An optical instrument for producing an optical image to be viewed by an observer, the optical instrument comprising: an optical system for producing an optical image of an object which is viewable by an observer at an exit pupil on a viewing plane; and a diffractive element located at an image plane of the optical system for producing an array of exit pupils, which are perceivable as a single, enlarged exit pupil by the observer; wherein the diffractive element comprises a surface on a substantially flat plane which has an array of diffractive units disposed at increasing radial distance outwardly from the optical axis of the diffractive element, each of which generates one of the exit pupils of the array of exit pupils, the diffractive units each comprising replications of a pattern of a plurality of separated areas which are effective to produce diffractive interference of light and generate a plurality of exit pupils which are displaced relative to one another in the form of an array of exit pupils, such as to be viewable as a single, continuous enlarged exit pupil, and the areas comprise irregular features of different sizes, both in horizontal and vertical section, which have curved surfaces at lateral faces thereof; characterized in that the diffractive units progressively provide for an increasing angular offset (β x, β y, β z) of the optical path in relation to the optical axis of the diffractive element by providing the areas within each progressively-radially outward diffractive unit to be of different size, shape and position, such that, independent of location on the aperture of the diffractive element and without any lens arrangement between the diffractive element and the viewing plane, light from the received image is relayed to a common region on the viewing plane across the aperture of the diffractive element. an optical system for producing an optical image of an object which is viewable by an observer at an exit pupil on a viewing plane; and a diffractive element located at an image plane of the optical system for producing an array of exit pupils, which are perceivable as a single, enlarged exit pupil by the observer; wherein the diffractive element comprises a surface on a substantially flat plane which has an array of diffractive units disposed at increasing radial distance outwardly from the optical axis of the diffractive element, each of which generates one of the exit pupils of the array of exit pupils, the diffractive units each comprising replications of a pattern of a plurality of separated areas which are effective to produce diffractive interference of light and generate a plurality of exit pupils which are displaced relative to one another in the form of an array of exit pupils, such as to be viewable as a single, continuous enlarged exit pupil, and the areas comprise irregular features of different sizes, both in horizontal and vertical section, which have curved surfaces at lateral faces thereof; characterized in that the diffractive units progressively provide for an increasing angular offset (β x, β y, β z) of the optical path in relation to the optical axis of the diffractive element by providing the areas within each progressively-radially outward diffractive unit to be of different size, shape and position, such that, independent of location on the aperture of the diffractive element and without any lens arrangement between the diffractive element and the viewing plane, light from the received image is relayed to a common region on the viewing plane across the aperture of the diffractive element.