Optical system and imaging device having the same

Abstract

To provide an optical system that has high optical performance despite a large aperture ratio and is capable of high-speed focusing. [Solution] An optical system consisting of a front group having positive refractive power, an image-side focusing group having positive refractive power, and a rear group, arranged in that order from the object side to the image side, wherein when focusing from infinity to a close distance, the image-side focusing group moves relative to the image plane so that the distance between the front group and the image-side focusing group and the distance between the image-side focusing group and the rear group change, and when focusing from infinity to a close distance, the rear group remains stationary relative to the image plane, an aperture stop that determines the axial light beam is arranged inside the front group or adjacent to the image side of the front group, and the front group has a positive lens Gp, and when the Abbe number of the material of the positive lens Gp is ​​vdp, the partial dispersion ratio is θgFp, and the anomalous partial dispersion is ΔθgFp, a predetermined conditional expression is satisfied.

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 with large aperture ratios that are compact yet provide high image quality with well-corrected aberrations, 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 a first lens group, a second lens group, and a third lens group, arranged in this order from the object side to the image side, in which the second lens group moves relative to the image plane during focusing, and an aperture stop is arranged in the second lens group. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-152773 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the optical system disclosed in Patent Document 1, the mass of the second lens group that moves during focusing is large, making high-speed focusing difficult and possibly resulting in a degradation of optical performance 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 front group having positive refractive power, an image-side focusing group having positive refractive power, and a rear group, wherein, during focusing from infinity to a close distance, the image-side focusing group moves relative to the image plane so that a distance between the front group and the image-side focusing group and a distance between the image-side focusing group and the rear group change, and wherein, during focusing from infinity to a close distance, the rear group remains stationary relative to the image plane, an aperture stop which determines an axial ray bundle is arranged within the front group or adjacent to the front group on the image side, the front group has a positive lens Gp, and wherein, when the Abbe number of the material of the positive lens Gp is ​​vdp, the partial dispersion ratio is θgFp, and the anomalous partial dispersion is ΔθgFp, the optical system satisfies the following condition: 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:

[0006] Another aspect of the present invention is an optical system consisting of a front group having positive refractive power, an image-side focusing group having positive refractive power, and a rear group, arranged in that order from the object side to the image side, wherein the image-side focusing group moves relative to the image plane so that the distance between the front group and the image-side focusing group and the distance between the image-side focusing group and the rear group change when focusing from infinity to a close distance, and the image-side focusing group has at least two negative lenses. [Effects of the Invention]

[0007] It is possible to provide an optical system that has high optical performance despite its large aperture ratio and is capable of high-speed focusing. [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] 10 is a cross-sectional view of the optical system of Example 8 when focused at infinity. [Figure 16] Longitudinal aberration diagrams of the optical system of Example 8 when focusing to (A) infinity and (B) the distance at which the lateral magnification is −0.1 [Figure 17] Schematic diagram of the imaging device [Figure 18] 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 duplicated descriptions will be omitted.

[0010] 1, 3, 5, 7, 9, 11, 13, and 15 are cross-sectional views of the optical systems of Examples 1 to 8 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 denotes the entire optical system, and lens group Li denotes the i-th lens group (i is a natural number) counting from the object side among the lens groups that move or are fixed integrally with respect to the image plane during focusing. In other words, the air spacing between adjacent lens groups changes during focusing, but the air spacing between lenses within each lens group does not change during focusing. Furthermore, each lens group may be composed of one lens or multiple lenses.

[0013] In the present disclosure, the inside of a lens group refers to the space between the lens arranged closest to the object and the lens arranged closest to the image among the lenses constituting the lens group.

[0014] In optical system L0, LFR denotes the image-side focusing group that is positioned closest to the image among the lens groups that move during focusing from infinity to a close distance. LF denotes the front group, which is a group of all lenses that are positioned closer to the object than the image-side focusing group LFR. LR denotes the rear group, which is a group of all lenses that are positioned closer to the image than the image-side focusing group LFR.

[0015] Furthermore, at least some of the lenses included in the front group LF may move in the optical axis direction during focusing as a front focusing group.

[0016] Furthermore, Gk represents the kth (k is a natural number) lens counted from the object side among the lenses included in the optical system L0. Furthermore, the lens surface of each lens may have a metasurface.

[0017] 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, during focusing from infinity to a close distance, the image-side focusing group LFR, which will be described later, moves from the image side to the object side.

[0018] 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.

[0019] 2, 4, 6, 8, 10, 12, 14, and 16 are aberration diagrams when the optical systems L0 of Examples 1 to 8 are focused at (A) infinity and (B) a distance at which the lateral magnification is −0.1, respectively.

[0020] 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 astigmatism 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 lateral chromatic aberration for the g-line. Additionally, ω is the imaging half angle of view (°).

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

[0022] The optical system L0 in each embodiment comprises, arranged in order from the object side to the image side, a front group LF having positive refractive power, an image-side focusing group LFR having positive refractive power, and a rear group LR. During focusing from infinity to a close distance, the image-side focusing group LFR moves relative to the image plane so that the distance between the front group LF and the image-side focusing group LFR and the distance between the image-side focusing group LFR and the rear group LR change.

[0023] The optical system L0 is configured so that a light beam converged by the front lens unit LF, which has positive refractive power, enters the image-side focusing group LFR, which also has positive refractive power. This allows the lens diameter of the image-side focusing group LFR, which moves relative to the image plane during focusing, to be reduced, and the weight of the image-side focusing group LFR to be reduced, enabling high-speed focusing.

[0024] Furthermore, by locating the rear group LR at a position far from the aperture stop SP, 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.

[0025] Next, the configuration that is preferably satisfied in the optical system L0 of each embodiment will be described.

[0026] In the optical system L0 of each embodiment, it is preferable to position an aperture stop SP inside the front group LF or adjacent to it on the image side. This makes it possible to reduce the height of off-axial rays incident on the image-side focusing group LFR, and to reduce the lens diameter of the image-side focusing group LFR. Furthermore, by making the aperture stop SP immovable during focusing, it is no longer necessary to move the mechanical components that make up the aperture stop SP during focusing. This makes it possible to reduce the weight of the image-side focusing group LFR, which is preferable because it enables high-speed focusing.

[0027] In the optical system L0 of each embodiment, it is preferable that the front group LF has at least two negative lenses. In a wide-angle lens, to ensure sufficient back focus, a strong negative refractive power is required on the object side of the optical system L0. By sharing this strong negative refractive power among at least two negative lenses, the refractive power per negative lens can be reduced, thereby suppressing the occurrence of distortion and curvature of field.

[0028] In the optical system L0 of each embodiment, it is preferable that the image-side focusing group LFR has at least two positive lenses and at least one negative lens. To reduce the amount of movement of the image-side focusing group LFR during focusing from infinity to a close distance, the refractive power of the image-side focusing group LFR must be increased. By sharing this strong refractive power with at least two positive lenses, the refractive power per positive lens can be reduced, thereby reducing fluctuations in spherical aberration and field curvature during focusing. Furthermore, having at least one negative lens can suppress fluctuations in axial chromatic aberration that occur during focusing.

[0029] 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 image-side focusing group LFR has a concave shape facing the object side. This allows off-axial light beams that have passed through the aperture stop SP to be incident on the surface closest to the object in the image-side focusing group LFR in a substantially concentric manner, thereby reducing the refraction of light rays at that surface. This makes it possible to suppress fluctuations in astigmatism and coma, as well as fluctuations in the angle of view, during focusing.

[0030] In the optical system L0 of each embodiment, it is preferable that the image-side lens surface of the lens arranged closest to the image side in the image-side focusing group LFR has a convex shape facing the image side. This allows off-axial light beams emerging from the image-side focusing group LFR to emerge approximately concentrically from the surface closest to the image side in the image-side focusing group LFR, thereby reducing the refraction of light rays at that surface. This makes it easier to suppress fluctuations in astigmatism and coma aberration, as well as fluctuations in the angle of view, during focusing.

[0031] In the optical system L0 of each embodiment, it is preferable to position a negative lens closest to the image side of the rear group LR, 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 rear group LR. Furthermore, by positioning 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, thereby enabling good correction of field curvature.

[0032] In the optical system L0 of each embodiment, the positive lens Gp is ​​preferably arranged as a triplet cemented lens Gcomp consisting of, in order from the object side, a positive lens, a positive lens Gp, and a negative lens, or a negative lens, a positive lens Gp, and a positive lens, thereby improving the effect of correcting axial chromatic aberration.

[0033] In addition, in the optical system L0 of each embodiment, by cementing the object-side and image-side lens surfaces of the positive lens Gp with other lenses, when the positive lens Gp is ​​made of a resin material, the degree of moisture absorption of the positive lens Gp can be reduced. This reduces deformation of the positive lens Gp and the lenses cemented thereto, making it possible to suppress changes in spherical aberration, etc., even in a high-humidity environment.

[0034] Next, conditions that the optical system L0 of each embodiment should preferably satisfy will be described.

[0035] It is preferable that the optical system L0 of each embodiment satisfies one or more of the following conditional expressions (1) to (18): In each conditional expression, the various numerical values ​​are expressed as follows.

