Zoom lens and imaging apparatus

Abstract

To provide a zoom lens having high magnification and high optical performance.SOLUTION: A zoom lens (L1) includes, in order from an object side to an image side, a first lens unit (L0) having a negative refractive power, a second lens unit (L2) having a positive refractive power, and a third lens unit (L3) having a positive refractive power, wherein during zooming from a wide-angle end to a telephoto end, the second lens unit moves and a distance between adjacent lens units changes, and the second lens unit includes at least five lenses and satisfies a predetermined conditional equation.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a zoom lens and an imaging device. [Background technology]

[0002] Conventionally, a negative-lead zoom lens has been known which consists of, in order from the object side to the image side, a negative first lens group, a positive second lens group, and a positive third lens group, in which the first lens group and the second lens group move during zooming. Summary of the Invention [Problem to be solved by the invention]

[0003] There is a demand for a zoom lens that has a higher magnification and higher optical performance than conventional zoom lenses. [Means for solving the problem]

[0004] A zoom lens according to one aspect of the present invention is a zoom lens comprising, in order from the object side to the image side, a first lens group with negative refractive power, a second lens group with positive refractive power, and a third lens group with positive refractive power, wherein, during zooming from the wide-angle end to the telephoto end, the second lens group moves and the spacing between adjacent lens groups changes, the second lens group has at least five lenses, and satisfies a predetermined conditional expression.

[0005] Other objects and features of the present invention are illustrated in the following examples. [Brief explanation of the drawings]

[0006] [Figure 1] FIG. 1 is a cross-sectional view of a zoom lens at a wide-angle end in a first embodiment. [Figure 2] 3A to 3C are aberration diagrams of the zoom lens at the wide-angle end, at the intermediate zoom position, and at the telephoto end in Example 1. [Figure 3] FIG. 10 is a cross-sectional view of a zoom lens at a wide-angle end in a second embodiment. [Figure 4]10A to 10C are aberration diagrams of the zoom lens at the wide-angle end, at the intermediate zoom position, and at the telephoto end in Example 2. [Figure 5] FIG. 10 is a cross-sectional view of a zoom lens at the wide-angle end in Example 3. [Figure 6] 10A to 10C are aberration diagrams of the zoom lens at the wide-angle end, at the intermediate zoom position, and at the telephoto end in Example 3. [Figure 7] FIG. 10 is a cross-sectional view of a zoom lens at the wide-angle end in Example 4. [Figure 8] 10A to 10C are aberration diagrams of the zoom lens at the wide-angle end, at the intermediate zoom position, and at the telephoto end in Example 4. [Figure 9] FIG. 1 is a diagram illustrating the configuration of an imaging device equipped with a zoom lens in each embodiment. [Figure 10] FIG. 1 is a diagram illustrating the configuration of an imaging device equipped with a zoom lens in each embodiment. [Figure 11] FIG. 1 is a diagram illustrating the configuration of an imaging device equipped with a zoom lens in each embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0007] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0008] The zoom lens L0 in each embodiment is a zoom lens used in imaging devices such as digital video cameras, digital still cameras, broadcast cameras, silver halide film cameras, surveillance cameras, and vehicle-mounted cameras.

[0009] 1, 3, 5, and 7 are cross-sectional views of the zoom lens L0 of Examples 1 to 4 at the wide-angle end when focusing on infinity. In each cross-sectional view, the left side is the object side and the right side is the image side. The zoom lens L0 of each Example may be used as a projection lens for a projector or the like. In this case, the left side is the screen side (enlargement side) and the right side is the projected image side (reduction side).

[0010] The solid arrows pointing downward in each cross-sectional view represent the movement locus of each lens group during zooming from the wide-angle end to the telephoto end. Focusing is achieved by moving the first lens group L1 along the optical axis OA. Of the movement locus of the first lens group L1 depicted in each cross-sectional view, the solid curve represents the movement locus for correcting image plane fluctuations that occur when zooming from the wide-angle end to the telephoto end while focusing on an object at infinity. The dotted curve represents the movement locus for correcting image plane fluctuations that occur when zooming from the wide-angle end to the telephoto end while focusing on a close-up object. Note that in each embodiment, focusing may be achieved by moving the second lens group L2 or the third lens group L3 along the optical axis OA instead of the first lens group L1.

[0011] In each cross-sectional view, P denotes an optical block such as an optical filter, faceplate, low-pass filter, or infrared cut filter. I denotes an image plane. When the zoom lens L0 of each embodiment is used as the imaging optical system of a digital still camera or digital video camera, the imaging surface of an imaging element (photoelectric conversion element) such as a CCD sensor or CMOS sensor is disposed on the image plane I. When the zoom lens 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 disposed on the image plane I.

