Zoom lens and imaging device

Abstract

To provide a zoom lens advantageous in terms of a wide angle of view, small size, and high optical performance.SOLUTION: A zoom lens has a first lens group B1 having a negative refractive power, a second lens group B2 having a positive refractive power, intermediate groups B3, B4 including two or more lens groups, and a rear group B5 including one or more lens groups and having a positive refractive power, which are arranged in order from an object side to an image side. The first lens group does not move for zooming, the second lens group moves in zooming, and the interval between the adjacent lens groups changes. Of all the lens groups included in the zoom lens, the second lens group has the maximum amount of movement and zoom ratio between a wide angle end and a telephoto end. The minimum focal length f2p of the focal lengths of positive lenses in the second lens group, the maximum focal length f2n of the focal lengths of negative lenses in the second lens group, and the focal length f2 of the second lens group satisfy the conditions of 0.65≤f2p / f2≤2.00 and -0.85≤f2n / f2<0.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Wider angle of view and smaller size are desired for zoom lenses used in imaging devices such as surveillance cameras, digital still cameras, video cameras, and broadcast cameras. Patent Documents 1 and 2 disclose negative-lead type zoom lenses as compact wide-angle zoom lenses. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-047813 [Patent Document 2] Japanese Patent Application Laid-Open No. 2014-109761 Summary of the Invention [Problem to be solved by the invention]

[0004] Zoom lenses like those mentioned above are also required to have high optical performance that can support high image quality such as 8K resolution.

[0005] An object of the present invention is to provide a zoom lens that is advantageous in terms of, for example, a wide angle of view, compact size, and high optical performance. [Means for solving the problem]

[0006] A zoom lens according to one aspect of the present invention comprises two lens groups, arranged in order from the object side to the image side, a first lens group having negative refractive power and a second lens group having positive refractive power. Or three Lens group Consists of Intermediate group and 1 one Lens group Made up of The rear group has positive refractive power. , consisting ofThis is a zoom lens in which the first lens group does not move during zooming, but the second lens group moves during zooming, and the spacing between adjacent lens groups changes. Of all the lens groups included in the zoom lens, the second lens group has the largest amount of movement and the largest zoom ratio between the wide-angle end and the telephoto end. Let f2p be the smallest focal length of at least one positive lens included in the second lens group, f2n be the largest focal length of at least one negative lens included in the second lens group, and f2 be the focal length of the second lens group. 0.65≦f2p / f2≦2.00 -0.85≦f2n / f2<0 The present invention is characterized in that the following conditions are satisfied: An imaging device including the zoom lens described above also constitutes another aspect of the present invention. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a zoom lens that is advantageous in terms of, for example, a wide angle of view, compact size, and high optical performance. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a cross-sectional view of a zoom lens according to a first embodiment. [Figure 2] 5A to 5C are aberration diagrams of the zoom lens of Example 1 at the wide-angle end, at the intermediate zoom position, and at the telephoto end. [Figure 3] FIG. 10 is a cross-sectional view of a zoom lens according to a second embodiment. [Figure 4] 10A to 10C are aberration diagrams of the zoom lens of Example 2 at the wide-angle end, at the intermediate zoom position, and at the telephoto end. [Figure 5] FIG. 10 is a cross-sectional view of a zoom lens according to a third embodiment. [Figure 6] 10A to 10C are aberration diagrams of the zoom lens of Example 3 at the wide-angle end, at the intermediate zoom position, and at the telephoto end. [Figure 7] FIG. 10 is a cross-sectional view of a zoom lens according to a fourth embodiment. [Figure 8] 10A to 10C are aberration diagrams of the zoom lens of Example 4 at the wide-angle end, at the intermediate zoom position, and at the telephoto end. [Figure 9] FIG. 10 is a cross-sectional view of a zoom lens according to a fifth embodiment. [Figure 10] 10A to 10C are aberration diagrams of the zoom lens of Example 5 at the wide-angle end, at the intermediate zoom position, and at the telephoto end. [Figure 11] FIG. 10 is a cross-sectional view of a zoom lens according to a sixth embodiment. [Figure 12] 13A to 13C are aberration diagrams of the zoom lens of Example 6 at the wide-angle end, at the intermediate zoom position, and at the telephoto end. [Figure 13] FIG. 1 is a diagram showing an imaging device equipped with a zoom lens according to any one of Examples 1 to 6. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0010] Prior to describing specific Examples 1 to 6, we will first explain matters common to all Examples. The zoom lens of each Example is used as an imaging lens for various imaging devices such as digital still cameras, video cameras, broadcast cameras, surveillance cameras, and cameras for silver halide film. The imaging lens may be replaceable with respect to the imaging device, or may be provided integrally with the imaging device. The zoom lens of each Example can also be used as a projection optical system for an image projection device (projector).

