Optical system and image pickup apparatus including the same

Abstract

Provided are an object distance shortening optical system capable of focusing and having high optical performance, and an image pickup apparatus including the optical system. The optical system includes a first lens group having a positive refractive power, a second lens group having a positive refractive power, and a third lens group, the first lens group, the second lens group, and the third lens group being arranged in order from an object side toward an image side. The second lens group is configured to move in the optical axis direction with respect to the image plane during focusing, and the first lens group and the third lens group are configured to remain stationary with respect to the image plane during focusing. The first lens group includes three negative lenses continuously arranged in the optical axis direction and positioned closest to the object plane. The second lens group includes two or more lenses.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to an optical system and an image pickup apparatus including the optical system, and is suitable for an image pickup apparatus such as a digital video camera, a digital still camera, a broadcast camera, a silver halide film camera, a surveillance camera, and a vehicle-mounted camera. BACKGROUND

[0002] An optical system is used in an image pickup apparatus such as a digital still camera and a video camera using a solid-state image sensor. There has recently been a demand for a compact optical system capable of focusing at a closer distance. Japanese Patent Application Publication No. 2023-008471 discusses an optical system composed of, in order from an object side to an image side, a first lens group having positive refractive power, a second lens group having positive refractive power, and a third lens group having positive refractive power. The second lens group is configured to move relative to an image plane during focusing.

[0003] However, in the optical system discussed in Japanese Patent Application Publication No. 2023-008471, the refractive power of the positive second lens group that moves during focusing is small. This causes the object distance at which the optical system focuses by focusing to be far from the image plane. In addition, various aberrations that occur during focusing become difficult to correct. SUMMARY

[0004] According to an aspect of the present disclosure, an optical system includes a first lens group having positive refractive power, a second lens group having positive refractive power, and a third lens group, the first lens group, the second lens group, and the third lens group being arranged in order from an object side to an image side, wherein the second lens group is configured to move in an optical axis direction relative to the image plane during focusing, and the first lens group and the third lens group are configured to remain stationary relative to the image plane during focusing, wherein the first lens group includes three negative lenses that are continuously arranged in the optical axis direction and positioned closest to the object side, wherein the second lens group includes two or more lenses, and wherein the following conditional expressions are satisfied: 0.50 < f2 / f < 3.00, 0.20 < sk / f ≤ 1.075, and 0.00 < sk / |f3| < 0.80, where f is a focal length of the entire optical system, sk is an air equivalent back focal length in a case where the optical system focuses at infinity, f2 is a focal length of the second lens group, and f3 is a focal length of the third lens group.

[0005] According to another aspect of the present disclosure, an image pickup apparatus includes the above-described optical system.

[0006] Further features of the present disclosure will become apparent from the following description of exemplary embodiments with reference to the drawings. BRIEF DESCRIPTION OF DRAWINGS

[0007] Figure 1 is a cross-sectional view of the optical system of Example 1 when the optical system is focused at infinity.

[0008] Figure 2A and Figure 2B are longitudinal aberration diagrams of the optical system of Example 1 when the optical system is focused at (A) infinity and (B) a distance where the lateral magnification is -0.1, respectively.

[0009] Figure 3 is a cross-sectional view of the optical system of Example 2 when the optical system is focused at infinity.

[0010] Figure 4A and Figure 4B are longitudinal aberration diagrams of the optical system of Example 2 when the optical system is focused at (A) infinity and (B) a distance where the lateral magnification is -0.1, respectively.

[0011] Figure 5 is a cross-sectional view of the optical system of Example 3 when the optical system is focused at infinity.

[0012] Figure 6A and Figure 6B are longitudinal aberration diagrams of the optical system of Example 3 when the optical system is focused at (A) infinity and (B) a distance where the lateral magnification is -0.1, respectively.

[0013] Figure 7 is a cross-sectional view of the optical system of Example 4 when the optical system is focused at infinity.

[0014] Figure 8A and Figure 8B are longitudinal aberration diagrams of the optical system of Example 4 when the optical system is focused at (A) infinity and (B) a distance where the lateral magnification is -0.1, respectively.

[0015] Figure 9 is a cross-sectional view of the optical system of Example 5 when the optical system is focused at infinity.

[0016] Figure 10A and Figure 10B are longitudinal aberration diagrams of the optical system of Example 5 when the optical system is focused at (A) infinity and (B) a distance where the lateral magnification is -0.1, respectively.

[0017] Figure 11 is a cross-sectional view of the optical system of Example 6 when the optical system is focused at infinity.

[0018] Figure 12A and Figure 12Bare longitudinal aberration diagrams of the optical system of Example 6 when the optical system is focused at (A) infinity and (B) a distance where the lateral magnification is -0.1, respectively.

[0019] Figure 13 is a cross-sectional view of the optical system of Example 7 when the optical system is focused at infinity.

[0020] Figure 14A and Figure 14B are longitudinal aberration diagrams of the optical system of Example 7 when the optical system is focused at (A) infinity and (B) a distance where the lateral magnification is -0.1, respectively.

[0021] Figure 15 is a schematic view of an example imaging device.

[0022] Figure 16 is a schematic view of an example lens device. DETAILED DESCRIPTION

[0023] Typical embodiments of the present disclosure will be explained in detail below with reference to the drawings. For convenience, each drawing can be drawn in a scale different from the actual scale. In each drawing, like components are denoted by like reference numerals, and redundant explanation thereof will be omitted.

[0024] Figure 1 , Figure 3 , Figure 5 , Figure 7 , Figure 9 , Figure 11 and Figure 13 are cross-sectional views of the optical systems of Example 1, Example 2, Example 3, Example 4, Example 5, Example 6, and Example 7 when the optical systems are focused at infinity, respectively.

[0025] In each cross-sectional view, the object side is on the left side, and the image side is on the right side. The optical system according to the example is suitable for an imaging device such as a digital video camera, a digital still camera, a broadcast camera, a silver halide film camera, a surveillance camera, and a vehicle-mounted camera. The optical system according to the example can be used as a projection lens of a projector, in which case the screen side is on the left side, and the image-to-be-projected side is on the right side.

[0026] In each cross-sectional view, the entire optical system is denoted by L0, and the i-th (i is a natural number) lens group from the object side among the lens groups divided by the aperture stop between the object side and the image side is denoted by Li. The k-th (k is a natural number) lens from the object side among the lenses included in each lens group is denoted by Gk. As employed herein, the inside of a lens group refers to the space between the lens located closest to the object plane and the lens located closest to the image plane among the lenses constituting the lens group.

[0027] The lens group Li is a lens group that is integrally moved with respect to the image plane during focusing or is fixed with respect to the image plane. In other words, the air gaps between adjacent lens groups vary during focusing. The air gaps within each lens group do not vary during focusing.

[0028] The arrow parallel to the optical axis in each sectional view indicates the direction of movement of the lens group during focusing from infinity to the closest distance. In each example, only the second lens group L2 to be described below moves from the image side to the object side during focusing.

[0029] In each sectional view, the aperture stop SP determines the light flux at an opening F number. In the case where the optical system of each example is used as an imaging optical system of a digital still camera or a digital video camera, an imaging plane of a solid-state image sensor or a photoelectric conversion element such as a charge-coupled device (CCD) sensor and a complementary metal-oxide semiconductor (CMOS) sensor is located on the image plane IP. The optical system Lo of each example can be used as an imaging optical system of a silver halide film camera, in which case a photosensitive plane corresponding to a film plane is located on the image plane IP.

[0030] Figure 2A and Figure 2B , Figure 4A and Figure 4B , Figure 6A and Figure 6B , Figure 8A and Figure 8B , Figure 10A and Figure 10B , Figure 12A and Figure 12B , and Figure 14A and Figure 14B are aberration diagrams when the optical system Lo of Example 1, Example 2, Example 3, Example 4, Example 5, Example 6, and Example 7 is focused at (A) infinity and (B) a distance at which the lateral magnification is -0.1, respectively.

