GB2474762A

GB2474762A - Thermal imaging device with objective having five lens groups

Info

Publication number: GB2474762A
Application number: GB1017422A
Authority: GB
Inventors: Bertram Achtner
Original assignee: Carl Zeiss Optronics GmbH
Current assignee: Hensoldt Optronics GmbH
Priority date: 2009-10-23
Filing date: 2010-10-15
Publication date: 2011-04-27
Anticipated expiration: 2030-10-15
Also published as: DE102009045970A1; GB2474762B; GB201017422D0; DE102009045970B4

Abstract

A thermal imaging device or reimager 100 for the detection of infrared radiation has an objective OB, an inverting system UM and an image capture unit BE The objective OB has a first lens group G1, a second lens group G2, a third lens group G3, a fourth lens group G4 and a fifth lens group G5. Each of the second lens group G2 — which may be a single lens L3 — and the third lens group G3 — which may be a single lens L4 — has negative refractive power, and may have focal lengths in the ranges -15 mm to -25 mm (G2) and -35 mm to -90 mm (G3). The inverting system UM comprises a sixth lens group G6 and a seventh lens group G7. The first lens group G1 has a first lens unit L1 with positive refractive power. The second and third lens groups may be movable along optical axis A in the direction of the first optical group or the image capture unit. The device may have adjustable focal length, and figures 1a, 1b and 1c show three zoom positions in which the objective has focal lengths of 207 mm, 115.8 mm and 23 mm respectively. Beam deflection means (S1, S2, S3) may be provided to realise a small structure.

Description

INTELLECTUAL

. .... PROPERTY OFFICE Application No. GB 1017422.5 RTM Date:9 February 2011 The following terms are registered trademarks and should be read as such wherever they occur in this document: UMICORE and GAS JR Intellectual Property Office is an operating name of the Patent Office www.ipo.gov.uk Thermal Imaging Device The invention relates to a thermal imaging device with at least one objective, with at least one inverting system and with at least one image capture unit. The thermal imaging device is provided for the detection of infrared radiation to be used, for example, for recognising an object or a person.

An optical system with an objective, an inverting system and an image capture unit is often also referred to as a reimager. The objective projects an object located at infinity or at a finite distance onto an intermediate image. This intermediate image is projected by the inverting system onto the image capture unit, which is arranged in an image plane. Such an optical system is used in particular in a thermal imaging device, which is configured for the detection of infrared radiation. By means of the thermal imaging device it is possible to generate images on the basis of the process of thermography. In this case, thermography is an image-forming process that makes heat radiation (middle infrared) of an object or body that is invisible to the human eye visible. Temperature distributions on surfaces as well as objects are detected and displayed.

An optical system for a thermal imaging device is known from patent document DE 196 00 336 Al, for example, wherein the optical system has a fixed focal length. It is not designed for a variable focal length, which is desirable in many applications.

A further optical system for a thermal imaging device is known from patent document DE 198 07 093 C2. In this optical system an objective, an inverting system and an image capture unit are likewise arranged from a reproducible object in the direction of the image capture unit. In addition, from a reproducible object in the direction of the image capture unit, the objective has a first lens group, a second lens group and a third lens group. Moreover, the inverting system is formed by two further lens groups. The first lens group of the known optical system has a first lens unit with positive refractive power. This optical system also has the disadvantage that it is only designed for a fixed focal length.

Moreover, deliberations have shown that it is desirable that an optical system (and therefore also a thermal imaging device, which has the optical system) has a small structural space.

I

Therefore, the object forming the basis of the invention is to propose a thermal imaging device that at least provides the possibility of adjusting a focal length as well as making the structural space small.

This object is achieved by means of a thermal imaging device with the features of claim 1.

Further features of the invention may be seen from the following description, the following claims and/or the attached figures.

The thermal imaging device according to the invention has at least one objective, at least one inverting system and at least one image capture unit. The objective, the inverting system and the image capture unit are arranged from a reproducible object in the direction of the image capture unit. In other words, the inverting system is arranged between the objective and the image capture unit. The objective is, moreover, provided with multiple lens groups. Thus, from a reproducible object in the direction of the image capture unit, it has a first lens group, a second lens group, a third lens group, a fourth lens group and a fifth lens group. The inverting system is also provided with multiple lens groups. Thus, from a reproducible object in the direction of the image capture unit, the inverting system has a sixth lens group and a seventh lens group. In addition, the first lens group has a first lens unit with positive refractive power. Moreover, both the second lens group and the third lens group have negative refractive power.

In the preceding and following text, a lens group is understood to mean either a group of at least two lenses or only a single lens. Therefore, a lens group can consist of only one single lens. In addition, in the preceding and following text, a lens unit is understood to mean a unit with at least two lenses or also only one unit with a single lens.

Deliberations have shown that the claimed refractive powers of the individual lens groups and/or lens units enable an optical system to be provided in a thermal imaging device that at least provides the possibility of adjusting a focal length and also making the structural space of the thermal imaging device small. Moreover, deliberations have shown that the optical system can have a relatively high aperture. This and further considerations as well as embodiments will be outlined in more detail below.

The optical system of the thermal imaging device according to the invention is a reimager, which has already been described above. Thus, the objective projects an object located at infinity or at a finite distance onto an intermediate image. This intermediate image is projected by the inverting system onto the image capture unit, which is arranged in an image plane.

