Zoom lens and imaging apparatus

Abstract

To provide a zoom lens having a simple configuration, a long entire length, and excellent optical performance.SOLUTION: The zoom lens (L0) includes a first lens group (L1) having positive refractive power, a second lens group (L2) having negative refractive power, a third lens group (L3) having positive refractive power, and a fourth lens group (L4) having positive refractive power, in order from an object side to an image side, wherein the first lens group is immovable during zooming from a wide-angle end to a telephoto end, and a distance between adjacent lens groups changes, and the zoom lens satisfies a predetermined conditional expression.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] 2. Description of the Related Art Conventionally, a zoom lens has been known that is made up of lens groups having, in order from the object side to the image side, positive, negative, positive and positive refractive powers. Summary of the Invention [Problem to be solved by the invention]

[0003] A zoom lens having a simpler configuration, a longer overall length, and better optical performance than conventional zoom lenses is desired. [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 having positive refractive power, a second lens group having negative refractive power, a third lens group having positive refractive power, and a fourth lens group having positive refractive power, wherein, during zooming from the wide-angle end to the telephoto end, the first lens group remains stationary and the spacing between adjacent lens groups changes, and a predetermined conditional expression is satisfied.

[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. 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 focused at 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] In each cross-sectional view, L1 is the first lens group, L2 is the second lens group, L3 is the third lens group, and L4 is the fourth lens group. When changing magnification (zooming) from the wide-angle end to the telephoto end, each lens group moves as shown by the arrows in each diagram. The solid and dotted arrows indicate the movement trajectories when focusing on an object at infinity and a close distance, respectively.

[0011] In each cross-sectional view, P denotes a glass block such as a CCD faceplate or low-pass 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 placed 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 equivalent to the film surface is placed on the image plane I.

[0012] In each cross-sectional view, SP denotes an aperture stop. The aperture stop SP forms part of the third lens unit L3. During zooming, the aperture stop P moves together with the third lens unit L3. 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 occurs significantly at the telephoto end, thereby achieving better optical performance.

[0013] The zoom lens L0 in each embodiment is composed of, in order from the object side to the image side, a first lens unit L1 having positive refractive power, a second lens unit L2 having negative refractive power, a third lens unit L3 having positive refractive power, and a fourth lens unit L4 having positive refractive power. This configuration makes it possible to efficiently achieve a large zoom ratio.

[0014] During zooming from the wide-angle end to the telephoto end, the first lens group is immobile (fixed), and the heavy first lens group L1 is not moved.

[0015] In each embodiment, when the focal length of the first lens unit L1 is f1 and the total optical length at the telephoto end is Lt, it is preferable to satisfy the following conditional expression (1).

[0016] 1.00 <f1 / Lt<1.50 ···(1) The total optical length is the distance from the object side surface of the first lens unit L1 to the image side surface of the fourth lens unit L4 plus the back focus. If there is a glass block or the like in the back focus, the back focus extension caused by the glass block or the like is also added.

[0017] Conditional formula (1) defines the ratio between the focal length of the first lens unit L1 and the total optical length at the telephoto end. Exceeding the upper limit of conditional formula (1) is undesirable because it becomes difficult to achieve the desired zoom ratio and angle of view. On the other hand, falling below the lower limit of conditional formula (1) is undesirable because it becomes difficult to correct spherical aberration and coma, particularly at the telephoto end, or the total optical length becomes long.

[0018] More preferably, the upper limit of conditional expression (1) is set to 1.47, 1.44, 1.40, 1.37, 1.34, or 1.31, and more preferably, the lower limit of conditional expression (1) is set to 1.001, 1.002, 1.003, or 1.004.

[0019] In each embodiment, when the focal length of the entire zoom lens system L0 at the telephoto end is ft, it is preferable to satisfy the following conditional expression (2).

