Optical Systems and Optical Instruments

Abstract

To provide an optical system with less fluctuation in an angle of view upon focusing.SOLUTION: An optical system OL comprises a preceding lens group GA having negative refractive power and a succeeding lens group GB having positive refractive power, arranged in order from an object side along an optical axis. The succeeding lens group GB includes a focusing group GF having positive refractive power disposed closest to the object side of the succeeding lens group GB and an image-side group GC disposed closer to an image side than the focusing group GF. The focusing group GF moves toward the image side along the optical axis while focusing from an infinitely distant object to a short-distance object. The image-side group GC has a lens group having negative refractive power disposed closest to the image side.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an optical system and an optical instrument. [Background technology]

[0002] Conventionally, optical systems suitable for photo cameras, electronic still cameras, video cameras, etc. have been proposed (see, for example, Patent Document 1). In such optical systems, it is required to suppress fluctuations in the angle of view when focusing. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-117419 Summary of the Invention

[0004] A first optical system according to the present invention comprises, arranged in order from the object side along the optical axis, a first lens group having negative refractive power and a subsequent lens group having positive refractive power, the subsequent lens group comprising, arranged in order from the object side along the optical axis, a second lens group having positive refractive power and an image-side group having a plurality of lens groups, the second lens group moving during focusing to change the spacing between adjacent lens groups, and satisfying the following conditional expression: 1.00<βB / βC<10.00 however, βB: Magnification of the subsequent lens group when focusing on an object at infinity βC: Magnification of the image-side group when focusing on an object at infinity

[0005] A second optical system according to the present invention comprises, arranged in order from the object side along the optical axis, a first lens group having negative refractive power and a subsequent lens group having positive refractive power, the subsequent lens group comprising, arranged in order from the object side along the optical axis, a second lens group having positive refractive power and an image-side group having a plurality of lens groups, the second lens group moving during focusing to change the spacing between adjacent lens groups, and satisfying the following conditional expression: 0.78 <fB / fC<1.00 however, fB: focal length of the subsequent group when focusing on an object at infinity fC: focal length of the image-side group when focusing on an object at infinity

[0006] An optical device according to the present invention includes the optical system described above. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 2 is a diagram showing the lens configuration of an optical system according to Example 1. [Figure 2] 2A and 2B are diagrams showing various aberrations of the optical system according to Example 1 when focused at infinity and when focused at a close distance, respectively. [Figure 3] FIG. 10 is a diagram showing the lens configuration of an optical system according to a second example. [Figure 4] 4A and 4B are diagrams showing various aberrations of the optical system according to Example 2 when focused at infinity and when focused at a close distance, respectively. [Figure 5] FIG. 10 is a diagram showing the lens configuration of an optical system according to Example 3. [Figure 6] 6A and 6B are diagrams showing various aberrations of the optical system according to Example 3 when focused at infinity and when focused at a close distance, respectively. [Figure 7] FIG. 1 is a diagram showing the configuration of a camera including an optical system according to each embodiment. [Figure 8] 1 is a flowchart illustrating a method for manufacturing an optical system according to each embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0008] Preferred embodiments of the present invention will be described below. First, a camera (optical device) equipped with an optical system according to each embodiment will be described with reference to FIG. 7. As shown in FIG. 7, this camera 1 is composed of a main body 2 and a photographic lens 3 attached to the main body 2. The main body 2 is equipped with an image sensor 4, a main body control unit (not shown) that controls the operation of the digital camera, and an LCD screen 5. The photographic lens 3 is equipped with an optical system OL consisting of multiple lens groups, and a lens position control mechanism (not shown) that controls the position of each lens group. The lens position control mechanism is composed of a sensor that detects the position of the lens groups, a motor that moves the lens groups back and forth along the optical axis, a control circuit that drives the motor, etc.

[0009] Light from the subject is collected by the optical system OL of the photographing lens 3 and reaches the image plane I of the image sensor 4. The light from the subject that reaches the image plane I is photoelectrically converted by the image sensor 4 and recorded as digital image data in a memory (not shown). The digital image data recorded in the memory can be displayed on the liquid crystal screen 5 in response to a user operation. Note that this camera may be a mirrorless camera or a single-lens reflex camera with a quick-return mirror.

[0010] Next, an optical system according to a first embodiment will be described. As shown in FIG. 1, an optical system OL(1) as an example of an optical system (photographing lens) OL according to the first embodiment is composed of, in order from the object side along the optical axis, a leading lens group GA having negative refractive power and a trailing lens group GB having positive refractive power. The trailing lens group GB has a focusing group GF having positive refractive power and arranged closest to the object side of the trailing lens group GB, and an image-side group GC arranged closer to the image side than the focusing group GF. When focusing from an object at infinity to a close-distance object, the focusing group GF moves toward the image side along the optical axis.

[0011] With the above-described configuration, the optical system OL according to the first embodiment satisfies the following conditional expression (1). 0.78 <fB / fC<1.00 ···(1) where fB is the focal length of the subsequent lens group GB when focusing on an object at infinity fC: focal length of the image-side group GC when focusing on an object at infinity

[0012] According to the first embodiment, it is possible to obtain an optical system with little fluctuation in the angle of view during focusing, and an optical device equipped with this optical system. The optical system OL according to the first embodiment may be the optical system OL(2) shown in Fig. 3 or the optical system OL(3) shown in Fig. 5.

[0013] Conditional expression (1) defines an appropriate relationship between the focal length of the rear lens group GB when focusing on an object at infinity and the focal length of the image-side lens group GC when focusing on an object at infinity. By satisfying conditional expression (1), fluctuations in the angle of view during focusing can be reduced.

[0014] If the value corresponding to conditional expression (1) falls outside the above range, it becomes difficult to suppress fluctuations in the angle of view during focusing. By setting the lower limit of conditional expression (1) to 0.79, 0.80, 0.81, 0.82, or even 0.83, the effects of this embodiment can be more reliably achieved. Furthermore, by setting the upper limit of conditional expression (1) to 0.98, 0.96, 0.95, or even 0.94, the effects of this embodiment can be more reliably achieved.

[0015] It is desirable that the optical system OL according to the first embodiment satisfy the following conditional expression (2). 0.010 <BLDF / TL<0.160 ···(2) However, TL: total length of optical system OL BLDF: Length of focusing group GF on the optical axis

[0016] Condition (2) defines the appropriate relationship between the axial length of the focusing group GF and the overall length of the optical system OL. Satisfying condition (2) makes it possible to reduce the weight of the focusing group and achieve high-speed focusing.

[0017] If the value corresponding to conditional expression (2) falls outside the above range, it becomes difficult to reduce the weight of the focusing group. The effects of this embodiment can be further ensured by setting the lower limit of conditional expression (2) to 0.015, 0.020, 0.023, 0.025, 0.028, 0.030, 0.033, or even 0.035. Furthermore, the effects of this embodiment can be further ensured by setting the upper limit of conditional expression (2) to 0.150, 0.130, 0.110, 0.080, 0.060, or even 0.050.

