Optical system and imaging apparatus having the same

Abstract

To provide an optical system that suppresses aberration and a change in angle of view occurring in focusing despite its small size.SOLUTION: An optical system has a first lens group, a second lens group having a negative refractive power, a third lens group, and a fourth lens group having a positive refractive power, which are arranged in order from an object side to an image side, wherein the interval between the adjacent lens groups changes in focusing. The optical system has an aperture stop between the second lens group and the fourth lens group. In focusing from infinity to the closest distance, the second lens group moves to the image side, and the fourth lens group moves to the object side. The optical system satisfies predetermined conditional expressions.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an optical system suitable for use in imaging devices such as digital video cameras, digital still cameras, broadcast cameras, and cameras for silver halide film. [Background technology]

[0002] In recent years, optical systems used in image pickup apparatuses are required to be compact and to perform high-speed focusing.

[0003] Therefore, as a compact configuration for reducing the weight of the lens groups that move during focusing while suppressing the fluctuation of aberrations that occur during focusing, a system in which a plurality of lens groups move during focusing is known.

[0004] Patent Document 1 discloses an optical system in which a second lens group and a fourth lens move during focusing. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2022-140076 A Summary of the Invention [Problem to be solved by the invention]

[0006] The optical system of Patent Document 1 is composed of a first lens group with positive refractive power, a second lens group with negative refractive power, a third lens group with positive refractive power, a fourth lens group with positive refractive power, and a fifth lens group with negative refractive power, which are arranged in this order from the object side to the image side. However, the surface closest to the object of the second lens group that moves during focusing faces the object side as a concave surface, and has a small absolute value of the radius of curvature, or the surface closest to the object of the fourth lens group faces the object side as a convex surface, and has a small radius of curvature. As a result, the off-axis light rays are greatly bent by the lens surface described above, and the fluctuation of the angle of view that occurs during focusing, so-called breathing, becomes large.

[0007] SUMMARY OF THE PRESENT EMBODIMENTS An object of the present invention is to provide an optical system that is compact and yet suppresses aberrations and fluctuations in the angle of view that occur during focusing. [Means for solving the problem]

[0008] An optical system according to one embodiment of the present invention has, arranged in order from an object side to an image side, a first lens group, a second lens group having negative refractive power, a third lens group, and a fourth lens group having positive refractive power, in which a distance between adjacent lens groups changes during focusing, the optical system has an aperture stop between the second lens group and the fourth lens group; During focusing from infinity to a close distance, the second lens group moves toward the image side, and the fourth lens group moves toward the object side, Let R21 be the radius of curvature of the surface of the second lens group closest to the object side, R22 be the radius of curvature of the surface of the second lens group closest to the image side, R41 be the radius of curvature of the surface of the fourth lens group closest to the object side, and R42 be the radius of curvature of the surface of the fourth lens group closest to the image side. 0.90<(R21+R22) / (R21-R22)<4.00 -10.00<(R41+R42) / (R41-R42)<-2.00 The present invention is characterized in that the following conditional expression is satisfied: Effect of the Invention

[0009] According to the present invention, it is possible to provide an optical system that is compact and yet suppresses aberrations and fluctuations in the angle of view that occur during focusing. [Brief description of the drawings]

[0010] [Figure 1] 1 is a cross-sectional view of the lens when focusing at infinity in the optical system of Example 1. [Diagram 2] In the optical system of Example 1, (A) is an aberration diagram when focusing at infinity, and (B) is an aberration diagram when focusing at a close distance. [Diagram 3] 1 is a cross-sectional view of a lens when focusing at infinity in the optical system of Example 2. [Figure 4] In the optical system of Example 2, (A) is an aberration diagram when focusing at infinity, and (B) is an aberration diagram when focusing at a close distance. [Diagram 5] 1 is a cross-sectional view of a lens when focusing at infinity in the optical system of Example 3. [Figure 6] In the optical system of Example 3, (A) is an aberration diagram when focusing at infinity, and (B) is an aberration diagram when focusing at a close distance. [Figure 7] 1 is a cross-sectional view of the lens when focusing at infinity in the optical system of Example 4. [Figure 8] In the optical system of Example 4, (A) is an aberration diagram when focusing at infinity, and (B) is an aberration diagram when focusing at a close distance. [Figure 9] 13 is a cross-sectional view of the lens when focusing at infinity in the optical system of Example 5. [Figure 10] In the optical system of Example 5, (A) is an aberration diagram when focusing at infinity, and (B) is an aberration diagram when focusing at a close distance. [Figure 11] 13 is a cross-sectional view of the lens when focusing at infinity in the optical system of Example 6. [Figure 12] In the optical system of Example 6, (A) is an aberration diagram when focusing at infinity, and (B) is an aberration diagram when focusing at a close distance. [Figure 13] 13 is a cross-sectional view of the lens when focusing at infinity in the optical system of Example 7. [Figure 14] In the optical system of Example 7, (A) is an aberration diagram when focusing at infinity, and (B) is an aberration diagram when focusing at a close distance. [Figure 15] Diagram showing flare cut aperture placement [Figure 16] Schematic diagram showing an imaging device DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of an optical system and an image pickup apparatus having the same according to the present invention will be described with reference to the accompanying drawings.

[0012] 1, 3, 5, 7, 9, 11, and 13 are lens cross-sectional views when focusing at infinity in the optical system L0 of Examples 1 to 7. The optical system L0 of each Example is an optical system used in imaging devices such as digital video cameras, digital still cameras, broadcast cameras, silver halide film cameras, surveillance cameras, and vehicle-mounted cameras.

[0013] In each lens cross-sectional view, the left side is the object side and the right side is the image side. The optical system L0 of each embodiment may be used as a projection lens for a projector, etc. In this case, the left side is the screen side and the right side is the projected image side.

[0014] The optical system L0 of each embodiment has a first lens group L1, a second lens group L2 with negative refractive power, a third lens group L3, and a fourth lens group L4 with positive refractive power, which are arranged in this order from the object side to the image side, and the interval between adjacent lens groups changes during focusing. Each lens group may be composed of one lens or multiple lenses. The lens group may also include an aperture stop. In addition, when a lens element A that moves during image blur correction is arranged, the lens element A is considered to be included in the lens group.

[0015] Here, a lens element refers to one lens or multiple lenses.

[0016] The solid arrows pointing downward in each lens cross-sectional view represent the movement locus of each lens group during focusing from infinity to a close distance.

[0017] In each lens cross-sectional view, SP is an aperture stop. IP is an image plane, and when the optical system L0 of each embodiment is used in a digital still camera or digital video camera, the imaging surface of a solid-state image sensor (photoelectric conversion element) such as a CCD sensor or CMOS sensor is disposed thereon. When the optical system L0 of each embodiment is used as a photographic optical system for a silver halide film camera, a photosensitive surface equivalent to the film surface is disposed on the image plane IP.

[0018] GB is an optical block equivalent to an optical filter, a face plate, a crystal low-pass filter, an infrared cut filter, etc.

[0019] 2(A), 4(A), 6(A), 8(A), 10(A), 12(A), and 14(A) are aberration diagrams when focusing at infinity in the optical systems of Examples 1 to 7, respectively.

[0020] 2(B), 4(B), 6(B), 8(B), 10(B), 12(B), and 14(B) are aberration diagrams when focusing at close range in the optical systems of Examples 1 to 7, respectively.

