Zoom lens and imaging device

Abstract

To provide a compact zoom lens which offers high optical performance.SOLUTION: A zoom lens provided herein consists of four or more lens groups including first through third lens groups L1 to L3 respectively having positive, negative, and positive power in order from the object side. The first lens group consists of three or less lenses, while the second lens group consists of a first single lens in the form of a negative spherical lens, a cemented lens consisting of a negative and positive lenses that are cemented together, and a second single lens in the form of a negative spherical lens. The zoom lens satisfies the following condition expressions: 1.35≤|f2| / skm≤5.00, 3.0≤d21 / d22≤10.0, where skm represents a minimum back focus over an entire zoom range of the zoom lens, f2 represents a focal length of the second lens group, d21 represents a distance between an image-side surface of the first single lens to a lens surface of the cemented lens on the most object side along an optical axis, and d22 represents a distance between a lens surface of the cemented lens B on the most image side and an object-side surface of the second single lens along the optical axis.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a zoom lens suitable for use in image pickup devices such as still cameras and video cameras. [Background technology]

[0002] Zoom lenses include inner focus type and rear focus type, which perform focusing by moving a lens group closer to the image side than a first lens group closest to the object side. Patent Document 1 discloses a rear focus type zoom lens that is composed of first to fifth lens groups with positive, negative, positive, negative and positive refractive powers in order from the object side to the image side, and the fourth lens group and the fifth lens group are composed of two or less lenses. Patent Document 2 discloses a high-magnification and thin zoom lens that has first and second lens groups with positive and negative refractive powers in order from the object side to the image side, and is provided with a prism element in the first lens group that bends the optical path. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2016-156902 A [Patent Document 2] JP 2005-181635 A Summary of the Invention [Problem to be solved by the invention]

[0004] Zoom lenses are required to have high optical performance and be robust against manufacturing errors while being compact. However, the zoom lens of Patent Document 1 has a long overall lens length and is not sufficiently compact. In addition, the zoom lens of Patent Document 2 has a problem in that the overall lens length increases in the wide-angle range because it is difficult to move the first lens group including a large prism element.

[0005] The present invention provides a compact zoom lens that is robust to manufacturing errors and has high optical performance. [Means for solving the problem]

[0006] A zoom lens according to one aspect of the present invention comprises four or more lens groups, including a first lens group having positive refractive power, a second lens group having negative refractive power, and a third lens group having positive refractive power, arranged in this order from the object side to the image side. The distance between adjacent lens groups changes during zooming from the wide-angle end to the telephoto end, and the first lens group moves during zooming, the distance between the first lens group and the second lens group increases during zooming from the wide-angle end to the telephoto end, and the distance between the second lens group and the third lens group decreases during zooming from the wide-angle end to the telephoto end. The first lens group is composed of three or less lenses, and the second lens group comprises a first single lens as a spherical lens having negative refractive power, a cemented lens in which a spherical lens having negative refractive power and a spherical lens having positive refractive power are cemented together, and a second single lens as a spherical lens having negative refractive power, arranged in this order from the object side to the image side. The minimum value of the back focus of the zoom lens in the entire zoom range is skm, the focal length of the second lens group is f2, the distance on the optical axis between the lens surface on the image side of the first single lens and the lens surface on the most object side of the cemented lens is d21, the distance on the optical axis between the lens surface on the most image side of the cemented lens and the lens surface on the object side of the second single lens is d22, and the focal length of the first lens group is f1. The average Abbe number of the material of the negative refractive power lens and the second single lens in the cemented lens based on the d-line is νBC. When 1.35≦|f2| / skm≦5.00 3.1≦d21 / d22≦10.0 4.0≦|f1 / f2|≦8.0 48≦νBC≦80 The present invention is characterized in that the above conditions are satisfied. An image pickup apparatus including the above zoom lens also constitutes another aspect of the present invention. Effect of the Invention

[0007] According to the present invention, it is possible to provide a compact zoom lens that is robust against manufacturing errors and has high optical performance. [Brief description of the drawings]

[0008] [Figure 1] 1A to 1C are cross-sectional views of a zoom lens according to a first embodiment at a wide-angle end, at a middle zoom position, and at a telephoto end. [Diagram 2] 5A to 5C are aberration diagrams of the zoom lens of Example 1 at the wide-angle end, at a middle zoom position, and at the telephoto end. [Diagram 3] 11A to 11C are cross-sectional views of a zoom lens according to a second embodiment at a wide-angle end, at a middle zoom position, and at a telephoto end. [Figure 4] 11A to 11C are aberration diagrams of the zoom lens of Example 2 at the wide-angle end, at the intermediate zoom position, and at the telephoto end. [Diagram 5] 11A to 11C are cross-sectional views of a zoom lens according to a third embodiment at a wide-angle end, at a middle zoom position, and at a telephoto end. [Figure 6] 11A to 11C are aberration diagrams of the zoom lens of Example 3 at the wide-angle end, at a middle zoom position, and at the telephoto end. [Figure 7] 11A to 11C are cross-sectional views of a zoom lens according to a fourth embodiment at a wide-angle end, at a middle zoom position, and at a telephoto end. [Figure 8] 11A to 11C are aberration diagrams of the zoom lens of Example 4 at the wide-angle end, at the intermediate zoom position, and at the telephoto end. [Figure 9] FIG. 1 is a diagram showing an imaging device equipped with a zoom lens according to any one of the first to fourth embodiments. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Figures 1, 3, 5, and 7 respectively show cross sections of the zoom lenses of Examples 1, 2, 3, and 4 at the wide-angle end (shortest focal length), the intermediate zoom position, and the telephoto end (longest focal length). In each cross section, the left side is the object side, and the right side is the image side.

[0010] The zoom lens of each embodiment is composed of four or more lens groups including a first lens group L1 with positive refractive power (= the reciprocal of the focal length), a second lens group L2 with negative refractive power, and a third lens group L3 with positive refractive power, arranged in this order from the object side to the image side. During zooming from the wide-angle end to the telephoto end, the distance between the first lens group L1 and the second lens group L2 increases, and the distance between the second lens group L2 and the third lens group L3 decreases. During zooming, the first lens group L1 moves. During zooming, the distances between the adjacent lens groups of the multiple lens groups (L4 to L7) on the image side of the third lens group L3 also change.

