Automatic camera focusing system - measures light received from object illuminated at two distances from illumination source

摘要

Automatic camera focusing system measures the illumination by a source of an object at different distances and analyses the resulting signals using the equation E = I/r2 where E is the illumination with the object at a distance r and I is the light intensity provided by the system. For a given distance between camera and object the latter is illuminated from two different distances. The two illumination values are measured and the signals are analysed using E = I/r2. The quotient of the signals is used to product a focus control signal corresponding to the range detected. This compensates for variations in light source strength and reflective qualities of the object.