Optical system and optical device

Abstract

To provide an optical system that is compact and has excellent optical performance.SOLUTION: An optical system OL comprises an object side lens group GA having positive refractive power, at least one or more focusing lens groups GF1, GF2 having positive refractive power, and a subsequent lens group GR, the object side lens group has a first lens L11 that is disposed in the furthest object side and has negative refractive power, and a second lens L12 that is disposed adjacent to the image side of the first lens and has negative refractive power, the object side lens group has a cemented lens CL disposed in the furthest image surface side, the cemented lens has mutually cemented negative lens L19 and positive lens L110, a focusing lens group travels along a light axis at the time of focusing, the object side lens group and the subsequent lens group are fixed relative to the image surface, further has an aperture diaphragm S disposed in the image surface side relative to the object side lens group. The optical system OL satisfies the following expression: 1.00<Da / f<2.00 1.70<(-fa) / f<4.00 0.03<Dn / Dp<0.30.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Conventionally, optical systems suitable for photo cameras, electronic still cameras, video cameras, etc. have been proposed (see, for example, Patent Document 1). However, it is difficult to achieve good optical performance while making such optical systems compact. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-63966 Summary of the Invention

[0004] An optical system according to the present invention includes, arranged in order from the object side along an optical axis, an object-side lens group having positive refractive power, at least one focusing lens group having positive refractive power, and a subsequent lens group, wherein the object-side lens group includes a first lens arranged closest to the object side and having negative refractive power, and a second lens arranged adjacent to the image side of the first lens and having negative refractive power, the object-side lens group includes a cemented lens arranged closest to the image plane of the object-side lens group, the cemented lens including a negative lens and a positive lens cemented together, the at least one focusing lens group moving along the optical axis during focusing, the object-side lens group and the subsequent lens group being fixed with respect to the image plane, and the optical system further includes an aperture stop arranged closer to the image plane than the object-side lens group.

[0005] The optical system according to the present invention further satisfies the following condition: 1.00 <Da / f<2.00 1.70<(-fa) / f<4.00 0.03 <Dn / Dp<0.30 where f is the focal length of the optical system when focused at infinity Da: the distance on the optical axis from the aperture stop to the image plane when focused at infinity fa: the focal length of the first lens arranged closest to the object in the object-side lens group Dn: the thickness of the negative lens in the cemented lens on the optical axis Dp: the thickness of the positive lens in the cemented lens on the optical axis

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

[0007] [Figure 1] FIG. 2 is a diagram showing the lens configuration of an optical system according to Example 1. [Figure 2] 2A and 2B are diagrams showing various aberrations of the optical system according to Example 1 when focused at infinity and when focused at a close distance, respectively. [Figure 3] FIG. 10 is a diagram showing the lens configuration of an optical system according to a second example. [Figure 4] 4A and 4B are diagrams showing various aberrations of the optical system according to Example 2 when focused 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. 13 is a diagram showing the lens configuration of an optical system according to Example 6. [Figure 12] 12A and 12B are diagrams showing various aberrations of the optical system according to Example 6 when focused on infinity and when focused on a close distance, respectively. [Figure 13] 1 is a diagram showing the configuration of a camera equipped with an optical system according to an embodiment of the present invention. [Figure 14] 10 is a flowchart illustrating a method for manufacturing an optical system according to the present embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0008] A preferred embodiment of the present invention will now be described. First, a camera (optical device) equipped with an optical system according to this embodiment will be described with reference to FIG. 13. As shown in FIG. 13, 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 includes 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 includes an optical system OL consisting of multiple lens groups, and a lens position control mechanism (not shown) that controls the position of each lens group. The lens position control mechanism is composed of a sensor that detects the position of the lens groups, a motor that moves the lens groups back and forth along the optical axis, a control circuit that drives the motor, etc.

[0009] Light from the subject is collected by the optical system OL of the photographing lens 3 and reaches the image plane I of the image sensor 4. The light from the subject that reaches the image plane I is photoelectrically converted by the image sensor 4 and recorded as digital image data in a memory (not shown). The digital image data recorded in the memory can be displayed on the 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. 13 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.

[0010] Next, an optical system according to this embodiment will be described. As shown in FIG. 1, an optical system OL(1) as an example of the optical system OL according to this embodiment is configured to include, in order from the object side along the optical axis, an object-side lens group GA having positive refractive power, at least one focusing lens group (GF1, GF2) having positive refractive power, and a subsequent lens group GR. During focusing, the at least one focusing lens group moves along the optical axis, and the object-side lens group GA and the subsequent lens group GR are fixed with respect to the image plane I. The optical system OL according to this embodiment also includes an aperture stop S arranged closer to the image plane than the object-side lens group GA.

[0011] With the above-described configuration, the optical system OL according to this embodiment satisfies the following conditional expressions (1) and (2). 1.00 <Da / f<2.00 ···(1) 1.70<(-fa) / f<4.00 (2) where f is the focal length of the optical system OL when focused at infinity Da: the distance on the optical axis from the aperture stop S to the image plane I when focused at infinity fa: focal length of the first lens La located closest to the object in the object-side lens group GA

[0012] According to this embodiment, it is possible to obtain an optical system that is small yet has good optical performance, and an optical device equipped with this optical system. Furthermore, since the focusing lens group can be made small, it is possible to obtain an optical system that can achieve high-speed and quiet autofocus (AF). The optical system OL according to this embodiment may be the optical system OL(2) shown in FIG. 3, the optical system OL(3) shown in FIG. 5, or the optical system OL(4) shown in FIG. 7. Furthermore, the optical system OL according to this embodiment may be the optical system OL(5) shown in FIG. 9 or the optical system OL(6) shown in FIG. 11.

[0013] Conditional expression (1) defines the appropriate relationship between the distance on the optical axis from aperture stop S to image plane I when focused at infinity, and the focal length of optical system OL when focused at infinity. Satisfying conditional expression (1) makes it possible to effectively correct various aberrations, including spherical aberration when focused at infinity, despite the compact size.

[0014] If the value corresponding to conditional expression (1) exceeds the upper limit, the distance on the optical axis from the aperture stop S to the image plane I when focused at infinity becomes too large, making it difficult to correct various aberrations, including spherical aberration, when focused at infinity. By setting the upper limit of conditional expression (1) to 1.98, or even 1.96, the effect of this embodiment can be further ensured.

[0015] If the corresponding value of conditional expression (1) falls below the lower limit, the distance on the optical axis from the aperture stop S to the image plane I when focused at infinity becomes too small, and the object-side lens group GA becomes large, making it difficult to correct various aberrations including spherical aberration while maintaining a compact size. By setting the lower limit of conditional expression (1) to 1.15, 1.25, 1.50, or even 1.60, the effects of this embodiment can be further ensured.

[0016] Conditional expression (2) defines the appropriate relationship between the focal length of the first lens La, which is located closest to the object in the object-side lens group GA, and the focal length of the optical system OL when focused at infinity. By satisfying conditional expression (2), it is possible to effectively correct various aberrations, including coma when focused at infinity, while still maintaining a compact size.

[0017] If the corresponding value of conditional expression (2) exceeds the upper limit, the refractive power of the first lens La becomes too weak, making it difficult to correct various aberrations such as coma while maintaining a compact size. By setting the upper limit of conditional expression (2) to 3.75, 3.50, 3.25, or even 3.00, the effect of this embodiment can be further ensured.

[0018] If the corresponding value of conditional expression (2) is below the lower limit, the refractive power of the first lens La becomes too strong, making it difficult to correct various aberrations, including coma when focused at infinity. By setting the lower limit of conditional expression (2) to 1.85, 2.00, 2.10, or even 2.20, the effect of this embodiment can be further ensured.

[0019] It is desirable that the optical system OL according to this embodiment satisfy the following conditional expression (3). 1.00 <f1 / f<4.40 ···(3) where f1 is the focal length of the object-side lens group GA

[0020] Conditional expression (3) defines the appropriate relationship between the focal length of the object-side lens group GA and the focal length of the optical system OL when focused at infinity. By satisfying conditional expression (3), it is possible to effectively correct various aberrations, including spherical aberration when focused at infinity, while still maintaining a compact size.

[0021] If the value corresponding to conditional expression (3) exceeds the upper limit, the refractive power of the object-side lens group GA becomes too weak, making it difficult to correct various aberrations including spherical aberration while maintaining a compact size. By setting the upper limit of conditional expression (3) to 4.00, 3.50, 3.00, or even 2.50, the effect of this embodiment can be further ensured.

[0022] If the value corresponding to conditional expression (3) falls below the lower limit, the refractive power of the object-side lens group GA becomes too strong, making it difficult to correct various aberrations, including spherical aberration, when focused at infinity. By setting the lower limit of conditional expression (3) to 1.15, 1.30, 1.40, or even 1.50, the effect of this embodiment can be further ensured.

[0023] In the optical system OL according to this embodiment, the object-side lens group GA preferably includes, in order from the object side along the optical axis, a first lens La having negative refractive power and a second lens Lb having negative refractive power, which allows for excellent correction of various aberrations, including coma when focused at infinity.

