Optical system and imaging device having the same

Abstract

To provide an optical system in which a focusable object distance is shortened while having high optical performance.SOLUTION: An optical system including, in order from an object side to an image side, a first lens group having a positive refractive power, a second lens group having a positive refractive power, and a third lens group, wherein, during focusing, the second lens group moves in an optical axis direction with respect to an image plane, the first lens group and the third lens group do not move with respect to the image plane, and the first lens group includes three negative lenses that are disposed consecutively in the optical axis direction on a side closest to the object, where f represents a focal distance of the entire optical system, sk represents an air-equivalent back focal distance when focusing is performed at infinity, and f2 represents a focal distance of the second lens unit.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 such as digital video cameras, digital still cameras, broadcast cameras, silver halide film cameras, surveillance cameras, and vehicle-mounted cameras. [Background technology]

[0002] In recent years, there has been a demand for optical systems that are compact yet capable of focusing at ever closer distances, for use in imaging devices using solid-state imaging elements, such as digital still cameras and video cameras. Patent Document 1 discloses an optical system that includes, in order from the object side to the image side, a first lens group having positive refractive power, a second lens group having positive refractive power, and a third lens group having positive refractive power, and in which the second lens group moves relative to the image plane during focusing. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2023-008471 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the optical system disclosed in Patent Document 1, the refractive power of the two positive groups that move during focusing is small, so the object distance at which focusing is achieved becomes far from the image plane, and it becomes difficult to correct various aberrations that occur during focusing. [Means for solving the problem]

[0005] An optical system according to one aspect of the present invention is an optical system comprising, arranged in order from the object side to the image side, a first lens group having positive refractive power, a second lens group having positive refractive power, and a third lens group, wherein during focusing, the second lens group moves in the optical axis direction relative to an image plane, while the first lens group and the third lens group are stationary relative to the image plane, the first lens group has three negative lenses arranged consecutively in the optical axis direction on a side closest to the object, the second lens group has two to four lenses, and the second lens group has two or more positive lenses, wherein the optical system satisfies the following conditional expression, where f is a focal length of the entire system, L is the total optical length of the optical system, sk is an air-equivalent back focus when focused to infinity, f1 is the focal length of the first lens group, f2 is the focal length of the second lens group, and f3 is the focal length of the third lens group. 0.50 <f2 / f<3.00 0.20 <sk / f≦1.075 0.00 <sk / |f3|≦0.282 4.00 <L / f<15.00 -1.50 <f / f3≦0.018 0.50 <f1 / f<5.00

[0006] Another aspect of the present invention provides an optical system including, in order from an object side to an image side, a first lens group having positive refractive power, a second lens group having positive refractive power, and a third lens group, wherein, during focusing, the second lens group moves in the optical axis direction relative to an image plane, and the first lens group and the third lens group are stationary relative to the image plane; When the focal length of the entire optical system is f and the focal length of the second lens group is f2, the following conditional expression is satisfied: 0.50 <f2 / f<3.00 [Effects of the Invention]

[0007] It is possible to provide an optical system that has high optical performance and shortens the focusable object distance. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a cross-sectional view of the optical system of Example 1 when focused at infinity. [Figure 2] Longitudinal aberration diagrams of the optical system of Example 1 when focusing to (A) infinity and (B) the distance at which the lateral magnification is −0.1 [Figure 3] 10 is a cross-sectional view of the optical system of Example 2 when focused at infinity. [Figure 4] Longitudinal aberration diagrams of the optical system of Example 2 when focusing to (A) infinity and (B) the distance at which the lateral magnification is −0.1 [Figure 5] 10 is a cross-sectional view of the optical system of Example 3 when focused at infinity. [Figure 6] Longitudinal aberration diagrams of the optical system of Example 3 when focusing to (A) infinity and (B) the distance at which the lateral magnification is −0.1 [Figure 7] 10 is a cross-sectional view of the optical system of Example 4 when focused at infinity. [Figure 8] Longitudinal aberration diagrams of the optical system of Example 4 when focusing to (A) infinity and (B) the distance at which the lateral magnification is −0.1 [Figure 9] 10 is a cross-sectional view of the optical system of Example 5 when focused at infinity. [Figure 10] Longitudinal aberration diagrams of the optical system of Example 5 when focusing to (A) infinity and (B) the distance at which the lateral magnification is −0.1 [Figure 11] 10 is a cross-sectional view of the optical system of Example 6 when focused at infinity. [Figure 12] Longitudinal aberration diagrams of the optical system of Example 6 when focusing to (A) infinity and (B) the distance at which the lateral magnification is −0.1 [Figure 13] 10 is a cross-sectional view of the optical system of Example 7 when focused at infinity. [Figure 14] Longitudinal aberration diagrams of the optical system of Example 7 when focusing to (A) infinity and (B) the distance at which the lateral magnification is −0.1 [Figure 15] Schematic diagram of the imaging device [Figure 16] Schematic diagram of a lens device DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments disclosed in this specification will be described in detail with reference to the drawings. Note that the drawings may be drawn at a scale different from the actual scale for convenience. In addition, the same reference numerals are used for the same components in the drawings, and duplicate descriptions will be omitted.

[0010] 1, 3, 5, 7, 9, 11, and 13 are cross-sectional views of the optical systems of Examples 1 to 7 when focused at infinity, respectively.

[0011] In each cross-sectional view, the left side is the object side and the right side is the image side. The optical system of each embodiment is suitable for imaging devices such as digital video cameras, digital still cameras, broadcast cameras, silver halide film cameras, surveillance cameras, and vehicle-mounted cameras. The optical system of each embodiment may also be used as a projection lens for a projector, in which case the left side is the screen side and the right side is the projected image side.

[0012] In each cross-sectional view, L0 represents the entire optical system, Li represents the i-th lens group (i is a natural number) counting from the object side among the lens groups separated from the object side by the aperture stop, and Gk represents the k-th lens (k is a natural number) counting from the object side among the lenses included in each lens group. Note that, in this disclosure, the interior of a lens group refers to the space between the lens located closest to the object and the lens located closest to the image among the lenses constituting the lens group.

[0013] Lens group Li is a group of lenses that move or are fixed together relative to the image plane during focusing. That is, the air gaps between adjacent lens groups change during focusing, but the air gaps within each lens group do not change during focusing.

[0014] The arrows parallel to the optical axis shown in each cross-sectional view indicate the direction of movement of the lens groups during focusing from infinity to a close distance. In each embodiment, only the second lens group L2, which will be described later, moves from the image side to the object side during focusing.

[0015] In each cross-sectional view, SP denotes an aperture stop that determines the light beam with a maximum aperture F-number. IP denotes an image plane, and when the optical system of each embodiment is used as the photographic optical system of a digital still camera or digital video camera, the imaging surface of a solid-state image sensor such as a CCD sensor or CMOS sensor or a photoelectric conversion element is disposed thereon. Note that the optical system of each embodiment may also be used as the photographic optical system of a silver halide film camera, in which case a photosensitive surface corresponding to the film surface is disposed at the image plane IP.

[0016] 2, 4, 6, 8, 10, 12, and 14 are aberration diagrams when the optical system L0 of each of Examples 1 to 7 is focused at (A) infinity and (B) a distance at which the lateral magnification is −0.1.

[0017] In the spherical aberration diagram, Fno is the F-number, the solid line represents the amount of spherical aberration for the d-line (wavelength 587.6 nm), and the two-dot chain line represents the amount of spherical aberration for the g-line (wavelength 435.8 nm). In the aberration diagram, the solid line S represents the amount of aberration on the sagittal image plane, and the dashed line M represents the amount of aberration on the meridional image plane. In the distortion diagram, the solid line represents the amount of distortion for the d-line. In the chromatic aberration diagram, the two-dot chain line represents the amount of chromatic aberration of magnification for the g-line. Additionally, ω is the imaging half angle of view (°).

[0018] Next, the characteristic configuration of the optical system of each embodiment will be described.

[0019] The optical system L0 in each embodiment comprises, arranged in order from the object side to the image side, a first lens group L1 having positive refractive power, a second lens group L2 having positive refractive power, and a third lens group L3. In addition, in the optical system L0 in each embodiment, during focusing, the second lens group L2 moves in the optical axis direction relative to the image plane, while the first lens group L1 and the third lens group L3 are stationary relative to the image plane.

[0020] The optical system L0 is configured such that a light beam converged by a first lens group L1 having positive refractive power enters a second lens group L2 having positive refractive power, which allows the diameter of the second lens group L2, which moves relative to the image plane during focusing, to be reduced, and the weight of the second lens group L2 to be reduced, enabling high-speed focusing.

[0021] The optical system L0 of each embodiment is characterized in that it satisfies the following conditional expression, where f is the focal length of the entire optical system L0 and f2 is the focal length of the second lens group. 0.50 <f2 / f<3.00···(1)

[0022] Conditional expression (1) relates to the refractive power of the second lens unit L2. By satisfying conditional expression (1), the focal length f2 of the second lens unit L2 becomes small, and the object distance at which focus can be achieved by focusing can be brought closer to the image plane. In addition, the overall length of the optical system can be shortened while suppressing changes in optical performance during focusing.

[0023] If the focal length f2 of the positive second lens unit L2 becomes short by falling below the lower limit of conditional expression (1), the refractive power of the second lens unit L2 becomes too strong, which is undesirable because it results in significant performance changes such as spherical aberration, curvature of field, and fluctuations in the angle of view that occur during focusing.

[0024] If the positive focal length f2 of the second lens unit L2 increases beyond the upper limit of conditional expression (1), the position sensitivity of the second lens unit L2, i.e., the ratio of the movement amount of the image plane to the movement amount of the focus unit, becomes too small. As a result, the object distance at which focus can be achieved by focusing becomes farther from the image plane, which is undesirable. Also, in order to ensure the air gap that allows focusing, the overall length of the optical system L0 increases, which is undesirable.

[0025] It is more preferable that the numerical range of conditional expression (1) be set to the range of the following conditional expression (1a). 0.70 <f2 / f<2.80···(1a)

[0026] It is more preferable that the numerical range of conditional expression (1) be set to the range of the following conditional expression (1b). 0.90 <f2 / f<2.60···(1b)

[0027] Furthermore, it is more preferable that the numerical range of conditional expression (1) be set to the range of the following conditional expression (1c). 1.10 <f2 / f<2.40···(1c)

[0028] Next, the configurations that are preferably satisfied in the optical systems of the respective embodiments will be described.

