Optical system and imaging device

Abstract

This makes it possible to provide an optical system and imaging device with a larger aperture and higher imaging magnification while maintaining an overall compact size. [Solution] The optical system has a plurality of lens groups (G1 to G5) in which the distance between adjacent lens groups changes during focusing, and an aperture diaphragm S. It is characterized in that when the distance between the exit pupil of the axial light rays and the image plane due to the aperture diaphragm in the infinity focus state, the first close-range object focus state with imaging magnification β1, and the second close-range object focus state with imaging magnification β2 are Pinf, P1, and P2, respectively, it satisfies predetermined conditions. The imaging device also comprises the optical system and an image sensor.

Description

Technical Field

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[0001] The present invention relates to an optical system and an imaging device, and more particularly to an optical system and an imaging device suitable for an imaging device using a solid-state imaging device (such as a CCD or a CMOS) such as a digital still camera or a digital video camera.

Background Art

[0002] Conventionally, imaging devices using various solid-state imaging devices such as video cameras, digital still cameras, single-lens reflex cameras, and mirrorless single-lens cameras have become widespread. Along with the progress of high performance and miniaturization of these imaging devices, further high performance and miniaturization are required for their imaging lenses (optical systems), and macro lenses are no exception. A macro lens generally refers to an imaging lens with a maximum imaging magnification of 0.5 to 1 times.

[0003] In particular, for macro lenses, it is required to suppress aberration variations during focusing, such as variations in spherical aberration and field curvature, and to achieve high optical performance over the entire focus range. However, many of the currently commercially available macro lenses are about F2.8. A zoom lens can also achieve a similar imaging magnification with a brightness of about F2.8, and a zoom lens may be used as a substitute for a macro lens. Therefore, there is a growing demand for macro lenses that are smaller and more high-performance, and that pursue imaging expressions unique to macro lenses and have higher added value.

[0004] As such macro lenses, the optical systems disclosed in Patent Document 1 and Patent Document 2 are known. The optical system disclosed in Patent Document 1 is composed of a front group having a positive refractive power and a rear group having a negative refractive power in order from the object side to the image side. During focusing, the rear group is fixed, and the front group is used as a focus group and moved along the optical axis direction toward the object side to focus on the subject.

[0005] Furthermore, the optical system disclosed in Patent Document 2 has multiple lens groups in which the spacing between adjacent lens groups changes during focusing. This optical system employs a floating focus method, and focuses on the subject by moving a second lens group having negative refractive power and a fourth lens group having positive refractive power along the optical axis. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2021-39304 [Patent Document 2] Japanese Patent Publication No. 2020-60661 [Overview of the project] [Problems that the invention aims to solve]

[0007] However, although the optical system disclosed in Patent Document 1 has an F2.0 aperture ratio and achieves a large aperture ratio, the weight and movement of the focus group are large, making it difficult to further improve imaging magnification and focusing speed while suppressing the increase in size of the macro lens.

[0008] Furthermore, in the optical system disclosed in Patent Document 2, a strong positive refractive force is placed in the third lens group to reduce the diameter of the fourth lens group, which is the focusing group. In this case, if one attempts to further increase the aperture and improve the imaging magnification, it is necessary to increase the number of lenses constituting the other lens groups in order to adequately correct the aberrations occurring in the third lens group, which results in a larger optical system.

[0009] Therefore, the object of the present invention is to provide an optical system and imaging device with a larger aperture and higher imaging magnification while maintaining a compact overall size. [Means for solving the problem]

[0010] To solve the above problems, the optical system according to the present invention is an optical system having a plurality of lens groups in which the spacing between adjacent lens groups changes when focusing, and an aperture diaphragm, When the distances between the exit pupil of the axial ray and the image plane due to the aperture diaphragm in the state of focusing on an object at infinity, the first state of focusing on a near-range object with an imaging magnification of β1, and the second state of focusing on a near-range object with an imaging magnification of β2 are denoted as Pinf, P1, and P2, respectively, The lens group positioned closest to the image plane is fixed in the direction of the optical axis when focusing. The lens groups that move in the direction of the optical axis during focusing all have cemented lenses. It is characterized by meeting the following conditions. |β1| < |β2| ···(1) |Pinf|> |P1| ···(2) |P2| > |P1| ···(3) However, when βmax is the imaging magnification (maximum imaging magnification) at the closest focusing state in the optical system, |β2| ≤ |βmax|.

[0011] Furthermore, in order to solve the above-mentioned problems, the imaging device according to the present invention is characterized by comprising the optical system and an image sensor that converts the optical image formed by the optical system into an electrical signal. [Effects of the Invention]

[0012] According to the present invention, it is possible to provide an optical system and imaging device with a larger aperture and higher imaging magnification while maintaining a compact overall size. [Brief explanation of the drawing]