[0021] In the spherical aberration diagram, Fno is the F-number, the solid line shows the amount of spherical aberration for the d-line (wavelength 587.6 nm) and the dashed line shows the amount of spherical aberration for the g-line (wavelength 435.8 nm). In the astigmatism diagram, the solid line shows the amount of aberration on the sagittal image plane, and the dashed line shows the amount of aberration on the meridional image plane. The distortion aberration diagram shows the amount of distortion aberration for the d-line. The chromatic aberration diagram shows the amount of lateral chromatic aberration for the g-line. ω is the half angle of view (°).

[0022] 15 is a diagram showing the arrangement of flare cut diaphragms for blocking light rays in the optical system L0 of Example 2. FC1 denotes a flare cut diaphragm arranged in the first lens unit L1, and FC4 denotes a flare cut diaphragm arranged in the fourth lens unit L4.

[0023] Next, the characteristic configuration of the optical system of each embodiment will be described.

[0024] The optical system L0 in each embodiment has, in order from the object side to the image side, a first lens group L1, a second lens group L2 with negative refractive power, a third lens group L3, and a fourth lens group L4 with positive refractive power, and the spacing between adjacent lens groups changes during focusing. The movement of the multiple lens groups during focusing suppresses fluctuations in various aberrations that occur during focusing.

[0025] Also, when focusing from infinity to a close distance, the second lens group L2 moves toward the image side, and the fourth lens group L4 moves toward the object side. The second lens L2 and the fourth lens group L4, which have refractive powers with different signs, move so that the distance on the optical axis between the second lens group L2 and the fourth lens group L4 becomes smaller. As a result, when focusing from infinity to a close distance, the fluctuation in the height of off-axis light rays incident on each lens group is suppressed, and the fluctuation in the angle of view that occurs when focusing from infinity to a close distance is suppressed.

[0026] Moreover, it is preferable that the optical system L0 in each embodiment satisfies the following conditional expression. 0.90<(R21+R22) / (R21-R22)<4.00...(1) -10.00<(R41+R42) / (R41-R42)<-2.00...(2)

[0027] Here, the radius of curvature of the surface of the second lens group L2 closest to the object side is R21, the radius of curvature of the surface of the second lens group L2 closest to the image side is R22, the radius of curvature of the surface of the fourth lens group L4 closest to the object side is R41, and the radius of curvature of the surface of the fourth lens group L4 closest to the image side is R42.

[0028] Conditions (1) and (2) are intended to suppress aberrations and fluctuations in the angle of view that occur during focusing.

[0029] If the upper limit of conditional expression (1) is exceeded, the surface closest to the image side of the second lens group L2 will be concave toward the image side, and the radius of curvature will be small. As a result, fluctuations in coma aberration and the like that occur during focusing are likely to become large. If the lower limit of conditional expression (1) is not reached, the surface closest to the object side of the second lens group L2 will be concave toward the object side, and the absolute value of the radius of curvature will be small. As a result, off-axis rays will be significantly bent by the surface closest to the object side of the second lens group L2, and fluctuations in the angle of view that occur during focusing are likely to become large.

[0030] When the upper limit of conditional expression (2) is exceeded, the surface closest to the object in the fourth lens group L4 faces a concave surface toward the object side, and the absolute value of the radius of curvature becomes small. As a result, it becomes difficult to suppress fluctuations in coma aberration and the like that occur during focusing. When the lower limit of conditional expression (2) is not reached, the surface closest to the image in the fourth lens group L4 faces a convex surface toward the image side, and the absolute value of the radius of curvature becomes large. As a result, off-axis rays are significantly bent by the surface closest to the image in the fourth lens group L4, and fluctuations in the angle of view that occur during focusing tend to become large.

[0031] It is preferable that at least one of the upper limit and the lower limit of the numerical range of conditional expression (1) is set to the numerical value of the following conditional expression (1a). 1.00<(R21+R22) / (R21-R22)<3.80...(1a) -9.60<(R41+R42) / (R41-R42)<-2.05...(2a)

[0032] Furthermore, it is preferable that at least one of the upper limit and the lower limit of any numerical range of conditional formula (1) satisfies the range of the following conditional formula (1b). 1.05<(R21+R22) / (R21-R22)<3.70...(1b) -9.30<(R41+R42) / (R41-R42)<-2.08...(2b)

[0033] In the optical system L0 of each embodiment, it is preferable that the fifth lens unit L5 has a positive lens and a negative lens, thereby suppressing fluctuations in lateral chromatic aberration and the like that occur during focusing.

[0034] In addition, in the optical system L0 of each embodiment, the surface closest to the object side of the second lens group L2 has a convex shape toward the object side, and the surface closest to the image side of the second lens group L2 has a concave shape toward the image side. It is also preferable that the radius of curvature of the surface closest to the image side of the second lens group L2 is smaller than the radius of curvature of the surface closest to the object side of the second lens group L2. This makes the surface closest to the object side and the surface closest to the image side of the second lens group L2 concentric with the aperture, suppressing the fluctuation of the angle of view that occurs during focusing in the second lens group L2.

[0035] The surface of the fourth lens group L4 closest to the object side has a concave shape toward the object side, and the surface of the fourth lens group L4 closest to the image side has a convex shape toward the image side. It is preferable that the absolute value of the radius of curvature of the surface of the fourth lens group L4 closest to the object side is smaller than the absolute value of the radius of curvature of the surface of the fourth lens group L4 closest to the image side. This makes the surface of the fourth lens group L4 closest to the object side and the surface of the fourth lens group L4 closest to the image side concentric with the aperture, suppressing the fluctuation of the angle of view that occurs during focusing in the fourth lens group L4.

[0036] Next, a more preferable configuration of the optical system L0 in each embodiment will be described.

[0037] During image blur correction, it is preferable that all or some of the lens elements of the third lens group L3 move so as to include a component in a direction perpendicular to the optical axis. In order to obtain a desired amount of peripheral light during image blur correction, the diameter of the lens that moves during image blur correction is increased. Therefore, it is possible to prevent the optical system L0 from becoming large in the radial direction by moving the lens elements of the third lens group L3, which have a relatively small radial size.

[0038] In addition, when the third lens group L3 has a positive refractive power, it is easy to arrange the principal point of the optical system L0 on the object side, and it is easy to reduce the overall lens length. In addition, when the third lens group L3 has a negative refractive power, it is easy to correct spherical aberration.

[0039] It is preferable that the optical system L0 in each embodiment satisfies one or more of the following conditional expressions. -3.5 <M2 / M4<-0.5···(3) -7.00 <f2 / f4<-2.50···(4) 0.05<|f1 / f2|<0.50 (5) 2.0<|fR / f|<500.0 (6) 0.30 <BF / f<1.50···(7) 0.45 <Da / TL<0.70···(8) 0.15 <D4 / Da<0.35···(9) 0.70<(1-β4 2 ) × βR 2 <3.00···(10) 70.0<ν4p<96.0 (11)

[0040] Here, M2 and M4 are the amounts of movement of the second lens unit L2 and the fourth lens unit L4, respectively, when focusing from infinity to an object distance where the lateral magnification of the entire system is −0.1, where the sign of the amount of movement toward the image side is positive.

[0041] f4 is the focal length of the fourth lens group L4, f2 is the focal length of the second lens group L2, and f1 is the focal length of the first lens group L1. f is the focal length of the entire system. fR is the focal length of the lens group arranged closest to the image side in the optical system L0. BF is the back focus when focusing to infinity.

[0042] The optical system L0 has an aperture stop SP. Da is the distance on the optical axis from the aperture stop SP to the image plane when focusing at infinity. TL is the total lens length of the optical system L0. D4 is the distance on the optical axis from the aperture stop SP to the surface of the fourth lens group L4 closest to the object.

