WO2015029645A1

WO2015029645A1 - Far infrared lens, photographing lens system and camera system

Info

Publication number: WO2015029645A1
Application number: PCT/JP2014/069343
Authority: WO
Inventors: 杭迫　真奈美
Original assignee: コニカミノルタ株式会社
Priority date: 2013-08-28
Filing date: 2014-07-22
Publication date: 2015-03-05
Also published as: JPWO2015029645A1

Abstract

A far infrared lens has a lens core made of an inorganic crystal material having a refractive index of 1.74 or less at a wavelength of 10 µm, and a coating layer made of an organic material relatively thinly covering the entire surface of the lens core. At least one surface of the lens core is formed into a spherical surface and a diffraction grating is provided on the surface of the coating layer located on at least one spherical surface. Alternatively, both surfaces of the lens core are formed into spherical surfaces and an aspheric surface is provided on the surface of the coating layer located on at least one spherical surface.

Description

Far-infrared lens, photographing lens system and camera system

The present invention relates to a far-infrared lens, a photographing lens system, and a camera system. For example, the far-infrared lens as an optical element used in the far-infrared band (wavelength 8 to 12 μm band) and the light-receiving of an imaging element The present invention relates to a far-infrared photographing lens system for forming a far-infrared optical image of a subject on a surface, and a far-infrared camera system (for example, a night vision device, a thermography, etc.) on which the photographing lens system is mounted.

With the spread of surveillance cameras and security cameras, there is a need for a small and inexpensive photographic lens system that uses far infrared rays. However, the lens material used in the far-infrared photographing lens system is more expensive than general optical glass. Even a relatively inexpensive lens material has problems such as low transmittance and processability, and depletion due to deliquescence. In order to solve these problems, various types of lenses and lens materials for far infrared rays have been proposed in Patent Documents 1 to 3 and the like.

Patent Document 1 describes an optical material in which an inorganic crystal material (including deliquescent materials) is moisture-proof by coating with a resin material (polyvinylidene chloride, phenol resin, benzene resin, etc.). Although the thickness of the coating material is 0.05 to 1 μm or less, the deliquescent inorganic crystal material can be moisture-proof to prevent the transmittance from decreasing.

Patent Document 2 describes a lens base material prepared by mixing an inorganic crystal material having a particle size of 500 nm or less with a polyethylene resin. The transmittance of the far-infrared band is as low as about 30% for the polyethylene resin, but 95% or more for NaCl or KBr of the inorganic crystal material. For this reason, by mixing the inorganic crystal material, the transmittance can be made higher than that of the resin-only material.

Patent Document 3 describes an optical element in which a flat plate or plano-convex lens made of NaCl or the like is covered with polyethylene or the like and a Fresnel surface is formed on the plane. The thickness of polyethylene covering the surface is λ / 4 (λ: wavelength), and is about 1.7 μm at a wavelength of 10 μm. If the Fresnel surface is used, it is possible to reduce the thickness by dividing the surface of the thick lens into an annular zone. Therefore, the Fresnel surface is effective for manufacturing a lens using a material having low transmittance.

JP-A-6-347607 JP 2010-204245 A US 6,441,956

The inorganic crystal material as described in Patent Document 1 has a considerably lower refractive index than that of Ge, Si, ZnSe, and ZnS conventionally used for far-infrared lenses, and the dispersion is also compared with that of Ge and Si. And pretty big. Such optical characteristics are disadvantageous for aberration correction in designing a lens system. In other words, simply applying a moisture-proof coating to an inorganic crystal material to prevent deliquescence will cause aberrations that are too large to use in place of conventional lenses, and will sufficiently correct aberrations even when the number of lenses is increased. I can't. In addition, since the crystal material used as the substrate is difficult to process, it is difficult to produce an aspherical surface or a diffraction grating surface. Furthermore, a thin organic material coating under harsh usage conditions may only be able to withstand a moisture-proof effect for about one to two years.

In the lens described in Patent Document 2, the low transmittance of polyethylene is improved by the high transmittance of inorganic crystal material by mixing nano-sized inorganic crystal material (NaCl or KBr) in polyethylene. Yes. However, considering lens molding, the proportion of polyethylene as a base material cannot be made 30% or less. For this reason, the transmittance increases only to about 65%. If a single lens does not have a transmittance of 80% or more, when a system composed of a plurality of lenses is configured, such as a photographing lens system of a camera, no resolution is obtained. For example, in these materials having a low refractive index, a thick lens is indispensable for increasing the curvature. However, when a thick lens is manufactured, a decrease in transmittance becomes a problem. In addition, NaCl and KBr are more likely to absorb moisture as the particle size is smaller, and a coating layer with higher air barrier properties is required. Therefore, if the coating layer is thickly covered with polyethylene or the like, the transmittance is further reduced.

In the Fresnel surface described in Patent Document 3, the inclination of the surface increases toward the periphery of the surface. This is the same for a normal lens surface, but on the Fresnel surface, it is difficult to process because it is necessary to make the interval closer to the peripheral ring zone, and there is a limit to making it thinner. Moreover, since the surface reflectance is increased due to the large inclination of the peripheral surface, it is impossible to prevent the overall transmittance from being lowered even though the refractive index of the material is small.

In addition, an increase in curvature due to the low refractive index of the lens material leads to an increase in aberrations, and the aberration correction effect is determined by the position of the lens surface in the lens system. Absent. In other words, in order to compensate for the low refractive index and large dispersion of the inorganic crystal material, it is necessary to provide a correction effect on the surface where the power (power: the amount defined by the reciprocal of the focal length) is large and the aberration is greatly generated. In addition, even if aberration correction is performed on a surface with low power, a sufficient effect cannot be obtained. Accordingly, it is not sufficient to provide a Fresnel surface or a diffraction grating surface on the plane, and sufficient aberration correction cannot be realized in a lens system using such an optical element.

The present invention has been made in view of such a situation, and an object of the present invention is to provide a lens that is inexpensive and easy to process, has excellent far-infrared transmittance, and has high aberration correction capability, and a photographic lens system including the same. And providing a camera system.

In order to achieve the above object, the far-infrared lens of the first invention is a lens used in the far-infrared band,
A lens core made of an inorganic crystal material having a refractive index with respect to a wavelength of 10 μm of 1.74 or less, and a coating layer made of an organic material that covers the entire lens core relatively thinly;
At least one surface of the lens core is a spherical surface, and a diffraction grating is provided on the surface of the coating layer located on at least one spherical surface.

In order to achieve the above object, the far-infrared lens of the second invention is a lens used in the far-infrared band,
A lens core made of an inorganic crystal material having a refractive index with respect to a wavelength of 10 μm of 1.74 or less, and a coating layer made of an organic material that covers the entire lens core relatively thinly;
Both surfaces of the lens core are spherical surfaces, and an aspherical surface is provided on the surface of the coating layer located on at least one spherical surface.

The far-infrared lens of the third invention is characterized in that, in the first or second invention, the thickness of the coating layer is 10 μm or more at the thinnest and 500 μm or less at the thickest. .