[0013] [Figure 1] This is a cross-sectional view of the lens of the optical system of Embodiment 1 of the present invention, with the upper section showing the state of focus on an object at infinity, the middle section showing the state of focus on a first close-range object (imaging magnification β1), and the lower section showing the state of focus on a second close-range object (imaging magnification β2) (the same applies to the following cross-sectional views of the lens). [Figure 2] These are the spherical aberration diagram, astigmatism diagram, and distortion aberration diagram of the optical system of Example 1 in the state of focusing on an object at infinity. [Figure 3] Spherical aberration diagram, astigmatism diagram, and distortion aberration diagram [in] the first close-distance object in-focus state of the optical system of Example 1. [Figure 4] Spherical aberration diagram, astigmatism diagram, and distortion aberration diagram [in] the second close-distance object in-focus state of the optical system of Example 1. [Figure 5] Lens cross-sectional view of the optical system of Example 2 of the present invention. [Figure 6] Spherical aberration diagram, astigmatism diagram, and distortion aberration diagram [in] the infinite-distance object in-focus state of the optical system of Example 2. [Figure 7] Spherical aberration diagram, astigmatism diagram, and distortion aberration diagram [in] the first close-distance object in-focus state of the optical system of Example 2. [Figure 8] Spherical aberration diagram, astigmatism diagram, and distortion aberration diagram [in] the second close-distance object in-focus state of the optical system of Example 2. [Figure 9] Lens cross-sectional view of the optical system of Example 3 of the present invention. [Figure 10] Spherical aberration diagram, astigmatism diagram, and distortion aberration diagram [in] the infinite-distance object in-focus state of the optical system of Example 3. [Figure 11] Spherical aberration diagram, astigmatism diagram, and distortion aberration diagram [in] the first close-distance object in-focus state of the optical system of Example 3. [Figure 12] Spherical aberration diagram, astigmatism diagram, and distortion aberration diagram [in] the second close-distance object in-focus state of the optical system of Example 3. [Figure 13] Lens cross-sectional view of the optical system of Example 4 of the present invention. [Figure 14] Spherical aberration diagram, astigmatism diagram, and distortion aberration diagram [in] the infinite-distance object in-focus state of the optical system of Example 4. [Figure 15] Spherical aberration diagram, astigmatism diagram, and distortion aberration diagram [in] the first close-distance object in-focus state of the optical system of Example 4. [Figure 16] Spherical aberration diagram, astigmatism diagram, and distortion aberration diagram [in] the second close-distance object in-focus state of the optical system of Example 4.

Mode for Carrying Out the Invention

[0014] 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.

[0015] 1.Optical system The optical system comprises multiple lens groups, the spacing between adjacent lens groups changes during focusing, and an aperture diaphragm. Here, "lens group" refers to a group consisting of one or more lenses arranged adjacent to each other, and the air spacing between adjacent lens groups changes during focusing. Furthermore, when referring to "one lens group," the air spacing between each lens included in that "one lens group" does not change during focusing. Hereafter, a lens group that moves in the direction of the optical axis during focusing will be referred to as the focus group. Since the optical system has at least one focus group, it is composed of at least two lens groups. The following describes the conditions that the optical system should or preferably satisfy, and its operation during focusing.

[0016] 1-1. Conditional expression 1-1-1. Conditional expressions (1) to (3) The optical system satisfies the following conditions when the distances between the exit pupil of the on-axial rays and the image plane due to the aperture diaphragm are Pinf, P1, and P2, respectively, in the state of focusing on an object at infinity, the first state of focusing on a close-range object with an imaging magnification of β1, and the second state of focusing on a close-range object with an imaging magnification of β2. |β1| < |β2| ···(1) |Pinf|> |P1| ···(2) |P2| > |P1| ···(3) However, when βmax is the imaging magnification (maximum imaging magnification) at the closest focusing state in the optical system, |β2| ≤ |βmax|. The first near-field object focus state refers to the state in which, when the target subject is in focus at the first imaging distance, an image of the subject with a size of |β1| times the actual size of the subject is formed on the image plane. The second near-field object focus state refers to the state in which, when the target subject is in focus at the second imaging distance, an image of the subject with a size of |β2| times the actual size of the subject is formed on the image plane.

[0017] In this optical system, when focusing from an object at infinity to a near-range object, the distance between adjacent lens groups is changed to focus on the target subject. When conditions (1) to (3) above are satisfied according to the imaging distance, the exit pupil position moves towards the image side when focusing from an object at infinity to the first near-range object. When focusing from the first near-range object to the second near-range object, the exit pupil position moves towards the object side. In this way, when focusing from an object at infinity to the second near-range object, the exit pupil position is moved towards the image side and then towards the object side, so when viewed across the entire focus range, the fluctuation of the exit pupil position during focusing is reduced, and image plane fluctuations during focusing can be suppressed. Therefore, the number of lenses required for aberration correction can be reduced, and even when the maximum imaging magnification is increased, an optical system with high imaging performance can be obtained while maintaining a compact overall size.

[0018] Furthermore, by satisfying conditions (2) and (3), the position of the exit pupil does not deviate significantly from the position when the object is in focus at infinity, even when imaging up close to the subject (when the imaging magnification is greater than β1). Also, as mentioned above, high imaging performance can be obtained with a small number of lenses, so the decrease in brightness that occurs with an increase in the number of lenses can be suppressed. For these reasons, it is easy to increase the aperture while maintaining a compact overall size. As described above, by satisfying the above conditions (1) to (3), it is possible to obtain an optical system with a larger aperture and higher imaging magnification while maintaining a compact overall size.

[0019] 1-1-2. Conditional expressions (4) and (5) In the optical system, it is preferable that the first imaging magnification β1 and the second imaging magnification β2 each satisfy the following conditions. |β1| > 0.2 ···(4) |β2| ≥ 0.8 ···(5)

[0020] If the above condition (5) is satisfied, the optical system can be made into a macro lens with a maximum imaging magnification of 0.8x or more. In this case, by satisfying the above condition (4), even when an optical system with a large maximum imaging magnification is used, the effects obtained by satisfying the above conditions (1) to (3) can be fully obtained, and a large-aperture optical system with high imaging performance can be realized while maintaining a compact overall size.

