Observation instrument for observing a celestial body

Abstract

Observation instrument (12) for observing a celestial body (14) with • an entrance plane (18) with an entrance slit (20) for admitting at least part of a celestial body image, • a spectrograph (22) for splitting light (24) entering through the entrance slit (20) into spectral lines (26), • an image generating device (28) for generating the celestial body image on the input plane (18), comprising ◯ a first reflection element (30) with a first optical axis (32), ◯ a second reflection element (34) with a second optical axis (36), wherein the first reflection element (30) is in optical operative connection with the second reflection element (34), wherein the second optical axis (36) has a translational and / or angular offset with respect to the first optical axis (32), and wherein the first reflection element (30) is concave.

Description

[0001] The invention relates to an observation instrument for observing a celestial body.

[0002] An observation instrument for observing celestial bodies, known since the 1930s, is the so-called Schiefspiegler telescope. Until the late 1980s, such telescopes were regularly used by amateur astronomers and in observatories. A further development of the Schiefspiegler is described in US 8 947 778 B2. An application is also shown in US 2011 / 0 051 121 A1. DE 36 06 547 A1 is also cited as prior art.

[0003] Spectroheliographs, among other instruments, are used to observe the Sun. A spectroheliograph is used to create a monochromatic image of the Sun. Sunlight passes through the lens of a telescope onto an entrance slit of the spectroheliograph, creating an image of the Sun at the entrance slit.

[0004] A narrow section of the solar image passes through the entrance slit and is broken down into its spectral lines, for example by means of a diffraction grating. By recording one of the spectral lines individually using a photographic plate, a monochromatic image of that section of the solar image can be created. In newer designs of spectroheliographs, the photographic plate is often replaced by an electronic image sensor. A corresponding spectroheliograph is known, for example, from US 7 209 229 B2 or US 2005 / 0 275 838 A1. In order to be able to image not just a section of the solar image but the entire solar image, it is necessary to move the solar image evenly across the entrance slit. This type of movement of an image of a celestial body across the observation instrument is also referred to as "scanning". It is essential to coordinate the speed of movement of the image of the celestial body with the photographic plate orthe electronic image sensor.

[0005] In order to be able to image details on the sun using the spectroheliograph, the width of the entrance slit in relation to the diameter of the solar image must not exceed a certain limit. However, a narrow entrance slit has the disadvantage, among other things, of being difficult to manufacture. Particular challenges lie in producing the slit edges with sufficient parallelism and surface quality to avoid irregularities in the image. Furthermore, a narrow slit is sensitive to contamination. A correspondingly small solar image also has the effect of generating considerable heat at the focal point, which can lead to atmospheric turbulence and tension, particularly in the area of ​​the entrance slit, and thus impairing image quality. Various measures are known to overcome these disadvantages. For example, one can try to create the largest possible image of the sun.The use of cooling measures, such as water cooling or the use of heat shields, is also known.

[0006] For the telescope types used in spectroheliographs, such as refractors or Gregory telescopes, such measures result in large installation space requirements and high costs. Furthermore, the images produced with such optics exhibit field curvature due to their inherent design.

[0007] The object of the present invention is therefore to provide a spectroheliograph which has a high image quality with a small installation space requirement and is simple and inexpensive to manufacture.

[0008] The object is achieved according to the invention by an observation instrument having the features of patent claim 1.

[0009] Advantageous embodiments and further developments of the invention are specified in the dependent claims.

[0010] An observation instrument according to the invention for observing a celestial body comprises an entrance plane with an entrance slit for admitting at least part of a celestial body image, a spectrograph for decomposing light incident through the entrance slit into spectral lines, and an image generation device for generating the celestial body image on the entrance plane. The image generation device comprises a first reflection element with a first optical axis and a second reflection element with a second optical axis, wherein the first reflection element is in optically operative connection with the second reflection element, and wherein the second optical axis has a translational and / or angular offset with respect to the first optical axis. The image generation device can thus be designed in particular according to the principle of a slanting mirror. The observation instrument is preferably designed as a spectroheliograph.

