Zoom lens and image pickup apparatus

Abstract

The problem is to provide a zoom lens and an imaging device which are small and light and have high optical performance. The solution is that the zoom lens of the present invention has, in order from the object side, a first lens group having negative refractive power, and a second lens group having positive refractive power, and performs a zoom action by changing the interval between adjacent lens groups. The zoom lens has a specific optical characteristic represented by four formulas related to the second lens group.

Description

Technical Field

[0001] This invention relates to zoom lenses (zoom lenses) and imaging devices. Background Technology

[0002] Currently, imaging devices equipped with solid-state imaging elements such as CCD (Charge Coupled Device) and CMOS (Complementary Metal Oxide Semiconductor) are rapidly becoming widespread across a wide range of fields. Examples of such imaging devices include SLR cameras, digital cameras, camcorders, and surveillance cameras. With this increasing prevalence, the demand for lenses corresponding to the solid-state imaging elements in these devices continues to grow.

[0003] In recent years, the increasing pixel count and sensitivity of solid-state camera elements have created a demand for high-resolution and bright lenses. Furthermore, the miniaturization and widespread adoption of camera devices have led to a desire for smaller, lighter, and cheaper lenses for camera devices, such as zoom lenses. Moreover, advancements in artificial intelligence and image recognition technologies have created a need for high-performance lenses in camera devices that can correct aberrations across a wide spectral range, enabling photography day and night.

[0004] In the lenses of the imaging devices described above, for example, a zoom lens is known that consists of a first lens group with negative optical power and a second lens group with positive optical power. This zoom lens is small and lightweight, and possesses bright and good optical performance. It is designed to achieve small size, large aperture ratio, and high performance in wide-angle systems, while suppressing performance changes due to temperature variations, thereby achieving cost reduction. Furthermore, the second lens group includes a resin lens with anomalous dispersion (see, for example, Patent Document 1).

[0005] Furthermore, among zoom lenses, a wide-angle zoom lens is known that comprises a first lens group with negative optical power, a second lens group with positive optical power, and a third lens group with positive optical power. This lens has a large aperture and good optical performance. The second lens group includes a resin lens with anomalous dispersion as a positive lens (see, for example, Patent Documents 2 and 3).

[0006] Prior art literature

[0007] Patent documents

[0008] [Patent Document 1] Japanese Patent Application Publication No. 2011-242517

[0009] [Patent Document 2] Japanese Patent Application Publication No. 2013-134498

[0010] [Patent Document 3] Japanese Patent Application Publication No. 2014-202841 Summary of the Invention

[0011] The problem that the invention aims to solve

[0012] The zoom lens described in Patent Document 1 is difficult to miniaturize because the overall positive optical power of the second lens group is weak. The zoom lenses described in Patent Documents 2 and 3 each have weak positive optical power in their respective resin lenses, failing to fully realize the effect of resin lenses with aberrant dispersion. Therefore, the zoom lenses described in Patent Documents 2 and 3 cannot adequately correct chromatic aberration over a wide wavelength range. Furthermore, the weak overall positive optical power of the second lens group in the zoom lenses described in Patent Documents 2 and 3 further hinders miniaturization.

[0013] As such, there is still room for exploration in the viewpoint of fully realizing miniaturization, lightweighting, and high optical performance in conventional zoom lenses.

[0014] One aspect of the present invention is to provide a small, lightweight zoom lens and a camera device with high optical performance.

[0015] Methods for solving problems

[0016] To address the aforementioned issues, one aspect of the present invention relates to a zoom lens (zoom lens) that, from the object side, sequentially comprises a first lens group having negative optical power and a second lens group having positive optical power. Zooming is achieved by varying the spacing between adjacent lens groups. The second lens group includes a lens Lp having positive optical power. The zoom lens satisfies the following equations (1) to (4):

[0017] 0.85 < f2 / f 2p <1.50···(1)

[0018] 0 < f2 / f w <3.25···(2)

[0019] -0.3<ΔPdt_2p<-0.1···(3)

[0020] 1.50 < Nd2 < 2.00 ···(4)

[0021] in,

[0022] f2: Focal length of the second lens group

[0023] f 2p The focal length of the lens Lp

[0024] f wThe focal length at the wide-angle end of the zoom lens when focusing at infinity.

[0025] ΔPdt_2p: Anomalous dispersion between the d-line and t-line of the lens Lp.

[0026] Nd2: The refractive index at the d-line of the lens Lp.

[0027] In addition, in order to solve the above-mentioned problems, an imaging device according to one aspect of the present invention includes: the above-mentioned zoom lens, and a solid-state imaging element disposed on the image side of the zoom lens and converting the optical image formed by the zoom lens into an electrical signal.

[0028] Invention Effects

[0029] According to one aspect of the present invention, it is possible to provide a small, lightweight zoom lens and a camera device with high optical performance. Attached Figure Description

[0030] Figure 1 This is a schematic diagram illustrating the optical structure of the zoom lens of Embodiment 1 when focusing at infinity at the wide-angle end.

[0031] Figure 2 This is a diagram showing the longitudinal aberration of the zoom lens of Embodiment 1 when focusing at infinity at the wide-angle end.

[0032] Figure 3 This is a diagram showing the longitudinal aberration of the zoom lens of Embodiment 1 when focusing at infinity at the telephoto end.

[0033] Figure 4 This is a schematic diagram illustrating the optical structure of the zoom lens of Embodiment 2 when focusing at infinity at the wide-angle end.

[0034] Figure 5 This is a diagram showing the longitudinal aberration of the zoom lens of Embodiment 2 when focusing at infinity at the wide-angle end.

[0035] Figure 6 This is a diagram showing the longitudinal aberration of the zoom lens of Embodiment 2 when focusing at infinity at the telephoto end.

[0036] Figure 7 This is a schematic diagram illustrating the optical structure of the zoom lens of Embodiment 3 when focusing at infinity at the wide-angle end.

[0037] Figure 8 This is a diagram showing the longitudinal aberration of the zoom lens of Embodiment 3 when focusing at infinity at the wide-angle end.

[0038] Figure 9 This is a diagram showing the longitudinal aberration of the zoom lens of Embodiment 3 when focusing at infinity at the telephoto end.

[0039] Figure 10 This is a schematic diagram illustrating the optical structure of the zoom lens of Embodiment 4 when focusing at infinity at the wide-angle end.

[0040] Figure 11 This is a diagram showing the longitudinal aberration of the zoom lens of Example 4 when focusing at infinity at the wide-angle end.