[0021] To obtain the above effects, the lower limit of conditional equation (4) is more preferably 0.25, even more preferably 0.3, and even more preferably 0.4. Furthermore, the upper limit of conditional equation (4) is required to be less than |β2| as specified in conditional equation (1) above. If the optical system satisfies conditional equation (5), the upper limit of conditional equation (4) is more preferably 0.7, and more preferably 0.6. Furthermore, the lower limit of conditional equation (5) is more preferably 0.85, even more preferably 0.9, and even more preferably 0.95. Note that the inequality sign (<) in conditional equations (4) and (5) may be replaced with an equality sign with an inequality sign (≦). Also, regarding the upper limit of conditional equation (4), the numerical value of conditional equation (4) may be less than or equal to the numerical values ​​listed above, or less than the numerical values ​​listed above.

[0022] 1-2. Operation during focusing In this optical system, the subject is focused by moving one or more lens groups along the optical axis. In this case, as long as the above conditions (1) to (3) are satisfied, the focusing operation in this optical system is not particularly limited, but it is preferable to do so as follows.

[0023] 1-2-1. Between the state of focusing on an object at infinity and the state of focusing on a first object at close range. Between the state of focusing on an object at infinity and the first state of focusing on an object at close range, it is preferable to focus on the subject in the following manner.

[0024] (1) Inner focus system First, it is preferable that the lens group positioned closest to the object in the optical system (the lens group closest to the object) is fixed in the direction of the optical axis from the state of focus on an object at infinity to the state of focus on a first close-range object. In other words, it is preferable that the focus on the subject is achieved by an inner focus method from the state of focus on an object at infinity to the state of focus on a first close-range object.

[0025] When an inner focus system is adopted, the focus group can be smaller and lighter than the outermost lens group. This makes it easier to achieve high-speed autofocus. Also, compared to when the outermost lens group is used as the focus group, it becomes easier to suppress changes in the angle of view during focusing. When shooting video or live view, the focus group is vibrated (wobbled) at high speed in the optical axis direction with a small amplitude to find the optimal position of the focus group to achieve focus on the target subject, and then the focus group is moved to that optimal position. In this process, by using an inner focus system, it is possible to suppress changes in the angle of view caused by the vibration of the focus group during wobbling. Therefore, it is possible to suppress changes in the size of the subject image during wobbling and prevent the user from feeling any discomfort when shooting video or live view.

[0026] (2) Floating type It is preferable to move the two lens groups along the optical axis to achieve focus from the state of focusing on an object at infinity to the first state of focusing on a nearby object. At this time, it is preferable to position an aperture diaphragm between these two lens groups.

[0027] In this way, the subject can be focused using so-called floating focus from the state of focusing on an object at infinity to the first state of focusing on an object at close range, thereby suppressing aberration fluctuations during focusing.

[0028] (3) Single lens element Between the state of in-finity focus and the first state of close-range focus, it is preferable to use a lens group composed of a single lens element as the focus group and to focus on the subject by moving the focus group along the optical axis. In other words, it is preferable that the lens group that functions as the focus group between the state of in-finity focus and the first state of close-range focus is composed of a single lens element.

[0029] Here, "single lens element" refers to an element consisting of only one lens, or only one cemented lens formed by joining multiple lenses. By using a lens group composed of a single lens element to cover the range from the infinity focus state to the first near-range focus state as the focus group, the focus group can be made smaller and lighter, enabling high-speed autofocus. Furthermore, by making the focus group smaller and lighter, the drive mechanism for driving the focus group can also be made smaller and lighter, resulting in a smaller and lighter overall lens unit.

[0030] 1-2-2. Between the first near-field object focus state and the second near-field object focus state. Between the first state of focusing on a near-range object and the second state of focusing on a near-range object, it is preferable to achieve focus by moving multiple lens groups along the same trajectory along the optical axis.

[0031] In this way, multiple lens groups can be fixed to the same lens frame, and the lens frame can be driven by a single drive mechanism, allowing multiple lens groups to move simultaneously. In this case, there is no need to provide a drive mechanism for each lens group, which simplifies the focus drive mechanism and allows for a more compact overall lens unit. Note that the multiple lens groups may be two lens groups or three or more lens groups.

[0032] 1-2-3. Lens group closest to the object As described above, it is preferable to focus on the subject using an inner focus method from the state of focusing on an object at infinity to the first state of focusing on a close-range object, and it is preferable that the lens group closest to the object in this optical system is fixed in the direction of the optical axis.

[0033] Between the first near-field object focus state and the second near-field object focus state, the lens group closest to the object may be configured as a fixed group or as a focusing group during focusing.

[0034] If the lens group closest to the object is fixed between the first and second close-range object focus states, the inner focus system can be used to maintain focus on the subject during that time. This allows for miniaturization and weight reduction of the focus group, as well as simplification of the drive mechanism for the focus group, resulting in a more compact overall lens unit. Furthermore, since the barrel length does not change during focusing, the object-side of the barrel can be sealed, making it easier to create a waterproof and dustproof barrel.

