Zoom lens and image capturing device

Abstract

To provide a wide-angle, large-aperture zoom lens which offers high optical performance.SOLUTION: A zoom lens provided herein comprises a first lens group L1 having negative refractive power, and a rear group including at least three lens groups and having positive composite refractive power at the wide-angle end. The first lens group comprises three negative lenses arranged successively in order from the object side to the image side. A focal length f1 of the first lens group, a focal length fRw of the rear group at the wide-angle end, a back focus Bfw of the zoom lens at the wide-angle end, a focal length fw of the zoom lens at the wide-angle end, and a half angle ωw of the zoom lens at the wide-angle end satisfy conditions expressed as: -2.5≤f1 / fRw≤-0.5 and 0.3≤BFw / (fw×tanωw)≤0.8.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a zoom lens used for imaging and the like.

Background Art

[0002] As a retrofocus type zoom lens, those having a first lens group with negative refractive power and a rear group including a plurality of lens groups arranged in order from the object side to the image side are disclosed in Patent Documents 1 and 2. The zoom lens of Patent Document 1 is composed of a first lens group with negative refractive power, a second lens group with positive refractive power, an aperture stop, a third lens group with negative refractive power, a fourth lens group with positive refractive power, a fifth lens group with negative refractive power, and a sixth lens group with negative refractive power, which are arranged in order from the object side. The zoom lens of Patent Document 2 is composed of a first lens group with negative refractive power, a second lens group with positive refractive power including an aperture stop, a third lens group with negative refractive power, and a fourth lens group with negative refractive power, which are arranged in order from the object side.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] Such a zoom lens is required to be small, have a high magnification ratio, and have high optical performance. For this purpose, it is important to appropriately set the refractive power and configuration of each lens group, as well as the movement conditions during zooming.

[0005] In the zoom lens of Patent Document 1, the number of negative lenses included in the first lens group is small, and it is difficult to achieve wide-angle conversion while correcting off-axis aberrations such as field curvature. In the zoom lens of Patent Document 2, the refractive power of the first lens group is strong, which is advantageous for miniaturization. However, in order to obtain wide-angle conversion and high optical performance, it is necessary to arrange many aspherical lenses in the first lens group, which easily causes a decrease in optical performance due to molding variations of each aspherical lens.

[0006] The present invention provides a zoom lens that can obtain a wide-angle, large-aperture, and high optical performance.

Means for Solving the Problems

[0007] In the zoom lens as one aspect of the present invention, the lens groups arranged in order from the object side to the image side include a first lens group having a negative refractive power and a rear group including at least three lens groups and having a positive combined refractive power at the wide-angle end, and the interval between adjacent lens groups changes during zooming. The first lens group includes at least three negative lenses arranged continuously in order from the object side to the image side. When the focal length of the first lens group is f1, the focal length of the rear group at the wide-angle end is fRw, the back focus at the wide-angle end of the zoom lens is BFw, the focal length of the zoom lens at the wide-angle end is fw, and the half field angle at the wide-angle end of the zoom lens is ωw, -2.5 ≦ f1 / fRw ≦ -0.5 0.3 ≦ BFw / (fw × tan ωw) ≦ 0.8 It is characterized by satisfying the conditions. Note that an imaging device equipped with the above zoom lens also constitutes another aspect of the present invention.

Effects of the Invention

[0008] According to the present invention, it is possible to provide a zoom lens that can obtain a wide-angle, large-aperture, and high optical performance.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

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Figure 12

BEST MODE FOR CARRYING OUT THE INVENTION

[0010] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Here, before specifically describing the zoom lenses of Examples 1 to 5, matters common to the zoom lenses of each embodiment will be described. FIGS. 1, 3, 5, 7, and 9 respectively show cross-sections of the zoom lenses of Examples 1 to 5 at the wide-angle end and the telephoto end.

[0011] The zoom lens of each embodiment is used as an imaging optical system in an imaging device such as a video camera, a digital still camera, a silver halide film camera, a TV camera, an in-vehicle camera, and a surveillance camera. Also, the zoom lens of each embodiment can be used as a projection optical system in an image projection device (projector).

[0012] In each cross-sectional view, the left side is the object side (front side) and the right side is the image side (rear side). Also, let i be the order of the lens groups from the object side, and Li denote the i-th lens group. In a zoom lens, a lens group is a collection of one or more lenses that move together during zooming (variation in magnification) between the wide-angle end and the telephoto end. That is, the distance between adjacent lens groups changes during zooming. A lens group may include a diaphragm. Also, the wide-angle end and the telephoto end respectively indicate the zoom states of the maximum angle of view (shortest focal length) and the minimum angle of view (longest focal length) when the lens group that moves during zooming is located at both ends of the range where it can move mechanically or controllably on the optical axis.

[0013] SP is a diaphragm that determines (limits) the light beam of the open F-number Fno. IP is the image plane. On the image plane IP, the imaging surface (light-receiving surface) of an imaging device such as a CCD sensor or a CMOS sensor, or the film surface (photosensitive surface) of a silver halide film is arranged. The arrow marked with Focus indicates the moving direction of the lens group during focusing from infinity to a short distance.

[0014] The zoom lens of each embodiment is a zoom lens composed of a first lens group L1 having a negative refractive power (reciprocal of the focal length) and a rear group LR including at least three lens groups and having a positive combined refractive power at the wide-angle end, with the lens groups arranged in order from the object side to the image side. In order to ensure a wide angle of view in the wide-angle region and correct aberrations well throughout the zoom range to obtain high optical performance, the zoom lens of each embodiment has a configuration in which negative and positive refractive powers are arranged from the object side.

[0015] The first lens group L1 does not move during zooming and focusing. The first lens group L1 includes three lenses with negative refractive powers arranged continuously in order from the object side to the image side. With this configuration, while ensuring a wide angle of view in the wide-angle region, off-axis aberrations such as coma aberration and field curvature can be corrected well. In the case where the first lens group L1 includes one cemented lens in which two or more lenses are cemented, the cemented lens shall be counted as two or more lenses.

[0016] In addition, since the rear group LR includes at least three lens groups, coma aberration that changes during zooming can be corrected well, and particularly, spherical aberration and coma aberration that are likely to occur due to an increase in the light beam in the telephoto range can be corrected well.

[0017] And the zoom lens of each embodiment satisfies the conditions of the following formulas (1) and (2).

[0018] -2.5 ≦ f1 / fRw ≦ -0.5 (1) 0.3 ≦ BFw / (fw × tan ωw) ≦ 0.8 (2) In formulas (1) and (2), let the focal length of the first lens group L1 be f1, the focal length of the rear group LR at the wide-angle end be fRw, the back focus at the wide-angle end of the zoom lens be BFw, the focal length of the entire zoom lens system at the wide-angle end be fw, and the half field angle at the wide-angle end of the zoom lens be ωw. The back focus is the air-converted value of the distance on the optical axis from the most image-side surface (the final surface) of the zoom lens to the paraxial image plane. Note that an optical member such as an optical filter or a prism having no refractive power or having an extremely weak refractive power may be disposed between the zoom lens and the image plane.

[0019] The condition of formula (1) shows an appropriate relationship between the focal length of the first lens group L1 and the focal length of the rear group LR at the wide-angle end, and is a condition for enabling wide-angle conversion and good correction of field curvature and longitudinal chromatic aberration in the wide-angle range. When f1 / fRw exceeds the upper limit of formula (1), the refractive power of the first lens group L1 with respect to the rear group LR becomes strong, which is advantageous for miniaturization of the entire system, but correction of field curvature and longitudinal chromatic aberration generated in the first lens group L1 becomes difficult, which is not preferable. When f1 / fRw is below the lower limit of formula (1), the refractive power of the first lens group L1 with respect to the rear group LR becomes weak, which is advantageous for reducing various aberrations generated by off-axis light beams, but wide-angle conversion becomes difficult, which is not preferable. Furthermore, since miniaturization of the zoom lens becomes difficult, it is not preferable.

