Method of and apparatus for detecting precence or absence of photosensitive object at a prescribed position.

摘要

Photosensors (3, 4, 5) having light emitting elements and light receiving elements are provided in a path for carrying a film (1). The light emitting elements emit periodic pulsed light. When the film (1) is present in the positions of the photosensors (3, 4, 5), the periodic pulsed light is reflected by the film (1) to enter the light receiving elements, whereby presence of the film (1) is detected. Activation time and activation interval of the light emitting elements for generating the periodic pulsed light and determined so that accumulated exposure value in each portion on the film (1) is less than a critical exposure value of photosensitive material provided in the film (1).