Rigid endoscope optical system

Abstract

The purpose of the present invention is to provide a rigid endoscope optical system capable of observing or imaging high-resolution and high-contrast images while suppressing chromatic aberration in a wide wavelength region from the visible region to the near-infrared region for finer observation of biological tissue.　This rigid endoscope optical system comprises a plurality of lenses having an effective diameter of 7 mm or less, wherein the plurality of lenses include at least three or more lens groups including a first lens group on the light-entry side, a second lens group on the downstream side of the first lens group, and a third lens group located in front of a diaphragm surface. In the first lens group, a first lens on the most upstream side has positive power, and a lens on the downstream side of the first lens has negative power as a whole. The second lens group includes the longest lens, which is the longest among the plurality of lenses, and the third lens group is provided with one or more anomalous dispersion lenses.

Description

Rigid endoscope optical system

[0001] The present invention relates to a rigid endoscope optical system used for a rigid endoscope.

[0002] The rigid endoscope has a rigid insertion portion to be inserted into a hollow portion in a living body, one end of the insertion portion is inserted into the living body, and the other end side of the insertion portion is provided with a grip portion that is gripped by an operator to operate the insertion portion (for example, see Patent Document 1). Each of the insertion portion and the grip portion includes a relay lens system, and an image of a living tissue is observed or captured by a camera or the like connected to the grip portion.

[0003] For such a rigid endoscope, for more precise observation of living tissues, there is a demand for a rigid endoscope capable of observing or capturing high-contrast images with high resolution while suppressing chromatic aberration in a wide wavelength range extending from the visible region to the near-infrared region.

[0004] Japanese Unexamined Patent Application Publication No. 10-115788

[0005] In view of the above problems, an object of the present invention is to provide a rigid endoscope optical system capable of observing or capturing high-contrast images with high resolution while suppressing chromatic aberration in a wide wavelength range extending from the visible region to the near-infrared region, for more precise observation of living tissues.

[0006] A rigid endoscope optical system according to the present invention is a rigid endoscope optical system including a plurality of lenses having an effective diameter of 7 mm or less, wherein the plurality of lenses include at least three or more lens groups: a first lens group on the incident side, a second lens group located downstream of the first lens group, and a third lens group located in front of the stop surface. In the first lens group, the most upstream first lens has positive power, and the lenses located downstream of the first lens have negative power as a whole. The second lens group includes the longest lens among the plurality of lenses, and the third lens group includes one or more anomalous dispersion lenses.

[0007] Figure 1 is a schematic diagram of a rigid mirror 1 to which the rigid mirror optical system according to the first embodiment is applied. Figure 2 is an optical configuration diagram of the rigid mirror optical system 100 according to the first embodiment. Figure 3 is a table showing the characteristics of the lenses constituting the first lens group L1 to the third lens group L3 of the rigid mirror optical system 100 in the first embodiment. Figure 4 is a graph showing the modulation transfer function of the rigid mirror optical system 100 in the example of Figure 3 when the wavelength of the incident light is 450.0 nm (visible region). Figure 5 is a graph showing the modulation transfer function of the rigid mirror optical system 100 in the example of Figure 3 when the wavelength of the incident light is 587.6 nm (visible region). Figure 6 is a graph showing the modulation transfer function of the rigid mirror optical system 100 in the example of Figure 3 when the wavelength of the incident light is 900.0 nm (near-infrared region). Figure 7 is a graph showing the modulation transfer function of the rigid mirror optical system 100 in the example of Figure 3 when the wavelength of the incident light is 1450.0 nm (near-infrared region). Figure 8 is a graph showing the modulation transfer function of the rigid mirror optical system 100 in the example of Figure 3 when the incident light wavelength uniformly includes 450.0 to 1450.0 nm (visible region to near-infrared region) under white light illumination. Figure 9 is an aberration curve diagram of the rigid mirror optical system 100 in the example of Figure 3. Figure 10 is an optical configuration diagram illustrating the rigid mirror optical system 100 according to the second embodiment. Figure 11 is a table showing the characteristics of the lenses constituting the first lens group L1 to the third lens group L3 of the rigid mirror optical system 100 in the second embodiment. Figure 12 is a graph showing the modulation transfer function of the rigid mirror optical system 100 in the example of Figure 11 when the incident light wavelength is 450.0 nm (visible region). Figure 13 is a graph showing the modulation transfer function of the rigid mirror optical system 100 in the example of Figure 11 when the incident light wavelength is 587.6 nm (visible region). Figure 14 is a graph showing the modulation transfer function of the rigid mirror optical system 100 in the example of Figure 11 when the wavelength of the incident light is 900.0 nm (near-infrared region). Figure 15 is a graph showing the modulation transfer function of the rigid mirror optical system 100 in the example of Figure 11 when the wavelength of the incident light is 1450.0 nm (near-infrared region). Figure 16 is a graph showing the modulation transfer function of the rigid mirror optical system 100 in the example of Figure 11 when the incident light wavelength uniformly includes 450.0 to 1450.0 nm (visible region to near-infrared region) under white light illumination.Figure 17 is an aberration curve diagram of the rigid mirror optical system 100 in the example shown in Figure 11. Figure 18 is an optical configuration diagram illustrating the rigid mirror optical system 100 according to the third embodiment. Figure 19 is a table showing the characteristics of the lenses constituting the first lens group L1 to the third lens group L3 of the rigid mirror optical system 100 in the third embodiment. Figure 20 is a graph showing the modulation transfer function of the rigid mirror optical system 100 in the example shown in Figure 19 when the wavelength of the incident light is 450.0 nm (visible region). Figure 21 is a graph showing the modulation transfer function of the rigid mirror optical system 100 in the example shown in Figure 19 when the wavelength of the incident light is 587.6 nm (visible region). Figure 22 is a graph showing the modulation transfer function of the rigid mirror optical system 100 in the example shown in Figure 19 when the wavelength of the incident light is 900.0 nm (near-infrared region). Figure 23 is a graph showing the modulation transfer function of the rigid mirror optical system 100 in the example of Figure 19 when the wavelength of the incident light is 1450.0 nm (near-infrared region). Figure 24 is a graph showing the modulation transfer function of the rigid mirror optical system 100 in the example of Figure 19 when the incident light wavelength uniformly includes 450.0 to 1450.0 nm (visible region to near-infrared region) under white light illumination. Figure 25 is an aberration curve diagram of the rigid mirror optical system 100 in the example of Figure 19, showing the aberration curve for each wavelength of illumination light. Figure 26 is an optical configuration diagram illustrating the rigid mirror optical system 100 according to the fourth embodiment. Figure 27 is a table showing the characteristics of the lenses constituting the first lens group L1 to the third lens group L3 and the seventh lens group La of the rigid mirror optical system 100 in the fourth embodiment. Figure 28 is a graph showing the modulation transfer function of the rigid mirror optical system 100 in the example of Figure 27 when the incident light wavelength uniformly includes 450.0 to 1450.0 nm (visible region to near-infrared region) as white light illumination. Figure 29 is an optical configuration diagram illustrating the rigid mirror optical system 100 according to the fifth embodiment. Figure 30 is a table showing the characteristics of the lenses constituting the first lens group L1 to the third lens group L3 and the seventh lens group La of the rigid mirror optical system 100 in the fifth embodiment. Figure 31 is a graph showing the modulation transfer function of the rigid mirror optical system 100 in the example of Figure 30 when the incident light wavelength uniformly includes 450.0 to 1450.0 nm (visible region to near-infrared region) as white light illumination. Figure 32 is an optical configuration diagram illustrating the rigid mirror optical system 100 according to the sixth embodiment.Figure 33 is a table showing the characteristics of the lenses constituting the first lens group L1 to the third lens group L3 and the seventh lens group La of the rigid mirror optical system 100 in the sixth embodiment. Figure 34 is a graph showing the modulation transfer function of the rigid mirror optical system 100 of the example in Figure 33 when the incident light wavelength uniformly includes 450.0 to 1450.0 nm (visible region to near-infrared region) under white light illumination. Figure 35 is an optical configuration diagram illustrating the rigid mirror optical system 100 according to the seventh embodiment. Figure 36 is a table showing the characteristics of the lenses constituting the first lens group L1 to the third lens group L3 and the seventh lens group La of the rigid mirror optical system 100 in the seventh embodiment. Figure 37 is a graph showing the modulation transfer function of the rigid mirror optical system 100 of the example in Figure 36 when the incident light wavelength is 450.0 nm (visible region). Figure 38 is a graph showing the modulation transfer function of the rigid mirror optical system 100 in the example of Figure 36 when the wavelength of the incident light is 587.6 nm (visible region). Figure 39 is a graph showing the modulation transfer function of the rigid mirror optical system 100 in the example of Figure 36 when the wavelength of the incident light is 900.0 nm (near-infrared region). Figure 40 is a graph showing the modulation transfer function of the rigid mirror optical system 100 in the example of Figure 36 when the wavelength of the incident light is 1450.0 nm (near-infrared region). Figure 41 is a graph showing the modulation transfer function of the rigid mirror optical system 100 in the example of Figure 36 when the incident light wavelength uniformly includes 450.0 to 1450.0 nm (visible region to near-infrared region) under white light illumination. Figure 42 is an aberration curve diagram of the rigid mirror optical system 100 in the example of Figure 36.

