Optical system and imaging device

Abstract

To provide an optical system which is bright with a small F-number, has a large aperture, and yet offers suppressed image plane variation and chromatic aberration while shifting focus, and to provide an image capturing device.SOLUTION: An optical system is provided, comprising, in order from the object side, a first lens group (G1) having positive refractive power, a second lens group (G2) having negative refractive power, a third lens group (G3) having positive refractive power, and a fourth lens group (G4) having negative refractive power, the second lens group having at least one positive lens and at least one negative lens. When shifting focus from infinity to a shortest distance, the first and fourth lens groups are stationary relative to the image plane while the second and third lens groups move along an optical axis. The optical system satisfies given conditional expressions. An image capturing device comprising such optical system is also provided.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to an optical system and an imaging device. [Background technology]

[0002] In recent years, as demand for full-frame mirrorless cameras has expanded, there has been a growing need for high-resolution lenses that can handle the increased pixel count of sensors and the higher resolution of monitors and other components.

[0003] Generally, bright, large-aperture lenses with an f-number of around 1.4 have a shallow depth of field, requiring greater suppression of image plane fluctuations when focusing on objects from infinity to the closest distance. Furthermore, correction of axial chromatic aberration and lateral chromatic aberration, such as color fringing of the image on the sensor image plane and color fringing of the out-of-focus image, is becoming increasingly important.

[0004] Conventionally, optical systems with bright, large-aperture lenses with an F-number of around 1.4 have been known. For example, the optical systems disclosed in Patent Documents 1 and 2 consist of a first lens group with positive refractive power, a second lens group with negative refractive power, and a third lens group with positive refractive power, arranged in order from the object side to the image side, and employ an inner focus method in which the second lens group is moved along the optical axis to achieve focus. The optical system disclosed in Patent Document 3 consists of a first lens group with positive refractive power, a second lens group with negative refractive power, a third lens group with positive refractive power, and a fourth lens group with negative refractive power, arranged in order from the object side to the image side, and employs a floating focus method in which the second and third lens groups are moved along the optical axis to achieve focus. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2020-30383 [Patent Document 2] International Publication No. 2016 / 056310 [Patent Document 3] Patent No. 6631412 [Overview of the project] [Problems that the invention aims to solve]

[0006] However, in the optical system described in Patent Document 1, the power arrangement of the first and second lens groups is not appropriate, resulting in a relatively large diameter for the lenses constituting the first lens group. Consequently, the overall product becomes larger. Furthermore, image plane fluctuation and chromatic aberration correction during focusing are insufficient, and improvements in optical performance are required.

[0007] In the optical system described in Patent Document 2, focusing is achieved using a single lens group, resulting in large image plane fluctuations when focusing from infinity to the closest distance. Therefore, suppression of image plane fluctuations across the entire focusing range is required.

[0008] The optical system described in Patent Document 3 achieves focusing using a floating focus method. The lenses used in the lens group that moves during focusing are made of glass with low anomalous dispersion. As a result, the correction of axial chromatic aberration and lateral chromatic aberration across the entire focusing range is insufficient, and color fringing at the image plane becomes noticeable.

[0009] The object of this invention is to provide an optical system and imaging device that, while being a bright, large-aperture lens with a small F-number, suppresses image plane fluctuations and chromatic aberration across the entire focusing range. [Means for solving the problem]

[0010] To solve the above problems, the optical system according to the present invention is composed of, in order from the object side, a first lens group having positive refractive power, a second lens group having negative refractive power, a third lens group having positive refractive power, and a fourth lens group having negative refractive power, wherein the second lens group has at least one positive lens and at least one negative lens, and when focusing from infinity to the closest point, the first lens group and the fourth lens group are fixed with respect to the image plane, and the second lens group and the third lens group move along the optical axis, respectively, and satisfy the following equation. -0.55 ≦ f1 / f2 ≦ -0.01 ·····(1) ν2 ≦ 25.0 ·····(2) Wherein, f1: focal length of the first lens group f2: focal length of the second lens group ν2: the Abbe number at d-line of any one positive lens included in the second lens group

[0011] Further, in order to solve the above problem, an imaging apparatus according to the present invention includes the above optical system, and an image sensor that converts an optical image formed by the optical system into an electrical signal on the image side of the optical system. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] [Figure 1] It is a lens cross-sectional view of the optical system of Example 1 when focused at infinity. [Figure 2] It is a longitudinal aberration diagram of the optical system of Example 1 when focused at infinity. [Figure 3] It is a lateral aberration diagram of the optical system of Example 1 when focused at infinity. [Figure 4] It is a longitudinal aberration diagram of the optical system of Example 1 when focused at the closest distance. [Figure 5] It is a lateral aberration diagram of the optical system of Example 1 when focused at the closest distance. [Figure 6] It is a lens cross-sectional view of the optical system of Example 2 when focused at infinity. [Figure 7] It is a longitudinal aberration diagram of the optical system of Example 2 when focused at infinity. [Figure 8] It is a lateral aberration diagram of the optical system of Example 2 when focused at infinity. [Figure 9] It is a longitudinal aberration diagram of the optical system of Example 2 when focused at the closest distance. [Figure 10] It is a lateral aberration diagram of the optical system of Example 2 when focused at the closest distance. [Figure 11] It is a lens cross-sectional view of the optical system of Example 3 when focused at infinity. [Figure 12] It is a longitudinal aberration diagram of the optical system of Example 3 when focused at infinity. [Figure 13] It is a lateral aberration diagram of the optical system of Example 3 when focused at infinity. [Figure 14] It is a longitudinal aberration diagram of the optical system of Example 3 when focused at the closest distance. [Figure 15] It is a lateral aberration diagram of the optical system of Example 3 when focused at the closest distance. [Figure 16] It is a lens cross-sectional view of the optical system of Example 4 when focused at infinity. [Figure 17] It is a longitudinal aberration diagram of the optical system of Example 4 when focused at infinity. [Figure 18] It is a lateral aberration diagram of the optical system of Example 4 when focused at infinity. [Figure 19] It is a longitudinal aberration diagram of the optical system of Example 4 when focused at the closest distance. [Figure 20] It is a lateral aberration diagram of the optical system of Example 4 when focused at the closest distance. [Figure 21] It is a lens cross-sectional view of the optical system of Example 5 when focused at infinity. [Figure 22] It is a longitudinal aberration diagram of the optical system of Example 5 when focused at infinity. [Figure 23] It is a lateral aberration diagram of the optical system of Example 5 when focused at infinity. [Figure 24] It is a longitudinal aberration diagram of the optical system of Example 5 when focused at the closest distance. [Figure 25] It is a lateral aberration diagram of the optical system of Example 5 when focused at the closest distance. [Figure 26] It is a lens cross-sectional view of the optical system of Example 6 when focused at infinity. [Figure 27] It is a longitudinal aberration diagram of the optical system of Example 6 when focused at infinity. [Figure 28] It is a lateral aberration diagram of the optical system of Example 6 when focused at infinity. [Figure 29] It is a longitudinal aberration diagram of the optical system of Example 6 when focused at the closest distance. [Figure 30] It is a lateral aberration diagram of the optical system of Example 6 when focused at the closest distance. [Figure 31] It is a lens cross-sectional view of the optical system of Example 7 when focused at infinity. [Figure 32] It is a longitudinal aberration diagram of the optical system of Example 7 when focused at infinity. [Figure 33] This is a diagram of the lateral aberration of the optical system of Example 7 when it is focused at infinity. [Figure 34] This is a longitudinal aberration diagram of the optical system of Example 7 at its closest focusing point. [Figure 35] This is a diagram of the lateral aberration of the optical system in Example 7 at its closest focusing point. [Figure 36] This is a cross-sectional view of the lens of the optical system of Example 8 when it is in focus at infinity. [Figure 37] This is a longitudinal aberration diagram of the optical system of Example 8 when it is in focus at infinity. [Figure 38] This is a diagram showing the lateral aberration of the optical system of Example 8 when it is in focus at infinity. [Figure 39] This is a longitudinal aberration diagram of the optical system of Example 8 at its closest focusing point. [Figure 40] This is a diagram showing the lateral aberration of the optical system in Example 8 at its closest focusing point. [Figure 41] This figure schematically shows an example of the configuration of an imaging device according to one embodiment of the present invention. [Modes for carrying out the invention]

[0013] The embodiments of the optical system and imaging device according to the present invention will be described below. However, the optical system and imaging device described below are only one embodiment of the optical system and imaging device according to the present invention, and the optical system and imaging device according to the present invention are not limited to the embodiments described below.

