Optical system, lens device having the same, and imaging device

Abstract

To provide a compact optical system which offers good optical performance and is easy to manufacture.SOLUTION: An optical system consists of a front group with positive refractive power consisting of a lens group configured to move when focusing, and a negative lens group with negative refractive power, arranged in order from the object side to the image side, and is configured such that the lens group of the front group moves toward the object side so as to extend the distance between the front group and the negative lens group while shifting focus from infinity to a short distance. The front group includes a partial group with negative refractive power consisting of lenses located on the object side of a positive lens located on the most object side among all positive lenses included in the optical system. A foal length of the optical system when focused at infinity, a focal length of the partial group, an average refractive index of the partial group, a distance from an image-side surface of a lens located on the most object side in the optical system to an object-side surface of the positive lens along an optical axis when focused at infinity, a distance from a lens surface on the most object side in the optical system to the image plane along the optical axis when focused at infinity, and a back focus of the optical system when focused at infinity are each set appropriately.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] In recent years, with the increase in the number of pixels of image sensors such as CCD and CMOS sensors, it is desired that optical systems used in imaging devices equipped with image sensors have high optical performance. Patent Document 1 discloses a front focus type optical system that performs focusing by moving a lens group arranged on the object side toward the object side in order to suppress focus fluctuations caused by various aberrations. Patent Document 2 discloses an optical system in which a meniscus lens with negative refractive power having an aspheric surface is arranged closest to the object side in order to satisfactorily correct off-axis aberrations such as field curvature and distortion aberration. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2019-74632 A [Patent Document 2] JP 2017-161848 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, when the optical system of Patent Document 1 is made wider, the off-axis aberration increases as the angle of view increases. In order to satisfactorily correct the increased off-axis aberration, it is necessary to arrange a lens with a large diameter on the object side in the front group, which is the focus group, leading to an increase in the size of the optical system. Furthermore, since the mass of the focus group also increases, a high-output actuator is required for autofocusing, which may lead to an increase in the size of the actuator.

[0005] In addition, in the optical system of Patent Document 2, even when the angle is increased, various aberrations can be well corrected without increasing the size of the front group of the optical system. However, since it is necessary to place the aspherical lens at a position where the height from the optical axis of the off-axis light rays is large, the aspherical lens is highly sensitive to manufacturing, making it difficult to manufacture the optical system.

[0006] An object of the present invention is to provide an optical system that has good optical performance, is easy to manufacture, and is small in size, as well as a lens device and an imaging device that include the optical system. [Means for solving the problem]

[0007] An optical system according to one aspect of the present invention is an optical system which is composed of one or more lens groups arranged in order from the object side to the image side, and which comprises a front group having positive refractive power overall and a negative lens group having negative refractive power, in which the distance between adjacent lens groups changes during focusing, and in which, during focusing from infinity to a close distance, the distance on the optical axis between the lens surface of the front group closest to the image and the lens surface of the negative lens group closest to the object increases, and all of the lens groups arranged in the front group move toward the object side, The front group is , No. 1 cemented lens and , Located on the image side of the first cemented lens Aperture Diameter and , A The optical system has a second cemented lens, and the front group has a first subgroup with negative refractive power consisting of all lenses arranged on the object side of a first positive lens arranged closest to the object side among the positive lenses included in the optical system, and the focal length of the optical system when focusing at infinity is denoted as f, the focal length of the first subgroup as fFL1, the average refractive index of the first subgroup as Nave, the distance on the optical axis from the image side of the lens arranged closest to the object side of the optical system when focusing at infinity to the object side of the first positive lens as x, and the distance on the optical axis from the lens surface closest to the object side of the optical system when focusing at infinity to the image plane as x. When the distance on the optical axis at is TTL and the back focus of the optical system at infinity is BF, -4.00 <fFL1 / x<-0.95 1.40 <Nave<1.65 0.25 <BF / f<0.95 0.13 <x / TTL<0.35 The present invention is characterized in that the following conditional expression is satisfied: Effect of the Invention

[0008] According to the present invention, it is possible to provide an optical system that has good optical performance, is easy to manufacture, and is small in size, as well as a lens device and an imaging device that include the optical system. [Brief description of the drawings]

[0009] [Figure 1] 1 is a cross-sectional view of the optical system of Example 1 when focused on infinity. [Diagram 2] 4A and 4B are aberration diagrams of the optical system of Example 1 when focused at infinity and when focused at an object distance at which the lateral magnification is −0.5 times. [Diagram 3] FIG. 11 is a cross-sectional view of the optical system of Example 2 when focused on infinity. [Figure 4] 13A and 13B are aberration diagrams of the optical system of Example 2 when focused at infinity and when focused at an object distance at which the lateral magnification is −0.5 times. [Diagram 5] FIG. 11 is a cross-sectional view of the optical system of Example 3 when focused on infinity. [Figure 6] 13A and 13B are aberration diagrams of the optical system of Example 3 when focused at infinity and when focused at an object distance at which the lateral magnification is −0.5 times. [Figure 7] FIG. 11 is a cross-sectional view of the optical system of Example 4 when focused on an object at infinity. [Figure 8] 13A and 13B are aberration diagrams of the optical system of Example 4 when focused at infinity and when focused at an object distance at which the lateral magnification is −0.5 times. [Figure 9] FIG. 13 is a cross-sectional view of the optical system of Example 5 when focused on infinity. [Figure 10] 13A and 13B are aberration diagrams of the optical system of Example 5 when focused at infinity and when focused at an object distance at which the lateral magnification is −0.5 times. [Figure 11] FIG. 13 is a cross-sectional view of the optical system of Example 6 when focused on infinity. [Figure 12]13A and 13B are aberration diagrams of the optical system of Example 6 when focused at infinity and when focused at an object distance at which the lateral magnification is −0.5 times. [Figure 13] FIG. 1 is a schematic diagram of an imaging device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of an optical system and an image pickup apparatus having the same according to the present invention will be described with reference to the accompanying drawings.

[0011] 1, 3, 5, 7, 9, and 11 are cross-sectional views of the optical system L0 of each of the first to sixth embodiments when focused at infinity. The optical system L0 of each embodiment is an optical system used in imaging devices such as digital video cameras, digital still cameras, broadcast cameras, silver halide film cameras, and surveillance cameras. The optical system L0 of each embodiment is preferably used as a large-aperture wide-angle lens. Since it is assumed that image distortion caused by the distortion aberration generated in the optical system L0 of each embodiment is corrected by image processing, the optical system L0 of each embodiment is designed to allow the occurrence of distortion aberration. For example, in an imaging device equipped with a lens device having the optical system L0 of each embodiment, the acquired image is corrected by an image processing unit in the imaging device using information on the amount of distortion aberration related to the image formed by the optical system L0, which is stored in a storage unit in the lens device.

