ASA Exposure Indexes

While ASA film speeds do not apply directly to mo-tion-picture films, exposure meters calibrated to ASA, ANSI, or ISO standards specify exposure indexes (EI) related to film speeds (film speeds are calculated mathematically from sensitometric exposures; exposure indexes are numbers useful to the cinematographer in determining or specifying exposure in a given instance). All film manufacturers furnish EI numbers related to commercial exposure meters as a recommendation for a starting point in determining optimum exposure.

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