Abstract: A psssive display device comprises a first supporting plate (10) and a second supporting plate (11) at least one of which is transparent. The device comprises display elements each having at least one fixed electrode (12, 13) and an electrode 16 which is arranged so as to be movable with respect to the said electrode (12, 13) and has apertures. The movable electrode 16 can be moved by electrostatic forces between two final positions determined by engaging surfaces (14, 15). In each of the final positions the movable electrode 16 engages an engaging surface (14, 15) whose surface structure is not congruent with that of the surface of the electrode so that a finite number of discrete engaging points is formed between the movable electrode and its engaging surfaces. Furthermore methods are described for manufacturing such a display device.

Abstract: A binocular belonging to one type is provided with a focus adjusting device which allows one to select a desired ocular lens feed rate. A single annular piece is included in the device to be rotated by a manually operated focus adjusting ring to in turn drive a shaft associated with ocular lens barrels in a reciprocal movement. A bunch of such exchangeable annular pieces are prepared each being formed with a helical slot which differs in pitch from helical slots in the others.