Utilizing the concept of Ronchi interferometry, a simple and inexpensive surface testing technique is described which allows the testing of large flat first surface optical mirrors. The system sensitivity is variable and responsive to a number of imaging defects introduced by imperfect mirrors. While easiest to use in a qualitative or semi-quantitative mode based on empirical measurements, the testing technique can be quantified to any required degree. When used qualitatively, the system functions best in a large volume testing environment as a screening comparator.
David E. Stoltzmann,
"Application Of Ronchi Interferometry To Testing Large Aperture Flat Mirrors", Proc. SPIE 0153, Advances in Optical Metrology I, (15 December 1978); doi: 10.1117/12.938218; https://doi.org/10.1117/12.938218