DE102012018441B4 - IR zoom lens and thermal imaging device - Google Patents

Abstract

IR zoom lens (1) comprising an optical front group (2) arranged one after the other in the imaging direction, at least one optical zoom group (3, 4) displaceable along the imaging beam path, a main lens (5) for imaging an intermediate image in an intermediate image plane (12) and an optical one Relay group (9) for imaging the intermediate image on an IR detector (11), characterized in that the relay group (9) is followed by a warm screen (10b) which can be introduced into the imaging beam path, with between the main objective (5) and the relay group ( 9) an optical pupil compensation group (6) which can be displaced along the imaging beam path is arranged to compensate for the positional displacement of the entrance pupil by introducing the warm screen (10b).

Description

The invention relates to an IR zoom lens for imaging the thermal radiation of an object onto an electronic IR detector with a variable focal length. The invention also relates to a thermal imaging device comprising such an IR zoom lens with variable focal length and a corresponding IR detector. The invention is concerned with the technical problem that with IR lenses projecting into the optical beam path parts of the lens such. B. Sockets emit heat radiation that appears as stray light on the IR detector. If lens parts protrude into the optical beam path, this is also referred to as vignetting, which is the cause of undesired interference light on the IR detector in IR lenses. An IR lens should therefore always be free of vignetting. In particular, this applies to an IR zoom lens for the adjustable different focal lengths.

A zoom lens is characterized in that the magnification of the object to be imaged is changed. For example, if the object is at infinity, the object angle range to be imaged changes when zooming. Since an IR detector with constant geometry is mostly used to detect the IR radiation, the focal length of the objective must change when the object angle changes. A zoom lens changes its focal length between small and large values in particular by shifting an optical zoom group along the imaging beam path. Small focal lengths are called wide-angle focal lengths; large focal lengths as telephoto focal lengths. With the telephoto focal lengths, the object angle is smaller than with the wide angle focal lengths.

Eine kleine f-Zahl steht dabei für eine große Blendenöffnung und umgekehrt. Ändert sich der Abstand der Systemblende zu dem objektseitig davorstehenden Objektivteil, so ändert sich auch die Lage der Eintrittspupille.A zoom lens and in particular an IR zoom lens has the property that the diameter of the entrance pupil (ie the object-side image of the system aperture) scales with the zoom factor or with the focal length. The diameter of the entrance pupil EPD is linked to the f-number or f-number f _# and the focal length f of a lens by: $$EPD=\frac{\left|f\right|}{f_{\text{\#}}}.$$

A small f-number stands for a large aperture and vice versa. If the distance between the system aperture and the lens part in front of the object changes, the position of the entrance pupil also changes.

The diameter of a lens depends on the transmitted object angle range (with wide-angle lenses) and the diameter of the entrance pupil (with telephoto lenses). With telephoto lenses, the diameter of the entrance pupil is very large due to the large focal length. Therefore, the entrance pupil should be on the front lens of the lens if possible. If the entrance pupil lies behind the front lens, the diameter of the objective must become larger than the diameter of the entrance pupil due to the diverging beam path. As a result, larger lenses and thus more glass material are required, which undesirably increases both the weight of the lens and its cost. For this reason, the entrance pupil should be on the front lens with telephoto lenses and especially with zoom lenses.

To increase sensitivity, an electronic IR detector must be cooled to low temperatures, for example to the temperature of liquid nitrogen. So that the system screen of the thermal imaging device does not radiate heat radiation onto the IR detector, it is installed inside the cooling housing of the detector and is also cooled. Such a cooled screen is usually referred to as a cold screen. The system diaphragm of such a thermal imaging device is inevitably always arranged behind the lens in the imaging direction, so that beams of rays diverge in the lens. In other words, the entrance pupil lies behind the front lens on the image side and the diameter of the objective must then be chosen larger than the diameter of the entrance pupil to avoid vignetting.

Since the cold aperture lies behind the lens and the entrance pupil position results from the image of the cold aperture through the lens in front, the entrance pupil generally lies between the front lens and the image plane. In order to place the position of the entrance pupil in the vicinity of the front lens, you need an intermediate image and thus an additional lens group. The optics downstream of the intermediate image plane for imaging the intermediate image on the detector is usually referred to as a relay group.

In the case of an IR zoom lens with a large zoom factor of, for example, 50, the telephoto focal length being 50 times larger than the wide-angle focal length, the diameter of the entrance pupil would change from the wide-angle position, assuming the geometric opening of the lens remains the same Also enlarge the telephoto setting 50 times. However, the diameter of the objective and thus of the lenses used cannot be increased arbitrarily for both cost and technical reasons (increase in lens errors, limited diameter of the measuring instruments). Currently, for example, in the IR range, the maximum diameter of a lens that is technically feasible and technically feasible, in particular the front lens of a lens, is around 250 mm.

With a zoom lens with large focal lengths, the problem arises in that the diameter of the entrance pupil becomes larger than the diameter of the realizable front lens from a certain focal length. In the case of an IR zoom lens with large focal lengths, vignetting disadvantageously occurs again when a certain focal length is exceeded, and thus the undesired stray light occurs on the IR detector.

The WO 2008/145735 A2 relates to an infrared camera with an optical zoom, which comprises: a matrix detector which comprises a cooled screen, a matrix which can detect infrared radiation; a module for changing the focal length of the camera, the changing module being able to vary the focal length of the camera in order to ensure the optical zoom function of the camera; and an imaging module which can ensure, on the one hand, the focus of the infrared radiation on the matrix of the detector for all values of the focal length of the camera, and on the other hand the conjugation of the pupil of the camera on the cooled screen of the detector.

Furthermore, the WO 2007/144290 A1 a passive three-field optronic system.

The object of the invention is to provide an IR zoom lens which is particularly suitable for imaging the thermal radiation of an object on an IR detector with a cold diaphragm, an undesired interference light being reduced at long focal lengths.

This object is achieved according to the invention by an IR zoom lens, which is arranged one after the other in the imaging direction, an optical front group, at least one optical zoom group displaceable along the imaging beam path, a main lens for imaging an intermediate image in an intermediate image plane and an optical relay group for imaging the intermediate image on one IR detector, wherein the relay group is followed by a heat shield that can be introduced into the imaging beam path.

The invention is based on the consideration that the desired dimming of the IR zoom lens at long focal lengths cannot be achieved by a cold aperture arranged in the cooling housing. Due to the low temperatures prevailing there, a cold aperture located there cannot be used as a variable aperture such. B. an iris diaphragm. For technical reasons, such a solution is not available with the required functional reliability. However, if a warm screen outside the cooling housing (hence the term warm screen) is placed as close as possible to the IR detector, this stray light shields off the lens, while due to its proximity to the IR detector itself it is a source for a lower proportion of stray light represents. The warm screen is located on the image-side end of the lens. This means that when the lens is used in a thermal imaging device, it is located directly in front of the cooling housing of the IR detector or directly in front of the entrance window of the housing.

The warm aperture arranged at the image-side end of the objective is preferably introduced into the beam path when a limit of the system focal length is exceeded. This limit value of the system focal length is given in particular by the fact that from this limit value the diameter of the entrance pupil is larger than the diameter of the objective or the diameter of the front lens. Unwanted vignetting occurs from this focal length. The warm screen arranged directly in front of the cooling housing or the entrance window of the cooling housing reduces the undesired interference light that then occurs from the limit value of the system focal length.

A mechanical control curve, for example, can be introduced into the mount of the objective as a means of introducing the warm screen when the limit value is exceeded. When moving a zoom group when a certain travel range is exceeded, the warm screen is, for example, folded or swung into the beam path via the mechanical control curve. Alternatively, a dimming by means of a variable iris diaphragm is possible if the limit of the system focal length is exceeded.

Alternatively, the means for introducing the warm screen into the beam path can also be provided by a motor control of the movable components of the objective by means of a control unit. Via, for example, control tables or functional ones stored in a memory such as an EPROM The introduction of the warm screen can be linked to the adjustment path of a zoom group. Temperature-dependent tables or functional relationships are preferably stored in the control unit provided for motor control.

In an expedient embodiment, the warm screen is mirrored on the image side so as to emit as little heat radiation as possible.

