Optical system and imaging device

Abstract

This provides a compact optical system that offers a wide field of view, a large aperture ratio, and fast focusing capabilities. [Solution] The optical system L0 consists of a first lens group L1, a second lens group L2 with positive refractive power, a third lens group L3, a fourth lens group L4 with positive refractive power, and a fifth lens group L5, arranged sequentially from the object side to the image side. During focusing, the first, third, and fifth lens groups remain stationary, while the second and fourth lens groups move. The second lens group consists 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.

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 image sensors such as CCD sensors and CMOS sensors require optical systems that are compact, have a wide field of view and a large aperture ratio, and possess high optical performance. Furthermore, high-speed autofocus is also required in these optical systems. Patent documents 1 and 2 disclose an inner-focus type optical system that drives a group of focus lenses arranged inside the optical system during focusing. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2019-197125 [Patent Document 2] Japanese Patent Publication No. 2015-200845 [Overview of the Initiative] [Problems that the invention aims to solve]

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

[0005] The present invention provides a compact optical system that offers a wide field of view and a large aperture ratio while enabling high-speed focusing, as well as an imaging device equipped therewith. [Means for solving the problem]

[0006] An optical system, as one aspect of the present invention, consists of 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 order from the object side to the image side. During focusing, the first, third, and fifth lens groups remain stationary, while the second and fourth lens groups move. The first lens group has a negative lens positioned closest to the object, and the second lens group consists of one positive lens or one positive lens unit. The third lens group has one positive lens and one negative lens, and the fourth lens group has two positive lenses and one negative lens. An imaging device equipped with 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 field of view and a large aperture ratio while still being capable of high-speed focusing. [Brief explanation of the drawing]

[0008] [Figure 1] A cross-sectional view showing the configuration of the optical system in Example 1. [Figure 2] A diagram showing the longitudinal aberration of the optical system of Example 1 when it is in focus at infinity. [Figure 3] A diagram showing the longitudinal aberration of the optical system of Example 1 in the closest focus state. [Figure 4] A cross-sectional view showing the configuration of the optical system in Example 2. [Figure 5] Longitudinal aberration diagram of the optical system of Example 2 in the infinity focus state. [Figure 6] Longitudinal aberration diagram of the optical system of Example 2 in the closest focus state. [Figure 7] A cross-sectional view showing the configuration of the optical system in Example 3. [Figure 8] Longitudinal aberration diagram of the optical system of Example 3 in the infinity focus state. [Figure 9] A diagram showing the longitudinal aberration of the optical system of Example 3 in its closest focusing state. [Figure 10] A cross-sectional view showing the configuration of the optical system in Example 4. [Figure 11]Longitudinal aberration diagram in the infinity focus state of the optical system of Example 4. [Figure 12] Longitudinal aberration diagram in the closest focus state of the optical system of Example 4. [Figure 13] Diagram showing an imaging device equipped with the optical systems of Examples 1 to 4.

Mode for Carrying Out the Invention

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

[0010] FIG. 1, FIG. 4, FIG. 7, and FIG. 10 each show a cross-section of the optical systems of Examples 1, 2, 3, and 4 of the present invention in the infinity focus state. In each figure, the left side is the object side and the right side is the image side. The optical systems of each example 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 interchangeable with respect to the imaging device or may be provided integrally with the imaging device.

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

[0012] The optical system L0 of each embodiment includes, as lens groups arranged 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, when focusing, the first lens group L1, the third lens group L3, and the fifth lens group L5 are fixed (immovable) with respect to the image plane IMG, and the second lens group L2 and the fourth lens group L4 move. The arrows shown below the second lens group L2 and the fourth lens group L4 in each figure indicate the moving directions of the respective lens groups when focusing from an infinite object to the closest object.

[0013] In an optical system that is small and highly performant while achieving both a wide angle of view and a large aperture ratio, in order to achieve high-speed autofocus, it is important to appropriately arrange the lens groups constituting the optical system and configure and arrange the focus lens group. In the optical system of each embodiment, by moving some of the focus lens groups (L2, L4) among the plurality of lens groups (L1 to L5) constituting this, aberration correction and weight reduction of the focus lens group are achieved. Also, by making both of the two focus lens groups (L2, L4) positive lens groups and dispersing positive power to them, it becomes easy to suppress fluctuations in aberrations during focusing, particularly spherical aberration, coma aberration, and chromatic aberration of magnification.

