Zoom lens and imaging device having the same

Abstract

To obtain a zoom lens in which deterioration in optical performance accompanying focusing is suppressed while an entire system is compact.SOLUTION: A zoom lens comprises a first lens group having positive refractive power, a second lens group having negative refractive power, a third lens group having positive refractive power, and a fourth lens group, which are arranged in order from an object side to an image side, distances between adjacent lens groups changes when zooming, the second lens group is fixed when zooming, and the fourth lens group moves when focusing. The total sum TD4 of distances on an optical axis from an object-side surface to an image-side surface of each lens of the fourth lens group, distance TL3 on the optical axis from a surface closest to the object side to a surface closest to the image side of the third lens group on the optical axis, focal distance f4 of the fourth lens group, and focal distance ft of an entire system at a telephoto end are appropriately set.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a zoom lens and an imaging device having the same, and is suitable for imaging devices using an imaging element such as video cameras, electronic still cameras, broadcast cameras, and surveillance cameras. [Background technology]

[0002] Telephoto zoom lenses with long focal lengths at the telephoto end are known as imaging optical systems (Patent Document 1). Such zoom lenses are required to be compact, yet facilitate high-speed focusing, and to suppress degradation of optical performance due to focusing.

[0003] Patent Document 1 discloses a zoom lens that is composed of first to sixth lens groups arranged in order from the object side to the image side, with positive, negative, positive, positive, negative, and negative refractive powers. By increasing the number of lenses in the fourth lens group, which is the focusing group, the optical performance associated with focusing is improved. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 06690425 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the zoom lens of Patent Document 1 has a large number of lenses in the fourth lens group, which is the focus group, and also has a relatively strong refractive power, making it difficult to achieve both high-speed focusing and suppression of deterioration in optical performance due to focusing.

[0006] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a zoom lens system that is compact overall and that suppresses degradation of optical performance during focusing, and an image pickup apparatus having the same. [Means for solving the problem]

[0007] A zoom lens of the present invention comprises, arranged in order from the object side to the image side, a first lens group having positive refractive power, a second lens group having negative refractive power, a third lens group having positive refractive power, and a fourth lens group, wherein the spacing between adjacent lens groups changes during zooming, the second lens group is fixed during zooming, and the fourth lens group moves during focusing, the first lens group has a first positive lens and a second positive lens arranged in this order from the most object side to the image side, Let TD4 be the sum of the distances on the optical axis from the object-side surface of each lens in the fourth lens group to the image-side surface, TL3 be the distance on the optical axis from the surface closest to the object to the surface closest to the image in the third lens group, f4 be the focal length of the fourth lens group, and ft be the focal length of the entire system at the telephoto end. 0.001 <TD4 / TL3<0.090 0.01<|f4| / ft<0.16 The present invention is characterized in that the following conditional expressions are satisfied: [Effects of the Invention]

[0008] According to the present invention, a zoom lens can be obtained in which the overall system is compact and the degradation of optical performance due to focusing is suppressed. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a cross-sectional view of a zoom lens at a wide-angle end according to a first embodiment of the present invention; [Figure 2] Aberration diagrams of the zoom lens of Example 1 at (A) the wide-angle end, (B) an intermediate zoom position, and (C) the telephoto end. [Figure 3] 10 is a cross-sectional view of a zoom lens at the wide-angle end of Example 2. [Figure 4] Aberration diagrams of the zoom lens of Example 2 at (A) the wide-angle end, (B) the intermediate zoom position, and (C) the telephoto end. [Figure 5] 10 is a cross-sectional view of a zoom lens at the wide-angle end according to a third embodiment of the present invention; [Figure 6] Aberration diagrams of the zoom lens of Example 3 at (A) the wide-angle end, (B) an intermediate zoom position, and (C) the telephoto end. [Figure 7] 10 is a cross-sectional view of a zoom lens at the wide-angle end according to a fourth embodiment of the present invention; [Figure 8] Aberration diagrams of the zoom lens of Example 4 at (A) the wide-angle end, (B) the intermediate zoom position, and (C) the telephoto end. [Figure 9] 10 is a cross-sectional view of a zoom lens at the wide-angle end according to a fifth embodiment of the present invention; [Figure 10] Aberration diagrams of the zoom lens of Example 5 at (A) the wide-angle end, (B) the intermediate zoom position, and (C) the telephoto end. [Figure 11] 10 is a cross-sectional view of a zoom lens at the wide-angle end according to a sixth embodiment of the present invention; [Figure 12] Aberration diagrams of the zoom lens of Example 6 at (A) the wide-angle end, (B) the intermediate zoom position, and (C) the telephoto end. [Figure 13] 1 is a schematic diagram illustrating a main part of an imaging device according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0010] A preferred embodiment of the present invention will be described below with reference to the accompanying drawings. The zoom lens in this embodiment has, arranged in order from the object side to the image side, a first lens group with positive refractive power, a second lens group with negative refractive power, a third lens group with positive refractive power, and a fourth lens group, and the spacing between adjacent lens groups changes during zooming. The second lens group remains fixed during zooming, and the fourth lens group moves during focusing.

[0011] Fig. 1 is a cross-sectional view of the lens at the wide-angle end (short focal length end) of Example 1. Figs. 2(A), (B), and (C) are longitudinal aberration diagrams at the wide-angle end, at an intermediate zoom position, and at the telephoto end (long focal length end) of the zoom lens of Example 1, respectively, when focused on an object at infinity. Example 1 is a zoom lens with a zoom ratio of 3.78 and an F-number of approximately 5.71 to 9.18.

[0012] Fig. 3 is a cross-sectional view of the lens at the wide-angle end of Example 2. Figs. 4(A), (B), and (C) are longitudinal aberration diagrams of the zoom lens of Example 2 at the wide-angle end, at an intermediate zoom position, and at the telephoto end, respectively, when the lens is focused on an object at infinity. Example 2 is a zoom lens with a zoom ratio of 4.99 and an F-number of approximately 5.71 to 11.00.

