Optical system, optical instrument, and method for manufacturing an optical system

Abstract

To provide an optical system that is compact, bright, and capable of achieving good optical performance. [Solution] The optical system OL consists of a front group GA having positive refractive power, an aperture S, an intermediate group GM having positive refractive power, and a rear group GR having negative refractive power, all arranged in order from the object side along the optical axis. When focusing, the intermediate group GA moves along the optical axis, and the front group GA consists of a negative lens, a positive lens, a negative lens, and a positive lens, arranged in order from the object side, or a negative lens, a positive lens, a positive lens, and a negative lens, and the rear group GR consists of a positive lens, a negative lens, and a negative lens, satisfying the following conditional equation. 2.60 <DSE / DM<3.50 0.80

Description

[Technical Field]

[0001] The present invention relates to an optical system, an optical instrument, and a method for manufacturing an optical system. [Background technology]

[0002] Conventional optical systems suitable for photographic cameras, electronic still cameras, video cameras, etc., have been proposed (see, for example, Patent Document 1). In such optical systems, it is difficult to achieve brightness and good optical performance while keeping the device compact. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2019-200339 [Overview of the Initiative]

[0004] The first optical system according to the present invention consists of a front group having positive refractive power, an aperture, an intermediate group having positive refractive power, and a rear group having negative refractive power, all arranged in order from the object side along the optical axis. When focusing occurs, the intermediate group moves along the optical axis, the distance between the front group and the intermediate group changes, and the distance between the intermediate group and the rear group changes, satisfying the following conditional equation. 2.60 <DSE / DM<3.50 0.80 <fAM / f<1.00 However, DSE: distance along the optical axis from the aperture to the lens surface closest to the image plane of the rear group. DM: Length of the intermediate group along the optical axis in the state of infinity focus. fAM: Combined focal length of the front group and the intermediate group in the infinity focus state f: focal length of the optical system when in focus at infinity

[0005] The second optical system according to the present invention consists of a front group having positive refractive power, an aperture, an intermediate group having positive refractive power, and a rear group having negative refractive power, all arranged in order from the object side along the optical axis. When focusing occurs, the intermediate group moves along the optical axis, the distance between the front group and the intermediate group changes, and the distance between the intermediate group and the rear group changes, satisfying the following conditional equation. 0.80 <fAM / f<1.00 0.50 <DA / (DM+DR)<1.20 1.70 <DSR / DM<3.40 However, fAM: the combined focal length of the front group and the intermediate group in the infinity focus state. f: focal length of the optical system when in focus at infinity DA: Length along the optical axis of the front group in the state of infinity focus. DM: Length of the intermediate group along the optical axis in the state of infinity focus. DR: Length along the optical axis of the rear group in the infinity focus state. DSR: Distance along the optical axis from the aperture to the lens surface closest to the object in the rear group.

[0006] The optical instrument according to the present invention is configured to include the optical system described above.

[0007] The first method for manufacturing an optical system according to the present invention is a method for manufacturing an optical system comprising a front group having positive refractive power, an aperture, an intermediate group having positive refractive power, and a rear group having negative refractive power, arranged in order from the object side along the optical axis, wherein when focusing occurs, the intermediate group moves along the optical axis, the distance between the front group and the intermediate group changes, and the distance between the intermediate group and the rear group changes, and each lens is arranged in the lens barrel such that the following condition is satisfied. 2.60 <DSE / DM<3.50 0.80 <fAM / f<1.00 However, DSE: distance along the optical axis from the aperture to the lens surface closest to the image plane of the rear group. DM: Length of the intermediate group along the optical axis in the state of infinity focus. fAM: Combined focal length of the front group and the intermediate group in the infinity focus state f: Focal length of the optical system in the infinite focus state

[0008] A method for manufacturing an optical system according to a second invention is a method for manufacturing an optical system including a front group having a positive refractive power, an aperture stop, an intermediate group having a positive refractive power, and a rear group having a negative refractive power, arranged in order from the object side along the optical axis. When focusing, the intermediate group moves along the optical axis, the distance between the front group and the intermediate group changes, and the distance between the intermediate group and the rear group changes. Each lens is arranged in a lens barrel so as to satisfy the following conditional expressions. 0.80 < fAM / f < 1.00 0.50 < DA / (DM + DR) < 1.20 1.70 < DSR / DM < 3.40 However, fAM: Composite focal length of the front group and the intermediate group in the infinite focus state f: Focal length of the optical system in the infinite focus state DA: Length on the optical axis of the front group in the infinite focus state DM: Length on the optical axis of the intermediate group in the infinite focus state DR: Length on the optical axis of the rear group in the infinite focus state DSR: Distance on the optical axis from the aperture stop to the most object-side lens surface of the rear group

Brief Description of Drawings

[0009] [Figure 1] It is a diagram showing the lens configuration of the optical system according to the first embodiment. [Figure 2] FIG. 2(A) and FIG. 2(B) are aberration diagrams at the time of infinite focus and close focus of the optical system according to the first embodiment, respectively. [Figure 3] It is a diagram showing the lens configuration of the optical system according to the second embodiment. [Figure 4] FIG. 4(A) and FIG. 4(B) are aberration diagrams at the time of infinite focus and close focus of the optical system according to the second embodiment, respectively. [Figure 5] It is a diagram showing 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 configuration of a camera equipped with the optical system according to each embodiment. [Figure 16] It is a flowchart showing a manufacturing method of the optical system according to each embodiment.

Embodiments for Carrying Out the Invention

[0010] The following describes preferred embodiments of the present invention. First, a camera (optical device) equipped with an optical system according to each embodiment will be described with reference to Figure 15. As shown in Figure 15, this 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.

[0011] 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 15 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.

[0012] Next, the optical system according to the first embodiment will be described. Optical system OL(1), as an example of the optical system OL according to the first embodiment, consists of a front group GA having positive refractive power, an aperture (diaphragm) S, an intermediate group GM having positive refractive power, and a rear group GR having negative refractive power, all arranged in order from the object side along the optical axis, as shown in Figure 1. When focusing, the intermediate group GM moves along the optical axis, changing the distance between the front group GA and the intermediate group GM, and changing the distance between the intermediate group GM and the rear group GR.

[0013] Under the above configuration, the optical system OL according to the first embodiment satisfies the following conditions (1) and (2). 2.60 <DSE / DM<3.50 ···(1) 0.80 <fAM / f<1.00 ···(2) However, DSE: distance along the optical axis from aperture S to the lens surface closest to the image plane of the rear group GR. DM: Length of the intermediate group GM on the optical axis in the state of infinity focus. fAM: Combined focal length of the front group GA and the intermediate group GM at infinity focus. f: Focal length of the optical system OL at infinity focus.

[0014] According to the first embodiment, it is possible to obtain an optical system that is compact yet bright and has good optical performance, and an optical instrument equipped with this optical system. The optical system OL according to the first embodiment may be optical system OL(2) shown in Figure 3, optical system OL(3) shown in Figure 5, or optical system OL(4) shown in Figure 7. Furthermore, the optical system OL according to the first embodiment may be optical system OL(5) shown in Figure 9, optical system OL(6) shown in Figure 11, or optical system OL(7) shown in Figure 13.

[0015] Conditional equation (1) defines the appropriate relationship between the distance along the optical axis from the aperture S to the lens surface closest to the image plane of the rear group GR, and the length along the optical axis of the intermediate group GM when in focus at infinity. By satisfying conditional equation (1), it is possible to suppress variations in various aberrations such as spherical aberration, field curvature, and coma aberration during focusing, while maintaining a compact size.

[0016] If the corresponding value in conditional equation (1) exceeds the upper limit, the distance along the optical axis from the aperture S to the lens surface closest to the image plane of the rear group GR becomes longer. This makes it difficult to reduce the size of the optical system OL while suppressing fluctuations in various aberrations such as spherical aberration, field curvature, and coma aberration during focusing. By setting the upper limit of conditional equation (1) to 3.45, 3.40, 3.35, and further to 3.30, the effects of this embodiment can be made more reliable.

