Optical system, optical device, and method of manufacturing optical system

Abstract

To provide an optical system which offers good optical performance, an optical device having the same, and a method of manufacturing the optical system.SOLUTION: An optical system OL for use in optical devices such as cameras 1 is provided, the system comprising, in order from the object side, an objective optical system GO and an imaging optical system GI for forming an intermediate image IM formed by the objective optical system GO, and is configured to satisfy a condition expressed as: 0.40<fo / f<0.80, where fo represents a focal length of the objective optical system, and f represents a focal length of the entire optical system OL.SELECTED DRAWING: Figure 1

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] Conventionally, optical systems for capturing images of minute subjects or narrow spaces at close range have been proposed (see, for example, Patent Document 1). However, further improvements in optical performance are desired. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-133571 Summary of the Invention

[0004] An optical system according to a first aspect of the present invention comprises, in order from the object side, an objective optical system and an imaging optical system that images an intermediate image formed by the objective optical system, and satisfies the following condition: 0.40 < fo / f < 0.80 however, fo: focal length of the objective optical system f: focal length of the entire optical system

[0005] A method for manufacturing an optical system according to a first aspect of the present invention is a method for manufacturing an optical system comprising, in order from the object side, an objective optical system and an imaging optical system that images an intermediate image formed by the objective optical system, and the optical systems are arranged so as to satisfy the following condition: 0.40 < fo / f < 0.80 however, fo: focal length of the objective optical system f: focal length of the entire optical system [Brief explanation of the drawings]

[0006] [Figure 1] FIG. 2 is a cross-sectional view showing the lens configuration of the optical system according to the first example. [Figure 2] 5A to 5C are diagrams illustrating various aberrations of the optical system according to Example 1 when focused at infinity. [Figure 3] FIG. 10 is a cross-sectional view showing the lens configuration of an optical system according to a second example. [Figure 4] 10A to 10C are diagrams showing various aberrations of the optical system according to Example 2 when focused on infinity. [Figure 5] FIG. 10 is a cross-sectional view showing the lens configuration of an optical system according to Example 3. [Figure 6] 10A to 10C are diagrams showing various aberrations of the optical system according to Example 3 when focused at infinity. [Figure 7] FIG. 2 is a cross-sectional view of a camera equipped with the optical system. [Figure 8] 4 is a flowchart illustrating a method for manufacturing the optical system. DETAILED DESCRIPTION OF THE INVENTION

[0007] Preferred embodiments will now be described with reference to the drawings.

[0008] 1, the optical system OL according to this embodiment is composed of, in order from the object side, an objective optical system GO and an imaging optical system GI that images an intermediate image IM formed by the objective optical system GO. This configuration makes it possible to obtain good optical performance.

[0009] Moreover, it is desirable that the optical system OL according to this embodiment satisfy the following conditional expression (1).

[0010] 0.40 < fo / f < 0.80 (1) however, fo: focal length of the objective optical system GO f: focal length of the entire optical system (when focused on an object at infinity)

[0011] Conditional expression (1) defines the ratio of the focal length of the objective optical system GO to the focal length of the entire optical system OL. Satisfying conditional expression (1) allows the diameter of the object-side lens in the optical system OL to be reduced. Below the lower limit of conditional expression (1), the refractive power of the objective optical system GO becomes too strong, making it difficult to correct off-axis aberrations such as coma and astigmatism, which is undesirable. To ensure the effect of conditional expression (1), it is preferable to set the lower limit of conditional expression (1) to 0.42, 0.45, 0.48, or even 0.50. Above the upper limit of conditional expression (1), it is undesirable because the refractive power of the imaging optical system GI becomes too strong, making it difficult to correct spherical aberration and field curvature. To ensure the effect of conditional expression (1), it is preferable to set the upper limit of conditional expression (1) to 0.78, 0.75, 0.72, or even 0.70.

[0012] Furthermore, it is desirable that the optical system OL according to this embodiment have one intermediate image IM. With this configuration, it is possible to reduce the overall length of the optical system OL while keeping the lens diameter on the object side small.

[0013] In the optical system OL according to this embodiment, the imaging optical system GI preferably has at least two focusing groups (a first movable group G1 and a second movable group G2), and the spacing between adjacent lens groups changes during focusing. This configuration can reduce fluctuations in field curvature during focusing of the optical system OL.

[0014] Furthermore, the optical system OL according to this embodiment is preferably configured so that, during focusing, the focusing groups (the first movable group G1 and the second movable group G2) are moved along the optical axis to focus on an object at infinity. With this configuration, the optical system OL can be used as a photographic lens.

[0015] Moreover, it is desirable that the optical system OL according to this embodiment satisfy the following conditional expression (2).

[0016] 0.15 < fa / fr < 0.80 (2) however, fa: the focal length of the optical system (first fixed group GA) located closer to the object than the focusing group (first movable group G1) located closest to the object in the imaging optical system GI fr: focal length of the imaging optical system GI (when focusing on an object at infinity)

[0017] Conditional expression (2) defines the ratio of the focal length of the optical system (first fixed group GA) located closer to the object than the focusing group (first movable group G1) located closest to the object in the imaging optical system GI to the focal length of the imaging optical system GI. By satisfying conditional expression (2), good optical performance can be achieved. Below the lower limit of conditional expression (2), the refractive power of the first fixed group GA becomes too strong, making it difficult to correct axial chromatic aberration, which is undesirable. To ensure the effect of conditional expression (2), it is preferable to set the lower limit of conditional expression (2) to 0.16, 0.18, or even 0.20. Above the upper limit of conditional expression (2), it is undesirable to set the refractive power of the imaging optical system GI too strong, making it difficult to correct spherical aberration and field curvature. To ensure the effect of conditional expression (2), it is preferable to set the upper limit of conditional expression (2) to 0.78, 0.75, 0.72, or even 0.70.