[0014] 1.Optical system 1-1.Optical configuration The optical system of this embodiment is composed of, in order from the object side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, and a fourth lens group having a negative refractive power.

[0015] By employing the above refractive power configuration, this optical system can easily correct aberrations in bright, large-aperture optical systems with a small f-number of around 1.4.

[0016] (1) First lens group The first lens group is not particularly limited in its specific configuration, except that it is a lens group with positive refractive power. Having a first lens group with positive refractive power makes it easier to suppress aberrations and miniaturize the device. Furthermore, for example, if the first lens group has a negative lens, it is preferable as it is easier to suppress chromatic aberration and obtain good optical performance. Also, if the first lens group has a cemented lens of a positive lens and a negative lens, it is preferable as it is easier to suppress chromatic aberration and reduce the sensitivity of each lens. If the largest air gap is placed in the first lens group from the lens surface closest to the object in the first lens group to the lens surface closest to the image in the fourth lens group, it is preferable as it is easier to correct coma aberration.

[0017] Here, "lens group" refers to a group consisting of one or more adjacent lenses. Furthermore, when focusing, the spacing between adjacent lenses in a lens group changes along the optical axis. If a lens group consists of multiple lenses, the distance along the optical axis between each lens within that group is assumed to remain unchanged during focusing.

[0018] (2) Second lens group The second lens group is a group of lenses having negative refractive power, and its specific configuration is not particularly limited as long as it has one or more lenses with negative refractive power. The second lens group may have one or more lenses with positive refractive power and one or more lenses with negative refractive power. Furthermore, it is preferable for the second lens group to consist of a negative lens and a positive lens from the object side, as this can effectively suppress chromatic aberration.

[0019] (3) Third lens group The third lens group is a group of lenses having positive refractive power, and its specific configuration is not particularly limited as long as it has one or more lenses with positive refractive power. For example, the third lens group may have one or more lenses with positive refractive power and one or more lenses with negative refractive power. Furthermore, a configuration in the third lens group that includes a cemented lens of a positive lens and a negative lens is preferable because it makes it easier to suppress chromatic aberration and reduce the sensitivity of each lens. In order to suppress various aberrations, the shape of the lens positioned closest to the object in the third lens group is preferably convex on the object side. Similarly, the shape of the lens positioned closest to the image is preferably convex on the image side.

[0020] (3) Fourth lens group The fourth lens group is a group of lenses having negative refractive power, and its specific configuration is not particularly limited as long as it has one or more lenses with negative refractive power. It is preferable to have at least one negative lens, as this makes it easier to suppress chromatic aberration and obtain good optical performance. For example, if the fourth lens group has a positive lens, it is preferable as this makes it easier to suppress chromatic aberration and obtain good optical performance. It is also preferable to have a cemented lens of a positive lens and a negative lens in the fourth lens group, as this makes it easier to suppress chromatic aberration and reduce the sensitivity of each lens. Furthermore, it is preferable for the fourth lens group to have a positive lens, a negative lens, and another negative lens in that order from the object side, as this makes it easier to correct various aberrations.

[0021] (4) Aperture diaphragm In this optical system, the arrangement of the aperture diaphragm is not particularly limited. However, the aperture diaphragm referred to here is the aperture diaphragm that defines the diameter of the optical system, that is, the aperture diaphragm that defines the F-number of the optical system. Nevertheless, arranging the aperture diaphragm within the first lens group is preferable in order to miniaturize the aperture unit.

[0022] 1-2.Focus In this optical system, when focusing from infinity to the closest distance, the first and fourth lens groups are fixed relative to the image plane, and the second and third lens groups move along the optical axis, respectively. As long as these lens groups move along the optical axis, their specific operation is not particularly limited. Furthermore, when focusing from infinity to a close distance, a configuration in which the second lens group moves along the optical axis toward the image and the third lens group moves along the optical axis toward the object is preferable because it suppresses image plane fluctuations. Moreover, when focusing from infinity to a close distance, it is even more preferable that the second and third lens groups move along the optical axis by different amounts. This configuration makes it possible to have high optical performance when focusing from infinity to the closest distance. Furthermore, when focusing from infinity to the closest distance, it is even more preferable that the second lens group moves a larger amount along the optical axis relative to the image plane than the third lens group. This configuration makes it possible to have even higher optical performance when focusing from infinity to the closest distance.

[0023] 1-3.Formula In this optical system, it is preferable to adopt the configuration described above and satisfy one or more of the following equations.

[0024] 1-3-1.Formula (1) -0.55 ≦ f1 / f2 ≦ -0.01 (1) however, f1: Focal length of the first lens group f2: Focal length of the second lens group

[0025] Equation (1) defines the ratio of the focal lengths of the first lens group and the second lens group. By satisfying equation (1), it is possible to shorten the overall optical length while effectively correcting various aberrations, and it becomes easier to miniaturize the second lens group.

[0026] Conversely, if the value of equation (1) falls below the lower limit, the power of the first lens group weakens, making it difficult to miniaturize the optical system. On the other hand, if the value of equation (1) exceeds the upper limit, the power of the first lens group strengthens, increasing the fluctuations in coma aberration and distortion aberration occurring within the first lens group, making it difficult to correct various aberrations.

[0027] To obtain the above effect, the lower limit of equation (1) is preferably -0.53, and more preferably -0.50. Furthermore, the upper limit of equation (1) is preferably -0.02, and more preferably -0.03.

[0028] 1-3-2.Formula (2) ν² ≤ 25.0 ·····(2) however, ν2: The Abbe number on the d line of any one of the positive lenses included in the second lens group.

[0029] Equation (2) specifies the Abbe number on the d line for any one of the positive lenses included in the second lens group. By satisfying equation (2), it becomes possible to correct axial chromatic aberration and lateral chromatic aberration at the time of focusing, from objects at infinity to objects at close range. If the second lens group has multiple positive lenses, this effect can be obtained if only one of the lenses satisfies equation (2). Furthermore, it is more preferable for multiple lenses to satisfy equation (2) in order to obtain this effect.

[0030] In contrast, if the value in equation (2) exceeds the upper limit, the correction of axial chromatic aberration and lateral chromatic aberration becomes insufficient, resulting in noticeable color fringing of the image on the image plane and color fringing of the blurred image in the out-of-focus area, which is undesirable.

[0031] To obtain the above effect, the lower limit of equation (2) is preferably 10.0, and more preferably 15.0. Furthermore, the upper limit of equation (2) is preferably 24.0, and more preferably 22.0.

[0032] 1-3-3.Formula (3) -0.50 ≦ f / f2 ≦ -0.01 ····(3) however, f: Focal length when the optical system is in focus at infinity

[0033] Equation (3) defines the ratio of the focal length of the optical system at infinity focus to the focal length of the second lens group. By satisfying equation (3), the overall optical length can be shortened while aberrations are well corrected, and the second lens group can be easily miniaturized.

[0034] Conversely, if the value of equation (3) falls below the lower limit, the power of the second lens group weakens and the amount of movement increases, making it difficult to miniaturize while correcting various aberrations. On the other hand, if the value of equation (3) exceeds the upper limit, the power of the second lens group strengthens and it becomes more susceptible to the influence of manufacturing errors in the second lens group, resulting in increased eccentricity sensitivity. Furthermore, image plane fluctuations become more pronounced. In addition, it becomes difficult to suppress aberration fluctuations when focusing from infinity to the closest focus point.

[0035] To obtain the above effect, the lower limit of equation (3) is preferably -0.45, and more preferably -0.40. Furthermore, the upper limit of equation (3) is preferably -0.05, and more preferably -0.10.

[0036] 1-3-4.Formula (4) ν1 ≤ 25.0 ·····(4) however, ν1: Abbe number on the d line of the negative lens included in the first lens group.

[0037] Equation (4) is an equation that defines the Abbe number on the d line for the negative lens included in the first lens group. The first lens group has at least one negative lens that satisfies equation (4), which makes it possible to correct axial chromatic aberration and lateral chromatic aberration when focusing from infinity to the closest distance.

[0038] In contrast, if the value in equation (4) exceeds the upper limit, sagittal coma flare expands, and furthermore, the correction of axial chromatic aberration and lateral chromatic aberration becomes insufficient, resulting in noticeable color fringing of the image on the image plane and color fringing of the out-of-focus image, which is undesirable.