[0041] Figure 12 This is a diagram showing the longitudinal aberration of the zoom lens of Embodiment 4 when focusing at infinity at the telephoto end.

[0042] Figure 13 This is a schematic diagram illustrating the optical structure of the zoom lens of Embodiment 5 when focusing at infinity at the wide-angle end.

[0043] Figure 14 This is a diagram showing the longitudinal aberration of the zoom lens of Embodiment 5 when focusing at infinity at the wide-angle end.

[0044] Figure 15 This is a diagram showing the longitudinal aberration of the zoom lens of Embodiment 5 when focusing at infinity at the telephoto end.

[0045] Figure 16 This is a diagram schematically illustrating an example of the structure of a camera device according to one embodiment of the present invention.

[0046] Explanation of reference numerals in the attached figures:

[0047] 1. Mirrorless single-lens camera (video recording device)

[0048] 2. Main Body

[0049] 3. Lens tube

[0050] 21 CCD sensor (camera element)

[0051] 22 Protective Glass

[0052] 30mm zoom lens

[0053] 31. G1 First Lens Group

[0054] 32. G2 Second Lens Group

[0055] 33. G3 Third Lens Group

[0056] 34. S-diaphragm

[0057] G4 Fourth Lens Group

[0058] CG protective glass

[0059] F filter

[0060] OA optical axis. Detailed Implementation

[0061] 1. Zoom lens (zoom lens)

[0062] 1.1 Optical Structure

[0063] One embodiment of the present invention relates to a zoom lens having a first lens group having negative optical power and a second lens group having positive optical power arranged sequentially from the object side. Furthermore, the second lens group includes a positive lens with specific aberration dispersion properties. Therefore, this zoom lens can capture images with chromatic aberration corrected over a wide wavelength range, and is also small and lightweight.

[0064] Furthermore, in this specification, "lens group" means a collection of lenses that move in conjunction with the zoom operation. A lens group can consist of a single lens or multiple lenses. During the zoom operation, the lenses in the lens group move while maintaining their relative positional relationships. The zoom operation is performed by changing the spacing between lenses in the lens group; the spacing between lenses belonging to the same lens group remains unchanged during the zoom operation.

[0065] In addition, in this specification, the lens can be not only a single lens, but also a combined lens formed by integrating multiple single lenses without air gaps, or a composite lens formed by integrating a single lens with resin without air gaps.

[0066] Furthermore, in this specification, a lens with positive optical power will be referred to as a "positive lens," and a lens with negative optical power will be referred to as a "negative lens."

[0067] (1) First lens group

[0068] The first lens group is the lens group positioned closest to the object side in this zoom lens, and it has a negative optical power. The first lens group only needs to have a negative optical power as a whole, and it only needs to have at least one negative lens. The structure of the lenses in the first lens group can be appropriately determined within the range of having a negative optical power overall.

[0069] (2) Second lens group

[0070] The second lens group is a lens group arranged on the image side of the first lens group and has positive optical power. The second lens group only needs to have positive optical power as a whole and only needs to have at least one lens Lp. Lens Lp preferably has positive optical power and satisfies the conditions described later. From the viewpoint of effectively correcting chromatic aberration, it is more preferable that the second lens group has two or more lenses Lp. The structure of the lenses in the second lens group can be appropriately determined within the range of having positive optical power as a whole.

[0071] Lens Lp is preferably a plastic lens. From the perspectives of properly correcting various aberrations, reducing costs, and reducing the weight of the second lens group, it is preferable that the aforementioned lens Lp is a plastic lens. From the perspectives of cost reduction and achieving effective aberration correction, it is preferable that the plastic lens is an aspherical lens.

[0072] Furthermore, the second lens group may also include a negative lens, and preferably at least one negative lens in the second lens group is a plastic lens. The use of a plastic negative lens is advantageous from the perspectives of cost reduction and lightweighting of the second lens group. Additionally, from the perspectives of cost reduction and achieving effective aberration correction, the plastic lens is preferably an aspherical lens. Moreover, particularly from the perspective of achieving effective Purzval correction, it is preferable that at least one negative lens in the second lens group is a plastic lens.

[0073] (3) Focusing group

[0074] The zoom lens may also have a focusing group. The focusing group consists of at least one lens that moves along the optical axis of the zoom lens when focusing on an object moving from infinity to near. The focusing group can be either the entire lens group that moves along the optical axis for focusing, or at least one lens within the zoom lens that moves along the optical axis for focusing. The position and power of the focusing group during focusing are not limited.

[0075] (4) Aperture

[0076] The zoom lens may also have an aperture stop. Here, "aperture stop" refers to the aperture stop that defines the beam diameter of the zoom lens, that is, the aperture stop that defines the F-number of the zoom lens. The placement of this aperture stop in the zoom lens is not limited.

[0077] (5) Lens group structure

[0078] The zoom lens, starting from the object side, sequentially comprises a first lens group with negative optical power and a second lens group with positive optical power. In this embodiment, the zoom lens may also include other lens groups besides the first and second lens groups, within the range where the effects of this embodiment can be achieved. The arrangement of the lens groups in the zoom lens can be appropriately determined within the range that satisfies the aforementioned positional relationship between the first and second lens groups. For example, the other lens groups may be located further to the image side than the second lens group. There may be one or more other lens groups.

[0079] Furthermore, the zoom lens of this embodiment may also include other optical elements besides the lens group and aperture stop, within the range that achieves the effects of this embodiment. These other optical elements may be one or more. Examples of these other optical elements include a filter. The filter can be appropriately selected within the range that embodies the optical characteristics desired in this embodiment.

[0080] 1-2. Actions

[0081] (1) Actions during zoom

[0082] The zoom lens of this embodiment performs zoom operation by changing the spacing between adjacent lens groups. "Changing the spacing between adjacent lens groups" means changing the air gap between adjacent lens groups. In zooming, from the viewpoint of achieving a desired zoom ratio, it is preferable that the first lens group and the second lens group move relative to each other in a manner that reduces the air gap between the two lens groups from the wide-angle end to the telephoto end.

[0083] Furthermore, the zoom lens may also include other lens groups as described above, and the trajectory of these other lenses, formed by connecting the wide-angle end and the telephoto end of these other lens groups, includes a shape that faces the image side and then the object side. For example, the zoom lens may also have other lens groups positioned further towards the image side than the second lens group, and these other lens groups have a trajectory with the shape described above. This structure is preferred from the viewpoint of improving image plane performance at intermediate focal lengths.

