Optical system and imaging device having the same

Abstract

The present invention provides an optical system and imaging device that are equipped with a quiet and lightweight focusing group suitable for video recording, and that have high optical performance capable of effectively correcting various aberrations. [Solution] The optical system according to the present invention comprises, in order from the object side to the image side, a first lens group that does not move during focusing and has positive refractive power, and a second lens group that moves along the optical axis during focusing and has positive refractive power, wherein only the second lens group moves during focusing, the total number of lenses included in the optical system is nine or less, a negative lens is arranged on the object side of the first lens group, and the average value of the refractive index of each lens included in the second lens group, the focal length of the second lens group, the focal length of the first lens which has the largest absolute value of focal length among at least one lens included in the second lens group, the total optical length of the optical system, and the focal length of the optical system are appropriately set.

Description

Technical Field

[0001] The present invention relates to an optical system and an image pickup apparatus having the same, and particularly relates to an optical system suitably used in image pickup apparatuses such as digital video cameras, digital still cameras, cameras for silver halide film, broadcast cameras, and surveillance cameras.

Background Art

[0002] In recent years, optical systems used in image pickup apparatuses are required to be entirely compact and lightweight, and to have high optical performance that can sufficiently correct chromatic aberration. Further, in an optical system suitable for moving image shooting, it is important that focusing is performed quietly and a lightweight focus group is provided to suppress the occurrence of vibration.

[0003] Here, in order to achieve quiet operation and suppress the occurrence of vibration while maintaining high optical performance, it is important that the focus group is configured to be compact and lightweight, and the lens configuration of each lens group is appropriately set. Patent Document 1 discloses an optical system composed of, in order from an object side to an image side, a first lens unit having positive refractive power that does not move during focusing, a second lens unit having negative refractive power that moves along an optical axis during focusing, and a third lens unit having positive refractive power that does not move during focusing.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of Invention

Problems to be Solved by the Invention

[0005] The optical system disclosed in Patent Document 1 is not sufficiently miniaturized because a large number of lenses are provided to satisfactorily correct lateral chromatic aberration and field curvature. Therefore, the present invention aims to provide an optical system and imaging device having the same, which are equipped with a lightweight, quiet, and low-vibration focusing group suitable for video recording, and which have high optical performance capable of effectively correcting various aberrations, including chromatic aberration and field curvature. [Means for solving the problem]

[0006] One aspect of the present invention is an optical system comprising, in order from the object side to the image side, a first lens group that does not move during focusing and has positive refractive power, and a second lens group that moves along the optical axis during focusing and has positive refractive power, wherein only the second lens group moves during focusing, the total number of lenses included in the optical system is nine or less, a negative lens is arranged on the object side of the first lens group, when Nave2 is the average value of the refractive index of each lens included in the second lens group with respect to the d line, f2 is the focal length of the second lens group, f2lp is the focal length of the first lens with the largest absolute value of focal length among at least one lens included in the second lens group, TD is the total optical length of the optical system, and f is the focal length of the optical system, 1.45 <Nave2<1.67 -0.80 <f2 / f2lp<0.60 2.20 <TD / f<5.50 It is characterized by satisfying the following conditional expression. Another aspect of the present invention is an optical system comprising, in order from the object side to the image side, a first lens group that does not move during focusing and has positive refractive power, and a second lens group that moves along the optical axis during focusing and has positive refractive power, wherein only the second lens group moves during focusing, the total number of lenses included in the optical system is nine or less, and a negative lens is arranged on the object side of the first lens group. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide an optical system with high optical performance that is equipped with a lightweight focus group that is quiet and has little vibration, suitable for video recording, and that can effectively correct various aberrations including chromatic aberration and field curvature, as well as an imaging device having the same. [Brief explanation of the drawing]

[0008] [Figure 1] A cross-sectional view of the optical system according to Example 1 when focused to infinity. [Figure 2] A diagram showing the aberrations of the optical system according to Example 1 when focused to infinity. [Figure 3] Aberration diagram when focusing to the closest distance in the optical system according to Example 1. [Figure 4] A cross-sectional view of the optical system according to Example 2 when focused to infinity. [Figure 5] Aberration diagram of the optical system according to Example 2 when focused to infinity. [Figure 6] Aberration diagram when focusing to the closest distance in the optical system according to Example 2. [Figure 7] A cross-sectional view of the optical system according to Example 3 when focused to infinity. [Figure 8] A diagram showing the aberrations of the optical system according to Example 3 when focused to infinity. [Figure 9] Aberration diagram when focusing to the closest distance in the optical system according to Example 3. [Figure 10] A cross-sectional view of the optical system according to Example 4 when focused to infinity. [Figure 11] A diagram showing the aberrations of the optical system according to Example 4 when focused to infinity. [Figure 12] Aberration diagram when focusing to the closest distance in the optical system according to Example 4. [Figure 13] A cross-sectional view of the optical system according to Example 5 when focused to infinity. [Figure 14] Aberration diagram of the optical system according to Example 5 when focused to infinity. [Figure 15] Aberration diagram when the optical system according to Example 5 is focused at the closest distance. [Figure 16] Cross-sectional view when the optical system according to Example 6 is focused at infinity. [Figure 17] Aberration diagram when the optical system according to Example 6 is focused at infinity. [Figure 18] Aberration diagram when the optical system according to Example 6 is focused at the closest distance. [Figure 19] Cross-sectional view when the optical system according to Example 7 is focused at infinity. [Figure 20] Aberration diagram when the optical system according to Example 7 is focused at infinity. [Figure 21] Aberration diagram when the optical system according to Example 7 is focused at the closest distance. [Figure 22] Cross-sectional view when the optical system according to Example 8 is focused at infinity. [Figure 23] Aberration diagram when the optical system according to Example 8 is focused at infinity. [Figure 24] Aberration diagram when the optical system according to Example 8 is focused at the closest distance. [Figure 25] Cross-sectional view when the optical system according to Example 9 is focused at infinity. [Figure 26] Aberration diagram when the optical system according to Example 9 is focused at infinity. [Figure 27] Aberration diagram when the optical system according to Example 9 is focused at the closest distance. [Figure 28] Perspective view of an imaging apparatus comprising the optical system according to any one of Examples 1 to 9. [Modes for Carrying Out the Invention]

[0009] Hereinafter, the optical system according to the present embodiment will be described in detail based on the accompanying drawings. Note that the drawings shown below may be drawn on a different scale from the actual one to facilitate easy understanding of the present embodiment. Figures 1, 4, 7, 10, 13, 16, 19, 22, and 25 show schematic cross-sectional views of the optical system L0 according to Examples 1, 2, 3, 4, 5, 6, 7, 8, and 9 when focused to infinity.

[0010] Specifically, the optical systems L0 in each of Examples 1 to 9 are used in imaging devices such as digital video cameras, digital still cameras, silver halide film cameras, broadcast cameras, and surveillance cameras, but are not limited to these. In Figures 1, 4, 7, 10, 13, 16, 19, 22, and 25, the left side is the object side and the right side is the image side.

[0011] The optical system L0 in each of the 1 to 9 embodiments is formed by a plurality of lens groups. The term "lens group" as used herein refers to a single or multiple lenses that move together as a unit during focusing, or remain stationary (immovable), and may include the aperture diaphragm SP.

[0012] In other words, in the optical system L0 according to each of the 1 to 9 embodiments, the spacing between adjacent lens groups changes when focusing from infinity to the closest distance. Specifically in Figures 1, 4, 7, 10, 13, 16, 19, 22, and 25, Li (where i is a natural number) represents the i-th lens group from the object side among the multiple lens groups included in the optical system L0.

[0013] Of these, the first lens group L1 has positive refractive power, and the second lens group L2 also has positive refractive power. SP is the aperture diaphragm, and IP is the image plane. When the optical system L0 according to each of the 1 to 9 is used as an imaging optical system for a digital still camera or a digital video camera, the imaging surface of a solid-state image sensor (photoelectric conversion element) such as a CCD sensor or CMOS sensor is positioned at the location of the image plane IP.

