Optical system and camera device

Abstract

The challenge is to provide a compact optical system and imaging device with high optical performance from infinity to near. The solution lies in an optical system and an imaging device equipped with this optical system, wherein the optical system, from the object side, consists of a front group (G1), a first focusing lens group (G2) with negative optical power, and a rear group (G3-G5). The rear group (G3-G5) includes a second focusing lens group (G4) with negative optical power. During focusing, the front group (G1) is fixed relative to the image plane (IP), and the first and second focusing lens groups (G2 and G4) move along the optical axis. This optical system satisfies a specified condition.

Description

Technical Field

[0001] This invention relates to optical systems and imaging devices. Background Technology

[0002] In recent years, small imaging devices using solid-state imaging elements, such as digital cameras, have become increasingly popular. Along with this, there are high demands on small imaging systems, requiring miniaturization of the optical systems they incorporate. Furthermore, there is a high demand for high performance; in optical systems capable of high magnification for close-up photography, high optical performance is required from infinity to extremely close distances. Therefore, a so-called floating system, which suppresses aberrations by moving multiple lens groups during focusing, has been adopted. However, in optical systems employing the floating system, reducing the travel of each focusing lens group required for focusing significantly contributes to the miniaturization of the optical system and, consequently, the lens barrel. Therefore, minimizing this travel has become a key challenge.

[0003] Patent Document 1 discloses the following invention: it consists of a first lens group with positive optical power, a second lens group with negative optical power, a third lens group with positive optical power, and a fourth lens group with positive optical power, arranged sequentially from the object side, and employs a floating method in which the second and third lens groups move in the optical axis direction during focusing.

[0004] Patent documents 2 and 3 disclose the following invention: starting from the object side, it consists of a first lens group with positive optical power, a second lens group with negative optical power, a third lens group with negative optical power, and a fourth lens group with positive optical power, and adopts a floating method in which the second lens group and the third lens group move in the optical axis direction during focusing.

[0005] Prior art literature

[0006] Patent documents

[0007] [Patent Document 1] Japanese Patent Application Publication No. 9-211319

[0008] [Patent Document 2] Japanese Patent Application Publication No. 62-231918

[0009] [Patent Document 3] Japanese Patent Application Publication No. 59-116709 Summary of the Invention

[0010] The problem that the invention aims to solve

[0011] In the optical system of Patent Document 1, the focusing sensitivity of the third lens group with positive optical power is small, resulting in a large stroke, which hinders the miniaturization of the optical system.

[0012] In the optical systems of Patent Documents 2 and 3, the focusing sensitivity of the third lens group with negative optical power is low, resulting in a large stroke and hindering the miniaturization of the optical system.

[0013] Therefore, the objective of this invention is to provide an optical system that has high optical performance and is small in size, from infinity to near.

[0014] Methods for solving problems

[0015] To address the aforementioned issues, the optical system of the present invention is characterized by comprising, from the object side, a front group, a first focusing lens group having negative optical power, and a rear group in sequence.

[0016] The rear group includes a second focusing lens group with negative optical power.

[0017] During focusing, the front group is fixed relative to the image plane, while the first focusing lens group and the second focusing lens group move along the optical axis.

[0018] The optical system satisfies the following condition:

[0019] 2.00≤|(1-βfO1×βfO1)×βfO1r×βfO1r|····(1)

[0020] 2.00≤|(1-βfO2×βfO2)×βfO2r×βfO2r|····(2)

[0021] in,

[0022] βfO1: Horizontal magnification when the first focusing lens group is focused at infinity.

[0023] βfO1r: The combined horizontal magnification of all lenses positioned further on the image side than the first focusing lens group when focused at infinity.

[0024] βfO2: Horizontal magnification when the second focusing lens group is focused at infinity.

[0025] βfO2r: The combined horizontal magnification of all lenses positioned on the image side further than the second focusing lens group when focusing at infinity.

[0026] In addition, in order to solve the above-mentioned problems, the imaging device according to the present invention is characterized by comprising: the above-described optical system, and an imaging element that converts the optical image formed by the optical system into an electrical signal.

[0027] Invention Effects

[0028] According to the present invention, it is possible to provide an optical system and imaging device with high optical performance from infinity to near distance and in a small size. Attached Figure Description

[0029] Figure 1 This is a cross-sectional view of the optical system of Example 1.

[0030] Figure 2 This is an aberration diagram of the optical system of Example 1 at infinity focus.

[0031] Figure 3 This is an aberration diagram of the optical system in Example 1 under extremely close focusing conditions.

[0032] Figure 4 This is a cross-sectional view of the optical system in Example 2.

[0033] Figure 5 This is an aberration diagram of the optical system in Example 2 at infinity focus.

[0034] Figure 6 This is an aberration diagram of the optical system in Example 2 under extremely close focusing conditions.

[0035] Figure 7 This is a cross-sectional view of the optical system in Example 3.

[0036] Figure 8 This is an aberration diagram of the optical system in Example 3 at infinity focus.

[0037] Figure 9 This is an aberration diagram of the optical system in Example 3 under extremely close focusing conditions.

[0038] Figure 10 This is a cross-sectional view of the optical system in Example 4.

[0039] Figure 11 This is an aberration diagram of the optical system in Example 4 at infinity focus.

[0040] Figure 12 This is an aberration diagram of the optical system in Example 4 under extremely close focusing conditions.

[0041] Figure 13 This is a cross-sectional view of the optical system in Example 5.

[0042] Figure 14 This is an aberration diagram of the optical system in Example 5 at infinity focus.

[0043] Figure 15 This is an aberration diagram of the optical system in Example 5 under extremely close focusing conditions.

[0044] Figure 16 This is a diagram schematically illustrating an example of the configuration of a camera device according to one embodiment of the present invention.

[0045] Explanation of reference numerals in the attached figures

[0046] S···Aperture Stop

[0047] CG··· Protective Glass

[0048] IP... Image

[0049] G1···First Lens Group

[0050] G2···Second Lens Group

[0051] G3···Third Lens Group

[0052] G4...4th Lens Group

[0053] G5···5th Lens Group

[0054] G6···The 6th Lens Group

[0055] 1. Mirrorless single-lens camera

[0056] 2. Camera body

[0057] 3···Eye tube

[0058] 21···CCD Sensor

[0059] 22··· Protective Glass Detailed Implementation

[0060] The following describes embodiments of the optical system and imaging device according to the present invention. The optical system and imaging device described below are 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 this embodiment.

