History Three-mirror anastigmat

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1 history

1.1 paul
1.2 paul-baker
1.3 korsch





history

many combinations of 3 mirror figures can used cancel third-order aberrations. in general these involve solving relatively complex set of equations. few configurations simple enough, however, designed starting few intuitive concepts.


paul

the first proposed in 1935 maurice paul. basic idea behind paul s solution spherical mirrors, aperture stop @ centre of curvature, have spherical aberration - no coma or astigmatism (but produce image on curved surface of half radius of spherical mirror, mirror in air). if spherical aberration can corrected, wide field of view can obtained. similar conventional schmidt design, schmidt refractive corrector plate instead of third mirror.


paul s idea start mersenne beam compressor, looks cassegrain made 2 (confocal) paraboloids, both input , output beams collimated. compressed input beam directed spherical tertiary mirror, results in traditional spherical aberration. paul s key insight secondary can converted spherical mirror. 1 way @ imagine tertiary mirror, suffers spherical aberration, replaced schmidt telescope, correcting plate @ centre of curvature. if radii of secondary , tertiary of same magnitude, opposite sign, , if centre of curvature of tertiary placed directly @ vertex of secondary mirror, schmidt plate lie on top of paraboloid secondary mirror. therefore schmidt plate required make tertiary mirror schmidt telescope eliminated paraboloid figuring on convex secondary of mersenne system, each corrects same magnitude of spherical aberration, opposite sign. also, system of mersenne + schmidt sum of 2 anastigmats: mersenne system anastigmat, , schmidt system, resultant system anastigmat, third-order aberrations purely additive. in addition secondary easier fabricate. design called mersenne-schmidt, since uses mersenne configuration corrector schmidt telescope.


paul-baker

paul s solution had curved focal plane, corrected in paul-baker design, introduced in 1969 james gilbert baker. paul-baker design adds spacing , reshapes secondary elliptical, corrects field curvature obtain flat focal plane.


korsch

a more general set of solutions developed dietrich korsch in 1972. korsch telescope corrected spherical aberration, coma, astigmatism, , field curvature , can have wide field of view while ensuring there little stray light in focal plane.








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