WO2016208433A1 - Far-infrared lens system, imaging optical apparatus, and digital device - Google Patents

Abstract

The far-infrared lens system according to the present invention is a lens system used in the far-infrared band, and is configured from, in order from the object side, three single lenses including a first lens having a negative power, a second lens having a positive power, and a third lens having a positive power, the conditional expression 3.2 < f2/f < 17 (where f2 is the focal distance of the second lens and f is the focal distance of the far-infrared lens system as a whole) being satisfied, and the half field angle being greater than 30°.

Description

Far-infrared lens system, imaging optical device and digital equipment

The present invention relates to a far-infrared lens system, an imaging optical device, and a digital device. For example, an imaging lens system used in the far-infrared band (wavelength 8 to 12 μm band), and particularly has a brightness with a peripheral light amount ratio of 50% or more even at a wide angle where the half angle of view ω is greater than 30 °, A far-infrared lens system that can be used in an inexpensive camera system, an imaging optical device that captures far-infrared images obtained by the far-infrared lens system with a far-infrared sensor, and a digital device with an image input function equipped with a far-infrared lens system , About.

With the spread of surveillance cameras and security cameras, an inexpensive and small far-infrared lens system is required. Since the lens material used for the far-infrared lens system is more expensive than general optical glass, the smaller the lens volume, the lower the cost. Therefore, from the viewpoint of balance with optical performance and the like, Patent Documents 1 to 4 propose a relatively wide-angle infrared lens system including three lenses.

JP 2011-253006 A JP-A-4-128709 Japanese Unexamined Patent Publication No. 2009-63942 US2010 / 0232013 A1

The lens system described in Patent Document 1 is a three-element far-infrared lens system that covers a wide range from a standard angle of view to a wide angle with a half angle of view ω of 30 ° or more. In the case of the standard angle of view, the peripheral light amount ratio can be 50% or more if the off-axis light beam is restricted only by the diaphragm and is configured without vignetting. However, since the focal length of the second lens is shorter than the focal length of the entire system, and the second lens has a shorter focal length than the third lens, the half angle of view ω is 30 ° or more. When the wide-angle lens system is configured, the off-axis light beam becomes thin, and the angle at which the off-axis chief ray reaches the image plane is tilted to the same angle as the field angle. It becomes impossible to make it 50% or more. Normally, when the second lens has such a focal length, the peripheral light amount ratio is about 25% to 40%.

Although the lens system described in Patent Document 4 is a lens system for near infrared rays, it has the same focal length ratio of the second lens and that of the second and third lenses as those described in Patent Document 1. Yes. Therefore, in the lens system having a half angle of view ω of 30 ° or more, the peripheral light amount ratio is similarly less than 50%.

In the three-lens infrared lens system described in Patent Document 2, the focal length of the second lens is slightly longer, but this is not sufficient from the viewpoint of the peripheral light quantity ratio. In this type of lens system, the peripheral light amount ratio is not a problem when the angle of view is from standard to telephoto. However, if the lens is used in a wide-angle lens system having a half angle of view ω of 30 ° or more, the peripheral light amount ratio is less than 50%, which is not desirable as a lens system specification.

Further, in the lens systems described in Patent Documents 1 to 4, a material having a refractive index smaller than 2.9 is used for the first lens. For this reason, the first lens cannot have a very strong curvature, and the interval between the first lens and the second lens is narrowed to ensure performance. When configured in this manner, a lens system having a half angle of view ω of 30 ° or less can ensure a sufficient peripheral light amount ratio and lens performance. However, in a lens system in which the half angle of view ω is greater than 30 °, the off-axis light flux does not pass through a position higher than the optical axis in the first lens, and therefore, off-axis due to a local refractive power difference between the on-axis and the periphery. The effect of enlarging the pupil is hardly obtained, and the peripheral light amount ratio falls below 50%.

In the far-infrared lens system described in Patent Document 3, a diaphragm is arranged in the foreground in a three-lens lens system. By adopting such a configuration, the front lens diameter can be reduced even with a wide-angle lens system. However, since the off-axis light beam cannot be corrected by the lens for the reduction of the pupil area viewed from an oblique direction, the angle of view is determined by the cos 4th power law. The peripheral light amount ratio is reduced by that amount.

In the lens systems described in Patent Documents 1 and 2, the third lens has a strong convex surface facing the image side. With this configuration, the angle at which the off-axis light beam reaches the image plane can be easily controlled, but the off-axis light beam passes through a high position on the rear surface of the third lens and is refracted rapidly. An external coma aberration is generated and distortion is greatly negative, which is not preferable for a thermo camera.

The present invention has been made in view of such a situation. The object of the present invention is to have a peripheral light quantity ratio of 50% or more while the half angle of view ω is a wide angle larger than 30 ° and as few as three. An object of the present invention is to provide a high-performance and inexpensive far-infrared lens system in which aberrations are favorably corrected even with the number of lenses, an imaging optical device and a digital device including the same.

To achieve the above object, the far-infrared lens system of the first invention is a lens system used in the far-infrared band,
In order from the object side, the lens is composed of three single lenses of a first lens having negative power, a second lens having positive power, and a third lens having positive power. The following conditional expression ( 1) is satisfied, and the half angle of view is larger than 30 °.
3.2 <f2 / f <17 (1)
However,
f2: focal length of the second lens,
f: focal length of the entire far-infrared lens system,
It is.

A far-infrared lens system according to a second invention is characterized in that, in the first invention, the first lens is made of a material having a refractive index larger than 2.9 at a wavelength of 10 μm.

A far-infrared lens system according to a third aspect of the present invention is characterized in that, in the first or second aspect, the first lens has a negative meniscus shape having a convex surface facing the object side.

The far-infrared lens system of the fourth invention is characterized in that, in the third invention, the following conditional expression (2) is satisfied.
3.0 <d2 / f <9.0 (2)
However,
d2: axial distance between the image side surface of the first lens and the object side surface of the second lens,
f: focal length of the entire far-infrared lens system,
It is.

A far-infrared lens system according to a fifth invention is characterized in that, in any one of the first to fourth inventions, the second lens has a positive meniscus shape or plano-convex shape with a convex surface facing the object side. To do.

A far-infrared lens system according to a sixth invention is characterized in that, in any one of the first to fifth inventions, a diaphragm is provided between an image side surface of the first lens and an object side of the third lens. And

A far-infrared lens system according to a seventh invention is the bi-convex lens according to any one of the first to sixth inventions, wherein the third lens has a convex surface having a stronger power directed toward the object side when both surfaces are compared. It has a shape or a positive meniscus shape with a convex surface facing the object side.

The far-infrared lens system of the eighth invention is characterized in that, in any one of the first to seventh inventions, the following conditional expression (3) is satisfied.
1.7 <f23 / f <2.8 (3)
However,
f23: composite focal length of the second lens and the third lens,
f: focal length of the entire far-infrared lens system,
It is.

The far-infrared lens system of the ninth invention is characterized in that, in any one of the first to eighth inventions, the following conditional expression (4) is satisfied.
1.45 <f2 / f3 <8.0 (4)
However,
f2: focal length of the second lens,
f3: focal length of the third lens,
It is.

An imaging optical device according to a tenth aspect of the invention is a far-infrared lens system according to any one of the first to ninth inventions, and a far-infrared optical image formed on the imaging surface is converted to an electrical signal. An infrared sensor, and the far-infrared lens system is provided so that a far-infrared optical image of a subject is formed on an imaging surface of the far-infrared sensor.

The digital apparatus according to an eleventh aspect is characterized in that at least one of a still image photographing and a moving image photographing function of a subject is added by including the imaging optical device according to the tenth aspect.

A far-infrared camera system according to a twelfth aspect includes the far-infrared lens system according to any one of the first to ninth aspects.

According to the present invention, three bright and high-performance far-infrared lens systems capable of obtaining a peripheral light amount ratio of 50% or more while having a distortion within ± 5% and a half angle of view ω larger than 30 ° are provided. Thus, a wide-angle far-infrared lens system suitable for a thermo camera that requires temperature detection can be provided at a low cost. Therefore, it is possible to realize an inexpensive but high-performance far-infrared lens system and an imaging optical device including the same. By using the far-infrared lens system or the imaging optical device according to the present invention in a digital device such as a night vision device, a thermography, a portable terminal, a camera system (for example, a digital camera, a surveillance camera, a security camera, an in-vehicle camera). Therefore, it is possible to add a high-performance far-infrared image input function to a digital device at a low cost and in a compact manner.