[0031] In the spherical aberration diagram, the F number is indicated by Fno. The solid line indicates the spherical aberration amount on the d line (wavelength: 587.6 nm), and the double-dot chain line indicates the spherical aberration amount on the g line (wavelength: 435.8 nm). In the astigmatism diagram, the solid line S indicates the astigmatism amount on the sagittal image plane, and the broken line M indicates the astigmatism amount on the tangential image plane. In the distortion aberration diagram, the solid line indicates the distortion aberration amount on the d line. In the chromatic aberration diagram, the double-dot chain line indicates the lateral chromatic aberration amount on the g line. The half viewing angle (°) used for imaging is indicated by ω.

[0032] Next, the characteristic structures of the optical systems according to the examples will be described.

[0033] The optical system L0 of each example is composed of, in order from the object side toward the image side, a first lens group L1 having positive refractive power, a second lens group L2 having positive refractive power, and a third lens group L3. In the optical system L0 of each example, the second lens group L2 moves in the optical axis direction with respect to the image plane IP during focusing. The first lens group L1 and the third lens group L3 remain stationary with respect to the image plane IP during focusing.

[0034] The optical system L0 is configured so that a light flux converged by the first lens group L1 having positive refractive power is incident on the second lens group L2 having positive refractive power. Thereby, this allows the lens diameter of the second lens group L2 which moves with respect to the image plane IP during focusing to be reduced, and the weight of the second lens group L2 can be lightened for high-speed focusing.

[0035] The optical system L0 of each example is characterized in that the following conditional expression is satisfied:

[0036] 0.50 < f2 / f < 3.00... (1)

[0037] where f is the focal length of the entire optical system L0, and f2 is the focal length of the second lens group L2.

[0038] The conditional expression (1) is related to the refractive power of the second lens group L2. Satisfying the conditional expression (1) makes the focal length f2 of the second lens group L2 small, whereby it is possible to make the object distance which can be focused closer to the image plane IP. Furthermore, it is possible to reduce the total length of the optical system L0 while reducing the change in optical performance during focusing.

[0039] If the positive focal length f2 of the second lens group L2 is reduced so as to fall below the lower limit of the conditional expression (1), the refractive power of the second lens group L2 is too high. This undesirably increases the performance change such as the spherical aberration, the field curvature, and the variation in angle of view which occur during focusing.

[0040] If the positive focal length f2 of the second lens group L2 is increased so as to exceed the upper limit of the conditional expression (1), the position sensitivity of the second lens group L2 (i.e., the ratio of the amount of movement of the image plane IP to the amount of movement of the focusing lens group) is too low. This undesirably makes the object distance which can be focused farther from the image plane IP. Furthermore, in order to secure the air gap for focusing, the total length of the optical system L0 is undesirably increased.

[0041] The numerical range of the conditional expression (1) is desirably replaced with the numerical range of the following conditional expression (1a).

[0042] 0.70 < f2 / f < 2.80... (1a)

[0043] The numerical range of the conditional expression (1) is more desirably replaced with the numerical range of the following conditional expression (1b).

[0044] 0.90 < f2 / f < 2.60...(1b)

[0045] The numerical range of the conditional expression (1) is more desirably replaced with the numerical range of the following conditional expression (1c).

[0046] 1.10 < f2 / f < 2.40...(1c)

[0047] Next, the structure desirably satisfied in the optical system L0 of each example will be described.

[0048] In the optical system L0, the first lens group L1 desirably includes three negative lenses arranged successively in the optical axis direction and positioned closest to the object plane. In order to provide a sufficient back focal length for a wide-angle lens, a high negative power on the object side of the optical system L0 can be required.

[0049] Sharing the negative power among the three negative lenses can reduce the power of each single negative lens, whereby the occurrence of barrel distortion aberration and field curvature can be suppressed. In the present exemplary embodiment, three successively arranged negative lenses means that no positive lens is configured between the three negative lenses.

[0050] The third lens group L3 is positioned on the image side of the second lens group L2 which moves during focusing, at a position where the on-axis light beam and the peripheral light beam are sufficiently separated in a direction orthogonal to the optical axis. This can well correct the astigmatism aberration and the distortion aberration to improve the peripheral performance of the optical system L0.

[0051] In the optical system L0, the positive second lens group L2 includes at least two positive lenses and at least one negative lens. In order to reduce the amount of movement of the second lens group L2 during focusing from infinity to the closest distance, the second lens group L2 needs to be high power. Sharing the high power among the at least two positive lenses can reduce the power of each single positive lens, whereby the variation of the spherical aberration and the field curvature during focusing can be reduced. The inclusion of at least one negative lens can well correct the axial chromatic aberration.

[0052] In the optical system L0, the aperture stop SP for determining the on-axis light beam is desirably located inside or next to the image side of the first lens group L1, and remains stationary with respect to the image plane IP during focusing. This enables high-speed focusing since the weight of the second lens group L2 which moves during focusing can be lightened. In the case where the aperture stop SP is located inside or next to the image side of the first lens group L1, the imbalance of the lens diameter between the front and the rear of the optical system L0 can be reduced. This can reduce the diameter of the entire optical system L0.

[0053] In the optical system L0, the lens in the second lens group L2 that is located closest to the object side desirably has a concave object-side lens surface. This causes the off-axis light beams that pass through the aperture stop SP to be substantially concentrically incident on the surface in the second lens group L2 that is closest to the object side, where the refraction of the light rays is reduced. As a result, the variation in the image spread, the coma, and the angle of view during focusing can be reduced.

[0054] In the optical system L0, the lens in the second lens group L2 that is located closest to the image side desirably has a convex image-side lens surface. This causes the off-axis light beams that exit from the second lens group L2 to be substantially concentric with respect to the surface in the second lens group L2 that is closest to the image side, where the refraction of the light rays is reduced. This facilitates the reduction in the variation in the image spread, the coma, and the angle of view during focusing.

[0055] In the optical system L0, the negative lens desirably is located closest to the image side in the third lens group L3 (i.e., closest to the image side in the optical system L0). This can increase the angle that the off-axis light rays incident on the image plane IP make with the optical axis, thereby allowing the lens diameter of the third lens group L3 to be reduced. Since the negative lens is located at a position where the height of the off-axis light rays on the image side is high, the positive Petzval sum of the entire optical system L0 can be reduced without deteriorating the sagittal flare, and thus the curvature of field can be well corrected.

[0056] Next, the conditions that the optical system L0 of each example desirably satisfies will be described.

[0057] The optical system L0 of each example desirably satisfies one or more of the following conditional expressions (2) to (17).

[0058] 0.20 < sk / f < 1.20... (2)

[0059] 0.30 < f1 / f2 < 3.00... (3)

[0060] -1.50 < f / f3 < 1.50... (4)

[0061] -1.50 < (R22-R21) / (R22+R21) < 1.50... (5)

[0062] -0.015 < ΔθgFn < 0.015... (6)

[0063] -0.20 < Ndn-(-0.0145425 x Vdn+2.28725) < 0.05... (7)

[0064] 0.50 < (1-β2 2 ) x β32 <2.50...(8)

[0065] 0.00 < sk / f3 < 0.80...(9)

[0066] 0.20 < ΣDair / (L-sk) < 0.70...(10)

[0067] 2.00 < L / f < 15.00...(11)

[0068] 60.00 < νd2p < 100.00...(12)

[0069] -0.200 < M2 / DSP < -0.005...(13)

[0070] 60.00 < νd1n < 100.00...(14)

[0071] 0.050 < ΔθgFp < 0.250...(15)

[0072] 0.30 < (DSP+sk) / L < 0.80...(16)

[0073] 0.50 < f1 / f < 5.00...(17)

[0074] In the conditional expressions (2) to (17), various numerical values are indicated as follows.

[0075] sk is an air-equivalent back focus of the optical system L0.

[0076] f3 is a focal length of the third lens group L3.

[0077] R21 is a radius of curvature of a surface closest to an object in the second lens group L2, and R22 is a radius of curvature of a surface closest to an image.

[0078] Ndn is a refractive index at a d line of a negative lens Gn included in the optical system L0.

