Optical system and imaging device 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 image sensors 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] As a long-focal-length photographic optical system, a so-called telephoto type is known, in which an optical system with positive refractive power is placed on the object side and an optical system with negative refractive power is placed on the image side. Telephoto type photographic optical systems are used, for example, in fixed-focal-length super-telephoto lenses.

[0003] In super-telephoto lenses, axial chromatic aberration and lateral chromatic aberration generally increase as the focal length increases. A known method for effectively correcting these chromatic aberrations is to increase the number of lenses positioned on the object side, distributing the chromatic aberration correction function among the lenses. 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 method increases the weight of the imaging optical system.

[0004] In the imaging optical system described in Patent Document 1, axial chromatic aberration and lateral chromatic aberration are corrected by arranging positive lenses made from materials with low dispersion and anomalous dispersion in a continuous sequence from the object side. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2015-215561 [Overview of the project] [Problems that the invention aims to solve]

[0006] In the optical system described in Patent Document 1, chromatic aberration is corrected by arranging positive lenses formed from materials having low dispersion and anomalous dispersibility as close to the object side as possible. However, since the effective diameters of these positive lenses are large, the optical system cannot be sufficiently lightened.

[0007] In order to further lighten the optical system, it is important to find appropriate materials and arrangements not only for the positive lenses but also for the negative lenses.

[0008] An object of the present invention is to provide an optical system that is small and has good correction of aberrations such as chromatic aberration, and an imaging device having the same.

Means for Solving the Problems

[0009] The optical system of the present invention is composed of a first lens group, a second lens group, and a third lens group having positive refractive power, arranged in order from the object side to the image side. When focusing, the second lens group moves, and the interval between adjacent lens groups changes. The first lens group includes a positive lens G1p arranged closest to the object side, a lens G2 arranged adjacent to the image side of the positive lens G1p, and a negative lens G1n arranged closest to the object side among the negative lenses included in the first lens group. When correcting image blur, at least a part of the lenses of the optical system moves in a direction including a component perpendicular to the optical axis. 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 νdG1n, and the partial dispersion ratio is θgFG1n. Possesses positive refractive power 0.02 < BF / fG1p < 0.14 When the distance between the positive lens G1p and the lens G2 along the optical axis is D12, and the distance from the lens surface closest to the object in the first lens group to the image plane along the optical axis is LD, 2.00 < |fG1p / fG1n| < 10.00 20.0 < νdG1n < 40.0 -0.1000 < θgFG1n - (-1.665×10 ×νdG1n -7 ×νdG1n 3 +5.213×10 -5 ×νdG1n 2 -5.656×10 -3 ×νdG1n + 0.7268) < -0.0010 0.15 <D12 / LD<0.50 It is characterized by satisfying the following conditional expression. [Effects of the Invention]

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

[0011] [Figure 1] This is a cross-sectional view of the lens of the optical system in Example 1. [Figure 2] This is an aberration diagram of the optical system of Example 1 when it is in focus at infinity. [Figure 3] This is a cross-sectional view of the lens of the optical system in Example 2. [Figure 4] This is an aberration diagram of the optical system of Example 2 when it is in focus at infinity. [Figure 5] This is a cross-sectional view of the lens of the optical system in Example 3. [Figure 6] This is an aberration diagram of the optical system of Example 3 when it is in focus at infinity. [Figure 7] This is a schematic diagram of the main components of the imaging device. [Modes for carrying out the invention]

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

[0013] Figures 1, 3, and 5 are cross-sectional views of the optical systems of Examples 1 to 3, respectively. The optical systems of each example 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 view, the left side is the object side (front), and the right side is the image side (rear). Also, in the lens cross-sectional view, if j is the order of the lens groups from the object side to the image side, then Bj represents the j-th lens group.

[0014] In each embodiment, SP is an aperture diaphragm. In the optical system of each embodiment, the aperture diaphragm SP is positioned between the first lens group B1 and the second lens group B2.

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

[0016] Figures 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 the spherical aberration for the d-line (wavelength 587.6 nm) and the g-line (wavelength 435.8 nm). In the astigmatism diagram, S shows the amount of astigmatism at the sagittal image plane, and M shows the amount of astigmatism at the meridional image plane. Distortion is shown for the d-line. In the chromatic aberration diagram, chromatic aberration at the g-line is shown. ω is the half-angle of view of the image.