[0018] Next, an optical system according to a second embodiment will be described. As shown in FIG. 1, an optical system OL(1) as an example of an optical system (photographing lens) OL according to the second embodiment is composed of, arranged in order from the object side along the optical axis, a leading lens group GA having negative refractive power and a trailing lens group GB having positive refractive power. The trailing lens group GB has a focusing group GF having positive refractive power and arranged closest to the object side of the trailing lens group GB, and an image-side group GC arranged closer to the image side than the focusing group GF. When focusing from an object at infinity to a close-distance object, the focusing group GF moves toward the image side along the optical axis.

[0019] With the above-described configuration, the optical system OL according to the second embodiment satisfies the following conditional expression (3). 1.00<βB / βC<10.00 (3) where βB is the magnification of the subsequent lens group GB when focusing on an object at infinity. βC: Magnification of the image-side group GC when focusing on an object at infinity

[0020] According to the second embodiment, it is possible to obtain an optical system with little fluctuation in the angle of view during focusing, and an optical device equipped with this optical system. The optical system OL according to the second embodiment may be the optical system OL(2) shown in Fig. 3 or the optical system OL(3) shown in Fig. 5.

[0021] Conditional expression (3) defines an appropriate relationship between the magnification of the subsequent lens group GB when focusing on an object at infinity and the magnification of the image-side group GC when focusing on an object at infinity. By satisfying conditional expression (3), fluctuations in the angle of view during focusing can be reduced.

[0022] If the value corresponding to conditional expression (3) falls outside the above range, it becomes difficult to suppress fluctuations in the angle of view during focusing. By setting the lower limit of conditional expression (3) to 1.40, 1.80, 2.20, 2.50, or even 2.60, the effects of this embodiment can be further ensured. Furthermore, by setting the upper limit of conditional expression (3) to 8.00, 7.50, 7.00, 6.50, 6.00, 5.50, 5.00, or even 4.50, the effects of this embodiment can be further ensured.

[0023] It is desirable that the optical system OL according to the second embodiment satisfy the above-mentioned conditional expression (2). By satisfying conditional expression (2), high-speed focusing can be achieved, as in the first embodiment. By setting the lower limit of conditional expression (2) to 0.015, 0.020, 0.023, 0.025, 0.028, 0.030, 0.033, or even 0.035, the effects of this embodiment can be made more certain. Furthermore, by setting the upper limit of conditional expression (2) to 0.150, 0.130, 0.110, 0.080, 0.060, or even 0.050, the effects of this embodiment can be made more certain.

[0024] The optical system OL according to the second embodiment may satisfy the above-mentioned conditional expression (1). By satisfying conditional expression (1), it is possible to reduce fluctuations in the angle of view during focusing, as in the first embodiment. By setting the lower limit of conditional expression (1) to 0.79, 0.80, 0.81, 0.82, or even 0.83, it is possible to further ensure the effects of the second embodiment. Furthermore, by setting the upper limit of conditional expression (1) to 0.98, 0.96, 0.95, or even 0.94, it is possible to further ensure the effects of the second embodiment.

[0025] Furthermore, the optical system OL according to the first embodiment may satisfy the above-mentioned conditional expression (3). By satisfying conditional expression (3), it is possible to reduce fluctuations in the angle of view during focusing, as in the second embodiment. By setting the lower limit of conditional expression (3) to 1.40, 1.80, 2.20, 2.50, or even 2.60, it is possible to further ensure the effects of the first embodiment. By setting the upper limit of conditional expression (3) to 8.00, 7.50, 7.00, 6.50, 6.00, 5.50, 5.00, or even 4.50, it is possible to further ensure the effects of the first embodiment.

[0026] It is desirable that the optical systems OL according to the first and second embodiments satisfy the following conditional expression (4). 0.50<(-fA) / f<1.50 (4) where fA is the focal length of the leading lens group GA f: focal length of optical system OL when focusing on an object at infinity

[0027] Condition (4) defines the appropriate relationship between the focal length of the leading lens group GA and the focal length of the optical system OL when focused on an object at infinity. By satisfying condition (4), various aberrations such as field curvature can be effectively corrected.

[0028] If the value corresponding to conditional expression (4) falls outside the above range, it becomes difficult to correct various aberrations such as field curvature. By setting the lower limit of conditional expression (4) to 0.60, 0.70, 0.75, 0.80, 0.85, 0.90, 0.95, or even 0.98, the effects of each embodiment can be more reliably achieved. Furthermore, by setting the upper limit of conditional expression (4) to 1.45, 1.40, 1.35, 1.30, 1.25, 1.20, 1.18, or even 1.15, the effects of each embodiment can be more reliably achieved.

[0029] It is desirable that the optical systems OL according to the first and second embodiments satisfy the following conditional expression (5). -3.00<(rL1R2+rL1R1) / (rL1R2-rL1R1)<0.00 ···(5) where rL1R1 is the radius of curvature of the lens surface on the object side of the lens arranged closest to the object side in the optical system OL. rL1R2: Radius of curvature of the image-side lens surface of the lens located closest to the object in the optical system OL

[0030] Condition (5) defines an appropriate shape factor for the lens element located closest to the object in optical system OL. Satisfying condition (5) enables good correction of coma and curvature of field.

[0031] If the value corresponding to conditional expression (5) falls outside the above range, it becomes difficult to correct coma and curvature of field. By setting the lower limit of conditional expression (5) to -2.70, -2.50, -2.30, -2.00, -1.80, or -1.70, the effects of each embodiment can be more reliably achieved. Furthermore, by setting the upper limit of conditional expression (5) to -0.40, -0.60, -0.80, -1.00, -1.20, or -1.30, the effects of each embodiment can be more reliably achieved.

[0032] It is desirable that the optical systems OL according to the first and second embodiments satisfy the following conditional expression (6). -5.00<(rL2R2+rL2R1) / (rL2R2-rL2R1)<-2.00 ···(6) where rL2R1 is the radius of curvature of the object-side lens surface of the second lens element in the optical system OL, counting from the object side. rL2R2: Radius of curvature of the image-side lens surface of the second lens located from the object side of the optical system OL

[0033] Conditional formula (6) defines the appropriate shape factor for the second lens element in optical system OL, counting from the object side. Satisfying conditional formula (6) enables good correction of coma and curvature of field.

[0034] If the value corresponding to conditional expression (6) falls outside the above range, it becomes difficult to correct coma aberration and field curvature. By setting the lower limit of conditional expression (6) to -4.80, -4.60, -4.50, -4.40, or -4.30, the effects of each embodiment can be more reliably achieved. Furthermore, by setting the upper limit of conditional expression (6) to -2.20, -2.40, -2.50, -2.60, -2.70, or -2.80, the effects of each embodiment can be more reliably achieved.