[0020] 0.50 <Lt / ft<1.40 ···(2) Conditional expression (2) defines the ratio between the total optical length and the focal length at the telephoto end. Exceeding the upper limit of conditional expression (2) is undesirable because the total optical length becomes too long. On the other hand, falling below the lower limit of conditional expression (2) is undesirable because it becomes difficult to correct spherical aberration and coma, especially at the telephoto end.

[0021] More preferably, the upper limit of conditional expression (2) is set to 1.39, 1.38, 1.37, 1.36, or 1.35, and more preferably, the lower limit of conditional expression (2) is set to 0.53, 0.57, 0.60, 0.63, 0.67, or 0.69.

[0022] In each embodiment, it is preferable that the first lens unit L1 has three or more lenses. By having the first lens unit L1 have three or more lenses, various aberrations can be effectively corrected while moving the position of the principal point of the first lens unit L1.

[0023] In each embodiment, it is preferable that the first lens unit L1 has a negative lens with a concave image-side surface at the most image-side position, which allows the principal point of the first lens unit L1 to move toward the object side, thereby shortening the overall optical length.

[0024] In each embodiment, when the minimum Abbe number of the lenses in the first lens group L1 relative to the d-line (the smallest Abbe number among the Abbe numbers of the lenses in the first lens group L1) is ν1min, it is preferable to satisfy the following conditional expression (3):

[0025] 35.0<ν1min<55.0 (3) Conditional formula (3) defines the minimum Abbe number of the lenses in the first lens group L1 based on the d-line. Exceeding the upper limit of conditional formula (3) is undesirable because it makes it difficult to correct chromatic aberration in the first lens group L1. On the other hand, falling below the lower limit of conditional formula (3) is undesirable because it makes it difficult to shorten the overall optical length by moving the principal point of the first lens group L1 toward the object side, which is also undesirable.

[0026] More preferably, the upper limit of conditional expression (3) is set to 54.6, 53.9, 53.4, 52.8, 52.0, 51.6, or 51.0, and more preferably, the lower limit of conditional expression (3) is set to 36.5, 38.0, 39.5, 41.0, 42.5, 43.5, or 45.0.

[0027] In each embodiment, when the refractive index of the lens having the smallest Abbe number based on the d-line among the lenses in the first lens group L1 (the refractive index of the lens having the smallest Abbe number among the lenses in the first lens group L1) is denoted by nd_ν1min, it is preferable to satisfy the following conditional expression (4):

[0028] 1.50 <nd_ν1min<1.78···(4) Conditional expression (4) defines the refractive index of the lens in the first lens group L1 that has the smallest Abbe number based on the d-line. Exceeding the upper limit of conditional expression (4) is undesirable because it becomes difficult to achieve both a configuration that shifts the principal point of the first lens group L1 toward the object side and correction of field curvature. On the other hand, falling below the lower limit of conditional expression (4) is undesirable because it becomes difficult to select a material that can correct chromatic aberration in the first lens group L1.

[0029] More preferably, the upper limit of conditional expression (4) is set to 1.76, 1.74, 1.72, 1.70, 1.68, or 1.66, and more preferably, the lower limit of conditional expression (4) is set to 1.51, 1.52, 1.53, or 1.54.

[0030] In each embodiment, it is preferable that the third lens group L3 has a negative lens with a concave image-side surface at the most image-side position. By having the third lens group L3 have a negative lens with a concave image-side surface at the most image-side position, the principal point of the third lens group L3 can be moved toward the object side, thereby shortening the distance from the object-side surface of the third lens group L3 to the image plane. As a result, this also contributes to shortening the overall optical length.

[0031] In each embodiment, when the focal length of the third lens unit L3 is f3 and the focal length of the fourth lens unit L4 is f4, the following conditional expression (5) is satisfied.

[0032] 0.70 <f3 / f4<1.80 ···(5) Conditional expression (5) defines the ratio between the focal length of the third lens group L3 and the focal length of the fourth lens group L4. If the upper limit of conditional expression (5) is exceeded, the principal point position when the third lens group L3 and the fourth lens group L4 are combined will be shifted toward the image side, and the total optical length will increase, which is undesirable. On the other hand, if the lower limit of conditional expression (5) is exceeded, it will be difficult to correct spherical aberration and coma, or it will be difficult to perform image plane correction during zooming with the fourth lens group L4, which is also undesirable.

