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

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 used in imaging devices such as digital still cameras, video cameras, surveillance cameras, broadcast cameras, and silver halide cameras.

Background Art

[0002] In recent years, imaging devices such as digital still cameras, video cameras, surveillance cameras, broadcast cameras, and silver halide cameras using solid-state imaging devices have been highly functionalized. As an optical system used therefor, miniaturization of the entire focus group has been required. Furthermore, when focusing from infinity to the closest distance, it is required to be an optical system that can satisfactorily correct chromatic aberration and field curvature at the closest shooting while increasing the shooting magnification. In addition, with the mirrorless conversion of large-format cameras, there is a demand for a lens with a short back focus, small size, and large aperture. As an optical system that satisfies these requirements, an optical system having a lens group with a positive refractive power, a focus lens group with a positive refractive power, and a focus lens group with a positive refractive power, which are arranged in order from the object side to the image side, is known (Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the optical systems of Patent Document 1, the refractive power of the lens group with a positive refractive power (the reciprocal of the focal length) arranged on the outermost object side is too weak, so the back focus is long and miniaturization is insufficient. In addition, the number of lenses in the entire focus group is large, and it is not optimal for miniaturization and weight reduction of the focus group.

[0005] Therefore, an object of the present invention is to provide an optical system that can correct chromatic aberration, field curvature, etc. during shooting at all object distances from infinity to the closest distance while shortening the overall length and miniaturizing the entire focus group.

Means for Solving the Problems

[0006] The optical system of the present invention is an optical system having, in order from the object side to the image side, a first lens group with positive refractive power, a second lens group with positive refractive power, and a third lens group with positive refractive power, and focusing from infinity to the closest distance For , wherein the first lens group is fixed, the second lens group and the third lens group move such that the distance between the second lens group and the third lens group changes, the first lens group has a negative lens disposed on the object side with its convex surface facing the object side, the focal length of the entire 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 , the distance DG12 between the first lens group and the second lens group When 0.01 < f1 / f < 2.60 0.50 < f2 / f3 < 30.00 0.20 < DG12 / f1 < 1.00 satisfies the conditions.

[0007] Other objects and features of the present invention will be described in the following embodiments.

Effects of the Invention

[0008] According to the present invention, an optical system can be obtained that can correct chromatic aberration, field curvature, etc. during shooting at all object distances from infinity to the closest distance while shortening the overall length and miniaturizing the entire focus group.

Brief Description of the Drawings

[0009]

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Embodiments 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 a positive refractive power, a second lens group L2 with a positive refractive power, and a third lens group L3 with a positive refractive power, which are arranged in order from the object side to the image side. Further, when focusing from infinity to the closest distance, the first lens group L1 is fixed, and the second lens group L2 and the third lens group L3 are configured to move such 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 of magnification in the entire imaging range when focusing from infinity to the closest distance.

[0012] When the focal length of the entire 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 expression (1) is a conditional expression that appropriately sets the ratio of the focal length of the first lens group L1 to the focal length of the entire system at infinity focus. If the upper limit value of conditional expression (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. Also, if the lower limit value of conditional expression (1) is exceeded, the focal length of the first lens group L1 becomes too small, and it becomes difficult to correct mainly spherical aberration, axial chromatic aberration, etc., especially for large-aperture lenses.

[0014] Conditional expression (2) is a conditional expression 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 value of conditional expression (2) is exceeded, the focal length of the second lens group L2 becomes too large, and the second lens group L2, which is the focus group, becomes large, which is not preferable. Also, if the lower limit value of conditional expression (2) is exceeded, the focal length of the third lens group L3 becomes too large, and the third lens group L3, which is the focus group, becomes large, which is not preferable.

[0015] More preferably, the numerical ranges of each conditional expression are set as follows.

[0016] 0.01 < f1 / f < 2.55 ····(1a) 0.70 < f2 / f3 < 20.00 ····(2a) More preferably, the numerical ranges of the respective conditional expressions are set as follows.

[0017] 0.01 < f1 / f < 2.50 ····(1b) 0.90 < f2 / f3 < 10.00 ····(2b) By satisfying the above-described configuration and conditional expressions, the present invention can provide an optical system that can satisfactorily correct chromatic aberration, field curvature, etc. during shooting at all object distances from infinity to the closest distance while shortening the overall length and miniaturizing the entire focusing group.