The lens block diagram of 1st Embodiment (Example 1). FIG. 6 is an aberration diagram of Example 1. The lens block diagram of 2nd Embodiment (Example 2). FIG. 6 is an aberration diagram of Example 2. The lens block diagram of 3rd Embodiment (Example 3). FIG. 6 is an aberration diagram of Example 3. The lens block diagram of 4th Embodiment (Example 4). FIG. 6 is an aberration diagram of Example 4. The lens block diagram of 5th Embodiment (Example 5). FIG. 6 is an aberration diagram of Example 5. The lens block diagram of 6th Embodiment (Example 6). FIG. 10 is an aberration diagram of Example 6. The lens block diagram of 7th Embodiment (Example 7). FIG. 10 is an aberration diagram of Example 7. The lens block diagram of 8th Embodiment (Example 8). FIG. 10 is an aberration diagram of Example 8. The lens block diagram of 9th Embodiment (Example 9). FIG. 10 is an aberration diagram of Example 9. The lens block diagram of 10th Embodiment (Example 10). FIG. 10 is an aberration diagram of Example 10. The lens block diagram of 11th Embodiment (Example 11). FIG. 10 shows aberration diagrams of Example 11. The lens block diagram of 12th Embodiment (Example 12). FIG. 10 is an aberration diagram of Example 12. The lens block diagram of 13th Embodiment (Example 13). Aberration diagram of Example 13. The lens block diagram of 14th Embodiment (Example 14). Aberration diagram of Example 14. The lens block diagram of 15th Embodiment (Example 15). FIG. 18 shows aberration diagrams of Example 15. The lens block diagram of 16th Embodiment (Example 16). Aberration diagram of Example 16. The lens block diagram of 17th Embodiment (Example 17). Aberration diagram of Example 17. The schematic diagram which shows the schematic structural example of the digital apparatus carrying a far-infrared lens system.

Hereinafter, the far-infrared lens system, the imaging optical device, the digital device, and the like according to the present invention will be described. The far-infrared lens system according to the present invention is a lens system used in the far-infrared band, and in order from the object side, a first lens having a negative power, a second lens having a positive power, and a positive lens It consists of three single lenses with a third lens that has power (power: an amount defined by the reciprocal of the focal length), satisfies the following conditional expression (1), and has a half angle of view ω of 30 ° It is also characterized by being large.
3.2 <f2 / f <17 (1)
However,
f2: focal length of the second lens,
f: focal length of the entire far-infrared lens system,
It is.

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 emitted light having a wavelength of 8 to 12 μm, and most of the far infrared optical system is used at a wavelength of 8 to 12 μm. The far-infrared region with a wavelength of 8 to 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. Recently, far-infrared sensor manufacturing technology has advanced, and inexpensive thermopiles, uncooled microbolometers, and the like have been manufactured, and an inexpensive lens system that is compatible with these is desired. In addition, a lineup of far-infrared lens systems applicable to various fields is also desired, and in particular, a wide-angle lens system having a half angle of view ω larger than 30 ° is required.

However, at present, there are few far-infrared lens systems with a wide angle, and the reason is that it is not possible to prevent the decrease in the peripheral light amount ratio due to the angle of view of the lens system (peripheral light amount ratio: the image plane by the axial light beam). The ratio of the amount of light that reaches the image plane by the most off-axis light flux to the amount of light that reaches. The decrease in the peripheral light amount ratio due to the angle of view is known as the cosine fourth law (cosine fourth law). According to the cosine fourth law, the angle of the light beam incident on the lens system is θ, and the ratio of the light amount to the axis. However, in an ideal lens, it decreases to the fourth power of cos θ (theoretical value).

The distance from the object to the lens is off-axis and cos θ times on the axis, and the amount of light decreases in proportion to the square of the object distance. When the entrance pupil area (in the case of an ideal lens) is viewed obliquely, the area is reduced by a factor of cos θ and the amount of incident light is reduced. The image plane arrival angle (in the case of an ideal lens) is θ, and the amount of light when the lens reaches obliquely decreases by a factor of cos θ. At the same time, it is reduced to the fourth power of cos θ. That is, the difference in the object distance between the on-axis and the off-axis, the entrance pupil area viewed obliquely, and the oblique incidence of the off-axis light beam on the image plane are combined to reduce the amount of light corresponding to the cos 4th power of the angle of view. .

For example, in a lens system with a half angle of view ω of 30 °, the peripheral light quantity ratio is 56% or less even when the aperture efficiency is 100%, and in a lens system with a wider angle, it is less than 50%. Since the far-infrared lens system detects heat, a decrease in the peripheral light amount ratio is detected by the far-infrared sensor as a pseudo heat amount decrease. Although it is possible to perform temperature correction in consideration of a decrease in the peripheral light amount ratio by calibration for each lens system, the resolution with respect to the temperature change differs between the on-axis and the periphery by performing the correction. This difference becomes more significant as the angle of view of the lens system becomes wider. Particularly, when the half angle of view ω is larger than 30 °, sufficient resolution cannot be obtained for use as a thermo camera for measuring temperature.

As a method of compensating for the decrease in the peripheral light amount ratio due to the angle of view, it is conceivable to generate distortion in the negative direction. When distortion in the minus direction is generated, the image is reduced and projected toward the periphery. In this method, a wide range of heat is imaged in a smaller range, the light amount ratio is increased by the amount of distortion, and a decrease in the peripheral light amount ratio can be suppressed over the entire screen. For example, when the half angle of view ω is 30 °, a lens system in which the decrease in the peripheral light amount ratio is about 5% can be configured even with a general lens system by providing a distortion of minus 15%. However, when the half angle of view ω is larger than 30 °, the distortion that must be generated in order to make the peripheral light amount ratio substantially uniform becomes extremely large. Therefore, it is difficult to specify accurately, which is not desirable for the application of a thermo camera.

As described above, it is desirable that the half field angle ω of the far-infrared lens system is larger than 30 ° in order to enable application to various fields. Most conventional far-infrared sensors are expensive and can accurately display temperature resolution. In such a sensor, it is necessary to cool the periphery of the sensor with a refrigerant such as liquid nitrogen in order to sufficiently exhibit temperature resolution. Therefore, since a space for cooling is required, a wide-angle lens system in which the lens back tends to be relatively short has hardly been manufactured. However, there is a need to view a wider field of view, and in recent years, non-cooled sensors such as microbolometers that do not require cooling can be manufactured at low cost. Therefore, even a far-infrared lens system having a wide angle of half field angle ω greater than 30 ° can be realized.

The reason why the first lens has negative power is to secure a sufficient lens back with a wide-angle lens system in which the half angle of view ω is larger than 30 °. In an inexpensive uncooled sensor for far infrared rays, a cover glass is disposed and sealed in front of the light receiving surface to maintain the resolving power, and a vacuum is formed between the light receiving surface and the cover glass. For this reason, a space is required between the light receiving surface and the lens. In a lens system with a wide angle and a short focal length, it is necessary to bring the principal point as far back as possible. By making the first lens a negative lens, the principal point can be brought behind the final surface of the lens system, and a sufficient lens back can be secured even at a wide angle.

When the focal length f2 / f of the standardized second lens is set within a predetermined range longer than the conventional one so as to satisfy the conditional expression (1) in the configuration of three negative and positive lenses, the off-axis luminous flux width is set. It is possible to keep the lens system wide behind the lens system, and a lens system having a peripheral light amount ratio of 50% or more can be realized even with a lens system having a half angle of view ω wider than 30 °. By making f2 / f larger than the lower limit of conditional expression (1), it becomes possible to keep the off-axis luminous flux width large to the rear of the lens system, the half angle of view ω is larger than 30 °, and distortion is caused. Even within ± 5%, the peripheral light amount ratio can be brightened to 50% or more. In addition, since the angle at which the off-axis chief ray reaches the image plane can be made nearly vertical, an effect of increasing the peripheral light amount ratio can be obtained. By making f2 / f smaller than the upper limit of conditional expression (1), the power of the third lens can be prevented from becoming too strong, and the coma aberration of the off-axis light beam can be suppressed to provide a high-performance lens system. . Further, the arrival angle of the off-axis principal ray on the image plane can be prevented from being swung from the vertical direction to the reverse direction, and the light quantity ratio can be kept high.

According to the above-described characteristic configuration, a bright and high-performance far-infrared lens system capable of obtaining a peripheral light quantity ratio of 50% or more while having a distortion within ± 5% and a half angle of view ω larger than 30 °, This can be realized with a small number of three, and a wide-angle far-infrared lens system suitable for a thermocamera that requires temperature detection can be provided at low cost. Therefore, it is possible to realize an inexpensive but high-performance far-infrared lens system and an imaging optical device including the same. And by using the far-infrared lens system for camera systems such as digital cameras, surveillance cameras, security cameras, and in-vehicle cameras, or by using imaging optical devices for digital devices such as portable terminals, night vision devices, and thermography, It is possible to realize a high-performance far-infrared image input function at a low cost and in a compact manner, contributing to its compactness, high performance, and high functionality. The following describes how to obtain these effects in a well-balanced manner, as well as setting conditions for achieving higher optical performance, securing a peripheral light amount ratio, widening the angle, downsizing, and the like.

Regarding the focal length of the second lens, it is desirable to satisfy the following conditional expression (1a), and it is more desirable to satisfy the conditional expression (1b).
3.2 <f2 / f <9 (1a)
4.3 <f2 / f <5.6 (1b)
These conditional expressions (1a) and (1b) define more preferable condition ranges based on the above viewpoints, etc., among the condition ranges defined by the conditional expression (1). Therefore, the above effect can be further enhanced by preferably satisfying conditional expression (1a), more preferably satisfying conditional expression (1b). For example, the peripheral light quantity ratio can be further increased by exceeding the lower limit of the conditional expression (1a) or (1b).