The optical system of the thermal imaging system according to the invention is formed from materials, for example, that are transparent to infrared radiation. Therefore, infrared radiation can be detected with the optical system. The spectral range of the detectable infrared radiation covers the entire infrared spectral range. However, it is provided in an embodiment of the invention to detect in particular the spectral range of 3 tm to 12 pm. In a further exemplary embodiment it is provided in turn to detect a spectral range of 3 tm to 5 tm or 8 tm to 12 pm. The last-mentioned spectral range is of particular advantage, since the thermal radiation emission of a human body falls within this spectral range.

In an embodiment of the thermal imaging device, the first lens group additionally has a second lens unit with positive refractive power. The first lens group has positive refractive power overall in this exemplary embodiment.

In a further embodiment of the thermal imaging device, the second lens group and/or the third lens group is/are arranged to be movable along an optical axis of the optical system in the direction of the first lens group and/or in the direction of the image capture unit. Moreover, it is provided that the first lens group is configured to be immovable relative to the image capture unit. The second lens group is also referred to as variator, whereas the third lens group is also referred to as compensator. The focal length of the objective is adjustable because of the possibility of movement of the second lens group and the third lens group. It is provided in an embodiment in this case that the movement of the second lens group and/or of the third lens group is continuous, so that a continuous zoom action is possible. Alternatively to this, it is provided that the second lens group and/or the third lens group are moved to specific predefinable positions along the optical axis, so that specific (i.e. discrete) focal lengths are adjustable.

In a further embodiment of the thermal imaging device it is provided that the focal length of the objective is adjustable and that a magnification of the inverting system is constant. The focal length of the objective is adjusted as described above, for example. It is provided in an alternative embodiment that the focal length of the objective is constant and that the magnification of the inverting system is selectable.

The second lens group and the third lens group have a further function in a further embodiment. They ensure in this further embodiment that the optical system of the thermal imaging device is actively athermal. This is understood to mean the following. The refractive index is dependent on the prevailing temperature. Therefore, to ensure that a sharply defined image of an object to be projected is formed on the image capture unit, it is provided that the second lens group and the third lens group are moved at a temperature T substantially differing from 20°C (e.g. at T higher than or equal to 25°C or T lower than or equal to 15°C).

It is provided in this case that the second lens group and the third lens group are moved independently of one another. Thus, the second lens group and the third lens group can have two functions. On the one hand, the focal length of the objective is adjustable as a result of the movement of the second lens group and/or the third lens group. On the other hand, they serve to compensate the position of the image on the image capture unit by moving the second lens group and/or the third lens group.

In a further embodiment of the invention, the first lens group has precisely only the first lens unit and the second lens unit, i.e. no further lens units beyond the two aforementioned lens units. In a further embodiment, the second lens group has precisely only a single third lens unit, and/or the third lens group has precisely only a single fourth lens unit, and/or the fourth lens group has precisely only a single fifth lens unit, and/or the fifth lens group has precisely only a single sixth lens unit.

In a further embodiment of the thermal imaging device, the sixth lens group is provided with a seventh lens unit (e.g. with negative refractive power) and with an eighth lens unit (e.g. with positive refractive power). Moreover, the seventh lens group has a ninth lens unit. In addition, it can be provided, for example, that the sixth lens group has precisely only the seventh lens unit and the eighth lens unit, i.e. no further lens unit beyond this. In addition, the seventh lens group in this exemplary embodiment has precisely only the ninth lens unit.

The thermal imaging device is configured slightly differently in a further exemplary embodiment. Thus, it is provided in this exemplary embodiment that the sixth lens group has a seventh lens unit, and that the seventh lens group has an eighth lens unit and also a ninth lens unit. It is then provided in a ftirther exemplary embodiment that the sixth lens group has precisely only the seventh lens unit, and that the seventh lens group has precisely only the eighth lens unit and the ninth lens unit, i.e. no further lens units beyond this.

A further exemplary embodiment of the thermal imaging device is distinguished in that the fourth lens group has positive refractive power, and/or the fifth lens group has negative refractive power, and/or that the seventh lens group has positive refractive power.

If the first lens unit and the second lens unit are formed from a material with a high refractive index (e.g. germanium), then an exemplary embodiment provides to not configure an aspherical face on either the first lens unit or on the second lens unit. However, if the first lens unit and the second lens unit are made from a material with a low refractive index (e.g. zinc selenide), then at least one first lens face is configured to be aspherical on the first lens unit and/or the second lens unit. This enables a favourable correction of the image of an object. It is a similar case with a colour correction. If the first lens unit and the second lens unit are formed from a material with a low dispersion (e.g. germanium),then no diffractive surface is configured on the first lens unit and the second lens unit. However, if the first lens unit and the second lens unit are formed from a material with a high dispersion (e.g. zinc selenide), then it is provided in an embodiment that at least one face of the first lens unit and/or the second lens unit is diffractive in configuration.

In addition, deliberations have shown that a further favourable image correction can be achieved when the second lens group, the third lens group, the fourth lens group, the sixth lens group and/or the seventh lens group respectively has/have a second lens face, wherein the second lens face(s) is/are aspherical or spherical in configuration.

