Optical system

Abstract

To provide a lens unit for an infrared region that can easily generate a tilt error.SOLUTION: A lens unit (4) is a lens unit used for an infrared region including a wavelength in the 7-14 μm range, and includes: a first lens (1) and a second lens (2). The first lens (1) and / or the second lens (2) have notch parts (1d, 2d) in circumferential parts (1c, 2d). An adhesive (12) introduced in the notch parts (1d, 2d) makes the first lens (1) and the second lens (2) integrated with each other.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a lens unit used in a spectroscopic property measuring device or the like.

Background Art

[0002] Patent Document 1 discloses a near-infrared spectroscopic property measuring device including an objective lens that collimates signal light from a specimen, a phase shifter provided in the collimated light, and an imaging lens that forms an image of the specimen on a detection unit. Patent Document 2 discloses an imaging system including an optical system (objective lens) that collimates light from an object, a plurality of imaging lenses that form an image of a part of the collimated light on a detection unit, and filters provided in the respective imaging lenses, and describes the design of an objective lens in the visible region.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, it is known that in the infrared region on the longer wavelength side than the near-infrared region (for example, wavelength 7 to 14 μm), there is absorption associated with molecular vibrations inherent to substances. Therefore, for further development of spectroscopic measurement technology, development of spectroscopic property measuring devices such as hyperspectral cameras into such an infrared region is also expected. However, in a lens unit in a spectroscopic property measuring device of a finite system where the measurement object is at a short distance, the influence of the deviation of the mounting angle of the lens with respect to the lens barrel member (tilt error) on the optical characteristics is likely to be greater than that in a lens unit in a spectroscopic property measuring device of an infinite system where the subject is at a distance.

[0005] In view of the above problems, an object of the present invention is to provide a lens unit in the infrared region that is less likely to cause tilt errors.

Means for Solving the Problems

[0006] In order to solve the above problems, a lens unit according to an aspect of the present invention is a lens unit used in the infrared region including at least any wavelength within the range of 7 to 14 μm, and includes a first lens and a second lens. The first lens and / or the second lens has a notch at the peripheral portion, and the first lens and the second lens are integrated by an adhesive introduced into the notch.

Effects of the Invention

[0007] According to the lens unit according to an aspect of the present invention, it is easier to suppress the occurrence of tilt errors.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Embodiments for Carrying Out the Invention

[0009] [Embodiment] <Optical system> 1 is a cross-sectional view taken along an optical axis, showing the configuration of the main parts of an optical system 100 to which a lens unit according to an embodiment is applied. The optical system 100 forms an image of an object surface T on an image plane S on which an image sensor (detector) or the like corresponding to a wavelength region of the infrared region (7 μm to 14 μm) can be disposed. In the following, unless otherwise specified, the infrared region refers to the region of wavelengths of 7 μm to 14 μm.

[0010] The optical system 100 includes a first lens unit 4 and a second lens unit 5 according to an embodiment of the present invention, and an aperture 8. The first lens unit 4 is an objective lens that converts light incident from the object plane T side into parallel light. The first lens unit 4 is configured by arranging a first lens 1, a second lens 2, and a third lens 3 in this order from the aperture 8 side toward the object plane T side.

[0011] The second lens unit 5 is an imaging lens that converges parallel light onto the image plane S, and has a configuration similar to that of the first lens unit 4. Specifically, the second lens unit 5 is configured by arranging, in order from the diaphragm 8 side toward the image plane S side, a first lens 1, a second lens 2, and a third lens 3.

[0012] The second lens unit 5 has a similar configuration to the first lens unit 4, and is disposed in the optical system 100 so as to be symmetrical to the first lens unit 4 with respect to the aperture 8. The apertures of each lens unit are located on the parallel light side of the first lens 1. In the optical system 100, the apertures 8 of the lens units are configured to be common to each other.

[0013] The optical system 100 can be applied to a multispectral camera or a hyperspectral camera by, for example, placing a filter or a phase shifter near the position of the aperture 8. Note that the optical system 100 does not necessarily have to include the aperture 8.

[0014] By having a lens unit according to an aspect of the present invention, the optical system 100 is likely to suppress the occurrence of tilt errors. Therefore, it is possible to suppress a decrease in MTF (Modulation Transfer Function) associated with the occurrence of tilt errors, reduce the RMS radius of convergence on the image plane, and also suppress aberrations. In addition, the resolution is good.

[0015] [MTF of the optical system] The MTF in the wavelength range of 7 to 14 μm at a spatial frequency of 41.7 cycles / mm preferably satisfies 0.35 or more within the image circle, and more preferably satisfies 0.40 or more. With this configuration, the resolution on the image plane S becomes good. Note that the spatial frequency of 41.7 cycles / mm corresponds to the Nyquist frequency f of an image sensor with a pixel pitch of 12 μm. N corresponds to.

[0016] <Lens unit> Hereinafter, the lens unit according to an aspect of the present invention will be described. Since the second lens unit 5 has the same configuration as the first lens unit 4, the first lens unit 4 will be described unless otherwise specified. In addition, the first lens unit 4 may be described as the lens unit 4, and the second lens unit 5 may be described as the lens unit 5.

[0017] FIG. 2 is a cross-sectional view along the optical axis showing the configuration of the main part of the lens unit according to the embodiment. FIG. 3 is a cross-sectional view showing a state in which the lens unit according to the embodiment is housed and fixed in a lens barrel. FIG. 4 is a front view showing the lens unit according to the embodiment. The lens unit 4 includes a first lens 1, a second lens 2, a third lens 3, a lens barrel 6, a first ring portion 65, and a second ring portion 66. The first lens 1 and the second lens 2 are integrated by an adhesive 12.

