JP7832819B2 - Zoom lens and imaging device - Google Patents

Description

This invention relates to a zoom lens and an imaging device.

In recent years, imaging devices using solid-state image sensors, such as digital still cameras, have become widespread. Along with this, zoom lenses have become more high-performance and smaller, and compact imaging system systems are rapidly gaining popularity. For conventional lenses, particularly those for surveillance cameras, video cameras, digital still cameras, SLR cameras, and mirrorless cameras where short overall length and compact size are desired, the challenge lies in correcting aberrations to maintain high optical performance while ensuring performance during close-up shooting.

The zoom lenses described in Patent Documents 1 to 3 disclose a zoom lens consisting of a first lens group with positive refractive power, a second lens group with negative refractive power, 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, arranged in order from the object side to the image side. However, in Patent Documents 1 and 3, the refractive power of the negative lens in the fourth lens group is too strong, making it difficult to correct image field curvature when focusing at close range, and thus making close-range photography and maintaining performance difficult. Furthermore, in Patent Document 2, the correction of chromatic aberration by the negative lens in the fourth lens group is insufficient, making close-range photography and maintaining performance difficult.

Patent No. 5581730 Japanese Patent Publication No. 2017-134304 Japanese Patent Publication No. 2006-099130

Therefore, the objective of this invention is to provide a zoom lens capable of achieving high optical performance even when shooting at close range.

The lens system consists of, 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, a third lens group with positive refractive power, a fourth lens group with negative refractive power, and a rear lens group.
It is a zoom lens that changes magnification by changing the spacing between adjacent lens groups.
A zoom lens having a negative refractive power, wherein at least one of the lens group positioned on the image plane side of the aperture diaphragm has a negative lens Ln, and satisfies the following equation.
0.95 ≦ fn / fGN < 20.00 (1)
1.55 < Ndn < 1.70 (2)
15.0 < νdn < 32.0 (3)
however,
fn: focal length of the negative lens Ln fGN: focal length of the lens group having the negative lens Ln Ndn: refractive index of the negative lens Ln at the d line νdn: Abbe number of the negative lens Ln at the d line

Furthermore, in order to solve the above-mentioned problems, the imaging device according to the present invention is characterized by comprising the zoom lens and an image sensor that converts the optical image formed by the zoom lens into an electrical signal.

According to this invention, it is possible to provide a zoom lens that can achieve high optical performance even when shooting at close range.

This is a νd-PCt diagram of the material. This is a cross-sectional view of the zoom lens of Example 1. This is a longitudinal aberration diagram of the zoom lens of Example 1 at the wide-angle end. This is a longitudinal aberration diagram of the zoom lens of Example 1 in the intermediate region. This is a longitudinal aberration diagram of the zoom lens of Example 1 at its telephoto end. This is a cross-sectional view of the zoom lens of Example 2. This is an aberration diagram of the zoom lens of Example 2 at the wide-angle end. This is an aberration diagram of the zoom lens of Example 2 in the intermediate range. This is an aberration diagram of the zoom lens of Example 2 at its telephoto end. This is a cross-sectional view of the zoom lens of Example 3. This is an aberration diagram of the zoom lens of Example 3 at the wide-angle end. This is an aberration diagram of the zoom lens of Example 3 in the intermediate range. This is an aberration diagram of the zoom lens of Example 3 at its telephoto end. This diagram schematically shows an example of the configuration of an imaging device according to one embodiment of the present invention.

The following describes embodiments of the zoom lens and imaging device according to the present invention. However, the zoom lens and imaging device described below are merely one embodiment of the zoom lens and imaging device according to the present invention, and the zoom lens and imaging device according to the present invention are not limited to the embodiments described below.

1. Zoom Lens 1-1. Optical Configuration The zoom lens according to the present invention is configured to have, 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, a fourth lens group having negative refractive power, and a rear group. This configuration makes it easy to create a zoom lens with relatively high magnification. Furthermore, for higher performance, it is preferable for the rear group to have a fifth lens group and a sixth lens group.

(1) First Lens Group The first lens group is not particularly limited in its specific configuration as long as it is a lens group having positive refractive power. The first lens group is preferably composed of four or more lenses in order to correct axial chromatic aberration in the telephoto range. Furthermore, it is easier to improve the performance at the telephoto end if the first lens group is composed of a cemented lens in which a negative meniscus lens and a biconvex lens are joined, a positive lens and a positive lens in order from the object side to the image side.

Here, a "lens group" refers to a group of one or more adjacent lenses that move along the same trajectory and by the same amount along the optical axis during magnification. When a lens group consists of multiple lenses, the distance along the optical axis between each lens within that group does not change during magnification. However, the distance along the optical axis between adjacent lens groups does change during magnification.

(2) Second Lens Group The second lens group is not particularly limited in its specific configuration as long as it is a lens group having negative refractive power. The second lens group preferably has three negative lenses and one positive lens in order to correct chromatic aberration of magnification when changing magnification. Furthermore, it is more preferable that the second lens group consists of a negative meniscus lens, a negative meniscus lens, and a cemented lens formed by joining a biconcave lens and a biconvex lens, in order from the object side to the image side.

(3) Third Lens Group The third lens group is not particularly limited in its specific configuration, as long as it is a lens group having positive refractive power. Preferably, the third lens group has at least one negative lens. Furthermore, it is preferable that the third lens group consists of a positive lens, a negative lens, and a positive lens in the order from the object side to the image side. This configuration makes it easy to miniaturize while correcting aberrations.

(4) Fourth Lens Group The fourth lens group has negative refractive power and is a group of lenses that move along the optical axis during magnification, but its specific configuration is not particularly limited. This configuration makes it easy to miniaturize while correcting aberrations. It is preferable that the fourth lens group has a positive lens closest to the object. It is also preferable that the fourth lens group consists of a positive lens and a negative lens arranged from the object side toward the image side. This configuration makes it easy to miniaturize while correcting aberrations.

