Figure metrology of deep general aspherics using a conventional interferometer with CGH null

We present a simple and general method of aspheric figure metrology using a CGH null mounted in the test beam of a conventional Fizeau or Twyman-Green interferometer. A 'standard' reflective CGH is used to establish optical alignment with respect to the interferometer's spherical test beam. This alignment is then mechanically trnaferred to a custom CGH null. The accuaracy of the alignment transfer is readily verified. The test method has been modeled by raytracing and verified experimentally by testing a perforated 8 inch F/1.5 on-axis paraboloid and a 50 mm off-axis paraboloid from their centers of curvature.