Optical system and image pickup apparatus

Abstract

The invention discloses an optical system and an image pickup apparatus. The optical system includes, in order from an object side to an image side, a front group having a positive refractive power and including at least one lens unit, an intermediate lens unit having a positive refractive power, and a rear group having a negative refractive power and including at least one lens unit. The distance between adjacent lens units varies during focusing. The intermediate lens unit moves toward the object side during focusing from infinity to a close distance. The front group includes at least two positive lenses and at least one negative lens. The rear group includes at least one aspheric lens having an aspheric surface with a pole at a position separated from the optical axis.

Description

Technical Field

[0001] The present disclosure relates to an optical system suitable for imaging. Background Art

[0002] As an optical system having a large aperture diameter, reduced size, and high optical performance and capable of focusing, Japanese Unexamined Patent Application Publication No. 2019-148680 discloses an optical system including, in order from the object side to the image side, a front group having a positive refractive power, an aperture stop, and a rear group having a positive refractive power. Summary of the Invention

[0003] An optical system according to one aspect of the present disclosure includes, in order from the object side to the image side: a front group having a positive refractive power and including at least one lens unit, an intermediate lens unit having a positive refractive power, and a rear group having a negative refractive power and including at least one lens unit, or includes, in order from the object side to the image side: a front group having a positive refractive power, an intermediate lens unit, and a rear group including at least one lens unit. The distance between adjacent lens units changes during focusing. The intermediate lens unit moves toward the object side during focusing from infinity to a short distance. The front group includes at least two positive lenses and at least one negative lens. The rear group includes at least one aspherical lens having an aspherical surface with a vertex located at a position separated from the optical axis. An imaging device having the above optical system also constitutes another aspect of the present disclosure.

[0004] Other features of various embodiments of the present disclosure will become apparent from the following description of the embodiments with reference to the accompanying drawings. Brief Description of the Drawings

[0005] Figure 1 A cross-sectional view of the optical system according to Example 1 is shown.

[0006] [[ID=2,5]] Figure 2 Longitudinal and lateral aberration diagrams of the optical system according to Example 1 in a focused state at infinity (with respect to an object) are shown.

[0007] Figure 3 A cross-sectional view of the optical system according to Example 2 is shown.

[0008] Figure 4 Longitudinal and lateral aberration diagrams of the optical system according to Example 2 in a focused state at infinity are shown.

[0009] Figure 5 A cross-sectional view of the optical system according to Example 3 is shown.

[0010] Figure 6 Longitudinal and lateral aberration diagrams of the optical system according to Example 3 in a focused state at infinity are shown.

[0011] Figure 7Shows a cross-sectional view of the optical system according to Example 4.

[0012] Figure 8 Shows the longitudinal and lateral aberration diagrams of the optical system according to Example 4 in the infinite focus state.

[0013] Figure 9 Shows a cross-sectional view of the optical system according to Example 5.

[0014] Figure 10 Shows the longitudinal and lateral aberration diagrams of the optical system according to Example 5 in the infinite focus state.

[0015] Figure 11 Shows a cross-sectional view of the optical system according to Example 6.

[0016] Figure 12 Shows the longitudinal and lateral aberration diagrams of the optical system according to Example 6 in the infinite focus state.

[0017] Figure 13 Shows a cross-sectional view of the optical system according to Example 7.

[0018] Figure 14 Shows the longitudinal and lateral aberration diagrams of the optical system according to Example 7 in the infinite focus state.

[0019] Figure 15 Shows a cross-sectional view of the optical system according to Example 8.

[0020] Figure 16 Shows the longitudinal and lateral aberration diagrams of the optical system according to Example 8 in the infinite focus state.

[0021] Figure 17 Shows a cross-sectional view of the optical system according to Example 9.

[0022] Figure 18 Shows the longitudinal and lateral aberration diagrams of the optical system according to Example 9 in the infinite focus state.

[0023] Figure 19 Shows a cross-sectional view of the optical system according to Example 10.

[0024] Figure 20 Shows the longitudinal and lateral aberration diagrams of the optical system according to Example 10 in the infinite focus state.

[0025] Figure 21 Shows an imaging device having an optical system according to any one of Examples 1 to 10. Detailed Description

[0026] A description of examples according to the present disclosure will now be given with reference to the accompanying drawings.Figure 1 , Figure 3 , Figure 5 , Figure 7 , Figure 9 , Figure 11 , Figure 13 , Figure 15 , Figure 17 and Figure 19 respectively show cross - sections of the optical systems according to Examples 1 to 10. In each figure, the left side is the object side (front side) and the right side is the image side (rear side).

[0027] Before the detailed description of Examples 1 to 10, a description of matters common to each example will now be given. The optical systems according to each example are used in various imaging devices such as digital video cameras, digital still cameras, broadcast cameras, film - based cameras, and surveillance cameras.

[0028] The optical systems according to each example include a plurality of lens units. These lens units include, in order from the object side to the image side: a front group Lf including at least one lens unit, an intermediate lens unit Lm, and a rear group Lr including at least one lens unit. A lens unit is a group of one or more lenses that move as a whole or remain stationary during focusing. In other words, the distance between adjacent lens units changes during focusing.

[0029] Ln represents a negative lens arranged in the front group Lf, and LP1 and LP2 represent positive lenses arranged in the front group Lf. SP represents the aperture stop (iris). IP represents the (paraxial) image plane. The imaging surface (light - receiving surface) of a solid - state image sensor such as a CCD sensor or a CMOS sensor or the emulsion surface (photosensitive surface) of a silver film is arranged on the image plane IP.

[0030] A glass block having no refractive power, such as a cover glass or an IR - cut filter, may be arranged between the lens surface closest to the object and the image plane in the optical system.

[0031] In the optical systems according to each example, the front group Lf has a positive refractive power, the intermediate lens unit Lm has a positive refractive power, and the rear group Lr has a negative refractive power. This telephoto - type refractive - power configuration can reduce the overall length of the optical system. The refractive power of each lens unit and each lens represents the refractive power at the paraxial position and corresponds to the reciprocal of the focal length.

[0032] In the optical system according to each example, the intermediate lens unit Lm moves toward the object side during focusing from infinity to a close distance. This configuration can converge the light beam at the front group Lf, thereby reducing the diameter of the light beam incident on the intermediate lens unit Lm and the weight of the focusing mechanism for moving the intermediate lens unit Lm. In each figure, below the lens unit that moves during focusing, the moving direction of the lens unit during focusing from infinity to a close distance is indicated by a dashed arrow.

