JP7542975B2 - Zoom lens and imaging device - Google Patents

Description

The present invention relates to a zoom lens and an imaging device.

As a photographing optical system in imaging devices such as surveillance cameras, digital cameras, and video cameras that include an imaging element, there is a demand for an optical system with high optical performance corresponding to a high-definition imaging element. In recent years, with the rapid expansion of the surveillance camera market, there is a strong demand for miniaturized surveillance cameras from the viewpoint of installation and inconspicuousness. In addition, there is a demand for an optical system that is bright (has a small F-number) so that it can be used to photograph in dark places, and can also photograph with high optical performance even with near-infrared light. Patent Document 1 discloses a two-group zoom lens consisting of a negative lens group and a positive lens group arranged in that order from the object side to the image side.

JP 2009-230122 A

The zoom lens in Patent Document 1 has a relatively small F-number and corrects chromatic aberration even at near-infrared wavelengths, but is insufficient in terms of compactness.

The present invention aims to provide a zoom lens that is advantageous in terms of, for example, its small size, brightness, and high optical performance from visible light to near-infrared light.

A zoom lens according to one aspect of the present invention is a zoom lens comprising a negative first lens group and a positive second lens group arranged in that order from the object side to the image side, wherein the spacing between adjacent lens groups both changes during zooming, the second lens group comprises a positive lens, a negative lens, a positive lens, and a negative lens arranged in that order from the object side to the image side, the negative lens located closest to the image side among the negative lenses included in the second lens group has an aspheric surface, and the focal length f 1 of the first lens group, the average Abbe number vd2p of all positive lenses included in the second lens group, and the minimum value bfwt of the air-equivalent back focus at the wide end satisfy predetermined conditions.

Other objects and features of the present invention are described in the following examples.

The present invention can provide a zoom lens that is advantageous in terms of, for example, its small size, brightness, and high optical performance from visible light to near-infrared light.

3A and 3B are diagrams illustrating a cross section and a movement locus of the zoom lens at the wide-angle end of Example 1. 5A to 5C are aberration diagrams at the wide-angle end, at a middle zoom position, and at the telephoto end in Example 1. 11A and 11B are diagrams illustrating a cross section and a movement locus of a zoom lens at the wide-angle end of Example 2. 11A to 11C are aberration diagrams of Example 2 at the wide-angle end, at a middle zoom position, and at the telephoto end. 13A and 13B are diagrams illustrating a cross section and a movement locus of a zoom lens at the wide-angle end according to a third embodiment. 13A to 13C are aberration diagrams of Example 3 at the wide-angle end, at a middle zoom position, and at the telephoto end. 13A and 13B are diagrams illustrating a cross section and a movement locus of a zoom lens at the wide-angle end of Example 4. 13A to 13C are aberration diagrams of Example 4 at the wide-angle end, at the intermediate zoom position, and at the telephoto end. FIG. 2 is a cross-sectional view of a surveillance camera in each embodiment. FIG. 2 is a cross-sectional view of a surveillance camera in each embodiment. FIG. 2 is an explanatory diagram of a surveillance camera in each embodiment.

The following describes in detail embodiments of the present invention with reference to the drawings. Each embodiment relates to a zoom lens that is small in size, has a small F-number, and has high optical performance from visible light to the near infrared region, and an imaging device having the same.

Figures 1, 3, 5, and 7 are diagrams showing the cross sections and movement trajectories of zoom lenses 1a to 1d at the wide-angle end of Examples 1 to 4, respectively. Each of the zoom lenses 1a to 1d of the examples is a two-group zoom lens consisting of two lens groups, a first lens group L1 having negative refractive power and a second lens group L2 having positive refractive power, arranged in that order from the object side to the image side. During zooming, the first lens group L1 and the second lens group L2 both move independently in the direction of the arrow in each figure.

In each figure, SP is a diaphragm (aperture stop) that is arranged on the object side of the second lens group L2. G is an optical block that corresponds to an optical filter, face plate, etc. IP is an image plane that corresponds to the imaging surface of a solid-state imaging element (photoelectric conversion element) such as a CCD sensor or CMOS sensor when the zoom lenses 1a to 1d are used as an imaging optical system.

Figures 2, 4, 6, and 8 are aberration diagrams for Examples 1 to 4 at the wide-angle end, the mid-zoom position, and the telephoto end, respectively. In spherical aberration, d, g, and t respectively indicate the d-line (587.56 nm), g-line (435.84 nm), and t-line (1013.98 nm). In astigmatism, M and S respectively indicate the meridional image plane and sagittal image plane at the d-line. Distortion aberration is shown with respect to the d-line. In lateral chromatic aberration, aberrations for the g-line and t-line relative to the d-line are shown.

