Optical system and imaging apparatus

Abstract

To provide a compact and wide-angle optical system which has high image magnification and high optical performance and can support auto focusing as well.SOLUTION: An optical system includes a front lens group B1, a first focus lens group Bf arranged closer to an image side than the front lens group, and a second focus lens group Br arranged closer to the image side than the first focus lens group. For focusing, the front lens group is immobile and the first focus lens group and the second focus lens group move. The optical system can perform focusing from a focusing state on an infinity object to a focusing state where the lateral magnification β of the optical system becomes equal to or less than -1.0. When the focal length of the front lens group is defined as f1 and the focal length of at least one of the first and second focus lens groups is defined as ffr, the optical system satisfies a condition of -5.500≤|ffr| / f1≤0.380.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an optical system that can be used in macro imaging. [Background technology]

[0002] Wide-angle optical systems (macro lenses) used for close-up (macro) imaging include those disclosed in, for example, Patent Documents 1 and 2. Many conventional macro lenses have low image magnification, and the macro imaging techniques that can use them are limited. For this reason, there is a demand for macro lenses with high image magnification. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-139416 [Patent Document 2] Japanese Patent Application Laid-Open No. 2012-220828 Summary of the Invention [Problem to be solved by the invention]

[0004] Furthermore, like regular lenses, macro lenses are required not only to be compact, but also to have a bright F-number, to have various aberrations well corrected, and to support autofocusing and optical image stabilization to suppress image blur caused by camera shake, etc. To satisfy these requirements, it is necessary to appropriately set the refractive power arrangement within the macro lens and the focal length of each lens, etc.

[0005] The present invention provides a compact, wide-angle optical system that has a high image magnification, high optical performance, and is also compatible with autofocus. [Means for solving the problem]

[0006] An optical system according to one aspect of the present invention has a front lens group, a first focus lens group arranged closer to the image than the front lens group, and a second focus lens group arranged closer to the image than the first focus lens group, and the spacing between adjacent lens groups changes during focusing. For focusing, the front lens group does not move, but the first and second focus lens groups move. This optical system is capable of focusing from a state focused on an object at infinity to a state where the lateral magnification β of the optical system is −1.0 or less. Let f1 be the focal length of the front lens group, and ffr be the focal length of at least one of the first and second focus lens groups. -5.500≦|ffr| / f1≦0.380 The optical system is characterized by satisfying the following conditions: An imaging device including the optical system described above 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, wide-angle optical system that has a high image magnification, high optical performance, and is also compatible with autofocus. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a cross-sectional view of an optical system according to a first embodiment. [Figure 2] 1A is aberration diagram of the optical system of Example 1 in an infinity-focused state and a minimum-focused state; [Figure 3] FIG. 10 is a cross-sectional view of the optical system of the second embodiment. [Figure 4] 10A is aberration diagrams of the optical system of Example 2 in an infinity-focused state and a minimum-focused state; FIG. [Figure 5] FIG. 10 is a cross-sectional view of the optical system of the third embodiment. [Figure 6] 10A is an aberration diagram of the optical system of Example 3 in an infinity-focused state and a minimum-focused state; FIG. [Figure 7] FIG. 10 is a cross-sectional view of an optical system according to a fourth embodiment. [Figure 8]10A is aberration diagrams of the optical system of Example 4 in an infinity-focused state and a minimum-focused state; [Figure 9] 4A to 4C are diagrams showing lateral aberrations of the optical system of Example 1 in an image stabilization state. [Figure 10] FIG. 1 is a schematic diagram of an imaging device equipped with the optical system of Examples 1 to 4. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Prior to the specific description of embodiments 1 to 4, matters common to all embodiments will be described. The optical system of each embodiment is used as an imaging optical system for various imaging devices such as a digital still camera, a video camera, a surveillance camera, and an in-vehicle camera.

[0010] 1, 3, 5, and 7 show cross sections of optical systems of Examples 1 to 4, respectively. The optical system of each Example is composed of, arranged in order from the object side to the image side, a front lens group B1 that does not move for focusing, a first focus lens group Bff that moves for focusing, an intermediate lens group Bm that does not move for focusing, a second focus lens group Bfr that moves for focusing, and a rear lens group Bk that does not move for focusing. The lens group is a group of one or more lenses that may or may not move as a unit during focusing between a state focused on an object at infinity (hereinafter referred to as the infinity focused state) and a state focused on the closest object (hereinafter referred to as the closest focused state). In other words, the spacing between adjacent lens groups changes during focusing.

[0011] The optical system of each embodiment is capable of focusing from a state in which an object at infinity is focused to a state in which the lateral magnification β of the optical system is -1.0 or less. In other words, it is an optical system capable of imaging at infinity to so-called life-size macro imaging. In the following description, the first focus lens group will be abbreviated as the first focus lens group, and the second focus lens group will be abbreviated as the second focus lens group.

[0012] The optical system of each embodiment has an aperture stop SP in the intermediate lens group Bm. IP is an image plane. The image plane IP is where the imaging surface (light receiving surface) of an imaging element such as a CCD sensor or CMOS sensor or the film surface (photosensitive surface) of a silver halide film is located.

[0013] In order to achieve high optical performance even during macro imaging, the optical system of each embodiment satisfies the condition of the following equation (1), where f1 is the focal length of the front lens group B1 and ffr is the focal length of at least one of the first and second focus groups.

[0014] -5.500≦|ffr| / f1≦0.380 (1) The condition of formula (1) indicates the appropriate relationship between the focal length ffr (absolute value) of at least one of the first and second focus groups and the focal length f1 of the front lens group. If the focal length of at least one focus group becomes too long so that |ffr| / f1 exceeds the upper limit of formula (1), aberration correction becomes easier, but the amount of movement of at least one focus group during focusing increases, making it difficult to compact the optical system, which is undesirable. Also, if the focal length of at least one focus group becomes too short so that |ffr| / f1 falls below the lower limit of formula (1), it is effective in compacting the optical system, but it becomes difficult to correct spherical aberration during focusing, which is undesirable.