[0012] In each cross-sectional view, P denotes an aperture stop. The aperture stop P forms part of the second lens unit L2 and is located closest to the object side of the second lens unit L2. During zooming, the aperture stop P moves together with the second lens unit L2. The aperture diameter of the aperture stop SP may be constant during zooming, or may be changed during zooming. By changing the diameter of the aperture stop SP, it is possible to cut out underline coma flare caused by off-axial light beams that occur significantly at the telephoto end, thereby achieving better optical performance.

[0013] The zoom lens L0 in each embodiment comprises, in order from the object side to the image side, a first lens unit L1 with negative refractive power, a second lens unit L2 with positive refractive power, and a third lens unit L3 with positive refractive power. When zooming (varying magnification) from the wide-angle end to the telephoto end, the second lens unit L2 moves, changing the spacing between adjacent lens units. The second lens unit L2 has at least five lenses. This allows, for example, fluctuations in spherical aberration, coma, and other aberrations to be suppressed when zooming from the wide-angle end to the telephoto end.

[0014] In each embodiment, in order to realize a zoom lens that is small and has a wide angle, yet has a high magnification and high optical performance, it is preferable to satisfy at least one of the following conditional expressions.

[0015] In each embodiment, when the Abbe number of the lens closest to the object in the second lens unit L2 with reference to the d-line is νd21, it is preferable to satisfy the following conditional expression (1).

[0016] 65<νd21<100 (1) Conditional expression (1) defines the range of the Abbe number νd21 of the positive lens located closest to the object in the second lens unit L2. If the upper limit of conditional expression (1) is exceeded, the Abbe number νd21 becomes large, and no lens material can be selected. On the other hand, if the lower limit of conditional expression (1) is exceeded, the Abbe number νd21 becomes small, and correction of axial chromatic aberration and lateral chromatic aberration becomes insufficient throughout the zoom range, which is undesirable.

[0017] More preferably, the upper limit of conditional expression (1) is set to 99, 98, 97, 96, or 95. More preferably, the lower limit of conditional expression (1) is set to 66, 67, 68, 69, 70, or 71.

[0018] In each embodiment, when the focal length of the second lens unit L2 is f2 and the maximum movement amount of the second lens unit L2 during zooming from the wide-angle end to the telephoto end is M2, it is preferable to satisfy the following conditional expression (2): Here, the maximum movement amount of the second lens unit L2 is the difference between the position of the second lens unit L2 at the wide-angle end and the position of the second lens unit L2 at the telephoto end.

[0019] 0.0 <f2 / M2<1.0 ···(2) Conditional expression (2) defines the ratio between the focal length f2 of the second lens unit L2 and the maximum amount of movement M2. Exceeding the upper limit of conditional expression (2) is undesirable because the refractive power of the second lens unit L2 becomes weaker or the amount of movement becomes smaller, making it difficult to achieve high magnification. On the other hand, falling below the upper limit of conditional expression (2) is undesirable because the refractive power of the second lens unit L2 becomes stronger or the amount of movement becomes larger, resulting in larger fluctuations in spherical aberration and coma when zooming from the wide-angle end to the telephoto end.

[0020] More preferably, the upper limit of conditional expression (2) is set to 0.96, 0.92, 0.88, 0.84, 0.80, 0.76, or 0.72, and more preferably, the lower limit of conditional expression (2) is set to 0.04, 0.08, 0.12, 0.16, 0.20, 0.24, 0.28, 0.32, 0.36, or 0.40.

[0021] In each embodiment, when the focal length of the first lens unit L1 is f1, it is preferable to satisfy the following conditional expression (3).

[0022] -2.0 <f1 / f2<-1.0 ···(3) Conditional expression (3) defines the ratio of the focal length f1 of the first lens group L1 to the focal length f2 of the second lens group L2. Exceeding the upper limit of conditional expression (3) is undesirable because the refractive power of the first lens group L1 becomes stronger relative to the refractive power of the second lens group L2, making it difficult to obtain good curvature of field, particularly at the wide-angle end. On the other hand, falling below the lower limit of conditional expression (3) is undesirable because the refractive power of the first lens group L1 becomes weaker relative to the refractive power of the second lens group L2, making it difficult to achieve a wide angle.

[0023] More preferably, the upper limit of conditional expression (3) is set to −1.04, −1.08, −1.12, −1.16, −1.20, or −1.24, and the lower limit of conditional expression (3) is set to −1.96, −1.92, −1.88, −1.84, −1.80, −1.76, or −1.72.