(5) Rear group The rear group consists of one or more lens groups, and the number of lens groups is not particularly limited. The rear group may consist only of the fifth lens group, but it is preferable to have the fifth and sixth lens groups, and it may also have a seventh lens group. Furthermore, the fifth lens group is preferably a lens group having positive refractive power, and it is preferable to have at least one lens having negative refractive power. The sixth lens group is preferably having negative refractive power, and it is preferable to have at least one negative lens with a concave surface on the object side in order to correct the field curvature. The seventh lens group may have either positive or negative refractive power, and is not particularly limited.

(6) Aperture In the zoom lens, the arrangement of the aperture is not particularly limited. It is preferable to place the aperture closer to the object than the fourth lens group, and it is even more preferable to place it closer to the object than the third lens group, as this simplifies the lens configuration.

(7) Negative lens Ln
The negative lens Ln is included in at least one lens group of negative refractive power lenses positioned on the image plane side of the aperture diaphragm. The negative lens Ln preferably satisfies at least one of equations (2) and (3) described later, and more preferably satisfies both equations (2) and (3). From the viewpoint of good correction of chromatic aberration, it is more preferable that the negative lens Ln is included in the fourth lens group or the sixth lens group.

1-2. Operation (1) Magnification The specific operation of the zoom lens is not particularly limited as long as the fourth lens group moves along the optical axis when changing magnification from the wide-angle end to the telephoto end. In order to miniaturize the zoom lens, it is preferable that the first and third lens groups be fixed to the image plane when changing magnification.

(2) Focusing The zoom lens's specific operation is not particularly limited as long as the lens group with negative refractive power moves along the optical axis when focusing from infinity to close distance. When focusing from infinity to close distance, a configuration in which the fourth or sixth lens group moves towards the image side along the optical axis is preferable, because it allows for correction of chromatic aberration and field curvature at magnification.

1-3. Formulas The zoom lens should adopt the configuration described above and preferably satisfy at least one of the following formulas.

1-3-1. Formula (1)
0.95 ≦ fn / fGN < 20.00 (1)
however,
fn: Focal length of the negative lens Ln; fGN: Focal length of the lens group having the negative lens Ln

Equation (1) defines the ratio of the focal length of the negative lens Ln to the focal length of the lens group containing the negative lens Ln. Satisfying equation (1) suppresses field curvature during close-up photography across the entire zoom range, easily achieving high optical performance.

If the refractive power of the negative lens Ln falls below the lower limit of equation (1), the refractive power of the negative lens Ln increases, leading to increased field curvature and making it difficult to maintain optical performance during close-up photography. Conversely, if the refractive power exceeds the upper limit of equation (1), the refractive power of the negative lens Ln decreases, making it easier to suppress aberration variations at different focusing distances, but it becomes difficult to cancel out aberrations generated by the lens group with positive refractive power.

To achieve the above effect, the lower limit of equation (1) is preferably 1.00, and more preferably 1.10. Furthermore, the upper limit of equation (1) is preferably 19.00, and more preferably 18.00. When adopting these preferred lower or upper limits, the equality sign (≦) in equation (1) may be replaced with an inequality sign (＜). The same principle applies to other equations.

1-3-2. Formula (2)
1.55 < Ndn < 1.70 (2)
however,
Ndn: Refractive index of negative lens Ln at the d line

Equation (2) is the formula for defining the refractive index of the negative lens Ln.

If the value falls below the lower limit of equation (2), the correction of field curvature aberrations becomes insufficient, making it difficult to achieve high performance during close-up photography. Conversely, if the value exceeds the upper limit of equation (2), the correction of field curvature aberrations becomes excessive, also making it difficult to achieve high performance during close-up photography.

To achieve the above effect, the lower limit of equation (2) is preferably 1.56, and more preferably 1.57. Furthermore, the upper limit of equation (2) is preferably 1.69, and more preferably 1.68.

1-3-3. Formula (3)
15.0 < νdn < 32.0 (3)
however,
νdn: Abbe number on the d line of the negative lens Ln

Equation (3) is the formula for defining the Abbe number of the negative lens Ln.

If the value falls below the lower limit of equation (3), the correction of chromatic aberration becomes excessive, making it difficult to achieve high performance during close-up photography. Conversely, if the value exceeds the upper limit of equation (3), the correction of chromatic aberration becomes insufficient, making it difficult to achieve high performance during close-up photography.

To achieve the above effect, the lower limit of equation (3) is preferably 18.0, and more preferably 20.0. Furthermore, the upper limit of equation (3) is preferably 31.5, and more preferably 31.0.

By simultaneously satisfying equations (2) and (3), field curvature and chromatic aberration at magnification can be effectively suppressed, making it easier to achieve high performance during close-up photography. Furthermore, it is more preferable for the negative lens Ln to be a resin lens in order to simultaneously satisfy equations (2) and (3).

