Optical system and imaging apparatus having the same

Abstract

To obtain an optical system which is light and in which aberration such as chromatic aberration is satisfactorily corrected.SOLUTION: An optical system comprises a first lens group B1 having positive refractive power, a second lens group B2, and a third lens group B3 arranged in order from an object side to an image side. When performing focusing, the second lens group B2 moves, and an interval between adjacent lens groups changes. The first lens group B1 comprises a positive lens G1p disposed on the most object side, and a negative lens G1n disposed on the most object side among all negative lenses belonging to the first lens group B1. The optical system satisfies predetermined conditions.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an optical system and an imaging device having the same, and is suitable for imaging devices using imaging elements such as digital still cameras, video cameras, surveillance cameras, and broadcast cameras, or imaging devices such as cameras using silver halide photographic film. [Background technology]

[0002] A known example of a long focal length photographic optical system is a so-called telephoto type photographic optical system, which has an optical system with positive refractive power arranged on the object side and an optical system with negative refractive power arranged on the image side. Telephoto type photographic optical systems are used, for example, in single-focus super telephoto lenses.

[0003] In super-telephoto lenses, the longer the focal length, the greater the axial chromatic aberration and lateral chromatic aberration. One known method for effectively correcting these chromatic aberrations is to increase the number of lenses positioned on the object side and have each lens share the responsibility for correcting the chromatic aberration. However, the effective diameter of the lenses positioned on the object side of a super-telephoto lens tends to be large, and correcting chromatic aberration using the above-mentioned method would result in an increase in the weight of the photographic optical system.

[0004] In the photographic optical system of Patent Document 1, a positive lens made of a material having low dispersion and anomalous dispersion is arranged in succession from the most object side to correct axial chromatic aberration and chromatic aberration of magnification. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-215561 Summary of the Invention [Problem to be solved by the invention]

[0006] In the optical system described in Patent Document 1, positive lenses formed from materials with low dispersion and anomalous dispersion are positioned as close to the object as possible to correct chromatic aberration, but these positive lenses have large effective diameters, making it impossible to sufficiently reduce the weight of the optical system.

[0007] To achieve further weight reduction in the optical system, it is important to find appropriate materials and arrangements not only for the positive lens but also for the negative lens.

[0008] An object of the present invention is to provide an optical system that is small and in which aberrations such as chromatic aberration are well corrected, and an imaging device having the same. [Means for solving the problem]

[0009] The optical system of the present invention is composed of a first lens group, a second lens group, and a third lens group, all of which have positive refractive power, arranged in this order from the object side to the image side, and wherein the second lens group moves during focusing, changing the interval between adjacent lens groups; the first lens group includes a positive lens G1p arranged closest to the object, a lens G2 arranged adjacent to the image side of the positive lens G1p, and a negative lens G1n arranged closest to the object among the negative lenses included in the first lens group; and wherein during image blur correction, at least some of the lenses in the optical system move in a direction including a component perpendicular to the optical axis; and wherein when the back focus of the optical system is BF, the focal length of the positive lens G1p is fG1p, the focal length of the negative lens G1n is fG1n, the Abbe number of the material of the negative lens G1n is vdG1n, the partial dispersion ratio is θgFG1n, and the Abbe number of the material of the lens G2 is vdG2, 0.02 <BF / fG1p<0.14 2.00<|fG1p / fG1n|<10.00 20.0<νdG1n<40.0 -0.1000<θgFG1n-(-1.665×10 -7 ×νdG1n 3 +5.213×10 -5 ×νdG1n 2 -5.656×10 -3×νdG1n+0.7268)<-0.0010 The present invention is characterized in that the following conditional expression is satisfied: [Effects of the Invention]

[0010] According to the present invention, it is possible to obtain an optical system that is small in size and in which aberrations such as chromatic aberration are well corrected. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a cross-sectional view of a lens of an optical system according to a first embodiment. [Figure 2] 4A to 4C are aberration diagrams of the optical system of Example 1 when focused at infinity. [Figure 3] FIG. 10 is a cross-sectional view of a lens of an optical system according to a second embodiment. [Figure 4] 10A and 10B are aberration diagrams of the optical system of Example 2 when focused at infinity. [Figure 5] FIG. 10 is a cross-sectional view of a lens of an optical system according to a third embodiment. [Figure 6] 10A and 10B are aberration diagrams of the optical system of Example 3 when focused at infinity. [Figure 7] FIG. 1 is a schematic diagram of a main part of an imaging device. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, embodiments of an optical system and an imaging device including the same of the present invention will be described in detail with reference to the accompanying drawings. The optical system in each embodiment is composed of a first lens group, a second lens group, and a third lens group, all of which have positive refractive power, arranged in this order from the object side to the image side. During focusing, the second lens group moves, changing the spacing between adjacent lens groups. Here, the lens group refers to a lens element that moves integrally during focusing, and may include one or more lenses, but does not have to include multiple lenses.

