Optical system and optical device

Abstract

To provide an optical system which exhibits less aberration variations while focusing.SOLUTION: An optical system OL disclosed herein consists of a first lens group G1, a first focusing lens group GF1 having negative refractive power, and a second focusing lens group GF2 having positive refractive power, arranged in order from the object side along an optical axis, and is configured such that the first focusing lens group GF1 and the second focusing lens group GF2 move on different trajectories along the optical axis while shifting focus, and that the following conditional expression is satisfied: f1 / |f1R|<1.00, where f1 represents a focal length of the first lens group G1 and f1R represents a composite focal length of lens groups located on the image side of the first lens group G1 in infinity focus state.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 difficult to suppress aberration fluctuations during focusing. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2018-5099 Summary of the Invention

[0004] A first optical system according to the present invention has, arranged in order from the object side along the optical axis, a first lens group, a first focusing lens group having negative refractive power, a second focusing lens group having positive refractive power, and a subsequent lens group having negative refractive power, wherein, during focusing, the first focusing lens group and the second focusing lens group move along the optical axis on mutually different trajectories, and further has an aperture stop arranged closer to the object side than the first focusing lens group, and satisfies the following conditional expression: 0.60 <fF2 / (-fR)<1.10 where fF2 is the focal length of the second focusing lens group. fR: focal length of the subsequent lens group

[0005] A second optical system according to the present invention has, arranged in order from the object side along an optical axis, a first lens group, a first focusing lens group having negative refractive power, and a second focusing lens group having positive refractive power, wherein, during focusing, the first focusing lens group and the second focusing lens group move along the optical axis on different loci, and the optical system satisfies the following conditional expression: f1 / |f1R|<1.00 where f1 is the focal length of the first lens group f1R: composite focal length of the lens group located closer to the image than the first lens group when focused at infinity

[0006] A third optical system according to the present invention has, arranged in order from the object side along the optical axis, a first lens group, an aperture stop, a first focusing lens group, and a second focusing lens group, wherein, during focusing, the first focusing lens group and the second focusing lens group move along the optical axis on different trajectories, and the first focusing lens group has at least two negative lenses.

[0007] An optical device according to the present invention includes the optical system described above. [Brief explanation of the drawings]

[0008] [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 on infinity and when focused on 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] 4 is a flowchart showing a method for manufacturing the optical system according to the first embodiment. [Figure 9] 10 is a flowchart showing a method for manufacturing an optical system according to a second embodiment. [Figure 10] 10 is a flowchart showing a method for manufacturing an optical system according to a third embodiment. [Figure 11]10 is a flowchart showing a method for manufacturing an optical system according to a fourth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] 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.

[0010] 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 LCD 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. Also, the optical system OL shown in FIG. 7 is a schematic representation of an optical system provided in the photographing lens 3, and the lens configuration of the optical system OL is not limited to this configuration.

[0011] Next, an optical system according to the first embodiment will be described. As shown in FIG. 1, an optical system OL(1) as an example of the optical system OL according to the first embodiment is configured to include, in order from the object side along the optical axis, a first lens group G1, a first focusing lens group GF1 having negative refractive power, and a second focusing lens group GF2 having positive refractive power. During focusing, the first focusing lens group GF1 and the second focusing lens group GF2 move along the optical axis on different trajectories. The optical system OL according to the first embodiment also includes an aperture stop S located closer to the object side than the first focusing lens group GF1.

[0012] With the above-described configuration, the optical system OL according to the first embodiment satisfies the following conditional expression (1). 0.68<(-fF1) / fF2<3.60 (1) where fF1 is the focal length of the first focusing lens group GF1 fF2: focal length of the second focusing lens group GF2

[0013] According to the first embodiment, it is possible to obtain an optical system with little aberration fluctuation during focusing, and an optical device equipped with this optical system. Furthermore, since the focusing lens group can be made small and lightweight, it is possible to obtain an optical system that can achieve high-speed, quiet autofocus (AF) without increasing the size of the lens barrel. 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.

[0014] Conditional expression (1) defines an appropriate relationship between the focal length of the first focusing lens group GF1 and the focal length of the second focusing lens group GF2. By satisfying conditional expression (1), fluctuations in various aberrations, including spherical aberration, during focusing can be suppressed.

[0015] If the corresponding value of conditional expression (1) exceeds the upper limit, the refractive power of the second focusing lens group GF2 becomes too strong, making it difficult to suppress fluctuations in various aberrations, including spherical aberration, during focusing. The effect of this embodiment can be further ensured by setting the upper limit of conditional expression (1) to 3.50, 3.30, 3.00, 2.75, 2.50, 2.20, 2.00, or even 1.85.

[0016] If the corresponding value of conditional expression (1) falls below the lower limit, the refractive power of the first focusing lens group GF1 becomes too strong, making it difficult to suppress fluctuations in various aberrations, including spherical aberration, during focusing. By setting the lower limit of conditional expression (1) to 0.70, 0.72, 0.75, 0.78, 0.80, or even 0.82, the effects of this embodiment can be more reliably achieved.

[0017] 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 the optical system OL according to the second embodiment is configured to include, arranged in order from the object side along the optical axis, a first lens group G1, a first focusing lens group GF1 having negative refractive power, a second focusing lens group GF2 having positive refractive power, and a subsequent lens group GR having negative refractive power. During focusing, the first focusing lens group GF1 and the second focusing lens group GF2 move along the optical axis along different trajectories. The optical system OL according to the second embodiment also includes an aperture stop S located closer to the object side than the first focusing lens group GF1.

[0018] With the above-described configuration, the optical system OL according to the second embodiment satisfies the following conditional expression (2). 0.60 <fF2 / (-fR)<1.10 ···(2) where fF2 is the focal length of the second focusing lens group GF2 fR: focal length of the subsequent lens group GR

[0019] According to the second embodiment, it is possible to obtain an optical system with little aberration fluctuation during focusing, and an optical device equipped with this optical system. Furthermore, since the focusing lens group can be made small and lightweight, it is possible to obtain an optical system that can achieve high-speed, quiet autofocus (AF) without increasing the size of the lens barrel. 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.

[0020] Conditional expression (2) defines an appropriate relationship between the focal length of the second focusing lens group GF2 and the focal length of the subsequent lens group GR. By satisfying conditional expression (2), fluctuations in various aberrations, including spherical aberration, during focusing can be suppressed.

[0021] If the corresponding value of conditional expression (2) exceeds the upper limit, the refractive power of the subsequent lens group GR becomes too strong, making it difficult to suppress fluctuations in various aberrations, including spherical aberration, during focusing. By setting the upper limit of conditional expression (2) to 1.08, 1.05, 1.03, 1.00, or even 0.98, the effects of this embodiment can be further ensured.

