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    • 专利摘要:
    The invention relates to an anastigmat telescope with three aspherical mirrors comprising: - means (5) linear displacement of the third mirror (M3) on the optical axis of the telescope (O) so as to vary the focal length of the telescope between a focal length minimum (fmin) and a maximum focal length (fmax), - a deformable mirror (MD) and controllable, - means (10, 10 ') of variation of the optical path between the deformable mirror (MD) and the detector (D), the third mirror having a new taper (c'3) determined from an initial taper (c3), the initial taper (c3) being determined from the Korsch equation, the new taper (c'3) being determined so that the telescope has, without the presence of said deformable mirror and for the minimum and maximum focal lengths, compensable aberrations by said deformable mirror (MD), - said fixed median position (Pm) of said deformable mirror and the shape of its surface respectively po ur the values of minimum (Smin) and maximum (Smax) focal length, being determined so as to correct said compensable aberrations and to optimize the image quality in the focal plane of the telescope according to a predetermined criterion.
    公开号:FR3060134A1
    申请号:FR1601769
    申请日:2016-12-13
    公开日:2018-06-15
    发明作者:Nicolas TETAZ
    申请人:Thales SA；
    IPC主号:
    专利说明:

    The field of the invention is that of telescopes, in particular that of observation telescopes embedded in satellites. More specifically, the field of the invention relates to catoptric systems with large focal lengths.
    îo STATE OF THE ART
    Current space telescopes are single focal length. A known type of telescope is the Korsh type telescope. The Korsch type telescope, also called TMA (acronym of the English expression “Three Mirors Anastigmat”) is an anastigmat telescope with three aspherical mirrors (either of the Concave-Convex-Concave type) which comprises at least one first M1 mirror concave, a second convex mirror M2 and a third concave mirror M3. The three mirrors being aspherical and of classical shape for such a telescope. The first, second and third mirrors
    M1, M2 and M3 are aspherical, of fixed shapes, each mirror being characterized by at least two parameters, a radius of curvature R and a conic c.
    This optical system has an optical axis O well known to those skilled in the art, defined by the radius passing through the center of the entrance pupil Pe and perpendicular to this pupil.
    The three mirrors M1, M2 and M3 are arranged so that the first mirror and the second mirror form from an object to infinity an intermediate image located between the second mirror and the third mirror, the third mirror forming this intermediate image a final image in the focal plane of the telescope in which a detector D is placed. By application of the Korsch equations well known to those skilled in the art, the respective positions and parameters of the three mirrors are easily calculated. The theoretical solution is of very good quality, which makes all the interest of this type of telescope.
    The quality of an optical system is evaluated by comparison between the ideal light wave limited by diffraction and the real light wave at the output of the optical system taking into account the defects of the optical system crossed. The analysis of the difference between theoretical wave and real wave makes it possible to identify the types of defects or aberrations of the optical system.
    It is known that the main geometric aberrations are: spherical aberration, astigmatism, coma, field curvature (defocus in the field) and distortion.
    Polynomials, and more particularly Zernike polynomials, are conventionally used to more easily qualify the different types of aberrations of a wavefront (ie a surface) at the output of an optical system.
    Zernike surfaces are the most commonly used. A Zernike surface is defined in polar coordinates in a space (p, Θ, z), and if z (p, Θ) represents the z coordinate of a point on this surface, we have the relation:
    i + Vi-O + aW + Σ ( -Α
    Zj being a Zernike polynomial of order j and Cj being the constant associated with this polynomial, j being an index varying respectively between 0 and an integer, k being the conicity constant and c the curvature of the surface.
    Any surface decomposed according to polynomials is called φ-polynomial surface. This surface is therefore characterized by values of the coefficients of these polynomials.
    The advantage of decomposing waveforms into orthogonal Zernicke polynomials is that each polynomial of the base considered corresponds to a different aberration category. It is then possible to know the nature of the aberrations present in a wavefront.
    The table below illustrates the different "Fringe Zernike" polynomials according to their order (here 1 to 16), as well as the corresponding aberration type.
    Order Polynomial Aberration (s) 1 1 Piston 2 p Cos [0] Tilt in x 3 p Sin [9) Inclination in y 4 -1 + 2 p 2 Focus 5 p 2 Cos [2 ej 0 ° astigmatism 6 p 2 Sinl2 Θ] Astigmatism at 45 " 7 p (-2 + 3 p 2 ) Cos [0] Coma in x 8 p (-2 + 3 p 2 ) Sin [9J Coma in y 9 1- 6 p 2 + 6 p 4 Sphericity and focus 10 p 3 Cos [3 Θ] Sort sheet 11 p 3 Sin (3 Θ] Sort sheet 12 p 2 (-3 + 4 p 2 ) Cos [2 Θ] Astigmatism order 2 13 p 2 (-3 + 4 p 2 ) Sin [2 Θ] Astigmatism order 2 14 p (3 - 12 p 2 + 10 p *) Cos [6] Coma in x order 2 15 p (3 - 12 p 2 + 10 p 4 ) Sîn [0J Coma in order 2 16 -1 + 12 p 2 - 30 p 4 + 20 p® Sphericity order 2
    By adopting the definition of Fringe Zernike polynomials, the different types of aberration correspond to:
    -the focus corresponds to the term Z4, îo - astigmatism corresponds to the terms Z5 and Z6,
    -the coma at terms Z7 and Z8 and -the first order spherical aberration at Z9.
    - the second order spherical aberration at Z16
    Conventionally, it is known to improve the image quality of optical instruments by adding a deformable mirror MD as an exit pupil, commonly known as a "free form" or free form surface.
    The theoretical solution of the Korsch 3 mirror telescope being of very good quality, conventionally the deformable mirror does not intervene in the optical combination of the telescope and is used only to compensate for the defects due to the imperfection of realization of the real system compared to the theoretical solution.
    -on the ground to compensate for atmospheric turbulence (historical application of deformable mirrors),
    -in flight to compensate for defects in the M1 mirror. In fact, the mirror M1 being complex to produce, the deformable mirror makes it possible to relax the production constraints, while retaining good performance. Similarly, we can allow a lighter and less rigid M1 mirror, because its deformations will be compensated by the deformable mirror.
    Thus, a deformable mirror in exit pupil is generally used to correct the constant aberrations in the field. When positioned in the pupil of an instrument, the deformation of the deformable mirror by adding a Zernike polynomial introduces constant aberrations into the field. For example, if we introduce a non-zero value for the polynomial Z5 on the deformable mirror, each point of the field will be impacted by astigmatism.
    FIG. 1 illustrates a Korsch 10 type telescope having a deformable mirror MD arranged at the exit pupil Ps of the telescope.
    The surface S to be given to the deformable mirror to allow the correction of defects is called the "free form" surface, meaning that it has no symmetry of revolution.
