Optical system and imaging device having the same

Abstract

To provide a compact and light-weight optical system, which has high optical performance in which aberration variation by focusing is suppressed while enabling obtaining high shooting magnification when shooting the closest distance, in a wide angle lens.SOLUTION: An optical system L0 comprises a first lens group L1 having negative refractive power, and a second lens group L2 having positive refractive power, in order from an object side to an image side. In focusing from an infinite distance to the closest distance, the first lens group is fixed, and the second lens group moves. The first lens group includes two negative lenses continuously arranged in order from the side closest to an object side to the side closest to an image side. Thickness D1, on an optical axis, of the first lens group, thickness D2, on the optical axis, of the second lens group, a focal distance f1 of the first lens group, a focal distance f2 of the second lens group, a distance PD, on the optical axis, from a position of aperture diaphragm to an image surface in focusing the infinite distance, and an entire optical length LD of the optical system in focusing the infinite distance satisfy predetermined conditions.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an optical system suitable for digital video cameras, digital still cameras, broadcast cameras, cameras for silver halide film, surveillance cameras, and the like. [Background technology]

[0002] In recent years, there has been a demand for wide-angle lenses used in imaging devices that are compact overall yet capable of achieving high magnification when photographing at the closest distance, as well as lenses that have high optical performance when focusing from infinity to the closest distance.

[0003] In a wide-angle lens, in order to obtain a high magnification when shooting at the closest distance, it is necessary to increase the amount of movement of the focus lens group, which makes it difficult to reduce the size of the entire lens. In order to reduce the amount of movement of the focus lens group, it is necessary to increase the refractive power of the focus lens group, but this makes it difficult to maintain high optical performance when focusing from infinity to the closest distance. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2020 / 213337 [Patent Document 2] International Publication No. 2021 / 117429 Summary of the Invention [Problem to be solved by the invention]

[0005] Patent Document 1 discloses an optical system that has, arranged in order from the object side to the image side, a first lens group with positive refractive power and a second lens group with positive refractive power, and that moves during focusing. Because the refractive power of the second lens group is weaker than that of the first lens group, the amount of movement of the second lens group during focusing is large, and in order to obtain a high imaging magnification when shooting at the closest distance, the lens must be large.

[0006] Patent Document 2 discloses an optical system that consists of a front group with negative refractive power and a rear group with positive refractive power, arranged in that order from the object side to the image side, in which multiple single lenses in the rear group move during focusing. When taking photographs at the closest distances, which requires high magnification, it is difficult to correct various aberrations by moving multiple single lenses, and high optical performance cannot be achieved.

[0007] In order to realize a wide-angle lens system that is small and lightweight, provides high magnification at the closest focusing distance, and has high optical performance with reduced aberration fluctuations due to focusing, it is important to optimize the refractive power and thickness of the focus lens group and the lens group located on the object side of the focus lens group.

[0008] The present invention provides an optical system with a wide-angle lens that is small and lightweight, can obtain a high imaging magnification when photographing at the closest distance, and has high optical performance with reduced aberration fluctuation due to focusing, and an imaging device having the same. [Means for solving the problem]

[0009] An optical system according to one aspect of the present invention has a first lens group having negative refractive power and a second lens group having positive refractive power, arranged in that order from the object side to the image side, and the spacing between adjacent lens groups changes during focusing. During focusing from infinity to the closest point, the first lens group is fixed and the second lens group moves. The first lens group includes two negative lenses arranged consecutively in that order from the most object side to the image side. The optical system has an axial thickness of the first lens group of D1, an axial thickness of the second lens group of D2, a focal length of the first lens group of f1, a focal length of the second lens group of f2, a distance on the optical axis from the position of the aperture stop to the image plane when the optical system is focused at infinity of PD, and an overall optical length of the optical system when the optical system is focused at infinity of LD. The air-equivalent length of the distance on the optical axis from the image-side lens surface of the lens located closest to the image side to the image plane when the optical system is focused at infinity is sk When 0.6 <D1 / D2<2.0 -5.2 <f1 / f2<0.0 0.55 <PD / LD<0.80 1.5 <D2 / sk<4.5 The following condition is satisfied.

[0010] Other objects and features of the present invention will be described in the following embodiments. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide a wide-angle lens optical system that is small and lightweight, is capable of obtaining a high magnification when photographing at the closest distance, and has high optical performance with reduced aberration fluctuations due to focusing. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 2 is a cross-sectional view of the optical system of Example 1 when focused at infinity. [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 the optical system of Example 2 when focused at infinity. [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 the optical system of Example 3 when focused at infinity. [Figure 6] 10A and 10B are aberration diagrams of the optical system of Example 3 when focused at infinity. [Figure 7] FIG. 10 is a cross-sectional view of the optical system of Example 4 when focused at infinity. [Figure 8] 10A and 10B are aberration diagrams of the optical system of Example 4 when focused at infinity. [Figure 9] FIG. 1 is a schematic diagram of an imaging device. DETAILED DESCRIPTION OF THE INVENTION

[0013] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the optical system and the imaging device having the same according to the present invention will be described with reference to the accompanying drawings.

[0014] 1, 3, 5, and 7 are cross-sectional views of the optical system L0 of Examples 1 to 4 when focused at infinity. The optical system L0 of each Example is an optical system used in imaging devices such as digital video cameras, digital still cameras, broadcast cameras, silver halide film cameras, and surveillance cameras.

[0015] In each lens cross-sectional view, the left side is the object side and the right side is the image side. The optical system L0 in each embodiment is configured with multiple lens groups. In this specification, a lens group refers to a group of lenses that move or remain stationary as a unit during focusing. That is, in the optical system L0 in each embodiment, the spacing between adjacent lens groups changes during focusing from infinity to a close distance. Note that a lens group may be composed of a single lens or multiple lenses. The lens group may also include an aperture stop.

[0016] In each lens cross-sectional view, Li represents the i-th lens group (i is a natural number) counting from the object side among the lens groups included in the optical system L0.

