Depth of field
Depth of field (DoF): When a lens is focused on a particular object, some part in front of the object towards the camera and some part beyond also is acceptably sharp to human eye. The acceptable sharp range of focused area or field is known as DoF.
This DoF will depend on:
Distance between the lens and the object
Focal length of the lens
Lens aperture: Aperture plays very important role in DoF. Wider the opening of the lens (lower f no), lesser the DoF. Smaller the opening (higher f no), more the DoF.
This means that DoF will increase when we use a smaller aperture. In such case, we have to set a slower shutter speed to compensate for reduced amount of light reaching the film or digital image sensor. (or we have to set higher ISO value)
Distance between the lens and the object: When aperture is constant, at closer distance, we will get shallower DoF. It will increase when the distance is increased.
This has a good consideration when it comes to close up photography. In extreme close up shots, even at the smallest aperture, the DoF can be within a few millimeters. So a very careful focusing is required to record the most important part of the subject. Camera shake also has to be taken in to account as the small aperture will reduce the shutter speed in order to give the correct exposure. In such case, use of a good sturdy tripod is a must.
Focal length of the lens: Lens with less focal length (wide angle lens) will give more DoF. Tele lens will give much less DoF.
This has to be understand with the distance. As a tele lens brings the subject, which is far, close to the camera, virtually we are reducing the distance. That is the reason why we get a reduced DoF.
If we shoot with either a tele or a wide angle lens, in such a way, that the size of the subject remains almost the same in the photograph frame, then we will get the same DoF with irrespective of the focal length of the lens. Yes, the perspective in this case will change.
This happens because in order to maintain the size of a subject, with wide angle lens, we have to go close to the subject. Which means that the distance is reduced and with less distance, depth of field is also reduced.
DoF can be used creatively. When it is shallow, means the field is short. So the main subject remains focused and the background elements go out of focus - a real advantage when we are shooting a person or a child outdoors. Disturbing and distracting background becomes soft and out of focus and main subject is emphasized.
However, when we are shooting a product or an architectural picture, then we may need to have everything sharp. So use of smaller aperture (larger f-no) will give us more depth of field.
Read about how to set a lens for hyper-focal distance
Return back to Camera from depth of field
Learn more about:
Accessories in photography
Auto focus mechanism of camera
Other photographic accesso
Studio flash lights
Types of cameras
Wide angle lens
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