    There are different definitions of freeform surfaces. Generally, each definition responds to a particular need, is adapted to a specific calculation and optimization mode. Whatever the mathematical formulation used to define a "freeform" surface, one can pass from one formulation to another by a mathematical conversion. In other words, the same “freeform” surface can be defined by several mathematical formulations. As examples, the mathematical definitions of a "freeform" surface can be as follows:
    -Freeform surface defined by XY polynomials. Clearly, this surface being defined in a space (x, y, z), if z (x, y) represents the coordinate z of a point of this surface, we have the relation:
    c (x 2 + y 2 ) ï (x, y) = -j ---------- = - f- + yli- (ï + k) c 2 (x 2 + + Σ4 c being the curvature of the surface, k being the conicity constant, A, being constants, i, j and k being indices varying between 0 and three whole numbers respectively.
    This surface corresponds to an extension of the classical definition of aspherical surfaces by generalizing it to a surface without symmetry of revolution;
    -Free form surface defined by φ polynomials, such as the Zernike polynomials defined above or the Q-Forbes polynomials The GW Forbes publication entitled “Characterizing the shape of freeform optics” 30.01.2012 / Vol.20, N ° 3 / Optics Express 2483 describes the surfaces defined by Q-Forbes phi-polynomials.
    -Freeform surface defined by local equations of “freeform” subsurface of different definition.
    -Freeform surface defined by hybrid descriptions such as, for example, surfaces mixing phi-polynomial surfaces and so-called "NURBS" surfaces, acronym meaning "Non-Uniform Rational Basis
    Splines ”or“ Uniform Rational B-Splines ”surfaces.
    The MD mirror is deformable and controllable, that is to say that any desired surface can be obtained by driving the mirror, the desired surface of the MD being calculated so as to compensate for the defects of the real system.
    We decompose the desired surface using polynomials, and we generate this surface by applying the right coefficients in a controlled manner via the mirror control system. We can then change the shape of the surface by modifying the values of the coefficients.
    It is thus possible by directly controlling the value of the coefficients Cj to introduce the desired aberrations into the design.
    An example of an MD mirror is a MADRAS deformable mirror (Active Deformable and Regulated Mirror for Space Applications.
    It can be interesting to be able to change the focal length in flight. Indeed, changing the focal length in flight makes it possible to change the field of view and / or the resolution of the image with one and the same instrument.
    There are currently two families of telescopes:
    bifocal telescopes which make it possible to take a high resolution image but on a narrow field or an image on a wide field but at lower resolution, and
    - telescopes with continuous reflective zoom allowing a change of focal length in flight.
    Examples of bifocal telescopes include those based on a separation of a common channel into two different focal length channels. The separation can be done spectrally: the same field is separated by a dichroic plate if the wavelength domain allows this spectral separation (eg visible and infrared). It can be done by separating the received flux into reflected flux and transmitted flux, by means of an optical density if it is a non-disjoint wavelength domain (ex: 50% of the flux is reflected, 50% transmitted).
    Advantages of these bifocal solutions with common channel separation:
    - Simultaneous bifocal function,
    - Observation of a common field of view.
    Disadvantages of these solutions:
    - Addition of optical elements (dichroic blade / density + mirrors / lenses specific to each channel),
    - Detectors specific to each channel,
    - If the spectral range of the channels is not disjoint, this requires losing a significant part of the flow,
    - Only bifocal.
    We can also cite the separation telescopes in the field of view: the two channels do not have the same field of view.
    Advantage of these bifocal separation solutions in the field of view:
    - simultaneous bifocal function.
    Disadvantages of these solutions:
    - Addition of optical elements: mirrors / lenses specific to each channel, îo - Detectors specific to each channel,
    - Observation of a different field of view,
    - Only bifocal.
    Another bifocal solution described in US Pat. No. 6084727 makes it possible to change the focal length of the telescope by inserting reflective elements on the optical path.
    Advantages of this solution for inserting reflective elements:
    - A single detector,
    - Observation of a common field.
    Disadvantages of this solution:
    - Addition of optical elements: mirrors specific to one of the channels,
    - Only bifocal,
    - Non-simultaneous bifocal function.
    As an example of a telescope with continuous reflective zoom, mention may be made of the telescope described in US Pat. No. 6,333,811; it is based on a Cassegrain type telescope with image recovery, the magnification of which is variable, which enables continuous zooming.
    Advantages of this solution:
    - A single detector,
    - Continuous zoom,
    - Observation of a common field,
    - No modification of the shape of the mirrors.
    Disadvantages of this solution:
    - The number of mirrors: 7 mirrors including 3 aspherical, 2 "freeform" and 1 plane mirror,
    - Moving two freeform mirrors whose positioning can be sensitive,
    - Cassegrain type telescope, therefore with limited field.
    There are also zoom lenses using mirrors with deformable curvature radii, an example of which is illustrated in the publication by Kristof Seidl et al. : "Wide field-of-view all-reflective objectives designed for multispectral îo image acquisition in photogrammetric applications".
    Advantages of this solution:
    - A single detector,
    - Continuous zoom,
    - Observation of a common field,
    - No moving of the mirrors.
    Disadvantages of this solution:
    - Too bulky for long focal lengths, for example greater than 10m,
    - Deformable mirrors only work for spherical mirrors with small diameters of the order of a few cm: they are therefore not compatible with pupil sizes of space telescopes typically greater than 0.5m.
    An object of the present invention is to overcome the aforementioned drawbacks by proposing a telescope with three aspherical multifocal mirrors, mono detector and compact, operating for large pupil diameters, with a field of view larger than that of a Cassegrain (> 1), and having a very high image quality for all focal lengths.
    DESCRIPTION OF THE INVENTION
    The subject of the present invention is an anastigmat telescope with three aspherical mirrors comprising at least a first concave mirror, a second convex mirror, a third concave mirror and a detector, and having an optical axis,
    the three mirrors being arranged so that the first mirror and the second mirror form from an object to infinity an intermediate image situated between the second mirror and the third mirror, the third mirror forming from this intermediate image a final image in the focal plane of the telescope in which the detector is placed, the first, second and third mirrors being of fixed shape characterized by at least one radius of curvature and a taper, the telescope further comprising:
    means of linear displacement of the third mirror on the optical axis of the telescope so as to vary the focal length of the telescope between at least a minimum focal length and a maximum focal length, the telescope at the minimum focal length having a first exit pupil at a first position, and the telescope at maximum focal length having a second exit pupil at a second position,
    - a deformable and controllable mirror, having a deformable surface and disposed at a fixed central position located between the first and the second position,
    means for varying the optical path between the deformable mirror and the detector configured so that the detector remains positioned in the focal plane of the telescope,
    the third mirror having a new conicity determined from an initial conicity, the initial conicity being determined from the Korsch equations, the new conicity being determined so that the telescope presents, without the presence of said deformable mirror and for the minimum and maximum focal lengths, aberrations compensated by said deformable mirror,
    said fixed central position of said deformable mirror and the shape of its surface respectively for the minimum and maximum focal values, being determined so as to correct said compensable aberrations and to optimize the image quality in the focal plane of the telescope according to a criterion predetermined.