[0061] 1. Optical system

[0062] 1-1. Optical Components

[0063] The optical system of the present invention comprises, from the object side, a front group, a first focusing lens group with negative optical power that moves in the direction of the optical axis during focusing, and a rear group having at least a second focusing lens group with negative optical power that moves in the direction of the optical axis during focusing. During focusing, the front group is fixed relative to the image plane, while at least the first and second focusing lens groups move in a so-called floating manner, thereby enabling miniaturization of the optical system.

[0064] (1) Pre-group

[0065] The front group can be any lens group that is fixed relative to the image plane during focusing (front lens group), and its specific configuration is not particularly limited. Furthermore, it is preferred that the front group has at least one positive lens, which facilitates the suppression of chromatic aberration and achieves good optical performance. It is also preferred that the front group has a negative lens, which facilitates the suppression of chromatic aberration and achieves good optical performance. Furthermore, it is preferred that the front group has at least one combined lens formed by combining a positive lens and a negative lens, which facilitates the suppression of chromatic aberration and the suppression of the sensitivity of each lens. Furthermore, it is preferred that the front group is a lens group with positive optical power, which facilitates the suppression of various aberrations and achieves miniaturization. Furthermore, it is preferable that the front group has at least three positive lenses and one negative lens. Furthermore, it is preferable that the front group, from the object side, has at least one positive lens, one positive lens, one negative lens, and one positive lens in that order.

[0066] Here, a "lens group" consists of one or more adjacent lenses, and the spacing between it and adjacent lens groups along the optical axis changes during focusing. When a lens group consists of multiple lenses, it is assumed that the distance on the optical axis between the lenses contained in that lens group does not change during focusing.

[0067] (2) First focusing lens group

[0068] The first focusing lens group can be any lens group with negative optical power, and it may contain at least one lens with negative optical power; its specific configuration is not particularly limited. The first focusing lens group may also contain at least one lens with positive optical power and at least one lens with negative optical power. Furthermore, having at least one combined lens (composed of a positive lens and a negative lens) in the first focusing lens group is preferable as it facilitates the suppression of chromatic aberration and the sensitivity of each lens.

[0069] (3) Rear group

[0070] The rear group only needs to have a second focusing lens group, and its specific configuration is not particularly limited. The rear group may not only have a second focusing lens group, but also have more than one lens group with positive optical power, or it may have more than one lens group with positive optical power and more than one lens group with negative optical power.

[0071] The rear group preferably includes a lens group (intermediate lens group) with positive optical power located further on the object side than the second focusing lens group. This configuration converges the light incident on the second focusing lens group, thus enabling further miniaturization of the second focusing lens group. Furthermore, it is even more preferable to include a lens group with positive optical power located further on the image side than the second focusing lens group. This configuration effectively corrects field curvature, enabling a high-performance optical system. Additionally, it is more preferable that the lens of the rear group positioned closest to the image side has a convex shape on the image side. This configuration suppresses ghosting caused by reflections between the lens and the image plane, achieving a high-performance optical system. Furthermore, the rear group preferably includes a lens group on the image side that is fixed relative to the image plane during focusing. This lens group having negative optical power is preferable for suppressing field curvature.

[0072] (4) Second focusing lens group

[0073] The second focusing lens group simply needs to be a group with negative optical power and have at least one lens with negative optical power; its specific configuration is not particularly limited. The second focusing lens group may also have at least one lens with positive optical power and at least one lens with negative optical power. Furthermore, it is preferable that the second focusing lens group has at least one combined lens formed by combining a positive lens and a negative lens, as this facilitates the suppression of chromatic aberration and the sensitivity of each lens.

[0074] Furthermore, the rear group may not only have a second focusing lens group, but also a third focusing lens group that moves along the optical axis during focusing. This allows for focusing with higher precision. The third focusing lens group preferably has positive optical power and is positioned on the object side or image side of the second focusing lens group.

[0075] (5) Aperture stop

[0076] In this optical system, the configuration of the aperture stop is not particularly limited. Here, the aperture stop refers to the aperture stop that defines the beam diameter of the optical system, i.e., the aperture stop that defines the Fno of the optical system. It is preferable to place the aperture stop within the rear group for miniaturization of the aperture stop unit. Furthermore, when the rear group includes a lens group with negative optical power, it is preferable to place the aperture stop closer to the object side than the lens group with negative optical power. To counteract the negative distortion and negative field curvature generated in the front group, it is preferable to generate aberrations in the same direction before and after the aperture stop. Therefore, by placing the aperture stop closer to the image side than the first lens group and closer to the object side than the lens group with negative optical power in the rear group, aberrations can be efficiently counteracted before and after the aperture stop, resulting in an optical system with high optical performance.

[0077] The aperture stop is preferably positioned between the first focusing lens group and the second focusing lens group, and more preferably positioned before or after an intermediate lens group or within an intermediate lens group that is positioned closer to the object side than the second focusing lens group. With this configuration, excellent aberration correction can be achieved in extremely close focusing conditions, enabling the construction of a high-performance optical system.

[0078] 1-2. Actions

[0079] (1) Focusing

[0080] This optical system only requires that at least the first and second focusing lens groups move along the optical axis when focusing from infinity to near, and the specific operation is not particularly limited. For example, it is preferable that the first and second focusing lens groups move along the optical axis to the image side when focusing from infinity to near. Furthermore, it is more preferable that the first and second focusing lens groups move along the optical axis with different amounts of movement when focusing from infinity to near. With this configuration, higher optical performance can be achieved from infinity to near. Even more preferable is that, when focusing from infinity to near, the second focusing lens group moves a greater amount of movement along the optical axis relative to the image plane compared to the first focusing lens group. With this configuration, particularly high optical performance can be achieved from infinity to near. Furthermore, it is even more preferable that, in addition to the first and second focusing lens groups, there is also a lens group that moves when focusing from infinity to near. This configuration enables higher optical performance from infinity to near.

