Infrared lens, infrared optical system, and infrared imaging device

Abstract

To provide an infrared lens suitable for infrared applications, and an infrared optical system and an infrared imaging device including the same.SOLUTION: An infrared lens L is configured to transmit infrared rays and is formed of resin. This makes it possible to reduce material costs and to achieve aspherical shaping due to good moldability. The infrared lens L has an average thickness within an optically effective diameter of 0.5 mm or less, thereby achieving a favorable infrared transmittance. Accordingly, the infrared lens L suitable for infrared applications can be obtained.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Infrared optical systems, which generally use infrared light (infrared rays) with wavelengths of 3-5μm and 8-14μm, are able to detect radiant heat and are therefore used as thermal cameras to measure body temperature without contact.In addition, because they are less susceptible to disturbances (fog, haze, darkness, backlight, etc.) that visible light optical systems are not good at, and they can measure temperature, they are also used for surveillance, security, inspection, etc. However, despite their versatility, infrared optical systems have not been widely adopted due to their higher cost compared to visible light optical systems, one of the main reasons for this high cost being the high cost of lenses.

[0003] Known lens materials used in infrared optical systems include Ge, Si, ZnSe, ZnS, chalcogenide glass, and polyethylene resin (PE resin). Of these, Ge has good infrared transmittance (transmittance of infrared rays), but is expensive and has problems with processability. Si has relatively good infrared transmittance and is cheaper than Ge, but like Ge, it has problems with processability. For this reason, these materials are often used to form spherical lenses by polishing, and are not suitable for aspheric lenses. ZnSe, ZnS, and chalcogenide glass have relatively good infrared transmittance and can be molded to make them aspherical, but they are expensive materials and toxic.

[0004] In this regard, PE resin is inexpensive and has good moldability, making it possible to make it aspherical, but it has the problem of low infrared transmittance. For example, in the technology described in Patent Document 1, an imaging optical system is constructed using a single lens made of PE resin. However, forming an image with a single lens requires thickness at the center of the lens, which reduces infrared transmittance. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 5584870 Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention has been made in view of the above circumstances, and has an object to provide an infrared lens suitable for infrared applications, and an infrared optical system and an infrared imaging device including the same. [Means for solving the problem]

[0007] In order to achieve the above object, the present invention provides: An infrared lens that transmits infrared rays, It is made of resin, The average thickness within the optical effective diameter is 0.5 mm or less. It is characterized by: [Effects of the Invention]

[0008] According to the present invention, an infrared lens suitable for infrared applications can be obtained. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a schematic cross-sectional view of an infrared imaging device according to an embodiment. [Figure 2] 1A and 1B are graphs showing the effect of the thickness of a polyethylene resin on the transmittance in the far-infrared region, where FIG. 1A shows the transmittance in the far-infrared region of a polyethylene resin depending on the thickness, and FIG. 1B shows the average transmittance in the wavelength range of 8 to 12 μm. [Figure 3]Graph (a) shows the relationship between the thickness of the edge and the internal stress of the infrared lens when both ends of the outer surface are held with tweezers or the like, and graph (b) shows the relationship between the optical effective diameter and the thickness of the edge when the yield stress or half of the yield stress is reached. [Figure 4] FIG. 2 is an enlarged cross-sectional view of a first infrared lens. [Figure 5] 1 shows lens configuration diagrams and MTF curves for explaining the influence of the annular zones on the Fresnel surface, where (a) is for one annular zone, (b) is for two annular zones, and (c) is for three annular zones. [Figure 6] These are examples of ray diagrams for Fresnel lenses. (a) shows a Fresnel lens with a curved optical surface opposite the Fresnel surface, and (b) shows a Fresnel lens with a flat optical surface. [Figure 7] FIG. 10 is a diagram illustrating a modified example of the infrared optical system according to the embodiment. [Figure 8] FIG. 10 is a diagram illustrating a modified example of the infrared optical system according to the embodiment. [Figure 9] This is a lens configuration diagram and MTF curves for comparing the performance of a two-element resin infrared lens configuration and a single inorganic lens (chalcogenide glass lens) configuration. [Figure 10] This is a lens configuration diagram and MTF curves for comparing the performance of a configuration consisting of one resin infrared lens and two inorganic lenses (chalcogenide glass lenses) with a configuration consisting of three inorganic lenses (chalcogenide glass lenses). [Figure 11] FIG. 10 is a diagram illustrating a support structure for an infrared lens and an infrared imaging element in the case of a single lens configuration. [Figure 12] 10A and 10B are diagrams for explaining a support structure for each infrared lens and an infrared imaging element in the case of a configuration with multiple lenses. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0011] [Overall configuration of infrared imaging device] FIG. 1 is a schematic cross-sectional view of an infrared imaging device 100 according to this embodiment. The infrared imaging device 100 is an infrared camera that captures and visualizes light rays including infrared rays, and is used, for example, as a night vision camera, a thermometer, etc. Specifically, as shown in FIG. 1, the infrared imaging device 100 includes an infrared optical system 10 and a sensor unit 50.

