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

Abstract

To provide a compact variable magnification optical system with good optical performance. [Solution] The optical system OL has a front group GF, an aperture S, and a rear group GR arranged in order from the object side along the optical axis. The rear group GR has an image plane side subgroup Gp2 located closest to the image plane and an object side subgroup Gp1 located closer to the object than the image plane side subgroup Gp2. The image plane side subgroup Gp2 has an image plane side positive lens Lp2 having positive refractive power and an image plane side negative lens Ln2 having negative refractive power. The object side subgroup Gp1 has an object side positive lens Lp1 having positive refractive power and an object side negative lens Ln1 having negative refractive power, satisfying a predetermined conditional equation.

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] Optical systems suitable for photographic cameras, electronic still cameras, video cameras, etc., have been proposed conventionally (see, for example, Patent Document 1). Further improvements in optical performance are desired for such optical systems. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2021-92694 [Overview of the project]

[0004] The optical system according to the first invention has a front group, an aperture, and a rear group arranged in order from the object side along the optical axis, the rear group having an image-plane side subgroup located closest to the image plane and an object-side subgroup located closer to the object than the image-plane side subgroup, the image-plane side subgroup having an image-plane side positive lens having positive refractive power and an image-plane side negative lens having negative refractive power, and the object-side subgroup having an object-side positive lens having positive refractive power and an object-side negative lens having negative refractive power, satisfying the following conditional equation. 0.6455<θgFLp1+0.0017×νdLp1 θgFLn1-0.000023×(νdLn1)^2+0.004106×νdLn1<0.706984 0.6455<θgFLp2+0.0017×νdLp2 θgFLn2-0.000023×(νdLn2)^2+0.004106×νdLn2<0.706984 However, νdLp1: Abbe number of the object-side positive lens νdLn1: Abbe number of the object-side negative lens νdLp2: Abbe number of the positive lens on the image plane side νdLn2: Abbe number of the negative lens on the image plane side θgFLp1 is the partial dispersion ratio of the object-side positive lens, and is defined by the following equation, where ngLp1 is the refractive index of the object-side positive lens Lp1 with respect to the g line, nFLp1 is the refractive index with respect to the F line, and nCLp1 is the refractive index with respect to the C line. θgFLp1=(ngLp1-nFLp1) / (nFLp1-nCLp1) θgFLp2 is the partial dispersion ratio of the positive lens on the image plane side, and is defined by the following equation, where ngLp2 is the refractive index of the positive lens on the image plane side Lp2 with respect to the g line, nFLp2 is the refractive index with respect to the F line, and nCLp2 is the refractive index with respect to the C line. θgFLp2=(ngLp2-nFLp2) / (nFLp2-nCLp2) θgFLn1 is the partial dispersion ratio of the object-side negative lens, and is defined by the following equation, where ngLn1 is the refractive index of the object-side negative lens Ln1 with respect to the g line, nFLn1 is the refractive index with respect to the F line, and nCLn1 is the refractive index with respect to the C line. θgFLn1=(ngLn1-nFLn1) / (nFLn1-nCLn1) θgFLn2 is the partial dispersion ratio of the negative lens on the image plane side, and is defined by the following equation, where ngLn2 is the refractive index of the negative lens Ln2 on the g line, nFLn2 is the refractive index on the F line, and nCLn2 is the refractive index on the C line. θgFLn2=(ngLn2-nFLn2) / (nFLn2-nCLn2)

[0005] The optical system according to the second invention comprises a front group, an aperture, and a rear group, arranged in order from the object side along the optical axis. The rear group has at least two positive lenses and at least two negative lenses, the at least two positive lenses include at least two image-plane positive lenses positioned closest to the image plane, and the at least two negative lenses include at least two image-plane negative lenses positioned closest to the image plane, satisfying the following condition. ndLn2-ndLp2<0.35 νdLp2-νdLn2<55.00 0.6455<θgFLp2+0.0017×νdLp2 However, ndLp2: Refractive index based on the d line of the positive lens on the image plane side. ndLn2: Refractive index based on the d-line of the negative lens on the image plane. νdLp2: Abbe number of the positive lens on the image plane side νdLn2: Abbe number of the negative lens on the image plane side θgFLp2 is the partial dispersion ratio of the positive lens on the image plane side, and is defined by the following equation, where ngLp2 is the refractive index of the positive lens on the image plane side Lp2 with respect to the g line, nFLp2 is the refractive index with respect to the F line, and nCLp2 is the refractive index with respect to the C line. θgFLp2=(ngLp2-nFLp2) / (nFLp2-nCLp2)

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

[0007] A method for manufacturing an optical system according to the first invention comprises a front group, an aperture, and a rear group arranged in order from the object side along the optical axis, wherein the rear group comprises an image-plane side subgroup located closest to the image plane and an object-side subgroup located closer to the object than the image-plane subgroup, the image-plane side subgroup comprises an image-plane side positive lens having positive refractive power and an image-plane side negative lens having negative refractive power, and the object-side subgroup comprises an object-side positive lens having positive refractive power and an object-side negative lens having negative refractive power, and the method for manufacturing an optical system comprises the step of arranging each lens in the lens barrel such that the following condition is satisfied. 0.6455<θgFLp1+0.0017×νdLp1 θgFLn1-0.000023×(νdLn1)^2+0.004106×νdLn1<0.706984 0.6455<θgFLp2+0.0017×νdLp2 θgFLn2-0.000023×(νdLn2)^2+0.004106×νdLn2<0.706984 However, νdLp1: Abbe number of the object-side positive lens νdLn1: Abbe number of the object-side negative lens νdLp2: Abbe number of the positive lens on the image plane side νdLn2: Abbe number of the negative lens on the image plane side θgFLp1: Partial dispersion ratio of the positive lens on the object side. When the refractive index of the object-side positive lens Lp1 with respect to the g-line is ngLp1, the refractive index with respect to the F-line is nFLp1, and the refractive index with respect to the C-line is nCLp1, it is defined by the following formula θgFLp1 = (ngLp1 - nFLp1) / (nFLp1 - nCLp1) θgFLp2: Partial dispersion ratio of the positive lens on the image plane side. When the refractive index of the image-plane-side positive lens Lp2 with respect to the g-line is ngLp2, the refractive index with respect to the F-line is nFLp2, and the refractive index with respect to the C-line is nCLp2, it is defined by the following formula θgFLp2 = (ngLp2 - nFLp2) / (nFLp2 - nCLp2) θgFLn1: Partial dispersion ratio of the negative lens on the object side. When the refractive index of the object-side negative lens Ln1 with respect to the g-line is ngLn1, the refractive index with respect to the F-line is nFLn1, and the refractive index with respect to the C-line is nCLn1, it is defined by the following formula θgFLn1 = (ngLn1 - nFLn1) / (nFLn1 - nCLn1) θgFLn2: Partial dispersion ratio of the negative lens on the image plane side. When the refractive index of the image-plane-side negative lens Ln2 with respect to the g-line is ngLn2, the refractive index with respect to the F-line is nFLn2, and the refractive index with respect to the C-line is nCLn2, it is defined by the following formula θgFLn2 = (ngLn2 - nFLn2) / (nFLn2 - nCLn2)

[0008] The manufacturing method of the optical system according to the second invention has a front group, an aperture stop, and a rear group arranged in order from the object side along the optical axis. The rear group has at least two positive lenses and at least two negative lenses. At least two positive lenses include the image-plane-side positive lens arranged closest to the image plane among the at least two positive lenses, and at least two negative lenses include the image-plane-side negative lens arranged closest to the image plane among the at least two negative lenses. The manufacturing method of the optical system includes a step of arranging each lens in the lens barrel so as to satisfy the following conditional expressions. ndLn2 - ndLp2 < 0.35 νdLp2 - νdLn2 < 55.00 0.6455 < θgFLp2 + 0.0017 × νdLp2 However, ndLp2: refractive index based on the d-line of the positive lens on the image plane side ndLn2: refractive index based on the d-line of the negative lens on the image plane side νdLp2: Abbe number of the positive lens on the image plane side νdLn2: Abbe number of the negative lens on the image plane side θgFLp2: partial dispersion ratio of the positive lens on the image plane side. When the refractive index with respect to the g-line of the positive lens Lp2 on the image plane side is ngLp2, the refractive index with respect to the F-line is nFLp2, and the refractive index with respect to the C-line is nCLp2, it is defined by the following formula θgFLp2 = (ngLp2 - nFLp2) / (nFLp2 - nCLp2)

Brief Description of the Drawings

[0009] [Figure 1] It is a diagram showing the lens configuration of the optical system according to the first embodiment. [Figure 2] It is a diagram showing various aberrations of the optical system according to the first embodiment when focused at infinity. [Figure 3] It is a diagram showing various aberrations of the optical system according to the first embodiment when focused at a short distance. [Figure 4] It is a diagram showing the lens configuration of the optical system according to the second embodiment. [Figure 5] It is a diagram showing various aberrations of the optical system according to the second embodiment when focused at infinity. [Figure 6] It is a diagram showing various aberrations of the optical system according to the second embodiment when focused at a short distance. [Figure 7] It is a diagram showing the lens configuration of the optical system according to the third embodiment. [Figure 8] It is a diagram showing various aberrations of the optical system according to the third embodiment when focused at infinity. [Figure 9] It is a diagram showing various aberrations of the optical system according to the third embodiment when focused at a short distance. [Figure 10] It is a diagram showing the lens configuration of the optical system according to the fourth embodiment. [Figure 11] It is a diagram showing various aberrations of the optical system according to the fourth embodiment when focused at infinity. [Figure 12] It is a diagram showing various aberrations of the optical system according to the fourth embodiment when focused at a short distance. [Figure 13] This figure shows the lens configuration of the optical system according to the fifth embodiment. [Figure 14] This is a diagram showing the various aberrations of the optical system according to the fifth embodiment when it is in focus at infinity. [Figure 15] This is a diagram showing the various aberrations of the optical system according to the fifth embodiment when it is in close focus. [Figure 16] This figure shows the configuration of a camera equipped with an optical system according to each embodiment. [Figure 17] This is a flowchart showing a method for manufacturing an optical system according to the first embodiment. [Figure 18] This is a flowchart showing a method for manufacturing an optical system according to the second embodiment. [Modes 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 16. As shown in Figure 16, 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 a memory (not shown). The digital image data recorded in the 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 16 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, an optical system according to the first embodiment will be described. An example of the optical system OL according to the first embodiment, optical system OL(1), as shown in Figure 1, has a front group GF, an aperture diaphragm S, and a rear group GR arranged in order from the object side along the optical axis. The rear group has an image plane side subgroup Gp2 and an object side subgroup Gp1 which is located closer to the object than the image plane side subgroup Gp2. The image plane side subgroup Gp2 has an image plane side positive lens Lp2 having a positive refractive power and an image plane side negative lens Ln2 having a negative refractive power. The object side subgroup Gp1 has an object side positive lens Lp1 having a positive refractive power and an object side negative lens Ln1 having a negative refractive power. In each embodiment, "lens" means one of either a single lens or a cemented lens.

