Optical Systems and Optical Instruments

Abstract

To provide an optical system which offers superior optical performance over a focus range of infinity to a short distance.SOLUTION: An optical system OL disclosed herein comprises a first lens group G1 having positive refractive power, a second lens group G2, a third lens group G3, and a fourth lens group G4 arranged in order from the object side along an optical axis, and is configured such that the second lens group G2 and the third lens group G3 move along the optical axis on different trajectories when shifting focus from an object at infinity to a nearby object. The optical system satisfies a the following conditional expression: 0.010<(Δx2A+Δx3A) / D1<0.200, where Δx2A represents an absolute value of a displacement of the second lens group G2 when shifting focus from an object at infinity to a nearby object, Δx3A represents an absolute value of a displacement of the third lens group G3 when shifting focus from an object at infinity to a nearby object, and D1 represents an optical axial length of the first lens group G1.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 digital still cameras, video cameras, etc. have been proposed (see, for example, Patent Document 1). Such optical systems are required to maintain excellent optical performance from focusing at infinity to focusing at close distances. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-194630 Summary of the Invention

[0004] The optical system according to the present invention comprises a first lens group, a second lens group, a third lens group, and a fourth lens group, all of which have positive refractive power, arranged in this order from the object side along an optical axis. Made up of When focusing from an object at infinity to an object at a close distance, the second lens group and the third lens group move along different trajectories along the optical axis, two positive lenses are arranged in the first lens group in order from the most object side to the image side, and a positive lens, a negative lens and a positive lens are arranged in the first lens group in order from the most image side to the object side, The following conditional expression is satisfied: 0.010<(Δx2A+Δx3A) / D1<0.200 where Δx2A 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. Δx3A: 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 D1: The length of the first lens group on the optical axis

[0005] An optical device according to the present invention includes the optical system described above. [Brief explanation of the drawings]

[0006] [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. 10 is a diagram showing the lens configuration of an optical system according to Example 4. [Figure 8] 8A and 8B are diagrams showing various aberrations of the optical system according to Example 4 when focused at infinity and when focused at a close distance, respectively. [Figure 9] FIG. 10 is a diagram showing the lens configuration of an optical system according to Example 5. [Figure 10] 10A and 10B are diagrams showing various aberrations of the optical system according to Example 5 when focused on infinity and when focused on a close distance, respectively. [Figure 11] FIG. 1 is a diagram showing the configuration of a camera including an optical system according to each embodiment. [Figure 12] 1 is a flowchart illustrating a method for manufacturing an optical system according to each embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0007] Preferred embodiments of the present invention will be described below. First, the optical A camera (optical device) equipped with such a system will be described with reference to FIG. 11. As shown in FIG. 11, 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.

[0008] 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. The optical system OL shown in FIG. 11 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.

[0009] 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 configured to include, in order from the object side along the optical axis, a first lens group G1 having positive refractive power, a second lens group G2, a third lens group G3, and a fourth lens group G4. When focusing from an object at infinity to an object at close range, the second lens group G2 and the third lens group G3 move along the optical axis on different trajectories. Furthermore, the second lens group G2 and the third lens group G3 are configured to include a total of three or fewer lenses.

[0010] According to the first embodiment, it is possible to obtain an optical system that has excellent optical performance from focusing at infinity to focusing at close distances, and an optical device that includes this optical system. The optical system OL according to the first embodiment may be the optical system OL(2) shown in Fig. 3, the optical system OL(3) shown in Fig. 5, the optical system OL(4) shown in Fig. 7, or the optical system OL(5) shown in Fig. 9.

[0011] 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 configured to include, in order from the object side along the optical axis, a first lens group G1 having positive refractive power, a second lens group G2, a third lens group G3, and a fourth lens group G4. When focusing from an object at infinity to an object at a close distance, the second lens group G2 and the third lens group G3 move along the optical axis on different trajectories.

[0012] With the above-described configuration, the optical system OL according to the second embodiment satisfies the following conditional expression (1). 0.010<(Δx2A+Δx3A) / D1<0.200 ···(1) where Δx2A: absolute value of the movement amount of the second lens group G2 when focusing from an object at infinity to an object at a close distance Δx3A: Absolute value of the movement amount of the third lens group G3 when focusing from an object at infinity to an object at a close distance D1: Length of the first lens group G1 on the optical axis

[0013] According to the second embodiment, it is possible to obtain an optical system that has excellent optical performance from focusing at infinity to focusing at close distances, and an optical device that includes this optical system. The optical system OL according to the second embodiment may be the optical system OL(2) shown in Fig. 3, the optical system OL(3) shown in Fig. 5, the optical system OL(4) shown in Fig. 7, or the optical system OL(5) shown in Fig. 9.

[0014] Conditional expression (1) defines an appropriate relationship between the sum of the movement amounts of the second lens group G2 and the third lens group G3 during focusing and the axial length of the first lens group G1. By satisfying conditional expression (1), it is possible to suppress aberration fluctuations during focusing from an object at infinity to an object at a close distance.

[0015] If the corresponding value of conditional expression (1) falls below the lower limit, the movement amount of the second lens group G2 and the third lens group G3 that perform focusing becomes small, which tends to increase the power of the second lens group G2 and the third lens group G3, making it difficult to suppress aberration fluctuations during focusing. The effect of this embodiment can be further ensured by setting the lower limit of conditional expression (1) to 0.015, 0.020, 0.025, 0.030, 0.035, 0.040, or even 0.042.

[0016] If the corresponding value of conditional expression (1) exceeds the upper limit, the first lens group G1 becomes shorter, which tends to increase the power of the first lens group G1, making it difficult to correct various aberrations such as axial chromatic aberration and spherical aberration. By setting the upper limit of conditional expression (1) to 0.175, 0.160, 0.150, 0.125, 0.115, 0.110, or even 0.100, the effects of this embodiment can be further ensured.

[0017] It is desirable that the optical systems OL according to the first and second embodiments satisfy the following conditional expression (2). -0.20<Δx2 / f2<0.00 (2) where Δx2 is the amount of movement of the second lens group G2 when focusing from an object at infinity to an object at a close distance (the sign of the amount of movement toward the image plane side is +, and the sign of the amount of movement toward the object side is -). f2: Focal length of the second lens group G2

[0018] Conditional expression (2) defines an appropriate relationship between the amount of movement of the second lens group G2 during focusing and the focal length of the second lens group G2. By satisfying conditional expression (2), it is possible to suppress aberration fluctuations during focusing from an object at infinity to an object at a close distance.

[0019] If the corresponding value of conditional expression (2) falls below the lower limit, the power of the second lens group G2, which performs focusing, becomes stronger, making it difficult to suppress aberration fluctuations during focusing. Furthermore, the amount of movement of the second lens group G2, which performs focusing, becomes larger, resulting in an increase in the overall length of the optical system OL. In order to prevent an increase in the overall length of the optical system OL, for example, it is necessary to shorten the first lens group G1 and increase the power of the first lens group G1, which makes it difficult to correct various aberrations such as axial chromatic aberration and spherical aberration. Setting the lower limit of conditional expression (2) to -0.18, -0.15, -0.13, -0.10, -0.09, or even -0.08 can further enhance the effects of each embodiment.

[0020] If the corresponding value of conditional expression (2) reaches the upper limit, it becomes difficult to ensure the power or movement amount of the second lens group G2 that performs focusing, which is undesirable. By setting the upper limit of conditional expression (2) to -0.01, or even -0.02, the effects of each embodiment can be made more certain.

[0021] It is desirable that the optical systems OL according to the first and second embodiments satisfy the following conditional expression (3). -0.20<Δx3 / f3<0.00 (3) where Δx3 is the amount of movement of the third lens group G3 when focusing from an object at infinity to an object at a close distance (the sign of the amount of movement toward the image plane side is +, and the sign of the amount of movement toward the object side is -). f3: Focal length of the third lens group G3

[0022] Conditional expression (3) defines an appropriate relationship between the amount of movement of the third lens group G3 during focusing and the focal length of the third lens group G3. By satisfying conditional expression (3), it is possible to suppress aberration fluctuations during focusing from an object at infinity to an object at a close distance.

[0023] If the corresponding value of conditional expression (3) falls below the lower limit, the power of the third lens group G3, which performs focusing, becomes stronger, making it difficult to suppress aberration fluctuations during focusing. Furthermore, the amount of movement of the third lens group G3, which performs focusing, becomes larger, resulting in an increase in the overall length of the optical system OL. In order to prevent an increase in the overall length of the optical system OL, for example, it is necessary to shorten the first lens group G1 and increase the power of the first lens group G1, which makes it difficult to correct various aberrations such as axial chromatic aberration and spherical aberration. Setting the lower limit of conditional expression (3) to -0.18, -0.16, or even -0.15 can further ensure the effects of each embodiment.

