Andrew Bailey

Ilfracombe, United Kingdom

After a working lifetime spent in visual communication of one sort of another, Andrew is now happily retired and living in peace and...

Yet More Photographic terms

These two definitions ought to be of prime importance to the serious photographer

Depth of Focus
This is a phenomenon which occurs only inside the camera. It is the distance through which an image may be moved either side of the principal focus without, apparently, losing acuity or sharpness. The degree of movement available is in direct relation to the f-number or stop (aperture) used when exposure is made. An aperture of f16 will allow greater movement than an aperture of f11.

Depth of Field
This should not be confused with depth of focus above as the two as distinctly different. When a camera is focused to give a sharp image of a particular object, other objects closer or farther away do not appear equally sharp.
The decline in sharpness is gradual and there is a zone extending in front of and behind the focused distance where the blur is too small to be noticeable.
This zone is known as the depth of field and its extent depends, among other things, on how great a degree of blur we are prepared to accept as sharp, i.e., the size of the circles of confusion (q.v.). The stricter the standards of sharpness, the smaller the circles of confusion and the shorter the depth of field. Depth of field also depends on the aperture and the focal length of the lens in use as well as the distance from lens to subject. The smaller the aperture and the shorter the focal length of the lens, the greater the depth of field. The closer the object, the smaller the depth of field.

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