[0014] Furthermore, in the optical system 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 term "positive lens" here also includes a cemented lens that is positive as a whole, formed by bonding multiple lenses together. In addition, by configuring the fixed third lens group L3 during focusing to have a positive lens and a negative lens, it becomes easier to correct axial chromatic aberration and spherical aberration while suppressing the increase in weight of the focusing lens group. By configuring L4 to have at least two positive lenses and one negative lens, it becomes easier to suppress aberration fluctuations during focusing, especially fluctuations in axial chromatic aberration and spherical aberration.

[0015] Next, we will describe the preferred configuration that satisfies the optical system of each embodiment.

[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 the Petzval sum. Therefore, having one positive lens and two negative lenses in the fifth lens group L5 makes it easier to correct field curvature.

[0017] Furthermore, it is preferable that the fourth lens group L4 is composed of a cemented lens, a biconvex positive lens, and another positive lens, arranged in order from the object side to the image side. By placing the cemented lens on the object side, where the lens diameter is relatively easy to keep down, it is possible to easily correct axial chromatic aberration while suppressing the increase in weight of the focusing lens group. Also, by placing two positive lenses in the fourth lens group L4 and making the positive lens on the object side a biconvex lens, it is possible to distribute the positive power to facilitate aberration correction and suppress the amount of movement of the focusing lens group, thereby facilitating faster autofocus. If the number of lenses constituting the fourth lens group L4 is too large, it becomes difficult to reduce the weight of the focusing lens group, which is undesirable.

[0018] Furthermore, it is preferable to provide an aperture diaphragm SP in the third lens group L3. By placing the aperture diaphragm SP in the third lens group L3, which is located near the center of the entire optical system, the symmetry of the aperture diaphragm SP in the optical system is improved, making it easier to correct coma aberration and distortion aberration.

[0019] Furthermore, it is preferable that the third lens group L3 is composed of a positive lens and a negative lens arranged in order from the object side to the image side. By placing the positive lens on the object side, the axial light beam is focused, making it easier to suppress the lens diameter of the fourth lens group L4, which is located on the image side of the third lens group L3. As a result, it becomes easier to reduce the weight of the fourth lens group L4, which is the focusing lens group. If the number of lenses in the third lens group L3 is three or more, the third lens group L3 and, consequently, the optical system will become larger, which is undesirable.

[0020] Furthermore, it is preferable that the negative lens in the first lens group L1 is positioned closest to the object. By positioning the negative lens closest to the object, the power configuration becomes that of a retrofocus lens, making it easier to achieve a wide angle of view.

[0021] Furthermore, it is preferable that the second lens group L2 and the fourth lens group L4 move by different amounts during focusing. This facilitates aberration correction in the closest focusing state.

[0022] Next, we will describe the conditions that the optical system of each embodiment preferably satisfies. The optical system of each embodiment preferably satisfies at least one of the following conditions of equations (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 / f ≤ -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 of the fourth lens group L4 when focusing from an object at infinity to the nearest object. The movement of the fourth lens group L4 here is the difference in the position of a particular lens surface in the fourth lens group L4 when it is focused on the object at infinity and when it is focused on the nearest object. The sign of the movement is positive when the fourth lens group is located closer to the object when it is focused on the nearest object compared to when it is focused on the object at infinity, and negative when it is located closer to the image. The movement amounts (absolute values) of the other lens groups are defined similarly. The nearest object is the object located at the closest distance (closest distance) within the distance at which imaging is possible using the optical system of each embodiment.

[0024] Furthermore, f is the focal length of the entire optical system when it is in focus on an object at infinity (hereinafter referred to as the infinity focus state). M2 is the absolute value of the amount of movement of the second lens group L2 when focusing from an object at infinity to the nearest 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 it is in focus at infinity, and b4 is the lateral magnification of the fourth lens group L4 when it is in focus at infinity. T1 is the distance along the optical axis from the lens surface closest to the object in the first lens group L1 to the lens surface closest to the image in the first lens group L1. T2 is the distance along the optical axis from the lens surface closest to the object in the second lens group L2 to the lens surface closest to the image in the second lens group L2. T3 is the distance along the optical axis from the lens surface closest to the object in the third lens group L3 to the lens surface closest to the image in the third lens group L3. T4 is the distance along the optical axis from the lens surface closest to the object in the fourth lens group L4 to the lens surface closest to the image in the fourth lens group L4. T5 is the distance along the optical axis from the lens surface closest to the object in the fifth lens group L5 to the lens surface closest to the image in the fifth lens group L5.