[0033] In the optical system according to each example, the front group Lf includes at least two positive lenses LP1 and LP2 and at least one negative lens Ln. This configuration can satisfactorily correct chromatic aberration. In the case where two lenses are joined together to form a joined lens, the number of lenses is counted as two.

[0034] The rear group Lr includes at least one aspherical lens La(Lb) having an aspherical surface whose pole is located at a position separated from the optical axis (hereinafter referred to as the periphery). This aspherical lens provides a refractive power difference between the central light beam and the peripheral light beam, thereby satisfactorily correcting the sagittal coma flare.

[0035] The pole is defined as the point on the lens surface where the tangent plane of the lens surface is perpendicular to the optical axis within the effective diameter.

[0036] The optical system according to each example having the above configuration has a reduced size, high optical performance, and a large aperture diameter, and can perform high-speed focusing (autofocus: AF).

[0037] In the optical system according to each embodiment, TTL is the total optical length (hereinafter referred to as the total lens length), which is the distance on the optical axis from the lens surface closest to the object (the frontmost) of the optical system to the lens surface closest to the image surface (the final surface) of the optical system plus the back focal length. The back focal length is the air equivalent length on the optical axis from the final surface of the optical system to the image surface IP. f is the focal length of the optical system, and ω is the half field of view (°). In this case, the optical system according to each embodiment can satisfy the following inequality (1):

[0038] 3.0 ≤ TTL / (f×tanω) ≤ 10.0 (1)

[0039] Inequality (1) defines an appropriate relationship between the total lens length and the image height of the optical system. When TTL / (f×tanω) becomes higher than the upper limit of inequality (1), the total lens length increases. When the total lens length decreases such that TTL / (f×tanω) becomes lower than the lower limit of inequality (1), the refractive power of each lens increases, and it becomes difficult to correct the curvature of field and distortion.

[0040] The optical system according to each example can satisfy the following inequality (2):

[0041] 1.50 ≤ PNdave ≤ 2.00 (2)

[0042] Wherein, PNdave is the average value of the refractive indices of the d-lines (wavelength 587.56 nm) of all the positive lenses included in the optical system (of the material).

[0043] Inequality (2) defines an appropriate average refractive index of all the positive lenses included in the optical system. When the average refractive index increases such that PNdave becomes higher than the upper limit of inequality (2), the dispersion increases, and it becomes difficult to correct the longitudinal chromatic aberration. When the average refractive index decreases such that PNdave becomes lower than the lower limit of inequality (2), the Petzval sum of the entire system increases, and it becomes difficult to correct the curvature of field.

[0044] The optical system according to each example can satisfy the following inequality (3):

[0045] 0.01 ≤ sk / TTL ≤ 0.50 (3)

[0046] Wherein, sk is the back focal length.

[0047] Inequality (3) defines an appropriate relationship between the back focal length and the total lens length. When sk / TTL becomes higher than the upper limit of inequality (3), the total lens length increases. When the back focal length is short such that sk / TTL becomes lower than the lower limit of inequality (3), the effective diameter of the lens arranged on the image side increases, and the size of the optical system increases in the radial direction.

[0048] The optical system according to each example can satisfy the following inequality (4):

[0049] 2.0 ≤ ff / sk ≤ 10.0 (4)

[0050] Wherein, ff is the focal length of the front group Lf.

[0051] Inequality (4) defines an appropriate relationship between the front focal length and the back focal length of the front group Lf. In the case where the refractive power of the front group Lf increases such that ff / sk becomes lower than the lower limit of inequality (4), the Petzval sum of the entire system increases, and it becomes difficult to correct field curvature and chromatic aberration. In the case where the refractive power of the front group Lf decreases such that ff / sk becomes higher than the upper limit of inequality (4), there is a deviation from the telephoto refractive power configuration, and the total lens length increases.

[0052] The optical system according to each example can satisfy the following inequality (5):

[0053] 0.1 ≤ -fm / fr ≤ 1.0 (5)

[0054] where fm is the focal length of the intermediate lens unit Lm, and fr is the focal length of the rear group Lr.

[0055] Inequality (5) defines an appropriate relationship between the focal length of the intermediate lens unit Lm and the focal length of the rear group Lr. In the case where the refractive power of the rear group Lr decreases such that -fm / fr becomes lower than the lower limit of inequality (5), the lens deviates from the telephoto refractive power configuration, and the total lens length increases. In the case where the refractive power of the rear group Lr increases such that -fm / fr becomes higher than the upper limit of inequality (5), the incident angle of off-axis light on the image plane increases, and the peripheral light loss called vignetting becomes significant.

[0056] The optical system according to each example can satisfy the following inequality (6):

[0057] 0.1≤Df / f≤1.0 (6)

[0058] where Df is the distance on the optical axis between the front group Lf and the intermediate lens unit Lm.

[0059] Inequality (6) defines an appropriate relationship between the distance between the front group Lf and the intermediate lens unit Lm and the focal length of the optical system. In the case where Df decreases such that Df / f becomes lower than the lower limit of inequality (6), the amount of movement of the intermediate lens unit Lm during focusing decreases, and short-distance imaging becomes difficult. In the case where Df increases such that Df / f becomes higher than the upper limit of inequality (6), the total lens length increases.

[0060] The optical system according to each example can satisfy the following inequality (7):

[0061] 0.1≤-ff / fr≤2.0 (7)

[0062] Inequality (7) defines an appropriate relationship between the focal length of the front group Lf and the focal length of the rear group Lr. In the case where the refractive power of the rear group Lr is decreased such that -ff / fr becomes lower than the lower limit of inequality (7), the refractive power configuration shifts relative to the telephoto type, and the total lens length increases. In the case where the refractive power of the rear group Lr is increased such that -ff / fr becomes higher than the upper limit of inequality (7), the incident angle of off-axis light on the image plane increases, and the shading becomes significant.

[0063] In the case where LP1 represents the positive lens having the largest Abbe number based on the d-line among all the positive lenses included in the front group Lf, the optical system according to each example can satisfy the following inequality (8):

[0064] 55 ≤ νdp1 ≤ 97 (8)

[0065] where νdp1 is the Abbe number of the positive lens LP1 based on the d-line.

[0066] Inequality (8) defines an appropriate range for the Abbe number of the positive lens LP1. In the case where the Abbe number of the positive lens LP1 is decreased such that νdp1 becomes lower than the lower limit of inequality (8), the dispersion increases and it becomes difficult to correct chromatic aberration. In the case where the Abbe number of the positive lens LP1 is increased such that νdp1 becomes higher than the upper limit of inequality (8), a glass material cannot be selected.

