinite) d13 2.76 d15 12.57 d17 5.91 d30 41.80 (When object distance is -2.5m) d13 11.85 d15 5.19 d17 4.20 d30 41.80 Lens group data Group starting plane focal length 1 1 133.36 2 14 -46.01 3 16 -71.60 4 18 75.71

[0067] [Table 1]

[0068] [Imaging device] 13 shows the configuration of a digital still camera (imaging device) that uses the optical system of Examples 1 to 6 as its imaging optical system. Reference numeral 10 denotes a camera body, and 11 denotes an imaging optical system configured using any of the optical systems of Examples 1 to 6. Reference numeral 12 denotes an imaging element that is built into the camera body and is configured with a photoelectric conversion element such as a CCD sensor or CMOS sensor that photoelectrically converts the optical image formed by the imaging optical system 11 (i.e., captures an image of a subject through the imaging optical system 11).

[0069] The camera body 10 may be a single-lens reflex camera with a quick-turn mirror, or a mirrorless camera without a quick-turn mirror. The camera body 10 may also be a lens-interchangeable type or an integrated lens type.

[0070] In this way, by applying the optical system of each embodiment to an imaging device such as a digital still camera, it is possible to obtain an imaging device equipped with a compact optical system.

[0071] The above embodiment includes the following configurations.

[0072] (Configuration 1) An optical system including a front lens group, an intermediate lens group, and a rear lens group, each having a positive refractive power, arranged in this order from the object side to the image side, wherein the distance between adjacent lens groups changes during focusing, wherein the front lens group includes the largest air gap in the optical system, For focusing, the front lens group and the rear lens group do not move, the intermediate group includes two or more focus lens groups that move independently of each other for focusing; The focus sensitivity B of each focus lens group is expressed as βf, the lateral magnification of the focus lens group is expressed as βr, and the combined lateral magnification of all lenses arranged on the image side of the focus lens group is expressed as βr. B=(1-βf 2 )βr 2 and the smallest absolute value of the focus sensitivity B of each of the two or more focus lens groups is Bab_min, and the maximum F-number of the optical system is Fno, then: 0.10≦Bab_min / Fno≦0.95 An optical system characterized by satisfying the following conditions: (Configuration 2) When the length on the optical axis from the lens surface closest to the object side of the optical system to the image plane is OTL and the focal length of the optical system is f, 0.45≦OTL / f≦1.20 The optical system according to configuration 1, characterized in that the following condition is satisfied: (Configuration 3) When the smallest absolute value of the focal lengths of the two or more focus lens groups is fab_min, 0.06≦fab_min / f≦0.60 3. The optical system according to configuration 1 or 2, wherein the following condition is satisfied: (Configuration 4) When the largest absolute value of the focal lengths of the two or more focus lens groups is defined as fab_max, 0.10≦fab_max / f≦2.00 4. The optical system according to any one of configurations 1 to 3, wherein the following condition is satisfied: (Configuration 5) When the length of the maximum air gap on the optical axis is Dmax, 0.15≦Dmax / OTL≦0.60 5. The optical system according to any one of configurations 1 to 4, wherein the following condition is satisfied: (Configuration 6) When the focal length of the front lens group is f1, 0.2≦f1 / f≦0.8 6. The optical system according to any one of configurations 1 to 5, wherein the following condition is satisfied: (Configuration 7) the optical system includes an aperture stop that determines an F-number; The optical system according to any one of configurations 1 to 6, wherein two of the two or more focus lens groups are arranged closer to the image side than the aperture stop. (Configuration 8) the optical system includes an aperture stop that determines an F-number; When the distance on the optical axis from the aperture diaphragm to the lens surface of the focus lens group farthest from the aperture diaphragm among the two or more focus lens groups is defined as Df_max, 0.01≦|Df_max| / OTL≦0.15 8. The optical system according to any one of configurations 1 to 7, wherein the following condition is satisfied: (Configuration 9) Let BF be the air-equivalent length on the optical axis from the lens surface closest to the image side of the optical system to the image plane, and IH be the maximum image height. 1.3≦BF / IH≦5.0 9. The optical system according to any one of configurations 1 to 8, wherein the following condition is satisfied: (Configuration 10) When the largest absolute value of the focus sensitivities of the two or more focus lens groups is defined as Bab_max, 0.5≦Bab_max / Fno≦2.0 10. The optical system according to any one of configurations 1 to 9, wherein the following condition is satisfied: (Configuration 11) When the focal length of the object-side partial lens unit among the partial lens units located on the object side and the image side with the maximum air gap in between in the front lens unit is denoted by f1a, 0.2≦f1a / f≦1.0 11. The optical system according to any one of configurations 1 to 10, wherein the following condition is satisfied: (Configuration 12) 12. The optical system according to configuration 11, wherein the object-side partial lens group is composed of one or two positive lenses. (Configuration 13) 13. The optical system according to any one of configurations 1 to 12, wherein the two or more focus lens groups all have negative refractive power. (Configuration 14) the intermediate group is composed of two adjacent focus lens groups each having negative refractive power, 14. The optical system according to any one of configurations 1 to 13, wherein the two focus lens groups move toward the image side during focusing from infinity to a close distance. (Configuration 15) the intermediate group is composed of a focus lens group with positive refractive power, an aperture stop, and two focus lens groups with negative refractive power, arranged in this order from the object side to the image side; 15. The optical system according to any one of configurations 1 to 14, wherein, during focusing from infinity to a close distance, the focus lens group having positive refractive power moves toward the object side, and the two focus lens groups having negative refractive power move toward the image side. (Configuration 16) 16. The optical system according to any one of configurations 1 to 15, wherein at least a portion of the rear lens group moves relative to the optical axis for optical vibration isolation. (Configuration 17) The optical system according to any one of configurations 1 to 16; and an image sensor that captures an image of a subject through the optical system.