[0033] More preferably, the upper limit of conditional expression (5) is set to 1.75, 1.70, 1.65, 1.60, 1.55, 1.50, 1.45, 1.40, or 1.35, and more preferably, the lower limit of conditional expression (5) is set to 0.72, 0.74, 0.76, 0.78, 0.81, or 0.83.

[0034] In each embodiment, the fourth lens group L4 is preferably composed of a positive lens and a negative lens, and the distance between the positive lens and the negative lens increases with increasing distance from the optical axis OA (the distance at the lens periphery is greater than the distance on the optical axis). By configuring the fourth lens group L4 with two lenses, a positive lens and a negative lens, it is possible to achieve both weight reduction and chromatic aberration correction. Furthermore, by increasing the distance between the positive lens and the negative lens in the fourth lens group L4 with increasing distance from the optical axis OA, it is possible to appropriately correct field curvature and chromatic aberration of magnification.

[0035] In each embodiment, when the focal length of the second lens unit L2 is f2, it is preferable to satisfy the following conditional expression (6).

[0036] -4.50 <f1 / f2<-2.00 ···(6) Conditional expression (6) defines the ratio between the focal length of the first lens group L1 and the focal length of the second lens group L2. Exceeding the upper limit of conditional expression (6) is undesirable because it makes it difficult to correct curvature of field. On the other hand, falling below the lower limit of conditional expression (6) is undesirable because it makes it difficult to increase the focal length of the zoom lens L0 at the telephoto end.

[0037] More preferably, the upper limit of conditional expression (6) is set to −2.10, −2.20, −2.30, −2.40, −2.44, or −2.55, and the lower limit of conditional expression (6) is set to −4.30, −4.10, −3.90, −3.70, −3.50, −3.36, −3.24, or −3.12.

[0038] In each embodiment, it is preferable to satisfy the following conditional expression (7).

[0039] 0.70 <f1 / ft<2.00 ···(7) Conditional expression (7) defines the ratio between the focal length of the first lens group L1 and the focal length of the zoom lens L0 at the telephoto end. Exceeding the upper limit of conditional expression (7) is undesirable because it becomes difficult to achieve the desired zoom ratio and angle of view. On the other hand, falling below the lower limit of conditional expression (7) is undesirable because it becomes difficult to correct spherical aberration and coma, particularly at the telephoto end.

[0040] More preferably, the upper limit of conditional expression (7) is set to 1.96, 1.92, 1.88, 1.84, or 1.80, and more preferably, the lower limit of conditional expression (7) is set to 0.71, 0.72, 0.73, 0.74, 0.75, or 0.76.

[0041] In each embodiment, it is preferable that the fourth lens unit L4 moves during focusing. By moving the fourth lens unit L4 during focusing, it is possible to minimize changes in the angle of view when the focal length changes.

[0042] In each embodiment, when the focal length of the lens arranged closest to the image in the first lens unit L1 is taken as f1i, it is preferable to satisfy the following conditional expression (8).

[0043] -0.50 <f1i / f1<-0.20 ···(8) Conditional expression (8) defines the ratio between the focal length of the lens in the first lens group L1 that is located closest to the image and the focal length of the first lens group L1. Exceeding the upper limit of conditional expression (8) is undesirable because it makes it difficult to correct coma and curvature of field. On the other hand, falling below the lower limit of conditional expression (8) is undesirable because it makes it difficult to move the principal point of the first lens group L1 toward the object side and shorten the overall optical length.

[0044] More preferably, the upper limit of conditional expression (8) is set to −0.21, −0.22, −0.23, −0.24, −0.25, −0.26, or −0.27, and more preferably, the lower limit of conditional expression (8) is set to −0.49, −0.48, −0.48, −0.47, −0.46, or −0.45.