[0011] The zoom lens of each embodiment is a negative-lead zoom lens having, arranged 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, an intermediate group including two or more lens groups, and a rear group with positive refractive power including one or more lens groups. Because the negative first lens group and positive second lens group are arranged on the object side, this zoom lens is suitable for wide-angle applications.

[0012] A "lens group" refers to a group of one or more lenses that move together during zooming (variable magnification) between the wide-angle end and the telephoto end. That is, the spacing between adjacent lens groups changes during zooming. The lens group may include an aperture stop. The wide-angle end and the telephoto end refer to the zoom states with the maximum angle of view (shortest focal length) and the minimum angle of view (maximum focal length), respectively, when the lens group that moves during zooming is positioned at the ends of its mechanically or controllably movable range on the optical axis.

[0013] In the zoom lens of each embodiment, the first lens group does not move (remains stationary) during zooming, but the second lens group and at least one intermediate lens group move, changing the spacing between adjacent lens groups. By providing the lens groups from the second lens group onwards with a magnification-varying function, changes in various aberrations during magnification variation are corrected, and image plane fluctuations associated with magnification variation are also corrected.

[0014] In each embodiment, the second lens group is primarily responsible for changing magnification. That is, when the absolute value of the lateral magnification at the telephoto end divided by the lateral magnification at the wide-angle end for each lens group is defined as the magnification ratio (zoom ratio) of that lens group, the magnification ratio of the second lens group is the largest of all the lens groups.

[0015] Furthermore, when varying the magnification, at least one intermediate lens group (hereinafter also referred to as the focus lens group) moves mainly to correct image plane fluctuations. The focus lens group also moves when focusing on objects at various distances from infinity to close objects. Furthermore, the intermediate lens groups other than the focus lens group include a lens group that moves to more accurately correct aberration changes when varying the magnification.

[0016] Positive refractive power rear This group corrects chromatic aberration of magnification that occurs in the first lens group, where off-axial rays are high, and also has the effect of reducing the angle of incidence of rays onto the image plane.

[0017] In each embodiment, when comparing the amount of movement of each lens group that moves during magnification change between the wide-angle end and the telephoto end, the amount of movement of the second lens group is the greatest. The "amount of movement" of the second lens group here refers to the absolute value of the difference in position between a lens surface included in the second lens group at the wide-angle end and the telephoto end.

[0018] Furthermore, in each embodiment, the second lens group includes at least one positive lens and at least one negative lens. If the second lens group includes a cemented lens in which a positive lens and a negative lens are cemented together, the positive lens and the negative lens are treated as a single lens that is not cemented together. The zoom lens in each embodiment satisfies the following formulas (1) and (2), where f2p is the smallest focal length of the positive lenses included in the second lens group, f2n is the largest focal length of the negative lenses included in the second lens group, and f2 is the focal length of the second lens group.

[0019] 0.65≦f2p / f2≦2.00 (1) -0.85≦f2n / f2<0 (2) If f2p / f2 is below the lower limit of formula (1), the refractive power of the second lens group becomes too small, which increases the amount of movement of the second lens group during zooming, making it difficult to reduce the size of the zoom lens, which is undesirable.If f2p / f2 is above the upper limit of formula (1), the refractive power of the second lens group becomes too large, which causes problems in terms of aberration correction, which is undesirable.

