Zoom lens and imaging device

Abstract

To achieve a wide field angle, a high zoom ratio and excellent aberration correction in a small-sized zoom lens.SOLUTION: A zoom lens is constituted of a first negative lens group, a second positive lens group, a third negative lens group and a fourth positive lens group. When zooming from a wide angle end to a telephoto end, the first, second and third lens groups move, and the fourth lens group is immovable; the second lens group includes at least two aspheric lenses; when setting the focal distance of the first lens group to f1, the focal distance of the second lens group to f2, the movement amount of the second lens group on the side of an object when zooming from the wide angle end to the telephoto end to m2 and a length on the optical axis from the lens surface of the zoom lens at the telephoto end on the side closest to the object to an image surface to TLt, the conditions of 0.1≤|f1 / f2|≤1.0 and 0.35≤m2 / TLt≤1.00 are satisfied.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a zoom lens suitable for imaging.

Background Art

[0002] Zoom lenses are required to have high optical performance capable of supporting high-definition imaging. Particularly in surveillance cameras, it is required to be small in size, have a wide angle of view at the wide-angle end, and have a high zoom ratio. As a wide-angle and small-sized zoom lens, as disclosed in Patent Documents 1 to 3, a negative-lead type zoom lens in which the lens group closest to the object side has a negative refractive power is known.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0004] In a negative-lead type zoom lens, in order to achieve a wide angle of view, a high zoom ratio, and miniaturization, it is necessary to increase the refractive power of each lens group. However, when the refractive power is increased, in addition to off-axis aberrations such as coma aberration and field curvature, the spherical aberration of the entire system tends to increase, and it becomes difficult to correct these aberrations simultaneously.

[0005] The present invention provides a small-sized zoom lens that has a wide angle of view and a high zoom ratio, and in which various aberrations are well corrected over the entire zoom range.

Means for Solving the Problems

[0006] A zoom lens according to one aspect of the present invention is composed of a first lens group having a negative refractive power, a second lens group having a positive refractive power, a third lens group having a negative refractive power, and a fourth lens group having a positive refractive power, which are arranged in order from the object side to the image side. During zooming, the distance between adjacent lens groups changes. When zooming from the wide-angle end to the telephoto end, the first lens group, the second lens group, and the third lens group move, and the fourth lens group remains stationary. The second lens group includes at least two aspherical lenses. Let the focal length of the first lens group be f1, the focal length of the second lens group be f2, the amount of movement of the second lens group toward the object side during zooming from the wide-angle end to the telephoto end be m2, and the length on the optical axis from the most object-side lens surface of the zoom lens at the telephoto end to the image plane be TLt. 0.1 ≦ |f1 / f2| ≦ 1.0 0.35 ≦ m2 / TLt ≦ 1.00 It is characterized by satisfying the above conditions. Note that an imaging device equipped with the above zoom lens also constitutes another aspect of the present invention.

Effects of the Invention

[0007] According to the present invention, it is possible to provide a small-sized zoom lens that has a wide angle of view and a high zoom ratio, and in which various aberrations are well corrected over the entire zoom range.

Brief Description of the Drawings

[0008] [Figure 1] Cross-sectional view of the zoom lens of Example 1. [Figure 2] Aberration diagrams of the zoom lens of Example 1 at the wide-angle end, intermediate focal length, and telephoto end. [Diagram 3] Cross-sectional view of the zoom lens of Example 2. [Figure 4] Aberration diagrams of the zoom lens of Example 2 at the wide-angle end, intermediate focal length, and telephoto end. [Diagram 5] Cross-sectional view of the zoom lens of Example 3. [Figure 6] Aberration diagrams of the zoom lens of Example 3 at the wide-angle end, intermediate focal length, and telephoto end. [Figure 7] FIG. 10 is a cross-sectional view of a zoom lens according to a fourth embodiment. [Figure 8] 10A to 10C are aberration diagrams of the zoom lens of Example 4 at the wide-angle end, at the intermediate focal length, and at the telephoto end. [Figure 9] FIG. 10 is a cross-sectional view of a zoom lens according to a fifth embodiment. [Figure 10] 10A to 10C are aberration diagrams of the zoom lens of Example 5 at the wide-angle end, at the intermediate focal length, and at the telephoto end. [Figure 11] FIG. 10 is a cross-sectional view of a zoom lens according to a sixth embodiment. [Figure 12] 13A to 13C are aberration diagrams of the zoom lens of Example 6 at the wide-angle end, at the intermediate focal length, and at the telephoto end. [Figure 13] 1A and 1B are schematic diagrams of an imaging device equipped with a zoom lens according to each embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, embodiments of the present invention will be described with reference to the drawings. First, prior to describing specific embodiments 1 to 6, matters common to all embodiments will be described.

[0010] The zoom lenses of the respective embodiments are used in various imaging devices such as cinema cameras, broadcast cameras, video cameras, surveillance cameras, digital still cameras, and cameras for silver halide film.

[0011] In a zoom lens, a lens group is a group of one or more lenses that may or may not move as a unit during zooming between the wide-angle and telephoto ends. That is, the spacing between adjacent lens groups changes during zooming. The lens group may include an aperture stop. The wide-angle and telephoto ends refer to the zoom states with the maximum and minimum angles of view (shortest focal lengths) when the lens group that moves during zooming is located at the ends of its mechanically or controllably movable range on the optical axis.

[0012] 1, 3, 5, 7, 9, and 11 show cross sections of the zoom lenses of Examples 1 to 6 at the wide-angle end, respectively. In these figures, the left side is the object side (front side) and the right side is the image side (rear side). Bi is the i-th lens group counting from the object side, and Lim is the m-th lens in the i-th lens group Bi counting from the object side. AP is an aperture stop, and G is a glass block such as an image sensor cover glass, low-pass filter, or infrared cut filter. IM is an image plane. The image plane IM is where the image sensor's image sensing surface (light receiving surface) or the film surface (photosensitive surface) of a silver halide film in an imaging device is located.

