Optical systems and optical instruments

Abstract

This optical system (OL) comprises a front group (GA), a stop (S), and a rear group (GB) that are arranged in order from the object side along an optical axis. The rear group (GB) has a focusing lens group (GF1) disposed closest to the object side in the rear group (GB) and having negative refractive power, during focusing, the focusing lens group moves along the optical axis, and the spacing between adjacent lens groups changes, and the following conditional expression is satisfied.　0.50 < ST / TL < 0.95, where ST is the distance on the optical axis from the stop (S) to an image surface (I), and TL is the total length of the optical system (OL).

Description

Technical Field

[0001] The present invention relates to an optical system and optical instruments .

Background Art

[0002] Conventionally, optical systems suitable for photographic cameras, digital still cameras, video cameras, etc. have been proposed (see, for example, Patent Document 1). In such an optical system, it is required to suppress the change in the angle of view during focusing.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

[0005] The second optical system according to the present invention consists of a front group, an aperture, and a rear group, arranged in order from the object side along the optical axis. The front group consists of a first lens group having positive refractive power. The rear group consists of a second lens group having negative refractive power, which is arranged closest to the object side, forming a first focusing lens group having negative refractive power; a third lens group having positive refractive power; a fourth lens group having negative refractive power, which is forming a second focusing lens group having negative refractive power; and a fifth lens group having negative refractive power. When focusing, the second and fourth lens groups move along the optical axis, changing the spacing between adjacent lens groups and satisfying the following condition. 0.50 <ST / TL<0.95 0.65 < (-fF) / fA < 1.15 0.65 <f / (-fF)<1.40 0.05 <Bf / TL<0.25 However, ST: distance along the optical axis from the aperture to the image plane. TL: Total length of the optical system fF: The above The second lens group that constitutes the first focusing lens group. focal length fA: Focal length of the front group f: focal length of the optical system Bf: Back focus of the optical system

[0006] According to the present invention The optical instrument is configured with the optical system described above. [Brief explanation of the drawing]

[0007] [Figure 1] This figure shows the lens configuration of the optical system according to the first embodiment. [Figure 2] Figures 2(A) and 2(B) show the aberrations of the optical system according to the first embodiment when it is focused at infinity and when it is focused at close range, respectively. [Figure 3] This figure shows the lens configuration of the optical system according to the second embodiment. [Figure 4] Figures 4(A) and 4(B) show the aberrations of the optical system according to the second embodiment when it is focused at infinity and when it is focused at close range, respectively. [Figure 5] This figure shows the lens configuration of the optical system according to the third embodiment. [Figure 6] FIG. 6(A) and FIG. 6(B) are aberration diagrams at infinity focus and close focus of the optical system according to the third embodiment, respectively. [Figure 7] It is a diagram showing the lens configuration of the optical system according to the fourth embodiment. [Figure 8] FIG. 8(A) and FIG. 8(B) are aberration diagrams at infinity focus and close focus of the optical system according to the fourth embodiment, respectively. [Figure 9] It is a diagram showing the lens configuration of the optical system according to the fifth embodiment. [Figure 10] FIG. 10(A) and FIG. 10(B) are aberration diagrams at infinity focus and close focus of the optical system according to the fifth embodiment, respectively. [Figure 11] It is a diagram showing the lens configuration of the optical system according to the sixth embodiment. [Figure 12] FIG. 12(A) and FIG. 12(B) are aberration diagrams at infinity focus and close focus of the optical system according to the sixth embodiment, respectively. [Figure 13] It is a diagram showing the lens configuration of the optical system according to the seventh embodiment. [Figure 14] FIG. 14(A) and FIG. 14(B) are aberration diagrams at infinity focus and close focus of the optical system according to the seventh embodiment, respectively. [Figure 15] It is a diagram showing the lens configuration of the optical system according to the eighth embodiment. [Figure 16] FIG. 16(A) and FIG. 16(B) are aberration diagrams at infinity focus and close focus of the optical system according to the eighth embodiment, respectively. [Figure 17] It is a diagram showing the configuration of a camera equipped with the optical system according to the present embodiment. [Figure 18] It is a flowchart showing a manufacturing method of the optical system according to the present embodiment.

Embodiments for Carrying Out the Invention

[0008] [[ID=4�]] The following describes preferred embodiments of the present invention. First, a camera (optical device) equipped with the optical system according to this embodiment will be described with reference to Figure 17. As shown in Figure 17, the camera 1 consists of a main body 2 and a shooting 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 a liquid crystal screen 5. The shooting lens 3 includes an optical system OL consisting of a plurality of lens groups and a lens position control mechanism (not shown) that controls the position of each lens group. The lens position control mechanism consists 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, and a control circuit that drives the motor.

[0009] Light from the subject is focused by the optical system OL of the photographic 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 memory (not shown). The digital image data recorded in memory can be displayed on the liquid crystal screen 5 according to the user's operation. This camera may be a mirrorless camera or a single-lens reflex type camera with a quick-return mirror. Also, the optical system OL shown in Figure 17 is a schematic representation of the optical system provided in the photographic lens 3, and the lens configuration of the optical system OL is not limited to this configuration.

[0010] Next, the optical system according to this embodiment will be described. As an example of the optical system (photographic lens) OL according to this embodiment, optical system OL(1) consists of a front group GA, an aperture (aperture diaphragm) S, and a rear group GB, which are arranged in order from the object side along the optical axis, as shown in Figure 1. The rear group GB is composed of a focusing lens group (GF1) having negative refractive power, which is located closest to the object in the rear group GB. When focusing, the focusing lens group moves along the optical axis, and the spacing between adjacent lens groups changes.

[0011] Under the above configuration, the optical system OL according to this embodiment satisfies the following condition (1). 0.50 <ST / TL<0.95 ···(1) However, ST: distance along the optical axis from aperture S to image plane I. TL: Total length of optical system OL

[0012] According to this embodiment, it is possible to obtain an optical system that exhibits little variation in the angle of view during focusing, and an optical instrument equipped with this optical system. The optical system OL according to this embodiment may be optical system OL(2) shown in Figure 3, optical system OL(3) shown in Figure 5, optical system OL(4) shown in Figure 7, or optical system OL(5) shown in Figure 9. Furthermore, the optical system OL according to this embodiment may be optical system OL(6) shown in Figure 11, optical system OL(7) shown in Figure 13, or optical system OL(8) shown in Figure 15.

[0013] Conditional equation (1) defines the appropriate relationship between the distance along the optical axis from the aperture S to the image plane I and the total length of the optical system OL. By satisfying conditional equation (1), the change in the angle of view during focusing can be reduced.

[0014] If the corresponding value in conditional equation (1) falls outside the above range, it becomes difficult to suppress the angle of view fluctuation during focusing. By setting the lower limit of conditional equation (1) to 0.53, 0.55, 0.58, 0.60, 0.63, and further to 0.65, the effect of this embodiment can be made more reliable. Furthermore, by setting the upper limit of conditional equation (1) to 0.93, 0.90, 0.88, 0.85, 0.83, 0.80, and further to 0.78, the effect of this embodiment can be made more reliable.

[0015] The optical system OL according to this embodiment is preferably satisfied with the following condition (2). 0.65 < (-fF) / fA < 1.20 ... (2) However, fF: focal length of the focusing lens group. fA: Focal length of the front group GA

[0016] Condition (2) defines the appropriate relationship between the focal length of the focusing lens group and the focal length of the front group GA. By satisfying condition (2), the change in the angle of view during focusing can be reduced.

[0017] If the corresponding value in conditional equation (2) falls outside the above range, it becomes difficult to suppress the angle of view fluctuation during focusing. Setting the lower limit of conditional equation (2) to 0.68, 0.70, 0.73, 0.75, and further to 0.77 makes the effect of this embodiment more reliable. Furthermore, setting the upper limit of conditional equation (2) to 1.18, 1.15, 1.13, 1.00, and further to 1.09 makes the effect of this embodiment more reliable.

[0018] In the optical system OL according to this embodiment, the rear lens group GB preferably has at least one lens group positioned on the image plane side of the focusing lens group and satisfies the following condition (3). 0.70 < (-fF) / fR < 1.80 ... (3) However, fF: focal length of the focusing lens group. fR: Combined focal length of at least one lens group

[0019] Condition (3) defines an appropriate relationship between the focal length of the focusing lens group and the combined focal length of at least one lens group positioned on the image plane side of the focusing lens group. The combined focal length of the at least one lens group is the combined focal length when an object at infinity is in focus. Furthermore, if there is only one lens group, the combined focal length of the at least one lens group is the focal length of that single lens group; if there are multiple lens groups, it is the combined focal length of the multiple lens groups. By satisfying condition (3), the change in the angle of view during focusing can be reduced.

[0020] If the corresponding value in conditional equation (3) falls outside the above range, it becomes difficult to suppress the angle of view fluctuation during focusing. Setting the lower limit of conditional equation (3) to 0.73, 0.75, 0.78, 0.80, and further to 0.83 makes the effect of this embodiment more reliable. Furthermore, setting the upper limit of conditional equation (3) to 1.78, 1.75, 1.73, 1.70, 1.68, 1.65, and further to 1.63 makes the effect of this embodiment more reliable.

[0021] In the optical system OL according to this embodiment, the rear lens group GB has a successor lens group GR1 arranged adjacent to the image plane side of the focusing lens group, and it is desirable that the following condition (4) is satisfied. 0.00 < βR1 / βF < 0.25 ... (4) However, βR1: Horizontal magnification of the subsequent lens group GR1 when focusing on an object at infinity. βF: Lateral magnification of the focusing lens group when focusing on an object at infinity.