[0036] The Abbe number of the material of the positive lens Gp in the front group LF is νdp, the partial dispersion ratio is θgFp, and the anomalous partial dispersion is ΔθgFp, where the various values ​​are expressed as follows: 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

[0037] The air-equivalent back focus of the optical system L0 when focused at infinity is denoted by sk.

[0038] The focal length of the entire optical system L0 is defined as f.

[0039] The focal length of the front group LF is defined as fLF, the focal length of the image-side focusing group LFR as fLFR, and the focal length of the rear group LR as fLR.

[0040] The radius of curvature of the lens surface closest to the object in the image-side focusing group LFR is defined as RLFR1, and the radius of curvature of the lens surface closest to the image is defined as RLFR2.

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

[0042] The anomalous partial dispersion ΔθgFn of the material 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] When focused at infinity, the lateral magnification of the image-side focusing group LFR is βLFR, and the lateral magnification of the rear group LR is βLR.

[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 defined as L. The total optical length is the distance from the first lens surface to the final lens surface plus the back focus in air.

[0046] The Abbe number of the material of the negative lens G1n in the front group LF is denoted by νd1n.

[0047] The Abbe number of the material of the positive lens G2p in the image-side focusing group LFR is denoted by νd2p.

[0048] The amount of movement of the image-side focusing group LFR during focusing from infinity to an object distance at which the lateral magnification of the entire system becomes −0.1 times is defined as MLFR.

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

[0050] The focal length of the cemented lens Gcomp including the positive lens Gp in the front group LF is represented by fGcomp.

[0051] 0.050<ΔθgFp<0.250 (1) 0.10 <sk / f<1.80 ···(2) 0.30 <fLF / fLFR<3.00 ···(3) -1.50 <f / fLR<1.50 ···(4) -1.50<(RLFR2-RLFR1) / (RLFR2+RLFR1)<1.50...(5) -0.015<ΔθgFn<0.015 (6) -0.200 <Ndn-(-1.454×10 -2 ×νdn+2.287)<0.05 (7) 0.50<(1-βLFR 2 )×βLR 2 <2.50 (8) 0.00 <sk / |fLR|<0.80 ···(9) 0.20<ΣDair / (L-sk)<0.70 ···(10) 1.50 <L / f<15.00 ···(11) 60.00<νd2p<100.00 (12) -0.200 <MLFR / DSP<-0.005 ···(13) 60.00<νd1n<100.00 (14) 0.50 <fLFR / f<3.00 ···(15) 0.30<(DSP+sk) / L<0.80 (16) 0.50 <fLF / f<5.00 ···(17) 0.00 <f / fGcomp<2.00 ···(18)

[0052] Next, the technical meaning of the above-mentioned conditional expressions (1) to (18) will be explained.

[0053] Condition (1) defines the anomalous partial dispersion ΔθgFp of the positive lens Gp arranged in the front group LF.

[0054] Axial chromatic aberration in the short wavelength region, 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, the axial chromatic aberration for the g-line tends to become excessive. Therefore, by using a material with a large ΔθgFp for the positive lens, the excessive axial chromatic aberration in the short wavelength region, such as the g-line, can be selectively converged, thereby making it possible to effectively correct the axial chromatic aberration.

[0055] If ΔθgFp becomes small below the lower limit of conditional expression (1), it becomes difficult to correct longitudinal chromatic aberration, which is not preferable.

[0056] If ΔθgFp becomes large beyond the upper limit of conditional expression (1), then the longitudinal chromatic aberration will be overcorrected, which is not desirable.

[0057] Conditional expression (2) relates to the air-equivalent back focal length sk of optical system L0. By satisfying conditional expression (2), the rear group LR can be positioned at a position where the height of off-axial rays is large, making it possible to selectively correct distortion and astigmatism while minimizing the effect on correction of spherical aberration and sagittal flare. This improves the peripheral performance of optical system L0.

[0058] If the back focal length sk falls below the lower limit of conditional expression (2) and becomes small, interference will occur between the optical system L0 and components such as a camera to which the optical system L0 is attached, making it difficult to arrange lenses in the rear group LR, which is undesirable.

[0059] If the back focal length sk exceeds the upper limit of the condition (2) and becomes large, it becomes difficult to correct distortion, curvature of field, and astigmatism, which is not preferable.

[0060] Condition (3) defines the ratio of the refractive power of the front lens unit LF to the refractive power of the image-side focusing lens unit LFR.

[0061] If fLFR becomes large, falling below the lower limit of conditional expression (3), the positive refractive power of the image-side focusing unit LFR becomes too small. This increases the amount of movement of the lens units during focusing, undesirably increasing the overall length of the optical system. Furthermore, if fLF becomes small, it becomes difficult to correct spherical aberration and axial chromatic aberration, undesirably.

[0062] If fLFR becomes small beyond the upper limit of conditional expression (3), the refractive power of the image-side focusing group LFR becomes too strong, which is undesirable because it causes excessive performance changes during focusing, such as spherical aberration, curvature of field, and fluctuations in the angle of view.Furthermore, if fLF becomes too large, the overall length of the optical system becomes large, which is also undesirable.

[0063] Conditional expression (4) defines the ratio of the focal length fLR of the rear group LR to the focal length f of the entire optical system L0. Near the lower limit of conditional expression (4), fLR takes a negative value. If the absolute value of fLR falls below the lower limit of conditional expression (4) and becomes small, the negative refractive power of the rear group LR 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 prone to cause color irregularities when an image is captured using a solid-state image sensor such as a CMOS sensor.

[0064] Near the upper limit of conditional expression (4), fLR takes a positive value. If the absolute value of fLR decreases beyond the upper limit of conditional expression (4), the positive refractive power of the rear group LR becomes too strong. In this case, the positive Petzval sum of the entire optical system L0 becomes too large, making it difficult to correct curvature of field, which is undesirable.

[0065] Conditional expression (5) defines the shape of the image-side focusing group LFR, and relates to the condition for suppressing aberrations that occur during focusing and fluctuations in the angle of view.

[0066] 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 image-side focusing group LFR closest to the object becomes large. In this case, the concentricity of the surface of the image-side focusing group LFR closest to the object with respect to off-axial light beams incident on the image-side focusing group LFR becomes small. Furthermore, because the absolute value of the radius of curvature of the convex surface of the image-side focusing group LFR closest to the image becomes small, the off-axial light beams are significantly refracted by the surface of the image-side focusing group LFR closest to the image. As a result, fluctuations in the angle of view that occur during focusing tend to become large, which is undesirable.

[0067] If the upper limit of conditional expression (5) is exceeded, the absolute value of the radius of curvature of the concave surface of the image-side focusing group LFR closest to the object becomes small. In this case, the concentricity of the surface of the image-side focusing group LFR closest to the object with respect to off-axial light beams incident on the image-side focusing group LFR 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 image-side focusing group LFR closest to the image becomes large. This is undesirable because it tends to increase fluctuations in aberrations such as coma and astigmatism during focusing.

[0068] Condition (6) defines the anomalous partial dispersion of the negative lens Gn in at least one of the front group LF and the image-side focusing group LFR.

[0069] 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.

[0070] 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.

[0071] Condition (7) defines the dispersibility of the material of the negative lens Gn in at least one of the front group LF and the image-side focusing group LFR.

[0072] If the lower limit of conditional expression (7) is not reached, the Abbe number of the negative lens Gn becomes too large, which is undesirable because it results in excessive correction of longitudinal chromatic aberration.

[0073] If the upper limit of conditional expression (7) is exceeded, the Abbe number of the negative lens Gn becomes too small, which is undesirable because the correction of axial chromatic aberration is insufficient.Furthermore, the refractive power of the negative lens Gn becomes too large, which is undesirable because it becomes difficult to correct spherical aberration.

[0074] Axial chromatic aberration in the g-line and other short wavelength regions 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. For this reason, by using a material for the negative lens element Gn that satisfies conditional expressions (6) and (7), the degree of divergence of the g-line caused by the negative lens element can be made relatively small, and axial chromatic aberration in the g-line and other short wavelength regions can be prevented from becoming excessive.

[0075] By arranging at least one negative lens Gn that satisfies both conditional expressions (6) and (7) in at least one of the front group LF and the image-side focusing group LFR, the effect of correcting axial chromatic aberration described above can be obtained.

[0076] Furthermore, by including two negative lenses Gn in at least one of the front group LF and the image-side focusing group LFR, the effect of the aforementioned longitudinal chromatic aberration correction can be enhanced, and by including three or more negative lenses Gn, the effect of the aforementioned longitudinal chromatic aberration correction can be further enhanced.

[0077] Furthermore, it is more preferable to dispose at least one negative lens Gn in each of the front group LF and the image-side focusing group LFR. By disposing a negative lens Gn in the front group LF, axial chromatic aberration can be effectively corrected throughout the entire optical system L0. By disposing a negative lens Gn in the image-side focusing group LFR, axial chromatic aberration can be easily corrected within the image-side focusing group LFR, and fluctuations in axial chromatic aberration during focusing can be suppressed.

