Optical system and image pickup apparatus including the same

Abstract

To provide an optical system capable of satisfactorily correcting aberration over a wide object distance range while achieving miniaturization of a focus lens group.SOLUTION: The optical system L0 includes, in order from the object side to the image side, a first lens unit L1 having a positive refractive power, a second lens unit L2 having a negative refractive power, a third lens unit L3 having a positive refractive power, and a fourth lens unit L4 having a positive refractive power. During focusing, the first lens unit and the fourth lens unit are fixed, and the second lens unit and the third lens unit are moved. The first lens group includes a lens having a positive refractive power that is disposed closest to the object side, and the fourth lens group includes a lens having a negative refractive power that is disposed closest to the image side.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an optical system suitable for digital video cameras, digital still cameras, broadcast cameras, cameras for silver halide film, surveillance cameras, and the like. [Background technology]

[0002] In recent years, optical systems used in imaging devices have been required to achieve a reduction in the overall lens diameter of the focus lens group, and to be able to effectively correct chromatic aberration, field curvature, and the like during shooting at the closest distance while increasing the shooting magnification.As an optical system that satisfies these requirements, Patent Document 1 discloses an optical system that has, arranged in order from the object side to the image side, a first lens group with positive refractive power, a focus lens group with negative refractive power, and a focus lens group with positive refractive power.

[0003] The optical system described in Patent Document 1 reduces aberration fluctuations, particularly chromatic aberration fluctuations, during focusing, and has high optical performance over a wide range of object distances. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2017-173409 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the optical system described in Patent Document 1, when the diameter of the optical system is increased, the focal length of the focus lens group with positive refractive power and the focal length of the fourth lens group disposed on the image side of the focus lens group are not appropriately set, which makes it difficult to suppress aberration fluctuations during focusing in the optical system described in Patent Document 1 when the diameter of the optical system is increased.

[0006] The present invention provides an optical system that can effectively correct aberrations over a wide range of object distances while achieving a compact focus lens group. [Means for solving the problem]

[0007] An optical system according to one aspect of the present invention is an optical system comprising, arranged in order from the object side to the image side, a first lens group with positive refractive power, a second lens group with negative refractive power, a third lens group with positive refractive power, and a fourth lens group with positive refractive power, wherein, during focusing, the first lens group and the fourth lens group are fixed, and the second lens group and the third lens group move, and the first lens group includes a lens with positive refractive power arranged closest to the object, and the fourth lens group includes a lens with negative refractive power arranged closest to the image.

[0008] Other objects and features of the present invention will be described in the following embodiments. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide an optical system that can achieve a compact focus lens group and can effectively correct aberrations over a wide range of object distances. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a cross-sectional view of an optical system according to a first embodiment. [Figure 2] FIG. 2 is a longitudinal aberration diagram of the optical system of Example 1 when focused at infinity. [Figure 3] FIG. 2 is a longitudinal aberration diagram of the optical system of Example 1 when focused at a close distance (0.70 m). [Figure 4] FIG. 10 is a cross-sectional view of an optical system according to a second embodiment. [Figure 5] FIG. 10 is a longitudinal aberration diagram of the optical system of Example 2 when focused at infinity. [Figure 6] FIG. 10 is a longitudinal aberration diagram of the optical system of Example 2 when focused at a close distance (0.60 m). [Figure 7] FIG. 10 is a cross-sectional view of an optical system according to a third embodiment. [Figure 8] FIG. 10 is a longitudinal aberration diagram of the optical system of Example 3 when focused at infinity. [Figure 9] FIG. 10 is a longitudinal aberration diagram of the optical system of Example 3 when focused at a close distance (0.70 m). [Figure 10] FIG. 10 is a cross-sectional view of an optical system according to a fourth embodiment. [Figure 11] FIG. 10 is a longitudinal aberration diagram when the optical system of Example 4 is focused at infinity. [Figure 12] FIG. 10 is a longitudinal aberration diagram of the optical system of Example 4 when focused at a close distance (0.85 m). [Figure 13] FIG. 1 is a schematic diagram of an imaging device. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, embodiments of an optical system and an imaging apparatus having the same according to the present invention will be described with reference to the accompanying drawings.

[0012] 1, 4, 7, and 10 are cross-sectional views of the optical systems of Examples 1 to 4 when focused at infinity. The optical system L0 in each example is an optical system used in imaging devices such as digital video cameras, digital still cameras, broadcast cameras, silver halide film cameras, and surveillance 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 in each embodiment is configured with multiple lens groups. In this specification, a lens group refers to a group of lenses that move or remain stationary as a unit during focusing. That is, in the optical system L0 in each embodiment, the spacing between adjacent lens groups changes during focusing from infinity to a close distance. Note that a lens group may be composed of a single lens or multiple lenses. The lens group may also include an aperture stop.