[0079] ΔθgFn is an anomalous partial dispersion of the negative lens Gn included in the optical system L0, which is given by:

[0080] ΔθgFn = θgFn - (-0.0025116 x νdn + 0.67449)

[0081] where νdn is an Abbe number, and θgFn is a partial dispersion ratio on the g line and the F line.

[0082] β2 is a lateral magnification of the second lens group L2 when the optical system L0 is focused at infinity, and β3 is a lateral magnification of the third lens group L3 when the optical system L0 is focused at infinity.

[0083] ∑Dair is a sum of air gaps on the optical axis from the surface closest to the object plane up to the surface closest to the image plane in the optical system L0.

[0084] L is a total optical length of the optical system L0.

[0085] νd1n is an Abbe number of the negative lens G1n included in the first lens group L1.

[0086] νd2p is an Abbe number of the positive lens G2p included in the second lens group L2.

[0087] M2 is a moving amount of the second lens group L2 during focusing from infinity to an object distance at which the lateral magnification of the entire system is -0.1 times.

[0088] DSP is a distance on the optical axis from the aperture stop SP up to the surface closest to the image plane in the optical system L0 when the optical system L0 is focused at infinity.

[0089] ΔθgFp is an anomalous partial dispersion of the positive lens Gp included in the first lens group L1 or the second lens group L2, which is given by:

[0090] ΔθgFp = θgFp - (B3 x νdp 3 + B2 x νdp 2 + B1 x νdp + B0)

[0091] where,

[0092] B3 = -1.665 x 10 -7

[0093] B2 = 5.213 x 10 -5

[0094] B1 = -5.656 x 10 -3

[0095] B0 = 7.278 x 10 -1

[0096] where, νdp is an Abbe number, and θgFp is a partial dispersion ratio.

[0097] Next, the technical meanings of the above-described conditional expressions (2) to (17) will be explained.

[0098] Conditional expression (2) relates to the air equivalent back focal length sk of the optical system L0. In a case where conditional expression (2) is satisfied, the third lens group L3 can be located at a position where the height of the off-axis light ray is large. This makes it possible to selectively correct the distortion aberration and the astigmatism while minimizing the influence on the correction of the spherical aberration and the sagittal flare. As a result, it is possible to improve the peripheral performance of the optical system L0.

[0099] If the back focal length sk falls below the lower limit of conditional expression (2) or exceeds the upper limit of conditional expression (2), the third lens group L3 is difficult to be located at a position where the height of the off-axis light ray is large. This is undesirable because the distortion aberration, the field curvature, and the astigmatism become difficult to be sufficiently corrected.

[0100] Conditional expression (3) relates to the ratio of the refractive power of the first lens group L1 and the refractive power of the second lens group L2.

[0101] If f2 increases and the ratio falls below the lower limit of conditional expression (3), the positive refractive power of the second lens group L2 is too low, which undesirably increases the amount of movement during focusing and increases the total length. A small f1 is undesirable because the spherical aberration and the axial chromatic aberration become difficult to be corrected.

[0102] If f2 decreases and the ratio exceeds the upper limit of conditional expression (3), the positive refractive power of the second lens group L2 is too large. This is undesirable because the performance variation such as the spherical aberration, the field curvature, and the variation of the angle of view during focusing becomes too large. A large f1 is undesirable because the total length increases.

[0103] Conditional expression (4) defines the ratio of the focal length f3 of the third lens group L3 and the focal length f of the entire optical system L0.

[0104] In the vicinity of the lower limit of conditional expression (4), f3 has a negative value. If the absolute value of f3 increases and the ratio falls below the lower limit of conditional expression (4), the negative refractive power of the third lens group L3 is too high. This makes the incident angle of the off-axis light beam incident on the image plane IP too large, which is undesirable because color unevenness easily occurs when an image is captured using a solid-state image sensor such as a CMOS sensor.

[0105] In the vicinity of the upper limit of conditional expression (4), f3 has a positive value. If the absolute value of f3 decreases and the ratio exceeds the upper limit of conditional expression (4), the positive refractive power of the third lens group L3 is too high. This makes the positive Petzval sum and the total length of the entire optical system L0 too large, which is undesirable because the field curvature becomes difficult to be corrected.

[0106] The conditional expression (5) defines the shape of the second lens group L2 and is related to a condition for reducing variation in aberration and angle of view that occurs during focusing.

[0107] In a case where the lower limit of the conditional expression (5) is exceeded, the curvature radius of the concave surface closest to the object in the second lens group L2 has a large absolute value. Here, the concentricity of the surface closest to the object in the second lens group L2 with respect to an off-axis light beam incident on the second lens group L2 deteriorates. In addition, the curvature radius of the convex surface closest to the image in the second lens group L2 has a small absolute value, and the off-axis light beam is significantly refracted at the surface closest to the image in the second lens group L2. This is undesirable because variation in the angle of view that occurs during focusing tends to be large.

[0108] In a case where the upper limit of the conditional expression (5) is exceeded, the curvature radius of the concave surface closest to the object in the second lens group L2 has a small absolute value. Here, the concentricity of the surface closest to the object in the second lens group L2 with respect to an off-axis light beam incident on the second lens group L2 deteriorates. As a result, variation in the angle of view that occurs during focusing tends to be large. In addition, the curvature radius of the convex surface closest to the image in the second lens group L2 has a large absolute value. This is undesirable because aberration variation such as coma and astigmatism during focusing tends to be large.

[0109] The conditional expression (6) defines the anomalous partial dispersion of the negative lens Gn included in the first lens group LI or the second lens group L2.

[0110] In a case where the lower limit of the conditional expression (6) is exceeded, the on-axis chromatic aberration at the g line is undesirably overcorrected.

[0111] In a case where the upper limit of the conditional expression (6) is exceeded, the on-axis chromatic aberration at the g line is undesirably undercorrected.

[0112] The conditional expression (7) defines the dispersion of the negative lens Gn included in at least one of the first lens group LI and the second lens group L2.

[0113] In a case where the lower limit of the conditional expression (7) is exceeded, the on-axis chromatic aberration is undesirably overcorrected.

[0114] In a case where the upper limit of the conditional expression (7) is exceeded, the on-axis chromatic aberration is undesirably undercorrected, or the refractive power of the negative lens Gn is so high that spherical aberration becomes difficult to correct.

[0115] A large-diameter lens tends to have a problem of axial chromatic aberration at a shorter wavelength such as the g-line. In particular, primary achromatization on the C-line and the F-line tends to cause excessive axial chromatic aberration on the g-line. Use of a lens material satisfying the conditional expressions (6) and (7) for a negative lens can relatively reduce the degree of divergence of the g-line passing through the negative lens, whereby it is possible to prevent axial chromatic aberration at a shorter wavelength such as the g-line from becoming excessive.

[0116] By configuring at least one negative lens Gn satisfying both of the conditional expressions (6) and (7) in at least one of the first lens group LI and the second lens group L2, it is possible to obtain the above-described effect for correcting axial chromatic aberration.

[0117] It is possible to enhance the effect by including two negative lenses Gn. It is possible to further enhance the effect by including three or more negative lenses Gn.

[0118] More desirably, at least one lens Gn is configured in the first lens group LI, and at least one lens Gn is configured in the second lens group L2.

[0119] Inclusion of a negative lens Gn in the first lens group LI can effectively correct axial chromatic aberration of the entire optical system LO. Inclusion of a negative lens Gn in the second lens group L2 facilitates correction of axial chromatic aberration inside the second lens group L2, whereby it is possible to reduce variation in axial chromatic aberration during focusing.

[0120] The conditional expression (8) is related to the position sensitivity of the second lens group L2, and defines a ratio of the amount of movement of the image plane IP with respect to the amount of movement of the second lens group L2.

[0121] In a case lower than the lower limit of the conditional expression (8), the position sensitivity of the second lens group L2 is too low.

[0122] As a result, the distance enabling focusing becomes undesirably long. This is also undesirable because the total length of the optical system LO is difficult to reduce in order to secure an air gap for focusing.