[0013] Below the first lens group B1, the second lens group B2, and the third lens group B3, which move during zooming, arrows indicate the movement locus of each lens group during zooming from the wide-angle end to the telephoto end. The solid arrow and dashed arrow below the third lens group B3 indicate the movement locus of the third lens group B3 for correcting image plane fluctuations that accompany zooming from the wide-angle end to the telephoto end when focused on an object at infinity (hereinafter referred to as the infinity focused state) and when focused on a close object, respectively. Note that the aperture stop AP moves integrally with the second lens group B2 during zooming.

[0014] Below the third lens unit B3 that moves during focusing, an arrow labeled FC indicates the direction in which this lens unit moves during focusing from infinity to close range.

[0015] The zoom lens of each embodiment is composed of, arranged in order from the object side to the image side, a first lens unit B1 with negative refractive power, a second lens unit B2 with positive refractive power, a third lens unit B3 with negative refractive power, and a fourth lens unit B4 with positive refractive power. During zooming from the wide-angle end to the telephoto end, the first lens unit B1, the second lens unit B2, and the third lens unit B3 move, while the fourth lens unit B4 remains stationary (fixed).

[0016] When zooming, the first lens group B1, the second lens group B3, and the third lens group B3 move. By using the intervals between the lens groups, various aberrations are effectively corrected while miniaturizing the zoom lens. Also, when zooming, the fourth lens group B4 is kept stationary, reducing the number of motors for driving the lens groups for zooming, improving controllability, and further miniaturizing the zoom lens.

[0017] In addition, the second lens group B2 includes at least two aspherical lenses. Thereby, fluctuations in various aberrations such as spherical aberration and coma aberration during zooming from the wide-angle end to the telephoto end are effectively corrected, and the number of lenses constituting the second lens group B2 is reduced. As a result, it is possible to achieve both miniaturization of the zoom lens and a high zoom ratio while ensuring the moving amount of the second lens group B2 during zooming.

[0018] In the above configuration, let the focal length of the first lens group B1 be f1, the focal length of the second lens group B2 be f2, and the amount of movement of the second lens group B2 toward the object side during zooming from the wide-angle end to the telephoto end be m2. The amount of movement here is the difference between the position of the second lens group B2 at the wide-angle end and the position at the telephoto end, excluding the reciprocating movement amount, and is positive when the second lens group B2 is positioned closer to the object side at the telephoto end than at the wide-angle end. Also, let the length on the optical axis from the most object-side lens surface of the zoom lens at the telephoto end to the image plane IM (optical overall length: hereinafter, also referred to as the lens overall length) be TLt. At this time, the zoom lens of each embodiment satisfies the conditions of the following formulas (1) and (2).

[0019] 0.1 ≦ |f1 / f2| ≦ 1.0 (1) 0.35 ≦ m2 / TLt ≦ 1.00 (2) The condition of Equation (1) indicates an appropriate relationship between the focal lengths f1 and f2 of the first lens group B1 and the second lens group B2. If |f1 / f2| exceeds the upper limit of Equation (1), the refractive power of the first lens group B1 becomes too weak relative to the refractive power of the second lens group B2, making it difficult to achieve a wide-angle effect, which is not preferable. If |f1 / f2| is below the lower limit of Equation (1), the refractive power of the first lens group B1 becomes too strong relative to the refractive power of the second lens group B2, especially increasing the field curvature at the wide-angle end, which is not preferable.

[0020] The condition of Equation (2) indicates an appropriate relationship between the movement amount m2 of the second lens group B2 during zooming from the wide-angle end to the telephoto end and the overall lens length TLt at the telephoto end. If m2 / TLt exceeds the upper limit of Equation (2), the movement amount m2 of the second lens group B2 exceeds the overall lens length TLt at the telephoto end, making it impossible to form a zoom lens, which is not preferable. If m2 / TLt is below the lower limit of Equation (2), the movement amount m2 of the second lens group B2 becomes too small relative to the overall lens length TLt at the telephoto end, making it difficult to achieve both a high zoom ratio and miniaturization of the zoom lens, which is not preferable.

[0021] It is more preferable to set the numerical ranges of Equations (1) and (2) as follows.

[0022] 0.3 ≦ |f1 / f2| ≦ 1.0 (1a) 0.35 ≦ m2 / TLt ≦ 0.90 (2a) It is even more preferable to set the numerical ranges of Equations (1) and (2) as follows.

[0023] 0.5 ≦ |f1 / f2| ≦ 1.0 (1b) 0.35 ≦ m2 / TLt ≦ 0.70 (2b) By satisfying the above configuration and conditions, it is possible to realize a small-sized zoom lens with a wide-angle and high zoom ratio while well correcting various aberrations in the entire zoom range.

[0024] Also, the zoom lens (and the imaging device including the zoom lens) of each embodiment preferably satisfies at least one of the following configurations and the conditions of formulas (3) to (12).

[0025] The second lens group B2 is preferably composed of four or fewer lenses. Thereby, an increase in the thickness of the second lens group B2 can be suppressed, it becomes easy to secure the movement amount of the second lens group B2, and it becomes easy to realize a high zoom ratio. When the second lens group B2 includes a cemented lens in which two lenses are cemented, this cemented lens shall be counted as two lenses.

[0026] In the second lens group B2, it is preferable that at least two aspherical lenses each have a positive refractive power, and when the average of the focal lengths of these aspherical lenses is f2_asph, the condition of the following formula (3) is satisfied.

[0027] 0.1 ≦ f2 / f2_asph ≦ 2.0 (3) In order to give a strong positive refractive power to the second lens group B2, which is the main variable magnification group in a zoom lens with a high zoom ratio as in each embodiment, it is necessary to include a positive lens with a strong refractive power in the second lens group B. Since the amount of various aberrations generated is large in a lens with a strong refractive power, by making the positive lens in the second lens group B2 an aspherical lens, various aberrations generated in the second lens group B2 can be effectively suppressed.

