Optical system and imaging device having the same

Abstract

To provide an optical system that offers high optical performance while shortening the focusing distance for objects. [Solution] An optical system comprising a first lens group having positive refractive power, a second lens group having positive refractive power, and a third lens group arranged in order from the object side to the image side, wherein during focusing, the second lens group moves in the optical axis direction relative to the image plane, the first lens group and the third lens group remain stationary relative to the image plane, the first lens group has three negative lenses arranged continuously in the optical axis direction closest to the object, and when the focal length of the entire optical system is f, the air-equivalent back focus when focused to infinity is sk, and the focal length of the second lens group is f2, a predetermined conditional equation 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 in-vehicle cameras. [Background technology]

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

[0003] [Patent Document 1] Japanese Patent Publication No. 2023-008471 [Overview of the Initiative] [Problems that the invention aims to solve]

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

[0005] One aspect of the present invention is an optical system comprising a first lens group having positive refractive power, a second lens group having positive refractive power, and a third lens group, arranged in order from the object side to the image side, wherein during focusing, the second lens group moves in the optical axis direction relative to the image plane, the first lens group and the third lens group remain stationary relative to the image plane, the first lens group has three negative lenses arranged continuously in the optical axis direction closest to the object, and when the focal length of the entire optical system is f, the air-equivalent back focus when focused to infinity is sk, and the focal length of the second lens group is f2, the following conditional equation is satisfied. 0.50 <f2 / f<3.00 0.20 <sk / f<1.20 Furthermore, another aspect of the present invention is an optical system comprising a first lens group having positive refractive power, a second lens group having positive refractive power, and a third lens group arranged in order from the object side to the image side, wherein during focusing, the second lens group moves in the optical axis direction relative to the image plane, while the first and third lens groups remain stationary relative to the image plane. When the focal length of the entire optical system is f and the focal length of the second lens group is f2, the following condition is satisfied. 0.50 <f2 / f<3.00 [Effects of the Invention]

[0006] This allows us to provide an optical system that offers high optical performance while shortening the focusing distance of objects. [Brief explanation of the drawing]

[0007] [Figure 1] Cross-sectional view of the optical system of Example 1 at infinity focus. [Figure 2] Longitudinal aberration diagram of the optical system of Example 1 when focused at (A) infinity and (B) the distance at which the lateral magnification is -0.1. [Figure 3] Cross-sectional view of the optical system of Example 2 at infinity focus. [Figure 4]Longitudinal aberration diagrams at focus for the optical system of Example 2 at (A) infinity and (B) a distance corresponding to a lateral magnification of -0.1 [Figure 5] Cross-sectional view of the optical system of Example 3 at infinity focus [Figure 6] Longitudinal aberration diagrams at focus for the optical system of Example 3 at (A) infinity and (B) a distance corresponding to a lateral magnification of -0.1 [Figure 7] Cross-sectional view of the optical system of Example 4 at infinity focus [Figure 8] Longitudinal aberration diagrams at focus for the optical system of Example 4 at (A) infinity and (B) a distance corresponding to a lateral magnification of -0.1 [Figure 9] Cross-sectional view of the optical system of Example 5 at infinity focus [Figure 10] Longitudinal aberration diagrams at focus for the optical system of Example 5 at (A) infinity and (B) a distance corresponding to a lateral magnification of -0.1 [Figure 11] Cross-sectional view of the optical system of Example 6 at infinity focus [Figure 12] Longitudinal aberration diagrams at focus for the optical system of Example 6 at (A) infinity and (B) a distance corresponding to a lateral magnification of -0.1 [Figure 13] Cross-sectional view of the optical system of Example 7 at infinity focus [Figure 14] Longitudinal aberration diagrams at focus for the optical system of Example 7 at (A) infinity and (B) a distance corresponding to a lateral magnification of -0.1 [Figure 15] Schematic diagram of an imaging device [Figure 16] Schematic diagram of a lens device

Embodiments for Carrying Out the Invention

[0008] Hereinafter, the embodiments disclosed in this specification will be described in detail with reference to the drawings. Note that each drawing may be drawn at a scale different from the actual for convenience. Also, in each drawing, the same members are denoted by the same reference numerals, and redundant explanations are omitted.

[0009] Figures 1, 3, 5, 7, 9, 11, and 13 are cross-sectional views of the optical systems of Examples 1 to 7 when they are focused at infinity.

[0010] In each cross-sectional view, the left side is the object side and the right side is the image side. The optical systems of each embodiment are suitable for imaging devices such as digital video cameras, digital still cameras, broadcast cameras, silver halide film cameras, surveillance cameras, and in-vehicle cameras. Furthermore, the optical systems of each embodiment may also be used as projection lenses for projectors, in which case the left side is the screen side and the right side is the projected image side.

[0011] In each cross-sectional view, L0 represents the entire optical system, and Li represents the i-th lens group from the object side (where i is a natural number) among the lens groups separated from the object side and the image side by an aperture diaphragm. Gk represents the k-th lens from the object side (where k is a natural number) among the lenses included in each lens group. In this disclosure, the interior of a lens group refers to the space between the lens positioned furthest towards the object and the lens positioned furthest towards the image among the lenses constituting the lens group.

[0012] Lens group Li is a collection of lenses that move or remain fixed as a single unit relative to the image plane during focusing. That is, the air gap between adjacent lens groups changes during focusing, while the air gap within each lens group remains unchanged during focusing.

[0013] The arrows parallel to the optical axis shown in each cross-sectional view represent the direction of movement of the lens group during focusing from infinity to near. In each embodiment, during focusing, only the second lens group L2, described later, moves from the image side to the object side.

[0014] In each cross-sectional view, SP is the aperture diaphragm that determines the light beam at the open F-number. IP is the 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 image plane of a solid-state image sensor such as a CCD sensor or CMOS sensor or a photoelectric conversion element is located there. 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 plane is located on the image plane IP.

[0015] Figures 2, 4, 6, 8, 10, 12, and 14 show the aberration diagrams when the optical system L0 of Examples 1 to 7 is focused at (A) infinity and (B) a distance where the lateral magnification is -0.1, respectively.

[0016] 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 dashed line represents the amount of spherical aberration for the g-line (wavelength 435.8 nm). In the aberration diagram, the solid line S represents the amount of aberration at the sagittal image plane, and the dashed line M represents the amount of aberration at 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 dashed line represents the amount of lateral chromatic aberration at the g-line. Also, ω is the half-angle of view (°).

[0017] Next, we will describe the characteristic configurations of the optical systems in each embodiment.

[0018] The optical system L0 of each embodiment consists of a first lens group L1 having positive refractive power, a second lens group L2 having positive refractive power, and a third lens group L3, arranged in order from the object side to the image side. Furthermore, in the optical system L0 of each embodiment, during focusing, the second lens group L2 moves in the optical axis direction relative to the image plane, while the first lens group L1 and the third lens group L3 remain stationary relative to the image plane.

[0019] The optical system L0 is configured such that the light beam, focused by the first lens group L1 which has positive refractive power, is incident on the second lens group L2 which also has positive refractive power. This reduces the lens diameter of the second lens group L2, which moves relative to the image plane during focusing, and makes the second lens group L2 lighter, thus enabling high-speed focusing.

[0020] Furthermore, the optical system L0 of each embodiment is characterized in that, when the focal length of the entire optical system L0 is f and the focal length of the second lens group is f2, it satisfies the following conditional equation. 0.50 <f2 / f<3.00···(1) Condition (1) relates to the refractive power of the second lens group L2. By satisfying condition (1), the focal length f2 of the second lens group L2 becomes smaller, allowing the object distance that can be focused to be brought closer to the image plane. Furthermore, the overall length of the optical system can be shortened while suppressing changes in optical performance during focusing.

[0021] If the focal length f2 of the positive second lens group L2 falls below the lower limit of condition (1), the refractive power of the second lens group L2 becomes too large. This is undesirable because it results in large changes in performance such as spherical aberration, field curvature, and angle of view fluctuations that occur during focusing.

[0022] If the focal length f2 of the positive second lens group L2 increases beyond the upper limit of condition (1), the positional sensitivity of the second lens group L2, i.e., the ratio of the movement of the image plane to the movement of the focusing group, becomes too small. This is undesirable because the object distance that can be focused by focusing moves further away from the image plane. Furthermore, the overall length of the optical system L0 increases in order to ensure sufficient air distance for focusing, which is also undesirable.

[0023] Furthermore, it is more preferable to set the numerical range of condition (1) to the range of condition (1a) below. 0.70 <f2 / f<2.80···(1a) Furthermore, it is more preferable to set the numerical range of condition (1) to the range of condition (1b) below. 0.90 <f2 / f<2.60···(1b) Furthermore, it is more preferable to set the numerical range of condition (1) to the range of condition (1c) below. 1.10 <f2 / f<2.40···(1c) Next, we will describe the configurations that are preferable to satisfy in the optical system of each embodiment.