[0078] Condition (8) defines the position sensitivity of the image-side focusing group LFR, that is, the ratio of the amount of movement of the image plane to the amount of movement of the image-side focusing group LFR during focusing.

[0079] If the lower limit of conditional expression (8) is exceeded, the position sensitivity of the image-side focusing group LFR becomes too small, which is undesirable because it increases the focusing distance. It is also undesirable because it becomes difficult to shorten the overall length of the optical system L0 in order to ensure sufficient air space for focusing.

[0080] If the upper limit of conditional expression (8) is exceeded, the refractive power of the image-side focusing group LFR 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.

[0081] Condition (9) defines the ratio between the focal length fLR of the rear group LR and the air-equivalent back focal length sk.

[0082] If sk becomes small by falling below the lower limit of conditional expression (9), the image plane of optical system L0 will be located closer to the object than the lens surface of the lens included in the rear group LR that is closest to the image, or at a position equivalent to the lens surface that is closest to the image, which makes it difficult to capture an image, which is undesirable.

[0083] If sk becomes large beyond the upper limit of conditional expression (9), the absolute value of the refractive power of the rear group LR becomes too large. If the negative refractive power of the rear group LR becomes too large, the angle of incidence of off-axial 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 of the rear group LR 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.

[0084] 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.

[0085] 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. Also, to give the negative lens in the first lens group a sufficiently positive curvature, an air gap on the optical axis between the adjacent lens elements is necessary, but this becomes difficult to achieve, which undesirably makes it difficult to make the optical system L0 a wide angle lens or to correct distortion.

[0086] 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 positive lens with sufficient refractive power, and making it difficult to correct spherical aberration and axial chromatic aberration, which is undesirable. Alternatively, if each positive lens is to be provided with sufficient refractive power, the total length would increase, which is undesirable.

[0087] 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.

[0088] 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.

[0089] If L becomes large beyond the upper limit of conditional expression (11), the overall length of the lens device L0 becomes large, which is not preferable.

[0090] Conditional expression (12) defines the Abbe number νd2p of the material of at least one positive lens G2p in the image-side focusing group LFR, and defines the condition for favorably correcting axial chromatic aberration.

[0091] If νd2p becomes small below the lower limit of conditional expression (12), it becomes difficult to correct axial chromatic aberration, which is not preferable.

[0092] If vd2p increases beyond the upper limit of conditional expression (12), lateral chromatic aberration will be overcorrected, which is not preferable.

[0093] It is more preferable to dispose two or more positive lenses G2p that satisfy conditional expression (12) in the image-side focusing group LFR, as this can enhance the above-mentioned effect.

[0094] Conditional expression (13) defines the ratio between the amount of movement MLFR of the image-side focusing unit LFR during focusing from infinity to an object distance where the lateral magnification of the entire system is −0.1, and the distance DSP on the optical axis from the aperture stop SP to the surface closest to the image side. Note that the sign of the amount of movement MLFR is positive when moving from the object side to the image side.

[0095] If the lower limit of condition (13) is not reached, the refractive power of the image-side focusing unit LFR becomes too strong, which is undesirable because it increases the fluctuations in spherical aberration and curvature of field during focusing.

[0096] If MLFR becomes large beyond the upper limit of conditional expression (13), the amount of movement of the image-side focusing group LFR becomes large, and the overall length becomes large to ensure space for that movement, which is undesirable.

[0097] Conditional expression (14) defines the Abbe number νd1n of the material of the negative lens G1n in the front group LF, and defines the condition for favorably correcting lateral chromatic aberration.

[0098] 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.

[0099] 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.

[0100] It is more preferable to dispose two or more negative lenses G1n that satisfy conditional expression (14) in the front lens unit LF, since this can enhance the above-mentioned effect.

[0101] Conditional expression (15) relates to the refractive power of the image-side focusing group LFR. By satisfying conditional expression (15), the focal length fLFR of the image-side focusing group LFR 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.

[0102] If the focal length fLFR of the positive image-side focusing unit LFR becomes short by falling below the lower limit of conditional expression (15), the refractive power of the image-side focusing unit LFR becomes too strong, which is undesirable because it increases performance changes such as spherical aberration, curvature of field, and fluctuations in the angle of view that occur during focusing.

[0103] If the focal length fLFR of the positive image-side focusing unit LFR increases beyond the upper limit of conditional expression (15), the position sensitivity of the image-side focusing unit LFR, i.e., the ratio of the amount of movement of the image plane to the amount of movement 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.

[0104] 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.

[0105] It is also preferable that the triplet cemented lens be located adjacent to the object side or image side of the aperture stop SP located in the front group LF, which places the triplet cemented lens at a position where the height of axial rays is large, thereby improving the effect of correcting axial chromatic aberration.

[0106] Furthermore, it is preferable that the triplet cemented lens and aperture diaphragm SP be located in the front lens unit LF, which does not move during focusing. As mentioned above, it is preferable to locate 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 results in larger lenses and heavier lenses. Therefore, it is preferable that the aperture diaphragm SP and the triplet cemented lens including the positive lens Gp be configured to not move during focusing.

[0107] Conditional expression (16) defines the position DSP of the aperture stop SP, and defines the condition for configuring the optical system L0 in a compact size.

[0108] 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.

[0109] If DSP becomes larger beyond the upper limit of conditional expression (16), the diameter of the lens arranged on the image side of the aperture stop SP becomes large, which is undesirable because it increases the overall mass and diameter of the optical system L0.

[0110] Condition (17) defines the focal length fLF of the front lens unit LF.

[0111] If fLF becomes small by going below the lower limit of conditional expression (17), the positive refractive power of the front lens unit LF becomes too strong, making it difficult to correct spherical aberration and distortion, which is undesirable.

[0112] If fLF increases beyond the upper limit of conditional expression (17), the lens diameter of the image-side focusing unit LFR increases, which undesirably increases the mass of the image-side focusing unit LFR and makes high-speed focusing difficult.

[0113] Condition (18) defines the focal length fGcomp of the cemented lens Gcomp.

[0114] If fGcomp falls below the lower limit of condition (18) and takes a negative value, it becomes difficult to correct axial chromatic aberration, which is undesirable.

[0115] If the upper limit of conditional expression (18) is exceeded and fGcomp becomes small, the positive refractive power of the cemented lens Gcomp becomes too large, which is undesirable because the longitudinal chromatic aberration is overcorrected.

[0116] It is more preferable that the numerical ranges of the conditional expressions (1) to (18) be the numerical ranges of the following conditional expressions (1a) to (18a). 0.060<ΔθgFp<0.220 (1a) 0.20 <sk / f<1.60···(2a) 0.50 <fLF / fLFR<2.70···(3a) -1.20 <f / fLR<1.20···(4a) -1.20<(RLFR2-RLFR1) / (RLFR2+RLFR1)<1.20...(5a) -0.010<ΔθgFn<0.010 (6a) -0.180 <Ndn-(-1.454×10 -2 ×νdn+2.287)<0.030···(7a) 0.60<(1-βLFR 2 )×βLR 2 <2.20···(8a) 0.00 <sk / |fLR|<0.70···(9a) 0.25<ΣDair / (L-sk)<0.64 (10a) 2.00 <L / f<13.50···(11a) 62.00<νd2p<99.00 (12a) -0.160 <MLFR / DSP<-0.008···(13a) 62.00<νd1n<99.00 (14a) 0.70 <fLFR / f<2.80···(15a) 0.35<(DSP+sk) / L<0.74 (16a) 0.70 <fLF / f<4.50···(17a) 0.01 <f / fGcomp<1.80···(18a)

[0117] It is more preferable that the numerical ranges of the conditional expressions (1) to (18) be the numerical ranges of the following conditional expressions (1b) to (18b). 0.070<ΔθgFp<0.190 (1b) 0.30 <sk / f<1.40···(2b) 0.70 <fLF / fLFR<2.30···(3b) -0.90 <f / fLR<0.50···(4b) -0.80<(RLFR2-RLFR1) / (RLFR2+RLFR1)<0.80...(5b) -0.008<ΔθgFn<0.007 (6b) -0.15 <Ndn-(-1.454×10 -2 ×νdn+2.287)<0.02···(7b) 0.55<(1-βLFR 2 )×βLR 2 <1.90 (8b) 0.00 <sk / |fLR|<0.60···(9b) 0.30<ΣDair / (L-sk)<0.59 (10b) 2.20 <L / f<12.00···(11b) 64.00<νd2p<98.00 (12b) -0.120 <MLFR / DSP<-0.012···(13b) 64.00<νd1n<98.00 (14b) 0.90 <fLFR / f<2.60···(15b) 0.40<(DSP+sk) / L<0.68 (16b) 1.00 <fLF / f<4.00···(17b) 0.02 <f / fGcomp<1.60···(18b)

[0118] Furthermore, it is more preferable that the numerical ranges of the conditional expressions (1) to (18) be set to the numerical ranges of the following conditional expressions (1c) to (18c). 0.080<ΔθgFp<0.160 (1c) 0.38 <sk / f<1.20···(2c) 0.90 <fLF / fLFR<1.80···(3c) -0.70 <f / fLR<0.20···(4c) -0.50<(RLFR2-RLFR1) / (RLFR2+RLFR1)<0.50...(5c) -0.006<ΔθgFn<0.004 (6c) -0.13 <Ndn-(-0.0145425×νdn+2.28725)<0.01···(7c) 0.65<(1-βLFR 2 )×βLR 2 <1.60···(8c) 0.00 <sk / |fLR|<0.40···(9c) 0.33<ΣDair / (L-sk)<0.57 (10c) 2.60 <L / f<11.00···(11c) 66.00<νd2p<97.00···(12c) -0.080 <MLFR / DSP<-0.016···(13c) 66.00<νd1n<97.00···(14c) 1.00 <fLFR / f<2.40···(15c) 0.45<(DSP+sk) / L<0.65 (16c) 1.30 <fLF / f<3.50···(17c) 0.04 <f / fGcomp<1.40···(18c)

[0119] Furthermore, by setting the lower limit of conditional expression (1) to 0.10, 0.12, 0, or 13, the effect implied by the lower limit of conditional expression (1) can be further enhanced.