[0024] If the value corresponding to conditional expression (3) reaches the upper limit, it becomes difficult to ensure the power or movement amount of the third lens group G3 that performs focusing, which is undesirable. By setting the upper limit of conditional expression (3) to -0.01, the effects of each embodiment can be more reliably achieved.

[0025] It is desirable that the optical systems OL according to the first and second embodiments satisfy the following conditional expression (4). 1.00 <f2 / (-f3)<4.00 ···(4) However, f2 is the focal length of the second lens group G2. f3: Focal length of the third lens group G3

[0026] Conditional expression (4) defines an appropriate relationship between the focal length of the second lens group G2 and the focal length of the third lens group G3. By satisfying conditional expression (4), it is possible to suppress aberration fluctuations when focusing from an object at infinity to an object at a close distance.

[0027] If the corresponding value of conditional expression (4) falls below the lower limit, the power of the second lens group G2, which performs focusing, becomes strong, making it difficult to suppress aberration fluctuations during focusing. By setting the lower limit of conditional expression (4) to 1.05, 1.10, 1.15, 1.20, 1.25, 1.30, or even 1.35, the effects of each embodiment can be more reliably achieved.

[0028] If the corresponding value of conditional expression (4) exceeds the upper limit, the power of the third lens group G3, which performs focusing, becomes strong, making it difficult to suppress aberration fluctuations during focusing. By setting the upper limit of conditional expression (4) to 3.80, 3.50, 3.25, 3.00, 2.85, 2.80, 2.75, or even 2.70, the effects of each embodiment can be further ensured.

[0029] It is desirable that the optical systems OL according to the first and second embodiments satisfy the following conditional expression (5). -3.00<Δx2 / Δx3<-0.20 (5) where Δx2 is the amount of movement of the second lens group G2 when focusing from an object at infinity to an object at a close distance (the sign of the amount of movement toward the image plane side is +, and the sign of the amount of movement toward the object side is -). Δx3: the amount of movement of the third lens group G3 when focusing from an object at infinity to an object at a close distance (the sign of the amount of movement toward the image plane side is +, and the sign of the amount of movement toward the object side is -)

[0030] Condition (5) defines an appropriate relationship between the amount of movement of the second lens group G2 during focusing and the amount of movement of the third lens group G3 during focusing. By satisfying condition (5), various aberrations such as axial chromatic aberration and spherical aberration can be effectively corrected.

[0031] If the value of conditional expression (5) falls below the lower limit, the amount of movement of the second lens group G2, which performs focusing, increases, which leads to an increase in the overall length of the optical system OL. For example, it would be necessary to shorten the length of the first lens group G1 and increase the power of the first lens group G1, which would make it difficult to correct various aberrations such as axial chromatic aberration and spherical aberration. By setting the lower limit of conditional expression (5) to -2.85, -2.70, -2.60, -2.50, -2.45, or even -2.40, the effects of each embodiment can be more reliably achieved.

[0032] If the value corresponding to conditional expression (5) exceeds the upper limit, the movement amount of the third lens group G3, which performs focusing, increases, resulting in an increase in the overall length of the optical system OL. To prevent the overall length of the optical system OL from increasing, for example, it is necessary to shorten the first lens group G1 and increase the power of the first lens group G1, which makes it difficult to correct various aberrations such as axial chromatic aberration and spherical aberration. By setting the upper limit of conditional expression (5) to -0.25, -0.30, -0.35, -0.40, -0.45, or even -0.50, the effects of each embodiment can be further ensured.

[0033] In the optical systems OL according to the first and second embodiments, it is desirable that the fourth lens group G4 have an image stabilization group with negative refractive power that is movable so as to have a displacement component in a direction perpendicular to the optical axis in order to correct image blur, thereby suppressing aberration fluctuations when correcting image blur.

[0034] In the optical systems OL according to the first and second embodiments, it is desirable that the vibration reduction group be composed of two or more lenses, which makes it possible to suppress aberration fluctuations when correcting image blur.

[0035] It is desirable that the optical systems OL according to the first and second embodiments satisfy the following conditional expression (6). -8.50 <f1 / fVR<-3.00 ···(6) where f1 is the focal length of the first lens group G1 fVR: focal length of vibration isolation group

[0036] Conditional expression (6) defines an appropriate relationship between the focal length of the first lens group G1 and the focal length of the vibration reduction group. By satisfying conditional expression (6), it is possible to suppress aberration fluctuations when correcting image blur.

[0037] If the corresponding value of conditional expression (6) falls below the lower limit, the power of the image stabilization group becomes strong, making it difficult to suppress aberration fluctuations when correcting image blur. By setting the lower limit of conditional expression (6) to -8.25, -8.10, -8.00, -7.85, -7.70, -7.50, -7.30, or even -7.25, the effects of each embodiment can be further ensured.

[0038] If the corresponding value of conditional expression (6) exceeds the upper limit, the power of the first lens group G1 becomes strong, making it difficult to correct various aberrations such as axial chromatic aberration and spherical aberration. By setting the upper limit of conditional expression (6) to -3.15, -3.30, -3.50, -3.65, -3.80, -4.00, -4.10, -4.20, or even -4.25, the effects of each embodiment can be further ensured.

[0039] It is desirable that the optical systems OL according to the first and second embodiments satisfy the following conditional expression (7). 0.45<β2<0.80 (7) β2: Magnification of the second lens group G2 when focusing on an object at infinity

[0040] Conditional expression (7) defines an appropriate range for the magnification of the second lens group G2 when focusing on an object at infinity. By satisfying conditional expression (7), fluctuations in various aberrations, including spherical aberration, during focusing can be suppressed.

[0041] If the corresponding value of conditional expression (7) falls below the lower limit, it becomes difficult to suppress fluctuations in various aberrations during focusing. By setting the lower limit of conditional expression (7) to 0.46, 0.47, 0.48, or even 0.49, the effects of each embodiment can be more reliably achieved.

[0042] If the corresponding value of conditional expression (7) exceeds the upper limit, it becomes difficult to suppress fluctuations in various aberrations during focusing. By setting the upper limit of conditional expression (7) to 0.78, 0.75, 0.73, or even 0.70, the effects of each embodiment can be further ensured.

[0043] It is desirable that the optical systems OL according to the first and second embodiments satisfy the following conditional expression (8). 0.20<1 / β3<0.50 (8) However, β3 is the magnification of the third lens group G3 when focusing on an object at infinity.

[0044] Conditional expression (8) defines an appropriate range for the magnification of the third lens group G3 when focusing on an object at infinity. By satisfying conditional expression (8), fluctuations in various aberrations, including spherical aberration, during focusing can be suppressed.

[0045] If the corresponding value of conditional expression (8) falls below the lower limit, it becomes difficult to suppress fluctuations in various aberrations during focusing. By setting the lower limit of conditional expression (8) to 0.22, 0.24, 0.25, or even 0.26, the effects of each embodiment can be further ensured.

[0046] If the corresponding value of conditional expression (8) exceeds the upper limit, it becomes difficult to suppress fluctuations in various aberrations during focusing. By setting the upper limit of conditional expression (8) to 0.48, 0.46, 0.45, or even 0.44, the effects of each embodiment can be further ensured.

[0047] It is desirable that the optical systems OL according to the first and second embodiments satisfy the following conditional expression (9). {β2+(1 / β2)} -2 <0.25 (9) β2: Magnification of the second lens group G2 when focusing on an object at infinity

[0048] Conditional expression (9) defines an appropriate range for the magnification of the second lens group G2 when focusing on an object at infinity. By satisfying conditional expression (9), it is possible to reduce the amount of movement of the focus group while suppressing fluctuations in various aberrations, such as spherical aberration, distortion, and coma, when focusing.

[0049] It is preferable that the value corresponding to conditional expression (9) is within the range of the conditional expression, and if the lower limit value of conditional expression (9) is set to 0.10, 0.12, 0.14, or even 0.15, the effects of each embodiment can be more reliably achieved.

[0050] If the corresponding value of conditional expression (9) exceeds the upper limit, it becomes difficult to suppress fluctuations in various aberrations during focusing. By setting the upper limit of conditional expression (9) to 0.24, or even 0.23, 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 (10). {β3+(1 / β3)} -2 <0.18 (10) However, β3 is the magnification of the third lens group G3 when focusing on an object at infinity.

