The most important lesson for any photographer to learn is mastering the exposure triangle.
Understanding these three elements of control are the building blocks to producing the results you desire and understanding which to adjust to master the conditions you find yourself shooting in.
Aperture (Depth of Field)
Aperture controls the amount of light entering into the camera via the lens. Think of it compared to the Iris and Pupil of the human eye. In low light the iris dilates the pupil to let more more light into the retina, in harsh light it contracts the pupil to a pin hole to restrict the amount of light hitting the retina. The exact same is true of how a lens aperture effects the light hitting the camera sensor.
Aperture is expressed in terms of f-stop, also known as the speed of the lens, f-number or f-ratio. In simple terms, it is the ratio of the systems focal length to the diameter of the entrance pupil. The lower the value of the f-stop, the wider the diaphragm of the lens can open, hence allowing more light to hit the camera sensor. The higher the value of the f-stop, the narrower the diaphragm of the lens, hence allowing less light to hit the camera sensor.
This of course has a secondary effect on the image captured in regards to the depth of objects that are in clear focus vs those out of focus, known as Depth of Field.
Large apertures (small f-number) cause a narrow depth of field where the background can blur beautifully which is excellent for portraiture and wildlife photographs. Small (large f-number) apertures cause a much greater depth of field where objects near and far are in clear focus ideally suited for landscape photography. Mastering the art of controlling depth of field can lead to a large range of creativity in image capture.
The image below illustrates this, firstly showing the effect of a large aperture (f1.4 for example) and the narrow depth of field, the bottom image showing a small aperture (f8 for example) and the large depth of field it generates.
In the next blog post we will cover off shutter speed and ISO.