[0043] β4 is the lateral magnification of the fourth lens unit L4 when focusing at infinity, and βR is the combined lateral magnification of all lens units arranged on the image side of the fourth lens unit L4 when focusing at infinity.

[0044] ν4p is the Abbe number of at least one positive lens disposed in the fourth lens unit L4.

[0045] Next, the technical meanings of the above-mentioned conditional expressions (3) to (11) will be explained.

[0046] If the upper limit of conditional expression (3) is exceeded and the amount of movement of the fourth lens group L4 becomes too large, the fluctuation in the height of off-axis light rays incident on each lens group becomes large when focusing from infinity to a close distance. As a result, the fluctuation in the angle of view that occurs when focusing from infinity to a close distance becomes large, which is not preferable. If the lower limit of conditional expression (3) is exceeded, the amount of movement of the second lens group L2 becomes too large and the fluctuation in the height of off-axis light rays incident on each lens group becomes large when focusing from infinity to a close distance. As a result, the fluctuation in the angle of view that occurs when focusing from infinity to a close distance becomes large, which is not preferable.

[0047] If the upper limit of conditional expression (4) is exceeded, the refractive power of the second lens group L2 becomes too strong. As a result, the fluctuation in the angle of view that occurs during focusing becomes too large, which is undesirable. If the lower limit of conditional expression (4) is exceeded, the refractive power of the fourth lens group L4 becomes too strong. As a result, the fluctuation in the angle of view and the curvature of field that occurs during focusing becomes too large, which is undesirable.

[0048] If the upper limit of conditional expression (5) is exceeded, the refractive power of the first lens group L1 becomes too weak. As a result, the overall lens length becomes long and the radial size of the first lens group L1 becomes large, which is undesirable. If the lower limit of conditional expression (5) is not reached, the refractive power of the first lens group L1 becomes too strong. As a result, spherical aberration, chromatic aberration of magnification, and the like generated in the first lens group L1 become too large and difficult to correct.

[0049] If the upper limit of conditional expression (6) is exceeded, the refractive power of the lens group arranged closest to the image side in the optical system L0 becomes too weak. As a result, it becomes difficult for the lens group arranged closest to the image side in the optical system L0 to suppress the field curvature generated in each lens group arranged in the optical system L0. If the lower limit of conditional expression (6) is not reached, the refractive power of the lens group arranged closest to the image side becomes too strong. As a result, it becomes difficult to correct the chromatic aberration of magnification generated in the lens group arranged closest to the image side.

[0050] If the back focus becomes long by exceeding the upper limit of conditional expression (7), the overall lens length becomes too long.If the back focus becomes short by falling below the lower limit of conditional expression (7), when an image sensor is disposed, ghost light generated by reflection between the image sensor and the image-side surface of the lens disposed closest to the image side is likely to be imaged by the image sensor, which is undesirable.

[0051] If the upper limit of conditional expression (8) is exceeded and the aperture stop SP is disposed on the object side in the optical system L0, the radial size of the lens group disposed closest to the image side becomes large, which is not preferable. If the lower limit of conditional expression (8) is exceeded and the aperture stop SP is disposed on the image side in the optical system L0, the radial size of the first lens group L1 becomes large, which is not preferable.

[0052] If the upper limit of conditional expression (9) is exceeded and the distance on the optical axis from the aperture stop SP to the surface of the fourth lens group L4 closest to the object becomes long, the fourth lens group L4 will be disposed at a position where the height from the optical axis of off-axis rays is high, which is undesirable because it increases the fluctuation in the angle of view that occurs during focusing.

[0053] If the lower limit of conditional expression (9) is exceeded and the distance on the optical axis from the aperture stop SP to the surface of the fourth lens group L4 closest to the object becomes short, the fourth lens group L4 will be disposed at a position where the height of the axial light beam from the optical axis is high, which undesirably increases the fluctuation of spherical aberration that occurs during focusing.

[0054] Conditional expression (10) relates to the position sensitivity of the fourth lens group L4. In other words, it expresses the amount of change in the image plane position when the fourth lens group L4 is moved by a unit amount in the optical axis direction. If the upper limit of conditional expression (10) is exceeded and the position sensitivity of the fourth lens group L4 becomes large, the refractive power of the fourth lens group L4 becomes too strong. As a result, the fluctuations in various aberrations that occur during focusing become too large, which is undesirable.

[0055] If the lower limit of conditional expression (10) is not reached and the position sensitivity of the fourth lens group L4 becomes small, the amount of movement of the second lens group L2 becomes too large in order to focus from infinity to a desired object distance, resulting in a long overall lens length.

[0056] If the upper limit of conditional expression (11) is exceeded, the refractive index of at least one positive lens arranged in the fourth lens group L4 becomes too low, making it difficult to correct field curvature, etc. If the lower limit of conditional expression (11) is exceeded, the Abbe number of at least one positive lens arranged in the fourth lens group L4 becomes too small, making it difficult to correct lateral chromatic aberration.

[0057] It is more preferable to set at least one of the upper and lower limits of the conditional expressions (3) to (11) within the following numerical ranges. -3.3 <M2 / M4<-0.6···(3a) -6.95 <f2 / f4<-2.55···(4a) 0.10<|f1 / f2|<0.47 (5a) 2.1<|fR / f|<450.0 (6a) 0.35 <BF / f<1.30···(7a) 0.50 <Da / TL<0.67···(8a) 0.17 <D4 / Da<0.33···(9a) 0.75<(1-β4×β4)×βR×βR<2.80 (10a) 72.0<ν4p<95.5 (11a)

[0058] Moreover, it is more preferable to set at least one of the upper and lower limits of the conditional expressions (2) to (10) to the following numerical ranges. -3.1 <M2 / M4<-0.7···(3b) -6.90 <f2 / f4<-2.60···(4b) 0.15<|f1 / f2|<0.45 (5b) 2.2<|fR / f|<400.0 (6b) 0.40 <BF / f<1.20···(7b) 0.55 <Da / TL<0.65···(8b) 0.20 <D4 / Da<0.31···(9b) 0.78<(1-β4 2 ) × βR 2 <2.50···(10b) 75.0<ν4p<95.0 (11b)

[0059] Next, the configuration of the optical system L0 in each embodiment will be described in detail. From embodiment 2 onwards, differences from embodiment 1 will be mainly described.

[0060] [Example 1] The optical system L0 of the first embodiment is composed of a positive, negative, positive, positive, negative lens group arranged in that order from the object side to the image side, and the interval between adjacent lens groups changes during focusing. By appropriately arranging the lens groups having positive refractive power and the lens groups having negative refractive power, the fluctuation of various aberrations that occur during focusing is suppressed.

[0061] During focusing from infinity to close range, the second lens unit L2 moves toward the image side. The fourth lens unit L4 moves toward the object side to suppress fluctuations in the height of off-axis rays incident on each lens unit, thereby suppressing fluctuations in the angle of view that occur when focusing from infinity to a close distance.

[0062] In addition, the second lens unit L2 is composed of a negative meniscus lens with a convex surface facing the object side, which achieves both weight reduction and suppression of fluctuations in spherical aberration that occur during focusing.

[0063] [Example 2] The fourth lens unit L4 in the second embodiment has a negative meniscus lens with a convex surface facing the image side, which makes it easier to suppress fluctuations in the curvature of field that occur during focusing.

[0064] [Example 3] The optical system L0 of the third embodiment has a negative meniscus lens with a convex surface facing the image side, which is arranged closest to the image side, making it easy to correct the curvature of field.