[0014] On the other hand, when the optical system L0 according to each of Examples 1 to 9 is used as the imaging optical system of a silver halide film camera, a photosensitive surface corresponding to the film surface is placed at the position of the image plane IP. Furthermore, the arrows related to focus shown in Figures 1, 4, 7, 10, 13, 16, 19, 22, and 25 represent the direction of movement of the second lens group L2 during focusing from infinity to the closest distance.

[0015] Figures 2, 5, 8, 11, 14, 17, 20, 23, and 26 show the longitudinal aberration diagrams of the optical system L0 according to Examples 1 to 9 when focused to infinity. Figures 3, 6, 9, 12, 15, 18, 21, 24, and 27 show longitudinal aberration diagrams when the optical system L0 according to Examples 1 to 9 is focused to the closest distance.

[0016] In the spherical aberration diagram, Fno indicates the F number, and the amount of spherical aberration at the d line (wavelength 587.56 nm) and the g line (wavelength 435.835 nm) is also shown. In the astigmatism diagram, S represents the sagittal image plane and M represents the meridional image plane.

[0017] The distortion diagram shows the amount of distortion on the d line, and the chromatic aberration diagram shows the amount of chromatic aberration on the g line. In the astigmatism, distortion, and chromatic aberration diagrams, ω represents the half-angle of view (degrees) calculated using paraxial calculations.

[0018] Next, we will describe the characteristic configurations of the optical system L0 in each of the 1 to 9 examples. The optical system L0 in each of Examples 1 to 9 includes, in order from the object side to the image side, a first lens group L1 with positive refractive power that does not move (is stationary) during focusing, and a second lens group L2 with positive refractive power that moves along the optical axis during focusing.

[0019] In the optical system L0 according to each of Examples 1 to 9, the lens configuration is appropriately set so that the first lens group L1 and the second lens group L2 each have positive refractive power, thereby reducing the diameter of the light beam incident on the second lens group L2. This makes it possible to make the focus group smaller and lighter. Furthermore, in the optical system L0 according to each of the 1 to 9 embodiments, only the second lens group L2 moves during focusing, thereby achieving both suppression of angle of view fluctuations during focusing and weight reduction.

[0020] Furthermore, the number of lenses (total number) included in the optical system L0 for each of Examples 1 to 9 is nine or less. Furthermore, in the optical system L0 according to each of the 1 to 9 embodiments, a lens with negative refractive power (negative lens) is arranged at the object-side of the first lens group L1.

[0021] Furthermore, the optical system L0 for each of Examples 1 to 9 satisfies the following conditions (1), (2), and (3). 1.45 <Nave2<1.67 ···(1) -0.80 <f2 / f2lp<0.60 ···(2) 2.20 <TD / f<5.50 ···(3)

[0022] In condition (1), Nave2 represents the average value of the refractive index of each lens included in the second lens group L2 with respect to the d line. In condition (2), f2 represents the focal length of the second lens group L2, and f2lp represents the focal length of the lens Gb2lp (the first lens) which has the largest absolute value of focal length among at least one lens included in the second lens group L2.

[0023] In conditional equation (3), TD represents the total optical length of the optical system L0, and f represents the focal length of the entire optical system L0. Here, the total optical length of the optical system L0 is the distance along the optical axis between the lens surface closest to the object in the optical system L0 (i.e., the lens surface closest to the object in the optical system L0) and the image plane IP.

[0024] Condition (1) is a condition for the average value of the refractive index of at least one lens included in the second lens group L2. To reduce the weight of the focusing group, it is necessary to select a glass material for at least one lens in the focusing group that has a low specific gravity and a low refractive index while still possessing sufficient optical performance.

[0025] If the proportion of lenses made of a high refractive index among at least one lens in the second lens group L2 increases to the point where it exceeds the upper limit of condition (1), then the proportion of lenses with high specific gravity increases, making it difficult to lighten the focus group. On the other hand, as the value falls below the lower limit of condition (1), the proportion of lenses made of materials with a low refractive index among at least one lens in the second lens group L2 increases, making it difficult to obtain sufficient optical performance due to the limited range of selectable materials.

[0026] Conditional equation (2) is a conditional equation for the focal length f2lp of lens Gb2lp, which has the largest absolute value of focal length among at least one lens included in the second lens group L2, normalized by the focal length f2 of the second lens group L2. Specifically, condition (2) specifies the lens power suitable for reducing the weight of the focus group and reducing field curvature. If the absolute value of the focal length of each lens included in the second lens group L2 becomes so small that it exceeds the upper limit of condition (2) or falls below the lower limit, it becomes difficult to achieve both a reduction in field curvature and a reduction in chromatic aberration.

[0027] Conditional equation (3) is a conditional equation for the total optical length TD normalized by the focal length f in the entire optical system L0, that is, it defines the range of the focal length f and the total optical length TD in the entire optical system L0. If the upper limit of condition (3) is exceeded, the optical total length TD will increase, making it difficult to achieve sufficient weight reduction. On the other hand, if the value falls below the lower limit of condition (3), the optical total length TD can be shortened, which can significantly reduce weight, but it becomes difficult to obtain sufficient optical performance.

[0028] In addition, for each of the 1 to 9 examples, the optical system L0 preferably satisfies the following conditions (1a), (2a), and (3a) instead of conditions (1) to (3). 1.47 <Nave2<1.66 ···(1a) -0.70 <f2 / f2lp<0.59 ···(2a) 2.23 <TD / f<5.48 ···(3a)

[0029] Furthermore, it is more preferable that the optical system L0 in each of Examples 1 to 9 satisfies the following conditions (1b), (2b), and (3b) instead of conditions (1a) to (3a). 1.50 <Nave2<1.65 ···(1b) -0.60 <f2 / f2lp<0.58 ···(2b) 2.26 <TD / f<5.46 ···(3b)

[0030] Furthermore, it is preferable that the optical system L0 for each of Examples 1 to 9 satisfies at least one of the following conditions (4), (5), (6), (7), (8), (9), (10), (11), (12), (13), and (14). 0.60 <SPD / TD<0.80 ···(4) 1.50 <f2 / f<3.00 ···(5) 0.20 <f1r / f1<1.10 ···(6) 0.50 <f1 / f2<2.00 ···(7) -3.00<(Rn2+Rn1) / (Rn2-Rn1)<-0.01 ···(8) 1.40 <f1 / f<3.70 ···(9) 0.05 <DF / TD<0.18 ···(10) 0.15 <SK / TD<0.46 ···(11) 0.10 <Db1 / TD<0.24 ···(12) 0.10 <Db2 / TD<0.26 ···(13) 0.80 <d<3.10 ···(14)

[0031] In conditional equation (4), SPD represents the distance along the optical axis between the aperture diaphragm SP and the image plane IP. In conditional equation (6), f1r is the focal length of the lens located closest to the image in the first lens group L1, and f1 is the focal length of the first lens group L1.

[0032] In conditional equation (8), Rn1 and Rn2 represent the radius of curvature of the object-side and image-side lens surfaces of the negative refractive lens located closest to the object in the first lens group L1, respectively. In conditional equation (10), DF represents the distance on the optical axis between the object-side lens surface of the second lens group L2 and the image-side lens surface or aperture diaphragm SP of a lens adjacent to it on the object side of the second lens group L2 when focused at infinity.

[0033] In other words, the object-side lens surface of the second lens group L2 is the object-side lens surface of the lens (the second lens) that is positioned closest to the object in the second lens group L2. Furthermore, adjacent lenses on the object side of the second lens group L2 refer to the lenses located adjacent to the object side of the lens that is positioned closest to the object in the second lens group L2.