[0017] If the corresponding value in conditional equation (1) falls below the lower limit, the distance along the optical axis from the aperture S to the lens surface closest to the image plane of the rear group GR becomes shorter, and the amount of movement of the intermediate group GM at the time of focusing is restricted, making it difficult to suppress fluctuations in various aberrations such as spherical aberration, field curvature, and coma aberration at the time of focusing. By setting the lower limit of conditional equation (1) to 2.65, 2.68, 2.70, and further to 2.73, the effect of this embodiment can be made more reliable.

[0018] Conditional equation (2) defines the appropriate relationship between the combined focal length of the front group GA and the intermediate group GM at infinity focus and the focal length of the optical system OL at infinity focus. By satisfying conditional equation (2), it is possible to correct various aberrations such as spherical aberration, chromatic aberration, and coma aberration well, while maintaining a compact size.

[0019] If the corresponding value in conditional equation (2) exceeds the upper limit, it becomes difficult to correct field curvature and astigmatism when miniaturizing the optical system (OL). By setting the upper limit of conditional equation (2) to 0.98, and further to 0.96, the effects of this embodiment can be made more reliable.

[0020] If the corresponding value in conditional equation (2) falls below the lower limit, the magnification of the rear group GR becomes too large, making it difficult to correct various aberrations such as spherical aberration, chromatic aberration, and coma aberration. By setting the lower limit of conditional equation (2) to 0.82, 0.84, and further to 0.86, the effect of this embodiment can be made more reliable.

[0021] Next, an optical system according to the second embodiment will be described. The optical system OL according to the second embodiment has the same configuration as the optical system OL according to the first embodiment, and will be described using the same reference numerals as in the first embodiment. An example of the optical system OL according to the second embodiment, optical system OL(1), as shown in Figure 1, consists of a front group GA having positive refractive power, an aperture (diaphragm) S, an intermediate group GM having positive refractive power, and a rear group GR having negative refractive power, all arranged in order from the object side along the optical axis. When focusing, the intermediate group GM moves along the optical axis, changing the distance between the front group GA and the intermediate group GM, and changing the distance between the intermediate group GM and the rear group GR.

[0022] Under the above configuration, the optical system OL according to the second embodiment satisfies the following conditions (2) to (4). 0.80 <fAM / f<1.00 ···(2) 0.50 <DA / (DM+DR)<1.20 ···(3) 1.70 <DSR / DM<3.40 ···(4) However, fAM: the combined focal length of the front group GA and the intermediate group GM in the state of infinity focus. f: Focal length of the optical system OL at infinity focus. DA: Length of the front group GA on the optical axis in the state of focus at infinity DM: Length of the intermediate group GM on the optical axis in the state of infinity focus. DR: Length of the rear group GR along the optical axis when in focus at infinity. DSR: Distance along the optical axis from aperture S to the lens surface of the rear group GR closest to the object.

[0023] According to the second embodiment, it is possible to obtain an optical system that is compact yet bright and has good optical performance, and an optical instrument equipped with this optical system. The optical system OL according to the second embodiment may be optical system OL(2) shown in Figure 3, optical system OL(3) shown in Figure 5, or optical system OL(4) shown in Figure 7. Furthermore, the optical system OL according to the second embodiment may be optical system OL(5) shown in Figure 9, optical system OL(6) shown in Figure 11, or optical system OL(7) shown in Figure 13.

[0024] Conditional equation (2) defines an appropriate relationship between the combined focal length of the front group GA and the intermediate group GM in the infinity focus state and the focal length of the optical system OL in the infinity focus state. By satisfying conditional equation (2), various aberrations such as spherical aberration, chromatic aberration, and coma aberration can be well corrected while maintaining a compact size, similar to the first embodiment. By setting the upper limit of conditional equation (2) to 0.98 and further to 0.96, the effect of this embodiment can be made more reliable. Furthermore, by setting the lower limit of conditional equation (2) to 0.82, 0.84 and further to 0.86, the effect of this embodiment can be made more reliable.

[0025] Conditional equation (3) defines an appropriate relationship between the length of the front group GA on the optical axis in the infinity focus state and the sum of the lengths of the intermediate group GM and the rear group GR on the optical axis in the infinity focus state. By satisfying conditional equation (3), aberrations that are generally difficult to correct in lenses with a wide angle of view (e.g., field curvature, distortion, chromatic aberration, etc.) and aberrations that are generally difficult to correct in lenses with a small F-number (e.g., spherical aberration, coma aberration, etc.) can be well corrected.

[0026] If the corresponding value in conditional equation (3) exceeds the upper limit, the front group GA becomes too long relative to the intermediate group GM and the rear group GR, making it difficult to correct spherical aberration, coma aberration, etc. By setting the upper limit of conditional equation (3) to 1.18, 1.15, and further to 1.13, the effects of this embodiment can be made more reliable.

[0027] If the corresponding value in conditional equation (3) falls below the lower limit, the intermediate group GM and the rear group GR become too long relative to the front group GA, making it difficult to correct field curvature, distortion, chromatic aberration, etc. By setting the lower limit of conditional equation (3) to 0.52, and further to 0.55, the effects of this embodiment can be made more reliable.

[0028] Conditional equation (4) defines the appropriate relationship between the distance along the optical axis from the aperture S to the lens surface of the rear group GR closest to the object, and the length along the optical axis of the intermediate group GM in the infinity focus state. By satisfying conditional equation (4), it is possible to suppress variations in various aberrations during focusing while maintaining a compact size.

[0029] If the corresponding value in conditional equation (4) exceeds the upper limit, the distance along the optical axis from the aperture S to the lens surface closest to the object in the rear group GR becomes longer, making it difficult to reduce the size of the optical system OL while suppressing variations in various aberrations during focusing. By setting the upper limit of conditional equation (4) to 3.35, 3.30, and further to 3.25, the effects of this embodiment can be made more reliable.

[0030] If the corresponding value in conditional equation (4) falls below the lower limit, the distance along the optical axis from the aperture S to the lens surface of the rear group GR closest to the object becomes shorter, and the amount of movement of the intermediate group GM at the time of focusing is restricted, making it difficult to suppress variations in various aberrations during focusing. By setting the lower limit of conditional equation (4) to 1.75, 1.80, and further to 1.82, the effect of this embodiment can be made more reliable.

[0031] The optical system OL according to the second embodiment may satisfy the aforementioned condition (1). By satisfying condition (1), it is possible to suppress variations in various aberrations during focusing while maintaining a compact size, similar to the first embodiment. The effect of this embodiment can be made more reliable by setting the upper limit of condition (1) to 3.45, 3.40, 3.35, and further to 3.30. Furthermore, the effect of this embodiment can be made more reliable by setting the lower limit of condition (1) to 2.65, 2.68, 2.70, and further to 2.73.

[0032] The optical system OL according to the first and second embodiments preferably satisfies the following condition (5). 0.60 <fM / f<1.30 ···(5) However, fM: focal length of the intermediate group GM in the infinity focus state.

[0033] Condition (5) defines the appropriate relationship between the focal length of the intermediate group GM in the infinity focus state and the focal length of the optical system OL in the infinity focus state. By satisfying condition (5), spherical aberration, coma aberration, etc. can be well corrected while maintaining a small F-number and compact size.

[0034] If the corresponding value in conditional equation (5) exceeds the upper limit, the refractive power of the intermediate group GM becomes too weak, making it difficult to reduce the size of the optical system OL while simultaneously reducing the F-number. By setting the upper limit of conditional equation (5) to 1.25, 1.20, 1.15, and further to 1.10, the effects of each embodiment can be made more reliable.