[0013] 1, 3, and 5 are cross-sectional views of optical systems according to Examples 1 to 3, respectively. The optical systems of the respective Examples are photographic lens systems used in imaging devices such as video cameras, digital cameras, silver halide film cameras, and television cameras. In the lens cross-sectional views, the left side is the object side (front) and the right side is the image side (rear). In addition, in the lens cross-sectional views, if j is the order of the lens groups from the object side to the image side, then Bj indicates the j-th lens group.

[0014] In each embodiment, SP is an aperture stop. In the optical system of each embodiment, the aperture stop SP is disposed between the first lens unit B1 and the second lens unit B2.

[0015] IP is the image plane. When the optical system is used as an imaging optical system for a video camera or digital camera, the image plane IP corresponds to a solid-state imaging element (photoelectric conversion element) such as a CCD sensor or CMOS sensor. When the optical system of each embodiment is used as an imaging optical system for a silver halide film camera, the image plane IP corresponds to the film plane.

[0016] 2, 4, and 6 are aberration diagrams of the optical systems of Examples 1 to 3 when focused at infinity, respectively.

[0017] In the spherical aberration diagram, Fno is the F-number, and shows spherical aberration for the d-line (wavelength 587.6 nm) and g-line (wavelength 435.8 nm). In the astigmatism diagram, S shows the amount of astigmatism on the sagittal image plane, and M shows the amount of astigmatism on the meridional image plane. Distortion is shown for the d-line. In the chromatic aberration diagram, chromatic aberration for the g-line is shown. ω is the half angle of view.

[0018] In the optical system of each embodiment, as shown by the arrow in the lens cross-sectional view, the second lens unit B2 moves toward the image side during focusing from infinity to a close distance, changing the spacing between adjacent lens units. That is, in the optical system of each embodiment, the second lens unit B2 corresponds to the focus unit.

[0019] In addition, in the optical systems of the embodiments, some of the lenses in the optical system are used as image stabilization groups, and the image formation position can be changed by moving the image stabilization groups in a direction having a component perpendicular to the optical axis. This makes it possible to perform image blur correction. Any of the first lens group B1, the second lens group B2, and the third lens group B3 may be used as the image stabilization group, or some of the lenses included in a specific lens group may be used as the image stabilization group.

[0020] In the optical systems of each embodiment, chromatic aberration is effectively corrected by using a material with high dispersion and anomalous dispersion for the negative lens included in the first lens group B1. In conventional super telephoto lenses, the amount of chromatic aberration is reduced by appropriately selecting the material for the positive lens included in the first lens group B1, but the chromatic aberration correction effect of the negative lens included in the first lens group B1 is insufficient. Therefore, in the optical systems of each embodiment, a material with high dispersion and anomalous dispersion is used for the negative lens included in the first lens group B1, thereby improving the chromatic aberration correction effect of the negative lens included in the first lens group B1 and effectively correcting chromatic aberration in the entire optical system.

[0021] Here, the Abbe number vd and the partial dispersion ratio θgF are known as parameters related to the correction of chromatic aberration in an optical system. When the refractive indices of materials for the g-line (wavelength 435.8 nm), F-line (486.1 nm), C-line (656.3 nm), and d-line (587.6 nm) are Ng, NF, NC, and Nd, respectively, the Abbe number vd and the partial dispersion ratio θgF are respectively expressed by the following equations. νd=(Nd-1) / (NF-NC) θgF=(Ng-NF) / (NF-NC)

[0022] Generally, the use of a high-dispersion material for a negative lens element in a lens group that has a positive overall refractive power can effectively correct first-order chromatic aberration, while the use of a high-anomalous dispersion material for a negative lens element in a lens group that has a positive overall refractive power can effectively correct second-order lateral chromatic aberration.

[0023] Here, the anomalous dispersion of the material used for the lens will be explained. In this specification, the index of the strength of the anomalous dispersion, ΔθgF, is defined by the following formula: ΔθgF=θgF-(-1.665×10 -7 ×νd 3 +5.213×10 -5 ×νd 2 -5.656×10 -3 ×νd+0.7268)

[0024] For many optical materials, the value of ΔθgF is close to zero. The further away from zero the value of ΔθgF is, the higher the anomalous dispersion of the material.