[0008] This embodiment will be described below with reference to the attached drawings. The attached drawings show embodiments in accordance with the principles of this disclosure, but they are for the purpose of understanding this disclosure and are not to be used in any way to restrict the interpretation of this disclosure. The descriptions herein are merely typical examples and do not limit in any way the claims or applications of this disclosure. Although this embodiment is described in sufficient detail for those skilled in the art to implement this disclosure, other implementations and forms are possible, and it is important to understand that the configuration and structure can be changed and various elements replaced without departing from the scope and spirit of the technical idea of ​​this disclosure. Therefore, the following description should not be interpreted as limiting to this.

[0009] [First Embodiment] Figure 1 is a schematic diagram of a rigid endoscope 1 to which the rigid endoscope optical system according to the first embodiment is applied. The rigid endoscope 1 is composed of an insertion portion 10 and a gripping portion 20 provided on the other end of the insertion portion 10 and gripped by an operator.

[0010] The insertion section 10 has a rigid housing as a whole and is configured to be inserted into a living organism (such as the human body). The gripping section 20 is provided at the end of the insertion section 10 and is configured to be grasped by an operator, and has buttons and levers (not shown) necessary for various operations (such as turning on, switching, and dimming the light source). The insertion section 10 and the gripping section 20 have a rigid mirror optical system 100 and a light guide 200 inside. The rigid mirror 1 is connected to the light source device 30 via the light guide 200. The camera Cm is connected to the computer 40 via signal wiring, etc.

[0011] As will be described later, the rigid endoscope optical system 100 has an objective lens at the tip of the insertion section 10, and is equipped with various relay lens systems, eyepiece lens systems, and imaging lens systems to form an image of a living organism on the camera Cm. The camera Cm can be configured to be detachably attached to the gripping section 20.

[0012] When the rigid endoscope 1 is in use, illumination light (visible light to near-infrared light) emitted by the light source device 30 is irradiated onto the object to be observed in the living body at the tip of the insertion section 10 via the light guide 200. An optical image of the object to be observed is formed on the light-receiving surface of the camera Cm by the rigid endoscope optical system 100. The camera Cm has a high resolution, such as 4K or 8K resolution. The image captured by the camera Cm is transmitted as an image signal to the computer 40 and displayed on a display or the like.

[0013] The rigid mirror optical system 100 will be described with reference to Figure 2. The rigid mirror optical system 100 is a relay optical system that includes multiple lenses with an effective diameter of 7 mm or less. The multiple lenses include a first lens group L1, a second lens group L2, a third lens group L3, a field diaphragm AP, a fourth lens group L4, a fifth lens group L5, and a sixth lens group L6. The first lens group L1 is located at the very front of the insertion section 10 and receives light from the object to be imaged. The second lens group L2 is located downstream of the first lens group L1. The third lens group L3 is located further downstream than the second lens group L2 and is positioned in front of the field diaphragm AP.

[0014] The rigid mirror optical system 100 is configured symmetrically with respect to the field diaphragm AP. That is, the fourth lens group L4, the fifth lens group L5, and the sixth lens group L6 are symmetrical with respect to the third lens group L3, the second lens group L2, and the first lens group L1, respectively, and have similar optical characteristics. Downstream of the field diaphragm AP, the rigid mirror optical system 100 has the fourth lens group L4, the fifth lens group L5, and the sixth lens group L6 in that order. Each lens group is formed by arranging multiple lenses, but a pair of symmetrical lens groups can be configured by arranging multiple lenses of the same type symmetrically. In addition, the rigid mirror optical system 100 may include another single lens at a position between the first to sixth lens groups L1 to L6.

