What does aperture control in a camera?

Aperture in a camera refers to the opening in the lens through which light enters the camera body. It is measured in f-stops, with lower f-stop numbers corresponding to larger openings that allow more light to pass through. The primary function of aperture is to control depth of field, which is the range of distance in a photo that appears acceptably sharp. A wider aperture (lower f-stop number) results in a shallow depth of field, meaning that the subject can be in focus while the background is blurred. This effect is often used in portrait photography to isolate the subject from the background, creating a sense of depth.

Conversely, a narrower aperture (higher f-stop number) increases the depth of field, bringing more elements in the scene into focus. This is particularly useful in landscape photography where it's desirable to have both the foreground and background elements sharp.

The other choices relate to different aspects of photography; for instance, shutter speed affects motion blur, ISO sensitivity controls the camera's sensitivity to light and affects grain, and image stabilization helps in reducing blur caused by camera shake. While all these elements work together to create a well-exposed photograph, aperture specifically pertains to manipulating depth of field.