![]() ![]() History īetween 19, Leitz (Leica) patented an array of autofocus and corresponding sensor technologies. 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 teleconverters. 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. F-stops of around f/2 to f/2.8 are generally considered best for focusing speed and accuracy. The speed of the AF system is highly dependent on the widest aperture offered by the lens at the current focal length. 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 data collected from AF sensors is used to control an electromechanical system that adjusts the focus of the optical system. Canon cameras call this AI servo Nikon cameras call it "continuous focus". Some AF cameras are able to detect whether the subject is moving towards or away from the camera, including speed and acceleration, and keep focus - a function used mainly in sports and other action photography. ![]() 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. 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. Through-the-lens optical autofocusing is usually speedier and more precise than manual focus with an ordinary viewfinder, although more precise manual focus can be achieved with special accessories such as focusing magnifiers. Most modern SLR cameras use through-the-lens optical sensors, with a separate sensor array providing light metering, although the latter can be programmed to prioritize its metering to the same area as one or more of the AF sensors. ![]() Some AF systems rely on a single sensor, while others use an array of sensors. Autofocus methods are distinguished as active, passive or hybrid types.Īutofocus systems rely on one or more sensors to determine correct focus. An electronic rangefinder has a display instead of the motor the adjustment of the optical system has to be done manually until indication. One selected green focus point using pinpoint autofocusĪn autofocus (or AF) optical system uses a sensor, a control system and a motor to focus on an automatically or manually selected point or area. ![]()
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