Film Speed measures the degree to which film is sensitive to light. The International Organization for Standardization (ISO) or the American Standards Association (ASA) are both responsible for setting the ranges of film speed. Both digital and manual cameras depend on film speed ratings.
While higher film speeds require less exposure to light, slower speeds need more light (or longer periods exposed to the light) to take the same pictures. Film speeds can be calculated through either linear or logarithmic equations.
To accommodate the film speed with the appropriate exposure, a photographer can widen his camera’s aperture, increase or decrease the shutter speed or alter the lighting in a given scene.
Film speed is also related to the granularity of the resulting photograph. Portrait photographers and those looking for more detailed pictures tend to use “slow film” (film with slower film speeds) that require more light and decreased shutter speeds.
However, photographers shooting in darker scenes with poor lighting situations should opt for fast film that renders a grainer printed photo. Similarly, if a photographer is looking to produce a photo with more contrast, he should also opt for fast film. The choice of film speed will depend on whether you are looking for a more convenient and versatile film (faster film speeds) or film that will produce higher quality photos (slower film speeds).