[0120] Furthermore, by setting the upper limit of conditional expression (1) to 0.155, 0.15, or 0.145, the effect implied by the upper limit of conditional expression (1) can be further enhanced.

[0121] Furthermore, by setting the lower limit of conditional expression (12) to 68.00, 70.00, 73.00, 75.00, or 80.00, the effect implied by the lower limit of conditional expression (12) can be further enhanced.

[0122] Moreover, by setting the upper limit of conditional expression (18) to 1.20, 1.00, 0.80, 0.60, or 0.40, the effect implied by the upper limit of conditional expression (18) can be further enhanced.

[0123] Next, a detailed description will be given of the configuration of the optical system L0 of Examples 1 to 8. Note that, in the optical system L0 of each Example, a description of the same configuration as the optical system L0 of Example 1 will be omitted, and differences from Example 1 will be mainly described.

[0124] [Example 1] The optical system L0 of the first embodiment is made up 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.

[0125] In the optical system L0 of the first embodiment, the front group LF having positive refractive power corresponds to the first lens group L1, the image-side focusing group LFR having positive refractive power corresponds to the second lens group L2, and the rear group LR corresponds to the third lens group L3.

[0126] By providing the rear group LR with negative refractive power, it becomes easier to correct the positive Petzval sum, and field curvature can be corrected well.

[0127] In the optical system L0 of Example 1, the front group LF is made up of lenses G1 to G12, the image-side focusing group LFR is made up of lenses G13 to G16, and the rear group is made up of lenses G17 and G18. The front group LF has seven negative lenses.

[0128] In the optical system L0 of Example 1, the aperture stop SP is located inside the front group LF. Furthermore, by using aspherical lenses for the G1 lens and the G3 lens, distortion and astigmatism can be corrected well.

[0129] In the optical system L0 of Example 1, the lens closest to the image side of the image-side focusing group LFR is an aspherical lens. This allows for excellent correction of spherical aberration, field curvature, and astigmatism. Furthermore, by locating this aspherical lens closest to the image side of the image-side focusing group LFR where the light beam is converged, it is possible to reduce the rate of performance degradation due to deviations from the desired surface shape caused by manufacturing errors.

[0130] 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.

[0131] In the optical system L0 of Example 1, G11 is a positive lens Gp having positive anomalous partial dispersion, and is cemented between a positive lens G10 and a negative lens G12 to form a triplet cemented lens Gcomp, which enables excellent correction of axial chromatic aberration in the short wavelength region, such as the g-line.

[0132] During focusing, the image-side focusing group LFR moves in the direction of the optical axis from the image side to the object side relative to the image plane, while the front group LF and rear group LR remain stationary relative to the image plane.

[0133] [Example 2] In the optical system L0 of the second embodiment, the front group LF is made up of lenses G1 to G10, the image-side focusing group LFR is made up of lenses G11 to G14, and the rear group is made up of lenses G15 and G16.

[0134] In the optical system L0 of Example 2, the G4 and G5 lenses, the G8 to G10 lenses, the G11 and G12 lenses, and the G15 and G16 lenses are cemented together to form a cemented lens. The front group LF has six negative lenses.

[0135] In the optical system L0 of Example 2, G9 is a positive lens Gp having positive anomalous partial dispersion, and is cemented between a positive lens G8 and a negative lens G10 to form a triplet cemented lens Gcomp, which enables excellent correction of axial chromatic aberration in the short wavelength region, such as the g-line.

[0136] [Example 3] The optical system L0 of Example 3 is composed of a first lens group L1 having positive refractive power, a second lens group L2 having negative refractive power, a third lens group L3 having positive refractive power, a fourth lens group L4 having positive refractive power, and a fifth lens group L5 having negative refractive power.

[0137] The front group LF having positive refractive power is made up of a first lens group L1, a second lens group L2, and a third lens group L3, the image-side focusing group LFR also having positive refractive power corresponds to the fourth lens group L4, and the rear group LR corresponds to the fifth lens group L5.

[0138] In the optical system L0 of Example 3, the front group LF is composed of lenses G1 to G8, the image-side focusing group LFR is composed of lenses G9 to G12, and the rear group is composed of lenses G13 to G15. The front group LF has five negative lenses. An aperture stop SP is located inside the front group LF.

[0139] In the optical system L0 of Example 3, the G3 and G4 lenses, the G7 to G9 lenses, the G10 and G11 lenses, and the G14 and G15 lenses are each cemented to form one cemented lens.

[0140] In the optical system L0 of Example 3, G8 is a positive lens Gp having positive anomalous partial dispersion, and is cemented between a positive lens G7 and a negative lens G9 to form a triplet cemented lens Gcomp, which enables excellent correction of axial chromatic aberration in the short wavelength region, such as the g-line.

[0141] In the optical system L0 of Example 3, the second lens unit L2 moves from the object side to the image side during focusing from infinity to a close distance, and the fourth lens unit L4 moves from the image side to the object side. By moving the second lens unit L2 in addition to the fourth lens unit L4, which is the image-side focusing unit LFR, during focusing, it is possible to suppress fluctuations in field curvature and breathing.

[0142] Alternatively, instead of the second lens unit L2, any lens in the front lens unit LF may be moved from the object side to the image side or from the image side to the object side. As an example, by moving the G5 lens from the image side to the object side, fluctuations in field curvature during focusing can be suppressed.

[0143] Furthermore, during focusing from infinity to a close distance, the first lens unit L1, the third lens unit L3, and the fifth lens unit L5 do not move relative to the image plane.

[0144] [Example 4] In the optical system L0 of Example 4, the front group LF is made up of lenses G1 to G11, the image-side focusing group LFR is made up of lenses G12 to G15, and the rear group is made up of lenses G16 and G17. The front group LF has seven negative lenses.

[0145] In the optical system L0 of Example 4, the G5 and G6 lenses, the G9 to G11 lenses, the G12 and G13 lenses, and the G16 and G17 lenses are each cemented to form one cemented lens.

[0146] In the optical system L0 of Example 4, G10 is a positive lens Gp having positive anomalous partial dispersion, and is cemented between a positive lens G9 and a negative lens G11 to form a triplet cemented lens Gcomp, which enables excellent correction of axial chromatic aberration in the short wavelength region, such as the g-line.

[0147] [Example 5] In the optical system L0 of Example 5, the front group LF is composed of lenses G1 to G12, the image-side focusing group LFR is composed of lenses G13 to G16, and the rear group is composed of lenses G17 and G18. The front group LF has seven negative lenses. Furthermore, by using aspherical lenses for the G1 and G3 lenses, distortion and astigmatism can be effectively corrected.

[0148] 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.

[0149] [Example 6] The optical system L0 of the sixth embodiment is made up 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 positive refractive power.

[0150] The front group LF having positive refractive power corresponds to the first lens group L1, the image-side focusing group LFR having positive refractive power corresponds to the second lens group L2, and the rear group LR corresponds to the third lens group L3.

[0151] The optical system L0 of Example 6 comprises a front group LF having positive refractive power, an image-side focusing group LFR having positive refractive power, and a rear group LR having positive refractive power. By providing the rear group LR with positive refractive power, the angle of incidence of off-axial 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.

[0152] In the optical system L0 of Example 6, the front group LF is composed of lenses G1 to G10, the image-side focusing group LFR is composed of lenses G11 to G14, and the rear group is composed of lenses G15 and G16. The front group LF has six negative lenses. Furthermore, by using aspherical lenses for the G1 and G3 lenses, distortion and astigmatism can be effectively corrected.

[0153] 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.

[0154] In the optical system L0 of Example 6, G9 is a positive lens Gp having positive anomalous partial dispersion, and is cemented between a positive lens G8 and a negative lens G10 to form a triplet cemented lens Gcomp, which enables excellent correction of axial chromatic aberration in the short wavelength region, such as the g-line.