[0015] The first lens group L1 has a positive power in its first lens, which is the most upstream lens, and a negative power overall in the lenses downstream of that first lens. The second lens group L2 includes the longest lens among the multiple lenses, which has the longest length (thickness) along the optical axis of the rigid mirror optical system 100. The third lens group L3 and the fourth lens group L4 each include one or more anomalous dispersion lenses. An anomalous dispersion lens is a lens made of a material that has anomalous partial dispersion, and anomalous partial dispersion refers to the property of anomalous partial dispersion or special dispersion, which means that the partial dispersion changes uniquely depending on the wavelength. Examples of materials include fluorite and calcium fluoride. With a configuration using an anomalous dispersion lens, chromatic aberration correction is achieved over a wide range from the visible region to the near-infrared region (450 nm to 1700 nm) (less than 0.1 mm), and furthermore, a resolution of 200 line / mm or higher (4K) is obtained in the visible region (400 to 750 nm), and a resolution of 100 line / mm or higher (2K) is obtained in the near-infrared region (750 to 1700 nm). In addition, it is preferable that the rigid mirror optical system 100 satisfies the following two conditions when one wavelength in the near-infrared region (1000 nm to 1700 nm) is designated as λIR, one wavelength in the non-λIR wavelength range (450 nm to 1700 nm) is designated as λ2, the focal length of the rigid mirror optical system 100 at wavelength λIR is designated as FIR, and the focal length of the rigid mirror optical system 100 at wavelength λ2 is designated as F2. [Conditional Expression 1] | FIR-F2 | <0.1 [Conditional Expression 2] | λIR-λ2 | >100 nm

[0016] Figure 3 is a table showing the characteristics (radius of curvature of the front surface, thickness, material (glass), semi-diameter, product name, and conicity) of the lenses constituting the first lens group L1 to the third lens group L3 of the rigid mirror optical system 100 that satisfies the above-mentioned conditions 1 and 2 in the first embodiment. In the table, numbers 1 to 3 indicate the lenses constituting the first lens group L1. Numbers 5 to 11 indicate the diameter of curvature of the front surface, thickness, material, radius, and conicity of the lenses constituting the second lens group L2. Numbers 13 to 15 indicate the radius of curvature of the front surface, thickness, material, radius, and conicity of the lenses constituting the third lens group L3.

[0017] Numbers 4, 12, and 16 are single lenses located before and after the first to third lens groups L1 to L3, OBJ is the objective lens located at the front of the rigid endoscope optical system 100, and STO is the exit lens located at the rear end of the rigid endoscope optical system 100. Note that the fourth lens group L4 to the sixth lens group L6 are symmetrical to the first lens group L1 to the third lens group L3, so they are omitted from the table.

[0018] Lenses 1 to 3 that make up the first lens group L1 have positive power for lens 1, and the remaining two (numbers 2 and 3) have negative power as a whole. In addition, one of the lenses 5 to 11 that make up the second lens group L2 is the longest lens among the lenses that make up the rigid mirror optical system 100. In this example in Figure 3, lens 7 is the longest (thickest). Also, one or more of the lenses 13 to 15 that make up the third lens group L3 are anomalous dispersion lenses, but in the example in Figure 3, lens 15 is an anomalous dispersion lens (for example, OHARA GmbH, S-FPL55).

[0019] Figure 4 is a graph showing the modulation transfer function of the rigid mirror optical system 100 in the example shown in Figure 3, when the wavelength of the incident light is 450.0 nm (visible region). The horizontal axis of the graph is spatial frequency, and the vertical axis is contrast (modulation) (the same applies to the following graphs). In the rigid mirror 1 having the rigid mirror optical system 100, a contrast of 0.2 or higher is obtained at a spatial frequency of around 200 (Cycles / mm), and a high-contrast image with high resolution is obtained.

[0020] Figure 5 is a graph showing the modulation transfer function of the rigid mirror optical system 100 in the example shown in Figure 3, when the wavelength of the incident light is 587.6 nm (visible region). In the rigid mirror 1 having the rigid mirror optical system 100, a contrast of 0.2 or higher is obtained at a spatial frequency of around 200 (Cycles / mm), and a high-contrast image with high resolution is obtained.

[0021] Figure 6 is a graph showing the modulation transfer function of the rigid mirror optical system 100 in the example shown in Figure 3, when the wavelength of the incident light is 900.0 nm (near-infrared region). In the rigid mirror 1 having the rigid mirror optical system 100, a contrast of 0.1 or higher is obtained in the near-infrared light region when the spatial frequency is around 200 (Cycles / mm), and a high-contrast image with sufficiently high resolution is obtained for near-infrared observation images.

[0022] Figure 7 is a graph showing the modulation transfer function of the rigid mirror optical system 100 in the example shown in Figure 3, when the wavelength of the incident light is 1450.0 nm (near-infrared region). In the rigid mirror 1 having the rigid mirror optical system 100, a contrast of 0.1 or higher is obtained in the near-infrared light region when the spatial frequency is around 100 (Cycles / mm), and a high-contrast image with sufficiently high resolution is obtained for near-infrared observation images.

[0023] Figure 8 is a graph showing the modulation transfer function of the rigid mirror optical system 100 in the example shown in Figure 3, when the incident light is illuminated with white light that uniformly includes wavelengths from 450.0 to 1450.0 nm (visible region to near-infrared region). In the rigid mirror 1 having the rigid mirror optical system 100, a contrast of 0.2 or higher is obtained at a spatial frequency of around 200 (Cycles / mm), and high-contrast images with sufficiently high resolution are obtained over a wide wavelength range from the visible region to the near-infrared region.

[0024] Figure 9 shows the aberration curves of the rigid mirror optical system 100 in the example shown in Figure 3, with curves shown for each wavelength of illumination light. Axial chromatic aberration is also suppressed to less than 0.02 mm, and images with sufficient resolution and contrast can be obtained even when imaging with white light.

[0025] [Second Embodiment] Next, a rigid mirror optical system 100 according to the second embodiment will be described with reference to Figures 10 to 17. As shown in Figure 10, the rigid mirror optical system 100 of the second embodiment is a relay optical system including a plurality of lenses with an effective diameter of 7 mm or less, similar to the first embodiment, and the plurality of lenses include a first lens group L1, a second lens group L2, a third lens group L3, a field diaphragm AP, a fourth lens group L4, a fifth lens group L5, and a sixth lens group L6, similar to the first embodiment.

[0026] The first lens group L1 is located at the very front of the insertion section 10 and receives light from the object to be imaged. The second lens group L2 is located downstream of the first lens group L1. The third lens group L3 is located further downstream than the second lens group L2 and is positioned in front of the field diaphragm AP. The rigid mirror optical system 100 is configured symmetrically with respect to the field diaphragm AP. That is, the fourth lens group L4, the fifth lens group L5, and the sixth lens group L6 are symmetrical with respect to the third lens group L3, the second lens group L2, and the first lens group L1, respectively, and have similar optical characteristics. Each lens group is formed by arranging multiple lenses, but a pair of symmetrical lens groups can be configured by arranging multiple lenses of the same type symmetrically. The rigid mirror optical system 100 may also include other single lenses at positions between the first to sixth lens groups L1 to L6. Furthermore, the first lens group L1 may be composed of a doublet lens.