[0018] The lens barrel 6 includes a first hole 61, a second hole 62, and a third hole 63. The first hole 61 is connected to the second hole 62 and has a larger diameter than the second hole 62. The second hole 62 is connected to the third hole 63 and has a larger diameter than the third hole 63. The third hole 63 has an edge portion 63a protruding with respect to the axis on the opening side.

[0019] The third lens 3 is fitted into the third hole 63. The second lens 2 and the first lens 1 are fitted into the second hole 62 with a second ring portion 66 interposed therebetween and the third lens 3. A first ring portion 65 that presses the first lens 1 is fitted into the first hole 61. Each of the ring portions 65 and 66 positions each lens at a required position in the lens barrel 6 or fixes it at a required position on the optical axis of the lens barrel 6. Specifically, the first ring portion 65 presses the peripheral edge portion (the first surface 1a) of the first lens 1 that does not contact the second lens 2.

[0020] Each lens is fixed in a state where the peripheral edge portions 1c, 2c, and 3c are in contact with at least one of the lens barrel 6 and / or the ring portions 65 and 66. The peripheral edge portions 1c, 2c, and 3c are regions including flange portions (flange parts), and include the first surfaces 1a, 2a, 3a, the second surfaces 1b, 2b, 3b, and the lens end faces. The peripheral edge portions 1c, 2c, and 3c may include a part of the optical surface. In the present embodiment, the third lens 3 is fixed in a state where the second surface 3b is locked to the edge portion 63a of the lens barrel 6 and the first surface 3a is in contact with the second ring portion 66. The second lens 2 is fixed in a state where the second surface 2b is in contact with the second ring portion 66 and the first surface 2a is in contact with the second surface 1b of the first lens 1. The first lens 1 is fixed in a state where the second surface 1b is in contact with the first surface 2a of the second lens 2 and the first surface 1a is pressed by the first ring portion 65. That is, each lens of the lens unit 4 is accommodated and fixed in the lens barrel 6 by being pressed by the first ring portion 65 from the first lens 1 side.

[0021] The first surface and the second surface are, for example, regions within 10 mm, within 8 mm, within 5 mm, within 3 mm, within 2 mm from the end face (side face) of the lens. The lower limit is, for example, 0.5 mm or more, 1 mm or more.

[0022] [Material of the lens barrel] It is preferable to use an aluminum alloy, such as A5052 or A5056, as the material of the lens barrel 6. Further, such an aluminum alloy may be satin-finished (roughened). Furthermore, it may be used in a state of being black anodized. The material of the lens barrel 6 is not limited to an aluminum alloy, and for example, it may be made of SUS304 (austenitic stainless steel) and may have black trivalent chromium plating on the surface layer.

[0023] [Notch portion] As shown in the enlarged view of Fig. 3, the first lens 1 and the second lens 2 have notch portions 1d and 2d. Specifically, the first lens 1 has a notch portion 1d on the second surface 1b side. The second lens 2 has a notch portion 2d on the first surface 2a side. The notch portion 1d is formed at the corner of the second surface 1b, and the notch portion 2d is formed at the corner of the first surface 2a. The notch portions 1d and 2d are inclined surfaces that form a predetermined angle (for example, about 45°) with respect to the optical axis. That is, the notch portions 1d and 2d are formed by chamfering. Note that by appropriately adjusting the above angle, the depth and width of the notch portions 1d and 2d can be adjusted.

[0024] The notch portion may be formed in either one of the first lens 1 and the second lens 2, or may be formed in both the first lens 1 and the second lens 2.

[0025] It is preferable that the notch portions 1d and 2d are formed over the entire circumference of the corners of the second surface 1b and the first surface 2a. This makes it easier to firmly integrate the first lens 1 and the second lens 2. The notch portions 1d and 2d may be formed intermittently along the circumferential direction of the corners of the second surface 1b and the first surface 2a.

[0026] The notches 1d and 2d preferably have a width in the lens diameter direction of 1 mm to 5 mm and 2 mm to 4 mm. In this case, the portion of the second surface 1b where the notch 1d is not formed (the lens surface on the second surface 1b side) and the portion of the first surface 2a where the notch 2d is not formed (the lens surface on the first surface 2a side) can be made to abut well, and it becomes difficult for the second lens 2 to be integrated with the first lens 1 in an inclined state.

[0027] The notches 1d and 2d preferably have a width in the lens optical axis direction of 1 mm to 5 mm and 2 mm to 4 mm. In this case, the portion of the lens end face where the notches 1d and 2d are not formed can be made to abut well with the lens barrel 6, and it becomes easier to suppress the occurrence of tilt error when attaching the lens to the lens barrel 6.

[0028] [Integration of lenses] The first lens 1 and the second lens 2 are integrated by the adhesive 12 introduced into the notches 1d and 2d. In other words, they are integrated by the adhesive 12 introduced into the space (void 20) formed by the notches 1d and 2d. With the above configuration, the intrusion of impurities between the lenses can be suppressed.

[0029] As the adhesive 12, an adhesive commonly used for adhesive applications can be used. For example, when classified by focusing on the curing method of the adhesive, an ultraviolet curable type, a heat curable type, a solvent volatilization type, an anaerobic curable type, a hardener mixed type, and a combination type thereof can be used. From the perspective of versatility, it is preferable to use an ultraviolet curable type and a heat curable type.

[0030] It is preferable that no adhesive 12 is introduced between the surfaces of the first lens 1 and the second lens 2 that face each other in the optical axis direction except for the notches 1d and 2d. That is, it is preferable that the portion where the notch 1d is not formed and the portion where the notch 2d is not formed are in direct contact. Thereby, it becomes difficult for the second lens 2 to be integrated with the first lens 1 in an inclined state.