[0022] Condition (4) defines an appropriate relationship between the lateral magnification of the trailing lens group GR1 when an object at infinity is in focus and the lateral magnification of the focusing lens group when an object at infinity is in focus. By satisfying condition (4), the fluctuation in image magnification during focusing can be reduced.

[0023] If the corresponding value in conditional equation (4) falls outside the above range, it becomes difficult to suppress fluctuations in image magnification during focusing. Setting the lower limit of conditional equation (4) to 0.01 makes the effect of this embodiment more reliable. Furthermore, setting the upper limit of conditional equation (4) to 0.23, 0.20, 0.18, 0.16, and even 0.15 makes the effect of this embodiment more reliable.

[0024] The optical system OL according to this embodiment is preferably satisfied with the following condition (5). 0.03 < Δx / f < 0.35 ... (5) However, Δx: the amount of movement of the focusing lens group when focusing from an object at infinity to an object at a close distance. f: focal length of optical system OL

[0025] Conditional equation (5) defines the appropriate relationship between the amount of movement of the focusing lens group during focusing and the focal length of the optical system OL. By satisfying conditional equation (5), field curvature, spherical aberration, coma aberration, etc., can be effectively corrected. In this embodiment, the sign of the amount of movement of the focusing lens group toward the image plane is set to +, and the sign of the amount of movement toward the object is set to -.

[0026] If the corresponding value in conditional equation (5) falls outside the above range, it becomes difficult to correct field curvature, spherical aberration, coma aberration, etc. By setting the lower limit of conditional equation (5) to 0.04, 0.06, and further to 0.08, the effects of this embodiment can be made more reliable. Furthermore, by setting the upper limit of conditional equation (5) to 0.33, 0.30, 0.28, 0.25, 0.23, 0.20, and further to 0.18, the effects of this embodiment can be made more reliable.

[0027] The optical system OL according to this embodiment is preferably satisfied with the following condition (6). 0.65 <f / (-fF)<1.60 ···(6) However, f: focal length of the optical system OL fF: Focal length of the focusing lens group

[0028] Conditional equation (6) defines the appropriate relationship between the focal length of the optical system OL and the focal length of the focusing lens group. By satisfying conditional equation (6), chromatic aberration, field curvature, etc., can be effectively corrected.

[0029] If the corresponding value in conditional equation (6) falls outside the above range, it becomes difficult to correct chromatic aberration, field curvature, etc. Setting the lower limit of conditional equation (6) to 0.68, 0.70, and further to 0.73 makes the effects of this embodiment more reliable. Furthermore, setting the upper limit of conditional equation (6) to 1.58, 1.55, 1.53, 1.50, 1.48, 1.45, 1.43, and further to 1.40 makes the effects of this embodiment more reliable.

[0030] The optical system OL according to this embodiment preferably satisfies the following condition (7). 2.00 <TL / (FNO×Bf)<10.00 ···(7) However, FNO: F number of the optical system OL Bf: Back focus of the optical system (OL)

[0031] Conditional equation (7) defines the appropriate relationship between the total length of the optical system OL, the F-number of the optical system OL, and the back focus. By satisfying conditional equation (7), it is possible to create an optical system that has sufficient peripheral illumination, a large aperture, and a short back focus. Note that the back focus of the optical system OL in conditional equation (7) and conditional equation (14) described later refers to the distance along the optical axis (air-equivalent distance) from the lens surface on the image plane side to the image plane I of the lens positioned closest to the image plane in the optical system OL.

[0032] If the corresponding value in conditional equation (7) falls outside the above range, it becomes difficult to secure sufficient light at the edges of the field of view. The effect of this embodiment can be made more reliable by setting the lower limit of conditional equation (7) to 2.10, 2.15, 2.20, 2.25, 2.30, 2.35, 2.40, and further to 2.43. Furthermore, the effect of this embodiment can be made more reliable by setting the upper limit of conditional equation (7) to 9.85, 9.65, 9.60, 9.55, 9.50, 9.45, and further to 9.40.

[0033] In the optical system OL according to this embodiment, it is desirable that the focusing lens group be composed of a single negative lens component. This makes the focusing lens group lighter, enabling high-speed focusing from an object at infinity to an object at a close distance. In this embodiment, the lens component refers to a single lens or a cemented lens.

[0034] The optical system OL according to this embodiment is preferably satisfied with the following condition (8). -2.50<(rFR2+rFR1) / (rFR2-rFR1)<-0.25 ...(8) However, rFR1: radius of curvature of the lens surface closest to the object in the focusing lens group. rFR2: Radius of curvature of the lens surface closest to the image plane in the focusing lens group.

[0035] Condition (8) defines an appropriate range for the shape factor of the lenses constituting the focusing lens group. By satisfying condition (8), spherical aberration, coma aberration, etc., can be corrected effectively.

[0036] If the corresponding value in conditional equation (8) falls outside the above range, it becomes difficult to correct spherical aberration, coma aberration, etc. By setting the lower limit of conditional equation (8) to -2.45, -2.40, -2.35, -2.30, -2.25, and further to -2.23, the effect of this embodiment can be made more reliable. Furthermore, by setting the upper limit of conditional equation (8) to -0.30, -0.33, -0.35, -0.38, -0.40, -0.43, -0.45, -0.48, and further to -0.50, the effect of this embodiment can be made more reliable.

[0037] The optical system OL according to this embodiment is preferably satisfied with the following condition (9). 0.90<(rNR2+rNR1) / (rNR2-rNR1)<2.65 ...(9) However, rNR1: radius of curvature of the object-side lens surface at the lens positioned closest to the image plane in the optical system OL. rNR2: Radius of curvature of the image-plane lens surface at the lens positioned closest to the image plane in the optical system OL.

[0038] Condition (9) defines an appropriate range for the shape factor of the lens positioned closest to the image plane in the optical system OL. By satisfying condition (9), spherical aberration and distortion can be effectively corrected.

[0039] If the corresponding value in conditional equation (9) falls outside the above range, it becomes difficult to correct spherical aberration and distortion. The effect of this embodiment can be made more reliable by setting the lower limit of conditional equation (9) to 0.93, 0.95, 0.98, 1.00, and further to 1.02. Furthermore, the effect of this embodiment can be made more reliable by setting the upper limit of conditional equation (9) to 2.60, 2.58, 2.55, 2.53, 2.50, 2.48, and further to 2.45.

[0040] The optical system OL according to this embodiment is preferably satisfied with the following condition (10). 0.08 < 1 / βF < 0.55 ···(10) However, βF: Lateral magnification of the focusing lens group when focusing on an object at infinity.

[0041] Condition (10) defines an appropriate range for the lateral magnification of the focusing lens group when an object at infinity is in focus. By satisfying condition (10), various aberrations such as spherical aberration and field curvature can be effectively corrected when an object at infinity is in focus.

[0042] If the corresponding value in conditional equation (10) falls outside the above range, it becomes difficult to correct various aberrations such as spherical aberration and field curvature when focusing on an object at infinity. By setting the lower limit of conditional equation (10) to 0.10, 0.12, and further to 0.14, the effect of this embodiment can be made more reliable. Furthermore, by setting the upper limit of conditional equation (10) to 0.53, 0.50, 0.48, 0.45, and further to 0.43, the effect of this embodiment can be made more reliable.

[0043] The optical system OL according to this embodiment is preferably satisfied with the following condition (11). {βF + (1 / βF)} -2 <0.15 ···(11) However, βF: Lateral magnification of the focusing lens group when focusing on an object at infinity.

[0044] Condition (11) defines an appropriate range for the lateral magnification of the focusing lens group when an object at infinity is in focus. By satisfying condition (11), various aberrations such as spherical aberration and field curvature can be effectively corrected when an object at infinity is in focus.

[0045] If the corresponding value in conditional equation (11) falls outside the above range, it becomes difficult to correct various aberrations such as spherical aberration and field curvature when focusing on an object at infinity. By setting the upper limit of conditional equation (11) to 0.14, and further to 0.13, the effect of this embodiment can be made more reliable.

[0046] The optical system OL according to this embodiment is preferably satisfied with the following condition (12). 0.003 <BLDF / TL<0.060 ···(12) However, BLDF: Length of the focusing lens group along the optical axis

[0047] Condition (12) defines the appropriate relationship between the length of the focusing lens group along the optical axis and the total length of the optical system OL. By satisfying condition (12), the focusing lens group can be made lighter, and variations in aberrations during focusing can be suppressed.

[0048] If the corresponding value of conditional equation (12) falls outside the above range, it becomes difficult to correct the fluctuations in various aberrations during focusing. Setting the lower limit of conditional equation (12) to 0.004, 0.006, and further to 0.008 makes the effect of this embodiment more reliable. Furthermore, setting the upper limit of conditional equation (12) to 0.058, 0.055, 0.053, 0.050, 0.048, 0.045, and further to 0.043 makes the effect of this embodiment more reliable.

[0049] The optical system OL according to this embodiment preferably satisfies the following condition (13). 0.05 < βB / βF < 0.50 ···(13) However, βB: Lateral magnification of the rear group GB when focusing on an object at infinity. βF: Lateral magnification of the focusing lens group when focusing on an object at infinity.

[0050] Conditional equation (13) defines an appropriate relationship between the lateral magnification of the rear lens group GB when an object at infinity is in focus and the lateral magnification of the focusing lens group when an object at infinity is in focus. By satisfying conditional equation (13), the angle of view fluctuation when an object at infinity is in focus can be suppressed.

