An autostereoscopic display comprises an SLM which is controlled to provide an image display and a signal display. A parallax optic has a first portion which cooperates with the image display to form a plurality of viewing windows. A second portion of the parallax optic forms first and second images visible to an observer to allow the observer to distinguish between a desired orthoscopic viewing zone and undesirable viewing positions such as pseudoscopic positions. The pitch of parallax elements in the second portion is one and a half times the parallax element pitch in the first portion.