Optical system and imaging apparatus

Abstract

To provide a small-size optical system that has a wide angle of view and a large aperture ratio, and can perform high-speed focusing.SOLUTION: An optical system L0 is composed of a first lens group L1, a second lens group L2 having a positive refractive power, a third lens group L3, a fourth lens group L4 having a positive refractive power, and a fifth lens group L5, as lens groups arranged in order from an object side to an image side. In focusing, the first lens group, the third lens group, and the fifth lens group do not move, and the second lens group and the fourth lens group move. The second lens group is composed of one positive lens or one positive lens unit. The third lens group has at least one positive lens and one negative lens, and the fourth lens group has at least two positive lenses and one negative lens.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an optical system suitable for imaging devices such as digital still cameras, video cameras, and surveillance cameras. [Background technology]

[0002] Imaging devices using solid-state imaging elements such as CCD sensors and CMOS sensors are required to have optical systems that are compact and have high optical performance while having a wide angle of view and a large aperture ratio. High-speed autofocusing is also required for optical systems. Patent documents 1 and 2 disclose inner-focusing optical systems that drive a focus lens group disposed inside the optical system during focusing. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-197125 [Patent Document 2] Japanese Patent Application Laid-Open No. 2015-200845 Summary of the Invention [Problem to be solved by the invention]

[0004] Optical systems with wide angles of view and large aperture ratios face the problem of difficulty in correcting various aberrations. In particular, when the focus lens group is made lightweight to enable high-speed focusing (autofocus), it becomes difficult to suppress aberration fluctuations when focusing from an object at infinity to a close object.

[0005] The present invention provides a compact optical system that has a wide angle of view and a large aperture ratio, yet is capable of high-speed focusing, and an imaging device equipped with the same. [Means for solving the problem]

[0006] An optical system according to one aspect of the present invention comprises a first lens group, a second lens group with positive refractive power, a third lens group, a fourth lens group with positive refractive power, and a fifth lens group arranged in that order from the object side to the image side. During focusing, the first lens group, the third lens group, and the fifth lens group remain stationary, while the second lens group and the fourth lens group move. The second lens group comprises one positive lens or one positive lens unit. The third lens group has at least one positive lens and one negative lens, and the fourth lens group has at least two positive lenses and one negative lens. An imaging device including the above optical system also constitutes another aspect of the present invention. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a compact optical system that has a wide angle of view, a large aperture ratio, and yet is capable of high-speed focusing. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a cross-sectional view showing the configuration of an optical system according to a first embodiment. [Figure 2] 4A and 4B are longitudinal aberration diagrams of the optical system of Example 1 in a state where the optical system is focused at infinity. [Figure 3] 4A and 4B are longitudinal aberration diagrams in the closest focusing state of the optical system of Example 1. [Figure 4] FIG. 10 is a cross-sectional view showing the configuration of an optical system according to a second embodiment. [Figure 5] FIG. 10 is a longitudinal aberration diagram of the optical system of Example 2 in a state where the optical system is focused at infinity. [Figure 6] 10A and 10B are longitudinal aberration diagrams in the closest focusing state of the optical system of Example 2. [Figure 7] FIG. 10 is a cross-sectional view showing the configuration of an optical system according to a third embodiment. [Figure 8] 10A and 10B are longitudinal aberration diagrams of the optical system of Example 3 in a state where the optical system is focused at infinity. [Figure 9] 10A and 10B are longitudinal aberration diagrams in the closest focusing state of the optical system of Example 3. [Figure 10] FIG. 10 is a cross-sectional view showing the configuration of an optical system according to a fourth embodiment. [Figure 11]10A and 10B are longitudinal aberration diagrams of the optical system of Example 4 in a state where the optical system is focused at infinity. [Figure 12] 10A and 10B are longitudinal aberration diagrams in the closest focusing state of the optical system of Example 4. [Figure 13] FIG. 1 is a diagram showing an imaging device equipped with an optical system according to first to fourth embodiments. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0010] 1, 4, 7, and 11 show cross sections of optical systems according to first, second, third, and fourth embodiments of the present invention, respectively, in a state of focusing at infinity. In each figure, the left side is the object side, and the right side is the image side. The optical systems of the respective embodiments are used as imaging optical systems in imaging devices such as video cameras, digital still cameras, broadcast cameras, silver halide film cameras, and surveillance cameras. The imaging lens may be replaceable with respect to the imaging device, or may be integrally provided in the imaging device.

[0011] The optical system L0 in each embodiment has multiple lens groups (L1 to L5). A lens group is a group of one or more lenses that move together during focusing or zooming. That is, the spacing between adjacent lens groups changes during focusing or zooming. The lens groups may include an aperture stop. In each figure, SP is the aperture stop, and IMG is the image plane. The image plane IMG is where the imaging surface of a solid-state image sensor (photoelectric conversion element) such as a CCD sensor or CMOS sensor, or the film surface (photosensitive surface) of a silver halide film, is located.