A far-infrared lens according to a fourth aspect of the invention is characterized in that, in the second aspect of the invention, the aspherical surface provided on the surface of the coating layer has a shape in which the positive power decreases as the distance from the optical axis increases. And

A far-infrared lens according to a fifth invention is characterized in that, in any one of the first to fourth inventions, the inorganic crystal material constituting the lens core is made of a substantially pure crystal. .

A far-infrared imaging lens system according to a sixth aspect of the present invention includes a lens core made of an inorganic crystal material having a refractive index of 1.74 or less with respect to a wavelength of 10 μm, and a coating layer made of an organic material that covers the entire lens core relatively thinly. And at least one of them includes the lens according to any one of the first to fifth inventions.

A far-infrared camera system according to a seventh aspect of the invention is characterized by including the photographing lens system according to the sixth aspect of the invention.

By adopting the configuration of the present invention, a far-infrared lens that is inexpensive, easy to process, has excellent far-infrared transmittance, and has high aberration correction capability, and a far-infrared imaging lens system and camera system including the same (For example, night vision devices, thermography, etc.) can be realized. The photographic lens system according to the present invention is used in a camera system such as a digital camera, a surveillance camera, a security camera, and an in-vehicle camera, or the camera system according to the present invention is used in a digital device such as a portable terminal. It is possible to realize a far-infrared image input function with low cost.

The schematic diagram which shows the example of a manufacturing process of a far-infrared lens in cross section. The schematic diagram which shows in cross section the specific example of the far-infrared lens by which the diffraction grating was given to the surface of the coating layer. The schematic diagram which shows in cross section the specific example of the far-infrared lens by which the aspherical surface was given to the surface of the coating layer. 1 is an optical configuration diagram of a first embodiment (Example 1) of a taking lens system. FIG. Aberration diagram of Example 1 of the photographing lens system. The optical block diagram of 2nd Embodiment (Example 2) of a photographic lens system. Aberration diagram of Example 2 of the photographing lens system. The optical block diagram of 3rd Embodiment (Example 3) of a photographic lens system. Aberration diagram of Example 3 of the photographing lens system. The optical block diagram of 4th Embodiment (Example 4) of a photographic lens system. Aberration diagram of Example 4 of the photographing lens system. FIG. 10 is an optical configuration diagram of a fifth embodiment (Example 5) of the taking lens system. Aberration diagram of Example 5 of the photographing lens system. The optical block diagram of 6th Embodiment (Example 6) of an imaging lens system. Aberration diagram of Example 6 of the photographing lens system. The optical block diagram of 7th Embodiment (Example 7) of an imaging lens system. Aberration diagram of Example 7 of the photographing lens system. The optical block diagram of 8th Embodiment (Example 8) of a taking lens system. Aberration diagram of Example 8 of the photographing lens system. The schematic diagram which shows the schematic structural example of the camera system for far infrared rays.

Hereinafter, a far infrared lens, a photographing lens system, a camera system, and the like according to the present invention will be described. The far-infrared lens according to the present invention is a lens used in the far-infrared band, and compares the entire lens core with a lens core made of an inorganic crystal material having a refractive index with respect to a wavelength of 10 μm of 1.74 or less. And a far-infrared lens as an optical element having a coating layer made of an organic material that is thinly covered. Among them, the first type of lens is characterized in that at least one surface of the lens core is a spherical surface, and a diffraction grating is provided on the surface of the covering layer located on at least one spherical surface. The second type lens is characterized in that both surfaces of the lens core are spherical and an aspheric surface is provided on the surface of the coating layer located on at least one of the spherical surfaces.

The lens core is a portion whose shape and material are the basis of the lens, and when considering a single lens, it is a small portion except for a thin material layer such as a coating, a diffraction grating, and an aspherical portion. In the first type lens, at least one surface of the lens core is spherical, but in the second type lens, both surfaces of the lens core are spherical. This is to make it possible to correct other aberrations as much as possible even in the presence of chromatic aberration. The edge shape is not particularly defined, but may be any shape that is easy to make.

The coating layer that covers the entire lens core relatively thinly is thicker than a general antireflection coating in the visible region and thinner than the lens core. However, unlike the antireflection coating in the visible region, it is not in the nm unit because it is used in the far-infrared band having a long wavelength and also for maintaining the moisture-proof effect for a long time. For example, the antireflection coating represented by 10 μm of far-infrared is about 3 μm for λ / 4 polyethylene, but it is thick because it is insufficient for moisture prevention. In addition, since the refractive index of the organic material (for example, polyethylene) which comprises a coating layer is low, the reflection prevention of a far-infrared lens is unnecessary.

Refractive index is the ratio of the traveling speed of light in the substance to the vacuum, and is displayed for the d-line (587 nm) in the visible region. However, since this value has no meaning in the far-infrared region, the refractive index for a wavelength of 10 μm is typically representative. For example, the refractive index at a wavelength of 10 μm of far-infrared optical materials conventionally used is Ge = 4.004, Si = 3.418, ZnS = 2.200, ZnSe = 2.407, and the like.

As a value representing the nature of dispersion, the Abbe number νd of d-line is used for visible light. This Abbe number is expressed by νd = (Nd−1) / (Nf−Nc) (where Nd: refractive index of d-line, Nf is refractive index of F-line, Nc is refractive index of C-line, is there.). However, since this value has no meaning in the far-infrared region, ν = (N10-1) / (N8-N12) is used as a value representing the nature of dispersion in the first and second type lenses. (N10: Refractive index at a wavelength of 10 μm, N8: Refractive index at a wavelength of 8 μm, N12: Refractive index at a wavelength of 12 μm). The larger this value, the smaller the difference in refractive index between colors, and the smaller the dispersion. For example, dispersions of far-infrared optical materials conventionally used are Ge = 785, Si = 1860, ZnS = 23 (used for achromatization), ZnSe = 57 (used for achromatization), and the like.

Far infrared rays are mainly infrared rays having a wavelength in the range of 7 to 14 μm. The body temperature of humans and animals is 8 to 12 μm, and most of far-infrared optical systems are used at 8 to 12 μm. The far-infrared region in the wavelength band 8-12 μm is the range in which the temperature of a substance can be detected, and there are many things that can be applied such as temperature measurement, human detection in the dark, and security. However, the reason why far-infrared cameras are not widely used at present is that the lens material that transmits far-infrared rays is an expensive crystal material, or the processing is difficult and the cost is high.

Among the inorganic crystal materials having a refractive index with respect to a wavelength of 10 μm of 1.74 or less, all materials considered as far-infrared lens materials have a transmittance with respect to a wavelength of 10 μm of 90% or more. Among inorganic crystal materials, NaCl (sodium chloride), KCl (potassium chloride), KBr (potassium bromide), CsI (cesium iodide), CsBr (cesium bromide) and the like have a refractive index of a wavelength of 10 μm of 1.74 or less. Are relatively inexpensive and non-toxic, or few if any. However, these materials have a high internal transmittance of 90% or more in the far-infrared band, but have deliquescence, and the surface transmittance decreases with the passage of time unless cut off from air and moisture. On the other hand, among organic materials, polyethylene and the like are stable in the air, but the internal transmittance of far infrared rays is as low as about 30%. Even if the permeability is improved by increasing the molecular weight, it seems to be about 50%. For this reason, it cannot be used for thick lenses.

