WO2016027784A1 - Far-infrared lens, image-acquisition optical device, and digital equipment - Google Patents

Abstract

This far-infrared lens is a lens system used in the far-infrared band. The lens is formed of two single lenses, namely, a first lens and a second lens in this order from the object side, satisfies the conditional expression 7.3 < (r1 + r2)/(r1 - r2) < 27.5, where r1 is the paraxial radius of curvature of the object-side surface of the first lens, and r2 is the paraxial radius of curvature of the image-side surface of the first lens, and has a half angle of view greater than 30°.

Description

Far-infrared lens, imaging optical device and digital equipment

The present invention relates to a far-infrared lens, an imaging optical device, and a digital device. For example, an imaging lens system used in the far-infrared (wavelength 8 to 12 μm band), especially with a wide angle with a half angle of view ω of 30 ° or more, the number of lenses is as few as 2, and aberration correction is performed well. It relates to a far-infrared lens that can be used in an inexpensive camera system, an imaging optical device that captures a far-infrared image obtained by the far-infrared lens with an imaging device, and a digital device with an image input function equipped with a far-infrared lens. is there.

With the spread of surveillance cameras and security cameras, cheap and small far-infrared lenses are required. Since the lens material used for the far-infrared lens is more expensive than general optical glass, the smaller the lens volume, the lower the cost. From such a viewpoint, Patent Documents 1 to 4 propose a relatively wide-angle far-infrared lens composed of two lenses.

US2013 / 0271852 A1 JP 2013-19595 A US2012 / 0229892 A1 US6292293 B1

In the far-infrared lenses described in Patent Documents 1 to 4, the core thickness of the second lens normalized by the focal length is thin. In order to accommodate large far-infrared sensors, if the lens diameter is increased, the material cost will increase, so it will be compensated, or the size of the homogeneous lens material will be limited, so the lens core thickness has been reduced. It is thought that it is designed. However, recently, a far infrared sensor having a small size has been manufactured at a low cost. In addition, there are an increasing number of sensors with a large number of pixels even though they are inexpensive. For such a sensor, a higher-performance and higher-definition lens system is required, but it is difficult to correct different aberrations between the front and rear surfaces of the lens when the core thickness of the second lens is thin. In the system of the number of lenses, sufficient aberration correction cannot be performed.

In the above Patent Documents 1 to 3, the back focus normalized by the focal length is long. In the far-infrared lens, since the brightness of the system also affects the resolving power, the F number is as bright as about 1.2, and the off-axis light beam is not cut as much as possible. In such a lens system, when the back focus is long and the distance from the image plane to the second lens is long, the F-number light beam passes through a high position from the optical axis of the second lens. The burden will increase. In addition, since the on-axis light beam and the off-axis light beam pass through almost the same height, it is difficult to effectively correct off-axis performance (correction of field curvature or the like). For this reason, sufficient performance cannot be obtained with a system having a small number of lenses.

In the above Patent Document 4, the back focus normalized by the focal length is shortened. This is considered to be because the numerical system is a lens system for an inch and the sensor screen size is large. When this is applied in a proportionally reduced manner so as to correspond to an inexpensive and small sensor, the cover glass of the sensor cannot be inserted into the back focus. Since the sensor cover glass is indispensable for ensuring performance even if it is small and inexpensive, such a lens system with an excessively short back focus cannot be used.

In Patent Documents 1 and 4, a first lens having a relatively weak meniscus is disposed with the concave surface facing the object side. The meniscus degree is determined by the paraxial radius of curvature of the front and rear surfaces of the lens, and is represented by (r1 + r2) / (r1-r2) where r1 is the radius of curvature of the front surface and r2 is the radius of curvature of the rear surface. When considering the value of the radius of curvature including the sign, in the case of a positive lens, the larger the value, the closer the radius of curvature of the front and rear surfaces, and the greater the meniscus degree. In the one described in Patent Document 1, the positive lens has a weak meniscus degree and a high power (power: an amount defined by the reciprocal of the focal length), and the first lens also exhibits spherical aberration and field curvature due to the positive power. generate. Although the aberration due to the positive power in the second lens is slightly reduced, the first lens does not actively correct the aberration, so the aberration cannot be reduced sufficiently with a small number of lenses, and the performance is deteriorated particularly in a wide-angle lens system. It is easy to do.

In the above Patent Documents 2 and 3, the first lens is a negative lens. At this time, if the meniscus degree is weak, the negative power is strong. Although there is an effect of generating aberration by the negative power of the first lens and canceling out aberration due to the positive second lens, the negative power is too strong, so that the light passes through a higher position from the optical axis in the second lens and becomes larger. Aberrations are generated, and a wide-angle lens system deteriorates the performance.

In Patent Documents 1 and 4, the focal length of the first lens normalized by the focal length of the entire system takes a small positive value, and the positive power of the first lens is relatively strong. As in the case where the degree of meniscus is weak, the first lens also causes spherical aberration and curvature of field due to positive power, and the aberration is not corrected so much, so good performance cannot be obtained with a small number of lenses.

In the above Patent Documents 2 and 3, the focal length of the first lens normalized by the focal length of the entire system takes a small negative value, and the negative power is strong. Similar to the case where the meniscus degree is weak, if the negative power is too strong, the power condensed by the second lens becomes stronger, which deteriorates the performance.

In the above Patent Documents 1, 3, and 4, the total lens length normalized by the focal length of the entire system is small. In the case where the number of lenses is as small as two, if the entire lens length is small, the surfaces are arranged close to each other, so that it is difficult to correct different aberrations on each surface, and sufficient performance cannot be obtained.

In Patent Document 2, the total lens length standardized by the focal length of the entire system is large. In such a lens system, the off-axis light beam passes through a high position on the first surface and the effective diameter becomes large. Although each surface can be spaced apart and different aberration correction is possible, the coma aberration of the off-axis light beam becomes large and sufficient performance cannot be obtained.

