Optical system and imaging device

Abstract

To provide an optical system and imaging apparatus with high imaging performance, whose various aberrations are favorably corrected in a whole area from a visible light range to a near-infrared range.SOLUTION: An optical system comprises, with a variable interval closest to an object side in focusing interposed therebetween, a first lens group G1 having refractive power, disposed at the object side and a second lens group G2 having positive refractive power, disposed at an image side. The first lens group G1 includes, in order from the image side, a positive lens, and at least one or more negative lenses, while the second lens group G2 includes, in order from the object side, a second A group G2A having positive refractive power, an aperture stop S, and a second B group G2B having positive refractive power, where the second B group G2B includes, in order from the object side, a negative lens, and a positive lens. The optical system satisfies a prescribed condition expression, and an imaging apparatus includes the optical system.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] Conventionally, imaging devices have been used in various fields, such as single-lens reflex cameras, digital cameras, video cameras, surveillance cameras, and industrial cameras. In all fields, image sensors (imaging elements) have become increasingly pixelated, and as a result, brighter and higher-resolution optical systems are required. In recent years, the importance of industrial cameras, particularly industrial cameras for machine vision (FA / MV) that are connected to image analysis devices and used for inspections using image analysis, has been increasing. In particular, industrial cameras that can sense not only the external structure of an object but also its internal structure by using light rays in a wide wavelength range from the visible light range to the near-infrared range, have attracted attention. For such imaging devices, optical systems with high imaging performance and good aberration correction in a wide wavelength range from the visible light range to the near-infrared range are required. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2004-245967 A [Patent Document 2] JP 2019-53236 A Summary of the Invention [Problem to be solved by the invention]

[0004] For example, Patent Document 1 discloses a bright optical system having an F-number of about 1.4, which is composed of, from the object side, a first lens group having negative refractive power and a second lens group having positive refractive power. Patent Document 2 discloses a relatively bright optical system having an F-number of about 2.8, which is composed of, from the object side, a first lens group having a refractive power and a second lens group having a positive refractive power. However, it cannot be said that the optical systems disclosed in Patent Documents 1 and 2 adequately correct various aberrations over the entire range from the visible light region to the near infrared region.

[0005] SUMMARY OF THE PRESENT EMBODIMENT An object of the present invention is to provide an optical system and an imaging apparatus having high imaging performance in which various aberrations are well corrected over the entire range from the visible light region to the near infrared region. [Means for solving the problem]

[0006] In order to solve the above problem, the optical system of the present invention is composed of a first lens group having refractive power and arranged on the object side, and a second lens group having positive refractive power and arranged on the image side, with a variable interval that is closest to the object side during focusing. The first lens group includes, from the image side, a positive lens and at least one or more negative lenses. The second lens group includes, from the object side, a 2A group having positive refractive power, an aperture stop, and a 2B group having positive refractive power, and has at least one or more negative lenses that satisfy the following conditional expressions (1) and (2). The 2B group includes, from the object side, a negative lens and a positive lens, and satisfies the following conditional expressions (3) and (4). (1) θct ≧ 0.800 (2) νd ≦ 55 (3) nd_pave <1.70 (4) νd_pave >50 however, θct: partial dispersion ratio from C-line to T-line of the negative lens in the second lens group The partial dispersion ratio θct from line C to line t is defined by the following equation. θct=(nC-nt) / (nF-nC) nC: Refractive index at C line nt: Refractive index at t rays nF: Refractive index at F line νd: Abbe number at the d line of the negative lens in the second lens group nd_pave: the average value of the refractive index at the d line of all the positive lenses arranged in the second B group νd_pave: the average value of the Abbe numbers at the d-line of all the positive lenses arranged in the 2B group

[0007] In order to solve the above problem, the imaging device according to the present invention is characterized by including the above optical system and an imaging element that converts an optical image formed by the optical system into an electrical signal. Effect of the Invention

[0008] According to the present invention, it is possible to provide an optical system and an imaging device having high imaging performance in which various aberrations are well corrected over the entire range from the visible light region to the near infrared region. [Brief description of the drawings]

[0009] [Figure 1] FIG. 2 is a cross-sectional view of the optical system of the first embodiment. [Diagram 2] 4A to 4C are aberration diagrams of the optical system of Example 1. [Diagram 3] FIG. 11 is a cross-sectional view of an optical system according to a second embodiment. [Figure 4] 11A to 11C are aberration diagrams of the optical system of Example 2. [Diagram 5] FIG. 11 is a cross-sectional view of an optical system according to a third embodiment. [Figure 6] 11A to 11C are aberration diagrams of the optical system of Example 3. [Figure 7] 1 is a diagram illustrating an example of a configuration of an imaging device according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, an embodiment of the optical system and the imaging device according to the present invention will be described. However, the optical system and the imaging device described below are one aspect of the optical system and the imaging device according to the present invention, and the optical system and the imaging device according to the present invention are not limited to the following aspects.