In a ftirther embodiment of the thermal imaging device a means for beam deflection is provided, e.g. a minor (in particular a plane minor) or a prism. This embodiment assures in particular a highly compact configuration of the thermal imaging device, so that this only requires a very small structural space. It is provided in particular that a first means for beam deflection is arranged between the fourth lens group and the fifth lens group. Alternatively or additionally hereto, it is provided that a second means for beam deflection is arranged between the fifth lens group and the sixth lens group. Likewise alternatively or additionally hereto, it is provided that a third means for beam deflection is arranged between the sixth lens group and the seventh lens group. The distances between the aforementioned lens groups are selected in such a manner that the means for beam deflection can be inserted without any problem. In a further embodiment it is provided that the second means for beam deflection, which is arranged between the fifth lens group and the sixth lens group, is not arranged in the vicinity of the intermediate image plane. A specification of the distance range of the second means for beam deflection from the intermediate image plane is given further below. The likelihood of smears that can be present on the second means for beam deflection being visible in the image is reduced as a result of this.

In a further embodiment of the thermal imaging device according to the invention, the first means for beam deflection, which is arranged between the fourth lens group and the fifth lens group, is configured as a microscanner. This is distinguished in that it is tiltable around an axis at a predefinable angle and that it is tilted back and forth between a first position and a second position. An offset of the image on the image capture unit of about half a pixel is achieved as a result of this. The resolution of the image on the image capture unit is increased in this way.

In a ftirther embodiment of the thermal imaging device, it is provided that at least one of the aforementioned lens groups, in particular the first lens unit and/or the second lens unit, is formed from germanium, zinc selenide, zinc sulphide, gallium arsenide or chalcogenide. For example, materials composed of chalcogenide are provided that are known under the designations AMTIR (in particular AMTIR1 or AMTIR3), GASIR (in particular GASIR1 or GASIR2) and IG (in particular 1G2, 1G3, 1G4, 1G5 or 1G6). Manufacturers' specifications for these materials are specified further below.

A further embodiment of the thermal imaging device is based on the following consideration.

In order to obtain a compact arrangement of the thermal imaging device, it is desirable that the distance between a first vertex of the first lens unit and the first means for beam deflection is as small as possible, e.g. the distance amounts to approximately 90 mm to 110 mm. The second lens group and the third lens group, which serve to adjust the focal length and therefore a zoom action, are arranged between the first lens unit and the first means for beam deflection. This means that the focal lengths of the individual units are relatively short.

For example, the focal lengths can lie within the following ranges (Table 1):

Table 1:

Lens Group Focal Length Range [mm] First lens group 60 to 190 Second lens group (-15) to (-25) Third lens group (-35) to (-90) Fourth lens group 20 to 35 Fifth lens group (-130) to (-180) Sixth lens group 35 to 60 Seventh lens group 20 to 45 An alternative embodiment provides for the following focal length ranges (Table 2):

Table 2:

Lens Group Focal Length Range [mm] First lens group 60 to 190 Second lens group (-15) to (-25) Third lens group (-35) to (-90) Fourth lens group 20 to 35 Fifth lens group (-120) to (-200) Sixth lens group 30 to 90 Seventh lens group 20 to 45 As a result of this, the aperture of the first lens unit and therefore also of the first lens group can be very large. This will be discussed in more detail below. If one were now to select germanium, for example, as material for the first lens group and provide a single aspherical lens as first lens group, then the orderly function of the thermal imaging device would no longer be assured with high temperature fluctuations, since the aberrations in the image would increase substantially because of a substantial change in the refractive index at specific temperatures. This is undesirable. For this reason, an embodiment of the thermal imaging device provides to configure the first lens unit and the second lens unit respectively as a spherical lens and also respectively form them from germanium. It is provided in a further embodiment to configure both the first lens unit and the second lens unit from a material, in which the temperature coefficient of the refractive index is substantially lower than in the case of germanium. For example, zinc selenide is provided. The value for in the case of germanium amounts to 408 i06/°K. For zinc selenide the value for amounts to 60i06/°K.

Moreover, at least one aspherical face is provided in the case of the first lens unit and/or the second lens unit. It is provided in a further embodiment that the first lens unit is made from germanium and the second lens unit is configured as an aspherical diffractive lens. All the aforementioned exemplary embodiments assure a good function in a very large temperature range, e.g. from -40°C to 70°C.

The invention shall be explained in more detail below on the basis of exemplary embodiments.

Figure 1 shows a first exemplary embodiment of a thermal imaging device according to the invention; Figure 2 shows a second exemplary embodiment of a thermal imaging device according to the invention; Figure 3 shows a third exemplary embodiment of a thermal imaging device according to the invention.

Figure 1 shows a first exemplary embodiment of a thermal imaging device 100 according to the invention, which is configured with an optical system. From an object to be projected (not shown) in the direction of an image capture unit BE, the thermal imaging device 100 has an objective OB, an inverting system UM and also the image capture unit BE. The objective OB projects an object arranged at infinity or at a finite distance onto an intermediate image ZE.

The intermediate image ZE is projected as an image onto the image capture unit BE by the inverting system UM. An exit pupil is located between the inverting system UM and the image capture unit BE. A cold-light diaphragm KB is arranged here, which will be discussed in more detail below.

The thermal imaging device 100 is shown in three zoom positions. Figure 1 a shows a first zoom position, in which the objective OB has a focal length of 207 mm. Figure lb shows a second zoom position, in which the objective OB has a focal length of 115.8 mm. A further, i.e. third zoom position is shown in Figure lc. In the third zoom position the objective OB has a focal length of 23 mm.

