Optical system, and imaging device and lens device having the same.

Abstract

To provide an optical system which has a reduced total length and more compact focusing group as a whole, and is well corrected for chromatic aberration, field curvature, and the like while shooting over an entire object distance range from infinity to a short distance.SOLUTION: An optical system is provided, comprising a first lens group L1 having positive refractive power, a second lens group L2 having positive refractive power, and a third lens group L3 having positive refractive power arranged in order from the object side to the image side. When shifting focus from infinity to a short distance, the first lens group is stationary while the second and third lens groups move such that a distance therebetween changes. A focal length f of the entire system when focused on infinity and focal lengths f1, f2, f3 of the first, second, and third lens groups satisfy given conditions.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an optical system and an imaging device having the same, and is particularly suitable as a lens for use in imaging devices such as digital still cameras, video cameras, surveillance cameras, broadcast cameras, and silver halide photographic cameras. [Background technology]

[0002] In recent years, imaging devices such as digital still cameras, video cameras, surveillance cameras, broadcast cameras, and silver halide cameras using solid-state image sensors have become more sophisticated. Consequently, there is a demand for miniaturization of the entire focusing group in the optical system used in these devices. Furthermore, there is a need for an optical system that can effectively correct chromatic aberration and field curvature at the closest focusing distance while increasing the magnification during focusing from infinity to close-up. Additionally, with the shift towards mirrorless large-format cameras, there is a demand for compact, large-aperture lenses with short back focus. An optical system that satisfies these requirements is known, comprising a group of positive refractive power lenses arranged sequentially from the object side to the image side, a group of positive refractive power focusing lenses, and another group of positive refractive power focusing lenses (Patent Document 1). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2014-48488 [Overview of the project] [Problems that the invention aims to solve]

[0004] In the optical system described in Patent Document 1, the refractive power of the positive refractive power (reciprocal of the focal length) lens group located closest to the object is too weak, resulting in a long back focus and insufficient miniaturization. Furthermore, the total number of elements in the focusing group is large, making it unsuitable for miniaturizing and lightening the focusing group.

[0005] Therefore, the present invention aims to provide an optical system that can shorten the overall length and miniaturize the entire focus group while effectively correcting chromatic aberration and field curvature during shooting at all object distances from infinity to the closest distance. [Means for solving the problem]

[0006] The optical system of the present invention comprises a first lens group with positive refractive power, a second lens group with positive refractive power, and a third lens group with positive refractive power, arranged in order from the object side to the image side, wherein when focusing from infinity to near, the first lens group is fixed, and the second and third lens groups move such that the distance between them changes, and the second lens group has a negative lens positioned closest to the object, with its concave surface facing the object side. The third lens group consists of two or one lens. When the total focal length of the system at infinity focus is f, and the focal lengths of the first lens group, the second lens group, and the third lens group are f1, f2, and f3, respectively, 0.01 <f1 / f<2.60 0.50 <f2 / f3<30.00 The conditions are met.

[0007] Other objects and features of the present invention are described in the following embodiments. [Effects of the Invention]

[0008] According to the present invention, an optical system is obtained that can shorten the overall length and miniaturize the entire focusing group while effectively correcting chromatic aberration and field curvature during shooting at all object distances from infinity to the closest distance. [Brief explanation of the drawing]

[0009] [Figure 1] This is a cross-sectional view of the lens of the optical system of Example 1 when it is in focus at infinity. [Figure 2] This is a diagram showing the various aberrations of the optical system of Example 1 when it is focused at infinity. [Figure 3] This is a diagram of the aberrations of the optical system of Example 1 at close focus. [Figure 4] It is a lens cross-sectional view at infinity focus of the optical system of Example 2. [Figure 5] It is a diagram of various aberrations at infinity focus of the optical system of Example 2. [Figure 6] It is a diagram of various aberrations in the closest focus state of the optical system of Example 2. [Figure 7] It is a lens cross-sectional view at infinity focus of the optical system of Example 3. [Figure 8] It is a diagram of various aberrations at infinity focus of the optical system of Example 3. [Figure 9] It is a diagram of various aberrations in the closest focus state of the optical system of Example 3. [Figure 10] It is a lens cross-sectional view at infinity focus of the optical system of Example 4. [Figure 11] It is a diagram of various aberrations at infinity focus of the optical system of Example 4. [Figure 12] It is a diagram of various aberrations in the closest focus state of the optical system of Example 4. [Figure 13] It is a lens cross-sectional view at infinity focus of the optical system of Example 5. [Figure 14] It is a diagram of various aberrations at infinity focus of the optical system of Example 5. [Figure 15] It is a diagram of various aberrations in the closest focus state of the optical system of Example 5. [Figure 16] It is a schematic diagram of a main part as an example of an imaging device. [Figure 17] It is an external perspective view of the lens device in the present embodiment.