[0017] Furthermore, SP denotes an aperture stop. IP denotes an image plane, on which the imaging surface of a solid-state imaging element (photoelectric conversion element) such as a CCD sensor or CMOS sensor is placed when the optical system L0 of each embodiment is used as the imaging optical system of a digital still camera or digital video camera. When the optical system L0 of each embodiment is used as the imaging optical system of a silver halide film camera, a photosensitive surface corresponding to the film surface is placed on the image plane IP.

[0018] Furthermore, the optical system L0 of each embodiment is configured so that at least the second lens unit L2 is moved during focusing.

[0019] 2, 4, 6, and 8 are aberration diagrams of the optical systems L0 of Examples 1 to 4 when focused at infinity.

[0020] In the spherical aberration diagram, Fno is the F-number, and shows the amount of spherical aberration for the d-line (wavelength 587.6 nm) and g-line (wavelength 435.8 nm). In the astigmatism diagram, ΔS shows the amount of astigmatism on the sagittal image plane, and ΔM shows the amount of astigmatism on the meridional image plane. In the distortion diagram, the amount of distortion for the d-line is shown. In the chromatic aberration diagram, the amount of chromatic aberration for the g-line is shown. ω is the half angle of view (°).

[0021] Next, the characteristic configuration of the optical system L0 of each embodiment will be described.

[0022] The optical system L0 in each embodiment has a first lens group L1 with negative refractive power and a second lens group L2 with positive refractive power, arranged in that order from the object side to the image side. The optical system L0 in each embodiment is an optical system in which the spacing between adjacent lens groups changes during focusing. During focusing from infinity to the closest distance, the first lens group L1 does not move (is fixed), and the second lens group L2 moves. The first lens group L1 includes two lenses with negative refractive power (negative lenses) arranged consecutively in that order from the closest object side to the image side.

[0023] Furthermore, the optical system L0 of each embodiment satisfies the following conditional expressions (1) to (3).

[0024] 0.6 <D1 / D2<2.0 ···(1) -5.2 <f1 / f2<0.0 ···(2) 0.55 <PD / LD<0.80 ···(3) Here, D1 is the axial thickness of the first lens group L1. D2 is the axial thickness of the second lens group L2. The axial thickness of a lens group is the axial distance from the lens surface closest to the object to the lens surface closest to the image. f1 is the focal length of the first lens group L1. f2 is the focal length of the second lens group L2. PD is the axial distance from the position of the aperture stop SP to the image plane IP when the optical system L0 is focused at infinity. LD is the total optical length (total lens length) of the optical system L0 when the optical system L0 is focused at infinity.

[0025] Conditional formula (1) defines the ratio between the thickness of the first lens group L1 and the thickness of the second lens group L2. In a wide-angle lens, by appropriately setting the thickness of the lens group that remains fixed during focusing and the thickness of the focus lens group that moves during focusing, it is possible to achieve both high optical performance and an even wider angle of view. Exceeding the upper limit of conditional formula (1) strengthens the positive refractive power of the lens group positioned closest to the image side in optical system L0, thereby lengthening the exit pupil and reducing shading and other effects. However, because the refractive power of the lens group positioned closest to the image side is strong, this is advantageous for reducing the overall lens length, but it also worsens field curvature aberrations, which are primarily caused by off-axial light rays. Falling below the lower limit of conditional formula (1) strengthens the overall lens length, but worsens distortion and lateral chromatic aberrations, which are caused by off-axial light rays.

[0026] Conditional expression (2) defines the ratio between the focal length of the first lens group L1 and the focal length of the second lens group L2. By optimizing the focal lengths of the focus lens group and the lens group located closer to the object than the focus lens group, it becomes possible for light rays incident on the focus lens group to be incident at an angle nearly parallel to the optical axis (afocal light rays). This suppresses aberration fluctuations during focusing, allowing the optical system L0 to be compact and achieving high magnification when shooting at the closest distance. If the upper limit of conditional expression (2) is exceeded, the focal length of the first lens group L1 will be positive, which is advantageous for reducing the overall length but makes it difficult to achieve a wide angle of view for the entire lens system. If the lower limit of conditional expression (2) is exceeded, the focal length of the first lens group L1 will be long and its refractive power will be weak, which is advantageous for suppressing aberration fluctuations during focusing but results in an increase in the size of the front lens element.

[0027] Conditional expression (3) defines the ratio of the distance PD on the optical axis from the position of the aperture stop SP to the image plane IP when the optical system L0 is focused at infinity to the total optical length LD of the optical system L0. By appropriately positioning the aperture stop SP, it is possible to achieve a compact optical system L0. If the upper limit of conditional expression (3) is exceeded, the distance from the aperture stop SP to the image plane IP becomes longer than the total optical length, and the aperture stop SP must be positioned closer to the object than the lens closest to the object. This makes it difficult to position the lenses in a way that is suitable for a wide-angle lens. If the lower limit of conditional expression (3) is not met, the back focal length can be shortened, which is advantageous for reducing the total length, but the front lens element becomes larger.

[0028] Furthermore, it is more preferable that the numerical ranges of the conditional expressions (1) to (3) be within the ranges of the following conditional expressions (1a) to (3a).

[0029] 0.75 <D1 / D2<1.80 ···(1a) -5.0 <f1 / f2<0.0 ···(2a) 0.56 <PD / LD<0.70 ···(3a) It is more preferable that the numerical ranges of the conditional expressions (1) to (3) be within the ranges of the following conditional expressions (1b) to (3b).

[0030] 0.9 <D1 / D2<1.5 ···(1b) -4.8 <f1 / f2<0.0 ···(2b) 0.57 <PD / LD<0.66 ···(3b) As described above, the optical system L0 of each embodiment has the above configuration and satisfies conditional expressions (1) to (3), thereby realizing a wide-angle lens that is small and lightweight, can obtain a high imaging magnification when photographing at the closest distance, and has high optical performance with reduced aberration fluctuations due to focusing.