[0014] In each lens cross-sectional view, Li represents the i-th lens group (i is a natural number) counting from the object side among the lens groups included in the optical system L0.

[0015] Furthermore, SP denotes an aperture stop. IP denotes an image plane, on which the imaging surface of a solid-state imaging element (photoelectric conversion element) such as a CCD sensor or CMOS sensor is placed when the optical system L0 of each embodiment is used as the imaging optical system of a digital still camera or digital video camera. When the optical system L0 of each embodiment is used as the imaging optical system of a silver halide film camera, a photosensitive surface corresponding to the film surface is placed on the image plane IP.

[0016] In each lens cross-sectional view of Examples 1 to 4, L1 is a first lens group with positive refractive power, L2 is a second lens group with negative refractive power, L3 is a third lens group with positive refractive power, and L4 is a fourth lens group with positive refractive power.

[0017] In addition, in the optical systems L0 of Examples 1 to 4, the second lens group L2 moves toward the image side and the third lens group L3 moves toward the object side as shown by the arrows during focusing from infinity to a close distance. The first lens group L1 and the fourth lens group L4 remain stationary (fixed) during focusing from infinity to a close distance. The second lens group L2 and the third lens group L3 move along different trajectories during focusing.

[0018] 2, 5, 8, and 11 are aberration diagrams of the optical systems L0 of Examples 1 to 4 when focused at infinity, respectively.

[0019] 3, 6, 9, and 12 are aberration diagrams of the optical systems L0 of Examples 1 to 4 when focused at close distances.

[0020] In the spherical aberration diagram, Fno is the F-number, and shows the amount of spherical aberration for the d-line (wavelength 587.6 nm) and g-line (wavelength 435.8 nm). In the astigmatism diagram, dS shows the amount of astigmatism on the sagittal image plane, and dM shows the amount of astigmatism on the meridional image plane. In the distortion diagram, the amount of distortion for the d-line is shown. In the chromatic aberration diagram, the amount of chromatic aberration for the g-line is shown. ω is the half angle of view (°).

[0021] Next, the characteristic configuration of the optical system L0 of each embodiment will be described.

[0022] The optical system L0 of each embodiment comprises, arranged in order from the object side to the image side, a first lens group L1 with positive refractive power, a second lens group L2 with negative refractive power, a third lens group L3 with positive refractive power, and a fourth lens group L4 with positive refractive power. In the optical system L0 of each embodiment, the first lens group L1 and the fourth lens group L4 are fixed during focusing, while the second lens group L2 and the third lens group L3 move during focusing. As described above, the optical system L0 of each embodiment is characterized by a four-group configuration with positive, negative, positive, and positive refractive powers, and the second lens group L2 and the third lens group L3 move independently during focusing. By making the fourth lens group, the final lens group, positive, have positive refractive power, it is possible to weaken the refractive power of the third lens group L3 with positive refractive power, which moves during focusing, and spherical aberration can be effectively corrected at close distances.

[0023] Furthermore, the first lens group L1 is characterized by including a lens with positive refractive power that is positioned closest to the object, which allows the diameters of the second and third lens groups L2 and L3, which are focus lens groups, to be reduced, making it possible to make the focus lens groups smaller and lighter.

[0024] Furthermore, the fourth lens unit L4 is characterized by including a lens with negative refractive power that is positioned closest to the image side, which makes it possible to adopt a telephoto type power arrangement and shorten the overall lens length.

[0025] Next, the configuration that is preferably satisfied in the optical system L0 of each embodiment will be described.

[0026] When focusing from infinity to a close distance, it is preferable that the second lens group L2 move toward the image side. This makes it possible to suppress field curvature and spherical aberration when focusing from infinity to the closest possible distance, while also suppressing changes in the angle of view during video shooting. Also, it is preferable that the third lens group L3 move toward the object side when focusing from infinity to a close distance. By moving the third lens group L3, which has a refractive power of the opposite sign to that of the second lens group L2 (the main focus group), in the opposite direction to the second lens group L2, it is possible to more effectively correct spherical aberration and field curvature.

[0027] In the optical system L0, it is preferable that the axial distance between the second lens group L2 and the third lens group L3 be the widest after the axial distance between adjacent lens groups. This ensures a sufficient amount of movement for the focus lens group, making it possible to shorten the minimum focusing distance. Furthermore, the refractive power of the focus lens group can be weakened, making it possible to suppress curvature of field and spherical aberration during focusing.

[0028] It is preferable that the second lens group L2 and the third lens group L3 each be composed of three or fewer lenses. By configuring the focus lens group with a small number of lenses, quick focusing is possible even with a large aperture.