The present invention has been made in view of such a situation, and an object of the present invention is to provide a high-performance and inexpensive far-off lens in which aberrations are satisfactorily corrected for an on-axis light beam and an off-axis light beam even with a small number of two lenses. An object of the present invention is to provide an infrared lens, an imaging optical apparatus and a digital apparatus including the infrared lens.

In order to achieve the above object, the far-infrared lens of the first invention is a lens system used in the far-infrared band,
It is composed of two single lenses of the first lens and the second lens in order from the object side, satisfies the following conditional expression (2), and has a half field angle larger than 30 °.
7.3 <(r1 + r2) / (r1-r2) <27.5 (2)
However,
r1: Paraxial radius of curvature of the object side surface of the first lens,
r2: paraxial radius of curvature of the image side surface of the first lens,
It is.

The far-infrared lens of the second invention is characterized in that, in the first invention, the following conditional expression (4) is satisfied.
0.63 <dL2 / f <2.55 (4)
However,
dL2: center thickness of the second lens,
f: Focal length of the entire far-infrared lens system,
It is.

A far-infrared lens according to a third aspect of the invention is characterized in that, in the first or second aspect of the invention, the following conditional expression (6) is satisfied.
0.9 <f2 / f <4.5 (6)
However,
f2: focal length of the second lens,
f: Focal length of the entire far-infrared lens system,
It is.

A far-infrared lens of a fourth invention is characterized in that, in any one of the first to third inventions, the first lens and the second lens have a refractive index larger than 2 at a design wavelength. .

An imaging optical device according to a fifth aspect of the invention is a far-infrared lens according to any one of the first to fourth aspects, and an imaging element that converts a far-infrared optical image formed on the imaging surface into an electrical signal. And the far-infrared lens is provided so that a far-infrared optical image of a subject is formed on the imaging surface of the imaging device.

The digital device according to a sixth aspect of the invention is characterized in that at least one of a still image shooting and a moving image shooting of a subject is added by including the imaging optical device according to the fifth invention.

A far-infrared camera system according to a seventh aspect of the invention includes the far-infrared lens according to any one of the first to fourth aspects.

In the present invention, by adopting the above-described configuration, it becomes possible to perform positive aberration correction on the on-axis light beam and off-axis light beam even with a small number of lenses, that is, good aberration correction. As a result, high performance and high definition are possible, and it is possible to deal with newly manufactured inexpensive far-infrared sensors. Therefore, it is possible to realize an inexpensive but high-performance far-infrared lens and an imaging optical device including the same. And, by using the far-infrared lens 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), A high-performance far-infrared image input function can be added to a digital device at a low cost and in a compact manner.

1 is a lens cross-sectional view of a first embodiment (Example 1). FIG. FIG. 6 is an aberration diagram of Example 1. FIG. 6 is a lens cross-sectional view of a second embodiment (Example 2). FIG. 6 is an aberration diagram of Example 2. FIG. 6 is a lens cross-sectional view of a third embodiment (Example 3). FIG. 6 is an aberration diagram of Example 3. FIG. 10 is a lens cross-sectional view of a fourth embodiment (Example 4). FIG. 6 is an aberration diagram of Example 4. FIG. 10 is a lens cross-sectional view of a fifth embodiment (Example 5). FIG. 6 is an aberration diagram of Example 5. FIG. 10 is a lens cross-sectional view of a sixth embodiment (Example 6). FIG. 10 is an aberration diagram of Example 6. FIG. 10 is a lens cross-sectional view of a seventh embodiment (Example 7). FIG. 10 is an aberration diagram of Example 7. FIG. 10 is a lens cross-sectional view of an eighth embodiment (Example 8). FIG. 10 is an aberration diagram of Example 8. FIG. 10 is a lens cross-sectional view of a ninth embodiment (Example 9). FIG. 10 is an aberration diagram of Example 9. FIG. 10 is a lens cross-sectional view of a tenth embodiment (Example 10). FIG. 10 is an aberration diagram of Example 10. The lens sectional view of the 11th embodiment (Example 11). FIG. 10 shows aberration diagrams of Example 11. A lens sectional view of a twelfth embodiment (Example 12). FIG. 10 is an aberration diagram of Example 12. FIG. 18 is a lens cross-sectional view of a thirteenth embodiment (Example 13). Aberration diagram of Example 13. The schematic diagram which shows the schematic structural example of the digital apparatus carrying a far-infrared lens.

Hereinafter, a far-infrared lens, an imaging optical device, a digital device, and the like according to embodiments of the present invention will be described. A far-infrared lens according to an embodiment of the present invention is a lens system used in a far-infrared band, and is composed of two single lenses, a first lens and a second lens, in order from the object side. Conditional expression (2) is satisfied, and the half angle of view is larger than 30 °.
7.3 <(r1 + r2) / (r1-r2) <27.5 (2)
However,
r1: Paraxial radius of curvature of the object side surface of the first lens,
r2: paraxial radius of curvature of the image side surface of the first lens,
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. Nonetheless, far-infrared cameras are not widely used at present because lens materials that transmit far-infrared rays are materials containing expensive rare metals or materials that are difficult to process. This is because a lens system using several or more lenses increases the cost. 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 the far-infrared lens according to the embodiment of the present invention, the processing cost of the lens system is configured by forming the single lens of the first lens and the second lens in order from the object side to form a small number of lens systems. This makes it possible to provide an inexpensive lens system.

Also, most of the conventional far infrared sensors are expensive and can accurately display the 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. For this reason, even a wide-angle far-infrared lens having a half angle of view ω larger than 30 ° can be realized. The far-infrared lens according to the embodiment of the present invention assumes a lens configuration suitable for a wide-angle system in which the half angle of view ω is larger than 30 °, even though it has a wide-angle lens configuration composed of two single lenses. The following is a description of conditions and the like that are desirable in order to enable even two lenses while achieving such a wide angle and high performance.