[0031] When the lens is viewed from the end face direction, it is preferable that the area of the adhesive 12 introduced into the cutout portions 1d and 2d is 10% or more and 100% or less, 10% or more and 90% or less with respect to the areas of the cutout portions 1d and 2d. Thereby, it becomes difficult for the adhesive 12 to protrude from the cutout portions 1d and 2d, and it becomes easy to suppress the occurrence of tilt errors caused by the adhesive 12.

[0032] It is preferable that the volume of the adhesive 12 introduced into the cutout portions 1d and 2d is 10% or more and 100% or less, 10% or more and 90% or less with respect to the volumes of the cutout portions 1d and 2d. In other words, it is preferable that the volume of the adhesive 12 introduced into the space (gap 20) formed by the cutout portions 1d and 2d is 10% or more and 100% or less, 10% or more and 90% or less with respect to the volume of the gap 20. Thereby, it is possible to suppress the adhesive 12 from protruding from the gap 20, and it becomes easy to suppress the occurrence of tilt errors caused by the adhesive 12. It is preferable that the adhesive 12 is in contact with the cutout portions 1d and 2d and is not in contact with the lens barrel 6. Thereby, it becomes easy to suppress the occurrence of tilt errors when the lens is attached to the lens barrel 6.

[0033] [Optical axis thickness and interval of the lens] In the present embodiment, the effective diameter of the first lens 1 is larger than the effective diameter of the third lens 3. Also, the optical axis thickness t3 of the third lens 3 is larger than the optical axis thickness of either the first lens 1 or the second lens 2. With these configurations, when the lens unit 4 is used as an imaging lens, the resolution is good.

[0034] It is preferable that the optical axis thickness t3 of the third lens 3 is 0.5 times to 2 times the second distance d2, which is the distance on the optical axis between the second lens 2 and the third lens 3 (the surface-to-surface distance between the opposing surfaces). In this case, the MTF in the tangential direction and the sagittal direction at the spatial frequency of 41.7 cycles / mm of the optical system 100 becomes high.

[0035] That is, the lens unit 4 has a good resolution corresponding to an infrared image sensor having a pixel pitch on the order of the wavelength. The high MTF at the spatial frequency described above means having a good resolution corresponding to an image sensor with a narrow pitch on the order of the wavelength.

[0036] The first distance d1, which is the distance on the optical axis between the first lens 1 and the second lens 2, is preferably smaller than the second distance d2. In this case, the NA (numerical aperture) on the image side becomes larger, and the RMS radius of convergence on the image plane can be reduced.

[0037] The ratio of the second distance d2 to the first distance d1 is preferably 9 or less.

[0038] [Material of the lens] Examples of the lens material include germanium (Ge), silicon (Si), chalcogenide glass, zinc selenide (ZnSe), zinc sulfide (ZnS), etc. The chalcogenide glass preferably contains 20 to 90% of tellurium (Te) in mol%, and at least one of 0 to 50% of germanium (Ge) or 0 to 50% of gallium (Ga). Note that the content of Te is preferably 30 to 88%, 40 to 84%, 50 to 82%, particularly 60 to 80%. Such chalcogenide glass has extremely low light absorption over a wide wavelength range in the infrared region, such as a wavelength of 7 to 14 μm, and the internal transmittance tends to be good, at least in the above wavelength range. The internal transmittance refers to the transmittance inside the material and does not include the reflection loss at the material surface. Specifically, as the internal transmittance at a thickness of 2 mm, it can achieve 90% or more, particularly 95% or more, at a wavelength of 10 μm. Such chalcogenide glass was developed by the applicant (see International Publication WO2020 / 105719A1).

[0039] The chalcogenide glass preferably has an Abbe number of 100 or more, 150 or more, particularly 200 or more, at a wavelength of 10 μm. The Abbe number (ν10) is calculated by the following formula. Thereby, chromatic aberration can be suppressed. ν10 = (Refractive index at wavelength 10 μm - 1) / (Refractive index at wavelength 8 μm - Refractive index at wavelength 12 μm)

[0040] The refractive index of the chalcogenide glass at a wavelength of 10 μm is preferably 2.5 to 4.0, 2.74 to 3.92, 2.8 to 3.8, and particularly preferably 2.9 to 3.7. A low refractive index requires a smaller radius of curvature for the lens than a material with a high refractive index, which increases the difficulty of lens processing. In addition, the thickness in the optical axis direction may increase, which may impair optical freedom.

[0041] It is preferable that the chalcogenide glass does not contain toxic substances such as As, Se, Tl, etc. This reduces the environmental impact.

[0042] The third lens 3 is preferably made of a material whose internal transmittance at a wavelength of 10 μm is equal to or higher than that of the material making up the second lens 2 and equal to or higher than that of the material making up the first lens 1. This configuration improves the resolution of the image formed by the optical system 100. For example, the internal transmittance of the material making up the third lens 3 at a thickness of 2 mm at a wavelength of 10 μm is preferably 90% or higher, and particularly 95% or higher. For example, the third lens 3 is preferably made of the chalcogenide glass described above.

[0043] The third lens 3 is preferably made of chalcogenide glass having a refractive index of 2.5 to 4.0 at a wavelength of 10 μm. With the above configuration, the resolution of the image formed by the optical system 100 is improved.

[0044] The second lens 2 is preferably made of chalcogenide glass having a refractive index of 2.5 to 4.0 at a wavelength of 10 μm. With the above configuration, the resolution of the image formed by the optical system 100 becomes better.

[0045] The first lens 1 is preferably made of germanium, which improves the durability and hardness of the first lens 1.