[0031] Next, conditions that are preferably satisfied in the optical system L0 of each embodiment will be described. It is preferable that the optical system L0 of each embodiment satisfy one or more of the following conditional expressions (4) to (16).

[0032] 0.0 <f1n2 / f1<0.4 ···(4) 0.0 <f1n3 / f1<0.3 ···(5) 1.5 <D1 / sk<5.0 ···(6) 1.5 <D2 / sk<4.5 ···(7) 0.7 <ESinf<1.4 ···(8) 0.0 <f2 / f3<0.5 ···(9) -15 <f1 / f<-3 ···(10) 2.0 <f2 / f<4.0 ···(11) 0.20<βmod (12) 90°<2ω<180° (13) -5.0 <R2f / R2r<2.0 ···(14) 0.05 <L23 / LD<0.20 ···(15) 0.05 <sk / LD<0.22 ···(16) Here, f1n2 is the composite focal length of two negative lenses in the first lens group L1 when the two negative lenses are arranged consecutively in order from the most object side to the image side. f1n3 is the composite focal length of three negative lenses in the first lens group L1 when the three negative lenses are arranged consecutively in order from the most object side to the image side. sk is the air-equivalent length (back focus) of the distance on the optical axis from the image-side lens surface of the lens arranged closest to the image side to the image plane IP when the optical system L0 is focused at infinity. ESinf is the focus sensitivity of the second lens group L2 when the optical system L0 is focused at infinity. The focus sensitivity ESi of an arbitrary lens group Li is given by ESi=(1-βi 2 )×βr 2 is defined as follows. f3 is the focal length of the third lens group L3, when the third lens group L3 is a lens group including all lenses arranged closer to the image side than the second lens group L2. f is the focal length of the optical system L0. βmod is the imaging magnification when the optical system L0 is focused at the closest distance. ω is the half angle of view (°) of the optical system L0. R2f is the radius of curvature of the object-side lens surface of the lens arranged closest to the object in the second lens group L2. R2r is the radius of curvature of the image-side lens surface of the lens arranged closest to the image in the second lens group L2. L23 is the distance on the optical axis from the lens surface closest to the image in the second lens group L2 to the lens surface closest to the object in the third lens group L3 (the distance between the second lens group L2 and the third lens group L3).

[0033] Conditional expression (4) defines the ratio of the combined focal length f1n2 of the two negative lenses to the focal length f1 of the first lens unit L1. If the upper limit of conditional expression (4) is exceeded, the negative refractive power of the two negative lenses relative to the refractive power of the first lens unit L1 becomes weak, making it impossible to bend off-axis rays, making it difficult to achieve a wide angle of view and resulting in an increase in the overall size of the lens, which is undesirable. If the lower limit of conditional expression (4) is exceeded, the negative refractive power of the two negative lenses relative to the refractive power of the first lens unit L1 becomes strong, which is advantageous for achieving a wide angle of view, but is undesirable because it worsens distortion and chromatic aberration of magnification caused by off-axis rays.

[0034] Conditional expression (5) defines the ratio of the combined focal length f1n3 of the three negative lenses to the focal length f1 of the first lens unit L1. If the upper limit of conditional expression (5) is exceeded, the negative refractive power of the three negative lenses relative to the refractive power of the first lens unit L1 becomes weak, making it impossible to bend off-axis light rays, making it difficult to achieve a wide angle of view and resulting in an increase in the overall size of the lens, which is undesirable. If the lower limit of conditional expression (5) is exceeded, the negative refractive power of the three negative lenses relative to the refractive power of the first lens unit L1 becomes strong, which is advantageous for achieving a wide angle of view, but is undesirable because it worsens distortion and chromatic aberration of magnification caused by off-axis light rays.

[0035] Conditional expression (6) defines the ratio between the thickness D1 of the first lens unit L1 and the back focal length sk. If the upper limit of conditional expression (6) is exceeded, the thickness D1 of the first lens unit L1 increases, making it impossible to position a lens close to the image sensor. This is advantageous for improving field curvature and lateral chromatic aberration, but undesirably leads to an increase in the overall size of the lens. If the lower limit of conditional expression (6) is exceeded, the thickness D1 of the first lens unit L1 decreases, which is advantageous for making the entire lens more compact, but undesirably makes it difficult to improve field curvature and lateral chromatic aberration.

[0036] Conditional expression (7) defines the ratio between the thickness D2 of the second lens unit L2 and the back focal length sk. If the upper limit of conditional expression (7) is exceeded, the thickness D2 of the second lens unit L2 increases, which is advantageous for suppressing fluctuations in various aberrations due to focusing, but this undesirably results in an increase in the size of the second lens unit L2, which is the focus lens unit. If the lower limit of conditional expression (7) is exceeded, the thickness D2 of the second lens unit L2 decreases, which reduces the size of the second lens unit L2, which is the focus lens unit, leading to an increase in focusing speed, but this undesirably results in an increase in fluctuations in various aberrations due to focusing.

[0037] Conditional expression (8) defines the focus sensitivity ESinf of the second lens group L2 when the optical system L0 is focused at infinity. Exceeding the upper limit of conditional expression (8) is undesirable because the change in the angle of view relative to the amount of movement of the second lens group L2, which is the focus lens group, during focusing becomes large. It is also undesirable because it becomes difficult to suppress fluctuations in spherical aberration and curvature of field during focusing. Falling below the lower limit of conditional expression (8) makes it easier to suppress changes in spherical aberration and curvature of field during focusing, but it is undesirable because the amount of movement of the second lens group L2, which is the focus lens group, during focusing increases, resulting in an increase in the overall lens length.