[0015] It is more preferable to set the numerical range of the formula (1) as follows:

[0016] -4.500≦|ffr| / f1≦0.370 (1a) Furthermore, it is more preferable to set the numerical range of formula (1) as follows:

[0017] -4.000≦|ffr| / f1≦0.360 (1b) By satisfying the above configuration and conditions, it is possible to realize a compact, wide-angle optical system that has high image magnification, a bright F-number, high optical performance, and is also compatible with autofocus and optical image stabilization.

[0018] It is preferable that the optical system of each embodiment satisfies at least one of the conditions and configurations of the following expressions (2) to (14).

[0019] The optical system of each embodiment preferably satisfies the condition of the following formula (2), where ff is the focal length of the first focus group and f is the focal length of the entire optical system when focused at infinity.

[0020] 1.340≦|ff| / f≦6.370 (2) The condition in equation (2) indicates the appropriate relationship between the focal length ff (absolute value) of the first focus group and the focal length f of the entire optical system. If the focal length of the first focus group becomes too large, such that |ff| / f exceeds the upper limit of equation (2), it becomes easier to correct aberrations, but the amount of movement of the first focus group during focusing increases, making it difficult to achieve a compact optical system, which is undesirable. If the focal length of the first focus group becomes too small, such that |ff| / f falls below the lower limit of equation (2), it becomes effective in achieving a compact optical system, but it becomes difficult to correct field curvature during focusing, which is undesirable.

[0021] The optical system of each embodiment preferably satisfies the condition of the following formula (3), where dltf is the amount of movement of the first focus group during focusing from infinity to the closest point, and d1 is the thickness of the front lens group (the length on the optical axis from the surface closest to the object to the surface closest to the image): Note that the amount of movement of the focus group is the difference between the position of the focus group in a state focused at infinity and the position of the focus group in a state focused at the closest point, and does not include the amount of reciprocation, and is considered positive when the focus group is located closer to the image in the state focused at infinity.

[0022] -1.500≦|dltf| / d1≦0.800 (3) The condition of formula (3) indicates the appropriate relationship between the movement amount dltf (absolute value) of the first focus unit during focusing from infinity to the closest distance and the thickness d1 of the front lens unit.

[0023] If the amount of movement of the first focus group becomes too large so that |dltf| / d1 exceeds the upper limit of equation (3), it becomes difficult to make the optical system compact, which is undesirable. If the amount of movement of the first focus group becomes too small so that |dltf| / d1 falls below the lower limit of equation (3), it is possible to make the optical system compact, but it is also undesirable because fluctuations in spherical aberration during focusing increase.

[0024] It is preferable that the optical system of each embodiment satisfies the condition of the following formula (4), where dltr is the movement amount of the second focus group during focusing from infinity to the closest distance and d1 is the thickness of the front lens group.

[0025] 0.060≦|dltr| / d1≦2.000 (4) The condition of equation (4) indicates an appropriate relationship between the movement amount dltr (absolute value) of the second focus group during focusing from infinity to the closest distance and the thickness d1 of the front lens group.

[0026] If the amount of movement of the second focus group becomes too large so that |dltr| / d1 exceeds the upper limit of equation (4), it becomes difficult to make the optical system compact, which is not preferable. If the amount of movement of the second focus group becomes too small so that |dltr| / d1 falls below the lower limit of equation (4), it is possible to make the optical system compact, but it is also undesirable because it increases the fluctuation of spherical aberration during focusing.

[0027] It is preferable that the optical system of each embodiment satisfies the condition of the following equation (5), where df is the thickness of the first focus group (the length on the optical axis from the surface closest to the object to the surface closest to the image) and f is the focal length of the entire optical system when focused at infinity.

[0028] 0.020≦df / f≦0.400 (5) The condition of equation (5) indicates the appropriate relationship between the thickness df of the first focus group and the focal length f of the entire optical system. If the thickness of the first focus group becomes too large so that df / f exceeds the upper limit of equation (5), it becomes difficult to ensure the amount of movement of the first focus group during focusing, which is undesirable for compactness. If the thickness of the first focus group becomes too small so that df / f falls below the lower limit of equation (5), this is favorable for compactness of the optical system, but is undesirable because it makes the lenses that make up the first focus group more susceptible to deformation during processing, which can easily cause fluctuations in optical performance.

[0029] It is preferable that the optical system of each embodiment satisfies the condition of the following equation (6), where dr is the thickness of the second focus group (the length on the optical axis from the surface closest to the object to the surface closest to the image) and f is the focal length of the entire optical system when focused at infinity.

[0030] 0.090≦dr / f≦0.500 (6) The condition of formula (6) indicates the appropriate relationship between the thickness of the second focus group and the focal length of the entire optical system. If the thickness of the second focus group becomes too large so that dr / f exceeds the upper limit of formula (6), it becomes difficult to ensure the movement amount of the second focus group during focusing, which is undesirable for miniaturizing the optical system. If the thickness of the second focus group becomes too small so that dr / f falls below the lower limit of formula (6), it is favorable for miniaturizing the optical system, but it is undesirable because deformation and the like are more likely to occur during processing of the lenses that make up the second focus group, which makes the optical performance more likely to fluctuate.

[0031] It is preferable that the optical system of each embodiment satisfies the condition of the following formula (7), where f1 is the focal length of the front lens group and sk is the back focus of the optical system (the air-equivalent distance from the surface closest to the image side to the paraxial image plane).

[0032] 0.660≦|f1| / sk≦23.100 (7) The condition of equation (7) indicates the appropriate relationship between the focal length f1 (absolute value) of the front lens group and the back focal length sk. If the focal length of the front lens group becomes too large, such that |f1| / sk exceeds the upper limit of equation (7), aberration correction becomes easier, but the overall length of the optical system becomes longer, making compactness difficult, which is undesirable. If the focal length of the front lens group becomes too small, such that |f1| / sk falls below the lower limit of equation (7), this is favorable for compactness of the optical system, but makes spherical aberration correction difficult, which is undesirable.