    Preferably, the shape of the surface of the deformable mirror comprises at least a first and a second category of aberration. Advantageously, the first category of aberration is first-order spherical aberration and the second category of aberration is focus.
    Preferably, the shape of the surface of the deformable mirror further comprises a second order spherical aberration to further improve the image quality according to said criterion.
    Advantageously, the new taper deviates from the initial taper by more than 5% and less than 30%.
    According to one embodiment, a new conicity of the first mirror and a new conicity of the second mirror are determined from an initial conicity of the first mirror and an initial conicity of the second mirror respectively, the initial conicities being determined from the equations of Korsch, the new conicities being determined so as to further improve the image quality of said telescope according to said criterion.
    Preferably, the surface of the deformable mirror is defined from coefficients of polynomials. Advantageously, the coefficients are the coefficients of the Fringe Zernike polynomials.
    According to one embodiment, we define:
    -a positive astigmatism such as an astigmatism for which a tangential focus is located before a sagittal focus,
    -a negative astigmatism such as an astigmatism for which a sagittal focus is located before a tangential focus,
    -a positive coma like a coma for which a shape of the spot image of a source point is a "comet" whose tail moves away from the optical axis and,
    -a negative coma like a coma for which a shape of the spot image of a source point is a "comet" whose tail is directed towards the optical axis, the compensable aberrations being of positive astigmatism and positive coma for maximum focal length, positive astigmatism and negative coma for minimum focal length.
    According to one embodiment, the new taper of the third mirror is determined so as to modify the sign of the telescope's astigmatism for the minimum focal length, without the presence of an aspherical component.
    Preferably, the predetermined criterion consists in minimizing a waveform error.
    According to one embodiment, the telescope according to the invention has a plurality of intermediate focal lengths, the shape of the surface of the deformable mirror associated with each intermediate focal length being calculated from the shape of the surface for the minimum and maximum focal values .
    Other characteristics, objects and advantages of the present invention will appear on reading the detailed description which follows and with reference to the appended drawings given by way of nonlimiting examples and in which:
    FIG. 1, already cited, illustrates a monofocal Korsch type telescope having a deformable mirror placed at the level of the exit pupil of the telescope.
    FIG. 2 illustrates a multifocal Korsch type telescope seen in a YZ plane, the focal length being made variable by deglazing the third mirror on the optical axis. Figure 2a describes the optical system for maximum focal length and Figure 2b describes the optical system for minimum focal length.
    Figure 3 illustrates the telescope of Figure 2 seen in the XZ plane, Figure 3a describes the optical system for maximum focal length and Figure 3b describes the optical system for minimum focal length.
    FIG. 4a describes a first variant of means for varying the optical path between the third mirror and the detector D.
    FIG. 4b illustrates a second variant of means for varying the optical path between the third mirror and the detector D in which the detector
    D is fixed, the means for varying the optical path comprising two roof-shaped mirrors T1 and T2, for a position of the mirror T2.
    FIG. 4c illustrates the second variant of means for varying the optical path between the third mirror and the detector D in which the detector D is fixed, the means for varying the optical path comprising two mirrors T1 and T2 in the form of a roof, for a other position of the T2 mirror.
    FIG. 5 illustrates the aberrations present in the focal plane for the bifocal telescope whose aspherical mirrors M1, M2 and M3 have the initial parameters obtained by solving the Korsch equations. Figure 5a illustrates these aberrations when the telescope operates at maximum focal length, and Figure 5b illustrates these aberrations when the telescope operates at minimum focal length.
    Figure 6 describes the sign convention used for certain categories of aberrations.
    Figure 7 shows schematically a Korsh type telescope according to the invention.
    FIG. 8 illustrates, for the initial system, the resulting aberrations following the introduction of spherical aberration Z9md on a deformable mirror as a function of its relative position relative to the effective exit pupil, when MD is placed downstream of the effective exit pupil. Figure 8a corresponds to Z9 M d <0 and Figure 8b corresponds to Z9 M d> 0.
    FIG. 9 illustrates, for the initial system, the resulting aberrations following the introduction of spherical aberration Z9md on a deformable mirror as a function of its relative position relative to the effective exit pupil, when MD is placed upstream of the effective exit pupil. Figure 9a corresponds to Z9md <0 and Figure 9b corresponds to Z9md> 0.
    FIG. 10 describes the evolution of the mean value of the telescope astigmatism as a function of the taper value of the M3.
    Figure 11 illustrates the different aberrations present in the focal plane of the telescope, with M3 having a conicity c’3 = -0.52. Figure 11a illustrates the different aberrations for the max focal length and Figure 11b for the min focal length.
    Figure 12 illustrates the evolution of I quadratic mean value of the WFE RMS waveform error as a function of the taper value u M3.
    FIG. 13 illustrates the various aberrations in the focal plane of a telescope according to the invention, the telescope having a new conicity c'3 of the mirror M3, and for the deformable mirror, a middle position Pm and values of Z9md and of Z4md (Z9 | / iD / max and Z9MD / min; Z4 | 4D / max and Z4MD / min) optimized. Figure 13a illustrates the different aberrations for the max focal length and Figure 13b for the min focal length.
    Figure 14 describes the variation of the average focus <Z4> of the 3 Mirror telescope without deformable mirror as a function of the value of the cone of M3.
    Figure 15 illustrates the evolution of the main aberrations as a function of the value of the conicity of M2, for the min and max focal lengths.
    Figure 16 illustrates the evolution of the main aberrations as a function of the value of the taper of M1 for the min and max focal lengths.
    FIG. 17 illustrates the different aberrations in the focal plane of a telescope according to the invention, the telescope having new conicities c'1, c'2 and c'3 respectively of the mirrors M1, M2 and M3, and for the mirror deformable MD, a median position Pm and values of Z9md, Z4md and Z16 M d optimized. Figure 17a illustrates the different aberrations for the max focal length and Figure 17b for the min focal length.
    FIG. 18 illustrates the method for determining the parameters of an anastigmat telescope according to the invention
    Figure 19 illustrates the evolution of the WFE averaged over the different focal lengths, after each step of the process.
    DETAILED DESCRIPTION OF THE INVENTION
    We will first describe a Korsch type telescope rendered with variable focal length. FIGS. 2 and 3 describe a Korsch type telescope 20 with 3 multifocal mirrors or having a zoom function, the focal length being made variable by displacement of the third mirror M3 on the optical axis of the telescope O using displacement means 5 linear. Document US 4993818 briefly describes the principle of such a system.