[0084] (2) Focusing action

[0085] In this zoom lens, focusing can be achieved through the focusing group described above. The focusing group that moves when focusing on an object from infinity towards a closer object can also be any lens or lens group, as described above. Furthermore, the direction of movement of the focusing group during focusing is not limited.

[0086] 1-3. Formulas representing the conditions of a zoom lens

[0087] The zoom lens involved in this embodiment preferably adopts the structure described above and satisfies one or more of the formulas described below.

[0088] Equation (1) specifies the ratio of the focal length of the second lens group to the focal length of the lens Lp arranged in the second lens group.

[0089] 0.85 < f2 / f 2p <1.50···(1)

[0090] in,

[0091] f2: Focal length of the second lens group

[0092] f2p The focal length of lens Lp

[0093] Satisfying Equation (1) is preferred from the viewpoint of properly setting the focal length of the positive lens included in the second lens group, and is also preferred from the viewpoint of properly correcting the spherical aberration and axial chromatic aberration generated in the second lens group.

[0094] At f2 / f 2p When the value is below the lower limit of equation (1), the focal length of the positive lens included in the second lens group is sometimes too short. Therefore, the spherical aberration and axial chromatic aberration generated in the second lens group increase, sometimes making it difficult to obtain good optical performance. At f2 / f 2p When the value exceeds the upper limit of Equation (1), the focal length of the positive lens included in the second lens group is sometimes too long. Therefore, the correction of spherical aberration and axial chromatic aberration generated in the second lens group is sometimes insufficient, and it is difficult to achieve miniaturization of the zoom lens.

[0095] From the perspective of achieving good optical performance, f2 / f 2p More preferably, it should be greater than 0.87, and even more preferably, it should be greater than 0.89. Furthermore, from the viewpoints of achieving good optical performance and miniaturizing zoom lenses, f2 / f 2p More preferably less than 1.45, more preferably less than 1.40.

[0096] Equation (2) specifies the ratio of the focal length of the second lens group to the focal length of the zoom lens when focusing at infinity at the wide-angle end.

[0097] 0 < f2 / f w <3.25···(2)

[0098] in,

[0099] f2: Focal length of the second lens group

[0100] f w The focal length at the wide-angle end when a zoom lens is focused at infinity.

[0101] Satisfying Equation (2) is preferred from the viewpoint of properly setting the focal length of the second lens group and properly correcting the spherical aberration, astigmatism and axial chromatic aberration generated in the second lens group.

[0102] At f2 / f w When the focal length is below the lower limit of equation (2), the focal length of the second lens group is sometimes too short. Therefore, spherical aberration, astigmatism, and axial chromatic aberration increase in the second lens group, sometimes making it difficult to achieve good optical performance. At f2 / f wWhen the focal length of the second lens group exceeds the upper limit of Equation (2), it may sometimes be too long. Therefore, the correction of spherical aberration, astigmatism and axial chromatic aberration generated in the second lens group may become insufficient, and it may be difficult to miniaturize the zoom lens.

[0103] From the perspective of achieving good optical performance, f2 / f w More preferably, it exceeds 1.00; even more preferably, it exceeds 1.50; and still more preferably, it exceeds 2.00. Furthermore, from the viewpoints of achieving good optical performance and miniaturizing zoom lenses, f2 / f... w More preferably less than 3.00, and even more preferably less than 2.80.

[0104] Equation (3) specifies the anomalous dispersion of the lens Lp contained in the second lens group corresponding to the d-line and t-line.

[0105] -0.30<ΔPdt_2p<-0.10···(3)

[0106] in,

[0107] ΔPdt_2p: Anomalous dispersion between the d-line and t-line of lens Lp

[0108] Here, the "abnormal dispersion between the d-line and the t-line" is manifested as follows: when the vertical axis is set as the partial dispersion ratio between the d-line and the t-line, and the horizontal axis is set as the Abbe number vd, and the straight line passing through the coordinates of C7 (partial dispersion ratio between the d-line and the t-line: 1.1337, vd: 60.49) and F2 (partial dispersion ratio between the d-line and the t-line: 1.0009, vd: 36.30) is set as the baseline, the deviation between the point on the baseline corresponding to the Abbe number of the lens Lp and the partial dispersion ratio of the lens Lp.

[0109] Satisfying equation (3) is preferred from the viewpoint that the second lens group includes not only the visible light domain from the d line to the C line but also the near-infrared domain from the C line to the t line in a wide band, including both axial chromatic aberration and magnification chromatic aberration.

[0110] When ΔPdt_2p is below the lower limit of equation (3), the absolute value of the anomalous dispersion of the positive lens included in the second lens group is sometimes too large. Therefore, the chromatic aberration correction in the band including the t-line is excessive, sometimes making it difficult to obtain good optical performance for light in the band from the d-line to the t-line. When ΔPdt_2p is above the upper limit of equation (3), the absolute value of the anomalous dispersion of the positive lens included in the second lens group is sometimes too small. Therefore, the chromatic aberration becomes large in the band including the t-line, sometimes making it difficult to obtain good optical performance for light in the band from the d-line to the t-line.

[0111] The value of ΔPdt_2p can be appropriately determined from the range shown in equation (3) within the wide band range that can be used to properly correct chromatic aberration as described above.

[0112] Equation (4) specifies the refractive index of lens Lp corresponding to the d line.

[0113] 1.50 < Nd2 < 2.00 ···(4)

[0114] in,

[0115] Nd2: Refractive index at the d-line of lens Lp

[0116] Satisfying equation (4) is preferred from the viewpoint of properly setting the refractive index of the lens Lp included in the second lens group corresponding to the d line, and is also preferred from the viewpoint of properly correcting the spherical aberration and axial chromatic aberration generated in the second lens group.

[0117] When Nd2 is below the lower limit of equation (4), the correction of spherical aberration generated in the second lens group sometimes becomes insufficient, and it is difficult to achieve miniaturization of the zoom lens. When Nd2 is above the upper limit of equation (4), the axial chromatic aberration generated in the second lens group increases, and it is sometimes difficult to obtain good optical performance.

[0118] The value of Nd2 can be appropriately determined from the range shown in equation (4) within the range that properly corrects the spherical aberration and axial chromatic aberration generated in the second lens group.

[0119] Equation (5) specifies the ratio of the focal length of the lens Lp configured in the second lens group to the focal length of the zoom lens at the wide-angle end when focusing at infinity.