In the first and second type lenses, a thick lens shape is made of an inorganic crystal material having a high transmittance, and the entire surface is thinly covered with a stable organic material. It can be produced. Further, since the refractive index of the organic material is about 1.4 to 1.6, there is almost no reflection or refraction at the interface with the inorganic crystal material having a refractive index of 1.74 or less, which is optically preferable. For example, Ge (germanium) and Si (silicon), which have been used conventionally, have a high refractive index (3.0 or more) and have a very large surface reflection at the interface with air. In this case, the organic material constituting the coating layer is preferable because the refractive index is low as described above and the surface reflection at the interface with air is small.

An inexpensive inorganic crystal material has a refractive index lower than 1.74. Therefore, Ge (germanium), Si (silicon), ZnSe (zinc selenide), ZnS (zinc sulfide), which have been used for far-infrared lenses. ) Etc., the curvature of each surface must be increased to achieve the same focal length. When the curvature is large (that is, the curvature radius is small), spherical aberration and other aberrations increase. In addition, since the inclination increases near the periphery of the surface and the incident angle of the light beam also increases, the reflectance at the air interface increases. Therefore, if a diffraction grating is provided to supplement the refractive power as in the first type of lens and thereby the tilt angle around the surface is reduced, a lens with reduced aberration and reduced surface reflection can be produced. .

Inorganic crystal materials that are cheaper than Ge, Si, ZnSe, and ZnS conventionally used for far-infrared lenses have a low refractive index, and as described above, to achieve the same focal length as these lenses. The curvature must be increased. When the curvature is large (that is, the curvature radius is small), spherical aberration and other aberrations become large, so that it is difficult to manufacture a lens having sufficient performance. Therefore, in the second type of lens, first, the lens core is formed into a double-sided spherical shape, and aberration correction is shared between both sides, thereby preventing the performance from being reduced. Next, after covering the entire lens core with a coating layer made of an organic material, an aspheric surface is formed on the surface, thereby making it possible to suppress aberrations to a small level. This aspherical surface can be produced in the same manner as when a resin aspherical surface is formed on the glass surface. The organic material has a refractive index in the vicinity of a wavelength of 10 μm and is close to that of these inorganic crystal materials, and performance comparable to that obtained when an inorganic crystal material is directly aspherically processed can be obtained. Since it is difficult to process the aspherical surface of the crystal material, it may be processed into a spherical surface.

As described above, the first type of lens includes a lens core made of an inorganic crystal material having a refractive index with respect to a wavelength of 10 μm of 1.74 or less, and a coating layer made of an organic material that covers the entire lens core relatively thinly. The lens core has a configuration in which at least one surface of the lens core is a spherical surface, and a diffraction grating is provided on the surface of the covering layer located on at least one of the spherical surfaces. An inexpensive far-infrared lens can be produced by constituting most of the lens with a material having a high far-infrared transmittance of 90% or more and a low price. The deliquescence which is a defect of these materials can be prevented by covering the entire lens core with a coating layer made of a stable organic material. The disadvantage of aberration correction due to the use of a low refractive index material is compensated by applying a diffraction grating to the coating layer on the spherical surface, and the same focus as a lens made of a conventional material with a high refractive index but an expensive price. A distance lens is obtained. In addition, the inclination around the surface can be kept small, and a lens with higher transmittance can be realized by reducing the surface reflectance.

As described above, the second type of lens includes a lens core made of an inorganic crystal material having a refractive index with respect to a wavelength of 10 μm of 1.74 or less, and a coating layer made of an organic material that covers the entire lens core relatively thinly. The lens core has a spherical surface, and an aspheric surface is provided on the surface of the coating layer located on at least one spherical surface. Similar to the first type of lens, an inexpensive far-infrared lens can be produced by constituting most of the lens with a material having a high far-infrared transmittance of 90% or more and an inexpensive price. In order to compensate for the deterioration of the aberration due to the low refractive index of the material, the aberration is corrected by applying an aspherical surface to the coating layer on the spherical surface. In addition, by using an inorganic crystal material having a refractive index close to that of an organic material, an effect comparable to that obtained when an aspheric surface is directly made of an inorganic crystal material can be obtained. Most of organic materials have a refractive index of 1.49 to 1.75, but far-infrared lens materials of inorganic crystal materials of 1.74 or more do not have a refractive index of 2.2 or more. It can be said that the refractive index is close to the organic material.

The lens materials Ge, Si, ZnSe, and ZnS that have been used for far infrared rays are expensive, but the refractive index is high as 2.2 to 4.0, so that the curvature of the surface can be relaxed. It is effective for the production of small lenses. Disadvantages of inexpensive materials NaCl, KCl, KBr, CsI, and CsBr include low refractive index and deliquescence. However, as described above, the deliquescence is compensated by applying an organic material coating layer. It is possible.

In the first and second type lenses, the aberration reduction due to the low refractive index and strong curvature is corrected by applying a diffraction grating or an aspherical surface to the surface of the coating layer on the spherical surface. By adopting such a configuration, it is possible to obtain a far-infrared lens that is highly inexpensive and stable while having high optical performance, like a lens made of a conventional high refractive index material. These lenses have considerably higher transmittance than organic materials that are transparent to far-infrared rays, and the same performance as conventional lenses made of expensive materials can be obtained in terms of transmittance. By constructing a lens system including at least one of these lenses, it is possible to obtain a lens system that is comparable to a conventional lens system composed of an expensive material having a high refractive index. In addition, an inexpensive camera system can be manufactured.

According to the above characteristic configuration, a far-infrared lens that is inexpensive, easy to process, has excellent far-infrared transmittance, and has high aberration correction capability, and a far-infrared photographing lens system and camera system (for example, dark Visual devices, thermography, etc.). By using the photographing lens system for a camera system such as a digital camera, a surveillance camera, a security camera, and a vehicle-mounted camera, or using a far-infrared camera system for a digital device such as a portable terminal, a high-performance far-infrared ray The image input function can be realized at low cost, and can contribute to the downsizing, high performance, high functionality, and the like. The conditions for achieving such effects in a well-balanced manner and achieving higher optical performance, downsizing, etc. will be described below.

In the first and second type lenses, it is desirable that the thickness of the coating layer is 10 μm or more at the thinnest and 500 μm or less at the thickest. In order to shield and protect the inorganic crystal material from air and moisture, the coating layer must have a certain thickness. The thicker the coating layer, the better the air barrier property, but the higher the molecular weight and the higher the density, the better the barrier property, so the thickness may be about 10 μm, and the smaller molecular weight must be thicker than this. Don't be. However, if the coating layer is thicker than 500 μm, the far-infrared transmittance deteriorates and is not suitable for lenses.