The first lens is preferably made of a material having a refractive index larger than 2.9 at a wavelength of 10 μm. The refractive index is the ratio of the traveling speed of light in the material 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 used conventionally is germanium (Ge) = 4.004, silicon (Si) = 3.418, zinc sulfide (ZnS) = 2.200, selenium. Zinc halide (ZnSe) = 2.407 or the like. Furthermore, sodium chloride (NaCl) or potassium bromide (KBr) having a refractive index of around 1.5, metallic materials having a refractive index larger than 2.9, and the like are included, and there are many variations in the refractive index.

By using a material with a high refractive index for the first lens, the curvature of the lens surface can be relaxed. For this reason, even when the off-axis light beam passes through a high position from the optical axis, the coma aberration is suppressed to be small, and the distortion is also suppressed to be not greatly negative. Therefore, a lens system with good optical performance can be realized. In addition, since the first lens can be disposed relatively apart, the pupil size of the off-axis light beam can be controlled. That is, by using a material having a refractive index greater than 2.9 at a wavelength of 10 μm for the first lens, the distance between the first lens and the second lens can be made longer than before, so that the first lens Due to the effect of expanding the pupil of the off-axis light beam passing through a high position, it becomes possible to realize a lens system having a higher peripheral light amount ratio.

It is desirable that the first lens has a negative meniscus shape with a convex surface facing the object side. When the first lens has a convex surface directed toward the object side, the off-axis light beam passes through a high position from the optical axis. As a result, the pupil becomes larger as it is off-axis, so that the peripheral light amount ratio can be effectively increased.

It is desirable to satisfy the following conditional expression (2), and it is further desirable to satisfy the conditional expression (2) using a negative meniscus lens having a convex surface facing the object side as the first lens.
3.0 <d2 / f <9.0 (2)
However,
d2: axial distance between the image side surface of the first lens and the object side surface of the second lens,
f: focal length of the entire far-infrared lens system,
It is.

If the standardized first and second lens intervals d2 / f are set within a predetermined range so as to satisfy the conditional expression (2), the peripheral light amount ratio can be further increased. When d2 / f is made larger than the lower limit of conditional expression (2), the off-axis light beam passes through a high position from the optical axis of the first lens. When the object side surface of the first lens has a strong convex shape, the local refractive power is stronger than on the axis at a position higher than the optical axis of the convex surface. For this reason, it is possible to increase the pupil diameter with respect to the off-axis light beam, and the effect of increasing the peripheral light amount ratio is given, so that the peripheral light amount ratio can be effectively increased to 50% or more. By making d2 / f smaller than the upper limit of the conditional expression (2), it is possible to prevent the off-axis light beam from passing through a position that is too high on the first lens, and to prevent a large coma aberration or distortion from being caused by a strong convex surface. Can be configured.

It is more desirable to satisfy the following conditional expression (2a).
4.3 <d2 / f <7.3 (2a)
This conditional expression (2a) defines a more preferable condition range based on the above viewpoints, etc., among the condition ranges defined by the conditional expression (2). Therefore, the above effect can be further increased preferably by satisfying conditional expression (2a). For example, the peripheral light amount ratio can be further increased by exceeding the lower limit of the conditional expression (2a).

It is desirable that the second lens has a positive meniscus shape or plano-convex shape with a convex surface facing the object side. Since the first lens has negative power, the light flux is converged for the first time by the second lens. By converging the light beam on the first surface of the second lens, it is possible to suppress the spherical aberration and the curvature of field without reducing the light beam width too much.

If the second lens has a biconvex shape, the second lens can have a strong positive power. However, from the condition (1), the second lens needs to have a strong power. There is not much sex. When the power of the second lens is not so strong, if the object side surface is first given a positive power as described above, the image side surface is inevitably weakened to correct spherical aberration and field curvature. Or it has weak negative power. In addition, since a material having a higher refractive index has a smaller surface curvature and a smaller aberration, a material having a higher refractive index than 2.9, such as Ge and Si, is used in each of the examples described later. In a design using a lens material having a low refractive index, there is a case where it is necessary to give positive power to both surfaces even if the power of the second lens is within the range of the conditional expression (1). Conceivable.

It is desirable to have a stop between the image side surface of the first lens and the object side of the third lens. The object side of the first lens is also conceivable as the position where the aperture is placed. However, when the diaphragm is placed on the object side of the first lens, if the off-axis light beam is incident obliquely, the pupil is reduced by cos times the incident angle, even if there is no vignetting by the lens, and the peripheral light quantity ratio is reduced. Resulting in. By placing the stop closer to the image side than the first lens, the first lens or the first lens and the second lens can increase the pupil diameter with respect to the off-axis light beam, and the peripheral light amount ratio is increased. It becomes. Further, in order to sufficiently obtain the pupil enlargement effect due to the off-axis light beam passing through the high position of the first lens, the position of the stop is set to be the second lens than 1/2 of the interval between the first lens and the second lens. It is more preferable to be close to.

It is desirable that the third lens has a biconvex shape in which the convex surface with the higher power is directed toward the object side when comparing both surfaces, or a positive meniscus shape with the convex surface directed toward the object side. In other words, the shape of the third lens having a relatively strong positive power is a biconvex shape in which the strong convex surface of both convex surfaces having positive power faces the object side, or the convex surface faces the object side. A positive meniscus shape is desirable. By adopting such a shape, it is possible to condense a light beam that reaches the third lens with a large light beam width in a shape that minimizes aberration. Since spherical aberration and coma generated by the third lens can be reduced, aberration correction can be performed efficiently by the negative power of the first lens.

It is desirable to satisfy the following conditional expression (3).
1.7 <f23 / f <2.8 (3)
However,
f23: composite focal length of the second lens and the third lens,
f: focal length of the entire far-infrared lens system,
It is.

When the normalized second and third combined focal lengths f23 / f are set within a predetermined range so as to satisfy the conditional expression (3), the positive power concentrates behind the lens system. However, it is possible to secure a lens back while the lens system is larger than 30 ° and has a wide angle and a short focal length. By making f23 / f smaller than the upper limit of conditional expression (3), a short focal length can be realized, and a lens system with a small front lens diameter can be obtained even at a wide angle so that the total lens length does not become too large. This is possible, and the configuration is such that off-axis coma and distortion are reduced. By making f23 / f larger than the lower limit of conditional expression (3), it is possible to prevent the positive power concentrated behind the lens system from becoming too strong, and to reduce spherical aberration and curvature of field. It becomes.

It is more desirable to satisfy the following conditional expression (3a).
2.0 <f23 / f <2.7 (3a)
This conditional expression (3a) defines a more preferable condition range based on the above viewpoints, etc., among the condition ranges defined by the conditional expression (3). Therefore, the above effect can be further increased preferably by satisfying conditional expression (3a).

It is desirable to satisfy the following conditional expression (4).
1.45 <f2 / f3 <8.0 (4)
However,
f2: focal length of the second lens,
f3: focal length of the third lens,
It is.

When the power ratio f2 / f3 between the second lens and the third lens is set within a predetermined range so as to satisfy the conditional expression (4), an off-axis principal ray image plane that is closely related to the peripheral light amount ratio is obtained. It is possible to control the angle of arrival. For this reason, even if the half angle of view ω is a wide angle of 30 ° or more and the distortion is within ± 5%, it is possible to obtain a configuration in which the peripheral light amount ratio is sufficiently secured. The peripheral light amount ratio and the angle of light rays reaching the image plane have a deep relationship as indicated by the cos 4th law. That is, if the light rays reaching the image plane are close to vertical, the decrease in the peripheral light amount ratio can be reduced.

By making f2 / f3 larger than the lower limit of conditional expression (4), the off-axis light beam is refracted behind the lens system, and the off-axis principal ray reaches at an angle close to the image plane. By making f2 / f3 smaller than the upper limit of conditional expression (4), the arrival angle of the off-axis principal ray on the image plane can be prevented from deviating from vertical in the reverse direction. Further, the configuration is such that the off-axis coma aberration is reduced by preventing the third lens power from becoming too strong. In addition, when the angle of arrival of the off-axis chief ray on the image plane is nearly vertical, the aperture image is formed at a position far from the light receiving surface, so that ghosting due to the aperture can be prevented, which is suitable for a far infrared camera. It becomes a lens type.

It is more desirable to satisfy the following conditional expression (4a).
1.9 <f2 / f3 <2.3 (4a)
The conditional expression (4a) defines a more preferable condition range based on the above viewpoints, etc., among the condition ranges defined by the conditional expression (4). Therefore, the above effect can be further increased preferably by satisfying conditional expression (4a). For example, when the lower limit of conditional expression (4a) is exceeded, the off-axis principal ray arrives at an angle that is closer to the image plane, and the reduction in the peripheral light amount ratio can be further reduced.

It is desirable that at least one of the second lens and the third lens is made of a material having a refractive index larger than 2.9 at a wavelength of 10 μm. As described above, when a wide-angle lens system in which the half angle of view ω is larger than 30 ° is assumed, the focal length of the entire system becomes short, and the powers of the second lens and the third lens, which are positive lenses, tend to be strong. For this reason, if a material having a high refractive index capable of obtaining a strong power even if the lens has a gentle curvature, the aberration due to the positive lens can be reduced, so that a lens system with good optical performance can be easily realized.