[0012] The optical system L0 of each embodiment comprises, in order from the object side to the image side, a first lens group L1 (with positive or negative refractive power), a second lens group L2 (with positive refractive power), a third lens group L3 (with positive or negative refractive power), a fourth lens group L4 (with positive refractive power), and a fifth lens group L5 (with positive or negative refractive power). In the optical system L0 of each embodiment, during focusing, the first lens group L1, the third lens group L3, and the fifth lens group L5 are fixed (unmoving) relative to the image plane IMG, while the second lens group L2 and the fourth lens group L4 move. The arrows below the second lens group L2 and the fourth lens group L4 in each figure indicate the direction of movement of each lens group during focusing from an object at infinity to a closest object.

[0013] In order to achieve high-speed autofocus in a compact, high-performance optical system that combines a wide angle of view with a large aperture ratio, it is important to appropriately configure and arrange the lens groups constituting the optical system and the focus lens group. In the optical system of each embodiment, aberration correction and weight reduction of the focus lens group are achieved by moving some of the focus lens groups (L2, L4) among the multiple lens groups (L1 to L5) that make up the optical system. In addition, by using both focus lens groups (L2, L4) as positive lens groups and distributing positive power among them, it becomes easy to suppress fluctuations in aberrations during focusing, particularly astigmatism, coma, and chromatic aberration of magnification.

[0014] In the optical systems of each embodiment, the second lens group L2 consists of one positive lens or a positive lens unit. The third lens group L3 has at least one positive lens and one negative lens. The fourth lens group L4 has at least two positive lenses and one negative lens. By configuring the second lens group L2, which moves during focusing, with one positive lens, it becomes easier to increase the speed of autofocus. The positive lens here also includes a cemented lens composed of multiple lenses cemented together that is positive overall. Furthermore, by configuring the third lens group L3, which remains stationary during focusing, with a positive lens and a negative lens, it becomes easier to correct axial chromatic aberration and spherical aberration while minimizing the weight increase of the focus lens group. By configuring L4 with at least two positive lenses and one negative lens, it becomes easier to suppress aberration fluctuations during focusing, particularly fluctuations in axial chromatic aberration and spherical aberration.

[0015] Next, a description will be given of the configuration that the optical system of each embodiment preferably satisfies.

[0016] The fifth lens group L5 preferably has one positive lens and two negative lenses. Since the fifth lens group L5 is the lens group closest to the image plane in the optical system, it is effective in correcting Petzval sum. Therefore, by having the fifth lens group L5 have one positive lens and two negative lenses, it becomes easier to correct field curvature.

[0017] Furthermore, the fourth lens group L4 is preferably composed of, arranged in order from the object side to the image side, a cemented lens, a biconvex positive lens, and a positive lens. By arranging the cemented lens on the object side, where it is relatively easy to reduce the lens diameter, it is possible to suppress an increase in the weight of the focus lens group while facilitating correction of axial chromatic aberration. Furthermore, by arranging two positive lenses in the fourth lens group L4 and making the object-side positive lens a biconvex lens, it is possible to distribute the positive power to facilitate aberration correction, while reducing the amount of movement of the focus lens group, thereby facilitating high-speed autofocus. It is not preferable to configure the fourth lens group L4 with too many lenses, as this makes it difficult to reduce the weight of the focus lens group.

[0018] It is also preferable to provide an aperture stop SP in the third lens unit L3. By locating the aperture stop SP in the third lens unit L3, which is located near the center of the entire optical system, the symmetry of the optical system in front of and behind the aperture stop SP is improved, making it easier to correct coma and distortion.

[0019] Furthermore, it is preferable that the third lens group L3 be composed of a positive lens and a negative lens arranged in this order from the object side to the image side. By arranging the positive lens on the object side, it becomes easier to converge the axial light beam and reduce the lens diameter of the fourth lens group L4 arranged on the image side of the third lens group L3, which results in easier weight reduction of the fourth lens group L4, which is the focus lens group. It is not preferable to have three or more lenses in the third lens group L3 because this increases the size of the third lens group L3 and, ultimately, the optical system.

[0020] It is also preferable that the first lens group L1 has a negative lens positioned closest to the object. By positioning the negative lens closest to the object, a power arrangement is achieved on the retrofocus side, making it easier to achieve a wide angle of view.

[0021] It is also preferable that the second lens group L2 and the fourth lens group L4 move by different amounts during focusing, which makes it easier to correct aberrations when in focus at the closest distance.

[0022] Next, conditions that the optical system of each example should preferably satisfy will be described. The optical system of each example should preferably satisfy at least one of the following conditions (1) to (18).

[0023] 0.05≦M4 / f≦0.40 (1) 0.01≦M2 / f≦0.45 (2) -0.3≦f / f1≦0.2 (3) 0.05≦f / f2≦1.10 (4) -1.0≦f / f3≦0.5 (5) 0.5≦f / f4≦1.5 (6) -1.00≦f / f5≦-0.01 (7) -0.99≦b2≦0.20 (8) 0.3≦b4≦0.8 (9) 0.1≦T1 / f≦1.5 (10) 0.01≦T2 / f≦0.40 (11) 0.01≦T3 / f≦0.50 (12) 0.1≦T4 / f≦1.0 (13) 0.15≦T5 / f≦0.90 (14) 0.05≦sk / f≦1.00 (15) 1≦TD / f≦6 (16) -2.0≦f / f11≦-0.1 (17) 0.2≦(r2b+r2a) / (r2b-r2a)≦4.0 (18) In equations (1) to (18), M4 is the absolute value of the movement amount of the fourth lens group L4 when focusing from an object at infinity to the closest object. The movement amount of the fourth lens group L4 here refers to the difference in the position of a lens surface in the fourth lens group L4 between when the lens surface is focused on an object at infinity and when the lens surface is focused on the closest object. The sign of the movement amount is positive when the fourth lens group is closer to the object when the lens surface is focused on the closest object than when the lens surface is focused on an object at infinity, and negative when the lens surface is closer to the image. The movement amounts (absolute values) of the other lens groups are defined similarly. The closest object is the object located at the closest distance (nearest point) that can be imaged using the optical system of each embodiment.