Next, referring to FIG. 1, FIG. 3, FIG. 5, and FIG. 7, the method of moving each lens group constituting the zoom lenses 1a to 1d will be described. Zooming from the wide-angle end to the telephoto end is performed by moving the first lens group L1 and the second lens group L2 independently. As mentioned above, the zoom type of the zoom lenses 1a to 1d in each embodiment is a negative-lead (negative group leading) two-group configuration. This is a configuration suitable for widening the angle by changing the spacing between each lens group while giving the first lens group L1 negative power. Zooming is performed by moving the positive second lens group L2 located on the image side, and the associated image plane fluctuation is corrected by the negative first lens group L1. According to each embodiment, by having only two movable groups, it is possible to simplify the lens barrel structure, resulting in a configuration advantageous for miniaturization. Focusing is performed by moving the first lens group L1.

The zoom lenses 1a to 1d in each embodiment are composed of a negative first lens group L1 and a positive second lens group L2 arranged in order from the object side to the image side, and the spacing between adjacent lens groups changes during zooming. The second lens group L2 includes at least two positive lenses G21, G23 and at least two negative lenses G22, G24. Of the at least two negative lenses, the negative lens G24 located on the image side has an aspheric surface (the negative lens G24 in each embodiment has aspheric surfaces on both sides). The focal length of the first lens group L1 is f1, the focal length of the second lens group L2 is f2, the average Abbe number of the at least two positive lenses G21, G22 is νd2p, and the minimum value of the air-equivalent back focus at the wide end (or the entire magnification range) is bfwt. In this case, the following conditional expressions (1) to (3) are satisfied.

-1.20<f1/f2<-0.80...(1)
68.00<νd2p<90.00...(2)
0.40<bfwt/f2<0.90...(3)
Conditional expressions (1) and (3) are conditions for obtaining high optical performance and the effect of compactness by defining the relationship between the second lens unit L2 and the back focus with respect to the first lens unit L1. The first lens group L1 has a relatively strong power (short focal length) as a wide-angle zoom lens. The second lens group L2 has an appropriate power as a magnification varying group. Condition (2) satisfies the following conditions: These are conditions necessary for correcting chromatic aberration not only in the light region but also in the near-infrared region, and are the conditions for appropriately using glass that is highly effective in correcting chromatic aberration.

If the upper limit of conditional expression (1) is exceeded, the power of the first lens group L1 becomes too strong, causing significant chromatic aberration, which is undesirable. On the other hand, if the lower limit of conditional expression (1) is exceeded, the power of the first lens group L1 becomes weak, which is undesirable for compactness.

If the upper limit of conditional expression (2) is exceeded, the effect of correcting chromatic aberration can be obtained, but glass that satisfies this condition generally has a characteristic of having a low refractive index, making it difficult to obtain power as a single lens, which is not desirable for miniaturization. On the other hand, if the lower limit of conditional expression (2) is exceeded, chromatic aberration correction becomes insufficient, which is not desirable.

Conditional expression (3) specifies the relationship between the minimum necessary back focus and the power of the second lens group L2. For compactness, it is preferable to have a configuration in which the back focus of the second lens group L2 is shortest at the wide-angle end. If the upper limit of conditional expression (3) is exceeded, the back focus becomes too long, which is not preferable for compactness. On the other hand, if the lower limit of conditional expression (3) is exceeded, the power of the second lens group L2 tends to become weaker, and accordingly the amount of movement of the second lens group L2 for zooming becomes too large, which is not preferable for compactness.

The zoom lenses 1a to 1d of each embodiment are realized by satisfying the above configuration. In each embodiment, it is preferable to satisfy at least one of the following conditional expressions. Each conditional expression and its technical aspects are explained below.

When the focal length of the negative lens G24 having an aspheric surface in the second lens group L2 is f2n_asph, the following conditional expression is satisfied.