[0033] It is preferable that the optical system of each embodiment satisfies the condition of the following formula (8), where the focal length of the first focus group is ff and the focal length of the second focus group is fr.

[0034] -3.200≦|ff| / |fr|≦1.700 (8) The condition in equation (8) indicates the appropriate relationship between the focal length ff (absolute value) of the first focus group and the focal length fr (absolute value) of the second focus group. If the focal length of the first focus group becomes too long, such that |ff| / |fr| exceeds the upper limit of equation (8), aberration correction becomes easier, but the amount of movement of the first focus group during focusing increases, making it difficult to compact the optical system, which is undesirable. If the focal length of the first focus group becomes too short, such that |ff| / |fr| falls below the lower limit of equation (8), it is favorable for compacting the optical system, but spherical aberration correction becomes difficult, which is undesirable.

[0035] In the optical systems of each embodiment, it is preferable that the intermediate lens unit Bm, located on the image side of the first focus unit, does not move during focusing, includes an aperture stop SP and an aspherical lens, and has positive refractive power as a whole, which enables good correction of spherical aberration.

[0036] In the optical system of each embodiment, it is preferable to satisfy the condition of the following expression (9), where the focal length of the intermediate lens group is fm and the focal length of the front lens group is f1.

[0037] 0.050≦fm / |f1|≦1.000 (9) The condition of equation (9) indicates the appropriate relationship between the focal length fm of the intermediate lens group and the focal length f1 (absolute value) of the front lens group. If the focal length of the intermediate lens group becomes too long, such that fm / |f1| exceeds the upper limit of equation (9), aberration correction becomes easier, but the overall length of the optical system increases, making compactness difficult, which is undesirable. If the focal length of the intermediate lens group becomes too short, such that fm / |f1| falls below the lower limit of equation (9), this is favorable for compactness of the optical system, but makes spherical aberration correction difficult, which is undesirable.

[0038] The optical system of each embodiment preferably satisfies the condition of the following equation (10), where fm is the focal length of the intermediate lens group and f is the focal length of the entire optical system when focused at infinity.

[0039] 0.440≦fm / f≦8.400 (10) The condition of equation (10) indicates the appropriate relationship between the focal length fm of the intermediate lens group and the focal length f of the entire optical system. If the focal length of the intermediate lens group becomes too large, such that fm / f exceeds the upper limit of equation (10), it becomes easier to correct aberrations, but this is undesirable because the overall length of the optical system increases and compactness becomes difficult. If the focal length of the intermediate lens group becomes too small, such that fm / f falls below the lower limit of equation (10), it becomes easier to correct spherical aberrations, but this is undesirable because it becomes difficult to correct spherical aberrations.

[0040] In the optical system of each embodiment, it is preferable to satisfy the condition of the following formula (11), where the focal length of the intermediate lens group is fm and the focal length of the second focus group is fr.

[0041] 0.120≦fm / |fr|≦0.800 (11) The condition of equation (11) indicates the appropriate relationship between the focal length fm of the intermediate lens group and the focal length fr (absolute value) of the second focus group. If the focal length of the intermediate lens group becomes too long, such that fm / |fr| exceeds the upper limit of equation (11), aberration correction becomes easier, but the overall length of the optical system increases, making compactness difficult, which is undesirable. If the focal length of the intermediate lens group becomes too short, such that fm / |fr| falls below the lower limit of equation (11), this is favorable for compactness of the optical system, but it becomes difficult to correct spherical aberration, which is undesirable.

[0042] In the optical systems of each embodiment, the rear lens unit Bk, which is located on the image side of the second focus unit and does not move during focusing, preferably has positive or negative refractive power and includes an aspherical lens. This configuration enables excellent correction of field curvature and lateral chromatic aberration.

[0043] In the optical system of each embodiment, it is preferable to satisfy the condition of the following expression (12), where the focal length of the rear lens group is fk and the focal length of the front lens group is f1.

[0044] 0.150≦|fk| / |f1|≦6.900 (12) The condition of equation (12) indicates the appropriate relationship between the focal lengths fk (absolute value) and f1 (absolute value) of the rear and front lens groups. If the focal length of the rear lens group becomes too long, such that |fk| / |f1| exceeds the upper limit of equation (12), aberration correction becomes easier, but the back focus increases, making it difficult to reduce the size of the optical system, which is undesirable. On the other hand, if the focal length of the rear lens group becomes too short, such that |fk| / |f1| falls below the lower limit of equation (12), it is favorable for reducing the size of the optical system, but it becomes difficult to correct chromatic aberration of magnification, which is undesirable.

[0045] The optical system of each embodiment preferably satisfies the condition of the following equation (13), where fk is the focal length of the rear lens group and f1 is the focal length of the entire optical system when focused at infinity.

[0046] 0.490≦|fk| / f≦4.500 (13) The condition of equation (13) indicates the appropriate relationship between the focal length fk (absolute value) of the rear lens group and the focal length f of the entire optical system. If the focal length of the rear lens group becomes too large, such that |fk| / f exceeds the upper limit of equation (13), aberration correction becomes easier, but the back focus increases, making it difficult to reduce the size of the optical system, which is undesirable. If the focal length of the rear lens group becomes too small, such that |fk| / f falls below the lower limit of equation (13), it is favorable for reducing the size of the optical system, but it becomes difficult to correct chromatic aberration of magnification, which is undesirable.

[0047] Furthermore, it is preferable that the optical system of each embodiment satisfies the condition of the following equation (14), where the focal length of the rear lens unit is fk and the focal length of the second focus unit is ff.

[0048] 0.610≦|fk| / |ff|≦4.000 (14) The condition of equation (14) indicates the appropriate relationship between the focal length fk (absolute value) of the rear lens group and the focal length ff (absolute value) of the second focus group. If the focal length of the rear lens group becomes too long, such that |fk| / |ff| exceeds the upper limit of equation (14), aberration correction becomes easier, but the back focus increases, making it difficult to downsize the optical system, which is undesirable. If the focal length of the rear lens group becomes too short, such that |fk| / |ff| falls below the lower limit of equation (14), it is favorable for downsizing the optical system, but it becomes difficult to correct chromatic aberration of magnification, which is undesirable.

