Optical system and imaging device

Abstract

To make it possible to provide an optical system and an imaging device that have a larger diameter and a higher imaging magnification while keeping the whole compact.SOLUTION: An optical system has a plurality of lens groups (G1 to G5) in which the interval between adjacent lens groups changes during focusing and an aperture stop S. When the intervals between an exit pupil and an image plane of an on-axis ray by the aperture stop in an infinity object focus state, a first close-distance object in-focus state in which an imaging magnification is β1, and a second close-distance object in-focus state in which the imaging magnification is β2 are set as a Pinf, P1, P2, respectively, predetermined conditions are satisfied. Further, the imaging device includes the optical system and an imaging element.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[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 imaging devices using solid-state imaging elements (CCD, CMOS, etc.) such as digital still cameras and digital video cameras. [Background technology]

[0002] Imaging devices using various solid-state imaging elements, such as video cameras, digital still cameras, single-lens reflex cameras, and mirrorless single-lens cameras, have become widespread. As these imaging devices become more powerful and smaller, their imaging lenses (optical systems) are also required to be more powerful and smaller, and macro lenses are no exception. A macro lens generally refers to an imaging lens with a maximum imaging magnification of 0.5x to 1x.

[0003] Macro lenses are required to achieve high optical performance throughout the entire focusing range, particularly by suppressing fluctuations in aberrations that occur during focusing, such as spherical aberration and field curvature. However, most macro lenses currently on the market have an aperture of around F2.8. Zoom lenses can also achieve a similar imaging magnification with a brightness of around F2.8, and zoom lenses are sometimes used as substitutes for macro lenses. For this reason, there is a growing demand for macro lenses that are smaller, have higher performance, and offer higher added value by pursuing the imaging capabilities unique to macro lenses.

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

[0005] 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 system in which a second lens group with negative refractive power and a fourth lens group with positive refractive power are moved along the optical axis to focus on a subject. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent Publication No. 2021-39304 [Patent Document 2] Japanese Patent Application Publication No. 2020-60661 Summary of the Invention [Problem to be solved by the invention]

[0007] However, although the optical system disclosed in Patent Document 1 has a large aperture ratio of F2.0, the weight and movement amount of the focus group are large, making it difficult to further improve the imaging magnification and focus speed while preventing the macro lens from becoming larger.

[0008] Furthermore, in the optical system disclosed in Patent Document 2, a strong positive refractive power is provided in the third lens group, and the diameter of the fourth lens group, which is the focus group, is reduced. In this case, if an attempt is made 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 satisfactorily correct aberrations that occur in the third lens group, which results in an increase in the size of the optical system.

[0009] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an optical system and an imaging device that have a larger aperture and a higher imaging magnification while maintaining a compact overall size. [Means for solving the problem]

[0010] In order to solve the above-mentioned problems, the optical system of the present invention is an optical system having a plurality of lens groups in which the spacing between adjacent lens groups changes during focusing, and an aperture stop, and is characterized in that, when Pinf, P1, and P2 are the spacings between the exit pupil of an axial ray and the image plane defined by the aperture stop in an infinity object focusing state, a first close object focusing state with an imaging magnification of β1, and a second close object focusing state with an imaging magnification of β2, respectively, the optical system satisfies the following condition: |β1| < |β2| (1) |Pinf|> |P1| (2) |P2| > |P1| (3) However, when the imaging magnification (maximum imaging magnification) in the closest focusing state in the optical system is βmax, |β2|≦|βmax| is satisfied.