[0123] In a case higher than the upper limit of the conditional expression (8), the refractive power of the second lens group L2 is too high. This is undesirable because variations in performance such as spherical aberration, field curvature, and variation in angle of view during focusing become excessively large.

[0124] The conditional expression (9) defines a ratio of the focal length f3 of the third lens group L3 to the air equivalent back focal length sk.

[0125] If sk decreases so as to fall below the lower limit of conditional expression (9), the image plane IP of the optical system L0 falls on the most object- side surface in the optical system L0. This is undesirable because imaging is difficult.

[0126] If sk increases so as to exceed the upper limit of conditional expression (9), this is undesirable because the effect of correcting the distortion aberration and the field curvature decreases, or the diameter of the front lens element increases.

[0127] If |f3| decreases and the ratio exceeds the upper limit of conditional expression (9), the absolute value of the refractive power of the third lens group L3 is too large. Too high negative refractive power is undesirable because the incident angle of the off-axis light beams incident on the image plane IP is too large, and color unevenness easily occurs when an image is captured using an image sensor such as a CMOS sensor. Too high positive refractive power is undesirable because the positive Petzval sum of the entire optical system L0 is so large that the field curvature becomes difficult to correct.

[0128] Conditional expression (10) defines the ratio of the sum ΣDair of the air gaps on the optical axis from the most object- side surface up to the most image- side surface in the optical system L0 to the total optical length L of the optical system L0.

[0129] If ΣDair decreases so as to fall below the lower limit of conditional expression (10), it is difficult to provide sufficient space for the lens groups to move during focusing. This is undesirable because the negative lens included in the first lens group L is difficult to configure with sufficient positive curvature, and it is difficult to constitute a wide-angle optical system L0 or correct the distortion aberration.

[0130] If ΣDair increases so as to exceed the upper limit of conditional expression (10), the ratio of the air gap to the total optical length is too high. This is undesirable because the lens is difficult to configure with sufficient refractive power, and the spherical aberration and the axial chromatic aberration become difficult to correct. In other words, if the lens is configured with sufficient refractive power, the total length undesirably increases.

[0131] Conditional expression (11) defines the ratio of the total optical length L of the optical system L0 to the focal length f of the entire optical system L0.

[0132] If L decreases so as to fall below the lower limit of conditional expression (11), the refractive power of the lens groups is too high. This is undesirable because the aberrations such as the distortion aberration, the astigmatism, and the spherical aberration become difficult to correct.

[0133] If L increases so as to exceed the upper limit of conditional expression (11), the total length undesirably increases.

[0134] The conditional expression (12) is an expression defining Abbe number vd2p of at least one positive lens G2p included in the second lens group L2. The conditional expression (12) defines a condition for well correcting axial chromatic aberration.

[0135] If vd2p falls below the lower limit of the conditional expression (12), this is undesirable because axial chromatic aberration becomes difficult to correct.

[0136] If vd2p exceeds the upper limit of the conditional expression (12), this is undesirable because magnification chromatic aberration is overcorrected, or the degree of wear of the lens material is too high to make processing difficult or to be easily broken.

[0137] It is more desirable to configure two or more positive lenses G2p satisfying the conditional expression (12) in the second lens group L2 because the above-described effects can be enhanced.

[0138] The conditional expression (13) defines a ratio of a movement amount M2 of the second lens group L2 during focusing from infinity to an object distance at which the lateral magnification of the entire system is -0.1 times to a distance DSP on the optical axis from the stop SP up to the surface closest to the image plane. The sign of the movement amount M2 is positive when the second lens group L2 moves from the object side to the image side.

[0139] If M2 decreases to fall below the lower limit of the conditional expression (13), the refractive power of the second lens group L2 is too high. This is undesirable because variations in spherical aberration and field curvature during focusing increase.

[0140] If M2 increases to exceed the upper limit of the conditional expression (13), the movement amount M2 of the second lens group L2 is too large. This undesirably increases the total length to secure a movement space.

[0141] The conditional expression (14) is an expression defining Abbe number vd1n of at least one negative lens G1n included in the first lens group L1. The conditional expression (14) defines a condition for well correcting magnification chromatic aberration.

[0142] If vd1n falls below the lower limit of the conditional expression (14), this is undesirable because magnification chromatic aberration becomes difficult to correct.

[0143] If vd1n exceeds the upper limit of the conditional expression (14), this is undesirable because magnification chromatic aberration is overcorrected, or the degree of wear of the negative lens G1n is too high to make processing difficult or to be easily broken.

[0144] It is more desirable to configure two or more negative lenses G1n satisfying the conditional expression (14) in the first lens group L1 because the above-described effects can be enhanced.

[0145] The conditional expression (15) defines the anomalous partial dispersion AgFp of the positive lens Gp included in the first lens group LI or the second lens group L2.

[0146] A large diameter lens tends to have a problem of axial chromatic aberration at a shorter wavelength such as g-line. In particular, primary chromatic aberration on C-line and F-line tends to cause excessive axial chromatic aberration on g-line. Use of a material having high AgFp for the positive lens enables good correction by selectively converging excessive axial chromatic aberration at a shorter wavelength such as g-line.

[0147] If AgFp falls below the lower limit of the conditional expression (15), this is undesirable because axial chromatic aberration becomes difficult to correct.

[0148] If AgFp exceeds the upper limit of the conditional expression (15), this is undesirable because axial chromatic aberration is overcorrected.

[0149] By configuring the positive lens Gp in the form of a three-cemented triplet composed of a positive lens, a positive lens Gp, and a negative lens or a three-cemented triplet composed of a negative lens, a positive lens Gp, and a positive lens, it is possible to further enhance the effect of correcting axial chromatic aberration.

[0150] The negative lens constituting the three-cemented triplet can be a negative lens satisfying the conditional expressions (6) and (7), in which case it is possible to effectively correct axial chromatic aberration.

[0151] The three-cemented triplet desirably locates on the object side or the image side next to the aperture stop SP configured in the first lens group LI. Thus, the three-cemented triplet locates at a position where the axial ray height is large, which can enhance the effect of axial chromatic aberration correction.

[0152] The three-cemented triplet and the aperture stop SP desirably are configured in the first lens group LI that remains stationary during focusing. Although the three-cemented triplet can locate in front of or behind the aperture stop SP as described above, the beam diameter is large on the axis in front of or behind the aperture stop SP, which leads to a large lens diameter and increased lens weight. For such a reason, the aperture stop SP and the three-cemented triplet including the positive lens Gp desirably are configured to be stationary during focusing.

[0153] The conditional expression (16) is an expression defining the position of the aperture stop SP and defines a condition for miniaturizing the optical system LO.

[0154] If the DSP decreases to fall below the lower limit of the conditional expression (16), the diameter of the lens located on the object side of the aperture stop SP becomes large. This is undesirable because the quality and diameter of the entire optical system L0 increase. In addition, the angle of the off-axis light beam incident on the image plane IP becomes too large, which is undesirable because color unevenness easily occurs when an image is captured using a solid-state image sensor such as a CMOS sensor.

[0155] If the DSP increases to exceed the upper limit of the conditional expression (16), the diameter of the lens located on the image side of the aperture stop SP becomes large. This is undesirable because the quality and diameter of the entire optical system L0 increase.

[0156] The conditional expression (17) defines the focal length fl of the first lens group LI.

[0157] If fl decreases to fall below the lower limit of the conditional expression (17), the positive refractive power of the first lens group LI becomes too high. This is undesirable because spherical aberration and distortion aberration become difficult to correct.

[0158] If fl increases to exceed the upper limit of the conditional expression (17), the diameter and quality of the second lens group L2 increase. This is undesirable because high-speed focusing becomes difficult.

[0159] The numerical ranges of the conditional expressions (2) to (17) are desirably replaced with the numerical ranges of the following conditional expressions (2a) to (17a).

