Advanced autofocus

In the early days of digital photography we had a pixel count race with camera manufacturers trying to outdo each other with a higher resolution sensor that could produce bigger and better images. That’s now settled down and there are cameras with a range of pixel counts to suit different requirements, photographers and budgets. The battleground has moved to AF systems, particularly where artificial intelligence (AI) helps with subject detection.

New developments in AF technology add an extra layer of complexity with more settings to choose from, but once you understand how it all works it makes capturing sharp images much easier.

Set the focus mode

One of the first decisions that needs to be made when photographing a subject is which focus mode is most appropriate. Most cameras offer three settings: manual focus, single autofocus and continuous autofocus. Single AF mode (S-AF or AF-S) is designed for use when subjects aren’t moving. When selected, the camera will focus the lens when the shutter button is pressed half-way. Once focus is achieved, the lens stays focused at that distance until the shutter button is released, then pressed.

Continuous autofocus (C-AF or AF-C and either AI Servo or Servo AF with Canon cameras) is intended for use with moving subjects and the camera continues to assess the focus and adjust if necessary while the shutter button is pressed. If the subject isn’t moving, the focus may adjust backwards and forwards a little in C-AF mode, making S-AF a better choice. Some cameras also offer an Auto AF mode, which will switch between S-AF and C-AF if it detects that the subject is moving and if it decides that the subject is motionless, it will use S-AF.

Focus-area modes

In the early days of AF systems, there was one AF point at the centre of the image frame. Today’s cameras have many focus points and modes to help with their selection. Options range from using a single point to allowing the camera