[0011] A lens group is a group of one or more lenses whose spacing between adjacent lens groups changes during zooming or focusing. The wide-angle end and telephoto end refer to the states (zoom positions) when the lens group is located at both ends of the range in which it can mechanically move in the optical axis direction during zooming.

[0012] The zoom lens of each of the above-mentioned embodiments has, in order from the object side to the image side, a positive, a negative and a positive lens group in order to correct aberrations well over the entire zoom range while shortening the overall lens length at the wide-angle end. Also, by having four or more lens groups, spherical aberration and coma aberration occurring in the first lens group L1 and the second lens group L2 can be corrected well.

[0013] Furthermore, in the telephoto zoom range, variations in spherical aberration and coma aberration due to manufacturing errors are likely to become significant. By making the first lens group L1 a positive lead type with positive refractive power, it is possible to reduce the height of incidence of the axial light ray to the lens on the image side of the second lens group L2, thereby achieving compactness and improved robustness against manufacturing errors.

[0014] Furthermore, in order to ensure a high zoom ratio while maintaining a compact size, during zooming, the lens groups are moved so that the distance between the first lens group L1 and the second lens group L2 is wider at the telephoto end and the distance between the second lens group L2 and the third lens group L3 is narrower at the telephoto end than at the wide-angle end.

[0015] In the zoom lens of each embodiment, the first lens group L1 is composed of three or less lenses. In this way, by reducing the number of lenses constituting the first lens group L1, which has a large lens diameter, it is possible to achieve a compact and lightweight lens. Moreover, the height of the light beam emerging from the first lens group L1 can be lowered, and off-axis aberrations such as coma aberration and curvature of field can be effectively corrected.

[0016] Furthermore, in the zoom lens of each embodiment, the second lens group L2 is composed of a single lens A (first single lens) as a spherical lens having negative refractive power, a cemented lens B in which a lens having negative refractive power and a lens having positive refractive power are cemented together, and a single lens C (second single lens) as a spherical lens having negative refractive power, which are arranged in this order from the object side to the image side. By configuring the second lens group L2 using a spherical lens, it is possible to suppress surface shape errors (errors due to non-rotationally symmetric components and spherical shape change components) that tend to occur in aspherical lenses. In addition, while increasing the refractive power of the second lens group L2, it is possible to satisfactorily correct the field curvature in the wide-angle range and the spherical aberration in the telephoto range, thereby realizing the miniaturization of the entire system.

[0017] Furthermore, by arranging the negative single lens A closest to the object side in the second lens unit L2, the power arrangement in the second lens unit L2 can be of the retrofocus type, making it possible to satisfactorily correct curvature of field in the wide-angle range.

[0018] In addition, by disposing a cemented lens B consisting of a negative lens and a positive lens on the image side of the negative single lens A, it is possible to satisfactorily correct field curvature in the wide-angle range and spherical aberration in the telephoto range, and further to suppress variations in spherical aberration and coma aberration in the telephoto range due to manufacturing errors (decentration errors), thereby ensuring good optical performance.

[0019] Furthermore, by disposing a negative single lens C on the image side of the cemented lens B, it is possible to ensure that the second lens unit L2 is able to share the refractive power and the magnification, while also making it possible to satisfactorily correct off-axis coma and field curvature in the wide-angle range.

[0020] In the zoom lens of each embodiment, the third lens group L3 has an aperture stop SP that determines (limits) the light flux at the maximum F-number (Fno), and focusing is performed by moving the lens group on the image side of the third lens group L3. In each cross-sectional view, the arrow indicates the movement direction of the lens group when focusing from infinity to a close distance.

[0021] In each cross-sectional view, IP is an image plane. When the zoom lens of each embodiment is used as an imaging optical system of an imaging device such as a video camera, a digital still camera, a TV camera, or a silver halide film camera, the imaging surface of a solid-state imaging element (photoelectric conversion element) such as a CCD sensor or a CMOS sensor, or the film surface (photosensitive surface) of a silver halide film is disposed on the image plane IP. The zoom lens of each embodiment can also be used as a projection optical system for an image projection device (projector).

[0022] The zoom lens of each embodiment will be described in more detail below.

[0023] The zoom lens of Example 1 shown in Fig. 1 has a zoom ratio of 3.3 and an aperture ratio of about 2.9 to 2.9. The zoom lens of Example 2 shown in Fig. 3 has a zoom ratio of 7.1 and an aperture ratio of about 2.9 to 2.9. In the zoom lenses of Examples 1 and 2, the first, second and third lens groups L1, L2 and L3 have positive, negative and positive refractive powers, respectively, as described above, the fourth lens group L4 has negative refractive power, and the fifth lens group L5 has positive refractive power. In the zoom lenses of Examples 1 and 2, during zooming from the wide-angle end to the telephoto end, the first lens group L1 moves monotonically toward the object side, and the second lens group L2 to the fifth lens group L5 move such that the distance between the first lens group L1 and the second lens group L2 increases, the distance between the second lens group L2 and the third lens group L3 decreases, the distance between the third lens group L3 and the fourth lens group L4 changes, and further the distance between the fourth lens group L4 and the fifth lens group L5 increases. During focusing from infinity to a close distance, the fourth lens group L4 moves toward the image side.

[0024] 5 is a zoom lens having a zoom ratio of 9.3 and an aperture ratio of about 4.1 to 6.4. In the zoom lens of Example 3, the first, second and third lens groups L1, L2 and L3 have positive, negative and positive refractive powers, respectively, as described above, the fourth lens group L4 has positive refractive power, the fifth lens group L5 has negative refractive power and the sixth lens group L6 has negative refractive power. In the zoom lens of Example 3, during zooming from the wide-angle end to the telephoto end, the first lens group L1 moves monotonically toward the object side, and the second lens group L2 to the sixth lens group L6 move so that the distance between the first lens group L1 and the second lens group L2 increases, the distance between the second lens group L2 and the third lens group L3 decreases, the distance between the third lens group L3 and the fourth lens group L4 decreases, the distance between the fourth lens group L4 and the fifth lens group L5 decreases, and further the distance between the fifth lens group L5 and the sixth lens group L6 increases. During focusing from infinity to a close distance, the fifth lens group L5 moves toward the image side.

