What does the aperture control in photography?

Aperture primarily controls the depth of field in photography. Depth of field refers to the range within a photo that appears sharp and in focus. By adjusting the aperture, which is the opening in the lens through which light enters the camera, a photographer can determine how much of the scene in front of and behind the subject is in focus.

A wider aperture (represented by smaller f-stop numbers, like f/1.8) allows more light to enter the camera and results in a shallower depth of field. This effect is often used to create a blurred background, drawing attention to the subject in focus. Conversely, a narrower aperture (larger f-stop numbers, like f/16) reduces the amount of light entering the lens and increases the depth of field, allowing more of the scene to be in focus.

While the aperture also influences exposure by controlling how much light hits the sensor, its primary role related to this question is its impact on depth of field, making it a crucial element in composition and creativity in photography.