[0013] Fig. 5 is a cross-sectional view of the lens at the wide-angle end of Example 3. Figs. 6(A), (B), and (C) are longitudinal aberration diagrams of the zoom lens at the wide-angle end, at an intermediate zoom position, and at the telephoto end, respectively, when focused on an object at infinity in Example 3. Example 3 is a zoom lens with a zoom ratio of 3.77 and an F-number of approximately 5.77 to 9.20.

[0014] Fig. 7 is a cross-sectional view of the lens at the wide-angle end of Example 4. Figs. 8(A), (B), and (C) are longitudinal aberration diagrams of the zoom lens at the wide-angle end, at an intermediate zoom position, and at the telephoto end, respectively, when focused on an object at infinity in Example 4. Example 4 is a zoom lens with a zoom ratio of 3.78 and an F-number of approximately 5.71 to 9.18.

[0015] Fig. 9 is a cross-sectional view of the lens at the wide-angle end of Example 5. Figs. 10(A), (B), and (C) are longitudinal aberration diagrams of the zoom lens at the wide-angle end, at an intermediate zoom position, and at the telephoto end when focused on an object at infinity in Example 5. Example 5 is a zoom lens with a zoom ratio of 3.77 and an F-number of approximately 5.83 to 8.00.

[0016] Fig. 11 is a cross-sectional view of the lens at the wide-angle end of Example 6. Figs. 12(A), (B), and (C) are longitudinal aberration diagrams of the zoom lens of Example 6 at the wide-angle end, at an intermediate zoom position, and at the telephoto end, respectively, when focused on an object at infinity. Example 6 is a zoom lens with a zoom ratio of 3.77 and an F-number of approximately 5.77 to 9.20.

[0017] The zoom lens of each embodiment is a zoom lens used in imaging devices such as digital cameras, video cameras, broadcast cameras, surveillance cameras, and silver halide cameras. In the lens cross-sectional views, the left is the object side (front) and the right is the image side (rear). Note that the zoom lens of each embodiment may also be used as a projection optical system for a projection device (projector), in which case the left is the screen side and the right is the projection side. In the lens cross-sectional views, L0 represents the entire zoom lens system. i represents the order of the lens groups from the object side, and Li represents the ith lens group.

[0018] SP is the aperture stop (maximum aperture F-number). IP is the image plane. In digital cameras and video cameras, the image plane IP of a zoom lens corresponds to the imaging plane of a solid-state image sensor (photoelectric conversion element) such as a CCD sensor or CMOS sensor. In a silver halide film camera, the image plane IP of a zoom lens corresponds to the film plane. The arrows show the movement trajectory of the lens group when zooming from the wide-angle end to the telephoto end while focused at infinity. The arrow labeled FOCUS shows the movement direction of the lens group when focusing from an object at infinity to a close-up object. IS is a lens group that corrects image blur; by moving in a direction that includes a component perpendicular to the optical axis, it corrects image blur that occurs when the lens is tilted due to camera shake, etc.

[0019] In the spherical aberration diagram, Fno is the F-number. The solid line d represents the d-line (wavelength 587.6 nm), and the two-dot chain line g represents the g-line (wavelength 435.8 nm). In the astigmatism diagram, the dotted line ΔM represents the meridional image plane at the d-line, and the solid line ΔS represents the sagittal image plane at the d-line. The distortion diagram shows the d-line. The lateral chromatic aberration diagram shows the g-line. ω is the half angle of view (degrees).

[0020] The zoom lens of each embodiment has, arranged in order from the object side to the image side, a first lens group L1 with positive refractive power, a second lens group L2 with negative refractive power, a third lens group L3 with positive refractive power, and a fourth lens group L4, with the spacing between adjacent lens groups changing during zooming. The second lens group L2 remains fixed during zooming, while the fourth lens group L4 moves during focusing. By making the first lens group L1 have positive refractive power and the second lens group L2 have negative refractive power, the front principal point is positioned on the object side, resulting in a telephoto-type configuration, thereby reducing the size of the entire zoom lens system L0. By making the second lens group L2 with negative refractive power fixed during zooming, degradation of optical performance due to manufacturing errors is reduced. By making the third lens group L3 have positive refractive power, the axial light beam incident on the fourth lens group L4 is reduced, resulting in a smaller focus lens group.

[0021] The sum of the distances on the optical axis from the object-side surface to the image-side surface of each lens in the fourth lens group L4 is TD4, and the distance on the optical axis from the surface closest to the object to the surface closest to the image in the third lens group L3 is TL3. The focal length of the fourth lens group L4 is f4, and the focal length of the entire zoom lens system L0 at the telephoto end is ft. In this case, the zoom lenses of each embodiment are as follows: 0.001 <TD4 / TL3<0.090···(1) 0.01<|f4| / ft<0.16 (2) The following condition is satisfied.

[0022] Next, the technical meaning of each of the aforementioned conditional expressions will be explained. Conditional expression (1) is intended to reduce the size and weight of the fourth lens group L4, which is a focus lens group, and to suppress aberration fluctuations that occur during focusing. Here, TD4 is the sum of the axial distances from the object-side surface to the image-side surface of each lens constituting the fourth lens group L4, and does not include the air gaps between the lenses. If the sum of the axial distances from the object-side surface to the image-side surface of each lens constituting the fourth lens group L4 becomes large, exceeding the upper limit of conditional expression (1), the lens unit of the fourth lens group L4, which is a focus lens group, becomes large. As a result, it becomes difficult to achieve high-speed focusing. If the lower limit of conditional expression (1) is not satisfied, and the axial distance from the surface closest to the object to the surface closest to the image in the third lens group L3 becomes large, the overall length of the zoom lens system L0 becomes long.

[0023] Conditional expression (2) is intended to achieve both high-speed focusing and suppression of fluctuations in aberrations that occur during focusing. If the upper limit of conditional expression (2) is exceeded and the focal length of the fourth lens unit L4 becomes long, the refractive power of the fourth lens unit L4 weakens. As a result, the amount of movement of the focus unit during focusing becomes large, making it difficult to achieve high-speed focusing. If the lower limit of conditional expression (2) is exceeded and the focal length of the fourth lens unit L4 becomes short, the refractive power of the fourth lens unit L4 becomes too strong, making it difficult to suppress fluctuations in spherical aberration and coma that occur during focusing, particularly at the telephoto end.