[0018] In the optical system of the present invention, more preferably, one or more of the following conditional expressions 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 overall back focus at infinity focus, TG2 and TG3 are the thicknesses of the second lens group L2 and the third lens group L3 in the optical axis direction respectively, and DG12 is the distance between the first lens group L1 and the second lens group L2. Also, FL2 and FL3 are the movement amounts (extension amounts, positive when extended toward the object side) 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, and X1 is the distance from the aperture to the image plane at infinity focus. Note that the thickness of a lens group in the optical axis direction refers to the distance on the optical axis from the lens surface closest to the object of that lens group to the lens surface closest to the image of that lens group.

[0020] Conditional expression (3) is a conditional expression that appropriately sets the ratio of the overall focal length to the back focus at infinity focus. If the upper limit value of conditional expression (3) is exceeded, the back focus becomes too long compared to the overall focal length, making it difficult to shorten the overall length. Also, if the lower limit value of conditional expression (3) is exceeded, the back becomes too short compared to the overall focal length, increasing the incident angle on the sensor, which is not preferable because the peripheral chromatic aberration deteriorates.

[0021] Conditional expression (4) is a conditional expression that appropriately sets the ratio of the focal length of the second lens group L2 to the back focus at infinity focus. If the upper limit value of conditional expression (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. Also, if the lower limit value of conditional expression (4) is exceeded, the focal length of the second lens group L2 becomes too small, and the movement amount during focusing at the closest distance becomes relatively large compared to the back focus, increasing the overall length, which is not preferable.

[0022] Conditional expression (5) is a conditional expression that appropriately sets the ratio of the thickness of the second lens group L2, which is the first focus group, to the focal length. If the upper limit value of conditional expression (5) is exceeded, the thickness of the second lens group L2 becomes too thick, which hinders the weight reduction of the focus lens group, so it is not preferable. Also, if the lower limit value of conditional expression (5) is exceeded, the power of the focus lens group becomes too loose, increasing the focus movement amount and hindering miniaturization, so it is not preferable.

[0023] Conditional expression (6) is a conditional expression that appropriately sets the ratio of the thickness of the second lens group L2, which is the first focus group, to the thickness of the third lens group L3, which is the second focus lens group. If the upper limit value of conditional expression (6) is exceeded, the thickness of the second lens group L2 becomes too thick. Therefore, the weight of the first focus lens group becomes too heavy compared to the weight of the second focus lens group, which is not preferable because it hinders weight reduction. Also, if the lower limit value of conditional expression (6) is exceeded, the thickness of the third lens group L3 becomes too thick, and the weight of the second focus lens group becomes too heavy compared to the weight of the first focus lens group. For this reason, it hinders miniaturization and weight reduction and is not preferable.

[0024] Conditional expression (7) is a conditional expression that appropriately sets the ratio of the distance DG12 between the first lens group L1 and the second lens group L2 to the focal length of the first lens group L1. If the upper limit value of conditional expression (7) is exceeded, the overall length becomes long, which hinders miniaturization and is not preferable. Also, if the lower limit value of conditional expression (7) is exceeded, the power of the first lens group L1 becomes too loose, resulting in an increase in the front lens diameter, which is not preferable. Also, the distance DG12 between the first lens group L1 and the second lens group L2 becomes too narrow, making it difficult to focus at the closest distance, which is not preferable.

[0025] Conditional expression (8) is a conditional expression that appropriately sets the ratio of the movement amount FL2 of the second lens group L2 from infinity focus to focusing on an object 500 mm from the image plane to the focal length f2 of the second lens group L2, which is the first focus lens group. If the upper limit value of conditional expression (8) is exceeded, the power of the second lens group L2 becomes too strong, deteriorating the performance during focusing at the closest distance. Also, if the lower limit value of conditional expression (8) is exceeded, the power of the second lens group L2 becomes too loose, resulting in a large focus movement amount, which hinders miniaturization.

[0026] Conditional expression (9) is a conditional expression that appropriately sets the ratio of the movement amount FL2 of the second lens group L2 from infinity focus to focusing on an object 500 mm from the image plane and the movement amount FL3 of the third lens group L3 from infinity focus to focusing on an object 500 mm from the image plane. If the upper limit value of conditional expression (9) is exceeded, the movement amount of the second lens group L2 becomes too large, and the mechanical mechanism for moving the second lens group L2, which is the first focus group, becomes large, which is not preferable. Also, the change in the angle of view during video shooting becomes large, which is not preferable. If the lower limit value of conditional expression (9) is exceeded, the movement amount of the third lens group L3 becomes too large, and the mechanical mechanism for moving the third lens group L3, which is the second focus group, becomes large, which is not preferable.