The diffraction grating for the far-infrared wavelength of 10 μm needs a depth of about 10 μm. Therefore, when a diffraction grating is applied to the surface of the coating layer, the thickness of the coating layer must be 10 μm or more. Further, when an aspheric surface is applied to the surface of the coating layer, the surface is molded using a mold or the like. At this time, molding is performed by applying a certain amount of pressure. However, if the coating layer is too thin, it is difficult to apply pressure so that the lens core is not broken, and molding becomes difficult. Therefore, the coating layer needs to have a minimum thickness of about 10 μm.

The internal transmittance of organic materials such as polyethylene around a wavelength of 10 μm is about 30% at a thickness of about 3 mm. Considering the resolving power of the captured image, it is considered that the overall transmittance is required to be about 80%. For example, when using a system consisting of a single lens in which an inorganic crystal material such as NaCl (with a transmittance of 98%) is covered with an organic material such as polyethylene, the thickness of the organic material must be a maximum of 800 μm at the distance that the light passes. Don't be. Since there are two layers of organic material in one lens, even if the thinnest one is 10 μm in thickness, considering that the condensed light beam passes diagonally, the transmittance on the other side must be less than 500 μm at most. Cannot be secured.

In the second type of lens, it is desirable that the aspherical surface provided on the surface of the coating layer has a shape in which the positive power becomes weaker as the distance from the optical axis increases. A lens in which a lens core is made of an inorganic crystal material and the surface thereof is covered with an organic material has a low refractive index and thus has a large surface curvature, and thus has a large aberration. In addition, the inclination around the surface is large, and the surface reflectance is also high. In order to improve the aberration of the lens and reduce the reflectance as much as possible, the positive power becomes weaker toward the periphery (away from the optical axis) of the aspherical shape applied to the surface of the coating layer made of the organic material. Like that. When an aspheric surface is provided on the convex surface, the inclination of the peripheral surface is reduced, and the reflectance of the surface can be kept low together with aberration correction. Concave surfaces generally have a light incident angle on the surface close to 90 ° when a lens system is configured. Therefore, even if the concave shape becomes somewhat tight for aberration correction, the incident angle on the surface of the light beam does not become too large. The reflectivity does not change much.

In the first and second type lenses, it is desirable that the inorganic crystal material constituting the lens core is made of a substantially pure crystal. As described above, inexpensive inorganic crystal materials such as NaCl, KCl, KBr, CsI, and CsBr have deliquescence properties, but it is known that the liquefaction property is weakened as the material is pure and large crystals. This is because water molecules are less likely to enter the interior by reducing the surface area of the material as much as possible and reducing crystal defects. A lens core that is difficult to deliquesce with a substantially pure material is manufactured, and a lens that is stable over a long period of time can be obtained by covering the surface with an organic material as described above.

The far-infrared photographing lens system includes a lens core made of an inorganic crystal material having a refractive index of 1.74 or less with respect to a wavelength of 10 μm, and a coating layer made of an organic material that covers the entire lens core relatively thinly. It is preferable that the lens includes at least one lens, and at least one of them includes the first and second type lenses. Since the inorganic crystal material has a thin coating layer covering its surface, it determines most of its optical properties. In addition, since most of the inorganic crystal materials have a refractive index of 1.74 or less and a dispersion of 70 or less, the optical performance is improved as compared with materials having a refractive index of 3 or more and a dispersion of 700 or more, such as Si and Ge. Is disadvantageous. Nevertheless, the material is inexpensive, and it is suitable when it is desired to manufacture a far-infrared lens system at a low cost.

At this time, as described above, the surface is covered with an organic material, and a diffraction grating or an aspheric surface is applied to the surface to reduce the aberration of a single lens, and a lens system composed of a plurality of single lenses including such a single lens is adopted. Thus, an inexpensive far-infrared photographing lens system can be realized with good aberration correction. In addition to the first and second types of lenses, the photographic lens system may include a lens that is not provided with a diffraction grating or an aspherical surface. Further, it may include a lens having a coating layer in which both the diffraction grating and the aspheric surface are applied to the same surface, or may include a lens in which at least one of the diffraction grating and the aspheric surface is applied to both surfaces. Good.

The far-infrared camera system is preferably provided with the far-infrared imaging lens system. As described above, one of the reasons why far-infrared cameras are not widespread is that lens materials and lens processing are expensive. Low-cost photographic lens system and camera system by covering the lens core made of inorganic crystal material with a coating layer made of organic material and further including a lens system with a diffraction grating or aspherical surface on the surface of the coating layer Can be realized. This is expected to increase the application to fields where far-infrared cameras have not been used.

The inorganic crystal material preferably has a dispersion with a wavelength of 8 to 12 μm smaller than 70. That is, it is preferable that the conditional expression: ν = (N10-1) / (N8−N12) <70 is satisfied.

Among the materials that have been mainly used conventionally, the Ge dispersion is 800 and the Si dispersion is about 1600. The dispersion ν indicates that the larger the value, the smaller the difference in refractive index due to color. Except for special cases, these materials need not be considered for color correction in the far-infrared band, but are expensive materials. On the other hand, if the inorganic crystal material has a dispersion ν of 70 or less, the cost becomes considerably low, but correction of chromatic aberration is necessary. Therefore, it is possible to correct chromatic aberration by giving a part of positive power to the diffraction grating. In contrast to the refracting surface, the diffraction grating surface has a positive power to generate negative chromatic aberration. By utilizing this, even an inexpensive inorganic crystal material having a large dispersion in the far-infrared wavelength band can be dispersed by covering the surface with an organic material having a diffraction grating on the surface.

In Examples to be described later, NaCl and KBr are used as inorganic crystal materials, but KCl (N10 = 1.46, ν = 29.98), CsI (N10 = 1.72, ν = 70), Similarly, CsBr (N10 = 1.64, ν = 65) and the like can be used because they have a high far-infrared transmittance. In addition to polyethylene, polyolefin resins, polyvinylidene chloride, phenol resins, benzene resins, and the like can be used as the organic material. At that time, it is important to determine the maximum thickness according to the internal transmittance of each organic material.

In addition, a highly toxic material such as ZnS or ZnSe is covered with an organic material to protect it, and a lens having a diffraction grating on the surface of the coating layer may be manufactured in order to correct the dispersion being larger than that of Ge or the like. Is possible. Since ZnS and ZnSe have large dispersion, it is preferable to use a diffraction grating mainly for color correction and to produce a positive lens. Since the refractive index is relatively high, there is little need for aberration correction.