[0012] The infrared optical system 10 is a single-focus optical system for forming a subject image on the imaging surface (projection surface) I of the infrared imaging element 51, and is housed in a lens barrel (lens frame) 41. The lens barrel 41 has an opening OP through which light from the object side is incident. The infrared optical system 10 includes at least one infrared lens L (two in this embodiment). The configuration of the infrared optical system 10 will be described in detail later.

[0013] The sensor unit 50 includes an infrared imaging element 51 that captures the subject image formed by the infrared optical system 10 . The infrared imaging element 51 is an imaging element (solid-state imaging element) sensitive to infrared light, such as a thermal microbolometer. The infrared imaging element 51 is fixed in a state where it is positioned relative to the optical axis Ax of the infrared optical system 10. The infrared imaging element 51 has a conversion unit as an imaging surface I, around which a signal processing circuit (not shown) is formed. Pixels, that is, conversion elements, are arranged two-dimensionally in the conversion unit. Note that the infrared imaging element 51 is not limited to a thermal microbolometer, and may be one incorporating a quantum or other thermal imaging element.

[0014] [Specific configuration of infrared optical system] Next, the infrared optical system 10 will be described in more detail. As shown in FIG. 1, the infrared optical system 10 of this embodiment is substantially composed of, in order from the object side, an aperture stop AP and two infrared lenses L (a first infrared lens L1 and a second infrared lens L2).

[0015] Each infrared lens L is a lens that transmits infrared rays and is made of resin. Because the infrared lenses L are made of resin, material costs can be reduced and good moldability can be achieved. Among these, it is preferable to use an olefin-based resin (high-density polyethylene, ultra-high molecular weight PE, TPX, etc.) or a fluorine-based resin, which have low absorption in the infrared region.

[0016] FIG. 2 is a graph based on actual measurements showing the effect of the thickness of the polyethylene resin on the far-infrared transmittance (transmittance in the far-infrared region), in which (a) shows the far-infrared transmittance of the polyethylene resin depending on the thickness, and (b) shows the average far-infrared transmittance at wavelengths of 8 to 12 μm. The average thickness within the optical effective diameter of each infrared lens L is 0.5 mm or less. This allows for a far-infrared transmittance of 60% or more, as shown in Figures 2(a) and 2(b), even for resin lenses, which have a high absorption coefficient and therefore a high sensitivity of transmittance to thickness. The average thickness within the optically effective diameter of each infrared lens L is preferably 0.3 mm or less, and more preferably 0.2 mm or less. By setting the average thickness to 0.3 mm or less, a far-infrared transmittance of 70% or more can be obtained, and by setting the average thickness to 0.2 mm or less, an even higher far-infrared transmittance can be obtained. In this specification, the "thickness" or "thickness" of a lens (or a part thereof) refers to the thickness in the axial direction along the optical axis Ax, unless otherwise specified. Furthermore, the "optical effective diameter" of a lens refers to the diameter of a bundle of parallel rays that emerge from an object point at infinity on the optical axis Ax and pass through the optical surface of the lens.

