F-stop is a consistent way to measure lens aperture, and helps photographers control exposure and depth of field. It is noted with an f followed by a slash and number, for example f/2.8.

The maximum aperture is noted in the lens – for instance, a Nikon AF-S 85mm f/1.8G sports a maximum aperture of f/1.8, while a Canon EF 16-35mm f/4L IS USM features a maximum aperture of f/4.