[0020] The upper limit of formula (2) is determined by the fact that the refractive power of the second lens group is positive and f2n is a negative focal length. If f2n / f2 falls below the lower limit of formula (2), the power of the negative lens included in the second lens group becomes too small, resulting in insufficient correction of various aberrations, particularly spherical aberration and coma, which is undesirable. By reducing the aberrations of the second lens group, which is the main variable magnification group, it is possible to further suppress aberration fluctuations during magnification.

[0021] By having the above configuration and satisfying the conditions of expressions (1) and (2), it is possible to provide a zoom lens that is advantageous in terms of optical performance corresponding to a wide angle of view, compactness, and high resolution. It is more preferable to set the numerical ranges of the formulas (1) and (2) as follows:

[0022] 0.68≦f2p / f2≦1.50 (1a) -0.80≦f2n / f2<0 (2a) Furthermore, it is more preferable to set the numerical ranges of the formulas (1) and (2) as follows:

[0023] 0.72≦f2p / f2≦0.90 (1b) -0.76≦f2n / f2<0 (2b) It is preferable that the zoom lens of each embodiment satisfies at least one of the conditions of the following expressions (3) to (9).

[0024] It is preferable that the focal lengths f2p and f2n satisfy the condition of the following formula (3).

[0025] -2.00≦f2p / f2n≦-0.95 (3) If f2p / f2n is outside the range of the formula (3), it is not preferable in terms of various aberrations caused by the second lens group, particularly spherical aberration and coma.

[0026] Furthermore, when the amount of movement of the second lens group between the wide-angle end and the telephoto end is m2 and the amount of movement of the third lens group, which is in the intermediate group and adjacent to the second lens group on the image side, between the wide-angle end and the telephoto end is m3, it is preferable to satisfy the condition of the following formula (4):

[0027] 1.0 <m2 / m3≦2.5 (4) It is more preferable to provide an aperture stop in either the second or third lens group while satisfying the condition of formula (4), which can reduce the change in the height of light rays in the second lens group during zooming, making it easier to suppress aberration fluctuations during zooming.

[0028] In the zoom lens of each embodiment, which is a negative lead type zoom lens suitable for widening the angle of view, it is preferable to satisfy the condition of the following formula (5), where f1 is the focal length of the first lens group.

[0029] -0.85≦f1 / f2≦-0.55 (5) If f1 / f2 is below the lower limit of formula (5), the negative refractive power of the first lens group becomes too weak, which is undesirable in terms of widening the angle of view, whereas if f1 / f2 is above the upper limit of formula (5), the negative refractive power of the first lens group becomes too strong, which is undesirable in terms of correcting axial chromatic aberration.

[0030] Furthermore, in order to correct axial chromatic aberration, it is preferable that the first lens group include at least one positive lens, and where νd1p is the Abbe number of the at least one positive lens with respect to the d-line as the reference lens and θgF1p is the partial dispersion ratio of the positive lens with respect to the g-line and the F-line, the first lens group satisfy the following expressions (6) and (7):

[0031] νd1p≦40 (6) θgF1p+0.00162×νd1p-0.64146≦0.006 (7) Since the first lens group has negative refractive power, in order to correct axial chromatic aberration, it is preferable that at least one of the positive lenses included in the first lens group has high dispersion so as to satisfy the condition of formula (6). Furthermore, when secondary spectrum is taken into consideration, it is preferable that the condition of formula (7) is satisfied. The Abbe number νd1p is given by, where nd, nF, and nC are the refractive indices of the positive lens (or its material) at the d-line (wavelength 587.6 nm), F-line (wavelength 486.1 nm), and C-line (wavelength 656.3 nm), respectively. νd1p=(nd-1) / (nF-nC) In addition, the partial dispersion ratio θgF1p is expressed as follows, where the refractive indices of the positive lens for the g-line (wavelength 435.8 nm), F-line, and C-line are ng, nF, and nC, respectively: θgF1p=(ng-nF) / (nF-nC) It is expressed as:

[0032] Furthermore, it is more preferable for the correction of axial chromatic aberration that the positive lens in the first lens group is cemented with a negative lens.

