Panasonic GH4 Quick Start Manual page 58

Use A FC f or c ontinuous a uto f ocus w hile s hooting.
Press t he s hutter t o s et t he i nitial f ocal p oint.
Set L ever t o AFC Green indicates i n focus
Note: A uto F ocus c an b ecome a p roblem i n l ow l ight.