Apparatus for detecting the in-focusing conditions

An apparatus for detecting in-focusing conditions of an optical system comprising:

• a plurality of optical fibers of different lengths which are closely arranged to each other and have light inlet ends arranged side by side along a given line and located at different levels when viewed in a direction of an optical axis of the optical system and light outlet ends located on a same plane, the inlet end of a centrally arranged optical fiber being situated on a predetermined focal plane of the optical system;
• a like number of charge transfer elements arranged at the respective outlet ends of the optical fibers to receive light rays emerging from respective picture elements and transmitted through the respective optical fibers and to produce illuminance signals;
• and means for receiving the illuminance signals from the charge transfer elements and processing the received illuminance signals in accordance with a predetermined function to produce a signal which represents a focusing condition of the optical system.