From an object to be projected in the direction of the image capture unit BE, the objective OB has five lens groups, namely a first lens group Gi, a second lens group G2, a third lens group G3, a fourth lens group G4 and a fifth lens group G5. The inverting system UM is likewise composed of multiple lens groups. Thus, from an object to be projected in the direction of the image capture unit BE, a sixth lens group G6 and a seventh lens group G7 are provided.

The first lens group G 1 has a first lens unit Li and a second lens unit L2. Both the first lens unit Li and the second lens unit L2 are respectively configured as a single lens and respectively have positive refractive power. The first lens group G 1 has positive refractive power overall. The first lens unit Li and the second lens unit L2 respectively have a first face (first face i or first face 3 respectively) directed towards an object to be projected and a second face (second face 2 or second face 4 respectively) directed towards the image capture unit BE. The faces i to 4 are respectively spherical in configuration. Moreover, the first lens group Gi is configured to be immovable relative to the image capture unit BE.

The second lens group G2 is formed from a third lens unit L3 that has a single lens. The third lens unit L3 has negative refractive power and is formed from germanium. The third lens group G3 is similar in structure to the second lens group G2. Thus, the third lens group G3 is formed from a fourth lens unit L4 that has a single lens. The fourth lens unit L4 is formed from zinc selenide. Both the third lens unit L3 and the fourth lens unit L4 respectively have a first face (first face 5 or first face 7 respectively) directed towards an object to be projected and a second face (second face 6 or second face 8 respectively) directed towards the image capture unit BE. The first face 5 of the third lens unit L3 and the second face 8 of the fourth lens unit L4 are aspherical in configuration. Moreover, the second lens group G2 (variator) and the third lens group G3 (compensator) are arranged to be movable along an optical axis A of the thermal imaging device i 00 in the direction of the first lens group G i and/or in the direction of the image capture unit BE. The focal length of the objective OB is adjustable because of the possibility of movement of the second lens group G2 and the third lens group G3. In this case, it is provided in an embodiment that the movement of the second lens group G2 and/or the third lens group G3 occurs continuously, so that a continuous zoom action is possible. Alternatively, it is provided that the second lens group G2 and/or the third lens group G3 are moved to specific predefinable positions (e.g. the positions illustrated in Figures ia to ic) along the optical axis, so that specific (i.e. discrete) focal lengths are

adjustable.

The second lens group G2 and the third lens group G3 have a further function in this embodiment. They ensure that the optical system of the thermal imaging device 100 is actively athermal, which has already been explained above. Thus, to ensure that a sharply defined image of an object to be projected is formed on the image capture unit BE, it is provided that the second lens group G2 and the third lens group G3 are moved at a temperature T substantially differing from 20°C (e.g. at T higher than or equal to 25°C or T lower than or equal to 15°C). It is provided in this case that the second lens group G2 and the third lens group G3 are moved independently of one another.

As mentioned above, the objective OB also has a fourth lens group G4 and a fifth lens group G5. Both the fourth lens group G4 and the fifth lens group G5 are arranged to be immovable relative to the image capture unit BE.

The fourth lens group G4, which is formed from germanium, for example, is formed from a fifth lens unit L5 that is configured as a single lens. The fifth lens unit L5 has positive refractive power and -as mentioned -is formed from germanium. The fifth lens group G5 is formed from a sixth lens unit L6 that is configured as a single lens. It has negative refractive power and is also formed from germanium. Both the fifth lens unit L5 and the sixth lens unit L6 have a first face (first face 9 or first face 11 respectively) directed towards an object to be projected and a second face (second face 10 or second face 12 respectively) directed towards the image capture unit BE. The second face 10 is aspherical in configuration.

The sixth lens group G6 has a seventh lens unit L7 made of zinc sulphide and an eighth lens unis L8 made of germanium. Both the seventh lens unit L7 and the eighth lens unit L8 are respectively formed from a single lens. Both the seventh lens unit L7 and the eighth lens unit L8 have a first face (first face 13 or first face 15 respectively) directed towards an object to be projected and a second face (second face 14 or second face 16 respectively) directed towards the image capture unit BE. The second faces 14 and 16 are aspherical in configuration.

The seventh lens group G7 has a ninth lens unit L9 that is formed by a single lens made of zinc selenide. It has a first face (first face 17) directed towards an object to be projected and a second face (second face 18) directed towards the image capture unit BE. The second face 18 is aspherical in configuration.

The sixth lens group G6 and the seventh lens group G7 are arranged to be immovable relative to the image capture unit BE.

The aspherical configurations of some faces explained above are advantageous because a good image correction can be achieved in this way.

The image capture unit BE is configured as a CMOS, for example. However, the invention is not restricted to a CMOS and any desired image capture unit suitable for the invention is usable. In particular, it is provided to configure the image capture unit BE with a plane or curved capture surface.

In the exemplary embodiment shown in Figure 1, the cold-light diaphragm KB, which is cooled, is arranged between the seventh lens group G7 and the image capture unit BE. The cold-light diaphragm KB assures that only the infrared radiation emanating from an object viewed with the thermal imaging device 100 is captured by the image capture unit BE.

Further radiation from the direct surroundings of the image capture unit BE that emanates from ftirther structural parts (e.g. a wall) is suppressed as far as possible by this, so that this frirther radiation does not disturb the imaging. The cold-light diaphragm KB is the active aperture stop. It is arranged at the location of the exit pupil.