[0035] On the other hand, between the first close-range object focus state and the second close-range object focus state, if the lens group closest to the object is used as the focusing group and the subject is focused by moving the lens group closest to the object along the optical axis, it becomes easier to improve the maximum imaging magnification and shorten the minimum imaging distance while making the overall structure compact. This is for the following reasons. First, if the lens group closest to the object is fixed throughout the entire focus range, it becomes difficult to shorten the minimum imaging distance or improve the maximum magnification while maintaining a compact overall optical system due to constraints on the optical configuration. On the other hand, if the lens group closest to the object is extended towards the object, for example, according to the imaging distance during focusing, the degree of freedom in the optical configuration increases, making it easier to shorten the minimum imaging distance or improve the maximum magnification. Furthermore, by moving the closest lens group towards the image when not imaging, it becomes possible to make the entire system compact.

[0036] When the imaging magnification is small, it is relatively easy to capture the subject with the user's intended point of focus even when using an autofocus system. However, when capturing the subject at a large imaging magnification, it is generally difficult to focus on the intended point of focus using an autofocus system. Therefore, high-speed autofocus is achieved by fixing the lens group closest to the object in the optical axis direction and focusing on the subject using an inner focus system from the state of focusing on an object at infinity to the first state of focusing on an object at close range. From the first state of focusing on an object at close range to the second state of focusing on an object at close range, the subject is focused using a manual focus system, improving user convenience. Furthermore, from the first state of focusing on an object at close range to the second state of focusing on an object at close range, if the lens group closest to the object is extended forward by a cam mechanism provided on the lens barrel, it becomes unnecessary to provide a focus drive mechanism to drive the lens group closest to the object, thus enabling miniaturization and weight reduction of the entire lens unit.

[0037] 1-2-4. Final lens group In this optical system, the lens group positioned closest to the image plane (the final lens group) is preferably fixed in the direction of the optical axis during focusing. By making the final lens group a fixed group in this way, there is no need to place a drive mechanism to drive the final lens group on the image plane side, thus simplifying the lens barrel structure. Furthermore, by making the final lens group a fixed group, the image plane side of the lens barrel can be sealed, preventing dust, dirt, water, etc. from entering from the image plane side.

[0038] However, the final lens group is not limited to a fixed group; it may also be used as the focusing group. For example, between the first close-range focusing state and the second close-range focusing state, the lens group closest to the object may be fixed in the direction of the optical axis, and the final lens group may be moved along the optical axis to focus on the subject.

[0039] 1-2-5. Lens group configuration The lens group configuration in the optical system is not particularly limited, but by using different lens groups as focus groups between the state of infinity focus on a first close-range object and between the first close-range focus and the second close-range focus, it becomes easier to obtain an optical system that satisfies conditions (1) to (3). Specifically, it is preferable to have a first focus group that moves along the optical axis direction from the state of infinity focus on a first close-range object to the state of first close-range object focus, and a second focus group that moves along the optical axis direction from the first close-range object focus to the second close-range object focus, wherein the second focus group is fixed along the optical axis direction from the state of infinity focus on a first close-range object focus, and the first focus group is fixed along the optical axis direction from the first close-range object focus to the second close-range object focus.

[0040] In the optical system, when an inner focus system is employed from the state of focusing on an object at infinity to the first state of focusing on a nearby object, as described above, the first focus group is required to be a lens group positioned closer to the image plane than the lens group closest to the object. Furthermore, when a floating focus system is employed, it is required to have two or more first focus groups, and it is preferable that an aperture diaphragm is placed between the first focus groups. It is also preferable that the first focus group is composed of a single lens element.

[0041] Furthermore, it is preferable to have one or more second focus groups in the optical system. For example, the second focus group can be a lens group positioned between the first focus groups, or the lens group closest to the object.

[0042] 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 imaging lens according to the present invention and an image sensor that converts the optical image formed by the imaging lens into an electrical signal. Preferably, the image sensor is provided on the image side of the optical system.

[0043] 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 these solid-state image sensors, such as digital cameras and video cameras. Furthermore, the imaging device can be applied to various imaging devices such as single-lens reflex cameras, mirrorless cameras, digital still cameras, surveillance cameras, in-vehicle cameras, and drone cameras. These imaging devices may be interchangeable-lens imaging devices or fixed-lens imaging devices in which the lens is fixed to the housing. In particular, the imaging lens has a maximum imaging magnification of 0.5x or more and is suitable as a so-called macro lens that allows imaging at close range to the subject, making it suitable for imaging devices such as single-lens reflex cameras and mirrorless cameras, and for applications where it is necessary to image the subject at a large size, such as industrial imaging devices.

[0044] Next, the present invention will be specifically described with reference to examples. However, the present invention is not limited to the following examples. [Examples]

[0045] (1) Optical configuration Figure 1 is a cross-sectional view of the lens of the optical system of Embodiment 1 according to the present invention. The upper section shows the state of focus on an object at infinity, the middle section shows the state of focus on a first close-range object (imaging magnification β1), and the lower section shows the state of focus on a second close-range object (imaging magnification β2). The same applies to the cross-sectional view of the lens shown in each embodiment below, so the explanation will be omitted below.

[0046] As shown in Figure 1, the optical system comprises, 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, a fourth lens group G4 having negative refractive power, and a fifth lens group G5 having positive refractive power. The aperture diaphragm S is located on the object side of the third lens group G3. The configuration of each lens group is as shown in the figure.