Mode for Carrying Out the Invention

[0010] An object of the present invention is to provide an optical system that can achieve a reduction in the overall length and miniaturization of the entire focus group, and can satisfactorily correct chromatic aberration, field curvature, etc. during shooting at all object distances from infinity to the closest distance.

[0011] The optical system of the present invention has a first lens group L1 with positive refractive power, a second lens group L2 with positive refractive power, and a third lens group L3 with positive refractive power, arranged in order from the object side to the image side. Furthermore, when focusing from infinity to close, the first lens group L1 is fixed, while the second lens group L2 and the third lens group L3 move so that the distance between them changes. By adopting the above configuration, the optical system of the present invention can suppress spherical aberration, field curvature, and chromatic aberration across the entire shooting range when focusing from infinity to close.

[0012] When the total focal length of the system at infinity focus is f, and the focal lengths of the first lens group L1, the second lens group L2, and the third lens group L3 are f1, f2, and f3, respectively, the optical system of the present invention satisfies the following conditions.

[0013] 0.01 <f1 / f<2.60 ····(1) 0.50 <f2 / f3<30.00 ····(2) Conditional equation (1) is a conditional equation that appropriately sets the ratio between the focal length of the first lens group L1 and the total focal length of the entire system when focused at infinity. If the upper limit of conditional equation (1) is exceeded, the focal length of the first lens group L1 becomes too large, the back focus becomes long, and it becomes difficult to shorten the overall length. Conversely, if the lower limit of conditional equation (1) is exceeded, the focal length of the first lens group L1 becomes too small, and correction of spherical aberration and axial chromatic aberration becomes difficult, especially with large-aperture lenses.

[0014] Conditional equation (2) is a conditional equation that appropriately sets the ratio of the focal length of the second lens group L2 to the focal length of the third lens group L3. If the upper limit of conditional equation (2) is exceeded, the focal length of the second lens group L2 becomes too large, which is undesirable as it makes the second lens group L2, the focusing group, larger. Also, if the lower limit of conditional equation (2) is exceeded, the focal length of the third lens group L3 becomes too large, which is undesirable as it makes the third lens group L3, the focusing group, larger.

[0015] More preferably, the numerical ranges for each conditional expression should be set as follows:

[0016] 0.01 <f1 / f<2.55 ····(1a) 0.70 <f2 / f3<20.00 ····(2a) More preferably, the numerical ranges for each conditional expression should be set as follows:

[0017] 0.01 <f1 / f<2.50 ····(1b) 0.90 <f2 / f3<10.00 ····(2b) By satisfying the above configuration and conditions, the present invention provides an optical system that can shorten the overall length and miniaturize the entire focusing group while effectively correcting chromatic aberration and field curvature during shooting at all object distances from infinity to the closest distance.

[0018] In the optical system of the present invention, it is more preferable that one or more of the following conditions are satisfied.

[0019] 0.01 <sk / f<1.00 ····(3) 0.01 <sk / f2<0.30 ····(4) 0.01 <TG2 / f2<0.10 ····(5) 0.10 <TG2 / TG3<3.00 ····(6) 0.20 <DG12 / f1<1.00 ····(7) 0.01 <FL2 / f2<0.20 ····(8) 1.00 <FL2 / FL3<3.00 ····(9) 0.05 <f / X1<3.00 ····(10) However, sk is the back focus of the entire system when focused at infinity, TG2 and TG3 are the thicknesses in the optical axis direction of the second lens group L2 and the third lens group L3, respectively, and DG12 is the distance between the first lens group L1 and the second lens group L2. Also, FL2 and FL3 are the amount of movement (extension amount) of the second lens group L2 and the third lens group L3 from infinity focus to focusing on an object 500 mm from the image plane, respectively, and X1 is the distance from the aperture to the image plane when focused at infinity. Note that the thickness in the optical axis direction of a lens group refers to the distance along the optical axis from the lens surface closest to the object to the lens surface closest to the image to that lens group.

[0020] Conditional equation (3) is a conditional equation that appropriately sets the ratio of the total focal length to the back focus when the system is in focus at infinity. If the upper limit of conditional equation (3) is exceeded, the back focus becomes too long compared to the total focal length of the system, making it difficult to shorten the overall length. Conversely, if the lower limit of conditional equation (3) is exceeded, the back becomes too short compared to the total focal length of the system, resulting in a steeper angle of incidence to the sensor, which worsens chromatic aberration in the peripheral areas and is therefore undesirable.

