Stereo digital image correlation with improved depth of field using tilt-shift photography

Abstract

Stereo digital image correlation (DIC) is a non-contacting technique to obtain full-field displacement and strain fields from the surface of a deforming object by comparing images recorded before and after deformation. With stereo measurement techniques, out-of-plane measurements are often limited by the depth of field achieved in an image. Tilt-shift photography uses the Scheimpflug principle to improve depth of field by rotating the image plane with respect to the camera sensor. This is implemented using a tilt-shift lens mount, which imposes an angle of tilt between the lens and the camera sensor. In this stereo-DIC study, images were taken using a range of stereo camera angles with either the lens tilted or not tilted to impose the Scheimpflug effect. A series of rigid body displacements were then measured for each combination of stereo and tilt angles. An evaluation of the means and standard deviations of the measurements shows that Scheimpflug adjustment offers minimal improvement when measuring rigid body displacements, but significant improvement at reducing artificial strains.