Optical system and imaging device

Abstract

To provide a compact optical system capable of high-speed focusing.SOLUTION: An optical system L0 comprises, in order from an object side to an image side, a front group Lf having a positive refractive power and including a plurality of lens groups, an aperture stop SP, and a rear group Lr having a positive refractive power and including a plurality of lens groups. During focusing, a first focus lens group L2 included in the front group and a second focus lens group L4 included in the rear group move, thereby changing intervals between the adjacent lens groups. The front group includes a first lens having the positive refractive power disposed closest to the object side, and a second lens having a negative refractive power disposed adjacent to the first lens on the image side.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an optical system suitable for imaging. [Background technology]

[0002] Imaging requires optical systems that are compact and have high optical performance despite their large aperture ratio, and also require high-speed focusing (autofocus).

[0003] Patent Documents 1 and 2 disclose an inner focus type optical system in which a focus lens group arranged inside the optical system is driven during focusing. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2019-197125 [Patent Document 2] Japanese Patent Publication No. 2023-120952 Summary of the Invention [Problem to be solved by the invention]

[0005] In optical systems with a large aperture ratio, it is difficult to correct various aberrations. In particular, if the focus lens group is made lightweight to enable high-speed focusing, it becomes difficult to suppress aberration fluctuations when focusing from an object at infinity to a close object.

[0006] The present invention provides a compact optical system that has a large aperture ratio, is lightweight, and is capable of high-speed focusing, and an imaging device equipped with the same. [Means for solving the problem]

[0007] An optical system according to one aspect of the present invention comprises, arranged in order from the object side to the image side, a front group having positive refractive power and including multiple lens groups, an aperture stop, and a rear group having positive refractive power and including multiple lens groups. During focusing, the first focus lens group included in the front group and the second focus lens group included in the rear group move, thereby changing the spacing between adjacent lens groups. The front group includes a first lens having positive refractive power and located closest to the object, and a second lens having negative refractive power and adjacent to the first lens on the image side. An imaging device including the above optical system also constitutes another aspect of the present invention. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a compact optical system that has a large aperture ratio, is lightweight, and is capable of high-speed focusing. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a cross-sectional view showing the configuration of an optical system according to a first embodiment. [Figure 2] 1A and 1B are longitudinal aberration diagrams of the optical system of Example 1 in a state where the optical system is focused at infinity and a state where the optical system is focused at the closest possible distance. [Figure 3] FIG. 10 is a cross-sectional view showing the configuration of an optical system according to a second embodiment. [Figure 4] 10A and 10B are longitudinal aberration diagrams of the optical system of Example 2 when focused at infinity and when focused at the closest possible distance. [Figure 5] FIG. 10 is a cross-sectional view showing the configuration of an optical system according to a third embodiment. [Figure 6] 10A and 10B are longitudinal aberration diagrams of the optical system of Example 3 when focused at infinity and when focused at the closest possible distance. [Figure 7] FIG. 10 is a cross-sectional view showing the configuration of an optical system according to a fourth embodiment. [Figure 8] 10A and 10B are longitudinal aberration diagrams of the optical system of Example 4 when focused at infinity and when focused at the closest possible distance. [Figure 9] 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

[0010] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0011] 1, 3, 5, and 7 show cross sections of optical systems L0 of Examples 1, 2, 3, and 4 of the present invention, respectively, when focused on an object at infinity (hereinafter referred to as the infinity focused state). In each figure, the left side is the object side (front side), and the right side is the image side (rear side).

[0012] The optical system L0 in each embodiment is used as an imaging optical system for various imaging devices such as a video camera, a digital still camera, a broadcast camera, a silver halide film camera, a surveillance camera, etc. The optical system L0 may be replaceable with respect to the imaging device, or may be provided integrally with the imaging device.

[0013] The optical system L0 in each embodiment is composed of, arranged in order from the object side to the image side, a front group Lf with positive refractive power, an aperture stop SP, and a rear group Lr with positive refractive power. IP is an image plane. The image plane IP is where the imaging surface (light-receiving surface) of an imaging element (photoelectric conversion element) such as a CCD sensor or CMOS sensor, or the film surface (photosensitive surface) of a silver halide film, is located.

[0014] In Examples 1 to 3, the front group Lf is composed of, arranged in order from the object side to the image side, a first lens group L1 with positive refractive power, a second lens group L2 with positive or negative refractive power, and a third lens group L3 with positive or negative refractive power. A lens group is a group of one or more lenses that may or may not move together during focusing between infinity and the closest focus. That is, the spacing between adjacent lens groups changes during focusing. In addition, the rear group Lr in Examples 1 to 3 is composed of a fourth lens group L4 with positive refractive power and a fifth lens group L5 with positive or negative refractive power.

[0015] In Examples 1 to 3, the first lens group L1, the third lens group L3, and the fifth lens group L5 are fixed (unmoving) relative to the image plane IP during focusing, and the second lens group L2 and the fourth lens group L4 move. In each diagram, the direction of movement (toward the object or toward the image) of the lens group that moves during focusing from infinity to a close distance is indicated below the lens group that moves during focusing.

[0016] The front group Lf in Example 4 is composed of a first lens group L1 and a second lens group L2 with negative refractive power, arranged in this order from the object side to the image side. The rear group Lr in Example 4 is composed of a third lens group L3 with positive refractive power and a fourth lens group L4 with positive or negative refractive power. In Example 4, during focusing, the first lens group L1 and the fourth lens group L4 are fixed (unmoving) with respect to the image plane IP, and the second lens group L2 and the third lens group L3 move.

[0017] In order to speed up focusing (autofocus) in a compact, high-performance optical system that has a wide angle of view and a large aperture ratio, it is important to appropriately arrange the lens groups that make up the optical system and the arrangement and configuration of the focus lens group that moves during focusing. The optical system L0 in each embodiment achieves aberration correction and a lightweight focus lens group by moving some of the multiple lens groups that make up the optical system.

[0018] Furthermore, by distributing the power between the two focus lens groups, it becomes easier to suppress fluctuations in aberrations during focusing, particularly fluctuations in astigmatism, coma, and chromatic aberration of magnification.