[0012] In each cross-sectional view, the left side is the object side and the right side is the image side. The optical system L0 in each embodiment is configured to have multiple lens groups. In this specification, a lens group is a group of lenses that move or stand still as a unit during focusing. That is, in the optical system L0 in each embodiment, the distance between adjacent lens groups changes during focusing from infinity to a close distance. Note that the lens group may be composed of one lens or multiple lenses. The lens group may also include an aperture stop.

[0013] The optical system L0 of each embodiment is composed of a front group FL having positive refractive power, which is composed of one or more lens groups arranged in order from the object side to the image side and which move during focusing, and a rear group (negative lens group) RL having negative refractive power. The optical systems of embodiments 1, 2, 3, 5, and 6 are composed of one lens group (first lens group) having positive refractive power as the front group FL, and a second lens group having negative refractive power as the rear group RL. The optical system of embodiment 4 is composed of a first lens group having negative refractive power and a second lens group having positive refractive power as the front group FL, and a third lens group having negative refractive power as the rear group RL.

[0014] In each cross-sectional view, FLi denotes the i-th lens group (i is a natural number) counted from the object side among the lens groups included in the front group FL.

[0015] Also, SP is an aperture stop. IP is an image plane, and when the optical system L0 of each embodiment is used as a photographing optical system of a digital still camera or a digital video camera, the imaging surface of a solid-state image sensor (photoelectric conversion element) such as a CCD sensor or a CMOS sensor is disposed thereon. When the optical system L0 of each embodiment is used as a photographing optical system of a silver halide film camera, a photosensitive surface equivalent to the film surface is disposed on the image plane IP. Also, in the optical system L0 of embodiments 1 to 4 and 6, IS is a correction lens group, which can correct image blur caused by camera shake or the like by moving in a direction perpendicular to the optical axis.

[0016] In the optical system L0 of each embodiment, when focusing from infinity to a close distance, the lens group included in the front group FL moves toward the object side so as to increase the distance between the front group FL and the rear group RL. The arrows shown in each cross-sectional view indicate the direction of movement of the lens group when focusing from infinity to a close distance.

[0017] The optical system L0 of this embodiment is a front focus type optical system, which can focus on a wide range of object distances from infinity to close range, and can be made compact. In addition, the amount of movement during focusing can be reduced, and the fluctuation of various aberrations such as spherical aberration and curvature of field during focusing can be suppressed well. As in the optical system L0 of Example 4, the first subgroup FL1 (first lens group) with negative refractive power and the second subgroup FL2 (second lens group) with positive refractive power included in the front group FL may be moved toward the object side along different trajectories. With this configuration, the amount of movement of the first subgroup FL1 can be reduced, and the working distance during close range shooting can be secured. Note that, although only examples in which the front group FL is composed of one or two lens groups are disclosed in this specification, even if the front group FL is composed of three or more lens groups, the effect of the present invention, which will be described in detail later, can be obtained.

[0018] Also, the rear group RL may be moved toward the object side to suppress variation in field curvature during focusing, as in the optical system L0 of Example 6. However, since this type of configuration increases the amount of movement of the front group FL during focusing, it is also preferable that the rear group RL is fixed during focusing, as in the optical systems L0 of Examples 1 to 5.

[0019] 2, 4, 6, 8, 10, and 12 are aberration diagrams of the optical system L0 of Examples 1 to 6. In each aberration diagram, (A) is an aberration diagram when focused at infinity, and (B) is an aberration diagram when focused at a close distance.

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

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

[0022] The front group FL has a first subgroup FL1 having a negative refractive power and composed of a lens arranged closer to the object than the first positive lens arranged closest to the object among the positive lenses included in the optical system L0. With this configuration, the optical system L0 can be made wider-angle and the curvature of field can be corrected well. From the viewpoint of aberration correction, it is preferable that the lens arranged closest to the object in the first subgroup FL1 is a negative meniscus lens with a concave surface facing the image surface side. It is also preferable that the number of lenses included in the first subgroup FL1 is two or less. If the number of lenses included in the first subgroup FL1 is three or more, the front group FL, which is a focus group, becomes large, which is not preferable.

[0023] The optical system L0 of each embodiment satisfies the following conditional expressions (1) to (4). Here, f is the focal length of the optical system L0 when focusing at infinity. fFL1 is the focal length of the first sub-group FL1. Nave is the average refractive index of the first sub-group FL1. x is the distance from the image side surface of the lens arranged on the most object side of the optical system L0 on the optical axis when focusing at infinity to the object side surface of the first positive lens. TTL is the distance (total optical length) from the most object side lens surface of the optical system L0 on the optical axis when focusing at infinity to the image surface IP of the optical system L0. BF is the back focus of the optical system L0 when focusing at infinity.

[0024] -4.00 <fFL1 / x<-0.95 (1) 1.40 <Nave<1.65 (2) 0.25 <BF / f<0.95 (3) 0.13 <x / TTL<0.35 (4) Conditional formula (1) specifies the focal length fFL1 and the distance x. By satisfying conditional formula (1), when the optical system L0 is made wider-angle, the ray bundle of the light beam incident on the first positive lens can be increased within a range in which the optical path length is short and the spherical aberration can be suppressed. If the upper limit of conditional formula (1) is exceeded and the negative refractive power of the first subgroup FL1 becomes large, the spherical aberration cannot be corrected well, or the optical path length is extended and the optical system L0 becomes large, which is not preferable. If the negative refractive power of the first subgroup FL1 becomes small and the lower limit of conditional formula (1) is exceeded, the ray bundle of the light beam incident on the first subgroup FL1 cannot be made sufficiently large before it is incident on the first positive lens (for example, the height from the optical axis of the axial light beam cannot be made sufficiently large). This is not preferable because the subsequent lens groups cannot perform good aberration correction.

[0025] Conditional formula (2) specifies the average refractive index Nave of the first subgroup FL1. By satisfying conditional formula (2), when the angle of the optical system L0 is increased, the field curvature can be corrected satisfactorily within a range in which spherical aberration can be suppressed. If the average refractive index Nave increases beyond the upper limit of conditional formula (2), the Petzval sum of the optical system L0 increases, which is undesirable as the field curvature cannot be corrected satisfactorily. If the average refractive index Nave decreases below the lower limit of conditional formula (2), the curvature of the negative meniscus lens in the first subgroup FL1 increases, which is undesirable as the spherical aberration cannot be corrected satisfactorily.

[0026] Conditional expression (3) specifies the back focus BF and focal length f. By satisfying conditional expression (3), the optical system L0 can be made compact. If the back focus BF is increased beyond the upper limit of conditional expression (3), the overall length of the optical system L0 will be increased, which is not preferable. If the back focus BF is decreased below the lower limit of conditional expression (3), the distance between the image side principal point and the final surface will increase, which will result in a larger effective diameter required for the final lens, and therefore the optical system L0 will be larger, which is not preferable.