[0024] In each embodiment, when the focal length of the third lens unit L3 is f3, it is preferable to satisfy the following conditional expression (4).

[0025] 0.3 <f2 / f3<1.2 ···(4) Conditional expression (4) defines the ratio of the focal length f2 of the second lens group L2 to the focal length f3 of the third lens group L3. Exceeding the upper limit of conditional expression (4) is undesirable because the refractive power of the second lens group L2 becomes smaller relative to the refractive power of the third lens group L3, making it difficult to achieve high magnification. On the other hand, falling below the lower limit of conditional expression (4) is undesirable because the refractive power of the second lens group L2 becomes larger relative to the refractive power of the third lens group L3, causing large fluctuations in spherical aberration and coma during zooming from the wide-angle end to the telephoto end.

[0026] More preferably, the upper limit of conditional expression (4) is set to 1.18, 1.16, 1.14, 1.12, 1.10, 1.08, 1.06, 1.04, or 1.02, and more preferably, the lower limit of conditional expression (4) is set to 0.32, 0.34, 0.36, 0.38, 0.40, 0.42, 0.44, 0.46, 0.48, or 0.50.

[0027] In each embodiment, when the focal length of the entire zoom lens system L0 at the wide-angle end is fw, it is preferable to satisfy the following conditional expression (5):

[0028] 1.4 <f2 / fw<2.2 ···(5) Conditional expression (5) defines the ratio between the focal length f2 of the second lens group L2 and the focal length fw of the entire zoom lens system L0 at the wide-angle end. Exceeding the upper limit of conditional expression (5) undesirably increases the focal length of the second lens group L2 relative to the focal length of the zoom lens L0 at the wide-angle end, i.e., decreases the refractive power, making it difficult to reduce the size of the zoom lens L0 throughout the entire zoom range. On the other hand, exceeding the upper limit of conditional expression (5) undesirably increases the focal length of the second lens group L2 relative to the focal length of the zoom lens L0 at the wide-angle end, i.e., increases the refractive power. As a result, the refractive power of the first lens group L1 becomes excessively large due to the wide-angle end, making it difficult to obtain a satisfactory curvature of field, particularly at the wide-angle end.

[0029] More preferably, the upper limit of conditional expression (5) is set to 2.18, 2.16, 2.14, 2.12, 2.10, 2.08, 2.06, 2.04, 2.02, or 2.00. More preferably, the lower limit of conditional expression (5) is set to 1.42, 1.44, 1.46, 1.48, 1.50, 1.52, 1.54, 1.56, 1.58, 1.60, 1.62, 1.64, or 1.66.

[0030] In each embodiment, when the total lens length at the wide-angle end is TLw, it is preferable to satisfy the following conditional expression (6).

[0031] 0.1 <M2 / TLw<0.8 ···(6) Conditional expression (6) defines the ratio of the maximum movement amount M2 of the second lens group L2 to the total lens length TLw at the wide-angle end. Exceeding the upper limit of conditional expression (6) is undesirable because the maximum movement amount M2 of the second lens group L2 relative to the total lens length at the wide-angle end becomes too large, making it difficult to reduce the size of the zoom lens L0. On the other hand, falling below the lower limit of conditional expression (6) is undesirable because the maximum movement amount M2 of the second lens group L2 relative to the total lens length at the wide-angle end becomes too small, which increases the refractive power of the second lens group L2 for higher magnification and increases fluctuations in spherical aberration and coma.

[0032] More preferably, the upper limit of conditional expression (6) is set to 0.76, 0.72, 0.68, 0.64, 0.60, 0.56, or 0.52, and more preferably, the lower limit of conditional expression (6) is set to 0.14, 0.18, 0.22, 0.26, or 0.30.

[0033] In each embodiment, it is preferable that the first lens group L1 consists of three or fewer lenses. By limiting the number of lenses in the first lens group L1, the zoom lens L0 can be made compact.

[0034] Here, the distance from the lens surface of the zoom lens L0 closest to the image plane to the image plane is defined as the back focus. In each embodiment, when the back focus at the wide-angle end is represented by bfw, it is preferable that the following conditional expression (7) be satisfied:

[0035] 0.1 <bfw / f2<0.5 ···(7) Conditional expression (7) defines the ratio of the back focal length bfw at the wide-angle end to the focal length f2 of the second lens unit L2. Exceeding the upper limit of conditional expression (7) undesirably increases the back focal length at the wide-angle end relative to the focal length of the second lens unit L2, making it difficult to reduce the size of the zoom lens L0. Conversely, falling below the lower limit of conditional expression (8) undesirably decreases the back focal length at the wide-angle end relative to the focal length of the second lens unit L2, making the refractive power of the first lens unit L1 excessively weak and making it difficult to achieve a wider angle.