[0155] [Example 7] In the optical system L0 of Example 7, the front group LF is made up of lenses G1 to G8, the image-side focusing group LFR is made up of lenses G9 to G12, and the rear group is made up of lenses G13 and G14. Furthermore, by making the G14 lens closest to the image side an aspherical lens, distortion and astigmatism can be effectively corrected.

[0156] Furthermore, by constructing the G12 lens from plastic resin, the image-side focusing group LFR can be made lighter, enabling high-speed focusing.

[0157] In the optical system L0 of Example 7, the G5 to G7 lenses, the G9 and G10 lenses, and the G13 and G14 lenses are each cemented to form one cemented lens.

[0158] In the optical system L0 of Example 7, the G8 lens included in the front group LF moves so as to include a component perpendicular to the optical axis, thereby enabling image blur correction and suppressing fluctuations in coma aberration and one-sided blur during image blur correction.

[0159] In the optical system L0 of each embodiment, it is preferable to position a negative lens closest to the image side of the rear group LR, 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 rear group LR. Furthermore, by positioning 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.

[0160] [Example 8] In the optical system L0 of Example 8, the front group LF is made up of lenses G1 to G8, the image-side focusing group LFR is made up of lenses G9 to G11, and the rear group is made up of lenses G12 and G13. The front group LF has four negative lenses.

[0161] In the optical system L0 of Example 8, G7 is a positive lens Gp having positive anomalous partial dispersion, and is cemented between a positive lens G6 and a negative lens G8 to form a triplet cemented lens Gcomp, which enables excellent correction of axial chromatic aberration in the short wavelength region, such as the g-line.

[0162] In the optical system L0 of Example 8, the aperture stop SP is disposed adjacent to the front group LF on the image side, which allows the aperture diameter of the aperture stop SP to be small.

[0163] Next, the configuration that the optical system L0 of each embodiment preferably satisfies will be described.

[0164] In the optical system L0 of each embodiment, it is preferable that at least one of the air lenses, from the first to third air lenses from the object side, has a biconvex shape. This allows a lens with strong negative refractive power to be located at a position away from the aperture stop SP, and it is possible to reduce the positive Petzval sum while suppressing sagittal flare caused by strong negative refractive power, thereby enabling good correction of field curvature.

[0165] In the optical system L0 of each embodiment, it is preferable that the front group LF has, in order from the object side, a negative lens G1, a negative lens G2, a negative lens G3, and a positive lens G4. By making the lens G4 a positive lens, barrel-side distortion and chromatic aberration of magnification generated by the lenses G1 to G3 can be effectively corrected.

[0166] In the optical systems L0 of Examples 1, 2, 4, 5, and 6, it is preferable that the front group LF has two negative meniscus lenses arranged consecutively on the most object side, with the object-side lens surface having a convex shape facing the object side, which enables excellent correction of distortion, curvature of field, and astigmatism.

[0167] In Examples 1, 2, 4, 5, and 6, it is preferable that the front group LF has three negative lenses arranged consecutively in the optical axis direction at the position closest to the object. 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.

[0168] In the optical systems L0 of Examples 1, 2, 4, 5, and 6, it is preferable that the front group LF has at least one aspherical lens among the three negative lenses arranged consecutively on the object side. This allows for excellent correction of distortion and astigmatism. 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.

[0169] In the optical systems L0 of Examples 1 and 5, it is preferable that the G4 lens be 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 whose object-side lens surface is convex toward the object side, or a positive meniscus lens whose image-side lens surface is convex toward the image side.

[0170] In the optical system L0 of each embodiment, it is preferable that the front group LF 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 that satisfies conditional expressions (6) and (7) as the negative lens in the cemented lens, it is possible to effectively correct longitudinal chromatic aberration for the g-line.

[0171] In the optical system L0 of each embodiment, image blur correction can be performed by moving at least some of the lenses constituting the front group LF so as to include a component in a direction perpendicular to the optical axis. For example, in Examples 7 and 8, the G8 lens moves during image blur correction so as to include a component perpendicular to the optical axis, but this is not limited to this. Furthermore, by ensuring that 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.

[0172] In the optical system L0 of each embodiment, the image-side focusing group LFR has a negative lens and a positive lens arranged in that order in the optical axis direction. This allows for better correction of 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 and positive lenses are arranged.

[0173] In the optical system L0 of each embodiment, it is preferable that the object-side lens surface of the lens that is located closest to the object among the lenses that make up the image-side focusing group LFR be concave toward the object side. It is also preferable that the image-side lens surface of the second lens, counting from the object side, be convex toward the image side. This makes the lens surface approximately concentric with respect to off-axial light beams that enter the image-side focusing group LFR, thereby suppressing aberrations and fluctuations in the angle of view during focusing.

[0174] In the optical system L0 of each embodiment, the image-side focusing group LFR includes 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.

[0175] It is also preferable that the cemented lens be located closest to the object in the image-side focusing group LFR, which allows the cemented lens to be located at a position where the height from the optical axis of the axial marginal ray is high, thereby enabling even better correction of axial chromatic aberration.

[0176] Furthermore, it is preferable that the lens surface closest to the object side of the cemented lens has a concave shape facing the object side, and the lens surface closest to the image side has a convex shape facing the image side. This results in a nearly concentric shape for off-axial light beams incident on the image-side focusing group LFR, making it possible to suppress aberrations and fluctuations in the angle of view during focusing. Note that the cemented lens may also be formed by cementing a biconcave lens and a biconvex lens together in that order from the object side.

[0177] In the optical system L0 of each embodiment, it is preferable that the image-side focusing group LFR be composed of five or fewer lenses. This allows the weight of the lenses in the image-side focusing group LFR 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. To enhance the above-mentioned effects, it is more preferable that the image-side focusing group LFR be composed of four or fewer lenses. It is even more preferable that the image-side focusing group LFR be composed of three or fewer lenses.

[0178] 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 image-side focusing group LFR has a concave shape facing the object side. This allows off-axial light beams that have passed through the aperture stop to be incident on the surface closest to the object in the image-side focusing group LFR in a substantially concentric manner, making it easy to suppress fluctuations in astigmatism and coma and fluctuations in the angle of view during focusing.

[0179] In the optical system L0 of each embodiment, it is preferable that the image-side focusing group LFR 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 image-side focusing group LFR aspherical is more preferable, as this reduces errors in the surface shape during molding. Furthermore, it is more preferable that the lens closest to the image side or the second-nearest lens from the image side in the image-side focusing group LFR is aspherical, as this allows for excellent correction of off-axis aberrations such as astigmatism and coma.

[0180] In the optical systems L0 of Examples 1 to 6, it is preferable that the rear group LR has a cemented lens made up of a positive lens and a negative lens, which makes it possible to effectively correct chromatic aberration of magnification and astigmatism.

[0181] 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.

[0182] In the optical system L0 of each embodiment of Example 7, the aspherical lens G12 arranged in the image-side focusing group LFR is made of a plastic material. In this way, by making at least one of the lenses arranged in the image-side focusing group LFR out of a plastic material, it is possible to reduce the weight of the image-side focusing group LFR, which is preferable.

[0183] In the optical system L0 of each embodiment, it is preferable that the composite focal length fGcomp of the triplet cemented lens Gcomp arranged in the front group LF be a positive value, which allows for good correction of axial chromatic aberration and enables the diameter of the lens arranged on the object side of the image-side focusing group LFR to be reduced.

[0184] In the optical system L0 of each embodiment, it is preferable that the positive lens Gp is ​​made of an organic resin material. This allows the overall weight of the optical system L0 to be reduced. Also, the anomalous partial dispersion required for the positive lens Gp as defined in conditional formula (1) can be obtained.

[0185] Materials that satisfy conditional expression (1) include, for example, resins and mixtures of resins and inorganic oxide particles. Examples of inorganic oxides include TiO2 (nd=2.304, νd=13.8), Nb2O5 (nd=2.367, νd=14.0), and ITO (nd=1.8571, νd=5.69). Other examples include CrO3 (nd=2.2178, νd=13.4) and BaTiO3 (nd=2.4362, νd=11.3). The refractive index of each material at the d line is denoted as nd.

[0186] A material satisfying conditional formula (1) can be obtained by dispersing the inorganic oxide particles in a solid material at an appropriate volume ratio. Considering the scattering of the material, the particle size of the particles is preferably 2 nm to 50 nm. A dispersant or the like may be added to suppress aggregation.

[0187] In the optical system L0 of each embodiment, it is preferable that the refractive index of the positive lens with the greatest refractive power among the positive lenses constituting the triplet lens Gcomp is 1.65 or more and 2.1 or less.

[0188] If the positive lens Gp constituting the triplet cemented lens Gcomp is made of a resin material, the positive lens Gp may deform due to external environmental changes such as temperature changes and moisture absorption, and the positive lens cemented to the object side or image side may also deform. If the refractive index of the positive lens cemented to the positive lens Gp is ​​less than 1.65, the mechanical hardness of the positive lens, i.e., the Young's modulus and Knoop hardness of the material of the positive lens, becomes small. This is undesirable because it tends to increase the deformation of the positive lens and increase fluctuations in aberrations such as spherical aberration. Furthermore, it is more preferable for the refractive index to be 1.70 or higher, and even more preferably 1.75 or higher.

