Optical system and imaging device

Abstract

To provide an optical system which offers high optical performance while reducing a size and weight of a lens group that moves for focusing.SOLUTION: An optical system provided herein consists of, in order from an object side to an image side, a first lens group L1 having positive refractive power, a second lens group L2 having negative refractive power, and a third lens group L3 having positive refractive power, configured such that distances therebetween change while focusing. A lens located on the most image side in the third lens group has negative refractive power and a concave object-side surface. The optical system satisfies conditions expressed as: 0.51≤f1 / f≤0.93 and 0.01≤sk / OTL≤0.16, where f represents a focal length of the entire system, f1 represents a focal length of the first lens group, OTL represents a total optical length of the optical system, and sk represents an air-equivalent distance from a most image-side lens surface of the third lens group to an image plane.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an optical system suitable for an imaging device. [Background technology]

[0002] BACKGROUND ART In imaging devices such as digital still cameras and video cameras, as imaging elements such as CCD sensors and CMOS sensors have become increasingly multi-pixel, optical systems that form subject images on the imaging elements are required to have high optical performance.

[0003] Furthermore, as disclosed in Patent Documents 1 and 2, large-aperture lenses with small F-numbers require that the lens groups that move during focusing be made small and lightweight so that they can move at high speed. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2017-122871 [Patent Document 2] Japanese Patent Application Publication No. 2018-060078 Summary of the Invention [Problem to be solved by the invention]

[0005] To reduce the size and weight of a lens group, it is necessary to reduce the number of lenses constituting the lens group and the diameter of the lenses. However, reducing the number of lenses results in significant fluctuations in field curvature and chromatic aberration during focusing, leading to a deterioration in optical performance. Furthermore, to reduce the diameter of a lens, it is necessary to reduce the diameter of the light beam incident on that lens. To achieve this, it is necessary to position a lens group with a higher refractive power closer to the object than the lens group containing that lens. As a result, spherical aberration and axial chromatic aberration increase.

[0006] The present invention provides an optical system in which a lens group that moves during focusing is made smaller and lighter while still providing high optical performance, and an imaging apparatus having the same. [Means for solving the problem]

[0007] An optical system according to one aspect of the present invention comprises 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, arranged in this order from the object side to the image side, and the distance between which changes during focusing. The lens in the third lens group closest to the image side has negative refractive power and has a concave surface facing the object side. When the optical system is focused at infinity, the focal length of the entire system is f, the focal length of the first lens group is f1, the total optical length of the entire system is OTL, the air-equivalent distance from the lens surface in the third lens group closest to the image plane is sk, the axial thickness from the lens surface in the third lens group closest to the object side to the lens surface closest to the image side is D3, and the axial length from the lens surface in the first lens group closest to the object side to the lens surface in the third lens group closest to the image side is TL. 0.51≦f1 / f≦0.93 0.01≦sk / OTL≦0.1 3 0.430≦D3 / TL≦0.6 An imaging device using the above optical system also constitutes another aspect of the present invention. [Effects of the Invention]

[0008] According to the present invention, it is possible to obtain high optical performance while reducing the size and weight of the lens group that moves during focusing. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 2 is a cross-sectional view of the optical system of the first embodiment (in a state focused at infinity). [Figure 2] 4A to 4C are aberration diagrams of the optical system of Example 1 (infinity focused state). [Figure 3] FIG. 10 is a cross-sectional view of the optical system of the second embodiment (in a state focused at infinity). [Figure 4] 10A and 10B are aberration diagrams of the optical system of Example 2 (infinity focused state). [Figure 5] FIG. 10 is a cross-sectional view of the optical system of Example 3 (in a state focused at infinity). [Figure 6] 10A and 10B are aberration diagrams of the optical system of Example 3 (infinity focused state). [Figure 7] FIG. 1 is a schematic diagram of an imaging device using the optical systems of Examples 1 to 3. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Figures 1, 3, and 5 show cross sections of optical systems according to first to third embodiments of the present invention, respectively, when focused at infinity. Figures 2, 4, and 6 show various aberrations of the optical systems according to first to third embodiments, respectively, when focused at infinity. The optical systems of the respective embodiments are used in imaging devices such as digital still cameras, video cameras, surveillance cameras, and vehicle-mounted cameras, as well as in various optical devices including interchangeable lenses.