If the warm aperture is used to stop the IR zoom lens from reaching a system focal length limit, the position of the system aperture in a thermal imaging device jumps from the cold aperture inside the cooling housing of the IR detector to the warm aperture, which is inserted directly in front of the cooling housing in the beam path . Such a change in the position of the system diaphragm changes the pupil image and accordingly the size and position of the entrance pupil. This undesirably results in vignetting in the lens or on the front lens.

In order to correct the effect of vignetting by introducing the warm aperture, the relay group could be exchanged, for example, or an additional optical group can be introduced into the lens with the warm aperture. However, such compensation only works for a single system focal length.

According to the invention, an optical pupil compensation group that is displaceable along the imaging beam path is arranged between the main objective and the relay group to compensate for the positional shift of the entrance pupil by introducing the warm diaphragm.

By introducing a further displaceable component within the IR zoom lens, it is not only possible to coordinate the entrance pupil for the limit value of the system focal length and for telephoto positioning on the front lens of the IR zoom lens. Continuous movement of the optical pupil compensation group even makes it possible to correct the position of the entrance pupil for the range of the system focal length between the limit value and the telephoto position on the front lens. In other words, by introducing a displaceable optical pupil compensation group, the effect of a jump in the entrance pupil when the warm diaphragm is introduced can be corrected. This avoids renewed vignetting in the IR zoom lens at long focal lengths.

The pupil compensation group is preferably arranged between the main objective and the intermediate image plane. At this position there is enough space in the lens for the necessary displacement of the pupil compensation group along the imaging beam path. At the same time, this position is close to the intermediate image, so that the position of the entrance pupil can be easily corrected. This position is also well suited for a correction of the radiation beams, since these are far from the pupil and close to the intermediate image.

The optical pupil compensation group can consist of one or more lenses. The pupil compensation group expediently has a positive refractive power. In a preferred embodiment, the pupil compensation group comprises an individual collecting lens, in particular. The converging lens is in turn expediently spherical.

So that the overall length of the lens does not become too long, the lens can be built at an angle. For this purpose, in an advantageous embodiment, at least one deflection element for deflecting the imaging beam path is arranged between the main objective and the relay group. It is further preferred that the imaging beam path is bent again by arranging a first deflection element between the pupil compensation group and the intermediate image plane and a second deflection element between the intermediate image plane and the relay group. The latter arrangement makes it possible to redirect the imaging beam path twice, and thus in particular by 180 °, so that the objective can be constructed very compactly. In this arrangement, the intermediate image plane is preferably located between the two deflection elements.

The deflection elements can be designed as plane mirrors or prisms. The latter can optionally be optically active for correcting imaging errors. Again, alternatively, the deflection elements can also be designed as spherical or aspherical mirror elements, so that lens elements are saved. Face mirrors are preferred because the positioning tolerances are less critical.

If the imaging beam path is angled by means of at least one deflecting element, the pupil compensation group can also be arranged in the angled imaging beam path. For adjustment reasons, however, in the case of an angled imaging beam path, the pupil compensation group is arranged in the imaging direction in front of the first deflection element. Otherwise the optical elements of the pupil compensation group would possibly be perpendicular to the optical axis of the main objective.

In a further preferred embodiment of the IR zoom lens, a displaceable first zoom group and a displaceable second zoom group are provided. The first zoom group acts in particular as a variator that is moved along the optical axis to vary the focal length. The second zoom group acts as a compensator and is used as a focus lens.

The first zoom group advantageously has a negative refractive power. Again, the second zoom group preferably comprises a single lens.

To reproduce the intermediate image, the main objective preferably has a positive refractive power as a group as a whole.

As a means for displacing the pupil compensation group, a mechanical control cam is expediently provided, which moves the pupil compensation group as a function of the travel range of the zoom group and thus as a function of the system focal length. As an alternative and according to the current state of the art, a control unit is used which moves the pupil compensation group by motor depending on the desired system focal length or depending on the associated travel of the zoom group. For this purpose, a non-volatile memory, e.g. be stored in an EPROM or in an EEPROM, according to control tables or functional relationships.

Both the mechanical control curve and the control unit for adjusting the pupil compensation group are expediently combined or combined with the mechanical control curve or the control unit for introducing the warm screen. In particular, the means for shifting the pupil compensation group are also designed to shift the pupil compensation group only when a limit value of the system focal length is exceeded.

The above-mentioned object is also achieved according to the invention by a thermal imaging device with a previously described IR zoom lens. The thermal imaging device in this case comprises an IR detector arranged within a cooling housing, onto which the IR zoom lens images the object.

To avoid interference radiation, a cold screen is preferably connected upstream of the IR detector in the cooling housing.

The advantages mentioned for advantageous configurations of the IR zoom lens can be analogously transferred to the thermal imaging device.

• 1: den typischen Verlauf der Lage der Eintrittspupille für ein Zoomobjektiv in Abhängigkeit von der Systembrennweite,
• 2: den Verlauf der Lage der Eintrittspupille entsprechend 1 bei Einschwenken einer Warmblende ab einem Grenzwert der Systembrennweite,
• 3: den Verlauf der Lage der Eintrittspupille entsprechend 1, wobei eine Pupillenkompensationsgruppe ab Einschwenken der Warmblende verfahren wird,
• 4, 8, 12, 16: ein erstes, ein zweites, ein drittes und ein viertes Ausführungsbeispiel für ein IR-Zoomobjektiv mit verschiebbarer Pupillenkompensationsgruppe,
• 5, 9, 13, 17: den Verlauf der Lage der Eintrittspupille für das erste, das zweite, das dritte und das vierte Ausführungsbeispiel eines IR-Zoomobjektivs, wobei die Pupillenkompensationsgruppe ab Einschwenken der Warmblende verfahren wird,
• 6, 10, 14, 18: die Verschiebung der beweglichen Gruppen für das erste, das zweite, das dritte und das vierte Ausführungsbeispiel eines IR-Zoomobjektivs aufgetragen über der Systembrennweite und
• 7, 11, 15, 19 eine Weitwinkelposition, eine Teleposition und eine Zwischenposition eines IR-Zoomobjektivs entsprechend der ersten, der zweiten, der dritten und der vierten Ausführungsform.

Embodiments of the invention are explained in more detail with reference to a drawing. Show:

• 1 : the typical course of the position of the entrance pupil for a zoom lens as a function of the system focal length,
• 2nd : the course of the position of the entrance pupil accordingly 1 when a warm screen is swung in from a limit of the system focal length,
• 3rd : the course of the position of the entrance pupil accordingly 1 , where a pupil compensation group is moved from the pivoting of the warm shield,
• 4th , 8th , 12th , 16 a first, a second, a third and a fourth exemplary embodiment of an IR zoom lens with a displaceable pupil compensation group,
• 5 , 9 , 13 , 17th the course of the position of the entrance pupil for the first, the second, the third and the fourth exemplary embodiment of an IR zoom lens, the pupil compensation group being moved from the pivoting in of the warm aperture,
• 6 , 10th , 14 , 18th : the displacement of the movable groups for the first, the second, the third and the fourth embodiment of an IR zoom lens plotted against the system focal length and
• 7 , 11 , 15 , 19th a wide-angle position, a teleposition and an intermediate position of an IR zoom lens according to the first, second, third and fourth embodiments.

To understand the invention is as an example in 1 the typical course of the position of the entrance pupil as a function of the system focal length for a zoom system is shown. The reference point for the position of the entrance pupil is always the apex of the front lens. Out 1 it can be seen that the position of the entrance pupil has a maximum deviation at medium focal lengths and is almost corrected for the two extreme focal lengths of the wide-angle position and the telephoto position. Also shown is the limit value f _WS for the system focal length, from which the diameter of the entrance pupil is larger than the diameter of the lenses of the objective. The indices ws stand for "Warm Shield", since from this limit the system should be swung in to shield the system. It becomes clear that the position of the entrance pupil is not at zero even at the focal length f _WS and thus vignetting occurs on the front lens. In 1 the course can be seen without swiveling in a warm screen.

Will now be accordingly 2nd the warming aperture swung in from focal length f _WS , the position of the entrance pupil changes abruptly from this focal length. The position of the entrance pupil jumps by more than 4000 mm at the focal length f _WS = -1157 mm, which leads to undesired vignetting, among other things, on the front lens.

To avoid this effect, an optical pupil compensation group that can be moved along the imaging beam path is integrated into the zoom objective. By moving the pupil compensation group, the position of the entrance pupil can be corrected so that for the focal lengths f _WS and the telephoto position, the entrance pupil lies on the front lens (and thus at zero). By continuously moving the pupil compensation group, it is also possible to correct the position of the entrance pupil for the focal length range from f _WS to telephoto position to zero. This will be 3rd evident.