[0035] It is desirable that the optical systems OL according to the first and second embodiments satisfy the following conditional expression (7). 60.00°<2ω<130.00° ···(7) However, 2ω: the total angle of view of the optical system OL when focusing on an object at infinity

[0036] Conditional expression (7) defines an appropriate range for the total angle of view of the optical system OL when focusing on an object at infinity. Satisfying conditional expression (7) is preferable because it provides an optical system with a wide angle of view. Setting the lower limit of conditional expression (7) to 64.00°, 68.00°, 72.00°, 76.00°, or even 80.00° can further ensure the effects of each embodiment. Furthermore, setting the upper limit of conditional expression (7) to 125.00°, 120.00°, 115.00°, 110.00°, or even 105.00° can further ensure the effects of each embodiment.

[0037] It is desirable that the optical systems OL according to the first and second embodiments satisfy the following conditional expression (8). 1.20 <FNO<3.00 ···(8) However, FNO: F-number of the optical system OL when focusing on an object at infinity

[0038] Conditional expression (8) defines an appropriate range for the F-number of the optical system OL when focusing on an object at infinity. Satisfying conditional expression (8) is preferable because it results in a bright optical system. Setting the lower limit of conditional expression (8) to 1.25, 1.30, 1.40, 1.50, 1.60, 1.70, or even 1.75 can further ensure the effects of each embodiment. Furthermore, setting the upper limit of conditional expression (8) to 2.80, 2.65, 2.50, 2.40, 2.30, or even 2.20 can further ensure the effects of each embodiment.

[0039] In the optical systems OL according to the first and second embodiments, it is desirable that an aperture stop S is disposed in the subsequent lens group GB and that the following conditional expression (9) is satisfied: 0.35 <STL / TL<0.70 ···(9) However, STL: Distance on the optical axis from aperture stop S to image plane I when focusing on an object at infinity TL: Total length of optical system OL

[0040] Condition (9) defines an appropriate position for the aperture stop S. By satisfying condition (9), the amount of peripheral light can be ensured.

[0041] If the value corresponding to conditional expression (9) falls outside the above range, it becomes difficult to ensure the amount of peripheral light. By setting the lower limit of conditional expression (9) to 0.38, 0.40, 0.42, 0.45, or even 0.48, the effects of each embodiment can be more reliably achieved. Furthermore, by setting the upper limit of conditional expression (9) to 0.68, 0.65, 0.63, 0.60, 0.58, or even 0.57, the effects of each embodiment can be more reliably achieved.

[0042] It is desirable that the optical systems OL according to the first and second embodiments satisfy the following conditional expression (10). 0.05 <Bf / TL<0.30 ···(10) However, Bf is the back focus of the optical system OL. TL: Total length of optical system OL

[0043] Condition (10) defines an appropriate relationship between the back focal length of the optical system OL and the overall length of the optical system OL. By satisfying condition (10), various aberrations such as field curvature and distortion can be effectively corrected.

[0044] If the value corresponding to conditional expression (10) falls outside the above range, it becomes difficult to correct various aberrations such as curvature of field and distortion. By setting the lower limit of conditional expression (10) to 0.06, 0.07, 0.08, 0.09, or even 0.10, the effects of each embodiment can be more reliably achieved. Furthermore, by setting the upper limit of conditional expression (10) to 0.27, 0.25, 0.23, 0.20, 0.18, 0.16, or even 0.15, the effects of each embodiment can be more reliably achieved.

[0045] It is desirable that the optical systems OL according to the first and second embodiments satisfy the following conditional expression (11). 1.50 <fF / f<4.50 ···(11) where fF is the focal length of the focusing group GF f: focal length of optical system OL when focusing on an object at infinity

[0046] Conditional expression (11) defines an appropriate relationship between the focal length of the focusing group GF and the focal length of the optical system OL when focusing on an object at infinity. By satisfying conditional expression (11), good optical performance can be obtained both when focusing on an object at infinity and when focusing on a close object.

[0047] If the value corresponding to conditional expression (11) falls outside the above range, it becomes difficult to obtain good optical performance both when focusing on an object at infinity and when focusing on an object at close range. By setting the lower limit of conditional expression (11) to 1.60, 1.80, 2.20, 2.30, 2.40, 2.45, 2.50, or even 2.55, the effects of each embodiment can be further ensured. Furthermore, by setting the upper limit of conditional expression (11) to 4.20, 4.00, 3.80, 3.60, 3.50, 3.40, or even 3.30, the effects of each embodiment can be further ensured.

[0048] It is desirable that the optical systems OL according to the first and second embodiments satisfy the following conditional expression (12). 1.00 <fF / fB<3.00 ···(12) where fF is the focal length of the focusing group GF fB: focal length of the subsequent lens group GB when focusing on an object at infinity

[0049] Conditional expression (12) defines an appropriate relationship between the focal length of the focusing group GF and the focal length of the subsequent lens group GB when focusing on an object at infinity. By satisfying conditional expression (12), good optical performance can be obtained both when focusing on an object at infinity and when focusing on a close object.

[0050] If the value corresponding to conditional expression (12) falls outside the above range, it becomes difficult to obtain good optical performance both when focusing on an object at infinity and when focusing on an object at close range. By setting the lower limit of conditional expression (12) to 1.20, 1.30, 1.40, 1.50, 1.55, 1.60, or even 1.65, the effects of each embodiment can be further ensured. Furthermore, by setting the upper limit of conditional expression (12) to 2.80, 2.70, 2.60, 2.50, 2.40, 2.35, 2.30, 2.25, 2.20, or even 2.18, the effects of each embodiment can be further ensured.

[0051] It is desirable that the optical systems OL according to the first and second embodiments satisfy the following conditional expression (13). 0.15 <dF / TL<0.40 ···(13) where dF is the distance on the optical axis from the lens surface of the optical system OL closest to the object to the lens surface of the focusing group GF closest to the object when focusing on an object at infinity. TL: Total length of optical system OL

[0052] Conditional expression (13) defines an appropriate range for the distance on the optical axis from the lens surface closest to the object in the optical system OL to the lens surface closest to the object in the focusing group GF. Satisfying conditional expression (13) is preferable because it allows the focusing group GF to be positioned closer to the object in the optical system OL. Setting the lower limit of conditional expression (13) to 0.18, 0.20, 0.22, or even 0.23 can further enhance the effects of each embodiment. Setting the upper limit of conditional expression (13) to 0.38, 0.35, 0.33, or even 0.30 can further enhance the effects of each embodiment.