[0011] The optical axis is preferably the axis that runs through the center of an optical effective surface of the corresponding reflection element and is aligned orthogonal to the optical effective surface at the center. If the second optical axis has a translational offset with respect to the first optical axis, the first optical axis and the second optical axis preferably do not lie on top of one another. In this case, the first optical axis and the second optical axis are particularly preferably arranged parallel to one another. If the second optical axis has an angular offset with respect to the first optical axis, the first optical axis and the second optical axis preferably intersect at an axis intersection point and thus enclose an axis angle. The axis intersection point can lie inside or outside the imaging device or the observation instrument.If the second optical axis has a translational and an angular offset relative to the first optical axis, the first optical axis and the second optical axis are preferably arranged skewed relative to one another.

[0012] The beam path preferably runs in such a way that the light incident on the observation instrument is guided from the first reflection element to the second reflection element and from the second reflection element to the input plane. Particularly preferably, the beam path from the second reflection element to the input plane is guided past the first reflection element. This makes it possible, in particular, to avoid the need for the light emanating from the second reflection element to be guided through the first reflection element, for example by means of an opening in the first reflection element, or to be guided past the first reflection element by means of an additional optical element. Such guidance of the beam path can be made possible by the second optical axis having a translational and / or angular offset relative to the first optical axis.

[0013] Starting from the second reflection element, the beam path preferably extends to the input plane, whereby a portion of the light incident on the input plane can pass through the input slit onto the spectrograph. To decompose the light incident through the input slit into spectral lines, the spectrograph can, in particular, comprise a diffraction grating.

[0014] A collimating lens of the spectrograph can be arranged in the beam path between the entrance slit and the diffraction grating. The collimating lens is preferably designed as a Schiefspiegler lens. The advantages of the Schiefspiegler lens, particularly color purity and the long focal length in a small installation space, can also have positive effects.

[0015] The first reflection element is preferably arranged facing the second reflection element. The first reflection element and the second reflection element are preferably referred to as facing each other if they are arranged such that light incident on the first reflection element can impinge directly on the second reflection element after being reflected by the first reflection element, i.e., without further deflection. Such an arrangement, particularly in combination with the translational and / or angular offset of the two optical axes, makes it possible to achieve a folded beam path. In particular, a long beam path can be accommodated in a comparatively short installation space.

[0016] Particularly preferably, the second reflection element is arranged outside an incident beam path of the first reflection element. This avoids stray light and diffraction phenomena that can be caused by a second reflection element arranged in the incident beam path of the first reflection element. Furthermore, the first reflection element is not shaded by the second reflection element, so that such an imaging device can be designed to be comparatively bright.

[0017] According to the invention, the first reflection element is concave. The first reflection element can, in particular, be spherically concave. The term "concave" used here and below preferably describes the shape of a first optical effective surface of the first reflection element, onto which the incident light impinges. Due to the concave design, the first reflection element can have a first focal point. With a spherically concave design of the first reflection element, the first optical effective surface preferably has a constant first radius of curvature.

[0018] The second reflection element can be convex, in particular spherically convex, concave, or flat. The term "convex" used here and below preferably describes the shape of a second optical effective surface of the second reflection element, onto which the incident light emanating from the first reflection element impinges. Due to its convex shape, the second reflection element can have a second focal point. With a spherically convex shape of the second reflection element, the second optical effective surface preferably has a constant second radius of curvature.

[0019] As an alternative to a spherical cross-section, each of the optical concave or convex effective surfaces described here and below can have a conical, in particular a parabolic, elliptical, or flattened elliptical, cross-section. For fine correction of image aberrations, the first reflection element and / or the second reflection element can have a non-rotationally symmetrical design, for example a cardioid or toroidal shape. Spherical surfaces can have the advantage of being cost-effective to manufacture. Furthermore, they can be easy to center because their radius of curvature is constant, in contrast to a surface with a parabolic cross-section, for example. In the case of a concave or convex design of one of the reflection elements, the corresponding optical axis preferably runs as a normal through a vertex of curvature of the respective reflection element.

[0020] A convex design of the second reflection element is preferably used in combination with a concave design of the first reflection element. This combination allows a long focal length and thus a comparatively large image of celestial bodies to be achieved in a relatively small installation space.