[0022] If the corresponding value of conditional expression (2) falls below the lower limit, the refractive power of the second focusing lens group GF2 becomes too strong, making it difficult to suppress fluctuations in various aberrations, including spherical aberration, during focusing. By setting the lower limit of conditional expression (2) to 0.62, or even 0.64, the effects of this embodiment can be made even more certain.

[0023] In the optical system OL according to the second embodiment, it is desirable for the rear lens group GR to have at least two lens components. This allows for excellent correction of various aberrations, including coma when focused at infinity. Note that in each embodiment, the lens components refer to single lenses or cemented lenses.

[0024] Next, an optical system according to a third embodiment will be described. As shown in Fig. 1, an optical system OL(1) as an example of the optical system OL according to the third embodiment is configured to include, arranged in order from the object side along the optical axis, a first lens group G1, a first focusing lens group GF1 having negative refractive power, and a second focusing lens group GF2 having positive refractive power. During focusing, the first focusing lens group GF1 and the second focusing lens group GF2 move along the optical axis on different trajectories.

[0025] With the above-described configuration, the optical system OL according to the third embodiment satisfies the following conditional expression (3). f1 / |f1R|<1.00 (3) where f1 is the focal length of the first lens group G1 f1R: The composite focal length of the lens group located closer to the image than the first lens group G1 when focused at infinity

[0026] According to the third embodiment, it is possible to obtain an optical system with little aberration fluctuation during focusing, and an optical device equipped with this optical system. Furthermore, since the focusing lens group can be made small and lightweight, it is possible to obtain an optical system that can achieve high-speed, quiet autofocus (AF) without increasing the size of the lens barrel. The optical system OL according to the third embodiment may be the optical system OL(2) shown in FIG. 3 or the optical system OL(3) shown in FIG. 5.

[0027] Conditional expression (3) defines an appropriate relationship between the focal length of the first lens group G1 and the combined focal length of the lens groups located closer to the image than the first lens group G1 when focused at infinity. By satisfying conditional expression (3), various aberrations, including spherical aberration, can be effectively corrected when focused at infinity.

[0028] If the value corresponding to conditional expression (3) exceeds the upper limit, the refractive power of the lens group disposed closer to the image side than the first lens group G1 becomes too strong, making it difficult to correct various aberrations, including spherical aberration, when focused at infinity. The effect of this embodiment can be further ensured by setting the upper limit of conditional expression (3) to 0.90, 0.80, 0.75, 0.70, 0.65, 0.60, 0.55, 0.50, or even 0.45. Furthermore, the effect of this embodiment can be further ensured by setting the lower limit of conditional expression (3) to 0.05, 0.10, 0.15, 0.20, 0.25, or even 0.30.

[0029] The optical system OL according to the third embodiment preferably further includes an aperture stop S located closer to the object than the first focusing lens group GF1, thereby making it possible to suppress fluctuations in various aberrations, including spherical aberration, during focusing.

[0030] Next, an optical system according to a fourth embodiment will be described. As shown in FIG. 1, an optical system OL(1) as an example of the optical system OL according to the fourth embodiment is configured to include, in order from the object side along the optical axis, a first lens group G1, an aperture stop S, a first focusing lens group GF1, and a second focusing lens group GF2. During focusing, the first focusing lens group GF1 and the second focusing lens group GF2 move along the optical axis on different trajectories. The first focusing lens group GF1 also has at least two negative lenses.

[0031] According to the fourth embodiment, it is possible to obtain an optical system with little aberration fluctuation during focusing, and an optical device equipped with this optical system. Furthermore, since the focusing lens group can be made small and lightweight, it is possible to obtain an optical system that can achieve high-speed, quiet autofocus (AF) without increasing the size of the lens barrel. The optical system OL according to the fourth embodiment may be the optical system OL(2) shown in FIG. 3 or the optical system OL(3) shown in FIG. 5.

[0032] In the optical system OL according to the fourth embodiment, it is desirable that the first focusing lens group GF1 has negative refractive power and the second focusing lens group GF2 has positive refractive power, which makes it possible to suppress fluctuations in various aberrations, including spherical aberration, during focusing without increasing the size of each focusing lens group.

[0033] The optical systems OL according to the second, third, and fourth embodiments preferably satisfy the aforementioned conditional expression (1). Satisfying conditional expression (1) can suppress fluctuations in various aberrations, including spherical aberration, during focusing, as in the first embodiment. Setting the upper limit of conditional expression (1) to 3.50, 3.30, 3.00, 2.75, 2.50, 2.20, 2.00, or even 1.85 can further enhance the effects of each embodiment. Setting the lower limit of conditional expression (1) to 0.70, 0.72, 0.75, 0.78, 0.80, or even 0.82 can further enhance the effects of each embodiment.

[0034] The optical systems OL according to the first, third, and fourth embodiments preferably further include a subsequent lens group GR having negative refractive power and arranged closer to the image than the second focusing lens group GF2, and preferably satisfy the aforementioned conditional expression (2). Satisfying conditional expression (2) can suppress fluctuations in various aberrations, including spherical aberration, during focusing, as in the second embodiment. Setting the upper limit of conditional expression (2) to 1.08, 1.05, 1.03, 1.00, or even 0.98 can further enhance the effects of each embodiment. Furthermore, setting the lower limit of conditional expression (2) to 0.62 or even 0.64 can further enhance the effects of each embodiment.

[0035] In this case, it is desirable that the rear lens group GR has at least two lens components, which allows for excellent correction of various aberrations, including coma when focused at infinity.

[0036] The optical systems OL according to the first, second, and fourth embodiments preferably satisfy the aforementioned conditional expression (3). By satisfying conditional expression (3), various aberrations, including spherical aberration, can be effectively corrected when focused at infinity, as in the third embodiment. The effects of each embodiment can be further enhanced by setting the upper limit of conditional expression (3) to 0.90, 0.80, 0.75, 0.70, 0.65, 0.60, 0.55, 0.50, or even 0.45. Furthermore, the effects of each embodiment can be further enhanced by setting the lower limit of conditional expression (3) to 0.05, 0.10, 0.15, 0.20, 0.25, or even 0.30.

[0037] The optical system OL according to the third embodiment preferably further includes an aperture stop S located closer to the object than the first focusing lens group GF1, thereby making it possible to suppress fluctuations in various aberrations, including spherical aberration, during focusing.

[0038] It is desirable that the optical systems OL according to the first, second, and fourth embodiments satisfy the following conditional expression (4): Moreover, it is desirable that the optical system OL according to the third embodiment further includes an aperture stop S arranged closer to the object than the first focusing lens group GF1, and that it also satisfy the following conditional expression (4): 0.50 <Lre / Lfr<4.00 ···(4) where Lfr is the distance on the optical axis from the lens surface closest to the object in the optical system OL to the aperture stop S. Lre: Distance on the optical axis from the aperture stop S to the image plane I

[0039] Conditional expression (4) defines an appropriate relationship between the optical axial distance from the lens surface closest to the object in optical system OL to aperture stop S and the optical axial distance from aperture stop S to image plane I. Satisfying conditional expression (4) enables good correction of various aberrations, including spherical aberration, when focused at infinity.

