Autofocus: Difference between revisions

Most multi-sensor AF cameras allow manual selection of the active sensor, and many offer automatic selection of the sensor using [[algorithms]] which attempt to discern the location of the subject. Some AF cameras are able to detect whether the subject is moving towards or away from the camera, including speed and acceleration data, and keep focus on the subject — afocus — a function used mainly in sports and other action photography;. on Canon cameras call this is known as [[AI servo]], while on; Nikon cameras call it is known as "continuous focus".

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 ''[[Rangefinder camera#Digital rangefinder|electronic rangefinder]]'', a system 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-stop]]s of around {{f/}}2 to {{f/}}2.8 are generally considered optimalbest in terms offor focusing speed and accuracy. Faster lenses than this (e.g.: {{f/}}1.4 or {{f/}}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 {{f/}}5.6, whilst professional models can often cope with a widest aperture of {{f/}}8, which is particularly useful for lenses used in conjunction with [[teleconverter]]s. {{Citation needed|reason=Looks like original research.|date=October 2016}}