Zoom lens and imaging device

Abstract

This provides a zoom lens that is compact and has a short overall length, yet offers a long focal length and high optical performance across the entire zoom range. [Solution] The zoom lens 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, and at least one subsequent lens group. When zooming from the wide-angle end to the telephoto end, the third lens group remains stationary with respect to the image plane, the spacing between adjacent lens groups changes, and the at least one subsequent lens group includes a focus lens group that moves when focusing from infinity to near distance. The third lens group includes at least two positive lenses, and the focal length of the second lens group, the focal length of the third lens group, the focal length of the focus lens group, and the average of the focal lengths of the lens with the strongest refractive power and the lens with the second strongest refractive power among the positive lenses included in the third lens group are appropriately set.

Description

Technical Field

[0005]

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

Background Art

[0002] In recent years, the high definition of monitors has advanced, and high image quality is required for zoom lenses mounted on surveillance cameras, network cameras, video cameras, etc. As the high definition of monitors advances, it is desired that the mounted zoom lens be an optical system having high optical performance with good correction of various aberrations such as chromatic aberration and field curvature. At the same time, for a zoom lens mounted on a surveillance camera or the like, miniaturization of the entire optical system is desired in order to reduce the size of the entire device. Further, in long-distance surveillance, it is desired that the entire optical system has a long focal length.

[0003] As a small and long-focal-length zoom lens, as disclosed in Patent Documents 1 to 3, a zoom lens including a positive first lens group, a negative second lens group, a positive third lens group, and at least one subsequent lens group is known. <000​​​​​​​​​​​​​​​​​​​​​​​​​​​​​In order to miniaturize zoom lenses, increasing the refractive power of each lens group tends to increase various aberrations such as spherical aberration, coma aberration, and field curvature. Furthermore, axial chromatic aberration tends to increase, especially at long focal lengths, making it difficult to correct all of these aberrations simultaneously.

[0006] The present invention aims to provide a zoom lens that is compact and has a short overall length, yet has a long focal length and delivers high optical performance throughout the entire zoom range. [Means for solving the problem]

[0007] A zoom lens according to one aspect of the present invention comprises, 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, and at least one subsequent lens group, wherein the spacing between adjacent lens groups changes when zooming from the wide-angle end to the telephoto end, the third lens group is stationary with respect to the image plane, the at least one subsequent lens group includes a focus lens group that moves when focusing from infinity to near distance, the third lens group includes at least two positive lenses, and when the focal length of the second lens group is f2, the focal length of the third lens group is f3, the focal length of the focus lens group is f_focus, and the average value of the focal lengths of the lens with the strongest refractive power and the second strongest refractive power among the positive lenses included in the third lens group is f3p12_ave, 1.00 <f3p12_ave / f3<1.55 0.90 < |f2 / f3| < 1.25 1.20 < |f_focus / f3| < 1.90 It is characterized by satisfying the following conditions. Another embodiment of the present invention is a zoom lens comprising, 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, and at least one subsequent lens group, wherein the spacing between adjacent lens groups changes when zooming from the wide-angle end to the telephoto end, the first lens group and the third lens group are immovable with respect to the image plane, the at least one subsequent lens group includes a focus lens group that moves when focusing from infinity to near distance, and the third lens group includes at least two positive lenses. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a zoom lens that is compact and has a short overall length, yet has a long focal length, and can obtain high optical performance throughout the entire zoom range, as well as an imaging device having the same. [Brief explanation of the drawing]

[0009] [Figure 1] This is a cross-sectional view of the zoom lens of Example 1 at the wide-angle end when it is focused at infinity. [Figure 2] This is an aberration diagram of the zoom lens of Example 1 at the wide-angle end, intermediate focal length, and telephoto end when focused at infinity. [Figure 3] This is a cross-sectional view of the zoom lens of Example 2 when it is focused at infinity at the wide-angle end. [Figure 4] This is an aberration diagram of the zoom lens of Example 2 at the wide-angle end, intermediate focal length, and telephoto end when focused at infinity. [Figure 5] This is a cross-sectional view of the zoom lens of Example 3 at the wide-angle end when it is focused at infinity. [Figure 6] This is an aberration diagram of the zoom lens of Example 3 at the wide-angle end, intermediate focal length, and telephoto end when focused at infinity. [Figure 7] This is a cross-sectional view of the zoom lens of Example 4 when it is focused at infinity at its wide-angle end. [Figure 8] This is an aberration diagram of the zoom lens of Example 4 at the wide-angle end, intermediate focal length, and telephoto end when focused at infinity. [Figure 9] This is a cross-sectional view of the zoom lens of Example 5 at the wide-angle end when it is focused at infinity. [Figure 10] This is an aberration diagram of the zoom lens of Example 5 at the wide-angle end, intermediate focal length, and telephoto end when focused at infinity. [Figure 11] This is a schematic diagram of an imaging device equipped with a zoom lens for each embodiment. [Modes for carrying out the invention]

[0010] The embodiments of the present invention will be described below with reference to the drawings. First, before describing the specific embodiments 1 to 5, we will explain the matters common to each embodiment. The zoom lenses of each embodiment are used in various imaging devices such as cinema cameras, broadcast cameras, video cameras, surveillance cameras, digital still cameras, and silver halide film cameras. In a zoom lens, a lens group is a collection of one or more lenses that move together or remain stationary during zooming between the wide-angle end and the telephoto end. That is, the distance between adjacent lens groups changes during zooming. The lens group may include an aperture diaphragm. The wide-angle end and telephoto end represent the zoom states at the maximum angle of view (shortest focal length) and minimum angle of view (longest focal length), respectively, when the lens group that moves during zooming is positioned at both ends of the range that is mechanically or controllly movable along the optical axis.