    The displacement of the mirror M3 between two extreme positions Pmin and Pmax makes it possible to produce a variable focal length between respectively a minimum focal length fmin and a maximum focal length fmax. By zoom is meant an instrument which comprises at least two focal lengths fmin and fmax, and which is capable of operating for intermediate focal lengths by displacement of the mirror M3.
    According to a variant, the telescope comprises only two focal lengths, fmin and fmax, it is then called bifocal.
    FIG. 2 illustrates the telescope seen from the side in a YZ plane, FIG. 2a illustrates the telescope operating with the maximum focal length and FIG. 2b with the minimum focal length. FIG. 3 illustrates the telescope seen from the side in an XZ plane, FIG. 3a illustrates the telescope operating with the maximum focal length and FIG. 3b with the minimum focal length.
    For M3 at one of the extreme positions Pmin, the telescope has the minimum focal length fmin, a first exit pupil PS1 at a first position P1 and a focal plane PFmin (FIGS. 2b, 3b). For M3 at the other extreme position Pmax, the telescope has the maximum focal length fmax, a second exit pupil PS2 at a second position P2 and a focal plane Pmax (FIGS. 2a, 3a).
    Since the position of the focal plane of the telescope varies with the focal length, it is necessary to integrate means for varying the optical path between the third mirror M3 and the detector D configured so that the detector remains positioned in the focal plane of the telescope. These means are described below for the case of a standard multifocal telescope 20, and will be applied later to a telescope according to the invention.
    According to a first variant, the means for varying the optical path between the third mirror M3 and the detector D comprise means of translation 10 of the detector D along the optical axis O and along the axis Y defined in FIG. 2a, 2a), such that 'illustrated in Figure 4a.
    According to a second variant illustrated in FIGS. 4b and 4c the detector D is fixed and the means for varying the optical path comprise two mirrors T1, T2 in the form of a roof (that is to say having two faces at approximately 90 ° one on the other) located between the third mirror M3 and the detector D, and means 10 'for linear translation of one of the two roof-shaped mirrors, T2 in the example, the other remaining fixed, along an axis not parallel to the optical axis, so as to vary the optical path. The slopes of T1 preferably at 45 ° are not necessarily parallel to those of T2. FIG. 4b illustrates a first position of the roof mirror T2 corresponding to a first position of the mirror M3 (short focal length), and FIG. 4c illustrates a second position of the roof mirror T2 corresponding to a second position of the mirror M3 (longer focal length) ). A plane MO mirror allows the beam to be folded back for better readability of the overall optical system.
    In order to fully understand the path that led to the invention, we will first describe how to calculate a zoom Korsch type telescope. Parameters called initial parameters of the first, second and third mirrors compatible with both the minimum focal length fmin and the maximum focal length fmax are determined, using optical optimization software known in the prior art.
    Using the Korsch equations, we determine the radii of curvature and initial conics for the two extreme focal lengths of our zoom.
    For example, it is possible to answer the Korsch equations simultaneously for the two focal lengths fmin and fmax by having an identical radius of curvature M1 for the 2 focal lengths.
    The starting point is therefore constituted by the values: R1, R2_fmax, R2_fmin, R3_fmax, R3_fmin, C1_fmax, C1_fmin, C2_fmax, C2_fmin, C3_fmax, C3_fmin.
    The continuation of the optimization consists in constraining the radii of curvature and the conicities to be identical for the 2 extreme focal lengths.
    Optimization is carried out conventionally using optical calculation software (CodeV, Zemax, Oslo, ...). This software works on the principle of minimizing an error function. Typically the error function includes image quality at the focal plane and the constraint of the focal lengths fmin and fmax.
    Thus, with a first optimization of the image quality in the focal plane of the telescope according to a predetermined criterion, we arrive at the initial parameters:
    Initial radii of curvature: R1, R2, R3 for M1, M2 and M3 respectively Conic initials: C1, C2, C3 for M1, M2 and M3 respectively
    3060134,
    The predetermined criterion consists for example of minimizing a waveform error or WFE for Wave Front Error in English, averaged over a plurality of points of the field, well known to those skilled in the art, typically we seek to minimize the quadratic mean value or WFE RMS.
    In this type of solution, the shapes of the mirrors M1, M2 and M3, defined by the parameters radius of curvature and constant taper, meet the equations established by M. Korsch in order to obtain an aplanatic and anastigmate solution, without field curvature. However these equations cannot be rigorously solved simultaneously the two extreme focal lengths fmin and fmax.
    This is a compromise and the image quality is affected. The image quality remains acceptable for telescopes with little volume constraint (that is to say for which the rays are incident on the mirrors with small angles). In the space domain, the volume constraint is essential. This solution is therefore not conceivable for spatial instruments of focal length and large pupil size in which the rays are incident on the mirrors with high angles.
    An illustrative example is a bifocal telescope with:
    Max focal length = 37.5 m
    Min focal length: 15 m
    Zoom Ratio: 2.5
    Diameter of mirror M1: 1.1 m
    Distance between M1 and M2: 1600 mm
    Distances between the two extreme positions of M3: 250 mm
    Distances between PS1 and PS2: 250 mm
    Distance between PFmax and PFmin: 1600 mm (PF: focal plane).
    The step of determining the initial parameters by a first optimization as described above results in an initial configuration of the telescope with the following values:
    R1 = 4000 mm R2 = 1000 mm R3 = 1200 mm
    C1 = -1 C2 = -2.1 C3 = -0.61
    FIG. 5 illustrates the aberrations present in the focal plane (positon of the detector) for the bifocal telescope whose three aspherical mirrors M1, M2 and M3 have the initial parameters obtained by solving the equations of
    Korsch as explained above.
    Figure 5a illustrates the aberrations for the maximum focal length fmax, and Figure 5b for the minimum focal length fmin.
    As a reminder, the focus corresponds to Z4, the astigmatism to Z5 and Z6 (Z5 / 6), the coma to Z7 and Z8 (Z7 / 8) and the spherical aberration to Z9.
    In order to characterize more precisely the different categories of aberrations studied we will adopt a sign convention illustrated in Figure 6.
    We will name:
    - "radial" astigmatism: astigmatism for which the tangential focus is located before the sagittal focus. In the following this astigmatism will be considered by convention as positive and noted A + ;
    - "tangential" astigmatism: astigmatism for which the sagittal focus is located before the tangential focus. In the following this astigmatism will be considered by convention as negative and noted A '.