[0011] In the cross-sectional view of the optical system, the left side is the object side (front side) and the right side is the image side (rear side). The optical system in each embodiment is composed of a first lens group L1 with positive refractive power, a second lens group L2 with negative refractive power, and a third lens group L3 with positive refractive power, arranged in this order from the object side to the image side, with the spacing between them changing during focusing. SP denotes an aperture that determines (limits) the light beam at the maximum F-number (Fno), and in each embodiment, is arranged between the first lens group L1 and the second lens group L2. IP denotes the image plane of the optical system, where the imaging surface of an imaging element such as a CCD sensor or CMOS sensor or the film surface (photosensitive surface) of a film camera is located. GB denotes a glass block such as an optical filter.

[0012] In the aberration diagrams, Fno represents the F-number, and ω represents the half angle of view (°) based on paraxial calculations. In the spherical aberration diagrams, d represents the spherical aberration for the d-line (wavelength 587.56 nm), and g represents the spherical aberration for the g-line (wavelength 435.835 nm). In the astigmatism diagrams, ΔS represents the astigmatism for the d-line on the d-sagittal image plane, and ΔM represents the astigmatism for the d-line on the meridional image plane. Distortion aberration is shown for the d-line. Magnification chromatic aberration is shown for the g-line.

[0013] When the focal length of the entire optical system is f, the focal length of the first lens unit L1 is f1, the length on the optical axis from the lens surface closest to the object to the image plane when focused at infinity (total optical length) is OTL, and the air-equivalent distance on the optical axis from the lens surface closest to the image to the image plane when focused at infinity (hereinafter referred to as back focus) is sk, the following conditions of formulas (1) and (2) are satisfied.

[0014] 0.51≦f1 / f ≦ 0.93 (1) 0.01≦sk / OTL≦0.16 (2) By appropriately setting the focal length of the first lens group L1 relative to the focal length of the entire system so as to satisfy these conditions, it is possible to reduce the size of the entire system and the size and weight of the lens group that moves during focusing (hereinafter referred to as the focusing group). As a result of reducing the size of the focusing group, fluctuations in various aberrations, particularly field curvature and chromatic aberration, become greater when focusing from infinity to the closest object. By shortening the back focus, it is possible to position lenses closer to the image plane, making it possible to correct various aberrations that are mainly caused by off-axial rays. In this case, by appropriately setting the focal length of each lens group, it is possible to achieve both a reduction in size and weight of the focusing group and suppression of various aberrations.

[0015] The condition in formula (1) is a condition regarding the focal length f1 of the first lens group L1 relative to the focal length f of the entire optical system when focused at infinity. By appropriately setting the ratio of the focal length of the first lens group L1 to the focal length of the entire system, the diameter of the light beam incident on the second lens group L2 becomes smaller, making it possible to reduce the size and weight of the focusing group. If f1 / f exceeds the upper limit of formula (1), the focal length of the first lens group L1 becomes longer and the diameter of the light beam incident on the second lens group L2 becomes larger, making it difficult to reduce the size and weight of the focusing group. In addition, since the light beam cannot be properly focused, the overall lens length of the entire system (the length on the optical axis from the lens surface closest to the object to the lens surface closest to the image) increases, which is undesirable. If f1 / f falls below the lower limit of expression (1), the focal length of the first lens unit L1 becomes short, which is advantageous for making the focusing unit smaller and lighter and shortening the overall length of the entire system, but it becomes difficult to correct spherical aberration and chromatic aberration, which leads to a decrease in image quality, and is therefore undesirable.

[0016] The condition in equation (2) is the condition regarding the back focal length sk relative to the total optical length OTL of the entire system when focused at infinity. By appropriately setting sk, it is possible to suppress fluctuations in field curvature and chromatic aberration with changes in object distance, which have become difficult to achieve with the focus group's compactness and weight reduction. If sk / OTL exceeds the upper limit of equation (2), the back focal length sk increases, making it impossible to position a lens close to the image plane IP. This makes it difficult to improve field curvature and lateral chromatic aberration, resulting in poor image quality, which is undesirable. If sk / OTL falls below the lower limit of equation (2), the back focal length sk becomes shorter, allowing a lens to be positioned closer to the image plane IP, which is advantageous for improving field curvature and lateral chromatic aberration. However, this is undesirable because it makes it difficult to position a shutter, optical filter, etc.