[0045] In each embodiment, when the distance on the optical axis between the first lens unit L1 and the second lens unit L2 at the telephoto end is D1t and the distance on the optical axis between the second lens unit L2 and the third lens unit L3 at the telephoto end is D2t, it is preferable to satisfy the following conditional expression (9):

[0046] 0.010 <D2t / D1t<0.100 ···(9) Conditional expression (9) defines the ratio of the distance between the second lens group L2 and the third lens group L3 at the telephoto end to the distance between the first lens group L1 and the second lens group L2 at the telephoto end. Exceeding the upper limit of conditional expression (9) is undesirable because it becomes difficult to efficiently obtain a sufficient zoom ratio. On the other hand, falling below the lower limit of conditional expression (9) is undesirable because the total optical length becomes too long.

[0047] More preferably, the upper limit of conditional expression (9) is set to 0.095, 0.090, 0.085, 0.080, or 0.075, and more preferably, the lower limit of conditional expression (9) is set to 0.012, 0.016, 0.020, 0.024, or 0.028.

[0048] 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 (10):

[0049] 1.20 <f1 / fw<4.20 ···(10) Conditional expression (10) defines the ratio between the focal length of the first lens unit L1 and the focal length of the zoom lens L0 at the wide-angle end. Exceeding the upper limit of conditional expression (10) is undesirable because the total optical length increases. On the other hand, falling below the lower limit of conditional expression (10) is undesirable because it becomes difficult to correct various aberrations.

[0050] More preferably, the upper limit of conditional expression (10) is set to 4.10, 4.00, 3.90, 3.80, 3.75, 3.70, 3.65, or 3.60, and more preferably, the lower limit of conditional expression (10) is set to 1.25, 1.30, 1.35, 1.40, 1.45, 1.50, or 1.55.

[0051] In each embodiment, it is preferable to satisfy the following conditional expression (11).

[0052] -1.50 <f2 / fw<-0.20 ···(11) Conditional expression (11) defines the ratio between the focal length of the second lens unit L2 and the focal length of the zoom lens L0 at the wide-angle end. Exceeding the upper limit of conditional expression (11) is undesirable because it becomes difficult to correct astigmatism and field curvature. On the other hand, falling below the lower limit of conditional expression (11) is undesirable because the power of the second lens unit L2 is too weak, requiring the first lens unit L1 to be large, which increases the size of the zoom lens L0.

[0053] More preferably, the upper limit of conditional expression (11) is set to −0.25, −0.30, −0.35, −0.40, −0.45, or −0.50, and more preferably, the lower limit of conditional expression (11) is set to −1.45, −1.40, −1.35, or −1.30.

[0054] 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 telephoto zoom lens with a simple configuration, a short overall length, and good optical performance. Also, by arbitrarily combining a plurality of conditional expressions, the effects of each embodiment can be further enhanced.

[0055] The zoom lens L0 of Examples 1 to 3 comprises, in order from the object side to the image side, a first lens unit L1 having positive refractive power, a second lens unit L2 having negative refractive power, a third lens unit L3 having positive refractive power, and a fourth lens unit L4 having positive refractive power. During zooming from the wide-angle end to the telephoto end, the first lens unit L1 and the third lens unit L3 remain stationary, while the second lens unit L2 and the fourth lens unit L4 move.

[0056] The zoom lens L0 of Example 4 comprises, in order from the object side to the image side, a first lens unit L1 having positive refractive power, a second lens unit L2 having negative refractive power, a third lens unit L3 having positive refractive power, and a fourth lens unit L4 having positive refractive power. During zooming from the wide-angle end to the telephoto end, the first lens unit L1 remains stationary, while the second lens unit L2, the third lens unit L3, and the fourth lens unit L4 move.

[0057] 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.

[0058] 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 (°).

[0059] 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:

[0060] 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 value obtained by adding BF (back focus) to the length from the surface (lens surface) closest to the object of the zoom lens to the final lens surface (the lens surface closest to the image). The lens group is not limited to being composed of multiple lenses, and may be composed of a single lens.