[0120] 1.80 < f 2p / f w <3.50···(5)

[0121] in,

[0122] f 2p The focal length of lens Lp

[0123] f w The focal length at the wide-angle end when a zoom lens is focused at infinity.

[0124] Satisfying equation (5) is preferred from the viewpoint of properly setting the focal length of the positive lens included in the second lens group, and is also preferred from the viewpoint of properly correcting spherical aberration mainly generated in the second lens group.

[0125] In f 2p / f w Below the lower limit of equation (5), the correction for spherical aberration generated in the second lens group sometimes becomes insufficient, and miniaturization of the zoom lens becomes difficult. At f2p / f w When the value exceeds the upper limit of equation (5), the spherical aberration generated in the second lens group may increase. Therefore, the spherical aberration correction in the entire system may be excessive, and it may be difficult to obtain good optical performance.

[0126] f 2p / f w From the perspectives of properly correcting spherical aberration generated in the second lens group and miniaturizing the zoom lens, a value exceeding 2.00 is more preferred, and even more preferred is a value exceeding 2.20. Additionally, f 2p / f w From the viewpoint of properly correcting the spherical aberration in the entire system, a value of less than 3.30 is more preferred, and even more preferred is a value of less than 3.10.

[0127] Equation (6) specifies the horizontal magnification of the second lens group at the telephoto end relative to the horizontal magnification of the second lens group at the wide-angle end.

[0128] 1.5 < β 2t / β 2w <4.0···(6)

[0129] in,

[0130] β 2t Horizontal magnification of the second lens group at the telephoto end

[0131] β 2w Horizontal magnification of the second lens group at the wide-angle end

[0132] Satisfying equation (6) is preferred from the perspectives of achieving an appropriate zoom ratio from the wide-angle end to the telephoto end of the second lens group, miniaturizing the zoom lens, and suppressing aberrations during zooming.

[0133] In β 2t / β 2w Below the lower limit of equation (6), the zoom ratio obtained by moving the second lens group becomes smaller, sometimes making it difficult to miniaturize the zoom lens. In β 2t / β 2w When the magnification exceeds the upper limit of equation (6), the zoom ratio obtained by moving the second lens group becomes larger, making it easier to miniaturize the zoom lens. However, the aberration variation during zooming increases, sometimes making it difficult to obtain high optical performance across the entire zoom range.

[0134] β 2t / β 2w From the viewpoint of achieving high optical performance across the entire zoom range, a value less than 3.80 is more preferable, and more preferably less than 3.60. Furthermore, β... 2t / β 2wThe lower limit can be appropriately determined from the range shown in Equation (6) from the perspectives of achieving the desired zoom ratio and miniaturizing the zoom lens.

[0135] Equation (7) specifies the ratio of the focal length of the joint lens arranged in the second lens group to the radius of curvature of the joint surface of the joint lens.

[0136] 3.0 < |f s / R s |<20.0···(7)

[0137] in,

[0138] f s The focal length of the aforementioned combined lens

[0139] R s The radius of curvature of the joint surface of the aforementioned joint lens

[0140] Satisfying equation (7) is preferred from the viewpoint of properly setting the focal length of the joint lens included in the second lens group and the radius of curvature of the joint surface of the joint lens, and is also preferred from the viewpoint of properly correcting the chromatic aberration mainly generated in the second lens group.

[0141] In |f s / R s When the value is below the lower limit of equation (7), the radius of curvature of the joint surface in the joint lens of the second lens group is too large, and therefore, the optical power of the joint surface is sometimes weakened. Consequently, the correction of axial chromatic aberration and magnification chromatic aberration generated in the second lens group becomes insufficient, and sometimes it is difficult to obtain good optical performance. In |f s / R s When the value exceeds the upper limit of equation (7), the radius of curvature of the joint surface in the joint lens of the second lens group is too small, and therefore, the optical power of the joint surface sometimes becomes stronger. As a result, the axial chromatic aberration and magnification chromatic aberration generated in the second lens group increase, and sometimes it is difficult to obtain good optical performance.

[0142] |f s / R s From the viewpoint of properly correcting axial chromatic aberration and magnification chromatic aberration generated in the second lens group, a value exceeding 3.50 is more preferred, and a value exceeding 4.00 is even more preferred. Additionally, |f s / R s From the viewpoint of properly correcting the axial chromatic aberration and magnification chromatic aberration generated in the second lens group, a value of less than 15.0 is more preferred, and a value of less than 10.0 is even more preferred.

[0143] Equation (8) specifies the focal length of the first lens group at the wide-angle end when focusing relative to infinity of the zoom lens.

[0144] -2.8 < f1 / f w <-1.5···(8)

[0145] in,

[0146] f1: Focal length of the first lens group

[0147] f w The focal length at the wide-angle end when a zoom lens is focused at infinity.

[0148] Satisfying equation (8) is preferred from the perspectives of achieving an appropriate focal length for the first lens group, the main viewpoint of wide-angle zoom lens, the viewpoint of miniaturization of zoom lens, and the viewpoint of properly correcting coma and field curvature.

[0149] In f1 / f w Below the lower limit of equation (8), the optical focal length of the first lens group is too weak, sometimes making it difficult to achieve wide-angle and miniaturized zoom lenses. At f1 / f w If the light intensity exceeds the upper limit of Equation (8), the light focal length of the first lens group is too strong, and it is sometimes difficult to correct coma and field curvature.

[0150] f1 / f w From the viewpoint of widening the angle and miniaturizing the zoom lens, a value exceeding -2.50 is more preferable, and even more preferable is a value exceeding -2.20. Additionally, f1 / f w From the viewpoint of properly correcting coma and field curvature, a value less than -1.60 is more preferred, and a value less than -1.70 is even more preferred.

[0151] 2. Camera device

[0152] Next, an imaging device according to one embodiment of the present invention will be described. This imaging device includes a zoom lens as described in the above embodiment, and an imaging element that converts the optical image formed by the zoom lens into an electrical signal. The imaging element is disposed on the image plane side of the zoom lens.

[0153] Here, the imaging element is not limited and can be a solid-state imaging element such as a CCD sensor or a CMOS sensor. The imaging device according to this embodiment is suitable for imaging devices such as digital cameras and camcorders that use the aforementioned solid-state imaging element. Furthermore, this imaging device can be a fixed-lens imaging device where the lens is fixed to the housing, or a lens-changing imaging device such as an SLR camera or a mirrorless single-lens reflex camera. In particular, the zoom lens according to this embodiment ensures a suitable back focus for lens-changing systems. Therefore, it is suitable for imaging devices such as SLR cameras that include an optical viewfinder, a phase difference sensor, and a mirror for branching light to these components.