[0019] The features of the optical system L0 of each embodiment will be described below.

[0020] In Examples 1 to 4, the first lens group L1, which is closest to the object among the front group Lf having positive refractive power, has a first lens with positive refractive power closest to the object. The term "lens" as used here includes various types of lenses, such as a single lens, a cemented lens in which lenses made of different materials are bonded together, and a lens made of an inorganic material such as glass on the surface of which a layer made of an organic material such as resin is provided. In Numerical Examples 1 to 4 corresponding to Examples 1 to 4, respectively, the first lens is composed of a single lens. By imparting positive refractive power to the first lens, the incident light beam is converged, and the diameters of the lenses on the image side of the first optical element in the first lens group L1 and the lenses in the second lens group L2 can be reduced, thereby making it possible to reduce the weight of each lens.

[0021] In Examples 1 to 4, the first lens group L1 has a second lens with negative refractive power adjacent to the first lens on the image side. In each numerical example, the second lens has a configuration in which a resin layer is provided on the object-side surface of a single lens. Furthermore, in Examples 1 to 4, the second lens has an aspherical surface. In each numerical example, the object-side surface of the resin layer is aspherical.

[0022] In Examples 1 and 2, the second lens group L2, which is the first focus lens group in the front group Lf that moves during focusing, is composed of a single lens with positive refractive power or a cemented lens with positive refractive power. In Numerical Examples 1 and 2, the second lens group L2 is composed of a single lens with positive refractive power. In Examples 1 and 2, the second lens group L2 moves toward the object side during focusing from infinity to a close distance.

[0023] In Examples 3 and 4, the second lens unit L2, which is the first focus lens unit in the front group Lf that moves during focusing, is composed of a single lens with negative refractive power or a cemented lens with negative refractive power. In Numerical Examples 3 and 4, the second lens unit L2 is composed of a single lens with negative refractive power. In Examples 3 and 4, the second lens unit L2 moves toward the image side during focusing from infinity to a close distance.

[0024] By configuring the second lens group L2, which moves during focusing, with a single lens in this way, it becomes easier to increase the focusing speed.

[0025] In Examples 1 and 2, the third lens group L3, which is the closest to the image in the front group Lf, is composed of a single lens with negative refractive power or a cemented lens with negative refractive power. In Numerical Examples 1 and 2, the third lens group L3 is composed of a single lens with negative refractive power. In Example 3, the third lens group L3, which is the closest to the image in the front group Lf, is composed of a single lens with positive refractive power or a cemented lens with positive refractive power. In Numerical Example 3, the third lens group L3 is composed of a single lens with positive refractive power.

[0026] In Examples 1 to 3, an aperture diaphragm SP is disposed between the third lens unit L3 and the fourth lens unit L4. In Example 4, an aperture diaphragm SP is disposed between the second lens unit L2 and the third lens unit L3.

[0027] The fourth lens group L4 in Examples 1 to 3 and the third lens group L3 in Example 4 are second focus lens groups that move toward the object side during focusing from infinity to a close distance. The fourth lens group L4 in Examples 1 to 3 and the third lens group L3 in Example 4 each include at least two positive lenses and one negative lens. A cemented lens in which a positive lens and a negative lens are cemented together is counted as one positive lens and one negative lens. This configuration makes it easy to suppress aberration fluctuations during focusing, particularly fluctuations in axial chromatic aberration and spherical aberration.

[0028] Furthermore, in Examples 1 to 3, by arranging the third lens unit L3 which is stationary during focusing, it becomes easy to correct axial chromatic aberration and spherical aberration while suppressing an increase in the weight of the focus lens unit.

[0029] Next, a description will be given of the configuration that the optical system L0 of each embodiment preferably satisfies.

[0030] In Examples 1 to 4, the first lens group L1 preferably has an aspherical surface. By having the aspherical surface of the first lens group L1, where off-axis rays are positioned high, it becomes possible to effectively correct field curvature, astigmatism, and distortion.

[0031] It is preferable that the second rear lens unit Lr2 (fifth lens unit L5 in Examples 1 to 3, fourth lens unit L4 in Example 4) closest to the image side of the rear group Lr in Examples 1 to 4 has at least one positive lens and two negative lenses. In each example, the lens unit closest to the image side has the above configuration, which is effective in correcting Petzval sum and makes it easy to correct curvature of field.

[0032] In Examples 1 to 4, the first rear lens group Lr1 (the fourth lens group L4 in Examples 1 to 3, and the third lens group L3 in Example 4) located closest to the object side of the rear group Lr is preferably composed of, in order from the object side to the image side, a cemented lens, a biconvex positive lens, and a positive lens. Moreover, by reducing the number of lenses constituting the first rear lens group Lr1, it is possible to achieve a lightweight focus lens group.

[0033] By arranging a cemented lens in the first rear lens unit Lr1, which is closest to the object side of the rear unit Lr and in which the lens diameter can be easily reduced, it is possible to suppress an increase in the weight of the focus lens unit and to facilitate correction of axial chromatic aberration.

[0034] In Examples 1 to 4, the first rear lens unit Lr1 includes two single lenses with positive refractive power, and it is preferable that the single lens with positive refractive power closer to the object side is a biconvex lens. This distributes the positive power to facilitate aberration correction, while reducing the amount of movement of the focus lens unit, making it easy to increase the focusing speed.

[0035] It is preferable to dispose an aperture stop SP in the lens group closest to the image side of the front group Lf (the third lens group L3 in Examples 1 to 3, and the second lens group L2 in Example 4) or in a position adjacent to that lens group on the image side (between the front group Lf and the rear group Lr) in Examples 1 to 4. Disposing the aperture stop SP near the center of the entire optical system L0 improves the symmetry of the optical system L0 before and after the aperture stop SP, making it easier to correct coma and distortion.

[0036] In Examples 1 to 4, it is preferable that the focusing lens group in the front group Lf and the focusing lens group in the rear group Lr move by different amounts during focusing, which facilitates aberration correction when focused on the closest object (hereinafter referred to as the closest focused state).