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

[0028] By satisfying the above configuration and conditional expressions, an optical system can be obtained that can correct chromatic aberration, field curvature, etc. during shooting at all object distances from infinity to the closest distance while shortening the overall length and miniaturizing the entire focus group.

[0029] More preferably, the numerical ranges of the respective conditional expressions (3) to (10) are 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 the respective conditional expressions (3a) to (10a) may 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) Also, in the optical system of the present invention, among various aberrations, the correction of distortion aberration and magnification chromatic aberration may be corrected by electrical image processing. By doing so, while achieving miniaturization of the entire lens diameter, when shooting at the closest distance in the optical system, it is possible to satisfactorily correct chromatic aberration and field curvature at the closest shooting while increasing the shooting magnification.

[0032] Also, in the optical system of the present invention, when focusing from infinity to the closest distance, by moving the second lens group L2 and the third lens group L3 toward the object side, it is possible to easily suppress the change in the angle of view during video shooting. (Examples 1 to 5) Hereinafter, embodiments of the optical system of the present invention will be described with reference to the drawings.

[0033] FIG. 1 is a lens cross-sectional view at infinity focus of the optical system in Example 1 of the present invention. FIGS. 2 and 3 are aberration diagrams in the infinity and closest focus states of the optical system, respectively.

[0034] FIG. 4 is a lens cross-sectional view at infinity focus of the optical system in Example 2 of the present invention. FIGS. 5 and 6 are aberration diagrams in the infinity and closest focus states of the optical system, respectively.

[0035] FIG. 7 is a lens cross-sectional view at infinity focus of the optical system in Example 3 of the present invention. FIGS. 8 and 9 are aberration diagrams in the infinity and closest focus states of the optical system, respectively.

[0036] FIG. 10 is a lens cross-sectional view at infinity focus of the optical system in Example 4 of the present invention. FIGS. 11 and 12 are aberration diagrams in the infinity and closest focus states of the optical system, respectively.

[0037] FIG. 13 is a lens cross-sectional view at infinity focus of the optical system in Example 5 of the present invention. FIGS. 14 and 15 are aberration diagrams in the infinity and closest focus states of the optical system, respectively.

[0038] The optical systems of Examples 1 to 5 are imaging lens systems used in an imaging device. In the lens cross-sectional view, the left side is the object side and the right side is the image side. In each of the lens cross-sectional views of Examples 1 to 5, L1 is a first lens group having a positive refractive power, L2 is a second lens group having a positive refractive power, and L3 is a third lens group having a positive refractive power. SP is the aperture stop and IP is the image plane. In the lens cross-sectional view of Example 4, L4 is a fourth lens group having a negative refractive power. In Examples 1 to 5, during focusing, the second lens group L2 is moved toward the object side and the third lens group L3 is moved toward the object side as indicated by the arrows to perform zooming.

[0039] The configurations within each lens group in Examples 1 to 5 will be described. The first lens group L1 is composed of a negative lens, a positive lens, a cemented lens of a negative lens and a positive lens, a cemented lens of a negative lens and a positive lens, a cemented lens of a positive lens and a negative lens, or two lenses of a positive lens and a negative lens. Thereby, while suppressing the longitudinal chromatic aberration at the wide-angle end, the power of the first lens group L1 is reduced, contributing to miniaturization. The second lens group L2 is composed of two lenses, a negative lens and a positive lens. Thereby, while suppressing the sagittal coma aberration when the aperture is increased, it contributes to the miniaturization and weight reduction of the second lens group L2, which is the first focusing lens group, with the minimum necessary number of lenses. The third lens group L3 is composed of two or one lens. Thereby, while suppressing the sagittal coma aberration when the aperture is increased, it contributes to the miniaturization and weight reduction of the third lens group L3, which is the second focusing lens group, with the minimum necessary number of lenses. The fourth lens group L4 in Example 4 is composed of one negative lens, contributing to shortening the overall length. In addition, in the lens configurations shown in Examples 1, 2, and 3, a fourth lens group L4 with a negative refractive power may be further added.

[0040] Note that in each aberration diagram, d and g represent the d-line and the g-line, and ΔM and ΔS represent the meridional image plane and the sagittal image plane. F is the F-number, and ω is the semi-field angle (°). In spherical aberration, the d-line (solid line) and the g-line (dotted line) are displayed. In astigmatism, ΔM and ΔS for the d-line are displayed, and in distortion, the d-line is displayed. In longitudinal chromatic aberration, the aberration of the g-line with respect to the d-line is displayed, and in longitudinal chromatic aberration, the aberration of the g-line with respect to the d-line is displayed.