1-3-4. Formula (4)
-0.100 < ΔPcti < 0.000 (4)
however,
ΔPcti: Anomalous dispersion of C-line and t-line in material i of negative lens Ln

First, we will describe the partial variance ratio and anomalous variance.
Let each spectral line and its wavelength be the t-line (1013.98 nm), the C-line (656.27 nm), and the d-line (587.56 nm). When arbitrary letters x and y are associated with each spectral line, the refractive indices for the x-line and y-line are defined as nx and ny. For example, the refractive index for the d-line is expressed as nd, and the refractive index for the F-line is expressed as nF. Furthermore, the partial dispersion ratio for the x-line and y-line is expressed as Pxy, and defined as Pxy = (nx - ny) / (nF - nC). For example, the partial dispersion ratio PCt for the C-line and t-line is PCt = (nC - nt) / (nF - nC).
This section explains the anomalous dispersion for the C-line and t-line. Figure 1 is a graph illustrating the anomalous dispersion for the C-line and t-line. As shown in Figure 1, first, the Abbe number νd for the d-line is plotted on the X-axis of the XY coordinate plane, and the partial dispersion ratio PCt for the C-line and t-line is plotted on the Y-axis. Then, two points are defined on the coordinate plane for two reference materials relating to the C-line and t-line, and the straight line connecting these two points is defined as the standard line Ct relating to the C-line and t-line. In this invention, the standard line Ct is defined as a straight line with a slope of 0.0047 and an intercept of 0.546, and is given by "Standard line Ct:PCt = 0.546 + 0.0047 × νd". Thus, the anomalous dispersion for the C-line and t-line can be defined as the deviation ΔPCt of PCt from the standard line Ct for a given material's νd. For example, if the Abbe number for d-lines of any material i is νdi, and the partial dispersion ratio for C-lines and t-lines is PCti, then the anomalous dispersion ΔPCti of any material i with respect to C-lines and t-lines can be calculated as ΔPCti = PCti - (0.546 + 0.0047 × νdi). This defined ΔPCti represents the anomalous dispersion with respect to C-lines and t-lines.

Equation (4) is a formula for defining the anomalous dispersion of the C-line and t-line in material i of the negative lens Ln. It can correct axial chromatic aberration and lateral chromatic aberration in the near-infrared region from the C-line to the t-line, facilitating high performance during close-range imaging.

If the value falls below the lower limit of equation (4), the absolute value of the anomalous dispersion of the negative lens Ln becomes too large, resulting in excessive correction of aberrations in the near-infrared region including the t-line. This makes it difficult to obtain good optical performance for light in the wavelength range including the near-infrared. Conversely, if the value exceeds the upper limit of equation (4), the absolute value of the anomalous dispersion of the negative lens Ln becomes too small, resulting in large chromatic aberrations in the near-infrared region including the t-line. This also makes it difficult to obtain good optical performance for light in the wavelength range including the near-infrared. Furthermore, it is more preferable for the negative lens Ln to be a resin lens to satisfy the conditions of equation (4).

To achieve the above effect, the lower limit of equation (4) is preferably -0.090, and more preferably -0.080. Furthermore, the upper limit of equation (4) is preferably -0.005, and more preferably -0.010.

1-3-5. Formula (5)
3.0≦f1/｜f2｜≦10.0...(5)
however,
f1: Focal length of the first lens group f2: Focal length of the second lens group

Equation (5) is a formula for defining the ratio of the absolute values of the focal lengths of the first lens group and the second lens group. Satisfying equation (5) allows for good aberration correction at the telephoto end, making it easier to obtain high optical performance.

If the value falls below the lower limit of equation (5), the aberration variation due to the magnification of the second lens group becomes smaller, but aberration correction at the telephoto end becomes difficult, making high performance challenging. On the other hand, if the value exceeds the upper limit of equation (5), aberration correction at the telephoto end becomes easier, but the aberration variation due to the magnification of the second lens group becomes too large, making aberration correction across the entire zoom range difficult, making high performance challenging.

To achieve the above effect, the lower limit of equation (5) is preferably 4.0, and more preferably 5.0. Furthermore, the upper limit of equation (5) is preferably 9.0, and more preferably 8.0.

1-3-6. Formula (6)
1.0 ≦ |f2| / fw ≦ 2.0...(6)
however,
f2: Focal length of the second lens group; fw: Focal length of the zoom lens at infinity focus at the wide-angle end.

Equation (6) defines the ratio of the absolute value of the focal length of the second lens group to the focal length of the zoom lens at infinity focus at the wide-angle end. Satisfying equation (6) allows for good aberration correction at the wide-angle end, facilitating high performance.

If the value falls below the lower limit of equation (6), the amount of movement due to the magnification of the second lens group becomes small, but the field curvature at the wide-angle end becomes large, making correction difficult and hindering high performance. On the other hand, if the value exceeds the upper limit of equation (6), aberration correction of field curvature at the wide-angle end becomes easier, but the amount of movement due to the magnification of the second lens group becomes too large, making high performance difficult.

To obtain the above effect, the lower limit of equation (6) is preferably 1.1, and more preferably 1.2. Furthermore, the upper limit of equation (6) is preferably 1.9, and more preferably 1.8.

1-3-7. Formula (7)
0.5≦f3/｜f4｜≦2.0...(7)
however,
f3: Focal length of the third lens group f4: Focal length of the fourth lens group

Equation (7) is used to define the ratio of the absolute values of the focal lengths of the third lens group and the fourth lens group. Satisfying equation (7) allows for good correction of spherical aberration and field curvature, facilitating high performance.

If the value falls below the lower limit of equation (7), spherical aberration correction becomes easier, but field curvature aberration correction becomes impossible, making high performance difficult. Conversely, if the value exceeds the upper limit of equation (7), field curvature aberration correction becomes easier, but spherical aberration cannot be suppressed, making high performance difficult.

To achieve the above effect, the lower limit of equation (7) is preferably 0.6, and more preferably 0.7. Furthermore, the upper limit of equation (7) is preferably 1.9, and more preferably 1.8.

1-3-8. Formula (8)
3.0≦D2rw/fw≦10.0...(8)
however,
fw: Focal length of the zoom lens at infinity focus at the wide-angle end. D2rw: Distance between the second and third lens groups at infinity focus at the wide-angle end.

Equation (8) defines the ratio of the distance between the second and third lens groups at infinity focus at the wide-angle end to the focal length of the zoom lens at infinity focus at the wide-angle end. Satisfying equation (8) facilitates miniaturization of the lens and widening of the focal length at the wide-angle end.