The conditional expression (2) defines a desirable condition regarding the shaping factor of the first lens of the far-infrared lens. It is further desirable to satisfy the following conditional expression (2a), and by satisfying conditional expression (2a), the effects described later can be further increased.
9.4 <(r1 + r2) / (r1-r2) <27.1 (2a)
However,
r1: Paraxial radius of curvature of the object side surface of the first lens,
r2: paraxial radius of curvature of the image side surface of the first lens,
It is.

The shaping factor indicates the shape of one lens. If the paraxial curvature radius of the front surface (object side surface) of the lens including the sign is r1, and the paraxial curvature radius of the rear surface (image side surface) is r2, then (r1 + r2) / (r1-r2). When the values of the paraxial curvature radii on both sides are close to each other including the sign, the lens has a strong meniscus degree, and the absolute value of the shaping factor becomes large. The sign plus or minus differs depending on the direction of the lens surface. When the paraxial radii of curvature on both sides are separated including the sign, the lens has a low meniscus degree, and the absolute value of the shaping factor is small. The sign plus or minus differs depending on the direction of the lens surface as described above.

In the far-infrared lens according to the embodiment of the present invention, it is preferable to set the shaping factor of the first lens within a predetermined range. The conditional expressions (2) and (2a) define the range, and indicate that the value of the shaping factor is large, that is, the degree of meniscus is large. When the meniscus degree is large, the first lens has a weak positive power or a weak negative power. The first lens is mainly responsible for correction of spherical aberration and curvature of field, and by weakening the light condensing function, sufficient back focus can be secured and aberration correction can be made even with a wide angle specification.

When the value of the shaping factor becomes smaller than the lower limit of the conditional expression (2), the first lens has a weak meniscus and has a slightly strong positive power. Since it has a condensing function to some extent, the back focus is shortened and aberration correction is insufficient, and the second lens cannot be corrected. Further, if the value of the shaping factor exceeds the upper limit of the conditional expression (2), the aberration correction power of the first lens is almost lost, and the second lens alone needs to collect light. A large amount of aberration will occur.

Accordingly, if the conditional expression (2) is satisfied, and preferably the conditional expression (2a) is satisfied, the first lens becomes a positive lens or negative lens having a strong meniscus degree, and the first lens has spherical aberration, curvature of field, etc. Thus, it is possible to improve the performance by canceling out aberration due to the positive power generated in the second lens.

Regarding the back focus of the entire far-infrared lens system, it is desirable to satisfy the following conditional expression (1). Furthermore, it is desirable to satisfy the following conditional expression (1a), and it is further desirable to satisfy the following conditional expression (1b). Therefore, the effect described later can be further enhanced by preferably satisfying conditional expression (1a), more preferably satisfying conditional expression (1b).
0.38 <fB / f <1.35 (1)
0.38 <fB / f <0.97 (1a)
0.38 <fB / f <0.85 (1b)
However,
fB: Air-converted distance from the image side surface of the second lens to the image surface
f: Focal length of the entire far-infrared lens system,
It is.

In the far-infrared lens according to the embodiment of the present invention, it is preferable to set the back focus normalized by the focal length of the entire system within a predetermined range. The conditional expressions (1), (1a), and (1b) define the range, and the back focus is relatively short compared to a general far-infrared lens system. By shortening the back focus, the distance from the image plane to the second lens is shortened, so that the F-number light beam on the axis passes through a relatively low position of the second lens and suppresses the generation amount of spherical aberration. It becomes possible. However, in the far-infrared lens, since the brightness of the lens system determines the resolving power, the brightness of the F number: about 1.2 is required. For this reason, if the upper limit of conditional expression (1) is exceeded, spherical aberration tends to occur, making it difficult to construct a lens system with a small number of lenses. If the generation amount of spherical aberration is reduced so as not to exceed the upper limit of conditional expression (1), off-axis aberrations can be corrected efficiently by an aspherical surface, etc., and a wide-angle lens system is configured with a small number of lenses. Is possible. Further, if the back focus is shortened beyond the lower limit of the conditional expression (1), it is difficult to secure a space for disposing the far-infrared sensor cover glass and an interval between the cover glass and the sensor light receiving surface. Become. In the far infrared sensor, such a space is indispensable in order to ensure the performance. Therefore, the far infrared lens must be designed to ensure such a space.

Therefore, if the conditional expression (1) is satisfied, and preferably the conditional expression (1a) or (1b) is satisfied, the distance from the image plane to the second lens is not excessively increased, and the low position of the second lens is set. Thus, the spherical aberration can be suppressed by passing the F-number light beam, and at the same time, the field curvature correction can be effectively performed for the off-axis light beam. In addition, a sufficient space for inserting the far-infrared sensor cover glass can be secured.

Regarding the total length of the far-infrared lens, it is desirable to satisfy the following conditional expression (3). Furthermore, it is desirable to satisfy the following conditional expression (3a), and it is more desirable to satisfy the following conditional expression (3b). Therefore, the effect described later can be further enhanced by preferably satisfying conditional expression (3a), more preferably satisfying conditional expression (3b).
1.75 <TL / f <5.7 (3)
1.75 <TL / f <5.0 (3a)
1.75 <TL / f <3.2 (3b)
However,
TL: full length of far infrared lens (when back focus is converted to air),
f: Focal length of the entire far-infrared lens system,
It is.

In the far-infrared lens according to the embodiment of the present invention, it is preferable to set the total lens length normalized by the focal length of the entire system within a predetermined range. The conditional expressions (3), (3a), and (3b) define the range. When the lower limit of conditional expression (3) is exceeded, when the number of lenses is as small as two, the surfaces are arranged close to each other due to the small total lens length, making it difficult to correct different aberrations on each surface. Sufficient performance cannot be obtained. If the upper limit of conditional expression (3) is exceeded, in such a lens system, the off-axis light beam passes through a high position on the first surface, so that the effective diameter becomes large. Different aberrations can be corrected because the surfaces can be arranged apart from each other, but sufficient performance cannot be obtained because the coma aberration of the off-axis light beam increases.

