Zoom lens and imaging device

Abstract

To provide a zoom lens that is advantageous in terms of, for example, high optical performance, a high zoom ratio, and a compact size.SOLUTION: A zoom lens has a first lens group having a positive refractive power (B1), a second lens group having a negative refractive power (B2), and a rear group including one or more lens groups (B3, B4, B5), which are arranged in order from an object side to an image side. In zooming, the first lens group does not move, and each interval between the adjacent lens groups changes. The second lens group includes at least two positive lenses (LP1, LP2). The lateral magnification β2W of the second lens group at a wide angle end, the lateral magnification β2T of the second lens group at a telephoto end, the focal distance fW of the zoom lens at the wide angle end, the focal distance fT of the zoom lens at the telephoto end, and the distance Dt from a lens surface on the most object side to an image surface satisfy predetermined conditional expressions.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] There is a demand for zoom lenses that have good optical performance, a high zoom ratio, and a small size, as zoom lenses used in surveillance cameras, digital still cameras, video cameras, broadcast cameras, etc. Patent Document 1 discloses a zoom lens with a zoom ratio of about 30. Patent Document 2 discloses a zoom lens with a zoom ratio of about 20. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-126057 [Patent Document 2] Japanese Patent Application Laid-Open No. 2018-25625 Summary of the Invention [Problem to be solved by the invention]

[0004] The zoom lens disclosed in Patent Document 1 is insufficient in terms of compactness. The zoom lens disclosed in Patent Document 2 is insufficient in terms of zoom ratio. An object of the present invention is to provide a zoom lens that is advantageous in terms of, for example, high optical performance, a high zoom ratio, and compactness. [Means for solving the problem]

[0005] A zoom lens according to one aspect of the present invention includes, arranged in order from an object side to an image side, a first lens group having a positive refractive power, and a second lens group having a negative refractive power; It consists of a third lens group with positive refractive power, a fourth lens group with negative refractive power, and a fifth lens group with positive refractive power. In the zoom lens, the first lens group does not move during zooming, and the intervals between adjacent lens groups change. The lateral magnification β of the second lens group at the wide-angle end is 2W , the lateral magnification β of the second lens group at the telephoto end2T , the focal length f of the zoom lens at the wide-angle end W , the focal length f of the zoom lens at the telephoto end T , the distance D from the lens surface closest to the object to the image plane t satisfies a predetermined conditional expression.

[0006] Other objects and features of the present invention are illustrated in the following examples. [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, high optical performance, a high zoom ratio, and compact size. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a cross-sectional view of a zoom lens according to a first embodiment. [Figure 2] 4A to 4C are aberration diagrams of the zoom lens in 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 in 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 in 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 in 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 in 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 in Example 6 at the wide-angle end, at the intermediate zoom position, and at the telephoto end. [Figure 13] 1 is a schematic diagram of an imaging device equipped with a zoom lens in each embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0010] The zoom lens of each embodiment is a positive-lead zoom lens having, arranged in order from the object side to the image side, a first lens group with positive refractive power, a second lens group with negative refractive power, and a rear group including one or more lens groups, making it suitable for achieving high zoom ratios. Furthermore, in the zoom lens of each embodiment, the first lens group does not move during zooming, and the spacing between adjacent lens groups changes. In this way, the zoom lens of each embodiment is configured to provide the lens groups from the second lens group onwards with a zooming function and to compensate for the movement of the image plane associated with zooming. The second lens group includes at least two lenses with positive refractive power, and primarily corrects the spherical aberration of the second lens group while canceling and correcting the residual axial chromatic aberration of the first lens group at the telephoto end. Note that if a cemented lens is included, the refractive power of each lens is calculated as a single uncemented lens to determine whether it is positive or negative.

[0011] The zoom lens of each embodiment also satisfies the following conditional expressions (1) and (2).

[0012] 0.220≦(f W β 2T ) / (f T β 2W )≦0.597 (1) 0.300 <D t / f T <0.815 (2) Here, β 2W is the lateral magnification of the second lens group at the wide-angle end, and β2T is the lateral magnification of the second lens group at the telephoto end, and f W is the focal length of the zoom lens (total system) at the wide-angle end, f T is the focal length of the zoom lens (total system) at the telephoto end, D t is the distance from the lens surface closest to the object to the image plane.