[0061] (Numerical Example 1) Unit: mm Surface Data Surface number rd nd νd 1 37.014 6.79 1.49700 81.5 2 -225.588 2.07 3 34.232 5.32 1.49700 81.5 4 125.532 2.52 5 -190.869 2.05 1.54072 47.2 6 23.802 (variable) 7 -77.914 0.72 1.67790 55.3 8 21.684 1.48 2.05090 26.9 9 35.050 (variable) 10 28.293 2.97 1.49700 81.5 11 -66.431 0.17 12 30.238 1.86 1.49700 81.5 13 105.023 2.42 14 21.130 4.45 1.49700 81.5 15 -40.900 1.05 1.90525 35.0 16 20.225 3.25 17 (Aperture) ∞ 9.38 18 87.629 2.16 1.96300 24.1 19 -29.000 0.60 1.71300 53.9 20 23.021 (variable) 21 34.011 4.10 1.83481 42.7 22 -86.113 0.17 23 -164.685 0.96 1.95906 17.5 24 107.927 (variable) 25 ∞ 1.20 1.51633 64.1 26∞1.00 Image plane ∞ Various data Zoom ratio 2.00 Wide-angle Mid-range Telephoto Focal length 74.13 121.13 148.26 F-number 4.12 4.02 4.12 Half angle of view 8.33 5.06 4.09 Image height 10.75 10.75 10.75 Lens length 127.61 127.61 127.61 BF 30.50 24.44 16.55 d 6 3.09 25.78 33.34 d 9 31.77 9.08 1.52 d20 7.77 13.83 21.73 d24 28.71 22.65 14.76 Zoom lens group data Group starting plane focal length 1 1 137.95 2 7 -46.85 3 10 56.85 4 21 49.97 (Numerical Example 2) Unit: mm Surface Data Surface number rd nd νd 1 57.051 2.95 1.49700 81.5 2 250.149 0.17 3 140.528 1.81 1.49700 81.5 4 -2721.711 0.17 5 34.532 4.21 1.49700 81.5 6 169.953 4.40 7 338.543 1.09 1.54814 45.8 8 28.361 (variable) 9 -113.790 0.74 1.63854 55.4 10 39.192 0.97 11 726.758 0.71 1.51633 64.1 12 38.043 1.40 13 37.505 1.19 2.05090 26.9 14 75.499 (variable) 15 29.350 2.53 1.49700 81.5 16 -96.420 0.29 17 38.812 1.43 1.72916 54.7 18 207.245 0.17 19 26.856 3.75 1.49700 81.5 20 -43.842 0.17 21 -43.157 1.05 1.89190 37.1 22 24.576 5.79 23 (Aperture) ∞ 8.66 24 127.808 1.84 1.96300 24.1 25 -36.336 2.27 26 -30.671 0.60 1.65412 39.7 27 22.532 (variable) 28 34.691 4.36 1.80400 46.5 29 -70.728 0.17 30 -125.915 0.97 1.92286 18.9 31 166.429 (variable) 32 ∞ 1.20 1.51633 64.1 33∞1.00 Image plane ∞ Various data Zoom ratio 2.00 Wide-angle Mid-range Telephoto Focal length 60.85 99.70 121.70 F-number 4.11 4.04 4.12 Half angle of view 10.20 6.17 5.01 Image height 10.75 10.75 10.75 Lens length 127.40 127.40 127.40 BF 28.51 23.48 17.30 d 8 2.73 26.40 34.28 d14 32.58 8.91 1.02 d27 9.70 14.74 20.91 d31 26.72 21.69 15.51 Zoom lens group data Group starting plane focal length 1 1 128.45 2 9 -49.96 3 15 60.77 4 28 45.65 (Numerical Example 3) Unit: mm Surface Data Surface