[0017] Each infrared lens L has an edge F formed to a predetermined thickness on the outer diameter side (outside the optical effective diameter) of the optical surface. If the edge F is thin, the lens may be deformed or damaged when held with tweezers or the like, making it difficult to handle, so it is preferable that the thickness t (t1, t2) of the edge F be a predetermined thickness or more. Figure 3(a) is a graph based on structural analysis showing the relationship between the thickness t of the edge F and the internal stress of the infrared lens L when both ends of the outer peripheral surface are grasped with tweezers or the like (optical surface diameter: φ10 mm, φ5 mm, and φ2.5 mm, radial width of the edge F: 1 mm, thickness of the optical surface: 0.3 mm, grasping force: 1 N). Figure 3(b) is a graph showing the relationship between the optical effective diameter and the thickness t of the edge F when the yield stress or half of the yield stress is reached. As shown in Figure 3(a), for example, if the material of the infrared lens L is polyethylene resin, in order to keep the stress during gripping below the yield stress of 27 MPa, the thickness t of the edge F must be 0.4 mm or more for a φ10 mm lens, 0.25 mm or more for a φ5 mm lens, and 0.175 mm or more for a φ2.5 mm lens. The thickness t [mm] of the edge F to keep it below the yield stress can be roughly expressed by the following equation (1), where D [mm] is the optical effective diameter, as shown in Figure 3(b), and it is preferable that the thickness t be equal to or greater than the value on the right side of the equation. t≧0.03D+0.1 (1) Furthermore, in order to safely keep the stress below 13.5 MPa, the thickness t of the edge portion F can also be roughly expressed by the following equation (2) (it must be 0.65 mm or more for φ10 mm, 0.45 mm or more for φ5 mm, and 0.3 mm or more for φ2.5 mm), so it is more preferable that it be greater than or equal to the value on the right side of the equation. t≧0.045D+0.2 (2)

[0018] As shown in Fig. 4, the first infrared lens L1 is a Fresnel lens in which the object-side surface (optical surface on the object side) S11 is a Fresnel surface having a sawtooth cross-section on the periphery. This allows the first infrared lens L1 to be made thin even when power is required, which in turn makes it easier to ensure high infrared transmittance. More specifically, the object-side surface S11, which is a Fresnel surface, has four or less annular zones R (first annular zone R1 to fourth annular zone R4 in the example of FIG. 4) within the optically effective diameter (i.e., the number of divisions of annular zones R is five or less). Here, the "annular zone" of the Fresnel surface refers to an annular sawtooth portion centered on the optical axis Ax that has an optically effective size, and in this embodiment refers to an annular zone with an axial annular zone height h of 0.02 mm or more. Figure 5 shows a lens construction diagram (the edge portion is omitted) and MTF curves to explain the effect of the annular zone R on the Fresnel surface of a resin Fresnel lens with an average thickness of 0.2 mm within the optically effective diameter, where (a) is for one annular zone (two divisions), (b) is for two annular zones (three divisions), and (c) is for three annular zones (four divisions). As shown in these figures, the annular zones R of the Fresnel surface generate phase differences depending on their number and radial position, resulting in changes in optical performance. Specifically, the fewer the number of annular zones or the farther the annular zones R are from the optical axis Ax, the better the optical performance. In this embodiment, as described above, the number of annular zones within the optical effective diameter is four or less, and the first annular zone R1, the innermost radial zone, is located outside more than 50% of the optical effective diameter. However, there are no particular limitations on the number or radial position of the annular zones R. Furthermore, if the annular zone R of the Fresnel surface is positioned inside the diameter of the aperture stop AP, the optical performance may be degraded. Therefore, in this embodiment, the diameter of the second annular zone R2, which is the second from the inner diameter side, is formed to be larger than the diameter (inner diameter) of the aperture stop AP. This minimizes the above-mentioned performance degradation. That is, the fewer the number of annular zones, the better, and even fewer the number of annular zones within the aperture stop AP. Also, the farther the annular zone R is from the optical axis Ax, the better. The number of annular zones within the optical effective diameter should be four or less, the number of annular zones within the diameter of the aperture stop AP should be one or less (aperture stop diameter < second annular zone diameter), and the first annular zone should be outside more than 50% of the effective diameter (optical effective diameter / 2 < first annular zone diameter). It is preferable to satisfy at least one of these conditions, and it is even more preferable to satisfy all of them. Although FIG. 5 shows an example of a lens with an average thickness of 0.2 mm, the above-described tendency in performance according to the position and number of annular zones does not depend on the lens thickness.