[0013] Under the above configuration, the optical system OL according to the first embodiment satisfies the following conditions (1) to (4). 0.6455<θgFLp1+0.0017×νdLp1...(1) θgFLn1-0.000023×(νdLn1)^2+0.004106×νdLn1<0.706984...(2) 0.6455<θgFLp2+0.0017×νdLp2...(3) θgFLn2-0.000023×(νdLn2)^2+0.004106×νdLn2<0.706984...(4) However, νdLp1: Abbe number of the object-side positive lens νdLn1: Abbe number of the object-side negative lens νdLp2: Abbe number of the positive lens on the image plane side νdLn2: Abbe number of the negative lens on the image plane side θgFLp1 is the partial dispersion ratio of the object-side positive lens, and is defined by the following equation, where ngLp1 is the refractive index of the object-side positive lens Lp1 with respect to the g line, nFLp1 is the refractive index with respect to the F line, and nCLp1 is the refractive index with respect to the C line. θgFLp1=(ngLp1-nFLp1) / (nFLp1-nCLp1) θgFLp2 is the partial dispersion ratio of the positive lens on the image plane side, and is defined by the following equation, where ngLp2 is the refractive index of the positive lens on the image plane side Lp2 with respect to the g line, nFLp2 is the refractive index with respect to the F line, and nCLp2 is the refractive index with respect to the C line. θgFLp2=(ngLp2-nFLp2) / (nFLp2-nCLp2) θgFLn1 is the partial dispersion ratio of the object-side negative lens, and is defined by the following equation, where ngLn1 is the refractive index of the object-side negative lens Ln1 with respect to the g line, nFLn1 is the refractive index with respect to the F line, and nCLn1 is the refractive index with respect to the C line. θgFLn1=(ngLn1-nFLn1) / (nFLn1-nCLn1) θgFLn2 is the partial dispersion ratio of the negative lens on the image plane side, and the partial dispersion ratio of the negative lens Ln2 on the image plane side is defined by the following equation, where ngLn2 is the refractive index of the negative lens Ln2 with respect to the g line, nFLn2 is the refractive index of the F line, and nCLn2 is the refractive index of the C line. θgFLn2=(ngLn2-nFLn2) / (nFLn2-nCLn2)

[0014] According to the first embodiment, it is possible to obtain an optical system having good optical performance and an optical instrument equipped with this optical system. The optical system OL according to the first embodiment may be the optical system OL(2) shown in Figure 4, the optical system OL(3) shown in Figure 7, and the optical system OL(4) shown in Figure 10. Alternatively, the optical system OL(5) shown in Figure 13 may also be used.

[0015] Condition (1) appropriately defines the anomalous dispersion of the object-side positive lens. By satisfying condition (1), in addition to correcting first-order chromatic aberration, the second-order spectrum can be corrected well. The Abbe number νdLp1 of the object-side positive lens is defined by the following equation, where ndLp1 is the refractive index of the object-side positive lens Lp1 with respect to the d line, nFLp1 is the refractive index with respect to the F line, and nCLp1 is the refractive index with respect to the C line. Hereafter, the equations defining the Abbe number only change the symbol of the lens indicated by the symbol L, and redundant descriptions are omitted. νdLp1=(ndLp1-1) / (nFLp1-nCLp1)

[0016] If the corresponding value in conditional equation (1) falls below the lower limit, the anomalous dispersion of the object-side positive lens decreases, making it difficult to correct the secondary spectrum. By setting the lower limit of conditional equation (1) to 0.6500, 0.6600, 0.6700, and further to 0.6800, the effect of this embodiment can be made more reliable.

[0017] Condition (2) appropriately defines the anomalous dispersion of the object-side negative lens. By satisfying condition (2), in addition to correcting first-order chromatic aberration, secondary spectra can be corrected effectively.

[0018] If the corresponding value in conditional equation (2) exceeds the upper limit, the anomalous dispersion of the object-side negative lens increases, making it difficult to correct the secondary spectrum. By setting the upper limit of conditional equation (2) to 0.7030, 0.7000, and further to 0.6990, the effect of this embodiment can be made more reliable.

[0019] Condition (3) appropriately defines the anomalous dispersion of the positive lens on the image plane. By satisfying condition (3), in addition to correcting first-order chromatic aberration, secondary spectra can be corrected effectively.

[0020] If the corresponding value in conditional equation (3) falls below the lower limit, the anomalous dispersion of the positive lens on the image plane becomes smaller, making it difficult to correct the secondary spectrum. By setting the lower limit of conditional equation (3) to 0.6480, 0.6500, and further to 0.6520, the effect of this embodiment can be made more reliable.

[0021] Condition (4) appropriately defines the anomalous dispersion of the negative lens on the image plane. By satisfying condition (4), in addition to correcting first-order chromatic aberration, secondary spectra can be corrected effectively.

[0022] If the corresponding value in conditional equation (4) exceeds the upper limit, the anomalous dispersion of the negative lens on the image plane side increases, making it difficult to correct the secondary spectrum. By setting the upper limit of conditional equation (4) to 0.7030, 0.7000, and further to 0.6990, the effect of this embodiment can be made more reliable.

[0023] In the optical system OL according to the first embodiment, the following condition (9) may be satisfied. νdLn1<45.00···(9)

[0024] Condition (9) specifies the Abbe number of the object-side negative lens within an appropriate range. By satisfying condition (9), first-order chromatic aberration can be corrected effectively.

[0025] If the corresponding value in conditional equation (9) exceeds the upper limit, it becomes difficult to correct axial chromatic aberration, therefore it is preferable to... Not ideal. By setting the upper limit of conditional expression (9) to 34.00, 33.00, 32.00, 31.00, and further to 30.00, the effect of this embodiment can be made more reliable.

[0026] In the optical system OL according to the first embodiment, the object-side subgroup may consist of an object-side positive lens and an object-side negative lens arranged sequentially from the object side along the optical axis. This allows for correction of various aberrations and improvement of the performance of the optical system.

[0027] In the optical system OL according to the first embodiment, the object-side subgroup may be arranged alongside the image plane-side subgroup on the object side. This allows for correction of various aberrations and improvement of the performance of the optical system.

[0028] In the optical system OL according to the first embodiment, the following condition (10) may be satisfied. -0.50 <f / fp2<0.50···(10) However, fp2: focal length of the image plane subgroup f: focal length of the optical system

[0029] Condition (10) specifies an appropriate range for the ratio of the focal lengths of the entire optical system to that of the image plane subgroup. By satisfying condition (10), various aberrations such as spherical aberration, coma aberration, field curvature, and distortion can be effectively corrected.

[0030] If the corresponding value in conditional equation (10) exceeds the upper limit, it becomes difficult to secure back focus, which is undesirable because it physically interferes with the camera body equipped with the optical system. Furthermore, forcibly securing back focus would increase the overall size of the optical system, which is also undesirable. By setting the upper limit of conditional equation (10) to 0.30, 0.20, 0.10, and even 0.01, the effects of this embodiment can be made more reliable.

[0031] If the corresponding value in conditional equation (10) falls below the lower limit, the exit pupil of the optical system approaches the image plane, and the telecentricity deteriorates. The image sensor has an incident angle characteristic in which the effective sensitivity decreases as the incident angle increases due to the effects of vignetting of the photodiode, which is undesirable as it reduces peripheral light intensity and causes color shading. By setting the lower limit of conditional equation (10) to -0.30, -0.20, and further to -0.17, the effect of this embodiment can be made more reliable.

[0032] In the optical system OL according to the first embodiment, the following condition (11) may be satisfied. 0.50 <fLp1 / (-fLn1)<4.00···(11) However, fLp1: focal length of the object-side positive lens fLn1: Focal length of the negative lens on the object side

[0033] Condition (11) specifies an appropriate range for the ratio of the focal lengths of the positive and negative lens on the object side. By satisfying condition (11), axial chromatic aberration can be effectively corrected.

[0034] If the corresponding value in conditional expression (11) exceeds the upper limit, it results in overcorrection, which is undesirable. By setting the upper limit of conditional expression (11) to 3.00, 2.90, 2.80, and further to 2.70, the effect of this embodiment can be made more reliable.

[0035] If the corresponding value in conditional equation (11) falls below the lower limit, it becomes difficult to correct axial chromatic aberration, which is undesirable. By setting the lower limit of conditional equation (11) to 0.60, 0.80, 1.00, and even 1.50, the effect of this embodiment can be made more reliable.

[0036] In the optical system OL according to the first embodiment, the object-side positive lens and the object-side negative lens may be joined together. By joining the positive lens and the negative lens, the eccentricity error during assembly and adjustment can be reduced, and the optical performance can be improved.

[0037] In the optical system OL according to the first embodiment, the following condition (12) may be satisfied. 0.30<(L1r1+L2r2) / (L2r2-L1r1)<6.00...(12) However, L1r1: radius of curvature of the lens surface closest to the image plane in the object-side subgroup. L2r2: Radius of curvature of the lens surface closest to the object in the image plane subgroup.

[0038] Condition (12) defines an appropriate range for the relationship between the radius of curvature of the lens surface closest to the image plane in the object-side subgroup and the lens surface closest to the object in the image-side subgroup. By satisfying condition (12), spherical aberration and coma aberration can be effectively corrected.

[0039] If the corresponding value in conditional equation (12) exceeds the upper limit, the curvature difference between the lens surface closest to the image plane in the object-side subgroup and the lens surface closest to the object in the image-side subgroup becomes too small, making it difficult to correct various aberrations such as spherical aberration. By setting the upper limit of conditional equation (12) to 5.00, 4.00, 3.00, and even 2.00, the effect of this embodiment can be made more reliable.

[0040] If the corresponding value in conditional equation (12) falls below the lower limit, the lens surface closest to the image plane in the object-side subgroup becomes too gentle, making it difficult to correct spherical aberration. By setting the lower limit of conditional equation (12) to 0.40, 0.50, 0.60, 0.70, and even 1.00, the effect of this embodiment can be made more reliable.

[0041] In the optical system OL according to the first embodiment, the image plane-side subgroup may consist of an image plane-side positive lens and an image plane-side negative lens arranged sequentially from the object side along the optical axis. This allows for good correction of axial chromatic aberration.

[0042] Next, an optical system according to the second embodiment will be described. In the conditional expressions described below, the same symbols are used when the same conditional expressions as in the first embodiment are used. Optical system OL(1), as an example of the optical system OL according to the second embodiment, has a front group GF, an aperture diaphragm S, and a rear group GR arranged in order from the object side along the optical axis, as shown in Figure 1. The rear group is composed of at least two positive lenses and at least two negative lenses. These at least two positive lenses include an image-plane positive lens which is positioned closest to the image plane, and the at least two negative lenses include an image-plane negative lens which is positioned closest to the image plane.

[0043] Under the above configuration, the optical system OL according to the second embodiment satisfies the following conditions (5), (6), and (3). ndLn2 - ndLp2 < 0.35 ···(5) νdLp2-νdLn2<55.00···(6) 0.6455<θgFLp2+0.0017×νdLp2...(3) However, ndLp2: Refractive index based on the d line of the positive lens on the image plane side. ndLn2: Refractive index based on the d-line of the negative lens on the image plane. νdLp2: Abbe number of the positive lens on the image plane side νdLn2: Abbe number of the negative lens on the image plane side θgFLp2: This is the partial dispersion ratio of the positive lens on the image plane side, where ngLp2 is the refractive index of the positive lens on the image plane side Lp2 with respect to the g line, nFLp2 is the refractive index with respect to the F line, and nFLp2 is the refractive index with respect to the C line. When the refractive index is nCLp2, it is defined by the following equation. θgFLp2=(ngLp2-nFLp2) / (nFLp2-nCLp2)

[0044] According to the second embodiment, it becomes possible to obtain an optical system having good optical performance and an optical instrument equipped with this optical system. The optical system OL according to the second embodiment may be the optical system OL(2) shown in Figure 4, the optical system OL(3) shown in Figure 7, the optical system OL(4) shown in Figure 10, or the optical system OL(5) shown in Figure 13.

[0045] Condition (5) specifies an appropriate range for the difference in refractive index between the positive and negative lenses on the image plane. By satisfying condition (5), aberrations can be corrected while ensuring telecentricity.

[0046] If the corresponding value in conditional equation (5) exceeds the upper limit, the refractive index of the positive lens on the image plane decreases, worsening the Petzval sum and making it difficult to maintain image plane flatness, which is undesirable. Furthermore, if one attempts to maintain the refractive power necessary to sufficiently move the exit pupil of the optical system away from the positive lens on the image plane with a low refractive index in an attempt to ensure telecentricity, the curvature of the lens becomes excessively sharp, making it difficult to correct peripheral image field curvature, astigmatism, and coma aberration, which is also undesirable. By setting the upper limit of conditional equation (5) to 0.28, 0.25, and further to 0.21, the effects of this embodiment can be made more reliable. Furthermore, by setting the lower limit of conditional equation (5) to 0.10 and further to 0.12, the effects of this embodiment can be made more reliable.