[0011] 1.Optical system 1-1.Optical configuration The optical system is composed of a first lens group having refractive power arranged on the object side and a second lens group having positive refractive power arranged on the image side, with a variable interval on the most object side during focusing. Furthermore, in this optical system, the first lens group includes, in order from the image side, a positive lens and at least one or more negative lenses. Furthermore, the second lens group includes, in order from the object side, a second A group having positive refractive power, an aperture stop, and a second B group having positive refractive power. Furthermore, the second B group includes, in order from the object side, a negative lens and a positive lens. By employing such an optical configuration and satisfying at least one or more of the conditional expressions described below, an optical system with high imaging performance in which aberrations are well corrected from the visible light region to the near infrared region can be obtained.

[0012] (1) First lens group The first lens group has refractive power and is composed of at least two lenses, a positive lens and a negative lens, in that order from the image side, and may have another lens on the object side of the negative lens. For example, if the first lens group is configured to have a positive lens closest to the object side, it is preferable because it is possible to ensure a wide angle of view while satisfactorily correcting distortion aberration. The sign of the refractive power of the first lens group may be positive or negative, but it is more preferable that it is negative in order to achieve a wide angle of view.

[0013] (2) Second lens group The second lens group is disposed on the image side of the first lens group via a variable interval that is closest to the object when focusing. Here, the lens interval that changes when focusing is referred to as the "variable interval when focusing." The "variable interval closest to the object when focusing" refers to the one that is closest to the object among the "variable intervals when focusing" in the optical system. Therefore, the second lens group includes all lenses that are disposed on the image side of the variable interval that is closest to the object when focusing.

[0014] The second lens group may include, in order from the object side, a second A group having a positive refractive power, an aperture stop, and a second B group having a positive refractive power. The second lens group may also include a "variable interval during focusing", and may include one or more other groups having positive or negative refractive power via a variable interval during focusing on the image side of the second B group. The interval between the second A group and the second B group may not change during focusing, or may change. However, regardless of the presence or absence of a variable interval during focusing, it is preferable to configure the second lens group from the second A group and the second B group, since this makes it easier to configure the optical system in a compact size.

[0015] The specific lens configuration of the 2A group is not particularly limited as long as it has a positive refractive power as a whole and includes at least one positive lens. The specific lens configuration of the 2B group is not particularly limited as long as it has a positive refractive power as a whole and includes, in order from the object side, a negative lens and a positive lens.

[0016] 1-2.Operation In this optical system, focusing from an infinite object to a close object is performed by moving one or more lens groups along the optical axis. For example, focusing may be performed by moving the first lens group along the optical axis, and the lens group to be moved during focusing is not particularly limited. However, in this optical system, focusing from an infinite object to a close object is preferably performed by moving the entire second lens group along the optical axis, or by moving the second A group and the second B group along the optical axis on different trajectories. If focusing is performed by the entire second lens group, the configuration of the driving mechanism during focusing is simplified, which is preferable for achieving overall miniaturization and weight reduction. Furthermore, by performing focusing by the entire second lens group arranged on the image side, it is possible to suppress the fluctuation of various aberrations and the fluctuation of the angle of view during focusing, and good imaging performance can be obtained regardless of the object position from an infinite object to a close object. On the other hand, if focusing is performed using both the 2A group and the 2B group, the amount of movement of each group during focusing can be reduced, making it easier to achieve a compact optical system in the optical axis direction. In this case, it is preferable to configure the second lens group from the 2A group and the 2B group, which makes it easier to achieve a compact optical system in the optical axis direction. It is more preferable to fix the first lens group in the optical axis direction during focusing.

[0017] 1-3.Conditional Expressions It is preferable that the optical system has the above-mentioned configuration and satisfies at least one of the following conditional expressions.

[0018] 1-3-1. Conditional formula (1) and conditional formula (2) It is preferable that the second lens group has at least one negative lens that satisfies the following conditional expression.

[0019] (1) θct ≧ 0.800 (2) νd ≦ 55 however, θct: partial dispersion ratio from C-line to t-line of the negative lens in the second lens group The partial dispersion ratio θct from line C to line t is defined by the following equation. θct=(nC-nt) / (nF-nC) nC: Refractive index at C line, where C line refers to light with a wavelength of 656.2800 nm. nt: Refractive index at the t-line, where t-line refers to light with a wavelength of 1013.9800 nm. nF: Refractive index at the F line, where the F line refers to light with a wavelength of 486.1300 nm. νd: Abbe number at the d line of the negative lens in the second lens group

[0020] The above conditional formula (1) defines the partial dispersion ratio of the glass material from the C-line to the t-line, and the conditional formula (2) defines the Abbe number of the glass material at the d-line. By configuring the second lens group to include a negative lens made of a glass material that satisfies the above conditional formulas (1) and (2), chromatic aberration can be effectively corrected from the visible light region to the near infrared region.