[0081] 1-3.Conditional expression

[0082] The optical system preferably adopts the above-described configuration and satisfies at least one of the conditions described below.

[0083] 1-3-1.Conditional expression (1)

[0084] 2.00≤|(1-βfO1×βfO1)×βfO1r×βfO1r|····(1)

[0085] in,

[0086] βfO1: Horizontal magnification when focusing at infinity using the first focusing lens group.

[0087] βfO1r: The combined horizontal magnification of all lenses positioned on the image side further from the first focusing lens group at infinity when focused.

[0088] Condition (1) is a condition that specifies the focusing sensitivity of the first focusing lens group. By satisfying condition (1), the amount of movement during focusing can be suppressed, making it easier to miniaturize the lens barrel. Here, focusing sensitivity refers to the change in the image plane relative to the amount of focusing movement.

[0089] In contrast, if the value of condition (1) is lower than the lower limit, the focusing sensitivity of the first focusing lens group becomes lower and the amount of movement during focusing becomes larger, making it difficult to achieve miniaturization.

[0090] Regarding achieving the aforementioned effect, the lower limit of conditional expression (1) is preferably 2.10, more preferably 2.20. Furthermore, the upper limit of conditional expression (1) is preferably 20.00, more preferably 10.00, and even more preferably 8.00.

[0091] Furthermore, when using these preferred lower or upper limits, the inequality sign (≤) with an equal sign can be replaced with an inequality sign (<) in condition (1). The same principle applies to other conditional expressions.

[0092] 1-3-2.Conditional expression (2)

[0093] 2.00≤|(1-βfO2×βfO2)×βfO2r×βfO2r|····(2)

[0094] in,

[0095] βfO2: Horizontal magnification at infinity when focusing on the second focusing lens group.

[0096] βfO2r: The combined horizontal magnification of all lenses positioned further to the image side than the second focusing lens group at infinity when focused.

[0097] Condition (2) is a condition that specifies the focusing sensitivity of the second focusing lens group. By satisfying condition (2), the amount of movement during focusing can be suppressed, making it easier to miniaturize the lens barrel.

[0098] In contrast, if the value of condition (2) is lower than the lower limit, the focusing sensitivity of the second focusing lens group becomes lower and the amount of movement during focusing becomes larger, making it difficult to achieve miniaturization.

[0099] Regarding achieving the aforementioned effect, the lower limit of conditional expression (2) is preferably 2.10, more preferably 2.20. Furthermore, the upper limit of conditional expression (2) is preferably 20.00, more preferably 10.00, and even more preferably 8.00.

[0100] 1-3-3.Conditional expression (3)

[0101] 0.005≤dPgF····(3)

[0102] in,

[0103] dPgF: The anomalous dispersion of a lens with positive optical power at the g-line (435.83nm) and F-line (486.13nm) is expressed by the following formula.

[0104] dPgF=PgF+0.0018×vd-0.6483

[0105] Here,

[0106] vd: The Abbe number of a lens with positive optical power.

[0107] PgF: Partial dispersion ratio of a lens with positive optical power at the g-line and F-line.

[0108] In addition, the partial dispersion ratio is defined by PgF=(ng-nF) / (nF-nC), where ng, nF, and nC represent the refractive indices corresponding to the g-line, F-line, and C-line (656.28nm), respectively.

[0109] Condition (3) is a condition that specifies the aberrant dispersion of the positive lenses included in the front group. By having at least one of the positive lenses included in the front group satisfy condition (3), chromatic aberration can be well corrected, and a high-performance optical system can be easily realized.

[0110] In contrast, if the value of condition (3) is lower than the lower limit, the abnormal dispersion of the positive lens becomes smaller, and it cannot correct chromatic aberration well, thus making it difficult to achieve high performance.

[0111] Regarding achieving the aforementioned effect, the lower limit of conditional expression (3) is preferably 0.007, more preferably 0.009. Furthermore, the upper limit of conditional expression (3) is preferably 0.060, more preferably 0.050, and even more preferably 0.040.

[0112] 1-3-4.Conditional expression (4)

[0113] 0.05≤ff / f≤0.70····(4)

[0114] in,

[0115] ff: Focal length of the front element

[0116] f: Focal length of the optical system when focusing at infinity

[0117] Condition (4) is a condition that specifies the ratio of the focal length of the front group to the focal length of the optical system when focusing at infinity. By satisfying condition (4), various aberrations can be well corrected, and the overall optical length can be shortened, making it easy to miniaturize the lens barrel.

[0118] In contrast, if the value of condition (4) is lower than the lower limit, the optical power of the front group becomes stronger, making it difficult to correct various aberrations. On the other hand, if the value of condition (4) exceeds the upper limit, the optical power of the front group becomes weaker, and the overall optical length becomes longer, making it difficult to achieve miniaturization.

[0119] Regarding achieving the aforementioned effect, the lower limit of conditional expression (4) is preferably 0.10, more preferably 0.20. Furthermore, the upper limit of conditional expression (4) is preferably 0.60, more preferably 0.50, and even more preferably 0.45.

[0120] 1-3-5.Conditional expression (5)

[0121] -0.90≤fr / f≤-0.05····(5)

[0122] in,

[0123] fr: The combined focal length at infinity of all lenses positioned further to the image side than the previous group when focusing.

[0124] f: Focal length of the optical system when focusing at infinity

[0125] Condition (5) is a condition that specifies the ratio of the combined focal length of all lenses positioned closer to the image side than the front group when focusing at infinity to the focal length of the optical system when focusing at infinity. By satisfying condition (5), various aberrations can be well corrected, and the overall optical length can be shortened by increasing the telescope, making it easy to miniaturize the lens barrel.

[0126] In contrast, if the value of condition (5) is lower than the lower limit, the negative optical power of the lens group positioned closer to the image side than the previous group becomes weaker, the overall optical length becomes longer, and it is difficult to achieve miniaturization of the lens barrel. On the other hand, if the value of condition (5) exceeds the upper limit, the negative optical power of the lens group positioned closer to the image side than the previous group becomes stronger, and it is difficult to correct various aberrations.