[0025] The back focus of the optical system is BF, the focal length of the positive lens G1p, which is located closest to the object among the positive lenses in the first lens group B1, is fG1p, and the focal length, Abbe number, and partial dispersion ratio of the negative lens G1n, which is located closest to the object among the negative lenses in the first lens group B1, are fG1n, νdG1n, and θgFG1n, respectively. The optical system of each example satisfies the following expressions (1) to (4). 0.02 <BF / fG1p<0.14 (1) 2.00<|fG1p / fG1n|<10.00 (2) 20.00<νdG1n<40.00 (3) -0.1000<θgFG1n-(-1.665×10 -7 ×νdG1n 3 +5.213×10 -5 ×νdG1n 2 -5.656×10 -3 ×νdG1n+0.7268)<-0.0010 (4)

[0026] Conditional formula (1) defines the relationship between the back focal length of the optical system and the focal length of the positive lens G1p. Satisfying conditional formula (1) enables the realization of a compact optical system with a short overall length. Exceeding the upper limit of conditional formula (1) undesirably increases the back focal length too long, resulting in an increase in the size of the optical system and the imaging device to which the optical system is attached along the optical axis. Also, falling below the lower limit of conditional formula (1) undesirably increases the back focal length too short. In this case, the diameter of the lens located closest to the image side of the optical system becomes too large, resulting in an increase in the diameter of the mount for attaching the optical system to the imaging device. As a result, it becomes difficult to achieve a compact and lightweight optical system and imaging device. Furthermore, attempting to reduce the diameter of the final lens in the optical system while reducing the back focal length so as to fall below the lower limit of conditional formula (1) undesirably increases the angle of incidence of light rays on the imaging element, resulting in a deterioration in image quality, particularly at the periphery of the image.

[0027] Conditional formula (2) defines the ratio of the focal length fG1p of the positive lens G1p to the focal length fG1n of the negative lens G1n. If the focal length fG1p of the positive lens G1p becomes short below the lower limit of conditional formula (2), the refractive power of the positive lens G1p becomes too strong, which is undesirable because a large amount of on-axis chromatic aberration occurs in the positive lens G1p. In order to correct the on-axis chromatic aberration occurring in the positive lens G1p with the negative lens included in the first lens group B1, it becomes necessary to increase the number of negative lenses, which is undesirable because it increases the weight of the optical system.

[0028] Furthermore, if the focal length fG1p of the positive lens G1p becomes longer beyond the upper limit of conditional expression (2), the refractive power of the positive lens G1p becomes too weak, which results in the positive lens G1p being unable to sufficiently converge light, and the effective diameter of the lens located on the image side of the positive lens G1p becomes large, which is undesirable as it increases the weight of the optical system.

[0029] Conditional formula (3) defines the Abbe number νdG1n of the material of the negative lens G1n. By using a high-dispersion material as the material of the negative lens G1n included in the first lens group B1 with positive refractive power, first-order chromatic aberration can be effectively corrected. If the lower limit of conditional formula (3) is exceeded, lateral chromatic aberration is overcorrected in the negative lens G1n, which is undesirable. Furthermore, if the upper limit of conditional formula (3) is exceeded, it becomes difficult to sufficiently correct lateral chromatic aberration in the negative lens G1n, which is also undesirable.

[0030] Conditional formula (4) defines the anomalous dispersion ΔθgFG1n of the material of the negative lens G1n. By using a material with high anomalous dispersion to form the negative lens G1n, the effect of correcting second-order lateral chromatic aberration can be improved. A material below the lower limit of conditional formula (4) is less practical for use as a photographic optical system. Using a material above the upper limit of conditional formula (4) as the material for the negative lens G1n is undesirable because it makes it difficult to sufficiently correct second-order lateral chromatic aberration.

[0031] In the optical systems of the embodiments, NBFD15 (manufactured by HOYA Corporation; νd=33.27, θgF=0.5883, ΔθgF=-0.0019) is used as the material for the negative lens G1n, taking into consideration the balance of aberration correction for the entire optical system. The negative lens G1n of the present invention may be made of a material that satisfies both equations (3) and (4). An example of a material that satisfies both equations (3) and (4) is S-LAH79 (manufactured by OHARA Corporation; νd=28.27, θgF=0.5980, ΔθgF=-0.0068). Alternatively, S-NBH56 (manufactured by OHARA Corporation; νd=24.80, θgF=0.6122, ΔθgF=-0.0039) may also be used.

[0032] As explained above, in each embodiment, the elements are appropriately set so as to satisfy conditional expressions (1) to (4), thereby making it possible to obtain a compact optical system in which aberrations such as chromatic aberration are well corrected.

[0033] In each embodiment, it is preferable to set the numerical ranges of the conditional expressions (1) to (4) as follows. 0.02 <BF / fG1p<0.11 (1a) 2.50<|fG1p / fG1n|<8.00 (2a) 21.00<νdG1n<39.00 (3a) -0.0300<θgFG1n-(-1.665×10 -7 ×νdG1n 3 +5.213×10 -5 ×νdG1n 2 -5.656×10 -3 ×νdG1n+0.7268)<-0.0013 (4a)

[0034] It is more preferable to set the numerical ranges of the conditional expressions (1) to (4) as follows: 0.04 <BF / fG1p<0.09 (1b) 2.20<|fG1p / fG1n|<7.00 (2b) 23.00<νdG1n<36.00 (3b) -0.0020<θgFG1n-(-1.665×10 -7 ×νdG1n 3 +5.213×10 -5 ×νdG1n 2 -5.656×10 -3 ×νdG1n+0.7268)<-0.0015 (4b)

[0035] In this way, by using a material with high anomalous dispersion as the material for the negative lens G1n, the positive lens included in the first lens unit B1 can be positioned relatively closer to the image side, which effectively reduces the weight of the first lens unit B1 and enables both a compact optical system and good correction of chromatic aberration.