The focal lengths of the individual units of the thermal imaging device 100 are relatively short. For example, the focal lengths can lie within the following ranges (Table 3):

Table 3:

Lens Group Focal Length Range [mm] First lens group Gi 60 to 190 Second lens group G2 (-15) to (-25) Third lens group G3 (-35) to (-90) Fourth lens group G4 20 to 35 Fifth lens group GS (-130) to (-180) Sixth lens group G6 35 to 60 Seventh lens group G7 20 to 45 The aforementioned properties of the individual lens groups as well as further properties of the individual lens groups may be seen from the following Tables 4 and 5, wherein the properties given in brackets will be explained frirther below.

Table 4:

Lens Group Refractive Power Lens Unit Refractive Power Glass ___________ Lens Group ___________ Lens Unit ______________ Gi Positive Li Positive Germanium ______________ ____________________ (Zinc selenide) L2 Positive Germanium ______________ ____________________ ______________ ____________________ (Zinc selenide) G2 Negative L3 Negative Germanium G3 Negative L4 Negative Zinc selenide G4 Positive L5 Positive Germanium G5 Negative L6 Negative Germanium G6 Positive L7 Negative Zinc suiphide ___________ ________________ L8 Positive Germanium G7 Positive L9 Positive Zinc selenide

Table 5:

Face Configuration 1 Spherical 2 Spherical (DOE) 3 Spherical 4 Spherical (aspherical) Aspherical 6 Spherical 7 Spherical 8 Aspherical 9 Spherical Aspherical ii Spherical 12 Spherical 13 Spherical 14 Aspherical Spherical 16 Aspherical 17 Spherical 18 Aspherical Figure 2 shows a further exemplary embodiment of a thermal imaging device 100 according to the invention, This corresponds, in principle, to the exemplary embodiment according to Figure 1, and therefore reference is firstly made to the above explanations. Means for beam deflection are additionally provided. Thus, a first deflection unit Si is arranged between the fifth lens unit L5 (fourth lens group G4) and the sixth lens unit L6 (fifth lens group G5).

Moreover, a second deflection unit S2 is arranged between the sixth lens unit L6 (fifth lens group G5) and the seventh lens unit L7 (sixth lens group G6). In addition, a third deflection unit S3 is arranged between the eighth lens unit L8 (sixth lens group G6) and the ninth lens unit L9 (seventh lens group G7). In the exemplary embodiment illustrated here, the aforementioned deflection units are configured as mirrors. Alternatively to this, individual or all deflection units can also be configured as prisms.

The first deflection unit Si, the second deflection unit S2 and the third deflection unit S3 deflect rays entering the thermal imaging device 100 substantially by 90°, e.g. in a range of 80° to 100°. In this way, a very compact arrangement of the thermal imaging device 100 can be achieved that only requires a very small structural space. Moreover, it is provided that the second deflection unit S2 is arranged not quite in the vicinity of the intermediate image plane ZE, but at a distance of approximately 5 mm to 15 mm therefrom, for example. The likelihood of smears that can be present on the second deflection unit S2 being visible in the image on the image capture unit BE is reduced as a result of this.

The distance covered by radiation entering the thermal imaging device 100 up to the image capture unit BE lies substantially in a range of 290 mm to 340 mm, e.g. approximately 305 mm.

The distance between a first vertex of the first face 1 and the first deflection unit Si is as short as possible, e.g. approximately 90 mm to 110 mm. Moreover, the aperture of the first lens group Gi is large, e.g. in the range of f= 0.6 to f= 1.4, preferably f= 0.8. In order to obtain adequate function over a large temperature range (e.g. from -40°C to 70°C) on the basis of the above-described criteria, the first lens unit Li and the second lens unit L2 in this exemplary embodiment are respectively configured as a spherical lens as well as being respectively made from germanium.

A further exemplary embodiment is based on the exemplary embodiment according to Figure 2, and therefore reference is made to the above explanations. In contrast to the exemplary embodiment according to Figure 2, the first lens group Gi is configured slightly differently.

Thus, the first lens unit Li and the second lens unit L2 are formed from zinc selenide. In addition, the second face 2 of the first lens unit Li has a diffractive optical element (DOE).

Moreover, the second face 4 of the second lens unit L2 is aspherical in configuration. This embodiment has the properties of Tables 3 to 5, but with the difference that the lens group G 1 has the properties in the brackets. All further properties of the individual lens groups are identical and do not change. This embodiment also assures adequate function over a large temperature range (e.g. from -40°C to 70°C). Deliberations have shown that the use of zinc selenide, which has a refractive index of relatively low temperature dependence, with an aspherical face and a DOE is well suited for this.

The DOE is provided because the first lens unit Li and the second lens unit L2 are formed from a material with a high dispersion (zinc selenide) in the above-described embodiment. A favourable colour correction in the imaging is obtained in this way.

In the above-described embodiments, germanium, zinc sulphide and zinc selenide are specified as materials for the individual lens units. However, the invention is not restricted to these materials. Rather, any material suitable for the invention is usable. In particular, the first lens unit Li and the second lens unit L2 can also be formed from chalcogenide. For example, materials composed of chalcogenide are provided that are available under the designations AMTIR (in particular AMTIR1 or AMTIR3) from Amorphous Materials Inc. This additionally includes materials that are available from UMICORE under the designation GASIR (in particular GASIR1 or GASIR2). Also included are materials that are available from VITRON Spezialwerkstoffe GmbH under the designation IG (in particular 1G2, 1G3, 1G4, 1G5 or 1G6). In this exemplary embodiment, at least one of the faces of the first lens unit Li or the second lens unit L2 has an aspherical face. Alternatively to this, it is provided to configure the first lens unit Li as a spherical lens made of germanium and the second lens unit L2 as an aspherical and diffractive lens.