[0029] In the optical system L0, the first lens group L1 preferably has three negative lenses arranged consecutively in the optical axis direction at the object side. In a wide-angle lens, a strong negative refractive power is required on the object side of the optical system L0 to ensure sufficient back focus. By sharing this negative refractive power among three negative lenses, the refractive power per negative lens can be reduced, thereby suppressing barrel distortion and curvature of field. In this disclosure, three negative lenses arranged consecutively means that no positive lenses are arranged between the three negative lenses.

[0030] Furthermore, by arranging the third lens group L3 on the image side of the second lens group L2, which moves during focusing, at a position where the axial light beam and the peripheral light beam are sufficiently separated in the direction perpendicular to the optical axis, astigmatism and distortion can be effectively corrected, thereby improving the peripheral performance of the optical system L0.

[0031] In the optical system L0, it is preferable that the positive second lens unit L2 has at least two positive lenses and at least one negative lens. To reduce the amount of movement of the second lens unit L2 during focusing from infinity to a close distance, it is necessary to increase the refractive power of the second lens unit L2. By sharing this strong refractive power with at least two positive lenses, the refractive power per positive lens can be reduced, thereby minimizing fluctuations in spherical aberration and field curvature during focusing. Furthermore, having at least one negative lens enables excellent correction of axial chromatic aberration.

[0032] In the optical system L0, it is preferable that the aperture diaphragm SP, which determines the axial light beam, is located inside the first lens group L1 or adjacent to the first lens group L1 on the image side, and that the aperture diaphragm SP is stationary relative to the image plane during focusing. This allows the weight of the second lens group L2, which moves during focusing, to be reduced, thereby enabling high-speed focusing. Furthermore, by locating the aperture diaphragm SP inside the first lens group L1 or adjacent to the first lens group L1 on the image side, it is possible to reduce the imbalance in lens diameters between the front and rear portions of the optical system L0, thereby reducing the diameter of the entire optical system L0.

[0033] In the optical system L0, it is preferable that the object-side lens surface of the lens arranged closest to the object in the second lens group L2 has a concave shape. This allows off-axis light beams that have passed through the aperture stop SP to be incident on the surface closest to the object in the second lens group L2 in a substantially concentric manner, reducing the refraction of light rays at that surface. As a result, fluctuations in astigmatism and coma, as well as fluctuations in the angle of view, during focusing can be suppressed.

[0034] In the optical system L0, it is preferable that the image-side lens surface of the lens arranged closest to the image side in the second lens group L2 has a convex shape. This allows off-axis light beams emerging from the second lens group L2 to emerge approximately concentrically from the surface closest to the image side in the second lens group L2, thereby reducing the refraction of light rays at that surface. As a result, it becomes easier to suppress fluctuations in astigmatism and coma aberration, and fluctuations in the angle of view during focusing.

[0035] In the optical system L0, it is preferable to dispose a negative lens closest to the image side of the third lens group L3, i.e., closest to the image side of the optical system L0. This allows the angle of off-axial rays incident on the image plane from the optical axis to be increased, making it possible to reduce the lens diameter of the third lens group L3. Furthermore, by disposing a negative lens at a position on the image side where the height of off-axial rays is high, it is possible to reduce the positive Petzval sum of the entire optical system L0 without worsening sagittal flare, and to effectively correct field curvature.

[0036] Next, conditions that the optical system L0 of each embodiment should preferably satisfy will be described.

[0037] It is preferable that the optical system of each embodiment satisfies one or more of the following conditional expressions (2) to (17): In each conditional expression, the various numerical values ​​are expressed as follows.

[0038] The air-equivalent back focus of the optical system L0 is denoted by sk.

[0039] The focal length of the third lens unit L3 is f3.

[0040] The radius of curvature of the surface of the second lens unit L2 closest to the object side is R21, and the radius of curvature of the surface closest to the image side is R22.

[0041] The refractive index of the negative lens Gn in the optical system L0 at the d-line is set to Ndn.

[0042] The anomalous partial dispersion ΔθgFn of the negative lens Gn in the optical system L0 is calculated by using the Abbe number νdn and the partial dispersion ratios for the g-line and F-line θgFn: ΔθgFn=θgFn-(-0.0025116×νdn+0.67449) Let's say.

[0043] The lateral magnification of the second lens unit L2 when focused on infinity is denoted by β2, and the lateral magnification of the third lens unit L3 when focused on infinity is denoted by β3.

[0044] The sum of the air spaces on the optical axis from the surface of the optical system L0 closest to the object to the surface closest to the image is denoted by ΣDair.

[0045] The total optical length of the optical system L0 is L.

[0046] The Abbe number of the negative lens G1n included in the first lens unit L1 is denoted by νd1n.

[0047] The Abbe number of the positive lens G2p in the second lens unit L2 is denoted by νd2p.

[0048] The amount of movement of the second lens unit L2 during focusing from infinity to an object distance at which the lateral magnification of the entire system becomes -0.1 is denoted by M2.

[0049] The distance on the optical axis from the aperture stop SP to the surface closest to the image side when the optical system L0 is focused at infinity is defined as DSP.

[0050] The anomalous partial dispersion ΔθgFp of the positive lens Gp in the first lens unit L1 or the second lens unit L2 is expressed as follows using the Abbe number νdp and the partial dispersion ratio θgFp: ΔθgFp=θgFp-(B3×νdp 3 +B2×νdp 2 +B1×νdp+B0) B3=-1.665×10 -7 B2=5.213×10 -5 B1=-5.656×10 -3 B0=7.278×10 -1 0.20 <sk / f<1.20···(2) 0.30 <f1 / f2<3.00···(3) -1.50 <f / f3<1.50···(4) -1.50<(R22-R21) / (R22+R21)<1.50...(5) -0.015<ΔθgFn<0.015 (6) -0.20 <Ndn-(-0.0145425×νdn+2.28725)<0.05···(7) 0.50<(1-β2 2 )×β3 2 <2.50···(8) 0.00 <sk / |f3|<0.80···(9) 0.20<ΣDair / (L-sk)<0.70 (10) 2.00 <L / f<15.00···(11) 60.00<νd2p<100.00 (12) -0.200 <M2 / DSP<-0.005···(13) 60.00<νd1n<100.00 (14) 0.050<ΔθgFp<0.250 (15) 0.30<(DSP+sk) / L<0.80···(16) 0.50 <f1 / f<5.00···(17)

[0051] Next, the technical meaning of the above-mentioned conditional expressions (2) to (17) will be explained.

[0052] Conditional expression (2) relates to the air-equivalent back focal length sk of the optical system L0. By satisfying conditional expression (2), the third lens unit L3 can be disposed at a position where the height of off-axial rays is large, thereby enabling selective correction of distortion and astigmatism while minimizing the effect on correction of spherical aberration and sagittal flare. As a result, the peripheral performance of the optical system L0 can be improved.

[0053] If the lower limit of conditional expression (2) is exceeded or the upper limit is exceeded, it becomes difficult to position the third lens unit L3 at a position where the height of off-axial rays is large, which is undesirable because it becomes difficult to sufficiently correct distortion, curvature of field, and astigmatism.

[0054] Condition (3) relates to the ratio of the refractive power of the first lens unit L1 to the refractive power of the second lens unit L2.

[0055] If f2 becomes large below the lower limit of conditional expression (3), the positive refractive power of the second lens unit L2 becomes too small, which increases the amount of movement during focusing and increases the overall length, which is undesirable.Furthermore, if f1 becomes small, it becomes difficult to correct spherical aberration and axial chromatic aberration, which is undesirable.

[0056] If the upper limit of conditional expression (3) is exceeded and f2 becomes small, the refractive power of the second lens unit L2 becomes large. This can cause performance changes such as spherical aberration, field curvature, and fluctuations in the angle of view when focusing. This is not desirable because the size becomes too large. Also, if f1 becomes large, the overall length becomes large. Therefore, it is not desirable.

[0057] Conditional expression (4) defines the ratio of the focal length f3 of the third lens unit L3 to the focal length f of the entire optical system L0.

[0058] Near the lower limit of conditional expression (4), f3 takes a negative value. If the absolute value of f3 falls below the lower limit of conditional expression (4) and becomes small, the negative refractive power of the third lens unit L3 becomes too strong. In this case, the angle of incidence of the off-axial light beam incident on the image plane becomes too large, which is undesirable because it is likely to cause color unevenness when an image is captured using a solid-state image sensor such as a CMOS sensor.

[0059] Near the upper limit of conditional expression (4), f3 takes a positive value. If the absolute value of f3 becomes small by exceeding the upper limit of conditional expression (4), the positive refractive power of the third lens unit L3 becomes too strong, and in this case, the positive Petzval sum of the entire optical system L0 becomes too large, making it difficult to correct the curvature of field, which is undesirable.

[0060] Conditional expression (5) defines the shape of the second lens unit L2 and relates to the condition for suppressing aberrations that occur during focusing and fluctuations in the angle of view.

[0061] If the lower limit of conditional expression (5) is not reached, the absolute value of the radius of curvature of the concave surface of the second lens group L2 closest to the object becomes large. In this case, the concentricity of the surface of the second lens group L2 closest to the object with respect to off-axis light beams incident on the second lens group L2 becomes small. Furthermore, because the absolute value of the radius of curvature of the convex surface of the second lens group L2 closest to the image becomes small, the surface of the second lens group L2 closest to the image largely refracts off-axis light beams. As a result, the fluctuation in the angle of view that occurs during focusing tends to become large, which is undesirable.

[0062] If the upper limit of conditional expression (5) is exceeded, the absolute value of the radius of curvature of the concave surface of the second lens unit L2 closest to the object becomes small. In this case, the concentricity of the surface of the second lens unit L2 closest to the object with respect to off-axial light beams incident on the second lens unit L2 becomes small. As a result, fluctuations in the angle of view that occur during focusing tend to become large. In addition, the absolute value of the radius of curvature of the convex surface of the second lens unit L2 closest to the image becomes large. This is undesirable because it tends to increase fluctuations in aberrations such as coma and astigmatism during focusing.

