Phase detection autofocus measures the direction and distance to focus in one step, so it tracks moving subjects smoothly in video. Contrast detection autofocus adjusts focus until the image looks sharpest, which can be accurate but tends to hunt back and forth. For video, phase detection, or a hybrid of both, is usually the better choice.
How each system works
Phase detection compares light from two sides of the lens. The camera sees how far out of focus the subject is and which way to move, so it can go straight to the right spot. Contrast detection analyzes the image itself and moves the focus back and forth until edges look as crisp as possible. Many modern cameras combine the two in a hybrid system, using phase detection to get near and contrast detection to fine-tune.
What this means for video
- Smooth transitions: phase detection knows which way to move, so focus pulls look steadier. Contrast detection can overshoot and pulse, which shows on screen.
- Moving subjects: phase detection follows people, pets and vehicles better, especially at wide apertures.
- Low light: both struggle in dim scenes, but contrast detection can be slow and uncertain with low-contrast subjects.
- Accuracy on still subjects: contrast detection can be very exact for static subjects, such as product shots on a tripod.
- Camera support: which system you get depends on the camera, so check the maker’s description of its video autofocus.
Comparison
| Trait | Phase detection | Contrast detection |
|---|---|---|
| Speed | Fast | Slower |
| Focus hunting | Rare | More likely |
| Subject tracking | Strong | Limited |
| Static subjects | Good | Very good |
Settings to try
- Use continuous autofocus for moving subjects and single autofocus for static ones.
- Choose a focus area that fits the scene, such as a small point for a fixed subject or a tracking mode for a person.
- Set the focus transition speed, if your camera offers it, to a moderate level so pulls look natural.
- Use face or eye detection when filming people.
- Add light if the scene is dim, since both systems work better with more light.
- Switch to manual focus for planned shots where you want complete control.
A practical test
Record a short clip of a person walking toward the camera, then away from it, with the same settings each time. Watch for focus that pulses or lags, and repeat in dim light. A few minutes of this tells you more about your camera than a feature list.
FAQ
Which system is better for vlogging?
Phase detection or a hybrid system is usually more convenient, since you move around and need the camera to follow your face without constant hunting.
Does a lens affect autofocus quality?
Yes. A lens with a quiet, fast motor helps both systems, and older lenses can slow things down or make noise in recordings.
The Short Version
Phase detection is the stronger choice for video that involves movement, while contrast detection is accurate for still subjects but can pulse. Many cameras use a hybrid of the two. Check your camera’s manual for how its video autofocus works.