[0038] Conditional expression (9) defines the ratio of the focal length f2 of the second lens group L2 to the focal length f3 of the third lens group L3. Exceeding the upper limit of conditional expression (9) makes the ratio of the refractive power of the second lens group L2 to the refractive power of the third lens group L3 approach 1, which is advantageous for improving spherical aberration and curvature of field when the optical system L0 is focused at infinity, leading to higher image quality. However, this weakens the refractive power of the second lens group L2, lengthening the focus movement distance during focusing and increasing the overall size of the lens, which is undesirable. Falling below the lower limit of conditional expression (9) weakens the refractive power of the third lens group L3 relative to the second lens group L2, making it difficult for the third lens group L3 to bend off-axial rays. A larger angle of incidence of off-axial rays on the imaging surface makes it difficult to ensure an exit pupil, which increases color shading on the imaging surface and undesirably degrades image quality.

[0039] Conditional expression (10) defines the ratio of the focal length f1 of the first lens unit L1 to the focal length f of the optical system L0. If the upper limit of conditional expression (10) is exceeded, the focal length of the first lens unit L1 becomes short, which is advantageous for reducing the size of the entire lens system, but is undesirable because it worsens curvature of field and chromatic aberration of magnification. If the lower limit of conditional expression (10) is exceeded, the focal length of the first lens unit L1 becomes long, which is advantageous for correcting curvature of field and chromatic aberration of magnification, but is undesirable because it makes it difficult to reduce the size of the entire lens system.

[0040] Conditional expression (11) defines the ratio of the focal length f2 of the second lens group L2 to the focal length f of the optical system L0. Exceeding the upper limit of conditional expression (11) weakens the refractive power of the second lens group L2, reducing fluctuations in aberrations caused by focusing, which is advantageous for improving image quality. However, this undesirably increases the amount of focus movement required during focusing, resulting in an increase in the overall size of the lens. Falling below the lower limit of conditional expression (11), the refractive power of the second lens group L2 increases, reducing the amount of focus movement required during focusing, which is advantageous for reducing the overall size of the lens and increasing the magnification when shooting at the closest distance. However, this undesirably increases fluctuations in aberrations caused by focusing.

[0041] Conditional expression (12) defines the magnification βmod when the optical system L0 is focused at the closest distance. If the lower limit of conditional expression (12) is exceeded, it is not preferable because the magnification at the closest distance cannot be increased.

[0042] Conditional expression (13) defines the angle of view (°) of optical system L0. Exceeding the upper limit of conditional expression (13) makes it possible to take photographs with a wider angle of view than desired, which is undesirable because it results in the overall lens becoming larger. Falling below the lower limit of conditional expression (13) makes it difficult to achieve a wider angle of view, which is undesirable.

[0043] Conditional expression (14) defines the ratio between the radius of curvature R2f of the object-side lens surface of the lens located closest to the object in the second lens unit L2 and the radius of curvature R2r of the image-side lens surface of that lens. If the upper limit of conditional expression (14) is exceeded, the refractive power of the second lens unit L2 will be weak, which is advantageous for suppressing fluctuations in spherical aberration during focusing, but it will undesirably increase the overall lens length. If the lower limit of conditional expression (14) is exceeded, the refractive power of the second lens unit L2 will be strong, which is advantageous for reducing the overall lens length, but it will undesirably increase fluctuations in spherical aberration during focusing.

[0044] Conditional expression (15) defines the ratio of the distance L23 between the second lens group L2 and the third lens group L3 to the total optical length LD. Exceeding the upper limit of conditional expression (15) is advantageous because it allows the lens diameter of the second lens group L2 to be reduced and the weight of the second lens group L2, which serves as the focus lens group, to be reduced. However, this is undesirable because it becomes difficult to ensure the amount of movement of the second lens group L2 during focusing. Falling below the lower limit of conditional expression (15) allows the overall lens to be made more compact, but is undesirable because it becomes difficult to arrange mechanical components such as motors required to move the second lens group L2 as the focus lens group.

[0045] Conditional expression (16) defines the ratio of the back focal length sk to the total optical length LD. If the upper limit of conditional expression (16) is exceeded, the back focal length sk increases, making it impossible to position the lens close to the image sensor, making it difficult to improve curvature of field and chromatic aberration of magnification, and as a result, resulting in poor image quality, which is undesirable. If the lower limit of conditional expression (16) is exceeded, the back focal length sk decreases, making it possible to position the lens closer to the image sensor, which is advantageous for improving curvature of field and chromatic aberration of magnification, but it is undesirable because it makes it difficult to position the shutter component, etc.

[0046] It is more preferable that the numerical ranges of the conditional expressions (4) to (16) be within the ranges of the following conditional expressions (4a) to (16a).

[0047] 0.05 <f1n2 / f1<0.35 ···(4a) 0.00 <f1n3 / f1<0.25 ···(5a) 1.7 <D1 / sk<4.5 ···(6a) 1.7 <D2 / sk<4.0 ···(7a) 0.75 <ESinf<1.20 ···(8a) 0.05 <f2 / f3<0.40 ···(9a) -13 <f1 / f<-4 ···(10a) 2.2 <f2 / f<3.3 ···(11a) 0.22<βmod (12a) 95°<2ω<180° (13a) -4.0 <R2f / R2r<1.5 ···(14a) 0.06 <L23 / LD<0.15 ···(15a) 0.08 <sk / LD<0.20 ···(16a) It is more preferable that the numerical ranges of the conditional expressions (4) to (16) be within the ranges of the following conditional expressions (4b) to (16b).

[0048] 0.08 <f1n2 / f1<0.30 ···(4b) 0.0 <f1n3 / f1<0.2 ···(5b) 2.0 <D1 / sk<4.0 ···(6b) 2.0 <D2 / sk<3.5 ···(7b) 0.78 <ESinf<1.05 ···(8b) 0.10 <f2 / f3<0.35 ···(9b) -11 <f1 / f<-5 ···(10b) 2.4 <f2 / f<2.8 ···(11b) 0.24<βmod (12b) 100°<2ω<180° (13b) -3.0 <R2f / R2r<1.3 ···(14b) 0.065 <L23 / LD<0.100 ···(15b) 0.10 <sk / LD<0.16 ···(16b) Next, the configuration that is preferably satisfied in the optical system L0 of each embodiment will be described.

