Method and apparatus for compensating for shutter speed variations

An exposure control system for a photographic camera employing a scanning type shutter that includes a pair of cooperating shutter blade elements automatically compensates for exposure altering variations in shutter blade element speed that may occur from one exposure interval to another. The exposure control system includes an encoder to provide information on the actual position of the shutter blade elements as a function of time during an exposure cycle. The encoder generates a series of pulses representative of relative blade element position as the blades are moved during the exposure cycle. The time between these pulses is measured and directly converted into a signal representative of shutter blade element speed or velocity. This shutter blade speed signal is then employed to alter the duration of an exposure interval to compensate for any shutter blade element speed variations.