[0053] It is desirable that the optical systems OL according to the first and second embodiments satisfy the following conditional expression (14). 0.00<1 / βF<0.60 (14) where βF is the magnification of the focusing group GF when focusing on an object at infinity

[0054] Condition (14) defines an appropriate range for the magnification of the focusing group GF when focusing on an object at infinity. By satisfying condition (14), fluctuations in the angle of view when focusing can be reduced.

[0055] If the value corresponding to conditional expression (14) falls outside the above range, it becomes difficult to suppress fluctuations in the angle of view during focusing. By setting the lower limit of conditional expression (14) to 0.04, 0.05, 0.08, 0.10, 0.13, 0.15, 0.18, 0.20, or even 0.22, the effects of each embodiment can be more reliably achieved. Furthermore, by setting the upper limit of conditional expression (14) to 0.55, 0.53, 0.50, 0.48, 0.45, 0.42, 0.40, 0.38, or even 0.36, the effects of each embodiment can be more reliably achieved.

[0056] It is desirable that the optical systems OL according to the first and second embodiments satisfy the following conditional expression (15). {βF+(1 / βF)} -2 <0.18 (15) where βF is the magnification of the focusing group GF when focusing on an object at infinity

[0057] Condition (15) defines an appropriate range for the magnification of the focusing group GF when focusing on an object at infinity. By satisfying condition (15), fluctuations in the angle of view when focusing can be reduced.

[0058] If the value corresponding to conditional expression (15) is outside the above range, it becomes difficult to suppress fluctuations in the angle of view during focusing. By setting the upper limit of conditional expression (15) to 0.16, 0.15, 0.14, 0.13, 0.12, or even 0.11, the effects of each embodiment can be more reliably achieved.

[0059] Next, with reference to FIG. 8, a manufacturing method of the optical system OL according to the first and second embodiments will be outlined. First, a leading lens group GA having negative refractive power and a trailing lens group GB having positive refractive power are arranged, in order from the object side along the optical axis (Step ST1). Next, a focusing group GF having positive refractive power is arranged closest to the object side of the trailing lens group GB, and an image-side group GC is arranged closer to the image side than the focusing group GF of the trailing lens group GB (Step ST2). Next, the focusing group GF is configured to move toward the image side along the optical axis when focusing from an object at infinity to a close object (Step ST3). Then, in the case of the optical system OL according to the first embodiment, each lens is arranged in the lens barrel so as to satisfy at least the above conditional expression (1) (Step ST4). In the case of the optical system OL according to the second embodiment, each lens is arranged in the lens barrel so as to satisfy at least the above conditional expression (3) (Step ST4). This manufacturing method makes it possible to manufacture an optical system with little fluctuation in the angle of view during focusing. [Example]

[0060] Optical systems OL according to examples of each embodiment will be described below with reference to the drawings. Figures 1, 3, and 5 are cross-sectional views showing the configuration and refractive power distribution of optical systems OL {OL(1) to OL(3)} according to first to third examples. In the cross-sectional views of the optical systems OL(1) to OL(3) according to first to third examples, arrows indicate the direction of movement of each lens group along the optical axis when focusing from infinity to a close-distance object.

[0061] 1, 3, and 5, each lens group and each group is represented by a combination of the symbol G and a number, and each lens is represented by a combination of the symbol L and a number. In this case, to prevent the symbols and numbers from becoming too numerous and complicated, each embodiment uses its own unique combination of symbols and numbers to represent the lens groups, etc. Therefore, even if the same combination of symbols and numbers is used between embodiments, this does not mean that the embodiments have the same configuration.

[0062] Tables 1 to 3 are shown below, with Table 1 showing data on various elements in Example 1, Table 2 showing data on various elements in Example 2, and Table 3 showing data on various elements in Example 3. In each example, the d-line (wavelength λ=587.6 nm) and g-line (wavelength λ=435.8 nm) were selected as the targets for calculating aberration characteristics.

[0063] In the [Overall Specifications] table, f is the focal length of the entire lens system, FNO is the F-number, 2ω is the angle of view (units: ° (degrees), where ω is half the angle of view), and Y is the image height. TL is the distance from the frontmost lens surface to the last lens surface on the optical axis when focusing at infinity plus BF, and BF is the distance from the last lens surface on the optical axis to the image plane I when focusing at infinity (back focus). Also, in the [Overall Specifications] table, fA is the focal length of the leading lens group. fB is the focal length of the trailing lens group when focusing at infinity. fC is the focal length of the image-side group when focusing at infinity. fF is the focal length of the focusing group. βB is the magnification of the trailing lens group when focusing at infinity. βC is the magnification of the image-side group when focusing at infinity. βF is the magnification of the focusing group when focusing at infinity.

[0064] In the [Lens Specifications] table, the surface number indicates the order of the optical surface from the object side along the direction of light ray travel, R is the radius of curvature of each optical surface (surfaces whose center of curvature is on the image side have a positive value), D is the surface spacing, which is the distance on the optical axis from each optical surface to the next optical surface (or image plane), nd is the refractive index of the optical element material with respect to the d-line, and νd is the Abbe number of the optical element material with respect to the d-line. The "∞" next to the radius of curvature indicates a flat surface or an aperture, and (stop S) indicates the aperture stop S. The refractive index of air, nd = 1.00000, is omitted. If the optical surface is aspherical, an * is added to the surface number, and the paraxial radius of curvature is shown in the "radius of curvature R" column.

[0065] In the [Aspherical Data] table, the shape of the aspherical surface shown in [Lens Specifications] is shown by the following formula (A). X(y) is the distance (amount of sag) along the optical axis from the tangent plane at the vertex of the aspherical surface to the position on the aspherical surface at height y, R is the radius of curvature of the reference sphere (paraxial radius of curvature), κ is the conic constant, and Ai is the ith aspherical coefficient. "En" is the square root of the square root of the aspherical surface. -n For example, 1.234E-05 = 1.234 x 10 -5 The second-order aspherical coefficient A2 is 0, and is therefore omitted.

[0066] X(y)=(y 2 / R) / {1+(1-κ×y 2 / R 2 ) 1 / 2}+A4×y 4 +A6×y 6 +A8×y 8 +A10×y 10 +A12×y 12 …(A)

[0067] The [Variable Distance Data] table shows the surface spacing for surface number i, where the surface spacing in the [Lens Specifications] table is (Di). In the [Variable Distance Data] table, f indicates the focal length of the entire lens system, and β indicates the magnification.

[0068] The [Lens Group Data] table shows the starting surface (the surface closest to the object) and focal length of each lens group.

[0069] In the following, for all specifications, the focal length f, radius of curvature R, surface spacing D, and other lengths are generally expressed in "mm" unless otherwise specified, but this is not limited to this, as the same optical performance can be obtained even when the optical system is proportionally enlarged or reduced.

[0070] The explanation of the tables up to this point is common to all the embodiments, and duplicate explanations will be omitted below.