[0024] It is desirable that the optical system OL according to this embodiment satisfy the following conditional expression (4). 1.00<(-fb) / f<30.00 (4) However, fb: focal length of second lens Lb

[0025] Conditional expression (4) defines an appropriate relationship between the focal length of second lens Lb and the focal length of optical system OL when focused at infinity. By satisfying conditional expression (4), various aberrations, including coma when focused at infinity, can be effectively corrected.

[0026] If the corresponding value of conditional expression (4) exceeds the upper limit, the refractive power of the second lens Lb becomes too weak, and it becomes necessary to increase the refractive power of the first lens La, making it difficult to correct various aberrations, including coma aberration, when focused at infinity. By setting the upper limit of conditional expression (4) to 25.00, 20.00, 15.00, or even 10.00, the effect of this embodiment can be further ensured.

[0027] If the value corresponding to conditional expression (4) falls below the lower limit, the refractive power of the second lens Lb becomes too strong, making it difficult to correct various aberrations, including coma when focused at infinity. By setting the lower limit of conditional expression (4) to 1.50, 2.00, 2.50, or even 2.75, the effect of this embodiment can be further ensured.

[0028] In the optical system OL according to this embodiment, it is desirable that the object-side lens group GA includes a plurality of positive lenses, which allows for excellent correction of various aberrations, including chromatic aberration, when focused at infinity.

[0029] It is desirable that the optical system OL according to this embodiment satisfy the following conditional expression (5). 15.0<νp1<35.0 (5) where νp1 is the Abbe number of the positive lens having the smallest Abbe number among the plurality of positive lenses in the object-side lens group GA.

[0030] Conditional expression (5) defines an appropriate range for the Abbe number of the positive lens having the smallest Abbe number among the plurality of positive lenses in the object-side lens group GA. By satisfying conditional expression (5), various aberrations, including chromatic aberration, can be effectively corrected when focused at infinity.

[0031] If the value corresponding to conditional expression (5) exceeds the upper limit, the Abbe number of the positive lens having the smallest Abbe number among the plurality of positive lenses in the object-side lens group GA becomes too large, making it difficult to correct various aberrations, including chromatic aberration, when focused at infinity. By setting the upper limit of conditional expression (5) to 32.5, 30.0, or even 27.5, the effect of this embodiment can be further ensured.

[0032] If the value corresponding to conditional expression (5) falls below the lower limit, the Abbe number of the positive lens having the smallest Abbe number among the plurality of positive lenses in the object-side lens group GA will become too small, making it difficult to correct various aberrations, including chromatic aberration, when focused at infinity. The effect of this embodiment can be further ensured by setting the lower limit of conditional expression (5) to 17.0, 20.0, 22.5, or even 24.0.

[0033] It is desirable that the optical system OL according to this embodiment satisfy the following conditional expression (6). 15.0<νp2<40.0 (6) where νp2 is the Abbe number of the positive lens having the second smallest Abbe number among the plurality of positive lenses in the object-side lens group GA.

[0034] Conditional expression (6) defines an appropriate range for the Abbe number of the positive lens having the second smallest Abbe number among the plurality of positive lenses in the object-side lens group GA. By satisfying conditional expression (6), various aberrations, including chromatic aberration, can be effectively corrected when focused at infinity.

[0035] If the value corresponding to conditional expression (6) exceeds the upper limit, the Abbe number of the positive lens having the second smallest Abbe number among the plurality of positive lenses in the object-side lens group GA becomes too large, making it difficult to correct various aberrations, including chromatic aberration, when focused at infinity. By setting the upper limit of conditional expression (6) to 39.0, 38.0, or even 37.0, the effect of this embodiment can be further ensured.

[0036] If the value corresponding to conditional expression (6) falls below the lower limit, the Abbe number of the positive lens having the second smallest Abbe number among the plurality of positive lenses in the object-side lens group GA will become too small, making it difficult to correct various aberrations, including chromatic aberration, when focused at infinity. The effect of this embodiment can be further ensured by setting the lower limit of conditional expression (6) to 17.0, 20.0, 25.0, or even 27.5.

[0037] It is desirable that the optical system OL according to this embodiment satisfy the following conditional expression (7). 0.30 <fp1 / fp2<2.20 ···(7) where fp1 is the focal length of the positive lens with the smallest Abbe number among the plurality of positive lenses in the object-side lens group GA. fp2: The focal length of the positive lens with the second smallest Abbe number among the multiple positive lenses in the object-side lens group GA

[0038] Conditional expression (7) defines an appropriate relationship between the focal length of the positive lens with the smallest Abbe number among the plurality of positive lenses in the object-side lens group GA and the focal length of the positive lens with the second smallest Abbe number among the plurality of positive lenses in the object-side lens group GA. By satisfying conditional expression (7), various aberrations, including chromatic aberration, can be effectively corrected when focused at infinity.

[0039] If the value corresponding to conditional expression (7) exceeds the upper limit, the refractive power of the positive lens having the smallest Abbe number among the plurality of positive lenses in the object-side lens group GA becomes too weak, making it difficult to correct various aberrations, including chromatic aberration, when focused at infinity. The effect of this embodiment can be further ensured by setting the upper limit of conditional expression (7) to 2.00, 1.75, 1.50, or even 1.20.

[0040] If the value corresponding to conditional expression (7) falls below the lower limit, the refractive power of the positive lens having the second smallest Abbe number among the plurality of positive lenses in the object-side lens group GA becomes too weak, making it difficult to correct various aberrations, including chromatic aberration, when focused at infinity. By setting the lower limit of conditional expression (7) to 0.50, 0.65, or even 0.80, the effect of this embodiment can be further ensured.

[0041] It is desirable that the optical system OL according to this embodiment satisfy the following conditional expression (8). 0.10 <fp1 / (-fa)<2.80 ···(8) where fp1 is the focal length of the positive lens with the smallest Abbe number among the plurality of positive lenses in the object-side lens group GA.

[0042] Conditional expression (8) defines an appropriate relationship between the focal length of the positive lens with the smallest Abbe number among the plurality of positive lenses in the object-side lens group GA and the focal length of the first lens La, which is located closest to the object in the object-side lens group GA. By satisfying conditional expression (8), various aberrations, including chromatic aberration, can be effectively corrected when focused at infinity.

[0043] If the value corresponding to conditional expression (8) exceeds the upper limit, the refractive power of the positive lens having the smallest Abbe number among the plurality of positive lenses in the object-side lens group GA becomes too weak, making it difficult to correct various aberrations, including chromatic aberration, when focused at infinity. The effect of this embodiment can be further ensured by setting the upper limit of conditional expression (8) to 2.50, 2.00, 1.50, or even 1.00.

[0044] If the value corresponding to conditional expression (8) falls below the lower limit, the refractive power of the positive lens having the smallest Abbe number among the plurality of positive lenses in the object-side lens group GA becomes too strong, making it difficult to correct various aberrations, including chromatic aberration, when focused at infinity. The effect of this embodiment can be further ensured by setting the lower limit of conditional expression (8) to 0.20, 0.25, 0.35, or even 0.40.

[0045] It is desirable that the optical system OL according to this embodiment satisfy the following conditional expression (9). 0.10 <fp2 / (-fa)<2.80 ···(9) where fp2 is the focal length of the positive lens with the second smallest Abbe number among the multiple positive lenses in the object-side lens group GA.

[0046] Conditional expression (9) defines an appropriate relationship between the focal length of the positive lens having the second smallest Abbe number among the plurality of positive lenses in the object-side lens group GA and the focal length of the first lens La, which is located closest to the object in the object-side lens group GA. By satisfying conditional expression (9), various aberrations, including chromatic aberration, can be effectively corrected when focused at infinity.

[0047] If the value corresponding to conditional expression (9) exceeds the upper limit, the refractive power of the positive lens having the second smallest Abbe number among the plurality of positive lenses in the object-side lens group GA becomes too weak, making it difficult to correct various aberrations, including chromatic aberration, when focused at infinity. The effect of this embodiment can be further ensured by setting the upper limit of conditional expression (9) to 2.50, 2.00, 1.50, or even 1.00.

[0048] If the value corresponding to conditional expression (9) falls below the lower limit, the refractive power of the positive lens having the second smallest Abbe number among the plurality of positive lenses in the object-side lens group GA becomes too strong, making it difficult to correct various aberrations, including chromatic aberration, when focused at infinity. The effect of this embodiment can be further ensured by setting the lower limit of conditional expression (9) to 0.20, 0.25, 0.35, or even 0.45.

[0049] In the optical system OL according to this embodiment, it is desirable that at least two lens surfaces in the at least one focusing lens group are aspherical, which makes it possible to suppress fluctuations in various aberrations, including coma, when focusing from an object at infinity to a close object.

[0050] In the optical system OL according to this embodiment, it is desirable that at least one lens surface in the at least one focusing lens group be an aspheric surface with a stronger positive refractive power on the periphery than on the center, thereby suppressing fluctuations in various aberrations, including coma, when focusing from an object at infinity to a close object.

[0051] In the optical system OL according to this embodiment, it is desirable that at least one lens surface in the at least one focusing lens group be an aspheric surface with a stronger negative refractive power on the periphery than on the center, thereby suppressing fluctuations in various aberrations, including coma, when focusing from an object at infinity to a close object.