[0040] If the corresponding value of conditional expression (4) exceeds the upper limit, the distance on the optical axis from the aperture stop S to the image plane I becomes too large, making it difficult to correct various aberrations, including spherical aberration, when focused at infinity. By setting the upper limit of conditional expression (4) to 3.80, 3.65, 3.50, 3.40, 3.30, 3.20, or even 3.10, the effects of each embodiment can be further ensured.

[0041] If the corresponding value of conditional expression (4) falls below the lower limit, the distance on the optical axis from the lens surface closest to the object in optical system OL to aperture stop S becomes too large, making it difficult to correct various aberrations, including spherical aberration, when focused at infinity. By setting the lower limit of conditional expression (4) to 0.60, 0.70, 0.80, 0.90, 1.00, 1.10, 1.20, or even 1.30, the effects of each embodiment can be further ensured.

[0042] It is desirable that the optical systems OL according to the first to fourth embodiments satisfy the following conditional expression (5). 0.45 <f1 / (-fF1)<2.50 ···(5) where f1 is the focal length of the first lens group G1 fF1: focal length of the first focusing lens group GF1

[0043] Conditional expression (5) defines an appropriate relationship between the focal length of the first lens group G1 and the focal length of the first focusing lens group GF1. By satisfying conditional expression (5), various aberrations, including spherical aberration, can be effectively corrected when focused at infinity, and fluctuations in various aberrations, including spherical aberration, can be suppressed when focusing from an object at infinity to a close object.

[0044] If the corresponding value of conditional expression (5) exceeds the upper limit, the refractive power of the first focusing lens group GF1 becomes too strong, making it difficult to suppress fluctuations in various aberrations, including spherical aberration, when focusing from an object at infinity to a close object. By setting the upper limit of conditional expression (5) to 2.35, 2.20, 2.10, 2.00, 1.85, 1.70, 1.50, 1.40, or even 1.35, the effects of each embodiment can be more reliably achieved.

[0045] If the corresponding value of conditional expression (5) falls below the lower limit, the refractive power of the first lens group G1 becomes too strong, making it difficult to correct various aberrations, including spherical aberration, when focused at infinity. By setting the lower limit of conditional expression (5) to 0.50, 0.55, 0.60, 0.65, 0.70, 0.75, or even 0.80, the effects of each embodiment can be more reliably achieved.

[0046] It is desirable that the optical systems OL according to the first to fourth embodiments satisfy the following conditional expression (6). 0.55 <f1 / fF2<3.00 ···(6) where f1 is the focal length of the first lens group G1 fF2: focal length of the second focusing lens group GF2

[0047] Conditional expression (6) defines an appropriate relationship between the focal length of the first lens group G1 and the focal length of the second focusing lens group GF2. By satisfying conditional expression (6), various aberrations, including spherical aberration, can be effectively corrected when focused at infinity, and fluctuations in various aberrations, including spherical aberration, can be suppressed when focusing from an object at infinity to a close object.

[0048] If the corresponding value of conditional expression (6) exceeds the upper limit, the refractive power of the second focusing lens group GF2 becomes too strong, making it difficult to suppress fluctuations in various aberrations, including spherical aberration, when focusing from an object at infinity to a close object. By setting the upper limit of conditional expression (6) to 2.85, 2.70, 2.60, 2.50, 2.40, 2.30, 2.20, or even 3.15, the effects of each embodiment can be more reliably achieved.

[0049] If the corresponding value of conditional expression (6) falls below the lower limit, the refractive power of the first lens group G1 becomes too strong, making it difficult to correct various aberrations, including spherical aberration, when focused at infinity. By setting the lower limit of conditional expression (6) to 0.60, 0.65, 0.68, 0.70, 0.73, or even 0.75, the effects of each embodiment can be more reliably achieved.

[0050] It is desirable that the optical systems OL according to the first to fourth embodiments satisfy the following conditional expression (7). 0.10 <f1 / f<1.25 ···(7) where f1 is the focal length of the first lens group G1 f: focal length of optical system OL when focused at infinity

[0051] Conditional expression (7) defines an appropriate relationship between the focal length of the first lens group G1 and the focal length of the optical system OL when focused at infinity. By satisfying conditional expression (7), various aberrations, including spherical aberration when focused at infinity, can be effectively corrected without increasing the size of the lens barrel.

[0052] If the corresponding value of conditional expression (7) exceeds the upper limit, the refractive power of the first lens group G1 becomes too weak, and the lens barrel becomes large. By setting the upper limit of conditional expression (7) to 1.20, 1.18, 1.15, 1.13, or even 1.10, the effects of each embodiment can be more reliably achieved.

[0053] If the value corresponding to conditional expression (7) falls below the lower limit, the refractive power of the first lens group G1 becomes too strong, making it difficult to correct various aberrations, including spherical aberration, when focused at infinity. By setting the lower limit of conditional expression (7) to 0.15, 0.20, 0.25, 0.30, 0.35, 0.40, 0.45, or even 0.48, the effects of each embodiment can be further ensured.

[0054] It is desirable that the optical systems OL according to the first to fourth embodiments satisfy the following conditional expression (8). 0.05 <Bf / f<0.65 ···(8) where Bf is the back focus of the optical system OL when focused at infinity. f: focal length of optical system OL when focused at infinity

[0055] Conditional expression (8) defines an appropriate relationship between the back focus of the optical system OL when focused at infinity and the focal length of the optical system OL when focused at infinity. By satisfying conditional expression (8), various aberrations, including coma when focused at infinity, can be effectively corrected.

[0056] If the value corresponding to conditional expression (8) exceeds the upper limit, the back focus becomes large relative to the focal length of the optical system OL, making it difficult to correct various aberrations, including coma when focused at infinity. By setting the upper limit of conditional expression (8) to 0.60, 0.55, 0.50, 0.45, 0.40, or even 0.35, the effects of each embodiment can be further ensured.

[0057] If the corresponding value of conditional expression (8) is below the lower limit, the back focus becomes small relative to the focal length of the optical system OL, making it difficult to correct various aberrations, including coma when focused at infinity. By setting the lower limit of conditional expression (8) to 0.08, 0.10, or even 0.12, the effects of each embodiment can be more reliably achieved.

[0058] In the optical systems OL according to the first to fourth embodiments, it is desirable that the first lens group G1 has at least one positive lens and satisfies the following conditional expression (9). νP<42.00 (9) where νP is the Abbe number of the positive lens having the smallest Abbe number among at least one positive lens in the first lens group G1.

