Zoom lens, and imaging device

Abstract

To provide a standard zoom lens that is high in optical performance while achieving a lightweight focus group, and to provide an imaging device that includes the zoom lens.SOLUTION: A zoom lens according to the present invention comprises, with the broadest air gap at a wide-angle end as a boundary: a front group (G1 and G2) that has negative refractive power on an object side; and a rear group (G3, G4, and G5) on an image side. The zoom lens is configured to vary power from the wide-angle end to a telephoto end by changing an air gap between lens groups so as to reduce at least an air gap between the front group and the rear group, in which the rear group includes a focus group F that consists of a cemented lens having a lens Lp with positive refractive power and a lens Ln with the negative refractive power cemented; move the focus group F in an optical axis direction to thereby focus on a close object from infinity; and satisfy a predetermined condition.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a zoom lens and an imaging device, and more particularly to a zoom lens and an imaging device suitable for imaging devices using solid-state imaging elements (CCD, CMOS, etc.) such as digital still cameras and digital video cameras. [Background technology]

[0002] Imaging devices using solid-state imaging elements, such as digital still cameras, digital video cameras, single-lens reflex cameras, and mirrorless cameras, have become widespread. These imaging devices commonly use imaging lenses known as standard zoom lenses. A standard zoom lens generally refers to a zoom lens whose zoom range includes a focal length equivalent to 50 mm in 35 mm format.

[0003] For example, Patent Document 1 proposes a standard zoom lens that is composed of, in order from the object side, a first lens group having positive refractive power, a second lens group having negative refractive power, a third lens group having positive refractive power, and a fourth lens group having positive refractive power. In this zoom lens, the second lens group is moved toward the object side to focus on a subject. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-3195 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the zoom lens disclosed in Patent Document 1, the second lens group, which is primarily responsible for the zooming function, is used as the focusing group. The second lens group has a large number of lenses and is heavy compared to the other lens groups. This makes it difficult to perform quick autofocus. Furthermore, because the second lens group is heavy, the drive mechanism for moving the second lens group during focusing also becomes large. This results in an increase in the size and weight of the entire lens unit, including the lens barrel.

[0006] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a standard zoom lens system that has a lightweight focus group and high optical performance, and an imaging device equipped with the zoom lens system. [Means for solving the problem]

[0007] In order to solve the above-mentioned problems, a zoom lens according to one aspect of the present invention provides a zoom lens, wherein a lens group located closer to the object side than the widest air space at the wide-angle end is defined as a front group and a lens group located closer to the image side than the widest air space at the wide-angle end is defined as a rear group, the front group has negative refractive power as a whole and the rear group has positive refractive power as a whole, the zoom lens changes magnification from the wide-angle end to the telephoto end by changing the air space between the lens groups so as to reduce at least the air space between the front group and the rear group, the rear group includes a focus group formed of a cemented lens in which a lens Lp having positive refractive power and a lens Ln having negative refractive power are cemented together, and focusing from infinity to a close object is performed by moving the focus group in the optical axis direction, the rear group has at least one lens Lrn having negative refractive power located closer to the object than the focus group, at least one lens group is fixed in the optical axis direction during zooming, and the following conditions are satisfied: (1) 15.0 < νdLp < 35.0 (2) 53.186 ≦ νdLn < 98.0 (7-4)2.5 < |{1-(βft×βft)}×βftr×βftr|< 15.00 (15-3)1.962 ≦ NdLrn < 2.10 however, νdLp: Abbe number at the d line of the lens Lp νdLn: Abbe number of the lens Ln at the d line βft: lateral magnification of the focus group at the telephoto end when focused at infinity βftr: the combined lateral magnification of all lenses arranged on the image side of the focus group at the telephoto end when focused at infinity NdLrn: refractive index at the d line of the lens Lrn In order to solve the above-mentioned problems, a zoom lens according to another aspect of the present invention provides a zoom lens, wherein a lens group located closer to the object side than the widest air space at the wide-angle end is defined as a front group and a lens group located closer to the image side than the widest air space at the wide-angle end is defined as a rear group, the front group has negative refractive power as a whole and the rear group has positive refractive power as a whole, the magnification is changed by changing the air space between the lens groups so as to reduce at least the air space between the front group and the rear group, the rear group includes a focus group formed of a cemented lens in which a lens Lp having positive refractive power and a lens Ln having negative refractive power are cemented together, and focusing from infinity to a close object is performed by moving the focus group in the optical axis direction, and the rear group has at least one lens Lrn having negative refractive power located closer to the object than the focus group, and the following condition is satisfied: (1) 15.0 < νdLp < 35.0 (2) 53.186 ≦ νdLn < 98.0 (4-1)5.10 < Cr1f / fw (7-4)2.50 < |{1-(βft×βft)}×βftr×βftr|< 15.00 (15-3)1.962 ≦ NdLrn < 2.10 however, νdLp: Abbe number at the d line of the lens Lp νdLn: Abbe number of the lens Ln at the d line Cr1f: Radius of curvature of the surface of the zoom lens closest to the object fw: focal length of the zoom lens at the wide-angle end βft: lateral magnification of the focus group at the telephoto end when focused at infinity βftr: the combined lateral magnification of all lenses arranged on the image side of the focus group at the telephoto end when focused at infinity NdLrn: refractive index at the d line of the lens Lrn

[0008] In addition, in order to solve the above problem, the imaging device of the present invention is characterized by comprising the zoom lens of the present invention and an imaging element on the image side of the zoom lens that converts an optical image formed by the zoom lens into an electrical signal. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a standard zoom lens with high optical performance while reducing the weight of the focus group, and an imaging device equipped with the zoom lens. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a cross-sectional view showing an example of the lens configuration of a zoom lens according to a first embodiment of the present invention at the wide-angle end when focusing on infinity. [Figure 2] 3A to 3C are diagrams illustrating spherical aberration, astigmatism, and distortion of the zoom lens of Example 1 at the wide-angle end when focused on infinity. [Figure 3] 3A to 3C are diagrams illustrating spherical aberration, astigmatism, and distortion of the zoom lens of Example 1 when focused on infinity in an intermediate focal length state. [Figure 4] 3A to 3C are diagrams illustrating spherical aberration, astigmatism, and distortion of the zoom lens of Example 1 at the telephoto end when focused on infinity. [Figure 5] FIG. 10 is a cross-sectional view showing an example of the lens configuration of a zoom lens according to Reference Example 2 of the present invention at the wide-angle end when focusing on infinity. [Figure 6] 10A to 10C are diagrams illustrating spherical aberration, astigmatism, and distortion of the zoom lens of Reference Example 2 when focused on infinity at the wide-angle end. [Figure 7] 10A to 10C are diagrams illustrating spherical aberration, astigmatism, and distortion of the zoom lens of Reference Example 2 when focused on infinity in an intermediate focal length state. [Figure 8]10A to 10C are diagrams illustrating spherical aberration, astigmatism, and distortion of the zoom lens of Reference Example 2 when focused on infinity at the telephoto end. [Figure 9] FIG. 11 is a cross-sectional view showing an example of the lens configuration of a zoom lens of Reference Example 3 at the wide-angle end when focusing on infinity. [Figure 10] 10A to 10C are diagrams illustrating spherical aberration, astigmatism, and distortion of the zoom lens of Reference Example 3 when focused on infinity at the wide-angle end. [Figure 11] 10A to 10C are diagrams illustrating spherical aberration, astigmatism, and distortion of the zoom lens of Reference Example 3 when focused on infinity in an intermediate focal length state. [Figure 12] 10A to 10C are diagrams illustrating spherical aberration, astigmatism, and distortion of the zoom lens of Reference Example 3 when focused on infinity at the telephoto end. [Figure 13] FIG. 10 is a cross-sectional view showing an example of the lens configuration of a zoom lens according to a second embodiment of the present invention at the wide-angle end when focusing on infinity. [Figure 14] 10A to 10C are diagrams illustrating spherical aberration, astigmatism, and distortion of the zoom lens of Example 2 when focused on infinity at the wide-angle end. [Figure 15] 10A to 10C are diagrams illustrating spherical aberration, astigmatism, and distortion of the zoom lens of Example 2 when focused on infinity in an intermediate focal length state. [Figure 16] 10A to 10C are diagrams illustrating spherical aberration, astigmatism, and distortion of the zoom lens of Example 2 when focused on infinity at the telephoto end. DETAILED DESCRIPTION OF THE INVENTION

[0011] The following describes an embodiment of a zoom lens and an imaging device according to the present invention. However, the zoom lens and imaging device described below are one aspect of the zoom lens and imaging device according to the present invention, and the zoom lens and imaging device according to the present invention are not limited to the following aspects.

[0012] 1. Zoom Lens 1-1.Optical structure of a zoom lens First, the optical configuration of the zoom lens of this embodiment will be described. In the zoom lens of this embodiment, the lens group located closer to the object than the widest air space at the wide-angle end is defined as the front group, and the lens group located closer to the image than the rear group. The front group has negative refractive power as a whole, and the rear group has positive refractive power as a whole. In this zoom lens, when changing magnification from the wide-angle end to the telephoto end, the air space between the lens groups is changed so as to reduce at least the air space between the front group and the rear group. The rear group includes a focus group formed by a cemented lens in which a lens Lp having positive refractive power and a lens Ln having negative refractive power are cemented together, and focusing from infinity to a close object is performed by moving the focus group along the optical axis.

[0013] This zoom lens employs a retrofocus power arrangement in which the front group has a diverging effect and the rear group has a converging effect, with the widest air gap at the wide-angle end as the boundary. This facilitates achieving a wide angle of view at the wide-angle end without increasing the size of the zoom lens. In other words, because this zoom lens employs a power arrangement suitable for standard zoom lenses, it achieves a wide angle of view at the wide-angle end, while ensuring a back focus suitable for interchangeable lens systems such as single-lens reflex cameras and achieving a compact overall design. However, this zoom lens must have a focal length equivalent to 50mm in 35mm format within its zoom range, and the half angle of view (ω) of the zoom lens at the wide-angle end must be greater than 24°.

[0014] In this zoom lens, the front group has negative refractive power and the rear group has positive refractive power, reducing the air gap between the front and rear groups when changing magnification from the wide-angle end to the telephoto end. While the angle of incidence of light on the front group fluctuates with magnification, the angle of incidence of light on the rear group fluctuates only slightly. Therefore, by placing the focus group in the rear group, fluctuations in the angle of view during focusing can be suppressed. Therefore, fluctuations in the angle of view are small even when wobbling is performed, making this a zoom lens that is also suitable for video capture.

[0015] Furthermore, in this zoom lens, the diameter of the light beam incident on the rear group is smaller than the diameter of the light beam incident on the front group. Therefore, by placing the focus group in the rear group, it is possible to reduce the size and weight of the focus group compared to when the focus group is placed in the front group. Furthermore, in this zoom lens, because the focus group is composed of the above-mentioned cemented lens, it is even easier to reduce the size and weight of the focus group compared to when the focus group is composed of multiple single lenses spaced apart by air. Next, the optical configuration of this zoom lens will be described in more detail.

[0016] (1) The widest air gap at the wide-angle end First, we will explain the air spacing between the front and rear groups. This zoom lens is composed of multiple lens groups. The air spacing between each lens group changes when zooming from the wide-angle end to the telephoto end. The size of the air spacing between each lens group changes depending on the zoom position of the zoom lens. Therefore, in this invention, the air spacing between each lens group constituting the zoom lens, that is widest at the wide-angle end of the zoom lens, is referred to as the "widest air spacing at the wide-angle end." Here, when the air spacing between lens groups that changes depending on the zoom position of the zoom lens is referred to as a variable spacing, the "widest air spacing at the wide-angle end" refers to the largest variable spacing at the wide-angle end among the variable spacings between the lens group located closest to the object and the lens group located closest to the image in the zoom lens, and does not include the air spacing (back focus) between the lens group located closest to the image in the zoom lens and the imaging plane. One or more lens groups arranged on the object side of the "widest air gap at the wide-angle end" are referred to as the front group, and one or more lens groups arranged on the image side are referred to as the rear group.

[0017] (2) Front group The front group is a collective term for one or more lens groups that are located closer to the object than the "widest air gap at the wide-angle end." The front group has negative refractive power as a whole, and therefore includes at least one lens group with negative refractive power.

[0018] Among the lens groups with negative refractive power included in the front group, the lens group with the largest negative refractive power is referred to as negative lens group n. As long as the front group has this negative lens group n and has a negative refractive power as a whole, the configuration of the other lens groups is not particularly limited. For example, the front group may have two or more lens groups with negative refractive power, or one or more lens groups with positive refractive power.

[0019] However, from the viewpoint of being effective in increasing the diameter of the zoom lens, it is preferable that the front group has a lens group with positive refractive power closest to the object, and locating a lens group with negative refractive power on the image side of the lens group with positive refractive power in the front group is also effective in increasing the magnification of the zoom lens.