[0036] More preferably, the upper limit of conditional expression (7) is set to 0.48, 0.46, 0.44, 0.42, 0.40, 0.38, or 0.36, and more preferably, the lower limit of conditional expression (7) is set to 0.12, 0.14, 0.16, 0.18, 0.20, or 0.22.

[0037] In each embodiment, when the Abbe number of the lens having the smallest dispersion among the lenses constituting the cemented lens included in the second lens unit L2 is νd2c, it is preferable to satisfy the following conditional expression (8).

[0038] 25<νd2c<60 (8) Conditional expression (8) defines the range of the Abbe number of the lens that has the smallest dispersion among the lenses that make up the cemented lens in the second lens group L2. If the upper limit of conditional expression (8) is exceeded, it is not preferable because a material with a high refractive index cannot be used, making it difficult to achieve high magnification. On the other hand, if the lower limit of conditional expression (8) is exceeded, optical performance such as chromatic aberration deteriorates, which is also not preferable.

[0039] More preferably, the upper limit of conditional expression (8) is set to 59, 58, 57, or 56. More preferably, the lower limit of conditional expression (8) is set to 26, 27, 28, 29, 30, 31, or 32.

[0040] In each embodiment, during zooming from the wide-angle end to the telephoto end, it is preferable that the first lens unit L1 moves along a locus that is convex toward the image side, the second lens unit L2 moves monotonically from the image side to the object side, and the third lens unit L3 does not move (is fixed).

[0041] In each embodiment, during zooming from the wide-angle end to the telephoto end, it is preferable that the first lens unit L1 moves along a locus that is convex toward the image side, the second lens unit L2 moves monotonically from the image side to the object side, and the third lens unit L3 moves monotonically from the object side to the image side.

[0042] In each embodiment, by having the respective configurations as described above or by satisfying at least one of the conditional expressions, it is possible to obtain, for example, a zoom lens that is compact and has a wide angle, yet has a high magnification and excellent optical performance. Furthermore, by arbitrarily combining a plurality of conditional expressions, the effects of each embodiment can be further enhanced.

[0043] In the zoom lens L0 of Examples 1 and 2, the first lens group L1 consists of, from the object side to the image side, two negative lenses and one positive lens. The second lens group L2 consists of, from the object side to the image side, a positive lens, a cemented lens formed by cementing a positive lens and a negative lens, a positive lens, and a negative lens. The third lens group L3 consists of a positive lens.

[0044] In the zoom lens L0 of Example 3, the first lens group L1 consists of, in order from the object side to the image side, a negative lens and a positive lens. The second lens group L2 consists of, in order from the object side to the image side, a positive lens, a cemented lens formed by cementing a positive lens and a negative lens, a positive lens, and a negative lens. The third lens group L3 consists of a single positive lens.

[0045] In the zoom lens L0 of Example 4, the first lens group L1 consists of, from the object side to the image side, two negative lenses and a positive lens. The second lens group L2 consists of, from the object side to the image side, two positive lenses, a cemented lens formed by cementing a positive lens and a negative lens, a positive lens, and a negative lens. The third lens group consists of one positive lens.

[0046] 2, 4, 6, and 8 are aberration diagrams of the zoom lens in Examples 1 to 4 when focused on infinity at (A) the wide-angle end, (B) the intermediate zoom position, and (C) the telephoto end, respectively.

[0047] In the spherical aberration diagram, Fno is the F-number, the solid line shows the amount of spherical aberration for the d-line (wavelength 587.6 nm), and the dashed line shows the amount of spherical aberration for the g-line (wavelength 435.8 nm). In the astigmatism diagram, the solid line shows the amount of aberration on the sagittal image plane, and the dashed line shows the amount of aberration on the meridional image plane. In the distortion diagram, the amount of distortion for the d-line is shown. In the chromatic aberration diagram, the amount of lateral chromatic aberration for the g-line is shown. ω is the half angle of view (°).

[0048] Numerical Examples 1 to 4 corresponding to Examples 1 to 4, respectively, are shown below. In each numerical example, ri is the radius of curvature of the ith surface, in order from the object side, di is the distance between the ith surface and the (i+1)th surface (lens thickness or air distance), and ndi and νdi are the refractive index and Abbe number of the material of the ith lens at the d-line, respectively. Note that the Abbe number νd of a certain material is given by: 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. νd=(Nd-1) / (NF-NC) It is expressed as:

[0049] In each numerical example, d, focal length (mm), F-number, and half angle of view (°) are all values ​​when the zoom lens of each example is focused at infinity. BF (back focus) 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, and is a value that does not include the glass block. The total lens length is the length from the surface (lens surface) of the zoom lens closest to the object to the image plane. The lens group is not limited to being composed of multiple lenses, and may be composed of a single lens.