[0059] Conditional expression (9) defines an appropriate range for the Abbe number of the positive lens having the smallest Abbe number among the at least one positive lens in the first lens group G1. By satisfying conditional expression (9), chromatic aberration in the infinity focused state can be effectively corrected without increasing the size of the lens barrel.

[0060] If the value corresponding to conditional expression (9) exceeds the upper limit, the Abbe number of the positive lens with the smallest Abbe number among the at least one positive lens in first lens group G1 becomes too large, making it difficult to correct chromatic aberration when focused at infinity without increasing the size of the lens barrel. By setting the upper limit of conditional expression (9) to 40.00, 37.00, 35.00, or even 32.00, the effects of each embodiment can be more reliably achieved.

[0061] In the optical systems OL according to the first to fourth embodiments, it is desirable that the first focusing lens group GF1 moves toward the image along the optical axis when focusing from an object at infinity to an object at a close distance, thereby suppressing fluctuations in various aberrations, including spherical aberration, when focusing from an object at infinity to an object at a close distance.

[0062] In the optical systems OL according to the first to fourth embodiments, it is desirable that the second focusing lens group GF2 moves toward the object along the optical axis when focusing from an object at infinity to an object at a close distance, thereby suppressing fluctuations in various aberrations, including spherical aberration, when focusing from an object at infinity to an object at a close distance.

[0063] It is desirable that the optical systems OL according to the first to fourth embodiments satisfy the following conditional expression (10). 0.10 <MF1 / MF2<20.00 ···(10) where MF1 is the absolute value of the movement of the first focusing lens group GF1 when focusing from an object at infinity to an object at a close distance. MF2: Absolute value of the movement of the second focusing lens group GF2 when focusing from an object at infinity to an object at a close distance

[0064] Conditional expression (10) defines an appropriate relationship between the absolute value of the amount of movement of the first focusing lens group GF1 when focusing from an object at infinity to a close object and the absolute value of the amount of movement of the second focusing lens group GF2 when focusing from an object at infinity to a close object. By satisfying conditional expression (10), fluctuations in various aberrations, including spherical aberration, can be suppressed when focusing from an object at infinity to a close object.

[0065] If the value corresponding to conditional expression (10) exceeds the upper limit, the amount of movement of the first focusing lens group GF1 when focusing from an object at infinity to an object at a close distance becomes too large, making it difficult to suppress fluctuations in various aberrations, including spherical aberration, when focusing from an object at infinity to an object at a close distance. By setting the upper limit of conditional expression (10) to 18.50, 17.00, 15.00, 13.50, 12.00, 11.50, 11.00, 10.50, or even 10.00, the effects of each embodiment can be more reliably achieved.

[0066] If the corresponding value of conditional expression (10) falls below the lower limit, the amount of movement of the second focusing lens group GF2 when focusing from an object at infinity to an object at a close distance becomes too large, making it difficult to suppress fluctuations in various aberrations, including spherical aberration, when focusing from an object at infinity to an object at a close distance. By setting the lower limit of conditional expression (10) to 0.25, 0.40, 0.50, 0.60, 0.70, 0.80, or even 0.90, the effects of each embodiment can be more reliably achieved.

[0067] It is desirable that the optical systems OL according to the first to fourth embodiments satisfy the following conditional expression (11). 0.50<βF1<15.00 (11) where βF1 is the lateral magnification of the first focusing lens group GF1 when focused at infinity.

[0068] Conditional expression (11) defines an appropriate range for the lateral magnification of the first focusing lens group GF1 when focused at infinity. By satisfying conditional expression (11), fluctuations in various aberrations, including spherical aberration, can be suppressed when focusing from an object at infinity to a close object.

[0069] If the value corresponding to conditional expression (11) exceeds the upper limit, the lateral magnification of the first focusing lens group GF1 when focused at infinity becomes too large, making it difficult to suppress fluctuations in various aberrations, including spherical aberration, when focusing from an object at infinity to an object at a close distance. By setting the upper limit of conditional expression (11) to 14.50, 14.00, 13.50, 13.00, 12.50, 12.00, or even 11.50, the effects of each embodiment can be more reliably achieved.

[0070] If the value corresponding to conditional expression (11) falls below the lower limit, the lateral magnification of the first focusing lens group GF1 when focused at infinity becomes too small, making it difficult to suppress fluctuations in various aberrations, including spherical aberration, when focusing from an object at infinity to an object at a close distance. By setting the lower limit of conditional expression (11) to 0.60, 0.70, 0.85, 1.00, 1.25, 1.50, 1.74, or even 2.00, the effects of each embodiment can be more reliably achieved.

[0071] It is desirable that the optical systems OL according to the first to fourth embodiments satisfy the following conditional expression (12). 0.05<βF2<1.00 (12) where βF2 is the lateral magnification of the second focusing lens group GF2 when focused at infinity.

[0072] Conditional expression (12) defines an appropriate range for the lateral magnification of the second focusing lens group GF2 when focused at infinity. By satisfying conditional expression (12), fluctuations in various aberrations, including spherical aberration, can be suppressed when focusing from an object at infinity to a close object.

[0073] If the value corresponding to conditional expression (12) exceeds the upper limit, the lateral magnification of the second focusing lens group GF2 when focused at infinity becomes too large, making it difficult to suppress fluctuations in various aberrations, including spherical aberration, when focusing from an object at infinity to an object at a close distance. By setting the upper limit of conditional expression (12) to 0.95, 0.90, 0.85, 0.80, 0.70, 0.60, 0.50, 0.40, or even 0.30, the effects of each embodiment can be further ensured.

[0074] If the corresponding value of conditional expression (12) falls below the lower limit, the lateral magnification of the second focusing lens group GF2 when focused at infinity becomes too small, making it difficult to suppress fluctuations in various aberrations, including spherical aberration, when focusing from an object at infinity to an object at a close distance. By setting the lower limit of conditional expression (12) to 0.06, 0.07, 0.08, 0.09, or even 0.10, the effects of each embodiment can be more reliably achieved.

[0075] It is desirable that the optical systems OL according to the first to fourth embodiments satisfy the following conditional expression (13). 1.00<βF1 / βF2 (13) where βF1 is the lateral magnification of the first focusing lens group GF1 when focused at infinity. βF2: Lateral magnification of the second focusing lens group GF2 when focused at infinity

[0076] Conditional expression (13) defines an appropriate relationship between the lateral magnification of the first focusing lens group GF1 when focused at infinity and the lateral magnification of the second focusing lens group GF2 when focused at infinity. By satisfying conditional expression (13), fluctuations in various aberrations, including spherical aberration, can be suppressed when focusing from an object at infinity to a close object.