[0013] Conditional expression (1) defines the ratio of the second lens group's contribution to the zoom ratio of the zoom lens. If the lower limit of conditional expression (1) is not met, the absolute value of the refractive power of the second lens group becomes too small, and the amount of movement of the second lens group associated with zooming becomes large, making it difficult to reduce the size of the zoom lens. On the other hand, if the upper limit of conditional expression (1) is met, the absolute value of the refractive power of the second lens group becomes too large, or if the refractive power of the second lens group is kept to a level that does not pose a problem in terms of aberration correction, the amount of movement of the second lens group associated with zooming becomes large, making it difficult to reduce the size of the zoom lens.

[0014] Conditional expression (2) defines the ratio between the overall length of the zoom lens and the focal length of the zoom lens at the telephoto end. The smaller this ratio, the more compact the zoom lens. If the lower limit of conditional expression (2) is not met, the refractive power of the first lens group becomes too strong, making it difficult to correct spherical aberration and axial chromatic aberration at the telephoto end. It also makes it difficult to correct fluctuations in field curvature associated with zooming and spherical aberration at the telephoto end. On the other hand, if the upper limit of conditional expression (2) is exceeded, the zoom lens becomes too large.

[0015] Preferably, at least one of the numerical ranges of conditional expressions (1) and (2) is set as shown in the following conditional expressions (1a) and (2a), respectively.

[0016] 0.221≦(f W β 2T ) / (f T β 2W )≦0.596 (1a) 0.350 <D t / f T <0.813 (2a) More preferably, at least one of the numerical ranges of conditional expressions (1) and (2) is set as shown in the following conditional expressions (1b) and (2b), respectively.

[0017] 0.222≦(f W β 2T ) / (f T β 2W )≦0.595 (1b) 0.400 <D t / f T <0.811 (2b) It is also preferable that the zoom lens of each embodiment satisfies the following conditional expressions (3) and (4).

[0018] 1.90 <n ave ···(3) ν ave <35 (4) where n ave is the average refractive index of at least two positive lenses in the second lens group, ν ave is the average Abbe number of at least two positive lenses in the second lens group. Note that the average refractive index n ave and the average Abbe number ν ave are defined as the following expressions (5) and (6), respectively, where N is the number of at least two positive lenses in the second lens group.

[0019]

number

[0020] where n i d is the refractive index of the glass material of the i-th positive lens at the d line, ν i d is the Abbe number of the glass material of the i-th positive lens element based on the d-line. By satisfying conditional expression (3), spherical aberration in the second lens group can be corrected more effectively. By satisfying conditional expression (4), axial chromatic aberration on the telephoto side can be corrected more effectively.

[0021] It is also preferable that at least one of the at least two positive lenses included in the second lens group satisfies the following conditional expression (7).

[0022] θ gF +0.00162ν d -0.64146>0.02 (7) where ν d is the Abbe number based on the d-line of at least one positive lens among at least two positive lenses included in the second lens group, and θ gF is the partial dispersion ratio. Partial dispersion ratio θ gF are the refractive indices for the g-line, F-line, and C-line of at least one positive lens among at least two positive lenses included in the second lens group, respectively. g , n F , n C is defined as the following equation (8).

[0023] θ gF =(n g -n F ) / (n F -n C ) ···(8) By satisfying conditional expression (7), the secondary spectrum can be corrected more effectively with respect to the axial chromatic aberration on the telephoto side.

[0024] Also, preferably, in terms of correcting spherical aberration and longitudinal chromatic aberration, the at least two positive lenses included in the second lens group include a positive lens cemented with a negative lens.

[0025] It is also preferable that the positive lens included in the second lens group satisfy the following conditional expression (9).

[0026] -0.4<φ p / φ2<0 (9) where φ pis the maximum refractive power of the positive lenses included in the second lens group, and φ2 is the refractive power of the second lens group. If the positive lenses are cemented together, the refractive power calculated for a single lens when the lenses are not cemented together is used. The upper limit of conditional expression (9) is determined by the fact that the signs of the respective refractive powers are opposite. It is not preferable to exceed the lower limit of conditional expression (9) because spherical aberration will be over-corrected.

[0027] It is also preferable that the second lens group satisfy the following conditional expression (10):

[0028] -3 <f2 / f W <0 ···(10) Here, f2 is the focal length of the second lens group. The upper limit of conditional expression (10) is determined by the fact that the refractive power of the second lens group is negative. If the lower limit of conditional expression (10) is not reached, the absolute value of the refractive power of the second lens group becomes large, which is undesirable in terms of fluctuations in field curvature associated with magnification and correction of spherical aberration on the telephoto side.