[0018] Moreover, it is desirable that the optical system OL according to this embodiment satisfy the following conditional expression (3).

[0019] 0.10 < TLo / TL < 0.30 (3) however, TLo: The distance on the optical axis from the lens surface closest to the object of the objective optical system GO to the intermediate image IM TL: Total optical length of optical system OL (when focusing on an object at infinity)

[0020] Conditional expression (3) defines the ratio of the axial distance from the lens surface of the objective optical system GO closest to the object to the intermediate image IM (the overall optical length of the objective optical system GO) to the overall optical length of the optical system OL. Satisfying conditional expression (3) enables both reduction in performance degradation due to manufacturing errors and a compact lens barrel. Below the lower limit of conditional expression (3), the refractive power of the objective optical system GO becomes too strong, significantly reducing performance degradation due to manufacturing errors. To ensure the effect of conditional expression (3), it is preferable to set the lower limit of conditional expression (3) to 0.11, 0.12, 0.13, 0.14, or even 0.15. Above the upper limit of conditional expression (3), it is preferable to set the upper limit of conditional expression (3) to 0.29, 0.27, or even 0.25, since the refractive power of the objective optical system GO becomes too weak, making it difficult to reduce the diameter of the optical system OL. To ensure the effect of conditional expression (3), it is preferable to set the upper limit of conditional expression (3) to 0.29, 0.27, or even 0.25.

[0021] Moreover, it is desirable that the optical system OL according to this embodiment satisfy the following conditional expression (4).

[0022] 0.30 < |fb / fr| < 0.80 (4) however, fb: the focal length of the optical system (second fixed group GB) that is closer to the image plane than the focusing group (second movable group G2) that is closest to the image plane in the imaging optical system GI fr: focal length of the imaging optical system GI (when focusing on an object at infinity)

[0023] Conditional expression (4) defines the ratio of the focal length of the optical system (second fixed group GB) located closer to the image plane than the focusing group (second movable group G2) located closest to the image plane in the imaging optical system GI to the focal length of the imaging optical system GI. By satisfying conditional expression (4), good optical performance can be achieved. Below the lower limit of conditional expression (4), the refractive power of the second fixed group GB becomes too strong, making it difficult to correct coma, which is undesirable. To ensure the effect of conditional expression (4), it is preferable to set the lower limit of conditional expression (4) to 0.32, 0.35, 0.38, or even 0.40. Above the upper limit of conditional expression (4), the refractive power of the imaging optical system GI becomes too strong, making it difficult to correct spherical aberration and field curvature, which is undesirable. In order to ensure the effect of conditional expression (4), it is more desirable to set the upper limit of conditional expression (4) to 0.78, 0.75, 0.72, and more preferably 0.70.

[0024] Moreover, it is desirable that the optical system OL according to this embodiment satisfy the following conditional expression (5).

[0025] 0.10 < Lsum / TLr < 0.60 (5) however, Lsum: total lens thickness of the imaging optical system GI TLr: Distance on the optical axis from intermediate image IM to image plane I (when focusing on an object at infinity)

[0026] Conditional expression (5) defines the ratio of the total lens thickness of the imaging optical system GI (the sum of the thicknesses of all the lenses constituting the imaging optical system GI) to the axial distance from the intermediate image IM to the image plane I. Satisfying conditional expression (5) ensures excellent optical performance. Below the lower limit of conditional expression (5), the number of lenses in the imaging optical system GI is reduced, making it difficult to sufficiently correct spherical aberration and curvature of field, which is undesirable. To ensure the effect of conditional expression (5), it is preferable to set the lower limit of conditional expression (5) to 0.11, or even 0.12. Above the upper limit of conditional expression (5), the total thickness of the glass in the imaging optical system GI increases, resulting in a decrease in the amount of light. This makes it difficult to obtain a clear image, which is undesirable. To ensure the effect of conditional expression (5), it is preferable to set the upper limit of conditional expression (5) to 0.58, 0.55, 0.52, or even 0.50.

[0027] Furthermore, it is desirable that the optical system OL according to this embodiment has a stop (aperture stop S) in the imaging optical system GI. This configuration allows the diameter of the optical system OL to be reduced, and further allows for excellent correction of field curvature and distortion.

[0028] In the optical system OL according to this embodiment, it is desirable that the lens L1 arranged closest to the object side of the objective optical system GO is a spherical lens. This configuration can reduce performance degradation due to manufacturing errors in the optical system OL.

[0029] In the optical system OL according to this embodiment, it is desirable that the lens L1 located closest to the object side of the objective optical system GO has negative refractive power, which allows for excellent correction of the field curvature and astigmatism of the optical system OL.

[0030] Moreover, it is desirable that the optical system OL according to this embodiment satisfy the following conditional expression (6).