[0047] Condition (6) specifies an appropriate range for the difference in Abbe numbers between the positive and negative lenses on the image plane. By satisfying condition (6), the second-order spectrum of chromatic aberration, in particular, can be effectively corrected.

[0048] If the corresponding value in conditional equation (6) exceeds the upper limit, it becomes difficult to correct both the first-order achromaticity and the second-order spectrum simultaneously, which is undesirable. Setting the upper limit of conditional equation (6) to 50.00, 47.50, 45.00, 42.50, and further to 40.00 can make the effect of this embodiment more reliable. Furthermore, setting the lower limit of conditional equation (6) to 28.00, 30.00, and further to 33.00 can make the effect of this embodiment more reliable.

[0049] As mentioned above, condition (3) appropriately defines the anomalous dispersion of the image-plane positive lens Lp2. By satisfying condition (3), in addition to correcting first-order chromatic aberration, secondary spectra can be corrected effectively. Setting the lower limit of condition (3) to 0.6480, 0.6500, and further to 0.6520 makes the effects of this embodiment even more reliable.

[0050] In the optical system OL according to the second embodiment, at least two negative lenses may include an object-side negative lens positioned closer to the object than the image-plane-side negative lens, and satisfy the following conditions (2) and (4). θgFLn1-0.000023×(νdLn1)^2+0.004106×νdLn1<0.706984...(2) θgFLn2-0.000023×(νdLn2)^2+0.004106×νdLn2<0.706984...(4) However, θgFLn1 is the partial dispersion ratio of the object-side negative lens, and when the refractive index of the object-side negative lens Ln1 with respect to the g line is ngLn1, the refractive index with respect to the F line is nFLn1, and the refractive index with respect to the C line is nCLn1, it is defined by the following equation. θgFLn1=(ngLn1-nFLn1) / (nFLn1-nCLn1) νdLn1: Abbe number of the object-side negative lens θgFLn2 is the partial dispersion ratio of the negative lens on the image plane side, and is defined by the following equation, where ngLn2 is the refractive index of the negative lens Ln2 on the g line, nFLn2 is the refractive index on the F line, and nCLn2 is the refractive index on the C line. θgFLn2=(ngLn2-nFLn2) / (nFLn2-nCLn2)

[0051] As mentioned above, condition (2) appropriately defines the anomalous dispersion of the object-side negative lens. By satisfying condition (2), in addition to correcting first-order chromatic aberration, secondary spectra can be corrected effectively. Setting the upper limit of condition (2) to 0.7030, 0.7000, and further to 0.6990 makes the effects of this embodiment even more reliable.

[0052] As mentioned above, condition (4) appropriately defines the anomalous dispersion of the negative lens on the image plane. By satisfying condition (4), in addition to correcting the first-order chromatic aberration, the second-order spectrum can be corrected well. By setting the upper limit of condition (4) to 0.7030, 0.7000, and further to 0.6990, the effect of this embodiment can be made even more reliable.

[0053] In the optical system OL according to the second embodiment, at least two positive lenses include object-side positive lenses positioned closer to the object than the image-plane side positive lens, and at least two negative lenses include object-side negative lenses positioned closer to the object than the image-plane side negative lens, and the following conditions (7) and (8) may be satisfied. ndLp1-ndLn1<0.35···(7) νdLn1-νdLp1<20.00···(8) However, ndLp1: Refractive index based on the d line of the object-side positive lens. ndLn1: Refractive index of an object negative lens with reference to the d line. νdLp1: Abbe number of the object-side positive lens νdLn1: Abbe number of the object-side negative lens

[0054] Condition (7) specifies an appropriate range for the difference in refractive index between the object-side positive lens and the object-side negative lens. By satisfying condition (7), the refractive index of the object-side positive lens increases, which reduces the Petzval sum and ensures image plane flatness. Furthermore, even with the same refractive power, a flat lens with a larger radius of curvature can be used, allowing for efficient placement of lenses in the limited space near the mount, thus enabling a smaller overall optical system.

[0055] If the corresponding value in conditional equation (7) exceeds the upper limit, the refractive power of the object-side negative lens weakens, and the curvature of the lens surface of the object-side negative lens becomes too sharp, which is undesirable. Furthermore, it becomes difficult to miniaturize the optical system, which is also undesirable. By setting the upper limit of conditional equation (7) to 0.33, 0.30, 0.25, 0.20, and further to 0.17, the effect of this embodiment can be made more reliable. Also, by setting the lower limit of conditional equation (7) to 0.10, and further to 0.12, the effect of this embodiment can be made more reliable.

[0056] Condition (8) specifies an appropriate range for the difference in Abbe numbers between the negative and positive lens on the object side. By satisfying condition (8), axial chromatic aberration can be effectively corrected.

[0057] If the corresponding value in conditional equation (8) exceeds the upper limit, it becomes difficult to correct axial chromatic aberration, which is undesirable. By setting the upper limit of conditional equation (8) to 18.00, 16.50, 15.00, and further to 13.50, the effect of this embodiment can be made more reliable. By setting the lower limit of equation (8) to 8.00 and further to 9.00, the effects of this embodiment can be made more reliable.

[0058] In the optical system OL according to the second embodiment, at least two positive lenses include object-side positive lenses positioned closer to the object than the image-plane side positive lens, and at least two negative lenses include object-side negative lenses positioned closer to the object than the image-plane side negative lens, and the object-side negative lens is joined to the object-side positive lens, and the image-plane side lens of the object-side negative lens may be concave. By joining the object-side positive lens and the object-side negative lens, eccentricity errors during assembly and adjustment can be reduced and optical performance can be improved. Furthermore, because the image-plane side lens surface of the object-side negative lens is concave, various aberrations of the optical system can be corrected effectively.

[0059] In the optical system OL according to the first and second embodiments, the following condition (13) may be satisfied. νdLn2<45.0···(13)

[0060] Condition (13) specifies the Abbe number of the negative lens on the image plane to be within an appropriate range. By satisfying condition (13), first-order chromatic aberration can be corrected effectively.

[0061] If the corresponding value in conditional equation (13) exceeds the upper limit, it becomes difficult to correct chromatic aberration, which is undesirable. By setting the upper limit of conditional equation (13) to 44.0, 43.0, 42.0, 41.0, and even 40.0, the effect of this embodiment can be made more reliable.

[0062] In the optical system OL according to the first and second embodiments, the following condition (14) may be satisfied. 0.50 <fLp2 / (-fLn2)<2.00···(14) However, fLp2: focal length of the positive lens on the image plane side fLn2: Focal length of the negative lens on the image plane

[0063] Conditional equation (14) defines the ratio of the focal lengths of the positive and negative image-plane lenses in the first and second embodiments to be within an appropriate range. By satisfying conditional equation (14), chromatic aberration can be effectively corrected.

[0064] If the corresponding value in conditional expression (14) exceeds the upper limit, it results in overcorrection, which is undesirable. By setting the upper limit of conditional expression (14) to 1.90, 1.80, 1.70, 1.60, 1.50, and even 1.35, the effect of this embodiment can be made more reliable.

[0065] If the corresponding value in conditional equation (14) falls below the lower limit, it becomes difficult to correct chromatic aberration, which is undesirable. By setting the lower limit of conditional equation (14) to 0.60, 0.70, 0.80, 0.90, and even 1.00, the effect of this embodiment can be made more reliable.

[0066] In the optical system OL according to the first and second embodiments, the following condition (15) may be satisfied. 0.30 <BFa / f<1.00···(15) However, BFa: The length along the optical axis from the lens surface closest to the image plane to the image plane (air-equivalent distance). f: focal length of the optical system

[0067] Condition (15) specifies the ratio of the back focus of the optical system OL to the focal length of the entire optical system within an appropriate range. By satisfying condition (15), a good optical system can be obtained while achieving miniaturization.

[0068] If the corresponding value in conditional equation (15) exceeds the upper limit, it becomes difficult to miniaturize the optical system, which is undesirable. By setting the upper limit of conditional equation (15) to 0.95, 0.90, 0.85, 0.80, and further to 0.70, the effects of this embodiment can be made more reliable.

[0069] If the corresponding value in conditional expression (15) falls below the lower limit, it interferes with the camera body, which is undesirable. By setting the lower limit of conditional expression (15) to 0.35, 0.40, 0.45, and further to 0.50, the effect of this embodiment can be made more reliable.

[0070] In the optical system OL according to the first and second embodiments, the following condition (16) may be satisfied. 32.0°<ω<65.0°···(16) However, ω: half-angle of view when the optical system is in focus on an object at infinity.

[0071] Conditional equation (16) defines the half-angle of view of the optical system OL within an appropriate range. By satisfying conditional equation (16), chromatic aberration can be effectively corrected.

[0072] If the corresponding value in conditional expression (16) exceeds the upper limit, it becomes difficult to obtain the effects of this embodiment, which is undesirable. By setting the upper limit of conditional expression (16) to 62.0°, 58.0°, 54.0°, 51.0°, and even 46.0°, the effects of this embodiment can be made more reliable.

[0073] If the corresponding value in conditional equation (16) falls below the lower limit, it becomes difficult to miniaturize the optical system, which is undesirable. By setting the lower limit of conditional equation (16) to 35.0°, 37.0°, 40.0°, and even 42.0°, the effects of this embodiment can be made more reliable.

[0074] In the optical system OL according to the first and second embodiments, the following condition (17) may be satisfied. 0.80 <FNO<4.20···(17) However, FNO: F-number of the optical system

[0075] Conditional equation (17) specifies the F-number of the optical system OL within an appropriate range.

[0076] If the corresponding value in conditional equation (17) exceeds the upper limit, it becomes difficult to miniaturize the optical system relative to the specifications, which is undesirable. By setting the upper limit of conditional equation (17) to 3.00, 2.50, 1.60, 1.40, 1.30, and further to 1.25, the effects of this embodiment can be made more reliable.

[0077] Furthermore, by setting the lower limit of conditional expression (17) to 0.85, 0.90, 0.95, 1.00, and 1.20, the effects of this embodiment can be made more reliable.

[0078] In the optical system OL according to the first and second embodiments, the following condition (18) may be satisfied. 2.50 <fF / f<5.50···(18) However, fF: focal length of the front group f: focal length of the optical system

[0079] Conditional equation (18) defines the ratio of the front group and focal length of the optical system OL according to the first and second embodiments to an appropriate range. By satisfying conditional equation (18), the optical system It can be miniaturized.

[0080] If the corresponding value in conditional equation (18) exceeds the upper limit, it becomes difficult to miniaturize the optical system, which is undesirable. By setting the upper limit of conditional equation (18) to 5.40, 5.30, and 5.20, the effects of this embodiment can be made more reliable.

[0081] If the corresponding value in conditional equation (18) falls below the lower limit, it becomes difficult to miniaturize the optical system, which is undesirable. By setting the lower limit of conditional equation (18) to 2.60, 2.70, 2.80, 2.90, and even 3.00, the effects of this embodiment can be made more reliable.

[0082] In the optical system OL according to the first and second embodiments, the following condition (19) may be satisfied. 1.20 <fR / f<4.00···(19) However, fR: focal length of the rear group f: focal length of the optical system

[0083] Conditional equation (19) defines the ratio of the focal length of the rear group OL of the optical system and the focal length of the entire optical system to be within an appropriate range according to the first and second embodiments. By satisfying conditional equation (19), the optical system can be miniaturized.

[0084] If the corresponding value in conditional equation (19) exceeds the upper limit, it becomes difficult to miniaturize the optical system, which is undesirable. By setting the upper limit of conditional equation (19) to 3.40, 3.20, 3.00, 2.90, and further to 2.80, the effects of this embodiment can be made more reliable.