[0027] The first lens group L1 has a first lens, the upstreammost lens, which has positive power, and the lenses downstream of that first lens, as a whole, have negative power. The second lens group L2 includes the longest lens among the multiple lenses. The third lens group L3 and the fourth lens group L4 each include one or more lenses with anomalous dispersion.

[0028] Figure 11 is a table showing the characteristics (radius of curvature of the front surface, thickness, material (glass), semi-diameter, product name, and conicity) of the lenses constituting the first lens group L1 to the third lens group L3 of the rigid mirror optical system 100 that satisfies the above-mentioned conditions 1 and 2 in the second embodiment. In the table, numbers 1 to 3 indicate the lenses constituting the first lens group L1. Numbers 5 to 11 indicate the diameter of curvature of the front surface, thickness, material, radius, and conicity of the lenses constituting the second lens group L2. Numbers 13 to 15 indicate the radius of curvature of the front surface, thickness, material, radius, and conicity of the lenses constituting the third lens group L3. Numbers 4, 12, and 16 are single lenses located before and after the first to third lens groups L1 to L3, OBJ is the objective lens located at the front of the rigid mirror optical system 100, and STO is the exit lens located at the rear end of the rigid mirror optical system 100.

[0029] Similar to the first embodiment, the lenses 1 to 3 constituting the first lens group L1 have positive power for lens 1 and negative power for the remaining two as a whole. In addition, one of the lenses 5 to 11 constituting the second lens group L2 is the longest lens among the lenses constituting the rigid mirror optical system 100. In this example of Figure 11, lens 9 is the longest (thickest). Also, one or more of the lenses 13 to 15 constituting the third lens group L3 are anomalous dispersion lenses, but in the example of Figure 11, lens 15 is an anomalous dispersion lens (S-FPL55).

[0030] Figure 12 is a graph showing the modulation transfer function of the rigid mirror optical system 100 in the example shown in Figure 11 when the wavelength of the incident light is 450.0 nm (visible region). In the rigid mirror 1 having the rigid mirror optical system 100, a contrast of 0.2 or higher is obtained at a spatial frequency of around 200 (Cycles / mm), and a high-contrast image with high resolution is obtained.

[0031] Figure 13 is a graph showing the modulation transfer function of the rigid mirror optical system 100 in the example shown in Figure 11, when the wavelength of the incident light is 587.6 nm (visible region). In the rigid mirror 1 having the rigid mirror optical system 100, a contrast of 0.2 or higher is obtained at a spatial frequency of around 200 (Cycles / mm), and a high-contrast image with high resolution is obtained.

[0032] Figure 14 is a graph showing the modulation transfer function of the rigid mirror optical system 100 in the example shown in Figure 11 when the wavelength of the incident light is 900.0 nm (near-infrared region). In the rigid mirror 1 having the rigid mirror optical system 100, a contrast of 0.1 or higher is obtained in the near-infrared light region when the spatial frequency is around 200 (Cycles / mm), and a high-contrast image with sufficiently high resolution is obtained for near-infrared observation images.

[0033] Figure 15 is a graph showing the modulation transfer function of the rigid mirror optical system 100 in the example shown in Figure 11 when the wavelength of the incident light is 1450.0 nm (near-infrared region). In the rigid mirror 1 having the rigid mirror optical system 100, a contrast of 0.1 or higher is obtained in the near-infrared light region when the spatial frequency is around 120 (Cycles / mm), and a high-contrast image with sufficiently high resolution is obtained for near-infrared observation images.

[0034] Figure 16 is a graph showing the modulation transfer function of the rigid mirror optical system 100 in the example shown in Figure 11, when the incident light wavelength uniformly includes 450.0 to 1450.0 nm (visible region to near-infrared region) under white light illumination. In the rigid mirror 1 having the rigid mirror optical system 100, a contrast of 0.2 or higher is obtained at a spatial frequency of around 200 (Cycles / mm), and high-contrast images with sufficiently high resolution are obtained over a wide wavelength range from the visible region to the near-infrared region.

[0035] Figure 17 shows the aberration curves of the rigid mirror optical system 100 in the example shown in Figure 11, with the aberration curves shown for each wavelength of illumination light. Axial chromatic aberration is also suppressed to less than 0.02 mm, and images with sufficient resolution and contrast can be obtained even when imaging with white light.

[0036] [Third Embodiment] Next, a rigid mirror optical system 100 according to the third embodiment will be described with reference to Figures 18 to 25. As shown in Figure 18, the rigid mirror optical system 100 of the third embodiment is a relay optical system including a plurality of lenses with an effective diameter of 7 mm or less, similar to the embodiments described above, and the plurality of lenses include a first lens group L1, a second lens group L2, a third lens group L3, a field diaphragm AP, a fourth lens group L4, a fifth lens group L5, and a sixth lens group L6, similar to the embodiments described above.

[0037] The first lens group L1 is located at the very front of the insertion section 10 and receives light from the object to be imaged. In this third embodiment, the lens group L1 is composed of a so-called doublet lens. A doublet lens is a lens made by combining two pieces of glass with different refractive indices, and as an effect on its optical system, it cancels out or reduces chromatic aberration and spherical aberration that tend to occur with single lenses. By using a doublet lens, chromatic aberration and spherical aberration are improved. The second lens group L2 is located downstream of the first lens group L1. The third lens group L3 is located even further downstream than the second lens group L2 and is positioned in front of the field diaphragm AP. The rigid mirror optical system 100 is configured symmetrically with respect to the field diaphragm AP. That is, the fourth lens group L4, the fifth lens group L5, and the sixth lens group L6 are symmetrical with respect to the third lens group L3, the second lens group L2, and the first lens group L1, respectively, and have similar optical characteristics. Each lens group is formed by arranging multiple lenses, but a pair of symmetrical lens groups can be constructed by arranging multiple lenses of the same type symmetrically. The rigid mirror optical system 100 may also include a separate single lens at a position between the first to sixth lens groups L1 to L6.

[0038] The first lens group L1 has a first lens, the upstreammost lens, which has positive power, and the lenses downstream of that first lens, as a whole, have negative power. The second lens group L2 includes the longest (thickest) lens among the multiple lenses. The third lens group L3 and the fourth lens group L4 each include one or more lenses with anomalous dispersion.