[0051] If the corresponding value in conditional equation (13) falls outside the above range, it becomes difficult to suppress the angle of view fluctuation when focusing on an object at infinity. By setting the lower limit of conditional equation (13) to 0.06, 0.08, 0.10, and further to 0.12, the effect of this embodiment can be made more reliable. Furthermore, by setting the upper limit of conditional equation (13) to 0.48, 0.45, 0.43, 0.40, and further to 0.38, the effect of this embodiment can be made more reliable.

[0052] The optical system OL according to this embodiment is preferably satisfied with the following condition (14). 0.05 <Bf / TL<0.25 ···(14) However, Bf: back focus of the optical system OL

[0053] Conditional equation (14) defines an appropriate relationship between the back focus of the optical system OL and the total length of the optical system OL. Satisfying conditional equation (14) allows the back focus to be shortened relative to the total length of the optical system, which enables miniaturization of the optical system and is therefore desirable.

[0054] If the corresponding value in conditional equation (14) falls outside the above range, the back focus becomes long relative to the total length of the optical system, making it difficult to miniaturize the optical system. Setting the lower limit of conditional equation (14) to 0.06 and further to 0.08 can make the effects of this embodiment more reliable. Furthermore, setting the upper limit of conditional equation (14) to 0.24 and further to 0.22 can make the effects of this embodiment more reliable.

[0055] The optical system OL according to this embodiment is preferably satisfied with the following condition (15). 1.00 <FNO<3.00 ···(15) However, FNO: F number of the optical system OL

[0056] Conditional equation (15) defines an appropriate range for the F-number of the optical system OL. Satisfying conditional equation (15) is preferable because it results in a bright optical system. Setting the lower limit of conditional equation (15) to 1.10, 1.15, and further to 1.20 can make the effects of this embodiment more reliable. Furthermore, setting the upper limit of conditional equation (15) to 2.85, 2.70, 2.60, 2.50, 2.40, 2.30, 2.20, and further to 2.10 can make the effects of this embodiment more reliable.

[0057] The optical system OL according to this embodiment is preferably satisfied with the following condition (16). 12.00°<2ω<40.00° ···(16) However, 2ω: the entire field of view of the optical system OL

[0058] Conditional equation (16) defines an appropriate range for the entire field of view of the optical system OL. Satisfying conditional equation (16) is preferable because it allows for an optical system with a wide field of view. Setting the lower limit of conditional equation (16) to 12.50°, 13.00°, 13.50°, 14.00°, and further to 14.50° makes the effect of this embodiment more reliable. Furthermore, setting the upper limit of conditional equation (16) to 38.50°, 37.00°, 36.00°, and further to 35.50° makes the effect of this embodiment more reliable.

[0059] Next, with reference to Figure 18, the manufacturing method of the optical system OL according to this embodiment will be outlined. First, the front group GA, the aperture (diaphragm) S, and the rear group GB are arranged in order from the object side along the optical axis (step ST1). Next, the focusing lens group (GF1) having negative refractive power is placed on the object side of the rear group GB (step ST2). Next, the focusing lens group is configured to move along the optical axis when focusing, and the spacing between adjacent lens groups changes (step ST3). Then, each lens is arranged in the lens barrel so as to satisfy at least the above condition (1) (step ST4). With this manufacturing method, it is possible to manufacture an optical system with little variation in the angle of view when focusing. [Examples]

[0060] The optical system OL according to the embodiment of this model will be described below based on the drawings. Figures 1, 3, 5, 7, 9, 11, 13, and 15 are cross-sectional views showing the configuration and refractive power distribution of the optical system OL{OL(1) to OL(8)} according to the first to eighth embodiments. In the cross-sectional views of the optical system OL(1) to OL(8) according to the first to eighth embodiments, the direction of movement along the optical axis of each focusing lens group when focusing from infinity to a near-field object is indicated by an arrow along with the word "focus".

[0061] In Figures 1, 3, 5, 7, 9, 11, 13, and 15, 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, in order to prevent the number and types of symbols and numbers from becoming too large and complicated, each embodiment uses a separate combination of symbols and numbers to represent the lens groups, etc. Therefore, even if the same combination of symbols and numbers is used between embodiments, it does not mean that they have the same configuration.

[0062] Tables 1 to 8 are shown below. Table 1 shows the specifications for the first example, Table 2 for the second example, Table 3 for the third example, Table 4 for the fourth example, Table 5 for the fifth example, Table 6 for the sixth example, Table 7 for the seventh example, and Table 8 for the eighth example. In each example, the d-line (wavelength λ=587.6nm) and the g-line (wavelength λ=435.8nm) were selected as the targets for calculating aberration characteristics.

[0063] In the [Overall Specifications] table, f is the focal length of the entire lens system, FNO is the F number, 2ω is the angle of view (in degrees, where ω is half the angle of view), and Y is the image height. TL is the distance from the frontmost lens to the final lens surface on the optical axis when focused at infinity, plus Bf, and Bf is the distance from the final lens surface on the optical axis to the image plane I (back focus) when focused at infinity. Bf(a) is the distance on the optical axis from the lens surface on the image plane side to the image plane I for the lens positioned closest to the image plane in the optical system (air equivalent distance). Also, in the [Overall Specifications] table, fA is the focal length of the front group. fR is the combined focal length of at least one lens group in the rear group that is positioned closer to the image plane than the object-side focusing lens group. Δx is the amount of movement of the focusing lens group when focusing from an object at infinity to a nearby object. βF is the lateral magnification of the focusing lens group when focusing on an object at infinity. βB indicates the lateral magnification of the rear lens group when an object at infinity is in focus. βR1 indicates the lateral magnification of the subsequent lens group when an object at infinity is in focus.

[0064] In the [Lens Specifications] table, the surface number indicates the order of the optical surfaces from the object side along the direction of light propagation; R is the radius of curvature of each optical surface (a positive value is given for surfaces where the center of curvature is located on the image side); D is the interplanar spacing, which is the distance along the optical axis from each optical surface to the next optical surface (or image plane); nd is the refractive index of the optical component material with respect to the d line; and νd is the Abbe number with respect to the d line of the optical component material. "∞" for the radius of curvature indicates a plane or aperture, and (Aperture S) indicates an aperture diaphragm S. The refractive index of air nd = 1.00000 is omitted.

[0065] The [Variable Interval Data] table shows the inter-plane spacing at surface number i, where the inter-plane spacing is (Di) in the [Lens Specifications] table. Note that D0 represents the distance from the object to the optical surface closest to the object in the optical system. In the [Variable Interval Data] table, f represents the focal length of the entire lens system, and β represents the magnification.

[0066] The [Lens Group Data] table shows the starting surface (the surface closest to the object) and focal length for each lens group.

[0067] In all specifications listed below, the focal length f, radius of curvature R, interplanar spacing D, and other lengths are generally expressed in "mm" unless otherwise specified. However, since optical systems can achieve equivalent optical performance even when proportionally enlarged or reduced, this is not the only way to express them.

[0068] The explanations in the tables up to this point are common to all examples, and any redundant explanations below will be omitted.

[0069] (First embodiment) The first embodiment will be described using Figures 1 and 2 and Table 1. Figure 1 is a diagram showing the lens configuration of the optical system according to the first embodiment. The optical system OL(1) according to the first embodiment consists of a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, a third lens group G3 having positive refractive power, a fourth lens group G4 having negative refractive power, and a fifth lens group G5 having negative refractive power, all arranged in order from the object side along the optical axis. When focusing from an object at infinity to an object at a close distance, the second lens group G2 and the fourth lens group G4 move towards the image side along the optical axis, and the spacing between adjacent lens groups changes. At the time of focusing, the first lens group G1, the third lens group G3, and the fifth lens group G5 are fixed with respect to the image plane I. The sign (+) or (-) attached to each lens group symbol indicates the refractive power of each lens group, and this is the same in all the embodiments described below.

[0070] The aperture diaphragm S is positioned between the first lens group G1 and the second lens group G2. When focusing, the aperture diaphragm S is fixed relative to the image plane I. In this embodiment, the first lens group G1 constitutes the front group GA, and the second lens group G2, third lens group G3, fourth lens group G4, and fifth lens group G5 constitute the rear group GB. The second lens group G2 corresponds to the first focusing lens group GF1, which is positioned closest to the object in the rear group GB. The third lens group G3 corresponds to the subsequent lens group GR1, which is positioned adjacent to the first focusing lens group GF1 on the image plane side. The fourth lens group G4 corresponds to the second focusing lens group GF2, which is positioned closer to the image plane than the first focusing lens group GF1.

[0071] The first lens group G1 consists of a positive meniscus lens L11 with its convex surface facing the object, arranged in order from the object side along the optical axis; a positive meniscus lens L12 with its convex surface facing the object; a cemented lens formed by joining a positive meniscus lens L13 with its convex surface facing the object and a negative meniscus lens L14 with its convex surface facing the object; a negative meniscus lens L15 with its convex surface facing the object; and a positive meniscus lens L16 with its convex surface facing the object. The second lens group G2 consists of a negative meniscus lens L21 with its convex surface facing the object.

[0072] The third lens group G3 consists of a cemented lens formed by joining a biconcave negative lens L31 and a biconvex positive lens L32, arranged in order from the object side along the optical axis, a biconvex positive lens L33, and a biconvex positive lens L34. The fourth lens group G4 consists of a biconcave negative lens L41.

