In its simplest form, a transmission Fresnel zone plate lens consists of alternate transparent and opaque rings. Note that the second term on the right-hand side of Eq. Most applications are dominated by the choice of photon energy w , and thus by l . Thus, for many applications, l , D r , and N constitute a natural set of zone plate defining parameters. For uniform plane-wave illumination, as in Fig.
Alternate zones are opaque in the simple transmission zone plate.
With a total number of zones, N, the zone plate lens is fully specified. Lens characteristics such as the focal length f, diameter D, and numerical aperture NA are described in terms of l , N, and D r, the outer zone width. The lens is shown as having a diameter D and outer zone width D r. The object and image distances are p and q, respectively. A full-field image is formed concurrently in this manner.