Camera autofocus: PDAF, laser and how a camera gets sharp

Autofocus is the camera system that automatically moves the lens so the subject becomes sharp. Phones use contrast, phase-detection (PDAF, Dual Pixel) and laser autofocus, often together.

Autofocus sharpens the image like a binocular focus wheel

In plain words

Remember binoculars with a focus wheel? You turn it until the picture is clear. Autofocus does the same in a fraction of a second: a tiny motor shifts the lens and the sensor checks whether it got sharper. Phase-detection autofocus even knows straight away which way to turn.

How it works

Contrast autofocus moves the lens back and forth looking for maximum sharpness - slower.
Phase detection (PDAF) uses special pixels that "see" the image shift and know the direction at once.
Dual Pixel and all-pixel PDAF use most of the pixels for this - the fastest.
Laser or ToF autofocus measures the distance to the subject, helping in the dark.
Neural networks recognise eyes, faces and animals to keep focus on them.

Autofocus keeps a moving subject sharp

Where you'll see it

In camera specs: "PDAF", "Dual Pixel PDAF", "laser AF", "fixed focus". Front and ultra-wide cameras on budget phones often have fixed focus with no autofocus.

Does it matter when buying

Yes, especially for photos of kids, pets and movement. Phase-detection autofocus on the main camera is a must. Autofocus on the front camera makes selfies sharper at different distances. And macro shots from the ultra-wide are only possible if it has autofocus.

Myths

Myth: More megapixels means sharper photos. Reality: Without accurate focus even 200 MP gives a blurry photo.
Myth: Fixed focus is always bad. Reality: For ultra-wide cameras it is sometimes a reasonable trade-off, but less flexible.

FAQ

How do I focus manually?

Tap the spot you want on the camera screen.

Why does the camera "hunt" for focus in the dark?

There is too little light for the PDAF sensors; laser or ToF helps.

What is fixed focus?

The lens does not move; sharpness is set for a certain distance.