[0052] Condition (10) defines an appropriate range for the magnification of the third lens group G3 when focusing on an object at infinity. By satisfying conditional expression (10), it is possible to reduce the amount of movement of the focus group while suppressing fluctuations in various aberrations, such as spherical aberration, distortion, and coma, during focusing.

[0053] It is preferable that the value corresponding to conditional expression (10) is within the range of the conditional expression. If the lower limit of conditional expression (10) is set to 0.03, or even 0.05, the effects of each embodiment can be more reliably achieved.

[0054] If the corresponding value of conditional expression (10) exceeds the upper limit, it becomes difficult to suppress fluctuations in various aberrations during focusing. By setting the upper limit of conditional expression (10) to 0.16, 0.15, or even 0.14, the effects of each embodiment can be further ensured.

[0055] In the optical systems OL according to the first and second embodiments, it is desirable that the first lens group G1 has a positive lens (L15) that satisfies the following conditional expressions (11) to (13). ndL1+(0.01425×νdL1)<2.12 (11) νdL1<35.00 (12) 0.702<θgFL1+(0.00316×νdL1)...(13) where ndL1 is the refractive index of the positive lens for the d line νdL1: Abbe number based on the d-line of the positive lens θgFL1: The partial dispersion ratio of the positive lens, which is defined by the following formula when the refractive index of the positive lens for the g-line is ngL1, the refractive index of the positive lens for the F-line is nFL1, and the refractive index of the positive lens for the C-line is nCL1. θgFL1=(ngL1-nFL1) / (nFL1-nCL1) The Abbe number νdL1 of the positive lens based on the d-line is defined by the following formula: νdL1=(ndL1-1) / (nFL1-nCL1)

[0056] Conditional expression (11) defines an appropriate relationship between the refractive index of the positive lens in the first lens group G1 at the d-line and the Abbe number of the positive lens with the d-line as the reference. Satisfying conditional expression (11) enables good correction of basic aberrations such as spherical aberration and coma, and good correction of first-order chromatic aberration (achromatism).

[0057] If the corresponding value of conditional expression (11) exceeds the upper limit, for example, the Petzval sum becomes small, which makes it difficult to correct field curvature, and is therefore undesirable. By setting the upper limit of conditional expression (11) to 2.11, 2.10, 2.09, 2.08, 2.07, or even 2.06, the effects of each embodiment can be made more certain.

[0058] The lower limit of conditional expression (11) may be set to 1.83. If the corresponding value of conditional expression (11) falls below this lower limit, the base aberration and chromatic aberration will be overcorrected, which is undesirable. By setting the lower limit of conditional expression (11) to 1.85, 1.90, 1.95, or even 1.98, the effects of each embodiment can be further ensured.

[0059] Conditional expression (12) defines an appropriate range for the Abbe number of the positive lens in the first lens group G1, with reference to the d-line. Satisfying conditional expression (12) enables favorable correction of basic aberrations such as spherical aberration and coma, as well as favorable correction of first-order chromatic aberration (achromatism).

[0060] If the value corresponding to conditional expression (12) exceeds the upper limit, it becomes difficult to correct axial chromatic aberration, for example, in a lens group located closer to the image plane than the positive lens, which is undesirable. By setting the upper limit of conditional expression (12) to 32.50, 32.00, 31.50, 31.00, 30.50, 30.00, or even 29.50, the effects of each embodiment can be further ensured.

[0061] The lower limit of conditional expression (12) may be set to 18.00. If the corresponding value of conditional expression (12) falls below this lower limit, the base aberration and chromatic aberration will be overcorrected, which is undesirable. By setting the lower limit of conditional expression (12) to 18.50, 19.00, 19.50, or even 20.00, the effects of each embodiment can be further ensured.

[0062] Conditional expression (13) appropriately defines the anomalous dispersion of the positive lens in the first lens group G1. By satisfying conditional expression (13), in the correction of chromatic aberration, in addition to first-order achromatism, second-order spectrum can be effectively corrected.

[0063] If the corresponding value of conditional expression (13) falls below the lower limit, the anomalous dispersion of the positive lens becomes small, making it difficult to correct chromatic aberration. By setting the lower limit of conditional expression (13) to 0.704, 0.708, 0.710, 0.712, or even 0.715, the effects of each embodiment can be further ensured.

[0064] The upper limit of conditional expression (13) may be set to 0.900. If the corresponding value of conditional expression (13) exceeds this upper limit, chromatic aberration will be overcorrected, which is undesirable. By setting the upper limit of conditional expression (13) to 0.880, 0.850, 0.825, or even 0.800, the effects of each embodiment can be further ensured.

[0065] The optical systems OL according to the first and second embodiments preferably have lenses (L12, L13) that satisfy the following conditional expression (14): Note that, to distinguish it from other lenses, a lens that satisfies conditional expression (14) may be referred to as a specific lens. 80.00<νdL2 (14) where νdL2 is the Abbe number based on the d line of a specific lens

[0066] Conditional expression (14) defines an appropriate range for the Abbe number of a specific lens based on the d-line. By satisfying conditional expression (14), axial chromatic aberration and lateral chromatic aberration can be effectively corrected.

[0067] If the corresponding value of conditional expression (14) falls below the lower limit, it becomes difficult to correct axial chromatic aberration and lateral chromatic aberration. By setting the lower limit of conditional expression (14) to 81.00, 81.80, 82.50, 84.00, 85.50, 87.00, or even 90.00, the effects of each embodiment can be further ensured.

[0068] The upper limit of conditional expression (14) may be set to 110.00. If the corresponding value of conditional expression (14) exceeds this upper limit, axial chromatic aberration and lateral chromatic aberration will be overcorrected, which is undesirable. By setting the upper limit of conditional expression (14) to 107.50, 105.00, 102.50, 100.00, or even 98.00, the effects of each embodiment can be further ensured.

[0069] It is desirable that the optical systems OL according to the first and second embodiments satisfy the following conditional expression (15). 3.50°<2ω<8.50° (15) However, 2ω: full field angle of optical system OL

[0070] Conditional expression (15) defines an appropriate range for the total angle of view of the optical system OL. Satisfying conditional expression (15) is preferable because it allows for a telephoto optical system with a long focal length. By setting the lower limit of conditional expression (15) to 3.80° or even 4.00°, the effects of each embodiment can be made more certain. Furthermore, by setting the upper limit of conditional expression (15) to 8.00°, , 7.50°, 7.00°, and even 6.50°, the effects of each embodiment can be more reliably achieved.

[0071] In the optical systems OL according to the first and second embodiments, when focusing from an object at infinity to a close object, it is desirable that the second lens group G2 move toward the object along the optical axis and the third lens group G3 move toward the image plane along the optical axis. This makes it possible to effectively correct aberration fluctuations when focusing from an object at infinity to a close object. Furthermore, this also makes it possible to effectively use the space in the optical system OL, thereby shortening the overall length of the optical system OL while maintaining good optical performance.

[0072] In the optical systems OL according to the first and second embodiments, it is desirable that the second lens group G2 be composed of a single lens. This makes the second lens group G2 lightweight, enabling high-speed focusing from an object at infinity to a close-up object. Furthermore, since there is no need to reduce the lens diameter in order to reduce the weight of the focus group, the power of the first lens group G1, for example, does not become too strong, making it possible to effectively correct various aberrations such as axial chromatic aberration and spherical aberration.

[0073] In the optical systems OL according to the first and second embodiments, it is desirable that the third lens group G3 be composed of a single lens component. This makes the third lens group G3 lightweight, enabling high-speed focusing from an object at infinity to a close-up object. Furthermore, since there is no need to reduce the lens diameter in order to reduce the weight of the focus group, the power of the first lens group G1, for example, does not become too strong, making it possible to effectively correct various aberrations such as axial chromatic aberration and spherical aberration. Note that in each embodiment, the lens component refers to a single lens or a cemented lens.

[0074] The optical system OL according to the first and second embodiments preferably has a diaphragm (aperture diaphragm S) located closer to the image plane than the second lens group G2, which allows the diaphragm to be located at a position in the optical system OL where the diameter of the light beam is small, making it possible to reduce the outer diameter of the lens barrel.

[0075] Furthermore, it is desirable to position the diaphragm (aperture diaphragm S) closer to the image plane than the third lens group G3, which places the diaphragm at a location in the optical system OL where the diameter of the light beam is small, making it possible to reduce the outer diameter of the lens barrel.

