Testing the trueness of circular surfaces by laser speckle photography

In an earlier article (1979), the authors suggested a new type of holographic interferometry where the motion or deformation of the object under study is transferred to a probe touching the object for the analysis. The method was developed for circular, cylindrical, or spherical objects using a precision self-centering lens holder as the probe. The present paper intends to show that laser speckle photography can also be used for such studies. The method simply involves illuminating the object surface by a laser beam and taking two photographs on the same film - one before and the other after - the deformation. A large number of double-exposure photographs can be taken, and after the film has been developed, they can readily be analyzed by the scanning method. The discussion covers the analysis and the measurement range for a circular object of variable radius.