Electronic flash control system for use in a fixed focus lens camera for increasing depth of field by the timing of flash actuation

Claim 1

An exposure control system for photographic apparatus having means for defining a film plane and a fixed focus lens for directing light along an optical path from a scene onto photosensitive material located in the film plane, said exposure control system comprising: a blade mechanism mounted for movement between a blocking arrangement in which said blade mechanism is in light blocking relation with respect to the optical path so as to preclude scene light from being transmitted along the optical path to the film plane and an unblocking arrangement in which said blade mechanism is in light unblocking relation with respect to the optical path so as to allow the passage of scene light to the film plane, said blade mechanism serving to provide an exposure aperture through which scene light passes and whose size varies in a predetermined manner when said blade mechanism is actuated between its said light blocking and unblocking arrangements to produce an exposure interval; drive means for displacing said blade mechanism between its said blocking and unblocking arrangements to define said exposure interval; a light source for illuminating the scene with artificial light that is energizable for a period of time before and for a period of time during the exposure interval; light sensitive means for detecting, prior to an exposure interval, light emitted by said light source and reflected from a subject within the scene that is located at a distance less than a predetermined magnitude and for generating a first signal representative thereof comprising means for storing a reference signal representative of the near distance of the normal depth of field of the fixed focus lens, means responsive to the light emitted by said light source and reflected from the subject within the scene and for generating a signal representative of subject reflectivity and a comparator for comparing said reference signal to said subject reflectivity signal, and for detecting light emitted by said light source and reflected from the scene during the exposure interval and for generating a second signal representative thereof; and control means 1) for actuating said drive means to effect displacement of said blade mechanism to produce said exposure interval, 2) for energizing and de-energizing said light source to illuminate the scene and a subject included therein, before said exposure interval, 3) responsive to said first signal for energizing said light source a fixed period of time after actuating said drive means to initiate said blade mechanism displacement, said fixed period of time being just sufficient for the aperture to reach a size which is smaller than that which would be normally used, and 4) responsive to said second signal for de-energizing said light source during said exposure interval.