[0035] If the corresponding value in conditional equation (5) falls below the lower limit, the refractive power of the intermediate group GM becomes too strong, making it difficult to correct spherical aberration, coma aberration, etc. By setting the lower limit of conditional equation (5) to 0.65, and further to 0.70, the effects of each embodiment can be made more reliable.

[0036] The optical system OL according to the first and second embodiments preferably satisfies the following condition (6). 0.60 <fA / (-fR)<1.50 ···(6) However, fA: focal distance of the front group GA in the state of focus at infinity. fR: Focal length of the rear group GR when in focus at infinity

[0037] Conditional equation (6) defines the appropriate relationship between the focal length of the front group GA and the focal length of the rear group GR when in focus at infinity. By satisfying conditional equation (6), field curvature, astigmatism, spherical aberration, coma aberration, etc., can be effectively corrected.

[0038] If the corresponding value in conditional equation (6) exceeds the upper limit, the refractive power of the rear group GR becomes too strong compared to the front group GA, making it difficult to correct spherical aberration and coma aberration. By setting the upper limit of conditional equation (6) to 1.45, 1.40, 1.35, and further to 1.30, the effects of each embodiment can be made more reliable.

[0039] If the corresponding value in conditional equation (6) falls below the lower limit, the refractive power of the rear group GR becomes too weak compared to the front group GA, making it difficult to correct field curvature and astigmatism. By setting the lower limit of conditional equation (6) to 0.65, 0.70, and further to 0.75, the effects of each embodiment can be made more reliable.

[0040] The optical system OL according to the first and second embodiments preferably satisfies the following condition (7). 0.60 < {1-(βM) 2}×(βR) 2 <1.50 ···(7) However, βM: Horizontal magnification of the intermediate group GM in the infinity focus state. βR: Lateral magnification of the rear group GR in the infinity focus state.

[0041] Conditional equation (7) defines the appropriate relationship between the lateral magnification of the intermediate group GM and the lateral magnification of the rear group GR in the infinity focus state. By satisfying conditional equation (7), it is possible to maintain the image plane position change during focusing appropriately while suppressing variations in various aberrations during focusing.

[0042] If the corresponding value in conditional equation (7) falls outside the above range, it becomes difficult to maintain proper image plane position changes during focusing while suppressing fluctuations in various aberrations during focusing. Setting the upper limit of conditional equation (7) to 1.45, 1.40, 1.35, 1.30, and further to 1.25 makes the effects of each embodiment more reliable. Setting the lower limit of conditional equation (7) to 0.65, 0.70, 0.75, and further to 0.80 makes the effects of each embodiment more reliable.

[0043] The optical system OL according to the first and second embodiments preferably satisfies the following condition (8). 0.70 <DA / DM<2.30 ···(8) However, DA: length of the front group GA on the optical axis in the state of focus at infinity. DM: Length of the intermediate group GM on the optical axis in the state of infinity focus.

[0044] Conditional equation (8) defines the appropriate relationship between the length of the front group GA on the optical axis and the length of the intermediate group GM on the optical axis when in focus at infinity. By satisfying conditional equation (8), various aberrations such as spherical aberration, coma aberration, and field curvature can be corrected effectively.

[0045] If the corresponding value in conditional equation (8) falls outside the above range, it becomes difficult to correct various aberrations such as spherical aberration, coma aberration, and field curvature. Setting the upper limit of conditional equation (8) to 2.25, 2.20, 2.15, and further to 2.10 makes the effects of each embodiment more reliable. Setting the lower limit of conditional equation (8) to 0.75, 0.80, 0.85, 0.90, and further to 0.95 makes the effects of each embodiment more reliable.

[0046] In the optical system OL according to the first and second embodiments, it is desirable that the lens positioned closest to the image plane is a negative lens. This allows for good correction of field curvature and astigmatism.

[0047] In the optical system OL according to the first and second embodiments, it is desirable that the second lens positioned from the object side be a positive lens. This allows for good correction of spherical aberration and coma aberration.

[0048] In the optical system OL according to the first and second embodiments, it is desirable that the third lens positioned from the image plane is a positive lens. This allows for good correction of spherical aberration and coma aberration.

[0049] In the optical system OL according to the first and second embodiments, the intermediate group GM consists of a first focusing lens group and a second focusing lens group arranged in order from the object side along the optical axis, and it is desirable that when focusing, the first focusing lens group and the second focusing lens group move along the optical axis on different trajectories from each other, satisfying the following condition (9). 9.00 < |fF1| / f < 90.00 ···(9) However, fF1: Focal length of the first focusing lens group

[0050] Conditional equation (9) defines the appropriate relationship between the focal length of the first focusing lens group and the focal length of the optical system OL. By satisfying conditional equation (9), various aberrations such as spherical aberration, coma aberration, and field curvature can be well corrected, and fluctuations in various aberrations during focusing can be suppressed.

[0051] If the corresponding value of conditional equation (9) falls outside the above range, it becomes difficult to correct various aberrations such as spherical aberration, coma aberration, and field curvature, and to suppress fluctuations in various aberrations during focusing. Setting the upper limit of conditional equation (9) to 88.00, 85.00, and further to 83.00 makes the effects of each embodiment more reliable. Setting the lower limit of conditional equation (9) to 9.50, 10.00, 10.50, 11.00, and further to 11.50 makes the effects of each embodiment more reliable.

[0052] In the optical system OL according to the first and second embodiments, the intermediate group GM consists of a first focusing lens group and a second focusing lens group having positive refractive power, which are arranged in order from the object side along the optical axis. When focusing, it is desirable that the first focusing lens group and the second focusing lens group move along the optical axis on different trajectories and satisfy the following condition (10). 0.30 <fF2 / f<2.00 ···(10) However, fF2: Focal length of the second focusing lens group

[0053] Conditional equation (10) defines the appropriate relationship between the focal length of the second focusing lens group and the focal length of the optical system OL. By satisfying conditional equation (10), various aberrations such as spherical aberration, coma aberration, and field curvature can be well corrected, and fluctuations in various aberrations during focusing can be suppressed.

[0054] If the corresponding value of conditional equation (10) falls outside the above range, it becomes difficult to correct various aberrations such as spherical aberration, coma aberration, and field curvature, and to suppress fluctuations in various aberrations during focusing. Setting the upper limit of conditional equation (10) to 1.85, 1.75, 1.50, 1.45, and further to 1.40 makes the effects of each embodiment more reliable. Setting the lower limit of conditional equation (10) to 0.40, 0.50, 0.55, 0.60, 0.65, and further to 0.70 makes the effects of each embodiment more reliable.

[0055] The optical system OL according to the first and second embodiments preferably satisfies the following condition (11). 0.80 < (-fE) / f < 16.00 ···(11) However, fE: the focal length of the lens positioned closest to the image plane in the rear group GR.

[0056] Conditional equation (11) defines the appropriate relationship between the focal length of the lens positioned closest to the image plane in the rear group GR and the focal length of the optical system OL. By satisfying conditional equation (11), field curvature, chromatic aberration, distortion, etc., can be effectively corrected.

[0057] If the corresponding value of conditional equation (11) falls outside the above range, it becomes difficult to correct field curvature, chromatic aberration, distortion, etc. Setting the upper limit of conditional equation (11) to 15.50, 15.25, 15.00, and 14.75 makes the effects of each embodiment more reliable. Setting the lower limit of conditional equation (11) to 0.85, 0.90, 0.95, and further to 1.00 makes the effects of each embodiment more reliable.

[0058] The optical system OL according to the first and second embodiments preferably satisfies the following condition (12). 1.00 < (-fR) / f < 3.90 ... (12) However, fR: focal length of the rear group GR in the infinity focus state.

[0059] Conditional equation (12) defines the appropriate relationship between the focal length of the rear group GR in the infinity focus state and the focal length of the optical system OL in the infinity focus state. By satisfying conditional equation (12), field curvature, chromatic aberration, distortion, etc., can be effectively corrected.