[0034] In conditional equation (11), SK represents the air-equivalent distance on the optical axis between the image-side lens surface of the lens positioned closest to the image in the optical system L0 and the image plane IP. In conditional equation (12), Db1 represents the sum of the lens thicknesses along the optical axis between the lens surface closest to the object and the lens surface closest to the image of the first lens group L1, that is, the sum of the lens thicknesses along the optical axis of each lens included in the first lens group L1.

[0035] In condition (13), Db2 represents the sum of the lens thicknesses along the optical axis between the lens surface closest to the object and the lens surface closest to the image of the second lens group L2, that is, the sum of the lens thicknesses along the optical axis of each lens included in the second lens group L2. In condition (14), d represents the specific gravity of the lens with the largest absolute focal length among at least one lens included in the second lens group L2.

[0036] Conditional equation (4) is a conditional equation for the distance SPD between the aperture diaphragm SP and the image plane IP, normalized by the total optical length TD of the optical system L0, and specifically defines the position of the aperture diaphragm SP. If the aperture diaphragm SP is positioned so close to the object that it exceeds the upper limit of condition (4), the number of lenses that can be positioned closer to the object than the aperture diaphragm SP will decrease, making it difficult to reduce spherical aberration and axial chromatic aberration. On the other hand, if the value falls below the lower limit of condition (4), the aperture diaphragm SP is positioned closer to the image plane IP, which increases the angle of incidence relative to the image plane IP around the maximum image height, resulting in color shading.

[0037] Conditional equation (5) is a conditional equation for the focal length f2 of the second lens group L2, normalized by the focal length f of the optical system L0. Specifically, it defines the conditions under which the closest focusing distance can be shortened while suppressing changes in optical performance during focusing. If the positive focal length f2 of the second lens group L2 becomes large enough to exceed the upper limit of condition (5), the focus position sensitivity of the second lens group L2 (the ratio of the movement of the image plane IP to the movement of the focus group) becomes too small. As a result, it becomes difficult to shorten the closest focusing distance, or it becomes difficult to shorten the overall length of the optical system L0 in order to secure a focusing distance. On the other hand, if the positive focal length f2 of the second lens group L2 becomes smaller, falling below the lower limit of condition equation (5), the refractive power of the second lens group L2 becomes too large, resulting in excessive changes in optical performance such as spherical aberration, field curvature, and angle of view fluctuations during focusing.

[0038] Conditional equation (6) is a conditional equation for the focal length f1r of the lens located closest to the image in the first lens group L1, normalized by the focal length f1 of the first lens group L1. If the upper limit of condition (6) is exceeded, the diameter of the light beam incident on the second lens group L2 increases, which in turn increases the lens diameter on the object side of the focusing group, resulting in an increase in weight. On the other hand, if the value falls below the lower limit of condition (6), the refractive power of the first lens group L1 increases, resulting in increased spherical aberration and axial chromatic aberration.

[0039] Conditional equation (7) is a conditional equation that defines the relationship between the focal length f1 of the first lens group L1 and the focal length f2 of the second lens group L2. If the focal length f2 of the second lens group L2 becomes so small that it exceeds the upper limit of condition (7), the refractive power of the second lens group L2 becomes too large, causing excessive changes in optical performance such as spherical aberration, field curvature, and angle of view fluctuations during focusing.

[0040] Furthermore, as the focal length f1 of the first lens group L1 increases beyond the upper limit of condition (7), the total length of the optical system L0 increases. On the other hand, as the focal length f2 of the second lens group L2 increases to the point below the lower limit of condition equation (7), the refractive power of the second lens group L2 becomes too small, increasing the amount of movement required during focusing, and thus increasing the overall length of the optical system L0. Furthermore, as the focal length f1 of the first lens group L1 decreases below the lower limit of condition equation (7), it becomes difficult to correct spherical aberration and axial chromatic aberration.

[0041] Conditional equation (8) is a conditional equation that defines the range of shape factors of the negative refractive lens located closest to the object in the optical system L0. When the upper limit of condition (8) is exceeded, the radius of curvature of the lens surface on the object side becomes smaller than the radius of curvature of the lens surface on the image side, resulting in increased field curvature. On the other hand, if the value falls below the lower limit of condition (8), it is advantageous in reducing field curvature, but the lens diameter of the lens becomes larger, resulting in a larger overall size.

[0042] Conditional equation (9) is a conditional equation for the focal length f1 of the first lens group L1, normalized by the focal length f of the optical system L0. When the upper limit of condition (9) is exceeded, the refractive power of the first lens group L1 decreases, which increases the overall length of the optical system L0. On the other hand, if the value falls below the lower limit of condition equation (9), it is advantageous for miniaturizing the focus group, but spherical aberration and axial chromatic aberration increase.

[0043] Conditional equation (10) is a conditional equation for the distance DF between the object-side lens surface of the second lens group L2 and the image-side lens surface or aperture diaphragm SP of the lens adjacent to the object-side lens of the second lens group L2 when focused at infinity, normalized by the total optical length TD of the optical system L0. If the upper limit of condition (10) is exceeded, the optical system L0 becomes larger as the total optical length TD increases in order to suppress the reduction in optical performance. On the other hand, if the value falls below the lower limit of condition (10), it becomes difficult to achieve both miniaturization and suppression of the reduction in optical performance for focusing.

[0044] Conditional equation (11) is a conditional equation for the air-equivalent distance SK between the image-side lens surface and the image plane IP of the optical system L0, normalized by the total optical length TD of the optical system L0. If the upper limit of condition (11) is exceeded, the spacing between each lens in the optical system L0 becomes smaller, making it difficult to reduce spherical aberration and chromatic aberration. On the other hand, if the value falls below the lower limit of condition (11), the air-equivalent distance SK between the image-side lens surface and the image plane IP of the optical system L0 becomes smaller, which increases spherical aberration and coma aberration.

[0045] Conditional equation (12) is a conditional equation for the sum of the wall thicknesses Db1 of each lens included in the first lens group L1, normalized by the total optical length TD of the optical system L0. If the upper limit of condition (12) is exceeded, the thickness of each lens included in the first lens group L1 increases, making weight reduction difficult. On the other hand, if the value falls below the lower limit of condition equation (12), it becomes difficult to reduce axial chromatic aberration.

[0046] Conditional equation (13) is a conditional equation for the sum of the wall thicknesses Db2 of each lens included in the second lens group L2, normalized by the total optical length TD of the optical system L0. If the upper limit of condition (13) is exceeded, the thickness of each lens included in the second lens group L2 increases, which enlarges the focusing group and makes miniaturization difficult. On the other hand, if the value falls below the lower limit of condition equation (13), it becomes difficult to reduce chromatic aberration.

[0047] Conditional equation (14) is a conditional equation for the specific gravity d of the lens with the largest absolute value of focal length among at least one lens included in the second lens group L2. If the upper limit of condition (14) is exceeded, the weight of the focus group will increase. On the other hand, if the refractive power falls below the lower limit of condition equation (14), it becomes difficult to create a lens with a refractive power suitable for focusing.