[0085] If the corresponding value in conditional equation (19) falls below the lower limit, it becomes difficult to miniaturize the optical system, which is undesirable. By setting the lower limit of conditional equation (19) to 1.40, 1.60, 1.80, and even 2.00, the effects of this embodiment can be made more reliable.

[0086] In the optical system OL according to this embodiment, the following conditional expression may be satisfied. 0.35 <TL / Lr<3.20···(20) However, TL: The length along the optical axis from the lens surface closest to the object to the image plane (air-equivalent distance). Lr: Length along the optical axis from the aperture to the image plane (air-equivalent distance)

[0087] Conditional equation (20) defines the ratio of the length along the optical axis from the lens surface closest to the object to the image plane to the length along the optical axis from the aperture to the image plane within an appropriate range for the optical system OL according to the first and second embodiments. By satisfying conditional equation (20), the optical system can be miniaturized.

[0088] If the corresponding value in conditional equation (20) exceeds the upper limit, it becomes difficult to miniaturize the optical system, which is undesirable. By setting the upper limit of conditional equation (20) to 3.10, 3.00, 2.90, 2.80, and further to 2.70, the effects of this embodiment can be made more reliable.

[0089] If the corresponding value in conditional equation (20) falls below the lower limit, it becomes difficult to miniaturize the optical system, which is undesirable. By setting the lower limit of conditional equation (20) to 0.50, 1.00, 1.50, and even 1.90, the effects of this embodiment can be made more reliable.

[0090] In the optical system OL according to the first and second embodiments, the following conditional expression may be satisfied. 1.00 <Lr / f<10.00···(21) However, Lr: Length along the optical axis from the aperture to the image plane (air-equivalent distance) f: focal length of the optical system

[0091] Conditional equation (21) defines the ratio of the length along the optical axis from the aperture to the image plane of the optical system OL according to the first and second embodiments to the focal length of the entire optical system within an appropriate range. By satisfying conditional equation (21), miniaturization can be achieved.

[0092] If the corresponding value in conditional equation (21) exceeds the upper limit, it becomes difficult to miniaturize the optical system, which is undesirable. By setting the upper limit of conditional equation (21) to 8.00, 5.00, 4.00, and 3.90, the effects of this embodiment can be made more reliable.

[0093] If the corresponding value in conditional equation (21) falls below the lower limit, it becomes difficult to miniaturize the optical system, which is undesirable. By setting the lower limit of conditional equation (21) to 1.50, 2.00, and 2.50, the effects of this embodiment can be made more reliable.

[0094] In addition, in the optical system OL according to the first and second embodiments, at least one of the lens surfaces of the positive lens on the image plane side and the negative lens on the image plane side may be an aspherical surface. By doing so, various aberrations of the optical system can be corrected well, and the exit pupil of the optical system can be appropriately controlled to ensure telecentricity with respect to the image sensor. The aspherical surface may have a positive refractive power that weakens and a negative refractive power that strengthens as it moves away from the optical axis. That is, if it is a convex surface, the curvature may become gentler as it moves away from the optical axis, and if it is a concave surface, the curvature may become steeper as it moves away from the optical axis. By doing so, various aberrations such as coma aberration and field curvature can be corrected well, and the exit pupil of the optical system can be appropriately controlled to ensure telecentricity with respect to the image sensor.

[0095] Here, the manufacturing method of the optical system OL according to the first embodiment will be described with reference to Figure 17. First, a front group, an aperture, and a rear group are arranged in order from the object side along the optical axis (step ST10). The rear group is arranged to have an image-plane side subgroup located on the image plane side of the rear group, and an object-side subgroup located on the object side of the image-plane subgroup (step ST11). The image-plane side subgroup is configured to have an image-plane side positive lens having a positive refractive power and an image-plane side negative lens having a negative refractive power (step ST12). The object-side subgroup is configured to have an object-side positive lens having a positive refractive power and an object-side negative lens having a negative refractive power (step ST13). Then, each lens is arranged in the lens barrel so as to satisfy at least conditional equations (1) to (4) (step ST14). By such a manufacturing method, an optical system OL with good optical performance can be obtained.

[0096] Next, the manufacturing method of the optical system OL according to the second embodiment will be described with reference to Figure 18. First, a front group, an aperture, and a rear group are arranged in order from the object side along the optical axis (step ST20), and the rear group is configured to have at least two positive lenses and at least two negative lenses (step ST21). Furthermore, the at least two positive lenses are configured to include an image-plane positive lens which is positioned closest to the image plane among at least two lenses (step ST22). Furthermore, the at least two negative lenses are configured to include an image-plane negative lens which is positioned closest to the image plane among at least two lenses (step ST23). Then, each lens is arranged in the lens barrel so as to satisfy at least conditional equations (5), (6), and (3) (step ST24). By such a manufacturing method, an optical system OL with good optical performance can be obtained. [Examples]

[0097] The optical system OL according to the embodiment of this present invention will be described below based on the drawings. Figures 1, 4, 7, 10, and 13 show the optical system OL {OL(1) to OL(5)} according to the first to fifth embodiments. This is a cross-sectional view showing the configuration of the lens. In Figures 1, 4, 7, 10, and 13, the direction of movement of each lens group along the optical axis when focusing from infinity to a near object is indicated by an arrow along with the word (focus).

[0098] In Figures 1, 4, 7, 10, and 13, each lens group is represented using the designations GF (front group) and GR (rear group). However, each embodiment represents the lens group independently. Therefore, the use of the same designations between embodiments does not necessarily mean that they have the same configuration.

[0099] Tables 1 to 5 are shown below. Table 1 shows the specifications for the first embodiment, Table 2 for the second embodiment, Table 3 for the third embodiment, Table 4 for the fourth embodiment, and Table 5 for the fifth embodiment. In each embodiment, the d-line (λ=587.6nm), g-line (λ=435.8nm), C-line (λ=656.3nm), and F-line (λ=486.1nm) were selected as the parameters for calculating aberration characteristics.

[0100] In the [Overall Specifications] table, f is the focal length of the entire optical system, FNO is the F number, ω is the half-angle of view (in degrees), and Y is the image height. TL indicates the total length of the optical system, and more specifically, it is the value obtained by adding the distance from the lens surface closest to the object to the lens surface closest to the image plane on the optical axis when focused at infinity, to the air-equivalent distance from the last lens surface on the optical axis to the image plane I when focused at infinity. Lr indicates the air-equivalent distance on the optical axis from the aperture of the optical system to the image plane. BFa indicates the air-equivalent distance (back focus) from the last lens surface on the optical axis to the image plane I when focused at infinity. fF indicates the focal length of the front group, and fR indicates the focal length of the rear group. Also, fp1 indicates the focal length of the object-side subgroup Gp1 in the first embodiment, and fp2 indicates the focal length of the image plane-side subgroup Gp2 in the first embodiment. fLp2 represents the focal length of the positive lens on the image plane side, fLn2 represents the focal length of the negative lens on the image plane side, fLp1 represents the focal length of the positive lens on the object side, and fLn1 represents the focal length of the negative lens on the object side.

[0101] 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 (surfaces with the center of curvature on the image plane side are given a positive value), 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), and nd is the refractive index based on the d line of the optical material. "∞" for the radius of curvature indicates a plane or aperture, and (S) indicates an aperture diaphragm. The refractive index of air is nd = 1.00000. Details have been omitted. If the lens surface is aspherical, an asterisk (*) is placed next to the surface number, and the radius of curvature R column shows the radius of paraxial curvature.

[0102] The table in [Aspherical Data] shows the shape of the aspherical surface shown in [Lens Specifications] using the following equation (A). X(y) is the distance along the optical axis (sag) 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 cone constant, and Ai is the i-th aspherical coefficient. "En" is "×10 -n This shows that 1.234E-05 = 1.234 × 10 -5It should be noted that the second-order aspherical coefficient A2 is 0, and its description is omitted.

[0103] X(y)=(y 2 / R) / {1+(1-κ×y 2 / R 2 ) 1 / 2}+A4×y 4 +A6×y 6 +A8×y 8 +A10×y 10 +A12×y 12 ···(A)

[0104] [Lens group data] table shows the starting surface (the most object-side surface) and the focal length of each lens group.

[0105] [Variable interval data] table shows the surface intervals (d1~d3) described for the surface numbers where the surface interval is (variable) in the [Lens specifications] table, and shows the surface intervals in the infinity focus state and the surface intervals in the close-distance focus state, respectively. Here, f represents the focal length of the entire lens system, β represents the shooting magnification, respectively. Also, D0 represents the distance from the object to the most object-side optical surface in the optical system.

[0106] Hereinafter, in all the specification values, the published focal length, radius of curvature R, surface interval D, and other lengths, etc., generally use "mm" when not otherwise specified, but the optical system can obtain the same optical performance even if it is proportionally enlarged or reduced, so it is not limited to this.

[0107] The explanations of the tables so far are common to all the embodiments, and the overlapping explanations below are omitted.

[0108] [[ID=4​The first embodiment will be described using Figures 1 to 3 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, an aperture diaphragm S, a second lens group G2, a third lens group G3, and a fourth lens group G4, which are 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 different trajectories (amount of movement), and the spacing between adjacent lens groups changes. An optical filter FL (for example, a low-pass filter) is placed between the fourth lens group G4 and the image plane I.

[0109] The first lens group G1 consists of the following lenses arranged in order from the object side along the optical axis: a meniscus-shaped negative lens L11 with its convex surface facing the object side, a meniscus-shaped negative lens L12 with its convex surface facing the object side, a meniscus-shaped negative lens L13 with its convex surface facing the object side, a meniscus-shaped positive lens L14 with its convex surface facing the object side, a cemented lens formed from a plano-concave negative lens L15 with its concave surface facing the object side and a plano-convex positive lens L16 with its convex surface facing the image plane side, a biconvex positive lens L17, and a cemented lens formed from a biconvex positive lens L18 and a biconcave negative lens L19. The object-side and image-side lens surfaces of the negative lens L13 are formed in an aspherical shape.

[0110] The second lens group G2 consists of a biconcave negative lens L21 and a biconvex positive lens L22, arranged in order from the object side along the optical axis. When focusing from an object at infinity to a nearby object, the second lens group G2 moves towards the object.

[0111] The third lens group G3 consists of a meniscus-shaped positive lens L31 with its convex surface facing the object, and a biconvex-shaped positive lens L32, arranged sequentially from the object side along the optical axis. When focusing from an object at infinity to a nearby object, the third lens group G3 moves towards the object side. The image-plane side of the positive lens L31 and the object-side lens surface of the positive lens L32 are formed in an aspherical shape.

[0112] The fourth lens group G4 consists of a biconvex positive lens L41, a cemented lens formed from a biconvex positive lens L42 and a biconcave negative lens L43, and a cemented lens formed from a biconvex positive lens L44 and a biconcave negative lens L45, all arranged in order from the object side along the optical axis. The object-side lens surface of the positive lens L44 is formed in an aspherical shape.

[0113] The aperture diaphragm S, which is intended to adjust the amount of light, is positioned between the first lens group G1 and the second lens group G2.

[0114] In this embodiment, the first lens group G1 constitutes the front group GF. The second lens group G2, the third lens group G3, and the fourth lens group G4 constitute the rear group GR. In the fourth lens group G4, the positive lens L42 corresponds to the object-side positive lens Lp1, and the negative lens L43 corresponds to the object-side negative lens Ln1. In addition, the positive lens L44 in the fourth lens group G4 is the image plane-side positive lens. Lp2 corresponds to negative lens L45, which corresponds to negative lens Ln2 on the image plane side. In addition, positive lens L42 and negative lens L43 constitute object-side subgroup Gp1 according to the first embodiment. Furthermore, positive lens L44 and negative lens L45 constitute image-side subgroup Gp2 according to the first embodiment.