[0067] In the case where LP2 represents the positive lens having the smallest Abbe number based on the d-line among all the positive lenses included in the front group Lf, the optical system according to each example can satisfy the following inequality (9):

[0068] 15 ≤ νdp2 ≤ 40 (9)

[0069] where νdp2 is the Abbe number of the positive lens LP2 based on the d-line.

[0070] Inequality (9) defines an appropriate range for the Abbe number of the positive lens LP2. In the case where the Abbe number of the positive lens LP2 is decreased such that νdp2 becomes lower than the lower limit of inequality (9), a glass material cannot be selected. In the case where the Abbe number of the positive lens LP2 is increased such that νdp2 becomes higher than the upper limit of inequality (9), the anomalous partial dispersion decreases, and it becomes difficult to correct chromatic aberration on the short wavelength side.

[0071] In the case where Ln represents the negative lens closest to the object among all the negative lenses included in the front group Lf, the optical system according to each example can satisfy the following inequality (10):

[0072] 15 ≤ vdn ≤ 40 (10)

[0073] Among them, νdn is the Abbe number of the negative lens Ln with respect to the d-line as a reference.

[0074] Inequality (10) defines an appropriate range of the Abbe number of the negative lens Ln. When the Abbe number of the negative lens Ln decreases such that νdn becomes lower than the lower limit of inequality (10), a glass material cannot be selected. When the Abbe number of the negative lens Ln increases such that νdn becomes higher than the upper limit of inequality (10), it becomes difficult to correct chromatic aberration.

[0075] In the optical system according to each example, the negative lens Ln included in the front group Lf may have a biconcave shape to satisfactorily correct spherical aberration.

[0076] The optical system according to each example may satisfy the following inequality (11) to satisfactorily correct field curvature and distortion:

[0077] 0 < Ra1 / f

[0078] 0 < Ra2 / f (11)

[0079] Among them, Ra1 is the paraxial curvature radius of the object-side lens surface of the aspherical lens La, and Ra2 is the paraxial curvature radius of the image-side lens surface of the aspherical lens La.

[0080] The optical system according to each example may satisfy the following inequality (12) to satisfactorily correct field curvature and chromatic aberration:

[0081] 1.44 ≤ Nda ≤ 1.77 (12)

[0082] Among them, Nda is the refractive index of the d-line of the aspherical lens La.

[0083] The optical system according to each example may include an aspherical lens Lb in the rear group Lr and satisfy the following inequality (13) to satisfactorily correct field curvature and distortion:

[0084] Rb1 / f < 0

[0085] Rb2 / f < 0 (13)

[0086] Among them, Rb1 is the paraxial curvature radius of the object-side lens surface of the aspherical lens Lb, and Rb2 is the paraxial curvature radius of the image-side lens surface of the aspherical lens Lb.

[0087] In the optical system according to each example, the aspherical lens Lb may have poles at the periphery to satisfactorily reduce the sagittal coma spot.

[0088] Inequalities (1) to (13) can be replaced by the following inequalities (1a) to (13a):

[0089] 4.0 ≤ TTL / (f × tan ω) ≤ 7.0 (1a)

[0090] 1.60 ≤ PNdave ≤ 1.90 (2a)

[0091] 0.05 ≤ sk / TTL ≤ 0.30 (3a)

[0092] 3.0 ≤ ff / sk ≤ 8.0 (4a)

[0093] 0.3 ≤ -fm / fr ≤ 0.7 (5a)

[0094] 0.2 ≤ Df / f ≤ 0.5 (6a)

[0095] 0.5 ≤ -ff / fr ≤ 1.5 (7a)

[0096] 60 ≤ νdp1 ≤ 96 (8a)

[0097] 16 ≤ νdp2 ≤ 30 (9a)

[0098] 18 ≤ νdn ≤ 30 (10a)

[0099] 0.5 ≤ Ra1 / f ≤ 10.0

[0100] 0.2 ≤ Ra2 / f ≤ 10.0 (11a)

[0101] 1.500 ≤ Nda ≤ 1.728 (12a)

[0102] -10.0 ≤ Rb1 / f ≤ -0.1

[0103] -10.0 ≤ Rb2 / f ≤ -0.1 (13a)

[0104] Inequalities (1) to (13) can be replaced by the following inequalities (1b) to (13b):

[0105] 5.0 ≤ TTL / (f × tan ω) ≤ 6.0 (1b)

[0106] 1.70 ≤ PNdave ≤ 1.85 (2b)

[0107] 0.09 ≤ sk / TTL ≤ 0.15 (3b)

[0108] 4.0 ≤ ff / sk ≤ 7.0 (4b)

[0109] 0.40 ≤ -fm / fr ≤ 0.60(5b)

[0110] 0.3 ≤ Df / f ≤ 0.4 (6b)

[0111] 0.7 ≤ -ff / fr ≤ 1.0 (7b)

[0112] 65 ≤ νdp1 ≤ 95 (8b)

[0113] 17 ≤ νdp2 ≤ 25 (9b)

[0114] 20 ≤ νdn ≤ 28 (10b)

[0115] 0.8 ≤ Ra1 / f ≤ 2.0

[0116] 0.4 ≤ Ra2 / f ≤ 0.5 (11b)

[0117] 1.55 ≤ Nda ≤ 1.70 (12b)

[0118] -1.0 ≤ Rb1 / f ≤ -0.2

[0119] -1.0 ≤ Rb2 / f ≤ -0.2 (13b)

[0120] The optical systems according to Examples 1 to 10 will now be described in detail.

[0121] In the optical system according to Example 1, the front group Lf includes the first lens unit L1. The first lens unit L1 includes, in order from the object side to the image side, a biconcave negative lens Ln, a positive lens, a cemented lens of a positive lens and a negative lens LP2, a cemented lens of a positive lens and a negative lens, and a cemented lens of a positive lens LP1 and a negative lens. The aperture stop SP is disposed between the first lens unit L1 and the second lens unit L2 serving as an intermediate lens unit Lm.

[0122] The second lens unit L2 includes, in order from the object side to the image side, a cemented lens of a negative lens and a positive lens and a cemented lens of a positive lens and a negative lens. The rear group Lr includes the third lens unit L3. The third lens unit L3 includes, in order from the object side to the image side, an aspherical lens Lb, an aspherical lens La, and a positive lens.

[0123] In the optical systems according to Examples 2, 3, 4, and 6, the front group Lf includes the first lens unit L1. The first lens unit L1 includes, in order from the object side to the image side, a biconcave negative lens Ln, a positive lens LP2, a cemented lens of a positive lens and a negative lens, and a cemented lens of a positive lens LP1 and a negative lens. The aperture stop SP is disposed between the first lens unit L1 and the second lens unit L2 serving as an intermediate lens unit Lm.