[0076] In the optical systems OL according to the first and second embodiments, the second lens group G2 is the first focusing lens group that moves during focusing, and may have either positive or negative refractive power. Also, the third lens group G3 is the second focusing lens group that moves during focusing, and may have either positive or negative refractive power.

[0077] In the optical systems OL according to the first and second embodiments, the second lens group G2 is the first focusing lens group that moves during focusing, and the third lens group G3 is the second focusing lens group that moves during focusing, but one or more lenses having positive or negative refractive power may be provided between the first focusing lens group and the second focusing lens group.

[0078] Next, a manufacturing method of the optical system OL according to the first embodiment will be outlined with reference to Fig. 12. First, a first lens group G1 having positive refractive power, a second lens group G2, a third lens group G3, and a fourth lens group G4 are arranged in order from the object side along the optical axis (Step ST1). Next, when focusing from an object at infinity to an object at close range, the second lens group G2 and the third lens group G3 are configured to move along different trajectories along the optical axis (Step ST2). Furthermore, the lenses are arranged within the lens barrel so that the second lens group G2 and the third lens group G3 are composed of a total of three or less lenses. This manufacturing method makes it possible to manufacture an optical system with excellent optical performance from infinity focusing to close-up focusing. Next, as with the first embodiment, a manufacturing method for the optical system OL according to the second embodiment will be outlined with reference to FIG. 12 . First, a first lens group G1 having positive refractive power, a second lens group G2, a third lens group G3, and a fourth lens group G4 are arranged in order from the object side along the optical axis (Step ST1). Next, when focusing from an object at infinity to a close-up object, the second lens group G2 and the third lens group G3 are configured to move along different trajectories along the optical axis (Step ST2). Furthermore, the lenses are arranged within the lens barrel so as to satisfy at least the above conditional expression (1). This manufacturing method makes it possible to manufacture an optical system with excellent optical performance from infinity focusing to close-up focusing. [Example]

[0079] Optical systems OL according to examples of each embodiment will be described below with reference to the drawings. FIGS. 1, 3, 5, 7, and 9 are cross-sectional views showing the configurations and refractive power distributions of optical systems OL {OL(1) to OL(5)} according to Examples 1 to 5. In the cross-sectional views of the optical systems OL(1) to OL(5) according to Examples 1 to 5, the direction of movement of the second and third lens groups along the optical axis when focusing from infinity to a close-up object is indicated by an arrow accompanied by the word "focusing." Furthermore, the direction of movement of a portion of the fourth lens group when it acts as an image stabilization group to correct image blur is indicated by an arrow accompanied by the word "stabilization."

[0080] 1, 3, 5, 7, and 9, 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.

[0081] Tables 1 to 5 are shown below, with Table 1 showing data on the various elements in Example 1, Table 2 in Example 2, Table 3 in Example 3, Table 4 in Example 4, and Table 5 in Example 5. 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.

[0082] 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: °, 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, fVR is the focal length of the vibration-reduction group. Δx2 is the amount of movement of the second lens group when focusing from an object at infinity to a close object. Δx3 is the amount of movement of the third lens group when focusing from an object at infinity to a close object. Note that for the amount of movement of the lens groups, the sign for movement toward the image plane is positive, and the sign for movement toward the object is negative. β2 is the magnification of the second lens group when focusing on an object at infinity. β3 represents the magnification of the third lens group when focusing on an object at infinity.

[0083] In the [Lens Specifications] table, the surface number indicates the order of the optical surfaces from the object side along the direction of light travel, R is the radius of curvature of each optical surface (surfaces whose center of curvature is located on the image side are given 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 surface), nd is the refractive index of the optical element material with respect to the d-line, νd is the Abbe number of the optical element material with the d-line as the reference, and θgF is the partial dispersion ratio of the optical element material. The "∞" in the radius of curvature indicates a plane or an aperture, and (stop S) indicates the aperture stop S. The refractive index of air is nd=1.00000. The details are omitted.

[0084] Let ng be the refractive index of the optical member material at the g-line (wavelength λ=435.8 nm), nF be the refractive index of the optical member material at the F-line (wavelength λ=486.1 nm), and nC be the refractive index of the optical member material at the C-line (wavelength λ=656.3 nm). In this case, the partial dispersion ratio θgF of the optical member material is defined by the following equation (A).

[0085] θgF=(ng-nF) / (nF-nC) …(A)

[0086] 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.

[0087] The [Lens Group Data] table shows the starting surface (the surface closest to the object) and focal length of each lens group.

[0088] 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.

[0089] The explanation of the tables up to this point is common to all the embodiments, and duplicate explanations will be omitted below.

[0090] (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 positive refractive power, a third lens group G3 having negative refractive power, and a fourth lens group G4 having positive refractive power. When focusing from an object at infinity to a close object, the second lens group G2 moves toward the object along the optical axis, and the third lens group G3 moves toward the image along the optical axis, changing the spacing between adjacent lens groups. During focusing, the first lens group G1 and the fourth lens group G4 are fixed relative to the image plane I. An aperture stop S is disposed between the third lens group G3 and the fourth lens group G4. 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.

[0091] 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 positive meniscus lens L12 with its convex surface facing the object side, a biconvex positive lens L13, a biconcave negative lens L14, a biconvex positive lens L15, and a cemented lens formed by cementing together a biconcave negative lens L16 and a positive meniscus lens L17 with its convex surface facing the object side.

[0092] The second lens group G2 is composed of a positive meniscus lens L21 with a convex surface facing the object side. The third lens group G3 is composed of a negative meniscus lens L31 with a convex surface facing the object side. In other words, the second lens group G2 and the third lens group G3 are composed of a total of two lenses.

[0093] The fourth lens group G4 includes, arranged in order from the object side along the optical axis, a biconcave negative lens L41, a cemented lens formed by cementing a positive meniscus lens L42 with its concave surface facing the object side and a biconcave negative lens L43, a biconvex positive lens L44, a biconvex positive lens L45, a negative meniscus lens L46 with its convex surface facing the object side and a biconvex positive lens L47. The fourth lens group G4 is composed of a cemented lens having a positive lens L45 and a biconcave negative lens L48. An optical filter FL is disposed between the positive lens L45 and the negative meniscus lens L46 (of the cemented lens) in the fourth lens group G4. An image plane I is disposed on the image side of the fourth lens group G4.

[0094] In this embodiment, the negative lens L41, positive meniscus lens L42, and negative lens L43 of the fourth lens group G4 constitute an image stabilization group that is movable in a direction perpendicular to the optical axis and corrects displacement of the imaging position (image blur on the image plane I) due to camera shake or the like. The positive lens L15 of the first lens group G1 corresponds to the positive lens that satisfies the above-mentioned conditional expressions (11) to (13). The positive meniscus lens L12, positive lens L13, and positive meniscus lens L17 of the first lens group G1, the positive meniscus lens L21 of the second lens group G2, and the negative lens L43 of the fourth lens group G4 correspond to the lenses (specific lenses) that satisfy the above-mentioned conditional expression (14).

[0095] Table 1 below lists the values ​​of the specifications of the optical system according to the first example.

[0096] (Table 1) [Overall specifications] f=390.00001 fVR=-65.65418 FNO=2.90297 Δx2=-11.7496 2ω=6.29588 Δx3=7.7093 Y=21.60 β2=0.63393 TL=405.3186 β3=2.52874 Bf=54.0003 [Lens specifications] Surface number RD nd νd θgF 1 439.8093 8.2000 1.518600 69.89 0.532 2 -1741.2521 0.1000 3 222.5379 12.0000 1.433852 95.25 0.540 4 1393.9654 97.1809 5 139.4073 11.0000 1.433852 95.25 0.540 6 -380.4635 0.1050 7 -416.7878 3.0000 1.683760 37.64 0.578 8 192.2903 59.0562 9 102.4273 6.6000 1.663820 27.35 0.632 10 -401.4769 0.1362 11 -360.0793 1.8000 1.737999 32.26 0.590 12 58.7393 8.8000 1.497820 82.57 0.539 13 1167.4655 (D13) 14 83.8395 6.2000 1.497820 82.57 0.539 15 10090.0640 (D15) 16 690.6259 1.8000 1.755000 52.33 0.548 17 60.0805 (D17) 18 ∞ 7.0861 (Aperture S) 19 -246.8276 1.8000 1.910822 35.25 0.582 20 116.7166 3.8112 21 -73.3878 4.1000 1.846663 23.78 0.619 22 -39.7299 1.8000 1.497820 82.57 0.539 23 433.0885 4.6000 24 89.2307 3.8000 1.612660 44.46 0.564 25 -1734.6597 40.2586 26 55.6338 5.5000 1.696800 55.52 0.543 27 -779.8112 10.0000 28 ∞ 1.5000 1.516800 63.88 0.536 29 ∞ 0.1000 30 63.5589 1.5000 1.804000 46.60 0.557 31 26.0339 8.8000 1.612660 44.46 0.564 32 -212.3772 4.7866 33 -69.8293 1.5000 2.000694 25.46 0.614 34 198.2621 Bf [Variable Interval Data] Focused at infinity Focused at mid-range distance Focused at close range f=390.00001 β=-0.0333 β=-0.1682 D13 16.0689 13.7323 23.5588 D15 4.1000 8.0022 23.4588 D17 14.2286 12.6630 6.5193 [Lens group data] Group starting plane focal length G1 1 282.01395 G2 14 169.78939 G3 16 -87.26627 G4 19 310.88872

[0097] 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.