[0039] To obtain the above effect, the lower limit of equation (4) is preferably 10.0, and more preferably 15.0. Furthermore, the upper limit of equation (4) is preferably 24.0, and more preferably 22.0.

[0040] 1-3-5.Formula (5) 39.0 ≦ f1R ≦ 85.0 (5) however, f1R: The combined focal length (mm) of the lenses in the first lens group that are on the image side of the aperture.

[0041] Equation (5) defines the combined focal length of the lenses in the first lens group that are on the image side of the aperture. By satisfying equation (5), the light rays incident on the second lens group are restricted, and the aberration fluctuations when the second lens group is in focus can be suppressed, thereby enabling good correction.

[0042] Conversely, if the value in equation (5) falls below the lower limit, the angle of incidence of light on the second lens group increases. This also increases the aberration sensitivity of the second lens group, increases the eccentricity sensitivity of the lens group due to lens manufacturing errors, and makes it difficult to obtain an optical system with high optical performance. On the other hand, if the value in equation (5) exceeds the upper limit, the angle of incidence of light on the second lens group decreases. While it is possible to lower the aberration sensitivity of the lens group, this leads to an increase in the size and weight of the second lens group, and further increases the outer diameter of the product, which is undesirable.

[0043] To obtain the above effect, the lower limit of equation (5) is preferably 40.0, and more preferably 41.0. Furthermore, the upper limit of equation (5) is preferably 83.0, more preferably 80.0, and even more preferably 75.0.

[0044] 1-3-6.Formula (6) -10.0≦(R1f+R1r) / (R1f-R1r)≦1.2 (6) however, R1f: Radius of curvature of the image surface of the lens positioned on the object side, straddling the maximum air gap within the first lens group. R1r: Radius of curvature of the object side of the lens positioned on the image side, straddling the maximum air gap within the first lens group.

[0045] Equation (6) defines the radius of curvature of the object-side and image-side lens surfaces in the first lens group, with the maximum air gap between them. By satisfying equation (6), sagittal coma aberration and chromatic aberration occurring in the first lens group can be effectively corrected.

[0046] Conversely, if the value in equation (6) falls below the lower limit, the incident angle of off-axis rays changes. In particular, the change in the g-line becomes larger, and chromatic aberration increases. Also, sagittal coma aberration, which is a problem with large-aperture lenses, is amplified, making aberration correction difficult. On the other hand, if the value in equation (6) exceeds the upper limit, the fluctuations in sagittal coma aberration and distortion aberration become large, making aberration correction difficult.

[0047] To obtain the above effect, the lower limit of equation (6) is preferably -9.5, and more preferably -9.3. Furthermore, the upper limit of equation (6) is preferably 1.0, and more preferably 0.8.

[0048] 1-3-7.Formula (7) 0.5 ≦ BF / Y ≦ 1.3 (7) however, BF: Distance along the optical axis from the apex of the outermost surface of the fourth lens group to the image plane. Y: Maximum image height of the optical system

[0049] Equation (7) defines the distance from the top of the outermost image surface of the fourth lens group to the image plane and the maximum image height of the image plane in the optical system. Satisfying equation (7) minimizes the effect of peripheral light. Furthermore, the overall length of the optical system can be shortened, making miniaturization easier.

[0050] Conversely, if the value in equation (7) falls below the lower limit, the incident angle of the principal ray entering the image plane from the outermost side of the optical system (the incident angle of the principal ray that the pixels on the sensor's light-receiving surface can tolerate) becomes steeper, leading to peripheral light deficiency (shading) and chromatic aberration. On the other hand, if the value in equation (7) exceeds the upper limit, the back focus becomes longer, and the overall length of the optical system increases. This also makes it difficult to miniaturize the optical system, making it unsuitable for mirrorless cameras.

[0051] To obtain the above effect, the lower limit of equation (7) is preferably 0.52, and more preferably 0.55. Furthermore, the upper limit of equation (7) is preferably 1.2, and more preferably 1.1.

[0052] 1-3-8.Formula (8) 0.80 ≦ FD / f ≦ 1.50 (8) however, FD: Distance along the optical axis from the lens surface closest to the object in the second lens group to the lens surface closest to the image in the fourth lens group when in focus at infinity. f: Focal length when the optical system is in focus at infinity

[0053] Equation (8) defines the ratio of the distance along the optical axis from the object-side lens surface of the second lens group to the image-side lens surface of the fourth lens group to the focal length of the optical system when it is in focus at infinity. By satisfying equation (8), it is possible to optimize the size of the second lens group while suppressing aberration fluctuations during focusing. Furthermore, the effect of peripheral light intensity becomes minimal. In addition, the overall length of the optical system can be shortened, making miniaturization easier.

[0054] Conversely, if the value in equation (8) falls below the lower limit, the overall length cannot be kept down, making miniaturization difficult. On the other hand, if the value in equation (8) exceeds the upper limit, the aberration fluctuations at the time of focusing become large, making it difficult to correct various aberrations.

[0055] To obtain the above effect, the lower limit of equation (8) is preferably 0.85, and more preferably 0.90. Furthermore, the upper limit of equation (8) is preferably 1.45, and more preferably 1.40.

[0060] 1-3-10.Formula (10) 0.95 ≦ βb ≦ 1.50 (10) however, βb: Lateral magnification of the fourth lens group when focused at infinity.

[0061] Equation (10) defines the lateral magnification of the fourth lens group. Satisfying equation (10) enables miniaturization of the optical system and correction of various aberrations.

[0062] Conversely, if the value in equation (10) falls below the lower limit, the overall length cannot be kept down, making miniaturization difficult. On the other hand, if the value in equation (10) exceeds the upper limit, the aberration fluctuations at focus become large, making it difficult to correct various aberrations.

[0063] To obtain the above effect, the lower limit of equation (10) is preferably 0.98, and more preferably 1.00. Furthermore, the upper limit of equation (10) is preferably 1.48, and more preferably 1.46.

[0064] 2. Imaging device Next, the imaging device according to the present invention will be described. The imaging device according to the present invention is characterized by comprising the optical system according to the present invention and an image sensor provided on the image side of the optical system, which converts the optical image formed by the optical system into an electrical signal.

[0065] Here, there are no particular limitations on the image sensor, and solid-state image sensors such as CCD (Charge Coupled Device) sensors and CMOS (Complementary Metal Oxide Semiconductor) sensors can also be used. The imaging device according to the present invention is suitable for imaging devices using such solid-state image sensors, such as digital cameras and video cameras. Furthermore, the imaging device may be a fixed-lens type imaging device in which the lens is fixed to the housing, or it may be an interchangeable-lens type imaging device such as an SLR camera or a mirrorless interchangeable-lens camera.

[0066] Figure 41 is a schematic diagram showing an example of the configuration of the imaging device 1. The camera 2 has a detachable optical system 3, an image sensor 21 (CCD sensor or CMOS sensor) positioned on the image plane IP of the optical system 3, and a cover glass 22 positioned on the object side of the image sensor 21. The optical system 3 has an aperture diaphragm 31.

[0067] Next, the present invention will be specifically described with reference to examples. However, the present invention is not limited to the following examples. [Examples]

[0068] (1) Optical configuration of the optical system Figure 1 is a cross-sectional view of the lens configuration of the optical system of Embodiment 1 according to the present invention when it is in focus at infinity.

[0069] The optical system consists of, in order from the object side, a first lens group G1 with positive refractive power, a second lens group G2 with negative refractive power, a third lens group G3 with positive refractive power, and a fourth lens group G4 with negative refractive power. When focusing from an object at infinity to a nearby object, the first lens group G1 and the fourth lens group G4 are fixed in the direction of the optical axis, while the second lens group G2 moves towards the image side and the third lens group G3 moves towards the object side. The aperture diaphragm S is located inside the first lens group G1.

[0070] The configuration of each lens group is described below. The first lens group G1 consists of, in order from the object side, a positive refractive power cemented lens formed by joining a positive meniscus lens L1 with a concave surface facing the object side and a negative meniscus lens L2 with a concave surface facing the object side, a negative meniscus lens L3 with a convex surface facing the object side, a biconvex lens L4, a negative meniscus lens L5 with a convex surface facing the object side, a negative refractive power cemented lens formed by joining a biconcave lens L6 and a biconvex lens L7, an aperture diaphragm S, and a biconvex lens L8.

[0071] The second lens group G2 consists of a plano-concave lens L9 with a flat surface facing the object, and a biconvex lens L10.

[0072] The third lens group G3 consists of a positive meniscus lens L11 with its concave surface facing the object.