[0049] In the optical systems of the embodiments, it is preferable that the first focus group Bff and the second focus group Bfr each be composed of two or fewer lenses, which allows the focus mechanism that drives each focus group during autofocusing to be made smaller.

[0050] In the optical system of each embodiment, it is preferable to move (shift) all or part of the intermediate lens group Bm in a direction including a directional component perpendicular to the optical axis for optical image stabilization. Because the intermediate lens group is a lens group with a relatively small diameter in the optical system, shifting at least some of its lenses using an image stabilization mechanism can facilitate the miniaturization of the optical system including the image stabilization mechanism.

[0051] In the optical system of each embodiment, the lens closest to the object in the rear lens group Bk may be shifted for optical image stabilization. Because the lens closest to the object in the rear lens group Bk has a relatively small diameter in the optical system, shifting it using an image stabilization mechanism can facilitate the miniaturization of the optical system, including the image stabilization mechanism.

[0052] Furthermore, it is preferable that the optical system of each embodiment has a five-group configuration having, arranged in order from the object side to the image side, a front lens unit B1 having positive or negative refractive power, a first focus unit Bff having negative refractive power, an intermediate lens unit Bm having positive refractive power including an aperture stop SP, a second focus unit Bfr having negative or positive refractive power, and a rear lens unit Bk having negative or positive refractive power, which makes it possible to reduce the size of the optical system while effectively correcting various aberrations.

[0053] It is more preferable that the numerical ranges of the formulas (2) to (14) are as follows:

[0054] 1.610≦|ff| / f≦5.310 (2a) -1.360≦|dltf| / d1≦0.620 (3a) 0.070≦|dltr| / d1≦1.600 (4a) 0.030≦df / f≦0.290 (5a) 0.110≦dr / f≦0.410 (6a) 0.800≦|f1| / sk≦19.210 (7a) -2.950≦|ff| / |fr|≦1.350 (8a) 0.070≦fm / |f1|≦0.810 (9a) 0.530≦fm / f≦6.980 (10a) 0.140≦fm / |fr|≦0.630 (11a) 0.180≦|fk| / |f1|≦5.700 (12a) 0.590≦|fk| / f≦3.730 (13a) 0.730≦|fk| / |ff|≦3.320 (14a) Furthermore, it is more preferable to set the numerical ranges of the formulas (2) to (14) as follows:

[0055] 1.830≦|ff| / f≦4.670 (2b) -1.180≦|dltf| / d1≦0.550 (3b) 0.080≦|dltr| / d1≦1.400 (4b) 0.030≦df / f≦0.250 (5b) 0.120≦dr / f≦0.360 (6b) 0.910≦|f1| / sk≦16.900 (7b) -2.630≦|ff| / |fr|≦1.190 (8b) 0.080≦fm / |f1|≦0.710 (9b) 0.600≦fm / f≦6.140 (10b) 0.160≦fm / |fr|≦0.560 (11b) 0.210≦|fk| / |f1|≦5.020 (12b) 0.670≦|fk| / f≦3.280 (13b) 0.830≦|fk| / |ff|≦2.920 (14b) Examples 1 to 4 will be specifically described below along with corresponding Numerical Examples 1 to 4. 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.

[0056] 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).

[0057] β is the imaging magnification in paraxial calculations, and here it represents the lateral magnification (-1.0) of the optical system at the closest focusing position. f is the focal length, Fno is the F-number, ω is the half angle of view (°), and sk is the back focus (mm). As mentioned above, back focus is the distance on the optical axis from the lens surface closest to the image (the final surface) of the optical system to the paraxial image plane, expressed as the air-equivalent length. The total lens length is the distance on the optical axis from the lens surface closest to the object to the final surface of the optical system, plus the back focus.

[0058] An "*" next to a surface number indicates that the surface has an aspherical shape. The aspherical shape is expressed by the following formula, where 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, the direction of light travel is positive, R is the paraxial radius of curvature, K is the conic constant, and A4, A6, A8, A10, and A12 are aspherical coefficients. The "e±x" of the conic constant and aspherical coefficients is x 10 ±x means.

[0059]

number

[0060] Moreover, values ​​corresponding to the conditions of the above-mentioned formulas (1) to (14) 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 (14). [Example]

[0061] 1 is composed of, arranged in order from the object side to the image side, a front lens group (first lens group) B1 having negative refractive power, a first focus lens group (second lens group) Bff having negative refractive power, an intermediate lens group (third lens group) Bm having positive refractive power, a second focus lens group (fourth lens group) Bfr having negative refractive power, and a rear lens group (fifth lens group) Bk having positive refractive power. During focusing from infinity to the closest point, the first focus lens group Bff and the second focus lens group Bfr move toward the object side and the image side, respectively, as indicated by the arrows in the figure.

[0062] The shift lens Bs in the rear lens group Bk, which is closest to the object, shifts relative to the optical axis to perform optical image stabilization while suppressing chromatic aberration fluctuations. Optical image stabilization is also performed by shifting the cemented lens in the intermediate lens group Bm, which is closer to the image side than the aperture stop SP, relative to the optical axis.

[0063] The optical system of Numerical Example 1 is a macro imaging lens with a wide angle of view and a large aperture, with a half angle of view ω of about 44°, an F-number of about 2.8, and an imaging magnification β of about -1.0 at the closest focus position.

[0064] Figure 2(A) shows the longitudinal aberration (spherical aberration, astigmatism, distortion, and chromatic aberration) of the optical system of Numerical Example 1 when focused at infinity. Figure 2(B) shows the longitudinal aberration of the optical system of Numerical Example 1 when focused at the closest possible distance. In the spherical aberration diagram, Fno indicates the F-number, the solid line indicates the spherical aberration for the d-line (wavelength 587.6 nm), and the two-dot chain line indicates the spherical aberration for the g-line (wavelength 435.8 nm). In the astigmatism diagram, the solid line S indicates the astigmatism at the sagittal image plane, and the dashed line M indicates the astigmatism at the meridional image plane. The distortion diagram shows distortion at the d-line. The chromatic aberration diagram shows chromatic aberration of magnification at the g-line. ω is the half angle of view (°). The explanations for these aberration diagrams are the same for other numerical examples.

