A camera shutter is set to various speeds, each of which determine the length of time a film is exposed. Shutter mechanisms are commonly blinds-like components that open progressively. Most often, they open up vertically, althought they can also open up horizontally. Some devices, especially motion-picture cameras, have rotating shutters.

If the blades move slowly, a bigger slit opens and more light comes in. This is useful for dark environments or ones where there isn’t a lot of motion. (Fast-moving objects, like a car racing by, blur when shutter speed is set too low.)

If the blades move fast, the slit is smaller and less light travels through the lens. This is useful for fast-moving action or bright environments with sun, snow, and sand.