[0036] Furthermore, in each embodiment, it is more preferable to satisfy one or more of the following conditional expressions: 0.13 <D12 / LD<0.50 (5) 1.50 <fG1p / fG2<5.00 (6) νdG2>73.00 (7) 0.0100<θgFG2-(-1.665×10 -7 ×νdG2 3 +5.213×10 -5 ×νdG2 2 -5.656×10 -3 ×νdG2+0.7268)<0.1000(8) 0.05 <BF / IH<2.20 (9) 0.05 <BF / fG2<0.23 (10) 1.02<|fGkp / fGkn|<2.50 (11)

[0037] Here, LD is the distance on the optical axis from the lens surface closest to the object in the first lens group B1 to the image plane, D12 is the distance on the optical axis between the positive lens G1p and the lens G2 arranged adjacent to the image side of the positive lens G1p, fG2 is the focal length of the lens G2, νdG2 is the Abbe number of the material of the lens G2, and θgFG2 is the partial dispersion ratio of the material of the lens G2.

[0038] Furthermore, IH is the maximum image height, which refers to half the diagonal length of the usable range of the image sensor used to form the output image.

[0039] Furthermore, the focal length of the positive lens located closest to the image among the positive lenses included in the third lens group B3 is defined as fGkp, and the focal length of the negative lens located closest to the image among the negative lenses included in the third lens group B3 is defined as fGkn.

[0040] Conditional formula (5) defines the ratio of the axial distance D12 between the positive lens G1p and the lens G2 located adjacent to the image side of the positive lens G1p to the total lens length LD. If the distance D12 between the positive lens G1p and the lens G2 becomes short by falling below the lower limit of conditional formula (5), the effective diameter of the lens G2 becomes large, which increases the weight of the lens G2, which is undesirable. If the distance D12 between the positive lens G1p and the lens G2 becomes long by exceeding the upper limit of conditional formula (5), it becomes difficult to correct the spherical aberration and chromatic aberration generated by the positive lens G1p with the lenses subsequent to the lens G2, which is undesirable.

[0041] Furthermore, it is preferable that lens G2 has positive refractive power. By arranging two positive lenses consecutively from the most object side of the optical system, it is possible to greatly converge light rays passing through the lenses, and as a result, it is possible to reduce the effective diameter of the lens arranged closer to the image side than lens G2. This makes it possible to further reduce the weight of the entire optical system.

[0042] Conditional formula (6) defines the ratio of the focal length fG1p of the positive lens G1p to the focal length fG2 of the lens G2. If the focal length fG1p of the positive lens G1p becomes short below the lower limit of conditional formula (6), the refractive power of the positive lens G1p becomes too strong, which is undesirable because a large amount of on-axis chromatic aberration occurs in the positive lens G1p. In order to correct the on-axis chromatic aberration occurring in the positive lens G1p with a negative lens included in the first lens group B1, it becomes necessary to increase the number of negative lenses, which is undesirable because it increases the weight of the optical system.

[0043] Furthermore, if the focal length fG1p of the positive lens G1p becomes longer beyond the upper limit of conditional expression (6), the refractive power of the positive lens G1p becomes too weak, which results in the positive lens G1p being unable to sufficiently converge light, and the effective diameter of the lens located on the image side of the positive lens G1p becomes large, which is undesirable as it increases the weight of the optical system.

[0044] Conditional expression (7) defines the Abbe number νdG2 of the material of lens G2. If the Abbe number νdG2 falls below the lower limit of conditional expression (7) and becomes small, a large amount of chromatic aberration occurs in lens G2, which is not preferable.

[0045] Conditional expression (8) defines the anomalous dispersion of the material of lens G2. By using a material with high anomalous dispersion to construct lens G2, the effect of correcting second-order lateral chromatic aberration can be improved. Materials below the lower limit of conditional expression (8) are not practical as optical materials used in photographic optical systems. Using a material above the upper limit of conditional expression (8) as the material for lens G2 is undesirable because it makes it difficult to sufficiently correct second-order lateral chromatic aberration.

[0046] In the optical systems of the examples, FCD100 (manufactured by HOYA Corporation; νd=95.10, θgF=0.5334, ΔθgF=0.0162) is used as the material for lens G2, taking into consideration the balance of aberration correction for the entire optical system. Other materials that satisfy both equations (3) and (4) include S-FPL53 (manufactured by OHARA Corporation; νd=94.93, θgF=0.5340, ΔθgF=0.0168). S-FPL51 (manufactured by OHARA Corporation; νd=81.54, θgF=0.5375, ΔθgF=0.0168) may also be used.