[0029] The fourth lens unit L4 preferably includes two or more negative lenses, which makes it possible to correct Petzval sum and effectively correct curvature of field while shortening the overall lens length.

[0030] Next, conditions that the optical system L0 of each embodiment should preferably satisfy will be described. The optical system L0 of each embodiment should preferably satisfy one or more of the following conditional expressions (1) to (9).

[0031] 0.4 <f1 / f<1.5 ···(1) -1.0 <f2 / f<-0.3 ···(2) 0.8 <f3 / f<5.0 ···(3) 0.5 <f4 / f<4.0 ···(4) -1.5 <M3 / M2<0.0 ···(5) 0.5<(rf+rr) / (rf-rr)<1.5 (6) 0.5 <D23 / sk<3.0 ···(7) 3.0 <f4 / sk<40.0 ···(8) -2.0 <fno×f2 / f3<0.0 ···(9) Here, f is the focal length of the optical system L0. f1 is the focal length of the first lens group L1. f2 is the focal length of the second lens group L2. f3 is the focal length of the third lens group L3. f4 is the focal length of the fourth lens group L4. M2 is the relative movement amount of the second lens group L2 with respect to the image plane IP during focusing from infinity to the closest point, with the direction in which the second lens group L2 moves from the object side to the image side being positive. M3 is the relative movement amount of the third lens group L3 with respect to the image plane IP during focusing from infinity to the closest point, with the direction in which the third lens group L3 moves from the object side to the image side being positive. rf is the radius of curvature of the object-side lens surface of the lens in the second lens group L2 located closest to the object. rr is the radius of curvature of the image-side lens surface of the lens in the second lens group L2 located closest to the image side. sk is the back focus of the optical system L0 when focusing at infinity. D23 is the axial distance between the second lens unit L2 and the third lens unit L3 when focusing at infinity. In other words, D23 is the axial distance from the lens surface of the second lens unit L2 closest to the image to the lens surface of the third lens unit L3 closest to the object when focusing at infinity. fno is the F-number of the optical system L0.

[0032] Conditional expression (1) defines the focal length f1 of the first lens group L1. By satisfying conditional expression (1), it is possible to shorten the overall lens length and reduce the weight of the focus lens group. If the focal length f1 of the first lens group L1 becomes too short, falling below the lower limit of conditional expression (1), it becomes difficult to correct spherical aberration, which is undesirable. If the focal length f1 of the first lens group L1 becomes too long, exceeding the upper limit of conditional expression (1), the converging action of the first lens group L1 weakens, and the overall lens length increases. As a result, the diameters of the second lens group L2 and the third lens group L3 become large, which makes it difficult to reduce the weight of the focus lens group, which is undesirable.

[0033] Conditional expression (2) defines the focal length f2 of the second lens group L2. If the focal length f2 of the second lens group L2 falls below the lower limit of conditional expression (2) and becomes too long, the amount of movement of the second lens group L2 during focusing increases. This makes it difficult to shorten the overall lens length, which is undesirable. If the focal length f2 of the second lens group L2 exceeds the upper limit of conditional expression (2) and becomes too short, it makes it difficult to suppress field curvature and spherical aberration during focusing, which is undesirable.

[0034] Conditional expression (3) defines the focal length f3 of the third lens group L3. If the focal length f3 of the third lens group L3 falls below the lower limit of conditional expression (3) and becomes too short, it becomes difficult to suppress curvature of field and spherical aberration during focusing, which is undesirable. If the focal length f3 of the third lens group L3 exceeds the upper limit of conditional expression (3) and becomes too long, the amount of movement of the third lens group L3 during focusing becomes large. This makes it difficult to shorten the overall lens length, which is undesirable.

[0035] Conditional expression (4) defines the focal length f4 of the fourth lens group L4. If the focal length f4 of the fourth lens group L4 falls below the lower limit of conditional expression (4) and becomes too short, the positive refractive power of the third lens group L3 becomes relatively weak, and the amount of movement of the second lens group L2 during focusing increases. This makes it difficult to shorten the overall lens length, which is undesirable. If the focal length f4 of the fourth lens group L4 exceeds the upper limit of conditional expression (4) and becomes too long, the positive refractive power of the third lens group L3 becomes relatively strong, which makes it difficult to suppress field curvature and spherical aberration during focusing, which is undesirable.

[0036] Conditional expression (5) defines the ratio of the amount of movement M2 of the second lens group L2, which is a focus lens group, to the amount of movement M3 of the third lens group L3, which is a focus lens group. If the amount of movement M2 of the second lens group L2 becomes too small, falling below the lower limit of conditional expression (5), it becomes difficult to suppress spherical aberration during focusing, which is undesirable. If the upper limit of conditional expression (5) is exceeded, the third lens group L3 moves toward the object side, which makes it difficult to shorten the minimum shooting distance and increases the overall lens length, which is undesirable.

