Film Speed, ASA, ISO

A measure of the sensitivity of a film emulsion to light. A film emulsion with a high ASA number will be more sensitive to light and can be used when there is little light available, such as unlit interiors, dark overcast days or dusk exteriors. The ASA system is also applied when using electronic sensors in video and digital stills cameras. There is usually an increase in grain or noise with higher ASA ratings. In summary: High ASA = high sensitivity, low light conditions, increased grain or noise. Low ASA = low sensitivity, bright light conditions, fine grain, little or no noise.