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A type of camera lens that can adjust the distance of what is in focus (focal length).

Auto-focus usually provide better photo quality than fixed-focus, since auto-focus lenses can be larger and allow more light to reach the camera sensor. The downside of auto-focus is usually a delay when taking a photo (shutter lag).

Unlike fixed-focus lenses, auto-focus lenses provide "depth of field", meaning objects not at the focus distance appear out of focus (blurry).

Most auto-focus cameras mechanically change the distance between two lenses to do this using a small motor or ultrasonic actuator. Newer technologies use lenses that can change shape, providing the same functionality in a smaller package.

See: Fixed-focus

Basic auto-focus systems use contrast detection (CDAF), which does an electronic version of what how you would focus with your own eyes: adjusting the lens until edges appear sharp.

More advanced auto-focus systems in phones use lasers and/or dedicated focus pixels on the main sensor. A system using focus pixels is known as phase detection (PDAF).


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