[0019] The image side surface (image-side optical surface) S12 of the first infrared lens L1, which is a Fresnel lens, is formed in a flat surface that is approximately perpendicular to the optical axis Ax. FIG. 6 shows examples of ray diagrams for Fresnel lenses, where (a) shows a Fresnel lens with a curved optical surface on the side opposite the Fresnel surface, and (b) shows a Fresnel lens with a flat optical surface on the side opposite the curved optical surface. As shown in Figure 6(a), if the optical surface is a curved Fresnel surface, it is possible to design it, but the thickness deviation (difference in thickness) between the center and periphery will be large, which will result in disadvantages such as differences in infrared transmittance and deterioration of formability. On the other hand, as shown in Figure 6(b), when the optical surface is a flat Fresnel surface, thickness unevenness (difference in thickness) between the center and periphery can be suppressed, which makes it possible to uniform the infrared transmittance, improve formability, and reduce the number of annular zones. In particular, from the perspective of the effect on infrared transmittance, it is preferable that the image-side surface S12 be a surface close to a flat surface within the optical effective diameter, with a sag of 0.1 or less from a plane perpendicular to the optical axis Ax. While Fig. 5 shows an example in which the image-side surface is a Fresnel surface, the same holds true for the case in which the object-side surface is a Fresnel surface as in Fig. 1. Furthermore, as will be described later, when the infrared lens L is a Fresnel lens, any optical surface may be a Fresnel surface.

[0020] FIG. 7 is a diagram showing a modified example of the infrared optical system 10. In FIG. As shown in this figure, the first infrared lens L1 may have an integrally formed window member W on the side opposite to the Fresnel surface. The window member W is made of a general-purpose material that transmits infrared rays (for example, an inorganic material mainly composed of Ge, Si, chalcogenide glass, or ZnS). In this way, by integrally providing the window member W with the first infrared lens L1 (Fresnel lens), when an optical window is required, it is possible to reduce the height and increase the rigidity of the first infrared lens L1.

[0021] As shown in FIG. 1, at least one optical surface of the second infrared lens L2 (both optical surfaces in this embodiment) has an aspherical shape with an inflection point. In other words, at least one optical surface has a point where the angle between the normal to the surface and the optical axis increases and then decreases, or decreases and then increases. More preferably, at least one optical surface has an extremum. Here, an "extremum" refers to a point on the aspherical surface where, in the curve of the cross-sectional shape of the second infrared lens L2 within the optical effective diameter, the tangent plane of the vertex of the aspherical surface is a plane perpendicular to the optical axis Ax. This enables excellent correction of astigmatism and other aberrations. Furthermore, the second infrared lens L2 has a thickness variation ratio (minimum thickness / maximum thickness) of 0.5 or more within the optical effective diameter, which prevents excessive thickness variation and reduces variations in infrared transmittance throughout the second infrared lens L2.

[0022] The number of infrared lenses L in the infrared optical system 10 is not particularly limited, and it is sufficient that there is at least one. When infrared optical system 10 is configured with a single lens, it is preferable that the infrared lens L be a Fresnel lens like first infrared lens L1 in order to ensure sufficient power, as shown in Figures 8(a) and 8(b). The Fresnel surface may be either the object-side surface S11 or the image-side surface S12. In this way, by configuring infrared optical system 10 with a single Fresnel lens, it is possible to achieve both infrared transmittance and resolution performance.

[0023] Furthermore, if the desired performance cannot be obtained with the infrared optical system 10 consisting of a single lens, it may be configured with multiple infrared lenses L, as in this embodiment, for example. In this case, as shown in FIG. 8(c), it is also possible to have three or more infrared lenses L. Specifically, as shown in Figures 9(a) and (b), when a configuration using two resin infrared lenses L (Figure 9(a)) is used, performance equal to or better than a configuration using one thick inorganic lens G (Figure 9(b)) can be expected. In other words, performance can be maximized by using Fresnel lenses for lenses that require power and aspherical lenses without Fresnel lenses for lenses that do not require as much power. Furthermore, as shown in FIG. 10(a), a resin infrared lens L may be combined with inorganic lenses G (two lenses in the example of FIG. 10(a)). In this case, performance can be expected to be roughly equivalent to that of a configuration using only inorganic lenses G (three lenses in the example of FIG. 10(b)) as shown in FIG. 10(b). In this way, by combining a resin infrared lens L with a lens made of an inorganic material (for example, one whose main component is Ge, chalcogenide glass, or ZnS), it is possible to achieve a reduction in weight, height, cost, etc.