[0020] The condition of Equation (2) shows an appropriate relationship between the back focus in the wide-angle range, the focal length in the wide-angle range, and the tangent of the half field angle in the wide-angle range, and shows an appropriate relationship between the back focus and the image height on the image plane. If the back focus at the wide-angle end becomes long such that BFw / (fw×tanωw) exceeds the upper limit of Equation (2), the height of the off-axis light beam passing through the final lens group becomes low, making it difficult to correct field curvature and magnification chromatic aberration, which is not preferable. If the back focus at the wide-angle end becomes short such that BFw / (fw×tanωw) is below the lower limit of Equation (2), the distance between the lens arranged closest to the image side and the image plane (image sensor) becomes short, making it difficult to arrange a mount that ensures a predetermined strength, which is not preferable.

[0021] Note that it is more preferable if the numerical ranges of Equations (1) and (2) are as follows.

[0022] -2.0 ≦ f1 / fRw ≦ -0.8 (1a) 0.4 ≦ BFw / (fw×tanωw) ≦ 0.6 (2a) By satisfying the condition of Equation (1a), it becomes easier to suppress the spherical aberration generated by the on-axis light beam in the wide-angle range and to suppress the field curvature and magnification chromatic aberration generated by the off-axis light beam. Also, by satisfying the condition of Equation (2a), it becomes easier to achieve wide-angle conversion and downsizing of the entire system.

[0023] Also, it is even more preferable if the numerical ranges of Equations (1) and (2) are as follows.

[0024] -1.5 ≦ f1 / fRw ≦ -1.0 (1b) 0.45 ≦ BFw / (fw×tanωw) ≦ 0.55 (2b) By satisfying the above configuration and conditions, it is possible to realize a zoom lens with a wide field angle at the wide-angle end, a large aperture, and high optical performance.

[0025] Also, the zoom lens of each embodiment preferably satisfies at least one of the conditions of the following Equations (3) to (14).

[0026] -3.0 ≤ f1 / fw ≤ -1.0 (3) -2.0 ≤ f1 / ft ≤ -0.5 (4) 0.10 ≤ LD1 / TLt ≤ 0.30 (5) 0.70 ≤ TLt / TLw ≤ 1.10 (6) 0.10 ≤ LD12w / TLw ≤ 0.30 (7) -0.40 ≤ f1 / TLw ≤ -0.20 (8) -2.5 ≤ SF11 ≤ -1.2 (9) -4.5 ≤ SF12 ≤ -1.2 (10) -0.40 ≤ nd1n - nd1p ≤ -0.20 (11) 1.2 ≤ νd1n / νd1p ≤ 2.5 (12) 0.05 ≤ DRMAX ≤ 0.40 (13) 45° ≤ ωw ≤ 60° (14) In formulas (3) to (14), let ft be the focal length at the telephoto end of the entire zoom lens system, LD1 be the length on the optical axis (lens group thickness) of the first lens group L1, and LD12w be the interval on the optical axis between the first lens group L1 and the second lens group L2 at the wide-angle end. Let TLw and TLt be the overall optical lengths at the wide-angle end and the telephoto end of the entire zoom lens system, respectively. The overall optical length is the length obtained by adding the back focus to the length on the optical axis from the most object-side surface (frontmost surface) of the zoom lens to the final surface (added retrospectively).

[0027] The first lens group L1 preferably has at least three negative lenses from the most object side. In this case, let R1 be the radius of curvature of the object-side surface of the negative lens arranged on the most object side in the first lens group L1, R2 be the radius of curvature of the image-side surface, and SF11 be the shape factor. Also, let R3 be the radius of curvature of the object-side surface of the second negative lens from the object side in the first lens group L1, R4 be the radius of curvature of the image-side surface, and SF12 be the shape factor.

[0028] The shape factor SF is defined by the following formula when the radius of curvature of the object-side surface of the lens is Ra and the radius of curvature of the image-side surface is Rb.

[0029] SF = (Rb + Ra) / (Rb - Ra) That is SF11 = (R2 + R1) / (R2 - R1) SF12 = (R4 + R3) / (R4 - R3) When the surface has an aspherical shape, Ra and Rb are the radius R of the base surface (reference quadratic surface) of the aspherical surface.

[0030] Let the average refractive index of at least one positive lens included in the first lens group L1 at the d-line be nd1p, and the average refractive index of at least three negative lenses included in the first lens group L1 at the d-line be nd1n. Let the average Abbe number based on the d-line of at least one positive lens included in the first lens group L1 be νd1p, and the average Abbe number based on the d-line of at least three negative lenses included in the first lens group L1 be νd1n. For the Abbe number νd based on the d-line, when the refractive indices at the d-line (587.56 nm), F-line (486.1 nm), and C-line (656.3 nm) of the Fraunhofer lines are Nd, NF, and NC respectively νd = (Nd - 1) / (NF - NC) It is defined as

[0031] Let the maximum value of the absolute value of the aspherical amount of the aspherical lens included in the first lens group L1 be DRMAX. The aspherical amount will be described with reference to FIG. 11. The aspherical amount is the position difference in the optical axis direction between an arbitrary position on the reference spherical surface, which is a spherical surface connecting the position P corresponding to the effective diameter of the aspherical surface and the vertex of the aspherical surface, and the position at the same height as the arbitrary position on the aspherical surface. Therefore, the aspherical amount DR is represented by DR = X - Xr in FIG. 11. DRMAX is the maximum value of the absolute value of DR.

[0032] The condition of Equation (3) shows an appropriate relationship between the focal length of the first lens group L1 and the focal length at the wide-angle end of the entire zoom lens system, and is a condition for ensuring a wide angle of view at the wide-angle end. If the focal length of the first lens group L1 with respect to the focal length at the wide-angle end of the entire system becomes longer such that f1 / fw exceeds the upper limit of Equation (3), the divergence effect of the light beam emitted from the first lens group L1 weakens, leading to an increase in the size of the rear lens group LR, which is not preferable. If the focal length of the first lens group L1 with respect to the focal length at the wide-angle end of the entire system becomes shorter such that f1 / fw is below the lower limit of Equation (3), the refractive power of the light beam emitted from the first lens group L1 increases, leading to an increase in field curvature and longitudinal chromatic aberration, which is not preferable.

[0033] The condition of Equation (4) shows an appropriate relationship between the focal length of the first lens group L1 and the focal length at the telephoto end of the entire zoom lens system, and is a condition for ensuring a wide angle of view at the wide-angle end and a high magnification ratio. If the focal length of the first lens group L1 with respect to the focal length at the telephoto end of the entire system becomes longer such that f1 / ft exceeds the upper limit of Equation (4), it becomes difficult to ensure a wide angle of view at the wide-angle end, which is not preferable. If the focal length of the first lens group L1 with respect to the focal length at the telephoto end of the entire system becomes shorter such that f1 / ft is below the lower limit of Equation (4), the divergence effect of the light beam emitted from the first lens group L1 increases, making it difficult to ensure a long focal length (high magnification ratio) in the telephoto range, which is not preferable.