Therefore, if the conditional expression (3) is satisfied, and preferably the conditional expression (3a) or (3b) is satisfied, the surfaces can be arranged sufficiently apart from each other, so that even with a lens configuration of as few as two lenses It is possible to obtain a lens system with good performance by correcting different aberrations. Further, it is possible to prevent an increase in the front lens diameter due to an excessively large lens total length, and to suppress the coma aberration of the off-axis light beam caused by the first lens.

Regarding the center thickness (core thickness) of the second lens of the far-infrared lens, it is desirable to satisfy the following conditional expression (4), and it is more desirable to satisfy the following conditional expression (4a). Therefore, preferably, by satisfying conditional expression (4a), the effects described later can be further increased.
0.63 <dL2 / f <2.55 (4)
0.68 <dL2 / f <2.5 (4a)
However,
dL2: center thickness of the second lens,
f: Focal length of the entire far-infrared lens system,
It is.

In the far-infrared lens according to the embodiment of the present invention, it is preferable to set the core thickness of the second lens normalized by the focal length of the entire system within a predetermined range. The conditional expressions (4) and (4a) define the range, and the core thickness of the second lens is relatively thick compared to the conventional far-infrared lens. By increasing the thickness of the lens, different aberration correction can be performed on the front surface and the rear surface of the second lens, and good performance can be ensured even with a small number of lenses.

If the core thickness of the second lens is reduced beyond the lower limit of conditional expression (4), the same aberration correction can only be performed on the front surface and the rear surface of the second lens. It will be difficult to do. Also, if the core thickness of the second lens increases beyond the upper limit of conditional expression (4), it becomes difficult to obtain a homogeneous material due to lens material restrictions, or uniform heat molding is difficult in the case of an aspherical surface. For this reason, it becomes difficult to obtain the performance of a single lens as designed, and it becomes impossible to obtain a lens system with good performance.

Regarding the focal length of the first lens of the far-infrared lens, it is desirable to satisfy the following conditional expression (5). Furthermore, it is more desirable to satisfy the following conditional expressions (5a), (5b) or (5c). That is, it is more preferable that the conditional expressions (5), (5a), (5b), and (5c) are satisfied in this order. Therefore, the effect described later can be further increased by satisfying conditional expression (5a), more preferably conditional expression (5b) or (5c).
1.1 <f1 / f <97.5 (5)
1.1 <f1 / f <8.0 (5a)
1.1 <f1 / f <3.8 (5b)
1.3 <f1 / f <3.8 (5c)
However,
f1: focal length of the first lens,
f: Focal length of the entire far-infrared lens system,
It is.

In the far-infrared lens according to the embodiment of the present invention, it is preferable to set the focal length of the first lens normalized by the focal length of the entire system within a predetermined range. The conditional expressions (5), (5a), (5b), and (5c) define the range, and the first lens has a relatively weak positive power. If the power of the first lens exceeds the upper limit of the conditional expression (5), it becomes difficult to secure a sufficient back focus, and even in a wide-angle optical system, it is difficult to even insert a sensor cover glass. End up. Further, when the power of the first lens becomes smaller than the lower limit of the conditional expression (5), most of the light condensing action must be performed by the second lens, and a large spherical aberration occurs in the second lens.

Regarding the focal length of the second lens of the far-infrared lens, it is desirable to satisfy the following conditional expression (6). Furthermore, it is desirable to satisfy the following conditional expression (6a), and it is more desirable to satisfy the following conditional expression (6b). Therefore, the effect described later can be further enhanced by preferably satisfying conditional expression (6a), more preferably satisfying conditional expression (6b).
0.9 <f2 / f <4.5 (6)
0.9 <f2 / f <2.9 (6a)
0.9 <f2 / f <1.3 (6b)
However,
f2: focal length of the second lens,
f: Focal length of the entire far-infrared lens system,
It is.

In the far-infrared lens according to the embodiment of the present invention, it is preferable to set the focal length of the second lens normalized by the focal length of the entire system within a predetermined range. The conditional expressions (6), (6a), and (6b) define the range. If the lower limit of conditional expression (6) is exceeded, the power of the second lens is not too strong, so that curvature of field, distortion, etc. that occur in this lens are kept small, and eccentricity errors and lens shape errors that occur during manufacturing. The performance degradation due to the lens interval error can be kept small. If the upper limit of conditional expression (6) is not reached, the power of the second lens is not too weak, so the optical system does not become too large, and the volume and weight of the lens can be kept within an appropriate range.

In the far-infrared lens according to the embodiment of the present invention, it is preferable that a refractive index at a design wavelength of the first lens and the second lens is larger than 2. The first lens and the second lens are made of a far-infrared lens material having a high refractive index. Specifically, chalcogenide glass containing chalcogen as a main component (refractive index of about 2.5 to 2.8 at a wavelength of 10 μm), silicon (Si, refractive index of about 3 at a wavelength of 10 μm), germanium (Ge, at a wavelength of 10 μm) For example, a refractive index of about 4). Since these lens materials have a high refractive index, the curvature of the lens surface can be relaxed and the aberration of each surface can be reduced. Therefore, even when the number of lenses is small, good aberration correction can be performed. Some far-infrared lens materials have a low refractive index. However, even if they are inexpensive, it is necessary to increase the curvature of the lens surface. Therefore, it is difficult to construct a lens system with a small number of sheets, which ultimately increases the cost of the lens system.

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.

Also, 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, the far-infrared lens uses ν = (N10-1) / (N8-N12) as a value representing the nature of dispersion (however, 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 = 1250 to 1252, Si = 1860, ZnS = 23 (used for achromatic), ZnSe = 57 (used for achromatic), and the like. .

In the far-infrared lens according to the embodiment of the present invention, it is preferable that at least one of the lens surfaces of the first and second lenses is a diffraction grating surface. By having a diffraction grating surface, it is possible to satisfactorily correct axial chromatic aberration. As a cross-sectional shape of the diffraction grating, a step shape or a kinoform may be used in addition to the binary shape. In either case, the phase difference at the diffraction wavelength can be calculated by the equation (DS) described later.

