AF points explained
The amount of autofocus points varies between cameras – but in short, the more you pay, the more you get
Entry-level SLRs have around 7-9 AF points, whereas a high-end CSCs like the Sony A7 Mark III squeezes in 693. Cameras that offer a densely populated array of AF points across the viewfinder make it easier to focus on subjects that aren’t in the centre of the picture. A large number of AF points also makes for smoother focus tracking, as the camera can ‘hand off’ autofocus from one AF point to the next to more accurately follow a subject moving across the picture.
AF point array
AF points are clustered towards the centre of an SLR viewfinder. An AF point array typically contains standard AF sensors that measure sharpness in one plane and ‘cross-type’ AF sensors that are more precise.
How they work
The AF sensor detects a line of contrast that ‘breaks’ the line of the sensor – such as the horizon here. The AF system pushes the lens’ focusing back and forth until the active sensor is able to find this high-contrast point.
Types of AF points
Beginner cameras may have one cross-type point, whereas high-end models have many.