[0011] In order to solve the above problem, the imaging device according to the present invention is characterized by including the above optical system and an imaging element that converts an 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 an imaging device that have a larger aperture and a higher imaging magnification while maintaining a small overall size. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a lens cross-sectional view of an optical system according to a first embodiment of the present invention, in which the upper row shows a state focused on an object at infinity, the middle row shows a state focused on a first close-up object (imaging magnification β1), and the lower row shows a state focused on a second close-up object (imaging magnification β2) (the same applies to the following lens cross-sectional views). [Figure 2] 3A to 3C are diagrams showing spherical aberration, astigmatism, and distortion of the optical system of Example 1 in a state where the optical system is focused on an object at infinity. [Figure 3] 3A to 3C are diagrams illustrating spherical aberration, astigmatism, and distortion of the optical system of Example 1 in a first close-distance object-focused state. [Figure 4]10A to 10C are diagrams illustrating spherical aberration, astigmatism, and distortion of the optical system of Example 1 in a second close object focused state. [Figure 5] FIG. 10 is a cross-sectional view of a lens of an optical system according to a second embodiment of the present invention. [Figure 6] 10A to 10C are diagrams showing spherical aberration, astigmatism, and distortion of the optical system of Example 2 when focused on an object at infinity. [Figure 7] 10A to 10C are diagrams illustrating spherical aberration, astigmatism, and distortion of the optical system of Example 2 in a first close-distance object-focused state. [Figure 8] 10A to 10C are diagrams illustrating spherical aberration, astigmatism, and distortion of the optical system of Example 2 in a second close object focused state. [Figure 9] FIG. 10 is a cross-sectional view of a lens of an optical system according to a third embodiment of the present invention. [Figure 10] 10A to 10C are diagrams showing spherical aberration, astigmatism, and distortion of the optical system of Example 3 when focused on an object at infinity. [Figure 11] 10A to 10C are diagrams illustrating spherical aberration, astigmatism, and distortion of the optical system of Example 3 in a first close-distance object-focused state. [Figure 12] 10A to 10C are diagrams illustrating spherical aberration, astigmatism, and distortion of the optical system of Example 3 in a second close object focused state. [Figure 13] FIG. 10 is a cross-sectional view of a lens of an optical system according to a fourth embodiment of the present invention. [Figure 14] 10A to 10C are diagrams showing spherical aberration, astigmatism, and distortion of the optical system of Example 4 when focused on an object at infinity. [Figure 15] 10A to 10C are diagrams illustrating spherical aberration, astigmatism, and distortion of the optical system of Example 4 in a first close-distance object-focused state. [Figure 16] 10A to 10C are diagrams illustrating spherical aberration, astigmatism, and distortion of the optical system of Example 4 in a second close object focused state. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, an embodiment of the optical system and the imaging device according to the present invention will be described. However, the optical system and the imaging device described below are one aspect of the optical system and the imaging device according to the present invention, and the optical system and the imaging device according to the present invention are not limited to the following aspects.

[0015] 1.Optical system The optical system has multiple lens groups, the spacing between adjacent lens groups changing during focusing, and an aperture stop. Here, a "lens group" refers to a group consisting of one or more adjacent lenses, and the air spacing between adjacent lens groups changes during focusing. Furthermore, when referring to a "lens group," it is assumed that the air spacing between lenses included in that "lens group" does not change during focusing. Hereinafter, a lens group that moves along the optical axis during focusing will be referred to as a "focus group." Since the optical system has at least one focus group, it is composed of at least two lens groups. Below, we will discuss conditional expressions that the optical system should or preferably satisfy, and its operation during focusing.