[0011] The zoom lens in each embodiment includes, 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, and at least one successor lens group. When zooming from the wide-angle end to the telephoto end, the third lens group remains stationary with respect to the image plane, and the spacing between each lens group changes. The at least one successor lens group includes a focusing lens group that moves when focusing from infinity to near distance. The third lens group also includes at least two positive lenses.

[0012] FIG. 1, FIG. 3, FIG. 5, FIG. 7, and FIG. 9 each show a cross-sectional view of the zoom lens according to Embodiments 1 to 5 at the wide-angle end in an infinitely focused state. 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 counted from the object side, and Lim is the m-th lens counted from the object side in the i-th lens group Bi. AP is the aperture stop, and G is a glass block such as a cover glass, a low-pass filter, and an infrared cut filter that protects the imaging device. IM is the image plane. On the image plane IM, the imaging surface (light receiving surface) of the imaging element in the imaging device or the film surface (photosensitive surface) of the silver halide film is arranged.

[0013] Under each lens group that moves during zooming, the movement locus from the wide-angle end to the telephoto end during zooming is indicated by an arrow. The solid arrow and the broken arrow under the focus lens group respectively indicate the movement locus of the focus lens group for correcting the image plane variation associated with zooming from the wide-angle end to the telephoto end in a state of being focused on an infinite object (hereinafter referred to as an infinitely focused state) and a state of being focused on a close object. Note that the aperture stop AP is stationary with respect to the image plane during zooming. Also, under the focus lens group that moves during focusing, the movement direction of the focus lens group during focusing from infinity to the closest distance is indicated by an arrow with the symbol FC attached.

[0014] In this way, during zooming, while effectively correcting various aberrations by using the intervals between the lens groups, the zoom lens is miniaturized. Also, by making the third lens group B3 stationary during zooming, the number of motors for driving the lens groups for zooming is reduced to improve controllability, or the zoom lens is further miniaturized.

[0015] Also, during focusing, by adopting a configuration in which any one focus lens group located on the image side of the third lens group B3 moves, the number of motors for driving the lens groups for focusing is minimized to improve controllability.

[0016] Furthermore, the third lens group B3 includes at least two positive lenses. This allows the refractive power of each positive lens included in the third lens group B3 to be reduced, thereby suppressing the occurrence of various aberrations such as spherical aberration and coma aberration.

[0017] In the above configuration, when the focal length of the second lens group B2 is f2, the focal length of the third lens group B3 is f3, the focal length of the focusing lens group is f_focus, and the average of the focal lengths of the lens with the strongest refractive power and the lens with the second strongest refractive power among the positive lenses included in the third lens group B3 is f3p12_ave, 1.00 <f3p12_ave / f3<1.55 ···(1) 0.90 < |f2 / f3| < 1.25 ... (2) 1.20<|f_focus / f3|<1.90 ···(3) The conditions are met.

[0018] Condition (1) indicates an appropriate relationship between the focal length f3 of the third lens group B3 and the average value of the focal lengths f3p12_ave of the positive lenses included in the third lens group B3, specifically the lens with the strongest refractive power and the lens with the second strongest refractive power. Exceeding the upper limit of condition (1) is undesirable because the refractive power of the positive lenses included in the third lens group B3 becomes too small relative to the refractive power of the third lens group B3, increasing the number of lenses required to obtain the desired refractive power of the third lens group B3 and making it larger. Exceeding the lower limit of condition (1) is undesirable because the refractive power of the positive lenses included in the third lens group B3 becomes too large relative to the refractive power of the third lens group B3, increasing various aberrations.

[0019] The condition in equation (2) indicates an appropriate relationship between the focal length f3 of the third lens group B3 and the focal length f2 of the second lens group B2. If the value exceeds the upper limit of equation (2), the refractive power of the second lens group B2 becomes too weak relative to the refractive power of the third lens group B3, making miniaturization difficult, which is undesirable. If the value falls below the lower limit of equation (2), the refractive power of the second lens group B2 becomes too strong relative to the refractive power of the third lens group B3, increasing various aberrations, which is also undesirable.

[0020] The condition in equation (3) indicates an appropriate relationship between the focal length f3 of the third lens group B3 and the focal length f_focus of the focusing lens group. If the value exceeds the upper limit of equation (3), the refractive power of the focusing lens group becomes too weak relative to the refractive power of the third lens group B3, making miniaturization difficult, which is undesirable. If the value falls below the lower limit of equation (3), the refractive power of the focusing lens group becomes too strong relative to the refractive power of the third lens group B3, increasing various aberrations, which is also undesirable.

[0021] Furthermore, it is preferable to set the numerical ranges of conditional expressions (1), (2), and (3) as follows. 1.10 <f3p12_ave / f3<1.50 ···(1a) 0.94 < |f2 / f3| < 1.20 ···(2a) 1.24<|f_focus / f3|<1.85 ···(3a) Furthermore, it is even preferable to set the numerical ranges of conditional expressions (1), (2), and (3) as follows. 1.15 <f3p12_ave / f3<1.45 ···(1b) 0.94 < |f2 / f3| < 1.15 ···(2b) 1.24<|f_focus / f3|<1.81 ···(3b)

[0022] By satisfying the above configuration and conditions, it is possible to realize a zoom lens that is short in overall length and compact, yet has a long focal length and high optical performance throughout the entire zoom range. Furthermore, it is preferable that the zoom lens of each embodiment and the imaging device equipped with the zoom lens satisfy at least one of the following configurations and conditions (4) to (8).

[0023] When the focal length of the first lens group B1 is f1, 2.00 <f1 / f3<4.50 ···(4) It is preferable that the following conditions be satisfied. The condition in equation (4) indicates an appropriate relationship between the focal length f3 of the third lens group B3 and the focal length f1 of the first lens group B1. If the value exceeds the upper limit of equation (4), the refractive power of the first lens group B1 becomes too small relative to the refractive power of the third lens group B3, making miniaturization difficult, which is undesirable. If the value falls below the lower limit of equation (4), the refractive power of the first lens group B1 becomes too large relative to the refractive power of the third lens group B3, increasing various aberrations, which is also undesirable.

