This invention relates to the use of a standing acoustic wave charge storage device 11 as an image readout device. A frequency f.sub.1 22 is applied to the storage transfer device to create a traveling electric field in the device in one direction along a straight line. A second frequency f.sub.2 23 which is a harmonic of f.sub.1, has the same amplitude as f.sub.1, and is phase stable with f.sub.1 is applied to the charge transfer device to create a traveling electric field in the opposite direction to the first traveling electric field. Consequently, a standing wave (FIG. 2) is created in the charge transfer device along the straight line. When an image 25 is focused on the charge transfer device, light is stored in the wells of the standing wave. Thereafter when the frequency f.sub.2 is removed from the device, the standing wave tends to break up (FIG. 3) and the charges stored therein are moved to an electrode 18 which is connected to an output terminal 19. This terminal is connected to a utilization device 28 where the received charges represent the image on the surface of the charge transfer device along a projection of said straight line.