[0028] The condition of formula (3) shows an appropriate relationship between the focal length f2 of the second lens group B2 and the average focal length f2 / f2_asph of at least two aspherical positive lenses included in the second lens group B2. When f2 / f2_asph exceeds the upper limit of formula (3), the refractive power of the aspherical lens becomes too weak with respect to the refractive power of the second lens group B2, and it becomes difficult to effectively suppress various aberrations generated in the second lens group B2, which is not preferable. When f2 / f2_asph is below the lower limit of formula (3), the refractive power of the aspherical lens becomes too strong, the sensitivity to aberration correction increases, and the performance variation due to manufacturing variations increases, which is not preferable.

[0029] At least two aspherical lenses in the second lens group B2 are all single lenses. When the average Abbe number based on the d-line of these aspherical lenses is νd2_asph, it is preferable to satisfy the conditions of the following formula (4).

[0030] 55.0 ≦ νd2_asph ≦ 100.0 (4) The Abbe number νd based on the d-line is given by the following formula when the refractive indices for the F-line (486.1 nm), d-line (587.6 nm), and C-line (656.3 nm) of the Fraunhofer lines are nF, nd, and nC, respectively.

[0031] νd = (nd - 1) / (nF - nC) The condition of formula (4) indicates an appropriate range of the average Abbe number νd2_asph of the aspherical single lenses included in at least two in the second lens group B2. If νd2_asph exceeds the upper limit of formula (4), there will be no options for actual optical materials, which is not preferable. If νd2_asph is below the lower limit of formula (4), the dispersion becomes too large, making it difficult to correct the axial chromatic aberration of the entire zoom lens system, which is not preferable.

[0032] When zooming from the wide-angle end to the telephoto end, the first lens group B1 preferably moves toward the object side after moving toward the image side, that is, it moves along a locus that is convex toward the image side. By moving the first lens group B1 in this way, it is possible to suppress an increase in the overall lens length while ensuring a high zoom ratio.

[0033] The first lens group B1 includes at least one aspherical lens with a negative refractive power. When the average focal length of these aspherical lenses is f1n_asph, it is preferable to satisfy the conditions of the following formula (5).

[0034] 0.1 ≦ f1n_asph / f1 ≦ 3.0 (5) In order to give a strong negative refractive power to the first lens group B1 in a wide-angle zoom lens like each embodiment, it is necessary to include a negative lens with a strong refractive power in the first lens group B1. Among various aberrations in the negative lens of the first lens group B1, the amount of field curvature generated is particularly large. Therefore, by using an aspherical lens as the negative lens of the first lens group B1, the field curvature generated in the first lens group B1 can be effectively suppressed.

[0035] The condition of Equation (5) shows an appropriate relationship between the focal length f1 of the first lens group B1 and the average focal length f1n_asph of the aspherical negative lens included in the first lens group B1 at least once. When f1n_asph / f1 exceeds the upper limit of Equation (5), the refractive power of the aspherical lens becomes too weak with respect to the refractive power of the first lens group B1, making it difficult to effectively suppress the field curvature generated in the first lens group B1 by the aspherical surface, which is not preferable. When f1n_asph / f1 is below the lower limit of Equation (5), the refractive power of the aspherical lens becomes too strong, increasing the sensitivity to aberration correction and the performance variation due to manufacturing variations, which is not preferable.

[0036] When the focal length of the third lens group B3 is f3, it is preferable to satisfy the condition of the following Equation (6).

[0037] 1.0 ≦ |f3 / f2| ≦ 3.0 (6) The condition of Equation (6) shows an appropriate relationship between the focal lengths f2 and f3 of the second lens group B2 and the third lens group B3. When |f3 / f2| exceeds the upper limit of Equation (6), the refractive power of the third lens group B3 becomes too weak with respect to the refractive power of the second lens group B2, making it difficult to miniaturize the zoom lens, which is not preferable. When |f3 / f2| is below the lower limit of Equation (6), the refractive power of the third lens group B3 becomes too strong with respect to the refractive power of the second lens group B2, increasing various aberrations, which is not preferable.

[0038] When the focal length of the fourth lens group B4 is f4, it is preferable to satisfy the condition of the following Equation (7).

[0039] 1.0 ≦ |f4 / f2| ≦ 3.0 (7) The condition of formula (7) shows an appropriate relationship between the focal lengths f2 and f4 of the second lens group B2 and the fourth lens group B4. When |f4 / f2| exceeds the upper limit of formula (7), the refractive power of the fourth lens group B4 becomes too weak relative to the refractive power of the second lens group B2, making it difficult to miniaturize the zoom lens, which is not preferable. When |f4 / f2| is below the lower limit of formula (7), the refractive power of the fourth lens group B4 becomes too strong relative to the refractive power of the second lens group B2, increasing various aberrations, which is not preferable.

[0040] When the focal length of the entire zoom lens at the wide-angle end is fw and the air equivalent distance (back focus) from the most image-side lens surface of the zoom lens to the image plane IM at the wide-angle end is BFw, it is preferable to satisfy the condition of the following formula (8).

[0041] 0 < BFw / fw ≤ 1.5 (8) The condition of formula (8) shows an appropriate relationship between the focal length and the back focus of the zoom lens at the wide-angle end. When BFw / fw exceeds the upper limit of formula (8), the back focus becomes too large, making it difficult to miniaturize the zoom lens, which is not preferable. When BFw / fw is below the lower limit of formula (8), the most image-side lens surface gets too close to the image plane IM, which is not preferable.

[0042] Note that it is more preferable to set the numerical ranges of formulas (3) to (8) as follows.

[0043] 0.6 ≤ f2 / f2_asph ≤ 1.7 (3a) 60.0 ≤ νd2_asph ≤ 90.0 (4a) 0.4 ≤ f1n_asph / f1 ≤ 2.8 (5a) 1.3 ≤ |f3 / f2| ≤ 3.0 (6a) 1.0 ≤ |f4 / f2| ≤ 2.5 (7a) 0.5 ≤ BFw / fw ≤ 1.5 (8a) Also, it is even more preferable to set the numerical ranges of formulas (3) to (8) as follows.