[0065] [Example 4] The optical system L0 of the fourth embodiment is composed of negative, negative, positive, positive, negative lens groups arranged in this order from the object side to the image side, and the interval between adjacent lens groups changes during focusing.

[0066] The first lens unit L1 in the fourth embodiment has a positive meniscus lens with a convex surface facing the object side, which makes it easier to correct spherical aberration.

[0067] [Example 5] The optical system L0 of the fifth embodiment is composed of positive, negative, positive, positive, negative, negative lens groups arranged in this order from the object side to the image side, and the interval between adjacent lens groups changes during focusing.

[0068] During focusing from infinity to close range, the second lens unit L2 moves toward the image side. The fourth lens unit L4 moves toward the object side, and the fifth lens unit L5 moves along a convex locus toward the object side. When focusing from infinity to a close distance, the movement of the three lens units makes it easier to suppress fluctuations in various aberrations.

[0069] Furthermore, by making the refractive powers of the fifth lens group L5 and the sixth lens group L6 negative, the principal point of the optical system L0 is located on the object side, making it easier to reduce the overall lens length.

[0070] [Example 6] The optical system L0 of the sixth embodiment is composed of positive, negative, positive, positive, negative, positive lens groups arranged in this order from the object side to the image side, and the spacing between adjacent lens groups changes during focusing.

[0071] During focusing from infinity to close range, the second lens unit L2 moves toward the image side. The fourth lens unit L4 moves toward the object side, and the fifth lens unit L5 moves along a convex locus toward the object side. When focusing from infinity to a close distance, the movement of the three lens units makes it easier to suppress fluctuations in primary aberrations.

[0072] In addition, the fifth lens group L5 and the sixth lens group L6 have refractive powers with different signs, which makes it easier to cancel out lateral chromatic aberration and field curvature occurring in the fifth lens group L5 and the sixth lens group L6.

[0073] [Example 7] The optical system L0 of the seventh embodiment is composed of positive, negative, positive, positive, positive lens groups arranged in this order from the object side to the image side, and the interval between adjacent lens groups changes during focusing.

[0074] The fifth lens group L5 has a positive refractive power, which reduces the angle of incidence of light rays with respect to the normal direction of the image plane, making it easier to suppress color shift (color shading) that occurs when an image sensor is disposed.

[0075] In addition, the positive lens and the negative lens constituting the cemented lens arranged in the optical system L0 of each embodiment are preferably bonded with an adhesive having an axial thickness of 0.005 mm or more and 0.050 mm or less. If it is less than 0.005 mm, the lenses are likely to peel off, and if it is more than 0.030 mm, the axial distance from the surface of the cemented lens closest to the object to the surface closest to the image becomes long, resulting in a long overall lens length. More preferably, it is preferable to satisfy 0.008 mm or more and 0.020 mm or less.

[0076] Furthermore, the second lens group L2 may have two or more lenses. When the second lens group L2 has two or more lenses, it becomes easier to suppress fluctuations in spherical aberration and the like that occur in the second lens group L2 during focusing.

[0077] At least one lens arranged in the optical system L0 of each embodiment is provided with an anti-reflection film for preventing reflection, and the anti-reflection film is preferably composed of a plurality of layers. Here, when the refractive index of the layer closest to the air interface with respect to the d-line is Nd, it is preferable that the anti-reflection film PC has Nd of 1.32 or less. By making Nd 1.32 or less, the difference in refractive index with air can be reduced, so that the reflectance of light can be further reduced, and ghosts can be reduced.

[0078] Specific examples of the configuration of the antireflection film PC include, but are not limited to, multilayer films formed using a wet method, as described in JP-A-2012-230211, JP-A-2014-95877, etc. More preferably, Nd is set to 1.30 or less to further reduce ghosts.

[0079] Here, among the negative lenses arranged in optical system L0 with their concave surfaces facing the image side, it is preferable to provide an anti-reflection coating PC on the image side surface of lens A arranged closest to the object, or lens B arranged second closest to the object. The image side surfaces of lenses A and B tend to have large open angles, and light reflected within a large open angle range tends to be reflected at a large angle with respect to the normal direction of the lens surface, resulting in a high reflectance.

[0080] In addition, light reflected by a negative lens with a concave surface facing the image side tends to be focused on the image plane, making ghosting more noticeable. Therefore, ghosting can be reduced by applying an anti-reflection coating PC to the image-side surface of lens A or lens B.

[0081] In each embodiment, it is preferable to provide a flare cut diaphragm that blocks light rays. Fig. 15 is a diagram showing the arrangement of a flare cut diaphragm in the optical system L0 of the embodiment 2. A preferable configuration for providing a flare cut diaphragm will be described with reference to Fig. 15.

[0082] It is preferable to dispose at least one flare cut aperture FC1 in the first lens group L1, which can appropriately block the lower line of off-axis marginal rays entering the first lens group L1 from below on the object side in FIG. 15, thereby reducing coma aberration.

[0083] It is preferable to dispose at least one flare cut aperture FC4 in the fourth lens group L4, which can appropriately block the upper ray of the off-axis marginal ray entering the first lens group L1 from below on the object side in FIG. 15, thereby reducing coma aberration.

[0084] The preferable arrangement of the flare cut diaphragm described above is not limited to that in the first embodiment, and coma aberration can be reduced in the second to seventh embodiments by using a similar arrangement.

[0085] Numerical examples 1 to 7 corresponding to the first to seventh embodiments, respectively, are shown below.

[0086] In the surface data of each numerical example, r represents the radius of curvature of each optical surface, and d (mm) represents the axial spacing (distance on the optical axis) between the mth surface and the (m+1)th surface. Here, m is the surface number counted from the light incident side. In addition, nd represents the refractive index of each optical member with respect to the d-line, and νd represents the Abbe number of the optical member. The Abbe number νd of a certain material is given by Nd, NF, and NC, respectively, when the refractive indices at the Fraunhofer lines d-line (wavelength 587.6 nm), F-line (wavelength 486.1 nm), C-line (wavelength 656.3 nm), and g-line (wavelength 435.8 nm) are: νd=(Nd-1) / (NF-NC) It is expressed as:

[0087] BF is the back focus.

[0088] If the optical surface is aspheric, a * symbol is added to the right of the surface number. The aspheric shape is expressed as follows, where X is the displacement from the apex 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 the aspheric coefficients of each order: 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 each aspheric coefficient is "×10± XX " It means.

[0089] The lens arrangement length represents the distance on the optical axis from the surface closest to the object side to the surface closest to the image side in each lens group.

[0090] In addition, the various data shows the distance on the optical axis between adjacent lens groups when the lateral magnification of the entire system is 0.0x (INF), -0.1x, close range, etc. INF represents infinity.