[0124] The second lens unit L2 includes, in order from the object side to the image side, a cemented lens of a negative lens and a positive lens and a cemented lens of a positive lens and a negative lens. The rear group Lr includes a third lens unit L3. The third lens unit L3 includes, in order from the object side to the image side, an aspherical lens Lb, an aspherical lens La, and a positive lens.

[0125] In the optical system according to Example 5, the front group Lf includes a first lens unit L1 and a second lens unit L2. The first lens unit L1 includes, in order from the object side to the image side, a biconcave negative lens Ln, a positive lens LP2, and a cemented lens of a positive lens and a negative lens. The second lens unit L2 includes a cemented lens of a positive lens LP1 and a negative lens. The second lens unit L2 moves toward the image side during focusing from infinity to a short distance. The aperture stop SP is disposed between the second lens unit L2 and the third lens unit L3 which serves as an intermediate lens unit Lm.

[0126] In the optical system according to Example 5, the front group Lf includes a first lens unit L1 and a second lens unit L2. The first lens unit L1 includes, in order from the object side to the image side, a biconcave negative lens Ln, a positive lens LP2, and a cemented lens of a positive lens and a negative lens. The second lens unit L2 includes a cemented lens of a positive lens LP1 and a negative lens. The aperture stop SP is disposed between the second lens unit L2 and the third lens unit L3 which serves as an intermediate lens unit Lm.

[0127] The third lens unit L3 includes, in order from the object side to the image side, a cemented lens of a negative lens and a positive lens and a cemented lens of a positive lens and a negative lens. The rear group Lr includes a fourth lens unit L4. The fourth lens unit L4 includes, in order from the object side to the image side, an aspherical lens Lb, an aspherical lens La, and a positive lens.

[0128] In the optical system according to Example 7, the front group Lf includes a first lens unit L1. The first lens unit L1 includes, in order from the object side to the image side, a biconcave negative lens Ln, a positive lens LP2, a cemented lens of a positive lens and a negative lens, and a cemented lens of a positive lens LP1 and a negative lens. The aperture stop SP is disposed between the first lens unit L1 and the second lens unit L2 which serves as an intermediate lens unit Lm.

[0129] The second lens unit L2 includes, in order from the object side to the image side, a cemented lens of a negative lens and a positive lens and a cemented lens of a positive lens and a negative lens. The rear group Lr includes a third lens unit L3 and a fourth lens unit L4. The third lens unit L3 includes, in order from the object side to the image side, an aspherical lens Lb and an aspherical lens La. The third lens unit L3 moves toward the image side during focusing from infinity to a short distance. The fourth lens unit L4 includes a positive lens.

[0130] In the optical systems according to Examples 8 and 9, the front group Lf includes a first lens unit L1. The first lens unit L1 includes, in order from the object side to the image side, a positive lens, a biconcave negative lens Ln, a positive lens, a positive lens LP2, a cemented lens of a positive lens and a negative lens, and a cemented lens of a positive lens LP1 and a negative lens. The aperture stop SP is disposed between the first lens unit L1 and the second lens unit L2 serving as an intermediate lens unit Lm.

[0131] The second lens unit L2 includes, in order from the object side to the image side, a cemented lens of a negative lens and a positive lens and a cemented lens of a positive lens and a negative lens. The rear group Lr includes a third lens unit L3. The third lens unit L3 includes, in order from the object side to the image side, an aspherical lens Lb and an aspherical lens La.

[0132] In the optical system according to Example 10, the front group Lf includes a first lens unit L1. The first lens unit L1 includes, in order from the object side to the image side, a biconcave negative lens Ln, a positive lens, a positive lens LP2, a cemented lens of a positive lens and a negative lens, and a cemented lens of a positive lens LP1 and a negative lens. The aperture stop SP is disposed between the first lens unit L1 and the second lens unit L2 serving as an intermediate lens unit Lm.

[0133] The second lens unit L2 includes, in order from the object side to the image side, a cemented lens of a negative lens and a positive lens and a cemented lens of a positive lens and a negative lens. The rear group Lr includes a third lens unit L3. The third lens unit L3 includes, in order from the object side to the image side, an aspherical lens Lb, an aspherical lens La, and a negative lens.

[0134] In Examples 1 to 10, the front group and the intermediate lens unit each have positive refractive power and the rear group has negative refractive power, but the front group may have negative refractive power, or the intermediate lens unit may have negative refractive power. The rear group may have positive refractive power. In other words, the combination of positive and negative refractive powers in the front group, the intermediate group, and the rear group is not limited. In Examples 1 to 10, the intermediate lens unit moves toward the object side during focusing from infinity to a close distance, but it may also move toward the image side. In other words, the moving direction of the intermediate lens unit is not limited. The front group may include at least two positive lenses and at least two negative lenses. In these cases, at least one of Inequalities (1) to (13) can be satisfied.

[0135] Descriptions of Numerical Examples 1 to 10 corresponding to Examples 1 to 10 will now be given. In the surface data of each example, the surface number m indicates the order of the surface counted from the object side. r represents the radius of curvature (mm) of the m-th surface, and d (mm) represents the distance on the optical axis between the m-th surface and the (m + 1)-th surface. nd represents the refractive index of the d-line of the optical material between the m-th surface and the (m + 1)-th surface, and νd represents the Abbe number based on the d-line of the optical material. The Abbe number νd based on the d-line is expressed as follows:

[0136] νd = (Nd - 1) / (NF - NC)

[0137] where Nd, NF, and NC are the refractive indices of the d-line, F-line (wavelength 486.13 nm), and C-line (wavelength 656.27 nm) in the Fraunhofer lines. The effective diameter (mm) indicates the diameter of the region through which the light rays contributing to imaging on the optical surface pass.

[0138] In each numerical example, the focal length (mm), F-number, and half angle of view (°) are values when the optical system is focused on an object at infinity. BK and the total lens length correspond to the back focal length sk and the total optical length TTL, respectively.

[0139] The asterisk "*" next to the surface number means that the surface has an aspherical shape. The aspherical shape is represented by the following equation:

[0140]

[0141] where X is the displacement amount from the surface vertex in the optical axis direction, H is the height from the optical axis in the direction perpendicular to the optical axis, the light traveling direction is positive, R is the paraxial radius of curvature, K is the conic constant, and A3 to A14 are the aspherical coefficients. "e±x" in the conic constant and aspherical coefficients means "×10 ±x ".