number rd nd νd 1 48.004 5.47 1.55200 70.7 2 -171.910 0.17 3 48.960 3.04 1.49700 81.5 4 259.325 0.99 5 -246.252 1.26 1.65844 50.9 6 40.282 (variable) 7 -975.236 0.88 1.69680 55.5 8 26.244 4.30 9 27.775 1.21 1.96300 24.1 10 37.939 (variable) 11 41.602 1.72 1.74400 44.8 12 -170.323 0.17 13 23.545 1.87 1.52841 76.5 14 123.112 0.17 15 22.168 3.26 1.49700 81.5 16 -46.526 0.17 17 -45.098 1.05 1.69895 30.1 18 18.771 3.10 19 (Aperture) ∞ 5.12 20 57.447 1.81 1.92286 18.9 21 -32.718 0.52 22 -30.221 0.60 1.71736 29.5 23 15.295 (variable) 24 32.305 4.86 1.85150 40.8 25 -66.112 0.17 26 -174.575 1.55 1.89286 20.4 27 67.412 (variable) 28 ∞ 1.20 1.51633 64.1 29∞1.00 Image plane ∞ Various data Zoom ratio 2.00 Wide-angle Mid-range Telephoto Focal length 47.45 78.10 94.90 F-number 4.12 4.07 4.12 Half angle of view 12.90 7.81 6.39 Image height 10.75 10.75 10.75 Lens length 127.59 127.59 127.59 BF 12.52 14.19 12.54 d 6 2.41 34.15 44.73 d10 44.20 12.46 1.88 d23 25.01 23.34 24.98 d27 10.73 12.40 10.75 Zoom lens group data Group starting plane focal length 1 1 167.59 2 7 -59.83 3 11 48.44 4 24 45.99 (Numerical Example 4) Unit: mm Surface Data Surface number rd nd νd 1 46.086 3.75 1.49700 81.5 2 1423.828 0.17 3 38.180 3.87 1.49700 81.5 4 334.250 0.17 5 44.066 4.24 1.49700 81.5 6 -173.480 1.97 1.60738 56.8 7 52.315 5.52 8 276.090 1.56 1.61772 49.8 9 23.164 (variable) 10 -81.040 0.65 1.77250 49.6 11 22.953 1.42 2.05090 26.9 12 43.342 (variable) 13 32.732 2.30 1.49700 81.5 14 -76.350 0.17 15 35.314 1.60 1.49700 81.5 16 863.692 1.85 17 19.284 3.79 1.57135 53.0 18 -65.317 0.93 1.90366 31.3 19 19.712 4.64 20 (Aperture) ∞ 8.64 21 64.713 2.49 1.80810 22.8 22 -26.749 0.60 1.74100 52.6 23 21.422 (variable) 24 38.115 3.91 1.80100 35.0 25 -65.592 0.27 26 -116.891 0.93 1.95906 17.5 27 104.990 (variable) 28 ∞ 1.20 1.51633 64.1 29∞1.00 Image plane ∞ Various data Zoom ratio 2.00 Wide-angle Mid-range Telephoto Focal length 91.38 148.03 182.76 F-number 4.90 5.33 5.77 Half angle of view 6.70 4.14 3.32 Image height 10.75 10.75 10.75 Lens length 127.53 127.53 127.53 BF 28.51 22.26 13.85 d 9 2.66 17.24 22.10 d12 31.06 8.70 1.55 d23 9.87 23.91 34.60 d27 26.72 20.46 12.06 Zoom lens group data Group starting plane focal length 1 1 142.44 2 10 -46.19 3 13 51.83 4 24 61.04 Table 1 shows the relationship between the above-mentioned conditional expressions and the respective numerical examples.