[0154] Figure 16This is a diagram schematically illustrating an example of the structure of the camera device according to this embodiment. Figure 16 As shown, the mirrorless single-lens camera 1 has a main body 2 and a lens barrel 3 that can be detached from the main body 2. The mirrorless single-lens camera 1 is one type of imaging device.

[0155] The lens barrel 3 has a zoom lens 30. The zoom lens 30 includes a first lens group 31, a second lens group 32, and a third lens group 33. The zoom lens 30 is configured, for example, such that the first lens group 31 and the second lens group 32 at least satisfy the above-described equations (1) to (4). In addition, an aperture stop 34 is disposed between the first lens group 31 and the second lens group 32.

[0156] The first lens group 31 has negative optical power, the second lens group 32 has positive optical power, and the third lens group 33 has negative optical power. The second lens group 32 has the aforementioned lens Lp, which has positive optical power.

[0157] The main body 2 has a CCD sensor 21 as an imaging element and a protective glass 22. The CCD sensor 21 is positioned in the main body 2 such that the optical axis OA of the zoom lens 30, which is mounted in the lens barrel 3 of the main body 2, is the central axis.

[0158] The camera apparatus according to this embodiment more preferably includes: an image processing unit that performs electrical processing on camera image data acquired by the camera element and changes the shape of the camera image, and an image correction data holding unit that holds image correction data and image correction programs used for processing the camera image data in the image processing unit.

[0159] When miniaturizing a zoom lens, the shape of the image captured in the imaging plane is prone to distortion. In this case, it is preferable to correct the distortion of the image shape. For example, by having an image correction data holding unit pre-store distortion correction data for correcting the distortion of the image shape, the image processing unit can perform the correction using the distortion correction data held in the image correction data holding unit. With such an imaging device, it is possible to further miniaturize the zoom lens, obtain beautiful image quality, and achieve overall miniaturization of the imaging device.

[0160] Furthermore, in the imaging apparatus according to this embodiment, it is preferable that the image correction data holding unit holds the magnification chromatic aberration correction data in advance. Additionally, in the image processing unit, it is preferable to use the magnification chromatic aberration correction data held in the image correction data holding unit to perform magnification chromatic aberration correction on the captured image. By correcting the magnification chromatic aberration, i.e., color distortion aberration, through the image processing unit, the number of lenses constituting the optical system can be reduced. Therefore, according to such an imaging apparatus, it is possible to further miniaturize the zoom lens, obtain a beautiful captured image, and achieve overall miniaturization of the imaging apparatus.

[0161] This invention is not limited to the embodiments described above, and various modifications can be made within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included within the technical scope of this invention.

[0162] [Example]

[0163] The following describes embodiments of the present invention. Furthermore, in the following tables, all lengths are in "mm" and all field of view angles are in "°".

[0164] [Example 1]

[0165] Figure 1 This diagram schematically illustrates the optical structure of the zoom lens of Embodiment 1 when focusing at infinity at the wide-angle end. The lens of Embodiment 1, from the object side, consists of a first lens group G1 with negative optical power, a second lens group G2 with positive optical power, and a third lens group G3 with positive optical power. An aperture stop S is positioned closest to the object side of the second lens group G2. A protective glass CG is positioned between the third lens group G3 and the image plane IMG. The second lens group G2, from the object side, is composed of a lens with positive optical power (lens Lp), a lens with negative optical power, and a combined lens of a lens with positive optical power and a lens with negative optical power.

[0166] The zoom lens of Example 1 performs zoom operation by changing the air gap between the lens groups. In the figure, the arrows shown below each lens group indicate the trajectory of the lens group as it moves from the wide-angle end through the intermediate focal length to the telephoto end. When zooming from the wide-angle end to the telephoto end, the first lens group G1 is fixed in the optical axis direction. The second lens group G2 gradually moves towards the object side. The third lens group G3 moves towards the image side and then towards the object side. More specifically, zooming is performed by moving the second lens group G2 towards the object side as described above, and focusing and correction of the focal position based on zoom are performed by moving the third lens group G3 as described above.

[0167] Next, examples of specific numerical values ​​applied to the zoom lens will be explained. Table 1 is a table of surface data for the zoom lens of Example 1.

[0168] In the table, "r" represents the radius of curvature, and "d" represents the lens thickness or lens spacing. Additionally, "Nd" represents the refractive index corresponding to the d-line (wavelength λ = 587.56 nm), and "vd" represents the Abbe number corresponding to the d-line. Furthermore, "ΔPdt" represents the deviation between a point on the baseline corresponding to the Abbe number associated with the d-line and t-line and the partial dispersion ratio. More specifically, "ΔPdt" represents the deviation between a point on the baseline corresponding to the Abbe number of a lens and the partial dispersion ratio of that lens when the vertical axis is set to the partial dispersion ratio between the d-line and t-line, the horizontal axis is set to the Abbe number vd, and the straight line passing through coordinates C7 (partial dispersion ratio between d-line and t-line: 1.1337, vd: 60.49) and F2 (partial dispersion ratio between d-line and t-line: 1.0009, vd: 36.30) is set as the baseline.

[0169] Additionally, the symbol “*” in the table indicates an aspherical lens, “S” represents an aperture stop, and “INF” means infinity. The “d” column shows “D(6)”, etc., indicating that the spacing on the optical axis of the lens surface is a variable spacing that changes during zooming or focusing.

[0170] In Table 1, surfaces 1-6 are the surface numbers of the lenses in the first lens group G1, and surfaces 7-13 are the surface numbers of the lenses in the second lens group G2. Surface 7 represents the aperture stop and also represents the surface of the lens closest to the object side in the second lens group G2. Surfaces 14 and 15 are the surface numbers of the lenses in the third lens group G3. Surfaces 16 and 17 represent the protective glass, and surface 18 represents the image plane.

[0171] [Table 1] Lens surface data

[0172]

[0173]

[0174] Table 2 shows various data of the zoom lens of Example 1. In Table 2, "F" represents the focal length of the zoom lens when focusing at infinity, "FNo" represents the F-number, "ω" represents the half field of view, and "Y" represents the image height.