[0031] 1.70 < nL1 (6) however, nL1: refractive index for the d-line of the medium of the lens L1 located closest to the object in the objective optical system GO

[0032] Conditional expression (6) defines the refractive index at the d-line of the medium of lens L1 located closest to the object in objective optical system GO. By satisfying conditional expression (6), field curvature and astigmatism can be corrected well. To ensure the effect of conditional expression (6), it is more desirable to set the lower limit of conditional expression (6) to 1.72, 1.74, 1.76, 1.78, or even 1.80.

[0033] Moreover, it is desirable that the optical system OL according to this embodiment satisfy the following conditional expression (7).

[0034] 0.80 < ωn / ωi < 1.20 (7) however, ωn: Half angle of view when optical system OL is focused on a close object ωi: Half angle of view when optical system OL is focused on an object at infinity

[0035] Conditional expression (7) defines the ratio of the half angle of view of the optical system OL when focused on a close object to the half angle of view when focused on an object at infinity. Conditional expression (7) relates to lens breathing, and satisfying conditional expression (7) can reduce the sense of incongruity felt during video shooting. To ensure the effectiveness of conditional expression (7), it is preferable to set the lower limit of conditional expression (7) to 0.82, 0.85, 0.88, or even 0.90. To ensure the effectiveness of conditional expression (7), it is preferable to set the upper limit of conditional expression (7) to 1.18, 1.15, 1.12, or even 1.10.

[0036] It should be noted that the conditions and configurations described above each exert the effects described above, and are not limited to those that satisfy all of the conditions and configurations; the effects described above can be obtained by satisfying any one of the conditions or configurations, or a combination of any one of the conditions or configurations.

[0037] Next, a camera, which is an optical device equipped with the optical system OL according to this embodiment, will be described with reference to FIG. 7. This camera 1 is a so-called mirrorless camera with interchangeable lenses, which is equipped with the optical system OL according to this embodiment as a photographing lens 2. In this camera 1, light from an object (subject) (not shown) is collected by the photographing lens 2 and forms a subject image on the imaging plane of the imaging unit 3 via an OLPF (Optical low pass filter) (not shown). The subject image is then photoelectrically converted by a photoelectric conversion element (imaging element) provided in the imaging unit 3 to generate an image of the subject. This image is displayed on an EVF (Electronic Viewfinder) 4 provided in the camera 1. This allows the photographer to observe the subject through the EVF 4.

[0038] Furthermore, when the photographer presses a release button (not shown), an image photoelectrically converted by the imaging unit 3 is stored in a memory (not shown). In this way, the photographer can photograph a subject using this camera 1. Note that although an example of a mirrorless camera has been described in this embodiment, the same effects as those of the camera 1 can be achieved even when the optical system OL according to this embodiment is mounted on a single-lens reflex camera that has a quick-return mirror in the camera body and observes a subject through a viewfinder optical system.

[0039] The following contents can be appropriately adopted within the scope that does not impair the optical performance.

[0040] In this embodiment, the optical system OL is configured with an objective optical system GO and a four-group imaging optical system GI. However, the above-described configuration conditions can also be applied to other group configurations, such as five or six groups. Furthermore, a configuration in which a lens or lens group is added closest to the object, or closest to the image plane, may also be used. Specifically, a configuration in which a lens group whose position relative to the image plane is fixed during focusing is added closest to the image plane of the imaging optical system GI. Furthermore, unless a specific boundary is specified, a lens group refers to a portion having at least one lens separated by an air gap that changes during focusing. Furthermore, a lens component refers to a single lens or a cemented lens in which multiple lenses are cemented together.

[0041] Alternatively, a single or multiple lens groups, or a partial lens group, may be moved in the optical axis direction to function as a focusing group that focuses from an object at infinity to a close-up object. In this case, the focusing group can be used for autofocusing and is suitable for driving a motor (such as an ultrasonic motor) for autofocusing. In particular, it is preferable to use the first and second movable groups G1 and G2 of the combined optical system GI as focusing groups, and to fix the positions of the other lenses relative to the image plane during focusing.

[0042] Alternatively, a lens group or a partial lens group may be moved so as to have a displacement component perpendicular to the optical axis, or rotated (oscillated) in a plane including the optical axis, to serve as an image stabilization group that corrects image blur caused by camera shake.

[0043] The lens surface may be spherical, flat, or aspherical. A spherical or flat lens surface is preferable because it facilitates lens processing and assembly adjustment and prevents degradation of optical performance due to errors in processing and assembly adjustment. It is also preferable because degradation of imaging performance is minimal even when the image plane is misaligned. If the lens surface is aspherical, the aspherical surface may be any of the following aspherical surfaces: a ground aspherical surface, a glass-molded aspherical surface in which glass is molded into an aspherical shape, or a hybrid aspherical surface in which a resin is molded into an aspherical shape on the surface of glass. The lens surface may also be a diffractive surface, and the lens may be a gradient index lens (GRIN lens) or a plastic lens.

[0044] The aperture stop S is preferably disposed within the imaging optical system GI, but it is also possible to use the lens frame to perform the role of the aperture stop without providing a component serving as the aperture stop.

[0045] Furthermore, each lens surface may be coated with an anti-reflection coating that has high transmittance over a wide wavelength range in order to reduce flare and ghosting and achieve high contrast and high optical performance.

