Telescope

Abstract

Telescope. The present invention relates to a telescope (10) comprising: a first concave mirror (M1), a second convex mirror (M2), a focal plane (PF), the first mirror (M1) and the second mirror (M2) being arranged such that: the optical axes of the first mirror (M1) and the second mirror (M2) are coincident, each of the first mirror (M1) and the second mirror (M2) is used at least in double reflection, no intermediate image is formed between the first mirror (M1) and the second mirror (M2). Figure for the abstract: 1

Description

Title of the invention: Telescope

[0001] The present invention relates to a telescope.

[0002] In particular, the invention is particularly suitable for compact long focal length telescopes.

[0003] There are two families of solutions for compact long focal length telescopes: Cassegrain type telescopes and Korsch type telescopes.

[0004] Cassegrain-type telescopes consist of two aspherical mirrors M1 and M2 and several lenses in front of the focal plane. This solution is compact, but limited in field of view (<0.8-1°). In addition, the lenses introduce chromatic aberration, limiting the spectral band of use.

[0005] Korsch-type telescopes consist of two aspherical mirrors M1 and M2 forming the front cavity, and an aspherical mirror M3. A reflecting mirror is also used. The aspherical mirror M3 and the reflecting mirror form the rear cavity. A Korsch-type telescope achieves linear fields of view of up to 2 or 3°. However, Korsch-type telescopes have a larger volume due to the use of an additional mirror in the rear cavity.

[0006] Thus, the volume of a telescope is generally cylindrical (for Cassegrain-type solutions), or cylindrical on a parallelepiped-shaped base (for Korsch-type solutions). The aim is to reduce this volume as much as possible.

[0007] The reduction in volume can be achieved by three means: - Reducing the diameter of the cylinder: but this is done at the expense of the amount of light collected by the instrument (the diameter of the cylinder being linked to the diameter of the entrance pupil of the telescope) and is therefore not a usable lever. - Reduce the volume of the rear cavity. - Reduce the volume of the front cavity: i.e., the distance between M1 and M2.

[0008] In particular, for the front cavity, from a theoretical point of view, it is possible to reduce the length of the front cavity (distance M1-M2) while maintaining a nominal image quality (i.e. theoretical, with a perfect realization of the mirrors and a perfect positioning of the mirrors).

[0009] However, such a very compact M1-M2 distance combination also becomes very sensitive to positioning errors (mainly the error in the longitudinal position of mirror M2). Such a solution, although theoretically sound, becomes completely impractical with accuracies of realization and stability (errors due to vibrations, thermal expansion), beyond the current capabilities of the technology.

[0010] There is therefore a need for a telescope that is more compact than current solutions, without increasing the sensitivity to positioning errors of the telescope mirrors.

[0011] To this end, the invention relates to a telescope comprising: - a first concave mirror, - a second convex mirror, - a focal plane,

[0012] the first mirror and the second mirror being arranged such that: - the optical axes of the first mirror and the second mirror are coincident, - each of the first and second mirrors is used at least in double reflection so that: • The first mirror is designed to collect an incident beam of light and reflect it towards the second mirror, to obtain a first reflected beam. • The second mirror is designed to reflect the first reflected beam back towards the first mirror, to obtain a second reflected beam. • The first mirror is designed to reflect the second reflected beam towards the second mirror, to obtain a third reflected beam. • The second mirror is designed to reflect the third reflected beam, to obtain a fourth reflected beam. • the focal plane is suitable for receiving the fourth reflected beam in the case of double reflection, or a beam resulting from reflections of the fourth reflected beam on the first mirror and the second mirror in the case of additional reflection, - no intermediate image is formed between the first mirror and the second mirror.

[0013] According to other advantageous aspects of the invention, the telescope comprises one or more of the following features, taken individually or in all technically possible combinations:

[0014] - the telescope has a field greater than or equal to 30°.