[0037] Next, conditions that the optical system L0 of each embodiment should preferably satisfy will be described. The optical system L0 of each embodiment should preferably satisfy at least one of the conditions of the following expressions (1) to (15).

[0038] 0.5≦f1 / f≦4.0 (1) 0.02≦LD1 / f≦0.15 (2) 0.1≦SK / f≦0.6 (3) 15≦νd1≦30 (4) 0.2≦T1 / f≦1.5 (5) 0.01≦T2 / f≦0.30 (6) 0.1≦Tr1 / f≦0.9 (7) 0.2≦Tr2 / f≦0.9 (8) 0.5≦fLf / f≦5.0 (9) 0.2≦fLr / f≦5.0 (10) 0.5≦fLf / fLr≦4.0 (11) 0.2≦fL1 / f≦5.0 (12) 0.5≦|fL2| / f≦5.0 (13) 0.1≦fLr1 / f≦4.0 (14) -7.0≦fLr2 / f≦-0.2 (15) In equations (1) to (15), f is the focal length of the entire optical system L0 when focused at infinity. f1 is the focal length of the first lens in the first lens group L1, and f2 is the focal length of the second lens in the first lens group L1. LD1 is the air distance on the optical axis between the first and second lenses. SK is the air-equivalent distance (back focus) on the optical axis from the lens surface closest to the image in the optical system L0 to the image plane (paraxial image plane) IP. T1 is the distance on 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 on 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. Tr1 is the distance (thickness) on the optical axis from the lens surface closest to the object in the first rear lens group Lr1 in the rear group Lr to the lens surface closest to the image in the lens group closest to the object. Tr2 is the distance (thickness) on the optical axis from the lens surface closest to the object of the second rear lens unit Lr2 in the rear group Lr to the lens surface closest to the image of the lens unit closest to the image.

[0039] νd1 is the Abbe number based on the d-line of the first lens. fLf is the focal length of the front lens unit Lf, and fLr is the focal length of the rear lens unit Lr. fL1 is the focal length of the first lens unit L1, fL2 is the focal length of the second lens unit L2, and fLr1 is the focal length of the first rear lens unit Lr1 in the rear lens unit Lr. fLr2 is the focal length of the second rear lens unit Lr2.

[0040] The condition of formula (1) indicates the appropriate relationship between the focal length f1 of the first lens and the focal length f of the entire optical system L0. If f1 / f is below the lower limit of formula (1), the focal length of the first lens becomes too short, i.e., the refractive power of the first lens becomes too strong, making it difficult to correct astigmatism and spherical aberration, which is undesirable. Conversely, if f1 / f is above the upper limit of formula (1), the focal length of the first lens becomes too long, i.e., the refractive power of the first lens becomes too weak, making it impossible to sufficiently converge the light beam entering the optical system L0. As a result, it becomes difficult to reduce the diameter of the lens in the first lens group L1 that is closer to the image than the first lens, which increases the weight of the entire optical system L0, which is undesirable.

[0041] The condition of formula (2) indicates the appropriate relationship between the air gap LD1 between the first and second lenses and the focal length f of the entire optical system L0. If the gap between the first and second lenses is too narrow, such that LD1 / f falls below the lower limit of formula (2), it becomes necessary to position the second and subsequent lenses in the first lens group L1 before the light beam incident on the first lens converges. This results in larger diameters for the second and subsequent lenses, which undesirably increases the overall weight of the optical system L0. If the gap between the first and second lenses is too wide, such that LD1 / f exceeds the upper limit of formula (2), it becomes necessary to increase the overall length of the optical system L0, which undesirably increases the size of the optical system L0.

[0042] The condition of formula (3) indicates the appropriate relationship between the back focal length SK and the focal length f of the entire optical system L0. If the back focal length is long so that SK / f exceeds the upper limit of formula (3), the optical system L0 will become large, which is undesirable. If the back focal length is short so that SK / f falls below the lower limit of formula (3), it will be difficult to lay out optical blocks such as the image sensor and low-pass filter near the image plane, which is also undesirable.

[0043] Equation (4) shows the appropriate range for the Abbe number νd1 of the first lens, which is a positive lens. If νd1 falls below the lower limit of equation (4), excessive axial chromatic aberration will occur in the first lens, which is undesirable. If νd1 exceeds the upper limit of equation (4), correction of axial chromatic aberration will be insufficient, which is undesirable.

[0044] The condition of formula (5) indicates the appropriate relationship between the thickness T1 of the first lens unit L1 and the focal length f of the entire optical system L0. If the thickness of the first lens unit L1 is increased so that T1 / f exceeds the upper limit of formula (5), the optical system L0 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 formula (5), it will become difficult to correct aberrations, particularly distortion, that occur in the first lens unit L1, which is also undesirable.

[0045] The condition of formula (6) indicates the appropriate relationship between the thickness T2 of the second lens unit L2 and the focal length f of the entire optical system L0. If the thickness of the second lens unit L2 is increased so that T2 / f exceeds the upper limit of formula (6), the optical system L0 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 formula (6), it will become difficult to correct aberrations, particularly distortion, that occur in the second lens unit L2, which is also undesirable.

[0046] The condition of formula (7) shows the appropriate relationship between the thickness Tr1 of the first rear lens unit Lr1 and the focal length f of the entire optical system L0. If the thickness of the first rear lens unit Lr1 is so large that Tr1 / f exceeds the upper limit of formula (7), the weight of the first rear lens unit Lr1 increases, making it difficult to achieve high-speed focusing, which is undesirable. If the thickness of the first rear lens unit Lr1 is so small that Tr1 / f falls below the lower limit of formula (7), it becomes difficult to correct aberrations generated in the first rear lens unit Lr1, particularly spherical aberration and astigmatism, which is also undesirable.

