Optical Systems and Optical Instruments

Abstract

To provide an optical system with small aberration fluctuation during focusing.SOLUTION: An optical system OL comprises, in order from an object side along an optical axis, 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, the second lens group G2 and the third lens group G3 move along the optical axis, distances between respective lens groups adjacent to each other change, and the following conditional expression is satisfied: 0.75<f1 / (-f2)<1.30, where f1 is a focal length of the first lens group G1, and f2 is a focal length of the second lens group G2.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 have been proposed in which multiple lens groups are moved along the optical axis to achieve focusing (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 Publication No. 2018-141888 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 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, wherein, during focusing, the second lens group and the third lens group move along the optical axis, changing the interval between adjacent lens groups, and the optical system satisfies the following conditional expression: 0.75 <f1 / (-f2)<1.30 where f1 is the focal length of the first lens group f2: focal length of the second lens group

[0005] A second optical system according to the present invention has, 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, wherein, during focusing, the second lens group and the third lens group move along the optical axis, changing the interval between adjacent lens groups, and the optical system satisfies the following conditional expression: 3.00<(LnR2+LnR1) / (LnR2-LnR1)<5.00 where LnR1 is the radius of curvature of the object-side lens surface of the negative lens arranged closest to the image side of the optical system. LnR2: the radius of curvature of the image-side lens surface of the negative lens arranged closest to the image side of the optical system

[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 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, wherein, during focusing, the second lens group and the third lens group move along the optical axis and the interval between adjacent lens groups changes, and the first lens group has a negative lens that satisfies the following conditional expression: 1.80 <ndM1 νdM1<26.00 θgFM1-(0.6415-0.00162×νdM1)<0.0120 where ndM1 is the refractive index of the negative lens in the first lens group with respect to the d-line νdM1: Abbe number of the negative lens in the first lens group θgFM1: partial dispersion ratio of the negative lens of the first lens group, where ngM1 is the refractive index of the negative lens of the first lens group with respect to the g-line, nFM1 is the refractive index of the negative lens of the first lens group with respect to the F-line, and nFM2 is the refractive index of the negative lens of the first lens group with respect to the C-line. When the refractive index for the θgFM1=(ngM1-nFM1) / (nFM1-nCM1)

[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 in the infinity-focused state and the closest distance-focused state of the optical system according to Example 1, 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 in the infinity-focused state and the closest distance-focused state of the optical system according to the second example, 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 in the infinity-focused state and the closest distance-focused state of the optical system according to Example 3, 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 in the infinity-focused state and the closest distance-focused state of the optical system according to Example 4, 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 in the infinity-focused state and the closest distance-focused state of the optical system according to Example 5, respectively. [Figure 11] FIG. 1 is a diagram showing the configuration of a camera including an optical system according to each embodiment. [Figure 12] 5 is a flowchart showing a method for manufacturing the optical system according to the first to third embodiments. [Figure 13] 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. 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.

[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. 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.

[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, arranged in order from the object side along the optical axis, 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. During focusing, the second lens group G2 and the third lens group G3 move along the optical axis. , the spacing between adjacent lens groups changes.

[0012] With the above-described configuration, the optical system OL according to the first embodiment satisfies the following conditional expression (1). 0.20 <DG4 / TL<0.40 ···(1) However, DG4: The length of the fourth lens group G4 on the optical axis TL: Total length of optical system OL when focused at infinity

[0013] According to the first embodiment, it is possible to obtain an optical system with little aberration fluctuation during focusing, and an optical apparatus including 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.

[0014] Conditional expression (1) defines an appropriate relationship between the axial length of the fourth lens group G4 and the overall length of the optical system OL. By satisfying conditional expression (1), the axial length of the fourth lens group G4 becomes large relative to the overall length of the optical system OL, thereby enabling excellent correction of curvature of field and coma in the peripheral area over the entire range of magnification. In each embodiment, the overall length of the optical system OL is the axial distance from the lens surface of the optical system OL closest to the object to the image plane I (the distance from the lens surface of the optical system OL closest to the image to the image plane I is the air-equivalent distance).

[0015] If the value corresponding to conditional expression (1) falls outside the above range, it becomes difficult to correct curvature of field and coma in the peripheral area within a portion of the magnification range. By setting the lower limit of conditional expression (1) to 0.21, 0.23, or even 0.25, the effect of this embodiment can be further ensured. Furthermore, by setting the upper limit of conditional expression (1) to 0.38, 0.36, 0.35, or even 0.33, the effect of this embodiment can be further ensured.

[0016] Next, an optical system according to a second embodiment will be described. The optical system according to the second embodiment has the same configuration as the optical system OL according to the first embodiment, and will therefore be described using the same reference numerals as in the first embodiment. 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, in order from the object side along the optical axis, 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. During focusing, the second lens group G2 and the third lens group G3 move along the optical axis, changing the spacing between adjacent lens groups.

[0017] With the above-described configuration, the optical system OL according to the second embodiment satisfies the following conditional expression (2). 3.00<(LnR2+LnR1) / (LnR2-LnR1)<5.00 ···(2) where LnR1 is the radius of curvature of the object-side lens surface of the negative lens arranged closest to the image side in the optical system OL. LnR2: Radius of curvature of the image-side lens surface of the negative lens located closest to the image side of the optical system OL

[0018] According to the second embodiment, it is possible to obtain an optical system with little aberration fluctuation during focusing, and an optical apparatus including 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.

[0019] Conditional expression (2) defines an appropriate range for the shape factor of the negative lens element located closest to the image side in optical system OL. By satisfying conditional expression (2), it is possible to uniformly correct curvature of field and coma within the image plane over the entire range of magnification.

[0020] If the value corresponding to conditional expression (2) falls outside the above range, it becomes difficult to uniformly correct field curvature and coma within the image plane within a portion of the magnification range. The effects of this embodiment can be further ensured by setting the lower limit of conditional expression (2) to 3.05, 3.10, 3.15, 3.20, or even 3.23. Furthermore, the effects of this embodiment can be further ensured by setting the upper limit of conditional expression (2) to 4.90, 4.80, 4.70, 4.60, 4.50, or even 4.40.

[0021] Next, an optical system according to a third embodiment will be described. The optical system according to the third embodiment has the same configuration as the optical system OL according to the first embodiment, and will therefore be described using the same reference numerals as in the first embodiment. As shown in FIG. 1 , an optical system OL(1) as an example of the optical system OL according to the third embodiment includes, arranged in order from the object side along the optical axis, 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. During focusing, the second lens group G2 and the third lens group G3 move along the optical axis, changing the spacing between adjacent lens groups.

[0022] With the above-described configuration, the optical system OL according to the third embodiment satisfies the following conditional expression (3). 0.75 <f1 / (-f2)<1.30 ···(3) where f1 is the focal length of the first lens group G1 f2: Focal length of the second lens group G2

[0023] According to the third embodiment, it is possible to obtain an optical system with little aberration fluctuation during focusing, and an optical apparatus including this optical system. The optical system OL according to the third 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.

[0024] Conditional expression (3) defines an appropriate relationship between the focal length of the first lens group G1 and the focal length of the second lens group G2. By satisfying conditional expression (3), fluctuations in spherical aberration and curvature of field can be suppressed when focusing from an object at infinity to a close object.

[0025] If the value corresponding to conditional expression (3) falls outside the above range, it becomes difficult to suppress fluctuations in spherical aberration and field curvature during focusing. The effects of this embodiment can be further ensured by setting the lower limit of conditional expression (3) to 0.80, 0.90, 0.95, 1.00, 1.05, or even 1.10. Furthermore, the effects of this embodiment can be further ensured by setting the upper limit of conditional expression (3) to 1.28, 1.25, 1.23, or even 1.20.