[0020] (3) Rear group The rear group is a collective term for one or more lens groups arranged closer to the image side than the "widest air gap at the wide-angle end." Since the rear group has positive refractive power overall, it includes at least one lens group with positive refractive power. The rear group is not particularly limited in its other lens group configuration, as long as it includes the focus group and has positive refractive power overall. For example, it may include two or more lens groups with positive refractive power, or one or more lens groups with negative refractive power. To achieve compactness in the zoom lens, it is preferable to arrange a lens group with positive refractive power closest to the object side of the rear group, but this is not particularly limited.

[0021] It is preferable that the rear group has at least one lens on the image side of the focus group. By arranging at least one lens on the image side of the focus group, it becomes easier to correct aberration fluctuations that accompany movement of the focus group during focusing on the image side of the focus group. In this case, the refractive power of the lens may be positive, but it is preferable that the lens have at least one lens surface Sr with negative refractive power. By arranging a lens having at least one lens surface Sr on the image side of the focus group, it becomes easier to reduce field curvature.

[0022] Furthermore, it is preferable that the rear group has at least one lens Lrn having negative refractive power on the object side of the focus group. By arranging the lens Lrn having negative refractive power closer to the object side than the focus group, it is possible to reduce the curvature of field and make it easier to reduce chromatic aberration. At the same time, the lens Lrn can reduce the aberrations that occur in the focus group. Therefore, it is easy to realize a zoom lens that has a small amount of aberrations that need to be corrected during focusing and has high optical performance throughout the entire focusing range.

[0023] (4) Focus group The focus group is one of the lens groups constituting the rear group, or a part thereof. As described above, the focus group is composed of a cemented lens in which a lens Lp having positive refractive power is cemented to a lens Ln having negative refractive power, and the order in which the lenses Lp and Ln are arranged is not particularly limited. Here, the lenses Lp and Ln are each single lenses. Note that in this specification, the single lenses may be either spherical lenses or aspherical lenses. Furthermore, the aspherical lenses also include so-called composite aspherical lenses with an aspherical film attached to their surfaces.

[0024] Because the focus group is composed of a cemented lens formed by cementing together lenses Lp and Ln, there is no air gap in the focus group. Therefore, compared to a focus group composed of multiple single lenses arranged with an air gap in between, the focus group in this zoom lens can be made smaller and lighter. As a result, the mechanical component for moving the focus group along the optical axis during focusing (hereinafter referred to as the "focus drive mechanism") can be made smaller and lighter, thereby enabling the entire zoom lens unit to be made smaller and lighter. It should be noted that the zoom lens unit includes, in addition to the zoom lens, a drive mechanism for moving each lens group relative to one another during magnification change (hereinafter referred to as the zoom drive mechanism), the focus drive mechanism, and a lens barrel that houses these components.

[0025] Furthermore, compared to a configuration in which the focus group is made up of multiple single lenses arranged with an air gap between them, by configuring the focus group only with the cemented lens, it is possible to reduce various manufacturing errors such as decentering errors and errors in the air gap between the single lenses. This makes it possible to reduce the degradation of optical performance caused by manufacturing errors and to reduce variations in performance between products. As a result, zoom lenses with high optical performance can be manufactured with a good yield.

[0026] Furthermore, it is preferable that the focus group has negative refractive power. In other words, it is preferable that the combined refractive power of the lenses Lp and Ln is negative. When the focus group has negative refractive power, the focus group can offset the curvature of field and distortion that occur in the front group, which has negative refractive power. This makes it possible to obtain a zoom lens with even higher optical performance.

[0027] Here, in the focus group, it is preferable that the lenses Lp and Ln are cemented in this order from the object side. As described above, the focus group is disposed in the rear group. In this case, compared with on-axis rays, off-axial rays pass through more peripheral portions of the cemented lenses that make up the focus group. In order to more effectively correct lateral chromatic aberration, it is preferable to dispose a lens with negative refractive power on the image side. Therefore, it is preferable that the lenses Lp and Ln are cemented in this order from the object side.

[0028] The focus group can also be configured from only one single lens, rather than a cemented lens. In this case, the same effects as those described above can be obtained compared to a configuration in which the focus group is configured from multiple single lenses with an air gap between them. Compared to a configuration in which the focus group is configured from a cemented lens, a focus group configured from only one single lens can be made lighter and more compact.

[0029] (5) Aperture diaphragm In the zoom lens, the arrangement of the aperture diaphragm is not particularly limited, but the aperture diaphragm referred to here refers to the aperture diaphragm that determines the diameter of the light beam of the zoom lens, i.e., the aperture diaphragm that determines the Fno of the zoom lens.

[0030] However, locating the aperture stop on the object side of the rear group or within the rear group is preferable in order to obtain good optical performance throughout the entire focusing range. As mentioned above, there is little variation in the diameter of the light beam incident on the rear group. Therefore, locating the aperture stop on the object side of the rear group or within the rear group can suppress aberration fluctuations during focusing.

[0031] (6) Lens group configuration The number of lens groups constituting the zoom lens is not particularly limited, but may be, for example, a five-group zoom lens consisting of a first lens group having positive refractive power, a second lens group having negative refractive power, a third lens group having positive refractive power, a fourth lens group having negative refractive power, and a fifth lens group having positive refractive power, with the third lens group and subsequent lens groups being rear groups, or a first lens group having negative refractive power, a second lens group having positive refractive power, and a third lens group having negative refractive power. Various lens group configurations can be employed, such as a four-group zoom lens consisting of a first lens group having positive refractive power, a second lens group having negative refractive power, a third lens group having positive refractive power, a fourth lens group having positive refractive power, a fifth lens group having negative refractive power, and a sixth lens group having positive refractive power, with the second lens group and subsequent lens groups being the rear group, or a six-group zoom lens consisting of a first lens group having positive refractive power, a second lens group having negative refractive power, a third lens group having positive refractive power, a fourth lens group having positive refractive power, a fifth lens group having negative refractive power, and a sixth lens group having positive refractive power, with the third lens group and subsequent lens groups being the rear group.The specific lens group configuration of the zoom lens is not particularly limited as long as it is configured to have, with the widest air space at the wide-angle end as the boundary, a front group having negative refractive power on the object side and a rear group having positive refractive power on the image side.

[0032] 1-2.Operation (1) Operation when changing magnification In this zoom lens, when changing magnification from the wide-angle end to the telephoto end, the air gap between the lens groups is changed so that the air gap between at least the front group and the rear group is reduced.

[0033] Here, if the front group and / or rear group includes multiple lens groups, the air spacing between each lens group also changes during zooming. When zooming from the wide-angle end to the telephoto end, it is sufficient that the air spacing between at least the front group and the rear group decreases, and there are no particular limitations on the increase or decrease in the air spacing between the other lens groups. Furthermore, during zooming, all of the lens groups constituting the zoom lens may move along the optical axis, or some of the lens groups may be fixed along the optical axis and the remaining lens groups may move along the optical axis. There are no particular limitations on whether or not each lens group moves, and the direction of movement.

[0034] Here, if the first lens group, which is located closest to the object in the zoom lens, is moved toward the object when changing magnification from the wide-angle end to the telephoto end, the overall optical length of the zoom lens at the wide-angle end can be shortened. In this case, if the lens barrel has a nested structure in which the inner barrel portion is housed in the outer barrel portion so that it can be extended, for example, when changing magnification from the wide-angle end to the telephoto end, the inner barrel portion is extended to move the first lens group toward the object, and when changing magnification from the telephoto end to the wide-angle end, the inner barrel portion is housed in the outer barrel, the lens barrel length at the wide-angle end can be shortened, and the zoom lens unit can be made more compact.

[0035] (2) Focusing behavior In this zoom lens, when focusing from infinity to a close object, the focus group disposed in the rear group moves in the direction of the optical axis. The direction of movement of the focus group when focusing is not particularly limited, but it is preferable that the focus group move toward the image side when focusing from infinity to a close object, for example.

[0036] Here, if the front group located on the object side has negative refractive power, the rear group located on the image side has positive refractive power, and a focus group consisting of the cemented lens is arranged in the rear group, the amount of axial chromatic aberration and spherical aberration occurring when capturing close-up images of a subject is smaller at the wide-angle end than at the telephoto end. Therefore, even if the shortest imaging distance at the wide-angle end is shorter than the shortest imaging distance at the telephoto end, the amount of each of the above aberrations occurring at the wide-angle end is small. Therefore, by shortening the shortest imaging distance at the wide-angle end compared to the shortest imaging distance at the telephoto end, the imaging angle of view can be appropriately selected according to the distance to the subject and the size of the subject, and the range of scenes that can be captured with the zoom lens can be expanded. Here, the shortest imaging distance (shortest shooting distance) refers to the shortest distance from the imaging plane to the subject.

[0037] In addition to the focus group consisting of the cemented lens, other lens groups or parts of the lens groups may also be moved during focusing. That is, focusing may be performed using a floating system. In an imaging lens that employs a retrofocus power arrangement, using a floating system makes it easier to correct aberrations during focusing, so focusing using the floating system is preferable in order to achieve a zoom lens with high optical performance.

[0038] However, the floating system requires moving multiple lens groups during focusing, which complicates the configuration of the focus drive mechanism. Therefore, in order to reduce the size and weight of the zoom lens, it is preferable to not use the floating system, but to move only the focus group composed of the cemented lens during focusing. In other words, it is preferable that the zoom lens does not include any lens group that moves on the optical axis during focusing other than the focus group.

[0039] In the present invention, even when focusing is performed by the floating method, it is sufficient that the focus group consisting of cemented lenses meets the configuration and conditions described in this specification. In other words, there are no particular limitations on the other lens groups or parts of lens groups that move together with the focus group during focusing.

[0040] 1-2.Conditional Expressions In this zoom lens, it is preferable that the above-mentioned configuration be adopted and that at least one of the following conditional expressions be satisfied.

[0041] 1-2-1.Conditional Expression (1) (1) 15.0 < νdLp < 35.0 νdLp: Abbe number at the d line of lens Lp

[0042] Conditional expression (1) defines the Abbe number of the lens Lp having positive refractive power that constitutes the cemented lens. When conditional expression (1) is satisfied, chromatic aberration is well corrected, and a zoom lens with high optical performance can be realized.

[0043] On the other hand, if the value of conditional formula (1) is equal to or less than the lower limit, chromatic aberration will be overcorrected, making it difficult to correct axial chromatic aberration when focusing on an object at a finite distance, which is undesirable. Furthermore, glass materials for which the value of conditional formula (1) is equal to or less than the lower limit are high refractive index materials and are expensive. Therefore, from the viewpoint of cost, it is undesirable for the value of conditional formula (1) to be equal to or less than the lower limit. On the other hand, if the value of conditional formula (1) is equal to or greater than the upper limit, chromatic aberration will be undercorrected, which is also undesirable.

[0044] To obtain the above effects, the lower limit of conditional formula (1) is preferably 18.0, and more preferably 22.0, and the upper limit of conditional formula (1) is preferably 34.0, more preferably 33.0, even more preferably 32.0, still more preferably 31.0, and even more preferably 30.0.

[0045] 1-2-2.Conditional Expression (2) (2) 45.0 < νdLn < 98.0 however, νdLn: Abbe number at the d line of lens Ln

[0046] Conditional formula (2) above defines the Abbe number of the lens Ln that constitutes the cemented lens. When conditional formula (2) is satisfied, chromatic aberration is well corrected, making it easy to realize a zoom lens with high optical performance. Furthermore, many glass materials that satisfy conditional formula (2) have a relatively low specific gravity, which is also effective in reducing the weight of the focus group.

[0047] On the other hand, if the value of conditional formula (2) is below the lower limit, the chromatic dispersion of the lens Ln becomes large, making it difficult to correct axial chromatic aberration when focusing on an object at a finite distance, which is undesirable. On the other hand, if the value of conditional formula (2) is above the upper limit, the chromatic dispersion of the lens Ln becomes small, which is preferable in terms of correcting chromatic aberration. However, glass materials with large Abbe numbers are more expensive than glass materials with small Abbe numbers. Using glass materials with Abbe numbers above the upper limit is effective in correcting chromatic aberration, but the effect is small in terms of cost-effectiveness. Therefore, it is undesirable from a cost perspective to have the value of conditional formula (2) exceed the upper limit.

[0048] To obtain these effects, the lower limit of conditional formula (2) is preferably 45.5, and more preferably 46.0, while the upper limit of conditional formula (2) is preferably 82.0, and more preferably 76.0, and even more preferably 68.0, and even more preferably 65.0, and even more preferably 62.0.

[0049] Here, as mentioned above, the focus group can be configured with only one single lens instead of a cemented lens. In that case, it is preferable that the focus group be configured with a single lens having negative refractive power, i.e., a lens similar to the lens Ln. Even when the focus group is configured with only a lens similar to the lens Ln, the same effect as above can be obtained.