[0044] 0.8 ≤ f2 / f2_asph ≤ 1.5 (3b) 65.0 ≤ νd2_asph ≤ 85.0 (4b) 0.8 ≤ f1n_asph / f1 ≤ 2.6 (5b) 1.5 ≤ |f3 / f2| ≤ 2.9 (6b) 1.1 ≤ |f4 / f2| ≤ 2.0 (7b) 0.9 ≤ BFw / fw ≤ 1.4 (8b) Hereinafter, Examples 1 to 6 will be specifically described. After Example 6, Numerical Examples 1 to 6 corresponding to each of Examples 1 to 6 are shown. In the following description, the lens groups and the lenses constituting each lens group are arranged in order from the object side to the image side.

Example

[0045] The zoom lens of Example 1 (Numerical Example 1) shown in FIG. 1 is composed of a first lens group B1 with negative refractive power, a second lens group B2 with positive refractive power, a third lens group B3 with negative refractive power, and a fourth lens group B4 with positive refractive power.

[0046] The first lens group B1 is composed of negative lenses L11, L12, and a positive lens L13. The second lens group B2 is composed of a positive lens L21, a cemented lens of a positive lens L22 and a negative lens L23, and a positive lens L24. The positive lens L21 and the positive lens L24 are aspherical single lenses. An aperture stop AP is included on the most object side of the second lens group B2. The third lens group B3 is composed of a negative lens L31. The fourth lens group B4 is composed of a positive lens L41.

[0047] FIGS. 2(A), (B), and (C) show the longitudinal aberration (spherical aberration, astigmatism, distortion, and chromatic aberration) at the wide-angle end, intermediate focal length, and telephoto end in the infinity-focus state of the zoom lens of Numerical Example 1, respectively.

[0048] In the spherical aberration diagram, Fno indicates the F-number. The solid line represents the spherical aberration for the d-line (wavelength 587.6 nm), and the two-dot chain line represents the spherical aberration for the g-line (wavelength 435.8 nm). Also, the one-dot chain line represents the spherical aberration for the C-line (wavelength 656.3 nm), and the long dashed line represents the spherical aberration for the F-line (wavelength 486.1 nm). In the astigmatism diagram, the solid line S represents the astigmatism at the sagittal image plane, and the dashed line M represents the astigmatism at the meridional image plane. The distortion aberration diagram shows the distortion aberration for the d-line. The chromatic aberration diagram shows the longitudinal chromatic aberration for the g-line, C-line, and F-line. The astigmatism diagram and the chromatic aberration diagram show the aberration amounts when the central ray of the light beam at the aperture position is taken as the chief ray. ω is the paraxial half field angle (°). The above explanations for the aberration diagrams are the same for the aberration diagrams of the following numerical examples.

Example

[0049] The zoom lens of Example 2 (numerical example 2) shown in Fig. 3 is composed of a first lens group B1 with negative refractive power, a second lens group B2 with positive refractive power, a third lens group B3 with negative refractive power, and a fourth lens group B4 with positive refractive power.

[0050] The first lens group B1 is composed of negative lenses L11, L12, and a positive lens L13. The second lens group B2 is composed of a positive lens L21, a cemented lens of a positive lens L22 and a negative lens L23, and a positive lens LL24. The positive lens L21 and the positive lens L24 are aspherical single lenses. The aperture stop AP is included on the most object side of the second lens group B2. The third lens group B3 is composed of a negative lens L31. The fourth lens group B4 is composed of a positive lens L41.

[0051] Figs. 4(A), (B), and (C) show the longitudinal aberration at the wide-angle end, intermediate focal length, and telephoto end in the infinity-focus state of the zoom lens of numerical example 2, respectively.

Example

[0052] The zoom lens of Example 3 (Numerical Example 3) shown in Fig. 5 is composed of a first lens group B1 with negative refractive power, a second lens group B2 with positive refractive power, a third lens group B3 with negative refractive power, and a fourth lens group B4 with positive refractive power.

[0053] The first lens group B1 is composed of negative lenses L11, L12 and a positive lens L13. The second lens group B2 is composed of a positive lens L21, a cemented lens of a positive lens L22 and a negative lens L23, and a positive lens LL24. The positive lens L21 and the positive lens L24 are aspherical single lenses. An aperture stop AP is included on the most object side of the second lens group B2. The third lens group B3 is composed of a negative lens L31. The fourth lens group B4 is composed of a positive lens L41.

[0054] Figs. 6(A), (B) and (C) show the longitudinal chromatic aberrations at the wide-angle end, the intermediate focal length, and the telephoto end in the infinity-focus state of the zoom lens of Numerical Example 3, respectively.

Example

[0055] The zoom lens of Example 4 (Numerical Example 4) shown in Fig. 7 is composed of a first lens group B1 with negative refractive power, a second lens group B2 with positive refractive power, a third lens group B3 with negative refractive power, and a fourth lens group B4 with positive refractive power.

[0056] The first lens group B1 is composed of negative lenses L11, L12 and a positive lens L13. The second lens group B2 is composed of a positive lens L21, a cemented lens of a positive lens L22 and a negative lens L23, and a positive lens LL24. The positive lens L21 and the positive lens L24 are aspherical single lenses. An aperture stop AP is included on the most object side of the second lens group B2. The third lens group B3 is composed of a negative lens L31. The fourth lens group B4 is composed of a positive lens L41.

[0057] Figs. 8(A), (B) and (C) show the longitudinal chromatic aberrations at the wide-angle end, the intermediate focal length, and the telephoto end in the infinity-focus state of the zoom lens of Numerical Example 4, respectively. [Example]

[0058] The zoom lens of Example 5 (Numerical Example 5) shown in Figure 9 is composed of a first lens group B1 with negative refractive power, a second lens group B2 with positive refractive power, a third lens group B3 with negative refractive power, and a fourth lens group B4 with positive refractive power.