[0034] The condition of Equation (5) shows an appropriate relationship between the lens group thickness of the first lens group L1 and the overall optical length at the telephoto end of the zoom lens, and is a condition for achieving miniaturization of the entire system at the telephoto end. If LD1 / TLt exceeds the upper limit of Equation (5), arranging a large number of lenses in the first lens group L1 is advantageous for correcting field curvature, longitudinal chromatic aberration, and wide-angle conversion generated in the first lens group L1, but it is not preferable because the focal length at the telephoto end cannot be lengthened to ensure the required magnification ratio. If LD1 / TLt is below the lower limit of Equation (5), it is impossible to ensure the moving distance of the first lens group L1 during zooming, making it difficult to ensure the required magnification ratio, which is not preferable.

[0035] The condition of Equation (6) shows an appropriate relationship between the overall optical lengths at the wide-angle end and the telephoto end of the zoom lens, and is a condition for achieving both high magnification and miniaturization. When TLt / TLw exceeds the upper limit of Equation (6), it becomes difficult to secure the moving distance of the lens group that moves during zooming within the rear group LR, which is not preferable. When TLt / TLw is below the lower limit of Equation (6), although it is advantageous for miniaturization at the wide-angle end, the moving distance of the lens group that moves during zooming becomes long, and the variations in various aberrations such as spherical aberration associated with zooming become large, which is not preferable.

[0036] The condition of Equation (7) shows an appropriate relationship between the interval on the optical axis between the first lens group L1 and the second lens group L2 at the wide-angle end and the overall optical length at the wide-angle end of the zoom lens, and is a condition for securing the moving distance of the first lens group L1 during zooming. When LD12w / TLw exceeds the upper limit of Equation (7), the moving distance of the first lens group L1 during zooming becomes long, and the variations in various aberrations such as spherical aberration associated with zooming become large, which is not preferable. When LD12w / TLw is below the lower limit of Equation (7), the moving distance of the first lens group L1 during zooming cannot be secured, and it becomes difficult to achieve the required magnification ratio, which is not preferable.

[0037] The condition of Equation (8) shows an appropriate relationship between the focal length of the first lens group L1 and the overall optical length at the wide-angle end of the zoom lens, and is a condition for securing a wide angle of view and a high magnification ratio at the wide-angle end. When the focal length of the first lens group L1 becomes longer relative to the focal length of the second lens group L2 such that f1 / TLw exceeds the upper limit of Equation (8), it becomes difficult to secure a wide angle of view at the wide-angle end, which is not preferable. When the focal length of the first lens group L1 becomes shorter relative to the focal length of the second lens group L2 such that f1 / TLw is below the lower limit of Equation (8), the divergence effect of the light beam emitted from the first lens group L1 is enhanced, and it becomes difficult to secure a long focal length (high magnification ratio) in the telephoto range, which is not preferable.

[0038] The condition of Equation (9) is a condition regarding the shape factor of the most object-side negative lens (hereinafter referred to as the first negative lens) of the first lens group L1, and is a condition for achieving both wide-angleization and suppression of field curvature occurring in off-axis light beams. When the SF11 of the first negative lens is -1, the first negative lens has a plano-concave shape with a concave surface facing the image side. If the refractive power of the first negative lens becomes stronger such that SF11 exceeds the upper limit of Equation (9), it is advantageous for wide-angleization, but since the curvature of the object-side surface becomes smaller and coma and field curvature increase, it is not preferable. Also, since the curvature of the object-side surface becomes smaller, processing and molding of the first negative lens become difficult, which is not preferable. If the curvature of the object-side surface of the first negative lens becomes larger such that SF11 is below the lower limit of Equation (9), it is advantageous for correcting longitudinal chromatic aberration, but wide-angleization becomes difficult, which is not preferable.

[0039] The condition of Equation (10) shows a condition regarding the shape factor of the second negative lens (hereinafter referred to as the second negative lens), which is the second lens from the object side in the first lens group L1, and is a condition for achieving both wide-angleization and suppression of longitudinal chromatic aberration occurring in off-axis light beams. When the SF12 of the second negative lens is -1, the second negative lens has a plano-concave shape with a concave surface facing the image side. If the refractive power of the second negative lens becomes stronger such that SF12 exceeds the upper limit of Equation (10), it is advantageous for wide-angleization, but since the curvature of the object-side surface becomes smaller and longitudinal chromatic aberration increases, it is not preferable. Also, since the curvature of the object-side surface becomes smaller, processing and molding of the second negative lens become difficult, which is not preferable. If the curvature of the object-side surface of the second negative lens becomes larger such that SF12 is below the lower limit of Equation (10), it is advantageous for correcting longitudinal chromatic aberration, but wide-angleization becomes difficult, which is not preferable.

[0040] The condition of Equation (11) shows an appropriate relationship between the average refractive index of at least three negative lenses included in the first lens group L1 and the average refractive index of at least one positive lens included therein. By optimizing the refractive indices of the lenses within the first lens group L1 so as to satisfy this condition, it is possible to achieve both miniaturization of each lens diameter and suppression of the field curvature generated within the first lens group L1. When nd1n - nd1p exceeds the upper limit of Equation (11), although it is possible to correct the field curvature and astigmatism well, it causes an increase in axial chromatic aberration, which is not preferable. Also, it becomes difficult to optimize the refractive power of these negative lenses, leading to an increase in the lens diameter, which is not preferable. When nd1n - nd1p is below the lower limit of Equation (11), it becomes difficult to correct the field curvature and distortion aberration mainly caused by off-axis rays, which is not preferable. Also, it becomes difficult to optimize the Abbe number of these negative lenses, leading to an increase in the longitudinal chromatic aberration, which is not preferable.

[0041] The condition of Equation (12) shows an appropriate relationship between the average Abbe number of at least three negative lenses included in the first lens group L1 and the average Abbe number of at least one positive lens included therein. By optimizing the Abbe numbers of the lenses within the first lens group L1, it is possible to achieve both miniaturization of the lens diameter and suppression of the longitudinal chromatic aberration generated within the first lens group L1. When νd1n / νd1p exceeds the upper limit of Equation (12), it is possible to correct the longitudinal chromatic aberration well, but it causes an increase in axial chromatic aberration, and it also becomes difficult to optimize the refractive power of the negative lens, leading to an increase in its lens diameter, which is not preferable. When νd1n / νd1p is below the lower limit of Equation (12), although it becomes easy to suppress the field curvature and distortion aberration mainly caused by off-axis rays, it becomes difficult to correct the longitudinal chromatic aberration, which is not preferable.

[0042] The condition of Equation (13) shows an appropriate range of the aspheric amount of the aspheric lens included in the first lens group L1. When DRMAX exceeds the upper limit value of Equation (13), it becomes difficult to manufacture the aspheric lens, which is not preferable. When DRMAX is below the lower limit of Equation (13), it becomes difficult to correct the spherical aberration and coma aberration, which is not preferable.

[0043] The condition of Equation (14) indicates an appropriate range of the half angle at the wide-angle end. If ωw exceeds the upper limit of Equation (14), it results in an excessive angle of view and leads to an increase in the size of the zoom lens, which is not preferable. If ωw is below the lower limit of Equation (14), it becomes difficult to widen the angle of view, which is not preferable.

[0044] Note that it is more preferable if the numerical ranges of Equations (3) to (14) are as follows.

[0045] -2.7 ≦ f1 / fw ≦ -1.5 (3a) -1.7 ≦ f1 / ft ≦ -0.5 (4a) 0.12 ≦ LD1 / TLt ≦ 0.27 (5a) 0.80 ≦ TLt / TLw ≦ 1.00 (6a) 0.12 ≦ LD12w / TLw ≦ 0.25 (7a) -0.35 ≦ f1 / TLw ≦ -0.22 (8a) -2.3 ≦ SF11 ≦ -1.4 (9a) -4.2 ≦ SF12 ≦ -1.5 (10a) -0.35 ≦ nd1n - nd1p ≦ -0.22 (11a) 1.4 ≦ νd1n / νd1p ≦ 2.2 (12a) 0.08 ≦ DRMAX ≦ 0.35 (13a) 47° ≦ ωw ≦ 57° (14a) Moreover, it is even more preferable if the numerical ranges of Equations (3) to (14) are as follows.