[0047] Conditional expression (9) expresses the relationship between the back focal length of the optical system and the maximum image height. Exceeding the upper limit of conditional expression (9) results in an excessively long overall length, increasing the weight of the mechanical components (such as the lens barrel) that support the optical system, making it difficult to reduce the optical system's weight. Furthermore, falling below the lower limit of conditional expression (9) results in an excessively short back focal length. In this case, the diameter of the lens positioned closest to the image side of the optical system becomes too large, resulting in an increase in the diameter of the mount for attaching the optical system to the imaging device. As a result, it becomes difficult to achieve a compact and lightweight optical system and imaging device. Furthermore, attempting to reduce the diameter of the final lens in the optical system while reducing the back focal length so as to fall below the lower limit of conditional expression (9) is undesirable because it increases the angle of incidence of light rays on the imaging element, which can lead to a deterioration in image quality, particularly at the periphery of the image.

[0048] Conditional expression (10) expresses the relationship between the back focal length of the optical system and the focal length of lens G2. Exceeding the upper limit of conditional expression (10) results in an excessively long overall length, increasing the weight of the mechanical components (such as the lens barrel) that support the optical system, making it difficult to reduce the optical system's weight. Furthermore, falling below the lower limit of conditional expression (10) results in an excessively short back focal length. In this case, the diameter of the lens positioned closest to the image side of the optical system becomes too large, resulting in an increase in the diameter of the mount for attaching the optical system to the imaging device. As a result, it becomes difficult to achieve a compact and lightweight optical system and imaging device. Furthermore, attempting to reduce the diameter of the final lens in the optical system while reducing the back focal length so as to fall below the lower limit of conditional expression (10) is undesirable because it increases the angle of incidence of light rays on the imaging element, which can lead to a deterioration in image quality, especially at the periphery of the image.

[0049] Conditional expression (11) defines the relationship between the focal lengths of the positive lens Gkp, which is located closest to the image, and the negative lens Gkn, which is located closest to the image, among the positive lenses in the third lens group B3. By satisfying conditional expression (11), it is possible to shorten the overall length of the optical system while effectively correcting distortion and lateral chromatic aberration.

[0050] Exceeding the upper limit of condition (11) is advantageous in shortening the overall length of the optical system, but is undesirable because it tends to result in insufficient correction of distortion and lateral chromatic aberration.

[0051] If the lower limit of condition (11) is exceeded, curvature of field and distortion become large, which is undesirable.

[0052] It is preferable to set the numerical ranges of the conditional expressions (5) to (11) as follows: 0.15 <D12 / LD<0.45 (5a) 1.55 <fG1p / fG2<4.50 (6a) νdG2>80.00 (7a) 0.0120<θgFG2-(-1.665×10 -7 ×νdG2 3 +5.213×10 -5 ×νdG2 2-5.656×10 -3 ×νdG2+0.7268)<0.0600(8a) 0.06 <BF / IH<2.00 (9a) 0.06 <BF / fG2<0.21 (10a) 1.04<|fGkp / fGkn|<2.20 (11a)

[0053] It is more preferable to set the numerical ranges of the conditional expressions (5) to (8) as follows: 0.17 <D12 / LD<0.40 (5b) 1.60 <fG1p / fG2<4.00 (6b) νdG2>90.00 (7b) 0.0150<θgFG2-(-1.665×10 -7 ×νdG2 3 +5.213×10 -5 ×νdG2 2 -5.656×10 -3 ×νdG2+0.7268)<0.0170(8b) 0.07 <BF / IH<1.80 (9b) 0.07 <BF / fG2<0.20 (10b) 1.06<|fGkp / fGkn|<1.90 (11b)

[0054] It is preferable that the second lens unit B2, which moves during focusing, consists of a single negative lens. This allows for a reduction in the size and weight of the mechanism for driving the second lens unit B2, and also facilitates quick focusing.

[0055] Furthermore, in the optical systems of each embodiment, it is preferable that the first lens group B1 does not move during focusing. Of the lens groups constituting the optical system, the first lens group B1, which is positioned closest to the object, has a large effective diameter and is heavy. In order to move the heavy first lens group B1 during focusing, a large drive mechanism is required, which is undesirable because it increases the weight of the optical system and the image pickup device including the optical system.

[0056] In addition, in the optical systems of each embodiment, it is preferable that the third lens group B3 has a positive lens and a negative lens, in that order from the image plane side. That is, it is preferable that the third lens group B3 has a positive lens Gkp arranged closest to the image plane and a negative lens Gkn arranged adjacent to the positive lens Gkp on the object side. By adopting a configuration in which a negative lens and a positive lens are arranged, in that order from the object side, on the closest image plane side of the optical system, it is possible to reduce the angle of incidence on the imaging surface. This makes it possible to suppress the reduction in light intensity and degradation of image quality in the peripheral areas of an image, which are problems when a CMOS sensor or CCD sensor is used as the imaging element.