[0024] When the Abbe number with respect to the d line is νd, the refractive index with respect to the g line is ng, the refractive index with respect to the F line is nF, and the refractive index with respect to the C line is nC, the partial dispersion ratio θgF is: θgF = (ng - nF) / (nF - nC) It is represented as follows, and the third lens group B3 is, 65.00 < νd < 105.00 ···(5) 0.640<θgF+0.00167×νd<0.715 (6) It is preferable to include at least two positive lenses that satisfy the following conditions.

[0025] In the third lens group B3, which has positive refractive power, the amount of axial chromatic aberration can be reduced by using low-dispersion glass material for the positive lens. Furthermore, by selecting glass material with a higher partial dispersion ratio, the secondary spectrum of axial chromatic aberration can be reduced. The condition in equation (5) indicates the appropriate Abbe number range for at least two positive lenses included in the third lens group B3. Exceeding the upper limit of equation (5) is undesirable because it effectively eliminates the selection of glass material. Exceeding the lower limit of equation (5) is also undesirable because it results in excessively high dispersion and increased axial chromatic aberration.

[0026] Conditional equation (6) indicates the appropriate range of partial dispersion ratios for at least two positive lenses included in the third lens group B3. Exceeding the upper limit of conditional equation (6) is undesirable because it effectively eliminates the selection of suitable glass materials. Exceeding the lower limit of conditional equation (6) is also undesirable because the partial dispersion ratio becomes too small, particularly increasing the secondary spectrum of axial chromatic aberration at the telephoto end.

[0027] The third lens group B3 preferably includes at least two negative lenses. This configuration effectively corrects spherical aberration, coma aberration, and other distortions that tend to occur in the third lens group B3, thereby achieving high optical performance throughout the entire zoom range. When zooming from the wide-angle end to the telephoto end, it is preferable that the first lens group B1 remains stationary relative to the image plane. This configuration eliminates the need for a motor to drive the first lens group B1, which has a large lens diameter and is heavy, thereby improving controllability.

[0028] The focusing lens group preferably includes at least one positive lens and at least one negative lens. This configuration reduces aberrations occurring in the focusing lens group, suppresses fluctuations in aberrations during focusing, and allows for high optical performance from infinity to close distances.

[0029] When D_B1APt is defined as the distance along the optical axis from the lens surface closest to the object to the aperture diaphragm AP at the telephoto end of the zoom lens, and the total length of the lens is defined as the distance along the optical axis from the lens surface closest to the object to the image plane, then TLt is the total length of the lens at the telephoto end. 0.35 <D_B1APt / TLt<0.55 ···(7) It is preferable that the following conditions be satisfied.

[0030] Condition (7) indicates an appropriate relationship between the distance along the optical axis from the lens surface closest to the object at the telephoto end of the zoom lens to the aperture diaphragm AP, and the total length of the lens at the telephoto end. If the upper limit of condition (7) is exceeded, the position of the aperture diaphragm AP is too close to the image side, which is undesirable because it increases the lens diameter, especially of the first lens group B1, making miniaturization difficult. If the lower limit of condition (7) is exceeded, the aperture diaphragm AP is too close to the object side, which increases the lens diameter, especially of the third lens group B3 and beyond, making miniaturization difficult, and it is also undesirable because it becomes difficult to secure space for components such as motors to drive the lens groups.

[0031] When the focal length at the wide-angle end is defined as fw, and the air-equivalent distance from the lens surface closest to the image to the image plane IM is defined as the back focus, then the back focus at the wide-angle end is denoted as bfw, 0.05 <bfw / fw<0.35 ···(8) It is preferable that the following conditions be satisfied.

[0032] The condition in equation (8) indicates an appropriate relationship between the focal length at the wide-angle end and the back focus at the wide-angle end. Exceeding the upper limit of condition (8) is undesirable because the back focus becomes too long, making miniaturization difficult. Exceeding the lower limit of condition (8) is also undesirable because the back focus becomes too short, bringing the optical elements too close to the image plane.

[0033] Furthermore, it is preferable to set the numerical ranges of conditional expressions (4) to (8) as follows. 2.50 <f1 / f3<4.00 ···(4a) 71.00 < νd < 105.00 ···(5a) 0.650<θgF+0.00167×νd<0.710 (6a) 0.40 <D_B1APt / TLt<0.53 ···(7a) 0.10 <bfw / fw<0.30 ···(8a)

[0034] Furthermore, it is even preferable to set the numerical ranges of conditional expressions (4) to (8) as follows. 3.00 <f1 / f3<3.70 ···(4b) 80.00 < νd < 102.00 ···(5b) 0.655<θgF+0.00167×νd<0.705 (6b) 0.40 <D_B1APt / TLt<0.51 ···(7b) 0.10 <bfw / fw<0.28 ···(8b)

[0035] Examples 1 to 5 will be described in detail below. After Example 5, the numerical values ​​corresponding to Examples 1 to 5 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. [Examples]

[0036] Figure 1 shows a cross-sectional view of the zoom lens of Example 1 at the wide-angle end when focused at infinity. The zoom lens of Example 1 is composed of a first lens group B1 with positive refractive power, a second lens group B2 with negative refractive power, a third lens group B3 with positive refractive power, a fourth lens group B4 with negative refractive power, and a fifth lens group B5 with positive refractive power, arranged in order from the object side to the image side. When zooming from the wide-angle end to the telephoto end, the second lens group B2 moves towards the image side, and the fourth lens group B4 moves towards the image side along a convex trajectory. The first lens group B1, the third lens group B3, and the fifth lens group B5 are immovable (fixed). In addition, in the zoom lens of Example 1, the focusing lens group is the fourth lens group B4, which moves towards the image side when focusing from infinity to close.