[0127] Regarding achieving the aforementioned effect, the lower limit of conditional expression (5) is preferably -0.80, more preferably -0.70. Furthermore, the upper limit of conditional expression (5) is preferably -0.10, more preferably -0.20, and even more preferably -0.30.

[0128] 1-3-6.Conditional expression (6)

[0129] -1.00≤ffO1 / f≤-0.05····(6)

[0130] in,

[0131] ffO1: Focal length of the first focusing lens group

[0132] f: Focal length of the optical system when focusing at infinity

[0133] Condition (6) is a condition used to specify the ratio of the focal length of the first focusing lens group to the focal length of the optical system when focusing at infinity. By satisfying condition (6), various aberrations can be well corrected and the amount of movement during focusing can be suppressed, making it easy to achieve miniaturization of the lens barrel.

[0134] In contrast, if the value of condition (6) is lower than the lower limit, the optical power of the first focusing lens group becomes weaker, and the amount of movement during focusing becomes larger, making it difficult to achieve miniaturization. On the other hand, if the value of condition (6) exceeds the upper limit, the negative optical power of the first focusing lens group becomes stronger, making it difficult to correct various aberrations.

[0135] Regarding achieving the aforementioned effect, the lower limit of condition (6) is preferably -0.90, more preferably -0.80, further preferably -0.60, and even more preferably -0.50. Additionally, the upper limit of condition (6) is preferably -0.10, more preferably -0.20, and even more preferably -0.30.

[0136] 1-3-7.Conditional expression (7)

[0137] -1.00≤ffO2 / f≤-0.05····(7)

[0138] in,

[0139] ffO2: Focal length of the second focusing lens group

[0140] f: Focal length of the optical system when focusing at infinity

[0141] The above condition (7) is a condition used to specify the ratio of the focal length of the second focusing lens group to the focal length of the optical system when focusing at infinity. By satisfying condition (7), various aberrations can be well corrected and the amount of movement during focusing can be suppressed, making it easy to achieve miniaturization of the lens barrel.

[0142] In contrast, if the value of condition (7) is lower than the lower limit, the optical power of the second focusing lens group becomes weaker, thus increasing the amount of movement during focusing and making it difficult to achieve miniaturization of the lens barrel. On the other hand, if the value of condition (7) exceeds the upper limit, the negative optical power of the second focusing lens group becomes stronger, making it difficult to correct various aberrations.

[0143] Regarding achieving the aforementioned effect, the lower limit of condition (7) is preferably -0.90, more preferably -0.80, and even more preferably -0.60. Furthermore, the upper limit of condition (7) is preferably -0.10, more preferably -0.20, and even more preferably -0.30.

[0144] 1-3-8.Conditional expression (8)

[0145] -2.50≤ff / ffO1≤-0.80····(8)

[0146] in,

[0147] ff: Focal length of the front element

[0148] ffO1: Focal length of the first focusing lens group

[0149] The above condition (8) is used to specify the ratio of the focal length of the front group to the focal length of the first focusing lens group. By satisfying condition (8), various aberrations can be well corrected, and the overall optical length can be shortened, making it easy to achieve miniaturization of the lens barrel.

[0150] In contrast, if the value of condition (8) is lower than the lower limit, the optical power of the front group becomes weaker and the overall optical length becomes longer, making it difficult to miniaturize the lens barrel. On the other hand, if the value of condition (8) exceeds the upper limit, the optical power of the front group becomes stronger, making it difficult to correct various aberrations.

[0151] Regarding achieving the aforementioned effect, the lower limit of conditional expression (8) is preferably -2.40, more preferably -2.30, further preferably -2.00, and even more preferably -1.60. Additionally, the upper limit of conditional expression (8) is preferably -0.85, more preferably -0.90, further preferably -0.95, and even more preferably -1.00.

[0152] 2. Camera device

[0153] 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 described above, and an imaging element that converts the optical image formed by the optical system into an electrical signal. Furthermore, the imaging element is preferably disposed on the image side of the optical system.

[0154] Here, the imaging element is not particularly limited, and solid-state imaging elements such as CCD (Charge Coupled Device) sensors and CMOS (Complementary Metal Oxide Semiconductor) sensors can also be used. The imaging device according to this invention is suitable for imaging devices such as digital cameras and camcorders that use these solid-state imaging elements. Furthermore, this imaging device is applicable to various imaging devices such as SLR cameras, mirrorless single-lens cameras, digital cameras, surveillance cameras, vehicle-mounted cameras, and drone-mounted cameras. Moreover, these imaging devices can be either interchangeable-lens or fixed-lens types where the lens is fixed to the housing. The optical system according to this invention is particularly suitable as an optical system for imaging devices that mount large, full-size imaging elements. This optical system is small and lightweight overall and has high optical performance, thus enabling the acquisition of high-quality images when used as an optical system for such imaging devices.

[0155] Figure 16This diagram schematically illustrates an example of the configuration of the camera device according to this embodiment. Figure 16 As shown, the mirrorless single-lens camera 1 has a camera body 2 and a lens barrel 3 that can be detached from the camera body 2. The mirrorless single-lens camera 1 is one type of imaging device.

[0156] The camera body 2 has a CCD sensor 21 as an image-receiving element and a protective glass 22. The CCD sensor 21 is located at the central axis of the optical system 30, which is disposed in the camera body 2 and mounted in the lens barrel 3 on the camera body 2. The camera body 2 may also have an IR cutoff filter or a parallel plate without substantial optical power instead of the protective glass 22.

[0157] The present invention will now be illustrated with examples and described in detail. However, the present invention is not limited to the following examples.

[0158] [Example 1]

[0159] (1) Optical structure

[0160] Figure 1 This is a cross-sectional view of the optical system of Embodiment 1 of the present invention during infinity focusing and extremely close focusing. The optical system, from the object side, consists of a first lens group G1 (front group) with positive optical power, a second lens group G2 (first focusing lens group) with negative optical power, a third lens group G3 with positive optical power, a fourth lens group G4 (second focusing lens group) with negative optical power, and a fifth lens group G5 with positive optical power. In this embodiment, the rear group consists of the third lens group G3 to the fifth lens group G5.