[0073] The fifth lens group G5 consists of a cemented lens formed by joining a biconvex positive lens L51 and a negative meniscus lens L52 with its concave surface facing the object, arranged in order from the object side along the optical axis, and a negative meniscus lens L53 with its concave surface facing the object. The image plane I is positioned on the image side of the fifth lens group G5. A parallel plate PP is positioned between the fifth lens group G5 and the image plane I.

[0074] Table 1 below lists the specifications of the optical system according to the first embodiment.

[0075] (Table 1) [Overall Specifications] f=87.000 fA=89.351 FNO=1.424 fR=64.417 2ω = 28.285 Δx = 12.719 Y=21.600 βF=2.601 TL=129.013 βB=0.974 Bf=1.000 βR1=0.359 Bf(a) = 11.168 [Lens Specifications] Face number RD nd νd 1 69.6342 5.430 1.9591 17.47 2 132.1539 0.116 3 55.3642 5.244 2.0010 29.13 4 89.6665 0.100 5 40.4445 8.778 1.5503 75.49 6 140.0000 1.200 1.8548 24.80 7 29.5861 5.360 8 63.3783 1.200 1.9229 20.88 9 31.8132 0.100 10 31.2943 8.078 1.7292 54.67 11 237.3897 2.787 12 ∞ (D12) (Aperture S) 13 438.3400 1.200 1.5163 64.14 14 38.4472 (D14) 15 -65.9934 1.200 1.7783 23.91 16 39.9168 8.673 1.8040 46.53 17 -723.3882 0.100 18 70.0000 9.587 1.8160 46.62 19 -124.9732 0.100 20 135.5192 4.257 1.9591 17.47 21 -631.3761 (D21) 22 -255.5306 1.200 1.6989 30.13 23 1196.1373 (D23) 24 148.6618 10.553 1.9591 17.47 25 -40.7482 1.000 1.8929 20.36 26 -348.6817 5.247 27 -43.6865 1.200 1.7783 23.91 28 -175.9036 9.113 29 ∞ 1.600 1.5168 63.88 30 ∞ Bf [Variable interval data] Infinity focus state, intermediate distance focus state, very close distance focus state f=87.000 β=-0.034 β=-0.126 D0 ∞ 2570.805 728.956 D12 1.500 4.805 14.219 D14 19.979 16.674 7.260 D21 2.293 4.042 10.530 D23 10.820 9.071 2.583 [Lens group data] Group starting plane focal length G1 1 89.351 G2 13 -81.705 G3 15 54.836 G4 22 -301.138 G5 24 -611.471

[0076] Figure 2(A) is an aberration diagram of the optical system according to the first embodiment when focused at infinity. Figure 2(B) is an aberration diagram of the optical system according to the first embodiment when focused at close range. In each aberration diagram when focused at infinity, FNO indicates the F number and Y indicates the image height. In each aberration diagram when focused at close range, 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 and distortion diagrams show the maximum image height, and the coma aberration diagram shows the values ​​of each image height. d indicates the d line (wavelength λ=587.6nm), and g indicates the g line (wavelength λ=435.8nm). 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 reference numerals as in this embodiment are used in the aberration diagrams of the embodiments shown below, and redundant explanations are omitted.

[0077] From the various aberration diagrams, it can be seen that the optical system according to the first embodiment has excellent image-forming performance, with aberrations well corrected throughout the entire range from infinity focus to close-up focus. Therefore, even when focusing on close-up objects, it is possible to maintain good optical performance while minimizing changes in the angle of view during focusing.

[0078] (Second example) The second embodiment will be described using Figures 3-4 and Table 2. Figure 3 is a diagram showing the lens configuration of the optical system according to the second embodiment. The optical system OL(2) according to the second embodiment consists of a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, a third lens group G3 having positive refractive power, a fourth lens group G4 having negative refractive power, and a fifth lens group G5 having negative refractive power, all arranged in order from the object side along the optical axis. When focusing from an object at infinity to an object at a close distance, the second lens group G2 and the fourth lens group G4 move towards the image side along the optical axis, and the spacing between adjacent lens groups changes. At the time of focusing, the first lens group G1, the third lens group G3, and the fifth lens group G5 are fixed with respect to the image plane I.

[0079] The aperture diaphragm S is positioned between the first lens group G1 and the second lens group G2. When focusing, the aperture diaphragm S is fixed relative to the image plane I. In this embodiment, the first lens group G1 constitutes the front group GA, and the second lens group G2, third lens group G3, fourth lens group G4, and fifth lens group G5 constitute the rear group GB. The second lens group G2 corresponds to the first focusing lens group GF1, which is positioned closest to the object in the rear group GB. The third lens group G3 corresponds to the subsequent lens group GR1, which is positioned adjacent to the first focusing lens group GF1 on the image plane side. The fourth lens group G4 corresponds to the second focusing lens group GF2, which is positioned closer to the image plane than the first focusing lens group GF1.

[0080] The first lens group G1 consists of a positive meniscus lens L11 with its convex surface facing the object, arranged in order from the object side along the optical axis; a positive meniscus lens L12 with its convex surface facing the object; a cemented lens formed by joining a biconvex positive lens L13 and a biconcave negative lens L14; and a positive meniscus lens L15 with its convex surface facing the object. The second lens group G2 consists of a negative meniscus lens L21 with its convex surface facing the object.

[0081] The third lens group G3 consists of a cemented lens formed by joining a negative meniscus lens L31 with its convex surface facing the object and a positive meniscus lens L32 with its convex surface facing the object, arranged in order from the object side along the optical axis, and a biconvex positive lens L33. The fourth lens group G4 consists of a negative meniscus lens L41 with its convex surface facing the object.

[0082] The fifth lens group G5 consists of a positive meniscus lens L51 with its convex surface facing the object and a negative meniscus lens L52 with its concave surface facing the object, arranged in order from the object side along the optical axis. The image plane I is positioned on the image side of the fifth lens group G5. A parallel plate PP is positioned between the fifth lens group G5 and the image plane I.

[0083] Table 2 below lists the specifications of the optical system according to the second embodiment.

[0084] (Table 2) [Overall Specifications] f=84.853 fA=83.808 FNO=1.855 fR=70.031 2ω = 28.002 Δx = 8.031 Y=21.600 βF=4.398 TL=114.050 βB=1.012 Bf=1.000 βR1=0.165 Bf(a) = 11.205 [Lens Specifications] Face number RD nd νd 1 57.5903 6.716 1.8081 22.76 2 250.0000 4.134 3 54.4191 3.242 1.7725 49.60 4 87.8376 0.100 5 42.6165 6.392 1.4560 91.37 6 -1029.0613 1.200 2.0007 25.46 7 30.7264 7.020 8 33.1538 7.106 1.4978 82.57 9 2847.8763 2.046 10 ∞ (D10) (Aperture S) 11 1361.3846 1.200 1.5530 55.07 12 35.8243 (D12) 13 105.7816 1.200 1.8052 25.46 14 30.0129 5.549 1.7292 54.67 15 177.6261 7.465 16 70.0000 6.745 2.0007 25.46 17 -91.9564 (D17) 18 135.9285 1.200 1.6730 38.26 19 50.2105 (D19) 20 85.3901 2.439 2.0010 29.13 21 157.8735 6.189 22 -36.1082 4.843 1.8081 22.76 23 -200.0000 9.150 24 ∞ 1.600 1.5168 63.88 25 ∞ Bf [Variable interval data] Infinity focus state, intermediate distance focus state, very close distance focus state f=84.853 β=-0.034 β=-0.120 D0 ∞ 2544.448 725.082 D10 1.500 3.593 9.531 D12 11.802 9.709 3.771 D17 6.374 7.694 11.374 D19 7.839 6.518 2.839 [Lens group data] Group starting plane focal length G1 1 83.808 G2 11 -66.556 G3 13 40.059 G4 18 -118.979 G5 20 -84.660

[0085] Figure 4(A) shows the aberrations of the optical system according to the second embodiment when focused at infinity. Figure 4(B) shows the aberrations of the optical system according to the second embodiment when focused at close range. From each aberration diagram, it can be seen that the optical system according to the second embodiment has excellent imaging performance, with aberrations well corrected across the entire range from infinity focus to close range focus. Therefore, even when focusing on close objects, it is possible to maintain good optical performance while reducing the angle of view fluctuation during focusing.

[0086] (Third embodiment) The third embodiment will be explained using Figures 5-6 and Table 3. Figure 5 is a diagram showing the lens configuration of the optical system according to the third embodiment. The optical system OL(3) according to the third embodiment consists of a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, a third lens group G3 having positive refractive power, a fourth lens group G4 having negative refractive power, and a fifth lens group G5 having negative refractive power, all arranged in order from the object side along the optical axis. When focusing from an object at infinity to an object at a close distance, the second lens group G2 and the fourth lens group G4 move towards the image side along the optical axis, and the spacing between adjacent lens groups changes. At the time of focusing, the first lens group G1, the third lens group G3, and the fifth lens group G5 are fixed with respect to the image plane I.

[0087] The aperture diaphragm S is positioned between the first lens group G1 and the second lens group G2. When focusing, the aperture diaphragm S is fixed relative to the image plane I. In this embodiment, the first lens group G1 constitutes the front group GA, and the second lens group G2, third lens group G3, fourth lens group G4, and fifth lens group G5 constitute the rear group GB. The second lens group G2 corresponds to the first focusing lens group GF1, which is positioned closest to the object in the rear group GB. The third lens group G3 corresponds to the subsequent lens group GR1, which is positioned adjacent to the first focusing lens group GF1 on the image plane side. The fourth lens group G4 corresponds to the second focusing lens group GF2, which is positioned closer to the image plane than the first focusing lens group GF1.