[0024] It is preferable to set the conditions (1) and (2) as follows: 0.002 <TD4 / TL3<0.085···(1a) 0.03<|f4| / ft<0.15 (2a)

[0025] It is more preferable to set the conditions (1a) and (2a) as follows: 0.003 <TD4 / TL3<0.075···(1b) 0.04<|f4| / ft<0.14 (2b)

[0026] Furthermore, in the zoom lens of each embodiment, it is preferable that one or more of the following conditional expressions be satisfied. 0.35 <TL1 / |f4|<2.50···(3) 3.00<|(1-βft 2 )×βrt 2 |<25.0···(4) 0.70 <f1 / fw<3.20···(5) -1.00 <f2 / fw<-0.10···(6) 0.10 <f3 / fw<1.20···(7) 5.0 <ft / skw<50.0···(8) 2.00 <TTDw / skw<25.0···(9) -1.00 <m1 / f1<-0.05···(10)

[0027] Let TL1 be the distance on the optical axis from the surface of the first lens group L1 closest to the object to the surface closest to the image, and f4 be the focal length of the fourth lens group L4. Let βft be the lateral magnification of the fourth lens group L4 when focused on an object at infinity at the telephoto end. Let βrt be the lateral magnification of all lens groups located closer to the image than the fourth lens group L4 when focused on an object at infinity at the telephoto end. However, if no lens group is located closer to the image than the fourth lens group L4, then βrt = 1.00 is used in the calculation. Let f1 be the focal length of the first lens group L1, and fw be the focal length of the entire system at the wide-angle end. Let f2 be the focal length of the second lens group L2. Let f3 be the focal length of the third lens group L3. Let skw be the back focal length at the wide-angle end. Let TTDw be the total lens length at the wide-angle end. Let m1 be the movement amount of the first lens group L1 when zooming from the wide-angle end to the telephoto end. The total lens length TTDw at the wide-angle end is the distance on the optical axis from the lens surface closest to the object to the lens surface closest to the image plus the value of the back focus in air. Back focus is the length, in air terms, from the lens surface closest to the image to the image plane. The amount of movement of a lens group during zooming corresponds to the difference between its position on the optical axis at the wide-angle end and its position on the optical axis at the telephoto end. The sign of the movement amount is positive when the lens group is closer to the image at the telephoto end than at the wide-angle end, and negative when the lens group is closer to the object at the telephoto end than at the wide-angle end.

[0028] Next, the technical meaning of each of the above-mentioned conditional expressions will be explained.

[0029] Condition (3) relates to the miniaturization of the entire zoom lens system L0 and the increase in focusing speed.

[0030] If the upper limit of conditional expression (3) is exceeded and the distance TL1 on the optical axis from the surface of the first lens unit L1 closest to the object to the surface closest to the image becomes large, it becomes difficult to make the entire zoom lens system L0 compact.If the lower limit of conditional expression (3) is not reached and the focal length of the fourth lens unit L4 becomes long, it becomes necessary to ensure a large amount of movement of the fourth lens unit L4 during focusing, which makes it difficult to achieve high-speed focusing.

[0031] Conditional expression (4) defines the focus sensitivity of the fourth lens unit L4 at the telephoto end.

[0032] If the upper limit of conditional expression (4) is exceeded and focus sensitivity becomes high, the focus changes significantly in response to a slight movement of the focus group in the optical axis direction, making it difficult to control focus with high precision.If the lower limit of conditional expression (4) is exceeded and focus sensitivity becomes low, the movement amount of the fourth lens group L4 during focusing must be increased, making it difficult to achieve high-speed focusing.

[0033] Conditional expression (5) is intended to reduce the size of the entire zoom lens system L0. If the upper limit of conditional expression (5) is exceeded and the focal length of the first lens unit L1 becomes long, the front principal point will be located on the image plane side, and the entire zoom lens system L0 will become large. If the lower limit of conditional expression (5) is not satisfied and the focal length of the first lens unit L1 becomes short, it will become difficult to correct spherical aberration and coma.

[0034] Condition (6) is intended to achieve both compactness of the entire zoom lens system L0 and good optical performance.

[0035] If the upper limit of conditional expression (6) is exceeded and the focal length of the second lens group L2 becomes shorter, the axial light beam incident on the lens group closer to the image side than the second lens group L2 becomes larger. As a result, the fourth lens group L4, which is the focus group, becomes larger. If the lower limit of conditional expression (6) is not reached and the absolute value of the focal length of the second lens group L2 becomes longer, the amount of movement of the first lens group L1 and the third lens group L3 must be increased to achieve the desired zoom magnification, resulting in a larger overall zoom lens system L0.

[0036] Condition (7) is for achieving both a compact zoom lens system L0 and a lightweight fourth lens unit L4.

[0037] If the upper limit of conditional expression (7) is exceeded and the focal length f3 of the third lens unit L3 becomes large, the amount of movement of the third lens unit L3 during zooming must be increased to ensure the desired zoom ratio. As a result, the overall zoom lens system L0 becomes larger. If the lower limit of conditional expression (7) is not reached and the focal length f3 of the third lens unit L3 becomes short, the angle of the marginal ray of the axial light beam incident on the fourth lens unit L4, which is the focus unit, becomes too large with respect to the optical axis. This makes it difficult to suppress fluctuations in aberrations such as spherical aberration during focusing.

[0038] Condition (8) is for achieving both optical performance and compactness of the entire zoom lens system L0.

[0039] If the upper limit of conditional expression (8) is exceeded and the focal length ft at the telephoto end becomes long, it becomes difficult to correct various aberrations at the telephoto end, particularly axial chromatic aberration.If the lower limit of conditional expression (8) is not reached and the back focus skw at the wide-angle end of the entire zoom lens system L0 becomes large, the entire zoom lens system L0 becomes large.

[0040] Condition (9) is for achieving both the desired optical performance and compactness of the entire zoom lens system L0.

[0041] If the upper limit of conditional expression (9) is exceeded and the total optical length TTDw at the wide-angle end becomes large, the overall zoom lens system L0 becomes large, which is undesirable.If the lower limit of conditional expression (9) is not reached and the total optical length TTDw at the wide-angle end becomes small, the refractive power of each group in the overall zoom lens system L0 becomes too strong, which makes it difficult to achieve the desired optical performance.