[0046] [Shape of the lens] It is preferable that each lens of the lens unit 4 has the following configuration. The first lens 1 preferably has a positive power and preferably has a concave meniscus shape on the side of the second lens 2. The second lens 2 preferably has a negative power. The third lens 3 preferably has a positive power and preferably has a convex meniscus shape on the side of the second lens 2. With these configurations, the lens unit can be made compact.

[0047] [Coating film] It is preferable that at least one of the surfaces of the first lens 1 and the second lens 2 has a coating film, and it is more preferable that each lens surface including the third lens has a coating film. The coating film is formed for the purpose of reducing reflection on the lens surface to improve transmittance, protecting the lens surface, etc. The coating film preferably consists of at least one selected from germanium (Ge), silicon (Si), fluoride, zinc selenide (ZnSe), zinc sulfide (ZnS), and diamond-like carbon. For example, it is more preferable that the first lens 1 has a coating film and the coating film contains diamond-like carbon. In this case, the durability and hardness of the first lens 1 are improved. Note that a lens without a coating film may be included.

[0048] It is preferable that the peripheral portions 1c, 2c, 3c have a region (non-adhesion region) where no coating film is adhered to at least a part of the barrel 6 and / or each ring portion that is in contact. For example, it is preferable to have a non-adhesion region on at least one of the first surfaces 1a, 3a and the second surfaces 2b, 3b.

[0049] If there are film formation misalignments, film thickness unevenness, film bleeding, etc. in the coating film on the lens, when the lens is housed and fixed in the lens barrel 6, the lens may tilt with respect to the lens barrel 6. When such tilting occurs, there is a risk of tilt error caused by the coating film. Therefore, by adopting a configuration in which the non-adhesive region is in direct contact with the lens barrel 6 and / or the ring portion, it is possible to suppress the tilting of the lens caused by the coating film.

[0050] It is preferable that the non-adhesive region is provided in a portion where the notch portion 1d of the second surface 1b is not formed and a portion where the notch portion 2d of the first surface 2a is not formed. This makes it difficult to integrate the second lens 2 with the first lens 1 in a tilted state.

[0051] It is preferable that the non-adhesive region is provided at the peripheral edge of the lens surface in contact with (locked to) the lens barrel 6. In the present embodiment, the peripheral edge of the lens surface locked to the lens barrel 6 is the second surface 3b. This makes it easier to suppress the occurrence of tilt error.

[0052] It is particularly preferable that the non-adhesive region is provided on each of the first surfaces 1a, 2a, 3a and the second surfaces 1b, 2b, 3b. In this case, it becomes easier to effectively suppress the occurrence of tilt error.

[0053] The thickness of the coating film is preferably 1 μm or more. Since the larger the thickness of the coating film, the easier it is for tilt error to occur, the above configuration can effectively suppress the occurrence of tilt error. The upper limit of the thickness of the coating film is preferably 5 μm or less.

[0054] The flange portion of the lens preferably has a width in the lens diameter direction of 2 mm or more, and more preferably 5 mm or more. According to the above configuration, it becomes easier to fix the lens to the lens barrel 6 and / or the ring portion, and it is easier to suppress the occurrence of tilt error. The upper limit can be, for example, 10 mm or less, 9 mm or less.

[0055] The outer diameter of the lens is preferably 10 mm or more and 100 mm or less. Since the influence of tilt error on optical characteristics is likely to increase for a lens with such an outer diameter, it is easier to enjoy the effects of the present invention. For a lens with an outer diameter of less than 10 mm, it becomes difficult to secure a non-adhesion area while ensuring the optical effective diameter. For a lens with an outer diameter of more than 100 mm, the tilt error suppression effect due to the non-adhesion area becomes small.

[0056] It is preferable that a non-adhesion area is formed over the entire circumference of the peripheral edge. Here, "a non-adhesion area is formed over the entire circumference of the peripheral edge" means having a continuous non-adhesion area in the circumferential direction of the peripheral edge. According to the above configuration, the occurrence of tilt error during lens attachment is effectively suppressed.

[0057] It is preferable that an area of 1 mm or more, more preferably 1.5 mm or more, in the radial direction from the end face (side face) of the lens is a non-adhesion area. By having a non-adhesion area in the above-mentioned area, the occurrence of tilt error is effectively suppressed.

[0058] [Aperture] The first lens 1 may have an aperture 8 (see FIG. 1) on the side opposite to the second lens 2 in the optical axis direction. Also, the ratio of the diameter of the image of the aperture 8 to the effective diameter of the image is preferably 3 to 4.5. With this configuration, when the lens unit 4 is an imaging lens (the first lens unit 4), the NA on the image side increases. Also, when the lens unit 4 is an objective lens (the second lens unit 5), the NA on the object surface side increases.

[0059] [Shape of the lens surface] Of the opposing surfaces of the first lens 1 and the second lens 2, at least one surface may be a diffractive surface. Specifically, at least one of the optical surfaces on the second surface 1b side and the optical surfaces on the first surface 2a side may be a diffractive surface. Since the first lens 1 and the second lens 2 are integrated, even if the opposing optical surfaces on the inner side are diffractive surfaces, breakage and contamination of the diffractive surfaces do not occur, and aberrations are also suppressed. In addition, it is possible to provide a lens unit in which chromatic aberration is less likely to occur. The step of the unevenness of the diffractive surface can be appropriately designed according to the wavelength of the diffracted light. For example, when diffracting light in the infrared region, the step of the unevenness is preferably 1 μm to 10 μm, 2 μm to 9 μm. In this case, it becomes easier to suppress chromatic aberration.

