WO2001059488A1 - Procede destine a obtenir des surfaces optiques biquadratiques et en particulier des correcteurs de schmidt - Google Patents

Procede destine a obtenir des surfaces optiques biquadratiques et en particulier des correcteurs de schmidt Download PDF

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Publication number
WO2001059488A1
WO2001059488A1 PCT/IT2000/000043 IT0000043W WO0159488A1 WO 2001059488 A1 WO2001059488 A1 WO 2001059488A1 IT 0000043 W IT0000043 W IT 0000043W WO 0159488 A1 WO0159488 A1 WO 0159488A1
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WO
WIPO (PCT)
Prior art keywords
plates
accordance
biquadratic
corrector
optical
Prior art date
Application number
PCT/IT2000/000043
Other languages
English (en)
Inventor
Pietro Sgarbi
Original Assignee
Pietro Sgarbi
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Pietro Sgarbi filed Critical Pietro Sgarbi
Priority to PCT/IT2000/000043 priority Critical patent/WO2001059488A1/fr
Publication of WO2001059488A1 publication Critical patent/WO2001059488A1/fr

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Classifications

    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B17/00—Systems with reflecting surfaces, with or without refracting elements
    • G02B17/08—Catadioptric systems
    • G02B17/0884—Catadioptric systems having a pupil corrector
    • G02B17/0888—Catadioptric systems having a pupil corrector the corrector having at least one aspheric surface, e.g. Schmidt plates
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B17/00—Systems with reflecting surfaces, with or without refracting elements
    • G02B17/08—Catadioptric systems
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B23/00—Telescopes, e.g. binoculars; Periscopes; Instruments for viewing the inside of hollow bodies; Viewfinders; Optical aiming or sighting devices
    • G02B23/02—Telescopes, e.g. binoculars; Periscopes; Instruments for viewing the inside of hollow bodies; Viewfinders; Optical aiming or sighting devices involving prisms or mirrors
    • G02B23/06—Telescopes, e.g. binoculars; Periscopes; Instruments for viewing the inside of hollow bodies; Viewfinders; Optical aiming or sighting devices involving prisms or mirrors having a focussing action, e.g. parabolic mirror
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
    • G02B27/0025—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00 for optical correction, e.g. distorsion, aberration
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B3/00—Simple or compound lenses
    • G02B3/12—Fluid-filled or evacuated lenses

