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→History: Removed bayonet misspelling and brought into same terminology as the next reference to the EF mount
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→top: Sensor link, but perhaps someone can supply a more relevant definition
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An '''autofocus''' (or '''AF''') [[optical]] system uses a [[sensor]], a [[control system]] and a [[Electric motor|motor]] to [[Focus (optics)|focus]] on an [[wikt:automatic|automatic]]ally or manually selected point or area. An [[Rangefinder camera#Digital rangefinder|electronic rangefinder]] has a display instead of the motor; the adjustment of the optical system has to be done manually until indication. Autofocus methods are distinguished by their type as being either [[Passivity (engineering)|active]], [[Passivity (engineering)|passive]] or hybrid variants.
 
Autofocus systems rely on one or more sensors[[sensor]]<nowiki/>s to determine correct focus. Some AF systems rely on a single sensor, while others use an array of sensors. Most modern [[SLR camera]]s use [[Through-the-lens metering|through-the-lens]] optical sensors, with a separate sensor array providing light [[Metering mode|metering]], although the latter can be programmed to prioritize its metering to the same area as one or more of the AF sensors.
 
Through-the-lens optical autofocusing is now often speedier and more precise than can be achieved manually with an ordinary viewfinder, although more precise manual focus can be achieved with special accessories such as focusing magnifiers. Autofocus accuracy within 1/3 of the [[depth of field]] (DOF) at the widest [[aperture]] of the lens is common in professional AF SLR cameras.
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