[0016] 1-1.Conditional Expressions 1-1-1. Conditional expressions (1) to (3) The optical system satisfies the following condition when the distances between the exit pupil of an axial ray and the image plane defined by the aperture stop are Pinf, P1, and P2, respectively, in an infinity object focused state, a first close object focused state with an imaging magnification of β1, and a second close object focused state with an imaging magnification of β2. |β1| < |β2| (1) |Pinf|> |P1| (2) |P2| > |P1| (3) However, when the imaging magnification (maximum imaging magnification) in the closest focusing state in the optical system is βmax, |β2|≦|βmax| is satisfied. The first close-distance object focusing state refers to a state in which, when a target subject is focused at a first imaging distance, an object image that is |β1| times larger than the actual size of the subject is formed on the image plane, and the second close-distance object focusing state refers to a state in which, when a target subject is focused at a second imaging distance, an object image that is |β2| times larger than 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 an object at a close distance, the spacing between adjacent lens groups is changed to focus on the target subject. If conditional expressions (1) to (3) above are satisfied depending on the imaging distance, the exit pupil position moves toward the image side when focusing from an object at infinity to a first close object. When focusing from the first close object to a second close object, the exit pupil position moves toward the object side. In this way, when focusing from an object at infinity to a second close object, the exit pupil position moves toward the image side and then toward the object side. This reduces fluctuations in the exit pupil position during focusing across the entire focus range, thereby suppressing image plane fluctuations during focusing. This reduces the number of lenses required for aberration correction, and allows for an optical system with high imaging performance while maintaining a compact overall size, even when the maximum imaging magnification is increased.

[0018] Furthermore, by satisfying conditional expressions (2) and (3), it is possible to prevent the position of the exit pupil from fluctuating significantly from the position when the lens is focused on an object at infinity, even when capturing an image close to the subject (even when the imaging magnification is greater than β1). Furthermore, as described above, high imaging performance can be achieved with a small number of lenses, and therefore the decrease in brightness that accompanies an increase in the number of lenses can be suppressed. These factors make it easy to increase the aperture while maintaining a compact overall size. As described above, by satisfying the above conditional expressions (1) to (3), it is possible to obtain an optical system with a larger aperture and a 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 condition. |β1| > 0.2 (4) |β2| ≧ 0.8 (5)

[0020] When the above conditional expression (5) is satisfied, the optical system can be a macro lens with a maximum imaging magnification of 0.8 or more. In this case, by satisfying the above conditional expression (4), even when an optical system with a large maximum imaging magnification is configured, the effects obtained by satisfying the above conditional expressions (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] In order to obtain the above effect, the lower limit of conditional formula (4) is more preferably 0.25, even more preferably 0.3, and even more preferably 0.4. Furthermore, the upper limit of conditional formula (4) is required to be less than |β2| as defined in the above conditional formula (1). When the optical system satisfies conditional formula (5), the upper limit of conditional formula (4) is preferably 0.7, and more preferably 0.6. Furthermore, the lower limit of conditional formula (5) is more preferably 0.85, even more preferably 0.9, and even more preferably 0.95. Note that in conditional formulas (4) and (5), the inequality sign (<) may be replaced with an inequality sign with an equal sign (≦). Regarding the upper limit of conditional formula (4), the numerical value of conditional formula (4) may be equal to or less than the numerical values ​​listed above.

[0022] 1-2.Focusing operation In this optical system, one or more lens groups are moved along the optical axis to focus on a subject. In this case, as long as the above conditional expressions (1) to (3) are satisfied, there are no particular restrictions on the operation of the optical system during focusing, but it is preferable to do so as follows.

[0023] 1-2-1. From infinity to first close-up focus During the period from the infinity object focus state to the first close object focus state, it is preferable to focus on the subject as follows.

[0024] (1) Inner focus method First, it is preferable that the lens group disposed closest to the object side in the optical system (the lens group closest to the object) is fixed in the optical axis direction from the infinity object focusing state to the first close object focusing state, i.e., it is preferable that the subject is focused by the inner focus method from the infinity object focusing state to the first close object focusing state.

[0025] When the inner focus system is adopted, a smaller and lighter lens group can be used as the focus group compared to the lens group closest to the object. This makes it easier to achieve high-speed autofocus. Furthermore, compared to when the lens group closest to the object is used as the focus group, it makes it easier to suppress fluctuations in the angle of view during focusing. During video capture, live view capture, and other such captures, the focus group is wobbled at high speed with a small amplitude along the optical axis to determine the optimal position for the focus group so that the target subject is in focus, and then the focus group is moved to that optimal position. In this case, using the inner focus system can suppress fluctuations in the angle of view associated with the vibration of the focus group during wobbling. Therefore, fluctuations in the size of the subject image during wobbling can be suppressed, preventing the user from experiencing discomfort during video capture, live view capture, and other such captures.