[0050] However, by configuring the focus group from a cemented lens, and by having the lenses Lp and Ln that make up the cemented lens satisfy conditional expressions (1) and (2), respectively, it is possible to prevent problems such as good correction of longitudinal chromatic aberration at the wide-angle end but large lateral chromatic aberration, or good correction of longitudinal chromatic aberration at the telephoto end but large lateral chromatic aberration. In other words, it is possible to correct longitudinal chromatic aberration and lateral chromatic aberration in a well-balanced manner at both the wide-angle end and the telephoto end. Therefore, compared to a case in which the focus group is configured from only one single lens, chromatic aberration is corrected better throughout the entire zoom range, making it possible to achieve a zoom lens with even higher optical performance.

[0051] 1-2-3.Conditional Expression (3) (3)0.50 < (-ffw+Dfrw) / FBw < 1.95 however, ffw: Combined focal length of the front group at the wide-angle end Dfrw: The distance on the optical axis between the front group's surface closest to the image and the rear group's surface closest to the object at the wide-angle end FBw: Air equivalent length from the side of the zoom lens closest to the image plane at the wide-angle end

[0052] Conditional formula (3) defines the ratio of the focal point of the light beam entering the rear group to the focal point of the light beam emerging from the rear group at the wide-angle end. In conditional formula (3), the numerator represents the axial distance from the focal point of the light beam entering the rear group to the surface of the rear group closest to the object, and the denominator represents the so-called back focus, which represents the axial distance from the focal point of the light beam emerging from the rear group to the surface of the rear group closest to the image. Satisfying conditional formula (3) ensures an appropriate back focus suitable for an interchangeable lens system while enabling the zoom lens to be made compact. Here, the surface closest to the object in the front group refers to the lens surface of the front group that is located closest to the object, and the surface closest to the image in the rear group refers to the lens surface of the rear group that is located closest to the image.

[0053] On the other hand, if the value of conditional expression (3) is equal to or greater than the upper limit, the back focal length at the wide-angle end becomes short. This makes it difficult to ensure a back focal length suitable for an interchangeable lens system. Furthermore, if the value of conditional expression (3) is equal to or greater than the upper limit, this means that the focal point of the light beam entering the rear group is far away. In other words, the focal point of the light beam entering the rear group is closer to the object side, which increases the overall optical length at the wide-angle end, making it difficult to reduce the size of the zoom lens. For these reasons, it is preferable that the value of conditional expression (3) be less than the upper limit.

[0054] On the other hand, if the value of conditional expression (3) is equal to or less than the lower limit, the back focal length at the wide-angle end becomes long, making it easier to ensure a back focal length suitable for an interchangeable lens system. However, if the back focal length becomes too long, the total optical length at the wide-angle end becomes long. Therefore, in this case too, it becomes difficult to achieve a compact zoom lens. For these reasons, it is preferable that the value of conditional expression (3) be greater than the lower limit.

[0055] In order to obtain these effects, the lower limit of conditional formula (3) is preferably 0.60, more preferably 0.70, even more preferably 0.80, still more preferably 0.90, even more preferably 1.05, and still more preferably 1.15, and the upper limit of conditional formula (3) is preferably 1.93, and more preferably 1.91.

[0056] 1-2-4.Conditional Expression (4) (4) 2.00 < Cr1f / fw however, Cr1f: Radius of curvature of the surface of the zoom lens closest to the object fw: focal length of the zoom lens at the wide-angle end

[0057] Conditional expression (4) defines the ratio between the radius of curvature of the surface of the zoom lens closest to the object and the focal length of the zoom lens at the wide-angle end. A positive value for conditional expression (4) means that the surface of the zoom lens closest to the object is flat or has a convex shape facing the object. By satisfying conditional expression (4), the radius of curvature of the surface of the zoom lens closest to the object falls within an appropriate range for the focal length of the zoom lens at the wide-angle end, enabling well-balanced correction of distortion and curvature of field.

[0058] On the other hand, if the value of conditional expression (4) is equal to or less than the lower limit, the radius of curvature of the surface of the zoom lens closest to the object becomes too small relative to the focal length of the zoom lens at the wide-angle end, which is undesirable because distortion is overcorrected and correction of field curvature becomes difficult.

[0059] In order to obtain the above effects, the lower limit of conditional formula (4) is more preferably 2.50, even more preferably 3.00, even more preferably 4.00, even more preferably 4.20, even more preferably 4.50, even more preferably 4.80, and most preferably 5.10. There are no particular restrictions on the upper limit of conditional formula (4), but if an upper limit is set, it is preferably 500.00, more preferably 100.00, even more preferably 50.00, and even more preferably 40.00.

[0060] 1-2-5.Conditional Expression (5) (5)0.00 <(Crff+Crfr) / (Crff-Crfr)< 5.00 however, Crff: Radius of curvature of the focal group closest to the object Crfr: Radius of curvature of the focal group closest to the image

[0061] The above conditional expression (5) defines the shape of the cemented lens that constitutes the focus group. By ensuring that the shape of the cemented lens that constitutes the focus group satisfies the above conditional expression (5), it becomes possible to effectively correct spherical aberration, reduce aberration fluctuations when focusing on a close subject, and realize a zoom lens with high optical performance throughout the entire focusing range.

[0062] In order to obtain these effects, the lower limit of conditional formula (5) is more preferably 0.05, even more preferably 0.08, even more preferably 0.10, and even more preferably 0.15, and the upper limit of conditional formula (5) is more preferably 4.50, even more preferably 4.00, and even more preferably 3.00.

[0063] 1-2-6.Conditional Expression (6) In the zoom lens, it is preferable that the front group has at least one lens group having negative refractive power, and when the lens group having the largest negative refractive power in the front group is designated as negative lens group n, the zoom lens satisfies the following condition:

[0064] (6) -2.00 < fn / fw < -0.55 however, fn: focal length of negative lens group n fw: focal length of the zoom lens at the wide-angle end

[0065] Conditional expression (6) defines the ratio between the focal length of the negative lens group n included in the front group and the focal length of the zoom lens at the wide-angle end. Satisfying conditional expression (6) makes it easy to widen the angle of view at the wide-angle end while preventing the zoom lens from becoming too large. Furthermore, it is possible to correct curvature of field, coma, distortion, and other aberrations with a small number of lenses, thereby achieving a compact zoom lens with high optical performance.

[0066] On the other hand, if the value of conditional expression (6) is equal to or less than the lower limit, the refractive power of the negative lens group n, which has the strongest refractive power and is included in the front group, becomes small relative to the focal length of the zoom lens at the wide-angle end, thereby reducing the effect of widening the angle of view by the negative lens group n arranged in the front group. In this case, to widen the angle of view at the wide-angle end, it is necessary to increase the outer diameter of the so-called front lens, making it difficult to achieve a compact zoom lens. On the other hand, if the value of conditional expression (6) is equal to or greater than the upper limit, the refractive power of the negative lens group n, which has the strongest refractive power and is included in the front group, becomes large relative to the focal length of the zoom lens at the wide-angle end. This makes it difficult to correct various aberrations such as field curvature, coma, and distortion. Therefore, to achieve a zoom lens with high optical performance, it is necessary to increase the number of lenses for aberration correction, making it difficult to achieve a compact zoom lens.

[0067] In order to obtain these effects, the lower limit of conditional formula (6) should preferably be −1.90, more preferably −1.80, and even more preferably −1.60, and the upper limit of conditional formula (6) should preferably be −0.58, more preferably −0.62, and even more preferably −0.68.

[0068] 1-2-7.Conditional Expression (7) (7) 1.20 < |{1-(βft×βft)}×βftr×βftr| < 15.00 however, βft: Lateral magnification of the focus group at the telephoto end when focused at infinity βftr: The combined lateral magnification of all lenses positioned on the image side of the focus group in a telephoto lens when focused at infinity

[0069] Conditional expression (7) defines the focus sensitivity of the focus group. Here, focus sensitivity represents the amount of movement of the image plane when the focus group moves a unit amount. When conditional expression (7) is satisfied, the amount of movement of the focus group when focusing from an object at infinity to a close object can be kept within an appropriate range, enabling rapid autofocusing and facilitating the miniaturization of the zoom lens.

[0070] On the other hand, if the value of conditional expression (7) is below the lower limit, the focus sensitivity of the focus group becomes too low. As a result, the amount of movement of the focus group when focusing from an object at infinity to a close object becomes large, and the overall optical length becomes long, which is undesirable as it makes it difficult to reduce the size of the zoom lens. Also, if the value of conditional expression (7) is above the upper limit, the focus sensitivity of the focus group becomes too high. As a result, the amount of movement of the focus group required to correct a positional shift in the focus position becomes too small, which is undesirable as it requires highly accurate position control.

[0071] In order to obtain the above effects, the lower limit of conditional formula (7) is more preferably 1.50, even more preferably 2.00, even more preferably 2.50, even more preferably 3.00, and even more preferably 3.60, and the upper limit of conditional formula (7) is more preferably 14.00, even more preferably 13.00, and even more preferably 12.00.

[0072] (7-1) |βft|>1 Here, it is preferable that the absolute value of "βft" in conditional formula (7) be greater than 1. As mentioned above, "βft" refers to the lateral magnification of the focus group at the telephoto end when focusing at infinity. The focus group is included in the rear group. By giving the lens group included in the rear group (focus group) a lateral magnification greater than 1, the overall optical length and radial dimensions of the zoom lens can be reduced.

[0073] 1-2-8.Conditional Expression (8) As described above, it is preferable that the first lens group of the zoom lens moves toward the object side when changing magnification from the wide-angle end to the telephoto end. In this case, it is preferable that the following conditional expression (8) be satisfied:

[0074] (8) 0.01 < |X1| / ft < 0.65 however, X1: the amount of movement of the first lens group when the first lens group moves from the most image-side position to the most object-side position where the first lens group can be located during zooming from the wide-angle end to the telephoto end ft: focal length of the zoom lens at the telephoto end

[0075] Conditional expression (8) above defines the amount of movement of the first lens group toward the object side when changing magnification from the wide-angle end to the telephoto end. When conditional expression (8) is satisfied, the refractive power of the first lens group is appropriate, and the amount of movement during magnification change is within an appropriate range. Therefore, while ensuring a predetermined magnification ratio, the overall optical length of the zoom lens at the wide-angle end can be shortened, allowing for the zoom lens to be made more compact.

[0076] On the other hand, when the value of conditional expression (8) is equal to or less than the lower limit, the amount of movement of the first lens group during zooming becomes small. In this case, the refractive power of each lens group must be increased to ensure a predetermined zoom ratio. Increasing the refractive power of each lens group requires a larger number of lenses to correct aberrations such as axial chromatic aberration and spherical aberration, making it difficult to achieve a compact zoom lens. Furthermore, when the value of conditional expression (8) is equal to or greater than the upper limit, the amount of movement of the first lens group during zooming becomes large. In this case, if the lens barrel has a nested structure in which an inner barrel portion is housed within an outer barrel portion, designing the lens barrel length to match the overall optical length at the wide-angle end would require doubling the inner barrel portion to house it within the outer barrel portion, complicating the lens barrel structure and increasing the outer diameter of the lens barrel, which is undesirable.

[0077] However, the "amount of movement of the first lens group from the most image-side position to the most object-side position where the first lens group can be located during zooming from the wide-angle end to the telephoto end" is equal to the "difference in the optical axial distance between the most image-side position where the first lens group can be located during zooming from the wide-angle end to the telephoto end and the most object-side position where the first lens group can be located." Therefore, "X1" can be rephrased as "the optical axial distance between the most image-side position where the first lens group can be located during zooming from the wide-angle end to the telephoto end and the most object-side position where the first lens group can be located." For example, if the first lens group moves toward the object while tracing a convex locus toward the image side during zooming from the wide-angle end to the telephoto end, X1 is the distance between the apex of the convex locus traced by the first lens group during zooming (the most image-side position) and the position where the first lens group is closest to the object (the most object-side position) at the wide-angle end or the telephoto end. The locus of movement of the first lens group is not particularly limited and may be convex toward the image side as described above, or may be convex toward the object side, or may form an S-shape. Of course, the locus of movement of the first lens group may also be a straight line.

[0078] In order to obtain these effects, the lower limit of conditional expression (8) is more preferably 0.05, even more preferably 0.10, even more preferably 0.15, and even more preferably 0.20, while the upper limit of conditional expression (8) is more preferably 0.60, even more preferably 0.55, even more preferably 0.48, and even more preferably 0.46.

