ASA, an acronym for American Standards Association, refers to an archaic scale for
speeds of films made by Kodak in
the 1940s. The sensitivity of the film to measure the
degree to which the film is
sensitive to light. For example,
a higher speed of the film indicates that the film
has less exposure to light or shorter exposure
to capture an image. Conversely, the decrease in ASA or ISO means that the film is a "slow film" that needs more
light exposure to capture the same image.Today, the velocity measurements ASA film was replaced by ISO (International Organization for Standardization), which includes the dimensions of both linear and logarithmic.
The ASA and ISO sensitivity ranges of the film are important because they determine the quality of the photos: the grain of a photo finish. The sequence is: large grains of the film, the faster the film, less light exposure required. Therefore, the well-defined and detailed images such as portraits are usually taken at a slow fine grain film. However, the scenes that have a limited perspective or are in motion in general, should be taken with more rapid film grain capturing an image with minimal light exposure.
The various film companies (such as Canon, Fuji and Kodak) to reach speeds very different films. Choose a film with a speed appropriate to the type of photos you want to take.