When the dispersion ν at a wavelength of 8 to 12 μm is defined by the following formula (FD), it is desirable that the dispersion ν of the lens material constituting at least one of the first to third lenses is larger than 100.
ν = (N10-1) / (N8-N12) (FD)
However,
N8: refractive index at a wavelength of 8 μm,
N10: refractive index at a wavelength of 10 μm,
N12: refractive index at a wavelength of 12 μm,
It is.

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 is the refractive index at the d-line, Nf is the refractive index at the F-line, and Nc is the refractive index at the C-line. Rate.). However, since this value has no meaning in the far-infrared region, in the far-infrared lens system, it is expressed by the formula (FD): ν = (N10-1) / (N8-N12) as a value representing the nature of dispersion. The value ν is used. The larger the value ν, the smaller the difference in refractive index due to color, and the smaller the dispersion. For example, dispersions of far-infrared optical materials conventionally used are Ge = 1250, Si = 1860, ZnS = 23 (used for achromatic), ZnSe = 57 (used for achromatic), and the like.

In the far-infrared lens system, it is necessary to correct aberrations in a wide wavelength range when measuring any temperature. In the telephoto lens system, color correction is performed by using materials with different dispersions for the positive lens and the negative lens, but in a wide-angle lens system with a short focal length, a combination of chromatic aberrations that minimizes each lens. Color correction by is not necessary. However, if a far-infrared sensor with higher definition than ever is developed in the future, as in the telephoto lens system, color correction will be performed using a material with a large dispersion value ν (ie, a low dispersion material) for the positive lens. There is a need to do. As described above, if a lens material (for example, Ge, Si) having a dispersion ν larger than 100 is used, this can be dealt with.

In the far-infrared lens system, aberration correction may be performed using a diffraction grating as long as the peripheral light amount ratio is not significantly reduced. By providing a diffraction grating, it is possible to satisfactorily correct axial chromatic aberration and the like. As a cross-sectional shape of the diffraction grating, a step shape or a kinoform may be used in addition to the binary shape.

The far-infrared lens system according to the present invention is suitable as an imaging lens system for a far-infrared camera system. The reason why there are few wide-angle lenses in the conventional far-infrared lens system is considered to be that the peripheral light amount ratio is lowered by the angle of view as described above. By using a simple three-lens lens system as described above, a lens system having a high peripheral light amount ratio can be obtained even at a wide angle. In combination with an inexpensive far-infrared sensor, an inexpensive system that can be used for a thermocamera even at a wide angle can be configured.

By adopting each of the conditions set as described above alone or in combination as necessary, positive aberration correction can be performed on the on-axis light beam and off-axis light beam even with a small number of three lenses. Will be able to. For this reason, it is possible to achieve a wide angle with a high peripheral light quantity ratio with good aberration correction, while achieving both high performance and high definition, even with three lenses, and the newly manufactured inexpensive far-infrared rays The sensor can also be used. Therefore, it is possible to realize an inexpensive but high-performance far-infrared lens system and an imaging optical device including the same.

Using far-infrared lens systems or imaging optical devices for digital devices such as night vision devices, thermography, portable terminals, camera systems (for example, digital cameras, surveillance cameras, security cameras, in-vehicle cameras) makes high performance for digital devices. A far-infrared image input function with high performance can be added at a low cost and in a compact manner, contributing to the compactness, high performance, high functionality, and the like. One of the reasons why far-infrared cameras are not widespread is that the lens material and lens processing are expensive. Therefore, by using a simple three-lens lens system as the far-infrared lens system, Therefore, it is possible to realize an inexpensive camera system.

The far-infrared lens system according to the present invention is suitable for use as an imaging optical system for a digital device with a far-infrared image input function (for example, a portable terminal, a drive recorder, etc.). By combining them, it is possible to configure a far-infrared imaging optical device that optically captures a far-infrared image of a subject and outputs it as an electrical signal. 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 far-infrared ray that forms a far-infrared optical image of an object in order from the object (that is, subject) side. It comprises a lens system and a far infrared sensor (imaging device) that converts a far infrared optical image formed by the far infrared lens system into an electrical signal. The far-infrared lens system 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 far-infrared sensor. Therefore, it is possible to realize an imaging optical device having high performance and a digital device including the same.

Examples of digital devices with a far-infrared image input function include camera systems such as infrared cameras, surveillance cameras, security cameras, in-vehicle cameras, aircraft cameras, digital cameras, video cameras, videophone cameras, and personal computers. , Night vision devices, thermography, portable digital devices (for example, small and portable information device terminals such as mobile phones, smart phones (high-function mobile phones), tablet terminals, mobile computers, etc.), and peripheral devices (scanners, printers) , Mouse, etc.), other digital devices (drive recorders, defense devices, etc.), etc., which have a camera function built in or externally mounted. As can be seen from these examples, it is possible not only to configure an infrared camera system by using an imaging optical device for far infrared rays, but also to provide an infrared camera function and a night vision function by installing the imaging optical device in various devices. , A temperature measurement function can be added. 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. 35 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. 35 is a far-infrared lens system LN (AX: light) that forms a far-infrared optical image (image plane) IM of an object in order from the object (that is, subject) side. Axis) and a far infrared sensor (imaging device) SR that converts an optical image IM formed on the light receiving surface (imaging surface) SS by the far infrared lens system LN into an electrical signal. On the image plane IM side of the far-infrared lens system LN, the cover glass of the far-infrared sensor SR, an optical filter arranged as necessary, and the like are positioned as parallel plates (not shown). 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.

The far-infrared lens system LN is a three-lens single focal point lens composed of three lenses of the first to third lenses in order from the object side. As described above, the light-receiving surface SS of the far-infrared sensor SR. An optical image IM composed of far infrared rays is formed on the top. As the far-infrared sensor SR, for example, a far-infrared image sensor (thermosensor or the like) having a plurality of pixels (for example, several thousand to several hundred thousand pixels) and using a wavelength of about 8 to 12 μm is used. Since the far-infrared 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 far-infrared sensor SR, the optical image formed by the far-infrared lens system LN. IM is converted into an electrical signal by the far-infrared sensor SR.

Specific examples of the far infrared sensor SR include a pyroelectric sensor, a microbolometer, and a thermopile. The pyroelectric sensor uses a pyroelectric effect in which ceramic containing lead zirconate titanate or the like spontaneously polarizes due to a change in temperature. In most cases, the pyroelectric sensor has a single light receiving surface and is an inexpensive temperature sensor. The microbolometer is a temperature sensor that has a light receiving surface in which heat sensitive materials such as amorphous silicon and vanadium oxide are two-dimensionally arranged by a microfabrication technique and detects a change in resistance value due to a temperature rise. Common microbolometers currently used have 80 × 80, 320 × 240, 640 × 480 and the like. In the past, most of the sensors were cooled with liquid nitrogen to provide sufficient temperature resolution. However, in recent years, manufacturing technology has advanced, and products with a high temperature detection capability have been manufactured without cooling. It is coming. The thermopile is a temperature sensor that uses thermocouples capable of converting heat into electric energy in series or in parallel to form a sensor surface, and is the second cheapest sensor after a pyroelectric sensor.

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 far-infrared sensor SR is subjected to predetermined digital image processing, image compression processing, and the like as required by the signal processing unit 1 and recorded as a digital video signal in the memory 3 (semiconductor memory, optical disk, etc.). In some cases, the signal is transmitted to another device 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 performs control of functions such as a photographing function (still image photographing function, moving image photographing function, etc.), an image reproduction function, and the like; and a lens moving mechanism for focusing. 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 far infrared 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.

FIGS. 1, 3,..., 31 and 33 show first to seventeenth embodiments of the far-infrared lens system LN in an infinitely focused state in optical cross sections. The far-infrared lens system LN according to the first to seventeenth embodiments includes, in order from the object side, a first lens L1 having negative power, a second lens L2 having positive power, and a third lens L3 having positive power. It consists of. In each embodiment, a parallel plate PT corresponding to the protective cover glass of the far infrared sensor SR is disposed on the image plane IM side of each far infrared lens system LN.

The far-infrared lens system LN of the first and eighth embodiments (EX1, 8) includes, in order from the object side, a negative power first lens L1, an aperture stop ST, and a positive power second lens L2. And a third lens L3 having a positive power. When viewing each lens with a paraxial surface shape, the first lens L1 is a negative meniscus lens convex toward the object side, the second lens L2 is a positive meniscus lens convex toward the object side, and the third lens L3 is A positive meniscus lens convex toward the object side. The object side surface of the first lens L1, the object side surface of the second lens L2, and the image side surface of the third lens L3 are aspheric.

The far-infrared lens systems LN of the second to seventh, tenth, and eleventh embodiments (EX2 to 7, 10, and 11), in order from the object side, the first lens L1 having a negative power, the aperture stop ST, , A positive power second lens L2 and a positive power third lens L3. When viewing each lens with a paraxial surface shape, the first lens L1 is a negative meniscus lens convex toward the object side, the second lens L2 is a positive meniscus lens convex toward the object side, and the third lens L3 is A positive meniscus lens convex toward the object side. The object side surface of the first lens L1, the object side surface of the second lens L2, and both surfaces of the third lens L3 are aspherical surfaces. The second lens L2 in the eleventh embodiment can be said to have a plano-convex shape because the image side surface has a meniscus shape close to a planar shape. In the fourth to seventh embodiments, the object side surface of the first lens L1 is an aspheric surface for each zone.