[0050] If the optical surface is aspherical, a "*" is added to the right of the surface number. When the displacement in the optical axis direction at a position of height h from the optical axis with the vertex of the surface as the reference is x, the aspherical shape is expressed as follows: x=(h 2 / R) / [1+{1-(1+k)(h / R) 2} 1 / 2 ]+A4h 4 +A6h 6 +A8h 8 +A10h 10 It is expressed as:

[0051] Here, R is the paraxial radius of curvature, k is the conic constant (eccentricity), and A4, A6, A8, and A10 are the 4th, 6th, 8th, and 10th order aspheric coefficients, respectively. -Z " means.

[0052] (Numerical Example 1) Unit: mm Surface Data Surface number rd nd νd 1 -30.634 0.60 1.88300 40.8 2 317.342 0.96 3 -20.843 0.60 1.59522 67.7 4 11.863 0.58 5 13.620 1.44 1.95906 17.5 6 29.878 (variable) 7 (Aperture) ∞ 0.09 8* 5.531 2.73 1.49710 81.6 9* -26.636 0.17 10 8.436 2.21 1.81600 46.6 11 -15.799 0.60 1.78880 28.4 12 4.770 1.47 13* 10.570 1.81 1.58313 59.4 14* -18.152 1.27 15 -4.325 0.60 1.61800 63.3 16 -14.015 (variable) 17 23.669 1.28 1.95906 17.5 18 -50.514 (variable) 19 ∞ 1.00 1.51000 60.0 20 ∞ (variable) Image plane ∞ Aspheric data Side 8 K =-1.50342e-01 A 4=-1.58830e-04 A 6=-4.01153e-06 A 8= 1.10090e-06 9th page K =-2.86005e+00 A 4= 8.33919e-04 A 6=-7.46575e-07 A 8= 1.44774e-06 Page 13 K =-1.12087e-01 A 4= 8.40534e-04 A 6= 2.88530e-05 A 8=-1.39592e-05 Page 14 K =-1.57897e+00 A 4= 1.13146e-04 A 6=-1.43270e-05 A 8=-8.74763e-06 Various data Zoom ratio 4.90 Wide-angle Mid-range Telephoto Focal length 5.12 11.50 25.08 F-number 1.99 2.99 5.09 Half angle of view 43.4 16.0 7.26 Image height 3.20 3.20 3.20 Lens length 35.81 29.64 34.91 BF 2.22 2.22 2.22 d 6 16.40 5.53 0.81 d16 0.80 5.50 15.48 d18 0.56 0.56 0.56 d20 1.00 1.00 1.00 Zoom lens group data Group starting plane focal length 1 1 -13.85 2 7 8.59 3 17 16.95 4 19 ∞ (Numerical Example 2) Unit: mm Surface Data Surface number rd nd νd 1 -28.108 0.60 1.85150 40.8 2 204.442 0.17 3 -567.477 0.60 1.59522 67.7 4 11.061 0.26 5 10.943 1.73 1.95906 17.5 6 17.068 (variable) 7 (Aperture) ∞ 0.09 8 5.940 1.46 1.43875 94.7 9 12.965 0.17 10* 4.728 2.20 1.85150 40.8 11 24.590 0.60 1.80810 22.8 12 3.572 0.78 13* 8.677 1.47 1.85150 40.8 14* 451.664 2.22 15 -2.856 1.05 1.80518 25.4 16 -4.310 (variable) 17 11.808 2.12 2.00100 29.1 18 -66.260 (variable) 19 ∞ 1.00 1.51000 60.0 20 ∞ (variable) Image plane ∞ Aspheric data Side 10 K =-9.22875e-01 A 4= 9.62474e-04 A 6= 5.07787e-06 A 8= 2.71152e-06 Page 13 K =-4.94070e+00 A 4=-2.24034e-03 A 6=-1.53757e-04 A 8=-6.95757e-05 Page 14 K = 2.86603e+04 A 4=-3.49416e-03 A 6=-3.67199e-04 A 8=-1.84829e-05 Various data Zoom ratio 4.30 Wide-angle Mid-range Telephoto Focal length 5.15 10.59 22.14 F-number 2.06 3.02 5.09 Half angle of view 42.4 17.5 8.18 Image height 3.20 3.20 3.20 Lens length 37.21 30.04 34.16 BF 2.36 2.36 2.36 d 6 18.54 6.67 0.81 d16 0.80 5.50 15.48 