Automatic Focussing Devices for Photographic Cameras

摘要

High-aperture cameras and photography under poor light conditions make focussing with conventional methods very difficult. Hence, the need for autofocussing systems. Initial requirements for autofocussing systems for both still and cine cameras were defined and active and passive systems examined. In particular, optimizing rules were derived for passive autofocussing systems using contrast-measurement methods or auto-correlation based on image scanning, these rules being used in the development of related models. As regards the active autofocussing systems, working models employing triangulation with infrared light sources and ultra-sonic-wave reflection times were constructed. The advantages and disadvantages of the various systems were considered in relation to ultimate range and measurement accuracy and duration, and practical active and passive autofocussing systems successfully demonstrated. In selecting the most suitable autofocussing system for a camera, the degree of technological complexity has to be considered with respect to the differing requirements of the electronic and optical systems.