Electronically operating automatic focussing system - uses multielement photosensitive sensor which scans optical field and results of successive scans are compared

摘要

An automatic focussing device for cameras or projectors based on the use of electronics and light-sensitive elements. A sensor containing a number of light sensitive elements generates signals according to the intensity of light received, and it can be controlled in its distance from a point in the optical system by a control sginal. A circuit derives a mean signal value from all the individual sensor elements, whilst a second circuit determines the difference between each individual signal and this mean value. A third circuit forms the sum of all the positive or negative difference generated in the second circuit over a scanning cycle covering all the individual elements. The output signal from the third circuit over one cycle is compared in a fourth circuit for successive scanning cycles and according as the result is greater or smaller, generates a control signal to shift the focus in one sense or the other.