In 3rd the position of the entrance pupil as a function of the system focal length is shown for the compensated case. It can be seen that the effects of the jump are corrected when the warm screen is swung in. The entrance pupil lies on the front lens after the warm shield has been swung in.

In 4th is the construction of an IR zoom lens 1 shown according to a first embodiment. This is a 50x continuous zoom system, which means that any focal length from wide-angle to telephoto can be used. This can be achieved using a mechanical zoom curve or motorized movements.

The front group 2nd consists only of a front lens and has a positive refractive power and is fixed. To correct the spherical aberration, it is aspherical on one side. In addition, a diffractive optical element (DOE) is applied. The asphere and the diffractive optical element are usually applied on the same side of the lens, since they are realized in one operation. They are preferably applied on the back since they are protected against mechanical damage. The focal length of the front lens, in this case the front group 2nd overall, is chosen so that the f-number or aperture f _# front lens of the front lens is not too small. The condition 0.8 <f _{# front lens} <2 should preferably apply.

The first zoom group 3rd has a negative refractive power and consists of three lenses, the first and the last of the three lenses having a preferred negative refractive power. The middle of the three lenses can also have a positive refractive power. At least one of the three lenses has an aspherical surface. The first zoom group 3rd is also called a variator (for varying the focal length) and moves along the optical axis. The second zoom group 4th has a positive refractive power and preferably consists of only a single lens. The second zoom group is also called a compensator, also moves along the optical axis and is used as a focus lens.

The main lens 5 with positive refractive power consists of 3 lenses with at least two aspherical surfaces. The main lens 5 is certain.

The pupil compensation group 6 has a positive refractive power. It is fixed until the warm screen is swiveled in and is then moved to correct the entrance pupil so that there is no vignetting occurs on the front lens. The pupil compensation group 6 is constructed in this embodiment from a purely spherical lens.

So that the overall length of the lens 1 not too long, the lens can 1 be built angled. There are two deflection elements here 7 and 8th provided, which are each designed as a plane mirror. However, only a single deflection element can be used. With two deflection elements 7 , 8th becomes the lens 1 more compact because of the detector 11 due to the cooling unit has a not negligible expansion. The two or one of the two deflecting mirrors can also be made spherical or aspherical so that lens elements are saved.

For adjustment reasons there is no lens between the two deflection elements 7 , 8th attached, as this would be perpendicular to the optical axis of the main lens. The main lens 5 forms the object on an intermediate image level 12th from which is between the two deflection elements 7 , 8th located. It can also be advantageous to place one or more lenses here because you are close to the intermediate image and can therefore correct the pupil position well. This position is also well suited for a correction of the field bundles, since these are far from the pupil and close to the intermediate image.

There is a positive relay group behind the second deflecting mirror 9 that the intermediate image on the detector 11 maps. It preferably consists of two lenses, one lens having an aspherical surface. In the exemplary embodiment shown, it consists of three lenses, preferably with an aspherical surface on the first lens (third to last lens). The image scale of the relay group 9 is selected so that the intermediate image is displayed in a reduced size. This has the advantage that the chromatic longitudinal error of the lens 1 is shown reduced in the tele position. The imaging scale of the relay group should be preferred 9 are between 0.7 and 1.3.

Behind the relay group 9 sits a swiveling warm screen 10 b and the detector 11 . Inside the detector 11 is the cold aperture 10 a placed. The exact arrangement of the detector 11 , Warm screen 10 b and cold aperture 10 a becomes from in 4th inserted detail view Y recognizable. So the detector is 11 inside a cooling case 13 arranged, in which the heat radiation to be imaged through an entrance window 14 occurs. The cold aperture 10 a is located inside the cooling housing. The warm screen 10 b of the lens 1 is immediately in front of the entrance window 14 arranged of the cooling housing. The cold aperture 10 a is designed as an IR-transparent filter.

In summary, there is the IR zoom lens 1 from the front group 2nd , the first zoom group 3rd , the second zoom group 4th , the main lens 5 , the pupil compensation group 6 , the deflection elements 7 , 8th , the relay group 9 and the pourable warm filter 10 b . The IR zoom lens 1 and the detector unit with cooling housing 13 , IR detector 11 and cold aperture 10 a together form a thermal imaging device 15 .

Table 1 below shows the radii, thicknesses and materials of the exemplary embodiment according to 1 listed. The respective entry and exit surfaces of the optical components are numbered consecutively from the object side to the image side. These areas are also referred to below as S1 to Sn. The radii of the surfaces and the distance between the surfaces are each shown in mm. TABLE 1 Radii, thick materials for example 1 No radius distance Glass 1 381.94555 25,000 'SI' Front group 2nd 650.04260 0,000 3rd INFINITY (variable) 4th 45.48253 5,065 'SI' Variator 5 36.91074 47.158 6 -57.02914 3,771 'SI' Variator 7 -66.93962 24,689 8th -94.55676 3,240 'SI' Variator 9 -531.11259 0,000 10th INFINITY (variable) 11 -216.45432 6,591 'SI' Compensator 12th -132.38315 0,000 13 INFINITY (variable) 14 113.92537 7,230 'SI' Main lens 15 504.65573 5,378 16 1015.38468 5,506 'GE' Main lens 17th 234.06589 33,410 18th 170.29812 4,294 'SI' Main lens 19th 87.90094 (variable) 20 -1640.43767 6,417 'SI' Pupil compensator 21 -226.85319 (variable) 22 INFINITY 23,000 23 INFINITY 52,716 optional deflecting mirror 1 24th INFINITY 34,257 Intermediate picture ZB 25th INFINITY 30,000 optional deflecting mirror 2 26 144.30242 3,385 'SI' Relay group 27 281.22758 0.200 28 30.98301 4,796 'SI' Relay group 29 41.40469 2,478 30th 83.26706 3,000 'CAF' Relay group 31 51.19879 12,493 32 INFINITY 5,000 33 INFINITY 0.500 Warm glare 34 INFINITY 1,000 'SI' Detector entry window 35 INFINITY 1,000 36 INFINITY 0.300 'GE' 37 INFINITY 0,000 38 INFINITY 30,000 Cold fade 39 INFINITY 0,000 40 INFINITY 0,000 Detector / image plane

The material designation SI stands for silicon with a refractive index of n _4200nm = 3.428682, the material designation GE for germanium with n _4200nm = 4.022109 and the material designation CAF for calcium fluoride with n _4200nm = 1.407708. The distances or airspaces marked with "variable" are given below for a number of focal lengths.

The following list gives the aspherical constants for the above areas from Table 1 for the first exemplary embodiment according to 4th on. Aspherical constants Example 1 Aspheric surface area S2: Development constants: A: 5.177e-010 B: 6.168e-016 C: -5.626e-020 D: 1.489e-024 Aspheric area S5: Development constants: A: -9.918e-008 B: -1.157e-010 C: 4.823e-014 D: -1.619e-016 Aspheric area S9: Development constants: A: -2.934e-007 B: -6.617e-012 C: 1.332e-013 D: -1.104e-016 Aspheric surface S15: Development constants: A: 3.186e-007 B: -2.241e-010 C: -1.000e-013 D: 5.367e-017 Aspheric area S17: Development constants: A: -3.803e-007 B: 4.306e-010 C: 9.319e-014 D: -2.063e-017 Aspheric area S19: Development constants: A: -2.130e-008 B: -3.823e-010 C: -1.440e-013 D: 1.220e-016 Aspheric surface S27: development constants: A: 6.199e-007 B: 9.695e-011 C: 3.203e-013 D: 1.416e-017

Dabei bezeichnet z die Pfeilhöhe der Fläche parallel zur z-Achse; c ist die Krümmung am Scheitel der Fläche; k ist die konische Konstante und bei den hier angegebenen Beispielen immer Null und deshalb nicht aufgeführt. r ist der radiale Abstand zur z-Achse. A, B, C und D sind die Entwicklungs-Koeffizienten der 4., 6., 8., und 10. Ordnung.The aspherical shape is given by the following formula: $$\mathrm{e.g.}=\frac{c{r}^{\mathrm{2nd}}}{1+\sqrt{1-\left(1+k\right)c^{\mathrm{2nd}}{r}^{\mathrm{2nd}}}}+A{r}^{\mathrm{4th}}+\mathrm{<figure-callout\; id="6"\; label="B\; r"\; filenames="DE102012018441B4\_0016.png,DE102012018441B4\_0018.png"\; state="\{\{state\}\}">B\; </figure-callout>}{r}^{}{}^6+\mathrm{C.}{r}^{\mathrm{8th}}+D{r}^{\mathrm{10th}}$$

Z denotes the arrow height of the surface parallel to the z-axis; c is the curvature at the apex of the surface; k is the conical constant and is always zero in the examples given here and therefore not listed. r is the radial distance to the z-axis. A, B, C and D are the development coefficients of the 4th, 6th, 8th, and 10th . Order.

