Abstract: A video signal processing circuit for producing a dissolve control signal to control dissolving of a video signal uses primarily digital circuitry to derive the dissolve signal. A phase locked loop is used to produce a clock signal having a frequency which is a multiple of the vertical synchronizing signal in the video signal, and which is frequency divided by a fraction determined by a programmable counter which defines the rate of dissolve. The divided signal is processed by a signal processor and delivered to an up/down counter controlling a digital to analogue converter, the output of which is processed to produce as said control signal a ramp signal of which the slope is determined by the programmable counter.To provide a dissolving operation of long duration the counter is temporarily halted at midcount Also, the perceived duration of the dissolve operation is made equal to the actual duration by altering the shape of the dissolve control signal.

Abstract: A diascope for a television camera comprises a support, a slide holder and an objective lens. In the support is provided a longitudinal slot with a V-shaped cross-section; the slide holder and the objective lens are placed in the slot and are maintained therein by means of leaf springs attached to the support. The slide holder has a cylindrical shape; the angular position of a test pattern integral with the slide holder is adjusted by rotation of the latter about its longitudinal axis. The longitudinal position of the objective lens is adjusted by causing the objective lens to slide towards one end or the other of the slot.