[0046] An outline of a manufacturing method for the optical system OL according to this embodiment will be explained below with reference to Fig. 8. First, in order from the object side, an objective optical system GO and an imaging optical system GI that forms an intermediate image IM formed by the objective optical system GO are prepared (step S100). Then, these lens groups are arranged so as to satisfy a predetermined condition (for example, the above-mentioned conditional formula (1)) (step S200).

[0047] As described above, it is possible to provide an optical system, an optical device, and a method for manufacturing this optical system, which are capable of close-range photography, have a small lens diameter on the object side, and have good optical performance. [Example]

[0048] Each embodiment will be described below with reference to the drawings. Figures 1, 3, and 5 are cross-sectional views showing the configuration and refractive power distribution of an optical system OL (OL1 to OL3) according to each embodiment. In addition, in the cross-sectional views of these optical systems OL1 to OL3, arrows indicate the movement direction of each lens group G1, G2 along the optical axis when focusing from an object at infinity (∞) to a close-distance object (short distance).

[0049] In the second embodiment, the aspherical surface is expressed by the following formula (a), where y is the height in the direction perpendicular to the optical axis, S(y) is the distance (amount of sag) along the optical axis from the tangent plane of the vertex of each aspherical surface at the height y to each aspherical surface, r is the radius of curvature (paraxial radius of curvature) of the reference spherical surface, K is the conic constant, and An is the n-th order aspherical coefficient. Note that in the following embodiments, "en" is expressed as "×10 -n " indicates.

[0050] S(y)=(y 2 / r) / {1+(1-K×y 2 / r 2 ) 1 / 2} +A4×y 4 +A6×y 6 +A8×y 8 +A10×y 10 (a)

[0051] In the second embodiment, the second-order aspherical coefficient A2 is 0. In the table of the second embodiment, aspherical surfaces are marked with an * to the right of the surface number.

[0052] [First Example] 1 is a diagram showing the configuration of an optical system OL1 according to Example 1. This optical system OL1 is composed of, from the object side, an objective optical system GO having positive refractive power, and an imaging optical system GI having positive refractive power that images an intermediate image IM formed by the objective optical system GO. Furthermore, the imaging optical system GI is composed of, from the object side, a first fixed group GA having positive refractive power, a first movable group G1 having negative refractive power, a second movable group G2 having negative refractive power, and a second fixed group GB having positive refractive power.

[0053] The objective optical system GO is composed of, in order from the object side, a meniscus negative lens L11 (L1) with its convex surface facing the object side, a biconvex positive lens L12, a cemented positive lens formed by cementing a biconcave negative lens L13 and a biconvex positive lens L14, a cemented negative lens formed by cementing a biconcave negative lens L15 and a biconvex positive lens L16, a biconvex positive lens L17, a biconvex negative lens L18, and a biconvex positive lens L19.

[0054] The first fixed lens group GA of the imaging optical system GI is composed of, from the object side, a meniscus positive lens L21 with a convex surface facing the object side, a biconcave negative lens L22, a meniscus positive lens L23 with a concave surface facing the object side, a biconvex positive lens L24, and a cemented positive lens formed by cementing together a meniscus negative lens L25 with a convex surface facing the object side and a biconvex positive lens L26. The first movable lens group G1 is composed of, from the object side, a cemented negative lens L31 and a meniscus positive lens L32 with a convex surface facing the object side. The second movable lens group G2 is composed of, from the object side, a biconcave negative lens L41 and a meniscus positive lens L42 with a concave surface facing the object side. The second fixed group GB is composed of, in order from the object side, a cemented positive lens formed by cementing together a meniscus negative lens L51 with its convex surface facing the object side and a biconvex positive lens L52.

[0055] In this optical system OL1, an intermediate image IM is formed between the objective optical system GO and the imaging optical system GI. An aperture stop S is disposed between the first fixed group GA and the first movable group G1 of the imaging optical system GI. A filter group FL is disposed between the imaging optical system GI and the image plane I.

[0056] Furthermore, when focusing from an object at infinity to an object at a close distance, the first fixed group GA and the second fixed group GB of the imaging optical system GI are fixed relative to the image plane I, and the first movable group G1 and the second movable group G2, which are the focusing groups, move in the optical axis direction (the first movable group G1 moves toward the image plane, and the second movable group G2 moves toward the object side once and then moves toward the image plane).

[0057] Table 1 below lists the specifications of optical system OL1. In Table 1, the overall specifications include f, the focal length of the entire system, Fno, the F-number, ω, the half angle of view [°], Y, the maximum image height, TL, the total optical length, and Bf, the back focus, all of which represent values ​​when focusing on an object at infinity. Here, the back focus Bf represents the distance on the optical axis, in terms of air equivalent length, from the lens surface closest to the image (surface No. 39) to the image plane I. The total optical length TL represents the distance on the optical axis from the lens surface closest to the object (surface No. 1) to the lens surface closest to the image plane (surface No. 39) plus the back focus, in terms of air equivalent length. In the lens data, the first column m indicates the order of the lens surfaces (surface number) from the object side along the direction of light travel, the second column r indicates the radius of curvature of each lens surface, the third column d indicates the distance on the optical axis from each optical surface to the next optical surface (surface spacing), and the fourth column nd and fifth column vd indicate the refractive index and Abbe number for the d-line (λ=587.6 nm). A radius of curvature of ∞ indicates a flat surface, and the refractive index of air, 1.00000, is omitted. The lens group focal length indicates the surface number and focal length of the first surface of each lens group.