[0063] Condition (6) defines the anomalous partial dispersion of the negative lens Gn in the first lens unit L1 or the second lens unit L2.

[0064] If the lower limit of conditional expression (6) is not reached, the longitudinal chromatic aberration for the g-line will be overcorrected, which is not preferable.

[0065] If the upper limit of conditional expression (6) is exceeded, correction of axial chromatic aberration for the g-line will be insufficient, which is not preferable.

[0066] Condition (7) defines the dispersibility of the negative lens Gn in at least one of the first lens unit L1 and the second lens unit L2.

[0067] If the lower limit of conditional expression (7) is exceeded, the longitudinal chromatic aberration will be overcorrected, which is not preferable.

[0068] If the upper limit of conditional expression (7) is exceeded, the correction of axial chromatic aberration will be insufficient or the refractive power of the negative lens Gn will become too large, making it difficult to correct spherical aberration, which is undesirable.

[0069] Axial chromatic aberration in the short wavelength range, such as the g-line, can easily become an issue with large-diameter lenses. In particular, when first-order achromatization is performed for the C-line and F-line, axial chromatic aberration for the g-line tends to become excessive. By using glass materials that satisfy conditional expressions (6) and (7) for the negative lens element, the degree of divergence for the g-line caused by the negative lens element can be made relatively small, and axial chromatic aberration for short wavelengths, such as the g-line, can be prevented from becoming excessive.

[0070] By arranging at least one negative lens Gn that satisfies both conditional expressions (6) and (7) in at least one of the first lens group L1 and the second lens group L1, the effect of correcting the axial chromatic aberration described above can be obtained.

[0071] In addition, the effect can be enhanced by providing two negative lenses Gn, and the effect can be further enhanced by providing three or more negative lenses Gn.

[0072] It is more preferable that at least one negative lens Gn is disposed in each of the first lens group L1 and the second lens group L2.

[0073] By disposing the negative lens Gn in the first lens unit L1, it is possible to effectively correct axial chromatic aberration throughout the entire optical system L0. By disposing the negative lens Gn in the second lens unit L2, it becomes easier to correct axial chromatic aberration within the second lens unit L2, and it is possible to suppress fluctuations in axial chromatic aberration during focusing.

[0074] Condition (8) defines the ratio of the movement amount of the image plane to the movement amount of the second lens unit L2, in relation to the position sensitivity of the second lens unit L2.

[0075] If the lower limit of conditional expression (8) is not met, the position sensitivity of the second lens unit L2 becomes too small. As a result, the focusing distance becomes too long, which is undesirable. Also, in order to ensure the air gap that allows focusing, it becomes difficult to shorten the overall length of the optical system L0, which is undesirable.

[0076] If the upper limit of conditional expression (8) is exceeded, the refractive power of the second lens unit L2 becomes too strong, which is undesirable because it causes excessive changes in performance such as spherical aberration, curvature of field, and fluctuations in the angle of view during focusing.

[0077] Conditional expression (9) defines the ratio between the focal length f3 of the third lens unit L3 and the air-equivalent back focus sk.

[0078] If sk becomes small below the lower limit of conditional expression (9), the image plane of the optical system L0 will be located closer to the object side than the surface of the optical system L0 closest to the image side, which makes it difficult to take an image, which is undesirable.

[0079] If sk becomes large beyond the upper limit of conditional expression (9), the effect of correcting distortion and curvature of field becomes small, and the diameter of the front lens becomes large, which is not preferable.

[0080] If |f3| becomes small, exceeding the upper limit of conditional expression (9), the absolute value of the refractive power of the third lens unit L3 becomes too large. If the negative refractive power becomes too large, the angle of incidence of off-axis light beams incident on the image plane becomes too large, which is undesirable because it makes it more likely that color irregularities will occur when an image is captured using an image sensor such as a CMOS sensor. If the positive refractive power becomes too large, the positive Petzval sum of the entire optical system L0 becomes too large, which is undesirable because it makes it difficult to correct field curvature.

[0081] Condition (10) defines the ratio of the total air gap ΣDair on the optical axis from the surface closest to the object to the surface closest to the image in the optical system L0 to the total optical length L of the optical system L0.

[0082] If ΣDair falls below the lower limit of conditional expression (10) and becomes small, it becomes difficult to ensure sufficient space for the lens groups to move during focusing. It also becomes difficult to give the negative lens in the first lens group a sufficiently positive curvature, which is undesirable because it becomes difficult to make the optical system L0 wide-angle and correct distortion.

[0083] If ΣDair becomes large beyond the upper limit of conditional expression (10), the ratio of the air gap to the total optical length becomes too large, making it difficult to provide each lens with sufficient refractive power, which is undesirable as it makes it difficult to correct spherical aberration and axial chromatic aberration.Alternatively, if each lens is provided with sufficient refractive power, the total length becomes large, which is undesirable.

[0084] Conditional expression (11) defines the ratio of the total optical length L of the optical system L0 to the focal length f of the entire optical system L0.

[0085] If L becomes small below the lower limit of conditional expression (11), the refractive power of each lens group becomes too strong, making it difficult to correct aberrations such as distortion, astigmatism, and spherical aberration, which is undesirable.

[0086] If L becomes large beyond the upper limit of conditional expression (11), the overall length becomes large, which is not preferable.

[0087] Conditional expression (12) defines the Abbe number νd2p of at least one positive lens G2p in the second lens unit L2, and defines the condition for favorably correcting axial chromatic aberration.

[0088] If νd2p becomes small below the lower limit of conditional expression (12), it becomes difficult to correct axial chromatic aberration, which is not preferable.

[0089] If νd2p becomes large beyond the upper limit of conditional expression (12), lateral chromatic aberration will be overcorrected, or the glass material will be worn too much, making processing difficult and prone to cracking, which is undesirable.

[0090] It is more preferable to dispose two or more positive lenses G2p that satisfy conditional expression (12) in the second lens unit L2, as this can enhance the above-mentioned effect.

[0091] Conditional expression (13) defines the ratio of the amount of movement M2 of the second lens unit L2 during focusing from infinity to an object distance at which the lateral magnification of the entire system is −0.1, to the distance DSP on the optical axis from the aperture stop SP to the surface closest to the image. Note that the sign of the amount of movement M2 is positive when moving from the object side to the image side.

[0092] If M2 becomes small below the lower limit of conditional expression (13), the refractive power of the second lens unit L2 becomes too strong, which is undesirable because it increases the fluctuations in spherical aberration and curvature of field during focusing.

[0093] If M2 becomes large beyond the upper limit of conditional expression (13), the amount of movement of the second lens group becomes large, and the overall length becomes large to ensure space for that movement, which is undesirable.

[0094] Conditional expression (14) defines the Abbe number νd1n of at least one negative lens G1n in the first lens unit L1, and defines the condition for favorably correcting lateral chromatic aberration.

[0095] If the lower limit of conditional expression (14) is exceeded and νd1n becomes small, it becomes difficult to correct chromatic aberration of magnification, which is not preferable.

[0096] If vd1n becomes large beyond the upper limit of conditional expression (14), lateral chromatic aberration will be overcorrected, or the negative lens Gn1 will be worn too much, making processing difficult and prone to cracking, which is undesirable.

[0097] It is more preferable to dispose two or more negative lenses G1n that satisfy conditional expression (14) in the first lens unit L1, since this can enhance the above-mentioned effect.

[0098] Conditional expression (15) defines the anomalous partial dispersion ΔθgFp of the positive lens Gp arranged in the first lens unit L1 or the second lens unit L2.

[0099] Axial chromatic aberration in the short wavelength range, such as the g-line, can easily become an issue with large-diameter lenses. In particular, when first-order achromatization is performed for the C-line and F-line, axial chromatic aberration for the g-line tends to become excessive. Therefore, by using a material with a large ΔθgFp for the positive lens, excessive axial chromatic aberration for short wavelengths, such as the g-line, can be selectively converged, making it possible to effectively correct it.

[0100] If ΔθgFp becomes small below the lower limit of conditional expression (15), it becomes difficult to correct longitudinal chromatic aberration, which is not preferable.

[0101] If ΔθgFp becomes large beyond the upper limit of conditional expression (15), then the longitudinal chromatic aberration will be overcorrected, which is not desirable.

[0102] The positive lens Gp can be arranged as a triplet cemented lens consisting of a positive lens, a positive lens Gp, and a negative lens, or as a triplet cemented lens consisting of a negative lens, a positive lens Gp, and a positive lens, thereby further improving the effect of correcting axial chromatic aberration.

[0103] Furthermore, by using the negative lens Gn that constitutes the triplet of cemented lenses as a negative lens that satisfies the conditional expressions (6) and (7), it is possible to effectively correct longitudinal chromatic aberration.

[0104] Furthermore, it is preferable that the triplet cemented lens be located adjacent to the object side or image side of the aperture stop SP located in the first lens unit L1, which allows the triplet to be located at a position where the height of axial rays is large, thereby enhancing the effect of correcting axial chromatic aberration.

[0105] Furthermore, it is preferable that the triplet cemented lens and aperture diaphragm SP are disposed in the first lens group L1, which does not move during focusing. As mentioned above, it is preferable to dispose the triplet cemented lens before and after the aperture diaphragm SP, but the axial light beam diameter is large before and after the aperture diaphragm SP, which would result in the lenses becoming larger in diameter and becoming too heavy. Therefore, it is preferable that the aperture diaphragm SP and the triplet cemented lens including the positive lens Gp are configured to not move during focusing.

[0106] Conditional expression (16) defines the position of the aperture stop SP, and defines the condition for configuring the optical system L0 in a compact size.

[0107] If DSP falls below the lower limit of conditional expression (16) and becomes small, the diameter of the lens positioned closer to the object than the aperture stop SP becomes large, which is undesirable because it increases the mass and diameter of the entire optical system L0. Also, the angle of the off-axial light beam incident on the image plane becomes too large, which is undesirable because it is likely to cause color irregularities when an image is captured using a solid-state image sensor such as a CMOS sensor.

[0108] If DSP becomes larger beyond the upper limit of conditional expression (16), the diameter of the lens positioned closer to the image side than the aperture stop SP becomes large, which is undesirable because it increases the mass and diameter of the entire optical system L0.

[0109] Conditional expression (17) defines the focal length f1 of the first lens unit L1.