[0048] The optical system L0 for each of Examples 1 to 9 is more preferably satisfied by the following conditions (4a), (5a), (6a), (7a), (8a), (9a), (10a), (11a), (12a), (13a), and (14a) instead of conditions (4) to (14). 0.61 <SPD / TD<0.79 ···(4a) 1.53 <f2 / f<2.98 ···(5a) 0.25 <f1r / f1<1.07 ···(6a) 0.55 <f1 / f2<1.80 ···(7a) -2.95<(Rn2+Rn1) / (Rn2-Rn1)<-0.03 (8a) 1.45 <f1 / f<3.65 ···(9a) 0.06 <DF / TD<0.17 ···(10a) 0.16 <SK / TD<0.45 ···(11a) 0.11 <Db1 / TD<0.22 ···(12a) 0.11 <Db2 / TD<0.24 ···(13a) 0.90 <d<3.08 ···(14a)

[0049] Furthermore, it is even more preferable that the optical system L0 in each of Examples 1 to 9 satisfies the following conditions (4b), (5b), (6b), (7b), and (8b) instead of conditions (4a) to (8a). Furthermore, it is even more preferable that the optical system L0 in each of Examples 1 to 9 satisfies the following conditions (9b), (10b), (11b), (12b), (13b), and (14b) instead of the conditions (9a) to (14a). 0.62 <SPD / TD<0.78 ···(4b) 1.56 <f2 / f<2.96 ···(5b) 0.30 <f1r / f1<1.04 ···(6b) 0.60 <f1 / f2<1.60 ···(7b) -2.90<(Rn2+Rn1) / (Rn2-Rn1)<-0.05 (8b) 1.50 <f1 / f<3.60 ···(9b) 0.07 <DF / TD<0.16 ···(10b) 0.17 <SK / TD<0.44 ···(11b) 0.12 <Db1 / TD<0.20 ···(12b) 0.12 <Db2 / TD<0.22 ···(13b) 1.00 <d<3.06 ···(14b)

[0050] Furthermore, in the optical system L0 according to each of Examples 1 to 9, it is preferable that the second lens group L2 is composed of four or fewer lenses. This makes it easy to achieve both a lightweight focus group and high optical performance.

[0051] Furthermore, it is preferable that the optical system L0 in each of Examples 1 to 9 is composed of six or more lenses. This makes it easy to achieve both a lightweight optical system (L0) and high optical performance.

[0052] Furthermore, in the optical system L0 according to each of the 1 to 9 examples, it is preferable that the lens with the largest absolute focal length among the at least one lens included in the second lens group L2 is positioned closest to the image in the second lens group L2. This makes it easy to suppress distortion fluctuations during focusing. Furthermore, in the optical system L0 according to each of Examples 1 to 9, it is preferable that the lens with the largest absolute value of focal length among at least one lens included in the second lens group L2 is an aspherical lens.

[0053] Next, the detailed configuration of the optical system L0 for each of Examples 1 to 9 will be described. Figure 1 shows a schematic cross-sectional view of the optical system L0 according to Example 1 when it is focused to infinity.

[0054] In the optical system L0 according to Embodiment 1, a first lens group L1 is provided, which is located closest to the object, and a second lens group L2 is provided, which is located adjacent to the first lens group L1. The first lens group L1 consists of the following four lenses. Specifically, the first lens group L1 includes, in order from the object side to the image side, a meniscus lens that is convex toward the object side and has negative refractive power, a meniscus lens that is convex toward the object side and has negative refractive power, and a lens that is biconvex and has positive refractive power. Furthermore, the first lens group L1 includes a meniscus lens that is concave toward the object side on the image side and has positive refractive power.

[0055] The second lens group L2 consists of the following four lenses. Specifically, the second lens group L2 includes, in order from the object side to the image side, a meniscus lens that is concave on the object side and has positive refractive power, and a meniscus lens bonded to the said meniscus lens that is concave on the object side and has negative refractive power. Furthermore, the second lens group L2 includes a lens that is biconvex on the image side and also has positive refractive power.

[0056] Furthermore, the second lens group L2 includes a lens on the image side in which, on the paraxial direction, the lens surface on the object side is concave toward the object side, and the lens surface on the image side is convex toward the image side, and also has a positive refractive power. In the optical system L0 according to Example 1, the lens Gb2lp, which has the largest absolute focal length among at least one lens included in the second lens group L2, is positioned closest to the image in the second lens group L2. The focusing group is the second lens group L2.

[0057] Figure 4 shows a schematic cross-sectional view of the optical system L0 according to Example 2 when it is focused to infinity. In the optical system L0 according to Embodiment 2, a first lens group L1 is positioned closest to the object, a second lens group L2 is positioned adjacent to the first lens group L1, and a third lens group L3 is positioned closest to the image.

[0058] The first lens group L1 consists of the following four lenses. Specifically, the first lens group L1 includes, in order from the object side to the image side, a meniscus lens that is convex toward the object side and has negative refractive power, and a meniscus lens that is convex toward the object side and has negative refractive power. Furthermore, the first lens group L1 includes, in order from the object side to the image side, a biconvex lens with positive refractive power and a meniscus lens that is concave on the object side with positive refractive power.

[0059] The second lens group L2 consists of the following four lenses. Specifically, the second lens group L2 includes, in order from the object side to the image side, a meniscus lens that is concave on the object side and has positive refractive power, and a lens bonded to the meniscus lens that is biconcave and has negative refractive power. Furthermore, the second lens group L2 includes a lens that is biconvex on the image side and also has positive refractive power. Furthermore, the second lens group L2 includes a lens on the image side in which, on the paraxial direction, the lens surface on the object side is concave toward the object side, and the lens surface on the image side is convex toward the image side, and also has a negative refractive power.

[0060] The third lens group L3 consists of a meniscus lens that is concave towards the object and has positive refractive power. In the optical system L0 according to Embodiment 2, the lens Gb2lp, which has the largest absolute focal length among at least one lens included in the second lens group L2, is positioned on the image side of the second lens group L2. The focusing group is the second lens group L2.

[0061] Figure 7 shows a schematic cross-sectional view of the optical system L0 according to Example 3 when it is focused to infinity. In the optical system L0 according to Embodiment 3, a first lens group L1 is provided that is located closest to the object, and a second lens group L2 is provided that is located adjacent to the first lens group L1.

[0062] The first lens group L1 consists of the following four lenses. Specifically, the first lens group L1 includes, in order from the object side to the image side, a meniscus lens that is convex toward the object side and has negative refractive power, and a meniscus lens that is convex toward the object side and has negative refractive power. Furthermore, the first lens group L1 includes, in order from the object side to the image side, a biconvex lens with positive refractive power and a meniscus lens that is concave on the object side with positive refractive power.

[0063] The second lens group L2 consists of the following four lenses. Specifically, the second lens group L2 includes, in order from the object side to the image side, a biconvex lens with positive refractive power, and a meniscus lens bonded to the said lens, which is concave on the object side and has negative refractive power. Furthermore, the second lens group L2 includes a meniscus lens that is concave towards the object side on the image side and has positive refractive power.

[0064] Furthermore, the second lens group L2 includes a lens on the image side in which, on the paraxial direction, the lens surface on the object side is concave toward the object side, and the lens surface on the image side is convex toward the image side, and also has a negative refractive power. In the optical system L0 according to Embodiment 3, the lens Gb2lp, which has the largest absolute focal length among at least one lens included in the second lens group L2, is positioned on the image side of the second lens group L2. The focusing group is the second lens group L2.

[0065] Figure 10 shows a schematic cross-sectional view of the optical system L0 according to Example 4 when it is focused to infinity. In the optical system L0 according to Embodiment 4, a first lens group L1 is provided that is located closest to the object, and a second lens group L2 is provided that is located adjacent to the first lens group L1.

[0066] The first lens group L1 consists of the following four lenses. Specifically, the first lens group L1 includes, in order from the object side to the image side, a biconcave lens with negative refractive power and a biconvex lens with positive refractive power. Furthermore, the first lens group L1 includes, in order from the object side to the image side, a biconcave lens with negative refractive power and a biconvex lens with positive refractive power.

[0067] The second lens group L2 consists of the following four lenses. Specifically, the second lens group L2 includes, in order from the object side to the image side, a meniscus lens that is concave on the object side and has positive refractive power, and a lens bonded to the meniscus lens that is biconcave and has negative refractive power. Furthermore, the second lens group L2 includes a lens that is biconvex on the image side and also has positive refractive power.

[0068] Furthermore, the second lens group L2 includes a lens on the image side in which, on the paraxial direction, the lens surface on the object side is concave toward the object side, and the lens surface on the image side is convex toward the image side, and also has a negative refractive power. In the optical system L0 according to Embodiment 4, the lens Gb2lp, which has the largest absolute focal length among at least one lens included in the second lens group L2, is positioned on the image side of the second lens group L2. The focusing group is the second lens group L2.