[0142] Figure 2 , Figure 4 , Figure 6 , Figure 8 , Figure 10 , Figure 12 , Figure 14 , Figure 16 , Figure 18 and Figure 20Longitudinal aberrations (spherical aberration, astigmatism, distortion, and chromatic aberration) and lateral aberrations of the optical systems according to Numerical Examples 1 to 10 in an infinitely focused state are shown respectively. In the spherical aberration diagram, Fno represents the F-number. The solid line indicates the amount of spherical aberration for the d-line, and the two-dot chain line indicates the amount of spherical aberration for the g-line (wavelength of 435.8 nm). In the astigmatism diagram, the solid line S indicates the amount of astigmatism on the sagittal image plane, and the dashed line M indicates the amount of astigmatism on the meridional image plane. The distortion diagram shows the amount of distortion for the d-line. The chromatic aberration diagram shows the lateral chromatic aberration for the g-line. ω is the semi-field angle (°).

[0143] The lateral aberration diagram shows the amount of lateral aberration for the d-line. The solid line M indicates the amount of lateral aberration on the meridional section, and the dashed line S indicates the amount of lateral aberration on the sagittal section.

[0144] Numerical Example 1

[0145] Unit: mm

[0146]

[0147]

[0148] Aspherical data

[0149] The 17th surface

[0150] K = 0.00000e+00 A4 = 5.37646e-05 A6 = 1.55863e-06 A8 = 6.05348e-09 A10 = 1.82198e-12

[0151] A3 = -1.65820e-04 A5 = -1.24402e-05 A7 = -1.24659e-07 A9 = -1.62280e-10 The 20th surface

[0152] K = -4.27441e+00 A4 = 1.78716e-05 A6 = -6.05510e-06 A8 = -2.51039e-08 A10 = -6.98524e-12

[0153] A3 = 5.33362e-04 A5 = 3.06426e-05 A7 = 5.26407e-07 A9 = 6.44512e-10 The 21st surface

[0154] K = -4.40654e+00 A4 = 6.44848e-04 A6 = 9.25388e-06 A8 = 2.81051e-08 A10 = 9.86621e-12

[0155] A 3 = -3.46691e-04 A 5 = -9.85179e-05 A 7 = -6.15848e-07 A 9 = -7.80055e-10 The 22nd surface

[0156] K = 0.00000e+00 A 4 = 5.80061e-04 A 6 = 7.76706e-06 A 8 = -6.95980e-08 A10 = -1.91328e-10 A12 = -1.81766e-14

[0157] A 3 = -1.22295e-04 A 5 = -1.17096e-04 A 7 = 1.86177e-07 A 9 = 5.23501e-09 A11 = 3.30660e-12

[0158] The 23rd surface

[0159] K = 0.00000e+00 A 4 = -2.19737e-04 A 6 = -1.00699e-05 A 8 = -1.69644e-07 A10 = -4.30350e-10 A12 = -9.61000e-14

[0160] A 3 = 7.95396e-04 A 5 = 3.69643e-05 A 7 = 1.67386e-06 A 9 = 1.08448e-08 A11 = 9.72341e-12

[0161]

[0162]

[0163] Lens unit data

[0164] Numerical example 2 Unit: mm Surface data

[0165]

[0166] Aspherical data

[0167] The 15th surface

[0168] K = 0.00000e+00 A 4 = 3.32972e-05 A 6 = 1.11752e-06 A 8 = 4.14369e-09 A10 = 1.04564e-12

[0169] A 3=-1.00111e-04A 5=-8.89535e-06A 7=-8.84820e-08A 9=-1.04206e-10The 18th face

[0170] K=-5.88757e+00A 4=-2.71472e-04A 6=-1.48622e-05A 8=-5.67023e-08A10=-1.61539e-11

[0171] A 3=7.95535e-04A 5=9.96883e-05A 7=1.20415e-06A 9=1.46692e-09The 19th face

[0172] K=-3.35640e+00A 4=6.15817e-04A 6=1.66019e-06A 8=-8.55019e-09A10=-5.05019e-14

[0173] A 3=-1.43247e-04A 5=-6.16012e-05A 7=1.05295e-07A 9=1.76563e-10The 20th face

[0174] K=0.00000e+00A 4=6.51831e-04A 6=1.02975e-05A 8=-7.77252e-08A10=-3.25677e-10A12=-6.51157e-14

[0175] A 3=-4.72892e-04A 5=-1.34367e-04A 7=3.46845e-08A 9=7.21992e-09A11=7.39708e-12

[0176] The 21st side

[0177] K=0.00000e+00A 4=-2.90800e-04A 6=-1.41705e-05A 8=-2.40217e-07A10=-6.85583e-10A12=-1.74180e-13

[0178] A 3=6.44304e-04A 5=5.83963e-05A 7=2.30041e-06A 9=1.62058e-08A11=1.65507e-11

[0179]

[0180]

[0181] Lens unit data

[0182] Numerical example 3 Unit: mm Surface data

[0183]

[0184] Aspherical data

[0185] The 15th surface

[0186] K = 0.00000e+00 A4 = 3.33689e-05 A6 = 1.12024e-06 A8 = 4.13811e-09 A10 = 1.04675e-12

[0187] A3 = -9.89037e-05 A5 = -8.92891e-06 A7 = -8.85418e-08 A9 = -1.03939e-10 The 18th surface

[0188] K = -5.59343e+00 A4 = -2.48212e-04 A6 = -1.44824e-05 A8 = -5.60354e-08 A10 = -1.60139e-11

[0189] A3 = 7.60344e-04 A5 = 9.56402e-05 A7 = 1.18371e-06 A9 = 1.45357e-09 The 19th surface

[0190] K = -3.18771e+00 A4 = 6.12209e-04 A6 = 1.74522e-06 A8 = -7.07541e-09 A10 = 8.53125e-13

[0191] A3 = -1.41291e-04 A5 = -6.14094e-05 A7 = 8.77888e-08 A9 = 1.17866e-10 The 20th surface

[0192] K = 0.00000e+00 A4 = 6.38602e-04 A6 = 9.77458e-06 A8 = -7.78300e-08 A10 = -3.15421e-10 A12 = -6.15155e-14

[0193] A 3 = -4.51554e-04 A 5 = -1.30558e-04 A 7 = 6.85395e-08 A 9 = 7.07611e-09 A11 = 7.08707e-12

[0194] The 21st surface

[0195] K = 0.00000e+00 A 4 = -2.90901e-04 A 6 = -1.42728e-05 A 8 = -2.38720e-07 A10 = -6.76314e-10 A12 = -1.71301e-13

[0196] A 3 = 6.33038e-04 A 5 = 5.91833e-05 A 7 = 2.29968e-06 A 9 = 1.60352e-08 A11 = 1.62948e-11

[0197]

[0198]