[0077] If the corresponding value of conditional expression (13) falls below the lower limit, the lateral magnification of the second focusing lens group GF2 when focused at infinity becomes too large, making it difficult to suppress fluctuations in various aberrations, including spherical aberration, when focusing from an object at infinity to a close object. Setting the lower limit of conditional expression (13) to 1.50, 2.00, 2.50, 3.00, 3.50, 5.00, 7.50, or even 10.00 can further enhance the effects of each embodiment. Setting the upper limit of conditional expression (13) to 110.00, 100.00, 80.00, 65.00, 50.00, or even 40.00 can further enhance the effects of each embodiment.

[0078] It is desirable that the optical systems OL according to the first to fourth embodiments satisfy the following conditional expression (14). {βF1+(1 / βF1)} -2 <0.250 (14) where βF1 is the lateral magnification of the first focusing lens group GF1 when focused at infinity.

[0079] Conditional expression (14) defines an appropriate range for the lateral magnification of the first focusing lens group GF1 when focused at infinity. By satisfying conditional expression (14), it is possible to suppress fluctuations in various aberrations, including spherical aberration, when focusing from an object at infinity to an object at a close distance.

[0080] If the corresponding value of conditional expression (14) exceeds the upper limit, it becomes difficult to suppress fluctuations in various aberrations, including spherical aberration, when focusing from an object at infinity to a close object. By setting the upper limit of conditional expression (14) to 0.230, 0.200, 0.185, 0.170, 0.150, 0.125, or even 0.100, the effects of each embodiment can be further ensured. Furthermore, by setting the lower limit of conditional expression (14) to 0.000, 0.001, 0.003, or even 0.005, the effects of each embodiment can be further ensured.

[0081] It is desirable that the optical systems OL according to the first to fourth embodiments satisfy the following conditional expression (15). {βF2+(1 / βF2)} -2 <0.250 (15) where βF2 is the lateral magnification of the second focusing lens group GF2 when focused at infinity.

[0082] Conditional expression (15) defines an appropriate range for the lateral magnification of the second focusing lens group GF2 when focused at infinity. By satisfying conditional expression (15), fluctuations in various aberrations, including spherical aberration, can be suppressed when focusing from an object at infinity to a close object.

[0083] If the corresponding value of conditional expression (15) exceeds the upper limit, it becomes difficult to suppress fluctuations in various aberrations, including spherical aberration, when focusing from an object at infinity to a close object. By setting the upper limit of conditional expression (15) to 0.230, 0.200, 0.185, 0.170, 0.150, 0.125, or even 0.100, the effects of each embodiment can be more reliably achieved. Furthermore, by setting the lower limit of conditional expression (15) to 0.000, 0.001, 0.003, 0.005, 0.008, or even 0.010, the effects of each embodiment can be more reliably achieved.

[0084] Next, a manufacturing method of the optical system OL according to the first embodiment will be outlined with reference to FIG. 8. First, a first lens group G1, a first focusing lens group GF1 having negative refractive power, and a second focusing lens group GF2 having positive refractive power are arranged, in order from the object side along the optical axis (Step ST1). Next, the first focusing lens group GF1 and the second focusing lens group GF2 are configured to move along the optical axis on different trajectories during focusing (Step ST2). Furthermore, an aperture stop S is arranged closer to the object than the first focusing lens group GF1 (Step ST3). Then, each lens is arranged within the lens barrel so as to satisfy at least the above-mentioned conditional expression (1) (Step ST4). This manufacturing method makes it possible to manufacture an optical system with minimal aberration fluctuation during focusing.

[0085] Next, a manufacturing method of the optical system OL according to the second embodiment will be outlined with reference to FIG. 9. First, the first lens group G1, the first focusing lens group GF1 having negative refractive power, the second focusing lens group GF2 having positive refractive power, and the subsequent lens group GR having negative refractive power are arranged along the optical axis in this order from the object side (step ST11). Next, the first focusing lens group GF1 and the second focusing lens group GF2 are configured to move along the optical axis on different trajectories during focusing (step ST12). Furthermore, an aperture stop S is arranged closer to the object than the first focusing lens group GF1 (step ST13). Then, the lenses are arranged in the lens barrel so as to satisfy at least the above conditional expression (2) (step ST14). This manufacturing method makes it possible to manufacture an optical system with minimal aberration fluctuation during focusing.

[0086] Next, a manufacturing method of the optical system OL according to the third embodiment will be outlined with reference to FIG. 10. First, the first lens group G1, the first focusing lens group GF1 having negative refractive power, and the second focusing lens group GF2 having positive refractive power are arranged along the optical axis in this order from the object side (step ST21). Next, the first focusing lens group GF1 and the second focusing lens group GF2 are configured to move along the optical axis on different trajectories during focusing (step ST22). Then, the lenses are arranged within the lens barrel so as to satisfy at least conditional expression (3) above (step ST23). This manufacturing method makes it possible to manufacture an optical system with minimal aberration fluctuation during focusing.

[0087] Next, a manufacturing method of the optical system OL according to the fourth embodiment will be outlined with reference to FIG. 11. First, the first lens group G1, aperture stop S, first focusing lens group GF1, and second focusing lens group GF2 are arranged along the optical axis in this order from the object side (step ST31). Next, the first focusing lens group GF1 and the second focusing lens group GF2 are configured to move along the optical axis on different trajectories during focusing (step ST32). Then, the lenses are arranged within the lens barrel so that the first focusing lens group GF1 has at least two negative lenses (step ST33). This manufacturing method makes it possible to manufacture an optical system with minimal aberration fluctuation during focusing. [Example]

[0088] 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.

[0089] 1, 3, and 5, each lens 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 example 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 examples, this does not mean that the examples have the same configuration.

[0090] 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.

[0091] 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 are ° (degrees), where ω is half the angle of view), and Ymax is the maximum image height. TL is the distance from the frontmost lens surface to the last lens surface on the optical axis when focused at infinity plus Bf, and Bf is the distance from the last lens surface on the optical axis to the image plane I when focused at infinity (back focus).

[0092] In the table under "Overall Specifications," βF1 indicates the lateral magnification of the first focusing lens group when focused at infinity. βF2 indicates the lateral magnification of the second focusing lens group when focused at infinity. MF1 indicates the absolute value of the movement amount of the first focusing lens group when focusing from an object at infinity to a close object. MF2 indicates the absolute value of the movement amount of the second focusing lens group when focusing from an object at infinity to a close object. Lfr indicates the distance on the optical axis from the lens surface closest to the object in the optical system to the aperture stop. Lre indicates the distance on the optical axis from the aperture stop to the image plane. f1R indicates the composite focal length of the lens group located closer to the image than the first lens group when focused at infinity.

[0093] 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.

[0094] 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.