[0052] In the optical system OL according to this embodiment, the at least one focusing lens group comprises a first focusing lens group GF1 and a second focusing lens group GF2 that is disposed closer to the image plane than the first focusing lens group GF1, and it is desirable that the first focusing lens group GF1 and the second focusing lens group GF2 move along the optical axis on different trajectories during focusing, thereby suppressing fluctuations in various aberrations, including coma, during focusing from an object at infinity to a close object.

[0053] It is desirable that the optical system OL according to this embodiment satisfy the following conditional expression (10). 0.10 <fF1 / fF2<20.00 ···(10) where fF1 is the focal length of the first focusing lens group GF1 fF2: focal length of the second focusing lens group GF2

[0054] Conditional expression (10) defines an appropriate relationship between the focal length of the first focusing lens group GF1 and the focal length of the second focusing lens group GF2. By satisfying conditional expression (10), fluctuations in various aberrations, including coma, can be suppressed when focusing from an object at infinity to a close object.

[0055] If the value corresponding to conditional expression (10) exceeds the upper limit, the refractive power of the second focusing lens group GF2 becomes too strong, making it difficult to suppress fluctuations in various aberrations, including coma, when focusing from an object at infinity to a close object. By setting the upper limit of conditional expression (10) to 17.50, 15.00, 12.50, or even 10.00, the effects of this embodiment can be made more certain.

[0056] If the corresponding value of conditional expression (10) falls below the lower limit, the refractive power of the first focusing lens group GF1 becomes too strong, making it difficult to suppress fluctuations in various aberrations, including coma, when focusing from an object at infinity to an object at a close distance. By setting the lower limit of conditional expression (10) to 0.25, 0.50, 0.75, or even 1.00, the effect of this embodiment can be made more certain.

[0057] It is desirable that the optical system OL according to this embodiment satisfy the following conditional expression (11). 0.10 <MF1 / MF2<10.00 ···(11) where MF1 is the absolute value of the movement of the first focusing lens group GF1 when focusing from an object at infinity to an object at a close distance. MF2: Absolute value of the movement of the second focusing lens group GF2 when focusing from an object at infinity to an object at a close distance

[0058] Conditional expression (11) defines an appropriate relationship between the amount of movement of the first focusing lens group GF1 and the amount of movement of the second focusing lens group GF2 when focusing from an object at infinity to an object at a close distance. By satisfying conditional expression (11), fluctuations in various aberrations, including coma, can be suppressed when focusing from an object at infinity to an object at a close distance.

[0059] If the value corresponding to conditional expression (11) exceeds the upper limit, the amount of movement of the first focusing lens group GF1 when focusing from an object at infinity to an object at a close distance becomes too large, making it difficult to suppress fluctuations in various aberrations, including coma, when focusing from an object at infinity to an object at a close distance. The effect of this embodiment can be further ensured by setting the upper limit of conditional expression (11) to 7.50, 5.00, 3.50, or even 2.00.

[0060] If the value corresponding to conditional expression (11) is below the lower limit, the amount of movement of the second focusing lens group GF2 when focusing from an object at infinity to an object at a close distance becomes too large, making it difficult to suppress fluctuations in various aberrations, including coma, when focusing from an object at infinity to an object at a close distance. The effect of this embodiment can be further ensured by setting the lower limit of conditional expression (11) to 0.30, 0.50, 0.75, or even 0.90.

[0061] It is desirable that the optical system OL according to this embodiment satisfy the following conditional expression (12). 0.10<βF1 / βF2<3.00 (12) where βF1 is the lateral magnification of the first focusing lens group GF1 when focused at infinity. βF2: Lateral magnification of the second focusing lens group GF2 when focused at infinity

[0062] Conditional expression (12) defines an appropriate relationship between the lateral magnification of the first focusing lens group GF1 when focused at infinity and the lateral magnification of the second focusing lens group GF2 when focused at infinity. By satisfying conditional expression (12), fluctuations in various aberrations, including coma, can be suppressed when focusing from an object at infinity to a close object.

[0063] If the value corresponding to conditional expression (12) exceeds the upper limit, the lateral magnification of the first focusing lens group GF1 when focused at infinity becomes too large, making it difficult to suppress fluctuations in various aberrations, including coma, when focusing from an object at infinity to an object at a close distance. The effect of this embodiment can be further ensured by setting the upper limit of conditional expression (12) to 2.75, 2.50, 2.25, or even 2.00.

[0064] If the value corresponding to conditional expression (12) falls below the lower limit, the lateral magnification of the second focusing lens group GF2 when focused at infinity becomes too large, making it difficult to suppress fluctuations in various aberrations, including coma, when focusing from an object at infinity to an object at a close distance. By setting the lower limit of conditional expression (12) to 0.20, 0.35, or even 0.50, the effects of this embodiment can be made even more certain.

[0065] It is desirable that the optical system OL according to this embodiment satisfy the following conditional expression (13). 0.20 <Bf / f<0.63 ···(13) where Bf is the back focus of the optical system OL when focused at infinity.

[0066] Conditional expression (13) defines an appropriate relationship between the back focus of the optical system OL when focused at infinity and the focal length of the optical system OL when focused at infinity. In this embodiment, the back focus of the optical system OL is the air-equivalent distance on the optical axis from the lens surface of the optical system OL closest to the image plane to the image plane I. By satisfying conditional expression (13), various aberrations, including coma when focused at infinity, can be effectively corrected.

[0067] If the value corresponding to conditional expression (13) exceeds the upper limit, the back focus of the optical system OL when focused at infinity becomes large relative to the focal length of the optical system OL when focused at infinity, making it difficult to correct various aberrations such as coma when focused at infinity. The effect of this embodiment can be further ensured by setting the upper limit of conditional expression (13) to 0.55, 0.50, 0.45, or even 0.40.

[0068] If the value corresponding to conditional expression (13) is below the lower limit, the back focus of the optical system OL when focused at infinity becomes small relative to the focal length of the optical system OL when focused at infinity, making it difficult to correct various aberrations such as coma when focused at infinity. The effect of this embodiment can be further ensured by setting the lower limit of conditional expression (13) to 0.22, 0.25, 0.27, or even 0.30.

[0069] It is desirable that the optical system OL according to this embodiment satisfy the following conditional expression (14). 1.00<(-fR) / f<7.20 (14) where fR is the focal length of the subsequent lens group GR

[0070] Conditional expression (14) defines an appropriate relationship between the focal length of the subsequent lens group GR and the focal length of the optical system OL when focused at infinity. By satisfying conditional expression (14), various aberrations, including coma when focused at infinity, can be effectively corrected.

[0071] If the value corresponding to conditional expression (14) exceeds the upper limit, the refractive power of the subsequent lens group GR becomes too weak, making it difficult to correct various aberrations, including coma when focused at infinity. By setting the upper limit of conditional expression (14) to 7.00, 6.50, 6.00, or even 5.50, the effect of this embodiment can be made even more certain.

[0072] If the value corresponding to conditional expression (14) falls below the lower limit, the refractive power of the subsequent lens group GR becomes too strong, making it difficult to correct various aberrations, including coma when focused at infinity. By setting the lower limit of conditional expression (14) to 1.20, 1.50, 2.00, or even 2.50, the effect of this embodiment can be made even more certain.

[0073] It is desirable that the optical system OL according to this embodiment satisfy the following conditional expression (15). 1.00 <D1 / D2R<4.00 ···(15) where D1 is the distance on the optical axis from the lens surface of the object-side lens group GA closest to the object to the lens surface of the object-side lens group GA closest to the image plane. D2R: The distance on the optical axis from the lens surface of the focusing lens group closest to the object to the lens surface of the succeeding lens group GR closest to the image plane when focused at infinity.

[0074] Conditional expression (15) defines an appropriate relationship between the axial distance from the lens surface of the object-side lens group GA closest to the object to the lens surface of the object-side lens group GA closest to the image plane, and the axial distance from the lens surface of the focusing lens group closest to the object to the lens surface of the subsequent lens group GR closest to the image plane when focused at infinity. By satisfying conditional expression (15), various aberrations, including spherical aberration, can be effectively corrected when focused at infinity.

[0075] If the value corresponding to conditional expression (15) exceeds the upper limit, the distance on the optical axis from the lens surface in the object-side lens group GA closest to the object to the lens surface in the object-side lens group GA closest to the image plane becomes too long, making it difficult to correct various aberrations, including spherical aberration, when focused at infinity. The effect of this embodiment can be further ensured by setting the upper limit of conditional expression (15) to 3.75, 3.50, 3.00, or even 2.50.

[0076] If the value corresponding to conditional expression (15) falls below the lower limit, the distance on the optical axis from the lens surface of the focusing lens group closest to the object to the lens surface of the subsequent lens group GR closest to the image plane when focused at infinity becomes too large, making it difficult to correct various aberrations, including spherical aberration, when focused at infinity. By setting the lower limit of conditional expression (15) to 1.20, 1.50, or even 1.75, the effects of this embodiment can be further ensured.