-4.50<f2n_asph/f2<-0.80...(4)
Conditional expression (4) is a condition for reducing the number of lenses by using an aspheric surface in the second lens unit L2 and for obtaining a large effect of size reduction by appropriately setting the power of the lenses. If the upper limit of 4) is exceeded, the power of the negative lens having an aspherical surface becomes too strong, the characteristics such as astigmatism and curvature of field deteriorate, and the resolution (MTF) at a high image height cannot be obtained, which is undesirable. On the other hand, if the lower limit of conditional expression (4) is exceeded, the power of the negative lens G24 having an aspheric surface becomes too weak, making it impossible to reduce the number of glass sheets in the optical system and making it difficult to reduce the size, which is undesirable. .

When the average Abbe number of at least two positive lenses G21 and G23 is νd2p and the average Abbe number of at least two negative lenses G22 and G24 is νd2n, the following conditional formula (5) is satisfied.

25.00<νd2p−νd2n<45.00 (5)
Condition (5) is a condition for correcting axial and lateral chromatic aberrations, and in particular, a condition for effectively correcting chromatic aberration of near-infrared light relative to visible light. If the lower limit of conditional expression (5) is exceeded, the balance of the Abbe numbers of the positive lens and the negative lens in the second lens unit L2 is lost, and favorable correction cannot be performed, which is not preferable. This is not preferable because the correction of chromatic aberration is insufficient, and in particular, axial chromatic aberration of near-infrared light relative to visible light occurs, resulting in insufficient resolution under a light source that is a mixture of visible light and near-infrared light.

The first lens group L1 includes at least one positive lens G13. When the Abbe number of the positive lens G13 of the first lens group L1 is νd1p and the refractive index of the positive lens G13 of the first lens group L1 is Nd1p, the following conditional expressions (6) and (7) are satisfied.

13.00<νd1p<20.00 (6)
1.85<Nd1p<2.10 (7)
Conditional expressions (6) and (7) are conditions that stipulate the material characteristics of the positive lens G13 of the first lens unit L1. The Abbe number is By using a relatively high dispersion material for the positive lens G13, the lateral chromatic aberration occurring in the positive lens G13 can be cancelled. If the upper limit of the conditional expression (6) is exceeded, the correction of the lateral chromatic aberration will be insufficient, which is not preferable. On the other hand, if the lower limit of the conditional expression (6) is exceeded, the lateral chromatic aberration will be overcorrected, which is not preferable. If the upper limit of the conditional expression (7) is exceeded, the Petzval sum of the entire system of the zoom lenses 1a to 1d will become On the other hand, if the lower limit of the conditional expression (7) is exceeded, the refractive index becomes low and the lens diameter of the first lens unit L1 becomes large, which is not preferable. , which is undesirable from the viewpoint of miniaturization.

The second lens group L2 is composed of, in order from the object side to the image side, a positive lens G21, a negative lens G22, a positive lens G23, and a negative lens G24. This is a stipulation of the configuration of the second lens group L2 in order to reduce the F-number and the size of the entire system of the zoom lenses 1a to 1d. A diaphragm SP is provided on the most image side of the second lens group L2. For this reason, by making the lens closest to the object side, where the light beam diameter is largest, the positive lens G21, spherical aberration is effectively corrected. The group following the positive lens G21 is composed of a negative lens G22, a positive lens G23, and a negative lens G24, which makes it easier to correct off-axis aberrations such as astigmatism while correcting residual spherical aberration.

The positive lens G21, which is disposed closest to the object side in the second lens group L2, and the negative lens G22, which is disposed next to the positive lens G21, each consist of a single lens. The positive lens G12 and the negative lens G22 are separated by air (air lens), and when the radius of curvature on the image side of the positive lens G21 is R12 and the radius of curvature on the object side of the negative lens G22 is R21, the following conditional expression (8) is satisfied.

-0.10<(R12-R21)/(R12+R21)<0.70...(8)
Conditional expression (8) is a condition for optimizing the correction of spherical aberration in particular by utilizing the effect of the air lens with respect to the shape of the air lens located closest to the object side. If the lower limit of condition (8) is exceeded, the power of the air lens becomes too large, resulting in overcorrection. , not desirable.

In each embodiment, when the central thickness of the positive lens G21 on the object side of the two positive lenses G21 and G23 is d2p1 and the central thickness of the positive lens G23 on the image side of the two positive lenses G21 and G23 is d2p2, the following conditional formula (9) is satisfied.

0.50<(d2p1+d2p2)/f2<1.20 (9)
Condition (9) is a condition for satisfactorily correcting axial and lateral chromatic aberrations. Although a glass material with a relatively large Abbe number is used for the positive lens, by appropriately setting the glass thickness, If the upper limit of conditional expression (9) is exceeded, the thickness of the positive lens becomes too large, which is undesirable from the viewpoint of compactness. On the other hand, if the lower limit of conditional expression (9) is exceeded, This is not preferable because it makes it difficult to obtain the effect of correcting chromatic aberration.

