PDAF

Phase-detection autofocus works by measuring the phase difference between two offset images captured by dedicated pixels on the image sensor. Because the camera can detect both the direction and the amount of defocus from a single reading, it moves the lens directly to the correct focus position in one step. This is fundamentally different from contrast-detection AF, which repeatedly moves the lens back and forth through the focus range, testing multiple positions to find peak sharpness. PDAF eliminates the searching process and focuses significantly faster.

PDAF arrived relatively late in the M43 system compared to other mirrorless formats. Many M43 cameras from Olympus and Panasonic used contrast-detection AF for most of their product history, employing advanced predictive algorithms to improve tracking performance. On-sensor PDAF became available in M43 cameras in the early 2020s, starting with flagship bodies. Cameras without PDAF remain capable for general and portrait photography, but phase-detection bodies perform noticeably better for tracking fast-moving subjects and in lower light.

M43 cameras with PDAF support AI-based subject recognition, which uses machine learning to detect and track specific categories of subjects including humans, birds, animals, and vehicles. The phase-detection data provides the camera with real-time distance information that helps subject recognition maintain focus as subjects move unpredictably through the frame. Subject recognition does not function the same way on contrast-detection-only M43 bodies.

Current M43 cameras with on-sensor PDAF include the OM System OM-1 and OM-1 Mark II, the OM-3, OM-5 II, and from Panasonic the G9 II and GH7. These represent the top performance tier of the M43 system for tracking, action, and wildlife photography. Both OM System and Panasonic continue to improve subject recognition performance on PDAF bodies through firmware updates after initial release.