[0037] The first lens group B1 consists of positive lenses L11 and L12, and a cemented lens formed by positive lens L13 and negative lens L14. The second lens group B2 consists of negative lens L21, and a cemented lens formed by negative lens L22 and positive lens L23. The third lens group B3 consists of positive lens L31, a cemented lens formed by positive lens L32 and negative lens L33, positive lens L34, a cemented lens formed by positive lens L35 and negative lens L36, positive lens L37, and negative lens L38. An aperture diaphragm AP is positioned adjacent to the object side of the third lens group B3. The fourth lens group B4 consists of a cemented lens formed by positive lens L41 and negative lens L42. The fifth lens group B5 consists of positive lens L51.

[0038] Figures 2(A), (B), and (C) show the longitudinal aberrations (spherical aberration, astigmatism, distortion, and chromatic aberration) of the zoom lens of Example 1 at the wide-angle end, intermediate focal length, and telephoto end, respectively, when the lens is in focus at infinity. As shown in Figure 2, the zoom lens of Example 1 has well corrected aberrations throughout the entire zoom range, achieving high optical performance.

[0039] In the spherical aberration diagram, Fno indicates the F number, the solid line represents the spherical aberration at the d line (wavelength 587.6 nm), the dashed line represents the spherical aberration at the g line (wavelength 435.8 nm), the dashed line represents the spherical aberration at the C line (wavelength 656.3 nm), and the long dashed line represents the spherical aberration at the F line (wavelength 486.1 nm). In the astigmatism diagram, the solid line S and the dashed line M represent the field curvature at the d line in the sagittal and meridional image planes, respectively. The distortion diagram shows the distortion at the d line. The chromatic aberration diagram shows the lateral chromatic aberration at the g, C, and F lines. The astigmatism and chromatic aberration diagrams show the amount of aberration when the central ray of the light beam at the aperture position is considered the principal ray. ω is the paraxial half-angle of view (°). The above explanation of the aberration diagrams is the same for the aberration diagrams of Examples 2 to 5 described later. Furthermore, Table 1 shows the values ​​corresponding to the conditions (1) to (8) in the numerical example 1. The zoom lens of numerical example 1 satisfies all of the conditions (1) to (8), has a short overall length and is compact, yet has a long focal length and achieves high optical performance throughout the entire zoom range. [Examples]

[0040] Figure 3 shows a cross-sectional view of the zoom lens of Example 2 at the wide-angle end when focused at infinity. The zoom lens of Example 2 is composed of a first lens group B1 with positive refractive power, a second lens group B2 with negative refractive power, a third lens group B3 with positive refractive power, a fourth lens group B4 with negative refractive power, and a fifth lens group B5 with positive refractive power, arranged in order from the object side to the image side. When zooming from the wide-angle end to the telephoto end, the second lens group B2 moves towards the image side, and the fourth lens group B4 moves towards the image side along a convex trajectory. The first lens group B1, the third lens group B3, and the fifth lens group B5 are immovable (fixed). In addition, in the zoom lens of Example 2, the focusing lens group is the fourth lens group B4, which moves towards the image side when focusing from infinity to close.

[0041] The first lens group B1 consists of positive lenses L11 and L12, and a cemented lens formed by positive lens L13 and negative lens L14. The second lens group B2 consists of positive lens L21, negative lens L22, and a cemented lens formed by negative lens L23 and positive lens L24. The third lens group B3 consists of positive lens L31, a cemented lens formed by positive lens L32 and negative lens L33, positive lens L34, a cemented lens formed by positive lens L35 and negative lens L36, positive lens L37, and negative lens L38. An aperture diaphragm AP is positioned adjacent to the object side of the third lens group B3. The fourth lens group B4 consists of a cemented lens formed by positive lens L41 and negative lens L42. The fifth lens group B5 consists of positive lens L51.

[0042] Figures 4(A), (B), and (C) show the longitudinal aberrations (spherical aberration, astigmatism, distortion, and chromatic aberration) of the zoom lens of Example 2 at the wide-angle end, intermediate focal length, and telephoto end, respectively, when the lens is in focus at infinity. As shown in Figure 4, the zoom lens of Example 2 has well corrected aberrations throughout the entire zoom range, achieving high optical performance. Furthermore, Table 1 shows the values ​​corresponding to the conditions (1) to (8) in Numerical Example 2. The zoom lens of Numerical Example 2 satisfies all of the conditions (1) to (8), has a short overall length and is compact, yet has a long focal length and achieves high optical performance throughout the entire zoom range. [Examples]

[0043] Figure 5 shows a cross-sectional view of the zoom lens of Example 3 at the wide-angle end when focused at infinity. The zoom lens of Example 3 is composed of a first lens group B1 with positive refractive power, a second lens group B2 with negative refractive power, a third lens group B3 with positive refractive power, and a fourth lens group B4 with positive refractive power, arranged in order from the object side to the image side. When zooming from the wide-angle end to the telephoto end, the second lens group B2 moves towards the image side, and the fourth lens group B4 moves towards the object side along a convex trajectory. The first lens group B1 and the third lens group B3 are immovable (fixed). In addition, in the zoom lens of Example 3, the focusing lens group is the fourth lens group B4, which moves towards the object side when focusing from infinity to close.

[0044] The first lens group B1 consists of positive lenses L11 and L12, and a cemented lens formed by positive lens L13 and negative lens L14. The second lens group B2 consists of negative lens L21, and a cemented lens formed by negative lens L22 and positive lens L23. The third lens group B3 consists of positive lens L31, a cemented lens formed by positive lens L32 and negative lens L33, positive lens L34, a cemented lens formed by positive lens L35 and negative lens L36, positive lens L37, and negative lens L38. An aperture diaphragm AP is positioned adjacent to the object side of the third lens group B3. The fourth lens group B4 consists of negative lens L41 and positive lens L42.