[0025] 7 is a zoom lens having a zoom ratio of 2.4 and an aperture ratio of about 2.9 to 2.9. In the zoom lens of Example 4, the first, second and third lens groups L1, L2 and L3 have positive, negative and positive refractive powers, respectively, as described above, the fourth lens group L4 has negative refractive power, the fifth lens group L5 has positive refractive power, the sixth lens group L6 has negative refractive power and the seventh lens group L7 has negative refractive power. In the zoom lens of Example 4, during zooming from the wide-angle end to the telephoto end, the first lens group L1 moves monotonically toward the object side, and the second lens group L2 to the seventh lens group L7 move in such a manner that the distance between the first lens group L1 and the second lens group L2 increases, the distance between the second lens group L2 and the third lens group L3 decreases, the distance between the third lens group L3 and the fourth lens group L4 increases, the distance between the fourth lens group L4 and the fifth lens group L5 decreases, the distance between the fifth lens group L5 and the sixth lens group L6 changes, and further the distance between the sixth lens group L6 and the seventh lens group L7 increases. During focusing from infinity to a close distance, the fourth lens group L4 moves toward the object side, and the sixth lens group L6 moves toward the image side.

[0026] Although the zoom lenses in the first to fourth embodiments are configured with five to seven lens groups, the number of lens groups may be four or more, including the first to third lens groups described above.

[0027] The conditions that the zoom lens of each embodiment satisfies will be described below.

[0028] The minimum value of the back focus in the entire zoom range is skm, the focal length of the second lens group L2 is f2, the distance on the optical axis between the image-side lens surface of the single lens A and the lens surface closest to the object of the cemented lens B is d21, and the distance on the optical axis between the lens surface closest to the image of the cemented lens B and the lens surface closest to the object of the single lens C is d22. In this case, the following conditional formula (1) is satisfied. 1.35≦|f2| / skm≦5.00 (1) 3.0≦d21 / d22≦10.0 (2) Conditional formula (1) shows the condition regarding the relationship between the focal length f2 of the second lens group L2 and the minimum back focus skm in order to shorten the overall lens length at the wide-angle end and ensure high optical performance. The overall lens length is the length obtained by adding the back focus as an air-equivalent value to the distance on the optical axis from the lens surface closest to the object to the lens surface closest to the image. The back focus is the distance on the optical axis from the lens surface closest to the image (the lens surface closest to the image when a parallel plate such as a filter is removed) to the paraxial image plane for an infinite object point.

[0029] In a positive lead type zoom lens, the wide angle is achieved by generally adopting a retrofocus type refractive power arrangement as a whole at the wide angle end, and generally adopting a telephoto type refractive power arrangement as a whole at the telephoto end. This allows a high zoom ratio to be achieved. Therefore, in order to shorten the overall lens length at the wide angle end, it is necessary to appropriately set the refractive power of the second lens group L2. By satisfying conditional expression (1), it is possible to achieve both compactness and high performance.

[0030] If |f2| / skm exceeds the upper limit of conditional formula (1), the refractive power of the second lens unit L2 is small, and the overall lens length increases to ensure the necessary angle of view at the wide-angle end, which is undesirable.If |f2| / skm falls below the lower limit of conditional formula (1), the refractive power of the second lens unit L2 is large, making it difficult to correct lateral chromatic aberration and curvature of field on the telephoto side, and furthermore, correction of spherical aberration and coma on the telephoto side is insufficient, which is undesirable.

[0031] Conditional formula (2) shows a condition related to the relationship between the distances d21 and d22 for achieving a wide angle while suppressing the variation of the curvature of field during zooming. If the single lens A is positioned closer to the object side in the second lens group L2 so that d21 / d22 exceeds the upper limit of conditional formula (2), this is advantageous for correcting the curvature of field, but it is undesirable because it increases the diameter of the first lens group L1 and hinders size reduction. If the single lens C is positioned closer to the image side in the second lens group L2 so that d21 / d22 falls below the lower limit of conditional formula (2), it is undesirable because it becomes difficult to effectively correct the spherical aberration and coma aberration on the telephoto side.

[0032] It is more preferable to set the numerical ranges of the conditional expressions (1) and (2) as follows: 1.38≦|f2| / skm≦3.00 (1a) 3.0≦d21 / d22≦6.0 (2a) By satisfying condition (1a), it becomes easier to suppress the variation in lateral chromatic aberration for each wavelength while suppressing astigmatic difference on the wide-angle side, and by satisfying condition (2a), it becomes possible to shorten the overall lens length while suppressing spherical aberration on the telephoto side.

[0033] It is more preferable that the numerical ranges of the conditional expressions (1) and (2) are as follows: 1.41≦|f2| / skm≦2.00 (1b) 3.1≦d21 / d22≦4.0 (2b) As described above, by appropriately configuring each lens group and simultaneously satisfying conditional expressions (1) and (2), it is possible to satisfactorily correct various aberrations such as spherical aberration and coma aberration, and it is possible to realize a zoom lens that is compact in size as a whole, yet is robust against manufacturing errors and has high optical performance. It is preferable that the zoom lens of each embodiment satisfies at least one of the following conditional expressions (3) to (12).

[0034] Let fw and ft be the focal lengths of the zoom lens at the wide-angle end and the telephoto end, respectively, and f1 and f3 be the focal lengths of the first lens group L1 and the third lens group L3, respectively. Let SFA be the shape factor of single lens A, and SFbc be the shape factor of the air lens formed between cemented lens B and single lens C. Let RBm be the radius of curvature of the cemented surface of cemented lens B. Let nBC be the average value of the refractive index for the d-line of the negative lens in cemented lens B and single lens C, and νBC be the average value of the Abbe numbers based on the d-line. Let V be the third-order aberration coefficient of the distortion aberration occurring in the zoom lens at the wide-angle end, and dmin be the percentage of the distortion aberration at the maximum image height at the wide-angle end.