[0042] Condition (10) is for achieving both the desired optical performance and compactness of the entire zoom lens system L0.

[0043] If the upper limit of conditional expression (10) is exceeded and the absolute value of the movement amount m1 of the first lens unit L1 during zooming from the wide-angle end to the telephoto end becomes small, the movement amount of the subsequent lens units becomes large in order to obtain the desired telephoto end focal length. As a result, it becomes difficult to suppress zoom fluctuations such as field curvature aberration. If the lower limit of conditional expression (10) is not reached and the absolute value of the movement amount m1 of the first lens unit L1 becomes large, the entire zoom lens system L0 at the telephoto end becomes large.

[0044] It is preferable to set the conditions (3) to (10) as follows: 0.50 <TL1 / |f4|<2.00···(3a) 4.00<|(1-βft 2 )×βrt 2 |<20.0···(4a) 0.90 <f1 / fw<2.50···(5a) -0.50 <f2 / fw<-0.15···(6a) 0.15 <f3 / fw<1.00···(7a) 8.0 <ft / skw<30.0···(8a) 3.00 <TTDw / skw<20.0···(9a) -0.80 <m1 / f1<-0.08···(10a)

[0045] It is more preferable to set the conditions (3a) to (10a) as follows: 0.60 <TL1 / |f4|<1.70···(3b) 5.00<|(1-βft 2 )×βrt 2 |<15.0···(4b) 1.10 <f1 / fw<2.00···(5b) -0.40 <f2 / fw<-0.25···(6b) 0.20 <f3 / fw<0.80···(7b) 10.0 <ft / skw<25.0···(8b) 4.00 <TTDw / skw<12.0···(9b) -0.40 <m1 / f1<-0.12···(10b)

[0046] Furthermore, in order to obtain good imaging performance even when the lens barrel becomes decentered due to camera shake, etc., it is preferable to have a lens group whose lenses are decentered in a direction that includes a component perpendicular to the optical axis. For example, performing image blur correction using the entire second lens group L2 or part of the second lens group L2 is more preferable, as it allows good image blur correction to be performed with a small, lightweight lens unit from the wide-angle end to the telephoto end.

[0047] Furthermore, in order to perform focusing by the fourth lens unit L4 at high speed, it is necessary to reduce the weight of the fourth lens unit L4, and therefore it is preferable that the fourth lens unit L4 be constructed of a cemented lens or one single lens.

[0048] In order to suppress fluctuations in field curvature during zooming, it is preferable that the fourth lens unit L4 be a lens unit with negative refractive power.

[0049] Furthermore, in order to suppress fluctuations in the field curvature aberration with respect to the object distance during focusing, it is preferable that the surface of the fourth lens unit L4 closest to the image side has a concave shape facing the image side.

[0050] In order to achieve both compactness and suppression of axial aberrations, it is preferable to arrange a first positive lens and a second positive lens in the first lens unit L1 in this order from the object side to the image side.

[0051] Furthermore, in order to suppress field curvature and distortion, it is preferable that the third lens group L3 has an aperture stop therein for determining the F-number, and that the lenses that make up the third lens group L3 are disposed on the object side and the image side of the aperture stop.

[0052] In each embodiment, by specifying each element as described above, a zoom lens is obtained in which the overall system is small and the degradation of optical performance due to focusing is suppressed.

[0053] Next, the lens configuration of each embodiment will be described in detail. The zoom lens of Embodiment 1 is composed of a first lens group with positive refractive power, a second lens group with negative refractive power, a third lens group with positive refractive power, a fourth lens group with negative refractive power, a fifth lens group with positive refractive power, and a sixth lens group with negative refractive power. The lens group configuration of the zoom lens of Embodiment 2 is the same as that of Embodiment 1. The six-group configuration provides excellent correction of optical performance throughout the entire zoom range. During zooming from the wide-angle end to the telephoto end, all lens groups except the second lens group L2 move toward the object side. The second lens group L2 remains stationary during zooming. During focusing from infinity to the closest distance, the fourth lens group L4 moves toward the image side. In addition, the three lenses in the second lens group closest to the image are designated as a subgroup IS, and are moved in a direction approximately perpendicular to the optical axis to perform image blur correction. Image blur correction is performed using three lenses, suppressing aberrations that occur when the lenses are decentered. The aperture that determines the F-number is located inside the third lens group L3.

[0054] The zoom lens of Example 3 consists of a first lens group with positive refractive power, a second lens group with negative refractive power, a third lens group with positive refractive power, a fourth lens group with positive refractive power, and a fifth lens group with negative refractive power. The five-group configuration reduces the weight of the entire zoom lens system L0 compared to a six-group configuration. When zooming from the wide-angle end to the telephoto end, all lens groups except the second lens group L2 move toward the object. The second lens group L2 remains stationary during zooming. When focusing from infinity to a close-up distance, the fourth lens group L4 moves toward the object. Furthermore, the three image-side lenses of the second lens group, designated as a subgroup IS, are moved in a direction approximately perpendicular to the optical axis to compensate for image blur. The aperture diaphragm, which determines the F-number, is located within the third lens group L3.

[0055] The zoom lens of Example 4 consists of a first lens group with positive refractive power, a second lens group with negative refractive power, a third lens group with positive refractive power, a fourth lens group with positive refractive power, a fifth lens group with positive refractive power, and a sixth lens group with negative refractive power. When zooming from the wide-angle end to the telephoto end, all lens groups except the second lens group move toward the object. The second lens group L2 remains stationary during zooming. When focusing from infinity to a close-up distance, the fourth lens group L4 moves toward the object. Furthermore, the three image-side lenses of the second lens group L2, designated as a subgroup IS, are moved in a direction approximately perpendicular to the optical axis to compensate for image blur. The aperture, which determines the F-number, is located within the third lens group L3.

