An aperture is a hole or opening at the back of the lens through which light enters into the camera. When the aperture is low the hole is completely open and when we set aperture to a higher value we get a tiny hole. Therefore it’s clear that, larger the hole more the light it captures and the smaller the less light it captures.
The measurement of aperture is done in ‘f-stops’ for example you must have seen f/2.8, f/4, f/5.6, f/8, f/22. When we change the setting from one f stop to other it changes the size of the hole either to double or to half that directly affects the amount of light entering into through it. A smaller f-stop means a larger aperture, while a larger f-stop means a smaller aperture. For example, f/1.4 is larger than f/2.0 and much larger than f/8.0.
Depth of field is another factor that is affected directly by the aperture setting of the camera. Depth of field is simply the area of the image that remains in focus. While shooting at small aperture (large f stop) the camera will focus on both the foreground and background objects while shooting at large aperture the camera will eradicate focusing on the background objects and hence the background remains blurred.
What is the actual need of D.O.F.?
When we want to focus mainly on the subject or a body then we must use higher aperture as it excludes the background from being focused. Higher aperture mostly benefits the user while shooting portrait.
On the other hand, when we want to focus on both the subject and the background objects we must ensure that the camera’s aperture is set to lowest. For example while shooting landscape the photographer wants to capture the whole scene so he must use small aperture in order to get better results.
A sample that clearly show you the size of lens opening at the end w.r.t different aperture.
Easiest way to control the depth of field:
To control depth of field, the easiest way know to us is the aperture setting of your DSLR, the AV mode allows to to control your aperture with mode dial button or via aperture ring. To achieve higher depth of field one must set its aperture setting to the lowest and to achieve shallow depth of field on must set its aperture to the maximum.