[0026] Next, an optical system according to a fourth embodiment will be described. The optical system according to the fourth embodiment has the same configuration as the optical system OL according to the first embodiment, and will therefore be described using the same reference numerals as in the first embodiment. As shown in FIG. 1 , an optical system OL(1) as an example of the optical system OL according to the fourth embodiment includes, arranged in order from the object side along the optical axis, 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. During focusing, the second lens group G2 and the third lens group G3 move along the optical axis, changing the spacing between adjacent lens groups.

[0027] With the above-described configuration, the optical system OL according to the fourth embodiment satisfies the following conditional expressions (4) to (6). 1.80 <ndM1 ···(4) νdM1<26.00 (5) θgFM1-(0.6415-0.00162×νdM1)<0.0120 ···(6) where ndM1 is the refractive index of the negative lens in the first lens group G1 at the d-line νdM1: Abbe number of the negative lens in the first lens group G1 θgFM1: partial dispersion ratio of the negative lens in the first lens group G1, which is defined by the following equation, where ngM1 is the refractive index of the negative lens in the first lens group G1 for the g-line, nFM1 is the refractive index of the negative lens in the first lens group G1 for the F-line, and nCM1 is the refractive index of the negative lens in the first lens group G1 for the C-line. θgFM1=(ngM1-nFM1) / (nFM1-nCM1)

[0028] According to the fourth embodiment, it is possible to obtain an optical system with little aberration fluctuation during focusing, and an optical apparatus including this optical system. The optical system OL according to the fourth 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.

[0029] Conditional formula (4) defines an appropriate range for the refractive index of the negative lens in the first lens group G1 at the d-line. Conditional formula (5) defines an appropriate range for the Abbe number of the negative lens in the first lens group G1. Conditional formula (6) defines an appropriate relationship between the partial dispersion ratio and the Abbe number of the negative lens in the first lens group G1. By satisfying conditional formulas (4) to (6), axial chromatic aberration and lateral chromatic aberration can be effectively corrected over the entire range of magnification.

[0030] If the value corresponding to conditional expression (4) is outside the above range, it becomes difficult to correct axial chromatic aberration and lateral chromatic aberration within a part of the magnification range. By setting the lower limit of conditional expression (4) to 1.82, 1.83, or even 1.84, the effect of this embodiment can be further ensured.

[0031] If the value corresponding to conditional expression (5) is outside the above range, it becomes difficult to correct axial chromatic aberration and lateral chromatic aberration within a part of the magnification range. By setting the upper limit of conditional expression (5) to 25.90, 25.85, 25.70, 25.50, or even 25.35, the effect of this embodiment can be further ensured.

[0032] If the value corresponding to conditional expression (6) falls outside the above range, it becomes difficult to correct axial chromatic aberration and lateral chromatic aberration within a portion of the magnification range. The effect of this embodiment can be further ensured by setting the upper limit of conditional expression (6) to 0.0115, 0.0110, 0.0105, 0.0100, or even 0.0098. The lower limit of conditional expression (6) may also be set to greater than 0.0000.

[0033] It is desirable that the optical systems OL according to the second to fourth embodiments satisfy the above-mentioned conditional expression (1). By satisfying conditional expression (1), it is possible to satisfactorily correct curvature of field and coma in the peripheral area over the entire range of magnification, as in the first embodiment. By setting the lower limit of conditional expression (1) to 0.21, 0.23, or even 0.25, it is possible to further ensure the effects of each embodiment. Furthermore, by setting the upper limit of conditional expression (1) to 0.38, 0.36, 0.35, or even 0.33, it is possible to further ensure the effects of each embodiment.

[0034] It is desirable that the optical systems OL according to the third and fourth embodiments satisfy the above-mentioned conditional expression (2). By satisfying conditional expression (2), it is possible to uniformly correct curvature of field and coma within the image plane over the entire range of magnification, as in the second embodiment. By setting the lower limit of conditional expression (2) to 3.05, 3.10, 3.15, 3.20, or even 3.23, the effects of each embodiment can be further ensured. Furthermore, by setting the upper limit of conditional expression (2) to 4.90, 4.80, 4.70, 4.60, 4.50, or even 4.40, This makes it possible to further ensure the effects of each embodiment.

[0035] It is desirable that the optical system OL according to the fourth embodiment satisfy the above-mentioned conditional expression (3). By satisfying conditional expression (3), fluctuations in spherical aberration and field curvature can be suppressed when focusing from an object at infinity to a close object, as in the third embodiment. The effects of this embodiment can be further ensured by setting the lower limit of conditional expression (3) to 0.80, 0.90, 0.95, 1.00, 1.05, or even 1.10. Furthermore, the effects of this embodiment can be further ensured by setting the upper limit of conditional expression (3) to 1.28, 1.25, 1.23, or even 1.20.

[0036] It is desirable that the optical systems OL according to the first to fourth embodiments satisfy the following conditional expression (7). 0.75 <f1 / f3<1.20 ···(7) where f1 is the focal length of the first lens group G1 f3: Focal length of the third lens group G3

[0037] Conditional expression (7) defines an appropriate relationship between the focal length of the first lens group G1 and the focal length of the third lens group G3. By satisfying conditional expression (7), fluctuations in spherical aberration and curvature of field can be suppressed when focusing from an object at infinity to a close object.

[0038] If the value corresponding to conditional expression (7) falls outside the above range, it becomes difficult to suppress fluctuations in spherical aberration and field curvature during focusing. By setting the lower limit of conditional expression (7) to 0.80, 0.85, 0.90, 0.95, or even 1.00, the effects of each embodiment can be more reliably achieved. Furthermore, by setting the upper limit of conditional expression (7) to 1.18, 1.15, 1.13, or even 1.10, the effects of each embodiment can be more reliably achieved.

[0039] It is desirable that the optical systems OL according to the first to fourth embodiments satisfy the following conditional expression (8). 0.45<(-β) (8) where β is the lateral magnification of the optical system OL

[0040] Conditional expression (8) defines an appropriate range for the lateral magnification of the entire optical system OL. Satisfying conditional expression (8) is preferable because it enables close-up photography. Setting the lower limit of conditional expression (8) to 0.52, 0.55, 0.60, 0.70, 0.75, or even 0.80 can further ensure the effects of each embodiment.

[0041] It is desirable that the optical systems OL according to the first to fourth embodiments satisfy the following conditional expression (9). 35.0<β2 / β3<350.0 (9) β2: Lateral magnification of the second lens group G2 when focused at infinity β3: Lateral magnification of the third lens group G3 when focused at infinity

[0042] Conditional expression (9) defines an appropriate relationship between the lateral magnification of the second lens group G2 when focused at infinity and the lateral magnification of the third lens group G3 when focused at infinity. By satisfying conditional expression (9), fluctuations in field curvature and spherical aberration during focusing can be suppressed.

[0043] If the value corresponding to conditional expression (9) is outside the above range, it becomes difficult to suppress fluctuations in field curvature and spherical aberration during focusing. By setting the lower limit of conditional expression (9) to 35.50, 36.00, 36.50, 37.00, or 37.30, the effects of each embodiment can be more clearly achieved. Furthermore, by setting the upper limit of conditional expression (9) to 300.00, 250.00, 200.00, 150.00, 100.00, 85.00, or even 75.00, the effects of each embodiment can be made more certain.

[0044] The optical systems OL according to the first to fourth embodiments may satisfy the following conditional expression (10). 0.005<β3 / β2<0.035 (10) β2: Lateral magnification of the second lens group G2 when focused at infinity β3: Lateral magnification of the third lens group G3 when focused at infinity

[0045] Conditional expression (10) defines an appropriate relationship between the lateral magnification of the second lens group G2 and the lateral magnification of the third lens group G3 when focused at infinity. By satisfying conditional expression (10), fluctuations in field curvature and spherical aberration during focusing can be suppressed.