[0018] In the optical systems of each embodiment, as indicated by the arrows in the lens cross-sectional diagrams, the second lens group B2 moves toward the image side when focusing from infinity to near distance, and the spacing between adjacent lens groups changes. In other words, in the optical systems of each embodiment, the second lens group B2 corresponds to the focusing group.

[0019] Furthermore, in the optical system of each embodiment, some of the lenses in the optical system are designated as an image-stabilizing group, and the image formation position can be changed by moving the image-stabilizing group in a direction having a component perpendicular to the optical axis. This allows for image blur correction. The image-stabilizing group may be any of the lens groups of the first lens group B1, the second lens group B2, or the third lens group B3, or some of the lenses included in a specific lens group may be designated as an image-stabilizing 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 setting the material of 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 was not sufficient. Therefore, in the optical systems of each embodiment, the chromatic aberration correction effect of the negative lens included in the first lens group B1 is enhanced by using a material with high dispersion and anomalous dispersion for the negative lens included in the first lens group B1, thereby effectively correcting chromatic aberration in the entire optical system.

[0021] Here, the Abbe number νd and the partial dispersion ratio θgF are known as parameters related to the correction of chromatic aberration in optical systems. When the refractive indices of the 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 νd and the partial dispersion ratio θgF are expressed by the following equations. νd = (Nd-1) / (NF-NC) θgF = (Ng - NF) / (NF - NC)

[0022] Generally, by using a highly dispersed material as the negative lens material within a lens group that has a positive refractive power as a whole, a correction effect for first-order chromatic aberration can be obtained. Furthermore, by using a material with high anomalous dispersion as the negative lens material within a lens group that has a positive refractive power as a whole, second-order chromatic aberration can be effectively corrected.

[0023] Here, the anomalous dispersibility of the material used for the lens will be described. In the present specification, the index ΔθgF of the strength of anomalous dispersibility 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] In many optical materials, the value of ΔθgF becomes a value near zero. The farther the value of ΔθgF is from zero, the higher the anomalous dispersibility of the material.

[0025] Let the back focus of the optical system be BF, and the focal length of the positive lens G1p that is most disposed on the object side among the positive lenses included in the first lens group B1 be fG1p. Also, when the focal length, Abbe number, and partial dispersion ratio of the negative lens G1n that is most disposed on the object side among the negative lenses included in the first lens group B1 are fG1n, νdG1n, and θgFG1n, respectively, the optical systems of each embodiment satisfy the following formulas (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] Condition (1) defines the relationship between the back focus of the optical system and the focal length of the positive lens G1p. Satisfying condition (1) allows for the realization of a compact optical system with a short overall length. Exceeding the upper limit of condition (1) results in an excessively long back focus, which is undesirable as it causes the optical system and the imaging device to which it is mounted to become larger in the optical axis direction. Conversely, falling below the lower limit of condition (1) results in an excessively short back focus. In this case, the diameter of the lens positioned closest to the image in the optical system becomes too large, and the diameter of the mount for attaching the optical system to the imaging device also becomes larger. As a result, it becomes difficult to design a compact and lightweight optical system and imaging device. Furthermore, attempting to reduce the diameter of the final lens in the optical system while simultaneously reducing the back focus to the point below the lower limit of condition (1) results in a larger angle of incidence of light rays to the image sensor, which is undesirable as it tends to degrade image quality, especially at the edges of the image.

[0027] Conditional equation (2) is a conditional equation that 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 shorter than the lower limit of conditional equation (2), the refractive power of the positive lens G1p becomes too strong, causing a lot of axial chromatic aberration in the positive lens G1p, which is undesirable. Correcting the axial chromatic aberration generated in the positive lens G1p with the negative lenses included in the first lens group B1 would require increasing the number of negative lenses, which would increase the weight of the optical system and is therefore undesirable.

[0028] Furthermore, if the focal length fG1p of the positive lens G1p becomes longer than the upper limit of condition (2), the refractive power of the positive lens G1p becomes too weak. As a result, the light cannot be sufficiently focused in the positive lens G1p, the effective diameter of the lens positioned on the image side of the positive lens G1p becomes larger, and this leads to an increase in the weight of the optical system, which is undesirable.