[0056] The zoom lens of Example 5 consists of a first lens group with positive refractive power, a second lens group with negative refractive power, a third lens group with positive refractive power, a fourth lens group with negative refractive power, a fifth lens group with negative refractive power, and a sixth lens group with positive refractive power. When zooming from the wide-angle end to the telephoto end, all lens groups except the second and sixth lens groups move toward the object. The second lens group L2 and the sixth lens group L6 are fixed during zooming. By keeping the sixth lens group L6 fixed during zooming, degradation of optical performance due to manufacturing errors is suppressed. When focusing from infinity to a close distance, the fourth lens group L4 moves toward the object. Furthermore, the four image-side lenses of the second lens group L2 are designated as a subgroup IS and are moved in a direction approximately perpendicular to the optical axis to perform image blur correction. Performing image blur correction using four lenses provides better optical performance during image blur correction than image blur correction using three lenses. The aperture that determines the Fno is located inside the third lens unit L3.

[0057] The zoom lens of Example 6 is a four-group zoom lens consisting of a first lens group with positive refractive power, a second lens group with negative refractive power, a third lens group with positive refractive power, and a fourth lens group with negative refractive power. The four-group configuration reduces the weight of the entire zoom lens system L0 by using a five-group configuration. When zooming from the wide-angle end to the telephoto end, all lens groups except the second lens group move toward the object. When focusing from infinity to the closest distance, the fourth lens group L4 moves toward the image. Furthermore, the three image-side lenses of the second lens group L2 are designated as a subgroup IS, and are moved in a direction approximately perpendicular to the optical axis to perform image blur correction. The aperture, which determines the F-number, is located within the third lens group L3.

[0058] In addition, in Examples 1 to 6, it is preferable that all the lenses that are used are spherical lenses in order to prevent degradation of optical performance due to manufacturing errors.

[0059] Next, an example of a digital still camera (imaging device) that uses the optical system (zoom lens) of this embodiment as an imaging optical system will be described with reference to Fig. 13. In Fig. 13, 10 denotes a camera body, and 11 denotes an imaging optical system configured using any of the optical systems described in Examples 1 to 6. 12 denotes a solid-state imaging element (photoelectric conversion element) such as a CCD sensor or CMOS sensor that is built into the camera body and receives and photoelectrically converts an optical image formed by the imaging optical system 11. The camera body 10 may be a so-called single-lens reflex camera that has a quick-turn mirror, or a so-called mirrorless camera that does not have a quick-turn mirror.

[0060] In this way, by applying the optical system of this embodiment to an imaging device such as a digital still camera, an imaging device with a small lens and high-speed focusing can be obtained.

[0061] Specific numerical examples 1 to 6 corresponding to the first to sixth embodiments are shown below.

[0062] In the surface data of each numerical example, r represents the radius of curvature of each optical surface, and d (mm) represents the axial spacing (distance on the optical axis) between the mth surface and the (m+1)th surface. Here, m is the surface number counted from the light incident side. Also, nd represents the refractive index of each optical element with respect to the d-line, and vd represents the Abbe number of the optical element. Note that the Abbe number vd of a certain material is given by the following when the refractive indices at the d-line (587.6 nm), F-line (486.1 nm), and C-line (656.3 nm) of the Fraunhofer lines are Nd, NF, and NC, respectively: It is expressed as νd=(Nd-1) / (NF-NC).

[0063] In each numerical example, d, focal length (mm), F-number, and half angle of view (°) are all values ​​when the optical system of each example is focused on an object at infinity. "Back focus BF" is the distance on the optical axis from the final lens surface (the lens surface closest to the image) to the paraxial image plane, expressed as an air-equivalent length. "Total lens length" is the distance on the optical axis from the frontmost lens surface (the lens surface closest to the object) of the zoom lens to the final lens surface plus the back focus. "Lens group" is not limited to cases where it is composed of multiple lenses, but also includes cases where it is composed of a single lens.

[0064] Table 1 shows the relationship between each of the above-mentioned conditional expressions and each of the numerical examples.

[0065] [Numerical Example 1] Unit: mm Surface Data Surface number rd nd νd 1 144.748 9.32 1.48749 70.2 2∞48.43 3 89.287 10.89 1.49700 81.6 4 -847.726 3.00 1.61340 44.3 5 74.191 1.97 6 100.080 4.93 1.51823 58.9 7 174.640 (variable) 8 ∞ 4.76 1.65412 39.7 9 -63.154 2.00 1.58913 61.1 10 767.732 3.37 11 682.775 1.50 1.72916 54.7 12 82.889 2.86 13 -101.488 1.50 1.69680 55.5 14 101.488 3.53 1.78472 25.7 15 ∞ (variable) 16 49.739 7.15 1.49700 81.6 17 -138.331 0.19 18 64.996 1.70 1.72916 54.7 19 27.598 9.12 1.53775 74.7 20 -231.045 0.97 21 -86.744 1.90 1.90525 35.0 22 1464.098 16.96 23 (Aperture) ∞ 24.36 24 64.330 4.61 1.61340 44.3 25 -43.939 1.30 1.89190 37.1 26 -157.290 (variable) 27 271.506 2.33 1.85478 24.8 28 -74.228 1.00 1.83481 42.7 29 39.368 (variable) 30 67.122 1.70 1.92286 20.9 31 38.251 6.33 1.65412 39.7 32 -60.563 (variable) 33 -76.617 1.30 1.59522 67.7 34 166.663 1.15 35 -165.426 1.50 1.59522 67.7 36 23.838 6.86 1.61340 44.3 37 181.816 (variable) Image plane ∞ Various data Zoom ratio 3.78 Wide-angle Mid-range Telephoto Focal length 206.00 384.91 778.20 F-number 5.71 6.70 9.18 Angle of view 6.00 3.22 1.59 Image height 21.64 21.64 21.64 Lens total length 330.11 387.57 420.11 BF 40.03 58.26 96.02 d 7 7.95 65.40 97.95 d15 41.76 29.34 2.97 d26 15.09 8.51 3.09 d29 17.80 24.37 29.79 d32 18.99 13.18 1.79 d37 40.03 58.26 96.02 Zoom lens group data Group starting plane focal length 1 1 298.92 2 8 -73.88 3 16 72.61 4 27 -56.61 5 30 58.15 6 33 -55.76