When using the thermal imaging device 100 in the range from 3 pm to 5 jim, it is preferred to use silicon as lens material in place of germanium.

The different embodiments of the thermal imaging device 100 are provided for the detection of infrared radiation. They are used for recognition of an object or a person. The spectral range of the detectable infrared radiation covers the entire infrared spectral range. However, in one embodiment of the invention it is provided in particular to detect the spectral range of 3 tm to 12 pm. In a further embodiment it is in turn provided to detect a spectral range of 3 tm to 5 tm or 8 tm to 12 pm. In particular the last-mentioned spectral range is advantageous since the thermal radiation emission of a human body falls within this spectral range.

Some additional properties of embodiments of the thermal imaging device 100 are specified

below (Table 6):

Table 6:

Properties Example 1 Example 2 Example 3 Zoom factor 7x 9x lix Aperture number (f) 2.5 2.1 1.9 Detectable wavelength 7.5 tmto 9.0 tm 7.1 tmto 9.5 tm 7.0 prnto 12.0 tm range X Temperature range 0°C to 40°C -20°C to 60°C -40°C to 70°C Structural length 180mm 110 mmto 130 mm 100mm (vertex first face 1 to Si) ________________ __________________ __________________ Figure 3 shows a third exemplary embodiment of a thermal imaging device 100 according to the invention that is configured with an optical system. The thermal imaging device 100 of this exemplary embodiment is used in a spectral range of 3 pm to 5 jLm, for example. The third exemplary embodiment of Figure 3 is based on the first exemplary embodiment according to Figure 1. Therefore, the same structural parts have been given the same reference numeral.

Again, from an object to be projected (not shown) in the direction of an image capture unit BE, the thermal imaging device 100 has an objective OB, an inverting system UM and also the image capture unit BE. The objective OB projects an object arranged at infinity or at a finite distance onto an intermediate image ZE. The intermediate image ZE is projected as an image onto the image capture unit BE by the inverting system UM. An exit pupil is located between the inverting system UM and the image capture unit BE. Again, a cold-light diaphragm KB is arranged here, which has the same function as that already explained above.

The thermal imaging device 100 is shown in two zoom positions. Figure 3a shows a first zoom position, in which the objective OB has a focal length of 27.2 mm. Figure 3b shows a second zoom position, in which the objective OB has a focal length of 275 mm.

In contrast to the exemplary embodiment of Figure 1, the first lens group G 1 of this exemplary embodiment only has a single lens unit, namely the first lens unit Li. The first lens unit Li is configured as a single lens and has positive refractive power. The first lens unit Li has a first face 1 directed towards an object to be projected and a second face 2 directed towards the image capture unit BE. The first face 1 is spherical in configuration. The second face 2 is diffractive and aspherical in configuration. Moreover, the first lens group Gi is configured to be immovable relative to the image capture unit BE.

The further configuration of the exemplary embodiment of Figure 3 corresponds, in principle, to the exemplary embodiment of Figure 1. Thus, the second lens group G2 is formed from a third lens unit L3 that has a single lens. The third lens unit L3 has negative refractive power and is formed from silicon. The third lens group G3 is similar in structure to the second lens group G2. Thus, the third lens group G3 is formed from a fourth lens unit L4 that has a single lens. The fourth lens unit L4 is formed from gallium arsenide. The fourth lens unit can also be formed from chalcogenide. Both the third lens unit L3 and the fourth lens unit L4 respectively have a first face (first face 5 or first face 7 respectively) directed towards an object to be projected and a second face (second face 6 or second face 8 respectively) directed towards the image capture unit BE. The first face 5 of the third lens unit L3 and the second face 8 of the fourth lens unit L4 are aspherical in configuration. Moreover, in this exemplary embodiment the second lens group G2 (variator) and the third lens group G3 (compensator) are arranged to be movable along an optical axis A of the thermal imaging device 100 in the direction of the first lens group Gi and/or in the direction of the image capture unit BE. In this exemplary embodiment, the focal length of the objective OB is also adjustable because of the possibility of movement of the second lens group G2 and the third lens group G3. In this case, it is provided in a further embodiment that the movement of the second lens group G2 and/or the third lens group G3 occurs continuously, so that a continuous zoom action is possible. Alternatively, it is provided that the second lens group G2 and/or the third lens group G3 are moved to specific predefinable positions (e.g. the positions illustrated in Figures 3a to 3c) along the optical axis A, so that specific (i.e. discrete) focal lengths are adjustable.

The second lens group G2 and the third lens group G3 also have a further function in this exemplary embodiment. They ensure that the optical system of the thermal imaging device is actively athermal, which has already been explained above. Thus, to ensure that a sharply defined image of an object to be projected is formed on the image capture unit BE, it is provided that the second lens group G2 and the third lens group G3 are moved at a temperature T substantially differing from 20°C (e.g. at T higher than or equal to 25°C or T lower than or equal to 15°C). It is provided in this case that the second lens group G2 and the third lens group G3 are moved independently of one another.

