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All light-sensitive photographic materials—film or photographic print paper—produce their finest results when given the optimum exposure. Precise exposure, coupled with consistent development, is the technical key to excellent photographs. A photographer can change the amount of exposure the film receives by adjusting either the shutter speed or the aperture setting. A one-stop change in shutter speed is equivalent to an aperture change of one f-stop, and vice versa. Thus, for a given lighting situation, several different combinations of f-stop and shutter speed result in the same amount of light hitting the film. For example, an exposure of f/5.6 at 1/15 second allows the same amount of light to strike the film as an exposure of f/2.8 at 1/60 second—the aperture is two stops larger, but the speed is two stops faster. The exposures are thus comparable, but they produce different pictorial results. If the photographer is holding the camera by hand, the second option is preferable, because at speeds below 1/60 second, movement of the camera or of the subject is likely to blur the image. If the photographer is using a tripod to hold the camera still and photographing a still subject, the first option may be preferable because the smaller aperture provides greater depth of field. When film is developed according to the manufacturer's specifications, every stop of increase in the exposure (one step up in either f-stop or shutter speed) effectively doubles the density of the negative. For example, an exposure at f/5.6 for 1/15 second produces twice the density of an exposure at the same f-stop for 1/30 second, and therefore a print made from it will be twice as light, unless the print exposure time is doubled. However, there are limits to this relationship, called reciprocity, between exposure and density. At the extremes of very little and very great amounts of exposure, this rule is less consistent and the resulting images will be noticeably underexposed. |