[0189] Furthermore, it is preferable to set the refractive index of the positive lens cemented to the positive lens Gp to 2.1 or less, since this allows for good correction of longitudinal chromatic aberration.

[0190] In the optical system L0 of each embodiment, it is preferable that the Abbe number for the d-line of the positive lens with the greatest refractive power among the positive lenses constituting the triplet lens Gcomp is 25 or more and 60 or less.

[0191] If the Abbe number for the d-line of the positive lens cemented to the positive lens Gp exceeds 60, the mechanical hardness of the positive lens decreases, which tends to increase the deformation of the positive lens associated with the deformation of the positive lens Gp, resulting in large fluctuations in aberrations such as spherical aberration, which is undesirable. Furthermore, it is more preferable to set the Abbe number to 56 or less, and even more preferably 53 or less.

[0192] Furthermore, if the Abbe number for the d-line of the positive lens cemented to the positive lens Gp is ​​smaller than 25, it becomes difficult to correct axial chromatic aberration, which is not preferable.

[0193] Numerical Examples 1 to 8 corresponding to Examples 1 to 8, respectively, are shown below.

[0194] 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 the material of each optical element at the d-line, and vd represents the Abbe number of the material of each 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)

[0195] 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.

[0196] 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.

[0197] [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 Side 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

[0198] [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

[0199] [Numerical Example 3] Unit: mm Surface Data Surface number rd nd νd 1 53.831 1.05 1.72916 54.7 2 22.346 14.69 3 -29.419 1.00 1.48749 70.2 4 188.029 3.89 5 -203.116 8.40 1.83481 42.7 6 -20.865 1.05 1.85478 24.8 7 -47.144 0.20 8 49.538 4.97 2.00069 25.5 9 -184.719 (variable) 10 115.985 1.10 1.61340 44.3 11 45.795 (variable) 12 (Aperture) ∞ 1.48 13 74.195 6.89 1.75500 52.3 14 -31.627 0.50 1.57060 20.1 15 -29.087 1.00 1.66565 35.6 16 87.405 (variable) 17 -34.716 5.17 1.49700 81.7 18 -16.180 1.00 1.85478 24.8 19 -210.624 0.20 20 56.336 8.47 1.49700 81.7 21 -27.668 0.94 22* 90.528 6.73 1.80400 46.5 23* -46.782 (variable) 24 119.008 6.50 1.92286 20.9 25 -55.757 1.05 1.66565 35.6 26 38.876 5.37 27 -85.461 1.00 1.51742 52.4 28 -595.711 15.00 Image plane ∞ Aspheric data Page 22 K = 0.00000e+00 A 4=-8.63588e-06 A 6= 2.87015e-09 A 8=-1.46350e-11 A10= 5.23093e-14 A12=-1.23076e-16 Page 23 K = 0.00000e+00 A 4= 3.58608e-06 A 6= 3.19398e-09 A 8=-1.61487e-11 A10= 1.02393e-13 A12=-1.58745e-16 Focal length 24.72 F-number 1.46 Angle of view 37.40 Image height 18.90 Lens length 117.50 BF 15.00 When focused at infinity When focused at an object distance with a lateral magnification of -0.1x From object surface to first surface Infinity 226.884 d 9 0.50 2.71 d11 8.51 6.31 d16 8.64 6.89 d23 2.20 3.95 Lens group data Group starting plane Focal length Lens length Front principal point position Rear principal point position L1 1 41.33 35.24 34.50 28.24 L2 10 -124.11 1.10 1.13 0.45 L3 12 183.91 9.87 -3.63 -9.67 L4 17 34.38 22.51 16.76 6.16 L5 24 -106.17 13.92 10.87 0.43 Single lens data Lens initial surface focal length θgF 1 1 -53.14 2 3 -52.11 3 5 27.28 4 6 -44.61 0.6122 5 8 39.45 6 10 -124.11 0.5633 7 13 30.22 8 14 592.30 0.7782 9 15 -32.67 0.5824 10 17 55.81 11 18 -20.55 0.6122 12 20 38.63 13 22 39.22 14 24 41.89 15 25 -34.26 16 27 -192.96

[0200] [Numerical Example 4] Unit: mm Surface Data Surface number rd nd νd 1* 61.501 2.00 1.58313 59.4 2* 20.184 9.47 3 1901.390 1.80 1.49700 81.7 4 42.169 2.76 5 159.837 2.00 1.76802 49.2 6* 92.467 10.72 7 -28.269 1.20 1.43387 95.1 8 80.363 0.50 9 44.572 9.93 1.72916 54.7 10 -25.481 1.05 1.84666 23.8 11 -53.627 0.25 12 82.209 5.46 1.81600 46.6 13 -50.551 1.71 14 -37.489 1.10 1.62205 41.1 15 -87.960 2.83 16 (Aperture) ∞ 2.32 17 147.999 4.55 2.00069 25.5 18 -49.961 1.00 1.57060 20.1 19 -35.594 1.10 1.66565 35.6 20 67.510 (variable) 21 -39.085 5.89 1.43875 94.7 22 -15.511 1.00 1.77047 29.7 23 -82.267 0.20 24 39.313 7.60 1.49700 81.7 25 -35.308 2.28 26* 99.752 5.96 1.80400 46.5 27* -45.519 (variable) 28 575.113 7.49 1.59282 68.6 29 -25.634 1.05 1.66565 35.6 30 61.536 17.78 Image plane ∞ Aspheric data Front page K = 0.00000e+00 A 4= 1.29176e-06 A 6=-2.09110e-09 A 8= 4.38333e-12 2nd side K =-3.24571e-01 A 4=-5.71201e-06 A 6=-1.03383e-08 A 8=-7.16243e-11 Side 6 K =-7.00000e+00 A 4= 1.58032e-05 A 6= 1.44025e-08 A 8= 2.02465e-10 A10=-6.06022e-13 A12= 1.67729e-15 Page 26 K = 0.00000e+00 A 4=-1.06246e-05 A 6=-7.22658e-09 A 8= 2.73322e-11 A10= 9.27530e-14 A12=-1.23176e-16 Page 27 K = 0.00000e+00 A 4= 5.05881e-06 A 6=-6.17326e-09 A 8= 4.07297e-11 A10= 1.05263e-13 A12=-6.79698e-17 Focal length 18.45 F-number 1.46 Angle of view: 45.46 Image height 18.75 Lens length 121.17 BF 17.78 d20 7.96 d27 2.20 Lens group data Group starting plane Focal length Lens length Front principal point position Rear principal point position L1 1 47.25 61.75 44.85 39.61 L2 21 30.00 22.93 15.17 1.79 L3 28 -79.53 8.54 5.66 0.30 Single lens data Lens initial surface focal length θgF 1 1 -52.46 2 3 -86.80 3 5 -289.37 4 7 -48.04 5 9 23.65 6 10 -58.34 7 12 39.08 8 14 -105.92 0.5690 9 17 37.76 10 18 211.58 0.7782 11 19 -34.86 0.5824 12 21 54.46 13 22 -24.97 0.5951 14 24 38.74 15 26 39.60 16 28 41.59 17 29 -27.06

[0201] [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 Side 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

[0202] [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

[0203] [Numerical Example 7] Unit: mm Surface Data Surface number rd nd νd 1 64.036 1.25 1.59270 35.3 2 19.134 5.47 3 29.144 6.99 2.05090 26.9 4 -164.343 0.20 5 -214.914 1.10 1.67270 32.1 6 20.824 6.60 7 -23.834 0.90 1.58144 40.8 8 120.560 0.44 9 40.779 7.75 1.75500 52.3 10 -22.714 0.50 1.60401 20.8 11 -20.733 0.90 1.85478 24.8 12 -31.966 4.45 13 (Aperture) ∞ 4.13 14 75.325 2.30 1.81600 46.6 15 30549.322 (variable) 16 -17.256 3.03 1.49700 81.7 17 -14.230 0.75 1.77047 29.7 18 -22.527 0.20 19 67.123 6.11 1.49700 81.7 20 -28.721 4.28 21* -64.055 4.45 1.53500 56.0 22* -24.736 (variable) 23 513.689 1.00 1.51742 52.4 24 60.438 7.24 25* -28.526 2.25 1.53500 56.0 26* -69.691 14.00 Image plane ∞ Aspheric data Page 21 K = 0.00000e+00 A 4=-9.95374e-06 A 6= 7.57077e-08 A 8=-1.20581e-10 A10= 2.35597e-13 Page 22 K = 0.00000e+00 A 4= 1.95965e-05 A 6= 4.39915e-08 A 8= 1.12423e-10 A10=-5.83395e-13 A12= 1.49458e-15 Page 25 K = 0.00000e+00 A 4=-6.90991e-06 A 6=-3.19089e-08 A 8=-1.15341e-10 Page 26 K = 0.00000e+00 A 4=-2.04198e-05 A 6=-1.90671e-08 A 8=-2.89877e-11 Focal length 34.00 F-number 1.85 Angle of view 30.41 Image height 19.96 Lens length 98.50 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 313.087 d15 10.02 7.80 d22 2.20 4.41 Lens group data Group starting plane focal length L1 1 56.50 L2 16 35.52 L3 23 -52.86 Single lens data Lens initial surface focal length θgF 1 1 -46.52 2 3 24.00 3 5 -28.17 4 7 -34.15 5 9 20.39 6 10 359.44 0.7230 7 11 -71.67 0.6122 8 14 92.53 9 16 122.53 10 17 -52.20 0.5951 11 19 41.35 12 21 72.47 13 23 -132.48 14 25 -92.02