[0066] [Numerical Example 2] Unit: mm Surface Data Surface number rd nd νd 1 159.699 11.19 1.55200 70.7 2 -9253.167 29.40 3 124.859 11.82 1.43875 94.7 4 -1594.386 3.00 1.61340 44.3 5 90.657 1.88 6 112.075 7.30 1.52249 59.8 7 268.277 (variable) 8 379.010 4.72 1.65412 39.7 9 -95.619 2.00 1.58913 61.1 10 133.911 4.36 11 1360.740 1.50 1.72916 54.7 12 99.116 2.70 13 -93.784 1.50 1.69680 55.5 14 93.784 3.64 1.78472 25.7 15 ∞ (variable) 16 42.748 8.09 1.43875 94.7 17 -244.321 9.41 18 61.253 1.70 1.72916 54.7 19 25.121 10.52 1.53775 74.7 20 -145.036 1.15 21 -64.802 1.90 1.90525 35.0 22 -371.091 20.41 23 (Aperture) ∞ 5.58 24 57.372 6.20 1.61340 44.3 25 -39.197 1.30 1.89190 37.1 26 -116.455 (variable) 27 323.331 3.60 1.85478 24.8 28 -43.383 1.00 1.83481 42.7 29 38.104 (variable) 30 105.754 1.70 1.92286 20.9 31 40.781 4.94 1.65412 39.7 32 -52.073 (variable) 33 -70.909 1.30 1.59522 67.7 34 166.620 1.46 35 -80.692 1.50 1.59522 67.7 36 27.051 6.68 1.61340 44.3 37 -192.918 (variable) Image plane ∞ Various data Zoom ratio 4.99 Wide-angle Mid-range Telephoto Focal length 200.00 384.79 998.33 F-number 5.71 8.00 11.00 Angle of view 6.17 3.22 1.24 Image height 21.64 21.64 21.64 Lens total length 346.80 414.38 456.78 BF 43.85 57.79 105.49 d 7 27.82 95.40 137.81 d15 48.96 40.25 2.94 d26 19.01 13.14 3.03 d29 16.52 22.39 32.50 d32 17.16 11.93 1.54 d37 43.85 57.79 105.49 Zoom lens group data Group starting plane focal length 1 1 306.41 2 8 -64.76 3 16 67.47 4 27 -53.60 5 30 68.64 6 33 -65.43

[0067] [Numerical Example 3] Unit: mm Surface Data Surface number rd nd νd 1 150.352 9.09 1.51823 58.9 2 -2220.884 47.50 3 109.107 10.05 1.49700 81.5 4 -311.952 2.70 1.61340 44.3 5 85.891 2.62 6 151.247 4.38 1.49700 81.5 7 297.213 (variable) 8 105.941 4.54 1.59270 35.3 9 -572.784 4.71 10 451.610 1.65 1.83481 42.7 11 93.220 3.35 12 494.132 1.65 1.59522 67.7 13 172.589 2.14 14 -116.509 1.65 1.77250 49.6 15 102.552 2.75 1.84666 23.8 16 284.801 (variable) 17 135.888 3.96 1.49700 81.5 18 -198.755 0.20 19 68.386 6.98 1.49700 81.5 20 -75.459 1.80 1.90043 37.4 21 -1059.696 35.54 22 (Aperture) ∞ 11.24 23 -78.564 1.30 1.62041 60.3 24 63.938 5.79 1.57501 41.5 25 -50.115 7.21 26 73.938 1.50 1.84666 23.8 27 50.694 (variable) 28 56.532 3.97 1.54072 47.2 29 -45.496 1.00 1.95375 32.3 30 -102.766 (variable) 31 -171.505 1.00 1.53775 74.7 32 21.201 4.27 1.51742 52.4 33 64.491 3.78 34 -46.262 1.50 1.49700 81.5 35 37.451 5.23 1.53172 48.8 36 -86.653 (variable) Image plane ∞ Various data Zoom ratio 3.77 Wide-angle Mid-range Telephoto Focal length 205.98 384.96 775.84 F-number 5.77 6.80 9.20 Angle of view 6.00 3.22 1.60 Image height 21.64 21.64 21.64 Lens total length 336.95 386.89 426.95 BF 38.57 65.58 108.88 d 7 2.00 51.94 92.00 d16 57.03 34.81 2.21 d27 7.65 15.35 26.04 d30 36.66 24.17 2.79 d36 38.57 65.58 108.88 Zoom lens group data Group starting plane focal length 1 1 337.68 2 8 -93.52 3 17 118.61 4 28 102.47 5 31 -64.57

[0068] [Numerical Example 4] Unit: mm Surface Data Surface number rd nd νd 1 143.068 9.33 1.48749 70.2 2∞46.81 3 105.831 10.49 1.49700 81.6 4 -421.308 3.00 1.61340 44.3 5 81.155 1.41 6 101.264 5.86 1.51823 58.9 7 246.538 (variable) 8 ∞ 3.16 1.65412 39.7 9 -67.730 2.00 1.58913 61.1 10 18081.804 3.28 11 1218.430 1.50 1.72916 54.7 12 83.015 2.91 13 -105.215 1.50 1.69680 55.5 14 105.215 3.51 1.78472 25.7 15 ∞ (variable) 16 39.645 7.02 1.49700 81.6 17 809.672 10.80 18 73.120 1.70 1.72916 54.7 19 22.924 10.35 1.53775 74.7 20 -122.755 2.89 21 -54.461 1.90 1.90525 35.0 22 -218.508 8.12 23 (Aperture) ∞ 18.65 24 71.191 5.13 1.61340 44.3 25 -44.461 1.30 1.89190 37.1 26 -109.673 (variable) 27 181.380 0.30 1.77250 49.6 28 40.522 (variable) 29 113.502 1.70 1.92286 20.9 30 91.813 4.15 1.65412 39.7 31 -64.870 (variable) 32 -85.727 1.30 1.59522 67.7 33 166.663 11.70 34 -110.554 1.50 1.59522 67.7 35 31.223 6.66 1.61340 44.3 36 4143.568 (variable) Image plane ∞ Various data Zoom ratio 3.78 Wide-angle Mid-range Telephoto Focal length 206.00 384.79 778.20 F-number 5.71 6.70 9.18 Angle of view 6.00 3.22 1.59 Image height 21.64 21.64 21.64 Lens total length 330.12 386.42 420.13 BF 34.33 53.24 93.04 d 7 2.50 58.81 92.52 d15 43.10 31.02 2.97 d26 23.43 13.41 0.97 d28 16.49 26.51 38.95 d31 20.32 13.49 1.75 d36 34.33 53.24 93.04 Zoom lens group data Group starting plane focal length 1 1 274.14 2 8 -76.47 3 16 78.95 4 27 -67.61 5 29 66.21 6 32 -62.01