[0021] In order to obtain the above effects, the lower limit of conditional formula (1) is more preferably 0.810, and even more preferably 0.815. The upper limit of conditional formula (2) is more preferably 53. When these preferable lower or upper limits are adopted, the inequality sign (<) in conditional formula (1) may be replaced with an inequality sign with an equal sign (≦). The same applies in principle to other formulas. The inequality sign with an equal sign (≦) in other formulas may be replaced with an inequality sign (<).

[0022] 1-3-2. Conditional formula (3) and conditional formula (4) It is preferable for the positive lens arranged in the 2B group to satisfy the following condition: (3) nd_pave <1.70 (4) νd_pave >50 however, nd_pave: The average value of the refractive index at the d line of all the positive lenses arranged in the 2B group νd_pave: The average Abbe number at the d line of all positive lenses in the 2B group

[0023] The above conditional formula (3) defines the average value of the Abbe number at the d-line of the positive lens included in the second lens group, and the conditional formula (4) defines the average value of the refractive index at the d-line of the positive lens included in the second lens group. By disposing a positive lens made of a glass material that satisfies both conditional formulas (3) and (4) in the second lens group, it is possible to prevent the dispersion caused by the positive lens in the second lens group from becoming too large, and it is possible to satisfactorily correct chromatic aberration from the visible light region to the near-infrared light region.

[0024] In order to obtain the above-mentioned effects, it is more preferable that the upper limit value of conditional expression (3) be 1.67, and it is even more preferable that the lower limit value of conditional expression (4) be 55, and it is even more preferable that the lower limit value be 63.

[0025] 1-3-3.Conditional expression (5) It is preferable that the negative lens arranged closest to the object in the 2B group satisfies the following condition:

[0026] (5) -0.007< 0.00558×νd_n2B+0.531-θct_n2B < 0.000 however, νd_n2B: Abbe number at d line of the negative lens located closest to the object in the 2B group θct_n2B: partial dispersion ratio for the C-line and t-line of the negative lens located closest to the object in the 2B group

[0027] The above conditional formula (5) prescribes the glass material of the negative lens arranged closest to the object in the 2B group. By making the negative lens arranged closest to the object in the 2B group a lens made of a glass material that satisfies this conditional formula (5), it becomes easier to effectively correct chromatic aberration from the visible light region to the near infrared light region. In addition, by making the negative lens arranged immediately behind the aperture stop out of such a glass material, chromatic aberration can be corrected more effectively than if other lenses were made of the same glass material.

[0028] In order to obtain the above effect, the lower limit of condition (5) is preferably −0.006, and more preferably −0.005.

[0029] 1-3-4.Conditional expression (6) It is preferable that the positive lens located closest to the object in the 2A group satisfies the following condition:

[0030] (6) 0.623 < θgF_p2A however, θgF_p2A: The partial dispersion ratio for the g-line and F-line of the positive lens located closest to the object in the 2A group The partial dispersion ratio θgF from the g-line to the F-line is defined by the following formula. θgF=(ng-nF) / (nF-nC) ng: The refractive index at the g-line, which refers to light with a wavelength of 435.8400 nm.

[0031] The above conditional formula (6) prescribes the glass material of the positive lens located closest to the object in group 2A. By using a glass material that satisfies conditional formula (6) for the positive lens located closest to the object in group 2A, it becomes possible to effectively correct chromatic aberration for light with wavelengths in the visible light range, particularly for light with wavelengths on the short wavelength side.

[0032] In order to obtain the above effect, the lower limit of condition (6) should preferably be 0.625, and more preferably be 0.630.

[0033] 1-3-5.Conditional expression (7) (7) -0.050 < θIRp-θIRn < 0.050 however, θIRp: The average value of (nF-nd) / (n1700nm-nd) of all the positive lenses in the second lens group θIRn: Average value of (nF-nd) / (n1700nm-nd) of all negative lenses included in the second lens group n1700nm: Refractive index at a wavelength of 1700nm

[0034] The above conditional expression (7) is an expression relating to the dispersion characteristics of the positive lens and the negative lens included in the second lens group. By satisfying the conditional expression (7), it is possible to obtain an optical system with high imaging performance in which chromatic aberrations are well corrected from the visible light region to the near infrared region, and various aberrations are well corrected from the visible light region to the near infrared region. The value of the above conditional expression (7) may be 0.

