Abstract: A system to automatically regulate input light and television camera tube gain to maximize scene viewing continuity while protecting against overloads. An electro-optical input assembly, an image intensifier, SEC vidicon and video pre-amplifier produce required video signals. The signals are fed along a common path comprising a keyed clamp and field gating circuit, parallelly connected peak and average detectors, detector output weighting, amplifying and attenuator circuits. The path branches to a control function stage and a high voltage power supply to form a fast vidicon accelerating voltage adjusting loop. The path also branches to iris threshold and dead zone stages, to cause an iris motor to control the iris position in accordance with ambient durational and transient light conditions.