[0110] If f1 becomes small below the lower limit of conditional expression (17), the positive refractive power of the first lens unit L1 becomes too strong, making it difficult to correct spherical aberration and distortion, which is undesirable.

[0111] If f1 becomes large beyond the upper limit of conditional expression (17), the diameter of the second lens unit L2 becomes large, and the mass becomes large, which is undesirable because it makes high-speed focusing difficult.

[0112] It is more preferable that the numerical ranges of the conditional expressions (2) to (17) be the numerical ranges of the following conditional expressions (2a) to (17a). 0.30 <sk / f<1.18···(2a) 0.50 <f1 / f2<2.70···(3a) -1.20 <f / f3<1.20···(4a) -1.20<(R22-R21) / (R22+R21)<1.20...(5a) -0.010<ΔθgFn<0.010 (6a) -0.18 <Ndn-(-0.0145425×νdn+2.28725)<0.03···(7a) 0.60<(1-β2 2 )×β3 2 <2.20···(8a) 0.00 <sk / |f3|<0.70···(9a) 0.25<ΣDair / (L-sk)<0.64 (10a) 3.00 <L / f<13.50···(11a) 62.00<νd2p<99.00 (12a) -0.160 <M2 / DSP<-0.008···(13a) 62.00<νd1n<99.00 (14a) 0.060<ΔθgFp<0.210 (15a) 0.35<(DSP+sk) / L<0.74 (16a) 0.70 <f1 / f<4.50···(17a)

[0113] It is more preferable that the numerical ranges of the conditional expressions (2) to (17) be the numerical ranges of the following conditional expressions (2b) to (17b). 0.40 <sk / f<1.14···(2b) 0.70 <f1 / f2<2.30···(3b) -0.90 <f / f3<0.50···(4b) -0.80<(R22-R21) / (R22+R21)<0.80...(5b) -0.008<ΔθgFn<0.007 (6b) -0.15 <Ndn-(-0.0145425×νdn+2.28725)<0.02···(7b) 0.55<(1-β2 2 )×β3 2 <1.90 (8b) 0.00 <sk / |f3|<0.60···(9b) 0.30<ΣDair / (L-sk)<0.56 (10b) 3.50 <L / f<12.00···(11b) 64.00<νd2p<98.00 (12b) -0.120 <M2 / DSP<-0.012···(13b) 64.00<νd1n<98.00 (14b) 0.070<ΔθgFp<0.180 (15b) 0.40<(DSP+sk) / L<0.68 (16b) 1.00 <f1 / f<4.00···(17b)

[0114] Furthermore, it is more preferable that the numerical ranges of the conditional expressions (2) to (17) be the numerical ranges of the following conditional expressions (2c) to (17c). 0.50 <sk / f<1.10···(2c) 0.90 <f1 / f2<1.80···(3c) -0.50 <f / f3<0.20···(4c) -0.50<(R22-R21) / (R22+R21)<0.50...(5c) -0.006<ΔθgFn<0.004 (6c) -0.13 <Ndn-(-0.0145425×νdn+2.28725)<0.01···(7c) 0.65<(1-β2 2 )×β3 2 <1.60···(8c) 0.00 <sk / |f3|<0.40···(9c) 0.33<ΣDair / (L-sk)<0.50 (10c) 4.00 <L / f<11.00···(11c) 66.00<νd2p<97.00···(12c) -0.080 <M2 / DSP<-0.016···(13c) 66.00<νd1n<97.00···(14c) 0.080<ΔθgFp<0.160 (15c) 0.45<(DSP+sk) / L<0.65 (16c) 1.30 <f1 / f<3.50···(17c)

[0115] Next, a detailed description will be given of the configuration of the optical system L0 of Examples 1 to 7. Note that, in the zoom lens L0 of each Example, a description of the same configuration as the zoom lens L0 of Example 1 will be omitted, and differences from Example 1 will be mainly described.

[0116] [Example 1] The optical system L0 of Example 1 is composed of a first lens unit L1 having a positive refractive power, a second lens unit L2 having a positive refractive power, and a third lens unit L3 having a negative refractive power. By making the third lens unit L3 have a negative refractive power, it becomes easier to correct the positive Petzval sum, and field curvature can be corrected well.

[0117] In the optical system L0 of Example 1, the first lens group L1 is composed of lenses G1 to G12, the second lens group L2 is composed of lenses G13 to G16, and the third lens group is composed of lenses G17 and G18. The first lens group L1 includes an aperture stop SP. Furthermore, by using aspherical lenses for the G1 and G3 lenses, distortion and astigmatism can be effectively corrected.

[0118] In the optical system L0 of the first embodiment, the G6 and G7 lenses, the G10 to G12 lenses, the G13 and G14 lenses, and the G17 and G18 lenses are each cemented to form one cemented lens.

[0119] During focusing, the second lens group L2 moves in the optical axis direction relative to the image plane, while the first lens group L1 and the third lens group L3 remain stationary relative to the image plane.

[0120] [Example 2] In the optical system L0 of the second embodiment, the first lens group L1 is made up of G1 to G10 lenses, the second lens group L2 is made up of G11 to G14 lenses, and the third lens group is made up of G15 and G16 lenses.

[0121] In the optical system L0 of the second embodiment, the G4 and G5 lenses, the G8 to G10 lenses, the G11 and G12 lenses, and the G15 and G16 lenses are each cemented to form one cemented lens.

[0122] [Example 3] In the optical system L0 of Example 3, the first lens group L1 is composed of G1 to G8 lenses, the second lens group L2 is composed of G9 to G12 lenses, and the third lens group is composed of G13 and G14 lenses. The first lens group L1 includes an aperture stop SP. Furthermore, by using aspherical lenses for the G1 and G3 lenses, distortion and astigmatism can be effectively corrected.

[0123] In the optical system L0 of Example 3, the G4 and G5 lenses, the G6 and G7 lenses, the G9 and G10 lenses, and the G13 and G14 lenses are each cemented to form one cemented lens.

[0124] In the optical system L0 of the third embodiment, the G8 lens included in the first lens unit L1 moves so as to include a component in the direction orthogonal to the optical axis, thereby making it possible to suppress fluctuations in chromatic aberration during image blur correction.

[0125] [Example 4] In the optical system L0 of the fourth embodiment, the first lens group L1 is made up of G1 to G9 lenses, the second lens group L2 is made up of G10 to G14 lenses, and the third lens group is made up of G15 to G17 lenses.

[0126] In the optical system L0 of Example 4, the G4 and G5 lenses, the G8 and G9 lenses, the G10 to G12 lenses, and the G15 and G16 lenses are each cemented to one another to form one cemented lens.

[0127] [Example 5] In the optical system L0 of Example 5, the first lens group L1 is composed of lenses G1 to G12, the second lens group L2 is composed of lenses G13 to G16, and the third lens group is composed of lenses G17 and G18. In addition, by using aspherical lenses for the G1 and G3 lenses, distortion and astigmatism can be effectively corrected.

[0128] In the optical system L0 of Example 5, the G6 and G7 lenses, the G10 to G12 lenses, the G13 and G14 lenses, and the G17 and G18 lenses are each cemented to form one cemented lens.

[0129] [Example 6] The optical system L0 of Example 6 includes a first lens group L1 having a positive refractive power, a second lens group L2 having a positive refractive power, and a third lens group L3 having a positive refractive power. By providing the third lens group L3 with a positive refractive power, the angle of incidence of off-axis light beams incident on the image plane can be reduced, which makes it easier to suppress color unevenness when capturing an image using a solid-state image sensor such as a CMOS sensor.

[0130] In the optical system L0 of Example 6, the first lens group L1 is composed of G1 to G10 lenses, the second lens group L2 is composed of G11 to G14 lenses, and the third lens group is composed of G15 and G16 lenses. In addition, by using aspherical lenses for the G1 and G3 lenses, distortion and astigmatism can be effectively corrected.

[0131] In the optical system L0 of Example 6, the G4 and G5 lenses, the G8 to G10 lenses, the G11 and G12 lenses, and the G15 and G16 lenses are each cemented to form one cemented lens.

[0132] [Example 7] In the optical system L0 of Example 7, the first lens group L1 is composed of G1 to G8 lenses, the second lens group L2 is composed of G9 to G12 lenses, and the third lens group is composed of G13 and G14 lenses. In addition, by using aspherical lenses for the G1 and G3 lenses, distortion and astigmatism can be effectively corrected.

[0133] In the optical system L0 of Example 7, the G4 and G5 lenses, the G9 and G10 lenses, and the G13 and G14 lenses are each cemented to form one cemented lens.

[0134] In the optical system L0 of Example 7, the G8 lens included in the first lens unit L1 moves so as to include a component in the direction orthogonal to the optical axis, thereby making it possible to suppress fluctuations in chromatic aberration during image blur correction.

[0135] In the optical system L0 of each embodiment, it is preferable to arrange a negative lens closest to the image side of the third lens unit L3, i.e., closest to the image side of the optical system L0. This allows the angle of off-axial rays incident on the image surface from the optical axis to be increased, making it possible to reduce the lens diameter of the third lens unit L3. Furthermore, by arranging a negative lens at a position where the height of off-axial rays on the image side is high, it is possible to reduce the positive Petzval sum of the entire optical system L0 without worsening sagittal flare, and to effectively correct field curvature.

[0136] In the optical system L0 of each embodiment, it is preferable that the first lens unit L1 has two consecutive negative meniscus lenses with convex object-side surfaces arranged closest to the object, which enables excellent correction of distortion, curvature of field, and astigmatism.

[0137] In the optical system L0 of each embodiment, it is preferable that at least one of the three negative lenses arranged consecutively closest to the object in the first lens group L1 be an aspherical lens. This allows for excellent correction of distortion and astigmatism. In addition, in Examples 1 and 5, the G1 lens and the G3 lens are aspherical lenses, thereby enhancing the above-mentioned effects. Furthermore, by shaping the aspherical lens so that the absolute value of the curvature on the periphery is smaller than the absolute value of the curvature on the optical axis, distortion can be effectively corrected.

[0138] In the optical system L0 of each embodiment, it is preferable that the image-side lens surface of the negative G2 lens is concave, and the object-side lens surface of the negative G3 lens is concave. This increases the refractive power of the negative air lens formed by the image-side lens surface of the G2 lens and the object-side lens surface of the G3 lens, making it easier to reduce the positive Petzval sum and effectively correct field curvature.