[0017] It is more preferable to set the numerical ranges of the formulas (1) and (2) as shown in the following formulas (1a) and (2a).

[0018] 0.53≦f1 / f ≦ 0.92 (1a) 0.05≦sk / OTL≦0.16 (2a) It is more preferable to set the numerical ranges of the formulas (1) and (2) as shown in the following formulas (1b) and (2b).

[0019] 0.55≦f1 / f ≦ 0.90 (1b) 0.10≦sk / OTL≦0.16 (2b) By satisfying the conditions of expressions (1) and (2) in this way, it is possible to make the focusing group small and lightweight and achieve high optical performance in a large-aperture optical system with a small F-number.

[0020] It is more preferable that the optical system of each embodiment satisfies at least one of the conditions of the following expressions (3) to (13). Here, the focal length of the second lens group L2 is f2, and the focal length of the third lens group L3 is f3. The total lens length, which is the length on the optical axis from the lens surface closest to the object to the lens surface closest to the image, is TL. The lens group thickness, which is the length on the optical axis from the lens surface closest to the object in the first lens group L1 to the lens surface closest to the image, is D1, and the lens group thickness of the third lens group L3 is D3. The lens group spacing, which is the length on the optical axis from the lens surface closest to the image in the first lens group L1 to the lens surface closest to the object in the third lens group L3, is D13. The refractive index of the lenses with positive refractive power included in the first lens group L1 is rate The average of the negative refractive power of the lens included in the first lens unit L1 is Nd1p. rate The average of the Abbe numbers of the positive lenses included in the first lens unit L1 is denoted by νd1p, and the average of the Abbe numbers of the negative lenses is denoted by νd1n. The refraction of the positive lenses included in the third lens unit L3 rate The average of Nd3p and the refraction of the negative lens included in the third lens unit L3 rate Let the average be Nd3n.

[0021] -0.9≦f2 / f≦-0.3 (3) 0.1≦f3 / f≦0.9 (4) 0 <D1·sk / OTL 2 ≦0.1 (5) 0.1≦D13 / OTL≦0.4 (6) 0.4≦D3 / TL≦0.6 (7) 0.1≦D1 / TL≦0.4 (8) 1.7≦f1 / D1≦2.5 (9) 1.0≦f3 / D3≦1.5 (10) -0.20≦Nd1p-Nd1n≦-0.05 (11) 25.0≦νd1p-νd1n≦38.0 (12) 0.01≦Nd3p-Nd3n≦0.2 (13) The condition in formula (3) is a condition regarding the focal length f2 of the second lens group L2 relative to the focal length f of the entire system when the second lens group L2 moves as a focusing group. By optimizing the focal length of the second lens group L2, the amount of movement of the second lens group L2 during focusing can be reduced, thereby shortening the overall lens length. If f2 / f exceeds the upper limit of formula (3), the refractive power of the second lens group L2 becomes weak, thereby reducing fluctuations in spherical aberration and field curvature during focusing. However, this undesirably increases the amount of movement of the second lens group L2 during focusing, thereby lengthening the overall lens length. If f2 / f falls below the lower limit of formula (3), the refractive power of the second lens group L2 becomes strong, which is advantageous for shortening the overall lens length, but undesirably increases fluctuations in spherical aberration and field curvature during focusing.

[0022] The condition in formula (4) is a condition regarding the focal length f3 of the third lens unit L3 relative to the focal length f of the entire system. By optimizing the focal length of the third lens unit L3, it is possible to both suppress various aberrations caused mainly by off-axial light rays and shorten the overall lens length. If f3 / f exceeds the upper limit of formula (4), the refractive power of the third lens unit L3 becomes weak, which is advantageous for suppressing various aberrations, but the overall lens length increases, which is undesirable. If f3 / f falls below the lower limit of formula (4), the refractive power of the third lens unit L3 becomes strong, which is advantageous for shortening the overall lens length, but it becomes difficult to correct field curvature and chromatic aberration of magnification, which results in poor image quality, which is undesirable.