The diffractive development coefficients for the first embodiment can be found in the following table: Diffractive surface for example 1 Diffractive surface S2: development const C1: -8.055e-006 S2: C2: -1.200e-012 Design wavelength diffraction order: 1 4400nm

mit der Furchenzahl N(y) $$N\left(y\right)=\frac{C_1{y}^2}{\lambda }+\frac{C_2{y}^4}{\lambda },$$

wobei y der radiale Abstand zur z-Achse, λ die Designwellenlänge, C₁ der Koeffizient der 2. Ordnung und C₂ der Koeffizient 4. Ordnung ist,
und der Furchentiefe $$T=\frac{\lambda }{n-1},$$

wobei n der Brechungsindex ist.The diffractive removal Z (DOE) parallel to the optical axis results from the following formula: $$\text{Z}\left(\text{DOE}\right)=\text{T *}\left(\text{N}\left(\text{y}\right)-\text{SIGN}\left(\text{N}\left(\text{y}\right)\right)*\text{INTEGER}\left(\text{SECTION}\left(\text{N}\left(\text{y}\right)\right)\right)\right),$$

with the number of furrows N (y) $$N\left(y\right)=\frac{{\mathrm{C.}}_1{y}^{\mathrm{2nd}}}{\lambda }+\frac{{\mathrm{C.}}_{\mathrm{2nd}}{y}^{\mathrm{4th}}}{\lambda },$$

where y is the radial distance to the z-axis, λ is the design wavelength, C _{1 is} the 2nd order coefficient and C _{2 is} the coefficient 4th . Okay is
and the furrow depth $$T=\frac{\lambda }{n-1},$$

where n is the refractive index.

The following table shows the variable airspaces for ten focal lengths and the position as well as the diameter of the system aperture. From this you can also see the pivoting of the warm screen 10 b from the zoom position Z8 (Focal length 1200mm). The position of the system cover jumps from the surface S38 (Cold aperture 10 a ) on surface S33 (Warm fade 10 b ). The distance between the warm screen 10 b and the cold aperture 10 a can be taken from the list of radii and distances above (Table 1) and is 2.8 mm here. The pupil compensation group 6 (see airspace S19 and S21 ) only moves after the warm fade 10 b was swung in. Before that she is certain. This can be the columns Z1 to Z7 be removed. The distances are the same here.

The group focal lengths for the first exemplary embodiment are given in the following table. From this, the structure of the IR zoom lens 1 be read. A positive front group 2nd follows a negative variable first zoom group 3rd . Then comes a positive variable second zoom group 4th that are in front of the positive fixed main lens 5 stands. The pupil compensation group 6 is variable again and has a positive refractive power. The two deflection elements 7 , 8th have no refractive power and therefore do not appear here. The relay group then forms 9 the intermediate image from the intermediate image plane with a magnification of 0.932 12th scaled down to the detector 11 from. The focal length up to the intermediate image is also given for the wide-angle position. Group focal lengths Ex.1: Front group S1..3: 355.839mm Variator S4..10: -21.207mm Compensator S11..13: 132.997mm Main lens S14..19: 621.957mm Pupil compensation group S20..21: 108.081mm Relay group S26..31: 30.325mm Front group up to ZB S1..24: 38.626mm for Z1 Image scale relay group: 0.932

To clarify the function of the pupil compensation group 6 the following table "Vignetting for Ex. 1" is given. The diameter of the front lens is 251.6 mm. For the respective zoom or focal length positions, the aperture or f-number (F #), the entrance pupil diameter (EPD), the entrance pupil position (EP position) in relation to the apex of the front lens and the maximum diameter of the beam for the respective zoom position Zx (max . DM Pos Zx) listed. If the maximum diameter of the beam is smaller than the value of the diameter of the front lens, no vignetting occurs. All values in the line max. DM Pos Zx are smaller than the diameter of the front lens. Therefore, vignetting does not occur. The location of the entrance pupil of the zoom positions Z8 and Z9 can be larger than that of the zoom position Z10 , because here the entrance pupil diameter is smaller than the lens diameter.

The variation in the position of the entrance pupil for the first embodiment of an IR zoom lens 1 according to 4th is in 5 represented graphically. The jump of the entrance pupil position into the negative is due to the shift of the pupil compensation group 6 corrected.

The course of the movement of the zoom groups 3rd , 4th and the pupil compensation group 6 is in 6 to see. The history 20 gives the movement of the first zoom group 3rd (Variator), the course 21 the movement of the second zoom group (compensator) again. The history 22 describes the distance between the first and the second zoom group 3rd or. 4th . The history 23 shows the movement of the pupil compensation group 6 . The variator shifts to get from the wide-angle position to the tele position 3rd from the object side to the image side. The compensator 4th drives in front of the variator 3rd forth, but has a turning point at longer focal lengths and runs back slightly towards the object. This reduces the distance between the variators 3rd and compensator 4th . This distance is at a minimum when telephoto. In addition to the pupil compensation group 6 become a variator 3rd and compensator 4th slightly offset to adjust the focal length and focus.

For motorized adjustment of the movable first and second zoom group 3rd , 4th , the pupil compensation group 6 according to the movements 6 as well as for inserting or folding in the warm panel 10 b In the beam path from the focal length f _WS is a control unit 16 (please refer 4th ) intended.

In 7 are three zoom positions for the IR zoom lens 1 acc. 4th drawn. The lower lens section a) shows the wide-angle position, the upper c) the telephoto position. Here you can clearly see that the variator 3rd and the compensator 4th have moved towards the picture. Also the pupil compensation group 6 has moved and moved towards the image. The middle picture b) shows the IR zoom lens 1 immediately before the warm screen is swung in 10 a . The pupil compensation group has the same position as in the wide-angle position a). It can be seen that the central bundle fills the full front lens. A further enlargement would lead to vignetting, which is why the warm screen is at this point 10 a introduced.

In 8th is the construction of an IR zoom lens 1 shown according to a second embodiment. The difference to the example is that here the variator 3rd , the main lens 5 as well as the relay system 9 are constructed differently. Even with the IR zoom lens 1 acc. 8th is a 50x continuous zoom system.

The front group 2nd (here again it only consists of the front lens) has a positive refractive power and is fixed. To correct the spherical aberration, it is aspherical on one side. In addition, a diffractive optical element (DOE) is applied. The asphere and the diffractive element are mostly applied on the same side of the lens, since they are realized in one operation. They are preferably applied on the back since they are protected against mechanical damage. The focal length of the front lens is selected so that the f-number or aperture f _# front lens of the front lens is not too small. The condition 0.8 <f _{# front lens} <2 should preferably apply.

The first zoom group 3rd (has a negative refractive power and consists of two lenses, both lenses having a preferred negative refractive power. At least one of the two lenses has an aspherical surface. The first zoom group 3rd moves along the optical axis. The second zoom group 4th has a positive refractive power and preferably consists of only a single lens. Also the second zoom group 4th moves along the optical axis. It is used as a focus lens.

The main lens 5 with positive refractive power consists of three lenses with at least two aspherical surfaces. The main lens 5 stands and forms the object on an intermediate image level 12th from.

The pupil compensation group 6 has a positive refractive power. It is fixed until the warm panel is swung in 10 b and is then shifted to correct the entrance pupil so that there is no vignetting on the front lens. The pupil compensation group 6 in this example, too, is made up of a purely spherical lens.

So that the overall length of the lens does not become too long, the lens can be adjusted using two deflection elements 7 , 8th be built angled. The deflection elements 7 , 8th are also designed as a flat mirror here.

However, only a single deflection element can be used. With two deflection elements 7 , 8th becomes the lens 1 more compact because of the detector 11 due to the cooling unit has a not negligible expansion. The two or one of the two deflecting mirrors can also be made spherical or aspherical so that lens elements are saved.