[0024] In the optical system L0, it is preferable that the first lens group L1 has three negative lenses arranged continuously in the optical axis direction on the object side. In wide-angle lenses, a strong negative refractive force is required on the object side of the optical system L0 in order to ensure sufficient back focus. By sharing this negative refractive force among three negative lenses, the refractive force per negative lens can be reduced, thereby suppressing barrel distortion and field curvature. In this disclosure, three continuously arranged negative lenses means that no positive lenses are arranged between the three negative lenses.

[0025] Furthermore, by positioning the third lens group L3 at a location on the image side of the second lens group L2, which moves during focusing, where the on-axial light beam and peripheral light beam are sufficiently separated in the direction perpendicular to the optical axis, astigmatism and distortion can be effectively corrected, improving the peripheral performance of the optical system L0.

[0026] In the optical system L0, it is preferable that the positive second lens group L2 has at least two positive lenses and at least one negative lens. To reduce the amount of movement of the second lens group L2 when focusing from infinity to close range, the refractive power of the second lens group L2 needs to be increased. By sharing this strong refractive power among 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. In addition, having at least one negative lens allows for good correction of axial chromatic aberration.

[0027] In the optical system L0, it is preferable that the aperture diaphragm SP, which determines the on-axial light beam, is located inside the first lens group L1 or adjacent to the image side of the first lens group L1, and that the aperture diaphragm SP is immovable relative to the image plane during focusing. This makes it possible to reduce the weight of the second lens group L2, which moves during focusing, thus enabling high-speed focusing. Furthermore, by arranging the aperture diaphragm SP inside or adjacent to the image side of the first lens group L1, the imbalance in lens diameters between the front and rear of the optical system L0 can be reduced, thereby reducing the overall diameter of the optical system L0.

[0028] In the optical system L0, it is preferable that the object-side lens surface of the lens positioned closest to the object in the second lens group L2 is concave. This allows the off-axis light beam that has passed through the aperture diaphragm SP to be incident approximately concentrically on the object-side surface of the second lens group L2, reducing the refraction of light rays at that surface. As a result, variations in astigmatism, coma aberration, and angle of view during focusing can be suppressed.

[0029] In the optical system L0, it is preferable that the image-side lens surface of the lens positioned closest to the image in the second lens group L2 is convex. This causes the off-axis light beam emitted from the second lens group L2 to be emitted approximately concentrically toward the image-side surface of the second lens group L2, thereby reducing the refraction of light rays at that surface. As a result, it becomes easier to suppress variations in astigmatism, coma aberration, and angle of view during focusing.

[0030] In the optical system L0, it is preferable to place the negative lens on the image side of the third lens group L3, i.e., the image side of the optical system L0. This allows for a larger angle of the off-axis rays incident on the image plane from the optical axis, thereby reducing the lens diameter of the third lens group L3. Furthermore, by placing the negative lens at a position where the height of the off-axis rays on the image side is high, the positive Petzval sum of the entire optical system L0 can be reduced without worsening sagittal flare, and image field curvature can be effectively corrected.

[0031] Next, we will describe the conditions that the optical system L0 of each embodiment should preferably satisfy.

[0032] The optical system of each embodiment preferably satisfies one or more of the following conditional equations (2) to (17). In each conditional equation, the numerical values ​​are expressed as follows.

[0033] Let sk be the air-equivalent back focus of the optical system L0.

[0034] Let the focal length of the third lens group L3 be f3.

[0035] Let R21 be the radius of curvature of the object-side surface of the second lens group L2, and R22 be the radius of curvature of the image-side surface.

[0036] Let Ndn be the refractive index of the d-line of the negative lens Gn in the optical system L0.

[0037] The anomalous partial dispersion ΔθgFn of the negative lens Gn of the optical system L0 is expressed using the Abbe number νdn and the partial dispersion ratios for the g-line and F-line as θgFn. ΔθgFn=θgFn-(-0.0025116×νdn+0.67449) Let's assume that.

[0038] Let β2 be the lateral magnification when the second lens group L2 is focused at infinity, and let β3 be the lateral magnification when the third lens group L3 is focused at infinity.

[0039] Let ΣDair be the sum of the air gaps along the optical axis from the object-side surface to the image-side surface of the optical system L0.

[0040] Let L be the total optical length of the optical system L0.

[0041] Let νd1n be the Abbe number of the negative lens G1n in the first lens group L1.

[0042] Let νd2p be the Abbe number of the positive lens G2p in the second lens group L2.

[0043] Let M2 be the amount of movement of the second lens group L2 when focusing from infinity to an object distance where the lateral magnification of the entire system becomes -0.1x.

[0044] DSP is defined as the distance along the optical axis from the aperture diaphragm SP to the image-side plane when the optical system L0 is focused to infinity.

[0045] The anomalous partial dispersion ΔθgFp of the positive lens Gp of the first lens group L1 or the second lens group L2 is expressed as follows, using the Abbe number νdp and the partial dispersion ratio θgFp. ΔθgFp = θgFp - (B3 × νdp 3 +B2×νdp 2 (+B1×νdp+B0) B3 = -1.665 × 10 -7 B2 = 5.213 × 10 -5 B1 = -5.656 × 10 -3 B0 = 7.278 × 10 -1 0.20 <sk / f<1.20···(2) 0.30 <f1 / f2<3.00···(3) -1.50 <f / f3<1.50···(4) -1.50<(R22-R21) / (R22+R21)<1.50...(5) -0.015 < ΔθgFn < 0.015 ···(6) -0.20 <Ndn-(-0.0145425×νdn+2.28725)<0.05···(7) 0.50<(1-β2 2 )×β3 2 <2.50···(8) 0.00 <sk / |f3|<0.80···(9) 0.20<ΣDair / (L-sk)<0.70 (10) 2.00 <L / f<15.00···(11) 60.00 < νd2p < 100.00 ... (12) -0.200 <M2 / DSP<-0.005···(13) 60.00 < νd1n < 100.00 ... (14) 0.050 < ΔθgFp < 0.250 ... (15) 0.30<(DSP+sk) / L<0.80···(16) 0.50 <f1 / f<5.00···(17) Next, we will explain the technical meaning of the aforementioned conditional expressions (2) through (17).

[0046] Condition (2) relates to the air-equivalent back focus sk of the optical system L0. By satisfying condition (2), the third lens group L3 can be positioned at a location with a large off-axis ray height, thereby selectively correcting distortion and astigmatism while minimizing the impact on correcting spherical aberration and sagittal flare. As a result, the peripheral performance of the optical system L0 can be improved.

[0047] If the back focus sk becomes small below the lower limit of condition (2), it becomes difficult to position the lens near the image plane, which is undesirable.

[0048] If the back focus sk becomes large beyond the upper limit of condition (2), it becomes difficult to position the third lens group L3 at a position with a large off-axis ray height, making it difficult to adequately correct distortion, field curvature, and astigmatism, which is undesirable. Condition (3) relates to the ratio of the refractive powers of the first lens group L1 and the second lens group L2.

[0049] If f2 becomes large below the lower limit of condition (3), the positive refractive power of the second lens group L2 becomes too small, which is undesirable because it increases the amount of movement required during focusing and increases the overall length. Also, if f1 becomes small, it becomes difficult to correct spherical aberration and axial chromatic aberration, which is undesirable.

[0050] If f2 becomes too small, exceeding the upper limit of condition (3), the refractive power of the second lens group L2 becomes too large, which is undesirable because it leads to excessive changes in performance such as spherical aberration, field curvature, and angle of view during focusing. Also, if f1 becomes too large, the overall length increases, which is undesirable.

[0051] Conditional equation (4) defines the ratio of the focal length f3 of the third lens group L3 to the focal length f of the entire optical system L0.

[0052] Near the lower limit of condition (4), f3 takes a negative value. When the absolute value of f3 becomes small below the lower limit of condition (4), the negative refractive power of the third lens group L3 becomes too large. At this time, the angle of incidence of the off-axis light beam incident on the image plane becomes too large, which is undesirable because it makes color unevenness more likely to occur when imaging with a solid-state image sensor such as a CMOS sensor.

[0053] Near the upper limit of condition (4), f3 takes a positive value. If the absolute value of f3 becomes small beyond the upper limit of condition (4), the positive refractive power of the third lens group L3 becomes too large, which is undesirable because it causes the positive Petzval sum of the entire optical system L0 to become too large, making it difficult to correct the field curvature.