[0029] Conditional equation (3) is a conditional equation that specifies the Abbe number νdG1n of the material for the negative lens G1n. By using a highly dispersed material for the negative lens G1n included in the first lens group B1 with positive refractive power, first-order chromatic aberration can be corrected well. If the value falls below the lower limit of conditional equation (3), the lateral chromatic aberration in the negative lens G1n will be overcorrected, which is undesirable. Conversely, if the value exceeds the upper limit of conditional equation (3), it will be difficult to adequately correct the lateral chromatic aberration in the negative lens G1n, which is also undesirable.

[0030] Conditional equation (4) is a conditional equation that defines the anomalous dispersion ΔθgFG1n of the material of the negative lens G1n. By constructing the negative lens G1n using a material with high anomalous dispersion, the correction effect of second-order chromatic aberration can be enhanced. Materials below the lower limit of conditional equation (4) have poor practicality as an imaging optical system. Using a material above the upper limit of conditional equation (4) as the material for the negative lens G1n is undesirable because it becomes difficult to adequately correct second-order chromatic aberration.

[0031] In each embodiment, considering the balance of aberration correction for the entire optical system, NBFD15 (manufactured by HOYA Corporation; νd=33.27, θgF=0.5883, ΔθgF=-0.0019) is used as the material constituting the negative lens G1n. The negative lens G1n of the present invention only needs to be composed 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), etc., may also be used.

[0032] In each embodiment, as described above, each element is appropriately set to satisfy the conditions (1) to (4). This makes it possible to obtain a compact optical system with well-corrected aberrations such as chromatic aberration.

[0033] In each embodiment, it is preferable to set the numerical ranges of 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] Furthermore, it is preferable to set the numerical ranges of 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] Thus, by using a material with high anomalous dispersion as the material for the negative lens G1n, the positive lens included in the first lens group B1 can be positioned relatively towards the image side. This effectively reduces the weight of the first lens group B1, enabling both miniaturization of the optical system and good correction of chromatic aberration.

[0036] Furthermore, it is more preferable that each embodiment satisfies one or more of the following conditions. 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 along the optical axis from the lens surface closest to the object in the first lens group B1 to the image plane. Also, D12 is the distance along the optical axis between lens G2, which is positioned adjacent to the image side of positive lens G1p, and positive lens G1p, fG2 is the focal length of lens G2, νdG2 is the Abbe number of the material of lens G2, and θgFG2 is the partial dispersion ratio of the material of lens G2.

[0038] Furthermore, IH is defined as the maximum image height. Note that the maximum image height IH refers to half the diagonal length of the usable area 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 denoted 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 denoted as fGkn.

[0040] Conditional equation (5) defines the ratio of the optical axis distance D12 between the positive lens G1p and lens G2, which is positioned 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 lens G2 becomes shorter, below the lower limit of conditional equation (5), the effective diameter of lens G2 increases, which is undesirable because it increases the weight of lens G2. If the distance D12 between the positive lens G1p and lens G2 becomes longer, above the upper limit of conditional equation (5), it becomes difficult to correct spherical aberration and chromatic aberration generated in the positive lens G1p with lenses G2 and subsequent lenses, which is also undesirable.

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

[0042] Conditional equation (6) is a conditional equation that defines the ratio of the focal length fG1p of the positive lens G1p to the focal length fG2 of lens G2. If the focal length fG1p of the positive lens G1p becomes shorter than the lower limit of conditional equation (6), the refractive power of the positive lens G1p becomes too strong, causing a lot of axial chromatic aberration in the positive lens G1p, which is undesirable. Correcting the axial chromatic aberration generated in the positive lens G1p with the negative lenses included in the first lens group B1 would require increasing the number of negative lenses, which would increase the weight of the optical system, and is therefore undesirable.

[0043] Furthermore, if the focal length fG1p of the positive lens G1p becomes longer than the upper limit of condition (6), the refractive power of the positive lens G1p becomes too weak. As a result, the positive lens G1p cannot sufficiently focus the light, the effective diameter of the lens positioned on the image side of the positive lens G1p becomes larger, and this leads to an increase in the weight of the optical system, which is undesirable.

[0044] Conditional equation (7) is a conditional equation that defines the Abbe number νdG2 of the material of lens G2. If the Abbe number νdG2 falls below the lower limit of conditional equation (7) and becomes small, a large amount of chromatic aberration occurs in lens G2, which is undesirable.

[0045] Conditional equation (8) is a conditional equation that defines the anomalous dispersion of the material of lens G2. By constructing lens G2 using a material with high anomalous dispersion, the correction effect of second-order chromatic aberration can be enhanced. Materials below the lower limit of conditional equation (8) have poor practical use as optical materials for photographic optical systems. Using a material above the upper limit of conditional equation (8) as the material for lens G2 is undesirable because it becomes difficult to adequately correct second-order chromatic aberration.

