When we run our courses, especially Getting Started, we’re often pleased to see the reaction of our delegates when we cover aperture. It seems to be the one element of exposure that causes the most confusion – and we like it when it all becomes clear.
Let’s keep this simple – an aperture is a hole – a door or a window is an aperture in a wall. A camera lens has a “hole” through which the light passes through to the film or sensor in a digital camera. When we talk about aperture in photography, all we’re talking about is the size of the hole.
So where does f-stop come into it? Well without going into the mathematics of it all, f-stop or f-number, is simply a measurement of the size of that hole or aperture. So in reality, aperture and f-stop are one and the same thing.
How does the numbering work – like I said don’t worry about the mathematics, just remember these key points:
- The smaller the f-number, e.g. f/2, f/4 the bigger the hole or aperture – meaning more light can pass through the lens
- The bigger the f-number, e.g. f/8, f/11 the smaller the hole or aperture – meaning less light can pass through the lens
Each time the area of the aperture or hole doubles, twice as much light can get in. Conversely, each time the area halves, half as much light can get in. And this halving or doubling is known as a stop – hence f-stop.
Don’t worry about how the numbers are calculated, but the scale looks like this:
- f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22 and so on
But why have different values? Well, there are various reasons, but two of the most important are the effect this has on the length of the exposure – more light, less time, less light, more time. The second is control of depth of field – a great creative tool at the photographers disposal.