[0060] The optical surface on the second surface 3b side of the third lens 3 may be an aspherical surface. Since the second surface 3b side is usually arranged at a position where displacement is unlikely to occur, even if it is an aspherical surface, tilt error is unlikely to occur when attaching the lens to the lens barrel 6. In this case, since the second surface b has a non-adhesion region, tilt error is less likely to occur.

[0061] [NA] When the lens unit 4 is an imaging lens, the NA on the image side preferably satisfies 0.35 or more. Since the NA on the image side is directly related to the resolution, the resolution of the optical system 100 is improved.

[0062] <Modification Example 1 of the Lens Unit> Hereinafter, the lens unit 13 of Modification Example 1 will be described. FIG. 5 is a cross-sectional view showing a state in which the lens unit 13 of Modification Example 1 is housed and fixed in a lens barrel 7. The lens unit 13 includes a first lens 1, a second lens 2, a third lens 3, a lens barrel 7, a first ring portion 75, and a second ring portion 76.

[0063] The lens barrel 7 is provided with a first hole 71, a second hole 72, a third hole 73, and a fourth hole 74. The first hole 71 is continuous with the second hole 72 and has a larger diameter than the second hole 72. The first hole 71 has a locking portion 71a. The second hole 72 is a tapered hole connecting the first hole 71 and the third hole 73. The third hole 73 is continuous with the fourth hole 74 and has a smaller diameter than the fourth hole 74. The third hole 73 has a locking portion 73a.

[0064] A second ring portion 76 is fitted into the fourth hole 74. A third lens 3 is fitted into the third hole 73. In the first hole 71, a second lens 2, a first lens 1, and a first ring portion 75 are fitted in order from the side of the third lens 3. Each of the ring portions 75 and 76 positions each lens at a required position in the lens barrel 7 or fixes it at a required position on the optical axis of the lens barrel 7. Specifically, the first ring portion 75 presses the peripheral edge portion (the first surface 1a) of the first lens 1 that does not contact the second lens 2. The second ring portion 76 presses the peripheral edge portion (the second surface 3b) of the third lens 3 that does not contact the lens barrel 7.

[0065] Each lens is fixed in a state where the peripheral edge portions 1c, 2c, and 3c are in contact with at least one of the lens barrel 7 and / or the ring portions 75 and 76. In this modified example, the third lens 3 is fixed in a state where the second surface 3b is pressed by the second ring portion 76 and the first surface 3a is locked by the locking portion 73a. The second lens 2 is fixed in a state where the second surface 2b is locked by the locking portion 71a and the first surface 2a is in contact with the first lens 1. The first lens 1 is fixed in a state where the second surface 1b is in contact with the second lens 2 and the first surface 1a is pressed by the first ring portion 75. That is, each lens of the lens unit 13 is accommodated and fixed in the lens barrel 7 by being pressed by the first ring portion 75 from the side of the first lens 1 and by being pressed by the second ring portion 76 from the side of the third lens 3.

[0066] As shown in the enlarged view of FIG. 5, the first lens 1 has a notch 1d on the second surface 1b, and the second lens 2 has a notch 2d on the first surface 2a. The notches 1d and 2d are formed at the corners of the second surface 1b and the first surface 2a, and are inclined surfaces forming a predetermined angle (for example, about 45°) with respect to the optical axis. That is, the notches 1d and 2d are formed by chamfering. Note that by appropriately adjusting the above angle, the depth and width of the notches 1d and 2d can be adjusted.

[0067] It is preferable that the notches 1d and 2d are formed over the entire circumference of the corners of the second surface 1b and the first surface 2a. This makes it easier to firmly integrate the first lens 1 and the second lens 2. The notches 1d and 2d may be formed intermittently along the circumferential direction of the corners of the second surface 1b and the first surface 2a.

[0068] It is preferable that the notches 1d and 2d have a width in the lens diameter direction of 1 mm to 5 mm, preferably 2 to 4 mm. In this case, when assembling, the portion where the notch 1d on the second surface 1b is not formed and the portion where the notch 2d on the first surface 2a is not formed can be brought into good contact, and it becomes difficult to integrate the second lens 2 with respect to the first lens 1 in an inclined state.

[0069] Also in this modified example, it is preferable that a coating film is formed on the surface of each lens, and it is preferable that there is a non-adhesion region at the peripheral edge of the lens. By such a non-adhesion region coming into direct contact with the lens barrel 7 and / or the ring portion, the inclination of the lens due to the coating film can be suppressed. That is, according to this modified example, it becomes easy to suppress the occurrence of tilt error due to the coating film.

[0070] It is preferable that a non-adhesion region is formed at least in a portion in contact with at least one of the lens barrel 7 and / or each ring portion. For example, it is preferable to have a non-adhesion region on at least one of the first surfaces 1a and 3a and the second surfaces 2b and 3b.

[0071] For example, if there are problems such as film formation deviation, film thickness unevenness, and film bleeding in the coating film on the lens, when the lens is accommodated and fixed in the lens barrel 7, the lens may tilt with respect to the lens barrel 7. When such tilting occurs, there is a risk of tilt error caused by the coating film. Therefore, by directly contacting the non-adhesive region with the lens barrel 7 and / or the ring portion, it is possible to suppress the tilting of the lens caused by the coating film.

[0072] It is preferable that the non-adhesive region is provided in a portion where the notch portion 1d of the second surface 1b is not formed and a portion where the notch portion 2d of the first surface 2a is not formed. This makes it difficult to integrate the second lens 2 with the first lens 1 in a tilted state.

[0073] It is preferable that the non-adhesive region is provided at the peripheral edge of the lens surface in contact with (locked to) the lens barrel 7. In the present embodiment, the peripheral edges of the lens surfaces locked to the lens barrel 7 are the second surface 2b and the first surface 3a. This makes it easier to suppress the occurrence of tilt error.