[0204] [Numerical Example 8] Unit: mm Surface Data Surface number rd nd νd 1 53.821 1.25 1.59270 35.3 2 19.792 6.70 3 32.079 6.96 2.05090 26.9 4 -197.061 0.20 5 -219.698 1.10 1.69895 30.1 6 22.445 7.32 7 -22.851 0.90 1.53172 48.8 8 128.035 0.20 9 42.517 8.54 1.81600 46.6 10 -20.253 0.60 1.60401 20.8 11 -18.556 0.90 1.85451 25.2 12 -34.216 9.36 13 63.514 2.28 1.81600 46.6 14 406.615 1.50 15 (Aperture) ∞ (Variable) 16 -15.762 0.90 1.85451 25.2 17 -24.463 0.20 18 90.261 6.30 1.49700 81.7 19 -23.179 3.61 20* -159.864 4.42 1.76802 49.2 21* -36.419 (variable) 22 -433.667 1.00 1.56732 42.8 23 85.888 6.84 24* -26.724 2.25 1.53500 56.0 25* -63.795 13.00 Image plane ∞ Aspheric data Page 20 K = 0.00000e+00 A 4= 8.94338e-06 A 6= 4.88458e-08 A 8= 5.93594e-11 A10=-7.78918e-13 Page 21 K = 0.00000e+00 A 4= 2.50680e-05 A 6= 3.79676e-08 A 8= 2.03086e-10 A10=-1.01428e-12 A12=-1.35233e-16 Page 24 K = 0.00000e+00 A 4=-5.82583e-06 A 6=-2.82269e-08 A 8=-1.68916e-10 Page 25 K = 0.00000e+00 A 4=-1.70437e-05 A 6=-3.50373e-08 A 8=-3.50671e-11 Focal length 34.00 F-number 1.85 Angle of view 30.41 Image height 21.64 Lens length 98.50 BF 13.00 When focused at infinity When focused at an object distance with a lateral magnification of -0.1x From object surface to first surface Infinity 310.391 d15 9.97 7.59 d21 2.20 4.58 Lens group data Group starting plane focal length L1 1 49.70 L2 16 36.67 L3 22 -50.42 Single lens data Lens initial surface focal length θgF 1 1 -53.55 2 3 26.67 3 5 -29.08 4 7 -36.39 5 9 17.91 6 10 323.61 0.7230 7 11 -48.74 0.6103 8 13 91.97 9 16 -54.46 0.6103 10 18 37.81 11 20 60.47 12 22 -126.28 13 24 -87.82

[0205] Various values ​​in each numerical example are summarized in Tables 1 and 2 below.

[0206] [Table 1]

[0207] The lenses that satisfy the conditional expressions (1), (6), (7), (12), and (14) in each numerical example and their numerical values ​​are summarized in Table 2 below.

[0208] [Table 2]

[0209] [Imaging device] Next, an embodiment of an imaging device including the optical system L0 of this embodiment will be described.

[0210] 17 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 8, and a light receiving element 12 that photoelectrically converts an image formed by the optical system 11.

[0211] 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.

[0212] 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.

[0213] The optical system L0 of each of the above-described embodiments can be applied not only to the digital still camera shown in Fig. 17 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.

[0214] [Lens device] Next, an embodiment of a lens device including the optical system L0 of this embodiment will be described.

[0215] Fig. 18 is a schematic diagram showing the appearance of a lens device 20 equipped with the optical system L0 of this embodiment. The lens device 20 of Fig. 18 is a so-called interchangeable lens that is detachably attached to a camera body (not shown).

[0216] The lens device 20 includes a photographing optical system 21 similar to any one of the above-described embodiments 1 to 8. The lens device 20 includes a focus operation means 22 and an operation means 23 for changing the photographing mode.

[0217] 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.

[0218] 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.

[0219] The disclosure of this specification also includes the following configurations.

[0220] (Configuration 1) An optical system comprising, arranged in order from the object side to the image side, a front group having positive refractive power, an image-side focusing group having positive refractive power, and a rear group, the image-side focusing group moves relative to an image plane so that a distance between the front group and the image-side focusing group and a distance between the image-side focusing group and the rear group change during focusing from infinity to a close distance; During focusing from infinity to a close distance, the rear group remains stationary relative to the image plane. an aperture stop that determines an axial light beam is disposed within the front group or adjacent to the front group on the image side; the front group has a positive lens Gp, the aperture stop and the positive lens Gp are stationary relative to the image plane during focusing; An optical system characterized in that the following conditional expression is satisfied, where νdp is the Abbe number, θgFp is the partial dispersion ratio, and ΔθgFp is the anomalous partial dispersion of the material of the positive lens Gp. 0.050<ΔθgFp<0.250 however, ΔθgFp=θgFp-(B3×νdp3+B2×νdp2+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:

[0221] (Configuration 2) An optical system comprising, arranged in order from the object side to the image side, a front group having positive refractive power, an image-side focusing group having positive refractive power, and a rear group, the image-side focusing group moves relative to an image plane so that a distance between the front group and the image-side focusing group and a distance between the image-side focusing group and the rear group change during focusing from infinity to a close distance; During focusing, the rear group remains stationary relative to the image plane, An optical system characterized in that the image-side focusing group has at least two negative lenses.

[0222] (Configuration 3) The optical system according to configuration 1 or 2, wherein the air-equivalent back focus of the optical system when focused at infinity is sk and the focal length of the entire optical system is f, satisfies the following conditional expression: 0.10 <sk / f<1.80

[0223] (Configuration 4) An optical system according to any one of Configurations 1 to 3, wherein the following condition is satisfied, where fLF is the focal length of the front group and fLFR is the focal length of the image-side focusing group: 0.30 <fLF / fLFR<3.00

[0224] (Configuration 5) An optical system according to any one of configurations 1 to 4, characterized in that the following condition is satisfied, where f is the focal length of the entire optical system and fLR is the focal length of the rear group. -1.50 <f / fLR<1.50

[0225] (Configuration 6) 6. The optical system according to any one of configurations 1 to 5, wherein the image-side focusing group has at least two positive lenses and at least one negative lens.

[0226] (Configuration 7) the object-side lens surface of the lens arranged closest to the object side in the image-side focusing group is concave; an image-side lens surface of the image-side focusing group that is disposed closest to the image side has a convex shape; 7. The optical system according to any one of configurations 1 to 6, wherein the following conditional expression is satisfied, where RLFR1 is the radius of curvature of the object-side lens surface and RLFR2 is the radius of curvature of the image-side lens surface: -1.50<(RLFR2-RLFR1) / (RLFR2+RLFR1)<1.50

[0227] (Configuration 8) at least one of the front group and the image-side focusing group has a negative lens Gn; The optical system according to any one of configurations 1 to 7, 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. -0.20 <Ndn-(-0.0145425×νdn+2.28725)<0.05 -0.015<ΔθgFn<0.015 where ΔθgFn=θgFn-(-0.0025116×νdn+0.67449) It is expressed as:

[0228] (Configuration 9) 9. The optical system according to any one of configurations 1 to 8, wherein the front group has at least one negative lens Gn.

[0229] (Configuration 10) 10. The optical system according to any one of configurations 1 to 9, wherein the image-side focusing group includes at least one negative lens Gn.

[0230] (Configuration 11) The optical system described in any one of Configurations 1 to 10, wherein the following conditional expression is satisfied, when the lateral magnification of the image-side focusing group when focused at infinity is βLFR and the lateral magnification of the rear group is βLR: 0.50<(1-βLFR2)×βLR2<2.50

[0231] (Configuration 12) 12. The optical system according to any one of configurations 1 to 11, wherein the aperture stop is fixed in the optical axis direction relative to the image plane during focusing.

