ABSTRACT
Image sharpness is seen to vary in depth. Detail both in front of and behind the point of optimum focus may also be rendered adequately sharp to give a zone of acceptably sharp focus, termed depth of field. Depth of field can be quantified and calculated in terms of these parameters and others, but first some consideration is needed of the sharpness of the photographic record, such as a print viewed in the hand. Manipulation of almost any camera will demonstrate that depth of field may be controlled by the choice of the focal length and aperture of the lens in use together with the focused subject distance. Normal vision uses muscular action to alter the refractive state of the eye in order to focus. The use of modulation transfer function analysis allows assessment of performance of an optical system with components other than lenses by means of through-focus traces at specific spatial frequencies.
