Understanding autofocusing - Part 1

Autofocusing systems in cameras have developed along two lines: contrast detection (CDAF) and phase difference detection (PDAF). Although they operate quite differently, in recent years many cameras have included both types in the quest for faster, more accurate autofocusing.

This Insider will concentrate on how they work; not the actual mechanisms used to drive autofocusing. (Readers interested in the nuts and bolts of autofocusing systems can find an excellent article by Roger Cicala of Lens Rentals at www.bit.ly/pr79-autofocus.)

Contrast detection

CDAF systems are technologically simple, relatively cheap to implement, and more likely to focus accurately. They work by analysing the pixel array on the image sensor and scanning through possible focus points, looking for edges with the