[0024] Furthermore, f is the focal length of the entire optical system when focused on an object at infinity (hereinafter referred to as the infinity focused state). M2 is the absolute value of the movement amount of the second lens group L2 when focusing from an object at infinity to the closest object. f1 is the focal length of the first lens group L1, f2 is the focal length of the second lens group L2, f3 is the focal length of the third lens group L3, f4 is the focal length of the fourth lens group L4, and f5 is the focal length of the fifth lens group L5.

[0025] Furthermore, b2 is the lateral magnification of the second lens group L2 when focused at infinity, and b4 is the lateral magnification of the fourth lens group L4 when focused at infinity. T1 is the axial distance from the lens surface of the first lens group L1 closest to the object to the lens surface of the first lens group L1 closest to the image. T2 is the axial distance from the lens surface of the second lens group L2 closest to the object to the lens surface of the second lens group L2 closest to the image. T3 is the axial distance from the lens surface of the third lens group L3 closest to the object to the lens surface of the third lens group L3 closest to the image. T4 is the axial distance from the lens surface of the fourth lens group L4 closest to the object to the lens surface of the fourth lens group L4 closest to the image. T5 is the axial distance from the lens surface of the fifth lens group L5 closest to the object to the lens surface of the fifth lens group L5 closest to the image.

[0026] Furthermore, sk is the distance on the optical axis from the image-side lens surface of the lens closest to the image in the optical system (lenses having power) to the image plane (back focus). TD is the distance on the optical axis from the object-side lens surface of the lens closest to the object in the optical system (lenses having power) to the image plane (total lens length). f11 is the focal length of the lens closest to the object in the optical system (lenses having power). r2a is the radius of curvature of the lens surface closest to the object in the second lens group L2, and r2b is the radius of curvature of the lens surface closest to the image in the second lens group L2.

[0027] Equation (1) indicates the condition regarding the amount of movement of the second lens unit L2 during focusing. If the amount of movement is large so that M4 / f exceeds the upper limit of equation (1), it becomes difficult to increase the speed of autofocus, which is undesirable. If the amount of movement is small so that M4 / f falls below the lower limit of equation (1), it becomes difficult to correct fluctuations in aberrations, especially astigmatism, during focusing, which is also undesirable.

[0028] Equation (2) indicates the condition regarding the amount of movement of the fourth lens unit L4 during focusing. If the amount of movement is large so that M2 / f exceeds the upper limit of equation (2), the optical system becomes large, which is not desirable. If the amount of movement is small, below the lower limit, it becomes difficult to correct aberration fluctuations during focusing, particularly spherical aberration, which is not desirable.

[0029] Equation (3) indicates a condition related to the focal length of the first lens unit L1. If the focal length of the first lens unit L1 is short (refractive power is large) so that f / f1 exceeds the upper limit of equation (3), the power arrangement becomes telephoto side, making it difficult to ensure back focus, which is undesirable. If the focal length of the first lens unit L1 is long (refractive power is small) so that f / f1 falls below the lower limit of equation (3), the overall length of the optical system becomes long, making it difficult to reduce its size, which is also undesirable.

[0030] Equation (4) indicates a condition related to the focal length of the second lens unit L2. If the focal length of the second lens unit L2 is short so that f / f2 exceeds the upper limit of equation (4), the weight of the second lens unit L2 increases, making it difficult to achieve high-speed autofocus, which is undesirable. If the focal length of the second lens unit L2 is long so that f / f2 falls below the lower limit of equation (4), it becomes difficult to correct fluctuations in aberrations, particularly astigmatism, during focusing, which is also undesirable.

[0031] Formula (5) indicates a condition related to the focal length of the third lens group L3. If the focal length of the third lens group L3 is short so that f / f3 exceeds the upper limit of formula (5), it becomes difficult to correct aberrations generated in the third lens group L3, particularly spherical aberration and axial chromatic aberration, which is undesirable. If the focal length of the third lens group L3 is long so that f / f3 falls below the lower limit of formula (5), it becomes difficult to reduce the lens diameter of the fourth lens group L4, which makes it difficult to increase the speed of autofocus by moving the fourth lens group L4, which is undesirable.

[0032] Equation (6) indicates a condition related to the focal length of the fourth lens unit L4. If the focal length of the fourth lens unit L4 is short so that f / f4 exceeds the upper limit of equation (6), the weight of the second lens unit L2, which moves together during focusing, increases, making it difficult to achieve high-speed autofocusing, which is undesirable. If the focal length of the fourth lens unit L4 is long so that f / f4 falls below the lower limit of equation (6), it becomes difficult to correct fluctuations in aberrations, particularly spherical aberration and axial chromatic aberration, during focusing, which is also undesirable.