[0029] Preferably, the rear group includes at least three lens groups. Such a configuration reduces the magnification variation share of the second lens group, making it easier to fall within the range of conditional formula (1). Preferably, the rear group includes at least one lens group with negative refractive power. More preferably, the lens group with negative refractive power includes a lens group that moves for focusing, and by moving this lens group for focusing when the object distance changes, the amount of movement of the focus lens group required for focusing can be reduced, contributing to further miniaturization of the zoom lens.

[0030] More preferably, at least one of the numerical ranges of conditional expressions (3), (4), (7), (9), and (10) is set to satisfy the following conditional expressions (3a), (4a), (7a), (9a), and (10a), respectively.

[0031] 1.92 <n ave (3a) ν ave <30 (4a) θ gF +0.00162νd -0.64146>0.03 (7a) -0.38<φ p / φ2<-0.10 (9a) -2.8 <f2 / f W <-0.5 (10a) More preferably, at least one of the numerical ranges of conditional expressions (3), (4), (7), (9), and (10) is set to satisfy the following conditional expressions (3b), (4b), (7b), (9b), and (10b), respectively.

[0032] 1.95 <n ave (3b) ν ave <25 (4b) θ gF +0.00162ν d -0.64146>0.04 (7b) -0.37<φ p / φ2<-0.15 (9b) -2.5 <f2 / f W <-1.0 (10b) Next, the zoom lenses of the respective examples will be described with reference to Figures 1 to 12. Figures 1, 3, 5, 7, 9, and 11 are cross-sectional views of zoom lenses 1a to 1f of Examples 1 to 6 at the wide-angle end, respectively.

[0033] Each of the zoom lenses 1a to 1f in the embodiments comprises, arranged in order from the object side to the image side, a first lens group B1 with positive refractive power, a second lens group B2 with negative refractive power, and a rear group including one or more lens groups (third lens group B3, fourth lens group B4, fifth lens group B5). The first lens group B1 does not move during magnification variation, but the spacing between adjacent lens groups changes during magnification variation. The second lens group B2 includes at least two positive lenses LP1 and LP2. AP denotes an aperture stop, DP denotes a glass block such as a cover glass for a CCD sensor or CMOS sensor or a low-pass filter, and IM denotes an image plane.

[0034] When changing magnification from the wide-angle end to the telephoto end, each lens group moves as shown by the arrows in each cross-sectional view. The fourth lens group B4 is a focus lens group with negative refractive power and moves during focusing. The solid and dashed lines indicate the movement locus of the fourth lens group B4, which corrects image plane fluctuations during magnification when focusing on an object at infinity and a close distance, respectively.

[0035] 2, 4, 6, 8, 10, and 12 are aberration diagrams of the zoom lenses 1a to 1f of Examples 1 to 6, respectively, showing aberration diagrams at (A) the wide-angle end, (B) the intermediate zoom position, and (C) the telephoto end. In each aberration diagram, d and g represent the d-line and g-line, respectively, and M and S represent the meridional and sagittal image planes, respectively. Distortion is shown for the d-line, and chromatic aberration of magnification is shown for the g-line.

[0036] Numerical Examples 1 to 6 corresponding to Examples 1 to 6 are listed below in Tables 1 to 6. In each numerical example, r is the radius of curvature (paraxial radius of curvature) of the ith surface, in order from the object side, d is the surface distance (lens thickness or air distance) between the ith surface and the (i+1)th surface, and n and v are the refractive index and Abbe number of the material of the ith lens, respectively. The Abbe number v of a certain material is calculated by dividing the refractive index at the d-line (587.6 nm), F-line (486.1 nm), and C-line (656.3 nm) of the Fraunhofer lines by n. d , n F , n C When ν=(n d -1) / (n F -n C ) It is expressed as:

[0037] In each numerical example, d, focal length f (mm), F-number Fno, and half angle of view ω (°) are all values ​​when the zoom lens of each example is focused on an object at infinity. If the optical surface is aspherical, a "*" is added to the right of the surface number. The aspherical shape is expressed by the following equation (11), where y is the radial distance from the optical axis, z is the surface sag in the optical axis direction, r is the paraxial radius of curvature, k is the Conic coefficient, and B is the aspherical coefficient, with the sign of z being positive in the direction from the object side to the image plane.