[0047] In the optical system of Embodiment 1, the "imaging magnification β1" = -0.5 and the "imaging magnification β2" = -1.0, with imaging magnification β2 corresponding to the maximum imaging magnification βmax in the optical system. In this optical system, from the state of focusing on an object at infinity to the state of focusing on a first close-range object, the subject is focused by moving the second lens group G2 and the fourth lens group G4 along the optical axis, and during this time, the first lens group G1, the third lens group G3 and the fifth lens group G5 are fixed along the optical axis. Furthermore, from the state of focusing on a first close-range object to the state of focusing on a second close-range object, the subject is focused by moving the first lens group G1 and the third lens group G3 along the optical axis on the same trajectory, and during this time, the second lens group G2, the fourth lens group G4 and the fifth lens group G5 are fixed along the optical axis. The second lens group G2 and the fourth lens group G4 are the first focusing group, and the first lens group G1 and the third lens group G3 are the second focusing group.

[0048] In Figure 1, "Pinf," "P1," and "P2" indicate the exit pupil position in the state of focus on an object at infinity, the state of focus on a first near-range object, and the state of focus on a second near-range object, respectively. As shown in Figure 1, fluctuations in the exit pupil position are suppressed throughout the entire focus range. In Figure 1, "IMG" refers to the image 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. The object side of the IP is also equipped with a cover glass CG, etc. This point is the same as in the cross-sectional view of the lenses shown in other embodiments, so further explanation will be omitted.

[0049] (2) Numerical Examples Next, a numerical example of the optical system will be described. Below are the surface data, various data, variable interval at focus, and focal length of each lens group of the optical system. In the table showing surface data, "No." indicates the order of the lens surfaces (surface number) counted from the object side, "R" indicates the radius of curvature of the lens surface, "D" indicates the spacing of the lens surfaces along the optical axis, "Nd" indicates the refractive index for the d line (wavelength λ=587.6nm), and "ABV" indicates the Abbe number for the d line. In the "No." column, "STOP" displayed in the column following the surface number represents the aperture diaphragm. In the "D" column, "D○○" (D7 in this embodiment, for example) indicates the variable spacing when in focus. In all the tables below, the unit of length is "mm" and the unit of field of view is "°". In each table, "∞" represents infinity.

[0050] In the table showing various data, "f" is the focal length of the optical system, "β" is the magnification ratio, "Fno" is the F-number, "ω" is the half-angle of view, "Y" is the image height, "BF" is the back focus, and "TL" is the total optical length, each representing the values ​​for the infinity focus state, the first close-range focus state, and the second close-range focus state, respectively. However, the values ​​in the table include a 2.5 mm thick cover glass (Nd=1.5168), and the same applies to the back focus shown in other embodiments.

[0051] The table showing the variable interval when focusing indicates the variable interval for the state of focusing on an object at infinity, the state of focusing on the first near-field object, and the state of focusing on the second near-field object, along with the focal length (f) and imaging distance at those times. The table showing the focal lengths of each lens group indicates the lens surfaces included in each lens group and the focal length of each lens group.

[0052] Furthermore, the numerical values ​​used in each condition (1) to condition (5) are shown in Table 1 (shown below). Since the same applies to the tables shown in other examples, the explanation is omitted below.

[0053] Figures 2, 3, and 4 show the longitudinal aberration diagrams of the optical system in the state of infinity focus, the first near-field focus state (imaging magnification β1), and the second near-field focus state (imaging magnification β2). In each longitudinal aberration diagram, spherical aberration, astigmatism, and distortion are shown from left to right. In the diagram showing spherical aberration, the vertical axis is the ratio to the maximum aperture, and the horizontal axis is defocus. The solid line shows the spherical aberration at the d line (wavelength λ=587.56nm), the dashed line shows the spherical aberration at the C line (wavelength λ=656.28nm), and the dashed line shows the spherical aberration at the F line (wavelength λ=486.13nm). In the diagram showing astigmatism, the vertical axis is the half-angle of view (ω), and the horizontal axis is defocus. The solid line shows the sagittal image plane relative to the d line, and the dotted line shows the meridional image plane relative to the d line. In the diagrams representing distortion, the vertical axis represents the half-angle of view (ω), and the horizontal axis represents the percentage (%). The details regarding these diagrams are the same as those shown in the longitudinal aberration diagrams in other examples, so further explanation is omitted below.

[0054] (Surface data) No. RD Nd ABV 1 179.9617 4.1633 1.77250 49.62 2 -384.0735 6.8484 3 79.7721 4.2145 1.49700 81.61 4 2266.2517 0.2000 5 59.6990 6.1353 1.59282 68.62 6 -126.8915 1.0000 1.84666 23.78 7 169.6620 D7 8 -250.8703 0.8000 1.80400 46.53 9 106.3512 4.5353 1.92286 20.88 10 -86.6084 0.8000 1.83481 42.74 11 43.7378 D11 12STOP ∞ 1.0000 13 77.9391 1.0000 1.76174 26.71 14 30.2075 7.6150 1.51106 77.74 15 -89.5658 0.2000 16 38.8444 5.7779 1.62620 59.44 17 -122.0103 D17 18 ∞ 0.0000 19 116.2374 4.0000 1.69671 31.70 20 -38.1606 0.8000 1.86180 38.82 21 31.2754 D21 22 55.8335 5.4512 1.90925 35.35 23 -46.7074 0.9110 24 -69.5328 1.3000 1.51004 68.81 25 38.2703 12.9013 26 -23.6330 1.0000 1.84666 23.78 27 -47.7349 15.0000 28 ∞ 2.5000 1.51633 64.14 29 ∞ 1.0000

