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] As a photographic optical system with a long focal length, a so-called telephoto type photographic optical system is known in which an optical system with positive refractive power is arranged on the object side and an optical system with negative refractive power is arranged on the image side. The telephoto type photographic optical system is used, for example, in a single-focus super telephoto lens.

[0003] In super telephoto lenses, the longer the focal length, the more axial chromatic aberration and lateral chromatic aberration occur. A known method for effectively correcting these chromatic aberrations is to increase the number of lenses arranged on the object side and have each lens share the role of correcting the chromatic aberration. However, the effective diameter of the lenses arranged on the object side of a super telephoto lens tends to be large, and correcting chromatic aberration using the above-mentioned method results 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 lateral chromatic aberration. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2015-215561 A 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 having low dispersion and anomalous dispersion are positioned as close to the object as possible to correct chromatic aberration. However, since these positive lenses have large effective diameters, it is not possible to sufficiently reduce the weight of the optical system.

[0007] In order to achieve further weight reduction in 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 which is small and in which aberrations such as chromatic aberration are well corrected, and an imaging apparatus 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 the second lens group moves during focusing, changing the distance 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 the negative lens G1n has a concave surface facing the image side. 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: Effect of the Invention

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

[0011] [Figure 1] 1 is a lens sectional view of an optical system according to a first embodiment. [Diagram 2] 4A to 4C are aberration diagrams of the optical system of Example 1 when focused on infinity. [Diagram 3] FIG. 11 is a cross-sectional view of a lens of an optical system according to a second embodiment. [Figure 4] 11A to 11C are aberration diagrams of the optical system of Example 2 when focused on infinity. [Diagram 5] FIG. 11 is a lens sectional view of the optical system of Example 3. [Figure 6] 11A to 11C are aberration diagrams of the optical system of Example 3 when focused on infinity. [Figure 7] FIG. 2 is a schematic diagram of a main part of the imaging device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, embodiments of the optical system and the imaging device having the same of the present invention will be described in detail with reference to the accompanying drawings. The optical system of 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, and the distance between adjacent lens groups changes. Here, the lens group refers to a lens element that moves integrally during focusing, and may include one or more lenses, but does not necessarily have to include multiple lenses.

[0013] 1, 3, and 5 are cross-sectional views of the optical systems of 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 an image plane. When the optical system is used as an imaging optical system for a video camera or a digital camera, the image plane IP corresponds to a solid-state imaging element (photoelectric conversion element) such as a CCD sensor or a 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 surface.

[0016] 2, 4 and 6 are aberration diagrams of the optical systems of Examples 1 to 3 when focused on 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 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 aberration is shown for the d-line. The chromatic aberration diagram shows chromatic aberration for the g-line. 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 group B2 moves toward the image side during focusing from infinity to a close distance, and the distance between adjacent lens groups changes. That is, in the optical system of each embodiment, the second lens group B2 corresponds to the focus group.

[0019] In the optical system of each embodiment, a part of the lenses in the optical system is used as an anti-vibration group, and the image formation position can be changed by moving the anti-vibration group 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 anti-vibration group, or some of the lenses included in a specific lens group may be used as the anti-vibration group.

[0020] In the optical system of each embodiment, chromatic aberration is well 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, and the chromatic aberration correction effect of the negative lens included in the first lens group B1 is not sufficient. Therefore, in the optical system 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 well 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 expressed by the following equations. νd=(Nd-1) / (NF-NC) θgF=(Ng-NF) / (NF-NC)

[0022] In general, the use of a high dispersion material for a negative lens arranged in a lens group having a positive refractive power as a whole can provide a correction effect for first-order chromatic aberration. Also, the use of a high anomalous dispersion material for a negative lens arranged in a lens group having a positive refractive power as a whole can provide good correction for second-order lateral chromatic aberration.

[0023] Here, the anomalous dispersion of the material used for the lens will be described. 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 farther the value of ΔθgF is from zero, 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 located closest to the object among the positive lenses included in the first lens group B1 is fG1p, and the focal length, Abbe number, and partial dispersion ratio of the negative lens G1n located closest to the object among the negative lenses included in the first lens group B1 are fG1n, νdG1n, and θgFG1n, respectively. The optical system of each embodiment satisfies 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] Conditional formula (1) defines the relationship between the back focus of the optical system and the focal length of the positive lens G1p. By satisfying conditional formula (1), a small optical system with a short overall length can be realized. If the upper limit of conditional formula (1) is exceeded, the back focus becomes too long, which is undesirable because the optical system and the imaging device to which the optical system is attached become large in the optical axis direction. Also, if the lower limit of conditional formula (1) is exceeded, the back focus becomes too short. In this case, the diameter of the lens arranged closest to the image side of the optical system becomes too large, and the diameter of the mount for mounting the optical system on the imaging device becomes large. As a result, it becomes difficult to configure the optical system and the imaging device to be small and lightweight. Also, if the back focus is reduced while the diameter of the final lens of the optical system is reduced to a value below the lower limit of conditional formula (1), the angle of incidence of the light beam on the imaging element increases, which is undesirable because the image quality is likely to deteriorate, especially at the periphery of the image.