[0060] If the corresponding value of conditional equation (12) falls outside the above range, it becomes difficult to correct field curvature, chromatic aberration, distortion, etc. Setting the upper limit of conditional equation (12) to 3.80, 3.70, 3.60, and further to 3.50 makes the effects of each embodiment more reliable. Setting the lower limit of conditional equation (12) to 1.05, 1.10, 1.15, and further to 1.18 makes the effects of each embodiment more reliable.

[0061] Next, with reference to Figure 16, the manufacturing method of the optical system OL according to the first embodiment will be outlined. First, along the optical axis, in order from the object side, a front group GA having positive refractive power, an aperture S, an intermediate group GM having positive refractive power, and a rear group GR having negative refractive power are arranged (step ST1). Next, when focusing, the intermediate group GM moves along the optical axis, changing the distance between the front group GA and the intermediate group GM, and changing the distance between the intermediate group GM and the rear group GR (step ST2). Then, each lens is arranged in the lens barrel so as to satisfy at least the above conditions (1) and (2) (step ST3). With this manufacturing method, it is possible to manufacture an optical system that is small yet bright and has good optical performance.

[0062] Next, we will outline the manufacturing method of the optical system OL according to the second embodiment. The manufacturing method of the optical system OL according to the second embodiment is the same as the manufacturing method described in the first embodiment, so we will explain it with reference to the same Figure 16 as in the first embodiment. First, along the optical axis, in order from the object side, a front group GA having positive refractive power, an aperture S, an intermediate group GM having positive refractive power, and a rear group GR having negative refractive power are arranged (step ST1). Next, when focusing, the intermediate group GM moves along the optical axis, changing the distance between the front group GA and the intermediate group GM, and changing the distance between the intermediate group GM and the rear group GR (step ST2). Then, each lens is arranged in the lens barrel so as to satisfy at least the above conditional equations (2) to (4) (step ST3). With such a manufacturing method, it is possible to manufacture an optical system that is small yet bright and has good optical performance. [Examples]

[0063] The optical system OL according to each embodiment will be described below based on the drawings. Figures 1, 3, 5, 7, 9, 11, and 13 are cross-sectional views showing the configuration and refractive power distribution of the optical system OL{OL(1) to OL(7)} according to the first to seventh embodiments. In the cross-sectional views of the optical system OL(1) to OL(7) according to the first to seventh embodiments, the direction of movement of each lens group along the optical axis when focusing from infinity to a near-field object is indicated by arrows.

[0064] In Figures 1, 3, 5, 7, 9, 11, and 13, 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.

[0065] Tables 1 to 7 are shown below. Table 1 shows the specifications for the first embodiment, Table 2 for the second embodiment, and Table 3 for the third embodiment. In each embodiment, the d-line (wavelength λ=587.6nm) and the g-line (wavelength λ=435.8nm) were selected as the targets for calculating aberration characteristics.

[0066] 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 (in degrees), and Y is the image height. TL is the distance along the optical axis from the lens surface closest to the object to the lens surface closest to the image plane when the optical system is focused at infinity, plus Bf (back focus). Bf is the distance along the optical axis from the lens surface closest to the image plane to the image plane when the optical system is focused at infinity (air equivalent distance).

[0067] Also, in the [Overall Specifications] table, βM indicates the lateral magnification of the intermediate group in the infinity focus state. βR indicates the lateral magnification of the rear group in the infinity focus state. fAM indicates the combined focal length of the front group and the intermediate group in the infinity focus state. fM indicates the focal length of the intermediate group in the infinity focus state. fE indicates the focal length of the lens arranged closest to the image plane side of the rear group.

[0068] In the [Lens Specifications] table, the surface number indicates the order of the optical surfaces from the object side along the direction of light ray propagation. R is the radius of curvature of each optical surface (a surface with the center of curvature located on the image side is defined as a positive value), D is the surface interval, which is the distance on the optical axis from each optical surface to the next optical surface (or the image plane), nd is the refractive index of the material of the optical member with respect to the d-line, and νd is the Abbe number of the material of the optical member with respect to the d-line. "∞" for the radius of curvature indicates a plane or an aperture, and (stop S) indicates the aperture stop S. The description of the refractive index of air nd = 1.00000 is omitted. When an optical surface is an aspherical surface, an asterisk is attached to the surface number, and the paraxial radius of curvature is shown in the column of the radius of curvature R.

[0069] In the [Aspherical Data] table, for the aspherical surfaces shown in [Lens Specifications], the shape is expressed by the following formula (A). X(y) is the distance (sag amount) 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 i-th order aspherical coefficient. "E-n" indicates "×10 -n ". For example, 1.234E-05 = 1.234×10 -5 . Note that the second-order aspherical coefficient A2 is 0, and its description is omitted.

[0070] 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)

[0071] 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. The [Variable Interval Data] table also shows the inter-plane spacing at infinity focus and at close focus. In the [Variable Interval Data] table, f represents the focal length of the entire lens system, and β represents the magnification. D0 represents the distance from the object to the optical surface closest to the object in the optical system.

[0072] The [Lens Group Data] table shows the starting surface (the surface closest to the object) and focal length for each lens group.

[0073] 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.

[0074] The explanations in the table above are common to all examples, and any redundant explanations below will be omitted.

[0075] (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, an aperture diaphragm S, a second lens group G2 having positive refractive power, and a third lens group G3 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 object side along the optical axis, and the spacing between adjacent lens groups changes. At the time of focusing, the positions of the first lens group G1 and the third lens group G3 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.

[0076] 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 in position relative to the image plane I. In this embodiment, the first lens group G1 constitutes the front group GA, which as a whole has a positive refractive power. The second lens group G2 constitutes the intermediate group GM, which as a whole has a positive refractive power. The third lens group G3 constitutes the rear group GR, which as a whole has a negative refractive power. In this embodiment, the second lens group G2 corresponds to the focusing lens group GF.

[0077] The first lens group G1 consists of a biconcave negative lens L11, a biconvex positive lens L12, and a bonded negative lens formed by joining a biconcave negative lens L13 and a biconvex positive lens L14, all arranged in order from the object side along the optical axis.

[0078] The second lens group G2 consists of a bonded negative lens formed by joining a biconcave negative lens L21 and a biconvex positive lens L22, which are arranged in order from the object side along the optical axis; a positive meniscus lens L23 with its concave surface facing the object side; and a positive meniscus lens L24 with its concave surface facing the object side. The positive meniscus lens L23 has an aspherical lens surface on the image plane side.

[0079] The third lens group G3 consists of a bonded negative lens formed by joining a biconvex positive lens L31 and a biconcave negative lens L32, which are arranged in order from the object side along the optical axis, and a negative meniscus lens L33 with its concave surface facing the object side. The negative meniscus lens L33 has an aspherical lens surface on the object side. The image plane I is positioned on the image side of the third lens group G3. An optical filter FL is positioned between the third lens group G3 and the image plane I.

[0080] Table 1 below lists the specifications of the optical system according to the first embodiment.