[0037] Conditional expression (6) defines the shape factor of the second lens unit L2, which is a focus lens unit. If the radius of curvature rf of the lens surface closest to the object in the second lens unit L2 becomes negatively small by falling below the lower limit of conditional expression (6), it becomes difficult to suppress spherical aberration during focusing, which is undesirable. If the radius of curvature rr of the lens surface closest to the image in the second lens unit L2 becomes small by exceeding the upper limit of conditional expression (6), it becomes difficult to suppress field curvature during focusing, which is undesirable.

[0038] Conditional expression (7) defines the axial distance D23 between the second lens group L2 and the third lens group L3. If the distance D23 between the second lens group L2 and the third lens group L3 falls below the lower limit of conditional expression (7) and becomes too narrow, it becomes difficult to shorten the minimum focusing distance, which is undesirable. It also becomes difficult to suppress curvature of field and spherical aberration during focusing, which is undesirable. If the distance D23 between the second lens group L2 and the third lens group L3 exceeds the upper limit of conditional expression (7), it becomes difficult to shorten the overall lens length, which is undesirable.

[0039] Conditional expression (8) defines the ratio of the focal length f4 of the fourth lens group L4 to the back focal length sk. If the focal length f4 of the fourth lens group L4 falls below the lower limit of conditional expression (8), the focal length f4 of the fourth lens group L4 becomes too short, which is undesirable because it becomes difficult to shorten the overall lens length. If the focal length f4 of the fourth lens group L4 exceeds the upper limit of conditional expression (8), the focal length f4 of the fourth lens group L4 becomes too long, which is undesirable because it becomes difficult to ensure the back focal length sk.

[0040] Conditional formula (9) defines the relationship between the F-number fno of the optical system L0 and the focal lengths f2 and f3 of the focus lens groups L2 and L3. If the focal length f2 of the second lens group L2 becomes too long by falling below the lower limit of conditional formula (9), the amount of movement of the second lens group L2 during focusing increases. This makes it difficult to shorten the overall lens length, which is undesirable. It also makes it difficult to achieve the desired large aperture ratio, which is undesirable. If the focal length f2 of the second lens group L2 becomes too short by exceeding the upper limit of conditional formula (9), it makes it difficult to suppress field curvature and spherical aberration during focusing, which is undesirable.

[0041] It is more preferable that the numerical ranges of the conditional expressions (1) to (9) be within the ranges of the following conditional expressions (1a) to (9a).

[0042] 0.5 <f1 / f<1.3 ···(1a) -0.9 <f2 / f<-0.35 ···(2a) 1.0 <f3 / f<4.5 ···(3a) 0.6 <f4 / f<3.0 ···(4a) -1.5 <M3 / M2<-0.05 ···(5a) 0.6<(rf+rr) / (rf-rr)<1.3 (6a) 0.8 <D23 / sk<2.5 ···(7a) 4.0 <f4 / sk<30.0 ···(8a) -1.5 <fno×f2 / f3<-0.05 ···(9a) It is more preferable that the numerical ranges of the conditional expressions (1) to (9) be within the ranges of the following conditional expressions (1b) to (9b).

[0043] 0.6 <f1 / f<1.1 ···(1b) -0.8 <f2 / f<-0.4 ···(2b) 1.2 <f3 / f<4.0 ···(3b) 0.7 <f4 / f<2.0 ···(4b) -1.5 <M3 / M2<-0.08 ···(5b) 0.7<(rf+rr) / (rf-rr)<1.2 (6b) 1.0 <D23 / sk<2.0 ···(7b) 5.0 <f4 / sk<20.0 ···(8b) -1.0 <fno×f2 / f3<-0.1 ···(9b) By satisfying at least one of the above conditional expressions, it becomes easy to achieve a reduction in the size of the focus lens group and to correct aberrations well over a wide range of object distances.

[0044] Next, the optical system L0 of each embodiment will be described in detail. [Example 1] FIG. 1 is a cross-sectional view of the optical system L0 of Example 1 when focused at infinity, FIG. 2 is an aberration diagram of the optical system L0 of Example 1 when focused at infinity, and FIG. 3 is an aberration diagram of the optical system L0 of Example 1 when focused at a close distance (0.70 m).

[0045] The optical system L0 according to Example 1 comprises, arranged in order from the object side to the image side, a first lens unit L1 with positive refractive power, a second lens unit L2 with negative refractive power, a third lens unit L3 with positive refractive power, and a fourth lens unit L4 with positive refractive power. An aperture stop SP is arranged between the second lens unit L2 and the third lens unit L3. During focusing from infinity to a close distance, the second lens unit L2 moves toward the image side, and the third lens unit L3 moves toward the object side.

