text: The data collected from AF sensors is used to control an electromechanical system that adjusts the focus of the optical system. A variation of autofocus is an electronic rangefinder, in which focus data are provided to the operator, but adjustment of the optical system is still performed manually.
  The speed of the AF system is highly dependent on the widest aperture offered by the lens at the current focal length.  F-stops of around 2 to 2.8 are generally considered best for focusing speed and accuracy.  Faster lenses than this (e.g.: 1.4 or 1.8) typically have very low depth of field, meaning that it takes longer to achieve correct focus, despite the increased amount of light.  Most consumer camera systems will only autofocus reliably with lenses that have a widest aperture of at least 5.6, whilst professional models can often cope with a widest aperture of 8, which is particularly useful for lenses used in conjunction with teleconverters.
  History
  Between 1960 and 1973, Leitz (Leica) patented an array of autofocus and corresponding sensor technologies.  At photokina 1976, Leica had presented a camera based on their previous development, named Correfot, and in 1978 they displayed an SLR camera with fully operational autofocus.
  The first mass-produced autofocus camera was the Konica C35 AF, a simple point and shoot model released in 1977. The Polaroid SX-70 Sonar OneStep was the first autofocus single-lens reflex camera, released in 1978.