[0077] In the optical system OL according to this embodiment, the object-side lens group GA has a cemented lens CL arranged closest to the image plane in the object-side lens group GA, and the cemented lens CL of the object-side lens group GA has a negative lens and a positive lens cemented together, and it is desirable that the cemented lens CL satisfy the following conditional expression (16): 0.03 <Dn / Dp<0.30 ···(16) where Dn is the thickness on the optical axis of the negative lens in the cemented lens CL of the object-side lens group GA. Dp: the thickness of the positive lens on the optical axis in the cemented lens CL of the object-side lens group GA

[0078] Conditional expression (16) defines an appropriate relationship between the axial thickness of the negative lens in the cemented lens CL of the object-side lens group GA and the axial thickness of the positive lens in the cemented lens CL of the object-side lens group GA. By satisfying conditional expression (16), various aberrations, including spherical aberration, can be effectively corrected when focused at infinity.

[0079] If the value corresponding to conditional expression (16) exceeds the upper limit, the thickness of the negative lens in the cemented lens CL of the object-side lens group GA becomes too large on the optical axis, making it difficult to correct various aberrations, including spherical aberration, when focused at infinity. By setting the upper limit of conditional expression (16) to 0.25, 0.20, 0.17, or even 0.15, the effect of this embodiment can be further ensured.

[0080] If the value corresponding to conditional expression (16) is below the lower limit, the thickness on the optical axis of the positive lens in the cemented lens CL of the object-side lens group GA becomes too large, making it difficult to correct various aberrations, including spherical aberration, when focused at infinity. By setting the lower limit of conditional expression (16) to 0.05, 0.08, or even 0.10, the effect of this embodiment can be made more certain.

[0081] Next, a manufacturing method of the optical system OL according to this embodiment will be outlined with reference to FIG. 14. First, an object-side lens group GA having positive refractive power, at least one focusing lens group (GF1, GF2) having positive refractive power, and a subsequent lens group GR are arranged, in order from the object side along the optical axis (Step ST1). Next, the at least one focusing lens group moves along the optical axis during focusing, and the object-side lens group GA and the subsequent lens group GR are fixed relative to the image plane I (Step ST2). An aperture stop S is also arranged closer to the image plane than the object-side lens group GA (Step ST3). Then, each lens is arranged in the lens barrel so as to satisfy at least the above conditional expressions (1) and (2) (Step ST4). This manufacturing method makes it possible to manufacture an optical system that is compact yet has good optical performance. [Example]

[0082] Optical systems OL according to examples of this embodiment will be described below with reference to the drawings. Figures 1, 3, 5, 7, 9, and 11 are cross-sectional views showing the configurations and refractive power distributions of optical systems OL {OL(1) to OL(6)} according to examples 1 to 6. In the cross-sectional views of the optical systems OL(1) to OL(6) according to examples 1 to 6, arrows indicate the direction of movement of each lens group along the optical axis when focusing from infinity to a close-distance object.

[0083] 1, 3, 5, 7, 9, and 11, 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.

[0084] Tables 1 to 6 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, Table 5 for Example 5, and Table 6 for Example 6. 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.

[0085] In the [Overall Specifications] table, f is the focal length of the entire lens system, FNO is the F-number, ω is the half angle of view (unit: ° (degrees)), and Y is the image height. TL is the distance on the optical axis from the lens surface closest to the object to the lens surface closest to the image plane when focused at infinity, plus Bf (back focus), and Bf is the distance on the optical axis from the lens surface closest to the image plane to the image plane when focused at infinity (air equivalent distance).

[0086] In the table of "Overall Specifications," Da indicates the distance on the optical axis from the aperture stop to the image plane when focused at infinity. fa indicates the focal length of the first negative lens. fb indicates the focal length of the second negative lens. fp1 indicates the focal length of the positive lens with the smallest Abbe number among the multiple positive lenses in the object-side lens group. fp2 indicates the focal length of the positive lens with the second smallest Abbe number among the multiple positive lenses in the object-side lens group. MF1 indicates the absolute value of the movement amount of the first focusing lens group when focusing from an object at infinity to a close object. MF2 indicates the absolute value of the movement amount of the second focusing lens group when focusing from an object at infinity to a close object. βF1 indicates the lateral magnification of the first focusing lens group when focused at infinity. βF2 indicates the lateral magnification of the second focusing lens group when focused at infinity. D1 denotes the distance on the optical axis from the lens surface of the object-side lens group closest to the object to the lens surface of the object-side lens group closest to the image plane, and D2R denotes the distance on the optical axis from the lens surface of the focusing lens group closest to the object to the lens surface of the subsequent lens group closest to the image plane when focused at infinity.

[0087] In the [Lens Specifications] table, the surface number indicates the order of the optical surface from the object side along the direction of light ray travel, R is the radius of curvature of each optical surface (surfaces whose center of curvature is on the image side have a positive value), D is the surface spacing, which is the distance on the optical axis from each optical surface to the next optical surface (or image plane), nd is the refractive index of the optical element material with respect to the d-line, and νd is the Abbe number of the optical element material with respect to the d-line. The "∞" next to the radius of curvature indicates a flat surface or an aperture, and (stop S) indicates the aperture stop S. The refractive index of air, nd = 1.00000, is omitted. If the optical surface is aspherical, an * is added to the surface number, and the paraxial radius of curvature is shown in the "radius of curvature R" column.

[0088] In the [Aspherical Data] table, the shape of the aspherical surface shown in [Lens Specifications] is shown by the following formula (A). X(y) is the distance (amount of sag) along the optical axis from the tangent plane at the vertex of the aspherical surface to the position on the aspherical surface at height y, R is the radius of curvature of the reference sphere (paraxial radius of curvature), κ is the conic constant, and Ai is the ith aspherical coefficient. "En" is the square root of the square root of the aspherical surface. -nFor example, 1.234E-05 = 1.234 x 10 -5 The second-order aspherical coefficient A2 is 0, and is therefore omitted.

[0089] X(y)=(y 2 / R) / {1+(1-κ×y 2 / R 2 ) 1 / 2}+A4×y 4 +A6×y 6 +A8×y 8 +A10×y 10 …(A)

[0090] The [Variable Distance Data] table shows the surface spacing for surface number i, which is specified as (Di) in the [Lens Specifications] table. The [Variable Distance Data] table also shows the surface spacing when focused at infinity and when focused at close distances. In the [Variable Distance Data] table, f represents the focal length of the entire lens system, and β represents the magnification. Furthermore, D0 represents the distance from the object to the optical surface closest to the object in the optical system.

[0091] The [Lens Group Data] table shows the starting surface (the surface closest to the object) and focal length of each lens group.

[0092] 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.

[0093] The explanation of the tables up to this point is common to all the embodiments, and duplicate explanations will be omitted below.

[0094] (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 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 and the third lens group G3 move along the optical axis toward the object side along different trajectories (movement amounts), changing the spacing between adjacent lens groups. During focusing, the positions of the first lens group G1 and the fourth lens group G4 are fixed relative to the image plane I. The sign (+) or (-) attached to each lens group symbol indicates the refractive power of the lens group, and this is the same in all the following embodiments.

[0095] An aperture stop S is disposed between the first lens group G1 and the second lens group G2. During focusing, the position of the aperture stop S is fixed relative to the image plane I. In this embodiment, the first lens group G1 corresponds to the object-side lens group GA, the second lens group G2 corresponds to the first focusing lens group GF1, the third lens group G3 corresponds to the second focusing lens group GF2, and the fourth lens group G4 corresponds to the subsequent lens group GR.

[0096] The first lens group G1 is composed of, arranged in order from the object side along the optical axis, a negative meniscus lens L11 with a convex surface facing the object side, a negative meniscus lens L12 with a convex surface facing the object side, a cemented positive lens formed by cementing a biconvex positive lens L13 and a biconcave negative lens L14, a cemented negative lens formed by cementing a biconcave negative lens L15 and a biconvex positive lens L16, a biconvex positive lens L17, a biconvex positive lens L18, and a cemented negative lens formed by cementing a biconcave negative lens L19 and a biconvex positive lens L110. The lens surface of the negative meniscus lens L12 facing the image plane is aspheric. In this embodiment, the negative meniscus lens L11 corresponds to the first lens La, and the negative meniscus lens L12 corresponds to the second lens Lb. The cemented negative lens formed by cementing the negative lens L19 and the positive lens L110 corresponds to the cemented lens CL of the object-side lens group GA.

[0097] 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 biconvex positive lens L22.

[0098] The third lens group G3 is composed of, arranged in order from the object side along the optical axis, a positive meniscus lens L31 with a convex surface facing the object side and a positive meniscus lens L32 with a convex surface facing the object side. The image-side lens surface of the positive meniscus lens L31 is an aspheric surface with a stronger positive refractive power on the periphery side than on the center side. The image-side lens surface of the positive meniscus lens L32 is an aspheric surface with a stronger negative refractive power on the periphery side than on the center side.

[0099] The fourth lens group G4 is composed of, arranged in order from the object side along the optical axis, a positive meniscus lens L41 with its concave surface facing the object side and a biconcave negative lens L42. An image surface I is located on the image side of the fourth lens group G4.

[0100] Table 1 below lists the values ​​of the specifications of the optical system according to the first example.