As mentioned above, the objective OB also has a fourth lens group G4 and a fifth lens group G5. Both the fourth lens group G4 and the fifth lens group G5 are arranged to be immovable relative to the image capture unit BE. The fourth lens group G4 is formed from a fifth lens unit L5 that is configured as a single lens. The fifth lens unit L5 has positive refractive power and is formed from silicon. The fifth lens group G5 is formed from a sixth lens unit L6 that is configured as a single lens. It has negative refractive power and is also formed from silicon.

Both the fifth lens unit L5 and the sixth lens unit L6 have a first face (first face 9 or first face 11 respectively) directed towards an object to be projected and a second face (second face 10 or second face 12 respectively) directed towards the image capture unit BE. The first face 9 is aspherical in configuration.

The sixth lens group G6 of the inverting system UM has a seventh lens unit L7 made of silicon and an eighth lens unit L8 made of zinc sulphide. Both the seventh lens unit L7 and the eighth lens unit L8 are respectively formed from a single lens. Both the seventh lens unit L7 and the eighth lens unit L8 have a first face (first face 13 or first face 15 respectively) directed towards an object to be projected and a second face (second face 14 or second face 16 respectively) directed towards the image capture unit BE. The first face 15 is aspherical in configuration.

The seventh lens group G7 of the inverting system UM has a ninth lens unit L9 that is formed by a single lens made of silicon. It in turn has a first face (first face 17) directed towards an object to be projected and a second face (second face 18) directed towards the image capture unit BE. The first face 17 is aspherical in configuration.

The aspherical configurations of some faces explained above are advantageous because a good image conection can be achieved in this way.

The image capture unit BE is configured as a CMOS, for example. The statements given above concerning the image capture unit BE of the exemplary embodiment according to Figure 1 also apply here.

The focal lengths of the individual units of the thermal imaging device 100 according to Figure 3 are specified by way of example in ranges in the following table (Table 7):

Table 7:

Lens Group Focal Length Range [mm] First lens group Gi 60 to 190 Second lens group G2 (-15) to (-25) Third lens group G3 (-35) to (-90) Fourth lens group G4 20 to 35 Fifth lens group G5 (-120) to (-200) Sixth lens group G6 30 to 90 Seventh lens group G7 20 to 45 In this case, the seventh lens unit L7 of the sixth lens group G6 has a focal length range of 20 mm to 60 mm. In contrast, the eighth lens unit L8 of the sixth lens group G6 has a focal length range of(-30) mm to (-100) mm.

The aforementioned properties of the individual lens groups as well as further properties of the individual lens groups may be seen from the following Tables 8 and 9.

Table 8:

Lens Group Refractive Power Lens Unit Refractive Power Glass ___________ Lens Group ___________ Lens Unit ______________ Gi Positive Li Positive Silicon G2 Negative L3 Negative Silicon G3 Negative L4 Negative Gallium arsenide G4 Positive L5 Positive Silicon G5 Negative L6 Negative Silicon G6 Positive L7 Positive Silicon L8 Negative Zinc sulphide G7 Positive L9 Positive Silicon

Table 9:

Face Configuration 1 Spherical 2 Aspherical with DOE Aspherical 6 Spherical 7 Spherical 8 Aspherical 9 Aspherical Spherical 11 Spherical 12 Spherical 13 Spherical 14 Spherical Aspherical 16 Spherical 17 Aspherical 18 Spherical The exemplary embodiment shown in Figure 3 can also be provided with means for beam deflection, as is provided in the exemplary embodiment shown in Figure 2. In principle, the exemplary embodiment shown in Figure 3 then corresponds to the exemplary embodiment of Figure 2, but with the difference that the first lens group G 1 is only provided with the first lens unit Li. Thus, the first deflection unit Si is arranged between the fifth lens unit L5 (fourth lens group G4) and the sixth lens unit L6 (fifth lens group G5). Moreover, the second deflection unit S2 is arranged between the sixth lens unit L6 (fifth lens group US) and the seventh lens unit L7 (sixth lens group G6). In addition, the third deflection unit S3 is arranged between the eighth lens unit L8 (sixth lens group G6) and the ninth lens unit L9 (seventh lens group G7). In the exemplary embodiment illustrated here, the aforementioned deflection units are configured as minors. Alternatively to this, individual or all deflection units can also be configured as prisms.

The exemplary embodiment of Figure 3 equipped with the first deflection unit Si, the second deflection unit S2 and the third deflection unit S3 has the same properties and advantages with respect to the focal length range, zoom factor, aperture number, structural length and also the position of the aforesaid deflection units Si to S3 as that already explained with respect to Figures i and 2. Moreover, all the suitable materials for the individual lens units, e.g. germanium, silicon, zinc sulphide, zinc selenide, gallium arsenide and chalcogenide, are also usable in this exemplary embodiment.