In addition, in each embodiment, when the total center thickness of all lenses constituting the second lens group L2 is d2G and the total length of the second lens group L2 (the length from the object side surface of the lens closest to the object to the image side surface of the lens closest to the image) is TL2G, the following conditional formula (10) is satisfied.

0.70<d2G/TL2G<0.99 (10)
Condition (10) is a condition for obtaining good optical performance while being compact. Reducing the number of glass sheets is good for making the lens compact, but this makes it difficult to correct various aberrations. This problem can be solved by balancing the optical path length between the glass medium through which the light passes and the air. If the upper limit of condition (10) is exceeded, the area through which the light passes through the air becomes smaller. If the lower limit of condition (10) is exceeded, the lens cannot have a proper refractive power (power as glass) for correcting aberrations, and field curvature, astigmatism, and the like cannot be corrected, which is not preferable. If it exceeds this value, the power of each lens tends to become weak, which is not preferable for correcting astigmatism, coma, and the like.

The zoom lenses 1a to 1d of each embodiment are used in an imaging device. The imaging device has an imaging element 12 that receives (captures) an image formed by the zoom lenses 1a to 1d. The imaging element 12 is a CCD (Charge Coupled Device) sensor or a CMOS (Complementary Metal Oxide Semiconductor) sensor for digitally processing the image.

In this embodiment, it is preferable to set the numerical range of at least one of the conditional expressions (1) to (10) as shown in the following conditional expressions (1a) to (10a).

-1.15<f1/f2<-0.82...(1a)
70.00<νd2p<89.50...(2a)
0.45<bfwt/f2<0.90...(3a)
-4.00<f2n_asph/f2<-1.00...(4a)
26.50<νd2p−νd2n<43.50 (5a)
14.00<νd1p<19.50...(6a)
1.86<Nd1p<2.09 (7a)
0.05<(R12-R21)/(R12+R21)<0.65...(8a)
0.60<(d2p1+d2p2)/f2<1.15...(9a)
0.74<d2G/TL2G<0.97...(10a)
It is more preferable that the numerical range of at least one of the conditional expressions (1) to (10) is set as in the following conditional expressions (1b) to (10b), respectively.

-1.10<f1/f2<-0.85...(1b)
72.00<νd2p<89.00...(2b)
0.50<bfwt/f2<0.90...(3b)
-3.50<f2n_asph/f2<-1.20...(4b)
28.00<νd2p−νd2n<42.00 (5b)
15.00<νd1p<19.00...(6b)
1.88<Nd1p<2.08...(7b)
0.02<(R12-R21)/(R12+R21)<0.60...(8b)
0.70<(d2p1+d2p2)/f2<1.10...(9b)
0.78<d2G/TL2G<0.95...(10b)
Next, the lens configurations of the zoom lenses 1a to 1d of the respective embodiments will be described. The lens configurations will be described below in the order of arrangement from the object side to the image side, unless otherwise specified. 3, 5, and 7, the left side is the subject side (object side), and the right side is the image side. The zoom positions refer to the ends of the range in which the lens can move along the zoom lens axis. The movement of each lens group from the wide-angle end to the telephoto end follows a locus as indicated by the arrows (solid lines) in each cross-sectional view.

The solid curve and dotted curve of the second lens group L2 are the movement trajectories for correcting image plane fluctuations when focusing on an object at infinity and a close distance object, respectively, from the wide-angle end to the telephoto end zoom position. For example, when focusing from an object at infinity to a close distance object at the telephoto end zoom position, the lens is moved as shown by the arrow F in each cross-sectional view.

The aperture diaphragm SP is provided in front of the second lens group L2 and moves integrally with the second lens group L2 during zooming. Alternatively, the aperture diaphragm SP may be configured to move independently, which has the advantage of making it easier to cut off light rays that cause flare.

The lens configuration of each embodiment and the imaging device having the same are described in detail below. The zoom lens of each embodiment has a two-group configuration with negative and positive power arrangement. The first lens group L1 and the second lens group L2 move during zooming. When zooming from the wide-angle end to the telephoto end, the first lens group L1 follows a trajectory that forms a convex shape toward the image side, and the second lens group L2 moves monotonically toward the object side.