[0069] Figure 13 shows a schematic cross-sectional view of the optical system L0 according to Example 5 when it is focused to infinity. In the optical system L0 according to Embodiment 5, a first lens group L1 is provided that is located closest to the object, and a second lens group L2 is provided that is located adjacent to the first lens group L1.

[0070] The first lens group L1 consists of the following four lenses. Specifically, the first lens group L1 includes, in order from the object side to the image side, a meniscus lens that is convex toward the object side and has negative refractive power, and a meniscus lens that is convex toward the object side and has negative refractive power. Furthermore, the first lens group L1 includes, in order from the object side to the image side, a biconvex lens with positive refractive power and a meniscus lens that is concave on the object side with positive refractive power.

[0071] The second lens group L2 consists of the following four lenses. Specifically, the second lens group L2 includes, in order from the object side to the image side, a biconvex lens with positive refractive power, and a meniscus lens bonded to the said lens, which is concave on the object side and has negative refractive power. Furthermore, the second lens group L2 includes a meniscus lens that is concave towards the object side on the image side and has positive refractive power.

[0072] Furthermore, the second lens group L2 includes a lens on the image side in which, on the paraxial direction, the lens surface on the object side is concave toward the object side, and the lens surface on the image side is convex toward the image side, and also has a positive refractive power. In the optical system L0 according to Example 5, the lens Gb2lp, which has the largest absolute focal length among at least one lens included in the second lens group L2, is positioned on the image side of the second lens group L2. The focusing group is the second lens group L2.

[0073] Figure 16 shows a schematic cross-sectional view of the optical system L0 according to Example 6 when it is focused to infinity. In the optical system L0 according to Embodiment 6, a first lens group L1 is provided that is located closest to the object, and a second lens group L2 is provided that is located adjacent to the first lens group L1.

[0074] The first lens group L1 consists of the following four lenses. Specifically, the first lens group L1 includes, in order from the object side to the image side, a biconcave lens with negative refractive power and a biconvex lens with positive refractive power. Furthermore, the first lens group L1 includes, in order from the object side to the image side, a biconcave lens with negative refractive power and a biconvex lens with positive refractive power.

[0075] The second lens group L2 consists of the following four lenses. Specifically, the second lens group L2 includes, in order from the object side to the image side, a meniscus lens that is concave on the object side and has positive refractive power, and a lens bonded to the meniscus lens that is biconcave and has negative refractive power. Furthermore, the second lens group L2 includes a lens on the image side that is both biconvex and has positive refractive power.

[0076] Furthermore, the second lens group L2 includes a lens on the image side in which, on the paraxial direction, the lens surface on the object side is concave toward the object side, and the lens surface on the image side is convex toward the image side, and also has a positive refractive power. In the optical system L0 according to Example 6, the lens Gb2lp, which has the largest absolute focal length among at least one lens included in the second lens group L2, is positioned on the image side of the second lens group L2. The focusing group is the second lens group L2.

[0077] Figure 19 shows a schematic cross-sectional view of the optical system L0 according to Example 7 when it is focused to infinity. In the optical system L0 according to Embodiment 7, a first lens group L1 is positioned closest to the object, a second lens group L2 is positioned adjacent to the first lens group L1, and a third lens group L3 is positioned closest to the image.

[0078] The first lens group L1 consists of, in order from the object side to the image side, a biconcave lens with negative refractive power and a biconvex lens with positive refractive power. The second lens group L2 consists of, in order from the object side to the image side, a meniscus lens that is concave on the object side and has negative refractive power, a lens that is biconvex and has positive refractive power, and a meniscus lens that is concave on the object side in the paraxial direction and has positive refractive power.

[0079] The third lens group L3 consists of a meniscus lens that is convex towards the object and has negative refractive power. In the optical system L0 according to Example 7, the lens Gb2lp, which has the largest absolute focal length among at least one lens included in the second lens group L2, is positioned on the image side of the second lens group L2. The focusing group is the second lens group L2.

[0080] Figure 22 shows a schematic cross-sectional view of the optical system L0 according to Example 8 when it is focused to infinity. In the optical system L0 according to Embodiment 8, a first lens group L1 is provided that is located closest to the object, and a second lens group L2 is provided that is located adjacent to the first lens group L1.

[0081] The first lens group L1 consists of the following four lenses. Specifically, the first lens group L1 includes, in order from the object side to the image side, a meniscus lens that is convex toward the object side and has negative refractive power, and a meniscus lens that is convex toward the object side and has negative refractive power. Furthermore, the first lens group L1 includes, in order from the object side to the image side, a biconvex lens with positive refractive power and a meniscus lens that is concave on the object side with positive refractive power.

[0082] The second lens group L2 consists of the following four lenses. Specifically, the second lens group L2 includes, in order from the object side to the image side, a meniscus lens that is convex toward the object side and has positive refractive power, and a meniscus lens bonded to the said meniscus lens that is concave toward the object side and has negative refractive power. Furthermore, the second lens group L2 includes a meniscus lens on the image side that is concave toward the object side and has positive refractive power.

[0083] Furthermore, the second lens group L2 includes a lens on the image side in which, on the paraxial direction, the lens surface on the object side is concave toward the object side, and the lens surface on the image side is convex toward the image side, and also has a negative refractive power. In the optical system L0 according to Example 8, the lens Gb2lp, which has the largest absolute focal length among at least one lens included in the second lens group L2, is positioned on the image side of the second lens group L2. The focusing group is the second lens group L2.

[0084] Figure 25 shows a schematic cross-sectional view of the optical system L0 according to Example 9 when it is focused to infinity. In the optical system L0 according to Embodiment 9, a first lens group L1 is provided that is located closest to the object, and a second lens group L2 is provided that is located adjacent to the first lens group L1.

[0085] The first lens group L1 consists of the following four lenses. Specifically, the first lens group L1 includes, in order from the object side to the image side, a biconcave lens with negative refractive power and a biconvex lens with positive refractive power. Furthermore, the first lens group L1 includes, in order from the object side to the image side, a meniscus lens that is concave on the object side and has negative refractive power, and a lens that is biconvex and has positive refractive power.

[0086] The second lens group L2 consists of the following three lenses. Specifically, the second lens group L2 includes, in order from the object side to the image side, a biconcave lens with negative refractive power and a biconvex lens with positive refractive power. Furthermore, the second lens group L2 includes a lens on the image side in which, on the paraxial direction, the lens surface on the object side is concave toward the object side, and the lens surface on the image side is convex toward the image side, and also has a positive refractive power. In the optical system L0 according to Example 9, the lens Gb2lp, which has the largest absolute focal length among at least one lens included in the second lens group L2, is positioned on the image side of the second lens group L2. The focusing group is the second lens group L2.

[0087] Next, the numerical values ​​corresponding to each of Examples 1 to 9 are shown below. Examples 1 to 9 are shown below. In the surface data of each numerical example, when m is the number of the optical surface counted from the object side, r m d is the radius of curvature of the m-th surface, m This represents the interplanar spacing (distance along the optical axis) between the m-th plane and the (m+1)-th plane.

[0088] Also, nd m νd is the refractive index of the optical element between the m-th plane and the (m+1)-th plane with respect to the d-line. m This represents the Abbe number of the optical element between the m-th plane and the (m+1)-th plane. Here, the Abbe number νd is expressed by the following equation (A), where Nd, NF, and NC are the refractive indices for the Fraunhofer lines d (587.56 nm), F (486.13 nm), and C (656.27 nm), respectively. νd = (Nd-1) / (NF-NC) ... (A)

[0089] Furthermore, θgF represents the partial dispersion ratio with respect to the g-line (435.84 nm) and the F-line, and specifically, when the refractive index of the Fraunhofer line with respect to the g-line is Ng, it is expressed by the following equation (B). θgF=(Ng-NF) / (NF-NC) ···(B)

[0090] In each numerical example, the plane spacing d, focal length, F-number, and half-angle of view calculated by paraxial calculation are the values ​​obtained when the optical system L0 is focused on an object at infinity. Furthermore, the back focus (BF) represents the distance between the final surface and the image plane (IP), and the total lens length is the distance between the first surface (the lens surface closest to the object) and the final surface (the lens surface closest to the image) plus the back focus (BF).