[0073] The fourth lens group G4 consists of, in order from the object side, a biconvex lens L12, a biconcave lens L13, and a negative meniscus lens L14 with its convex surface facing the object side.

[0074] In Figure 1, "IP" represents the imaging plane, specifically the imaging surface of a solid-state image sensor such as a CCD sensor or CMOS sensor, or the film surface of a silver halide film. Furthermore, the object side of the imaging plane IP is equipped with a parallel plate, such as a cover glass CG, that has virtually no refractive power. These points are the same in the cross-sectional lens diagrams shown in other embodiments, and therefore will not be explained further below.

[0075] (2) Numerical Examples Next, we will describe a numerical example in which specific numerical values ​​of the optical system are applied. Below, we show the "surface data," "various data," "variable interval (when in focus)," "focal length of each lens group," and "aspherical data" of the optical system. The values ​​of each equation (values ​​corresponding to the conditional equations) are shown together after Example 8.

[0076] In the "Surface Data," the "Surface Number" is the order of the lens surfaces counted from the object side, "R" is the radius of curvature of the lens surface, "D" is the distance of the lens surfaces along the optical axis, "Nd" is the refractive index for the d line (wavelength λ=587.6nm), and "νd" is the Abbe number for the d line. In addition, "ASPH" displayed after the surface number indicates that the lens surface is aspherical, and "STOP" indicates the aperture diaphragm. Furthermore, "D(15)", "D(19)", etc., in the column for the distance of the lens surfaces along the optical axis means that the distance of the lens surfaces along the optical axis is a variable distance that changes when the focus is achieved at the shooting distance. Note that all units of length in each table are "mm", and all units of angle of view are "°". Also, "0.0000" in the radius of curvature column means a plane. Note that surfaces 29 and 30 in Table 1 are surface data for the cover glass CG.

[0077] "Various Data" indicates the focal length ("F"), f-number ("Fno"), half-angle of view ("W"), image height ("Y"), and back focus ("BF") of the optical system at infinity focus and closest focus. Note that the "BF" value of the optical system includes a 2.5 mm thick cover glass (Nd=1.5168), and the same applies to the back focus shown in other embodiments.

[0078] "Variable interval (when in focus)" indicates the variable interval when in focus at a given shooting distance.

[0079] "Focal length of each lens group" indicates the focal length of each lens group that constitutes the optical system.

[0080] The "Aspherical Data" shows the aspherical coefficient for each aspherical surface. However, an aspherical surface is defined by the following equation, where x is the displacement from the surface vertex in the optical axis direction. x=( h 2 / r) / [1+{1-(1+k)×(h / r) 2} 1 / 2 )] +A4×h 4 +A6×h 6 +A8×h 8 +A10×h 10 +A12×h 12 In the above formula, h represents the height from the optical axis, r represents the paraxial radius of curvature, k represents the conic constant, and An represents the n-th order aspheric coefficient. In addition, "E±XX" represents exponential notation and means "×10 ±XX ". The matters regarding these tables also apply to each table shown in other examples, so description thereof will be omitted below.

[0081] Further, FIGS. 2, 3, 4 and 5 show longitudinal aberration diagrams and lateral aberration diagrams of the optical system when focused at infinity and when focused at the closest distance. The longitudinal aberration diagrams shown in each figure are, in order from the left side when facing the drawing, spherical aberration (mm), astigmatism (mm), and distortion (%), respectively. In the spherical aberration diagram, the solid line shows the spherical aberration for the d-line (wavelength 587.6 nm), and the broken line shows the spherical aberration for the g-line (wavelength 435.8 nm). In the astigmatism diagram, the vertical axis represents the half angle of view (ω), the horizontal axis represents defocus, the solid line represents the sagittal image plane (ds) for the d-line, and the broken line represents the meridional image plane (dm) for the d-line, respectively. In the distortion diagram, the vertical axis represents the half angle of view (ω), and the horizontal axis represents distortion. The lateral aberration diagrams shown in each figure are, in order from the left side when facing the drawing, coma in the meridional direction (mm) and coma in the sagittal direction (mm), respectively. These are coma at half angles of view (ω) in a ratio of 1.0 to 0.0 in order from the top to the bottom of the drawing. The solid line shows coma for the d-line, and the broken line shows coma for the g-line. These matters also apply to each aberration diagram shown in other examples, so description thereof will be omitted below.

[0082] [Surface Data] Surface Number R D Nd νd 1 -1112.3474 5.8449 1.83481 42.72 2 -76.9745 1.3000 1.92286 20.88 3 -210.0000 0.2000 4 912.7674 1.5500 1.72947 51.78 5 29.2979 12.6247 6 37.4056 8.0335 1.77012 24.46 7 -184.3239 9.3213 8ASPH 73.0859 1.3200 1.58313 59.42 9ASPH 26.8077 5.9985 10 -44.5673 1.2500 1.84666 23.78 11 26.5193 10.3945 1.74126 51.15 12 -39.7111 2.0000 13STOP 0.0000 2.0000 14 78.5899 7.1050 1.77250 49.62 15 -55.6186 D(15) 16 0.0000 1.2000 1.74167 32.84 17 37.9326 4.3916 18 81.4598 3.7061 1.92286 20.88 19 -538.5562 D(19) 20 -1603.1667 4.9642 1.70802 53.04 21 -49.8250 D(21) 22 32.7713 9.4981 1.49700 81.61 23 -69.7355 0.2000 24 -241.3847 1.0000 1.65620 29.82 25 28.7255 4.6346 26ASPH 107.2719 1.8500 1.85108 40.12 27ASPH 42.7204 3.0998 28 0.0000 10.9000 29 0.0000 2.5000 1.51680 64.20 30 0.0000 D(30)

[0083] [Various items] The closest shooting distance to INF. F 33.3896 32.2974 Fno 1.4500 1.4500 W 32.8185 31.2228 Y 21.633 21.633 BF 17,500 17,500

[0084] [Variable interval (when in focus)] Shooting distance INF Closest D(0) ∞ 320.0288 D(15) 2.1937 8.9177 D(19) 9.5193 2.2299 D(21) 0.4000 0.9654 D(30) 1.0000 1.0000

[0085] [Focal length of each lens group] Group Surface number Focal length G1 1-15 37.8392 G2 16-19 -186.367 G3 20-21 72.5337 G4 22-27 -85.4053

[0086] [Aspherical data] Surface number k A4 A6 A8 A10 8 0.00000E+00 -1.64135E-05 -2.94174E-08 8.96861E-11 8.35605E-14 9 -8.23823E-01 1.20196E-06 -2.58683E-08 3.11021E-11 3.67239E-13 26 0.00000E+00 -1.75503E-05 -8.41385E-09 -3.09446E-11 6.41687E-14 27 0.00000E+00 -5.70161E-06 7.86503E-10 4.91575E-13 4.95011E-14 Face number A12 8 -5.23312E-16 9 -1.28157E-15 26 0.00000E+00 27 0.00000E+00 [Examples]

[0087] (1) Optical configuration of the optical system Figure 6 is a cross-sectional view of the lens configuration of the optical system of Embodiment 2 according to the present invention when it is in focus at infinity.

[0088] The optical system consists of, in order from the object side, a first lens group G1 with positive refractive power, a second lens group G2 with negative refractive power, a third lens group G3 with positive refractive power, and a fourth lens group G4 with negative refractive power. When focusing from an object at infinity to a nearby object, the first lens group G1 and the fourth lens group G4 are fixed in the direction of the optical axis, while the second lens group G2 moves towards the image side and the third lens group G3 moves towards the object side. The aperture diaphragm S is located inside the first lens group G1.

[0089] The configuration of each lens group is described below. The first lens group G1 consists of, in order from the object side, a negative refractive power cemented lens formed by joining a positive meniscus lens L1 and a biconcave lens L2 with the concave surface facing the object side, a biconvex lens L3, a negative meniscus lens L4 with the convex surface facing the object side, a positive refractive power cemented lens formed by joining a biconcave lens L5 and a biconvex lens L6, an aperture diaphragm S, and a biconvex lens L7.

[0090] The second lens group G2 consists of a negative refractive power cemented lens formed by joining a biconvex lens L8 and a biconcave lens L9, and a biconvex lens L10, in that order from the object side.

[0091] The third lens group G3 consists of a biconvex lens L11.

[0092] The fourth lens group G4 consists of, in order from the object side, a biconvex lens L12, a biconcave lens L13, and a biconcave lens L14.