[0073] The embodiments described above are merely representative examples, and various modifications and alterations are possible to each embodiment when implementing the present invention. [Explanation of symbols]

[0074] Lf Front lens group Lm intermediate lens group Lr rear lens group Lf1, Lf2, Lf3 focus lens group

Claims

1. An optical system including a front lens group, an intermediate lens group, and a rear lens group, each having a positive refractive power, arranged in this order from the object side to the image side, wherein the distance between adjacent lens groups changes during focusing, wherein the front lens group includes the largest air gap in the optical system, For focusing, the front lens group and the rear lens group do not move, the intermediate group includes two or more focus lens groups that move independently of each other for focusing; The focus sensitivity B of each focus lens group is expressed as follows: the lateral magnification of the focus lens group is βf, and the combined lateral magnification of all lenses arranged on the image side of the focus lens group is βr. B=(1-β&) ２ )br ２ and the smallest absolute value of the focus sensitivity B of each of the two or more focus lens groups is Bab_min, and the maximum F-number of the optical system is Fno. 0.10≦Bab_min / Fno≦0.95 An optical system characterized by satisfying the following conditions:

2. When the length on the optical axis from the lens surface closest to the object side of the optical system to the image plane is OTL and the focal length of the optical system is f, 0.45≦OTL / f≦1.20 2. The optical system according to claim 1, wherein the following condition is satisfied:

3. When the smallest absolute value of the focal lengths of the two or more focus lens groups is defined as fab_min, 0.06≦fab_min / f≦0.60 2. The optical system according to claim 1, wherein the following condition is satisfied:

4. When the largest absolute value of the focal lengths of the two or more focus lens groups is defined as fab_max, 0.10≦fab_max / f≦2.00 2. The optical system according to claim 1, wherein the following condition is satisfied:

5. When the length of the maximum air gap on the optical axis is Dmax, 0.15≦Dmax / OTL≦0.60 2. The optical system according to claim 1, wherein the following condition is satisfied:

6. When the focal length of the front lens group is f1, 0.2≦f1 / f≦0.8 2. The optical system according to claim 1, wherein the following condition is satisfied:

7. the optical system includes an aperture stop that determines an F-number; 2. The optical system according to claim 1, wherein two of the two or more focus lens groups are arranged closer to the image side than the aperture stop.

8. the optical system includes an aperture stop that determines an F-number; When the distance on the optical axis from the aperture diaphragm to the lens surface of the focus lens group farthest from the aperture diaphragm among the two or more focus lens groups is defined as Df_max, 0.01≦|Df_max| / OTL≦0.15 2. The optical system according to claim 1, wherein the following condition is satisfied:

9. When the air-equivalent length on the optical axis from the lens surface closest to the image side of the optical system to the image plane is BF and the maximum image height is IH, 1.3≦BF / IH≦5.0 2. The optical system according to claim 1, wherein the following condition is satisfied:

10. When the largest absolute value of the focus sensitivities of the two or more focus lens groups is denoted by Bab_max, 0.5≦Bab_max / Fno≦2.0 2. The optical system according to claim 1, wherein the following condition is satisfied:

11. When the focal length of the object-side partial lens unit among the partial lens units located on the object side and the image side with the maximum air gap in between in the front lens unit is denoted by f1a, 0.2≦f1a / f≦1.0 2. The optical system according to claim 1, wherein the following condition is satisfied:

12. 12. The optical system according to claim 11, wherein the object-side partial lens group is composed of one or two positive lenses.

13. 2. The optical system according to claim 1, wherein the two or more focus lens groups all have negative refractive power.

14. the intermediate group is composed of two adjacent focus lens groups each having negative refractive power, 2. The optical system according to claim 1, wherein the two focus lens groups move toward the image side during focusing from infinity to a close distance.

15. the intermediate group is composed of a focus lens group with positive refractive power, an aperture stop, and two focus lens groups with negative refractive power, arranged in this order from the object side to the image side; 2. The optical system according to claim 1, wherein, during focusing from infinity to a close distance, the focus lens group having positive refractive power moves toward the object side, and the two focus lens groups having negative refractive power move toward the image side.

16. 2. The optical system according to claim 1, wherein at least a portion of the rear lens group moves relative to the optical axis for optical vibration reduction.

17. An optical system according to any one of claims 1 to 16; and an image sensor that captures an image of a subject through the optical system.

Images