contrastdetect

Contrast-detect autofocus (contrast-detect AF) is an autofocus method used in digital cameras and image sensors. It adjusts lens focus to maximize image contrast on the sensor, based on the principle that sharp focus increases local contrast and edge definition.

Operation: The camera analyzes a focusing region and computes a contrast metric. The lens is moved and the metric is re-evaluated, typically via a hill-climbing search, until peak contrast is reached or a threshold is met. In many mirrorless cameras, CDAF is performed entirely on the imaging sensor during live view.

Advantages: It uses only image data, so it works with any lens and does not require phase-detection hardware. It can be highly accurate and integrates with manual focus aids such as magnification and focus peaking.

Limitations: CDAF can be slower than phase-detect autofocus, especially in low-contrast scenes or during continuous AF. It may hunt in poor lighting or with macro subjects, and video AF can appear less smooth.

Hybrid approaches: Some cameras combine contrast-detect with phase-detect sensors to gain speed while preserving the accuracy of CDAF, particularly for continuous AF and video.

See also: autofocus, phase-detect autofocus, hybrid autofocus, live view.