[0027] Conditional formula (4) specifies the distance x and the total optical length TTL. By satisfying conditional formula (4), when the optical system L0 is made wider, the ray bundle of the light beam incident on the first positive lens can be increased while keeping the optical path length short and within a range where spherical aberration can be suppressed. If the distance x is longer than the upper limit of conditional formula (4), it is not preferable because there is no space to arrange a lens group for correcting spherical aberration and the like subsequent to the first positive lens. If the distance x is shorter than the lower limit of conditional formula (4), it is not preferable because when the optical system L0 is made wider, the ray bundle of the light beam incident on the first positive lens cannot be made sufficiently large, and good aberration correction cannot be performed by the subsequent lens group.

[0028] It is preferable that the numerical ranges of the conditional expressions (1) to (4) are set to the numerical ranges of the following conditional expressions (1a) to (4a).

[0029] -3.50 <fFL1 / x<-0.98 (1a) 1.42 <Nave<1.60 (2a) 0.3 <BF / f<0.8 (3a) 0.15 <x / TTL<0.32 (4a) It is further preferable that the numerical ranges of the conditional expressions (1) to (4) be the numerical ranges of the following conditional expressions (1b) to (4b).

[0030] -3 <fFL1 / x<-1 (1b) 1.45 <Nave<1.55 (2b) 0.35 <BF / f<0.70 (3b) 0.16 <x / TTL<0.30 (4b) With the above-mentioned configuration, it is possible to realize an optical system L0 that has good optical performance, is easy to manufacture, and is small in size.

[0031] It is preferable that the optical system L0 in each embodiment satisfies the following conditional expression (5), where the maximum refractive index of the positive lens included in the first cemented lens arranged on the object side of the aperture stop SP is Ndp and the minimum refractive index of the negative lens included in the first cemented lens is Ndn.

[0032] 0.07 <Ndp-Ndn<0.25 (5) Conditional expression (5) specifies the maximum refractive index Ndp and the minimum refractive index Ndn. By satisfying conditional expression (5), the Petzval sum can be reduced to a range in which axial chromatic aberration can be suppressed when correcting the field curvature of the optical system L0. If the upper limit of conditional expression (5) is exceeded, it is not preferable because the first cemented lens cannot sufficiently achromatize when selecting a general lens glass material. If the lower limit of conditional expression (5) is exceeded, it is not preferable because the Petzval sum cannot be sufficiently reduced when selecting a general lens glass material.

[0033] It is preferable that the optical system L0 in each embodiment satisfies the following conditional expression (6), where the maximum Abbe number of the positive lens included in the second cemented lens arranged on the image side of the aperture stop SP is vdp and the minimum Abbe number of the negative lens included in the second cemented lens is vdn.

[0034] 25<νdp-νdn<70 (6) Conditional formula (6) specifies the maximum Abbe number νdp and the minimum Abbe number νdn. By satisfying conditional formula (6), achromatism can be achieved within a range in which curvature of field can be suppressed when reducing the chromatic aberration of the optical system L0. Exceeding the upper limit of conditional formula (6) is not preferable because the Petzval sum increases when selecting a general lens glass material, making it impossible to fully suppress curvature of field. Falling below the lower limit of conditional formula (6) is not preferable because chromatic aberration cannot be sufficiently corrected.

[0035] It is preferable that the optical system L0 in each embodiment satisfies the following conditional expression (7), where φr is the maximum effective diameter of the lens located closest to the image side of the optical system L0 and φmax is the maximum effective diameter of the lenses included in the optical system L0.

[0036] 0.63<φr / φmax≦1.00 (7) Conditional expression (7) defines the maximum effective diameters φr and φmax. By satisfying conditional expression (7), it is possible to prevent the diameter of the front lens of the optical system L0 from becoming large. If the lower limit of conditional expression (7) is not satisfied, the diameter of the front lens of the optical system L0 becomes too large, which leads to an increase in the size of the optical system L0, which is not preferable.

[0037] It is preferable that the optical system L0 in each embodiment satisfies the following conditional expression (8), where φf is the maximum effective diameter of the lens located closest to the object side of the optical system L0.

[0038] 0.7<φf / φr<1.3 (8) Conditional expression (8) specifies the maximum effective diameters φf and φr. By satisfying conditional expression (8), the lens shape of optical system L0 can be made closer to symmetrical when off-axis aberrations such as coma and curvature of field of optical system L0 are effectively corrected. If the upper limit of conditional expression (8) is exceeded or the lower limit is exceeded, the symmetry of the lens shape is lost and off-axis aberrations such as coma and curvature of field cannot be effectively corrected, which is not preferable.

[0039] It is preferable that the optical system L0 in each embodiment satisfies the following conditional expression (9).

[0040] 0.06 <BF / TTL<0.35 (9) Conditional formula (9) specifies the back focus BF and the total optical length TTL. By satisfying conditional formula (9), the total length of the optical system L0 can be shortened. If the back focus BF is increased beyond the upper limit of conditional formula (9), the total length of the optical system L0 will be increased, which is undesirable. If the back focus BF is decreased below the lower limit of conditional formula (9), the distance between the optical system L0 and the imaging surface on which the imaging element and the like are arranged will be narrowed, which is undesirable because the arrangement space for the color filter and the like will be insufficient.

[0041] It is preferable that the optical system L0 in each embodiment satisfies the following conditional expression (10).

[0042] -2.0 <fFL1 / f<-0.1 (10) Conditional expression (10) specifies the focal length fFL1,f. By satisfying conditional expression (10), when the angle of the optical system L0 is increased, the optical path length is short and the ray bundle of the light beam incident on the first positive lens can be increased within a range in which spherical aberration can be suppressed. If the upper limit of conditional expression (10) is exceeded and the negative refractive power of the first sub-group FL1 is increased, it is not preferable because the spherical aberration cannot be corrected well. If the lower limit of conditional expression (10) is exceeded and the negative refractive power of the first sub-group FL1 is decreased, the optical path length required to increase the ray bundle of the light beam incident on the first positive lens is extended, and the optical system L0 becomes large, which is not preferable.

[0043] It is preferable that the optical system L0 in each embodiment satisfies the following conditional expression (11), when the focal length of the rear group RL is fRL.

[0044] -twenty two <fRL / f<-5 (11) Conditional expression (11) defines the focal length fRL,f. By satisfying conditional expression (11), it is possible to suppress focus fluctuations due to coma aberration when reducing the amount of movement of the front group FL, which is the focus group, during focusing. If the upper limit of conditional expression (11) is exceeded and the refractive power of the positive lens in the rear group RL becomes small, it is not preferable because it is not possible to effectively suppress focus fluctuations due to coma aberration during focusing. If the lower limit of conditional expression (11) is exceeded and the negative refractive power of the rear group RL becomes small, it is not preferable because the amount of movement of the front group FL during focusing becomes large.

[0045] It is preferable that the optical system L0 in each embodiment satisfies the following conditional expression (12), where V is a third-order distortion aberration coefficient that the optical system L0 has when focused at infinity.