[0098] 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 over the entire range from focusing at infinity to focusing at close distances.

[0099] (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 positive refractive power, a third lens group G3 having negative refractive power, and a fourth lens group G4 having positive refractive power. When focusing from an object at infinity to a close object, the second lens group G2 moves toward the object along the optical axis, and the third lens group G3 moves toward the image along the optical axis, changing the spacing between adjacent lens groups. During focusing, the first lens group G1 and the fourth lens group G4 are fixed relative to the image plane I. An aperture stop S is disposed between the third lens group G3 and the fourth lens group G4.

[0100] 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 positive meniscus lens L12 with its convex surface facing the object side, a biconvex positive lens L13, a biconcave negative lens L14, a biconvex positive lens L15, and a cemented lens formed by cementing together a biconcave negative lens L16 and a positive meniscus lens L17 with its convex surface facing the object side.

[0101] The second lens group G2 is composed of a biconvex positive lens L21. The third lens group G3 is composed of a cemented lens (having negative refractive power) in which, from the object side, a positive meniscus lens L31 with its concave surface facing the object side and a biconcave negative lens L32 are cemented together. In other words, the second lens group G2 and the third lens group G3 are composed of a total of three lenses.

[0102] The fourth lens group G4 is composed of, arranged in order from the object side along the optical axis, a cemented lens formed by cementing a positive meniscus lens L41 with its concave surface facing the object side and a biconcave negative lens L42, a biconcave negative lens L43, a biconvex positive lens L44, a cemented lens formed by cementing a biconvex positive lens L45 and a negative meniscus lens L46 with its concave surface facing the object side, a biconvex positive lens L47, and a negative meniscus lens L48 with its concave surface facing the object side. An image plane I is located on the image side of the fourth lens group G4.

[0103] In this embodiment, the positive meniscus lens L41 and negative lens L42 of the fourth lens group G4, and the negative lens L43 constitute an image stabilization group that is movable in a direction perpendicular to the optical axis, and corrects displacement of the imaging position (image blur on the image plane I) due to camera shake or the like. The positive lens L15 of the first lens group G1 corresponds to the positive lens that satisfies the above-mentioned conditional expressions (11) to (13). The positive meniscus lens L12, positive lens L13, and positive meniscus lens L17 of the first lens group G1 correspond to the lenses (specific lenses) that satisfy the above-mentioned conditional expression (14).

[0104] Table 2 below lists the values ​​of the specifications of the optical system according to the second example.

[0105] (Table 2) [Overall specifications] f=389.99986 fVR=-63.58427 FNO=2.90000 Δx2=-5.0000 2ω=6.31216 Δx3=11.7806 Y=21.60 β2=0.50377 TL=374.8074 β3=2.39339 Bf=40.8074 [Lens specifications] Surface number RD nd νd θgF 1 411.5072 9.6000 1.518600 69.89 0.532 2 -1780.5743 2.0000 3 176.8633 11.9000 1.433837 95.16 0.539 4 650.5128 88.9014 5 139.4073 11.2000 1.433837 95.16 0.539 6 -454.4554 3.8410 7 -416.7878 2.7000 1.770470 29.74 0.595 8 280.1935 40.5654 9 144.0688 8.0000 1.663820 27.35 0.632 10 -152.3486 0.1000 11 -156.0200 1.8000 1.749504 35.33 0.582 12 58.8242 9.0000 1.437001 95.10 0.534 13 808693.5500 (D13) 14 80.8416 6.0000 1.593190 67.90 0.544 15 -1732.6760 (D15) 16 -1283.1947 3.5000 1.850260 32.35 0.595 17 -277.4866 1.5000 1.517420 52.20 0.558 18 45.9700 (D18) 19 ∞ 6.6883 (Aperture S) 20 -769.1919 3.0000 1.805181 25.46 0.616 21 -74.8338 1.2000 1.593190 67.90 0.544 22 88.8291 2.9101 23 -151.9699 1.2000 1.755000 52.33 0.548 24 133.0301 4.6000 25 78.5763 3.0000 1.654115 39.68 0.574 26 -531.2778 38.2139 27 106.4326 6.2000 1.654115 39.68 0.574 28 -65.3375 1.5000 1.922859 20.88 0.628 29 -494.2887 3.9085 30 214.9436 5.0000 1.770470 29.74 0.595 31 -127.9388 20.8915 32 -77.1790 1.5000 1.902650 35.77 0.581 33 -511.7909 Bf [Variable Interval Data] Focused at infinity Focused at mid-range distance Focused at close range f=389.99986 β=-0.0333 β=-0.1699 D13 9.4718 8.7870 4.4718 D15 4.0000 7.1614 20.7806 D18 20.1082 17.6315 8.3276 [Lens group data] Group starting plane focal length G1 1 341.63982 G2 14 130.36832 G3 16 -93.23698 G4 20 491.53462

[0106] 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. From the diagrams of various aberrations, 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 range.

[0107] (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 of Example 3 when focused at infinity. The optical system OL(3) of 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 positive refractive power, a third lens group G3 having negative refractive power, and a fourth lens group G4 having positive refractive power. When focusing from an object at infinity to a close object, the second lens group G2 moves toward the object along the optical axis, and the third lens group G3 moves toward the image along the optical axis, changing the spacing between adjacent lens groups. During focusing, the first lens group G1 and the fourth lens group G4 are fixed relative to the image plane I. An aperture stop S is disposed between the third lens group G3 and the fourth lens group G4.

[0108] 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 biconvex positive lens L13, a biconcave negative lens L14, a biconvex positive lens L15, and a cemented lens formed by cementing together a biconcave negative lens L16 and a positive meniscus lens L17 with a convex surface facing the object side.

[0109] The second lens group G2 is composed of a positive meniscus lens L21 with a convex surface facing the object side. The third lens group G3 is composed of a negative meniscus lens L31 with a convex surface facing the object side. In other words, the second lens group G2 and the third lens group G3 are composed of a total of two lenses.

[0110] The fourth lens group G4 is composed of, arranged along the optical axis from the object side, a biconvex positive lens L41, a cemented lens formed by cementing a biconvex positive lens L42 and a biconcave negative lens L43, a biconcave negative lens L44, a biconvex positive lens L45, a cemented lens formed by cementing a biconvex positive lens L46 and a biconcave negative lens L47, a biconvex positive lens L48, and a negative meniscus lens L49 with its concave surface facing the object side. An image plane I is located on the image side of the fourth lens group G4.

[0111] In this embodiment, the positive lens L42 and negative lens L43 of the fourth lens group G4, and the negative lens L44, constitute an image stabilization group that is movable in a direction perpendicular to the optical axis, and corrects displacement of the imaging position (image blur on the image plane I) due to camera shake or the like. The positive lens L15 of the first lens group G1 corresponds to the positive lens that satisfies the above-mentioned conditional expressions (11) to (13). The positive meniscus lens L12, positive lens L13, and positive meniscus lens L17 of the first lens group G1 correspond to the lenses (specific lenses) that satisfy the above-mentioned conditional expression (14).

[0112] Table 3 below lists the values ​​of the specifications of the optical system according to the third example.

