Exposure latitude is important for traditional film cameras.
Exposure latitude is the range of brightnesses that an emulsion can record while still maintaining detail. It is normally described in f-stops, which are the standard measures of camera apertures. For black and white art photography, the "zone system" of Ansel Adams is sometimes used to describe the tonal variations in an image.
Definition
Look around you on a sunny day. The eye can distinguish highlight details, such as wrinkles in a white shirt, and shadow details, such as the fur texture of a black cat in a shadow. No single photograph can manage that. Either the highlight details will "wash out" or the shadows will "block up". Exposure latitude is the difference within a single image between the brightest and darkest areas for which the film can record full detail.
Aperture
A diaphragm within the lens of a traditional camera is positioned to allow light to enter the camera and fall on the film when the camera shutter is opened. The size of this opening is called the "aperture" and is measured in a unit called "f-stops". The higher the f-stop, the smaller the aperture. F-stops are also used to describe exposure. If you set the camera to an average exposure and certain areas of the area you wish to photograph are more than three f-stops lighter or darker than that average, you will lose details in the image. Transparency films with very narrow exposure latitudes are unforgiving, in the sense that you will lose highlight or shadow detail if you miscalculate your exposure even slightly.
The Zone System
Ansel Adams' "Zone System" was originally designed for determining ideal exposures in black and white photography. It divided an image into 10 tonal zones, ranging from pure black, Zone I, through pure white, Zone X. Middle gray, which is the average tone of most outdoor scenes, is Zone V. Each zone differs from the next by one f-stop. Using a spot meter, determine the exposure of a middle grey object or a special "gray card" in the area you intend to shoot. That exposure becomes your Zone V. Next, meter other objects in the intended photographic field to see if they are within the exposure latitude of your film. If they are not, decide whether you wish to sacrifice highlight or shadow detail, and whether it might be possible to keep both by under or over-exposing by one or two stops.
Film Types
Slide films have a latitude of approximately five stops, digital SLRs six, color negative film about seven stops and black and white films up to eight. Generally, the higher the contrast of the film, the narrower the exposure latitude. Different brands and speeds of film vary in their abilities to maintain highlight and shadow detail within a given exposure latitude. Certain processing techniques can also affect exposure latitude or compensate for under or over-exposed film to some degree.
Tags: black white, highlight shadow, highlight shadow detail, shadow detail, Ansel Adams, black white photography
