A folded optical arrangement for use in a view-through display to transmit an image from an image source to a user's eye, the arrangement providing a folded optical transmission path and comprising: an optical system having a first optical element comprising a first plurality of optically powered surfaces (618, 620, 622), and a second optical element comprising at least one optically powered surface (626, 628), the optical system configured to receive light forming the image from the image source, and configured to present a virtual image of the image source to the user with an apparent focus between a predetermined distance and optical infinity; and a compensator element located between the first optical element and an external view to receive the external view for combination with the image output from the optical system, wherein the first plurality of optically powered surfaces and the at least one optically powered surface of the second optical element are arranged to define a plurality of interfaces along the folded optical path and wherein a refractive index change at each interface is predetermined to control the direction of light passing through the interface; and wherein one surface of the first optical element and one surface of the second optical element are adjacent to one another and each define an angle (902, 904) with a respective other surface (622, 628) of the relevant optical element at opposing ends of the adjacent surfaces and wherein the opposing angles are not equal, characterised in that the adjacent surfaces (620, 626) are non-complementary or non-sympathetic such that there is no way to place the surfaces (620, 626) together without leaving a gap. an optical system having a first optical element comprising a first plurality of optically powered surfaces (618, 620, 622), and a second optical element comprising at least one optically powered surface (626, 628), the optical system configured to receive light forming the image from the image source, and configured to present a virtual image of the image source to the user with an apparent focus between a predetermined distance and optical infinity; and a compensator element located between the first optical element and an external view to receive the external view for combination with the image output from the optical system, wherein the first plurality of optically powered surfaces and the at least one optically powered surface of the second optical element are arranged to define a plurality of interfaces along the folded optical path and wherein a refractive index change at each interface is predetermined to control the direction of light passing through the interface; and wherein one surface of the first optical element and one surface of the second optical element are adjacent to one another and each define an angle (902, 904) with a respective other surface (622, 628) of the relevant optical element at opposing ends of the adjacent surfaces and wherein the opposing angles are not equal, characterised in that the adjacent surfaces (620, 626) are non-complementary or non-sympathetic such that there is no way to place the surfaces (620, 626) together without leaving a gap.