[0049] In the optical system L0 of each embodiment, it is preferable that the third lens unit L3 is fixed during focusing from infinity to the closest distance. Furthermore, it is preferable that only one lens unit moves during focusing from infinity to the closest distance. This makes it possible to reduce the number of parts, such as motors, required to move the focus unit, thereby making it possible to reduce weight.

[0050] In the optical system L0 of each embodiment, it is preferable that the first lens unit L1 has two lenses with positive refractive power (positive lenses), which makes it possible to correct both the chromatic aberration of magnification and the axial chromatic aberration that occur in the first lens unit L1.

[0051] Preferably, the first lens group L1 includes three negative lenses arranged consecutively from the object side to the image side. It is even more preferable that the first lens group L1 includes four negative lenses arranged consecutively from the object side to the image side. This allows for both correction of chromatic aberration of magnification that occurs in the first lens group L1 and a wider angle of view.

[0052] In addition, it is preferable that the lens closest to the image side in the first lens group L1 has positive refractive power and that the image-side lens surface of this lens is convex toward the image side, which makes it possible to correct spherical aberration while also reducing the overall lens length.

[0053] Preferably, the first lens group L1 includes a cemented lens composed of a lens with positive refractive power and a lens with negative refractive power. More preferably, the first lens group L1 includes two cemented lenses composed of a lens with positive refractive power and a lens with negative refractive power. This allows for correction of axial chromatic aberration and chromatic aberration of magnification.

[0054] It is also preferable that the first lens group L1 includes an aspherical lens. It is even more preferable that the aspherical lens is disposed closest to the object in the first lens group L1. This makes it possible to appropriately correct fluctuations in field curvature caused by focusing, which are primarily caused by off-axis rays.

[0055] It is also preferable that the second lens group L2 includes a cemented lens composed of a lens with positive refractive power and a lens with negative refractive power. It is even more preferable that the second lens group L2 includes two cemented lenses composed of a lens with positive refractive power and a lens with negative refractive power. This makes it possible to suppress fluctuations in axial chromatic aberration and chromatic aberration of magnification during focusing.

[0056] It is also preferable that the third lens group L3 is composed of one lens (single lens) with positive refractive power, which makes it possible to secure an exit pupil while reducing the weight of the entire lens.

[0057] Furthermore, when the image blur correction group is moved in a direction perpendicular to the optical axis to correct the image blur, some lenses in the optical system L0 may be moved in a direction perpendicular to the optical axis.

[0058] Next, the optical system L0 of each embodiment will be described in detail.

[0059] The optical system L0 of the first embodiment is made up of a first lens unit L1, a second lens unit L2, and a third lens unit L3, arranged in this order from the object side to the image side.

[0060] The lenses that make up the first lens group L1, in order from the object side to the image side, are a negative aspherical lens, a negative lens, a negative lens, a positive lens, and a cemented lens consisting of a negative lens and a positive lens. The aperture stop SP is located closest to the object in the second lens group L2. The lenses that make up the second lens group L2, in order from the object side to the image side, are a cemented lens consisting of a positive lens and a negative lens, a positive lens, a cemented lens consisting of a negative lens and a positive lens, and a negative aspherical lens. The third lens group L3 is composed of a positive single lens.

[0061] The optical system L0 of the second embodiment is made up of a first lens unit L1, a second lens unit L2, and a third lens unit L3, arranged in this order from the object side to the image side.

[0062] The lenses that make up the first lens group L1, in order from the object side to the image side, are a negative aspherical lens, a negative lens, a negative lens, a cemented lens of a negative lens and a positive lens, and a cemented lens of a negative lens and a positive lens. The aperture stop SP is located closest to the object in the second lens group L2. The lenses that make up the second lens group L2, in order from the object side to the image side, are a cemented lens of a positive lens and a negative lens, a cemented lens of a positive lens and a negative lens, a negative lens, a positive lens, and a negative aspherical lens. The third lens group L3 is composed of a positive single lens.

[0063] The optical system L0 of the third embodiment is composed of a first lens unit L1, a second lens unit L2, and a third lens unit L3, arranged in this order from the object side to the image side.

[0064] The lenses that make up the first lens group L1, in order from the object side to the image side, are a negative aspherical lens, a negative lens, a negative lens, a negative lens, a negative lens, a positive lens, and a cemented lens consisting of a negative lens and a positive lens. The aperture stop SP is located closest to the object in the second lens group L2. The lenses that make up the second lens group L2, in order from the object side to the image side, are a negative lens, a cemented lens consisting of a positive lens and a negative lens, a positive lens, a cemented lens consisting of a positive lens and a negative lens, a cemented lens consisting of a negative lens and a positive lens, and a negative aspherical lens. The third lens group L3 is composed of a positive single lens.

[0065] The optical system L0 of the fourth embodiment is made up of a first lens unit L1 and a second lens unit L2, which are arranged in this order from the object side to the image side.

[0066] The lenses that make up the first lens group L1, in order from the object side to the image side, are a negative aspherical lens, a negative lens, a negative lens, a positive lens, and a cemented lens of a negative lens and a positive lens. The aperture stop SP is located closest to the object in the second lens group L2. The lenses that make up the second lens group L2, in order from the object side to the image side, are a cemented lens of a negative lens and a positive lens, a positive lens, a cemented lens of a positive lens and a negative lens, a cemented lens of a negative lens and a positive lens, and a negative aspherical lens.

[0067] Numerical Examples 1 to 4 corresponding to Examples 1 to 4, respectively, are shown below.