[0055] (Various data) INF β1 β2 f 92.7002 56.4352 38.4725 β 0 -0.5 -1.0 Fno 2.110 3.200 4.200 ω 12.5792 6.5626 3.7783 Y 21.633 21.633 21.633 BF 18,500 18,500 18,500 TL 134.619 134.619 145.676

[0056] (Variable interval) INF β1 β2 f 92.7002 56.4352 38.4725 Imaging distance INF 334.90 263.79 D7 3.0674 18.3151 29.3727 D11 29.5683 14.3206 3.2630 D17 2.2000 10.2615 21.3192 D21 10.6298 2.5682 2.5682

[0057] (Focal length of each lens group) Group Surface number Focal length G1 1-7 65.4594 G2 8-11 -49.3120 G3 12-17 36.1356 G4 18-20 -39.3439 G5 21-26 267.9377 [Examples]

[0058] (1) Optical configuration Figure 5 is a cross-sectional view of the lens of the optical system of Embodiment 2 according to the present invention. As shown in Figure 5, the optical system comprises, 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, a fourth lens group G4 having negative refractive power, and a fifth lens group G5 having positive refractive power. The aperture diaphragm S is located on the object side of the third lens group G3. The configuration of each lens group is as shown in the figure.

[0059] In the optical system of Embodiment 2, the "imaging magnification β1" = -0.5 and the "imaging magnification β2" = -0.8, with imaging magnification β2 corresponding to the maximum imaging magnification βmax in this optical system. In this optical system, from the state of focusing on an object at infinity to the state of focusing on a first close-range object, the subject is focused by moving the second lens group G2 and the fourth lens group G4 along the optical axis, and during this time, the first lens group G1, the third lens group G3 and the fifth lens group G5 are fixed along the optical axis. Furthermore, from the state of focusing on a first close-range object to the state of focusing on a second close-range object, the subject is focused by moving the third lens group G3 along the optical axis, and during this time, the first lens group G1, the second lens group G2, the fourth lens group G4 and the fifth lens group G5 are fixed along the optical axis. The second lens group G2 and the fourth lens group G4 are the first focusing group, and the third lens group G3 is the second focusing group.

[0060] (2) Numerical Examples Next, a numerical example of the optical system will be described. Below are the surface data, various data, variable interval at focus, focal length of each lens group, and aspherical data of the optical system.

[0061] In the "No." column of the surface data, the "ASPH" displayed in the column following the surface number indicates that the surface is aspherical. "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=(h2 / r) / [1+{1-(1+k)×(h / r)2}1 / 2] +A4×h4+A6×h6+A8×h8+A10×h10+A12×h12 In the above equation, h is the height from the optical axis, r is the radius of paraxial curvature, k is the conicity coefficient, and An is the nth order. This represents the aspheric coefficient. Furthermore, "E±XX" represents exponential notation, meaning "×10±XX". The following explanations regarding aspheric surfaces are the same and will be omitted.

[0062] Furthermore, Figures 6, 7, and 8 show longitudinal aberration diagrams of the optical system in the state of infinity focus, the first near-field focus state (imaging magnification β1), and the second near-field focus state (imaging magnification β2).

[0063] (Surface data) No. RD Nd ABV 1 268.6607 3.3383 1.76169 50.13 2 -288.1781 0.6336 3 79.9614 5.1240 1.49700 81.61 4 -257.8755 0.2000 5 74.5842 5.5062 1.59282 68.62 6 -132.5628 1.0000 1.84666 23.78 7 243.9703 D7 8 -133.7219 0.8000 1.76665 49.89 9 102.8476 0.5442 10 133.0884 4.4475 1.92286 20.88 11 -83.2619 0.8000 1.80817 44.37 12 49.2117 D12 13STOP ∞ 1.0000 14 32.0346 1.0000 1.81052 24.88 15 21.5241 10.3613 1.51502 76.75 16 -146.3724 0.4168 17ASPH 84.8960 3.7046 1.57154 66.04 18 -186.2521 D18 19 106.0691 6.4737 1.76700 26.49 20 -24.4352 0.8000 1.84872 33.72 21 28.9820 D21 22 51.8305 5.5661 1.86838 38.28 23 -47.7138 1.5121 24 -76.4518 1.3000 1.51214 58.15 25 53.2939 12.9816 26 -25.4575 1.0000 1.84666 23.78 27 -58.6778 15.0000 28 ∞ 2.5000 1.51633 64.14 29 ∞ 1.0000

[0064] (Various data) INF β1 β2 f 92.7001 61.6892 46.4780 β 0 -0.5 -0.8 Fno 2.1549 3.2000 3.8000 ω 12.5935 5.8338 5.7301 Y 21.633 21.633 21.633 BF 18,500 18,500 18,500 TL 136.903 136.903 136.903

[0065] (Variable interval) INF β1 β2 f 92.7001 61.6892 46.4780 Imaging distance INF 367.88 297.08 D7 3.4132 20.3409 20.3409 D12 31.4879 14.5603 3.4745 D18 2.2000 6.4277 17.5134 D21 12.7918 8.5641 8.5641

[0066] (Focal length of each lens group) Group Surface number Focal length G1 1-7 61.2857 G2 8-12 -46.1949 G3 13-18 42.3498 G4 19-21 -40.8445 G5 22-27 125.6290

[0067] (Aspherical data) No. K A4 A6 A8 A10 17 0.00000E+00 0.00000E+00 1.51299E-09 9.60398E-12 -2.04325E-14 No. A12 17 8.36539E-17 [Examples]

[0068] (1) Optical configuration Figure 9 is a cross-sectional view of the lens of the optical system of Embodiment 3 according to the present invention. As shown in Figure 9, the optical system comprises, 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, a fourth lens group G4 having negative refractive power, and a fifth lens group G5 having positive refractive power. The aperture diaphragm S is located on the object side of the third lens group G3. The configuration of each lens group is as shown in the figure.

