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Published online by Cambridge University Press: 28 May 2003
This paper is describing the fundamental notions of phase contrastmethod introduced by F. Zernike (Zernike 1934) and how it can beapplied to coronagraphy. These techniques were first designed foroptical surface testing and therefore their use as coronagraphicinstrument is not straightforward. This paper is mainly describingthe Foucault knife edge test, its later improvement by Zernike andBurch and their effects as coronagraphic concepts. A formaldemonstration is given in the case of the Phase Knife Coronagraph.