[0046] 0.2 <V<0.6 (12) Conditional expression (12) defines the distortion coefficient V. By satisfying conditional expression (12), when the optical system L0 is made compact, the negative refractive power of the first subgroup FL can be increased to move the entrance pupil position toward the object side, thereby making it possible to reduce the diameter of the front lens and satisfactorily correct various aberrations other than distortion. Here, the distortion coefficient V is a general formula explained in third-order aberration theory, and is expressed by the following formula.

[0047] V = ΣV ν (ν is a natural number) Here, the subscript ν indicates the surface numbers of all lenses included in the optical system L0 of each embodiment, and V ν indicates the distortion coefficient of the n-th lens surface from the object side obtained by paraxial ray tracing. ν is expressed by the following formula: JPEG0007625379000001.jpg8141

[0048] The formulas constituting the above formula are expressed as follows: JPEG0007625379000002.jpg29117

[0049] In addition, the nine variables used in the above formula are TIFF0007625379000003.tif11112

[0050] h represents the radius of curvature and refractive index of the ray passing through the νth lens surface when performing paraxial ray tracing. ν is the height of a ray from the optical axis at the intersection point when the ray originating from an axial object point passes through the v-th lens surface. JPEG0007625379000004.jpg910

[0051] is the height of the ray from the optical axis at the intersection point when the ray from the off-axis object point passes through the νth lens surface. ν is the converted inclination angle between the light ray emitted from an axial object point and the optical axis when the light ray is incident on the v-th lens surface. JPEG0007625379000005.jpg711

[0052] is the conversion inclination angle between the light ray from an off-axis object point and the optical axis when the light ray is incident on the νth lens surface. ν ' is the converted inclination angle between the light ray from an axial object point and the optical axis when it emerges from the νth lens surface. JPEG0007625379000006.jpg715

[0053] is the conversion inclination angle between the light ray from an off-axis object point and the optical axis when it emerges from the νth lens surface. r ν is the radius of curvature of the νth lens surface. N ν is the refractive index of the space on the object side of the νth lens surface. ν ' is the refractive index of the space on the image side of the νth lens surface.

[0054] Here, the distortion coefficient V in the present invention uses a value when focusing at infinity in air. Therefore, as an initial condition for ray tracing to obtain the distortion coefficient V, h1 of a ray emerging from an on-axis object point and incident on the first lens surface is 1, and α1 is 0. In addition, JPEG0007625379000007.jpg1011

[0055] is -t (t is the distance from the first lens surface on the optical axis to the entrance pupil of the optical system L0), JPEG0007625379000008.jpg811

[0056] is -1. The refractive index N of air is 1. The power φ of the νth lens surface is ν (N ν '-N ν ) / r ν , the conversion distance e from the νth lens surface to the (ν+1)th lens surface ν ' is d ν ' / N ν '(d ν' is the surface spacing on the optical axis from the νth lens surface to the (ν+1)th lens surface. Ray tracing from an axial object point is performed using the following three equations.

[0057] α ν '= α ν +h ν φ ν h ν+1 =h ν -e ν 'α ν ' α ν+1 = α ν ' Ray tracing from an off-axis object point is performed using the following three equations. TIFF0007625379000009.tif3155

[0058] If the distortion coefficient V increases beyond the upper limit of condition (12), it is not preferable because the optical system L0 cannot satisfactorily correct various aberrations such as field curvature. If the distortion coefficient V decreases below the lower limit of condition (12), it is not preferable because the negative refractive power of the first subgroup FL cannot be made sufficiently large, and the front lens becomes large, which in turn increases the size of the optical system L0.

[0059] It is preferable that the optical system L0 in each embodiment satisfies the following conditional expression (13), where dist(ω) is the amount of distortion at the maximum half angle of view ω when focused at infinity.

[0060] -20 <dist(ω)<-5 (13) Conditional formula (13) specifies the amount of distortion dist(ω). By satisfying conditional formula (13), when the optical system L0 is made compact, the negative refractive power of the first subgroup FL is increased to move the entrance pupil position toward the object side, thereby making it possible to reduce the diameter of the front lens and to satisfactorily correct various aberrations other than distortion. Here, the amount of distortion dist(ω) is calculated using the relational expression (y'-y0) / y0×100[%] between the ideal image height y0 and the real image height y' in the projection method of y=f×tanω. The ideal image height y0 is given by the specifications of the optical system L0 (focal length f and maximum half angle of view ω), and the real image height y' is given by the ray height from the optical axis at the image plane IP of the chief ray incident on the optical system L0 from infinity to the maximum half angle of view ω. If the amount of distortion dist(ω) increases beyond the upper limit of conditional expression (13), it is not preferable because the optical system L0 cannot satisfactorily correct various aberrations such as field curvature. If the amount of distortion dist(ω) decreases below the lower limit of conditional expression (13), it is not preferable because the negative refractive power of the first subgroup FL cannot be made sufficiently large, and the front lens becomes large, thereby increasing the size of the optical system L0.

[0061] It is preferable that the numerical ranges of the conditional expressions (5) to (13) be the numerical ranges of the following conditional expressions (5a) to (13a).

[0062] 0.08 <Ndp-Ndn<0.22 (5a) 30<νdp-νdn<65 (6a) 0.73<φr / φmax≦1.00 (7a) 0.85<φf / φr<1.29 (8a) 0.08 <BF / TTL<0.25 (9a) -1.8 <fFL1 / f<-0.5 (10a) -twenty two <fRL / f<-6 (11a) 0.23 <V<0.55 (12a) -18.0 <dist(ω)<-5.5 (13a) It is further preferable that the numerical ranges of the conditional expressions (5) to (13) be the numerical ranges of the following conditional expressions (5b) to (13b).

[0063] 0.09 <Ndp-Ndn<0.20 (5b) 32<νdp-νdn<60 (6b) 0.78<φr / φmax≦1.00 (7b) 0.90<φf / φr<1.28 (8b) 0.09 <BF / TTL<0.20 (9b) -1.5 <fFL1 / f<-0.8 (10b) -20 <fRL / f<-7 (11b) 0.26 <V<0.50 (12b) -16 <dist(ω)<-6 (13b) In the optical system L0 of each embodiment, the front group FL preferably has an aperture stop SP arranged on the image side of the first positive lens. In the front group FL, the first positive lens, the first cemented lens, and the second cemented lens, which are arranged with a convex surface facing the object side and separated from the first subgroup FL1 by the maximum air space, are preferably concentrated near the aperture stop SP where the marginal ray height is large. This makes it possible to satisfactorily correct various aberrations such as spherical aberration and axial chromatic aberration, which increase with increasing aperture diameter. Furthermore, in order to satisfactorily correct curvature of field, the front group FL preferably includes at least one aspherical lens on the image side of the first subgroup FL1, the surface of which has a shape in which the negative refractive power becomes stronger from the center to the periphery. With the above-mentioned configuration, it is possible to realize an optical system L0 that is small in size and has good optical performance when focusing at infinity.