[0054] Conditional equation (5) defines the shape of the second lens group L2 and relates to the conditions for suppressing aberrations and changes in the angle of view that occur during focusing.

[0055] When the value falls below the lower limit of condition (5), the absolute value of the radius of curvature of the concave surface closest to the object in the second lens group L2 increases. In this case, the concentricity of the surface closest to the object in the second lens group L2 with respect to the off-axis light beam incident on the second lens group L2 decreases. Also, because the absolute value of the radius of curvature of the convex surface closest to the image in the second lens group L2 decreases, the off-axis light beam is significantly refracted by the surface closest to the image in the second lens group L2. As a result, the fluctuation in the angle of view that occurs during focusing tends to increase, which is undesirable.

[0056] When the upper limit of condition (5) is exceeded, the absolute value of the radius of curvature of the concave surface closest to the object in the second lens group L2 becomes smaller. At this time, the concentricity of the surface closest to the object in the second lens group L2 with respect to the off-axis light beam incident on the second lens group L2 becomes smaller. As a result, the fluctuation in the angle of view that occurs during focusing tends to become larger. Also, the absolute value of the radius of curvature of the convex surface closest to the image in the second lens group L2 becomes larger. This is undesirable because it tends to increase the fluctuation of aberrations such as coma and astigmatism during focusing.

[0057] Condition (6) defines the anomalous partial dispersion of the negative lens Gn of the first lens group L1 or the second lens group L2.

[0058] If the value falls below the lower limit of condition (6), the correction of axial chromatic aberration on the g line becomes excessive, which is undesirable.

[0059] If the upper limit of condition (6) is exceeded, the correction of axial chromatic aberration on the g line will be insufficient, which is undesirable.

[0060] Condition (7) defines the dispersion of the negative lens Gn possessed by at least one of the first lens group L1 or the second lens group L2.

[0061] If the value falls below the lower limit of condition equation (7), the correction of axial chromatic aberration becomes excessive, which is undesirable.

[0062] If the upper limit of condition (7) is exceeded, it is undesirable because either the correction of axial chromatic aberration will be insufficient, or the refractive power of the negative lens Gn will become too large, making it difficult to correct spherical aberration.

[0063] Large-aperture lenses often suffer from axial chromatic aberration in the short-wavelength range, such as the g-line. In particular, when first-order achromatic correction is performed on the C-line and F-line, axial chromatic aberration of the g-line tends to become excessive. By using glass material that satisfies conditions (6) and (7) in the negative lens, the degree of divergence of the g-line due to the negative lens can be relatively reduced, thereby suppressing excessive axial chromatic aberration of short wavelengths such as the g-line.

[0064] By placing at least one negative lens Gn that satisfies both conditions (6) and (7) in at least one of the first lens group L1 or the second lens group L1, the above-described effect of axial chromatic aberration correction can be obtained.

[0065] Furthermore, the effect can be enhanced by having two negative lenses (Gn). The effect can be further enhanced by having three or more negative lenses (Gn).

[0066] Furthermore, it is preferable to place at least one negative lens Gn in each of the first lens group L1 and the second lens group L2.

[0067] By placing a negative lens Gn in the first lens group L1, axial chromatic aberration correction can be effectively performed for the entire optical system L0. By placing a negative lens Gn in the second lens group L2, axial chromatic aberration correction within the second lens group L2 is facilitated, and fluctuations in axial chromatic aberration during focusing can be suppressed.

[0068] Conditional equation (8) specifies the ratio of the movement of the image plane to the movement of the second lens group L2, relating to the positional sensitivity of the second lens group.

[0069] If the value falls below the lower limit of condition (8), the positional sensitivity of the second lens group L2 becomes too low. This is undesirable because it increases the focusing distance. Furthermore, it is undesirable because it becomes difficult to shorten the overall length of the optical system L0 in order to secure a focusing distance.

[0070] If the upper limit of condition (8) is exceeded, the refractive power of the second lens group L2 becomes too large, which is undesirable because it leads to excessive changes in performance such as spherical aberration, field curvature, and angle of view during focusing.

[0071] Conditional equation (9) specifies the ratio of the focal length f3 of the third lens group L3 to the air-equivalent back focus sk.

[0072] When sk becomes small, falling below the lower limit of condition (9), the image plane of the optical system L0 is positioned closer to the object than the image-side plane of the optical system L0, making imaging difficult and undesirable.

[0073] If sk exceeds the upper limit of condition (9), it is undesirable because the correction effect for distortion and field curvature decreases, and the front lens diameter increases.

[0074] If |f3| becomes smaller than the upper limit of condition (9), the absolute value of the refractive power of the third lens group L3 becomes too large. If the negative refractive power becomes too large, the angle of incidence of the off-axis light beam incident on the image plane becomes too large, which is undesirable because it makes it easier for color unevenness to occur when imaging with an image sensor such as a CMOS sensor. If the positive refractive power becomes too large, the positive Petzval sum of the entire optical system L0 becomes too large, which is undesirable because it makes it difficult to correct the field curvature.

[0075] Conditional equation (10) defines the ratio of the total air gap ΣDair on the optical axis from the object-side surface to the image-side surface of the optical system L0 to the total optical length L of the optical system L0.

[0076] If ΣDair becomes small below the lower limit of condition (10), it becomes difficult to secure sufficient space for the lens group to move during focusing, which is undesirable. Furthermore, it becomes difficult to give sufficient positive curvature to the negative lens of the first lens group, making it difficult to widen the optical system L0 and correct distortion aberrations, which is also undesirable.

[0077] If ΣDair becomes larger than the upper limit of condition (10), the ratio of the air gap to the total optical length becomes too large, making it difficult to provide each lens with sufficient refractive power, and thus difficult to correct spherical aberration and axial chromatic aberration, which is undesirable. Alternatively, if one attempts to provide each lens with sufficient refractive power, the total length becomes larger, which is also undesirable.

[0078] Conditional equation (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.

[0079] If L becomes small below the lower limit of condition (11), the refractive power of each lens group becomes too large, making it difficult to correct aberrations such as distortion, astigmatism, and spherical aberration, which is undesirable.

[0080] If L exceeds the upper limit of condition (11), the overall length increases, which is undesirable.

[0081] Conditional equation (12) is an equation that defines the Abbe number νd2p of at least one positive lens G2p in the second lens group L2, and defines the conditions for good correction of axial chromatic aberration.

[0082] If νd2p becomes small below the lower limit of condition equation (12), it becomes difficult to correct axial chromatic aberration, which is undesirable.

[0083] If νd2p exceeds the upper limit of condition (12), it is undesirable because it can lead to excessive correction of chromatic aberration, excessive wear of the glass material making processing difficult, and increased cracking.

[0084] Furthermore, it is preferable to arrange two or more positive lenses G2p that satisfy condition (12) in the second lens group L2, as this can enhance the effects described above.

[0085] Conditional equation (13) defines the ratio of the amount of movement M2 when focusing the second lens group L2 from infinity to an object distance where the lateral magnification of the entire system is -0.1x, and the distance on the optical axis from the aperture diaphragm SP to the image-side plane, which is DSP. Note that the sign of the amount of movement M2 is positive when moving from the object side to the image side. If M2 becomes small below the lower limit of condition (13), the refractive power of the second lens group L2 becomes too large, which is undesirable because it increases the fluctuations in spherical aberration and field curvature during focusing.

[0086] If M2 exceeds the upper limit of condition (13), the amount of movement of the second lens group increases, and the overall length increases in order to secure space for that movement, which is undesirable.

[0087] Conditional equation (14) is an equation that defines the Abbe number νd1n of at least one negative lens G1n in the first lens group L1, and defines the conditions for good correction of chromatic aberration.

[0088] If νd1n becomes small below the lower limit of condition equation (14), it becomes difficult to correct chromatic aberration, which is undesirable.

[0089] If νd1n becomes larger than the upper limit of condition equation (14), it is undesirable because it can lead to excessive correction of chromatic aberration, excessive wear of the negative lens Gn1 making processing difficult, and increased susceptibility to cracking.

[0090] Furthermore, it is even more preferable to arrange two or more negative lenses G1n that satisfy condition (14) in the first lens group L1, as this can enhance the effects described above.

[0091] Conditional equation (15) defines the anomalous partial dispersion ΔθgFp of the positive lens Gp located in the first lens group L1 or the second lens group L2.

[0092] Large-aperture lenses often suffer from axial chromatic aberration in the short-wavelength range, such as the g-line. In particular, applying first-order achromatic correction to the C-line and F-line tends to result in excessive axial chromatic aberration in the g-line. Therefore, by using a material with a large ΔθgFp for the positive lens, the excessive axial chromatic aberration in the short-wavelength range, such as the g-line, can be selectively focused and effectively corrected.