[0033] Furthermore, when the maximum refractive index of at least one positive lens included in the rear group having positive refractive power is represented by Ndp, it is preferable that the condition of the following expression (8) be satisfied.

[0034] 1.85≦Ndp (8) Ndp is the formula ( 8 ) is low enough to fall outside the range of the positive lens, the curvature of each surface of the positive lens increases, which increases various aberrations, and is therefore undesirable.

[0035] It is also preferable that the Abbe number νdp of the positive lens with the maximum refractive index in the rear group, with reference to the d-line, satisfies the condition of the following formula (9).

[0036] νdp≦25 (9) By satisfying the condition of expression (9) in the rear group that corrects lateral chromatic aberration, the effect of the correction can be further improved.

[0037] Furthermore, it is preferable that the intermediate group includes at least one lens group with negative refractive power. By using this negative lens group as the focus lens group, the amount of movement of the focus lens group during focusing can be reduced, allowing for further miniaturization of the zoom lens.

[0038] It is more preferable that the numerical ranges of the formulas (3) to (9) are as follows:

[0039] -1.90≦f2p / f2n≦-0.97 (3a) 1.0 <m2 / m3≦2.2 (4a) -0.80≦f1 / f2≦-0.56 (5a) νd1p≦39 (6a) θgF1p+0.00162×νd1p-0.64146≦0.004 (7a) 1.90≦Ndp (8a) νdp≦23 (9a) Furthermore, it is more preferable to set the numerical ranges of the formulas (3) to (9) as follows:

[0040] -1.80≦f2p / f2n≦-0.98 (3b) 1.0 <m2 / m3≦1.9 (4b) -0.76≦f1 / f2≦-0.57 (5b) νd1p≦38 (6b) θgF1p+0.00162×νd1p-0.64146≦0.002 (7b) 1.95≦Ndp (8b) νdp≦21 (9b) Examples 1 to 6 will be described below. FIGS. 1, 3, 5, 7, 9, and 11 show the configurations of the zoom lenses of Examples 1 to 6 at the wide-angle end, respectively. The zoom lenses of Examples 1 to 4 include, arranged in order from the object side to the image side, a first lens group B1 with negative refractive power, a second lens group B2 with positive refractive power, a third lens group B3 with positive refractive power and a fourth lens group B4 with negative refractive power included in the intermediate group, and a fifth lens group B5 with positive refractive power as the rear group. The zoom lens of Example 5 includes a first lens group B1 with negative refractive power, a second lens group B2 with positive refractive power, a third lens group B3 with positive refractive power and a fourth lens group B4 with negative refractive power included in the intermediate group, and a sixth lens group B6 with positive refractive power as the rear group. Furthermore, the zoom lens of Example 6 has a first lens group B1 with negative refractive power, a second lens group B2 with positive refractive power, a third lens group B3 with negative refractive power included in an intermediate group, a fourth lens group B4 with positive refractive power, a fifth lens group B5 with negative refractive power, and a sixth lens group B6 with positive refractive power as a rear group.

[0041] In each figure, AP denotes an aperture stop. In Examples 1 to 5, the aperture stop AP is included in the second lens unit B2, and in Example 6, the aperture stop AP is included in the third lens unit B3.

[0042] DP is a glass block such as a cover glass or low-pass filter attached to an image sensor such as a CCD sensor or CMOS sensor. IM is the image plane, where the image sensor's image plane is located. In a silver halide film camera, the film surface (photosensitive surface) of the silver halide film is located on the image plane IM.

[0043] In each embodiment, the first lens group B1 includes a positive lens LP1. The second lens group B2 includes a positive lens LP2 with the shortest focal length among the positive lenses included in the second lens group B2 and a negative lens LN2 with the longest focal length among the negative lenses included in the second lens group B2. The rear group includes a positive lens LP3 with the greatest refractive power among the positive lenses included in the rear group.

[0044] In each figure, arrows below the lens groups that move during magnification change indicate the movement loci of those lens groups during magnification change from the wide-angle end to the telephoto end. In Examples 1 to 4, the second lens group B2, the third lens group B3, and the fourth lens group B4 move toward the object side during magnification change from the wide-angle end to the telephoto end. In Examples 5 and 6, the second lens group B2, the third lens group B3, the fourth lens group B4, and the fifth lens group B5 move toward the object side during magnification change from the wide-angle end to the telephoto end.