[0027] Conditional formula (2) specifies 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 axial chromatic aberration occurs in the positive lens G1p. In order to correct the axial 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 formula (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 disposed on the image side of the positive lens G1p becomes large, undesirably increasing the weight of the optical system.

[0029] Conditional formula (3) specifies 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 corrected well. If the lower limit of conditional formula (3) is exceeded, the lateral chromatic aberration is overcorrected in the negative lens G1n, which is not preferable. Also, if the upper limit of conditional formula (3) is exceeded, it becomes difficult to sufficiently correct the lateral chromatic aberration in the negative lens G1n, which is not preferable.

[0030] Conditional formula (4) is a conditional formula that specifies the anomalous dispersion ΔθgFG1n of the material of the negative lens G1n. By forming the negative lens G1n using a material with high anomalous dispersion, 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. It is not preferable to use a material above the upper limit of conditional formula (4) as the material of the negative lens G1n, since it becomes difficult to sufficiently correct second-order lateral chromatic aberration.

[0031] In the optical system of each embodiment, NBFD15 (manufactured by HOYA Corporation; νd=33.27, θgF=0.5883, ΔθgF=-0.0019) is used as the material constituting the negative lens G1n, taking into consideration the balance of aberration correction of the entire optical system. The negative lens G1n of the present invention may be made of a material that satisfies both expressions (3) and (4). An example of a material that satisfies both expressions (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 be used.

[0032] As explained above, in each embodiment, the elements are appropriately set so as to satisfy the conditions (1) to (4), thereby making it possible to obtain an optical system that is compact and 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 group B1 can be positioned relatively closer to the image side, which effectively reduces the weight of the first lens group B1 and enables both a compact optical system and good correction of chromatic aberration.

[0036] Furthermore, in each embodiment, it is more preferable that one or more of the following conditional expressions be satisfied. 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, the distance on the optical axis from the lens surface closest to the object in the first lens group B1 to the image plane is denoted as LD, the distance on the optical axis between the lens G2 arranged adjacent to the image side of the positive lens G1p and the positive lens G1p is denoted as D12, the focal length of the lens G2 is denoted as fG2, the Abbe number of the material of the lens G2 is denoted as νdG2, and the partial dispersion ratio of the material of the lens G2 is denoted as θgFG2.

[0038] Also, IH is the maximum image height, which is 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 side among the positive lenses included in the third lens group B3 is fGkp, and the focal length of the negative lens located closest to the image side among the negative lenses included in the third lens group B3 is fGkn.

[0040] Conditional formula (5) defines the ratio of the distance D12 on the optical axis between the positive lens G1p and the lens G2 arranged 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 is short below the lower limit of conditional formula (5), the effective diameter of the lens G2 becomes large, and the weight of the lens G2 increases, which is not preferable. If the distance D12 between the positive lens G1p and the lens G2 is long above the upper limit of conditional formula (5), it is not preferable because it becomes difficult to correct the spherical aberration and chromatic aberration generated in the positive lens G1p by the lenses after the lens G2.

[0041] In addition, it is preferable that the lens G2 has a positive refractive power. By arranging two positive lenses consecutively from the most object side of the optical system, it is possible to greatly converge the light rays passing through the lenses, and as a result, it is possible to reduce the effective diameter of the lens arranged on the image side of the 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 axial chromatic aberration occurs in the positive lens G1p. In order to correct the axial 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.

[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 disposed on the image side of the positive lens G1p becomes large, undesirably increasing 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 formula (8) regulates the anomalous dispersion of the material of lens G2. By forming lens G2 using a material with high anomalous dispersion, the effect of correcting second-order lateral chromatic aberration can be improved. A material below the lower limit of conditional formula (8) is not practical as an optical material used in a photographic optical system. It is not preferable to use a material above the upper limit of conditional formula (8) as the material of lens G2, since it becomes difficult to sufficiently correct second-order lateral chromatic aberration.

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

[0047] Conditional formula (9) is a relational expression between the back focus of the optical system and the maximum image height. If the upper limit of conditional formula (9) is exceeded, the overall length becomes too long, and the weight of the mechanical members (such as the lens barrel) that hold the optical system becomes large, making it difficult to reduce the weight of the optical system. If the lower limit of conditional formula (9) is exceeded, the back focus becomes too short. In this case, the diameter of the lens disposed closest to the image side of the optical system becomes too large, and the diameter of the mount for mounting the optical system on the imaging device becomes large. As a result, it becomes difficult to configure the optical system and the imaging device to be small and lightweight. If the back focus is reduced while the diameter of the final lens of the optical system is reduced so as to fall below the lower limit of conditional formula (9), the angle of incidence of the light beam on the imaging element becomes large, which is undesirable because it tends to deteriorate the image quality, especially at the periphery of the image.