[0161] When focusing from an object at infinity to a closer object, the second lens group G2 and the fourth lens group G4 move along the optical axis from the object side to the image side by different amounts of movement.

[0162] The aperture stop S is configured within the third lens group G3.

[0163] The first lens group G1 consists of, from the object side, a biconvex lens, a combined lens formed by combining a biconvex lens with a negative concave-convex lens, and a biconvex lens with aspherical surfaces on both sides.

[0164] The second lens group G2 is composed of a combined lens formed by sequentially joining a negative concave-convex lens and a positive concave-convex lens from the object side.

[0165] The third lens group G3, starting from the object side, consists of a combined lens formed by combining a biconvex lens and a biconcave lens, an aperture stop S, and a biconvex lens.

[0166] The fourth lens group G4 is composed of a combined lens formed by sequentially joining a biconcave lens and a positive concave-convex lens, starting from the object side.

[0167] The fifth lens group G5 consists of, from the object side, a combined lens formed by joining a biconvex lens and a biconcave lens, and a negative concave-convex lens.

[0168] In addition, Figure 1 In this context, "IP" stands for image plane, specifically referring to the imaging plane of a solid-state imaging element such as a CCD sensor or CMOS sensor, or the thin film surface of a silver halide film. Furthermore, on the object side of the image plane IP, there is a parallel plate, such as a protective glass CG, which does not possess substantial optical power. These aspects are the same in the lens cross-sectional views shown in other embodiments, and therefore will not be described further hereafter.

[0169] (2) Numerical Examples

[0170] Next, numerical embodiments of the optical system with specific numerical values ​​will be described. Hereinafter, "lens data", "variable specification table", "variable spacing", "aspheric coefficient", and "lens group data" will be used. In addition, the values ​​of each conditional expression (Table 1) will be summarized after Embodiment 5.

[0171] In the (lens data) section, "Surface Number" indicates the sequence number of the lens surface, counting from the object side; "R" indicates the radius of curvature of the lens surface; "D" indicates the lens wall thickness or air gap along the optical axis; "Nd" indicates the refractive index at the d-line (wavelength λ = 587.56 nm); "ABV" indicates the Abbe number at the d-line; and "dPgF" indicates the anomalous dispersion of the lens at the g-line (435.83 nm) and F-line (486.13 nm). Additionally, in the "Surface Number" column, "ASP" appended after the surface number indicates that the lens surface is aspherical, and "S" indicates that the surface is an aperture stop. In the "D" column, "D(7)", "D(10)", etc., indicate that the spacing along the optical axis of the lens surface is a variable spacing that changes during focusing. Furthermore, "∞" in the radius of curvature column means infinity, implying that the lens surface is planar.

[0172] In the various specification tables, "f" is the focal length of the optical system, "Fno." is the F-number, and "ω" is the half field of view. These represent the values ​​for focusing at infinity and focusing at extremely close distances, respectively.

[0173] In (variable interval), the values ​​represent the values ​​for focusing at infinity and focusing at extremely close distances, respectively. The same applies to other embodiments.

[0174] (Aspherical coefficient) is defined as follows for aspherical shapes. Where x is the displacement relative to the reference plane along the optical axis, r is the paraxial radius of curvature, H is the height relative to the optical axis in the direction perpendicular to the optical axis, k is the conic coefficient, and An is the aspherical coefficient of order n. Additionally, in the "Aspherical Coefficients" table, "E±XX" represents an exponential marker, meaning "×10⁻⁶". ±XX ".

[0175] [Formula 1]

[0176]

[0177] The items in the above tables are the same as those in the tables shown in other embodiments, and therefore are omitted in the following description.

[0178] In addition, Figure 2 , Figure 3 The figures show the longitudinal aberration diagrams for focusing on objects at infinity and at extremely close distances using the optical system. From left to right, the longitudinal aberration diagrams represent spherical aberration (mm), astigmatism (mm), and distortion aberration (%). In the spherical aberration diagram, the solid line represents the spherical aberration at the d-line (wavelength 587.56 nm), the long dashed line represents the spherical aberration at the F-line (wavelength 486.13 nm), and the short dashed line represents the spherical aberration at the C-line (wavelength 656.28 nm). In the astigmatism diagram, the vertical axis is the half-field angle (ω), and the horizontal axis is defocus; the solid line represents the sagittal image plane (S) of the d-line, and the dashed line represents the meridional image plane (T) of the d-line. In the distortion aberration diagram, the vertical axis is the half-field angle (ω), and the horizontal axis is the distortion aberration. These properties are the same in the aberration diagrams shown in other embodiments, and therefore, descriptions are omitted below.

[0179] (Lens data)

[0180]

[0181]

[0182] (Various specifications)

[0183] Infinity Very close f 103.0119 39.6323 Fno. 2.9099 5.7631 ω 11.7947 5.9246

[0184] (Variable interval)

[0185] Infinity Very close magnification - -1.0 D(7) 2.0000 10.3740 D(10) 12.1146 3.7407 D(16) 2.0022 20.7626 D(19) 26.5836 7.8232

[0186] (Astronomical coefficient)

[0187] Face number K A4 A6 A8 A10 6 0.00000E+00 -2.07070E-06 -2.05319E-09 -5.07994E-12 1.31403E-14 7 0.00000E+00 3.30845E-06 -4.59751E-09 7.06002E-12 -5.12319E-16 11 0.00000E+00 7.21661E-06 9.98081E-09 0.00000E+00 0.00000E+00

[0188] (Lens group data)

[0189] Group Face number focal length G1 1-7 35.6813 G2 8-10 -34.4254 G3 11-16 47.1619 G4 17-19 -48.0117 G5 20-24 496.9200

[0190] [Example 2]

[0191] (1) Optical structure

[0192] Figure 4 This is a cross-sectional view of the optical system of Embodiment 2 of the present invention during infinity focusing and extremely close focusing. The optical system, from the object side, consists of a first lens group G1 (front group) with positive optical power, a second lens group G2 (first focusing lens group) with negative optical power, a third lens group G3 with positive optical power, a fourth lens group G4 (second focusing lens group) with negative optical power, a fifth lens group G5 with positive optical power, and a sixth lens group G6 with negative optical power. In this embodiment, the rear group consists of the third lens group G3 to the sixth lens group G6. In Embodiment 2, the fifth lens group G5 functions as the aforementioned third focusing lens group, so that when focusing from an object at infinity to a close object, the second lens group G2, the fourth lens group G4, and the fifth lens group G5 move along the optical axis from the object side to the image side by different amounts of movement.