[0074] At least one of the opposing surfaces of the first lens 1 and the second lens 2 may be a diffractive surface. In this case, it is possible to provide a lens unit in which chromatic aberration is less likely to occur.

[0075] <Modified Example 2 of Lens Unit> Hereinafter, the lens unit 14 of the modified example 2 will be described. FIG. 6 is a cross-sectional view showing a state in which the lens unit 14 of the modified example 2 is accommodated and fixed in the lens barrel 7. In FIG. 6, the same parts as those in FIG. 5 are denoted by the same reference numerals and detailed description thereof is omitted.

[0076] As shown in the enlarged view of FIG. 6, the first lens 1 has a groove portion 1e as a notch portion that extends in the optical axis direction at a position slightly on the optical axis side from the end face of the second surface 1b. The second lens 2 has a groove portion 2e that extends in the optical axis direction at a position slightly on the optical axis side from the end face of the first surface 2a. The first lens 1 and the second lens 2 are integrated by an adhesive 12 introduced into a space (gap 21) formed by aligning the openings of the groove portions 1e and 2e.

[0077] The groove portions 1e and 2e are preferably formed over the entire circumferences of the second surface 1b and the first surface 2a. The groove portions 1e and 2e may be formed intermittently along the circumferential direction of the second surface 1b and the first surface 2a.

[0078] The groove portions 1e and 2e have a width in the lens diameter direction of 0.5 mm to 5 mm, more preferably 0.5 mm to 3 mm. In this case, the first lens 1 and the second lens 2 can be adhered well, and the portion of the second surface 1b where the groove portion 1e is not formed and the portion of the first surface 2a where the groove portion 2e is not formed can be brought into good contact, making it difficult for the second lens 2 to be integrated with the first lens 1 in an inclined state. The groove portions are not limited to having one each at the peripheral edge portion 1c and the peripheral edge portion 2c, and may have a plurality. Also, a groove portion may be provided on either one of the peripheral edge portion 1c and the peripheral edge portion 2c.

[0079] <Spectral characteristic device> FIG. 7 is a cross-sectional view showing a spectral characteristic measuring device 200 to which the lens unit according to the embodiment is applied. The spectral characteristic measuring device 200 includes a lens unit 4, a lens unit 5, a sample support plate 10, a detection unit 11, and a phase shifter 9. The configurations of the lens unit 4 and the lens unit 5 of the spectral characteristic measuring device 200 are the same as the configurations of the lens unit 4 and the lens unit 5 of the optical system 100.

[0080] In the spectroscopic characteristic measurement apparatus 200, the third lens 3 of the lens unit 4 faces the sample support plate 10, and the third lens 3 of the lens unit 5 faces the detection unit 11 and is arranged. A phase shifter 9 is arranged between the lens unit 4 and the lens unit 5. The optical axis of the lens unit 4 and the optical axis of the lens unit 5 are orthogonal at the phase shifter 9. In the spectroscopic characteristic measurement apparatus 200, the optical axis is bent vertically by the reflection-type phase shifter 9, but the basic optical configuration is the same as that of the above-described transmission-type optical system 100. The phase shifter 9 is arranged near the position of the aperture 8 of the optical system 100. That is, the lens unit 4 and the lens unit 5 are arranged symmetrically with the phase shifter 9 as the center.

[0081] In the present embodiment, the spectroscopic characteristic measurement apparatus 200 uses a reflection-type phase shifter 9. The phase shifter 9 includes a fixed mirror unit 91, a movable mirror unit 92, and a drive unit 93. The fixed mirror unit 91 and the movable mirror unit 92 are arranged so as to be aligned in a direction (x-axis direction) perpendicular to the plane of FIG. 6, with the movable mirror unit 92 on the back side in the x-axis direction with respect to the fixed mirror unit 91. The fixed mirror unit 91 and the movable mirror unit 92 are arranged so as to be inclined by α degrees (about 45 degrees) with respect to the optical axis of the lens unit 4. The fixed mirror unit 91 and the movable mirror unit 92 are arranged so as to be inclined by β degrees (about 45 degrees) with respect to the optical axis of the lens unit 5. The movable mirror unit 92 is configured to be movable in a direction perpendicular to the surface of the movable mirror unit 92. Thereby, a phase difference occurs between the first light beam reflected by the fixed mirror unit 91 and the second light beam reflected by the movable mirror unit 92. Note that the phase shifter 9 is not limited to the reflection type, and a transmission-type phase shifter may be used.

[0082] With a sample (not shown) supported on the sample support plate 10, infrared light is irradiated from a light source (not shown) toward the sample. The infrared light is scattered by various components of the sample, and the scattered light enters the third lens 3 of the lens unit 4. The scattered light becomes a parallel light beam by the lens unit 4 and reaches the fixed mirror portion 91 and the movable mirror portion 92 of the phase shifter 9. A part of the light is reflected by the fixed mirror portion 91 as the first light beam, and the remaining light is reflected by the movable mirror portion 92 as the second light beam, and each enters the first lens 1 of the lens unit 5. The first light beam and the second light beam incident on the lens unit 5 are imaged on the light receiving surface of the detection unit 11, and an interferogram (change in imaging intensity (change in interference light intensity)) is formed.

[0083] By moving the movable mirror portion 92 to impart a phase difference to the first light beam and the second light beam, a waveform of the interferogram can be obtained. By performing a Fourier transform on the interferogram, the spectral characteristics of the sample can be obtained. Since the spectroscopic characteristic measuring device 200 includes the lens unit according to one aspect of the present invention, tilt errors during lens attachment can be suppressed, the resolution of the image formed on the detection unit 11 becomes good, and the spectral characteristics of the sample can be acquired.