Definitions

  • the present invention refers to a process to obtain biquadratic optical surfaces, in particular Schmidt correctors, and product acquired with the aforementioned process.
  • the aim of the present invention is to dramatically reduce the cost of manufacturing the corrector plate used in all the types of instruments which are derived from the original
  • this object is achieved by means of a process for obtaining biquadratic surfaces, in particular Schmidt correctors, characterised in that it includes the use of two transparent piano- parallel plates, adequately distanced from one another and connected to one another at the periphery in order to allow their radial expansion, and the application of an equally distributed deforming force on these plates so that their distance at the centre is greater than that at their periphery, thereby inducing a biquadratic deformation on the surface of the plates so that the two plates will assume a shape similar to a single plate worked on both surfaces an expansion compensator being placed at the centre of the two plates.
  • an optical fluid medium is inserted between the two piano-parallel plates to exercise the said deforming force in an equal manner on the surface of the two plates.
  • the present invention it is not necessary to complete an initial piano-parallel processing of the internal surfaces of the two plates if the optical medium adopted has the same refraction index as the material used for the plate.
  • the new process overcomes the inconvenience of a manual working of the plate because a curve automatically deformed to the maximum extremity of the plate itself is achieved without further processing.
  • the new process devised is applicable to all of the optical combinations which foresee a Schmidt-type corrector, and more precisely: classic Schmidt, Schmidt - Cassegrain, Baker - Schmidt, Newton - Baker; moreover, it is applicable to the classic Newton in order to improve the general performance.
  • a further advantage introduced by the new process is the dramatic reduction in the intermediate optical controls required to verify the shape of the surface obtained.
  • Figure 1 shows a classic configuration of the Schmidt system in accordance with the known technique
  • Figure 2 shows a classic configuration of the Schmidt - Cassegrain system in accordance with the known technique
  • Figure 3 illustrates a classic configuration of the Newton - Baker system in accordance with the known technique
  • Figure 4 illustrates a configuration of the Newton classic system
  • Figure 5 shows the family of curves utilised by all correctors for the reduction of optical aberrations
  • Figure 6 shows the course of the two plates deformed by the process according to the present invention
  • Figure 9 shows the final configuration of the corrector obtained in this way.
  • the mirror 2 has a radius r and an apex V, positioned on an optical axis 6, whilst the focal surface 3 has a radius rl and is concentric on the surface of the focal F mirror 2.
  • the corrector 1 deviates the incident rays 4 and 5 to compensate for the spherical aberration of mirror 2, whilst the coma is eliminated by positioning the corrector 1 in the centre of curvature C.
  • 'Spherical aberration' is intended as the inability of a spherical mirror to carry parallel incident rays onto the same focal point in different positions on its surface, whilst “coma” is intended as the comet tail shaped image which is caused by the impossibility of focalising a punctiform image if this lies outside the optical axis as a consequence of the incidence of oblique beams.
  • the corrector 1 is realised by means of a highly accurate surface processing starting from a piano-parallel plate of glass with hand-made zonal works subsequently executed to give the corrector a very slight spherical curvature.
  • the shape to be given to the corrector 1 plate surface is not unique. That is to say that there is not only one but an entire family of valid equations which eliminate the aberrations caused by mirror 2; for practical reasons a specific shape is chosen, as for example that which allows a lesser removal of glass when the same correction is required (see Figure 5).
  • the shape of the corrector 1 must be able to keep the residual chromatic aberration caused by the corrector itself at a minimum, which aberration, however, in the case of traditional correctors, is always kept to very low values due to the thinness of the plate.
  • the main prerogative of this type of instrument is to obtain systems shorter than that shown in Figure 1 because the longer the optical tube, that is the longer the telescope is, the higher is the cost of the entire instrument with a ratio estimated at 1 :6 (for example a 2m telescope would be six times the price of a lm long telescope).
  • Figure 4 illustrates a classic Newton system which can be distinguished from the previous Newton - Baker system in that its configuration can be reduced to a primary parabolic mirror 9 and a secondary elliptic plane mirror 60, whose function is to perpendicularly deviate the image to the optical axis.
  • Figure 6 shows the course of two plates deformed by the process according to the present invention.
  • the process according to the invention takes advantage of the elastic property of the glass to deform the plates maintaining the surfaces parallel between them in order to obtain a permanent shape, such as that shown in Figure 6.
  • This consists of a bending corresponding to the biquadratic surface required, the shape being acquired by means of an equally distributed pressure. This is practicable in as much as the deformations undergone by the plates are extremely small and are, therefore, rigorously elastic (Hooke's law).
  • optical medium 13 will be a fluid, such as distilled water and 60% to 98% glycerine solution or a mineral oil with a low viscosity and a low freezing point (such as the type used for achromatic doublets) for applications with diameters greater than 10 - 13 cm, otherwise it is possible to use a case-hardening vegetable resin or other synthetic case-hardening resins (such as cyano-acrylate, epoxy, etc.) for applications with diameters less than 10 - 13 cm.