[0139] In the optical system L0 of each embodiment, the first lens group L1 preferably includes, in order from the object side, a negative lens G1, a negative lens G2, a negative lens G3, and a positive lens G4. By using the lens G4 as a positive lens, barrel-side distortion and chromatic aberration of magnification generated by the lenses G1 to G3 can be effectively corrected.

[0140] In Examples 1 and 5, the G4 lens is preferably a meniscus lens with positive refractive power. This makes it possible to correct barrel-side distortion and lateral chromatic aberration. The G4 lens may be a positive meniscus lens with a convex object-side lens surface, or a positive meniscus lens with a convex image-side lens surface.

[0141] In the optical system L0 of each embodiment, it is preferable that the first lens unit L1 has at least one cemented lens consisting of a positive lens and a negative lens. This makes it possible to effectively correct longitudinal chromatic aberration and chromatic aberration of magnification. Furthermore, as in Examples 2, 3, 4, 6, and 7, by using a negative lens Gn in the cemented lens that satisfies conditional expressions (6) and (7), it is possible to effectively correct longitudinal chromatic aberration for the g-line.

[0142] In the optical system L0 of each embodiment, the first lens group L1 can perform image blur correction by moving at least a part of the first lens group L1 so as to include a component in the direction orthogonal to the optical axis.

[0143] In Examples 3 and 7, the G8 lens moves during image blur correction so as to include a component perpendicular to the optical axis, but this is not limiting. Furthermore, if the lenses that move during image blur correction include at least a positive lens and a negative lens, fluctuations in chromatic aberration during image blur correction can be suppressed. Furthermore, a configuration in which three or more lenses move during image blur correction may also be used.

[0144] In the optical system L0 of each embodiment, the second lens unit L2 has a negative lens and a positive lens arranged in that order in the optical axis direction. This makes it possible to more effectively correct axial chromatic aberration when focusing at infinity and fluctuations in axial chromatic aberration during focusing. Note that the above-mentioned effects can be obtained regardless of the order in which the negative lens and positive lens are arranged.

[0145] In the second lens group L2, it is preferable that the object-side lens surface of the second lens element counting from the object side be concave, and that the image-side lens surface be convex, which results in a substantially concentric shape for off-axis light beams incident on the second lens group L2, thereby suppressing aberrations and fluctuations in the angle of view during focusing.

[0146] In the optical system L0 of each embodiment, the second lens group L2 has a cemented lens formed by cementing together at least one of the negative lenses Gn and at least one of the positive lenses G2p, thereby enabling excellent correction of axial chromatic aberration during infinity focusing and fluctuations in axial chromatic aberration during focusing.

[0147] It is also preferable that the cemented lens be located closest to the object in the second lens group L2, whereby the cemented lens is located at a position where the height of off-axial rays is high, thereby enabling good correction of axial chromatic aberration.

[0148] It is also preferable that the lens surface closest to the object side of the cemented lens be concave and the lens surface closest to the image side be convex. This results in a nearly concentric shape for off-axis light beams incident on the second lens group L2, making it possible to suppress aberrations and fluctuations in the angle of view during focusing. The cemented lens may also be formed by cementing a biconcave lens and a biconvex lens together in that order from the object side.

[0149] In the optical system L0 of each embodiment, the second lens unit L2 is composed of four lenses, which makes it possible to reduce the refractive power of each lens and suppress fluctuations in spherical aberration, curvature of field, and chromatic aberration during focusing.

[0150] In the optical system L0 of each embodiment, it is preferable that the second lens group L2 be composed of five or fewer lenses. This allows the weight of the lenses in the second lens group L2 to be reduced, enabling high-speed focusing. It also allows the refractive power per lens to be reduced, making it possible to suppress fluctuations in spherical aberration, field curvature, and chromatic aberration during focusing. In order to enhance the above-mentioned effects, it is more preferable that the second lens group L2 be composed of four or fewer lenses.

[0151] In the optical system L0 of each embodiment, it is preferable that the object-side lens surface of the lens arranged closest to the object in the second lens unit L2 has a concave shape, so that off-axis light passing through the aperture stop is incident on the surface closest to the object in the second lens unit L2 in a substantially concentric manner, making it easy to suppress fluctuations in astigmatism and coma and fluctuations in the angle of view during focusing.

[0152] In the optical system L0 of each embodiment, it is preferable that the second lens group L2 includes an aspherical lens having at least one aspherical surface. This allows for excellent correction of spherical aberration, astigmatism, and coma. Furthermore, making any of the surfaces of the positive lenses included in the second lens group L2 aspherical is more preferable because it reduces errors in the surface shape during molding. Furthermore, it is more preferable to make the lens closest to the image side or the second-nearest lens from the image side in the second lens group L2 aspherical because it allows for excellent correction of off-axis aberrations such as astigmatism and coma.

[0153] In the optical system L0 of each embodiment, it is preferable that the third lens unit L3 has a cemented lens made up of a positive lens and a negative lens, which allows for excellent correction of chromatic aberration of magnification and astigmatism.

[0154] In the optical system L0 of each embodiment, the aspherical lens material may be an organic material such as plastic, or a glass material. Alternatively, an aspherical lens made of an organic material may be formed on a spherical glass by molding, joining, or adhering an organic material such as plastic with a thickness of approximately 0.01 mm to 1.00 mm onto the spherical glass.

[0155] Numerical Examples 1 to 7 corresponding to Examples 1 to 7, respectively, are shown below.

[0156] In the surface data of each numerical example, r represents the radius of curvature of each optical surface, and d (mm) represents the 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. nd represents the refractive index of each optical element at the d-line, and vd represents the Abbe number of the optical element. The Abbe number vd and partial dispersion ratio θgF of a certain material can be expressed as follows, where Nd, NF, NC, and Ng are the refractive indices at the Fraunhofer d-line (587.6 nm), F-line (486.1 nm), C-line (656.3 nm), and g-line (wavelength 435.8 nm). νd=(Nd-1) / (NF-NC) θgF=(Ng-NF) / (NF-NC)

[0157] 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. The back focus BF is the air-equivalent distance from the final lens surface to the image plane. The total optical length is the value obtained by adding the air-equivalent back focus to the distance from the first lens surface to the final lens surface. However, this does not include optical components such as optical filters, face plates, crystal low-pass filters, and infrared cut filters.

[0158] Furthermore, for each lens, if the lens surface is aspherical, an * symbol is added to the right of the surface number. The aspherical shape is expressed as follows, where X is the displacement from the vertex of the surface in the optical axis direction, h is the height from the optical axis in a direction perpendicular to the optical axis, R is the paraxial radius of curvature, k is the conic constant, and A4, A6, A8, A10, A12, A14, and A16 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×h 12 +A14×h 14 +A16×h 16 In addition, "e±XX" in each aspherical coefficient is "×10± XX " means.

[0159] [Numerical Example 1] Unit: mm Surface Data Surface number rd nd νd 1* 30.434 2.50 1.58313 59.4 2* 12.960 14.47 3 -8220.485 1.60 1.49700 81.7 4 48.726 5.09 5 -52.293 2.00 1.80400 46.5 6* 61.254 0.20 7 30.423 3.13 1.66565 35.6 8 60.805 4.01 9 -38.272 1.20 1.43387 95.1 10 89.263 0.20 11 33.379 9.18 1.75500 52.3 12 -25.609 1.05 1.84666 23.8 13 -50.774 0.20 14 121.888 4.07 1.83481 42.7 15 -55.780 3.62 16 -26.631 1.10 1.77047 29.7 17 -79.426 2.00 18 (Aperture) ∞ 2.43 19 52.498 5.84 2.00100 29.1 20 -45.067 1.00 1.57060 20.1 21 -32.493 1.10 1.66565 35.6 22 71.141 (variable) 23 -120.281 7.55 1.43875 94.7 24 -14.562 1.00 1.77047 29.7 25 -57.242 0.20 26 39.251 8.64 1.49700 81.7 27 -31.928 0.60 28* 137.086 4.68 1.85400 40.4 29* -65.817 (variable) 30 -1214.157 7.51 1.59282 68.6 31 -22.877 1.05 1.91650 31.6 32 331.855 14.00 Image plane ∞ Aspheric data Front page K = 0.00000e+00 A 4=-9.44889e-06 A 6=-2.78211e-09 A 8= 1.38292e-11 A10=-1.87056e-14 A12= 7.67401e-18 2nd side K =-6.82090e-01 A 4=-2.16920e-06 A 6=-9.17628e-09 A 8=-2.33882e-10 A10= 8.26939e-13 A12=-1.85607e-15 Page 6 K = 0.00000e+00 A 4= 2.29625e-05 A 6= 1.76297e-08 A 8= 4.18666e-10 A10=-2.45395e-12 A12= 6.29348e-15 Page 28 K = 0.00000e+00 A 4=-2.17900e-05 A 6=-7.22596e-09 A 8=-1.48661e-10 A10= 1.85432e-12 A12=-3.03305e-15 Page 29 K = 0.00000e+00 A 4=-1.07831e-05 A 6=-3.03321e-09 A 8=-5.03844e-11 A10= 1.22127e-12 A12=-1.50312e-15 Focal length 14.42 F-number 1.46 Half angle of view 52.34 Image height 18.68 Optical total length 118.50 BF 14.00 When focused at infinity When focused at an object distance with a lateral magnification of -0.1x From object surface to first surface Infinity 240.532 d22 5.08 4.08 d29 2.20 3.21 Lens group data Group starting plane focal length L1 1 36.30 L2 23 28.35 L3 30 -57.28 Single lens data Lens initial surface focal length θgF 1 1 -40.86 2 3 -97.46 3 5 -34.81 4 7 87.86 5 9 -61.56 6 11 20.57 7 12 -62.22 8 14 46.32 9 16 -52.47 0.5951 10 19 24.97 11 20 198.38 0.7782 12 21 -33.37 0.5824 13 23 36.96 14 24 -25.61 0.5951 15 26 36.91 16 28 52.63 17 30 39.24 18 31 -23.32