    -coma "external": coma for which the shape of the spot image of a source point is a "comet" whose tail (widest part) moves away from the optical axis. It is the coma created by a bifocal lens. In the following this coma will be considered by convention as positive, and noted C + ;
    - "internal" coma: coma for which the shape of the image spot of a source point is a "comet" whose tail is directed towards the optical axis. In the following this coma will be considered by convention as negative and noted C
    It can be seen in FIG. 5 that these aberrations, with the exception of the spherical aberration Z9, are variable in the field (X, Y) of the telescope. The dominant aberrations for this initial configuration of the telescope are: Initial dominant aberrations for the maximum focal length (Figure 5a): Astigmatism (Z5 / 6)> 0 denoted A + , and Coma (Z7 / 8)> 0 denoted C +
    Initial dominant aberrations for a minimal focal length (figure 5b): Astigmatism (Z5 / 6) <0 noted A and Coma (Z7 / 8) <noted C '
    The telescope as it is cannot be used due to excessive aberrations.
    The Korsh 30 type telescope according to the invention, illustrated in FIG. 7, is a telescope 20 as illustrated in FIGS. 2 to 4 and which also comprises a deformable mirror MD as described above. To limit the size of the deformable mirror MD, it is disposed at a fixed central position Pm situated between the first position P1 of the exit pupil PS1 (minimum focal length) and the second position P2 of the exit pupil PS2 (maximum focal length) .
    The means for varying the optical path configured so that the detector remains positioned in the focal plane of the telescope, as described above (for example 10 and 10 ′) are then placed between the deformable mirror MD and the detector D, such that illustrated in figure 7.
    In the case of a telescope 30 according to the invention, the exit pupil is not fixed according to the focal length of the zoom. The exit pupil moves (order of magnitude ~ 200mm) according to the focal length chosen: the deformable mirror MD cannot therefore be used as exit pupil for all focal lengths, and its position relative to the effective exit pupil varies according to of the chosen focal length. This has a very significant impact: given the orders of magnitude of displacement of the exit pupil, the deformable mirror will work in the field: the impact of the aberrations applied by deformation of the surface of the mirror MD to try to compensate for the aberrations of the system as illustrated in figure 5, is no longer constant in the field. And so the aberrations applied to the deformable mirror will create new aberrations in the system. For example as explained below, the introduction of spherical aberration on the deformable mirror, which is distant from the exit pupil, introduced into the telescope of astigmatism and coma in much greater proportions than spherical aberration.
    Now let’s study what aberrations can be corrected by a deformable mirror placed in the interpupillary area.
    For the following, the aberrations of the telescope, corresponding to the defects of the telescope as an optical system, should not be confused with the aberrations introduced in the form of the deformable mirror, noted with the index MD.
    Figure 8 illustrates, for the initial system, the resulting aberrations following the introduction of spherical aberration on a deformable mirror Z9md (Z9md > 0 for Figure 8a and Z9md <0 for Figure 8b), depending on its relative position relative to the effective exit pupil PS, when it is located downstream of PS compared to the mirror M3.
    Figure 9 illustrates, for the initial system, the resulting aberrations following the introduction of spherical aberration Z9md on deformable mirror, with Z9md> 0 for figure 9a and Z9md <0 for figure 9b, according to its relative position with respect to the effective exit pupil PS, when it is located upstream of PS with respect to the mirror M3.
    The mirror MD being disposed between P1 and P2, it is located according to FIG. 8 for the maximum focal length (downstream from PS2 relative to M3) and according to FIG. 9 for the minimum focal length (upstream from PS1 relative to M3) .
    We see in Figures 8 and 9 that the introduction of spherical aberration Z9md on the deformable mirror MD introduces aberrations such as astigmatism and coma in the telescope. This means that the deformable mirror MD can compensate for the inverse aberrations of those created by Z9mdOn deduced from Figure 8 that for the max focal length fmax:
    -introducing Z9md> 0 creates astigmatism <0 and coma <0, which makes it possible to correct astigmatism> 0 and coma> 0 -introducing Z9md <0 creates astigmatism> 0 and coma> 0, which corrects astigmatism <0 and coma <0
    We deduce from Figure 9 that for the focal length min fmin:
    -introducing Z9md> 0 creates astigmatism <0 and coma> 0, which allows to correct astigmatism> 0 and coma <0 -introducing Z9md <0 creates astigmatism> 0 and coma <0 which corrects astigmatism <0 and coma> 0
    Thus, by placing the deformable mirror MD between P1 and P2, Z9md of a given sign makes it possible to correct simultaneously for the two extreme focal lengths, astigmatism of the same given sign and coma of opposite sign.
    For example Z9 M d> 0 corrects A + and C + for fmax and A + and C for fmin.
    This correction capacity is not compatible with the initial system whose aberrations to be corrected are illustrated in FIG. 5.
    Thus by applying to the bifocal telescope a classic method of optimizing its parameters using Korsch equations (initial configuration of the 3-mirror telescope) and by trying to compensate for aberrations using a deformable mirror, at an impasse: MD placed in the interpupillary area cannot simultaneously correct astigmatism and coma present in the system operating at minimum focal length and at maximum focal length
    After numerous calculations, the inventors identified a way of making a Korsch type telescope with a zoom having very good image quality.
    In the telescope 30 according to the invention, the third mirror M3 has a new conicity c’3 determined from the initial conicity c3 (calculated from the Korsch equations during the first optimization as explained above).
    The new conicity c’3 is determined so that the anastigmat telescope with three aspherical mirrors presents, without the presence of the MD, and for the minimum and maximum focal lengths, aberrations compensable by the MD. Given the teaching of FIGS. 8 and 9, we seek to obtain a configuration of the M1 / M2 / M3 telescope (without MD) having:
    For maximum focal length: positive astigmatism A + and positive coma C +
    For the minimum focal length: positive astigamism A + and negative coma C '
    In Figure 5 we see that the astigmatism for the minimum focal length is negative. The new conicity c'3 is therefore determined so as to modify the sign of the telescope astigmatism without the presence of the deformable mirror, for the minimum focal length, ie transform the negative astigmatism of the system into a positive astigmatism for the minimum focal length. .
    Figure 10 describes the evolution of the average value of the astigmatism of the 3-mirror telescope (without the MD) <Z5 / 6> according to an arbitrary unit, for the min focal (curve 11) and the max focal (curve 12 ), depending on the taper value of M3. We find for the initial taper c3 = -0.61 a positive astigmatism for fmax and negative for fmin.
    This figure highlights the existence of a value of c’3f for which the sign of astigmatism for the focal min reverses, here -0.56. For a new conicity c'3 greater than or equal to c'3inf, the astigmatism of the focal point îo min changes sign. The new value of c'3 cannot moreover stray too far from the initial value c3 in order to maintain the convergence of the optical system.