[0015] - each of the first mirror and the second mirror is used in triple reflection so that : • The first mirror is designed to reflect the fourth reflected beam towards the second mirror, to obtain a fifth reflected beam. • The second mirror is designed to reflect the fifth reflected beam, to obtain a sixth reflected beam. • the focal plane is suitable for receiving the sixth reflected beam;

[0016] - the telescope comprises a single detector or a plurality of detectors, forming the focal plane;

[0017] - the single detector has a curvature or the plurality of detectors are arranged so as to form a curve;

[0018] - the single detector is spherical or cylindrical, or the plurality of detectors are arranged so that the focal plane is spherical or cylindrical;

[0019] - the telescope is devoid of lenses;

[0020] -the first mirror has a hole on the optical axis of the first mirror so that the last beam reflected by the second mirror is sent to the focal plane through the hole in the first mirror;

[0021] - the telescope includes a flat mirror between the first mirror and the second mirror, the plane mirror being arranged so as to send, onto the focal plane, the last beam reflected by the second mirror;

[0022] - the telescope includes a flat mirror attached to the first mirror so as to send, on the focal plane, the last beam reflected by the second mirror.

[0023] The invention will become clearer upon reading the following description, given solely by way of non-limiting example, and made with reference to the drawings in which:

[0024] [Fig-1] [Fig.1] is an example of a schematic representation of a telescope according to a first embodiment,

[0025] [Fig.2] [Fig.2] is an example of a schematic representation of a telescope according to a second embodiment, and

[0026] [Fig.3] [Fig.3] is an example of a schematic representation of a telescope according to a third embodiment.

[0027] Different embodiments of a telescope 10 are illustrated by figures 1 to 3.

[0028] The telescope 10 is, for example, a long focal length telescope, used for example for observation from a satellite. For example, the telescope 10 has a focal length greater than or equal to 3000 mm. For example, the telescope 10 has an exit pupil greater than or equal to 300 mm and a linear field greater than or equal to 1°.

[0029] Preferably, the telescope 10 has a large field, typically a field greater than or equal to 30°.

[0030] The field of view of a telescope, also called the field of view or linear field of view, is the portion of space captured by the telescope in transverse.

[0031] As illustrated by figures 1 to 3, the telescope 10 comprises a first mirror M1, a second mirror M2 and a focal plane PF.

[0032] Preferably, the telescope 10 is lens-free.

[0033] The first mirror Ml is concave. The first mirror Ml is the only concave mirror of the telescope 10.

[0034] The second mirror M2 is convex. The second mirror M2 is the only convex mirror in telescope 10.

[0035] The first mirror M1 and the second mirror M2 are arranged such that: - the optical axes of the first mirror M1 and the second mirror M2 are coincident (or coincident). - each of the first mirror M1 and the second mirror M2 is used at least in double reflection so that: • The first mirror M1 is suitable for collecting an incident light beam F1 and reflecting it towards the second mirror M2, to obtain a first reflected beam FL. In particular, the incident light beam F1 is a beam originating from an object at infinity (the rays collected by the first mirror M1 are therefore parallel to each other). • the second mirror M2 is suitable for reflecting the first reflected beam Fl towards the first mirror Ml, to obtain a second reflected beam F2. • the first mirror M1 is suitable for reflecting the second reflected beam F2 towards the second mirror M2, to obtain a third reflected beam F3. • the second mirror M2 is suitable for reflecting the third reflected beam F3, to obtain a fourth reflected beam F4. • the focal plane PF is suitable for receiving the fourth reflected beam F4 in case of double reflection or a beam resulting from reflections of the fourth reflected beam F4 on the first mirror M1 and the second mirror M2 in case of additional reflection. - no intermediate image is formed between the first mirror M1 and the second mirror M2. The mirrors are therefore positioned at a relatively close distance from each other, preventing the formation of intermediate images.