[0033] Equation (7) shows a condition related to the focal length of the fifth lens unit L5. If the focal length of the fifth lens unit L5 is short so that f / f5 exceeds the upper limit of equation (7), it becomes difficult to correct the Petzval sum and to suppress the curvature of field, which is undesirable. If the focal length of the fifth lens unit L5 is long so that f / f5 falls below the lower limit of equation (7), it becomes difficult to ensure the back focus, which is also undesirable.

[0034] Equation (8) shows the condition for the lateral magnification of the second lens unit L2 when focused at infinity. If b2 exceeds the upper limit of equation (8), the change in the height of the axial ray during focusing becomes large, and the fluctuation in spherical aberration in particular becomes large, which is undesirable. If b2 falls below the lower limit of equation (8), the lens diameter of the second lens unit L2 increases, making it difficult to reduce the weight of the second lens unit L2 as a focus lens unit, which is also undesirable.

[0035] Equation (9) expresses a condition related to the lateral magnification of the fourth lens unit L4 when focused at infinity. If b4 exceeds the upper limit of equation (9), the change in the height of the axial ray during focusing becomes large, and the fluctuation in spherical aberration in particular becomes large, which is undesirable. If b4 falls below the lower limit of equation (9), the lens diameter of the fourth lens unit L4 increases, making it difficult to reduce the weight of the fourth lens unit L4 as a focus lens unit, which is also undesirable.

[0036] Expression (10) indicates a condition regarding the thickness of the first lens unit L1 in the optical axis direction. If the thickness of the first lens unit L1 is increased so that T1 / f exceeds the upper limit of expression (10), the optical system will become larger, which is undesirable. If the thickness of the first lens unit L1 is decreased so that T1 / f falls below the lower limit of expression (10), it will become difficult to correct aberrations, particularly distortion, that occur in the first lens unit L1, which is undesirable.

[0037] Expression (11) indicates a condition regarding the thickness of the second lens unit L2 in the optical axis direction. If the thickness of the second lens unit L2 is increased so that T2 / f exceeds the upper limit of expression (11), the optical system will become larger, which is undesirable. If the thickness of the second lens unit L2 is decreased so that T2 / f falls below the lower limit of expression (11), it will become difficult to correct aberrations, particularly distortion, that occur in the second lens unit L2, which is undesirable.

[0038] Expression (12) indicates a condition regarding the thickness of the third lens unit L3 in the optical axis direction. If the thickness of the third lens unit L3 is so large that T3 / f exceeds the upper limit of expression (12), the optical system becomes large, which is undesirable. If the thickness of the third lens unit L3 is so small that T3 / f falls below the lower limit of expression (12), it becomes difficult to correct aberrations generated in the third lens unit L3, particularly axial chromatic aberration and spherical aberration, which is also undesirable.

[0039] Expression (13) indicates a condition regarding the thickness of the fourth lens unit L4 in the optical axis direction. If the thickness of the fourth lens unit L4 is so large that T4 / f exceeds the upper limit of expression (13), the weight of the fourth lens unit L4 increases, making it difficult to achieve high-speed autofocus, which is undesirable. If the thickness of the fourth lens unit L4 is so small that T4 / f falls below the lower limit of expression (12), it becomes difficult to correct aberrations generated in the fourth lens unit L4, particularly spherical aberration and astigmatism, which is undesirable.

[0040] Expression (14) indicates a condition regarding the thickness of the fifth lens unit L5 in the optical axis direction. If the thickness of the fifth lens unit L5 is so large that T5 / f exceeds the upper limit of expression (14), the optical system becomes large, which is undesirable. If the thickness of the fifth lens unit L5 is so small that T5 / f falls below the lower limit of expression (14), it becomes difficult to correct curvature of field and distortion, which is undesirable.

[0041] Equation (15) shows a condition related to the back focus. If the back focus is large so that sk / f exceeds the upper limit of equation (15), the optical system becomes large, which is not preferable. If the back focus is small so that sk / f falls below the lower limit of equation (15), it becomes difficult to lay out optical blocks such as the image sensor and low-pass filter near the image plane, which is also not preferable.

[0042] Equation (16) indicates a condition related to the total lens length. If the total lens length is long enough that TD / f exceeds the upper limit of equation (16), the lens diameters of the first lens group L1 and the second lens group L2 increase, making it difficult to miniaturize the optical system, which is undesirable. If the total lens length is short enough that TD / f falls below the lower limit of equation (16), the refractive power of each lens group increases, making it particularly difficult to correct coma and field curvature, which is undesirable.

[0043] Expression (17) indicates a condition regarding the focal length of the lens arranged closest to the object in the optical system (first lens group L1). If f / f11 exceeds the upper limit of expression (17), it becomes difficult to achieve a wide angle of view of the optical system, which is undesirable. If f / f11 falls below the lower limit of expression (17), it becomes difficult to correct distortion, which is undesirable.

[0044] Equation (18) shows a condition related to the shape of the second lens unit L2. If (r2b+r2a) / (r2b-r2a) exceeds the upper limit of equation (18), the focus fluctuation due to spherical aberration becomes large, which is undesirable. If (r2b+r2a) / (r2b-r2a) falls below the lower limit of equation (18), it becomes difficult to correct the focus fluctuation due to astigmatism, which is undesirable.