[0095] 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 …(A)

[0096] The [Variable Distance Data] table shows the surface spacing for surface number i, which is specified as (Di) in the [Lens Specifications] table. The [Variable Distance Data] table also shows the surface spacing when focused at infinity and when focused at close distances. In the [Variable Distance Data] table, f represents the focal length of the entire lens system, and β represents the magnification. Furthermore, D0 represents the distance from the object to the optical surface closest to the object in the optical system.

[0097] The [Lens Group Data] table shows the starting surface (the surface closest to the object) and focal length of each lens group.

[0098] 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.

[0099] The explanation of the tables up to this point is common to all the embodiments, and duplicate explanations will be omitted below.

[0100] (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 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. 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 third lens group G3 moves along the optical axis toward the object side, changing the spacing between adjacent lens groups. During focusing, the positions of the first lens group G1 and the fourth lens group G4 are fixed relative to the image plane I. The sign (+) or (-) attached to each lens group symbol indicates the refractive power of the lens group, and this is the same in all the following embodiments.

[0101] An aperture stop S is disposed between the first lens group G1 and the second lens group G2. During focusing, the position of the aperture stop S is fixed relative to the image plane I. In this embodiment, the second lens group G2 corresponds to the first focusing lens group GF1, the third lens group G3 corresponds to the second focusing lens group GF2, and the fourth lens group G4 corresponds to the subsequent lens group GR.

[0102] 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 positive meniscus lens L12 with a convex surface facing the object side, a negative meniscus lens L13 with a convex surface facing the object side, a biconvex positive lens L14, a biconvex positive lens L15, and a cemented negative lens formed by cementing a biconcave negative lens L16 and a biconvex positive lens L17 together.

[0103] The second lens group G2 is composed of, arranged in order from the object side along the optical axis, a negative meniscus lens L21 with its convex surface facing the object side, a biconcave negative lens L22, and a biconvex positive lens L23.

[0104] The third lens group G3 is composed of, arranged in order from the object side along the optical axis, a biconvex positive lens L31 and a biconvex positive lens L32. The object-side lens surface of the positive lens L32 is aspherical.

[0105] The fourth lens group G4 is composed of, arranged in order from the object side along the optical axis, a biconcave negative lens L41 and a positive meniscus lens L42 with its convex surface facing the object side. An image surface I is located on the image side of the fourth lens group G4.

[0106] Table 1 below lists the values ​​of the specifications of the optical system according to the first example.

[0107] (Table 1) [Overall specifications] f=58.199 FNO=2.884 2ω=41.16 Ymax=21.600 TL=129.454 Bf=18.233 βF1=6.285 βF2=0.193 MF1=1.071 MF2=1.092 Lfr=44.026 Lre=85.428 f1R=-73.793 [Lens specifications] Surface number RD nd νd Object plane ∞ 1 70.9676 1.000 1.81600 46.59 2 24.5834 8.377 3 39.1849 3.877 1.90366 31.27 4 359.9017 12.338 5 80.4619 1.000 1.85026 32.35 6 27.7147 2.519 7 270.1842 2.882 1.80400 46.60 8 -69.3419 0.200 9 30.8966 6.189 1.59319 67.90 10 -36.3993 0.200 11 -50.2592 1.000 1.84666 23.80 12 77.1654 3.308 1.81600 46.59 13 -73.3678 1.136 14∞ (D14) (Aperture S) 15 3039.8536 1.000 1.90366 31.27 16 26.6247 3.179 17 -37.1406 1.000 1.72047 34.71 18 105.9932 0.237 19 69.8034 3.653 1.94595 17.98 20 -54.1523 (D20) 21 285.7257 6.480 1.59319 67.90 22 -41.9044 0.362 23* 127.2840 4.094 1.59349 67.00 24 -137.6180 (D24) 25 -42.9609 1.000 1.80518 25.45 26 61.3138 0.200 27 36.3529 4.660 1.48749 70.31 28 95.2752 Bf Image plane ∞ [Aspherical data] Page 23 κ=1.0000,A4=-1.09713E-06,A6=2.87783E-09,A8=-1.07908E-11,A10=1.55910E-14 [Variable Interval Data] Infinity focus Close focus f=58.199 β=-0.100 D0 ∞ 567.971 D14 2.000 3.071 D20 24.282 22.120 D24 15.048 16.140 [Lens group data] Group starting plane focal length G1 1 31.774 G2 15 -39.196 G3 21 40.437 G4 25 -41.889

[0108] 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.

[0109] From the various aberration diagrams, it can be seen that the optical system according to Example 1 has excellent imaging performance, with various aberrations being well corrected not only when focusing at infinity but also when focusing at close distances.

[0110] (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 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. 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 third lens group G3 moves along the optical axis toward the object side, changing the spacing between adjacent lens groups. During focusing, the positions of the first lens group G1 and the fourth lens group G4 are fixed relative to the image plane I.

[0111] An aperture stop S is disposed between the first lens group G1 and the second lens group G2. During focusing, the position of the aperture stop S is fixed relative to the image plane I. In this embodiment, the second lens group G2 corresponds to the first focusing lens group GF1, the third lens group G3 corresponds to the second focusing lens group GF2, and the fourth lens group G4 corresponds to the subsequent lens group GR.

[0112] The first lens group G1 is composed of, arranged in order from the object side along the optical axis, a biconvex positive lens L11, a cemented negative lens formed by cementing a biconcave negative lens L12 and a biconvex positive lens L13, and a cemented positive lens formed by cementing a positive meniscus lens L14 with its concave surface facing the object side, a biconcave negative lens L15 and a biconvex positive lens L16. The object side surface of the positive meniscus lens L14 is aspheric.

[0113] The second lens group G2 is composed of, arranged in order from the object side along the optical axis, a negative meniscus lens L21 with a convex surface facing the object side, a biconcave negative lens L22, and a positive meniscus lens L23 with a convex surface facing the object side.

[0114] The third lens group G3 is composed of, in order from the object side along the optical axis, a negative meniscus lens L31 with its convex surface facing the object side and a biconvex positive lens L32 cemented together. The object-side lens surface of the negative meniscus lens L31 is aspherical.

[0115] The fourth lens group G4 is composed of, arranged in order from the object side along the optical axis, a negative meniscus lens L41 with a convex surface facing the object side, a cemented negative lens formed by cementing together a negative meniscus lens L42 with a convex surface facing the object side and a positive meniscus lens L43 with a convex surface facing the object side, a cemented positive lens formed by cementing together a negative meniscus lens L44 with a convex surface facing the object side and a biconvex positive lens L45, a negative meniscus lens L46 with a concave surface facing the object side, and a positive meniscus lens L47 with a convex surface facing the object side. An image plane I is located on the image side of the fourth lens group G4.