[0065] Fig. 9 shows the lateral aberration when the shift lens Bs is shifted to correct image blur of about 0.3° at an angle of a paraxial ray from the optical axis in the optical system of Numerical Example 1. The figure shows the change in aberration at the center position on the image plane and at positions (±) 10 mm above and below in the image height direction. [Example]

[0066] 3 is composed of, arranged in order from the object side to the image side, a front lens group (first lens group) B1 having negative refractive power, a first focus lens group (second lens group) Bff having negative refractive power, a middle lens group (third lens group) Bm having positive refractive power, a second focus lens group (fourth lens group) Bfr having negative refractive power, and a rear lens group (fifth lens group) Bk having positive refractive power. During focusing from infinity to the closest distance, both the first focus lens group Bff and the second focus lens group Bfr move toward the object side, as indicated by the arrows in the figure.

[0067] The optical system of Numerical Example 2 is a macro imaging lens with a wide angle of view and a large aperture, with a half angle of view ω of approximately 42°, an F-number of approximately 2.8, and an imaging magnification β of approximately -1.0 at the closest focus position.

[0068] 4A shows longitudinal aberrations in the infinity-focused state of the optical system of Numerical Example 2. FIG. 4B shows longitudinal aberrations in the closest-focused state of the optical system of Numerical Example 2. [Example]

[0069] 5 is composed of, arranged in order from the object side to the image side, a front lens group (first lens group) B1 having negative refractive power, a first focus lens group (second lens group) Bff having negative refractive power, a middle lens group (third lens group) Bm having positive refractive power, a second focus lens group (fourth lens group) Bfr having positive refractive power, and a rear lens group (fifth lens group) Bk having negative refractive power. During focusing from infinity to the closest distance, both the first focus lens group Bff and the second focus lens group Bfr move toward the object side, as indicated by the arrows in the figure.

[0070] The optical system of Numerical Example 3 is a macro imaging lens with a wide angle of view and a large aperture, with a half angle of view ω of approximately 39°, an F-number of approximately 2.8, and an imaging magnification β of approximately -1.2 when focused at the closest distance.

[0071] 6A shows longitudinal aberrations in the infinity-focused state of the optical system of Numerical Example 3. FIG. 6B shows longitudinal aberrations in the closest-focused state of the optical system of Numerical Example 3. [Example]

[0072] 7 is composed of, arranged in order from the object side to the image side, a front lens group (first lens group) B1 having positive refractive power, a first focus lens group (second lens group) Bff having negative refractive power, a middle lens group (third lens group) Bm having positive refractive power, a second focus lens group (fourth lens group) Bfr having negative refractive power, and a rear lens group (fifth lens group) Bk having positive refractive power. During focusing from infinity to the closest distance, the first focus lens group Bff and the second focus lens group Bfr move toward the object side and the image side, respectively, as indicated by the arrows in the figure.

[0073] The optical system of Numerical Example 4 is a macro imaging lens with a wide angle of view and a large aperture, with a half angle of view ω of about 44°, an F-number of about 2.8, and an imaging magnification β of about -1.2 when focused at the closest point.

[0074] 8A shows longitudinal aberrations in the infinity-focused state of the optical system of Numerical Example 4. FIG. 8B shows longitudinal aberrations in the closest-focused state of the optical system of Numerical Example 4.