[0071] (First Example) The first embodiment will be described with reference to FIGS. 1 and 2 and Table 1. FIG. 1 illustrates the lens configuration of the optical system according to the first embodiment. The optical system OL(1) according to the first embodiment is composed of, arranged along the optical axis from the object side, a first lens group G1 having negative refractive power, a second lens group G2 having positive 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 negative refractive power. When focusing from an object at infinity to a close object, the second lens group G2 moves along the optical axis toward the image side, and the fourth lens group G4 moves along the optical axis toward the object side, changing the spacing between adjacent lens groups. During focusing, the first lens group G1, the third lens group G3, and the fifth lens group G5 are fixed relative to the image plane I. An aperture stop S is disposed within the third lens group G3. The sign (+) or (-) attached to each lens group symbol indicates the refractive power of the lens group, and this also applies to all the following examples.

[0072] The first lens group G1 is composed of, arranged along the optical axis from the object side, a negative meniscus lens L11 with a convex surface facing the object side, a negative meniscus lens L12 with a convex surface facing the object side, and a cemented lens consisting of a biconcave negative lens L13 and a positive meniscus lens L14 with a convex surface facing the object side. The negative meniscus lens L12 is a hybrid lens composed of a glass lens body with a resin layer provided on the object side surface. The image side surface of the resin layer is aspherical, making the negative meniscus lens L12 a hybrid aspherical lens. In the "Lens Specifications" section described below, surface number 3 indicates the object side surface of the lens body, surface number 4 indicates the image side surface of the lens body and the object side surface of the resin layer (the surface where the two are cemented), and surface number 5 indicates the image side surface of the resin layer.

[0073] The second lens group G2 is composed of a biconvex positive lens L21.

[0074] The third lens group G3 is composed of, arranged in order from the object side, a cemented lens of a biconvex positive lens L31 and a biconcave negative lens L32, a biconcave negative lens L33, a biconvex positive lens L34, a cemented lens of a biconvex positive lens L35 and a negative meniscus lens L36 with its concave surface facing the object side, and a biconvex positive lens L37. An aperture diaphragm S is disposed between the negative lens L32 and the negative lens L33 in the third lens group G3.

[0075] The fourth lens group G4 is composed of a negative meniscus lens L41 with its concave surface facing the object side, and both lens surfaces of the negative meniscus lens L41 are aspherical.

[0076] The fifth lens group G5 is composed of a negative meniscus lens L51 with its concave surface facing the object side. An image surface I is located on the image side of the fifth lens group G5. Both lens surfaces of the negative meniscus lens L51 are aspherical.

[0077] In this embodiment, the first lens group G1 constitutes the leading lens group GA, which has a negative refractive power as a whole. The second lens group G2, the third lens group G3, the fourth lens group G4, and the fifth lens group G5 constitute the trailing lens group GB, which has a positive refractive power as a whole. The second lens group G2 constitutes the focusing group GF in the trailing lens group GB, and the third lens group G3, the fourth lens group G4, and the fifth lens group G5 constitute the image-side group GC in the trailing lens group GB.

[0078] Table 1 below lists the values ​​of the specifications of the optical system according to the first example.

[0079] (Table 1) [Overall specifications] f=19.752 fA=-21.416 FNO=1.850 fB=32.742 2ω=94.000 fC=36.880 Y=21.700 fF=54.915 TL=119.425 βB=-0.922 Bf=13.307 βC=-0.223 βF=4.143 [Lens specifications] Surface number RD nd νd 1 95.9736 2.200 1.69680 55.53 2 22.7534 8.128 3 44.6575 1.550 1.77250 49.62 4 23.5501 0.050 1.51380 52.97 5* 19.5320 10.056 6 -2091.0337 1.600 1.49782 82.57 7 28.5475 5.100 1.95375 32.33 8 62.5330 (D8) 9 49.0421 4.800 1.80400 46.60 10 -423.4257 (D10) 11 62.2274 5.000 1.95375 32.33 12 -31.1515 1.100 1.84666 23.80 13 109.4389 7.476 14 ∞ 4.522 (Aperture S) 15 -21.9847 1.100 1.63980 34.55 16 180.9758 0.200 17 28.8999 6.500 1.49782 82.57 18 -32.6652 0.200 19 40.2245 7.600 1.49782 82.57 20 -21.1001 1.200 1.95375 32.33 21 -133.5276 0.200 22 46.5098 4.369 1.96300 24.11 23 -174.4889 (D23) 24* -114.5192 1.600 1.86100 37.10 [[ID=2⑧]]25* -200.0000 (D25) 26* -41.2363 2.000 1.86100 37.10 27* -52.6527 Bf [Aspherical Data] The 5th surface κ = 0.0000, A4 = 2.25913E - 06, A6 = -1.46119E - 09 A8 = -3.65260E - 11, A10 = 7.29186E - 14, A12 = -0.12250E - 15 The 24th surface κ = 1.0000, A4 = -2.36949E - 05, A6 = 4.59449E - 08 A⑧ = -2.40149E - 10, A10 = 4.37008E - 14, A12 = 0.00000E + 00 The 25th surface κ = 1.0000, A4 = 1.03885E - 05, A6 = -1.05283E - 08<0, Note: There seems to be a small error in the original text where is written as with a comma in the tag in the provided translation task. I've translated it as as per the instruction to preserve tags exactly, but it should be double - checked if this was a typo in the original task setup. Also, the "絞りS" was translated as "Aperture S" which is a common translation for "aperture" in optical contexts, but again, the specific meaning might need to be verified based on the overall technical domain.A8=2.53730E-10,A10=-2.36282E-12,A12=0.56556E-14 Page 26 κ=1.0000,A4=5.70338E-05,A6=-5.96569E-07 A8=1.49791E-09,A10=-2.21943E-12,A12=0.00000E+00 Page 27 κ=1.0000,A4=6.20655E-05,A6=-5.08156E-07 A8=1.34161E-09,A10=-1.31454E-12,A12=0.00000E+00 [Variable Interval Data] Focused at infinity Focused at mid-range distance Focused at close range f=19.7523 β=-0.0324 β=-0.1844 Object distance ∞ 583.6824 81.5339 D8 3.83333 4.66117 8.49234 D10 9.69148 8.86123 5.03506 D23 7.98377 7.83192 7.06806 D25 8.05896 8.21231 8.97413 [Lens group data] Group starting plane focal length G1 1 -21.416 G2 9 54.915 G3 11 33.632 G4 24 -313.917 G5 26 -240.369

[0080] FIG. 2A shows various aberration diagrams for the optical system of Example 1 when focusing at infinity. FIG. 2B shows various aberration diagrams for the optical system of Example 1 when focusing at close distances. In each aberration diagram for when focusing at infinity, FNO indicates the F-number, and Y indicates the image height. In each aberration diagram for when focusing at close distances, NA indicates the numerical aperture, and Y indicates the image height. Note that the spherical aberration diagram shows the F-number or numerical aperture value corresponding to the maximum aperture, the astigmatism diagram and distortion diagram show the maximum image height, and the coma diagram shows the value of each image height. d indicates the d-line (wavelength λ=587.6 nm), and g indicates the g-line (wavelength λ=435.8 nm). In the astigmatism diagram, the solid line indicates the sagittal image plane, and the dashed line indicates the meridional image plane. Note that the same symbols as in this example are used in the aberration diagrams of each example shown below, and redundant explanations will be omitted.

