Perfect perspective projection using a varifocal mirror and its application to three-dimensional close-up imaging

An imaging system with a focusing mechanism based on perfect perspective projection was devised using a varifocal mirror to achieve high-quality three-dimensional imaging and precise measurement of shapes. It was constructed so that the varifocal mirror was placed at the object focal point of the image-taking lens. The focal point of the lens was fixed when focusing with the varifocal mirror. Magnification was exactly equal to the ratio of the focal length and the object point distance from the object focal point of the lens. This held at magnifications larger than unity. The surface shape of a spherical dent (3.5 mm in diameter) could accurately be measured with the shape-from-focus method because the dent could be viewed from the side in the perspective projection system.