[0047] The condition of formula (8) indicates the appropriate relationship between the thickness Tr2 of the second rear lens unit Lr2 and the focal length f of the entire optical system L0. If the thickness of the second rear lens unit Lr2 is large enough that Tr2 / f exceeds the upper limit of formula (8), the optical system L0 will become large, which is undesirable. If the thickness of the second rear lens unit Lr2 is small enough that Tr2 / f falls below the lower limit of formula (8), it will be difficult to correct field curvature and distortion, which is undesirable.

[0048] The condition of equation (9) indicates the appropriate relationship between the focal length fLf of the front group Lf and the focal length f of the entire optical system L0. If the focal length of the front group Lf is increased so that fLf / f exceeds the upper limit of equation (9), i.e., if the refractive power of the front group Lf is weakened, the light beam convergence effect will be weakened. As a result, the diameter of the light beam passing through the second lens group L2 and the aperture stop SP will increase, making it difficult to miniaturize the optical system L0, which is undesirable. If the focal length of the front group Lf is decreased so that fLf / f falls below the lower limit of equation (9), i.e., if the refractive power of the front group Lf is strong, it will be difficult to correct the spherical aberration and astigmatism that occur within the front group Lf, which is also undesirable.

[0049] The condition of equation (10) indicates the appropriate relationship between the focal length fLr of the rear group Lr and the focal length f of the entire optical system L0. If the focal length of the rear group Lr becomes longer so that fLr / f exceeds the upper limit of equation (10), i.e., if the refractive power of the rear group Lr becomes weaker, it becomes difficult to correct off-axial aberrations generated in the front group Lf, particularly lateral chromatic aberration and distortion, which is undesirable. If the focal length of the rear group Lr becomes shorter so that fLr / f falls below the lower limit of equation (10), i.e., if the refractive power of the rear group Lr becomes stronger, it becomes difficult to correct off-axial aberrations generated in the rear group Lr, particularly lateral chromatic aberration and distortion, which is also undesirable.

[0050] The condition of equation (11) indicates the appropriate relationship between the focal length fLf of the front group Lf and the focal length fLr of the rear group Lr. If the focal length of the rear group Lr becomes short so that fLf / fLr exceeds the upper limit of equation (11), i.e., if the refractive power of the second lens group L2 becomes strong, the curvature of field generated in the rear group Lr increases and becomes difficult to correct, which is undesirable. If the focal length of the front group Lf becomes short so that fLf / fLr falls below the lower limit of equation (11), i.e., if the refractive power of the front group Lf becomes strong, it becomes difficult to correct the spherical aberration and astigmatism generated in the front group Lf, which is also undesirable.

[0051] The condition of equation (12) indicates the appropriate relationship between the focal length fL1 of the first lens group L1 and the focal length f of the entire optical system L0. If the focal length of the first lens group L1 is short so that fL1 / f exceeds the upper limit of equation (12), i.e., if the refractive power of the first lens group L1 is strong, it becomes difficult to correct the spherical aberration and astigmatism that occur within the first lens group L1, which is undesirable. On the other hand, if the focal length of the first lens group L1 is long so that fL1 / f falls below the lower limit of equation (12), i.e., if the refractive power of the first lens group L1 is weak, the overall length of the optical system L0 becomes long, making it difficult to achieve compactness, which is also undesirable.

[0052] The condition of equation (13) indicates the appropriate relationship between the focal length fL2 of the second lens unit L2 and the focal length f of the entire optical system L0. If the focal length of the second lens unit L2 is short so that |fL2| / f exceeds the upper limit of equation (13), the weight of the second lens unit L2 increases, making it difficult to achieve high-speed focusing, which is undesirable. If the focal length of the second lens unit L2 is long so that |fL2| / f falls below the lower limit of equation (13), it becomes difficult to correct fluctuations in aberrations, especially astigmatism, during focusing, which is also undesirable.

[0053] The condition of equation (14) indicates the appropriate relationship between the focal length fLr1 of the first rear lens unit Lr1 in the rear group Lr and the focal length f of the entire optical system L0. If the focal length of the first rear lens unit Lr1 is short so that fLr1 / f exceeds the upper limit of equation (14), the weight of the second lens unit L2, which moves together with the first rear lens unit Lr1 during focusing, increases, making it difficult to achieve high-speed focusing, which is undesirable. If the focal length of the first rear lens unit Lr1 is long so that fLr1 / f falls below the lower limit of equation (14), it becomes difficult to correct fluctuations in aberrations, particularly spherical aberration and axial chromatic aberration, during focusing, which is also undesirable.

[0054] The condition of formula (15) indicates the appropriate relationship between the focal length fLr2 of the second rear lens unit Lr2 and the focal length f of the entire optical system L0. If the focal length of the second rear lens unit Lr2 is short so that fLr2 / f exceeds the upper limit of formula (15), it becomes difficult to correct the Petzval sum and to suppress the curvature of field, which is undesirable. If the focal length of the second rear lens unit Lr2 is long so that fLr2 / f falls below the lower limit of formula (15), it becomes difficult to ensure the back focus, which is undesirable.

[0055] It is more preferable that the numerical ranges of the formulas (1) to (15) are as follows:

[0056] 1.0≦f1 / f≦3.5 (1a) 0.025≦LD1 / f≦0.130 (2a) 0.15≦SK / f≦0.40 (3a) 17≦νd1≦28 (4a) 0.5≦T1 / f≦1.2 (5a) 0.015≦T2 / f≦0.150 (6a) 0.3≦Tr1 / f≦0.7 (7a) 0.25≦Tr2 / f≦0.70 (8a) 1.0≦fLf / f≦3.0 (9a) 0.3≦fLr / f≦3.0 (10a) 0.7≦fLf / fLr≦3.0 (11a) 0.3≦fL1 / f≦3.0 (12a) 0.7≦|fL2| / f≦3.0 (13a) 0.2≦fLr1 / f≦3.0 (14a) -5.0≦fLr2 / f≦-0.5 (15a) Furthermore, it is more preferable to set the numerical ranges of the formulas (1) to (15) as follows.