The first lens group L1 is composed of a meniscus negative lens G11 having a convex shape toward the object side, a biconcave negative lens G12, and a meniscus negative lens G13 having a convex shape toward the object side. The second lens group L2 is composed of a biconvex positive lens G21, a biconcave (Examples 1 and 2) or meniscus (Examples 3 and 4) negative lens G22 having a convex shape toward the image side, a biconvex positive lens G23, and a biconcave negative lens G24. The negative lens G24 is aspheric on both sides, and aberrations such as astigmatism and curvature of field are well corrected. The material of the aspheric surface is not limited to glass, and plastic materials with good moldability may be used. The positive lenses G21 and G23 are made of low-dispersion glass with a large Abbe number, and they well correct lateral chromatic aberration and axial chromatic aberration.

Next, referring to FIG. 9 and FIG. 10, a surveillance camera equipped with the zoom lenses 1a to 1d of each embodiment will be described. FIG. 9 is a cross-sectional view of the surveillance camera 100a. The surveillance camera 100a is equipped with the zoom lens 1a of the first embodiment (or the zoom lenses 1b to 1d of the second to fourth embodiments) and a dome cover 15. The dome cover 15 is molded with a thickness of about several millimeters from a plastic material such as polymethyl methacrylate (PMMA) or polycarbonate (PC). As a result, when making an imaging device that is assumed to have a dome cover, the influence of the dome cover 15 (focal length and material) can be taken into consideration in the design, and various aberrations can be corrected. FIG. 10 is a cross-sectional view of the surveillance camera 100b. The surveillance camera 100b is equipped with the zoom lens 1a of the first embodiment (or the zoom lenses 1b to 1d of the second to fourth embodiments) and a flat protective cover 17.

Next, referring to FIG. 11, an imaging device (surveillance camera 100) that uses zoom lens 1a (1b-1d) as an imaging optical system will be described. FIG. 11 is an explanatory diagram of the surveillance camera 100, with FIG. 11(A) showing an external view of the surveillance camera 100 and FIG. 11(B) showing an example of how the surveillance camera 100 is used.

In FIG. 11(A), 11 is the surveillance camera body, and 12 is an imaging element (photoelectric conversion element) such as a CCD sensor or CMOS sensor that is built into the camera body 11 and receives the subject image formed by the zoom lens 1a (1b-1d). 13 is a memory section that records information corresponding to the subject image photoelectrically converted by the imaging element 12. 14 is a network cable for transferring the subject image photoelectrically converted by the imaging element 12. FIG. 11(B) shows an example in which the surveillance camera 100 is attached to the ceiling with a dome cover 15 attached. Note that the imaging device is not limited to a surveillance camera, and the present invention can also be applied to other imaging devices such as video cameras and digital cameras.

Each embodiment can provide a zoom lens and imaging device that is compact, has a small F-number, and has high optical performance from visible light to the near infrared range.

An imaging system (surveillance camera system) may be configured that includes the zoom lenses 1a to 1d of each embodiment and a control unit that controls the zoom lenses. In this case, the control unit can control the zoom lens so that each lens group moves as described above during zooming. In this case, the control unit does not need to be configured integrally with the zoom lens, and the control unit may be configured separately from the zoom lens. For example, a configuration may be adopted in which a control unit (control device) that is located remotely from a drive unit that drives each lens of the zoom lens includes a transmission unit that sends a control signal (command) for controlling the zoom lens. Such a control unit allows the zoom lens to be remotely operated.

In addition, the control unit may be provided with an operation unit (operation member) such as a controller or buttons for remotely operating the zoom lens, so that the zoom lens is controlled in response to a user's input to the operation unit. For example, a zoom-in button and a zoom-out button may be provided as the operation unit. In this case, the control unit may be configured to send a signal to the drive unit of the zoom lens so that the magnification of the zoom lens increases when the user presses the zoom-in button, and decreases when the user presses the zoom-out button.

The imaging system may also have a display unit such as a liquid crystal panel that displays information (movement state) related to the zoom of the zoom lens. Information related to the zoom of the zoom lens is, for example, the zoom magnification (zoom state) and the movement amount (movement state) of each lens group. In this case, the user can remotely operate the zoom lens via the operation unit while viewing the information related to the zoom of the zoom lens displayed on the display unit. In this case, the display unit and the operation unit may be integrated by using, for example, a touch panel.

