Understanding the Camera Auto-focus

The auto-focus system is what tracks the subject and adjusts the lens in order to bring the subject into focus. Learning what auto-focus mode to use for certain situation allows the photographer to be in control of the situation. Knowing which mode to use can mean the difference between tack sharp photos and unfocused ones.

Canon AF mode selector

Auto-focus modes

One Shot or Single Shot Focusing Mode – One-Shot AF (Canon)/AF-S (Nikon)

Single shot mode is usually used for subjects that don’t move. Once the subject is in focus, it will no longer refocus on the subject unless the shutter button is released and half pressed again. It is usually used for portraits, and shooting still life photos. This mode conserves battery as it only focuses on the subject once.

Penguin toy - Image: FreeDigitalPhotos.net

Continuous Focusing Mode – AI Servo AF (Canon)/AF-C (Nikon)
As the name implies, continuously tracks and focuses on the subject. It detects the subject’s movement and refocuses the lens to keep the subject in focus. The continuous focus mode is useful for subjects that continuously move. This can be useful for sports and wildlife photography. However, this mode consumes more battery as the camera will adjust the focus continuously.

Deer running- Image: arztsamui / FreeDigitalPhotos.net

Automatic Autofocus Mode – AI Focus AF (Canon)/AF-A (Nikon)

This mode automatically switches between one shot and AI servo mode depending on the current situation.