[0081] (Table 1) [Overall Specifications] f=36.000 FNO=1.46 ω=31.58 Y=21.70 TL=90.455 Bf=12.055 βM=0.365 βR=1.129 fAM=31.881 fM=35.176 fE = -103.632 [Lens Specifications] Face number RD nd νd 1 -684.4027 1.200 1.48749 70.32 2 30.7344 3.000 3 72.1530 5.200 1.81600 46.59 4 -97.7224 2.836 5 -48.4219 1.000 1.58144 40.98 6 22.6564 8.200 1.80400 46.60 7 -88.5075 2.500 8 ∞ (D8) (Aperture S) 9 -20.3873 0.800 1.75520 27.57 10 408.5856 4.400 1.77250 49.62 11 -40.1434 0.200 12 -359.9200 4.400 1.77250 49.62 13* -40.3978 2.500 14 -320.2237 7.300 1.77250 49.62 15 -32.4972 (D15) 16 1000.0000 8.300 1.80400 46.60 17 -30.0000 1.200 1.62004 36.40 18 81.1828 7.900 19* -46.2636 1.200 1.48749 70.32 20 -553.8512 10.500 21 ∞ 1.600 1.51680 64.20 22 ∞ 0.500 [Aspherical data] Page 13 κ=1.0000,A4=1.10781E-05,A6=2.99496E-09,A8=2.33937E-11,A10=-4.46052E-14 Page 19 κ=1.0000,A4=-1.04347E-05,A6=1.44032E-08,A8=-6.35354E-11,A10=9.26712E-14 [Variable interval data] Infinity focus state Close focus state f = 36.000 β = -0.100 D0 ∞ 341.8 D8 13.764 10.624 D15 2.500 5.640 [Lens group data] Group starting plane focal length G1 1 87.279 G2 9 35.176 G3 16 -97.362

[0082] 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.

[0083] From the various aberration diagrams, it can be seen that the optical system according to the first embodiment has excellent imaging performance, with aberrations well corrected not only when focused at infinity but also when focused at close range.

[0084] (Second example) The second embodiment will be explained 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, an aperture diaphragm S, 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, 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 third lens group G3 move toward the object side along the optical axis on different trajectories (amount of movement), and the spacing between adjacent lens groups changes. At the time of focusing, the positions of the first lens group G1 and the fourth lens group G4 are fixed with respect to the image plane I.

[0085] 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 in position relative to the image plane I. In this embodiment, the first lens group G1 constitutes the front group GA, which as a whole has a positive refractive power. The second lens group G2 and the third lens group G3 constitute the intermediate group GM, which as a whole has a positive refractive power. The fourth lens group G4 constitutes the rear group GR, which as a whole has a negative refractive power. In this embodiment, the second lens group G2 corresponds to the first focusing lens group GF1, and the third lens group G3 corresponds to the second focusing lens group GF2.

[0086] The first lens group G1 consists of a biconcave negative lens L11, a biconvex positive lens L12, and a bonded negative lens formed by joining a biconcave negative lens L13 and a biconvex positive lens L14, all arranged in order from the object side along the optical axis.

[0087] The second lens group G2 consists of a bonded negative lens formed by joining a biconcave negative lens L21 and a biconvex positive lens L22, which are arranged in order from the object side along the optical axis, and a biconvex positive lens L23.

[0088] The third lens group G3 consists of a biconvex positive lens L31. The positive lens L31 is a composite lens in which a resin layer is provided on the image-plane side surface of a glass lens body. The image-plane side surface of the resin layer is aspherical, and the positive lens L31 is a composite aspherical lens. In the [Lens Specifications] described later, surface number 14 indicates the object-side surface of the lens body, surface number 15 indicates the image-plane side surface of the lens body and the object-side surface of the resin layer (the surface where the two are joined), and surface number 16 indicates the image-plane side surface of the resin layer.

[0089] The fourth lens group G4 consists of a biconvex positive lens L41, a biconcave negative lens L42, and a negative meniscus lens L43 with its concave surface facing the object, arranged in order from the object side along the optical axis. The negative meniscus lens L43 is a composite lens in which a resin layer is provided on the object-side surface of a glass lens body. The object-side surface of the resin layer is aspherical, and the negative meniscus lens L43 is a composite aspherical lens. In the [Lens Specifications] described later, surface number 21 indicates the object-side surface of the resin layer, surface number 22 indicates the image-side surface of the resin layer and the object-side surface of the lens body (the surface where the two are joined), and surface number 23 indicates the image-side surface of the lens body. The image plane I is positioned on the image side of the fourth lens group G4. An optical filter FL is positioned between the fourth lens group G4 and the image plane I.

[0090] Table 2 below lists the specifications of the optical system according to the second embodiment.

[0091] (Table 2) [Overall Specifications] f=36.000 FNO=1.46 ω=31.93 Y=21.70 TL=94.455 Bf=12.055 βM=0.364 βR=1.109 fAM=32.455 fM=38.495 fE = -82.849 [Lens Specifications] Face number RD nd νd 1 -241.3564 1.200 1.48749 70.32 2 28.6776 3.700 3 67.6343 5.500 1.80400 46.60 4 -87.5063 4.500 5 -39.7460 1.000 1.62004 36.40 6 28.7182 8.800 1.80400 46.60 7 -51.6012 2.500 8 ∞ (D8) (Aperture S) 9 -20.9092 0.800 1.67270 32.19 10 151.7550 2.500 1.71300 53.96 11 -390.5795 0.100 12 160.0000 6.550 1.77250 49.62 13 -33.2181 (D13) 14 98.3039 6.650 1.77250 49.62 15 -68.9149 0.200 1.56093 36.64 16* -54.3985 (D16) 17 100.0000 7.000 1.60311 60.69 18 -52.7466 0.100 19 -102.2448 1.200 1.75520 27.57 20 75.3981 8.600 21* -38.9850 0.200 1.56093 36.64 22 -34.7338 1.100 1.51680 63.88 23 -500.0000 10.500 24 ∞ 1.600 1.51680 64.20 25 ∞ 0.500 [Aspherical data] Page 16 κ=1.0000,A4=9.32563E-06,A6=-9.72867E-10,A8=4.82410E-12,A10=1.29999E-15 Page 21 κ=1.0000,A4=-7.71632E-06,A6=6.32250E-09,A8=-4.09121E-11,A10=7.56697E-14 [Variable interval data] Infinity focus state Close focus state f = 36.000 β = -0.100 D0 ∞ 340.5 D8 16.200 10.637 D13 2.000 4.298 D16 2.000 5.227 [Lens group data] Group starting plane focal length G1 1 89.058 G2 9 481.615 G3 14 48.005 G4 17 -88.510

[0092] 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 not only when focused at infinity but also when focused at close range.

[0093] (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, an aperture diaphragm S, 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, 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 third lens group G3 move toward the object side along the optical axis along different trajectories (amount of movement), and the spacing between adjacent lens groups changes. At the time of focusing, the positions of the first lens group G1 and the fourth lens group G4 are fixed with respect to the image plane I.

[0094] 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 in position relative to the image plane I. In this embodiment, the first lens group G1 constitutes the front group GA, which as a whole has a positive refractive power. The second lens group G2 and the third lens group G3 constitute the intermediate group GM, which as a whole has a positive refractive power. The fourth lens group G4 constitutes the rear group GR, which as a whole has a negative refractive power. In this embodiment, the second lens group G2 corresponds to the first focusing lens group GF1, and the third lens group G3 corresponds to the second focusing lens group GF2.

[0095] The first lens group G1 consists of a negative meniscus lens L11 with its convex surface facing the object, arranged in order from the object side along the optical axis; a biconvex positive lens L12; and a bonded negative lens formed by joining a biconvex positive lens L13 and a biconcave negative lens L14.

[0096] The second lens group G2 consists of a negative meniscus lens L21 with its concave surface facing the object, and a biconvex positive lens L22, which are arranged in order from the object side along the optical axis.

[0097] The third lens group G3 consists of a biconvex positive lens L31. The positive lens L31 has an aspherical surface on the image plane side.

[0098] The fourth lens group G4 consists of a bonded negative lens formed by joining a biconvex positive lens L41 and a biconcave negative lens L42, which are arranged in order from the object side along the optical axis, and a negative meniscus lens L43 with its concave surface facing the object side. The negative meniscus lens L43 has an aspherical lens surface on the object side. The image plane I is positioned on the image side of the fourth lens group G4. An optical filter FL is positioned between the fourth lens group G4 and the image plane I.

[0099] Table 3 below lists the specifications of the optical system according to the third embodiment.