[0024] 11(a), the infrared lens L and the infrared imaging element 51 may be positioned in the axial and radial directions via the lens barrel 41 by supporting (fixing) the infrared lens L to the lens barrel 41. The lens barrel 41 is fixed to a sensor box 52 that supports the infrared imaging element 51. The infrared lens L is supported by the lens barrel 41, for example, at its edge F. 11(b), the edge F of the infrared lens L (or the outer periphery of the lens corresponding to the edge F) may be fixed directly to the infrared imaging element 51 (sensor box 52) without using the lens barrel 41. In this case, the lens barrel 41 may be omitted, leaving a light-shielding member 15 that shields the outer periphery of the first infrared lens L1 on the object side. This makes it possible to eliminate factors that deteriorate the positioning accuracy due to the fixing structure (e.g., adhesive) between the lens barrel 41 and the infrared lens L, compared to when the lens barrel 41 is used, and improves the positioning accuracy of the infrared lens L.

[0025] Furthermore, even if the infrared lens L is configured with multiple lenses, each infrared lens L may be supported (fixed) on a lens barrel 41, as shown in Figure 12(a), so that each infrared lens L and the infrared imaging element 51 can be positioned in the axial and radial directions via the lens barrel 41. 12(b), two (multiple) consecutive infrared lenses L may be directly positioned to each other without using the lens barrel 41 by mutually supporting (fixing) the edge portions F (or the lens peripheries corresponding to the edge portions F) of the two (multiple) consecutive infrared lenses L. This eliminates factors that deteriorate the positioning accuracy due to the fixing structure (e.g., adhesive) between the lens barrel 41 and the infrared lenses L, compared to when the lens barrel 41 is used, and improves the positioning accuracy of the infrared lenses L. Furthermore, the shape of the lens barrel 41 can be simplified by the amount that the shape required for fitting to the edge portion F of the second infrared lens L2 can be eliminated. 12(c), the edge F of each infrared lens L (or the lens outer periphery corresponding to the edge F) may be fixed to the adjacent infrared lens L (the edge F) and the infrared imaging element 51 (sensor box 52) without the lens barrel 41. In this case, the lens barrel 41 may be omitted, leaving a light-shielding member 15 that shields the outer periphery of the first infrared lens L1 on the object side. This eliminates factors that deteriorate the positioning accuracy due to the fixing structure (e.g., adhesive) between the lens barrel 41 and the infrared lens L, compared to when the lens barrel 41 is interposed, and improves the positioning accuracy of the infrared lens L. Furthermore, by centering (fitting) adjacent infrared lenses L, eccentricity between the infrared lenses L can be reduced. 12(a) to 12(c) show an example in which there are two infrared lenses L, but the same configuration can be used in the case of three or more infrared lenses L. Furthermore, the positioning by the edge portion F of the infrared lens L only needs to be performed in at least one of the radial direction and the axial direction.

[0026] [Technical effect of this embodiment] As described above, according to this embodiment, the infrared lens L that transmits infrared light is made of resin. This makes it possible to reduce material costs, and the excellent moldability allows for aspheric surfaces. The infrared lens L has an average thickness of 0.5 mm or less within its optically effective diameter, which allows for good infrared transmittance. Therefore, an infrared lens L suitable for infrared applications can be obtained.

[0027] Furthermore, according to this embodiment, by setting the average thickness within the optically effective diameter to 0.3 mm or less, it is possible to obtain even better infrared transmittance. Furthermore, by setting the thickness of the edge portion F of the infrared lens L, which is located on the outer diameter side of the optical surface, to satisfy the above formula (1), internal stress can be effectively suppressed even when the edge portion F is grasped with tweezers or the like.

[0028] Furthermore, according to this embodiment, by setting the average thickness within the optically effective diameter to 0.2 mm or less, it is possible to obtain even better infrared transmittance. Furthermore, by setting the thickness of the edge portion F of the infrared lens L, which is located on the outer diameter side of the optical surface, to satisfy the above formula (2), internal stress can be further effectively suppressed even when the edge portion F is grasped with tweezers or the like.

