Apparatus measures the radius of curvature of a reflective or partially reflective surface 18, and comprises first and second lasers 2, 4 which generate two parallel beams a known distance apart. A lens 12 focuses the beams, which are passed via a beam splitter 14 and transform lens 16 to the surface 18. The beams are reflected back via the transform lens 16 and the beam splitter 14 onto a detector 20. A processor 22 calculates the radius of curvature of the surface using the known distance (X, fig 2) separating the beams and the positions of the beams on the detector 20. The lasers 2, 4 can be replaced by a discrete beam generator (24, fig 3) which generates a plurality of parallel beams. Add-on optics (28, fig 4) may be positioned between tranform lens 16 and surface 18 to increase or decrease beam separation.
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