[0057] 1.5≦f1 / f≦3.0 (1b) 0.03≦LD1 / f≦0.12 (2b) 0.20≦SK / f≦0.35 (3b) 20≦νd1≦26 (4b) 0.7≦T1 / f≦0.9 (5b) 0.02≦T2 / f≦0.07 (6b) 0.4≦Tr1 / f≦0.5 (7b) 0.3≦Tr2 / f≦0.4 (8b) 1.5≦fLf / f≦2.5 (9b) 0.5≦fLr / f≦1.5 (10b) 1.0≦fLf / fLr≦2.0 (11b) 0.5≦fL1 / f≦1.5 (12b) 1.0≦|fL2| / f≦2.0 (13b) 0.3≦fLr1 / f≦1.5 (14b) -3.5≦fLr2 / f≦-1.0 (15b) Numerical Examples 1 to 4 are shown below. In each numerical example, surface number i indicates the order of the surface when counted from the object side. r is the radius of curvature (mm) of the ith surface from the object side, d is the lens thickness or air gap (mm) on the optical axis between the ith and (i+1)th surfaces, and nd is the refractive index at the d-line of the optical material between the ith and (i+1)th surfaces. νd is the Abbe number based on the d-line of the optical material between the ith and (i+1)th surfaces.

[0058] The Abbe number νd based on the d-line is expressed as νd=(Nd-1) / (NF-NC), where Nd, NF, and NC are the refractive indices at the Fraunhofer d-line (587.6 nm), F-line (486.1 nm), and C-line (656.3 nm).

[0059] The distance d, focal length, F-number, and half angle of view (°) are all values when the lens is focused at infinity.

[0060] SK represents the back focal length (mm) mentioned above. The total length of a lens is the distance on the optical axis from the lens surface closest to the object to the lens surface closest to the image, plus the back focal length.

[0061] 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}] +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.

[0062] The distance between lens groups indicates the distance when the lens is focused at infinity and when it is focused at the closest possible distance (object distance is shown in parentheses). The object distance is the distance from the image plane to the object position.

[0063] Moreover, values corresponding to the conditions of the above-mentioned formulas () to (15) in Numerical Examples 1 to 4 are summarized in Table 1. Each of the numerical examples satisfies all of the conditions of formulas (1) to (15).

[0064] Figures 2, 4, 6, and 8 respectively show longitudinal aberrations (spherical aberration, astigmatism, distortion, and chromatic aberration) of the optical system L0 of Numerical Examples 1 to 4 in (a) the infinity-focused state and (b) the closest focus state. 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 two-dot chain line indicates spherical aberration for the g-line (wavelength 435.8 nm). In the astigmatism diagrams, the solid line S indicates astigmatism at the sagittal image plane, and the dashed line M indicates astigmatism at the meridional image plane. The distortion diagrams show distortion at the d-line. The chromatic aberration diagrams show lateral chromatic aberration at the g-line. ω is the half angle of view (°).

