The failure of the reciprocity law to apply. This occurs at one second and longer when the normal ratio of aperture and shutter speed will underexpose the film and at 1/10,000 second and faster. When using black-and-white film with exposures of one second or longer, exposures just need to be increased to avoid underexposure. When using color film in these conditions, color shifts will occur because the three emulsions do not respond to the reciprocity effect in the same manner. To compensate, follow exposure and filtering instructions provided with the film, along with a little trial and error.
Loss of predictable sensitivity in a photographic emulsion due to very long (more than one second) and very short (faster than 1/10,000th) exposures.
When a film's speed cannot be relied upon for proper exposure at slow shutter speed, reciprocity failure (or the "Reciprocity effect") is said to occur. Additional exposure is required in order to achieve proper exposure for that film, even though your light meter may say differently. The additional problem of a shift in color balance that occurs with reciprocity failure can be more troublesome. RECIPROCITY FAILURE results in underexposure and a shift in color balance.
anomolous behavior of films that manifests with long (or very short) exposure times.
A loss of film speed occurs when film is exposed for very short (one ten thousandth second or less) or very long exposures (hours). This is not usually a problem under normal circumstances. This can be a problem in astronomical photography where very long exposures are routine. Time Exposure
Deviation from the reciprocity law. Typically, this deviation occurs at either low intensity or at short interval exposures & high intensity AND/OR long interval exposure.
At extreme shutter speeds (extremely fast or slow) the reciprocal relationship between shutter speed and -stop begins to break down and results in a loss of image quality.
Films that slow down as the exposure time increases are said to be suffering from 'reciprocity failure'. For an example a 1600 ASA can, after a few minutes exposure end, up performing like a 100ASA. Different makes of film slwo down at different rates. The information is usually printed on the film box or enclosed leaflet.
When exposure TIME reaches a certain point (either VERY long or VERY short), the reciprocity relationship fails, and more exposure TIME is needed.
Photosensitive materials require a linear sensitivity within a certain range. Beyond that their sensitivity requires that exposure times be increased in larger amounts than normal.
in photographic emulsions occurs when exposure times fall outside a films normal range. At these times an increase in exposure is required in addition to the assessed amount. This can be achieved either by increasing intensity or time.