Autofocus

Autofocus - device used in certain cameras, projectors and enlargers that focuses the image automatically. There are basically two main AF methods in digital camera: the focus detecting method, or passive auto focus usually employs a CCD and works by evaluating the amount of con- trast or the phase difference in a scene. Distance metering or active autofocus utilises an (infrared) light emitter and receiver in a triangular surveying system. Alternatively, the camera uses ultrasound (sonar) and measures the time taken for the sound signal to return. This data is converted by a microprocessor into information about distance and thereby enables the automatic focusing of the lens.