[0023] The condition in equation (5) is a condition regarding the lens group thickness D1 of the first lens group L1 and the back focal length sk relative to the total optical length OTL of the optical system: D1·sk / OTL 2If D1·sk / OTL exceeds the upper limit of equation (5), at least one of the lens group thickness D1 of the first lens group L1 relative to the total optical length and the back focal length sk becomes long, which is advantageous for correcting spherical aberration and coma aberration that occur mainly due to axial rays, but it becomes difficult to correct field curvature and distortion that occur mainly due to off-axial rays, which is undesirable. 2 If falls below the lower limit of expression (5), at least one of the lens group thickness D1 of the first lens group L1 relative to the total optical length OTL and the back focal length sk becomes short, which is advantageous for correcting the curvature of field and distortion aberration that occurs mainly due to off-axial rays, but it becomes difficult to correct the spherical aberration and coma aberration that occurs mainly due to on-axial rays, which is not preferable.

[0024] The condition of formula (6) is a condition regarding the lens group spacing D13 between the first lens group L1 and the third lens group L3 relative to the total optical length OTL of the optical system. If D13 / OTL exceeds the upper limit of formula (6), the movement distance of the second lens group L2 becomes longer, which is advantageous for suppressing aberration fluctuations due to focusing, but it undesirably increases the total lens length. If D13 / OTL falls below the lower limit of formula (6), the movement distance of the second lens group L2 becomes shorter, which is advantageous for shortening the total lens length OTL, but it undesirably increases fluctuations in spherical aberration and field curvature during focusing.

[0025] The condition of formula (7) is a condition regarding the lens group thickness D3 of the third lens group L3 relative to the total lens length TL of the optical system. If D3 / TL exceeds the upper limit of formula (7), the lens group thickness D3 of the third lens group L3 will be increased, which is advantageous for correcting field curvature and distortion aberrations mainly caused by off-axial rays, but this is undesirable because it results in an increase in the total lens length TL. If D3 / TL falls below the lower limit of formula (7), the lens group thickness D3 of the third lens group L3 will be shortened, which is advantageous for shortening the total lens length OTL, but this is undesirable because it makes it difficult to correct field curvature and distortion aberrations mainly caused by off-axial rays.

[0026] The condition of formula (8) is a condition regarding the lens group thickness D1 of the first lens group L1 relative to the total lens length TL of the optical system. If D1 / TL exceeds the upper limit of formula (8), the lens group thickness D1 of the first lens group L1 will be long, which is advantageous for correcting spherical aberration and coma aberration caused mainly by axial rays, but this is undesirable because it results in an increase in the total lens length TL. If D1 / TL falls below the lower limit of formula (8), the lens group thickness D1 of the first lens group L1 will be short, which is advantageous for shortening the total lens length TL, but this is undesirable because it makes it difficult to correct spherical aberration and coma aberration caused mainly by axial rays.

[0027] The condition of formula (9) is a condition regarding the focal length f1 of the first lens unit L1 relative to the lens unit thickness D1 of the first lens unit L1. If f1 / D1 exceeds the upper limit of formula (9), the focal length f1 relative to the lens unit thickness D1 becomes long, causing light rays to pass through without having appropriate refractive power, which is undesirable because it increases the lens unit thickness D1 and the size of the focusing unit. If f1 / D1 falls below the lower limit of formula (9), the focal length f1 relative to the lens unit thickness D1 becomes short and the refractive power becomes strong, which is advantageous for reducing the size of the first lens unit L1, but it is undesirable because it makes it difficult to correct spherical aberration and coma aberration, which are mainly caused by axial rays.

[0028] The condition of formula (10) is a condition regarding the focal length f3 of the third lens unit L3 relative to the lens unit thickness D3 of the third lens unit L3. If f3 / D3 exceeds the upper limit of formula (10), the focal length f3 relative to the lens unit thickness D3 becomes long, causing light rays to pass through without having appropriate refractive power, which undesirably increases the lens unit thickness D3. If f3 / D3 falls below the lower limit of formula (10), the focal length f3 relative to the lens unit thickness D3 becomes short, which increases the refractive power, which is advantageous for reducing the size of the third lens unit L3, but it is undesirable because it makes it difficult to correct field curvature and distortion aberrations that occur mainly due to off-axial light rays.

[0029] The condition of the formula (11) is that the refraction of the positive lens included in the first lens unit L1 rate Average Nd1p and refraction of negative lens rateThis is a condition regarding the difference between Nd1p and the average Nd1n of the above. If Nd1p - Nd1n exceeds the upper limit of formula (11), the difference becomes large, which is advantageous for correcting curvature of field, but it becomes difficult to suppress spherical aberration and coma, which is undesirable. If Nd1p - Nd1n falls below the lower limit of formula (11), the difference becomes small, which is advantageous for suppressing spherical aberration and coma, but it becomes difficult to correct curvature of field, which is undesirable.