[0075] [Numerical example 1] Unit: mm Surface Data Surface number rd nd νd 1* 91.974 1.50 1.85400 40.4 2* 13.412 9.12 3 -22.593 1.20 1.95375 32.3 4 -474.273 3.67 1.59270 35.3 5 -35.125 0.20 6 63.572 1.20 1.95375 32.3 7 17.804 7.22 1.73037 32.2 8 -81.098 2.63 9 36.135 3.41 1.92286 20.9 10 602.792 (variable) 11 227.269 1.00 1.84666 23.8 12 40.035 (variable) 13* 31.456 4.82 1.58313 59.4 14 -55.834 1.50 15 (Aperture) ∞ 1.50 16 71.801 7.17 1.49700 81.5 17 -12.824 1.46 2.00100 29.1 18 -22.731 (variable) 19 57.479 1.00 1.61800 63.4 20 12.223 3.19 1.49700 81.5 21 25.103 (variable) 22* -3097.967 6.24 1.58313 59.4 23 -19.131 10.19 24 -23.488 1.20 2.00100 29.1 25 -1016.452 0.20 26 102.877 4.64 1.84666 23.8 27 -63.033 14.72 28 ∞ 2.00 1.51633 64.1 29∞1.09 Image plane ∞ Surface Spacing Infinite focus β=-1.0 Surface 10 9.91 1.50 Surface 12 1.11 9.52 Surface 18 3.20 8.75 Surface 21 9.35 3.80 Aspheric data Front page K = 0.00000e+00 A 4= 2.14517e-05 A 6=-3.78053e-08 A 8=-4.66959e-11 A10= 3.13496e-13 2nd side K = 0.00000e+00 A 4=-1.18205e-05 A 6=-9.65940e-08 A 8= 2.70156e-10 A10=-8.80968e-12 Page 13 K = 0.00000e+00 A 4=-2.95785e-06 A 6= 5.64931e-08 A 8= 2.04301e-10 A10= 7.35767e-13 Page 22 K = 0.00000e+00 A 4=-1.22787e-05 A 6= 1.55870e-08 A 8= 1.02243e-10 Various data f 21.00 F-number 2.80 Half angle of view (°) 43.60 Image height 20.00 Lens length 116.37 sk 17.14 [Numerical example 2] Unit: mm Surface Data Surface number rd nd νd 1* -99695.669 1.27 1.59379 69.6 2* 10.171 6.31 3 -48.929 0.98 1.43875 94.9 4 1421.039 0.64 5 23.876 3.01 1.56840 63.3 6 352.054 (variable) 7 -19.363 0.70 1.72381 55.2 8 139.133 1.24 1.83873 24.1 9 -156.496 (variable) 10 22.725 4.95 1.61023 67.7 11 -37.363 0.57 12 (Aperture) ∞ 1.00 13* 35.186 0.87 1.76312 33.6 14 17.380 0.15 15 16.589 3.90 1.72017 55.5 16 -1414.625 (variable) 17 -150.733 0.66 1.77790 36.5 18 26.937 0.10 19 18.322 2.45 1.53528 77.4 20 83.476 (variable) 21 144.296 1.94 1.72536 55.0 22 -42.603 2.59 23 -35.529 4.92 1.79065 26.0 24 -11.195 0.83 1.91616 31.6 25* -870.412 0.34 26 32.338 6.08 1.43875 94.9 27 -34.929 25.78 Image plane ∞ Surface Spacing Infinite focus β=-1.0 Surface 7 8.42 2.38 Surface 10 0.99 7.04 Surface 17 8.21 2.17 Surface 21 1.11 7.15 Aspheric data Front page K = 0.00000e+00 A 4= 2.26030e-05 A 6=-1.33022e-07 A 8= 4.52409e-10 A10=-5.76179e-13 2nd side K =-1.15870e+00 A 4= 7.33037e-05 A 6= 1.98964e-07 A 8=-3.11894e-09 A10= 1.74666e-11 Page 13 K = 0.00000e+00 A 4=-3.51798e-05 A 6=-5.95737e-08 A 8=-5.56655e-10 A10= 2.81885e-13 Page 25 K = 0.00000e+00 A 4= 3.77972e-05 A 6= 3.44816e-08 A 8= 3.26135e-10 Various data f 21.00 F-number 2.80 Half angle of view (°) 40.91 Image height 18.20 Lens total length 90.00 sk 25.78 [Numerical example 3] Unit: mm Surface Data Surface number rd nd νd 1* -216.033 2.00 1.60300 65.5 2* 16.469 13.45 3 -140.410 2.00 1.83500 43.0 4 42.899 0.20 5 19.915 3.40 1.63636 35.4 6 -138.375 (variable) 7 -17.356 1.00 1.92250 36.0 8 -75.181 (variable) 9 24.908 4.13 2.00330 28.3 10 -69.572 0.50 11 (Aperture) ∞ 1.00 12* 103.012 1.20 2.00330 28.3 13 40.999 0.30 14 21.304 9.93 1.49700 81.6 15 -11.030 1.72 1.95375 32.3 16 -15.940 (variable) 17 28.523 1.50 2.00069 25.5 18 11.629 5.36 1.64000 60.2 19 -59.569 (variable) 20* -58.105 1.50 1.92250 36.0 21 35.176 2.17 22 -29.259 2.61 1.92286 20.9 23 -16.016 1.95 24 -10.609 1.00 1.88300 40.8 25 -45.661 0.30 26 61.135 5.21 1.96300 24.1 27 -71.423 10.08 28 ∞ 2.00 1.51633 64.1 29∞1.11 Image plane ∞ Surface Spacing Infinite focus β=-1.2 Face 6 7.19 4.77 Surface 8 1.00 3.42 Surface 16 3.20 1.20 Side 19 3.00 5.00 Aspheric data Front page K = 0.00000e+00 A 4= 3.30712e-05 A 6=-1.87196e-07 A 8= 5.21628e-10 A10=-5.40728e-13 2nd side K =-3.01956e-01 A 4= 1.15321e-05 A 6=-1.02655e-07 A 8=-1.21336e-09 A10= 4.82736e-12 Side 12 K = 0.00000e+00 A 4=-5.91935e-05 A 6=-8.66204e-08 A 8= 3.64043e-10 A10= 6.15794e-12 Page 20 K = 0.00000e+00 A 4=-7.94163e-06 A 6= 1.52938e-07 A 8=-1.28541e-09 Various data f 23.00 F-number 2.80 Half angle of view (°) 38.35 Image height 18.20 Lens length 89.33 sk 12.51 [Numerical example 4] Unit: mm Surface Data Surface number rd nd νd 1* 52.912 1.50 1.85400 40.4 2* 12.359 9.14 3 -20.143 1.00 2.05090 26.9 4 39.583 5.03 1.73037 32.2 5 -41.488 2.17 6 107.435 1.20 2.00100 29.1 7 28.791 6.86 1.73037 32.2 8 -41.755 0.17 9 51.389 3.64 1.92286 20.9 10 -141.608 12.09 11 54.468 1.58 1.49700 81.5 12 122.581 1.18 1.85478 24.8 13 35.896 1.41 14* 34.320 4.32 1.58313 59.4 15 -87.170 1.50 16 (Aperture) ∞ 1.50 17 56.568 6.95 1.49700 81.5 18 -14.491 1.12 2.00100 29.1 19 -24.022 3.20 20 84.175 1.00 1.88300 40.8 21 12.801 3.84 1.51742 52.4 22 64.729 6.36 23* 60.132 6.67 1.58313 59.4 24 -19.746 6.41 25 -20.996 1.00 2.00100 29.1 26 52.617 2.03 27 70.732 5.96 1.92286 20.9 28 -49.070 14.08 29 ∞ 2.00 1.51633 64.1 30∞1.11 Image plane ∞ Surface Spacing Infinite focus β=-1.0 Surface 10 12.09 1.50 Face 13 1.41 12.00 Face 19 3.20 8.36 Surface 22 6.36 1.20 Aspheric data Front page K = 0.00000e+00 A 4= 1.01124e-05 A 6= 2.46220e-08 A 8=-2.13800e-10 A10= 7.54306e-13 2nd side K = 0.00000e+00 A 4=-2.25419e-05 A 6=-9.42665e-08 A 8= 1.75807e-10 A10=-1.04562e-11 Side 14 K = 0.00000e+00 A 4=-4.28045e-06 A 6= 2.52685e-08 A 8= 8.86186e-11 A10= 6.51757e-13 Page 23 K = 0.00000e+00 A 4=-6.60563e-06 A 6= 4.67801e-08 A 8=-4.30325e-11 Various data f 20.94 F-number 2.80 Half angle of view (°) 43.69 Image height 20.00 Lens length 115.33 sk 16.51

[0076] [Table 1]

[0077] [Imaging device] 10 shows a schematic configuration of an imaging device (digital still camera) that uses as its imaging optical system any of the optical systems of Examples 1 to 4. Reference numeral 10 denotes a camera body, and 11 denotes an imaging optical system configured using any of the optical systems of Examples 1 to 4.