[0160] 0.30 < sk / f < 1.18... (2a)

[0161] 0.50 < fl / f2 < 2.70... (3a)

[0162] -1.20 < f / f3 < 1.20... (4a)

[0163] -1.20 < (R22-R21) / (R22+R21) < 1.20... (5a)

[0164] -0.010 < ΔθgFn < 0.010... (6a)

[0165] -0.18 < Ndn-(-0.0145425 x Vdn+2.28725) < 0.03... (7a)

[0166] 0.60 < (1-β2 2 ) x β3 2 < 2.20... (8a)

[0167] 0.00 < sk / |f3| < 0.70... (9a)

[0168] 0.25 < ΣDair / (L-sk) < 0.64...(10a)

[0169] 3.00 < L / f < 13.50...(11a)

[0170] 62.00 < νdn < 99.00...(12a)

[0171] -0.160 < M2 / DSP < -0.008...(13a)

[0172] 62.00 < νdn < 99.00...(14a)

[0173] 0.060 < ΔθgFp < 0.210...(15a)

[0174] 0.35 < (DSP+sk) / L < 0.74...(16a)

[0175] 0.70 < f1 / f < 4.50...(17a)

[0176] The numerical ranges of the conditional expressions (2) to (17) are more desirably replaced with the numerical ranges of the following conditional expressions (2b) to (17b).

[0177] 0.40 < sk / f < 1.14...(2b)

[0178] 0.70 < f1 / f2 < 2.30...(3b)

[0179] -0.90 < f / f3 < 0.50...(4b)

[0180] -0.80 < (R22-R21) / (R22+R21) < 0.80...(5b)

[0181] -0.008 < ΔθgFn < 0.007...(6b)

[0182] -0.15 < Ndn-(-0.0145425 x νdn+2.28725) < 0.02...(7b)

[0183] 0.55 < (1-β2 2 ) x β3 2 < 1.90...(8b)

[0184] 0.00 < sk / |f3| < 0.60...(9b)

[0185] 0.30 < ΣDair / (L-sk) < 0.56...(10b)

[0186] 3.50 < L / f < 12.00... (lib)

[0187] 64.00 < νdn< 98.00... (12b)

[0188] -0.120 < M2 / DSP < -0.012... (13b)

[0189] 64.00 < νdn< 98.00... (14b)

[0190] 0.070 < ΔθgFp< 0.180... (15b)

[0191] 0.40 < (DSP + sk) / L < 0.68... (16b)

[0192] 1.00 < f1 / f < 4.00... (17b)

[0193] The numerical ranges of the conditional expressions (2) to (17) are more desirably replaced with the numerical ranges of the following conditional expressions (2c) to (17c), respectively.

[0194] 0.50 < sk / f < 1.10... (2c)

[0195] 0.90 < f1 / f2< 1.80... (3c)

[0196] -0.50 < f / f3< 0.20... (4c)

[0197] -0.50 < (R22- R21) / (R22+ R21) < 0.50... (5c)

[0198] -0.006 < ΔθgFn< 0.004... (6c)

[0199] -0.13 < Ndn- (-0.0145425 x νdn+ 2.28725) < 0.01... (7c)

[0200] 0.65 < (1- β2 2 ) x β3 2 < 1.60... (8c)

[0201] 0.00 < sk / |f3| < 0.40... (9c)

[0202] 0.33 < ΣDair / (L-sk) < 0.50... (10c)

[0203] 4.00 < L / f < 11.00... (11c)

[0204] 66.00 < Vd2p < 97.00...(12c)

[0205] -0.080 < M2 / DSP < -0.016...(13c)

[0206] 66.00 < Vdln < 97.00...(14c)

[0207] 0.080 < AGFp < 0.160...(15c)

[0208] 0.45 < (DSP + sk) / L < 0.65...(16c)

[0209] 1.30 < fl / f < 3.50...(17c)

[0210] Next, the detailed structure of the optical system L0 of Examples 1 to 7 will be described. For the optical system (zoom lens) L0 of Examples 2 to 7, the description of the components similar to those of the zoom lens L0 of Example 1 will be omitted, and the differences from Example 1 will be mainly described.

[0211] The optical system L0 of Example 1 is composed of a first lens group L1 having a positive refractive power, a second lens group L2 having a positive refractive power, and a third lens group L3 having a negative refractive power. The third lens group L3 is configured to have a negative refractive power, which facilitates correction of the positive Petzval sum and can well correct field curvature.

[0212] In the optical system L0 of Example 1, the first lens group L1 is composed of lenses G1 to G12. The second lens group L2 is composed of lenses G13 to G16. The third lens group is composed of lenses G17 and G18. The first lens group L1 includes an aperture stop SP. The lenses G1 and G3 are configured as aspherical lenses, which can well correct distortion aberration and astigmatism.

[0213] In the optical system L0 of Example 1, the lenses G6 and G7, the lenses G10 to G12, the lenses G13 and G14, and the lenses G17 and G18 are cemented to each other to constitute respective cemented lenses.

[0214] During focusing, the second lens group L2 moves in the optical axis direction with respect to the image plane IP, and the first lens group L1 and the third lens group L2 remain stationary with respect to the image plane IP.

[0215] In the optical system L0 of Example 2, the first lens group L1 is composed of lenses G1 to G10. The second lens group L2 is composed of lenses G11 to G14. The third lens group L3 is composed of lenses G15 and G16.

[0216] In the optical system L0 of Example 2, the lenses G4 and G5, the lenses G8 to G10, the lenses G11 and G12, and the lenses G15 and G16 are cemented to each other to form respective cemented lenses.

[0217] In the optical system L0 of Example 3, the first lens group L1 is composed of the lenses G1 to G8. The second lens group L2 is composed of the lenses G9 to G12. The third lens group L3 is composed of the lenses G13 and G14. The first lens group L1 includes the aperture stop SP. The lenses G1 and G3 are configured as aspherical lenses, which can well correct distortion aberration and astigmatism.

[0218] In the optical system L0 of Example 3, the lenses G4 and G5, the lenses G6 and G7, the lenses G9 and G10, and the lenses G13 and G14 are cemented to each other to form respective cemented lenses.

[0219] In the optical system L0 of Example 3, the lens G8 included in the first lens group L1 is moved in a direction including a component orthogonal to the optical axis. Thereby, variation of chromatic aberration can be reduced during image stabilization correction.

[0220] In the optical system L0 of Example 4, the first lens group L1 is composed of the lenses G1 to G9. The second lens group L2 is composed of the lenses G10 to G14. The third lens group L3 is composed of the lenses G15 to G17.

[0221] In the optical system L0 of Example 4, the lenses G4 and G5, the lenses G8 and G9, the lenses G10 to G12, and the lenses G15 and G16 are cemented to each other to form respective cemented lenses.

[0222] In the optical system L0 of Example 5, the first lens group L1 is composed of the lenses G1 to G12. The second lens group L2 is composed of the lenses G13 to G16. The third lens group L3 is composed of the lenses G17 and G18. The lenses G1 and G3 are configured as aspherical lenses, which can well correct distortion aberration and astigmatism.

[0223] In the optical system L0 of Example 5, the lenses G6 and G7, the lenses G10 to G12, the lenses G13 and G14, and the lenses G17 and G18 are cemented to each other to form respective cemented lenses.

[0224] The optical system L0 of Example 6 is composed of the first lens group L1 having positive refractive power, the second lens group L2 having positive refractive power, and the third lens group L3 having positive refractive power. Configuring the third lens group L2 to have positive refractive power can reduce the incidence angle of off-axis light beams incident on the image plane IP. This facilitates suppression of color unevenness when an image is captured using a solid-state image sensor such as a CMOS sensor.

[0225] In the optical system L0 of Example 6, the first lens group L1 is composed of the lenses G1 to G10. The second lens group L2 is composed of the lenses G11 to G14. The third lens group L3 is composed of the lenses G15 and G16. The lenses G1 and G3 are configured as aspherical lenses, which can well correct the distortion aberration and the astigmatism.

[0226] In the optical system L0 of Example 6, the lenses G4 and G5, the lenses G8 to G10, the lenses G11 and G12, and the lenses G15 and G16 are cemented to each other to form respective cemented lenses.

