We've talked about the triangle of photography: Shutter Speed, Aperture, and ISO. But have you ever stopped to think what ISO means? Prepare to get nerdier than you've ever been about that elusive third dial in the exposure triumvirate.
ISO is the winner of a vicious battle that has been raging for... Okay, maybe not all that long. And perhaps it was less of a war, and more of a gentlemen's scuffle, between the American Standards Association (ASA), the Deutsches Institut für Normung (DIN) standards, and ISO. Both of the former were in use until the end of the 1970s. Then, the International Organization for Standardization (ISO) stuck an oar in and added their own initial set of definitions.
Today's ISO values are defined by ISO 12232:2006 (that is, ISO standard number 12232, revised in 2006). This ISO standard "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. ISO 12232:2006 is applicable to both monochrome and colour digital still cameras."
So now you know. For the ultimate piece of photographic trivia, memorise "ISO 12232", and the next time your unworthy photography friends start harping on on about 'ISO', you can pull your smug face and go "Well, actually, did you know..."
For extra nerd cred, dig out your credit card and shell out the 92 Swiss Francs (£67) it costs to buy the full ISO standard and read the whole thing. Just don't learn it completely off by heart, as nobody likes a smartarse...