[0068] In the surface data of each numerical example, r represents the radius of curvature of each optical surface, and d (mm) represents the axial spacing (distance on the optical axis) between the mth surface and the (m+1)th surface. Here, m is the surface number counted from the light incident side. Also, nd represents the refractive index of each optical element with respect to the d-line, and vd represents the Abbe number of the optical element. Note that the Abbe number vd of a certain material is given by the following when the refractive indices at the d-line (587.6 nm), F-line (486.1 nm), and C-line (656.3 nm) of the Fraunhofer lines are Nd, NF, and NC, respectively: νd=(Nd-1) / (NF-NC) It is expressed as:

[0069] In each numerical example, d, focal length (mm), F-number, and half angle of view (°) are all values ​​when the optical system of each example is focused on an object at infinity. "Back focus (BF)" is the distance on the optical axis from the final lens surface (the lens surface closest to the image) to the paraxial image plane, expressed as an air-equivalent length. "Total lens length" is the distance on the optical axis from the forefront lens surface (the lens surface closest to the object) to the final lens surface plus the back focus. "Lens group" is not limited to cases where it is composed of multiple lenses, but also includes cases where it is composed of a single lens.

[0070] If the optical surface is aspherical, an asterisk (*) is added to the right of the surface number. The aspherical shape is expressed as follows: X is the displacement from the vertex of the surface in the optical axis direction, h is the height from the optical axis in the direction perpendicular to the optical axis, R is the paraxial radius of curvature, k is the conic constant, and A4, A6, A8, A10, and A12 are the aspherical coefficients of each order. x=(h 2 / R) / [1+{1-(1+k)(h / R) 2} 1 / 2 +A4×h 4 +A6×h 6 +A8×h 8 +A10×h 10 +A12×h12 In addition, "e±XX" in each aspherical coefficient is "×10± XX " means.

[0071] [Numerical Example 1] Unit: mm Surface Data Surface number rd nd νd 1* 80.171 1.60 1.85400 40.4 2* 17.429 12.13 3 28.322 1.60 1.49700 81.5 4 14.876 5.67 5 170.561 1.30 1.49700 81.5 6 26.221 0.37 7 30.433 4.73 1.59551 39.2 8 -51.651 2.35 9 -20.166 1.20 1.49700 81.5 10 17.569 8.71 1.57135 53.0 11 -24.290 (variable) 12 (Aperture) ∞ 1.88 13 67.872 3.30 1.49700 81.5 14 -17.690 1.00 1.92119 24.0 15 -28.577 8.23 16 20.132 6.57 1.49700 81.5 17 -65.823 0.08 18 38.603 1.00 1.77250 49.6 19 11.923 4.76 1.49700 81.5 20 27.088 4.29 21* -20.649 1.80 1.85400 40.4 22* -25.792 (variable) 23 -65.506 4.31 1.48749 70.2 24 -29.600 (variable) Image plane ∞ Aspheric data Front page K = 0.00000e+00 A 4=-4.29349e-07 A 6= 1.28741e-08 A 8=-2.67886e-11 A10= 2.93208e-14 2nd side K = 0.00000e+00 A 4=-1.34999e-05 A 6=-4.37562e-08 A 8= 1.81207e-10 A10=-7.75902e-13 Page 21 K = 0.00000e+00 A 4= 2.78062e-05 A 6= 1.29191e-06 A 8=-1.62457e-08 A10= 5.22894e-11 Page 22 K = 0.00000e+00 A 4= 6.66745e-05 A 6= 1.13310e-06 A 8=-1.14081e-08 A10= 3.72567e-11 Various data Focal length 14.83 F-number 2.91 Half angle of view (°) 52.03 Image height 19.00 Lens length 105.19 BF 10.83 Magnification ∞ -0.5 d11 10.22 0.56 d22 7.25 16.92 d24 10.83 10.83 Lens group data Group starting plane focal length 1 1 -80.00 2 12 36.66 3 23 106.58 [Numerical Example 2] Unit: mm Surface Data Surface number rd nd νd 1* 51.981 2.20 1.85400 40.4 2* 20.569 8.08 3 36.511 1.80 1.43875 94.7 4 15.979 4.55 5 24.967 1.80 1.49700 81.5 6 16.463 10.13 7 -17.964 1.20 1.86966 20.0 8 368.738 5.03 1.83481 42.7 9 -22.155 0.20 10 273.200 1.00 1.49700 81.5 11 31.498 5.17 1.92286 18.9 12 -176.232 (variable) 13 (Aperture) ∞ 1.88 14 34.652 7.62 1.49700 81.5 15 -15.895 1.00 1.89190 37.1 16 -23.257 1.60 