sensitivity and image capture
3PTP[H[PVUZ VM ÄST JHW[\YL Expiry date
At the time of manufacture all film products have an expiry date printed on their packaging. Do not use film once this date expires. The manufacturer will not guarantee correct rendition of color and reliable results cannot be predicted. Store unexposed film at a constant temperature, preferably in a refrigerator, but do not freeze.
Color temperature and white balance It is not important to fully understand the theory of color temperature other than to know that capturing color images requires the correct match between capture medium and light source to avoid excessive color casts. Black and white film is relatively unaffected by color temperature although a small increase in exposure (as indicated by the MIE reading) is often required when using tungsten lights. Tungsten film is rated at 3200K and used with tungsten lighting. Daylight film is rated at 5500K and used with flash and daylight. To render correct color, the use of a ‘white balance’ or filtration can be used to balance any image sensor or film to any lighting situation. The filtration required for film is listed in the manufacturer’s specifications packaged with the film.
Reciprocity Reciprocity, more correctly referred to as reciprocity failure, is a measure of the film’s ability or inability to handle extreme exposure times. Reciprocity, in general terms, takes effect when shutter speeds are greater than 1 second when using daylight color film, greater than 30 seconds when using tungsten color film and 1 second when using black and white. All manufacturers issue a technical information sheet with their professional film packaging stating the reciprocity values relevant to that batch (manufacturing identification) of film. This should be followed closely. Without going into the causes of reciprocity the remedy is to reduce shutter speed (time) and compensate by increasing aperture (intensity). Increasing exposure by increasing time will only compound the problem. The results of not compensating for reciprocity is an underexposed image, varying shifts in color rendition and unpredictable results.
Activity 1 Photograph a subject of average contrast using the capture medium of your choosing. Adjust shutter speed and the intensity of light so exposure times start at 1 second with the aperture at f2.8 or f4. In one stop increments increase exposure time to 64 seconds. Label the results for reference, comparison and discussion. At what exposure time did the images suffer reciprocity failure or excessive levels of noise?
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