[0035] 1.0≦SFA≦10.0 (3) -2.0≦SFbc≦1.0 (4) 0.6≦|RBm / f2|≦3.0 (5) 1.51≦nBC≦1.85 (6) 40≦νBC≦80 (7) 4.0≦|f1 / f2|≦8.0 (8) 3.5≦|f1 / fw|≦10.0 (9) 0.2≦|f3 / ft|≦0.6 (10) 0.3≦V≦1.0 (11) -15.0≦dmin≦-4.4 (12) The Abbe number νd based on the d-line is given by the following, where Nd, NF, and NC are the refractive indices for the d-line (587.6 nm), F-line (486.1 nm), and C-line (656.3 nm) of the Fraunhofer lines: νd=(Nd-1) / (NF-NC) The shape factor SFA is the shape factor of single lens A, and is expressed by the following formula, where the radius of curvature of the lens surface on the object side of single lens A is RA1 and the radius of curvature of the lens surface on the image side is R22. When the surface has an aspheric shape, the radius of curvature means the radius of the quadratic curved surface that serves as the reference (base R).

[0036] SFA = -(RA2 + RA1) / (RA2 - RA1) The shape factor SFbc is expressed by the following formula, where RB2 is the radius of curvature of the lens surface of the cemented lens B closest to the image side, and RC1 is the radius of curvature of the lens surface of the single lens C closest to the object side. When the surface has an aspheric shape, this means its base R.

[0037] SFbc = (RC1 + RB2) / (RC1 - RB2) Conditional formula (3) shows a condition related to the shape factor of single lens A for properly correcting curvature of field in the wide-angle range and miniaturizing the second lens group L2 while optimizing its share of the magnification change. When SFA is 1, which is the lower limit of conditional formula (3), single lens A becomes a plano-convex lens with its concave surface facing the image side. If SFA exceeds the upper limit of conditional formula (3), it becomes difficult to properly correct curvature of field and astigmatism in the wide-angle range, and zoom fluctuation of curvature of field becomes large, which is not preferable. If SFA falls below the lower limit of conditional formula (3), the angle of view fluctuation of chromatic aberration of magnification in the wide-angle format becomes large, which is also not preferable.

[0038] Conditional formula (4) shows a condition regarding the shape of the air lens for suppressing spherical aberration on the telephoto side while suppressing astigmatic difference in the wide-angle range. The air lens has a strong convex surface on the image side, and is sandwiched on both sides by media with a refractive index of 1 or more, which creates a refractive index difference, so it can be considered as a lens with a refractive action similar to that of a negative lens. By giving the air lens such a shape, the number of lenses constituting the second lens group L2 can be reduced. If SFbc exceeds the upper limit of conditional formula (4), the curvature of the image-side surface of the air lens becomes strong, which leads to insufficient correction of spherical aberration on the telephoto side, which is not preferable. If SFbc falls below the lower limit of conditional formula (4), the curvature of the object-side surface of the air lens becomes strong, which leads to an increase in astigmatic difference in the wide-angle range, which is not preferable.

[0039] Conditional formula (5) indicates a condition regarding the relationship between the radius of curvature RBm of the cemented surface of the cemented lens B and the focal length of the second lens group L2 in order to optimize the aberration correction burden of the cemented lens B in the second lens group L2. If |RBm / f2| exceeds the upper limit of conditional formula (5), the radius of curvature of the cemented surface becomes too large, which is undesirable as it causes insufficient correction of curvature of field in the wide angle range. Also, if |RBm / f2| falls below the lower limit of conditional formula (5), the radius of curvature of the cemented surface becomes too small, which is undesirable as it causes high-order aberrations and causes variations in spherical aberration and curvature of field for each wavelength.

[0040] Conditional expressions (6) and (7) show conditions for the materials of the negative lens of the cemented lens B and the single lens (negative lens) C, which are used to suppress the occurrence of lateral chromatic aberration at the wide-angle end while suppressing the curvature of field on the wide-angle side. If the refractive index nBC and the Abbe number νBC are within the numerical ranges of conditional expressions (6) and (7), respectively, the primary achromatic effect can be easily optimized.

[0041] Conditional formula (8) shows a condition related to the relationship between the focal length f1 of the first lens group L1 and the focal length f2 of the second lens group L2 in order to miniaturize the entire system while ensuring an appropriate zoom ratio. In a zoom lens that is bright in the telephoto range, if the refractive power of the first lens group L1 is not set appropriately within a range in which aberrations can be corrected, the total lens length in the telephoto range increases, and the diameter of the first lens group L1 is increased in order to ensure the amount of peripheral light. If |f1 / f2| exceeds the upper limit of conditional formula (8), the refractive power of the first lens group L1 decreases, so the total lens length increases and it becomes difficult to ensure the amount of peripheral light, which is undesirable. If |f1 / f2| falls below the lower limit of conditional formula (8), the aberration fluctuation due to the movement of the first lens group L1 and the second lens group L2 during zooming becomes large, and it becomes difficult to correct spherical aberration in particular, which is undesirable.

[0042] Conditional formula (9) shows a condition regarding the relationship between the focal length f1 of the first lens group L1 and the focal length fw at the wide-angle end of the zoom lens in order to optimize the share of the first lens group L1 in the zooming while miniaturizing the zoom lens. The first lens group L1 has an appropriate refractive power, so that the movement amount of the first lens group L1 during zooming can be reduced. If |f1 / fw| exceeds the upper limit of conditional formula (9), the refractive power of the first lens group L1 is weak and the zooming action is weakened, so that it becomes necessary to increase the movement amount of the first lens group L1 during zooming to compensate for the zooming action, and the total lens length at the telephoto end increases, which is not preferable. Moreover, the lens groups after the third lens group L3 must ensure the share of the zooming action, and various aberrations such as spherical aberration and coma aberration occur frequently in the telephoto range, and it becomes necessary to increase the number of lenses and aspherical lenses to correct them, which is not preferable because it reduces robustness against manufacturing errors. If |f1 / fw| falls below the lower limit of conditional expression (9), the refractive power of the first lens unit L1 becomes too strong, causing more spherical aberration in the telephoto range than in the first lens unit L1, which is undesirable.