[0039] Figure 19 is a table showing the characteristics (radius of curvature of the front surface, thickness, material (glass), semi-diameter, product name, and conicity) of the lenses constituting the first lens group L1 to the third lens group L3 of the rigid endoscope optical system 100 that satisfies the above-mentioned conditions 1 and 2 in the third embodiment. In the table, numbers 1 to 3 indicate the lenses constituting the first lens group L1. Numbers 5 to 11 indicate the diameter of curvature of the front surface, thickness, material, radius, and conicity of the lenses constituting the second lens group L2. Numbers 13 to 15 indicate the radius of curvature of the front surface, thickness, material, radius, and conicity of the lenses constituting the third lens group L3. Numbers 4, 12, and 16 are single lenses located before and after the first to third lens groups L1 to L3, OBJ is the objective lens located at the front of the rigid endoscope optical system 100, and STO is the exit lens located at the rear end of the rigid endoscope optical system 100.

[0040] Similar to the previously described embodiment, the lenses 1 to 3 constituting the first lens group L1 have positive power for lens 1 and negative power for the remaining two as a whole. In addition, one of the lenses 5 to 11 constituting the second lens group L2 is the longest lens among the lenses constituting the rigid mirror optical system 100. In this example of Figure 19, lens 7 is the longest (thickest). Lens 5, which is the leading lens of the second lens group L2, has positive power. In addition, one or more of the lenses 13 to 15 constituting the third lens group L3 are anomalous dispersion lenses, but in the example of Figure 19, lens 15 is an anomalous dispersion lens (S-FPL55).

[0041] Figure 20 is a graph showing the modulation transfer function of the rigid mirror optical system 100 in the example shown in Figure 19 when the wavelength of the incident light is 450.0 nm (visible region). In the rigid mirror 1 having the rigid mirror optical system 100, a contrast of 0.2 or higher is obtained at a spatial frequency of around 200 (Cycles / mm), and a high-contrast image with high resolution is obtained.

[0042] FIG. 21 is a graph showing the modulation transfer function of the rigid endoscope optical system 100 of the example in FIG. 19 when the wavelength of incident light is 587.6 nm (in the visible region). In the rigid endoscope 1 having the rigid endoscope optical system 100, a contrast of 0.2 or higher is obtained at a spatial frequency around 200 (Cycle / mm), and an image with high resolution and high contrast is obtained.

[0043] FIG. 22 is a graph showing the modulation transfer function of the rigid endoscope optical system 100 of the example in FIG. 19 when the wavelength of incident light is 900.0 nm (in the near-infrared region). In the rigid endoscope 1 having the rigid endoscope optical system 100, a contrast of 0.1 or higher is obtained at a spatial frequency around 200 (Cycle / mm) in the near-infrared light region, and a sufficiently high-resolution and high-contrast image is obtained as a near-infrared observation image.

[0044] FIG. 23 is a graph showing the modulation transfer function of the rigid endoscope optical system 100 of the example in FIG. 19 when the wavelength of incident light is 1450.0 nm (in the near-infrared region). In the rigid endoscope 1 having the rigid endoscope optical system 100, a contrast of 0.1 or higher is obtained at a spatial frequency around 120 (Cycle / mm) in the near-infrared light region, and a sufficiently high-resolution and high-contrast image is obtained as a near-infrared observation image.

[0045] FIG. 24 is a graph showing the modulation transfer function of the rigid endoscope optical system 100 of the example in FIG. 19 in the case of white light illumination that uniformly includes incident light wavelengths of 450.0 to 1450.0 nm (visible region to near-infrared region). In the rigid endoscope 1 having the rigid endoscope optical system 100, a contrast of 0.2 or higher is obtained at a spatial frequency around 200 (Cycle / mm), and a sufficiently high-resolution and high-contrast image is obtained in a wide wavelength range extending from the visible region to the near-infrared region.

[0046] FIG. 25 is an aberration curve diagram of the rigid endoscope optical system 100 of the example in FIG. 19, which shows aberration curves for each wavelength of illumination light. The axial chromatic aberration is also suppressed to less than 0.02 mm, and an image with sufficient resolution and contrast can be obtained even in imaging with white light.

[0047] [Fourth Embodiment] Next, a rigid endoscope optical system 100 according to the fourth embodiment will be described with reference to FIGS. 26 to 28. As shown in FIG. 26, the rigid endoscope optical system 100 of the fourth embodiment is a relay optical system including a plurality of lenses with an effective diameter of 7 mm or less, similar to the aforementioned embodiments, and the plurality of lenses include, similarly to the aforementioned embodiments, a first lens group L1, a second lens group L2, a third lens group L3, a field stop AP, a fourth lens group L4, a fifth lens group L5, and a sixth lens group L6. In addition to this, this relay optical system includes a seventh lens group La (first additional lens group) between the first lens group L1 and the second lens group L2, and an eighth lens group Lb (second additional lens group) between the fifth lens group L5 and the sixth lens group L6. The seventh lens group La and the eighth lens group Lb are arranged symmetrically with respect to the field stop AP and have identical characteristics.

[0048] The first lens group L1 is provided at the most distal end side of the insertion portion 10, and allows light from an imaging target to enter. The lens group L1 of this fourth embodiment is constituted by a so-called doublet lens. This achieves improvement of chromatic aberration and spherical aberration. The second lens group L2 is located on the downstream surface side relative to the first lens group L1 and the seventh lens group La. The third lens group L3 is located further downstream than the second lens group L2, and is positioned in front of the field stop AP. The rigid endoscope optical system 100 is configured to be bilaterally symmetric with respect to the field stop AP. That is, the fourth lens group L4, the fifth lens group L5, the eighth lens group Lb, and the sixth lens group L6 are bilaterally symmetric to the third lens group L3, the second lens group L2, the seventh lens group La, and the first lens group L1 respectively, and have similar optical characteristics. Each lens group is formed by arranging a plurality of lenses, and a pair of bilaterally symmetric lens groups may be configured by arranging a plurality of lenses of the same type in bilateral symmetry. Note that the rigid endoscope optical system 100 may additionally include another single lens at a position between the first to sixth lens groups L1 to L6.

[0049] In the first lens group L1, the first lens furthest upstream has positive power, and the lenses downstream of the first lens have negative power as a whole. The second lens group L2 includes the longest (thickest) lens among the multiple lenses. The third lens group L3 and the fourth lens group L4 each include one or more anomalous dispersion lenses. In this fourth embodiment, not only the third lens group L3 and the fourth lens group L4, but also the second lens group L2, the fifth lens group L5, and the seventh lens group La are each equipped with one or more anomalous dispersion lenses.