[0046] If the value corresponding to conditional expression (10) falls outside the above range, it becomes difficult to suppress fluctuations in field curvature and spherical aberration during focusing. By setting the lower limit of conditional expression (10) to 0.008, 0.010, or even 0.012, the effects of each embodiment can be more reliably achieved. Furthermore, by setting the upper limit of conditional expression (10) to 0.033, 0.030, or even 0.029, the effects of each embodiment can be more reliably achieved.

[0047] It is desirable that the optical systems OL according to the first to fourth embodiments satisfy the following conditional expression (11). {β2+(1 / β2)} -2 <0.10 (11) β2: Lateral magnification of the second lens group G2 when focused at infinity

[0048] Conditional expression (11) defines an appropriate range for the lateral magnification of the second lens group G2 when focused at infinity. By satisfying conditional expression (11), various aberrations such as spherical aberration and curvature of field when focused at infinity can be effectively corrected.

[0049] If the value corresponding to conditional expression (11) is outside the above range, it becomes difficult to correct various aberrations such as spherical aberration and curvature of field when focused at infinity. By setting the upper limit of conditional expression (11) to 0.08, 0.06, or even 0.05, 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 (12). {β3+(1 / β3)} -2 <0.10 (12) However, β3 is the lateral magnification of the third lens group G3 when focused at infinity.

[0051] Conditional expression (12) defines an appropriate range for the lateral magnification of the third lens group G3 when focused at infinity. By satisfying conditional expression (12), various aberrations such as spherical aberration and curvature of field when focused at infinity can be effectively corrected.

[0052] If the value corresponding to conditional expression (12) is outside the above range, it becomes difficult to correct various aberrations such as spherical aberration and curvature of field when focused at infinity. By setting the upper limit of conditional expression (12) to 0.08, 0.06, or even 0.05, the effects of each embodiment can be more reliably achieved.

[0053] It is desirable that the optical systems OL according to the first to fourth embodiments satisfy the following conditional expression (13). 0.05 <Bf / TL<0.35 ···(13) However, Bf is the back focus of the optical system OL when focused at infinity. TL: Total length of optical system OL when focused at infinity

[0054] Conditional expression (13) defines an appropriate relationship between the back focus of the optical system OL and the overall length of the optical system OL. In each embodiment, the back focus of the optical system OL is the distance on the optical axis (air-equivalent distance) from the lens surface of the optical system OL closest to the image to the image plane I. By satisfying conditional expression (13), it is possible to obtain an optical system with a short back focus while effectively suppressing the occurrence of various aberrations. By setting the lower limit of conditional expression (13) to 0.06, 0.07, or even 0.08, the effects of each embodiment can be further ensured. Furthermore, by setting the upper limit of conditional expression (13) to 0.33, 0.30, 0.25, 0.20, 0.18, or even 0.15, the effects of each embodiment can be further ensured.

[0055] It is desirable that the optical systems OL according to the first to fourth embodiments satisfy the following conditional expression (14). 0.10 <Bf / f<0.50 ···(14) However, Bf is the back focus of the optical system OL when focused at infinity. f: focal length of optical system OL

[0056] Conditional expression (14) defines an appropriate relationship between the back focus of the optical system OL and the focal length of the optical system OL. By satisfying conditional expression (14), it is possible to obtain an optical system with a short back focus while effectively suppressing the occurrence of various aberrations. By setting the lower limit of conditional expression (14) to 0.12, 0.14, or even 0.15, the effects of each embodiment can be more reliably achieved. Furthermore, by setting the upper limit of conditional expression (20) to 0.45, 0.40, 0.35, 0.30, 0.25, or even 0.20, the effects of each embodiment can be more reliably achieved.

[0057] The optical systems OL according to the first to fourth embodiments have a diaphragm (aperture diaphragm) S, and it is desirable that the following conditional expression (15) be satisfied. 0.50 <L1S / SLn<1.00 ···(15) However, L1S 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 when focused at infinity. SLn: The distance on the optical axis from the aperture stop S to the lens surface closest to the image side of the optical system OL when focused at infinity

[0058] Conditional expression (15) defines an appropriate relationship between the axial distance from the lens surface closest to the object in the optical system OL to the aperture stop S and the axial distance from the aperture stop S to the lens surface closest to the image in the optical system OL. By satisfying conditional expression (15), it is possible to obtain an optical system in which various aberrations in the peripheral area are effectively suppressed. By setting the lower limit of conditional expression (15) to 0.52, 0.55, 0.58, or even 0.60, the effects of each embodiment can be further ensured. Furthermore, by setting the upper limit of conditional expression (15) to 0.95, 0.90, 0.88, 0.85, 0.83, or even 0.80, the effects of each embodiment can be further ensured. It is preferable that the aperture stop (aperture stop) S be disposed between the second lens group G2 and the third lens group G3.

[0059] It is desirable that the optical systems OL according to the first to fourth embodiments satisfy the following conditional expression (16). 0.70 <Mf2 / Mf3<1.10 ···(16) where Mf2 is the absolute value of the movement of the second lens group G2 when focusing from an object at infinity to the closest object. Mf3: Absolute value of the movement of the third lens group G3 when focusing from an object at infinity to the closest object

[0060] Conditional expression (16) defines an appropriate relationship between the amount of movement of the second lens group G2 and the amount of movement of the third lens group G3 during focusing. The closest object distance corresponds to the shortest shooting distance. By satisfying conditional expression (16), fluctuations in spherical aberration and curvature of field during focusing from an object at infinity to an object at a close distance can be suppressed.

[0061] If the value corresponding to conditional expression (16) falls outside the above range, it becomes difficult to suppress fluctuations in spherical aberration and field curvature during focusing. By setting the lower limit of conditional expression (16) to 0.73, 0.75, 0.78, 0.80, or even 0.82, the effects of each embodiment can be more reliably achieved. Furthermore, by setting the upper limit of conditional expression (16) to 0.99, 0.98, or even 0.97, the effects of each embodiment can be more reliably achieved.

[0062] In the optical systems OL according to the first to fourth embodiments, it is desirable that the third lens group G3 has a negative lens that satisfies the following conditional expressions (17) to (19). 1.80 <ndM3 ···(17) νdM3<26.00 (18) θgFM3-(0.6415-0.00162×νdM3)<0.0120 ···(19) where ndM3 is the refractive index of the negative lens in the third lens group G3 at the d line νdM3: Abbe number of the negative lens in the third lens group G3 θgFM3: partial dispersion ratio of the negative lens in the third lens group G3, which is defined by the following equation when the refractive index of the negative lens in the third lens group G3 for the g-line is ngM3, the refractive index of the negative lens in the third lens group G3 for the F-line is nFM3, and the refractive index of the negative lens in the third lens group G3 for the C-line is nCM3 θgFM3=(ngM3-nFM3) / (nFM3-nCM3)

[0063] Conditional expression (17) defines an appropriate range for the refractive index of the negative lens in the third lens group G3 at the d-line. Conditional expression (18) defines an appropriate range for the Abbe number of the negative lens in the third lens group G3. Conditional expression (19) defines an appropriate relationship between the partial dispersion ratio and the Abbe number of the negative lens in the third lens group G3. By satisfying conditional expressions (17) to (19), it is possible to suppress fluctuations in axial chromatic aberration when focusing from an object at infinity to an object at a close distance.

[0064] If the value corresponding to conditional expression (17) is outside the above range, it becomes difficult to suppress fluctuations in axial chromatic aberration during focusing. By setting the lower limit of conditional expression (17) to 1.82, 1.83, or even 1.84, the effects of each embodiment can be further ensured.

[0065] If the value corresponding to conditional expression (18) falls outside the above range, it becomes difficult to suppress fluctuations in axial chromatic aberration during focusing. By setting the upper limit of conditional expression (18) to 25.90, 25.85, 25.70, 25.50, or even 25.35, the effects of each embodiment can be further ensured.