The far-infrared lens systems LN of the ninth, twelfth, and thirteenth embodiments (EX9, 12, and 13) are, in order from the object side, the negative lens first lens L1, the aperture stop ST, and the positive power first lens L1. 2 lenses L2 and a positive power third lens L3. When viewing each lens with a paraxial surface shape, the first lens L1 is a negative meniscus lens convex toward the object side, the second lens L2 is a positive meniscus lens convex toward the object side, and the third lens L3 is A positive meniscus lens convex toward the object side. Both sides of the first lens L1, both sides of the second lens L2, and the image side surface of the third lens L3 are aspheric.

The far-infrared lens system LN of the fourteenth to sixteenth embodiments (EX14 to 16) includes, in order from the object side, a negative power first lens L1, an aperture stop ST, a positive power second lens L2, And a third lens L3 having a positive power. When viewing each lens with a paraxial surface shape, the first lens L1 is a negative meniscus lens convex toward the object side, the second lens L2 is a positive meniscus lens convex toward the object side, and the third lens L3 is It is a biconvex positive lens. Both sides of the first lens L1, both sides of the second lens L2, and the image side surface of the third lens L3 are aspheric.

The far-infrared lens system LN according to the seventeenth embodiment (EX17) includes, in order from the object side, a negative lens first lens L1, a positive power second lens L2, an aperture stop ST, and a positive power third lens. And a lens L3. When viewing each lens with a paraxial surface shape, the first lens L1 is a negative meniscus lens convex toward the object side, the second lens L2 is a positive meniscus lens convex toward the object side, and the third lens L3 is A positive meniscus lens convex toward the object side. The second lens L2 can be said to have a plano-convex shape because the image side surface has a meniscus shape close to a planar shape. The image side surface of the second lens L2 forms an aperture stop ST at the edge portion. Both sides of the first lens L1, both sides of the second lens L2, and the image side surface of the third lens L3 are aspheric.

Hereinafter, the configuration and the like of the far-infrared lens system embodying the present invention will be described more specifically with reference to the construction data of the examples. Examples 1 to 17 (EX1 to 17) listed here are numerical examples corresponding to the first to seventeenth embodiments, respectively, and are lens configuration diagrams showing the first to seventeenth embodiments. (FIG. 1, FIG. 3,..., FIG. 33) show optical configurations such as the lens cross-sectional shape and lens arrangement of the corresponding Examples 1 to 17, respectively.

In the construction data of each embodiment, as surface data, in order from the left column, surface number i (OB: object surface, ST: aperture surface, IM: image surface), radius of curvature r (mm) in paraxial, axial upper surface An interval d (mm), a refractive index N10 at a design wavelength λ0 of 10 μm, and a dispersion ν at a wavelength of 8 to 12 μm are shown (none: air).

The surface with * in the surface number i is an aspheric surface, and the surface shape is defined by the following formula (AS) using a local orthogonal coordinate system (x, y, z) with the surface vertex as the origin. The 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 (Aj · h ^j ) (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 (reciprocal of paraxial radius of curvature r),
K: conic constant,
Aj: j-order aspheric coefficient (Σ represents the sum of the fourth to ∞ orders for j),
It is.

The aspheric surface for each zone is also expressed by the above formula (AS) in the same way as a normal aspheric surface. However, the radius of curvature R (mm) and the aspherical coefficient Aj take different values for each zone according to the height h (mm) from the optical axis AX, and j is a zero-order and fourth-order or higher natural number of a constant term. take.

As the refractive index and dispersion data of the optical material constituting each lens, the refractive index N10 at a wavelength of 10 μm and the dispersion ν = (N10-1) / (N8-N12) at a wavelength of 8 to 12 μm are as follows: Show. The parallel plate PT in front of the image plane IM is a silicon protective plate (cover glass) of the far-infrared sensor SR.
Germanium (Ge) ... N10 = 4.004, ν = 1251
Silicon (Si): N10 = 3.4178, ν = 1860

As various data (specs), the design wavelength λ 0 (nm), the focal length f (mm) of the entire system, the F number (FNO), the total length TL (the distance from the lens front surface to the image plane IM (however, the parallel plate PT is Actual dimensions), mm) and half angle of view ω (°). Table 1 shows values corresponding to the conditional expressions of each example and related data.

2, 4, 6,..., 32, and 34 are aberration diagrams corresponding to Examples 1 to 17 (EX1 to 17), respectively, (A) is a spherical aberration diagram, and (B) is a non-aberration diagram. Point aberration diagram, (C) is a distortion diagram. The spherical aberration diagram (A) shows the amount of spherical aberration at a design wavelength (evaluation wavelength) of 10000 nm indicated by a solid line, the amount of spherical aberration at a wavelength of 8000 nm indicated by an alternate long and short dash line, and the amount of spherical aberration at a wavelength of 12000 nm indicated by a broken line. The vertical axis represents a value obtained by normalizing the incident height to the pupil by the maximum height (that is, the relative pupil height). In the astigmatism diagram (B), the broken line T is the tangential image plane at the design wavelength of 10000 nm, the solid line S is the sagittal image plane at the design wavelength of 10000 nm, and the deviation (mm) in the optical axis AX direction from the paraxial image plane. The vertical axis represents the image height (IMG HT, mm). In the distortion diagram (C), the horizontal axis represents distortion (%) at a design wavelength of 10,000 nm, and the vertical axis represents image height (IMG HT, mm). The maximum value of the image height IMG HT corresponds to half the diagonal length of the light receiving surface SS of the far infrared sensor SR.

Example 1
Unit: mm
Surface data i r (mm) d (mm) N10 ν
OB INFINITY INFINITY
1 * 19.97442 4.259916 4.004 1251
2 11.34338 24.142077
3 (ST) INFINITY 0.500000
4 * 30.58615 1.500000 4.004 1251
5 63.48804 12.450600
6 18.06938 7.000000 4.004 1251
7 * 33.47349 3.247407
8 INFINITY 1.000000 3.4178 1860
9 INFINITY 0.900000
IM INFINITY 0.000000

Various data λ0 = 10000.0nm
f = 3.9450
FNO = 1.3000
TL = 55.0
ω = 52.0179 °

Aspheric data Aspheric surface: i = 1 *
K = 0.000000
A4 = 0.112980E-04
A6 = -0.115701E-07
A8 = 0.127064E-09
A10 = 0.000000E + 00

Aspheric data Aspheric surface: i = 4 *
K = 0.000000
A4 = 0.000000E + 00
A6 = -0.136039E-05
A8 = 0.434985E-07
A10 = 0.000000E + 00

Aspheric data Aspheric surface: i = 7 *
K = -1.003103
A4 = 0.756826E-04
A6 = 0.000000E + 00
A8 = 0.000000E + 00
A10 = 0.000000E + 00

Example 2
Unit: mm
Surface data i r (mm) d (mm) N10 ν
OB INFINITY INFINITY
1 * 18.98745 3.933550 4.004 1251
2 11.39073 21.941429
3 (ST) INFINITY 3.188808
4 * 31.63379 1.500000 4.004 1251
5 61.27521 12.046530
6 * 18.51782 7.000000 4.004 1251
7 * 40.54304 3.489683
8 INFINITY 1.000000 3.4178 1860
9 INFINITY 0.900001
IM INFINITY 0.000000

Various data λ0 = 10000.0nm
f = 3.9588
FNO = 1.3000
TL = 55.0
ω = 51.9210 °

Aspheric data Aspheric surface: i = 1 *
K = 0.000000
A4 = 0.117838E-04
A6 = -0.317272E-07
A8 = 0.240204E-09
A10 = 0.000000E + 00

Aspheric data Aspheric surface: i = 4 *
K = -2.088591
A4 = -0.109544E-04
A6 = 0.356402E-06
A8 = -0.549585E-08
A10 = 0.000000E + 00

Aspheric data Aspheric surface: i = 6 *
K = 0.520593
A4 = -0.809827E-05
A6 = 0.153916E-08
A8 = 0.000000E + 00
A10 = 0.000000E + 00

Aspheric data Aspheric surface: i = 7 *
K = -2.244124
A4 = 0.720723E-04
A6 = 0.000000E + 00
A8 = 0.000000E + 00
A10 = 0.000000E + 00

Example 3
Unit: mm
Surface data i r (mm) d (mm) N10 ν
OB INFINITY INFINITY
1 * 18.98745 3.937538 4.004 1251
2 11.26822 22.848958
3 (ST) INFINITY 1.946879
4 * 31.24766 1.500000 4.004 1251
5 59.99565 12.389216
6 * 17.88176 7.000000 4.004 1251
7 * 35.04051 3.477409
8 INFINITY 1.000000 3.4178 1860
9 INFINITY 0.899996
IM INFINITY 0.000000