[0030] The condition of formula (12) is a condition regarding the difference between the average Abbe number vd1p of the positive lenses in the first lens unit L1 and the average Abbe number vd1n of the negative lenses. If vd1p-vd1n exceeds the upper limit of formula (12), the difference becomes large, which is advantageous for correcting chromatic aberration, but it becomes difficult to suppress spherical aberration and coma, which is undesirable. If vd1p-vd1n falls below the lower limit of formula (12), the difference becomes small, which is advantageous for suppressing spherical aberration and coma, but it becomes difficult to correct chromatic aberration, which is undesirable.

[0031] The condition of the formula (13) is that the refraction of the positive lens included in the third lens unit L3 rate Average Nd3p and negative lens refraction rate This condition relates to the difference between the average Nd3p and the average Nd3n. If Nd3p - Nd3n exceeds the upper limit of equation (13), the difference becomes large, which is advantageous for correcting field curvature, but it is undesirable because it makes it difficult to correct lateral chromatic aberration. If Nd3p - Nd3n falls below the lower limit of equation (13), the difference becomes small, which is advantageous for correcting field curvature, but it is undesirable because it makes it difficult to correct field curvature.

[0032] It is more preferable to set the numerical ranges of the formulas (3) to (13) as shown in the following formulas (3a) to (13a).

[0033] -0.75≦f2 / f≦-0.34 (3a) 0.4≦f3 / f≦0.8 (4a) 0 <D1·sk / OTL 2 ≦0.1 (5a) 0.07≦D13 / OTL≦0.2 (6a) 0.43≦D3 / TL≦0.58 (7a) 0.20≦D1 / TL≦0.36 (8a) 1.7≦f1 / D1≦2.4 (9a) 1.0≦f3 / D3≦1.4 (10a) -0.19≦Nd1p-Nd1n≦-0.07 (11a) 27.0≦νd1p-νd1n≦36.0 (12a) 0.02≦Nd3p-Nd3n≦0.16 (13a) It is more preferable to set the numerical ranges of the formulas (3) to (13) as shown in the following formulas (3b) to (13b).

[0034] -0.66≦f2 / f≦-0.37 (3b) 0.65≦f3 / f≦0.75 (4b) 0.02≦D1·sk / OTL 2 ≦0.05 (5b) 0.15≦D13 / OTL≦0.2 (6b) 0.45≦D3 / TL≦0.55 (7b) 0.27≦D1 / TL≦0.31 (8b) 1.7≦f1 / D1≦2.2 (9b) 1.0≦f3 / D3≦1.2 (10b) -0.18≦Nd1p-Nd1n≦-0.10 (11b) 29.0≦νd1p-νd1n≦34.5 (12b) 0.03≦Nd3p-Nd3n≦0.11 (13b) Furthermore, it is desirable that the optical system of each embodiment satisfy at least one of the following configurations. First, it is desirable that the lens group that moves as the focusing group is at least one of the second lens group L2 and the third lens group L3. Also, when focusing from infinity to the closest distance, it is desirable that the second lens group L2 moves from the object side to the image side, and the third lens group L3 moves from the image side to the object side. This makes it possible to efficiently suppress fluctuations in various aberrations during focusing.

[0035] Furthermore, it is desirable that the first lens unit L1 be fixed (unmoving) during focusing, which can improve the operability of focusing.

[0036] It is also desirable that the second lens unit L2 be composed of two lenses, which makes it possible to achieve both a compact and lightweight focusing unit and suppression of fluctuations in aberrations due to focusing.

[0037] Furthermore, it is desirable that the refractive power of the lens located closest to the object in the first lens group L1 be positive, which makes it possible to efficiently correct spherical aberration caused by off-axis rays.

[0038] It is also desirable that the first lens group L1 includes three or more positive lenses and one or more negative lenses, which makes it possible to achieve both an optimal focal length for the first lens group L1 and good correction of various aberrations such as spherical aberration and chromatic aberration.

[0039] It is also desirable that the third lens group L3 includes three or more positive lenses and three or more negative lenses, which makes it possible to efficiently correct curvature of field and chromatic aberration.