[0046] -2.5 ≦ f1 / fw ≦ -2.0 (3b) -1.5 ≦ f1 / ft ≦ -1.1 (4b) 0.15 ≦ LD1 / TLt ≦ 0.25 (5b) 0.85 ≦ TLt / TLw ≦ 0.96 (6b) 0.15 ≦ LD12w / TLw ≦ 0.22 (7b) -0.33 ≦ f1 / TLw ≦ -0.25 (8b) -2.1 ≦ SF11 ≦ -1.6 (9b) -4.0 ≦ SF12 ≦ -1.7 (10b) -0.33 ≦ nd1n - nd1p ≦ -0.24 (11b) 1.6 ≦ νd1n / νd1p ≦ 2.0 (12b) 0.10 ≦ DRMAX ≦ 0.32 (13b) 50° ≦ ωw ≦ 55° (14b) The zoom lens of each embodiment preferably satisfies at least one of the following configurations.

[0047] The first lens group L1 preferably has three negative lenses continuously in order from the object side. Further, the first lens group L1 preferably has at least one positive lens. In particular, it is more preferable that the first lens group L1 is composed of three negative lenses and one positive lens continuously in order from the object side. With such a configuration, the degree of freedom in selecting the optical material of the negative lens increases, and various aberrations such as magnification chromatic aberration can be corrected well.

[0048] Also, it is preferable that the negative lens in the first lens group L1 has an aspherical surface. Thereby, while effectively correcting the field curvature at the wide-angle end, it becomes easy to reduce the size of the first lens group L1. However, if the negative lens has two or more aspherical surfaces, although it is advantageous for correcting field curvature and distortion aberration, the manufacturing error of the lens increases and the manufacturing difficulty becomes high, and it becomes difficult to ensure the optical performance. Therefore, it is desirable that the aspherical surface is one surface.

[0049] Also, the second lens group L2 is preferably arranged on the object side of the aperture stop SP and is composed of a single lens as one positive lens. Thereby, the light beam diverged by the first lens group L1 can be converged and made to enter the third lens group L3 almost telecentrically, and it becomes easy to suppress the variation of spherical aberration due to focusing.

[0050] Also, the rear group LR preferably includes aspherical surfaces on at least two surfaces. Thereby, while effectively correcting the field curvature in the wide-angle range and the spherical aberration in the telephoto range, it becomes easy to reduce the size of the rear group LR.

[0051] Also, it is preferable that the rearmost lens group of the rear group LR has a configuration in which it does not move during zooming or the amount of movement during zooming becomes short. Thereby, the number of lens groups that move a long distance during zooming can be reduced, making it easier to configure a zoom drive mechanism. Also, by arranging a lens near the image plane in the telephoto range, various aberrations such as field curvature and longitudinal chromatic aberration generated by off-axis rays can be corrected well. In particular, since the rearmost lens group does not move during zooming, it is possible to reduce the intrusion of foreign matters such as dust into the zoom lens, which is a problem when the zoom lens is removable from the imaging device like an interchangeable lens, and it becomes easier to ensure the durability of the zoom lens.

[0052] Also, it is preferable that the rear group LR has at least two cemented lenses in which a positive lens and a negative lens are cemented together. Thereby, various aberrations such as variations in spherical aberration for each wavelength and longitudinal chromatic aberration in the telephoto range can be corrected well.

[0053] Furthermore, it is desirable that the rearmost lens on the image side in the rearmost lens group is a lens convex toward the image side. Thereby, it becomes easy to secure the back focus, and it is possible to suppress the condensation of unnecessary light (ghost) caused by the imaging element.

[0054] Also, it is preferable that the rearmost lens group is composed of one single lens having a positive refractive power. Thereby, the weight of the entire system can be reduced, the incident angle of the off-axis light beam incident on the image plane can be made gentle, and the occurrence of color separation generated on the image plane can be suppressed.

[0055] Further, in the zoom lens of each embodiment, the whole or a part of any lens group may be used as an anti-shake group that reduces image blur by moving it (shifting in a direction including a component orthogonal to the optical axis or rotating around a point on the optical axis) with respect to the optical axis. In the zoom lens of each embodiment, the whole or a part of the lens group disposed on the image side of the aperture stop SP in the rear group LR is used as the anti-shake group. Note that there are no particular restrictions on the number and shape of the lenses constituting the anti-shake group. Further, the anti-shake group preferably has a negative refractive power, and more preferably is constituted by one cemented lens in which one negative lens and one positive lens are cemented together.

[0056] In the zoom lens of each embodiment, it is preferable to perform focusing by moving the whole or a part of any lens group as a focusing group in the optical axis direction. At this time, it is desirable that the focusing group is disposed on the object side of the aperture stop SP. By disposing the focusing group on the object side in this way, it becomes easy to suppress fluctuations in axial chromatic aberration due to focusing. Further, the focusing group is preferably constituted by one negative lens. This makes it easy to reduce the weight of the focusing group and suppress fluctuations in magnification chromatic aberration due to focusing.

[0057] Further, the zoom lens of each embodiment preferably does not include a diffractive optical element. When a diffractive optical element is included, it is advantageous from the viewpoint of chromatic aberration correction, but it is not preferable because diffractive flare occurs in the diffractive optical element.

[0058] Next, the configuration of the zoom lens of each embodiment will be specifically described. Further, after Example 5, Numerical Examples 1 to 5 corresponding to each of Examples 1 to 5 are shown. In each embodiment (numerical example), a zoom lens having high imaging performance is obtained by appropriately setting the power arrangement of the lens groups that move during zooming and the variable magnification burden due to the configuration of each lens group.

Example

[0059] The zoom lens of Example 1 shown in Fig. 1 is composed of a first lens group L1 with negative refractive power, a second lens group L2 with positive refractive power, a third lens group L3 with negative refractive power, a fourth lens group L4 with positive refractive power including an aperture stop SP, and a fifth lens group L5 with positive refractive power as the final lens group. The second lens group L2 to the fifth lens group L5 constitute a rear group LR with positive refractive power. When zooming from the wide-angle end to the telephoto end, the first lens group L1 moves toward the image side, the second lens group L2 to the fourth lens group L4 move toward the object side, and the fifth lens group L5 does not move. When focusing from an infinite object to a close object, the third lens group L3 moves toward the object side.

[0060] The zoom lens of Numerical Example 1 is a zoom lens with a zoom ratio of 1.7 and an aperture ratio of about 2.9. Figs. 2(A) and (B) show the longitudinal aberrations (spherical aberration, astigmatism, distortion, and chromatic aberration) at the wide-angle end and the telephoto end of the zoom lens of Numerical Example 1, respectively. In the spherical aberration diagram, Fno indicates the F-number. The solid line represents the spherical aberration for the d-line (wavelength 587.6 nm), and the two-dot chain line represents the spherical aberration for the g-line (wavelength 435.8 nm). In the astigmatism diagram, the solid line ΔS represents the astigmatism in the sagittal image plane, and the broken line ΔM represents the astigmatism in the meridional image plane. The distortion aberration diagram shows the distortion aberration at the d-line. The chromatic aberration diagram shows the lateral chromatic aberration at the g-line. ω is the semi-field angle (°) as a ray tracing value. The explanation of this aberration diagram is the same for other numerical examples described later.