    A second optimization of the image quality, from the value c'3inf is is then carried out, in order to determine the new conicity c'3, the median position Pm of MD, as well as the shapes of its surface, Smin for fmin and
    Smax for fmax to obtain the best image quality according to the predetermined criterion.
    With a priori knowledge of the aberrations capable of being compensated for by the mirror, as illustrated in FIGS. 8 and 9, it is known that the shape of the surface S of the deformable mirror MD capable of compensating for the aberrations of the optical system comprising M1, M2 , and M3 of conicity c'3, must include a first type of aberration, here in the example of the first order spherical aberration Z9md, and more particularly of the positive Z9md.
    Thus the exact value of my new conicity c'3, the fixed median position Pm of the deformable mirror, common to the two focal lengths, and the surface shapes of MD, Smin for fmin and Smax for fmax, are determined by a second optimization of the optical paths in the instrument, so as to correct the aberrations of the 3-mirror telescope having a new conicity c'3 and to optimize the image quality in the focal plane of the telescope according to the predetermined criterion, typically the minimization of an error WFE wavefront.
    The modification of the taper of M3 makes it possible to reverse the sign of the astigmatism of the focal min, and thus to introduce into the optical system aberrations such that the resulting aberrations of the optical system are compensable by an MD at a fixed position in the interpupillary area.
    Figure 11 illustrates the different aberrations present in the focal plane of the 3-mirror telescope whose M3 has the conicity c'3 = -0.52 The new value c'3 of the conic of M3 makes it possible to obtain positive astigmatism for all focal lengths and opposite comas for extreme focal lengths.
    In the example, the new conicity c’3 deviates by about 20% from the value of the initial conic c3. Preferably, the new conicity c’3 deviates from the initial conicity c3 by more than 5% and less than 30%.
    FIG. 12 illustrates the evolution of the mean square value of the WFE RMS waveform error as a function of the taper value of M3, for the min focal lengths (curve 15) and the maximum focal lengths (curve 16). It can be seen that the initial conicity c3 corresponded to the optimized image quality value, a new conicity value c'3 greater than -0.56 causing an increase in the WFE, that is to say a decrease in the quality of 'picture. The change in value of the conic section of M3 does not meet a need for image quality, but makes it possible to obtain aberrations compensable by the MD. We are moving away from the optimum image quality in order to allow correction of aberrations.
    The introduction of Z9md spherical aberration at the level of the deformable mirror greatly reduces the Z7 / 8 (coma) and Z5 / 6 (astigmatism) of the system, but does not reduce the Z4 focus. On the contrary, Z9md will also cause an increase in the Z4 of the telescope as illustrated in Figure 14, which describes the variation of the average focus <Z4> of the system (3 Mirrors telescope without MD) as a function of the value of the cone of M3, for the min focal (curve 17) and max focal (curve 18): it can be seen that the focus Z4 increases appreciably, particularly for the min focal.
    It is therefore advisable to introduce a second type of aberration in the shape of the surface of the MD, to compensate for the focus present in the system.
    In the example we introduce focus Z4 MD to compensate for the Z4 of the system (the one initially present and the one introduced by Z9md (first aberration). The introduction of Z4md also makes it possible to balance the values of astigmatism and coma, c that is to say to make the values of the respective coefficients close, which makes it possible to improve the compensation by the Z9md ·
    From the range identified for c'3, the determination of the final value of c'3, of the Pm value, of the Z9md and of the Z4md for Smax (area of the MD for fmax) and for Smin (area of the MD for fmin ), is performed by a second optimization.
    FIG. 13 illustrates the different aberrations in the focal plane of a telescope 30 according to the invention, the telescope having a new conicity c'3 of the mirror M3, and for the deformable mirror, a middle position Pm and values of Z9md Ot of Z4md (Z9MD / max and Z9 | viD / min; Z4MD / max and Z4MD / min) optimized. Figure 13a illustrates the different aberrations for the max focal length and Figure 13b for the min focal length.
    The surface shape for the max focal length Smax therefore includes Z9Mç> / max and Z4 M D / max. The surface shape for the min Smin focal length includes Z9 | / | D / min and Z4 | / | D / min.
    In the example c’3 = -0.52, the deformable mirror MD is positioned 110 mm after the PS1 and 140mm before the PS2.
    It can be seen by comparing this FIG. 13 with FIG. 5 (see the change of scale), that the quality of the telescope is greatly improved.
    According to one embodiment, to further improve the image quality, the taper of the mirrors M2 and M1 of the telescope 30 according to the invention is slightly modified.
    In the example, the performance of the telescope can be further improved, the Z7 / 8 and the Z9 being compensated only by the Z9md Modifying the taper of M2 (new value c’2) precisely allows to play on these two aberrations. However, this new conicity c’2 also provides significant amounts of Z4. This excess of Z4 is offset by the modification of the taper of the M1 (new value c’1), which also plays on the Z9.
    Thus a new conicity of the first mirror c'1 and a new conicity of the second mirror c'2 are determined respectively from a first initial conicity c1 of the first mirror and from a second initial conicity c2 of the second mirror, so as to further improve the image quality of the telescope according to the predetermined criterion.
    For the example, these modifications are illustrated in FIGS. 15 and 16. îo FIG. 15 illustrates the evolution of the main aberrations as a function of the value of the taper of M2, for the min and max focal lengths, and FIG. 16 the evolution of the main aberrations as a function of the value of the taper of M1.
    By a third optimization we determine the new taper values c’2 and c’1, illustrated in Figures 15 and 16:
    C’1 = -0.98 C’2 = -2.1
    By comparing them to the initial values c1 = -1 and c2 = -2, we see that these variations in taper are small (less than 10%, see less than 5% for c1), but nevertheless allow the quality of d to be further improved. 'picture.
    As a variant, a third type of aberration is also added, here Z16md or spherical aberration of the second order, which influences Z16, Z9, Z4 Z5 / 6 and Z7 / 8 and makes it possible to further increase the quality of picture.
    FIG. 17 illustrates the various aberrations in the focal plane of a telescope 30 according to the invention, the telescope having new conicities c'1, c'2 and c'3 respectively of the mirrors M1, M2 and M3, and for the deformable mirror MD, a middle position Pm and values of Z9md, Z4md and Z16md optimized. Figure 17a illustrates the different aberrations for the max focal length and Figure 17b for the min focal length.
    It can be seen by comparing this FIG. 17 with FIG. 13 (see change of scale), that the quality of the telescope is further improved. The final image quality obtained is compatible with the constraint of a WFE RMS <λ / 15, which for the visible corresponds to a WFE RMS <50 nm. (see figure 19 below).
    Contrary to what is conventionally practiced, in the telescope 30 5 according to the invention the MD mirror is an integral part of the optical combination of the instrument.