[0045] Figures 6(A), (B), and (C) show the longitudinal aberrations (spherical aberration, astigmatism, distortion, and chromatic aberration) of the zoom lens of Example 3 at the wide-angle end, intermediate focal length, and telephoto end, respectively, when the lens is in focus at infinity. As shown in Figure 6, the zoom lens of Example 3 has well corrected aberrations throughout the entire zoom range, achieving high optical performance. Furthermore, Table 1 shows the values ​​corresponding to the conditional equations (1) to (8) in Example 3. The zoom lens of Example 3 satisfies all of the conditional equations (1) to (8), has a short overall length and is compact, yet has a long focal length and achieves high optical performance throughout the entire zoom range. [Examples]

[0046] Figure 7 shows a cross-sectional view of the zoom lens of Example 4 at the wide-angle end when focused at infinity. The zoom lens of Example 4 is composed of a first lens group B1 with positive refractive power, a second lens group B2 with negative refractive power, a third lens group B3 with positive refractive power, a fourth lens group B4 with negative refractive power, a fifth lens group B5 with positive refractive power, and a sixth lens group B6 with negative refractive power, arranged in order from the object side to the image side. When zooming from the wide-angle end to the telephoto end, the second lens group B2 moves toward the image side, the fourth lens group B4 moves toward the image side along a convex trajectory, and the fifth lens group B5 also moves toward the image side. The first lens group B1, the third lens group B3, and the sixth lens group B6 are fixed. In addition, in the zoom lens of Example 4, the focusing lens group is the fourth lens group B4, which moves toward the image side when focusing from infinity to close.

[0047] The first lens group B1 consists of positive lenses L11, L12, L13, and a cemented lens of positive lens L14 and negative lens L15. The second lens group B2 consists of positive lens L21, negative lens L22, and a cemented lens of negative lens L23 and positive lens L24. The third lens group B3 consists of positive lens L31, a cemented lens of positive lens L32 and negative lens L33, positive lens L34, negative lens L35, positive lens L36, and negative lens L37. An aperture diaphragm AP is positioned adjacent to the object side of the third lens group B3. The fourth lens group B4 consists of a cemented lens of positive lens L41 and negative lens L42. The fifth lens group B5 consists of positive lens L51. The sixth lens group B6 consists of negative lens L61.

[0048] Figures 8(A), (B), and (C) show the longitudinal aberrations (spherical aberration, astigmatism, distortion, and chromatic aberration) of the zoom lens of Example 4 at the wide-angle end, intermediate focal length, and telephoto end, respectively, when the lens is in focus at infinity. As shown in Figure 8, the zoom lens of Example 4 has well corrected aberrations throughout the entire zoom range, achieving high optical performance. Furthermore, Table 1 shows the values ​​corresponding to the conditions (1) to (8) in the numerical example 4. The zoom lens of numerical example 4 satisfies all of the conditions (1) to (8), has a short overall length and is compact, yet has a long focal length and achieves high optical performance throughout the entire zoom range. [Examples]

[0049] Figure 9 shows a cross-sectional view of the zoom lens of Example 5 at the wide-angle end when focused at infinity. The zoom lens of Example 5 is composed of a first lens group B1 with positive refractive power, a second lens group B2 with negative refractive power, a third lens group B3 with positive refractive power, a fourth lens group B4 with positive refractive power, and a fifth lens group B5 with negative refractive power, arranged in order from the object side to the image side. When zooming from the wide-angle end to the telephoto end, the second lens group B2 moves toward the image side, and the fourth lens group B4 moves toward the object side along a convex trajectory. The first lens group B1, the third lens group B3, and the fifth lens group B5 are immovable (fixed). In addition, in the zoom lens of Example 5, the focusing lens group is the fourth lens group B4, which moves toward the object side when focusing from infinity to close.

[0050] The first lens group B1 consists of positive lenses L11 and L12, and a cemented lens formed by positive lens L13 and negative lens L14. The second lens group B2 consists of negative lens L21, and a cemented lens formed by negative lens L22 and positive lens L23. The third lens group B3 consists of positive lens L31, a cemented lens formed by positive lens L32 and negative lens L33, positive lens L34, a cemented lens formed by positive lens L35 and negative lens L36, positive lens L37, and negative lens L38. An aperture diaphragm AP is positioned adjacent to the object side of the third lens group B3. The fourth lens group B4 consists of negative lens L41 and positive lens L42. The fifth lens group B5 consists of negative lens L51.

[0051] Figures 10(A), (B), and (C) show the longitudinal aberrations (spherical aberration, astigmatism, distortion, and chromatic aberration) of the zoom lens of Example 5 at the wide-angle end, intermediate focal length, and telephoto end, respectively, when the lens is in focus at infinity. As shown in Figure 10, the zoom lens of Example 5 has well corrected aberrations throughout the entire zoom range, achieving high optical performance. Furthermore, Table 1 shows the values ​​corresponding to the conditions (1) to (8) in Example 5. The zoom lens of Example 5 satisfies all of the conditions (1) to (8), has a short overall length and is compact, yet has a long focal length and achieves high optical performance throughout the entire zoom range.

[0052] The following shows the numerical examples 1 to 5 corresponding to each example. In each numerical example, the surface number i indicates the order of the surfaces 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 gap on the optical axis between the i-th and (i+1)-th surfaces (mm), and nd is the refractive index of the optical material at the d-line between the i-th and (i+1)-th surfaces. νd is the Abbe number with respect to the d-line of the optical material between the i-th and (i+1)-th surfaces.

[0053] BF represents the back focus (mm) mentioned above. The total length of the lens is the distance along the optical axis from the lens surface closest to the object (frontmost) to the lens surface closest to the image (final surface) of the zoom lens, plus the back focus.

