An optical configuration for measurement of in-plane displacement and for contouring is reported. In this method an object point is viewed symmetrically with respect to surface normal and combined coherently at the image plane of the imaging system. Because the beams are combined by small apertures at the image plane, decorrelation sets in rather slowly. Owing to low decorrelation, fringes have been obtained for large in-plane deformations and large angular tilts. The method is simple to implement, and its sensitivity can be varied over a wide range. The configuration, therefore, extends the range of measurement.
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