[0045] By satisfying at least one of the above conditions, it becomes easier to obtain a compact optical system that has a wide angle of view, a large aperture ratio, and yet is capable of high-speed autofocusing.

[0046] It is more preferable that the numerical ranges of the formulas (1) to (18) are as follows:

[0047] 0.08≦M4 / f≦0.30 (1a) 0.015≦M2 / f≦0.350 (2a) -0.25≦f / f1≦0.15 (3a) 0.1≦f / f2≦0.9 (4a) -0.8≦f / f3≦0.4 (5a) 0.6≦f / f4≦1.3 (6a) -0.80≦f / f5≦-0.06 (7a) -0.9≦b2≦0.1 (8a) 0.4≦b4≦0.7 (9a) 0.2≦T1 / f≦1.4 (10a) 0.05≦T2 / f≦0.30 (11a) 0.06≦T3 / f≦0.42 (12a) 0.2≦T4 / f≦0.9 (13a) 0.25≦T5 / f≦0.80 (14a) 0.1≦sk / f≦0.7 (15a) 1.5≦TD / f≦5.0 (16a) -1.6≦f / f11≦-0.2 (17a) 0.4≦(r2b+r2a) / (r2b-r2a)≦3.0 (18a) Furthermore, it is more preferable to set the numerical ranges of the formulas (1) to (18) as follows:

[0048] 0.09≦M4 / f≦0.20 (1b) 0.02≦M2 / f≦0.25 (2b) -0.20≦f / f1≦0.09 (3b) 0.15≦f / f2≦0.80 (4b) -0.7≦f / f3≦0.3 (5b) 0.70≦f / f4≦1.15 (6b) -0.600≦f / f5≦-0.115 (7b) -0.87≦b2≦0.08 (8b) 0.44≦b4≦0.60 (9b) 0.25≦T1 / f≦1.30 (10b) 0.08≦T2 / f≦0.20 (11b) 0.12≦T3 / f≦0.38 (12b) 0.3≦T4 / f≦0.8 (13b) 0.35≦T5 / f≦0.70 (14b) 0.2≦sk / f≦0.6 (15b) 1.8≦TD / f≦4.0 (16b) -1.3≦f / f11≦-0.3 (17b) 0.5≦(r2b+r2a) / (r2b-r2a)≦2.5 (18b) Next, the optical systems of Examples 1 to 4 will be described in detail. As described above, the optical system of each Example is composed of a first lens group L1, a positive second lens group L2, a third lens group L3, a positive fourth lens group L4, and a fifth lens group L5, arranged in this order from the object side to the image side. When focusing from an object at infinity to a closest object, the second lens group L2 and the fourth lens group L4 move, while the first lens group L1, the third lens group L3, and the fifth lens group L5 do not move. The second lens group L2 is composed of one positive lens or a positive lens unit. The third lens group L3 has at least one positive lens and one negative lens. The fourth lens group L4 has at least two positive lenses and one negative lens. An aperture stop SP is located in the third lens group L3.

[0049] Numerical Examples 1 to 4 described below show examples of various numerical values ​​for the optical systems of Examples 1 to 4, respectively. In each numerical example, surface number i indicates the order of the optical surface when counted from the object, and r (mm) indicates the radius of curvature of the optical surface. d (mm) indicates the distance (distance) on the optical axis between the i-th surface and the (i+1)-th surface. nd is the refractive index at the d-line of the optical material between the i-th surface and the (i+1)-th surface. νd is the Abbe number based on the d-line of the optical material between the i-th surface and the (i+1)-th surface. The Abbe number νd is given by Nd, NF, NC, and Ng, respectively, when the refractive indices at the d-line (587.6 nm), F-line (486.1 nm), C-line (656.3 nm), and g-line (wavelength 435.8 nm) of the Fraunhofer lines of the optical material are Nd, NF, NC, and Ng, respectively. νd=(Nd-1) / (NF-NC) It is expressed by:

[0050] In each numerical example, the distance d, focal length, F-number, and half angle of view (°) are all values ​​when the optical system is focused at infinity. sk represents the back focus (mm). The back focus is the distance on the optical axis from the final surface of the optical system (the lens surface closest to the image) to the paraxial image plane, expressed as an air-equivalent length. The total lens length is the distance on the optical axis from the front surface of the optical system (the lens surface closest to the object) to the final surface plus the back focus.

[0051] Furthermore, an asterisk (*) next to a surface number indicates that the lens surface has an aspherical shape. When x is the displacement from the vertex of the surface in the optical axis direction, h is the height from the optical axis in a direction perpendicular to the optical axis, R is the paraxial radius of curvature, k is the conic constant, and A4, A6, A8, A10, and A12 are aspherical coefficients, the aspherical shape is expressed as follows: x=(h 2 / R) / [1+{1-(1+k)(h / R) 2} 1 / 2 +A4×h 4 +A6×h 6 +A8×h 8 +A10×h 10 +A12×h 12 The "e±XX" in the conic constant and aspherical coefficient is expressed as "×10 ±XX " means.

[0052] The lens group spacing is shown when the lens is focused at infinity and when it is focused on the closest object (closest focus state). The object distance when the lens is focused at the closest object is shown in parentheses. The object distance is the distance from the image plane to the object position.

