What does aperture control in photography?

Aperture primarily controls exposure in photography. It refers to the opening in a camera lens through which light passes. The size of this opening can be adjusted to allow more or less light to reach the camera sensor. A wider aperture (a lower f-number, such as f/1.8) lets in more light, which is beneficial in low-light situations or when you want to create a shallow depth of field, producing a blurred background effect (bokeh). Conversely, a narrower aperture (a higher f-number, such as f/16) restricts the amount of light entering the camera, which can be advantageous in bright conditions or when a greater depth of field is desired, keeping more of the scene in focus.

While aperture does indeed impact focus indirectly by affecting depth of field, its primary and most direct function is the control of light exposure. The other options—focus, zoom level, and speed—are influenced by other factors in photography such as focal length of the lens, camera settings like shutter speed, and the overall composition techniques employed by the photographer.