[0091] [Numerical Example 1] Unit: mm Surface Data Surface number rd nd νd 1 66.406 1.30 1.59349 67.0 2* 23.697 15.11 3 -29.349 1.20 1.49815 62.7 4 73.097 2.32 5 85.690 10.64 1.76385 48.5 6 -23.402 1.30 1.85478 24.8 7 -48.343 0.20 8 58.989 4.89 2.00098 28.6 9 -151.967 (variable) 10 163.200 1.50 1.61314 44.3 11 51.990 (variable) 12(Aperture) ∞ 5.44 13 226.152 6.34 1.76385 48.5 14 -22.862 1.10 1.72047 34.7 15 -412.253 (variable) 16 -30.434 5.20 1.49700 81.5 17 -16.763 1.00 1.77047 29.7 18 -269.583 2.09 19 53.782 7.99 1.49700 81.5 20 -31.544 0.53 21* 162.397 6.89 1.80400 46.5 22* -44.046 (variable) 23 118.583 5.99 1.92286 20.9 24 -61.303 1.74 1.77047 29.7 25 45.530 5.00 26 -77.584 1.76 1.39156 32.0 27 145.502 12.97 28 ∞ 1.00 1.51633 64.1 29∞1.00 Image plane ∞ Aspheric Data 2nd side K = 0.00000e+00 A 4= 6.14218e-07 A 6= 5.28540e-09 A 8=-2.21840e-11 A10= 6.93534e-14 Page 21 K = 0.00000e+00 A 4=-8.89677e-06 A 6=-5.76603e-09 A 8= 2.46003e-11 A10=-1.08980e-13 A12= 1.29068e-16 Page 22 K = 0.00000e+00 A 4= 2.85669e-06 A 6=-6.12974e-09 A 8= 2.49444e-11 A10=-5.50422e-14 A12= 4.81648e-17 Various data Focal length 28.80 F-number 1.46 Angle of view: 33.89 Lens length 119.74 BF 14.63 Lateral magnification of the entire system 0.00(INF) -0.026 -0.10 -0.19 d 9 0.60 1.24 2.90 4.65 d11 7.35 6.71 5.05 3.30 d15 6.43 5.95 4.53 2.52 d22 1.20 1.68 3.10 5.11 Lens Group Data Lens group Focal length Lens length L1 1 38.08 36.95 L2 10 -125.07 1.50 L3 12 143.42 12.88 L4 16 35.48 23.71 L5 23 -72.03 28.46

[0092] [Numerical Example 2] Unit: mm Surface Data Surface number rd nd νd 1 72.978 1.30 1.59349 67.0 2* 19.349 14.73 3 -34.011 1.50 1.59678 66.9 4 45.153 2.74 5 50.272 13.45 1.76385 48.5 6 -23.235 1.30 1.85478 24.8 7 -52.852 0.72 8 54.430 3.79 2.00107 28.9 9 -332.088 (variable) 10 800.000 1.50 1.61120 44.5 11 72.250 (variable) 12 (Aperture) ∞ 1.86 13 182.727 3.29 1.76385 48.5 14 -64.432 1.75 1.72047 34.7 15 -83.994 (variable) 16 -28.776 4.69 1.49700 81.5 17 -15.444 1.00 1.77047 29.7 18 246.210 2.00 19 41.743 7.52 1.49700 81.5 20 -28.002 0.20 21* 71.189 6.98 1.80400 46.5 22* -41.928 (variable) 23 58.473 3.10 1.92286 20.9 24 384.629 1.25 1.77047 29.7 25 24.024 5.01 26 -2493.166 2.00 1.77043 29.7 27 692.822 13.78 28 ∞ 1.00 1.51633 64.1 29∞1.00 Image plane ∞ Aspheric Data 2nd side K = 0.00000e+00 A 4=-1.54852e-06 A 6=-1.39851e-08 A 8= 4.03181e-11 A10=-1.18272e-13 Page 21 K = 0.00000e+00 A 4=-1.44287e-05 A 6=-1.34545e-08 A 8= 2.95087e-11 A10=-3.61239e-13 A12= 6.97332e-16 Page 22 K = 0.00000e+00 A 4= 5.35853e-06 A 6=-2.56320e-08 A 8= 1.20016e-10 A10=-4.84989e-13 A12= 8.09237e-16 Various data Focal length 20.63 F-number 1.46 Angle of view: 42.73 Lens length 112.63 BF 15.44 Lateral magnification of the entire system 0.00(INF) -0.020 -0.10 -0.14 d 9 0.60 1.06 2.94 3.79 d11 5.19 4.73 2.84 2.00 d15 8.53 8.30 7.29 6.79 d22 1.20 1.43 2.43 2.94 Lens Group Data Lens group Focal length Lens length L1 1 42.82 39.54 L2 10 -130.05 1.50 L3 12 75.09 6.91 L4 16 28.27 22.39 L5 23 -58.79 26.13

[0093] [Numerical Example 3] Unit: mm Surface Data Surface number rd nd νd 1 72.288 1.30 1.59349 67.0 2 21.526 13.44 3 -29.716 1.22 1.54814 45.8 4 57.813 3.61 5 84.776 10.56 1.76385 48.5 6 -23.162 1.30 1.85478 24.8 7 -45.112 0.19 8 60.450 4.94 2.00069 25.5 9 -152.845 (variable) 10 147.080 1.49 1.62004 36.3 11 60.717 (variable) 12(Aperture) ∞ 1.99 13 1242.125 7.29 1.76385 48.5 14 -21.123 1.09 1.72047 34.7 15 -166.674 (variable) 16 -33.613 5.21 1.49700 81.5 17 -15.879 1.00 1.77047 29.7 18 834.948 1.99 19 49.688 8.75 1.49700 81.5 20 -30.861 0.20 21* 80.138 7.00 1.80400 46.5 22* -47.206 (variable) 23 130.745 4.30 1.92286 20.9 24 -78.962 1.25 1.77047 29.7 25 44.799 4.93 26 -80.385 1.20 1.65412 39.7 27 -289.464 13.52 28 ∞ 1.00 1.51633 64.1 29∞1.00 Image plane ∞ Aspheric Data Page 21 K = 0.00000e+00 A 4=-7.68130e-06 A 6=-9.12882e-10 A 8= 2.65012e-11 A10=-7.89662e-14 A12= 1.31928e-16 Page 22 K = 0.00000e+00 A 4= 4.42473e-06 A 6=-2.12367e-09 A 8= 3.53558e-11 A10=-6.57718e-14 A12= 1.35297e-16 Various data Focal length 24.72 F-number 1.46 Angle of view: 37.14 Lens length 118.17 BF 15.18 Lateral magnification of the entire system 0.00(INF) -0.022 -0.10 -0.17 d 9 1.20 1.69 3.37 4.82 d11 8.91 8.41 6.73 5.28 d15 6.78 6.40 5.08 3.91 d22 1.85 2.23 3.55 4.73 Lens Group Data Lens group Focal length Lens length L1 1 38.50 36.56 L2 10 -167.88 1.49 L3 12 143.52 10.38 L4 16 31.67 24.14 L5 23 -72.41 26.19

[0094] [Numerical Example 4] Unit: mm Surface Data Surface number rd nd νd 1 47.721 1.30 1.59349 67.0 2* 21.373 13.33 3 -61.952 1.18 1.49700 81.5 4 31.860 4.92 5 1053.852 8.08 1.91082 35.2 6 -23.698 1.30 1.84666 23.9 7 -103.763 0.18 8 34.315 4.93 1.85478 24.8 9 47.457 (variable) 10 2234.784 1.44 1.61340 44.3 11 105.403 (variable) 12(Aperture) ∞ 1.44 13 72.289 7.46 1.90043 37.4 14 -29.201 1.49 1.54814 45.8 15 323.072 (variable) 16 -35.927 6.57 1.49700 81.5 17 -15.755 1.00 1.77047 29.7 18 -59.765 1.98 19 30.174 9.15 1.49700 81.5 20 -35.862 0.16 21* 245.125 5.40 1.80400 46.5 22* -44.909 (variable) 23 -306.228 2.58 1.92286 20.9 24 -63.551 2.01 1.77047 29.7 25 25.357 1.91 26 44.412 3.91 1.73800 32.3 27 141.498 19.03 28 ∞ 1.00 1.51633 64.1 29∞2.08 Image plane ∞ Aspheric Data 2nd side K = 0.00000e+00 A 4=-7.52192e-07 A 6=-6.39173e-09 A 8= 1.90775e-11 A10=-4.34826e-14 Page 21 K = 0.00000e+00 A 4=-1.59674e-05 A 6= 1.32646e-09 A 8=-1.63157e-10 A10= 1.83632e-12 A12=-4.38378e-15 Page 22 K = 0.00000e+00 A 4= 4.55728e-06 A 6=-5.06476e-09 A 8= 5.47838e-12 A10= 1.16038e-12 A12=-3.04625e-15 Various data Focal length 21.22 F-number 1.46 Angle of view: 41.03 Lens length 120.82 BF 21.77 Lateral magnification of the entire system 0.00(INF) -0.020 -0.10 -0.15 d 9 2.58 3.14 5.75 7.65 d11 6.89 6.33 3.71 1.82 d15 6.76 6.53 5.54 4.89 d22 1.11 1.34 2.33 2.97 Lens Group Data Lens group Focal length Lens length L1 1 -79.50 35.21 L2 10 -180.39 1.44 L3 12 44.73 10.39 L4 16 26.29 24.25 L5 23 -52.20 30.45