[0081] From the various aberration diagrams, it can be seen that the optical system of Example 1 has excellent imaging performance, with various aberrations being well corrected across the entire range from focusing at infinity to focusing at close distances. As a result, even when focusing on close objects, good optical performance can be maintained and fluctuations in the angle of view during focusing can be reduced.

[0082] (Second Example) The second example will be described with reference to FIGS. 3 and 4 and Table 2. FIG. 3 shows the lens configuration of the optical system according to the second example. The optical system OL(2) according to the second example is composed of, arranged along the optical axis from the object side, a first lens group G1 having negative refractive power, a second lens group G2 having positive 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 negative refractive power. When focusing from an object at infinity to a close object, the second lens group G2 moves along the optical axis toward the image side, and the fourth lens group G4 moves along the optical axis toward the object side, changing the spacing between adjacent lens groups. During focusing, the first lens group G1, the third lens group G3, and the fifth lens group G5 are fixed relative to the image plane I. An aperture stop S is disposed within the third lens group G3.

[0083] In the second embodiment, the first lens group G1, the second lens group G2, the third lens group G3, the fourth lens group G4, and the fifth lens group G5 are configured in the same manner as in the first embodiment, so the same reference numerals as in the first embodiment are used and detailed descriptions of these lenses are omitted. In this embodiment, the first lens group G1 constitutes the leading lens group GA, which has a negative refractive power as a whole. The second lens group G2, the third lens group G3, the fourth lens group G4, and the fifth lens group G5 constitute the trailing lens group GB, which has a positive refractive power as a whole. The second lens group G2 constitutes the focusing group GF in the trailing lens group GB, and the third lens group G3, the fourth lens group G4, and the fifth lens group G5 constitute the image-side group GC in the trailing lens group GB.

[0084] Table 2 below lists the values ​​of the specifications of the optical system according to the second example.

[0085] (Table 2) [Overall specifications] f=18.300 fA=-20.673 FNO=2.040 fB=33.525 2ω=100.000 fC=36.254 Y=21.700 fF=56.730 TL=115.432 βB=-0.885 Bf=13.305 βC=-0.228 βF=3.889 [Lens specifications] Surface number RD nd νd 1 90.2277 2.200 1.69680 55.53 2 22.3259 8.564 3 46.5688 1.550 1.77250 49.62 4 22.8095 0.050 1.51380 52.97 5* 18.7517 10.444 6 -695.4342 1.600 1.49782 82.57 7 28.3462 5.100 1.95375 32.33 8 67.1568 (D8) 9 47.3685 4.800 1.80400 46.60 10 -1173.5659 (D10) 11 57.0678 5.000 1.95375 32.33 12 -28.3547 1.100 1.84666 23.80 13 124.7137 6.930 14 ∞ 4.437 (Aperture S) 15 -21.8487 1.100 1.66464 34.18 16 83.7472 0.200 17 26.4652 6.000 1.49782 82.57 18 -34.8619 0.200 19 32.6847 7.800 1.49782 82.57 20 -21.1000 1.200 1.95481 31.10 21 -238.7056 0.200 22 41.9717 4.400 1.96300 24.11 23 -115.3109 (D23) 24* -48.7305 1.600 1.86100 37.10 25* -76.3867 (D25) 26* -50.5083 2.000 1.86100 37.10 27* -52.6316 Bf [Aspherical Data] Fifth Surface κ = 0.0000, A4 = 1.73336E-06, A6 = -5.18373E-09 A8 = -6.72613E-12, A10 = -1.17084E-14, A12 = -0.28865E-16 Twenty-fourth Surface κ = 1.0000, A4 = -2.54179E-05, A6 = 1.75260E-07 A8=-4.68333E-10, A10=-2.00453E-12, A12=0.00000E+00 The 25th surface κ=1.0000, A4=1.77608E-05, A6=9.96131E-08 A8=3.73519E-10, A10=-6.29138E-12, A12=0.11757E-13 The 26th surface κ=1.0000, A4=5.28778E-05, A6=-4.96309E-07 A8=9.50586E-10, A10=-1.55937E-12, A12=0.00000E+00 The 27th surface κ=1.0000, A4=5.89841E-05, A6=-4.03867E-07 A8=6.73316E-10, A10=-1.78482E-13, A12=0.00000E+00 [Variable interval data] Infinity focus state, intermediate distance focus state, closest distance focus state f=18.3000 β=-0.0300 β=-0.1722[[ID=2B]] Object distance ∞ 585.1748 81.2627 D8 4.34275 5.13609 8.85548 D10 9.47662 8.68285 4.96440[[ID=3B]] D23 7.13601 7.03337 6.49123 D25 7.52933 7.63252 8.17487 [Lens group data] Group, starting surface, focal length G1 1 -20.673 G2 9 56.730 G3 11 32.335 G4 24 -160.622 G5 26 -2577.184

[0086] Fig. 4(A) is a diagram showing various aberrations of the optical system according to Example 2 when focusing at infinity. Fig. 4(B) is a diagram showing various aberrations of the optical system according to Example 2 when focusing at close distances. From these aberration diagrams, it can be seen that the optical system according to Example 2 has excellent imaging performance, with various aberrations being well corrected across the entire range from focusing at infinity to focusing at close distances. Therefore, even when focusing on close-distance objects, it is possible to reduce fluctuations in the angle of view when focusing while maintaining good optical performance.

[0087] (Third Example) Example 3 will be described with reference to FIGS. 5 to 6 and Table 3. FIG. 5 shows the lens configuration of an optical system according to Example 3 of this embodiment when focused at infinity. The optical system OL(3) according to Example 3 is composed of, arranged along the optical axis from the object side, a first lens group G1 having negative refractive power, a second lens group G2 having positive 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 negative refractive power. When focusing from an object at infinity to a close object, the second lens group G2 moves along the optical axis toward the image side, and the fourth lens group G4 moves along the optical axis toward the object side, changing the spacing between adjacent lens groups. During focusing, the first lens group G1, the third lens group G3, and the fifth lens group G5 are fixed relative to the image plane I. An aperture stop S is disposed within the third lens group G3.