[0193] The aperture stop S is configured within the third lens group G3.

[0194] The first lens group G1 consists of, from the object side, a biconvex lens, a combined lens formed by joining a biconvex lens and a biconcave lens, and a biconvex lens with aspherical surfaces on both sides.

[0195] The second lens group G2 is composed of a combined lens formed by sequentially joining a negative concave-convex lens and a positive concave-convex lens from the object side.

[0196] The third lens group G3, starting from the object side, consists of a combined lens formed by combining a biconvex lens and a biconcave lens, an aperture stop S, and a biconvex lens.

[0197] The fourth lens group G4 is composed of a combined lens formed by sequentially joining a biconcave lens and a positive concave-convex lens, starting from the object side.

[0198] The fifth lens group G5 consists of a combined lens formed by joining a biconvex lens and a biconcave lens, starting from the object side.

[0199] The sixth lens group, G6, consists of negative concave and convex lenses.

[0200] (2) Numerical Examples

[0201] Next, as a numerical embodiment of this optical system, specific numerical values ​​are used, representing "lens data," "variable specification tables," "variable spacing," "aspheric coefficient," and "lens group data." Additionally, in... Figure 5 and Figure 6The diagram shows the longitudinal aberrations of the optical system when focusing at infinity and at very close distances.

[0202] (Lens data)

[0203] Face number R D Nd ABV dPgF 1 171.4013 2.7631 1.72916 54.67 -0.0046 2 -1000.0000 0.2000 3 101.9923 3.5372 1.55032 75.50 0.0276 4 -250.0000 1.0000 1.85478 24.80 0.0109 5 272.4347 0.2000 6ASP 35.2020 5.8033 1.72903 54.04 -0.0064 7ASP -381.8077 D(7) 8 172.7373 1.0000 1.90366 31.31 0.0028 9 16.1798 3.8816 1.92286 20.88 0.0283 10 25.3271 D(10) 11ASP 45.9389 3.1994 1.69350 53.20 -0.0059 12 -500.0000 1.0000 1.92286 20.88 0.0283 13 29.1683 3.1643 14S ∞ 1.5582 15 53.8704 4.2483 1.83400 37.34 -0.0021 16 -43.7564 D(16) 17 -80.3963 0.8000 1.83481 42.72 -0.0067 18 26.3128 2.4748 1.94595 17.98 0.0386 19 81.0145 D(19) 20 54.4198 8.5163 1.90366 31.31 0.0028 21 -25.8712 1.0000 1.84666 23.78 0.0137 22 108.3208 D(22) 23 -35.1520 1.2000 1.92286 20.88 0.0283 24 -61.4852 17.0000 25 ∞ 2.5000 1.51680 64.20 0.0015 26 ∞ 1.0000 27 ∞

[0204] (Various specifications)

[0205] Infinity Very close f 99.6297 38.9937 Fno. 2.8846 5.7624 ω 12.1849 6.0032

[0206] (Variable interval)

[0207] Infinity Very close magnification - -1.0 D(7) 2.0000 10.8284 D(10) 12.5654 3.7370 D(16) 2.0021 27.4699 D(19) 23.3076 2.0242 D(22) 9.0785 4.8940

[0208] (Astronomical coefficient)

[0209] Face number K A4 A6 A8 A10 6 0.00000E+00 -1.60414E-06 -1.84631E-09 -3.59417E-12 1.06097E-14 7 0.00000E+00 2.86807E-06 -3.58717E-09 6.09781E-12 -5.45644E-16 11 0.00000E+00 7.70963E-06 8.85545E-09 0.00000E+00 0.00000E+00

[0210] (Lens group data)

[0211] Group Face number focal length G1 1-7 36.0592 G2 8-10 -33.9550 G3 11-16 49.9438 G4 17-19 -55.6759 G5 20-22 87.0475 G6 23-24 -90.9253

[0212] [Example 3]

[0213] (1) Optical structure

[0214] Figure 7 This is a cross-sectional view of the optical system of Embodiment 3 of the present invention during infinity focusing and extremely close focusing. From the object side, the optical system consists of a first lens group G1 (front group) with positive optical power, a second lens group G2 (first focusing lens group) with negative optical power, a third lens group G3 with positive optical power, a fourth lens group G4 (second focusing lens group) with negative optical power, and a fifth lens group G5 with positive optical power. The rear group consists of the third lens group G3 to the fifth lens group G5.

[0215] In Embodiment 3, the third lens group G3 functions as the third focusing lens group described above, so that when focusing from an object at infinity to a closer object, the second lens group G2, the third lens group G3 and the fourth lens group G4 move along the optical axis from the object side to the image side by different amounts of movement.

[0216] The aperture stop S is configured within the third lens group G3.

[0217] The first lens group G1 consists of, from the object side, a positive concave-convex lens, a combined lens formed by joining a biconvex lens and a biconcave lens, and a biconvex lens with aspherical surfaces on both sides.

[0218] The second lens group G2 is composed of a combined lens formed by sequentially joining a negative concave-convex lens and a positive concave-convex lens from the object side.

[0219] The third lens group G3, starting from the object side, consists of a combined lens formed by combining a biconvex lens and a biconcave lens, an aperture stop S, and a biconvex lens.

[0220] The fourth lens group G4 is composed of a combined lens formed by sequentially joining a biconcave lens and a positive concave-convex lens, starting from the object side.

[0221] The fifth lens group G5 consists of, from the object side, a combined lens formed by joining a biconvex lens and a biconcave lens, and a negative concave-convex lens.

[0222] (2) Numerical Examples

[0223] Next, as a numerical embodiment of this optical system, specific numerical values ​​are used, representing "lens data," "variable specification tables," "variable spacing," "aspheric coefficient," and "lens group data." Additionally, in... Figure 8 and Figure 9 The diagram shows the longitudinal aberrations of the optical system when focusing at infinity and at very close distances.