[0160] [Numerical Example 2] Unit: mm Surface Data Surface number rd nd νd 1 52.423 1.40 1.60311 60.6 2 19.691 5.03 3 29.399 2.00 1.58313 59.4 4* 17.890 16.43 5 -23.409 1.20 1.43875 94.7 6 -99.819 0.50 7 167.077 8.86 1.75500 52.3 8 -20.287 1.05 1.85478 24.8 9 -46.575 0.25 10 70.946 5.42 1.90043 37.4 11 -70.946 0.96 12 184.489 1.10 1.54072 47.2 13 50.592 4.99 14 (Aperture) ∞ 2.18 15 124.113 3.80 2.00069 25.5 16 -86.925 0.70 1.57060 20.1 17 -58.110 1.10 1.66565 35.6 18 92.703 (variable) 19 -31.832 5.02 1.49700 81.7 20 -16.428 1.00 1.77047 29.7 21 -103.188 0.20 22 40.261 8.11 1.49700 81.7 23 -34.315 2.75 24* 87.489 5.76 1.80400 46.5 25* -54.320 (variable) 26 326.711 6.95 1.59282 68.6 27 -29.793 1.05 1.66565 35.6 28 59.878 18.44 Image plane ∞ Aspheric data Side 4 K =-4.88704e+00 A 4= 9.85206e-05 A 6=-4.60796e-07 A 8= 2.61477e-09 A10=-1.06987e-11 A12= 2.62680e-14 A14=-2.76184e-17 Page 24 K = 0.00000e+00 A 4=-8.28107e-06 A 6= 7.81678e-09 A 8=-5.60781e-11 A10= 2.06771e-13 A12=-4.03084e-16 Page 25 K = 0.00000e+00 A 4= 6.09726e-06 A 6= 5.11495e-09 A 8=-1.22444e-11 A10= 1.38078e-13 A12=-2.89951e-16 Focal length 20.60 F-number 1.46 Half angle of view: 42.54 Image height 18.90 Optical total length 117.50 BF 18.44 When focused at infinity When focused at an object distance with a lateral magnification of -0.1x From object surface to first surface Infinity 300.024 d18 9.05 7.44 d25 2.20 3.81 Lens group data Group starting plane focal length L1 1 45.15 L2 19 32.25 L3 26 -85.88 Single lens data Lens initial surface focal length θgF 1 1 -53.14 2 3 -83.73 3 5 -70.04 4 7 24.46 5 8 -42.84 0.6122 6 10 40.12 7 12 -129.29 8 15 51.55 9 16 304.54 0.7782 10 17 -53.51 0.5824 11 19 61.63 12 20 -25.49 0.5951 13 22 38.67 14 24 42.45 15 26 46.39 16 27 -29.75

[0161] [Numerical Example 3] Unit: mm Surface Data Surface number rd nd νd 1 34.785 1.25 1.79360 37.1 2 17.108 5.10 3 29.757 2.00 1.53500 56.0 4* 19.213 10.91 5 -21.843 1.20 1.49700 81.7 6 -59.460 0.38 7 108.499 9.23 1.72916 54.7 8 -17.093 1.00 1.85478 24.8 9 -37.633 0.20 10 40.930 4.97 2.00100 29.1 11 -42.422 1.00 1.57501 41.5 12 30.464 5.24 13 (Aperture) ∞ 2.53 14 83.477 1.85 2.00100 29.1 15 595.325 (variable) 16 -22.125 4.05 1.49700 81.7 17 -11.634 0.90 1.77047 29.7 18 -78.451 0.20 19 72.224 6.30 1.72916 54.7 20 -22.067 0.20 21* -169.027 4.15 1.53500 56.0 22* -27.901 (variable) 23 -131.373 8.10 1.59282 68.6 24 -17.133 1.05 1.65412 39.7 25 111.091 17.25 Image plane ∞ Aspheric data Side 4 K = 0.00000e+00 A 4=-6.65980e-06 A 6=-3.24494e-08 A 8= 5.25976e-11 A10=-5.17248e-13 Page 21 K = 0.00000e+00 A 4=-3.01742e-05 A 6= 1.03918e-08 A 8=-2.78416e-10 A10= 2.38934e-12 A12=-1.19202e-14 Page 22 K = 0.00000e+00 A 4= 6.71096e-06 A 6= 2.88119e-08 A 8=-2.08523e-10 A10= 2.35578e-12 A12=-9.87781e-15 Focal length 20.60 F-number 1.85 Half angle of view: 42.64 Image height 18.97 Optical total length 98.50 BF 17.25 When focused at infinity When focused at an object distance with a lateral magnification of -0.1x From object surface to first surface Infinity 283.670 d15 7.24 5.62 d22 2.20 3.81 Lens group data Group starting plane focal length L1 1 33.12 L2 16 31.34 L3 23 -70.29 Single lens data Lens initial surface focal length θgF 1 1 -43.79 2 3 -108.52 3 5 -70.21 4 7 20.90 5 8 -37.48 0.6122 6 10 21.45 7 11 -30.68 8 14 96.82 9 16 43.76 10 17 -17.83 0.5951 11 19 23.85 12 21 61.83 13 23 32.38 14 24 -22.62

[0162] [Numerical Example 4] Unit: mm Surface Data Surface number rd nd νd 1 71.542 1.05 1.62004 36.3 2 20.538 9.22 3 536.237 1.80 1.53500 56.0 4* 195.727 6.51 5 -25.880 1.00 1.58144 40.8 6 -45.968 0.23 7 -81.956 9.01 1.87070 40.7 8 -20.977 1.05 1.85478 24.8 9 -41.688 1.33 0.6122 10 35.061 4.85 2.00069 25.5 11 788.676 0.99 0.7230 12 29.284 1.10 1.51742 52.4 0.6122 13 19.707 11.37 14 -30.397 4.97 1.59282 68.6 15 -16.310 1.00 1.85478 24.8 16 -23.209 0.50 17 (Aperture) ∞ (Variable) 18 -23.769 3.97 1.49700 81.7 19 -15.307 0.70 1.60401 20.8 20 -14.297 1.00 1.85478 24.8 21 -46.845 0.20 22 66.641 9.32 1.49700 81.7 23 -27.000 0.15 24* 119.785 6.50 1.80400 46.5 25* -47.701 (variable) 26 57.367 4.83 1.92286 20.9 27 -215.059 1.05 1.77047 29.7 28 35.159 6.22 29 -64.493 1.00 1.77047 29.7 30 -11124.715 12.50 Image plane ∞ Aspheric data Side 4 K = 0.00000e+00 A 4=-7.78923e-07 A 6=-4.74554e-09 A 8=-3.40498e-12 Page 24 K = 0.00000e+00 A 4=-5.94169e-06 A 6= 1.89102e-08 A 8=-1.30969e-10 A10= 5.43367e-13 A12=-9.16322e-16 Page 25 K = 0.00000e+00 A 4= 4.36873e-06 A 6= 1.94417e-08 A 8=-1.21992e-10 A10= 5.31778e-13 A12=-8.61502e-16 Focal length 24.00 F-number 1.50 Half angle of view 38.29 Image height 18.95 Optical total length 113.00 BF 12.50 When focused at infinity When focused at an object distance with a lateral magnification of -0.1x From object surface to first surface Infinity 325.872 d17 7.40 5.34 d25 2.20 4.25 Lens group data Group starting plane focal length L1 1 47.04 L2 18 31.80 L3 26 -64.02 Single lens data Lens initial surface focal length θgF 1 1 -46.83 2 3 -577.20 3 5 -103.75 4 7 30.30 5 8 -50.58 6 10 36.55 7 12 -121.22 8 14 52.48 9 15 -68.79 0.6122 10 18 74.86 11 19 284.54 0.7230 12 20 -24.42 0.6122 13 22 39.98 14 24 43.18 15 26 49.49 16 27 -39.15 17 29 -84.20

[0163] [Numerical Example 5] Unit: mm Surface Data Surface number rd nd νd 1* 31.090 2.50 1.58313 59.4 2* 13.099 14.59 3 -530.553 1.70 1.49700 81.7 4 47.214 5.63 5 -49.986 2.00 1.80400 46.5 6* 87.783 0.20 7 31.641 3.06 1.66565 35.6 8 68.370 3.74 9 -36.085 1.20 1.43387 95.1 10 60.775 0.20 11 32.009 8.73 1.75500 52.3 12 -25.657 1.05 1.84666 23.8 13 -54.614 0.20 14 167.133 3.92 1.83481 42.7 15 -53.249 4.34 16 -24.473 1.10 1.77047 29.7 17 -65.694 2.00 18 (Aperture) ∞ 1.68 19 50.345 6.13 2.00100 29.1 20 -44.102 1.00 1.57060 20.1 21 -32.378 1.10 1.66565 35.6 22 87.176 (variable) 23 -140.226 7.75 1.43875 94.7 24 -14.948 1.00 1.77047 29.7 25 -65.160 0.20 26 40.856 8.72 1.49700 81.7 27 -31.383 0.20 28* 128.494 4.66 1.85400 40.4 29* -70.134 (variable) 30 -319.132 7.26 1.59282 68.6 31 -23.023 1.05 1.91650 31.6 32 -1191.612 15.50 Image plane ∞ Aspheric data Front page K = 0.00000e+00 A 4=-1.01110e-05 A 6= 8.17661e-10 A 8= 8.93040e-12 A10=-1.54052e-14 A12= 7.63241e-18 2nd side K =-6.44184e-01 A 4=-6.39936e-06 A 6=-1.43284e-08 A 8=-2.16244e-10 A10= 7.31957e-13 A12=-1.78412e-15 Page 6 K = 0.00000e+00 A 4= 2.13738e-05 A 6= 2.10113e-08 A 8= 3.60161e-10 A10=-2.14645e-12 A12= 6.19796e-15 Page 28 K = 0.00000e+00 A 4=-2.11705e-05 A 6=-5.23668e-09 A 8=-1.83281e-10 A10= 1.81505e-12 A12=-2.71601e-15 Page 29 K = 0.00000e+00 A 4=-1.02347e-05 A 6=-7.27343e-09 A 8=-3.83789e-11 A10= 1.01331e-12 A12=-1.00325e-15 Focal length 14.42 F-number 1.46 Half angle of view 52.34 Image height 18.68 Optical total length 119.50 BF 15.50 When focused at infinity When focused at an object distance with a lateral magnification of -0.1x From object surface to first surface Infinity 241.623 d22 4.90 3.89 d29 2.20 3.21 Lens group data Group starting plane focal length L1 1 36.74 L2 23 29.10 L3 30 -65.56 Single lens data Lens initial surface focal length θgF 1 1 -40.91 2 3 -87.15 3 5 -39.36 4 7 85.64 5 9 -51.99 6 11 20.18 7 12 -58.12 8 14 48.77 9 16 -51.22 0.5951 10 19 24.27 11 20 207.03 0.7782 12 21 -35.34 0.5824 13 23 37.43 14 24 -25.40 0.5951 15 26 37.20 16 28 53.71 17 30 41.48 18 31 -25.63