[0058] Here, the focal length f, radius of curvature r, surface spacing d, and other length units listed in the following specifications are generally in millimeters, but this is not a limitation because the optical system can achieve the same optical performance even when proportionally enlarged or reduced. The explanations of these symbols and specifications tables also apply to the following examples.

[0059] (Table 1) First Example [Overall specifications] f = 9.913 Fno = 8.000 ω[°] = 56.998 Y = 14.500 TL (air equivalent length) = 179.975 Bf (air equivalent length) = 30.552 [Lens data] mrd nd νd Object surface ∞ D0 1 6.2691 1.4889 2.001000 29.12 2 2.5778 1.7437 3 51.3647 4.0000 1.696800 55.52 4 -54.6413 0.1000 5 -128.3143 3.0000 2.000690 25.46 6 6.9062 2.3618 1.902000 25.26 7 -6.1780 0.1000 8 -11.9935 3.0000 1.950000 29.37 9 9.1860 3.5769 1.755000 52.34 10 -10.0483 0.2903 11 15.0001 3.8374 1.593190 67.90 12 -12.0371 0.3921 13 -13.2963 3.0000 1.755200 27.57 14 12.6877 0.3383 15 16.0580 4.0000 2.000690 25.46 16 -62.9620 6.0263 17 ∞ 8.5834 Intermediate Image IM 18 14.0000 2.0651 2.000690 25.46 19 28.8428 3.9851 20 -15.9087 1.0000 1.805180 25.45 21 50.5249 0.9953 22 -42.6940 2.1974 1.883000 40.69 23 -14.9810 25.3889 24 101.0649 2.1044 1.592550 67.86 25 -28.6555 19.0122 26 31.4214 1.0000 2.001000 29.12 27 12.0376 1.7535 1.729160 54.61 28 -78.2539 1.0000 29 ∞ D29 Aperture Stop S 30 -19.2721 1.0000 1.647690 33.72 31 9.4162 1.9777 1.808090 22.74 32 257.3835 D32 33 -235.1104 1.0000 1.950000 29.37 34 25.0805 1.4374 35 -64.3294 2.0127 1.953750 32.33 36 -19.2897 D36 37 62.4958 1.0000 2.000690 25.46 38 18.2928 4.8801 1.620410 60.24 39 -31.3885 28.4975 40 ∞ 1.6000 1.516800 63.88 41 ∞ 0.9999 Image plane ∞ [Lens group focal length] Lens group First surface Focal length GO 1 5.371 objective Imaging optical system GI 18 113.248 1st fixed group GA 18 43.759 1st movable group G1 30 -51.321 2nd movable group G2 33 -439.203 2nd fixed group GB 37 65.481

[0060] In this optical system OL1, the axial air gap D29 between the first fixed group GA and the first movable group G1, the axial air gap D32 between the first movable group G1 and the second movable group G2, and the axial air gap D36 between the second movable group G2 and the second fixed group GB change during focusing. Table 2 below shows the variable gaps during focusing on an object at infinity and when focusing on an object at close range. Note that D0 indicates the distance from the lens surface (first surface) closest to the object in the optical system OL1 to the object, f indicates the focal length, and β indicates the magnification. This explanation also applies to the following examples.

[0061] (Table 2) [Variable Interval Data] Infinite object Near object f 9.913 - β - 1.241 D0 ∞ 5.0000 D29 12.1044 18.9021 D32 12.1744 9.2270 D36 4.9502 1.1000

[0062] FIG. 2 shows the spherical aberration, astigmatism, distortion, and coma diagrams of this optical system OL1 when focused on an object at infinity. In each aberration diagram, FNo indicates the F-number, and A indicates the half angle of view. Note that the spherical aberration diagram indicates the F-number value corresponding to the maximum aperture, the astigmatism and distortion diagrams indicate the maximum half angle of view, and the coma diagram indicates the value of each half angle of view. d indicates the d-line (λ=587.6 nm), and g indicates the g-line (λ=435.8 nm). In the astigmatism diagram, the solid line indicates the sagittal image plane, and the dashed line indicates the meridional image plane. In the coma diagram, the solid line indicates the meridional image plane. The same symbols as in this embodiment are used in the aberration diagrams of each embodiment shown below. These aberration diagrams demonstrate that this optical system OL1 provides excellent correction for various aberrations and exhibits excellent imaging performance.

[0063] [Second Example] 3 is a diagram showing the configuration of an optical system OL2 according to Example 2. This optical system OL2 is composed of, from the object side, an objective optical system GO having positive refractive power, and an imaging optical system GI having positive refractive power that images an intermediate image IM formed by the objective optical system GO. Furthermore, the imaging optical system GI is composed of, from the object side, a first fixed group GA having positive refractive power, a first movable group G1 having negative refractive power, a second movable group G2 having positive refractive power, and a second fixed group GB having negative refractive power.

[0064] The objective optical system GO is composed of, in order from the object side, a meniscus negative lens L11 (L1) with its convex surface facing the object side, a meniscus negative lens L12 with its convex surface facing the object side, a cemented positive lens formed by cementing a biconcave negative lens L13 and a biconvex positive lens L14, a cemented positive lens formed by cementing a biconcave negative lens L15 and a biconvex positive lens L16, a biconvex positive lens L17, a cemented negative lens formed by cementing a biconcave negative lens L18 and a biconvex positive lens L19, and a biconvex positive lens L110.