[0026] Furthermore, sk is the distance along the optical axis from the image-side lens surface to the image plane of the lens closest to the image in the optical system (power lens) (back focus). TD is the distance along the optical axis from the object-side lens surface to the image plane of the lens closest to the object in the optical system (power lens) (total lens length). f11 is the focal length of the lens closest to the object in the optical system (power lens). 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) shows the conditions regarding the amount of movement of the fourth lens group L4 during focusing. If the amount of movement is large, such 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, such that M4 / f falls below the lower limit of equation (1), it becomes difficult to correct the variation in aberrations during focusing, especially astigmatism, which is also undesirable.

[0028] Equation (2) shows the conditions regarding the amount of movement of the second lens group L2 during focusing. If the amount of movement is large, such that M2 / f exceeds the upper limit of equation (2), the optical system becomes larger, which is undesirable. If the amount of movement is small, falling below the lower limit, it becomes difficult to correct aberration fluctuations during focusing, especially spherical aberration, which is also undesirable.

[0029] Equation (3) shows the conditions regarding the focal length of the first lens group L1. If the focal length of the first lens group L1 is short (high refractive power) so that f / f1 exceeds the upper limit of equation (3), it becomes a telephoto power configuration and it becomes difficult to secure back focus, which is undesirable. If the focal length of the first lens group L1 is long (low refractive power) 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 miniaturize, which is also undesirable.

[0030] Equation (4) shows the conditions regarding the focal length of the second lens group L2. If the focal length of the second lens group L2 is short such that f / f2 exceeds the upper limit of equation (4), it is undesirable because the weight of the second lens group L2 increases, making it difficult to increase the speed of autofocus. If the focal length of the second lens group L2 is long such that f / f2 falls below the lower limit of equation (4), it is undesirable because it becomes difficult to correct the variation in aberrations during focusing, especially astigmatism.

[0031] Equation (5) shows the conditions regarding the focal length of the third lens group L3. If the focal length of the third lens group L3 is short such that f / f3 exceeds the upper limit of equation (5), it is undesirable because it becomes difficult to correct aberrations occurring in the third lens group L3, especially spherical aberration and axial chromatic aberration. If the focal length of the third lens group L3 is long such that f / f3 falls below the lower limit of equation (5), it is undesirable because it becomes difficult to reduce the lens diameter of the fourth lens group L4, and it becomes difficult to increase the speed of autofocus that moves the fourth lens group L4.

[0032] Equation (6) shows the conditions regarding the focal length of the fourth lens group L4. If the focal length of the fourth lens group L4 is short such that f / f4 exceeds the upper limit of equation (6), it is undesirable because the weight of the second lens group L2, which moves together during focusing, increases, making it difficult to increase the speed of autofocus. If the focal length of the fourth lens group L4 is long such that f / f4 falls below the lower limit of equation (6), it is undesirable because it becomes difficult to correct the fluctuations of aberrations during focusing, especially spherical aberration and axial chromatic aberration.

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

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

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

[0036] Equation (10) shows the conditions regarding the thickness of the first lens group L1 in the optical axis direction. If the thickness of the first lens group L1 increases so that T1 / f exceeds the upper limit of equation (10), the optical system becomes larger, which is undesirable. If the thickness of the first lens group L1 decreases so that T1 / f falls below the lower limit of equation (10), it becomes difficult to correct aberrations, especially distortion, that occur in the first lens group L1, which is also undesirable.

[0037] Equation (11) shows the conditions regarding the thickness of the second lens group L2 in the optical axis direction. If the thickness of the second lens group L2 increases so that T2 / f exceeds the upper limit of equation (11), the optical system becomes larger, which is undesirable. If the thickness of the second lens group L2 decreases so that T2 / f falls below the lower limit of equation (11), it becomes difficult to correct aberrations, especially distortion, that occur in the second lens group L2, which is also undesirable.

