Automatic focussing appliance for telephotographic system

摘要

The appliance has a focus detector for detecting the focussing sharpness of several symmetrically formed detection areas of different sizes. For this purpose the centre of the field of view of the telephotographic system is evaluated as the centre of the telephotographic system. A device then determines that smallest detection area as the effective one in which reliability of focus does not fall below a preset level. Several light collection devices can be provided for the reflected light of the telephotographic system in which the sharpness of focus of the reflected light is determined from the output signals of the light collection device which lies in a detection area symmetrical about the centre of the field of view