[0079] 1-2-9.Conditional Expression (9) (9) 0.01 < Crrf / ft however, Crrf: Radius of curvature of the rear group's surface closest to the object ft: focal length of the zoom lens at the telephoto end

[0080] Conditional expression (9) above defines the ratio of the radius of curvature of the surface of the rear group closest to the object to the focal length of the zoom lens at the telephoto end. A positive value for conditional expression (9) means that the surface of the rear group closest to the object is flat or has a convex shape facing the object. When conditional expression (9) is satisfied, the radius of curvature of the surface of the rear group closest to the object falls within an appropriate range for the focal length of the zoom lens at the telephoto end, resulting in a good balance of correction of spherical aberration and coma.

[0081] In order to obtain these effects, the lower limit of conditional formula (9) is more preferably 0.03, even more preferably 0.06, and even more preferably 0.09. There are no particular restrictions on the upper limit of conditional formula (9), but if an upper limit is set, it is preferably 500.00, more preferably 50.00, even more preferably 25.00, and even more preferably 12.00.

[0082] 1-2-10.Conditional Expression (10) (10)-0.70 < ff / ft < -0.05 however, ff: focal length of the focus group ft: focal length of the zoom lens at the telephoto end

[0083] Conditional expression (10) above defines the ratio between the focal length of the focus group and the focal length of the zoom lens at the telephoto end. When conditional expression (10) is satisfied, the occurrence of axial chromatic aberration, spherical aberration, curvature of field, and other aberrations can be suppressed when focusing on a close subject, resulting in a zoom lens with high optical performance throughout the entire focusing range. Furthermore, when conditional expression (10) is satisfied, the refractive power of the focus group falls within an appropriate range, thereby enabling focus sensitivity to be kept within an appropriate range. When focus sensitivity is within an appropriate range, the amount of movement of the focus group when focusing from an object at infinity to a close object can be kept within an appropriate range, enabling fast autofocusing and facilitating the miniaturization of the zoom lens.

[0084] On the other hand, if the value of conditional expression (10) is below the lower limit, the focal length of the focus group becomes larger relative to the focal length of the zoom lens at the telephoto end. In other words, the refractive power of the focus group becomes too weak. In this case, the focus sensitivity of the focus group becomes too low, resulting in a large amount of movement of the focus group when focusing on a close subject. This requires an air gap for the focus group to move, which undesirably increases the overall optical length of the zoom lens. On the other hand, if the value of conditional expression (10) is above the upper limit, the focal length of the focus group becomes smaller relative to the focal length of the zoom lens at the telephoto end. In other words, the refractive power of the focus group becomes too strong. In this case, axial chromatic aberration, spherical aberration, and curvature of field become large when focusing on a close subject, making it difficult to maintain high optical performance throughout the entire focusing range, which is undesirable. Furthermore, in this case, the focus sensitivity of the focus group becomes too high. Excessive focus sensitivity is undesirable because it requires highly accurate position control to correct misalignment of the focusing position.

[0085] In order to obtain these effects, the lower limit of conditional formula (10) should preferably be −0.65, even more preferably −0.60, even more preferably −0.55, and even more preferably −0.45, and the upper limit of conditional formula (10) should preferably be −0.08, even more preferably −0.10, and even more preferably −0.12.

[0086] 1-2-11.Conditional Expression (11) (11) 0.10 < ffft / ft < 1.00 however, ffft: The composite focal length of all lenses located on the object side of the focus group at the telephoto end ft: focal length of the zoom lens at the telephoto end

[0087] Conditional expression (11) defines the ratio of the combined focal length at the telephoto end of all lenses located closer to the object than the focus group to the focal length of the zoom lens at the telephoto end. When conditional expression (11) is satisfied, the combined lateral magnification of all lens groups located closer to the image than the focus group falls within an appropriate range, making it easy to achieve a compact zoom lens that ensures a predetermined zoom ratio and has high optical performance.

[0088] On the other hand, when the value of conditional expression (11) is equal to or less than the lower limit, the composite focal length of all lenses located closer to the object than the cemented lens constituting the focus group becomes shorter than the focal length of the zoom lens at the telephoto end. In this case, the composite lateral magnification of all lens groups located closer to the image than the focus group becomes larger. This increases spherical aberration and curvature of field, making it difficult to realize a compact zoom lens with high optical performance, which is undesirable. On the other hand, when the value of conditional expression (11) is equal to or greater than the upper limit, the composite focal length of all lenses located closer to the object than the cemented lens constituting the focus group becomes longer than the focal length of the zoom lens at the telephoto end. In this case, the composite lateral magnification of all lens groups located closer to the image than the focus group becomes smaller. Therefore, to ensure a predetermined zoom ratio, the movement distance of each lens group during zooming must be increased, which makes it difficult to achieve a compact zoom lens along the optical axis, which is undesirable.

[0089] In order to obtain these effects, the lower limit of conditional formula (11) is more preferably 0.15, even more preferably 0.20, even more preferably 0.25, and even more preferably 0.30, and the upper limit of conditional formula (11) is more preferably 0.90, even more preferably 0.80, even more preferably 0.70, and even more preferably 0.60.

[0090] 1-2-12.Conditional Expression (12) When the lens surface arranged closest to the focus group in the direction in which the focus group moves when focusing from infinity to a close object is defined as lens surface Lnf, it is preferable that the following condition be satisfied.

[0091] (12) 0.015 < Drfrt / ft < 1.000 however, Drfrt: the distance on the optical axis between the focus group at the telephoto end and the lens surface Lnf when focused at infinity ft: focal length of the zoom lens at the telephoto end

[0092] Conditional expression (12) defines the distance (distance on the optical axis) between the focus group and the lens surface Lnf that is closest to the focus group in the direction in which the focus group moves when focusing from infinity to a close object. Satisfying conditional expression (12) ensures a sufficient distance for the focus group to move in a predetermined direction when focusing, making it possible to shorten the minimum focusing distance. Satisfying conditional expression (12) is also effective in shortening the minimum focusing distance at the wide-angle end.

[0093] On the other hand, if the value of conditional expression (12) is equal to or less than the lower limit, it is possible to ensure a sufficient distance for the focus group to move in a predetermined direction during focusing, and it becomes impossible to shorten the minimum imaging distance, which is undesirable.On the other hand, if the value of conditional expression (12) is equal to or greater than the upper limit, the total optical length at the telephoto end becomes long, which is undesirable in terms of miniaturizing the zoom lens.

[0094] The direction in which the focus group moves when focusing from infinity to a close object may be toward the object side or toward the image side. If the direction in which the focus group moves when focusing from infinity to a close object is toward the object side, the lens surface Lnf will be the lens surface located closest to the object side of the focus group. If the direction in which the focus group moves when focusing from infinity to a close object is toward the image side, the lens surface Lnf will be the lens surface located closest to the image side of the focus group.

[0095] In order to obtain these effects, the lower limit of conditional expression (12) is more preferably 0.020, even more preferably 0.030, and even more preferably 0.040, and the upper limit of conditional expression (12) is more preferably 0.8000, even more preferably 0.600, even more preferably 0.400, even more preferably 0.300, and even more preferably 0.250.

[0096] 1-2-13.Conditional Expression (13) (13)-1.50 < fw / ffw < -0.50 however, fw: focal length of the zoom lens at the wide-angle end ffw: Combined focal length of the front group at the wide-angle end

[0097] Conditional expression (13) defines the ratio between the focal length of the zoom lens at the wide-angle end and the combined focal length of the front group at the wide-angle end. By satisfying conditional expression (13), it becomes easier to realize a zoom lens with high optical performance using a small number of lens elements.

[0098] On the other hand, if the value of conditional expression (13) is equal to or less than the lower limit, the composite focal length of the front group at the wide-angle end becomes shorter relative to the focal length of the zoom lens at the wide-angle end, making it difficult to correct aberrations such as curvature of field, coma, and distortion. Therefore, to achieve a zoom lens with high optical performance, it is necessary to increase the number of lenses for aberration correction. In other words, it is not possible to achieve a zoom lens with high optical performance with a small number of lenses, which makes it difficult to miniaturize the zoom lens, which is undesirable. On the other hand, if the value of conditional expression (13) is equal to or greater than the upper limit, the composite focal length of the front group at the wide-angle end becomes longer relative to the length of the zoom lens at the wide-angle end, which reduces the effect of the front group in widening the angle of view. Therefore, to achieve a wider angle of view at the wide-angle end, it is necessary to increase the diameter of the front lens, which makes it difficult to miniaturize the zoom lens, which is undesirable.

[0099] In order to obtain these effects, the lower limit of conditional expression (13) should preferably be −1.40, more preferably −1.30, and even more preferably −1.20, and the upper limit of conditional expression (13) should preferably be −0.55, more preferably −0.60, and even more preferably −0.63.

[0100] 1-2-14.Conditional Expression (14) As described above, it is preferable that the zoom lens has at least one lens surface Sr having negative refractive power located closer to the image side than the focus unit. In this case, it is more preferable that the following conditional expression be satisfied:

[0101] (14)-0.400 <|fw×tanωw| / (fsr-FBw)< -0.002 however, ωw: Half angle of view of the most off-axis chief ray of the zoom lens at the wide-angle end fsr: focal length of lens surface Sr

[0102] Conditional expression (14) is an equation that approximates the ratio between the light-converging point of lens surface Sr and the image height of the most off-axis ray on the image plane. Here, the chief ray refers to the ray that passes through the center of the aperture stop. By locating lens surface Sr that satisfies conditional expression (14) on the image side of the focus group, field curvature can be effectively corrected by that lens surface Sr. This makes it easy to achieve even higher performance for the zoom lens.

[0103] On the other hand, if the value of conditional expression (14) is equal to or greater than the upper limit, the negative refractive power of the lens surface Sr becomes too small. In this case, the curvature of field falls too far to the underside, making it difficult to achieve high performance in the zoom lens, which is undesirable. On the other hand, if the value of conditional expression (14) is equal to or less than the lower limit, the negative refractive power of the lens surface Sr becomes too large. In this case, the Petzval sum is insufficiently corrected, making it difficult to achieve high performance in the zoom lens, which is undesirable. Furthermore, two or more lens surfaces Sr may be provided, and in this case, it is sufficient that any one of the surfaces satisfies conditional expression (14). More preferably, all of the lens surfaces Sr satisfy conditional expression (14), which makes it easier to achieve high performance.

[0104] In order to obtain these effects, the upper limit of conditional formula (14) is more preferably -0.004, even more preferably -0.006, even more preferably -0.008, even more preferably -0.010, and even more preferably -0.012. The lower limit of conditional formula (14) is more preferably -0.350, even more preferably -0.300, even more preferably -0.250, even more preferably -0.230, and even more preferably -0.220.

[0105] 1-2-15.Conditional Expression (15) In the zoom lens, it is preferable that the rear group has at least one lens Lrn having negative refractive power located closer to the object side than the focus group, as described above. In this case, it is preferable that the following condition is satisfied:

[0106] (15) 1.84 < NdLrn < 2.10 however, NdLrn: refractive index of lens Lrn at the d line

[0107] Conditional formula (15) defines the refractive index of lens Lrn at the d-line. Here, the rear group has positive refractive power as a whole. Therefore, in order to effectively correct Petzval's sum, it is necessary to dispose a lens having negative refractive power and made of a glass material with a high refractive index in the rear group. Glass materials that satisfy conditional formula (15) provide a good balance between Petzval's sum correction and glass material costs. Therefore, by having the rear group include lens Lrn that satisfies conditional formula (15) on the object side of the focus group, it is possible to achieve a zoom lens with high optical performance while preventing costs from becoming too high.

[0108] On the other hand, if the value of conditional expression (15) is below the lower limit, the refractive index of the lens Lrn at the d-line becomes small, and Petzval sum cannot be sufficiently corrected, which is undesirable. On the other hand, if the value of conditional expression (15) is above the upper limit, the refractive index of the lens Lrn at the d-line becomes large, which is preferable in terms of correcting Petzval sum. However, glass materials with a high refractive index at the d-line are generally more expensive than glass materials with a low refractive index at the d-line. Using a glass material with a refractive index at the d-line that is above the upper limit will be effective in correcting Petzval sum, but the effect is small in terms of cost-effectiveness. Therefore, it is undesirable from the perspective of cost to set the value of conditional expression (15) above the upper limit.

[0109] In order to obtain these effects, the lower limit of conditional formula (15) should preferably be 1.860, even more preferably 1.870, and even more preferably 1.880, while the upper limit of conditional formula (15) should preferably be 2.070, even more preferably 2.010, and even more preferably 1.960.

[0110] 1-2-16.Conditional Expression (16) In the zoom lens, it is preferable that the rear group has at least one lens Lrn having negative refractive power located closer to the object side than the focus group, as described above. In this case, it is preferable that the following condition is satisfied:

[0111] (16)-0.015 < ΔPgF < 0.022 however, ΔPgF: In a coordinate system with the partial dispersion ratio on the vertical axis and the Abbe number νd for the d line on the horizontal axis, the deviation of the partial dispersion ratio from the reference line is measured by a line passing through the coordinates of glass material C7, which has a partial dispersion ratio of 0.5393 and νd of 60.49, and the coordinates of glass material F, which has a partial dispersion ratio of 0.5829 and νd of 36.30.