17 -64.358 5.80 1.52841 76.5 18 -13.659 1.20 1.83481 42.7 19 -18.337 0.50 20 -22.096 1.20 1.90366 31.3 21 315.102 0.50 22 28.758 7.76 1.52841 76.5 23 -30.985 7.03 24* -42.698 2.00 1.85400 40.4 25* -61.258 (variable) 26 -35.535 2.32 1.48749 70.2 27 -29.600 (variable) Image plane ∞ Aspheric data Front page K = 0.00000e+00 A 4= 2.73272e-05 A 6=-7.46033e-08 A 8= 1.09580e-10 A10=-5.39795e-14 2nd side K = 0.00000e+00 A 4= 2.55638e-05 A 6=-1.22607e-09 A 8=-3.79502e-10 A10= 8.88604e-13 Page 24 K = 0.00000e+00 A 4=-1.02089e-04 A 6= 4.45475e-07 A 8= 2.57836e-10 A10=-4.84481e-12 Page 25 K = 0.00000e+00 A 4=-6.24451e-05 A 6= 4.90597e-07 A 8=-1.05304e-10 A10=-2.55556e-12 Various data Focal length 14.70 F-number 2.06 Half angle of view (°) 52.27 Image height 19.00 Lens total length 110.00 BF 12.16 Magnification ∞ -0.25 d12 9.01 5.14 d25 7.25 11.13 d27 12.16 12.16 Lens group data Group starting plane focal length 1 1 -150.00 2 13 37.22 3 26 322.33 [Numerical Example 3] Unit: mm Surface Data Surface number rd nd νd 1* 46.326 1.60 1.85150 40.8 2* 14.244 5.61 3 26.949 1.60 1.43875 94.7 4 12.294 4.46 5 27.129 1.20 1.43875 94.7 6 13.975 2.94 7 164.743 1.20 1.49700 81.5 8 23.325 0.26 9 27.563 3.77 1.59270 35.3 10 -36.572 0.91 11 -21.172 0.80 1.49700 81.5 12 10.946 7.09 1.56384 60.7 13 -20.157 (variable) 14 (Aperture) ∞ 1.50 15 -23.993 1.00 1.89286 20.4 16 -91.684 1.50 17 21.948 6.88 1.49700 81.5 18 -11.764 0.80 1.95375 32.3 19 -19.425 1.00 20 69.883 2.40 1.98612 16.5 21 -62.856 0.10 22 27.517 8.18 1.59282 68.6 23 -12.806 1.00 2.00100 29.1 24 -18.451 0.50 25 -22.502 1.00 1.95375 32.3 26 16.604 4.93 1.49700 81.5 27 -41.599 1.00 28* -15.160 1.80 1.85400 40.4 29* -19.821 (variable) 30 -75.683 3.84 1.48749 70.2 31 -29.600 (variable) Image plane ∞ Aspheric data Front page K = 0.00000e+00 A 4= 1.89838e-05 A 6=-4.59219e-08 A 8= 1.01446e-10 A10=-6.52209e-14 2nd side K = 0.00000e+00 A 4= 2.09660e-06 A 6=-3.44717e-08 A 8=-6.81241e-11 A10=-4.12512e-13 Page 28 K = 0.00000e+00 A 4= 1.79358e-04 A 6= 1.23745e-06 A 8=-2.96566e-08 A10= 1.24751e-10 Page 29 K = 0.00000e+00 A 4= 2.04257e-04 A 6= 1.28357e-06 A 8=-2.24094e-08 A10= 8.78005e-11 Various data Focal length 12.47 F-number 2.83 Half angle of view (°) 56.72 Image height 19.00 Lens total length 90.60 BF 10.19 Magnification ∞ -0.25 d13 4.31 0.35 d29 7.25 11.21 d31 10.19 10.19 Lens group data Group starting plane focal length 1 1 -78.38 2 14 31.44 3 30 97.07 [Numerical Example 4] Unit: mm Surface Data Surface number rd nd νd 1* 49.186 1.60 1.85400 40.4 2* 14.646 6.53 3 36.397 1.60 1.43875 94.7 4 13.270 5.45 5 95.887 1.20 1.49700 81.5 6 20.374 1.90 7 44.748 3.25 1.83400 37.3 8 -69.471 7.00 9 -24.900 1.00 1.48749 70.2 10 13.067 6.82 1.51823 58.9 11 -18.928 (variable) 12 (Aperture) ∞ 1.99 13 28.657 9.27 1.52841 76.5 14 -12.183 0.80 1.87070 40.7 15 -21.540 1.00 16 33.419 4.86 1.49700 81.5 17 -19.286 0.49 18 -23.625 6.16 1.85478 24.8 19 -11.418 0.96 1.95375 32.3 20 -46.181 0.50 21 -94.254 0.94 1.83481 42.7 22 12.905 8.06 1.52841 76.5 23 -151.530 2.96 24* -46.831 2.00 1.85400 40.4 25* -42.786 (variable) Image plane ∞ Aspheric data Front page K = 0.00000e+00 A 4= 9.55905e-06 A 6=-1.43725e-08 A 8= 3.98210e-11 A10=-2.50400e-14 2nd side K = 0.00000e+00 A 4= 8.22924e-08 A 6=-1.60691e-08 A 8=-7.30553e-11 A10= 7.34071e-14 Page 24 K = 0.00000e+00 A 4= 1.00010e-05 A 6= 6.17869e-07 A 8=-6.18367e-09 A10= 1.91334e-11 Page 25 K = 0.00000e+00 A 4= 3.26827e-05 A 6= 5.50249e-07 A 8=-4.73191e-09 A10= 1.16696e-11 Various data Focal length 15.00 F-number 2.83 Half angle of view (°) 51.72 Image height 19.00 Lens length 95.50 BF 14.12 Magnification ∞ -0.25 d11 5.05 1.23 d25 14.12 17.94 Lens group data Group starting plane focal length 1 1 -160.00 2 12 37.37 The various values ​​in each numerical example are summarized in Table 1 below.