[0113] (Table 3) [Overall specifications] f=389.99987 fVR=-43.21297 FNO=2.93355 Δx2=-5.0178 2ω=6.31206 Δx3=10.3311 Y=21.63 β2=0.54598 TL=357.8074 β3=3.37032 Bf=40.8075 [Lens specifications] Surface number RD nd νd θgF 1 274.6094 9.6000 1.518600 69.89 0.532 2 1444.1407 3.0000 3 189.5245 11.9000 1.433837 95.16 0.539 4 876.8340 89.3809 5 139.4073 11.2000 1.433837 95.16 0.539 6 -496.1675 1.4595 7 -541.6390 2.7000 1.770470 29.74 0.595 8 350.5591 38.4092 9 122.5377 8.4000 1.663820 27.35 0.632 10 -159.9948 0.1000 11 -161.0621 1.8000 1.720467 34.71 0.583 12 53.9862 8.5000 1.437001 95.10 0.534 13 268.4116 (D13) 14 69.4230 6.0000 1.593190 67.90 0.544 15 529.0836 (D15) 16 11438.0050 1.5000 1.696800 55.52 0.543 17 50.3745 (D17) 18 ∞ 22.9851 (Aperture S) 19 497.7845 4.5000 1.729160 54.61 0.544 20 -104.8775 4.5000 21 135.7675 3.0000 1.922859 20.88 0.628 22 -574.7517 1.2000 1.593190 67.90 0.544 23 36.8702 4.6409 24 -98.5151 1.2000 1.729160 54.61 0.544 25 106.1474 4.6000 26 54.3694 4.0000 1.654115 39.68 0.574 27 -1515.8814 0.1000 28 53.4516 6.7000 1.620040 36.40 0.588 29 -53.9119 1.5000 1.808090 22.74 0.629 30 71.0492 15.0246 31 79.3722 6.5000 1.770470 29.74 0.595 32 -62.5659 6.1388 33 -46.9005 1.5000 1.903658 31.31 0.595 34 -495.5352 Bf [Variable Interval Data] Focused at infinity Focused at mid-range distance Focused at close range f=389.99987 β=-0.0333 β=-0.1714 D13 11.4406 10.6069 6.4228 D15 4.5919 7.4922 19.9407 D17 18.9286 16.8620 8.5975 [Lens group data] Group starting plane focal length G1 1 310.67557 G2 14 134.05749 G3 16 -72.61779 G4 19 266.10963

[0114] 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. From the diagrams of various aberrations, 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 range.

[0115] (Fourth Example) Example 4 will be described with reference to FIGS. 7 to 8 and Table 4. FIG. 7 shows the lens configuration of the optical system of Example 4 when focused at infinity. The optical system OL(4) of Example 4 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 positive refractive power, a third lens group G3 having negative 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 toward the object along the optical axis, and the third lens group G3 moves toward the image along the optical axis, changing the spacing between adjacent lens groups. During focusing, the first lens group G1 and the fourth lens group G4 are fixed relative to the image plane I. An aperture stop S is disposed within the fourth lens group G4.

[0116] 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 biconvex positive lens L12, a biconvex positive lens L13, a biconcave negative lens L14, a positive meniscus lens L15 with a concave surface facing the object side, and a cemented lens formed by cementing together a negative meniscus lens L16 with a convex surface facing the object side and a positive meniscus lens L17 with a convex surface facing the object side.

[0117] The second lens group G2 is composed of a positive meniscus lens L21 with a convex surface facing the object side. The third lens group G3 is composed of a negative meniscus lens L31 with a convex surface facing the object side. In other words, the second lens group G2 and the third lens group G3 are composed of a total of two lenses.

[0118] The fourth lens group G4 is composed of, arranged in order from the object side along the optical axis, a biconvex positive lens L41, a cemented lens formed by cementing a biconvex positive lens L42 and a biconcave negative lens L43, a biconcave negative lens L44, a biconvex positive lens L45, a cemented lens formed by cementing a biconvex positive lens L46 and a negative meniscus lens L47 with its concave surface facing the object side, a cemented lens formed by cementing a biconvex positive lens L48 and a negative meniscus lens L49 with its concave surface facing the object side, and a negative meniscus lens L50 with its concave surface facing the object side. An aperture stop S is disposed between the positive lens L41 and the positive lens L42 (of the cemented lens) in the fourth lens group G4. An image plane I is disposed on the image side of the fourth lens group G4. An optical filter FL is disposed between the negative meniscus lens L50 of the fourth lens group G4 and the image plane I.

[0119] In this embodiment, the positive lens L42 and negative lens L43 of the fourth lens group G4, and the negative lens L44, constitute an image stabilization group that is movable in a direction perpendicular to the optical axis, and corrects displacement of the imaging position (image blur on the image plane I) due to camera shake or the like. The positive meniscus lens L15 of the first lens group G1 corresponds to the positive lens that satisfies the above-mentioned conditional expressions (11) to (13). The positive lens L12, positive lens L13, and positive meniscus lens L17 of the first lens group G1, and the negative meniscus lens L49 of the fourth lens group G4 correspond to the lenses (specific lenses) that satisfy the above-mentioned conditional expression (14).

[0120] Table 4 below lists the values ​​of the specifications of the optical system according to the fourth example.

[0121] (Table 4) [Overall specifications] f=587.99970 fVR=-61.09024 FNO=4.09990 Δx2=-9.2038 2ω=4.15318 Δx3=2.0000 Y=21.70 β2=0.53805 TL=457.9999 β3=3.07318 Bf=33.4999 [Lens specifications] Surface number RD nd νd θgF 1 320.0114 9.4987 1.487490 70.32 0.529 2 1556.2771 70.0000 3 200.0000 14.7065 1.433837 95.16 0.539 4 -1850.8679 66.5961 5 112.1065 14.0539 1.433837 95.16 0.539 6 -411.9826 3.0994 7 -271.7122 2.6000 1.749504 35.33 0.582 8 273.2070 41.9524 9 -276.2752 2.9954 1.663820 27.35 0.632 10 -151.1038 0.1000 11 165.8791 1.9000 1.804400 39.61 0.572 12 56.1791 10.0000 1.437001 95.10 0.534 13 246.7321 (D13) 14 72.7085 5.0000 1.627496 59.24 0.556 15 437.2023 (D15) 16 608.4245 1.4000 1.804400 39.61 0.572 17 59.2420 (D17) 18 1662.7369 3.0000 1.808090 22.74 0.629 19 -268.2959 7.9411 20 ∞ 6.5000 (Aperture S) 21 173.1949 4.4983 1.846663 23.78 0.619 22 -93.9126 1.2000 1.755000 52.33 0.548 23 68.9486 3.7146 24 -79.9737 1.2000 1.729160 54.61 0.544 25 319.8993 8.0984 26 65.6157 3.8964 1.647690 33.72 0.593 27 -6303.3612 57.0554 28 1057.7056 6.4549 1.770470 29.74 0.595 29 -30.5390 1.2600 1.922860 20.88 0.639 30 -363.6860 0.1000 31 143.0814 7.4994 1.595510 39.21 0.581 32 -33.2229 1.2000 1.497820 82.57 0.539 33 -1263.0104 19.8180 34 -48.8063 1.2000 1.848500 43.79 0.562 35 -70.0018 8.7649 36 ∞ 2.0000 1.516800 64.13 0.536 37∞Bf [Variable Interval Data] Focused at infinity Focused at mid-range distance Focused at close range f=587.99970 β=-0.0333 β=-0.1450 D13 15.5701 13.4060 6.3663 D15 4.2356 6.8823 15.4394 D17 15.3905 14.9079 13.3905 [Lens group data] Group starting plane focal length G1 1 348.13120 G2 14 138.25340 G3 16 -81.68490 G4 18 -6571.80060

[0122] Fig. 8(A) is a diagram showing various aberrations when the optical system according to Example 4 is focused at infinity. Fig. 8(B) is a diagram showing various aberrations when the optical system according to Example 4 is focused at close distances. From the diagrams of various aberrations, it can be seen that the optical system according to Example 4 has excellent imaging performance, with various aberrations being well corrected across the entire range from focusing at infinity to focusing at close distances.

[0123] (Fifth Example) Example 5 will be described with reference to FIGS. 9 and 10 and Table 5. FIG. 9 shows the lens configuration of the optical system of Example 5 when focused at infinity. The optical system OL(5) of Example 5 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 positive refractive power, a third lens group G3 having negative refractive power, and a fourth lens group G4 having positive refractive power. When focusing from an object at infinity to a close object, the second lens group G2 moves toward the object side along the optical axis, and the third lens group G3 moves toward the image side along the optical axis, changing the spacing between adjacent lens groups. During focusing, the first lens group G1 and the fourth lens group G4 are fixed relative to the image plane I. An aperture stop S is disposed between the third lens group G3 and the fourth lens group G4.