[0021] Conditional equation (4) is a conditional equation that appropriately sets the ratio of the focal length of the second lens group L2 to the back focus when focused at infinity. If the upper limit of conditional equation (4) is exceeded, the back focus becomes too long compared to the focal length of the second lens group L2, making it difficult to shorten the overall length. Conversely, if the lower limit of conditional equation (4) is exceeded, the focal length of the second lens group L2 becomes too small, and the amount of movement when focusing to close objects becomes relatively large compared to the back focus, resulting in a longer overall length, which is undesirable.

[0022] Conditional equation (5) is a conditional equation that appropriately sets the ratio of the thickness of the second lens group L2, which is the first focusing group, to its focal length. If the upper limit of conditional equation (5) is exceeded, the thickness of the second lens group L2 becomes too thick, which is undesirable as it hinders the weight reduction of the focusing lens group. Conversely, if the lower limit of conditional equation (5) is exceeded, the power of the focusing lens group becomes too loose, resulting in a large amount of focus shift, which is undesirable as it hinders miniaturization.

[0023] Conditional equation (6) is a conditional equation that appropriately sets the ratio of the thickness of the second lens group L2, which is the first focusing lens group, to the thickness of the third lens group L3, which is the second focusing lens group. If the upper limit of conditional equation (6) is exceeded, the thickness of the second lens group L2 becomes too thick. As a result, the weight of the first focusing lens group becomes too heavy compared to the weight of the second focusing lens group, which is undesirable as it hinders weight reduction. Also, if the lower limit of conditional equation (6) is exceeded, the thickness of the third lens group L3 becomes too thick, and the weight of the second focusing lens group becomes too heavy compared to the weight of the first focusing lens group. As a result, it hinders miniaturization and weight reduction, which is undesirable.

[0024] Conditional equation (7) is a conditional equation that appropriately sets the ratio between the distance DG12 between the first lens group L1 and the second lens group L2 and the focal length of the first lens group L1. If the upper limit of conditional equation (7) is exceeded, the overall length will increase, which is undesirable as it hinders miniaturization. Conversely, if the lower limit of conditional equation (7) is exceeded, the power of the first lens group L1 will become too weak, resulting in an increased front element diameter, which is also undesirable. Furthermore, if the distance DG12 between the first lens group L1 and the second lens group L2 becomes too narrow, it will be difficult to focus on close objects, which is also undesirable.

[0025] Conditional equation (8) is a conditional equation that appropriately sets the ratio between the amount of movement FL2 of the second lens group L2 from infinity focus to focusing on an object 500mm from the image plane, and the focal length f2 of the second lens group L2, which is the first focusing lens group. If the upper limit of conditional equation (8) is exceeded, the power of the second lens group L2 becomes too strong, and the performance when focusing on close objects deteriorates. Conversely, if the lower limit of conditional equation (8) is exceeded, the power of the second lens group L2 becomes too weak, resulting in a large amount of focus movement, which hinders miniaturization.

[0026] Conditional equation (9) is a conditional equation that appropriately sets the ratio between the amount of movement FL2 of the second lens group L2 from infinity focus to focusing on an object 500mm from the image plane and the amount of movement FL3 of the third lens group L3 from infinity focus to focusing on an object 500mm from the image plane. If the upper limit of conditional equation (9) is exceeded, the amount of movement of the second lens group L2 becomes too large, which is undesirable because it makes the mechanical mechanism for moving the second lens group L2, which is the first focusing group, larger. Also, it is undesirable because it makes the angle of view change during video recording larger. If the lower limit of conditional equation (9) is exceeded, the amount of movement of the third lens group L3 becomes too large, which is undesirable because it makes the mechanical mechanism for moving the third lens group L3, which is the second focusing group, larger.

[0027] Conditional equation (10) is a conditional equation that appropriately sets the ratio of the distance X1 from the aperture to the image plane and the overall focal length f of the optical system when focused at infinity. If the upper limit of conditional equation (10) is exceeded, the distance from the aperture to the image plane and the overall focal length of the optical system become too small when focused at infinity, causing the exit pupil position in the optical system to approach the image plane. As a result, it becomes difficult to ensure telecentricity within a range that is compatible with electronic image sensors (solid-state image sensors). Conversely, if the lower limit of conditional equation (10) is exceeded, the distance from the aperture to the image plane and the overall focal length of the optical system become too large when focused at infinity, making it difficult to suppress the overall length of the optical system.

[0028] By satisfying the above configuration and conditions, an optical system can be obtained that shortens the overall length and miniaturizes the entire focusing group, while effectively correcting chromatic aberration and field curvature during shooting at all object distances from infinity to close.