d18 0.69 0.69 0.69 d20 1.00 1.00 1.00 Zoom lens group data Group starting plane focal length 1 1 -17.31 2 7 10.14 3 17 10.15 4 19 ∞ (Numerical Example 3) Unit: mm Surface Data Surface number rd nd νd 1* -21.468 0.60 1.69350 53.2 2* 9.484 3.00 3 9.256 1.06 1.95906 17.5 4 11.268 (variable) 5 (Aperture) ∞ 0.07 6* 9.912 1.87 1.55332 71.7 7* -19.496 0.17 8 5.082 1.87 1.69680 55.5 9 27.998 0.60 1.90110 27.1 10 4.734 1.72 11* 8.207 1.80 1.58313 59.4 12* -11.452 0.76 13 -5.059 0.60 1.59522 67.7 14 29.560 (variable) 15 -153.309 1.63 1.69680 55.5 16 -10.602 (variable) 17 ∞ 1.00 1.51000 60.0 18 ∞ (variable) Image plane ∞ Aspheric data Front page K =-6.73160e-01 A 4= 2.93490e-04 A 6=-3.44944e-06 A 8= 2.11249e-08 2nd side K =-4.75482e+00 A 4= 1.06069e-03 A 6=-7.04542e-06 A 8= 1.17440e-07 Side 6 K =-1.13215e+00 A 4=-1.35965e-04 A 6=-1.02895e-05 A 8= 4.32228e-08 Side 7 K =-7.79122e-01 A 4=-1.35794e-05 A 6= 2.14248e-06 A 8=-9.44737e-07 Page 11 K = 5.91960e+00 A 4= 6.87504e-04 A 6= 1.84208e-04 A 8= 2.57823e-06 Side 12 K =-6.40003e-01 A 4= 3.13753e-03 A 6= 1.60450e-04 A 8= 6.64830e-05 Various data Zoom ratio 4.50 Wide-angle Mid-range Telephoto Focal length 4.40 9.20 19.80 F-number 2.42 3.46 5.77 Half angle of view 47.5 20.0 9.42 Image height 3.20 3.20 3.20 Lens length 35.84 29.24 32.43 BF 2.72 2.56 2.22 d 4 16.58 6.05 0.88 d14 0.80 4.89 13.59 d16 1.06 0.90 0.56 d18 1.00 1.00 1.00 Zoom lens group data Group starting plane focal length 1 1 -12.47 2 5 8.60 3 15 16.27 4 17 ∞ (Numerical Example 4) Unit: mm Surface Data Surface number rd nd νd 1 20.056 0.80 1.75500 52.3 2 8.895 2.43 3 254.804 0.60 1.80400 46.6 4 5.610 0.83 5 6.519 2.08 1.95906 17.5 6 11.286 (variable) 7 (Aperture) ∞ 0.09 8* 7.041 2.05 1.55332 71.7 9* -9.317 0.17 10 -5.172 0.61 1.49700 81.5 11 -5.045 0.17 12 6.451 1.53 1.95375 32.3 13 -55.283 0.60 1.95906 17.5 14 3.144 0.17 15 3.968 1.24 1.95906 17.5 16 8.681 0.17 17* 4.175 0.60 1.58313 59.5 18* 2.501 (variable) 19 14.878 2.38 2.00100 29.1 20 -20.873 (variable) 21 ∞ 1.00 1.51000 60.0 22 ∞ (variable) Image plane ∞ Aspheric data Side 8 K =-1.00126e+00 A 4=-2.68008e-03 A 6=-3.94645e-04 A 8= 2.59361e-06 9th page K =-1.00523e+00 A 4=-3.96176e-03 A 6=-8.23337e-05 A 8=-6.83234e-06 Page 17 K =-9.53463e-01 A 4=-3.49379e-02 A 6= 6.71923e-03 A 8=-9.10670e-04 Side 18 K =-4.24653e+00 A 4=-1.05008e-02 A 6= 2.39069e-03 A 8=-3.00385e-04 Various data Zoom ratio 4.90 Wide-angle Mid-range Telephoto Focal length 3.23 7.27 15.84 F-number 2.07 3.25 5.77 Half angle of view 58.2 24.4 11.6 Image height 3.20 3.20 3.20 Lens length 28.96 27.63 35.00 BF 2.19 2.19 2.19 d 6 9.45 3.42 0.81 d18 0.79 5.49 15.47 d20 0.53 0.53 0.53 d22 1.00 1.00 1.00 Zoom lens group data Group starting plane focal length 1 1 -8.13 2 7 6.39 3 19 8.98 4 21 ∞ Table 1 shows the relationship between the above-mentioned conditional expressions and the respective numerical examples.