[0088] The first lens group G1 consists of a positive meniscus lens L11 with its convex surface facing the object, a positive meniscus lens L12 with its convex surface facing the object, and a cemented lens formed by joining a biconvex positive lens L13 and a biconcave negative lens L14, all arranged in order from the object side along the optical axis. The second lens group G2 consists of a negative meniscus lens L21 with its convex surface facing the object.

[0089] The third lens group G3 consists of a biconvex positive lens L31. The fourth lens group G4 consists of a negative meniscus lens L41 with its convex surface facing the object.

[0090] The fifth lens group G5 consists of a positive meniscus lens L51 with its convex surface facing the object and a negative meniscus lens L52 with its concave surface facing the object, arranged in order from the object side along the optical axis. The image plane I is positioned on the image side of the fifth lens group G5. A parallel plate PP is positioned between the fifth lens group G5 and the image plane I.

[0091] Table 3 below lists the specifications of the optical system according to the third embodiment.

[0092] (Table 3) [Overall Specifications] f=82.010 fA=102.479 FNO=2.060 fR=82.146 2ω = 28.969 Δx = 10.381 Y=21.600 βF=2.495 TL=90.023 βB=0.800 Bf=1.000 βR1=0.202 Bf(a) = 17.858 [Lens Specifications] Face number RD nd νd 1 46.5771 5.350 1.7725 49.60 2 179.4303 0.100 3 40.3285 4.836 1.4970 81.61 4 129.0466 0.100 5 33.5684 6.218 1.4560 91.37 6 -229.0734 1.000 1.9004 37.37 7 29.9047 5.182 8 ∞ (D8) (Aperture S) 9 88.7347 1.000 1.4875 70.23 10 33.2383 (D10) 11 40.9864 8.072 1.7130 53.87 12 -66.9077 (D12) 13 159.0319 1.157 1.5814 40.75 14 37.2505 (D14) 15 46.6687 2.874 1.8590 22.73 16 78.4005 7.093 17 -26.5540 3.000 1.9037 31.31 18 -63.6154 15.803 19 ∞ 1.600 1.5168 63.88 20 ∞ Bf [Variable interval data] Infinity focus state, intermediate distance focus state, very close distance focus state f=82.010 β=-0.032 β=-0.113 D0 ∞ 2519.887 756.709 D8 1.066 3.911 11.447 D10 17.056 14.211 6.675 D12 1.148 2.146 4.829 D14 6.369 5.372 2.688 [Lens group data] Group starting plane focal length G1 1 102.479 G2 9 -109.666 G3 11 36.793 G4 13 -83.956 G5 15 -101.166

[0093] Figure 6(A) shows the aberrations of the optical system according to the third embodiment when focused at infinity. Figure 6(B) shows the aberrations of the optical system according to the third embodiment when focused at close range. From each aberration diagram, it can be seen that the optical system according to the third embodiment has excellent imaging performance, with aberrations well corrected across the entire range from infinity focus to close range focus. Therefore, even when focusing on close objects, it is possible to maintain good optical performance while reducing the angle of view fluctuation during focusing.

[0094] (Fourth embodiment) The fourth embodiment will be explained using Figures 7-8 and Table 4. Figure 7 is a diagram showing the lens configuration of the optical system according to the fourth embodiment. The optical system OL(4) according to the fourth embodiment consists of a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, a third lens group G3 having positive refractive power, a fourth lens group G4 having negative refractive power, and a fifth lens group G5 having negative refractive power, all arranged in order from the object side along the optical axis. When focusing from an object at infinity to an object at a close distance, the second lens group G2 and the fourth lens group G4 move towards the image side along the optical axis, and the spacing between adjacent lens groups changes. At the time of focusing, the first lens group G1, the third lens group G3, and the fifth lens group G5 are fixed with respect to the image plane I.

[0095] The aperture diaphragm S is positioned between the first lens group G1 and the second lens group G2. When focusing, the aperture diaphragm S is fixed relative to the image plane I. In this embodiment, the first lens group G1 constitutes the front group GA, and the second lens group G2, third lens group G3, fourth lens group G4, and fifth lens group G5 constitute the rear group GB. The second lens group G2 corresponds to the first focusing lens group GF1, which is positioned closest to the object in the rear group GB. The third lens group G3 corresponds to the subsequent lens group GR1, which is positioned adjacent to the first focusing lens group GF1 on the image plane side. The fourth lens group G4 corresponds to the second focusing lens group GF2, which is positioned closer to the image plane than the first focusing lens group GF1.

[0096] The first lens group G1 consists of a positive meniscus lens L11 with its convex surface facing the object, arranged in order from the object side along the optical axis; a cemented lens formed by joining a positive meniscus lens L12 with its convex surface facing the object and a negative meniscus lens L13 with its convex surface facing the object; and a cemented lens formed by joining a biconvex positive lens L14 and a biconcave negative lens L15. The second lens group G2 consists of a negative meniscus lens L21 with its convex surface facing the object.

[0097] The third lens group G3 consists of a negative meniscus lens L31 with its concave surface facing the object, a positive meniscus lens L32 with its concave surface facing the object, and a biconvex positive lens L33, all arranged in order from the object side along the optical axis. The fourth lens group G4 consists of a negative meniscus lens L41 with its convex surface facing the object.

[0098] The fifth lens group G5 consists of three lenses arranged in order from the object side along the optical axis: a negative meniscus lens L51 with its convex surface facing the object, a positive meniscus lens L52 with its convex surface facing the object, and a negative meniscus lens L53 with its concave surface facing the object. The image plane I is positioned on the image side of the fifth lens group G5. A parallel plate PP is positioned between the fifth lens group G5 and the image plane I.

[0099] Table 4 below lists the specifications of the optical system according to the fourth embodiment.

[0100] (Table 4) [Overall Specifications] f=84.453 fA=118.522 FNO=1.242 fR=61.307 2ω = 28.622 Δx = 10.784 Y=21.600 βF=3.780 TL=130.011 βB=0.713 Bf=1.000 βR1=0.153 Bf(a) = 11.185 [Lens Specifications] Face number RD nd νd 1 73.2143 10.224 1.8929 20.36 2 453.0360 0.100 3 54.5976 9.054 1.5503 75.49 4 258.6524 1.000 1.7283 28.46 5 39.1638 1.660 6 45.1558 12.609 1.5928 68.62 7 -100.3906 1.000 1.9229 20.88 8 119.0758 4.000 9 ∞ (D9) (Aperture S) 10 361.2899 1.000 1.5530 55.07 11 47.0735 (D11) 12 -36.4250 1.300 1.6398 34.47 13 -49.6895 0.100 14 -131.6092 5.891 1.7292 54.67 15 -54.7849 0.100 16 50.6772 14.609 1.7725 49.60 17 -230.5704 (D17) 18 113.4024 1.000 1.8081 22.74 19 52.3424 (D19) 20 89.2568 1.000 1.9229 20.88 21 36.4463 0.100 22 36.3836 9.726 1.9591 17.47 23 183.6004 8.074 24 -38.1283 1.000 1.7408 27.79 25 -98.0949 9.130 26 ∞ 1.600 1.5168 63.88 27 ∞ Bf [Variable interval data] Infinity focus state, intermediate distance focus state, very close distance focus state f=84.453 β=-0.043 β=-0.087 D0 ∞ 2018.279 1007.763 D9 2.000 6.974 12.784 D11 21.625 16.651 10.841 D17 2.000 4.186 6.592 D19 9.109 6.923 4.518 [Lens group data] Group starting plane focal length G1 1 118.522 G2 10 -97.991 G3 12 43.900 G4 18 -121.185 G5 20 -251.050

[0101] Figure 8(A) shows the aberrations of the optical system according to the fourth embodiment when focused at infinity. Figure 8(B) shows the aberrations of the optical system according to the fourth embodiment when focused at close range. From each aberration diagram, it can be seen that the optical system according to the fourth embodiment has excellent imaging performance, with aberrations well corrected across the entire range from infinity focus to close range focus. Therefore, even when focusing on close objects, it is possible to maintain good optical performance while reducing the angle of view fluctuation during focusing.

[0102] (Fifth example) The fifth embodiment will be explained using Figures 9 to 10 and Table 5. Figure 9 is a diagram showing the lens configuration of the optical system according to the fifth embodiment. The optical system OL(5) according to the fifth embodiment consists of a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, a third lens group G3 having positive refractive power, a fourth lens group G4 having negative refractive power, and a fifth lens group G5 having negative refractive power, all arranged in order from the object side along the optical axis. When focusing from an object at infinity to an object at a close distance, the second lens group G2 and the fourth lens group G4 move towards the image side along the optical axis, and the spacing between adjacent lens groups changes. At the time of focusing, the first lens group G1, the third lens group G3, and the fifth lens group G5 are fixed with respect to the image plane I.

[0103] The aperture diaphragm S is positioned between the first lens group G1 and the second lens group G2. When focusing, the aperture diaphragm S is fixed relative to the image plane I. In this embodiment, the first lens group G1 constitutes the front group GA, and the second lens group G2, third lens group G3, fourth lens group G4, and fifth lens group G5 constitute the rear group GB. The second lens group G2 corresponds to the first focusing lens group GF1, which is positioned closest to the object in the rear group GB. The third lens group G3 corresponds to the subsequent lens group GR1, which is positioned adjacent to the first focusing lens group GF1 on the image plane side. The fourth lens group G4 corresponds to the second focusing lens group GF2, which is positioned closer to the image plane than the first focusing lens group GF1.

