1. Aperture Priority for controlling depth of field
The aperture is the opening in the lens, formed by a set of diaphragm blades. By changing the aperture setting, these blades can be made to open and close and consequently allow more or less light to hit the camera sensor.
As well as its role in exposure, the choice of aperture also has an effect on the depth of field. There are many situations where you’ll want precise control over the depth of field: when photographing landscapes, for instance, you’re likely to want as much depth of field as possible to give the picture plenty of foreground-to-background sharpness.
But when you’re photographing a portrait you’ll want to reduce the depth of field, in order to make the person you’re photographing stand out from the background.
To give you this flexibility, switch the camera to Aperture Priority mode. This is indicated by Av or A on the camera’s shooting mode dial. Aperture Priority is a semi-automatic mode: you control the aperture and the camera can do the rest.
Choose small apertures (represented by high f-numbers like f/11 and f/16) to increase the depth of field and select large apertures (represented by low f-numbers like f/2.8 and f/4) to reduce the depth of field.