[0053] Moreover, values ​​corresponding to the conditions of the above-mentioned formulas (1) to (18) in Numerical Examples 1 to 4 are summarized in Table 1.

[0054] Figures 2, 5, 8, and 12 respectively show longitudinal aberrations (spherical aberration, astigmatism, distortion, and chromatic aberration) of the optical systems of Numerical Examples 1 to 4 at the closest focus position. In the spherical aberration diagrams, Fno indicates the F-number, the solid line indicates spherical aberration for the d-line (wavelength 587.6 nm), and the dash-dotted line indicates spherical aberration for the g-line (wavelength 435.8 nm). In the astigmatism diagrams, the solid line ΔS indicates the sagittal image plane, and the dashed line ΔM indicates the meridional image plane. In the distortion diagrams, distortion for the d-line is shown. In the chromatic aberration diagrams, chromatic aberration of magnification for the g-line is shown. ω is the half angle of view (°).

[0055] [Numerical example 1] Unit: mm Surface Data Surface number rd nd νd 1 268.127 1.20 1.61800 63.4 2 25.391 10.49 3 -27.729 1.00 1.49700 81.5 4 58.394 2.18 5 4572.062 10.07 1.72916 54.7 6 -20.881 1.20 1.64769 33.8 7 -52.141 0.15 8 93.762 2.47 2.05090 26.9 9 -2255.545 (variable) 10 50.628 3.33 1.49700 81.5 11 213.010 (variable) 12 36.449 7.37 1.49700 81.5 13 -86.700 0.15 14 52.111 1.30 1.77047 29.7 15 31.825 4.80 16 (Aperture) ∞ (Variable) 17 -35.175 5.46 1.43875 94.7 18 -15.761 1.00 1.72047 34.7 19 -108.234 0.15 20 35.518 7.83 1.49700 81.5 21 -28.098 0.15 22* -10000.000 3.72 1.85400 40.4 23* -39.933 (variable) 24 53.749 1.00 1.72047 34.7 25 27.162 6.72 26 -29.555 1.00 1.59270 35.3 27 35.766 6.29 2.00100 29.1 28 -255.727 12.72 Image plane ∞ Aspheric data Page 22 K = 0.00000e+000 A 4=-2.63160e-005 A 6=-2.82840e-008 A 8=-1.20483e-010 A10= 7.73278e-013 Page 23 K = 0.00000e+000 A 4=-5.94014e-006 A 6=-2.25330e-008 A 8=-2.39058e-011 A10= 5.34837e-013 Focal length 24.36 F-number 1.44 Half angle of view (°) 41.61 Image height 21.64 Lens length 106.56 sk 12.72 Lens group spacing Infinity Closest (-240mm) d 9 6.42 1.00 d11 1.00 6.42 d16 6.41 3.85 d23 1.00 3.55 Lens group data Group starting plane focal length 1 1 -162.08 2 10 132.73 3 12 92.59 4 17 29.48 5 24 -57.44 [Numerical example 2] Unit: mm Surface Data Surface number rd nd νd 1 88.572 2.00 1.58313 59.4 2* 34.245 9.15 3 -30.590 1.20 1.56732 42.8 4 53.915 2.30 5 62.944 11.42 1.83481 42.7 6 -23.941 1.40 1.85478 24.8 7 -47.250 (variable) 8 57.044 4.07 1.92286 20.9 9 -2074.345 (variable) 10 30.498 3.70 1.59522 67.7 11 58.291 1.20 1.85478 24.8 12 27.083 5.61 13 (Aperture) ∞ (Variable) 14 -27.657 5.45 1.43875 94.7 15 -15.312 1.00 1.77047 29.7 16 -76.877 0.15 17 78.338 10.14 1.49700 81.5 18 -26.670 0.15 19* -351.940 4.90 1.80400 46.5 20 -39.592 (variable) 21 65.421 7.46 2.00100 29.1 22 -63.240 1.20 1.73800 32.3 23 35.661 6.94 24 -52.972 1.00 1.61340 44.3 25 110.397 0.20 26 59.973 4.12 1.59522 67.7 27 1144.661 13.67 Image plane ∞ Aspheric data 2nd side K = 0.00000e+000 A 4= 2.12964e-006 A 6=-1.52028e-009 A 8= 1.93728e-011 Page 19 K = 0.00000e+000 A 4=-8.83374e-006 A 6=-2.00315e-009 A 8=-1.99539e-012 A10=-1.41539e-014 Focal length 34.09 F-number 1.45 Half angle of view (°) 32.40 Image height 21.64 Lens length 113.84 sk 13.67 Lens group spacing Infinity Closest (-280mm) d 7 3.03 1.00 d 9 0.99 3.03 d13 10.38 4.52 d20 1.00 6.86 d27 13.67 7.88 Lens group data Group starting plane focal length 1 1 -470.22 2 8 60.21 3 10 -170.04 4 14 41.65 5 21 -139.70 [Numerical example 3] Unit: mm Surface Data Surface number rd nd νd 1 -57.015 1.70 1.85478 24.8 2 87.168 5.45 3 117.013 7.06 1.90043 37.4 4 -62.441 (variable) 5 45.119 4.86 2.00069 25.5 6 151.320 (variable) 7 30.379 7.86 1.53775 74.7 8 -16569.845 1.40 1.72047 34.7 9 20.608 7.27 10 (Aperture) ∞ (Variable) 11 -27.131 5.48 1.53775 74.7 12 -15.613 1.00 1.62004 36.3 13 -435.824 0.07 14 77.464 8.58 1.59522 67.7 15 -35.901 0.15 16* 181.874 4.79 1.80400 46.5 17* -88.705 (variable) 18 -163.432 8.81 1.95375 32.3 19 -28.024 1.40 1.85478 24.8 20 -80.143 10.95 21 -32.474 1.40 1.54814 45.8 22 -118.962 11.47 Image plane ∞ Aspheric data Page 16 K = 0.00000e+000 A 4=-1.81642e-006 A 6=-1.42419e-008 A 8= 4.16156e-011 A10=-1.15770e-013 Page 17 K = 0.00000e+000 A 4= 9.43411e-007 A 6=-1.31177e-008 A 8= 3.85556e-011 A10=-9.80429e-014 Focal length 48.50 F-number 1.45 Half angle of view (°) 24.04 Image height 21.64 Lens length 108.70 sk 11.47 Lens group spacing Infinity Closest (-450mm) d 4 2.07 0.98 d 6 0.95 2.03 d10 11.98 4.73 d17 3.99 11.24 Lens group data Group starting plane focal length 1 1 738.19 2 5 62.80 3 7 -73.53 4 11 51.43 5 18 -376.44 [Numerical example 4] Unit: mm Surface Data Surface number rd nd νd 1 1008.881 2.20 1.58313 59.4 2* 37.867 9.77 3 -33.792 2.26 1.51633 64.1 4 150.220 0.92 5 56.563 11.24 1.72916 54.7 6 -25.521 1.40 1.85478 24.8 7 -47.329 (variable) 8 69.263 4.62 1.92286 20.9 9 -143.958 1.40 1.77047 29.7 10 -372.741 (variable) 11 34.774 6.44 1.59522 67.7 12 -159.435 1.20 1.77047 29.7 13 39.476 4.14 14 (Aperture) ∞ (Variable) 15 -20.038 1.20 1.77047 29.7 16 65.751 3.53 1.59522 67.7 17 -138.789 0.15 18 69.921 9.71 1.59522 67.7 19 -32.397 0.15 20* 99.627 7.27 1.76450 49.1 21* -39.978 (variable) 22 312.128 7.93 2.00100 29.1 23 -44.888 1.20 1.73800 32.3 24 49.387 7.45 25 -38.427 1.20 1.61340 44.3 26 -100.507 11.50 Image plane ∞ Aspheric data 2nd side K = 0.00000e+000 A 4= 3.40116e-006 A 6= 3.03750e-010 A 8= 2.83362e-011 Page 20 K = 0.00000e+000 A 4=-7.25520e-006 A 6=-5.03423e-009 A 8=-4.06550e-012 A10= 1.24966e-014 Page 21 K = 0.00000e+000 A 4= 4.93121e-006 A 6=-4.25761e-009 A 8=-7.38139e-012 A10= 3.02796e-014 Focal length 34.00 F-number 1.45 Half angle of view (°) 32.47 Image height 21.64 Lens length 113.49 sk 11.50 Lens group spacing Infinity Closest (-280mm) d 7 5.00 3.48 d10 1.00 2.52 d14 9.61 4.92 d21 1.00 5.69 Lens group data Group starting plane focal length 1 1 -424.23 2 8 61.25 3 11 -536.77 4 15 32.54 5 22 -63.86