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 two lenses. Will be able to. For this reason, it is possible to achieve a wide angle with two lenses while achieving high performance and high definition through good aberration correction, and it can also be used for newly manufactured inexpensive far-infrared sensors. Become. Therefore, it is possible to realize an inexpensive but high-performance far-infrared lens and an imaging optical device including the same.

High performance for digital devices by using far-infrared lenses or imaging optical devices for digital devices such as night vision devices, thermography, portable terminals, camera systems (eg, digital cameras, surveillance cameras, security cameras, in-vehicle cameras) The far-infrared image input function can be added at a low cost and in a compact manner, contributing to its compactness, high performance, and high functionality. As described above, 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 two-lens lens system as a far-infrared lens. Further, it is possible to realize an inexpensive camera system in which the processing cost of the lens is suppressed.

The far-infrared lens according to the embodiment of 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 mobile terminal, a drive recorder, etc.). By combining with a sensor or the like, 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. The lens includes a lens and an imaging element (far infrared sensor) that converts a far infrared optical image formed by the far infrared lens into an electrical signal. Then, the far-infrared lens 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 image sensor, so that the size and cost are high. An imaging optical device having performance and a digital device including the same can be realized.

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. 27 shows a schematic configuration example of the digital device DU in a schematic cross section. The imaging optical device LU mounted in the digital device DU shown in FIG. 27 has a far-infrared lens LN (AX: optical axis) that forms a far-infrared optical image (image plane) IM of the object in order from the object (that is, 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 far-infrared lens LN. And an imaging element (far infrared 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.

The far-infrared lens LN is a two-lens single-focus lens composed of two single lenses, a first lens and a second lens, in order from the object side. As described above, the light receiving surface SS of the image sensor SR. An optical image IM composed of far infrared rays is formed on the top. As the image 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 LN is provided so that the optical image IM of the subject is formed on the light-receiving surface SS that is the photoelectric conversion unit of the imaging element SR, the optical image IM formed by the far-infrared lens LN is It is converted into an electrical signal by the image sensor SR.

Specific examples of the image 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 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 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 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.

FIG. 1, FIG. 3,..., FIG. 25 show first to thirteenth embodiments of the far-infrared lens LN in an infinitely focused state in optical sections. The far-infrared lenses LN according to the first to thirteenth embodiments include, in order from the object side, a first lens L1 having positive power and a second lens L2 having positive power.

In the first, second, ninth to twelfth embodiments, the first lens L1 and the second lens L2 have a meniscus shape that is paraxial and convex to the image side. In the third and thirteenth embodiments, the first lens L1 has a meniscus shape that is paraxial and concave on the image side, and the second lens L2 has a biconvex shape that is paraxial. In the fourth to eighth embodiments, the first lens L1 has a meniscus shape that is paraxial and convex to the image side, and the second lens L2 has a biconvex shape that is paraxial.

In the first to thirteenth embodiments, the first lens L1 and the second lens L2 are double-sided aspheric lenses. In the first, second, fourth to twelfth embodiments, the aperture stop ST is disposed closest to the object side. In the third and thirteenth embodiments, the first lens L1 and the second lens L2 are arranged. An aperture stop ST is disposed between the two. A parallel plate PT (for example, a parallel plate of Ge crystal) corresponding to the protective cover glass of the image sensor SR is disposed on the image side of each far-infrared lens LN.

Hereinafter, the configuration and the like of the far-infrared lens embodying the present invention will be described more specifically with reference to construction data of the examples. Examples 1 to 13 (EX1 to 13) listed here are numerical examples corresponding to the first to thirteenth embodiments, respectively, and are lens configuration diagrams showing the first to thirteenth embodiments. (FIG. 1, FIG. 3,..., FIG. 25) respectively show the lens cross-sectional shape, lens arrangement, and the like of the corresponding Examples 1 to 13.

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), paraxial radius of curvature R (mm), axial top surface spacing d (mm), a refractive index N10 for a design wavelength of 10 μm, and a dispersion value ν for wavelengths of 8 to 12 μm. The dispersion value ν represents the nature of dispersion and is defined by ν = (N10-1) / (N8-N12) (where N8: refractive index for a wavelength of 8 μm, refractive index N10 for a wavelength of 10 μm, N12: for a wavelength of 12 μm) Refractive index.) The optical material with a refractive index of 4.000400 is germanium (GE), and the optical material with a refractive index of 2.77810 is chalcogenide glass. The parallel flat plate PT in front of the image plane IM is a protective plate (cover glass) of the far infrared sensor SR.

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 (reciprocal of paraxial 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. A phase coefficient is shown as diffraction plane data. It should be noted that the coefficient of the term not described in the diffraction surface 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.

Table 1 shows various data as the focal length f (mm), F number (Fno), half angle of view ω (°), image height Y ′ (real image height, mm), lens total length TL (mm), The back focus fB (mm), the focal length f1 (mm) of the first lens L1, and the focal length f2 (mm) of the second lens L2 are shown, and Table 2 shows the values corresponding to the conditional expressions of each embodiment (design wavelength: 10,000 nm). The back focus BF in Table 1 expresses the distance from the lens final surface to the paraxial image surface by the air conversion length, and the total lens length TL indicates the back focus BF at the distance from the lens front surface to the lens final surface. In addition, when the first surface is the stop ST (EX1, 2, 4 to 12), the total lens length TL is the distance from the stop ST to the paraxial image point IM.