[0227] In the optical system L0 of Example 7, the first lens group L1 is composed of the lenses G1 to G8. The second lens group L2 is composed of the lenses G9 to G12. The third lens group is composed of the lenses G13 and G14. The lenses G1 and G3 are configured as aspherical lenses, which can well correct the distortion aberration and the astigmatism.

[0228] In the optical system L0 of Example 7, the lenses G4 and G5, the lenses G9 and G10, and the lenses G13 and G14 are cemented to each other to form respective cemented lenses.

[0229] In the optical system L0 of Example 7, the lens G8 included in the first lens group L1 is moved in a direction including a component orthogonal to the optical axis. Thereby, variation of the chromatic aberration can be reduced during the image stabilization correction.

[0230] In the optical system L0 of each example, the negative lens is desirably located at a position closest to the image plane in the third lens group L3 (that is, a position closest to the image plane in the optical system L0). This can increase an angle formed by an off-axis light ray incident on the image plane IP and the optical axis, thereby making it possible to reduce the lens diameter of the third lens group L3. Since the negative lens is located at a position where the height of the off-axis light ray on the image side is large, it is possible to reduce the positive Petzval sum of the entire optical system L0 without deteriorating the sagittal flare, and to well correct the field curvature.

[0231] In the optical system L0 of each example, the first lens group L1 desirably includes two negative meniscus lenses having convex object side lens surfaces which are arranged continuously and located closest to the object. This makes it possible to well correct the distortion aberration, the field curvature, and the astigmatism.

[0232] In the optical system L0 of each example, the first lens group L1 desirably includes an aspherical lens as at least one of the three negative lenses that are arranged continuously and positioned closest to the object. This makes it possible to correct the distortion aberration and the coma well. In Example 1 and Example 5, the two lenses G1 and G3 are configured as aspherical lenses to enhance the above-described effects. By shaping the aspherical lens so that the peripheral curvature has a smaller absolute value than the absolute value of the curvature on the optical axis, the distortion aberration can be corrected well.

[0233] In the optical system L0 of each example, the negative lens G2 desirably has a concave image-side lens surface, and the negative lens G3 desirably has a concave object-side lens surface. This increases the refractive power of the negative air lens constituted by the image-side lens surface of the lens G2 and the object-side lens surface of the lens G3. Thus, the positive Petzval sum can be easily reduced to correct the field curvature well.

[0234] In the optical system L0 of each example, the first lens group L1 desirably includes a negative lens G1, a negative lens G2, a negative lens G3, and a positive lens G4 in this order from the object side. Configuring the lens G4 as a positive lens makes it possible to correct the barrel distortion aberration and the magnification chromatic aberration that occur from the lenses G1 to G3 well.

[0235] In Example 1 and Example 5, the lens G4 desirably is a meniscus lens having a positive refractive power. This makes it possible to correct the barrel distortion aberration and the magnification chromatic aberration. The lens G4 can be a positive meniscus lens having a convex object-side lens surface, or a positive meniscus lens having a convex image-side lens surface.

[0236] In the optical system L0 of each example, the first lens group L1 desirably includes at least one cemented lens composed of a positive lens and a negative lens. This makes it possible to correct the axial chromatic aberration and the magnification chromatic aberration well. By configuring the negative lens in the cemented lens to be the negative lens Gn that satisfies the conditional expressions (6) and (7) as in Example 2, Example 3, Example 4, Example 6, and Example 7, the axial chromatic aberration on the g line can be corrected more well.

[0237] In the optical system L0 of each example, the first lens group L1 can achieve the image stabilization correction by moving at least a part of the first lens group L1 in a direction including a component orthogonal to the optical axis direction.

[0238] In Example 3 and Example 7, the lens G8 is moved in a direction including a component orthogonal to the optical axis during the image stabilization correction. However, this is not limiting. At least a positive lens and a negative lens can be moved during the image stabilization correction, where in this case, the variation in the chromatic aberration during the image stabilization correction can be reduced. The optical system L0 can be configured to move three or more lenses during the image stabilization correction.

[0239] In the optical system L0 of each example, the second lens group L2 includes a negative lens and a positive lens arranged in order in the optical axis direction. Thereby, axial chromatic aberration during infinity focusing and variation of axial chromatic aberration during focusing can be corrected more favorably. This effect can be obtained regardless of the order in which the negative lens and the positive lens are arranged.

[0240] In the second lens group L2, the lens positioned second closest to the object plane desirably has a concave object side lens surface, and the lens positioned closest to the image plane desirably has a convex image side lens surface. This results in a substantially concentric structure with respect to an off-axis light beam incident on the second lens group L2, whereby variation of aberration and angle of view during focusing can be reduced.

[0241] In the optical system L0 of each example, the second lens group L2 includes a cemented lens formed by cementing at least one of the negative lenses Gn and at least one of the positive lenses G2p. This enables axial chromatic aberration during infinity focusing and variation of axial chromatic aberration during focusing to be corrected favorably.

[0242] The cemented lens is desirably positioned closest to the object plane in the second lens group L2.

[0243] Since the cemented lens is thus positioned at a position where the height of an off-axis light ray is large, axial chromatic aberration can be corrected favorably.

[0244] In the cemented lens, a concave lens surface is desirably positioned closest to the object plane, and a convex lens surface is desirably positioned closest to the image plane. This results in a substantially concentric structure with respect to an off-axis light beam incident on the second lens group L2, and variation of aberration and angle of view during focusing can be reduced. The cemented lens can be formed by cementing a double-concave lens and a double-convex lens in order from the object side.

[0245] In the optical system L0 of each example, the second lens group L2 is composed of four lenses. This can reduce the refractive power of each lens, and variation of spherical aberration, field curvature, and chromatic aberration during focusing can be reduced.

[0246] In the optical system L0 of each example, the second lens group L2 desirably is composed of five or fewer lenses. This can reduce the weight of the lenses in the second lens group L2 and enable high-speed focusing. Furthermore, the refractive power of each lens can be reduced to reduce variation of spherical aberration, field curvature, and chromatic aberration during focusing. To enhance the above effects, the second lens group L2 more desirably is composed of four or fewer lenses.

[0247] In the optical system L0 of each example, the lens closest to the object plane in the second lens group L2 desirably has a concave object side lens surface. As a result, the off-axis light flux that has passed through the aperture stop SP is incident approximately concentrically to the surface closest to the object plane in the second lens group L2. This facilitates reduction of the variation in the image spread, the coma, and the angle of view during focusing.

[0248] In the optical system L0 of each example, the second lens group L2 desirably includes an aspherical lens having at least one aspherical surface. This enables good correction of the spherical aberration, the image spread, and the coma. It is more desirable to configure one of the surfaces of the positive lens included in the second lens group L2 as an aspherical surface because the error in the surface shape during molding can be reduced. It is more desirable to configure the lens closest to the image plane or the lens second closest to the image plane in the second lens group L2 as an aspherical surface because the off-axis aberration such as the image spread and the coma can be well corrected.

[0249] In the optical system L0 of each example, the third lens group L3 desirably includes a cemented lens composed of a positive lens and a negative lens. This can well correct the magnification chromatic aberration and the image spread.

[0250] In the optical system L0 of each example, the aspherical lens can be made of a plastic or other organic material or a glass material. A layer of the plastic or other organic material having a thickness of about 0.01 to 1.00 mm can be molded and cemented or bonded to a spherical glass to form an aspherical lens made of the organic material on the spherical glass.

[0251] Numerical example 1 to numerical example 7 corresponding to example 1 to example 7, respectively, will now be described.

[0252] In the surface data of each numerical example, r is the radius of curvature, and d is the distance on the optical axis between the mth surface and the (m+1)th surface. Here, m is the number of the surface from the light incident side. nd is the refractive index of each optical member on the d line, and vd is the Abbe number of the optical member. The Abbe number vd and the partial dispersion ratio θgF of a certain material are given by the following:

[0253] vd = (Nd - 1) / (NF - NC)

[0254] θgF = (Ng - NF) / (NF - NC)

[0255] where Nd, NF, NC, and Ng are the refractive indices on the d line (wavelength: 587.6 nm), the F line (wavelength: 486.1 nm), the C line (wavelength: 656.3 nm), and the g line (wavelength: 435.8 nm) of Fraunhofer, respectively.

