Device for detecting a magnification error in an optical imaging system
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United States of America Patent
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-
Sep 20, 1988
Grant Date -
N/A
app pub date -
Oct 14, 1986
filing date -
May 21, 1986
priority date (Note) -
Expired
status (Latency Note)
Importance
Abstract
A device is described for detecting a magnification error in an optical imaging system comprising a lens system (L.sub.1, L.sub.2) which is telecentric at one side. Two gratings (RG.sub.1, RG.sub.2) arranged in the object plane (MA) are imaged onto two gratings (WG.sub.1, WG.sub.2) arranged in the image plane (W; WT) and the radiation beams (b.sub.1, b.sub.2) by means of which these images are formed are incident on two radiation-sensitive detection systems (D.sub.1, D.sub.2) which supply periodic signals (S.sub.1, S.sub.2). By phase comparison of these signals a magnification error (S.sub.ME) and, if desired, a focussing error can be measured very accurately.
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