[0088] The first lens group G1 is composed of, arranged in order from the object side along the optical axis, a negative meniscus lens L11 with a convex surface facing the object side, a negative meniscus lens L12 with a convex surface facing the object side, and a cemented lens consisting of a negative meniscus lens L13 with a convex surface facing the object side and a positive meniscus lens L14 with a convex surface facing the object side. The negative meniscus lens L12 is a hybrid lens composed of a glass lens body with a resin layer provided on the object side surface. The image side surface of the resin layer is aspherical, making the negative meniscus lens L12 a hybrid aspherical lens. In the "Lens Specifications" described below, surface number 3 indicates the object side surface of the lens body, surface number 4 indicates the image side surface of the lens body and the object side surface of the resin layer (the surface where the two are cemented), and surface number 5 indicates the image side surface of the resin layer.

[0089] The second lens group G2 is composed of a biconvex positive lens L21.

[0090] The third lens group G3 is composed of, arranged in order from the object side, a cemented lens of a biconvex positive lens L31 and a biconcave negative lens L32, a biconcave negative lens L33, a biconvex positive lens L34, a cemented lens of a biconvex positive lens L35 and a negative meniscus lens L36 with its concave surface facing the object side, and a biconvex positive lens L37. An aperture diaphragm S is disposed between the negative lens L32 and the negative lens L33 in the third lens group G3.

[0091] The fourth lens group G4 is composed of a biconcave negative meniscus lens L41, both of whose lens surfaces are aspherical.

[0092] The fifth lens group G5 is composed of a negative meniscus lens L51 with its concave surface facing the object side. An image surface I is located on the image side of the fifth lens group G5. Both lens surfaces of the negative meniscus lens L51 are aspherical.

[0093] In this embodiment, the first lens group G1 constitutes the leading lens group GA, which has a negative refractive power as a whole. The second lens group G2, the third lens group G3, the fourth lens group G4, and the fifth lens group G5 constitute the trailing lens group GB, which has a positive refractive power as a whole. The second lens group G2 constitutes the focusing group GF in the trailing lens group GB, and the third lens group G3, the fourth lens group G4, and the fifth lens group G5 constitute the image-side group GC in the trailing lens group GB.

[0094] Table 3 below lists the values ​​of the specifications of the optical system according to the third example.

[0095] (Table 3) [Overall specifications] f=23.400 fA=-24.637 FNO=1.850 fB=28.542 2ω=84.000 fC=34.083 Y=21.700 fF=60.973 TL=108.428 βB=-0.950 Bf=14.958 βC=-0.327 βF=2.902 [Lens specifications] Surface number RD nd νd 1 142.4574 1.800 1.65844 50.83 2 21.6000 6.396 3 38.1000 1.550 1.51680 64.13 4 23.6120 0.050 1.51380 52.97 5* 19.2059 6.142 6 63.1783 1.600 1.49782 82.57 7 23.3698 6.266 1.95000 29.37 8 36.0387 (D8) 9 54.5725 3.900 1.80400 46.60 10 -466.6331 (D10) 11 39.5691 5.000 1.95375 32.33 12 -40.6795 1.100 1.84666 23.80 13 54.0179 4.380 14 ∞ 4.408 (Aperture S) 15 -24.1356 1.100 1.62004 36.40 16 75.2494 0.200 17 28.7803 7.300 1.49782 82.57 18 -30.0589 0.200 19 35.1599 8.100 1.49782 82.57 20 -19.4891 1.200 1.95375 32.33 21 -97.0841 0.200 22 53.3925 4.200 1.96300 24.11 23 -93.6556 (D23) 24* -501.9657 1.400 1.86100 37.10 25* 126.9062 (D25) 26* -29.3391 1.600 1.86100 37.10 27* -35.7143 Bf [Aspherical surface] Page 5 κ=0.0000,A4=4.66669E-07,A6=-6.88717E-09 A8=-2.30899E-11,A10=5.43815E-14,A12=-0.19200E-15 Page 24 κ=1.0000,A4=-1.88541E-05,A6=-8.03342E-08 A8=2.03164E-10,A10=1.24201E-12,A12=-0.10143E-13 Page 25 κ=1.0000,A4=6.60646E-06,A6=-1.50187E-07 A8=7.59419E-10,A10=-1.80547E-12,A12=-0.21528E-14 Page 26 κ=1.0000,A4=2.96788E-05,A6=-5.54230E-07 A8=1.09418E-09,A10=8.51720E-13,A12=0.35278E-15 Page 27 κ=1.0000,A4=4.49265E-05,A6=-4.55643E-07 A8=1.16960E-09,A10=1.42886E-12,A12=-0.54944E-14 [Can change the interval データ] Infinite distance focusing state, intermediate distance focusing state, and near distance focusing state. f=23.4000 β=-0.0397 β=-0.1410 Object distance ∞ 562.7256 138.9454 D8 3.68884 5.07863 8.66216 D10 6.97027 5.57838 2.00000 D23 7.70512 7.31418 6.15913 D25 7.01357 7.40825 8.56537 [Lens group data] Group starting plane focal length G1 1 -24.637 G2 9 60.973 G3 11 29.756 G4 24 -117.529 G5 26 -215.972

[0096] Fig. 6(A) is a diagram showing various aberrations of the optical system according to Example 3 when focusing at infinity. Fig. 6(B) is a diagram showing various aberrations of the optical system according to Example 3 when focusing at close distances. From these aberration diagrams, it can be seen that the optical system according to Example 3 has excellent imaging performance, with various aberrations being well corrected across the entire range from focusing at infinity to focusing at close distances. Therefore, even when focusing on close-distance objects, it is possible to reduce fluctuations in the angle of view when focusing while maintaining good optical performance.

[0097] Next, the table of [Values ​​Corresponding to Conditional Expressions] is shown below: This table shows the values ​​corresponding to each of the conditional expressions (1) to (14) for all the examples (Examples 1 to 3). Condition (1) 0.78 <fB / fC<1.00 Condition (2) 0.010 <BLDF / TL<0.160 Conditional expression (3) 1.00<βB / βC<10.00 Condition (4) 0.50<(-fA) / f<1.50 Conditional expression (5) -3.00<(rL1R2+rL1R1) / (rL1R2-rL1R1)<0.00 Conditional expression (6) -5.00<(rL2R2+rL2R1) / (rL2R2-rL2R1)<-2.00 Conditional expression (7) 60.00°<2ω<130.00° Condition (8) 1.20 <FNO<3.00 Condition (9) 0.35 <STL / TL<0.70 Condition (10) 0.05 <Bf / TL<0.30 Condition (11) 1.50 <fF / f<4.50 Condition (12) 1.00 <fF / fB<3.00 Condition (13) 0.15 <dF / TL<0.40 Conditional expression (14) 0.00<1 / βF<0.60 Conditional expression (15) {βF+(1 / βF)} -2 <0.18

[0098] [Conditional expression corresponding value] Conditional Expression First Example Second Example Third Example (1) 0.888 0.925 0.837 (2) 0.040 0.042 0.036 (3) 4.143 3.889 2.902 (4) 1.084 1.130 1.053 (5) -1.622 -1.658 -1.357 (6) -3.231 -2.920 -4.260 (7) 94,000 100,000 84,000 (8) 1.850 2.040 1.850 (9) 0.493 0.511 0.550 (10) 0.111 0.115 0.138 (11) 2.780 3.100 2.606 (12) 1.677 1.692 2.136 (13) 0.272 0.293 0.254 (14) 0.241 0.257 0.345 (15) 0.052 0.058 0.095

[0099] According to each of the above embodiments, an optical system with little fluctuation in the angle of view during focusing can be realized.

