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Film Speed
A typical roll of film. |
Speed is defined as the sensitivity of film to light. Film Speed can be measured by ASA (American Standards Association) or ISO (International Organization for Standardization). Fast film (High ASA, 400 or 800) reacts to light quicker than slow film (Lower ASA, 100 or 200). Therefore, faster film requires faster shutter speeds. Slower film requires longer shutter speeds. Speed is determined by the grain size on the film. When large grain is used (high ASA), each grain activated by the light creates more density on the developed film (see diagram below). |
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If 1 ray of light activates 2 grain, a larger percent of the larger grain (left) is darkened than the smaller grain (right).
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Tips for choosing Film
- When shooting in a wide variety of conditions, use 400 speed.
- Always use 800 or 400 speed for sports photography, especially when using a zoom lens.
- If you plan to enlarge photos you take, use slower film (smaller grain looks better when enlarged).
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