Abstract: A lens, suitable for directing radiation, comprises an array of planar reflecting elements or slats. Each reflecting element is of non-uniform extent or surface area t and/or is of non-uniformly spacing d from adjacent elements. The elements may be parallel or non-parallel. Each element is positioned such that the ratio of spacing d.sub.n to extent t.sub.n is determined by the angle of incidence on the nth element .gamma..sub.n as is given by the relationship (a) where d.sub.n is the spacing between the nth and (n+1)th adjacent elements of the lens, t.sub.n is the length of the nth element and M is the magnification of the lens.