[0100] The above-described examples are merely illustrative examples of the present invention, and the present invention is not limited to these.

[0101] The following contents can be appropriately adopted within the scope that does not impair the optical performance of the optical system of this embodiment.

[0102] Although a five-group configuration has been shown as an example of the optical system of this embodiment, the present application is not limited to this, and variable magnification optical systems with other group configurations (e.g., six groups) can also be configured. Specifically, a lens or lens group may be added to the optical system of this embodiment closest to the object or closest to the image plane. Note that a lens group refers to a portion having at least one lens separated by an air gap that changes during focusing.

[0103] The lens group or partial lens group may be moved so as to have a component in a direction perpendicular to the optical axis, or may be rotated (oscillated) in a plane including the optical axis, to serve as an image stabilization lens group that corrects image blur caused by camera shake.

[0104] The lens surface may be spherical, flat, or aspherical. Spherical or flat lens surfaces are preferred because they facilitate lens processing and assembly adjustment, and prevent degradation of optical performance due to errors in processing and assembly adjustment. Furthermore, they are preferred because they minimize degradation of imaging performance even when the image plane is misaligned.

[0105] If the lens surface is aspherical, the aspherical surface may be any of the following: a ground aspherical surface, a glass-molded aspherical surface in which glass is molded into an aspherical shape, or a hybrid aspherical surface in which a resin is formed into an aspherical shape on the surface of glass. The lens surface may also be a diffractive surface, or the lens may be a gradient index lens (GRIN lens) or a plastic lens.

[0106] It is preferable that the aperture stop be disposed in the third lens group, but it is also possible to use the lens frame to fulfill that role instead of providing a member serving as an aperture stop.

[0107] Each lens surface may be coated with an anti-reflection coating that has high transmittance over a wide wavelength range in order to reduce flare and ghosting and achieve high-contrast optical performance. [Explanation of symbols]

[0108] G1 First lens group G2 Second lens group G3 3rd lens group G4 4th lens group G5 5th lens group I Image plane S Aperture stop

Claims

1. the first lens group having negative refractive power and the subsequent lens group having positive refractive power, arranged in order from the object side along the optical axis; the subsequent group includes, in order from the object side along the optical axis, a second lens group having positive refractive power and an image-side group including a plurality of lens groups; the image-side group includes, arranged in order from the object side along the optical axis, a third lens group having positive refractive power, a fourth lens group having negative refractive power, and a fifth lens group having negative refractive power; When focusing from an object at infinity to an object at a close distance, the second lens group moves along the optical axis toward the image side, and the fourth lens group moves along the optical axis toward the object side, An optical system that satisfies the following condition: 1.00<βB / βC<10.00 however, βB: Magnification of the subsequent lens group when focusing on an object at infinity βC: Magnification of the image-side group when focusing on an object at infinity

2. 2. The optical system according to claim 1, wherein the following condition is satisfied: 0.78<fB / fC<1.00 however, fB: focal length of the subsequent lens group when focusing on an object at infinity fC: focal length of the image-side group when focusing on an object at infinity

3. 3. The optical system according to claim 1, wherein the following condition is satisfied: 0.010<BLDF / TL<0.160 however, TL: total length of the optical system BLDF: the length of the second lens group on the optical axis

4. 4. The optical system according to claim 1, wherein the following condition is satisfied: 0.50<(-fA) / f<1.50 however, fA: focal length of the first lens group f: focal length of the optical system when focused on an object at infinity

5. 5. The optical system according to claim 1, wherein the following condition is satisfied: -3.00<(rL1R2+rL1R1) / (rL1R2-rL1R1) ＜０．００ however, rL1R1: Radius of curvature of the object-side lens surface of the lens arranged closest to the object side in the optical system rL1R2: Radius of curvature of the image-side lens surface of the lens located closest to the object side in the optical system

6. 6. The optical system according to claim 1, wherein the following condition is satisfied: -5.00<(rL2R2+rL2R1) / (rL2R2-rL2R1) ＜－２．００ however, rL2R1: the radius of curvature of the object-side lens surface of the second lens located from the object side of the optical system rL2R2: the radius of curvature of the image-side lens surface of the second lens located from the object side of the optical system

7. 7. The optical system according to claim 1, wherein the following condition is satisfied: 60.00°<2ω<130.00° however, 2ω: full angle of view of the optical system when focused on an object at infinity

8. 8. The optical system according to claim 1, wherein the following condition is satisfied: 1.20<FNO<3.00 however, FNO: F-number of the optical system when focused on an object at infinity

9. an aperture stop is disposed in the subsequent lens group; 9. The optical system according to claim 1, wherein the following condition is satisfied: 0.35<STL / TL<0.70 however, STL: distance on the optical axis from the aperture stop to the image plane when focusing on an object at infinity TL: total length of the optical system

10. 10. The optical system according to claim 1, wherein the following condition is satisfied: 0.05<Bf / TL<0.30 however, Bf: back focus of the optical system TL: total length of the optical system

11. 11. The optical system according to claim 1, wherein the following condition is satisfied: 1.50<fF / f<4.50 however, fF: focal length of the second lens group f: focal length of the optical system when focused on an object at infinity

12. 12. The optical system according to claim 1, wherein the following condition is satisfied: 1.00<fF / fB<3.00 however, fF: focal length of the second lens group fB: focal length of the subsequent lens group when focusing on an object at infinity

13. 13. The optical system according to claim 1, wherein the following condition is satisfied: 0.15<dF / TL<0.40 however, dF: the distance on the optical axis from the lens surface of the optical system closest to the object to the lens surface of the second lens group closest to the object when focusing on an object at infinity TL: total length of the optical system

14. 14. The optical system according to claim 1, wherein the following condition is satisfied: 0.00<1 / βF<0.60 however, βF: Magnification of the second lens group when focusing on an object at infinity

15. 15. The optical system according to claim 1, wherein the following condition is satisfied: {βF+(1 / βF)}-2<0.18 however, βF: Magnification of the second lens group when focusing on an object at infinity

16. An optical instrument comprising the optical system according to any one of claims 1 to 15.

Images