Recently a photographer friend of mine was talking shop with me and she referred to the camera ISO as, “Izzo.” I had heard the debate between the two pronunciations of Eye Ess Oh versus Eye So, but I had never before heard Izzo. I soon realized that I didn’t know which way it was supposed to be and so I decided to do a little research.
Jared Polin, Matt Grainger and a lot of other professional or near professional photographers who are doing a lot of instructional videos on YouTube are all pronouncing ISO as individual letters, as if ISO were an acronym. This is a common misconception. ISO is often said to be an acronym of the International Standards Organization. But if you do a search for this organization, you will not find it. However, there is an organization called the International Organization of Standardization which just so happens to set the standards for camera sensor sensitivity for manufacturers along with nearly 20,000 other standards. On their website, they describe why they adopted the name ISO instead of IOS.
Because ‘International Organization for Standardization’ would have different acronyms in different languages (IOS in English, OIN in French for Organisation internationale de normalisation), our founders decided to give it the short form ISO. ISO is derived from the Greek isos, meaning equal. Whatever the country, whatever the language, the short form of our name is always ISO.
So since ISO is a shortened form of the Greek “isos”, it is pronounced “EyeSo”, and not, “Eye Ess Oh”. Case closed.
If you are interested in learning more about ISO 12232: 2006 which specifies the method for assigning and reporting ISO speed ratings, ISO speed latitude ratings, standard output sensitivity values, and recommended exposure index values for digital still cameras, you can purchase a PDF from ISO or ANSI.