[0232] (Configuration 13) The optical system according to any one of configurations 1 to 12, wherein the following conditional expression is satisfied, where sk is the air-equivalent back focus of the optical system when focused at infinity, and fLR is the focal length of the rear group: 0.00 <sk / |fLR|<0.80

[0233] (Configuration 14) The optical system according to any one of Configurations 1 to 13, wherein the following conditional expression is satisfied: ΣDair is the sum of air spaces on the optical axis from the object-side lens surface of the lens in the front group that is positioned closest to the object to the image-side lens surface of the lens in the rear group that is positioned closest to the image, L is the total optical length of the optical system, and sk is the air-equivalent back focus of the optical system when focused at infinity. 0.20<ΣDair / (L-sk)<0.70

[0234] (Configuration 15) The optical system according to any one of configurations 1 to 14, wherein the following condition is satisfied, where L is the total optical length of the optical system and f is the focal length of the entire optical system: 1.50 <L / f<15.00

[0235] (Configuration 16) the image-side focusing group includes a positive lens G2p, The optical system according to any one of Configurations 1 to 15, 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

[0236] (Configuration 17) The optical system described in any one of Configurations 1 to 16, wherein the following conditional expression is satisfied: MLFR is the amount of movement of the image-side focusing group when focusing from infinity to an object distance where the lateral magnification of the entire system is -0.1 times; MLFR is the amount of movement of the image-side focusing group 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 the distance on the optical axis from the aperture stop of the optical system to the image plane when focused at infinity. -0.200 <MLFR / DSP<-0.005

[0237] (Configuration 18) the front group includes a negative lens G1n, The optical system according to any one of Configurations 1 to 17, wherein the following condition is satisfied, where νd1n is the Abbe number of the negative lens G1n: 60.00<νd1n<100.00

[0238] (Configuration 19) 19. The optical system according to any one of configurations 1 to 18, wherein the following condition is satisfied, where fLFR is the focal length of the image-side focusing group and f is the focal length of the entire optical system: 0.50 <fLFR / f<3.00

[0239] (Configuration 20) The optical system according to any one of configurations 1 to 19, wherein the following conditional expression is satisfied, where DSP is the distance on the optical axis from the aperture stop of the optical system to the image plane when focused at infinity, sk is the back focus in air, and L is the total optical length of the optical system: 0.30<(DSP+sk) / L<0.80

[0240] (Configuration 21) The optical system according to any one of configurations 1 to 20, wherein the following condition is satisfied, where fLF is the focal length of the front group and f is the focal length of the entire optical system: 0.50 <fLF / f<5.00

[0241] (Configuration 22) The optical system according to any one of Configurations 1 to 21, wherein a negative lens is disposed closest to the image side of the rear group.

[0242] (Configuration 23) the front group includes a cemented lens Gcomp made up of a positive lens, the positive lens Gp, and a negative lens, The optical system according to any one of configurations 1 to 22, wherein the following conditional expression is satisfied, where f is the focal length of the entire optical system and fGcomp is the focal length of the cemented lens Gcomp. 0.00 <f / fGcomp<2.00

[0243] (Configuration 24) the front group has an object-side focusing group, 24. The optical system according to any one of configurations 1 to 23, wherein the object-side focusing group moves relative to the image plane during focusing from infinity to a close distance.

[0244] (Configuration 25) The optical system according to any one of configurations 1 to 24, wherein the rear group has positive refractive power.

[0245] (Configuration 26) The optical system according to any one of configurations 1 to 25, wherein the rear group has negative refractive power.

[0246] (Configuration 27) the front group includes, arranged in order from the object side, a first lens group having positive refractive power, a second lens group having negative refractive power, and a third lens group having positive refractive power; 27. The optical system according to any one of configurations 1 to 26, wherein, during focusing from infinity to a close distance, the second lens group moves relative to an image plane so that a distance between the first lens group and the second lens group and a distance between the second lens group and the third lens group change.

[0247] (Configuration 28) 28. An imaging device comprising: the optical system according to any one of configurations 1 to 27; and an imaging element that receives an image formed by the optical system. [Explanation of symbols]

[0248] L0 optical system LF front group LFR image side focusing group LR rear group SP aperture stop GP positive lens

Claims

1. An optical system comprising, arranged in order from the object side to the image side, a front group having positive refractive power, an image-side focusing group having positive refractive power, and a rear group, the image-side focusing group moves relative to an image plane so that a distance between the front group and the image-side focusing group and a distance between the image-side focusing group and the rear group change during focusing from infinity to a close distance; During focusing from infinity to a close distance, the rear group remains stationary relative to the image plane. an aperture stop that determines an axial light beam is disposed within the front group or adjacent to the front group on the image side; the front group has a positive lens Gp, An optical system characterized in that the following conditional expression is satisfied, where νdp is the Abbe number of the material of the positive lens Gp, θgFp is the partial dispersion ratio, and ΔθgFp is the anomalous partial dispersion. 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:

2. 2. The optical system according to claim 1, wherein the following condition is satisfied, where sk is the air-equivalent back focus of the optical system when focused at infinity, and f is the focal length of the entire optical system: 0.10<sk / f<1.80

3. 2. The optical system according to claim 1, wherein the following condition is satisfied, where fLF is the focal length of the front group and fLFR is the focal length of the image-side focusing group: 0.30<fLF / fLFR<3.00

4. 2. The optical system according to claim 1, wherein the following condition is satisfied, where f is the focal length of the entire optical system and fLR is the focal length of the rear group: -1.50<f / fLR<1.50

5. 2. The optical system according to claim 1, wherein the image-side focusing group comprises at least two positive lenses and at least one negative lens.

6. an object-side lens surface of the lens arranged closest to the object side in the image-side focusing group has a concave shape toward the object side; an image-side lens surface arranged closest to the image side in the image-side focusing group has a convex shape toward the image side; 2. The optical system according to claim 1, wherein the following condition is satisfied, where RLFR1 is the radius of curvature of the object-side lens surface and RLFR2 is the radius of curvature of the image-side lens surface: -1.50<(RLFR2-RLFR1) / (RLFR2+RLFR1)<1.50

7. at least one of the front group and the image-side focusing 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: -0.2000<N~~~~~(-1.454×10) －２ ×ν+2.287)<0050 -0.015<ΔθgFn<0.015 where ΔθgFn = θgFn - (-2.511 × 10 －３ ×νdn+0.674) It is expressed as:

8. 8. The optical system according to claim 7, wherein the front group includes at least one negative lens Gn.

9. 8. The optical system according to claim 7, wherein the image-side focusing group includes at least one negative lens Gn.

10. 2. The optical system according to claim 1, wherein the following condition is satisfied, where βLFR is the lateral magnification of the image-side focusing group when focused at infinity, and βLR is the lateral magnification of the rear group: 0.50<(1-βLFR ２ )×βLR ２ <2.50

11. 2. The optical system according to claim 1, wherein at least one of the aperture stop and the positive lens Gp is ​​stationary relative to the image plane during focusing.

12. 2. The optical system according to claim 1, wherein the following condition is satisfied, where sk is the air-equivalent back focus of the optical system when focused at infinity, and fLR is the focal length of the rear group: 0.00<sk / |fLR|<0.80

13. 2. The optical system according to claim 1, wherein the following conditional expression is satisfied: ΣDair is a sum of air spaces on the optical axis from the object-side lens surface of the lens in the front group that is positioned closest to the object to the image-side lens surface of the lens in the rear group that is positioned closest to the image, L is a total optical length of the optical system, and sk is an air-equivalent back focus of the optical system when focused at infinity. 0.20<ΣDair / (L-sk)<0.70

14. 2. The optical system according to claim 1, wherein the following condition is satisfied, where L is the total optical length of the optical system and f is the focal length of the entire optical system: 1.50<L / f<15.00

15. the image-side focusing group has a 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

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

17. the front group has 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

18. 2. The optical system according to claim 1, wherein the following condition is satisfied, where fLFR is the focal length of the image-side focusing group and f is the focal length of the entire optical system: 0.50<fLFR / f<3.00

19. 2. The optical system according to claim 1, wherein the following conditional expression is satisfied, where DSP is the distance on the optical axis from the aperture stop of the optical system to the image plane when focused at infinity, sk is the back focus in air, and L is the total optical length of the optical system. 0.30<(DSP+sk) / L<0.80

20. 2. The optical system according to claim 1, wherein the following condition is satisfied, where fLF is the focal length of the front group and f is the focal length of the entire optical system: 0.50<fLF / f<5.00

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

22. the front group includes a cemented lens Gcomp made up of a positive lens, the positive lens Gp, and a negative lens, 2. The optical system according to claim 1, wherein the following condition is satisfied, where f is a focal length of the entire optical system and fGcomp is a focal length of the cemented lens Gcomp. 0.00<f / fGcomp<2.00

23. the front group has an object-side focusing group, 2. The optical system according to claim 1, wherein the object-side focusing group moves relative to the image plane during focusing from infinity to a close distance.

24. 2. The optical system according to claim 1, wherein the rear group has positive refractive power.

25. 2. The optical system according to claim 1, wherein the rear group has negative refractive power.

26. the front group includes, arranged in order from the object side, a first lens group having positive refractive power, a second lens group having negative refractive power, and a third lens group having positive refractive power; 2. The optical system according to claim 1, wherein the second lens group moves relative to the image plane so that a distance between the first lens group and the second lens group and a distance between the second lens group and the third lens group change during focusing from infinity to a close distance.

27. An optical system comprising, arranged in order from the object side to the image side, a front group having positive refractive power, an image-side focusing group having positive refractive power, and a rear group, the image-side focusing group moves relative to an image plane so that a distance between the front group and the image-side focusing group and a distance between the image-side focusing group and the rear group change during focusing from infinity to a close distance; An optical system characterized in that the front group has at least two negative lenses.

28. 28. 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