[0045] The fourth lens group B4 in Examples 1 to 4 and the fifth lens group B5 in Examples 5 and 6 move to correct image plane fluctuations during magnification. Below these lens groups in each figure, solid and dashed lines indicate the movement loci of the lens groups during magnification change when focusing on an object at infinity and a close-up object, respectively. The fourth lens group B4 in Examples 1 to 4 and the fifth lens group B5 in Examples 5 and 6 move as a focus lens group during focusing. Specifically, they move toward the image side during focusing from an object at infinity to a close-up object.

[0046] Numerical examples 1 to 6 corresponding to Examples 1 to 6, respectively, are shown in Tables 1 to 6. In each numerical example, f is the focal length (mm), Fno is the F-number, and ω is the half angle of view (°).

[0047] The surface number i indicates the order of the surface when counted from the object side. r is the radius of curvature (mm) of the ith surface from the object side, d is the lens thickness or air gap (mm) between the ith and (i+1)th surfaces, and n is the refractive index at the d-line of the optical material between the ith and (i+1)th surfaces. ν is the Abbe number based on the d-line of the optical material between the ith and (i+1)th surfaces.

[0048] An asterisk (*) next to a surface number indicates that the surface has an aspherical shape. The aspherical shape is expressed by the following equation, where z is the displacement (sag) from the vertex of the surface in the optical axis direction, y is the height from the optical axis in a direction perpendicular to the optical axis, the direction of light travel is positive, r is the paraxial radius of curvature, k is the conic constant, and Bj (j = 1 to 16) are aspherical coefficients.

[0049]

number

[0050] In each table, "E±x" is "10 ±x " Also, all coefficients that are not specifically stated are 0.

[0051] Table 7 shows the values ​​corresponding to the above-mentioned conditional expressions (1) to (9) in Numerical Examples 1 to 6.

[0052] Figures 2, 4, 6, 8, 10, and 12 respectively show longitudinal aberrations (spherical aberration, astigmatism, distortion, and chromatic aberration) for Numerical Examples 1 to 6 at (A) the wide-angle end, (B) the mid-zoom position, and (C) the telephoto end. In the spherical aberration diagrams, Fno indicates the F-number, the solid line indicates spherical aberration for the d-line, the two-dot chain line indicates spherical aberration for the C-line, and the one-dot chain line indicates spherical aberration for the g-line. The separation amount at the bottom end indicates axial chromatic aberration. In the astigmatism diagrams, the solid line S indicates the sagittal image plane, and the dashed line M indicates the meridional image plane. In the distortion diagrams, distortion for the d-line is shown. In the chromatic aberration diagrams, the two-dot chain line indicates lateral chromatic aberration for the C-line, and the one-dot chain line indicates lateral chromatic aberration for the g-line. ω is the half angle of view (°).

[0053] The configurations of the zoom lenses in Examples 1 to 6 are merely examples, and the number of lenses in each lens group, the number of aspherical lenses, and the number of lens groups included in the intermediate group may be changed. Also, the zoom lenses in Examples 1 to 6 have, from the object side, negative, positive, positive, negative, positive. ,or, negative, positive, positive , positive, negative, positive, or negative, positive, negative, positive , negative, positive However, other lens group arrangements may also be employed.

[0054] [Table 1]

[0055] [Table 2]

[0056] [Table 3]

[0057] [Table 4]

[0058] [Table 5]

[0059] [Table 6]

[0060] [Table 7]

[0061] [Imaging device] Fig. 13 shows an imaging device (monitoring camera) that uses a zoom lens according to any one of Examples 1 to 6 as an imaging optical system. In Fig. 13, 16 is an imaging optical system configured using any one of the zoom lenses according to Examples 1 to 6. 11 is a camera body, and 12 is an imaging element such as a CCD sensor or CMOS sensor that captures (photoelectrically converts) an object image formed by the imaging optical system 16. 13 is a recording medium that records image information generated from an output signal from the imaging element 12. 14 is a cable that serves as transfer means for transferring image information to the outside.