[0043] Conditional expression (10) indicates a condition regarding the relationship between the focal length f3 of the third lens group L3 and the focal length ft at the telephoto end of the zoom lens in order to ensure the third lens group L3's share of the variable magnification after favorably correcting spherical aberration and coma aberration. If |f3 / ft| exceeds the upper limit of conditional expression (10), the refractive power of the third lens group L3 becomes weak, weakening the variable magnification effect, and it becomes necessary to increase the amount of movement of the third lens group L3 during zooming, which is undesirable. If |f3 / ft| falls below the lower limit of conditional expression (10), the refractive power of the third lens group L3 becomes too strong, causing spherical aberration and coma aberration in the telephoto range, and further causing astigmatic difference in the central area of ​​the image plane, which is undesirable.

[0044] Conditional expression (11) indicates a condition related to the third-order aberration coefficient V of distortion in order to appropriately correct curvature of field and astigmatism, and to suppress degradation of resolution due to enlargement when electronic distortion correction is performed on captured image data in an imaging device. If V exceeds the upper limit of conditional expression (11), distortion becomes large, and degradation of resolution due to enlargement becomes large, which is undesirable. If V falls below the lower limit of conditional expression (11), it becomes difficult to satisfactorily correct curvature of field and lateral chromatic aberration, which is undesirable.

[0045] Conditional expression (12) indicates a condition related to the percentage dmin of distortion at the maximum image height at the wide-angle end in order to appropriately correct curvature of field and lateral chromatic aberration. If dmin exceeds the upper limit of conditional expression (12), it is advantageous for size reduction, but it is undesirable because distortion increases and the deterioration of resolution due to enlargement increases. If dmin falls below the lower limit of conditional expression (12), it is undesirable because it becomes difficult to suppress the change in lateral chromatic aberration (especially short wavelength components) with respect to image height.

[0046] The first lens group L1 is preferably composed of a cemented lens of a negative lens and a positive lens, and a single lens of a meniscus shape having positive refractive power, which makes it possible to effectively correct lateral chromatic aberration over the entire zoom range, and facilitates effective correction of spherical aberration and axial chromatic aberration in the telephoto range.

[0047] The third lens group L3 is preferably configured with a single lens having positive refractive power and convex toward the object side at its most object side. The light beam entering the third lens group L3 from the second lens group L2, which is mainly responsible for the magnification change, has a high ray height, which causes high-order spherical aberration and coma aberration. Therefore, by arranging a single lens having positive refractive power and convex toward the object side at the most object side of the third lens group L3, it becomes easier to ensure the positive refractive power required to converge the light beam diverged by the second lens group L2, and the occurrence of spherical aberration and coma aberration can be effectively suppressed.

[0048] In the lens group closest to the image side, it is preferable that the lens closest to the image side is a positive lens convex toward the image side, which makes it easier to ensure the back focus and suppresses the collection of unwanted light (ghost) caused by the image sensor in the image pickup device.

[0049] Furthermore, it is preferable that the lens group closer to the image side than the third lens group L3 has an aspheric surface, which makes it possible to effectively correct the curvature of field at the wide-angle end while making the zoom lens more compact.

[0050] It is more preferable to set the numerical ranges of the conditional expressions (3) to (12) as follows:

[0051] 1.1≦SFA≦9.0 (3a) -1.7≦SFbc≦0.3 (4a) 0.8≦|RBm / f2|≦1.8 (5a) 1.52≦nBC≦1.82 (6a) 44≦νBC≦78 (7a) 5.0≦|f1 / f2|≦7,2 (8a) 4.0≦|f1 / fw|≦9.0 (9a) 0.22≦|f3 / ft|≦0.55 (10a) 0.31≦V≦0.60 (11a) -14.0≦dmin≦-4.6 (12a) By satisfying conditional expression (3a), the correction of curvature of field in the wide-angle range becomes more appropriate, and it becomes easier to correct the curvature of field even when the angle of view of the zoom lens is widened. By satisfying conditional expression (4a), it becomes easier to correct spherical aberration and coma aberration in the telephoto range. By satisfying conditional expression (5a), it becomes easier to suppress the variation of curvature of field for each wavelength in the wide-angle range. By satisfying conditional expressions (6a) and (7a), it becomes easier to suppress the fluctuation of chromatic aberration of magnification during zooming. By satisfying conditional expression (8a), the division of magnification load between the first lens group L1 and the second lens group L2 becomes more appropriate, and it becomes easier to make the lens compact even when the magnification is increased. By satisfying conditional expression (9a), it becomes easier to correct chromatic aberration of magnification in the wide-angle range and spherical aberration on the telephoto side. By satisfying conditional expression (10a), the magnification variation share of the third lens group L3 is more appropriately adjusted, and it becomes easier to suppress the fluctuation of coma due to zooming. By satisfying conditional expressions (10a) and (11a), it becomes easier to effectively correct the curvature of field, the astigmatism, and the lateral chromatic aberration.

[0052] It is even more preferable to set the numerical ranges of the conditional expressions (3) to (12) as follows:

[0053] 1.1≦SFA≦8.4 (3b) -1.5≦SFbc≦0.1 (4b) 1.0≦|RBm / f2|≦1.5 (5b) 1.53≦nBC≦1.79 (6b) 48≦νBC≦76 (7b) 5.1≦|f1 / f2|≦6.8 (8b) 4.3≦|f1 / fw|≦8.6 (9b) 0.24≦|f3 / ft|≦0.50 (10b) 0.32≦V≦0.50 (11b) -13.0≦dmin≦-4.9 (12b) Numerical Examples 1 to 4 corresponding to Examples 1 to 4 are shown below. In each numerical example, 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) between the i-th and (i+1)-th surfaces, and nd is the refractive index at the d-line of the material of the i-th optical component. νd is the Abbe number based on the d-line of the material of the i-th optical component and is expressed as described above. BF is the back focus (mm) described above, and the total lens length is as described above.

[0054] An "*" next to a surface number means that the surface has an aspheric shape. The aspheric shape is expressed by the following formula, where the position in the optical axis direction is X, the height in the direction perpendicular to the optical axis is H, the direction of light travel is positive, R is the paraxial radius of curvature, K is the conic constant, and A4, A6, A8, A10, A12, and A14 are aspheric coefficients. The conic constant and the aspheric coefficient ex are expressed as x 10 -x means...