[0224] (Lens data)

[0225]

[0226]

[0227] (Various specifications)

[0228] Infinity Very close f 101.8439 38.9171 Fno. 2.8838 5.7665 ω 11.9476 5.6524

[0229] (Variable interval)

[0230] Infinity Very close magnification - -1.0 D(7) 2.0000 12.3089 D(10) 11.9899 3.6811 D(16) 2.0011 27.8904 D(19) 29.9728 2.0835

[0231] (Astronomical coefficient)

[0232] Face number K A4 A6 A8 A10 6 0.00000E+00 -2.23064E-06 -1.21617E-09 0.00000E+00 0.00000E+00 7 0.00000E+00 1.64206E-06 -1.67521E-10 0.00000E+00 0.00000E+00 11 0.00000E+00 8.72527E-06 1.00191E-08 0.00000E+00 0.00000E+00

[0233] (Lens group data)

[0234]

[0235]

[0236] [Example 4]

[0237] (1) Optical structure

[0238] Figure 10This is a cross-sectional view of the optical system of Embodiment 4 of the present invention during infinity focusing and extremely close focusing. From the object side, the optical system consists of a first lens group G1 (front group) with positive optical power, a second lens group G2 (first focusing lens group) with negative optical power, a third lens group G3 with positive optical power, a fourth lens group G4 (second focusing lens group) with negative optical power, and a fifth lens group G5 with positive optical power. The rear group consists of the third lens group G3 to the fifth lens group G5.

[0239] In Embodiment 4, the fifth lens group G5 functions as the third focusing lens group described above, so that when focusing from an object at infinity to a closer object, the second lens group G2, the fourth lens group G4, and the fifth lens group G5 move along the optical axis from the object side to the image side by different amounts of movement.

[0240] The aperture stop S is configured within the third lens group G3.

[0241] The first lens group G1 consists of, from the object side, a biconvex lens, a combined lens formed by joining a biconvex lens and a biconcave lens, and a biconvex lens with aspherical surfaces on both sides.

[0242] The second lens group G2 is composed of a combined lens formed by sequentially joining a negative concave-convex lens and a positive concave-convex lens from the object side.

[0243] The third lens group G3, starting from the object side, consists of a combined lens formed by combining a biconvex lens and a biconcave lens, an aperture stop S, and a biconvex lens.

[0244] The fourth lens group G4 is composed of a combined lens formed by sequentially joining a biconcave lens and a positive concave-convex lens, starting from the object side.

[0245] The fifth lens group G5 consists of, from the object side, a combined lens formed by joining a biconvex lens and a biconcave lens, and a negative concave-convex lens.

[0246] (2) Numerical Examples

[0247] Next, as a numerical embodiment of this optical system, specific numerical values ​​are used, representing "lens data," "variable specification tables," "variable spacing," "aspheric coefficient," and "lens group data." Additionally, in... Figure 11 and Figure 12 The diagram shows the longitudinal aberrations of the optical system when focusing at infinity and at very close distances.

[0248] (Lens data)

[0249] Face number R D Nd ABV dPgF 1 171.4013 2.7631 1.72916 54.67 -0.0046 2 -1000.0000 0.2000 3 97.3312 3.6350 1.55032 75.50 0.0276 4 -250.0000 1.0000 1.85478 24.80 0.0109 5 229.8772 0.2000 6ASP 35.6320 5.8808 1.72903 54.04 -0.0064 7ASP -346.8031 D(7) 8 147.3737 1.0000 1.90366 31.31 0.0028 9 16.0234 4.0835 1.92286 20.88 0.0283 10 25.0977 D(10) 11ASP 42.3167 3.4178 1.69350 53.20 -0.0059 12 -500.0000 1.0000 1.92286 20.88 0.0283 13 28.0206 3.2841 14S ∞ 1.2154 15 52.6342 4.3848 1.83400 37.34 -0.0021 16 -41.6370 D(16) 17 -76.2421 0.8000 1.83481 42.72 -0.0067 18 24.2431 2.5401 1.94595 17.98 0.0386 19 71.5090 D(19) 20 54.2631 8.9441 1.90366 31.31 0.0028 21 -25.9057 1.0000 1.84666 23.78 0.0137 22 117.0780 4.7455 23 -40.2514 1.2000 1.92286 20.88 0.0283 24 -80.9946 D(24) 25 ∞ 2.5000 1.51680 64.20 0.0015 26 ∞ 1.0000 27 ∞

[0250] (Various specifications)

[0251] Infinity Very close f 101.8258 39.4173 Fno. 2.8861 5.7635 ω 11.9377 5.9449

[0252] (Variable interval)

[0253]

[0254]

[0255] (Astronomical coefficient)

[0256] Face number K A4 A6 A8 A10 6 0.00000E+00 -1.89258E-06 -2.22936E-09 -4.20496E-12 1.33158E-14 7 0.00000E+00 2.63438E-06 -3.83575E-09 7.17849E-12 -5.46403E-16 11 0.00000E+00 7.42847E-06 1.02339E-08 0.00000E+00 0.00000E+00

[0257] (Lens group data)

[0258] Group Face number focal length G1 1-7 36.5830 G2 8-10 -34.7779 G3 11-16 47.0502 G4 17-19 -50.6477 G5 20-24 436.8180

[0259] [Example 5]

[0260] (1) Optical structure

[0261] Figure 13 This is a cross-sectional view of the optical system of Embodiment 5 of the present invention during infinity focusing and extremely close focusing. From the object side, the optical system consists of, in sequence, a first lens group G1 (front group) with positive optical power, a second lens group G2 (first focusing lens group) with negative optical power, a third lens group G3 with positive optical power, a fourth lens group G4 (second focusing lens group) with negative optical power, and a fifth lens group G5 with positive optical power. The rear group consists of the third lens group G3 to the fifth lens group G5.

[0262] When focusing from an object at infinity to a closer object, the second lens group G2 and the fourth lens group G4 move along the optical axis from the object side to the image side by different amounts of movement.

