What is ISO in photography?

What is ISO in photography?
(Image credit: James Artaius)

It's a simple question: what is ISO in photography? Well, the answer isn't as simple as the question.

It involves a bit of backtracking, and asking what is ISO in photography when it comes to the pre-digital age. Back in those days, film came in a variety of different speeds. The ‘faster’ the film (the higher the ISO), the more sensitive it was to light – enabling you to use faster shutter speeds than with ‘slower’ film. Using these higher-sensitivity film emulsions was useful for moving subjects – and particularly so in low light. 

Chris George

Chris George has worked on Digital Camera World since its launch in 2017. He has been writing about photography, mobile phones, video making and technology for over 30 years – and has edited numerous magazines including PhotoPlus, N-Photo, Digital Camera, Video Camera, and Professional Photography. 

His first serious camera was the iconic Olympus OM10, with which he won the title of Young Photographer of the Year - long before the advent of autofocus and memory cards. Today he uses a Nikon D800, a Fujifilm X-T1, a Sony A7, and his iPhone 15 Pro Max.

He has written about technology for countless publications and websites including The Sunday Times Magazine, The Daily Telegraph, Dorling Kindersley, What Cellphone, T3 and Techradar.

With contributions from