[0056] [Table 1]

[0057] [Imaging device] 13 shows a digital still camera (imaging device) that uses the optical system of Examples 1 to 4 as its imaging optical system. Reference numeral 10 denotes a camera body, and 11 denotes an imaging optical system configured using any of the optical systems of Examples 1 to 4. Reference numeral 12 denotes a solid-state imaging element (photoelectric conversion element) such as a CCD sensor or CMOS sensor that is built into the camera body 10 and captures (photoelectrically converts) the optical image formed by the imaging optical system 11. The camera body 10 may be a single-lens reflex camera that has a quick-turn mirror, or may be a mirrorless camera that does not have a quick-turn mirror.

[0058] By applying the optical systems of Examples 1 to 4 to an imaging device such as a digital still camera, it is possible to obtain an imaging device that has a wide angle of view, a large aperture ratio, a small size, high optical performance, and high-speed autofocus.

[0059] The embodiments described above are merely representative examples, and various modifications and alterations are possible to each embodiment when implementing the present invention. [Explanation of symbols]

[0060] L0 optical system L1 First lens group L2 Second lens group L3: Third lens group L4 4th lens group L5 Fifth lens group IMG image plane

Claims

1. the first lens group, the second lens group having a positive refractive power, the third lens group, the fourth lens group having a positive refractive power, and the fifth lens group, which are arranged in this order from the object side to the image side, During focusing, the first lens group, the third lens group, and the fifth lens group are stationary, and the second lens group and the fourth lens group are moved, the second lens group is composed of one positive lens or one positive lens unit, the third lens group has one positive lens and one negative lens, The optical system according to claim 1, wherein the fourth lens group has two positive lenses and one negative lens.