  • a fluid such as distilled water and 60% to 98% glycerine solution or a mineral oil with a low viscosity and a low freezing point (such as the type used for achromatic doublets) for applications with diameters greater than 10 - 13 cm, otherwise it is possible to use a case-hardening vegetable resin or other synthetic case-hardening resins (such as cyano-acrylate, epoxy, etc.) for applications with diameters less than 10 - 13 cm.
  • the process always requires the presence of two plates adequately distanced and supported at the edge by a fixed support or free support.
  • the plates which constitute the corrector can be of different thicknesses (that which involves a deformation different from one plate to another) in such a way that it is possible to obtain a better chromatic correction as foreseen in the solution indicated by Linfoot.
  • the fundamental parameters are: a) elasticity coefficient; b) rigidity coefficient (or flexural rigidity); c) elasticity module; d) Poisson's module (or Poisson's ratio); e) thickness of the plate; f) refraction index; g) dispersion index; h) total inner pressure.
  • the only optical control required is to be carried out on the already assembled corrector and consists of testing the calibration of the inner pressure between the two plates, simultaneously verifying the quality of the image obtained by means of an interferometer or Ronchi reticule positioned in the focus of the instrument.
  • the maximum deformation is calculated on the basis of the physical characteristics of the glass employed in order to realise the plates constituting the corrector.
  • the various physical parameters of the calculation provide a large degree of freedom in obtaining a series of curves, greater than with the processing system for removal of the material.
  • the applied weight P force must always be symmetrical in respect to the centre of the plate.
  • ⁇ (x 4 - krV) / [4(n - 1) R 3 ] (6)
  • ⁇ is the deviation of the plate surface
  • k is the shape factor and is comprised between - 1 and + 3
  • r is the semi-diameter of the plate
  • R is the curvature radius of the primary mirror
  • n is the refraction index of the plate.
  • the two plates 18 and 19, of glass and other transparent material, with adequate space between them, have a central hole 29 through which it is possible to obtain the connections for the external collimation of a secondary mirror 40 connected to a small disc 47.
  • the two plates 18 and 19 are hermetically sealed thanks to the presence of a couple of gaskets 42 with a predetermined thickness glued to the external wall of an expansion compensator 49 and another couple of gaskets
  • the barrel 21 in this way allows a radial expansion of the two plates 18 and 19 that is, one plate "slides” onto the other, so that the traction generated by the bending at the centre can be discharged without creating an undesired deformation.
  • the two plates are spaced by a suitably sized annular gasket 62 placed near to the external edge.
  • the optical medium 41 is inserted between plates 18 and 19.
  • the optical medium 41 is a fluid in cases where the diameter of plates 18 and 19 is greater than approximately 10 - 13 cm, but can also be a vegetable case- hardening resin, as for example the so-called Canada balsam, or synthetic if the diameter of plates 18 and 19 is lower.
  • the fluid can be inserted after the corrector has been assembled with the exception of membrane 50. In fact there is only air between the two plates 18 and 19 and the fluid is injected, through a needle (not shown in the Figure) with the same diameter as the special holes 63 made on the body of the compensator 49, until it goes out of the other holes. The air present between the two plates 18 and 19 is vented in this way.
  • the deformation of the two plates 18 and 19, as shown in Figure 6, is therefore caused by the optical medium inserted, with a predetermined pressure obtained thanks to the screwing down of a threaded and graduated ring 52 which compresses the optical medium 41 thereby creating the deformations foreseen by the theory described previously in accordance with equation 1.
  • the expansion compensator 49 is located centrally on plates 18 and 19 and acts by means of an elastic membrane 50 so as to maintain the difference in pressure between the outside (ambient pressure) and the inside (pressure exerted on the optical medium 41 by the membrane 50) constant thanks to the holes 63 in order to guarantee a constant deformation, which must imprint a shape such as that shown in Figure 6.
  • the function of the membrane 50 of the expansion compensator 49 is to absorb the volumetric variations induced by variations in temperature and/or variations in atmospheric pressure caused by the different heights at which the instrument is operated.
  • the difference in pressure between the inside and outside is kept constant thanks to the variability in volume of the optical medium determined by the movement of membrane 50.
  • optical medium 41 is inside plates 18 and 19
  • fluids accomplishing this function can be used thanks to their selective fransmissivity, as for example certain fluorides or oils or also the compounds used for the production of gelatine filters.
  • Other fluids besides those already mentioned, may also be used (a solution of distilled water and 60% to 98% glycerine, low viscosity mineral oil), according to the glass employed for the two plates 18 and 19.
  • the corrector in accordance with the invention is applicable to any of the optical systems cited.
  • glasses with high refraction indexes especially those with lanthanum, turn out to be more suitable; to this purpose it is calculated that if it were possible to deposit a layer of germanium even of only 0.5 microns on the external surfaces of both plates, the glass employed could be normal glass with a low index, BK3 type, which is much more economical than the lanthanum type.
  • the fluid must have a refraction index analogous to that of the glass employed and, as stated previously, it is better if it is identical.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Astronomy & Astrophysics (AREA)
  • Telescopes (AREA)