[0112] Here, if the refractive indices of glass for the g-line (435.8 nm), F-line (486.1 nm), d-line (587.6 nm), and C-line (656.3 nm) are Ng, NF, Nd, and NC, respectively, the Abbe number (νd) and partial dispersion ratio (PgF) can be expressed as follows: νd = (Nd-1) / (NF-NC) PgF = (Ng-NF) / (NF-NC)

[0113] Conditional formula (16) defines the anomalous dispersion of lens Lrn. Here, the rear group has positive refractive power as a whole. To correct chromatic aberration in a lens group having positive refractive power, it is common to combine a negative lens made of a high-dispersion glass material with a positive lens made of a low-dispersion glass material. However, the dispersion characteristics of high-dispersion glass material with respect to wavelength are quadratic, while the dispersion characteristics of low-dispersion glass material with respect to wavelength are linear. Therefore, when a negative lens made of a high-dispersion glass material is combined with a positive lens made of a low-dispersion glass material, even if chromatic aberration can be eliminated at some wavelengths, chromatic aberration remains at other wavelengths, making it impossible to correct chromatic aberration over the entire wavelength range.

[0114] Therefore, by combining the lens Lrn having negative refractive power and made of a glass material with low anomalous dispersion that satisfies the above conditional expression (16) with, for example, a positive lens made of a glass material with high anomalous dispersion, as will be explained below, it becomes possible to correct chromatic aberrations over the entire wavelength range used. Therefore, by locating the lens Lrn having negative refractive power that satisfies the conditional expression (16) on the object side of the focus group, it becomes possible to realize a zoom lens with high optical performance and good chromatic aberrations over the entire wavelength range used. Note that, in terms of good correction of chromatic aberrations, it is more preferable for the lens Lrn to satisfy the above conditional expression (15) and also satisfy the conditional expression (16).

[0115] In order to obtain these effects, the lower limit of conditional expression (16) should preferably be −0.012, and more preferably be −0.010, and the upper limit of conditional expression (16) should preferably be 0.014, and even more preferably be 0.013, and even more preferably be 0.012.

[0116] In this zoom lens, it is preferable that the rear group has a lens Lrn that satisfies the above conditional expression (16) on the object side of the focus group, and also has a lens Lrp that has positive refractive power and satisfies the following conditional expression (16-1):

[0117] (16-1) 0.009< ΔPgFp < 0.060 however, ΔPgFp: In a coordinate system with the partial dispersion ratio on the vertical axis and the Abbe number νd for the d line on the horizontal axis, the deviation of the partial dispersion ratio from the reference line is measured by a line passing through the coordinates of glass material C7, which has a partial dispersion ratio of 0.5393 and νd of 60.49, and the coordinates of glass material F, which has a partial dispersion ratio of 0.5829 and νd of 36.30.

[0118] Glass materials that satisfy conditional expression (16-1) have high anomalous dispersion and have dispersion characteristics that are quadratic with respect to wavelength. Therefore, by arranging a lens Lrp having positive refractive power that satisfies conditional expression (16-1) together with a lens Lrn that satisfies conditional expression (16) in the rear group, it is possible to realize a zoom lens that exhibits good chromatic aberrations over the entire wavelength range in use.

[0119] The zoom lens described above can provide a standard zoom lens with high optical performance while reducing the weight of the focus group, and an imaging device equipped with the zoom lens. In particular, the zoom lens can have a focal length of 50 mm (35 mm equivalent) within its zoom range, and the half angle of view (ω) at the wide-angle end can be made larger than 24°.

[0120] 2. Imaging device Next, we will explain the imaging device of the present invention, which is characterized by including the zoom lens of the present invention described above and an imaging element provided on the image plane side of the zoom lens, which converts an optical image formed by the zoom lens into an electrical signal.

[0121] Here, the imaging element is not particularly limited, and solid-state imaging elements such as CCD (Charge Coupled Device) sensors and CMOS (Complementary Metal Oxide Semiconductor) sensors can also be used. The imaging device of the present invention is suitable for imaging devices using such solid-state imaging elements, such as digital cameras and video cameras. The imaging device may also be a fixed-lens imaging device in which the lens is fixed to the housing, or an interchangeable-lens imaging device such as a single-lens reflex camera or a mirrorless single-lens camera. In particular, the zoom lens of the present invention can ensure a back focus suitable for an interchangeable lens system. Therefore, it is suitable for imaging devices such as single-lens reflex cameras equipped with an optical viewfinder, a phase difference sensor, a reflex mirror for splitting light to these, etc.

[0122] The imaging device of the present invention preferably includes an image processing unit that electrically processes captured image data acquired by the imaging element to change the shape of the captured image, and an image correction data storage unit that stores image correction data, an image correction program, etc., used to process the captured image data in the image processing unit. When a zoom lens is made smaller, distortion (curvature) of the captured image formed on the imaging plane is likely to occur. In this case, it is preferable to store distortion correction data for correcting the distortion of the captured image shape in advance in the image correction data storage unit, and for the image processing unit to correct the distortion of the captured image shape using the distortion correction data stored in the image correction data storage unit. Such an imaging device allows for even smaller zoom lenses, resulting in clearer captured images and a more compact imaging device overall.

[0123] Furthermore, in the imaging device according to the present invention, it is preferable that the image correction data storage unit stores magnification chromatic aberration correction data in advance, and the image processing unit corrects the magnification chromatic aberration of the captured image using the magnification chromatic aberration correction data stored in the image correction data storage unit. By correcting the magnification chromatic aberration, i.e., chromatic distortion, using the image processing unit, it is possible to reduce the number of lenses constituting the optical system. Therefore, with such an imaging device, it is possible to further reduce the size of the zoom lens, thereby obtaining beautiful captured images and reducing the size of the entire imaging device.

[0124] 3. Supplementary invention The problem of the present invention can also be solved by the following invention, in which a focus group consisting of only one single lens is used instead of the focus group consisting of a cemented lens in which the lens Lp having positive refractive power and the lens Ln having negative refractive power are cemented together.

[0125] [Appendix 1] With the widest air gap at the wide-angle end as the boundary, the lens group located on the object side is the front group, and the lens group located on the image side is the rear group, the front group has a negative refractive power as a whole, the rear group has a positive refractive power as a whole, and the magnification is changed from the wide-angle end to the telephoto end by changing the air space between the lens groups so as to reduce the air space between the front group and the rear group; The rear group includes a focus group consisting of one single lens, and focuses from infinity to a nearby object by moving the focus group in the optical axis direction; A zoom lens characterized by satisfying the following conditions: (2) 45.0 < νdLn < 98.0 (3)0.50 < (-ffw+Dfrw) / FBw < 1.95 however, ffw: composite focal length of the front group at the wide-angle end Dfrw: The distance on the optical axis between the surface of the front group closest to the image side and the surface of the rear group closest to the object side at the wide-angle end FBw: Air equivalent length from the side of the zoom lens closest to the image plane at the wide-angle end The matters relating to the focus group described above can be applied as long as they are applicable to a focus group consisting of only one single lens, as described above.

[0126] In the zoom lenses described in 1 and 2 above, the "focus group" is a cemented lens formed by cementing together a lens Lp having positive refractive power and a lens Ln having negative refractive power. The appended invention includes a focus group consisting of only one single lens, instead of the focus group consisting of the cemented lens. Due to the difference in the configuration of the focus group, the matters related to conditional formula (1) cannot be applied to the zoom lens, but other matters can be applied to the appended invention as long as they are applicable to the appended invention. The reference example described below is an example of the appended invention. Furthermore, it is preferable in the appended invention that a lens Lp having positive refractive power that satisfies conditional formula (1) be disposed in a lens group other than the focus group. The reference example described below is an example of the appended invention.

[0127] Next, the present invention will be described in detail with reference to examples. However, the present invention is not limited to the following examples. The zoom lenses of the following examples are applicable to imaging devices (optical devices) such as digital cameras, video cameras, and silver halide film cameras. In each lens cross-sectional view, the left side is the object side and the right side is the image plane side. [Example]

[0128] (1) Optical structure of the zoom lens FIG. 1 is a cross-sectional view of a zoom lens according to a first embodiment of the present invention, showing the lens configuration at the wide-angle end when focusing on infinity. The zoom lens is composed of, in order from the object side, a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, a third lens group G3 having positive refractive power, a fourth lens group G4 having negative refractive power, and a fifth lens group G5 having positive refractive power. When focusing from an object at infinity to a close object, the fourth lens group G4 moves toward the image along the optical axis. An aperture stop S is located on the object side of the third lens group G3. In this embodiment, the front group consists of the first lens group G1 and the second lens group, and the rear group consists of the third lens group G3, the fourth lens group G4, and the fifth lens group G5. The distance between the second lens group G2 and the third lens group G3 is the "widest air gap at the wide-angle end."

[0129] The configuration of each lens group will be described below. The first lens group G1 is composed of, in order from the object side, a cemented lens formed by cementing a negative meniscus lens L1 having a convex shape facing the object side and a convex lens L2, and a positive meniscus lens L3 having a convex shape facing the object side.

[0130] The second lens group G2 is composed of, in order from the object side, a negative meniscus lens L4 with a convex surface facing the object side, a biconcave lens L5, a biconvex lens L6, and a negative meniscus lens L7 with a concave surface facing the object side. The object side surface of the negative meniscus lens L4 is aspheric. Both surfaces of the negative meniscus lens L7 are aspheric.

[0131] The third lens group G3 is composed of, in order from the object side, an aperture stop S, a biconvex lens L8, a cemented lens formed by cementing a biconcave lens L9 and a biconvex lens L10, a cemented lens formed by cementing a biconcave lens L11 and a positive meniscus lens L12 having a convex surface facing the object side, a biconvex lens L13, a cemented lens formed by cementing a biconcave lens L14 and a biconvex lens L15, and a biconvex lens L16. The image side surface of the biconvex lens L8 is aspheric, and the object side surface of the biconcave lens L11 is aspheric. The biconcave lens L14 is the lens Lrn. The ΔPgF of the biconcave lens L14 is 0.000, and the ΔPgFp of the biconvex lens is 0.0375.

[0132] The fourth lens group G4 is composed of, in order from the object side, a cemented lens formed by cementing together a positive meniscus lens L17 having a convex shape facing the image side and a biconcave lens L18. The fourth lens group G4 is composed only of cemented lenses having negative refractive power, and the positive meniscus lens L17 is the lens Lp referred to in the present invention, and the biconcave lens L18 is the lens Ln referred to in the present invention.

[0133] The fifth lens group G5 is composed of, in order from the object side, a biconvex lens L19 and a negative meniscus lens L20 with a concave shape facing the object side.

[0134] In the zoom lens of Example 1, when changing magnification from the wide-angle end to the telephoto end, the first lens group G1 moves toward the object side relative to the image plane, the second lens group G2 moves toward the image side, the third lens group G3 moves toward the object side, the fourth lens group G4 moves toward the object side, and the fifth lens group G5 is fixed in the optical axis direction.

[0135] Furthermore, when image blur occurs due to camera shake or the like during image capture, it is preferable to use at least one lens among the lenses constituting the zoom lens as an image stabilization group and decenter the image stabilization group to shift the image and perform image blur correction. For example, it is preferable to use a cemented lens, in which a biconcave lens L11 and a positive meniscus lens L12 with a convex shape facing the object side, included in the third lens group G3, are cemented together, as the image stabilization group.

[0136] Furthermore, "IMG" in Figure 1 denotes an image plane, specifically the imaging surface of a solid-state imaging device such as a CCD sensor or a CMOS sensor, or the film surface of a silver halide film. A parallel plate with no substantial refractive power, such as a cover glass CG, is provided on the object side of the image plane IMG. These points are the same in the lens cross-sectional views shown in other embodiments, and therefore will not be described below.

[0137] (2) Numerical examples Next, we will explain numerical examples that apply specific numerical values ​​of this zoom lens. Table 1 shows the surface data of this zoom lens. In Table 1, the "surface number" indicates the order of the lens surface counted from the object side, "r" indicates the radius of curvature of the lens surface, "d" indicates the axial spacing of the lens surface, "Nd" indicates the refractive index for the d-line (wavelength λ=587.6 nm), "νd" indicates the Abbe number for the d-line, and "H" indicates the effective radius. Additionally, "ASP" displayed in the column following the surface number indicates that the lens surface is aspherical, and "S" indicates the aperture stop. Furthermore, "D5," "D13," and other characters in the column indicating the axial spacing of the lens surface indicate that the axial spacing of the lens surface is a variable spacing that changes during magnification or focusing. Note that all length values ​​in each table are in millimeters, and all angle of view values ​​are in degrees. Furthermore, "0.0000" for the radius of curvature indicates a flat surface. Note that surfaces 37 and 38 in Table 1 represent surface data for cover glass CG.

