I've been shooting video exclusively with Sony A7xxx cameras this year. While auto focus is pretty good, and unlike DSLRs, available while shooting video, it's not perfect. Just good is not good enough, and I've been burned a couple of times when the camera and I don't agree on the principal subject. I've found a pretty good work-around. It's simple enough to add follow focus, either with a manual knob or motorized. Most non-video AF lenses don't have direct coupling and hard focusing stops, which are required for conventional follow focus setup. Reaching around the camera to put two fingers on the focusing ring is possible, but awkward without disturbing the shot or setup. Sony cameras have a DMF mode, which reverts to manual focusing once AF is locked on. Keeping the shutter release (or AF button) depressed lets you fine-tune the focus manually, using very little rotation of the focus ring. Focus assist magnification turns on, if enabled, while AE is engaged. The focus remains fixed when you release the shutter button or the AF button until you repeat the process. The magnification you see in the viewfinder is not recorded to the memory card, nor transmitted via HDMI to an external recorder/monitor. You can't pre-set focusing stops, or use a marked dial, but you get the job done quickly. You can use straight manual focus-by-wire too, but you have to guess how far, how fast, and in which direction to turn the dial.