[0093] If ΔθgFp falls below the lower limit of condition equation (15) and becomes small, it becomes difficult to correct axial chromatic aberration, which is undesirable.

[0094] If ΔθgFp exceeds the upper limit of condition equation (15), the correction of axial chromatic aberration becomes excessive, which is undesirable.

[0095] Furthermore, the correction effect of axial chromatic aberration can be further enhanced by arranging the positive lens Gp as a three-element cemented lens consisting of a positive lens, a positive lens Gp, and a negative lens, or as a three-element cemented lens consisting of a negative lens, a positive lens Gp, and a positive lens.

[0096] Furthermore, by using a negative lens Gn that satisfies conditions (6) and (7) as the negative lens constituting the three-element cemented lens, axial chromatic aberration can be effectively corrected.

[0097] Furthermore, it is preferable that the three-element cemented lens be positioned adjacent to the object-side or image-side of the aperture diaphragm SP located in the first lens group L1. This positions the lens at a location with a large axial ray height, thereby enhancing the effect of axial chromatic aberration correction.

[0098] Furthermore, it is preferable that the three-element cemented lens and the aperture diaphragm SP be positioned in the first lens group L1, which remains stationary during focusing. As mentioned above, it is preferable to position the three-element cemented lens before and after the aperture diaphragm SP, but the axial light beam diameter is large before and after the aperture diaphragm SP, resulting in larger lens diameters and excessively heavy lenses. Therefore, it is preferable to configure the three-element cemented lens, including the aperture diaphragm SP and the positive lens Gp, to remain stationary during focusing.

[0099] Conditional equation (16) defines the position of the aperture diaphragm SP and specifies the conditions for making the optical system L0 compact.

[0100] If the DSP becomes small below the lower limit of condition (16), the diameter of the lens positioned on the object side of the aperture diaphragm SP becomes larger, which is undesirable because it increases the overall mass and diameter of the optical system L0. Also, the angle of the off-axis light beam incident on the image plane becomes too large, which is undesirable because it makes color unevenness more likely to occur when imaging with a solid-state image sensor such as a CMOS sensor.

[0101] When the DSP becomes large exceeding the upper limit of conditional expression (16), the aperture of the lens arranged on the image side becomes larger than the aperture stop SP, and the mass and diameter of the entire optical system L0 increase, which is not preferable.

[0102] Conditional expression (17) defines the focal length f1 of the first lens group L1.

[0103] When f1 becomes small below the lower limit of conditional expression (17), the positive refractive power of the first lens group L1 becomes too large, and it becomes difficult to correct spherical aberration and distortion aberration, which is not preferable.

[0104] When f1 becomes large exceeding the upper limit of conditional expression (17), the aperture of the second lens group L2 becomes large and the mass becomes large, making high-speed focusing difficult, which is not preferable.

[0105] It is more preferable that the numerical ranges of conditional expressions (2) to (17) are the numerical ranges of conditional expressions (2a) to (17a) below. 0.30 < sk / f < 1.18 ··· (2a) 0.50 < f1 / f2 < 2.70 ··· (3a) -1.20 < f / f3 < 1.20 ··· (4a) -1.20 < (R22 - R21) / (R22 + R21) < 1.20 ··· (5a) -0.010 < ΔθgFn < 0.010 ··· (6a) -0.18 < Ndn - (-0.0145425 × νdn + 2.28725) < 0.03 ··· (7a) 0.60 < (1 - β2 2 ) × β3 2 < 2.20 ··· (8a) 0.00 < sk / |f3| < 0.70 ··· (9a) 0.25 < ΣDair / (L - sk) < 0.64 ··· (10a) 3.00 < L / f < 13.50 ··· (11a) 62.00 < νd2p < 99.00 ··· (12a) -0.160 < M2 / DSP < -0.008 ··· (13a) 62.00 < νd1n < 99.00 ... (14a) 0.060<ΔθgFp<0.210 (15a) 0.35<(DSP+sk) / L<0.74 (16a) 0.70 <f1 / f<4.50···(17a) Furthermore, it is more preferable to use the numerical ranges of the following conditional expressions (2) to (17) as the numerical ranges of the conditional expressions (2b) to (17b). 0.40 <sk / f<1.14···(2b) 0.70 <f1 / f2<2.30···(3b) -0.90 <f / f3<0.50···(4b) -0.80<(R22-R21) / (R22+R21)<0.80...(5b) -0.008<ΔθgFn<0.007 (6b) -0.15 <Ndn-(-0.0145425×νdn+2.28725)<0.02···(7b) 0.55<(1-β2 2 )×β3 2 <1.90···(8b) 0.00 <sk / |f3|<0.60···(9b) 0.30<ΣDair / (L-sk)<0.56 (10b) 3.50 <L / f<12.00···(11b) 64.00 < νd2p < 98.00 ···(12b) -0.120 <M2 / DSP<-0.012···(13b) 64.00 < νd1n < 98.00 ... (14b) 0.070<ΔθgFp<0.180 (15b) 0.40<(DSP+sk) / L<0.68 (16b) 1.00 <f1 / f<4.00···(17b) Furthermore, it is more preferable to use the numerical ranges of the following conditional expressions (2) to (17) as the numerical ranges of the conditional expressions (2c) to (17c). 0.50 <sk / f<1.10···(2c) 0.90 <f1 / f2<1.80···(3c) -0.50 <f / f3<0.20···(4c) -0.50<(R22-R21) / (R22+R21)<0.50...(5c) -0.006<ΔθgFn<0.004 (6c) -0.13 <Ndn-(-0.0145425×νdn+2.28725)<0.01···(7c) 0.65<(1-β2 2 )×β3 2 <1.60···(8c) 0.00 <sk / |f3|<0.40···(9c) 0.33<ΣDair / (L-sk)<0.50 (10c) 4.00 <L / f<11.00···(11c) 66.00 < νd2p < 97.00 ···(12c) -0.080 <M2 / DSP<-0.016···(13c) 66.00 < νd1n < 97.00 ···(14c) 0.080<ΔθgFp<0.160 (15c) 0.45<(DSP+sk) / L<0.65 (16c) 1.30 <f1 / f<3.50···(17c) Next, we will describe the detailed configuration of the optical system L0 in Examples 1 to 7. Note that for the zoom lens L0 in each example, we will omit the explanation of configurations similar to the zoom lens L0 in Example 1, and will mainly describe the differences from Example 1.

[0106] [Example 1] The optical system L0 of Example 1 consists of a first lens group L1 having positive refractive power, a second lens group L2 having positive refractive power, and a third lens group L3 having negative refractive power. By making the third lens group L3 have negative refractive power, it becomes easier to correct the positive Petzval sum, and the field curvature can be corrected well.

[0107] In the optical system L0 of Example 1, the first lens group L1 consists of G1 to G12 lenses, the second lens group L2 consists of G13 to G16 lenses, and the third lens group consists of G17 and G18 lenses. The first lens group L1 includes an aperture diaphragm SP. Furthermore, by making the G1 and G3 lenses aspherical lenses, distortion and astigmatism can be corrected effectively.

[0108] In the optical system L0 of Example 1, lenses G6 and G7, lenses G10 to G12, lenses G13 and G14, and lenses G17 and G18 are each joined together to form a single cemented lens.

[0109] During focusing, the second lens group L2 moves in the optical axis direction relative to the image plane, while the first lens group L1 and the third lens group L3 remain stationary relative to the image plane.

[0110] [Example 2] In the optical system L0 of Example 2, the first lens group L1 consists of G1 to G10 lenses, the second lens group L2 consists of G11 to G14 lenses, and the third lens group consists of G15 and G16 lenses.

[0111] In the optical system L0 of Example 2, lenses G4 and G5, lenses G8 to G10, lenses G11 and G12, and lenses G15 and G16 are joined together to form a single cemented lens.

[0112] [Example 3] In the optical system L0 of Example 3, the first lens group L1 consists of G1 to G8 lenses, the second lens group L2 consists of G9 to G12 lenses, and the third lens group consists of G13 and G14 lenses. The first lens group L1 includes an aperture diaphragm SP. Furthermore, by making the G1 and G3 lenses aspherical lenses, distortion and astigmatism can be corrected effectively.

[0113] In the optical system L0 of Example 3, lenses G4 and G5, lenses G6 and G7, lenses G9 and G10, and lenses G13 and G14 are joined together to form a single cemented lens.

[0114] In the optical system L0 of Example 3, the G8 lens included in the first lens group L1 moves to include a component perpendicular to the optical axis. This makes it possible to suppress fluctuations in chromatic aberration during image blur correction.