[0175] [Table 2] Various Data

[0176] Wide-angle end Telephoto end F 3.1000 7.2000 FNo 2.06 3.19 ω 65.9 27.1 Y 3.4000 3.4000 D(6) 7.9134 0.8000 D(13) 1.0853 3.9675 D(15) 3.0732 7.3044

[0177] Table 3 shows the aspherical data of the zoom lens in Example 1. The aspherical shape of the aspherical lens is represented by the following formula when the height perpendicular to the optical axis is set to H, the displacement in the optical axis direction at height H with the apex of the surface as the origin is set to X(H), the paraxial radius of curvature is set to R, the conic coefficient is set to k, and the aspherical coefficients for the 2nd, 4th, 6th, 8th, 10th, 12th, and 14th orders are set to A, B, C, D, E, F, and G, respectively. Additionally, in Table 3, "E-a" indicates "×10". －a ".

[0178] [Formula 1]

[0179]

[0180] [Table 3] Aspherical Data

[0181] k A B C D E 3 0 0.00000E+00 -1.34231E-04 2.91731E-05 -3.17502E-06 8.79015E-08 4 0 0.00000E+00 -6.55936E-04 4.47569E-05 -4.85539E-06 2.04348E-07 7 0 0.00000E+00 -4.41251E-05 1.01065E-04 -1.36958E-05 1.25568E-06 8 0 0.00000E+00 2.94274E-03 2.43504E-05 -3.40187E-05 4.82792E-06 9 0 0.00000E+00 -3.19738E-03 6.71729E-05 -7.76154E-05 7.07428E-06 10 0 0.00000E+00 -6.46741E-03 5.99391E-05 -9.33305E-05 5.50843E-06 14 0 0.00000E+00 5.87296E-04 -5.94224E-05 6.43191E-06 -2.49953E-07 15 0 0.00000E+00 7.23970E-04 -8.82632E-05 9.19860E-06 -3.57017E-07

[0182] Table 4 shows the lens group data for Example 1. The lens group data shows the surface number of the starting surface, the surface number of the ending surface, and the focal length of each lens group constituting the zoom lens.

[0183] [Table 4] Lens Group Data

[0184] Lens group Initial interview - Final interview focal length G1 1-6 -5.10 G2 8-13 7.94 G3 14-15 31.53

[0185] Figure 2 This is a diagram showing the longitudinal aberration of the zoom lens of Embodiment 1 when focusing at infinity at the wide-angle end. Figure 3 This is a graph showing the longitudinal aberrations of the zoom lens of Embodiment 1 when focusing at infinity at the telephoto end. The longitudinal aberration graphs shown in each figure, from left to right facing the figure, represent spherical aberration (mm), astigmatism (mm), and distortion aberration (%).

[0186] In a graph representing spherical aberration, the vertical axis is set to the ratio of the open F-number, and the horizontal axis is set to defocus. In the graph representing spherical aberration, the dotted line represents the longitudinal aberration at the g-line (wavelength λ = 435.84 nm), the solid line represents the longitudinal aberration at the d-line (wavelength λ = 587.56 nm), the dashed line represents the longitudinal aberration at the C-line (wavelength λ = 656.27 nm), and the double-dotted line represents the longitudinal aberration at the near-infrared (wavelength λ = 850 nm) spectral density.

[0187] In the diagram representing astigmatism, the vertical axis is set to image height (mm), and the horizontal axis is set to defocus. In the diagram representing astigmatism, the solid line represents the sagittal image plane (S) corresponding to the d-line, and the dotted line represents the meridional image plane (T) corresponding to the d-line.

[0188] In a graph representing distortion aberrations, the vertical axis is set to image height (mm), and the horizontal axis is set to %.

[0189] [Example 2]

[0190] Figure 4 This diagram schematically illustrates the optical structure of the zoom lens of Embodiment 2 when focusing at infinity at the wide-angle end. The lens of Embodiment 2, from the object side, consists of a first lens group G1 with negative optical power, a second lens group G2 with positive optical power, and a third lens group G3 with positive optical power. An aperture stop S is positioned closest to the object side of the second lens group G2. A protective glass CG is positioned between the third lens group G3 and the image plane IMG. The second lens group G2, from the object side, consists of a lens with positive optical power (lens Lp), a lens with negative optical power, and a combined lens of a lens with positive optical power and a lens with negative optical power.

[0191] The zoom lens of Example 2 performs zoom operation by changing the air gap between the lens groups. In the figure, the arrows shown below each lens group indicate the trajectory of the lens group as it moves from the wide-angle end through the intermediate focal length to the telephoto end. When zooming from the wide-angle end to the telephoto end, the first lens group G1 is fixed in the optical axis direction. The second lens group G2 gradually moves towards the object side. The third lens group G3 moves towards the image side and then towards the object side. More specifically, zooming is performed by moving the second lens group G2 towards the object side as described above, and focus is performed by moving the third lens group G3 as described above to correct the focal position based on the zoom.

[0192] Next, examples of specific numerical values ​​for the zoom lens will be explained. Table 5 is a table of surface data for the zoom lens of Example 2. In Table 5, surfaces 1 to 6 are the surface numbers of the lenses in the first lens group G1, and surfaces 7 to 13 are the surface numbers of the lenses in the second lens group G2. Surface 7 represents the aperture stop and the surface of the lens closest to the object side of the second lens group G2. Surfaces 14 and 15 are the surface numbers of the lenses in the third lens group G3. Surfaces 16 and 17 represent the protective glass, and surface 18 represents the image plane.

[0193] [Table 5] Data for lens surfaces

[0194]

[0195]

[0196] Table 6 shows various data for the zoom lens of Example 2. Table 7 shows the aspherical data of Example 2. Table 8 shows the lens group data of Example 2.

[0197] [Table 6] Various Data

[0198] Wide-angle end Telephoto end F 3.1000 7.2000 FNo 2.04 3.13 ω 64.0 27.2 Y 3.4000 3.4000 D(6) 7.6572 0.8000 D(13) 1.1693 3.1536 D(15) 3.3182 8.1910

[0199] [Table 7] Aspherical Data

[0200]

[0201]

[0202] [Table 8] Lens Group Data

[0203] Lens group Initial interview - Final interview focal length G1 1-6 -5.36 G2 8-13 8.13 G3 14-15 25.68

[0204] Figure 5 This is a diagram showing the longitudinal aberration of the zoom lens of Embodiment 2 when focusing at infinity at the wide-angle end. Figure 6 This is a diagram showing the longitudinal aberration of the zoom lens of Embodiment 2 when focusing at infinity at the telephoto end.