[0021] In a preferred embodiment of the invention, the Petzval sum of the image generation device is 0. As a result, the celestial body image generated on the input plane has no image curvature. Preferably, the first radius of curvature and the second radius of curvature are equal or almost equal in magnitude. Thus, the Petzval sum of 0 can be realized exclusively with the first reflection element and the second reflection element. If the first radius of curvature and the second radius of curvature are equal or almost equal in magnitude, a first focal length of the first reflection element and a second focal length of the second reflection element can also be equal or almost equal in magnitude. Preferably, the image generation device is designed such that it has a total focal length that corresponds approximately to 1 2 / 3 times (1.67 times) the first focal length or the second focal length.

[0022] In a further development of the invention, the first reflection element is arranged so as to be tiltable about a first scanning axis, preferably arranged parallel to the entrance slit, and / or the second reflection element is arranged so as to be tiltable about a second scanning axis, preferably arranged parallel to the entrance slit. By tilting the first reflection element and / or the second reflection element, the celestial body image can be moved on the entrance plane and thus across the entrance slit. The scanning of the celestial body image can thus take place by tilting the first reflection element and / or the second reflection element about the first scanning axis or the second scanning axis. The arrangement of the first scanning axis and / or the second scanning axis parallel to the entrance slit makes it easy to guide the celestial body image across the entrance slit orthogonal to the entrance slit.

[0023] Alternatively, the first scanning axis and / or the second scanning axis can be arbitrarily oriented with respect to the entrance slit, and at least one deflecting element can be arranged in the beam path between the first reflection element and / or the second reflection element and the entrance plane. The at least one deflecting element can deflect the light emanating from the first reflection element and / or the second reflection element in such a way that, even when the first scanning axis and / or the second scanning axis are arranged non-parallel to the entrance slit, tilting the first reflection element about the first scanning axis and / or tilting the second reflection element about the second scanning axis causes the celestial body image to move orthogonally to the entrance slit. This configuration is preferably described such that the first scanning axis and / or the second scanning axis are arranged mechanically non-parallel but optically parallel to the entrance slit.

[0024] Preferably, the first reflection element and / or the second reflection element is / are arranged so as to be tiltable when installed in the observation instrument. This allows the corresponding reflection element to be movable during the intended use of the observation instrument. The first reflection element can be arranged on the first scan axis such that it is intersected by the first scan axis. Correspondingly, the second reflection element can be arranged on the second scan axis such that it is intersected by the second scan axis. Preferably, the respective scan axis runs through the apex of curvature of the corresponding reflection element, particularly preferably to the respective optical axis. Preferably, only the first reflection element is arranged so as to be tiltable about the first scan axis. This allows the design effort to be reduced and the scanning process to be simplified.

[0025] The image generation device is preferably designed as a mirror optics system. The optical elements that have a significant influence on the image quality or the image scale are therefore preferably designed as essentially reflective elements. This makes it possible to generate a high-quality image of a celestial body on the input plane, the quality of which is not significantly impaired, in particular by the wavelength or the angle of the incident light. Preferably, the first reflection element and the second reflection element are each designed as a mirror. The image generation device designed as a mirror optics system can comprise at least one field lens, which is preferably arranged in the beam path close to the input plane. This allows an exit pupil of the image generation device to be imaged onto an entrance pupil of the collimating objective.The at least one field lens usually has no significant influence on the image quality or the image scale.

[0026] The imaging device can be arranged in an instrument housing of the observation instrument. This simplifies transport to and installation at the site of use of the observation instrument, particularly because the positioning and adjustment of the imaging device does not have to be adjusted to the other components of the observation instrument at each new site of use. Preferably, the imaging device is arranged entirely within the instrument housing. The observation instrument preferably has precisely one instrument housing, in which, particularly preferably, the entire observation instrument is arranged.

[0027] The observation instrument can be combined with a compensation device designed to compensate for the relative movement between the celestial body image and the observation instrument caused by the Earth's rotation. The compensation device can be designed, in particular, as a celostat or heliostat. The compensation device can be arranged, in particular directly, on the observation instrument. Furthermore, the compensation device can be arranged in the instrument housing.