Example

[0061] The zoom lens of Example 2 shown in FIG. 3 is composed of a first lens group L1 with negative refractive power, a second lens group L2 with negative refractive power, a third lens group L3 with positive refractive power including an aperture stop SP, and a fourth lens group L4 with positive refractive power as the final lens group. The second lens group L2 to the fifth lens group L4 constitute a rear group LR with positive refractive power. When zooming from the wide-angle end to the telephoto end, the first lens group L1 moves toward the image side, the second lens group L2 and the third lens group L3 move toward the object side, and the fourth lens group L4 does not move. When focusing from an infinite object to a close object, the second lens group L2 moves toward the object side.

[0062] The zoom lens of Numerical Example 2 is a zoom lens with a zoom ratio of 1.6 and an aperture ratio of about 2.9. FIGS. 4(A) and (B) show the longitudinal chromatic aberration at the wide-angle end and the telephoto end of the zoom lens of Numerical Example 2, respectively.

Example

[0063] The zoom lens of Example 3 shown in FIG. 5 is composed of a first lens group L1 with negative refractive power, a second lens group L2 with positive refractive power, a third lens group L3 with negative refractive power, a fourth lens group L4 with positive refractive power including an aperture stop SP, a fifth lens group L5 with positive refractive power, and a sixth lens group L6 with positive refractive power as the final lens group. The second lens group L2 to the sixth lens group L6 constitute a rear group LR with positive refractive power. When zooming from the wide-angle end to the telephoto end, the first lens group L1 moves toward the image side, the second lens group L2 to the fifth lens group L5 move toward the object side, and the sixth lens group L6 does not move. When focusing from an infinite object to a close object, the third lens group L3 moves toward the object side.

[0064] The zoom lens of Numerical Example 3 is a zoom lens with a zoom ratio of 1.8 and an aperture ratio of about 2.9. FIGS. 6(A) and (B) show the longitudinal chromatic aberration at the wide-angle end and the telephoto end of the zoom lens of Numerical Example 3, respectively.

Example

[0065] The zoom lens of Example 4 shown in FIG. 7 is composed of a first lens group L1 with negative refractive power, a second lens group L2 with positive refractive power, a third lens group L3 with negative refractive power, a fourth lens group L4 with positive refractive power including an aperture stop SP, and a fifth lens group L5 with positive refractive power as the final lens group. The second lens group L2 to the fifth lens group L5 constitute a rear group LR with positive refractive power. When zooming from the wide-angle end to the telephoto end, the first lens group L1 moves toward the image side, the second lens group L2 to the fourth lens group L4 move toward the object side, and the fifth lens group L5 does not move. When focusing from an infinite object to a close object, the third lens group L3 moves toward the object side.

[0066] The zoom lens of Numerical Example 4 is a zoom lens with a zoom ratio of 1.7 and an aperture ratio of about 2.9. FIGS. 8(A) and (B) show the longitudinal aberration at the wide-angle end and the telephoto end of the zoom lens of Numerical Example 4, respectively.

Example

[0067] The zoom lens of Example 5 shown in FIG. 9 is composed of a first lens group L1 with negative refractive power, a second lens group L2 with positive refractive power, a third lens group L3 with negative refractive power, a fourth lens group L4 with positive refractive power including an aperture stop SP, and a fifth lens group L5 with negative refractive power as the final lens group. The second lens group L2 to the fifth lens group L5 constitute a rear group LR with positive refractive power. When zooming from the wide-angle end to the telephoto end, the first lens group L1 moves toward the image side, and the second lens group L2 to the fifth lens group L5 move toward the object side. When focusing from an infinite object to a close object, the third lens group L3 moves toward the object side.

[0068] The zoom lens of Numerical Example 5 is a zoom lens with a zoom ratio of 1.7 and an aperture ratio of about 2.9. FIGS. 10(A) and (B) show the longitudinal aberration at the wide-angle end and the telephoto end of the zoom lens of Numerical Example 4, respectively.

[0069] The following shows Numerical Examples 1 to 5. In each numerical example, the surface number i indicates the order of the surface when counted from the object side. r is the radius of curvature (mm) of the i-th surface from the object side, d is the lens thickness or air gap (mm) on the optical axis between the i-th and (i + 1)-th surfaces, nd is the refractive index at the d-line of the optical material between the i-th and (i + 1)-th surfaces. νd is the Abbe number based on the d-line of the optical material between the i-th and (i + 1)-th surfaces. BF represents the back focus (mm). The overall lens length (mm) corresponds to the aforementioned overall optical length.

[0070] The "*" attached to the surface number means that the surface has an aspherical shape. The aspherical shape is represented by the following equation when X is the displacement amount from the vertex of the surface in the optical axis direction, H is the height from the optical axis in the direction perpendicular to the optical axis, the direction of light propagation is positive, R is the paraxial radius of curvature, K is the conic constant, and A4, A6, A8, A10, A12 are the aspherical coefficients. The "e±x" of the conic constant and aspherical coefficients means ×10 ±x is meant.

[0071]

