A complex technique of preventing picture highlights from “comet-tailing” due to lack of beam current in the camera tube.

(The usually coloured trail behind a moving, very bright light/reflection in a picture is called a “comet-tail” since the effect looks similar to an astronomical comet.) The technique involves a special tube and circuitry to drive it. Basically, the charge due to a very bright object is never allowed to build up to an unmanageable level by discharging the target above a preset level during horizontal retrace time when the ACT action is turned on, with an increased beam current.