[0029] More preferably, the numerical ranges for each conditional expression (3) to (10) should be set as follows.

[0030] 0.05 <sk / f<0.90 ····(3a) 0.01 <sk / f2<0.25 ····(4a) 0.01 <TG2 / f2<0.09 ····(5a) 0.2 <TG2 / TG3<2.50 ····(6a) 0.20 <DG12 / f1<0.80 ····(7a) 0.01 <FL2 / f2<0.15 ····(8a) 1.00 <FL2 / FL3<2.50 ····(9a) 0.05 <f / X1<2.00 ····(10a) More preferably, the numerical ranges of each conditional expression (3a) to (10a) should be set as follows.

[0031] 0.10 <sk / f<0.80 ····(3b) 0.05 <sk / f2<0.20 ····(4b) 0.010 <TG2 / f2<0.071 ····(5b) 0.30 <TG2 / TG3<2.00 ····(6b) 0.20 <DG12 / f1<0.70 ····(7b) 0.01 <FL2 / f2<0.10 ····(8b) 1.00 <FL2 / FL3<2.00 ····(9b) 0.05 <f / X1<1.00 ···(10b) Furthermore, the optical system of the present invention may correct distortion and chromatic aberration among various aberrations by electrical image processing. By doing so, it is possible to achieve a smaller overall lens diameter while increasing the magnification when shooting at the closest point in the optical system, and to effectively correct chromatic aberration and field curvature when shooting at the closest point.

[0032] Furthermore, the optical system of the present invention makes it easy to suppress changes in the angle of view during video recording by having the second lens group L2 and the third lens group L3 move toward the object when focusing from infinity to close. (Examples 1-5) Embodiments of the optical system of the present invention will be described below with reference to the drawings.

[0033] Figure 1 is a cross-sectional view of the lens of the optical system in Embodiment 1 of the present invention when it is in focus at infinity. Figures 2 and 3 are aberration diagrams of the optical system in the infinity and near focus states, respectively.

[0034] Figure 4 is a cross-sectional view of the lens of the optical system in Embodiment 2 of the present invention when it is in focus at infinity. Figures 5 and 6 are aberration diagrams of the optical system in the infinity and near focus states, respectively.

[0035] Figure 7 is a cross-sectional view of the lens of the optical system in Embodiment 3 of the present invention when it is in focus at infinity. Figures 8 and 9 are aberration diagrams of the optical system in the infinity and near focus states, respectively.

[0036] Figure 10 is a cross-sectional view of the lens of the optical system in Embodiment 4 of the present invention when it is in focus at infinity. Figures 11 and 12 are aberration diagrams of the optical system in the infinity and near focus states, respectively.

[0037] Figure 13 is a cross-sectional view of the lens of the optical system in Embodiment 5 of the present invention when it is in focus at infinity. Figures 14 and 15 are aberration diagrams of the optical system in the infinity and near focus states, respectively.

[0038] The optical systems of Examples 1 to 5 are photographic lens systems used in imaging devices, and in the lens cross-section diagrams, the left side is the object side and the right side is the image side. In the lens cross-section diagrams of Examples 1 to 5, L1 is the first lens group with positive refractive power, L2 is the second lens group with positive refractive power, and L3 is the third lens group with positive refractive power. SP is the aperture diaphragm, and IP is the image plane. In the lens cross-section diagram of Example 4, L4 is the fourth lens group with negative refractive power. In Examples 1 to 5, during focusing, magnification is performed by moving the second lens group L2 towards the object side and the third lens group L3 towards the object side, as indicated by the arrows.

[0039] The configuration within each lens group in Examples 1 to 5 will now be described. The first lens group L1 consists of a negative lens, a cemented lens of a positive and negative lens, a cemented lens of a negative and positive lens, a cemented lens of a positive and negative lens, or two lenses, a positive lens and a negative lens. This suppresses chromatic aberration at the wide-angle end while reducing the power of the first lens group L1, contributing to miniaturization. The second lens group L2 consists of two lenses, a negative lens and a positive lens. This suppresses sagittal coma aberration when the aperture is increased, while contributing to the miniaturization and weight reduction of the second lens group L2, which is the first focusing lens group, by using the minimum necessary number of lenses. The third lens group L3 consists of two or one lens. This suppresses sagittal coma aberration when the aperture is increased, while contributing to the miniaturization and weight reduction of the third lens group L3, which is the second focusing lens group, by using the minimum necessary number of lenses. The fourth lens group L4 in Example 4 consists of a single negative lens, contributing to a reduction in overall length. Note that in the lens configurations shown in Examples 1, 2, and 3, a fourth lens group L4 with negative refractive power may also be added.