For adjustment reasons there is no lens between the two deflection elements 7 , 8th attached, as this would be perpendicular to the optical axis of the main lens. The main lens 5 forms the object on an intermediate image level 12th from which is between the two deflection elements 7 , 8th located. It can also be advantageous to place one or more lenses here because you are close to the intermediate image and can therefore correct the pupil position well. This position is also well suited for a correction of the field bundles, since these are far from the pupil and close to the intermediate image.

Behind the second deflecting mirror 8th is the positive relay group 9 that the intermediate image from the intermediate image level 12th on the detector 11 maps. It preferably consists of two lenses, one lens having an aspherical surface, preferably on the first lens (second to last lens). The two lenses preferably consist of a material with low dispersion (eg silicon) and a material with high dispersion (eg CaF). This allows the chromatic magnification difference of the relay system 9 keep very small. The image scale of the relay group 9 is selected so that the intermediate image is displayed in a reduced size. This has the advantage that the chromatic longitudinal error of the lens 1 is shown reduced in the tele position. The imaging scale of the relay group should be preferred 9 are between 0.7 and 1.3.

The retractable warm cover sits behind the relay group 10 b and the detector 11 . Inside the cooling case 13 of the detector 11 is appropriate 4th the cold aperture 10 a placed.

In the following Table 2, the radii, thicknesses and materials of the second embodiment are gem. 8th listed. The radii of the surfaces and the distances are given in mm. TABLE 2 Radii, thick materials for Ex. 2 No radius distance Glass 1 389.72450 25,000 'SI' Front group 2nd 689.26509 0,000 3rd INFINITY (variable) 4th 58.20467 5,000 'SI' Variator 5 44.98148 67,048 6 -65.56128 3,500 'SI' Variator 7 -345.85501 0,000 8th INFINITY (variable) 9 -196.03093 8,200 'SI' Compensator 10th -125.39586 0,000 11 INFINITY (variable) 12th 107.29455 9,000 'SI' Main lens 13 348.34727 31.502 14 1984.53839 4,000 'GE' Main lens 15 75.83787 4,008 16 72.42336 7,000 'SI' Main lens 17th 81.31705 (variable) 18th 283.75802 6,600 'SI' Pupil compensator 19th -1207.82940 (variable) 20 INFINITY 24.001 21 INFINITY 57,049 optional deflecting mirror 22 INFINITY 33,728 Intermediate image 23 INFINITY 38,303 optional deflecting mirror 24th 47.31920 5,044 'SI' Relay group 25th 111.53300 3,333 26 -188.85732 6,000 'CAF' Relay group 27 -538.95942 15.193 28 INFINITY 5,000 29 INFINITY 0.500 Warm glare 30th INFINITY 1,000 'SI' Detector entry window 31 INFINITY 1,600 32 INFINITY 0.300 'GE' 33 INFINITY 0,000 34 INFINITY 30,000 Cold fade 35 INFINITY 0,000 36 INFINITY 0,000 Detector / image plane

The material designations are according to Table 1. The distances or air spaces marked with (variable) are given below for a number of focal lengths.

The following list gives the aspherical constants for the above areas from Table 2 of the second exemplary embodiment. Aspherical constants Ex. 2 Aspheric surface S2: Development constants: A: 5.162e-010 B: 9.196e-016 C: -7.274e-020 D: 1.834e-024 Aspheric surface S7: Development constants: A: -4.601e-007 B: 2.793e-010 C: -9.742e-013 D: 1.468e-015 Aspheric surface S13: Development constants: A: 9.155e-008 B: -3.095e-011 C: 1.456e-014 D: -1.958e-018 Aspheric surface S15: Development constants: A: -1.070e-006 B: 2.821e-009 C: -4.290e-012 D: 9.352e-016 Aspheric surface S17: Development constants: A: 7.844e-007 B: -2.477e-009 C: 3.736e-012 D: -9.255e-016 Aspheric surface S25: Development constants: A: 9.295e-007 B: -4.488e-010 C: 3.723e-013 D: -3.484e-016

The diffractive development coefficients for the second embodiment according to 8th can be found in the following table: Diffractive surface for example 2 Diffractive surface S2: Development costs: C1: -8.163e-006 C2: 4.042e-012 Design wavelength: 4400 nm Diffraction order: 1

The following table shows the variable airspaces for ten focal lengths and the position as well as the diameter of the system aperture. From this you can also see the pivoting of the warm screen 10 b from zoom position Z8 (Focal length approx. 1200mm). The position of the system cover changes from surface S34 (Cold aperture 10 a ) on surface S29 (Warm fade 10 b ). The distance between the warm screen 10 a and the cold aperture 10 b can be found in the list of radii and distances above (Table 2) and is 3.4 mm here. The pupil compensation group 6 (see airspace S17 and S19 ) only moves after the warm fade 10 a was swung in. Before that she is certain. This can be seen in columns Z1 to Z7. The distances are the same here.

The group focal lengths for the second exemplary embodiment are given in the following table. From this, the structure of the IR zoom lens 1 acc. 8th be read. A positive front group 2nd follows a negative variable first zoom group 3rd . Then comes a positive variable second zoom group 4th that are in front of the positive fixed main lens 5 stands. The pupil compensation group 6 is variable again and has a positive refractive power. The two deflecting mirrors 7 , 8th have no refractive power and therefore do not appear. The relay group then forms 9 with an imaging scale of 0.874, the intermediate image is reduced to the detector 11 from. The focal length up to the intermediate image is also given for the wide-angle position. Group focal lengths for example 2: Front group S1..3: 347.424mm Variator S4..8: -18.299mm Compensator S9..11: 132.662mm Main lens S12..17: 411.240mm Pupil compensation group S18..19: 95.088mm Relay group S24..27: 33.452mm Front group up to ZB S1..22: 41.199mm for Z1 Image scale relay group: 0.874

To clarify the function of the pupil compensation group 6 the following table "Vignetting for Example 2" is given. The diameter of the front lens is 257.2 mm. For the respective zoom or focal length settings, the opening (F #), the entrance pupil diameter (EPD), the entrance pupil position (EP position) in relation to the apex of the first lens and the maximum diameter of the beam for the respective zoom position Zx (max. DM Pos Zx) listed. If the maximum diameter of the beam is max. DM Pos Zx smaller than the value of the diameter of the front lens, so there is no vignetting on. All values in the line max. DM Pos Zx are smaller than the diameter of the front lens. Therefore, vignetting does not occur.

The position of the entrance pupil of the zoom positions Z7 to Z10 is set to zero here. Between the focal length of 1157 mm and 1833 mm, this is done by shifting the pupil compensation group 6 .

The variation in the position of the entrance pupil is in 9 represented graphically. The jump of the entrance pupil position into the negative is due to the shift of the pupil compensation group 6 corrected. By shifting the pupil compensation group 6 the position of the entrance pupil is placed on the front lens.

The course of the movement of the zoom groups 3rd , 4th and the pupil compensation group 6 is in 10th to see. The history 20 gives the movement of the first zoom group 3rd (Variator), the course 21 the movement of the second zoom group (compensator) again. The history 22 describes the distance between the first and the second zoom group 3rd or. 4th . The history 23 shows the movement of the pupil compensation group 6 . The variator shifts in order to move from the wide-angle position to the telephoto position 3rd from the object side to the image side. The compensator 4th drives in front of the variator 3rd forth, but has a turning point at longer focal lengths and runs back slightly towards the object. This reduces the distance between the variators 3rd and compensator 4th . This distance is at a minimum when telephoto. In addition to the pupil compensation group 6 become a variator 3rd and compensator 4th slightly offset to adjust the focal length and focus. To simplify matters, only the positions of the ten focal lengths presented are drawn here. The intermediate values can be easily determined using an optimization calculation.

For motorized adjustment of the movable first and second zoom group 3rd , 4th , the pupil compensation group 6 according to the movements 10th as well as for inserting or folding in the warm panel 10 b In the beam path from the focal length f _WS is a control unit 16 (corresponding 4th ) intended.