Various data λ0 = 10000.0nm
f = 3.9588
FNO = 1.3000
TL = 55.0
ω = 51.9211 °

Aspheric data Aspheric surface: i = 1 *
K = 0.000000
A4 = 0.129183E-04
A6 = -0.346024E-07
A8 = 0.252758E-09
A10 = 0.000000E + 00

Aspheric data Aspheric surface: i = 4 *
K = -2.031676
A4 = -0.109474E-04
A6 = 0.465683E-06
A8 = -0.882319E-08
A10 = 0.000000E + 00

Aspheric data Aspheric surface: i = 6 *
K = 0.558144
A4 = -0.113023E-04
A6 = -0.322402E-07
A8 = 0.000000E + 00
A10 = 0.000000E + 00

Aspheric data Aspheric surface: i = 7 *
K = -0.872388
A4 = 0.649402E-04
A6 = 0.000000E + 00
A8 = 0.000000E + 00
A10 = 0.000000E + 00

Example 4
Unit: mm
Surface data i r (mm) d (mm) N10 ν
OB INFINITY INFINITY
1 * 18.98128 3.937538 4.004 1251
2 11.25300 22.848958
3 (ST) INFINITY 1.946879
4 * 32.38273 1.500000 4.004 1251
5 64.92274 12.389216
6 * 17.92470 7.000000 4.004 1251
7 * 35.04051 3.477409
8 INFINITY 1.000000 3.4178 1860
9 INFINITY 0.899995
IM INFINITY 0.000000

Various data λ0 = 10000.0nm
f = 3.9588
FNO = 1.3000
TL = 55.0
ω = 51.9211 °

Aspheric surfaces by aspheric data zone: i = 1 *
Zone 1 (0 ≦ h ≦ 1.5000)
R = 18.98128
A0 = 0.0000E + 00
A4 = 2.4117E-04
A6 = -1.1648E-04
A8 = 1.8285E-05
Zone 2 (1.5000 ≦ h ≦ 8.0000)
R = 1.8907E + 01
A0 = 7.9089E-05
A4 = 1.0107E-05
A6 = 7.8539E-09
A8 = 1.2421E-11
Zone 3 (8.0000 ≦ h)
R = 1.8866E + 01
A0 = -2.3935E-03
A4 = 1.0861E-05
A6 = -2.4951E-08
A8 = 2.2983E-10

Aspheric data Aspheric surface: i = 4 *
K = 0.478972
A4 = -0.237710E-04
A6 = 0.674554E-06
A8 = -0.132720E-07
A10 = 0.000000E + 00

Aspheric data Aspheric surface: i = 6 *
K = 0.734098
A4 = -0.147960E-04
A6 = -0.760821E-07
A8 = 0.000000E + 00
A10 = 0.000000E + 00

Aspheric data Aspheric surface: i = 7 *
K = -1.527333
A4 = 0.629146E-04
A6 = 0.000000E + 00
A8 = 0.000000E + 00
A10 = 0.000000E + 00

Example 5
Unit: mm
Surface data i r (mm) d (mm) N10 ν
OB INFINITY INFINITY
1 * 18.95171 3.937538 4.004 1251
2 11.21692 22.848958
3 (ST) INFINITY 1.946879
4 * 32.51597 1.500000 4.004 1251
5 65.92705 12.389216
6 * 17.97350 7.000000 4.004 1251
7 * 35.04051 3.477409
8 INFINITY 1.000000 3.4178 1860
9 INFINITY 0.900000
IM INFINITY 0.000000

Various data λ0 = 10000.0nm
f = 3.9588
FNO = 1.3000
TL = 55.0
ω = 51.9211 °

Aspheric surfaces by aspheric data zone: i = 1 *
Zone 1 (0 ≦ h ≦ 1.5000)
R = 18.95171
A0 = 0.0000E + 00
A4 = 2.4022E-04
A6 = -1.1577E-04
A8 = 1.8163E-05
Zone 2 (1.5000 ≦ h ≦ 8.0000)
R = 1.8878E + 01
A0 = 7.7705E-05
A4 = 1.0204E-05
A6 = 5.7692E-09
A8 = 3.1249E-11
Zone 3 (8.0000 ≦ h)
R = 1.8880E + 01
A0 = -1.1137E-03
A4 = 1.2098E-05
A6 = -3.2803E-08
A8 = 2.5595E-10

Aspheric data Aspheric surface: i = 4 *
K = 0.444630
A4 = -0.238076E-04
A6 = 0.694811E-06
A8 = -0.138261E-07
A10 = 0.000000E + 00

Aspheric data Aspheric surface: i = 6 *
K = 0.877702
A4 = -0.158038E-04
A6 = -0.102131E-06
A8 = 0.000000E + 00
A10 = 0.000000E + 00

Aspheric data Aspheric surface: i = 7 *
K = -1.233054
A4 = 0.674509E-04
A6 = 0.000000E + 00
A8 = 0.000000E + 00
A10 = 0.000000E + 00

Example 6
Unit: mm
Surface data i r (mm) d (mm) N10 ν
OB INFINITY INFINITY
1 * 18.95450 3.937538 4.004 1251
2 11.23809 22.848958
3 (ST) INFINITY 1.946879
4 * 33.05246 1.500000 4.004 1251
5 67.89601 12.389216
6 * 17.93397 7.000000 4.004 1251
7 * 35.04051 3.477409
8 INFINITY 1.000000 3.4178 1860
9 INFINITY 0.900000
IM INFINITY 0.000000

Various data λ0 = 10000.0nm
f = 3.9588
FNO = 1.3000
TL = 55.0
ω = 51.9211 °

Aspheric Data Zone 1 *
Zone 1 (0 ≦ h ≦ 1.5)
R = 18.95450
A0 = 0.0000E + 00
A4 = 2.0606E-04
A6 = -9.5905E-05
A8 = 1.4866E-05
Zone 2 (1.5 ≦ h ≦ 8.0)
R = 1.8882E + 01
A0 = 5.0511E-05
A4 = 1.0004E-05
A6 = 4.1273E-09
A8 = 4.9068E-11
Zone 3 (8.0 ≦ h)
R = 1.8877E + 01
A0 = -1.1443E-03
A4 = 1.1441E-05
A6 = -2.7680E-08
A8 = 2.3819E-10

Aspheric data Aspheric surface: i = 4 *
K = 0.649039
A4 = -0.230427E-04
A6 = 0.561985E-06
A8 = -0.999886E-08
A10 = 0.000000E + 00

Aspheric data Aspheric surface: i = 6 *
K = 0.667460
A4 = -0.109646E-04
A6 = -0.551889E-07
A8 = 0.000000E + 00
A10 = 0.000000E + 00

Aspheric data Aspheric surface: i = 7 *
K = -0.841862
A4 = 0.704026E-04
A6 = 0.000000E + 00
A8 = 0.000000E + 00
A10 = 0.000000E + 00

Example 7
Unit: mm
Surface data i r (mm) d (mm) N10 ν
OB INFINITY INFINITY
1 * 18.98744 3.263229 4.004 1251
2 11.95292 23.301818
3 (ST) INFINITY 3.628419
4 * 22.64137 1.500000 4.004 1251
5 33.26157 11.303538
6 * 17.80384 6.518600 4.004 1251
7 * 35.04051 3.584397
8 INFINITY 1.000000 3.4178 1860
9 INFINITY 0.900018
IM INFINITY 0.000000

Various data λ0 = 10000.0nm
f = 3.9588
FNO = 1.3000
TL = 55.0
ω = 51.9211 °

Aspheric surfaces by aspheric data zone: i = 1 *
Zone 1 (0 ≦ h ≦ 1.5000)
R = 18.98744
A0 = 0.0000E + 00
A4 = 2.1536E-04
A6 = -9.9496E-05
A8 = 1.5308E-05
Zone 2 (1.5000 ≦ h ≦ 8.0000)
R = 1.8904E + 01
A0 = 4.3477E-05
A4 = 8.3934E-06
A6 = 1.3349E-08
A8 = 1.9987E-11
Zone 3 (8.0000 ≦ h)
R = 1.9031E + 01
A0 = 2.4671E-03
A4 = 1.3479E-05
A6 = -4.1061E-08
A8 = 2.6257E-10

Aspheric data Aspheric surface: i = 4 *
K = 0.168718
A4 = -0.252402E-04
A6 = 0.506894E-06
A8 = -0.765910E-08
A10 = 0.000000E + 00

Aspheric data Aspheric surface: i = 6 *
K = 0.879655
A4 = -0.835647E-05
A6 = -0.105864E-06
A8 = 0.000000E + 00
A10 = 0.000000E + 00

Aspheric data Aspheric surface: i = 7 *
K = -1.277704
A4 = 0.943038E-04
A6 = 0.000000E + 00
A8 = 0.000000E + 00
A10 = 0.000000E + 00

Example 8
Unit: mm
Surface data i r (mm) d (mm) N10 ν
OB INFINITY INFINITY
1 * 19.28986 4.067793 3.4178 1860
2 10.86650 20.951878
3 (ST) INFINITY 7.291065
4 * 19.72855 1.500000 3.4178 1860
5 34.10096 10.213553
6 17.43825 5.567141 3.4178 1860
7 * 44.22484 3.508571
8 INFINITY 1.000000 3.4178 1860
9 INFINITY 0.900420
IM INFINITY 0.000000