[0062] By applying the zoom lenses of Examples 1 to 6 to an imaging device such as a surveillance camera, it is possible to realize a small imaging device that has good optical performance corresponding to a wide angle and high resolution.

[0063] The imaging device using the zoom lenses of Examples 1 to 6 is not limited to a surveillance camera, but can also be used in other imaging devices such as a video camera, a digital still camera, etc. In addition to the zoom lens, the imaging device may also have an image processing circuit that electrically performs aberration correction.

[0064] The embodiments described above are merely representative examples, and various modifications and changes can be made to each embodiment when implementing the present invention. [Explanation of symbols]

[0065] B1 First lens group B2 Second lens group B3 Third lens group B4 4th lens group B5 5th lens group B6 6th lens group LP2: Positive lens in the second lens group LN2 negative lens in the second lens group

Claims

1. A zoom lens comprising, arranged 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, an intermediate group consisting of two or three lens groups, and a rear group consisting of one lens group having positive refractive power, wherein the first lens group does not move during zooming, but the second lens group moves during zooming, and the distance between adjacent lens groups changes, the second lens group has the largest amount of movement and the largest zoom ratio between the wide-angle end and the telephoto end among all the lens groups included in the zoom lens, Let f2p be the smallest focal length among the focal lengths of at least one positive lens included in the second lens group, f2n be the largest focal length among the focal lengths of at least one negative lens included in the second lens group, and f2 be the focal length of the second lens group, 0.65≦f2p / f2≦2.00 -0.85≦f2n / f2<0 A zoom lens characterized by satisfying the following conditions:

2. -2.00≦f2p / f2n≦-0.95 2. The zoom lens according to claim 1, wherein the following condition is satisfied:

3. the intermediate group includes a third lens group adjacent to the second lens group, When the movement amounts of the second lens group and the third lens group between the wide-angle end and the telephoto end are m2 and m3, respectively, 1.0<m2 / m3≦2.5 3. The zoom lens according to claim 1, wherein the following condition is satisfied:

4. 4. The zoom lens according to claim 3, wherein either the second lens group or the third lens group includes an aperture stop.

5. When the focal length of the first lens group is f1, −0.85≦f1 / f2≦−0.55 5. The zoom lens according to claim 1, wherein the following condition is satisfied:

6. When the Abbe number with respect to the d-line is νd1p and the partial dispersion ratio for the g-line and the F-line is θgF1p, the first lens group is νd1p≦40 θgF1p+0.00162×νd1p−0.64146≦0.006 6. The zoom lens according to claim 1, further comprising a positive lens element that satisfies the following condition:

7. 7. The zoom lens according to claim 6, wherein the positive lens included in the first lens group is cemented with a negative lens.

8. When the refractive index of the positive lens having the largest refractive index at the d-line among at least one positive lens included in the rear group is Ndp, 1.85≦Ndp 8. The zoom lens according to claim 1, wherein the following condition is satisfied:

9. When the Abbe number of the positive lens having the maximum refractive index included in the rear group and based on the d-line is νdp, νdp≦25 9. The zoom lens according to claim 8, wherein the following condition is satisfied:

10. 10. The zoom lens according to claim 1, wherein the intermediate group includes at least one lens group having negative refractive power.

11. 11. The zoom lens according to claim 10, wherein the intermediate group includes a lens group with negative refractive power that moves for focusing.

12. the intermediate group includes, in order from the object side to the image side, a third lens group having a positive refractive power and a fourth lens group having a negative refractive power; 12. The zoom lens according to claim 1, wherein the rear group includes a fifth lens group having a positive refractive power.

13. the intermediate group includes, in order from the object side to the image side, a third lens group having a positive refractive power, a fourth lens group having a positive refractive power, and a fifth lens group having a negative refractive power; 12. The zoom lens according to claim 1, wherein the rear group includes a sixth lens group having a positive refractive power.

14. a zoom lens according to any one of claims 1 to 13; an image sensor for capturing an image formed by the zoom lens.

Images