[0095] [Numerical Example 5] Unit: mm Surface Data Surface number rd nd νd 1 195.819 1.30 1.59349 67.0 2* 25.288 13.99 3 -26.717 1.20 1.51633 64.1 4 1357.161 1.46 5 -1541.751 9.96 1.76385 48.5 6 -24.641 1.30 1.85478 24.8 7 -37.622 0.20 8 43.194 4.87 1.91082 35.2 9 -6279.728 (variable) 10 68.044 1.50 1.61340 44.3 11 39.028 (variable) 12 (Aperture) ∞ 1.35 13 57.301 6.26 1.76385 48.5 14 -28.945 1.10 1.72047 34.7 15 78.466 (variable) 16 -38.636 4.09 1.49700 81.5 17 -17.611 1.00 1.77047 29.7 18 -124.360 2.87 19 44.078 8.67 1.49700 81.5 20 -36.107 0.20 21* 97.208 5.16 1.80400 46.5 22* -108.884 (variable) 23 -1166.557 6.00 1.91650 31.6 24 -38.579 1.74 1.59551 39.2 25 63.518 (variable) 26 -144.259 1.20 1.54072 47.2 27 38.210 4.61 1.90366 31.3 28 99.227 10.97 29 ∞ 1.00 1.51633 64.1 30∞1.00 Image plane ∞ Aspheric Data 2nd side K = 0.00000e+00 A 4= 5.82869e-08 A 6= 3.28093e-10 A 8=-7.30293e-12 A10= 1.73470e-14 Page 21 K = 0.00000e+00 A 4= 2.29294e-06 A 6=-2.98460e-09 A 8= 1.20199e-10 A10=-4.29392e-13 A12= 2.82932e-16 Page 22 K = 0.00000e+00 A 4= 1.40841e-05 A 6=-8.55175e-09 A 8= 1.99012e-10 A10=-6.29223e-13 A12= 4.48042e-16 Various data Focal length 27.52 F-number 1.46 Angle of view 34.12 Lens length 121.21 BF 12.63 Lateral magnification of the entire system 0.00(INF) -0.025 -0.10 -0.20 d 9 2.24 3.04 5.66 9.65 d11 12.92 12.12 9.49 5.50 d15 8.23 ​​7.60 5.84 3.70 d22 1.20 1.46 2.82 5.73 d25 3.98 4.34 4.74 3.98 Lens Group Data Lens group Focal length Lens length L1 1 46.28 34.28 L2 10 -152.19 1.50 L3 12 164.00 8.71 L4 16 41.15 21.98 L5 23 -566.31 7.74 L6 26 -309.77 17.77

[0096] [Numerical Example 6] Unit: mm Surface Data Surface number rd nd νd 1 364.760 1.30 1.59349 67.0 2* 26.392 13.61 3 -26.967 1.20 1.51633 64.1 4 535.718 1.59 5 -2988.087 10.39 1.76385 48.5 6 -24.893 1.30 1.85478 24.8 7 -37.779 0.20 8 44.621 4.86 1.91082 35.2 9 -2618.689 (variable) 10 75.335 1.50 1.61340 44.3 11 39.000 (variable) 12 (Aperture) ∞ 1.25 13 47.897 6.20 1.76385 48.5 14 -34.180 1.10 1.72047 34.7 15 65.262 (variable) 16 -37.971 4.08 1.49700 81.5 17 -17.944 1.00 1.77047 29.7 18 -142.210 2.80 19 47.678 8.51 1.49700 81.5 20 -34.054 0.20 21* 102.030 5.06 1.80400 46.5 22* -107.005 (variable) 23 -528.497 6.00 1.91650 31.6 24 -37.503 1.71 1.59551 39.2 25 59.447 (variable) 26 -63.467 1.20 1.54072 47.2 27 39.740 6.66 1.90043 37.4 28 -578.466 10.97 29 ∞ 1.00 1.51633 64.1 30∞1.00 Image plane ∞ Aspheric Data 2nd side K = 0.00000e+00 A 4=-2.77516e-07 A 6=-1.54577e-09 A 8= 6.44179e-13 A10= 7.64354e-16 Page 21 K = 0.00000e+00 A 4= 1.80120e-06 A 6=-4.51707e-09 A 8= 9.41454e-11 A10=-3.12742e-13 A12= 1.29042e-16 Page 22 K = 0.00000e+00 A 4= 1.25407e-05 A 6=-9.09304e-09 A 8= 1.59275e-10 A10=-4.78303e-13 A12= 2.76852e-16 Various data Focal length 27.55 F-number 1.46 Angle of view 34.09 Lens length 125.79 BF 12.63 Lateral magnification of the entire system 0.00(INF) -0.025 -0.10 -0.21 d 9 3.59 4.34 6.76 10.71 d11 12.62 11.87 9.45 5.50 d15 8.73 8.04 6.20 3.88 d22 1.20 1.46 2.85 6.05 d25 5.30 5.73 6.18 5.30 Lens Group Data Lens group Focal length Lens length L1 1 47.69 34.45 L2 10 -133.93 1.50 L3 12 146.07 8.55 L4 16 42.39 21.65 L5 23 -319.83 7.71 L6 26 463.88 19.83

[0097] [Numerical Example 7] Unit: mm Surface Data Surface number rd nd νd 1 599.457 1.30 1.59349 67.0 2* 28.774 12.78 3 -27.081 1.20 1.51633 64.1 4 219.970 1.75 5 803.402 10.37 1.76385 48.5 6 -24.961 1.30 1.85478 24.8 7 -37.785 0.20 8 45.294 5.02 1.91082 35.2 9 -1051.130 (variable) 10 91.363 1.50 1.61340 44.3 11 39.018 (variable) 12 (Aperture) ∞ 1.26 13 46.494 6.38 1.76385 48.5 14 -34.876 1.10 1.72047 34.7 15 63.458 (variable) 16 -35.902 4.00 1.49700 81.5 17 -18.127 1.00 1.77047 29.7 18 -175.857 2.00 19 48.068 9.65 1.49700 81.5 20 -33.486 0.20 21* 95.577 5.66 1.80400 46.5 22* -101.180 (variable) 23 -290.592 6.00 1.91650 31.6 24 -37.181 1.25 1.59551 39.2 25 63.256 5.00 26 -67.855 1.20 1.54072 47.2 27 35.261 7.56 1.90043 37.4 28 -578.466 10.97 29 ∞ 1.00 1.51633 64.1 30∞2.23 Image plane ∞ Aspheric Data 2nd side K = 0.00000e+00 A 4= 3.61761e-07 A 6=-6.66364e-10 A 8= 3.81905e-12 A10=-2.19217e-15 Page 21 K = 0.00000e+00 A 4= 2.67559e-06 A 6=-2.93730e-09 A 8= 6.58324e-11 A10=-1.79203e-13 A12=-8.74999e-18 Page 22 K = 0.00000e+00 A 4= 1.30939e-05 A 6=-7.05155e-09 A 8= 1.25332e-10 A10=-3.09303e-13 A12= 8.07445e-17 Various data Focal length 28.79 F-number 1.46 Angle of view: 32.90 Lens length 128.09 BF 13.86 Lateral magnification of the entire system 0.00(INF) -0.026 -0.10 -0.22 d 9 4.21 5.00 7.13 10.41 d11 11.70 10.91 8.78 5.50 d15 9.43 8.80 7.01 3.99 d22 1.20 1.83 3.62 6.63 Lens Group Data Lens group Focal length Lens length L1 1 46.32 33.93 L2 10 -112.24 1.50 L3 12 141.88 8.75 L4 16 42.91 22.51 L5 23 9800.00 32.98