[0054] [Numerical Example 1] Unit: mm Surface data Face number rd nd vd 1 143.301 4.00 1.49700 81.5 2 -143.301 0.86 3 43.346 4.50 1.49700 81.5 4 204.347 5.32 5 64.250 3.16 1.49700 81.5 6 -443.596 1.37 1.83481 42.7 7 53.168 (variable) 8 ∞ 0.95 1.59522 67.7 9 32.344 4.70 10 -33.796 0.95 1.49700 81.5 11 45.658 1.61 1.85478 24.8 12 162.512 (variable) 13 (aperture) ∞ 1.62 14 64.625 3.67 1.49700 81.5 15 -106.104 0.20 16 65.536 4.63 1.43875 94.7 17 -28.392 0.90 1.83481 42.7 18 -74.232 0.20 19 21.767 5.18 1.49700 81.5 20 -222.111 0.20 21 19.664 4.06 1.49700 81.5 22 175.622 1.00 1.61340 44.3 23 14.186 9.91 24 115.698 1.81 1.59551 39.2 25 -35.993 1.10 26 -16.761 0.70 1.49700 81.5 27 ∞ (Variable) 28 -198.571 1.33 1.51742 52.4 29 -32.801 0.70 1.49700 81.5 30 19.836 (Variable) 31 23.374 6.44 1.49700 81.5 32 -80.043 5.48 33 ∞ 1.20 1.51633 64.1 34 ∞ 5.35 Image plane ∞ Various data Zoom ratio 1.99 Wide-angle, Medium, Telephoto Focal length 58.51 82.24 116.49 F-number 3.30 3.30 3.30 Half-angle 10.40 7.35 5.19 Image height 10.75 10.75 10.75 Lens length 128.00 128.00 128.00 BF 5.35 5.35 5.35 d 7 2.77 13.87 24.96 d12 25.02 13.92 2.82 d27 2.50 4.56 2.50 d30 14.59 12.53 14.59 Zoom lens group data Group starting plane focal length 1 1 104.22 2 8 -31.60 3 13 29.73 4 28 -36.88 5 31 37.17

[0055] [Numerical Example 2] Unit: mm Surface data Face number rd nd vd 1 88.493 5.34 1.43875 94.7 2 -215.190 0.20 3 50.708 5.71 1.43875 94.7 4 1241.649 0.96 5 59.863 4.84 1.43875 94.7 6 -282.076 1.37 1.75500 52.3 7 52.783 (variable) 8 -128.132 1.10 1.68893 31.1 9 -84.507 0.28 10 -60.277 0.95 1.49700 81.5 11 23.351 3.09 12 -36.802 0.95 1.43875 94.7 13 27.297 2.00 1.83481 42.7 14 97.331 (Variable) 15 (aperture) ∞ 1.85 16 65.387 1.91 1.49700 81.5 17 -128.825 0.20 18 68.148 4.11 1.43875 94.7 19 -22.383 0.90 1.74100 52.6 20 -89.436 0.20 21 23.129 4.46 1.53775 74.7 22 -82.940 1.10 23 20.149 3.95 1.43875 94.7 24 -172.560 1.00 1.61340 44.3 25 15.298 8.18 26 8215.510 1.71 1.83481 42.7 27 -29.834 1.02 28 -17.232 0.70 1.69680 55.5 29 -52.439 (variable) 30 -174.925 1.07 1.62004 36.3 31 -42.673 0.70 1.49700 81.5 32 18.803 (Variable) 33 19.631 7.89 1.43875 94.7 34 -121.740 4.00 35 ∞ 1.20 1.51633 64.1 36 ∞ 5.35 Image plane ∞ Various data Zoom ratio 3.01 Wide-angle, Medium, Telephoto Focal length 38.70 64.87 116.50 F-number 3.30 3.30 3.30 Half-angle 16.20 9.39 5.20 Image height 10.75 10.75 10.75 Lens length 135.00 135.00 135.00 BF 5.35 5.35 5.35 d 7 3.37 20.82 38.28 d14 37.82 20.36 2.90 d29 2.50 6.38 3.96 d32 13.03 9.15 11.57 Zoom lens group data Group starting plane focal length 1 1 109.22 2 8 -29.88 3 15 29.59 4 30 -36.82 5 33 39.20

[0056] [Numerical Example 3] Unit: mm Surface data Face number rd nd vd 1 74.819 4.55 1.49700 81.5 2 -241.355 0.20 3 40.414 4.49 1.49700 81.5 4 160.126 3.42 5 45.446 3.75 1.43875 94.7 6 3037.472 1.37 1.78800 47.4 7 35.650 (Variable) 8 -143.023 0.95 1.53775 74.7 9 34.815 2.54 10 -39.285 0.95 1.49700 81.5 11 40.987 1.49 1.85478 24.8 12 110.132 (variable) 13 (aperture) ∞ 1.72 14 69.277 2.75 1.49700 81.5 15 -69.443 0.20 16 71.912 3.65 1.43875 94.7 17 -35.566 0.90 1.90525 35.0 18 -166.264 0.20 19 30.989 3.73 1.49700 81.5 20 -136.894 9.59 21 20.029 4.60 1.49700 81.5 22 -54.959 2.38 1.53996 59.5 23 13.577 8.30 24 -50.805 1.52 1.95906 17.5 25 -30.717 1.15 26 -16.694 0.81 1.43875 94.7 27 -105.727 (variable) 28 -46.095 1.00 1.95906 17.5 29 -118.240 0.20 30 46.662 3.64 1.77250 49.6 31 -61.707 (variable) 32 ∞ 1.20 1.51633 64.1 33 ∞ 5.35 Image plane ∞ Various data Zoom ratio 1.99 Wide-angle, Medium, Telephoto Focal length 58.50 78.43 116.50 F-number 3.30 3.30 3.30 Half-angle 10.50 7.84 5.21 Image height 10.75 10.75 10.75 Lens length 128.00 128.00 128.00 BF 5.35 5.35 5.35 d 7 3.58 15.11 26.64 d12 26.00 14.47 2.94 d27 14.92 9.00 12.65 d31 6.89 12.82 9.17 Zoom lens group data Group starting plane focal length 1 1 109.25 2 8 -31.60 3 13 33.20 4 28 59.74