[0100] (Table 3) [Overall Specifications] f=28.840 FNO=1.46 ω=36.89 Y=21.70 TL=99.455 Bf=12.055 βM=0.322 βR=1.145 fAM=25.181 fM=30.516 fE = -419.431 [Lens Specifications] Face number RD nd νd 1 212.1379 1.200 1.48749 70.32 2 23.3713 20.636 3 49.7144 5.200 1.80400 46.60 4 -274.4623 0.200 5 36.2277 7.800 1.80400 46.60 6 -36.1361 1.000 1.64769 33.72 7 24.9178 3.500 8 ∞ (D8) (Aperture S) 9 -16.2749 1.000 1.71736 29.57 10 -58.1572 0.200 11 182.4646 7.500 1.77250 49.62 12 -29.4929 (D12) 13 91.4430 6.700 1.77250 49.62 14* -41.8675 (D14) 15 232.3455 8.300 1.74100 52.77 16 -32.5776 1.200 1.69895 30.13 17 56.4353 4.500 18* -293.0076 1.200 1.77250 49.62 19 -3067.6687 10.500 20 ∞ 1.600 1.51680 64.20 21 ∞ 0.500 [Aspherical data] Page 14 κ=1.0000,A4=1.40329E-05,A6=-5.80050E-09,A8=7.49771E-12,A10=0.00000E+00 Page 18 κ=1.0000,A4=-2.37073E-06,A6=-9.54689E-09,A8=-3.12635E-11,A10=4.17230E-14 [Variable interval data] Infinity focus state Close focus state f = 28.840 β = -0.100 D0 ∞ 264.4 D8 12.764 10.564 D12 2.000 1.810 D14 2.500 4.891 [Lens group data] Group starting plane focal length G1 1 78.172 G2 9 336.592 G3 13 38.009 G4 15 -98.824

[0101] 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 not only when focused at infinity but also when focused at close range.

[0102] (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, an aperture diaphragm S, a second lens group G2 having negative refractive power, a third lens group G3 having positive refractive power, and a fourth lens group G4 having negative refractive power, 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 third lens group G3 move toward the object side along the optical axis along different trajectories (amount of movement), and the spacing between adjacent lens groups changes. At the time of focusing, the positions of the first lens group G1 and the fourth lens group G4 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 in position relative to the image plane I. In this embodiment, the first lens group G1 constitutes the front group GA, which as a whole has a positive refractive power. The second lens group G2 and the third lens group G3 constitute the intermediate group GM, which as a whole has a positive refractive power. The fourth lens group G4 constitutes the rear group GR, which as a whole has a negative refractive power. In this embodiment, the second lens group G2 corresponds to the first focusing lens group GF1, and the third lens group G3 corresponds to the second focusing lens group GF2.

[0104] The first lens group G1 consists of a biconcave negative lens L11, a biconvex positive lens L12, and a bonded negative 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 negative lens L11 is a composite lens in which a resin layer is provided on the image-plane side surface of a glass lens body. The image-plane side surface of the resin layer is aspherical, and the negative lens L11 is a composite aspherical lens. In the [Lens Specifications] described later, surface number 1 indicates the object-side surface of the lens body, surface number 2 indicates the image-plane side surface of the lens body and the object-side surface of the resin layer (the surface where the two are joined), and surface number 3 indicates the image-plane side surface of the resin layer.

[0105] The second lens group G2 consists of a negative meniscus lens L21 with its concave surface facing the object, and a biconvex positive lens L22, which are arranged in order from the object side along the optical axis.

[0106] The third lens group G3 consists of a biconvex positive lens L31. The positive lens L31 is a composite lens in which a resin layer is provided on the image-plane side surface of a glass lens body. The image-plane side surface of the resin layer is aspherical, and the positive lens L31 is a composite aspherical lens. In the [Lens Specifications] described later, surface number 14 indicates the object-side surface of the lens body, surface number 15 indicates the image-plane side surface of the lens body and the object-side surface of the resin layer (the surface where the two are joined), and surface number 16 indicates the image-plane side surface of the resin layer.

[0107] The fourth lens group G4 consists of a bonded positive lens formed by joining a biconvex positive lens L41 and a negative meniscus lens L42 with its concave surface facing the object, arranged in order from the object side along the optical axis, and a biconcave negative lens L43. The image plane I is positioned on the image side of the fourth lens group G4. An optical filter FL is placed between the fourth lens group G4 and the image plane I.

[0108] Table 4 below lists the specifications of the optical system according to the fourth embodiment.

[0109] (Table 4) [Overall Specifications] f=51.500 FNO=1.46 ω=23.07 Y=21.70 TL=96.455 Bf=12.055 βM=0.477 βR=1.049 fAM=49.080 fM=45.487 fE = -53.954 [Lens Specifications] Face number RD nd νd 1 -177.4706 1.200 1.61272 58.54 2 86.9619 0.200 1.56093 36.64 3* 102.9016 4.800 4 53.4789 7.000 1.83481 42.73 5 -187.8110 0.200 6 41.5072 9.600 1.77250 49.62 7 -59.7672 1.000 1.67270 32.19 8 25.4591 6.000 9 ∞ (D9) (Aperture S) 10 -19.6066 0.800 1.67270 32.19 11 -141.5164 0.200 12 620.7750 6.300 1.77250 49.62 13 -31.0101 (D13) 14 152.3899 7.000 1.77250 49.62 15 -54.2708 0.200 1.56093 36.64 16* -50.4347 (D16) 17 864.8117 8.500 1.77250 49.62 18 -32.5318 1.200 1.53172 48.78 19 -587.8875 5.000 20 -37.6797 1.200 1.67270 32.19 21 1000.0000 10.500 22 ∞ 1.600 1.51680 64.20 23 ∞ 0.500 [Aspherical data] 3rd page κ=1.0000,A4=2.85829E-06,A6=4.78816E-10,A8=9.44053E-13,A10=0.00000E+00 Page 16 κ=1.0000,A4=4.47165E-06,A6=1.34225E-09,A8=0.00000E+00,A10=0.00000E+00 [Variable interval data] Infinity focus state Close focus state f = 51.500 β = -0.100 D0 ∞ 488.2 D9 17.100 11.418 D13 2.400 2.457 D16 4.500 10.126 [Lens group data] Group starting plane focal length G1 1 102.992 G2 10 -4133.359 G3 14 50.566 G4 17 -120.130

[0110] 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 not only when focused at infinity but also when focused at close range.

[0111] (Fifth example) The fifth embodiment will be described 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, an aperture diaphragm S, a second lens group G2 having positive refractive power, and a third lens group G3 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 object side along the optical axis, and the spacing between adjacent lens groups changes. At the time of focusing, the positions of the first lens group G1 and the third lens group G3 are fixed with respect to the image plane I.

[0112] 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 in position relative to the image plane I. In this embodiment, the first lens group G1 constitutes the front group GA, which as a whole has a positive refractive power. The second lens group G2 constitutes the intermediate group GM, which as a whole has a positive refractive power. The third lens group G3 constitutes the rear group GR, which as a whole has a negative refractive power. In this embodiment, the second lens group G2 corresponds to the focusing lens group GF.

[0113] The first lens group G1 consists of a biconcave negative lens L11, a biconvex positive lens L12, and a bonded negative 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 negative lens L11 has an aspherical lens surface on the image plane side.

[0114] The second lens group G2 consists of a negative meniscus lens L21 with its concave surface facing the object, a biconvex positive lens L22, and a biconvex positive lens L23, all arranged in order from the object side along the optical axis. The lens surface of the positive lens L23 on the image plane side is aspherical.

[0115] The third lens group G3 consists of a bonded positive lens formed by joining a positive meniscus lens L31 with its concave surface facing the object side and a negative meniscus lens L32 with its concave surface facing the object side, arranged in order from the object side along the optical axis, and a biconcave negative lens L33. The image plane I is positioned on the image side of the third lens group G3. An optical filter FL is placed between the third lens group G3 and the image plane I.