[0199] Lens unit data

[0200] Numerical example 4 Unit: mm Surface data

[0201]

[0202] Aspherical surface data

[0203] The 15th surface

[0204] K = 0.00000e+00 A 4 = 5.41546e-05 A 6 = 1.45093e-06 A 8 = 4.26187e-09 A10 = 7.39216e-13

[0205] A 3 = -1.76505e-04 A 5 = -1.24650e-05 A 7 = -1.03377e-07 A 9 = -9.14957e-11 The 18th surface

[0206] K = -8.40074e+00 A 4 = -1.58789e-04 A 6 = -7.00442e-06 A 8 = -1.79131e-08 A10 = -2.32428e-12

[0207] A 3 = 7.86549e-04 A 5 = 5.33971e-05 A 7 = 4.78090e-07 A 9 = 3.38563e-10 The 19th surface

[0208] K = -5.78545e+00 A 4 = 6.52084e-04 A 6 = 1.00083e-05 A 8 = 3.62759e-08 A10 = 1.40337e-11

[0209] A 3 = -3.20449e-04 A 5 = -1.00889e-04 A 7 = -7.25492e-07 A 9 = -1.07937e-09 The 20th surface

[0210] K = 0.00000e+00 A 4 = 4.05205e-04 A 6 = 6.56796e-06 A 8 = -7.47369e-08 A10 = -3.30628e-10 A12 = - 8.87165e-14

[0211] A 3 = -2.22625e-04 A 5 = -8.95434e-05 A 7 = 1.59019e-07 A 9 = 6.92079e-09 A11 = 8.35416e-12

[0212] The 21st surface

[0213] K = 0.00000e+00 A 4 = -4.71817e- 04 A 6 = -1.58142e-05 A 8 = -1.99245e-07 A10 = -5.19029e-10 A12 = -1.29054e-13

[0214] A 3 = 1.07100e-03 A 5 = 8.81324e-05 A 7 = 2.12198e-06 A 9 = 1.26705e-08 A11 = 1.23288e-11

[0215]

[0216] Lens unit data

[0217] Numerical example 5 Unit: mm Surface data

[0218]

[0219] Aspherical surface data

[0220] The 15th surface

[0221] K = 0.00000e+00 A4 = 5.74684e-05 A6 = 1.51200e-06 A8 = 4.35527e-09 A10 = 7.22714e-13

[0222] A3 = -1.85812e-04 A5 = -1.30857e-05 A7 = -1.06798e-07 A9 = -9.20134e-11 The 18th surface

[0223] K = -7.08229e+00 A4 = -1.68119e-04 A6 = -8.97552e-06 A8 = -2.78675e-08 A10 = -5.45973e-12

[0224] A3 = 8.44342e-04 A5 = 6.28773e-05 A7 = 6.68687e-07 A9 = 6.12342e-10 The 19th surface

[0225] K = -4.64706e+00 A4 = 7.60583e-04 A6 = 1.02069e-05 A8 = 3.24402e-08 A10 = 1.24833e-11

[0226] A3 = -4.38725e-04 A5 = -1.12557e-04 A7 = -6.78666e-07 A9 = -9.55775e-10 The 20th surface

[0227] K = 0.00000e+00 A4 = 5.18854e-04 A6 = 8.60317e-06 A8 = -7.51418e-08 A10 = -3.34287e-10 A12 = -8.49540e-14

[0228] A3 = -4.04452e-04 A5 = -1.11096e-04 A7 = 7.12499e-08 A9 = 7.09873e-09 A11 = 8.23498e-12

[0229] The 21st surface

[0230] K = 0.00000e+00 A4 = -4.61864e-04 A6 = -1.56818e-05 A8 = -1.99763e-07 A10 = -5.20986e-10 A12 = -1.28244e-13

[0231] A 3 = 1.04929e-03 A 5 = 8.66417e-05 A 7 = 2.11760e-06 A 9 = 1.27305e-08 A11 = 1.23271e-11

[0232]

[0233] Lens unit data

[0234]

[0235]

[0236] Numerical example 6 Unit: mm Surface data

[0237]

[0238] Aspherical surface data

[0239] The 15th surface

[0240] K = 0.00000e+00 A 4 = 4.78352e-05 A 6 = 1.37566e-06 A 8 = 4.44487e-09 A10 = 9.60554e-13

[0241] A 3 = -1.57093e-04 A 5 = -1.14446e-05 A 7 = -1.02173e-07 A 9 = -1.03240e-10 The 18th surface

[0242] K = -1.29274e+01 A 4 = -1.45405e-04 A 6 = -4.67476e-06 A 8 = -9.99426e-09 A10 = -9.34234e-13

[0243] A 3 = 6.80273e-04 A 5 = 4.00711e-05 A 7 = 2.91510e-07 A 9 = 1.68767e-10 The 19th surface

[0244] K = -4.58640e+00 A 4 = 5.12047e-04 A 6 = 9.18831e-06 A 8 = 3.85546e-08 A10 = 1.55327e-11

[0245] A 3 = -2.27546e-05 A 5 = -8.37482e-05 A 7 = -7.29744e-07 A 9 = -1.17802e-09 The 20th surface

[0246] K = 0.00000e+00 A4 = 2.13459e-04 A6 = 4.17605e-06 A8 = -6.33667e-08 A10 = -2.82786e-10 A12 = -7.61168e-14

[0247] A3 = 1.18437e-04 A5 = -5.72546e-05 A7 = 1.81175e-07 A9 = 5.85598e-09 A11 = 7.19340e-12

[0248] The 21st surface

[0249] K = 0.00000e+00 A4 = -5.43258e-04 A6 = -1.65813e-05 A8 = -1.96156e-07 A10 = -5.22183e-10 A12 = -1.34334e-13

[0250] A3 = 1.10691e-03 A5 = 1.00494e-04 A7 = 2.11678e-06 A9 = 1.25576e-08 A11 = 1.26205e-11

[0251]

[0252] Lens unit data

[0253]

[0254] Numerical example 7 Unit: mm Surface data

[0255]

[0256] Aspherical data

[0257] The 15th surface

[0258] K = 0.00000e+00 A4 = 4.76767e-05 A6 = 1.37160e-06 A8 = 4.43564e-09 A10 = 9.58782e-13

[0259] A3 = -1.56923e-04 A5 = -1.14141e-05 A7 = -1.01904e-07 A9 = -1.03065e-10 The 18th surface

[0260] K = -1.30224e+01 A4 = -1.40575e-04 A6 = -4.55413e-06 A8 = -9.60966e-09 A10 = -8.15633e-13