[0104] The first lens group G1 consists of a positive meniscus lens L11 with its convex surface facing the object, arranged in order from the object side along the optical axis; a cemented lens formed by joining a biconvex positive lens L12 and a biconcave negative lens L13; and a cemented lens formed by joining a negative meniscus lens L14 with its convex surface facing the object and a positive meniscus lens L15 with its convex surface facing the object. The second lens group G2 consists of a cemented lens with negative refractive power, formed by joining a positive meniscus lens L21 with its concave surface facing the object and a biconcave negative lens L22, arranged in order from the object side.

[0105] The third lens group G3 consists of a biconvex positive lens L31 and a negative meniscus lens L32 with its concave surface facing the object, arranged in order from the object side along the optical axis. The fourth lens group G4 consists of a cemented lens with negative refractive power, formed by joining a biconvex positive lens L41 and a biconcave negative lens L42, arranged in order from the object side.

[0106] The fifth lens group G5 consists of a cemented lens formed by joining a negative meniscus lens L51 with a convex surface facing the object side and a biconvex positive lens L52, arranged in order from the object side along the optical axis, and a negative meniscus lens L53 with a concave surface facing the object side. The image plane I is positioned on the image side of the fifth lens group G5. A parallel plate PP is positioned between the fifth lens group G5 and the image plane I.

[0107] Table 5 below lists the specifications of the optical system according to the fifth embodiment.

[0108] (Table 5) [Overall Specifications] f=68.369 fA=75.680 FNO=1.850 fR=52.672 2ω = 35.083 Δx = 11.502 Y=21.600 βF=6.768 TL=116.082 βB=0.903 Bf=1.000 βR1=0.110 Bf(a) = 11.055 [Lens Specifications] Face number RD nd νd 1 113.3605 3.581 1.9229 18.90 2 259.4789 2.000 3 64.8154 7.756 1.7495 35.28 4 -305.8877 1.000 1.9229 18.90 5 89.4171 9.650 6 42.6939 1.000 1.9037 31.34 7 24.8498 8.072 1.6584 50.88 8 195.3643 2.647 9 ∞ (D9) (Aperture S) 10 -123.7398 2.263 1.8590 22.73 11 -60.4222 1.000 1.5225 59.84 12 34.0422 (D12) 13 35.0724 8.638 1.6584 50.88 14 -72.0999 0.816 15 -53.1994 6.085 2.0033 28.27 16 -57.0661 (D16) 17 200.0000 4.047 1.5503 75.50 18 -70.0000 1.000 1.7888 28.43 19 88.7178 (D19) 20 146.9186 1.000 1.7847 26.29 21 35.2338 8.408 2.0010 29.14 22 -294.1634 5.492 23 -25.4180 1.000 1.6889 31.07 24 -199.9991 9.000 25 ∞ 1.600 1.5168 63.88 26 ∞ Bf [Variable interval data] Infinity focus state, intermediate distance focus state, very close distance focus state f=68.369 β=-0.028 β=-0.148 D0 ∞ 2500.000 500.000 D9 2.021 4.185 13.522 D12 20.093 17.929 8.591 D16 1.418 1.749 4.177 D19 5.496 5.164 2.737 [Lens group data] Group starting plane focal length G1 1 75.680 G2 10 -59.462 G3 13 39.475 G4 17 -105.696 G5 20 -171.475

[0109] Figure 10(A) shows the aberrations of the optical system according to the fifth embodiment when focused at infinity. Figure 10(B) shows the aberrations of the optical system according to the fifth embodiment when focused at close range. From each aberration diagram, it can be seen that the optical system according to the fifth embodiment has excellent imaging performance, with aberrations well corrected across the entire range from infinity focus to close range focus. Therefore, even when focusing on close objects, it is possible to maintain good optical performance while reducing the angle of view fluctuation during focusing.

[0110] (Sixth embodiment) The sixth embodiment will be described using Figures 11-12 and Table 6. Figure 11 is a diagram showing the lens configuration of the optical system according to the sixth embodiment. The optical system OL(6) according to the sixth embodiment consists of a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, a third lens group G3 having positive refractive power, a fourth lens group G4 having negative refractive power, and a fifth lens group G5 having negative refractive power, all arranged in order from the object side along the optical axis. When focusing from an object at infinity to an object at a close distance, the second lens group G2 and the fourth lens group G4 move towards the image side along the optical axis, and the spacing between adjacent lens groups changes. At the time of focusing, the first lens group G1, the third lens group G3, and the fifth lens group G5 are fixed with respect to the image plane I.

[0111] The aperture diaphragm S is positioned between the first lens group G1 and the second lens group G2. When focusing, the aperture diaphragm S is fixed relative to the image plane I. In this embodiment, the first lens group G1 constitutes the front group GA, and the second lens group G2, third lens group G3, fourth lens group G4, and fifth lens group G5 constitute the rear group GB. The second lens group G2 corresponds to the first focusing lens group GF1, which is positioned closest to the object in the rear group GB. The third lens group G3 corresponds to the subsequent lens group GR1, which is positioned adjacent to the first focusing lens group GF1 on the image plane side. The fourth lens group G4 corresponds to the second focusing lens group GF2, which is positioned closer to the image plane than the first focusing lens group GF1.

[0112] The first lens group G1 consists of a positive meniscus lens L11 with its convex surface facing the object, a positive meniscus lens L12 with its convex surface facing the object, a cemented lens formed by joining a positive meniscus lens L13 with its convex surface facing the object and a negative meniscus lens L14 with its convex surface facing the object, a negative meniscus lens L15 with its convex surface facing the object, and a positive meniscus lens L16 with its convex surface facing the object, all arranged in order from the object side along the optical axis. The second lens group G2 consists of a cemented lens with negative refractive power formed by joining a negative meniscus lens L21 with its convex surface facing the object and a negative meniscus lens L22 with its convex surface facing the object, all arranged in order from the object side.

[0113] The third lens group G3 consists of a cemented lens formed by joining a biconcave negative lens L31 and a biconvex positive lens L32, which are arranged in order from the object side along the optical axis, a positive meniscus lens L33 with its convex surface facing the object side, and a biconvex positive lens L34. The fourth lens group G4 consists of a negative meniscus lens L41 with its convex surface facing the object side.

[0114] The fifth lens group G5 consists of a cemented lens formed by joining a biconvex positive lens L51 and a negative meniscus lens L52 with its concave surface facing the object, arranged in order from the object side along the optical axis, and a negative meniscus lens L53 with its concave surface facing the object. The image plane I is positioned on the image side of the fifth lens group G5. A parallel plate PP is positioned between the fifth lens group G5 and the image plane I.

[0115] Table 6 below lists the specifications of the optical system according to the sixth embodiment.

[0116] (Table 6) [Overall Specifications] f=79.983 fA=80.002 FNO=1.650 fR=58.141 2ω = 14.994 Δx = 8.575 Y=21.600 βF=3.011 TL=127.000 βB=1.000 Bf=1.000 βR1=0.280 Bf(a) = 12.166 [Lens Specifications] Face number RD nd νd 1 110.5878 4.985 1.9630 24.11 2 283.6905 0.100 3 63.6059 4.396 2.0033 28.27 4 89.9017 3.000 5 80.0000 5.550 1.6935 53.20 6 383.6873 1.200 1.8929 20.36 7 84.9195 5.586 8 48.6443 1.000 1.8467 23.78 9 28.2642 0.248 10 28.4061 10.976 1.4970 81.61 11 231.2679 2.922 12 ∞ (D12) (Aperture S) 13 267.2771 1.500 1.6230 58.16 14 36.6616 3.000 1.8590 22.73 15 35.7069 (D15) 16 -36.0649 1.000 1.7380 32.33 17 92.6451 8.190 1.7725 49.62 18 -48.8133 0.100 19 64.0592 4.832 1.7725 49.60 20 306.9860 1.122 21 88.0545 5.785 1.9229 20.88 22 -184.9624 (D22) 23 140.5931 1.505 1.6910 54.82 24 48.6168 (D24) 25 83.3736 11.265 1.8515 40.78 26 -30.3564 1.000 1.8081 22.74 27 -217.6682 3.835 28 -42.0504 1.000 1.7783 23.91 29 -2185.7734 10.111 30 ∞ 1.600 1.5168 63.88 31 ∞ Bf [Variable interval data] Infinity focus state, intermediate distance focus state, very close distance focus state f=79.983 β=-0.032 β=-0.113 D0 ∞ 2544.448 725.082 D12 1.300 3.613 9.875 D15 18.706 16.393 10.131 D22 1.300 2.156 4.812 D24 8.887 8.031 5.375 [Lens group data] Group starting plane focal length G1 1 80.002 G2 13 -67.065 G3 16 41.282 G4 23 -108.270 G5 25 -1174.941

[0117] Figure 12(A) shows the aberrations of the optical system according to the sixth embodiment when focused at infinity. Figure 12(B) shows the aberrations of the optical system according to the sixth embodiment when focused at close range. From each aberration diagram, it can be seen that the optical system according to the sixth embodiment has excellent imaging performance, with aberrations well corrected across the entire range from infinity focus to close range focus. Therefore, even when focusing on close objects, it is possible to maintain good optical performance while reducing the angle of view fluctuation during focusing.