[0124] 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 biconvex positive lens L13, a biconcave negative lens L14, a biconvex positive lens L15, and a cemented lens formed by cementing together a biconcave negative lens L16 and a positive meniscus lens L17 with a convex surface facing the object side.

[0125] The second lens group G2 is composed of a positive meniscus lens L21 with a convex surface facing the object side. The third lens group G3 is composed of a negative meniscus lens L31 with a convex surface facing the object side. In other words, the second lens group G2 and the third lens group G3 are composed of a total of two lenses.

[0126] The fourth lens group G4 is composed of, arranged along the optical axis from the object side, the following: a biconvex positive lens L41, a cemented lens formed by cementing a biconvex positive lens L42 and a biconcave negative lens L43, a biconcave negative lens L44, a cemented lens formed by cementing a negative meniscus lens L45 with its convex surface facing the object side and a biconvex positive lens L46, a cemented lens formed by cementing a biconvex positive lens L47 and a biconcave negative lens L48, and a cemented lens formed by cementing a biconvex positive lens L49 and a biconcave negative lens L50. An image plane I is located on the image side of the fourth lens group G4.

[0127] In this embodiment, the positive lens L42 and negative lens L43 of the fourth lens group G4, and the negative lens L44, constitute an image stabilization group that is movable in a direction perpendicular to the optical axis, and corrects displacement of the imaging position (image blur on the image plane I) due to camera shake or the like. The positive lens L15 of the first lens group G1 corresponds to the positive lens that satisfies the above-mentioned conditional expressions (11) to (13). The positive meniscus lens L12, positive lens L13, and positive meniscus lens L17 of the first lens group G1, the positive meniscus lens L21 of the second lens group G2, and the negative lens L43 of the fourth lens group G4 correspond to the lenses (specific lenses) that satisfy the above-mentioned conditional expression (14).

[0128] Table 5 below lists the values ​​of the specifications of the optical system according to the fifth example.

[0129] (Table 5) [Overall specifications] f=587.99791 fVR=-34.34884 FNO=4.10847 Δx2=-6.1704 2ω=4.19942 Δx3=6.3894 Y=21.63 β2=0.67768 TL=438.8073 β3=3.63831 Bf=49.6725 [Lens specifications] Surface number RD nd νd θgF 1 320.9434 9.6000 1.518600 69.89 0.532 2 1936.3786 40.0000 3 197.3125 12.4000 1.433837 95.16 0.539 4 1249.9826 92.9991 5 139.4073 11.2000 1.433837 95.16 0.539 6 -595.5149 0.1000 7 -679.6046 2.7000 1.770470 29.74 0.595 8 257.1482 46.6155 9 111.7807 8.9000 1.663820 27.35 0.632 10 -211.8183 0.1000 11 -214.3458 1.8000 1.720467 34.71 0.583 12 63.9295 8.0000 1.437001 95.10 0.534 13 643.8176 (D13) 14 78.4833 5.5000 1.497820 82.57 0.539 15 379.7982 (D15) 16 1600.8170 1.5000 1.772500 49.62 0.552 17 54.9089 (D17) 18 ∞ 46.4752 (Aperture S) 19 149.0722 3.5000 1.552981 55.07 0.545 20 -96.2480 4.5000 21 114.2466 3.0000 1.922859 20.88 0.628 22 -195.3936 1.2000 1.497820 82.57 0.539 23 27.7113 4.6409 24 -60.3668 1.2000 1.729160 54.61 0.544 25 78.7651 4.9250 26 43.5209 1.5000 1.696800 55.52 0.543 27 26.5639 5.7000 1.654115 39.68 0.574 28 -233.7026 0.1000 29 71.9613 5.0000 1.654115 39.68 0.574 30 -41.4429 1.5000 1.808090 22.74 0.629 31 171.1519 25.5905 32 63.7147 7.5000 1.603420 38.03 0.583 33 -38.1075 1.5000 1.910822 35.25 0.582 34 300.4346 Bf [Variable Interval Data] Focused at infinity Focused at mid-range distance Focused at close range f=587.99791 β=-0.0333 β=-0.1485 D13 11.7675 10.1988 5.5971 D15 4.7905 7.6839 17.3503 D17 13.3307 12.0060 6.9412 [Lens group data] Group starting plane focal length G1 1 282.59807 G2 14 197.51986 G3 16 -73.63528 G4 19 2049.50489

[0130] Fig. 10(A) is a diagram showing various aberrations when the optical system according to Example 5 is focused at infinity. Fig. 10(B) is a diagram showing various aberrations when the optical system according to Example 5 is focused at close distances. From the diagrams of various aberrations, it can be seen that the optical system according to Example 5 has excellent imaging performance, with various aberrations being well corrected across the entire range from focusing at infinity to focusing at close distances.

[0131] 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 5). Conditional expression (1) 0.010<(Δx2A+Δx3A) / D1<0.200 Conditional expression (2) -0.20<Δx2 / f2<0.00 Conditional expression (3) -0.20<Δx3 / f3<0.00 Condition (4) 1.00 <f2 / (-f3)<4.00 Conditional expression (5) -3.00<Δx2 / Δx3<-0.20 Condition (6) -8.50 <f1 / fVR<-3.00 Conditional expression (7) 0.45<β2<0.80 Conditional expression (8) 0.20<1 / β3<0.50 Conditional expression (9) {β2+(1 / β2)} -2 <0.25 Conditional expression (10) {β3+(1 / β3)} -2 <0.18 Condition (11) ndL1+(0.01425×νdL1)<2.12 Conditional expression (12) νdL1<35.00 Conditional expression (13) 0.702<θgFL1+(0.00316×νdL1) Conditional expression (14) 80.00<νdL2 Conditional expression (15) 3.50°<2ω<8.50°

[0132] [Conditional Expression Corresponding Values] (First to Third Examples) Conditional Expression First Example Second Example Third Example (1) 0.094 0.089 0.082 (2) -0.07 -0.04 -0.04 (3) -0.09 -0.13 -0.14 (4) 1.95 1.40 1.85 (5) -0.66 -2.36 -2.06 (6) -4.30 -5.37 -7.19 (7) 0.63 0.50 0.55 (8) 0.40 0.42 0.30 (9) 0.20 0.16 0.18 (10) 0.12 0.13 0.07 (11) 2.054 2.054 2.054 (12) 27.35 27.35 27.35 (13) 0.718 0.718 0.718 (14) 95.25 95.16 95.16 82.57 - - (15) 6.296 6.312 6.312 [Conditional Expression Corresponding Values] (Fourth and Fifth Examples) Conditional Expressions Fourth Example Fifth Example (1) 0.044 0.054 (2) -0.07 -0.03 (3) -0.02 -0.09 (4) 1.69 2.68 (5) -0.22 -1.04 (6) -5.70 -8.23 (7) 0.54 0.68 (8) 0.33 0.27 (9) 0.17 0.22 (10) 0.09 0.07 (11) 2.054 2.054 (12) 27.35 27.35 (13) 0.718 0.718 (14) 95.16 95.16 82.57 82.57 (15) 4.153 4.199

[0133] According to each of the above embodiments, it is possible to realize a bright optical system with a long focal length that has excellent optical performance from focusing at infinity to focusing at close distances.

[0134] The above-described examples are merely illustrative examples of the present invention, and the present invention is not limited to these.

[0135] The following contents can be appropriately adopted within the scope that does not impair the optical performance of the optical system of this embodiment.

[0136] 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) can also be configured. Specifically, a configuration in which a lens or lens group is added to the most object side or the most image side of the optical system of this embodiment, or a configuration in which a lens or lens group is added between the second lens group (first focusing lens group) and the third lens group (second focusing lens group) can also be used. Note that a lens group refers to a portion having at least one lens separated by an air gap that changes during focusing.

[0137] Although an example of the optical system of this embodiment has been shown to have a configuration with an anti-shake function, the present invention is not limited to this, and the optical system may also have a configuration without an anti-shake function.

[0138] 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.

[0139] 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.

[0140] The aperture diaphragm is preferably located between the third and fourth lens groups or within the fourth lens group, but it is also possible to use the lens frame to fulfill that role without providing a member serving as an aperture diaphragm.