Number

[0072] Also, the values corresponding to the aforementioned formulas (1) to (14) in Numerical Examples 1 to 5 are summarized in Table 1. Each numerical example satisfies all the conditions of formulas (1) to (14). Also, Numerical Examples 1 to 4 satisfy all the conditions of formulas (1a) to (14a) and formulas (1b) to (14b), and Numerical Example 5 satisfies the conditions of (1a), (3a) to (14a) and formulas (1b), (3b) to (14b). [Numerical Example 1] Unit: mm Surface Data Surface Number r d nd νd 1 88.348 1.40 1.95375 32.3 2 23.448 0.05 1.53344 52.7 3* 20.527 6.84 4 79.576 1.20 1.48749 70.2 5 23.135 8.51 6 -45.566 1.10 1.49700 81.7 7 54.458 0.12 8 41.235 6.10 1.90043 37.4 9 -79.023 (variable) 10 48.326 2.05 1.77250 49.6 11 167.459 (variable) 12 -27.423 0.85 1.60311 60.6 13 ∞ (variable) 14 (aperture) ∞ 0.84 15 65.416 5.06 1.49700 81.7 16 -27.205 0.15 17 41.064 7.35 1.49700 81.7 18 -19.198 0.95 1.83481 42.7 19 -81.206 5.25 20 -64.814 2.07 1.90366 31.3 21 -28.769 0.90 1.61340 44.3 22 108.154 1.82 23 31.407 7.09 1.49700 81.7 24 -31.407 0.25 25 30.238 7.77 1.53775 74.7 26 -22.679 1.00 1.83481 42.7 27 29.093 3.93 28* -69.646 1.70 1.58283 59.5 29* -1000.000 (variable) 30 -104.423 6.93 1.48749 70.2 31 -28.354 10.24 Image plane ∞ Aspherical data The third surface K = 0.00000e+00 A 4=-1.09451e-05 A 6= 4.50666e-10 A 8=-1.50489e-10 A10= 4.73240e-13 A12=-9.51176e-16 The 28th surface K = 0.00000e+00 A 4=-9.63028e-05 A 6= 7.20183e-08 A 8= 1.66700e-09 A10=-1.33893e-11 A12= 3.80428e-14 The 29th surface K = 0.00000e+00 A 4=-4.66095e-05 A 6= 1.56445e-07 A 8= 1.63379e-09 A10=-1.04456e-11 A12= 2.08882e-14 Various data Zoom ratio 1.65 Wide angle, middle, telephoto Focal length 16.48 20.00 27.17 F-number 2.88 2.88 2.88 Half field angle (°) 47.52 43.53 37.44 Image height 18.00 19.00 20.80 Overall lens length 130.34 124.44 119.83 BF 10.24 10.24 10.24 d 9 23.28 13.64 1.33 d11 6.26 7.23 8.47 d13 4.76 3.79 2.54 d29 4.52 8.26 15.96 Lens group data Group, starting surface, focal length 1 1 -38.49 2 10 87.28 3 12 -45.47 4 14 23.93 5 30 77.53 [Numerical Example 2] Unit: mm Surface data Surface number r d nd νd 1 61.904 1.40 1.95375 32.3 2 20.247 0.05 1.51640 52.2 3* 18.373 5.67 4 44.033 1.20 1.71828 55.3 5 25.653 6.21 6 -106.598 1.00 1.49700 81.7 7 32.583 0.15 8 29.498 5.11 2.02677 28.4 9 288.201 (Variable) 10 -18.019 1.20 1.51588 64.6 11 -30.092 (Variable) 12 (Aperture) ∞ 1.80 13 117.663 5.12 1.49700 81.7 14 -23.189 0.15 15 36.389 7.48 1.53775 74.7 16 -18.380 1.30 1.91082 35.2 17 -66.282 4.31 18 -61.062 2.40 1.84666 23.9 19 -25.843 1.00 1.61340 44.3 20 110.697 4.38 21 42.465 6.11 1.49700 81.7 22 -27.481 0.15 23 23.479 7.82 1.53775 74.7 24 -24.794 1.00 1.83481 42.7 25 21.148 4.28 26* -55.112 1.70 1.58313 59.4 27* -378.334 (Variable) 28 -762.923 8.13 1.48749 70.2 29 -30.263 10.79 Image plane ∞ Aspherical data The third surface K = 0.00000e+00 A 4=-9.89514e-06 A 6= 5.32321e-08 A 8=-1.00711e-09 A10= 7.77335e-12 A12=-3.77833e-14 A14= 9.76335e-17 A16=-1.12886e-19 The 26th surface K = 0.00000e+00 A 4=-3.77487e-05 A 6= 4.15778e-08 A 8=-2.33823e-09 A10= 4.73379e-12 A12= 3.16760e-14 The 27th surface K = 0.00000e+00 A 4= 5.51540e-06 A 6= 9.32432e-09 A 8=-6.53949e-10 A10= 1.29016e-12 A12= 1.57567e-14 Various data Zoom ratio 1.64 Wide angle Middle Telephoto Focal length 16.48 23.24 27.08 F-number 2.90 2.90 2.90 Half field angle (°) 47.52 39.27 37.53 Image height 18.00 19.00 20.80 Overall lens length 121.45 116.36 115.52 BF 10.79 10.79 10.79 d 9 25.15 13.50 8.50 d11 3.90 2.69 2.66 d27 2.49 10.26 14.44 Lens group data Group starting surface Focal length 1 1 -33.05 2 10 -90.10 3 12 22.59 4 28 64.41 [Numerical example 3] Unit: mm Surface data Surface number r d nd νd 1 95.821 1.40 1.95375 32.3 2 24.913 0.05 1.53344 52.7 3* 20.931 6.56 4 72.105 1.20 1.48749 70.2 5 21.713 8.96 6 -48.789 1.10 1.49700 81.7 7 41.515 0.44 8 37.589 6.19 1.90043 37.4 9 -93.472 (Variable) 10 56.409 2.01 1.90043 37.4 11 762.938 (Variable) 12 -29.371 0.85 1.80400 46.5 13 -1412.490 (Variable) 14 (Aperture) ∞ 0.32 15 46.742 5.41 1.49700 81.7 16 -27.837 0.15 17 65.203 6.69 1.49700 81.7 18 -18.965 0.95 1.83481 42.7 19 -69.379 (Variable) 20 -74.743 1.89 1.90366 31.3 21 -33.041 0.90 1.61340 44.3 22 151.062 1.42 23 40.382 1.82 1.49700 81.7 24 67.668 0.25 25 32.853 6.24 1.49700 81.7 26 -39.046 0.25 27 27.936 7.63 1.49700 81.7 28 -24.955 1.00 1.83481 42.7 29 28.187 4.54 30* -48.034 1.70 1.58313 59.4 31* -500.000 (Variable) 32 -276.116 8.07 1.48749 70.2 33 -28.078 (Variable) Image plane ∞ Aspherical data The third surface K = 0.00000e+00 A 4=-1.51906e-05 A 6= 1.91375e-08 A 8=-2.94966e-10 A10= 8.97817e-13 A12=-1.34384e-15 The 30th surface K = 0.00000e+00 A 4=-1.45126e-04 A 6= 7.06611e-07 A 8=-2.79426e-09 A10= 7.89144e-12 A12= 1.23197e-15 The 31st surface K = 0.00000e+00 A 4=-8.48617e-05 A 6= 6.91573e-07 A 8=-1.40031e-09 A10=-1.74538e-12 A12= 1.19952e-14 Various data Zoom ratio 1.76 Wide-angle Medium Telephoto Focal length 15.45 20.00 27.17 F-number 2.88 2.88 2.94 Half field angle (°) 49.36 43.53 37.44 Image height 18.00 19.00 20.80 Overall lens length 131.80 125.47 122.18 BF 10.54 10.14 14.33 d 9 24.92 12.85 1.23 d11 5.11 5.74 7.42 d13 4.69 4.06 2.38 d19 6.56 7.42 5.94 d31 2.00 7.27 12.88 d33 10.54 10.14 14.33 Lens group data Group Starting surface Focal length 1 1 -35.33 2 10 67.56 3 12 -37.32 4 14 32.96 5 20 269.82 6 32 63.44 [Numerical example 4] Unit: mm Surface data Surface number r d nd νd 1 69.329 1.40 1.95375 32.3 2 23.558 5.82 3 78.570 1.20 1.48749 70.2 4 21.518 0.05 1.53344 52.7 5* 18.450 8.99 6 -54.735 1.10 1.49700 81.6 7 136.639 0.12 8 47.103 4.83 1.95375 32.3 9 - 146.332 (variable) 10 49.001 2.05 1.77250 49.6 11 220.527 (variable) 12 - 29.277 0.85 1.62230 53.2 13 ∞ (variable) 14 (aperture) ∞ 1.13 15 85.690 4.90 1.49700 81.6 16 - 26.257 0.15 17 35.427 7.61 1.49700 81.6 18 - 19.398 0.95 1.83481 42.7 19 - 123.444 4.09 20 - 68.817 2.18 1.90366 31.3 21 - 28.087 0.90 1.61340 44.3 22 120.221 1.83 23 31.663 7.03 1.49700 81.6 24 - 31.663 0.25 25 28.484 6.49 1.53775 74.7 26 - 33.812 1.00 1.83481 42.7 27 28.124 5.39 28* - 16.956 1.70 1.58313 59.4 29* - 24.111 (variable) 30 - 60.268 6.63 1.48749 70.2 31 - 25.904 10.38 Image plane ∞ Aspherical data The 5th surface K = 0.00000e+00 A 4 = - 1.61047e - 05 A 6 = 1.19890e - 08 A 8 = - 4.59302e - 10 A10 = 1.71508e - 12 A12 = - 3.77878e - 15 The 28th surface K = 0.00000e+00 A 4 = 1.75135e-05 A 6 = 6.78596e-07 A 8 = -8.10492e-09 A10 = 5.66788e-11 A12 = -1.89397e-13 The 29th surface K = 0.00000e+00 A 4 = 5.68500e-05 A 6 = 5.16256e-07 A 8 = -3.95802e-09 A10 = 2.01200e-11 A12 = -5.46951e-14 Various data Zoom ratio 1.66 Wide angle, Medium, Telephoto Focal length 17.51 20.00 29.10 F-number 2.88 2.88 2.89 Half field angle (°) 45.79 43.53 35.56 Image height 18.00 19.00 20.80 Overall lens length 127.77 125.15 118.54 BF 10.38 10.38 10.38 d9 22.36 17.12 1.30 d11 6.29 7.66 9.16 d13 5.44 4.08 2.58 d29 4.67 7.28 16.50 Lens group data Group, Starting surface, Focal length 1 1 -38.90 2 10 81.13 3 12 -47.05 4 14 25.19 5 30 87.65 [Numerical example 5] Unit: mm Surface data Surface number, r, d, nd, νd 1 74.640 1.40 1.95375 32.3 2 23.024 0.05 1.53344 52.7 3* 20.291 7.18 4 78.770 1.20 1.48749 70.2 5 22.698 8.88 6 -42.275 1.10 1.49700 81.7 7 65.581 0.28 8 44.155 5.88 1.90043 37.4 9 -77.800 (variable) 10 59.947 2.04 1.77250 49.6 11 -497.873 (variable) 12 -27.717 0.85 1.80400 46.5 13 -816.567 (variable) 14 (aperture) ∞ 0.61 15 54.261 5.36 1.49700 81.7 16 -26.826 0.15 17 35.997 7.28 1.49700 81.7 18 -20.476 0.95 1.83481 42.7 19 -62.913 (variable) 20 -81.113 1.90 1.90366 31.3 21 -34.112 0.90 1.61340 44.3 22 151.041 2.98 23 27.944 7.98 1.49700 81.7 24 -27.944 0.25 25 -74.984 6.77 1.53775 74.7 26 -15.360 1.00 1.87070 40.7 27 729.466 1.42 28* -161.561 1.70 1.58283 59.5 29* 769.541 (variable) Image plane ∞ Aspherical data The third surface K = 0.00000e+00 A 4=-1.18963e-05 A 6= 1.98677e-08 A 8=-2.70116e-10 A10= 8.62807e-13 A12=-1.49474e-15 The 28th surface K = 0.00000e+00 A 4=-1.07322e-04 A 6= 5.64090e-07 A 8=-5.66215e-09 A10= 4.05030e-11 A12=-9.87271e-14 The 29th surface K = 0.00000e+00 A 4=-6.27071e-05 A 6= 4.21985e-07 A 8=-2.67643e-09 A10= 1.64691e-11 A12=-3.83373e-14 Various data Zoom ratio 1.65 Wide angle Middle Telephoto Focal length 16.48 20.00 27.17 F-number 2.88 2.88 2.88 Half field angle (°) 47.52 43.53 37.44 Image height 18.00 19.00 20.80 Overall lens length 126.45 119.00 112.83 BF 16.21 19.66 27.57 d 9 24.37 13.82 1.32 d11 4.89 5.80 7.29 d13 4.91 4.00 2.51 d19 7.96 7.60 6.03 d29 16.21 19.66 27.57 Lens group data Group Starting surface Focal length 1 1 -39.36 2 10 69.37 3 12 -35.70 4 14 26.52 5 20 -670.07