    For zoom operation, the telescope 30 according to the invention has a plurality of intermediate focal lengths fi, whole index. The shape of the surface îo of the deformable mirror Sfi associated with each intermediate focal length fi is calculated from the shape of the surface for the minimum focal length values Smin and maximum Smax, in order to apply the correct correction to MD.
    For the example, once the aberrations Z9md, Z4md and Z16md 15 have been optimized for fmin and fmax, i.e. values of coefficients of the Fringe Zernike polynomials determined for fmin and fmax, the values of the coefficients of polynomials for each focal value, from the values of coefficients of the Fringe Zernike polynomials determined for fmin and fmax.
    According to a variant, the telescope according to the invention comprises an aperture diaphragm placed in the interpupillary zone and adjustable in aperture to keep a numerical aperture substantially constant when the focal length varies.
    According to another aspect, the invention relates to a method 50 for determining parameters of an anastigmat telescope illustrated in FIG. 18 and comprising: three aspherical mirrors, a first concave mirror M1, a second convex mirror M2, a third concave mirror M3,
    -a detector D,
    -a deformable and controllable MD mirror and,
    means 5 for linear displacement of the third mirror on the optical axis O of the telescope so as to vary the focal length of the telescope between a minimum focal length fmin and a maximum focal length fmax.
    The three mirrors M1, M2 and M3 are arranged so that the first mirror and the second mirror form an object at infinity of an intermediate image located between the second mirror and the third mirror, the third mirror forming this intermediate image a final image in the focal plane of the telescope in which the detector D is placed
    The first, second and third mirrors are of fixed shape characterized by a conical and a radius of curvature.
    Furthermore, the telescope at minimum focal length has a first exit pupil PS1 at a first position P1, and the telescope at maximum focal length has a second exit pupil PS2 at a second position P2.
    The deformable mirror MD has a deformable surface and is disposed at a fixed central position Pm located between the first and the second position.
    The method 50 comprises a first step 100 which determines values of conics and radii of curvature, called initial values, of the first, second and third mirrors of the telescope:
    M1 (c1, R1); M2 (c2, R2), M3 (c3, R3).
    These initial values are compatible with the minimum focal length fmin and the maximum focal length fmax, without the presence of the deformable mirror MD, are determined from the Korsh equations, by a first optimization of the image quality in the focal plane of the telescope according to a predetermined criterion.
    According to a second step 200, a taper value of the third mirror c'3inf is determined, from the initial taper c3 of the third mirror, from which the telescope presents, without the presence of the deformable mirror MD and for the minimum focal lengths and maximum, aberrations compensated by the deformable mirror MD.
    Then in a step 300 a new conicity value of the third mirror c'3 is determined, the fixed middle position Pm of MD, the shape of its surface Smin for the minimum focal value and the shape of its surface Smax for the value of maximum focal length, by a second optimization, so as to correct the compensable aberrations and to optimize the image quality in the focal plane of the telescope according to the predetermined criterion. The determination of the shape of the surface of the deformable mirror is based on the application of at least a first and a second aberration.
    For the intermediate focal lengths if necessary, the shape of the deformable mirror associated with each intermediate focal length is calculated from Smin and Smax.
    Preferably, the method 50 further comprises a step 400 consisting in determining a new conicity of the first mirror c’1 and a new conicity c’2 of the second mirror M2, so as to further improve the image quality according to the predetermined criterion.
    Preferably, the method 50 according to also comprises a step 500 consisting in refining the determination of the shape of the surface Smin of the deformable mirror for fmin and the shape of the surface Smax of the deformable mirror for fmax by integrating a third aberration Z16md, so as to improve still the image quality according to the predetermined criterion.
    Similarly for the intermediate focal lengths where appropriate, the shape of the deformable mirror associated with each intermediate focal length and integrating the third aberration is calculated, from Smin and Smax.
    Typically the predetermined criterion is to minimize a WFE waveform error.
    FIG. 19 illustrates the evolution of the WFE RMS averaged over the different focal lengths at the end of each step of the method, that is to say as a function of the different modifications introduced into the optical system, for the example of the telescope given above.
    The WFE obtained after the first optimization based on the Korsch equations is of the order of 560 nm, incompatible with the WFE RMS constraint <50 nm. By modifying the taper value of M3 to modify the sign of astigmatism, the WFE is degraded (no optically active deformable mirror yet: its surface is flat). On the other hand, by introducing first order spherical aberration and focus to the deformable mirror surface, the WFE is greatly improved at around a hundred nm. The modification of the conicities of M1 and M2 allows the WFE to be reduced below fifty nm, and the final optimization, introducing second order spherical aberration, makes it possible to further decrease it to ten nm.
    权利要求:
    Claims (17)
    [1" id="c-fr-0001]
    1. Anastigmat telescope with three aspherical mirrors comprising at least a first concave mirror (M1), a second convex mirror, a third concave mirror (M3) and a detector (D), and having an optical axis (O),
    -the three mirrors being arranged so that the first mirror (M1) and the second mirror (M2) form from an object to infinity an intermediate image located between the second mirror and the third mirror, the third mirror (M3) forming of this intermediate image a final image in the focal plane of the telescope in which the detector is placed, the first, second and third mirrors being of fixed shape characterized by at least one radius of curvature and a taper, the telescope further comprising:
    - means (5) for linear displacement of the third mirror (M3) on the optical axis of the telescope (O) so as to vary the focal length of the telescope between at least a minimum focal length (fmin) and a maximum focal length (fmax) , the telescope at minimum focal length having a first exit pupil (PS1) at a first position (P1), and the telescope at maximum focal length having a second exit pupil (PS2) at a second position (P2),
    - a deformable (MD) and controllable mirror, having a deformable surface and disposed at a fixed central position (Pm) situated between the first and the second position,
    - means (10, 10 ’) for varying the optical path between the deformable mirror (MD) and the detector (D) configured so that the detector remains positioned in the focal plane of the telescope,
    -the third mirror having a new conicity (c'3) determined from an initial conicity (c3), the initial conicity (c3) being determined from the Korsch equations, the new conicity (c'3) being determined so that the telescope presents, without the presence of said deformable mirror and for the minimum and maximum focal lengths, aberrations compensable by said deformable mirror (MD),
    - Said fixed central position (Pm) of said deformable mirror and the shape of its surface respectively for the minimum focal values (Smin) and maximum (Smax), being determined so as to correct said compensable aberrations and to optimize the image quality in the focal plane of the telescope according to a predetermined criterion.
    [2" id="c-fr-0002]
    2. Telescope according to claim 1 wherein said shape of the surface of the deformable mirror comprises at least a first and a second category of aberration.
