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Fotothek df tg Optik Dioptrik Licht Brechung Linse konvex konkav. Scan Deutsche Fotothek dftg color MIKCenter Berlin GmbH Figur Wrzburg Frankfurt Main Lichtbrechung an konvexen und konkaven Linsen Papier Kupferstich cm Optik Dioptrik Licht Brechung Linse konvex konkav ppn Druck Deutsche Fotothek gefrdert von der Deutschen