[0073]

Table 1

[0074] [Imaging device] FIG. 12 shows a digital still camera as an imaging device using the zoom lenses of Examples 1 to 5 as an imaging optical system. In FIG. 12, 10 is a camera body, and 11 is an imaging optical system composed of any one of the zoom lenses of Examples 1 to 5.

[0075] 12 is incorporated in the camera body 10 and is an imaging element such as a CCD sensor or a CMOS sensor that photoelectrically converts the subject image formed by the imaging optical system 11 (i.e., captures the subject).

[0076] The camera body 10 may be a single-lens reflex camera having a quick-return mirror or a mirrorless camera without a quick-return mirror.

[0077] By applying the zoom lens of each example to an imaging device such as a digital still camera in this way, an imaging device capable of acquiring a high-quality image while being small can be obtained.

[0078] The above embodiments include the following configurations.

[0079] [Configuration 1] A zoom lens in which lens groups arranged in order from the object side to the image side are composed of a first lens group having a negative refractive power and a rear group including at least three lens groups and having a positive combined refractive power at the wide-angle end, and in which the interval between adjacent lens groups changes during zooming, The first lens group includes three negative lenses arranged continuously in order from the object side to the image side. When the focal length of the first lens group is f1, the focal length at the wide-angle end of the rear group is fRw, the back focus at the wide-angle end of the zoom lens is BFw, the focal length at the wide-angle end of the zoom lens is fw, and the half field angle at the wide-angle end of the zoom lens is ωw, -2.5 ≤ f1 / fRw ≤ -0.5 0.3 ≤ BFw / (fw × tan ωw) ≤ 0.8 A zoom lens characterized by satisfying the following conditions. [Configuration 2] -3.0 ≤ f1 / fw ≤ -1.0 The zoom lens according to Configuration 1, characterized by satisfying the following conditions. [Configuration 3] When the focal length at the telephoto end of the zoom lens is ft, -2.0 ≤ f1 / ft ≤ -0.5 The zoom lens according to Configuration 1 or 2, characterized by satisfying the following conditions. [Configuration 4] When the length on the optical axis of the first lens group L1 is LD1 and the overall optical length at the telephoto end of the zoom lens is TLt, 0.10 ≤ LD1 / TLt ≤ 0.30 The zoom lens according to any one of Configurations 1 to 3, characterized by satisfying the following conditions. [Configuration 5] When the overall optical length at the wide-angle end of the zoom lens is TLw and the overall optical length at the telephoto end is TLt, 0.70 ≤ TLt / TLw ≤ 1.10 The zoom lens according to any one of Configurations 1 to 4, characterized by satisfying the following conditions. [Configuration 6] The rear group has a second lens group closest to the object side. When the interval on the optical axis between the first lens group and the second lens group L2 at the wide-angle end is LD12w and the overall optical length at the wide-angle end of the zoom lens is TLw, 0.10 ≤ LD12w / TLw ≤ 0.30 The zoom lens according to any one of Configurations 1 to 5, characterized by satisfying the following conditions. [Configuration 7] When the overall optical length at the wide-angle end of the zoom lens is TLw, -0.40 ≦ f1 / TLw ≦ -0.20 The zoom lens according to any one of Configurations 1 to 6, characterized by satisfying the following conditions. [Configuration 8] The first lens group has a negative lens on the object side most distant from the image plane. Let the radius of curvature of the object-side surface of the negative lens on the object side most distant from the image plane be R1, and the radius of curvature of the image-side surface be R2. SF11 = (R2 + R1) / (R2 - R1) When -2.5 ≦ SF11 ≦ -1.2 The zoom lens according to any one of Configurations 1 to 7, characterized by satisfying the following conditions. [Configuration 9] The first lens group L1 has a negative lens second from the object side. Let the radius of curvature of the object-side surface of the second negative lens be R3, and the radius of curvature of the image-side surface be R4. SF12 = (R4 + R3) / (R4 - R3) When -4.5 ≦ SF12 ≦ -1.2 The zoom lens according to any one of Configurations 1 to 8, characterized by satisfying the following conditions. [Configuration 10] The first lens group includes at least one positive lens and at least three negative lenses. When the average refractive index of the at least one positive lens at the d-line is nd1p, and the average refractive index of the at least three negative lenses at the d-line is nd1n, -0.40 ≦ nd1n - nd1p ≦ -0.20 The zoom lens according to any one of Configurations 1 to 9, characterized by satisfying the following conditions. [Configuration 11] The first lens group includes at least one positive lens and at least three negative lenses. When the average Abbe number based on the d-line of the at least one positive lens is νd1p and the average Abbe number based on the d-line of the at least three negative lenses is νd1n, 1.2 ≦ νd1n / νd1p ≦ 2.5 The zoom lens according to any one of Configurations 1 to 10, characterized by satisfying the condition. [Configuration 12] The first lens group includes an aspherical lens, When the maximum value of the absolute value of the aspherical amount of the aspherical lens is DRMAX, 0.05 ≦ DRMAX ≦ 0.40 The zoom lens according to any one of Configurations 1 to 11, characterized by satisfying the condition. [Configuration 13] When the half field angle at the wide-angle end of the zoom lens is ωw, 45° ≦ ωw ≦ 60° The zoom lens according to any one of Configurations 1 to 12, characterized by satisfying the condition. [Configuration 14] The lens groups arranged in order from the object side to the image side are composed of the first lens group, a second lens group with positive refractive power, a third lens group with negative refractive power, a fourth lens group with positive refractive power, and a fifth lens group with positive refractive power, the zoom lens according to any one of Configurations 1 to 13. [Configuration 15] The lens groups arranged in order from the object side to the image side are composed of the first lens group, a second lens group with negative refractive power, a third lens group with positive refractive power, and a fourth lens group with positive refractive power, the zoom lens according to any one of Configurations 1 to 13. [Configuration 16] The lens groups arranged in order from the object side to the image side are composed of the first lens group, a second lens group with positive refractive power, a third lens group with negative refractive power, a fourth lens group with positive refractive power, a fifth lens group with positive refractive power, and a sixth lens group with positive refractive power, the zoom lens according to any one of Configurations 1 to 13. [Configuration 17] The zoom lens according to any one of Configurations 1 to 13, characterized in that a lens group arranged in order from the object side to the image side comprises the first lens group, a second lens group having a positive refractive power, a third lens group having a negative refractive power, a fourth lens group having a positive refractive power, and a fifth lens group having a negative refractive power. [Configuration 18] A zoom lens according to any one of Configurations 1 to 17, and an imaging device comprising an imaging element that images a subject through the zoom lens.

