How to Pronounce “ISO”


Fuji X-T1 ISO dial.

For many years film speed, and more recently the amplification level of of a digital sensor, has been described by the ISO number. I have always pronounced ISO as “eye-ess-oh” and this is how I have generally heard others pronounce it.

Recently, I noticed some people using the one-word pronunciation “eye-so”. One such person is Tony Northrup, who states in his book Stunning Digital Photography that this is the correct pronunciation, and explains why in this video.

ISO is the abbreviation for the International Organization for Standardization (so it is not an acronym, which would have to be “IOS”). This abbreviation was chosen because the translation of the title into different languages leads to different abbreviations, so one was declared official, with “ISO” justified on the ISO website as being “derived from the Greek isos, meaning equal”.

This choice of abbreviation has led to confusion. Looking at photography books on my shelves, I find that The Complete Photography Course (by M. Joseph and D. Saunders, Weidenfeld and Nicolson, 1993), Digital Food Photography (L. Manna, Thomson, 2005), and The Art of Black and White Photography (J. Garrett, Amphoto, 1990) all state that ISO is an abbreviation for the “International Standards Organization”. This is what you would guess if you reverse engineer the abbreviation, but it is not correct.

But this is besides the point. There is no reason to pronounce ISO letter by letter. It is a pronounceable word, just like GIFF, NATO, and UNESCO. So “eye-so” it is.


One thought on “How to Pronounce “ISO”

  1. Many of us are old school, and used the ASA rating long before it was replaced by ISO. We pronounced the individual letters in ASA and did the same with ISO when it appeared. Hard to break old habits. Just as some people feel that the trend of just typing “RIP” instead of taking the extra few seconds to type “Rest in Peace” isn’t as respectful. Certainly the “RIP” usage has been around for centuries, but it was mainly due to peasants not being able to afford to have the complete phrase engraved on headstones, and saved money by abbreviating it. There was a real reason for it back then, but not so much these days when the extra few letters come free on a keyboard.

    Liked by 1 person

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