Focussing system

Abstract

A first photodetector arrangement comprises three adjoining photodetectors, and a second comprises six. First and second optics, and the two photodetector arrangements, are located immovable on the camera, and the optics project onto the first arrangement an image of a subject which is to form the basis of a subject-distance measurement, without shift between image and photodetectors of the first arrangement so long as the subject-distance is within one of the ranges the system is to furnish; whereas the image projected onto the second photodetector arrangement shifts relative thereto in dependence upon the distance to the subject. The six photodetectors of the second arrangement are subdivided, for signal-processing purposes, into four successive groups, respectively comprised of the first, second and third photodetector, the second, third and fourth, the third, fourth and fifth, etc. A plurality of comparisons are performed by signal-evaluating circuitry, on the basis of absolute-value versions of the differences between the output signals of individual photodetectors in the first arrangement and in successive photodetector-groups within the second arrangement, to automatically ascertain, sequentially or non-sequentially, which photodetector-group in the second photodetector arrangement is in receipt of an image best corresponding to that cast onto the first photodetector arrangement, thereby determining the subject-distance setting best corresponding to the true subject-distance value.