Of the crystal materials used in the near infrared (wavelength 800 nm to 1 μm) and mid infrared (wavelength 1 to 7 μm), it can be protected by coating an organic material on a material that is vulnerable to impact and difficult to process. These materials include CaF ₂ (fluorite), BaF ₂ (barium fluoride), MgF ₂ (magnesium fluoride), etc., but it is difficult to process them into an aspherical surface. Even with such a material, first, a spherical lens shape is processed, the whole is covered with an organic material, and the surface thereof is aspherical. Since these materials also have a refractive index close to that of an organic material, reflection and refraction at the interface hardly occur, and almost the same effect as that obtained when an aspherical surface is made of a crystalline material can be obtained. It is possible to obtain a lens system in which aberrations are favorably corrected from near infrared to mid infrared. At that time, it is necessary to determine the thickness by paying attention to how much the transmittance of the organic material is at the wavelength used.

FIG. 1 is a cross-sectional view showing a manufacturing process example of a far-infrared lens. First, a crystal of an inorganic material (NaCl, KBr, etc.) is cut or polished to produce a lens core CR having a spherical lens shape as shown in FIG. The lens shape is not limited to a biconvex shape, and may be a positive meniscus shape or a negative meniscus shape. The core thickness is about 1.5 to 4.5 mm.

Next, high-density polyethylene as an organic material is coated on the lens core CR by dip coating or the like, and the entire lens core CR is covered with a coating layer CT1 by about 10 μm as shown in FIG. When the curvature of the surface is close to a flat surface, high-density polyethylene can be applied by spin coating. Moreover, when it does not reach 10 μm by one coating, the application may be repeated a plurality of times. Here, the second coating is performed before the surface transmittance of the inorganic crystal material decreases due to deliquescence.

When the coating layer CT2 made of the same material as the coating layer CT1 is provided on the coating layer CT1, as shown in FIG. 1C, a two-layer coating layer CT made of the same material is obtained. Precise molding is performed on the surface with a mold. At this time, if a die provided with a diffraction grating, an aspherical surface, or both is used on at least one surface, the precise shape is transferred to the lens surface to complete the far-infrared lens LE.

Since the coating thickness of polyethylene is larger than the general coating thickness, the initial coating will cause the lens core CR to be non-uniformly attached. Even when the coating layer CT having a single layer structure is formed by one coating, A uniform polyethylene layer can be obtained by later molding using a mold. Further, since the aspherical surface and the diffraction grating surface are partially uneven in thickness, polyethylene may be further applied to the surface as necessary when the diffraction grating or the aspherical surface is formed.

FIG. 2 is a sectional view showing a specific example of the far-infrared lens LE in which the diffraction grating GR is applied to the surface of the coating layer CT. FIG. 2A shows a far-infrared lens LE in which a diffraction grating GR is provided on a high-power convex coating layer CT, and FIG. 2B shows an enlarged main portion P thereof. . The diffraction grating GR is a surface relief-like diffraction grating surface formed by pressing a heated mold against the coating layer CT. The cross-sectional shape of the diffraction grating GR is not limited to the binary shape shown in FIG. For example, a step (stair) shape or kinoform may be used. In any case, the phase difference at the diffraction wavelength is, for example, a value calculated from an example described later.

FIG. 3 is a cross-sectional view showing a specific example of the far-infrared lens LE in which the surface of the coating layer CT is aspherical AS. 3A shows a state where an aspheric surface is formed on the concave surface side of the spherical lens core CR, and FIG. 3B shows an aspheric surface formed on the convex surface side of the spherical lens core CR. Indicates the state. Since all the covering layers CT are thicker toward the periphery, the aspherical surface formed on the surface of the covering layer CT has a shape in which the positive power becomes weaker (the negative power becomes stronger) as the distance from the optical axis AX increases. Have.

FIG. 4, FIG. 6, FIG. 8,..., FIG. 18 show first to eighth embodiments of the far-infrared photographing lens system LN in an infinitely focused state in optical cross sections together with optical paths. The photographic lens system LN of the first to fifth embodiments includes three far-infrared lenses LE, which are a first lens L1, a second lens L2, and a third lens L3. A diaphragm (aperture diaphragm) ST is disposed between the lens L2. The photographic lens system LN of the sixth embodiment includes four far-infrared lenses LE, which are a first lens L1, a second lens L2, a third lens L3, and a fourth lens L4. A diaphragm ST is disposed between the third lens L3 and the third lens L3. The photographic lens system LN of the seventh and eighth embodiments is composed of two far-infrared lenses LE, which are a first lens L1 and a second lens L2, between the first lens L1 and the second lens L2. The aperture stop ST is arranged in FIG. A parallel plate PT (for example, a parallel plate of Ge crystal) corresponding to the protective cover glass of the image sensor (far infrared sensor) is disposed on the image side of each photographing lens system LN.

In the first embodiment (FIG. 4), diffraction gratings are provided on the object side surface of the first lens L1 and the object side surface of the second lens L2. In the second embodiment (FIG. 6), a diffraction grating is provided on the object side surface of the first lens L1, and a diffraction grating and an aspheric surface are provided on the object side surface of the second lens L2. In the third embodiment (FIG. 8), an aspheric surface is provided on the object side surface of the second lens L2. In the fourth embodiment (FIG. 10), an aspheric surface is provided on the object side surface of the second lens L2. In the fifth embodiment (FIG. 12), a diffraction grating is provided on the object side surface of the second lens L2. In the sixth embodiment (FIG. 14), a diffraction grating and an aspheric surface are provided on the object side surfaces of the first lens L1, the second lens L2, and the third lens L3, and the object side surface of the fourth lens L2 is provided. An aspheric surface is provided. In the seventh embodiment (FIG. 16), aspheric surfaces are provided on both surfaces of the first lens L1 and both surfaces of the second lens L2. In the eighth embodiment (FIG. 18), the first lens L1 is provided with aspheric surfaces, and the second lens L2 is provided with diffraction gratings.

The far-infrared imaging lens system LN according to the present invention is suitable for use as an imaging optical system for a far-infrared camera system (for example, a night vision device, a thermography, a surveillance camera, a security camera, an in-vehicle camera, etc.). By combining this with an image sensor (far infrared sensor) or the like, a far infrared imaging optical device that optically captures a far infrared image of a subject and outputs it as an electrical signal can be configured. The imaging optical device is an optical device that constitutes a main component of a camera used for still image shooting or moving image shooting of a subject, for example, a photographing lens that forms a far-infrared optical image of an object in order from the object (that is, subject) side. And an imaging device (far infrared sensor) that converts a far infrared optical image formed by the photographing lens system into an electrical signal. Then, the photographic lens system LN having the above-described characteristic configuration is arranged so that the far-infrared optical image of the subject is formed on the light receiving surface (that is, the imaging surface) of the imaging element, thereby reducing the size and cost. An imaging optical device having high performance and a camera system including the same can be realized.

Examples of digital devices with a far-infrared image input function include cameras such as infrared cameras, surveillance cameras, security cameras, in-vehicle cameras, aircraft cameras, digital cameras, video cameras, and personal computers, portable terminals (for example, For mobile phones, smart phones (high-function mobile phones), small and portable information device terminals such as mobile computers, peripheral devices (scanners, printers, etc.), and other digital devices (drive recorders, defense devices, etc.) An internal or external camera can be mentioned. As can be seen from these examples, it is possible not only to configure a night vision device by using an imaging optical device for far infrared rays, but also to add a night vision function by installing the imaging optical device in various devices. Is possible. For example, a digital device having a far-infrared image input function such as a smartphone with an infrared camera can be configured.