[0059] The first lens group B1 is composed of negative lenses L11 and L12, and a positive lens L13. The second lens group B2 is composed of a positive lens L21, a cemented lens consisting of a positive lens L22 and a negative lens L23, and a positive lens LL24. The positive lens L21 and the positive lens L24 are aspherical single lenses. The second lens group B2 includes an aperture stop AP closest to the object. The third lens group B3 is composed of a negative lens L31. The fourth lens group B4 is composed of a positive lens L41.

[0060] 10A, 10B, and 10C show longitudinal aberrations of the zoom lens of Numerical Example 5 at the wide-angle end, at the intermediate focal length, and at the telephoto end in a state focused at infinity, respectively. [Example]

[0061] The zoom lens of Example 6 (Numerical Example 6) shown in FIG. 11 is composed of a first lens group B1 with negative refractive power, a second lens group B2 with positive refractive power, a third lens group B3 with negative refractive power, and a fourth lens group B4 with positive refractive power.

[0062] The first lens group B1 is composed of negative lenses L11 and L12, and a positive lens L13. The second lens group B2 is composed of a positive lens L21, a cemented lens of a positive lens L22 and a negative lens L23, and a positive lens LL24. The positive lens L21 and the positive lens L24 are aspherical single lenses. The second lens group B2 includes an aperture stop AP closest to the object. The third lens group B3 is composed of a cemented lens of a positive lens L31 and a negative lens L32. The fourth lens group B4 is composed of a positive lens L41.

[0063] Figures 12(A), (B), and (C) show the longitudinal aberration at the wide-angle end, the intermediate focal length, and the telephoto end, respectively, in the infinity focus state of the zoom lens of Numerical Example 6.

[0064] The following shows Numerical Examples 1 to 6. In each numerical example, the surface number i indicates the order of the surface when counted from the object side. r is the radius of curvature (mm) of the i-th surface from the object side, d is the lens thickness or air interval (mm) on the optical axis between the i-th and (i + 1)-th surfaces, nd is the refractive index at the d-line of the optical material between the i-th surface and the (i + 1)-th surface. νd is the Abbe number based on the d-line of the optical material between the i-th surface and the (i + 1)-th surface.

[0065] BF represents the back focus (mm) described above. The overall length of the lens is the length obtained by adding the back focus to the distance on the optical axis from the lens surface closest to the object side (the frontmost surface) to the lens surface closest to the image side (the final surface) of the zoom lens.

[0066] The "*" attached to the surface number means that the surface has an aspherical shape. The aspherical shape is represented by the following formula when x is the displacement amount from the vertex of the surface in the optical axis direction, h is the height from the optical axis in the direction perpendicular to the optical axis, the direction of light propagation is positive, R is the paraxial radius of curvature, K is the conic constant, and A4, A6, A8, A10 are the aspherical coefficients. Note that "e±Z" of the conic constant and the aspherical coefficient means ×10 ±Z means.