[0115] Table 1 below shows the specifications for the optical system according to the first embodiment. Note that in the [Lens Specifications], the third surface is a virtual surface.

[0116] (Table 1) [Overall Specifications] f=24.74 Y=21.70 ω=45.59 FNO=1.23 TL=152.37 Lr=71.03 BFa = 12.45 fF=91.07 fR=51.63 fp1 = -46.38 fp2 = -182.20 fLp1 = 76.27 fLn1 = -28.47 fLp2 = 35.84 fLn2 = -29.12 [Lens Specifications] Surface number RD nd νd θg-F 1 54.0463 2.500 1.67798 54.89 2 24.2745 15.496 3 ∞ 0.083 4 14801.6410 2.500 1.49700 81.61 5 42.4817 3.231 6* 121.5477 3.000 1.51680 64.13 7* 42.5835 1.000 8 52.0232 5.652 1.92119 23.96 9 332.6351 10.433 10 -32.0475 2.100 1.73800 32.26 11 ∞ 6.819 1.95375 32.33 12 -54.8425 0.100 13 57.2867 10.670 1.59319 67.90 14 -73.4504 0.200 15 50.3056 12.426 1.51860 69.89 16 -37.4332 1.600 1.73800 32.26 17 110.1534 3.608 18 ∞ d1 (variable) (aperture) 19 -34.1298 1.500 1.73800 32.26 20 501.5244 0.100 21 54.7023 8.714 1.49700 81.61 22 -57.1769 d2 (variable) 23 36.8595 7.890 1.59255 67.86 24* 351.3727 0.100 25* 74.6447 3.500 1.85108 40.12 26 -141.8899 d3 (variable) 27 159.8139 3.442 1.94594 17.98 28 -259.6439 0.100 29 371.6677 3.999 1.94594 17.98 0.6546 30 -89.0537 1.400 1.78880 28.42 0.6006 31 30.2378 5.459 32* 125.2663 8.703 1.59255 67.86 0.5440 33 -24.9101 1.400 1.78880 28.42 0.6006 34 302.7448 11.300 35 ∞ 1.600 1.51680 64.13 36 ∞ 0.100 [Aspherical surface] Page 6 κ=1.0000,A4=1.66242E-06,A6=1.56004E-09,A8=8.69756E-12,A10=-2.80813E-14,A12=0.46258E-16 Page 7 κ=1.0000,A4=-4.27967E-06,A6=-6.94044E-10,A8=-2.12271E-12,A10=-1.41132E-14,A12=0.37644E-16 Page 24 κ=1.0000,A4=-1.05676E-05,A6=2.42614E-08,A8=-1.28275E-10,A10=2.44478E-13,A12=-0.18533E-15 Page 25 κ=1.0000,A4=-1.65439E-05,A6=1.47319E-08,A8=-1.00744E-10,A10=3.02846E-13,A12=-0.83526E-15 Page 32 κ=1.0000,A4=-1.03369E-05,A6=-9.20246E-09,A8=4.66420E-11,A10=-2.50880E-13,A12=0.00000E+00 [Variable interval data] Infinity focus state Close focus state f=24.74 β=-0.099 D0 ∞ 214.851 d1 11.387 8.034 d2 0.100 1.820 d3 0.788 2.421 [Lens group data] Group starting plane focal length G1 1 91.074 G2 19 -234.139 G3 23 33.081 G4 27 -57.648

[0117] Figure 2 shows the aberration diagrams for the optical system according to the first embodiment when focused at infinity, and Figure 3 shows the aberration diagrams 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. In the spherical aberration diagram, the F number or numerical aperture value corresponding to the maximum aperture is shown, in the astigmatism and distortion diagrams the maximum image height is shown, and in the coma aberration diagram each image height value is shown. d indicates the aberration at the d line (λ=587.6nm), g indicates the aberration at the g line (λ=435.8nm), C indicates the aberration at the C line (λ=656.3nm), and F indicates the aberration at the F line (λ=486.1nm). In the aberration diagram showing astigmatism, the solid line indicates the sagittal image plane and the dashed line indicates the meridional image plane. The distortion diagram shows the distortion relative to the d line. In the aberration diagrams of the embodiments shown below, the same reference numerals as in this embodiment are used, and redundant explanations are omitted.

[0118] From the various aberration diagrams, it can be seen that the optical system according to the first embodiment has good aberration correction and excellent imaging performance.

[0119] (Second example) The second embodiment will be described using Figures 4 to 6 and Table 2. Figure 4 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, an aperture diaphragm S, a second lens group G2, a third lens group G3, and a fourth lens group G4, which are 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 different trajectories (amount of movement), and the spacing between adjacent lens groups changes. An optical filter FL (for example, a low-pass filter) is placed between the fourth lens group G4 and the image plane I.

[0120] The first lens group G1 consists of, arranged in order from the object side along the optical axis, a meniscus-shaped negative lens L11 with its convex surface facing the object, a biconcave-shaped negative lens L12, a biconcave-shaped negative lens L13, a biconvex-shaped positive lens L14, a cemented lens formed by a plano-concave-shaped negative lens L15 with its concave surface facing the object and a plano-convex-shaped positive lens L16 with its convex surface facing the image plane, a biconvex-shaped positive lens L17, and a cemented lens formed by a biconvex-shaped positive lens L18 and a meniscus-shaped negative lens L19 with its concave surface facing the object. The object-side and image-side lens surfaces of the positive lens L11 and the object-side and image-side lens surfaces of the negative lens L13 are formed in an aspherical shape.

[0121] The second lens group G2 consists of a biconcave negative lens L21 and a biconvex positive lens L22, arranged in order from the object side along the optical axis. When focusing from an object at infinity to a nearby object, the second lens group G2 moves towards the object.

[0122] The third lens group G3 consists of a plano-convex positive lens L31 with its convex surface facing the object, and a biconvex positive lens L32. When focusing from an object at infinity to a nearby object, the third lens group G3 moves towards the object. The image-plane side of the positive lens L31 and the object-plane side of the positive lens L32 are formed aspherical.

[0123] The fourth lens group G4 consists of a biconvex positive lens L41, a cemented lens formed from a biconvex positive lens L42 and a biconcave negative lens L43, and a cemented lens formed from a biconvex positive lens L44 and a meniscus-shaped negative lens L45 with its concave side facing the object. The object-side lens surface of the positive lens L44 is formed in an aspherical shape.

[0124] The aperture diaphragm S, which is intended to adjust the amount of light, is positioned between the first lens group G1 and the second lens group G2.

[0125] In this embodiment, the first lens group G1 constitutes the front group GF. The second lens group G2, the third lens group G3, and the fourth lens group G4 constitute the rear group GR. In the fourth lens group G4, the positive lens L42 corresponds to the object-side positive lens Lp1, and the negative lens L43 corresponds to the object-side negative lens Ln1. In the fourth lens group G4, the positive lens L44 corresponds to the image plane-side positive lens Lp2, and the negative lens L45 corresponds to the image plane-side negative lens Ln2. Furthermore, the positive lens L42 and the negative lens L43 constitute the object-side subgroup Gp1 according to the first embodiment. Furthermore, the positive lens L44 and the negative lens L45 constitute the image plane-side subgroup Gp2 according to the first embodiment.

[0126] Table 2 below shows the values ​​of the parameters for the optical system according to the second embodiment.

[0127] (Table 2) [Overall Specifications] f=24.72 Y=21.70 ω=42.59 FNO=1.24 TL=152.44 Lr=79.56 BFa = 12.45 fF=99.05 fR=51.14 fp1 = -44.18 fp2 = 21504.53 fLp1 = 71.99 fLn1 = -27.14 fLp2 = 35.07 fLn2 = -33.88 [Lens Specifications] Surface number RD nd νd θg-F 1* 104.7869 2.500 1.58286 59.50 2* 23.0394 14.423 3 -287.9600 2.100 1.49700 81.61 4 157.6059 2.761 5* -103.1047 3.000 1.51680 64.13 6* 47.8546 1.000 7 52.8641 6.647 1.92119 23.96 8 -484.4586 5.466 9 -35.4455 2.100 1.73800 32.26 10 ∞ 4.949 1.95375 32.33 11 -70.8304 0.104 12 65.4267 10.445 1.59319 67.90 13 -61.0393 0.200 14 69.2418 13.670 1.51860 69.89 15 -31.6762 1.600 1.73800 32.26 16 -2301.9657 1.917 17 ∞ d1 (variable) (aperture) 18 -34.1079 1.500 1.73800 32.26 19 244.6353 0.100 20 57.6670 9.959 1.49700 81.61 21 -51.0813 d2 (variable) 22 39.1567 8.583 1.59255 67.86 23* ∞ 1.500 24* 83.2420 3.501 1.85108 40.12 25 -247.7735 d3 (variable) 26 131.9006 3.710 1.94594 17.98 27 -323.2819 0.100 28 1928.8605 4.389 1.94594 17.98 0.6546 29 -70.5141 1.400 1.78880 28.42 0.6006 30 31.0136 3.958 31* 98.3198 9.704 1.59255 67.86 0.5440 32 -25.3834 1.400 1.78880 28.42 0.6006 33 -518.4605 11.300 34 ∞ 1.600 1.51680 64.13 35 ∞ 0.100 [Aspherical surface] Page 1 κ=5.8911,A4=4.18472E-06,A6=-2.47036E-09,A8=2.52770E-13,A10=7.43401E-16,A12=-2.84970E-18 Page 2 κ=1.0172,A4=3.15623E-06,A6=-1.72824E-09,A8=3.90050E-11,A10=-4.72795E-14,A12=- 1.34120E-17 Page 5 κ=1.0000,A4=1.01469E-06,A6=6.79448E-09,A8=-8.26721E-12,A10=9.89108E-15,A12=1.43980E-17 Page 6 κ=1.0000,A4=-2.94917E-07,A6=-2.08112E-09,A8=-1.67690E-12,A10=-4.35517E-14,A12=-1.37260E-16 Page 23 κ=1.0000,A4=-1.16825E-05,A6=2.96738E-08,A8=-1.01356E-10,A10=2.49807E-13,A12=-3.57980E-16 Page 24 κ=1.0000,A4=-1.56826E-05,A6=1.77316E-08,A8=-8.59133E-11,A10=3.19552E-13,A12=-8.68080E-16 Page 31 κ=1.0000,A4=-6.36848E-06,A6=-1.00946E-08,A8=2.97753E-11,A10=-1.88653E-13,A12=0.00000E+00 [Variable interval data] Infinity focus state Close focus state f = 24.72 β = -0.150 D0 ∞ 137.748 d1 13.197 8.378 d2 0.100 2.158 d3 4.006 6.768 [Lens group data] Group starting plane focal length G1 1 99.052 G2 18 -202.245 G3 22 36.751 G4 26 -84.069

[0128] Figure 5 shows the aberration diagrams for the optical system according to the second embodiment when focused at infinity, and Figure 6 shows the aberration diagrams when focused at close range. From each aberration diagram, it can be seen that the optical system according to the second embodiment has good aberration correction and excellent imaging performance.

[0129] (Third embodiment) The third embodiment will be explained using Figures 7 to 9 and Table 3. Figure 7 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, an aperture diaphragm S, a second lens group G2, a third lens group G3, and a fourth lens group G4, which are 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 different trajectories (amount of movement), and the spacing between adjacent lens groups changes. An optical filter FL (for example, a low-pass filter) is placed between the fourth lens group G4 and the image plane I.

[0130] The first lens group G1 consists of the following lenses arranged in order from the object side along the optical axis: a meniscus-shaped negative lens L11 with its convex surface facing the object, a meniscus-shaped negative lens L12 with its convex surface facing the object, a meniscus-shaped negative lens L13 with its concave surface facing the image plane, a meniscus-shaped negative lens L14 with its convex surface facing the object, a meniscus-shaped positive lens L15 with its convex surface facing the object, a cemented lens formed by a plano-concave negative lens L16 with its concave surface facing the object and a plano-convex positive lens L17 with its convex surface facing the image plane, a biconvex positive lens L18, and a cemented lens formed by a biconvex positive lens L19 and a biconcave L20. The image-plane side lens surface of lens 3, and the object-side and image-plane side lens surfaces of negative lens L14 are formed in an aspherical shape.