[0040] In each aberration diagram, d and g represent the d-line and g-line, respectively, and ΔM and ΔS represent the meridional and sagittal image planes. F is the F-number, and ω is the half-angle of view (°). For spherical aberration, the d-line (solid line) and g-line (dotted line) are shown. For astigmatism, ΔM and ΔS on the d-line are shown, and for distortion, the d-line is shown. For chromatic aberration, the aberration of the g-line relative to the d-line is shown, and for chromatic aberration, the aberration of the g-line relative to the d-line is shown.

[0041] The following shows numerical examples 1 to 5 corresponding to each of the embodiments of the present invention.

[0042] In the surface data of each numerical example, the surface numbers are shown in order from the object side. Here, r represents the radius of curvature of each optical surface, and d (mm) represents the axial distance (distance on the optical axis) between the m-th surface and the (m + 1)-th surface. Note that m is the surface number counted from the light incident side. Also, nd represents the refractive index with respect to the d-line of each optical member, and νd represents the Abbe number of the optical member. The Abbe number νd of a certain material is expressed as νd = (Nd - 1) / (NF - NC), where Nd, NF, and NC are the refractive indices at the d-line (587.6 nm), F-line (486.1 nm), and C-line (656.3 nm) of the Fraunhofer lines, respectively.

[0043] In each numerical example, d, focal length (mm), F-number, and half angle (°) are all the values when the optical system of each example is focused on an infinite object. "BF (back focus)" is the distance on the optical axis from the final lens surface (the lens surface closest to the image side) to the paraxial image plane, expressed in terms of the air-equivalent length. "Total lens length" is the length obtained by adding the back focus to the distance on the optical axis from the frontmost surface (the lens surface closest to the object side) to the final surface of the zoom lens. "Lens group" includes not only cases composed of multiple lenses but also cases composed of a single lens.

[0044] When the optical surface is an aspherical surface, an asterisk (*) is attached to the right side of the surface number. The aspherical shape is expressed as x=(h / R) / [1+{1-(1+k)(h / R) 2}^2 2 +A4×h 1 / 2 ^4 4 +A6×h 6 ^6 8 +A8×h 10 ^8 12 ^10 XX +A12×h