[0029] Furthermore, according to this embodiment, one optical surface of the first infrared lens L1 is a Fresnel surface, which allows the lens to be thinned while maintaining power, and therefore infrared transmittance can be maintained.

[0030] Furthermore, according to this embodiment, the other optical surface of the first infrared lens L1 opposite the Fresnel surface has a sag of 0.1 mm or less from a plane perpendicular to the optical axis Ax. By making the optical surface opposite the Fresnel surface nearly flat, it is possible to reduce the thickness difference between the center and periphery. This makes it possible to uniform the infrared transmittance, improve moldability, and reduce the number of annular zones.

[0031] Furthermore, according to this embodiment, the number of ring zones R on the Fresnel surface within the optical effective diameter is four or less, so the number of ring zones can be reduced and optical performance can be improved. Furthermore, according to this embodiment, the first annular zone R1, which is the innermost one of the Fresnel surface, is located outside 50% of the effective optical diameter, and therefore the annular zone R can be positioned away from the optical axis Ax to improve optical performance.

[0032] Furthermore, according to this embodiment, the first infrared lens L1 has a window member W integrally formed on the side opposite to the Fresnel surface, which allows the infrared lens L to have a low profile and high rigidity when an optical window is required. Furthermore, according to this embodiment, the window member W is made of an inorganic material containing Ge, Si, chalcogenide glass, or ZnS as a main component. In other words, the window member W can be made of a general-purpose material that transmits infrared rays.

[0033] Furthermore, according to this embodiment, at least one optical surface of the second infrared lens L2 has an aspherical shape with an inflection point. This allows for good correction of astigmatism and other aberrations. By making the infrared lens L from resin to ensure processability (moldability), it becomes possible to manufacture an aspherical surface.

[0034] Furthermore, according to this embodiment, the second infrared lens L2 has a thickness deviation ratio, calculated by dividing the minimum thickness by the maximum thickness, of 0.5 or more within the effective optical diameter, which prevents excessive thickness deviation in the second infrared lens L2 and reduces variations in the infrared transmittance of the entire second infrared lens L2.

[0035] Furthermore, according to this embodiment, the infrared lens L is made of an olefin resin or a fluorine resin. By using these resins that have little absorption in the infrared region, good infrared transmittance can be obtained.

[0036] Furthermore, according to this embodiment, the infrared optical system 10 includes one infrared lens L, one optical surface of which is a Fresnel surface. By configuring the infrared optical system 10 with a single thin Fresnel lens, it is possible to achieve both high infrared transmittance and high resolution.

[0037] Furthermore, according to this embodiment, the infrared optical system 10 includes an infrared lens L having a resin window member W. In other words, all of the infrared lenses L, including those having the window member W, are made of resin. This allows the infrared optical system 10 to be made less expensive and lighter.

[0038] Furthermore, according to this embodiment, the infrared optical system 10 includes infrared lenses L having one optical surface that is a Fresnel surface and at least one optical surface that is aspherical. In other words, performance can be maximized by using Fresnel lenses for lenses that require power and aspherical lenses without Fresnel lenses for lenses that do not require as much power.

[0039] Furthermore, according to this embodiment, the infrared optical system 10 includes an inorganic lens G formed of an inorganic material containing Ge, chalcogenide glass, or ZnS as a main component, in addition to the infrared lens L. In this way, by combining the resin infrared lens L with an inorganic lens, it is possible to achieve a reduction in weight, height, cost, etc.

[0040] Furthermore, according to this embodiment, the diameter of the second annular zone R2, which is the second from the inner diameter side of the Fresnel surface of the first infrared lens L1, is larger than the diameter of the aperture stop AP, thereby suppressing deterioration in optical performance that may occur when the annular zone R of the Fresnel surface is positioned inside the diameter of the aperture stop AP.

[0041] Furthermore, according to this embodiment, the infrared lens L is positioned relative to another adjacent infrared lens L or the infrared imaging element 51 by the edge F (outer periphery) of the infrared lens L, which is located radially outward from the optical surface. In other words, the lens shape determines the spacing between the infrared lenses L or the spacing between the infrared lens L and the infrared imaging element 51. This improves the positioning accuracy of the infrared lenses L, allowing for stable assembly, and also enables a simple configuration by omitting at least a portion of the lens barrel 41.