[0041] Numerical Examples 1 to 5 corresponding to Examples 1 to 5 of the present invention are shown below.

[0042] In the surface data of each numerical example, the surface numbers are shown in order from the object side, r is 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. Here, m is the surface number counted from the light incident side. Also, 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. Note that 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 values when the optical system of each example is focused on an infinitely distant 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. "Overall 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 a plurality of 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) + A4×h + A6×h + A8×h + A10×h + A12×h}, 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. Note that "e±XX" in each aspherical coefficient means "×10±". 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 is expressed. Note that "e±XX" in each aspherical coefficient means "×10± XX ".

[0045] (Numerical Example 1) Unit: mm Surface data Surface number r d 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 The 9th surface K = 0.00000e+000 A4 = -1.95201e-007 A6 = 5.56469e-010 A8 = -1.84169e-012 The 17th surface 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 field angle (°) 38.93 Image height 21.64 Overall lens length 134.78 BF 13.00 d11 11.85 d16 15.72 d20 13.00 Zoom lens group data Group Starting surface Focal length 1 1 51.01 2 12 106.20 3 17 94.79 (Numerical Example 2) Unit: mm Surface data Surface number r d 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 Surface 9 K = 0.00000e+000 A4 = 4.42691e-007 A6 = -7.15232e-009 A8 = 3.90599e-011 Surface 10 K = 0.00000e+000 A4 = 4.53281e-006 A6 = -8.69501e-009 A8 = 5.39734e-011 Surface 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 field angle (°) 39.10 Image height 21.64 Overall lens length 131.96 BF 20.00 d13 15.13 d17 7.48 d21 20.00 Zoom lens group data Group Start surface Focal length 1 1 67.64 2 14 175.19 3 18 54.82 (Numerical Example 3) Unit: mm Surface data Surface No. r d 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 (Diaphragm) ∞ (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 The 9th surface K = 0.00000e+000 A4 = 6.46101e-007 A6 = -1.56132e-009 A8 = 4.53013e-012 The 10th surface K = 0.00000e+000 A4 = 1.93058e-006 A6 = -2.70735e-009 A8 = 7.75395e-012 The 18th surface 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 field angle (°) 32.68 Image height 21.64 Overall lens length 143.92 BF 20.00 d13 18.16 d17 10.39 d21 20.00 Zoom lens group data Group Starting surface Focal length 1 1 68.33 2 14 167.14 3 18 69.96 (Numerical Example 4) Unit: mm Surface data Surface number r d 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 (Diaphragm) ∞ (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 Surface 9 K = 0.00000e+000 A4 = -1.94572e-006 A6 = -1.87272e-009 A8 = 2.79637e-013 Surface 10 K = 0.00000e+000 A4 = 4.97742e-008 A6 = -1.52803e-009 A8 = 2.61249e-012 Surface 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 drawing angle (°) 32.57 Image height 21.64 Overall 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 surface 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 Surface number r d 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 The 9th surface K = 0.00000e+000 A4 = -4.79445e-007 A6 = -2.54333e-010 A8 = 3.69344e-013 The 10th surface K = 0.00000e+000 A4 = 3.41648e-006 A6 = -2.47237e-009 A8 = 2.27433e-012 The 18th surface 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 field angle (°) 39.02 Image height 21.64 Overall lens length 133.24 BF 20.00 d12 12.74 d17 5.54 d21 20.00 Zoom lens group data Group Starting surface Focal length 1 1 50.52 2 13 125.52 3 18 84.29 Table 1 below shows the numerical values corresponding to conditional expressions (1) to (10) in each example.

[0046] [Table 1]

[0047] Next, embodiments of an imaging device and a lens device using the optical system as shown in each example will be described with reference to FIGS. 16 and 17.

[0048] FIG. 16 is a schematic diagram of a main part of a digital still camera (imaging device) using the optical system of the present invention as an imaging optical system. In FIG. 16, 10 is a camera body, 11 is an imaging optical system constituted by the optical system of the present invention, 12 is a solid-state imaging device (photoelectric conversion element) such as a CCD sensor or a CMOS sensor built in the camera body and receiving the subject image formed by the imaging optical system 11. Further, 13 is a recording means for recording the subject image received by the imaging device 12, and 14 is a finder for observing the subject image displayed on a display element (not shown). The display element is constituted by a liquid crystal panel or the like, and the subject image formed on the imaging device 12 is displayed. The camera body 10 may be a so-called single-lens reflex camera having a quick return mirror, or a so-called mirrorless camera having no quick return mirror.