[0062] [Table 1]

[0063] Next, with reference to FIG. 9, an imaging device (surveillance camera) using the zoom lens of each embodiment as an imaging optical system will be described. FIG. 9 is a configuration diagram of the imaging device of each embodiment. In FIG. 9, reference numeral 16 denotes an imaging optical system configured with any of the zoom lenses of Embodiments 1 to 4. Reference numeral 15 in FIG. 9(B) denotes a dome cover (protective cover) that protects the imaging optical system 16. The dome cover 15 is molded with a thickness of about 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.

[0064] In Figures 9(A) and 9(B), 11a and 11b denote surveillance camera bodies. Figure 9(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.

[0065] 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.

[0066] According to each embodiment, for example, it is possible to provide a telephoto zoom lens and an imaging device that have a simple configuration, a short overall length, and good optical performance.

[0067] 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 positive refractive power, a second lens group having negative refractive power, a third lens group having positive refractive power, and a fourth lens group having positive refractive power, During zooming from the wide-angle end to the telephoto end, the first lens group remains stationary, and the spacing between adjacent lens groups changes. When the focal length of the first lens group is f1, the total optical length at the telephoto end is Lt, and the focal length of the zoom lens at the telephoto end is ft, 1.00 <f1 / Lt<1.50 0.50 <Lt / ft<1.40 A zoom lens characterized by satisfying the following conditional expressions: (Configuration 2) The zoom lens according to configuration 1, wherein the first lens group has three or more lenses. (Configuration 3) 3. The zoom lens according to configuration 1 or 2, wherein the first lens group has, at the most image side, a negative lens whose image-side surface is concave. (Configuration 4) When the smallest Abbe number based on the d-line among the lenses in the first lens group is νmin, 35.0<ν1min<55.0 4. The zoom lens according to any one of the configurations 1 to 3, wherein the following condition is satisfied: (Configuration 5) When the refractive index of the lens with the smallest Abbe number based on the d-line among the lenses in the first lens group is nd_ν1min, 1.50 <nd_ν1min<1.78 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 third lens group has, at the most image side, a negative lens whose image-side surface is concave. (Configuration 7) When the focal length of the third lens group is f3 and the focal length of the fourth lens group is f4, 0.70 <f3 / f4<1.80 7. The zoom lens according to any one of configurations 1 to 6, wherein the following condition is satisfied: (Configuration 8) the fourth lens group is composed of a positive lens and a negative lens, 8. The zoom lens according to any one of configurations 1 to 7, wherein the distance between the positive lens and the negative lens increases with increasing distance from the optical axis. (Configuration 9) When the focal length of the second lens group is f2, -4.50 <f1 / f2<-2.00 9. A zoom lens according to any one of configurations 1 to 8, wherein the following condition is satisfied: (Configuration 10) 0.70 <f1 / ft<2.00 10. The zoom lens according to any one of configurations 1 to 9, wherein the following condition is satisfied: (Configuration 11) 11. A zoom lens according to any one of configurations 1 to 10, wherein the fourth lens group moves during focusing. (Configuration 12) When the focal length of the lens arranged closest to the image in the first lens group is f1i, -0.50 <f1i / f1<-0.20 12. A zoom lens according to any one of configurations 1 to 11, characterized in that the following conditional expression is satisfied: (Configuration 13) When the distance on the optical axis between the first lens group and the second lens group at the telephoto end is D1t and the distance on the optical axis between the second lens group and the third lens group at the telephoto end is D2t, 0.010 <D2t / D1t<0.100 13. A zoom lens according to any one of configurations 1 to 12, wherein the following condition is satisfied: (Configuration 14) When the focal length of the zoom lens at the wide-angle end is fw, 1.20 <f1 / fw<4.20 14. A zoom lens according to any one of configurations 1 to 13, wherein the following condition is satisfied: (Configuration 15) When the focal length of the second lens group is f2 and the focal length of the zoom lens at the wide-angle end is fw, -1.50 <f2 / fw<-0.20 15. A zoom lens according to any one of configurations 1 to 14, wherein the following condition is satisfied: (Configuration 16) A zoom lens comprising, in order from the object side to the image side, a first lens group having positive refractive power, a second lens group having negative refractive power, a third lens group having positive refractive power, and a fourth lens group having positive refractive power, During zooming from the wide-angle end to the telephoto end, the first lens group remains stationary, and the spacing between adjacent lens groups changes. When the focal length of the first lens group is f1, the total optical length at the telephoto end is Lt, and the focal length of the zoom lens at the telephoto end is ft, 1.00 <f1 / Lt<1.50 A zoom lens characterized by satisfying the following conditional expressions: (Configuration 17) 17. An imaging device comprising the zoom lens according to any one of configurations 1 to 16, and an imaging element that receives an image formed by the zoom lens.