[0078] Reference numeral 12 denotes an imaging element (photoelectric conversion element) such as a CCD sensor or CMOS sensor that is built into the camera body 10 and captures the subject image formed by the imaging optical system 11 (that is, the subject through the imaging optical system 11).

[0079] By using the optical system according to Examples 1 to 4 as the imaging optical system 11, it is possible to perform excellent macro imaging and other wide-angle imaging.

[0080] The camera body 10 may be of an interchangeable lens type or an integrated lens type, and may further be of a single-lens reflex type having a quick-return mirror, or a mirrorless type having no quick-return mirror.

[0081] The above embodiment includes the following configurations.

[0082] (Configuration 1) An optical system having a front lens group, a first focus lens group arranged closer to the image side than the front lens group, and a second focus lens group arranged closer to the image side than the first focus lens group, wherein the distance between adjacent lens groups changes during focusing, For focusing, the front lens group does not move, and the first focus lens group and the second focus lens group move, the optical system is capable of focusing from a state in which an object at infinity is focused to a state in which the lateral magnification β of the optical system is −1.0 or less; When the focal length of the front lens group is f1 and the focal length of at least one of the first focus lens group and the second focus lens group is ffr, -5.500≦|ffr| / f1≦0.380 An optical system characterized by satisfying the following conditions: (Configuration 2) When the focal length of the first focus lens group is ff and the focal length of the optical system in a state where an object at infinity is focused is f, 1.340≦|ff| / f≦6.370 The optical system according to configuration 1, characterized in that the following condition is satisfied: (Configuration 3) When the movement amount of the first focus lens group during focusing from infinity to the closest point is dltf and the length on the optical axis from the surface of the front lens group closest to the object side to the surface of the front lens group closest to the image side is d1, -1.500≦|dltf| / d1≦0.800 3. The optical system according to configuration 1 or 2, wherein the following condition is satisfied: (Configuration 4) When the amount of movement of the second focus lens group during focusing from infinity to the closest point is dltr and the length on the optical axis from the surface of the front lens group closest to the object side to the surface of the front lens group closest to the image side is d1, 0.060≦|dltr| / d1≦2.000 4. The optical system according to any one of configurations 1 to 3, wherein the following condition is satisfied: (Configuration 5) Let df be the length on the optical axis from the surface of the first focus lens group closest to the object side to the surface of the first focus lens group closest to the image side, and f be the focal length of the optical system when focused on an object at infinity. 0.020≦df / f≦0.400 5. The optical system according to any one of configurations 1 to 4, wherein the following condition is satisfied: (Configuration 6) Let dr be the length on the optical axis from the surface of the second focus lens group closest to the object side to the surface of the second focus lens group closest to the image side, and f be the focal length of the optical system when focused on an object at infinity. 0.090≦dr / f≦0.500 6. The optical system according to any one of configurations 1 to 5, wherein the following condition is satisfied: (Configuration 7) Let f1 be the focal length of the first front lens unit, and sk be the air-equivalent distance on the optical axis from the surface of the optical system closest to the image side to the image plane. 0.660≦|f1| / sk≦23.100 7. The optical system according to any one of configurations 1 to 6, wherein the following condition is satisfied: (Configuration 8) When the focal length of the first focus lens group is ff and the focal length of the second focus lens group is fr, -3.200≦|ff| / |fr|≦1.700 8. The optical system according to any one of configurations 1 to 7, wherein the following condition is satisfied: (Configuration 9) an intermediate lens group that does not move for focusing is provided between the first focus lens group and the second focus lens group; The optical system according to any one of configurations 1 to 8, wherein the intermediate lens group includes an aperture stop and an aspherical lens, and has a positive refractive power as a whole. (Configuration 10) When the focal length of the intermediate lens group is fm and the focal length of the front lens group is f1, 0.050≦fm / |f1|≦1.000 10. The optical system according to any one of configurations 9, wherein the following condition is satisfied: (Configuration 11) When the focal length of the intermediate lens group is fm and the focal length of the optical system when focused on an object at infinity is f, 0.440≦fm / f≦8.400 The optical system according to any one of configurations 9 and 0, wherein the following condition is satisfied: (Configuration 12) When the focal length of the intermediate lens group is fm and the focal length of the second focus lens group is fr, 0.120≦fm / |fr|≦0.800 12. The optical system according to any one of configurations 9 to 11, wherein the following condition is satisfied: (Configuration 13) a rear lens group that is disposed closer to the image side than the second focus lens group and does not move for focusing; 13. The optical system according to any one of configurations 1 to 12, wherein the rear lens group has positive or negative refractive power and includes an aspherical lens. (Configuration 14) When the focal length of the rear lens group is fk and the focal length of the front lens group is f1, 0.150≦|fk| / |f1|≦6.900 14. The optical system according to configuration 13, wherein the following condition is satisfied: (Configuration 15) When the focal length of the rear lens group is fk and the focal length of the optical system when focused on an object at infinity is f, 0.490≦|fk| / f≦4.500 15. The optical system according to configuration 13 or 14, wherein the following condition is satisfied: (Configuration 16) When the focal length of the rear lens group is fk and the focal length of the second focus lens group is ff, 0.610≦|fk| / |ff|≦4.000 16. The optical system according to any one of configurations 13 to 15, wherein the following condition is satisfied: (Configuration 17) the front lens group has negative refractive power, the first focus lens group has negative refractive power, 17. The optical system according to any one of configurations 1 to 16, wherein the second focus lens group has negative refractive power. (Configuration 18) the front lens group has negative refractive power, the first focus lens group has negative refractive power, 17. The optical system according to any one of configurations 1 to 16, wherein the second focus lens group has a positive refractive power. (Configuration 19) the front lens group has positive refractive power, the first focus lens group has negative refractive power, 17. The optical system according to any one of configurations 1 to 16, wherein the second focus lens group has negative refractive power. (Configuration 20) The optical system according to any one of configurations 1 to 19; and an image sensor that captures an image of a subject through the optical system.