[0057] [Numerical Example 4] Unit: mm Surface data Face number rd nd vd 1 165.501 4.33 1.49700 81.5 2 -281.358 0.20 3 54.623 5.29 1.43875 94.7 4 180.189 0.20 5 34.133 5.92 1.43875 94.7 6 69.592 0.20 7 37.484 9.07 1.49700 81.5 8 71.908 2.97 1.88300 40.8 9 23.358 (variable) 10 265.298 1.28 1.95906 17.5 11 -251.546 2.64 12 -178.936 0.95 1.88300 40.8 13 39.103 2.85 14 -44.324 0.95 1.53775 74.7 15 41.711 2.09 1.85478 24.8 16 251.569 (variable) 17 (aperture) ∞ 1.69 18 78.368 2.03 1.69680 55.5 19 -227.140 0.20 20 59.844 4.40 1.41390 101.0 21 -34.604 0.90 2.00069 25.5 22 -103.041 0.20 23 23.751 5.38 1.43875 94.7 24 -111.822 4.70 25 15.921 1.21 1.95906 17.5 26 13.597 6.60 27 -86.936 1.61 1.77830 23.9 28 -27.955 1.10 29 -19.641 0.70 1.63854 55.4 30 -107.207 (variable) 31 200.885 1.92 1.59551 39.2 32 -33.166 0.70 1.59522 67.7 33 24.527 (Variable) 34 35.208 7.01 1.59551 39.2 35 -42.335 (variable) 36 -47.444 0.60 1.92286 18.9 37 -112.482 6.64 38 ∞ 1.20 1.51633 64.1 39 ∞ 5.35 Image plane ∞ Various data Zoom ratio 1.52 Wide-angle, Medium, Telephoto Focal length 105.00 129.96 160.00 F-number 3.30 3.30 3.30 Half-angle 5.79 4.67 3.78 Image height 10.75 10.75 10.75 Lens length 139.00 139.00 139.00 BF 5.35 5.35 5.35 d 9 5.00 11.45 17.89 d16 15.63 9.19 2.74 d30 7.54 6.77 2.50 d33 10.13 13.46 20.29 d35 7.62 5.06 2.50 Zoom lens group data Group starting plane focal length 1 1 118.53 2 10 -36.16 3 17 38.05 4 31 -47.22 5 34 33.41 6 36 -89.31

[0058] [Numerical Example 5] Unit: mm Surface data Face number rd nd vd 1 81.876 3.97 1.49700 81.5 2 -300.066 0.20 3 39.410 3.39 1.49700 81.5 4 78.961 0.20 5 39.859 4.63 1.49700 81.5 6 110.375 1.37 1.80400 46.5 7 32.779 (variable) 8 -126.412 0.95 1.49700 81.5 9 52.997 2.00 10 -60.985 0.95 1.43875 94.7 11 45.932 1.27 1.85478 24.8 12 81.109 (variable) 13 (aperture) ∞ 1.46 14 57.697 2.23 1.49700 81.5 15 -500.414 0.20 16 78.300 4.12 1.43875 94.7 17 -31.803 0.90 1.88300 40.8 18 -92.678 0.20 19 27.974 4.28 1.49700 81.5 20 -153.901 5.58 21 21.895 3.57 1.49700 81.5 22 63.417 3.00 1.61340 44.3 23 15.039 9.83 24 -207.893 1.80 1.84666 23.8 25 -37.990 1.15 26 -16.864 0.80 1.49700 81.5 27 115.660 (variable) 28 -57.831 1.80 1.95906 17.5 29 -117.240 0.02 30 37.980 5.44 1.51823 58.9 31 -53.023 (variable) 32 -43.504 0.60 1.43875 94.7 33 -54.960 4.00 34 ∞ 1.20 1.51633 64.1 35 ∞ 5.35 Image plane ∞ Various data Zoom ratio 1.99 Wide-angle, Medium, Telephoto Focal length 58.50 80.12 116.50 F-number 3.30 3.30 3.30 Half-angle 10.60 7.66 5.20 Image height 10.75 10.75 10.75 Lens length 128.00 128.00 128.00 BF 5.35 5.35 5.35 d 7 4.17 18.74 33.32 d12 32.36 17.78 3.21 d27 6.08 4.73 12.10 d31 8.93 10.28 2.91 Zoom lens group data Group starting plane focal length 1 1 128.40 2 8 -44.72 3 13 39.97 4 28 65.34 5 32 -483.42

[0059] [Table 1]

[0060] [Imaging device] An embodiment of an imaging device (surveillance camera) using the zoom lens of the present invention as an imaging optical system will be described with reference to Figure 11. Figure 11 shows an example of a surveillance camera as an imaging device equipped with any of the zoom lenses of Embodiments 1 to 5. In Figure 11, 15 is an imaging optical system composed of any of the zoom lenses of Embodiments 1 to 5, and 11 is the camera body. 12 is an image sensor (photoelectric conversion element) such as a CCD sensor or CMOS sensor that photoelectrically converts the subject image formed by the imaging optical system 15 (that is, it images the subject through the zoom lens).

[0061] 13 is a recording unit that records image data generated from the signal from the image sensor 12. 14 is a transfer cable for transferring image data. In addition, in surveillance cameras that have both daytime and nighttime imaging modes, optical filters such as IR cut filters and visible light cut filters may be inserted and removed using an insertion / removal mechanism (not shown).

[0062] Furthermore, the zoom lenses of each embodiment may be used with various imaging devices other than surveillance cameras, such as video cameras and digital cameras. In addition, the imaging device may be equipped with a circuit to electrically correct aberration components in the image data.

