The above image of three glasses demonstrates a pitfall of depth of field about which photographers should be mindful. Shot at f/1.4, 1/125th of a second and ISO 100, the image appears as if the photographer simply blew the focus. Upon close inspection, however, the front part of the rim of the glass (about where the light is reflecting) actually is in sharp focus. The remainder of the picture, including the rest of the same glass, is out of focus. The blurred focus, however, results from the use of f/1.4 and not the poor eyesight of the photographer.
When a photographer uses a wide aperture, like f/1.4 or f/2.0, great care must be taken to avoid making the area of focus so limited that the photographer blurs out a part intended to be in focus.
In the picture to the right, the photographer’s choices of f/4, 1/15th of a second, and ISO 100, correctly expose the image while providing enough depth of field to make most of the front glass in focus while maintaining the focus blur on the back glasses.
So, along with distance to subject and focal length of the lens, aperture plays a crucial role in determining the depth of field of the final image.
Expert Street Photographer, Dan Scott, uses a 50mm f/1.4 lens to get the left eye of the subject, yet the rest of the face very gradually falls out of focus. Had Dan been using a telephoto lens and/or been standing closer to the subject, he would have risked a very shallow depth of field – perhaps only getting the eyelash or pupil and iris in focus. As can be learned through basic experimentation, the impact of aperture on depth of field will lessen as one moves farther away from the main subject or shoots with a wider focal length lens.
For example. flash is often not allowed during the wedding ceremony. Without flash, wedding photographers must rely on lenses that gather as much light as possible as quickly as possible. An f/2.8 lens with a focal length of 28mm (wide angle lens) imaged the shot on the right. The wide angle of the lens counteracted the depth of field of the f/2.8 aperture and allowed a picture in low light that still kept most of the church in focus.
Uses of Different Apertures
The gallery below provides examples of common uses of depth of field and apertures of various sizes. Click on a photo to see the aperture and other camera settings and a description of the resulting effect.