[0138] Table 2 shows the specifications of this zoom lens. This table shows the focal length (f), F-number (Fno), half angle of view (ω), image height (Y), and total optical length (TL) of the zoom lens when focused at infinity. However, Table 2 shows the respective values ​​at the wide-angle end, mid-focal length state, and telephoto end, from left to right.

[0139] Table 3 shows the variable spacing on the optical axis of the zoom lens when changing magnification. Starting from the left, Table 3 shows the values ​​at the wide-angle end, at the mid-focal length state, and when focusing on infinity at the telephoto end. In the table, "INF" stands for "∞ (infinity)."

[0140] Table 4 shows the variable distances on the optical axis of the zoom lens when in focus. Table 4 also shows the values ​​when the shooting distance (image capture distance) is 380.00 mm, 400.00 mm, and 400.00 mm at the wide-angle end, mid-focal length state, and telephoto end, respectively. These shooting distances are the shortest image capture distances for each focal length.

[0141] Table 5 shows the focal length of each lens group that makes up the zoom lens.

[0142] Table 6 shows the aspherical coefficients of each aspherical surface. The aspherical coefficients are values ​​when each aspherical shape is defined by the following formula. Table 25 also shows the values ​​of each of conditional formulas (1) to (16-1).

[0143] X(Y)=CY 2 / [1+{1-(1+Κ)·C 2 Y 2} 1 / 2 ]+A4·Y 4 +A6·Y 6 +A8·Y 8 +A10·Y 10 +A12·Y 12

[0144] However, in Table 6, "Ea" is "×10 -a In the above formula, "X" is the amount of displacement from the reference surface in the optical axis direction, "C" is the curvature at the surface vertex, "Y" is the height from the optical axis in the direction perpendicular to the optical axis, "K" is the conic coefficient, and "An" is the n-th order aspheric coefficient. The matters relating to these tables are the same as those in the tables shown in the other embodiments, and therefore, explanations thereof will be omitted below.

[0145] [Table 1] Surface number rd Nd vd H 1 164.8841 1.300 2.00069 25.46 31.000 2 106.9087 5.753 1.59282 68.62 30.327 3 2049.3432 0.200 30.056 4 64.4678 5.097 1.59282 68.62 28.300 5 127.7370 D5 27.808 6 ASP 66.2535 1.400 1.87483 41.12 18.405 7 16.5245 8.916 13.821 8 -116.2454 0.800 1.85680 41.86 13.668 9 56.4149 0.200 13.446 10 61.8227 9.135 1.73319 26.22 13.451 11 -25.7135 0.300 13.288 12 ASP -22.4217 1.200 1.70845 51.27 13.182 13 ASP -103.8458 D13 13.108 14 S 0.0000 1.200 8.858 15 44.2087 3.473 1.69350 53.18 12.906 16 ASP -219.2615 1.536 12.944 17 -866.8618 0.800 1.84984 37.32 13.064 18 94.5183 4.469 1.59282 68.62 13.156 19 -44.7943 0.300 13.283 20 ASP -82.7341 0.900 1.74007 48.57 13.312 21 56.0779 2.635 1.84666 23.78 13.331 22 183.1346 2.578 13.356 23 41.0183 5.387 1.74192 48.43 13.775 24 -63.8393 0.200 13.624 25 -539.6209 0.800 1.97110 29.19 13.071 26 20.6597 6.228 1.49700 81.61 12.253 27 -111.4492 0.238 12.264 28 51.0216 5.332 1.61800 63.39 12.159 29 -79.8317 D29 11.800 30 -139.9604 2.500 1.80809 22.76 9.380 31 -31.1560 0.900 1.69350 53.18 9.408 32 ASP 23.4283 D32 9.411 33 246.3353 7.306 1.59282 68.62 14.773 34 -27.2244 0.200 15.146 35 -31.7701 0.800 1.80897 38.14 15.013 36 -80.5852 D36 15.522 37 0.0000 2.000 1.51680 64.20 20.964 38 0.0000 1.000 21.170

[0146] [Table 2] f 24.695 59.995 101.989 Fno 4.119 4.120 4.119 ω 42.156 19.074 11.409 Y 21.633 21.633 21.633 TL 170.000 186.493 207.607

[0147] [Table 3] f 24.695 59.995 101.989 Shooting distance INF INF INF D5 1.000 27.253 51.899 D13 38.860 10.474 1.300 D29 1.242 8.791 13.609 D32 7.117 18.194 19.019 D36 36.700 36.700 36.700

[0148] [Table 4] Photography distance 380.000 400.000 400.000 D29 1.825 11.176 19.899 D32 6.535 15.809 12.728

[0149] [Table 5] Group face number focus distance G1 1-5 150.486 G2 6-13 -21.265 G3 14-29 27.830 G4 30-32 -31.313 G5 33-36 114.076

[0150] [Table 6] Noodle Number K A4 A6 A8 A10 A12 6 0 -1.8735E-06 2.9593E-09 -1.3867E-11 1.5854E-14 -8.4316E-18 12 0 3.0985E-05 -3.0498E-07 2.1696E-09 -7.7151E-12 1.1327E-14 13 0 1.7444E-05 -3.0958E-07 2.0521E-09 -7.3574E-12 1.0024E-14 16 0 1.2534E-05 -6.6064E-09 8.6021E-11 -4.2944E-13 9.2479E-16 20 0 2.1197E-06 -8.9016E-09 6.0935E-11 -2.0221E-13 2.6903E-16 32 0 1.9583E-06 1.0589E-08 -4.3641E-10 3.7956E-12 -1.3630E-14

[0151] 2 to 4 show longitudinal aberration diagrams of the zoom lens of Example 1 at the wide-angle end, the intermediate focal length state, and the telephoto end when focusing on infinity. The longitudinal aberration diagrams shown in each diagram, from left to right, show spherical aberration (mm), astigmatism (mm), and distortion (%), respectively. In the diagrams showing spherical aberration, the vertical axis represents the ratio to the maximum aperture F-number, and the horizontal axis represents defocus. The solid line represents spherical aberration at the d-line (wavelength λ=587.6 nm), the dashed-dotted line represents spherical aberration at the g-line (wavelength λ=435.8 nm), and the dotted line represents spherical aberration at the C-line (wavelength λ=656.3 nm). In the diagrams showing astigmatism, the vertical axis represents image height, the horizontal axis represents defocus, and the solid line represents the sagittal image plane (ds) relative to the d-line, and the dotted line represents the meridional image plane (dm) relative to the d-line. In the diagrams showing distortion, the vertical axis represents image height and the horizontal axis represents distortion in %. The matters relating to these longitudinal aberration diagrams are the same as those shown in the longitudinal aberration diagrams of other examples, and therefore will not be described below.

[0152] The back focus "fb" of the zoom lens at the wide-angle end when focused on infinity is as follows: Note that the following value does not include the cover glass (Nd=1.5168), and the same applies to the back focus shown in other examples. fb= 39.019(mm) [Reference example 2]

[0153] (1) Optical structure of the zoom lens FIG. 5 is a cross-sectional view showing the lens configuration of a zoom lens according to Reference Example 2 of the present invention when focusing on infinity at the wide-angle end. This zoom lens is composed of, in order from the object side, a first lens group G1 having negative refractive power, a second lens group G2 having positive refractive power, a third lens group G3 having negative refractive power, and a fourth lens group G4 having positive refractive power. When focusing from an object at infinity to a close object, the third lens group G3 moves toward the image along the optical axis. An aperture stop S is located closest to the image side of the second lens group G2. In this example, the front group consists of the first lens group G1, and the rear group consists of the second lens group G2, the third lens group G3, and the fourth lens group G4. The distance between the first lens group G1 and the second lens group G2 is the "widest air gap at the wide-angle end."

[0154] The configuration of each lens group will be explained below. The first lens group G1 is composed of, in order from the object side, a negative meniscus lens L1 with a convex shape facing the object side, a negative meniscus lens L2 with a convex shape facing the object side, and a positive meniscus lens L3 with a convex shape facing the object side. The image side surface of the negative meniscus lens L1 is aspheric.

[0155] The second lens group G2 is composed of, in order from the object side, a positive meniscus lens L4 with a convex surface facing the object side, a cemented lens formed by cementing together a negative meniscus lens L5 with a convex surface facing the object side and a biconvex lens L6, and an aperture stop S. Both surfaces of the positive meniscus lens L4 are aspheric. The negative meniscus lens L5 is the above-mentioned lens Lrn. The ΔPgF of the negative meniscus lens L5 is 0.0137.

[0156] The third lens group G3 is composed of, in order from the object side, a cemented lens formed by cementing together a positive meniscus lens L7 with a convex shape facing the image side and a biconcave lens L8. The third lens group G3 is composed only of cemented lenses having negative refractive power, with the positive meniscus lens L7 being the lens Lp referred to in the present invention and the biconcave lens L8 being the lens Ln referred to in the present invention. The ΔPgFp of the positive meniscus lens L9 is 0.0375. The object-side surface of the negative meniscus lens L11 is the lens surface Sr.

[0157] The fourth lens group G4 is composed of, in order from the object side, a positive meniscus lens L9 convex on the image side, and a cemented lens formed by cementing a biconvex lens L10 and a negative meniscus lens L11 concave on the object side.

[0158] In the zoom lens of Reference Example 2, when changing magnification from the wide-angle end to the telephoto end, the first lens group G1 moves toward the image side, the second lens group G2 moves toward the object side, the third lens group G3 moves toward the object side, and the fourth lens group G4 moves toward the object side relative to the image plane.

[0159] Furthermore, when image blur occurs due to camera shake or the like during image capture, it is preferable to use at least one lens among the lenses constituting the zoom lens as an image stabilization group and to perform image blur correction by decentering the image stabilization group.

[0160] (2) Numerical examples Next, we will explain numerical examples that apply specific numerical values ​​of the zoom lens. Table 7 shows surface data of the zoom lens, and Table 8 shows a specification table of the zoom lens. Note that surfaces 21 and 22 in Table 7 are surface data of the cover glass CG.

[0161] Table 9 shows the variable distances on the optical axis of the zoom lens when changing magnification, and Table 10 shows the variable distances on the optical axis of the zoom lens when focusing. Table 10 also shows values ​​when the shooting distances (image capture distances) are 230.00 mm, 250.00 mm, and 250.00 mm at the wide-angle end, mid-focal length state, and telephoto end, respectively. These shooting distances are the shortest image capture distances for each focal length.

[0162] Table 11 shows the focal length of each lens group that constitutes the zoom lens. Table 12 shows the aspherical coefficients of each aspherical surface. Table 25 shows the values ​​of conditional expressions (1) to (16-1).

[0163] 6 to 8 show longitudinal aberration diagrams of the zoom lens of Reference Example 2 at the wide-angle end, in the intermediate focal length state, and at the telephoto end when focused on infinity, respectively.

[0164] Furthermore, the back focus of the zoom lens when focused at infinity at the wide-angle end is as follows: fb = 38.002(mm)

[0165] [Table 7] Surface number rd Nd vd H 1 664.2203 2.000 1.59201 67.02 19.685 2 ASP 12.4206 9.063 14.659 3 99.0474 1.700 1.83400 37.34 14.679 4 44.9342 0.382 14.536 5 27.4552 4.648 1.76182 26.61 15.052 6 82.1402 D6 14.800 7 ASP 27.5225 4.248 1.61881 63.85 8.001 8 ASP 341.9552 3.733 7.928 9 41.6779 1.000 1.84666 23.78 7.889 10 17.5890 4.766 1.51680 64.20 7.701 11 -20.4065 1.000 7.687 12 S 0.0000 D12 6.788 13 -43.8890 2.597 1.84666 23.78 6.245 14 -13.2199 1.000 1.80420 46.50 6.132 15 29.7835 D15 5.859 16 -217.0738 2.391 1.49700 81.61 5.867 17 -18.3135 0.300 5.905 18 63.0476 2.475 1.49700 81.61 5.747 19 -21.3360 1.000 1.83481 42.72 5.607 20 -161.5834 D20 5.569 21 0.0000 2.000 1.51680 64.20 13.865 22 0.0000 1.000 14.225

[0166] [Table 8] f 18.538 28.896 53.339 Fno 3.605 4.550 5.767 ω 38.587 26.428 14.755 Y 14.200 14.200 14.200 TL 133.849 122.674 120.000

[0167] [Table 9] f 18.538 28.896 53.339 Shooting distance INF INF INF D6 43.626 20.912 1.273 D12 2.450 4.207 10.084 D15 6.788 8.311 7.450 D20 35.683 43.942 55.891

[0168] [Table 10] Shooting distance 230.000 250.000 250.000 D12 3.300 5.738 15.028 D15 5.938 6.780 2.500

[0169] [Table 11] Group Surface number Focal length G1 1-6 -28.619 G2 7-12 23.772 G3 13-15 -22.745 G4 16-20 44.047

[0170] [Table 12] Surface number Κ A4 A6 A8 A10 A12 2 -0.864 9.3680E-06 2.0539E-09 4.6218E-11 7.4937E-15 0.0000E+00 7 0 -1.1011E-05 5.5255E-08 -2.4435E-09 0.0000E+00 0.0000E+00 8 0 2.2843E-05 7.6512E-08 -2.5280E-09 0.0000E+00 0.0000E+00

[0171] [Reference example 3] (1) Optical structure of the zoom lens FIG. 9 is a cross-sectional view of a zoom lens according to Reference Example 3, showing its lens configuration at the wide-angle end when focusing on infinity. The zoom lens is composed of, in order from the object side, a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, a third lens group G3 having positive refractive power, a fourth lens group G4 having positive refractive power, a fifth lens group G5 having negative refractive power, and a sixth lens group G6 having positive refractive power. When focusing from an object at infinity to a close object, the fifth lens group G5 moves toward the image along the optical axis. An aperture stop S is located closest to the object side of the third lens group G3. In this Reference Example, the front group consists of the first lens group G1 and the second lens group G2, and the rear group consists of the third lens group G3, the fourth lens group G4, the fifth lens group G5, and the sixth lens group G6. The distance between the second lens group G2 and the third lens group G3 is the "widest air gap at the wide-angle end."