[0049] FIG. 17 is a schematic external view 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 have a focus operation means 21 and an operation means 22 for changing the mode. Further, when the user operates the focus operation means 21, the arrangement of the lens group of the imaging optical system 11 may be changed mechanically or electrically to change the focal position. Further, when the user operates the operation means 22 for changing the mode, the arrangement of the lens group of the imaging optical system 11 may be changed mechanically or electrically to change the aberration.

[0050] By applying the optical system of the present invention to an imaging device and a lens device in this way, it is possible to obtain an imaging device and a lens device that can correct chromatic aberration, field curvature, etc. during shooting at all object distances from infinity to the closest distance while shortening the overall length and miniaturizing the entire focus group.

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

Explanation of Reference Numerals

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

Claims

1. An optical system having a first lens group having a positive refractive power, a second lens group having a positive refractive power, and a third lens group having a positive refractive power, which are arranged in this order from an object side to an image side, for focusing from infinity to a close distance, the first lens group is fixed, and the second lens group and the third lens group move so that a distance between the second lens group and the third lens group changes; the first lens group has a negative lens arranged closest to the object and having a convex surface facing the object side, Let f be the focal length of the entire system when focused at infinity, f1, f2, and f3 be the focal lengths of the first lens group, the second lens group, and the third lens group, respectively, and DG12 be the distance between the first lens group and the second lens group. 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.

2. An optical system comprising a first lens group having positive refractive power, a second lens group having positive refractive power, and a third lens group having positive refractive power, arranged in this order from an object side to an image side, for focusing from infinity to a close distance, the first lens group is fixed, and the second lens group and the third lens group move so that a distance between the second lens group and the third lens group changes; the first lens group has a negative lens arranged closest to the object and having a convex surface facing the object side, When the focal length of the entire system when focused at infinity 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.

3. An optical system having a first lens group having a positive refractive power, a second lens group having a positive refractive power, and a third lens group having a positive refractive power, which are arranged in this order from an object side to an image side, for focusing from infinity to a close distance, the first lens group is fixed, and the second lens group and the third lens group move so that a distance between the second lens group and the third lens group changes; the first lens group has a negative lens arranged closest to the object and having a convex surface facing the object side, When the focal length of the entire system when focused at infinity 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≦2.026 0.50<f2 / f3<30.00 An optical system characterized by satisfying the following conditions.

4. When s k is the back focus of the entire system when focused at infinity, 0.01<sk / f<1.00 4. The optical system according to claim 1, wherein the following condition is satisfied:

5. When s k is the back focus of the entire system when focused at infinity, 0.01<sk / f2<0.30 5. The optical system according to claim 1, wherein the following condition is satisfied:

6. When the thickness of the second lens group in the optical axis direction is TG2, 0.01<TG2 / f2<0.10 6. The optical system according to claim 1, wherein the following condition is satisfied:

7. 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 7. The optical system according to claim 1, wherein the following condition is satisfied:

8. When the amount of movement of the second lens group from focusing at infinity to focusing on an object 500 mm away from the image plane is FL2, 0.01<FL2 / f2<0.20 8. The optical system according to claim 1, wherein the following condition is satisfied:

9. Let FL2 and FL3 be the amounts of movement of the second lens group and the third lens group from focusing on infinity to focusing on an object 500 mm away from the image plane, respectively. 1.00<FL2 / FL3<3.00 9. The optical system according to claim 1, wherein the following condition is satisfied:

10. The optical system has a diaphragm, When the distance from the aperture to the image plane when focusing at infinity is X1, 0.05<f / X1<3.00 10. The optical system according to claim 1, wherein the following condition is satisfied:

11. The first lens group is arranged in order from the object side to the image side. A negative lens; a cemented lens of a positive lens and a negative lens; a cemented lens of a negative lens and a positive lens; 11. The optical system according to claim 1, comprising a cemented lens of a positive lens and a negative lens, or two lenses of a positive lens and a negative lens.

12. 12. The optical system according to claim 1, wherein the second lens group is made up of two lenses, a negative lens and a positive lens, arranged in that order from the object side to the image side.

13. 13. The optical system according to claim 1, wherein the third lens group is made up of two lenses or one lens.

14. 14. The optical system according to claim 1, further comprising a fourth lens group composed of one negative lens arranged closer to the image side than the third lens group.

15. An optical system according to any one of claims 1 to 14; and an image sensor that receives an image formed by the optical system.

16. A lens device comprising the optical system according to claim 1 .

Images