[0116] Table 5 below lists the specifications of the optical system according to the fifth embodiment.

[0117] (Table 5) [Overall Specifications] f=51.500 FNO=1.46 ω=22.89 Y=21.70 TL=96.455 Bf=12.055 βM=0.477 βR=1.049 fAM=49.098 fM=43.754 fE = -53.954 [Lens Specifications] Face number RD nd νd 1 -1011.3026 1.200 1.61272 58.54 2* 71.1508 5.000 3 49.8099 6.800 1.83481 42.73 4 -340.2042 0.200 5 38.0076 9.800 1.77250 49.62 6 -69.4851 1.000 1.67270 32.19 7 24.0943 6.000 8 ∞ (D8) (Aperture S) 9 -19.9414 0.800 1.67270 32.19 10 -523.8033 0.200 11 771.8063 6.300 1.77250 49.62 12 -30.7112 2.300 13 94.8763 7.700 1.77250 49.62 14* -52.2961 (D14) 15 -472.2588 8.100 1.77250 49.62 16 -33.2104 1.200 1.53172 48.78 17 -120.9626 5.000 18 -37.6797 1.200 1.67270 32.19 19 1000.0000 10.500 20 ∞ 1.600 1.51680 64.20 21 ∞ 0.500 [Aspherical data] 2nd side κ=1.0000,A4=2.09682E-06,A6=5.08234E-10,A8=7.22650E-13,A10=0.00000E+00 Page 14 κ=1.0000,A4=2.94054E-06,A6=2.73765E-10,A8=0.00000E+00,A10=0.00000E+00 [Variable interval data] Infinity focus state Close focus state f = 51.500 β = -0.100 D0 ∞ 485.4 D8 17.100 11.486 D14 4.500 10.114 [Lens group data] Group starting plane focal length G1 1 102.950 G2 9 43.754 G3 15 -132.026

[0118] 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 not only when focused at infinity but also when focused at close range.

[0119] (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, an aperture diaphragm S, a second lens group G2 having negative refractive power, a third lens group G3 having positive refractive power, and a fourth lens group G4 having negative refractive power, 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 third lens group G3 move toward the object side along the optical axis along different trajectories (amount of movement), and the spacing between adjacent lens groups changes. At the time of focusing, the positions of the first lens group G1 and the fourth lens group G4 are fixed with respect to the image plane I.

[0120] 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 in position relative to the image plane I. In this embodiment, the first lens group G1 constitutes the front group GA, which as a whole has a positive refractive power. The second lens group G2 and the third lens group G3 constitute the intermediate group GM, which as a whole has a positive refractive power. The fourth lens group G4 constitutes the rear group GR, which as a whole has a negative refractive power. In this embodiment, the second lens group G2 corresponds to the first focusing lens group GF1, and the third lens group G3 corresponds to the second focusing lens group GF2.

[0121] 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 negative meniscus lens L13 with its convex surface facing the object, all arranged in order from the object side along the optical axis.

[0122] The second lens group G2 consists of negative meniscus lenses L21 with their concave surfaces facing the object, and biconvex positive lenses L22, arranged sequentially from the object side along the optical axis. The positive lens L22 is a composite lens in which a resin layer is provided on the image-plane side surface of a glass lens body. The image-plane side surface of the resin layer is aspherical, and the positive lens L22 is a composite aspherical lens. In the [Lens Specifications] described later, surface number 10 indicates the object-side surface of the lens body, surface number 11 indicates the image-plane side surface of the lens body and the object-side surface of the resin layer (the surface where the two are joined), and surface number 12 indicates the image-plane side surface of the resin layer.

[0123] The third lens group G3 consists of a positive meniscus lens L31 with its concave surface facing the object.

[0124] The fourth lens group G4 consists of a biconcave negative lens L41. The image plane I is positioned on the image side of the fourth lens group G4. An optical filter FL is positioned between the fourth lens group G4 and the image plane I.

[0125] Table 6 below lists the specifications of the optical system according to the sixth embodiment.

[0126] (Table 6) [Overall Specifications] f=77.600 FNO=2.04 ω=15.48 Y=21.70 TL=91.455 Bf=14.055 βM=0.590 βR=1.115 fAM=69.617 fM=55.148 fE = -127.561 [Lens Specifications] Face number RD nd νd 1 32.0851 8.800 1.60311 60.69 2 427.2670 0.200 3 27.4269 5.200 1.77250 49.62 4 46.4244 2.200 5 149.1282 1.000 1.68893 31.16 6 19.0570 7.300 7 ∞ (D7) (Aperture S) 8 -23.7246 0.800 1.56732 42.58 9 -365.7671 0.200 10 149.2853 5.500 1.77250 49.62 11 -53.9601 0.200 1.56093 36.64 12* -50.7397 (D12) 13 -1478.0798 8.000 1.60311 60.69 14 -33.2322 (D14) 15 -87.5938 1.200 1.48749 70.32 16 215.3355 12.500 17 ∞ 1.600 1.51680 64.20 18 ∞ 0.500 [Aspherical data] Side 12 κ=1.0000,A4=8.63577E-06,A6=-3.87641E-09,A8=4.23228E-11,A10=-7.82625E-14 [Variable interval data] Infinity focus state Close focus state f = 77.600 β = -0.100 D0 ∞ 731.9 D7 21.100 12.434 D12 2.000 2.135 D14 13.700 22.131 [Lens group data] Group starting plane focal length G1 1 117.952 G2 8 -957.754 G3 13 56.252 G4 15 -127.561

[0127] 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 not only when focused at infinity but also when focused at close range.

[0128] (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, an aperture diaphragm S, a second lens group G2 having positive refractive power, and a third lens group G3 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 object side along the optical axis, and the spacing between adjacent lens groups changes. At the time of focusing, the positions of the first lens group G1 and the third lens group G3 are fixed with respect to the image plane I.

[0129] 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 in position relative to the image plane I. In this embodiment, the first lens group G1 constitutes the front group GA, which as a whole has a positive refractive power. The second lens group G2 constitutes the intermediate group GM, which as a whole has a positive refractive power. The third lens group G3 constitutes the rear group GR, which as a whole has a negative refractive power. In this embodiment, the second lens group G2 corresponds to the focusing lens group GF.

[0130] The first lens group G1 consists of positive meniscus lenses L11, which are arranged in order from the object side along the optical axis and have their convex surfaces facing the object, and a bonded negative lens formed by joining a positive meniscus lens L12, which has its convex surface facing the object, and a negative meniscus lens L13, which also has its convex surface facing the object. The positive meniscus lens L11 has an aspherical lens surface on the image plane side.

[0131] The second lens group G2 consists of three lenses arranged in order from the object side along the optical axis: a negative meniscus lens L21 with its concave surface facing the object, a biconvex positive lens L22, and a positive meniscus lens L23 with its concave surface facing the object. The positive lens L22 has an aspherical lens surface on the image plane side.

[0132] The third lens group G3 consists of a biconcave negative lens L31. The image plane I is positioned on the image side of the third lens group G3. An optical filter FL is positioned between the third lens group G3 and the image plane I.

[0133] Table 7 below lists the specifications of the optical system according to the seventh embodiment.