Next, Numerical Examples 1 to 4 corresponding to Examples 1 to 4 are shown. In each Numerical Example, the surface numbers are shown in order from the object side, r is the radius of curvature, d is the distance, and nd and νd are the refractive index and Abbe number based on the d-line, respectively. Note that the Abbe number νd of a certain material is given by Nd, NF, and NC, where Nd, NF, and NC are the refractive indexes at the d-line (587.6 nm), F-line (486.1 nm), and C-line (656.3 nm) of the Fraunhofer lines, respectively.
νd=(Nd-1)/(NF-NC)
It is expressed as:

In each numerical example, d, focal length (mm), F-number (F value), and half angle of view (°) are all values when the zoom lens of each example is focused on an object at infinity. BF (back focus) is the distance on the optical axis from the final lens surface (the lens surface closest to the image) to the paraxial image surface expressed as an air-equivalent length, and is the value when the glass block is not included. "Total lens length" is the distance on the optical axis from the foremost lens surface (the lens surface closest to the object) of the zoom lens to the final surface plus the back focus. "Lens group" is not limited to cases where it is composed of multiple lenses, but also includes cases where it is composed of a single lens.

If the optical surface is aspheric, a "*" is added to the right of the surface number. The aspheric shape is expressed by the following formula, where the X-axis is in the direction of the optical axis, the h-axis is 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 A4, A6, A8, A10, and A12 are fourth-order, sixth-order, eighth-order, tenth-order, and twelfth-order aspheric coefficients, respectively.

x=(h2/r)/[1+{1-(1+K)(h/r)2}1/2]+A4・h4+A6・h6+A8・h8+A10・h10+A12・h12
For example, the notation "e-Z" means "10 ^-Z ." The half angle of view is the numerical value of the half angle of view (ω) related to the photographable angle of view taking distortion aberration into consideration.
Table 1 shows the relationship between each numerical example and each conditional expression.

[Numerical Example 1]
Surface Data
Surface number rd nd νd
1 413.852 0.90 1.77250 49.6
2 5.674 2.79
3 -19.601 0.60 1.52249 59.8
4 23.299 0.83
5 13.736 2.20 1.94595 18.0
6 37.216 (variable)
7(Aperture) ∞ 0.27
8 6.041 2.98 1.49700 81.5
9 -5.482 0.15
10 -5.027 0.50 1.65412 39.7
11 77.636 0.19
12 5.511 4.12 1.49700 81.5
13 -5.837 0.24
14* -43.185 1.70 1.58313 59.4
15* 8.054 (variable)
16 ∞ 0.50 1.52000 61.4
Image plane ∞

Aspheric Data
Page 14
K = 0.00000e+000 A 4=-7.71859e-003 A 6=-6.95253e-005 A 8= 3.43371e-006
Page 15
K = 0.00000e+000 A 4=-5.35636e-003 A 6= 1.60144e-004 A 8= 1.17287e-005
A10=-7.99639e-007 A12= 7.99768e-022

Various data
Zoom ratio 2.41
Wide Angle Mid-Telephoto
Focal length 3.60 6.14 8.68
F-number 2.24 2.89 3.55
Half angle of view 41.63 27.54 20.25
Image height 3.20 3.20 3.20
Lens length 33.16 29.34 29.29
BF(In air) 5.76 8.38 11.01

Interval Wide-angle Mid-range Telephoto
d 6 9.76 3.31 0.64
d15 1.26 3.88 6.51

Each group focal length
1 -7.37
2 7.62

Single lens (element) focal length
G11 -7.45
G12 -20.28
G13 22.01
G21 6.33
G22 -7.2
G23 6.48
G24 -11.5

[Numerical Example 2]
Surface Data
Surface number rd nd νd
1 230.235 0.90 1.69680 55.5
2 5.300 2.83
3 -17.804 0.60 1.51823 58.9
4 27.407 1.14
5 12.569 2.20 1.98612 16.5
6 22.003 (variable)
7(Aperture) ∞ 0.24
8 5.825 2.82 1.43700 95.1
9 -5.046 0.15
10 -4.697 0.50 1.60562 43.7
11 81.575 0.19
12 5.285 4.03 1.49700 81.5
13 -5.924 0.24
14* -120.201 1.80 1.53113 55.8
15* 7.687 (variable)
16 ∞ 0.50 1.52000 61.4
Image plane ∞

Aspheric Data
Page 14
K = 0.00000e+000 A 4=-7.81269e-003 A 6=-1.93114e-004 A 8= 1.11847e-005
Page 15
K = 0.00000e+000 A 4=-5.39641e-003 A 6= 2.02235e-005 A 8= 3.09969e-005
A10=-1.52457e-006 A12= 5.19989e-022