[0055]

number

[0056] 2, 4, 6 and 8 are aberration diagrams of the zoom lenses of Examples 1, 2, 3 and 4 (numerical Examples 1, 2, 3 and 4) at the wide-angle end, the intermediate zoom position and the telephoto end, respectively. In each aberration diagram, Fno is the F-number. ω is the half angle of view (°), which is the half angle of view based on the ray tracing value. In the spherical aberration diagrams, the solid line indicates the spherical aberration of the d-line (wavelength 587.6 nm), and the two-dot chain line indicates the spherical aberration of the g-line (wavelength 435.8 nm). In the astigmatism diagrams, the solid line S indicates the sagittal image plane, and the dashed line M indicates the meridional image plane. The distortion aberration is shown for the d-line. The chromatic aberration diagrams show the chromatic aberration of magnification at the g-line.

[0057] Moreover, values ​​corresponding to the above-mentioned conditional expressions (1) to (12) in Numerical Examples 1 to 4 are summarized in Table 1. (Numerical Example 1) Unit: mm Surface Data Surface number rd nd νd 1 141.907 1.80 1.84666 23.8 2 65.733 6.40 1.61997 63.9 3 375.431 0.15 4 49.725 6.89 1.75500 52.3 5 195.174 (variable) 6 59.541 1.50 1.91082 35.3 7 13.279 7.12 8 -34.401 1.00 1.61997 63.9 9 16.635 4.95 2.00069 25.5 10 3167.419 2.05 11 -18.970 1.00 1.81600 46.6 12 -27.118 (variable) 13* 63.703 2.89 1.68948 31.0 14* -99.524 1.99 15(Aperture) ∞ 1.60 16 34.995 1.00 1.92286 18.9 17 22.173 5.92 1.49700 81.5 18 -27.379 0.50 19 29.006 3.98 1.49700 81.5 20 -51.300 0.80 1.79952 42.2 21 17.375 1.25 22* 15.325 6.22 1.61881 63.9 23* -19.673 (variable) 24 -2180.198 0.80 1.61800 63.4 25 13.874 1.79 26 110.502 0.81 1.53172 48.8 27 12.881 3.31 1.69680 55.5 28 35.478 (variable) 29 -63.517 3.37 1.91082 35.3 30 -29.610 (variable) Image plane ∞ Aspheric Data Page 13 K = 0.00000e+000 A4=-5.42417e-005 A6=-3.16930e-007 A8= 6.13967e-009 A10=-6.00779e-011 A12= 2.86581e-013 Side 14 K = 0.00000e+000 A4=-3.80560e-005 A6=-4.63751e-008 A8= 1.22944e-009 Page 22 K = 0.00000e+000 A4=-5.29719e-005 A6=-2.59814e-007 A8= 1.05461e-008 A10=-2.66191e-010 A12= 3.17312e-012 A14=-1.46144e-014 Page 23 K = 0.00000e+000 A4= 3.28246e-005 A6=-3.67629e-007 A8= 1.07289e-008 A10=-2.30132e-010 A12= 2.56287e-012 A14=-1.12454e-014 Various data Zoom ratio 3.26 Wide Angle Mid-Telephoto Focal length 16.50 27.55 53.81 F-number 2.90 2.90 2.90 Half angle of view (°) 42.26 25.94 13.98 Image height 14.00 14.00 14.00 Lens length 103.55 109.78 129.89 BF 14.18 12.29 10.01 d 5 1.00 10.82 26.55 d12 14.42 5.47 1.17 d23 1.73 2.88 2.06 d28 3.14 9.24 21.03 d30 14.18 12.29 10.01 Lens Group Data Group starting plane focal length 1 1 81.38 2 6 -15.58 3 13 17.39 4 24 -20.78 5 29 58.15 (Numerical Example 2) Unit: mm Surface Data Surface number rd nd νd 1 83.118 1.40 1.84666 23.8 2 56.427 6.85 1.49700 81.5 3 -1326.263 0.20 4 48.649 5.26 1.59349 67.0 5 148.191 (variable) 6 183.953 0.80 1.75500 52.3 7 11.681 5.86 8 -51.451 0.80 1.43700 95.1 9 13.472 3.67 2.00069 25.5 10 34.940 1.76 11 -35.851 0.90 1.69350 53.2 12 892.261 (variable) 13(Aperture) ∞ 1.00 14* 18.698 3.68 1.59201 67.0 15* -155.400 2.76 16 26.703 5.55 1.59349 67.0 17 -12.422 1.00 1.74951 35.3 18 18.379 1.68 19* 14.044 5.71 1.61997 63.9 20* -17.299 (variable) 21* -87.154 0.95 1.69680 55.5 22* 13.514 (variable) 23* 66.645 3.62 1.85150 40.8 24* -24.723 (variable) Image plane ∞ Aspheric Data Side 14 K = 0.00000e+000 A4=-3.19336e-005 A6= 2.75554e-008 A8= 8.65981e-010 A10=-4.45959e-011 Page 15 K = 0.00000e+000 A4=-3.32402e-005 A6= 2.70013e-007 A8=-9.74804e-010 A10=-4.38601e-011 Page 19 K = 0.00000e+000 A4=-1.24687e-004 A6=-1.46779e-008 A8=-2.71966e-009 A10= 7.08977e-011 A12=-2.21430e-012 Page 20 K = 0.00000e+000 A4= 3.46001e-005 A6=-4.17983e-007 A8= 6.61896e-009 A10=-8.28361e-011 A12=-9.12824e-013 Page 21 K = 0.00000e+000 