[0134] (Table 7) [Overall Specifications] f=77.600 FNO=2.05 ω=15.48 Y=21.70 TL=91.155 Bf=13.288 βM=0.617 βR=1.145 fAM=67.754 fM=60.108 fE = -93.756 [Lens Specifications] Face number RD nd νd 1 36.1757 7.500 1.60311 60.69 2* 91.6415 0.200 3 26.4224 8.000 1.77250 49.62 4 60.5724 1.000 1.69895 30.13 5 18.5472 7.800 6 ∞ (D6) (Aperture S) 7 -24.0725 0.800 1.57501 41.51 8 -315.3193 0.100 9 127.7089 6.000 1.77250 49.62 10* -43.8778 2.500 11 -123.5831 7.000 1.48749 70.32 12 -29.0241 (D12) 13 -64.6872 1.200 1.48749 70.32 14 156.7010 11.500 15 ∞ 1.600 1.51680 64.20 16 ∞ 0.733 [Aspherical data] 2nd side κ=1.0000,A4=7.14080E-07,A6=-1.98200E-10,A8=0.00000E+00,A10=0.00000E+00 Side 10 κ=1.0000,A4=6.70063E-06,A6=3.97954E-09,A8=0.00000E+00,A10=0.00000E+00 [Variable interval data] Infinity focus state Close focus state f = 77.600 β = -0.100 D0 ∞ 738.2 D6 21.100 12.711 D12 14.900 23.289 [Lens group data] Group starting plane focal length G1 1 109.766 G2 7 60.108 G3 13 -93.756

[0135] 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 not only when focused at infinity but also when focused at close range.

[0136] Next, the table of [Conditional Expression Corresponding Values] is shown below. This table summarizes the values ​​corresponding to each conditional expression (1) to (12) for all examples (Examples 1 to 7). Condition (1) 2.60 <DSE / DM<3.50 Condition (2) 0.80 <fAM / f<1.00 Condition (3) 0.50 <DA / (DM+DR)<1.20 Condition (4) 1.70 <DSR / DM<3.40 Condition (5) 0.60 <fM / f<1.30 Condition (6) 0.60 <fA / (-fR)<1.50 Conditional expression (7) 0.60<{1-(βM) 2}×(βR) 2 <1.50 Condition (8) 0.70 <DA / DM<2.30 Conditional expression (9) 9.00<|fF1| / f<90.00 Condition (10) 0.30 <fF2 / f<2.00 Conditional expression (11) 0.80<(-fE) / f<16.00 Conditional expression (12) 1.00<(-fR) / f<3.90

[0137] [Conditional Expression Corresponding Values] (Examples 1-4) Conditional expression First example Second example Third example Fourth example (1) 2.779 2.936 2.751 3.219 (2) 0.886 0.902 0.873 0.953 (3) 0.561 0.668 1.105 0.732 (4) 1.830 1.968 1.877 2.278 (5) 0.977 1.069 1.058 0.883 (6) 0.896 1.006 0.791 0.857 (7) 1.105 1.067 1.176 0.851 (8) 1.094 1.314 2.071 1.420 (9) ― 13.378 11.671 80.259 (10) ― 1.333 1.318 0.982 (11) 2.879 2.301 14.543 1.048 (12) 2.704 2.459 3.427 2.333 [Conditional corresponding values] (Examples 5 to 7) Conditional expression Example 5 Example 6 Example 7 (1) 3.145 3.156 3.268 (2) 0.953 0.897 0.873 (3) 0.732 0.972 0.949 (4) 2.249 3.084 3.195 (5) 0.850 0.711 0.775 (6) 0.780 0.925 1.171 (7) 0.850 0.810 0.812 (8) 1.387 1.042 1.018 (9) ― 12.342 ― (10) ― 0.725 ― (11) 1.048 1.644 1.208 (12) 2.564 1.644 1.208

[0138] According to the above embodiments, it is possible to realize an optical system that is compact yet bright and has good optical performance.

[0139] The above embodiments illustrate specific examples of the present invention, and the present invention is not limited to these.

[0140] The following elements can be appropriately incorporated as long as they do not impair the optical performance of the optical system of this embodiment.

[0141] Although the optical system of this embodiment is shown with a 3-group or 4-group configuration, this application is not limited to these, and optical systems with other group configurations (e.g., 5-group, 6-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 during focusing.

[0142] 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.

[0143] 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.

[0144] 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.

[0145] The aperture diaphragm is preferably positioned between the first lens group (front group) and the second lens group (intermediate group), but its function may be substituted by the lens frame instead of providing a separate aperture diaphragm component.

[0146] 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]

[0147] G1 First lens group G2 Second lens group G3 3rd lens group G4 4th lens group I Image plane S Aperture diaphragm

Claims

1. It consists of a front group with positive refractive power, an aperture, an intermediate group with positive refractive power, and a rear group with negative refractive power, all arranged in order from the object side along the optical axis. During focusing, the intermediate group moves along the optical axis, the distance between the front group and the intermediate group changes, and the distance between the intermediate group and the rear group changes. The aforementioned front group consists of a negative lens, a positive lens, a negative lens, and a positive lens arranged in order from the object side, or a negative lens, a positive lens, a positive lens, and a negative lens arranged in order from the object side. The aforementioned rear group consists of a positive lens, a negative lens, and another negative lens. An optical system that satisfies the following conditions. 2.60<DSE / DM<3.50 0.80<fAM / f<1.00 However, DSE: distance along the optical axis from the aperture to the lens surface closest to the image plane of the rear group. DM: Length of the intermediate group along the optical axis in the state of infinity focus. fAM: Combined focal length of the front group and the intermediate group in the infinity focus state f: Focal length of the optical system when in focus at infinity

2. It consists of a front group with positive refractive power, an aperture, an intermediate group with positive refractive power, and a rear group with negative refractive power, all arranged in order from the object side along the optical axis. The aforementioned front group consists of a negative lens, a positive lens, a negative lens, and a positive lens arranged in order from the object side, or a negative lens, a positive lens, a positive lens, and a negative lens arranged in order from the object side, or a positive lens, a positive lens, and a negative lens arranged in order from the object side, The lens positioned closest to the image plane is the negative lens. When focusing from an object at infinity to an object at a close distance, the intermediate group moves toward the object along the optical axis, the distance between the front group and the intermediate group changes, and the distance between the intermediate group and the rear group changes. An optical system that satisfies the following conditions. 2.60<DSE / DM<3.50 0.80<fAM / f<1.00 However, DSE: distance along the optical axis from the aperture to the lens surface closest to the image plane of the rear group. DM: Length of the intermediate group along the optical axis in the state of infinity focus. fAM: Combined focal length of the front group and the intermediate group in the infinity focus state f: Focal length of the optical system when in focus at infinity

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

4. The optical system according to claim 1 or 2, satisfying the following conditional expression. 0.60<fM / f<1.30 However, fM: focal length of the intermediate group in the state of infinity focus.

5. The optical system according to claim 1 or 2, satisfying the following conditional expression. 0.60<{1-(βM) 2 }×(βR) 2 <1.50 However, βM: Lateral magnification of the intermediate group in the state of focus at infinity. βR: Lateral magnification of the rear group in the infinity focus state.

6. The optical system according to claim 1 or 2, satisfying the following conditional expression. 0.70<DA / DM<2.30 However, DA: Length of the front group along the optical axis in the state of infinity focus.

7. The aforementioned intermediate group consists of a first focusing lens group and a second focusing lens group, which are arranged in order from the object side along the optical axis. During focusing, the first focusing lens group and the second focusing lens group move along the optical axis on different trajectories. The optical system according to claim 1 or 2, satisfying the following conditional expression. 9.00<|fF1| / f<90.00 However, fF1: focal length of the first focusing lens group.

8. The aforementioned intermediate group consists of a first focusing lens group and a second focusing lens group, which are arranged in order from the object side along the optical axis. During focusing, the first focusing lens group and the second focusing lens group move along the optical axis on different trajectories. The optical system according to claim 1 or 2, satisfying the following conditional expression. 0.30<fF2 / f<2.00 However, fF2: focal length of the second focusing lens group.

9. The optical system according to claim 1 or 2, satisfying the following conditional expression. 0.80<(-fE) / f<16.00 However, fE: the focal length of the lens positioned closest to the image plane in the rear group.

10. The optical system according to claim 1 or 2, satisfying the following conditional expression. 1.00<(-fR) / f<3.90 However, fR: focal length of the rear group in the state of infinity focus.

11. An optical instrument comprising the optical system described in claim 1 or 2.

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