[0050] Figure 27 is a table showing the characteristics (radius of curvature of the front surface, thickness, material (glass), semi-diameter, product name, and conicity) of the lenses constituting the first lens group L1 to the third lens group L3 and the seventh lens group La of the rigid mirror optical system 100 that satisfies the above-mentioned conditions 1 and 2 in the fourth embodiment. In the table, numbers 1 to 3 indicate the lenses constituting the first lens group L1. Numbers 5 to 7 indicate the diameter of curvature of the front surface, thickness, material, radius, and conicity of the lenses constituting the seventh lens group La. Numbers 9 to 13 indicate the radius of curvature of the front surface, thickness, material, radius, and conicity of the lenses constituting the second lens group L2, and numbers 15 to 17 indicate the radius of curvature of the front surface, thickness, material, radius, and conicity of the lenses constituting the third lens group L3. Numbers 4, 8, 14, and 18 are single lenses located before and after the first to third lens groups L1 to L3, OBJ is an objective lens located at the front of the rigid endoscope optical system 100, and STO is an exit lens located at the rear end of the rigid endoscope optical system 100.

[0051] Similar to the previously described embodiment, the lenses 1 to 3 constituting the first lens group L1 have positive power for lens 1 and negative power for the remaining two as a whole. In addition, one of the lenses 9 to 13 constituting the second lens group L2 is the longest lens among the lenses constituting the rigid mirror optical system 100. In this example of Figure 27, lenses 9 and 11 are the longest (thickest). Furthermore, one or more of the lenses constituting the second lens group L2, the third lens group L3, and the additional lens group La are anomalous dispersion lenses, but in the example of Figure 27, lenses 7, 9, 11, 13, and 17 are anomalous dispersion lenses (S-FPL55).

[0052] Figure 28 is a graph showing the modulation transfer function of the rigid mirror optical system 100 in the example shown in Figure 27, when the incident light illumination is white light uniformly containing wavelengths from 450.0 to 1450.0 nm (visible region to near-infrared region). In the rigid mirror 1 having the rigid mirror optical system 100, a contrast of 0.2 or higher is obtained at a spatial frequency of around 200 (Cycles / mm), and high-contrast images with sufficiently high resolution are obtained over a wide wavelength range from the visible region to the near-infrared region.

[0053] [Fifth Embodiment] Next, a rigid mirror optical system 100 according to the fifth embodiment will be described with reference to Figures 29 to 31. As shown in Figure 29, the rigid mirror optical system 100 of the fifth embodiment is a relay optical system including a plurality of lenses with an effective diameter of 7 mm or less, similar to the embodiments described above. The plurality of lenses include a first lens group L1, a second lens group L2, a third lens group L3, a field diaphragm AP, a fourth lens group L4, a fifth lens group L5, and a sixth lens group L6, similar to the embodiments described above. In addition, this relay optical system includes a seventh lens group La (first additional lens group) between the first lens group L1 and the second lens group L2, and an eighth lens group Lb (second additional lens group) between the fifth lens group L5 and the sixth lens group L6. The seventh lens group La and the eighth lens group Lb are arranged symmetrically with respect to the field diaphragm AP and have the same characteristics.

[0054] The first lens group L1 is located at the very front of the insertion section 10 and receives light from the object to be imaged. The lens group L1 in this fifth embodiment is also composed of so-called doublet lenses. This improves chromatic aberration and spherical aberration. The second lens group L2 is located downstream of the first lens group L1 and the seventh lens group La. The third lens group L3 is located even further downstream than the second lens group L2 and is positioned in front of the field aperture AP. The rigid mirror optical system 100 is configured symmetrically with respect to the field aperture AP. That is, the fourth lens group L4, the fifth lens group L5, the eighth lens group Lb, and the sixth lens group L6 are symmetrical with respect to the third lens group L3, the second lens group L2, the seventh lens group La, and the first lens group L1, respectively, and have similar optical characteristics. Each lens group is formed by arranging multiple lenses, but a pair of symmetrical lens groups can be configured by arranging multiple lenses of the same type symmetrically. Furthermore, the rigid mirror optical system 100 may include additional single lenses at positions between the first to sixth lens groups L1 to L6.

[0055] The first lens group L1 has a positive power in its first lens, which is the most upstream lens, and the lenses downstream of that first lens have a negative power as a whole. The second lens group L2 includes the longest (thickest) lens among the multiple lenses.

[0056] Figure 30 is a table showing the characteristics (radius of curvature of the front surface, thickness, material (glass), semi-diameter, product name, and conicity) of the lenses constituting the first lens group L1 to the third lens group L3 and the seventh lens group La of the rigid mirror optical system 100 that satisfies the above-mentioned conditions 1 and 2 in the fifth embodiment. In the table, numbers 1 to 3 indicate the lenses constituting the first lens group L1. Numbers 5 to 7 indicate the diameter of curvature of the front surface, thickness, material, radius, and conicity of the lenses constituting the seventh lens group La. Numbers 9 to 13 indicate the diameter of curvature of the front surface, thickness, material, radius, and conicity of the lenses constituting the second lens group L2. Numbers 15 to 17 indicate the radius of curvature of the front surface, thickness, material, radius, and conicity of the lenses constituting the third lens group L3. Numbers 4, 8, 14, and 18 are single lenses located before and after the first to third lens groups L1 to L3, OBJ is an objective lens located at the front of the rigid endoscope optical system 100, and STO is an exit lens located at the rear end of the rigid endoscope optical system 100.

[0057] Similar to the previously described embodiment, the lenses 1 to 3 constituting the first lens group L1 have positive power for lens 1 and negative power for the remaining two as a whole. In addition, one of the lenses 9 to 13 constituting the second lens group L2 is the longest lens among the lenses constituting the rigid mirror optical system 100. In the example of Figure 30, lenses 9 and 11 are the longest (thickest). Furthermore, one or more of the lenses constituting the second lens group L2, the third lens group L3, and the additional lens group La are anomalous dispersion lenses, but in the example of Figure 30, lenses 7, 9, 11, 13, and 17 are anomalous dispersion lenses (S-FPL55).

[0058] Figure 31 is a graph showing the modulation transfer function of the rigid mirror optical system 100 in the example shown in Figure 30, when the incident light illumination is white light that uniformly includes wavelengths from 450.0 to 1450.0 nm (visible region to near-infrared region). In the rigid mirror 1 having the rigid mirror optical system 100, a contrast of 0.2 or higher is obtained at a spatial frequency of around 200 (Cycles / mm), and high-contrast images with sufficiently high resolution are obtained over a wide wavelength range from the visible region to the near-infrared region.

[0059] [Sixth Embodiment] Next, a rigid mirror optical system 100 according to the sixth embodiment will be described with reference to Figures 32 to 34. As shown in Figure 32, the rigid mirror optical system 100 of the sixth embodiment is a relay optical system including a plurality of lenses with an effective diameter of 7 mm or less, similar to the embodiments described above. The plurality of lenses include a first lens group L1, a second lens group L2, a third lens group L3, a field diaphragm AP, a fourth lens group L4, a fifth lens group L5, and a sixth lens group L6, similar to the embodiments described above. In addition, this relay optical system includes a seventh lens group La (first additional lens group) between the first lens group L1 and the second lens group L2, and an eighth lens group Lb (second additional lens group) between the fifth lens group L5 and the sixth lens group L6. The seventh lens group La and the eighth lens group Lb are arranged symmetrically with respect to the field diaphragm AP and have the same characteristics.