[0116] Table 2 below lists the values ​​of the specifications of the optical system according to the second example.

[0117] (Table 2) [Overall specifications] f=102.000 FNO=2.868 2ω=24.42 Ymax=21.600 TL=149.455 Bf=33.258 βF1=11.216 βF2=0.113 MF1=2.399 MF2=0.255 Lfr=36.974 Lre=112.481 f1R=-134.926 [Lens specifications] Surface number RD nd νd Object plane ∞ 1 73.3620 5.300 1.69680 55.52 2 -109.7468 8.200 3 -46.1075 1.000 1.84666 23.80 4 26.5543 7.524 1.92286 20.88 5 -145.9538 0.887 6* -339.5091 4.120 1.59319 67.90 7 -38.3498 1.000 1.71736 29.57 8 49.2404 6.944 1.80400 46.60 9 -43.5214 2.000 10∞ (D10) (S aperture) 11 219.1588 1.000 1.83400 37.18 12 26.1206 3.581 13 -165.9036 1.000 1.65160 58.62 14 62.1595 0.200 15 42.0615 2.965 1.94594 17.98 16 156.1083 (D16) 17* 51.1323 1.000 1.94594 17.98 18 29.4695 7.000 1.81600 46.59 19 -100.5432 (D19) 20 202.9270 1.000 1.59349 67.00 21 67.0793 2.320 22 372.0300 1.000 1.81600 46.59 23 22.8082 4.271 1.94594 17.98 24 30.7973 2.000 25 32.4194 2.177 2.00069 25.46 26 20.5772 10.299 1.83400 37.18 27 -230.0301 2.427 28 -48.5548 1.000 1.84666 23.80 29 -1535.4051 0.200 30 80.9334 2.419 1.81600 46.59 31 147.0046 Bf Image plane ∞ [Aspherical data] Page 6 κ=1.0000,A4=-5.87404E-06,A6=-2.70092E-09,A8=2.40290E-12,A10=-5.67289E-15 Page 17 κ=1.0000,A4=2.80605E-07,A6=3.18648E-09,A8=-2.06870E-11,A10=4.66027E-14 [Variable Interval Data] Infinity focus Close focus f=102.000 β=-0.100 D0 ∞ 1043.392 D10 2.000 4.399 D16 29.363 26.710 D19 2.000 2.255 [Lens group data] Group starting plane focal length G1 1 50.642 G2 11 -38.835 G3 17 46.021 G4 20 -70.977

[0118] 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 range. It can be seen from the diagrams that the optical system according to Example 2 has excellent imaging performance, with various aberrations being well corrected not only when focusing at infinity but also when focusing at close range.

[0119] (Third Example) Example 3 will be described with reference to FIGS. 5 to 6 and Table 3. FIG. 5 shows the lens configuration of the optical system according to Example 3. 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 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. 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 third lens group G3 moves along the optical axis toward the object side, changing the spacing between adjacent lens groups. During focusing, the positions of the first lens group G1 and the fourth lens group G4 are fixed relative to the image plane I.

[0120] An aperture stop S is disposed between the first lens group G1 and the second lens group G2. During focusing, the position of the aperture stop S is fixed relative to the image plane I. In this embodiment, the second lens group G2 corresponds to the first focusing lens group GF1, the third lens group G3 corresponds to the second focusing lens group GF2, and the fourth lens group G4 corresponds to the subsequent lens group GR.

[0121] The first lens group G1 is composed of, arranged in order from the object side along the optical axis, a positive meniscus lens L11 with a convex surface facing the object side, a positive meniscus lens L12 with a convex surface facing the object side, a cemented negative lens formed by cementing together a positive meniscus lens L13 with a convex surface facing the object side and a negative meniscus lens L14 with a convex surface facing the object side, a biconcave negative lens L15, a biconvex positive lens L16, and a plano-convex positive lens L17 with a flat surface facing the image side.

[0122] The second lens group G2 is composed of, arranged in order from the object side along the optical axis, a negative meniscus lens L21 with its convex surface facing the object side, a biconcave negative lens L22, and a biconvex positive lens L23.

[0123] The third lens group G3 is composed of, arranged in order from the object side along the optical axis, a biconvex positive lens L31, and a cemented positive lens formed by cementing together a positive meniscus lens L32 with its concave surface facing the object side and a negative meniscus lens L33 with its concave surface facing the object side.

[0124] The fourth lens group G4 is composed of, arranged along the optical axis from the object side, a cemented positive lens formed by cementing a biconcave negative lens L41 and a biconvex positive lens L42, a cemented negative lens formed by cementing a biconcave negative lens L43 and a biconvex positive lens L44, and a negative meniscus lens L45 with its concave surface facing the object side. An image plane I is located on the image side of the fourth lens group G4.

[0125] Table 3 below lists the values ​​of the specifications of the optical system according to the third example.

[0126] (Table 3) [Overall specifications] f=83.999 FNO=1.220 2ω=29.26 Ymax=21.600 TL=139.455 Bf=11.455 βF1=3.155 βF2=0.242 MF1=2.314 MF2=0.737 Lfr=56.098 Lre=83.356 f1R=268.037 [Lens specifications] Surface number RD nd νd Object plane ∞ 1 72.5291 8.949 1.89286 20.36 2 244.3860 0.200 3 56.2010 5.840 1.81600 46.59 4 89.2667 0.200 5 44.3978 10.589 1.49782 82.57 6 486.1002 1.400 1.85478 24.80 7 28.9470 10.930 8 -192.3591 1.300 1.80518 25.45 9 59.8849 3.010 10 203.7409 3.984 1.81600 46.59 11 -186.7775 0.200 12 45.7693 7.498 1.83481 42.73 13∞2.000 14∞ (D14) (Aperture S) 15 91.6235 1.300 1.84666 23.80 16 32.8343 7.655 17 -99.1075 1.300 1.80518 25.45 18 227.4050 0.200 19 93.7043 4.280 1.94595 17.98 20 -233.9384 (D20) 21 67.0639 6.000 1.77250 49.62 22 -96.8252 0.200 23 -319.2894 6.500 1.77250 49.62 24 -36.1643 1.200 1.84666 23.80 25 -88.0731 (D25) 26 -112.9422 2.905 1.72825 28.38 27 81.8139 8.711 1.94595 17.98 28 -92.3161 0.200 29 -205.4633 1.200 1.73800 32.26 30 53.3478 7.178 1.51742 52.20 31 -172.6355 4.534 32 -40.6984 1.200 1.80400 46.60 33 -456.5834 Bf Image plane ∞ [Variable Interval Data] Infinity focus Close focus f=83.999 β=-0.033 D0 ∞ 2517.498 D14 2.000 4.314 D20 13.339 10.288 D25 2.000 2.737 [Lens group data] Group starting plane focal length G1 1 90.124 G2 15 -75.916 G3 21 42.468 G4 26 -60.936

[0127] 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 range. It can be seen from the diagrams that the optical system according to Example 3 has excellent imaging performance, with various aberrations being well corrected not only when focusing at infinity but also when focusing at close range.

