For fast, accurate and robust shape measurement of specular surfaces there are several powerful measurement techniques based on deflectometry. For boundary surfaces of transparent objects like refractive optics, on the contrary, deflectometry is so far limited to the measurement of only one surface in reflection. This is unsatisfying from a metrological point of view as the geometrical relation between both surfaces, which substantially defines the optical function, is lost. In this work a new deflectometric approach is presented that works in transmission and allows the simultaneous measurement of both surfaces of refractive optics. The basic idea of the approach is calculating the unknown surface geometry of a transparent object by iteratively adapting a surface model to the observed light ray deflections. The main problem in this case is the ambiguity of the refraction at the two boundary surfaces of a lens, as there are multiple possible solutions that produce the same measurement results. This is solved by combining four different views on the object under test, which allows to find an unambiguous solution. An experimental measurement setup is presented and results of different simulations and tests are discussed in this paper.

Date Published: 19 January 2009
PDF: 8 pages
Proc. SPIE 7239, Three-Dimensional Imaging Metrology, 723906 (19 January 2009); doi: 10.1117/12.810530

Published in SPIE Proceedings Vol. 7239:
Three-Dimensional Imaging Metrology
J. Angelo Beraldin; Geraldine S. Cheok; Michael McCarthy; Ulrich Neuschaefer-Rube D.V.M., Editor(s)