[0026] (2) Floating method It is preferable that focusing is performed by moving two lens groups in the optical axis direction from the infinity object focusing state to the first close object focusing state, and that an aperture stop be disposed between the two lens groups.

[0027] By doing so, it is possible to focus on the subject by so-called floating focus during the period from the infinity object focus state to the first close object focus state, and it is possible to suppress aberration fluctuations during focusing.

[0028] (3) Single Lens Element From the infinity object focusing state to the first close object focusing state, it is preferable that a lens group consisting of a single lens element is used as a focus group, and that the focus group is moved in the optical axis direction to focus on the subject. In other words, it is preferable that the lens group that functions as the focus group from the infinity object focusing state to the first close object focusing state be composed of a single lens element.

[0029] Here, a "single lens element" refers to an element consisting of only one lens or a cemented lens formed by cementing multiple lenses together. By using a lens group consisting of a single lens element as the focus group for the range from an infinity focus state to a first close-up focus state, 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 be made smaller and lighter, thereby enabling the entire lens unit to be made smaller and lighter.

[0030] 1-2-2. From the first close-up focus state to the second close-up focus state It is preferable that focusing be performed by moving a plurality of lens groups along the same locus along the optical axis direction between the first close-distance object focusing state and the second close-distance object focusing state.

[0031] By doing so, multiple lens groups can be fixed to the same lens frame and moved simultaneously by driving the lens frame with a single drive mechanism. In this case, there is no need to provide a drive mechanism for each lens group, which simplifies the focus drive mechanism and allows the entire lens unit to be configured compactly. The multiple lens groups may be two lens groups, or three or more lens groups.

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

[0033] During focusing between the first close object focus state and the second close object focus state, the lens group closest to the object side may be configured as a fixed group or as a focus group.

[0034] If the lens group closest to the object is fixed between the first close-object focusing state and the second close-object focusing state, the subject can be focused by the inner focusing method during that period, which makes it possible to reduce the size and weight of the focus group and simplify the drive mechanism for driving the focus group, resulting in a compact lens unit overall. Also, because the lens barrel length does not change during focusing, the object side of the lens barrel can be sealed, making it easy to make the lens barrel waterproof and dustproof.

[0035] On the other hand, if the lens group closest to the object is used as the focus group during the transition from the first close-distance object focusing state to the second close-distance object focusing state, and the lens group closest to the object is moved in the optical axis direction to focus on the subject, it becomes easier to reduce the overall size while improving the maximum imaging magnification and shortening the minimum imaging distance. This is for the following reasons. First, if the lens unit closest to the object side is fixed throughout the entire focusing range, restrictions will arise in the optical configuration, making it difficult to shorten the minimum imaging distance or improve the maximum imaging magnification while maintaining a compact overall optical system. On the other hand, if the lens unit closest to the object side is extended, for example, toward the object side depending on the imaging distance during focusing, the degree of freedom in the optical configuration will increase, making it easier to shorten the minimum imaging distance or improve the maximum imaging magnification. Furthermore, by moving the lens unit closest to the object side toward the image side when not taking images, it will be possible to make the overall optical system compact.

[0036] When the imaging magnification is low, it is relatively easy to capture an image of a subject while focusing on the object point intended by the user, even when an autofocus system is used. However, when capturing an image of a subject at a higher imaging magnification closer to the subject, it is generally difficult to focus on the object point intended by the user using an autofocus system. Therefore, high-speed autofocus is achieved by fixing the most object-side lens group in the optical axis direction and focusing on the subject using an inner focus system from the infinity object-focused state to the first close-up object-focused state, and by focusing on the subject using a manual focus system from the first close-up object-focused state to the second close-up object-focused state, thereby improving user usability. Furthermore, if the most object-side lens group is configured to be extended forward by a cam mechanism provided in the lens barrel from the first close-up object-focused state to the second close-up object-focused state, there is no need to provide a focus drive mechanism for driving the most object-side lens group, and the entire lens unit can be made smaller and lighter.