[0060] The first lens group L1 is located at the very front of the insertion section 10 and receives light from the object to be imaged. The lens group L1 in this sixth embodiment is also composed of so-called doublet lenses. This improves chromatic aberration and spherical aberration. The second lens group L2 is located downstream of the first lens group L1. The third lens group L3 is located even further downstream than the second lens group L2 and is positioned in front of the field aperture AP. The rigid mirror optical system 100 is configured symmetrically with respect to the field aperture AP. That is, the fourth lens group L4, the fifth lens group L5, and the sixth lens group L6 are symmetrical with respect to the third lens group L3, the second lens group L2, and the first lens group L1, respectively, and have similar optical characteristics. Each lens group is formed by arranging multiple lenses, but a pair of symmetrical lens groups can be configured by arranging multiple lenses of the same type symmetrically. Furthermore, the rigid mirror optical system 100 may include additional single lenses at positions between the first to sixth lens groups L1 to L6.

[0061] The first lens group L1 has a positive power in its first lens, which is the most upstream lens, and the lenses downstream of that first lens have a negative power as a whole. The second lens group L2 includes the longest (thickest) lens among the multiple lenses.

[0062] Figure 33 is a table showing the characteristics (radius of curvature of the front surface, thickness, material (glass), semi-diameter, product name, and conicity) of the lenses constituting the first lens group L1 to the third lens group L3 and the seventh lens group La of the rigid mirror optical system 100 that satisfies the above-mentioned conditions 1 and 2 in the sixth embodiment. In the table, numbers 1 to 3 indicate the lenses constituting the first lens group L1. Numbers 5 to 7 indicate the diameter of curvature of the front surface, thickness, material, radius, and conicity of the lenses constituting the seventh lens group La. Numbers 9 to 13 indicate the diameter of curvature of the front surface, thickness, material, radius, and conicity of the lenses constituting the second lens group L2. Numbers 15 to 17 indicate the radius of curvature of the front surface, thickness, material, radius, and conicity of the lenses constituting the third lens group L3. Numbers 4, 8, 14, and 18 are single lenses located before and after the first to third lens groups L1 to L3, OBJ is an objective lens located at the front of the rigid endoscope optical system 100, and STO is an exit lens located at the rear end of the rigid endoscope optical system 100.

[0063] Similar to the previously described embodiment, the lenses 1 to 3 constituting the first lens group L1 have positive power for lens 1 and negative power for the remaining two as a whole. In addition, one of the lenses 9 to 13 constituting the second lens group L2 is the longest lens among the lenses constituting the rigid mirror optical system 100. In the example of Figure 33, lenses 9 and 11 are the longest (thickest). Furthermore, one or more of the lenses constituting the second lens group L2, the third lens group L3, and the additional lens group La are anomalous dispersion lenses, but in the example of Figure 33, lenses 7, 13, and 17 are anomalous dispersion lenses (S-FPL55).

[0064] Figure 34 is a graph showing the modulation transfer function of the rigid mirror optical system 100 of the example in Figure 33 when the incident light wavelength uniformly includes 450.0 to 1450.0 nm (visible region to near-infrared region) under white light illumination. In the rigid mirror 1 having the rigid mirror optical system 100, a contrast of 0.2 or more is obtained at a spatial frequency of around 200 (Cycles / mm), and high-contrast images with sufficiently high resolution are obtained in a wide wavelength range from the visible region to the near-infrared region while suppressing chromatic aberration. [Seventh Embodiment] Next, the rigid mirror optical system 100 according to the seventh embodiment will be described with reference to Figures 35 to 41. As shown in Figure 35, the rigid mirror optical system 100 of the seventh embodiment is a relay optical system including a plurality of lenses with an effective diameter of 7 mm or less, similar to the embodiments described above. The plurality of lenses include a first lens group L1, a second lens group L2, a third lens group L3, a field diaphragm AP, a fourth lens group L4, a fifth lens group L5, and a sixth lens group L6, similar to the embodiments described above. In addition, this relay optical system includes a seventh lens group La between the first lens group L1 and the second lens group L2, and an eighth lens group Lb between the fifth lens group L5 and the sixth lens group L6. The seventh lens group La and the eighth lens group Lb are arranged symmetrically with respect to the field diaphragm AP and have the same characteristics.

[0065] The first lens group L1 is located at the very front of the insertion section 10 and receives light from the object to be imaged. The second lens group L2 is located downstream of the first lens group L1. The third lens group L3 is located further downstream than the second lens group L2 and is positioned in front of the field diaphragm AP. The rigid mirror optical system 100 is configured symmetrically with respect to the field diaphragm AP. That is, the fourth lens group L4, the fifth lens group L5, and the sixth lens group L6 are symmetrical with respect to the third lens group L3, the second lens group L2, and the first lens group L1, respectively, and have similar optical characteristics. Each lens group is formed by arranging multiple lenses, but a pair of symmetrical lens groups can be configured by arranging multiple lenses of the same type symmetrically. The rigid mirror optical system 100 may also include other single lenses at positions between the first to sixth lens groups L1 to L6.

[0066] The first lens group L1 has a positive power in its first lens, which is the most upstream lens, and the lenses downstream of that first lens have a negative power as a whole. The second lens group L2 includes the longest (thickest) lens among the multiple lenses.

[0067] Figure 36 is a table showing the characteristics (radius of curvature of the front surface, thickness, material (glass), semi-diameter, product name, and conicity) of the lenses constituting the first lens group L1 to the third lens group L3 and the seventh lens group La of the rigid mirror optical system 100 that satisfies the above-mentioned conditions 1 and 2 in the seventh embodiment. In the table, numbers 1 to 3 indicate the lenses constituting the first lens group L1. Numbers 5 to 7 indicate the diameter of curvature of the front surface, thickness, material, radius, and conicity of the lenses constituting the seventh lens group La. Numbers 9 to 13 indicate the diameter of curvature of the front surface, thickness, material, radius, and conicity of the lenses constituting the second lens group L2. Numbers 15 to 17 indicate the radius of curvature of the front surface, thickness, material, radius, and conicity of the lenses constituting the third lens group L3. Numbers 4, 8, 14, and 18 are single lenses located before and after the first to third lens groups L1 to L3, OBJ is an objective lens located at the front of the rigid endoscope optical system 100, and STO is an exit lens located at the rear end of the rigid endoscope optical system 100.