[0067] x = (h 2 / R) / [1 + √{1 - (1 + k)(h / R) 2}] + A4 × h 4 + A6 × h 6 + A8 × h 8 + A10 × h 10 The values of the above-mentioned formulas (1) to (8) in Numerical Examples 1 to 6 are summarized in Table 1. The zoom lens of each numerical example satisfies all the conditions of formulas (1) to (8) and is a small-sized zoom lens having high optical performance in the entire zoom range while having a wide angle and a high zoom ratio. [Numerical Example 1] Unit: mm Surface data Surface number r d nd νd 1 -136.305 0.80 1.61800 63.3 2 8.103 5.30 3 -23.725 0.60 1.58313 59.4 4* 37.117 0.28 5 22.459 1.07 1.95906 17.5 6 55.723 (variable) 7 (aperture) ∞ -0.89 8* 12.229 1.82 1.55332 71.7 9* -551.755 0.22 10 9.505 3.49 1.83481 42.7 11 -24.196 1.56 1.78880 28.4 12 5.941 2.81 13* 10.211 2.33 1.58313 59.4 14 -16.279 (variable) 15 -54.352 0.60 1.72825 28.5 16 34.893 (variable) 17 14.940 2.26 1.72916 54.1 18 239.388 1.86 19 ∞ 0.80 1.51633 64.1 20 ∞ 1.99 Image plane ∞ Aspherical data The 4th surface K = 0.00000e+00 A 4=-6.46029e-05 A 6=-2.86338e-07 A 8= 4.08661e-09 A10=-1.30552e-10 The 8th surface K = 0.00000e+00 A 4=-1.14354e-04 A 6= 8.72413e-07 A 8=-4.76464e-08 A10 = 9.55837e-10 Face 9 K = 0.00000e+00 A4 = 1.81243e-06 A6 = 1.57254e-06 A8 = -4.48671e-08 A10 = 8.51979e-10 Face 13 K = 0.00000e+00 A4 = -2.11516e-04 A6 = 6.18098e-07 A8 = 4.05736e-08 A10 = -2.15196e-10 Various data Zoom ratio 4.91 Wide angle, Medium, Telephoto Focal length 3.53, 10.44, 17.31 F-number 1.44, 2.40, 3.40 Half angle of view (°) 61.87, 17.73, 10.56 Image height 3.20, 3.20, 3.20 Overall lens length 51.19, 44.05, 51.14 BF 1.99, 1.99, 1.99 d6 22.60, 5.00, 1.64 d14 0.80, 2.53, 3.06 d16 0.91, 9.63, 19.56 Lens group data Group, Starting face, Focal length 1, 1, -9.86 2, 7, 11.25 3, 15, -29.10 4, 17, 21.76 [Numerical example 2] Unit: mm Surface data Surface number, r, d, nd, νd 1, -859.214, 0.80, 1.69680, 55.5 2*, 7.985, 4.65 3 -20.424 0.60 1.86300 41.5 4 67.672 0.20 5 23.481 1.35 1.95906 17.5 6 ∞ (variable) 7 (Diaphragm) ∞ 2.38 8* 15.701 1.94 1.55332 71.7 9* -42.848 0.20 10 7.926 3.20 1.75500 52.3 11 107.700 2.00 1.78880 28.4 12 5.291 2.17 13* 8.720 2.09 1.55332 71.7 14 -26.113 (variable) 15 -68.638 0.60 1.72825 28.5 16 15.589 (variable) 17 11.246 2.47 1.86300 41.5 18 -154.632 1.42 19 ∞ 0.80 1.51633 64.1 20 ∞ 1.99 Image plane ∞ Aspherical data Second surface K = 0.00000e+00 A 4=-3.28314e-05 A 6=-1.13896e-06 A 8= 5.44235e-08 A10=-8.74129e-10 Eighth surface K = 0.00000e+00 A 4=-1.35035e-04 A 6= 3.35298e-06 A 8=-2.37829e-07 A10= 5.04914e-09 Ninth surface K = 0.00000e+00 A 4=-6.17513e-05 A 6= 3.53434e-06 A 8=-2.32254e-07 A10= 4.99809e-09 Page 13 K = 0.00000e+00 A 4=-2.37662e-04 A 6= 2.55994e-06 A 8=-2.24198e-07 A10= 1.06688e-08 Various data Zoom ratio 4.91 Wide angle Middle Telephoto Focal length 3.49 10.34 17.14 F-number 1.44 2.45 3.60 Half field angle (°) 62.16 17.85 10.65 Image height 3.20 3.20 3.20 Overall lens length 51.19 44.04 51.14 BF 1.99 1.99 1.99 d 6 19.88 2.84 0.05 d14 0.80 5.97 7.90 d16 1.65 6.36 14.33 Lens group data Group Starting surface Focal length 1 1 -9.48 2 7 11.01 3 15 -17.39 4 17 12.23 [Numerical example 3] Unit: mm Surface data Surface number r d nd νd 1 -96.378 0.80 1.85400 40.4 2* 9.517 4.51 3 -37.503 0.60 1.76385 48.5 4* 107.438 0.18 5 26.925 1.64 1.95906 17.5 6 ∞ (Variable) 7 (Aperture) ∞ 0.07 8 * 9.951 2.34 1.69680 55.5 9 * -314.921 0.21 10 7.642 2.83 1.77250 49.6 11 -96.217 0.50 1.78880 28.4 12 4.656 2.44 13 * 12.101 1.62 1.49700 81.5 14 * -38.411 (variable) 15 -43.221 0.59 1.72825 28.5 16 53.837 (variable) 17 14.827 1.97 1.81600 46.6 18 -107.079 1.41 19 ∞ 0.80 1.51633 64.1 20 ∞ 2.00 Image plane ∞ Aspherical data Second surface K = 0.00000e+00 A 4=-5.22150e-05 A 6= 7.71365e-07 A 8=-1.38182e-08 A10=-1.22451e-10 Fourth surface K = 0.00000e+00 A 4=-1.80443e-05 A 6=-2.03534e-07 A 8= 1.10130e-09 Eighth surface K = 0.00000e+00 A 4=-1.01905e-04 A 6= 2.45023e-06 A 8=-1.38408e-07 A10= 3.68417e-09 Ninth surface K = 0.00000e+00 A 4= 2.43549e-05 A 6= 3.40973e-06 A 8=-1.47994e-07 A10= 4.06697e-09 Thirteenth surface K = 0.00000e+00 A4 = 1.79443e-04 A6 = 1.06683e-05 A8 = 1.16676e-06 A10 = 6.54468e-09 The 14th surface K = 0.00000e+00 A4 = 1.65995e-04 A6 = 5.28941e-06 A8 = 9.41645e-07 Various data Zoom ratio 7.50 Wide angle, middle, telephoto Focal length 3.50 14.89 26.27 F-number 1.44 3.10 4.90 Half field angle (°) 61.79 12.23 6.91 Image height 3.20 3.20 3.20 Overall lens length 54.99 43.76 54.93 BF 2.00 2.00 2.00 d6 28.07 2.85 0.02 d14 0.86 6.98 8.31 d16 1.55 9.43 22.09 Lens group data Group, starting surface, focal length 1 1 -11.77 2 7 11.78 3 15 -32.84 4 17 16.08 [Numerical example 4] Unit: mm Surface data Surface number, r, d, nd, νd 1 545.239 0.80 1.83481 42.7 2* 6.753 5.08 3 -8.361 0.60 1.53775 74.7 4 -38.735 0.20 5 48.217 0.87 1.95906 17.5 6 -81.596 (variable) 7 (Aperture) ∞ 0.10 8* 13.936 2.74 1.55200 70.7 9* -21.991 2.73 10 8.676 2.57 1.77250 49.6 11 591.946 0.51 1.78880 28.4 12 6.287 3.68 13* 11.233 2.31 1.43875 94.7 14 -13.419 (variable) 15 18.473 0.60 1.86300 41.5 16 8.521 (variable) 17 7.492 2.69 1.43875 94.7 18 -69.512 1.38 19 ∞ 0.80 1.51633 64.1 20∞2.00 Image plane ∞ Aspheric data 2nd side K = 0.00000e+00 A 4=-1.82901e-04 A 6=-3.69714e-06 A 8= 1.34133e-07 A10=-4.93272e-09 Side 8 K = 0.00000e+00 A 4=-1.24020e-04 A 6= 2.15326e-06 A 8=-1.00295e-07 A10= 2.15295e-09 9th page K = 0.00000e+00 A 4= 3.36148e-05 A 6= 2.16397e-06 A 8=-1.02904e-07 A10= 2.27496e-09 Page 13 K = 0.00000e+00 A 4=-1.90185e-04 A 6= 6.37960e-07 A 8= 1.13021e-07 A10 = -3.18409e-09 Various data Zoom ratio 3.79 Wide angle, middle, telephoto Focal length 3.48, 8.18, 13.18 F-number 1.44, 2.41, 3.60 Half field angle (°) 62.37, 22.72, 13.96 Image height 3.20, 3.20, 3.20 Overall lens length 49.00, 44.66, 49.97 BF 2.00, 2.00, 2.00 d 6, 16.74, 3.58, 0.08 d14 1.74, 9.83, 16.98 d16 0.88, 1.60, 3.28 Lens group data Group, starting surface, focal length 1, 1, -6.84 2, 7, 12.33 3, 15, -18.85 4, 17, 15.58 [Numerical example 5] Unit: mm Surface data Surface number, r, d, nd, νd 1, -49.104, 0.80, 1.80400, 46.6 2*, 6.620, 3.65 3, -18.339, 0.60, 1.49700, 81.5 4, -339.852, 0.63 5, 24.643, 1.10, 1.95906, 17.5 6, 706.051 (variable) 7 (aperture), ∞, 0.10 8*, 8.291, 1.70, 1.61800, 63.3 9*, 27.429, 2.73 10, 9.025, 2.03, 1.83481, 42.7 11 -73.831 0.50 1.78880 28.4 12 5.456 1.82 13* 9.708 2.74 1.55332 71.7 14 -10.288 (variable) 15 -43.704 0.59 1.72825 28.5 16 47.988 (variable) 17 9.575 2.46 1.49700 81.7 18 -164.167 2.42 19 ∞ 0.80 1.51633 64.1 20∞2.01 Image plane ∞ Aspheric data 2nd side K = 0.00000e+00 A 4=-3.84703e-04 A 6=-9.50954e-06 A 8= 2.13196e-07 A10=-7.98746e-09 Side 8 K = 0.00000e+00 A 4=-6.01972e-05 A 6= 3.35756e-06 A 8=-1.54344e-07 A10= 5.93797e-09 9th page K = 0.00000e+00 A 4= 2.20005e-04 A 6= 8.04278e-06 A 8=-3.68167e-07 A10= 1.34895e-08 Page 13 K = 0.00000e+00 A 4=-1.70675e-04 A 6= 3.16960e-06 A 8= 1.95549e-07 A10= 1.73152e-09 Various data Zoom ratio 3.19 Wide-angle Mid-range Telephoto Focal length 3.37 7.15 10.75 F-number 1.44 2.14 2.84 Half drawing angle (°) 62.21 26.29 17.31 Image height 3.20 3.20 3.20 Overall lens length 42.99 39.42 43.97 BF 2.01 2.01 2.01 d 6 14.60 3.30 0.11 d14 0.80 1.46 1.41 d16 0.91 7.99 15.77 Lens group data Group Starting surface Focal length 1 1 -8.79 2 7 10.97 3 15 -31.32 4 17 18.29 [Numerical example 6] Unit: mm Surface data Surface number r d nd νd 1 -246.369 0.80 1.58313 59.4 2* 8.039 5.50 3 -22.438 0.60 1.75500 52.3 4 42.957 0.19 5 20.999 1.31 1.95906 17.5 6 83.878 (Variable) 7 (Aperture) ∞ 0.37 8* 11.339 2.11 1.55332 71.7 9* -91.082 0.18 10 8.908 3.56 1.80400 46.6 11 -27.714 1.01 1.78880 28.4 12 5.731 2.14 13* 9.899 1.83 1.58313 59.4 14* -33.383 (Variable) 15 55.734 1.02 1.49700 81.7 16 -14.211 0.60 1.73800 32.3 17 17.484 (variable) 18 17.798 1.86 2.05090 26.9 19 -76.926 1.33 20 ∞ 0.80 1.51633 64.1 21 ∞ 2.15 Image plane ∞ Aspherical data Second surface K = 0.00000e+00 A 4=-3.64358e-05 A 6= 2.43102e-07 A 8= 3.90179e-09 A10=-2.43515e-10 Eighth surface K = 0.00000e+00 A 4=-9.37420e-05 A 6= 2.70541e-06 A 8=-1.49603e-07 A10= 3.05071e-09 Ninth surface K = 0.00000e+00 A 4= 2.80751e-05 A 6= 3.00160e-06 A 8=-1.54665e-07 A10= 3.22407e-09 Thirteenth surface K = 0.00000e+00 A 4=-7.69750e-05 A 6= 4.65010e-06 A 8=-2.59833e-08 A10= 7.57957e-12 Fourteenth surface K = 0.00000e+00 A 4= 1.29199e-04 A 6= 4.57539e-06 Various data Zoom ratio 6.11 Wide angle Middle Telephoto Focal length 3.54 12.48 21.63 F number 1.44 2.62 4.00 Half field angle (°) 61.89 14.60 8.40 Image height 3.20 3.20 3.20 Overall lens length 51.65 43.14 51.59 BF 2.15 2.15 2.15 d 6 22.40 2.87 0.30 d14 0.87 6.78 8.46 d17 1.02 6.13 15.46 Lens group data Group Starting surface Focal length 1 1 -10.20 2 7 10.91 3 15 -20.00 4 17 13.90