[0035] On the other hand, when the value of conditional expression (7) is equal to or greater than the upper limit, or equal to or less than the lower limit, it becomes difficult to satisfactorily correct chromatic aberration over the entire range from the visible light range to the near infrared range. As a result, even if chromatic aberration can be satisfactorily corrected in the visible light range, the correction of chromatic aberration in the near infrared range may be insufficient or excessive, or conversely, even if chromatic aberration can be satisfactorily corrected in the near infrared range, the correction of chromatic aberration in the visible light range may be insufficient or excessive, which is not preferable.

[0036] In order to obtain the above-mentioned effects, the lower limit of condition (7) should more preferably be -0.040, and even more preferably be -0.030, and the upper limit of condition (7) should more preferably be 0.040, and even more preferably be 0.030.

[0037] 1-3-6.Conditional expression (8) (8) 1.50 < F2 / F < 2.60 however, F2: Focal length at d line of the second lens group F: focal length at d line of the optical system

[0038] The above conditional expression (8) defines the ratio of the focal length of the second lens group to the focal length of the optical system. By satisfying conditional expression (8), chromatic aberration can be corrected well over the entire range from the visible light region to the near infrared region, and various aberrations such as field curvature and astigmatism can also be corrected well, making it easier to obtain an optical system with high imaging performance.

[0039] On the other hand, if this value is equal to or less than the lower limit, the refractive power of the second lens group becomes strong, making it difficult to satisfactorily correct chromatic aberration, field curvature, and astigmatism over the entire range from the visible light region to the near infrared region, and making it difficult to obtain an optical system with high imaging performance. On the other hand, if this value is equal to or more than the upper limit, the refractive power of the second lens group becomes weak, making it difficult to achieve a large aperture and compact size.

[0040] In order to obtain the above-mentioned effects, the lower limit value of conditional formula (8) should more preferably be 1.70, and even more preferably be 1.85, and the upper limit value of conditional formula (8) should more preferably be 2.50, and even more preferably be 2.40.

[0041] 1-3-7. Conditional expression (9) (9) 1.50 < F2B / F < 2.60 however, F2B: focal length at d line of group 2B

[0042] The above conditional expression (9) prescribes the ratio of the focal length of the 2B group at the d-line to the focal length of the optical system. By satisfying conditional expression (9), it becomes possible to satisfactorily correct various aberrations such as spherical aberration and chromatic aberration, and it becomes easier to realize an optical system with high imaging performance over a wide wavelength range from the visible light region to the near infrared region.

[0043] On the other hand, if this value is below the lower limit, the refractive power of the 2B group becomes strong, and the correction of various aberrations, mainly spherical aberration and chromatic aberration, becomes excessive, making it difficult to obtain an optical system with high imaging performance over the entire range from the visible light range to the near infrared range.On the other hand, if this value is above the upper limit, the refractive power of the 2B group becomes weak, making it difficult to sufficiently correct spherical aberration and chromatic aberration.

[0044] In order to obtain the above-mentioned effects, the lower limit value of conditional formula (9) should preferably be 1.70, and more preferably be 1.85, and the upper limit value of conditional formula (9) should preferably be 2.50, and more preferably be 2.40.

[0045] 2. Imaging device Next, an imaging device according to the present invention will be described. The imaging device according to the present invention is characterized by comprising the optical system according to the present invention and an imaging element that converts an optical image formed by the optical system into an electrical signal. The imaging element is preferably provided on the image side of the optical system.

[0046] Here, the optical system according to the present invention has good imaging performance in a wide wavelength range from the visible light range to the near infrared range. Therefore, as the imaging element, not only a visible light image sensor having sensitivity to light rays with wavelengths in the visible light range, such as a CCD (Charge Coupled Device) sensor or a CMOS (Complementary Metal Oxide Semiconductor) sensor, but also a SWIR (Short Wave InfraRed) sensor having sensitivity to light rays with wavelengths in the near infrared range can be suitably used. In particular, by using an image sensor having sensitivity to light rays in the entire wavelength range from the visible light range to the near infrared range (for example, 400 nm to 1700 nm) and the optical system according to the present invention, it is possible to realize an industrial camera capable of sensing not only the external structure of an object but also its interior, etc., with light rays from the visible light range to the near infrared range using one imaging device, without using two imaging devices, one for visible light and one for near infrared light, as in the conventional case, which is more preferable. However, the imaging device of the present invention is not limited to industrial cameras used for applications such as material sorting, foreign object inspection, and semiconductor inspection, but can also be applied to imaging devices for various applications such as surveillance cameras, in-vehicle cameras, and drone-mounted cameras.

[0047] 7 is a diagram showing a schematic example of the configuration of the imaging device 10. The imaging device 10 has an imaging device body 1, a lens barrel 2 that is detachable from the imaging device body 1, and an image sensor 3 disposed on an image plane IP of the optical system 2. The lens barrel 2 accommodates the optical system according to the present invention and a driving mechanism for driving the lens group during focusing.