Various data λ0 = 10000.0nm
f = 3.9450
FNO = 1.3000
TL = 55.0
ω = 51.9787 °

Aspheric data Aspheric surface: i = 1 *
K = 0.000000
A4 = 0.142209E-04
A6 = -0.461850E-07
A8 = 0.322518E-09
A10 = 0.000000E + 00

Aspheric data Aspheric surface: i = 4 *
K = 0.000000
A4 = -0.205992E-04
A6 = 0.139786E-06
A8 = -0.101871E-08
A10 = 0.000000E + 00

Aspheric data Aspheric surface: i = 7 *
K = -1.595049
A4 = 0.943232E-04
A6 = 0.000000E + 00
A8 = 0.000000E + 00
A10 = 0.000000E + 00

Example 9
Unit: mm
Surface data i r (mm) d (mm) N10 ν
OB INFINITY INFINITY
1 * 18.98744 4.338460 3.4178 1860
2 * 10.58949 19.728667
3 (ST) INFINITY 0.500000
4 * 17.26847 1.899319 3.4178 1860
5 * 26.38188 7.365513
6 16.63593 7.000000 3.4178 1860
7 * 71.59766 2.918293
8 INFINITY 1.000000 3.4178 1860
9 INFINITY 0.900000
IM INFINITY 0.000000

Various data λ0 = 10000.0nm
f = 3.9588
FNO = 1.3000
TL = 44.7503
ω = 51.4362 °

Aspheric data Aspheric surface: i = 1 *
K = 0.000000
A4 = 0.724807E-04
A6 = -0.175182E-07
A8 = 0.136875E-09
A10 = 0.000000E + 00

Aspheric data Aspheric surface: i = 2 *
K = 0.000000
A4 = 0.180666E-03
A6 = 0.136761E-05
A8 = 0.000000E + 00
A10 = 0.000000E + 00

Aspheric data Aspheric surface: i = 4 *
K = 0.756983
A4 = 0.313930E-04
A6 = -0.199210E-05
A8 = -0.230607E-07
A10 = 0.000000E + 00

Aspheric data Aspheric surface: i = 5 *
K = 0.000000
A4 = 0.113532E-03
A6 = -0.361963E-05
A8 = 0.000000E + 00
A10 = 0.000000E + 00

Aspheric data Aspheric surface: i = 7 *
K = 50.000000
A4 = 0.122205E-03
A6 = 0.000000E + 00
A8 = 0.000000E + 00
A10 = 0.000000E + 00

Example 10
Unit: mm
Surface data i r (mm) d (mm) N10 ν
OB INFINITY INFINITY
1 * 22.09903 2.000000 4.004 1251
2 15.10708 27.821632
3 (ST) INFINITY 6.655555
4 * 22.64186 1.500 160 4.004 1251
5 29.55163 11.833675
6 * 20.26530 7.908087 4.004 1251
7 * 45.21025 4.054555
8 INFINITY 1.000000 3.4178 1860
9 INFINITY 0.910996
IM INFINITY 0.000000

Various data λ0 = 10000.0nm
f = 3.9600
FNO = 1.3000
TL = 63.6847
ω = 51.1586 °

Aspheric data Aspheric surface: i = 1 *
K = 0.000000
A4 = 0.950632E-05
A6 = -0.510581E-08
A8 = 0.310007E-10
A10 = 0.636941E-13

Aspheric data Aspheric surface: i = 4 *
K = -1.194268
A4 = -0.658200E-05
A6 = 0.244872E-06
A8 = -0.193847E-08
A10 = 0.000000E + 00

Aspheric data Aspheric surface: i = 6 *
K = 1.383115
A4 = 0.202002E-04
A6 = -0.556347E-07
A8 = 0.568506E-10
A10 = -0.107270E-11

Aspheric data Aspheric surface: i = 7 *
K = 27.756396
A4 = 0.155446E-03
A6 = 0.000000E + 00
A8 = 0.000000E + 00
A10 = 0.000000E + 00

Example 11
Unit: mm
Surface data i r (mm) d (mm) N10 ν
OB INFINITY INFINITY
1 * 18.72159 7.000000 4.004 1251
2 8.68331 17.091768
3 (ST) INFINITY 0.500000
4 * 37.85306 7.000000 4.004 1251
5 2247.90524 8.688493
6 * 13.95820 1.515826 4.004 1251
7 * 28.79085 3.541168
8 INFINITY 1.000000 3.4178 1860
9 INFINITY 0.899200
IM INFINITY 0.000000

Various data λ0 = 10000.0nm
f = 3.9586
FNO = 1.3000
TL = 47.2365
ω = 51.9214 °

Aspheric data Aspheric surface: i = 1 *
K = 0.000000
A4 = 0.100503E-04
A6 = -0.121120E-07
A8 = 0.147112E-09
A10 = 0.000000E + 00

Aspheric data Aspheric surface: i = 4 *
K = -8.763694
A4 = -0.978501E-05
A6 = 0.109269E-05
A8 = -0.306888E-07
A10 = 0.000000E + 00

Aspheric data Aspheric surface: i = 6 *
K = 0.545783
A4 = -0.339683E-05
A6 = -0.700369E-07
A8 = 0.000000E + 00
A10 = 0.000000E + 00

Aspheric data Aspheric surface: i = 7 *
K = 0.035719
A4 = 0.804669E-04
A6 = 0.000000E + 00
A8 = 0.000000E + 00
A10 = 0.000000E + 00

Example 12
Unit: mm
Surface data i r (mm) d (mm) N10 ν
OB INFINITY INFINITY
1 * 18.98747 5.077222 3.4178 1860
2 * 10.15611 17.724169
3 (ST) INFINITY 0.500000
4 * 18.97666 1.952454 3.4178 1860
5 * 31.84518 6.794438
6 16.53191 6.952777 3.4178 1860
7 * 90.71964 2.879810
8 INFINITY 1.000000 3.4178 1860
9 INFINITY 0.900078
IM INFINITY 0.000000

Various data λ0 = 10000.0nm
f = 3.9863
FNO = 1.3000
TL = 43.7809
ω = 51.7279 °

Aspheric data Aspheric surface: i = 1 *
K = 0.000000
A4 = 0.610326E-04
A6 = -0.165222E-07
A8 = 0.154246E-09
A10 = 0.000000E + 00

Aspheric data Aspheric surface: i = 2 *
K = 0.000000
A4 = 0.183727E-03
A6 = 0.144326E-05
A8 = 0.000000E + 00
A10 = 0.000000E + 00

Aspheric data Aspheric surface: i = 4 *
K = -0.720252
A4 = 0.754406E-07
A6 = -0.326664E-05
A8 = -0.448511E-07
A10 = 0.000000E + 00

Aspheric data Aspheric surface: i = 5 *
K = 0.000000
A4 = 0.370447E-04
A6 = -0.571978E-05
A8 = 0.000000E + 00
A10 = 0.000000E + 00

Aspheric data Aspheric surface: i = 7 *
K = 50.000000
A4 = 0.154209E-03
A6 = 0.000000E + 00
A8 = 0.000000E + 00
A10 = 0.000000E + 00

Example 13
Unit: mm
Surface data i r (mm) d (mm) N10 ν
OB INFINITY INFINITY
1 * 15.08506 3.774564 3.4178 1860
2 * 9.21001 16.941609
3 (ST) INFINITY 0.500000
4 * 25.58510 4.521797 3.4178 1860
5 * 53.02554 8.801469
6 17.86752 7.000000 3.4178 1860
7 * 55.36084 3.180317
8 INFINITY 1.000000 3.4178 1860
9 INFINITY 1.381468
IM INFINITY 0.000000

Various data λ0 = 10000.0nm
f = 5.6328
FNO = 1.3000
TL = 47.1012
ω = 41.5050 °

Aspheric data Aspheric surface: i = 1 *
K = 0.000000
A4 = 0.506985E-04
A6 = -0.330441E-06
A8 = 0.110154E-08
A10 = 0.000000E + 00

Aspheric data Aspheric surface: i = 2 *
K = 0.000000
A4 = 0.125451E-03
A6 = -0.136292E-05
A8 = 0.000000E + 00
A10 = 0.000000E + 00

Aspheric data Aspheric surface: i = 4 *
K = -0.179898
A4 = -0.156811E-05
A6 = -0.309452E-06
A8 = -0.332867E-08
A10 = 0.000000E + 00

Aspheric data Aspheric surface: i = 5 *
K = 0.000000
A4 = 0.180058E-04
A6 = -0.713969E-06
A8 = 0.000000E + 00
A10 = 0.000000E + 00

Aspheric data Aspheric surface: i = 7 *
K = -0.958318
A4 = 0.991081E-04
A6 = 0.000000E + 00
A8 = 0.000000E + 00
A10 = 0.000000E + 00

Example 14
Unit: mm
Surface data i r (mm) d (mm) N10 ν
OB INFINITY INFINITY
1 * 18.98744 3.218035 3.4178 1860
2 * 11.32068 22.063256
3 (ST) INFINITY 0.754851
4 * 15.53320 2.536553 3.4178 1860
5 * 16.77402 6.079129
6 26.23256 7.000000 3.4178 1860
7 * -61.42566 3.305275
8 INFINITY 1.000000 3.4178 1860
9 INFINITY 3.045988
IM INFINITY 0.000000