[0040] It is also desirable to perform vibration reduction (image blur correction) by displacing the optical image formed by the optical system in a direction perpendicular to the optical axis by moving some of the lenses in the third lens group L3 in a direction perpendicular to the optical axis (by translating them in a plane perpendicular to the optical axis or by moving them in an arc around a point on the optical axis). This makes it possible to correct image blur when vibrations such as camera shake occur during image capture.

[0041] Below are various values ​​for Numerical Examples 1 to 3 corresponding to the above Examples 1 to 3. In the surface data of each Numerical Example, surface number i indicates the ith surface counted from the object side. r is the radius of curvature of the ith surface (mm), d is the lens thickness or air gap (mm) between the ith and (i+1)th surfaces, and nd is the refractive index at the d-line of the material of the ith optical component. νd is the Abbe number based on the d-line of the material of the ith optical component. The Abbe number νd is expressed as νd = (Nd-1) / (NF-NC), where Nd, NF, and NC are the refractive indices at the Fraunhofer d-line (587.6 nm), F-line (486.1 nm), and C-line (656.3 nm).

[0042] An asterisk (*) next to a surface number indicates that the surface has an aspherical shape. The aspherical shape is expressed by the following equation, where x is the displacement in the optical axis direction at a position of height h from the optical axis relative to the vertex of the surface, R is the paraxial radius of curvature, k is the conic constant, and A4, A6, and A8 are aspherical coefficients.

[0043] 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 "e±XXX" in each aspherical coefficient is "×10 ±XXX " means.

[0044] The various data also include focal length (mm), F-number, half angle of view (°), image height (mm), total lens length (mm), and back focus sk (mm).

