Depth of Field in Photography

Everybody keeps asking me the question, “How do we blur the background in a photo so that the subject stands sharp?” I answer, “Using Depth of Field!”

Well, it’s a complicated topic and a bit technical too, so let me start with showing a few examples and then moving on to explaining the topic to my level best. Check out the two photos that I took of my daughter below to understand what we are trying to achieve.

Notice how the background is blurred keeping the subject of the photo very clear? Here is another one shot with a 75-300mm Canon Zoom Lens.

Notice how the crowd in the background is blurred to enhance the subject. Would have missed enjoying the priceless expression on my daughter’s face if the background was fully in focus.

So, in other words, what we want to achieve is the isolation of the subject. We specifically want to draw the viewer’s eyes to exactly what we want them to see in the photograph. This can be achieved by adjusting the Depth of Field (DoF). Understanding and mastering the Depth of Field in photography can basically turn a 2 dimensional snapshot in to an amazing photo.

What is Depth of Field?

As explained in Wikipedia, Depth of Field (DOF) is the distance between the nearest and farthest objects in a scene that appear acceptably sharp in an image. Bump!!!

Ok, let me give it another shot.

Cameras and human eyes have something called “Depth of Field” (or “DoF”), which makes objects in the background or foreground appear blurry. It is the amount that tells you whether or not your subject and background can be sharply focused at the same time. In short, Depth of Field is a technical term used to describe the “area of sharpness” between the near and far values of a subject in focus.

Depth of Field in photography is determined by several factors like the subject, the movement of the subject, the distance of the subject, aperture, the focal length of the lens, etc. We shall discuss the two important aspects for now to get our goal – background blur – the aperture or f-stop and distance of the subject.

For those who are new to the word aperture, I recommend to read my blog post on Aperture first.

Aperture and Background Blur

Changing the aperture is probably the easiest way to alter the Depth of Field in photography. There is a direct relationship between aperture and Depth of Field i.e. the smaller the aperture, the more extensive the Depth of Field. Check the comparative image below.

The part of the left in the above picture has a large aperture and so it gives a shallow depth of field while the part on the right has a small aperture and so everything is in focus. Notice how the background blur is affected because of the aperture settings. Most of the times while shooting landscapes, I normally shoot at f/16 or higher to ensure that I have everything in sharp focus. While on the other hand while shooting wildlife, I tend to shoot at f/5.6 or a larger aperture. This also helps me with getting faster Shutter Speed.

Subject Distance and Background Blur

Simple rule – the further the subject is from the background, the more blur we will get. If our subject is right up against a background, it will be much harder to not have it in focus. The idea is to separate our subject from the background as much as we possibly can. Here are some illustrations to explain this.

Aperture is large, subject is near to the lens and so the background is fully blurred

Aperture is small, subject is near to the lens and so the background is slightly blurred

Aperture is large, subject here is near to the background and so the background is slightly blurred

Aperture is small, subject here is near to the background and so the background is fully in focus

Summary

What I have found is that changing and controlling the aperture is the best way to get good results with the Depth of Field. It is simply not possible to alter the position of the subject or shift the angle from where we are shooting the picture most of the times. In that case, changing the aperture of the camera surely has helped in getting a sharp subject and a blurred background without affecting the composition of the photo.

Do you know any other methods to get blurred backgrounds in your photo? If so, share them here and make this article more interesting.