Open AccessExact optics – III. Schwarzschild's spectrograph camera revised
Author(s) -
Willstrop R. V.
Publication year - 2004
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1111/j.1365-2966.2004.07421.x
Subject(s) - physics , schwarzschild radius , spectrograph , coma (optics) , geometrical optics , optics , conic section , spherical aberration , quadratic equation , classical mechanics , astronomy , gravitation , geometry , mathematics , lens (geology) , spectral line
Karl Schwarzschild identified a system of two mirrors, each defined by conic sections, free of third‐order spherical aberration, coma and astigmatism, and with a flat focal surface. He considered it impractical, because the field was too restricted. This system was rediscovered as a quadratic approximation to one of Lynden‐Bell's ‘exact optics’ designs which have wider fields. Thus the ‘exact optics’ version has a moderate but useful field, with excellent definition, suitable for a spectrograph camera. The mirrors are strongly aspheric in both the Schwarzschild design and the exact optics version.