[0101] (Table 1) [Overall specifications] f=34.301 FNO=1.230 ω=32.681 Y=21.600 TL=145.455 Bf=11.456 Da=62.617 fa=-82.219 fb=-199.997 fp1=42.746 fp2=44.756 MF1=1.369 MF2=1.416 βF1=0.943 βF2=0.570 D1=80.839 D2R=38.009 [Lens specifications] Surface number RD nd νd 1 96.047 2.000 1.48749 70.31 2 28.087 9.219 3 66.416 1.800 1.58887 61.13 4* 42.041 2.388 5 47.837 8.233 2.00100 29.12 6 -645.006 1.500 1.49782 82.57 7 35.910 11.438 8 -33.782 1.500 1.85451 25.15 9 80.983 5.585 1.56732 42.58 10 -217.995 0.200 11 237.343 8.059 2.00069 25.46 12 -51.294 0.200 13 44.432 10.369 1.59349 67.00 14 -144.859 2.518 15 -99.402 1.500 1.69895 30.13 16 27.200 14.331 1.59319 67.90 17 -86.856 2.000 18∞ (D18) (S aperture) 19 -38.048 1.300 1.68376 37.64 20 178.836 0.200 21 41.104 9.000 1.59349 67.00 22 -68.514 (D22) 23 36.893 6.200 1.85108 40.12 24* 75.937 4.486 25 157.349 2.500 1.77387 47.25 26* 161.771 (D26) 27 -597.200 3.598 1.94595 17.98 28 -68.766 1.916 29 -40.274 1.500 1.73037 32.23 30 834.207 Bf [Aspherical data] Side 4 κ=1.0000,A4=-1.39004E-06,A6=-9.76153E-10,A8=-1.35116E-12,A10=-7.50960E-16 Page 24 κ=1.0000,A4=-4.67477E-06,A6=-5.48120E-09,A8=3.46635E-11,A10=-1.11525E-14 Page 26 κ=1.0000,A4=2.09207E-05,A6=2.10855E-08,A8=-1.68530E-11,A10=-2.78769E-14 [Variable Interval Data] Infinity focus Close focus f=34.301 β=-0.03333 D0 ∞ 993.600 D18 13.152 11.783 D22 2.047 2.000 D26 5.262 6.678 Bf 11.456 11.456 [Lens group data] Group starting plane focal length G1 1 60.284 G2 19 493.944 G3 23 77.173 G4 27 -155.922

[0102] 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.

[0103] From the various aberration diagrams, it can be seen that the optical system according to Example 1 has excellent imaging performance, with various aberrations being well corrected not only when focusing at infinity but also when focusing at close distances.

[0104] (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 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 and the third lens group G3 move along the optical axis toward the object side along different trajectories (movement amounts), 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.

[0105] An aperture stop S is disposed between the first lens group G1 and the second lens group G2. During focusing, the position of the aperture stop S is fixed relative to the image plane I. In this embodiment, the first lens group G1 corresponds to the object-side lens group GA, the second lens group G2 corresponds to the first focusing lens group GF1, the third lens group G3 corresponds to the second focusing lens group GF2, and the fourth lens group G4 corresponds to the subsequent lens group GR.

[0106] The first lens group G1 is composed of, arranged in order from the object side along the optical axis, a negative meniscus lens L11 with a convex surface facing the object side, a negative meniscus lens L12 with a convex surface facing the object side, a cemented positive lens formed by cementing a biconvex positive lens L13 and a biconcave negative lens L14, a cemented negative lens formed by cementing a biconcave negative lens L15 and a biconvex positive lens L16, a biconvex positive lens L17, a biconvex positive lens L18, and a cemented negative lens formed by cementing a biconcave negative lens L19 and a biconvex positive lens L110. The lens surface of the negative meniscus lens L12 facing the image plane is aspheric. In this embodiment, the negative meniscus lens L11 corresponds to the first lens La, and the negative meniscus lens L12 corresponds to the second lens Lb. The cemented negative lens formed by cementing the negative lens L19 and the positive lens L110 corresponds to the cemented lens CL of the object-side lens group GA.

[0107] 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 biconvex positive lens L22.

[0108] The third lens group G3 is composed of, arranged in order from the object side along the optical axis, a cemented positive lens formed by cementing together a biconvex positive lens L31 and a biconcave negative lens L32, and a negative meniscus lens L33 with its concave surface facing the object side. The lens surfaces on both sides of the negative meniscus lens L33 are aspheric, with stronger negative refractive power on the periphery than on the center.

[0109] The fourth lens group G4 is composed of, arranged in order from the object side along the optical axis, a positive meniscus lens L41 with its concave surface facing the object side and a biconcave negative lens L42. An image surface I is located on the image side of the fourth lens group G4.

[0110] Table 2 below lists the values ​​of the specifications of the optical system according to the second example.

[0111] (Table 2) [Overall specifications] f=34.300 FNO=1.230 ω=32.676 Y=21.600 TL=145.455 Bf=11.455 Da=62.644 fa=-90.291 fb=-183.628 fp1=43.749 fp2=46.312 MF1=1.365 MF2=1.340 βF1=0.935 βF2=0.532 D1=80.811 D2R=38.559 [Lens specifications] Surface number RD nd νd 1 72.093 2.000 1.48749 70.31 2 27.081 11.466 3 105.428 1.800 1.51680 64.13 4* 49.653 1.202 5 47.334 7.850 2.00100 29.12 6 -2063.273 1.500 1.49782 82.57 7 34.755 11.769 8 -32.107 1.500 1.85451 25.15 9 82.520 5.950 1.67003 47.14 10 -198.954 0.200 11 391.739 7.906 2.00069 25.46 12 -48.789 0.200 13 41.194 11.022 1.59349 67.00 14 -135.101 1.669 15 -112.838 1.500 1.73037 32.23 16 27.200 13.277 1.59319 67.90 17 -122.895 2.000 18 ∞ (D18) 19 -42.056 1.300 1.68376 37.64 20 240.838 0.200 21 38.726 7.500 1.59319 67.90 22 -118.915 (D22) 23 42.490 7.198 1.83481 42.73 24 -124.265 1.500 1.68376 37.64 25 96.988 5.998 26* -257.390 2.500 1.77387 47.25 27* -264.366 (D27) 28 -531.885 3.492 1.94595 17.98 29 -71.866 1.741 30 -43.260 1.500 1.73037 32.23 31 848.999 Bf [Aspherical surface] Page 4 κ=1.0000,A4=-1.34774E-06,A6=-9.46928E-10,A8=-1.46439E-12,A10=-3.40961E-16 Page 26 κ=1.0000,A4=-7.46350E-06,A6=6.20342E-08,A8=-1.63956E-10,A10=4.03734E-14 Page 27 κ=1.0000,A4=9.35182E-06,A6=7.30804E-08,A8=-1.33669E-10,A10=1.93285E-14 [Variable Interval Data] Infinity focus Close focus f=34.300 β=-0.03333 D0 ∞ 994.412 D18 12.611 11.246 D22 2.244 2.268 D27 3.404 4.744 Bf 11.455 11.455 [Lens group data] Group starting plane focal length G1 1 65.214 G2 19 629.134 G3 23 70.033 G4 27 -165.983

[0112] Fig. 4(A) is a diagram showing various aberrations of the optical system according to Example 2 when focusing at infinity. Fig. 4(B) is a diagram showing various aberrations of the optical system according to Example 2 when focusing at close range. It can be seen from the diagrams that the optical system according to Example 2 has excellent imaging performance, with various aberrations being well corrected not only when focusing at infinity but also when focusing at close range.

[0113] (Third Example) Example 3 will be described with reference to FIGS. 5 to 6 and Table 3. FIG. 5 shows the lens configuration of an optical system according to Example 3. 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 positive refractive power, and a third lens group G3 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 object side, changing the spacing between adjacent lens groups. During focusing, the positions of the first lens group G1 and the third lens group G3 are fixed relative to the image plane I.

[0114] An aperture stop S is disposed between the first lens group G1 and the second lens group G2. During focusing, the position of the aperture stop S is fixed relative to the image plane I. In this embodiment, the first lens group G1 corresponds to the object-side lens group GA, the second lens group G2 corresponds to the focusing lens group GF, and the third lens group G3 corresponds to the subsequent lens group GR.

[0115] The first lens group G1 is composed of, arranged in order from the object side along the optical axis, a negative meniscus lens L11 with a convex surface facing the object side, a negative meniscus lens L12 with a convex surface facing the object side, a cemented positive lens formed by cementing a biconvex positive lens L13 and a biconcave negative lens L14, a negative meniscus lens L15 with a concave surface facing the object side, a biconvex positive lens L16, a biconvex positive lens L17, and a cemented negative lens formed by cementing a biconcave negative lens L18 and a biconvex positive lens L19. The lens surface of the negative meniscus lens L12 facing the image plane is aspheric. In this embodiment, the negative meniscus lens L11 corresponds to the first lens La, and the negative meniscus lens L12 corresponds to the second lens Lb. The cemented negative lens formed by cementing the negative lens L18 and the positive lens L19 corresponds to the cemented lens CL of the object-side lens group GA.