2, FIG. 4,..., FIG. 26 are aberration diagrams corresponding to Examples 1 to 13 (EX1 to 13), respectively, (A) is a spherical aberration diagram, (B) is an astigmatism diagram, and (C ) Is a distortion diagram. The spherical aberration diagram shows a spherical aberration amount at a design wavelength (evaluation wavelength) of 10 μm indicated by a solid line, a spherical aberration amount at a wavelength of 8 μm indicated by a long broken line, and a spherical aberration amount at a wavelength of 12 μm indicated by a short broken line from the paraxial image plane. The amount of displacement in the optical axis AX direction (mm) is represented, the vertical axis represents the F number, and the vertical axis scale represents the value obtained by normalizing the incident height to the pupil by the maximum height (that is, the relative pupil height). ing. In the astigmatism diagram, the alternate long and short dash line M or broken line T is the meridional (tangential) image plane at the design wavelength of 10 μm, the solid line S is the sagittal image plane at the design wavelength of 10 μm, and the amount of deviation in the optical axis AX direction from the paraxial image plane. (Mm), and the vertical axis represents the half angle of view ω (°). In the distortion diagram, the horizontal axis represents the distortion (%) at the design wavelength of 10 μm, and the vertical axis represents the half angle of view ω (°).

Example 1
Unit: mm
Surface data Surface number R (mm) d (mm) N10 ν
Object ∞
1 (Aperture) ∞ 0.75
2 * -6.338 2.43 4.00400 1252
3 * -5.752 1.82
4 * -196.123 2.80 4.00400 1252
5 * -27.043 2.30
6 ∞ 0.50 4.00400 1252
7 ∞ 0.50
Paraxial image point

Aspheric data 2nd surface 3rd surface 4th surface 5th surface K 7.621 -3.868 -15.000 -15.000
A4 -2.7194E-03 -3.5463E-03 3.6807E-03 4.3449E-03
A6 3.6128E-05 1.1045E-05 -1.0679E-05 -7.6449E-05
A8 2.9521E-05 2.9216E-06 -2.9459E-06 3.8592E-05
A10 -3.8271E-06 -7.1261E-07 1.0359E-07 -8.1171E-08

Example 2
Unit: mm
Surface data Surface number R (mm) d (mm) N10 ν
Object ∞
1 (Aperture) ∞ 0.81
2 * -6.045 2.74 2.77810 160
3 * -4.887 1.94
4 * -29.093 3.22 2.77810 160
5 * -12.221 2.84
6 ∞ 0.50 4.00400 1252
7 ∞ 0.49
Paraxial image point

Aspheric data 2nd surface 3rd surface 4th surface 5th surface K 5.363 -4.100 -0.852 7.657
A4 -9.7358E-04 -3.6558E-03 3.2384E-03 2.8128E-03
A6 -5.5200E-04 2.4842E-05 -5.0326E-06 1.1594E-05
A8 2.5492E-04 1.4386E-05 -1.8198E-06 8.0515E-06
A10 -1.3497E-05 -1.0203E-06 4.4725E-08 -6.7964E-09

Example 3
Unit: mm
Surface data Surface number R (mm) d (mm) N10 ν
Object ∞
1 * 3.591 1.01 2.77810 160
2 * 3.335 1.04
3 (Aperture) ∞ 0.78
4 * 8.676 3.27 2.77810 160
5 * -65.586 1.02
6 ∞ 0.50 4.00400 1252
7 ∞ 1.02
Paraxial image point

Aspheric data 1st surface 2nd surface 4th surface 5th surface K -0.392 1.073 3.590 30.000
A3 -2.4094E-04 1.0642E-03 1.8151E-04 -1.0760E-03
A4 1.1585E-03 -3.0028E-03 6.0091E-04 4.2629E-03
A5 6.9918E-05 4.6961E-05 -1.6119E-05 -2.3812E-05
A6 -7.0756E-05 -3.9360E-06 -2.2481E-04 -4.8154E-04
A8 2.8321E-05 -2.5775E-04 2.7422E-05 6.9480E-05
A10 -1.4924E-05 -6.6923E-05 -1.9462E-06 -4.7962E-06

Example 4
Unit: mm
Surface data Surface number R (mm) d (mm) N10 ν
OB ∞ ∞
1 (ST) ∞ 0.802176
2 * -6.27915 2.587169 4.004 1250
3 * -5.80433 1.831465
4 * 90.73463 2.779481 4.004 1250
5 * -57.55095 2.272522
6 ∞ 0.500000 4.004 1250
7 ∞ 0.486000
IM ∞ 0.000000

Aspheric data Aspheric surface: 2 *
K = 7.620968
A4 = -0.232586E-02
A6 = -0.138789E-03
A8 = 0.123318E-03
A10 = -0.807669E-05

Aspheric data Aspheric surface: 3 *
K = -4.105717
A4 = -0.341885E-02
A6 = 0.203194E-04
A8 = 0.360199E-05
A10 = -0.661989E-06

Aspheric data Aspheric surface: 4 *
K = -15.000000
A4 = 0.364839E-02
A6 = -0.804332E-05
A8 = -0.282540E-05
A10 = 0.104786E-06

Aspheric data Aspheric: 5 *
K = -15.000000
A4 = 0.445355E-02
A6 = 0.514582E-04
A8 = 0.335483E-04
A10 = 0.966802E-06

Example 5
Unit: mm
Surface data Surface number R (mm) d (mm) N10 ν
OB ∞ ∞
1 (ST) ∞ 0.810319
2 * -7.27664 3.452702 4.004 1250
3 * -6.67025 2.600671
4 * 99.81599 2.344192 4.004 1250
5 * -46.41594 2.013546
6 ∞ 0.500000 4.004 1250
7 ∞ 0.486000
IM ∞ 0.000000

Aspheric data Aspheric surface: 2 *
K = 9.490200
A4 = -0.141396E-02
A6 = -0.111242E-03
A8 = 0.890495E-04
A10 = -0.676957E-05

Aspheric data Aspheric surface: 3 *
K = -4.035285
A4 = -0.221072E-02
A6 = 0.169514E-04
A8 = 0.271526E-06
A10 = -0.134928E-06

Aspheric data Aspheric surface: 4 *
K = -15.000000
A4 = 0.281935E-02
A6 = 0.685182E-04
A8 = -0.503968E-05
A10 = 0.143664E-06

Aspheric data Aspheric: 5 *
K = 15.000000
A4 = 0.336277E-02
A6 = 0.261324E-03
A8 = -0.144972E-04
A10 = 0.376420E-05

