What do the different types of autofocus mean?
By locking a point of focus, the camera won't assess any other areas or hunt around. You can then go on to recompose your image knowing that your subject will still be sharp.
Working off the main imaging sensor, this analyses contrast in a scene and determines focus by finding where there's most contrast.
This follows a subject if it moves away from a focused position, keeping it in focus.
An AF sensor, usually comprising two individual sensors, that is sensitive to movement over two axes, usually along the vertical and horizontal.
This disables the camera's autofocus mechanism, allowing the user to adjust it to their requirements, either by a focusing ring or through the camera.
The standard method of autofocusing on a DSLR, which utilises a separate sensor, typically underneath the mirror.