[0115] [Example 4] In the optical system L0 of Example 4, the first lens group L1 consists of G1 to G9 lenses, the second lens group L2 consists of G10 to G14 lenses, and the third lens group consists of G15 to G17 lenses.

[0116] In the optical system L0 of Example 4, lenses G4 and G5, lenses G8 and G9, lenses G10 to G12, and lenses G15 and G16 are each joined together to form a single cemented lens.

[0117] [Example 5] In the optical system L0 of Example 5, the first lens group L1 consists of G1 to G12 lenses, the second lens group L2 consists of G13 to G16 lenses, and the third lens group consists of G17 and G18 lenses. Furthermore, by making the G1 and G3 lenses aspherical lenses, distortion and astigmatism can be corrected effectively.

[0118] In the optical system L0 of Example 5, lenses G6 and G7, lenses G10 to G12, lenses G13 and G14, and lenses G17 and G18 are joined together to form a single cemented lens.

[0119] [Example 6] The optical system L0 of Example 6 consists of a first lens group L1 having positive refractive power, a second lens group L2 having positive refractive power, and a third lens group L3 having positive refractive power. By making the third lens group L3 have positive refractive power, the incident angle of the off-axis light beam incident on the image plane can be reduced, making it easier to suppress color unevenness when imaging with a solid-state image sensor such as a CMOS sensor.

[0120] In the optical system L0 of Example 6, the first lens group L1 consists of G1 to G10 lenses, the second lens group L2 consists of G11 to G14 lenses, and the third lens group consists of G15 and G16 lenses. Furthermore, by making the G1 and G3 lenses aspherical lenses, distortion and astigmatism can be corrected effectively.

[0121] In the optical system L0 of Example 6, lenses G4 and G5, lenses G8 to G10, lenses G11 and G12, and lenses G15 and G16 are joined together to form a single cemented lens.

[0122] [Example 7] In the optical system L0 of Example 7, the first lens group L1 consists of G1 to G8 lenses, the second lens group L2 consists of G9 to G12 lenses, and the third lens group consists of G13 and G14 lenses. Furthermore, by making the G1 and G3 lenses aspherical lenses, distortion and astigmatism can be corrected effectively.

[0123] In the optical system L0 of Example 7, the G4 and G5 lenses, the G9 and G10 lenses, and the G13 and G14 lenses are joined together to form a single cemented lens.

[0124] In the optical system L0 of Example 7, the G8 lens included in the first lens group L1 moves to include a component perpendicular to the optical axis. This makes it possible to suppress fluctuations in chromatic aberration during image blur correction.

[0125] In the optical system L0 of each embodiment, it is preferable to place the negative lens on the image side of the third lens group L3, i.e., on the image side of the optical system L0. This allows for a larger angle of the off-axis rays incident on the image plane from the optical axis, thereby reducing the lens diameter of the third lens group L3. Furthermore, by placing the negative lens at a position where the height of the off-axis rays on the image side is high, the positive Petzval sum of the entire optical system L0 can be reduced without worsening sagittal flare, and image field curvature can be corrected effectively.

[0126] In the optical system L0 of each embodiment, it is preferable that the first lens group L1 has two negative meniscus lenses with a convex shape on the object side, arranged consecutively at the object side. This allows for good correction of distortion, field curvature, and astigmatism.

[0127] In the optical system L0 of each embodiment, it is preferable that at least one of the three negative lenses arranged most continuously towards the object in the first lens group L1 be an aspherical lens. This allows for good correction of distortion and astigmatism. Furthermore, in embodiments 1 and 5, the above effect is enhanced by making both the G1 lens and the G3 lens as aspherical lenses. In addition, by shaping the aspherical lens such that the absolute value of curvature at the periphery is smaller than the absolute value of curvature along the optical axis, distortion can be well corrected.

[0128] In the optical system L0 of each embodiment, it is preferable that the image-side lens surface of the negative G2 lens is concave and the object-side lens surface of the negative G3 lens is concave. This increases the refractive power of the negative air lens formed by the image-side lens surface of the G2 lens and the object-side lens surface of the G3 lens, making it easier to reduce the positive Petzval sum and effectively correcting field curvature.

[0129] In the optical system L0 of each embodiment, it is preferable that the first lens group L1 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 lens G4 a positive lens, barrel distortion and chromatic aberration generated by lenses G1 to G3 can be effectively corrected.

[0130] In Examples 1 and 5, the G4 lens is preferably a meniscus lens with positive refractive power. This allows for correction of barrel distortion and chromatic aberration. The G4 lens may be a positive meniscus lens with a convex shape on the object side, or a positive meniscus lens with a convex shape on the image side.

[0131] In the optical system L0 of each embodiment, it is preferable that the first lens group L1 has at least one cemented lens consisting of a positive lens and a negative lens. This allows for good correction of axial chromatic aberration and lateral chromatic aberration. Furthermore, as in Examples 2, 3, 4, 6, and 7, by making the negative lens in the cemented lens a negative lens Gn that satisfies conditions (6) and (7), axial chromatic aberration of the g line can be corrected even more effectively.

[0132] In the optical system L0 of each embodiment, the first lens group L1 can perform image blur correction by moving at least a portion of the first lens group L1 to include a component in the direction perpendicular to the optical axis.

[0133] In Examples 3 and 7, the G8 lens moves to include components perpendicular to the optical axis during image blur correction, but this is not limited to this configuration. Furthermore, if the lens that moves during image blur correction includes at least a positive lens and a negative lens, fluctuations in chromatic aberration during image blur correction can be suppressed. Alternatively, a configuration in which three or more lenses move during image blur correction is also possible.

[0134] In the optical system L0 of each embodiment, the second lens group L2 has negative and positive lenses arranged sequentially in the optical axis direction. This allows for better correction of axial chromatic aberration at infinity focus and fluctuations in axial chromatic aberration during focusing. The above effect can be obtained regardless of the order in which the negative and positive lenses are arranged.

[0135] Furthermore, in the second lens group L2, it is preferable that the object-side lens surface of the second lens positioned from the object side is concave, and the image-side lens surface is convex. This results in a substantially concentric shape with respect to the off-axis light beam incident on the second lens group L2, thereby suppressing aberrations and changes in the angle of view during focusing.

[0136] In the optical system L0 of each embodiment, the second lens group L2 has a cemented lens formed by joining at least one negative lens Gn and at least one positive lens G2p. This allows for good correction of axial chromatic aberration at infinity focus and fluctuations in axial chromatic aberration during focusing.

[0137] Furthermore, it is preferable that the cemented lens be positioned closest to the object in the second lens group L2. This ensures that the cemented lens is positioned at a high off-axis ray height, thereby effectively correcting on-axis chromatic aberration.

[0138] Furthermore, it is preferable that the lens surface closest to the object is concave and the lens surface closest to the image is convex. This results in a substantially concentric shape with respect to the off-axis light beam incident on the second lens group L2, thereby suppressing aberrations and changes in the angle of view during focusing. In addition, the cemented lens may be made by bonding a biconcave lens and a biconvex lens in that order from the object side.

[0139] In the optical system L0 of each embodiment, the second lens group L2 consists of four lenses. This reduces the refractive power per lens, thereby suppressing fluctuations in spherical aberration, field curvature, and chromatic aberration during focusing.

[0140] In the optical system L0 of each embodiment, it is preferable that the second lens group L2 consists of five or fewer lenses. This reduces the weight of the lenses in the second lens group L2, enabling high-speed focusing. It also reduces the refractive power per lens, suppressing fluctuations in spherical aberration, field curvature, and chromatic aberration during focusing. To further enhance the aforementioned effects, it is even more preferable to configure the second lens group L2 with four or fewer lenses.

[0141] In the optical system L0 of each embodiment, it is preferable that the object-side lens surface of the lens positioned closest to the object in the second lens group L2 is concave. This allows the off-axis light beam that has passed through the aperture diaphragm to be incident on the object-side surface of the second lens group L2 in a substantially concentric manner, making it easier to suppress variations in astigmatism, coma aberration, and angle of view during focusing.

[0142] In the optical system L0 of each embodiment, the second lens group L2 preferably includes an aspherical lens in which at least one surface is aspherical. This allows for good correction of spherical aberration, astigmatism, and coma aberration. Furthermore, it is more preferable to make one of the surfaces of the positive lenses included in the second lens group L2 aspherical, as this reduces surface shape errors during molding. Moreover, it is more preferable to make the lens closest to the image or the second lens from the image side of the second lens group L2 aspherical, as this allows for good correction of off-axis aberrations such as astigmatism and coma aberration.

[0143] In the optical system L0 of each embodiment, it is preferable that the third lens group L3 has a cemented lens consisting of a positive lens and a negative lens. This allows for good correction of chromatic aberration and astigmatism.

