Controlling the aperture If depth of field is important to your pictures, use Aperture Priority
Despite the majority of lenses offering a range of apertures, they are usually described by their maximum or largest available aperture, such as ‘85mm f/1.8’ or ‘85mm f/1.4’. Many zoom lenses have what’s known as a ‘floating’ aperture, where the maximum changes as the lens is zoomed. For instance, an 18-55mm f/3.5-5.6 lens has a maximum aperture of f/3.5 at the wide end, but this narrows to f/5.6 when the lens is zoomed to the telephoto setting.