[0045] Furthermore, the values ​​of the formulas (1) to (13) in Numerical Examples 1 to 3 are summarized in Table 1. (Numerical example 1) Unit: mm Surface Data Surface number rd nd νd 1 83.030 5.57 2.00100 29.1 2 256.257 0.15 3 55.377 9.54 1.49700 81.5 4 -1562.618 2.10 1.88300 40.8 5 157.784 0.15 6 48.262 5.24 1.49700 81.5 7 110.153 2.00 1.74077 27.8 8 32.826 1.79 9 41.561 7.22 1.53775 74.7 10 731.529 1.99 11 (Aperture) ∞ 2.20 12 -800.577 2.28 1.92286 18.9 13 -167.395 2.00 1.64000 60.1 14 33.920 13.59 15 -1618.230 2.00 1.67270 32.1 16 30.098 3.79 2.00069 25.5 17 47.606 1.40 18 44.072 7.06 1.77250 49.6 19 -82.524 2.00 1.72825 28.5 20 46.850 0.15 21 42.101 2.00 1.92286 20.9 22 26.733 12.26 1.69680 55.5 23 -117.997 1.90 24 -54.665 2.00 1.53172 48.8 25 37.574 12.86 2.00100 29.1 26 -74.410 7.77 27* -48.385 2.50 1.76802 49.2 28 -200.196 11.66 29 ∞ 1.50 1.51633 64.1 30 ∞ 0.35 Image plane ∞ Aspheric data Page 27 K = 0.00000e+000 A 4=-6.78251e-006 A 6= 3.50939e-009 A 8=-1.05473e-011 A10= 1.32171e-014 Various data Focal length 82.87 F-number 1.45 Half angle of view 14.63 Image height 21.64 Lens length 126.50 BF 13.00 Lens group data Group starting plane focal length 1 1 68.40 2 11 -54.52 3 15 58.91 4 29 ∞ (Numerical example 2) Unit: mm Surface Data Surface number rd nd νd 1 84.993 4.95 2.00100 29.1 2 202.416 0.15 3 64.164 9.64 1.49700 81.5 4 -318.125 2.10 1.72000 43.7 5 221.142 0.15 6 44.553 6.17 1.49700 81.5 7 114.119 2.00 1.72151 29.2 8 33.254 2.07 9 44.079 6.85 1.48749 70.2 10 572.213 1.99 11 (Aperture) ∞ 2.00 12 ∞ 2.18 1.92286 18.9 13 -250.097 0.70 14 -206.496 2.00 1.64000 60.1 15 37.733 14.76 16 5598.365 2.00 1.67270 32.1 17 30.558 3.79 2.00069 25.5 18 47.606 1.10 19 42.007 6.85 1.88300 40.8 20 -114.771 0.50 21 -108.194 2.00 1.72825 28.5 22 53.452 0.49 23 61.357 2.00 1.92286 20.9 24 26.750 11.05 1.72916 54.7 25 -168.388 1.91 26 -60.234 2.00 1.56732 42.8 27 33.668 14.14 2.00100 29.1 28 -62.938 3.32 29* -59.800 2.50 1.76802 49.2 30 -1001.556 15.79 31 ∞ 1.50 1.51633 64.1 32 ∞ 0.35 Image plane ∞ Aspheric data Page 29 K = 0.00000e+000 A 4=-6.99383e-006 A 6= 2.04264e-009 A 8=-9.55132e-012 A10= 1.30188e-014 Various data Focal length 82.86 F-number 1.45 Half angle of view 14.63 Image height 21.64 Lens length 128.50 BF 17.13 Lens group data Group starting plane focal length 1 1 74.01 2 11 -61.34 3 16 57.80 4 31 ∞ (Numerical example 3) Unit: mm Surface Data Surface number rd nd νd 1 97.050 5.69 1.91082 35.3 2 808.610 0.15 3 68.009 5.40 1.88300 40.8 4 161.282 0.15 5 58.276 9.34 1.49700 81.5 6 -171.384 2.00 1.92286 18.9 7 125.448 0.10 8 88.179 4.07 1.72916 54.7 9 618.713 2.06 10 (Aperture) ∞ 2.22 11 -707.487 4.60 1.98612 16.5 12 -56.353 2.00 1.91082 35.3 13 28.743 9.18 14 -345.236 2.00 1.64769 33.8 15 29.434 3.79 2.00069 25.5 16 47.606 1.00 17* 36.642 2.00 2.00100 29.1 18 22.542 12.76 1.49700 81.5 19 -80.204 0.15 20 -854.942 6.19 1.80400 46.5 21 -42.105 1.50 1.89286 20.4 22 -112.460 0.15 23 84.665 9.81 2.00100 29.1 24 -49.304 2.00 1.48749 70.2 25 -398.028 4.75 26* -37.257 2.50 1.59270 35.3 27 -961.002 16.82 28 ∞ 1.50 1.51633 64.1 29 ∞ 0.35 Image plane ∞ Aspheric data Page 17 K = 0.00000e+000 A 4= 3.32169e-006 A 6= 4.54064e-009 A 8=-2.16254e-012 Page 26 K = 0.00000e+000 A 4= 4.71639e-006 A 6= 3.40498e-009 A 8=-1.36079e-011 A10= 1.36420e-014 Various data Focal length 82.64 F-number 1.45 Half angle of view 14.67 Image height 21.64 Lens length 113.70 BF 18.16 Lens group data Group starting plane focal length 1 1 46.25 2 10 -31.40 3 14 57.48 4 28 ∞

[0046] [Table 1]

[0047] Fig. 7 shows a digital still camera (imaging device) using the optical system of Examples 1 to 3. In Fig. 7, 10 denotes a camera body, and 11 denotes an imaging optical system using the optical system described in any of Examples 1 to 3. 12 denotes an imaging element such as a CCD sensor or CMOS sensor that is built into the camera body 10 and captures a subject image formed by the imaging optical system 21.

[0048] Note that an interchangeable lens having an imaging optical system using the optical system described in any one of Examples 1 to 3 is also included in the optical equipment as another Example.

[0049] The embodiments described above are merely representative examples, and various modifications and alterations are possible to each embodiment when implementing the present invention. [Explanation of symbols]

[0050] 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 negative refractive power, and a third lens group having positive refractive power, the first lens group having a distance therebetween that changes during focusing, the first lens group being arranged in this order from the object side to the image side, the lens arranged closest to the image side in the third lens group has negative refractive power and has a concave surface facing the object side, In a state where the optical system is focused at infinity, the focal length of the optical system is f, the focal length of the first lens group is f1, the total optical length of the optical system is OTL, the air-equivalent distance from the lens surface in the third lens group closest to the image plane is sk, the thickness on the optical axis from the lens surface in the third lens group closest to the object side to the lens surface in the third lens group closest to the image side is D3, and the length on the optical axis from the lens surface in the first lens group closest to the object side to the lens surface in the third lens group closest to the image side is TL. 0.51≦f1 / f≦0.93 0.01≦sk / OTL≦0.13 0.430≦D3 / TL≦0.6 An optical system characterized by satisfying the following conditions:

2. When the focal length of the second lens group is f2, −0.9≦f2 / f≦−0.3 2. The optical system according to claim 1, wherein the following condition is satisfied:

3. When the focal length of the third lens group is f3, 0.1≦f3 / f≦0.9 3. The optical system according to claim 1, wherein the following condition is satisfied:

4. When the thickness on the optical axis from the lens surface closest to the object side to the lens surface closest to the image side in the first lens group is D1, 0<D1・sk / OTL ２ ≦0.1 4. The optical system according to claim 1, wherein the following condition is satisfied:

5. When the distance on the optical axis from the lens surface in the first lens group closest to the image side to the lens surface in the third lens group closest to the object side in an infinity focused state is D13, 0.1≦D13 / OTL≦0.4 5. The optical system according to claim 1, wherein the following condition is satisfied:

6. In a state where the lens is focused at infinity, let D1 be the thickness on the optical axis from the lens surface in the first lens group closest to the object side to the lens surface in the third lens group closest to the image side, and TL be the length on the optical axis from the lens surface in the first lens group closest to the object side to the lens surface in the third lens group closest to the image side. 0.1≦D1 / TL≦0.4 6. The optical system according to claim 1, wherein the following condition is satisfied:

7. When the thickness on the optical axis from the lens surface closest to the object side to the lens surface closest to the image side in the first lens group is D1, 1.7≦f1 / D1≦2.5 7. The optical system according to claim 1, wherein the following condition is satisfied:

8. When the focal length of the third lens group is f3 and the thickness on the optical axis from the lens surface closest to the object side to the lens surface closest to the image side in the third lens group is D3, 1.0≦f3 / D3≦1.5 8. The optical system according to claim 1, wherein the following condition is satisfied:

9. An optical system comprising 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, the first lens group having a distance therebetween that changes during focusing, the first lens group being arranged in this order from the object side to the image side, the lens arranged closest to the image side in the third lens group has negative refractive power and has a concave surface facing the object side, In a state where the optical system is focused at infinity, the focal length of the optical system is f, the focal length of the first lens group is f1, the total optical length of the optical system is OTL, the air-equivalent distance from the lens surface in the third lens group closest to the image plane is sk, the focal length of the third lens group is f3, and the thickness on the optical axis from the lens surface in the third lens group closest to the lens surface closest to the image plane is D3. 0.51≦f1 / f≦0.93 0.01≦sk / OTL≦0.13 1.0≦f3 / D3≦1.200 An optical system characterized by satisfying the following conditions:

10. When the average refractive index of the positive lenses included in the first lens group is Nd1p and the average refractive index of the negative lenses included in the first lens group is Nd1n, −0.20≦Nd1p−Nd1n≦−0.05 10. The optical system according to claim 1, wherein the following condition is satisfied:

11. When the average Abbe number of the positive lenses included in the first lens group is νd1p and the average Abbe number of the negative lenses included in the first lens group is νd1n, 25.0≦νd1p−νd1n≦38.0 11. The optical system according to claim 1, wherein the following condition is satisfied:

12. When the average refractive index of the positive lenses included in the third lens group is Nd3p and the average refractive index of the negative lenses included in the third lens group is Nd3n, 0.01≦Nd3p−Nd3n≦0.2 12. The optical system according to claim 1, wherein the following condition is satisfied:

13. 13. The optical system according to claim 1, wherein the first lens group is stationary during focusing.

14. 14. The optical system according to claim 1, wherein the second lens group is made up of two lenses.

15. 15. The optical system according to claim 1, wherein the lens closest to the object side in the first lens group is a positive lens.

16. 16. The optical system according to claim 1, wherein the first lens group includes three or more positive lenses and one or more negative lenses.

17. 17. The optical system according to claim 1, wherein the third lens group includes three or more positive lenses and three or more negative lenses.

18. 18. The optical system according to claim 1, wherein, during image blur correction, at least one lens in the third lens group moves in a direction including a direction perpendicular to the optical axis.

19. An optical system according to any one of claims 1 to 18; and an image sensor that receives light from the optical system.

Images