[0116] The second lens group G2 is composed of, arranged in order from the object side along the optical axis, a negative meniscus lens L21 with a concave surface facing the object side, a biconvex positive lens L22, a positive meniscus lens L23 with a convex surface facing the object side, a negative meniscus lens L24 with a convex surface facing the object side, and a biconvex positive lens L25. The object-side lens surface of the positive lens L25 is an aspheric surface with a stronger positive refractive power on the periphery side than on the center side. The image-side lens surface of the positive lens L25 is an aspheric surface with a stronger negative refractive power on the periphery side than on the center side.

[0117] The third lens group G3 is composed of, arranged in order from the object side along the optical axis, a cemented positive lens formed by cementing together a biconvex positive lens L31 and a negative meniscus lens L32 with its concave surface facing the object side, and a biconcave negative lens L33. An image surface I is located on the image side of the third lens group G3.

[0118] Table 3 below lists the values ​​of the specifications of the optical system according to the third example.

[0119] (Table 3) [Overall specifications] f=34.300 FNO=1.231 ω=32.7 Y=21.600 TL=147.455 Bf=11.455 Da=66.886 fa=-87.362 fb=-200.000 fp1=42.090 fp2=44.233 MF1= ― MF2= ― βF1= ― βF2= ― D1=78.569 D2R=41.861 [Lens specifications] Surface number RD nd νd 1 89.962 2.000 1.51680 64.14 2 29.834 8.038 3 64.800 1.800 1.51680 64.13 4* 39.453 4.204 5 53.072 8.539 2.00069 25.46 6 -187.660 1.500 1.59319 67.90 7 36.874 12.363 8 -35.072 4.480 1.85451 25.15 9 -468.769 0.214 10 255.225 7.580 2.00100 29.12 11 -52.775 0.200 12 42.168 10.958 1.59349 67.00 13 -119.114 1.293 14 -123.398 1.500 1.77047 29.74 15 27.200 13.900 1.59319 67.90 16 -94.098 2.000 17 ∞ (D17) 18 -36.369 1.300 1.77047 29.74 19 -153.657 0.200 20 49.062 8.325 1.59319 67.90 21 -69.631 0.200 22 41.063 4.271 2.00100 29.12 23 159.398 2.397 24 140.617 1.500 1.73037 32.23 25 31.673 3.168 26* 140.558 2.500 1.85108 40.12 27* -307.951 (D27) 28 261.365 9.478 1.94595 17.98 29 -44.722 1.500 1.85451 25.15 30 -186.773 2.314 31 -54.858 1.500 1.85451 25.15 32 851.953 Bf [Aspherical surface] Page 4 κ=1.0000,A4=-6.88705E-07,A6=1.20385E-09,A8=-4.51400E-12,A10=5.17307E-15 Page 26 κ=1.0000,A4=4.20055E-06,A6=3.33468E-08,A8=1.34441E-10,A10=-5.18786E-13 Page 27 κ=1.0000,A4=1.48019E-05,A6=3.06066E-08,A8=2.37704E-10,A10=-6.93790E-13 [Can change the interval データ] Infinity focus state and close-up focus state f=34.300 β=-0.03333 D0 ∞ 997.4088 D17 13.570 12.207 D27 3.208 4.571 Bf 11.455 11.455 [Lens group data] Group starting plane focal length G1 1 73.146 G2 18 62.301 G3 28 -174.616

[0120] Fig. 6(A) is a diagram showing various aberrations of the optical system according to Example 3 when focusing at infinity. Fig. 6(B) is a diagram showing various aberrations of the optical system according to Example 3 when focusing at close range. It can be seen from the diagrams that the optical system according to Example 3 has excellent imaging performance, with various aberrations being well corrected not only when focusing at infinity but also when focusing at close range.

[0121] (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 according to Example 4. The optical system OL(4) according to 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 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 and the third lens group G3 move along the optical axis toward the object side along different trajectories (movement amounts), 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.

[0122] An aperture stop S is disposed between the first lens group G1 and the second lens group G2. During focusing, the position of the aperture stop S is fixed relative to the image plane I. In this embodiment, the first lens group G1 corresponds to the object-side lens group GA, the second lens group G2 corresponds to the first focusing lens group GF1, the third lens group G3 corresponds to the second focusing lens group GF2, and the fourth lens group G4 corresponds to the subsequent lens group GR.

[0123] The first lens group G1 is composed of, arranged in order from the object side along the optical axis, a negative meniscus lens L11 with a convex surface facing the object side, a cemented positive lens formed by cementing a biconvex positive lens L12 and a biconcave negative lens L13, a cemented negative lens formed by cementing a biconcave negative lens L14 and a positive meniscus lens L15 with a convex surface facing the object side, a cemented positive lens formed by cementing a biconvex positive lens L16 and a negative meniscus lens L17 with a concave surface facing the object side, a positive meniscus lens L18 with a convex surface facing the object side, and a cemented negative lens formed by cementing a biconvex positive lens L19 and a biconcave negative lens L110. In this embodiment, the negative meniscus lens L11 corresponds to the first lens La. The cemented negative lens formed by cementing the positive lens L19 and the negative lens L110 corresponds to the cemented lens CL of the object-side lens group GA.

[0124] The second lens group G2 is composed of, arranged in order from the object side along the optical axis, a negative meniscus lens L21 with a concave surface facing the object side, a biconvex positive lens L22, and a negative meniscus lens L23 with a concave surface facing the object side. The object-side lens surface of the negative meniscus lens L23 is an aspheric surface with a stronger positive refractive power on the periphery side than on the center side. The image-side lens surface of the negative meniscus lens L23 is an aspheric surface with a stronger negative refractive power on the periphery side than on the center side.

[0125] The third lens group G3 is composed of, arranged in order from the object side along the optical axis, a positive meniscus lens L31 with a concave surface facing the object side and a negative meniscus lens L32 with a concave surface facing the object side. The image-side lens surface of the positive meniscus lens L31 is an aspheric surface with a stronger negative refractive power on the periphery side than on the center side. The object-side lens surface of the negative meniscus lens L32 is an aspheric surface with a stronger positive refractive power on the periphery side than on the center side.

[0126] The fourth lens group G4 is composed of, in order from the object side along the optical axis, a positive meniscus lens L41 with its concave surface facing the object side and a biconcave negative lens L42 cemented together. An image surface I is located on the image side of the fourth lens group G4.

[0127] Table 4 below lists the values ​​of the specifications of the optical system according to the fourth example.

[0128] (Table 4) [Overall specifications] f=34.300 FNO=1.228 ω=32.697 Y=21.600 TL=155.455 Bf=11.455 Da=64.555 fa=-78.778 fb=45.033 fp1=70.013 fp2=45.033 MF1=1.122 MF2=0.591 βF1=0.490 βF2=0.744 D1=85.325 D2R=39.713 [Lens specifications] Surface number RD nd νd 1 81.239 2.000 1.59349 67.00 2 29.403 11.650 3 97.417 9.313 1.90265 35.77 4 -66.592 1.500 1.51742 52.20 5 37.688 11.679 6 -36.576 3.997 1.73037 32.23 7 57.862 5.275 1.94595 17.98 8 437.731 0.200 9 137.189 14.813 1.84850 43.79 10 -31.982 1.500 1.85451 25.15 11 -58.341 0.200 12 50.708 7.542 1.59319 67.90 13 173.475 0.200 14 50.175 13.955 1.59319 67.90 15 -45.041 1.500 1.64769 33.73 16 49.712 5.575 17∞ (D17) (Aperture S) 18 -42.349 1.500 1.61266 44.46 19 -303.712 0.200 20 30.793 9.330 1.59349 67.00 21 -73.903 0.200 22* -74.759 2.000 1.88202 37.23 23* -78.949 (D23) 24 -117.169 3.976 1.77387 47.25 25* -26.746 0.564 26* -30.019 3.648 1.58887 61.13 27 -41.705 (D27) 28 -65.973 6.366 1.94595 17.98 29 -27.107 1.500 1.77047 29.74 30 90.644 Bf [Aspherical data] Page 22 κ=1.0000,A4=1.73688E-05,A6=9.00046E-08,A8=-3.66508E-10,A10=3.45942E-13 Page 23 κ=1.0000,A4=2.84915E-05,A6=9.29029E-08,A8=-3.03655E-10,A10=1.96904E-13 Page 25 κ=1.0000,A4=5.79685E-05,A6=-1.66905E-07,A8=4.04878E-10,A10=-3.50430E-13 Page 26 κ=1.0000,A4=6.83994E-05,A6=-2.43826E-07,A8=5.82093E-10,A10=-5.75702E-13 [Variable Interval Data] Infinity focus Close focus f=34.300 β=-0.03333 D0 ∞ 988.825 D17 13.387 12.265 D23 8.429 8.961 D27 2.000 2.591 Bf 11.455 11.455 [Lens group data] Group starting plane focal length G1 1 75.723 G2 18 69.782 G3 24 58.312 G4 28 -60.553

[0129] Fig. 8(A) is a diagram showing various aberrations of the optical system according to Example 4 when focusing at infinity. Fig. 8(B) is a diagram showing various aberrations of the optical system according to Example 4 when focusing at close range. It can be seen from the diagrams that the optical system according to Example 4 has excellent imaging performance, with various aberrations being well corrected not only when focusing at infinity but also when focusing at close range.