In 11 are three zoom positions for the IR zoom lens 1 acc. 8th drawn. The lower lens cut a ) shows the wide-angle position, the upper c) the telephoto position. Here you can clearly see that the variator 3rd and the compensator 4th have moved towards the picture. Also the pupil compensation group 6 has moved and moved towards the image. The middle picture b ) shows the IR zoom lens 1 immediately before the warm screen is swung in 10 a . The pupil compensation group 6 has the same position as in the wide-angle position. It can be seen that the central bundle fills the full front lens. A further enlargement would lead to vignetting, which is why the warm screen is at this point 10 a introduced.

In 12th is the construction of an IR zoom lens 1 shown according to a third embodiment. The difference according to the second embodiment. 8th is that the main lens here 5 is built differently. This allows tolerances to be relaxed. Even with the IR zoom lens 1 acc. 12th is a 50x continuous zoom system.

The front group 2nd (here again it only consists of the front lens) has a positive refractive power and is fixed. To correct the spherical aberration, it is aspherical on one side. In addition, a diffractive optical element (DOE) is applied. The asphere and the diffractive optical element are usually applied on the same side of the lens, since they are realized in one operation. They are preferably applied on the back since they are protected against mechanical damage. The focal length of the front lens is selected so that the f-number or aperture f _# front lens of the front lens is not too small. The condition 0.8 <f _{# front lens} <2 should preferably apply.

The first zoom group 3rd has a negative refractive power and consists of three lenses, both lenses having a preferred negative refractive power. At least one of the two lenses has an aspherical one Surface. The first zoom group 3rd moves along the optical axis. The second zoom group 4th has a positive refractive power and preferably consists of only a single lens. Also the second zoom group 4th moves along the optical axis. It is used as a focus lens.

The main lens 5 with positive refractive power consists of four lenses with at least two aspherical surfaces. The main lens 5 is certain.

The pupil compensation group 6 has a positive refractive power. It is fixed until the warm panel is swung in 10 a and is then shifted to correct the entrance pupil so that there is no vignetting on the front lens. The pupil compensation group 6 in this example, too, is made up of a purely spherical lens.

So that the length of the IR zoom lens 1 acc. 12th is not too long, it is built angled. There are two deflection elements designed as plane mirrors 7 , 8th intended.

But it can also be a single deflecting element 7 , 8th be used. With two deflection elements 7 , 8th becomes the lens 1 more compact because of the detector 11 due to the cooling unit has a not negligible expansion. The two or one of the two deflecting mirrors can also be made spherical or aspherical so that lens elements are saved.

For adjustment reasons there is no lens between the two deflection elements 7 , 8th attached, as this would be perpendicular to the optical axis of the main lens. The main lens 5 forms the object on an intermediate image level 12th from which is between the two deflection elements 7 , 8th located. It can also be advantageous to place one or more lenses here because you are close to the intermediate image and can therefore correct the pupil position well. This position is also well suited for a correction of the field bundles, since these are far from the pupil and close to the intermediate image.

Behind the second deflection element 8th is the positive relay group 9 that the intermediate image on the detector 11 maps. It preferably consists of two lenses, one lens having an aspherical surface, preferably on the first lens (second to last lens). The two lenses preferably consist of a material with low dispersion (eg silicon) and a material with high dispersion (eg CaF). As a result, the chromatic magnification difference of the relay system can be kept very small.

The image scale of the relay group 9 is selected so that the intermediate image is displayed in a reduced size. This has the advantage that the chromatic longitudinal error of the lens 1 is shown reduced in the tele position. The imaging scale of the relay group should be preferred 9 are between 0.7 and 1.3.

Behind the relay group 9 the swiveling warm panel sits 10 b and the detector 11 . Inside the cooling case 13 of the detector 11 is according to the 4th and 8th the cold aperture 10 a placed.

In the following Table 3, the radii, thicknesses and materials of the embodiment are gem. 12th listed. The radii of the surfaces and the distances are given in mm. TABLE 3 Radii, thick materials for Ex. 3 No radius distance Glass 1 375.26606 25,000 'SI' Front group 2nd 658.77402 0,000 3rd INFINITY (variable) 4th 49.08217 5,200 'SI' Variator 5 35.87800 59,753 6 -75.87938 4,500 'SI' Variator 7 -361.75560 0,000 8th INFINITY (variable) 9 -194.73316 8,000 'SI' Compensator 10th -124.04115 0,000 11 INFINITY (variable) 12th 126.27843 8,800 'SI' Main lens 13 752.93557 13,433 14 488.47329 6,800 'GE' Main lens 15 238.16182 32,200 16 -304.44151 3,400 'GE' Main lens 17th 127.84437 6,263 18th 76.87607 4,800 'SI' Main lens 19th 89.79836 (variable) 20 304.48798 6,500 'SI' Pupil compensator 21 -842.12547 (variable) 22 INFINITY 20,983 23 INFINITY 57,396 optional deflecting mirror 24th INFINITY 27,733 Intermediate image 25th INFINITY 50,026 optional deflecting mirror 26 51.64112 5,900 'SI' Relay system 27 130.83986 4,298 28 -171.77663 8,000 'CAF' Relay system 29 -496.99228 13,907 30th INFINITY 5,000 31 INFINITY 0.500 Warm glare 32 INFINITY 1,000 'SI' Detector entry window 33 INFINITY 1,600 34 INFINITY 0.300 'GE' 35 INFINITY 0,000 36 INFINITY 30,000 Cold fade 37 INFINITY 0,000 38 INFINITY 0,000 Detector / image plane

The material designations are according to Table 1. The distances or air spaces marked with (variable) are given below for a number of focal lengths.

The following list gives the aspherical constants for the above surfaces from Table 3 of Example 3. Aspherical constants Ex. 3 Aspheric surface S2: Development constants: A: 5.817e-010 B: 0.000e + 000 C: 0.000e + 000 D: 0.000e + 000 Aspheric surface S7: development constants: A: -4.588e-007 B: 6.041e-011 C: -6.636e-014 D: 0.000e + 000 Aspheric surface S13: development constants: A: 4.142e-008 B: -1.278e-012 C: 0.000e + 000 D: 0.000e + 000 Aspheric surface S17: Development constants: A: 1.792e-008 B: 2.364e-010 C: -3.652e-013 D: 6.426e-016 Aspheric surface S27: development constants: A: 7.999e-007 B: -2.937e-010 C: 0.000e + 000 D: 0.000e + 000

The diffractive development coefficients for Example 3 can be found in the following table: Diffractive area for Example 3 Diffractive surface S2: Development constants: C1: -8.679e-006 C2: 0.000e + 000 Design wavelength: 4600nm Diffraction order: 1

In the table below are the variable airspaces for ten 10th Focal length positions and the position, as well as the diameter of the system aperture are given. From this you can also see the pivoting of the warm screen 10 b from zoom position Z8 (Focal length approx. 1200mm). The position of the system cover changes from surface 36 (Cold aperture 10 a ) on surface 31 (Warm fade 10 b ). The distance between the warm screen 10 b and the cold aperture 10 a can be taken from the list of radii and distances according to table 3 and amounts to 3.4 mm. The pupil compensation group 6 (see airspace S19 and S21 ) only moves after the warm fade 10 b was swung in. Before that she is certain. This can be seen in columns Z1 to Z7. The distances are the same here.

The group focal lengths for the third exemplary embodiment are given in the following table. From this, the structure of the IR zoom lens according to 12th be read. A positive front group 2nd follows a negative variable first zoom group 3rd . Then comes a positive variable second zoom group 4th that are in front of the positive fixed main lens 5 stands. The pupil compensation group 6 is variable again and has a positive refractive power. The two deflecting mirrors 7 , 8th have no refractive power and therefore do not appear. The relay group then forms 9 with a magnification of 0.834, the intermediate image is reduced to the detector 11 from. The focal length up to the intermediate image is also given for the wide-angle position. Group focal lengths for example 3: Front group S1..3: 336.791mm Variator S4..8: -17.979mm Compensator S9..11: 130.539mm Main lens S12..19: 324.620mm Pupil compensation group S20..21: 92.651mm Relay group S26..29: 35.016mm Front group up to ZB S1..24: 43.182mm for Z1 Image scale relay group : 0.834

To clarify the function of the pupil compensator, the following table "Vignetting for Ex. 3" is given. The diameter of the front lens is 257.2 mm. For the respective zoom or focal length settings, the opening (F #), the entrance pupil diameter (EPD), the entrance pupil position EP position in relation to the apex of the first lens and the maximum diameter of the beam for the respective zoom position Zx (max. DM Pos Zx) specified. If the value for max. DM Pos Zx smaller than the value of the diameter of the front lens, so there is no vignetting. All values in the line max. DM Pos Zx are smaller than the diameter of the front lens. Therefore, vignetting does not occur. The position of the entrance pupil of the zoom positions Z7 to Z10 is set to zero here. Between the focal length of 1157 mm and 1833 mm, this is done by shifting the pupil compensation group 6 .

