Three-dimensional imaging based on perfect projection using varifocal mirror

An imaging system with a focusing mechanism based on perfect projection was devised using a varifocal mirror to achieve high-quality three-dimensional imaging and precise measurement of shape. We treated two types of projection that were used as an analytical model for machine vision. First, an imaging system based on perspective projection was constructed so that the varifocal mirror was placed at the front focal point of the image taking lens. Magnification was exactly equal to the ratio of the focal length and an object point distance from the front focal point of the lens, which was fixed when focusing with the varifocal mirror. The surface shape of a spherical dent (3.5 mm in diameter) was precisely measured with the shape-from-focus-method because the dent could be viewed from the side. Second, we constructed an imaging system with a focus mechanism based on orthographic projection so that the varifocal mirror could be placed at the back focal point. The system was able to be focused on any object point at constant magnification. Taking advantage of parallel projection, an entirely focused 3-D image of a screw thread (2 mm in diameter) and its profile could successfully be obtained using the shape-from-focus method.