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Photography 101: Understanding ISO
Back in the days when film photography predominated, film was manufactured with various sensitivities to light and measured with a standard called “ASA” or “American Standards Association”.
Film sensitivity is refereed to as “film speed” and the methods of determining a film’s speed have evolved over the history of photography. The most familiar standard to any film user in the 70s – 80s was ASA or ANSI which traces its roots back to the 1940s.
The current International Standard for measuring the speed of color negative film is ISO or the International Standard. Gaining film speed has always been a trade off. To create faster films, manufactures have had to make the grains of photosensitive elements larger, thus faster films result in grainier negatives.
In digital photography ISO measures the sensitivity of the image sensor. The same principles apply as in film photography – the lower the number the less sensitive your camera is to light and the finer the “grain”. Higher ISO settings are generally used in darker situations to get faster shutter speeds.