A curved cylindrical segment platen has a concave touching surface. An interrogating slit light beam is scanned around the platen to scan a finger held against the touching surface. An optical imaging system images the zone illuminated onto an array of photo-transducers to provide a signal representing...http://www.google.com.au/patents/US4783167?utm_source=gb-gplus-sharePatent US4783167 - Finger imaging apparatus using curved platen