[0066] If the value corresponding to conditional expression (19) falls outside the above range, it becomes difficult to suppress fluctuations in axial chromatic aberration during focusing. By setting the upper limit of conditional expression (19) to 0.0115, 0.0110, 0.0105, 0.0100, or even 0.0098, the effects of each embodiment can be further ensured. The lower limit of conditional expression (19) may also be set to be greater than 0.0000.

[0067] It is desirable that the optical systems OL according to the first to fourth embodiments satisfy the following conditional expression (20). (L1R2+L1R1) / (L1R2-L1R1)<0.10 ···(20) where L1R1 is the radius of curvature of the object-side lens surface of the positive lens arranged closest to the object side in the optical system OL. L1R2: Radius of curvature of the image-side lens surface of the positive lens located closest to the object in the optical system OL

[0068] Conditional expression (20) defines an appropriate range for the shape factor of the positive lens located closest to the object in optical system OL. By satisfying conditional expression (20), spherical aberration can be effectively corrected when focused at infinity.

[0069] If the value corresponding to conditional expression (20) falls outside the above range, it becomes difficult to correct spherical aberration when the lens is focused at infinity. The effects of each embodiment can be further ensured by setting the upper limit of conditional expression (20) to 0.00, -0.01, -0.03, -0.08, -0.10, -0.30, -0.50, or even -0.60. The lower limit of conditional expression (20) may also be set to -2.00, -1.80, -1.50, -1.45, or even -1.40.

[0070] In the optical systems OL according to the first to fourth embodiments, it is desirable that the lens in the fourth lens group G4 located closest to the image side have negative refractive power, which allows for excellent correction of curvature of field and coma in the peripheral area over the entire range of magnification.

[0071] In the optical systems OL according to the first to fourth embodiments, when focusing from an object at infinity to an object at a close distance, it is desirable that 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. In the optical systems OL according to the first to fourth embodiments, it is desirable that the position of the first lens group G1 is fixed relative to the image plane I when focusing. In the optical systems OL according to the first to fourth embodiments, it is desirable that the position of the fourth lens group G4 is fixed relative to the image plane I when focusing. This makes it possible to suppress aberration fluctuations during focusing.

[0072] In the optical systems OL according to the first to fourth embodiments, it is desirable that at least one lens surface of the negative lens arranged closest to the image side of the optical system OL is aspheric, thereby making it possible to uniformly correct curvature of field within the image plane.

[0073] 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 having negative refractive power, a third lens group G3 having positive refractive power, and a fourth lens group G4 having negative refractive power are arranged, in order from the object side along the optical axis (Step ST1). Next, the second lens group G2 and the third lens group G3 are configured to move along the optical axis during focusing, changing the spacing between adjacent lens groups (Step ST2). Then, the lenses are arranged within the lens barrel so as to satisfy at least the above-mentioned conditional expression (1) (Step ST3). This manufacturing method makes it possible to manufacture an optical system with minimal aberration fluctuation during focusing.

[0074] Next, a manufacturing method of the optical system OL according to the second embodiment will be outlined. The manufacturing method of the optical system OL according to the second embodiment is the same as the manufacturing method described in the first embodiment, and will therefore be described with reference to FIG. 12, which is the same as the first embodiment. First, in order from the object side along the optical axis, 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 are arranged (step ST1). Next, during focusing, the second lens group G2 and the third lens group G3 are aligned along the optical axis. The lens barrel is configured so that the lens group moves along the axis of the lens barrel, changing the spacing between adjacent lens groups (step ST2). Then, the lenses are arranged within the lens barrel so as to satisfy at least conditional expression (2) above (step ST3). This manufacturing method makes it possible to manufacture an optical system with little aberration fluctuation during focusing.

[0075] Next, a manufacturing method for the optical system OL according to the third embodiment will be outlined. The manufacturing method for the optical system OL according to the third embodiment is similar to the manufacturing method described in the first embodiment, and will be described with reference to FIG. 12, as in the first embodiment. First, 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 are arranged, in order from the object side along the optical axis (Step ST1). Next, the second lens group G2 and the third lens group G3 are configured to move along the optical axis during focusing, changing the spacing between adjacent lens groups (Step ST2). Then, the lenses are arranged within the lens barrel so as to satisfy at least the above-mentioned conditional expression (3) (Step ST3). This manufacturing method makes it possible to manufacture an optical system with minimal aberration fluctuation during focusing.

[0076] Next, a manufacturing method of the optical system OL according to the fourth embodiment will be outlined with reference to FIG. 13. First, 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 are arranged, in order from the object side along the optical axis (Step ST11). Next, the second lens group G2 and the third lens group G3 are configured to move along the optical axis during focusing, changing the spacing between adjacent lens groups (Step ST12). Then, the lenses are arranged within the lens barrel so that at least the first lens group G1 has a negative lens that satisfies the above conditional expressions (4) to (6) (Step ST13). This manufacturing method makes it possible to manufacture an optical system with minimal aberration fluctuation during focusing. [Example]

[0077] Optical systems OL according to examples of each embodiment will be described below with reference to the drawings. Figures 1, 3, 5, 7, and 9 are cross-sectional views showing the configuration and refractive power distribution 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 each lens group along the optical axis when focusing from infinity to a close-distance object (a finite-distance object) is indicated by an arrow along with the word "focusing."

[0078] 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.

[0079] Tables 1 to 5 are shown below, with Table 1 showing data on the various specifications for Example 1, Table 2 for Example 2, Table 3 for Example 3, Table 4 for Example 4, and Table 5 for Example 5. In each example, the d-line (wavelength λ=587.6 nm), g-line (wavelength λ=435.8 nm), C-line (wavelength λ=656.3 nm), and F-line (wavelength λ=486.1 nm) are selected as the targets for calculating aberration characteristics.

[0080] In the [Overall Specifications] table, f is the focal length of the entire optical system, 2ω is the angle of view (unit: ° (degrees), 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 air-equivalent distance (back focus) from the last lens surface to the image plane on the optical axis when focused at infinity. In the table of overall specifications, β2 indicates the lateral magnification of the second lens group when focused at infinity. β3 indicates the lateral magnification of the third lens group when focused at infinity. Mf2 indicates the absolute value of the movement amount of the second lens group when focusing from an object at infinity to the closest object. Mf3 indicates the absolute value of the movement amount of the third lens group when focusing from an object at infinity to the closest object.

[0081] 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. If the optical surface is aspherical, an * is added to the surface number, and the paraxial radius of curvature is shown in the column for radius of curvature R.

[0082] 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).

[0083] θgF=(ng-nF) / (nF-nC) …(A)

[0084] In the [Aspherical Data] table, the shape of the aspherical surface shown in [Lens Specifications] is shown by the following formula (B). 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.

[0085] X(y)=(y 2 / R) / {1+(1-κ×y 2 / R 2 ) 1 / 2}+A4×y 4 +A6×y 6 +A8×y 8 +A10×y 10 +A12×y 12 …(B)

[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). Note that D0 indicates the distance from the object to the optical surface in the optical system that is closest to the object. In the [Variable Distance Data] table, f indicates the focal length of the entire optical system, β indicates the imaging magnification (lateral magnification) of the optical system, and FNO indicates the F-number of the optical system.

[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 example will be described with reference to FIGS. 1 and 2 and Table 1. FIG. 1 is a diagram showing the lens configuration of the optical system according to the first example. The optical system OL(1) according to the first example has a The lens 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 first lens group G1 and the fourth lens group G4 are fixed in position relative to the image plane I. An aperture stop S is disposed between the second lens group G2 and the third lens group G3. During focusing, the aperture stop S is fixed in position relative to the image plane I. The sign (+) or (-) attached to each lens group symbol indicates the refractive power of the respective lens group, and this is the same in all of the following embodiments.

[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 cemented lens formed by cementing together a negative meniscus lens L12 with a convex surface facing the object side and a positive meniscus lens L13 with a convex surface facing the object side, and a positive meniscus lens L14 with a convex surface facing the object side. In this embodiment, the negative meniscus lens L12 of the first lens group G1 corresponds to the negative lens that satisfies conditional expressions (4) to (6).