Various data
Zoom ratio 2.41
Wide Angle Mid-Telephoto
Focal length 3.60 6.14 8.67
F-number 2.24 2.89 3.55
Half angle of view 41.63 27.54 20.25
Image height 3.20 3.20 3.20
Lens length 32.82 29.47 29.68
BF(In air) 6.10 8.83 11.56

Interval Wide-angle Mid-range Telephoto
d 6 8.93 2.85 0.33
d15 0.94 3.68 6.41

Each group focal length
1 -7.01
2 7.55

Single lens (element) focal length
G11 -7.8
G12 -20.73
G13 26.64
G21 6.72
G22 -7.32
G23 6.38
G24 -13.54

[Numerical Example 3]
Surface Data
Surface number rd nd νd
1 20.199 0.90 1.67790 55.3
2 5.300 4.36
3 -20.814 0.60 1.48749 70.2
4 10.331 1.77
5 11.097 2.20 1.95906 17.5
6 17.079 (variable)
7(Aperture) ∞ 0.00
8 6.118 2.62 1.49700 81.5
9 -8.979 0.30
10 -6.757 0.50 1.75520 27.5
11 -28.531 0.57
12 5.446 3.50 1.49700 81.5
13 -9.682 0.76
14* -436.341 1.72 1.53113 55.8
15* 8.097 (variable)
16 ∞ 0.50 1.52000 61.4
Image plane ∞


Aspheric Data
Page 14
K = 0.00000e+000 A 4=-7.04738e-003 A 6=-1.93933e-004 A 8= 2.14349e-005
A10=-8.97559e-007 A12= 5.27016e-022
Page 15
K = 0.00000e+000 A 4=-3.98411e-003 A 6=-2.08018e-005 A 8= 3.21100e-005

Various data
Zoom ratio 2.39
Wide Angle Mid-Telephoto
Focal length 3.10 5.25 7.40
F-number 2.24 2.86 3.49
Half angle of view 45.91 31.37 23.39
Image height 3.20 3.20 3.20
Lens length 34.37 29.87 29.24
BF(In air) 4.40 6.55 8.69

Interval Wide-angle Mid-range Telephoto
d 6 10 3.36 0.58
d15 2.12 4.26 6.41

Each group focal length
1 -7.10
2 7.09

Single lens (element) focal length
G11 -10.86
G12 -14.07
G13 27.99
G21 7.77
G22 -11.84
G23 7.6
G24 -14.95

[Numerical Example 4]
Surface number rd nd νd
1 16.847 0.90 1.69680 55.5
2 5.300 4.64
3 -18.712 0.60 1.48749 70.2
4 10.321 1.28
5 9.819 2.20 1.92286 18.9
6 14.844 (variable)
7(Aperture) ∞ 0.00
8 5.683 2.48 1.49700 81.5
9 -19.805 0.30
10 -8.559 0.50 1.80518 25.4
11 -48.958 0.15
12 5.633 3.25 1.48749 70.2
13 -7.799 0.66
14* -84.062 1.78 1.53113 55.8
15* 9.837 (variable)
16 ∞ 0.50 1.52000 61.4
Image plane ∞

Aspheric Data
Page 14
K = 0.00000e+000 A 4=-7.17527e-003 A 6=-2.11347e-004 A 8= 2.12300e-005
Page 15
K = 0.00000e+000 A 4=-4.25345e-003 A 6=-1.48874e-006 A 8= 3.03069e-005
A10=-1.09958e-006 A12= 5.29696e-022

Various data
Zoom ratio 2.50
Wide Angle Mid-Telephoto
Focal length 3.45 6.04 8.63
F-number 2.14 2.79 3.44
Half angle of view 42.85 27.91 20.34
Image height 3.20 3.20 3.20
Lens length 35.58 31.56 31.62
BF(In air) 4.02 4.02 4.02

Interval Wide-angle Mid-range Telephoto
d6 10.79 4.01 1.30
d15 1.52 4.29 7.05

Each group focal length
1 -7.15
2 7.63

Single lens (element) focal length
G11 -11.46
G12 -13.55
G13 25.97
G21 9.18
G22 -12.95
G23 7.29
G24 -16.47

The above describes preferred embodiments of the present invention, but the present invention is not limited to these embodiments, and various modifications and variations are possible within the scope of the gist of the invention.