[0037] 1-2-4. Final lens group In this optical system, it is preferable that the lens group (final lens group) located closest to the image plane is fixed in the optical axis direction during focusing. By making the final lens group a fixed group in this way, there is no need to place a drive mechanism for driving the final lens group on the image plane side, which simplifies the lens barrel structure. Furthermore, by making the final lens group a fixed group, the image plane side of the lens barrel can be made into a sealed structure, which prevents dust, dirt, water, etc. from entering from the image plane side.

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

[0039] 1-2-5. Lens group configuration Although the lens group configuration in this optical system is not particularly limited, it is easy to obtain an optical system that satisfies conditional expressions (1) to (3) by using different lens groups as the focus group between the infinity object focus state and the first close object focus state and between the first close object focus state and the second close object focus state. Specifically, it is preferable that the optical system includes a first focus group that moves along the optical axis direction between the infinity object focus state and the first close object focus state, and a second focus group that moves along the optical axis direction between the first close object focus state and the second close object focus state, wherein the second focus group is fixed in the optical axis direction between the infinity object focus state and the first close object focus state, and the first focus group is fixed in the optical axis direction between the first close object focus state and the second close object focus state.

[0040] In this optical system, when the inner focus system is used from the infinity object focus state to the first close object focus state as described above, the first focus group is required to be a lens group located closer to the image plane than the lens group closest to the object. Furthermore, when the floating focus system is used, the optical system is required to have two or more first focus groups, and it is preferable to place an aperture stop between the first focus groups. Furthermore, it is preferable that the first focus group be composed of a single lens element.

[0041] In addition, it is preferable that the optical system has one or more second focus groups. For example, the second focus group can be a lens group arranged between the first focus groups, or a lens group closest to the object side.

[0042] 2. Imaging device Next, we will explain the imaging device of the present invention. The imaging device of the present invention is characterized by including the imaging lens of the present invention described above and an imaging element that converts an optical image formed by the imaging lens into an electrical signal. The imaging element is preferably provided on the image side of the optical system.

[0043] Here, the imaging element is not particularly limited, and solid-state imaging elements such as a CCD (Charge Coupled Device) sensor or a CMOS (Complementary Metal Oxide Semiconductor) sensor can also be used. The imaging device of the present invention is suitable for imaging devices using such solid-state imaging elements, such as digital cameras and video cameras. The imaging device can also be applied to various imaging devices, such as single-lens reflex cameras, mirrorless single-lens cameras, digital still cameras, surveillance cameras, in-vehicle cameras, and drone-mounted 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, making it suitable for so-called macro lenses capable of capturing images close to a subject. Therefore, the imaging lens is suitable for applications requiring large-scale imaging of a subject, such as single-lens reflex cameras, mirrorless single-lens cameras, and industrial imaging devices.

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

[0045] (1) Optical configuration 1 is a lens cross-sectional view of an optical system according to Example 1 of the present invention, with the upper diagram showing an infinity object focused state, the middle diagram showing a first close-up object focused state (imaging magnification β1), and the lower diagram showing a second close-up object focused state (imaging magnification β2). The same applies to the lens cross-sectional views shown in each of the following Examples, and therefore further explanation will be omitted below.