[0065] [Numerical example 1] Unit: mm Surface Data Surface number rd nd νd 1 57.769 3.57 1.92286 20.9 2 99.001 2.01 3* 174.690 0.11 1.53352 52.8 4 207.351 1.35 1.65412 39.7 5 39.088 9.65 6 -41.799 1.35 1.77047 29.7 7 41.799 10.34 1.76385 48.5 8 -56.227 0.15 9 55.362 7.44 1.91082 35.2 10 -126.226 (variable) 11 41.162 3.03 1.90043 37.4 12 62.716 (variable) 13 ∞ 1.20 1.77047 29.7 14 38.312 4.28 15 (Aperture) ∞ (Variable) 16 -22.567 3.89 1.59522 67.7 17 -17.388 1.20 1.73037 32.2 18 -66.069 0.16 19 65.372 8.43 1.49700 81.7 20 -31.807 0.37 21* 195.760 6.10 1.80400 46.5 22* -52.537 (variable) 23 ∞ 5.16 2.00100 29.1 24 -46.593 1.20 1.58144 40.8 25 46.593 9.09 26 -31.535 1.00 1.72825 28.5 27 -45.428 14.66 Image plane ∞ Aspheric data 3rd page K = 0.00000e+00 A 4=-3.43375e-07 A 6=-2.73639e-09 A 8= 6.57484e-12 A10=-1.50535e-14 A12= 9.83500e-18 Page 21 K = 0.00000e+00 A 4=-3.27084e-06 A 6= 6.22450e-10 A 8= 1.62557e-11 A10=-9.43111e-14 A12= 1.12652e-16 Page 22 K = 0.00000e+00 A 4= 6.07848e-06 A 6=-7.76772e-09 A 8= 6.38476e-11 A10=-1.90658e-13 A12= 1.91577e-16 Focal length 48.50 F-number 1.46 Half angle of view (°) 24.04 Image height 21.64 Lens length 117.49 SK 14.66 Infinity Closest (-400mm) d10 3.76 1.46 d12 3.66 5.96 d15 11.67 7.27 d22 2.68 7.08 Lens group data Group starting plane focal length 1 1 53.02 2 11 124.70 3 13 -49.73 4 16 38.05 5 23 -96.43 [Numerical example 2] Unit: mm Surface Data Surface number rd nd νd 1 61.356 4.23 2.00069 25.5 2 155.534 4.23 3* 836.451 0.14 1.53352 52.8 4 9065.248 1.30 1.72047 34.7 5 37.963 9.31 6 -41.519 1.30 1.77047 29.7 7 40.508 10.06 1.77250 49.6 8 -55.412 0.15 9 56.306 6.62 1.95375 32.3 10 -136.914 (variable) 11 43.381 2.94 1.91082 35.2 12 66.751 (variable) 13 730.270 1.23 1.73037 32.2 14 38.613 4.26 15 (Aperture) ∞ (Variable) 16 -23.950 3.09 1.59522 67.7 17 -18.367 1.10 1.77047 29.7 18 -89.141 0.15 19 61.370 9.03 1.49700 81.5 20 -32.482 0.69 21* 123.050 6.50 1.80400 46.5 22* -55.009 (variable) 23 397.215 4.95 2.00100 29.1 24 -55.804 1.30 1.58144 40.8 25 42.967 9.38 26 -32.640 1.82 1.62004 36.3 27 -48.951 13.26 Image plane ∞ Aspheric data 3rd page K = 0.00000e+00 A 4=-4.27090e-07 A 6=-1.54574e-09 A 8= 3.73197e-12 A10=-1.06510e-14 A12= 8.55869e-18 Page 21 K = 0.00000e+00 A 4=-3.25844e-06 A 6= 1.10049e-08 A 8=-3.65477e-11 A10= 1.02156e-13 A12=-9.95585e-17 Page 22 K = 0.00000e+00 A 4= 5.69279e-06 A 6= 6.86476e-09 A 8=-1.01569e-11 A10=5.22676e-14 A12=-5.29539e-17 Focal length 48.50 F-number 1.46 Half angle of view (°) 24.04 Image height 21.64 Lens length 118.50 SK 13.26 Infinity Closest (-400mm) d10 3.84 1.49 d12 3.38 5.73 d15 11.92 7.15 d22 2.30 7.08 Lens group data Group starting plane focal length 1 1 55.54 2 11 128.35 3 13 -55.86 4 16 39.26 5 23 -105.72 [Numerical example 3] Unit: mm Surface Data Surface number rd nd νd 1 73.465 4.72 1.96300 24.1 2 422.069 5.34 3* -247.661 0.36 1.53352 52.8 4 -121.885 1.30 1.73037 32.2 5 40.970 7.70 6 -54.419 1.30 1.73037 32.2 7 42.011 9.81 1.81600 46.6 8 -52.701 0.15 9 46.818 6.53 1.91082 35.2 10 -182.855 (variable) 11 130.723 1.00 1.73037 32.2 12 34.408 (variable) 13 34.823 2.61 1.65160 58.5 14 42.973 3.97 15 (Aperture) ∞ (Variable) 16 -25.856 5.09 1.67790 55.3 17 -16.086 1.12 1.77047 29.7 18 -97.823 0.52 19 -252.862 3.88 1.59522 67.7 20 -46.425 0.61 21* 118.091 8.68 1.80400 46.5 22* -36.782 (variable) 23 3113.777 6.13 2.00100 29.1 24 -48.745 1.70 1.59551 39.2 25 56.334 9.36 26 -31.432 1.10 1.63980 34.5 27 -44.734 12.35 Image plane ∞ Aspheric data 3rd page K = 0.00000e+00 A 4=-3.62263e-06 A 6=-1.08195e-09 A 8= 7.95075e-12 A10=-1.65697e-14 A12= 1.36913e-17 Page 21 K = 0.00000e+00 A 4=-3.04370e-06 A 6= 7.00824e-09 A 8=-1.23743e-11 A10= 1.20496e-14 A12= 3.82758e-17 Page 22 K = 0.00000e+00 A 4= 4.39376e-06 A 6=-7.07780e-10 A 8= 2.06014e-11 A10=-7.70118e-14 A12= 1.37782e-16 Focal length 48.50 F-number 1.46 Half angle of view (°) 24.04 Image height 21.64 Lens length 116.95 SK 12.35 Infinity Closest (-400mm) d10 3.13 5.35 d12 3.53 1.31 d15 12.14 6.60 d22 2.81 8.35 Lens group data Group starting plane focal length 1 1 42.31 2 11 -64.22 3 13 250.12 4 16 43.54 5 23 -129.66 [Numerical example 4] Unit: mm Surface Data Surface number rd nd νd 1 53.816 5.80 1.96300 24.1 2 206.917 1.91 3* 103.952 0.15 1.53352 52.8 4 127.076 1.35 1.61340 44.3 5 25.575 10.79 6 -42.093 1.35 1.78880 28.4 7 42.093 7.97 1.76385 48.5 8 -65.152 0.15 9 69.917 5.89 1.88300 40.8 10 -101.196 1.45 11 51.742 3.85 1.81600 46.6 12 246.678 (variable) 13 239.114 1.20 1.61340 44.3 14 28.689 8.48 15 (Aperture) ∞ (Variable) 16 -59.348 5.85 1.49700 81.5 17 -20.840 1.31 1.73037 32.2 18 324.994 1.68 19 103.121 7.44 1.61800 63.3 20 -32.793 0.15 21* 152.195 5.53 1.80400 46.5 22* -87.314 (variable) 23 9313.997 5.43 2.00100 29.1 24 -46.460 3.01 1.54072 47.2 25 46.460 9.63 26 -31.065 1.00 1.53172 48.8 27 -44.083 13.03 Image plane ∞ Aspheric data 3rd page K = 0.00000e+00 A 4=-1.99729e-06 A 6=-5.01657e-10 A 8= 1.00336e-12 A10= 1.92177e-15 A12=-4.72109e-18 Page 21 K = 0.00000e+00 A 4=-1.96390e-06 A 6=-8.86488e-09 A 8= 3.81302e-11 A10=-1.09819e-13 A12= 8.62521e-17 Page 22 K = 0.00000e+00 A 4= 2.83578e-06 A 6=-1.38704e-08 A 8= 5.99084e-11 A10=-1.43518e-13 A12= 1.10064e-16 Focal length 48.50 F-number 1.46 Half angle of view (°) 24.04 Image height 21.64 Lens length 117.40 SK 13.03 Infinity Closest (-400mm) d12 1.47 5.08 d15 7.97 4.85 d22 3.56 6.69 Lens group data Group starting plane focal length 1 1 37.97 2 13 -53.26 3 16 44.53 4 23 -159.39

[0066] [Table 1]

[0067] [Imaging device] FIG. 9 shows a digital still camera (image capture device) that uses the optical system L0 of Examples 1 to 4 as an image capture optical system.

[0068] Reference numeral 10 denotes a camera body, and 11 denotes an imaging optical system configured using the optical system L0 of any one 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 the optical image formed by the imaging optical system 11 (i.e., the subject through the imaging optical system 11).

[0069] The camera body 10 may be a single-lens reflex camera having a quick-turn mirror, or may be a mirrorless camera having no quick-turn mirror.