As an example of a digital device with a far-infrared image input function, FIG. 20 shows a schematic configuration example of the digital device DU in a schematic cross section. The imaging optical device LU mounted on the digital device DU shown in FIG. 20 is an imaging lens system LN (AX: optical axis) that forms a far-infrared optical image (image plane) IM of an object in order from the object (namely, subject) side. ), A parallel plate PT (corresponding to a cover glass of the image sensor SR, an optical filter arranged as necessary), and an optical image formed on the light receiving surface (imaging surface) SS by the photographing lens system LN. And an image sensor SR that converts IM into an electrical signal. When a digital device DU with an image input function is constituted by this imaging optical device LU, the imaging optical device LU is usually arranged inside the body, but when necessary to realize the camera function, a form as necessary is adopted. Is possible. For example, the unitized imaging optical device LU can be configured to be detachable or rotatable with respect to the main body of the digital device DU.

As described above, the photographing lens system LN is configured to form the optical image IM composed of far infrared rays on the light receiving surface SS of the imaging element SR. As the image sensor SR, for example, a far-infrared image sensor (thermosensor or the like) having a plurality of pixels (tens of thousands to hundreds of thousands of pixels) and using a wavelength of about 7 to 10 μm is used. Since the photographic lens system LN is provided so that the optical image IM of the subject is formed on the light receiving surface SS which is a photoelectric conversion unit of the imaging element SR, the optical image IM formed by the photographic lens system LN is It is converted into an electrical signal by the image sensor SR.

The digital device DU includes a signal processing unit 1, a control unit 2, a memory 3, an operation unit 4, a display unit 5 and the like in addition to the imaging optical device LU. The signal generated by the image sensor SR is subjected to predetermined digital image processing, image compression processing, and the like in the signal processing unit 1 as necessary, and recorded as a digital video signal in the memory 3 (semiconductor memory, optical disc, etc.) In some cases, it is transmitted to other devices via a cable or converted into an infrared signal or the like (for example, a communication function of a mobile phone). The control unit 2 is composed of a microcomputer, and controls functions such as a shooting function (still image shooting function, moving image shooting function, etc.), an image reproduction function, etc .; a lens moving mechanism for focusing, etc. For example, the control unit 2 controls the imaging optical device LU so as to perform at least one of still image shooting and moving image shooting of a subject. The display unit 5 includes a display such as a liquid crystal monitor, and performs image display using an image signal converted by the image sensor SR or image information recorded in the memory 3. The operation unit 4 is a part including operation members such as an operation button (for example, a release button) and an operation dial (for example, a shooting mode dial), and transmits information input by the operator to the control unit 2.

Hereinafter, the configuration of the far-infrared lens and the photographing lens system embodying the present invention will be described more specifically with reference to the construction data of the examples. Examples 1 to 8 (EX1 to 8) listed here are numerical examples corresponding to the first to eighth embodiments, respectively, and are optical configuration diagrams showing the first to eighth embodiments. (FIG. 4, FIG. 6, FIG. 8,..., FIG. 16, FIG. 18) respectively show the lens configuration (lens cross-sectional shape, lens arrangement, etc.), optical path, etc. of the corresponding Examples 1 to 8.

In the construction data of each embodiment, as surface data, in order from the left column, surface number (OB: object surface, ST: aperture surface, IM: image surface), radius of curvature r (mm) in paraxial, axial surface distance d (mm), material name (none: air).

A surface with * in the surface number is an aspheric surface, and the surface shape is defined by the following expression (AS) using a local orthogonal coordinate system (x, y, z) with the surface vertex as the origin. . As aspheric data, an aspheric coefficient or the like is shown. It should be noted that the coefficient of the term not described in the aspherical data of each embodiment is 0, and ^En = × 10 ⁻ⁿ for all data.
z = (C · h ² ) / [1 + √ {1− (1 + K) · C ² · h ² }] + Σ (Ai · h ⁱ ) (AS)
However,
h: height in the direction perpendicular to the z axis (optical axis AX) (h ² = x ² + y ² ),
z: the amount of sag in the direction of the optical axis AX at the position of the height h (based on the surface vertex),
C: curvature at the surface vertex (the reciprocal of the radius of curvature r),
K: conic constant,
Ai: i-th order aspheric coefficient (Σ represents the sum of 4th order to ∞ order for i),
It is.

The surface numbered with # is a diffraction grating surface, and the diffractive structure is expressed by the following equation using a local orthogonal coordinate system (x, y, z) having the surface vertex as the origin, like an aspheric surface. (DS). The diffraction grating is a rotationally symmetric grating with respect to the optical axis, and first-order diffraction with respect to a wavelength of 10 μm is used, and the shape is given by a phase difference Pz with respect to a wavelength of 10 μm. As diffraction grating surface data, a diffraction order, a diffraction wavelength, and a phase coefficient are shown. It should be noted that the coefficient of the term not described in the diffraction grating plane data of each example is 0, and ^En = × 10 ⁻ⁿ for all data.
Pz = Σ (Bj · h ^j ) (DS)
However,
h: height in the direction perpendicular to the z axis (optical axis AX) (h ² = x ² + y ² ),
Pz: phase difference,
Bj: j-th order phase coefficient (Σ represents the total from the second order to the ∞ order for j),
It is.

As the refractive index and dispersion data of the optical material constituting each lens, the refractive index N10 for a wavelength of 10 μm and the dispersion ν = (N10-1) / (N8−N12) for a wavelength of 8 to 12 μm are shown below (N8: Refractive index for wavelength 8 μm, N12: Refractive index for wavelength 12 μm). The parallel plate PT in front of the image plane IM is a protective plate for the far infrared sensor, and is made of Ge (germanium).
PE (polyethylene) N10 = 1.5226, ν = 15.10
NaCl (sodium chloride) N10 = 1.4947, ν = 20.11
KBr (potassium bromide) N10 = 1.5242, ν = 64.72
Ge (germanium): N10 = 4.0004312, ν = 784.54

Specs indicate design wavelength (nm), focal length (f, mm) of the entire system, F number (FNO), full length (mm), and half angle of view (°). Table 1 shows the focal lengths (f1 to f4, mm) of the first to fourth lenses L1 to L4 and the minimum and maximum thicknesses (μm) of the coating layer made of an organic material (PE). .