[0130] (Fifth Example) Example 5 will be described with reference to FIGS. 9 and 10 and Table 5. FIG. 9 shows the lens configuration of an optical system according to Example 5. The optical system OL(5) according to 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 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 and the third lens group G3 move along the optical axis toward the object side along different trajectories (movement amounts), 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.

[0131] An aperture stop S is disposed between the first lens group G1 and the second lens group G2. During focusing, the position of the aperture stop S is fixed relative to the image plane I. In this embodiment, the first lens group G1 corresponds to the object-side lens group GA, the second lens group G2 corresponds to the first focusing lens group GF1, the third lens group G3 corresponds to the second focusing lens group GF2, and the fourth lens group G4 corresponds to the subsequent lens group GR.

[0132] The first lens group G1 is composed of, arranged in order from the object side along the optical axis, a negative meniscus lens L11 with a convex surface facing the object side, a cemented positive 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, a cemented negative lens formed by cementing a biconvex positive lens L14 and a biconcave negative lens L15, a biconcave negative lens L16, a biconvex positive lens L17, a biconvex positive lens L18, and a cemented negative lens formed by cementing a biconcave negative lens L19 and a biconvex positive lens L110. In this embodiment, the negative meniscus lens L11 corresponds to the first lens La, and the negative meniscus lens L12 corresponds to the second lens Lb. The cemented negative lens formed by cementing the negative lens L19 and the positive lens L110 corresponds to the cemented lens CL of the object-side lens group GA.

[0133] The second lens group G2 is composed of, arranged in order from the object side along the optical axis, a negative meniscus lens L21 with its concave surface facing the object side, and a biconvex positive lens L22.

[0134] The third lens group G3 is composed of, arranged in order from the object side along the optical axis, a biconcave negative lens L31 and a biconvex positive lens L32. The image-side lens surface of the negative lens L31 is aspheric, with a stronger positive refractive power on the periphery than on the center. The lens surfaces on both sides of the positive lens L32 are aspheric, with a stronger negative refractive power on the periphery than on the center.

[0135] The fourth lens group G4 is composed of, arranged in order from the object side along the optical axis, a biconvex positive lens L41 and a biconcave negative lens L42. An image surface I is located on the image side of the fourth lens group G4.

[0136] Table 5 below lists the values ​​of the specifications of the optical system according to the fifth example.

[0137] (Table 5) [Overall specifications] f=34.300 FNO=1.230 ω=32.684 Y=21.600 TL=157.455 Bf=11.455 Da=66.183 fa=-79.255 fb=-101.280 fp1=48.829 fp2=― MF1=1.493 MF2=1.512 βF1=0.495 βF2=0.939 D1=89.272 D2R=38.569 [Lens specifications] Surface number RD nd νd 1 66.961 2.000 1.81600 46.59 2 32.457 11.809 3 128.665 1.800 1.59319 67.90 4 40.741 9.802 2.00069 25.46 5 215.641 0.200 6 110.947 7.041 1.81600 46.59 7 -112.594 1.500 1.51680 64.14 8 28.007 12.084 9 -40.962 8.018 1.73037 32.23 10 857.978 0.200 11 70.201 9.539 1.81600 46.59 12 -61.720 0.200 13 54.810 7.279 1.59349 67.00 14 -212.179 2.494 15 -66.201 1.500 1.73037 32.23 16 27.501 13.807 1.59319 67.90 17 -57.491 2.000 18∞ (D18) (S aperture) 19 -41.015 1.300 1.56732 42.58 20 -310.485 0.200 21 38.747 7.973 1.77250 49.62 22 -146.553 (D22) 23 -42.724 1.500 1.62004 36.40 24* 60.145 0.200 25* 58.069 3.682 1.85108 40.12 26* -62.761 (D26) 27 154.307 8.500 1.94595 17.98 28 -76.392 1.740 29 -47.089 3.595 1.75520 27.57 30 85.433 Bf [Aspherical data] Page 24 κ=1.0000,A4=-1.09574E-04,A6=3.34832E-07,A8=-5.81576E-10,A10=4.32381E-13 Page 25 κ=1.0000,A4=-7.33927E-05,A6=3.59893E-07,A8=-6.97315E-10,A10=4.91900E-13 Page 26 κ=1.0000,A4=1.43166E-05,A6=1.17989E-07,A8=-2.22684E-10,A10=1.31507E-13 [Variable Interval Data] Infinity focus Close focus f=34.300 β=-0.03333 D0 ∞ 987.480 D18 16.159 14.666 D22 7.879 7.859 D26 2.000 3.512 Bf 11.455 11.455 [Lens group data] Group starting plane focal length G1 1 70.486 G2 19 74.747 G3 23 247.083 G4 27 -192.806

[0138] 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 range. From these aberration diagrams, it can be seen that the optical system according to Example 5 has excellent imaging performance, with various aberrations being well corrected not only when focused at infinity but also when focused at close range.

[0139] (Sixth Example) Example 6 will be described with reference to FIGS. 11 and 12 and Table 6. FIG. 11 shows the lens configuration of an optical system according to Example 6. The optical system OL(6) according to Example 6 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 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 and the third lens group G3 move along the optical axis toward the object side along different trajectories (movement amounts), 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.

[0140] An aperture stop S is disposed between the first lens group G1 and the second lens group G2. During focusing, the position of the aperture stop S is fixed relative to the image plane I. In this embodiment, the first lens group G1 corresponds to the object-side lens group GA, the second lens group G2 corresponds to the first focusing lens group GF1, the third lens group G3 corresponds to the second focusing lens group GF2, and the fourth lens group G4 corresponds to the subsequent lens group GR.

[0141] The first lens group G1 is composed of, arranged along the optical axis from the object side, a negative meniscus lens L11 with a convex surface facing the object side, a negative meniscus lens L12 with a convex surface facing the object side, a cemented positive lens formed by cementing a positive meniscus lens L13 with a convex surface facing the object side and a negative meniscus lens L14 with a convex surface facing the object side, a cemented negative lens formed by cementing a biconcave negative lens L15 and a biconvex positive lens L16, a biconvex positive lens L17, a biconvex positive lens L18, and a cemented negative lens formed by cementing a biconcave negative lens L19 and a biconvex positive lens L110. The negative meniscus lens L12 has an aspheric lens surface facing the image plane. In this embodiment, the negative meniscus lens L11 corresponds to the first lens La, and the negative meniscus lens L12 corresponds to the second lens Lb. The cemented negative lens formed by cementing the negative lens L19 and the positive lens L110 corresponds to the cemented lens CL of the object-side lens group GA.

[0142] 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 biconvex positive lens L22.

[0143] The third lens group G3 is composed of, arranged in order from the object side along the optical axis, a positive meniscus lens L31 with a convex surface facing the object side and a biconvex positive lens L32. The image-side lens surface of the positive meniscus lens L31 is an aspheric surface with a stronger positive refractive power on the periphery side than on the center side. The image-side lens surface of the positive lens L32 is an aspheric surface with a stronger negative refractive power on the periphery side than on the center side.

[0144] The fourth lens group G4 is composed of, arranged in order from the object side along the optical axis, a positive meniscus lens L41 with its concave surface facing the object side and a negative meniscus lens L42 with its concave surface facing the object side. An image surface I is located on the image side of the fourth lens group G4.

[0145] Table 6 below lists the values ​​of the specifications of the optical system according to the sixth example.

[0146] (Table 6) [Overall specifications] f=35.000 FNO=1.230 ω=31.746 Y=21.600 TL=145.455 Bf=10.955 Da=58.955 fa=-102.829 fb=-200.000 fp1=44.357 fp2=51.712 MF1=1.405 MF2=1.487 βF1=0.939 βF2=0.596 D1=83.518 D2R=35.097 [Lens specifications] Surface number RD nd νd 1 67.860 2.000 1.48749 70.31 2 28.552 8.759 3 56.466 1.800 1.58887 61.13 4* 37.716 3.790 5 51.569 7.504 2.00100 29.12 6 12706.656 1.500 1.49782 82.57 7 39.896 11.204 8 -34.883 1.500 1.85451 25.15 9 63.438 8.797 1.56732 42.58 10 -166.403 0.200 11 208.847 8.476 2.00069 25.46 12 -55.223 0.200 13 42.842 9.992 1.59349 67.00 14 -402.195 2.085 15 -164.696 1.500 1.69895 30.13 16 27.200 14.211 1.59319 67.90 17 -118.275 2.983 18∞ (D18) (S aperture) 19 -41.627 1.300 1.68376 37.64 20 117.749 0.200 21 37.122 8.000 1.59349 67.00 22 -76.861 (D22) 23 32.715 5.200 1.85108 40.12 24* 46.365 4.147 25 212.737 2.500 1.77387 47.25 26* -1000.777 (D26) 27 -811.142 3.025 1.94595 17.98 28 -93.510 2.770 29 -37.711 1.500 1.73037 32.23 30 -558.335 Bf [Aspherical data] Side 4 κ=1.0000,A4=-1.76373E-06,A6=-1.17943E-09,A8=-1.59414E-12,A10=-1.08316E-15 Page 24 κ=1.0000,A4=-3.14395E-06,A6=-1.49476E-08,A8=-1.54681E-11,A10=1.13351E-13 Page 26 κ=1.0000,A4=1.94012E-05,A6=2.29617E-08,A8=1.02524E-10,A10=-2.34228E-13 [Variable Interval Data] Infinity focus Close focus f=35.000 β=-0.03333 D0 ∞ 1010.855 D18 12.903 11.498 D22 2.081 1.999 D26 4.374 5.861 Bf 10.955 10.955 [Lens group data] Group starting plane focal length G1 1 55.625 G2 19 489.379 G3 23 77.454 G4 27 -115.422

[0147] Fig. 12(A) is a diagram showing various aberrations when the optical system according to Example 6 is focused at infinity. Fig. 12(B) is a diagram showing various aberrations when the optical system according to Example 6 is focused at close range. From these aberration diagrams, it can be seen that the optical system according to Example 6 has excellent imaging performance, with various aberrations being well corrected not only when focused at infinity but also when focused at close range.