[0068] 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. [Explanation of symbols]

[0069] L0 zoom lens L1 First lens group L2 Second lens group L3: Third lens group L4 4th lens group

Claims

1. A zoom lens comprising, in order from the object side to the image side, a first lens group having positive refractive power, a second lens group having negative refractive power, a third lens group having positive refractive power, and a fourth lens group having positive refractive power, During zooming from the wide-angle end to the telephoto end, the first lens group remains stationary, and the spacing between adjacent lens groups changes. When the focal length of the first lens group is f1, the total optical length at the telephoto end is Lt, and the focal length of the zoom lens at the telephoto end is ft, 1.00<f1 / Lt<1.50 0.50<Lt / ft<1.40 A zoom lens characterized by satisfying the following conditional expressions:

2. 2. The zoom lens according to claim 1, wherein the first lens group includes three or more lenses.

3. 2. The zoom lens according to claim 1, wherein the first lens group has, at the most image side, a negative lens whose image-side surface is concave.

4. When the smallest Abbe number based on the d-line among the lenses in the first lens group is ν1min, 35.0<ν1min<55.0 2. The zoom lens according to claim 1, wherein the following condition is satisfied:

5. When the refractive index of the lens with the smallest Abbe number based on the d-line among the lenses in the first lens group is nd_ν1min, 1.50<nd_ν1min<1.78 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 third lens group has, at the most image side, a negative lens element whose image-side surface is concave.

7. When the focal length of the third lens group is f3 and the focal length of the fourth lens group is f4, 0.70<f3 / f4<1.80 2. The zoom lens according to claim 1, wherein the following condition is satisfied:

8. the fourth lens group is composed of a positive lens and a negative lens, 2. The zoom lens according to claim 1, wherein the distance between the positive lens and the negative lens increases with increasing distance from the optical axis.

9. When the focal length of the second lens group is f2, -4.50<f1 / f2<-2.00 2. The zoom lens according to claim 1, wherein the following condition is satisfied:

10. 0.70<f1 / ft<2.00 2. The zoom lens according to claim 1, wherein the following condition is satisfied:

11. 2. The zoom lens according to claim 1, wherein the fourth lens group moves during focusing.

12. When the focal length of the lens arranged closest to the image in the first lens group is f1i, -0.50<f1i / f1<-0.20 2. The zoom lens according to claim 1, wherein the following condition is satisfied:

13. When the distance on the optical axis between the first lens group and the second lens group at the telephoto end is D1t and the distance on the optical axis between the second lens group and the third lens group at the telephoto end is D2t, 0.010<D2t / D1t<0.100 2. The zoom lens according to claim 1, wherein the following condition is satisfied:

14. When the focal length of the zoom lens at the wide-angle end is fw, 1.20<f1 / fw<4.20 2. The zoom lens according to claim 1, wherein the following condition is satisfied:

15. When the focal length of the second lens group is f2 and the focal length of the zoom lens at the wide-angle end is fw, -1.50<f2 / fw<-0.20 2. The zoom lens according to claim 1, wherein the following condition is satisfied:

16. A zoom lens comprising, in order from the object side to the image side, a first lens group having positive refractive power, a second lens group having negative refractive power, a third lens group having positive refractive power, and a fourth lens group having positive refractive power, During zooming from the wide-angle end to the telephoto end, the first lens group remains stationary, and the spacing between adjacent lens groups changes. When the focal length of the first lens group is f1, the total optical length at the telephoto end is Lt, and the focal length of the zoom lens at the telephoto end is ft, 1.00<f1 / Lt<1.50 A zoom lens characterized by satisfying the following conditional expressions:

17. 17. 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