Abstract: A microcomputer is employed in an automatic exposure control system for developing and controlling execution of film exposure strategies for both ambient light exposures and flash and fill flash exposures wherein the scene is illuminated with a mixture of ambient light and artificial illumination provided by a photoflash lamp which may have light output characteristics that deviate from specification due to manufacturing variances. Using pre-exposure scene brightness and distance inputs the computer selects an appropriate one of a plurality of different preprogrammed trajectory signal programs which is to be fed to a stepper motor that drives a shutter blade mechanism in a manner whereby its operation is characterized by an aperture size versus time trajectory curve defined by the selected program.