A condenser (600) for use with a ring-field deep ultraviolet or extreme ultraviolet lithography system. A condenser includes a ripple-plate mirror (606) which is illuminated by a collimated or converging beam (603) at grazing incidence. The ripple plate comprises a flat or curved plate mirror into which is formed a series of channels along an axis (Z) of the mirror to produce a series of concave surfaces in an undulating pattern. Light incident along the channels of the mirror is reflected onto a series of cones. The distribution of slopes on the ripple plate leads to a distribution of angles of reflection of the incident beam. This distribution has the form of an arc (609), with extremes of the arc given by the greatest slope in the ripple plate. An imaging mirror (608) focuses this distribution to a ring-field arc (610) at the mask plane.