[0205] [Example 3]

[0206] Figure 7 This diagram schematically illustrates the optical structure of the zoom lens of Embodiment 3 when focusing at infinity at the wide-angle end. The lens of Embodiment 3, from the object side, consists of a first lens group G1 with negative optical power, a second lens group G2 with positive optical power, and a third lens group G3 with positive optical power. An aperture stop S is positioned closest to the object side of the second lens group G2. A protective glass CG is positioned between the third lens group G3 and the image plane IMG. The second lens group G2, from the object side, consists of a lens with positive optical power (lens Lp), a lens with negative optical power, and a combined lens of a lens with positive optical power and a lens with negative optical power.

[0207] The zoom lens in Example 3 performs zoom operation by changing the air gap between the lens groups. In the figure, the arrows below each lens group indicate the trajectory of the lens group as it moves from the wide-angle end through the intermediate focal length to the telephoto end. When zooming from the wide-angle end to the telephoto end, the first lens group G1 is fixed in the optical axis direction. The second lens group G2 gradually moves towards the object side. The third lens group G3 moves towards the image side and then towards the object side. More specifically, zooming is performed by moving the second lens group G2 towards the object side as described above, and focus is performed by moving the third lens group G3 as described above to correct the focal position based on the zoom.

[0208] Next, examples of specific numerical values ​​for the zoom lens will be explained. Table 9 is a table of surface data for the zoom lens of Example 3. In Table 9, surfaces 1 to 6 are the surface numbers of the lenses in the first lens group G1, and surfaces 7 to 13 are the surface numbers of the lenses in the second lens group G2. Surface 7 represents the aperture stop and the surface of the lens closest to the object side of the second lens group G2. Surfaces 14 and 15 are the surface numbers of the lenses in the third lens group G3. Surfaces 16 and 17 represent the protective glass, and surface 18 represents the image plane.

[0209] [Table 9] Lens surface data

[0210]

[0211]

[0212] Table 10 shows various data for the zoom lens of Example 3. Table 11 shows the aspherical data of Example 3. Table 12 shows the lens group data of Example 3.

[0213] [Table 10] Various Data

[0214] Wide-angle end Telephoto end F 3.0000 6.9690 FNo 2.0719 3.1174 ω 68.0 28.1 Y 3.400 3.400 D(6) 7.402 0.603 D(13) 0.963 2.6312 D(15) 2.938 8.070

[0215] [Table 11] Aspherical Data

[0216] k A B C D E 3 0 0.00000E+00 -4.40682e-03 5.89606e-04 -4.50110e-05 1.37059e-06 4 0 0.00000E+00 -5.26205e-03 6.36316e-04 -5.12937e-05 1.68395e-06 7 0 0.00000E+00 -5.45898e-04 -5.52899e-05 -3.32593e-06 2.15720e-07 8 0 0.00000E+00 4.21906e-03 -3.69892e-04 2.40970e-05 -5.05537e-07 9 0 0.00000E+00 -1.09461e-02 1.65307e-03 -1.44489e-04 7.34208e-06 10 0 0.00000E+00 -1.86790e-02 2.42790e-03 -2.73409e-04 1.19781e-05 14 0 0.00000E+00 5.03710e-04 -3.36589e-05 5.61529e-06 -1.49835e-07 15 0 0.00000E+00 5.10712e-04 -4.51321e-05 6.17581e-06 -1.39098e-07

[0217] [Table 12] Lens Group Data

[0218] Lens group Initial interview - Final interview focal length G1 1-6 -4.9356 G2 7-13 7.7848 G3 14-15 20.6753

[0219] Figure 8 This is a diagram showing the longitudinal aberration of the zoom lens of Embodiment 3 when focusing at infinity at the wide-angle end. Figure 9 This is a diagram showing the longitudinal aberration of the zoom lens of Embodiment 3 when focusing at infinity at the telephoto end.

[0220] [Example 4]

[0221] Figure 10This diagram schematically illustrates the optical structure of the zoom lens of Embodiment 4 when focusing at infinity at the wide-angle end. The lens of Embodiment 4, from the object side, consists of a first lens group G1 with negative optical power, a second lens group G2 with positive optical power, a third lens group G3 with negative optical power, and a fourth lens group G4 with positive optical power. An aperture stop S is disposed between the first lens group G1 and the second lens group G2. A protective glass CG is disposed between the fourth lens group G4 and the image plane IMG. The second lens group G2, from the object side, consists of a lens with positive optical power (lens Lp) and a combined lens of a lens with negative optical power and a lens with positive optical power.

[0222] The zoom lens in Example 4 performs zoom operation by changing the air gap between the lens groups. In the figure, the arrows below each lens group indicate the trajectory of the lens group as it moves from the wide-angle end through the intermediate focal length to the telephoto end. When zooming from the wide-angle end to the telephoto end, the first lens group G1 and the third lens group G3 are fixed in the optical axis direction. The second lens group G2 gradually moves towards the object side. The fourth lens group G4 moves towards the image side and then towards the object side. More specifically, zooming is performed by moving the second lens group G2 towards the object side as described above, and focus correction and focusing based on the zoom focal position are performed by moving the fourth lens group G4 as described above.

[0223] Next, examples of specific numerical values ​​for the zoom lens will be explained. Table 13 is a table of surface data for the zoom lens of Example 4. In Table 13, surfaces 1 to 6 are the surface numbers of the lens in the first lens group G1, surface 7 represents the aperture stop. Surfaces 8 to 12 are the surface numbers of the lens in the second lens group G2, surface numbers 13 and 14 are the surface numbers of the lens in the third lens group G3. Surface numbers 15 and 16 are the surface numbers of the lens in the fourth lens group G4. Surface numbers 17 and 18 represent the protective glass, and surface 19 represents the image plane.

[0224] [Table 13] Lens surface data

[0225]

[0226]

[0227] Table 14 shows various data for the zoom lens of Example 4. Table 15 shows the aspherical data of Example 4. Table 16 shows the lens group data of Example 4.