[0263] The aperture stop S is configured within the third lens group G3.

[0264] In this embodiment, the front group refers to the first lens group G1, the first focusing group refers to the second lens group G2, the rear group refers to the third lens group G3, the fourth lens group G4, and the fifth lens group G5, and the second focusing group refers to the fourth lens group G4. The configuration of each lens group will be described below.

[0265] The first lens group G1 consists of, from the object side, a biconvex lens, a combined lens formed by joining a biconvex lens and a biconcave lens, and a biconvex lens with aspherical surfaces on both sides.

[0266] The second lens group G2 is composed of a combined lens formed by sequentially joining a negative concave-convex lens and a positive concave-convex lens from the object side.

[0267] The third lens group G3, starting from the object side, consists of a combined lens formed by combining a biconvex lens and a biconcave lens, an aperture stop S, and a biconvex lens.

[0268] The fourth lens group G4 is composed of a combined lens formed by sequentially joining a biconcave lens and a positive concave-convex lens, starting from the object side.

[0269] The fifth lens group G5 consists of, from the object side, a combined lens formed by joining a biconvex lens and a biconcave lens, and a negative concave-convex lens.

[0270] (2) Numerical Examples

[0271] Next, as a numerical embodiment of this optical system, specific numerical values ​​are used, representing "lens data," "variable specification tables," "variable spacing," "aspheric coefficient," and "lens group data." Additionally, in... Figure 14 and Figure 15 The image in the middle represents the longitudinal aberration diagram when the optical system is focused at infinity and at extremely close focus.

[0272] (Lens data)

[0273]

[0274]

[0275] (Various specifications)

[0276] Infinity Very close f 97.0157 40.7187 Fno. 2.8845 5.7567 ω 12.6238 4.7035

[0277] (Variable interval)

[0278] Infinity Very close magnification - -1.0 D(7) 2.0000 14.7241 D(10) 16.2567 3.5326 D(16) 2.0017 22.9675 D(19) 22.9796 2.0138

[0279] (Astronomical coefficient)

[0280] Face number K A4 A6 A8 A10 6 0.00000E+00 -2.11926E-06 9.97877E-10 -4.80270E-12 -8.50359E-15 7 0.00000E+00 1.53597E-06 2.40122E-09 -1.19942E-11 6.80915E-15 11 0.00000E+00 6.64629E-06 5.28865E-09 0.00000E+00 0.00000E+00

[0281] (Lens group data)

[0282] Group Face number focal length G1 1-7 40.1514 G2 8-10 -36.3542 G3 11-16 48.6743 G4 17-19 -54.0779 G5 20-24 195.3350

[0283] [Table 1]

[0284]

[0285]

[0286] Industrial applicability

[0287] The optical system involved in this invention can be suitably applied, for example, to the imaging optical system of imaging devices such as thin-film cameras, digital cameras, and digital video cameras.

Claims

1. An optical system, characterized in that, The optical system, starting from the object side, consists of a front group, a first focusing lens group with negative optical power, and a rear group. The rear group includes a second focusing lens group with negative optical power. During focusing, the front group is fixed relative to the image plane, while the first focusing lens group and the second focusing lens group move along the optical axis. The optical system satisfies the following condition: 2.00 ≤ |(1-βfO1×βfO1)×βfO1r×βfO1r|····(1) 2.00 ≤ |(1-βfO2×βfO2)×βfO2r×βfO2r|····(2) 0.05 ≤ ff / f ≤ 0.413····(4) in, βfO1: Horizontal magnification when the first focusing lens group is focused at infinity. βfO1r: The combined horizontal magnification of all lenses positioned further on the image side than the first focusing lens group when focused at infinity. βfO2: Horizontal magnification when the second focusing lens group is focused at infinity. βfO2r: The combined horizontal magnification of all lenses positioned further on the image side than the second focusing lens group when focused at infinity. ff: Focal length of the front group f: The focal length of the optical system when focusing at infinity.

2. An optical system, characterized in that, The optical system, starting from the object side, consists of a front group, a first focusing lens group with negative optical power, and a rear group. The rear group includes a second focusing lens group with negative optical power. During focusing, the front group is fixed relative to the image plane, while the first focusing lens group and the second focusing lens group move along the optical axis. The optical system satisfies the following condition: 2.00 ≤ |(1-βfO1×βfO1)×βfO1r×βfO1r|····(1) 2.00 ≤ |(1-βfO2×βfO2)×βfO2r×βfO2r|····(2) -0.650 ≤ fr / f ≤ -0.05····(5) in, βfO1: Horizontal magnification when the first focusing lens group is focused at infinity. βfO1r: The combined horizontal magnification of all lenses positioned further on the image side than the first focusing lens group when focused at infinity. βfO2: Horizontal magnification when the second focusing lens group is focused at infinity. βfO2r: The combined horizontal magnification of all lenses positioned further on the image side than the second focusing lens group when focused at infinity. fr: The combined focal length at infinity of all lenses positioned further on the image side than the preceding group when focused. f: The focal length of the optical system when focusing at infinity.

3. The optical system as described in claim 1, The front group has one or more lenses with positive optical power that satisfy the following condition: 0.005 ≤ dPgF····(3) in, dPgF: The anomalous dispersion of the lens with positive optical power at the g-line and F-line.

4. The optical system as described in claim 1 or 2, The following condition must be satisfied: -1.00 ≤ ffO1 / f ≤ -0.05····(6) in, ffO1: Focal length of the first focusing lens group f: The focal length of the optical system when focusing at infinity.

5. The optical system as described in claim 1 or 2, The following condition must be satisfied: -1.00 ≤ ffO2 / f ≤ -0.05····(7) in, ffO2: Focal length of the second focusing lens group f: The focal length of the optical system when focusing at infinity.

6. The optical system as described in claim 1 or 2, The following condition must be satisfied: -2.50 ≤ ff / ffO1 ≤ -0.80····(8) in, ff: Focal length of the front group ffO1: The focal length of the first focusing lens group.

7. A camera device, characterized in that, have: The optical system as claimed in any one of claims 1 to 6; and The imaging element converts the optical image formed by the optical system into an electrical signal on the image side of the optical system.

Images