Understanding autofocus - Part 2

Having outlined the different autofocusing systems used by today's cameras, we turn our attention to the in-camera focus controls. These are many and varied and include focus points, focusing modes, focus area settings and the facilities in camera menus that allow settings within these categories to be tweaked.

Focus point arrays

The term 'focus points' refers to the tiny sensors that pick up the information needed for focusing. In a DSLR camera, these sensors are usually phase-difference detectors, which are located below the secondary mirror that sits behind the reflex mirror and is used to reflect light down to the AF sensor array. Entry-level DSLR cameras have simple arrays, often with fewer than 12 points.

Mirrorless cameras tend to rely on contrast detection but an increasing number have phase-detection pixels embedded in the surface of the image