Example 6
Unit: mm
Surface data Surface number R (mm) d (mm) N10 ν
OB ∞ ∞
1 (ST) ∞ 0.816782
2 * -7.33382 3.441187 4.004 1250
3 * -6.68192 2.620908
4 * 121.52350 2.344225 4.004 1250
5 * -42.01188 1.990185
6 ∞ 0.500000 4.004 1250
7 ∞ 0.486000
IM ∞ 0.000000

Aspheric data Aspheric surface: 2 *
K = 9.611185
A4 = -0.149260E-02
A6 = -0.127211E-03
A8 = 0.870872E-04
A10 = -0.701794E-05

Aspheric data Aspheric surface: 3 *
K = -3.727033
A4 = -0.211299E-02
A6 = 0.839648E-05
A8 = 0.648433E-06
A10 = -0.142336E-06

Aspheric data Aspheric surface: 4 *
K = -15.000000
A4 = 0.266175E-02
A6 = 0.802542E-04
A8 = -0.550920E-05
A10 = 0.148235E-06

Aspheric data Aspheric: 5 *
K = 15.000000
A4 = 0.319550E-02
A6 = 0.254845E-03
A8 = -0.138955E-04
A10 = 0.352979E-05

Example 7
Unit: mm
Surface data Surface number R (mm) d (mm) N10 ν
OB ∞ ∞
1 (ST) ∞ 0.864920
2 * -7.03526 2.975668 4.004 1250
3 * -6.27469 1.945048
4 * 173.51899 2.650012 4.004 1250
5 * -46.35185 2.243907
6 ∞ 0.500000 4.004 1250
7 ∞ 0.486000
IM ∞ 0.000000

Aspheric data Aspheric surface: 2 *
K = 8.897131
A4 = -0.207533E-02
A6 = -0.289646E-03
A8 = 0.143117E-03
A10 = -0.135917E-04

Aspheric data Aspheric surface: 3 *
K = -4.359018
A4 = -0.283678E-02
A6 = 0.282421E-04
A8 = 0.110501E-05
A10 = -0.292151E-06

Aspheric data Aspheric surface: 4 *
K = -15.000000
A4 = 0.358746E-02
A6 = 0.520212E-05
A8 = -0.298734E-05
A10 = 0.108580E-06

Aspheric data Aspheric: 5 *
K = 14.690149
A4 = 0.402099E-02
A6 = 0.235244E-03
A8 = -0.784096E-05
A10 = 0.409915E-05

Example 8
Unit: mm
Surface data Surface number R (mm) d (mm) N10 ν
OB ∞ ∞
1 (ST) ∞ 0.861697
2 * -7.31877 3.125049 4.004 1250
3 * -6.42076 1.971548
4 * 390.00777 2.576393 4.004 1250
5 * -41.75446 2.236701
6 ∞ 0.500000 4.004 1250
7 ∞ 0.486000
IM ∞ 0.000000

Aspheric data Aspheric surface: 2 *
K = 9.690032
A4 = -0.206297E-02
A6 = -0.234755E-03
A8 = 0.116301E-03
A10 = -0.938163E-05

Aspheric data Aspheric surface: 3 *
K = -4.433234
A4 = -0.268792E-02
A6 = 0.300845E-04
A8 = 0.548332E-06
A10 = -0.225286E-06

Aspheric data Aspheric surface: 4 *
K = 15.000000
A4 = 0.363317E-02
A6 = 0.926419E-05
A8 = -0.322586E-05
A10 = 0.115247E-06

Aspheric data Aspheric: 5 *
K = -14.377065
A4 = 0.399215E-02
A6 = 0.236360E-03
A8 = -0.817727E-05
A10 = 0.405203E-05

Example 9
Unit: mm
Surface data Surface number R (mm) d (mm) N10 ν
OB ∞ ∞
1 (ST) ∞ 0.845567
2 * -7.64106 3.351431 4.004 1250
3 * -6.60849 2.053915
4 * -887.07541 2.433648 4.004 1250
5 * -37.24419 2.220860
6 ∞ 0.500000 4.004 1250
7 ∞ 0.486000
IM ∞ 0.000000

Aspheric data Aspheric surface: 2 *
K = 10.741471
A4 = -0.192691E-02
A6 = -0.154892E-03
A8 = 0.884281E-04
A10 = -0.433345E-05

Aspheric data Aspheric surface: 3 *
K = -4.550159
A4 = -0.249158E-02
A6 = 0.326732E-04
A8 = -0.269045E-07
A10 = -0.159032E-06

Aspheric data Aspheric surface: 4 *
K = -15.000000
A4 = 0.374483E-02
A6 = 0.154127E-04
A8 = -0.359526E-05
A10 = 0.128983E-06

Aspheric data Aspheric: 5 *
K = -6.221728
A4 = 0.407323E-02
A6 = 0.244691E-03
A8 = -0.929228E-05
A10 = 0.411471E-05

Example 10
Unit: mm
Surface data Surface number R (mm) d (mm) N10 ν
OB ∞ ∞
1 (ST) ∞ 0.819818
2 * -5.91316 2.768638 2.7781 160.2
3 * -4.52183 1.371573
4 * -34.73754 4.000000 2.7781 160.2
5 * -18.19129 2.696316
6 ∞ 0.500000 4.004 1250
7 ∞ 0.486000
IM ∞ 0.000000

Aspheric data Aspheric surface: 2 *
K = 1.768390
A4 = -0.455419E-02
A6 = -0.961230E-03
A8 = 0.277633E-03
A10 = -0.325522E-04

Aspheric data Aspheric surface: 3 *
K = -2.612672
A4 = -0.260108E-02
A6 = -0.396228E-04
A8 = 0.959824E-05
A10 = -0.614360E-06

Aspheric data Aspheric surface: 4 *
K = 6.570084
A4 = 0.389940E-02
A6 = -0.730020E-04
A8 = 0.391424E-06
A10 = 0.157896E-07

