Portrait Photography

Focusing systems work by seeing light and dark between two planes and lock into this; if this distinction is not present, say for example in low levels of light or when the scene is fairly flat with no distinguishing features, the system will struggle. To illustrate this, try to focus the camera on a flat white wall or in low light, and the lens will take its time to settle on anything to focus upon; in these situations it may well be prudent to switch to manual focus.