A4=-1.41421e-005 A6= 1.31038e-007 A8= 3.35676e-008 A10=-5.80528e-010 A12=-4.18368e-012 Page 22 K = 0.00000e+000 A4=-4.16982e-005 A6= 9.65766e-007 A8= 1.61197e-009 A10=-2.42704e-010 Page 23 K = 0.00000e+000 A4=-5.15783e-005 A6=-8.15623e-008 A8= 3.11409e-009 A10=-2.21549e-011 Page 24 K = 0.00000e+000 A4=-2.28395e-005 A6=-8.86433e-008 A8= 3.44750e-009 A10=-2.40365e-011 Various data Zoom ratio 7.12 Wide Angle Mid-Telephoto Focal length 9.27 25.02 66.00 F-number 2.92 2.92 2.92 Half angle of view (°) 41.18 15.73 6.13 Image height 7.50 7.50 7.50 Lens length 93.25 104.11 132.73 BF 11.10 9.23 8.22 d 5 1.00 15.88 40.84 d12 21.37 6.03 3.87 d20 2.74 7.09 5.35 d22 3.59 12.45 21.01 d24 11.10 9.23 8.22 Lens Group Data Group starting plane focal length 1 1 79.43 2 6 -11.81 3 13 16.35 4 21 -16.73 5 23 21.57 (Numerical Example 3) Unit: mm Surface Data Surface number rd nd νd 1 137.130 1.85 2.00100 29.1 2 77.212 8.00 1.49700 81.5 3 -576.767 0.15 4 73.139 6.00 1.61800 63.4 5 640.146 (variable) 6 234.390 1.46 1.85150 40.8 7 24.687 4.95 8 -64.697 1.22 1.78800 47.4 9 26.551 4.64 1.89286 20.4 10 -188.141 1.53 11 -35.617 1.13 1.77250 49.6 12 -122.937 (variable) 13(Aperture) ∞ 0.40 14 26.891 4.07 1.76200 40.1 15 -1337.440 0.15 16 37.497 4.63 1.56732 42.8 17 -38.643 0.82 1.83400 37.2 18 29.821 2.75 19 33.110 0.80 2.00069 25.5 20 17.901 4.35 1.72000 43.7 21 -296.974 2.63 22 -27.276 0.80 1.90366 31.3 23 -70.600 (variable) 24* 32.376 5.72 1.49700 81.5 25* -39.478 0.15 26 826.864 1.40 1.85478 24.8 27 141.190 5.28 1.59282 68.6 28 -31.712 (variable) 29 83.236 2.37 1.63980 34.5 30 -217.841 1.00 1.63854 55.4 31 23.212 (variable) 32 -46.541 1.32 1.77250 49.6 33 79.652 4.36 1.84666 23.8 34 -121.577 (variable) Image plane ∞ Aspheric Data Page 24 K = 0.00000e+000 A4=-1.47986e-005 A6= 4.76484e-008 Page 25 K = 0.00000e+000 A4= 2.38781e-005 A6= 3.36467e-008 A8=-1.25459e-010 A10=1.78308e-012 A12=-5.29676e-015 Various data Zoom ratio 9.32 Wide Angle Mid-Telephoto Focal length 24.97 85.37 232.79 F-number 4.12 5.66 6.40 Half angle of view (°) 41.55 13.50 5.03 Image height 19.45 21.64 21.64 Lens length 140.70 180.88 210.70 BF 12.99 41.24 52.16 d 5 1.35 33.29 61.98 d12 24.60 10.03 2.26 d23 8.41 2.97 0.95 d28 4.31 4.10 1.33 d31 15.11 15.31 18.09 d34 12.99 41.24 52.16 Lens Group Data Group starting plane focal length 1 1 109.85 2 6 -18.42 3 13 62.29 4 24 23.83 5 29 -51.59 6 32 -119.78 (Numerical Example 4) Unit: mm Surface Data Surface number rd nd νd 1 97.752 2.10 1.84666 23.8 2 51.859 8.31 1.69680 55.5 3 -479.946 (variable) 4 126.411 1.50 1.65160 58.5 5 20.764 7.30 6 -69.567 1.30 1.59282 68.6 7 31.197 6.27 1.83400 37.2 8 -149.658 2.35 9 -28.416 1.30 1.49700 81.5 10 -218.301 (variable) 11 68.216 3.82 1.49700 81.5 12 -122.027 2.00 13(Aperture) ∞ 2.00 14 71.871 1.25 1.80610 40.9 15 38.009 5.48 1.49700 81.5 16 -126.656 0.50 17 48.382 4.76 1.59282 68.6 18 -116.174 (variable) 19 -62.029 1.30 1.85025 30.1 20 -158.006 (variable) 21 36.456 1.40 1.83481 42.7 22 19.142 7.88 1.59282 68.6 23 -103.001 (variable) 24 -839.204 1.30 1.61800 63.4 25 50.474 (variable) 26* -55.814 2.00 1.53110 55.9 27* 297.774 0.20 28 52.015 5.49 1.49700 81.5 29 -870.096 (variable) Image plane ∞ Aspheric Data Page 26 K = 0.00000e+000 A4=-6.72296e-005 A6= 1.99840e-007 A8=-2.01249e-011 A10=-5.49137e-013 Page 27 K = 0.00000e+000 A4=-4.73615e-005 A6= 2.37281e-007 A8=-2.89941e-010 Various data Zoom ratio 2.35 Wide Angle Mid-Telephoto Focal length 28.84 46.89 67.79 F-number 2.90 2.90 2.90 Half angle of view (°) 34.71 23.13 16.22 Image height 19.00 21.64 21.64 Lens length 141.90 147.87 158.37 BF 12.51 20.74 27.26 d 3 1.00 13.89 24.42 d10 27.04 12.25 5.09 d18 3.47 6.93 13.04 d20 15.58 9.00 1.27 d23 1.13 2.86 1.28 d25 11.36 12.40 16.19 d29 12.51 20.74 27.26 Lens Group Data Group starting plane focal length 1 1 138.96 2 4 -25.00 3 11 31.06 4 19 -120.85 5 21 63.15 6 24 -77.00 7 26 -958.71