[0144] 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 bonding an organic material such as plastic with a thickness of about 0.01 mm to 1.00 mm onto the spherical glass.

[0145] The numerical values ​​corresponding to Examples 1 to 7 are shown below.

[0146] In the surface data for each numerical example, r represents the radius of curvature of each optical surface, and d (mm) represents the distance along the optical axis between the m-th surface and the (m+1)-th surface. Here, m is the surface number counted from the light incident side. Also, nd represents the refractive index of each optical element with respect to the d line, and νd represents the Abbe number of the optical element. The Abbe number νd and partial dispersion ratio θgF of a certain material are expressed as follows, when the refractive indices at the Fraunhofer lines d line (587.6 nm), F line (486.1 nm), C line (656.3 nm), and g line (wavelength 435.8 nm) are Nd, NF, NC, and Ng, respectively. νd = (Nd-1) / (NF-NC) θgF = (Ng - NF) / (NF - NC) In each numerical example, d, focal length (mm), F-number, and half-angle of view (°) are all values ​​when the optical system of each example is focused on an object at infinity. Back focus BF is the air-equivalent distance from the final lens surface to the image plane. The total optical length is the distance from the first lens surface to the final lens surface plus the air-equivalent back focus. However, optical components such as optical filters, faceplates, quartz low-pass filters, and infrared cut filters are not included.

[0147] Furthermore, for each lens, if the lens surface is aspherical, the symbol * is added to the right of the surface number. The aspherical shape is defined as follows, where X is the displacement from the surface vertex in the optical axis direction, h is the height from the optical axis perpendicular to the optical axis, R is the paraaxial radius of curvature, k is the cone constant, and A4, A6, A8, A10, A12, A14, and A16 are the aspherical coefficients of their respective orders. 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 This is expressed as follows. Note that "e±XX" in each aspherical coefficient is "×10± XX It means "...".

[0148] [Numerical Example 1] Unit: mm Surface data Face 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 ∞ Aspherical 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 52.34 Image height 18.68 Optical total length 118.50 BF 14.00 When focused at infinity, when focused on an object at a horizontal magnification of -0.1x. From the object surface to the 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 starting plane, 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

[0149] [Numerical Example 2] Unit: mm Surface data Face 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 ∞ Aspherical 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 42.54 Image height 18.90 Optical total length 117.50 BF 18.44 When focused at infinity, when focused on an object at a horizontal magnification of -0.1x. 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 starting plane, 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

[0150] [Numerical Example 3] Unit: mm Surface data Face number rd nd νd 1 34.785 1.25 1.79360 37.1 2 17.108 5.10 3 29.757 2.00 1.53500 56.0 4* 19.213 10.91 5 -21.843 1.20 1.49700 81.7 6 -59.460 0.38 7 108.499 9.23 1.72916 54.7 8 -17.093 1.00 1.85478 24.8 9 -37.633 0.20 10 40.930 4.97 2.00100 29.1 11 -42.422 1.00 1.57501 41.5 12 30.464 5.24 13 (aperture) ∞ 2.53 14 83.477 1.85 2.00100 29.1 15 595.325 (variable) 16 -22.125 4.05 1.49700 81.7 17 -11.634 0.90 1.77047 29.7 18 -78.451 0.20 19 72.224 6.30 1.72916 54.7 20 -22.067 0.20 21* -169.027 4.15 1.53500 56.0 22* -27.901 (variable) 23 -131.373 8.10 1.59282 68.6 24 -17.133 1.05 1.65412 39.7 25 111.091 17.25 Image plane ∞ Aspherical data Side 4 K = 0.00000e+00 A 4=-6.65980e-06 A 6=-3.24494e-08 A 8= 5.25976e-11 A10=-5.17248e-13 Page 21 K = 0.00000e+00 A 4=-3.01742e-05 A 6= 1.03918e-08 A 8=-2.78416e-10 A10= 2.38934e-12 A12=-1.19202e-14 Page 22 K = 0.00000e+00 A 4= 6.71096e-06 A 6= 2.88119e-08 A 8=-2.08523e-10 A10= 2.35578e-12 A12=-9.87781e-15 Focal length 20.60 F-number 1.85 Half-angle 42.64 Image height 18.97 Optical total length 98.50 BF 17.25 When focused at infinity, when focused on an object at a horizontal magnification of -0.1x. From the object's surface to the first surface: Infinity 283.670 d15 7.24 5.62 d22 2.20 3.81 Lens group data Group starting plane focal length L1 1 33.12 L2 16 31.34 L3 23 -70.29 Single lens data Lens starting plane, focal length θgF 1 1 -43.79 2 3 -108.52 3 5 -70.21 4 7 20.90 5 8 -37.48 0.6122 6 10 21.45 7 11 -30.68 8 14 96.82 9 16 43.76 10 17 -17.83 0.5951 11 19 23.85 12 21 61.83 13 23 32.38 14 24 -22.62

[0151] [Numerical Example 4] Unit: mm Surface data Surface number r d nd νd 1 71.542 1.05 1.62004 36.3 2 20.538 9.22 3 536.237 1.80 1.53500 56.0 4* 195.727 6.51 5 -25.880 1.00 1.58144 40.8 6 -45.968 0.23 7 -81.956 9.01 1.87070 40.7 8 -20.977 1.05 1.85478 24.8 9 -41.688 1.33 0.6122 10 35.061 4.85 2.00069 25.5 11 788.676 0.99 0.7230 12 29.284 1.10 1.51742 52.4 0.6122 13 19.707 11.37 14 -30.397 4.97 1.59282 68.6 15 -16.310 1.00 1.85478 24.8 16 -23.209 0.50 17 (Aperture) ∞ (Variable) 18 -23.769 3.97 1.49700 81.7 19 -15.307 0.7​​​​​​​​​​​​​26 57.367 4.83 1.92286 20.9 27 -215.059 1.05 1.77047 29.7 28 35.159 6.22 29 -64.493 1.00 1.77047 29.7 30 -11124.715 12.50 Image plane ∞ Aspherical data Side 4 K = 0.00000e+00 A 4=-7.78923e-07 A 6=-4.74554e-09 A 8=-3.40498e-12 Page 24 K = 0.00000e+00 A 4=-5.94169e-06 A 6= 1.89102e-08 A 8=-1.30969e-10 A10= 5.43367e-13 A12=-9.16322e-16 Page 25 K = 0.00000e+00 A 4= 4.36873e-06 A 6= 1.94417e-08 A 8=-1.21992e-10 A10= 5.31778e-13 A12=-8.61502e-16 Focal length 24.00 F-number 1.50 Half-angle 38.29 Image height 18.95 Optical total length 113.00 BF 12.50 When focused at infinity, when focused on an object at a horizontal magnification of -0.1x. From the object's surface to the first surface: Infinity 325.872 d17 7.40 5.34 d25 2.20 4.25 Lens group data Group starting plane focal length L1 1 47.04 L2 18 31.80 L3 26 -64.02 Single lens data Lens start surface focal length θgF 1 1 -46.83 2 3 -577.20 3 5 -103.75 4 7 30.30 5 8 -50.58 6 10 36.55 7 12 -121.22 8 14 52.48 9 15 -68.79 0.6122 … 10 18 74.86 11 19 284.54 0.7230 12 20 -24.42 0.6122 13 22 39.98 14 24 43.18 15 26 49.49 16 27 -39.15 17 29 -84.20

[0152] [Numerical Example 5] Unit: mm Surface data Surface number r d 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 … 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 ∞ Aspherical 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 52.34 Image height 18.68 Optical total length 119.50 BF 15.50 When focused at infinity, when focused on an object at a horizontal magnification of -0.1x. From the object's surface to the 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 starting plane, 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

[0153] [Numerical Example 6] Unit: mm Surface data Face 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 ∞ Aspherical 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 42.57 Image height 18.93 Optical total length 125.00 BF 20.51 When focused at infinity, when focused on an object at a horizontal magnification of -0.1x. From the object's surface to the 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 starting plane, 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