[0093] (2) Numerical Examples Next, we will describe an example of applying specific numerical values ​​to the optical system. Below, we show the "surface data," "various data," "variable interval (when in focus)," "focal length of each lens group," and "aspherical data" of the optical system.

[0094] [Surface data] Face number RD Nd νd 1 -3861.4979 8.0746 1.61692 56.07 2 -45.3488 1.6500 1.59867 38.84 3 31.5068 6.7310 4 38.0602 6.9105 1.92119 23.96 5 -324.9412 7.5142 6ASPH 114.7520 1.3200 1.58313 59.42 7ASPH 25.8590 7.0110 8 -57.4174 1.2500 1.82140 22.97 9 26.6490 0.0010 1.56732 42.84 10 26.6490 11.7877 1.74320 49.34 11 -48.3089 2.0000 12STOP 0.0000 2.0000 13 74.6318 8.5601 1.77250 49.62 14 -57.8627 D(14) 15 552.0331 3.0000 1.72916 54.67 16 -179.6380 1.0000 1.94728 29.07 17 40.8417 4.1464 18 123.9079 4.0082 1.94595 17.98 19 -163.8626 D(19) 20 75.5778 7.9360 1.77250 49.62 21 -64.1003 D(21) 22 53.6737 6.6944 1.49700 81.61 23 -103.7803 0.2000 24 -295.5789 1.0000 1.68893 31.16 25 30.1757 5.7954 26ASPH 997.7596 1.8500 1.85108 40.12 27ASPH 81.6478 3.0987 28 0.0000 10.9000 29 0.0000 2.5000 1.51680 64.20 30 0.0000 D(30)

[0095] [Various items] The closest shooting distance to INF F 40.3989 38.4571 Fno 1.4100 1.4726 W 27.8608 26.1523 Y 21.633 21.633 BF 17.4987 17.4987

[0096] [Adjustable interval (when in focus)] The closest shooting distance to INF D( 0) ∞ 320.0781 D(14) 1.9972 8.4486 D(19) 9.0634 2.0835 D(21) 1.0000 1.5285 D(30) 1.0000 1.0000

[0097] [Focus distance of each レンズ group] Group face number focus distance G1 1-14 42.3197 G2 15-19 -121.959 G3 20-21 46.0380 G4 22-27 -50.5631

[0098] [Aspherical data] Surface number k A4 A6 A8 A10 6 0.00000E+00 -1.15559E-05 -1.81351E-08 4.30716E-11 8.09943E-14 7 -6.15033E-01 3.84438E-06 -1.43478E-08 -1.90530E-11 3.35123E-13 26 0.00000E+00 -1.51181E-05 -1.31262E-08 4.54774E-11 -2.16222E-14 27 0.00000E+00 -5.12939E-06 -7.00821E-09 7.14763E-11 -4.60828E-14 Face number A12 6 -2.64140E-16 7 -7.75048E-16 26 0.00000E+00 27 0.00000E+00 [Examples]

[0099] (1) Optical configuration of the optical system Figure 11 is a cross-sectional view of the lens configuration of the optical system of Embodiment 3 according to the present invention when it is in focus at infinity.

[0100] The optical system consists of, in order from the object side, a first lens group G1 with positive refractive power, a second lens group G2 with negative refractive power, a third lens group G3 with positive refractive power, and a fourth lens group G4 with negative refractive power. When focusing from an object at infinity to a nearby object, the first lens group G1 and the fourth lens group G4 are fixed in the direction of the optical axis, while the second lens group G2 moves towards the image side and the third lens group G3 moves towards the object side. The aperture diaphragm S is located inside the first lens group G1.

[0101] The configuration of each lens group is described below. The first lens group G1 consists of a negative refractive power cemented lens formed by joining a positive meniscus lens L1 with its concave surface facing the object and a negative meniscus lens L2 with its concave surface facing the object, a biconvex lens L3, a negative meniscus lens L4 with its convex surface facing the object, a positive refractive power cemented lens formed by joining a biconcave lens L5 and a biconvex lens L6, an aperture diaphragm S, and a biconvex lens L7.

[0102] The second lens group G2 consists of, in order from the object side, a negative meniscus lens L8 with its concave surface facing the image side, and a biconvex lens L9.

[0103] The third lens group G3 consists of a biconvex lens L10.

[0104] The fourth lens group G4 consists of a negative refractive power cemented lens formed by joining a biconvex lens L11 and a biconcave lens L12, and a biconcave lens L13, in that order from the object side.

[0105] (2) Numerical Examples Next, we will describe an example of applying specific numerical values ​​to the optical system. Below, we show the "surface data," "various data," "variable interval (when in focus)," "focal length of each lens group," and "aspherical data" of the optical system.

[0106] [Surface data] Face number RD Nd νd 1 -85.0429 8.0000 1.90366 31.31 2 -29.9056 1.6500 1.93211 23.42 3 -153.0497 0.2000 4 67.2583 6.9594 1.92119 23.96 5 -144.6815 1.2881 6ASPH 78.8292 1.3200 1.58313 59.42 7ASPH 26.5688 16.2436 8 -35.0794 1.2500 1.70287 27.15 9 41.0964 10.8441 1.77250 49.62 10 -43.8325 2.0000 11STOP 0.0000 2.0000 12 79.2385 5.2508 1.77250 49.62 13 -159.3262 D(13) 14 17575.3702 1.2000 1.74317 47.32 15 42.0250 3.5969 16 206.9434 3.0697 1.92286 20.88 17 -225.6701 D(17) 18 69.3808 8.5634 1.77250 49.62 19 -68.0892 D(19) 20 64.9150 8.1710 1.77250 49.62 21 -56.1403 1.0000 1.71823 26.74 22 32.8244 6.4330 23ASPH -535.2130 1.8500 1.85135 40.10 24ASPH 99.5002 3.7462 25 0.0000 10.9000 26 0.0000 2.5000 1.51680 64.20 27 0.0000 D(27)

[0107] [Various items] The closest shooting distance to INF. F 48.5017 45.4920 Fno 1.4399 1.5474 W 23.7670 21.4597 Y 21.633 21.633 BF 18.1462 18.1462

[0108] [Changeable interval (when focusing)] Shooting distance INF Closest D(0) ∞ 324.8170 D(13) 1.9888 12.4470 D(17) 13.4766 2.1062 D(19) 0.7500 1.6622 D(27) 1.0000 1.0000

[0109] [Focal length of each lens group] Group Surface number Focal length G1 1-13 55.2474 G2 14-17 -118.122 G3 18-19 45.7261 G4 20-24 -56.1795

[0110] [Aspherical data] Surface number k A4 A6 A8 A10 6 0.00000E+00 -3.08885E-06 -6.33741E-09 4.04863E-14 8.15307E-15 7 -3.99165E-01 4.84256E-06 1.26947E-09 5.26078E-12 -4.27315E-15 23 0.00000E+00 -2.43881E-05 2.84540E-08 -2.26609E-11 6.28328E-14 24 0.00000E+00 -1.62108E-05 3.28709E-08 -6.10781E-12 2.73903E-14 Face number A12 6 -7.30680E-18 7 3.48953E-17 23 0.00000E+00 24 0.00000E+00 [Examples]

[0111] (1) Optical configuration of the optical system Figure 16 is a cross-sectional view of the lens configuration of the optical system of Embodiment 4 according to the present invention when it is in focus at infinity.

[0112] The optical system consists of, in order from the object side, a first lens group G1 with positive refractive power, a second lens group G2 with negative refractive power, a third lens group G3 with positive refractive power, and a fourth lens group G4 with negative refractive power. When focusing from an object at infinity to a nearby object, the first lens group G1 and the fourth lens group G4 are fixed in the direction of the optical axis, while the second lens group G2 moves towards the image side and the third lens group G3 moves towards the object side. The aperture diaphragm S is located inside the first lens group G1.

[0113] The configuration of each lens group is described below. The first lens group G1 consists of a negative refractive power cemented lens formed by joining a negative meniscus lens L1 with a concave surface facing the object and a biconcave lens L2 facing the object, a biconvex lens L3, a negative meniscus lens L4 with a convex surface facing the object, a positive refractive power cemented lens formed by joining a biconcave lens L5 and a biconvex lens L6, an aperture diaphragm S, and a biconvex lens L7.

[0114] The second lens group G2 consists of, in order from the object side, a plano-concave lens L8 with a flat surface on the object side and a biconvex lens L9.

[0115] The third lens group G3 consists of a biconvex lens L10.