[0065] The first fixed lens group GA of the imaging optical system GI is composed of, from the object side, a biconvex positive lens L21, a biconcave negative lens L22, a biconvex positive lens L23, a biconvex positive lens L24, and a cemented positive lens formed by cementing a meniscus negative lens L25 with its convex surface facing the object side and a biconvex positive lens L26. The first movable lens group G1 is composed of, from the object side, a cemented negative lens formed by cementing a biconcave negative lens L31 and a biconvex positive lens L32. The second movable lens group G2 is composed of a meniscus positive lens L41 with its concave surface facing the object side and an aspheric lens surface facing the image plane. The second fixed lens group GB is composed of, from the object side, a biconvex positive lens L51 and a biconcave negative lens L52.

[0066] In this optical system OL2, an intermediate image IM is formed between the objective optical system GO and the imaging optical system GI. An aperture stop S is disposed between the first fixed group GA and the first movable group G1 of the imaging optical system GI. A filter group FL is disposed between the imaging optical system GI and the image plane I.

[0067] Furthermore, in this optical system OL2, when focusing from an object at infinity to an object at close range, the first fixed group GA and the second fixed group GB of the imaging optical system GI are fixed relative to the image plane I, and the first movable group G1 and the second movable group G2, which are the focusing groups, move in the optical axis direction (the first movable group G1 moves toward the image plane, and the second movable group G2 moves toward the object).

[0068] Table 3 below lists the specifications of the optical system OL2.

[0069] (Table 3) Second Example [Overall specifications] f = 9.913 Fno = 8.200 ω[°] = 56.998 Y = 14.500 TL (air equivalent length) = 179.993 Bf (air equivalent length) = 18.162 [Lens data] mrd nd νd Object surface ∞ D0 1 6.4294 1.0000 2.000690 25.46 2 2.9207 1.3328 3 11.0345 1.0000 1.848500 43.79 4 4.7132 0.5249 5 -266.0401 3.0000 1.620410 60.24 6 4.4622 2.6231 2.000690 25.46 7 -12.5434 0.1000 8 -9.3459 3.0000 1.903660 31.27 9 5.0267 2.2405 1.788000 47.35 10 -7.5163 0.1000 11 18.8774 2.2735 1.593190 67.90 12 -6.7988 0.3175 13 -9.6345 4.0000 2.000690 25.46 14 8.9520 2.3451 1.593190 67.90 15 -27.0018 1.9425 16 130.0606 4.0000 1.846660 23.80 17 -13.7963 10.0522 18 ∞ 6.2639 Intermediate image IM 19 17.2518 3.3220 1.834000 37.18 20 -28.6469 0.1409 21 -24.7060 1.0000 1.846660 23.80 22 15.2383 2.3866 23 33.7523 2.2950 1.612660 44.46 24 -42.9424 27.6523 25 69.7163 2.2205 1.618750 63.73 26 -28.3428 13.8705 27 133.5069 1.0000 1.883000 40.69 28 9.5675 2.0003 1.593190 67.90 29 -18.7491 2.9892 30 ∞ D30 Aperture Stop S 31 -24.1459 1.0000 1.755200 27.57 32 13.4727 2.1169 1.860740 23.08 33 -53.0346 D33 34 -177.6629 2.8878 1.848500 43.79 35* -20.6570 D35 36 34.0716 2.4959 1.729160 54.61 37 -219.3380 1.2842 38 -30.0842 1.0000 1.846660 23.80 39 24.7298 16.1068 40 ∞ 1.6000 1.516800 63.88 41∞1.0000 Image plane ∞ [Lens group focal length] Lens group First surface Focal length GO 1 5.663 objective Imaging optical system GI 19 63.767 1st fixed group GA 19 37.934 1st movable group G1 31 -157.381 2nd movable group G2 34 27.318 2nd fixed group GB 36 -29.507

[0070] In this optical system OL2, the surface No. 35 is formed to have an aspherical shape. Table 4 below shows data on the aspherical surface, that is, the values ​​of the conic constant K and each of the aspherical constants A4 to A10.

[0071] (Table 4) [Aspherical data] m K A4 A6 A8 A10 35 0.00000 3.74495e-05 2.23580e-08 3.41930e-11 1.88741e-12

[0072] In this optical system OL2, the axial air gap D30 between the first fixed group GA and the first movable group G1, the axial air gap D33 between the first movable group G1 and the second movable group G2, and the axial air gap D35 between the second movable group G2 and the second fixed group GB change during focusing. Table 5 below shows the variable gaps when focusing on an object at infinity and when focusing on an object at close range.

[0073] (Table 5) [Variable Interval Data] Infinite object Near object f 9.913 - β - 1.128 D0 ∞ 5.0000 D30 1.5087 13.4827 D33 42.6997 27.9431 D35 1.3000 4.0826

[0074] Fig. 4 shows diagrams of spherical aberration, astigmatism, distortion, and coma when this optical system OL2 is focused on an object at infinity. These aberration diagrams show that this optical system OL2 has excellent correction for various aberrations and has excellent imaging performance.

