Method and apparatus for ascertaining the positions of film frames

摘要

Film frames of each of a series of spliced-together exposed and developed photographic films are monitored by photoelectric detector means to ascertain the positions of their leading and trailing edges prior to identification of the frames by a punching device ahead of the copying station. Those film frames whose leading and/or trailing edges cannot be detected with a requisite degree of accuracy (e.g., due to overexposure or underexposure) are pinpointed by ascertaining their length on the basis of accurately ascertained length of other film frame or frames in the same film (a) by calculating the position of the trailing edge upon accurate determination of the leading edge (or vice versa), (b) by calculating the positions of both edges on the basis of the distance between two accurately pinpointed frames which flank the frame whose edges are not detectable, (c) by measuring back from a previously pinpointed frame, or (d) by measuring forwardly from a subsequently ascertained frame.