In the development of thin active mirrors for future x-ray telescopes there is a need for full field, non-null methods
of rapidly characterising highly distorted surfaces without contact. Phase measuring deflectometry, due to its
high dynamic range and flexibility, is a promising solution to this problem. In this paper is described a system
developed by the authors at University College London, as well as the results of surface measurements using this
methodology on thin sheets of actuated glass.