[0053] [Table 1]

[0054] Next, with reference to FIGS. 9 to 11, an imaging device (surveillance camera) using the zoom lens of each embodiment as an imaging optical system will be described. FIGS. 9 to 11 are configuration diagrams of the imaging device of each embodiment. In FIGS. 9 to 11, 16 denotes an imaging optical system configured with any of the zoom lenses of Examples 1 to 4. In FIGS. 9 and 11(B), 15 denotes a dome cover (protective cover) that protects the imaging optical system 16. The dome cover 15 is molded with a thickness of approximately several millimeters from a plastic material such as polymethyl methacrylate (PMMA) or polycarbonate (PC). Therefore, when an imaging device is designed to be equipped with a dome cover, the influence of the dome cover 15 (focal length and material) can be taken into consideration in the design, and various aberrations can be corrected. In FIG. 10, 17 denotes a flat protective cover that protects the imaging optical system 16.

[0055] In Figures 11(A) and 11(B), 11a and 11b denote surveillance camera bodies. Figure 11(B) shows an example in which surveillance camera body 11b is fitted with a dome cover 15 and attached to a ceiling. Surveillance camera body 11b is installed on the ceiling with dome cover 15 facing downward. Reference numeral 12 denotes an imaging element (photoelectric conversion element) such as a CCD sensor or CMOS sensor that is built into surveillance camera bodies 11a and 11b and receives an image (subject image) formed by imaging optical system 16. Reference numeral 13 denotes a memory that records information corresponding to the subject image photoelectrically converted by imaging element 12. Reference numeral 14 denotes a network cable for transferring the subject image photoelectrically converted by imaging element 12. Note that the zoom lenses of the respective embodiments are not limited to surveillance cameras and can also be used in other imaging devices such as video cameras and digital cameras.

[0056] Furthermore, the imaging device of each embodiment may include a circuit for electrically correcting either or both of distortion and chromatic aberration of magnification, along with the zoom lens of any of Embodiments 1 to 4. If the zoom lens is configured to tolerate distortion and other aberrations, the number of lenses in the entire zoom lens can be reduced, facilitating miniaturization. Furthermore, electrically correcting chromatic aberration of magnification reduces color bleeding in captured images, making it easier to improve resolution.

[0057] According to each embodiment, for example, it is possible to provide a zoom lens and an imaging device that are small and have a wide angle, yet have a high magnification and high optical performance.

[0058] The disclosure of each embodiment includes the following configuration. (Configuration 1) A zoom lens comprising, in order from the object side to the image side, a first lens group having negative refractive power, a second lens group having positive refractive power, and a third lens group having positive refractive power, During zooming from the wide-angle end to the telephoto end, the second lens group moves, and the spacing between adjacent lens groups changes. the second lens group has at least five lenses; Let vd21 be the Abbe number of the lens closest to the object side in the second lens group with respect to the d-line, f2 be the focal length of the second lens group, and M2 be the maximum movement amount of the second lens group during zooming from the wide-angle end to the telephoto end. 65<νd21<100 0.0 <f2 / M2<1.0 A zoom lens characterized by satisfying the following conditional expressions: (Configuration 2) When the focal length of the first lens group is f1, -2.0 <f1 / f2<-1.0 2. The zoom lens according to claim 1, wherein the following condition is satisfied: (Configuration 3) When the focal length of the third lens group is f3, 0.3 <f2 / f3<1.2 3. The zoom lens according to configuration 1 or 2, wherein the following condition is satisfied: (Configuration 4) When the focal length of the zoom lens at the wide-angle end is fw, 1.4 <f2 / fw<2.2 4. The zoom lens according to any one of the configurations 1 to 3, wherein the following condition is satisfied: (Configuration 5) When the total lens length at the wide-angle end is TLw, 0.1 <M2 / TLw<0.8 5. The zoom lens according to any one of the first to fourth aspects, wherein the following condition is satisfied: (Configuration 6) 6. A zoom lens according to any one of configurations 1 to 5, wherein the first lens group is made up of three or less lenses. (Configuration 7) When the back focus at the wide-angle end is bfw, 0.1 <bfw / f2<0.5 7. The zoom lens according to any one of configurations 1 to 6, wherein the following condition is satisfied: (Configuration 8) During zooming from the wide-angle end to the telephoto end, the first lens group moves along a locus that is convex toward the image side, the second lens group moves monotonically from the image side to the object side, and the third lens group remains stationary, 8. The zoom lens according to any one of configurations 1 to 7, wherein the second lens group includes an aperture stop. (Configuration 9) During zooming from the wide-angle end to the telephoto end, the first lens group moves along a locus convex toward the image side, the second lens group moves monotonically from the image side to the object side, and the third lens group moves monotonically from the object side to the image side, 8. The zoom lens according to any one of configurations 1 to 7, wherein the second lens group includes an aperture stop. (Configuration 10) When the Abbe number of the lens having the smallest dispersion among the lenses constituting the cemented lens included in the second lens group is νd2c, 25<νd2c<60 10. The zoom lens according to any one of configurations 1 to 9, wherein the following condition is satisfied: (Configuration 11) A zoom lens comprising, in order from the object side to the image side, a first lens group having negative refractive power, a second lens group having positive refractive power, and a third lens group having positive refractive power, During zooming from the wide-angle end to the telephoto end, the second lens group moves, and the spacing between adjacent lens groups changes. the second lens group has at least five lenses; When the focal length of the second lens group is f2 and the maximum movement amount of the second lens group during zooming from the wide-angle end to the telephoto end is M2, 0.0 <f2 / M2<1.0 A zoom lens characterized by satisfying the following conditional expressions: (Configuration 12) 12. An imaging device comprising the zoom lens according to any one of configurations 1 to 11, and an imaging element that receives an image formed by the zoom lens.

