Digital Speckle Pattern Interferometry (DSPI) is a non destructive testing optical method allowing the visualization of the defects of the deformations of an object submitted to static deformation or to vibration. This method can be applied to a lot of cases within a range of displacements between tens of nanometers and tens of micrometers. DSPI can be applied to detect the natural frequencies and to visualize the mode shapes of a vibrating object. It is very convenient to study small and weak objects because no contact is required comparing the classical modal analysis using accelerometers. DSPI was successfully applied to study a cantilever aluminum plate (5 cm X 10 cm X 1 mm). The experimental iso-displacement fringe maps are compared to computational results using a finite element method.