[0084] <Summary> Aspect 1 of the present invention is a lens unit used in the infrared region including at least any wavelength within the range of 7 to 14 μm, comprising a first lens and a second lens, having a notch portion at the peripheral portion of the first lens and / or the second lens, and the first lens and the second lens are integrated by an adhesive introduced into the notch portion. According to the above configuration, since the first lens and the second lens are integrated, the entry of impurities between the lenses can be suppressed. Further, by introducing the adhesive into the notch portion at the peripheral portion of the lens, the entry of the adhesive between the lens surfaces can be suppressed, and tilt errors caused by the adhesive can be suppressed.

[0085] Aspect 2 of the present invention is such that at least one of the opposing surfaces of the first lens and the second lens is a diffractive surface. Since the first lens and the second lens are integrated, even if the opposing surfaces have diffractive surfaces, breakage and contamination of the diffractive surfaces do not occur, and chromatic aberration can be reduced.

[0086] Aspect 3 of the present invention is such that the notch is formed at a corner of the peripheral portion and is an inclined surface forming a predetermined angle with respect to the optical axis. According to the above configuration, the adhesive can be introduced into the notch sufficiently without overflowing.

[0087] Aspect 4 of the present invention is such that the width of the notch in the lens diameter direction is 1 mm to 5 mm. According to the above configuration, the portions of the peripheral portions of the first lens and the second lens where no notches are formed can be brought into good contact with each other, and it becomes difficult to integrate the second lens with respect to the first lens in a tilted state.

[0088] Aspect 5 of the present invention is such that the notch is a groove portion formed in the peripheral portion. According to the above configuration, the adhesive is introduced into the notch without overflowing.

[0089] Aspect 6 of the present invention is such that the volume of the adhesive introduced into the notch is 50% or more and 100% or less of the volume of the notch. According to the above configuration, the occurrence of tilt error due to the overflow of the adhesive can be suppressed.

[0090] Aspect 7 of the present invention is such that no adhesive is introduced between the surfaces facing each other in the optical axis direction, excluding the notches of the first lens and the second lens. According to the above configuration, the occurrence of tilt error is suppressed.

[0091] Aspect 8 of the present invention is such that at least one of the first lens and the second lens has a coating film. According to the above configuration, reflection on the surface of the lens is reduced and the surface is protected.

[0092] Aspect 9 of the present invention is that the first lens has the coating film, and the coating film contains diamond-like carbon. According to the above configuration, the durability and hardness are good.

[0093] Aspect 10 of the present invention is that the first lens is made of germanium. According to the above configuration, the durability and hardness are good.

[0094] Aspect 11 of the present invention further includes a lens barrel and a third lens, and the first lens, the second lens, and the third lens are accommodated and fixed in the lens barrel. The effective diameter of the first lens is larger than the effective diameter of the third lens, and the optical axis thickness of the third lens is larger than the optical axis thickness of any of the first lens and the second lens. According to the above configuration, tilt errors during lens mounting can be suppressed. Therefore, when the lens unit is applied to a spectroscopic property measuring device, the resolution of the image formed on the detection unit is good, and it becomes easier to acquire the spectroscopic properties of the sample.

[0095] Aspect 12 of the present invention is that the optical axis thickness of the third lens is 0.5 times to 2 times the second distance, which is the distance on the optical axis between the second lens and the third lens. According to the above configuration, the NA on the image side can be increased, and the condensing RMS radius can be reduced. Also, chromatic aberration can be reduced.

[0096] Aspect 13 of the present invention is that the first distance, which is the distance on the optical axis between the first lens and the second lens, is smaller than the second distance, which is the distance on the optical axis between the second lens and the third lens. According to the above configuration, the NA on the image side can be increased, and the condensing RMS radius can be reduced.

[0097] Aspect 14 of the present invention is such that the lens barrel has a first hole, a second hole, and a third hole. The third hole has a third lens fitted therein. The second hole is connected to the third hole and has a larger diameter than the third hole. The second lens and the first lens are fitted therein with a second ring portion interposed therebetween and the third lens. The first hole is connected to the second hole and has a larger diameter than the second hole. A first ring portion that presses the first lens is fitted therein. According to the above configuration, the lens unit is compactly accommodated.

[0098] Aspect 15 of the present invention is such that at least one of a portion of the third lens in contact with the lens barrel and / or the first ring portion, a portion of the second lens in contact with the first ring portion, and a portion of the first lens in contact with the second ring portion has a region where a coating film is not attached. According to the above configuration, the occurrence of tilt errors due to the coating film is suppressed during attachment.

[0099] Aspect 16 of the present invention is such that the lens barrel has a first hole, a second hole, a third hole, and a fourth hole. The first hole and the third hole have locking portions for locking the peripheral edge portions of the lenses. The fourth hole is connected to the third hole and has a larger diameter than the third hole. A second ring portion that presses the third lens is fitted therein. The third hole connects the fourth hole and the second hole. The third lens is fitted in a state of being locked to the locking portion. The second hole connects the third hole and the first hole. The first hole is connected to the second hole and has a larger diameter than the second hole. From the second hole side, the second lens, the first lens, and the first ring portion are sequentially fitted therein. According to the above configuration, the lens unit is compactly accommodated.

[0100] Aspect 17 of the present invention is such that at least one of a portion of the third lens in contact with the second ring portion and / or the locking portion, a portion of the second lens in contact with the locking portion, and a portion of the first lens in contact with the first ring portion has a region where a coating film is not attached. According to the above configuration, the occurrence of tilt errors due to the coating film is suppressed during attachment.

