A simple device has been constructed to record accurately the parallelism of optically contacted Fabry-Perots immediately after their manufacture. In this a Fabry-Perot fringe is tuned to be a maximum on-axis by varying the pressure of the gas in which the etalon is emersed. An insect-eye lens is then used to photograph the different fringe patterns from a large number of separate small areas of the Fabry-Perot simultaneously.
J. Meaburn, F. Anderson, R. F. Harrington, J. Mortleman, and A. Peters, "Recording the parallelism of optically contacted Fabry-Perots," Appl. Opt. 15, 3006-3008 (1976)