Autofocus
Like the G5 and other Panasonic CSCs, the Lumix DMC-GH3 uses a contrast-detection-based AF system, which is extremely fast in good-contrast light and faster than many phase-detection-based systems used in DSLRs. It can snap into focus from infinity to its minimum focus distance with ease. In low-contrast situations, however, it’s a different story. These systems are not as effective as phase detection. At times in single-point continuous AF, the camera needs to hunt for its subject in low light.
I find that the touchscreen really improves the handling of the AF, because as with metering, coverage is over the entire frame. With a gentle press anywhere on the screen (that barely affects the stability of the camera), single-point and pinpoint AF are particularly effective. In single-point AF, the size of the spot can be adjusted from a mere 3% (approx) of the frame to around 25%.
The 23 areas in the multi-segment AF mode are placed around nine central ‘points’. A manual override is possible in this mode by pressing the screen for touch AF, at which point the camera identifies the closest of these nine points to the area touched on the screen and takes information from there.
As is the case with the G5, the touch functions of the rear screen are available even while the viewfinder is in use, which is an intuitive feature once you become used to it.
As a mirrorless system, full-time AF is possible during video recording. Face detection and tracking AF work well for slow-moving subjects, but increase the speed and erratic movement of a subject and the system often struggles to keep up. High-speed sports photographers are unlikely to be enticed by the GH3, but for all other purposes the camera works well.