[0069] [Numerical Example 5] Unit: mm Surface Data Surface number rd nd νd 1 343.853 6.59 1.48749 70.2 2 -1704.092 0.25 3 143.057 9.25 1.43875 94.7 4 920.875 57.99 5 83.225 11.21 1.49700 81.5 6 -1888.558 2.50 1.61340 44.3 7 70.227 (variable) 8 95.304 3.11 1.69895 30.1 9 -6637.939 3.45 10 460.040 1.30 1.83481 42.7 11 83.586 1.99 12 -419.016 1.40 1.72916 54.7 13 103.766 2.90 14 -76.364 1.50 1.76385 48.5 15 106.789 2.51 1.84666 23.8 16 -2625.038 (variable) 17 59.528 4.59 1.49700 81.5 18 -266.452 0.10 19 34.850 4.74 1.49700 81.5 20 113.383 11.22 21 (Aperture) ∞ 2.03 22 56.726 3.78 1.72825 28.5 23 -123.494 1.70 1.95375 32.3 24 23.868 2.07 25 55.166 6.32 1.73037 32.2 26 -25.789 1.80 1.95375 32.3 27 -416.226 0.46 28 31.114 5.75 1.49700 81.5 29 -65.683 (variable) 30 -660.978 1.31 1.76182 26.5 31 -167.980 4.80 32 -139.451 0.50 1.95375 32.3 33 68.177 (variable) 34 85.018 1.10 1.92286 18.9 35 35.859 2.82 36 -49.039 1.20 1.49700 81.5 37 36.417 5.43 1.80000 29.8 38 -45.190 38.31 39 -41.484 1.35 1.49700 81.5 40 61.869 3.38 1.77250 49.6 41 442.867 (variable) 42 127.363 5.10 1.48749 70.2 43 -131.827 (variable) Image plane ∞ Various data Zoom ratio 3.77 Focal length 206.00 390.62 775.95 F-number 5.83 7.10 8.00 Angle of view 6.00 3.17 1.60 Image height 21.64 21.64 21.64 Lens total length 330.08 375.10 420.12 BF 38.46 38.46 38.46 d 7 1.48 46.50 91.52 d16 45.59 23.96 2.32 d29 2.37 5.12 1.84 d33 25.37 25.19 24.99 d41 1.00 20.06 45.18 d43 38.46 38.46 38.46 Zoom lens group data Group starting plane focal length 1 1 338.79 2 8 -57.29 3 17 49.86 4 30 -58.37 5 34 -166.80 6 42 133.74

[0070] [Numerical Example 6] Unit: mm Surface Data Surface number rd nd νd 1 122.696 10.29 1.51823 58.9 2 2745.406 39.28 3 107.916 9.35 1.49700 81.5 4 -312.569 2.00 1.61340 44.3 5 74.818 2.64 6 116.678 4.35 1.49700 81.5 7 282.163 (variable) 8 125.299 3.85 1.59270 35.3 9 -833.037 8.71 10 93.874 1.60 1.83481 42.7 11 66.175 4.42 12 -175.768 1.00 1.59522 67.7 13 112.528 2.54 14 -97.348 1.00 1.77250 49.6 15 90.817 3.06 1.84666 23.8 16 477.677 (variable) 17 137.480 4.35 1.49700 81.5 18 -86.973 0.19 19 62.163 6.35 1.49700 81.5 20 -62.683 1.00 1.90043 37.4 21 764.966 36.48 22 (Aperture) ∞ 5.74 23 -82.267 0.85 1.62041 60.3 24 58.139 5.20 1.57501 41.5 25 -47.587 0.15 26 61.158 1.50 1.84666 23.8 27 47.147 26.90 28 57.497 4.91 1.54072 47.2 29 -51.358 1.00 1.95375 32.3 30 -127.493 (variable) 31 -171.476 0.85 1.49700 81.5 32 22.888 2.85 1.58144 40.8 33 42.447 (variable) Image plane ∞ Various data Zoom ratio 3.77 Wide-angle Mid-range Telephoto Focal length 205.93 384.94 775.51 F-number 5.77 6.80 9.20 Angle of view 6.00 3.22 1.60 Image height 21.64 21.64 21.64 Lens total length 338.29 388.39 428.30 BF 66.81 94.35 139.51 d 7 2.00 52.10 92.01 d16 47.27 28.13 0.85 d30 29.80 21.41 3.51 d33 66.81 94.35 139.51 Zoom lens group data Group starting plane focal length 1 1 311.48 2 8 -70.10 3 17 86.49 4 31 -77.50

[0071] [Table 1]

[0072] Although the preferred embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and various modifications and changes are possible within the scope of the gist of the present invention. [Explanation of symbols]

[0073] L0 zoom lens system L1 First lens group L2 Second lens group L3: Third lens group L4 4th lens group L5 Fifth lens group L6 6th lens group

Claims

1. A zoom lens having, arranged in order from the object side to the image side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, and a fourth lens group, wherein the spacing between adjacent lens groups changes during zooming, the second lens group is fixed during zooming, and the fourth lens group moves during focusing; the first lens group has a first positive lens and a second positive lens arranged in this order from the most object side to the image side, Let TD4 be the sum of the distances on the optical axis from the object-side surface to the image-side surface of each lens in the fourth lens group, TL3 be the distance on the optical axis from the surface closest to the object to the surface closest to the image in the third lens group, f4 be the focal length of the fourth lens group, and ft be the focal length of the entire system at the telephoto end. 0.001<TD4 / TL3<0.090 0.01<|f4| / ft<0.16 A zoom lens characterized by satisfying the following conditional expressions:

