What is Aperture?
Aperture is one of the three main functions in photography along with the shutter and the ISO.
The aperture is a ‘circular hole’ within the lens and is known as the ‘diaphragm’. To create an image, light passes through the ‘diaphragm’ and travels into the camera image sensor/film creating the image. The amount the ‘diaphragm’ is open to allow light through is measured in f-stops, i.e. f2.8, f4, f5.6, f11, f16, etc.
Beginners often get confused on what ‘f’ numbers mean and how they work. As a general rule: the smaller the ‘f’ number, the larger the opening of the aperture. The larger ‘f’ number, the smaller the opening of the aperture.
Therefore, f2.8 is considered as a large aperture. At f2.8 the diaphragm of the lens is larger and allows more light to come through and fall on the image sensor/film.
At f16, the aperture is small. The diaphragm of the lens is small limiting the amount of light passing through the lens and falling on the image sensor/film.
The below diagram shows the aperture in relation to its ‘f’ numbers: (not to scale)
How does the aperture work?
Just think about the human eye; the pupil controls the amount of light passing further into the eye by shrinking or expanding.
The aperture works exactly the same way. The amount of light is controlled by changing the f-stops on the camera. As you can see from the diagram, f2.8 allows much more light in than f32.
If the aperture is changed from one ‘f’ stop ‘either way’, it doubles or halves the size of aperture as well as the amount of light passing through.
Moving from f2.8 to f4 the amount of light is halved.
Moving from f8 to f5.6the amount of light is doubled.
When changing the aperture either way, it also affects the shutter speed (the amount of time the shutter is open) and the ‘Depth of Field’- (DOF is what controls the image sharpness).
Aperture and Focus
Choosing a large ‘f’ number such as f22 or f32 will bring all the foreground and background in focus. This aperture setting is always best to use when you want everything to be sharp and in focus.
This photograph has been taken using f22, as you can see everything is in focus from the foreground to the background.
On the other hand, a small ‘f’ numbers such as f2.8, f4 and f5.6 will blur the background, isolating the subject. This aperture setting is useful to use when you want to have parts of your photograph blurred to add impact as well as for photographing close-ups.
The 1st photograph has been taken using f2.8, as you can see the purple nail varnish bottle is in focus and the rest of the image is blurred. The 2nd photograph has been taken on f5.6.
For cameras that do not have aperture mode, use ‘Landscape’ mode for a large DOF.
And for a small DOF use the ‘Close-up’ or the ‘Portrait’ mode.