If the value falls below the lower limit of equation (8), it becomes easier to miniaturize the lens, but it becomes difficult to widen the focal length at the wide-angle end. Conversely, if the value exceeds the upper limit of equation (8), it becomes easier to widen the focal length at the wide-angle end, but it becomes difficult to miniaturize the lens.

To achieve the above effect, the lower limit of equation (8) is preferably 4.0, and more preferably 5.0. Furthermore, the upper limit of equation (8) is preferably 9.0, and more preferably 8.0.

1-3-9. Formula (9)
5.0 ≦ β2T/ β2W ≦ 50.0...(9)
however,
β2W: Lateral magnification of the second lens group when focused at infinity at the wide-angle end. β2T: Lateral magnification of the second lens group when focused at infinity at the telephoto end.

Equation (9) defines the ratio of the lateral magnification of the second lens group at infinity focus at the telephoto end to the lateral magnification of the second lens group at infinity focus at the wide-angle end. Satisfying equation (9) allows for a balance between the magnification ratio of the second lens group and the other groups, facilitating good aberration correction even at high magnifications.

If the value falls below the lower limit of equation (9), the magnification ratio obtained by moving the second lens group becomes smaller, and the amount of movement increases, making it difficult to achieve high magnification over the desired overall length. On the other hand, if the value exceeds the upper limit of equation (9), the refractive power of the second lens group increases, the aberration fluctuations during magnification increase, and it becomes difficult to obtain high optical performance across the entire zoom range.

To achieve the above effect, the lower limit of equation (9) is preferably 6.0, and more preferably 7.0. Furthermore, the upper limit of equation (9) is preferably 40.0, and more preferably 30.0.

2. Imaging Device Next, the imaging device according to the present invention will be described. The imaging device according to the present invention is characterized by comprising the zoom lens according to the present invention and an image sensor that converts the optical image formed by the zoom lens into an electrical signal. It is preferable that the image sensor is provided on the image side of the zoom lens.

Here, there are no particular limitations on the image sensor, and solid-state image sensors such as CCD (Charge Coupled Device) sensors and CMOS (Complementary Metal Oxide Semiconductor) sensors can also be used. The imaging device according to this invention is suitable for imaging devices using these solid-state image sensors, such as digital cameras and video cameras. Furthermore, this imaging device can be applied to various imaging devices such as single-lens reflex cameras, mirrorless cameras, digital still cameras, surveillance cameras, in-vehicle cameras, and drone cameras. These imaging devices may be interchangeable-lens imaging devices or fixed-lens imaging devices where the lens is fixed to the housing. In particular, the zoom lens according to the present invention is suitable as a zoom lens for imaging devices equipped with large image sensors such as full-frame sensors. Because this zoom lens is generally small, lightweight, and has high optical performance, high-quality images can be obtained even when used as a zoom lens for such imaging devices.

Figure 14 is a schematic diagram showing an example of the configuration of the imaging device according to this embodiment. As shown in Figure 14, the camera 1 has a main body 2 and a lens barrel 3 that is detachable from the main body 2. The camera 1 is one embodiment of the imaging device.

The main body 2 has a CCD sensor 21 as an image sensor and an optical filter 22. The CCD sensor 21 is positioned within the main body 2 at a location where the optical axis of the zoom lens 30 in the lens barrel 3 mounted on the main body 2 is the central axis. The main body 2 may have a cover glass or the like instead of the optical filter 22.

Next, the present invention will be specifically described with reference to examples. However, the present invention is not limited to the following examples.

(1) Optical configuration Figure 2 is a cross-sectional view of the zoom lens of Embodiment 1 of the present invention when it is in focus at infinity. The zoom lens is composed of, in order from the object side, a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, a third lens group G3 having positive refractive power, a fourth lens group G4 having negative refractive power, a fifth lens group G5 having positive refractive power, and a sixth lens group G6 having negative refractive power.

During magnification from the wide-angle end to the telephoto end, the second lens group G2 moves along the optical axis from the object side to the image plane side, the fourth lens group G4 moves towards the image side in a convex trajectory, the fifth lens group G5 moves from the object side to the image side, and the sixth lens group G6 moves towards the image side in a convex trajectory. The first lens group G1 and the third lens group G3 are fixed relative to the image plane IMG.

When focusing from an object at infinity to a nearby object, the sixth lens group G 6 moves along the optical axis from the object side to the image side .

The first lens group G1 consists, in order from the object side, of a cemented lens formed by joining a negative meniscus lens and a biconvex lens, a positive meniscus lens, and another positive meniscus lens.

The second lens group G2 consists, in order from the object side, of a negative meniscus lens, another negative meniscus lens, and a cemented lens formed by joining a biconcave lens and a biconvex lens.

The third lens group G3 consists, in order from the object side, of a biconvex lens and a cemented lens formed by joining a negative meniscus lens and a biconvex lens.

The fourth lens group G4 consists, in order from the object side, of a positive meniscus lens and a cemented lens formed by joining a biconcave lens.

The fifth lens group G5 consists, in order from the object side, of a biconvex lens and a cemented lens formed by joining a negative meniscus lens and a biconvex lens.

The sixth lens group G6 is composed of biconcave lenses, and in this embodiment, these biconcave lenses are negative lenses Ln.

The aperture diaphragm S is located on the object side of the third lens group G3 and is fixed relative to the image plane IMG during magnification changes from the wide-angle end to the telephoto end, and when focusing from an object at infinity to a close-up object.

In Figure 2, "IMG" represents the image plane, specifically the imaging surface of a solid-state image sensor such as a CCD sensor or CMOS sensor, or the film surface of a silver halide film. An optical filter CG is provided on the object side of the image plane IMG. "F" indicates the lens group that moves during focusing, and the arrow indicates the direction of movement of the lens group. This point is the same in the cross-sectional lens diagrams shown in other embodiments, so further explanation is omitted.