[0048] Next, the present invention will be described in detail with reference to examples, but the present invention is not limited to the following examples. EXAMPLES

[0049] (1) Optical configuration FIG. 1 is a cross-sectional view of an optical system according to a first embodiment of the present invention when focusing at infinity. The optical system includes a first lens group G1 having negative refractive power on the object side and a second lens group G2 having positive refractive power on the image side, with a variable interval closest to the object side when focusing. The second lens group includes, in order from the object side, a second A group G2A having positive refractive power, an aperture stop S, and a second B group G2B having positive refractive power. The optical system focuses from an object at infinity to an object at a close distance by moving the entire second lens group G2 toward the object side along the optical axis. Note that the first lens group G1 is fixed in the optical axis direction when focusing. The configuration of each lens group will be described below.

[0050] The first lens group G1 is composed of, in order from the object side, a biconvex lens L1, a negative meniscus lens L2 with a convex shape facing the object side, a biconcave lens L3, and a cemented lens in which a negative meniscus lens L4 with a convex shape facing the object side and a biconvex lens L5 are cemented together.

[0051] Next, the configuration of the second lens group G2 will be described. The second A group G2A is composed of a positive meniscus lens L6 with a convex shape on the object side. The second B group is composed of a cemented lens in which a biconcave lens L7 and a biconvex lens L8 are cemented together, a cemented lens in which a biconvex lens L9 and a negative meniscus lens L10 with a concave shape on the object side are cemented together, a cemented lens in which a biconvex lens L11 and a biconcave lens L12 are cemented together, and a biconvex lens L13.

[0052] In Fig. 1, "I" indicates an image plane, specifically, an imaging plane of an imaging element such as a SWIR sensor, a CCD sensor, or a CMOS sensor, or a film plane of a silver halide film. In addition, it is preferable that the SWIR sensor is a sensor having sensitivity to light with wavelengths from the visible light region to the near-infrared wavelength region. This point is the same in each lens cross-sectional view shown in the other embodiments, so the explanation will be omitted hereafter.

[0053] (2) Numerical examples Next, a numerical example in which specific numerical values ​​of the optical system are applied will be described. The "lens data", "specification table", and "lens group data" are shown below. The values ​​of each formula (Table 1) are summarized after Example 3.

[0054] In (Lens Data), "Surface No." indicates the order of the lens surface counted from the object side, "r" indicates the radius of curvature of the lens surface, "d" indicates the lens thickness or air space on the optical axis, "Nd" indicates the refractive index at the d line (wavelength λ=587.5618 nm), "νd" indicates the Abbe number at the d line, "θgF" indicates the partial dispersion ratio from the g line to the F line ((ng-nF) / (nF-nC)), "θCT" indicates the partial dispersion ratio from the C line to the t line ((nC-nt) / (nF-nC)), and "θIR" indicates the value of "(nF-nd) / (n1700nm-nd)". In the "d" column, "D(9)" and "D(23)" indicate that the distance on the optical axis of the lens surface is a variable distance that changes when focusing. In the "radius of curvature" column, "INF" indicates infinity, meaning that the surface is flat.

[0055] In the specification table, "F" is the focal length of the optical system, "Fno" is the F-number, "ω" is the half angle of view, "D(9)" and "D(23)" are the variable intervals mentioned above, and the table shows the respective values ​​when focusing on an object at infinity (INF) and when focusing on a close-up object (object distance 0.2 m).

[0056] (Lens group data) indicates the focal lengths of the first lens group G1, the second lens group G2, the secondA lens group G2A, and the secondB lens group G2B.

[0057] The items in these tables are the same as those in the tables shown in the other embodiments, so the explanation will be omitted below.

[0058] FIG. 2 shows longitudinal aberration diagrams of the optical system when focused at infinity. The longitudinal aberration diagrams shown in each diagram are, from the left to the right, spherical aberration (mm), astigmatism (mm), and distortion (%). In the spherical aberration diagrams, the two-dot chain line shows the spherical aberration for light with a wavelength of 1700 nm, the one-dot chain line shows the spherical aberration for the C-line (656.2800 nm), the solid line shows the spherical aberration for the d-line (wavelength 587.5618 nm), the short dashed line shows the spherical aberration for the F-line (wavelength 486.1300 nm), and the long dashed line shows the spherical aberration for the g-line (wavelength 435.8400 nm). In the astigmatism diagrams, the vertical axis shows the half angle of view (ω) and the horizontal axis shows the defocus, the solid line shows the sagittal image plane for the d-line, and the dashed line shows the meridional image plane for the d-line. In the distortion diagrams, the vertical axis shows the half angle of view (ω) and the horizontal axis shows the distortion. These points are the same in the aberration diagrams shown in the other embodiments, and therefore will not be described below.