[0072] [Table 1]

[0073] [Imaging device] Next, an embodiment of a digital still camera (imaging device) 10 that uses the optical system of the present invention as an imaging optical system will be described with reference to Fig. 9. In Fig. 9, 13 denotes a camera body, and 11 denotes an imaging optical system configured using any of the optical systems described in Examples 1 to 4. 12 denotes a solid-state imaging element (photoelectric conversion element) such as a CCD sensor or CMOS sensor that is built into the camera body 13 and receives and photoelectrically converts an optical image formed by the imaging optical system 11. The camera body 13 may be a so-called single-lens reflex camera that has a quick-turn mirror, or a so-called mirrorless camera that does not have a quick-turn mirror.

[0074] In this way, by applying the optical system of the present invention to an imaging device such as a digital still camera, an imaging device with a small lens can be obtained.

[0075] Although the preferred embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and various combinations, modifications, and alterations are possible within the scope of the gist of the present invention. [Explanation of symbols]

[0076] L0 optical system L1 First lens group L2 Second lens group

Claims

1. An optical system having a first lens group having a negative refractive power and a second lens group having a positive refractive power, which are arranged in this order from the object side to the image side, and in which the distance between adjacent lens groups changes during focusing, During focusing from infinity to the closest distance, the first lens group is fixed and the second lens group is moved, the first lens group includes two negative lenses arranged consecutively in order from the most object side to the image side, Let D1 be the thickness on the optical axis of the first lens group, D2 be the thickness on the optical axis of the second lens group, f1 be the focal length of the first lens group, f2 be the focal length of the second lens group, PD be the distance on the optical axis from the position of the aperture stop to the image plane when the optical system is focused at infinity, LD be the total optical length of the optical system when the optical system is focused at infinity, and sk be the air-equivalent length of the distance on the optical axis from the image-side lens surface of the lens located closest to the image to the image plane when the optical system is focused at infinity. 0.6<D1 / D2<2.0 -5.2<f1 / f2<0.0 0.55<PD / LD<0.80 1.5<D2 / sk<4.5 An optical system characterized by satisfying the following conditional expression:

2. When the composite focal length of the two negative lenses is f1n2, 0.0<f1n2 / f1<0.4 2. The optical system according to claim 1, wherein the following condition is satisfied:

3. the first lens group includes three negative lenses arranged consecutively in order from the most object side to the image side, When the composite focal length of the three negative lenses is f1n3, 0.0<f1n3 / f1<0.3 3. The optical system according to claim 1, wherein the following condition is satisfied:

4. 1.5<D1 / sk<5.0 4. The optical system according to claim 1, wherein the following condition is satisfied:

5. When the focus sensitivity of the second lens group when the optical system is focused at infinity is ESinf, 0.7<ESinf<1.4 5. The optical system according to claim 1, wherein the following condition is satisfied:

6. a third lens group arranged on the image side of the second lens group, When the focal length of the third lens group is f3, 0.0<f2 / f3<0.5 6. The optical system according to claim 1, wherein the following condition is satisfied:

7. An optical system having a first lens group with negative refractive power, a second lens group with positive refractive power, and a third lens group arranged in this order from the object side to the image side, wherein the spacing between adjacent lens groups changes during focusing, During focusing from infinity to the closest distance, the first lens group is fixed and the second lens group is moved, the first lens group includes two negative lenses arranged consecutively in order from the most object side to the image side, When the thickness of the first lens group on the optical axis is D1, the thickness of the second lens group on the optical axis is D2, the focal length of the first lens group is f1, the focal length of the second lens group is f2, the focal length of the third lens group is f3, the distance on the optical axis from the position of the aperture stop to the image plane when the optical system is focused at infinity is PD, and the total optical length of the optical system when the optical system is focused at infinity is LD, 0.6<D1 / D2<2.0 -5.2<f1 / f2<0.0 0.55<PD / LD<0.80 0.0<f2 / f3<0.5 An optical system characterized by satisfying the following conditional expression:

8. When the focal length of the optical system is f, -15<f1 / f<-3 8. The optical system according to claim 1, wherein the following condition is satisfied:

9. When the focal length of the optical system is f, 2.0<f2 / f<4.0 9. The optical system according to claim 1, wherein the following condition is satisfied:

10. When the imaging magnification of the optical system when the optical system is focused at the closest distance is β mod, 0.20<βmod 10. The optical system according to claim 1, wherein the following condition is satisfied:

11. An optical system having a first lens group with negative refractive power and a second lens group with positive refractive power, arranged in that order from the object side to the image side, in which the spacing between adjacent lens groups changes during focusing, During focusing from infinity to the closest distance, the first lens group is fixed and the second lens group is moved, the first lens group includes two negative lenses arranged consecutively in order from the most object side to the image side, When the thickness of the first lens group on the optical axis is D1, the thickness of the second lens group on the optical axis is D2, the focal length of the first lens group is f1, the focal length of the second lens group is f2, the distance on the optical axis from the position of the aperture stop to the image plane when the optical system is focused at infinity is PD, the total optical length of the optical system when the optical system is focused at infinity is LD, and the photographing magnification of the optical system when the optical system is focused at the minimum distance is βmod, 0.6<D1 / D2<2.0 -5.2<f1 / f2<0.0 0.55<PD / LD<0.80 0.20<βmod An optical system characterized by satisfying the following conditional expression:

12. When the half angle of view of the optical system is ω, 90°<2ω<180° 12. The optical system according to claim 1, wherein the following condition is satisfied:

13. When the radius of curvature of the object-side lens surface of the lens arranged closest to the object in the second lens group is R2f and the radius of curvature of the image-side lens surface of the lens arranged closest to the image in the second lens group is R2r, -5.0<R2f / R2r<2.0 13. The optical system according to claim 1, wherein the following condition is satisfied:

14. When the optical system is focused at infinity, the distance on the optical axis from the lens surface of the second lens group closest to the image side to the lens surface of the third lens group closest to the object side is denoted by L23. 0.05<L23 / LD<0.20 7. The optical system according to claim 6, wherein the following condition is satisfied:

15. 0.05<sk / LD<0.22 15. The optical system according to claim 1, wherein the following condition is satisfied:

16. 15. The optical system according to claim 6, wherein the third lens group is fixed during focusing from infinity to the closest distance.

17. 17. The optical system according to claim 1, wherein the first lens group includes two positive lenses.

18. 18. The optical system according to claim 1, wherein the first lens group includes four negative lenses arranged consecutively in order from the most object side to the image side.

19. 19. The optical system according to claim 1, wherein in the first lens group, the lens arranged closest to the image side has positive refractive power, and the image-side lens surface of the lens is convex toward the image side.

20. 20. The optical system according to claim 1, wherein the first lens group includes a cemented lens made up of a lens with positive refractive power and a lens with negative refractive power.

21. 21. The optical system according to claim 1, wherein the first lens group includes an aspherical lens.

22. 22. The optical system according to claim 21, wherein the aspherical lens is disposed closest to the object side in the first lens group.

23. 23. The optical system according to claim 1, wherein the second lens group includes a cemented lens made up of a lens with positive refractive power and a lens with negative refractive power.

24. 17. The optical system according to claim 6, wherein the third lens group is made up of a single lens having a positive refractive power.

25. 6. The optical system according to claim 1, wherein the optical system comprises the first lens group and the second lens group, arranged in this order from the object side to the image side.

26. 25. The optical system according to claim 1, wherein the optical system comprises the first lens group, the second lens group, and the third lens group, arranged in this order from the object side to the image side.

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

Images