We report the testing of a fast hyperbolic concave surface based on the null screen principles. The design of the null screen with drop shaped spots is described; its image, which is formed by reflection on the test surface, becomes an exact square array of circular spots if the surface is perfect. Any departure from this geometry is indicative of defects on the surface. Here the whole surface is tested at once. The test surface is 459mm in diameter (F/0.5087), with a conic constant of k=-1.34514. The surface departures from the best surface fit will be shown; in addition, we perform an error analysis in order to determine the accuracy of the test when we have errors in the determination of the coordinates of the centroids of the reflected images, and in the coordinates of the spots of the null screen, which are below 6μm.
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