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

[0047] Conditional equation (9) is the relationship between the back focus of the optical system and the maximum image height. If the value exceeds the upper limit of conditional equation (9), the overall length becomes too long, increasing the weight of the mechanical components (lens barrel, etc.) that hold the optical system, making it difficult to lighten the optical system. Conversely, if the value falls below the lower limit of conditional equation (9), the back focus becomes too short. In this case, the diameter of the lens positioned closest to the image in the optical system becomes too large, and the diameter of the mount for attaching the optical system to the imaging device becomes larger. As a result, it becomes difficult to design a compact and lightweight optical system and imaging device. Furthermore, if one tries to reduce the diameter of the final lens in the optical system while simultaneously reducing the back focus to the point below the lower limit of conditional equation (9), the angle of incidence of light rays to the image sensor increases, which is undesirable because it tends to degrade image quality, especially at the edges of the image.

[0048] Conditional equation (10) is the relationship between the back focus of the optical system and the focal length of lens G2. If the value exceeds the upper limit of conditional equation (10), the overall length becomes too long, increasing the weight of the mechanical components (lens barrel, etc.) that hold the optical system, making it difficult to lighten the optical system. Conversely, if the value falls below the lower limit of conditional equation (10), the back focus becomes too short. In this case, the diameter of the lens positioned closest to the image in the optical system becomes too large, and the diameter of the mount for attaching the optical system to the imaging device becomes larger. As a result, it becomes difficult to design a compact and lightweight optical system and imaging device. Furthermore, if one tries to reduce the diameter of the final lens in the optical system while simultaneously reducing the back focus to the point below the lower limit of conditional equation (10), the angle of incidence of light rays to the image sensor increases, resulting in a decrease in image quality, especially at the edges of the image, which is undesirable.

[0049] Conditional equation (11) defines the relationship between the focal lengths of the positive lens Gkp, which is located closest to the image among the positive lenses of the third lens group B3, and the negative lens Gkn, which is located closest to the image among the negative lenses. By satisfying conditional equation (11), the overall length of the optical system can be shortened while distortion and chromatic aberration are well corrected.

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

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

[0052] Preferably, the numerical ranges for conditional expressions (5) to (11) should be set 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] Furthermore, it is preferable to set the numerical ranges of 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] Furthermore, it is preferable that the second lens group B2, which moves during focusing, consists of a single negative lens. This allows for miniaturization and weight reduction of the mechanical mechanism for driving the second lens group B2. It also facilitates rapid focusing.

[0055] Furthermore, in the optical system of each embodiment, it is preferable that the first lens group B1 remains stationary during focusing. The first lens group B1, which is positioned closest to the object among the lens groups constituting the optical system, has a large effective diameter and is heavy. Moving the heavy first lens group B1 during focusing would require a large drive mechanism, which would increase the weight of the optical system and the imaging device including the optical system, so this is undesirable.

[0056] Furthermore, in the optical system 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 positioned closest to the image plane and a negative lens Gkn positioned adjacent to the positive lens Gkp on the object side. By adopting a configuration in which the negative lens and the positive lens are positioned in that order from the object side at the closest to the image plane of the optical system, it is possible to reduce the angle of incidence to the imaging plane. This makes it possible to suppress the decrease in light intensity and the decrease in image quality at the edges of the image, which are problems when using a CMOS sensor or CCD sensor as the image sensor.

[0057] Furthermore, in the optical systems of each embodiment, it is preferable that both the second lens group B2 and the third lens group B3 have negative refractive power. This strengthens the tendency toward a telephoto-type power arrangement and allows for a shorter overall length of the optical system.

[0058] Next, the numerical examples 1 to 3 corresponding to Examples 1 to 3 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 i-th optical surface (i-th surface), di is the distance between the i-th surface and the (i+1)-th surface when focused at infinity, and ndi and νdi are the refractive index and Abbe number of the i-th optical component material with respect to the d-line, respectively. Regarding the change in the spacing of the lens surfaces, the spacing of the lens surfaces when focused at infinity and the spacing of the lens surfaces when focused at the closest distance are described.