[0098] Various values ​​in each numerical example are summarized in Table 1 below.

[0099] [Table 1]

[0100] [Imaging device] Next, an embodiment of a digital still camera (imaging device) using the optical system of the present invention as an imaging optical system will be described with reference to Fig. 16. In Fig. 16, 11 denotes an imaging optical system constituted by any of the optical systems described in Examples 1 to 7. 12 denotes an imaging element (photoelectric conversion element) such as a CCD sensor or CMOS sensor that is built into a camera body 10 and receives an optical image formed by the imaging optical system 11 and photoelectrically converts it. The camera body 10 may be a so-called single-lens reflex camera having a quick-turn mirror, or a so-called mirrorless camera having no quick-turn mirror.

[0101] In this way, by applying the optical system L0 of the present invention to an imaging device such as a digital still camera, it is possible to obtain a high-resolution image with a wide angle of view.

[0102] The disclosure of each embodiment includes the following configuration.

[0103] (Configuration 1) An optical system having a first lens group, a second lens group having negative refractive power, a third lens group, and a fourth lens group having positive refractive power, which are arranged in this order from an object side to an image side, and in which the distance between adjacent lens groups changes during focusing, the optical system has an aperture stop between the second lens group and the fourth lens group; During focusing from infinity to a close distance, the second lens group moves toward the image side, and the fourth lens group moves toward the object side, Let R21 be the radius of curvature of the surface of the second lens group closest to the object side, R22 be the radius of curvature of the surface of the second lens group closest to the image side, R41 be the radius of curvature of the surface of the fourth lens group closest to the object side, and R42 be the radius of curvature of the surface of the fourth lens group closest to the image side. 0.90<(R21+R22) / (R21-R22)<4.00 -10.00<(R41+R42) / (R41-R42)<-2.00 An optical system characterized in that the following condition is satisfied:

[0104] (Configuration 2) Let M2 and M4 be the amounts of movement of the second lens group and the fourth lens group when focusing from infinity to an object distance at which the lateral magnification of the entire system is -0.1 times, respectively, and let the sign of the amount of movement toward the image side when focusing from infinity to an object distance at which the lateral magnification of the entire system is -0.1 times be positive. -3.5 <M2 / M4<-0.5 2. The optical system according to claim 1, wherein the following condition is satisfied:

[0105] (Configuration 3) When the focal length of the second lens group is f2 and the focal length of the fourth lens group is f4, -7.00 <f2 / f4<-2.50 3. The optical system according to configuration 1 or 2, wherein the following condition is satisfied:

[0106] (Configuration 4) When the focal length of the first lens group is f1 and the focal length of the second lens group is f2, 0.05<|f1 / f2|<0.50 4. The optical system according to any one of configurations 1 to 3, wherein the following condition is satisfied:

[0107] (Configuration 5) In the optical system, if the focal length of the lens group arranged closest to the image side is fR and the focal length of the entire system is f, then 2.0<|fR / f|<500.0 5. The optical system according to any one of configurations 1 to 4, wherein the following condition is satisfied:

[0108] (Configuration 6) When focusing at infinity, the back focus is BF and the focal length of the entire system is f. 0.30 <BF / f<1.50 6. The optical system according to any one of configurations 1 to 5, wherein the following condition is satisfied:

[0109] (Configuration 7) When focusing at infinity, the distance on the optical axis from the aperture stop to the image plane is Da, and the total lens length of the optical system is TL. 0.45 <Da / TL<0.70 7. The optical system according to any one of configurations 1 to 6, wherein the following condition is satisfied:

[0110] (Configuration 8) When focusing at infinity, the distance on the optical axis from the aperture stop to the surface of the fourth lens group closest to the object side is denoted by D4. 0.15 <D4 / Da<0.35 8. The optical system according to claim 7, wherein the following condition is satisfied:

[0111] (Configuration 9) When the lateral magnification of the fourth lens group during focusing at infinity is β4, and the combined lateral magnification of all the lens groups disposed on the image side of the fourth lens group is βR, 0.70<(1-β42)×βR2<3.00 9. The optical system according to any one of configurations 1 to 8, wherein the following condition is satisfied:

[0112] (Configuration 10) When the Abbe number of at least one positive lens disposed in the fourth lens group is ν4p, 70.0<ν4p<96.0 10. The optical system according to any one of configurations 1 to 9, wherein the following condition is satisfied:

[0113] (Configuration 11) 11. The optical system according to any one of configurations 1 to 10, wherein, during image blur correction, all or some of the lens elements of the third lens group move so as to include a component in a direction perpendicular to the optical axis.

[0114] (Configuration 12) 12. The optical system described in any one of configurations 1 to 11, comprising, arranged in order from the object side to the image side, the first lens group having positive refractive power, the second lens group, the third lens group having positive refractive power, the fourth lens group, and a fifth lens group having negative refractive power.

[0115] (Configuration 13) 12. The optical system according to any one of configurations 1 to 11, comprising, arranged in order from the object side to the image side, the first lens group having negative refractive power, the second lens group, the third lens group having positive refractive power, the fourth lens group, and a fifth lens group having negative refractive power.

[0116] (Configuration 14) 12. The optical system according to any one of configurations 1 to 11, comprising, arranged in order from the object side to the image side, the first lens group having positive refractive power, the second lens group, the third lens group having positive refractive power, the fourth lens group, a fifth lens group having negative refractive power, and a sixth lens group having negative refractive power.

[0117] (Configuration 15) 12. The optical system according to any one of configurations 1 to 11, comprising, arranged in order from the object side to the image side, the first lens group having positive refractive power, the second lens group, the third lens group having positive refractive power, the fourth lens group, a fifth lens group having negative refractive power, and a sixth lens group having positive refractive power.

[0118] (Configuration 16) 12. The optical system described in any one of configurations 1 to 11, comprising, arranged in order from the object side to the image side, the first lens group having positive refractive power, the second lens group, the third lens group having positive refractive power, the fourth lens group, and a fifth lens group having positive refractive power.

[0119] (Configuration 17) An optical system including a first lens group, a second lens group having negative refractive power, a third lens group, a fourth lens group having positive refractive power, and a fifth lens group, which are arranged in this order from the object side to the image side, and in which the distance between adjacent lens groups changes during focusing, the optical system has an aperture stop between the second lens group and the fourth lens group; During focusing from infinity to a close distance, the second lens group moves toward the image side, and the fourth lens group moves toward the object side, The optical system according to claim 1, wherein the fifth lens group includes a positive lens and a negative lens.

