Automatic focusing devices for photographic cameras

Automatic focusing systems for either still or movie cameras are defined. System requirements, depending on camera characteristics (aperture), lighting conditions or the use of high-speed color film, are identified. Passive and active systems are considered. Optimizing rules are derived for passive systems. Two functioning models were built, using modified cameras: one incorporating contrast measuring, the other, autocorrelation based on image scanning. Working models of active systems which measure distance as a focusing criterion were also constructed. Triangulation with IR optics, and time delay measurement of ultrasonic signals were tried. The various systems were evaluated for ultimate range, focusing quality, and time needed for accurate measurements. The practicability of both passive and active systems is demonstrated. However, electronic and optical complexity must be traded off against focusing requirements in choosing a suitable camera system.