(2) Numerical Examples Next, we will describe numerical examples in which the specific numerical values of the zoom lens are applied. The following shows the "Lens Data,""SpecificationsTable,""VariableInterval,""AsphericalCoefficient," and "Focal Length of Each Lens Group." The values of each formula (Table 1) are shown together after Example 3. In the following numerical examples, the unit of length is always "mm" for numerical values where the unit is not specified, and the unit of angle is always "°."

In the (Lens Data) section, "Surface No." indicates the order of the lens surfaces counted from the object side, "r" is the radius of curvature of the lens surface, "D" is the lens thickness or air gap on the optical axis, "Nd" is the refractive index at the d-line (wavelength λ = 587.56 nm), "νd" is the Abbe number at the d-line, "H" is the maximum luminous beam height, and "PCt" indicates the partial dispersion ratio for the C-line and t-line. Furthermore, in the "Surface No." column, an asterisk (*) after the number indicates that the lens surface is aspherical, and "S" indicates that the surface is an aperture diaphragm. In the "D" column, "D(7)", "D(14)", etc., indicate that the spacing of the lens surfaces on the optical axis is a variable spacing that changes when in focus. Also, "INF" in the radius of curvature column indicates that the lens surface is planar.

In the specifications table, "f" represents the focal length of the zoom lens, "FNO" represents the F-number, and "ω" represents the half-angle of view. The values shown are for the wide-angle end, the intermediate range, and the telephoto end at infinity focus.

The values for the (variable interval) at infinity focus at the wide-angle end, intermediate range, and telephoto end are shown, respectively.

The (aspheric coefficient) represents the aspheric coefficient when the aspheric shape is defined as follows: where x is the displacement from the reference plane in the direction of the optical axis, r is the radius of paraxial curvature, H is the height from the optical axis in the direction perpendicular to the optical axis, K is the conicity coefficient, and An is the nth-order aspheric coefficient. Also, in the "Aspheric Coefficient" table, "E±XX" represents exponential notation and means "×10 ^±XX ".

The details in each of these numerical examples are the same in other examples as well, therefore, further explanation will be omitted.

Furthermore, Figures 3, 4, and 5 show the longitudinal aberration diagrams of the zoom lens at its wide-angle, intermediate, and telephoto ends when an object at infinity is in focus. The longitudinal aberration diagrams shown in each figure, from left to right, represent spherical aberration (mm), astigmatism (mm), and distortion (%), respectively. In the spherical aberration diagram, the solid line represents the d-line (wavelength 587.56 nm), the short dashed line represents the F-line (wavelength 486.13 nm), and the long dashed line represents the C-line (wavelength 656.27 nm). In the astigmatism diagram, the vertical axis represents the half-angle of view (ω), and the horizontal axis represents defocus. The solid line represents the sagittal image plane of the d-line, and the dashed line represents the meridional image plane of the d-line. In the distortion diagram, the vertical axis represents the half-angle of view (ω), and the horizontal axis represents distortion. These matters are the same for the aberration diagrams shown in other embodiments, so further explanation is omitted.

(Lens data)
Surface No. r D Nd νd H
1 84.1708 1.0000 2.00330 28.32 17.54
2 42.6674 6.0000 1.49700 81.61 16.48
3 -330.8051 0.1500 17.40
4 37.6397 4.7000 1.43700 95.10 15.80
5 274.3137 0.1500 14.08
6 36.0323 3.0000 1.72916 54.67 13.50
7 80.5079 D(7) 13.11
8 81.6391 0.7000 1.91082 35.25 7.53
9 9.2031 3.1399 5.99
10* -27.7437 0.7000 1.85135 40.10 5.86
11* -88.0908 0.6267 5.75
12 -23.9020 0.6000 1.80420 46.50 5.73
13 14.0862 2.7383 1.98612 16.48 5.68
14 -1000.0000 D(14) 5.60
15S INF 0.5399 5.23
16* 16.3486 3.1759 1.55332 71.68 5.40
17* -77.1346 0.1500 5.33
18 17.5915 0.6000 1.92119 23.96 5.25
19 10.3224 3.5000 1.55032 75.50 5.04
20 -22.2379 D(20) 4.87
21 -24.8093 1.7000 1.92286 18.90 4.60
22 -12.6838 0.7000 1.76802 49.24 4.52
23* 14.0141 D(23) 4.32
24* 17.6940 2.2633 1.59201 67.02 5.10
25* -28.0053 0.6500 5.18
26 254.0251 0.6000 1.80450 39.64 5.20
27 13.2247 4.5778 1.49710 81.56 5.20
28* -9.8564 D(28) 5.38
29* -27.5952 0.6000 1.66134 20.37 3.78 PCt=0.595
30* 119.2187 D(30) 3.72
31 INF 0.7000 1.51633 64.14 3.61
32 INF 3.4483 3.56

(Specifications table)
Wide-angle end, Mid-range, Telephoto end
f 4.6766 49.8394 129.5653
FNO 1.8500 4.3000 4.8000
ω 34.6485 3.6083 1.3990

(Variable interval)
Wide-angle end, Mid-range, Telephoto end, Shooting distance, INF, INF, INF
D(7) 0.7401 23.7282 28.9922
D(14) 29.4523 6.4641 1.2002
D(20) 0.8000 8.7982 6.1642
D(23) 8.9878 2.4097 10.4317
D(28) 7.6908 5.7042 0.8500
D(30) 1.0673 1.6338 1.1000