[0046] With this configuration, it is possible to obtain an optical system that is compact and capable of correcting various aberrations well over the entire object distance, as shown in the aberration diagrams of FIGS. [Example 2] FIG. 4 is a cross-sectional view of the optical system L0 of Example 2 when focused at infinity, FIG. 5 is an aberration diagram of the optical system L0 of Example 2 when focused at infinity, and FIG. 6 is an aberration diagram of the optical system L0 of Example 2 when focused at a close distance (0.60 m).

[0047] The optical system L0 according to Example 2 comprises, arranged in order from the object side to the image side, a first lens unit L1 with positive refractive power, a second lens unit L2 with negative refractive power, a third lens unit L3 with positive refractive power, and a fourth lens unit L4 with positive refractive power. An aperture stop SP is disposed between the second lens unit L2 and the third lens unit L3. During focusing from infinity to a close distance, the second lens unit L2 moves toward the image side, and the third lens unit L3 moves toward the object side.

[0048] With this configuration, it is possible to obtain an optical system that is compact and capable of correcting various aberrations well over the entire object distance, as shown in the aberration diagrams of FIGS. [Example 3] FIG. 7 is a cross-sectional view of the optical system L0 of Example 3 when focused at infinity, FIG. 8 is an aberration diagram of the optical system L0 of Example 3 when focused at infinity, and FIG. 9 is an aberration diagram of the optical system L0 of Example 3 when focused at a close distance (0.70 m).

[0049] The optical system L0 according to Example 3 comprises, arranged in order from the object side to the image side, a first lens unit L1 with positive refractive power, a second lens unit L2 with negative refractive power, a third lens unit L3 with positive refractive power, and a fourth lens unit L4 with positive refractive power. An aperture stop SP is disposed between the second lens unit L2 and the third lens unit L3. During focusing from infinity to a close distance, the second lens unit L2 moves toward the image side, and the third lens unit L3 moves toward the object side.

[0050] With this configuration, it is possible to obtain an optical system that is compact and capable of correcting various aberrations well over the entire object distance, as shown in the aberration diagrams of FIGS. [Example 4] FIG. 10 is a cross-sectional view of the optical system L0 of Example 4 when focused at infinity, FIG. 11 is an aberration diagram of the optical system L0 of Example 4 when focused at infinity, and FIG. 12 is an aberration diagram of the optical system L0 of Example 4 when focused at a close distance (0.85 m).

[0051] The optical system L0 according to Example 4 comprises, arranged in order from the object side to the image side, a first lens unit L1 with positive refractive power, a second lens unit L2 with negative refractive power, a third lens unit L3 with positive refractive power, and a fourth lens unit L4 with positive refractive power. An aperture stop SP is arranged between the second lens unit L2 and the third lens unit L3. During focusing from infinity to a close distance, the second lens unit L2 moves toward the image side, and the third lens unit L3 moves toward the object side.

[0052] With this configuration, it is possible to obtain an optical system that is compact and capable of correcting various aberrations well over the entire object distance, as shown in the aberration diagrams of FIGS.

[0053] Numerical Examples 1 to 4 corresponding to Examples 1 to 4, respectively, are shown below.

[0054] 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. Also, nd represents the refractive index of each optical element with respect to the d-line, and vd represents the Abbe number of the optical element. Note that the Abbe number vd of a certain material is given by the following when the refractive indices at the d-line (587.6 nm), F-line (486.1 nm), and C-line (656.3 nm) of the Fraunhofer lines are Nd, NF, and NC, respectively: νd=(Nd-1) / (NF-NC) It is expressed as:

[0055] In each numerical example, d, focal length (mm), F-number, and half angle of view (°) are all values ​​when the optical system L0 of each example is focused on an object at infinity. The back focus BF is the distance on the optical axis from the final lens surface (the lens surface closest to the image) to the paraxial image plane, expressed as an air-equivalent length. The total lens length is the distance on the optical axis from the first lens surface (the lens surface closest to the object) to the final lens surface plus the back focus. The lens group is not limited to cases where it is composed of multiple lenses, but may also be composed of a single lens.

[0056] If the optical surface is aspherical, an asterisk (*) is added to the right of the surface number. The aspherical shape is expressed as follows: X is the displacement from the vertex of the surface in the optical axis direction, h is the height from the optical axis in the 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 aspherical 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 aspherical coefficient is "×10± XX " means.

