APPARATUS FOR USE IN FOCUSSING IMAGES

摘要

Apparatus for focussing images on screens in which a strip of the image is scanned by a radiation-sensitive device. The well-defined edges of a focussed image produce high-frequency components in the output of the radiation sensitive device which are absent when the image is out of focus. Scanning is produced by deflection coils of a television camera or by the pull-down mechanism of a projector which allows some radiation to reach the screen during pull-down. The focus may be determined in two planes, one in front of and the other behind the screen whereby an indication of the direction in which the lens should be moved to focus the image on the screen is given.