    [3" id="c-fr-0003]
    3. Telescope according to claim 2 wherein the first category of aberration is first order spherical aberration (Z9md) and the second category of aberration is focus (Z4 M d)
    [4" id="c-fr-0004]
    4. Telescope according to claim 3 wherein the shape of the surface of the deformable mirror further comprises a second order spherical aberration (Z16md) to further improve the image quality according to said criterion.
    [5" id="c-fr-0005]
    5. Telescope according to one of the preceding claims, in which the new conicity (c’3) deviates from the initial conicity by more than 5% and by less than 30%
    [6" id="c-fr-0006]
    6. Telescope according to. One of the preceding claims in which a new conicity of the first mirror (c'1) and a new conicity of the second mirror (c'2) are determined respectively from an initial conicity of the first mirror ( c1) and of an initial conicity of the second mirror (c2), the initial conicities being determined from the Korsch equations, the new conicities being determined so as to further improve the image quality of said telescope according to said criterion.
    [7" id="c-fr-0007]
    7. Anastigmat telescope according to one of the preceding claims, characterized in that the surface of the deformable mirror is defined on the basis of coefficients of polynomials.
    [8" id="c-fr-0008]
    8. The telescope according to claim 7, in which said coefficients are the coefficients of the Fringe Zernike polynomials.
    [9" id="c-fr-0009]
    9. Telescope according to one of the preceding claims, in which:
    -a positive astigmatism (A +) such as an astigmatism for which a tangential focus is located before a sagittal focus,
    -a negative astigmatism (A-) as an astigmatism for which a sagittal focus is located before a tangential focus,
    -a positive coma like a coma for which a shape of the spot image of a source point is a "comet" whose tail moves away from the optical axis and,
    -a negative coma like a coma for which a form of the image spot of a source point is a "comet" whose tail is directed towards the optical axis, the compensable aberrations being of positive astigmatism (A +) and of positive coma (C +) for maximum focal length, positive astigmatism (A +) and negative coma (C-) for minimum focal length.
    [10" id="c-fr-0010]
    10. Telescope according to one of the preceding claims, in which:
    -a positive astigmatism (A +) such as an astigmatism for which a tangential focus is located before a sagittal focus,
    -a negative astigmatism (A-) as an astigmatism for which a sagittal focus is located before a tangential focus, and in which the new conicity of the third mirror (c'3) is determined so as to modify the sign of the astigmatism of the telescope for minimum focal length, without the presence of an aspherical component.
    [11" id="c-fr-0011]
    11. Telescope according to one of the preceding claims for which the predetermined criterion consists in minimizing a waveform error (WFE).
    [12" id="c-fr-0012]
    12. Telescope according to one of the preceding claims, having a plurality of intermediate focal lengths, and for which the shape of the surface of the deformable mirror (Sfi) associated with each intermediate focal length (fi) is calculated from the shape of the surface for minimum focal length (Smin) and maximum focal length (Smax).
    [13" id="c-fr-0013]
    13. Method (50) for determining parameters of an anastigmat telescope comprising three aspherical mirrors, a first concave mirror (M1), a second convex mirror (M2), a third concave mirror (M3), a detector (D), a deformable and controllable mirror (MD) and means (5) for linear displacement of the third mirror on an optical axis (O) of the telescope so as to vary the focal length of the telescope between a minimum focal length (fmin) and a maximum focal length ( fmax), the three mirrors being arranged so that the first mirror and the second mirror form from an object to infinity an intermediate image situated between the second mirror and the third mirror, the third mirror forming from this intermediate image an image final in the focal plane of the telescope in which the detector is placed, the first, second and third mirrors being of fixed shape characterized by at least one conical and a radius of curvature, the telescope at focal length minimum having a first exit pupil (PS1) at a first position (P1), and the telescope at maximum focal length having a second exit pupil (PS2) at a second position (P2), the deformable mirror (MD) having a deformable surface and being disposed at a fixed central position (Pm) located between the first and second positions, the method comprising the steps consisting in:
    -determine (100) values of conics and radii of curvature called initial values of the first (c1, R1), second (c2, R2), and third (c3, R3) mirrors of said compatible telescope of minimum focal length (fmin) and the maximum focal length (fmax), without the presence of the deformable mirror, from the Korsh equations, by a first optimization of the image quality in the focal plane of the telescope according to a predetermined criterion,
    -determine (200) a taper value of the third mirror (c'3inf), from the initial taper of the third mirror (c3), from which the telescope presents, without the presence of said deformable mirror and for minimum focal lengths and maximum, aberrations compensated by said deformable mirror (MD),
    - determining (300) a new taper value of the third mirror (c'3), said fixed central position (Pm) of said deformable mirror and the shape of its surface, respectively for the minimum focal value (Smin) and maximum (Smax) ), by a second optimization, so as to correct said compensable aberrations and to optimize the image quality in the focal plane of the telescope according to the predetermined criterion,
    5 the determination of the shape of the surface of the deformable mirror being based on at least a first and a second category of aberration.
    [14" id="c-fr-0014]
    14. The method of claim 13 wherein the first aberration category is first order spherical aberration (Z9md) and the second aberration category is focus (Z4md).
    [15" id="c-fr-0015]
    15 Method according to one of claims 13 or 14 further comprising a step of determining (400) a new conicity of the first (c’1) and second (c’2) mirrors so as to further improve the quality
    15 image according to the predetermined criterion.
    [16" id="c-fr-0016]
    16. The method of claim 15 further comprising a step (500) of refining the determination of the shape of the surface of the deformable mirror (Smin, Smax) by further integrating a third category
    [17" id="c-fr-0017]
    20 of aberration (Z16md) so as to further improve the image quality according to the predetermined criterion.
    1/20
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    法律状态:
    2017-11-27| PLFP| Fee payment|Year of fee payment: 2 |
    2018-06-15| PLSC| Publication of the preliminary search report|Effective date: 20180615 |
    2019-11-28| PLFP| Fee payment|Year of fee payment: 4 |
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    优先权:
    申请号 | 申请日 | 专利标题
    FR1601769A|FR3060134B1|2016-12-13|2016-12-13|COMPACT TELESCOPE HAVING A PLURALITY OF FOCALS COMPENSATED BY A DEFORMABLE MIRROR|
    FR1601769|2016-12-13|FR1601769A| FR3060134B1|2016-12-13|2016-12-13|COMPACT TELESCOPE HAVING A PLURALITY OF FOCALS COMPENSATED BY A DEFORMABLE MIRROR|
    EP17205146.8A| EP3336595B1|2016-12-13|2017-12-04|Compact telescope having a plurality of focal distances compensated by a deformable mirror|
    ES17205146T| ES2878025T3|2016-12-13|2017-12-04|Compact telescope with a plurality of focal lengths compensated by a deformable mirror|
    US15/839,608| US10976537B2|2016-12-13|2017-12-12|Compact telescope having a plurality of focal lengths compensated for by a deformable mirror|
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