[0116] The fourth lens group G4 consists of a negative refractive power cemented lens formed by joining a biconvex lens L11 and a biconcave lens L12, and a biconcave lens L13, in that order from the object side.

[0117] (2) Numerical Examples Next, we will describe an example of applying specific numerical values ​​to the optical system. Below, we show the "surface data," "various data," "variable interval (when in focus)," "focal length of each lens group," and "aspherical data" of the optical system.

[0118] [Surface data] Face number RD Nd νd 1 -228.0707 9.2744 1.61207 56.13 2 -33.4559 1.6500 1.62434 32.26 3 52.8155 2.1424 4 49.1826 6.8951 1.92119 23.96 5 -138.7195 5.0245 6ASPH 76.0775 1.3200 1.82115 24.06 7ASPH 32.4415 10.4748 8 -26.6038 1.2500 1.64863 30.34 9 79.7838 8.9693 1.83559 40.92 10 -33.6165 2.0000 11STOP 0.0000 2.0000 12 52.7128 6.4330 1.49700 81.61 13 -115.2491 D(13) 14 0.0000 1.2000 1.86485 38.15 15 44.1417 2.5752 16 128.7199 3.3271 1.92286 20.88 17 -235.1172 D(17) 18 77.2245 8.0235 1.77250 49.62 19 -61.2723 D(19) 20 68.9607 8.6126 1.77250 49.62 21 -43.5976 1.1129 1.73256 25.83 22 35.5320 5.8861 23ASPH -846.2459 1.8500 1.85108 40.12 24ASPH 81.3907 3.1015 25 0.0000 10.9000 26 0.0000 2.5000 1.51680 64.20 27 0.0000 D(27)

[0119] [Various Data] Shooting distance INF Closest F 45.5424 42.9123 Fno 1.4500 1.5435 W 25.1291 22.9702 Y 21.633 21.633 BF 17.5015 17.5015

[0120] [Variable interval (when in focus)] Shooting distance INF Closest D(0) ∞ 326.9244 D(13) 1.9931 12.2469 D(17) 13.0915 2.0952 D(19) 0.5500 1.2926 D(27) 1.0000 1.0000

[0121] [Focal length of each lens group] Group Surface number Focal length G1 1-13 53.0404 G2 14-17 -127.289 G3 18-19 45.3719 G4 20-24 -53.7838

[0122] [Aspherical data] Surface number k A4 A6 A8 A10 6 0.00000E+00 -4.62733E-06 -1.30739E-08 -5.66238E-12 -1.65355E-14 7 -5.18276E-01 4.17552E-06 -3.40382E-09 -1.61178E-11 1.30079E-15 23 0.00000E+00 -3.32507E-05 5.31909E-08 -2.74049E-11 -5.47803E-15 24 0.00000E+00 -2.46297E-05 6.19703E-08 -2.71967E-11 -2.86687E-15 Face number A12 6 4.04711E-17 7 -2.40030E-17 23 0.00000E+00 24 0.00000E+00 [Examples]

[0123] (1) Optical configuration of the optical system Figure 21 is a cross-sectional view of the lens configuration of the optical system of Embodiment 5 according to the present invention when it is in focus at infinity.

[0124] The optical system consists of, in order from the object side, a first lens group G1 with positive refractive power, a second lens group G2 with negative refractive power, a third lens group G3 with positive refractive power, and a fourth lens group G4 with negative refractive power. When focusing from an object at infinity to a nearby object, the first lens group G1 and the fourth lens group G4 are fixed in the direction of the optical axis, while the second lens group G2 moves towards the image side and the third lens group G3 moves towards the object side. The aperture diaphragm S is located inside the first lens group G1.

[0125] The configuration of each lens group is described below. The first lens group G1 consists of a positive refractive power cemented lens formed by joining a biconvex lens L1 and a negative meniscus lens L2 with its concave surface facing the object, a biconcave lens L3, a biconvex lens L4, a negative meniscus lens L5 with its convex surface facing the object, a negative refractive power cemented lens formed by joining a biconcave lens L6 and a biconvex lens L7, an aperture diaphragm S, and a biconvex lens L8.

[0126] The second lens group G2 consists of, in order from the object side, a plano-concave lens L9 with a flat surface on the object side and a biconvex lens L10.

[0127] The third lens group G3 consists of a biconvex lens L11.

[0128] The fourth lens group G4 consists of, in order from the object side, a biconvex lens L12, a biconcave lens L13, and a biconcave lens L14.

[0129] (2) Numerical Examples Next, we will describe an example of applying specific numerical values ​​to the optical system. Below, we show the "surface data," "various data," "variable interval (when in focus)," "focal length of each lens group," and "aspherical data" of the optical system.

[0130] [Surface data] Face number RD Nd νd 1 771.1109 7.4367 1.83481 42.72 2 -55.3704 1.3000 1.92119 23.96 3 -212.2186 0.2000 4 -7833.9757 1.5500 1.48749 70.44 5 21.9033 15.3480 6 30.4735 6.6151 1.82898 23.95 7 -141.9773 1.2819 8ASPH 71.4042 1.3200 1.83441 37.28 9ASPH 23.2956 6.8381 10 -36.8428 1.2500 1.84666 23.78 11 26.3609 9.7232 1.75746 50.33 12 -37.4388 2.0000 13STOP 0.0000 2.0000 14 96.1773 6.5028 1.77250 49.62 15 -48.8457 D(15) 16 0.0000 1.2000 1.74218 36.71 17 39.5754 2.5352 18 91.1801 3.3773 1.92286 20.88 19 -413.4901 D(19) 20 318.6990 4.5321 1.75198 50.60 21 -55.4532 D(21) 22 31.2848 8.6005 1.49700 81.61 23 -64.8295 0.2000 24 -172.0204 1.0000 1.73842 25.60 25 29.9718 4.4796 26ASPH -271.4701 1.8500 1.85108 40.12 27ASPH 115.4858 3.1000 28 0.0000 10.9000 29 0.0000 2.5000 1.51680 64.20 30 0.0000 D(30)

[0131] [Various Data] Shooting distance INF Closest F 31.4732 30.5281 Fno 1.4601 1.4852 W 34.5150 32.9635 Y 21.633 21.633 BF 17.5000 17.5000

[0132] [Variable interval (when in focus)] Shooting distance INF Closest D(0) ∞ 330.0319 D(15) 1.9878 8.2936 D(19) 8.8217 2.0595 D(21) 0.5500 1.0064 D(30) 1.0000 1.0000

[0133] [Focal length of each lens group] Group Surface number Focal length G1 1-15 37.3918 G2 16-19 -172.976 G3 20-21 63.1415 G4 22-27 -79.3352

[0134] [Aspherical data] Surface number k A4 A6 A8 A10 8 0.00000E+00 -1.36185E-05 -2.39755E-08 8.40427E-11 -2.51782E-15 9 -5.83033E-01 3.26236E-06 -2.06282E-08 3.20478E-11 1.59786E-13 26 0.00000E+00 1.12564E-05 -6.68072E-08 -1.23570E-11 1.55764E-13 27 0.00000E+00 2.47794E-05 -5.75350E-08 1.93230E-11 1.39863E-13 Face number A12 8 -2.32666E-16 9 -6.55543E-16 26 0.00000E+00 27 0.00000E+00 [Examples]

[0135] (1) Optical configuration of the optical system Figure 26 is a cross-sectional view of the lens configuration of the optical system of Embodiment 6 according to the present invention when it is in focus at infinity.

[0136] The optical system consists of, in order from the object side, a first lens group G1 with positive refractive power, a second lens group G2 with negative refractive power, a third lens group G3 with positive refractive power, and a fourth lens group G4 with negative refractive power. When focusing from an object at infinity to a nearby object, the first lens group G1 and the fourth lens group G4 are fixed in the direction of the optical axis, while the second lens group G2 moves towards the image side and the third lens group G3 moves towards the object side. The aperture diaphragm S is located inside the first lens group G1.

[0137] The configuration of each lens group is described below. The first lens group G1 consists of, in order from the object side, a positive refractive power cemented lens formed by joining a biconvex lens L1 and a negative meniscus lens L2 with its concave surface facing the object side, a biconcave lens L3, a biconvex lens L4, a negative meniscus lens L5 with its convex surface facing the object side, a negative refractive power cemented lens formed by joining a biconcave lens L6 and a biconvex lens L7, an aperture diaphragm S, and a biconvex lens L8.