[0083] The embodiments described above are merely representative examples, and various modifications and alterations are possible to each embodiment when implementing the present invention. [Explanation of symbols]

[0084] B1 front lens group Bf First focus lens group Bm intermediate lens group Br 2nd focus lens group Bk rear lens group

Claims

1. An optical system comprising a front lens group, a first focusing lens group positioned closer to the image than the front lens group, a second focusing lens group positioned closer to the image than the first focusing lens group, and a rear lens group positioned closer to the image than the second focusing lens group that does not move for focusing, wherein the spacing between adjacent lens groups changes during focusing, For focusing, the front lens group and the rear lens group do not move, while the first focusing lens group and the second focusing lens group move. The optical system is capable of focusing from a state of focus on an object at infinity to a state of focus where the lateral magnification β of the optical system is -1.0 or less. The aforementioned rear lens group has a positive or negative refractive power and includes an aspherical lens. When the focal length of the front lens group is f1, and the focal length of at least one of the first and second focus lens groups is ffr, -5.500≦|ffr| / f1≦0.380 An optical system characterized by satisfying the following conditions.

2. When the focal length of the first focusing lens group is ff, and the focal length of the optical system when in focus on an object at infinity is f, 1.340≦|ff| / f≦6.370 The optical system according to claim 1, characterized in that it satisfies the following conditions.

3. When the amount of movement of the first focusing lens group during focusing from infinity to the closest focusing point is dltf, and the length along the optical axis from the object-side surface of the front lens group to the image-side surface of the front lens is d1, -1.500≦|dltf| / d1≦0.800 The optical system according to claim 1, characterized in that it satisfies the following conditions.

4. When the amount of movement of the second focusing lens group during focusing from infinity to the closest focusing point is dlr, and the length along the optical axis from the object-side surface of the front lens group to the image-side surface of the front lens is d1, 0.060≦|dltr| / d1≦2.000 The optical system according to claim 1, characterized in that it satisfies the following conditions.

5. When df is the length along the optical axis from the object-side surface of the first focusing lens group to the image-side surface of the first focusing lens group, and f is the focal length of the optical system when in focus on an object at infinity, 0.020 ≤ df / f ≤ 0.400 The optical system according to claim 1, characterized in that it satisfies the following conditions.

6. When dr is the length along the optical axis from the object-side surface of the second focusing lens group to the image-side surface of the second focusing lens group, and f is the focal length of the optical system when in focus on an object at infinity, 0.090 ≤ dr / f ≤ 0.500 The optical system according to claim 1, characterized in that it satisfies the following conditions.

7. When the focal length of the front lens group is f1, and the air-equivalent distance on the optical axis from the image-side surface of the optical system to the image plane is sk, 0.660≦|f1| / sk≦23.100 The optical system according to claim 1, characterized in that it satisfies the following conditions.

8. When the focal length of the first focusing lens group is ff and the focal length of the second focusing lens group is fr, -3.200≦|ff| / |fr|≦1.700 The optical system according to claim 1, characterized in that it satisfies the following conditions.

9. Between the first focusing lens group and the second focusing lens group, there is an intermediate lens group that does not move for focusing. The optical system according to claim 1, characterized in that the intermediate lens group includes an aperture diaphragm and an aspherical lens, and the whole has a positive refractive power.

10. When the focal length of the intermediate lens group is fm and the focal length of the front lens group is f1, 0.050≦fm / |f1|≦1.000 The optical system according to claim 9, characterized in that it satisfies the following conditions.

11. When the focal length of the intermediate lens group is fm, and the focal length of the optical system when in focus on an object at infinity is f, 0.440 ≤ fm / f ≤ 8.400 The optical system according to claim 9, characterized in that it satisfies the following conditions.

12. When the focal length of the intermediate lens group is fm and the focal length of the second focusing lens group is fr, 0.120≦fm / |fr|≦0.800 The optical system according to claim 9, characterized in that it satisfies the following conditions.

13. When the focal length of the rear lens group is fk and the focal length of the front lens group is f1, 0.150≦|fk| / |f1|≦6.900 The optical system according to claim 1, characterized in that it satisfies the following conditions.

14. When the focal length of the rear lens group is fk, and the focal length of the optical system when in focus on an object at infinity is f, 0.490≦|fk| / f≦4.500 The optical system according to claim 1, characterized in that it satisfies the following conditions.

15. When the focal length of the rear lens group is fk and the focal length of the second focusing lens group is ff, 0.610≦|fk| / |ff|≦4.000 The optical system according to claim 1, characterized in that it satisfies the following conditions.

16. The aforementioned front lens group has a negative refractive power, The first focusing lens group has a negative refractive power, The optical system according to claim 1, characterized in that the second focusing lens group has a negative refractive power.

17. The aforementioned front lens group has a negative refractive power, The first focusing lens group has a negative refractive power, The optical system according to claim 1, characterized in that the second focusing lens group has a positive refractive power.

18. The aforementioned front lens group has a positive refractive power, The first focusing lens group has a negative refractive power, The optical system according to claim 1, characterized in that the second focusing lens group has a negative refractive power.

19. An optical system according to any one of claims 1 to 18, An imaging device characterized by having an image sensor that captures an image of a subject through the optical system.

Images