I love shallowness

Shallow depth of field or short depth of focus in photography is normally caused by using a large aperture or a small f-number. How short the focus actually is depends on the focal length of the lens, the type of camera used, the distance between camera and focal point and even the print/image size. The technical aspects of the depth of field are interesting enough in themselves. However, this is not why I like a shallow depth of field.

Unusual/Original

It is hard to say accurately, but I estimate that the majority of photos are shot with an f-stop of around f/8. It is not so hard to guess that most people who are more than a little interested in photography wish to create original and interesting photographs. One tip on how to make more interesting photos is to do something different from what everybody else is doing. Shooting with a much smaller f-stop like f/32 will not result in photos that are very different from photos shot at f/8 when it comes to depth of field (though the much longer exposure may give other interesting effects). A scene shot with f/1.4 is more likely to yield an unusual photo than the same scene shot at f/8. Still, that does not mean that the f/1.4-version is better, but it is different.

Defining space and distance

Normally our brain uses our stereoscopic vision to determine the distances between objects in a scene. When we look at a photo on paper or on screen, the real 3d is gone, but our brain will still try to read clues that can tell something about scale and depth in the photo. Recognizable objects like people, trees and buildings show scale. Short depth of field always signifies small scale (more about that in my article about tilt & shift photography). So when used in a scene with objects that give conflicting clues about the scale, the photograph takes on an unreal or unnormal appearance. It is not always easy to point out consciously, but our brain sees it and lets us know by telling our consciousness that the photograph is special and perhaps even interesting.

Blurring away unwanted elements

The focus is also a strong compositional tool. It can be used to control what is allowed into the scene, and what is not, even if the element in question stays within the boundaries of the photo. A short depth of field will throw the background out of focus, thereby removing any disturbing objects so the main subject does not have to compete for attention. It is a very powerful and much used technique. Other compositional tools would be for example adjusting the field of view left, right, up or down or by zooming in and out. Or moving the camera to remove elements from or to include elements into the scene.

Let the light in

With a lens that can open up to say f/1.2 instead of say f/2.8 or f/3.5, the difference in required shutter speed or ISO is huge. Low light conditions become much less of an obstacle, especially for the autofocus in the camera. Take the example to the right. It was shot at ISO 3200, with a shutterspeed of 1/50th of a second and f-stop f/1.2. With a f-stop of f/3.5, the shutter speed would have had to be 1/6th of a second. That's more than 8 times as long, and very difficult to hold steady.

More

You can read more about the use of depth of field in my tips & tricks article.