Abstract: An X-ray tube is movable between a minimum distance from an image receptor and a maximum distance. Signals are generated representative of the X-ray tube focal spot-to-image distance (SID), the peak kilovoltage (kVp) that is to be applied to the X-ray tube anode during a fluorographic exposure and the desired brightness of the X-ray image. The signals are processed in a manner that results in a control signal being developed that adjusts the X-ray tube filament current in a way that produces an X-ray tube current (mA) during the exposure which results in a constant limited X-ray dose rate at the X-ray beam entrance plane of a patient at any permissible kVp and SID setting and assures that the dose rate limit will not be exceeded at minimum permissible SID regardless of the selected kVp.