[0057] [Numerical Example 1] Unit: mm Surface Data Surface number rd nd νd Effective diameter 1 83.161 4.61 1.92286 20.9 64.00 2 154.104 0.20 63.04 3 55.552 7.11 1.59522 67.7 58.36 4 140.805 0.20 56.63 5 36.359 7.19 1.59522 67.7 47.90 6 74.943 0.10 45.96 7 76.130 1.85 1.72825 28.5 45.92 8 27.070 2.28 39.06 9 33.607 9.78 1.49700 81.5 38.98 10 -136.952 1.60 1.85478 24.8 37.31 11 1655.784 (variable) 35.78 12 397.704 2.52 1.80810 22.8 33.49 13 -128.213 1.10 1.77250 49.6 32.86 14 29.115 (variable) 29.31 15 (Aperture) ∞ (Variable) 27.81 16 50.963 1.10 1.85478 24.8 27.01 17 22.681 8.99 1.61800 63.4 25.88 18 -192.160 (variable) 24.98 19 -442.565 1.30 1.78472 25.7 26.89 20 55.512 0.54 28.41 21 73.672 4.97 1.91082 35.2 28.57 22 -56.192 1.40 1.61293 37.0 29.34 23 34.359 11.27 2.00100 29.1 32.76 24 -55.407 0.20 33.35 25 -785.674 2.10 1.69350 53.2 32.33 26* 38.858 7.55 31.08 27 -39.599 1.40 1.60311 60.6 31.39 28 -69.004 13.00 33.00 Image plane ∞ Aspheric data Page 26 K = 0.00000e+00 A 4= 5.44228e-06 A 6= 1.32152e-09 A 8= 3.52234e-11 A10=-6.99292e-14 A12= 1.27529e-16 Various data Focal length 82.50 F-number 1.46 Half angle of view (°) 14.69 Image height 21.64 Lens length 112.50 BF 13.00 infinite close d11 2.00 9.00 d14 12.96 5.96 d15 2.99 1.50 d18 2.20 3.69 Lens group data Group starting plane focal length 1 1 60.14 2 12 -41.48 Aperture 15∞ 3 16 105.20 4 19 118.83 Single lens data Lens starting surface focal length 1 1 189.82 2 3 149.50 3 5 110.94 4 7 -58.61 5 9 55.35 6 10 -147.92 7 12 120.24 8 13 -30.62 9 16 -48.68 10 17 33.36 11 19 -62.79 12 21 35.65 13 22 -34.58 14 23 22.61 15 25 -53.34 16 27 -156.89 [Numerical Example 2] Unit: mm Surface Data Surface number rd nd νd Effective diameter 1 80.607 4.80 1.61997 63.9 49.49 2 411.893 0.20 49.09 3 45.020 4.06 1.59522 67.7 47.11 4 67.726 0.20 46.18 5 39.961 3.00 1.61340 44.3 44.47 6 29.889 1.62 40.80 7 34.960 10.39 1.49700 81.5 40.76 8 -127.023 1.70 1.85478 24.8 39.19 9 -2528.692 (variable) 37.74 10 -1992.975 2.91 1.80810 22.8 35.85 11 -86.475 1.30 1.72916 54.7 35.30 12 30.641 (variable) 31.42 13 (Aperture) ∞ (Variable) 30.84 14 65.425 1.20 1.85478 24.8 30.24 15 33.708 5.13 1.61800 63.4 29.53 16 -892.457 (variable) 29.28 17 84.924 1.20 1.51633 64.1 30.58 18 35.214 1.54 31.76 19 43.097 8.14 1.88300 40.8 33.43 20 -56.346 1.40 1.67270 32.1 33.76 21 32.150 8.98 1.88300 40.8 34.62 22 -85.053 0.19 34.49 23 147.493 2.10 1.69350 53.2 33.03 24* 29.488 10.03 30.74 25 -29.367 1.40 1.61340 44.3 31.06 26 -46.814 12.99 33.00 Image plane ∞ Aspheric data Page 24 K = 0.00000e+00 A 4= 4.83027e-06 A 6= 2.32354e-09 A 8= 2.60591e-11 A10= 2.17885e-14 A12= 8.59268e-18 Various data Focal length 72.10 F-number 1.46 Half angle of view (°) 16.70 Image height 21.64 Lens length 108.50 BF 12.99 infinite close d 9 2.01 8.80 d12 13.12 6.33 d13 7.37 1.50 d16 1.50 7.37 Lens group data Group starting plane focal length 1 1 56.65 2 10 -42.93 Aperture 13∞ 3 14 147.64 4 17 91.00 Single lens data Lens starting surface focal length 1 1 160.76 2 3 211.49 3 5 -218.02 4 7 56.36 5 8 -156.51 6 10 111.79 7 11 -30.88 8 14 -82.79 9 15 52.67 10 17 -117.48 11 19 28.76 12 20 -30.24 13 21 27.41 14 23 -53.54 15 25 -132.50 [Numerical Example 3] Unit: mm Surface Data Surface number rd nd νd Effective