* 1871: The first photographic emulsions were created, but they were very slow and required long exposure times.
* 1879: George Eastman introduced the first commercially successful roll film, paving the way for more portable photography. However, these early films still required relatively long exposures.
* 1920s: The first standardized film speed systems were introduced, aiming to quantify how sensitive a film was to light. These early systems were based on measuring the exposure needed to produce a certain level of density on the film.
* 1930s: The American Standards Association (ASA) introduced a standardized film speed system that became widely adopted. This system was based on the ISO (International Organization for Standardization) system, which is still used today.
So, while there wasn't a single "invention" year, the 1920s and 1930s mark the period where film speed became a standardized and quantifiable measurement.