[0256] In each numerical example, d (mm), focal length (mm), F number, and half view angle (°) are all values when the optical system of the example focuses on an object at infinity. The back focus BF is an air equivalent distance from the last lens surface to the image plane IP. The total optical length is a value obtained by adding the air equivalent back focus BF to the distance from the first lens surface to the last lens surface. Optical members corresponding to optical filters, face plates, crystal low-pass filters, and infrared cut filters are excluded.

[0257] In each lens, a spherical lens surface is marked with * on the right side of the surface number. The aspherical shape is expressed by:

[0258] x = (h 2 / R) / [1+{1-(1+k)(h / R) 2} 1 / 2 +A4xh 4 +A6xh 6 +A8xh 8 +A10x

[0259] h 10 +A12xh 12 +A14xh 14 +A16xh 16

[0260] where x is a displacement amount in the optical axis direction from the vertex of the surface, h is a height with respect to the optical axis in a direction orthogonal to the optical axis, R is the paraxial curvature radius, k is the conic constant, and A4, A6, A8, A10, A12, A14, and A16 are aspherical coefficients of each order. "e±XX" in the aspherical coefficients means "x 10 ±XX ".

[0261] [Numerical Example 1]

[0262] Unit: mm

[0263] Surface data

[0264]

[0265]

[0266] Aspherical data

[0267]

[0268] Miscellaneous data

[0269]

[0270]

[0271] lens group data

[0272] Group Start Face Focal Length L1 1 36.30 L2 23 28.35 L3 30 -57.28

[0273] single lens data

[0274]

[0275] [numeric example 2] units: mm surface data

[0276]

[0277] aspherical surface data

[0278] miscellaneous data

[0279]

[0280]

[0281] lens group data

[0282] Group Start Face Focal Length L1 1 45.15 L2 19 32.25 L3 26 -85.88

[0283] single lens data

[0284] Lens Start Face Focal Length Theta gF 1 1 -53.14 2 3 -83.73 3 5 -70.04 4 7 24.46 5 8 -42.84 0.6122 6 10 40.12 7 12 -129.29 8 15 51.55 9 16 304.54 0.7782 10 17 -53.51 0.5824 11 19 61.63 12 20 -25.49 0.5951 13 22 38.67 14 24 42.45 15 26 46.39 16 27 -29.75

[0285] [numeric example 3]

[0286] units: mm surface data

[0287] Face Number r d nd vd 1 34.785 1.25 1.79360 37.1 2 17.108 5.10 3 29.757 2.00 1.53500 56.0 4* 19.213 10.91 5 -21.843 1.20 1.49700 81.7 6 -59.460 0.38 7 108.499 9.23 1.72916 54.7 8 -17.093 1.00 1.85478 24.8 9 -37.633 0.20 10 40.930 4.97 2.00100 29.1 11 -42.422 1.00 1.57501 41.5 12 30.464 5.24 13 (SP) ∞ 2.53 14 83.477 1.85 2.00100 29.1 15 595.325 (variable) 16 -22.125 4.05 1.49700 81.7 17 -11.634 0.90 1.770477 29.7 18 -78.451 0.20 19 72.244 6.30 1.72916 54.7 20 -22.067 0.20 21* -169.027 4.15 1.53500 56.0 22* -27.901 (variable) 23 -131.373 8.10 1.59282 68.6 24 -17.133 1.05 1.65412 39.7 25 111.091 17.25 Image Face ∞

[0288] aspherical surface data

[0289]

[0290]

[0291] miscellaneous data

[0292]

[0293] lens group data

[0294]

[0295]

[0296] Single lens data

[0297] Lens Start Face Focal Length Theta gF 1 1 -43.79 2 3 -108.52 3 5 -70.21 4 7 20.90 5 8 -37.48 0.6122 6 10 21.45 7 11 -30.68 8 14 96.82 9 16 43.76 10 17 -17.83 0.5951 11 19 23.85 12 21 61.83 13 23 32.38 14 24 -22.62

[0298] [Num. Ex. 4]

[0299] Units: mm

[0300] Surface data

[0301]

[0302]

[0303] Aspherical data

[0304]

[0305] Miscellaneous data

[0306]

[0307] Lens group data

[0308] Group Start Face Focal Length L1 1 47.04 L2 18 31.80 L3 26 -64.02

[0309] Single lens data

[0310]

[0311] [Num. Ex. 5] Units: mm Surface data

[0312]

[0313] Aspherical data

[0314]

[0315] Miscellaneous data

[0316]

[0317] Lens group data

[0318]

[0319]

[0320] Single lens data

[0321] Lens Start Face Focal Length Theta gF 1 1 -40.91 2 3 -87.15 3 5 -39.36 4 7 85.64 5 9 -51.99 6 11 20.18 7 12 -58.12 8 14 48.77 9 16 -51.22 0.5951 10 19 24.27 11 20 207.03 0.7782 12 21 -35.34 0.5824 13 23 37.43 14 24 -25.40 0.5951 15 26 37.20 16 28 53.71 17 30 41.48 18 31 -25.63

[0322] [Num. Ex. 6]

[0323] Units: mm

[0324] Surface Data

[0325]

[0326]

[0327] Aspheric Data

[0328]

[0329] Miscellaneous Data

[0330]

[0331] Lens Group Data

[0332] Group Start Face Focal Length L1 1 63.61 L2 19 45.28 L3 26 1142.84

[0333] Individual Lens Data

[0334] Lens Start Face Focal Length Theta gF 1 1 -62.53 2 3 -64.71 3 5 -82.75 4 7 27.04 5 8 -41.47 0.6122 6 10 41.97 7 12 -183.95 8 15 47.13 9 16 300.65 0.7782 10 17 -42.93 0.5633 11 19 47.17 12 20 -23.65 0.5951 13 22 40.93 14 24 63.00 15 26 41.39 16 27 -40.54

[0335] [Num. Ex. 7]

[0336] Units: mm

[0337] Surface Data

[0338]

[0339]

[0340] Aspheric Data

[0341]

[0342] Miscellaneous Data

[0343]

[0344] Lens Group Data

[0345] Group Start Face Focal Length L1 1 39.40 L2 17 28.11 L3 24 -61.16

[0346] Individual Lens Data

[0347]

[0348]

[0349] The following Table 1 and Table 2 summarize various values of each numerical example.

[0350] Table 1

[0351]

[0352]

[0353] In the following Table 2, lenses and various values thereof satisfying the conditional expressions (6), (7), (12), (14), and (15) in each numerical example are summarized.

[0354] Table 2

[0355]

[0356]

[0357]

[0358] [Imaging apparatus]

[0359] Next, an example of an imaging apparatus including the optical system L0 according to the present exemplary embodiment will be described.

[0360] Figure 15 is a schematic view illustrating an imaging apparatus 10 including the optical system L0 according to the present exemplary embodiment. The imaging apparatus 10 includes a camera body 13, an optical system 11 similar to one of the above-described Examples 1 to 7, and a light-receiving element 12 for photoelectrically converting an image formed by the optical system 11.

[0361] The imaging apparatus 10 of this example can obtain a high-quality image formed by the optical system 11 having a wide angle with improved correction of distortion aberration and a marginal illumination ratio.

[0362] An image sensor such as a CCD sensor and a CMOS sensor can be used as the light-receiving element 12. Various aberrations of an image obtained by the light-receiving element 12 such as distortion aberration and chromatic aberration can be corrected, for example, using an electrical technique, whereby the output image quality can be enhanced.

[0363] The optical system L0 of the above-described example is not limited to Figure 15 the illustrated digital still camera, and can be applied to various optical devices such as a silver halide film camera, a video camera, and a telescope. Both an integrated lens camera and a replaceable lens camera are applicable.