[0046] As shown in Figure 1, the optical system includes, 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. An aperture stop 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 Example 1, the "imaging magnification β1" is -0.5 and the "imaging magnification β2" is -1.0, and the imaging magnification β2 corresponds to the maximum imaging magnification βmax of the optical system. In this optical system, from an infinity-object-focused state to a first close-distance object-focused state, the second lens group G2 and the fourth lens group G4 are moved along the optical axis to focus on the subject, and the first lens group G1, the third lens group G3, and the fifth lens group G5 are fixed in the optical axis direction. Also, from the first close-distance object-focused state to a second close-distance object-focused state, the first lens group G1 and the third lens group G3 are moved along the same locus along the optical axis to focus on the subject, and the second lens group G2, the fourth lens group G4, and the fifth lens group G5 are fixed in the optical axis direction. The second lens group G2 and the fourth lens group G4 are a first focus group, and the first lens group G1 and the third lens group G3 are a second focus group.

[0048] In Figure 1, "Pinf," "P1," and "P2" represent the exit pupil positions when the lens is focused on an object at infinity, the first close-up object focus state, and the second close-up object focus state, respectively. As shown in Figure 1, fluctuations in the exit pupil position are suppressed throughout the entire focus range. In FIG. 1, "IMG" denotes an image plane, specifically the imaging surface of a solid-state imaging device such as a CCD sensor or CMOS sensor, or the film surface of a silver halide film. A cover glass CG or the like is provided on the object side of the IP. This is the same for the lens cross-sectional views 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, showing the surface data, various data, variable distances during focusing, and focal lengths of each lens group of the optical system. In the tables showing surface data, "No." indicates the order of the lens surface counted from the object side (surface number), "R" indicates the radius of curvature of the lens surface, "D" indicates the spacing on the optical axis of the lens surface, "Nd" indicates the refractive index for the d-line (wavelength λ=587.6 nm), and "ABV" indicates the Abbe number for the d-line. In the "No." column, "STOP" displayed next to the surface number indicates the aperture stop. In the "D" column, "D○○" (e.g., D7 in this example) indicates the variable spacing during focusing. In the tables shown below, all length units are "mm," and all angle of view units are "°." In each table, "∞" indicates infinity.

[0050] In the tables showing various data, "f" is the focal length of the optical system, "β" is the imaging magnification, "Fno" is the F-number, "ω" is the half angle of view, "Y" is the image height, "BF" is the back focal length, and "TL" is the total optical length, which respectively show values ​​when the lens is focused on an object at infinity, when the lens is focused on a first close object, and when the lens is focused on a second close object. However, the values ​​in the tables include a 2.5 mm thick cover glass (Nd=1.5168), and the same applies to the back focal lengths shown in other examples.

[0051] The table showing the variable distances during focusing shows the variable distances when focusing on an object at infinity, when focusing on a first close object, and when focusing on a second close object, along with the focal length (f) and imaging distance at that time. The table showing the focal lengths of each lens group shows the lens surfaces included in each lens group and the focal lengths of each lens group.

[0052] Furthermore, the numerical values ​​used in each of the conditional expressions (1) to (5) are shown in Table 1 (to be shown later). The matters relating to these tables are the same as those in the tables shown in the other examples, and therefore will not be described below.

[0053] 2, 3, and 4 show longitudinal aberration diagrams of the optical system in an infinity object focused state, a first close object focused state (imaging magnification β1), and a second close object focused state (imaging magnification β2). In each longitudinal aberration diagram, spherical aberration, astigmatism, and distortion are shown, from left to right. In the diagrams showing spherical aberration, the vertical axis represents the ratio to the maximum aperture, and the horizontal axis represents defocus. The solid line represents spherical aberration at the d-line (wavelength λ=587.56 nm), the dashed line represents spherical aberration at the C-line (wavelength λ=656.28 nm), and the dash-dot line represents spherical aberration at the F-line (wavelength λ=486.13 nm). In the diagrams showing astigmatism, the vertical axis represents half angle of view (ω), the horizontal axis represents defocus, and the solid line represents the sagittal image plane for the d-line, and the dotted line represents the meridional image plane for the d-line. In the diagrams showing distortion, the vertical axis represents the half angle of view (ω) and the horizontal axis represents distortion in %. The matters relating to these diagrams are the same as those in the longitudinal aberration diagrams shown in other embodiments, so explanations thereof will be 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 [Example]