[0038] Equation (12) shows the conditions regarding the thickness of the third lens group L3 in the optical axis direction. If the thickness of the third lens group L3 is large such that T3 / f exceeds the upper limit of equation (12), the optical system becomes larger, which is undesirable. If the thickness of the third lens group L3 is small such that T3 / f falls below the lower limit of equation (12), it becomes difficult to correct aberrations occurring in the third lens group L3, especially axial chromatic aberration and spherical aberration, which is also undesirable.

[0039] Equation (13) shows the conditions regarding the thickness of the fourth lens group L4 in the optical axis direction. If the thickness of the fourth lens group L4 is large such that T4 / f exceeds the upper limit of equation (13), it is undesirable because the weight of the fourth lens group L4 increases, making it difficult to increase the speed of autofocus. If the thickness of the fourth lens group L4 is small such that T4 / f falls below the lower limit of equation (12), it is undesirable because it becomes difficult to correct aberrations occurring in the fourth lens group L4, especially spherical aberration and astigmatism.

[0040] Equation (14) shows the conditions regarding the thickness of the fifth lens group L5 in the optical axis direction. If the thickness of the fifth lens group L5 is large such that T5 / f exceeds the upper limit of equation (14), the optical system becomes large, which is undesirable. If the thickness of the fifth lens group L5 is small such that T5 / f falls below the lower limit of equation (14), it becomes difficult to correct field curvature and distortion, which is also undesirable.

[0041] Equation (15) shows the conditions related to the back focus. If the back focus is large, such that sk / f exceeds the upper limit of equation (15), the optical system becomes larger, which is undesirable. If the back focus is small, such 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 undesirable.

[0042] Equation (16) shows the conditions regarding the overall length of the lens. If the overall length of the lens 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 increase, making it difficult to miniaturize the optical system, which is undesirable. If the overall length of the lens is short enough that TD / f falls below the lower limit of equation (16), the refractive power of each lens group increases, making it difficult to correct coma aberration and field curvature in particular, which is also undesirable.

[0043] Equation (17) shows the condition regarding the focal length of the lens positioned closest to the object in the optical system (first lens group L1). If f / f11 exceeds the upper limit of equation (17), it becomes difficult to widen the field of view of the optical system, which is undesirable. If f / f11 falls below the lower limit of equation (17), it becomes difficult to correct distortion, which is also undesirable.

[0044] Equation (18) shows the conditions regarding the shape of the second lens group L2. If (r2b+r2a) / (r2b-r2a) exceeds the upper limit of equation (18), the focus variation 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 variation due to astigmatism, which is also undesirable.

[0045] Satisfying at least one of the above conditions makes it easier to obtain a compact optical system that offers a wide field of view and a large aperture ratio while also enabling high-speed autofocus.

[0046] Furthermore, it is preferable to set the numerical ranges for equations (1) to (18) 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 / f ≤ -0.2 (17a) 0.4≦(r2b+r2a) / (r2b-r2a)≦3.0 (18a) Furthermore, it is even preferable to set the numerical ranges of equations (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 / f ≤ -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 mentioned above, the optical system of each example consists 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 order from the object side to the image side. When focusing from an object at infinity to the nearest 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 remain stationary. 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. The aperture diaphragm SP is located in the third lens group L3.

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

[0050] Also, in each numerical example, the interval d, focal length, F-number, and half angle (°) are all values when the optical system is in an infinitely focused state. sk represents the back focus (mm). The back focus is defined as the distance on the optical axis from the final surface (the lens surface closest to the image side) to the paraxial image plane, expressed in air-equivalent length. The overall lens length is the length obtained by adding the back focus to the distance on the optical axis from the frontmost surface (the lens surface closest to the object side) to the final surface.

[0051] Also, "*" attached to the surface number means that the lens surface has an aspherical shape. The aspherical shape is defined as follows: when x is the displacement amount from the vertex of the surface in the optical axis direction, h is the height from the optical axis in the direction perpendicular to the optical axis, R is the paraxial curvature radius, k is the conic constant, and A4, A6, A8, A10, A12 are the aspherical coefficients, 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 [[ID=?]] is represented by. "e±XX" in the conic constant and aspherical coefficients means "×10 ±XX ".