[0131] The second lens group G2 consists of a biconcave negative lens L21 and a biconvex positive lens L22, arranged in order from the object side along the optical axis. When focusing from an object at infinity to a nearby object, the second lens group G2 moves towards the object.

[0132] The third lens group G3 consists of a meniscus-shaped positive lens L31 with its convex surface facing the object, and a biconvex-shaped positive lens L32. When focusing from an object at infinity to a nearby object, the third lens group G3 moves towards the object. The image-plane side of the positive lens L31 and the object-plane side of the positive lens L32 are formed aspherical.

[0133] The fourth lens group G4 consists of a biconvex positive lens L41, a cemented lens formed from a meniscus-shaped positive lens L42 with its convex side facing the image plane and a biconcave negative lens L43, and a cemented lens formed from a biconvex positive lens L44 and a biconcave negative lens L45. The object-side lens surface of the positive lens L44 is formed in an aspherical shape.

[0134] The aperture diaphragm S, which is intended to adjust the amount of light, is positioned between the first lens group G1 and the second lens group G2.

[0135] In this embodiment, the first lens group G1 constitutes the front group GF. The second lens group G2, the third lens group G3, and the fourth lens group G4 constitute the rear group GR. In the fourth lens group G4, the positive lens L42 corresponds to the object-side positive lens Lp1, and the negative lens L43 corresponds to the object-side negative lens Ln1. In the fourth lens group G4, the positive lens L44 corresponds to the image plane-side positive lens Lp2, and the negative lens L45 corresponds to the image plane-side negative lens Ln2. Furthermore, the positive lens L42 and the negative lens L43 constitute the object-side subgroup Gp1 according to the first embodiment. Furthermore, the positive lens L44 and the negative lens L45 constitute the image plane-side subgroup Gp2 according to the first embodiment.

[0136] Table 3 below shows the values ​​of the parameters for the optical system according to the third embodiment.

[0137] (Table 3) [Overall Specifications] f=18.54 Y=21.70 ω=50.93 FNO=1.24 TL=188.27 Lr=70.10 BFa = 12.45 fF=60.99 fR=51.26 fp1 = -49.85 fp2 = -331.20 fLp1 = 61.50 fLn1 = -27.36 fLp2 = 44.08 fLn2 = -38.10 [Lens Specifications] Surface number RD nd νd θg-F 1 58.8076 3.000 1.56384 60.71 2 36.2444 12.849 3 49.9591 2.500 1.59319 67.90 4 30.0483 20.325 5 335.0585 2.500 1.49710 81.56 6* 24.8890 10.973 7* 194.3076 5.402 1.51680 64.13 8* 97.5403 1.101 9 57.0767 8.816 1.92119 23.96 10 13481.8560 17.933 11 -40.3700 2.100 1.73800 32.26 12 ∞ 4.728 1.95375 32.33 13 -98.6307 0.100 14 68.5255 9.818 1.59319 67.90 15 -63.5197 0.200 16 63.3463 11.904 1.51860 69.89 17 -33.1319 1.600 1.73800 32.26 18 495.1033 2.325 19 ∞ d1 (variable) (aperture) 20 -35.9212 1.500 1.73800 32.26 21 199.0346 0.200 22 50.9175 9.516 1.49700 81.61 23 -49.0721 d2 (variable) 24 35.2293 7.397 1.59255 67.86 25* 164.9761 0.776 26* 75.3449 3.750 1.85108 40.12 27 -486.7153 d3(can be changed) 28 192.9959 3.569 1.94594 17.98 29 -135.2598 0.100 30 -1524.2303 4.257 1.94594 17.98 0.6546 31 -56.1126 1.400 1.78880 28.42 0.6006 32 35.4506 4.911 33* 107.2960 5.370 1.59255 67.86 0.5440 34 -33.8813 1.400 1.78880 28.42 0.6006 35 270.9450 10.400 36 ∞ 1.600 1.51680 64.13 37 ∞ 1.000 [Aspherical surface] Page 6 κ=0.5208,A4=-3.95701E-06,A6=2.55042E-10,A8=5.53966E-12,A10=-1.02639E-14,A12=0.00000E+00 Page 7 κ=1.0000,A4=8.55618E-07,A6=6.70291E-09,A8=4.97503E-12,A10=-2.22810E-14,A12=1.84890E-17 Page 8 κ=1.0000,A4=-7.47115E-07,A6=1.27978E-09,A8=8.32219E-12,A10=-3.91329E-14,A12=4.56920E-17 Page 25 κ=1.0000,A4=-1.99456E-05,A6=2.95135E-08,A8=-1.06451E-10,A10=2.80026E-13,A12=-2.97910E-16 Page 26 κ=1.0000,A4=-2.17446E-05,A6=1.43590E-08,A8=-7.91290E-11,A10=2.93377E-13,A12=-7.78200E-16 Page 33 κ=1.0000,A4=-1.74730E-05,A6=-1.56047E-08,A8=5.46200E-11,A10=-3.81321E-13,A12=0.00000E+00 [Variable interval data] Infinity focus state Close focus state f = 18.54 β = -0.150 D0 ∞ 78.264 d1 10.566 7.184 d2 0.100 1.142 d3 2.834 5.174 [Lens group data] Group starting plane focal length G1 1 60.990 G2 20 -327.081 G3 24 39.505 G4 28 -94.907

[0138] Figure 8 shows the aberration diagrams for the optical system according to the third embodiment when focused at infinity, and Figure 9 shows the aberration diagrams when focused at close range. From each aberration diagram, it can be seen that the optical system according to the third embodiment has good aberration correction and excellent imaging performance.

[0139] (Fourth embodiment) The fourth embodiment will be described using Figures 10 to 12 and Table 4. Figure 10 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, an aperture diaphragm S, a second lens group G2, a third lens group G3, and a fourth lens group G4, which are 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 different trajectories (amount of movement), and the spacing between adjacent lens groups changes. An optical filter FL (for example, a low-pass filter) is placed between the fourth lens group G4 and the image plane I.

[0140] The first lens group G1 consists of the following lenses arranged in order from the object side along the optical axis: a meniscus-shaped negative lens L11 with its convex surface facing the object side, a biconcave-shaped negative lens L12, a meniscus-shaped negative lens L13 with its convex surface facing the object side, a meniscus-shaped positive lens L14 with its convex surface facing the object side, a plano-concave-shaped negative lens L15 with its concave surface facing the object side, a plano-convex-shaped positive lens L16 with its convex surface facing the image plane side, a biconvex-shaped positive lens L17, a biconvex-shaped positive lens L18, and a biconcave-shaped negative lens L19. The object-side and image-plane-side lens surfaces of the negative lens L13 are formed in an aspherical shape.

[0141] The second lens group G2 consists of a biconcave negative lens L21 and a biconvex positive lens L22, arranged in order from the object side along the optical axis. When focusing from an object at infinity to a nearby object, the second lens group G2 moves towards the object.

[0142] The third lens group G3 consists of a biconvex positive lens L31 and a biconvex positive lens L32. When focusing from an object at infinity to a nearby object, the third lens group G3 moves toward the object. The image-plane side of the positive lens L31 and the object-plane side of the positive lens L32 are formed aspherical.

[0143] The fourth lens group G4 consists of a meniscus-shaped positive lens L41 with its convex side facing the object, a cemented lens formed from a biconvex positive lens L42 and a biconcave negative lens L43, and a cemented lens formed from a biconcave negative lens L44 and a biconvex positive lens L45. The image-plane side of the positive lens L45 is formed in an aspherical shape.

[0144] The aperture diaphragm S, which is intended to adjust the amount of light, is positioned between the first lens group G1 and the second lens group G2.

[0145] In this embodiment, the first lens group G1 constitutes the front group GF. The second lens group G2, the third lens group G3, and the fourth lens group G4 constitute the rear group GR. In the fourth lens group G4, the positive lens L42 corresponds to the object-side positive lens Lp1, and the negative lens L43 corresponds to the object-side negative lens Ln1. In the fourth lens group G4, the negative lens L44 corresponds to the image plane-side negative lens Ln2, and the positive lens L45 corresponds to the image plane-side positive lens Lp2. Furthermore, the positive lens L42 and the negative lens L43 constitute the object-side subgroup Gp1 according to the first embodiment. Furthermore, the negative lens L44 and the positive lens L45 constitute the image plane-side subgroup Gp2 according to the first embodiment.

[0146] Table 4 below shows the values ​​of the parameters for the optical system according to the fourth embodiment.

[0147] (Table 4) [Overall Specifications] f=23.52 Y=21.70 ω=42.78 FNO=1.27 TL=154.22 Lr=75.33 BFa = 12.33 fF=83.96 fR=46.09 fp1 = -112.03 fp2 = -152.10 fLp1 = 52.86 fLn1 = -34.03 fLp2 = 42.21 fLn2 = -32.38 [Lens Specifications] Surface number RD nd νd θg-F 1 50.5449 2.500 1.67798 54.89 2 23.0471 15.248 3 -9063.4263 2.500 1.49700 81.61 4 47.0583 3.237 5* 214.5948 3.000 1.51680 64.13 6* 43.4559 1.000 7 52.8964 5.741 1.92119 23.96 8 1110.0252 6.958 9 -34.1985 2.100 1.73800 32.26 10 ∞ 6.780 1.95375 32.33 11 -58.9797 2.367 12 53.0972 10.960 1.59319 67.90 13 -75.3099 0.200 14 52.8842 11.199 1.51860 69.89 15 -39.2684 1.600 1.73800 32.26 16 111.5130 3.493 17 ∞ d1(variable) (aperture) 18 -31.7632 1.500 1.73800 32.26 19 1853.7591 2.436 20 58.2028 8.733 1.49700 81.61 21 -55.6593 d2(variable) 22 38.2383 8.450 1.59255 67.86 23* -259.9371 1.503 24* 69.6437 3.499 1.85108 40.12 25 -1463.0026 d3(variable) 26 170.6627 1.763 1.94594 17.98 27 208.2194 0.100 28 71.1492 5.893 1.94594 17.98 0.6546 29 -161.5077 1.400 1.78880 28.42 0.6006 30 32.3154 5.314 31 -209.6010 1.400 1.78880 28.42 0.6006 32 29.1730 7.512 1.59255 67.86 0.5440 33* -158.4717 10.295 34 ∞ 1.600 1.51680 64.13 35 ∞ 0.979 [Aspherical surface] Page 5 κ=1.0000,A4=1.67501E-06,A6=1.76643E-10,A8=1.51202E-11,A10=-4.58473E-14,A12=7.57780E-17 Page 6 κ=1.0000,A4=-4.38907E-06,A6=-1.89170E-09,A8=4.57936E-12,A10=-4.28999E-14,A12=1.11830E-16 Page 23 κ=1.0000,A4=-8.84181E-06,A6=3.36131E-08,A8=-1.10871E-10,A10=2.31946E-13,A12=-2.62920E-16 Page 24 κ=1.0000,A4=-1.49185E-05,A6=2.22682E-08,A8=-1.07717E-10,A10=3.41160E-13,A12=-7.72780E-16 Page 33 κ=1.0000,A4=1.28837E-05,A6=-8.98876E-09,A8=3.10566E-11,A10=2.74802E-14,A12=0.00000E+00 [Can change the interval データ] Infinity focus state Close focus state f=23.52 β=-0.149 D0 ∞ 132.288 d1 11.345 6.518 d2 0.100 2.386 d3 0.500 3.041 [Lens group data] Group starting plane focal length G1 1 83.964 G2 18 -246.080 G3 22 34.521 G4 26 -70.939

[0148] Figure 11 shows the aberration diagrams for the optical system according to the fourth embodiment when focused at infinity, and Figure 12 shows the aberration diagrams when focused at close range. From each aberration diagram, it can be seen that the optical system according to the fourth embodiment has good aberration correction and excellent imaging performance.

