What is the purpose of the f-stop on a lens?

The purpose of the f-stop on a lens is to indicate the aperture setting of the lens. The f-stop is a standardized measure that describes the size of the lens opening through which light passes. A lower f-stop number signifies a wider aperture, allowing more light to enter the camera, while a higher f-stop number represents a narrower aperture, which lets in less light. This setting not only influences the exposure of an image but also affects the depth of field, determining how much of the scene appears in focus. Understanding the f-stop is essential for photographers to manage exposure and achieve desired effects in their images.

The other options, while related to photography, do not accurately represent the specific role of the f-stop. For instance, shutter speed is indicated by a different metric entirely, and focal length refers to the distance between the lens and the image sensor, not the aperture setting. Additionally, while the amount of light entering the camera is related to the aperture, the f-stop itself is specifically designated to denote the aperture setting.