[0045] where X is the displacement amount 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. Here, "e±XX" in each aspherical coefficient means "×10±(Numerical Example 1) Unit: mm Surface data Face number rd nd νd 1 146.993 2.26 1.58267 46.4 2 26.699 11.90 3 54.581 11.21 2.00100 29.1 4 -95.421 1.84 1.54072 47.2 5 22.307 15.32 6 -29.242 2.00 1.60342 38.0 7 39.731 12.00 1.77250 49.6 8 -34.655 0.40 9* 55.986 7.42 1.76802 49.2 10 -63.673 2.00 1.85478 24.8 11 1660.234 (variable) 12 (aperture) ∞ 10.02 13 -30.789 2.00 1.69895 30.1 14 -47.478 0.27 15 76.544 6.00 1.49700 81.5 16 -49.703 (variable) 17* -656.310 3.00 1.76802 49.2 18 -159.856 0.50 19 39.375 6.05 1.49700 81.5 20 81.209 (variable) Image plane ∞ Aspherical data 9th page K=0.00000e+000 A4=-1.95201e-007 A6= 5.56469e-010 A8=-1.84169e-012 Page 17 K=0.00000e+000 A4=-8.55938e-006 A6=-3.88001e-009 Various data Zoom ratio 1.00 Focal length 26.79 F-number 1.44 Half-angle (°): 38.93 Image height 21.64 Lens length: 134.78 BF 13.00 d11 11.85 d16 15.72 d20 13.00 Zoom lens group data Group starting plane focal length 1 1 51.01 2 12 106.20 3 17 94.79 (Numerical Example 2) Unit: mm Surface data Face number rd nd νd 1 119.621 2.26 1.58267 46.4 2 25.462 8.91 3 47.110 11.19 2.00100 29.1 4 -104.870 1.84 1.54072 47.2 5 19.669 12.95 6 -29.712 2.00 1.60342 38.0 7 26.908 12.00 1.77250 49.6 8 -38.784 0.40 9* 43.881 7.08 1.76802 49.2 10* -93.453 0.40 11 175.819 2.00 1.85478 24.8 12 42.301 6.98 13 (aperture) ∞ (variable) 14 -24.621 2.00 1.69895 30.1 15 -42.889 0.27 16 254.901 6.00 1.49700 81.5 17 -35.061 (variable) 18* -99.313 4.00 1.53110 55.9 19 -40.599 0.50 20 42.567 8.57 1.49700 81.5 21 303.803 (variable) Image plane ∞ Aspherical data 9th page K=0.00000e+000 A4=4.42691e-007 A6=-7.15232e-009 A8=3.90599e-011 Side 10 K=0.00000e+000 A4=4.53281e-006 A6=-8.69501e-009 A8= 5.39734e-011 Page 18 K=0.00000e+000 A4=-6.49149e-006 A6=-1.15124e-009 Various data Zoom ratio 1.00 Focal length 26.62 F-number 1.44 Half-angle (°): 39.10 Image height 21.64 Lens length: 131.96 BF 20.00 d13 15.13 d17 7.48 d21 20.00 Zoom lens group data Group starting plane focal length 1 1 67.64 2 14 175.19 3 18 54.82 (Numerical Example 3) Unit: mm Surface data Face number rd nd νd 1 116.638 2.26 1.58267 46.4 2 27.122 9.30 3 52.499 11.03 2.00100 29.1 4 -99.507 1.84 1.54072 47.2 5 24.138 14.45 6 -32.665 2.00 1.60342 38.0 7 36.327 12.00 1.77250 49.6 8 -38.237 0.40 9* 49.984 8.91 1.76802 49.2 10* -74.122 0.40 11 -97.086 2.00 1.85478 24.8 12 102.731 9.99 13 (aperture) ∞ (variable) 14 -29.000 2.00 1.69895 30.1 15 -85.904 0.27 16 427.013 6.00 1.80400 46.6 17 -43.849 (variable) 18* -120.876 3.00 1.76802 49.2 19 -86.309 0.50 20 48.129 9.02 1.49700 81.5 21 -376.318 (variable) Image plane ∞ Aspherical data 9th page K=0.00000e+000 A4=6.46101e-007 A6=-1.56132e-009 A8=4.53013e-012 Side 10 K=0.00000e+000 A4=1.93058e-006 A6=-2.70735e-009 A8=7.75395e-012 Page 18 K=0.00000e+000 A4=-3.87737e-006 A6=-1.96727e-009 Various data Zoom ratio 1.00 Focal length 33.73 F-number 1.44 Half-angle (°): 32.68 Image height 21.64 Lens length: 143.92 BF 20.00 d13 18.16 d17 10.39 d21 20.00 Zoom lens group data Group starting plane focal length 1 1 68.33 2 14 167.14 3 18 69.96 (Numerical Example 4) Unit: mm Surface data Face number rd nd νd 1 60.679 2.26 1.69895 30.1 2 29.765 6.74 3 53.110 7.39 2.00100 29.1 4 -237.078 1.84 1.51633 64.1 5 21.849 19.33 6 -35.613 2.00 1.64769 33.8 7 33.010 12.00 1.77250 49.6 8 -55.208 0.40 9* 49.095 9.44 1.76802 49.2 10* -80.124 0.40 11 56.508 1.26 1.76182 26.5 12 37.517 7.68 13 (aperture) ∞ (variable) 14 -27.708 1.38 1.85478 24.8 15 -86.615 0.27 16 87.508 6.00 1.77250 49.6 17 -43.137 (variable) 18* -421.067 4.00 1.76802 49.2 19 -60.846 (variable) 20 -46.936 1.64 1.51633 64.1 21 -76.686 (variable) Image plane ∞ Aspherical data 9th page K=0.00000e+000 A4=-1.94572e-006 A6=-1.87272e-009 A8=2.79637e-013 Side 10 K=0.00000e+000 A4=4.97742e-008 A6=-1.52803e-009 A8=2.61249e-012 Page 18 K=0.00000e+000 A4=-8.41605e-006 A6=-3.79274e-009 Various data Zoom ratio 1.00 Focal length 33.87 F-number 1.44 Half-angle (°): 32.57 Image height 21.64 Lens length: 131.26 BF 16.49 d13 18.47 d17 5.04 d19 7.23 d21 16.49 Zoom lens group data Group starting plane focal length 1 1 53.36 2 14 134.26 3 18 92.16 4 20 -238.81 (Numerical Example 5) Unit: mm Surface data Face number rd nd νd 1 118.771 2.26 1.70154 41.2 2 28.953 11.38 3 70.479 9.79 2.00100 29.1 4 -77.769 1.84 1.54072 47.2 5 28.154 17.02 6 -34.552 2.00 1.60342 38.0 7 46.372 14.34 1.77250 49.6 8 -38.790 0.40 9* 31.270 7.77 1.76802 49.2 10* -306.540 0.40 11 205.045 2.00 1.85478 24.8 12 37.510 (Variable) 13 (aperture) ∞ 10.03 14 -26.478 2.00 1.69895 30.1 15 -45.919 0.27 16 112.739 6.00 1.49700 81.5 17 -37.281 (variable) 18* -155.139 3.00 1.53110 55.9 19 -44.298 0.50 20 48.577 3.96 1.49700 81.5 21 67.258 (Variable) Image plane ∞ Aspherical data 9th page K=0.00000e+000 A4=-4.79445e-007 A6=-2.54333e-010 A8=3.69344e-013 Side 10 K=0.00000e+000 A4=3.41648e-006 A6=-2.47237e-009 A8=2.27433e-012 Page 18 K=0.00000e+000 A4=-1.18783e-005 A6=-3.76022e-009 Various data Zoom ratio 1.00 Focal length 26.70 F-number 1.44 Half-angle (°): 39.02 Image height 21.64 Lens length: 133.24 BF 20.00 d12 12.74 d17 5.54 d21 20.00 Zoom lens group data Group starting plane focal length 1 1 50.52 2 13 125.52 3 18 84.29 Table 1 below shows the numerical values ​​corresponding to conditional equations (1) to (10) in each example.