[0057] In the optical systems of the respective embodiments, it is preferable that both the second lens unit B2 and the third lens unit B3 have negative refractive power, which strengthens the tendency toward a telephoto type power arrangement and shortens the overall length of the optical system.

[0058] Next, Numerical Examples 1 to 3 corresponding to Examples 1 to 3, respectively, are shown. In each Numerical Example, i indicates the order of the optical surfaces from the object side. ri is the radius of curvature of the ith optical surface (ith surface), di is the distance between the ith surface and the (i+1)th surface when focusing at infinity, and ndi and νdi are the refractive index and Abbe number of the material of the ith optical member for the d-line, respectively. Regarding changes in the distance between the lens surfaces, the distance between the lens surfaces when focusing at infinity and the distance between the lens surfaces when focusing at the closest distance are shown.

[0059] In each numerical example, the back focus (BF) is the distance from the surface of the optical system closest to the image side to the image plane, expressed as an air-equivalent length.

[0060] In each embodiment, a protective glass for protecting the lens may be disposed on the object side of the first lens group B1. Also, a protective glass or low-pass filter may be disposed between the lens disposed closest to the image plane and the image plane. In this specification, optical elements with extremely weak refractive power, such as protective glass or low-pass filters disposed closest to the object or image side of the optical system, are not considered to be lenses constituting the optical system. The term "extremely weak refractive power" refers to an optical element whose absolute focal length is five or more times the focal length of the entire optical system.

[0061] In addition, if an optical element with extremely weak refractive power is placed between the optical system and the image sensor, the value of the back focus BF is used when the optical element with extremely weak refractive power placed between the optical system and the image sensor is converted to air.

[0062] [Numerical Example 1] Unit: mm Surface Data Surface number rd nd νd Effective diameter 1 208.863 12.81 1.59522 67.7 135.17 2 2382.509 111.80 134.54 3 102.362 15.74 1.43700 95.1 89.59 4 -468.113 0.00 87.76 5 -468.113 1.50 1.80610 33.3 87.76 6 114.870 2.04 83.37 7 100.771 11.33 1.43700 95.1 83.11 8 ∞ 16.95 82.34 9 82.389 5.78 1.89286 20.4 70.56 10 140.543 0.20 69.07 11 73.987 2.00 1.83400 37.2 65.93 12 42.707 11.70 1.43700 95.1 59.92 13 117.076 7.33 57.82 14 (Aperture) ∞ 5.00 54.98 15 2203.612 1.60 1.61800 63.4 51.02 16 70.804 55.04 48.37 17 90.626 1.40 1.89286 20.4 33.99 18 63.622 6.17 1.51742 52.4 33.76 19 -141.334 1.00 33.75 20 62.995 6.11 1.80610 33.3 33.21 21 -112.871 1.20 1.53775 74.7 32.36 22 28.360 7.05 29.59 23 -61.753 1.20 1.72916 54.7 29.57 24 49.029 1.23 30.62 25 58.720 3.29 1.65412 39.7 31.53 26 384.248 6.25 31.95 27 51.293 12.56 1.64769 33.8 36.97 28 -41.167 1.70 1.80810 22.8 36.94 29 -94.283 8.00 37.29 30 -67.868 2.00 1.85025 30.1 35.98 31 65.755 1.00 37.10 32 54.455 8.04 1.56732 42.8 38.88 33 -98.899 31.01 39.42 Image plane ∞ Various data Focal length 392.00 F-number 2.90 Angle of view 3.16 Image height 21.64 Lens total length 360.03 BF 31.01 Entrance pupil position 379.29 Exit pupil position -96.96 Front principal point position -429.43 Back principal point position -360.99 Lens group data Group Starting plane Focal length Lens length Front principal point position Rear principal point position 1 1 183.77 199.18 99.64 -110.90 2 15 -118.41 1.60 1.02 0.03 3 17 -2011.18 68.20 252.67 174.19 Single lens data Lens starting surface focal length 1 1 383.77 2 3 193.83 3 5 -114.29 4 7 230.60 5 9 213.02 6 11 -124.75 7 12 146.82 8 15 -118.41 9 17 -245.13 10 18 85.67 11 20 50.95 12 21 -42.02 13 23 -37.31 14 25 105.54 15 27 37.25 16 28 -91.74 17 30 -39.01 18 32 63.10