Abstract

L'invention concerne un procédé destiné à obtenir des surfaces biquadratiques, en particulier des correcteurs de Schmidt, caractérisé en ce qu'il consiste à positionner deux plaques optiques (18, 19) plan-parallèles transparentes avec un espacement approprié. Les plaques (18, 19) sont reliées à une autre, sur la périphérie, afin de permettre leur expansion radiale. En outre, l'application d'une force de déformation (P) uniformément distribuée est prévue, en particulier induite à l'aide d'un fluide optique (41), et régulée au moyen d'un compensateur d'expansion central (49), de façon à obtenir des surfaces biquadratiques.
PCT/IT2000/000043 2000-02-11 2000-02-11 Procede destine a obtenir des surfaces optiques biquadratiques et en particulier des correcteurs de schmidt WO2001059488A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
PCT/IT2000/000043 WO2001059488A1 (fr) 2000-02-11 2000-02-11 Procede destine a obtenir des surfaces optiques biquadratiques et en particulier des correcteurs de schmidt

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
PCT/IT2000/000043 WO2001059488A1 (fr) 2000-02-11 2000-02-11 Procede destine a obtenir des surfaces optiques biquadratiques et en particulier des correcteurs de schmidt

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Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2003081920A2 (fr) * 2002-03-25 2003-10-02 Living Ad Limited Production d'images 3-d simulees
US8857779B2 (en) 2009-03-30 2014-10-14 Ge Healthcare Bio-Sciences Ab Holder for a holographic grating
WO2015107362A1 (fr) * 2014-01-17 2015-07-23 The Centre For Vision In The Developing World Cic Procédé de fabrication d'une membrane souple et son moule, membrane et lentille à foyer variable
FR3122262A1 (fr) * 2021-04-23 2022-10-28 Safran Reosc Télescope compact pour la détection de débris spatiaux
WO2024089367A1 (fr) * 2022-10-26 2024-05-02 Safran Reosc Télescope de schmidt à performances améliorées, dispositifs et procédé de détection associés

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3641354A (en) * 1967-03-08 1972-02-08 Jack De Ment Optical modulation by fluidic optics utilizing chromatic aberration
US3889431A (en) * 1973-09-04 1975-06-17 Celestron Pacific Method for making schmidt corrector lenses
JPS54109320A (en) * 1978-02-15 1979-08-27 Matsushita Electronics Corp Projection image receiver
EP0410686A2 (fr) * 1989-07-25 1991-01-30 Chromex, Inc., Surfaces optiques asphériques
US5973852A (en) * 1998-03-26 1999-10-26 The United States Of America As Represented By The Secretary Of The Air Force Variable power fluid lens

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3641354A (en) * 1967-03-08 1972-02-08 Jack De Ment Optical modulation by fluidic optics utilizing chromatic aberration
US3889431A (en) * 1973-09-04 1975-06-17 Celestron Pacific Method for making schmidt corrector lenses
JPS54109320A (en) * 1978-02-15 1979-08-27 Matsushita Electronics Corp Projection image receiver
EP0410686A2 (fr) * 1989-07-25 1991-01-30 Chromex, Inc., Surfaces optiques asphériques
US5973852A (en) * 1998-03-26 1999-10-26 The United States Of America As Represented By The Secretary Of The Air Force Variable power fluid lens

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
PATENT ABSTRACTS OF JAPAN vol. 003, no. 131 (E - 148) 31 October 1979 (1979-10-31) *

Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2003081920A2 (fr) * 2002-03-25 2003-10-02 Living Ad Limited Production d'images 3-d simulees
WO2003081920A3 (fr) * 2002-03-25 2004-02-26 Living Ad Ltd Production d'images 3-d simulees
US8857779B2 (en) 2009-03-30 2014-10-14 Ge Healthcare Bio-Sciences Ab Holder for a holographic grating
WO2015107362A1 (fr) * 2014-01-17 2015-07-23 The Centre For Vision In The Developing World Cic Procédé de fabrication d'une membrane souple et son moule, membrane et lentille à foyer variable
GB2539822A (en) * 2014-01-17 2016-12-28 The Centre For Vision In The Dev World C I C Method of making a flexible membrane and mold therefor, membrane and variable focus lens
GB2539822B (en) * 2014-01-17 2020-10-07 The Centre For Vision In The Dev World C I C Variable focus lenses
FR3122262A1 (fr) * 2021-04-23 2022-10-28 Safran Reosc Télescope compact pour la détection de débris spatiaux
WO2024089367A1 (fr) * 2022-10-26 2024-05-02 Safran Reosc Télescope de schmidt à performances améliorées, dispositifs et procédé de détection associés
FR3141450A1 (fr) * 2022-10-26 2024-05-03 Safran Reosc Télescope de Schmidt à performances améliorées, dispositifs et procédé de détection associés

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