[0149] (Fifth example) The fifth embodiment will be explained using Figures 13 to 15 and Table 5. Figure 13 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, an aperture diaphragm S, a second lens group G2, a third lens group G3, and a fourth lens group G4, which are 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 different trajectories (amount of movement), and the spacing between adjacent lens groups changes. Between the fourth lens group G4 and the image plane I An optical filter (FL, such as a low-pass filter) is placed in between.

[0150] The first lens group G1 consists of the following lenses arranged in order from the object side along the optical axis: a meniscus-shaped negative lens L11 with its convex surface facing the object side; a biconcave-shaped negative lens L12; a meniscus-shaped positive lens L13 with its convex surface facing the object side; a cemented lens formed from a plano-concave-shaped negative lens L14 with its concave surface facing the object side and a plano-convex-shaped positive lens L15 with its convex surface facing the image plane side; a biconvex-shaped positive lens L16; and a cemented lens formed from a biconvex-shaped positive lens L17 and a biconcave-shaped negative lens L18. The object-side and image-plane-side lens surfaces of the negative lens L12 are formed in an aspherical shape.

[0151] The second lens group G2 consists of a meniscus-shaped negative lens L21 with its concave surface facing the object, and a biconvex-shaped positive lens L22, arranged sequentially from the object side along the optical axis. When focusing from an object at infinity to a nearby object, the second lens group G2 moves towards the object.

[0152] The third lens group G3 consists of a biconvex positive lens L31 and a biconvex positive lens L32. When focusing from an object at infinity to a nearby object, the third lens group G3 moves toward the object. The image-plane side of the positive lens L31 and the object-plane side of the positive lens L32 are formed aspherical.

[0153] The fourth lens group G4 consists of a cemented lens formed from a biconvex positive lens L41 and a biconcave negative lens L42, a meniscus-shaped negative lens L43 with its convex side facing the object, and a biconvex positive lens L44. The object-facing lens surface of the positive lens L44 is formed in an aspherical shape.

[0154] The aperture diaphragm S, which is intended to adjust the amount of light, is positioned between the first lens group G1 and the second lens group G2.

[0155] In this embodiment, the first lens group G1 constitutes the front group GF. Also, the second lens group G2, the third lens group G3, and the fourth lens group G4 constitute the rear group GR. The positive lens L41 in the fourth lens group G4 corresponds to the object-side positive lens Lp1, and the negative lens L42 corresponds to the object-side negative lens Ln1. Also, the negative lens L43 in the fourth lens group G4 corresponds to the image-side negative lens Ln2, and the positive lens L44 corresponds to the image-side positive lens Lp2. Also, the positive lens L41 and the negative lens L42 constitute the object-side subgroup Gp1 according to the first embodiment. Also, the negative lens L43 and the positive lens L44 constitute the image-side subgroup Gp2 according to the first embodiment.

[0156] The following Table 5 shows the values of the specifications in the optical system according to the fifth embodiment.

[0157] (Table 5) [Overall specifications] f = 33.92 Y = 21.70 ω = 32.90 FNO = 1.46 TL = 152.46 Lr = 74.31 BFa = 23.23 fF = 150.21 fR = 54.21 fp1 = -86.83 fp2 = -720.86 fLp1 = 76.89 fLn1 = -39.64 fLp2 = 130.59 fLn2 = -108.87 [Lens specifications] Surface number R D nd νd θg - F 1 53.1509 2.500 1.49710 81.56 2 24.0533 12.914 3* -411.5635 3.000 1.51680 64.13 4* 27.9665 2.121 5 37.4930 5.728 1.92119 23.96 6 84.1266 9.416 7 -30.2280 2.100 1.73800 32.26 8 ∞ 7.906 1.95375 32.33 9 -48.1326 0.421 10 47.9490 11.022 1.59319 67.90 11 -94.5766 0.200 12 51.1215 11.482 1.51860 69.89 13 -40.5950 1.600 1.73800 32.26 14 68.3454 7.738 15 ∞ d1 (variable) (aperture) 16 -32.0541 1.500 1.73800 32.26 17 -1596.5753 0.100 18 52.0894 8.790 1.49700 81.61 19 -56.8067 d2 (variable) 20 36.2395 7.965 1.59255 67.86 21* -288.3489 1.497 22* 74.9824 3.500 1.85108 40.12 23 -2281.0278 d3 (variable) 24 103.7187 3.896 1.94594 17.98 0.6546 25 -239.0369 1.400 1.67300 38.26 0.5754 26 30.1013 3.996 27 338.9640 1.600 1.73800 32.33 0.5899 28 64.8189 1.880 29* 94.0146 3.000 1.59255 67.86 0.5440 30 -432.1333 21.171 31 ∞ 1.600 1.51680 64.13 32 ∞ 1.000 [Aspherical data] 3rd page κ = 1.0000, A4 = 1.37496E - 06, A6 = -7.40064E - 09, A8 = 2.50028E - 11, A10 = -4.02001E - 14, A12 = 3.01970E - 17 The 4th surface κ = 1.0000, A4 = -4.81514E - 06, A6 = -1.11965E - 08, A8 = 5.82226E - 13, A10 = 3.74751E - 14, A12 = -1.29930E - 16 The 21st surface κ = 1.0000, A4 = -9.83539E - 06, A6 = 3.32263E - 08, A8 = -1.04697E - 10, A10 = 2.41015E - 13, A12 = -3.40750E - 16 The 22nd surface κ = 1.0000, A4 = -1.64286E - 05, A6 = 1.69173E - 08, A8 = -7.23919E - 11, A10 = 2.32039E - 13, A12 = -6.83470E - 16 The 29th surface[[ID=I5]] κ = 1.0000, A4 = -4.76754E - 06, A6 = 8.04010E - 10, A8 = 8.44710E - 12, A10 = -6.77979E - 14, A12 = 0.00000E + 00 [Variable interval data] Infinity focus state, close - up focus state f = 33.92, β = -0.150 D0 ∞ 193.109 dI 10.838 6.484 d2 0.100 1.760 d3 1.021 3.6I4 [Lens group data] Group, starting surface, focal length G1 1 150.207 G2 16 -312.533 G3 20 34.889 G4 24 -78.293

[0158] Figure 14 shows the aberration diagrams for the optical system according to the fifth embodiment when focused at infinity, and Figure 15 shows the aberration diagrams when focused at close range. From each aberration diagram, it can be seen that the optical system according to the fifth embodiment has good aberration correction and excellent imaging performance.

[0159] Next, the table of [Conditional Expression Corresponding Values] is shown below. This table summarizes the values ​​corresponding to each conditional expression (1) to (21) for all examples (Examples 1 to 5). Conditional expression (1) 0.6455<θgFLp1+0.0017×νdLp1 Conditional expression (2) θgFLn1-0.000023×(νdLn1)^2+0.004106×νdLn1<0.706984 Conditional expression (3) 0.6455<θgFLp2+0.0017×νdLp2 (3) Conditional expression (4) θgFLn2-0.000023×(νdLn2)^2+0.004106×νdLn2<0.706984 Condition (5) ndLn2 - ndLp2 < 0.35 Conditional expression (6) νdLp2-νdLn2<55.00 Conditional expression (7)ndLp1-ndLn1<0.35 Conditional expression (8) νdLn1-νdLp1<20.00 Conditional expression (9) νdLn1<45.00 Conditional expression (10) - 0.50 <f / fp2<0.50 Condition (11) 0.50 <fLp1 / (-fLn1)<4.00 Conditional expression (12) 0.30<(L1r1+L2r2) / (L2r2-L1r1)<6.00 Conditional expression (13)νdLn2<45.0 Condition (14) 0.50 <fLp2 / (-fLn2)<2.00 Condition (15) 0.30 <BFa / f<1.00 Conditional expression (16) 32.0°<ω<65.0° Condition (17) 0.80 <FNO<4.20 Conditional equation (18) 2.50 <fF / f<5.50 Conditional equation (19) 1.20 <fR / f<4.00 Condition (20) 0.35 <TL / Lr<2.50 Condition (21) 1.00 <Lr / f<10.00

[0160] [Conditional Expression Corresponding Values] (Examples 1-5) Conditional expression First example Second example Third example Fourth example Fifth example (1) 0.6852 0.6852 0.6852 0.6852 0.6852 (2) 0.6987 0.6987 0.6987 0.6987 0.6987 (3) 0.6594 0.6594 0.6594 0.6594 0.6594 (4) 0.6987 0.6987 0.6987 0.6987 0.6985 (5) 0.196 0.196 0.196 0.196 0.145 (6) 39.44 39.44 39.44 39.44 35.53 (7) 0.157 0.157 0.157 0.157 0.273 (8) 10.44 10.44 10.44 10.44 20.28 (9) 28.42 28.42 28.42 28.42 38.26 (10) -0.136 0.001 -0.056 -0.155 -0.047 (11) 2.679 2.652 2.248 1.554 1.940 (12) 1.636 1.922 1.987 0.733 1.195 (13) 28.42 28.42 28.42 28.42 32.30 (14) 1.231 1.035 1.157 1.303 1.199 (15) 0.503 0.504 0.672 0.524 0.685 (16) 45.59 42.59 50.93 42.78 32.90 (17) 1.231 1.238 1.235 1.268 1.455 (18) 3.671 4.007 3.290 3.569 4.428 (19) 2.087 2.069 2.765 1.959 1.598 (20) 2.145 1.916 2.686 2.047 2.052 (21) 2.871 3.218 3.781 3.203 2.191

[0161] As described above, according to each embodiment, it is possible to realize optical systems and optical instruments that have bright and good optical performance.

[0162] In the embodiments described above, the following elements can be appropriately adopted as long as they do not impair optical performance.

[0163] Although a four-group configuration is shown as an example of the optical system in this embodiment, this application is not limited to this, and optical systems with other group configurations (for example, five groups, six groups, seven groups, etc.) can also be constructed. Specifically, a configuration in which a lens or lens group is added to the optical system of this embodiment, either on the object side or the image plane side, is also acceptable. A configuration in which a third focusing lens group is added in addition to the two focusing lens groups is also acceptable. Note that a lens group refers to a portion having at least one lens, separated by an air gap that changes during focusing.

[0164] 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.

[0165] 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.

[0166] The aperture diaphragm can be replaced by the lens frame itself, rather than by providing a separate aperture diaphragm component.