[0058] (1) Optical configuration Figure 5 is a cross-sectional view of lenses in an optical system according to a second embodiment of the present invention. As shown in Figure 5, the optical system includes, 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. An aperture stop S is disposed 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 Example 2, the "imaging magnification β1" is -0.5 and the "imaging magnification β2" is -0.8, and the imaging magnification β2 corresponds to the maximum imaging magnification βmax of the optical system. In this optical system, from an infinity object focusing state to a first close object focusing state, the second lens group G2 and the fourth lens group G4 are moved along the optical axis to focus on the subject, and the first lens group G1, the third lens group G3, and the fifth lens group G5 are fixed in the optical axis direction. Also, from the first close object focusing state to a second close object focusing state, the third lens group G3 is moved along the optical axis to focus on the subject, and the first lens group G1, the second lens group G2, the fourth lens group G4, and the fifth lens group G5 are fixed in the optical axis direction. The second lens group G2 and the fourth lens group G4 are the first focus group, and the third lens group G3 is the second focus group.

[0060] (2) Numerical examples Next, a numerical example of the optical system will be described below, showing the surface data, various data, variable distances during focusing, focal lengths of each lens group, and aspherical surface data of the optical system.

[0061] In the "No." column of the surface data, "ASPH" displayed in the column next to the surface number indicates that the surface is aspherical. "Aspherical surface data" indicates the aspherical coefficients of each aspherical surface. However, an aspherical surface is defined by the following equation, where x is the amount of displacement from the vertex of the surface in the optical axis direction. x=(h 2 / r) / [1+{1-(1+k)×(h / r) 2} 1 / 2 ] +A4×h 4 +A6×h 6 +A8×h 8 +A10×h 10 +A12×h 12 In the above formula, h is the height from the optical axis, r is the paraxial radius of curvature, k is the conic coefficient, and An is the n-th order Represents the aspherical coefficient. Also, "E±XX" represents the exponential notation, "×10 ±XX The same applies to aspherical surfaces below, so the explanation will be omitted.

[0062] 6, 7 and 8 show longitudinal aberration diagrams of the optical system in an infinity object focused state, a first close object focused state (imaging magnification β1), and a second close object focused 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] (aspheric 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 [Example]

[0068] (1) Optical configuration Figure 9 is a cross-sectional view of lenses in an optical system according to a third embodiment of the present invention. As shown in Figure 9, the optical system includes, 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. An aperture stop S is disposed 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 Example 3, the "imaging magnification β1" is -1.0 and the "imaging magnification β2" is -2.0, and the imaging magnification β2 corresponds to the maximum imaging magnification βmax of the optical system. In this optical system, from an infinity object-focused state to a first close-distance object-focused state, the second lens group G2 and the fourth lens group G4 are moved along the optical axis to focus on the subject, while the first lens group G1, the third lens group G3, and the fifth lens group G5 are fixed in the optical axis direction. Also, from the first close-distance object-focused state to a second close-distance object-focused state, the first lens group G1 and the third lens group G3 are moved along the optical axis to focus on the subject, while the second lens group G2, the fourth lens group G4, and the fifth lens group G5 are fixed in the optical axis direction. The second lens group G2 and the fourth lens group G4 are a first focus group, and the first lens group G1 and the third lens group G3 are a second focus group.

[0070] (2) Numerical examples Next, a numerical example of the optical system will be described below, showing the surface data, various data, variable distances during focusing, focal lengths of each lens group, and aspherical surface data of the optical system.