[0080] Each of the embodiments described above is merely a representative example, and various modifications and changes can be made to each embodiment when implementing the present invention.

Explanation of Reference Numerals

[0081] L1 First lens group LR Rear group L2 to L6 Second to sixth lens groups

Claims

1. A zoom lens in which a lens group arranged in order from the object side to the image side includes a first lens group having a negative refractive power and a rear group including at least three lens groups and having a positive combined refractive power at the wide-angle end, and the distance between adjacent lens groups changes during zooming, the first lens group includes three negative lenses arranged continuously in order from the object side to the image side, when the focal length of the first lens group is f1, the focal length of the rear group at the wide-angle end is fRw, the back focus at the wide-angle end of the zoom lens is BFw, the focal length of the zoom lens at the wide-angle end is fw, and the half field angle at the wide-angle end of the zoom lens is ωw, -2.5 ≤ f1 / fRw ≤ -0.5 0.3 ≤ BFw / (fw × tanωw) ≤ 0.8 A zoom lens characterized by satisfying the above conditions.

2. -3.0 ≤ f1 / fw ≤ -1.0 A zoom lens according to claim 1, characterized by satisfying the above conditions.

3. when the focal length of the zoom lens at the telephoto end is ft, -2.0 ≤ f1 / ft ≤ -0.5 A zoom lens according to claim 1, characterized by satisfying the above conditions.

4. when the length on the optical axis of the first lens group L1 is LD1 and the overall optical length of the zoom lens at the telephoto end is TLt, 0.10 ≤ LD1 / TLt ≤ 0.30 A zoom lens according to claim 1, characterized by satisfying the above conditions.

5. when the overall optical length of the zoom lens at the wide-angle end is TLw and the overall optical length of the zoom lens at the telephoto end is TLt, 0.70 ≤ TLt / TLw ≤ 1.10 A zoom lens according to claim 1, characterized by satisfying the above conditions.

6. The rear group has a second lens group closest to the object side, When the distance between the first lens group and the second lens group L2 on the optical axis at the wide-angle end is LD12w and the overall optical length of the zoom lens at the wide-angle end is TLw, 0.10 ≤ LD12w / TLw ≤ 0.30 The zoom lens according to claim 1, characterized in that the condition is satisfied.

7. When the overall optical length of the zoom lens at the wide-angle end is TLw, -0.40 ≤ f1 / TLw ≤ -0.20 The zoom lens according to claim 1, characterized in that the condition is satisfied.

8. The first lens group has a negative lens closest to the object side, Let the radius of curvature of the object-side surface of the negative lens closest to the object side be R1 and the radius of curvature of the image-side surface be R2, SF11 = (R2 + R1) / (R2 - R1) When, -2.5 ≤ SF11 ≤ -1.2 The zoom lens according to claim 1, characterized in that the condition is satisfied.

9. The first lens group L1 has a negative lens second from the object side, Let the radius of curvature of the object-side surface of the second negative lens be R3 and the radius of curvature of the image-side surface be R4, SF12 = (R4 + R3) / (R4 - R3) When, -4.5 ≤ SF12 ≤ -1.2 The zoom lens according to claim 1, characterized in that the condition is satisfied.

10. The first lens group includes at least one positive lens and the at least three negative lenses, When the average refractive index of the at least one positive lens at the d-line is nd1p and the average refractive index of the at least three negative lenses at the d-line is nd1n, -0.40 ≤ nd1n - nd1p ≤ -0.20 The zoom lens according to claim 1, characterized in that it satisfies the condition:

11. The first lens group includes at least one positive lens and the at least three negative lenses. When the average Abbe number based on the d-line of the at least one positive lens is νd1p and the average Abbe number based on the d-line of the at least three negative lenses is νd1n, 1.2 ≤ νd1n / νd1p ≤ 2.5 The zoom lens according to claim 1, characterized in that it satisfies the condition:

12. The first lens group includes an aspherical lens. When the maximum value of the absolute value of the aspherical amount of the aspherical lens is DRMAX, 0.05 ≤ DRMAX ≤ 0.40 The zoom lens according to claim 1, characterized in that it satisfies the condition:

13. When the half field angle at the wide-angle end of the zoom lens is ωw, 45° ≤ ωw ≤ 60° The zoom lens according to claim 1, characterized in that it satisfies the condition:

14. The lens groups arranged in order from the object side to the image side are composed of the first lens group, a second lens group with a positive refractive power, a third lens group with a negative refractive power, a fourth lens group with a positive refractive power, and a fifth lens group with a positive refractive power. The zoom lens according to claim 1, characterized in that it is so.

15. The lens groups arranged in order from the object side to the image side are composed of the first lens group, a second lens group with a negative refractive power, a third lens group with a positive refractive power, and a fourth lens group with a positive refractive power. The zoom lens according to claim 1, characterized in that it is so.

16. The zoom lens according to claim 1, wherein the lens groups arranged in order from the object side to the image side are composed of the first lens group, a second lens group having a positive refractive power, a third lens group having a negative refractive power, a fourth lens group having a positive refractive power, a fifth lens group having a positive refractive power, and a sixth lens group having a positive refractive power.

17. The zoom lens according to claim 1, wherein the lens groups arranged in order from the object side to the image side are composed of the first lens group, a second lens group having a positive refractive power, a third lens group having a negative refractive power, a fourth lens group having a positive refractive power, and a fifth lens group having a negative refractive power.

18. The zoom lens according to any one of claims 1 to 17, and an imaging device having an imaging element that images a subject through the zoom lens.

Images