[0052] The lens group intervals are shown for the infinitely focused state and the state focused on the closest object (the closest focused state). The object distance in the closest focused state is shown in parentheses. The object distance is the distance from the image plane to the object position.

[0053] Also, the values corresponding to the conditions of the aforementioned formulas (1) to (18) in Numerical Examples 1 to 4 are summarized in Table 1.

[0054] It seems there is a tag "?" in the original text which might be a mistake. I've translated the text as accurately as possible while keeping all the tags intact. If you have any further clarifications or corrections regarding the original text, please let me know.Figures 3, 6, 9, and 12 show the longitudinal aberrations (spherical aberration, astigmatism, distortion, and chromatic aberration) of the optical systems of numerical examples 1 to 4 at their closest focusing state, respectively. In the spherical aberration diagram, Fno indicates the F number, the solid line shows the spherical aberration with respect to the d line (wavelength 587.6 nm), and the dashed line shows the spherical aberration with respect to the g line (wavelength 435.8 nm). In the astigmatism diagram, the solid line ΔS shows the sagittal image plane, and the dashed line ΔM shows the meridional image plane. The distortion aberration diagram shows the distortion aberration with respect to the d line. The chromatic aberration diagram shows the lateral chromatic aberration at the g line. ω is the half-angle of view (°).

[0055] [Numerical Example 1] Unit: mm Surface data Face 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 ∞ Aspherical 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 (°): 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 Face 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 ∞ Aspherical 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 (°): 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 Face 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 ∞ Aspherical 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 (°): 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 Face 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 ∞ Aspherical 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 (°): 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] Figure 13 shows a digital still camera (imaging device) using the optical systems of Examples 1 to 4 as the imaging optical system. 10 is the camera body, and 11 is the imaging optical system composed of any of the optical systems of Examples 1 to 4. 12 is a solid-state image sensor (photoelectric conversion element) such as a CCD sensor or CMOS sensor, which 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 with a quick-turn mirror, or a mirrorless camera without a quick-turn mirror.

[0058] By applying the optical systems of Examples 1 to 4 to imaging devices such as digital still cameras, it is possible to obtain an imaging device that is compact, has high optical performance, and achieves high-speed autofocus while having a wide field of view and a large aperture ratio.

[0059] The embodiments described above are merely representative examples, and various modifications and changes can be made 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 5th lens group IMG image plane

Claims

1. It consists of 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 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 first lens group has a negative lens positioned closest to the object, The second lens group consists of one positive lens or one positive lens unit. The third lens group has one positive lens and one negative lens, The optical system is characterized in that the fourth lens group has two positive lenses and one negative lens.

2. When M4 is the absolute value of the amount of movement of the fourth lens group when focusing from an object at infinity to the nearest object, and f is the focal length of the optical system when it is in focus on the object at infinity, 0.05 ≤ M4 / f ≤ 0.40 The optical system according to claim 1, characterized in that it satisfies the following conditions.

3. When M2 is the absolute value of the amount of movement of the second lens group when focusing from an object at infinity to the nearest object, and f is the focal length of the optical system when it is in focus on the object at infinity, 0.01 ≤ M² / f ≤ 0.45 The optical system according to claim 1 or 2, characterized in that it satisfies the following conditions.

4. When the focal length of the first lens group is f1 and the focal length of the optical system when in focus on an object at infinity is f, -0.3 ≤ f / f1 ≤ 0.2 An optical system according to any one of claims 1 to 3, characterized in that it satisfies the following conditions.

5. When the focal length of the second lens group is f2, and the focal length of the optical system when focused on an object at infinity is f, 0.05 ≤ f / f² ≤ 1.10 The optical system according to any one of claims 1 to 4, characterized in that it satisfies the following conditions.

6. When the focal length of the third lens group is f3 and the focal length of the optical system when focused on an object at infinity is f, -1.0 ≤ f / f3 ≤ 0.5 The optical system according to any one of claims 1 to 5, characterized in that it satisfies the following conditions.

7. When the focal length of the fourth lens group is f4 and the focal length of the optical system when focused on an object at infinity is f, 0.5 ≤ f / f4 ≤ 1.5 An optical system according to any one of claims 1 to 6, characterized in that it satisfies the following conditions.