[0154] [Numerical Example 7] Unit: mm Surface data Face number rd nd νd θgF 1 41.398 1.25 1.85026 32.3 2 16.925 7.52 3 62.508 2.00 1.53500 56.0 4* 39.199 8.09 5 -20.954 1.20 1.49700 81.7 0.6122 6 -34.367 0.20 7 1150.801 8.11 1.87070 40.7 8 -18.645 1.00 1.85478 24.8 9 -53.827 0.20 10 25.911 4.47 1.95375 32.3 0.5951 11 -857.774 0.63 12 -1141.763 1.00 1.51742 52.4 13 19.319 6.01 14 (aperture) ∞ 2.55 15 86.000 1.99 2.00100 29.1 16 ∞ (Variable) 17 -23.457 4.27 1.49700 81.7 18 -11.526 0.90 1.77047 29.7 19 -46.802 0.20 20 53.297 7.13 1.59282 68.6 21 -22.514 1.46 22* -204.835 4.59 1.80400 46.5 23* -34.800 (Variable) 24 -959.581 6.27 1.59282 68.6 25 -23.602 1.05 1.66565 35.6 26 52.918 17.22 Image plane ∞ Aspherical data Side 4 K = 0.00000e+00 A 4=-8.84221e-06 A 6=-2.21367e-08 A 8=-3.29970e-11 A10=-5.08866e-14 Page 22 K = 0.00000e+00 A 4=-2.21360e-05 A 6= 1.50179e-08 A 8=-4.23029e-10 A10= 3.18520e-12 A12=-1.12092e-14 Page 23 K = 0.00000e+00 A 4= 1.34397e-06 A 6= 2.33770e-08 A 8=-2.84542e-10 A10= 2.23920e-12 A12=-7.01230e-15 Various data Zoom ratio 1.00 Focal length 20.44 F-number 1.85 Half-angle 42.77 Image height 18.91 Optical total length 98.17 BF 17.22 When focused at infinity, when focused on an object at a horizontal magnification of -0.1x. From the object's surface to the first surface: Infinity 282.639 d16 6.65 5.21 d23 2.20 3.64 Lens group data Group starting plane focal length L1 1 39.40 L2 17 28.11 L3 24 -61.16 Single lens data Lens starting plane, focal length 1 1 -34.48 2 3 -202.55 3 5 -111.34 4 7 21.14 5 8 -33.82 6 10 26.44 7 12 -36.71 8 15 85.88 9 17 40.75 10 18 -20.07 11 20 27.67 12 22 51.52 13 24 40.72 14 25 -24.39 The various values ​​in each numerical example are summarized in Tables 1 and 2 below.

[0155] [Table 1]

[0156] The lenses and their corresponding numerical values ​​that satisfy the conditions (6), (7), (12), (14), and (15) in each numerical example are summarized in Table 2 below.

[0157] [Table 2]

[0158] [Imaging device] Next, an embodiment of an imaging device equipped with the optical system L0 of this embodiment will be described.

[0159] Figure 15 is a schematic diagram of an imaging device 10 equipped with the optical system L0 of this embodiment. The imaging device 10 comprises a camera body 13, an optical system 11 similar to that of any of the embodiments 1 to 7 described above, and a light-receiving element 12 that converts the image formed by the optical system 11 into photoelectricity.

[0160] The imaging device 10 of this embodiment can obtain high-quality images formed by an optical system 11 that is wide-angle and has improved distortion correction and peripheral illumination ratio.

[0161] Furthermore, an image sensor such as a CCD or CMOS sensor can be used as the light-receiving element 12. In this case, the output image can be made higher quality by correcting various aberrations such as distortion and chromatic aberration of the image acquired by the light-receiving element 12, for example, using an electrical method.

[0162] Furthermore, the optical system L0 in each of the above embodiments can be applied not only to the digital still camera shown in Figure 15, but also to various optical instruments such as silver halide film cameras, video cameras, and telescopes. The camera itself may be either a fixed-lens type or a lens-interchangeable type.

[0163] [Lens device] Next, an embodiment of a lens device equipped with the optical system L0 of this embodiment will be described.

[0164] Figure 16 is a schematic diagram of the external appearance of a lens device equipped with the optical system L0 of this embodiment. The lens device in Figure 16 is a so-called interchangeable lens that is detachably attached to a camera body (not shown).

[0165] The lens device 20 includes a photographic optical system 21, which is the same as in any of the embodiments 1 to 7 described above. The lens device 20 also has a focus operating means 22 and an operating means 23 for changing the shooting mode.

[0166] The user operates the focus control means 22, which mechanically or electrically changes the arrangement of the imaging optical system 21 and alters the focal position. Alternatively, the user may operate the control means 23 to change the arrangement of the lens group of the imaging optical system 21 for purposes other than focusing. For example, the arrangement of the lens group of the imaging optical system 21 may be changed mechanically or electrically in conjunction with the operation of the control means 23, thereby altering the aberrations of the imaging optical system 21. In this case, it is preferable that the focal position does not substantially change.

[0167] Although 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 its gist.

[0168] Each embodiment's disclosure includes the configuration of the disclosure.

[0169] (Composition 1) An optical system comprising a first lens group having positive refractive power, a second lens group having positive refractive power, and a third lens group, arranged in order from the object side to the image side, During focusing, the second lens group moves in the optical axis direction relative to the image plane, while the first and third lens groups remain stationary relative to the image plane. The first lens group has three negative lenses arranged continuously in the optical axis direction, closest to the object. An optical system characterized by satisfying the following condition, where f is the focal length of the entire optical system, sk is the air-equivalent back focus when focused to infinity, and f2 is the focal length of the second lens group. 0.50 <f2 / f<3.00 0.20 <sk / f<1.20 (Configuration 2) An optical system comprising a positive first lens group, a positive second lens group, and a third lens group, arranged in order from the object side to the image side, During focusing, the second lens group moves in the optical axis direction relative to the image plane, while the first and third lens groups remain stationary relative to the image plane. An optical system characterized by satisfying the following condition when the focal length of the entire optical system is f, the air-equivalent back focus when focused to infinity is sk, and the focal length of the second lens group is f2. 0.50 <f2 / f<3.00 (Composition 3) The optical system according to configuration 1 or 2, characterized in that when the focal length of the first lens group is f1, the following conditional expression is satisfied. 0.30 <f1 / f2<3.00 (Composition 4) The optical system according to any one of configurations 1 to 3, characterized in that when the focal length of the third lens group is f3, the following conditional expression is satisfied. -1.50 <f / f3<1.50 (Composition 5) The optical system according to any one of configurations 1 to 4, characterized in that the second lens group comprises at least two positive lenses and at least one negative lens.

[0170] (Composition 6) The object-side lens surface of the lens positioned closest to the object in the second lens group is concave. The image-side lens surface of the second lens group, which is located closest to the image, has a convex shape. The optical system according to any one of configurations 1 to 5, characterized in that, when R21 is the radius of curvature of the object-side surface of the lens positioned furthest towards the object in the second lens group, and R22 is the radius of curvature of the image-side surface of the lens positioned furthest towards the image in the second lens group, the following conditional expression is satisfied. -1.50<(R22-R21) / (R22+R21)<1.50 (Composition 7) At least one of the first lens group or the second lens group has a negative lens Gn, The optical system according to any one of configurations 1 to 6, characterized in that, when the refractive index of the negative lens Gn material with respect to the d line is Ndn, the Abbe number is νdn, the partial dispersion ratio with respect to the g line and the F line is θgFn, and the anomalous partial dispersion is ΔθgFn, the following conditional equation is satisfied. -0.015 < ΔθgFn < 0.015 -0.20 <Ndn-(-0.0145425×νdn+2.28725)<0.05 However, ΔθgFn = θgFn - (-0.0025116 × νdn + 0.67449) This is how it is expressed.

[0171] (Composition 8) The optical system according to any one of configurations 1 to 7, characterized in that the first lens group has at least one negative lens Gn.

[0172] (Composition 9) The optical system according to any one of configurations 1 to 8, characterized in that the second lens group has at least one negative lens Gn.

[0173] (Composition 10) The optical system according to any one of configurations 1 to 9, characterized in that, when the lateral magnification of the second lens group when focused at infinity is β2 and the lateral magnification of the third lens group when focused at infinity is β3, the following conditional equation is satisfied. 0.50<(1-β2 2 )×β3 2 <2.50 (Composition 11) The first lens group has an aperture diaphragm located inside the first lens group or adjacent to the image side of the first lens group, The optical system according to any one of configurations 1 to 10, characterized in that the aperture diaphragm is immovable in the optical axis direction with respect to the image plane during focusing.