(Aspherical coefficient)
Surface No. K A4 A6 A8 A10
10 -7.15001E-01 2.32389E-05 -2.07527E-07 8.90122E-10 -8.34913E-11
11 -9.98408E+00 1.84937E-06 9.90432E-08 -1.23943E-09 -2.91221E-11
16 3.64226E-01 -5.21326E-05 1.01929E-07 -2.45782E-08 1.27704E-10
17 0.00000E+00 5.94777E-05 1.47185E-07 -2.88838E-08 1.88672E-10
23 0.00000E+00 -4.62462E-05 -1.79184E-06 1.26354E-07 -2.51593E-09
24 1.61135E+00 -9.11952E-05 -3.15487E-06 1.71972E-07 -5.62861E-09
25 -8.27837E+00 1.20295E-04 -6.69060E-07 1.03799E-07 -4.31101E-09
28 0.00000E+00 5.54748E-05 -1.56757E-06 4.30038E-08 -6.18084E-10
29 0.00000E+00 1.98970E-05 2.57704E-07 -3.68079E-08 -8.03780E-09
30 0.00000E+00 -2.33972E-05 -2.80345E-07 -6.81682E-09 -9.77628E-09

(Focal length of each lens group)
Group plane NO. Focal length
G1 1-7 44.0063
G2 8-14 -7.1353
G3 16-20 13.2017
G4 21-23 -12.2357
G5 24-28 13.2545
G6 29-30 -33.8282

(1) Optical configuration Figure 6 is a cross-sectional view of the zoom lens of Embodiment 2 of the present invention when it is in focus at infinity. The zoom lens is composed of, in order from the object side, a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, a third lens group G3 having positive refractive power, a fourth lens group G4 having negative refractive power, a fifth lens group G5 having positive refractive power, and a sixth lens group G6 having negative refractive power.

During magnification from the wide-angle end to the telephoto end, the second lens group G2 moves along the optical axis from the object side to the image plane side, the fourth lens group G4 moves towards the image plane in a convex trajectory, and the fifth lens group G5 moves from the object side to the image plane side. The first lens group G1, the third lens group G3, and the sixth lens group G6 are fixed relative to the image plane IMG.

When focusing from an object at infinity to a nearby object, the fourth lens group G4 moves along the optical axis from the object side to the image side .

The first lens group G1 consists, in order from the object side, of a cemented lens formed by joining a negative meniscus lens and a biconvex lens, a positive meniscus lens, and another positive meniscus lens.

The second lens group G2 consists, in order from the object side, of a negative meniscus lens, another negative meniscus lens, and a cemented lens formed by joining a biconcave lens and a biconvex lens.

The third lens group G3 consists, in order from the object side, of a biconvex lens and a cemented lens formed by joining a negative meniscus lens and a biconvex lens.

The fourth lens group G4 consists, in order from the object side, of a positive meniscus lens and a cemented lens formed by joining a biconcave lens.

The fifth lens group G5 consists, in order from the object side, of a biconvex lens and a cemented lens formed by joining a negative meniscus lens and a biconvex lens.

The sixth lens group G6 is composed of biconcave lenses, and in this embodiment, these biconcave lenses are negative lenses Ln.

The aperture diaphragm S is located on the object side of the third lens group G3 and is fixed relative to the image plane IMG during magnification changes from the wide-angle end to the telephoto end, and when focusing from an object at infinity to a close-up object.

(2) Numerical Examples Next, numerical examples in which specific numerical values of the zoom lens are applied are shown. Figures 7, 8, and 9 show longitudinal aberration diagrams at the wide-angle end, intermediate range, and telephoto end of the zoom lens when in focus at infinity.

(Lens data)
Surface No. r D Nd νd H
1 84.5417 1.0000 2.00330 28.32 17.52
2 42.7719 6.0000 1.49700 81.61 16.47
3 -323.4660 0.1500 17.40
4 37.7574 4.7000 1.43700 95.10 15.80
5 279.1621 0.1500 14.08
6 36.1258 3.0000 1.72916 54.67 13.50
7 81.0791 D(7) 13.11
8 86.1257 0.7000 1.91082 35.25 7.51
9 9.2522 3.1275 5.99
10* -27.2993 0.7000 1.85135 40.10 5.86
11* -90.5967 0.6143 5.75
12 -24.4400 0.6000 1.80420 46.50 5.73
13 14.0846 2.7371 1.98612 16.48 5.68
14 -1000.0000 D(14) 5.60
15S INF 0.5006 5.22
16* 16.4530 3.2023 1.55332 71.68 5.39
17* -74.0555 0.1500 5.33
18 17.6792 0.6000 1.92119 23.96 5.24
19 10.3659 3.5000 1.55032 75.50 5.04
20 -22.0968 D(20) 4.87
21 -24.6008 1.7000 1.92286 18.90 4.59
22 -12.7029 0.7000 1.76802 49.24 4.52
23* 14.0479 D(23) 4.32
24* 17.6843 2.2606 1.59201 67.02 5.10
25* -28.0804 0.6500 5.18
26 250.0000 0.6000 1.80450 39.64 5.20
27 13.2271 4.5749 1.49710 81.56 5.20
28* -9.8587 D(28) 5.38
29* -26.7729 0.6000 1.66134 20.37 3.78 PCt=0.595
30* 146.3855 1.1000 3.72
31 INF 0.7000 1.51633 64.14 3.61
32 INF 3.4474 3.56

(Specifications table)
Wide-angle end, Mid-range, Telephoto end
f 4.6766 49.5229 129.5632
FNO 1.8490 4.3027 4.7986
ω 34.6483 3.6256 1.3971

(Variable interval)
Wide-angle end, Mid-range, Telephoto end, Shooting distance, INF, INF, INF
D(7) 0.7550 23.7330 28.9947
D(14) 29.4450 6.4670 1.2053
D(20) 0.8000 8.9955 6.1707
D(23) 8.9943 2.6133 10.4621
D(28) 7.6885 5.8741 0.8500