2. Let M be the absolute value of the amount of movement of the fourth lens group during focusing from an object at infinity to a nearest object, and f be the focal length of the optical system when focused on an object at infinity. 0.05≦M4 / f≦0.40 2. The optical system according to claim 1, which satisfies the following condition:

3. Let M2 be the absolute value of the amount of movement of the second lens group during focusing from an object at infinity to a nearest object, and f be the focal length of the optical system when focused on an object at infinity. 0.01≦M2 / f≦0.45 3. The optical system according to claim 1, wherein the following condition is satisfied:

4. Let f1 be the focal length of the first lens group, and f be the focal length of the optical system when focused on an object at infinity. −0.3≦f / f1≦0.2 4. The optical system according to claim 1, wherein the following condition is satisfied:

5. Let f2 be the focal length of the second lens group, and f be the focal length of the optical system when focused on an object at infinity. 0.05≦f / f2≦1.10 5. The optical system according to claim 1, wherein the following condition is satisfied:

6. Let f be the focal length of the third lens group, and f be the focal length of the optical system when focused on an object at infinity. −1.0≦f / f3≦0.5 6. The optical system according to claim 1, wherein the following condition is satisfied:

7. Let f be the focal length of the fourth lens group, and f be the focal length of the optical system when focused on an object at infinity. 0.5≦f / f4≦1.5 7. The optical system according to claim 1, wherein the following condition is satisfied:

8. Let f5 be the focal length of the fifth lens group, and f be the focal length of the optical system when focused on an object at infinity. -1.00≦f / f5≦-0.01 8. The optical system according to claim 1, wherein the following condition is satisfied:

9. When the lateral magnification of the second lens group when focused on an object at infinity is b2, −0.99≦b2≦0.20 9. The optical system according to claim 1, wherein the following condition is satisfied:

10. When the lateral magnification of the fourth lens group when focused on an object at infinity is b4, 0.3≦b4≦0.8 10. The optical system according to claim 1, wherein the following condition is satisfied:

11. Let T1 be the distance on the optical axis from the lens surface of the first lens group closest to the object side to the lens surface of the first lens group closest to the image side, and f be the focal length of the optical system when focused on an object at infinity. 0.1≦T1 / f≦1.5 11. The optical system according to claim 1, wherein the following condition is satisfied:

12. Let T2 be the distance on the optical axis from the lens surface of the second lens group closest to the object side to the lens surface of the second lens group closest to the image side, and f be the focal length of the optical system when focused on an object at infinity. 0.01≦T2 / f≦0.40 12. The optical system according to claim 1, wherein the following condition is satisfied:

13. Let T3 be the distance on the optical axis from the lens surface of the third lens group closest to the object side to the lens surface of the third lens group closest to the image side, and f be the focal length of the optical system when focused on an object at infinity. 0.01≦T3 / f≦0.50 13. The optical system according to claim 1, wherein the following condition is satisfied:

14. Let T4 be the distance on the optical axis from the lens surface of the fourth lens group closest to the object side to the lens surface of the fourth lens group closest to the image side, and f be the focal length of the optical system when focused on an object at infinity. 0.1≦T4 / f≦1.0 14. The optical system according to claim 1, wherein the following condition is satisfied:

15. Let T5 be the distance on the optical axis from the lens surface of the fifth lens group closest to the object side to the lens surface of the fifth lens group closest to the image side, and f be the focal length of the optical system when focused on an object at infinity. 0.15≦T5 / f≦0.90 15. The optical system according to claim 1, wherein the following condition is satisfied:

16. Let sk be the distance on the optical axis from the lens surface closest to the image side of the optical system to the image plane, and f be the focal length of the optical system when focused on an object at infinity. 0.05≦s k / f ≦1.00 16. The optical system according to claim 1, wherein the following condition is satisfied:

17. Let TD be the distance on the optical axis from the lens surface closest to the object side of the optical system to the image plane, and f be the focal length of the optical system when focused on an object at infinity. 1≦TD / f≦6 17. The optical system according to claim 1, wherein the following condition is satisfied:

18. When the focal length of the lens closest to the object in the optical system is f11 and the focal length of the optical system when focused on an object at infinity is f, -2.0≦f / f11≦-0.1 18. The optical system according to claim 1, wherein the following condition is satisfied:

19. When the radius of curvature of the lens surface of the second lens group closest to the object side is r2a and the radius of curvature of the lens surface of the second lens group closest to the image side is r2b, 0.2≦(r2b+r2a) / (r2b-r2a)≦4.0 19. The optical system according to claim 1, wherein the following condition is satisfied:

20. 20. The optical system according to claim 1, wherein the fifth lens group has one positive lens and two negative lenses.

21. 21. The optical system according to claim 1, wherein the fourth lens group consists of, arranged in order from the object side to the image side, a cemented lens, a biconvex positive lens, and a positive lens.

22. 22. The optical system according to claim 1, wherein an aperture stop is provided in the third lens group.

23. 23. The optical system according to claim 1, wherein the third lens group consists of a positive lens and a negative lens arranged in this order from the object side to the image side.

24. An optical system according to any one of claims 1 to 23; and an image sensor for capturing an image formed by the optical system.

Images