Aspheric data Aspheric: 5 *
K = 3.514999
A4 = 0.245290E-02
A6 = -0.573722E-05
A8 = 0.954888E-05
A10 = -0.151311E-06

Example 11
Unit: mm
Surface data Surface number R (mm) d (mm) N10 ν
OB ∞ ∞
1 (ST) ∞ 0.824233
2 * -5.82038 2.748465 2.7781 160.2
3 * -4.52696 1.423082
4 * -39.21930 4.000000 2.7781 160.2
5 * -18.48482 2.676865
6 ∞ 0.500000 4.004 1250
7 ∞ 0.486000
IM ∞ 0.000000

Aspheric data Aspheric surface: 2 *
K = 1.545042
A4 = -0.448727E-02
A6 = -0.100024E-02
A8 = 0.285638E-03
A10 = -0.335281E-04

Aspheric data Aspheric surface: 3 *
K = -2.533029
A4 = -0.252923E-02
A6 = -0.488205E-04
A8 = 0.102503E-04
A10 = -0.639718E-06

Aspheric data Aspheric surface: 4 *
K = 14.765852
A4 = 0.379131E-02
A6 = -0.676970E-04
A8 = 0.299986E-06
A10 = 0.162865E-07

Aspheric data Aspheric: 5 *
K = 3.960430
A4 = 0.245208E-02
A6 = -0.495538E-05
A8 = 0.944887E-05
A10 = -0.132525E-06

Example 12
Unit: mm
Surface data Surface number R (mm) d (mm) N10 ν
OB ∞ ∞
1 (ST) ∞ 0.853611
2 * -5.38831 2.594890 2.7781 160.2
3 * -4.52618 1.836368
4 * -69.46815 4.000000 2.7781 160.2
5 * -17.34124 2.520451
6 ∞ 0.500000 4.004 1250
7 ∞ 0.486000
IM ∞ 0.000000

Aspheric data Aspheric surface: 2 *
K = 2.176583
A4 = -0.323974E-02
A6 = -0.101787E-02
A8 = 0.273320E-03
A10 = -0.298276E-04

Aspheric data Aspheric surface: 3 *
K = -2.896526
A4 = -0.344650E-02
A6 = -0.197773E-04
A8 = 0.866588E-05
A10 = -0.633557E-06

Aspheric data Aspheric surface: 4 *
K = -9.499184
A4 = 0.289565E-02
A6 = -0.232867E-04
A8 = -0.843775E-06
A10 = 0.279536E-07

Aspheric data Aspheric: 5 *
K = 6.108008
A4 = 0.230698E-02
A6 = -0.799862E-05
A8 = 0.854639E-05
A10 = -0.974203E-07

Example 13
Unit: mm
Surface data Surface number R (mm) d (mm) N10 ν
OB ∞ ∞
1 * 3.57283 1.051131 2.7781 160.2
2 * 3.31299 1.007687
3 (ST) ∞ 1.149565
4 * 8.24988 3.710412 2.7781 160.2
5 * -76.52927 0.668753
6 ∞ 0.500000 4.004 1250
7 ∞ 1.042203
IM ∞ 0.000000

Aspheric data Aspheric surface: 1 *
K = -3.6694E-01
A3 = 1.4780E-03
A4 = 1.0131E-03
A5 = 3.2472E-04
A6 = 7.7471E-05
A8 = 5.2150E-05
A10 = -6.5105E-06

Aspheric data Aspheric surface: 2 *
K = 1.1377E + 00
A3 = 1.6247E-04
A4 = -1.5162E-03
A5 = 6.2043E-04
A6 = 3.6710E-04
A8 = -1.0639E-04
A10 = -4.1788E-05
Aspheric: 4 *
K = 4.4727E + 00
A3 = -1.2208E-03
A4 = 9.2382E-04
A5 = 3.0930E-05
A6 = -2.4440E-04
A8 = 2.1154E-05
A10 = -1.6421E-06

Aspheric data Aspheric: 5 *
K = 1.5000E + 01
A3 = 9.7846E-03
A4 = -3.0877E-04
A5 = 2.3391E-04
A6 = -2.0535E-04
A8 = 8.1670E-05
A10 = -6.2377E-06

DU Digital equipment LU Imaging optical device LN Far infrared lens L1 First lens L2 Second lens ST Aperture stop
SR image sensor (far infrared 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 (7)

1. A lens system used in the far-infrared band,
   A far-infrared lens comprising two single lenses, a first lens and a second lens, in order from the object side, satisfying the following conditional expression (2) and having a half angle of view greater than 30 ° ;
   7.3 <(r1 + r2) / (r1-r2) <27.5 (2)
   However,
   r1: Paraxial radius of curvature of the object side surface of the first lens,
   r2: paraxial radius of curvature of the image side surface of the first lens,
   It is.
2. The far-infrared lens according to claim 1, wherein the following conditional expression (4) is satisfied:
   0.63 <dL2 / f <2.55 (4)
   However,
   dL2: center thickness of the second lens,
   f: Focal length of the entire far-infrared lens system,
   It is.
3. The far-infrared lens according to claim 1, wherein the following conditional expression (6) is satisfied:
   0.9 <f2 / f <4.5 (6)
   However,
   f2: focal length of the second lens,
   f: Focal length of the entire far-infrared lens system,
   It is.
4. The far-infrared lens according to any one of claims 1 to 3, wherein the first lens and the second lens have a refractive index greater than 2 at a design wavelength.
5. An imaging surface of the imaging device, comprising: the far-infrared lens according to any one of claims 1 to 4; and an imaging device that converts a far-infrared optical image formed on the imaging surface into an electrical signal. An imaging optical apparatus, wherein the far-infrared lens is provided so that a far-infrared optical image of a subject is formed thereon.
6. 6. A digital apparatus comprising the imaging optical device according to claim 5 to which at least one function of still image shooting and moving image shooting of a subject is added.
7. A far-infrared camera system comprising the far-infrared lens according to any one of claims 1 to 4.

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