2. When the distance on the optical axis from the surface of the first lens group closest to the object side to the surface of the first lens group closest to the image side is TL1, 0.35<TL1 / |f4|<2.50 2. The zoom lens according to claim 1, wherein the following condition is satisfied:

3. When the lateral magnification of the fourth lens group at the telephoto end is βft, and the lateral magnification of the subsequent group formed by combining all lens groups arranged closer to the image side than the fourth lens group is βrt, 3.00<|(1-βft ２ )×βrt ２ |<25.0 3. The zoom lens according to claim 1, wherein the following condition is satisfied:

4. When the focal length of the first lens group is f1 and the focal length at the wide-angle end is fw, 0.70<f1 / fw<3.20 4. The zoom lens according to claim 1, wherein the following condition is satisfied:

5. When the focal length of the second lens group is f2 and the focal length at the wide-angle end is fw, -1.00<f2 / fw<-0.10 5. The zoom lens according to claim 1, wherein the following condition is satisfied:

6. When the focal length of the third lens group is f3 and the focal length at the wide-angle end is fw, 0.10<f3 / fw<1.20 6. The zoom lens according to claim 1, wherein the following condition is satisfied:

7. When the back focus at the wide-angle end is skw, 5.0<ft / skw<50.0 7. The zoom lens according to claim 1, wherein the following condition is satisfied:

8. When the total lens length at the wide-angle end is TTDw and the back focus at the wide-angle end is skw, 2.00<TTDw / skw<25.0 8. The zoom lens according to claim 1, wherein the following condition is satisfied:

9. When the movement amount of the first lens group during zooming from the wide-angle end to the telephoto end is m1 and the focal length of the first lens group is f1, -1.00<m1 / f1<-0.05 9. The zoom lens according to claim 1, wherein the following condition is satisfied:

10. 10. The zoom lens according to claim 1, wherein the fourth lens group is made up of a cemented lens or a single lens.

11. 11. The zoom lens according to claim 1, wherein the lens surface of the fourth lens group closest to the image side has a shape concave toward the image side.

12. 12. The zoom lens according to claim 1, wherein the fourth lens group has a negative refractive power.

13. 13. The zoom lens according to claim 1, wherein, during image blur correction, all or some of the lenses in the second lens group move in a direction including a component perpendicular to the optical axis.

14. 14. The zoom lens according to claim 1, wherein the third lens group has an aperture stop for determining an F-number, and lenses constituting the third lens group are arranged on the object side and the image side of the aperture stop, respectively.

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

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

17. 15. The zoom lens according to claim 1, wherein the zoom lens comprises, arranged in order from the object side to the image side, the first lens group, the second lens group, the third lens group, the fourth lens group with negative refractive power, a fifth lens group with negative refractive power, and a sixth lens group with positive refractive power.

18. 15. The zoom lens according to claim 1, wherein the zoom lens comprises, in order from the object side to the image side, the first lens group, the second lens group, the third lens group, and the fourth lens group having negative refractive power.

19. A zoom lens comprising the first lens group, the second lens group, the third lens group, the fourth lens group with negative refractive power, the fifth lens group with positive refractive power, and the sixth lens group with negative refractive power, arranged in this order from the object side to the image side, wherein the spacing between adjacent lens groups changes during zooming, the second lens group is fixed during zooming, and the fourth lens group moves during focusing; Let TD4 be the sum of the distances on the optical axis from the object-side surface to the image-side surface of each lens in the fourth lens group, TL3 be the distance on the optical axis from the surface closest to the object to the surface closest to the image in the third lens group, f4 be the focal length of the fourth lens group, and ft be the focal length of the entire system at the telephoto end. 0.001<TD4 / TL3<0.090 0.01<|f4| / ft<0.16 A zoom lens characterized by satisfying the following conditional expressions:

20. A zoom lens comprising the first lens group, the second lens group, the third lens group, the fourth lens group with positive refractive power, and the fifth lens group with negative refractive power, arranged in this order from the object side to the image side, wherein the spacing between adjacent lens groups changes during zooming, the second lens group is fixed during zooming, and the fourth lens group moves during focusing; Let TD4 be the sum of the distances on the optical axis from the object-side surface to the image-side surface of each lens in the fourth lens group, TL3 be the distance on the optical axis from the surface closest to the object to the surface closest to the image in the third lens group, f4 be the focal length of the fourth lens group, and ft be the focal length of the entire system at the telephoto end. 0.001<TD4 / TL3<0.090 0.01<|f4| / ft<0.16 A zoom lens characterized by satisfying the following conditional expressions:

21. A zoom lens comprising the first lens group, the second lens group, the third lens group, the fourth lens group with negative refractive power, the fifth lens group with negative refractive power, and the sixth lens group with positive refractive power, arranged in this order from the object side to the image side, wherein the spacing between adjacent lens groups changes during zooming, the second lens group is fixed during zooming, and the fourth lens group moves during focusing; Let TD4 be the sum of the distances on the optical axis from the object-side surface to the image-side surface of each lens in the fourth lens group, TL3 be the distance on the optical axis from the surface closest to the object to the surface closest to the image in the third lens group, f4 be the focal length of the fourth lens group, and ft be the focal length of the entire system at the telephoto end. 0.001<TD4 / TL3<0.090 0.01<|f4| / ft<0.16 A zoom lens characterized by satisfying the following conditional expressions:

22. A zoom lens comprising the first lens group, the second lens group, the third lens group, and the fourth lens group having negative refractive power, arranged in this order from the object side to the image side, wherein the spacing between adjacent lens groups changes during zooming, the second lens group is fixed during zooming, and the fourth lens group moves during focusing; Let TD4 be the sum of the distances on the optical axis from the object-side surface to the image-side surface of each lens in the fourth lens group, TL3 be the distance on the optical axis from the surface closest to the object to the surface closest to the image in the third lens group, f4 be the focal length of the fourth lens group, and ft be the focal length of the entire system at the telephoto end. 0.001<TD4 / TL3<0.090 0.01<|f4| / ft<0.16 A zoom lens characterized by satisfying the following conditional expressions:

23. a zoom lens according to any one of claims 1 to 22; and an image sensor that receives an image formed by the zoom lens.

Images