[0261] A3 = 6.77762e-04 A5 = 3.90339e-05 A7 = 2.82929e-07 A9 = 1.58676e-10 The 19th surface

[0262] K = -4.48730e+00 A4 = 5.12069e-04 A6 = 9.26009e-06 A8 = 3.91727e-08 A10 = 1.58266e-11

[0263] A3 = -2.10974e-05 A5 = -8.39538e-05 A7 = -7.39122e-07 A9 = -1.19902e-09 The 20th surface

[0264] K = 0.00000e+00 A4 = 2.09225e-04 A6 = 4.13181e-06 A8 = -6.34547e-08 A10 = -2.82812e-10 A12 = -7.56848e-14

[0265] A3 = 1.21537e-04 A5 = -5.66474e-05 A7 = 1.83081e-07 A9 = 5.86021e-09 A11 = 7.18175e-12

[0266] The 21st surface

[0267] K = 0.00000e+00 A4 = -5.40859e-04 A6 = -1.63457e-05 A8 = -1.93607e-07 A1 = -5.17563e-10 A12 = -1.33696e-13

[0268] A3 = 1.09739e-03 A5 = 9.94067e-05 A7 = 2.08612e-06 A9 = 1.24198e-08 A11 = 1.25353e-11

[0269]

[0270]

[0271] Lens unit data

[0272] Numerical example 8 Unit: mm Surface data

[0273]

[0274] Aspherical surface data

[0275] The 19th surface

[0276] K = 0.00000e+00 A4 = 6.32292e-05 A6 = 2.21434e-06 A8 = 9.48450e-09 A10 = 3.09432e-12

[0277] A3 = -1.70963e-04 A5 = -1.62090e-05 A7 = -1.87106e-07 A9 = -2.64337e-10 The 22nd surface

[0278] K = -3.43065e+00 A4 = 1.04387e-05 A6 = -9.73401e-06 A8 = -4.53649e-08 A10 = -1.34370e-11

[0279] A3 = 4.90633e-04 A5 = 4.68535e-05 A7 = 9.01074e-07 A9 = 1.21136e-09 The 23rd surface

[0280] K = -3.86397e+00 A4 = 8.03053e-04 A6 = 1.33760e-05 A8 = 4.37050e-08 A10 = 1.68143e-11

[0281] A3 = -5.11667e-04 A5 = -1.34444e-04 A7 = -9.23043e-07 A9 = -1.26929e-09 The 24th surface

[0282] K = 0.00000e+00 A4 = 7.88845e-04 A6 = 1.55975e-05 A8 = -1.88494e-08 A10 = -1.08563e-10 A12 = 1.94811e-15

[0283] A3 = -2.01869e-04 A5 = -1.72721e-04 A7 = -5.58477e-07 A9 = 2.77439e-09 A11 = 1.49300e-12

[0284] The 25th surface

[0285] K = 0.00000e+00 A4 = -2.37204e-04 A6 = -1.29810e-05 A8 = -2.21118e-07 A10 = -5.61060e-10 A12 = -1.26354e-13

[0286] A3 = 8.53219e-04 A5 = 4.46557e-05 A7 = 2.18381e-06 A9 = 1.41173e-08 A11 = 1.27265e-11

[0287] Various data

[0288] Focal length 48.50

[0289]

[0290] Lens unit data

[0291] Numerical example 9 Unit: mm Surface data

[0292]

[0293] Aspherical surface data, the 19th surface

[0294] K = 0.00000e+00 A4 = 6.03791e-05 A6 = 2.21892e-06 A8 = 9.65989e-09 A10 = 3.17596e-12

[0295] A3 = -1.55004e-04 A5 = -1.60217e-05 A7 = -1.89413e-07 A9 = -2.70138e-10, the 22nd surface

[0296] K = -3.47418e+00 A4 = 2.64139e-05 A6 = -9.66133e-06 A8 = -4.51978e-08 A10 = -1.34194e-11

[0297] A3 = 4.15841e-04 A5 = 4.56382e-05 A7 = 8.97296e-07 A9 = 1.20748e-09, the 23rd surface

[0298] K = -4.22528e+00 A4 = 8.07011e-04 A6 = 1.37783e-05 A8 = 4.44833e-08 A10 = 1.66680e-11

[0299] A3 = -5.47883e-04 A5 = -1.37042e-04 A7 = -9.49537e-07 A9 = -1.27441e-09 The 24th surface

[0300] K = 0.00000e+00 A4 = 7.63375e-04 A6 = 1.45509e-05 A8 = -1.86686e-08 A10 = -1.08001e-10 A12 = -8.56394e-16

[0301] A3 = -4.19469e-04 A5 = -1.61944e-04 A7 = -5.17042e-07 A9 = 2.70292e-09 A11 = 1.60470e-12

[0302] The 25th surface

[0303] K = 0.00000e+00 A4 = -2.55253e-04 A6 = -1.37547e-05 A8 = -2.19520e-07 A10 = -5.61626e-10 A12 = -1.27978e-13

[0304] A3 = 5.92881e-04 A5 = 5.44466e-05 A7 = 2.19254e-06 A9 = 1.40493e-08 A11 = 1.28176e-11

[0305]

[0306]

[0307] Lens unit data

[0308] Numerical example 10 Unit: mm Surface data

[0309]

[0310] Aspherical surface data

[0311] The 17th surface

[0312] K = 0.00000e+00 A4 = 7.62821e-05 A6 = 3.07168e-06 A8 = 1.45215e-08 A10 = 5.06023e-12

[0313] A3 = -1.86315e-04 A5 = -2.10917e-05 A7 = -2.74094e-07 A9 = -4.18974e-10 The 20th face

[0314] K = -6.88013e+00 A4 = -1.89303e-04 A6 = -1.02530e-05 A8 = -4.46873e-08 A10 = -1.37534e-11

[0315] A3 = 6.85791e-04 A5 = 6.61195e-05 A7 = 8.87808e-07 A9 = 1.21558e-09 The 21st face

[0316] K = -4.16417e+00 A4 = 1.08906e-03 A6 = 2.66900e-05 A8 = 9.56578e-08 A10 = 3.41491e-11

[0317] A3 = -5.97375e-04 A5 = -2.26804e-04 A7 = -1.99988e-06 A9 = -2.69826e-09 The 22nd face

[0318] K = 0.00000e+00 A4 = 7.37075e-04 A6 = 2.16848e-05 A8 = 2.96573e-08 A10 = -5.96693e-11 A12 = 1.67586e-14

[0319] A3 = -3.44779e-04 A5 = -1.89748e-04 A7 = -1.29702e-06 A9 = 8.64156e-10 A11 = 4.85021e-13

[0320] The 23rd face

[0321] K = 0.00000e+00 A4 = -5.61961e-04 A6 = -2.43268e-05 A8 = -3.21277e-07 A10 = -8.07403e-10 A12 = -1.87901e-13

[0322] A3 = 9.72704e-04, A5 = 1.25282e-04, A7 = 3.39021e-06, A9 = 2.01933e-08, A11 = 1.85964e-11

[0323]

[0324]

[0325] Lens unit data

[0326]

[0327] Table 1 summarizes the values of inequalities (1) to (13) in Numerical Examples 1 to 10. Each numerical example satisfies all of inequalities (1) to (13).

