Electronic focus tracking via laser or ultrasound — keeps focus on moving subjects hands-free. Essential for locked-off shots and 4K work.
Since digital cameras have become high-resolution, you need someone on set to pull focus exclusively—or you can get a system that does it itself. The automated follow focus system (Automated Follow Focus) solves exactly this problem: an electronic unit measures the distance to the object via laser or ultrasound and controls the focus motor in real-time. No human in between, no unsharpness from manual jitters.
The technology works on a simple principle—you mark the target object (e.g., a person's face), and the system continuously tracks it. The laser variant measures the exact distance by reflection; ultrasound works similarly but is more susceptible to obstacles and echoes. For static camera positions—interviews, product shots, documentary tableaux—automation shows its strength: while the person moves around the room, they remain consistently in focus. Especially with 4K and higher resolutions, every focus error is immediately noticeable; depth of field becomes relentlessly narrow, and manual adjustment turns into a tightrope walk.
In practice, however, you need to know where the limits lie. Reflective surfaces—water, glass, metal sheets—fundamentally confuse the systems. Even with fast movements through multiple planes (e.g., a person runs through a room with other people in the background), automation can get confused; it needs clear lines to the object. Therefore, the hybrid approach is common: a focus puller operates the automation, adjusts the target box when necessary, and intervenes manually—not constantly readjusting, but as a safety net.
Tech tip: Test every system in situ—on your set, with your lighting conditions and distances. Manufacturers promise a lot, but backlight and diffuse illumination are classic pitfalls. Connect the automation to your focus motor (e.g., motorized follow focus systems from Dana Dolly, Tilta, or similar), and you save an entire position—valuable for small crews, deadly for the tension in the image if it's set incorrectly.