The variation in the position of the entrance pupil is in 13 represented graphically. The jump of the entrance pupil position into the negative is due to the shift of the pupil compensation group 6 corrected. By shifting the pupil compensation group 6 the position of the entrance pupil from the focal length f _{WS is placed} on the front lens.

The course of the movement of the zoom groups 3rd , 4th and the pupil compensation group 6 is in 14 to see. The history 20 gives the movement of the first zoom group 3rd (Variator), the course 21 the movement of the second zoom group (compensator) again. The history 22 describes the distance between the first and the second zoom group 3rd or. 4th . The history 23 shows the movement of the pupil compensation group 6 . The variator shifts in order to move from the wide-angle position to the telephoto position 3rd from the object side to the image side. The compensator 4th drives in front of the variator 3rd forth, but has a turning point at longer focal lengths and runs back slightly towards the object. This reduces the distance between the variator and compensator. This distance is at a minimum when telephoto. In addition to the pupil compensation group 6 become a variator 3rd and compensator 4th slightly offset to adjust the focal length and focus.

For motorized adjustment of the movable first and second zoom group 3rd , 4th , the pupil compensation group 6 according to the movements 14 as well as for inserting or folding in the warm panel 10 b In the beam path from the focal length f _WS is a control unit 16 (corresponding 4th ) intended.

In 15 three zoom positions are drawn. The lower lens section a) shows the wide-angle position, the upper c) the telephoto position. Here you can clearly see that the variator 3rd and the compensator 4th have moved towards the picture. Also the pupil compensation group 6 has moved and moved towards the image. The middle picture b) shows the IR zoom lens 1 corresponding 12th immediately before the warm screen is swung in 10 b . The pupil compensation group 6 has the same position as in the wide-angle position a). It can be seen that the central bundle fills the full front lens. A further enlargement would lead to vignetting, which is why the warm screen is at this point 10 b introduced.

In 16 is the construction of an IR zoom lens 1 shown according to a fourth embodiment. The difference to the exemplary embodiments accordingly 4th , 8th and 12th is that the front group here 2nd and the main lens 5 are constructed differently, and the zoom groups 3rd , 4th have a different power distribution. Correspondingly also with the IR zoom lenses 16 is a 50x continuous zoom system.

The front group 2nd consists of two positive lenses, has a positive refractive power and is fixed. The combination of a spherical lens made of silicon and an aspherical lens made of zinc sulfide ZnS with a diffractive optical element (DOE) has proven to be very advantageous for color correction. A lens is aspherical on one side to correct spherical aberration. In addition, a diffractive optical element is applied. The asphere and the diffractive optical element are mostly applied on the same side of the lens, since they are realized in one operation.

The disadvantage of the ZnS lens is that its diameter must be relatively large and it is strongly bent. The strong deflection results, among other things, from the requirement for small angles of incidence so that the centering sensitivity and distance sensitivity do not become too strong. The strong deflection results in high material consumption, which makes the lens very expensive here. Another disadvantage of a divided front group is the relatively large volume and weight. The length can be extended by changing the structure of the two zoom groups 3rd , 4th be compensated. Through two negative zoom groups 3rd , 4th the overall length is reduced again.

The first zoom group 3rd has a negative refractive power and consists of two lenses, one lens having a negative refractive power and one lens having a positive refractive power. At least one of the two lenses has an aspherical surface. The first zoom group 3rd moves along the optical axis. The second zoom group 4th also has a negative refractive power and preferably consists of only a single lens. Also the second zoom group 4th moves along the optical axis.

The main lens 5 with positive refractive power consists of two lenses with at least two aspherical surfaces. The main lens 5 is certain.

The pupil compensation group 6 has a positive refractive power. It is fixed until the warm panel is swung in 10 b and is then shifted to correct the entrance pupil so that there is no vignetting on the front lens. The pupil compensation group 6 is made up of a purely spherical lens.

The IR zoom lens 1 acc. 16 is built angled. There are two deflection elements for this 7 , 8th provided, which are designed as a flat deflecting mirror.

Between the two deflection elements 7 , 8th is the intermediate image of the main lens 5 .

But it can also be a single deflecting element 7 , 8th be used. With two deflection elements 7 , 8th becomes the lens 1 more compact because of the detector 11 due to the cooling unit has a not negligible expansion. The two or one of the two deflecting mirrors can also be made spherical or aspherical so that lens elements are saved

For adjustment reasons there is no lens between the two deflection elements 7 , 8th attached, as this would be perpendicular to the optical axis of the main lens. The main lens 5 forms the object on an intermediate image level 12th from which is between the two deflection elements 7 , 8th located. It can also be advantageous to place one or more lenses here because you are close to the intermediate image and can therefore correct the pupil position well. This position is also well suited for a correction of the field bundles, since these are far from the pupil and close to the intermediate image.

Behind the second deflection element 8th is the positive relay group 9 that the intermediate image on the detector 11 maps. It preferably consists of two lenses, but here of three lenses, one lens having an aspherical surface, preferably on the first lens (third to last lens). The image scale of the relay group 9 is selected so that the intermediate image is shown enlarged. Because the chromatic longitudinal error of the lens due to the front group consisting of two lenses 2nd is corrected very well, the imaging scale of the relay group 9 also enlarge, which has the advantage that the maximum focal length of the zoom lens 1 in front of the relay group 9 can be chosen smaller. The imaging scale of the relay group should preferably be between 0.7 and 1.3.

Behind the relay group 9 the swiveling warm panel sits 10 b and the detector 11 . Inside the cooling case 13 of the detector 11 is according to the 4th , 8th , 12th the cold aperture 10 a contain.

The radii, thicknesses and materials of Example 4 are listed in Table 4 below. The radii and distances are given in mm. TABLE 4 Radii, thick materials for example 4 No radius distance Glass 1 610.47150 25,009 'SI' Front group 2nd 1118.42049 56,413 3rd 200,60448 14,986 'CNS' Front group 4th 277.95776 0,000 5 INFINITY (variable) 6 -9795.96625 11,283 'GE' Variator 7 -836.01064 15,218 8th -107.57092 0.434 'SI' Variator 9 96.32623 0,000 10th INFINITY (variable) 11 -129.83710 5,698 'SI' Compensator 12th -232.64791 (variable) 13 -3298.34795 7,304 'SI' Main lens 14 -115.17518 52,225 15 -350.97141 1,266 'GE' Main lens 16 232.02399 (variable) 17th 1098.95929 1,921 'SI' Pupil compensator 18th -304.42471 (variable) 19th INFINITY 32,574 20 INFINITY 48,759 optional deflecting mirror 21 INFINITY 37,216 Intermediate image 22 INFINITY 30,000 optional deflecting mirror 23 92.26527 2,727 'CNS' Relay group 24th -440.92045 0.100 25th 28.57661 3,621 'SI' Relay group 26 35.12150 5,836 27 44.34616 0.593 CAF Relay group 28 23.01446 11.056 29 INFINITY 5,000 30th INFINITY 0.500 Warm glare 31 INFINITY 1,000 'SI' Detector entry window 32 INFINITY 1,000 33 INFINITY 0.300 'GE' 34 INFINITY 0,000 35 INFINITY 30,000 Cold fade 36 INFINITY 0,000 Detector / image plane

The material designations are according to Table 1. The distances or air spaces marked with (variable) are given below for a number of focal lengths.