[0172] The configuration of each lens group will be described below. The first lens group G1 is composed of, in order from the object side, a cemented lens formed by cementing together a negative meniscus lens L1 with a convex shape facing the object side and a convex lens L2, and a positive meniscus lens L3 with a convex shape facing the object side.

[0173] The second lens group G2 is composed of, in order from the object side, a negative meniscus lens L4 convex toward the object side, a cemented lens formed by cementing together a biconcave lens L5 and a biconvex lens L6, and a negative meniscus lens L7 concave toward the object side. The object side surface of the negative meniscus lens L4 is aspheric, and both surfaces of the negative meniscus lens L7 are aspheric.

[0174] The third lens group G3 is composed of, in order from the object side, an aperture stop S, a cemented lens formed by cementing together three lenses: a negative meniscus lens L8 with a convex surface facing the object side, a biconvex lens L9, and a negative meniscus lens L10 with a concave surface facing the object side, and a biconvex lens L11. The ΔPgF of the biconvex lens L9 is 0.0194.

[0175] The fourth lens group G4 is composed of, in order from the object side, a cemented lens formed by cementing a biconvex lens L12 and a negative meniscus lens L13 with a concave surface facing the object side, a cemented lens formed by cementing a biconcave lens L14 and a positive meniscus lens L15 with a convex surface facing the image side, and a biconvex lens L16. The object side surface of the biconvex lens L12 is aspheric, and both surfaces of the biconvex lens L16 are aspheric. The biconcave lens L14 is the above-mentioned lens Lrn. The ΔPgF of the biconcave lens L14 is 0.0036, and the ΔPgFp of the positive meniscus lens L15 is 0.0194.

[0176] The fifth lens group G5 is composed of a biconcave lens L17 with aspherical surfaces on both sides, that is, it is composed of only one single lens having negative refractive power, and the biconcave lens L17 corresponds to the negative lens Ln.

[0177] The sixth lens group G6 is composed of a positive meniscus lens L18 having a convex shape facing the image side. The object side surface of the positive meniscus lens L18 is the lens surface Sr.

[0178] In the zoom lens of the reference example, when changing magnification from the wide-angle end to the telephoto end, the first lens group G1 moves toward the object side relative to the image plane, the second lens group G2 moves once toward the image side and then moves toward the object side, the third lens group G3 moves toward the object side, the fourth lens group G4 moves toward the object side, the fifth lens group G5 moves toward the object side, and the sixth lens group G6 moves once toward the image side and then moves toward the object side.

[0179] Furthermore, when image blur occurs due to camera shake or the like during image capture, it is preferable to use at least one lens among the lenses constituting the zoom lens as an image stabilization group and decenter the image stabilization group to perform image blur correction. For example, it is preferable to use a cemented lens formed by cementing together a biconvex lens L12 and a negative meniscus lens L13 with a concave object side shape included in the fourth lens group G4 as the image stabilization group, and to perform image blur correction by moving the cemented lens in a direction perpendicular to the optical axis to shift the image.

[0180] (2) Numerical examples Next, we will explain numerical examples that apply specific numerical values ​​of the zoom lens. Table 13 shows surface data of the zoom lens, and Table 14 shows a specification table of the zoom lens. Note that surfaces 33 and 34 in Table 13 are surface data of the cover glass CG.

[0181] Table 15 shows the variable distances on the optical axis of the zoom lens when changing magnification, and Table 16 shows the variable distances on the optical axis of the zoom lens when focusing. Table 16 also shows values ​​when the shooting distances (image capture distances) are 380.00 mm, 400.00 mm, and 400.00 mm at the wide-angle end, mid-focal length state, and telephoto end, respectively. These shooting distances are the shortest image capture distances for each focal length.

[0182] Table 17 shows the focal length of each lens group that constitutes the zoom lens. Table 18 shows the aspherical coefficients of each aspherical surface. Table 25 shows the values ​​of conditional expressions (1) to (16-1).

[0183] 10 to 12 show longitudinal aberration diagrams of the zoom lens of this reference example at the wide-angle end, in the intermediate focal length state, and at the telephoto end when focused on infinity, respectively.

[0184] Furthermore, the back focus of the zoom lens when focused at infinity at the wide-angle end is as follows: fb= 39.000(mm)

[0185] [Table 13] Surface number rd Nd vd H 1 323.7548 1.200 1.92119 23.96 31.000 2 162.8221 5.378 1.59282 68.62 30.511 3 -416.6201 0.200 30.309 4 52.5783 6.103 1.59282 68.62 27.700 5 117.8837 D5 27.204 6 ASP 205.3924 0.300 1.51460 49.96 17.800 7 92.8554 1.000 1.72916 54.67 17.549 8 16.2034 9.149 12.854 9 -33.2034 0.800 1.49700 81.61 12.685 10 23.5127 7.798 1.72047 34.71 11.846 11 -53.7846 2.177 11.330 12 ASP -24.1046 1.000 1.85135 40.10 11.000 13 ASP -39.5928 D13 11.078 14 S 0.0000 1.000 7.350 15 33.5262 0.800 2.00100 29.13 11.263 16 22.1705 7.146 1.59282 68.62 11.130 17 -24.7861 0.800 1.80610 40.73 11.214 18 -1553.7806 0.200 11.601 19 45.5555 3.337 1.94595 17.98 11.975 20 -11420.0602 D20 11.917 21 ASP 73.0633 5.117 1.59282 68.62 11.798 22 -34.4056 0.800 1.94595 17.98 11.608 23 -44.4387 0.200 12.500 24 -252.4796 0.800 2.00100 29.13 11.189 25 21.7316 3.716 1.59282 68.62 10.757 26 44.7795 0.200 10.768 27 ASP 32.9204 6.239 1.82098 42.50 10.900 28 ASP -56.3856 D28 10.951 29 ASP -177.3325 1.000 1.59201 67.02 11.450 30 ASP 29.2491 D30 11.132 31 -331.6955 2.594 1.87070 40.73 13.305 32 -82.1148 D32 13.500 33 0.0000 2.000 1.51680 64.20 21.332 34 0.0000 1.000 21.528

[0186] [Table 14] f 25.752 51.482 101.851 Fno 4.123 4.108 4.120 ω 41.307 22.170 11.633 Y 21.633 21.633 21.633 TL 150.364 161.368 203.864

[0187] [Table 15] f 25.752 51.482 101.851 Shooting distance INF INF INF D5 1.000 17.096 42.593 D13 25.849 6.747 1.000 D20 4.201 2.583 1.000 D28 0.997 5.217 1.003 D30 9.581 13.836 20.242 D32 36.681 43.834 65.971

[0188] [Table 16] Shooting distance 380.000 400.000 400.000 D28 1.933 7.951 7.855 D30 8.645 11.101 13.390

[0189] [Table 17] Group face number focus distance G1 1-5 114.642 G2 6-13 -20.988 G3 14-20 42.458 G4 21-28 45.184 G5 29-30 -42.335 G6 31-32 124.734

[0190] [Table 18] Noodle Number K A4 A6 A8 A10 A12 6 0 1.2837E-05 -2.1442E-08 5.5949E-11 -1.1996E-13 1.5377E-16 12 0 -8.7531E-06 8.6202E-08 -3.3258E-10 5.1244E-13 -9.3573E-16 13 0 -9.7742E-06 7.6139E-08 -3.0250E-10 3.5047E-13 0.0000E+00 21 0 -5.5002E-06 -1.6789E-08 8.7410E-11 -3.4776E-13 7.7049E-16 27 0 -3.5514E-06 2.9946E-08 3.3719E-10 -1.8317E-12 1.2820E-14 28 0 7.9983E-06 -1.0254E-09 7.7608E-10 -5.3802E-12 2.7034E-14 29 0 -1.2178E-05 1.5756E-07 -1.0359E-09 2.8436E-12 0.0000E+00 30 0 -1.5518E-05 1.5764E-07 -1.0926E-09 2.8672E-12 2.0668E-15

Example

[0191] (1) Optical structure of the zoom lens FIG. 13 is a cross-sectional view showing the lens configuration of the zoom lens of Example 2 at the wide-angle end when focusing on infinity. The zoom lens is composed of, in order from the object side, a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, a third lens group G3 having positive refractive power, a fourth lens group G4 having positive refractive power, a fifth lens group G5 having negative refractive power, and a sixth lens group G6 having positive refractive power. When focusing from an object at infinity to a close object, the fifth lens group G5 moves toward the image along the optical axis. An aperture stop S is located closest to the object side of the third lens group G3. In this example, the front group consists of the first lens group G1 and the second lens group G2, and the rear group consists of the third lens group G3, the fourth lens group G4, the fifth lens group G5, and the sixth lens group G6. The distance between the second lens group G2 and the third lens group G3 is the "widest air gap at the wide-angle end."

[0192] The configuration of each lens group will be described below. The first lens group G1 is composed of, in order from the object side, a cemented lens formed by cementing together a negative meniscus lens L1 with a convex shape facing the object side and a convex lens L2, and a positive meniscus lens L3 with a convex shape facing the object side.

[0193] The second lens group G2 is composed of, in order from the object side, a negative meniscus lens L4 with a convex surface facing the object side, a biconcave lens L5, a biconvex lens L6, and a negative meniscus lens L7 with a concave surface facing the object side. The object side surface of the negative meniscus lens L4 is aspheric, and both surfaces of the negative meniscus lens L7 are aspheric.

[0194] The third lens group G3 is composed of, from the object side, an aperture stop S, a biconvex lens L8, a cemented lens formed by cementing a biconcave lens L9 and a biconvex lens L10, and a cemented lens formed by cementing a biconcave lens L11 and a positive meniscus lens L12 with a convex shape facing the object side. The image-side surface of the biconvex lens L8 and the object-side surface of the biconcave lens L11 are aspheric. The ΔPgFp of the biconvex lens L10 is 0.0194.

[0195] The fourth lens group G4 is composed of, in order from the object side, a biconvex lens L13, a cemented lens formed by cementing a biconcave lens L14 and a biconvex lens L15, and a biconvex lens L16. The biconcave lens L14 is the above-mentioned lens Lrn. The ΔPgF of the biconcave lens L14 is 0.000, and the ΔPgFp of the biconvex lens L15 is 0.0375.

[0196] The fifth lens group G5 is composed of, in order from the object side, a cemented lens formed by cementing together a positive meniscus lens L17 having a convex shape facing the image side and a biconcave lens L18. The fifth lens group G5 is composed only of cemented lenses having negative refractive power, and the positive meniscus lens L17 is the lens Lp referred to in the present invention, and the biconcave lens L18 is the lens Ln referred to in the present invention.

[0197] The sixth lens group G6 is composed of a cemented lens in which, in order from the object side, a biconvex lens L19 and a negative meniscus lens L20 having a concave shape facing the object side are cemented together.

[0198] In the zoom lens of Example 2, when changing magnification from the wide-angle end to the telephoto end, the first lens group G1 moves toward the object side relative to the image plane, the second lens group G2 moves toward the image side, the third lens group G3 moves toward the object side, the fourth lens group G4 moves toward the object side, the fifth lens group G5 moves toward the object side, and the sixth lens group G6 is fixed in the optical axis direction.

[0199] Furthermore, when image blur occurs due to camera shake or the like during image capture, it is preferable to use at least one lens among the lenses constituting the zoom lens as an image stabilization group and decenter the image stabilization group to perform image blur correction. For example, it is preferable to use a cemented lens formed by cementing together a biconcave lens L11 and a positive meniscus lens L12 with a convex shape facing the object side, which is included in the third lens group G3, as the image stabilization group, and to perform image blur correction by moving the cemented lens in a direction perpendicular to the optical axis to shift the image.