[0028] If the first reflection element is arranged so as to be tiltable about the first scanning axis and / or the second reflection element is arranged so as to be tiltable about the second scanning axis, the respective tiltably arranged reflection element is preferably mounted so as to be tiltable about the corresponding scanning axis relative to the instrument housing.

[0029] In particular, if the image generation device is arranged in the instrument housing of the observation instrument, the observation instrument can be designed to be portable. The observation instrument is referred to here and below as portable if, due to its shape and weight, it can be carried by an average adult. For this purpose, the observation instrument has a mass of preferably 30 kg or less. This can simplify transport and significantly expand the range of applications of the observation instrument. In one embodiment of the invention, the mass of the observation instrument can be in the range of 20 to 30 kg. The observation instrument preferably has a length of approximately 2 m. In a further embodiment of the invention, the mass of the observation instrument can be in the range of 8 to 20 kg. The observation instrument preferably has a length of approximately 90 cm.

[0030] In a preferred embodiment of the invention, the observation instrument comprises at least one electronic image sensor for detecting at least one of the spectral lines. For this purpose, the spectral lines generated by the spectrograph can be incident on the electronic image sensor. By detecting at least one of the spectral lines, the electronic image sensor can create a monochrome image of the portion of the celestial body image passing through the entrance slit. By using an electronic image sensor, the spectral line to be recorded can be easily selected electronically and further processed.

[0031] A camera lens can be arranged between the spectrograph's diffraction grating and the electronic image sensor. The camera lens is preferably designed as a skewed mirror. The advantages of the skewed mirror, particularly color purity and the long focal length in a small installation space, can also have positive effects.

[0032] The image generation device is preferably correlated with the at least one electronic image sensor. The images taken by the at least one image sensor are generally composed of several individual images of each of the parts of the celestial body image passing through the entrance slit. By correlating the image generation device with the at least one image sensor, the function of the at least one image sensor and movement around the scan axis can be coordinated. The correlation is particularly advantageous with regard to the frequency at which the at least one image sensor takes the individual images and the order in which the individual images are combined to form an overall image of the celestial body image. In a simple case, the correlation can be purely temporal. The starting time and / or the speed of the tilting around the scan axis are known to the at least one electronic image sensor.The individual images can then be assembled by a computer, particularly based on these parameters. An electronic coupling of the movement around the at least one scanning axis and the at least one electronic image sensor is not required for this purpose. Preferably, the image generation device and the at least one electronic image sensor are electronically coupled to one another, particularly preferably by means of an electronic data processing unit.

[0033] In a preferred embodiment of the invention, the at least one electronic image sensor is arranged immovably relative to the spectrograph. This allows the observation instrument to be manufactured in a structurally simpler and more cost-effective manner. The at least one electronic image sensor preferably has a first dimension and a second dimension. The at least one image sensor can be arranged such that the at least one spectral line output by the spectrograph is aligned along the first dimension. If multiple spectral lines are output by the spectrograph, the spectral lines can be arranged parallel to one another in the direction of the second dimension. The first dimension of a detected spectral line can thus contain location information about the detected content. The second dimension of a detected spectral line can contain color information about the detected content.The selection of one of the at least one spectral line to be detected, falling at any point on the at least one image sensor, and its arrangement in the overall image of the celestial body can be carried out electronically.

[0034] The at least one electronic image sensor can be designed as a line sensor. This allows the installation space required by the at least one electronic image sensor to be reduced and the observation instrument to be manufactured more cheaply. The use of a line sensor can also reduce the computational effort required to create the image of the celestial body. The line sensor is preferably arranged parallel to the at least one spectral line output by the spectrograph such that the at least one spectral line to be detected falls on the line sensor. The line sensor is thus preferably arranged along the first dimension. The selection of the at least one spectral line to be detected can thus be made by arranging the line sensor along the second dimension. The additional acquisition of color information is therefore not necessary to create a monochrome image.A line sensor is therefore sufficient to create a monochromatic image of celestial bodies.

[0035] Preferably, at least one of the following components has an electronic interface: • the image forming device, • the spectrograph.

