Contrast Detect AF

Contrast detection autofocus works by analysing the contrast in the image being captured by the sensor and adjusting lens focus until contrast is maximised. A sharp image produces high contrast at fine detail edges; a blurred image produces lower contrast. The camera moves the lens toward the point of maximum contrast, which corresponds to sharpest focus. Because the system must evaluate image data from the sensor itself, it requires the mirror to be up and the sensor to be live — which is why contrast detection is native to mirrorless cameras and was used in early mirrorless M43 bodies before phase detection was added.

The limitation of contrast detection is that it requires the camera to seek the peak contrast point, which often involves moving the lens past the focus point, detecting that contrast has decreased, and moving back. This seeking behaviour, known as hunting, takes time and produces the characteristic back-and-forth movement visible in the viewfinder when contrast AF is active. For static subjects in good light, modern contrast detection systems are fast enough for practical use. For moving subjects, contrast detection cannot predict where the subject will be when the shutter fires, making it less effective for tracking.

Panasonic used contrast detection as the primary AF method across its M43 lineup for many years, and the brand developed a refined implementation called Depth From Defocus that significantly improved speed by using optical calculations to estimate the focus distance before initiating the seek. The G9 II and GH7 introduced phase-detect AF to Panasonic's M43 cameras in 2023. Earlier Panasonic bodies including the G97, G85, and GH5 series use contrast detection only, which remains a practical choice for stills with static or slow-moving subjects but limits performance in tracking scenarios.