diameter 1 108.420 3.43 1.84666 23.8 69.85 2 163.186 0.20 69.12 3 59.780 10.26 1.59522 67.7 65.22 4 348.885 0.20 64.03 5 39.748 7.99 1.59522 67.7 55.56 6 73.013 1.85 1.67300 38.3 53.46 7 28.938 3.29 44.75 8 36.860 11.63 1.49700 81.5 44.62 9 -135.341 1.60 1.85478 24.8 42.55 10 300.932 (variable) 40.24 11 2925.902 2.09 1.80810 22.8 38.16 12 -228.462 1.10 1.72916 54.7 37.49 13 31.448 (variable) 33.64 14 (Aperture) ∞ (Variable) 32.35 15 94.094 1.10 1.85478 24.8 31.71 16 27.297 7.18 1.61800 63.4 30.74 17 -262.440 (variable) 30.63 18 74.274 5.46 2.00100 29.1 29.90 19 -49.488 0.54 29.42 20 -41.113 1.40 1.61340 44.3 29.40 21 28.815 12.89 1.57099 50.8 30.49 22 -37.037 0.20 31.34 23 -2066.129 2.10 1.69350 53.2 30.33 24* 43.111 10.05 29.56 25 -24.537 1.40 1.48749 70.2 30.25 26 -43.452 13.00 32.67 Image plane ∞ Aspheric data Page 24 K = 0.00000e+00 A 4= 3.17490e-06 A 6= 1.08346e-09 A 8= 1.01991e-11 A10=2.69214e-14 A12=-5.03511e-17 Various data Focal length 97.50 F-number 1.46 Half angle of view (°) 12.51 Image height 21.64 Lens length 125.50 BF 13.00 infinite close d10 2.60 12.51 d13 16.79 6.87 d14 4.58 1.50 d17 2.57 5.65 Lens group data Group starting plane focal length 1 1 69.37 2 11 -44.35 Aperture 14 infinity 3 15 357.88 4 18 80.64 Single lens data Lens starting surface focal length 1 1 370.91 2 3 119.62 3 5 134.52 4 6 -72.45 5 8 59.63 6 9 -109.03 7 11 262.32 8 12 -37.84 9 15 -45.33 10 16 40.39 11 18 30.34 12 20 -27.41 13 21 30.56 14 23 -60.87 15 25 -118.50 [Numerical Example 4] Unit: mm Surface Data Surface number rd nd νd Effective diameter 1 84.066 6.61 1.92286 20.9 69.94 2 225.702 0.20 68.82 3 69.879 5.70 1.59522 67.7 63.17 4 143.304 0.20 62.09 5 49.670 5.87 1.59522 67.7 57.14 6 84.792 1.27 55.56 7 112.284 1.85 1.85478 24.8 55.47 8 40.959 1.98 49.50 9 50.505 10.71 1.49700 81.5 49.44 10 -134.731 1.60 1.85478 24.8 48.08 11 -2587.955 (variable) 46.50 12 -555.071 3.16 1.80810 22.8 44.72 13 -100.597 1.10 1.72916 54.7 44.25 14 42.976 (variable) 40.32 15 (Aperture) ∞ (Variable) 39.80 16 396.094 1.10 1.85478 24.8 39.66 17 28.593 10.04 1.61800 63.4 39.09 18 790.704 0.20 39.61 19 50.723 6.98 1.61800 63.4 41.20 20 -220.501 (variable) 40.99 21 47.712 1.30 1.85478 24.8 38.20 22 35.563 1.39 36.81 23 45.775 12.97 1.91082 35.2 36.80 24 -38.786 1.40 1.70154 41.2 36.74 25 55.768 4.62 2.00100 29.1 35.39 26 -448.122 0.20 35.08 27 196.346 1.40 1.51633 64.1 34.36 28 30.659 10.38 32.17 29 -50.491 2.10 1.69350 53.2 32.09 30* -167.232 15.03 33.30 Image plane ∞ Aspheric data Page 30 K = 0.00000e+00 A 4= 9.07055e-06 A 6=-3.64062e-09 A 8= 8.42101e-11 A10=-2.13940e-13 A12= 2.14692e-16 Various data Focal length 82.50 F-number 1.24 Half angle of view (°) 14.69 Image height 21.64 Lens length 135.50 BF 15.03 infinite close d11 2.38 12.73 d14 17.37 7.02 d15 2.65 1.50 d20 3.74 4.89 Lens group data Group starting plane focal length 1 1 80.89 2 12 -56.54 Aperture 15∞ 3 16 116.76 4 21 127.11 Single lens data Lens starting surface focal length 1 1 141.98 2 3 222.68 3 5 189.63 4 7 -76.35 5 9 75.36 6 10 -166.33 7 12 151.57 8 13 -41.16 9 16 -36.10 10 17 47.76 11 19 67.39 12 21 -171.87 13 23 24.87 14 24 -32.41 15 25 49.77 16 27 -70.57 17 29 -105.07 The various values ​​in each numerical example are summarized in Table 1 below.