[0075] [Third Example] 5 is a diagram showing the configuration of an optical system OL3 according to Example 3. This optical system OL3 is composed of, from the object side, an objective optical system GO having positive refractive power, and an imaging optical system GI having positive refractive power that images an intermediate image IM formed by the objective optical system GO. Furthermore, the imaging optical system GI is composed of, from the object side, a first fixed group GA having positive refractive power, a first movable group G1 having negative refractive power, a second movable group G2 having positive refractive power, and a second fixed group GB having negative refractive power.

[0076] The objective optical system GO is composed of, in order from the object side, a meniscus negative lens L11 (L1) with its convex surface facing the object side, a meniscus negative lens L12 with its convex surface facing the object side, a cemented positive lens formed by cementing a meniscus negative lens L13 with its convex surface facing the object side and a biconvex positive lens L14, a cemented positive lens formed by cementing a biconcave negative lens L15 and a biconvex positive lens L16, a biconvex positive lens L17, a cemented negative lens formed by cementing a biconcave negative lens L18 and a biconvex positive lens L19, a meniscus negative lens L110 with its convex surface facing the object side, and a biconvex positive lens L111.

[0077] The first fixed group GA of the imaging optical system GI is composed of, from the object side, a cemented positive lens formed by cementing a biconvex positive lens L21 and a biconcave negative lens L22, a meniscus positive lens L23 with its concave surface facing the object side, and a cemented positive lens formed by cementing a meniscus negative lens L24 with its convex surface facing the object side and a biconvex positive lens L25. The first movable group G1 is composed of, from the object side, a cemented negative lens formed by cementing a biconcave negative lens L31 and a biconvex positive lens L32. The second movable group G2 is composed of, from the object side, a biconvex positive lens L41, a meniscus negative lens L42 with its convex surface facing the object side, and a biconvex positive lens L43. The second fixed lens group GB is composed of, in order from the object side, a biconvex positive lens L51 and a meniscus negative lens L52 with its concave surface facing the object side.

[0078] The medium of the negative lens L11 (L1) in the objective optical system GO is optical glass manufactured using a new glass manufacturing method known as the floating melt method. This floating melt method makes it possible to vitrify unstable compositions that have previously been difficult to vitrify. This is making it increasingly possible to manufacture glass that has a high refractive index, relatively little dispersion, and high transmittance even at short wavelengths. Using such high-refractive-index glass in a meniscus-shaped negative lens can reduce the occurrence of astigmatism.

[0079] Specifically, the levitation melting method uses a laser levitation furnace to irradiate a sample with a laser such as carbon dioxide gas to melt the sample, levitate the melt using a levitation gas jet from a nozzle, and then cool and solidify the melt. The levitation gas can be any gas capable of levitating the sample. Depending on the application, it can be selected from inert gases such as air, nitrogen, oxygen, and argon, as well as dry air. The levitation melting method, also known as the containerless solidification method, involves heating and melting a material without the use of a container, such as a Pt alloy (e.g., Pt-Au, Pt-Au-Rh, etc.), followed by cooling and solidifying the material to obtain glass (see, for example, JP 2014-196236 A). Such optical glass can also be produced in a zero-gravity environment, not just by the levitation melting method.

[0080] In this optical system OL3, an intermediate image IM is formed between the objective optical system GO and the imaging optical system GI. An aperture stop S is disposed between the first fixed group GA and the first movable group G1 of the imaging optical system GI. A filter group FL is disposed between the imaging optical system GI and the image plane I.

[0081] Furthermore, in this optical system OL3, when focusing from an object at infinity to an object at close range, the first fixed group GA and the second fixed group GB of the imaging optical system GI are fixed relative to the image plane I, and the first movable group G1 and the second movable group G2, which are the focusing groups, move in the optical axis direction (the first movable group G1 moves toward the image plane, and the second movable group G2 moves toward the object).

[0082] Table 6 below lists the specifications of the optical system OL3.

[0083] (Table 6) Third Example [Overall specifications] f = 9.913 Fno = 8.200 ω[°] = 56.998 Y = 14.500 TL (air equivalent length) = 219.461 Bf (air equivalent length) = 11.589 [Lens data] mrd nd νd Object surface ∞ D0 1 7.7288 1.0000 1.950092 38.64 2 2.8432 1.7036 3 30.6552 1.0000 2.001000 29.12 4 4.2612 0.3951 5 6.3299 6.2779 1.737999 32.33 6 4.5963 2.9311 1.693500 53.18 7 -4.9199 0.1000 8 -10.5263 2.1705 1.903660 31.27 9 6.4600 3.6423 1.808095 22.76 10 -9.6717 2.3760 11 12.3275 3.9815 1.438750 94.94 12 -9.4542 0.1000 13 -12.0166 1.0000 2.000690 25.46 14 9.1880 3.8440 1.729157 54.68 15 -20.6122 2.0884 16 35.4760 11.4424 1.808095 22.76 17 20.3140 0.4002 18 27.2714 4.3888 1.808090 22.74 19 -35.6694 2.0000 20 ∞ 5.9754 Intermediate image IM 21 32.2462 15.0000 1.953750 32.33 22 -11.5610 15.0000 1.808090 22.74 23 13.1795 1.0663 24 -408.3316 14.3387 2.001000 29.12 25 -16.5109 5.3519 26 62.5855 3.2799 1.902650 35.77 27 12.4730 3.2799 1.438750 94.66 28 -15.0576 5.4369 29 ∞ D29 Aperture Stop S 30 -24.7452 2.0004 1.728250 28.46 31 14.1273 2.6004 1.846660 23.80 32 -59.2718 D32 33 269.5254 4.0206 1.622992 58.16 34 -45.5105 5.4669 35 56.2791 2.0000 2.001000 29.12 36 23.1440 2.3517 37 71.9097 4.5709 1.883000 40.69 38 -44.0449 D38 39 37.9637 4.0230 1.729157 54.68 40 -301.1112 2.9883 41 -22.3833 1.0000 1.922860 18.90 42 -1881.0445 9.5342 43 ∞ 1.6000 1.516800 63.88 44∞1.0000 Image plane ∞ [Lens group focal length] GO 1 objective optics 5.153 Imaging optical system GI 21 140.433 1st fixed group GA 21 31.176 1st movable group G1 30 -179.401 2nd movable group G2 33 44.074 2nd fixed group GB 39 -67.682