[0120] (Configuration 18) An optical system having a first lens group, a second lens group having negative refractive power, a third lens group, and a fourth lens group having positive refractive power, which are arranged in this order from an object side to an image side, and in which the distance between adjacent lens groups changes during focusing, the optical system has an aperture stop between the second lens group and the third lens group; During focusing from infinity to a close distance, the second lens group moves toward the image side, and the fourth lens group moves toward the object side, the surface closest to the object side of the second lens group has a convex shape toward the object side, the surface closest to the image side of the second lens group has a concave shape toward the image side, and the radius of curvature of the surface closest to the image side of the second lens group is smaller than the radius of curvature of the surface closest to the object side of the second lens group, an optical system comprising: a surface of the fourth lens group closest to the object side that has a concave shape facing the object side; a surface of the fourth lens group closest to the image side that has a convex shape facing the image side; and an absolute value of the radius of curvature of the surface of the fourth lens group closest to the object side that is smaller than an absolute value of the radius of curvature of the surface of the fourth lens group closest to the image side.

[0121] (Configuration 19) 19. An imaging apparatus comprising: the optical system according to any one of configurations 1 to 18; and an imaging element that receives an image formed by the optical system.

[0122] Although the preferred embodiments and examples of the present invention have been described above, the present invention is not limited to these embodiments and examples, and various combinations, modifications, and changes are possible within the scope of the gist of the present invention. [Explanation of symbols]

[0123] L0 optical system L1 First lens group L2 Second lens group L3: Third lens group L4 4th lens group SP aperture stop

Claims

1. An optical system having a first lens group, a second lens group having negative refractive power, a third lens group, and a fourth lens group having positive refractive power, which are arranged in this order from an object side to an image side, and in which a distance between adjacent lens groups changes during focusing, the optical system has an aperture stop between the second lens group and the fourth lens group; During focusing from infinity to a close distance, the second lens group moves toward the image side, and the fourth lens group moves toward the object side, Let R21 be the radius of curvature of the surface of the second lens group closest to the object side, R22 be the radius of curvature of the surface of the second lens group closest to the image side, R41 be the radius of curvature of the surface of the fourth lens group closest to the object side, and R42 be the radius of curvature of the surface of the fourth lens group closest to the image side. 0.90<(R21+R22) / (R21-R22)<4.00 -10.00<(R41+R42) / (R41-R42)<-2.00 An optical system characterized in that the following condition is satisfied:

2. Let M2 and M4 be the movement amounts of the second lens group and the fourth lens group when focusing from infinity to an object distance at which the lateral magnification of the entire system is −0.1 times, respectively, and let the sign of the movement amount when moving toward the image side when focusing from infinity to an object distance at which the lateral magnification of the entire system is −0.1 times be positive, then -3.5<M2 / M4<-0.5 2. The optical system according to claim 1, wherein the following condition is satisfied:

3. When the focal length of the second lens group is f2 and the focal length of the fourth lens group is f4, -7.00<f2 / f4<-2.50 2. The optical system according to claim 1, wherein the following condition is satisfied:

4. When the focal length of the first lens group is f1 and the focal length of the second lens group is f2, 0.05<|f1 / f2|<0.50 2. The optical system according to claim 1, wherein the following condition is satisfied:

5. In the optical system, if the focal length of the lens unit arranged closest to the image side is fR and the focal length of the entire system is f, then 2.0<|fR / f|<500.0 2. The optical system according to claim 1, wherein the following condition is satisfied:

6. When focusing at infinity, the back focus is BF and the focal length of the entire system is f. 0.30<BF / f<1.50 2. The optical system according to claim 1, wherein the following condition is satisfied:

7. When focusing at infinity, the distance on the optical axis from the aperture stop to the image plane is Da, and the total lens length of the optical system is TL. 0.45<Da / TL<0.70 2. The optical system according to claim 1, wherein the following condition is satisfied:

8. When focusing at infinity, the distance on the optical axis from the aperture stop to the surface of the fourth lens group closest to the object side is denoted by D4. 0.15<D4 / Da<0.35 8. The optical system according to claim 7, wherein the following condition is satisfied:

9. When the lateral magnification of the fourth lens group during focusing at infinity is β4, and the combined lateral magnification of all the lens groups disposed on the image side of the fourth lens group is βR, 0.70<(1-β4) ２ )×βR ２ <3.00 2. The optical system according to claim 1, wherein the following condition is satisfied:

10. When the Abbe number of at least one positive lens arranged in the fourth lens group is ν4p, 70.0<ν4p<96.0 2. The optical system according to claim 1, wherein the following condition is satisfied:

11. 2. The optical system according to claim 1, wherein, during image blur correction, all or some of the lens elements of the third lens group move so as to include a component in a direction perpendicular to the optical axis.

12. 2. The optical system according to claim 1, comprising, arranged in order from the object side to the image side, the first lens group having positive refractive power, the second lens group, the third lens group having positive refractive power, the fourth lens group, and a fifth lens group having negative refractive power.

13. 2. The optical system according to claim 1, comprising, arranged in order from the object side to the image side, the first lens group having negative refractive power, the second lens group, the third lens group having positive refractive power, the fourth lens group, and a fifth lens group having negative refractive power.

14. 2. The optical system according to claim 1, comprising, arranged in order from the object side to the image side, the first lens group having positive refractive power, the second lens group, the third lens group having positive refractive power, the fourth lens group, a fifth lens group having negative refractive power, and a sixth lens group having negative refractive power.

15. 2. The optical system according to claim 1, comprising, arranged in order from the object side to the image side, the first lens group having positive refractive power, the second lens group, the third lens group having positive refractive power, the fourth lens group, a fifth lens group having negative refractive power, and a sixth lens group having positive refractive power.

16. 2. The optical system according to claim 1, comprising, arranged in order from the object side to the image side, the first lens group having positive refractive power, the second lens group, the third lens group having positive refractive power, the fourth lens group, and a fifth lens group having positive refractive power.

17. An optical system including a first lens group, a second lens group having negative refractive power, a third lens group, a fourth lens group having positive refractive power, and a fifth lens group, which are arranged in this order from an object side to an image side, and in which a distance between adjacent lens groups changes during focusing, the optical system has an aperture stop between the second lens group and the fourth lens group; During focusing from infinity to a close distance, the second lens group moves toward the image side, and the fourth lens group moves toward the object side, The optical system according to claim 1, wherein the fifth lens group includes a positive lens and a negative lens.

18. An optical system having a first lens group, a second lens group having negative refractive power, a third lens group, and a fourth lens group having positive refractive power, which are arranged in this order from an object side to an image side, and in which a distance between adjacent lens groups changes during focusing, the optical system has an aperture stop between the second lens group and the third lens group; During focusing from infinity to a close distance, the second lens group moves toward the image side, and the fourth lens group moves toward the object side, the surface closest to the object side of the second lens group has a convex shape toward the object side, the surface closest to the image side of the second lens group has a concave shape toward the image side, and the radius of curvature of the surface closest to the image side of the second lens group is smaller than the radius of curvature of the surface closest to the object side of the second lens group, the surface of the fourth lens group closest to the object side has a concave shape toward the object side, the surface of the fourth lens group closest to the image side has a convex shape toward the image side, and the absolute value of the radius of curvature of the surface of the fourth lens group closest to the image side is smaller than the absolute value of the radius of curvature of the surface of the fourth lens group closest to the object side.

19. 19. An imaging apparatus comprising: an optical system according to claim 1; and an imaging element that receives an image formed by the optical system.

Images