[0036] The electronic interface of the spectrograph is preferably arranged on the diffraction grating. The diffraction grating can be arranged so as to be displaceable, in particular rotatable, relative to the entrance slit or the collimation lens, particularly for adjusting the wavelength. Preferably, the wavelength of the diffraction grating can thus be adjusted using the electronic interface of the spectrograph. Furthermore, the at least one electronic image sensor can also have an electronic interface.

[0037] The focusing of the observation instrument can be achieved by changing the arrangement, in particular the distance, of the respective components to each other in at least one of the following component pairs: • Image forming device - entrance slit, • Collimation lens - entrance slit, • Camera lens - image sensor.

[0038] Preferably, the focus is adjustable via the electronic interface of at least one of the corresponding components. In particular, at least one of the following components can also have the electronic interface: entrance slit, collimation lens, camera lens.

[0039] The electronic interface is preferably designed as an ASCOM interface. The ASCOM interface is a standardized software interface for astronomical equipment. This allows electronic communication between the individual components to take place via a standardized software interface, thus facilitating communication. Operation of the system using a central computer, which particularly preferably also has an ASCOM interface, is also significantly simplified. It is particularly advantageous if the spectrograph has an ASCOM interface. The ASCOM interface of the imaging device preferably comprises an ASCOM interface of the scan axis.

[0040] An embodiment of the invention is explained with reference to the following figure. It shows: Fig. 1 an embodiment of an observation instrument.

[0041] Fig. 1 shows an observation instrument 12 designed as a spectroheliograph 10 for observing a celestial body 14, in particular the sun 16. The observation instrument 12 comprises an entrance plane 18 with an entrance slit 20 for admitting at least part of a celestial body image, a spectrograph 22 for decomposing light 24 incident through the entrance slit 20 into spectral lines 26, and an image generating device 28 for generating the celestial body image on the entrance plane 18. The image generating device 28 comprises a first reflection element 30 with a first optical axis 32, and a second reflection element 34 with a second optical axis 36, wherein the first reflection element 30 is in optically operative connection with the second reflection element 34, and wherein the second optical axis 36 encloses an axial angle 38 with the first optical axis 32.Thus, the second optical axis 36 has an angular offset relative to the first optical axis.

[0042] The first optical axis 32 runs as a normal through a curvature vertex of a first optical effective surface 40 of the first reflection element 30. In a corresponding manner, the second optical axis 36 runs as a normal through a curvature vertex of a second optical effective surface 42 of the second reflection element 34.

[0043] Preferably, the beam path 44 extends such that the light 24 incident on the observation instrument 12 is guided from the first reflection element 30 to the second reflection element 34 and from the second reflection element 34 to the input plane 18. The beam path 44 can be guided from the second reflection element 34 to the input plane 18 past the first reflection element 30. This can, in particular, prevent light 45 emanating from the second reflection element 34 from having to be guided through the first reflection element 30, for example, by means of an opening in the first reflection element 30, or past the first reflection element 30 by means of an additional optical element.

[0044] Starting from the second reflection element 34, the beam path 44 preferably extends to the input plane 18, wherein a portion of the light 24 incident on the input plane 18 can pass through the input slit 20 onto the spectrograph 22. To decompose the light 24 incident through the input slit 20 into spectral lines 26, the spectrograph 22 can, in particular, have a diffraction grating 46.

[0045] A collimating lens 48 of the spectrograph 22 can be arranged in the beam path 44 between the entrance slit 20 and the diffraction grating 46. Preferably, the collimating lens 48 is designed as a Schiefspiegler. Fig. 1, the observation instrument 12 can be combined with a coelostat 49 to compensate for the relative movement between the celestial body image and the observation instrument 12 caused by the Earth's rotation. The coelostat 49 can comprise a first reflector 49a and a second reflector 49b. The coelostat 49 can be arranged in the beam path 44 of the light 24 emitted by the observed celestial body 14, between the observed celestial body 14 and the first reflection element 30.

[0046] As in Fig. As shown in Figure 1, the first reflection element 30 is preferably arranged facing the second reflection element 34. Together with the at least angular offset of the second optical axis 36 from the first optical axis 32, a folded beam path 50 can be achieved. Fig. 1 also shows that the second reflection element 34 is arranged outside an incident beam path 52 of the first reflection element 30.