[0068]

Table 1

[0069] [Imaging device] FIG. 13 shows two examples of a surveillance camera as an imaging device equipped with the zoom lenses of Examples 1 to 6. In FIG. 13, 16 is an imaging optical system constituted by any one of the zoom lenses of Examples 1 to 6, and 10 and 11 are camera bodies. 12 is an imaging element such as a CCD sensor or a CMOS sensor that photoelectrically converts a subject image formed by the imaging optical system 16 (that is, captures an image of a subject through the zoom lens). 13 is a recording unit that records image data generated from the signal from the imaging element 12. 14 is a transfer cable for transferring the image data. 15 is a cover that protects the camera body 11 and the imaging optical system 16, and may have refractive power.

[0070] Note that in a surveillance camera having a daytime imaging mode and a nighttime imaging mode, an optical filter such as an IR cut filter or a visible light cut filter may be inserted or removed by an insertion / removal mechanism (not shown).

[0071] In addition, a zoom lens may be used in various imaging devices such as video cameras and digital cameras other than surveillance cameras. Further, a circuit for electrically correcting aberration components on the image data may be provided in the imaging device.

[0072] By using the zoom lens of each embodiment in an imaging device such as a surveillance camera as described above, it is possible to perform imaging with a wide angle of view and a high zoom ratio, and a small imaging device capable of obtaining image data with good image quality over the entire zoom range can be realized.

[0073] The above embodiments include the following configurations.