[0063] [Numerical Example 2] Unit: mm Surface Data Surface number rd nd νd Effective diameter 1 246.184 9.84 1.59349 67.0 118.93 2 7777.408 144.07 118.42 3 90.915 12.21 1.43700 95.1 74.98 4 -527.016 0.00 73.66 5 -527.016 1.85 1.80610 33.3 73.66 6 112.626 0.14 70.68 7 80.019 8.30 1.43700 95.1 70.47 8 289.154 26.22 69.69 9 73.539 3.98 1.92286 18.9 57.85 10 116.802 0.15 56.90 11 84.384 2.10 1.83481 42.7 55.90 12 39.915 11.42 1.43700 95.1 51.21 13 217.108 6.41 49.52 14 (Aperture) ∞ 3.77 46.57 15 449.487 1.60 1.59522 67.7 44.02 16 69.954 46.69 42.28 17 200.917 1.30 1.89286 20.4 30.60 18 38.569 4.77 1.80610 33.3 29.82 19 -622.316 1.03 29.52 20 86.674 4.54 1.66680 33.0 28.63 21 -56.951 1.30 1.59522 67.7 28.06 22 48.644 2.97 26.48 23 -148.460 1.10 1.77250 49.6 26.54 24 72.673 4.75 26.94 25 68.402 3.23 1.76182 26.5 29.85 26 -451.612 44.09 30.00 27 54.085 4.62 1.66565 35.6 36.58 28 359.236 1.60 1.92286 20.9 36.20 29 86.966 17.75 35.63 30 -68.784 1.60 1.72916 54.7 35.92 31 238.667 1.00 37.04 32 206.217 4.27 1.58144 40.8 37.66 33 -83.915 33.39 37.99 Image plane ∞ Various data Focal length 490.00 F-number 4.12 Angle of view: 2.53 Image height 21.64 Lens total length 412.08 BF 33.39 Entrance pupil position 463.65 Exit pupil position -117.91 Front principal point position -633.29 Back principal point position -456.61 Lens group data Group Starting plane Focal length Lens length Front principal point position Rear principal point position 1 1 206.83 226.69 130.87 -127.55 2 15 -139.41 1.60 1.19 0.19 3 17 -556.34 99.94 59.24 -25.69 Single lens data Lens starting surface focal length 1 1 428.16 2 3 178.51 3 5 -114.97 4 7 250.15 5 9 206.04 6 11 -92.72 7 12 109.76 8 15 -139.41 9 17 -53.66 10 18 45.20 11 20 52.20 12 21 -43.88 13 23 -63.02 14 25 78.19 15 27 95.08 16 28 -124.69 17 30 -73.07 18 32 103.14

[0064] [Numerical Example 3] Unit: mm Surface Data Surface number rd nd νd Effective diameter 1 337.123 11.90 1.59349 67.0 142.72 2 -2141.571 163.62 142.22 3 122.803 16.05 1.43700 95.1 90.55 4 -259.830 0.00 88.96 5 -259.830 1.60 1.80610 33.3 88.96 6 155.285 0.15 85.83 7 92.998 10.91 1.43387 95.1 85.67 8 356.639 44.95 84.69 9 82.341 5.68 1.84666 23.9 66.50 10 174.332 0.15 65.45 11 120.575 2.00 1.80420 46.5 64.32 12 44.732 14.19 1.43700 95.1 58.51 13 682.520 17.80 56.74 14 (Aperture) ∞ 3.30 45.94 15 377.336 1.60 1.59349 67.0 43.47 16 61.273 24.90 41.50 17 214.060 1.50 1.89286 20.4 35.71 18 49.453 5.28 1.73800 32.3 34.86 19 -421.466 0.97 34.55 20 84.928 4.22 1.80518 25.5 33.47 21 -117.310 1.30 1.59349 67.0 32.93 22 47.131 4.55 30.55 23 -106.050 1.30 1.81600 46.6 30.22 24 94.264 3.59 30.00 25 67.803 5.46 1.85478 24.8 30.63 26 3886.804 50.06 30.13 27 72.986 9.82 1.63980 34.5 33.25 28 -57.663 1.60 1.89286 20.4 32.74 29 223.691 22.76 32.73 30 -78.575 1.60 1.53775 74.7 35.35 31 53.409 1.00 37.05 32 52.308 9.05 1.51742 52.4 38.24 33 -84.502 33.21 39.00 Image plane ∞ Various data Focal length 588.00 F-number 4.12 Angle of view 2.11 Image height 21.64 Lens total length 476.08 BF 33.21 Entrance pupil position 705.95 Exit pupil position -142.39 Front principal point position -675.02 Back principal point position -554.79 Lens group data Group Starting plane Focal length Lens length Front principal point position Rear principal point position 1 1 234.60 289.00 193.11 -160.97 2 15 -123.49 1.60 1.20 0.20 3 17 -1500.00 124.07 -7.97 -121.60 Single lens data Lens starting surface focal length 1 1 491.66 2 3 193.29 3 5 -120.37 4 7 286.37 5 9 179.23 6 11 -89.48 7 12 108.80 8 15 -123.49 9 17 -72.34 10 18 60.26 11 20 61.76 12 21 -56.49 13 23 -60.98 14 25 80.68 15 27 51.87 16 28 -51.21 17 30 -58.88 18 32 63.88

[0065] Various values ​​in the optical systems of the examples are summarized in Table 1 below. In the table, ΔθgFG1n is calculated by θgFG1n-(-1.665×10-7 ×νdG1n 3 +5.213×10 -5 ×νdG1n 2 -5.656×10 -3 ×νdG1n+0.7268) and ΔθgFG2 is θgFG2-(-1.665×10 -7 ×νdG2 3 +5.213×10 -5 ×νdG2 2 -5.656×10 -3 ×νdG2+0.7268).

