Aperture and Depth of Field

The depth of field or DOF is the portion of a scene that appears sharp in the image. Basically, when we take landscape pictures, we prefer a large depth of field. On the other hands, we would like to have a small or shallow DOF for portraits shots. One of factors determining the depth of field is the aperture and the f-number.

For normal scenarios, the DOF is determined by three things. First, the distance from a camera to subject(s) and the distance from subject(s) to the background. Secondly, the lens focal length. Lastly, the lens f-number which relates to the aperture. However, for the close-up distance between a camera and subject(s) or the macro shot, the DOF is determined by subject(s) magnification and the f-number.

As you could see, the f-number always determines the depth of field. The less f-number (wider aperture) we use, the shallower DOF we get. The shallow depth of field will throw the background out of focus and makes the subject stand out.

Here are sample images captured by using various f-numbers.

 f 5.6

 f 14

 f 22

The orange area in the picture below depicts the sharp area in the image. It is calculated by using the 50mm standard lens, and the distance between a camera and a subject is 3 meter.

(pictures source: go_med @ rpst-digital.org)


See also
Aperture and F-number

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