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.