[0048] Conditional formula (10) is a relational expression between the back focus of the optical system and the focal length of the lens G2. If the upper limit of conditional formula (10) is exceeded, the overall length becomes too long, and the weight of the mechanical members (such as the lens barrel) that hold the optical system becomes large, making it difficult to reduce the weight of the optical system. If the lower limit of conditional formula (10) is exceeded, the back focus becomes too short. In this case, the diameter of the lens disposed closest to the image side of the optical system becomes too large, and the diameter of the mount for mounting the optical system on the imaging device becomes large. As a result, it becomes difficult to configure the optical system and the imaging device to be small and lightweight. If the back focus is reduced while the diameter of the final lens of the optical system is reduced so as to fall below the lower limit of conditional formula (10), the angle of incidence of the light beam on the imaging element becomes large, which is undesirable because it tends to deteriorate the 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 the lens closest to the image, and the negative lens Gkn, which is the lens closest to the image, in the third lens group B3. By satisfying conditional expression (11), it is possible to reduce the overall length of the optical system while effectively correcting distortion and lateral chromatic aberration.

[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 since the correction of distortion and lateral chromatic aberration tends to become insufficient.

[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 group B2, which moves during focusing, is made up of one negative lens. This allows the mechanical mechanism for driving the second lens group B2 to be made smaller and lighter, and also facilitates quick focusing.

[0055] Furthermore, in the optical system of each embodiment, it is preferable that the first lens group B1 does not move during focusing. The first lens group B1, which is disposed closest to the object among the lens groups constituting the optical system, 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 imaging device including the optical system.

[0056] In addition, 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 order from the image surface side. That is, it is preferable that the third lens group B3 has a positive lens Gkp arranged on the most image side and a negative lens Gkn arranged adjacent to the object side of the positive lens Gkp. By adopting a configuration in which a negative lens and a positive lens are arranged in order from the object side on the most image surface side of the optical system, it is possible to reduce the angle of incidence to the imaging surface. This makes it possible to suppress the decrease in the amount of light and the deterioration of image quality in the peripheral part of the image, which is a problem when a CMOS sensor or a CCD sensor is used as an imaging element.

[0057] In the optical systems of the 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 indicates the radius of curvature of the i-th optical surface (i-th surface), di indicates the distance between the i-th surface and the (i+1)-th surface when focusing at infinity, and ndi and νdi indicate the refractive index and Abbe number of the material of the i-th optical member for the d-line, respectively. Regarding the change in the distance between the lens surfaces, the distance between the lens surfaces when focused at infinity and the distance between the lens surfaces when focused 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 arranged on the object side of the first lens group B1. A protective glass or a low-pass filter may be arranged between the lens arranged closest to the image plane and the image plane. In this specification, optical elements with extremely weak refractive power, such as protective glass and a low-pass filter arranged closest to the object side and the 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 5 times or more the focal length of the entire optical system.

[0061] In addition, when an optical component 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 component 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 addition, ΔθgFG1n in the table is θgFG1n-(-1.665×10-7 ×νdG1n 3 +5.213×10 -5 ×νdG1n 2 -5.656×10 -3 ×νdG1n+0.7268). Also, 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 (imaging device) using the optical system of each of the above-mentioned embodiments as an imaging optical system will be described with reference to Fig. 7. In Fig. 7, 10 denotes a camera body, and 11 denotes an imaging optical system constituted by any of the optical systems described in the first to third embodiments. 12 denotes a solid-state imaging element (photoelectric conversion element) such as a CCD sensor or a CMOS sensor that is built into the camera body and receives a subject image formed by the imaging 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 2nd lens group B3 3rd 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 an object side to an image side, wherein the second lens group moves during focusing, and an interval between adjacent lens groups changes, the first lens group has five or more lenses including 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; 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, the Abbe number of the material of the lens G2 is vdG2, the partial dispersion ratio of the material of the lens G2 is θgFG2, and the maximum image height is IH, 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 0.0100<θgFG2-(-1.665×10-7×νdG2 3 +5.213×10-5×νdG2 2-5.656×10-3×νdG2+0.7268)<0.1000 0.05<BF / IH<2.20 An optical system characterized in that the following condition is satisfied:

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 on the most object side of the first lens group 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. 6. 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.

7. 7. The optical system according to claim 6, wherein the second lens group is made up of one negative lens.

8. 8. The optical system according to claim 1, wherein the first lens group does not move during focusing.

9. The third lens group includes at least one positive lens and at least one negative lens. When the focal length of the positive lens arranged closest to the image among the positive lenses included in the third lens group is fGkp, and the focal length of the negative lens arranged closest to the image among the negative lenses included in the third lens group is fGkn, 1.02<|fGkp / fGkn|<2.50 9. The optical system according to claim 1, wherein the following condition is satisfied:

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

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

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

Images