(Aspherical coefficient)
Surface No. K A4 A6 A8 A10
10 -7.31033E-01 2.33806E-05 -2.08609E-07 9.43622E-10 -8.16699E-11
11 -9.97336E+00 1.75183E-06 9.97870E-08 -1.30430E-09 -3.17930E-11
16 3.65903E-01 -5.20864E-05 1.05952E-07 -2.43583E-08 1.38592E-10
17 0.00000E+00 5.95810E-05 1.53346E-07 -2.87058E-08 1.96333E-10
23 0.00000E+00 -4.67787E-05 -1.78738E-06 1.30299E-07 -2.58061E-09
24 1.61721E+00 -9.10466E-05 -3.15761E-06 1.78621E-07 -5.98264E-09
25 -8.25906E+00 1.20208E-04 -6.55185E-07 1.03668E-07 -4.56159E-09
28 0.00000E+00 5.54992E-05 -1.54453E-06 4.60072E-08 -6.24577E-10
29 0.00000E+00 1.66230E-05 2.67180E-07 -1.60477E-08 -5.97206E-09
30 0.00000E+00 -1.91214E-05 -2.31718E-07 -2.95664E-09 -6.40895E-09

(Focal length of each lens group)
Group plane NO. Focal length
G1 1-7 43.9857
G2 8-14 -7.1354
G3 16-20 13.1887
G4 21-23 -12.2036
G5 24-28 13.2529
G6 29-30 -34.1763

(1) Optical configuration Figure 10 is a cross-sectional view of the zoom lens of Embodiment 3 of the present invention when it is in focus at infinity. The zoom lens is composed of, in order from the object side, a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, a third lens group G3 having positive refractive power, a fourth lens group G4 having negative refractive power, a fifth lens group G5 having positive refractive power, and a sixth lens group G6 having negative refractive power.

During magnification from the wide-angle end to the telephoto end, the second lens group G2 moves along the optical axis from the object side to the image plane side, the fourth lens group G4 moves towards the image plane in a convex trajectory, and the fifth lens group G5 moves from the object side to the image plane side. The first lens group G1, the third lens group G3, and the sixth lens group G6 are fixed relative to the image plane IMG.

When focusing from an object at infinity to a nearby object, the fourth lens group G4 moves along the optical axis from the object side to the image side .

The first lens group G1 consists, in order from the object side, of a cemented lens formed by joining a negative meniscus lens and a biconvex lens, a positive meniscus lens, and another positive meniscus lens.

The second lens group G2 consists, in order from the object side, of a negative meniscus lens, another negative meniscus lens, and a cemented lens formed by joining a biconcave lens and a biconvex lens.

The third lens group G3 consists, in order from the object side, of a biconvex lens and a cemented lens formed by joining a negative meniscus lens and a biconvex lens.

The fourth lens group G4 consists, in order from the object side, a cemented lens formed by joining a positive meniscus lens and a biconcave lens, and a negative meniscus lens. In this embodiment, the negative meniscus lens in the fourth lens group G4 is the negative lens Ln.

The fifth lens group G5 consists, in order from the object side, of a biconvex lens and a cemented lens formed by joining a negative meniscus lens and a biconvex lens.

The sixth lens group, G6, is composed of a negative meniscus lens.

The aperture diaphragm S is located on the object side of the third lens group G3 and is fixed relative to the image plane IMG during magnification changes from the wide-angle end to the telephoto end, and when focusing from an object at infinity to a close-up object.

(2) Numerical Examples Next, numerical examples in which specific numerical values of the zoom lens are applied are shown. Figures 11, 12, and 13 show longitudinal aberration diagrams at the wide-angle end, intermediate range, and telephoto end of the zoom lens when focused at infinity.

(Lens data)
Surface No. r D Nd νd H
1 83.7736 1.0000 2.00331 28.32 17.59
2 42.8940 6.0000 1.49700 81.61 16.54
3 -344.3948 0.1500 17.40
4 37.9372 4.7000 1.43700 95.10 15.80
5 323.8865 0.1500 14.09
6 36.3202 3.0000 1.72916 54.67 13.50
7 79.5013 D(7) 13.10
8 80.4884 0.7000 1.91082 35.25 7.53
9 9.4071 2.9858 6.01
10* -32.3049 0.7000 1.85135 40.10 5.89
11* -280.6574 0.9516 5.75
12 -22.1548 0.6000 1.80420 46.50 5.68
13 14.6377 2.5500 1.98612 16.48 5.66
14 -297.2917 D(14) 5.60
15S INF 0.6724 5.27
16* 16.7269 3.0000 1.55332 71.68 5.46
17* -74.3910 0.1500 5.41
18 16.8923 0.6000 1.92119 23.96 5.32
19 9.9608 3.5500 1.55032 75.50 5.09
20 -21.5863 D(20) 4.92
21 -26.1507 1.7500 1.92286 18.90 4.61
22 -12.4823 0.6398 1.77250 49.62 4.52
23 14.7721 0.1000 4.29
24* 13.4564 0.6845 1.58250 30.18 4.29 PCt=0.660
25* 11.6782 D(25) 4.24
26* 17.6142 2.2500 1.59201 67.02 4.80
27* -28.0779 0.4843 4.88
28 251.4439 0.6000 1.80450 39.64 4.90
29 13.3774 4.2992 1.49710 81.56 4.91
30* -9.9022 D(30) 5.09
31 -29.7181 0.6000 1.92286 18.90 3.76
32 -262.3471 1.1000 3.73
33 INF 0.7000 1.51633 64.14 3.61
34 INF 3.5174 3.56

(Specifications table)
Wide-angle end, Mid-range, Telephoto end
f 4.6765 50.6794 129.5577
FNO 1.8490 4.3028 4.7984
ω 34.6488 3.5262 1.3900