[0046] [Table 1]

[0047] Next, embodiments of imaging devices and lens devices using the optical systems shown in each embodiment will be described with reference to Figures 16 and 17.

[0048] Figure 16 is a schematic diagram of the main parts of a digital still camera (imaging device) using the optical system of the present invention as an imaging optical system. In Figure 16, 10 is the camera body, 11 is the imaging optical system configured by the optical system of the present invention, and 12 is a solid-state image sensor (photoelectric conversion element) such as a CCD sensor or CMOS sensor built into the camera body that receives the subject image formed by the imaging optical system 11. Also, 13 is a recording means for recording the subject image received by the image sensor 12, and 14 is a viewfinder for observing the subject image displayed on an unshown display element. The display element is made up of a liquid crystal panel or the like, and displays the subject image formed on the image sensor 12. The camera body 10 may be a so-called single-lens reflex camera with a quick-turn mirror, or a so-called mirrorless camera without a quick-turn mirror.

[0049] Figure 17 is a schematic diagram of the external appearance of a lens device 20, such as an interchangeable lens. The lens device 20 includes an imaging optical system 11. The lens device 20 may also have a focus operation means 21 and an operation means 22 for changing the mode. Furthermore, the arrangement of the lens group of the imaging optical system 11 may be changed mechanically or electrically by the user operating the focus operation means 21, thereby changing the focal position. Furthermore, the arrangement of the lens group of the imaging optical system 11 may be changed mechanically or electrically by the user operating the operation means 22 for changing the mode, thereby changing the aberrations.

[0050] By applying the optical system of the present invention to an imaging device and a lens device, it is possible to obtain an imaging device and a lens device that can shorten the overall length and miniaturize the entire focusing group while effectively correcting chromatic aberration and field curvature during imaging at all object distances from infinity to the closest distance.

[0051] Although preferred embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and various modifications and changes are possible within the scope of its gist. [Explanation of symbols]

[0052] L1: First lens group L2: Second lens group L3: Third lens group

Claims

1. An optical system having a first lens group with positive refractive power, a second lens group with positive refractive power, and a third lens group with positive refractive power, arranged in order from the object side to the image side, When focusing from infinity to near, the first lens group is fixed, and the second and third lens groups move such that the distance between them changes. The second lens group has a negative lens positioned closest to the object, with its concave surface facing the object. The third lens group consists of two or one lens, When the total focal length of the system at infinity focus is f, and the focal lengths of the first lens group, the second lens group, and the third lens group are f1, f2, and f3, respectively, 0.01<f1 / f<2.60 0.50<f2 / f3<30.00 An optical system characterized by satisfying the following conditions.

2. When sk is the back focus of the entire system when focused at infinity, 0.01<sk / f<1.00 The optical system according to claim 1, characterized in that it satisfies the following conditions.

3. When sk is the back focus of the entire system when focused at infinity, 0.01<sk / f2<0.30 The optical system according to claim 1 or 2, characterized in that it satisfies the following conditions.

4. When the thickness of the second lens group in the optical axis direction is TG2, 0.01<TG2 / f2<0.10 An optical system according to any one of claims 1 to 3, characterized in that it satisfies the following conditions.

5. When the thickness of the second lens group in the optical axis direction is TG2 and the thickness of the third lens group in the optical axis direction is TG3, 0.10<TG2 / TG3<3.00 The optical system according to any one of claims 1 to 4, characterized in that it satisfies the following conditions.

6. When the distance between the first lens group and the second lens group is DG12, 0.20<DG12 / f1<1.00 The optical system according to any one of claims 1 to 5, characterized in that it satisfies the following conditions.