[0328]

[0329] Imaging device

[0330] Figure 21 A digital still camera is shown as an imaging device using an optical system according to any one of Examples 1 to 10 as an imaging optical system. Reference numeral 20 denotes a camera body, and reference numeral 21 denotes an imaging optical system including any one of the optical systems according to Examples 1 to 10. Reference numeral 22 denotes a solid-state image sensor such as a CCD sensor or a CMOS sensor that is built into the camera body 20 and captures an optical image (subject image) formed by the imaging optical system 21. Reference numeral 23 denotes a recorder configured to record image data generated by processing a captured signal from the image sensor 22. Reference numeral 24 denotes a rear display configured to display the image data.

[0331] The optical systems according to the respective examples used as the imaging optical system can provide a camera with a reduced size and high optical performance.

[0332] The camera can be a single-lens reflex camera with a quick-return mirror or a mirrorless camera without a quick-return mirror. The camera can be a camera with an integrated lens.

[0333] Although the present disclosure describes example embodiments, it should be understood that the present disclosure is not limited to the example embodiments. The scope of the appended claims should be accorded the broadest interpretation so as to cover all such modifications as well as equivalent structures and functions.

[0334] Each example can provide an optical system having a large aperture diameter, a reduced size, high optical performance, and capable of performing high-speed focusing.

Claims

1. An optical system, which sequentially includes, from the object side to the image side: A front group, which has a positive refractive power and includes at least one lens unit; An intermediate lens unit, which has a positive refractive power; and A rear group, which has a negative refractive power and includes at least one lens unit, It is characterized in that the distance between adjacent lens units changes during focusing, wherein, the intermediate lens unit moves toward the object side during focusing from infinity to a short distance, wherein, the front group includes at least two positive lenses and at least one negative lens, and wherein, the rear group includes at least one aspherical lens, and the at least one aspherical lens has an aspherical surface with a pole at a position separated from the optical axis.

2. The optical system according to claim 1, characterized in that, The following inequality is satisfied: 3.0≤TTL / (f×tanω)≤10.0, wherein, TTL is the sum of the following two items: the distance on the optical axis from the lens surface closest to the object of the optical system to the lens surface closest to the image of the optical system and the air equivalent length on the optical axis from the lens surface closest to the image of the optical system to the image surface, f is the focal length of the optical system, and ω is the semi-angle of view of the optical system.

3. The optical system according to claim 1, characterized in that, The following inequality is satisfied: 1.50≤PNdave≤2.00, wherein, PNdave is the average value of the refractive indices of the d lines of all the positive lenses included in the optical system.

4. The optical system according to claim 1, characterized in that, The following inequality is satisfied: 0.01≤sk / TTL≤0.50, wherein, TTL is the sum of the following two items: the distance on the optical axis from the lens surface closest to the object of the optical system to the lens surface closest to the image of the optical system and the air equivalent length on the optical axis from the lens surface closest to the image of the optical system to the image surface, and sk is the air equivalent length.

5. The optical system according to claim 1, wherein The following inequality is satisfied: 2.0≤ff / sk≤10.0, wherein, ff is the focal length of the front group, and sk is the air equivalent length on the optical axis from the lens surface closest to the image of the optical system to the image surface.

6. The optical system according to claim 1, characterized in that, The following inequality is satisfied: 0.1≤-fm / fr≤1.0, wherein, fm is the focal length of the intermediate lens unit, and fr is the focal length of the rear group.

7. The optical system according to claim 1, characterized in that The following inequality is satisfied: 0.1≤Df / f≤1.0, wherein, Df is the distance on the optical axis between the front group and the intermediate lens unit, and f is the focal length of the optical system.

8. The optical system according to claim 1, wherein The following inequality is satisfied: 0.1≤-ff / fr≤2.0, wherein, ff is the focal length of the front group, and fr is the focal length of the rear group.

9. The optical system according to claim 1, characterized in that, The following inequality is satisfied: 55≤νdp1≤96, wherein, νdp1 is the Abbe number of the positive lens with the largest Abbe number based on the d line among all the positive lenses included in the front group.

10. The optical system according to claim 1, characterized in that, The following inequality is satisfied: 15≤νdp2≤40, wherein, νdp2 is the Abbe number of the positive lens with the smallest Abbe number based on the d line among all the positive lenses included in the front group.

11. The optical system according to claim 1, characterized in that, The following inequality is satisfied: 15≤νdn≤40, Among them, νdn is the Abbe number of the negative lens closest to the object among all the negative lenses included in the front group.

12. The optical system according to claim 11, wherein The negative lens closest to the object among all the negative lenses included in the front group has a biconcave shape.

13. The optical system according to claim 1, characterized in that, The following inequalities are satisfied: 0 < Ra1 / f, 0 < Ra2 / f, where Ra1 and Ra2 are the paraxial curvature radii of the object-side lens surface and the image-side lens surface of the aspherical lens included in the at least one aspherical lens, respectively, and f is the focal length of the optical system.

14. The optical system according to claim 1, wherein The following inequalities are satisfied: 1.44 ≤ Nda ≤ 1.77, where Nda is the refractive index of the d-line of the at least one aspherical lens.

15. The optical system according to claim 13, wherein The at least one aspherical lens includes an aspherical lens that satisfies the following inequality: Rb1 / f < 0, Rb2 / f < 0, where Rb1 and Rb2 are the paraxial curvature radii of the object-side lens surface and the image-side lens surface, respectively.

16. An optical system, comprising, in order from the object side to the image side: a front group having a positive refractive power; an intermediate lens unit; and a rear group including at least one lens unit, characterized in that the distance between adjacent lens units changes during focusing, wherein the intermediate lens unit moves toward the object side during focusing from infinity to a close distance, wherein the front group includes at least two positive lenses and at least one negative lens, and wherein the rear group includes at least one aspherical lens having an aspherical surface with a pole at a position separated from the optical axis.

17. An imaging device, comprising: the optical system according to any one of claims 1 to 16; and an image sensor configured to image a subject through the optical system.

Images