[0118] (Seventh Example) The seventh embodiment will be described using Figures 13-14 and Table 7. Figure 13 is a diagram showing the lens configuration of the optical system according to the seventh embodiment. The optical system OL(7) according to the seventh embodiment consists of a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, and a third lens group G3 having positive refractive power, all arranged in order from the object side along the optical axis. When focusing from an object at infinity to an object at a close distance, the second lens group G2 moves towards the image side along the optical axis, and the spacing between adjacent lens groups changes. At the time of focusing, the first lens group G1 and the third lens group G3 are fixed with respect to the image plane I.

[0119] The aperture diaphragm S is positioned between the first lens group G1 and the second lens group G2. When focusing, the aperture diaphragm S is fixed relative to the image plane I. In this embodiment, the first lens group G1 constitutes the front group GA, and the second lens group G2 and the third lens group G3 constitute the rear group GB. The second lens group G2 corresponds to the focusing lens group GF, which is positioned closest to the object in the rear group GB. The third lens group G3 corresponds to the subsequent lens group GR1, which is positioned adjacent to the focusing lens group GF on the image plane side.

[0120] The first lens group G1 consists of a positive meniscus lens L11 with its convex surface facing the object, arranged in order from the object side along the optical axis; a cemented lens formed by joining a biconvex positive lens L12 and a biconcave negative lens L13; and a cemented lens formed by joining a negative meniscus lens L14 with its convex surface facing the object and a positive meniscus lens L15 with its convex surface facing the object. The second lens group G2 consists of a cemented lens with negative refractive power, formed by joining a positive meniscus lens L21 with its concave surface facing the object and a biconcave negative lens L22, arranged in order from the object side.

[0121] The third lens group G3 consists of, arranged in order from the object side along the optical axis: a biconvex positive lens L31, a cemented lens formed by joining a biconcave negative lens L32 and a biconvex positive lens L33, a cemented lens formed by joining a biconvex positive lens L34 and a biconcave negative lens L35, a negative meniscus lens L36 with its convex surface facing the object side, a biconvex positive lens L37, and a negative meniscus lens L38 with its concave surface facing the object side. The image plane I is positioned on the image side of the third lens group G3. A parallel plate PP is positioned between the third lens group G3 and the image plane I.

[0122] Table 7 below lists the specifications of the optical system according to the seventh embodiment.

[0123] (Table 7) [Overall Specifications] f=73.180 fA=65.047 FNO=1.857 fR=61.979 2ω = 32.805 Δx = 7.838 Y=21.600 βF=5.900 TL=119.318 βB=1.125 Bf=1.006 βR1=0.191 Bf(a) = 11.061 [Lens Specifications] Face number RD nd νd 1 86.3436 3.855 1.9229 18.90 2 240.9219 0.100 3 109.1989 5.811 1.7495 35.28 4 -148.8703 1.000 1.9229 20.88 5 100.0000 11.212 6 40.0083 1.000 1.9037 31.31 7 23.8536 8.324 1.6968 55.53 8 541.8771 3.546 9 ∞ (D9) (Aperture S) 10 -102.6387 2.695 1.8590 22.73 11 -47.9027 1.940 1.5530 55.07 12 32.6973 (D12) 13 34.2780 7.412 1.7015 41.24 14 -122.6095 0.204 15 -30343.0670 1.113 1.9537 32.32 16 31.2978 6.189 1.7639 48.49 17 -1254.1635 1.400 18 141.8350 5.000 1.5378 74.70 19 -48.4566 1.000 1.6398 34.47 20 90.6288 2.112 21 240.5167 1.001 1.8548 24.80 22 37.9682 0.100 23 37.4387 12.070 2.0007 25.46 24 -277.6337 5.753 25 -23.7721 1.076 1.6730 38.26 26 -96.5381 9.000 27 ∞ 1.600 1.5168 63.88 28 ∞ Bf [Variable interval data] Infinity focus state, intermediate distance focus state, very close distance focus state f=73.180 β=-0.029 β=-0.128 D0 ∞ 2558.661 610.735 D9 2.242 3.982 10.080 D12 21.558 19.818 13.719 [Lens group data] Group starting plane focal length G1 1 65.047 G2 10 -52.462 G3 13 61.979

[0124] Figure 14(A) shows the aberrations of the optical system according to the seventh embodiment when focused at infinity. Figure 14(B) shows the aberrations of the optical system according to the seventh embodiment when focused at close range. From each aberration diagram, it can be seen that the optical system according to the seventh embodiment has excellent imaging performance, with aberrations well corrected across the entire range from infinity focus to close range focus. Therefore, even when focusing on close objects, it is possible to maintain good optical performance while reducing the angle of view fluctuation during focusing.

[0125] (Eighth example) The eighth embodiment will be explained using Figures 15-16 and Table 8. Figure 15 is a diagram showing the lens configuration of the optical system according to the eighth embodiment. The optical system OL(8) according to the eighth embodiment consists of a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, a third lens group G3 having positive refractive power, a fourth lens group G4 having positive refractive power, and a fifth lens group G5 having negative refractive power, all arranged in order from the object side along the optical axis. When focusing from an object at infinity to an object at a close distance, the second lens group G2 moves towards the image side along the optical axis, and the fourth lens group G4 moves towards the object side along the optical axis, changing the spacing between adjacent lens groups. Note that when focusing, the first lens group G1, the third lens group G3, and the fifth lens group G5 are fixed with respect to the image plane I.

[0126] The aperture diaphragm S is positioned between the first lens group G1 and the second lens group G2. When focusing, the aperture diaphragm S is fixed relative to the image plane I. In this embodiment, the first lens group G1 constitutes the front group GA, and the second lens group G2, third lens group G3, fourth lens group G4, and fifth lens group G5 constitute the rear group GB. The second lens group G2 corresponds to the first focusing lens group GF1, which is positioned closest to the object in the rear group GB. The third lens group G3 corresponds to the subsequent lens group GR1, which is positioned adjacent to the first focusing lens group GF1 on the image plane side. The fourth lens group G4 corresponds to the second focusing lens group GF2, which is positioned closer to the image plane than the first focusing lens group GF1.

[0127] The first lens group G1 consists of a positive meniscus lens L11 with its convex surface facing the object, a positive meniscus lens L12 with its convex surface facing the object, and a cemented lens formed by joining a biconvex positive lens L13 and a biconcave negative lens L14, all arranged in order from the object side along the optical axis. The second lens group G2 consists of a negative meniscus lens L21 with its convex surface facing the object.

[0128] The third lens group G3 consists of a biconvex positive lens L31. The fourth lens group G4 consists of a positive meniscus lens L41 with its convex surface facing the object.

[0129] The fifth lens group G5 consists of a negative meniscus lens L51 with its concave surface facing the object. The image plane I is positioned on the image side of the fifth lens group G5. A parallel plate PP is positioned between the fifth lens group G5 and the image plane I.

[0130] Table 8 below lists the specifications of the optical system according to the eighth embodiment.

[0131] (Table 8) [Overall Specifications] f=82.010 fA=84.922 FNO=2.050 fR=72.581 2ω = 32.753 Δx = 8.605 Y=21.600 βF=3.508 TL=90.018 βB=0.966 Bf=1.322 βR1=0.219 Bf(a) = 16.376 [Lens Specifications] Face number RD nd νd 1 49.7600 5.102 1.7550 52.32 2 207.7589 0.100 3 43.3970 4.415 1.6180 63.33 4 120.3692 0.100 5 35.5101 6.189 1.5928 68.62 6 -216.6911 2.098 1.9053 35.04 7 28.2895 5.240 8 ∞ (D8) (Aperture S) 9 5405.8128 1.000 1.4875 70.23 10 35.3627 (D10) 11 41.2560 9.000 1.5174 52.43 12 -51.9830 (D12) 13 98.4043 2.467 1.8590 22.73 14 222.8980 (D14)[[ID=1,7]] 15 -31.6093 3.000 1.8502 30.05 16 -173.6461 14.000 17 ∞ 1.600 1.5168 63.88 18 ∞ Bf [Variable Interval Data] Infinity Focus State, Intermediate Distance Focus State, Closest Distance Focus State f = 82.010 β = -0.033 β = -0.115 D0 ∞ 2526.094 756.181 D8 1.985 4.234 10.591 D10 16.324 14.075 7.719 D12 10.523 8.452 4.434 D14 5.552 7.623 11.641 [Lens Group Data] Group, Starting Surface, Focal Length G1 1 84.922 G2 9 -73.023 G3 11 45.967 G4 13 203.256 G5 15 -45.895

[0132] Figure 16(A) shows the aberrations of the optical system according to the eighth embodiment when focused at infinity. Figure 16(B) shows the aberrations of the optical system according to the eighth embodiment when focused at close range. From each aberration diagram, it can be seen that the optical system according to the eighth embodiment has excellent imaging performance, with aberrations well corrected across the entire range from infinity focus to close range focus. Therefore, even when focusing on close objects, it is possible to maintain good optical performance while reducing the angle of view fluctuation during focusing.