[0036] In an optional embodiment, each of the first mirror M1 and the second mirror M2 is used in triple reflection such that: • The first mirror M1 is designed to reflect the fourth reflected beam F4 towards the second mirror M2, to obtain a fifth reflected beam F5. • the second mirror M2 is suitable for reflecting the fifth reflected beam F5, to obtain a sixth reflected beam F6. • In this example, the focal plane PF is suitable for receiving the sixth reflected beam F6.

[0037] Preferably, the telescope 10 comprises a single detector or a plurality of detectors, forming the focal plane PF.

[0038] Preferably, the single detector has a curvature or the plurality of detectors are arranged so as to form a curve.

[0039] Preferably, the single detector is spherical or cylindrical, or the plurality of detectors are arranged so that the focal plane PF is spherical or cylindrical.

[0040] In particular, in the case of double reflection, the use of a curved focal plane allows for a small distance between the second mirror M2 and the focal plane, thus avoiding field curvature problems. This makes it possible to maintain good image quality.

[0041] Alternatively, the detector is planar. This is particularly suitable for the case of triple reflection, or more, on the first mirror M1 and the second mirror M2.

[0042] In the first embodiment illustrated by [Fig. 1], the first mirror M1 has a hole T on the optical axis of the first mirror M1 such that the last beam reflected by the second mirror M2 is directed onto the focal plane PF through the hole T of the first mirror M1. In particular, in this embodiment, the focal plane PF is positioned behind (after) the first mirror M1.

[0043] In the second embodiment illustrated in [Fig. 2], the telescope 10 comprises a plane mirror 20 between the first mirror M1 and the second mirror M2, the plane mirror 20 being arranged so as to direct the last beam reflected by the second mirror M2 onto the focal plane PF. In particular, in this second embodiment, the plane mirror 20 is separate (not attached) from the first mirror M1 and the second mirror M2. This second embodiment allows the focal plane PF to be projected to the side, and avoids puncturing the first mirror M1 (mechanical simplification).

[0044] In the third embodiment illustrated in [Fig. 3], the telescope 10 comprises a flat mirror 22 attached to the first mirror M1 so as to direct the last beam reflected by the second mirror M2 onto the focal plane PF. The flat mirror 22 is, for example, attached to the first mirror M1 by bonding or molecular adhesion. This third embodiment simplifies the handling of the flat mirror and also avoids drilling into the first mirror M1.

[0045] An example of the operation of telescope 10 will now be described.

[0046] When the telescope 10 receives an incident light beam Fb such an incident light beam F! is collected by the first mirror Ml.

[0047] The first mirror M1 reflects the incident light beam F, in the direction of the second mirror M2, to obtain a first reflected beam FL

[0048] The second mirror M2 then reflects the first reflected beam Fl towards the first mirror Ml, to obtain a second reflected beam F2.

[0049] Then, the first mirror M1 reflects the second reflected beam F2 towards the second mirror M2, to obtain a third reflected beam F3.

[0050] The second mirror M2 reflects the third reflected beam F3, to obtain a fourth reflected beam F4.

[0051] In the case of a double reflection, the fourth reflected beam F4 is sent to the focal plane PF, either directly via the hole T of the first mirror Ml (first embodiment), or via a plane mirror 20, 22 (second and third embodiment).

[0052] In the case of a triple reflection, the first mirror M1 reflects the fourth reflected beam F4 towards the second mirror M2, to obtain a fifth reflected beam F5.

[0053] The second mirror M2 reflects the fifth beam, to obtain a sixth reflected beam F6.

[0054] The sixth reflected beam F6 is sent to the focal plane PF, either directly via the hole T of the first mirror Ml (first embodiment), or via a plane mirror 20, 22 (second and third embodiment).

[0055] Thus, telescope 10 uses only two curved mirrors (concave mirror M1 and convex mirror M2), which eliminates chromatic aberration problems and the volume problem by eliminating the rear cavity.