[0059] (Lens data) Surface NO. rd Nd νd θgF θCT θIR 1 108.811 3.000 1.8040 46.53 0.56 0.77 -0.39 2 -446.594 0.161 3 56.597 1.400 1.4970 81.54 0.54 0.83 -0.35 4 13.272 6.082 5 -356.688 1.200 1.8929 20.36 0.64 0.65 -0.53 6 16.385 12.235 7 204.061 1.200 1.5891 61.13 0.54 0.84 -0.33 8 24.678 6.250 1.7620 40.10 0.58 0.74 -0.43 9 -31.718 D(9) 10 21.216 4.970 1.8929 20.36 0.64 0.65 -0.53 11 32.712 5.034 12 (Aperture) INF 3.935 13 -63.937 1.000 1.7380 32.33 0.59 0.72 -0.44 14 12.933 5.150 1.4970 81.54 0.54 0.83 -0.35 15 -24.439 0.300 16 156.901 3.850 1.4970 81.54 0.54 0.83 -0.35 17 -13.080 1.000 1.8929 20.36 0.64 0.65 -0.53 18 -31.684 0.200 19 21.061 4.930 1.5952 67.73 0.54 0.79 -0.37 20 -14.693 1.000 1.5174 52.20 0.56 0.82 -0.35 21 14.693 1.602 22 28.185 3.800 1.9037 31.34 0.60 0.70 -0.47 23 -142.857 D(23)

[0060] (Specifications table) INF 0.2m F 12.000 - Fno 1.60 - ω 34.79 - D(9) 2.141 1.486 D(23) 15.034 15.688

[0061] (Lens group data) F1 -302.112 F2 28.160 F2A 56.162 F2B 28.351 EXAMPLES

[0062] (1) Optical configuration 3 is a cross-sectional view of an optical system according to a second embodiment of the present invention when focusing at infinity. The optical system includes a first lens group G1 having negative refractive power on the object side and a second lens group G2 having positive refractive power on the image side, with a variable interval closest to the object side when focusing. The second lens group includes, in order from the object side, a second A group having positive refractive power, an aperture stop S, and a second B group having positive refractive power. The optical system focuses from an object at infinity to an object at a close distance by moving the entire second lens group G2 toward the object side along the optical axis. The configuration of each lens group will be described below.

[0063] The first lens group G1 is composed of, in order from the object side, a biconvex lens L1, a negative meniscus lens L2 having a convex shape facing the object side, a biconcave lens L3, and a cemented lens in which a biconcave lens L4 and a biconvex lens L5 are cemented together.

[0064] Next, the configuration of the second lens group G2 will be described. The second A group G2A is composed of a positive meniscus lens L6 with a convex shape on the object side. The second B group is composed of a cemented lens in which a biconcave lens L7 and a biconvex lens L8 are cemented together, a cemented lens in which a biconvex lens L9 and a negative meniscus lens L10 with a concave shape on the object side are cemented together, a cemented lens in which a biconvex lens L11 and a biconcave lens L12 are cemented together, and a biconvex lens L13.

[0065] (2) Numerical examples Next, "Lens Data", "Specification Table", and "Lens Group Data" are shown as numerical examples using specific numerical values ​​of the optical system. Also, Fig. 4 shows longitudinal aberration diagrams of the optical system when focused at infinity.

[0066] (Lens data) Surface NO. rd Nd νd θgF θCT θIR 1 37.695 5.679 1.8040 46.53 0.56 0.77 -0.39 2 -3182.289 0.380 3 122.771 1.400 1.5163 64.14 0.54 0.87 -0.31 4 13.804 6.287 5 -47.382 1.200 1.9229 18.90 0.65 0.64 -0.54 6 19.501 7.665 7 -88.131 1.200 1.5163 64.14 0.54 0.87 -0.31 8 29.255 6.385 1.7995 42.22 0.57 0.75 -0.41 9 -29.201 D(9) 10 25.387 5.400 1.8929 20.36 0.64 0.65 -0.53 11 80.878 9.028 12 (Aperture) INF 2.625 13 -43.464 1.000 1.7380 32.33 0.59 0.72 -0.44 14 15.414 4.872 1.4970 81.54 0.54 0.83 -0.35 15 -25.594 0.400 16 200.000 4.287 1.4970 81.54 0.54 0.83 -0.35 17 -12.500 1.000 1.8929 20.36 0.64 0.65 -0.53 18 -26.107 0.200 19 42.310 5.048 1.5952 67.73 0.54 0.79 -0.37 20 -12.839 1.000 1.5174 52.20 0.56 0.82 -0.35 21 19.708 1.326 22 27.166 2.922 1.9037 31.34 0.60 0.70 -0.47 23 -141.413 D(23)

[0067] (Specifications table) INF 0.2m F 16.01 - Fno 1.60 - ω 26.86 - D(9) 2.742 1.489 D(23) 17.790 19.043

