Max Shutter speed
Panasonic GH6 can shoot continuously at max speed of
14.0 fps and has max shutter speed of
1/8000 sec. GH6 also has an electronic shutter which can shoot silently at max speed of
1/32000s. One thing to keep in mind is that electronic shutter may cause rolling shutter / jello effects, and also banding issues under artificial light on your images.
Flash
Unfortunately GH6 doesn't have a built-in flash but it has a flash shoe for mounting external flashes.
Focusing
Panasonic GH6 features a Contrast Detection autofocusing system. Panasonic GH6 also features
Face detection AF where it intelligently detects the faces in the frame and locks the focus automatically. In addition to the face detect AF, GH6 has a more sophisticated feature called
Eye Tracking AF which detects and locks focus to the selected eye of the person in the frame accurately and tracks as the subject moves. Eye tracking AF of Panasonic GH6 is a perfect feature for shooting portraits and is especially useful when fast lenses are used and the depth of field is very narrow.
Focus Stacking
Macro shooters will love Panasonic GH6's Focus Stacking feature. In this mode, GH6 automatically composites multiple shots taken at different focal positions using focus bracketing to create a single image with maximum depth of field.
Post Focus
Panasonic GH6 has a special Post Focus mode which uses its 4K video and focus bracketing features together to shoot and stack a burst of images into a single image which you can change the focus point on the LCD screen after it is taken.