[0164] [Numerical Example 6] Unit: mm Surface Data Surface number rd nd νd 1 43.024 1.40 1.61800 63.4 2 20.105 5.66 3 32.408 2.00 1.58313 59.4 4* 17.039 15.89 5 -23.276 1.20 1.43875 94.7 6 -65.876 0.50 7 1040.783 9.43 1.75500 52.3 8 -20.743 1.05 1.85478 24.8 9 -51.168 0.25 10 88.793 5.21 1.88100 40.1 11 -61.610 0.25 12 53.033 1.10 1.48749 70.2 13 33.098 6.53 14 (Aperture) ∞ 1.38 15 56.211 4.07 2.00069 25.5 16 -282.390 0.70 1.57060 20.1 17 -106.816 1.10 1.61340 44.3 18 35.085 (variable) 19 -55.827 6.01 1.49700 81.7 20 -17.101 1.00 1.77047 29.7 21 -285.670 0.20 22 49.100 7.70 1.49700 81.7 23 -32.916 4.78 24* 167.193 5.11 1.80400 46.5 25* -71.686 (variable) 26 64.441 8.97 1.59282 68.6 27 -37.571 1.05 1.66565 35.6 28 96.827 20.51 Image plane ∞ Aspheric data Side 4 K =-4.93669e+00 A 4= 1.15091e-04 A 6=-5.84829e-07 A 8= 3.36673e-09 A10=-1.32319e-11 A12= 2.98902e-14 A14=-2.80832e-17 Page 24 K = 0.00000e+00 A 4=-3.47747e-06 A 6=-1.65912e-09 A 8= 4.12770e-11 A10=-9.38830e-14 A12=-2.12904e-17 Page 25 K = 0.00000e+00 A 4= 3.21233e-06 A 6= 1.28708e-09 A 8= 3.52617e-11 A10=-2.24322e-14 A12=-1.03425e-16 Focal length 20.60 F-number 1.50 Half angle of view: 42.57 Image height 18.93 Optical total length 125.00 BF 20.51 When focused at infinity When focused at an object distance with a lateral magnification of -0.1x From object surface to first surface Infinity 309.542 d18 9.74 7.07 d25 2.20 4.88 Lens group data Group starting plane focal length L1 1 63.61 L2 19 45.28 L3 26 1142.84 Single lens data Lens initial surface focal length θgF 1 1 -62.53 2 3 -64.71 3 5 -82.75 4 7 27.04 5 8 -41.47 0.6122 6 10 41.97 7 12 -183.95 8 15 47.13 9 16 300.65 0.7782 10 17 -42.93 0.5633 11 19 47.17 12 20 -23.65 0.5951 13 22 40.93 14 24 63.00 15 26 41.39 16 27 -40.54

[0165] [Numerical Example 7] Unit: mm Surface Data Surface number rd nd νd θgF 1 41.398 1.25 1.85026 32.3 2 16.925 7.52 3 62.508 2.00 1.53500 56.0 4* 39.199 8.09 5 -20.954 1.20 1.49700 81.7 0.6122 6 -34.367 0.20 7 1150.801 8.11 1.87070 40.7 8 -18.645 1.00 1.85478 24.8 9 -53.827 0.20 10 25.911 4.47 1.95375 32.3 0.5951 11 -857.774 0.63 12 -1141.763 1.00 1.51742 52.4 13 19.319 6.01 14 (Aperture) ∞ 2.55 15 86.000 1.99 2.00100 29.1 16 ∞ (variable) 17 -23.457 4.27 1.49700 81.7 18 -11.526 0.90 1.77047 29.7 19 -46.802 0.20 20 53.297 7.13 1.59282 68.6 21 -22.514 1.46 22* -204.835 4.59 1.80400 46.5 23* -34.800 (variable) 24 -959.581 6.27 1.59282 68.6 25 -23.602 1.05 1.66565 35.6 26 52.918 17.22 Image plane ∞ Aspheric data Side 4 K = 0.00000e+00 A 4=-8.84221e-06 A 6=-2.21367e-08 A 8=-3.29970e-11 A10=-5.08866e-14 Page 22 K = 0.00000e+00 A 4=-2.21360e-05 A 6= 1.50179e-08 A 8=-4.23029e-10 A10= 3.18520e-12 A12=-1.12092e-14 Page 23 K = 0.00000e+00 A 4= 1.34397e-06 A 6= 2.33770e-08 A 8=-2.84542e-10 A10= 2.23920e-12 A12=-7.01230e-15 Various data Zoom ratio 1.00 Focal length 20.44 F-number 1.85 Half angle of view: 42.77 Image height 18.91 Optical total length 98.17 BF 17.22 When focused at infinity When focused at an object distance with a lateral magnification of -0.1x From object surface to first surface Infinity 282.639 d16 6.65 5.21 d23 2.20 3.64 Lens group data Group starting plane focal length L1 1 39.40 L2 17 28.11 L3 24 -61.16 Single lens data Lens starting surface focal length 1 1 -34.48 2 3 -202.55 3 5 -111.34 4 7 21.14 5 8 -33.82 6 10 26.44 7 12 -36.71 8 15 85.88 9 17 40.75 10 18 -20.07 11 20 27.67 12 22 51.52 13 24 40.72 14 25 -24.39

[0166] Various values ​​in each numerical example are summarized in Tables 1 and 2 below.

[0167] [Table 1]

[0168] The lenses that satisfy the conditional expressions (6), (7), (12), (14), and (15) in each numerical example and their numerical values ​​are summarized in Table 2 below.

[0169] [Table 2]

[0170] [Imaging device] Next, an embodiment of an imaging device including the optical system L0 of this embodiment will be described.

[0171] 15 is a schematic diagram of an image capturing device 10 equipped with the optical system L0 of this embodiment. The image capturing device 10 includes a camera body 13, an optical system 11 similar to any of the above-described embodiments 1 to 7, and a light receiving element 12 that photoelectrically converts an image formed by the optical system 11.

[0172] The imaging device 10 of this embodiment can obtain high-quality images formed by the optical system 11, which has a wide angle, corrects distortion aberration, and improves the peripheral illumination ratio.

[0173] It should be noted that an imaging element such as a CCD or CMOS sensor can be used as the light receiving element 12. In this case, various aberrations such as distortion and chromatic aberration of the image acquired by the light receiving element 12 can be corrected, for example, by an electrical method, thereby improving the image quality of the output image.

[0174] The optical system L0 of each of the above-described embodiments can be applied not only to the digital still camera shown in Fig. 15 but also to various optical devices such as silver halide film cameras, video cameras, telescopes, etc. Furthermore, the camera may be of an integrated lens type or an interchangeable lens type.

[0175] [Lens device] Next, an embodiment of a lens device including the optical system L0 of this embodiment will be described.

[0176] Fig. 16 is a schematic diagram showing the appearance of a lens device equipped with the optical system L0 of this embodiment. The lens device of Fig. 16 is a so-called interchangeable lens that is detachably attached to a camera body (not shown).

[0177] The lens device 20 includes a photographing optical system 21 similar to any one of the above-described embodiments 1 to 7. The lens device 20 includes a focus operation means 22 and an operation means 23 for changing the photographing mode.

[0178] When the user operates the focus operation means 22, the arrangement of the photographic optical system 21 is changed mechanically or electrically, thereby changing the focal position. Note that the user may operate the operation means 23 to change the arrangement of the lens groups in the photographic optical system 21 for purposes other than focusing. For example, the arrangement of the lens groups in the photographic optical system 21 may be changed mechanically or electrically in response to the operation of the operation means 23, thereby changing the aberration of the photographic optical system 21. In this case, it is preferable that the focal position does not substantially change.

[0179] Although the preferred embodiments and examples of the present invention have been described above, the present invention is not limited to these embodiments and examples, and various combinations, modifications, and changes are possible within the scope of the gist of the present invention.

[0180] The disclosure of each embodiment includes the disclosed configuration.

[0181] (Configuration 1) An optical system comprising a first lens group having positive refractive power, a second lens group having positive refractive power, and a third lens group, arranged in this order from the object side to the image side, During focusing, the second lens group moves in the optical axis direction relative to the image plane, and the first lens group and the third lens group are stationary relative to the image plane; the first lens group has three negative lenses arranged consecutively in the optical axis direction on the most object side, An optical system characterized in that the following conditional expression is satisfied, where f is the focal length of the entire optical system, sk is the back focus in air when focused to infinity, and f2 is the focal length of the second lens group: 0.50 <f2 / f<3.00 0.20 <sk / f<1.20

[0182] (Configuration 2) An optical system comprising a positive first lens group, a positive second lens group, and a third lens group, arranged in this order from the object side to the image side, During focusing, the second lens group moves in the optical axis direction relative to the image plane, and the first lens group and the third lens group are stationary relative to the image plane; An optical system characterized in that the following conditional expression is satisfied, where f is the focal length of the entire optical system, sk is the back focus in air when focused to infinity, and f2 is the focal length of the second lens group. 0.50 <f2 / f<3.00

[0183] (Configuration 3) 3. The optical system according to configuration 1 or 2, wherein the following condition is satisfied, where f1 is the focal length of the first lens group: 0.30 <f1 / f2<3.00

[0184] (Configuration 4) 4. The optical system according to any one of configurations 1 to 3, wherein the following condition is satisfied when the focal length of the third lens group is f3: -1.50 <f / f3<1.50

[0185] (Configuration 5) 5. The optical system according to any one of configurations 1 to 4, wherein the second lens group has at least two positive lenses and at least one negative lens.