[0068] (Lens group data) F1 -61.605 F2 29.743 F2A 39.623 F2B 29.413 EXAMPLES

[0069] (1) Optical configuration 5 is a cross-sectional view of an optical system according to a third embodiment of the present invention when focusing at infinity. The optical system includes a first lens group G1 having negative refractive power on the object side and a second lens group G2 having positive refractive power on the image side, with a variable interval closest to the object side when focusing. The second lens group includes, in order from the object side, a second A group having positive refractive power, an aperture stop S, and a second B group having positive refractive power. The optical system focuses from an object at infinity to an object at a close distance by moving the second A group G2A and the second B group G2B along different trajectories toward the object side along the optical axis. The configuration of each lens group will be described below.

[0070] The first lens group G1 is composed of, in order from the object side, a biconvex lens L1, a negative meniscus lens L2 having a convex shape facing the object side, a biconcave lens L3, and a cemented lens in which a biconcave lens L4 and a biconvex lens L5 are cemented together.

[0071] Next, the configuration of the second lens group G2 will be described. The second A group G2A is composed of a positive meniscus lens L6 with a convex shape on the object side. The second B group is composed of a cemented lens in which a biconcave lens L7 and a biconvex lens L8 are cemented together, a cemented lens in which a biconvex lens L9 and a negative meniscus lens L10 with a concave shape on the object side are cemented together, a cemented lens in which a biconvex lens L11 and a biconcave lens L12 are cemented together, and a biconvex lens L13.

[0072] (2) Numerical examples Next, "Lens Data", "Specification Table", and "Lens Group Data" are shown as numerical examples using specific numerical values ​​of the optical system. Also, Fig. 4 shows longitudinal aberration diagrams of the optical system when focused at infinity.

[0073] (Lens data) Surface NO. rd Nd νd θgF θCT θIR 1 37.600 5.526 1.8040 46.53 0.56 0.77 -0.39 2 -3183.846 0.380 3 122.865 1.400 1.5163 64.14 0.54 0.87 -0.31 4 13.764 6.317 5 -47.140 1.200 1.9229 18.90 0.65 0.64 -0.54 6 19.673 7.605 7 -87.937 1.200 1.5163 64.14 0.54 0.87 -0.31 8 29.255 6.357 1.7995 42.22 0.57 0.75 -0.41 9 -29.338 D(9) 10 25.625 5.400 1.8929 20.36 0.64 0.65 -0.53 11 83.743 D(11) 12 (Aperture) INF 2.625 13 -42.892 1.000 1.7380 32.33 0.59 0.72 -0.44 14 15.814 4.872 1.4970 81.54 0.54 0.83 -0.35 15 -25.453 0.400 16 200.000 4.287 1.4970 81.54 0.54 0.83 -0.35 17 -12.498 1.000 1.8929 20.36 0.64 0.65 -0.53 18 -26.273 0.200 19 41.159 5.048 1.5952 67.73 0.54 0.79 -0.37 20 -12.948 1.000 1.5174 52.20 0.56 0.82 -0.35 21 19.477 1.326 22 27.026 2.922 1.9037 31.34 0.60 0.70 -0.47 23 -142.591 D(23)

[0074] (Specifications Table) INF 0.2m F 16.00 - Fno 1.60 - ω 26.86 - D(9) 2.863 1.819 D(11) 9.155 8.920 D(23) 17.773 19.052

[0075] (Lens Group Data) F1 -60.454 F2 29.768 F2A 39.617 F2B 29.346

[0076] [Table 1] Example 1 Example 2 Example 3 Conditional Expression (1) θct 0.815 0.815 0.815 Conditional Expression (2) νd 52 52 52 Conditional Expression (3) n_pave 1.62 1.62 1.62 Conditional Expression (4) νd_pave 66 66 66 Conditional Expression (5) 0.00558×νd_n2B+0.531-θct_n2B -0.004 -0.004 -0.004 Conditional Expression (6) θgF_p2A 0.639 0.639 0.639 Conditional Expression (7) θIRp-θIRn 0.025 0.025 0.025 Conditional Expression (8) F2 / F 2.35 1.86 1.86 Conditional expression (9) F2B / F 2.36 1.84 1.83 [Industrial Applicability]

[0077] The optical system according to the present invention can be suitably applied as an imaging optical system for imaging devices equipped with an imaging element, such as industrial cameras (FA / MV), video cameras, digital cameras, and surveillance cameras. [Explanation of symbols]

[0078] S Aperture I...image plane G1: First lens group G2: Second lens group G2A...Group 2A G2B...Group 2B 1. Imaging device body 2. Telescope tube 3. Imaging element 10 Imaging device