[0138] The second lens group G2 consists of, in order from the object side, a plano-concave lens L9 with a flat surface on the object side and a biconvex lens L10.

[0139] The third lens group G3 consists of a biconvex lens L11.

[0140] The fourth lens group G4 consists of, in order from the object side, a biconvex lens L12, a biconcave lens L13, and a negative meniscus lens L14 with its convex surface facing the object side.

[0141] (2) Numerical Examples Next, we will describe an example of applying specific numerical values ​​to the optical system. Below, we show the "surface data," "various data," "variable interval (when in focus)," "focal length of each lens group," and "aspherical data" of the optical system.

[0142] [Surface data] Face number RD Nd νd 1 173.7978 8.9679 1.83481 42.72 2 -63.9488 1.3000 1.92119 23.96 3 -240.3604 1.5000 4 -220.5721 1.5500 1.48749 70.44 5 20.4720 16.0381 6 30.4538 5.9926 1.83284 23.72 7 -116.2805 0.2000 8ASPH 82.5260 1.3200 1.83441 37.28 9ASPH 23.7204 6.4492 10 -35.5547 1.2500 1.84666 23.78 11 26.7926 0.0010 1.56732 42.84 12 26.7926 9.2332 1.77250 49.62 13 -37.0378 2.0000 14STOP 0.0000 2.0000 15 91.7715 6.2826 1.77250 49.62 16 -51.1134 D(16) 17 0.0000 1.2000 1.74265 41.05 18 40.4868 2.4271 19 108.4402 3.2198 1.92119 23.96 20 -295.8316 D(20) 21 492.4813 4.2604 1.77250 49.62 22 -55.8168 D(22) 23 31.0567 8.5715 1.49700 81.61 24 -66.4032 0.2000 25 -193.7372 1.0000 1.71466 26.60 26 28.4787 4.7194 27ASPH 1926.3038 1.8500 1.85108 40.12 28ASPH 106.5676 3.1000 29 0.0000 10.9000 30 0.0000 2.5000 1.51680 64.20 31 0.0000 D(31)

[0143] [Various items] The closest shooting distance to INF. F 31.0124 30.1903 Fno 1.4400 1.4856 W 34.9133 33.3701 Y 21.633 21.633 BF 17,500 17,500

[0144] [Variable interval (when in focus)] Shooting distance INF Closest D(0) ∞ 330.0363 D(16) 1.9737 7.6918 D(20) 8.4445 2.0906 D(22) 0.5500 1.1858 D(31) 1.0000 1.0000

[0145] [Focal length of each lens group] Group Surface number Focal length G1 1-16 37.6960 G2 17-20 -162.130 G3 21-22 65.1197 G4 23-28 -102.190

[0146] [Aspherical data] Surface number k A4 A6 A8 A10 8 0.00000E+00 -1.01087E-05 -3.35865E-08 9.33889E-11 2.32372E-13 9 -4.61533E-01 5.22094E-06 -2.94241E-08 -9.54051E-12 8.66882E-13 27 0.00000E+00 -7.90613E-06 -1.41361E-09 -8.38477E-11 1.35651E-13 28 0.00000E+00 4.50209E-06 5.24274E-09 -4.18014E-11 1.14135E-13 Face number A12 8 -9.34433E-16 9 -2.41711E-15 27 0.00000E+00 28 0.00000E+00 EXAMPLE

[0147] (1) Optical configuration of the optical system Fig. 31 is a lens cross-sectional view showing the lens configuration of the optical system of Example 7 according to the present invention when focused at infinity.

[0148] The optical system comprises, in order from the object side: a first lens group G1 having a positive refractive power, a second lens group G2 having a negative refractive power, a third lens group G3 having a positive refractive power, and a fourth lens group G4 having a negative refractive power. During focusing from an infinite distance object to a close distance object, with the first lens group G1 and the fourth lens group G4 fixed in the optical axis direction, the second lens group G2 moves toward the image side and the third lens group G3 moves toward the object side. The aperture stop S is arranged inside the first lens group G1.

[0149] Hereinafter, the configuration of each lens group will be described. The first lens group G1 comprises, in order from the object side: a cemented lens with positive refractive power formed by cementing a negative meniscus lens L1 having a convex surface facing the object side and a biconvex lens L2; a negative meniscus lens L3 having a convex surface facing the object side; a biconvex lens L4; a negative meniscus lens L5 having a convex surface facing the object side; a cemented lens with negative refractive power formed by cementing a biconcave lens L6 and a biconvex lens L7; the aperture stop S; and a biconvex lens L8.

[0150] The second lens group G2 comprises, in order from the object side, a plano-concave lens L9 having a planar surface on the object side, and a biconvex lens L10.

[0151] The third lens group G3 consists of a biconvex lens L11.

[0152] The fourth lens group G4 comprises, in order from the object side, a biconvex lens L12, a negative meniscus lens L13 having a convex surface facing the object side, and a negative meniscus lens L14 having a convex surface facing the object side.

[0153] (2) Numerical Examples Next, we will describe an example of applying specific numerical values ​​to the optical system. Below, we show the "surface data," "various data," "variable interval (when in focus)," "focal length of each lens group," and "aspherical data" of the optical system.

[0154] [Surface data] Face number RD Nd νd 1 250.0000 1.5000 1.92286 20.88 2 91.3371 5.4833 1.66386 56.12 3 -284.4015 0.5000 4 864.4431 1.6500 1.49700 81.61 5 21.6476 20.8072 6 28.5497 6.1373 1.93107 23.11 7 -660.6291 0.2000 8ASPH 90.6064 1.3200 1.83441 37.28 9ASPH 23.9800 6.4664 10 -42.6079 1.2500 1.84666 23.78 11 24.0973 9.8154 1.77250 49.62 12 -40.4448 2.0000 13STOP 0.0000 2.0000 14 59.6619 5.2243 1.77250 49.62 15 -118.9867 D(15) 16 0.0000 1.2000 1.74077 27.76 17 42.1415 2.9042 18 212.5356 3.8056 1.92286 20.88 19 -83.7584 D(19) 20 52.7404 4.3972 1.77250 49.62 21 -1579.0980 D(21) 22 39.8190 7.1079 1.49700 81.61 23 -70.5632 0.2000 24 152.5886 1.0000 1.78322 24.04 25 23.2826 5.9758 26ASPH 378.8394 1.8500 1.85108 40.12 27ASPH 135.9702 3.1003 28 0.0000 10.9000 29 0.0000 2.5000 1.51680 64.20 30 0.0000 D(30)

[0155] [Various items] The closest shooting distance to INF F 29.0222 28.0795 Fno 1.4432 1.4628 W 36.7181 35.8784 Y 21.633 21.633 BF 17.5003 17.5003

[0156] [Adjustable interval (when in focus)] The closest shooting distance to INF D( 0) ∞ 330.0427 D(15) 1.9754 4.8815 D(19) 7.1799 2.3193 D(21) 0.5500 2.5044 D(30) 1.0000 1.0000

[0157] [Focus distance of each レンズ group] Group face number focus distance G1 1-15 41.5286 G2 16-19 -869.596 G3 20-21 66.1435 G4 22-27 -90.4289

[0158] [Aspherical data] Surface number k A4 A6 A8 A10 8 0.00000E+00 -4.28786E-06 -2.52717E-08 9.50604E-11 -1.29592E-14 9 -3.35657E-01 6.46108E-06 -1.37717E-08 -5.13782E-11 9.09925E-13 26 0.00000E+00 -4.23342E-05 7.45101E-08 -2.48716E-10 7.05368E-13 27 0.00000E+00 -3.10941E-05 8.91765E-08 -1.49046E-10 6.40234E-13 Face number A12 8 -2.99395E-16 9 -2.08971E-15 26 0.00000E+00 27 0.00000E+00 [Examples]

[0159] (1) Optical configuration of the optical system Figure 36 is a cross-sectional view of the lens configuration of the optical system of Embodiment 8 according to the present invention when it is in focus at infinity.

[0160] The optical system consists of, in order from the object side, a first lens group G1 with positive refractive power, a second lens group G2 with negative refractive power, a third lens group G3 with positive refractive power, and a fourth lens group G4 with negative refractive power. When focusing from an object at infinity to a nearby object, the first lens group G1 and the fourth lens group G4 are fixed in the direction of the optical axis, while the second lens group G2 moves towards the image side and the third lens group G3 moves towards the object side. The aperture diaphragm S is located inside the first lens group G1.