[0101] In Embodiment 18 of the present invention, the third lens is made of chalcogenide glass having a refractive index of 2.5 to 4.0 at a wavelength of 10 μm. According to the above configuration, the transmittance of the third lens is high.

[0102] In Embodiment 19 of the present invention, the second lens is made of chalcogenide glass having a refractive index of 2.5 to 4.0 at a wavelength of 10 μm. According to the above configuration, the transmittance of the second lens is high.

[0103] In Embodiment 20 of the present invention, the chalcogenide glass contains 20% to 80% of Te in mol%.

[0104] 〔Supplementary Notes〕 The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope shown in the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention.

Explanation of Reference Numerals

[0105] 1 First lens 2 Second lens 3 Third lens 1a, 2a, 3a First surface 1b, 2b, 3b Second surface 1c, 2c, 3c Peripheral portion 1d, 2d Notch portion 1e, 2e Groove portion 4 First lens unit 5 Second lens unit 13, 14 Lens unit 6, 7 Lens barrel 61, 71 First hole 62, 72 Second hole 63, 73 Third hole 74 Fourth hole 63a Edge 65, 75 First ring portion 66, 76 Second ring portion 71a, 73a Locking portion 8 Diaphragm 9 Phase Shifter 91 Fixed Mirror Unit 92 Movable Mirror Unit 93 Driving Unit 10 Sample Support Plate 11 Detection Unit 12 Adhesive 20, 21 Clearance 100 Optical System 200 Spectral Characteristic Measuring Device S Image Plane T Object Plane t3 Optical Axis Thickness d1 First Distance d2 Second Distance

Claims

1. An optical system used in the infrared region including at least any wavelength within the range of 7 to 14 μm, comprising two lens units arranged symmetrically about the aperture, each of said lens units comprising a first lens, a second lens, and a third lens, and a lens barrel, wherein the first lens, the second lens, and the third lens are accommodated and fixed in the lens barrel in this order from the aperture side, the effective diameter of the first lens is larger than the effective diameter of the third lens, the optical axis thickness of the third lens is larger than the optical axis thickness of either the first lens or the second lens, the peripheral portion of the first lens and / or the second lens has a notch, and the first lens and the second lens are integrated by an adhesive introduced into the notch, an optical system.

2. The optical system according to claim 1, wherein at least one of the opposing surfaces of the first lens and the second lens is a diffractive surface.

3. The optical system according to claim 1 or 2, wherein the notch is formed at a corner of the peripheral portion and is an inclined surface forming a predetermined angle with respect to the optical axis.

4. The optical system according to claim 3, wherein the width of the notch in the lens diameter direction is 1 mm to 5 mm.

5. The optical system according to any one of claims 1 to 4, wherein the notch is a groove formed in the peripheral portion.

6. The optical system according to any one of claims 1 to 5, wherein the volume of the adhesive introduced into the notch is 10% or more and 100% or less of the volume of the notch.

7. The optical system according to any one of claims 1 to 6, wherein the adhesive is not introduced between the opposing surfaces in the optical axis direction excluding the notches of the first lens and the second lens.

8. The optical system according to any one of claims 1 to 7, wherein at least one of the first lens and the second lens has a coating film.

9. The first lens has the coating film, and the coating film contains diamond-like carbon, the optical system according to claim 8.

10. The first lens is made of germanium, the optical system according to any one of claims 1 to 9.

11. The optical system according to any one of claims 1 to 10, wherein the on-axis thickness of the third lens is 0.5 times to 2 times the second distance which is the on-axis distance between the second lens and the third lens.

12. The optical system according to any one of claims 1 to 11, wherein the first distance which is the on-axis distance between the first lens and the second lens is smaller than the second distance which is the on-axis distance between the second lens and the third lens.

13. The lens barrel has a first hole, a second hole, and a third hole. The third lens is fitted into the third hole. The second hole is connected to the third hole, has a larger diameter than the third hole, and the second lens and the first lens are fitted in a state where a second ring portion is interposed between the second lens and the third lens. The first hole is connected to the second hole, has a larger diameter than the second hole, and a first ring portion that presses the first lens is fitted therein. The optical system according to any one of claims 1 to 12.

14. The optical system according to claim 13, wherein at least one of the portion of the third lens in contact with the lens barrel and / or the second ring portion, the portion of the second lens in contact with the second ring portion, and the portion of the first lens in contact with the first ring portion has a region where a coating film is not attached.

15. The lens barrel has a first hole, a second hole, a third hole, and a fourth hole. The first hole and the third hole have locking portions for locking the peripheral edge of the lens. The fourth hole is connected to the third hole, has a larger diameter than the third hole, and a second ring portion that presses the third lens is fitted therein. The third hole connects the fourth hole and the second hole, and the third lens is fitted in a state of being locked to the locking portion. The second hole connects the third hole and the first hole. The first hole is connected to the second hole, has a larger diameter than the second hole, and the second lens, the first lens, and the first ring portion are sequentially fitted from the second hole side. The optical system according to any one of claims 1 to 12.

16. The optical system according to claim 15, wherein at least one of the portion of the third lens in contact with the second ring portion and / or the locking portion, the portion of the second lens in contact with the locking portion, and the portion of the first lens in contact with the first ring portion has a region where a coating film is not attached.

17. The optical system according to any one of claims 1 to 16, wherein the third lens is made of chalcogenide glass having a refractive index of 2.5 to 4.0 at a wavelength of 10 μm.

18. The optical system according to any one of claims 1 to 17, wherein the second lens is made of chalcogenide glass having a refractive index of 2.5 to 4.0 at a wavelength of 10 μm.

19. The optical system according to claim 17 or 18, wherein the chalcogenide glass contains 20% to 80% of Te in mol%.

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