For example, the shapes and numbers of lenses described in each embodiment are not limited to those described above. In each embodiment, some lenses and lens groups may be moved so as to have a perpendicular component to the optical axis OA, thereby correcting image blur caused by vibrations such as camera shake. In each embodiment, distortion aberrations and chromatic aberrations may be corrected by electrical correction means.

1a to 1d: zoom lens L1: first lens group L2: second lens group G21, G23: positive lenses G22, G24: negative lenses

Claims (13)

A zoom lens comprising a negative first lens group and a positive second lens group arranged in this order from an object side to an image side,
The spacing between adjacent lens groups changes during zooming.
the second lens group includes, in order from the object side to the image side, a positive lens, a negative lens, a positive lens, and a negative lens;
the negative lens located closest to the image side among the negative lenses included in the second lens group has an aspheric surface,
The focal length of the first lens group is f1, the focal length of the second lens group is f2, the average Abbe number of all the positive lenses included in the second lens group is νd2p, and the minimum value of the air-equivalent back focus at the wide end is bfwt,
-1.20<f1/f2<-0.80
68.00<νd2p<90.00
0.40<bfwt/f2<0.90
A zoom lens characterized by satisfying the following conditional expressions: The focal length of the negative lens having the aspheric surface is f2n_asph,
-4.50<f2n_asph/f2<-0.80
2. The zoom lens according to claim 1, wherein the following condition is satisfied: The average Abbe number of all the negative lenses included in the second lens group is defined as νd2n,
25.00<νd2p−νd2n<45.00
3. The zoom lens according to claim 1, wherein the following condition is satisfied: The first lens group includes a positive lens.
The Abbe number of the positive lens in the first lens group is denoted by νd1p, the refractive index of the positive lens in the first lens group is denoted by Nd1p,
13.00<νd1p<20.00
1.85<Nd1p<2.10
4. The zoom lens according to claim 1, wherein the following condition is satisfied: The positive lens arranged closest to the object side in the second lens group and the negative lens arranged adjacent to the positive lens are each composed of a single lens, the positive lens and the negative lens are separated by air, the radius of curvature of the positive lens on the image side is R12, the radius of curvature of the negative lens on the object side is R21,
-0.10<(R12-R21)/(R12+R21)<0.70
5. The zoom lens according to claim 1, wherein the following condition is satisfied: The center thickness of the positive lens closest to the object among the positive lenses included in the second lens group is d2p1, and the center thickness of the positive lens closest to the image among the positive lenses included in the second lens group is d2p2,
0.50<(d2p1+d2p2)/f2<1.20
6. The zoom lens according to claim 1, wherein the following condition is satisfied: The sum of the center thicknesses of all the lenses constituting the second lens group is denoted by d2G, and the total length of the second lens group is denoted by TL2G,
0.70<d2G/TL2G<0.99
7. The zoom lens according to claim 1, wherein the following condition is satisfied: A zoom lens comprising a negative first lens group and a positive second lens group arranged in this order from an object side to an image side,
The spacing between adjacent lens groups changes during zooming.
the second lens group includes at least two positive lenses and at least two negative lenses;
the negative lens located closest to the image side among the at least two negative lenses has an aspheric surface;
a positive lens arranged closest to the object side in the second lens group and a negative lens arranged adjacent to the positive lens each consist of a single lens, the positive lens and the negative lens are separated by air, the radius of curvature of the positive lens on the image side is R12, and the radius of curvature of the negative lens on the object side is R21,
The focal length of the first lens group is f1, the focal length of the second lens group is f2, the average Abbe number of all of the at least two positive lenses is νd2p, and the minimum value of the air-equivalent back focus at the wide end is bfwt,
-1.20<f1/f2<-0.80
75.89≦νd2p<90.00
0.40<bfwt/f2<0.90
-0.10<(R12-R21)/(R12+R21)<0.70
A zoom lens characterized by satisfying the following conditional expressions: A zoom lens according to any one of claims 1 to 8;
an image sensor for capturing an image formed by the zoom lens, An imaging system comprising the imaging device according to claim 9 and a control unit that controls the zoom lens for zooming. The imaging system according to claim 10, characterized in that the control unit transmits a control signal to the zoom lens. The imaging system according to claim 10 or 11, characterized in that the control unit has an operating member for operating the zoom lens. The imaging system according to any one of claims 10 to 12, characterized in that it has a display unit that displays information regarding the zoom of the zoom lens.