[0059] Although the 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 the gist of the present invention.

[0060] For example, further aberration correction may be achieved by dividing the cemented lens to provide an air gap between the lenses, or by replacing the spherical lens with an aspherical lens. [Explanation of symbols]

[0061] L0 zoom lens L1 First lens group L2 Second lens group L3: Third lens group

Claims

1. A zoom lens comprising, in order from the object side to the image side, a first lens group having a negative refractive power, a second lens group having a positive refractive power, and a third lens group having a positive refractive power, During zooming from the wide-angle end to the telephoto end, the second lens group moves, and the interval between the adjacent lens groups changes. the second lens group has at least five lenses; When the Abbe number based on the d-line of the lens closest to the object side in the second lens group is νd21, the focal length of the second lens group is f2, and the maximum movement amount of the second lens group during zooming from the wide-angle end to the telephoto end is M2, 65<νd21<100 0.0<f2 / M2<1.0 A zoom lens characterized by satisfying the following conditional expressions:

2. When the focal length of the first lens group is f1, -2.0<f1 / f2<-1.0 2. The zoom lens according to claim 1, wherein the following condition is satisfied:

3. When the focal length of the third lens group is f3, 0.3<f2 / f3<1.2 2. The zoom lens according to claim 1, wherein the following condition is satisfied:

4. When the focal length of the zoom lens at the wide-angle end is fw, 1.4<f2 / fw<2.2 2. The zoom lens according to claim 1, wherein the following condition is satisfied:

5. When the total lens length at the wide-angle end is TLw, 0.1<M2 / TLw<0.8 2. The zoom lens according to claim 1, wherein the following condition is satisfied:

6. 2. The zoom lens according to claim 1, wherein the first lens group is composed of three or less lenses.

7. When the back focus at the wide-angle end is bfw, 0.1<bfw / f2<0.5 2. The zoom lens according to claim 1, wherein the following condition is satisfied:

8. During zooming from the wide-angle end to the telephoto end, the first lens group moves along a locus that is convex toward the image side, the second lens group moves monotonically from the image side to the object side, and the third lens group remains stationary, 2. The zoom lens according to claim 1, wherein the second lens group includes an aperture stop.

9. During zooming from the wide-angle end to the telephoto end, the first lens group moves along a locus convex toward the image side, the second lens group moves monotonically from the image side to the object side, and the third lens group moves monotonically from the object side to the image side, 2. The zoom lens according to claim 1, wherein the second lens group includes an aperture stop.

10. When the Abbe number of the lens having the smallest dispersion among the lenses constituting the cemented lens included in the second lens group is νd2c, 25<νd2c<60 2. The zoom lens according to claim 1, wherein the following condition is satisfied:

11. A zoom lens comprising, in order from the object side to the image side, a first lens group having a negative refractive power, a second lens group having a positive refractive power, and a third lens group having a positive refractive power, During zooming from the wide-angle end to the telephoto end, the second lens group moves, and the interval between the adjacent lens groups changes. the second lens group has at least five lenses; When the focal length of the second lens group is f2 and the maximum movement amount of the second lens group during zooming from the wide-angle end to the telephoto end is M2, 0.0<f2 / M2<1.0 A zoom lens characterized by satisfying the following conditional expressions:

12. 12. An imaging device comprising: the zoom lens according to claim 1; and an imaging element that receives an image formed by the zoom lens.

Images