[0058] [Table 1]

[0059] 9 shows a digital still camera as an imaging device using any one of the zoom lenses of Examples 1 to 4 as an imaging optical system. Reference numeral 10 denotes a camera body, and 11 denotes an imaging optical system. Reference numeral 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 10 and receives and photoelectrically converts an optical image formed by the imaging optical system 11. The camera body 10 may be a single-lens reflex camera having a quick-turn mirror, or may be a mirrorless camera without a quick-turn mirror.

[0060] In this way, by using any one of the zoom lenses according to Examples 1 to 4 as an imaging optical system of an imaging device, it is possible to realize an imaging device that is small overall and capable of obtaining high-quality captured images.

[0061] The embodiments described above are merely representative examples, and various modifications and alterations are possible for each embodiment when implementing the present invention. [Explanation of symbols]

[0062] L1 First lens group L2 Second lens group L3: Third lens group

Claims

1. A zoom lens including four or more lens groups including, in order from an object side to an image side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, and a third lens group having a positive refractive power, When zooming from the wide-angle end to the telephoto end, the spacing between adjacent lens groups changes. the first lens group moves during zooming, the distance between the first lens group and the second lens group increases during zooming from the wide-angle end to the telephoto end, the distance between the second lens group and the third lens group narrows during zooming from the wide-angle end to the telephoto end, the first lens group is composed of three or less lenses, the second lens group includes, arranged in order from the object side to the image side, a first single lens as a spherical lens having negative refractive power, a cemented lens in which a spherical lens having negative refractive power and a spherical lens having positive refractive power are cemented together, and a second single lens as a spherical lens having negative refractive power, Let skm be the minimum value of the back focus of the zoom lens in the entire zoom range, f2 be the focal length of the second lens group, d21 be the distance on the optical axis between the image side lens surface of the first single lens and the lens surface of the cemented lens closest to the object side, d22 be the distance on the optical axis between the image side lens surface of the cemented lens and the object side lens surface of the second single lens, f1 be the focal length of the first lens group, and νBC be the average Abbe number based on the d line of each material of the lens having negative refractive power and the second single lens in the cemented lens, 1.35≦|f2| / skm≦5.00 3.1≦d21 / d22≦10.0 4.0≦|f1 / f2|≦8.0 48≦νBC≦80 A zoom lens characterized by satisfying the following conditions.

2. When the radius of curvature of the lens surface on the object side of the first single lens is RA1 and the radius of curvature of the lens surface on the image side is RA2, 1.0≦-(RA2+RA1) / (RA2-RA1)≦10.0 2. The zoom lens according to claim 1, which satisfies the following condition:

3. When the radius of curvature of the lens surface of the cemented lens closest to the image side is RB2 and the radius of curvature of the lens surface of the second single lens closest to the object side is RC1, -2.0≦(RC1+RB2) / (RC1-RB2)≦1.0 3. The zoom lens according to claim 1, wherein the following condition is satisfied:

4. When the radius of curvature of the cemented surface of the cemented lens is RBm, 0.6≦|RBm / f2|≦3.0 4. The zoom lens according to claim 1, which satisfies the following condition:

5. When the average value of the refractive index at the d line of each material of the lens having the negative refractive power and the second single lens in the cemented lens is nBC, 1.51≦nBC≦1.85 5. The zoom lens according to claim 1, which satisfies the following condition:

6. When the focal length of the zoom lens at the wide-angle end is fw, 3.5≦|f1 / fw|≦10.0 6. The zoom lens according to claim 1, which satisfies the following condition:

7. When the focal length of the third lens group is f3 and the focal length of the zoom lens at the telephoto end is ft, 0.2≦|f3 / ft|≦0.6 7. The zoom lens according to claim 1, which satisfies the following condition:

8. When the percentage of distortion occurring at the maximum image height at the wide-angle end of the zoom lens is dmin, -15.0≦dmin≦-4.4 8. The zoom lens according to claim 1, which satisfies the following condition:

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

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

11. A zoom lens comprising, arranged in order from an object side to an 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, a fourth lens group having a positive refractive power, a fifth lens group having a negative refractive power, and a sixth lens group having a negative refractive power, When zooming from the wide-angle end to the telephoto end, the spacing between adjacent lens groups changes. the first lens group moves during zooming, the distance between the first lens group and the second lens group increases during zooming from the wide-angle end to the telephoto end, the distance between the second lens group and the third lens group narrows during zooming from the wide-angle end to the telephoto end, the first lens group is composed of three or less lenses, the second lens group includes, arranged in order from the object side to the image side, a first single lens as a spherical lens having negative refractive power, a cemented lens in which a spherical lens having negative refractive power and a spherical lens having positive refractive power are cemented together, and a second single lens as a spherical lens having negative refractive power, Let skm be the minimum value of the back focus in the entire zoom range of the zoom lens, f2 be the focal length of the second lens group, d21 be the distance on the optical axis between the image side lens surface of the first single lens and the lens surface of the cemented lens closest to the object side, d22 be the distance on the optical axis between the image side lens surface of the cemented lens and the object side lens surface of the second single lens, and f1 be the focal length of the first lens group. 1.35≦|f2| / skm≦5.00 3.1≦d21 / d22≦10.0 4.0≦|f1 / f2|≦8.0 A zoom lens characterized by satisfying the following conditions.

12. 9. The zoom lens according to claim 1, comprising, arranged in order from the object side to the image side, the first, second and third lens groups, a fourth lens group having a negative refractive power, a fifth lens group having a positive refractive power, a sixth lens group having a negative refractive power, and a seventh lens group having a negative refractive power.

13. A zoom lens comprising, arranged in order from the object side to the image side, a first lens group of positive refractive power, a second lens group of negative refractive power, a third lens group of positive refractive power, a fourth lens group of negative refractive power, a fifth lens group of positive refractive power, a sixth lens group of negative refractive power, and a seventh lens group of negative refractive power, When zooming from the wide-angle end to the telephoto end, the spacing between adjacent lens groups changes. the first lens group moves during zooming, the distance between the first lens group and the second lens group increases during zooming from the wide-angle end to the telephoto end, the distance between the second lens group and the third lens group narrows during zooming from the wide-angle end to the telephoto end, the first lens group is composed of three or less lenses, the second lens group includes, arranged in order from the object side to the image side, a first single lens as a spherical lens having negative refractive power, a cemented lens in which a spherical lens having negative refractive power and a spherical lens having positive refractive power are cemented together, and a second single lens as a spherical lens having negative refractive power, Let skm be the minimum value of the back focus in the entire zoom range of the zoom lens, f2 be the focal length of the second lens group, d21 be the distance on the optical axis between the image side lens surface of the first single lens and the lens surface of the cemented lens closest to the object side, d22 be the distance on the optical axis between the image side lens surface of the cemented lens and the object side lens surface of the second single lens, and f1 be the focal length of the first lens group. 1.35≦|f2| / skm≦5.00 3.1≦d21 / d22≦10.0 4.0≦|f1 / f2|≦8.0 A zoom lens characterized by satisfying the following conditions.

14. A zoom lens according to any one of claims 1 to 13; and an image sensor that receives an optical image formed by the zoom lens.

Images