[0364] [Lens apparatus]

[0365] Next, an example of a lens apparatus including the optical system L0 according to the present exemplary embodiment will be described.

[0366] Figure 16 is a schematic appearance view of a lens apparatus including the optical system L0 according to the present exemplary embodiment. Figure 16 The lens apparatus of is a replaceable lens that can be detachably attached to an unillustrated camera body.

[0367] The lens apparatus 20 includes an imaging optical system 21 similar to one of the above-described Examples 1 to 7. The lens apparatus 20 includes a focus operation unit 22 and an operation unit 23 for changing an imaging mode.

[0368] When the user operates the focus operation unit 22, the arrangement of the imaging optical system 21 is mechanically or electrically changed to change the focus position. When the user operates the operation unit 23, the arrangement of the lens group in the imaging optical system 21 can be changed for purposes other than focusing. For example, based on the operation of the operation unit 23, the arrangement of the lens group in the imaging optical system 21 can be mechanically or electrically changed to change the aberration of the imaging optical system 21. In so doing, the focus position desirably remains substantially unchanged.

[0369] The above has described exemplary embodiments and examples of the present disclosure. The present disclosure is not limited to the above-described embodiments and examples, and various combinations, changes, and modifications can be made without departing from the spirit of the present disclosure.

[0370] While the present disclosure has been described with reference to exemplary embodiments, it is to be understood that the disclosure is not limited to the disclosed exemplary embodiments. The scope of the following claims is compatible with the widest interpretation of the present disclosure under the law to include all such modifications and equivalent structures and functions.

Claims

1. An optical system comprising: a first lens group having positive refractive power; a second lens group having positive refractive power; and a third lens group, the first lens group, the second lens group, and the third lens group being arranged in order from an object side to an image side, wherein the second lens group is configured to move in an optical axis direction with respect to an image plane during focusing, and the first lens group and the third lens group are configured to remain stationary with respect to the image plane during focusing, wherein the first lens group includes three negative lenses that are arranged continuously in the optical axis direction and positioned closest to the object side, and wherein the following conditional expressions are satisfied: 0.50 < f2 / f < 3.00, and 0.20 < sk / f < 1.20, wherein f is a focal length of the entire optical system, sk is an air equivalent back focal length when the optical system is focused at infinity, and f2 is a focal length of the second lens group. the following conditional expression is satisfied:

2. The optical system of claim 1, wherein, 0.30 < f1 / f2 < 3.00, wherein f1 is a focal length of the first lens group. the following conditional expression is satisfied:

3. The optical system of claim 1, wherein, -1.50 < f / f3 < 1.50, wherein f3 is a focal length of the third lens group. the second lens group includes at least two positive lenses and at least one negative lens.

4. The optical system of claim 1, wherein, 5. The optical system according to claim 1, a lens positioned closest to the object side in the second lens group has a concave object side lens surface, wherein, wherein a lens positioned closest to the image side in the second lens group has a convex image side lens surface, and wherein the following conditional expression is satisfied: -1.50 < (R22-R21) / (R22+R21) < 1.50, wherein R21 is a radius of curvature of an object side lens surface of a lens positioned closest to the object side in the second lens group, and R22 is a radius of curvature of an image side lens surface of a lens positioned closest to the image side in the second lens group.

6. The optical system according to claim 1, at least one of the first lens group and the second lens group includes a negative lens Gn, and wherein, wherein the following conditional expressions are satisfied: -0.015 < AgFn < 0.015, and -0.20 < Ndn-(-0.0145425 x vdn+2.28725) < 0.05, wherein AgFn = 9gFn - (-0.0025116 x vdn+0.67449), and wherein Ndn is a refractive index of a material of the negative lens Gn at the d line, vdn is an Abbe number, 9gFn is a partial dispersion ratio at the g line and the F line, and AgFn is an anomalous partial dispersion. the first lens group includes at least one negative lens Gn.

7. The optical system of claim 6, wherein, the second lens group includes at least one negative lens Gn.

8. The optical system of claim 6, wherein, the following conditional expression is satisfied:

9. The optical system of claim 1, wherein, wherein 2 is a lateral magnification of the second lens group when the optical system is focused at infinity, and 3 is a lateral magnification of the third lens group when the optical system is focused at infinity. 0.50<(1-β2 2 )×β3 2 <2.50， ​ 10. The optical system according to claim 1, further comprising an aperture stop inside or next to an image side of the first lens group, wherein the aperture stop is configured to remain stationary in the optical axis direction with respect to the image plane during focusing.

11. The optical system of claim 1, wherein, a conditional expression below is satisfied: 0.00 < sk / |f3| < 0.80, where f3 is a focal length of the third lens group.

12. The optical system of claim 1, wherein, a conditional expression below is satisfied: 0.20 < ∑Dair / (L - sk) < 0.70, where ∑Dair is a sum of air gaps on the optical axis from an object side lens surface of a lens located closest to the object plane in the first lens group to an image side lens surface of a lens located closest to the image plane in the third lens group, and L is a total optical length of the optical system.

13. The optical system of claim 1, wherein, a conditional expression below is satisfied: 2.00 < L / f < 15.00, where L is a total optical length of the optical system.

14. The optical system according to claim 1, wherein, the second lens group includes at least one positive lens G2p, and where a conditional expression below is satisfied: 60.00 < νd2p < 100.00, where νd2p is an Abbe number of a material of the positive lens G2p.

15. The optical system of claim 1, wherein, a conditional expression below is satisfied: -0.200 < M2 / DSP < -0.005, where M2 is a moving amount of the second lens group during focusing from infinity to an object distance at which a lateral magnification of the entire optical system is -0.1 times, in a case where the second lens group moves toward the image side during focusing from infinity to an object distance at which a lateral magnification of the entire optical system is -0.1 times, a sign of the moving amount is positive, and DSP is a distance on the optical axis from an aperture stop to a lens surface closest to the image plane in the optical system in a case where the optical system is focused at infinity.

16. The optical system according to claim 1, wherein the first lens group includes a negative lens GIn, and where a conditional expression below is satisfied: 60.00 < νdIn < 100.00, where νdIn is an Abbe number of the negative lens GIn.

17. The optical system according to claim 1, wherein at least one of the first lens group and the second lens group includes a positive lens Gp, and where a conditional expression below is satisfied: 0.050 < ΔθgFp < 0.250, where ΔθgFp = θgFp - (B3 x vdp 3 + B2 x vdp 2 + B1 x vdp + B0), B3＝-1.665×10 -7 ， B2＝5.213×10 -5 ， B1 = -5.656 x 10 -3 and B0 = 7.278 x 10 -1 and where νdp is an Abbe number of a material of the positive lens Gp, θgFp is a partial dispersion ratio, and ΔθgFp is an anomalous partial dispersion.

18. The optical system of claim 1, wherein, a conditional expression below is satisfied: 0.30 < (DSP + sk) / L < 0.80, where DSP is a distance on the optical axis from an aperture stop to a lens surface closest to the image plane in the optical system in a case where the optical system is focused at infinity, and L is a total optical length of the optical system.

19. The optical system of claim 1, wherein, a conditional expression below is satisfied: 0.50 < f1 / f < 5.00, where f1 is a focal length of the first lens group.

20. The optical system of claim 1, wherein, A negative lens is located closest to the image plane in the third lens group.

21. An optical system comprising: a first lens group having positive refractive power; a second lens group having positive refractive power; and a third lens group, the first lens group, the second lens group, and the third lens group being arranged in order from an object side to an image side, wherein the second lens group is configured to move in an optical axis direction relative to an image plane during focusing, and the first lens group and the third lens group are configured to remain stationary relative to the image plane during focusing, and wherein the following conditional expression is satisfied: 0.50 < f2 / f < 3.00, wherein f is a focal length of an entire optical system, and f2 is a focal length of the second lens group.

22. An image pickup apparatus comprising: the optical system according to any one of claims 1 to 21; and an image sensor configured to receive an image formed by the optical system.

Images