Before understanding what ISO means for the photography, let’s take a look first at how film speed works in film photography. Film speed is the measure of the sensitivity of film to light. Films with different film speeds are available in the market e.g. 50, 100, 200, 400, 800, 1600, and so on.

Mostly people confuse film speed with the speed of the object it is capturing, like if a faster object needs to be captured (a racing car) then the film speed should be higher like 1600 or 3200 and if a steady object like a person is being photographed then we slow film like 50 or 100 is needed. However, the reality is that the film speed refers to the speed at which the film reacts to light, the faster the film the faster it reacts to light.

The sensitivity of light on a photographic film is measured on many numerical scales but the most updated and recent scale is ISO system.

Evolution of current ISO system

Leon Warnerke was the first person to invent a practical sensitometer to measure the speed of photographic materials. This system known as The Warnerke Standard Sensitometer was invented in 1880 and was commercialized in 1881. This was followed by different systems:

1. H&D system was invented in 1890 Ferdinand Hurter and Vero Charles Driffield.

2. Scheinergrade system was invented by Julius Scheiner in 1894.

3. DIN system was put forward in 1934 by German Institute for Standardization.

4. Weston film speed rating was invented by Edward Faraday Weston and Dr. Edward Weston in 1932.

5. ASA was recommended by American Standards Association in 1943.