List of References optical system A optical axis OB objective UM inverting system BE image capture unit Gi first lens group G2 second lens group G3 third lens group G4 fourth lens group G5 fifth lens group G6 sixth lens group G7 seventh tens group Li first lens unit L2 second lens unit L3 third lens unit L4 fourth lens unit L5 fifth lens unit L6 sixth lens unit L7 seventh lens unit L8 eighth lens unit L9 ninth lens unit 1 first face of the first lens unit 2 second face of the first lens unit 3 first face of the second lens unit 4 second face of the second lens unit first face of the third lens unit 6 second face of the third lens unit 7 first face of the fourth lens unit 8 second face of the fourth lens unit 9 first face of the fifth lens unit second face of the fifth lens unit 11 first face of the sixth lens unit 12 second face of the sixth lens unit 13 first face of the seventh lens unit 14 second face of the seventh lens unit first face of the eighth lens unit 16 second face of the eighth lens unit 17 first face of the ninth lens unit 18 second face of the ninth lens unit Si first deflection unit S2 second deflection unit S3 third deflection unit ZE intermediate image plane KB cold-light diaphragm

Claims

Patent Claims: Thermal imaging device (100) with at least one objective (OB), at least one inverting system (UM) and with at least one image capture unit (BE), wherein * the objective (OB), the inverting system (UM) and the image capture unit (BE) are arranged from a reproducible object in the direction of the image capture unit (BE), * from a reproducible object in the direction of the image capture unit (BE), the objective (OB) has a first lens group (Gi), a second lens group (G2) and a third lens group (G3), * from a reproducible object in the direction of the image capture unit (BE), the inverting system (UM) has a sixth lens group (G6) and a seventh lens group (G7), and wherein * the first lens group (G 1) has a first lens unit (Li) with positive refractive power, characterised in that * the objective (OB) from the third lens group (G3) in the direction of the image capture unit (BE) has a fourth lens group (G4) and a fifth lens group (G5), * the second lens group (G2) has negative refractive power, and that * the third lens group (G3) has negative refractive power.
2. Thermal imaging device (100) according to claim 1, characterised in that the first lens group (G 1) has a second lens unit (L2) with positive refractive power.
3. Thermal imaging device (100) according to claim 1 or 2, characterised in that * the second lens group (G2) and/or the third lens group (G3) is/are arranged to be movable along an optical axis of the thermal imaging device (100) in the direction of the first lens group (G 1) and/or in the direction of the image capture unit (BE), and that * the first lens group (G 1) is configured to be immovable relative to the image capture unit (BE).
4. Thermal imaging device (100) according to one of the preceding claims, characterised in that the first lens group (G 1) has precisely only the first lens unit (Li) and the second lens unit (L2).
5. Thermal imaging device (100) according to one of the preceding claims, characterised in that * the second lens group (G2) has precisely only a single third lens unit (L3), and/or * the third lens group (G3) has precisely only a single fourth lens unit (L4), and/or * the fourth lens group (G4) has precisely only a single fifth lens unit (L5), and/or that * the fifth lens group (G5) has precisely only a single sixth lens unit (L6).
6. Thermal imaging device (100) according to one of the preceding claims, characterised in that * the sixth lens group (G6) has a seventh lens unit (L7) and an eighth lens unit (L8), and that * the seventh lens group (G7) has a ninth lens unit (L9).
7. Thermal imaging device (100) according to claim 6, characterised in that * the sixth lens group (G6) has precisely only the seventh lens unit (L7) and the eighth lens unit (L8), and/or that * the seventh lens group (G7) has precisely only the ninth lens unit (L9).
8. Thermal imaging device (100) according to one of claims 1 to 5, characterised in that * the sixth lens group (G6) has a seventh lens unit, and that * the seventh lens group (G7) has an eighth lens unit and a ninth lens unit.
9. Thermal imaging device (100) according to claim 8, characterised in that * the sixth lens group (G6) has precisely only the seventh lens unit, and that * the seventh lens group (G7) has precisely only the eighth lens unit and the ninth lens unit.
10. Thermal imaging device (100) according to one of the preceding claims, characterised in that * the fourth lens group (G4) has positive refractive power, and/or * the fifth lens group (G5) has negative refractive power, and/or that * the seventh lens group (G7) has positive refractive power.
11. Thermal imaging device (100) according to one of the preceding claims, characterised in that the first lens group (Gi) has at least one first lens face, which is aspherical, spherical and/or diffractive in configuration.
12. Thermal imaging device (100) according to one of the preceding claims, characterised in that the second lens group (G2), the third lens group (G3), the fourth lens group (G4), the sixth lens group (G6) and/or the seventh lens group (G7) respectively has/have a second lens face, wherein the second lens face(s) is/are aspherical or spherical in configuration.
13. Thermal imaging device (100) according to one of the preceding claims, characterised in that the objective (OB) has a focal length and the inverting system (UM) has a magnification, wherein * the focal length of the objective (OB) is adjustable and the magnification of the inverting system (UM) is constant, or wherein * the focal length of the objective (OB) is constant and the magnification of the inverting system (UM) is selectable.
14. Thermal imaging device (100) according to one of the preceding claims, characterised in that the thermal imaging device (100) has at least one means (Si, S2, S3) for beam deflection.
15. Thermal imaging device (100) according to claim 14, characterised in that * a first means (Si) for beam deflection is arranged between the fourth lens group (G4) and the fifth lens group (G5), and/or * a second means (S2) for beam deflection is arranged between the fifth lens group (G5) and the sixth lens group (G6) and/or that * a third means (S3) for beam deflection is arranged between the sixth lens group (G6) and the seventh lens group (G7).
16. Thermal imaging device (100) according to one of the preceding claims, characterised in that at least one of the aforementioned lens groups (G 1 to G7), in particular the first lens unit (Li) and/or the second lens unit (L2), is formed from germanium, zinc selenide, zinc sulphide, gallium arsenide, silicon or chalcogenide.
17. A thermal imaging device substantially as hereinbefore described with reference to the accompanying description and any one of the Figures.