[0068] Similar to the previously described embodiment, the lenses 1 to 3 constituting the first lens group L1 have positive power for lens 1 and negative power for the remaining two as a whole. The lens group L1 of this seventh embodiment is also composed of so-called doublet lenses. This improves chromatic aberration and spherical aberration. In addition, one or more of the lenses constituting the second lens group L2, the third lens group L3, and the additional lens group La are anomalous dispersion lenses, but in the example of Figure 36, lenses 7, 13, and 17 are anomalous dispersion lenses (S-FPL55).

[0069] Figure 37 is a graph showing the modulation transfer function of the rigid mirror optical system 100 in the example shown in Figure 36 when the wavelength of the incident light is 450.0 nm (visible region). In the rigid mirror 1 having the rigid mirror optical system 100, a contrast of 0.2 or higher is obtained at a spatial frequency of around 200 (Cycles / mm), and a high-contrast image with high resolution is obtained.

[0070] Figure 38 is a graph showing the modulation transfer function of the rigid mirror optical system 100 in the example shown in Figure 36 when the wavelength of the incident light is 587.6 nm (visible region). In the rigid mirror 1 having the rigid mirror optical system 100, a contrast of 0.2 or higher is obtained at a spatial frequency of around 200 (Cycles / mm), and a high-contrast image with high resolution is obtained.

[0071] Figure 39 is a graph showing the modulation transfer function of the rigid mirror optical system 100 in the example shown in Figure 36 when the wavelength of the incident light is 900.0 nm (near-infrared region). In the rigid mirror 1 having the rigid mirror optical system 100, a contrast of 0.1 or higher is obtained in the near-infrared light region when the spatial frequency is around 200 (Cycles / mm), and a high-contrast image with sufficiently high resolution is obtained for near-infrared observation images.

[0072] Figure 40 is a graph showing the modulation transfer function of the rigid mirror optical system 100 in the example shown in Figure 36 when the wavelength of the incident light is 1450.0 nm (near-infrared region). In the rigid mirror 1 having the rigid mirror optical system 100, a contrast of 0.1 or higher is obtained in the near-infrared light region when the spatial frequency is around 200 (Cycles / mm), and a high-contrast image with sufficiently high resolution is obtained for near-infrared observation images.

[0073] Figure 41 is a graph showing the modulation transfer function of the rigid mirror optical system 100 in the example shown in Figure 36, when the incident light wavelength uniformly includes 450.0 to 1450.0 nm (visible region to near-infrared region) under white light illumination. In the rigid mirror 1 having the rigid mirror optical system 100, a contrast of 0.2 or higher is obtained at a spatial frequency of around 200 (Cycles / mm), and high-contrast images with sufficiently high resolution are obtained over a wide wavelength range from the visible region to the near-infrared region while suppressing chromatic aberration.

[0074] Figure 42 shows the aberration curves of the rigid mirror optical system 100 in the example shown in Figure 36, with curves for each wavelength of illumination light. Axial chromatic aberration is also suppressed to less than 0.02 mm, and images with sufficient resolution and contrast can be obtained even when imaging with white light.

[0075] [Other] The present invention is not limited to the embodiments described above, and includes various modifications. For example, the embodiments described above are described in detail to make the present invention easier to understand, and are not necessarily limited to those having all the configurations described. Furthermore, it is possible to replace parts of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add configurations from other embodiments to the configuration of one embodiment. In addition, it is possible to add, delete, or replace parts of the configuration of each embodiment with other configurations.

[0076] 1…Rigid endoscope 10…Insertion section 20…Gripping section Cm…Camera 30…Light source device 40…Computer 100…Rigid endoscope optical system 200…Light guide L1-L6, La, Lb…Lens group

Claims

1. A rigid mirror optical system comprising a plurality of lenses with an effective diameter of 7 mm or less, wherein the plurality of lenses comprises at least three lens groups, including a first lens group on the incident side, a second lens group located downstream of the first lens group, and a third lens group located in front of the aperture plane, wherein the first lens group has a positive power at the upstreammost first lens and the lenses downstream of the first lens as a whole have a negative power, the second lens group includes the longest lens among the plurality of lenses, and the third lens group comprises one or more lenses with anomalous dispersion.

2. The rigid mirror optical system according to claim 1, wherein the first lens group includes a doublet lens.

3. The rigid mirror optical system according to claim 1, further comprising an additional lens group disposed between the first lens group and the second lens group.

4. The rigid mirror optical system according to claim 3, wherein the second lens group, the third lens group, and the additional lens group each include one or more anomalous dispersion lenses.

5. The rigid mirror optical system according to claim 4, wherein the first lens group includes a doublet lens.

6. A rigid mirror optical system according to any one of claims 1 to 5, wherein when one wavelength in the near-infrared region is denoted as λIR, one wavelength in the 450 nm to 1700 nm range that is not λIR is denoted as λ2, the focal length of the rigid mirror optical system at wavelength λIR is denoted as FIR, and the focal length of the rigid mirror optical system at wavelength λ2 is denoted as F2, the conditions are met: |FIR - F2| < 0.1 and |λIR - λ2| > 100 nm.

7. The rigid mirror optical system according to claim 1, further comprising a fourth lens group located downstream of the aperture surface, a fifth lens group located downstream of the fourth lens group, and a sixth lens group located downstream of the fifth lens group, wherein the first to sixth lens groups are configured to be optically symmetric with respect to the aperture surface.

8. The rigid mirror optical system according to claim 7, wherein the first lens group and the sixth lens group include doublet lenses.

9. The rigid mirror optical system according to claim 7, further comprising a first additional lens group disposed between the first lens group and the second lens group, and a second additional lens group disposed between the fifth lens group and the sixth lens group, wherein the first additional lens group and the second additional lens group are arranged symmetrically with respect to the aperture plane, and the fourth lens group, the fifth lens group, and the sixth lens group are symmetrical with respect to the third lens group, the second lens group, and the first lens group, respectively, with respect to the aperture plane, and have similar optical properties.

10. The rigid mirror optical system according to claim 9, wherein the first lens group and the sixth lens group include doublet lenses.

11. The rigid mirror optical system according to claim 9, wherein the second lens group, the third lens group, the first additional lens group, and the second additional lens group each include one or more anomalous dispersion lenses.

12. The rigid mirror optical system according to claim 11, wherein the first lens group and the sixth lens group include doublet lenses.

13. A rigid mirror optical system according to any one of claims 7 to 12, wherein when one wavelength in the near-infrared region is defined as λIR, and one wavelength between 450 nm and 1700 nm that is not λIR is defined as λ2, the focal length of the rigid mirror optical system at wavelength λIR is defined as FIR, and the focal length of the rigid mirror optical system at wavelength λ2 is defined as F2, the conditions are met: |FIR - F2| < 0.1 and |λIR - λ2| > 100 nm.

Images