[0148] 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 (16) for all the examples (Examples 1 to 6). Condition (1) 1.00 <Da / f<2.00 Condition (2) 1.70<(-fa) / f<4.00 Condition (3) 1.00 <f1 / f<4.40 Conditional expression (4) 1.00<(-fb) / f<30.00 Conditional expression (5) 15.0<νp1<35.0 Conditional expression (6) 15.0<νp2<40.0 Condition (7) 0.30 <fp1 / fp2<2.20 Condition (8) 0.10 <fp1 / (-fa)<2.80 Condition (9) 0.10 <fp2 / (-fa)<2.80 Condition (10) 0.10 <fF1 / fF2<20.00 Condition (11) 0.10 <MF1 / MF2<10.00 Conditional expression (12) 0.10<βF1 / βF2<3.00 Condition (13) 0.20 <Bf / f<0.63 Conditional expression (14) 1.00<(-fR) / f<7.20 Condition (15) 1.00 <D1 / D2R<4.00 Condition (16) 0.03 <Dn / Dp<0.30

[0149] [Conditional Expression Corresponding Values] (First to Fourth Examples) Conditional Expression 1st Example 2nd Example 3rd Example 4th Example (1) 1.826 1.826 1.950 1.882 (2) 2.397 2.632 2.547 2.297 (3) 1.758 1.901 2.133 2.208 (4) 5.831 5.354 5.831 - (5) 25.46 25.46 25.46 17.98 (6) 29.12 29.12 29.12 35.77 (7) 0.955 0.945 0.952 1.555 (8) 0.520 0.485 0.482 0.889 (9) 0.544 0.513 0.506 0.572 (10) 6.400 8.983 - 1.197 (11) 0.967 1.018 - 1.899 (12) 1.655 1.755 - 0.659 (13) 0.334 0.334 0.334 0.334 (14) 4.546 4.839 5.091 1.765 (15) 2.127 2.096 1.877 2.149 (16) 0.105 0.113 0.108 0.107 [Conditional Expression Corresponding Values] (Fifth and Sixth Examples) Conditional Expression 5th Example 6th Example (1) 1.930 1.684 (2) 2.311 2.938 (3) 2.055 1.589 (4) 2.953 5.714 (5) 25.46 25.46 (6) - 29.12 (7) - 0.858 (8) 0.616 0.431 (9) — 0.503 (10) 0.303 6.318 (11) 0.987 0.945 (12) 0.527 1.576 (13) 0.334 0.313 (14) 5.621 3.298 (15) 2.315 2.380 (16) 0.109 0.106

[0150] According to each of the above embodiments, an optical system that is compact yet has good optical performance can be realized.

[0151] The above-described examples are merely illustrative examples of the present invention, and the present invention is not limited to these.

[0152] The following contents can be appropriately adopted within the scope that does not impair the optical performance of the optical system of this embodiment.

[0153] Although examples of the optical system of this embodiment have been shown with a three-group configuration and a four-group configuration, the present application is not limited to these, and optical systems with other group configurations (for example, five groups, six groups, seven groups, etc.) 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 can also be used. A configuration in which a third focusing lens group is added in addition to the first and second focusing lens groups 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.

[0154] 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.

[0155] 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.

[0156] 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.

[0157] The aperture diaphragm is preferably located between the first and second lens groups, but the lens frame may serve the role of the aperture diaphragm instead of providing a component for the aperture diaphragm.The aperture diaphragm may also be located closer to the image plane than the object-side lens group.

[0158] 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]

[0159] 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, arranged in order from the object side along the optical axis, an object-side lens group having positive refractive power, at least one focusing lens group having positive refractive power, and a subsequent lens group; the object-side lens group includes a first lens that is disposed closest to the object and has negative refractive power, and a second lens that is disposed adjacent to the image side of the first lens and has negative refractive power, the object-side lens group has a cemented lens arranged closest to an image plane in the object-side lens group, the cemented lens has a negative lens and a positive lens cemented together, During focusing, the at least one focusing lens group moves along the optical axis, and the object-side lens group and the subsequent lens group are fixed with respect to an image plane; an aperture stop disposed closer to the image plane than the object-side lens group; An optical system that satisfies the following condition: 1.00<Da / f<2.00 1.70<(-fa) / f<4.00 0.03<Dn / Dp<0.30 where f is the focal length of the optical system when focused at infinity Da: distance on the optical axis from the aperture stop to the image plane when focused at infinity fa: focal length of the first lens Dn: the thickness of the negative lens in the cemented lens on the optical axis Dp: the thickness of the positive lens in the cemented lens on the optical axis

2. 2. The optical system according to claim 1, wherein the following condition is satisfied: 1.00<f1 / f<4.40 where f1 is the focal length of the object-side lens group

3. 2. The optical system according to claim 1, which satisfies the following condition: 1.00<(-fb) / f<30.00 where fb is the focal length of the second lens.

4. The optical system according to claim 1 , wherein the object-side lens group includes a plurality of positive lenses.

5. 5. The optical system according to claim 4, which satisfies the following condition: 15.0<νp1<35.0 where νp1 is the Abbe number of the positive lens having the smallest Abbe number among the plurality of positive lenses in the object-side lens group.

6. 5. The optical system according to claim 4, which satisfies the following condition: 15.0<νp2<40.0 where νp2 is the Abbe number of the positive lens having the second smallest Abbe number among the plurality of positive lenses in the object-side lens group.

7. 5. The optical system according to claim 4, which satisfies the following condition: 0.30<fp1 / fp2<2.20 where fp1 is the focal length of the positive lens having the smallest Abbe number among the plurality of positive lenses in the object-side lens group. fp2: focal length of the positive lens having the second smallest Abbe number among the plurality of positive lenses in the object-side lens group

8. 5. The optical system according to claim 4, which satisfies the following condition: 0.10<fp1 / (-fa)<2.80 where fp1 is the focal length of the positive lens having the smallest Abbe number among the plurality of positive lenses in the object-side lens group.

9. 5. The optical system according to claim 4, which satisfies the following condition: 0.10<fp2 / (-fa)<2.80 where fp2 is the focal length of the positive lens having the second smallest Abbe number among the plurality of positive lenses in the object-side lens group.

10. 2. The optical system of claim 1, wherein at least two lens surfaces in said at least one focusing lens group are aspheric.

11. 2. The optical system according to claim 1, wherein at least one lens surface in said at least one focusing lens group is an aspheric surface having a stronger positive refractive power on the periphery side than on the center side.

12. 2. The optical system according to claim 1, wherein at least one lens surface in said at least one focusing lens group is an aspheric surface having a stronger negative refractive power on the periphery side than on the center side.

13. the at least one focusing lens group includes a first focusing lens group and a second focusing lens group disposed closer to the image plane than the first focusing lens group, 2. The optical system according to claim 1, wherein, during focusing, the first focusing lens group and the second focusing lens group move along the optical axis on different trajectories.

14. 14. The optical system according to claim 13, which satisfies the following condition: 0.10<fF1 / fF2<20.00 where fF1 is the focal length of the first focusing lens group fF2: focal length of the second focusing lens group

15. 14. The optical system according to claim 13, which satisfies the following condition: 0.10<MF1 / MF2<10.00 where MF1 is the absolute value of the movement amount of the first focusing lens group when focusing from an object at infinity to an object at a close distance. MF2: Absolute value of the movement amount of the second focusing lens group when focusing from an object at infinity to an object at a close distance

16. 14. The optical system according to claim 13, which satisfies the following condition: 0.10<βF1 / βF2<3.00 where βF1 is the lateral magnification of the first focusing lens group when focused at infinity. βF2: lateral magnification of the second focusing lens group when focused at infinity

17. 2. The optical system according to claim 1, wherein the following condition is satisfied: 0.20<Bf / f<0.63 where Bf is the back focus of the optical system when focused at infinity.

18. 2. The optical system according to claim 1, wherein the following condition is satisfied: 1.00<(-fR) / f<7.20 where fR is the focal length of the subsequent lens group

19. 2. The optical system according to claim 1, wherein the following condition is satisfied: 1.00<D1 / D2R<4.00 where D1 is the distance on the optical axis from the lens surface of the object-side lens group closest to the object to the lens surface of the object-side lens group closest to the image plane. D2R: the distance on the optical axis from the lens surface of the focusing lens group closest to the object to the lens surface of the subsequent lens group closest to the image plane when focused at infinity

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

Images