An f-stop is the setting on a camera lens that controls how wide the aperture opens. The aperture is the hole inside the lens that lets light reach the camera’s sensor. F-stops are written as numbers like f/2, f/4, f/8, and f/16. Here’s the counter-intuitive part: smaller numbers mean a wider opening, and larger numbers mean a smaller opening.
Each full f-stop change either doubles or halves the amount of light entering the camera. Going from f/4 to f/2 lets in twice as much light. Going from f/4 to f/8 cuts the light in half. This predictable pattern is why f-stops matter so much in exposure.
F-stops also control depth of field, which is how much of the scene appears sharp from front to back. Wide apertures (low f-numbers) create shallow depth of field, blurring backgrounds and isolating subjects. Narrow apertures (high f-numbers) increase depth of field, keeping more of the scene in focus.
In practice, you choose an f-stop based on creative intent first, then adjust shutter speed and ISO to balance exposure. Portraits often favor wide apertures for soft backgrounds, while landscapes usually need smaller apertures for overall sharpness and clarity.