(Variable interval)
Wide-angle end, Mid-range, Telephoto end, Shooting distance, INF, INF, INF
D(7) 0.7413 23.8925 29.0469
D(14) 29.5152 6.3641 1.2096
D(20) 0.8052 9.1605 6.0999
D(25) 8.5281 2.5760 10.0592
D(30) 7.6758 5.2725 0.8500

(Aspherical coefficient)
Surface No. K A4 A6 A8 A10
10 -2.69114E-01 2.21888E-05 -1.94036E-07 1.12795E-09 -6.07781E-11
11 -7.42412E+00 5.45067E-06 1.60092E-07 1.95829E-12 -2.91124E-11
16 3.89792E-01 -5.10708E-05 6.13931E-08 -2.32952E-08 1.05964E-10
17 0.00000E+00 6.09964E-05 1.44777E-07 -3.08881E-08 1.71970E-10
24 7.13698E-02 -3.42539E-06 -1.01403E-06 -1.56103E-07 -6.90293E-09
25 -9.77189E-02 -5.61743E-05 -2.52957E-06 -3.69247E-08 -1.00041E-08
26 1.48618E+00 -9.67572E-05 -3.28802E-06 1.82535E-07 -5.48857E-09
27 -7.60164E+00 1.17405E-04 -1.15963E-06 1.37077E-07 -4.37570E-09
30 0.00000E+00 4.52222E-05 -1.73940E-06 3.91609E-08 -6.47493E-10

(Focal length of each lens group)
Group plane NO. Focal length
G1 1-7 44.1296
G2 8-14 -7.0687
G3 16-20 13.014
G4 21-25 -11.7842
G5 26-30 13.1225
G6 31-32 -36.361

(Table 1)
Formula Example 1 Example 2 Example 3
(1) fn / fGN 1.00 1.00 15.00
(2) Ndn 1.66 1.66 1.58
(3) νdn 20.37 20.37 30.18
(4) ΔPcti -0.046 -0.046 -0.026
(5) f1 / | f2 | 6.17 6.16 6.24
(6) |f2| / fw 1.53 1.53 1.51
(7) f3 / | f4 | 1.08 1.08 1.10
(8) D2rw / fw 6.41 6.40 6.46
(9) β2T/ β2W 15.88 15.83 16.04
fw 4.68 4.68 4.68
f1 44.01 43.99 44.13
f2 -7.14 -7.14 -7.07
f3 13.20 13.19 13.01
f4 -12.24 -12.20 -11.78
fn -33.83 -34.18 -176.76
fGN -33.83 -34.18 -11.78
β2W -0.24 -0.24 -0.23
β2T -3.81 -3.80 -3.69
D2rw 29.99 29.95 30.19

The zoom lens according to this invention can be suitably applied as a zoom lens to imaging devices such as surveillance cameras, film cameras, digital still cameras, and digital video cameras.

S... Aperture diaphragm CG... Optical filter IMG... Image plane G1... First lens group G2... Second lens group G3... Third lens group G4... Fourth lens group G5... Fifth lens group G6... Sixth lens group 1... Camera 2... Main unit 3... Lens barrel 21... CCD sensor 22... Optical filter

Claims (7)

The lens system consists of, 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, a third lens group with positive refractive power, a fourth lens group with negative refractive power, and a rear group.
It is a zoom lens that changes magnification by changing the spacing between adjacent lens groups.
At least one of the lens group having negative refractive power, which is positioned on the image plane side of the aperture diaphragm, has a negative lens Ln.
The fourth lens group moves along the optical axis during magnification,
The aforementioned rear group consists of, in order from the object side to the image side, a fifth lens group having positive refractive power and a sixth lens group having negative refractive power.
A zoom lens that satisfies the following equation.
0.95 ≦ fn / fGN < 20.00 (1)
1.55 < Ndn < 1.70 (2)
15.0 < νdn < 32.0 (3)
0.5≦f3/｜f4｜≦2.0...(7)

however,
fn: focal length of the negative lens Ln fGN: focal length of the lens group having the negative lens Ln Ndn: refractive index of the negative lens Ln at the d line νdn: Abbe number of the negative lens Ln at the d line
f3: Focal length of the third lens group
f4: Focal length of the fourth lens group
A zoom lens according to claim 1 that satisfies the following formula.
-0.100 < ΔPcti < 0.000 (4)
however,
ΔPcti: Abnormal dispersion of C-line and t-line in material i of the negative lens Ln. A zoom lens according to claim 1 or claim 2 that satisfies the following formula.
3.0≦f1/｜f2｜≦10.0...(5)
however,
f1: Focal length of the first lens group f2: Focal length of the second lens group A zoom lens according to any one of claims 1 to 3, satisfying the following formula.
1.0 ≦ |f2| / fw ≦ 2.0...(6)
however,
f2: Focal length of the second lens group fw: Focal length of the zoom lens when focused at infinity at the wide-angle end A zoom lens according to any one of claims 1 to 4 , satisfying the following formula.
3.0≦D2rw/fw≦10.0...(8)
however,
fw: Focal length of the zoom lens when in focus at infinity at the wide-angle end. D2rw: Distance between the second lens group and the third lens group when in focus at infinity at the wide-angle end. A zoom lens according to any one of claims 1 to 5 , satisfying the following formula.
5.0 ≦ β2T/ β2W ≦ 50.0...(9)
however,
β2W: Lateral magnification of the second lens group when focused at infinity at the wide-angle end. β2T: Lateral magnification of the second lens group when focused at infinity at the telephoto end. An imaging device comprising a zoom lens according to any one of claims 1 to 6 , and an image sensor on the image side of the zoom lens that converts an optical image formed by the zoom lens into an electrical signal.