[0071] 10, 11 and 12 show longitudinal aberration diagrams of the optical system in an infinity object focused state, a first close object focused state (imaging magnification β1), and a second close object focused 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 D1 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 D1 19 463.2052 2.2000 1.84666 23.78 20 -53.0340 0.8000 1.77899 48.54 21 22.5173 D2 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] (Internet) 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] (aspheric 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 [Example]

[0077] (1) Optical configuration Figure 13 is a cross-sectional view of lenses in an optical system according to a fourth embodiment of the present invention. As shown in Figure 13, the optical system includes, 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. An aperture stop S is disposed 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 Example 4, the "imaging magnification β1" is -0.75 and the "imaging magnification β2" is -1.5, and the imaging magnification β2 corresponds to the maximum imaging magnification βmax of the optical system. In this optical system, from an infinity object focusing state to a first close object focusing state, the second lens group G2 and the fourth lens group G4 are moved along the optical axis to focus on the subject, and the first lens group G1 and the third lens group G3 are fixed in the optical axis direction. Also, from the first close object focusing state to a second close object focusing state, the first lens group G1 and the third lens group G3 are moved along the optical axis to focus on the subject, and the second lens group G2 and the fourth lens group G4 are fixed in the optical axis direction. The second lens group G2 and the fourth lens group G4 are a first focus group, and the first lens group G1 and the third lens group G3 are a second focus group.

[0079] (2) Numerical examples Next, a numerical example of the optical system will be described below, showing the surface data, various data, variable distances during focusing, focal lengths of each lens group, and aspherical surface data of the optical system.

[0080] 14, 15 and 16 show longitudinal aberration diagrams of the optical system in an infinity object focused state, a first close object focused state (imaging magnification β1) and a second close object focused 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 D1 19 -48.5273 2.2089 1.84666 23.78 20 -30.3491 0.8000 1.49700 81.61 21 30.5832 D2 22 ∞ 2.5000 1.51633 64.14 23 ∞ 1.0000

[0082] (Internet) 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] (aspheric 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 an imaging device that have a larger aperture and a higher imaging magnification while maintaining a small overall size.

Claims

1. An optical system having a plurality of lens groups in which the intervals between adjacent lens groups change during focusing, and an aperture stop, When the distances between the exit pupil of an axial ray and the image plane by the aperture stop in an infinity object focusing state, a first close object focusing state with an imaging magnification of β1, and a second close object focusing state with an imaging magnification of β2 are Pinf, P1, and P2, respectively, between the infinity object focused state and the first close object focused state, focusing is performed by moving two lens groups in the optical axis direction, and the aperture stop is disposed between the two lens groups; An optical system characterized by satisfying the following conditions: ｜β１｜ ＜ ｜β２｜ ・・・（１） |Pinf|> |P1| ...(2) |P2| > |P1| ...(3)

2. 2. The optical system according to claim 1, wherein the lens group disposed closest to the image plane is fixed in the optical axis direction during focusing.

3. 3. The optical system according to claim 1, wherein the following condition is satisfied: ｜β１｜ ＞ ０．２ ・・・（４） ｜β２｜ ≧ ０．８ ・・・（５）

4. 4. The optical system according to claim 1, wherein the lens group arranged closest to the object side is fixed in the optical axis direction from the infinity object-focused state to the first close-distance object-focused state.

5. 5. The optical system according to claim 1, wherein focusing is performed by moving a lens group consisting of a single lens element in the optical axis direction between the infinity object focusing state and the first close object focusing state.

6. 6. The optical system according to claim 1, wherein focusing is performed by moving a plurality of lens groups along the same trajectory along the optical axis direction between the first close-distance object focusing state and the second close-distance object focusing state.

7. a first focus group that moves along an optical axis direction from the infinity object focus state to the first close object focus state, and a second focus group that moves along the optical axis direction from the first close object focus state to the second close object focus state, 7. The optical system according to claim 1, wherein the second focus group is fixed in the optical axis direction from the infinity object focus state to the first close-distance object focus state, and the first focus group is fixed in the optical axis direction from the first close-distance object focus state to the second close-distance object focus state.

8. 8. An imaging apparatus comprising: the optical system according to claim 1; and an imaging element that converts an optical image formed by the optical system into an electrical signal.

Images