Video disc play-back unit - with aerodynamic stabiliser for disc acting on optical scanning system

The video disc play-back unit employs an optical scanning system and aerodynamic stabilising means for the disc (111). The convergence of the optical scanning system is variable, with the convergence being adjusted in dependence on the pressure developed by the stabilising means for the disc (111). Pref. the optical scanning system includes a deformable membrane (118) with a reflective mirror surface, the membrane (118) being subjected to at least part of the pressure developed by the stabilising means to obtain the convergence adjustment. The membrane (118) may form an integral part of the stabilising means, so as to be acted on directly by the pressure of the latter. Pref. the membrane (118) forms one wall of a pressure chamber (126) for the stabilising means.