[0064] In the optical system L0 of each embodiment, it is preferable that the rear group RL has a positive lens and a negative lens arranged in this order from the object side to the image side. By arranging the positive lens on the object side, it is possible to effectively suppress fluctuations in coma aberration during focusing.

[0065] In addition, in the optical system L0, since the occurrence of distortion is permitted, there is no need to place an aspherical lens in the first sub-group FL1, which is disposed at a position where the height from the optical axis of off-axis rays is large. By not including an aspherical lens, manufacturing sensitivity can be reduced.

[0066] Also, like the optical systems L0 of the first to fourth and sixth embodiments, the front group FL may have a correction lens group IS arranged adjacent to the aperture stop SP. The correction lens group IS can correct image blurring caused by camera shake by moving in a direction perpendicular to the optical axis of the optical system L0. It is preferable that the correction lens group IS is composed of one lens. If the correction lens group IS is composed of two or more lenses, the weight of the lens increases, and a high-output actuator is required to correct camera shake, which is undesirable since there is a concern that this could lead to an increase in the size of the optical system L0.

[0067] Numerical examples 1 to 6 corresponding to the first to sixth embodiments, respectively, are given below.

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

[0069] In each numerical example, d, focal length (mm), F-number, and half angle of view (degrees) are all values ​​when the optical system L0 of each example is focused on an object at infinity. "Back focus" is the distance on the optical axis from the final lens surface (the lens surface closest to the image) to the paraxial image surface expressed as an air-equivalent length. "Total optical length" is the distance on the optical axis from the foreground (the lens surface closest to the object) of the optical system L0 of each example to the final lens surface plus the back focus. The term "lens group" is not limited to cases where the optical system is composed of multiple lenses, but also includes cases where the optical system is composed of a single lens.

[0070] If the optical surface is aspheric, a * symbol is added to the right of the surface number. The aspheric shape is expressed as follows, where X is the displacement from the apex of the surface in the optical axis direction, h is the height from the optical axis in the direction perpendicular to the optical axis, R is the paraxial radius of curvature, k is the conic constant, and A4, A6, A8, A10, and A12 are the aspheric coefficients of each order: X = (h 2 / R) / [1+{1-(1+k)(h / R) 2} 1 / 2 ]+A4×h 4 + A6×h 6 +A8×h 8 +A10×h 10 +A12×h 12 In addition, "e±XX" in each aspheric coefficient means "×10±XX."

