Editing Autofocus (section)

===Contrast detection===
Contrast-detection autofocus is achieved by measuring [[contrast (vision)]] within a sensor field [[Through-the-lens metering|through the lens]]. The intensity difference between adjacent pixels of the sensor naturally increases with correct image focus. The optical system can thereby be adjusted until the maximal contrast is detected. In this method, AF does not involve actual distance measurement at all. This creates significant challenges when [[Video tracking|tracking moving subjects]], since a loss of contrast gives no indication of the direction of motion towards or away from the camera.

Contrast-detect autofocus is a common method in [[digital camera]]s that lack [[Shutter (photography)|shutter]]s and reflex mirrors.  Most [[digital single-lens reflex camera|DSLR]]s use this method (or a hybrid of both contrast and phase-detection autofocus) when focusing in their [[live-preview digital camera|live-view]] modes. A notable exception is Canon digital cameras with Dual Pixel CMOS AF. [[Mirrorless interchangeable-lens camera]]s typically used contrast-measurement autofocus, although phase detection has become the norm on most mirrorless cameras giving them significantly better AF tracking performance compared to contrast detection.

Contrast detection places different constraints on lens design when compared with phase detection. While phase detection requires the lens to move its focus point quickly and directly to a new position, contrast-detection autofocus instead employs lenses that can quickly sweep through the focal range, stopping precisely at the point where maximal contrast is detected. This means that lenses designed for phase detection often perform poorly on camera bodies that use contrast detection.