[0091] Additionally, an aspherical optical surface is denoted by an asterisk (*) to the right of its surface number. The aspherical shape is expressed by the following equation (C), where X is the displacement from the vertex of the surface in a direction parallel to the optical axis, h is the height from the optical axis in a direction perpendicular to the optical axis, R is the radius of paraxial curvature, K is the cone constant, and A4, A6, A8, A10, and A12 are aspherical coefficients.

number

[0092] Furthermore, "eX" in the aspherical coefficient is "×10 -X It means "...". Furthermore, the values ​​corresponding to conditional equations (1) to (14) in the optical system L0 for each of the numerical examples 1 to 9 are shown in Tables 1-1 and 1-2 described later.

[0093] [Numerical Example 1] Unit: mm Surface data Surface number rm dm ndm vdm 1 31.779 1.00 1.61800 63.4 2 8.912 3.60 3 49.545 0.75 1.49700 81.7 4 8.865 3.66 5 89.819 4.49 1.80400 46.6 6 -25.757 4.87 7 -24.458 1.95 1.48749 70.2 8 -10.415 1.50 9 (aperture) ∞ (variable) 10 -45.427 5.20 1.49700 81.7 11 -6.710 0.68 1.62205 41.1 12 -386.087 0.15 13 19.498 5.76 1.48749 70.2 14 -13.523 3.94 15* -12.585 1.69 1.53500 56.0 16* -13.044 (variable) Image plane ∞ Aspherical data Page 15 K = 6.41863e-01 A 4= 1.44387e-05 A 6= 7.00234e-06 A 8=-1.00059e-07 A10= 1.03099e-09 A12=-8.33358e-12 Page 16 K = 0.00000e+00 A 4= 1.02253e-04 A 6= 5.31173e-06 A 8=-4.42186e-08 A10= 2.43306e-10 A12=-2.36589e-12 Various data Object distance Infinity Closest Focal length 12.36 F-number 2.88 Half-angle 43.86 Image height 13.66 Lens length: 62.63 BF 18.37 20.69 d 9 5.02 2.70 d16 18.37 20.69 Lens group data Group starting plane focal length 1 1 43.55 2 10 28.67

[0094] [Numerical Example 2] Unit: mm Surface data Surface number rm dm ndm vdm 1 25.629 1.00 1.61800 63.4 2 9.737 3.79 3 627.519 0.75 1.49700 81.7 4 7.998 3.43 5 81.983 3.89 1.80400 46.6 6 -27.373 5.18 7 -28.725 2.13 1.48749 70.2 8 -10.106 2.00 9 (aperture) ∞ (variable) 10 -56.659 4.77 1.49700 81.7 11 -7.032 0.68 1.62205 41.1 12 526.147 0.15 13 18.534 5.56 1.48749 70.2 14 -15.007 5.66 15* -11.969 1.81 1.53500 56.0 16* -12.867 (variable) 17 -66.711 1.79 1.48749 70.2 18 -32.785 12.00 Image plane ∞ Aspherical data Page 15 K = 1.30951e-02 A 4=-2.61233e-05 A 6= 6.86185e-06 A 8=-1.33121e-07 A10= 1.69154e-09 A12=-1.26517e-11 Page 16 K = 0.00000e+00 A 4= 1.07609e-04 A 6= 4.74435e-06 A 8=-4.54631e-08 A10= 3.34596e-10 A12=-2.30579e-12 Various data Object distance Infinity Closest Focal length 12.32 F-number 2.88 Half-angle 43.96 Image height 13.66 Lens length 63.50 BF 12.00 d 9 4.98 2.16 d16 3.93 6.75 Lens group data Group starting plane focal length 1 1 43.56 2 10 32.53 3 17 130.00

[0095] [Numerical Example 3] Unit: mm Surface data Surface number rm dm ndm vdm 1 15.886 1.20 1.61997 63.9 2 7.746 3.86 3 29.749 1.51 1.49700 81.7 4 8.131 2.54 5 138.942 4.00 1.80610 40.7 6 -24.233 4.19 7 -18.756 2.32 1.51633 64.1 8 -9.210 1.50 9 (aperture) ∞ (variable) 10 219.015 4.18 1.51633 64.1 11 -7.464 1.20 1.80518 25.4 12 -58.332 0.15 13 -669.052 5.10 1.67270 32.1 14 -11.446 4.06 15* -9.250 1.50 1.53500 56.0 16* -12.467 (variable) Image plane ∞ Aspherical data Page 15 K = 0.00000e+00 A 4= 2.57866e-04 A 6=-5.92436e-07 A 8= 2.32606e-08 A10=-2.39480e-10 Page 16 K = 0.00000e+00 A 4= 2.56479e-04 A 6=-5.75800e-07 A 8= 7.99259e-09 A10=-1.20784e-10 Various data Object distance Infinity Closest Focal length 15.77 F-number 2.88 Half-angle 40.9 Image height 13.66 Lens length 62.50 BF 20.00 21.46 d 9 5.19 3.72 d16 20:00 21:46 Lens group data Group starting plane focal length 1 1 41.39 2 10 36.00

[0096] [Numerical Example 4] Unit: mm Surface data Surface number rm dm ndm vdm 1 -21.639 0.70 1.58913 61.1 2 14.601 1.94 3 115.762 2.70 2.00100 29.1 4 -17.394 0.48 5 -14.340 1.00 1.84666 23.8 6 104.892 0.15 7 32.292 3.99 1.80400 46.6 8 -17.804 3.97 9 (aperture) ∞ (variable) 10 -21.742 4.78 1.49700 81.7 11 -7.299 0.80 1.51742 52.4 12 143.111 0.15 13 19.237 5.76 1.48749 70.2 14 -19.417 4.00 15* -31.371 2.00 1.53500 56.0 16* -59.192 (variable) Image plane ∞ Aspherical data Page 15 K = 0.00000e+00 A 4=-4.59756e-06 A 6=-5.38359e-07 A 8= 2.93932e-09 A10=-4.00457e-11 Page 16 K = 0.00000e+00 A 4= 7.52901e-05 Various data Object distance Infinity Closest Focal length 27.16 F-number 2.83 Half-angle 25.94 Image height 13.66 Lens length 62.20 BF 21.88 26.77 d 9 7.89 3.00 d16 21.88 26.77 Lens group data Group starting plane focal length 1 1 44.78 2 10 57.59

[0097] [Numerical Example 5] Unit: mm Surface data Surface number rm dm ndm vdm 1 23.068 1.20 1.95375 32.3 2 8.858 4.12 3 70.483 0.80 1.49700 81.7 4 9.403 4.90 5 95.382 3.01 1.85883 30.0 6 -32.448 3.81 7 -98.802 3.51 1.56883 56.4 8 -13.054 1.50 9 (aperture) ∞ (variable) 10 150.421 4.01 1.49700 81.7 11 -8.440 0.80 1.85478 24.8 12 -20.921 3.05 13 -14.676 1.93 1.48749 70.2 14 -10.097 4.02 15* -104.288 1.98 1.53500 56.0 16* -32.566 (variable) Image plane ∞ Aspherical data Page 15 K = 0.00000e+00 A 4=-4.73505e-06 A 6=-1.77181e-08 A 8=-1.40397e-09 A10=-2.94384e-11 Page 16 K = 0.00000e+00 A 4= 9.10902e-05 A 6=-7.46501e-09 A 8= 4.83577e-09 A10=-4.89018e-11 Various data Object distance Infinity Closest Focal length 11.33 F-number 2.88 Half-angle 46.36 Image height 13.66 Lens length: 61.75 BF 16.57 18.19 d 9 6.52 4.90 d16 16.57 18.19 Lens group data Group starting plane focal length 1 1 25.42 2 10 33.31