[0047] The Fig. The first reflection element 30 shown in Figure 1 is spherically concave. The first optical effective surface 40 thus has a constant first radius of curvature 54. The second reflection element 34 can be spherically convex. The second optical effective surface 42 can thus have a constant second radius of curvature 56. The Petzval sum of the image generation device 28 is preferably 0. As a result, the celestial body image generated on the input plane 18 has no image curvature. The Petzval sum of 0 can be achieved by ensuring that the first radius of curvature 54 and the second radius of curvature 56 are equal in magnitude.

[0048] In the Fig. 1, the first reflection element 30 is arranged so as to be tiltable about a first scanning axis 58, which is preferably arranged mechanically and optically parallel to the entrance slit. By tilting the first reflection element 30, the celestial body image can be moved on the entrance plane 18 and thus across the entrance slit 20. The celestial body image can thus be scanned by tilting the first reflection element 30 about the first scanning axis 58. Due to the tiltable arrangement of the first reflection element 30, the first reflection element 30 can be moved during the intended use of the observation instrument 12. The first reflection element 30 can be arranged on the first scanning axis 58 such that it is intersected by the first scanning axis 58. Preferably, only the first reflection element 30 is arranged so as to be tiltable about the first scanning axis 58. The second reflection element 34, on the other hand, can be arranged immovably.This can reduce the design effort and simplify the scanning process.

[0049] The Fig. The image generation device 28 shown in Figure 1 can be designed as a pure mirror optics. Thus, preferably, only substantially reflective elements are located in the beam path 44 of the image generation device 28. Thus, the first reflection element 30 and the second reflection element 34 are each preferably designed as a mirror.

[0050] The imaging device 28 can be arranged in an instrument housing 60 of the observation instrument 12. Preferably, the imaging device 28 is arranged entirely within the instrument housing 60. Preferably, the observation instrument 12 has precisely one instrument housing 60, in which the entire observation instrument 12 is particularly preferably arranged. The first reflection element 30 is preferably mounted so as to be tiltable relative to the instrument housing 60 about the first scanning axis 58. In particular, by arranging the entire observation instrument 12 in the instrument housing 60, the observation instrument 12 can be designed to be portable.

[0051] The observation instrument 12 can include an electronic image sensor 62 for detecting at least one of the spectral lines 26. For this purpose, the spectral lines 26 generated by the spectrograph 22 can fall onto the electronic image sensor 62. A camera lens 64 can be arranged between the diffraction grating 46 of the spectrograph 22 and the electronic image sensor 62. The camera lens 64 is preferably designed as a Schiefspiegler lens. By detecting at least one of the spectral lines 26 by the electronic image sensor 62, a monochrome image of the part of the celestial body image passing through the entrance slit 20 can be created.

[0052] Preferably, the image generation device 28 is correlated with the electronic image sensor 62. Preferably, the image generation device 28, in particular in the form of the first scanning axis 58, and the electronic image sensor 62 are electronically coupled to one another by means of an electronic data processing unit 66.

[0053] The electronic image sensor 62 can be arranged immovably relative to the spectrograph 22. The electronic image sensor 62 preferably has a first dimension 68 and a second dimension 70. The image sensor 62 can be arranged such that the at least one spectral line 26 output by the spectrograph 22 is aligned along the first dimension 68. If there are multiple spectral lines 26 output by the spectrograph 22, the spectral lines 26 can be arranged parallel to one another in the direction of the second dimension 70. The first dimension 68 of a detected spectral line 26 can thus contain location information about the detected content. The second dimension 70 of a detected spectral line 26 can contain color information about the detected content.The selection of one of the at least one spectral line 26 to be detected, falling at any point on the image sensor 62, and its arrangement in the overall recording of the celestial body image can be carried out electronically.

[0054] Preferably, at least one of the following components has an electronic interface: • the image forming device 28, • the spectrograph 22.