[0092] The second lens group G2 is composed of, arranged in order from the object side along the optical axis, a biconcave negative lens L21, and a cemented lens formed by cementing together a negative meniscus lens L22 with its convex surface facing the object side and a positive meniscus lens L23 with its convex surface facing the object side.

[0093] 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 lens formed by cementing together a negative meniscus lens L32 with its convex surface facing the object side and a biconvex positive lens L33. In this embodiment, the negative meniscus lens L32 of the third lens group G3 corresponds to the negative lens that satisfies conditional expressions (17) to (19).

[0094] The fourth lens group G4 is composed of, arranged along the optical axis from the object side, a negative meniscus lens L41 with a convex surface facing the object side, a cemented lens formed by cementing 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 lens formed by cementing a negative meniscus lens L44 with a convex surface facing the object side and a positive meniscus lens L45 with a convex surface facing the object side, and a negative meniscus lens L46 with a concave surface facing the object side. The negative meniscus lens L46 has an aspheric lens surface facing the object side. An image plane I is located on the image side of the fourth lens group G4.

[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=102.86 β2=8.163 2ω=24.06 β3=0.151 Ymax=21.70 Mf2=18.956 TL=149.38 Mf3=20.740 Bf=16.78 [Lens specifications] Surface number RD nd νd θgF Object plane ∞ (D0) 1 1598.6404 3.330 1.83481 42.73 2 -179.4707 0.200 3 80.9451 1.200 1.85451 25.15 0.6103 4 38.9730 7.070 1.59319 67.90 5 865.5813 0.200 6 47.0836 4.570 1.59319 67.90 7 210.0810 (D7) 8 -242.9579 1.100 1.51860 69.89 9 48.3271 1.613 10 122.3852 1.100 1.72047 34.71 11 28.6090 2.660 1.94595 17.98 12 44.8866 (D12) 13∞ (D13) (Aperture S) 14 85.7680 2.400 1.83481 42.72 15 -644.4854 0.200 16 79.2129 1.100 1.85451 25.15 0.6103 17 32.8950 5.480 1.59319 67.90 18 -109.8711 (D18) 19 163.4895 1.100 1.95375 32.33 20 45.6740 1.840 21 85.0464 1.100 1.51860 69.89 22 23.8970 3.210 1.94595 17.98 23 29.2234 2.983 24 34.9435 1.500 2.00069 25.46 25 21.6656 8.800 1.80440 39.61 26 250.8917 21.970 27* -26.4605 1.530 1.51680 64.14 28 -47.3182 Bf Image plane ∞ [Aspherical data] Page 27 κ=1.000,A4=9.61768E-06,A6=1.56877E-08 A8=-4.92862E-11,A10=-1.29299E-13,A12=-7.46540E-17 [Variable Interval Data] Focused at infinity Focused at mid-range distance Focused at closest distance f=102.86 β=-0.5 β=-1.0 D0 ∞ 226.746 138.188 D7 3.662 12.980 22.619 D12 25.484 16.167 6.528 D13 24.986 14.031 4.245 D18 2.206 13.161 22.947 FNO 2.89 3.68 4.65 [Lens group data] Group starting plane focal length G1 1 56.05 G2 8 -49.08 G3 14 52.89 G4 19 -64.87

[0097] FIG. 2(A) is a diagram showing various aberrations in the infinity-focused state of the optical system according to Example 1. FIG. 2(B) is a diagram showing various aberrations in the closest distance-focused state of the optical system according to Example 1 (photographic magnification β=-1.0). In each aberration diagram in the infinity-focused state, FNO indicates the F-number, and Y indicates the image height. In each aberration diagram in the closest distance-focused state, NA indicates the numerical aperture, and Y indicates the image height. Note that in the spherical aberration diagram, the F-number or numerical aperture value corresponding to the maximum aperture is shown, and in the astigmatism diagram and distortion diagram, the maximum value of the image height is shown. In the astigmatism diagrams, the values for each image height are shown. d indicates the d-line (wavelength λ=587.6 nm), g indicates the g-line (wavelength λ=435.8 nm), C indicates the C-line (wavelength λ=656.3 nm), and F indicates the F-line (wavelength λ=486.1 nm). In the astigmatism diagrams, the solid line indicates the sagittal image plane, and the dashed line indicates the meridional image plane. Note that in the aberration diagrams of each embodiment shown below, the same symbols as in this embodiment are used, 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 infinity focused to the closest distance focused.

[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 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. An aperture stop S is disposed between the second lens group G2 and the third lens group G3. During focusing, the position of the aperture stop S is fixed relative to the image plane I.

[0100] In the second embodiment, the second lens group G2, the third lens group G3, and the fourth lens group G4 are configured in the same manner as in the first embodiment, and therefore the same reference numerals as in the first embodiment are used, and detailed description of each lens will be omitted. The first lens group G1 is configured, in order from the object side along the optical axis, to include a positive meniscus lens L11 with a concave surface facing the object side, a cemented lens formed by cementing a negative meniscus lens L12 with a convex surface facing the object side and a positive meniscus lens L13 with a convex surface facing the object side, and a positive meniscus lens L14 with a convex surface facing the object side. In this embodiment, the negative meniscus lens L12 of the first lens group G1 corresponds to a negative lens that satisfies conditional expressions (4) to (6). Furthermore, the negative meniscus lens L32 of the third lens group G3 corresponds to a negative lens that satisfies conditional expressions (17) to (19).

[0101] Table 2 below lists the values of the specifications of the optical system according to the second example.

[0102] (Table 2) [Overall specifications] f=102.90 β2=8.644 2ω=24.05 β3=0.140 Ymax=21.70 Mf2=18.759 TL=149.44 Mf3=20.918 Bf=16.84 [Lens specifications] Surface number RD nd νd θgF Object plane ∞ (D0) 1 -970.6344 3.130 1.83481 42.73 2 -155.1786 0.200 3 81.0511 1.200 1.85451 25.15 0.6103 4 39.5973 6.920 1.59319 67.90 5 1859.7639 0.200 6 47.279 4.100 1.59319 67.90 7 216.5762 (D7) 8 -224.7372 1.100 1.51860 69.89 9 47.2726 1.597 10 121.819 1.100 1.72047 34.71 11 29.0024 2.610 1.94595 17.98 12 45.9042 (D12) 13∞ (D13) (Aperture S) 14 78.5700 2.400 1.83481 42.73 15 -637.4162 0.200 16 79.2597 1.100 1.85451 25.15 0.6103 17 32.0633 5.300 1.59319 67.90 18 -121.6144 (D18) 19 152.5421 1.100 1.95375 32.33 20 46.0324 2.000 21 95.1769 1.100 1.51860 69.89 22 24.2848 3.200 1.94595 17.98 23 29.7026 3.000 24 36.4143 1.100 2.00069 25.46 25 22.7290 8.210 1.80440 39.61 26 309.1328 22.990 27* -23.6207 1.500 1.51680 64.14 28 -38.5736 Bf Image plane ∞ [Aspherical data] Page 27 κ=1.000,A4=1.19399E-05,A6=2.04728E-08 A8=-7.55581E-11,A10=2.43965E-13,A12=-1.86360E-16 [Variable Interval Data] Focused at infinity Focused at mid-range distance Focused at closest distance f=102.90 β=-0.5 β=-1.0 D0 ∞ 226.763 138.555 D7 4.600 13.875 23.358 D12 25.347 16.072 6.588 D13 25.096 14.117 4.178 D18 2.200 13.179 23.118 FNO 2.91 3.68 4.79 [Lens group data] Group starting plane focal length G1 1 56.46 G2 8 -48.99 G3 14 52.33 G4 19 -65.47

[0103] Fig. 4(A) is a diagram showing various aberrations of the optical system of Example 2 when focused at infinity. Fig. 4(B) is a diagram showing various aberrations of the optical system of Example 2 when focused at the closest distance (magnification β=-1.0). It can be seen from these aberration diagrams that the optical system of Example 2 has excellent imaging performance, with various aberrations being well corrected across the entire range from focused at infinity to focused at the closest distance.