Claims

1. the first lens group having a refractive power and arranged on the object side, and a second lens group having a positive refractive power and arranged on the image side, with a variable interval disposed on the most object side during focusing; the first lens group includes, in order from the image side, a positive lens and at least one negative lens, the second lens group includes, in order from the object side, a second A group having positive refractive power, an aperture stop, and a second B group having positive refractive power, and includes at least one negative lens that satisfies the following conditional expressions (1) and (2): the second B group includes, in order from the object side, a negative lens and a positive lens, An optical system characterized in that it satisfies the following conditional expressions (3) to (5): (1) θct ≧ 0.800 (2) vd≦55 (3) nd_pave <1.70 (4) νd_pave >50 (5) -0.007<0.00558×νd_n2B+0.531-θct_n2B<0.000 however, θct: partial dispersion ratio from C-line to t-line of the negative lens in the second lens group The partial dispersion ratio θct from line C to line t is defined by the following formula. θct=(nC-nt) / (nF-nC) nC: Refractive index at C line nt: refractive index at t-line nF: Refractive index at F line νd: Abbe number at the d line of the negative lens in the second lens group nd_pave: the average value of the refractive index at the d line of all the positive lenses arranged in the second B group νd_pave: average value of Abbe numbers at d-line of all positive lenses arranged in the second B group νd_n2B: the Abbe number at the d line of the negative lens arranged closest to the object in the 2B group θct_n2B: partial dispersion ratio for the C-line and the t-line of the negative lens arranged closest to the object side in the second B group

2. A focusing system comprising a first lens group having a refractive power and arranged on the object side, and a second lens group having a positive refractive power and arranged on the image side, the first lens group having a variable interval closest to the object side when focusing, the first lens group includes, in order from the image side, a positive lens and at least one negative lens, the second lens group includes, in order from the object side, a second A group having positive refractive power, an aperture stop, and a second B group having positive refractive power, and includes at least one negative lens that satisfies the following conditional expressions (1) and (2): the second B group includes, in order from the object side, a negative lens and a positive lens, An optical system characterized by satisfying the following conditional expressions (3), (4) and (6): (1) θct ≧ 0.800 (2) vd≦55 (3) nd_pave <1.70 (4) νd_pave >50 (6) 0.623 < θgF_p2A however, θct: partial dispersion ratio from C-line to t-line of the negative lens in the second lens group The partial dispersion ratio θct from line C to line t is defined by the following formula. θct=(nC-nt) / (nF-nC) nC: Refractive index at C line nt: refractive index at t-line nF: Refractive index at F line νd: Abbe number at the d line of the negative lens in the second lens group nd_pave: the average value of the refractive index at the d line of all the positive lenses arranged in the second B group νd_pave: average value of Abbe numbers at d-line of all positive lenses arranged in the second B group θgF_p2A: partial dispersion ratio for the g-line and F-line of the positive lens arranged closest to the object side in the 2A group The partial dispersion ratio θgF from the g-line to the F-line is defined by the following formula. θgF=(ng-nF) / (nF-nC) ng: refractive index at g line

3. A focusing system comprising a first lens group having a refractive power and arranged on the object side, and a second lens group having a positive refractive power and arranged on the image side, the first lens group having a variable interval closest to the object side when focusing, the first lens group includes, in order from the image side, a positive lens and at least one negative lens, the second lens group includes, in order from the object side, a second A group having positive refractive power, an aperture stop, and a second B group having positive refractive power, and includes at least one negative lens that satisfies the following conditional expressions (1) and (2): the second B group includes, in order from the object side, a negative lens and a positive lens, the first lens group has a positive lens closest to the object side, An optical system characterized by satisfying the following conditional expressions (3) and (4): (1) θct ≧ 0.800 (2) vd≦55 (3) nd_pave <1.70 (4) νd_pave >50 however, θct: partial dispersion ratio from C-line to t-line of the negative lens in the second lens group The partial dispersion ratio θct from line C to line t is defined by the following formula. θct=(nC-nt) / (nF-nC) nC: Refractive index at C line nt: refractive index at t-line nF: Refractive index at F line νd: Abbe number at the d line of the negative lens in the second lens group nd_pave: the average value of the refractive index at the d line of all the positive lenses arranged in the second B group νd_pave: average value of Abbe numbers at d-line of all positive lenses arranged in the second B group

4. 4. The optical system according to claim 1, wherein the following condition is satisfied: (8) 1.50 < F2B / F < 2.60 however, F2B: focal length at d line of the second B group

5. 5. The optical system according to claim 1, wherein focusing is performed from an object at infinity to an object at a close distance by moving the entire second lens group along the optical axis, or by moving the second A group and the second B group along the optical axis on different trajectories.

6. 6. An imaging apparatus comprising: the optical system according to claim 1; and an imaging element on an image side of the optical system for converting an optical image formed by the optical system into an electrical signal.

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