[0071] [Numerical Example 1] Unit: mm Surface Data Surface number rd nd νd Effective diameter 1 166.725 1.50 1.51633 64.1 31.47 2 17.847 13.73 25.56 3 30.903 3.94 1.90043 37.4 22.17 4 -170.378 3.36 21.98 5 -200.954 4.00 1.91082 35.3 20.73 6 -21.588 1.00 1.72825 28.5 20.50 7 90.491 2.02 19.36 8(Aperture) ∞ 3.27 18.88 9 70.847 1.74 1.80400 46.5 17.66 10 -300.114 3.64 17.35 11 -18.714 1.00 1.85478 24.8 16.23 12 38.885 5.54 1.49700 81.5 16.83 13* -28.697 0.15 20.57 14 248.946 4.85 1.95375 32.3 24.38 15 -29.607 (variable) 25.47 16 -66.159 2.20 1.72916 54.7 29.66 17 -40.851 10.00 30.07 18 -23.830 1.50 1.51742 52.4 31.01 19 -45.530 13.20 33.52 Image plane ∞ Aspheric Data Page 13 K = 0.00000e+000 A 4= 1.51499e-005 A 6=-1.89505e-008 A 8= 4.59451e-010 A10=-1.29807e-012 A12=-2.87757e-015 Various data Focal length 28.60 F-number 1.85 Half angle of view (degrees) 37.1 Image height 20.15 Optical total length 81.00 BF 13.20 Infinity Close d15 4.37 19.01 Lens Group Data Group starting plane focal length FL 1 28.89 RL 16 -394.81 Single lens data Lens starting surface focal length 1 1 -38.84 2 3 29.32 3 5 26.27 4 6 -23.84 5 9 71.44 6 11 -14.66 7 12 34.15 8 14 27.98 9 16 141.29 10 18 -98.96 [Numerical Example 2] Unit: mm Surface Data Surface number rd nd νd Effective diameter 1 50.658 1.57 1.48749 70.2 39.00 2 17.433 7.73 29.64 3 82.620 1.50 1.48749 70.2 28.85 4 22.068 13.94 25.42 5 28.055 5.75 1.90043 37.4 19.63 6 -26.190 1.00 1.80000 29.8 19.37 7 -678.364 6.06 18.87 8(Aperture) ∞ 2.86 16.75 9 74.460 1.40 1.77250 49.6 15.62 10 -3498.619 2.98 15.34 11 -20.479 1.00 1.85478 24.8 14.46 12 30.759 3.15 1.49700 81.5 14.74 13 -76.152 0.29 17.08 14 107.343 4.13 1.58313 59.4 19.96 15* -42.035 0.15 22.35 16 108.394 4.96 1.85150 40.8 25.38 17 -35.438 (variable) 26.28 18 -72.427 1.84 1.83481 42.7 27.19 19 -45.108 10.50 27.56 20 -23.819 1.57 1.51742 52.4 28.87 21 -53.298 11.00 31.31 Image plane ∞ Aspheric Data Page 15 K = 0.00000e+000 A 4= 2.14904e-005 A 6=-6.26885e-009 A 8= 3.11936e-010 A10=-1.96590e-012 A12= 3.25155e-015 Various data Focal length 20.60 F-number 1.85 Half angle of view (degrees) 46.4 Image height 18.71 Optical total length 84.87 BF 11.00 Infinity Close d17 1.50 11.92 Lens Group Data Group starting plane focal length FL 1 20.75 RL 18 -255.10 Single lens data Lens starting surface focal length 1 1 -55.38 2 3 -62.27 3 5 15.84 4 6 -34.08 5 9 94.40 6 11 -14.25 7 12 44.52 8 14 52.33 9 16 31.87 10 18 139.00 11 20 -84.77 [Numerical Example 3] Unit: mm Surface Data Surface number rd nd νd Effective diameter 1 352.223 1.57 1.51633 64.1 33.00 2 16.734 15.32 25.69 3 32.834 3.88 1.91082 35.3 20.54 4 -101.361 2.45 20.39 5 -173.026 3.85 1.90043 37.4 19.43 6 -20.106 1.00 1.72825 28.5 19.21 7 92.116 2.92 18.19 8(Aperture) ∞ 3.40 17.43 9 70.143 1.65 1.67790 55.3 16.24 10 -252.397 3.51 15.95 11 -15.958 1.00 1.85478 24.8 15.03 12 71.900 3.99 1.49700 81.5 19.50 13 -28.609 0.15 18.99 14 162.276 5.15 1.91082 35.3 22.80 15 -27.659 0.15 24.07 16 -83.020 2.50 1.53110 55.9 24.80 17* -48.642 (variable) 25.55 18 -79.703 2.09 1.72916 54.7 28.60 19 -45.710 10.30 29.00 20 -24.031 2.55 1.51742 52.4 30.41 21 -44.953 11.00 33.46 Image plane ∞ Aspheric Data Page 17 K = 0.00000e+000 A 4= 1.70126e-005 A 6=-2.50325e-009 A 8= 1.03885e-010 A10=-5.41918e-013 A12= 1.15952e-015 Various data Focal length 24.72 F-number 1.85 Half angle of view (degrees) 41.2 Image height 19.34 Optical total length 81.00 BF 11.00 Infinity Close d17 2.56 15.56 Lens Group Data Group starting plane focal length FL 1 25.09 RL 18 -459.74 Single lens data Lens starting surface focal length 1 1 -34.08 2 3 27.61 3 5 24.97 4 6 -22.58 5 9 81.14 6 11 -15.20 7 12 41.73 8 14 26.28 9 16 215.73 10 18 143.27 11 20 -104.12 [Numerical Example 4] Unit: mm Surface Data Surface number rd nd νd Effective diameter 1 67.195 1.57 1.48749 70.2 39.00 2 18.918 7.01 30.04 3 105.995 1.50 1.48749 70.2 29.39 4 25.853 (variable) 26.24 5 29.535 4.41 1.90043 37.4 18.94 6 -40.982 1.00 1.80000 29.8 18.75 7 -398.457 6.44 18.47 8(Aperture) ∞ 2.93 16.53 9 96.281 1.33 1.77250 49.6 15.57 10 -501.436 2.99 15.35 11 -19.791 1.00 1.85478 24.8 14.60 12 31.208 4.04 1.49700 81.5 15.05 13 -38.215 0.15 17.83 14* 99.997 3.68 1.58313 59.4 20.79 15* -55.869 0.45 23.06 16 418.363 5.30 1.85150 40.8 25.67 17 -28.156 (variable) 26.72 18 -110.776 1.87 1.83481 42.7 27.94 19 -57.108 10.50 28.22 20 -23.854 1.57 1.51742 52.4 28.97 21 -72.046 11.52 31.58 Image plane ∞ Aspheric Data Page 14 K = 0.00000e+000 A 4=-1.52854e-005 A 6=-2.71853e-008 A 8=-4.82286e-010 Page 15 K = 0.00000e+000 A 4= 1.02317e-005 A 6=-5.45429e-008 A 8=-1.79351e-010 A10=-8.19774e-013 A12=-9.61042e-016 Various data Focal length 20.50 F-number 1.85 Half angle of view (degrees) 46.5 Image height 18.60 Optical total length 84.95 BF 11.52 Infinity Close d4 14.19 13.54 d17 1.50 12.50 Lens Group Data Group starting plane focal length FL1 1 -28.94 FL2 5 28.89 RL 18 -160.42 Single lens data Lens starting surface focal length 1 1 -54.59 2 3 -70.57 3 5 19.64 4 6 -57.17 5 9 104.66 6 11 -14.04 7 12 35.25 8 14 62.01 9 16 31.15 10 18 139.00 11 20 -69.70 [Numerical Example 5] Unit: mm Surface Data Surface number rd nd νd Effective diameter 1 264.891 1.57 1.51742 52.4 32.60 2 15.736 14.57 25.06 3 29.703 3.45 1.90366 31.3 20.67 4 -1467.268 0.16 20.50 5 51.003 5.35 1.80400 46.5 20.23 6 -22.603 1.05 1.64769 33.8 19.59 7 43.603 4.03 17.74 8(Aperture) ∞ 2.26 16.32 9 -281.459 1.68 1.72916 54.7 15.33 10 -41.378 1.14 15.08 11 -17.748 1.00 1.85478 24.8 14.94 12 27.023 3.30 1.49700 81.5 15.26 13 -78.691 0.15 15.71 14 63.292 4.74 1.91082 35.3 18.21 15 -25.839 0.15 19.59 16 -44.636 2.10 1.53110 55.9 20.04 17* -44.385 (variable) 21.14 18 -91.245 1.94 1.67790 55.3 25.80 19 -46.955 10.30 26.25 20 -23.866 1.57 1.51742 52.4 28.94 21 -45.889 10.50 31.60 Image plane ∞ Aspheric Data Page 17 K = 0.00000e+000 A 4= 2.83931e-005 A 6=-5.17075e-008 A 8= 1.49551e-009 A10=-1.23012e-011 A12= 3.69169e-014 Various data Focal length 24.60 F-number 1.85 Half angle of view (degrees) 41.3 Image height 19.32 Optical total length 73.00 BF 10.50 Infinity Close d17 2.00 14.96 Lens Group Data Group starting plane focal length FL 1 25.25 RL 18 -409.03 Single lens data Lens starting surface focal length 1 1 -32.40 2 3 32.25 3 5 20.13 4 6 -22.84 5 9 66.33 6 11 -12.40 7 12 40.90 8 14 20.67 9 16 3810.00 10 18 140.21 11 20 -98.50 [Numerical Example 6] Unit: mm Surface Data Surface number rd nd νd Effective diameter 1 83.021 1.50 1.51633 64.1 33.00 2 18.741 3.88 26.63 3 43.536 1.50 1.48749 70.2 26.33 4 22.900 10.50 24.12 5 26.464 5.00 1.90043 37.4 20.26 6 -129.459 2.04 19.88 7 -120.297 4.88 1.83481 42.7 19.02 8 -23.035 1.01 1.72825 28.5 18.51 9 201.055 1.70 17.82 10 (Aperture) ∞ 4.54 17.34 11 59.005 1.51 1.80400 46.5 15.74 12 1194.251 3.16 15.44 13 -19.019 1.05 1.85478 24.8 14.53 14 38.000 6.43 1.58313 59.4 21.00 15* -27.217 0.15 21.84 16 80.132 5.24 1.91082 35.3 27.50 17 -43.861 (variable) 28.33 18 -117.059 2.41 1.77250 49.6 29.26 19 -49.631 10.50 29.57 20 -23.346 1.50 1.51742 52.4 29.83 21 -53.345 (variable) 32.24 Image plane ∞ Aspheric Data Page 15 K = 0.00000e+000 A 4= 1.37287e-005 A 6= 7.17992e-009 A 8= 3.79205e-010 A10=-1.27723e-012 A12=-3.75238e-016 Various data Focal length 24.72 F-number 1.85 Half angle of view (degrees) 41.2 Image height 19.54 Optical total length 81.00 BF 11.01 Infinity Close d17 1.50 14.93 d21 11.01 15.41 Lens Group Data Group starting plane focal length FL 1 26.07 RL 18 -460.55 Single lens data Lens starting surface focal length 1 1 -47.25 2 3 -101.52 3 5 24.78 4 7 33.37 5 8 -28.32 6 11 77.16 7 13 -14.70 8 14 28.22 9 16 31.76 10 18 109.83 11 20 -81.63 The various values ​​in each numerical example are summarized in Table 1 below.