[0104] (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. An aperture stop S is disposed between the second lens group G2 and the third lens group G3. During focusing, the position of the aperture stop S is fixed relative to the image plane I.

[0105] In the third embodiment, the second lens group G2, the third lens group G3, and the fourth lens group G4 are configured in the same manner as in the first embodiment, and therefore the same reference numerals as in the first embodiment are used, and detailed description of each lens will be omitted. 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 lens formed by cementing together a negative meniscus lens L12 with a convex surface facing the object side and a positive meniscus lens L13 with a convex surface facing the object side, and a positive meniscus lens L14 with a convex surface facing the object side. The positive meniscus lens L14 has an aspheric lens surface facing the object side. In this embodiment, the negative meniscus lens L12 of the first lens group G1 corresponds to a negative lens that satisfies conditional expressions (4) to (6). The negative meniscus lens L32 of the third lens group G3 corresponds to a negative lens that satisfies conditional expressions (17) to (19).

[0106] Table 3 below lists the values of the specifications of the optical system according to the third example.

[0107] (Table 3) [Overall specifications] f=112.70 β2=6.996 2ω=21.80 β3=0.187 Ymax=21.70 Mf2=18.085 TL=153.44 Mf3=20.338 Bf=18.23 [Lens specifications] Surface number RD nd νd θgF Object plane ∞ (D0) 1 355.1676 3.588 1.83327 42.78 2 -285.0651 4.067 3 69.2281 2.242 1.85451 25.15 0.6103 4 35.8609 7.035 1.59319 67.90 5 290.9476 0.200 6* 51.7012 5.811 1.59319 67.90 7 490.4661 (D7) 8 -343.8397 1.159 1.51860 69.89 9 43.0965 5.534 10 235.9802 1.189 1.72047 34.71 11 32.9473 2.618 1.94594 17.98 12 56.6601 (D12) 13∞ (D13) (Aperture S) 14 126.3547 2.400 1.83369 42.76 15 -603.5933 0.220 16 69.9801 1.100 1.85451 25.15 0.6103 17 34.3310 5.800 1.59319 67.90 18 -90.9674 (D18) 19 219.3497 1.198 1.94180 30.88 20 48.5362 2.000 21 113.6761 1.200 1.51860 69.89 22 26.146 3.256 1.94594 17.98 23 34.4512 3.000 24 38.6884 1.100 2.00069 25.46 25 23.5045 7.441 1.80610 40.97 26 293.6016 19.200 27* -20.7242 2.129 1.51680 64.13 28 -33.3932 Bf Image plane ∞ [Aspherical data] Side 6 κ=1.000,A4=-7.80076E-08,A6=7.83037E-11 A8=-1.44363E-13,A10=0.00000E+00,A12=0.00000E+00 Page 27 κ=1.000,A4=1.27301E-05,A6=1.49611E-08 A8=9.59928E-12,A10=-4.03456E-15,A12=3.26570E-16 [Variable Interval Data] Focused at infinity Focused at mid-range distance Focused at closest distance f=112.70 β=-0.5 β=-1.0 D0 ∞ 241.112 143.316 D7 2.233 10.886 20.318 D12 23.545 14.893 5.461 D13 22.608 11.511 2.270 D18 3.338 14.435 23.676 FNO 2.92 3.71 4.73 [Lens group data] Group starting plane focal length G1 1 55.98 G2 8 -47.61 G3 14 53.52 G4 19 -46.34

[0108] Fig. 6(A) is a diagram showing various aberrations of the optical system of Example 3 when focused at infinity. Fig. 6(B) is a diagram showing various aberrations of the optical system of Example 3 when focused at the closest distance (magnification β=-1.0). It can be seen from the various aberration diagrams that the optical system of Example 3 has excellent imaging performance, with various aberrations being well corrected across the entire range from focused at infinity to focused at the closest distance.

[0109] (Fourth Example) The fourth example will be described with reference to FIGS. 7 to 8 and Table 4. FIG. 7 is a diagram showing the lens configuration of the optical system according to the fourth example. The optical system OL(4) according to the fourth example is composed of, arranged in order from the object side along the optical axis, 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 an object at a close distance, 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 first lens group G1 and the fourth lens group G4 The lens group G4 is fixed in position relative to the image plane I. The aperture stop S is disposed between the second lens group G2 and the third lens group G3. The aperture stop S is fixed in position relative to the image plane I during focusing.

[0110] In the fourth embodiment, the second lens group G2 and the third lens group G3 are configured in the same manner as in the first embodiment, and therefore the same reference numerals as in the first embodiment are used, and detailed description of each lens will be omitted. The first lens group G1 is configured, arranged in order from the object side along the optical axis, to include a biconvex positive lens L11, a cemented lens formed by cementing a negative meniscus lens L12 with a convex surface facing the object side and a biconvex positive lens L13, and a positive meniscus lens L14 with a convex surface facing the object side. The positive meniscus lens L14 has an aspheric lens surface facing the object side. In this embodiment, the negative meniscus lens L12 of the first lens group G1 corresponds to a negative lens that satisfies conditional expressions (4) to (6). The negative meniscus lens L32 of the third lens group G3 corresponds to a negative lens that satisfies conditional expressions (17) to (19).

[0111] The fourth lens group G4 is composed of, arranged along the optical axis from the object side, a biconcave negative lens L41, a cemented lens formed by cementing 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 lens formed by cementing a negative meniscus lens L44 with a convex surface facing the object side and a biconvex positive lens L45, and a negative meniscus lens L46 with a concave surface facing the object side. The object-side lens surface of the negative meniscus lens L46 is aspheric. An image plane I is located on the image side of the fourth lens group G4.

[0112] Table 4 below lists the values of the specifications of the optical system according to the fourth example.

[0113] (Table 4) [Overall specifications] f=91.80 β2=9.291 2ω=26.86 β3=0.129 Ymax=21.70 Mf2=18.681 TL=144.30 Mf3=22.112 Bf=13.94 [Lens specifications] Surface number RD nd νd θgF Object plane ∞ (D0) 1 408.2969 3.380 1.83481 42.73 2 -272.198 0.200 3 88.8401 1.200 1.85451 25.15 0.6103 4 40.6806 7.283 1.59319 67.90 5 -2294.7045 0.200 6* 44.6204 4.666 1.59319 67.90 7 181.6868 (D7) 8 -474.3707 1.100 1.51860 69.89 9 37.2782 2.943 10 257.8909 1.100 1.72047 34.71 11 35.7865 2.739 1.94594 17.98 12 67.2338 (D12) 13∞ (D13) (Aperture S) 14 80.2960 2.599 1.85225 41.93 15 -261.2143 0.200 16 103.5562 1.127 1.85451 25.15 0.6103 17 33.2058 5.480 1.59319 67.90 18 -115.1949 (D18) 19 -489.7555 1.182 1.90412 28.78 20 84.0357 2.000 21 1584.8325 1.100 1.51860 69.89 22 30.4557 3.319 1.94594 17.98 23 42.4678 3.000 24 50.1735 1.100 2.00069 25.46 25 29.4301 7.673 1.81892 43.48 26 -234.4595 24.209 27* -20.3038 1.500 1.51680 64.13 28 -38.3517 Bf Image plane ∞ [Aspherical data] Side 6 κ=1.000,A4=-1.39939E-07,A6=-9.81797E-11 A8=-3.74424E-13,A10=1.22198E-15,A12=-1.93260E-18 Page 27 κ=1.000,A4=1.58902E-05,A6=1.67973E-08 A8=2.63185E-11,A10=-9.61351E-14,A12=5.69420E-16 [Variable Interval Data] Focused at infinity Focused at mid-range distance Focused at closest distance f=91.80 β=-0.5 β=-1.0 D0 ∞ 207.102 129.576 D7 2.004 11.344 20.685 D12 22.744 13.404 4.064 D13 23.943 12.265 1.831 D18 2.371 14.048 24.482 FNO 2.85 3.66 4.83 [Lens group data] Group starting plane focal length G1 1 55.98 G2 8 -47.61 G3 14 53.52 G4 19 -46.34

[0114] Fig. 8(A) is a diagram showing various aberrations of the optical system of Example 4 when focused at infinity. Fig. 8(B) is a diagram showing various aberrations of the optical system of Example 4 when focused at the closest distance (magnification β=-1.0). It can be seen from the various aberration diagrams that the optical system of Example 4 has excellent imaging performance, with various aberrations being well corrected across the entire range from focused at infinity to focused at the closest distance.

