Phase measuring Ronchi test.

Use of synchronous phase detection in the conventional Ronchi test is discussed to measure a large amount of wavefront aberration or an aspheric wavefront. This method provides a simple but powerful tool for aspheric surface evaluation. By moving the Ronchi grating sideways, a periodic phase shift in the Ronchigram is introduced for synchronous phase detection. A theoretical interpretation of the Ronchigram and the procedure for an analysis are presented, and experimental results are shown.