[0063] By using the zoom lenses of each embodiment in imaging devices such as surveillance cameras, it is possible to realize imaging devices that are compact and have a short overall length, yet have a long focal length and high optical performance across the entire zoom range.

[0064] This embodiment includes the following configuration. (Composition 1) 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, and at least one subsequent lens group. When zooming from the wide-angle end to the telephoto end, the spacing between adjacent lens groups changes, while the third lens group remains stationary with respect to the image plane. The aforementioned at least one subsequent lens group includes a focusing lens group that moves when focusing from infinity to near distance. The third lens group includes at least two positive lenses, When the focal length of the second lens group is f2, the focal length of the third lens group is f3, the focal length of the focusing lens group is f_focus, and the average of the focal lengths of the lens with the strongest refractive power and the lens with the second strongest refractive power among the positive lenses included in the third lens group is f3p12_ave, 1.00 <f3p12_ave / f3<1.55 0.90 < |f2 / f3| < 1.25 1.20 < |f_focus / f3| < 1.90 A zoom lens characterized by meeting certain conditions. (Configuration 2) When the focal length of the first lens group is f1, 2.00 <f1 / f3<4.50 A zoom lens according to configuration 1, characterized in that it satisfies the following conditions. (Composition 3) When the Abbe number with respect to the d line is νd and the partial dispersion ratio is θgF, the third lens group is 65.00 < νd < 105.00 0.640 < θgF + 0.00167 × νd < 0.715 A zoom lens according to configuration 1 or 2, characterized by including two or more positive lenses that satisfy the following conditions. (Composition 4) The zoom lens according to any one of configurations 1 to 3, characterized in that the third lens group includes at least two negative lenses. (Composition 5) The zoom lens according to any one of configurations 1 to 4, characterized in that the first lens group remains stationary during zooming. (Composition 6) The zoom lens according to any one of configurations 1 to 5, characterized in that the focusing lens group includes a positive lens and a negative lens. (Composition 7) Having an opening diaphragm, When D_B1APt is the distance along the optical axis from the lens surface closest to the object at the telephoto end to the aperture diaphragm, and TLt is the distance along the optical axis from the lens surface closest to the object at the telephoto end to the image plane, 0.35 <D_B1APt / TLt<0.55 A zoom lens described in any of configurations 1 to 6, characterized by satisfying the following conditions. (Composition 8) When the focal length at the wide-angle end is fw and the back focus at the wide-angle end is bfw, 0.05 <bfw / fw<0.35 A zoom lens described in any of configurations 1 to 7, characterized by satisfying the following conditions. (Composition 9) 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, and at least one subsequent lens group. When zooming from the wide-angle end to the telephoto end, the spacing between adjacent lens groups changes, while the first and third lens groups remain stationary with respect to the image plane. The aforementioned at least one subsequent lens group includes a focusing lens group that moves when focusing from infinity to near distance. The third lens group is characterized by including at least two positive lenses in the zoom lens. (Composition 10) An imaging device characterized by having a zoom lens as described in any of configurations 1 to 9, and an image sensor for capturing an image formed by the zoom lens. [Explanation of symbols]

[0065] B1 First lens group B2 Second lens group B3 Third lens group B4 4th lens group B5 5th lens group B6 6th lens group

Claims

1. 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, and at least one subsequent lens group. When zooming from the wide-angle end to the telephoto end, the spacing between adjacent lens groups changes, while the third lens group remains stationary with respect to the image plane. The aforementioned at least one subsequent lens group includes a focusing lens group that moves when focusing from infinity to near distance. The third lens group includes at least two positive lenses, When the focal length of the second lens group is f2, the focal length of the third lens group is f3, the focal length of the focusing lens group is f_focus, and the average of the focal lengths of the lens with the strongest refractive power and the lens with the second strongest refractive power among the positive lenses included in the third lens group is f3p12_ave, 1.00<f3p12_ave / f3<1.55 0.90<|f2 / f3|<1.25 1.20<|f_focus / f3|<1.90 A zoom lens characterized by meeting certain conditions.

2. When the focal length of the first lens group is f1, 2.00<f1 / f3<4.50 A zoom lens according to claim 1, characterized by satisfying the following conditions.

3. When the Abbe number with respect to the d line is νd and the partial dispersion ratio is θgF, the third lens group is 65.00<νd<105.00 0.640<θgF+0.00167×νd<0.715 The zoom lens according to claim 1, characterized by including two or more positive lenses that satisfy the following conditions.

4. The zoom lens according to claim 1, characterized in that the third lens group includes at least two negative lenses.

5. The zoom lens according to claim 1, characterized in that the first lens group remains stationary during zooming.

6. The zoom lens according to claim 1, characterized in that the focusing lens group includes a positive lens and a negative lens.

7. Having an opening diaphragm, When D_B1APt is the distance along the optical axis from the lens surface closest to the object at the telephoto end to the aperture diaphragm, and TLt is the distance along the optical axis from the lens surface closest to the object at the telephoto end to the image plane, 0.35<D_B1APt / TLt<0.55 A zoom lens according to claim 1, characterized by satisfying the following conditions.

8. When the focal length at the wide-angle end is fw and the back focus at the wide-angle end is bfw, 0.05<bfw / fw<0.35 A zoom lens according to claim 1, characterized by satisfying the following conditions.

9. 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, and at least one subsequent lens group. When zooming from the wide-angle end to the telephoto end, the spacing between adjacent lens groups changes, while the first and third lens groups remain stationary with respect to the image plane. The aforementioned at least one subsequent lens group includes a focusing lens group that moves when focusing from infinity to near distance. The zoom lens is characterized in that the third lens group includes at least two positive lenses.

10. An imaging device characterized by having a zoom lens according to any one of claims 1 to 9, and an image sensor for capturing an image formed by the zoom lens.

Images