5, FIG. 7, FIG. 9,..., FIG. 17, and FIG. 19 are aberration diagrams corresponding to Examples 1 to 8 (EX1 to 8), respectively. Point aberration diagram, (C) is a distortion diagram. The spherical aberration diagram shows a spherical aberration amount at a design wavelength (evaluation wavelength) of 10000 nm indicated by a solid line, a spherical aberration amount at a wavelength of 8000 nm indicated by a one-dot chain line, and a spherical aberration amount at a wavelength of 9000 nm indicated by a two-dot chain line (however, only in FIG. 15) The amount of spherical aberration at a wavelength of 7000 nm indicated by a dotted line and the amount of spherical aberration at a wavelength of 12000 nm indicated by a broken line (however, the amount of spherical aberration at a wavelength of 13000 nm indicated by a broken line in FIG. 15) are paraxial images. The amount of displacement (mm) in the optical axis AX direction from the surface is represented, and the vertical axis represents a value obtained by normalizing the height of incidence on the pupil by the maximum height (that is, the relative pupil height). In the astigmatism diagram, the broken line T represents the tangential image plane at the design wavelength of 10000 nm, and the solid line S represents the sagittal image plane at the design wavelength of 10000 nm as the amount of deviation (mm) in the optical axis AX direction from the paraxial image plane. The vertical axis represents the half angle of view ω (ANGLE, °). In the distortion diagram, the horizontal axis represents the distortion (%) at the design wavelength of 10000 nm, and the vertical axis represents the half angle of view ω (ANGLE, °). Note that the maximum value of the half field angle ω corresponds to the maximum image height Y ′ on the image plane IM (half the diagonal length of the light receiving surface SS of the image sensor SR).

Example 1
Unit: mm
Surface data surface number r d Material name OB: ∞ ∞
1 #: 12.42933 0.030000 PE
2: 12.39933 4.720351 NaCl
3: 52.47570 0.010000 PE
4: 52.46570 5.779114
5 (ST): ∞ 5.555470
6 #: -6.51473 0.030000 PE
7: -6.54473 3.598074 NaCl
8: -8.46453 0.010000 PE
9: -8.47453 1.241609
10: 8.80004 0.010000 PE
11: 8.79004 4.310264 NaCl
12: 590.02108 0.010000 PE
13: 590.01108 0.142410
14: ∞ 0.782095 Ge
15: ∞ 3.500000
IM: ∞ 0.000000

Spec Design wavelength 10000.0nm
Focal length f 17.6840
FNO 1.1000
Total length 26.2294
Half angle of view 15.5000 °

Diffraction grating plane data Diffraction grating plane 1 #:
Diffraction order: 1.000000
Diffraction wavelength: 10000.00nm
B2: -2.1816E-03

Diffraction grating plane data Diffraction grating plane 6 #:
Diffraction order: 1.000000
Diffraction wavelength: 10000.00nm
B2: -9.5902E-03

Example 2
Unit: mm
Surface data surface number r d Material name OB: ∞ ∞
1 #: 16.52849 0.030000 PE
2: 16.49849 4.000000 NaCl
3: 74.49885 0.010000 PE
4: 74.48885 7.818001
5 (ST): ∞ 4.752288
6 * #: -9.01426 0.030000 PE
7: -8.34454 4.000000 NaCl
8: -8.70413 0.010000 PE
9: -8.71413 1.727038
10: 10.37919 0.010000 PE
11: 10.36919 4.000000 NaCl
12: 96.57674 0.010000 PE
13: 96.56674 0.472797
14: ∞ 0.782095 Ge
15: ∞ 6.037271
IM: ∞ 0.000000

Spec Design wavelength 10000.0nm
Focal length f 17.6840
FNO 1.1000
Total length 27.6522
Half angle of view 15.5000 °

Aspheric data Aspheric surface 6 *:
K: 0.000000
A4: -0.387423E-03
A6: 0.104738E-04
A8: -0.271465E-06
A10: 0.000000E + 00

Diffraction grating plane data Diffraction grating plane 1 #:
Diffraction order: 1.000000
Diffraction wavelength: 10000.00nm
B2: -9.1544E-04

Diffraction grating plane data Diffraction grating plane 6 #:
Diffraction order: 1.000000
Diffraction wavelength: 10000.00nm
B2: -4.8603E-03

Example 3
Unit: mm
Surface data surface number r d Material name OB: ∞ ∞
1: 17.16593 0.010000 PE
2: 17.15593 4.000000 KBr
3: 77.02012 0.010000 PE
4: 77.01012 1.096627
5 (ST): ∞ 2.888307
6 *: -14.05563 0.030000 PE
7: -11.49406 4.000000 KBr
8: -10.91321 0.010000 PE
9: -10.92321 7.976511
10: 12.57432 0.010000 PE
11: 12.56432 4.500000 KBr
12: 195.56572 0.010000 PE
13: 195.55572 2.401918
14: ∞ 0.782095 Ge
15: ∞ 4.452996
IM: ∞ 0.000000

Spec Design wavelength 10000.0nm
Focal length f 17.6840
FNO 1.1000
Total length 27.7255
Half angle of view 15.5000 °

Aspheric data Aspheric surface 6 *:
K: 0.000000
A4: -0.199777E-03
A6: 0.126929E-05
A8: -0.259688E-07
A10: 0.000000E + 00

Example 4
Unit: mm
Surface data surface number r d Material name OB: ∞ ∞
1: 16.16531 0.010000 PE
2: 16.15531 4.000000 KBr
3: 124.87967 0.010000 PE
4: 124.86967 2.637166
5 (ST): ∞ 4.047532
6 *: -13.83649 0.030000 PE
7: -12.58750 4.000000 NaCl
8: -11.24155 0.010000 PE
9: -11.25155 6.212953
10: 10.88550 0.010000 PE
11: 10.87550 4.500000 KBr
12: 84.64196 0.010000 PE
13: 84.63196 0.833599
14: ∞ 0.782095 Ge
15: ∞ 4.766400
IM: ∞ 0.000000

Spec Design wavelength 10000.0nm
Focal length f 17.6838
FNO 1.1000
Total length 27.0933
Half angle of view 15.5000 °

Aspheric data Aspheric surface 6 *:
K: 0.000000
A4: -0.220312E-03
A6: 0.262848E-05
A8: -0.373105E-07
A10: 0.000000E + 00

Example 5
Unit: mm
Surface data surface number r d Material name OB: ∞ ∞
1: 19.79603 0.010000 PE
2: 19.78603 4.000000 KBr
3: -31.11348 0.010000 PE
4: -31.12348 0.100000
5 (ST): ∞ 2.518416
6 #: -11.54794 0.030000 PE
7: -11.57794 2.518416 KBr
8: -13.50903 0.010000 PE
9: -13.51903 9.622011
10: 8.99551 0.010000 PE
11: 8.98551 3.392883 KBr
12: 44.47568 0.010000 PE
13: 44.46568 0.628999
14: ∞ 0.782095 Ge
15: ∞ 4.209075
IM: ∞ 0.000000

Spec Design wavelength 10000.0nm
Focal length f 16.6196
FNO 1.1000
Total length 23.6428
Half angle of view 15.5000

Diffraction grating plane data Diffraction grating plane 6 #:
Diffraction order: 1.000000
Diffraction wavelength: 10000.00nm
B2: -8.9680E-04

