How to change Depth of Field and make blurred backgrounds

Sometimes when taking a photograph you don’t want your background to be focus as you might want the foreground. Normally you will want your subject to be in focus and the background to be either slightly out of focus or very out of focus.  In order to do this you need to take control of  your camera settings.
The Aperture controls the depth of field.

What is a Cameras Aperture?

The Aperture is basically the eye of the camera which has the main job in a camera lens of collecting light. The aperture of a lens, which is controlled by a series of blades, is the diameter of the lens opening. The larger the diameter of the opening or aperture, the more light reaches the cameras image sensor. The camera aperture is expressed as something called an F-stop, written as  f2.8 or f/2.8. The smaller the F-stop number (or f/value), the larger the aperture and thus the more light reaches the lens. If you are buying a lens you will see something like f2.8 – f5.6 , which is the range of apertures available on this lens. When an aperture is opened up by one f- Stop, the amount of light reaching the camera sensor is doubled. When an aperture is reduced up by one f- Stop, the amount of light reaching the camera sensor is therefore halved.

How can Aperture control Depth of Field – DOF ?

Depth of Field is sometimes written as DOF and some people refer to it as Bokeh.

The best way to achieve Depth of Field is to use Aperture Priority Mode often illustrated as A on your camera settings (e.g. Canon).

In the example below the F stops start at 2.8 then go to 11 and the on to 22.

How to create Depth Of Field at Aperture f2.8

Depth Of Field at Aperture f/2.8

Depth Of Field at Aperture f11

Depth Of Field at Aperture f/11

Depth Of Field at Aperture f22

Depth Of Field at Aperture f/22

Results of Using Aperture Priority for Depth of Field

As you can see, the background is most out of focus when the aperture is letting in most light at aperture f/2.8 but the background becomes sharper as the f-stop is increased, thus letting in less and less light. At f/22 the background is a lot sharper than f/2.8.

Problems with Adjusting the Aperture

As you increase the f-stops towards f22, less light is entering the lens. Therefore to get the same level of light into the camera you need to decrease the shutter speed. If the shutter speed gets too low, e.g. towards .3″ hand holding the camera is out of the question and a tripod is a necessity. If your lens uses Image Stabilization (IS) don’t forget to check out the item on how using IS (Image Stabalisation) on a Tripod can cause blurry images .You can also increase the ISO, e.g. ISO 400 or ISO800 but this may make the shot noisy.


Basically, the aperture can create great effects for your photos. blurring image backgrounds where the background is not part of your subject or scene. taking portraits you might use f/2.8 or f/4 to create a blurred background – However if you are taking landscape shots, probably f/18 to f/22 might be good settings as you want all the shot to be in focus.

Hope you enjoy this post !