[0072] [Table 1]

[0073] [Imaging device] Next, an embodiment of a digital still camera (imaging device) using the optical system of the present invention as an imaging optical system will be described with reference to Fig. 13. In Fig. 13, 10 denotes a camera body, and 11 denotes an imaging optical system constituted by any of the optical systems L0 described in the first to sixth embodiments. 12 denotes a solid-state imaging element (photoelectric conversion element) such as a CCD sensor or a CMOS sensor that is built into the camera body and receives an optical image formed by the imaging optical system 11 and photoelectrically converts it. The camera body 10 may be a so-called single-lens reflex camera having a quick-turn mirror, or a so-called mirrorless camera having no quick-turn mirror.

[0074] In this way, by applying the optical system L0 of the present invention to an imaging device such as a digital still camera, it is possible to obtain an imaging device with a small lens. [Imaging system] An imaging system (surveillance camera system) may be configured including the optical system L0 of each embodiment and a control unit that controls the optical system L0. In this case, the control unit can control the optical system L0 so that each lens group moves as described above during focusing and image blur correction. In this case, the control unit does not need to be configured integrally with the optical system L0, and the control unit may be configured separately from the optical system L0. For example, a configuration may be adopted in which a control unit (control device) disposed remotely from a drive unit that drives each lens of the optical system L0 includes a transmission unit that sends a control signal (command) for controlling the optical system L0. With such a control unit, the optical system L0 can be remotely controlled.

[0075] In addition, the control unit may be provided with an operation unit such as a controller or buttons for remotely controlling the optical system L0, so that the optical system L0 is controlled in response to a user's input to the operation unit. For example, an infinity button and a close button may be provided as the operation unit. In this case, the control unit may be configured to send a signal to a drive unit of the optical system L0 so that when the user presses the infinity button, the object distance at which the optical system L0 focuses becomes larger, and when the user presses the close button, the object distance at which the optical system L0 focuses becomes smaller.

[0076] The imaging system may also have a display unit such as a liquid crystal panel that displays information (movement state) related to the object distance of the optical system L0. The information related to the object distance of the optical system L0 is, for example, the shooting magnification (focus position) and the movement amount (movement state) of each lens group. In this case, the user can remotely operate the optical system L0 via the operation unit while viewing the information related to the object distance of the optical system L0 displayed on the display unit. In this case, the display unit and the operation unit may be integrated by adopting, for example, a touch panel.

[0077] Although the preferred embodiments and examples of the present invention have been described above, the present invention is not limited to these embodiments and examples, and various combinations, modifications, and changes are possible within the scope of the gist of the present invention. [Explanation of symbols]

[0078] L0 optical system FL front group FL1 1st subgroup RL Rear group (negative lens group) IP image plane

Claims

1. An optical system comprising one or more lens groups arranged in order from the object side to the image side, the optical system comprising a front group having a positive refractive power as a whole and a negative lens group having a negative refractive power, the distance between adjacent lens groups changing during focusing, During focusing from infinity to a close distance, the distance on the optical axis between the lens surface of the front lens group closest to the image side and the lens surface of the negative lens group closest to the object side increases, and all of the lens groups disposed in the front lens group move toward the object side. the front group includes a first cemented lens, an aperture stop arranged on the image side of the first cemented lens, and a second cemented lens arranged on the image side of the aperture stop, the front group has a first subgroup having a negative refractive power and including all lenses that are arranged closer to the object side than a first positive lens that is arranged closest to the object side among the positive lenses included in the optical system, Let f be the focal length of the optical system when focused at infinity, fFL1 be the focal length of the first subgroup, Nave be the average refractive index of the first subgroup, x be the distance on the optical axis from the image side surface of the lens arranged closest to the object in the optical system to the object side surface of the first positive lens when focused at infinity, TTL be the distance on the optical axis from the lens surface closest to the object in the optical system to the image surface when focused at infinity, and BF be the back focus of the optical system when focused at infinity. -4.00<fFL1 / x<-0.95 1.40<Nave<1.65 0.25<BF / f<0.95 0.13<x / TTL<0.35 An optical system characterized in that the following condition is satisfied:

2. The optical system according to claim 1 , wherein the aperture stop is disposed closer to an image side than the first positive lens.

3. When the maximum refractive index of the positive lens included in the first cemented lens is Ndp and the minimum refractive index of the negative lens included in the first cemented lens is Ndn, 0.07<Ndp-Ndn<0.25 3. The optical system according to claim 1, wherein the following condition is satisfied:

4. An optical system comprising one or more lens groups arranged in order from the object side to the image side, the optical system comprising a front group having a positive refractive power as a whole and a negative lens group having a negative refractive power, the distance between adjacent lens groups changing during focusing, During focusing from infinity to a close distance, the distance on the optical axis between the lens surface of the front lens group closest to the image side and the lens surface of the negative lens group closest to the object side increases, and all of the lens groups disposed in the front lens group move toward the object side. the front group includes, in order from the object side to the image side, a first cemented lens and an aperture stop, the front group includes a first subgroup which is made up of all lenses arranged closer to the object side than a first positive lens which is arranged closest to the object side among the positive lenses included in the optical system, and which has a negative refractive power as a whole; Let f be the focal length of the optical system when focused at infinity, fFL1 be the focal length of the first subgroup, Nave be the average refractive index of the first subgroup, x be the distance on the optical axis from the image side surface of the lens arranged closest to the object in the optical system to the object side surface of the first positive lens when focused at infinity, TTL be the distance on the optical axis from the lens surface closest to the object in the optical system to the image surface when focused at infinity, BF be the back focus of the optical system when focused at infinity, Ndp be the maximum refractive index of the positive lens included in the first cemented lens, and Ndn be the minimum refractive index of the negative lens included in the first cemented lens. -4.00<fFL1 / x<-0.95 1.40<Nave<1.65 0.25<BF / f<0.95 0.13<x / TTL<0.35 0.07<Ndp-Ndn<0.25 An optical system characterized in that the following condition is satisfied:

5. When the maximum Abbe number of the positive lens included in the second cemented lens is νdp and the minimum Abbe number of the negative lens included in the second cemented lens is νdn, 25<νdp−νdn<70 4. The optical system according to claim 1, wherein the following condition is satisfied:

6. 6. The optical system according to claim 1, wherein the front group includes at least one aspheric lens on the image side of the first subgroup.