[0128] 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 (15) for all the examples (Examples 1 to 3). Conditional expression (1) 0.68<(-fF1) / fF2<3.60 Condition (2) 0.60 <fF2 / (-fR)<1.10 Conditional expression (3) f1 / |f1R|<1.00 Condition (4) 0.50 <Lre / Lfr<4.00 Condition (5) 0.45 <f1 / (-fF1)<2.50 Condition (6) 0.55 <f1 / fF2<3.00 Condition (7) 0.10 <f1 / f<1.25 Condition (8) 0.05 <Bf / f<0.65 Conditional expression (9) νP<42.00 Condition (10) 0.10 <MF1 / MF2<20.00 Conditional expression (11) 0.50<βF1<15.00 Conditional expression (12) 0.05<βF2<1.00 Conditional expression (13) 1.00<βF1 / βF2 Conditional expression (14) {βF1+(1 / βF1)} -2 <0.250 Conditional expression (15) {βF2+(1 / βF2)} -2 <0.250

[0129] [Conditional Expression Corresponding Values] (First to Third Examples) Conditional Expression First Example Second Example Third Example (1) 0.969 0.844 1.788 (2) 0.965 0.648 0.697 (3) 0.431 0.375 0.336 (4) 1.940 3.042 1.486 (5) 0.811 1.304 1.187 (6) 0.786 1.100 2.122 (7) 0.546 0.496 1.073 (8) 0.313 0.326 0.136 (9) 31.270 20.880 20.360 (10) 0.981 9.417 3.139 (11) 6.285 11.216 3.155 (12) 0.193 0.113 0.242 (13) 32.550 98.894 13.039 (14) 0.024 0.008 0.083 (15) 0.035 0.013 0.052

[0130] According to each of the above embodiments, an optical system with little aberration fluctuation during focusing can be realized.

[0131] The above-described examples are merely illustrative examples of the present invention, and the present invention is not limited to these.

[0132] The following contents can be appropriately adopted within the scope that does not impair the optical performance of the optical system of this embodiment.

[0133] Although a four-group configuration has been shown as an example of the optical system of this embodiment, the present application is not limited to this, and optical systems with other group configurations (for example, five groups, six groups, etc.) 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.

[0134] 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.

[0135] 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.

[0136] 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.

[0137] The aperture diaphragm is preferably disposed between the first lens group and the second 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 diaphragm.

[0138] 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]

[0139] G1 First lens group G2 Second lens group G3 3rd lens group G4 4th lens group I Image plane S Aperture stop

Claims

1. The lens comprises, arranged in order from the object side along the optical axis, a first lens group having positive refractive power, a second lens group having negative refractive power, a third lens group having positive refractive power, and a fourth lens group having negative refractive power, During focusing, the second lens group and the third lens group move along different trajectories along the optical axis, An optical system that satisfies the following condition: f1 / |f1R|<1.00 where f1 is the focal length of the first lens group f1R: composite focal length of the lens group arranged closer to the image than the first lens group when focused at infinity

2. An optical system as described in claim 1, which satisfies the following conditional expression. 0.68<(-fF1) / fF2<3.60 where fF1 is the focal length of the second lens group fF2: focal length of the third lens group

3. An optical system according to claim 1 or 2, which satisfies the following conditional expression: 0.60<fF2 / (-fR)<1.10 where fF2 is the focal length of the third lens group fR: focal length of the fourth lens group

4. 4. The optical system according to claim 1, wherein the fourth lens group has at least two lens components.

5. Having an aperture stop, 5. The optical system according to claim 1, wherein the following condition is satisfied: 0.50<Lre / Lfr<4.00 where Lfr is the distance on the optical axis from the lens surface closest to the object side of the optical system to the aperture stop. Lre: distance on the optical axis from the aperture stop to the image plane

6. 6. The optical system according to claim 1, wherein the following condition is satisfied: 0.45<f1 / (-fF1)<2.50 where f1 is the focal length of the first lens group fF1: focal length of the second lens group

7. 7. The optical system according to claim 1, wherein the following condition is satisfied: 0.55<f1 / fF2<3.00 where f1 is the focal length of the first lens group fF2: focal length of the third lens group

8. 8. The optical system according to claim 1, wherein the following condition is satisfied: 0.10<f1 / f<1.25 where f1 is the focal length of the first lens group f: focal length of the optical system when focused at infinity

9. 9. The optical system according to claim 1, wherein the following condition is satisfied: 0.05<Bf / f<0.65 where Bf is the back focus of the optical system when focused at infinity. f: focal length of the optical system when focused at infinity

10. the first lens group has at least one positive lens; 10. The optical system according to claim 1, wherein the following condition is satisfied: νP<42.00 where νP is the Abbe number of the positive lens having the smallest Abbe number among the at least one positive lens in the first lens group.

11. 11. The optical system according to claim 1, wherein the second lens group moves along the optical axis toward the image side when focusing from an object at infinity to an object at a close distance.

12. 12. The optical system according to claim 1, wherein the third lens group moves along the optical axis toward the object when focusing from an object at infinity to an object at a close distance.

13. The optical system according to any one of claims 1 to 12, which satisfies the following conditional expression: 0.10<MF1 / MF2<20.00 where MF1 is the absolute value of the movement amount of the second lens group when focusing from an object at infinity to an object at a close distance. MF2: Absolute value of the movement amount of the third lens group when focusing from an object at infinity to an object at a close distance

14. The optical system according to any one of claims 1 to 13, which satisfies the following conditional expression: 0.50<βF1<15.00 where βF1 is the lateral magnification of the second lens group when focused at infinity.

15. The optical system according to any one of claims 1 to 14, which satisfies the following conditional expression: 0.05<βF2<1.00 where βF2 is the lateral magnification of the third lens group when focused at infinity.

16. The optical system according to any one of claims 1 to 15, which satisfies the following conditional expression: 1.00<βF1 / βF2 where βF1 is the lateral magnification of the second lens group when focused at infinity. βF2: lateral magnification of the third lens group when focused at infinity

17. 17. The optical system according to claim 1, wherein the following condition is satisfied: {βF1+(1 / βF1)} -2 <0.250 where βF1 is the lateral magnification of the second lens group when focused at infinity.

18. 18. The optical system according to claim 1, wherein the following condition is satisfied: {βF2+(1 / βF2)} -2 <0.250 where βF2 is the lateral magnification of the third lens group when focused at infinity.

19. An optical instrument comprising the optical system according to any one of claims 1 to 18.

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