[0174] (Composition 12) The optical system according to any one of configurations 1 to 11, characterized in that when the focal length of the third lens group is f3, the following conditional expression is satisfied. 0.00 <sk / |f3|<0.80 (Composition 13) The optical system according to any one of configurations 1 to 12, characterized in that, when ΣDair is the sum of the air gaps on the optical axis from the object-side lens surface of the lens positioned furthest towards the object in the first lens group to the image-side lens surface of the lens positioned furthest towards the image in the third lens group, and L is the total optical length of the optical system, the following conditional equation is satisfied. 0.20 < ΣDair / (L-sk) < 0.70 (Composition 14) The optical system according to any one of configurations 1 to 13, characterized in that, when the total optical length of the optical system is L, the following condition is satisfied. 2.00 <L / f<15.00 (Composition 15) The second lens group has at least one positive lens G2p, The optical system according to any one of configurations 1 to 14, characterized in that the following condition is satisfied when the Abbe number of the material of the positive lens G2p is νd2p. 60.00 < νd2p < 100.00 (Composition 16) An optical system according to any one of configurations 1 to 15, characterized in that, when focusing from infinity to an object distance at which the lateral magnification of the entire system becomes -0.1 times, the amount of movement of the second lens group when the second lens group moves toward the image side when focusing from infinity to an object distance at which the lateral magnification of the entire system becomes -0.1 times is positive, and the distance on the optical axis from the aperture diaphragm to the image plane when the optical system is focused to infinity is DSP, the following conditional equation is satisfied. -0.20 <M2 / DSP<-0.005 (Composition 17) The first lens group has a negative lens G1n, The optical system according to any one of configurations 1 to 16, characterized in that the following condition is satisfied when the Abbe number of the material of the negative lens G1n is νd1n. 60.00 < νd1n < 100.00 (Composition 18) At least one of the first lens group or the second lens group has a positive lens Gp, The optical system according to any one of configurations 1 to 17, characterized in that, when the Abbe number of the material of the positive lens Gp is ​​νdp, the partial dispersion ratio is θgFp, and the anomalous partial dispersion is ΔθgFp, the following conditional equation is satisfied. 0.050 < ΔθgFp < 0.250 however, ΔθgFp = θgFp - (B3 × νdp 3 +B2×νdp 2 (+B1×νdp+B0) B3 = -1.665 × 10 -7 B2 = 5.213 × 10 -5 B1 = -5.656 × 10 -3 B0 = 7.278 × 10 -1 This is how it is expressed.

[0175] (Composition 19) The optical system according to any one of configurations 1 to 18, characterized in that, when the optical system is focused to infinity, the distance on the optical axis from the aperture diaphragm to the image plane is denoted as DSP, and the total optical length of the optical system is L, the following conditional equation is satisfied. 0.30 < (DSP + sk) / L < 0.80 (Composition 20) The optical system according to any one of configurations 1 to 19, characterized in that when the focal length of the first lens group is f1, the following conditional expression is satisfied. 0.50 <f1 / f<5.00 (Composition 21) The optical system according to any one of configurations 1 to 20, characterized in that a negative lens is positioned on the image side of the third lens group.

[0176] (Composition 22) An imaging device comprising an optical system described in any one of configurations 1 to 21, and an image sensor that receives an image formed by the optical system. [Explanation of symbols]

[0177] L0 optical system L1 First lens group L2 Second lens group L3 Third lens group

Claims

1. An optical system comprising a first lens group having positive refractive power, a second lens group having positive refractive power, and a third lens group, arranged in order from the object side to the image side, During focusing, the second lens group moves in the optical axis direction relative to the image plane, while the first and third lens groups remain stationary relative to the image plane. The first lens group has three negative lenses arranged continuously in the optical axis direction, closest to the object. An optical system characterized by satisfying the following conditional equation, where f is the focal length of the entire optical system, sk is the air-equivalent back focus when focused to infinity, and f2 is the focal length of the second lens group. 0.50<f2 / f<3.00 0.20<sk / f<1.20

2. The optical system according to claim 1, characterized in that, when the focal length of the first lens group is f1, the following condition is satisfied. 0.30<f1 / f2<3.00

3. The optical system according to claim 1, characterized in that when the focal length of the third lens group is f3, the following condition is satisfied. -1.50<f / f3<1.50

4. The optical system according to claim 1, characterized in that the second lens group comprises at least two positive lenses and at least one negative lens.

5. The object-side lens surface of the lens positioned closest to the object in the second lens group is concave. The image-side lens surface of the second lens group, which is positioned closest to the image, has a convex shape. The optical system according to claim 1, characterized in that, when R21 is the radius of curvature of the object-side surface of the lens positioned furthest towards the object in the second lens group, and R22 is the radius of curvature of the image-side surface of the lens positioned furthest towards the image in the second lens group, the following condition is satisfied. -1.50<(R22-R21) / (R22+R21)<1.50

6. At least one of the first lens group or the second lens group has a negative lens Gn, The optical system according to claim 1, characterized in that when the refractive index of the negative lens Gn material with respect to the d line is Ndn, the Abbe number is νdn, the partial dispersion ratio with respect to the g line and the F line is θgFn, and the anomalous partial dispersion is ΔθgFn, the following conditional equation is satisfied. -0.015<ΔθgFn<0.015 -0.20<Ndn-(-0.0145425×νdn+2.28725)<0.05 However, ΔθgFn = θgFn - (-0.0025116 × νdn + 0.67449) This is how it is expressed.

7. The optical system according to claim 6, characterized in that the first lens group has at least one negative lens Gn.

8. The optical system according to claim 6, characterized in that the second lens group has at least one negative lens Gn.

9. The optical system according to claim 1, characterized in that, when the lateral magnification of the second lens group when focused at infinity is β2 and the lateral magnification of the third lens group when focused at infinity is β3, the following conditional equation is satisfied. ０．５０＜（１－β２ ２ ）×β３ ２ ＜２．５０

10. It has an aperture diaphragm located inside the first lens group or adjacent to the image side of the first lens group, The optical system according to claim 1, characterized in that the aperture diaphragm is immovable in the optical axis direction with respect to the image plane during focusing.

11. The optical system according to claim 1, characterized in that when the focal length of the third lens group is f3, the following condition is satisfied. 0.00<sk / |f3|<0.80

12. The optical system according to claim 1, characterized in that, when ΣDair is the sum of the air gaps on the optical axis from the object-side lens surface of the lens positioned furthest towards the object in the first lens group to the image-side lens surface of the lens positioned furthest towards the image in the third lens group, and L is the total optical length of the optical system, the following condition is satisfied. 0.20<ΣDair / (L-sk)<0.70

13. The optical system according to claim 1, characterized in that, when the total optical length of the optical system is L, the following condition is satisfied. 2.00<L / f<15.00

14. The second lens group has at least one positive lens G2p, The optical system according to claim 1, characterized in that the following condition is satisfied when the Abbe number of the material of the positive lens G2p is νd2p. 60.00<νd2p<100.00

15. The optical system according to claim 1, characterized in that, when focusing from infinity to an object distance at which the lateral magnification of the entire system becomes -0.1 times, the amount of movement of the second lens group is M2, when focusing from infinity to an object distance at which the lateral magnification of the entire system becomes -0.1 times, the sign of the amount of movement of the second lens group when it moves toward the image side is positive, and the distance on the optical axis from the aperture diaphragm to the image plane when the optical system is focused to infinity is DSP, the following conditional equation is satisfied. -0.200<M2 / DSP<-0.005

16. The first lens group includes a negative lens G1n. The optical system according to claim 1, characterized in that the following condition is satisfied when the Abbe number of the negative lens G1n is νd1n. 60.00<νd1n<100.00

17. At least one of the first lens group or the second lens group has a positive lens Gp, The optical system according to claim 1, characterized in that, when the Abbe number of the material of the positive lens Gp is ​​νdp, the partial dispersion ratio is θgFp, and the anomalous partial dispersion is ΔθgFp, the following conditional equation is satisfied. 0.050<ΔθgFp<0.250 however, ΔθgFp=θgFp-(B3×νdp ３ +B2×νdp ２ +B1×νdp+B0) B3=-1.665×10 －７ B2=5.21310 －５ B1=-5.656×� －３ B0 = 7.278 × 10 －１ This is how it is expressed.

18. The optical system according to claim 1, characterized in that when the optical system is focused to infinity, the distance on the optical axis from the aperture diaphragm to the image plane is DSP, and the total optical length of the optical system is L, the following conditional equation is satisfied. 0.30<(DSP+sk) / L<0.80

19. The optical system according to claim 1, characterized in that when the focal length of the first lens group is f1, the following condition is satisfied. 0.50<f1 / f<5.00

20. The optical system according to claim 1, characterized in that the negative lens is positioned on the image side of the third lens group.

21. An optical system comprising a first lens group having positive refractive power, a second lens group having positive refractive power, and a third lens group, arranged in order from the object side to the image side, During focusing, the second lens group moves in the optical axis direction relative to the image plane, while the first and third lens groups remain stationary relative to the image plane. An optical system characterized by satisfying the following condition when the focal length of the entire optical system is f and the focal length of the second lens group is f2. 0.50<f2 / f<3.00

22. An imaging device comprising an optical system according to any one of claims 1 to 21 and an image sensor that receives an image formed by the optical system.

Images