The following list gives the aspherical constants for the above areas from Table 4 of the fourth exemplary embodiment. Aspherical constants Ex. 4 Aspheric surface S4: Development constants: A: -5.103e-010 B: 1.061e-015 C: 0.000e + 000 D: 0.000e + 000 Aspheric surface S9: Development constants: A: -1.509e-006 B: -3.485e-010 C: 5.250e-013 D: 0.000e + 000 Aspheric surface S13: Development constants: A: -2.694e-007 B: 2.978e-011 C: -2.577e-015 D: 0.000e + 000 Aspheric surface S15: Development constants: A: 6.689e-007 B: -2.314e-010 C: 8.520e-014 D: 0.000e + 000 Aspheric surface S23: Development constants: A: -9.449e-007 B: 0.000e + 000 C: 0.000e + 000 D: 0.000e + 000

The diffractive development coefficients for Example 4 can be found in the following table: Diffractive area for Example 4 Diffractive area development constants: S4: C1: -2.795e-005 C2: -9.949e-011 Design wavelength: 4200nm Diffraction order: 1

The following table shows the variable airspaces for ten focal lengths and the position as well as the diameter of the system aperture. From this you can also see the pivoting of the warm screen 10 b from zoom position Z8 (Focal length approx. 1200 mm). The position of the system cover changes from surface 35 (Cold aperture 10 a ) on surface 30th (Warm fade 10 b ). The distance between the warm screen 10 b and the cold aperture 10 a can be taken from the radius and distance list from table 4 and is 2.8 mm here. The pupil compensation group 6 (see airspace S16 and S18 ) only moves after the warm fade 10 b was swung in. Before that she is certain. This can be the columns Z1 to Z7 be removed. The distances are the same here.

The group focal lengths are given in the following table. The structure of the zoom system can be read from this. A positive front group 2nd follows a negative variable first zoom group 3rd . Then comes a second negative variable zoom group 4th that are in front of the positive fixed main lens 5 stands. The pupil compensation group 6 is variable again and has a positive refractive power. The two deflecting mirrors 7 , 8th have no refractive power and therefore do not appear. The relay group then forms 9 with a magnification of 1,013 the intermediate image is enlarged on the detector 11 from. The focal length up to the intermediate image is also given for the wide-angle position. Group focal lengths for example 4: Front group S1..5: 275.314mm Variator S6..10: -23.753mm Compensator S11..12: -126.119mm Main lens S13..16: 45.954mm Pupil compensation group S17..18: 98.411mm Relay group S25..28: 64.262mm Front group up to ZB S1..21: 35.538mm for Z1 Image scale relay group: 1,013

To clarify the function of the pupil compensation group 6 the following table is given. The diameter of the front lens is 252 mm. For the respective zoom or focal length settings, the opening (F #), the entrance pupil diameter (EPD), the entrance pupil position (EP position) in relation to the apex of the first lens and the maximum diameter of the beam for the respective zoom position Zx (max. DM Pos Zx) specified. If the value for max. DM Pos Zx smaller than the value of the diameter of the front lens, so there is no vignetting. All values in the line max. DM Pos Zx are smaller than the diameter of the front lens. Therefore, vignetting does not occur. The position of the entrance pupil of the zoom positions Z7 and Z10 is here close to zero. Between the focal length of 1131 mm and 1796 mm, this is done by shifting the pupil compensation group 6 . Vignetting for example 4: Front lens diameter: 252.00mm Zoom position Z1 Z2 Z3 Z4 Z5 Z6 Z7 Z8 Z9 Z10 Focal length -36,000 -60,000 -110,000 -280,000 -660.006 -879,982 -1131.164 -1199,982 -1549,949 -1796.537 F # 4,700 4,667 4,644 4,648 4,599 4,591 4,582 6,949 7,021 7,176 EPD 7,660 12,857 23,688 60,235 143.502 191.693 246.898 172,695 220,754 250,362 EP location 200,834 377.364 675.406 1333.875 1750.813 1477.517 707.154 -1493.880 -3286.016 -276,745 max.DM Pos Zx 158,967 176,948 175,860 163,379 167,630 195,693 246.898 181.010 240,641 250,362

The variation in the position of the entrance pupil is in 17th represented graphically. The jump of the entrance pupil position into the negative is due to the pupil compensation group 6 reset to near zero. For the zoom positions Z8 and Z9 could change the position of the entrance pupil by shifting the pupil compensation group 6 can also be set to near zero. However, this is not necessary here, since the maximum value of the diameter of the beam bundle max.DM Pos Zx for the zoom positions Z8 and Z9 is smaller than the diameter of the front lens (252 mm). Thus, by shifting the pupil compensation group 6 the position of the entrance pupil placed near the front lens.

The course of the movement of the zoom groups 3rd , 4th and the pupil compensation group 6 is in 18th to see. The history 20 gives the movement of the first zoom group 3rd (Variator), the course 21 the movement of the second zoom group (compensator) again. The history 22 describes the distance between the first and the second zoom group 3rd or. 4th . The history 23 shows the movement of the pupil compensation group 6 . The variator shifts in order to move from the wide-angle position to the telephoto position 3rd from the object side to the image side. The compensator 4th runs the variator 3rd first towards and then runs back towards the picture. This results in a position with a minimal distance between the variator 3rd and compensator 4th . This distance is achieved with a focal length between 600 mm and 700 mm. To simplify matters, only the positions of the ten focal lengths presented are drawn here.

For motorized adjustment of the movable first and second zoom group 3rd , 4th , the pupil compensation group 6 according to the movements 18th as well as for inserting or folding in the warm panel 10 b In the beam path from the focal length f _WS is a control unit 16 (corresponding 4th ) intended.

In 19th are three zoom positions of the IR zoom lens acc. 16 drawn. The lower lens section a) shows the wide-angle position, the upper the telephoto position. Here you can clearly see that the variator 3rd and the compensator 4th have moved towards the picture. Also the pupil compensation group 6 has moved and moved towards the image. The middle picture b) shows the zoom system 1 immediately before the warm screen is swung in 10 b . The pupil compensation group 6 has the same position as in the wide-angle position a). It can be seen that the central bundle fills the full front lens. A further enlargement would lead to vignetting, which is why the warm screen is at this point 10 b introduced.

Reference list

1

IR zoom lens

2nd

Front group

3rd

first zoom group

4th

second zoom group

5

Main lens

6

Pupil compensation group

7

first deflecting element

8th

second deflection element

9

Relay group

10 a

Cold fade

10 b

Warm glare

11

detector

12th

Intermediate image level

13

Cooling case

14

Entry window

16

Control unit

20

First zoom group (variator)

21

Second zoom group (compensator)

22

History distance first, second zoom group

23

Course of the pupil compensation group

Claims (14)

IR zoom lens (1) comprising one optical front group (2), one at least one optical zoom group (3, 4) that can be moved along the imaging beam path, one main lens (5) for imaging an intermediate image in an intermediate image plane (12) and an optical one Relay group (9) for imaging the intermediate image on an IR detector (11), characterized in that the relay group (9) is followed by a heat shield (10b) which can be introduced into the imaging beam path, the main lens (5) and the relay group ( 9) an optical pupil compensation group (6) which is displaceable along the imaging beam path is arranged to compensate for the positional shift of the entrance pupil by introducing the warm diaphragm (10b). IR zoom lens (1) after Claim 1 , the pupil compensation group (6) being arranged between the main objective (5) and the intermediate image plane (12). IR zoom lens (1) after Claim 1 or 2nd , wherein the pupil compensation group (6) has a positive refractive power. IR zoom lens (1) according to one of the Claims 1 to 3rd , wherein the pupil compensation group (6) comprises a converging lens. IR zoom lens (1) according to one of the preceding claims, wherein at least one deflection element (7, 8) for deflecting the imaging beam path is arranged between the main lens (5) and the relay group (9). IR zoom lens (1) after Claim 5 , A first deflection element (7) being arranged between the pupil compensation group (6) and the intermediate image plane (12) and a second deflection element (8) between the intermediate image plane (12) and the relay group (9). IR zoom lens (1) according to one of the preceding claims, wherein a displaceable first zoom group (3) and a displaceable second zoom group (4) are provided. IR zoom lens (1) after Claim 7 , wherein the first zoom group (3) has a negative refractive power. IR zoom lens (1) after Claim 7 or 8th , wherein the second zoom group (4) comprises a single lens. IR zoom lens (1) according to any one of the preceding claims, wherein the main lens (5) has a positive refractive power. IR zoom lens (1) according to one of the preceding claims, wherein means (16) for introducing the warm aperture (10 b) are provided when a limit value of the system focal length is exceeded. IR zoom lens (1) according to one of the preceding claims, wherein means (16) are provided for shifting the pupil compensation group (6) when the limit value of the system focal length is exceeded. Thermal imaging device (15) with an IR zoom lens (1) according to one of the preceding claims, with an IR detector (11) arranged inside a cooling housing (13). Thermal imaging device (15) after Claim 13 , A cold diaphragm (10 a) being connected upstream of the IR detector (11) in the cooling housing (13).

Images