[0161] The configuration of each lens group is described below. The first lens group G1 consists of, in order from the object side, a positive refractive power cemented lens formed by joining a biconcave lens L1 and a biconvex lens L2, a negative meniscus lens L3 with its convex surface facing the object, a biconvex lens L4, a negative meniscus lens L5 with its convex surface facing the object, a negative refractive power cemented lens formed by joining a biconcave lens L6 and a biconvex lens L7, an aperture diaphragm S, and a biconvex lens L8.

[0162] The second lens group G2 consists of, in order from the object side, a negative meniscus lens L9 with its convex surface facing the object side, and a biconvex lens L10.

[0163] The third lens group G3 consists of a biconvex lens L11.

[0164] The fourth lens group G4 consists of, in order from the object side, a biconvex lens L12, a negative meniscus lens L13 with its convex surface facing the object side, and a negative meniscus lens L14 with its convex surface facing the object side.

[0165] (2) Numerical Examples Next, we will describe an example of applying specific numerical values ​​to the optical system. Below, we show the "surface data," "various data," "variable interval (when in focus)," "focal length of each lens group," and "aspherical data" of the optical system.

[0166] [Surface data] Face number RD Nd νd 1 -383.2756 1.5000 1.92286 20.88 2 159.6775 4.6368 1.89930 35.51 3 -206.6054 0.5000 4 192.7697 1.6500 1.49700 81.61 5 21.7668 17.9391 6 0.0000 2.8000 7 29.9836 6.1586 1.92439 23.96 8 -332.8322 0.2000 9ASPH 89.8504 1.3200 1.85135 40.10 10ASPH 24.7941 6.4858 11 -39.1059 1.2500 1.84666 23.78 12 25.8283 9.5478 1.77250 49.62 13 -39.9770 2.0000 14STOP 0.0000 2.0000 15 63.5839 5.5981 1.77250 49.62 16 -96.0612 D(16) 17 390.3404 1.2000 1.74077 27.76 18 40.4417 3.3313 19 237.4962 3.7739 1.92286 20.88 20 -89.6564 D(20) 21 56.9933 4.2450 1.77250 49.62 22 -1377.1300 D(22) 23 41.5995 7.1973 1.49700 81.61 24 -71.5673 0.2000 25 125.8501 1.5449 1.78667 23.94 26 24.2525 5.6791 27ASPH 424.4833 1.8500 1.85108 40.12 28ASPH 115.8130 3.1000 29 0.0000 10.9000 30 0.0000 2.5000 1.51680 64.20 31 0.0000 D(31)

[0167] [Various items] The closest shooting distance to INF. F 29.0933 28.1356 Fno 1.4500 1.4733 W 36.9290 36.0637 Y 21.633 21.633 BF 17.5000 17.5000

[0168] [Variable interval (when in focus)] Shooting distance INF Closest D(0) ∞ 330.0429 D(16) 1.9719 4.9204 D(20) 7.3703 2.3161 D(22) 0.5500 2.6557 D(31) 1.0000 1.0000

[0169] [Focal length of each lens group] Group Surface number Focal length G1 1-16 40.9541 G2 17-20 -825.245 G3 21-22 70.9373 G4 23-28 -95.2085

[0170] [Aspherical data] Surface number k A4 A6 A8 A10 9 0.00000E+00 -4.12277E-06 -2.81947E-08 8.70743E-11 3.56984E-14 10 -3.50599E-01 6.46480E-06 -1.84803E-08 -4.39047E-11 7.82031E-13 27 0.00000E+00 -3.82861E-05 8.62244E-08 -1.91624E-10 3.68250E-13 28 0.00000E+00 -2.72470E-05 1.02161E-07 -1.33095E-10 3.82708E-13 Face number A12 9 -3.35643E-16 10 -1.67421E-15 27 0.00000E+00 28 0.00000E+00

[0171] [Conditional expression corresponding value] Example 1 Example 2 Example 3 Example 4 Conditional expression (1) f1 / f2 -0.20 -0.35 -0.47 -0.42 Conditional expression (2) ν2 20.88 17.98 20.88 20.88 Conditional expression (3) f / f2 -0.18 -0.33 -0.41 -0.36 Conditional expression (4) ν1 20.88 22.97 23.42 24.06 Conditional expression (5) f1R 43.16 43.41 69.17 73.71 Condition (6) (R1f + R1r) / (R1f -R1r) -8.23 0.48 -0.14 0.10 Conditional expression (7) BF / Y 0.81 0.81 0.84 0.81 Conditional equation (8) FD / f 1.24 1.13 0.99 1.0 2 article Condition (10)βb 1.08 1.35 1.30 1.30 Example 5 Example 6 Example 7 Example 8 Conditional expression (1) f1 / f2 -0.22 -0.23 -0.05 -0.05 Conditional expression (2) ν2 20.88 23.96 20.88 20.88 Conditional expression (3) f / f2 -0.18 -0.19 -0.03 -0.04 Conditional expression (4) ν1 23.78 23.78 20.88 20.88 Conditional expression (5) f1R 42.77 43.33 52.10 50.30 Conditional expression (6) (R1f + R1r) / (R1f -R1r) -6.11 -5.10 -7.27 -6.30 Conditional expression (7) BF / Y 0.81 0.81 0.81 0.81 Conditional equation (8) FD / f 1.18 1.18 1.25 1.27 article Condition (10)βb 1.12 1.07 1.16 1.13 [Industrial applicability]

[0172] According to the present invention, it is possible to provide an optical system and imaging device that are bright, large-aperture lenses with a small F-number, while suppressing image plane fluctuations and chromatic aberration across the entire focusing range. [Explanation of Symbols]

[0173] G1...First lens group G2...Second lens group G3...Third lens group G4...4th lens group S ···Opening diaphragm CG...cover glass IP...Image plane

Claims

1. Starting from the object side, it consists of a first lens group with positive refractive power, a second lens group with negative refractive power, a third lens group with positive refractive power, and a fourth lens group with negative refractive power. The second lens group comprises at least one positive lens and at least one negative lens. An optical system that satisfies the following equations (2), (6), and (10) when focusing from infinity to the closest point, wherein the first lens group and the fourth lens group are fixed with respect to the image plane, and the second lens group and the third lens group move along the optical axis direction, respectively. ν2 ≦ 20.88 (2) -10.0≦(R1f+R1r) / (R1f-R1r)≦0.10 (6) 0.95 ≦ βb ≦ 1.35 (10) however, ν²: Abbe number on the d line of any one of the positive lenses included in the second lens group. R1f: Radius of curvature of the image surface of the lens positioned on the object side, straddling the maximum air gap within the first lens group. R1r: Radius of curvature of the object side of the lens positioned on the image side, straddling the maximum air gap within the first lens group. βb: Lateral magnification of the fourth lens group when focused at infinity.

2. The optical system according to claim 1, satisfying the following formula. -0.50 ≦ f / f2 ≦ -0.01 (3) however, f: Focal length of the optical system when focused at infinity f2: Focal length of the second lens group

3. The optical system according to claim 1 or claim 2, wherein the first lens group has at least one negative lens that satisfies the following formula. however, ν1 ≦ 25.0 (4) ν1: Abbe number of the negative lens included in the first lens group on the d line

4. The optical system according to any one of claims 1 to 3, wherein the first lens group has an aperture and satisfies the following formula. 39.0 ≦ f1R ≦ 85.0 (5) however, f1R: The combined focal length (mm) of the lenses in the first lens group that are on the image side of the aperture.

5. The optical system according to any one of claims 1 to 4, wherein the first lens group is provided with the largest possible air gap among the air gaps arranged between the lens surface of the first lens group closest to the object and the lens surface of the fourth lens group closest to the image.

6. An optical system according to any one of claims 1 to 5, satisfying the following formula. 0.5 ≦ BF / Y ≦ 1.3 (7) however, BF: Distance along the optical axis from the top of the outermost image-side surface of the fourth lens group to the image plane. Y: Maximum image height of the optical system

7. The optical system according to any one of claims 1 to 6, wherein the first lens group has at least one cemented lens.

8. An optical system according to any one of claims 1 to 7, satisfying the following formula. 0.80 ≦ FD / f ≦ 1.50 (8) however, FD: Distance along the optical axis from the lens surface closest to the object in the second lens group to the lens surface closest to the image in the fourth lens group when in focus at infinity. f: Focal length of the optical system when focused at infinity

9. An imaging device characterized by comprising an optical system according to any one of claims 1 to 8, and an image sensor on the image side of the optical system that converts an optical image formed by the optical system into an electrical signal.

Images