[0115] (Fifth Example) The fifth example will be described with reference to FIGS. 9 to 10 and Table 5. FIG. 9 shows the lens configuration of the optical system according to the fifth example. The optical system OL(5) according to the fifth example is composed of, arranged in order from the object side along the optical axis, 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 an object at a close distance, the second lens group G2 moves toward the image side along the optical axis, and the third lens group G3 moves toward the object side along the optical axis, 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 aperture stop S is located between the second lens group G2 and the fourth lens group G4. and the third lens group G3. The aperture stop S is fixed in position relative to the image plane I during focusing.

[0116] In the fifth embodiment, the second lens group G2 and the third lens group G3 are configured in the same manner as in the first embodiment, and therefore the same reference numerals as in the first embodiment are used, and detailed description of each lens will be omitted. The first lens group G1 is configured, in order from the object side along the optical axis, to include a biconvex positive lens L11, a cemented lens formed by cementing a negative meniscus lens L12 with a convex surface facing the object side and a biconvex positive lens L13, and a positive meniscus lens L14 with a convex surface facing the object side. In this embodiment, the negative meniscus lens L12 of the first lens group G1 corresponds to the negative lens that satisfies conditional expressions (4) to (6). Furthermore, the negative meniscus lens L32 of the third lens group G3 corresponds to the negative lens that satisfies conditional expressions (17) to (19).

[0117] The fourth lens group G4 is composed of, arranged along the optical axis from the object side, a negative meniscus lens L41 with a convex surface facing the object side, a cemented lens formed by cementing 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 positive meniscus lens L44 with a convex surface facing the object side, a cemented lens formed by cementing a negative meniscus lens L45 with a convex surface facing the object side and a biconvex positive lens L46, and a negative meniscus lens L47 with a concave surface facing the object side. The negative meniscus lens L47 has an aspheric lens surface facing the object side. An image plane I is located on the image side of the fourth lens group G4.

[0118] Table 5 below lists the values of the specifications of the optical system according to the fifth example.

[0119] (Table 5) [Overall specifications] f=102.90 β2=7.191 2ω=24.02 β3=0.167 Ymax=21.70 Mf2=17.513 TL=151.46 Mf3=18.500 Bf=16.67 [Lens specifications] Surface number RD nd νd θgF Object plane ∞ (D0) 1 281.4565 4.042 1.84850 43.79 2 -254.6508 2.526 3 114.5240 1.200 1.85451 25.15 0.6103 4 40.7834 7.528 1.59319 67.90 5 -338.1593 0.200 6 42.8169 3.939 1.59319 67.90 7 155.8083 (D7) 8 -223.9031 1.223 1.51860 69.89 9 42.8160 2.098 10 151.8246 1.200 1.74950 35.25 11 30.8506 3.790 1.94594 17.98 12 53.8828 (D12) 13∞ (D13) (Aperture S) 14 108.3408 3.055 1.84850 43.79 15 -203.4420 0.200 16 67.4695 1.200 1.85451 25.15 0.6103 17 31.8859 6.500 1.59319 67.90 18 -140.2381 (D18) 19 216.9695 1.200 1.89190 37.13 20 33.9171 3.218 21 126.0145 1.200 1.59349 67.00 22 27.2774 3.571 1.94594 17.98 23 40.9231 2.000 24 35.5779 5.995 1.83481 42.73 25 166.9394 1.000 26 117.0398 2.000 1.90200 25.26 27 22.6500 10.000 1.76200 40.11 28 -2467.5977 14.472 29* -19.9041 1.200 1.51680 64.13 30 -33.7790 Bf Image plane ∞ [Aspherical data] Page 29 κ=1.000,A4=1.95940E-05,A6=-1.65107E-08 A8=2.48794E-10,A10=-8.47293E-13,A12=1.57410E-15 [Variable Interval Data] Focused at infinity Focused at mid-range distance Focused at closest distance f=102.90 β=-0.5 β=-1.0 D0 ∞ 226.207 135.900 D7 3.000 11.595 20.513 D12 23.577 14.982 6.064 D13 21.246 11.581 2.746 D18 2.000 11.666 20.500 FNO 2.85 3.65 4.73 [Lens group data] Group starting plane focal length G1 1 53.71 G2 8 -47.46 G3 14 49.28 G4 19 -35.41

[0120] Fig. 10(A) is a diagram showing various aberrations of the optical system of Example 5 when focused at infinity. Fig. 10(B) is a diagram showing various aberrations of the optical system of Example 5 when focused at the closest distance (magnification β=-1.0). It can be seen from the various aberration diagrams that the optical system of Example 5 has excellent imaging performance, with various aberrations being well corrected across the entire range from focused at infinity to focused at the closest distance.

[0121] 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 (20) for all the examples (Examples 1 to 5). Condition (1) 0.20 <DG4 / TL<0.40 Conditional expression (2) 3.00<(LnR2+LnR1) / (LnR2-LnR1)<5.00 Condition (3) 0.75 <f1 / (-f2)<1.30 Condition (4) 1.80 <ndM1 Conditional expression (5) νdM1<26.00 Conditional expression (6) θgFM1-(0.6415-0.00162×νdM1)<0.0120 Condition (7) 0.75 <f1 / f3<1.20 Conditional expression (8) 0.45<(-β) Conditional expression (9) 35.0<β2 / β3<350.0 Conditional expression (10) 0.005<β3 / β2<0.035 Conditional expression (11) {β2+(1 / β2)} -2 <0.10 Conditional expression (12) {β3+(1 / β3)} -2 <0.10 Condition (13) 0.05 <Bf / TL<0.35 Condition (14) 0.10 <Bf / f<0.50 Condition (15) 0.50 <L1S / SLn<1.00 Condition (16) 0.70 <Mf2 / Mf3<1.10 Condition (17) 1.80 <ndM3 Conditional expression (18) νdM3<26.00 Conditional expression (19) θgFM3-(0.6415-0.00162×νdM3)<0.0120 Conditional expression (20) (L1R2+L1R1) / (L1R2-L1R1)<0.10

[0122] [Conditional Expression Corresponding Values] (First to Third Examples) Conditional Expression First Example Second Example Third Example (1) 0.294 0.295 0.263 (2) 3.537 4.159 4.272 (3) 1.142 1.152 1.176 (4) 1.855 1.855 1.855 (5) 25.15 25.15 25.15 (6) 0.0095 0.0095 0.0095 (7) 1.060 1.079 1.046 (8) 1.00 1.00 1.00 (9) 54.19 61.71 37.44 (10) 0.018 0.016 0.027 (11) 0.015 0.013 0.020 (12) 0.022 0.019 0.033 (13) 0.116 0.116 0.122 (14) 0.168 0.169 0.167 (15) 0.649 0.651 0.779 (16) 0.914 0.897 0.889 (17) 1.855 1.855 1.855 (18) 25.15 25.15 25.15 (19) 0.0095 0.0095 0.0095 (20) -0.798 -1.381 -0.109 [Conditional Expression Corresponding Values] (Fourth and Fifth Examples) Conditional Expressions Fourth Example Fifth Example (1) 0.311 0.302 (2) 3.250 3.869 (3) 1.115 1.132 (4) 1.855 1.855 (5) 25.15 25.15 (6) 0.0095 0.0095 (7) 1.042 1.090 (8) 1.00 1.00 (9) 72.20 42.96 (10) 0.014 0.023 (11) 0.011 0.019 (12) 0.016 0.027 (13) 0.100 0.115 (14) 0.158 0.170 (15) 0.613 0.679 (16) 0.845 0.947 (17) 1.855 1.855 (18) 25.15 25.15 (19) 0.0095 0.0095 (20) -0.200 -0.050

[0123] According to each of the above embodiments, an optical system with little aberration fluctuation during focusing can be realized.