[0070] By applying the optical system L0 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 is capable of high-speed autofocus.

[0071] The above embodiment includes the following configurations.

[0072] (Configuration 1) An optical system including a front group having positive refractive power and including a plurality of lens groups, an aperture stop, and a rear group having positive refractive power and including a plurality of lens groups, which are arranged in this order from the object side to the image side, During focusing, the first focus lens group included in the front group and the second focus lens group included in the rear group move, changing the spacing between adjacent lens groups; The front group is a first lens element having a positive refractive power and located closest to the object; An optical system comprising a second lens having negative refractive power adjacent to the first lens on the image side. (Configuration 2) The optical system according to configuration 1, wherein the first lens is a single lens. (Configuration 3) the second lens has a resin layer on the object-side surface of the single lens, 3. The optical system according to configuration 1 or 2, wherein the object-side surface of the resin layer is aspherical. (Configuration 4) When the focal length of the first lens is f1 and the focal length of the optical system when focused on an object at infinity is f, 0.5≦f1 / f≦4.0 4. The optical system according to any one of configurations 1 to 3, wherein the following condition is satisfied: (Configuration 5) When the air gap between the first lens and the second lens on the optical axis is LD1 and the focal length of the optical system when focused on an object at infinity is f, 0.02≦LD1 / f≦0.15 5. The optical system according to any one of configurations 1 to 4, wherein the following condition is satisfied: (Configuration 6) Let SK be the air-equivalent 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. 0.1≦SK / f≦0.6 6. The optical system according to any one of configurations 1 to 5, wherein the following condition is satisfied: (Configuration 7) When the Abbe number of the first lens based on the d-line is νd1, 15≦νd1≦30 7. The optical system according to any one of configurations 1 to 6, wherein the following condition is satisfied: (Configuration 8) the front group includes, arranged in order from the object side to the image side, a first lens group having positive refractive power and a second lens group having positive or negative refractive power; 8. The optical system according to any one of configurations 1 to 7, wherein the second lens group is the first focus lens group. (Configuration 9) 9. The optical system according to claim 8, wherein the front group comprises, arranged in order from the object side to the image side, the first lens group, the second lens group, and a third lens group having positive or negative refractive power. (Configuration 10) the front group includes, arranged in order from the object side to the image side, a first lens group having positive refractive power and a second lens group having positive or negative refractive power; 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. 0.2≦T1 / f≦1.5 10. The optical system according to any one of configurations 1 to 9, wherein the following condition is satisfied: (Configuration 11) the front group includes, arranged in order from the object side to the image side, a first lens group having positive refractive power and a second lens group having positive or negative refractive power; 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≦0.30 11. The optical system according to any one of configurations 1 to 10, wherein the following condition is satisfied: (Configuration 12) the rear group is composed of a first rear lens group having positive refractive power and a second rear lens group having positive or negative refractive power, arranged in this order from the object side to the image side; 12. The optical system according to any one of configurations 1 to 11, wherein the first rear lens group is the second focus lens. (Configuration 13) the rear group is composed of a first rear lens group having positive refractive power and a second rear lens group having positive or negative refractive power, arranged in this order from the object side to the image side; Let Tr1 be the distance on the optical axis from the lens surface of the first rear lens group closest to the object side to the lens surface of the first rear 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≦Tr1 / f≦0.9 13. The optical system according to any one of configurations 1 to 12, wherein the following condition is satisfied: (Configuration 14) the rear group is composed of a first rear lens group having positive refractive power and a second rear lens group having positive or negative refractive power, arranged in this order from the object side to the image side; Let Tr2 be the distance on the optical axis from the lens surface of the second rear lens group closest to the object side to the lens surface of the second rear lens group closest to the image side, and f be the focal length of the optical system when focused on an object at infinity. 0.2≦Tr2 / f≦0.9 14. The optical system according to any one of configurations 1 to 13, wherein the following condition is satisfied: (Configuration 15) Let fLf be the focal length of the front group, and f be the focal length of the optical system when focused on an object at infinity. 0.5≦fLf / f≦5.0 15. The optical system according to any one of configurations 1 to 14, wherein the following condition is satisfied: (Configuration 16) Let fLr be the focal length of the rear group, and f be the focal length of the optical system when focused on an object at infinity. 0.2≦fLr / f≦5.0 16. The optical system according to any one of configurations 1 to 15, wherein the following condition is satisfied: (Configuration 17) When the focal length of the front group is fLf and the focal length of the rear group is fLr, 0.5≦fLf / fLr≦4.0 17. The optical system according to any one of configurations 1 to 16, wherein the following condition is satisfied: (Configuration 18) the front group includes, arranged in order from the object side to the image side, a first lens group having positive refractive power and a second lens group having positive or negative refractive power; When the focal length of the first lens group is fL1 and the focal length of the optical system when focused on an object at infinity is f, 0.2≦fL1 / f≦5 18. The optical system according to any one of configurations 1 to 17, wherein the following condition is satisfied: (Configuration 19) the front group includes, arranged in order from the object side to the image side, a first lens group having positive refractive power and a second lens group having positive or negative refractive power; When the focal length of the second lens group is fL2 and the focal length of the optical system when focused on an object at infinity is f, 0.5≦|fL2| / f≦5.0 19. The optical system according to any one of configurations 1 to 18, wherein the following condition is satisfied: (Configuration 20) the rear group is composed of a first rear lens group having positive refractive power and a second rear lens group having positive or negative refractive power, arranged in this order from the object side to the image side; When the focal length of the first rear lens group is fLr1 and the focal length of the optical system when focused on an object at infinity is f, 0.1≦fLr1 / f≦4.0 20. The optical system according to any one of configurations 1 to 19, wherein the following condition is satisfied: (Configuration 21) the rear group is composed of a first rear lens group having positive refractive power and a second rear lens group having positive or negative refractive power, arranged in this order from the object side to the image side; When the focal length of the second rear lens group is fLr2 and the focal length of the optical system when focused on an object at infinity is f, -7.0≦fLr2 / f≦-0.2 21. The optical system according to any one of configurations 1 to 20, wherein the following condition is satisfied: (Configuration 22) The optical system according to any one of configurations 1 to 21; and an image sensor that captures an image of a subject through the optical system.