[0228] [Table 14] Various Data

[0229] Wide-angle end Telephoto end F 3.0996 7.2852 FNo 2.0905 3.3754 ω 65.5 26.6 Y 3.400 3.400 D(6) 8.041 0.800 D(12) 0.800 8.041 D(14) 0.843 1.008 D(16) 4.068 3.904

[0230] [Table 15] Aspherical Data

[0231]

[0232]

[0233] [Table 16] Lens Group Data

[0234] Lens group Initial interview - Final interview focal length G1 1-6 -5.9306 G2 8-12 8.2438 G3 13-14 -17.956 G4 15-16 11.122

[0235] Figure 11 This is a diagram showing the longitudinal aberration of the zoom lens of Example 4 when focusing at infinity at the wide-angle end. Figure 12 This is a diagram showing the longitudinal aberration of the zoom lens of Embodiment 4 when focusing at infinity at the telephoto end.

[0236] [Example 5]

[0237] Figure 13 This diagram schematically illustrates the optical structure of the zoom lens of Embodiment 5 when focusing at infinity at the wide-angle end. The lens of Embodiment 5, starting from the object side, consists of a first lens group G1 with negative optical power and a second lens group G2 with positive optical power. Between the first lens group G1 and the second lens group G2, a filter F and an aperture stop S are arranged in the order of the filter F and aperture stop S, starting from the object side. A protective glass CG is disposed between the second lens group G2 and the image plane IMG. The second lens group G2, starting from the object side, consists of a lens with positive optical power, a lens with positive optical power, a lens with negative optical power and a lens with positive optical power combined, and a lens with negative optical power.

[0238] The zoom lens in Example 5 performs zoom operation by changing the air gap between the lens groups. In the figure, the arrows below each lens group indicate the trajectory of the lens group as it moves from the wide-angle end through the intermediate focal length to the telephoto end. When zooming from the wide-angle end to the telephoto end, the first lens group G1 gradually moves towards the image side, and the second lens group G2 gradually moves towards the object side. More specifically, zooming is performed by moving the second lens group G2 towards the object side, and focusing and correction of the focal position based on zoom are performed by moving the first lens group G1 towards the image side.

[0239] Next, examples of specific numerical values ​​for the zoom lens will be explained. Table 17 is a table of surface data for the zoom lens of Example 5. In Table 17, surfaces 1 to 6 are the surface numbers of the lenses in the first lens group G1. Surface 7 represents the filter, and surface 8 represents the aperture stop. Surfaces 9 to 17 are the surface numbers of the lenses in the second lens group G2. Surfaces 18 and 19 represent the protective glass, and surface 20 represents the image plane.

[0240] [Table 17] Lens surface data

[0241]

[0242]

[0243] Table 18 shows various data for the zoom lens of Example 5. Table 19 shows the aspherical data of Example 5. Table 20 shows the lens group data of Example 5.

[0244] [Table 18] Various Data

[0245] Wide-angle end Telephoto end F 3.0000 4.9000 FNo 2.09 2.80 ω 66.2 39.4 Y 3.4000 3.4000 D(6) 4.5295 1.1163 D(13) 4.1832 1.7451 D(15) 3.6063 6.0444

[0246] [Table 19] Aspherical Data

[0247]

[0248]

[0249] [Table 20] Lens Group Data

[0250] Lens group Initial interview - Final interview focal length G1 1-6 -5.9383 G2 9-17 7.6234

[0251] Figure 14 This is a diagram showing the longitudinal aberration of the zoom lens of Embodiment 5 when focusing at infinity at the wide-angle end. Figure 15 This is a diagram showing the longitudinal aberration of the zoom lens of Embodiment 5 when focusing at infinity at the telephoto end.

[0252] Table 21 shows the calculated values ​​based on the above formulas in Examples 1 to 5.

[0253] [Table 21] Table of Calculated Values

[0254] Example 1 Example 2 Example 3 Example 4 Example 5 <![CDATA[f2 / f 2p ]]> 0.95 0.87 1.39 0.92 0.90 <![CDATA[f2 / f w ]]> 2.56 2.62 2.59 2.66 2.54 ΔPdt_2p -0.13 -0.13 -0.13 -0.13 -0.13 <![CDATA[Nd2]]> 1.54 1.54 1.54 1.54 1.54 <![CDATA[f 2p / f w ]]> 2.69 3.00 1.86 2.90 2.82 <![CDATA[β 2t / b 2w ]]> 2.87 2.95 3.58 2.32 1.63 <![CDATA[|f s / R s |]]> 4.62 5.00 8.58 9.24 8.74 <![CDATA[f1 / f w ]]> -1.65 -1.73 -1.65 -1.91 -1.98

Claims

1. A zoom lens comprising, in order from an object side, a first lens group having negative refractive power, and a second lens group having positive refractive power, which performs a zooming operation by changing the interval between the adjacent lens groups, the second lens group has a single lens Lp having positive refractive power, has, on the image side of the lens Lp, a single lens L22 having negative refractive power with a convex shape on the object side, and has, on the image side of the lens L22, a single lens L23 having positive refractive power, the zoom lens satisfies the following formulas (1) to (4): 0.85 < f2 / f 2p <1.50 (1) 0 < f2 / f w <3.25 (2) - 0.30 < ΔPdt_2p < -0.10 (3) 1.50 < Nd2 < 2.00 (4) wherein f2: focal length of the second lens group f 2p : focal length of the lens Lp f w : focal length at wide angle end at infinity focus of the zoom lens ΔPdt_2p: abnormal dispersion between d-line and t-line of the lens Lp Nd2: refractive index at d-line of the lens Lp.

2. The zoom lens according to claim 1, the lens Lp is a plastic lens.

3. The zoom lens according to claim 1, satisfies the following formula (5): 1.80 < f 2p / f w < 3.50 (5).

4. The zoom lens according to claim 1, satisfies the following formula (6): 1.5＜β 2t / β 2w ＜4.0 （6） wherein beta 2t : the lateral magnification of the second lens group at the telephoto end β 2w : the lateral magnification of the second lens group at the wide angle end.

5. The zoom lens according to claim 1, the second lens group has a cemented lens formed by cementing a lens having negative refractive power and a lens having positive refractive power, and satisfies the following formula (7): 3.0 < |f s / R s | < 20.0 (7) wherein f s : focal length of the joining lens R s : the radius of curvature of the joining surface of the joining lens.

6. The zoom lens according to claim 1, satisfies the following formula (8): - 2.8 < f1 / f w < -1.5 (8) wherein f1: focal length of the first lens group.

7. The zoom lens according to claim 1, at least one lens having negative refractive power disposed in the second lens group is a plastic lens.

8. An imaging apparatus comprising: the zoom lens according to any one of claims 1 to 7, and a solid-state imaging device disposed on the image side of the zoom lens and configured to convert an optical image formed by the zoom lens into an electric signal.

Images