[0200] (2) Numerical examples Next, we will explain numerical examples that apply specific numerical values ​​of the zoom lens. Table 19 shows surface data of the zoom lens, and Table 20 shows a specification table of the zoom lens. Note that surfaces 36 and 37 in Table 19 are surface data of the cover glass CG.

[0201] Table 21 shows the variable distances on the optical axis of the zoom lens when changing magnification, and Table 22 shows the variable distances on the optical axis of the zoom lens when focusing. Table 22 also shows values ​​when the shooting distances (image capture distances) are 380.00 mm, 400.00 mm, and 400.00 mm at the wide-angle end, mid-focal length state, and telephoto end, respectively. These shooting distances are the shortest image capture distances for each focal length.

[0202] Table 23 shows the focal length of each lens group that constitutes the zoom lens. Table 24 shows the aspherical coefficients of each aspherical surface. Table 25 shows the values ​​of conditional expressions (1) to (16-1).

[0203] 14 to 16 show longitudinal aberration diagrams of the zoom lens of Example 2 at the wide-angle end, in the intermediate focal length state, and at the telephoto end when focused on infinity, respectively.

[0204] Furthermore, the back focus of the zoom lens when focused at infinity at the wide-angle end is as follows: fb= 39.437(mm)

[0205] [Table 19] Surface number rd Nd vd H 1 234.7666 1.300 2.00069 25.46 31.000 2 138.4148 5.791 1.59282 68.62 30.558 3 -680.0462 0.200 30.302 4 69.5724 5.230 1.59282 68.62 28.400 5 161.1477 D5 27.926 6 ASP 79.5439 1.400 1.86791 41.50 18.481 7 16.1943 8.900 13.716 8 -318.2547 0.800 1.87450 36.30 13.541 9 45.1827 0.309 13.327 10 51.2199 8.660 1.73426 26.35 13.336 11 -25.6352 0.451 13.228 12 ASP -20.9608 1.200 1.77115 48.40 13.152 13 ASP -64.5265 D13 13.100 14 S 0.0000 1.200 8.750 15 53.1982 3.548 1.69350 53.18 12.260 16 ASP -79.4200 1.520 12.346 17 -266.2503 0.800 1.82595 41.71 12.461 18 88.0772 4.260 1.59282 68.62 12.571 19 -42.6289 0.624 12.691 20 ASP -78.1987 0.900 1.74974 49.75 12.900 21 60.1253 2.368 1.84666 23.78 12.727 22 185.3061 D22 12.759 23 47.5209 5.193 1.68881 54.43 13.170 24 -55.0964 0.200 13.066 25 -327.0636 0.800 1.96229 29.86 12.625 26 22.8885 6.220 1.49700 81.61 12.075 27 -77.0078 0.350 12.125 28 73.7860 5.020 1.61800 63.39 12.044 29 -73.2609 D29 11.750 30 -207.6716 2.500 1.80809 22.76 9.380 31 -36.7222 0.900 1.69350 53.18 9.429 32 ASP 22.1640 D32 9.493 33 52.7180 6.495 1.59282 68.62 15.993 34 -73.2205 0.800 1.69206 30.32 16.171 35 -416.6667 37.118 16.374 36 0.0000 2.000 1.51680 64.20 21.005 37 0.0000 1.000 21.342

[0206] [Table 20] f 24.839 59.958 102.474 Fno 4.121 4.119 4.120 ω 41.981 18.973 11.267 Y 21.633 21.633 21.633 TL 169.752 174.603 207.241

[0207] [Table 21] f 24.839 59.958 102.474 Shooting distance INF INF INF D5 1.000 20.275 53.597 D13 38.216 6.180 1.360 D22 4.143 3.278 2.700 D29 1.179 12.168 13.313 D32 7.156 14.643 18.212

[0208] [Table 22] Shooting distance 380.000 400.000 400.000 D29 1.849 15.198 20.630 D32 6.486 11.613 10.895

[0209] [Table 23] Group Surface number Focal length G1 1-5 140.430 G2 6-13 -21.836 G3 14-22 56.376 G4 23-29 39.322 G5 30-32 -31.033 G6 33-37 86.738

[0210] [Table 24] Surface number Κ A4 A6 A8 A10 A12 6 0 -3.5121E-07 1.2475E-09 -1.8924E-11 2.0318E-14 -9.3027E-18 12 0 3.4527E-05 -2.8731E-07 2.1583E-09 -7.5699E-12 1.1133E-14 13 0 1.8666E-05 -3.0289E-07 2.0678E-09 -7.5735E-12 1.0314E-14 16 0 1.3999E-05 -4.6523E-09 4.5363E-11 -3.1634E-13 9.7102E-16 20 0 2.6081E-06 -9.1362E-09 6.1882E-11 -2.3937E-13 3.9842E-16 32 0 -4.4734E-06 3.3579E-09 -4.8480E-10 4.0227E-12 -1.3728E-14

[0211] [Table 25] Example 1 Reference Example 2 Reference Example 3 Example 2 Conditional expression (1) νdLp 22.761 23.785 - 22.761 Conditional expression (2) νdLn 53.186 46.503 67.023 53.186 Conditional expression (3) (-ffw+Dfrw) / FBw 1.714 1.901 1.422 1.703 Conditional expression (4) Cr1f / fw 6.677 35.830 12.572 9.452 Conditional expression (5) (Crff+Crfr) / (Crff-Crfr) 0.713 0.191 0.717 0.807 Conditional expression (6) fn / fw -0.861 -1.544 -0.815 -0.879 Conditional expression (7) |{1-(βft²)}×βftr²| 5.419 4.437 5.061 4.609 Conditional expression (7-1) |βft| 3.756 5.520 5.034 4.451 Conditional expression (8) |X1| / ft 0.369 0.260 0.525 0.366 Conditional expression (9) Crrf / ft 0.433 0.516 0.329 0.519 Conditional expression (10) ff / ft -0.307 -0.426 -0.416 -0.303 Conditional expression (11) ffft / ft 0.414 0.467 0.435 0.454 Conditional expression (12) Drfrt / ft 0.186 0.140 0.199 0.178 Conditional expression (13) fw / ffw -0.920 -0.648 -0.900 -0.895 Conditional expression (14) |fw×tanωw| / (fsr-FBw) -0.197 -0.141 -0.029 -0.017 Conditional expression (15) NdLrn 1.971 1.847 2.001 1.962 Conditional expression (16) ΔPgF 0.000 0.014 0.004 0.000 Conditional expression (16-1) ΔPgFp 0.038 0.038 0.019 0.038 [Possibility of industrial utilization]

[0212] The present invention provides a standard zoom lens with high optical performance and a lightweight focus group, and an imaging device equipped with the zoom lens. The zoom lens is particularly suitable for a zoom lens with a focal length of 50 mm (35 mm equivalent) within its zoom range and a half angle of view (ω) of more than 24° at the wide-angle end. [Explanation of symbols]

[0213] G1: First lens group G2: Second lens group G3: Third lens group G4: Fourth lens group G5: Fifth lens group G6: 6th lens group F Focus group S Aperture CG ···Cover glass IMG...Image plane

Claims

1. With the widest air gap at the wide-angle end as the boundary, the lens group located on the object side is the front group, and the lens group located on the image side is the rear group, the front group has a negative refractive power as a whole, the rear group has a positive refractive power as a whole, and the magnification is changed from the wide-angle end to the telephoto end by changing the air space between the lens groups so as to reduce the air space between at least the front group and the rear group, the rear group includes a focus group formed of a cemented lens in which a lens Lp having a positive refractive power and a lens Ln having a negative refractive power are cemented together, and focusing from infinity to a nearby object is performed by moving the focus group in the optical axis direction; the rear group has at least one lens Lrn having negative refractive power located closer to the object side than the focus group, At least one lens group is fixed in the optical axis direction during zooming, A zoom lens characterized by satisfying the following conditions: (1) 15.0 < νdLp < 35.0 (2) 53.186 ≦ νdLn < 98.0 (7-4) 2.50 < | {1 - (βft × βft)} × βftr × βftr | < 15.00 (15-3) 1.962 ≦ NdLrn < 2.10 however, νdLp: Abbe number at the d line of the lens Lp νdLn: Abbe number at the d line of the lens Ln βft: lateral magnification of the focus group at the telephoto end when focused on infinity βftr: composite lateral magnification at the telephoto end when all lenses arranged on the image side of the focus group are focused at infinity NdLrn: refractive index of the lens Lrn at the d line

2. With the widest air gap at the wide-angle end as the boundary, the lens group located on the object side is the front group, and the lens group located on the image side is the rear group, the front group has a negative refractive power as a whole, the rear group has a positive refractive power as a whole, and the magnification is changed from the wide-angle end to the telephoto end by changing the air space between the lens groups so as to reduce the air space between at least the front group and the rear group, the rear group includes a focus group formed of a cemented lens in which a lens Lp having a positive refractive power and a lens Ln having a negative refractive power are cemented together, and focusing from infinity to a nearby object is performed by moving the focus group in the optical axis direction; the rear group has at least one lens Lrn having negative refractive power located closer to the object side than the focus group, A zoom lens characterized by satisfying the following conditions: (1) 15.0 < νdLp < 35.0 (2) 53.186 ≦ νdLn < 98.0 (4-1) 5.10 < Cr1f / fw (7-4) 2.50 < | {1 - (βft × βft)} × βftr × βftr | < 15.00 (15-3) 1.962 ≦ NdLrn < 2.10 however, νdLp: Abbe number at the d line of the lens Lp νdLn: Abbe number at the d line of the lens Ln Cr1f: radius of curvature of the surface of the zoom lens closest to the object fw: focal length of the zoom lens at the wide-angle end βft: lateral magnification of the focus group at the telephoto end when focused on infinity βftr: composite lateral magnification at the telephoto end when all lenses arranged on the image side of the focus group are focused at infinity NdLrn: refractive index of the lens Lrn at the d line

3. 3. The zoom lens according to claim 1, wherein the following condition is satisfied: (5) 0.00 <(Crff+Crfr) / (Crff-Crfr)<5.00 however, Crff: radius of curvature of the surface of the focus group closest to the object Crfr: radius of curvature of the surface closest to the image side of the focus group

4. 4. The zoom lens according to claim 1, wherein the focus group is formed by cementing, from the object side, the lens Lp having the positive refractive power and the lens Ln having the negative refractive power in this order.

5. 5. The zoom lens according to claim 1, wherein the front group has at least one lens group having negative refractive power, and the lens group having the largest negative refractive power in the front group is designated as negative lens group n, and the following condition is satisfied: (6) -2.00 < fn / fw < -0.55 however, fn: focal length of the negative lens unit n fw: focal length of the zoom lens at the wide-angle end

6. When the lens group arranged closest to the object in the front group is the first lens group, 2. The first lens group moves in the optical axis direction when zooming from the zoom position to the telephoto position. The zoom lens according to claim 1.

7. 7. The zoom lens according to claim 6, which satisfies the following condition: (8) 0.01 < |X1| / ft < 0.65 however, X1: the amount of movement of the first lens group when the first lens group moves from the most image-side position to the most object-side position where the first lens group can be located during zooming from the wide-angle end to the telephoto end

8. 8. The zoom lens according to claim 1, wherein the following condition is satisfied: (9) 0.01 < Crrf / ft however, Crrf: radius of curvature of the surface of the rear group closest to the object ft: focal length of the zoom lens at the telephoto end

9. 9. The zoom lens according to claim 1, wherein the focus group has negative refractive power.

10. 10. The zoom lens according to claim 9, which satisfies the following condition: (10) -0.70 < ff / ft < -0.05 however, ff: focal length of the focus group ft: focal length of the zoom lens at the telephoto end

11. 11. The zoom lens according to claim 1, wherein the following condition is satisfied: when the lens surface arranged closest to the focus group in the direction in which the focus group moves when focusing from infinity to a close object is defined as lens surface Lnf. (12) 0.015 < Drfrt / ft < 1.000 however, Drfrt: the distance on the optical axis between the focus group at the telephoto end and the lens surface Lnf when focused at infinity ft: focal length of the zoom lens at the telephoto end

12. 12. The zoom lens according to claim 1, wherein the shortest imaging distance at the wide-angle end is shorter than the shortest imaging distance at the telephoto end.

13. 13. The zoom lens according to claim 1, which satisfies the following condition: (13) -1.50 < fw / ffw < -0.50 however, fw: focal length of the zoom lens at the wide-angle end

14. 14. An imaging apparatus comprising: the zoom lens according to claim 1; and an image sensor, on the image side of the zoom lens, for converting an optical image formed by the zoom lens into an electrical signal.

Images