[0167] 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]

[0168] OL optical system GF front group GR rear group S Aperture diaphragm I Image plane FL Optical Filter

Claims

1. It has a front group, an aperture, and a rear group, arranged in order from the object side along the optical axis. The aforementioned rear group comprises an image plane-side subgroup located closest to the image plane and an object-side subgroup located closer to the object than the image plane-side subgroup. The image plane-side subgroup comprises an image plane-side positive lens having a positive refractive power and an image plane-side negative lens having a negative refractive power. The object-side subgroup comprises an object-side positive lens having a positive refractive power and an object-side negative lens having a negative refractive power. An optical system that satisfies the following conditions. 0.6455<θgFLp1+0.0017×νdLp1 θgFLn1-0.000023×(νdLn1)^2+0.004106×νdLn1<0.706984 0.6455<θgFLp2+0.0017×νdLp2 θgFLn2-0.000023×(νdLn2)^2+0.004106×νdLn2<0.706984 However, νdLp1: Abbe number of the positive lens on the object side νdLn1: Abbe number of the object-side negative lens νdLp2: Abbe number of the positive lens on the image plane side. νdLn2: Abbe number of the negative lens on the image plane side. θgFLp1 is the partial dispersion ratio of the object-side positive lens, and is defined by the following equation when the refractive index of the object-side positive lens Lp1 with respect to the g line is ngLp1, the refractive index with respect to the F line is nFLp1, and the refractive index with respect to the C line is nCLp1. θgFLp1=(ngLp1-nFLp1) / (nFLp1-nCLp1) θgFLp2 is the partial dispersion ratio of the positive lens on the image plane side, and is defined by the following equation when the refractive index of the positive lens on the image plane side Lp2 with respect to the g line is ngLp2, the refractive index with respect to the F line is nFLp2, and the refractive index with respect to the C line is nCLp2. θgFLp2=(ngLp2-nFLp2) / (nFLp2-nCLp2) θgFLn1 is the partial dispersion ratio of the object-side negative lens, and is defined by the following equation when the refractive index of the object-side negative lens Ln1 with respect to the g line is ngLn1, the refractive index with respect to the F line is nFLn1, and the refractive index with respect to the C line is nCLn1. θgFLn1=(ngLn1-nFLn1) / (nFLn1-nCLn1) θgFLn2 is the partial dispersion ratio of the negative lens on the image plane side, and is defined by the following equation when the refractive index of the negative lens on the image plane side Ln2 with respect to the g line is ngLn2, the refractive index with respect to the F line is nFLn2, and the refractive index with respect to the C line is nCLn2. θgFLn2=(ngLn2-nFLn2) / (nFLn2-nCLn2)

2. It has a front group, an aperture, and a rear group, arranged in order from the object side along the optical axis. The aforementioned rear group has at least two positive lenses and at least two negative lenses. The at least two positive lenses include the image-plane positive lens, which is positioned closest to the image plane among the at least two lenses. The at least two negative lenses include the image-plane side negative lens, which is positioned closest to the image plane among the at least two lenses. An optical system that satisfies the following conditions. ndLn2−ndLp2<0.35 νdLp2−νdLn2<55.00 0.6455<θgFLp2+0.0017×νdLp2 However, ndLp2: refractive index based on the d line of the positive lens on the image plane side. ndLn2: Refractive index based on the d-line of the negative lens on the image plane side. νdLp2: Abbe number of the positive lens on the image plane side. νdLn2: Abbe number of the negative lens on the image plane side. θgFLp2 is the partial dispersion ratio of the positive lens on the image plane side, and is defined by the following equation when the refractive index of the positive lens on the image plane side Lp2 with respect to the g line is ngLp2, the refractive index with respect to the F line is nFLp2, and the refractive index with respect to the C line is nCLp2. θgFLp2=(ngLp2-nFLp2) / (nFLp2-nCLp2)

3. The at least two negative lenses include an object-side negative lens positioned closer to the object than the image-plane-side negative lens. The optical system according to claim 2, satisfying the following conditional expression. θgFLn1-0.000023×(νdLn1)^2+0.004106×νdLn1<0.706984 θgFLn2-0.000023×(νdLn2)^2+0.004106×νdLn2<0.706984 However, νdLn1: Abbe number of the object-side negative lens. θgFLn1 is the partial dispersion ratio of the object-side negative lens, and is defined by the following equation when the refractive index of the object-side negative lens Ln1 with respect to the g line is ngLn1, the refractive index with respect to the F line is nFLn1, and the refractive index with respect to the C line is nCLn1. θgFLn1=(ngLn1-nFLn1) / (nFLn1-nCLn1) θgFLn2 is the partial dispersion ratio of the negative lens on the image plane side, and is defined by the following equation when the refractive index of the negative lens on the image plane side Ln2 with respect to the g line is ngLn2, the refractive index with respect to the F line is nFLn2, and the refractive index with respect to the C line is nCLn2. θgFLn2=(ngLn2-nFLn2) / (nFLn2-nCLn2)

4. The at least two positive lenses include an object-side positive lens positioned closer to the object than the image-plane-side positive lens. The at least two negative lenses include an object-side negative lens positioned closer to the object than the image-plane-side negative lens. The optical system according to claim 2 or 3, satisfying the following conditional expression. ndLp1−ndLn1<0.35 νdLn1−νdLp1<20.00 However, ndLp1: refractive index based on the d line of the positive lens on the object side. ndLn1: Refractive index of the object negative lens with reference to the d line. νdLp1: Abbe number of the positive lens on the object side. νdLn1: Abbe number of the object-side negative lens

5. The at least two positive lenses include an object-side positive lens positioned closer to the object than the image-plane-side positive lens. The at least two negative lenses include an object-side negative lens positioned closer to the object than the image-plane-side negative lens. The object-side positive lens and the object-side negative lens are joined together. The optical system according to claims 2 to 4, wherein the lens surface on the image plane side of the object-side negative lens is concave.

6. The optical system according to claim 1, satisfying the following conditional expression. νdLn1<45.00

7. The optical system according to claim 1 or 6, wherein the object-side subgroup comprises the object-side positive lens and the object-side negative lens, which are arranged in order from the object side along the optical axis.

8. The optical system according to any one of claims 1, 6, or 7, wherein the object-side subgroup is arranged alongside the image plane-side subgroup on the object side.

9. An optical system according to any one of claims 1, 6 to 8, satisfying the following conditional expression. -0.50<f / fp2<0.50 However, fp2: focal length of the image plane side subgroup. f: Focal length of the optical system

10. An optical system according to any one of claims 1, 6 to 9, satisfying the following conditional expression. 0.50<fLp1 / (-fLn1)<4.00 However, fLp1: focal length of the positive lens on the object side. fLn1: Focal length of the negative lens on the object side

11. The optical system according to any one of claims 1, 6 to 10, wherein the object-side positive lens and the object-side negative lens are joined together.

12. An optical system according to any one of claims 1, 6 to 11, satisfying the following conditional expression. 0.30<(L1r1+L2r2) / (L2r2-L1r1)<6.00 However, L1r1: radius of curvature of the lens surface closest to the image plane in the object-side subgroup. L2r2: Radius of curvature of the lens surface closest to the object in the image plane subgroup.

13. The optical system according to any one of claims 1, 6 to 12, wherein the image plane-side subgroup comprises the image plane-side positive lens and the image plane-side negative lens, which are arranged in order from the object side along the optical axis.

14. An optical system according to any one of claims 1 to 13 that satisfies the following conditional expression. νdLn2 < 45.0

15. An optical system according to any one of claims 1 to 14 that satisfies the following conditional expression. 0.50<fLp2 / (-fLn2)<2.00 However, fLp2: focal length of the positive lens on the image plane side. fLn2: Focal length of the negative lens on the image plane side

16. An optical system according to any one of claims 1 to 15 that satisfies the following conditional expression. 0.30<BFa / f<1.00 However, BFa: The length along the optical axis from the lens surface closest to the image plane of the optical system to the image plane (air equivalent distance). f: Focal length of the optical system

17. An optical system according to any one of claims 1 to 16 that satisfies the following conditional expression. 32.0°<ω<65.0° However, ω: Half-angle of view when the optical system is in focus on an object at infinity.

18. An optical system according to any one of claims 1 to 17 that satisfies the following conditional expression. 0.80<FNO<4.20 However, FNO: F-number of the optical system.

19. An optical system according to any one of claims 1 to 18 that satisfies the following conditional expression. 2.50<fF / f<5.50 However, fF: focal length of the front group. f: Focal length of the optical system

20. An optical system according to any one of claims 1 to 19 that satisfies the following conditional expression. 1.20<fR / f<4.00 However, fR: focal length of the rear group. f: Focal length of the optical system

21. An optical system according to any one of claims 1 to 20 that satisfies the following conditional expression. 0.35<TL / Lr<2.50 However, TL: The length along the optical axis from the lens surface closest to the object to the image plane (air-equivalent distance). Lr: Length along the optical axis from the aperture to the image plane (air-equivalent distance)

22. An optical system according to any one of claims 1 to 21 that satisfies the following conditional expression. 1.00<Lr / f<10.00 However, Lr: the length along the optical axis from the aperture to the image plane (air equivalent distance) f: Focal length of the optical system

23. An optical instrument configured to incorporate the optical system described in any one of claims 1 to 22.

24. It has a front group, an aperture, and a rear group, arranged in order from the object side along the optical axis. The aforementioned rear group comprises an image plane-side subgroup located closest to the image plane and an object-side subgroup located closer to the object than the image plane subgroup. The image plane-side subgroup comprises an image plane-side positive lens having a positive refractive power and an image plane-side negative lens having a negative refractive power. The object-side subgroup is a method for manufacturing an optical system having an object-side positive lens having a positive refractive power and an object-side negative lens having a negative refractive power, A method for manufacturing an optical system, comprising the step of arranging each lens in a lens barrel so as to satisfy the following condition. 0.6455<θgFLp1+0.0017×νdLp1 θgFLn1-0.000023×(νdLn1)^2+0.004106×νdLn1<0.706984 0.6455<θgFLp2+0.0017×νdLp2 θgFLn2-0.000023×(νdLn2)^2+0.004106×νdLn2<0.706984 However, νdLp1: Abbe number of the positive lens on the object side νdLn1: Abbe number of the object-side negative lens νdLp2: Abbe number of the positive lens on the image plane side. νdLn2: Abbe number of the negative lens on the image plane side. θgFLp1 is the partial dispersion ratio of the object-side positive lens Lp1, and is defined by the following equation when the refractive index of the object-side positive lens Lp1 with respect to the g line is ngLp1, the refractive index with respect to the F line is nFLp1, and the refractive index with respect to the C line is nCLp1. θgFLp1=(ngLp1-nFLp1) / (nFLp1-nCLp1) θgFLp2 is the partial dispersion ratio of the image plane-side positive lens Lp2, and is defined by the following equation when the refractive index of the image plane-side positive lens Lp2 with respect to the g line is ngLp2, the refractive index with respect to the F line is nFLp2, and the refractive index with respect to the C line is nCLp2. θgFLp2=(ngLp2-nFLp2) / (nFLp2-nCLp2) θgFLn1 is the partial dispersion ratio of the object-side negative lens Ln1, and is defined by the following equation when the refractive index of the object-side negative lens Ln1 with respect to the g line is ngLn1, the refractive index with respect to the F line is nFLn1, and the refractive index with respect to the C line is nCLn1. θgFLn1=(ngLn1-nFLn1) / (nFLn1-nCLn1) θgFLn2 is the partial dispersion ratio of the image plane-side negative lens Ln2, and is defined by the following equation when the refractive index of the image plane-side negative lens Ln2 with respect to the g line is ngLn2, the refractive index with respect to the F line is nFLn2, and the refractive index with respect to the C line is nCLn2. θgFLn2=(ngLn2-nFLn2) / (nFLn2-nCLn2)

25. It has a front group, an aperture, and a rear group, arranged in order from the object side along the optical axis. The aforementioned rear group has at least two positive lenses and at least two negative lenses. The at least two positive lenses include the image-plane positive lens, which is positioned closest to the image plane among the at least two lenses. The method for manufacturing an optical system includes the image-plane side negative lens, which is the image-plane side negative lens among the at least two negative lenses, and the image-plane side negative lens is the one positioned closest to the image plane. A method for manufacturing an optical system, comprising the step of arranging each lens in a lens barrel so as to satisfy the following condition. ndLn2−ndLp2<0.35 νdLp2−νdLn2<55.00 0.6455<θgFLp2+0.0017×νdLp2 However, ndLp2: refractive index based on the d line of the positive lens on the image plane side. ndLn2: Refractive index based on the d-line of the negative lens on the image plane side. νdLp2: Abbe number of the positive lens on the image plane side. νdLn2: Abbe number of the negative lens on the image plane side. θgFLp2 is the partial dispersion ratio of the positive lens on the image plane side, and is defined by the following equation when the refractive index of the positive lens on the image plane side Lp2 with respect to the g line is ngLp2, the refractive index with respect to the F line is nFLp2, and the refractive index with respect to the C line is nCLp2. θgFLp2=(ngLp2-nFLp2) / (nFLp2-nCLp2)

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