As you begin exploring photography, you’ll quickly come across the term ‘f-stop’, otherwise known as the f-number. It’s one of those bits of jargon that feels intentionally designed to confuse beginners, but luckily we’re here to explain what it is and how to use it in your snapping adventures.
Whether you’re using a compact, mirrorless camera, DSLR or even a smartphone, you’ll likely see that the f-stop symbol appear on your screen, and even on some lenses. So what exactly is the f-stop?
In purely literal terms, the ‘f’ stands for ‘focal length’ and a ‘stop’ is a unit of light, which refers to either the doubling or halving of the amount of light in your photo. But as that doesn’t exactly clear things up, here’s a more in-depth explanation of what an f-stop actually is – and how to use it in your photography.
What is an f-stop?
The f-stop is the number a camera (or lens) displays to indicate the size of the lens aperture (see ‘F-stop vs aperture’ below). Most camera lenses offer a range of f-stops (from large to small aperture), for instance one lens might have f/2.8, f/4, f/5.6, f/8, f/11, f/16 and f/22.
It is not possible to expand beyond a lens’s f-stop range. In the previous example, the maximum f-stop (aperture) is f/2.8 and the minimum is f/22. The same aperture might be displayed with a capital or lower case ‘f’ and with or without a forward slash. For example, f/5.6, F/5.6, f5.6 or F5.6 are all the same thing.
But why the confusing use of symbols? This is because an f-stop indicates a fraction. For example, f/4 is a quarter, making it larger than f/8 which is an 1/8th. Therefore, the smaller the f-stop number, the larger the aperture.
However, the ‘f’ in f-stop actually stands for focal length. It’s a little complicated, but there is an equation comprising lens focal length and f-stop to work out the physical size of the aperture. This equation is the lens’ focal length divided by the diameter of your effective aperture.
F-stop vs aperture: what’s the difference?
The ‘aperture’ is the opening in your camera lens, that lets light pass through to the camera. On most lenses, the size of this diaphragm, which is formed by aperture blades (and seen as an almost circular hole), can be adjusted by the f-stop number. Some lenses have a fixed aperture, including those in most smartphone cameras.
Consider the human eye. An iris expands to let in more light so we can see more clearly in dark environments, and decreases in size when in bright light so we don’t get blinded. The principle of a lens aperture is the same.
So, aperture is the opening in the lens, while f-stop indicates the size of lens aperture, as a fraction. In the previous example of an f-stop range, each ‘stop’ lets in twice as much light as the next. For example, f/2.8 is twice the size of f/4.
Lenses with a large maximum aperture tend to be larger, heavier and more expensive than equivalent ones with smaller openings. But they are desirable for the two main reasons explained in the ‘how to use f-stops in your photography’ section below.
What do f-stops mean in smartphone cameras?
Except for a couple of oddballs like the Samsung Galaxy S10, smartphone cameras generally have a fixed aperture, which means only one f-stop.
Current smartphone cameras typically have a f-stop of around f/1.8. For phones with multiple cameras, there is usually a slightly different f-stop for each camera, such as f/1.8, f/2.0 and f/2.4, but ultimately each of these has a fixed aperture.