[0038]

number

[0039] In each numerical example, "E±x" is "10 ±x ". All coefficients not specifically indicated are 0.

[0040] Table 7 shows the relationship between the various numerical values ​​in each numerical example and each conditional expression.

[0041] [Table 1]

[0042] [Table 2]

[0043] [Table 3]

[0044] [Table 4]

[0045] [Table 5]

[0046] [Table 6]

[0047] [Table 7]

[0048] Next, with reference to FIG. 13, an imaging device (surveillance camera) using the zoom lens of each embodiment as an imaging optical system will be described. FIG. 13 is a schematic diagram of an imaging device 100 equipped with a zoom lens of each embodiment. In FIG. 13, reference numeral 16 denotes an imaging optical system configured with any of the zoom lenses of Embodiments 1 to 6, and reference numeral 11 denotes a surveillance camera body. Reference numeral 12 denotes an imaging element (photoelectric conversion element) such as a CCD sensor or CMOS sensor built into surveillance camera body 11, which receives a subject image formed by imaging optical system 16 (capturing an image formed by the zoom lens). Reference numeral 13 denotes a memory (recording means) that records information corresponding to the subject image photoelectrically converted by imaging element 12. Reference numeral 14 denotes a network cable (transfer means) for transferring the subject image photoelectrically converted by imaging element 12. Note that the zoom lens of each embodiment is not limited to surveillance cameras and can also be used in other imaging devices such as video cameras and digital cameras. Furthermore, imaging device 100 may include an aberration correction means, such as a circuit that electrically corrects aberrations.

[0049] According to each embodiment, it is possible to provide a zoom lens and an imaging device that are advantageous in terms of, for example, high optical performance, a high zoom ratio, and compact size.

[0050] While the preferred embodiments of the present invention have been described above, the present invention is not limited to these embodiments and various modifications and variations are possible within the scope of the present invention. For example, the number of lens groups in the rear group may be changed, or the number of aspherical lenses may be increased. [Explanation of symbols]

[0051] 1a-1f zoom lens B1 First lens group B2 Second lens group B3 Third lens group (rear group) B4 4th lens group (rear group) B5 5th lens group (rear group) LP1, LP2 positive lenses

Claims

1. A zoom lens comprising, arranged in order from the object side to the image side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, a fourth lens group having a negative refractive power, and a fifth lens group having a positive refractive power, During zooming, the first lens group does not move, and the intervals between adjacent lens groups change. the second lens group includes at least two positive lenses, The lateral magnification of the second lens group at the wide-angle end is β2W, the lateral magnification of the second lens group at the telephoto end is β2T, the focal length of the zoom lens at the wide-angle end is fW, the focal length of the zoom lens at the telephoto end is fT, and the distance from the lens surface closest to the object side to the image plane is Dt, 0.220≦(f) Ｗ ・b ２Ｔ ) / (& Ｔ ・b ２Ｗ )≦0.597 0.300<D ｔ / f Ｔ <0.815 A zoom lens characterized by satisfying the following conditional expressions:

2. The average refractive index of the at least two positive lenses is n ａｖｅ , the average Abbe number of the at least two positive lenses is ν ａｖｅ As, 1.90<n ａｖｅ n ａｖｅ <35 2. The zoom lens according to claim 1, wherein the following condition is satisfied:

3. The at least two positive lenses have an Abbe number of ν ｄ , the partial dispersion ratio is θ ｇＦ As, i ｇＦ +0.00162n ｄ -0.64146>0.02 3. The zoom lens according to claim 1, further comprising a positive lens element that satisfies the following condition:

4. 4. The zoom lens according to claim 1, wherein the at least two positive lenses include a positive lens cemented with a negative lens.

5. The maximum refractive power of the at least two positive lenses is defined as φ ｐ , the refractive power of the second lens group is φ ２ As, -0.4<φ ｐ / φ ２ <0 5. The zoom lens according to claim 1, wherein the following condition is satisfied:

6. The focal length of the second lens group is f ２ As, -3<f ２ / f Ｗ <0 6. The zoom lens according to claim 1, wherein the following condition is satisfied:

7. A zoom lens according to any one of claims 1 to 6; an image sensor for capturing an image formed by the zoom lens.

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