[0098] [Numerical Example 6] Unit: mm Surface data Surface number rm dm ndm vdm 1 -39.972 0.70 1.51633 64.1 2 11.358 2.27 3 83.463 4.06 1.95375 32.3 4 -23.579 2.09 5 -15.384 2.34 1.84666 23.8 6 89.940 0.15 7 40.666 3.56 1.88300 40.8 8 -16.767 2.43 9 (aperture) ∞ (variable) 10 -20.361 4.76 1.49700 81.7 11 -7.310 0.80 1.51742 52.4 12 62.041 0.15 13 23.979 5.00 1.48749 70.2 14 -19.453 4.00 15* -4801.201 1.80 1.53500 56.0 16* -82.153 (variable) Image plane ∞ Aspherical data Page 15 K = 0.00000e+00 A 4=-3.84759e-05 A 6=-2.54975e-07 A 8= 1.27102e-09 A10=-1.51523e-11 Page 16 K = 0.00000e+00 A 4= 1.45357e-05 Various data Object distance Infinity Closest Focal length 23.28 F-number 2.83 Half-angle 28.46 Image height 13.66 Lens length 63.20 BF 20.54 26.08 d 9 8.54 3.00 d16 20.54 26.08 Lens group data Group starting plane focal length 1 1 36.82 2 10 46.86

[0099] [Numerical Example 7] Unit: mm Surface data Surface number rm dm ndm vdm 1 -18.699 0.60 1.51742 52.4 2 15.788 4.02 3 45.571 9.00 1.83481 42.7 4 -19.428 0.55 5 (aperture) ∞ (variable) 6 -13.024 0.91 1.75211 25.0 7 -51.744 0.84 8 21.802 5.75 1.49700 81.7 9 -19.593 0.19 10* -63.603 5.02 1.53500 56.0 11* -22.419 (variable) 12 108.711 0.85 1.53172 48.8 13 39.923 20.02 Image plane ∞ Aspherical data Side 10 K = 0.00000e+00 A 4= 2.38175e-05 A 6= 4.52345e-07 A 8=-2.01259e-09 A10= 1.05760e-11 A12=-1.99911e-13 Page 11 K = 0.00000e+00 A 4= 9.68682e-05 A 6= 6.62446e-07 A 8=-4.39094e-09 A10= 1.06537e-10 A12=-7.08731e-13 Various data Object distance Infinity Closest Focal length 22.66 F-number 2.06 Half-angle 27.91 Image height 12.00 Lens length: 60.96 BF 20.02 d 5 7.15 3.95 d11 6.06 9.26 Lens group data Group starting plane focal length 1 1 41.51 2 6 35.94 3 12 -119.17

[0100] [Numerical Example 8] Unit: mm Surface data Surface number rm dm ndm vdm 1 ∞ 1.50 2 17.460 1.20 1.58913 61.1 3 8.203 4.14 4 28.883 1.51 1.49700 81.7 5 7.652 2.35 6 61.637 4.00 1.80400 46.6 7 -26.181 3.94 8 -22.850 2.37 1.51633 64.1 9 -9.224 1.50 10 (aperture) ∞ (variable) 11 -160.364 4.10 1.51633 64.1 12 -7.374 1.20 1.76182 26.5 13 -587.099 0.15 14 -1982.237 4.58 1.72047 34.7 15 -10.861 2.95 16* -9.224 1.50 1.58313 59.4 17* -11.974 (variable) Image plane ∞ Aspherical data Page 16 K = 0.00000e+00 A 4=-5.84907e-05 A 6= 4.16087e-06 A 8=-3.77842e-08 A10= 1.73448e-10 Page 17 K = 0.00000e+00 A 4=-4.06831e-06 A 6= 2.73342e-06 A 8=-2.20246e-08 A10= 5.44826e-11 Various data Object distance Infinity Closest Focal length 15.96 F-number 2.88 Half-angle 40.6 40.4 Image height 13.66 Lens length: 62.05 BF 20.00 21.72 d10 5.08 3.36 d17 20.00 21.72 Lens group data Group First surface Focal length 1 1 30.32 2 11 38.79

[0101] [Numerical Example 9] Unit mm Surface data Surface number rm dm ndm vdm 1 -25.272 0.74 1.58913 61.1 2 13.157 3.16 3 73.056 5.50 1.80400 46.6 4 -22.304 1.60 5 -16.211 1.15 1.67270 32.1 6 -30.124 0.15 7 166.672 4.54 1.59522 67.7 8 -16.420 4.43 9(Stop) ∞ (Variable) 10 -20.253 1.02 1.72825 28.5 11 153.658 0.15 12 26.023 4.89 1.65160 58.5 13 -26.795 5.00 14* -27.341 1.81 1.53500 56.0 15* -19.433 (Variable) Image plane ∞ Aspheric surface data 14th surface K = 0.00000e+00 A4= 5.67295e-05 A6= 1.77063e-07 A8= 4.65930e-09 A10=-3.02196e-11 15th surface K = 0.00000e+00 A 4= 1.35675e-04 A 6= 1.94246e-07 A 8= 7.07613e-09 A10=-3.29617e-11 Various Data Object Distance Infinity Closest Focal Length 21.51 F-number 2.00 Half View Angle 30.17 Image Height 13.66 Total Lens Length 61.41 BF 20.00 23.71 d 9 7.25 3.54 d15 20.00 23.71 Lens Group Data Group Start Surface Focal Length 1 1 33.62 2 10 51.58

[0102] [Table 1-1] [Table 1-2]

[0103] [Imaging Apparatus] Next, an imaging apparatus including a solid-state image sensor that captures an image formed by the optical system L0 according to any one of Examples 1 to 9 will be described.

[0104] Figure 28 shows a schematic perspective view of a digital camera 10 (imaging apparatus) using the optical system L0 according to any one of Examples 1 to 9 as the imaging optical system 12. The digital camera 10 includes a camera body 11, an imaging optical system 12 constituted by the optical system L0 according to any one of Examples 1 to 9, and an image sensor 13.

[0105] Specifically, the image sensor 13 is a solid-state image sensor (photoelectric conversion element) that is built into the camera body 11 and is configured to receive and capture the subject image formed by the imaging optical system 12. More specifically, the image sensor 13 is formed by, for example, a CCD (Charge Coupled Device) sensor or a CMOS (Complementary Metal Oxide Semiconductor) sensor.

[0106] Furthermore, the optical system L0 according to any of Examples 1 to 9 can be used as an imaging optical system in so-called single-lens reflex cameras with a quick-return mirror, or so-called mirrorless cameras without a quick-return mirror, etc. Furthermore, the optical system L0 according to any of Examples 1 to 9 can also be used as an imaging optical system in surveillance cameras, video cameras, and the like.

[0107] In a digital camera 10 using the optical system L0 according to any of Examples 1 to 9 as the imaging optical system 12, it is possible to capture images that are quiet and lightweight, suitable for video recording, and with various aberrations well corrected. Although preferred embodiments and examples have been described above, the invention is not limited to these embodiments and examples, and various combinations, modifications, and changes are possible within the scope of the gist of the invention.