[0066] [Table 1]

[0067] [Imaging device] Next, a digital still camera (image capture device) using the optical system of each of the above-described embodiments as an image capture optical system will be described with reference to Fig. 7. In Fig. 7, 10 denotes a camera body, and 11 denotes an image capture optical system configured with any of the optical systems described in Examples 1 to 3. 12 denotes a solid-state image capture element (photoelectric conversion element) such as a CCD sensor or CMOS sensor that is built into the camera body and receives a subject image formed by the image capture optical system 11.

[0068] In this way, by applying the optical system of each embodiment to an imaging device such as a digital still camera, it is possible to obtain an imaging device that is lightweight and in which aberrations such as chromatic aberration are well corrected. [Explanation of symbols]

[0069] B1 First lens group B2 Second lens group B3 Third lens group SP aperture stop

Claims

1. An optical system comprising a first lens group, a second lens group, and a third lens group, all of which have positive refractive power, arranged in this order from the object side to the image side, wherein the second lens group moves during focusing, changing the interval between adjacent lens groups, the first lens group includes a positive lens G1p arranged closest to the object, a lens G2 arranged adjacent to the image side of the positive lens G1p, and a negative lens G1n arranged closest to the object among the negative lenses included in the first lens group, During image blur correction, at least a part of the lenses of the optical system moves in a direction including a component perpendicular to the optical axis, When the back focus of the optical system is BF, the focal length of the positive lens G1p is fG1p, the focal length of the negative lens G1n is fG1n, the Abbe number of the material of the negative lens G1n is vdG1n, the partial dispersion ratio is θgFG1n, and the Abbe number of the material of the lens G2 is vdG2, 0.02<BF / fG1p<0.14 2.00<|fG1p / fG1n|<10.00 20.0<νdG1n<40.0 -0.1000<θgFG1n-(-1.665×10 －７ ×νdG1n ３ +5.213×10 －５ ×νdG1n ２ -5.656×10 －３ ×νdG1n+0.7268)<-0.0010 An optical system characterized by satisfying the following conditional expression:

2. When the distance on the optical axis between the positive lens G1p and the lens G2 is D12, and the distance on the optical axis from the lens surface of the first lens group closest to the object side to the image plane is LD, 0.13<D12 / LD<0.50 2. The optical system according to claim 1, wherein the following condition is satisfied:

3. 3. The optical system according to claim 1, wherein the lens G2 has a positive refractive power.

4. When the focal length of the lens G2 is fG2, 0.05<BF / fG2<0.23 4. The optical system according to claim 1, wherein the following condition is satisfied:

5. When the focal length of the lens G2 is fG2, 1.5<fG1p / fG2<5.0 5. The optical system according to claim 1, wherein the following condition is satisfied:

6. When the partial dispersion ratio of the material of the lens G2 is θgFG2, 0.0100<θgFG2-(-1.665×10 －７ ×νdG2 ３ +5.213×10 －５ ×νdG2 ２ -5.656×10 －３ ×νdG2+0.7268)<0.1000 6. The optical system according to claim 1, wherein the following condition is satisfied:

7. 7. The optical system according to claim 1, wherein the second lens group has negative refractive power and moves toward the image side during focusing from infinity to a close distance.

8. 8. The optical system according to claim 7, wherein the second lens group consists of one negative lens.

9. 9. The optical system according to claim 1, wherein the first lens group is stationary during focusing.

10. The third lens group includes at least one positive lens and at least one negative lens, and when the focal length of the positive lens included in the third lens group that is located closest to the image side is defined as fGkp, and the focal length of the negative lens included in the third lens group that is located closest to the image side is defined as fGkn, 1.02<|fGkp / fGkn|<2.50 10. The optical system according to claim 1, wherein the following condition is satisfied:

11. 11. The optical system according to claim 1, wherein the third lens group includes a positive lens Gkp arranged closest to the image side, and a negative lens Gkn arranged adjacent to the positive lens Gkp on the object side.

12. 12. The optical system according to claim 1, wherein the third lens group has a negative refractive power.

13. 13. An imaging device comprising: the optical system according to claim 1; and an imaging element that receives an image formed by the optical system.

14. When the maximum image height in the imaging device is IH, 0.05<BF / IH<2.20 14. The imaging device according to claim 13, wherein the following condition is satisfied:

Images