7. An optical system comprising one or more lens groups arranged in order from the object side to the image side, the optical system comprising a front group having a positive refractive power as a whole and a negative lens group having a negative refractive power, the distance between adjacent lens groups changing during focusing, During focusing from infinity to a close distance, the distance on the optical axis between the lens surface of the front lens group closest to the image side and the lens surface of the negative lens group closest to the object side increases, and all of the lens groups disposed in the front lens group move toward the object side. the front group has a first subgroup having a negative refractive power and including all lenses that are arranged closer to the object side than a first positive lens that is arranged closest to the object side among the positive lenses included in the optical system, the front group includes at least one aspheric lens on the image side of the first subgroup, Let f be the focal length of the optical system when focused at infinity, fFL1 be the focal length of the first subgroup, Nave be the average refractive index of the first subgroup, x be the distance on the optical axis from the image side surface of the lens arranged closest to the object in the optical system to the object side surface of the first positive lens when focused at infinity, TTL be the distance on the optical axis from the lens surface closest to the object in the optical system to the image surface when focused at infinity, and BF be the back focus of the optical system when focused at infinity. -4.00<fFL1 / x<-0.95 1.40<Nave<1.65 0.25<BF / f<0.95 0.13<x / TTL<0.35 An optical system characterized in that the following condition is satisfied:

8. 8. The optical system according to claim 1, wherein the negative lens group includes a positive lens and a negative lens.

9. Let φr be the maximum effective diameter of the lens located closest to the image side of the optical system, and φmax be the maximum effective diameter of the lenses included in the optical system. 0.63<φr / φmax≦1.00 9. The optical system according to claim 1, wherein the following condition is satisfied:

10. Let φf be the maximum effective diameter of the lens arranged closest to the object side of the optical system, and φr be the maximum effective diameter of the lens arranged closest to the image side of the optical system. 0.7<φf / φr<1.3 10. The optical system according to claim 1, wherein the following condition is satisfied:

11. 0.06<BF / TTL<0.35 11. The optical system according to claim 1, wherein the following condition is satisfied:

12. -2.0<fFL1 / f<-0.1 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 number of lenses included in the first subgroup is two or less.

14. 14. The optical system according to claim 1, wherein the first partial group and the first positive lens are arranged to be separated by a maximum air gap in the front group.

15. 15. The optical system according to claim 1, wherein the lens in the first subgroup arranged closest to the object side is a negative meniscus lens having a concave surface facing the image surface side.

16. 16. The optical system according to claim 1, wherein the first positive lens has a lens surface on the object side that is a convex surface.

17. When the focal length of the negative lens group is fRL, -22<fRL / f<-5 17. The optical system according to claim 1, wherein the following condition is satisfied:

18. An optical system comprising one or more lens groups arranged in order from the object side to the image side, the optical system comprising a front group having a positive refractive power as a whole and a negative lens group having a negative refractive power, the distance between adjacent lens groups changing during focusing, During focusing from infinity to a close distance, the distance on the optical axis between the lens surface of the front lens group closest to the image side and the lens surface of the negative lens group closest to the object side increases, and all of the lens groups disposed in the front lens group move toward the object side. the front group has a first subgroup having a negative refractive power and including all lenses that are arranged closer to the object side than a first positive lens that is arranged closest to the object side among the positive lenses included in the optical system, Let f be the focal length of the optical system when focused at infinity, fFL1 be the focal length of the first subgroup, Nave be the average refractive index of the first subgroup, x be the distance on the optical axis from the image side surface of the lens arranged closest to the object in the optical system to the object side surface of the first positive lens when focused at infinity, TTL be the distance on the optical axis from the lens surface closest to the object in the optical system to the image surface when focused at infinity, BF be the back focus of the optical system when focused at infinity, and fRL be the focal length of the negative lens group. -4.00<fFL1 / x<-0.95 1.40<Nave<1.65 0.25<BF / f<0.95 0.13<x / TTL<0.35 -22<fRL / f<-5 An optical system characterized in that the following condition is satisfied:

19. When the third-order distortion coefficient of the optical system at infinity focus is V, 0.2<V<0.6 19. The optical system according to claim 1, wherein the following condition is satisfied:

20. An optical system comprising one or more lens groups arranged in order from the object side to the image side, the optical system comprising a front group having a positive refractive power as a whole and a negative lens group having a negative refractive power, the distance between adjacent lens groups changing during focusing, During focusing from infinity to a close distance, the distance on the optical axis between the lens surface of the front lens group closest to the image side and the lens surface of the negative lens group closest to the object side increases, and all of the lens groups disposed in the front lens group move toward the object side. the front group has a first subgroup having a negative refractive power and including all lenses that are arranged closer to the object side than a first positive lens that is arranged closest to the object side among the positive lenses included in the optical system, Let f be the focal length of the optical system when focused at infinity, fFL1 be the focal length of the first subgroup, Nave be the average refractive index of the first subgroup, x be the distance on the optical axis from the image side surface of the lens arranged closest to the object in the optical system to the object side surface of the first positive lens when focused at infinity, TTL be the distance on the optical axis from the lens surface closest to the object in the optical system to the image surface when focused at infinity, BF be the back focus of the optical system when focused at infinity, and V be the third-order distortion aberration coefficient of the optical system when focused at infinity. -4.00<fFL1 / x<-0.95 1.40<Nave<1.65 0.25<BF / f<0.95 0.13<x / TTL<0.35 0.2<V<0.6 An optical system characterized in that the following condition is satisfied:

21. When the maximum half angle of view of the optical system when focused at infinity is ω and the amount of distortion of the optical system when focused at infinity at the maximum half angle of view is dist(ω), -20<dist(ω)<-5 21. The optical system according to claim 1, wherein the following condition is satisfied:

22. An optical system comprising one or more lens groups arranged in order from the object side to the image side, the optical system comprising a front group having a positive refractive power as a whole and a negative lens group having a negative refractive power, the distance between adjacent lens groups changing during focusing, During focusing from infinity to a close distance, the distance on the optical axis between the lens surface of the front lens group closest to the image side and the lens surface of the negative lens group closest to the object side increases, and all of the lens groups disposed in the front lens group move toward the object side. the front group has a first subgroup having a negative refractive power and including all lenses that are arranged closer to the object side than a first positive lens that is arranged closest to the object side among the positive lenses included in the optical system, When the focal length of the optical system when focused at infinity is f, the focal length of the first subgroup is fFL1, the average refractive index of the first subgroup is Nave, the distance on the optical axis from the image side surface of the lens arranged closest to the object in the optical system when focused at infinity to the object side surface of the first positive lens is x, the distance on the optical axis from the lens surface closest to the object in the optical system to the image surface when focused at infinity is TTL, the back focus of the optical system when focused at infinity is BF, the maximum half angle of view of the optical system when focused at infinity is ω, and the amount of distortion aberration of the optical system when focused at infinity at the maximum half angle of view is dist(ω), -4.00<fFL1 / x<-0.95 1.40<Nave<1.65 0.25<BF / f<0.95 0.13<x / TTL<0.35 -20<dist(ω)<-5 An optical system characterized in that the following condition is satisfied:

23. An optical system according to any one of claims 1 to 22; and a storage unit for storing information on an amount of distortion relating to an image formed by the optical system.

24. An optical system according to any one of claims 1 to 23, and an image sensor that receives an image formed by the optical system.

Images