[0055] The electronic interface of the spectrograph 22 is preferably arranged on the diffraction grating 46. The diffraction grating 46 can be arranged displaceably, in particular rotatably, relative to the entrance slit 20 or the collimation lens 48, in particular for adjusting the wavelength. Preferably, the wavelength of the diffraction grating 46 can thus be adjusted using the electronic interface of the spectrograph 22. Furthermore, the at least one electronic image sensor 62 can also have an electronic interface.

[0056] The focusing of the observation instrument 12 can be achieved by changing the arrangement, in particular the distance, of the respective components to each other in at least one of the following component pairs: • Image forming device 28 - entrance slit 20, • Collimation lens 48 - entrance slit 20, • Camera lens 64 - Image sensor 62.

[0057] Preferably, the focus is adjustable via the electronic interface of at least one of the corresponding components. In particular, at least one of the following components can also have the electronic interface: entrance slit 20, collimation lens 48, camera lens 64. The electronic interface is preferably designed as an ASCOM interface. List of reference symbols 10 Spectroheliograph 12 Observation instrument 14 celestial bodies 16 Sun 18 Entrance level 20 Entrance gap 22 Spectrograph 24 light 26 spectral line 28 Image forming device 30 first reflection element 32 first optical axis 34 second reflection element 36 second optical axis 38 Axis angle 40 first optical effective area 42 second optical effective area 44 Beam path 45 light emanating from the second reflection element 46 diffraction gratings 48 Collimating lens 49 Celostat 49a first reflector 49b second reflector 50 folded beam path 52 incident beam path 54 first radius of curvature 56 second radius of curvature 58 first scan axis 60 instrument housings 62 image sensor 64 Camera lens 66 electronic data processing unit 68 first dimension 70 second dimension

Claims

[1] Observation instrument (12) for observing a celestial body (14) with • an entrance plane (18) with an entrance slit (20) for admitting at least part of a celestial body image, • a spectrograph (22) for splitting light (24) entering through the entrance slit (20) into spectral lines (26), • an image generating device (28) for generating the celestial body image on the input plane (18), comprising ◯ a first reflection element (30) with a first optical axis (32), ◯ a second reflection element (34) with a second optical axis (36), wherein the first reflection element (30) is in optical operative connection with the second reflection element (34), wherein the second optical axis (36) has a translational and / or angular offset with respect to the first optical axis (32), and wherein the first reflection element (30) is concave. [2] Observation instrument according to claim 1 characterized by that the first reflection element (30) is arranged facing the second reflection element (34). [3] Observation instrument according to one of the preceding claims, characterized by that the second reflection element (34) is arranged outside an incident beam path (52) of the first reflection element (30). [4] Observation instrument according to one of the preceding claims, characterized by that the first reflection element (30) is spherically concave. [5] Observation instrument according to one of the preceding claims, characterized by that the second reflection element (34) is convex, in particular spherically convex, concave or flat. [6] Observation instrument according to one of the preceding claims, characterized by that the Petzval sum of the image generating device (28) is 0. [7] Observation instrument according to one of the preceding claims, characterized by that the first reflection element (30) is arranged so as to be tiltable about a first scanning axis (58), preferably arranged parallel to the entrance slit (20), and / or the second reflection element (34) is arranged so as to be tiltable about a second scanning axis, preferably arranged parallel to the entrance slit (20). [8] Observation instrument according to one of the preceding claims, characterized by that the image generating device (28) is designed as a mirror optics. [9] Observation instrument according to one of the preceding claims, characterized by that the image generating device (28) is arranged in an instrument housing (60) of the observation instrument (12). [10] Observation instrument according to one of the preceding claims, characterized by that the observation instrument (12) is designed to be portable. [11] Observation instrument according to one of the preceding claims, characterized bythat the observation instrument (12) comprises at least one electronic image sensor (62) for detecting at least one of the spectral lines (26). [12] Observation instrument according to claim 11, characterized by that the image generating device (28) is correlated with the at least one electronic image sensor (62). [13] Observation instrument according to one of claims 11 to 12, characterized by that the at least one electronic image sensor (62) is arranged immovably relative to the spectrograph (22). [14] Observation instrument according to one of the preceding claims, characterized by that at least one of the following components has an electronic interface: • the image forming device (28), • the spectrograph (22).

Images