[0069] In the optical system of Embodiment 3, the "imaging magnification β1" = -1.0 and the "imaging magnification β2" = -2.0, with imaging magnification β2 corresponding to the maximum imaging magnification βmax in this optical system. In this optical system, from the state of focusing on an object at infinity to the state of focusing on a first close-range object, the subject is focused by moving the second lens group G2 and the fourth lens group G4 along the optical axis, and during this time, the first lens group G1, the third lens group G3 and the fifth lens group G5 are fixed along the optical axis. Furthermore, from the state of focusing on a first close-range object to the state of focusing on a second close-range object, the subject is focused by moving the first lens group G1 and the third lens group G3 along the optical axis, and during this time, the second lens group G2, the fourth lens group G4 and the fifth lens group G5 are fixed along the optical axis. The second lens group G2 and the fourth lens group G4 are the first focusing group, and the first lens group G1 and the third lens group G3 are the second focusing group.

[0070] (2) Numerical Examples Next, a numerical example of the optical system will be described. Below are the surface data, various data, variable interval at focus, focal length of each lens group, and aspherical data of the optical system.

[0071] Furthermore, Figures 10, 11, and 12 show longitudinal aberration diagrams of the optical system in the state of infinity focus, the first near-field focus state (imaging magnification β1), and the second near-field focus state (imaging magnification β2).

[0072] (Surface data) No. RD Nd ABV 1 98.1640 3.8639 1.92286 20.88 2 -784.3577 1.0000 1.49700 81.61 3 27.5834 17.1841 4 163.4552 6.9948 1.49700 81.61 5 -33.5015 0.9133 6 -29.4497 1.0000 1.84666 23.78 7 -57.3774 0.2000 8ASPH 49.1121 9.1606 1.59282 68.62 9ASPH -35.5559 D9 10 -85.4429 0.8000 1.55560 68.54 11 36.4897 D11 12STOP ∞ 1.0000 13 90.9642 0.8000 1.84666 23.78 14 32.0307 3.2946 15 266.9782 3.7448 1.82748 39.97 16 -54.3529 0.2000 17 28.2447 7.5604 1.43700 95.10 18 -41.2961 D18 19 463.2052 2.2000 1.84666 23.78 20 -53.0340 0.8000 1.77899 48.54 21 22.5173 D21 22 47.1906 5.6024 1.57279 42.61 23 -29.6587 2.2428 24 -29.5772 1.0000 1.56133 63.85 25 39.5661 34.3772 26 ∞ 2.5000 1.51633 64.14 27 ∞ 1.0000

[0073] (Various data) INF β1 β2 f 87.8766 39.7703 25.9505 β 0 -1.0 -2.0 Fno 2.9000 5.8500 8.7000 ω 12.9523 8.4795 5.1482 Y 21.633 21.633 21.633 BF 37.877 37.877 37.877 TL 145.000 145.000 154.112

[0074] (Variable interval) INF β1 β2 f 87.8766 39.7703 25.9505 Imaging distance INF 208.41 181.58 D9 1.5000 8.9551 18.0666 D11 21.0666 13.6116 4.5000 D18 2.2000 11.9944 21.1060 D21 12.7945 3.0000 3.0000

[0075] (Focal length of each lens group) Group Surface number Focal length G1 1-9 35.2989 G2 10-11 -45.9144 G3 12-18 33.6266 G4 19-21 -31.8769 G5 22-25 777.5670

[0076] (Aspherical data) No. K A4 A6 A8 A10 8 0.00000E+00 -1.99576E-06 -7.78596E-10 -1.67883E-12 5.30277E-15 9 0.00000E+00 5.38841E-06 -2.33885E-09 2.70945E-12 2.47653E-15 No. A12 8 0.00000E+00 9 0.00000E+00 [Examples]

[0077] (1) Optical configuration Figure 13 is a cross-sectional view of the lens of the optical system of Embodiment 4 according to the present invention. As shown in Figure 13, the optical system comprises, 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 aperture diaphragm S is located on the object side of the third lens group G3. The configuration of each lens group is as shown in the figure.

[0078] In the optical system of Embodiment 4, the "imaging magnification β1" = -0.75 and the "imaging magnification β2" = -1.5, with imaging magnification β2 corresponding to the maximum imaging magnification βmax in this optical system. In this optical system, from the state of focusing on an object at infinity to the state of focusing on a first close-range object, the subject is focused by moving the second lens group G2 and the fourth lens group G4 along the optical axis, while the first lens group G1 and the third lens group G3 are fixed along the optical axis. Furthermore, from the state of focusing on a first close-range object to the state of focusing on a second close-range object, the subject is focused by moving the first lens group G1 and the third lens group G3 along the optical axis, while the second lens group G2 and the fourth lens group G4 are fixed along the optical axis. The second lens group G2 and the fourth lens group G4 are the first focusing group, and the first lens group G1 and the third lens group G3 are the second focusing group.

[0079] (2) Numerical Examples Next, a numerical example of the optical system will be described. Below are the surface data, various data, variable interval at focus, focal length of each lens group, and aspherical data of the optical system.

