A metal or glass wire (W) is etched into a narrowly tapering cone which has the shape of the desired final capillary-optics bore. By controlling the rate of removal (V) of the wire from an etchant bath (B) using feedback control (C), a carefully controlled taper is produced. A sensor (S) measures the diameter of the wire as it leaves the surface of the etchant. The etched and smoothed wire is coated with a material for optimizing the reflectivity of the radiation being focused. The coated wire is either electroplated, built up with electroless plating, or encapsulated in a polymer cylinder such as epoxy to increase the diameter of the wire for easier handling and greater robustness. The original wire material is then chemically etched away through slits or otherwise withdrawn to leave the hollow internal bore of the final tapered-capillary optical element.
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