[0124] The above-described examples are merely illustrative examples of the present invention, and the present invention is not limited to these.

[0125] The following contents can be appropriately adopted within the scope that does not impair the optical performance of the optical system of this embodiment.

[0126] 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. Note that a lens group refers to a portion having at least one lens separated by an air gap that changes during focusing.

[0127] 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.

[0128] 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.

[0129] 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.

[0130] The aperture diaphragm is preferably disposed between the second lens group and the third lens group, but it is also possible to use the lens frame to fulfill that role instead of providing a member serving as an aperture diaphragm.

[0131] 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]

[0132] 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 the optical axis, and the interval between adjacent lens groups changes; An optical system that satisfies the following condition: 0.75<f1 / (-f2)<1.30 3.00<(LnR2+LnR1) / (LnR2-LnR1)<5.00 0.75<f1 / f3<1.20 where f1 is the focal length of the first lens group f2: focal length of the second lens group f3: focal length of the third lens group LnR1: the radius of curvature of the object-side lens surface of the negative lens arranged closest to the image side in the optical system LnR2: the radius of curvature of the image-side lens surface of the negative lens arranged closest to the image side in the optical system

2. 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 the optical axis, changing the spacing between adjacent lens groups, and the following condition is satisfied: 0.75<f1 / (-f2)<1.30 ３５．０＜β２／β３＜３５０．０ where f1 is the focal length of the first lens group f2: focal length of the second lens group β2: lateral magnification of the second lens group when focused at infinity β3: lateral magnification of the third lens group when focused at infinity The optical system has a negative lens in the third lens group that satisfies the following condition: 1.80<ndM3 νdM3<26.00 θgFM3-(0.6415-0.00162×νdM3)<0.0120 where ndM3 is the refractive index of the negative lens in the third lens group with respect to the d-line νdM3: Abbe number of the negative lens in the third lens group θgFM3: partial dispersion ratio of the negative lens of the third lens group, which is defined by the following formula when the refractive index of the negative lens of the third lens group with respect to the g-line is ngM3, the refractive index of the negative lens of the third lens group with respect to the F-line is nFM3, and the refractive index of the negative lens of the third lens group with respect to the C-line is nCM3 θgFM3=(ngM3-nFM3) / (nFM3-nCM3)

3. 3. The optical system according to claim 1, wherein the following condition is satisfied: 0.20<DG4 / TL<0.40 where DG4 is the length of the fourth lens group on the optical axis. TL: total length of the optical system when focused at infinity

4. 3. The optical system according to claim 2, wherein the following condition is satisfied: 3.00<(LnR2+LnR1) / (LnR2-LnR1)<5.00 where LnR1 is the radius of curvature of the object-side lens surface of the negative lens arranged closest to the image side of the optical system. LnR2: the radius of curvature of the image-side lens surface of the negative lens arranged closest to the image side in the optical system

5. The optical system according to any one of claims 2 to 4, which satisfies the following conditional expression: 0.75<f1 / f3<1.20 where f1 is the focal length of the first lens group f3: focal length of the third lens group

6. 6. The optical system according to claim 1, wherein the following condition is satisfied: ０．４５＜（－β） where β is the lateral magnification of the optical system

7. The optical system according to any one of claims 1 and 3 to 6, which satisfies the following conditional expression: ３５．０＜β２／β３＜３５０．０ where β2 is the lateral magnification of the second lens group when focused at infinity. β3: lateral magnification of the third lens group when focused at infinity

8. 8. The optical system according to claim 1, wherein the following condition is satisfied: ０．００５＜β３／β２＜０．０３５ where β2 is the lateral magnification of the second lens group when focused at infinity. β3: lateral magnification of the third lens group when focused at infinity

9. 9. The optical system according to claim 1, wherein the following condition is satisfied: ｛β２＋（１／β２）｝ -2 ＜０．１０ where β2 is the lateral magnification of the second lens group when focused at infinity.

10. 10. The optical system according to claim 1, wherein the following condition is satisfied: ｛β３＋（１／β３）｝ -2 ＜０．１０ where β3 is the lateral magnification of the third lens group when focused at infinity.

11. The optical system according to any one of claims 1 to 10, which satisfies the following conditional expression: 0.05<Bf / TL<0.35 where Bf is the back focus of the optical system when focused at infinity. TL: total length of the optical system when focused at infinity

12. 12. The optical system according to claim 1, wherein the following condition is satisfied: 0.10<Bf / f<0.50 where Bf is the back focus of the optical system when focused at infinity. f: focal length of the optical system

13. having an aperture, The optical system according to any one of claims 1 to 12, which satisfies the following conditional expression: 0.50<L1S / SLn<1.00 where L1S is the distance on the optical axis from the lens surface closest to the object side of the optical system to the stop when the lens is focused at infinity. SLn: the distance on the optical axis from the aperture to the lens surface of the optical system closest to the image when focused at infinity

14. The optical system according to any one of claims 1 to 13, which satisfies the following conditional expression: 0.70<Mf2 / Mf3<1.10 where Mf2 is the absolute value of the movement amount of the second lens group when focusing from an object at infinity to an object at the closest distance. Mf3: Absolute value of the movement amount of the third lens group when focusing from an object at infinity to an object at the closest distance

15. 15. The optical system according to claim 1, wherein the third lens group has a negative lens that satisfies the following condition: 1 / (f / f<f<1 / f) / f / f<f<1 / f)<f / f<f / f. 1.80<ndM3 νdM3<26.00 θgFM3-(0.6415-0.00162×νdM3)<0.0120 where ndM3 is the refractive index of the negative lens in the third lens group with respect to the d-line νdM3: Abbe number of the negative lens in the third lens group θgFM3: partial dispersion ratio of the negative lens of the third lens group, which is defined by the following formula when the refractive index of the negative lens of the third lens group with respect to the g-line is ngM3, the refractive index of the negative lens of the third lens group with respect to the F-line is nFM3, and the refractive index of the negative lens of the third lens group with respect to the C-line is nCM3 θgFM3=(ngM3-nFM3) / (nFM3-nCM3)

16. The optical system according to any one of claims 1 to 15, which satisfies the following conditional expression: (L1R2+L1R1) / (L1R2-L1R1)<0.10 where L1R1 is the radius of curvature of the object-side lens surface of the positive lens arranged closest to the object side of the optical system. L1R2: Radius of curvature of the image-side lens surface of the positive lens arranged closest to the object side in the optical system

17. 17. The optical system according to claim 1, wherein the lens in the fourth lens group arranged closest to the image side has negative refractive power.

18. The optical system according to any one of claims 1 to 17, 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 image side, and the third lens group moves along the optical axis toward the object side.

19. 19. The optical system according to claim 1, wherein the first lens group is fixed in position relative to the image plane during focusing.

20. 20. The optical system according to claim 1, wherein the fourth lens group is fixed in position relative to the image plane during focusing.

21. An optical device comprising the optical system according to any one of claims 1 to 20.

Images