[0074] (Configuration 1) A zoom lens composed of a first lens group having a negative refractive power, a second lens group having a positive refractive power, a third lens group having a negative refractive power, and a fourth lens group having a positive refractive power, which are arranged in order from the object side to the image side, and in which the interval between adjacent lens groups changes during zooming, During zooming from the wide-angle end to the telephoto end, the first lens group, the second lens group, and the third lens group move, and the fourth lens group is stationary, The second lens group includes at least two aspherical lenses, Let the focal length of the first lens group be f1, the focal length of the second lens group be f2, the amount of movement of the second lens group toward the object side during zooming from the wide-angle end to the telephoto end be m2, and the length on the optical axis from the most object-side lens surface of the zoom lens at the telephoto end to the image plane be TLt. Then, 0.1 ≦ |f1 / f2| ≦ 1.0 0.35 ≦ m2 / TLt ≦ 1.00 A zoom lens characterized by satisfying the following conditions. (Configuration 2) The zoom lens according to Configuration 1, wherein the second lens group includes four or fewer lenses. (Configuration 3) All of the at least two aspherical lenses have a positive refractive power. When the average of the focal lengths of the at least two aspherical lenses is f2_asph, 0.1 ≦ f2 / f2_asph ≦ 2.0 The zoom lens according to Configuration 1 or 2, characterized by satisfying the condition (Configuration 4) When all of the at least two aspherical lenses are single lenses, and the average of the Abbe numbers of the at least two aspherical lenses with respect to the d-line is νd2_asph, 55.0 ≦ νd2_asph ≦ 100.0 The zoom lens according to any one of Configurations 1 to 3, characterized by satisfying the condition (Configuration 5) The zoom lens according to any one of Configurations 1 to 4, characterized in that, when zooming from the wide-angle end to the telephoto end, the first lens group moves toward the image side and then moves toward the object side. (Configuration 6) When the first lens group includes at least one aspherical lens having a negative refractive power, and the average of the focal lengths of the at least one aspherical lens is f1n_asph, 0.1 ≦ f1n_asph / f1 ≦ 3.0 The zoom lens according to any one of Configurations 1 to 5, characterized by satisfying the condition (Configuration 7) When the focal length of the third lens group is f3, 1.0 ≦ |f3 / f2| ≦ 3.0 The zoom lens according to any one of Configurations 1 to 6, characterized by satisfying the condition (Configuration 8) When the focal length of the fourth lens group is f4, 1.0 ≦ |f4 / f2| ≦ 3.0 The zoom lens according to any one of Configurations 1 to 7, characterized by satisfying the condition (Configuration 9) When the focal length of the zoom lens at the wide-angle end is fw and the air-equivalent distance from the most image-side lens surface of the zoom lens at the wide-angle end to the image plane is BFw, 0 < BFw / fw ≦ 1.5 The zoom lens according to any one of Configurations 1 to 8, characterized by satisfying the following conditions. (Configuration 10) A zoom lens according to any one of Configurations 1 to 9, and an imaging device having an imaging element that images a subject through the zoom lens.

[0075] Each of the embodiments described above is merely a representative example, and various modifications and changes can be made to each embodiment when implementing the present invention.

Explanation of Reference Numerals

[0076] B1 First lens group B2 Second lens group B3 Third lens group B4 Fourth lens group IM Image plane AP Aperture stop

Claims

1. A zoom lens composed of a first lens group with negative refractive power, a second lens group with positive refractive power, a third lens group with negative refractive power, and a fourth lens group with positive refractive power, arranged in order from the object side to the image side, and in which the distance between adjacent lens groups changes during zooming, during zooming from the wide-angle end to the telephoto end, the first lens group, the second lens group, and the third lens group move, and the fourth lens group is stationary, the second lens group includes at least two aspherical lenses, when the focal length of the first lens group is f1, the focal length of the second lens group is f2, the amount of movement of the second lens group toward the object side during zooming from the wide-angle end to the telephoto end is m2, and the length on the optical axis from the most object-side lens surface of the zoom lens at the telephoto end to the image plane is TLt, 0.1 ≤ |f1 / f2| ≤ 1.0 0.35 ≤ m2 / TLt ≤ 1.00 A zoom lens characterized by satisfying the following conditions.

2. The zoom lens according to claim 1, wherein the second lens group includes four or fewer lenses.

3. When both of the at least two aspherical lenses have positive refractive power and the average of the focal lengths of the at least two aspherical lenses is f2_asph, 0.1 ≤ f2 / f2_asph ≤ 2.0 The zoom lens according to claim 1, characterized by satisfying the following conditions.

4. When both of the at least two aspherical lenses are single lenses and the average of the Abbe numbers of the at least two aspherical lenses with respect to the d-line is νd2_asph, 55.0 ≤ νd2_asph ≤ 100.0 The zoom lens according to claim 1, characterized by satisfying the following conditions.

5. The zoom lens according to claim 1, wherein the first lens group moves toward the object side after moving toward the image side during zooming from the wide-angle end to the telephoto end.

6. When the first lens group includes at least one aspherical lens with negative refractive power and the average of the focal lengths of the at least one aspherical lens is f1n_asph, 0.1 ≤ f1n_asph / f1 ≤ 3.0 The zoom lens according to claim 1, characterized by satisfying the following conditions.

7. When the focal length of the third lens group is f3, 1.0 ≤ |f3 / f2| ≤ 3.0 The zoom lens according to claim 1, characterized by satisfying the following conditions.

8. When the focal length of the fourth lens group is f4, 1.0 ≤ |f4 / f2| ≤ 3.0 The zoom lens according to claim 1, characterized in that the condition is satisfied.

9. When the focal length of the zoom lens at the wide-angle end is fw and the air-equivalent distance from the most image-side lens surface of the zoom lens at the wide-angle end to the image plane is BFw, 0 < BFw / fw ≤ 1.5 The zoom lens according to claim 1, characterized in that the condition is satisfied.

10. A zoom lens according to any one of claims 1 to 9, An imaging device comprising an imaging element that images a subject through the zoom lens.

Images