What aperture is and how to use f-stops

Aperture controls how much light enters the lens and how much of the photo is in focus. Learn the f-stop scale and when to open up or stop down.

The aperture is an adjustable opening inside the lens, formed by blades that open and close like the pupil of an eye. It is written as an f-number: f/1.4, f/2.8, f/8 and so on. The confusing part is that small numbers mean a large opening and large numbers mean a small one.

Full f-stops: each step to the right halves the light and increases depth of field.

The full-stop scale

The standard sequence is f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16 and f/22. Each step lets in half as much light as the one before it. Your camera also shows thirds of a stop in between, like f/3.2 and f/3.5.

Aperture and depth of field

Wide apertures (f/1.2 to f/2.8) give a shallow depth of field: the subject is sharp and the background melts away. This is the look of portrait lenses like an 85mm f/1.4. Narrow apertures (f/8 to f/11) keep the scene sharp from front to back, which is what you want for landscapes, architecture and group photos.

The sharpest aperture

Most lenses are sharpest two or three stops down from their widest setting, usually around f/5.6 to f/8. Past f/11 or f/16, diffraction starts to soften the image slightly, so avoid f/22 unless you need maximum depth or a sunstar effect.