[0058] [Table 1]

[0059] [Imaging device] Next, an embodiment of a digital still camera (imaging device) 10 that uses the optical system of the present invention as an imaging optical system will be described with reference to Fig. 13. In Fig. 13, 13 denotes a camera body, and 11 denotes an imaging optical system configured with any of the optical systems L0 described in Examples 1 to 4. 12 denotes a solid-state imaging element (photoelectric conversion element) such as a CCD sensor or CMOS sensor that is built into the camera body 13 and receives and photoelectrically converts an optical image formed by the imaging optical system 11. The camera body 13 may be a so-called single-lens reflex camera that has a quick-return mirror, or a so-called mirrorless camera that does not have a quick-return mirror.

[0060] In this way, by applying the optical system of the present invention to an imaging device such as a digital still camera, an imaging device with a small lens can be obtained.

[0061] 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]

[0062] L0 optical system L1 First lens group L2 Second lens group L3: Third lens group L4 4th lens group

Claims

1. An optical system comprising, arranged in order from the object side to the image side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, and a fourth lens group having a positive refractive power, During focusing, the first lens group and the fourth lens group are fixed, and the second lens group and the third lens group are movable, the first lens group includes a lens having a positive refractive power that is arranged closest to the object, an optical system, wherein the fourth lens group includes a lens having negative refractive power that is disposed closest to the image side;

2. When the focal length of the optical system is f and the focal length of the first lens group is f1, 0.4<f1 / f<1.5 2. The optical system according to claim 1, wherein the following condition is satisfied:

3. When the focal length of the optical system is f and the focal length of the second lens group is f2, -1.0<f2 / f<-0.3 3. The optical system according to claim 1, wherein the following condition is satisfied:

4. When the focal length of the optical system is f and the focal length of the third lens group is f3, 0.8<f3 / f<5.0 4. The optical system according to claim 1, wherein the following condition is satisfied:

5. When the focal length of the optical system is f and the focal length of the fourth lens group is f4, 0.5<f4 / f<4.0 5. The optical system according to claim 1, wherein the following condition is satisfied:

6. 6. The optical system according to claim 1, wherein the second lens group moves toward the image side during focusing from infinity to a close distance.

7. 7. The optical system according to claim 1, wherein the third lens group moves toward the object side during focusing from infinity to a close distance.

8. When the direction of movement from the object side to the image side is defined as positive, the amount of relative movement of the second lens group with respect to the image plane during focusing from infinity to the closest distance is defined as M2, and the amount of relative movement of the third lens group with respect to the image plane during focusing from infinity to the closest distance is defined as M3, -1.5<M3 / M2<0.0 8. The optical system according to claim 1, wherein the following condition is satisfied:

9. When the radius of curvature of the object-side lens surface of the lens arranged closest to the object in the second lens group is rf and the radius of curvature of the image-side lens surface of the lens arranged closest to the image in the second lens group is rr, 0.5<(rf+rr) / (rf-rr)<1.5 9. The optical system according to claim 1, wherein the following condition is satisfied:

10. 10. The optical system according to claim 1, wherein the distance on the optical axis between the second lens group and the third lens group is the widest among the distances on the optical axis between adjacent lens groups in the optical system.

11. When the back focus of the optical system when focused at infinity is sk and the distance on the optical axis between the second lens group and the third lens group when focused at infinity is D23, 0.5<D23 / sk<3.0 11. The optical system according to claim 1, wherein the following condition is satisfied:

12. When the back focus of the optical system at infinity is sk and the focal length of the fourth lens group is f4, 3.0<f4 / sk<40.0 12. The optical system according to claim 1, wherein the following condition is satisfied:

13. When the F-number of the optical system is fno, the focal length of the second lens group is f2, and the focal length of the third lens group is f3, -2.0<fno×f2 / f3<0.0 13. The optical system according to claim 1, wherein the following condition is satisfied:

14. 14. The optical system according to claim 1, wherein the second lens group is composed of three or less lenses.

15. 15. The optical system according to claim 1, wherein the third lens group is composed of three or less lenses.

16. 16. The optical system according to claim 1, wherein the fourth lens group includes two or more negative lenses.

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

Images