This contrast is highest when the camera is sharply focused on the subject. The system adjusts the focus to achieve the maximum contrast. Some autofocus systems can sense if a subject is moving. These systems make adjustments so that the subject is in focus during the instant the shutter is open. Types of cameras Fixed-focus cameras, the most basic of all cameras, have a nonadjustable lens.
Most models have a single aperture setting and only one or two shutter speeds.
In general, a fixed-focus camera can take satisfactory photographs in ordinary daylight but not in dim light, because its aperture does not admit much light. Many fixed-focus cameras can take flash pictures. Disposable or recyclable cameras are a kind of fixed-focus camera that combines a plastic lens, a shutter, and film in one small box. The entire camera is brought to the photo lab when the roll of film has been exposed. Single-lens reflex cameras appeal to skilled amateur photographers and to professional photographers.