Example 6
Unit: mm
Surface data surface number r d Material name OB: ∞ ∞
1 * #: 38.99978 0.030000 PE
2: 38.96978 3.085728 NaCl
3: -3096.13384 0.010000 PE
4: -3096.14384 5.178473
5 * #: 13.63702 0.030000 PE
6: 13.60702 2.500000 NaCl
7: 15.71786 0.010000 PE
8: 15.70786 5.701996
9 (ST): ∞ 7.196684
10 * #: 10.04766 0.030000 PE
11: 9.96744 2.500000 NaCl
12: 10.75369 0.010000 PE
13: 10.74369 0.204423
14 *: 10.75984 0.030000 PE
15: 10.72984 2.970754 NaCl
16: 1140.62601 0.010000 PE
17: 1140.61601 0.219847
18: ∞ 0.782095 Ge
19: ∞ 3.503308
IM: ∞ 0.000000

Spec Design wavelength 10000.0nm
Focal length f 17.6879
FNO 1.1000
Total length 30.5000
Half angle of view 15.5000 °

Aspheric data Aspheric surface 1 *:
K: 0.000000
A4: -0.755616E-05
A6: -0.438474E-07
A8: 0.175040E-09
A10: 0.000000E + 00

Aspheric data Aspheric surface 5 *:
K: 0.000000
A4: -0.594242E-04
A6: 0.160824E-05
A8: -0.116127E-07
A10: 0.000000E + 00

Aspheric data Aspheric surface 10 *:
K: 0.000000
A4: 0.000000E + 00
A6: 0.700646E-05
A8: -0.267079E-06
A10: 0.210065E-08

Aspheric data Aspheric surface 14 *:
K: 0.000000
A4: -0.499437E-03
A6: 0.105082E-04
A8: -0.319212E-08
A10: 0.000000E + 00

Diffraction grating plane data Diffraction grating plane 1 #:
Diffraction order: 1.000000
Diffraction wavelength: 10000.00nm
B2: -1.7691E-03

Diffraction grating plane data Diffraction grating plane 5 #:
Diffraction order: 1.000000
Diffraction wavelength: 10000.00nm
B2: -2.1959E-03

Diffraction grating plane data Diffraction grating plane 10 #:
Diffraction order: 1.000000
Diffraction wavelength: 10000.00nm
B2: -9.1656E-03

Example 7
Unit: mm
Surface data surface number r d Material name OB: ∞ ∞
1 *: 9.80068 0.030000 PE
2: 9.77068 6.222632 KBr
3: 125.53000 0.030000 PE
4 *: 125.50000 3.466049
5 (ST): ∞ 0.807162
6 *: -23.30025 0.030000 PE
7: -23.33025 4.500000 KBr
8: -12.44062 0.030000 PE
9 *: -12.47062 2.401918
10: ∞ 0.782095 Ge
11: ∞ 5.407036
IM: ∞ 0.000000

Spec Design wavelength 10000.0nm
Focal length f 17.6840
FNO 1.1000
Total length 18.2999
Half angle of view 15.5000 °

Aspheric data Aspheric surface 1 *:
K: 0.000000
A4: -0.512773E-04
A6: 0.719061E-06
A8: -0.159701E-07
A10: 0.000000E + 00

Aspheric data Aspheric surface 4 *:
K: 0.000000
A4: 0.134409E-03
A6: -0.318764E-05
A8: 0.301769E-07
A10: 0.000000E + 00

Aspheric data Aspheric surface 6 *:
K: 0.000000
A4: 0.000000E + 00
A6: -0.170174E-04
A8: 0.756780E-06
A10: -0.888117E-08

Aspheric data Aspheric 9 *:
K: 0.000000
A4: 0.000000E + 00
A6: 0.314293E-04
A8: -0.121623E-05
A10: 0.208014E-07

Example 8
Unit: mm
Surface data surface number r d Material name OB: ∞ ∞
1 *: 12.65484 0.030000 PE
2: 12.62484 5.598237 KBr
3: 80.65113 0.030000 PE
4 *: 80.62113 8.197523
5 (ST): ∞ 4.252863
6 #: 9.77789 0.030000 PE
7: 9.74789 3.890661 KBr
8: 40.06229 0.030000 PE
9 #: 40.03229 0.457441
10: ∞ 0.782095 Ge
11: ∞ 3.499998
IM: ∞ 0.000000

Spec Design wavelength 10000.0nm
Focal length f 17.6842
FNO 1.1000
Total length 23.2988
Half angle of view 15.5000

Aspheric data Aspheric surface 1 *:
K: 0.000000
A4: -0.917199E-05
A6: 0.227517E-06
A8: -0.440588E-08
A10: 0.000000E + 00

Aspheric data Aspheric surface 4 *:
K: 0.000000
A4: 0.884917E-04
A6: -0.919709E-06
A8: 0.362242E-08
A10: 0.000000E + 00

Diffraction grating plane data Diffraction grating plane 6 #:
Diffraction order: 1.000000
Diffraction wavelength: 10000.00nm
B2: -7.5507E-03

Diffraction grating plane data Diffraction grating plane 9 #:
Diffraction order: 1.000000
Diffraction wavelength: 10000.00nm
B2: 7.9087E-03

LE Far-infrared lens CR Lens core CT Coating layer DU Digital equipment (camera system)
LU imaging optical device LN photographing lens system L1 to L4 first to fourth lens (far infrared lens)
ST Aperture SR Image sensor SS Photosensitive surface
IM image plane (optical image)
AX Optical axis 1 Signal processing unit 2 Control unit 3 Memory 4 Operation unit 5 Display unit

Claims

A lens used in the far-infrared band,
A lens core made of an inorganic crystal material having a refractive index with respect to a wavelength of 10 μm of 1.74 or less, and a coating layer made of an organic material that covers the entire lens core relatively thinly;
A lens, wherein at least one surface of the lens core is a spherical surface, and a diffraction grating is provided on a surface of the coating layer located on at least one spherical surface.
A lens used in the far-infrared band,
A lens core made of an inorganic crystal material having a refractive index with respect to a wavelength of 10 μm of 1.74 or less, and a coating layer made of an organic material that covers the entire lens core relatively thinly;
2. The lens according to claim 1, wherein both surfaces of the lens core are spherical surfaces, and an aspheric surface is provided on a surface of the covering layer located on at least one spherical surface.
3. The lens according to claim 1, wherein the thickness of the coating layer is 10 μm or more at the thinnest and 500 μm or less at the thickest.
3. The lens according to claim 2, wherein the aspherical surface provided on the surface of the covering layer has a shape in which the positive power becomes weaker as the distance from the optical axis increases.
The lens according to any one of claims 1 to 4, wherein the inorganic crystal material constituting the lens core is made of a substantially pure crystal.
It comprises two or more lenses having a lens core made of an inorganic crystal material having a refractive index with respect to a wavelength of 10 μm of 1.74 or less, and a coating layer made of an organic material that covers the entire lens core relatively thinly, of which A photographic lens system comprising at least one lens according to any one of claims 1 to 5.
A camera system comprising the photographic lens system according to claim 6.