[0186] (Configuration 6) the object-side lens surface of the lens arranged closest to the object in the second lens group has a concave shape; an image-side lens surface of the second lens group that is located closest to the image side has a convex shape; The optical system according to any one of Configurations 1 to 5, wherein when a radius of curvature of the object-side surface of the lens in the second lens group that is located closest to the object is R21 and a radius of curvature of the image-side surface of the lens in the second lens group that is located closest to the image is R22, the optical system satisfies the following conditional expression: -1.50<(R22-R21) / (R22+R21)<1.50

[0187] (Configuration 7) at least one of the first lens group and the second lens group has a negative lens Gn; The optical system according to any one of configurations 1 to 6, characterized in that the following conditional expression is satisfied when the refractive index of the material of the negative lens Gn for the d-line is Ndn, the Abbe number is νdn, the partial dispersion ratio for the g-line and the F-line is θgFn, and the anomalous partial dispersion is ΔθgFn. -0.015<ΔθgFn<0.015 -0.20 <Ndn-(-0.0145425×νdn+2.28725)<0.05 where ΔθgFn=θgFn-(-0.0025116×νdn+0.67449) It is expressed as:

[0188] (Configuration 8) 8. The optical system according to any one of configurations 1 to 7, wherein the first lens group includes at least one negative lens Gn.

[0189] (Configuration 9) 9. The optical system according to any one of configurations 1 to 8, wherein the second lens group includes at least one negative lens Gn.

[0190] (Configuration 10) The optical system according to any one of configurations 1 to 9, wherein the following conditional expression is satisfied, where β2 is the lateral magnification of the second lens group when focused at infinity, and β3 is the lateral magnification of the third lens group when focused at infinity. 0.50<(1-β2 2 )×β3 2 <2.50 (Configuration 11) an aperture stop disposed inside the first lens group or adjacent to the first lens group on the image side; 11. The optical system according to any one of configurations 1 to 10, wherein the aperture stop is fixed in the optical axis direction relative to the image plane during focusing.

[0191] (Configuration 12) 12. The optical system according to any one of configurations 1 to 11, wherein the following condition is satisfied when the focal length of the third lens group is f3: 0.00 <sk / |f3|<0.80

[0192] (Configuration 13) The optical system according to any one of Configurations 1 to 12, wherein the following conditional expression is satisfied, where ΣDair is the sum of the air spaces on the optical axis from the object-side lens surface of the lens in the first lens group that is positioned closest to the object to the image-side lens surface of the lens in the third lens group that is positioned closest to the image, and L is the total optical length of the optical system: 0.20<ΣDair / (L-sk)<0.70

[0193] (Configuration 14) 14. The optical system according to any one of configurations 1 to 13, wherein the following condition is satisfied, where L is the total optical length of the optical system: 2.00 <L / f<15.00

[0194] (Configuration 15) the second lens group has at least one positive lens G2p, The optical system according to any one of Configurations 1 to 14, wherein the following condition is satisfied when the Abbe number of the material of the positive lens G2p is νd2p: 60.00<νd2p<100.00

[0195] (Configuration 16) The optical system according to any one of configurations 1 to 15, characterized in that the following conditional expression is satisfied: M2 is the amount of movement of the second lens group when focusing from infinity to an object distance where the lateral magnification of the entire system is −0.1; M2 is the amount of movement of the second lens group when moving toward the image side when focusing from infinity to an object distance where the lateral magnification of the entire system is −0.1; and DSP is the distance on the optical axis from the aperture stop to the image plane when the optical system is focused at infinity. -0.20 <M2 / DSP<-0.005

[0196] (Configuration 17) the first lens group includes a negative lens G1n, 17. The optical system according to any one of Configurations 1 to 16, wherein the following condition is satisfied when the Abbe number of the material of the negative lens G1n is νd1n: 60.00<νd1n<100.00

[0197] (Configuration 18) at least one of the first lens group and the second lens group has a positive lens Gp; The optical system described in any one of Configurations 1 to 17, characterized in that when the Abbe number of the material of the positive lens Gp is ​​νdp, the partial dispersion ratio is θgFp, and the anomalous partial dispersion is ΔθgFp, the following conditional expression is satisfied: 0.050<ΔθgFp<0.250 however, ΔθgFp=θgFp-(B3×νdp 3 +B2×νdp 2 +B1×νdp+B0) B3=-1.665×10 -7 B2=5.213×10 -5 B1=-5.656×10 -3 B0=7.278×10 -1 It is expressed as:

[0198] (Configuration 19) 19. The optical system according to any one of configurations 1 to 18, wherein the following conditional expression is satisfied, where DSP is the distance on the optical axis from the aperture stop to the image plane when the optical system is focused at infinity, and L is the total optical length of the optical system: 0.30<(DSP+sk) / L<0.80

[0199] (Configuration 20) 20. The optical system according to any one of Configurations 1 to 19, wherein the following condition is satisfied when the focal length of the first lens group is f1: 0.50 <f1 / f<5.00

[0200] (Configuration 21) 21. The optical system according to any one of configurations 1 to 20, wherein a negative lens is disposed closest to the image side of the third lens group.

[0201] (Configuration 22) 22. An imaging device comprising: the optical system according to any one of configurations 1 to 21; and an imaging element that receives an image formed by the optical system. [Explanation of symbols]

[0202] L0 optical system L1 First lens group L2 Second lens group L3: Third lens group

Claims

1. An optical system comprising a first lens group having positive refractive power, a second lens group having positive refractive power, and a third lens group, arranged in this order from an object side to an image side, During focusing, the second lens group moves in the optical axis direction relative to the image plane, and the first lens group and the third lens group are stationary relative to the image plane; the first lens group has three negative lenses disposed consecutively in the optical axis direction on the most object side, the second lens group has two or more lenses but not more than four lenses, the second lens group has two or more positive lenses, an optical system characterized in that the following conditional expression is satisfied, where f is a focal length of the entire optical system, L is an overall optical length of the optical system, sk is an air-equivalent back focus when focused to infinity, f1 is a focal length of the first lens group, f2 is a focal length of the second lens group, and f3 is a focal length of the third lens group: 0.50<f2 / f<3.00 0.20<sk / f≦1.075 0.00<sk / |f3|≦0.282 4.00<L / f<15.00 -1.50<f / f3≦0.018 0.50<f1 / f<5.00

2. 2. The optical system according to claim 1, wherein the following condition is satisfied: 0.30<f1 / f2<3.00

3. 2. The optical system according to claim 1, wherein the second lens group includes at least one negative lens.

4. the object-side lens surface of the lens arranged closest to the object side in the second lens group has a concave shape; an image-side lens surface of the second lens group that is disposed closest to the image side has a convex shape; 2. The optical system according to claim 1, wherein the following conditional expression is satisfied: R21 is a radius of curvature of the object-side surface of the lens in the second lens group that is arranged closest to the object, and R22 is a radius of curvature of the image-side surface of the lens in the second lens group that is arranged closest to the image. -1.50<(R22-R21) / (R22+R21)<1.50

5. At least one of the first lens group and the second lens group has a negative lens Gn, The optical system according to claim 1, wherein the following conditional expression is satisfied when the refractive index of the material of the negative lens Gn for the d-line is Ndn, the Abbe number is νdn, the partial dispersion ratio for the g-line and the F-line is θgFn, and the anomalous partial dispersion is ΔθgFn: -0.015<ΔθgFn<0.015 -0.20<Ndn-(-0.0145425×νdn+2.28725)<0.05 where ΔθgFn=θgFn-(-0.0025116×νdn+0.67449) It is expressed as:

6. 6. The optical system according to claim 5, wherein the first lens group includes at least one negative lens Gn.

7. 6. The optical system according to claim 5, wherein the second lens group includes at least one negative lens Gn.

8. 2. The optical system according to claim 1, wherein the following condition is satisfied, where β2 is the lateral magnification of the second lens group when focused at infinity, and β3 is the lateral magnification of the third lens group when focused at infinity: ０．５０＜（１－β２ ２ ）×β３ ２ ＜２．５０

9. an aperture stop disposed inside the first lens group or adjacent to the first lens group on the image side; 2. The optical system according to claim 1, wherein said aperture stop is fixed in the optical axis direction relative to the image plane during focusing.

10. 2. The optical system according to claim 1, wherein the following conditional expression is satisfied, where ΣDair is a sum of air spaces on the optical axis from the object-side lens surface of the lens in the first lens group that is located closest to the object to the image-side lens surface of the lens in the third lens group that is located closest to the image: 0.20<ΣDair / (L-sk)<0.70

11. the second lens group has at least one positive lens G2p, 2. The optical system according to claim 1, wherein the following condition is satisfied, where νd2p is the Abbe number of the material of said positive lens G2p: 60.00<νd2p<100.00

12. The optical system according to claim 1, wherein the following conditional expression is satisfied: M2 is a movement amount of the second lens group when focusing from infinity to an object distance where the lateral magnification of the entire system is −0.1 times; M2 is a movement amount of the second lens group when moving toward the image side when focusing from infinity to an object distance where the lateral magnification of the entire system is −0.1 times; and DSP is a distance on the optical axis from the aperture stop to the image plane when the optical system is focused at infinity. -0.200<M2 / DSP<-0.005

13. the first lens group includes a negative lens G1n, 2. The optical system according to claim 1, wherein the following condition is satisfied, where νd1n is the Abbe number of the negative lens G1n: 60.00<νd1n<100.00

14. At least one of the first lens group and the second lens group has a positive lens Gp, 2. The optical system according to claim 1, wherein the following condition is satisfied when the Abbe number of the material of said positive lens Gp is ​​vdp, the partial dispersion ratio is θgFp, and the anomalous partial dispersion is ΔθgFp. 0.050<ΔθgFp<0.250 however, ΔθgFp=θgFp-(B3×νdp ３ +B2×νdp ２ +B1×νdp+B0) B3=-1.665×10 －７ B2=5.21310 －５ B1=-5.656×� －３ B0 = 7.278 × 10 －１ It is expressed as:

15. 2. The optical system according to claim 1, wherein the following condition is satisfied, where DSP is the distance on the optical axis from the aperture stop to the image plane when the optical system is focused at infinity: 0.30<(DSP+sk) / L<0.80

16. 2. The optical system according to claim 1, wherein a negative lens is disposed closest to the image side of the third lens group.

17. 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