[0108] This embodiment includes the following configuration. (Configuration 1) An optical system comprising, in order from an object side to an image side: a first lens unit that does not move during focusing and has a positive refractive power; and a second lens unit that moves on an optical axis during focusing and has a positive refractive power, wherein only the second lens unit moves during focusing, the total number of lenses included in the optical system is 9 or less, a negative lens is disposed on the most object side of the first lens unit, and when an average value of refractive indices for d-line of respective lenses included in the second lens unit is Nave2, a focal length of the second lens unit is f2, a focal length of a first lens having the largest absolute value of focal length among at least one lens included in the second lens unit is f2lp, an entire optical length of the optical system is TD, and a focal length of the optical system is f, the optical system satisfies conditional expressions of 1.45<Nave2<1.67, -0.80<f2 / f2lp<0.60, and 2.20<TD / f<5.50. (Configuration 2) The optical system according to Configuration 1, further comprising an aperture stop, wherein when a distance on the optical axis between the aperture stop and an image plane is SPD, the optical system satisfies a conditional expression of 0.60<SPD / TD<0.80. (Configuration 3) The optical system according to Configuration 1 or 2, wherein the optical system satisfies a conditional expression of 1.50<f2 / f<3.00. (Configuration 4) The optical system according to any one of Configurations 1 to 3, wherein when a focal length of the first lens unit is f1, and a focal length of a lens disposed on the most image side in the first lens unit is f1r, the optical system satisfies a conditional expression of 0.20<f1r / f1<1.10. (Configuration 5) The optical system according to any one of Configurations 1 to 4, wherein when a focal length of the first lens unit is f1, the optical system satisfies a conditional expression of 0.50<f1 / f2<2.00. (Configuration 6) The optical system according to any one of Configurations 1 to 5, wherein when radii of curvature of an object-side lens surface and an image-side lens surface of the negative lens are respectively Rn1 and Rn2, the optical system satisfies a conditional expression of -3.00<(Rn2+Rn1) / (Rn2-Rn1)<-0.01. (Configuration 7) The optical system according to any one of Configurations 1 to 6, wherein when a focal length of the first lens unit is f1, the optical system satisfies a conditional expression of 1.40<f1 / f<3.70. (Configuration 8) The optical system according to any one of Configurations 1 to 7, wherein when focusing on an infinite distance, letting DF be the distance on the optical axis between the object-side lens surface of the second lens disposed closest to the object side in the second lens group and the image-side lens surface of the lens disposed adjacent to the object side of the second lens, or in the case where an aperture stop disposed adjacent to the object side of the second lens is provided, the distance on the optical axis between the object-side lens surface of the second lens and the aperture stop, the conditional expression 0.05<DF / TD<0.18 is satisfied. (Configuration 9) The optical system according to any one of Configurations 1 to 8, wherein letting SK be the air-equivalent distance on the optical axis between the image-side lens surface of the lens disposed closest to the image side in the optical system and the image plane, the conditional expression 0.15<SK / TD<0.46 is satisfied. (Configuration 10) The optical system according to any one of Configurations 1 to 9, wherein letting Db1 be the sum of the lens thicknesses on the optical axis of each lens included in the first lens group, the conditional expression 0.10<Db1 / TD<0.24 is satisfied. (Configuration 11) The optical system according to any one of Configurations 1 to 10, wherein letting Db2 be the sum of the lens thicknesses on the optical axis of each lens included in the second lens group, the conditional expression 0.10<Db2 / TD<0.26 is satisfied. (Configuration 12) The optical system according to any one of Configurations 1 to 11, wherein letting d be the specific gravity of the first lens, the conditional expression 0.80<d<3.10 is satisfied. (Configuration 13) The optical system according to any one of Configurations 1 to 12, wherein the number of lenses included in the second lens group is 4 or less. (Configuration 14) The optical system according to any one of Configurations 1 to 13, wherein the number of lenses included in the optical system is 6 or more. (Configuration 15) The optical system according to any one of Configurations 1 to 14, wherein the first lens is disposed closest to the image side in the second lens group. (Configuration 16) An optical system comprising, in order from the object side to the image side, a first lens group that does not move during focusing and has positive refractive power, and a second lens group that moves along the optical axis during focusing and has positive refractive power, wherein only the second lens group moves during focusing, the total number of lenses included in the optical system is nine or less, and a negative lens is arranged on the object side of the first lens group. (Configuration 17) An imaging device characterized by comprising an optical system described in any one of Configurations 1 to 16 and an image sensor that receives light from the optical system. [Explanation of Symbols]

[0109] L0 optical system L1 First lens group L2 Second lens group L3 Third lens group

Claims

1. An optical system comprising, in order from the object side to the image side, a first lens group that does not move during focusing and has positive refractive power, and a second lens group that moves along the optical axis during focusing and has positive refractive power, During focusing, only the second lens group moves. The total number of lenses included in the optical system is nine or less. A negative lens is positioned at the object-side end of the first lens group. When Nave2 is the average refractive index of each lens in the second lens group with respect to the d line, f2 is the focal length of the second lens group, f2lp is the focal length of the first lens among at least one lens in the second lens group that has the largest absolute value of focal length, TD is the total optical length of the optical system, and f is the focal length of the optical system, 1.45<Nave2<1.67 -0.80<f2 / f2lp<0.60 2.20<TD / f<5.50 An optical system characterized by satisfying the following conditional equation.

2. Equipped with an aperture diaphragm, When the distance on the optical axis between the aperture diaphragm and the image plane is denoted as the SPD, 0.60<SPD / TD<0.80 The optical system according to claim 1, characterized in that it satisfies the following condition.

3. 1.50<f2 / f<3.00 The optical system according to claim 1, characterized in that it satisfies the following condition.

4. When the focal length of the first lens group is f1, and the focal length of the lens located closest to the image in the first lens group is f1r, 0.20<f1r / f1<1.10 The optical system according to claim 1, characterized in that it satisfies the following condition.

5. When the focal length of the first lens group is f1, 0.50<f1 / f2<2.00 The optical system according to claim 1, characterized in that it satisfies the following condition.

6. When the radii of curvature of the object-side lens surface and the image-side lens surface of the negative lens are Rn1 and Rn2, respectively, -3.00<(Rn2+Rn1) / (Rn2-Rn1)<-0.01 The optical system according to claim 1, characterized in that it satisfies the following condition.

7. When the focal length of the first lens group is f1, 1.40<f1 / f<3.70 The optical system according to claim 1, characterized in that it satisfies the following condition.

8. When focusing to infinity, let DF be the distance on the optical axis between the object-side lens surface of the second lens group that is positioned closest to the object and the image-side lens surface of the lens adjacent to the object-side of the second lens, or, if an aperture diaphragm is provided adjacent to the object-side of the second lens, the distance on the optical axis between the object-side lens surface of the second lens and the aperture diaphragm. 0.05<DF / TD<0.18 The optical system according to claim 1, characterized in that it satisfies the following condition.

9. In the optical system described above, when SK is the air-equivalent distance on the optical axis between the image-side lens surface and the image plane of the lens positioned closest to the image, 0.15<SK / TD<0.46 The optical system according to claim 1, characterized in that it satisfies the following condition.

10. When Db1 is the sum of the lens thicknesses of each lens in the first lens group along the optical axis, 0.10<Db1 / TD<0.24 The optical system according to claim 1, characterized in that it satisfies the following condition.

11. When Db2 is the sum of the lens thicknesses of each lens in the second lens group along the optical axis, 0.10<Db2 / TD<0.26 The optical system according to claim 1, characterized in that it satisfies the following condition.

12. When the specific gravity of the first lens is d, 0.80<d<3.10 The optical system according to claim 1, characterized in that it satisfies the following condition.

13. The optical system according to claim 1, characterized in that the number of lenses included in the second lens group is four or less.

14. The optical system according to claim 1, characterized in that the number of lenses included in the optical system is six or more.

15. The optical system according to claim 1, characterized in that the first lens is positioned furthest towards the image in the second lens group.

16. An optical system comprising, in order from the object side to the image side, a first lens group that does not move during focusing and has positive refractive power, and a second lens group that moves along the optical axis during focusing and has positive refractive power, During focusing, only the second lens group moves. The total number of lenses included in the optical system is nine or less. An optical system characterized in that a negative lens is arranged on the object side of the first lens group.

17. An imaging device comprising an optical system according to any one of claims 1 to 16 and an image sensor that receives light from the optical system.

Images