8. When the focal length of the fifth lens group is f5, and the focal length of the optical system when in focus on an object at infinity is f, -1.00 ≤ f / f5 ≤ -0.01 The optical system according to any one of claims 1 to 7, characterized in that it satisfies the following conditions.

9. When the image lateral magnification of the second lens group when it is in focus on an object at infinity is denoted as b2, -0.99 ≤ b² ≤ 0.20 The optical system according to any one of claims 1 to 8, characterized in that it satisfies the following conditions.

10. When the image lateral magnification of the fourth lens group when it is in focus on an object at infinity is denoted as b4, 0.3 ≤ b4 ≤ 0.8 The optical system according to any one of claims 1 to 9, characterized in that it satisfies the following conditions.

11. When T1 is the distance along the optical axis from the lens surface closest to the object in the first lens group to the lens surface closest to the image in the first lens group, and f is the focal length of the optical system when in focus on an object at infinity, 0.1 ≤ T1 / f ≤ 1.5 The optical system according to any one of claims 1 to 10, characterized in that it satisfies the following conditions.

12. When T2 is the distance along the optical axis from the lens surface closest to the object in the second lens group to the lens surface closest to the image in the second lens group, and f is the focal length of the optical system when in focus on an object at infinity, 0.01 ≤ T² / f ≤ 0.40 The optical system according to any one of claims 1 to 11, characterized in that it satisfies the following conditions.

13. When T3 is the distance along the optical axis from the lens surface closest to the object in the third lens group to the lens surface closest to the image in the third lens group, and f is the focal length of the optical system when in focus on an object at infinity, 0.01 ≤ T3 / f ≤ 0.50 The optical system according to any one of claims 1 to 12, characterized in that it satisfies the following conditions.

14. When T4 is the distance along the optical axis from the lens surface closest to the object in the fourth lens group to the lens surface closest to the image in the fourth lens group, and f is the focal length of the optical system when in focus on an object at infinity, 0.1 ≤ T4 / f ≤ 1.0 An optical system according to any one of claims 1 to 13, characterized in that it satisfies the following conditions.

15. When T5 is the distance along the optical axis from the lens surface closest to the object in the fifth lens group to the lens surface closest to the image in the fifth lens group, and f is the focal length of the optical system when in focus on an object at infinity, 0.15 ≤ T5 / f ≤ 0.90 An optical system according to any one of claims 1 to 14, characterized in that it satisfies the following conditions.

16. When the distance along the optical axis from the lens surface closest to the image plane of the optical system to the image plane is sk, and the focal length of the optical system when focused on an object at infinity is f, 0.05 ≤ sk / f ≤ 1.00 The optical system according to any one of claims 1 to 15, characterized in that it satisfies the following conditions.

17. When TD is the distance along the optical axis from the lens surface closest to the object to the image plane of the optical system, and f is the focal length of the optical system when it is in focus on an object at infinity, 1 ≤ TD / f ≤ 6 An optical system according to any one of claims 1 to 16, characterized in that it satisfies the following conditions.

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 it is in focus on an object at infinity is f, -2.0 ≤ f / f ≤ -0.1 An optical system according to any one of claims 1 to 17, characterized in that it satisfies the following conditions.

19. When the radius of curvature of the lens surface closest to the object in the second lens group is r2a, and the radius of curvature of the lens surface closest to the image in the second lens group is r2b, 0.2≦(r2b+r2a) / (r2b-r2a)≦4.0 An optical system according to any one of claims 1 to 18, characterized in that it satisfies the following conditions.

20. The optical system according to any one of claims 1 to 19, characterized in that the fifth lens group has one positive lens and two negative lenses.

21. The optical system according to any one of claims 1 to 20, characterized in that the fourth lens group consists of a cemented lens, a biconvex positive lens, and a positive lens, arranged in order from the object side to the image side.

22. The optical system according to any one of claims 1 to 21, characterized in that the third lens group is provided with an aperture diaphragm.

23. The optical system according to any one of claims 1 to 22, characterized in that the third lens group consists of positive and negative lenses arranged in order from the object side to the image side.

24. An optical system according to any one of claims 1 to 23, An imaging device characterized by having an image sensor that captures an image formed by the optical system.

Images