[0073] The above-described embodiments are merely representative examples, and various modifications and alterations can be made to each embodiment when implementing the present invention. [Explanation of symbols]

[0074] L0 optical system Lf front group Lr posterior group SP aperture stop IP image plane

Claims

1. An optical system comprising a front group with positive refractive power containing multiple lens groups arranged sequentially from the object side to the image side, an aperture diaphragm, and a rear group with positive refractive power containing multiple lens groups, During focusing, the first focusing lens group included in the front group and the second focusing lens group included in the rear group move, which changes the distance between adjacent lens groups. The aforementioned group is, The first lens with positive refractive power, positioned closest to the object, The first lens includes a second lens with negative refractive power adjacent to it on the image side. When the focal length of the first lens is f1, the focal length of the optical system when focused on an object at infinity is f, and the air-equivalent distance on the optical axis from the lens surface closest to the image plane of the optical system to the image plane is SK, 1.0 ≤ f1 / f ≤ 4.0 0.1 ≤ SK / f ≤ 0.302 An optical system characterized by satisfying the following conditions.

2. The optical system according to claim 1, characterized in that the first lens is a single lens.

3. The second lens has a resin layer on the object-side surface of the single lens, The optical system according to claim 1, characterized in that the object-side surface of the resin layer is aspherical.

4. When the air distance between the first lens and the second lens on the optical axis is LD1, 0.02 ≤ LD1 / f ≤ 0.15 The optical system according to claim 1, characterized in that it satisfies the following conditions.

5. When the Abbe number with respect to the d line of the first lens is νd1, 15 ≤ νd1 ≤ 30 The optical system according to claim 1, characterized in that it satisfies the following conditions.

6. The aforementioned front group includes a first lens group with positive refractive power and a second lens group with positive or negative refractive power, arranged in order from the object side to the image side. The optical system according to claim 1, characterized in that the second lens group is the first focusing lens group.

7. The optical system according to claim 6, characterized in that the front group is composed of a first lens group, a second lens group, and a third lens group having positive or negative refractive power, arranged in order from the object side to the image side.

8. The aforementioned front group includes a first lens group with positive refractive power and a second lens group with positive or negative refractive power, arranged in order from the object side to the image side. When T1 is the distance along the optical axis from the lens surface of the first lens group closest to the object to the lens surface of the first lens group closest to the image, 0.2 ≤ T1 / f ≤ 1.5 The optical system according to claim 1, characterized in that it satisfies the following conditions.

9. The aforementioned front group includes a first lens group with positive refractive power and a second lens group with positive or negative refractive power, arranged in order from the object side to the image side. When T2 is the distance along the optical axis from the lens surface of the second lens group closest to the object to the lens surface of the second lens group closest to the image, 0.01 ≤ T² / f ≤ 0.30 The optical system according to claim 1, which satisfies the following conditions

10. The aforementioned rear group consists of a first rear lens group with positive refractive power and a second rear lens group with positive or negative refractive power, arranged sequentially from the object side to the image side. The optical system according to claim 1, characterized in that the first rear lens group is the second focusing lens group.

11. The aforementioned rear group consists of a first rear lens group with positive refractive power and a second rear lens group with positive or negative refractive power, arranged sequentially from the object side to the image side. When Tr1 is the distance along the optical axis from the lens surface closest to the object in the first rear lens group to the lens surface closest to the image in the first rear lens group, 0.1 ≤ Tr1 / f ≤ 0.9 The optical system according to claim 1, characterized in that it satisfies the following conditions.

12. The aforementioned rear group consists of a first rear lens group with positive refractive power and a second rear lens group with positive or negative refractive power, arranged sequentially from the object side to the image side. When Tr2 is the distance along the optical axis from the lens surface closest to the object in the second rear lens group to the lens surface closest to the image in the second rear lens group, 0.2 ≤ Tr² / f ≤ 0.9 The optical system according to claim 1, characterized in that it satisfies the following conditions.

13. When the focal length of the front group is fLf, 0.5 ≤ fLf / f ≤ 5.0 The optical system according to claim 1, characterized in that it satisfies the following conditions.

14. When the focal length of the rear group is fLr, 0.2 ≤ fLr / f ≤ 5.0 The optical system according to claim 1, characterized in that it satisfies the following conditions.

15. When the focal length of the front group is fLf and the focal length of the rear group is fLr, 0.5 ≤ fLf / fLr ≤ 4.0 The optical system according to claim 1, characterized in that it satisfies the following conditions.

16. The aforementioned front group includes a first lens group with positive refractive power and a second lens group with positive or negative refractive power, arranged in order from the object side to the image side. When the focal length of the first lens group is fL1, 0.2 ≤ fL1 / f ≤ 5 The optical system according to claim 1, characterized in that it satisfies the following conditions.

17. The aforementioned front group includes a first lens group with positive refractive power and a second lens group with positive or negative refractive power, arranged in order from the object side to the image side. When the focal length of the second lens group is fL2, 0.5≦|fL2| / f≦5.0 The optical system according to claim 1, characterized in that it satisfies the following conditions.

18. The aforementioned rear group consists of a first rear lens group with positive refractive power and a second rear lens group with positive or negative refractive power, arranged sequentially from the object side to the image side. When the focal length of the first rear lens group is fLr1, 0.1 ≤ fLr1 / f ≤ 4.0 The optical system according to claim 1, characterized in that it satisfies the following conditions.

19. The aforementioned rear group consists of a first rear lens group with positive refractive power and a second rear lens group with positive or negative refractive power, arranged sequentially from the object side to the image side. When the focal length of the second rear lens group is fLr2, -7.0 ≤ fLr² / f ≤ -0.2 The optical system according to claim 1, characterized in that it satisfies the following conditions.

20. An optical system according to any one of claims 1 to 19, An imaging device characterized by having an image sensor that captures an image of a subject through the optical system.

Images