[0133] Next, the table of [Conditional Expression Corresponding Values] is shown below. This table summarizes the values ​​corresponding to each conditional expression (1) to (16) for all examples (Examples 1 to 8). Condition (1) 0.50 <ST / TL<0.95 Condition (2) 0.65 < (-fF) / fA < 1.20 Conditional expression (3) 0.70<(-fF) / fR<1.80 Conditional expression (4) 0.00<βR1 / βF<0.25 Conditional expression (5) 0.03<Δx / f<0.35 Condition (6) 0.65 <f / (-fF)<1.60 Condition (7) 2.00 <TL / (FNO×Bf)<10.00 Conditional expression (8) -2.50<(rFR2+rFR1) / (rFR2-rFR1)<-0.25 Conditional expression (9) 0.90<(rNR2+rNR1) / (rNR2-rNR1)<2.65 Conditional expression (10) 0.08<1 / βF<0.55 Conditional expression (11) {βF+(1 / βF)} -2 <0.15 Condition (12) 0.003 <BLDF / TL<0.060 Conditional expression (13) 0.05<βB / βF<0.50 Condition (14) 0.05 <Bf / TL<0.25 Condition (15) 1.00 <FNO<3.00 Conditional expression (16) 12.00°<2ω<40.00°

[0134] [Conditional response values] (Examples 1 to 4) Conditional expression Example 1 Example 2 Example 3 Example 4 (1) 0.702 0.667 0.747 0.695 (2) 0.914 0.794 1.070 0.827 (3) 1.268 0.950 1.335 1.598 (4) 0.138 0.038 0.081 0.040 (5) 0.146 0.095 0.127 0.128 (6) 1.065 1.275 0.748 0.862 (7) 8.113 5.488 2.447 9.359 (8) -1.192 -1.054 -2.198 -1.300 (9) 1.661 1.441 2.433 2.272 (10) 0.384 0.227 0.401 0.265 (11) 0.112 0.047 0.119 0.061 (12) 0.009 0.011 0.011 0.008 (13) 0.374 0.230 0.321 0.188 (14) 0.087 0.098 0.198 0.086 (15) 1.424 1.855 2.060 1.242 (16) 28.285 28.002 28.969 28.622 [Conditional response values] (Examples 5 to 8) Conditional expression Example 5 Example 6 Example 7 Example 8 (1) 0.692 0.685 0.708 0.742 (2) 0.786 0.838 0.807 0.860 (3) 1.129 1.154 0.846 1.006 (4) 0.016 0.093 0.032 0.062 (5) 0.168 0.107 0.107 0.105 (6) 1.150 1.193 1.395 1.123 (7) 5.676 6.327 5.808 2.681 (8) -0.568 -1.308 -0.517 -1.013 (9) 1.291 1.039 1.653 1.445 (10) 0.148 0.332 0.169 0.285 (11) 0.021 0.089 0.027 0.070 (12) 0.028 0.035 0.039 0.011 (13) 0.133 0.332 0.191 0.275 (14) 0.095 0.096 0.093 0.182 (15) 1.850 1.650 1.857 2.050 (16) 35.083 14.994 32.805 32.753

[0135] According to the above embodiments, it is possible to realize an optical system with minimal fluctuation in the angle of view during focusing.

[0136] The above embodiments illustrate specific examples of the present invention, and the present invention is not limited to these.

[0137] The following elements can be appropriately incorporated as long as they do not impair the optical performance of the optical system of this embodiment.

[0138] Although three-group and five-group configurations have been shown as examples of the optical system in this embodiment, this application is not limited to these, and optical systems with other group configurations (e.g., four-group, six-group, etc.) can also be constructed. Specifically, the optical system of this embodiment may be configured by adding lenses or lens groups to the object side or the image plane side. A lens group refers to a portion having at least one lens, separated by an air gap that changes when focusing.

[0139] A lens group or partial lens group may be moved so that it has a component perpendicular to the optical axis, or rotated (oscillated) in an in-plane direction including the optical axis, to correct image blur caused by camera shake.

[0140] The lens surface may be formed as a spherical, flat, or aspherical surface. A spherical or flat lens surface is preferable because it facilitates lens processing and assembly adjustment, preventing degradation of optical performance due to processing and assembly errors. It is also preferable because it minimizes degradation of image rendering performance even if the image plane is misaligned.

[0141] If the lens surface is aspherical, it can be an aspherical surface created by grinding, a glass molded aspherical surface formed from glass using a mold, or a composite aspherical surface formed by creating an aspherical shape from resin on the surface of glass. Furthermore, the lens surface may also be a diffractive surface, and the lens may be a refractive index distributed lens (GRIN lens) or a plastic lens.

[0142] The aperture diaphragm is preferably positioned between the first and second lens groups, but its function may be substituted by the lens frame instead of providing a separate aperture diaphragm component.

[0143] Each lens surface may be coated with an anti-reflective 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]

[0144] G1 First lens group G2 Second lens group G3 3rd lens group G4 4th lens group G5 5th lens group I Image plane S Aperture diaphragm

Claims

1. It consists of a front group, an aperture, and a rear group, arranged in order from the object side along the optical axis. The aforementioned front group consists of a first lens group having positive refractive power, The aforementioned rear group consists of a second lens group that constitutes a first focusing lens group having negative refractive power, arranged in order from the object side, a third lens group having positive refractive power, a fourth lens group that constitutes a second focusing lens group having negative refractive power, and a fifth lens group having negative refractive power. When focusing occurs, the second lens group and the fourth lens group move along the optical axis, and the spacing between adjacent lens groups changes. An optical system that satisfies the following conditions. 0.63<ST / TL<0.95 0.65<f / (-fF)<1.40 0.05<Bf / TL<0.25 However, ST: distance along the optical axis from the aperture to the image plane. TL: Total length of the optical system f: Focal length of the optical system fF: Focal length of the second lens group constituting the first focusing lens group. Bf: Back focus of the optical system

2. It consists of a front group, an aperture, and a rear group, arranged in order from the object side along the optical axis. The aforementioned front group consists of a first lens group having positive refractive power, The aforementioned rear group consists of a second lens group that constitutes a first focusing lens group having negative refractive power, arranged in order from the object side, a third lens group having positive refractive power, a fourth lens group that constitutes a second focusing lens group having negative refractive power, and a fifth lens group having negative refractive power. When focusing occurs, the second lens group and the fourth lens group move along the optical axis, and the spacing between adjacent lens groups changes. An optical system that satisfies the following conditions. 0.50<ST / TL<0.95 0.65<(-fF) / fA<1.15 0.65<f / (-fF)<1.40 0.05<Bf / TL<0.25 However, ST: distance along the optical axis from the aperture to the image plane. TL: Total length of the optical system fF: Focal length of the second lens group constituting the first focusing lens group. fA: Focal length of the front group f: Focal length of the optical system Bf: Back focus of the optical system

3. The optical system according to claim 1 or 2, satisfying the following conditional expression. 0.65<f / (-fF)≦1.395

4. The aforementioned rear group has at least one lens group positioned closer to the image plane than the second lens group that constitutes the first focusing lens group, An optical system according to any one of claims 1 to 3 that satisfies the following conditional expression. 0.70<(-fF) / fR<1.80 However, fR: the combined focal length of at least one lens group.

5. The aforementioned rear group has a subsequent lens group arranged adjacent to the image plane side of the second lens group that constitutes the first focusing lens group, An optical system according to any one of claims 1 to 4 that satisfies the following conditional expression. 0.00<βR1 / βF<0.25 However, βR1: Lateral magnification of the subsequent lens group when an object at infinity is in focus. βF: Lateral magnification of the second lens group constituting the first focusing lens group when an object at infinity is in focus.

6. An optical system according to any one of claims 1 to 5 that satisfies the following conditional expression. 2.00<TL / (FNO×Bf)<10.00 However, FNO: F-number of the optical system. Bf: Back focus of the optical system

7. The optical system according to any one of claims 1 to 6, wherein the focusing lens group is composed of one negative lens component.

8. An optical system according to any one of claims 1 to 7 that satisfies the following conditional expression. -2.50<(rFR2+rFR1) / (rFR2-rFR1)<-0.25 However, rFR1: the radius of curvature of the lens surface closest to the object in the second lens group constituting the first focusing lens group. rFR2: Radius of curvature of the lens surface closest to the image plane in the second lens group constituting the first focusing lens group.

9. An optical system according to any one of claims 1 to 8 that satisfies the following conditional expression. 0.90<(rNR2+rNR1) / (rNR2-rNR1)<2.65 However, rNR1: radius of curvature of the object-side lens surface in the lens positioned closest to the image plane in the optical system. rNR2: Radius of curvature of the lens surface on the image plane side of the lens positioned closest to the image plane in the optical system.

10. An optical system according to any one of claims 1 to 9 that satisfies the following conditional expression. 0.08<1 / βF<0.55 However, βF: the lateral magnification of the second lens group constituting the first focusing lens group when an object at infinity is in focus.

11. An optical system according to any one of claims 1 to 10 that satisfies the following conditional expression. {βF+(1 / βF)} -2 <0.15 However, βF: the lateral magnification of the second lens group constituting the first focusing lens group when an object at infinity is in focus.

12. An optical system according to any one of claims 1 to 11 that satisfies the following conditional expression. 0.003<BLDF / TL<0.060 However, BLDF: the length along the optical axis of the second lens group constituting the first focusing lens group.

13. An optical system according to any one of claims 1 to 12 that satisfies the following conditional expression. 0.05<βB / βF<0.50 However, βB: Lateral magnification of the rear group when an object at infinity is in focus. βF: Lateral magnification of the second lens group constituting the first focusing lens group when an object at infinity is in focus.

14. An optical system according to any one of claims 1 to 13 that satisfies the following conditional expression. 1.00<FNO<3.00 However, FNO: F-number of the optical system.

15. An optical system according to any one of claims 1 to 14 that satisfies the following conditional expression. 12.00°<2ω<40.00° However, 2ω: the entire field of view of the optical system.

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

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