7. An optical system having a first lens group with positive refractive power, a second lens group with positive refractive power, and a third lens group with positive refractive power, arranged in order from the object side to the image side, When focusing from infinity to near, the first lens group is fixed, and the second and third lens groups move such that the distance between them changes. The second lens group has a negative lens positioned closest to the object, with its concave surface facing the object. When the total focal length of the system at infinity focus is f, the focal lengths of the first lens group, the second lens group, and the third lens group are f1, f2, and f3 respectively, and the distance between the first lens group and the second lens group is DG12, 0.01<f1 / f<2.60 0.50<f2 / f3<30.00 0.20<DG12 / f1<1.00 An optical system characterized by satisfying the following conditions.

8. When FL2 is the amount of movement of the second lens group from focusing at infinity to focusing on an object 500 mm from the image plane, 0.01<FL2 / f2<0.20 The optical system according to any one of claims 1 to 7, characterized in that it satisfies the following conditions.

9. When the amount of movement of the second lens group and the third lens group from focusing at infinity to focusing on an object 500 mm from the image plane is denoted as FL2 and FL3, respectively, 1.00<FL2 / FL3<3.00 The optical system according to any one of claims 1 to 8, characterized in that it satisfies the following conditions.

10. An optical system having a first lens group with positive refractive power, a second lens group with positive refractive power, and a third lens group with positive refractive power, arranged in order from the object side to the image side, When focusing from infinity to near, the first lens group is fixed, and the second and third lens groups move such that the distance between them changes. The second lens group has a negative lens positioned closest to the object, with its concave surface facing the object. When the total focal length of the system at infinity focus is f, the focal lengths of the first lens group, the second lens group, and the third lens group are f1, f2, and f3, respectively, and the amount of movement of the second lens group and the third lens group from infinity focus to focusing on an object 500 mm from the image plane is FL2 and FL3, respectively, 0.01<f1 / f<2.60 0.50<f2 / f3<30.00 1.00<FL2 / FL3<3.00 An optical system characterized by satisfying the following conditions.

11. The optical system has an aperture, When the distance from the aperture to the image plane at infinity focus is X1, 0.05<f / X1<3.00 The optical system according to any one of claims 1 to 10, characterized in that it satisfies the following conditions.

12. The first lens group is arranged in order from the object side to the image side. Negative lens and, A cemented lens consisting of a positive lens and a negative lens, A cemented lens of a negative lens and a positive lens, The optical system according to any one of claims 1 to 11, characterized in that it comprises a cemented lens of a positive lens and a negative lens, or two lenses, one positive lens and one negative lens.

13. An optical system having a first lens group with positive refractive power, a second lens group with positive refractive power, and a third lens group with positive refractive power, arranged in order from the object side to the image side, When focusing from infinity to near, the first lens group is fixed, and the second and third lens groups move such that the distance between them changes. The first lens group is arranged in order from the object side to the image side. Negative lens and, A cemented lens consisting of a positive lens and a negative lens, A cemented lens of a negative lens and a positive lens, It consists of a cemented lens with a positive and a negative lens, or two lenses, one positive and one negative. The second lens group has a negative lens positioned closest to the object, with its concave surface facing the object. When the total focal length of the system at infinity focus is f, and the focal lengths of the first lens group, the second lens group, and the third lens group are f1, f2, and f3, respectively, 0.01<f1 / f<2.60 0.50<f2 / f3<30.00 An optical system characterized by satisfying the following conditions.

14. The optical system according to any one of claims 1 to 13, characterized in that the second lens group consists of two lenses, a negative lens and a positive lens, arranged in order from the object side to the image side.

15. The optical system according to any one of claims 1 to 14, further comprising a fourth lens group consisting of a negative lens positioned on the image side of the third lens group.

16. An optical system having a first lens group with positive refractive power, a second lens group with positive refractive power, a third lens group with positive refractive power, and a fourth lens group with negative refractive power, arranged in order from the object side to the image side, When focusing from infinity to near, the first lens group is fixed, and the second and third lens groups move such that the distance between them changes. The second lens group has a negative lens positioned closest to the object, with its concave surface facing the object. The fourth lens group consists of a single lens, When the total focal length of the system at infinity focus is f, and the focal lengths of the first lens group, the second lens group, and the third lens group are f1, f2, and f3, respectively, 0.01<f1 / f<2.60 0.50<f2 / f3<30.00 An optical system characterized by satisfying the following conditions.

17. An optical system according to any one of claims 1 to 16, An imaging device characterized by having an image sensor that receives light from an image formed by the optical system.

18. A lens device characterized by having an optical system according to any one of claims 1 to 16.

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