Various data λ0 = 10000.0nm
f = 3.9450
FNO = 1.3000
TL = 49.0031
ω = 52.0172 °

Aspheric data Aspheric surface: i = 1 *
K = 0.000000
A4 = 0.911643E-04
A6 = 0.987159E-07
A8 = -0.173836E-09
A10 = 0.000000E + 00

Aspheric data Aspheric surface: i = 2 *
K = 0.000000
A4 = 0.166507E-03
A6 = 0.175796E-05
A8 = 0.000000E + 00
A10 = 0.000000E + 00

Aspheric data Aspheric surface: i = 4 *
K = -0.430051
A4 = -0.851999E-05
A6 = -0.321128E-05
A8 = -0.327390E-07
A10 = 0.000000E + 00

Aspheric data Aspheric surface: i = 5 *
K = 0.000000
A4 = 0.509101E-04
A6 = -0.702033E-05
A8 = 0.000000E + 00
A10 = 0.000000E + 00

Aspheric data Aspheric surface: i = 7 *
K = 16.929357
A4 = 0.732062E-04
A6 = 0.000000E + 00
A8 = 0.000000E + 00
A10 = 0.000000E + 00

Example 15
Unit: mm
Surface data i r (mm) d (mm) N10 ν
OB INFINITY INFINITY
1 * 18.98744 3.089206 3.4178 1860
2 * 11.30298 22.560322
3 (ST) INFINITY 0.500000
4 * 24.07684 6.694275 3.4178 1860
5 * 24.49200 4.479898
6 29.72505 7.000000 3.4178 1860
7 * -40.03624 3.305275
8 INFINITY 1.000000 3.4178 1860
9 INFINITY 3.482869
IM INFINITY 0.000000

Various data λ0 = 10000.0nm
f = 3.9448
FNO = 1.3000
TL = 52.1118
ω = 52.0203 °

Aspheric data Aspheric surface: i = 1 *
K = 0.000000
A4 = 0.960046E-04
A6 = 0.435981E-07
A8 = -0.762702E-10
A10 = 0.000000E + 00

Aspheric data Aspheric surface: i = 2 *
K = 0.000000
A4 = 0.172197E-03
A6 = 0.150421E-05
A8 = 0.000000E + 00
A10 = 0.000000E + 00

Aspheric data Aspheric surface: i = 4 *
K = -1.933623
A4 = -0.378265E-04
A6 = -0.740384E-06
A8 = -0.269592E-07
A10 = 0.000000E + 00

Aspheric data Aspheric surface: i = 5 *
K = 0.000000
A4 = -0.283749E-05
A6 = -0.317907E-05
A8 = 0.000000E + 00
A10 = 0.000000E + 00

Aspheric data Aspheric surface: i = 7 *
K = -0.453093
A4 = 0.618267E-04
A6 = 0.000000E + 00
A8 = 0.000000E + 00
A10 = 0.000000E + 00

Example 16
Unit: mm
Surface data i r (mm) d (mm) N10 ν
OB INFINITY INFINITY
1 * 18.98744 2.893883 3.4178 1860
2 * 11.45425 23.077726
3 (ST) INFINITY 0.500000
4 * 34.18158 7.000000 3.4178 1860
5 * 37.66610 4.601597
6 33.24701 7.000000 3.4178 1860
7 * -39.88293 3.305275
8 INFINITY 1.000000 3.4178 1860
9 INFINITY 4.266405
IM INFINITY 0.000000

Various data λ0 = 10000.0nm
f = 3.9450
FNO = 1.3000
TL = 53.6449
ω = 52.0181 °

Aspheric data Aspheric surface: i = 1 *
K = 0.000000
A4 = 0.101912E-03
A6 = 0.693718E-07
A8 = -0.164873E-09
A10 = 0.000000E + 00

Aspheric data Aspheric surface: i = 2 *
K = 0.000000
A4 = 0.174291E-03
A6 = 0.160023E-05
A8 = 0.000000E + 00
A10 = 0.000000E + 00

Aspheric data Aspheric surface: i = 4 *
K = -6.566177
A4 = -0.586856E-04
A6 = -0.664538E-06
A8 = -0.363904E-07
A10 = 0.000000E + 00

Aspheric data Aspheric surface: i = 5 *
K = 0.000000
A4 = -0.365029E-04
A6 = -0.218257E-05
A8 = 0.000000E + 00
A10 = 0.000000E + 00

Aspheric data Aspheric surface: i = 7 *
K = -0.428362
A4 = 0.536361E-04
A6 = 0.000000E + 00
A8 = 0.000000E + 00
A10 = 0.000000E + 00

Example 17
Unit: mm
Surface data i r (mm) d (mm) N10 ν
OB INFINITY INFINITY
1 * 19.61551 4.689940 3.4178 1860
2 * 11.19901 22.125190
3 * 26.04935 5.578011 3.4178 1860
4 * 71.54092 0.079921
3 (ST) INFINITY 6.487793
6 18.00186 6.727592 3.4178 1860
7 * 45.70953 2.868613
8 INFINITY 1.000000 3.4178 1860
9 INFINITY 0.900000
IM INFINITY 0.000000

Various data λ0 = 10000.0nm
f = 4.7236
FNO = 1.3000
TL = 50.4571
ω = 46.5710 °

Aspheric data Aspheric surface: i = 1 *
K = 0.000000
A4 = 0.568175E-04
A6 = 0.314376E-07
A8 = -0.486950E-10
A10 = 0.000000E + 00

Aspheric data Aspheric surface: i = 2 *
K = 0.000000
A4 = 0.150067E-03
A6 = 0.127442E-05
A8 = 0.000000E + 00
A10 = 0.000000E + 00

Aspheric data Aspheric surface: i = 3 *
K = -1.751781
A4 = -0.182176E-04
A6 = -0.367494E-06
A8 = -0.111601E-07
A10 = 0.000000E + 00

Aspheric data Aspheric surface: i = 4 *
K = 0.000000
A4 = -0.190607E-04
A6 = -0.122023E-05
A8 = 0.000000E + 00
A10 = 0.000000E + 00

Aspheric data Aspheric surface: i = 7 *
K = 50.000000
A4 = 0.669433E-04
A6 = 0.000000E + 00
A8 = 0.000000E + 00
A10 = 0.000000E + 00

DU digital equipment (camera system)
LU imaging optical device LN far infrared lens system L1 first lens L2 second lens L3 third lens ST aperture stop (stop)
SR far-infrared sensor (image sensor)
SS Photosensitive surface (imaging 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 (12)

1. A lens system used in the far-infrared band,
   In order from the object side, the lens is composed of three single lenses, a first lens having negative power, a second lens having positive power, and a third lens having positive power. The following conditional expression ( 1) and a far-infrared lens system characterized by having a half angle of view larger than 30 °;
   3.2 <f2 / f <17 (1)
   However,
   f2: focal length of the second lens,
   f: focal length of the entire far-infrared lens system,
   It is.
2. The far-infrared lens system according to claim 1, wherein the first lens is made of a material having a refractive index larger than 2.9 at a wavelength of 10 µm.
3. The far-infrared lens system according to claim 1 or 2, wherein the first lens has a negative meniscus shape with a convex surface facing the object side.
4. The far-infrared lens system according to claim 3, wherein the following conditional expression (2) is satisfied:
   3.0 <d2 / f <9.0 (2)
   However,
   d2: axial distance between the image side surface of the first lens and the object side surface of the second lens,
   f: focal length of the entire far-infrared lens system,
   It is.
5. The far-infrared lens system according to any one of claims 1 to 4, wherein the second lens has a positive meniscus shape or plano-convex shape with a convex surface facing the object side.
6. The far-infrared lens system according to any one of claims 1 to 5, further comprising a stop between an image side surface of the first lens and an object side of the third lens.
7. The third lens has a biconvex shape in which a convex surface having a higher power is directed toward the object side or a positive meniscus shape in which the convex surface is directed toward the object side when comparing both surfaces. The far-infrared lens system according to any one of 1 to 6.
8. The far-infrared lens system according to any one of claims 1 to 7, wherein the following conditional expression (3) is satisfied:
   1.7 <f23 / f <2.8 (3)
   However,
   f23: composite focal length of the second lens and the third lens,
   f: focal length of the entire far-infrared lens system,
   It is.
9. The far-infrared lens system according to any one of claims 1 to 8, wherein the following conditional expression (4) is satisfied:
   1.45 <f2 / f3 <8.0 (4)
   However,
   f2: focal length of the second lens,
   f3: focal length of the third lens,
   It is.
10. A far-infrared lens system according to any one of claims 1 to 9, and a far-infrared sensor that converts a far-infrared optical image formed on an imaging surface into an electrical signal. An imaging optical apparatus, wherein the far-infrared lens system is provided so that a far-infrared optical image of a subject is formed on the imaging surface.
11. 11. A digital apparatus comprising the imaging optical device according to claim 10 to which at least one function of still image shooting and moving image shooting of a subject is added.
12. A far-infrared camera system comprising the far-infrared lens system according to any one of claims 1 to 9.

Images