[0056] Furthermore, by moving from a simple reflection solution on the mirrors to a double, or even triple, reflection solution on the mirrors, the front cavity (distance M1-M2) is made less sensitive. This allows the telescope 10 (distance M1-M2) to be further compacted, while maintaining the same manufacturing performance, stability, and final image quality.

[0057] The telescope 10 is, therefore, perfectly suited to replace Korsch or Cassegrain type telescopes, for example for Earth observation satellites.

[0058] The person skilled in the art will understand that the embodiments and variants described above can be adapted for reflections strictly greater than triple reflections on the first mirror M1 and the second mirror M2.

[0059] More generally, a person skilled in the art will understand that the embodiments and variants described above can be combined to form new embodiments provided that they are technically compatible.

Claims

1. Demands Telescope (10) comprising: - a first concave mirror (Ml), - a second convex mirror (M2), - a focal plane (FP), the first mirror (M1) and the second mirror (M2) being arranged such that: - the optical axes of the first mirror (M1) and the second mirror (M2) are coincident, - each of the first mirror (M1) and the second mirror (M2) is used at least in double reflection so that: • the first mirror (M1) is suitable for collecting an incident light beam (FO) and reflecting it towards the second mirror (M2), to obtain a first reflected beam (F1), • the second mirror (M2) is designed to reflect the first reflected beam (Fl) back towards the first mirror (Ml), to obtain a second reflected beam (F2), • The first mirror (M1) is designed to reflect the second reflected beam (F2) towards the second mirror (M2), to obtain a third reflected beam (F3), • the second mirror (M2) is designed to reflect the third reflected beam (F3), to obtain a fourth reflected beam (F4), • the focal plane (PF) is suitable for receiving the fourth reflected beam (F4) in the case of double reflection or a beam resulting from reflections of the fourth reflected beam (F4) on the first mirror (M1) and the second mirror (M2) in the case of additional reflection, - no intermediate image is formed between the first mirror (M1) and the second mirror (M2).

2. Telescope (10) according to claim 1, wherein the telescope (10) has a field greater than or equal to 30°.

3. Telescope (10) according to claim 1 or 2, wherein each of the first mirror (M1) and the second mirror (M2) is used in triple reflection such that: • the first mirror (M1) is suitable for reflecting the fourth reflected beam (F4) towards the second mirror (M2), to obtain a fifth reflected beam (F5), • the second mirror (M2) is suitable for reflecting the fifth reflected beam (F5), to obtain a sixth reflected beam (F6), • the focal plane (PF) is suitable for receiving the sixth reflected beam (F6).

4. Telescope (10) according to any one of claims 1 to 3, wherein the telescope (10) comprises a single detector or a plurality of detectors, forming the focal plane (FP).

5. Telescope (10) according to claim 4, wherein the single detector has a curvature or the plurality of detectors are arranged so as to form a curve.

6. Telescope (10) according to claim 4, wherein the single detector is spherical or cylindrical, or the plurality of detectors are arranged so that the focal plane (PF) is spherical or cylindrical.

7. Telescope (10) according to any one of claims 1 to 6, wherein the telescope (10) is devoid of lenses.

8. Telescope (10) according to any one of claims 1 to 7, wherein the first mirror (M1) has a hole (T) on the optical axis of the first mirror (M1) such that the last beam reflected by the second mirror (M2) is sent to the focal plane (PF) through the hole (T) of the first mirror (M1).

9. Telescope (10) according to any one of claims 1 to 8, wherein the telescope (10) comprises a plane mirror (20) between the first mirror (M1) and the second mirror (M2), the plane mirror (20) being arranged so as to send, on the focal plane (PF), the last beam reflected by the second mirror (M2).

10. Telescope (10) according to any one of claims 1 to 8, wherein the telescope (10) comprises a flat mirror (22) attached to the first mirror (M1) so as to send, on the focal plane (PF), the last beam reflected by the second mirror (M2).

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