[0084] In this optical system OL3, the axial air gap D29 between the first fixed group GA and the first movable group G1, the axial air gap D32 between the first movable group G1 and the second movable group G2, and the axial air gap D38 between the second movable group G2 and the second fixed group GB change during focusing. Table 7 below shows the variable gaps when focusing on an object at infinity and when focusing on an object at close range.

[0085] (Table 7) [Variable Interval Data] Infinite object Near object f 9.913 - β - 1.124 D0 ∞ 5.0000 D29 3.0764 14.8572 D32 53.2020 34.1158 D38 1.0000 8.3055

[0086] Diagrams of spherical aberration, astigmatism, distortion, and coma for this optical system OL3 when focused on an object at infinity are shown in Figure 6. These aberration diagrams show that this optical system OL3 has excellent correction for various aberrations and has excellent imaging performance.

[0087] [Conditional expression corresponding value] The values ​​corresponding to the conditional expressions (1) to (7) in the first to third examples are shown in Table 6 below.

[0088] (Table 6) First Example Second Example Third Example (1)fo / f 0.542 0.571 0.520 (2) fa / fr 0.386 0.595 0.222 (3) TLo / TL 0.207 0.221 0.232 (4)|fb / fr| 0.578 0.463 0.482 (5) Lsum / TLr 0.154 0.152 0.428 (6)nL1 2.00100 2.00069 1.95009 (7)ωn / ωi 0.955 0.995 1.013 [Explanation of symbols]

[0089] 1 Camera (optical equipment) OL (OL1~OL3) Optical system GO Objective optical system GI Imaging optical system GA First fixed group G1 1st movable group (focusing group) G2 2nd movable group (focusing group) GB Second fixed group S Aperture stop

Claims

1. From the object side, an objective optical system; an imaging optical system that forms an intermediate image formed by the objective optical system, An optical system that satisfies the following condition: 0.40 < fo / f < 0.80 however, fo: focal length of the objective optical system f: focal length of the entire optical system

2. The optical system according to claim 1 , wherein the number of intermediate images is one.

3. the imaging optical system has at least two focusing groups; 3. The optical system according to claim 1, wherein the distance between adjacent lens groups changes during focusing.

4. 4. The optical system according to claim 3, wherein the focusing group is moved along the optical axis during focusing to focus on an object at infinity.

5. 5. The optical system according to claim 3, wherein the following condition is satisfied: 0.15 < fa / fr < 0.80 however, fa: the focal length of the optical system located closer to the object than the focusing group located closest to the object in the imaging optical system fr: focal length of the imaging optical system

6. 6. The optical system according to claim 1, wherein the following condition is satisfied: 0.10 < TLo / TL < 0.30 however, TLo: the distance on the optical axis from the lens surface of the objective optical system closest to the object to the intermediate image TL: total optical length of the optical system

7. 7. The optical system according to claim 1, wherein the following condition is satisfied: 0.30 < | fb / fr | < 0.80 however, fb: the focal length of the optical system located closer to the image plane than the focusing group located closest to the image plane in the imaging optical system fr: focal length of the imaging optical system

8. 8. The optical system according to claim 1, wherein the following condition is satisfied: 0.10 < Lsum / TLr < 0.60 however, Lsum: total lens thickness of the imaging optical system TLr: the distance on the optical axis from the intermediate image to the image plane

9. 9. The optical system according to claim 1, further comprising a stop in the imaging optical system.

10. 10. The optical system according to claim 1, wherein the lens arranged closest to the object side of the objective optical system is a spherical lens.

11. 11. The optical system according to claim 1, wherein the lens arranged closest to the object side of the objective optical system has negative refractive power.

12. 12. The optical system according to claim 1, wherein the following condition is satisfied: 1.70 < nL1 however, nL1: refractive index of the medium of the lens arranged closest to the object side in the objective optical system with respect to the d-line

13. 13. The optical system according to claim 1, which satisfies the following condition: 0.80 < ωn / ωi < 1.20 however, ωn: half angle of view when the optical system is focused on a close object ωi: half angle of view when the optical system is focused on an object at infinity

14. An optical instrument comprising the optical system according to any one of claims 1 to 13.

15. 1. A method for manufacturing an optical system including, in order from an object side, an objective optical system and an imaging optical system that forms an intermediate image formed by the objective optical system, A manufacturing method for an optical system that is arranged to satisfy the following condition: 0.40 < fo / f < 0.80 however, fo: focal length of the objective optical system f: focal length of the entire optical system

Images