[0042] The above describes one embodiment of the present invention, but embodiments to which the present invention can be applied are not limited to the above-described embodiment and its variations, and can be modified as appropriate within the scope of the spirit of the present invention.

[0043] For example, in the above embodiment, the infrared optical system 10 is used in the infrared imaging device 100. However, the uses of the infrared lens and infrared optical system according to the present invention are not particularly limited, and the infrared lens and infrared optical system can also be suitably applied to uses other than imaging, such as light projection, illumination, and light collection. [Explanation of symbols]

[0044] 100 Infrared imaging device 10 Infrared optical system 15 Light blocking material 41 Telescope tube 51 Infrared imaging element (imaging element) 52 Sensor Box AP aperture stop Ax optical axis F Edge (outer periphery) G inorganic lens L infrared lens L1 First infrared lens L2 Second infrared lens L3 Third infrared lens R ring R1 First ring R2 Second ring zone S11 Object side (Fresnel surface) S12 image side W window material

Claims

1. An infrared lens that transmits infrared rays, It is made of resin, The average thickness within the optical effective diameter is 0.5 mm or less. An infrared lens characterized by:

2. It has an edge portion located on the outer diameter side of the optical surface, The average thickness within the optical effective diameter is 0.3 mm or less, The thickness t of the edge portion satisfies the following formula (1):

2. The infrared lens according to claim 1. t≧0.03D+0.1 (1) where D is the effective optical diameter of the infrared lens

3. The average thickness within the optical effective diameter is 0.2 mm or less.

3. The infrared lens according to claim 2.

4. The thickness t of the edge portion satisfies the following formula (2):

3. The infrared lens according to claim 2. t≧0.045D+0.2 (2) where D is the effective optical diameter of the infrared lens

5. One of the optical surfaces is a Fresnel surface.

2. The infrared lens according to claim 1.

6. the other optical surface opposite to the Fresnel surface has a sag of 0.1 mm or less from a plane perpendicular to the optical axis; 6. The infrared lens according to claim 5.

7. the Fresnel surface has four or less annular zones within an optical effective diameter; 6. The infrared lens according to claim 5.

8. The Fresnel surface has a first annular zone on the innermost diameter side positioned outside 50% of the optical effective diameter.

6. The infrared lens according to claim 5.

9. a window member integrally formed on the opposite side to the Fresnel surface; 6. The infrared lens according to claim 5.

10. the window member is formed of an inorganic material containing Ge, Si, chalcogenide glass, or ZnS as a main component; 10. The infrared lens according to claim 9.

11. At least one of the optical surfaces has an aspherical shape having an inflection point.

2. The infrared lens according to claim 1.

12. The thickness deviation ratio obtained by dividing the minimum thickness by the maximum thickness is 0.5 or more within the optical effective diameter.

12. The infrared lens according to claim 11.

13. It is made of an olefin resin or a fluorine resin.

2. The infrared lens according to claim 1.

14. At least one infrared lens according to claim 1 is provided. An infrared optical system characterized by:

15. one of the infrared lenses having a Fresnel surface as one optical surface; 15. The infrared optical system according to claim 14.

16. The infrared lens includes an infrared lens having an integrally formed resin window member.

15. The infrared optical system according to claim 14.

17. The infrared lens is a lens having one optical surface that is a Fresnel surface; Another lens having at least one optical surface that is aspherical; Including, 15. The infrared optical system according to claim 14.

18. In addition to the infrared lens, The optical system includes an inorganic lens formed of an inorganic material containing Ge, chalcogenide glass, or ZnS as a main component.

15. The infrared optical system according to claim 14.

19. Equipped with an aperture stop, The infrared lens includes an infrared lens having one optical surface that is a Fresnel surface, the Fresnel surface has a second annular zone, the second from the inner diameter side, having a diameter larger than the diameter of the aperture stop; 15. The infrared optical system according to claim 14.

20. an infrared optical system according to claim 14; an imaging element for detecting an image formed by the infrared optical system; Equipped with An infrared imaging device characterized by:

21. the infrared lens has an outer circumferential portion located on the outer diameter side of the optical surface, the outer circumferential portion positions the infrared lens relative to another infrared lens adjacent to the infrared lens or the imaging element, 21. The infrared imaging device according to claim 20.

Images