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

[0060] In each embodiment, protective glass may be placed on the object side of the first lens group B1 to protect the lenses. Furthermore, protective glass or a low-pass filter may be placed between the lens closest to the image plane and the image plane. In this specification, optical components with extremely weak refractive power, such as protective glass and low-pass filters placed on the object side and the image side of the optical system, are not treated as lenses constituting the optical system. "Extremely weak refractive power" refers to optical components whose absolute focal length is five times or more the focal length of the entire optical system.

[0061] Furthermore, if an optical element with extremely weak refractive power is placed between the optical system and the image sensor, the back focus BF value used is the value obtained by converting the refractive power of the optical element with extremely weak refractive power placed between the optical system and the image sensor to air equivalent.

[0062] [Numerical Example 1] Unit: mm Surface data Face 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 Field of view 3.16 Image height 21.64 Lens 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 plane, 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 Face 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 Field of view 2.53 Image height 21.64 Lens 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 plane, 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 Face 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 Field of view 2.11 Image height 21.64 Lens 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 plane, 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] Table 1 below summarizes the various values ​​in the optical system of each embodiment. Note that ΔθgFG1n in the table is θgFG1n - (-1.665 × 10-7 ×νdG1n 3 +5.213 × 10 -5 ×νdG1n 2 -5.656 × 10 -3 The value of ×νdG1n + 0.7268) is given by ΔθgFG2 - (-1.665 × 10 -7 ×νdG2 3 +5.213 × 10 -5 ×νdG2 2 -5.656 × 10 -3 This is the value of ×νdG² + 0.7268).

[0066] [Table 1]

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

[0068] By applying the optical systems of each embodiment to imaging devices such as digital still cameras, it is possible to obtain imaging devices that are lightweight and have well-corrected aberrations such as chromatic aberration. [Explanation of Symbols]

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

Claims

1. An optical system consisting of a first lens group, a second lens group, and a third lens group, all having positive refractive power, arranged sequentially from the object side to the image side, wherein the second lens group moves during focusing, changing the spacing between adjacent lens groups, The first lens group includes a positive lens G1p positioned closest to the object, a lens G2 having positive refractive power positioned adjacent to the image side of the positive lens G1p, and a negative lens G1n positioned closest to the object among the negative lenses included in the first lens group. During image blur correction, at least some of the lenses of the optical system move in a direction that includes 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 νdG1n, the partial dispersion ratio is θgFG1n, the distance between the positive lens G1p and the lens G2 on the optical axis is D12, and the distance from the lens surface closest to the object to the image plane on the optical axis of the first lens group is LD, 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 0.15<D12 / LD<0.50 An optical system characterized by satisfying the following conditional equation.

2. When the focal length of the lens G2 is denoted as fG2, 0.05<BF / fG2<0.23 The optical system according to claim 1, characterized in that it satisfies the following condition.

3. When the focal length of the lens G2 is denoted as fG2, 1.5<fG1p / fG2<5.0 The optical system according to claim 1 or 2, characterized in that it satisfies the following conditional expression.

4. When the Abbe number of the material of lens G2 is νdG2 and the partial dispersion ratio of the material of 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 The optical system according to any one of claims 1 to 3, characterized in that it satisfies the following conditional expression.

5. The optical system according to any one of claims 1 to 4, characterized in that the second lens group has a negative refractive power and moves toward the image side when focusing from infinity to near distance.

6. The optical system according to claim 5, characterized in that the second lens group consists of a single negative lens.

7. The optical system according to any one of claims 1 to 6, characterized in that the first lens group remains stationary during focusing.

8. 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 located furthest towards the image among the positive lenses included in the third lens group is fGkp, and the focal length of the negative lens located furthest towards the image among the negative lenses included in the third lens group is fGkn, 1.02<|fGkp / fGkn|<2.50 The optical system according to any one of claims 1 to 7, characterized in that it satisfies the following conditional expression.

9. The optical system according to any one of claims 1 to 8, characterized in that the third lens group has a positive lens Gkp positioned closest to the image and a negative lens Gkn positioned adjacent to the positive lens Gkp on the object side.

10. The optical system according to any one of claims 1 to 9, characterized in that the third lens group has a negative refractive power.

11. An imaging device characterized by having an optical system according to any one of claims 1 to 10 and an image sensor that receives an image formed by the optical system.

12. When the maximum image height in the imaging device is IH, 0.05<BF / IH<2.20 The imaging device according to claim 11, characterized in that it satisfies the following conditional expression.

Images