[0080] Furthermore, Figures 14, 15, and 16 show longitudinal aberration diagrams of the optical system in the state of infinity focus, the first near-field focus state (imaging magnification β1), and the second near-field focus state (imaging magnification β2).

[0081] (Surface data) No. RD Nd ABV 1 212.2695 5.0000 1.92286 20.88 2 -139.1666 1.0000 1.59282 68.62 3 36.1996 10.3366 4 216.2681 6.0443 1.49700 81.61 5 -37.8837 2.2524 6 -28.7055 0.8000 1.84666 23.78 7 -50.9510 0.2000 8ASPH 43.9348 12.0000 1.49700 81.61 9ASPH -31.3294 D9 10 -98.0288 0.8000 1.49700 81.61 11ASPH 43.4918 D11 12STOP ∞ 1.0000 13 128.6684 0.8000 1.84052 25.16 14 34.3070 2.7517 15 -655.0362 2.7599 1.90043 37.37 16 -60.4366 2.7808 17 39.2806 5.8311 1.49700 81.61 18 -37.3238 D18 19 -48.5273 2.2089 1.84666 23.78 20 -30.3491 0.8000 1.49700 81.61 21 30.5832 D21 22 ∞ 2.5000 1.51633 64.14 23 ∞ 1.0000

[0082] (Various data) INF β1 β2 f 91.6041 50.1114 35.1898 β 0 -0.75 -1.5 Fno 2.9100 5.0000 6.5000 ω 12.7285 8.6295 5.5211 Y 21.633 21.633 21.633 BF 53.033 40.589 40.589 TL 143.520 143.520 154.229

[0083] (Variable interval) INF β1 β2 f 91.6041 50.1114 35.1898 Imaging distance INF 240.97 201.73 D9 4.1722 14.2867 24.9956 D11 23.4275 13.3130 2.6041 D18 5.5222 17.9655 28.6744 D21 49.5326 37.0893 37.0893

[0084] (Focal length of each lens group) Group Surface number Focal length G1 1-9 43.5649 G2 10-11 -60.5025 G3 12-18 41.1919 G4 19-21 -44.7940

[0085] (Aspherical data) No. K A4 A6 A8 A10 8 0.00000E+00 -3.39392E-06 -2.03399E-09 1.64767E-12 -3.05491E-15 9 0.00000E+00 6.07741E-06 -1.25563E-09 4.83644E-12 -1.70952E-15 11 0.00000E+00 -2.41579E-06 -5.58930E-11 5.89953E-12 -2.24425E-14 No. A12 8 0.00000E+00 9 0.00000E+00 11 0.00000E+00

[0086] [Table 1] Example 1 Example 2 Example 3 Example 4 β1 -0.5 -0.5 -1.0 -0.75 β2 -1.0 -0.8 -2.0 -1.5 Pinf -44.94 -47.77 -63.00 -68.52 P1 -41.99 -45.99 -57.42 -60.65 P2 -44.13 -48.72 -59.13 -63.58 [Industrial applicability]

[0087] According to the present invention, it is possible to provide an optical system and imaging device with a larger aperture and higher imaging magnification while maintaining a compact overall size.

Claims

1. An optical system having multiple lens groups in which the spacing between adjacent lens groups changes when focusing, and an aperture diaphragm, When the distances between the exit pupil of the axial ray and the image plane due to the aperture diaphragm in the state of infinity focus, the first near-range object focus state with imaging magnification β1, and the second near-range object focus state with imaging magnification β2 are Pinf, P1, and P2, respectively, The lens group positioned closest to the image plane is fixed in the direction of the optical axis when focusing. The lens groups that move in the direction of the optical axis during focusing all have cemented lenses. An optical system characterized by satisfying the following conditions. ｜β１｜ ＜ ｜β２｜ ・・・（１） |Pinf|> |P1| ...(2) |P2| > |P1| ...(3)

2. The optical system according to claim 1, wherein the lens group positioned closest to the image plane consists of a plurality of lenses, with an air gap between each adjacent lens.

3. An optical system according to claim 1 or claim 2 that satisfies the following conditions. ｜β１｜ ＞ ０．２ ・・・（４） ｜β２｜ ≧ ０．８ ・・・（５）

4. The optical system according to any one of claims 1 to 3, wherein the lens group positioned closest to the object is fixed in the direction of the optical axis from the state of focusing on an object at infinity to the first state of focusing on a close-range object.

5. The optical system according to any one of claims 1 to 4, wherein the transition from the state of focusing on an object at infinity to the first state of focusing on a nearby object is achieved by moving a lens group composed of a single lens element in the optical axis direction.

6. The optical system according to any one of claims 1 to 5, wherein the transition from the first near-field object focus state to the second near-field object focus state is achieved by moving a plurality of lens groups along the same trajectory along the optical axis.

7. The system comprises a first focus group that moves along the optical axis direction from the state of in-finity focus to the first state of close-range focus, and a second focus group that moves along the optical axis direction from the first state of close-range focus to the second state of close-range focus. The optical system according to any one of claims 1 to 6, wherein the second focus group is fixed in the optical axis direction from the state of focusing on an object at infinity to the state of focusing on a first close-range object, and the first focus group is fixed in the optical axis direction from the state of focusing on a first close-range object to the state of focusing on a second close-range object.

8. An imaging device comprising an optical system according to any one of claims 1 to 7, and an image sensor that converts an optical image formed by the optical system into an electrical signal.

Images