[0141] 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]

[0142] 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 optical system comprises a first lens group having positive refractive power, a second lens group, a third lens group, and a fourth lens group, which are arranged in this order from the object side along the optical axis, When focusing from an object at infinity to an object at a close distance, the second lens group and the third lens group move along different loci along the optical axis, two positive lenses are arranged in the first lens group in order from the most object side to the image side, and a positive lens, a negative lens and a positive lens are arranged in the first lens group in order from the most image side to the object side, An optical system that satisfies the following condition: 0.010<(Δx2A+Δx3A) / D1<0.200 1.00<f2 / (-f3)<4.00 where Δx2A 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. Δx3A: 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 D1: the length of the first lens group on the optical axis f2: focal length of the second lens group f3: focal length of the third lens group

2. The optical system comprises a first lens group having positive refractive power, a second lens group, a third lens group, and a fourth lens group, which are arranged in this order from the object side along the optical axis, When focusing from an object at infinity to an object at a close distance, the second lens group and the third lens group move along different loci along the optical axis, two positive lenses are arranged in the first lens group in order from the most object side to the image side, and a positive lens, a negative lens and a positive lens are arranged in the first lens group in order from the most image side to the object side, An optical system that satisfies the following condition: 0.010<(Δx2A+Δx3A) / D1<0.200 ０．４５＜β２＜０．８０ where Δx2A 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. Δx3A: 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 D1: the length of the first lens group on the optical axis β2: Magnification of the second lens group when focusing on an object at infinity

3. The optical system comprises a first lens group having positive refractive power, a second lens group, a third lens group, and a fourth lens group, which are arranged in this order from the object side along the optical axis, When focusing from an object at infinity to an object at a close distance, the second lens group and the third lens group move along different loci along the optical axis, two positive lenses are arranged in the first lens group in order from the most object side to the image side, and a positive lens, a negative lens and a positive lens are arranged in the first lens group in order from the most image side to the object side, The following conditional expression is satisfied: 0.010<(Δx2A+Δx3A) / D1<0.200 where Δx2A 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. Δx3A: 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 D1: the length of the first lens group on the optical axis The first lens group is an optical system having a positive lens that satisfies the following condition: ndL1+(0.01425×νdL1)<2.12 νdL1<35.00 0.702<θgFL1+(0.00316×νdL1) where ndL1 is the refractive index of the positive lens with respect to the d-line νdL1: Abbe number of the positive lens based on the d line θgFL1: partial dispersion ratio of the positive lens, which is defined by the following formula when the refractive index of the positive lens for the g-line is ngL1, the refractive index of the positive lens for the F-line is nFL1, and the refractive index of the positive lens for the C-line is nCL1. θgFL1=(ngL1-nFL1) / (nFL1-nCL1)

4. The optical system comprises a first lens group having positive refractive power, a second lens group, a third lens group, and a fourth lens group, which are arranged in this order from the object side along the optical axis, When focusing from an object at infinity to an object at a close distance, the second lens group moves toward the object along the optical axis, and the third lens group moves toward the image plane along the optical axis, two positive lenses are arranged in the first lens group in order from the most object side to the image side, and a positive lens, a negative lens and a positive lens are arranged in the first lens group in order from the most image side to the object side, An optical system that satisfies the following condition: 0.010<(Δx2A+Δx3A) / D1<0.200 where Δx2A 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. Δx3A: 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 D1: the length of the first lens group on the optical axis

5. The optical system comprises a first lens group having positive refractive power, a second lens group, a third lens group, and a fourth lens group, which are arranged in this order from the object side along the optical axis, When focusing from an object at infinity to an object at a close distance, the second lens group and the third lens group move along different loci along the optical axis, two positive lenses are arranged in the first lens group in order from the most object side to the image side, and a positive lens, a negative lens and a positive lens are arranged in the first lens group in order from the most image side to the object side, the second lens group is composed of one lens, An optical system that satisfies the following condition: 0.010<(Δx2A+Δx3A) / D1<0.200 where Δx2A 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. Δx3A: 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 D1: the length of the first lens group on the optical axis

6. The optical system comprises a first lens group having positive refractive power, a second lens group, a third lens group, and a fourth lens group, which are arranged in this order from the object side along the optical axis, a stop is disposed closer to the image plane than the third lens group; When focusing from an object at infinity to an object at a close distance, the second lens group and the third lens group move along different loci along the optical axis, two positive lenses are arranged in the first lens group in order from the most object side to the image side, and a positive lens, a negative lens and a positive lens are arranged in the first lens group in order from the most image side to the object side, An optical system that satisfies the following condition: 0.010<(Δx2A+Δx3A) / D1<0.200 where Δx2A 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. Δx3A: 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 D1: the length of the first lens group on the optical axis

7. 7. The optical system according to claim 1, wherein the following condition is satisfied: -0.20<Δx2 / f2<0.00 where Δx2 is the amount of movement of the second lens group when focusing from an object at infinity to an object at a close distance (the sign of the amount of movement toward the image plane side is +, and the sign of the amount of movement toward the object side is −). f2: focal length of the second lens group

8. 7. The optical system according to claim 1, wherein the following condition is satisfied: -0.20<Δx3 / f3<0.00 where Δx3 is the amount of movement of the third lens group when focusing from an object at infinity to an object at a close distance (the sign of the amount of movement toward the image plane side is +, and the sign of the amount of movement toward the object side is −). f3: focal length of the third lens group

9. The optical system according to any one of claims 2 to 6, which satisfies the following conditional expression: 1.00<f2 / (-f3)<4.00 where f2 is the focal length of the second lens group f3: focal length of the third lens group

10. 7. The optical system according to claim 1, wherein the following condition is satisfied: -3.00<Δx2 / Δx3<-0.20 where Δx2 is the amount of movement of the second lens group when focusing from an object at infinity to an object at a close distance (the sign of the amount of movement toward the image plane side is +, and the sign of the amount of movement toward the object side is −). Δx3: the amount of movement of the third lens group when focusing from an object at infinity to an object at a close distance (the sign of the amount of movement toward the image plane side is +, and the sign of the amount of movement toward the object side is −)

11. 7. The optical system according to claim 1, wherein the fourth lens group includes an image stabilization group having negative refractive power and movable to have a displacement component in a direction perpendicular to the optical axis in order to correct image blur.

12. The optical system according to claim 11 , wherein the vibration isolation group is composed of two or more lenses.

13. 12. The optical system according to claim 11, which satisfies the following condition: -8.50<f1 / fVR<-3.00 where f1 is the focal length of the first lens group fVR: focal length of the image stabilization group

14. The optical system according to any one of claims 1 and 3 to 6, which satisfies the following conditional expression: ０．４５＜β２＜０．８０ where β2 is the magnification of the second lens group when focusing on an object at infinity.

15. 7. The optical system according to claim 1, wherein the following condition is satisfied: ０．２０＜１／β３＜０．５０ where β3 is the magnification of the third lens group when focusing on an object at infinity.

16. 7. The optical system according to claim 1, wherein the following condition is satisfied: ｛β２＋（１／β２）｝ -2＜０．２５ where β2 is the magnification of the second lens group when focusing on an object at infinity.

17. 7. The optical system according to claim 1, wherein the following condition is satisfied: ｛β３＋（１／β３）｝ -2＜０．１８ where β3 is the magnification of the third lens group when focusing on an object at infinity.

18. 7. The optical system according to claim 1, wherein the first lens group has a positive lens that satisfies the following condition: 1<x<1 / ... ndL1+(0.01425×νdL1)<2.12 νdL1<35.00 0.702<θgFL1+(0.00316×νdL1) where ndL1 is the refractive index of the positive lens with respect to the d-line νdL1: Abbe number of the positive lens based on the d line θgFL1: partial dispersion ratio of the positive lens, which is defined by the following formula when the refractive index of the positive lens for the g-line is ngL1, the refractive index of the positive lens for the F-line is nFL1, and the refractive index of the positive lens for the C-line is nCL1. θgFL1=(ngL1-nFL1) / (nFL1-nCL1)

19. 7. The optical system according to claim 1, comprising a lens that satisfies the following conditional expression: 80.00<νdL2 where νdL2 is the Abbe number of the lens based on the d line

20. 7. The optical system according to claim 1, wherein the following condition is satisfied: 3.50°<2ω<8.50° where 2ω is the total angle of view of the optical system.

21. The optical system according to any one of claims 1 to 3 and 5 to 6, wherein, 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 object side, and the third lens group moves along the optical axis toward the image plane side.

22. 7. The optical system according to claim 1, wherein the second lens group is composed of one lens.

23. 7. The optical system according to claim 1, wherein the third lens group is composed of one lens component.

24. 6. The optical system according to claim 1, further comprising a stop arranged closer to the image plane than the second lens group.

25. 25. The optical system according to claim 24, wherein the diaphragm is disposed closer to the image plane than the third lens group.

26. An optical instrument comprising the optical system according to any one of claims 1 to 6.

Images