ISO (International Standard of Organization) refers to a standard scale for determining the film's sensitivity to light. ISO 64 is comparatively slow while an ISO 400 film is considered fast. The more popular ISO 100 film is considered as medium, together with the ISO 200 version. A fast film requires less light for exposure, and offers wide exposure latitudes in shooting situations. On the other hand, a fast film tends to be "grainy". The image may not seem as sharp, particularly if the picture is enlarged. Today's films are, however, of much higher quality than previously, even at the faster speeds, so consumers tend to use the ISO 200 film nowadays compared to them using the slower ISO 100 film a decade or so ago. << Back to Main . 1 . 2 . 3 . 4 . 5 . 6 . 7 . 8 . 9 . 10 . 11 . 12 .